Nothing Special   »   [go: up one dir, main page]

WO2024210144A1 - Poly(meth)acrylic acid (salt)-based water-absorbing resin and absorbent article - Google Patents

Poly(meth)acrylic acid (salt)-based water-absorbing resin and absorbent article Download PDF

Info

Publication number
WO2024210144A1
WO2024210144A1 PCT/JP2024/013704 JP2024013704W WO2024210144A1 WO 2024210144 A1 WO2024210144 A1 WO 2024210144A1 JP 2024013704 W JP2024013704 W JP 2024013704W WO 2024210144 A1 WO2024210144 A1 WO 2024210144A1
Authority
WO
WIPO (PCT)
Prior art keywords
water
absorbent resin
absorbent
nonwoven fabric
weight
Prior art date
Application number
PCT/JP2024/013704
Other languages
French (fr)
Japanese (ja)
Inventor
幸恵 北畑
智嗣 松本
加奈子 津留
Original Assignee
株式会社日本触媒
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by 株式会社日本触媒 filed Critical 株式会社日本触媒
Publication of WO2024210144A1 publication Critical patent/WO2024210144A1/en

Links

Images

Classifications

    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
    • A61F13/00—Bandages or dressings; Absorbent pads
    • A61F13/15—Absorbent pads, e.g. sanitary towels, swabs or tampons for external or internal application to the body; Supporting or fastening means therefor; Tampon applicators
    • A61F13/53—Absorbent pads, e.g. sanitary towels, swabs or tampons for external or internal application to the body; Supporting or fastening means therefor; Tampon applicators characterised by the absorbing medium
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
    • A61F13/00—Bandages or dressings; Absorbent pads
    • A61F13/15—Absorbent pads, e.g. sanitary towels, swabs or tampons for external or internal application to the body; Supporting or fastening means therefor; Tampon applicators
    • A61F13/53—Absorbent pads, e.g. sanitary towels, swabs or tampons for external or internal application to the body; Supporting or fastening means therefor; Tampon applicators characterised by the absorbing medium
    • A61F13/534—Absorbent pads, e.g. sanitary towels, swabs or tampons for external or internal application to the body; Supporting or fastening means therefor; Tampon applicators characterised by the absorbing medium having an inhomogeneous composition through the thickness of the pad
    • A61F13/537—Absorbent pads, e.g. sanitary towels, swabs or tampons for external or internal application to the body; Supporting or fastening means therefor; Tampon applicators characterised by the absorbing medium having an inhomogeneous composition through the thickness of the pad characterised by a layer facilitating or inhibiting flow in one direction or plane, e.g. a wicking layer
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/22—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising organic material
    • B01J20/26—Synthetic macromolecular compounds
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/28—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F2/00—Processes of polymerisation
    • C08F2/04—Polymerisation in solution
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F20/00—Homopolymers and copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical or a salt, anhydride, ester, amide, imide or nitrile thereof
    • C08F20/02—Monocarboxylic acids having less than ten carbon atoms, Derivatives thereof
    • C08F20/04—Acids, Metal salts or ammonium salts thereof
    • C08F20/06—Acrylic acid; Methacrylic acid; Metal salts or ammonium salts thereof

