JP6508947B2 - Method for producing polyacrylic acid (salt) -based water absorbing agent - Google Patents

Description

  The present invention relates to a method for producing a polyacrylic acid (salt) -based water absorbing agent. More specifically, the present invention relates to a method for producing a polyacrylic acid (salt) -based water absorbing agent in which the deodorizing function and the antifungal function are improved by adding an aqueous liquid having a slight amount of a bactericidal component to the water absorbing resin particles.

  Water-absorbent resin (SAP / Super Absorbent Polymer) refers to a water-swellable water-insoluble polymer gelling agent, and absorbent articles such as paper diapers and sanitary napkins, water retention agents for agriculture and horticulture, water stop for industrial use It is widely used in various fields such as medicines.

  As the water absorbent resin, many monomers and hydrophilic polymers are used as the raw materials. For example, a polyacrylic acid partially neutralized crosslinked polymer, a hydrolyzate of a starch-acrylic acid graft polymer, a saponified product of a vinyl acetate-acrylic acid ester copolymer, and the like can be mentioned. Among them, from the viewpoint of water absorption performance, polyacrylic acid (salt) -based water absorbent resin using acrylic acid and / or a salt thereof as a monomer is industrially most produced.

  The above-mentioned water-absorbent resin is required to have various functions (higher physical properties) along with the high performance of paper diapers, which is a main application. Specifically, gel strength, water soluble content, water content, water absorption rate, liquid permeability, particle size distribution, urine resistance, antibacterial property, in addition to basic physical properties such as absorption capacity under no pressure and absorption capacity under pressure, And damage resistance, powder flowability, deodorization, coloration resistance, low dust, low residual monomer, and the like.

  Among the above-mentioned physical properties, in recent years, it has been required to add functions such as "deodorant" and "antimicrobial" to a water-absorbent resin, and until now, compounds such as deodorants and antibacterial agents It has been considered to add it to the resin.

  Specifically, a long-lasting antibacterial deodorant consisting of horseradish extract, mustard extract, etc., and an antibacterial deodorizing agent (water absorbing gelling agent) (Patent Document 1), a water absorbing resin, ammonia production A powdery deodorant / antibacterial water-absorbing agent (patent document 2) comprising a compound having an antibacterial function against bacteria and a drug having a neutralizing ability against ammonia, or an agent having a neutralizing ability and an adsorptive ability Proposed.

  In addition, as a water-absorbent resin composition (water-absorbent agent) to which a deodorant or antibacterial function is imparted and a method for producing the same, a method of producing a water-absorbent resin composition for forming an antibacterial film on the water-absorbent resin surface (Patent Document 3) A water-absorbent resin composition containing an antibacterial phosphate (Patent Documents 4 and 5), a water-absorbing agent containing a natural antibacterial component extracted from grapefruit seeds and / or herbs (Patent Document 6), during surface treatment or treatment A manufacturing method (patent document 7) etc. which are added with an antibacterial agent and a polyol later are proposed.

  Furthermore, as a highly safe water absorbing agent having an antibacterial (antibacterial) function and a deodorizing function, a water absorbent resin composition (Patent Document 8) or the like in which a reflux extract of bamboo and green tea is mixed with a water absorbent resin is proposed. ing.

  On the other hand, as an attempt to impart a deodorizing function and an antibacterial function to an absorbent article, disposable diapers (patent document 9) and the like using a water-absorbent resin containing benzalkonium chloride and / or chlorhexidine gluconate are proposed. It is done.

  In addition, when there are many impurities contained in the raw material of the water-absorbent resin, especially acetic acid and propionic acid in acrylic acid, the water-absorbent resin manufactured using such raw material acid absorbed and swelled body fluid such as urine. In some cases, an odor was generated. Therefore, a water absorbent resin (patent document 10) etc. which made content of acetic acid in acrylic acid and propionic acid below fixed amount are proposed.

JP 2000-51339 A Unexamined-Japanese-Patent No. 2000-79159 JP-A-3-59075 Unexamined-Japanese-Patent No. 5-179053 JP-A-7-165981 JP-A-9-208787 Japanese Patent Publication No. 2010-540004 WO 2009/048145 pamphlet Japanese Patent Application Laid-Open No. 63-135501 International Publication No. 2003/955510 brochure

  As described above, it is required to add functions such as "deodorant" and "antimicrobial" to a water-absorbent resin, and compounds such as a deodorant and an antibacterial agent are added to the water-absorbent resin And using raw materials with reduced amounts of impurities have been considered.

  However, the above-mentioned patent documents are inventions made by paying attention to the odor which occurs at all at the time of paper diaper use, and have not paid attention to the odor generated at the time of disposal after paper diaper use.

  Therefore, the object of the present invention is to provide a polyacrylic acid (salt) -based water-absorbing agent that exhibits excellent deodorizing performance and antifungal performance both during use and after disposal of absorbent articles such as paper diapers. It is to provide a manufacturing method of

  In order to solve the above problems, as a result of earnestly studying, by controlling the amount of impurities contained in the raw material within a certain range, and further adding an aqueous liquid containing a trace of bactericidal component to the surface cross-linked water absorbent resin particles In addition to the odor generated during use of absorbent articles such as disposable diapers, the inventors have found that the odor generated during disposal after use can be suppressed, and the present invention has been completed.

  That is, in order to solve the above problems, the production method according to the present invention is a method for producing a polyacrylic acid (salt) -based water absorbing agent, including a polymerization step of a monomer aqueous solution, a drying step, and a surface crosslinking step The total amount of acetic acid and propionic acid contained in the monomer or its polymer is 200 to 2500 ppm, and the method further comprises the step of adding an aqueous liquid containing a bactericidal component to the surface cross-linked water absorbent resin particles It is a manufacturing method of a polyacrylic acid (salt) type water-absorbing agent.

  By using the polyacrylic acid (salt) -based water absorbing agent obtained by the manufacturing method according to the present invention for an absorbent article such as a paper diaper, there is no odor generated after swelling when using the absorbent article in actual use, and it is comfortable. At the time of disposal of the absorbent article (final treatment, specifically, waste collection), the generation of odor and mold can be suppressed.

  Furthermore, by adopting the manufacturing method according to the present invention, the occurrence of troubles in the manufacturing apparatus can be reduced and stable operation can be performed.

  Hereinafter, the present invention will be described in detail, but the scope of the present invention is not restricted by these descriptions, and other than exemplified below, the scope of the present invention is appropriately modified within the scope not impairing the spirit of the present invention. It is possible. Moreover, this invention is not limited to the following embodiment, A various change is possible in the range shown to the claim. Other embodiments obtained by appropriately combining the technical means respectively described for the plurality of embodiments are also included in the technical scope of the present invention.

[1] Definition of terms (1-1) "Water-absorbent resin""Water-absorbentagent"
The "water-absorbent resin" in the present invention refers to a water-swellable water-insoluble polymer gelling agent, and refers to those satisfying the following physical properties. That is, CRC (centrifuge holding capacity) specified by ERT 441.2-02 as water-swellable is 5 g / g or more, and Ext (water-soluble as water insoluble) is specified by ERT 470.2-02 Minute) refers to a high molecular weight gelling agent having 50% by weight or less.

  The water-absorbent resin can be designed according to its application and purpose, and is not particularly limited, but is preferably a hydrophilic crosslinked polymer obtained by crosslinking and polymerizing an unsaturated monomer having a carboxyl group. In addition, the composition is not limited to a form in which the entire amount is a crosslinked polymer, and may be a composition including an additive or the like as long as each of the physical properties (CRC, Ext) described above satisfy the above numerical range.

  The “water-absorbent resin” in the present invention is not limited to the final product before shipment, but is an intermediate in the production process of the water-absorbent resin (for example, water-containing gelled crosslinked polymer after polymerization, dried polymer after drying, surface crosslinking It may refer to the previous water-absorbent resin powder etc.). All of these (including the above composition) are collectively referred to as "water-absorbent resin".

  The shape of the water absorbent resin may be in the form of sheet, fiber, film, particles, gel, etc. In the present invention, the particulate water absorbent resin is preferred.

  Further, the “water absorbing agent” in the present invention refers to a composition obtained by adding an additive to the water absorbing resin particles after surface crosslinking among the above-described water absorbing resins, and a water absorbing resin after performing a curing operation. Say

(1-2) "Poly acrylic acid (salt)"
In the present invention, "polyacrylic acid (salt)" refers to polyacrylic acid and / or a salt thereof, and acrylic acid and / or a salt thereof (hereinafter referred to as "acrylic acid (salt)") is repeated as a main component It means a crosslinked polymer which is contained as a unit and contains a graft component as an optional component.

  The above-mentioned "main component" is preferably 50 to 100 mol%, more preferably the amount (content) of acrylic acid (salt) used with respect to the entire monomers (excluding the internal crosslinking agent) used for polymerization. It is preferably 70 to 100 mol%, more preferably 90 to 100 mol%, particularly preferably substantially 100 mol%.