Definitions

  • the present invention relates to a water-absorbent resin and an absorbent article. More specifically, the present invention relates to a poly(meth)acrylic acid (salt)-based water-absorbent resin and an absorbent article having an absorbent body containing the same.
  • water-absorbing resins have been widely used as absorbents in sanitary materials such as paper diapers, sanitary napkins, and incontinence pads from the viewpoint of absorbing bodily fluids.
  • water-absorbing resins include hydrolyzates of starch-acrylonitrile graft copolymers, neutralized starch-acrylic acid graft polymers, saponified vinyl acetate-acrylic acid ester copolymers, and crosslinked products of partially neutralized (meth)acrylic acid polymers.
  • poly(meth)acrylic acid (salt)-based water-absorbing resins that use (meth)acrylic acid and/or its salts as the main monomer component are the most widely produced industrially from the viewpoint of water-absorbing performance.
  • Patent Document 1 When actually used in absorbents such as disposable diapers, in order for the water-absorbent resin to exhibit excellent performance, it is necessary to increase the water absorption capacity without pressure and the absorption performance under pressure, and to increase the absorption capacity of the disposable diaper. In addition, by improving the diffusibility and liquid permeability of the disposable diaper, it is possible to reduce the amount of liquid returning to the absorbent (Patent Document 1).
  • the water-absorbent resin with improved liquid permeability as described above when used in an absorbent article such as a paper diaper comprising a water-absorbent resin and a water-permeable substrate, the liquid to be absorbed still may not be sufficiently distributed throughout the entire absorbent article, resulting in an increased amount of liquid return, and there is still room for improvement in terms of liquid retention.
  • the water-absorbent resin with improved liquid permeability as described above when used in an absorbent article such as a paper diaper comprising a water-absorbent resin and a water-permeable substrate, the liquid to be absorbed still may not be sufficiently distributed throughout the entire absorbent article, resulting in an increased amount of liquid return, and there is still room for improvement in terms of liquid diffusion.
  • One aspect of the present invention aims to provide an absorbent resin that reduces the amount of liquid returning to an absorbent article that includes a water-absorbent resin and a water-permeable substrate and has excellent liquid retention properties.
  • Another aspect of the present invention aims to provide an absorbent article that has excellent liquid diffusion properties.
  • the poly(meth)acrylic acid (salt)-based water absorbent resin is The present invention is a poly(meth)acrylic acid (salt)-based water-absorbing resin having a resistance to penetration between fibers of a water-permeable substrate of 60% by weight or more, which is determined by the following steps (1) to (3): (1) A nonwoven fabric cut to 6 cm x 9 cm is fixed with double-sided tape to the bottom of a rectangular polystyrene case having a bottom of 6 cm x 9 cm and a depth of 1 cm, both of which are the dimensions of the inner surface of the case.
  • an absorbent resin that has excellent liquid retention properties and reduces the amount of liquid returning to an absorbent article that includes a water-absorbent resin and a water-permeable substrate.
  • an absorbent article that has excellent liquid diffusion properties.
  • FIG. 10 shows an absorbent sheet for evaluating the amount of liquid return in an example, in which 1001 is a top view of the absorbent sheet, and 1002 is a cross-sectional view of the absorbent sheet.
  • FIG. 10 shows an absorbent article for evaluating liquid diffusion properties in an example, in which 1003 is a top view of the absorbent article, and 1004 is a cross-sectional view of the absorbent article.
  • FIG. 2 is a schematic diagram of a roll-type grinding device used in the grinding step in one embodiment of the present invention.
  • FIG. 2 is a schematic diagram showing a pair of rolls in a roll-type grinding device used in a grinding step in one embodiment of the present invention, where 2001 is a pair of rolls in which grooves are provided on the surfaces of both rolls, and 2002 is a pair of rolls in which grooves are provided on the surface of one roll and no grooves are provided on the surface of the other roll.
  • Water-absorbent resin refers to a water-swellable, water-insoluble polymer gelling agent that satisfies the following physical properties: “Water-swellable” refers to a polymer gelling agent that satisfies the physical properties of CRC of 5 g/g or more as specified in ERT441.2-02, and “Water-insoluble” refers to a polymer gelling agent that satisfies the physical properties of Ext of 50 wt% or less as specified in ERT470.2-02.
  • the water-absorbing resin can be designed according to its application, and is not particularly limited, but is preferably a hydrophilic cross-linked polymer obtained by cross-linking an unsaturated monomer having a carboxyl group.
  • the water-absorbing resin is not limited to a form in which the total amount (100% by weight) is a polymer, and may be a water-absorbing resin composition containing additives and the like within a range that satisfies the physical properties (CRC, Ext).
  • the water-absorbing resin in the present invention is not limited to a final product, and may also refer to intermediates in the manufacturing process of the water-absorbing resin (e.g., a hydrogel-like cross-linked polymer after polymerization, a dried polymer after drying, a water-absorbing resin before surface cross-linking, a water-absorbing resin after surface cross-linking, a water-absorbing resin after granulation, etc.), and all of these are collectively referred to as "water-absorbing resin” together with the water-absorbing resin composition.
  • the shape of the water-absorbing resin is not particularly limited, and examples thereof include a sheet-like, fibrous, film-like, and particulate shape, but particulate water-absorbing resin is preferred in the present invention.
  • poly(meth)acrylic acid (salt)-based water-absorbent resin refers to a water-absorbing resin that contains an arbitrary graft component and is mainly composed of a repeating unit derived from (meth)acrylic acid and/or a salt thereof (hereinafter referred to as "(meth)acrylic acid (salt)").
  • EDANA European Disposables and Nonwovens Associations
  • ERT is an abbreviation for EDANA Recommended Test Methods, a European standard (almost global standard) for measuring the properties of water-absorbent resins.
  • the physical properties of the water-absorbent resin are measured in accordance with the original ERT (revised in 2002/publicly known document).
  • water permeable substrate refers to a member that has a function of permeating and/or diffusing an introduced liquid and that is in direct contact with a water-absorbent resin in an absorbent body used in absorbent articles such as disposable diapers.
  • the material include hydrophilic fibers (e.g., pulp fibers, etc.), hydrophilic fiber stacks, hydrophilic nonwoven fabrics containing hydrophilic fibers as constituent fibers, and nonwoven fabrics containing synthetic fibers as constituent fibers. can be done.
  • Water-absorbent resin (2-1) Resistance to penetration between fibers of water-permeable substrate
  • the present inventors have found that in an absorbent article comprising a water-absorbent resin and a water-permeable substrate, the water-absorbent resin penetrates between fibers of the water-permeable substrate, causing clogging of the fibers, and the liquid permeability inside the water-permeable substrate is not fully exhibited, which causes a decrease in the absorption performance of the entire absorbent article and generates a liquid return amount, leading to the completion of the present invention.
  • the "resistance to penetration between fibers of a water-permeable substrate” is a new physical property value for evaluating the difficulty of the water-absorbent resin to penetrate between fibers of a water-permeable substrate in an absorbent article, and specifically, is a value measured by the measurement method described in the examples.
  • the resistance to penetration between fibers of a water-permeable substrate of the water-absorbent resin according to one embodiment of the present invention is 60% by weight or more, preferably 65% by weight or more, more preferably 70% by weight or more, and even more preferably 75% by weight or more.
  • a water-absorbent resin having a penetration resistance between fibers of a water-permeable substrate of 60% by weight or more has the advantage that it is less likely to cause clogging of the fibers of the water-permeable substrate in an absorbent article, and exhibits excellent water absorption performance, thereby reducing the amount of liquid return.
  • the upper limit of the penetration resistance between fibers of a water-permeable substrate is not particularly limited, but is 99% by weight or less, preferably 95% by weight or less, and more preferably 90% by weight or less.
  • the shape of the water-absorbent resin is preferably particulate, and specifically, the shape of irregularly crushed particles, spherical particles, football-shaped particles, aggregate particles, granule particles, etc. can be mentioned.
  • spherical is not limited to a perfect sphere, and also includes a nearly spherical shape with an aspect ratio of 1.0 to 1.2.
  • aggregate particles or granule particles are preferable from the viewpoint that they are difficult to penetrate between the fibers of the water-permeable substrate and the water absorption rate is improved by increasing the specific surface area.
  • the water absorbent resin may contain additives to exhibit various functions.
  • additives include surfactants, compounds having phosphorus atoms, oxidizing agents, organic reducing agents, water-insoluble inorganic fine particles, organic powders (e.g., metal soaps, etc.), deodorants, antibacterial agents, pulp, thermoplastic fibers, etc.
  • the water-insoluble inorganic fine particles the compounds disclosed in “[5] Water-insoluble inorganic fine particles” of International Patent Publication No. 2011/040530 are applicable to the present invention.
  • the content of the water-insoluble inorganic fine particles is preferably 0.01 to 5.00 parts by weight, more preferably 0.05 to 3.00 parts by weight, even more preferably 0.10 to 1.00 parts by weight, and particularly preferably 0.20 to 0.50 parts by weight, relative to 100 parts by weight of the water-absorbent resin, from the viewpoint of providing appropriate friction between the water-absorbent resin and the water-permeable substrate.
  • the water-insoluble inorganic fine particles have a size that is smaller than the size of the water-absorbent resin particles.
  • the average particle size of the water-insoluble inorganic fine particles is preferably 0.01 ⁇ m to 50.00 ⁇ m, and may be 0.10 ⁇ m to 30.00 ⁇ m, or 1.00 ⁇ m to 20.00 ⁇ m.
  • the average particle size can be measured by a pore electrical resistance method or a laser diffraction/scattering method depending on the characteristics of the particles.
  • CRC is an abbreviation for Centrifuge Retention Capacity, and means the water absorption capacity of a water-absorbent resin under no pressure.
  • CRC is measured in accordance with the EDANA method (ERT441.2-02).
  • FSC is an abbreviation for Free Swell Capacity, and means the water absorption capacity of a water absorbent resin when suspended under no pressure.
  • FSC is measured in accordance with the EDANA method (ERT440.2-02).
  • the value of FSC can be controlled by changing the type and amount of an internal crosslinking agent and a surface crosslinking agent.
  • the FSC is 40 g/g or more, the absorption capacity is sufficient and the material can be suitably used as an absorbent for absorbent articles such as paper diapers. If the FSC is 70 g/g or less, the rate at which the material absorbs body fluids (e.g., urine, blood, etc.) does not decrease, making the material suitable for use in paper diapers with high water absorption rates.
  • body fluids e.g., urine, blood, etc.
  • Ext is an abbreviation for Extractables, and means the amount of extractables extracted from the water-absorbing resin. In this specification, Ext is measured in accordance with the EDANA method (ERT470.2-02).
  • AAP is an abbreviation for Absorption against Pressure, and means the water absorption capacity of a water-absorbent resin under pressure.
  • AAP is measured in accordance with the EDANA method (ERT442.2-02) except that the load condition is changed to 4.83 kPa (0.7 psi). Specifically, 0.9 g of a water-absorbent resin is swollen under a pressure of 4.83 kPa for 1 hour using a 0.9% by mass aqueous sodium chloride solution, and then the AAP (water absorption capacity under pressure) (unit: g/g) is measured.
  • the AAP of the water-absorbent resin according to one embodiment of the present invention is preferably 15 g/g or more, more preferably 20 g/g or more, and even more preferably 23 g/g or more, from the viewpoint of improving the water absorption properties when used in sanitary materials.
  • Moisture Content is measured in accordance with the EDANA method (ERT430.2-02), except that the sample amount is changed to 1.0 g and the drying temperature is changed to 180°C.
  • Mass average particle diameter (D50) The “mass-average particle diameter (D50)” is defined in “(3) Mass-Average Particle Diameter (D50) and Logarithmic Standard Deviation ( ⁇ ) of Particle Diameter Distribution” in columns 27 and 28 of U.S. Pat. No. 7,638,570. Measured in accordance with.
  • the mass average particle diameter (D50) of the water-absorbent resin according to one embodiment of the present invention is preferably 250 ⁇ m to 800 ⁇ m, more preferably 300 ⁇ m to 700 ⁇ m, even more preferably 310 ⁇ m to 600 ⁇ m, and particularly preferably 320 ⁇ m to 500 ⁇ m, from the viewpoint of preventing the water-absorbent resin from penetrating between the fibers of the water-permeable substrate in the absorbent article.
  • the proportion of particles having a particle diameter of less than 150 ⁇ m is preferably 40% by mass or less, more preferably 30% by mass or less, even more preferably 20% by mass or less, and particularly preferably 10% by mass or less, from the viewpoint that it is preferable that the number of fine particles that can penetrate between the fibers of the water-permeable substrate in the absorbent article is small. If the mass average particle diameter is 250 ⁇ m or more, the penetration of the water-absorbent resin into the fibers of the water-permeable substrate in the absorbent article can be reduced, and there is an advantage that there is less dust and it is easy to handle. Furthermore, if the mass average particle size is 800 ⁇ m or less, the rate at which the material absorbs body fluids (e.g., urine, blood, etc.) is prevented from decreasing, making the material suitable for use in paper diapers with high water absorption rates.
  • body fluids e.g., urine, blood, etc.
  • the bulk density of the water-absorbent resin according to one embodiment of the present invention is preferably 0.60 g/mL to 1.00 g/mL, more preferably 0.62 g/mL to 0.90 g/mL, and even more preferably 0.64 g/mL to 0.80 g/mL. If the bulk density is 0.60 to 1.00 g/mL, a decrease in the water-absorbent resin's absorption rate of body fluids (e.g., urine, blood, etc.) is prevented, and the water-absorbent resin is suitable for use in high-absorption-rate paper diapers, etc.
  • body fluids e.g., urine, blood, etc.
  • the "water absorption rate" of a water absorbent resin means the “water absorption rate by a vortex method”.
  • the "water absorption rate by a vortex method” means the time required for a test liquid to be covered with 2.0 g of a water absorbent resin when 50 g of a 0.9% by mass aqueous sodium chloride solution stirred at 600 rpm with a stirrer tip is added to the stirrer tip.
  • a water-absorbent resin having excellent "absorption speed" is preferable because it can instantly absorb liquid and reduce the amount of liquid returning when used as an absorbent article.
  • the water-absorbent resin according to one embodiment of the present invention has an absorption speed of preferably 50 seconds or less, more preferably 45 seconds or less, more preferably 40 seconds or less, and even more preferably 30 seconds or less.
  • the lower limit of the water-absorption speed is not particularly limited, but is 10 seconds or more, preferably 15 seconds or more, and even more preferably 20 seconds or more.
  • the water-absorbent resin has an absorption speed of 45 seconds or less, it can quickly absorb the liquid diffused by the water-permeable substrate, and therefore has excellent liquid retention properties and is suitable for use in paper diapers with high water-absorption speed.
  • the faster the water-absorbent resin has an absorption speed the higher the risk of so-called "gel blocking," a phenomenon in which a rapidly swollen gel blocks the gaps between the water-absorbent resin and prevents liquid from passing through. Therefore, the advantage of using a water-absorbent resin with high resistance to penetration between fibers in a water-permeable substrate is greater in avoiding a decrease in diffusion within the fibers.
  • This step is a step of preparing an aqueous solution containing (meth)acrylic acid (salt) as a main component (hereinafter referred to as "monomer aqueous solution").
  • a monomer slurry liquid can also be used within a range in which the water absorption performance of the obtained water absorbent resin is not deteriorated, for the sake of convenience, the monomer aqueous solution will be described in this section.
  • the “main component” means that the amount (content) of (meth)acrylic acid (salt) used is preferably 50 mol % or more, more preferably 70 mol % or more, and even more preferably 90 mol % or more (upper limit 100 mol %), based on the total amount of monomers (excluding the internal crosslinking agent) used in the polymerization reaction of the water absorbent resin.
  • ((Meth)acrylic acid (salt)) In the method for producing a water-absorbent resin according to one embodiment of the present invention, a (meth)acrylic acid (salt) is used as a monomer from the viewpoint of improving the physical properties and productivity of the obtained water-absorbent resin.
  • the "(meth)acrylic acid” may be any known (meth)acrylic acid, and may contain, as a polymerization inhibitor, preferably methoxyphenols, more preferably p-methoxyphenol, preferably at 200 ppm or less, more preferably 10 ppm to 160 ppm, and even more preferably 20 ppm to 100 ppm, from the viewpoint of improving the polymerization of the (meth)acrylic acid and the color tone of the water-absorbing resin.
  • impurities in (meth)acrylic acid the compounds described in U.S. Patent Application Publication No. 2008/0161512 are also applicable to the present invention.
  • the "(meth)acrylic acid salt” is a neutralized product obtained by neutralizing the (meth)acrylic acid with the following basic composition.
  • a commercially available (meth)acrylic acid salt e.g., sodium (meth)acrylate, etc.
  • a salt obtained by neutralization in a water-absorbent resin manufacturing plant may be used.
  • base composition refers to a composition containing a basic compound.
  • basic compositions include commercially available aqueous sodium hydroxide solutions.
  • the basic compound examples include alkali metal carbonates, alkali metal hydrogen carbonates, alkali metal hydroxides, ammonia, and organic amines.
  • the basic compound is strongly basic. That is, the basic compound is preferably an alkali metal hydroxide (sodium hydroxide, potassium hydroxide, lithium hydroxide, etc.), and more preferably sodium hydroxide.
  • the neutralization may be selected from or used in combination with neutralization of (meth)acrylic acid (before polymerization) and neutralization of a hydrogel crosslinked polymer obtained by crosslinking and polymerizing (meth)acrylic acid (after polymerization) (hereinafter referred to as "post-neutralization").
  • post-neutralization a hydrogel crosslinked polymer obtained by crosslinking and polymerizing (meth)acrylic acid
  • These neutralization methods may be continuous or batch-type, and are not particularly limited, but the continuous type is preferred from the viewpoint of improving production efficiency, etc.
  • the neutralization rate is preferably 10 to 90 mol%, more preferably 40 to 85 mol%, even more preferably 50 to 80 mol%, and particularly preferably 60 to 75 mol%, based on the acid groups of the monomer.
  • the neutralization rate is 10 mol% or more, a significant decrease in water absorption capacity can be suppressed.
  • the neutralization rate is 90 mol% or less, a water-absorbent resin with a high water absorption capacity under pressure can be obtained.
  • neutralization rate of 75 mol% means a mixture of 25 mol% (meth)acrylic acid and 75 mol% (meth)acrylic acid salt. Such a mixture of (meth)acrylic acid and (meth)acrylic acid salt may also be referred to as a partially neutralized (meth)acrylic acid.
  • the term "other monomer” refers to a monomer other than the (meth)acrylic acid (salt).
  • the other monomer can be used in combination with the (meth)acrylic acid (salt) to produce a water-absorbing resin.
  • the other monomer may be, for example, a water-soluble unsaturated monomer or a hydrophobic unsaturated monomer.
  • a water-soluble unsaturated monomer or a hydrophobic unsaturated monomer.
  • the compounds described in U.S. Patent Application Publication No. 2005/0215734 are also applicable to the present invention.
  • Examples of the internal crosslinking agent used in the present invention include N,N'-methylenebis(meth)acrylamide, (poly)ethylene glycol di(meth)acrylate, (poly)propylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, trimethylolpropane di(meth)acrylate, glycerin tri(meth)acrylate, glycerin acrylate methacrylate, ethylene oxide modified trimethylolpropane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol tetra(meth)acrylate, and the like.
  • Examples of the internal crosslinking agent include hexa(meth)acrylate, triallyl cyanurate, triallyl isocyanurate, triallyl phosphate, triallylamine, poly(meth)allyloxyalkane, (poly)ethylene glycol diglycidyl ether, glycerol diglycidyl ether, ethylene glycol, polyethylene glycol, propylene glycol, glycerin, 1,4-butanediol, pentaerythritol, ethylenediamine, ethylene carbonate, propylene carbonate, polyethyleneimine, glycidyl (meth)acrylate, etc.
  • One or more types of the internal crosslinking agent may be selected.
  • the internal crosslinking agent is preferably a compound having two or more polymerizable unsaturated groups, more preferably a compound having two or more polymerizable unsaturated groups that are thermally decomposable at the drying temperature described below, and even more preferably a compound having two or more polymerizable unsaturated groups that have a (poly)alkylene glycol structural unit.
  • the polymerizable unsaturated group is preferably an allyl group or a (meth)acrylate group. Of these, from the viewpoint of improving water absorption performance, a (meth)acrylate group is more preferable.
  • the (poly)alkylene glycol structural unit is preferably polyethylene glycol from the viewpoint of improving water absorption performance.
  • the number n of the (poly)alkylene glycol structural unit is preferably 1 to 100, more preferably 6 to 50.
  • the amount of the internal crosslinking agent used is preferably 0.0001 to 10 mol %, more preferably 0.001 to 1 mol %, based on the total amount of monomers. By setting the amount used within the above range, the desired water-absorbent resin can be obtained. Note that if the amount used is 0.0001 mol % or more, the gel strength tends to increase and the water-soluble content tends to decrease, while if the amount used is 10 mol % or less, the water absorption capacity tends to increase, which is preferable.
  • the method of adding the internal crosslinking agent is not particularly limited, but examples include a method of adding the internal crosslinking agent to an aqueous monomer solution in advance and causing a crosslinking reaction simultaneously with polymerization, a method of adding an internal crosslinking agent during or after polymerization and causing post-crosslinking, a method of radical crosslinking using a radical polymerization initiator, and a method of radiation crosslinking using active energy rays such as electron beams and ultraviolet rays.
  • a method of adding the internal crosslinking agent to an aqueous monomer solution in advance and causing a crosslinking reaction simultaneously with polymerization is preferred. The above methods may be used in combination as long as they do not impair the effects of the present invention.
  • hydrophilic polymers such as starch, starch derivatives, cellulose, cellulose derivatives, polyvinyl alcohol, poly(meth)acrylic acid (salt), and crosslinked poly(meth)acrylic acid (salt) may be added in an amount of preferably 50% by weight or less, more preferably 20% by weight or less, even more preferably 10% by weight or less, and particularly preferably 5% by weight or less (lower limit: 0% by weight) based on the total monomers used in the polymerization (excluding the crosslinking agent).
  • foaming agents such as carbonates, azo compounds, and bubbles; surfactants; chelating agents; chain transfer agents, etc. may be added in amounts of preferably 5% by weight or less, more preferably 1% by weight or less, and even more preferably 0.5% by weight or less (the lower limit is 0% by weight) based on the total monomers (excluding the crosslinking agent) used in the polymerization.
  • the substance may be added to the aqueous monomer solution or during polymerization.
  • the above-mentioned methods of addition may be used in combination as long as they do not impair the effects of the present invention.
  • a graft polymer or water-absorbent resin composition for example, starch-acrylic acid polymer, PVA-acrylic acid polymer, etc.
  • these polymers and water-absorbent resin compositions also fall within the scope of the water-absorbent resin of the present invention.
  • the concentration of the monomer component in the aqueous monomer solution is not particularly limited, but from the viewpoint of improving the physical properties of the water absorbent resin, it is preferably 10 to 80% by weight, more preferably 20 to 75% by weight, and even more preferably 30 to 70% by weight.
  • a solvent other than water can be used in combination as necessary.
  • the type of solvent is not particularly limited.
  • the "monomer component concentration” is the value calculated by the following formula (2), and the weight of the aqueous monomer solution does not include the weight of the hydrophilic polymer graft component (e.g., starch, etc.), the fine powder of the water-absorbent resin generated during the manufacturing process and added for reuse, or the weight of the hydrophobic solvent in the reversed-phase suspension polymerization.
  • the hydrophilic polymer graft component e.g., starch, etc.
  • the fine powder of the water-absorbent resin generated during the manufacturing process and added for reuse or the weight of the hydrophobic solvent in the reversed-phase suspension polymerization.
  • Monomer component concentration (wt%) ⁇ (weight of monomer component) / (weight of aqueous monomer solution) ⁇ x 100 ... formula (2).
  • This step is a step of polymerizing the aqueous monomer solution obtained in the aqueous monomer solution preparation step to obtain a hydrogel-like crosslinked polymer (hereinafter referred to as "hydrogel").
  • the polymerization initiator used in one embodiment of the present invention is not particularly limited since it is selected depending on the polymerization form, etc., but examples thereof include a thermally decomposable polymerization initiator, a photodecomposable polymerization initiator, or a redox-based polymerization initiator used in combination with a reducing agent that promotes the decomposition of these polymerization initiators.
  • a thermally decomposable polymerization initiator e.g., a photodecomposable polymerization initiator, or a redox-based polymerization initiator used in combination with a reducing agent that promotes the decomposition of these polymerization initiators.
  • one or more of the polymerization initiators disclosed in U.S. Pat. No. 7,265,190 are used. From the viewpoint of improving the handling of the polymerization initiator and the physical properties of the water-absorbing resin, preferably a peroxide or an azo compound, more preferably a peroxide, and even more preferably
  • the amount of the polymerization initiator used is preferably 0.001 to 1 mol %, more preferably 0.001 to 0.5 mol %, based on the total monomers used in the polymerization (excluding the crosslinking agent).
  • the amount of the reducing agent used is preferably 0.0001 to 0.02 mol %, based on the total monomers used in the polymerization (excluding the crosslinking agent).
  • the polymerization reaction may be carried out by irradiating the material with active energy rays such as radiation, electron beams, and ultraviolet rays, and these active energy rays may be used in combination with the polymerization initiator.
  • active energy rays such as radiation, electron beams, and ultraviolet rays
  • the polymerization form applied in one embodiment of the present invention is not particularly limited, and examples thereof include aqueous solution polymerization, reversed-phase suspension polymerization, droplet polymerization, bulk polymerization, precipitation polymerization, etc. Among these, aqueous solution polymerization or reversed-phase suspension polymerization is preferred from the viewpoint of ensuring good water absorption properties and improving ease of polymerization control.
  • This step is a step of pulverizing the hydrogel obtained in the polymerization step with a gel crusher (for example, a kneader; a screw extruder such as a meat chopper; a cutter mill, etc.) to obtain a particulate hydrogel (hereinafter referred to as a "particulate hydrogel").
  • a gel crusher for example, a kneader; a screw extruder such as a meat chopper; a cutter mill, etc.
  • the polymerization step and the gel crushing step are carried out simultaneously.
  • the gel crushing step may not be carried out.
  • This step is a step of drying the particulate hydrogel obtained in the polymerization step and/or gel crushing step to a desired resin solid content to obtain a dry polymer.
  • the resin solid content is determined from the loss on drying (weight change when 1 g of the water-absorbent resin is heated at 180° C. for 3 hours), and is preferably 80% by weight or more, more preferably 85 to 99% by weight, and even more preferably 90 to 98% by weight.
  • the method for drying the particulate hydrogel is not particularly limited, but examples include heat drying, hot air drying, reduced pressure drying, fluidized bed drying, stirring drying, infrared drying, microwave drying, drum dryer drying, azeotropic dehydration with a hydrophobic organic solvent, and high humidity drying using high-temperature water vapor.
  • stirring drying is preferred from the viewpoint of improving drying efficiency and shape retention.
  • the pulverization step is a step of pulverizing the particulate dried polymer obtained through the drying step, or the granules or agglomerates obtained in the granulation step described below, or a dried product thereof (dried granules) to obtain a desired particle size and particle shape.
  • the grinding step after the formation of granules or aggregates of primary particles of the water-absorbent resin refers to, for example, a grinding step after the formation of granules or aggregates in a granulation step described below, and preferably refers to a grinding step of dried granules obtained by further drying after the formation of granules or aggregates in a granulation step described below.
  • the method for producing a water-absorbent resin according to one embodiment of the present invention may include, for example, in the case of aqueous solution polymerization, a plurality of pulverization steps, for example, a pulverization step in which a dried polymer obtained by drying a particulate hydrogel obtained in the polymerization step and/or gel pulverization step is pulverized, and a pulverization step in which a fine powder obtained from the particulate water-absorbent resin obtained by the pulverization step is granulated and dried to pulverize a dried granulated product.
  • a pulverization step in which a dried polymer obtained by drying a particulate hydrogel obtained in the polymerization step and/or gel pulverization step is pulverized
  • a pulverization step in which a fine powder obtained from the particulate water-absorbent resin obtained by the pulverization step is granulated and dried to pulverize a dried
  • the method for producing a water-absorbent resin according to one embodiment of the present invention may include, for example, a grinding step in which an aggregate of primary particles obtained by multi-stage reversed-phase suspension polymerization, adding an aggregating agent to a gel of primary particles after polymerization, etc., is dried to obtain a dried granulated product.
  • pulverizers can be used in this step, but in one embodiment of the present invention, it is preferable to use a specific roll-type pulverizer because it is easy to adjust the particulate dried polymer or dried granules to an optimal shape.
  • a specific roll-type pulverizer for example, a roll-type pulverizer consisting of a pair of rolls, in which at least one of the pair of rolls has a groove (longitudinal groove) extending parallel to the roll rotation direction on the surface, is used.
  • the particulate dried polymer or dried granules By passing the particulate dried polymer or dried granules through the clearance between the pair of rolls provided in this specific roll-type pulverizer, the particulate dried polymer or dried granules is compressed, sheared or compacted between the rolls, thereby pulverizing the particulate dried polymer or dried granules.
  • specific roll-type pulverizers include a roll granulator (manufactured by Nippon Granulator Co., Ltd.), a roll granulator (manufactured by Kurimoto Iron Works Co., Ltd.), and a GRAN-U-LIZER (manufactured by MPE Co., Ltd.).
  • rolls that have no grooves on the surface of either roll, or rolls that have grooves but that run perpendicular to the direction of roll rotation are not preferred because they result in many smooth surfaces on the surface of the water-absorbent resin after grinding.
  • the grinding device used in the grinding step before forming granules or aggregates of primary particles of the water absorbent resin for example, the grinding step performed before granulation, in which the particulate hydrogel obtained in the polymerization step and/or gel grinding step is dried to grind the dried polymer, is not particularly limited, and may be a grinding device other than the specific roll-type grinding device, but it is more preferable to select the specific roll-type grinding device (e.g., roll granulator).
  • FIG. 3 A schematic diagram of the specific roll-type grinding device used in the grinding process in one embodiment of the present invention is shown in FIG. 3.
  • the roll-type grinding device 200 is provided with a pipe 201 for supplying particulate dried polymer or dried granulated material to the device 200, an inlet 202 for supplying the dried polymer or dried granulated material into the device 200, and a pair of rolls 203 for grinding the supplied dried polymer or dried granulated material. These are arranged in this order in a direction from top to bottom. Note that the "direction from top to bottom” is not limited to the vertical direction, but is a concept that may also include an oblique direction.
  • the pair of rolls 203 is composed of two rolls 203a and 203b.
  • At least one pair (two rolls) of rolls may be provided, and for example, two pairs (four rolls) or more of rolls may be provided lined up in the vertical direction.
  • two pairs of rolls are arranged vertically, the dried polymer or dried granules are crushed by passing between the upper pair of rolls, and then crushed by passing between the lower pair of rolls.
  • the dried polymer or dried granulated material 20a fed between the rolls 203 passes between the rolls 203a and 203b of the pair of rolls 203, and is made into water-absorbent resin 20b, which is a pulverized product of the dried polymer or dried granulated material.
  • the roll-type pulverizing device 200 may be provided with a feeder between the feed port 202 and the pair of rolls 203 for quantitative supply.
  • the specific roll-type grinding device has grooves (uneven pattern) on the surface of at least one of the pair of rolls.
  • groove means unevenness on the roll surface, and in one embodiment of the present invention, means grooves arranged in a striped pattern.
  • the grooves are arranged in a row in the roll width direction (the direction of the rotation axis of the roll). That is, in the roll-type grinding device, at least one of the pair of rolls has a plurality of grooves (vertical grooves) arranged in a row in the roll width direction, which extend parallel to the roll rotation direction. Therefore, unevenness (concave and convex parts) is formed on the roll surface, extending parallel to the roll rotation direction.
  • the clearance between the pair of rolls does not substantially change due to the rotation of the rolls at any position in the roll width direction. Since the clearance between the rolls does not change at any position in the roll width direction, it is possible to apply an appropriate force to the dried polymer or dried granulated material passing between the rolls, and it is presumed that the particle size of the resulting ground product is uniform and a ground product having a sharp particle size distribution is obtained.
  • "clearance between the rolls” means the distance between a pair of opposing rolls.
  • grooves are provided on each of the two roll surfaces of a pair of rolls.
  • the clearance between the rolls can be made constant at any position in the roll width direction by meshing corresponding irregularities provided on the roll surfaces of the two rolls, and this makes it possible to apply a constant force to the dried material being pulverized. Therefore, it is presumed that, particularly in pulverizing aggregates of primary particles of the dried material or granulated products, the particle size of the pulverized product obtained is more likely to be uniform, and pulverized products with a sharper particle size distribution can be obtained.
  • the pair of rolls may be the same shape (groove shape, diameter) or different shapes, but it is preferable to use rolls of the same shape (including symmetrical relationship).
  • the roll type grinding device 200 has grooves (concave and convex portions) that extend parallel to the roll rotation direction on the roll surface of both of the pair of rolls 203. That is, as shown by 2001 in FIG. 4, both of the pair of rolls 203 (rolls 203a, 203b) have concave and convex portions on their roll surfaces that extend parallel to the roll rotation direction of the roll rotation axis A of the roll.
  • the convex portions provided on the roll surface of one of the pair of rolls are configured to mesh with the concave portions provided on the roll surface of the other of the pair of rolls upon rotation.
  • one of the pair of rolls 203 (e.g., roll 203a) has grooves on the roll surface that extend parallel to the roll rotation direction of the roll rotation axis A, and the other of the pair of rolls (e.g., roll 203b) has a smooth surface (flat surface) with no grooves on the roll surface.
  • the clearance between the rolls will be explained based on 2001 in FIG. 4 and 2002 in FIG. 4.
  • the clearance d is a constant value d at any position in the roll width direction.
  • the clearance d has a maximum value (dmax) and a minimum value (dmin) depending on the position in the roll width direction.
  • the grooves provided on the rolls are formed to extend parallel to the roll rotation direction, so they do not substantially change with the rotation of the rolls.
  • horizontal grooves grooves extending in the roll width direction
  • convex parts extending in the roll width direction may be formed in parts of the roll.
  • Such grooves or convex parts cause cutouts in parts of the vertical grooves of the roll.
  • the presence of some cutout parts formed in the vertical grooves of the roll causes changes in the clearance at any position in the roll width direction.
  • not substantially changing with the rotation of the roll includes “not changing the clearance over 70% or more of the length range of one rotation of the roll, preferably over 80% or more of the length range, more preferably over 90% or more of the length range, and even more preferably over 95% or more of the length range.” Therefore, even if there are cutout parts in some of the vertical grooves of the roll, if the above regulations are met, it is considered to be “not substantially changing with the rotation of the roll.”
  • the clearance d is the same at any position in the roll width direction, whereas in the embodiment of 2002 in FIG. 4, the clearance d differs depending on the position in the roll width direction. In the present invention, even if the clearance d differs depending on the position in the roll width direction, it is sufficient that the clearance d does not substantially change at any position due to the rotation of the roll.
  • the grooves are provided in a shape that extends substantially parallel (0 degrees) to the roll rotation direction.
  • substantially parallel means that grooves that are inclined at less than ⁇ 1° to the roll rotation direction are included in the configuration of the present invention.
  • the inclination angle may be either positive or negative with respect to the roll rotation direction.
  • the minimum clearance value dmin between the rolls is not particularly limited, but is preferably greater than 0 and equal to or less than 3 mm.
  • the minimum clearance value dmin between the rolls is more preferably 0.05 mm to 3 mm, even more preferably 0.05 mm to 2.5 mm, even more preferably 0.1 mm to 2 mm, particularly preferably 0.1 mm to 1.5 mm, and most preferably 0.2 mm to 1 mm.
  • the clearance d is regarded as the minimum clearance value dmin.
  • the clearance difference is not particularly limited, but is preferably 0 to 0.2 mm, more preferably 0 to 0.1 mm, and even more preferably 0 to 0.05 mm.
  • the pitch (spacing) of the grooves on the roll can be determined according to the size of the particles to be crushed. It is preferable to select a large groove pitch when the crushed particle size is large, and a small groove pitch when the crushed particle size is small.
  • the groove pitch is not particularly limited, but is preferably 0.1 mm to 2 mm, more preferably 0.2 mm to 1.5 mm, and even more preferably 0.3 mm to 1.2 mm.
  • the groove pitch p means the spacing between the crest of any groove and the crest of the adjacent groove, or the spacing between the valley of any groove and the valley of the adjacent groove, as shown in 2001 in FIG. 4.
  • a flat portion when a surface parallel to the circumferential direction (hereinafter referred to as a "flat portion") is provided between the crest and valley of the groove, it means the spacing between the crest and crest of adjacent grooves, including the flat portion, or the spacing between the valley of adjacent grooves.
  • the groove pitch may be different on one roll, but is preferably constant across the entire roll width. When grooves are provided on both of a pair of rolls, it is preferably constant across the entire pair of rolls.
  • the height of the groove is not particularly limited, but is preferably 0.1 mm to 2 mm, more preferably 0.2 mm to 1.5 mm, and even more preferably 0.3 mm to 1 mm.
  • the height of the groove means the difference in height between the apex of the crest of any groove and the bottom of the valley of that groove, as shown in 2001 in Figure 4.
  • the dried polymer or dried granules obtained in the drying process or the like and subjected to the pulverization process may be pulverized in its entirety in a pulverizer, preferably the specific roll-type pulverizer, but depending on the shape of the dried polymer or dried granules, they may be subjected to another process, for example, a rough crushing process, or may be subjected to a classification process before being pulverized in the pulverizer.
  • the "rough crushing process” refers to a process for loosening (disintegrating) aggregated particles.
  • the dried polymer or dried granules when the dried polymer or dried granules are aggregated in a block shape or the like, the dried polymer or dried granules may be roughly crushed in advance in order to efficiently perform pulverization in a pulverizer, preferably the specific roll-type pulverizer.
  • the particle size distribution of the dried polymer or dried granules fed into the grinding device is such that the proportion of particles with a diameter of 850 ⁇ m or more (the proportion of particles that did not pass through a sieve with an opening diameter of 850 ⁇ m) in 100% by mass of the dried polymer or dried granules is preferably 50% by mass or less, more preferably 45% by mass or less, and even more preferably 40% by mass or less (the lower limit is 0% by mass).
  • the proportion of particles with a diameter of 1400 ⁇ m or more (the proportion of particles that did not pass through a sieve with an opening diameter of 1400 ⁇ m) in 100% by mass of the dried polymer or dried granules is preferably 40% by mass or less, more preferably 35% by mass or less, and even more preferably 30% by mass or less (the lower limit is 0% by mass).
  • the resin solid content of the dried polymer or dried granules subjected to the pulverization step is, for example, preferably 80 to 99% by mass, more preferably 90 to 98.8% by mass, and even more preferably 95 to 98.5% by mass. That is, the moisture content of the dried polymer or dried granules of the present invention is preferably 1 to 20% by mass, more preferably 1.2 to 10% by mass, and even more preferably 1.5 to 5% by mass.
  • the size and hardness of the aggregates formed by the dried polymer or dried granules can be adjusted to be suitable for pulverization in the pulverization step, and the generation of particles with crushed flat surfaces exposed in the obtained pulverized product can be suppressed. Particles with exposed flat surfaces tend to easily slide and penetrate between the fibers of the water-permeable substrate in the absorbent article, and it is preferable to suppress the generation of such particles.
  • the method for determining the resin solid content of the dried polymer or dried granules is as explained in "(3-4) Drying step".
  • the relationship between the clearance between the pair of rolls and the mass average particle size of the dried polymer or dried granules fed to the roll-type grinding device is preferably 1:0.3 to 1:10.
  • a pressure suitable for breaking down agglomerates formed by the primary particles of the dried polymer or dried granules is applied to the dried polymer or dried granules during grinding, and the generation of particles with crushed, flat surfaces exposed, can be suppressed.
  • the relationship between the clearance between the pair of rolls and the mass average particle size of the dried polymer or dried granules fed to the roll-type grinding device is more preferably 1:0.5 to 1:5, and even more preferably 1:0.9 to 1:3.
  • the water absorbent resin for example, water absorbent resin powder
  • the particle size adjustment method in the classification step is not particularly limited, and examples thereof include sieve classification using a JIS standard sieve (JIS Z8801-1 (2000)) and air flow classification.
  • the water-absorbent resin (for example, water-absorbent resin powder) obtained through the pulverization step (and any subsequent step) is preferably surface-cross-linked with a surface cross-linking agent.
  • the surface cross-linking is a treatment for providing a portion with high cross-linking density in the surface layer of the water-absorbent resin (a region from the surface of the water-absorbent resin to the interior of the resin by several tens of ⁇ m). By carrying out the surface cross-linking treatment, various water-absorbing properties can be improved.
  • the water-absorbent resin also includes a surface-cross-linked water-absorbent resin.
  • the surface cross-linking agent used in this step is not particularly limited, but may be, for example, an organic or inorganic surface cross-linking agent. Among them, from the viewpoint of improving the physical properties of the water-absorbent resin and the handling of the surface cross-linking agent, an organic surface cross-linking agent that reacts with a carboxyl group is preferred. For example, one or more surface cross-linking agents disclosed in U.S. Patent No. 7,183,456 may be mentioned.
  • polyhydric alcohol compounds epoxy compounds, haloepoxy compounds, polyvalent amine compounds, condensates of polyvalent amine compounds and haloepoxy compounds, oxazoline compounds, oxazolidinone compounds, polyvalent metal salts, alkylene carbonate compounds, cyclic urea compounds, etc. may be mentioned.
  • the method for producing a water-absorbent resin according to one embodiment of the present invention preferably includes a granulation step for obtaining aggregates of primary particles.
  • aggregates of primary particles can be obtained by performing multiple reversed-phase suspension polymerizations and adding a flocculant to the gel of primary particles after polymerization. Therefore, these processes can be said to be granulation processes.
  • the granulation process may involve adding an aqueous liquid to fine powder of water-absorbent resin, for example, fine particles of water-absorbent resin that pass through a JIS standard sieve with 150 ⁇ m openings, and stirring and mixing the liquid.
  • water-absorbent resin for example, fine particles of water-absorbent resin that pass through a JIS standard sieve with 150 ⁇ m openings
  • the average particle size of the water-absorbent resin fine powder is preferably within the range of 150 ⁇ m to 10 ⁇ m.
  • the content of fine powder having a particle size of 150 ⁇ m or less relative to the total amount of the water-absorbent resin fine powder is preferably 70 mass% or more, and more preferably 90 mass% or more.
  • the temperature when mixing the aqueous liquid with the water-absorbent resin fine powder is usually 40°C or higher, preferably 50°C or higher, more preferably 60°C or higher, and even more preferably 70°C or higher.
  • the upper limit of the temperature when mixing the aqueous liquid with the water-absorbent resin fine powder is below the boiling point of the aqueous liquid.
  • the boiling point may be adjusted in various ways by adding salts or other solvents, changing the pressure (reduced or increased pressure), etc., but since there is no significant change even if the temperature exceeds 100°C, it is usually preferable to keep it below 100°C.
  • the amount of the aqueous liquid added is preferably less than 100 parts by mass, more preferably 80 parts by mass or less, and is preferably 10 parts by mass or more, more preferably 15 parts by mass or more, and even more preferably 20 parts by mass or more, relative to 100 parts by mass of the water-absorbent resin fine powder.
  • the heated aqueous liquid and the water-absorbent resin fine powder are preferably mixed at high speed.
  • high speed mixing refers to mixing in which the time from the contact of the aqueous liquid with the water-absorbent resin fine powder to the generation of a hydrous gel-like granule is short.
  • the mixing time is short, the aqueous liquid and the fine powder can be mixed uniformly, and it is possible to prevent the mixture from becoming a giant gel-like product integrated with the fine powder.
  • the mixing time is short, it is possible to prevent a decrease in the performance of the water-absorbent resin, such as an increase in the water-soluble content of the obtained water-absorbent resin and a decrease in the water absorption capacity under pressure.
  • the time from the contact of the aqueous liquid with the water-absorbent resin fine powder to the generation of a hydrous gel-like granule is preferably 3 minutes or less, more preferably 1 minute or less.
  • the time for adding the aqueous liquid is also preferably short, preferably 60 seconds or less, more preferably 30 seconds or less, and most preferably 10 seconds or less.
  • the mixer used, so long as the aforementioned high-speed mixing can be achieved.
  • a mechanical agitation type mixer is preferred.
  • Specific examples include the Turbulizer (manufactured by Hosokawa Micron Corporation), the Loedige Mixer (manufactured by Loedige Corporation), and the Mortar Mixer (manufactured by Nishinippon Shikenki Co., Ltd.).
  • Turbulizer manufactured by Hosokawa Micron Corporation
  • the Loedige Mixer manufactured by Loedige Corporation
  • the Mortar Mixer manufactured by Nishinippon Shikenki Co., Ltd.
  • Either a batch type mixer or a continuous type mixer may be used. If the processing volume is small, a small food processor or the like may be used.
  • hydrogel-like granules are preferably further dried to obtain dried granules with improved granulation strength.
  • the fine powder is more firmly integrated and the aggregate shape of the primary particles is maintained.
  • the same drying conditions as in (3-4) above can be applied.
  • the term "hydrogel-like granules" as used herein includes both the hydrogel-like granules obtained in the case of aqueous solution polymerization and the aggregates of primary particles obtained in the case of reversed-phase suspension polymerization.
  • the method for producing a water-absorbent resin according to one embodiment of the present invention includes a granulation step, and more preferably includes a crushing step in which the water-absorbent resin obtained in the granulation step is crushed using the specific roll-type crushing device described above. This makes it possible to produce a water-absorbent resin that has good resistance to penetration between fibers of a water-permeable substrate.
  • the method for producing a water-absorbent resin according to one embodiment of the present invention may include, in addition to the above-mentioned steps, a water-containing (rewetting) step, a step of adding other additives, a granulation step, and a fine powder reuse step, if necessary.
  • the method may further include a transport step, a storage step, a packaging step, a keeping step, and the like.
  • This step is a step of adding at least one kind of additive selected from the group consisting of a polyvalent metal salt, a cationic polymer, a chelating agent, an inorganic reducing agent, and an ⁇ -hydroxycarboxylic acid compound to the water absorbent resin (e.g., water absorbent resin particles) obtained in the surface cross-linking step.
  • a polyvalent metal salt e.g., a cationic polymer
  • a chelating agent e.g., an inorganic reducing agent
  • an ⁇ -hydroxycarboxylic acid compound e.g., water absorbent resin particles
  • the additive is preferably added to the water-absorbent resin (e.g., water-absorbent resin particles) as an aqueous solution or dispersion (slurry).
  • the additive may be added and mixed simultaneously with the above-mentioned surface cross-linking agent solution.
  • additives other than the additives described above may be added to impart various functions to the water-absorbent resin.
  • the other additives include surfactants, compounds having phosphorus atoms, oxidizing agents, organic reducing agents, water-insoluble inorganic fine particles, organic powders (e.g., metal soaps, etc.), deodorants, antibacterial agents, pulp, thermoplastic fibers, etc.
  • the water-insoluble inorganic fine particles disclosed in "[5] Water-insoluble inorganic fine particles" of International Patent Publication No. 2011/040530 can be applied to the present invention.
  • water-insoluble inorganic fine particles By adding these water-insoluble inorganic fine particles, appropriate friction occurs between the water-absorbent resin (particles) and the water-permeable substrate, and when used in an absorbent article, the water-absorbent resin is suppressed from penetrating between the fibers of the water-permeable substrate, which is preferable.
  • the water-insoluble inorganic fine particles it is particularly preferable to add silica (silicon dioxide).
  • the water-insoluble inorganic fine particles may also serve as a powdered inorganic flocculant added in the polymerization step or the like, or may be added separately.
  • the “size regulation step” means a step of loosening the water absorbent resin loosely aggregated through the surface cross-linking step to regulate the particle size.
  • This size regulation step includes a fine powder removal step and a classification step subsequent to the surface cross-linking step.
  • the size regulation step is preferably carried out from the viewpoint of regulating the particle size of the water absorbent resin and obtaining stable water absorption properties.
  • the "fine powder reuse step” means a step of supplying the fine powder generated by sieve classification or the like in each step to any of the steps as it is or after granulating the fine powder.
  • the fine powder reuse step is preferably carried out from the viewpoint of reducing production loss of the water absorbent resin.
  • water-absorbent resin The uses of the water-absorbent resin according to one embodiment of the present invention are not particularly limited, but are preferably used as absorbents in absorbent articles such as paper diapers (for infants and adults), sanitary napkins, incontinence pads, etc.
  • the water-absorbent resin can be suitably used as an absorbent for paper diapers that include a water-absorbent resin and a water-permeable substrate.
  • absorbent articles include, for example, soil water retention agents, seedling sheets, seed coating materials, condensation prevention sheets, drip absorbents, freshness-preserving materials, disposable hand warmers, cooling bandanas, ice packs, medical waste liquid solidifying agents, residual soil solidifying materials, water damage prevention waste liquid gelling agents, water-absorbing sandbags, disaster-use portable toilets, poultice materials, thickeners for cosmetics, water-stopping materials for electrical and electronic materials and communication cables, gasket packing, sustained-release agents for fertilizers, various sustained-release agents (space disinfectants, air fresheners, etc.), pet sheets, cat litter, wound protection dressing materials, condensation prevention building materials, oil moisture removers, paints, adhesives, resin additives (anti-blocking agents, light diffusing agents, matting agents, additives for decorative panels, additives for artificial marble, additives for toners, etc.), and the like.
  • An absorbent article includes, in this order, a liquid-impermeable back sheet, an absorbent body containing a poly(meth)acrylic acid (salt)-based water-absorbent resin having a resistance to penetration between fibers of 60% by weight or more in the water-permeable substrate and a water-permeable substrate, and a liquid-permeable top sheet.
  • the liquid-impermeable back sheet can be any known sheet that can be used as a liquid-impermeable sheet constituting an absorbent article, and is not particularly limited.
  • the liquid-impermeable back sheet can be, for example, a thin plastic film such as a polyethylene film.
  • a breathable film is more preferable in order to provide comfort to the user of the absorbent article.
  • the liquid-permeable top sheet may be any known sheet that can be used as a liquid-permeable sheet constituting an absorbent article, and is not particularly limited.
  • the liquid-permeable top sheet is usually a nonwoven fabric, and may be, for example, an air-through nonwoven fabric, a point-bonded nonwoven fabric, a spunbonded nonwoven fabric, a spunlace nonwoven fabric, a melt-blown nonwoven fabric, an air-laid nonwoven fabric, or a laminate of two or more nonwoven fabrics selected from these. Examples of laminates of two or more nonwoven fabrics include spunbond/melt-blown/spunbond (SMS) nonwoven fabric, spunbond/melt-blown/melt-blown/spunbond (SMMS) nonwoven fabric, etc.
  • SMS spunbond/melt-blown/spunbond
  • SMMS spunbond/melt-blown/melt-blown/spunbond
  • the material constituting the liquid-permeable top sheet is not particularly limited, and examples include synthetic fibers such as polypropylene, polyethylene, and polyester. These materials may be used alone or in combination of two or more. In addition, it is preferable that these synthetic fibers are hydrophilized with a surfactant.
  • the absorbent includes the above-mentioned water-absorbent resin and water-permeable substrate.
  • Typical absorbent structures include, for example, a structure in which water-absorbent resin particles and water-permeable substrate are uniformly mixed, a structure in which water-absorbent resin particles are sandwiched between sheet-shaped water-permeable substrates or fibrous water-permeable substrates formed in layers, and the like.
  • a structure in which the water-absorbent resin is not present inside the water-permeable substrate is preferred. That is, a structure in which the above-mentioned water-absorbent resin and the water-permeable substrate each form a layer is preferred.
  • the water-absorbent resin layer and the water-permeable substrate layer may each form one layer, or at least one of them may form multiple layers, and the water-absorbent resin layer and the water-permeable substrate layer may be alternately laminated.
  • the "water-permeable substrate layer” is intended to include a water-permeable substrate layer made of a sheet-shaped water-permeable substrate and a water-permeable substrate layer made of a fibrous water-permeable substrate formed in layers.
  • preferred configurations include a configuration in which a water-absorbent resin layer is disposed on a water-permeable substrate layer made of a sheet-like water-permeable substrate, a configuration in which a water-absorbent resin layer is disposed on a water-permeable substrate layer made of a fibrous water-permeable substrate formed in a layered form, a configuration in which the water-permeable substrate layer is disposed on a water-absorbent resin layer, and a configuration in which a water-absorbent resin layer is sandwiched between a plurality of the water-permeable substrate layers.
  • a nonwoven fabric can be used as the sheet-like water-permeable substrate.
  • it may be an air-through nonwoven fabric, a point-bonded nonwoven fabric, a spunbonded nonwoven fabric, a spunlace nonwoven fabric, a melt-blown nonwoven fabric, an air-laid nonwoven fabric, or a laminate of two or more nonwoven fabrics selected from these.
  • laminates of two or more nonwoven fabrics include spunbond/melt-blown/spunbond (SMS) nonwoven fabrics and spunbond/melt-blown/melt-blown/spunbond (SMMS) nonwoven fabrics.
  • the material constituting the sheet-like water-permeable substrate is not particularly limited, and examples include synthetic fibers such as polypropylene, polyethylene, and polyester. These materials may be used alone or in combination of two or more. In addition, it is preferable that these synthetic fibers are hydrophilized with a surfactant.
  • the weight per unit area of the sheet-like water-permeable substrate is preferably 30 g/ m2 or more as a lower limit, more preferably 40 g/m2 or more as a higher limit, and is preferably 100 g/m2 or less, more preferably 50 g/m2 or less as an upper limit.
  • fibrous water-permeable substrate examples include pulp fiber, cotton linter cross-linked cellulose fiber, rayon, cotton, wool, acetate, vinylon, etc.
  • the fibrous water-permeable substrate may be used alone or in combination of two or more kinds.
  • the amount of the water-absorbent resin used (basis weight) is preferably 50 to 300 g/m 2 , more preferably 100 to 200 g/m 2 , relative to the area of the water-absorbent resin-existing region.
  • the "water-absorbent resin-existing region" refers to the entire region in the absorbent body where the water-absorbent resin is dispersed.
  • the absorbent may contain an additive in addition to the water-absorbent resin and the water-permeable substrate.
  • the additive may be any additive that may be generally contained in absorbents in absorbent articles, and is not particularly limited. Specific examples of the additive include inorganic powders (e.g., amorphous silica), deodorants, pigments, dyes, antibacterial agents, fragrances, and adhesives.
  • the absorbent may contain inorganic powders in addition to the inorganic particles in the water-absorbent resin. Examples of the inorganic powder include silicon dioxide, zeolite, kaolin, and clay.
  • the absorbent article according to one embodiment of the present invention may have a core wrap or three-dimensional gathers that cover at least one surface of the absorbent body in order to maintain the shape of the absorbent body.
  • the core wrap of the absorbent article according to one embodiment of the present invention may be, for example, tissue paper, particularly crepe paper, nonwoven fabric, particularly air-through nonwoven fabric, point-bonded nonwoven fabric, spunbonded nonwoven fabric, spunlace nonwoven fabric, etc., made of synthetic fibers such as polypropylene, polyethylene, polyester, etc.
  • the core wrap may be a composite nonwoven fabric of these.
  • the composite nonwoven fabric include spunbond/meltblown/spunbond (SMS nonwoven fabric) and nonwoven fabrics such as spunbond/meltblown/meltblown/spunbond (SMMS nonwoven fabric). It is preferable that these core wraps are hydrophilized with a surfactant.
  • the thickness of the absorbent body in an absorbent article according to one embodiment of the present invention is preferably 1 mm to 10 mm, and more preferably 1 mm to 5 mm.
  • the thickness of the entire absorbent article according to one embodiment of the present invention is preferably 1.2 mm to 15 mm, and more preferably 1.2 mm to 10 mm.
  • the present invention has the following configuration.
  • a poly(meth)acrylic acid (salt)-based water-absorbing resin according to any one of [1] to [3], which contains water-insoluble inorganic fine particles.
  • the water-permeable substrate is a sheet-shaped water-permeable substrate,
  • 0.2 g of the water-absorbent resin was placed in a nonwoven bag, and then immersed in a large excess of 0.90% by mass sodium chloride aqueous solution for 30 minutes to allow free swelling. The bag was then removed and hung for 10 minutes to drain, after which the water absorption capacity (unit: g/g) was determined.
  • AAP Absorption capacity under pressure
  • Moisture content of water-absorbent resin The moisture content of the water-absorbent resin was measured according to the EDANA method (ERT430.2-02). Note that, during the measurement, the mass of the sample (water-absorbent resin) was changed to 1.0 g, the drying temperature was changed to 180° C., and the drying time was changed to 3 hours.
  • sample water-absorbent resin
  • total mass W1 (g) of the sample and aluminum cup was then accurately weighed.
  • the sample was placed in an aluminum cup and left to stand in an oven set at an atmospheric temperature of 180° C. After 3 hours, the sample was removed from the oven together with the aluminum cup, and the total mass W2 (g) of the dried sample and aluminum cup was accurately weighed.
  • the mass of the sample (water-absorbent resin) used in this measurement was M (1.0 g)
  • Mass average particle diameter (D50) of water absorbent resin The mass-average particle diameter (D50) of the water-absorbent resin was measured according to the method described in “(3) Mass-Average Particle Diameter (D50) and Logarithmic Standard Deviation ( ⁇ ) of Particle Diameter Distribution” in columns 27 and 28 of U.S. Pat. No. 7,638,570.
  • Water absorption rate of water-absorbent resin 0.02 parts by mass of edible blue No. 1, a food additive, was added to 1000 parts by mass of a 0.90% by mass aqueous solution of sodium chloride (physiological saline), and the liquid temperature was adjusted to 30° C. 50 ml of physiological saline was measured into a 100 ml beaker, and 2.0 g of water-absorbent resin was added at once while stirring at 600 rpm using a cylindrical stirrer tip with a length of 40 mm and a cross section perpendicular to the length direction and a magnetic stirrer. The time until the water-absorbent resin absorbed the physiological saline and covered the stirrer tip was calculated as the water absorption rate (seconds).
  • a nonwoven fabric cut to 6 cm x 9 cm was fixed to the bottom of a rectangular polystyrene case (bottom surface 6 cm x 9 cm, depth 1 cm (both dimensions of the inner surface of the case)) with double-sided tape.
  • the nonwoven fabric (3 mm thick, 41 g/ m2 weight per unit area, made of a mixture of polyethylene, polypropylene, and polyethylene terephthalate, the fiber diameter of the polyethylene and the fiber diameter of the polypropylene are 0.18 mm, and the fiber diameter of the polyethylene terephthalate is 0.27 mm) was cut to 6 cm x 9 cm.
  • the nonwoven fabric was fixed to the bottom of the rectangular polystyrene case (bottom surface 6 cm x 9 cm, depth 1 cm (both dimensions of the inner surface of the case) with double-sided tape.
  • 1.0 g of water-absorbing resin was uniformly sprayed over the entire surface of the air-through nonwoven fabric.
  • the nonwoven fabric with the water-absorbing resin sprayed thereon was turned upside down on a tray with a base area larger than that of the case, and the water-absorbing resin that had fallen onto the tray was collected.
  • the collected water-absorbing resin is the water-absorbing resin that did not penetrate between the fibers of the nonwoven fabric.
  • the penetration resistance between the fibers of the water-permeable substrate was calculated according to the following formula (1).
  • FIG. 1 is a view of absorbent sheet 100 as seen from directly above, and 1002 in Fig. 1 is a cross-sectional view of absorbent sheet 100 cut perpendicular to the X-Y plane and parallel to the X-axis or Y-axis.
  • 0.5 g of water-absorbent resin 1 was uniformly sprayed onto an area surrounded by four sides located 1 cm inward from each end of the four sides on the adhesive surface of adhesive tape 2 (vinyl tape No. 21S made by NITTO DENKO) cut to 10 cm x 11 cm.
  • a nonwoven fabric 3 (3 mm thick, 41 g/ m2 basis weight, air-through nonwoven fabric made of a mixture of polyethylene, polypropylene, and polyethylene terephthalate, the fiber diameters of the polyethylene and polypropylene being 0.18 mm, and the fiber diameter of the polyethylene terephthalate being 0.27 mm) was placed with the same area as the area where the water-absorbent resin was sprayed, i.e., 8 cm x 9 cm.
  • the thickness of the nonwoven fabric was measured using a large-type dial thickness gauge (thickness gauge) (manufactured by Ozaki Manufacturing Co., Ltd., model number: J-B, gauge head: anvil top and bottom ⁇ 50 mm).
  • the upper gauge head of the thickness gauge was brought close to a height position of 2 to 3 mm from the nonwoven fabric, and then the handle was slowly released so as to apply as little pressure as possible to the nonwoven fabric, and the thickness of the nonwoven fabric was measured.
  • the monomer aqueous solution (1) was stirred continuously, and when the temperature of the monomer aqueous solution (1) reached 78°C, 15.8 g of a 3.8 wt% aqueous solution of sodium persulfate was added. After that, the monomer aqueous solution (1) was immediately poured into a stainless steel vat-type reactor (bottom surface: 340 x 340 mm, height: 25 mm, inner surface: Teflon (registered trademark) coating), and the polymerization reaction started shortly thereafter.
  • a hot plate (NEO HOTPLATE HI-1000/Iuchi Seiei-do Co., Ltd.) was installed under the stainless steel vat-type reactor, and the inner surface temperature of the vat was preset to 50°C.
  • reaction liquid (1) gelled while generating water vapor, and the resulting gel expanded in all directions while foaming, and then contracted. This expansion and contraction ended in about 1 minute.
  • the product was then held in the reactor for 3 minutes to obtain a hydrogel-like crosslinked polymer (1). This series of operations was carried out in an open-air system.
  • the obtained hydrogel-like cross-linked polymer (1) was gel-pulverized using a meat chopper (No. 32 type/manufactured by Hiraga Manufacturing Co., Ltd.) equipped with a die having a die hole diameter of 9.5 mm to obtain a particulate hydrogel-like cross-linked polymer (1).
  • the gel-pulverization was performed by feeding 2.4 (kg/min) of the hydrogel-like cross-linked polymer (1) and 5.0 (kg/h) of steam into the meat chopper with the screw shaft rotation speed of the meat chopper set to 130 rpm.
  • the obtained particulate hydrogel-like crosslinked polymer (1) was dried using a cylindrical container rotary dryer. Specifically, the rotary container of the cylindrical container rotary dryer was rotated at 75 rpm in an atmosphere at a temperature of 200°C, and the particulate hydrogel-like crosslinked polymer (1) was supplied to the cylindrical container rotary dryer and dried until the moisture content reached 2% by mass, thereby obtaining a dried polymer (1).
  • the dried polymer (1) was pulverized using a roll mill (WML type roll pulverizer/manufactured by Inokuchi Giken Co., Ltd.) as a pulverizing device to obtain a water absorbent resin powder (1).
  • a roll mill WML type roll pulverizer/manufactured by Inokuchi Giken Co., Ltd.
  • a pair of rolls was installed in the first stage, and one-stage pulverization was performed. Note that, as the pair of rolls, a groove having a V-shaped cross section was provided on the roll surface of each of the rolls in a direction approximately perpendicular to the roll rotation direction was used.
  • one groove was provided continuously from one end of the roll to the other end (i.e., continuously in the roll width direction), and multiple grooves were provided continuously in a row at equal intervals around the entire circumference.
  • the roll grooves (groove tooth shape) of the pair of rolls were the same for both. Note that the clearance between the rolls means the distance between the two rolls.
  • the water-absorbent resin powder (1) was classified using a JIS standard sieve with a mesh size of 150 ⁇ m, and water-absorbent resin fine powder (1) that passed through the sieve was obtained. Next, 30 parts by mass of the water-absorbent resin fine powder (1) was placed in a food processor, and 20 parts by mass of 90°C ion-exchanged water was added over 5 seconds while stirring, and further stirred for 10 seconds to obtain hydrous gel-like granulated material (1). Thereafter, the obtained hydrous gel-like granulated material (1) was dried again under the same conditions using the cylindrical container rotary dryer until the moisture content reached 2% by mass, and dried granulated material (1) was obtained.
  • the dried granulated material (1) was classified using a JIS standard sieve with a mesh size of 150 ⁇ m, and the dried granulated material (1) remaining on the sieve was pulverized using a roll granulator (manufactured by Nippon Granulator Co., Ltd., roll size: diameter 115 mm x length 100 mm) as a pulverizing device.
  • the pulverized material obtained was further classified using a JIS standard sieve with a mesh size of 150 ⁇ m, and the granulated particles remaining on the sieve were obtained as water-absorbent resin particles (1).
  • a pair of rolls was installed in the first stage, and one-stage pulverization was performed.
  • a groove with a V-shaped cross section was provided on the roll surface in a direction parallel to the roll rotation direction (clearance difference: 0).
  • the grooves were provided around the entire circumference of the roll surface, and a plurality of grooves were provided in a row at equal intervals from one end of the roll to the other end.
  • the pitch (spacing) of the grooves of the pair of rolls was the same for both rolls.
  • the grooves in each roll were arranged so that the peaks of the grooves on one roll and the valleys of the grooves on the other roll were in the same position in the axial direction of the rolls, as shown by 2001 in Figure 4, and the clearance between the rolls was constant.
  • a surface cross-linking agent solution consisting of 0.373 parts by weight of ethylene carbonate, 0.74 parts by weight of propylene glycol, and 2.52 parts by weight of ion-exchanged water was uniformly mixed with 100 parts by weight of the water-absorbent resin particles (1), and the mixture was heat-treated at a temperature of 198°C for 30 minutes. Thereafter, the powder was forcibly cooled to 60°C, and the mixture was passed through a JIS standard sieve with an opening of 850 ⁇ m to size the mixture, thereby obtaining surface-cross-linked water-absorbent resin particles (1).
  • Example 2 800 g of n-heptane was placed in a 2000 mL four-neck separable flask equipped with a stirrer, a reflux condenser, a thermometer, a nitrogen gas inlet tube, and a dropping funnel, and 0.88 g of maleic anhydride-modified ethylene-propylene copolymer (product name: Hiwax (registered trademark) HW2203A/manufactured by Mitsui Chemicals, Inc.) was added and dissolved as a dispersant, and nitrogen gas was blown in to expel the dissolved oxygen.
  • Hiwax registered trademark
  • a dispersion obtained by dispersing 0.092 g of amorphous silica (product name: Reolosil (registered trademark) QS-20, manufactured by Oriental Silicas Corporation) as inorganic fine particles (powdered inorganic flocculant) in 100 g of n-heptane in advance was added to the polymerization slurry liquid, and the mixture was stirred for 10 minutes.
  • the organic solvent was then filtered off by suction filtration, and the residue was air-dried at room temperature overnight to obtain a hydrogel-like crosslinked polymer (2) in the form of an aggregate.
  • the hydrogel-like crosslinked polymer (2) was dried using the same cylindrical container rotary dryer as in Example 1. Specifically, the hydrogel-like crosslinked polymer (2) was supplied to the cylindrical container rotary dryer set at the same temperature and rotation speed as in Example 1, and dried until the water content reached 10% by mass, to obtain a dried polymer (2).
  • the dried polymer (2) was ground under the same grinding conditions as those for grinding the dried granulated material (1) in Example 1, to obtain aggregate-shaped water-absorbent resin particles (2).
  • 100 parts by weight of the water-absorbent resin particles (2) were mixed uniformly with a surface-crosslinking agent solution consisting of 0.003 parts by weight of ethylene glycol diglycidyl ether, 0.385 parts by weight of ethylene carbonate, 0.644 parts by weight of propylene glycol, and 2.6 parts by weight of ion-exchanged water, and the mixture was heated at a temperature of 195°C for 25 minutes, and then the powder temperature was forcibly cooled to 60°C to obtain surface-crosslinked water-absorbent resin particles (2).
  • a surface-crosslinking agent solution consisting of 0.003 parts by weight of ethylene glycol diglycidyl ether, 0.385 parts by weight of ethylene carbonate, 0.644 parts by weight of propylene glycol, and 2.6 parts by weight of ion-exchanged water
  • Comparative Example 1 The water-absorbent resin powder (1) of Example 1 was classified using a JIS standard sieve having an opening of 150 ⁇ m, and comparative water-absorbent resin particles (1) remaining on the sieve were obtained.
  • the comparative water-absorbent resin particles (1) were subjected to the surface cross-linking process and the silica addition process under the same conditions as in Example 1 to obtain a comparative water-absorbent resin (1).
  • the physical properties of the obtained comparative water-absorbent resin (1) are shown in Table 1.
  • the comparative hydrogel-like crosslinked polymer (2) was dried using the same cylindrical container rotary dryer as in Example 1. Specifically, the comparative hydrogel-like crosslinked polymer (2) was supplied to a cylindrical container rotary dryer set at the same temperature and rotation speed as in Example 1, and dried until the moisture content reached 2% by mass, to obtain a comparative dried polymer (2). Then, a pulverization step was carried out under the same conditions as in Example 1, to obtain a comparative water-absorbent resin powder (2). The comparative water-absorbent resin powder (2) was classified using a JIS standard sieve with a mesh size of 150 ⁇ m, to obtain comparative water-absorbent resin particles (2) remaining on the sieve.
  • the comparative water-absorbent resin particles (2) 100 parts by weight of the comparative water-absorbent resin particles (2) were mixed uniformly with a surface-crosslinking agent solution consisting of 0.25 parts by weight of ethylene carbonate, 0.02 parts by weight of ethylene glycol diglycidyl ether, 0.41 parts by weight of propylene glycol, and 1.66 parts by weight of ion-exchanged water, and the mixture was heat-treated at a temperature of 165°C for 30 minutes, and then the powder temperature was forcibly cooled to 60°C, and the mixture was passed through a JIS standard sieve with an opening of 850 ⁇ m for granulation, thereby obtaining surface-crosslinked comparative water-absorbent resin particles (2).
  • a surface-crosslinking agent solution consisting of 0.25 parts by weight of ethylene carbonate, 0.02 parts by weight of ethylene glycol diglycidyl ether, 0.41 parts by weight of propylene glycol, and 1.66 parts by weight of ion-exchange
  • the comparative water-absorbent resin particles (2) were subjected to a silica addition process under the same conditions as in Example 1 to obtain a comparative water-absorbent resin (2).
  • the physical properties of the obtained comparative water-absorbent resin (2) are shown in Table 1.
  • 341 g of acrylic acid, 0.38 g of polyethylene glycol diacrylate (molecular weight 522.66, average number of ethylene oxide units: n 9), 22.16 g of a 0.1 wt % aqueous solution
  • the comparative water-absorbent resin powder (3) was classified using a JIS standard sieve with a mesh size of 150 ⁇ m, and the comparative water-absorbent resin fine powder (3) that had passed through the sieve was subjected to the granulation process and drying process under the same conditions as in Example 1 to obtain a comparative dried granulated material (3).
  • the comparative dried granules (3) were pulverized using a roll mill (WML type roll pulverizer/manufactured by Inokuchi Giken Co., Ltd.) as a pulverizing device, and further classified using a JIS standard sieve with a mesh size of 150 ⁇ m, and the granule-shaped particles remaining on the sieve were obtained as comparative water-absorbent resin particles (3).
  • the pulverization conditions of the roll mill were the same as those for pulverizing the water-absorbent resin powder (1) in Example 1.
  • 100 parts by weight of the comparative water-absorbent resin particles (3) were uniformly mixed with a surface-crosslinking agent solution consisting of 0.018 parts by weight of ethylene glycol diglycidyl ether, 0.20 parts by weight of ethylene carbonate, 0.34 parts by weight of propylene glycol, and 1.04 parts by weight of ion-exchanged water, and the mixture was heated at a temperature of 165°C for 30 minutes, and then forcibly cooled to a powder temperature of 60°C to obtain surface-crosslinked comparative water-absorbent resin particles (3).
  • a surface-crosslinking agent solution consisting of 0.018 parts by weight of ethylene glycol diglycidyl ether, 0.20 parts by weight of ethylene carbonate, 0.34 parts by weight of propylene glycol, and 1.04 parts by weight of ion-exchanged water
  • Comparative Example 4 The same polymerization step as in Example 2 was carried out, and the obtained polymerization slurry liquid was cooled to room temperature, and then the step of adding inorganic fine particles to the polymerization slurry liquid and mixing was not carried out, and the organic solvent was filtered off by suction filtration, and the residue was air-dried at room temperature overnight to obtain a comparative hydrogel-like crosslinked polymer (4). Thereafter, the drying step, the pulverization step, and the surface crosslinking step were carried out under the same conditions as in Example 2 to obtain a surface-crosslinked comparative water-absorbent resin particle (4).
  • Comparative Example 5 The dried polymer (2) obtained in Example 2 was supplied to a roll mill (WML type roll grinder/manufactured by Inokuchi Giken Co., Ltd.) and pulverized under the same pulverization conditions as those for pulverizing the dried granulated material (1) in Example 1, thereby obtaining a comparative water absorbent resin particle (5).
  • a roll mill WML type roll grinder/manufactured by Inokuchi Giken Co., Ltd.
  • Example 3 2 is a view of the absorbent article 101 as seen from directly above, and 1004 is a cross-sectional view of the absorbent article 101 cut perpendicular to the X-Y plane and parallel to the X-axis or Y-axis.
  • a 6 cm x 9 cm nonwoven fabric (3 mm thick, 41 g/m2 basis weight, air-through nonwoven fabric made of a mixture of polyethylene, polypropylene, and polyethylene terephthalate, the fiber diameters of the polyethylene and polypropylene being 0.18 mm, and the fiber diameter of the polyethylene terephthalate being 0.27 mm) was placed on the adhesive surface of an adhesive tape (NITTO DENKO vinyl tape No. 21S) cut to 10 cm x 11 cm, which corresponds to the liquid-impermeable back sheet 5 , in the areas 1 cm from each end in the long side direction and 2 cm inward from each end in the short side direction, i.e., in the area of 6 cm x 9 cm in the center of the adhesive tape.
  • an adhesive tape NITTO DENKO vinyl tape No. 21S
  • Example 1 1.0 g of the water-absorbent resin (1) obtained in Example 1 was uniformly sprayed on the entire surface of the nonwoven fabric.
  • the part sprayed with the water-absorbent resin (1) corresponds to the absorbent body.
  • a 10 cm x 11 cm liquid-permeable nonwoven fabric (airlaid nonwoven fabric, basis weight 46.6 g/ m2 ) corresponding to the liquid-permeable top sheet 7 was placed on the part sprayed with the water-absorbent resin (1), and the adhesive surfaces of the four sides were bonded together to produce an absorbent article (1).
  • Example 4 An absorbent article (2) was produced in the same manner as in Example 3, except that the water-absorbent resin (2) obtained in Example 2 was used instead of the water-absorbent resin (1).
  • Comparative Example 6 A comparative absorbent article (1) was produced in the same manner as in Example 3, except that the comparative absorbent resin (2) obtained in Comparative Example 2 was used instead of the absorbent resin (1).
  • Comparative Example 7 A comparative absorbent article (2) was produced in the same manner as in Example 3, except that the comparative absorbent resin (3) obtained in Comparative Example 3 was used instead of the absorbent resin (1).
  • Comparative Example 8 A comparative absorbent article (3) was produced in the same manner as in Example 3, except that the comparative absorbent resin (4) obtained in Comparative Example 4 was used instead of the absorbent resin (1).
  • Comparative Example 9 A comparative absorbent article (4) was produced in the same manner as in Example 3, except that the comparative absorbent resin (5) obtained in Comparative Example 5 was used instead of the absorbent resin (1).
  • the water-absorbent resin composition according to one embodiment of the present invention can reduce the amount of liquid returning to an absorbent article comprising a water-absorbent resin and a water-permeable substrate, and can provide a water-absorbent resin with excellent liquid retention. Therefore, it can be suitably used in sanitary materials (sanitary products) such as disposable diapers, sanitary napkins, adult incontinence products (incontinence pads), and pet sheets.
  • sanitary materials such as disposable diapers, sanitary napkins, adult incontinence products (incontinence pads), and pet sheets.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Health & Medical Sciences (AREA)
  • Organic Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Engineering & Computer Science (AREA)
  • Vascular Medicine (AREA)
  • Analytical Chemistry (AREA)
  • Epidemiology (AREA)
  • Medicinal Chemistry (AREA)
  • Biomedical Technology (AREA)
  • Heart & Thoracic Surgery (AREA)
  • Polymers & Plastics (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Animal Behavior & Ethology (AREA)
  • General Health & Medical Sciences (AREA)
  • Public Health (AREA)
  • Veterinary Medicine (AREA)
  • Absorbent Articles And Supports Therefor (AREA)

Abstract

To provide a water-absorbing resin with excellent liquid retention that reduces the amount of liquid return in an absorbent article provided with a water-absorbing resin and water-permeable base material and to provide an absorbent article having excellent liquid diffusibility. The problem is solved by using an absorbent article comprising a poly(meth)acrylic acid (salt)-based water-absorbing resin having a resistance to penetration between fibers into a water-permeable base material of 60 wt% or more, a liquid-impermeable back sheet, an absorber containing a water-absorbing resin and a water-permeable base material, and a liquid-permeable top sheet in this order. The water-absorbing resin is a poly(meth)acrylic acid (salt)-based water-absorbing resin having a resistance to penetration between fibers into a water-permeable base material of 60 wt% or more.

Description

ポリ（メタ）アクリル酸（塩）系吸水性樹脂及び吸収性物品Poly(meth)acrylic acid (salt)-based water-absorbent resin and absorbent article
　本発明は、吸水性樹脂及び吸収性物品に関する。より具体的には、本発明は、ポリ（メタ）アクリル酸（塩）系吸水性樹脂及びそれを含む吸収体を備える吸収性物品に関する。 The present invention relates to a water-absorbent resin and an absorbent article. More specifically, the present invention relates to a poly(meth)acrylic acid (salt)-based water-absorbent resin and an absorbent article having an absorbent body containing the same.
　近年、紙オムツ、生理用ナプキン、失禁パット等の衛生材料には、体液吸収の観点から、その構成材に、吸水性樹脂が、吸水剤として幅広く利用されている。このような吸水性樹脂としては、例えば、澱粉－アクリロニトリルグラフト共重合体の加水分解物、澱粉－アクリル酸グラフト重合体の中和物、酢酸ビニル－アクリル酸エステル共重合体のケン化物、（メタ）アクリル酸部分中和物重合体の架橋物等が知られている。これらの中でも、吸水性能の観点から、（メタ）アクリル酸及び／又はその塩を単量体の主成分として用いたポリ（メタ）アクリル酸（塩）系吸水性樹脂が、工業的に最も多く生産されている。 In recent years, water-absorbing resins have been widely used as absorbents in sanitary materials such as paper diapers, sanitary napkins, and incontinence pads from the viewpoint of absorbing bodily fluids. Examples of such water-absorbing resins include hydrolyzates of starch-acrylonitrile graft copolymers, neutralized starch-acrylic acid graft polymers, saponified vinyl acetate-acrylic acid ester copolymers, and crosslinked products of partially neutralized (meth)acrylic acid polymers. Of these, poly(meth)acrylic acid (salt)-based water-absorbing resins that use (meth)acrylic acid and/or its salts as the main monomer component are the most widely produced industrially from the viewpoint of water-absorbing performance.
　かかるポリ（メタ）アクリル酸（塩）系吸水性樹脂に望まれる特性を示すパラメーターとしては、無加圧下吸水倍率（ＣＲＣ）、加圧下吸水倍率（ＡＡＰ）、吸水速度（ＦＳＲ／ｖｏｒｔｅｘ）、無加圧下通液性、加圧下通液性、耐衝撃性、耐尿性、流動性、ゲル強度、耐着色性、粒度等多くのパラメーターが知られている。更に、同じパラメーター、例えば、無加圧下吸水倍率の中でも種々の観点から、数多くのパラメーター測定法が提案されている。これら数多くの特性に着目して開発されてきた吸水性樹脂は、前記数多くの特性（例えば、「無加圧下吸水倍率（ＣＲＣ）」や「加圧下吸水倍率（ＡＡＰ）」等）をコントロールしても、未だ紙オムツ等の吸収体に用いて実使用した場合には、十分な性能を発揮しているとは言い難いという問題があった。 Many parameters are known to indicate the desired characteristics of such poly(meth)acrylic acid (salt)-based water-absorbent resins, such as water absorption capacity without load (CRC), water absorption capacity under load (AAP), water absorption rate (FSR/vortex), liquid permeability without load, liquid permeability under load, impact resistance, urine resistance, fluidity, gel strength, color resistance, and particle size. Furthermore, many methods for measuring the same parameter, such as water absorption capacity without load, have been proposed from various viewpoints. Water-absorbent resins that have been developed with a focus on these many characteristics have a problem in that, even if the many characteristics (such as "water absorption capacity without load (CRC)" and "water absorption capacity under load (AAP)") are controlled, it is still difficult to say that they exhibit sufficient performance when actually used in absorbents such as disposable diapers.
　紙オムツ等の吸収体に用いて実使用した場合に、吸水性樹脂が優れた性能を発揮するには、無加圧下吸水倍率及び加圧下吸収性能を高め、紙オムツの吸収量を高くすることはもちろんであるが、それに加えて、紙オムツでの拡散性、通液性を向上することにより、吸収体の液戻り量を少なくすることができる（特許文献１）。 When actually used in absorbents such as disposable diapers, in order for the water-absorbent resin to exhibit excellent performance, it is necessary to increase the water absorption capacity without pressure and the absorption performance under pressure, and to increase the absorption capacity of the disposable diaper. In addition, by improving the diffusibility and liquid permeability of the disposable diaper, it is possible to reduce the amount of liquid returning to the absorbent (Patent Document 1).
日本国公開特許公報特開２０１５－１０７４８８号公報Japanese Patent Publication No. 2015-107488
　しかしながら、上述のような通液性が改善された吸水性樹脂では、吸水性樹脂及び透水性基材を備える紙オムツ等の吸収性物品に使用した際、依然、吸液対象の液が吸収性物品全体に充分に行き渡らずに、液戻り量が増加する場合があり、液保持性の観点において、改善の余地があった。さらに、上述のような通液性が改善された吸水性樹脂及び透水性基材を備える紙オムツ等の吸収性物品では、依然、吸液対象の液が吸収性物品全体に充分に行き渡らない場合があり、液拡散性の観点において、改善の余地があった。 However, when the water-absorbent resin with improved liquid permeability as described above is used in an absorbent article such as a paper diaper comprising a water-absorbent resin and a water-permeable substrate, the liquid to be absorbed still may not be sufficiently distributed throughout the entire absorbent article, resulting in an increased amount of liquid return, and there is still room for improvement in terms of liquid retention.Furthermore, when the water-absorbent resin with improved liquid permeability as described above is used in an absorbent article such as a paper diaper comprising a water-absorbent resin and a water-permeable substrate, the liquid to be absorbed still may not be sufficiently distributed throughout the entire absorbent article, resulting in an increased amount of liquid return, and there is still room for improvement in terms of liquid diffusion.
　本発明の一態様は、吸水性樹脂及び透水性基材を備える吸収性物品の液戻り量を低減し、液保持性に優れた吸水性樹脂を提供することを目的とする。また、本発明の一態様は、液拡散性に優れた吸収性物品を提供することを目的とする。 One aspect of the present invention aims to provide an absorbent resin that reduces the amount of liquid returning to an absorbent article that includes a water-absorbent resin and a water-permeable substrate and has excellent liquid retention properties. Another aspect of the present invention aims to provide an absorbent article that has excellent liquid diffusion properties.
　本発明の一実施形態に係るポリ（メタ）アクリル酸（塩）系吸水性樹脂は、
　下記（１）～（３）の手順により決定される、透水性基材に対する繊維間への侵入抵抗性が６０重量％以上である、ポリ（メタ）アクリル酸（塩）系吸水性樹脂である：
　（１）いずれもケース内面の寸法で、底面６ｃｍ×９ｃｍ、深さ１ｃｍの、ポリスチレン製の直方体のケースの底面に、６ｃｍ×９ｃｍに切り取った不織布を両面テープで固定する
　　ここで、前記不織布は、厚み３ｍｍ、目付量４１ｇ／ｍ２であり、ポリエチレン、ポリプロピレン及びポリエチレンテレフタレートの混合物製のエアスルー不織布であって、ポリエチレンの繊維径及びポリプロピレンの繊維径は０．１８ｍｍ、ポリエチレンテレフタレートの繊維径は０．２７ｍｍである；
　（２）吸水性樹脂１．０ｇを、前記不織布の全面に均一に散布し、前記ケースよりも底面積が大きい受け皿の上で、前記吸水性樹脂を散布した前記不織布をケースごと逆さにし、前記受け皿上に脱落した吸水性樹脂を回収する；
　（３）下記式（１）に従い、透水性基材に対する繊維間への侵入抵抗性を算出する
透水性基材に対する繊維間への侵入抵抗性［重量％］＝回収した吸水性樹脂の重量［ｇ］／散布した吸水性樹脂の重量［ｇ］×１００　式（１）。 The poly(meth)acrylic acid (salt)-based water absorbent resin according to one embodiment of the present invention is
The present invention is a poly(meth)acrylic acid (salt)-based water-absorbing resin having a resistance to penetration between fibers of a water-permeable substrate of 60% by weight or more, which is determined by the following steps (1) to (3):
(1) A nonwoven fabric cut to 6 cm x 9 cm is fixed with double-sided tape to the bottom of a rectangular polystyrene case having a bottom of 6 cm x 9 cm and a depth of 1 cm, both of which are the dimensions of the inner surface of the case. Here, the nonwoven fabric is an air-through nonwoven fabric made of a mixture of polyethylene, polypropylene and polyethylene terephthalate, with a thickness of 3 mm and a basis weight of 41 g/ m2 , and the fiber diameter of the polyethylene and the polypropylene is 0.18 mm, and the fiber diameter of the polyethylene terephthalate is 0.27 mm;
(2) 1.0 g of a water-absorbent resin is uniformly spread over the entire surface of the nonwoven fabric, and the nonwoven fabric with the water-absorbent resin spread thereon is inverted together with the case over a tray having a bottom area larger than that of the case, and the water-absorbent resin that has fallen onto the tray is collected;
(3) Calculate the penetration resistance between fibers in the water-permeable substrate according to the following formula (1): Penetration resistance between fibers in the water-permeable substrate [wt %] = weight of recovered water absorbent resin [g] / weight of sprayed water absorbent resin [g] × 100 Formula (1).
　また、本発明の一実施形態に係る吸収性物品は、
　液不透過性のバックシート、吸水性樹脂と透水性基材とを含む吸収体、及び液透過性のトップシートをこの順に含む吸収性物品であって、
　前記吸水性樹脂は、ポリ（メタ）アクリル酸（塩）系吸水性樹脂であるとともに、
　下記（１）～（３）の手順により決定される、透水性基材に対する繊維間への侵入抵抗性が６０重量％以上の吸水性樹脂である、吸収性物品である：
　（１）いずれもケース内面の寸法で、底面６ｃｍ×９ｃｍ、深さ１ｃｍの、ポリスチレン製の直方体のケースの底面に、６ｃｍ×９ｃｍに切り取った不織布を両面テープで固定する
　　ここで、前記不織布は、厚み３ｍｍ、目付量４１ｇ／ｍ２であり、ポリエチレン、ポリプロピレン及びポリエチレンテレフタレートの混合物製のエアスルー不織布であり、ポリエチレンの繊維径及びポリプロピレンの繊維径は０．１８ｍｍ、ポリエチレンテレフタレートの繊維径は０．２７ｍｍである；
　（２）吸水性樹脂１．０ｇを、前記不織布の全面に均一に散布し、前記ケースよりも底面積が大きい受け皿の上で、前記吸水性樹脂を散布した前記不織布をケースごと逆さにし、前記受け皿上に脱落した吸水性樹脂を回収する；
　（３）下記式（１）に従い、透水性基材に対する繊維間への侵入抵抗性を算出する
透水性基材に対する繊維間への侵入抵抗性［重量％］＝回収した吸水性樹脂の重量［ｇ］／散布した吸水性樹脂の重量［ｇ］×１００　式（１）。 In addition, the absorbent article according to one embodiment of the present invention includes:
An absorbent article comprising, in this order, a liquid-impermeable back sheet, an absorbent body containing a water-absorbent resin and a water-permeable substrate, and a liquid-permeable top sheet,
The water-absorbing resin is a poly(meth)acrylic acid (salt)-based water-absorbing resin,
The absorbent article is an absorbent article comprising a water-absorbent resin having a resistance to penetration between fibers of a water-permeable substrate of 60% by weight or more, the resistance being determined by the following steps (1) to (3):
(1) A nonwoven fabric cut to 6 cm x 9 cm is fixed with double-sided tape to the bottom of a rectangular polystyrene case having a bottom of 6 cm x 9 cm and a depth of 1 cm, both of which are the dimensions of the inner surface of the case. Here, the nonwoven fabric is an air-through nonwoven fabric made of a mixture of polyethylene, polypropylene and polyethylene terephthalate, with a thickness of 3 mm and a basis weight of 41 g/ m2 , the fiber diameter of the polyethylene and the fiber diameter of the polypropylene being 0.18 mm, and the fiber diameter of the polyethylene terephthalate being 0.27 mm;
(2) 1.0 g of a water-absorbent resin is uniformly spread over the entire surface of the nonwoven fabric, and the nonwoven fabric with the water-absorbent resin spread thereon is inverted together with the case over a tray having a bottom area larger than that of the case, and the water-absorbent resin that has fallen onto the tray is collected;
(3) Calculate the penetration resistance between fibers in the water-permeable substrate according to the following formula (1): Penetration resistance between fibers in the water-permeable substrate [wt %] = weight of recovered water absorbent resin [g] / weight of sprayed water absorbent resin [g] × 100 Formula (1).
　本発明の一態様によれば、吸水性樹脂及び透水性基材を備える吸収性物品の液戻り量を低減し、液保持性に優れた吸水性樹脂を提供することができる。また、本発明の一態様によれば、液拡散性に優れた吸収性物品を提供することができる。 According to one aspect of the present invention, it is possible to provide an absorbent resin that has excellent liquid retention properties and reduces the amount of liquid returning to an absorbent article that includes a water-absorbent resin and a water-permeable substrate. In addition, according to one aspect of the present invention, it is possible to provide an absorbent article that has excellent liquid diffusion properties.
実施例における液戻り量評価用の吸収シートを示す図であり、１００１は前記吸収シートを真上から見た図であり、１００２は前記吸収シートの断面図である。FIG. 10 shows an absorbent sheet for evaluating the amount of liquid return in an example, in which 1001 is a top view of the absorbent sheet, and 1002 is a cross-sectional view of the absorbent sheet. 実施例における液拡散性評価用の吸収性物品を示す図であり、１００３は前記吸収性物品を真上から見た図であり、１００４は前記吸収性物品の断面図である。FIG. 10 shows an absorbent article for evaluating liquid diffusion properties in an example, in which 1003 is a top view of the absorbent article, and 1004 is a cross-sectional view of the absorbent article. 本発明の一実施形態において粉砕工程で用いられるロール式粉砕装置の模式図である。FIG. 2 is a schematic diagram of a roll-type grinding device used in the grinding step in one embodiment of the present invention. 本発明の一実施形態において粉砕工程で用いられるロール式粉砕装置の一対のロールを模式的に示す図であり、２００１は、両方のロールの表面において溝が設けられている、一対のロールであり、２００２は、一方のロールの表面において溝が設けられ、他方のロールの表面において溝が設けられていない、一対のロールである。FIG. 2 is a schematic diagram showing a pair of rolls in a roll-type grinding device used in a grinding step in one embodiment of the present invention, where 2001 is a pair of rolls in which grooves are provided on the surfaces of both rolls, and 2002 is a pair of rolls in which grooves are provided on the surface of one roll and no grooves are provided on the surface of the other roll.
　以下、本発明を最良の形態を示しながら説明する。本明細書において使用される用語は、特に言及しない限り、当該分野で通常用いられる意味で用いられることが理解されるべきである。したがって、他に定義されない限り、本明細書中で使用される全ての専門用語及び科学技術用語は、本発明の属する分野の当業者によって一般的に理解されるのと同じ意味を有する。矛盾する場合、本明細書（定義を含めて）が優先する。本発明は、下記の実施形態に限定されるものではなく、特許請求の範囲内で種々改変することができる。 The present invention will now be described with reference to the best mode thereof. It should be understood that the terms used in this specification are used in the sense commonly used in the art unless otherwise specified. Therefore, unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In the case of conflict, this specification (including definitions) will take precedence. The present invention is not limited to the following embodiments, and various modifications can be made within the scope of the claims.
　〔１〕用語の定義
　（１－１）「吸水性樹脂」
　本発明における「吸水性樹脂」とは、水膨潤性水不溶性の高分子ゲル化剤を指し、以下の物性を満たすものをいう。即ち、「水膨潤性」として、ＥＲＴ４４１．２－０２で規定されるＣＲＣが５ｇ／ｇ以上、かつ、「水不溶性」として、ＥＲＴ４７０．２－０２で規定されるＥｘｔが５０重量％以下の物性を満たす高分子ゲル化剤を指す。 [1] Definition of Terms (1-1) "Water-absorbent resin"
The "water-absorbent resin" in the present invention refers to a water-swellable, water-insoluble polymer gelling agent that satisfies the following physical properties: "Water-swellable" refers to a polymer gelling agent that satisfies the physical properties of CRC of 5 g/g or more as specified in ERT441.2-02, and "Water-insoluble" refers to a polymer gelling agent that satisfies the physical properties of Ext of 50 wt% or less as specified in ERT470.2-02.
　前記吸水性樹脂は、その用途に応じて設計が可能であり、特に限定されないが、カルボキシル基を有する不飽和単量体を架橋重合させた親水性架橋重合体であることが好ましい。また、前記吸水性樹脂は、全量（１００重量％）が重合体である形態に限定されず、前記物性（ＣＲＣ、Ｅｘｔ）を満足する範囲内で、添加剤等を含んだ吸水性樹脂組成物であってもよい。更に、本発明における前記吸水性樹脂は、最終製品に限らず、吸水性樹脂の製造工程における中間体（例えば、重合後の含水ゲル状架橋重合体、乾燥後の乾燥重合体、表面架橋前の吸水性樹脂、表面架橋後の吸水性樹脂、造粒後の吸水性樹脂等）を指す場合もあり、前記吸水性樹脂組成物と合わせて、これら全てを包括して「吸水性樹脂」と総称する。なお、吸水性樹脂の形状については特に限定されず、例えば、シート状、繊維状、フィルム状、及び粒子状等が挙げられるが、本発明では粒子状の吸水性樹脂が好ましい。 The water-absorbing resin can be designed according to its application, and is not particularly limited, but is preferably a hydrophilic cross-linked polymer obtained by cross-linking an unsaturated monomer having a carboxyl group. The water-absorbing resin is not limited to a form in which the total amount (100% by weight) is a polymer, and may be a water-absorbing resin composition containing additives and the like within a range that satisfies the physical properties (CRC, Ext). Furthermore, the water-absorbing resin in the present invention is not limited to a final product, and may also refer to intermediates in the manufacturing process of the water-absorbing resin (e.g., a hydrogel-like cross-linked polymer after polymerization, a dried polymer after drying, a water-absorbing resin before surface cross-linking, a water-absorbing resin after surface cross-linking, a water-absorbing resin after granulation, etc.), and all of these are collectively referred to as "water-absorbing resin" together with the water-absorbing resin composition. The shape of the water-absorbing resin is not particularly limited, and examples thereof include a sheet-like, fibrous, film-like, and particulate shape, but particulate water-absorbing resin is preferred in the present invention.
　（１－２）「ポリ（メタ）アクリル酸（塩）系吸水性樹脂」
　本発明における「ポリ（メタ）アクリル酸（塩）系吸水性樹脂」とは、任意にグラフト成分を含み、繰り返し単位として、（メタ）アクリル酸及び／又はその塩（以下、「（メタ）アクリル酸（塩）」と称する）に由来する構成単位を主成分とする吸水性樹脂を意味する。前記ポリ（メタ）アクリル酸（塩）系吸水性樹脂は、重合に用いられる総単量体（架橋剤を除く）に対し、（メタ）アクリル酸（塩）を、好ましくは５０～１００モル％、より好ましくは７０～１００モル％、更に好ましくは９０～１００モル％、特に好ましくは実質１００モル％含む吸水性樹脂である。 (1-2) "Poly(meth)acrylic acid (salt)-based water-absorbent resin"
In the present invention, the term "poly(meth)acrylic acid (salt)-based water-absorbing resin" refers to a water-absorbing resin that contains an arbitrary graft component and is mainly composed of a repeating unit derived from (meth)acrylic acid and/or a salt thereof (hereinafter referred to as "(meth)acrylic acid (salt)"). The poly(meth)acrylic acid (salt)-based water-absorbing resin is a water-absorbing resin that contains preferably 50 to 100 mol%, more preferably 70 to 100 mol%, even more preferably 90 to 100 mol%, and particularly preferably substantially 100 mol% of (meth)acrylic acid (salt) relative to the total monomers (excluding the crosslinking agent) used in the polymerization.
　（１－３）「ＥＤＡＮＡ」及び「ＥＲＴ」
　「ＥＤＡＮＡ」は、欧州不織布工業会（Ｅｕｒｏｐｅａｎ　Ｄｉｓｐｏｓａｂｌｅｓ　ａｎｄ　Ｎｏｎｗｏｖｅｎｓ　Ａｓｓｏｃｉａｔｉｏｎｓ）の略称であり、「ＥＲＴ」は、欧州標準（ほぼ世界標準）の吸水性樹脂の測定法（ＥＤＡＮＡ　Ｒｅｃｏｍｍｅｎｄｅｄ　Ｔｅｓｔ　Ｍｅｔｈｏｄｓ）の略称である。本発明では、特に断りのない限り、ＥＲＴ原本（２００２年改定／公知文献）に準拠して、吸水性樹脂の物性を測定する。 (1-3) "EDANA" and "ERT"
"EDANA" is an abbreviation for European Disposables and Nonwovens Associations, and "ERT" is an abbreviation for EDANA Recommended Test Methods, a European standard (almost global standard) for measuring the properties of water-absorbent resins. In the present invention, unless otherwise specified, the physical properties of the water-absorbent resin are measured in accordance with the original ERT (revised in 2002/publicly known document).
　（１－４）「透水性基材」
　本発明における「透水性基材」とは、紙オムツ等の吸収性物品に用いられる吸収体において、投入された液体を透過及び／又は拡散する機能を有し、吸水性樹脂に直接接触する部材を指す。具体的には、親水性繊維（例えば、パルプ繊維等）、親水性繊維の積繊体、親水性繊維を構成繊維として含む親水性不織布、合成繊維を構成繊維として含む不織布等が挙げられる。 (1-4) “Water permeable base material”
In the present invention, the term "water-permeable substrate" refers to a member that has a function of permeating and/or diffusing an introduced liquid and that is in direct contact with a water-absorbent resin in an absorbent body used in absorbent articles such as disposable diapers. Specifically, examples of the material include hydrophilic fibers (e.g., pulp fibers, etc.), hydrophilic fiber stacks, hydrophilic nonwoven fabrics containing hydrophilic fibers as constituent fibers, and nonwoven fabrics containing synthetic fibers as constituent fibers. can be done.
　（１－５）その他
　本明細書において、範囲を示す「Ｘ～Ｙ」は「Ｘ以上、Ｙ以下」を意味する。本明細書において、「重量」と「質量」、「重量％」と「質量％」、「重量部」と「質量部」は同義語として扱う。本明細書において、特記しない限り、「ｐｐｍ」は、「質量ｐｐｍ」を意味する。本明細書において、「～酸（塩）」は「～酸及び／又はその塩」を意味し、「（メタ）アクリル」は「アクリル及び／又はメタクリル」を意味する。本明細書において、体積の単位「リットル」を「ｌ」又は「Ｌ」と表記する場合がある。 (1-5) Others In this specification, the range "X to Y" means "X or more and Y or less". In this specification, "weight" and "mass", "weight %" and "mass %, "parts by weight" and "parts by mass" are treated as synonyms. In this specification, unless otherwise specified, "ppm" means "ppm by mass". In this specification, "acid (salt)" means "acid and/or its salt", and "(meth)acrylic" means "acrylic and/or methacrylic". In this specification, the unit of volume "liter" may be written as "l" or "L".
　〔２〕吸水性樹脂
　（２－１）透水性基材に対する繊維間への侵入抵抗性
　本発明者らは、吸収体の液拡散性に着目し検討した結果、吸水性樹脂自体の通液性だけでなく、吸水性樹脂及び透水性基材を備える吸収性物品において、吸水性樹脂が透水性基材の繊維間に侵入することにより、繊維の目詰まりを起こし、透水性基材内部の通液性が十分に発揮されないことが吸収性物品全体による吸収性能の低下を引き起こし、液戻り量を発生させていることを見出し、本発明の完成に至った。本発明における「透水性基材に対する繊維間への侵入抵抗性」とは、吸収性物品において透水性基材の繊維間への吸水性樹脂の侵入のしにくさを評価するための新規な物性値であり、具体的には実施例に記載の測定方法によって測定される値である。本発明の一実施形態に係る吸水性樹脂の、透水性基材に対する繊維間への侵入抵抗性は、６０重量％以上、好ましくは６５重量％以上、より好ましくは７０重量％以上、更に好ましくは７５重量％以上である。透水性基材に対する繊維間への侵入抵抗性が６０重量％以上である吸水性樹脂は、吸収性物品において透水性基材の繊維の目詰まりを起こし難く、優れた吸水性能を発揮することにより、液戻り量が低減されるという利点を有する。透水性基材に対する繊維間への侵入抵抗性の上限は、特に限定されないが、９９重量％以下、好ましくは９５重量％以下、より好ましくは９０重量％以下である。 [2] Water-absorbent resin (2-1) Resistance to penetration between fibers of water-permeable substrate As a result of focusing on and studying the liquid diffusion property of the absorbent body, the present inventors have found that in an absorbent article comprising a water-absorbent resin and a water-permeable substrate, the water-absorbent resin penetrates between fibers of the water-permeable substrate, causing clogging of the fibers, and the liquid permeability inside the water-permeable substrate is not fully exhibited, which causes a decrease in the absorption performance of the entire absorbent article and generates a liquid return amount, leading to the completion of the present invention. In the present invention, the "resistance to penetration between fibers of a water-permeable substrate" is a new physical property value for evaluating the difficulty of the water-absorbent resin to penetrate between fibers of a water-permeable substrate in an absorbent article, and specifically, is a value measured by the measurement method described in the examples. The resistance to penetration between fibers of a water-permeable substrate of the water-absorbent resin according to one embodiment of the present invention is 60% by weight or more, preferably 65% by weight or more, more preferably 70% by weight or more, and even more preferably 75% by weight or more. A water-absorbent resin having a penetration resistance between fibers of a water-permeable substrate of 60% by weight or more has the advantage that it is less likely to cause clogging of the fibers of the water-permeable substrate in an absorbent article, and exhibits excellent water absorption performance, thereby reducing the amount of liquid return. The upper limit of the penetration resistance between fibers of a water-permeable substrate is not particularly limited, but is 99% by weight or less, preferably 95% by weight or less, and more preferably 90% by weight or less.
　（２－２）吸水性樹脂の形状
　本発明の一実施形態において、吸水性樹脂の形状は粒子状であることが好ましく、具体的には、不定形破砕形状粒子、球状粒子、フットボール状粒子、凝集体状粒子又は造粒体状粒子等の形状が挙げられる。本明細書において、「球状」とは、真球に限定されるものではなく、アスペクト比が１．０～１．２である略球状のものも含む。これらの中でも、透水性基材の繊維間へ侵入しにくく、かつ、比表面積が増大することにより吸水速度が向上するとの観点から、凝集体状粒子又は造粒体状粒子であることが好ましい。 (2-2) Shape of water-absorbent resin In one embodiment of the present invention, the shape of the water-absorbent resin is preferably particulate, and specifically, the shape of irregularly crushed particles, spherical particles, football-shaped particles, aggregate particles, granule particles, etc. can be mentioned. In this specification, "spherical" is not limited to a perfect sphere, and also includes a nearly spherical shape with an aspect ratio of 1.0 to 1.2. Among these, aggregate particles or granule particles are preferable from the viewpoint that they are difficult to penetrate between the fibers of the water-permeable substrate and the water absorption rate is improved by increasing the specific surface area.
　（２－３）添加剤
　本発明の一実施形態において、吸水性樹脂は、種々の機能を発現するために、添加剤を含んでいてもよい。添加剤としては、例えば、界面活性剤、リン原子を有する化合物、酸化剤、有機還元剤、水不溶性無機微粒子、有機粉末（例えば、金属石鹸等）、消臭剤、抗菌剤、パルプ、熱可塑性繊維等が挙げられる。なお、前記水不溶性無機微粒子としては、国際特許公開第２０１１／０４０５３０号の「〔５〕水不溶性無機微粒子」に開示された化合物が本発明に適用される。これら水不溶性無機微粒子のうち、特に親水性微粒子（欧州特許第０６２９４１１号に記載されている親水性度（水／メタノール＝７０／３０の混合液中にコロイド状に懸濁する微粒子の割合で表される）が高い（例えば、７０％以上の）もの、及び、特許第６８３７１３９号に記載されている、水に対する接触角が低い（例えば、１０°以下の）もの、例えば、シリカ（二酸化珪素）を含むことにより、吸収性物品に使用した場合に、吸水性樹脂粒子と透水性基材との間に適度な摩擦が生じ、吸水性樹脂が透水性基材の繊維間へ侵入することを抑制することができることから好ましい。 (2-3) Additives In one embodiment of the present invention, the water absorbent resin may contain additives to exhibit various functions. Examples of additives include surfactants, compounds having phosphorus atoms, oxidizing agents, organic reducing agents, water-insoluble inorganic fine particles, organic powders (e.g., metal soaps, etc.), deodorants, antibacterial agents, pulp, thermoplastic fibers, etc. In addition, as the water-insoluble inorganic fine particles, the compounds disclosed in “[5] Water-insoluble inorganic fine particles” of International Patent Publication No. 2011/040530 are applicable to the present invention. Among these water-insoluble inorganic fine particles, hydrophilic fine particles (those having a high hydrophilicity (expressed as the ratio of fine particles suspended in a colloidal state in a mixed liquid of water/methanol = 70/30) (e.g., 70% or more) described in European Patent No. 0629411 and those having a low contact angle with water (e.g., 10° or less) described in Japanese Patent No. 6837139, such as silica (silicon dioxide), are preferred because, when used in absorbent articles, appropriate friction is generated between the water-absorbent resin particles and the water-permeable substrate, and the penetration of the water-absorbent resin into the spaces between the fibers of the water-permeable substrate can be suppressed.
　水不溶性無機微粒子の含有量は、吸水性樹脂と透水性基材との間に適度な摩擦を与える観点から、吸水性樹脂１００重量部に対して、好ましくは０．０１～５．００重量部であり、より好ましくは０．０５～３．００重量部であり、さらに好ましくは０．１０～１．００重量部であり、特に好ましくは０．２０～０．５０重量部である。 The content of the water-insoluble inorganic fine particles is preferably 0.01 to 5.00 parts by weight, more preferably 0.05 to 3.00 parts by weight, even more preferably 0.10 to 1.00 parts by weight, and particularly preferably 0.20 to 0.50 parts by weight, relative to 100 parts by weight of the water-absorbent resin, from the viewpoint of providing appropriate friction between the water-absorbent resin and the water-permeable substrate.
　前記水不溶性無機微粒子は、吸水性樹脂の粒子の大きさと比較して微小な大きさを有する。水不溶性無機微粒子の平均粒子径は、好ましくは０．０１μｍ～５０．００μｍであり、０．１０μｍ～３０．００μｍ、又は、１．００μｍ～２０．００μｍであってもよい。ここで、平均粒子径は、粒子の特性に応じて、細孔電気抵抗法又はレーザー回折・散乱法によって測定することができる。 The water-insoluble inorganic fine particles have a size that is smaller than the size of the water-absorbent resin particles. The average particle size of the water-insoluble inorganic fine particles is preferably 0.01 μm to 50.00 μm, and may be 0.10 μm to 30.00 μm, or 1.00 μm to 20.00 μm. Here, the average particle size can be measured by a pore electrical resistance method or a laser diffraction/scattering method depending on the characteristics of the particles.
　（２－４）ＣＲＣ
　「ＣＲＣ」は、Ｃｅｎｔｒｉｆｕｇｅ　Ｒｅｔｅｎｔｉｏｎ　Ｃａｐａｃｉｔｙ（遠心分離機保持容量）の略称であり、吸水性樹脂の無加圧下での吸水倍率を意味する。本明細書においては、ＣＲＣは、ＥＤＡＮＡ法（ＥＲＴ４４１．２－０２）に準拠して測定される。 (2-4) CRC
"CRC" is an abbreviation for Centrifuge Retention Capacity, and means the water absorption capacity of a water-absorbent resin under no pressure. In this specification, CRC is measured in accordance with the EDANA method (ERT441.2-02).
　（２－５）ＦＳＣ
　「ＦＳＣ」は、Ｆｒｅｅ　Ｓｗｅｌｌ　Ｃａｐａｃｉｔｙの略称であり、吸水性樹脂の無加圧下吊り下げ吸水倍率を意味する。本明細書においては、ＦＳＣは、ＥＤＡＮＡ法（ＥＲＴ４４０．２－０２）に準拠して測定される。ＦＳＣの値は、内部架橋剤及び表面架橋剤等の種類及び量を変更することにより制御することができる。 (2-5) FSC
"FSC" is an abbreviation for Free Swell Capacity, and means the water absorption capacity of a water absorbent resin when suspended under no pressure. In this specification, FSC is measured in accordance with the EDANA method (ERT440.2-02). The value of FSC can be controlled by changing the type and amount of an internal crosslinking agent and a surface crosslinking agent.
　本発明の一実施形態に係る吸水性樹脂のＦＳＣは、好ましくは４０ｇ／ｇ以上であり、より好ましくは４５ｇ／ｇ以上であり、更に好ましくは５０ｇ／ｇ以上である。上限は特に限定されず、より高いＦＳＣが好ましいが、他の物性とのバランスが良好であるとの観点から、好ましくは８０ｇ／ｇ以下であり、より好ましくは７５ｇ／ｇ以下、更に好ましくは７０ｇ／ｇ以下である。 The FSC of the water-absorbent resin according to one embodiment of the present invention is preferably 40 g/g or more, more preferably 45 g/g or more, and even more preferably 50 g/g or more. There is no particular upper limit, and a higher FSC is preferable, but from the viewpoint of a good balance with other physical properties, it is preferably 80 g/g or less, more preferably 75 g/g or less, and even more preferably 70 g/g or less.
　前記ＦＳＣが４０ｇ／ｇ以上であれば、吸収量が十分であり、紙オムツ等の吸収性物品の吸収体として好適に用いることができる。また、前記ＦＳＣが７０ｇ／ｇ以下であれば、体液（例えば、尿及び血液等）等を吸収する速度の低下が防止され、高吸水速度タイプの紙オムツ等への使用に適する。 If the FSC is 40 g/g or more, the absorption capacity is sufficient and the material can be suitably used as an absorbent for absorbent articles such as paper diapers. If the FSC is 70 g/g or less, the rate at which the material absorbs body fluids (e.g., urine, blood, etc.) does not decrease, making the material suitable for use in paper diapers with high water absorption rates.
　（２－６）Ｅｘｔ
　「Ｅｘｔ」は、Ｅｘｔｒａｃｔａｂｌｅｓ（水可溶分）の略称であり、吸水性樹脂から抽出される可溶分量を意味する。本明細書において、Ｅｘｔは、ＥＤＡＮＡ法（ＥＲＴ４７０．２－０２）に準拠して測定される。 (2-6) Ext
"Ext" is an abbreviation for Extractables, and means the amount of extractables extracted from the water-absorbing resin. In this specification, Ext is measured in accordance with the EDANA method (ERT470.2-02).
　（２－７）ＡＡＰ
　「ＡＡＰ」は、Ａｂｓｏｒｐｔｉｏｎ　Ａｇａｉｎｓｔ　Ｐｒｅｓｓｕｒｅの略称であり、吸水性樹脂の加圧下における吸水倍率を意味する。本発明においては、ＡＡＰは、荷重条件を４．８３ｋＰａ（０．７ｐｓｉ）に変更する以外は、ＥＤＡＮＡ法（ＥＲＴ４４２．２－０２）に準拠して測定される。具体的には、０．９質量％塩化ナトリウム水溶液を用い、吸水性樹脂０．９ｇを１時間、４．８３ｋＰａの加圧下で膨潤させた後、ＡＡＰ（加圧下吸水倍率）（単位：ｇ／ｇ）を測定する。 (2-7) AAP
"AAP" is an abbreviation for Absorption Against Pressure, and means the water absorption capacity of a water-absorbent resin under pressure. In the present invention, AAP is measured in accordance with the EDANA method (ERT442.2-02) except that the load condition is changed to 4.83 kPa (0.7 psi). Specifically, 0.9 g of a water-absorbent resin is swollen under a pressure of 4.83 kPa for 1 hour using a 0.9% by mass aqueous sodium chloride solution, and then the AAP (water absorption capacity under pressure) (unit: g/g) is measured.
　本発明の一実施形態に係る吸水性樹脂のＡＡＰは、衛生材料に用いた際の吸水特性が向上するとの観点から、好ましくは１５g／ｇ以上、より好ましくは２０ｇ／ｇ以上、更に好ましくは２３ｇ／ｇ以上である。又、前記吸水性樹脂のＡＡＰの上限は、特に制限されないが、好ましくは４０ｇ／ｇ以下である。 The AAP of the water-absorbent resin according to one embodiment of the present invention is preferably 15 g/g or more, more preferably 20 g/g or more, and even more preferably 23 g/g or more, from the viewpoint of improving the water absorption properties when used in sanitary materials. There is no particular upper limit to the AAP of the water-absorbent resin, but it is preferably 40 g/g or less.
　（２－８）含水率
　「含水率」は、試料量を１．０ｇ、乾燥温度を１８０℃にそれぞれ変更する以外は、ＥＤＡＮＡ法（ＥＲＴ４３０．２－０２）に準拠して測定される。 (2-8) Moisture Content The "moisture content" is measured in accordance with the EDANA method (ERT430.2-02), except that the sample amount is changed to 1.0 g and the drying temperature is changed to 180°C.
　（２－９）質量平均粒子径（Ｄ５０）
　「質量平均粒子径（Ｄ５０）」は、米国特許第７６３８５７０号のカラム２７、２８に記載された「(3)Mass-Average Particle Diameter (D50) and Logarithmic Standard Deviation (σζ) of Particle Diameter Distribution」に準拠して測定される。 (2-9) Mass average particle diameter (D50)
The "mass-average particle diameter (D50)" is defined in "(3) Mass-Average Particle Diameter (D50) and Logarithmic Standard Deviation (σζ) of Particle Diameter Distribution" in columns 27 and 28 of U.S. Pat. No. 7,638,570. Measured in accordance with.
　本発明の一実施形態に係る吸水性樹脂の質量平均粒子径（Ｄ５０）は、吸収性物品における透水性基材に対する繊維間への吸水性樹脂の侵入を防止する観点から、好ましくは２５０μｍ～８００μｍ、より好ましくは３００μｍ～７００μｍ、更に好ましくは３１０μｍ～６００μｍ、特に好ましくは３２０μｍ～５００μｍである。また、粒子径が１５０μｍ未満の粒子の割合、すなわち、目開き１５０μｍのＪＩＳ標準篩を通過する粒子の割合は、吸収性物品における透水性基材の繊維間に侵入し得る細粒が少ない方が好ましいとの観点から、好ましくは４０質量％以下、より好ましくは３０質量％以下、更に好ましくは２０質量％以下、特に好ましくは１０質量％以下である。前記質量平均粒子径が２５０μｍ以上であれば、吸収性物品における透水性基材に対する繊維間への吸水性樹脂の侵入を低減することができ、更に粉塵が少なく取り扱い性がよいという利点を有する。また、前記質量平均粒子径が８００μｍ以下であれば、体液（例えば、尿及び血液等）等を吸収する速度の低下が防止され、高吸水速度タイプの紙オムツ等への使用に適する。 The mass average particle diameter (D50) of the water-absorbent resin according to one embodiment of the present invention is preferably 250 μm to 800 μm, more preferably 300 μm to 700 μm, even more preferably 310 μm to 600 μm, and particularly preferably 320 μm to 500 μm, from the viewpoint of preventing the water-absorbent resin from penetrating between the fibers of the water-permeable substrate in the absorbent article. The proportion of particles having a particle diameter of less than 150 μm, that is, the proportion of particles passing through a JIS standard sieve with a mesh size of 150 μm, is preferably 40% by mass or less, more preferably 30% by mass or less, even more preferably 20% by mass or less, and particularly preferably 10% by mass or less, from the viewpoint that it is preferable that the number of fine particles that can penetrate between the fibers of the water-permeable substrate in the absorbent article is small. If the mass average particle diameter is 250 μm or more, the penetration of the water-absorbent resin into the fibers of the water-permeable substrate in the absorbent article can be reduced, and there is an advantage that there is less dust and it is easy to handle. Furthermore, if the mass average particle size is 800 μm or less, the rate at which the material absorbs body fluids (e.g., urine, blood, etc.) is prevented from decreasing, making the material suitable for use in paper diapers with high water absorption rates.
　（２－１０）嵩比重
　「嵩比重」は、ＥＤＡＮＡ法（ＥＲＴ４６０．２－０２）に準拠して測定される。 (2-10) Bulk density "Bulk density" is measured in accordance with the EDANA method (ERT460.2-02).
　本発明の一実施形態に係る吸水性樹脂の嵩比重は、好ましくは０．６０ｇ／ｍＬ～１．００ｇ／ｍＬ、より好ましくは０．６２ｇ／ｍＬ～０．９０ｇ／ｍＬ、さらに好ましくは０．６４ｇ／ｍＬ～０．８０ｇ／ｍＬである。前記嵩比重が０．６０～１．００ｇ／ｍＬであれば、吸水性樹脂における体液（例えば、尿及び血液等）等の吸水速度の低下が防止され、吸水性樹脂は、高吸水速度タイプの紙オムツ等への使用に適する。 The bulk density of the water-absorbent resin according to one embodiment of the present invention is preferably 0.60 g/mL to 1.00 g/mL, more preferably 0.62 g/mL to 0.90 g/mL, and even more preferably 0.64 g/mL to 0.80 g/mL. If the bulk density is 0.60 to 1.00 g/mL, a decrease in the water-absorbent resin's absorption rate of body fluids (e.g., urine, blood, etc.) is prevented, and the water-absorbent resin is suitable for use in high-absorption-rate paper diapers, etc.
　（２－１１）吸水速度
　本発明において、吸水性樹脂の「吸水速度」とは、「ボルテックス法（Ｖｏｒｔｅｘ）による吸水速度」を意図する。「ボルテックス法による吸水速度」とは、スターラーチップによって６００ｒｐｍで攪拌された０．９質量％塩化ナトリウム水溶液５０ｇ中に、吸水性樹脂２．０ｇを添加し、該スターラーチップが試験液に覆われるまでの時間を意味する。 (2-11) Water Absorption Rate In the present invention, the "water absorption rate" of a water absorbent resin means the "water absorption rate by a vortex method". The "water absorption rate by a vortex method" means the time required for a test liquid to be covered with 2.0 g of a water absorbent resin when 50 g of a 0.9% by mass aqueous sodium chloride solution stirred at 600 rpm with a stirrer tip is added to the stirrer tip.
　「吸水速度」に優れる吸水性樹脂は、吸収性物品として使用した場合において、即座に液を取り込み、液戻り量を低減することができるため好ましい。本発明の一実施形態に係る吸水性樹脂の吸水速度は、好ましくは５０秒以下、より好ましくは４５秒以下、より好ましくは４０秒以下、更に好ましくは３０秒以下である。吸水速度の下限は特に制限されないが、１０秒以上、好ましくは１５秒以上、更に好ましくは２０秒以上である。前記吸水性樹脂の吸水速度が４５秒以下であれば、透水性基材が拡散させた液を素早く取り込むことができるため、液保持性に優れ、高吸水速度タイプの紙オムツ等への使用に適する。また、吸水速度の速い吸水性樹脂ほど、急速に膨潤したゲルが吸水性樹脂間の隙間をふさいで通液を妨げる現象、いわゆる「ゲルブロッキング」のリスクが高いため、透水性基材に対する繊維間への侵入抵抗性が高い吸水性樹脂を使用することによる、繊維内での拡散性低下回避のメリットがより大きい。 A water-absorbent resin having excellent "absorption speed" is preferable because it can instantly absorb liquid and reduce the amount of liquid returning when used as an absorbent article. The water-absorbent resin according to one embodiment of the present invention has an absorption speed of preferably 50 seconds or less, more preferably 45 seconds or less, more preferably 40 seconds or less, and even more preferably 30 seconds or less. The lower limit of the water-absorption speed is not particularly limited, but is 10 seconds or more, preferably 15 seconds or more, and even more preferably 20 seconds or more. If the water-absorbent resin has an absorption speed of 45 seconds or less, it can quickly absorb the liquid diffused by the water-permeable substrate, and therefore has excellent liquid retention properties and is suitable for use in paper diapers with high water-absorption speed. In addition, the faster the water-absorbent resin has an absorption speed, the higher the risk of so-called "gel blocking," a phenomenon in which a rapidly swollen gel blocks the gaps between the water-absorbent resin and prevents liquid from passing through. Therefore, the advantage of using a water-absorbent resin with high resistance to penetration between fibers in a water-permeable substrate is greater in avoiding a decrease in diffusion within the fibers.
　〔３〕吸水性樹脂の製造方法
　以下に、本発明の一実施形態に係る吸水性樹脂の製造工程を示す。 [3] Method for Producing Water-Absorbent Resin Hereinafter, a process for producing a water-absorbent resin according to one embodiment of the present invention will be described.
　（３－１）単量体水溶液調製工程
　本工程は、（メタ）アクリル酸（塩）を主成分として含む水溶液（以下、「単量体水溶液」と称する）を調製する工程である。なお、得られる吸水性樹脂の吸水性能が低下しない範囲で、単量体のスラリー液を使用することもできるが、本項では便宜上、単量体水溶液について説明を行う。 (3-1) Monomer Aqueous Solution Preparation Step This step is a step of preparing an aqueous solution containing (meth)acrylic acid (salt) as a main component (hereinafter referred to as "monomer aqueous solution"). Note that, although a monomer slurry liquid can also be used within a range in which the water absorption performance of the obtained water absorbent resin is not deteriorated, for the sake of convenience, the monomer aqueous solution will be described in this section.
　また、前記「主成分」とは、（メタ）アクリル酸（塩）の使用量（含有量）が、吸水性樹脂の重合反応に供される単量体（内部架橋剤を除く）全体に対して、好ましくは５０モル％以上、より好ましくは７０モル％以上、更に好ましくは９０モル％以上（上限は１００モル％）であることをいう。 The "main component" means that the amount (content) of (meth)acrylic acid (salt) used is preferably 50 mol % or more, more preferably 70 mol % or more, and even more preferably 90 mol % or more (upper limit 100 mol %), based on the total amount of monomers (excluding the internal crosslinking agent) used in the polymerization reaction of the water absorbent resin.
　（（メタ）アクリル酸（塩））
　本発明の一実施形態に係る吸水性樹脂の製造方法では、得られる吸水性樹脂の物性及び生産性が向上するとの観点から、単量体として（メタ）アクリル酸（塩）が用いられる。 ((Meth)acrylic acid (salt))
In the method for producing a water-absorbent resin according to one embodiment of the present invention, a (meth)acrylic acid (salt) is used as a monomer from the viewpoint of improving the physical properties and productivity of the obtained water-absorbent resin.
　前記「（メタ）アクリル酸」としては、公知の（メタ）アクリル酸であればよく、重合禁止剤として、好ましくはメトキシフェノール類、より好ましくはｐ－メトキシフェノールを、（メタ）アクリル酸の重合性及び吸水性樹脂の色調が向上するとの観点から、好ましくは２００ｐｐｍ以下、より好ましくは１０ｐｐｍ～１６０ｐｐｍ、更に好ましくは２０ｐｐｍ～１００ｐｐｍ含んでいてもよい。また、（メタ）アクリル酸中の不純物については、米国特許出願公開第２００８／０１６１５１２号に記載された化合物が本発明にも適用される。 The "(meth)acrylic acid" may be any known (meth)acrylic acid, and may contain, as a polymerization inhibitor, preferably methoxyphenols, more preferably p-methoxyphenol, preferably at 200 ppm or less, more preferably 10 ppm to 160 ppm, and even more preferably 20 ppm to 100 ppm, from the viewpoint of improving the polymerization of the (meth)acrylic acid and the color tone of the water-absorbing resin. In addition, as for impurities in (meth)acrylic acid, the compounds described in U.S. Patent Application Publication No. 2008/0161512 are also applicable to the present invention.
　前記「（メタ）アクリル酸塩」は、前記（メタ）アクリル酸を下記塩基性組成物で中和して得られた中和物である。該（メタ）アクリル酸塩としては、市販の（メタ）アクリル酸塩（例えば、（メタ）アクリル酸ナトリウム等）を用いてもよいし、吸水性樹脂の製造プラント内で中和して得られたものを用いてもよい。 The "(meth)acrylic acid salt" is a neutralized product obtained by neutralizing the (meth)acrylic acid with the following basic composition. As the (meth)acrylic acid salt, a commercially available (meth)acrylic acid salt (e.g., sodium (meth)acrylate, etc.) may be used, or a salt obtained by neutralization in a water-absorbent resin manufacturing plant may be used.
　（塩基性組成物）
　本発明の一実施形態において、「塩基性組成物」とは、塩基性化合物を含有する組成物を意味する。塩基性組成物としては、例えば、市販の水酸化ナトリウム水溶液等が挙げられる。 (Basic Composition)
In one embodiment of the present invention, the term "basic composition" refers to a composition containing a basic compound. Examples of basic compositions include commercially available aqueous sodium hydroxide solutions.
　前記塩基性化合物として、具体的には、アルカリ金属の炭酸塩、アルカリ金属の炭酸水素塩、アルカリ金属の水酸化物、アンモニア、有機アミン等が挙げられる。これらの中でも、得られる吸水性樹脂の物性が向上するとの観点から、前記塩基性化合物は強塩基性であることが好ましい。即ち、前記塩基性化合物は、アルカリ金属の水酸化物（水酸化ナトリウム、水酸化カリウム、水酸化リチウム等）が好ましく、水酸化ナトリウムがより好ましい。 Specific examples of the basic compound include alkali metal carbonates, alkali metal hydrogen carbonates, alkali metal hydroxides, ammonia, and organic amines. Among these, from the viewpoint of improving the physical properties of the resulting water-absorbent resin, it is preferable that the basic compound is strongly basic. That is, the basic compound is preferably an alkali metal hydroxide (sodium hydroxide, potassium hydroxide, lithium hydroxide, etc.), and more preferably sodium hydroxide.
　（中和）
　本発明の一実施形態において、中和として、（メタ）アクリル酸に対する中和（重合前）及び（メタ）アクリル酸を架橋重合して得られる含水ゲル状架橋重合体に対する中和（重合後）（以下、「後中和」と称する）の何れかを選択又は併用することができる。これら中和の方法は、連続式でもバッチ式でもよく、特に限定されないが、生産効率等向上の観点から、連続式が好ましい。 (Neutralization)
In one embodiment of the present invention, the neutralization may be selected from or used in combination with neutralization of (meth)acrylic acid (before polymerization) and neutralization of a hydrogel crosslinked polymer obtained by crosslinking and polymerizing (meth)acrylic acid (after polymerization) (hereinafter referred to as "post-neutralization"). These neutralization methods may be continuous or batch-type, and are not particularly limited, but the continuous type is preferred from the viewpoint of improving production efficiency, etc.
　中和装置、中和温度、滞留時間等の条件については、国際公開第２００９／１２３１９７号や米国特許出願公開第２００８／０１９４８６３号に記載された条件が適用される。 Conditions such as neutralization equipment, neutralization temperature, and residence time are as described in International Publication No. 2009/123197 and U.S. Patent Application Publication No. 2008/0194863.
　本発明の一実施形態における中和率は、単量体の酸基に対して、好ましくは１０～９０モル％、より好ましくは４０～８５モル％、更に好ましくは５０～８０モル％、特に好ましくは６０～７５モル％である。該中和率が１０モル％以上の場合、吸水倍率の著しい低下を抑制することができる。一方、該中和率が９０モル％以下の場合、加圧下吸水倍率の高い吸水性樹脂を得ることができる。 In one embodiment of the present invention, the neutralization rate is preferably 10 to 90 mol%, more preferably 40 to 85 mol%, even more preferably 50 to 80 mol%, and particularly preferably 60 to 75 mol%, based on the acid groups of the monomer. When the neutralization rate is 10 mol% or more, a significant decrease in water absorption capacity can be suppressed. On the other hand, when the neutralization rate is 90 mol% or less, a water-absorbent resin with a high water absorption capacity under pressure can be obtained.
　前記中和率は、重合前の中和でも、後中和の場合でも同様である。又、最終製品としての吸水性樹脂の中和率についても、前記中和率が適用される。なお、本明細書において、「中和率７５モル％」とは、（メタ）アクリル酸２５モル％及び（メタ）アクリル酸塩７５モル％の混合物を意味する。又、このような（メタ）アクリル酸と（メタ）アクリル酸塩との混合物を（メタ）アクリル酸部分中和物と称する場合もある。 The above neutralization rate is the same whether it is neutralized before or after polymerization. The above neutralization rate is also applied to the neutralization rate of the water-absorbing resin as a final product. In this specification, "neutralization rate of 75 mol%" means a mixture of 25 mol% (meth)acrylic acid and 75 mol% (meth)acrylic acid salt. Such a mixture of (meth)acrylic acid and (meth)acrylic acid salt may also be referred to as a partially neutralized (meth)acrylic acid.
　（他の単量体）
　本明細書において、「他の単量体」とは、前記（メタ）アクリル酸（塩）以外の単量体を意味する。該他の単量体は、（メタ）アクリル酸（塩）と併用して、吸水性樹脂を製造することができる。 (Other monomers)
In the present specification, the term "other monomer" refers to a monomer other than the (meth)acrylic acid (salt). The other monomer can be used in combination with the (meth)acrylic acid (salt) to produce a water-absorbing resin.
　前記他の単量体としては、例えば、水溶性の不飽和単量体又は疎水性の不飽和単量体が挙げられる。具体的には、米国特許出願公開第２００５／０２１５７３４に記載された化合物（但し、（メタ）アクリル酸は除く）が本発明にも適用される。 The other monomer may be, for example, a water-soluble unsaturated monomer or a hydrophobic unsaturated monomer. Specifically, the compounds described in U.S. Patent Application Publication No. 2005/0215734 (excluding (meth)acrylic acid) are also applicable to the present invention.
　（内部架橋剤）
　本発明で使用される内部架橋剤としては、例えば、Ｎ，Ｎ’－メチレンビス（メタ）アクリルアミド、（ポリ）エチレングリコールジ（メタ）アクリレート、（ポリ）プロピレングリコールジ（メタ）アクリレート、トリメチロールプロパントリ（メタ）アクリレート、トリメチロールプロパンジ（メタ）アクリレート、グリセリントリ（メタ）アクリレート、グリセリンアクリレートメタクリレート、エチレンオキサイド変性トリメチロールプロパントリ（メタ）アクリレート、ペンタエリスリトールテトラ（メタ）アクリレート、ジペンタエリスリトールヘキサ（メタ）アクリレート、トリアリルシアヌレート、トリアリルイソシアヌレート、トリアリルホスフェート、トリアリルアミン、ポリ（メタ）アリロキシアルカン、（ポリ）エチレングリコールジグリシジルエーテル、グリセロールジグリシジルエーテル、エチレングリコール、ポリエチレングリコール、プロピレングリコール、グリセリン、１，４－ブタンジオール、ペンタエリスリトール、エチレンジアミン、エチレンカーボネート、プロピレンカーボネート、ポリエチレンイミン、グリシジル（メタ）アクリレート等を挙げることができる。前記内部架橋剤は、１種又は２種以上を選択することができる。 (Internal Crosslinking Agent)
Examples of the internal crosslinking agent used in the present invention include N,N'-methylenebis(meth)acrylamide, (poly)ethylene glycol di(meth)acrylate, (poly)propylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, trimethylolpropane di(meth)acrylate, glycerin tri(meth)acrylate, glycerin acrylate methacrylate, ethylene oxide modified trimethylolpropane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol tetra(meth)acrylate, and the like. Examples of the internal crosslinking agent include hexa(meth)acrylate, triallyl cyanurate, triallyl isocyanurate, triallyl phosphate, triallylamine, poly(meth)allyloxyalkane, (poly)ethylene glycol diglycidyl ether, glycerol diglycidyl ether, ethylene glycol, polyethylene glycol, propylene glycol, glycerin, 1,4-butanediol, pentaerythritol, ethylenediamine, ethylene carbonate, propylene carbonate, polyethyleneimine, glycidyl (meth)acrylate, etc. One or more types of the internal crosslinking agent may be selected.
　得られる吸水性樹脂の吸水性能等向上の観点から、前記内部架橋剤としては、重合性不飽和基を２個以上有する化合物が好ましく、後述する乾燥温度で熱分解性を有する重合性不飽和基を２個以上有する化合物がより好ましく、（ポリ）アルキレングリコール構造単位を有する重合性不飽和基を２個以上有する化合物が更に好ましい。 From the viewpoint of improving the water absorption performance of the obtained water absorbent resin, the internal crosslinking agent is preferably a compound having two or more polymerizable unsaturated groups, more preferably a compound having two or more polymerizable unsaturated groups that are thermally decomposable at the drying temperature described below, and even more preferably a compound having two or more polymerizable unsaturated groups that have a (poly)alkylene glycol structural unit.
　前記重合性不飽和基としては、好ましくはアリル基、（メタ）アクリレート基が挙げられる。この中でも、吸水性能向上の観点から、（メタ）アクリレート基がより好ましい。前記（ポリ）アルキレングリコール構造単位としては、吸水性能向上の観点から、ポリエチレングリコールが好ましい。前記（ポリ）アルキレングリコール構造単位のｎ数としては、好ましくは１～１００、より好ましくは６～５０である。 The polymerizable unsaturated group is preferably an allyl group or a (meth)acrylate group. Of these, from the viewpoint of improving water absorption performance, a (meth)acrylate group is more preferable. The (poly)alkylene glycol structural unit is preferably polyethylene glycol from the viewpoint of improving water absorption performance. The number n of the (poly)alkylene glycol structural unit is preferably 1 to 100, more preferably 6 to 50.
　前記内部架橋剤の使用量は、単量体全体に対して、好ましくは０．０００１～１０モル％、より好ましくは０．００１～１モル％である。該使用量を前記範囲内とすることで、所望する吸水性樹脂が得られる。なお、該使用量が０．０００１モル％以上である場合、ゲル強度が増加し水可溶分が低下する傾向にあり、該使用量が１０モル％以下である場合、吸水倍率が増加する傾向にあるため、好ましい。 The amount of the internal crosslinking agent used is preferably 0.0001 to 10 mol %, more preferably 0.001 to 1 mol %, based on the total amount of monomers. By setting the amount used within the above range, the desired water-absorbent resin can be obtained. Note that if the amount used is 0.0001 mol % or more, the gel strength tends to increase and the water-soluble content tends to decrease, while if the amount used is 10 mol % or less, the water absorption capacity tends to increase, which is preferable.
　本発明の一実施形態において、内部架橋剤を添加する方法は特に限定されないが、例えば、予め単量体水溶液に内部架橋剤を添加し、重合と同時に架橋反応を起こさせる方法、重合中又は重合後に内部架橋剤を添加して後架橋する方法、ラジカル重合開始剤を用いてラジカル架橋する方法、電子線、紫外線等の活性エネルギー線を用いて放射線架橋する方法等が挙げられる。これらの中でも、反応性向上の観点から、予め単量体水溶液に内部架橋剤を添加し、重合と同時に架橋反応を起こさせる方法が好ましい。前記方法は、本発明の効果を損なわない範囲でこれらを併用してもよい。 In one embodiment of the present invention, the method of adding the internal crosslinking agent is not particularly limited, but examples include a method of adding the internal crosslinking agent to an aqueous monomer solution in advance and causing a crosslinking reaction simultaneously with polymerization, a method of adding an internal crosslinking agent during or after polymerization and causing post-crosslinking, a method of radical crosslinking using a radical polymerization initiator, and a method of radiation crosslinking using active energy rays such as electron beams and ultraviolet rays. Among these, from the viewpoint of improving reactivity, a method of adding the internal crosslinking agent to an aqueous monomer solution in advance and causing a crosslinking reaction simultaneously with polymerization is preferred. The above methods may be used in combination as long as they do not impair the effects of the present invention.
　（その他、単量体水溶液に添加される物質）
　本発明の一実施形態において、得られる吸水性樹脂の物性向上の観点から、下記の物質を単量体水溶液の調製時に添加することもできる。 (Other substances added to the aqueous monomer solution)
In one embodiment of the present invention, from the viewpoint of improving the physical properties of the resulting water-absorbent resin, the following substances may be added during preparation of the aqueous monomer solution.
　具体的には、澱粉、澱粉誘導体、セルロース、セルロース誘導体、ポリビニルアルコール、ポリ（メタ）アクリル酸（塩）、ポリ（メタ）アクリル酸（塩）架橋体等の親水性高分子を、重合に用いられる総単量体（架橋剤を除く）に対して、好ましくは５０重量％以下、より好ましくは２０重量％以下、更に好ましくは１０重量％以下、特に好ましくは５重量％以下（下限は０重量％）添加してもよい。 Specifically, hydrophilic polymers such as starch, starch derivatives, cellulose, cellulose derivatives, polyvinyl alcohol, poly(meth)acrylic acid (salt), and crosslinked poly(meth)acrylic acid (salt) may be added in an amount of preferably 50% by weight or less, more preferably 20% by weight or less, even more preferably 10% by weight or less, and particularly preferably 5% by weight or less (lower limit: 0% by weight) based on the total monomers used in the polymerization (excluding the crosslinking agent).
　更に、炭酸塩、アゾ化合物、気泡等の発泡剤；界面活性剤；キレート剤；連鎖移動剤等を、重合に用いられる総単量体（架橋剤を除く）に対して、好ましくは５重量％以下、より好ましくは１重量％以下、更に好ましくは０．５重量％以下（下限は０重量％）添加してもよい。 Furthermore, foaming agents such as carbonates, azo compounds, and bubbles; surfactants; chelating agents; chain transfer agents, etc. may be added in amounts of preferably 5% by weight or less, more preferably 1% by weight or less, and even more preferably 0.5% by weight or less (the lower limit is 0% by weight) based on the total monomers (excluding the crosslinking agent) used in the polymerization.
　前記物質の添加の形態は、単量体水溶液に添加される形態であってもよく、重合途中で添加される形態であってもよい。前記添加の形態は、本発明の効果を損なわない範囲で、これらを併用してもよい。 The substance may be added to the aqueous monomer solution or during polymerization. The above-mentioned methods of addition may be used in combination as long as they do not impair the effects of the present invention.
　なお、親水性高分子として水溶性樹脂又は吸水性樹脂を使用する場合には、グラフト重合体又は吸水性樹脂組成物（例えば、澱粉－アクリル酸重合体、ＰＶＡ－アクリル酸重合体等）が得られる。これらの重合体、吸水性樹脂組成物も本発明の吸水性樹脂の範疇である。 When a water-soluble resin or water-absorbent resin is used as the hydrophilic polymer, a graft polymer or water-absorbent resin composition (for example, starch-acrylic acid polymer, PVA-acrylic acid polymer, etc.) is obtained. These polymers and water-absorbent resin compositions also fall within the scope of the water-absorbent resin of the present invention.
　（単量体成分の濃度）
　本工程において、単量体水溶液を調製する際に、前記の各物質が添加される。該単量体水溶液中の単量体成分の濃度としては特に限定されないが、吸水性樹脂の物性が向上するとの観点から、好ましくは１０～８０重量％、より好ましくは２０～７５重量％、更に好ましくは３０～７０重量％である。 (Monomer component concentration)
In this step, when preparing the aqueous monomer solution, the above-mentioned substances are added. The concentration of the monomer component in the aqueous monomer solution is not particularly limited, but from the viewpoint of improving the physical properties of the water absorbent resin, it is preferably 10 to 80% by weight, more preferably 20 to 75% by weight, and even more preferably 30 to 70% by weight.
　水溶液重合又は逆相懸濁重合を採用する場合、水以外の溶媒を必要に応じて併用することもできる。この場合、溶媒の種類は特に限定されない。 When aqueous solution polymerization or reversed-phase suspension polymerization is used, a solvent other than water can be used in combination as necessary. In this case, the type of solvent is not particularly limited.
　本明細書において、前記「単量体成分の濃度」とは、下記式（２）で求められる値であり、単量体水溶液の重量には、親水性高分子のグラフト成分（例えば、澱粉等）や、再利用のために添加される製造工程から発生した吸水性樹脂の微粉、逆相懸濁重合における疎水性溶媒の重量は含めない。 In this specification, the "monomer component concentration" is the value calculated by the following formula (2), and the weight of the aqueous monomer solution does not include the weight of the hydrophilic polymer graft component (e.g., starch, etc.), the fine powder of the water-absorbent resin generated during the manufacturing process and added for reuse, or the weight of the hydrophobic solvent in the reversed-phase suspension polymerization.
　単量体成分の濃度（重量％）＝｛（単量体成分の重量）／（単量体水溶液の重量）｝×１００・・・式（２）。 Monomer component concentration (wt%) = {(weight of monomer component) / (weight of aqueous monomer solution)} x 100 ... formula (2).
　（３－２）重合工程
　本工程は、前記単量体水溶液の調製工程で得られた単量体水溶液を重合させて、含水ゲル状架橋重合体（以下、「含水ゲル」と称する）を得る工程である。 (3-2) Polymerization Step This step is a step of polymerizing the aqueous monomer solution obtained in the aqueous monomer solution preparation step to obtain a hydrogel-like crosslinked polymer (hereinafter referred to as "hydrogel").
　（重合開始剤）
　本発明の一実施形態において使用される重合開始剤は、重合形態等によって選択されるため、特に限定されないが、例えば、熱分解型重合開始剤、光分解型重合開始剤、又はこれらの重合開始剤の分解を促進する還元剤を併用したレドックス系重合開始剤等が挙げられる。具体的には、米国特許第７２６５１９０号に開示された重合開始剤のうち、１種又は２種以上が用いられる。なお、重合開始剤の取扱性や吸水性樹脂の物性が向上するとの観点から、好ましくは過酸化物又はアゾ化合物、より好ましくは過酸化物、更に好ましくは過硫酸塩が使用される。 (Polymerization initiator)
The polymerization initiator used in one embodiment of the present invention is not particularly limited since it is selected depending on the polymerization form, etc., but examples thereof include a thermally decomposable polymerization initiator, a photodecomposable polymerization initiator, or a redox-based polymerization initiator used in combination with a reducing agent that promotes the decomposition of these polymerization initiators. Specifically, one or more of the polymerization initiators disclosed in U.S. Pat. No. 7,265,190 are used. From the viewpoint of improving the handling of the polymerization initiator and the physical properties of the water-absorbing resin, preferably a peroxide or an azo compound, more preferably a peroxide, and even more preferably a persulfate is used.
　前記重合開始剤の使用量は、重合に用いられる総単量体（架橋剤を除く）に対して、好ましくは０．００１～１モル％、より好ましくは０．００１～０．５モル％である。また、前記還元剤の使用量は、重合に用いられる総単量体（架橋剤を除く）に対して、好ましくは０．０００１～０．０２モル％である。 The amount of the polymerization initiator used is preferably 0.001 to 1 mol %, more preferably 0.001 to 0.5 mol %, based on the total monomers used in the polymerization (excluding the crosslinking agent). The amount of the reducing agent used is preferably 0.0001 to 0.02 mol %, based on the total monomers used in the polymerization (excluding the crosslinking agent).
　なお、前記重合開始剤に代えて、放射線、電子線、紫外線等の活性エネルギー線を照射して重合反応を実施してもよく、これらの活性エネルギー線と重合開始剤を併用してもよい。 In addition, instead of using the polymerization initiator, the polymerization reaction may be carried out by irradiating the material with active energy rays such as radiation, electron beams, and ultraviolet rays, and these active energy rays may be used in combination with the polymerization initiator.
　（重合形態）
　本発明の一実施形態においてに適用される重合形態としては、特に限定されないが、例えば、水溶液重合、逆相懸濁重合、液滴重合、バルク重合、沈殿重合等が挙げられる。これらの中でも、良好な吸水特性の確保や重合制御の容易性等が向上するとの観点から、水溶液重合又は逆相懸濁重合が好ましい。 (Polymerization form)
The polymerization form applied in one embodiment of the present invention is not particularly limited, and examples thereof include aqueous solution polymerization, reversed-phase suspension polymerization, droplet polymerization, bulk polymerization, precipitation polymerization, etc. Among these, aqueous solution polymerization or reversed-phase suspension polymerization is preferred from the viewpoint of ensuring good water absorption properties and improving ease of polymerization control.
　（３－３）ゲル粉砕工程
　本工程は、前記重合工程で得られた含水ゲルを、ゲル粉砕機（例えば、ニーダー；ミートチョッパー等のスクリュー押出し機；カッターミル等）でゲル粉砕し、粒子状の含水ゲル（以下、「粒子状含水ゲル」と称する）を得る工程である。なお、前記重合工程がニーダー重合の場合には、重合工程及びゲル粉砕工程は同時に実施される。液滴重合や逆相懸濁重合等、粒子状含水ゲルが重合過程で直接得られる場合には、該ゲル粉砕工程が実施されないこともある。 (3-3) Gel Crushing Step This step is a step of pulverizing the hydrogel obtained in the polymerization step with a gel crusher (for example, a kneader; a screw extruder such as a meat chopper; a cutter mill, etc.) to obtain a particulate hydrogel (hereinafter referred to as a "particulate hydrogel"). When the polymerization step is kneader polymerization, the polymerization step and the gel crushing step are carried out simultaneously. When a particulate hydrogel is obtained directly in the polymerization process, such as droplet polymerization or reversed-phase suspension polymerization, the gel crushing step may not be carried out.
　前記以外のゲル粉砕条件や形態については、国際公開第２０１１／１２６０７９号に開示される内容が、本発明に好ましく適用される。 　For gel crushing conditions and forms other than those described above, the contents disclosed in WO 2011/126079 are preferably applied to the present invention.
　（３－４）乾燥工程
　本工程は、前記重合工程及び／又はゲル粉砕工程で得られた粒子状含水ゲルを、所望する樹脂固形分まで乾燥させて乾燥重合体を得る工程である。該樹脂固形分は、乾燥減量（吸水性樹脂１ｇを１８０℃で３時間加熱した際の重量変化）から求められ、好ましくは８０重量％以上、より好ましくは８５～９９重量％、更に好ましくは９０～９８重量％である。 (3-4) Drying step This step is a step of drying the particulate hydrogel obtained in the polymerization step and/or gel crushing step to a desired resin solid content to obtain a dry polymer. The resin solid content is determined from the loss on drying (weight change when 1 g of the water-absorbent resin is heated at 180° C. for 3 hours), and is preferably 80% by weight or more, more preferably 85 to 99% by weight, and even more preferably 90 to 98% by weight.
　前記粒子状含水ゲルの乾燥方法としては、特に限定されないが、例えば、加熱乾燥、熱風乾燥、減圧乾燥、流動層乾燥、攪拌乾燥、赤外線乾燥、マイクロ波乾燥、ドラムドライヤー乾燥、疎水性有機溶媒との共沸脱水による乾燥、高温の水蒸気を利用した高湿乾燥等が挙げられる。中でも、乾燥効率と形状保持とが向上するとの観点から、攪拌乾燥が好ましい。 The method for drying the particulate hydrogel is not particularly limited, but examples include heat drying, hot air drying, reduced pressure drying, fluidized bed drying, stirring drying, infrared drying, microwave drying, drum dryer drying, azeotropic dehydration with a hydrophobic organic solvent, and high humidity drying using high-temperature water vapor. Among these, stirring drying is preferred from the viewpoint of improving drying efficiency and shape retention.
　（３－５）粉砕工程
　粉砕工程は、前記乾燥工程を経て得られた粒子状の乾燥重合体、或いは後述する造粒工程で得られた造粒物又は凝集物又はこれらの乾燥物（乾燥造粒物）を粉砕し、所望の粒子径及び粒子形状に調整する工程である。 (3-5) Pulverization Step The pulverization step is a step of pulverizing the particulate dried polymer obtained through the drying step, or the granules or agglomerates obtained in the granulation step described below, or a dried product thereof (dried granules) to obtain a desired particle size and particle shape.
　本発明の一実施形態においては、吸水性樹脂の一次粒子の造粒物又は凝集物を形成した後の粉砕工程において、粉砕条件を精密に制御することが重要である。本明細書において、吸水性樹脂の一次粒子の造粒物又は凝集物を形成した後の粉砕工程とは、例えば後述する造粒工程にて造粒物又は凝集物を形成した後の粉砕工程であり、好ましくは、後述する造粒工程にて造粒物又は凝集物を形成した後に、さらに乾燥を行うことにより得られる乾燥造粒物の粉砕工程である。 In one embodiment of the present invention, it is important to precisely control the grinding conditions in the grinding step after the formation of granules or aggregates of primary particles of the water-absorbent resin. In this specification, the grinding step after the formation of granules or aggregates of primary particles of the water-absorbent resin refers to, for example, a grinding step after the formation of granules or aggregates in a granulation step described below, and preferably refers to a grinding step of dried granules obtained by further drying after the formation of granules or aggregates in a granulation step described below.
　本発明の一実施形態に係る吸水性樹脂の製造方法は、例えば、水溶液重合の場合は、複数の粉砕工程、例えば、前記重合工程及び／又はゲル粉砕工程で得られた粒子状含水ゲルを乾燥させて得た乾燥重合体を粉砕する粉砕工程と、当該粉砕により得られた粒子状の吸水性樹脂から得られる微粉を造粒工程で造粒・乾燥して得られる乾燥造粒物を粉砕する粉砕工程と、を含み得る。 The method for producing a water-absorbent resin according to one embodiment of the present invention may include, for example, in the case of aqueous solution polymerization, a plurality of pulverization steps, for example, a pulverization step in which a dried polymer obtained by drying a particulate hydrogel obtained in the polymerization step and/or gel pulverization step is pulverized, and a pulverization step in which a fine powder obtained from the particulate water-absorbent resin obtained by the pulverization step is granulated and dried to pulverize a dried granulated product.
　また、本発明の一実施形態に係る吸水性樹脂の製造方法は、逆相懸濁重合の場合は、例えば、多段階の逆相懸濁重合、重合後の一次粒子のゲルに凝集剤を加えること等により得られた一次粒子の凝集体を、乾燥して得られる乾燥造粒物を粉砕する粉砕工程を含み得る。 In the case of reversed-phase suspension polymerization, the method for producing a water-absorbent resin according to one embodiment of the present invention may include, for example, a grinding step in which an aggregate of primary particles obtained by multi-stage reversed-phase suspension polymerization, adding an aggregating agent to a gel of primary particles after polymerization, etc., is dried to obtain a dried granulated product.
　（粉砕装置）
　本工程で用いられる粉砕装置としては、種々の粉砕装置が挙げられるが、本発明の一実施形態においては、粒子状の乾燥重合体又は乾燥造粒物を最適な形状に調整しやすいことから、特定のロール式粉砕装置を使用することが好ましい。前記特定のロール式粉砕装置としては、例えば、２本一対のロールから構成されており、一対のロールのうち少なくとも一方のロールの表面に、ロール回転方向に対して平行に延びる溝（縦溝）が設けられているロール式粉砕装置が用いられる。この特定のロール式粉砕装置に備えられた一対のロール間のクリアランスに粒子状の乾燥重合体又は乾燥造粒物を通すことによって、当該粒子状の乾燥重合体又は乾燥造粒物は、ロール間で圧縮、せん断又は圧密されて、これにより、当該粒子状の乾燥重合体又は乾燥造粒物が粉砕される。このような特定のロール式粉砕装置としては、例えば、ロールグラニュレーター（日本グラニュレーター株式会社製）、ロールグラニュレーター（株式会社栗本鐵工所製）、ＧＲＡＮ－Ｕ－ＬＩＺＥＲ（ＭＰＥ社製）等が挙げられる。この特定のロール式粉砕装置を使用することにより、得られる粉砕物において、破砕され平坦面が露出した粒子の発生が抑制され得る。平坦面が露出した粒子は、吸収性物品における透水性基材の繊維間へ滑り込んで侵入しやすくなる傾向にあるため、該粒子の発生を抑制することが好ましい。 (Crushing device)
Various types of pulverizers can be used in this step, but in one embodiment of the present invention, it is preferable to use a specific roll-type pulverizer because it is easy to adjust the particulate dried polymer or dried granules to an optimal shape. As the specific roll-type pulverizer, for example, a roll-type pulverizer consisting of a pair of rolls, in which at least one of the pair of rolls has a groove (longitudinal groove) extending parallel to the roll rotation direction on the surface, is used. By passing the particulate dried polymer or dried granules through the clearance between the pair of rolls provided in this specific roll-type pulverizer, the particulate dried polymer or dried granules is compressed, sheared or compacted between the rolls, thereby pulverizing the particulate dried polymer or dried granules. Examples of such specific roll-type pulverizers include a roll granulator (manufactured by Nippon Granulator Co., Ltd.), a roll granulator (manufactured by Kurimoto Iron Works Co., Ltd.), and a GRAN-U-LIZER (manufactured by MPE Co., Ltd.). By using this specific roll-type pulverizer, the generation of particles with crushed and exposed flat surfaces can be suppressed in the obtained pulverized product. Particles with exposed flat surfaces tend to easily slide into spaces between the fibers of the water-permeable substrate in absorbent articles, and it is therefore preferable to suppress the generation of such particles.
　一方、前記一対のロールにおいて、両方のロールの表面に溝が無いもの、溝を有していてもロール回転方向に対して垂直に延びる溝が設けられているもの等は、粉砕後の吸水性樹脂の表面に平滑面が多く生じるため、好ましくない。 On the other hand, in the pair of rolls, rolls that have no grooves on the surface of either roll, or rolls that have grooves but that run perpendicular to the direction of roll rotation, are not preferred because they result in many smooth surfaces on the surface of the water-absorbent resin after grinding.
　ここで、吸水性樹脂の一次粒子の造粒物又は凝集物を形成する前の粉砕工程、例えば前述の、造粒前に行う、前記重合工程及び／又はゲル粉砕工程で得られた粒子状含水ゲルを乾燥させて得た乾燥重合体を粉砕する粉砕工程において使用する粉砕装置は、特に限定されるものではなく、前記特定のロール式粉砕装置以外の粉砕装置であってもよいが、前記特定のロール式粉砕装置（例：ロールグラニュレーター）を選択することがより好ましい。 Here, the grinding device used in the grinding step before forming granules or aggregates of primary particles of the water absorbent resin, for example, the grinding step performed before granulation, in which the particulate hydrogel obtained in the polymerization step and/or gel grinding step is dried to grind the dried polymer, is not particularly limited, and may be a grinding device other than the specific roll-type grinding device, but it is more preferable to select the specific roll-type grinding device (e.g., roll granulator).
　本発明の一実施形態において粉砕工程で用いられる、前記特定のロール式粉砕装置の模式図を図３に示す。図３に示すように、ロール式粉砕装置２００は、粒子状の乾燥重合体又は乾燥造粒物を装置２００に供給するための配管２０１と、当該乾燥重合体又は乾燥造粒物を装置２００内に供給する投入口２０２と、供給された乾燥重合体又は乾燥造粒物を粉砕する一対のロール２０３と、を備えている。これらは、この順に上方から下方に向かう方向に配置されている。なお、当該「上方から下方に向かう方向」は鉛直方向に限らず、斜め方向も含み得る概念である。一対のロール２０３は、２本のロール２０３ａ、２０３ｂにより構成されている。なお、ロール式粉砕装置において、ロールは、少なくとも一対（２本）備えられていればよく、例えば、二対（４本）以上のロールが上下方向に並べて備えられていてもよい。例えば、二対のロールが上下方向に並べて配置された場合、乾燥重合体又は乾燥造粒物は、上に位置する一対のロール間を通過して粉砕された後、更に、下に位置する一対のロール間を通過して粉砕される。 A schematic diagram of the specific roll-type grinding device used in the grinding process in one embodiment of the present invention is shown in FIG. 3. As shown in FIG. 3, the roll-type grinding device 200 is provided with a pipe 201 for supplying particulate dried polymer or dried granulated material to the device 200, an inlet 202 for supplying the dried polymer or dried granulated material into the device 200, and a pair of rolls 203 for grinding the supplied dried polymer or dried granulated material. These are arranged in this order in a direction from top to bottom. Note that the "direction from top to bottom" is not limited to the vertical direction, but is a concept that may also include an oblique direction. The pair of rolls 203 is composed of two rolls 203a and 203b. Note that in the roll-type grinding device, at least one pair (two rolls) of rolls may be provided, and for example, two pairs (four rolls) or more of rolls may be provided lined up in the vertical direction. For example, when two pairs of rolls are arranged vertically, the dried polymer or dried granules are crushed by passing between the upper pair of rolls, and then crushed by passing between the lower pair of rolls.
　ロール２０３間に投入された乾燥重合体又は乾燥造粒物２０ａは、一対のロール２０３のロール２０３ａとロール２０３ｂとの間を通過し、乾燥重合体又は乾燥造粒物の粉砕物である吸水性樹脂２０ｂとされる。なお、図示していないが、ロール式粉砕装置２００は、投入口２０２と一対のロール２０３との間に、定量的に供給するフィーダを備えていてもよい。 The dried polymer or dried granulated material 20a fed between the rolls 203 passes between the rolls 203a and 203b of the pair of rolls 203, and is made into water-absorbent resin 20b, which is a pulverized product of the dried polymer or dried granulated material. Although not shown, the roll-type pulverizing device 200 may be provided with a feeder between the feed port 202 and the pair of rolls 203 for quantitative supply.
　前記特定のロール式粉砕装置は、一対のロールのうち少なくともひとつのロール表面に溝（凹凸パターン）を有する。本明細書において、「溝」とは、ロール表面上の凹凸を意味し、本発明の一実施形態においては、溝が縞模様状に並んだものを意味する。溝は、ロール幅方向（ロールの回転軸方向）に複数並んで設けられる。即ち、ロール式粉砕装置において、一対のロールのうち少なくとも一方のロール表面には、ロール回転方向に対して平行に延びる溝（縦溝）が、ロール幅方向に複数並んで設けられている。よって、ロール表面には、凹凸（凹部及び凸部）がロール回転方向に対して平行に延びて形成されている。これにより、一対のロール間のクリアランスが、ロール幅方向の任意の位置において、ロールの回転により実質的に変化しない。ロール幅方向の任意の位置においてロール間のクリアランスが変化しないため、ロール間を通過する乾燥重合体又は乾燥造粒物に適切な力を付与することができ、得られる粉砕物の粒子径が揃い、シャープな粒度分布を有する粉砕物が得られると推定される。なお、本明細書において、「ロール間のクリアランス」とは、対向する一対のロール間の距離を意味する。 The specific roll-type grinding device has grooves (uneven pattern) on the surface of at least one of the pair of rolls. In this specification, "groove" means unevenness on the roll surface, and in one embodiment of the present invention, means grooves arranged in a striped pattern. The grooves are arranged in a row in the roll width direction (the direction of the rotation axis of the roll). That is, in the roll-type grinding device, at least one of the pair of rolls has a plurality of grooves (vertical grooves) arranged in a row in the roll width direction, which extend parallel to the roll rotation direction. Therefore, unevenness (concave and convex parts) is formed on the roll surface, extending parallel to the roll rotation direction. As a result, the clearance between the pair of rolls does not substantially change due to the rotation of the rolls at any position in the roll width direction. Since the clearance between the rolls does not change at any position in the roll width direction, it is possible to apply an appropriate force to the dried polymer or dried granulated material passing between the rolls, and it is presumed that the particle size of the resulting ground product is uniform and a ground product having a sharp particle size distribution is obtained. In addition, in this specification, "clearance between the rolls" means the distance between a pair of opposing rolls.
　本発明の製造方法において好ましい実施形態としては、溝が、一対のロールの２つのロール表面にそれぞれ設けられる。この場合、２つのロールのロール表面に設けられた対応する凹凸が噛み合うことにより、ロール幅方向のどの位置においてもロール間のクリアランスを一定とすることができ、これにより粉砕される乾燥物に対して一定の力を付与することができると考えられる。よって、特に、前記乾燥物の一次粒子の凝集物や造粒物の粉砕において、得られる粉砕物の粒子径がより一層揃いやすく、より一層シャープな粒度分布を有する粉砕物が得られると推定される。一対のロールは同一形状（溝の形状、直径）でも異形状でもよいが、好ましくは同一形状（対称関係を含む）のロールが使用される。 In a preferred embodiment of the manufacturing method of the present invention, grooves are provided on each of the two roll surfaces of a pair of rolls. In this case, it is believed that the clearance between the rolls can be made constant at any position in the roll width direction by meshing corresponding irregularities provided on the roll surfaces of the two rolls, and this makes it possible to apply a constant force to the dried material being pulverized. Therefore, it is presumed that, particularly in pulverizing aggregates of primary particles of the dried material or granulated products, the particle size of the pulverized product obtained is more likely to be uniform, and pulverized products with a sharper particle size distribution can be obtained. The pair of rolls may be the same shape (groove shape, diameter) or different shapes, but it is preferable to use rolls of the same shape (including symmetrical relationship).
　例えば、一実施形態において、ロール式粉砕装置２００は、一対のロール２０３のうち両方のロール表面において、ロール回転方向に対して平行に延びる溝（凹部及び凸部）が設けられている。即ち、図４の２００１に示すように、一対のロール２０３の両方（ロール２０３ａ、２０３ｂ）は、そのロール表面にロールの回転軸Ａのロール回転方向に対して平行に延びる凹部と凸部とを有している。そうして、一対のロールの一方のロール表面に設けられた凸部が、一対のロールの他方のロール表面に設けられた凹部と、回転により噛み合うように構成されている。 For example, in one embodiment, the roll type grinding device 200 has grooves (concave and convex portions) that extend parallel to the roll rotation direction on the roll surface of both of the pair of rolls 203. That is, as shown by 2001 in FIG. 4, both of the pair of rolls 203 ( rolls 203a, 203b) have concave and convex portions on their roll surfaces that extend parallel to the roll rotation direction of the roll rotation axis A of the roll. Thus, the convex portions provided on the roll surface of one of the pair of rolls are configured to mesh with the concave portions provided on the roll surface of the other of the pair of rolls upon rotation.
　また、一実施形態において、図４の２００２に示すように、一対のロール２０３のうち一方（例えば、ロール２０３ａ）は、ロール表面にロールの回転軸Ａのロール回転方向に対して平行に延びる溝を有し、一対のロールのうち他方（例えば、ロール２０３ｂ）は、ロール表面に溝がない滑面（平滑面）を有する。 In one embodiment, as shown in 2002 in FIG. 4, one of the pair of rolls 203 (e.g., roll 203a) has grooves on the roll surface that extend parallel to the roll rotation direction of the roll rotation axis A, and the other of the pair of rolls (e.g., roll 203b) has a smooth surface (flat surface) with no grooves on the roll surface.
　ここで、ロール間のクリアランスについて、図４の２００１及び図４の２００２に基づいて説明する。図４の２００１に示すように、２つのロール２０３ａ、２０３ｂの表面において溝が設けられている場合、そのクリアランスｄは、ロール幅方向の任意の位置において、一定の値ｄとなっている。又、図４の２００２に示すように、一方のロール２０３ａの表面において溝が設けられ、他方のロール２０３ｂの表面において溝が設けられていない場合、そのクリアランスｄは、ロール幅方向の位置により最大値（ｄｍａｘ）と最小値（ｄｍｉｎ）とを有する。図４の２００１、図４の２００２のいずれの形態においても、ロールに設けられた溝はロール回転方向に対して平行に延びて形成されているため、ロールの回転により実質的に変化しない。 Here, the clearance between the rolls will be explained based on 2001 in FIG. 4 and 2002 in FIG. 4. As shown in 2001 in FIG. 4, when grooves are provided on the surfaces of the two rolls 203a and 203b, the clearance d is a constant value d at any position in the roll width direction. Also, as shown in 2002 in FIG. 4, when grooves are provided on the surface of one roll 203a and no grooves are provided on the surface of the other roll 203b, the clearance d has a maximum value (dmax) and a minimum value (dmin) depending on the position in the roll width direction. In both the forms 2001 in FIG. 4 and 2002 in FIG. 4, the grooves provided on the rolls are formed to extend parallel to the roll rotation direction, so they do not substantially change with the rotation of the rolls.
　なお、縦溝構造において、ロールの製造上の事情等により、ロールの一部に横溝（ロール幅方向に延びる溝）又はロール幅方向に延びる凸部が形成される場合がある。このような溝又は凸部により、ロールの縦溝の一部に切り欠き部分が生じる。この場合、ロールの縦溝において形成された一部の切り欠き部分の存在により、ロール幅方向の任意の位置において、クリアランスの変化が生じてしまう。ここで、「ロールの回転により実質的に変化しない」とは、「ロールが１回転するうちの７０％以上の長さ範囲で、好ましくは８０％以上の長さ範囲で、より好ましくは９０％以上の長さ範囲で、更に好ましくは９５％以上の長さ範囲でクリアランスが変化しない」ことを包含する。よって、ロールの縦溝の一部に切り欠き部分が存在する場合であっても、前記規定を満たしている場合は、「ロールの回転により実質的に変化しない」とみなされる。 In addition, in the vertical groove structure, due to circumstances in the manufacture of the roll, horizontal grooves (grooves extending in the roll width direction) or convex parts extending in the roll width direction may be formed in parts of the roll. Such grooves or convex parts cause cutouts in parts of the vertical grooves of the roll. In this case, the presence of some cutout parts formed in the vertical grooves of the roll causes changes in the clearance at any position in the roll width direction. Here, "not substantially changing with the rotation of the roll" includes "not changing the clearance over 70% or more of the length range of one rotation of the roll, preferably over 80% or more of the length range, more preferably over 90% or more of the length range, and even more preferably over 95% or more of the length range." Therefore, even if there are cutout parts in some of the vertical grooves of the roll, if the above regulations are met, it is considered to be "not substantially changing with the rotation of the roll."
　ここで、図４の２００１の形態では、ロール幅方向のどの位置においても、クリアランスｄは同じであるのに対して、図４の２００２の形態では、ロール幅方向の位置によってクリアランスｄが異なる。本発明では、ロール幅方向の位置によってクリアランスｄが異なっていたとしても、任意の位置において、そのクリアランスｄが、ロールの回転により実質的に変化しなければよい。 In the embodiment of 2001 in FIG. 4, the clearance d is the same at any position in the roll width direction, whereas in the embodiment of 2002 in FIG. 4, the clearance d differs depending on the position in the roll width direction. In the present invention, even if the clearance d differs depending on the position in the roll width direction, it is sufficient that the clearance d does not substantially change at any position due to the rotation of the roll.
　なお、図４の２００１及び２００２に示すロールでは、溝は、ロール回転方向に対して、実質的に平行（０度）に延びた形状で設けられている。本明細書において、「実質的に平行」とは、ロール回転方向に対し±１°未満で傾斜した溝は、本発明の構成に含まれることを意味する。当該傾斜角は、ロール回転方向に対してプラス方向又はマイナス方向のいずれでもよい。 In the rolls shown in 2001 and 2002 in FIG. 4, the grooves are provided in a shape that extends substantially parallel (0 degrees) to the roll rotation direction. In this specification, "substantially parallel" means that grooves that are inclined at less than ±1° to the roll rotation direction are included in the configuration of the present invention. The inclination angle may be either positive or negative with respect to the roll rotation direction.
　ロール間のクリアランス最小値ｄｍｉｎは、特に限定されないが、好ましくは０を超えて３ｍｍ以下である。ロール間のクリアランス最小値ｄｍｉｎは、より好ましくは０．０５ｍｍ～３ｍｍ、更に好ましくは０．０５ｍｍ～２．５ｍｍ、更により好ましくは０．１ｍｍ～２ｍｍ、特に好ましくは０．１ｍｍ～１．５ｍｍ、最も好ましくは０．２ｍｍ～１ｍｍである。ロール間のクリアランス最小値ｄｍｉｎが前記範囲であるように一対のロールが配置されることにより、粉砕物における平坦面が露出した粒子の低減効果が更に発揮できる。なお、クリアランス最小値ｄｍｉｎとクリアランス最大値ｄｍａｘとが同じである場合（即ち、図４の２００１の場合）、クリアランスｄがクリアランス最小値ｄｍｉｎとみなされる。粉砕工程で二対以上のロールを用いる場合は、各ロール間で設けられたクリアランス最小値の中で最小の値が前記範囲であればよい。 The minimum clearance value dmin between the rolls is not particularly limited, but is preferably greater than 0 and equal to or less than 3 mm. The minimum clearance value dmin between the rolls is more preferably 0.05 mm to 3 mm, even more preferably 0.05 mm to 2.5 mm, even more preferably 0.1 mm to 2 mm, particularly preferably 0.1 mm to 1.5 mm, and most preferably 0.2 mm to 1 mm. By arranging a pair of rolls so that the minimum clearance value dmin between the rolls is within the above range, the effect of reducing particles with exposed flat surfaces in the crushed product can be further exerted. Note that when the minimum clearance value dmin and the maximum clearance value dmax are the same (i.e., in the case of 2001 in Figure 4), the clearance d is regarded as the minimum clearance value dmin. When two or more pairs of rolls are used in the crushing process, it is sufficient that the smallest value among the minimum clearance values set between each roll is within the above range.
　又、図４の２００２のように、ロール幅方向の位置によってクリアランスｄが異なる場合、各位置でのクリアランスｄを算出し、その最大のクリアランスｄｍａｘと最小のクリアランスｄｍｉｎとの差を「クリアランス差」と称する。クリアランス差は、特に限定されないが、好ましくは０～０．２ｍｍ、より好ましくは０～０．１ｍｍ、更に好ましくは０～０．０５ｍｍである。 Also, as in 2002 in Figure 4, when the clearance d varies depending on the position in the roll width direction, the clearance d at each position is calculated, and the difference between the maximum clearance dmax and the minimum clearance dmin is called the "clearance difference." The clearance difference is not particularly limited, but is preferably 0 to 0.2 mm, more preferably 0 to 0.1 mm, and even more preferably 0 to 0.05 mm.
　ロールに設けられた溝のピッチ（間隔）は粉砕する粒子のサイズに合わせて決定することができる。粉砕粒子サイズが大きい場合は溝のピッチも大きいものを、小さい場合は溝のピッチも小さいものを選定するのが好ましい。溝のピッチは、特に限定されないが、好ましくは０．１ｍｍ～２ｍｍ、より好ましくは０．２ｍｍ～１．５ｍｍ、更に好ましくは０．３ｍｍ～１．２ｍｍの間隔で溝が設けられる。ここで、溝のピッチｐとしては、図４の２００１に示すように、任意の溝の山部分と、それに隣接する溝の山部分との間隔、又は任意の溝の谷部分と、それに隣接する溝の谷部分との間隔を意味する。例えば、溝の山部分及び谷部分との間に周方向に平行な面（以下、「平坦部分」と称する）が設けられている場合、平坦部分を含め、隣接する溝の山部分と山部分との間隔又は隣接する溝の谷部分と谷部分の間隔を意味する。当該溝のピッチは、一つのロール上で異なっていても良いが、ロール幅全体に亘って一定であることが好ましく、一対のロールの両方に溝が設けられている場合は当該一対のロール全体に亘って一定であることが好ましい。 The pitch (spacing) of the grooves on the roll can be determined according to the size of the particles to be crushed. It is preferable to select a large groove pitch when the crushed particle size is large, and a small groove pitch when the crushed particle size is small. The groove pitch is not particularly limited, but is preferably 0.1 mm to 2 mm, more preferably 0.2 mm to 1.5 mm, and even more preferably 0.3 mm to 1.2 mm. Here, the groove pitch p means the spacing between the crest of any groove and the crest of the adjacent groove, or the spacing between the valley of any groove and the valley of the adjacent groove, as shown in 2001 in FIG. 4. For example, when a surface parallel to the circumferential direction (hereinafter referred to as a "flat portion") is provided between the crest and valley of the groove, it means the spacing between the crest and crest of adjacent grooves, including the flat portion, or the spacing between the valley of adjacent grooves. The groove pitch may be different on one roll, but is preferably constant across the entire roll width. When grooves are provided on both of a pair of rolls, it is preferably constant across the entire pair of rolls.
　溝の高さは、特に限定されないが、好ましくは０．１ｍｍ～２ｍｍ、より好ましくは０．２ｍｍ～１．５ｍｍ、更に好ましくは０．３ｍｍ～１ｍｍの高さで溝が設けられる。ここで、溝の高さとしては、図４の２００１に示すように、任意の溝の山部分の頂点と、その溝の谷部分の底との高低差を意味する。 The height of the groove is not particularly limited, but is preferably 0.1 mm to 2 mm, more preferably 0.2 mm to 1.5 mm, and even more preferably 0.3 mm to 1 mm. Here, the height of the groove means the difference in height between the apex of the crest of any groove and the bottom of the valley of that groove, as shown in 2001 in Figure 4.
　（粉砕工程前の吸水性樹脂）
　本発明の一実施形態において、乾燥工程等で得られ、粉砕工程に供される乾燥重合体又は乾燥造粒物は、そのまま全量を粉砕装置、好ましくは前記特定のロール式粉砕装置で粉砕してもよいが、乾燥重合体又は乾燥造粒物の形状に応じて、粉砕装置で粉砕する前に、別の工程、例えば、粗解砕工程に供してもよく、更に分級工程に供してもよい。なお、「粗解砕工程」とは凝集粒子を解す（ほぐす）工程をいう。したがって、乾燥重合体又は乾燥造粒物がブロック状等に凝集している場合、粉砕装置、好ましくは前記特定のロール式粉砕装置での粉砕を効率よく行うため、予め乾燥重合体又は乾燥造粒物を粗解砕しておくこともできる。 (Water absorbent resin before grinding process)
In one embodiment of the present invention, the dried polymer or dried granules obtained in the drying process or the like and subjected to the pulverization process may be pulverized in its entirety in a pulverizer, preferably the specific roll-type pulverizer, but depending on the shape of the dried polymer or dried granules, they may be subjected to another process, for example, a rough crushing process, or may be subjected to a classification process before being pulverized in the pulverizer. The "rough crushing process" refers to a process for loosening (disintegrating) aggregated particles. Therefore, when the dried polymer or dried granules are aggregated in a block shape or the like, the dried polymer or dried granules may be roughly crushed in advance in order to efficiently perform pulverization in a pulverizer, preferably the specific roll-type pulverizer.
　本発明の一実施形態において、粉砕装置、好ましくは前記特定のロール式粉砕装置に投入される乾燥重合体又は乾燥造粒物の粒度分布としては、粒子径８５０μｍ以上の割合（目開き粒子径８５０μｍの篩を通過しなかった粒子の割合）は、乾燥重合体又は乾燥造粒物１００質量％中、好ましくは上限が５０質量％以下、より好ましくは４５質量％以下、更に好ましくは４０質量％以下である（下限は０質量％）。また、乾燥重合体又は乾燥造粒物１００質量％中の粒子径１４００μｍ以上の割合（目開き粒子径１４００μｍの篩を通過しなかった粒子の割合）は好ましくは上限が４０質量％以下、より好ましくは３５質量％以下、更に好ましくは３０質量％以下である（下限は０質量％）。 In one embodiment of the present invention, the particle size distribution of the dried polymer or dried granules fed into the grinding device, preferably the specific roll-type grinding device, is such that the proportion of particles with a diameter of 850 μm or more (the proportion of particles that did not pass through a sieve with an opening diameter of 850 μm) in 100% by mass of the dried polymer or dried granules is preferably 50% by mass or less, more preferably 45% by mass or less, and even more preferably 40% by mass or less (the lower limit is 0% by mass). Also, the proportion of particles with a diameter of 1400 μm or more (the proportion of particles that did not pass through a sieve with an opening diameter of 1400 μm) in 100% by mass of the dried polymer or dried granules is preferably 40% by mass or less, more preferably 35% by mass or less, and even more preferably 30% by mass or less (the lower limit is 0% by mass).
　本発明の一実施形態において、粉砕工程に供される乾燥重合体又は乾燥造粒物の樹脂固形分は、例えば、好ましくは８０～９９質量％、より好ましくは９０～９８．８質量％、更に好ましくは９５～９８．５質量％である。即ち、本発明の乾燥重合体又は乾燥造粒物の含水率は、好ましくは１～２０質量％、より好ましくは１．２～１０質量％、更に好ましくは１．５～５質量％である。乾燥重合体又は乾燥造粒物の固形分率を前記範囲とすることにより、乾燥重合体又は乾燥造粒物により形成される凝集体の大きさ及び硬さを、粉砕工程における粉砕に適したものへと調整することができ、得られる粉砕物において、破砕され平坦面が露出した粒子の発生が抑制できる。平坦面が露出した粒子は、吸収性物品における透水性基材の繊維間へ滑り込んで侵入しやすくなる傾向にあり、該粒子の発生を抑制することが好ましい。なお、乾燥重合体又は乾燥造粒物の樹脂固形分の決定方法は、「（３－４）乾燥工程」で説明したとおりである。 In one embodiment of the present invention, the resin solid content of the dried polymer or dried granules subjected to the pulverization step is, for example, preferably 80 to 99% by mass, more preferably 90 to 98.8% by mass, and even more preferably 95 to 98.5% by mass. That is, the moisture content of the dried polymer or dried granules of the present invention is preferably 1 to 20% by mass, more preferably 1.2 to 10% by mass, and even more preferably 1.5 to 5% by mass. By setting the solid content rate of the dried polymer or dried granules within the above range, the size and hardness of the aggregates formed by the dried polymer or dried granules can be adjusted to be suitable for pulverization in the pulverization step, and the generation of particles with crushed flat surfaces exposed in the obtained pulverized product can be suppressed. Particles with exposed flat surfaces tend to easily slide and penetrate between the fibers of the water-permeable substrate in the absorbent article, and it is preferable to suppress the generation of such particles. The method for determining the resin solid content of the dried polymer or dried granules is as explained in "(3-4) Drying step".
　本発明一実施形態において、一対のロールのロール間のクリアランスと、ロール式粉砕装置に供される乾燥重合体又は乾燥造粒物の質量平均粒子径とは、１：０．３～１：１０の関係であることが好ましい。この場合、乾燥重合体又は乾燥造粒物の一次粒子が形成する凝集体を解砕するのに適した圧力が、粉砕される際に乾燥重合体又は乾燥造粒物に付与され、破砕され平坦面が露出した粒子の発生が抑制できる。一対のロールのロール間のクリアランスと、ロール式粉砕装置に供される乾燥重合体又は乾燥造粒物の質量平均粒子径とは、より好ましくは１：０．５～１：５であり、更に好ましくは１：０．９～１：３である。 In one embodiment of the present invention, the relationship between the clearance between the pair of rolls and the mass average particle size of the dried polymer or dried granules fed to the roll-type grinding device is preferably 1:0.3 to 1:10. In this case, a pressure suitable for breaking down agglomerates formed by the primary particles of the dried polymer or dried granules is applied to the dried polymer or dried granules during grinding, and the generation of particles with crushed, flat surfaces exposed, can be suppressed. The relationship between the clearance between the pair of rolls and the mass average particle size of the dried polymer or dried granules fed to the roll-type grinding device is more preferably 1:0.5 to 1:5, and even more preferably 1:0.9 to 1:3.
　（３－６）分級工程
　前記粉砕工程を経て得られる吸水性樹脂（例えば吸水性樹脂粉末）は、必要に応じて、更に分級工程に供される。本発明の一実施形態において、分級工程での粒度調整方法としては、特に限定されないが、例えば、ＪＩＳ標準篩（ＪＩＳ　Ｚ８８０１－１（２０００））を用いた篩分級や気流分級等が挙げられる。 (3-6) Classification step The water absorbent resin (for example, water absorbent resin powder) obtained through the pulverization step is further subjected to a classification step, if necessary. In one embodiment of the present invention, the particle size adjustment method in the classification step is not particularly limited, and examples thereof include sieve classification using a JIS standard sieve (JIS Z8801-1 (2000)) and air flow classification.
　（３－７）表面架橋工程
　前記粉砕工程（及びその後の任意の工程）を経て得られる吸水性樹脂（例えば、吸水性樹脂粉末）は、表面架橋剤によって表面架橋されることが好ましい。該表面架橋は、吸水性樹脂の表面層（吸水性樹脂の表面から数１０μｍ内部までの領域）に架橋密度の高い部分を設ける処理である。表面架橋処理を行うことで各種吸水特性を向上させることができる。本明細書において、吸水性樹脂には、表面架橋された吸水性樹脂も含まれる。 (3-7) Surface Cross-Linking Step The water-absorbent resin (for example, water-absorbent resin powder) obtained through the pulverization step (and any subsequent step) is preferably surface-cross-linked with a surface cross-linking agent. The surface cross-linking is a treatment for providing a portion with high cross-linking density in the surface layer of the water-absorbent resin (a region from the surface of the water-absorbent resin to the interior of the resin by several tens of μm). By carrying out the surface cross-linking treatment, various water-absorbing properties can be improved. In this specification, the water-absorbent resin also includes a surface-cross-linked water-absorbent resin.
　（表面架橋剤）
　本工程で使用される表面架橋剤としては、特に限定されないが、例えば、有機又は無機の表面架橋剤が挙げられる。中でも、吸水性樹脂の物性や表面架橋剤の取扱性が向上するとの観点から、カルボキシル基と反応する有機表面架橋剤が好ましい。例えば、米国特許７１８３４５６号に開示される１種又は２種以上の表面架橋剤が挙げられる。具体的には、多価アルコール化合物、エポキシ化合物、ハロエポキシ化合物、多価アミン化合物、多価アミン化合物とハロエポキシ化合物との縮合物、オキサゾリン化合物、オキサゾリジノン化合物、多価金属塩、アルキレンカーボネート化合物、環状尿素化合物等が挙げられる。 (Surface Cross-Linking Agent)
The surface cross-linking agent used in this step is not particularly limited, but may be, for example, an organic or inorganic surface cross-linking agent. Among them, from the viewpoint of improving the physical properties of the water-absorbent resin and the handling of the surface cross-linking agent, an organic surface cross-linking agent that reacts with a carboxyl group is preferred. For example, one or more surface cross-linking agents disclosed in U.S. Patent No. 7,183,456 may be mentioned. Specifically, polyhydric alcohol compounds, epoxy compounds, haloepoxy compounds, polyvalent amine compounds, condensates of polyvalent amine compounds and haloepoxy compounds, oxazoline compounds, oxazolidinone compounds, polyvalent metal salts, alkylene carbonate compounds, cyclic urea compounds, etc. may be mentioned.
　（３－８）造粒工程
　本発明の一実施形態に係る吸水性樹脂の製造方法は、一次粒子の凝集体を得るための造粒工程を含むことが好ましい。 (3-8) Granulation Step The method for producing a water-absorbent resin according to one embodiment of the present invention preferably includes a granulation step for obtaining aggregates of primary particles.
　例えば、逆相懸濁重合の場合は、多段階の逆相懸濁重合、重合後の一次粒子のゲルに凝集剤を加えること等により、一次粒子の凝集体を得ることができる。したがってこれらの工程は、造粒工程であるといえる。 For example, in the case of reversed-phase suspension polymerization, aggregates of primary particles can be obtained by performing multiple reversed-phase suspension polymerizations and adding a flocculant to the gel of primary particles after polymerization. Therefore, these processes can be said to be granulation processes.
　水溶液重合の場合は、造粒工程としては、吸水性樹脂微粉、例えば、１５０μｍの目開きのＪＩＳ標準篩を通過する吸水性樹脂の微粒子に水性液を添加して攪拌・混合することが挙げられる。 In the case of aqueous solution polymerization, the granulation process may involve adding an aqueous liquid to fine powder of water-absorbent resin, for example, fine particles of water-absorbent resin that pass through a JIS standard sieve with 150 μm openings, and stirring and mixing the liquid.
　前記吸水性樹脂微粉の平均粒子径は、１５０μｍ～１０μｍの範囲内であることが好ましい。前記吸水性樹脂微粉全量に対する、１５０μｍ以下の粒径を有する微粉の含有量は、７０質量％以上が好ましく、９０質量％以上がより好ましい。 The average particle size of the water-absorbent resin fine powder is preferably within the range of 150 μm to 10 μm. The content of fine powder having a particle size of 150 μm or less relative to the total amount of the water-absorbent resin fine powder is preferably 70 mass% or more, and more preferably 90 mass% or more.
　前記水性液は前記吸水性樹脂微粉との混合前に加熱しておくことが好ましい。前記水性液の吸水性樹脂微粉との混合時の温度は、通常４０℃以上、好ましくは５０℃以上、より好ましくは６０℃以上、さらに好ましくは７０℃以上である。前記水性液の吸水性樹脂微粉との混合時の温度の上限は水性液の沸点以下である。沸点は塩類や他の溶媒の添加、圧力（減圧、加圧）等を変化させて種々調整してもよいが、温度が１００℃を越えても大きな変化はないため、通常１００℃以下とすることが好ましい。 It is preferable to heat the aqueous liquid before mixing it with the water-absorbent resin fine powder. The temperature when mixing the aqueous liquid with the water-absorbent resin fine powder is usually 40°C or higher, preferably 50°C or higher, more preferably 60°C or higher, and even more preferably 70°C or higher. The upper limit of the temperature when mixing the aqueous liquid with the water-absorbent resin fine powder is below the boiling point of the aqueous liquid. The boiling point may be adjusted in various ways by adding salts or other solvents, changing the pressure (reduced or increased pressure), etc., but since there is no significant change even if the temperature exceeds 100°C, it is usually preferable to keep it below 100°C.
　前記水性液の添加量は、吸水性樹脂微粉１００質量部に対して、好ましくは１００質量部未満、より好ましくは８０質量部以下であって、好ましくは１０質量部以上、より好ましくは１５質量部以上、更に好ましくは２０質量部以上である。 The amount of the aqueous liquid added is preferably less than 100 parts by mass, more preferably 80 parts by mass or less, and is preferably 10 parts by mass or more, more preferably 15 parts by mass or more, and even more preferably 20 parts by mass or more, relative to 100 parts by mass of the water-absorbent resin fine powder.
　本発明の一実施形態において、加熱された前記水性液と前記吸水性樹脂微粉とは高速混合することが好ましい。本明細書において、「高速混合」とは、水性液と吸水性樹脂微粉との接触時点から、含水ゲル状造粒物が生成するまでの時間が短時間である混合である。混合時間が短い場合には、水性液と微粉との均一な混合が可能であり、混合物が一体化した巨大なゲル状物となることを防ぐことができる。また、混合時間が短い場合、得られる吸水性樹脂の水可溶分の増加や加圧下吸水倍率の低下等、吸水性樹脂の性能低下を防ぐことができる。水性液と吸水性樹脂微粉との接触時点から含水ゲル状造粒物が生成するまでの時間は、好ましくは３分以下、より好ましくは１分以下である。水性液の投入時間も短い方が好ましく、６０秒以下であることが好ましく、３０秒以下であることがさらに好ましく、１０秒以下であることが最も好ましい。 In one embodiment of the present invention, the heated aqueous liquid and the water-absorbent resin fine powder are preferably mixed at high speed. In this specification, "high speed mixing" refers to mixing in which the time from the contact of the aqueous liquid with the water-absorbent resin fine powder to the generation of a hydrous gel-like granule is short. When the mixing time is short, the aqueous liquid and the fine powder can be mixed uniformly, and it is possible to prevent the mixture from becoming a giant gel-like product integrated with the fine powder. In addition, when the mixing time is short, it is possible to prevent a decrease in the performance of the water-absorbent resin, such as an increase in the water-soluble content of the obtained water-absorbent resin and a decrease in the water absorption capacity under pressure. The time from the contact of the aqueous liquid with the water-absorbent resin fine powder to the generation of a hydrous gel-like granule is preferably 3 minutes or less, more preferably 1 minute or less. The time for adding the aqueous liquid is also preferably short, preferably 60 seconds or less, more preferably 30 seconds or less, and most preferably 10 seconds or less.
　前述の高速混合が達成できれば、用いる混合機は特に限定されない。例えば、容器固定型混合機であれば、機械攪拌型混合機が好ましい。具体的には、タービューライザー（ホソカワミクロン社製）、レーディゲミキサー（レーディゲ社製）、及びモルタルミキサー（西日本試験機社製）等が挙げられる。バッチ式混合機及び連続式合機のいずれを用いてもよい。処理量が少ない場合は、小型のフードプロセッサー等を用いても良い。 　There are no particular limitations on the mixer used, so long as the aforementioned high-speed mixing can be achieved. For example, if the mixer is a fixed-container type, a mechanical agitation type mixer is preferred. Specific examples include the Turbulizer (manufactured by Hosokawa Micron Corporation), the Loedige Mixer (manufactured by Loedige Corporation), and the Mortar Mixer (manufactured by Nishinippon Shikenki Co., Ltd.). Either a batch type mixer or a continuous type mixer may be used. If the processing volume is small, a small food processor or the like may be used.
　得られる含水ゲル状造粒物は、さらに乾燥して造粒強度を向上させた乾燥造粒物とすることが好ましい。含水ゲル状造粒物を乾燥することにより、微粉はより強固に一体化され、一次粒子の凝集体形状が維持される。乾燥方法は前記（３－４）と同じ条件が適用できる。なお、ここで、「含水ゲル状造粒物」は、水溶液重合の場合に得られる前記含水ゲル状造粒物及び逆相懸濁重合の場合に得られる一次粒子の凝集体のいずれをも含む趣旨である。 The obtained hydrogel-like granules are preferably further dried to obtain dried granules with improved granulation strength. By drying the hydrogel-like granules, the fine powder is more firmly integrated and the aggregate shape of the primary particles is maintained. The same drying conditions as in (3-4) above can be applied. Note that the term "hydrogel-like granules" as used herein includes both the hydrogel-like granules obtained in the case of aqueous solution polymerization and the aggregates of primary particles obtained in the case of reversed-phase suspension polymerization.
　本発明の一実施形態に係る吸水性樹脂の製造方法は、造粒工程を含むとともに、造粒工程で得られた吸水性樹脂を、前述の特定のロール式粉砕装置を使用して粉砕する粉砕工程を含むことがさらに好ましい。これにより、透水性基材に対する繊維間への侵入抵抗性が好適な吸水性樹脂を製造することができる。 The method for producing a water-absorbent resin according to one embodiment of the present invention includes a granulation step, and more preferably includes a crushing step in which the water-absorbent resin obtained in the granulation step is crushed using the specific roll-type crushing device described above. This makes it possible to produce a water-absorbent resin that has good resistance to penetration between fibers of a water-permeable substrate.
　（３－９）その他の工程
　本発明の一実施形態に係る吸水性樹脂の製造方法は、上述した各工程以外に、必要に応じて、含水（再湿潤）工程、その他の添加剤添加工程、整粒工程、及び微粉再利用工程を含んでいてもよい。また、輸送工程、貯蔵工程、梱包工程、保管工程等を更に含んでいてもよい。 (3-9) Other Steps The method for producing a water-absorbent resin according to one embodiment of the present invention may include, in addition to the above-mentioned steps, a water-containing (rewetting) step, a step of adding other additives, a granulation step, and a fine powder reuse step, if necessary. In addition, the method may further include a transport step, a storage step, a packaging step, a keeping step, and the like.
　（再湿潤工程）
　任意に実施される本工程は、前記表面架橋工程で得られた吸水性樹脂（例えば、吸水性樹脂粒子）に、多価金属塩、カチオン性ポリマー、キレート剤、無機還元剤、α－ヒドロキシカルボン酸化合物からなる群から選択される少なくとも１種の添加剤を添加する工程である。 (Rewetting process)
This step, which is optionally performed, is a step of adding at least one kind of additive selected from the group consisting of a polyvalent metal salt, a cationic polymer, a chelating agent, an inorganic reducing agent, and an α-hydroxycarboxylic acid compound to the water absorbent resin (e.g., water absorbent resin particles) obtained in the surface cross-linking step.
　前記の添加剤は、水溶液又は分散液（スラリー）として吸水性樹脂（例えば、吸水性樹脂粒子）に添加することが好ましい。なお、当該添加剤は上述した表面架橋剤溶液と同時に添加・混合してもよい。 The additive is preferably added to the water-absorbent resin (e.g., water-absorbent resin particles) as an aqueous solution or dispersion (slurry). The additive may be added and mixed simultaneously with the above-mentioned surface cross-linking agent solution.
　具体的には、国際特許公開第２０１５／０５３３７２号「（２－７）再湿潤工程」に記載の方法が、本発明にも適用される。 Specifically, the method described in International Patent Publication No. 2015/053372, "(2-7) Rewetting step," is also applicable to the present invention.
　（添加剤添加工程）
　本発明の一実施形態に係る吸水性樹脂の製造方法においては、上述した添加剤以外の添加剤（以下、「その他の添加剤」と称する）を、吸水性樹脂に種々の機能を付加させるために添加することもできる。該その他の添加剤として、具体的には、界面活性剤、リン原子を有する化合物、酸化剤、有機還元剤、水不溶性無機微粒子、有機粉末（例えば、金属石鹸等）、消臭剤、抗菌剤、パルプや熱可塑性繊維等が挙げられる。なお、前記水不溶性無機微粒子は、国際特許公開第２０１１／０４０５３０号の「〔５〕水不溶性無機微粒子」に開示された化合物を本発明に適用できる。これら水不溶性無機微粒子を添加することにより、吸水性樹脂（粒子）と透水性基材との間に適度な摩擦が生じ、吸収性物品に使用した場合に、吸水性樹脂が透水性基材に対する繊維間へ侵入することが抑制されるため好ましい。該水不溶性無機微粒子の中でも、特にシリカ（二酸化珪素）を添加することが好ましい。ここで、前記水不溶性無機微粒子は、重合工程等で添加する粉末状無機凝集剤を兼ねても良いし、別途添加してもよい。 (Additive addition process)
In the method for producing a water-absorbent resin according to one embodiment of the present invention, additives other than the additives described above (hereinafter referred to as "other additives") may be added to impart various functions to the water-absorbent resin. Specific examples of the other additives include surfactants, compounds having phosphorus atoms, oxidizing agents, organic reducing agents, water-insoluble inorganic fine particles, organic powders (e.g., metal soaps, etc.), deodorants, antibacterial agents, pulp, thermoplastic fibers, etc. In addition, the water-insoluble inorganic fine particles disclosed in "[5] Water-insoluble inorganic fine particles" of International Patent Publication No. 2011/040530 can be applied to the present invention. By adding these water-insoluble inorganic fine particles, appropriate friction occurs between the water-absorbent resin (particles) and the water-permeable substrate, and when used in an absorbent article, the water-absorbent resin is suppressed from penetrating between the fibers of the water-permeable substrate, which is preferable. Among the water-insoluble inorganic fine particles, it is particularly preferable to add silica (silicon dioxide). Here, the water-insoluble inorganic fine particles may also serve as a powdered inorganic flocculant added in the polymerization step or the like, or may be added separately.
　（整粒工程）
　「整粒工程」とは、前記表面架橋工程を経て緩く凝集した吸水性樹脂をほぐして粒子径を整える工程を意味する。なお、この整粒工程は、表面架橋工程以降の微粉除去工程及び分級工程を含むものとする。整粒工程は吸水性樹脂の粒子径を整え、安定した吸水物性を得る観点から、実施されることが好ましい。 (Sizing process)
The "size regulation step" means a step of loosening the water absorbent resin loosely aggregated through the surface cross-linking step to regulate the particle size. This size regulation step includes a fine powder removal step and a classification step subsequent to the surface cross-linking step. The size regulation step is preferably carried out from the viewpoint of regulating the particle size of the water absorbent resin and obtaining stable water absorption properties.
　（微粉再利用工程）
　「微粉再利用工程」とは、前記各工程で篩分級等により発生した微粉を、そのまま又は微粉を造粒した後に、いずれかの工程に供給する工程を意味する。微粉再利用工程は、吸水性樹脂の生産ロスを低減する観点から、実施されることが好ましい。 (Fine powder recycling process)
The "fine powder reuse step" means a step of supplying the fine powder generated by sieve classification or the like in each step to any of the steps as it is or after granulating the fine powder. The fine powder reuse step is preferably carried out from the viewpoint of reducing production loss of the water absorbent resin.
　〔４〕吸水性樹脂の用途
　本発明の一実施形態に係る吸水性樹脂の用途は、特に限定されないが、紙オムツ（幼児用、成人用）、生理用ナプキン、失禁パッド等の吸収性物品の吸収体用途が好ましい。特に、吸水性樹脂及び透水性基材を備える、紙オムツの吸収体として好適に使用することができる。その他の吸収性物品としては、例えば、土壌保水剤、育苗用シート、種子コーティング材、結露防止シート、ドリップ吸収材、鮮度保持材、使い捨てカイロ、冷却用バンダナ、保冷剤、医療用廃液固化剤、残土固化材、水損防止廃液ゲル化剤、吸水土のう、災害用簡易トイレ、湿布材、化粧品用増粘剤、電気・電子材料通信ケーブル用止水材、ガスケットパッキング、肥料用徐放剤、各種徐放剤（空間除菌剤、芳香剤等）、ペットシート、ネコ砂、創傷保護用ドレッシング材、結露防止用建築資材、油中水分除去剤、塗料、接着剤、樹脂用添加剤（アンチブロッキング剤、光拡散剤、艶消し剤、化粧板用添加剤、人工大理石用添加剤、トナー用添加剤等）等が挙げられる。 [4] Uses of the water-absorbent resin The uses of the water-absorbent resin according to one embodiment of the present invention are not particularly limited, but are preferably used as absorbents in absorbent articles such as paper diapers (for infants and adults), sanitary napkins, incontinence pads, etc. In particular, the water-absorbent resin can be suitably used as an absorbent for paper diapers that include a water-absorbent resin and a water-permeable substrate. Other absorbent articles include, for example, soil water retention agents, seedling sheets, seed coating materials, condensation prevention sheets, drip absorbents, freshness-preserving materials, disposable hand warmers, cooling bandanas, ice packs, medical waste liquid solidifying agents, residual soil solidifying materials, water damage prevention waste liquid gelling agents, water-absorbing sandbags, disaster-use portable toilets, poultice materials, thickeners for cosmetics, water-stopping materials for electrical and electronic materials and communication cables, gasket packing, sustained-release agents for fertilizers, various sustained-release agents (space disinfectants, air fresheners, etc.), pet sheets, cat litter, wound protection dressing materials, condensation prevention building materials, oil moisture removers, paints, adhesives, resin additives (anti-blocking agents, light diffusing agents, matting agents, additives for decorative panels, additives for artificial marble, additives for toners, etc.), and the like.
　〔５〕吸収性物品
　本発明の一実施形態に係る吸収性物品は、液不透過性のバックシート、透水性基材に対する繊維間への侵入抵抗性が６０重量％以上のポリ（メタ）アクリル酸（塩）系吸水性樹脂と透水性基材とを含む吸収体、及び液透過性のトップシートをこの順に含む。 [5] Absorbent article An absorbent article according to one embodiment of the present invention includes, in this order, a liquid-impermeable back sheet, an absorbent body containing a poly(meth)acrylic acid (salt)-based water-absorbent resin having a resistance to penetration between fibers of 60% by weight or more in the water-permeable substrate and a water-permeable substrate, and a liquid-permeable top sheet.
　本発明の一実施形態において、前記液不透過性のバックシートとしては、吸収性物品を構成する液不透過性のシートとして使用できる公知のシートを使用することができ、特に限定されない。前記液不透過性のバックシートとしては、例えば、ポリエチレンフィルム等の薄いプラスチックフィルムを用いることができる。前記プラスチックフィルムの中でも、前記吸収性物品の使用者に快適さを提供するため、通気性のフィルムがより好ましい。 In one embodiment of the present invention, the liquid-impermeable back sheet can be any known sheet that can be used as a liquid-impermeable sheet constituting an absorbent article, and is not particularly limited. The liquid-impermeable back sheet can be, for example, a thin plastic film such as a polyethylene film. Among the plastic films, a breathable film is more preferable in order to provide comfort to the user of the absorbent article.
　本発明の一実施形態において、前記液透過性のトップシートとしては、吸収性物品を構成する液透過性のシートとして使用できる公知のシートを使用することができ、特に限定されない。前記液透過性のトップシートは、通常、不織布であり、例えば、エアスルー不織布、ポイントボンド不織布、スパンボンド不織布、スパンレース不織布、メルトブロー不織布、エアレイド不織布又はこれらから選ばれる２種以上の不織布の積層体であってよい。２種以上の不織布の積層体としては、例えば、スパンボンド／メルトブロー／スパンボンド（ＳＭＳ）不織布、スパンボンド／メルトブロー／メルトブロー／スパンボンド（ＳＭＭＳ）不織布等が挙げられる。 In one embodiment of the present invention, the liquid-permeable top sheet may be any known sheet that can be used as a liquid-permeable sheet constituting an absorbent article, and is not particularly limited. The liquid-permeable top sheet is usually a nonwoven fabric, and may be, for example, an air-through nonwoven fabric, a point-bonded nonwoven fabric, a spunbonded nonwoven fabric, a spunlace nonwoven fabric, a melt-blown nonwoven fabric, an air-laid nonwoven fabric, or a laminate of two or more nonwoven fabrics selected from these. Examples of laminates of two or more nonwoven fabrics include spunbond/melt-blown/spunbond (SMS) nonwoven fabric, spunbond/melt-blown/melt-blown/spunbond (SMMS) nonwoven fabric, etc.
　前記液透過性のトップシートを構成する物質は、特に限定されず、例えば、ポリプロピレン、ポリエチレン、ポリエステル等の合成繊維等を挙げることができる。これらの物質は、単独で使用されてもよいし、２種以上を併用してもよい。また、これらの前記合成繊維は界面活性剤で親水化処理されていることが好ましい。 The material constituting the liquid-permeable top sheet is not particularly limited, and examples include synthetic fibers such as polypropylene, polyethylene, and polyester. These materials may be used alone or in combination of two or more. In addition, it is preferable that these synthetic fibers are hydrophilized with a surfactant.
　本発明の一実施形態において、前記吸収体は、前述の吸水性樹脂と透水性基材とを含む。一般的な吸収体の構成としては、例えば、吸水性樹脂粒子及び透水性基材が均一混合された構成、シート状の透水性基材又は層状に形成された繊維状の透水性基材の間に吸水性樹脂粒子が挟まれた構成等が挙げられるが、本発明の一実施形態においては、シート状の透水性基材の内部又は層状に形成された繊維状の透水性基材間における、吸液対象の液の透過性を十分に発揮させる観点から、透水性基材内部に吸水性樹脂が存在しない構成が好ましい。即ち、前述の吸水性樹脂と透水性基材とがそれぞれ層を形成している構成が好ましい。吸水性樹脂層と透水性基材層とはそれぞれ１つの層を形成してもよいし、少なくとも一方が複数の層を形成し、吸水性樹脂層と透水性基材層とが交互に積層されていてもよい。なお、本発明において、「透水性基材層」とは、シート状の透水性基材からなる透水性基材層、及び、層状に形成された繊維状の透水性基材からなる透水性基材層を含む趣旨である。具体的には、シート状の透水性基材からなる透水性基材層の上に吸水性樹脂層が配置された構成、層状に形成された繊維状の透水性基材からなる透水性基材層の上に吸水性樹脂層が配置された構成、吸水性樹脂層の上に前記透水性基材層が配置された構成、複数の前記透水性基材層の間に吸水性樹脂層が挟まれた構成が好ましい。 In one embodiment of the present invention, the absorbent includes the above-mentioned water-absorbent resin and water-permeable substrate. Typical absorbent structures include, for example, a structure in which water-absorbent resin particles and water-permeable substrate are uniformly mixed, a structure in which water-absorbent resin particles are sandwiched between sheet-shaped water-permeable substrates or fibrous water-permeable substrates formed in layers, and the like. In one embodiment of the present invention, from the viewpoint of fully exerting the permeability of the liquid to be absorbed inside the sheet-shaped water-permeable substrate or between fibrous water-permeable substrates formed in layers, a structure in which the water-absorbent resin is not present inside the water-permeable substrate is preferred. That is, a structure in which the above-mentioned water-absorbent resin and the water-permeable substrate each form a layer is preferred. The water-absorbent resin layer and the water-permeable substrate layer may each form one layer, or at least one of them may form multiple layers, and the water-absorbent resin layer and the water-permeable substrate layer may be alternately laminated. In the present invention, the "water-permeable substrate layer" is intended to include a water-permeable substrate layer made of a sheet-shaped water-permeable substrate and a water-permeable substrate layer made of a fibrous water-permeable substrate formed in layers. Specifically, preferred configurations include a configuration in which a water-absorbent resin layer is disposed on a water-permeable substrate layer made of a sheet-like water-permeable substrate, a configuration in which a water-absorbent resin layer is disposed on a water-permeable substrate layer made of a fibrous water-permeable substrate formed in a layered form, a configuration in which the water-permeable substrate layer is disposed on a water-absorbent resin layer, and a configuration in which a water-absorbent resin layer is sandwiched between a plurality of the water-permeable substrate layers.
　前記シート状の透水性基材としては、不織布を用いることができる。例えば、エアスルー不織布、ポイントボンド不織布、スパンボンド不織布、スパンレース不織布、メルトブロー不織布、エアレイド不織布又はこれらから選ばれる２種以上の不織布の積層体であってよい。２種以上の不織布の積層体は、例えば、スパンボンド／メルトブロー／スパンボンド（ＳＭＳ）不織布、スパンボンド／メルトブロー／メルトブロー／スパンボンド（ＳＭＭＳ）不織布等が挙げられる。 A nonwoven fabric can be used as the sheet-like water-permeable substrate. For example, it may be an air-through nonwoven fabric, a point-bonded nonwoven fabric, a spunbonded nonwoven fabric, a spunlace nonwoven fabric, a melt-blown nonwoven fabric, an air-laid nonwoven fabric, or a laminate of two or more nonwoven fabrics selected from these. Examples of laminates of two or more nonwoven fabrics include spunbond/melt-blown/spunbond (SMS) nonwoven fabrics and spunbond/melt-blown/melt-blown/spunbond (SMMS) nonwoven fabrics.
　前記シート状の透水性基材を構成する物質は、特に限定されず、例えば、ポリプロピレン、ポリエチレン、ポリエステル等の合成繊維等を挙げることができる。これらの物質は、単独で使用されてもよいし、２種以上を併用してもよい。また、これらの前記合成繊維は界面活性剤で親水化処理されていることが好ましい。 The material constituting the sheet-like water-permeable substrate is not particularly limited, and examples include synthetic fibers such as polypropylene, polyethylene, and polyester. These materials may be used alone or in combination of two or more. In addition, it is preferable that these synthetic fibers are hydrophilized with a surfactant.
　前記シート状の透水性基材の厚みは、液拡散性を発揮する観点から、好ましくは１ｍｍ以上であり、より好ましくは３ｍｍ以上である。また、前記シート状の透水性基材の厚みは、吸収性物品の厚みを抑制する観点から、好ましくは９ｍｍ以下であり、より好ましくは４ｍｍ以下である。 The thickness of the sheet-like water-permeable substrate is preferably 1 mm or more, more preferably 3 mm or more, from the viewpoint of exerting liquid diffusibility. Also, the thickness of the sheet-like water-permeable substrate is preferably 9 mm or less, more preferably 4 mm or less, from the viewpoint of suppressing the thickness of the absorbent article.
　前記シート状の透水性基材の目付量は、液拡散性を発揮する観点から、好ましい下限は３０ｇ／ｍ２以上であり、より好ましくは４０ｇ／ｍ２以上である。また、上限は、好ましくは１００ｇ／ｍ２以下であり、より好ましくは５０ｇ／ｍ２以下である。 From the viewpoint of exerting liquid diffusibility, the weight per unit area of the sheet-like water-permeable substrate is preferably 30 g/ m2 or more as a lower limit, more preferably 40 g/m2 or more as a higher limit, and is preferably 100 g/m2 or less, more preferably 50 g/m2 or less as an upper limit.
　前記繊維状の透水性基材としては、例えば、パルプ繊維、コットンリンター架橋セルロース繊維、レーヨン、綿、羊毛、アセテート及びビニロン等を挙げることができる。前記繊維状の透水性基材は、単独で用いられてもよく、２種以上を組み合わせて用いられてもよい。 Examples of the fibrous water-permeable substrate include pulp fiber, cotton linter cross-linked cellulose fiber, rayon, cotton, wool, acetate, vinylon, etc. The fibrous water-permeable substrate may be used alone or in combination of two or more kinds.
　前記吸収体において、吸水性樹脂の使用量（坪量）は、吸水性樹脂存在領域の面積に対して、好ましくは５０～３００ｇ／ｍ２、より好ましくは１００～２００ｇ／ｍ２である。吸水性樹脂の使用量が前記範囲である場合、優れた液拡散性と高い液体吸収力を兼ね備えた吸収性物品とすることができる。なお、本発明において、前記「吸水性樹脂存在領域」とは、前記吸収体において前記吸水性樹脂が散布されている全領域を指す。 In the absorbent body, the amount of the water-absorbent resin used (basis weight) is preferably 50 to 300 g/m 2 , more preferably 100 to 200 g/m 2 , relative to the area of the water-absorbent resin-existing region. When the amount of the water-absorbent resin used is within the above range, an absorbent article having both excellent liquid diffusibility and high liquid absorption capacity can be obtained. In the present invention, the "water-absorbent resin-existing region" refers to the entire region in the absorbent body where the water-absorbent resin is dispersed.
　本発明の一実施形態において、吸収体は、前記吸水性樹脂及び透水性基材以外に、添加剤を含んでいてもよい。前記添加剤は、吸収性物品における吸収体に一般に含まれ得る添加剤を使用することができ、特に限定されない。前記添加剤の具体例としては、例えば、無機粉末（例えば非晶質シリカ）、消臭剤、顔料、染料、抗菌剤、香料及び粘着剤等を挙げることができる。前記吸水性樹脂が無機粒子を含む場合、前記吸収体は、当該吸水性樹脂中の無機粒子とは別に無機粉末を含んでいてもよい。前記無機粉末としては、例えば、二酸化ケイ素、ゼオライト、カオリン及びクレイ等が挙げられる。 In one embodiment of the present invention, the absorbent may contain an additive in addition to the water-absorbent resin and the water-permeable substrate. The additive may be any additive that may be generally contained in absorbents in absorbent articles, and is not particularly limited. Specific examples of the additive include inorganic powders (e.g., amorphous silica), deodorants, pigments, dyes, antibacterial agents, fragrances, and adhesives. When the water-absorbent resin contains inorganic particles, the absorbent may contain inorganic powders in addition to the inorganic particles in the water-absorbent resin. Examples of the inorganic powder include silicon dioxide, zeolite, kaolin, and clay.
　本発明の一実施形態に係る吸収性物品は、上述の構成以外に、吸収体の形状を維持するため、吸収体の少なくとも一面を覆うコアラップや立体ギャザーを有していてもよい。 In addition to the above-mentioned configuration, the absorbent article according to one embodiment of the present invention may have a core wrap or three-dimensional gathers that cover at least one surface of the absorbent body in order to maintain the shape of the absorbent body.
　本発明の一実施形態に係る吸収性物品のコアラップは、例えば、ティッシュペーパー、特にクレープ紙、不織布、特にポリプロピレン、ポリエチレン、ポリエステル等の合成繊維による、エアスルー不織布、ポイントボンド不織布、スパンボンド不織布、スパンレース不織布等であり得る。さらに、前記コアラップは、これらの複合不織布でもあり得る。前記複合不織布としては、例えば、スパンボンド／メルトブロー／スパンボンド（ＳＭＳ不織布）や、スパンボンド／メルトブロー／メルトブロー／スパンボンドのような不織布（ＳＭＭＳ不織布）が挙げられる。これらのコアラップは界面活性剤で親水化処理されていることが好ましい。 The core wrap of the absorbent article according to one embodiment of the present invention may be, for example, tissue paper, particularly crepe paper, nonwoven fabric, particularly air-through nonwoven fabric, point-bonded nonwoven fabric, spunbonded nonwoven fabric, spunlace nonwoven fabric, etc., made of synthetic fibers such as polypropylene, polyethylene, polyester, etc. Furthermore, the core wrap may be a composite nonwoven fabric of these. Examples of the composite nonwoven fabric include spunbond/meltblown/spunbond (SMS nonwoven fabric) and nonwoven fabrics such as spunbond/meltblown/meltblown/spunbond (SMMS nonwoven fabric). It is preferable that these core wraps are hydrophilized with a surfactant.
　本発明の一実施形態に係る吸収性物品における吸収体の厚みは、１ｍｍ～１０ｍｍであることが好ましく、１ｍｍ～５ｍｍであることがより好ましい。また、本発明の一実施形態に係る吸収性物品全体の厚みは、１．２ｍｍ～１５ｍｍであることが好ましく、１．２ｍｍ～１０ｍｍであることがより好ましい。 The thickness of the absorbent body in an absorbent article according to one embodiment of the present invention is preferably 1 mm to 10 mm, and more preferably 1 mm to 5 mm. The thickness of the entire absorbent article according to one embodiment of the present invention is preferably 1.2 mm to 15 mm, and more preferably 1.2 mm to 10 mm.
　すなわち、本発明は、以下の構成からなるものである。 In other words, the present invention has the following configuration.
　〔１〕下記（１）～（３）の手順により決定される、透水性基材に対する繊維間への侵入抵抗性が６０重量％以上である、ポリ（メタ）アクリル酸（塩）系吸水性樹脂：
　（１）いずれもケース内面の寸法で、底面６ｃｍ×９ｃｍ、深さ１ｃｍの、ポリスチレン製の直方体のケースの底面に、６ｃｍ×９ｃｍに切り取った不織布を両面テープで固定する
　　ここで、前記不織布は、厚み３ｍｍ、目付量４１ｇ／ｍ２であり、ポリエチレン、ポリプロピレン及びポリエチレンテレフタレートの混合物製のエアスルー不織布であって、ポリエチレンの繊維径及びポリプロピレンの繊維径は０．１８ｍｍ、ポリエチレンテレフタレートの繊維径は０．２７ｍｍである；
　（２）吸水性樹脂１．０ｇを、前記不織布の全面に均一に散布し、前記ケースよりも底面積が大きい受け皿の上で、前記吸水性樹脂を散布した前記不織布をケースごと逆さにし、前記受け皿上に脱落した吸水性樹脂を回収する；
　（３）下記式（１）に従い、透水性基材に対する繊維間への侵入抵抗性を算出する
透水性基材に対する繊維間への侵入抵抗性［重量％］＝回収した吸水性樹脂の重量［ｇ］／散布した吸水性樹脂の重量［ｇ］×１００　式（１）。 [1] A poly(meth)acrylic acid (salt)-based water-absorbing resin having a resistance to penetration between fibers of a water-permeable substrate of 60% by weight or more, as determined by the following steps (1) to (3):
(1) A nonwoven fabric cut to 6 cm x 9 cm is fixed with double-sided tape to the bottom of a rectangular polystyrene case having a bottom of 6 cm x 9 cm and a depth of 1 cm, both of which are the dimensions of the inner surface of the case. Here, the nonwoven fabric is an air-through nonwoven fabric made of a mixture of polyethylene, polypropylene and polyethylene terephthalate, with a thickness of 3 mm and a basis weight of 41 g/ m2 , and the fiber diameter of the polyethylene and the polypropylene is 0.18 mm, and the fiber diameter of the polyethylene terephthalate is 0.27 mm;
(2) 1.0 g of a water-absorbent resin is uniformly spread over the entire surface of the nonwoven fabric, and the nonwoven fabric with the water-absorbent resin spread thereon is inverted together with the case over a tray having a bottom area larger than that of the case, and the water-absorbent resin that has fallen onto the tray is collected;
(3) Calculate the penetration resistance between fibers in the water-permeable substrate according to the following formula (1): Penetration resistance between fibers in the water-permeable substrate [wt %] = weight of recovered water absorbent resin [g] / weight of sprayed water absorbent resin [g] × 100 Formula (1).
　〔２〕ボルテックス法による吸水速度が５０秒以下である、〔１〕に記載のポリ（メタ）アクリル酸（塩）系吸水性樹脂。 [2] The poly(meth)acrylic acid (salt)-based water-absorbing resin according to [1], which has a water absorption speed of 50 seconds or less as measured by the vortex method.
　〔３〕質量平均粒子径（Ｄ５０）が、２５０μｍ～８００μｍである、〔１〕または〔２〕に記載のポリ（メタ）アクリル酸（塩）系吸水性樹脂。 [3] A poly(meth)acrylic acid (salt)-based water-absorbing resin according to [1] or [2], having a mass average particle diameter (D50) of 250 μm to 800 μm.
　〔４〕水不溶性無機微粒子を含む、〔１〕～〔３〕のいずれか１つに記載のポリ（メタ）アクリル酸（塩）系吸水性樹脂。 [4] A poly(meth)acrylic acid (salt)-based water-absorbing resin according to any one of [1] to [3], which contains water-insoluble inorganic fine particles.
　〔５〕液不透過性のバックシート、吸水性樹脂と透水性基材とを含む吸収体、及び液透過性のトップシートをこの順に含む吸収性物品であって、
　前記吸水性樹脂は、ポリ（メタ）アクリル酸（塩）系吸水性樹脂であるとともに、
　下記（１）～（３）の手順により決定される、透水性基材に対する繊維間への侵入抵抗性が６０重量％以上の吸水性樹脂である、吸収性物品：
　（１）いずれもケース内面の寸法で、底面６ｃｍ×９ｃｍ、深さ１ｃｍの、ポリスチレン製の直方体のケースの底面に、６ｃｍ×９ｃｍに切り取った不織布を両面テープで固定する
　　ここで、前記不織布は、厚み３ｍｍ、目付量４１ｇ／ｍ２であり、ポリエチレン、ポリプロピレン及びポリエチレンテレフタレートの混合物製のエアスルー不織布であり、ポリエチレンの繊維径及びポリプロピレンの繊維径は０．１８ｍｍ、ポリエチレンテレフタレートの繊維径は０．２７ｍｍである；
　（２）吸水性樹脂１．０ｇを、前記不織布の全面に均一に散布し、前記ケースよりも底面積が大きい受け皿の上で、前記吸水性樹脂を散布した前記不織布をケースごと逆さにし、前記受け皿上に脱落した吸水性樹脂を回収する；
　（３）下記式（１）に従い、透水性基材に対する繊維間への侵入抵抗性を算出する
透水性基材に対する繊維間への侵入抵抗性［重量％］＝回収した吸水性樹脂の重量［ｇ］／散布した吸水性樹脂の重量［ｇ］×１００　式（１）。 [5] An absorbent article comprising, in this order, a liquid-impermeable back sheet, an absorbent body containing a water-absorbent resin and a water-permeable substrate, and a liquid-permeable top sheet,
The water-absorbing resin is a poly(meth)acrylic acid (salt)-based water-absorbing resin,
An absorbent article, comprising a water-absorbent resin having a penetration resistance between fibers of a water-permeable substrate of 60% by weight or more, as determined by the following procedures (1) to (3):
(1) A nonwoven fabric cut to 6 cm x 9 cm is fixed with double-sided tape to the bottom of a rectangular polystyrene case having a bottom of 6 cm x 9 cm and a depth of 1 cm, both of which are the dimensions of the inner surface of the case. Here, the nonwoven fabric is an air-through nonwoven fabric made of a mixture of polyethylene, polypropylene and polyethylene terephthalate, with a thickness of 3 mm and a basis weight of 41 g/ m2 , the fiber diameter of the polyethylene and the fiber diameter of the polypropylene being 0.18 mm, and the fiber diameter of the polyethylene terephthalate being 0.27 mm;
(2) 1.0 g of a water-absorbent resin is uniformly spread over the entire surface of the nonwoven fabric, and the nonwoven fabric with the water-absorbent resin spread thereon is inverted together with the case over a tray having a bottom area larger than that of the case, and the water-absorbent resin that has fallen onto the tray is collected;
(3) Calculate the penetration resistance between fibers in the water-permeable substrate according to the following formula (1): Penetration resistance between fibers in the water-permeable substrate [wt %] = weight of recovered water absorbent resin [g] / weight of sprayed water absorbent resin [g] × 100 Formula (1).
　〔６〕前記吸水性樹脂のボルテックス法による吸水速度が５０秒以下である、〔５〕に記載の吸収性物品。 [6] The absorbent article according to [5], in which the water-absorbing resin has a water-absorbing speed of 50 seconds or less when measured by a vortex method.
　〔７〕前記吸水性樹脂の質量平均粒子径（Ｄ５０）が、２５０μｍ～８００μｍである、〔５〕または〔６〕に記載の吸収性物品。 [7] The absorbent article according to [5] or [6], wherein the mass average particle diameter (D50) of the water-absorbent resin is 250 μm to 800 μm.
　〔８〕前記吸水性樹脂が、水不溶性無機微粒子を含む、〔５〕～〔７〕のいずれか１つに記載の吸収性物品。 [8] The absorbent article according to any one of [5] to [7], wherein the water-absorbent resin contains water-insoluble inorganic fine particles.
　〔９〕前記透水性基材が、シート状の透水性基材であり、
　前記シート状の透水性基材の厚みが１ｍｍ以上、目付量が５０ｇ／ｍ２以下である、〔５〕～〔８〕のいずれか１つに記載の吸収性物品。 [9] The water-permeable substrate is a sheet-shaped water-permeable substrate,
The absorbent article according to any one of [5] to [8], wherein the sheet-like water-permeable substrate has a thickness of 1 mm or more and a basis weight of 50 g/m2 or less .
　以下に示す実施例及び比較例に従って本発明をより具体的に説明するが、本発明はこれらに限定解釈されるものではなく、各実施例に記載された技術的手段を組み合わせて得られる実施例も、本発明の範囲に含まれることとする。なお、実施例において「部」あるいは「％」の表示を用いる場合があるが、特に断りがない限り、「質量部」あるいは「質量％」を表す。又、特記しない限り、各操作は、室温（２３℃±２℃）、相対湿度４０～５０％ＲＨ下で行われる。なお、実施例及び比較例で使用する電気機器（吸水性樹脂の物性測定も含む）は、特に注釈のない限り、２００Ｖ又は１００Ｖ、６０Ｈｚの条件で電源を使用した。 The present invention will be described in more detail with reference to the following examples and comparative examples, but the present invention is not limited to these examples. Examples obtained by combining the technical means described in each example are also included in the scope of the present invention. In the examples, the terms "parts" and "%" may be used, but unless otherwise specified, they represent "parts by mass" or "% by mass." Unless otherwise specified, each operation is performed at room temperature (23°C ± 2°C) and a relative humidity of 40-50% RH. Unless otherwise noted, the electrical equipment used in the examples and comparative examples (including the measurement of the physical properties of the water-absorbent resin) was powered by a power source of 200V or 100V, 60Hz.
　〔１．評価方法〕
　〔１－１〕吸水性樹脂の無加圧下吊り下げ吸水倍率（ＦＳＣ）
　吸水性樹脂の無加圧下吊り下げ吸水倍率（ＦＳＣ）は、ＥＤＡＮＡ法（ＥＲＴ４４０．２－０２）に準拠して測定した。 1. Evaluation Method
[1-1] Suspension absorption capacity without pressure (FSC) of water-absorbent resin
The free suspension water absorption capacity (FSC) of the water-absorbent resin was measured in accordance with the EDANA method (ERT440.2-02).
　具体的には、吸水性樹脂０．２ｇを不織布製の袋に入れた後、大過剰の０．９０質量％塩化ナトリウム水溶液中に３０分間浸漬して自由膨潤させた。その後、袋を引き上げ、１０分間吊り下げて水切りをした後の吸水倍率（単位：ｇ／ｇ）を求めた。 Specifically, 0.2 g of the water-absorbent resin was placed in a nonwoven bag, and then immersed in a large excess of 0.90% by mass sodium chloride aqueous solution for 30 minutes to allow free swelling. The bag was then removed and hung for 10 minutes to drain, after which the water absorption capacity (unit: g/g) was determined.
　〔１－２〕吸水性樹脂の加圧下吸水倍率（ＡＡＰ）
　吸水性樹脂のＡＡＰ（加圧下吸水倍率）は、ＥＤＡＮＡ法（ＥＲＴ４４２．２－０２）に準拠して測定した。なお、荷重条件は４．８３ｋＰａ（０．７ｐｓｉ）に変更した。 [1-2] Absorption capacity under pressure (AAP) of water-absorbent resin
The AAP (absorbency against pressure) of the water-absorbent resin was measured in accordance with the EDANA method (ERT442.2-02). Note that the load condition was changed to 4.83 kPa (0.7 psi).
　〔１－３〕吸水性樹脂の含水率
　吸水性樹脂の含水率は、ＥＤＡＮＡ法（ＥＲＴ４３０．２－０２）に準拠して測定した。なお、測定に際し、試料（吸水性樹脂）の質量を１．０ｇに、乾燥温度を１８０℃に、乾燥時間を３時間にそれぞれ変更した。 [1-3] Moisture content of water-absorbent resin The moisture content of the water-absorbent resin was measured according to the EDANA method (ERT430.2-02). Note that, during the measurement, the mass of the sample (water-absorbent resin) was changed to 1.0 g, the drying temperature was changed to 180° C., and the drying time was changed to 3 hours.
　具体的には、底面の直径が５０ｍｍのアルミカップに、試料（吸水性樹脂）１．０ｇを投入した後、前記試料及びアルミカップの総質量Ｗ１（ｇ）を正確に秤量した。 Specifically, 1.0 g of sample (water-absorbent resin) was placed in an aluminum cup with a bottom diameter of 50 mm, and the total mass W1 (g) of the sample and aluminum cup was then accurately weighed.
　次に、前記試料をアルミカップに投入した状態で、雰囲気温度１８０℃に設定されたオーブン内に静置した。３時間経過後、該試料をアルミカップとともに前記オーブンから取り出し、乾燥後の試料及びアルミカップの総質量Ｗ２（ｇ）を正確に秤量した。本測定に供された試料（吸水性樹脂）の質量をＭ（１．０ｇ）としたときに、下記式（３）にしたがって、試料の含水率（質量％）を算出した：
含水率（質量％）＝｛（Ｗ１－Ｗ２）／Ｍ｝×１００・・・式（３）。 Next, the sample was placed in an aluminum cup and left to stand in an oven set at an atmospheric temperature of 180° C. After 3 hours, the sample was removed from the oven together with the aluminum cup, and the total mass W2 (g) of the dried sample and aluminum cup was accurately weighed. When the mass of the sample (water-absorbent resin) used in this measurement was M (1.0 g), the moisture content (mass%) of the sample was calculated according to the following formula (3):
Moisture content (mass%) = {(W1-W2)/M}×100...Formula (3).
　〔１－４〕吸水性樹脂の質量平均粒子径（Ｄ５０）
　吸水性樹脂の質量平均粒子径（Ｄ５０）は、米国特許第７６３８５７０号のカラム２７、２８に記載された「（3）Mass-Average Particle Diameter(D50) and Logarithmic Standard Deviation(σζ) of Particle Diameter Distribution」に記載の方法に従って測定した。 [1-4] Mass average particle diameter (D50) of water absorbent resin
The mass-average particle diameter (D50) of the water-absorbent resin was measured according to the method described in “(3) Mass-Average Particle Diameter (D50) and Logarithmic Standard Deviation (σζ) of Particle Diameter Distribution” in columns 27 and 28 of U.S. Pat. No. 7,638,570.
　〔１－５〕吸水性樹脂の嵩比重
　吸水性樹脂の嵩比重は、ＥＤＡＮＡ法（ＥＲＴ４６０．２－０２）に準拠して測定した。 [1-5] Bulk density of water-absorbent resin The bulk density of the water-absorbent resin was measured in accordance with the EDANA method (ERT460.2-02).
　〔１－６〕吸水性樹脂の吸水速度（ボルテックス法）
　０．９０質量％塩化ナトリウム水溶液（生理食塩水）１０００質量部に、食品添加物である食用青色１号を０．０２質量部添加し、液温３０℃に調整した。生理食塩水５０ｍｌを１００ｍｌビーカーに計り取り、長さ４０ｍｍで、長さ方向に垂直な断面の直径８ｍｍの円筒形のスターラーチップ及びマグネチックスターラーを用いて６００ｒｐｍで攪拌しながら、吸水性樹脂２．０ｇを一度に投入した。吸水性樹脂が生理食塩水を吸液してスターラーチップを覆うまでの時間を吸水速度（秒）として算出した。 [1-6] Water absorption rate of water-absorbent resin (Vortex method)
0.02 parts by mass of edible blue No. 1, a food additive, was added to 1000 parts by mass of a 0.90% by mass aqueous solution of sodium chloride (physiological saline), and the liquid temperature was adjusted to 30° C. 50 ml of physiological saline was measured into a 100 ml beaker, and 2.0 g of water-absorbent resin was added at once while stirring at 600 rpm using a cylindrical stirrer tip with a length of 40 mm and a cross section perpendicular to the length direction and a magnetic stirrer. The time until the water-absorbent resin absorbed the physiological saline and covered the stirrer tip was calculated as the water absorption rate (seconds).
　〔１－７〕吸水性樹脂の透水性基材に対する繊維間への侵入抵抗性
　吸水性樹脂の「透水性基材に対する繊維間への侵入抵抗性」は、下記に示す手順にて測定した。 [1-7] Resistance of Water-Absorbent Resin to Penetration Between Fibers of Water-Permeable Substrate The "resistance of water-absorbent resin to penetration between fibers of water-permeable substrate" was measured by the following procedure.
　ポリスチレン製の直方体のケース（底面６ｃｍ×９ｃｍ、深さ１ｃｍ（いずれもケース内面の寸法））の底面に、６ｃｍ×９ｃｍに切り取った不織布（厚みが３ｍｍで、目付量が４１ｇ／ｍ２の、ポリエチレン、ポリプロピレン、及びポリエチレンテレフタレートの混合物製のエアスルー不織布であって、ポリエチレンの繊維径及びポリプロピレンの繊維径は０．１８ｍｍ、ポリエチレンテレフタレートの繊維径は０．２７ｍｍである。）を両面テープで固定した。吸水性樹脂１．０ｇを、前記エアスルー不織布の全面に均一に散布した。続いて、前記ケースよりも底面積が大きい受け皿の上で吸水性樹脂を散布した不織布をケースごと逆さにし、受け皿上に脱落した吸水性樹脂を回収した。ここで、回収された吸水性樹脂は、不織布の繊維間へ侵入しなかった吸水性樹脂である。下記式（１）に従って、透水性基材に対する繊維間への侵入抵抗性を算出した。 A nonwoven fabric cut to 6 cm x 9 cm was fixed to the bottom of a rectangular polystyrene case (bottom surface 6 cm x 9 cm, depth 1 cm (both dimensions of the inner surface of the case)) with double-sided tape. The nonwoven fabric (3 mm thick, 41 g/ m2 weight per unit area, made of a mixture of polyethylene, polypropylene, and polyethylene terephthalate, the fiber diameter of the polyethylene and the fiber diameter of the polypropylene are 0.18 mm, and the fiber diameter of the polyethylene terephthalate is 0.27 mm) was cut to 6 cm x 9 cm. The nonwoven fabric was fixed to the bottom of the rectangular polystyrene case (bottom surface 6 cm x 9 cm, depth 1 cm (both dimensions of the inner surface of the case) with double-sided tape. 1.0 g of water-absorbing resin was uniformly sprayed over the entire surface of the air-through nonwoven fabric. Next, the nonwoven fabric with the water-absorbing resin sprayed thereon was turned upside down on a tray with a base area larger than that of the case, and the water-absorbing resin that had fallen onto the tray was collected. Here, the collected water-absorbing resin is the water-absorbing resin that did not penetrate between the fibers of the nonwoven fabric. The penetration resistance between the fibers of the water-permeable substrate was calculated according to the following formula (1).
　透水性基材に対する繊維間への侵入抵抗性［重量％］＝回収した吸水性樹脂の重量［ｇ］／散布した吸水性樹脂の重量［ｇ］×１００・・・式（１）。 　Resistance to penetration between fibers in permeable substrate [wt %] = weight of recovered absorbent resin [g] / weight of sprayed absorbent resin [g] x 100 ... formula (1).
　〔１－８〕吸収シートの液戻り量評価
　（１）吸収シートの作製
　図１の１００１は吸収シート１００を真上から見た図、図１の１００２は吸収シート１００を、Ｘ－Ｙ平面に垂直、かつＸ軸又はＹ軸に平行な方向に切断したときの断面図である。１０ｃｍ×１１ｃｍにカットした粘着テープ２（ＮＩＴＴＯ　ＤＥＮＫＯ製ビニールテープＮｏ．２１Ｓ）の粘着面の、四辺の端部からそれぞれ１ｃｍずつ内側に位置する四辺に囲まれた領域に吸水性樹脂１を０．５ｇ均一に散布した。散布した吸水性樹脂の上に、吸水性樹脂を散布した領域と同面積、即ち、８ｃｍ×９ｃｍの不織布３（厚みが３ｍｍで、目付量が４１ｇ／ｍ２の、ポリエチレン、ポリプロピレン、及びポリエチレンテレフタレートの混合物製のエアスルー不織布であって、ポリエチレンの繊維径及びポリプロピレンの繊維径は０．１８ｍｍ、ポリエチレンテレフタレートの繊維径は０．２７ｍｍである。）を載せた。該エアスルー不織布の上に、更に、吸水性樹脂１を０．５ｇ、該エアスルー不織布全面に対して均一に散布し、１０ｃｍ×１１ｃｍの液透過性不織布４（エアレイド不織布、目付量４６．６ｇ／ｍ２）を載せ、四辺の粘着面と貼り合わせて、評価用吸収シート１００を作製した。 [1-8] Evaluation of Liquid Wet-back Amount of Absorbent Sheet (1) Preparation of Absorbent Sheet In Fig. 1, 1001 is a view of absorbent sheet 100 as seen from directly above, and 1002 in Fig. 1 is a cross-sectional view of absorbent sheet 100 cut perpendicular to the X-Y plane and parallel to the X-axis or Y-axis. 0.5 g of water-absorbent resin 1 was uniformly sprayed onto an area surrounded by four sides located 1 cm inward from each end of the four sides on the adhesive surface of adhesive tape 2 (vinyl tape No. 21S made by NITTO DENKO) cut to 10 cm x 11 cm. On the sprayed water-absorbent resin, a nonwoven fabric 3 (3 mm thick, 41 g/ m2 basis weight, air-through nonwoven fabric made of a mixture of polyethylene, polypropylene, and polyethylene terephthalate, the fiber diameters of the polyethylene and polypropylene being 0.18 mm, and the fiber diameter of the polyethylene terephthalate being 0.27 mm) was placed with the same area as the area where the water-absorbent resin was sprayed, i.e., 8 cm x 9 cm. Further, 0.5 g of water-absorbent resin 1 was sprayed uniformly on the entire surface of the air-through nonwoven fabric, and a liquid-permeable nonwoven fabric 4 (airlaid nonwoven fabric, 46.6 g/ m2 basis weight) of 10 cm x 11 cm was placed and attached to the adhesive surfaces on all four sides to prepare an absorbent sheet 100 for evaluation.
　（２）液戻り量（液保持性）の測定
　評価用吸収シート１００を、液透過性不織布４を上面として平坦な台上に設置した。シリンジ（シリンジ針のゲージ：２１Ｇ）を用いて、その先端を評価用吸収シート１００中央部に接触させながら、２０℃の０．９質量％塩化ナトリウム水溶液１０ｇを、４５秒間かけて評価用吸収シートに添加した（１回目液添加）。１回目液添加開始から１０分後に、１回目液添加と同様の手順で、２０℃の０．９質量％塩化ナトリウム水溶液２０ｇを、４５秒間かけて添加した（２回目液添加）。２回目液添加開始から１０分後に、２回目液添加と同様の手順で、２０℃の０．９質量％塩化ナトリウム水溶液２０ｇを、４５秒間かけて添加した（３回目液添加）。３回目液添加開始から１０分後に、５．５ｃｍ×５．５ｃｍにカットした、総重量Ｋ１（ｇ）のキッチンペーパー（王子ネピア株式会社製キッチンタオル）３２枚を、評価用吸収シートの中央部に載せ、それと同時に該キッチンペーパーの最上部に、Φ５．５ｃｍ、重量５００ｇの錘（荷重：０．３ｐsｉ）を載せた。該キッチンペーパー及び錘を載せてから１０秒後に、該キッチンペーパー及び錘を取り除いて、該キッチンペーパー３２枚の総重量Ｋ２（ｇ）を測定し、下記式（４）に基づいて、該キッチンペーパーが吸収した液量として液戻り量を算出した。
液戻り量（ｇ）＝Ｋ２－Ｋ１・・・式（４）。 (2) Measurement of Liquid Return Amount (Liquid Retention) The absorbent sheet 100 for evaluation was placed on a flat table with the liquid-permeable nonwoven fabric 4 on the upper surface. Using a syringe (gauge of syringe needle: 21G), 10 g of 0.9% by mass sodium chloride aqueous solution at 20°C was added to the absorbent sheet for evaluation over 45 seconds while the tip of the syringe was in contact with the center of the absorbent sheet for evaluation 100 (first liquid addition). 10 minutes after the start of the first liquid addition, 20 g of 0.9% by mass sodium chloride aqueous solution at 20°C was added over 45 seconds in the same manner as the first liquid addition (second liquid addition). 10 minutes after the start of the second liquid addition, 20 g of 0.9% by mass sodium chloride aqueous solution at 20°C was added over 45 seconds in the same manner as the second liquid addition (third liquid addition). Ten minutes after the start of the third liquid addition, 32 sheets of kitchen paper (Oji Nepia kitchen towels) cut to 5.5 cm x 5.5 cm and having a total weight K1 (g) were placed on the center of the absorbent sheet for evaluation, and at the same time, a weight (load: 0.3 psi) having a diameter of 5.5 cm and a weight of 500 g was placed on the top of the kitchen paper. 10 seconds after the kitchen paper and the weight were placed, the kitchen paper and the weight were removed, and the total weight K2 (g) of the 32 sheets of kitchen paper was measured, and the amount of liquid return was calculated as the amount of liquid absorbed by the kitchen paper based on the following formula (4).
Amount of liquid return (g)=K2−K1...Equation (4).
　〔１－９〕不織布の厚み測定
　不織布の厚みは、ダイヤルシックネスゲージ　大型タイプ（厚み測定器）（株式会社尾崎製作所製、型番：Ｊ－Ｂ、測定子：アンビル上下φ５０ｍｍ）を用い、厚み測定器の上部測定子を不織布から２～３ｍｍの高さ位置まで近づけた後、不織布に圧力が出来るだけかからないよう、ハンドルからゆっくりと手を離し、不織布の厚みを測定した。 [1-9] Measurement of Nonwoven Fabric Thickness The thickness of the nonwoven fabric was measured using a large-type dial thickness gauge (thickness gauge) (manufactured by Ozaki Manufacturing Co., Ltd., model number: J-B, gauge head: anvil top and bottom φ50 mm). The upper gauge head of the thickness gauge was brought close to a height position of 2 to 3 mm from the nonwoven fabric, and then the handle was slowly released so as to apply as little pressure as possible to the nonwoven fabric, and the thickness of the nonwoven fabric was measured.
　〔１－１０〕吸収性物品の液拡散性評価
　後述の実施例及び比較例にて製造された吸収性物品を、液透過性不織布を上面として平坦な台上に設置した。シリンジ（シリンジ針のゲージ：２１Ｇ）を用いて、その先端を吸収性物品の中央部に接触させながら、青色１号で着色した２０℃の０．９質量％塩化ナトリウム水溶液１０ｇを、４５秒間かけて吸収性物品に添加した。液添加開始から１分後に、塩化ナトリウム水溶液によって着色された着色域の、縦方向の最大長さ及び横方向の最大長さをそれぞれ測定し、吸収性物品の液拡散性を評価した。なお、本発明において、「縦方向」とは、吸収性物品の長辺方向を、「横方向」とは、吸収性物品の短辺方向を、それぞれ表す。 [1-10] Evaluation of Liquid Diffusion of Absorbent Articles The absorbent articles manufactured in the examples and comparative examples described below were placed on a flat table with the liquid-permeable nonwoven fabric on the upper surface. Using a syringe (gauge of syringe needle: 21G), 10 g of 0.9% by mass sodium chloride aqueous solution at 20°C colored with Blue No. 1 was added to the absorbent article over 45 seconds while the tip of the syringe was in contact with the center of the absorbent article. One minute after the start of liquid addition, the maximum length in the vertical direction and the maximum length in the horizontal direction of the colored area colored by the sodium chloride aqueous solution were measured, and the liquid diffusibility of the absorbent article was evaluated. In the present invention, the "vertical direction" refers to the long side direction of the absorbent article, and the "horizontal direction" refers to the short side direction of the absorbent article.
　〔１－１１〕不織布及び吸収体の厚み測定
　不織布及び吸収体の厚みは、ダイヤルシックネスゲージ　大型タイプ（厚み測定器）（株式会社　尾崎製作所製、型番：Ｊ－Ｂ、測定子：アンビル上下φ５０ｍｍ）を用い、厚み測定器の上部測定子を不織布及び吸収体から２～３ｍｍの高さ位置まで近づけた後、不織布及び吸収体に圧力が出来るだけかからないよう、ハンドルからゆっくりと手を離し、不織布及び吸収体の厚みを測定した。 [1-11] Measurement of thickness of nonwoven fabric and absorbent body The thickness of the nonwoven fabric and absorbent body was measured using a large-type dial thickness gauge (thickness measuring device) (manufactured by Ozaki Seisakusho Co., Ltd., model number: J-B, measuring probe: anvil top and bottom φ50 mm). The upper measuring probe of the thickness measuring device was brought close to a height of 2 to 3 mm from the nonwoven fabric and absorbent body, and then the handle was slowly released so as to apply as little pressure as possible to the nonwoven fabric and absorbent body, and the thickness of the nonwoven fabric and absorbent body was measured.
　〔２．吸水性樹脂〕
　〔２－１．吸水性樹脂の製造〕
　〔実施例１〕
　容量１Ｌのポリプロピレン製容器に、アクリル酸３６４ｇ、内部架橋剤としてポリエチレングリコールジアクリレート（分子量５２２．６６、平均エチレンオキサイドユニット数：ｎ＝９）２．１１ｇ、キレート剤として０．１重量％のジエチレントリアミン５酢酸・３ナトリウム水溶液２２．１６ｇ、４８．５重量％の水酸化ナトリウム水溶液２９６ｇ及びイオン交換水３３０ｇを投入して撹拌、混合して単量体水溶液（１）を作製した。なお、単量体水溶液（１）の液温は、中和熱によって約８０℃まで上昇した。 [2. Water-absorbent resin]
[2-1. Production of water-absorbent resin]
Example 1
In a 1 L polypropylene container, 364 g of acrylic acid, 2.11 g of polyethylene glycol diacrylate (molecular weight 522.66, average number of ethylene oxide units: n=9) as an internal crosslinking agent, 22.16 g of a 0.1 wt% aqueous solution of trisodium diethylenetriaminepentaacetate as a chelating agent, 296 g of a 48.5 wt% aqueous solution of sodium hydroxide, and 330 g of ion-exchanged water were charged and stirred to prepare an aqueous monomer solution (1). The liquid temperature of the aqueous monomer solution (1) was raised to about 80° C. due to heat of neutralization.
　前記単量体水溶液（１）の攪拌を継続し、前記単量体水溶液（１）の液温が７８℃となった時点で３．８重量％の過硫酸ナトリウム水溶液１５．８ｇを添加した。その後、直ちにステンレス製バット型反応装置（底面：３４０×３４０ｍｍ、高さ：２５ｍｍ、内表面：テフロン（登録商標）コーティング）に前記単量体水溶液（１）を注ぎ込んだところ、間もなく重合反応が開始した。なお、前記ステンレス製バット型反応装置の下には、ホットプレート（ＮＥＯ　ＨＯＴＰＬＡＴＥ　ＨＩ－１０００／株式会社井内盛栄堂製）が備えられており、バットの内表面温度が５０℃となるように予め設定した。前記重合反応が開始すると、反応液（１）は水蒸気を発生しながらゲル化し、生成したゲルは発泡しながら四方八方に膨張した後、収縮した。この膨張及び収縮は約１分で終了した。その後生成物を３分間反応装置内に保持することで、含水ゲル状架橋重合体（１）を得た。なお、これら一連の操作は大気開放系で行った。 The monomer aqueous solution (1) was stirred continuously, and when the temperature of the monomer aqueous solution (1) reached 78°C, 15.8 g of a 3.8 wt% aqueous solution of sodium persulfate was added. After that, the monomer aqueous solution (1) was immediately poured into a stainless steel vat-type reactor (bottom surface: 340 x 340 mm, height: 25 mm, inner surface: Teflon (registered trademark) coating), and the polymerization reaction started shortly thereafter. A hot plate (NEO HOTPLATE HI-1000/Iuchi Seiei-do Co., Ltd.) was installed under the stainless steel vat-type reactor, and the inner surface temperature of the vat was preset to 50°C. When the polymerization reaction started, the reaction liquid (1) gelled while generating water vapor, and the resulting gel expanded in all directions while foaming, and then contracted. This expansion and contraction ended in about 1 minute. The product was then held in the reactor for 3 minutes to obtain a hydrogel-like crosslinked polymer (1). This series of operations was carried out in an open-air system.
　得られた含水ゲル状架橋重合体（１）を、ダイス孔径９．５ｍｍを有するダイスを備え付けたミートチョッパー（Ｎｏ．３２型／株式会社平賀製作所製）を用いてゲル粉砕し、粒子状含水ゲル状架橋重合体（１）を得た。当該ゲル粉砕は、該ミートチョッパーのスクリュー軸回転数を１３０ｒｐｍとした状態で、含水ゲル状架橋重合体（１）２．４（ｋｇ／ｍｉｎ）及び水蒸気５．０（ｋｇ／ｈ）をミートチョッパーに投入することにより行った。 The obtained hydrogel-like cross-linked polymer (1) was gel-pulverized using a meat chopper (No. 32 type/manufactured by Hiraga Manufacturing Co., Ltd.) equipped with a die having a die hole diameter of 9.5 mm to obtain a particulate hydrogel-like cross-linked polymer (1). The gel-pulverization was performed by feeding 2.4 (kg/min) of the hydrogel-like cross-linked polymer (1) and 5.0 (kg/h) of steam into the meat chopper with the screw shaft rotation speed of the meat chopper set to 130 rpm.
　続いて、円筒容器回転型乾燥機を用いて、得られた粒子状含水ゲル状架橋重合体（１）を乾燥した。具体的には温度２００℃の雰囲気下で、円筒容器回転型乾燥機が備える回転容器を７５ｒｐｍにて回転させ、前記粒子状含水ゲル状架橋重合体（１）を円筒容器回転型乾燥機に供給して、含水率が２質量％になるまで乾燥し、乾燥重合体（１）を得た。 Then, the obtained particulate hydrogel-like crosslinked polymer (1) was dried using a cylindrical container rotary dryer. Specifically, the rotary container of the cylindrical container rotary dryer was rotated at 75 rpm in an atmosphere at a temperature of 200°C, and the particulate hydrogel-like crosslinked polymer (1) was supplied to the cylindrical container rotary dryer and dried until the moisture content reached 2% by mass, thereby obtaining a dried polymer (1).
　続いて、粉砕装置としてロールミル（ＷＭＬ型ロール粉砕機／井ノ口技研製）を用いて前記乾燥重合体（１）を粉砕し、吸水性樹脂粉末（１）を得た。ここで、前記ロールミルにおいては、一対のロールを一段目に設置し、一段粉砕とした。なお、一対のロールとしては、いずれのロールのロール表面にも、ロール回転方向に対してほぼ垂直方向に断面Ｖ字形状の溝が設けられているものを用いた。具体的には、ロール表面において、１つの溝がロールの一方の端から他方の端まで連続して（すなわち、ロール幅方向において連続して）設けられ、かつ、複数の溝が全周にわたって等間隔で連続して並んで設けられている。一対のロールのロール溝(溝の歯形)は、どちらも同じとした。なお、ロール間のクリアランスとは、２つのロール間の距離を意味する。 Then, the dried polymer (1) was pulverized using a roll mill (WML type roll pulverizer/manufactured by Inokuchi Giken Co., Ltd.) as a pulverizing device to obtain a water absorbent resin powder (1). Here, in the roll mill, a pair of rolls was installed in the first stage, and one-stage pulverization was performed. Note that, as the pair of rolls, a groove having a V-shaped cross section was provided on the roll surface of each of the rolls in a direction approximately perpendicular to the roll rotation direction was used. Specifically, on the roll surface, one groove was provided continuously from one end of the roll to the other end (i.e., continuously in the roll width direction), and multiple grooves were provided continuously in a row at equal intervals around the entire circumference. The roll grooves (groove tooth shape) of the pair of rolls were the same for both. Note that the clearance between the rolls means the distance between the two rolls.
　・ロール回転数：４８０／２００ｒｐｍ
　・溝のピッチ：１．１５ｍｍ
　・ロール間のクリアランス：１．０ｍｍ。 ・Roll rotation speed: 480/200 rpm
Groove pitch: 1.15 mm
-Clearance between rolls: 1.0 mm.
　目開き１５０μｍのＪＩＳ標準篩を用いて前記吸水性樹脂粉末（１）を分級し、前記篩を通過した吸水性樹脂微粉（１）を得た。続いて、前記吸水性樹脂微粉（１）３０質量部をフードプロセッサーに入れ、攪拌しながら５秒で９０℃のイオン交換水２０質量部を添加し、更に１０秒攪拌することにより、含水ゲル状造粒物（１）を得た。その後、得られた含水ゲル状造粒物（１）を、前記円筒容器回転型乾燥機を用いて再度同じ条件にて含水率が２質量％になるまで乾燥し、乾燥造粒物（１）を得た。 The water-absorbent resin powder (1) was classified using a JIS standard sieve with a mesh size of 150 μm, and water-absorbent resin fine powder (1) that passed through the sieve was obtained. Next, 30 parts by mass of the water-absorbent resin fine powder (1) was placed in a food processor, and 20 parts by mass of 90°C ion-exchanged water was added over 5 seconds while stirring, and further stirred for 10 seconds to obtain hydrous gel-like granulated material (1). Thereafter, the obtained hydrous gel-like granulated material (1) was dried again under the same conditions using the cylindrical container rotary dryer until the moisture content reached 2% by mass, and dried granulated material (1) was obtained.
　目開き１５０μｍのＪＩＳ標準篩を用いて前記乾燥造粒物（１）を分級し、前記篩上に残留した前記乾燥造粒物（１）を、粉砕装置としてロールグラニュレーター（日本グラニュレーター株式会社製、ロールサイズ：直径１１５ｍｍ×長さ１００ｍｍ）を使用して粉砕した。得られた粉砕物を、更に目開き１５０μｍのＪＩＳ標準篩を用いて分級し、前記篩上に残留した造粒体形状の粒子を吸水性樹脂粒子（１）として得た。ここで、前記ロールグラニュレーターにおいて、一対のロールを一段目に設置し、一段粉砕とした。なお、一対のロールとしては、いずれのロールのロール表面にも、ロール回転方向に対して平行方向に断面Ｖ字形状の溝が設けられているものを用いた(クリアランス差：０)。具体的には、溝は、ロール表面の全周にわたって、かつ、複数の溝がロールの一方の端から他方の端まで等間隔で連続して並んで設けられている。一対のロールの溝のピッチ（間隔）は、それぞれのロールにおいてどちらも同じとした。また、それぞれのロールにおける溝は、図４の２００１のように、一方のロールの溝の山部分と、他方のロールの溝の谷部分とが、ロールの軸方向に同じ位置となるように設けられており、ロール間のクリアランスは一定であった。 The dried granulated material (1) was classified using a JIS standard sieve with a mesh size of 150 μm, and the dried granulated material (1) remaining on the sieve was pulverized using a roll granulator (manufactured by Nippon Granulator Co., Ltd., roll size: diameter 115 mm x length 100 mm) as a pulverizing device. The pulverized material obtained was further classified using a JIS standard sieve with a mesh size of 150 μm, and the granulated particles remaining on the sieve were obtained as water-absorbent resin particles (1). Here, in the roll granulator, a pair of rolls was installed in the first stage, and one-stage pulverization was performed. Note that, as the pair of rolls, a groove with a V-shaped cross section was provided on the roll surface in a direction parallel to the roll rotation direction (clearance difference: 0). Specifically, the grooves were provided around the entire circumference of the roll surface, and a plurality of grooves were provided in a row at equal intervals from one end of the roll to the other end. The pitch (spacing) of the grooves of the pair of rolls was the same for both rolls. In addition, the grooves in each roll were arranged so that the peaks of the grooves on one roll and the valleys of the grooves on the other roll were in the same position in the axial direction of the rolls, as shown by 2001 in Figure 4, and the clearance between the rolls was constant.
　・ロール回転数：５６５／４６２ｒｐｍ（内回り）
　・溝の高さ（溝の傾斜角）：１．０ｍｍ(４５°)
　・溝のピッチ：２．０ｍｍ
　・ロール間のクリアランス：１ｍｍ。 ・Roll speed: 565/462 rpm (inner rotation)
・Groove height (groove inclination angle): 1.0 mm (45°)
Groove pitch: 2.0 mm
- Clearance between rolls: 1 mm.
　次に、前記吸水性樹脂粒子（１）１００重量部に対して、エチレンカーボネート０．３７３重量部、プロピレングリコール０．７４重量部及びイオン交換水２．５２重量部からなる表面架橋剤溶液を均一に混合し、温度１９８℃で３０分間加熱処理した。その後、粉温を６０℃まで強制的に冷却し、目開き８５０μｍのＪＩＳ標準篩を通過させることにより整粒し、表面架橋された吸水性樹脂粒子（１）を得た。 Next, a surface cross-linking agent solution consisting of 0.373 parts by weight of ethylene carbonate, 0.74 parts by weight of propylene glycol, and 2.52 parts by weight of ion-exchanged water was uniformly mixed with 100 parts by weight of the water-absorbent resin particles (1), and the mixture was heat-treated at a temperature of 198°C for 30 minutes. Thereafter, the powder was forcibly cooled to 60°C, and the mixture was passed through a JIS standard sieve with an opening of 850 μm to size the mixture, thereby obtaining surface-cross-linked water-absorbent resin particles (1).
　前記表面架橋された吸水性樹脂粒子（１）１００重量部に、微粒子状のシリカ（商品名：アエロジル（登録商標）２００、日本アエロジル株式会社製）０．３重量部を均一に混合して、吸水性樹脂（１）を得た。得られた吸水性樹脂（１）の物性を表１に示す。 100 parts by weight of the surface-crosslinked water-absorbent resin particles (1) were uniformly mixed with 0.3 parts by weight of fine silica (product name: Aerosil (registered trademark) 200, manufactured by Nippon Aerosil Co., Ltd.) to obtain water-absorbent resin (1). The physical properties of the obtained water-absorbent resin (1) are shown in Table 1.
　〔実施例２〕
　攪拌機、還流冷却器、温度計、窒素ガス導入管及び滴下ロートを付した２０００ｍＬの四つ口セパラブルフラスコにｎ－へプタン８００ｇを取り、分散剤として無水マレイン酸変性エチレン・プロピレン共重合体（商品名：ハイワックス（登録商標）ＨＷ２２０３Ａ／三井化学株式会社製）０．８８ｇを加えて溶解させ、窒素ガスを吹き込んで溶存酸素を追い出した。 Example 2
800 g of n-heptane was placed in a 2000 mL four-neck separable flask equipped with a stirrer, a reflux condenser, a thermometer, a nitrogen gas inlet tube, and a dropping funnel, and 0.88 g of maleic anhydride-modified ethylene-propylene copolymer (product name: Hiwax (registered trademark) HW2203A/manufactured by Mitsui Chemicals, Inc.) was added and dissolved as a dispersant, and nitrogen gas was blown in to expel the dissolved oxygen.
　これとは別に、フラスコ中で、アクリル酸ナトリウム１２７ｇ、アクリル酸３６ｇ、及びポリエチレングリコールジアクリレート（ｎ＝９）０．０７７ｇ、ジエチレントリアミン５酢酸・３ナトリウム０．００８ｇ、及びイオン交換水２１５ｇよりなる単量体水溶液（２）を調製し、窒素ガスを吹き込んで水溶液内に溶存する溶存酸素を追い出した。 Separately, in a flask, an aqueous monomer solution (2) was prepared consisting of 127 g of sodium acrylate, 36 g of acrylic acid, 0.077 g of polyethylene glycol diacrylate (n=9), 0.008 g of trisodium diethylenetriaminepentaacetate, and 215 g of ion-exchanged water, and nitrogen gas was blown in to expel the dissolved oxygen from the aqueous solution.
　次いで、このフラスコ内の前記単量体水溶液（２）に過硫酸ナトリウムの１５％水溶液１．５ｇを加えた後、全量を前記セパラブルフラスコに加えて、２３０ｒｐｍで攪拌することにより分散させた。その後、浴温を６０℃に昇温して重合反応を開始させ、２時間この浴温６０℃を保持した後、重合スラリー液を室温まで冷却した。 Next, 1.5 g of a 15% aqueous solution of sodium persulfate was added to the aqueous monomer solution (2) in the flask, and the entire amount was added to the separable flask and dispersed by stirring at 230 rpm. The bath temperature was then raised to 60°C to initiate the polymerization reaction, and the bath temperature was maintained at 60°C for 2 hours, after which the polymerization slurry liquid was cooled to room temperature.
　その後、撹拌機の回転数を１０００ｐｐｍに設定して攪拌しながら、該重合スラリー液に、無機微粒子（粉末状無機凝集剤）として非晶質シリカ（商品名：レオロシール（登録商標）ＱＳ－２０、オリエンタルシリカズコーポレーション社製）０．０９２ｇを予めｎ－ヘプタン１００ｇに分散させることにより得られた分散液を添加した後、１０分間攪拌して混合した。その後、吸引濾過により有機溶剤を濾別し、残渣を一晩室温で風乾させることにより、凝集体形状の含水ゲル状架橋重合体（２）を得た。 Then, while stirring with the agitator rotation speed set at 1000 ppm, a dispersion obtained by dispersing 0.092 g of amorphous silica (product name: Reolosil (registered trademark) QS-20, manufactured by Oriental Silicas Corporation) as inorganic fine particles (powdered inorganic flocculant) in 100 g of n-heptane in advance was added to the polymerization slurry liquid, and the mixture was stirred for 10 minutes. The organic solvent was then filtered off by suction filtration, and the residue was air-dried at room temperature overnight to obtain a hydrogel-like crosslinked polymer (2) in the form of an aggregate.
　続いて、実施例１と同じ円筒容器回転型乾燥機を用いて前記含水ゲル状架橋重合体（２）を乾燥した。具体的には、実施例１と同じ温度及び回転数に設定した円筒容器回転型乾燥機に、前記含水ゲル状架橋重合体（２）を供給して、含水率が１０質量％になるまで乾燥し、乾燥重合体（２）を得た。 Then, the hydrogel-like crosslinked polymer (2) was dried using the same cylindrical container rotary dryer as in Example 1. Specifically, the hydrogel-like crosslinked polymer (2) was supplied to the cylindrical container rotary dryer set at the same temperature and rotation speed as in Example 1, and dried until the water content reached 10% by mass, to obtain a dried polymer (2).
　続いて、粉砕装置としてロールグラニュレーター（日本グラニュレーター株式会社製、ロールサイズ：直径１１５ｍｍ×長さ１００ｍｍ）を使用して、実施例１における乾燥造粒物（１）の粉砕と同じ粉砕条件で前記乾燥重合体（２）を粉砕することにより、凝集体形状の吸水性樹脂粒子（２）を得た。 Then, using a roll granulator (manufactured by Nippon Granulator Co., Ltd., roll size: diameter 115 mm × length 100 mm) as a grinding device, the dried polymer (2) was ground under the same grinding conditions as those for grinding the dried granulated material (1) in Example 1, to obtain aggregate-shaped water-absorbent resin particles (2).
　前記吸水性樹脂粒子（２）１００重量部に対して、エチレングリコールジグリシジルエーテル０．００３重量部、エチレンカーボネート０．３８５重量部、プロピレングリコール０．６４４重量部及びイオン交換水２．６重量部からなる表面架橋剤溶液を均一に混合し、温度１９５℃で２５分間加熱処理した後、粉温を６０℃まで強制的に冷却することにより表面架橋された吸水性樹脂粒子（２）を得た。 100 parts by weight of the water-absorbent resin particles (2) were mixed uniformly with a surface-crosslinking agent solution consisting of 0.003 parts by weight of ethylene glycol diglycidyl ether, 0.385 parts by weight of ethylene carbonate, 0.644 parts by weight of propylene glycol, and 2.6 parts by weight of ion-exchanged water, and the mixture was heated at a temperature of 195°C for 25 minutes, and then the powder temperature was forcibly cooled to 60°C to obtain surface-crosslinked water-absorbent resin particles (2).
　前記表面架橋された吸水性樹脂粒子（２）１００重量部に対して、水１０．０重量部を均一に混合し、目開き１０００μｍのＪＩＳ標準篩を通過させて整粒した後、更に微粒子状のシリカ（商品名：アエロジル（登録商標）２００、日本アエロジル株式会社製）０．３重量部を均一に混合して、吸水性樹脂（２）を得た。得られた吸水性樹脂（２）の物性を表１に示す。 100 parts by weight of the surface-crosslinked water-absorbent resin particles (2) were uniformly mixed with 10.0 parts by weight of water, and the mixture was passed through a JIS standard sieve with a mesh size of 1000 μm to size it. Then, 0.3 parts by weight of fine silica particles (product name: Aerosil (registered trademark) 200, manufactured by Nippon Aerosil Co., Ltd.) were uniformly mixed to obtain water-absorbent resin (2). The physical properties of the obtained water-absorbent resin (2) are shown in Table 1.
　〔比較例１〕
　実施例１の吸水性樹脂粉末（１）について、目開き１５０μｍのＪＩＳ標準篩を用いて分級し、前記篩上に残留した比較吸水性樹脂粒子（１）を得た。 Comparative Example 1
The water-absorbent resin powder (1) of Example 1 was classified using a JIS standard sieve having an opening of 150 μm, and comparative water-absorbent resin particles (1) remaining on the sieve were obtained.
　前記比較吸水性樹脂粒子（１）について、実施例１と同じ条件の表面架橋工程及びシリカ添加工程を行い、比較吸水性樹脂（１）を得た。得られた比較吸水性樹脂（１）の物性を表１に示す。 The comparative water-absorbent resin particles (1) were subjected to the surface cross-linking process and the silica addition process under the same conditions as in Example 1 to obtain a comparative water-absorbent resin (1). The physical properties of the obtained comparative water-absorbent resin (1) are shown in Table 1.
　〔比較例２〕
　中和率が７５モル％である３３重量％のアクリル酸ナトリウム水溶液５０００ｇに、内部架橋剤としてポリエチレングリコールジアクリレート（分子量５２２．６６、平均エチレンオキサイドユニット数：ｎ＝９）２．１８９ｇを溶解させることで、比較単量体水溶液（２）を調製した。次いで、シグマ型羽根を２本有する内容積１０Ｌのジャケット付きステンレス製双腕型ニーダーに蓋を付けて形成した反応器に、前記比較単量体水溶液（２）を供給し、反応液を２５℃に保ちながら系を窒素ガス置換して溶存酸素を除いた。 Comparative Example 2
A comparative monomer aqueous solution (2) was prepared by dissolving 2.189 g of polyethylene glycol diacrylate (molecular weight 522.66, average number of ethylene oxide units: n=9) as an internal crosslinking agent in 5000 g of a 33 wt % aqueous sodium acrylate solution with a neutralization rate of 75 mol %. Next, the comparative monomer aqueous solution (2) was supplied to a reactor formed by attaching a lid to a jacketed stainless steel double-arm kneader having an internal volume of 10 L and two sigma-type blades, and the system was replaced with nitrogen gas while maintaining the reaction solution at 25° C. to remove dissolved oxygen.
　続いて、前記比較単量体水溶液（２）を攪拌しながら、重合開始剤として１５重量％の過硫酸アンモニウム水溶液１８．６ｇ及び０．１重量％のＬ－アスコルビン酸水溶液２３．３ｇを添加したところ、およそ１分後に重合が開始した。そして、２５～９０℃で重合を行い、重合を開始してから４０分後に、得られた比較含水ゲル状架橋重合体（２）を取り出した。当該比較含水ゲル状架橋重合体（２）は、約５ｍｍの粒子に細分化されていた。 Next, while stirring the comparative monomer aqueous solution (2), 18.6 g of a 15 wt % aqueous ammonium persulfate solution and 23.3 g of a 0.1 wt % aqueous L-ascorbic acid solution were added as polymerization initiators, and polymerization started after about 1 minute. Polymerization was then carried out at 25 to 90°C, and 40 minutes after the start of polymerization, the obtained comparative hydrous gel-like cross-linked polymer (2) was taken out. The comparative hydrous gel-like cross-linked polymer (2) was broken down into particles of about 5 mm.
　続いて、実施例１と同じ円筒容器回転型乾燥機を用いて、前記比較含水ゲル状架橋重合体（２）を乾燥した。具体的には、実施例１と同じ温度及び回転数に設定した円筒容器回転型乾燥機に、前記比較含水ゲル状架橋重合体（２）を供給して、含水率が２質量％になるまで乾燥し、比較乾燥重合体（２）を得た。続いて、実施例１と同じ条件の粉砕工程を行い、比較吸水性樹脂粉末（２）を得た。目開き１５０μｍのＪＩＳ標準篩を用いて前記比較吸水性樹脂粉末（２）を分級し、前記篩上に残留した比較吸水性樹脂粒子（２）を得た。 Then, the comparative hydrogel-like crosslinked polymer (2) was dried using the same cylindrical container rotary dryer as in Example 1. Specifically, the comparative hydrogel-like crosslinked polymer (2) was supplied to a cylindrical container rotary dryer set at the same temperature and rotation speed as in Example 1, and dried until the moisture content reached 2% by mass, to obtain a comparative dried polymer (2). Then, a pulverization step was carried out under the same conditions as in Example 1, to obtain a comparative water-absorbent resin powder (2). The comparative water-absorbent resin powder (2) was classified using a JIS standard sieve with a mesh size of 150 μm, to obtain comparative water-absorbent resin particles (2) remaining on the sieve.
　前記比較吸水性樹脂粒子（２）１００重量部に対して、エチレンカーボネート０．２５重量部、エチレングリコールジグリシジルエーテル０．０２重量部、プロピレングリコール０．４１重量部及びイオン交換水１．６６重量部からなる表面架橋剤溶液を均一に混合し、温度１６５℃で３０分間加熱処理した後、粉温を６０℃まで強制的に冷却し、目開き８５０μｍのＪＩＳ標準篩を通過させることにより整粒し、表面架橋された比較吸水性樹脂粒子（２）を得た。 100 parts by weight of the comparative water-absorbent resin particles (2) were mixed uniformly with a surface-crosslinking agent solution consisting of 0.25 parts by weight of ethylene carbonate, 0.02 parts by weight of ethylene glycol diglycidyl ether, 0.41 parts by weight of propylene glycol, and 1.66 parts by weight of ion-exchanged water, and the mixture was heat-treated at a temperature of 165°C for 30 minutes, and then the powder temperature was forcibly cooled to 60°C, and the mixture was passed through a JIS standard sieve with an opening of 850 μm for granulation, thereby obtaining surface-crosslinked comparative water-absorbent resin particles (2).
　前記比較吸水性樹脂粒子（２）について、実施例１と同じ条件のシリカ添加工程を行い、比較吸水性樹脂（２）を得た。得られた比較吸水性樹脂（２）の物性を表１に示す。 The comparative water-absorbent resin particles (2) were subjected to a silica addition process under the same conditions as in Example 1 to obtain a comparative water-absorbent resin (2). The physical properties of the obtained comparative water-absorbent resin (2) are shown in Table 1.
　〔比較例３〕
　実施例１の単量体水溶液調製工程において、アクリル酸を３４１ｇ、ポリエチレングリコールジアクリレート（分子量５２２．６６、平均エチレンオキサイドユニット数：ｎ＝９）を０．３８ｇ、０．１重量％のジエチレントリアミン５酢酸・３ナトリウム水溶液を２２．１６ｇ、４８．５重量％の水酸化ナトリウム水溶液を２９１ｇ、イオン交換水を２６３ｇに変更して使用する以外は、実施例１と同じ重合工程、ゲル粉砕工程、乾燥工程、ロールミルによる粉砕工程を実施して比較吸水性樹脂粉末（３）を得た。 Comparative Example 3
In the monomer aqueous solution preparation step of Example 1, except that 341 g of acrylic acid, 0.38 g of polyethylene glycol diacrylate (molecular weight 522.66, average number of ethylene oxide units: n=9), 22.16 g of a 0.1 wt % aqueous solution of trisodium diethylenetriaminepentaacetate, 291 g of a 48.5 wt % aqueous solution of sodium hydroxide, and 263 g of ion-exchanged water were used, a polymerization step, a gel crushing step, a drying step, and a crushing step by a roll mill were carried out in the same manner as in Example 1, thereby obtaining a comparative water absorbent resin powder (3).
　目開き１５０μｍのＪＩＳ標準篩を用いて前記比較吸水性樹脂粉末（３）を分級し、前記篩を通過した比較吸水性樹脂微粉（３）を用いて実施例１と同じ条件の造粒工程と乾燥工程を実施し、比較乾燥造粒物（３）を得た。 The comparative water-absorbent resin powder (3) was classified using a JIS standard sieve with a mesh size of 150 μm, and the comparative water-absorbent resin fine powder (3) that had passed through the sieve was subjected to the granulation process and drying process under the same conditions as in Example 1 to obtain a comparative dried granulated material (3).
　粉砕装置としてロールミル（ＷＭＬ型ロール粉砕機／井ノ口技研製）を用いて前記比較乾燥造粒物（３）を粉砕し、更に目開き１５０μｍのＪＩＳ標準篩を用いて分級し、前記篩上に残留した造粒体形状の粒子を比較吸水性樹脂粒子（３）として得た。ここで、前記ロールミルの粉砕条件は実施例１における吸水性樹脂粉末（１）の粉砕と同じとした。 The comparative dried granules (3) were pulverized using a roll mill (WML type roll pulverizer/manufactured by Inokuchi Giken Co., Ltd.) as a pulverizing device, and further classified using a JIS standard sieve with a mesh size of 150 μm, and the granule-shaped particles remaining on the sieve were obtained as comparative water-absorbent resin particles (3). Here, the pulverization conditions of the roll mill were the same as those for pulverizing the water-absorbent resin powder (1) in Example 1.
　前記比較吸水性樹脂粒子（３）１００重量部に対して、エチレングリコールジグリシジルエーテル０．０１８重量部、エチレンカーボネート０．２０重量部、プロピレングリコール０．３４重量部及びイオン交換水１．０４重量部からなる表面架橋剤溶液を均一に混合し、温度１６５℃で３０分間加熱処理した後、粉温を６０℃まで強制的に冷却することで表面架橋された比較吸水性樹脂粒子（３）を得た。 100 parts by weight of the comparative water-absorbent resin particles (3) were uniformly mixed with a surface-crosslinking agent solution consisting of 0.018 parts by weight of ethylene glycol diglycidyl ether, 0.20 parts by weight of ethylene carbonate, 0.34 parts by weight of propylene glycol, and 1.04 parts by weight of ion-exchanged water, and the mixture was heated at a temperature of 165°C for 30 minutes, and then forcibly cooled to a powder temperature of 60°C to obtain surface-crosslinked comparative water-absorbent resin particles (3).
　前記表面架橋された比較吸水性樹脂粒子（３）１００重量部に、微粒子状のシリカ（商品名：アエロジル（登録商標）２００、日本アエロジル株式会社製）０．３重量部を均一に混合して、比較吸水性樹脂（３）を得た。得られた比較吸水性樹脂（３）の物性を表１に示す。 100 parts by weight of the surface-crosslinked comparative water-absorbent resin particles (3) were uniformly mixed with 0.3 parts by weight of fine silica (product name: Aerosil (registered trademark) 200, manufactured by Nippon Aerosil Co., Ltd.) to obtain a comparative water-absorbent resin (3). The physical properties of the obtained comparative water-absorbent resin (3) are shown in Table 1.
　〔比較例４〕
　実施例２と同じ重合工程を実施し、得られた重合スラリー液を室温まで冷却した後、重合スラリー液に無機微粒子を添加し混合する工程を行わずに、吸引濾過により有機溶剤を濾別し、残渣を一晩室温で風乾させることにより比較含水ゲル状架橋重合体（４）を得た。その後、実施例２と同じ条件の乾燥工程、粉砕工程、表面架橋工程を行い、表面架橋された比較吸水性樹脂粒子（４）を得た。前記表面架橋された比較吸水性樹脂粒子（４）１００重量部に対して、水１０．０重量部を均一に混合し、目開き３００μｍのＪＩＳ標準篩に通過させて整粒した後、更に、微粒子状のシリカ（商品名：アエロジル（登録商標）２００、日本アエロジル株式会社製）０．３重量部を均一に混合して、比較吸水性樹脂（４）を得た。得られた比較吸水性樹脂（４）の物性を表１に示す。 Comparative Example 4
The same polymerization step as in Example 2 was carried out, and the obtained polymerization slurry liquid was cooled to room temperature, and then the step of adding inorganic fine particles to the polymerization slurry liquid and mixing was not carried out, and the organic solvent was filtered off by suction filtration, and the residue was air-dried at room temperature overnight to obtain a comparative hydrogel-like crosslinked polymer (4). Thereafter, the drying step, the pulverization step, and the surface crosslinking step were carried out under the same conditions as in Example 2 to obtain a surface-crosslinked comparative water-absorbent resin particle (4). 100 parts by weight of the surface-crosslinked comparative water-absorbent resin particle (4) was uniformly mixed with 10.0 parts by weight of water, and the particles were passed through a JIS standard sieve with an opening of 300 μm to size them, and then 0.3 parts by weight of finely divided silica (trade name: Aerosil (registered trademark) 200, manufactured by Nippon Aerosil Co., Ltd.) was uniformly mixed to obtain a comparative water-absorbent resin (4). The physical properties of the obtained comparative water-absorbent resin (4) are shown in Table 1.
　〔比較例５〕
　実施例２で得られた乾燥重合体（２）をロールミル（ＷＭＬ型ロール粉砕機／井ノ口技研製）に供給して、実施例１における乾燥造粒物（１）の粉砕と同じ粉砕条件で粉砕することにより、比較吸水性樹脂粒子（５）を得た。 Comparative Example 5
The dried polymer (2) obtained in Example 2 was supplied to a roll mill (WML type roll grinder/manufactured by Inokuchi Giken Co., Ltd.) and pulverized under the same pulverization conditions as those for pulverizing the dried granulated material (1) in Example 1, thereby obtaining a comparative water absorbent resin particle (5).
　前記比較吸水性樹脂粒子（５）１００重量部に対して、実施例２と同じ条件の表面架橋を実施した後、実施例２と同じ条件で水及びシリカの添加工程を行い、比較吸水性樹脂（５）を得た。得られた比較吸水性樹脂（５）の物性を表１に示す。 100 parts by weight of the comparative water-absorbent resin particles (5) were subjected to surface cross-linking under the same conditions as in Example 2, and then water and silica were added under the same conditions as in Example 2 to obtain a comparative water-absorbent resin (5). The physical properties of the obtained comparative water-absorbent resin (5) are shown in Table 1.
　〔２－２．吸水性樹脂の評価結果〕 [2-2. Evaluation results of water-absorbent resin]
Figure JPOXMLDOC01-appb-T000001
 　実施例及び比較例の対比により、透水性基材に対する繊維間への侵入抵抗性が６０重量％以上である吸水性樹脂は、吸水性樹脂及び透水性基材を備える紙オムツ等の吸収性物品に使用される吸収体を模した吸収シートの評価において、液戻り量が有意に低減されており、即ち、液保持性に優れることが分かった。
Figure JPOXMLDOC01-appb-T000001
 By comparing the Examples and Comparative Examples, it was found that a water-absorbent resin having a penetration resistance between fibers of a water-permeable substrate of 60% by weight or more significantly reduced the amount of liquid return in an evaluation of an absorbent sheet simulating an absorbent used in an absorbent article such as a disposable diaper, which comprises a water-absorbent resin and a water-permeable substrate, i.e., has excellent liquid retention properties.
　〔３．吸収性物品〕
　〔３－１．吸収性物品の製造〕
　〔実施例３〕
　図２の１００３は吸収性物品１０１を真上から見た図、図２の１００４は吸収性物品１０１を、Ｘ－Ｙ平面に垂直、かつＸ軸又はＹ軸に平行な方向に切断したときの断面図である。液不透過性のバックシート５に相当する、１０ｃｍ×１１ｃｍにカットした粘着テープ（ＮＩＴＴＯ　ＤＥＮＫＯ製ビニールテープＮｏ．２１Ｓ）の粘着面に、長辺方向の端部からそれぞれ１ｃｍずつ、短辺方向の端部からそれぞれ２ｃｍずつ内側の領域、すなわち粘着テープ中央６ｃｍ×９ｃｍの領域に、シート状の透水性基材６である６ｃｍ×９ｃｍの不織布（厚みが３ｍｍで、目付量が４１ｇ／ｍ２の、ポリエチレン、ポリプロピレン、及びポリエチレンテレフタレートの混合物製のエアスルー不織布であって、ポリエチレンの繊維径及びポリプロピレンの繊維径は０．１８ｍｍ、ポリエチレンテレフタレートの繊維径は０．２７ｍｍである。）を載せた。該不織布上の全面に、実施例１で得られた吸水性樹脂（１）を１．０ｇ均一に散布した。ここで、前記吸水性樹脂（１）を散布した部分は吸収体に相当する。その後、前記吸水性樹脂（１）を散布した部分の上に、液透過性のトップシート７に相当する、１０ｃｍ×１１ｃｍの液透過性不織布（エアレイド不織布、目付量４６．６ｇ／ｍ２）を載せ、四辺の粘着面と貼り合わせて、吸収性物品（１）を製造した。 [3. Absorbent Articles]
3-1. Manufacture of absorbent articles
Example 3
2 is a view of the absorbent article 101 as seen from directly above, and 1004 is a cross-sectional view of the absorbent article 101 cut perpendicular to the X-Y plane and parallel to the X-axis or Y-axis. A 6 cm x 9 cm nonwoven fabric (3 mm thick, 41 g/m2 basis weight, air-through nonwoven fabric made of a mixture of polyethylene, polypropylene, and polyethylene terephthalate, the fiber diameters of the polyethylene and polypropylene being 0.18 mm, and the fiber diameter of the polyethylene terephthalate being 0.27 mm) was placed on the adhesive surface of an adhesive tape (NITTO DENKO vinyl tape No. 21S) cut to 10 cm x 11 cm, which corresponds to the liquid-impermeable back sheet 5 , in the areas 1 cm from each end in the long side direction and 2 cm inward from each end in the short side direction, i.e., in the area of 6 cm x 9 cm in the center of the adhesive tape. 1.0 g of the water-absorbent resin (1) obtained in Example 1 was uniformly sprayed on the entire surface of the nonwoven fabric. Here, the part sprayed with the water-absorbent resin (1) corresponds to the absorbent body. Then, a 10 cm x 11 cm liquid-permeable nonwoven fabric (airlaid nonwoven fabric, basis weight 46.6 g/ m2 ) corresponding to the liquid-permeable top sheet 7 was placed on the part sprayed with the water-absorbent resin (1), and the adhesive surfaces of the four sides were bonded together to produce an absorbent article (1).
　〔実施例４〕
　吸水性樹脂（１）の代わりに、実施例２にて得られた吸水性樹脂（２）を用いた以外は、実施例３と同様の方法にて、吸収性物品（２）を製造した。 Example 4
An absorbent article (2) was produced in the same manner as in Example 3, except that the water-absorbent resin (2) obtained in Example 2 was used instead of the water-absorbent resin (1).
　〔比較例６〕
　吸水性樹脂（１）の代わりに、比較例２にて得られた比較吸水性樹脂（２）を用いた以外は、実施例３と同様の方法にて、比較吸収性物品（１）を製造した。 Comparative Example 6
A comparative absorbent article (1) was produced in the same manner as in Example 3, except that the comparative absorbent resin (2) obtained in Comparative Example 2 was used instead of the absorbent resin (1).
　〔比較例７〕
　吸水性樹脂（１）の代わりに、比較例３にて得られた比較吸水性樹脂（３）を用いた以外は、実施例３と同様の方法にて、比較吸収性物品（２）を製造した。 Comparative Example 7
A comparative absorbent article (2) was produced in the same manner as in Example 3, except that the comparative absorbent resin (3) obtained in Comparative Example 3 was used instead of the absorbent resin (1).
　〔比較例８〕
　吸水性樹脂（１）の代わりに、比較例４にて得られた比較吸水性樹脂（４）を用いた以外は、実施例３と同様の方法にて、比較吸収性物品（３）を製造した。 Comparative Example 8
A comparative absorbent article (3) was produced in the same manner as in Example 3, except that the comparative absorbent resin (4) obtained in Comparative Example 4 was used instead of the absorbent resin (1).
　〔比較例９〕
　吸水性樹脂（１）の代わりに、比較例５にて得られた比較吸水性樹脂（５）を用いた以外は、実施例３と同様の方法にて、比較吸収性物品（４）を製造した。 Comparative Example 9
A comparative absorbent article (4) was produced in the same manner as in Example 3, except that the comparative absorbent resin (5) obtained in Comparative Example 5 was used instead of the absorbent resin (1).
　〔３－２．吸収性物品の評価結果〕
　実施例３、４にて製造された吸収性物品（１）、（２）及び比較例６～９にて製造された比較吸収性物品（１）～（４）の液拡散性を、前述の方法にて測定した。その結果を以下の表２に示す。 [3-2. Evaluation results of absorbent articles]
The liquid diffusibility of the absorbent articles (1) and (2) produced in Examples 3 and 4 and the comparative absorbent articles (1) to (4) produced in Comparative Examples 6 to 9 was measured by the above-mentioned method. The results are shown in Table 2 below.
Figure JPOXMLDOC01-appb-T000002
 　実施例及び比較例の対比により、透水性基材に対する繊維間への侵入抵抗性が６０重量％以上のポリ（メタ）アクリル酸（塩）系吸水性樹脂を含む、実施例３及び４にて製造された吸収性物品は、透水性基材に対する繊維間への侵入抵抗性が６０重量％より小さいポリ（メタ）アクリル酸（塩）系吸水性樹脂を含む、比較例６～９にて製造された吸収性物品よりも、縦（長辺）方向、横（短辺）方向それぞれにおける液拡散長が大きい、すなわち液拡散性に優れることが示された。
Figure JPOXMLDOC01-appb-T000002
 Comparison between the Examples and Comparative Examples shows that the absorbent articles produced in Examples 3 and 4, which contain a poly(meth)acrylic acid (salt)-based water absorbent resin having a penetration resistance between fibers of a water-permeable substrate of 60% by weight or more, have a larger liquid diffusion length in each of the longitudinal (long side) direction and the lateral (short side) direction, i.e., are superior in liquid diffusion properties, than the absorbent articles produced in Comparative Examples 6 to 9, which contain a poly(meth)acrylic acid (salt)-based water absorbent resin having a penetration resistance between fibers of a water-permeable substrate of less than 60% by weight.
　本発明の実施の一形態に係る吸水性樹脂組成物によれば、吸水性樹脂及び透水性基材を備える吸収性物品の液戻り量を低減し、液保持性に優れた吸水性樹脂を提供することができる。それゆえ、紙オムツ、生理用ナプキン、成人向け失禁用製品（失禁パッド）、ペット用シート等の衛生材料（衛生用品）等において好適に利用することができる。 The water-absorbent resin composition according to one embodiment of the present invention can reduce the amount of liquid returning to an absorbent article comprising a water-absorbent resin and a water-permeable substrate, and can provide a water-absorbent resin with excellent liquid retention. Therefore, it can be suitably used in sanitary materials (sanitary products) such as disposable diapers, sanitary napkins, adult incontinence products (incontinence pads), and pet sheets.
　１　吸水性樹脂
　２　粘着テープ
　３　不織布
　４　液透過性不織布
　５　バックシート
　６　透水性基材
　７　トップシート
　２０ａ　乾燥重合体又は乾燥造粒物
　２０ｂ　乾燥重合体又は乾燥造粒物の粉砕物（吸水性樹脂粉末）
　１００　吸収シート
　１０１　吸収性物品
　２００　ロール式粉砕装置
　２０１　配管
　２０２　投入口
　２０３、２０３ａ、２０３ｂ　ロール REFERENCE SIGNS LIST 1 Water-absorbent resin 2 Adhesive tape 3 Nonwoven fabric 4 Liquid-permeable nonwoven fabric 5 Back sheet 6 Water-permeable substrate 7 Top sheet 20a Dried polymer or dried granules 20b Ground product of dried polymer or dried granules (water-absorbent resin powder)
REFERENCE SIGNS LIST 100 Absorbent sheet 101 Absorbent article 200 Roll-type crushing device 201 Pipe 202 Feeding port 203, 203a, 203b Roll

Claims (9)

  1. 　下記（１）～（３）の手順により決定される、透水性基材に対する繊維間への侵入抵抗性が６０重量％以上である、ポリ（メタ）アクリル酸（塩）系吸水性樹脂：
    　（１）いずれもケース内面の寸法で、底面６ｃｍ×９ｃｍ、深さ１ｃｍの、ポリスチレン製の直方体のケースの底面に、６ｃｍ×９ｃｍに切り取った不織布を両面テープで固定する
    　　ここで、前記不織布は、厚み３ｍｍ、目付量４１ｇ／ｍ２であり、ポリエチレン、ポリプロピレン及びポリエチレンテレフタレートの混合物製のエアスルー不織布であって、ポリエチレンの繊維径及びポリプロピレンの繊維径は０．１８ｍｍ、ポリエチレンテレフタレートの繊維径は０．２７ｍｍである；
    　（２）吸水性樹脂１．０ｇを、前記不織布の全面に均一に散布し、前記ケースよりも底面積が大きい受け皿の上で、前記吸水性樹脂を散布した前記不織布をケースごと逆さにし、前記受け皿上に脱落した吸水性樹脂を回収する；
    　（３）下記式（１）に従い、透水性基材に対する繊維間への侵入抵抗性を算出する
    透水性基材に対する繊維間への侵入抵抗性［重量％］＝回収した吸水性樹脂の重量［ｇ］／散布した吸水性樹脂の重量［ｇ］×１００　式（１）。     A poly(meth)acrylic acid (salt)-based water-absorbing resin having a resistance to penetration between fibers of a water-permeable substrate of 60% by weight or more, as determined by the following steps (1) to (3):
    (1) A nonwoven fabric cut to 6 cm x 9 cm is fixed with double-sided tape to the bottom of a rectangular polystyrene case having a bottom of 6 cm x 9 cm and a depth of 1 cm, both of which are the dimensions of the inner surface of the case. Here, the nonwoven fabric is an air-through nonwoven fabric made of a mixture of polyethylene, polypropylene and polyethylene terephthalate, with a thickness of 3 mm and a basis weight of 41 g/ m2 , and the fiber diameter of the polyethylene and the polypropylene is 0.18 mm, and the fiber diameter of the polyethylene terephthalate is 0.27 mm;
    (2) 1.0 g of a water-absorbent resin is uniformly spread over the entire surface of the nonwoven fabric, and the nonwoven fabric with the water-absorbent resin spread thereon is inverted together with the case over a tray having a bottom area larger than that of the case, and the water-absorbent resin that has fallen onto the tray is collected;
    (3) Calculate the penetration resistance between fibers in the water-permeable substrate according to the following formula (1): Penetration resistance between fibers in the water-permeable substrate [wt %] = weight of recovered water absorbent resin [g] / weight of sprayed water absorbent resin [g] × 100 Formula (1).
  2. 　ボルテックス法による吸水速度が５０秒以下である、請求項１に記載のポリ（メタ）アクリル酸（塩）系吸水性樹脂。 The poly(meth)acrylic acid (salt)-based water-absorbing resin according to claim 1, which has a water absorption speed of 50 seconds or less when measured by the vortex method.
  3. 　質量平均粒子径（Ｄ５０）が、２５０μｍ～８００μｍである、請求項１または２に記載のポリ（メタ）アクリル酸（塩）系吸水性樹脂。 The poly(meth)acrylic acid (salt)-based water-absorbing resin according to claim 1 or 2, having a mass average particle diameter (D50) of 250 μm to 800 μm.
  4. 　水不溶性無機微粒子を含む、請求項１～３のいずれか１項に記載のポリ（メタ）アクリル酸（塩）系吸水性樹脂。 The poly(meth)acrylic acid (salt)-based water-absorbing resin according to any one of claims 1 to 3, which contains water-insoluble inorganic fine particles.
  5. 　液不透過性のバックシート、吸水性樹脂と透水性基材とを含む吸収体、及び液透過性のトップシートをこの順に含む吸収性物品であって、
    　前記吸水性樹脂は、ポリ（メタ）アクリル酸（塩）系吸水性樹脂であるとともに、
    　下記（１）～（３）の手順により決定される、透水性基材に対する繊維間への侵入抵抗性が６０重量％以上の吸水性樹脂である、吸収性物品：
    　（１）いずれもケース内面の寸法で、底面６ｃｍ×９ｃｍ、深さ１ｃｍの、ポリスチレン製の直方体のケースの底面に、６ｃｍ×９ｃｍに切り取った不織布を両面テープで固定する
    　　ここで、前記不織布は、厚み３ｍｍ、目付量４１ｇ／ｍ２であり、ポリエチレン、ポリプロピレン及びポリエチレンテレフタレートの混合物製のエアスルー不織布であり、ポリエチレンの繊維径及びポリプロピレンの繊維径は０．１８ｍｍ、ポリエチレンテレフタレートの繊維径は０．２７ｍｍである；
    　（２）吸水性樹脂１．０ｇを、前記不織布の全面に均一に散布し、前記ケースよりも底面積が大きい受け皿の上で、前記吸水性樹脂を散布した前記不織布をケースごと逆さにし、前記受け皿上に脱落した吸水性樹脂を回収する；
    　（３）下記式（１）に従い、透水性基材に対する繊維間への侵入抵抗性を算出する
    透水性基材に対する繊維間への侵入抵抗性［重量％］＝回収した吸水性樹脂の重量［ｇ］／散布した吸水性樹脂の重量［ｇ］×１００　式（１）。     An absorbent article comprising, in this order, a liquid-impermeable back sheet, an absorbent body containing a water-absorbent resin and a water-permeable substrate, and a liquid-permeable top sheet,
    The water-absorbing resin is a poly(meth)acrylic acid (salt)-based water-absorbing resin,
    An absorbent article, comprising a water-absorbent resin having a penetration resistance between fibers of a water-permeable substrate of 60% by weight or more, as determined by the following procedures (1) to (3):
    (1) A nonwoven fabric cut to 6 cm x 9 cm is fixed with double-sided tape to the bottom of a rectangular polystyrene case having a bottom of 6 cm x 9 cm and a depth of 1 cm, both of which are the dimensions of the inner surface of the case. Here, the nonwoven fabric is an air-through nonwoven fabric made of a mixture of polyethylene, polypropylene and polyethylene terephthalate, with a thickness of 3 mm and a basis weight of 41 g/ m2 , the fiber diameter of the polyethylene and the fiber diameter of the polypropylene being 0.18 mm, and the fiber diameter of the polyethylene terephthalate being 0.27 mm;
    (2) 1.0 g of a water-absorbent resin is uniformly spread over the entire surface of the nonwoven fabric, and the nonwoven fabric with the water-absorbent resin spread thereon is inverted together with the case over a tray having a bottom area larger than that of the case, and the water-absorbent resin that has fallen onto the tray is collected;
    (3) Calculate the penetration resistance between fibers in the water-permeable substrate according to the following formula (1): Penetration resistance between fibers in the water-permeable substrate [wt %] = weight of recovered water absorbent resin [g] / weight of sprayed water absorbent resin [g] × 100 Formula (1).
  6. 　前記吸水性樹脂のボルテックス法による吸水速度が５０秒以下である、請求項５に記載の吸収性物品。 The absorbent article according to claim 5, wherein the water-absorbing resin has a water-absorbing speed of 50 seconds or less when measured by a vortex method.
  7. 　前記吸水性樹脂の質量平均粒子径（Ｄ５０）が、２５０μｍ～８００μｍである、請求項５または６に記載の吸収性物品。 The absorbent article according to claim 5 or 6, wherein the mass average particle diameter (D50) of the water-absorbent resin is 250 μm to 800 μm.
  8. 　前記吸水性樹脂が、水不溶性無機微粒子を含む、請求項５～７のいずれか１項に記載の吸収性物品。 The absorbent article according to any one of claims 5 to 7, wherein the water-absorbent resin contains water-insoluble inorganic fine particles.
  9. 　前記透水性基材が、シート状の透水性基材であり、
    　前記シート状の透水性基材の厚みが１ｍｍ以上、目付量が５０ｇ／ｍ２以下である、請求項５～８のいずれか１項に記載の吸収性物品。     The water-permeable substrate is a sheet-shaped water-permeable substrate,
    The absorbent article according to any one of claims 5 to 8, wherein the sheet-like water-permeable substrate has a thickness of 1 mm or more and a basis weight of 50 g/m2 or less .
PCT/JP2024/013704 2023-04-03 2024-04-03 Poly(meth)acrylic acid (salt)-based water-absorbing resin and absorbent article WO2024210144A1 (en)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
JP2023060396 2023-04-03
JP2023060395 2023-04-03
JP2023-060395 2023-04-03
JP2023-060396 2023-04-03

Publications (1)

Publication Number Publication Date
WO2024210144A1 true WO2024210144A1 (en) 2024-10-10

Family

ID=92971922

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/JP2024/013704 WO2024210144A1 (en) 2023-04-03 2024-04-03 Poly(meth)acrylic acid (salt)-based water-absorbing resin and absorbent article

Country Status (1)

Country Link
WO (1) WO2024210144A1 (en)

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2002121291A (en) * 2000-02-29 2002-04-23 Nippon Shokubai Co Ltd Water-absorbing resin powder and method for producing the same
WO2009028568A1 (en) * 2007-08-28 2009-03-05 Nippon Shokubai Co., Ltd. Process for producing water-absorbing resin
WO2011040472A1 (en) * 2009-09-29 2011-04-07 株式会社日本触媒 Particulate water absorbent and process for production thereof
WO2015030128A1 (en) * 2013-08-28 2015-03-05 株式会社日本触媒 Method for producing water-absorbing resin
WO2022265472A1 (en) * 2021-06-18 2022-12-22 주식회사 엘지화학 Preparation method of super absorbent polymer, and super absorbent polymer
JP2023064963A (en) * 2021-10-27 2023-05-12 株式会社日本触媒 Method for producing water-absorbing resin, and water-absorbing resin

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2002121291A (en) * 2000-02-29 2002-04-23 Nippon Shokubai Co Ltd Water-absorbing resin powder and method for producing the same
WO2009028568A1 (en) * 2007-08-28 2009-03-05 Nippon Shokubai Co., Ltd. Process for producing water-absorbing resin
WO2011040472A1 (en) * 2009-09-29 2011-04-07 株式会社日本触媒 Particulate water absorbent and process for production thereof
WO2015030128A1 (en) * 2013-08-28 2015-03-05 株式会社日本触媒 Method for producing water-absorbing resin
WO2022265472A1 (en) * 2021-06-18 2022-12-22 주식회사 엘지화학 Preparation method of super absorbent polymer, and super absorbent polymer
JP2023064963A (en) * 2021-10-27 2023-05-12 株式会社日本触媒 Method for producing water-absorbing resin, and water-absorbing resin

Similar Documents

Publication Publication Date Title
JP6093751B2 (en) Method for producing polyacrylic acid (salt) water absorbent resin powder and polyacrylic acid (salt) water absorbent resin powder
JP6532894B2 (en) Water-absorbent agent, method for producing the same, and evaluation method and measurement method
JP4758669B2 (en) Amorphous crushed particulate water-absorbing agent
CN109608661B (en) Gel crushing device, method for producing polyacrylic acid (salt) -based water-absorbent resin powder, and water-absorbent resin powder
US10646612B2 (en) Polyacrylic acid (salt) water absorbent, and method for producing same
JP5706351B2 (en) Particulate water-absorbing agent mainly composed of water-absorbing resin
WO2013002387A1 (en) Polyacrylic acid (salt) water-absorbent resin powder, and method for producing same
JP5587348B2 (en) Method for producing water absorbent resin
JP4261853B2 (en) Water absorbent resin, water absorbent resin particles, and production method thereof
JP2006055833A (en) Particulate water absorbing agent with water-absorbing resin as main component
JP2010053296A (en) Method for producing water-absorbing resin
JP2008018328A (en) Particulate water absorbent and its manufacturing method
KR20220123443A (en) Absorbents, absorbent resins and absorbent articles
WO2024210144A1 (en) Poly(meth)acrylic acid (salt)-based water-absorbing resin and absorbent article
JP2022175089A (en) Poly(meth)acrylic acid (salt)-based water-absorbing resin, and absorber
WO2024210052A1 (en) Particulate poly(meth)acrylic acid (salt)-based water-absorbing resin
US20220023113A1 (en) Absorption body and absorptive article
JP2024147407A (en) Poly(meth)acrylic acid (salt)-based water-absorbent resin
JP2024147408A (en) Poly(meth)acrylic acid (salt)-based water-absorbent resin
WO2022239628A1 (en) Poly(meth)acrylic acid (salt)-based water-absorbing resin, and absorbent body
WO2022181771A1 (en) Granular water absorbent, absorbent body containing said water absorbent, and absorbent article using said absorbent body
WO2023106205A1 (en) Absorbent article
JP7572800B2 (en) Manufacturing method of water absorbent
JP7058787B1 (en) Poly (meth) acrylic acid (salt) -based water-absorbent resin and absorber
WO2022163849A1 (en) Method for producing water-absorbent resin