  The "polyacrylate" as a crosslinked polymer comprises a water-soluble salt of polyacrylic acid, preferably a monovalent salt, more preferably an alkali metal salt or ammonium salt, more preferably an alkali metal salt, particularly preferably Contains sodium salt.

(1-3) "EDANA" and "ERT"
"EDANA" is an abbreviation of the European Disposables and Nonwovens Associations, and "ERT" is an abbreviation of the European standard (almost global standard) measurement method of water-absorbing resin (EDANA Recommended Test Methods) . In the present invention, physical properties of the water-absorbent resin are measured in accordance with the original ERT (revised in 2002) unless otherwise noted.

(A) "CRC" (ERT 441.2-02)
"CRC" is an abbreviation for Centrifuge Retention Capacity (centrifuge holding capacity), and means the absorption capacity without pressure (also sometimes referred to as "water absorption capacity") of the water-absorbent resin. Specifically, 0.2 g of a water absorbing resin is placed in a non-woven bag, and then it is immersed in a large excess of 0.9 wt% sodium chloride aqueous solution for 30 minutes to allow free swelling, and then a centrifuge (250 G) The water absorption capacity (unit; g / g) after draining for 3 minutes in.

(B) “AAP” (ERT 442.2-02)
"AAP" is an abbreviation of Absorption Against Pressure, and means the water absorption capacity under pressure of a water absorbent resin. Specifically, the water absorption magnification after swelling 0.9 g of a water-absorbent resin in a large excess of 0.9 wt% sodium chloride aqueous solution under a load of 21 g / cm ² (2.06 kPa) for 1 hour (Unit; g / g) Moreover, although it describes with ERT 442.2-02 as Absorption Under Pressure, it is substantially the same content.

(C) "Ext" (ERT 470.2-02)
"Ext" is an abbreviation of Extractables and means the water-soluble component (the amount of water-soluble component) of the water-absorbent resin. Specifically, 1.0 g of a water-absorbent resin is added to 200 ml of a 0.9 wt% aqueous sodium chloride solution, and after stirring for 16 hours at 500 rpm, the amount (unit: wt%) of the substance dissolved in the aqueous solution is said. . PH titration is used to measure the water solubles.

(D) "PSD" (ERT 420.2-02)
"PSD" is an abbreviation for Particle Size Distribution, and means the particle size distribution of the water absorbent resin measured by sieve classification. In addition, D50 (weight average particle diameter) and σζ (log standard deviation of particle size distribution) are described in US Pat. No. 7,638,570 “(3) Mass-Average Particle Diameter (D50) and Logarithmic Standard Deviation (σζ) of It is measured in the same way as "Particle Diameter Distribution".

(E) "Moisture Content" (ERT 430.2-02)
"Moisture Content" means the moisture content of the water absorbent resin. Specifically, it refers to a value (unit: weight%) calculated from the loss on drying when 4.0 g of the water absorbent resin is dried at 105 ° C. for 3 hours. In some cases, the water-absorbent resin may be changed to 1.0 g and the drying temperature to 180 ° C. for measurement.

(F) "Residual Monomers" (ERT 410.2-02)
"Residual Monomers" means the amount of monomers (monomers) remaining in the water absorbent resin. Hereinafter, the monomer remaining in the water absorbent resin is referred to as "residual monomer". Specifically, 1.0 g of a water-absorbent resin is added to 200 ml of a 0.9 wt% aqueous sodium chloride solution, and after stirring for 1 hour at 500 rpm, the amount of monomer (unit: ppm) dissolved in the aqueous solution is said. High performance liquid chromatography (HPLC) is used to measure the amount of residual monomer.

(1-4) Others In the present specification, “X to Y” indicating a range means “X or more and Y or less”. Also, unless otherwise noted, the unit of weight "t (ton)" means "Metric ton", and "ppm" means "weight ppm" or "mass ppm".

  Moreover, "-acid (salt)" means "-acid and / or a salt thereof", and "(meth) acryl" means "acryl and / or methacryl", respectively.

[2] Process for Producing Polyacrylic Acid (Salt) -Based Water Absorbent Hereinafter, production steps (2-1) to (2-9) of the polyacrylic acid (salt) -based water absorbent according to the present invention will be described.

(2-1) Step of Preparing a Monomer Aqueous Solution This step is a step of preparing an aqueous solution containing acrylic acid (salt) as a main component (hereinafter referred to as “monomer aqueous solution”). In the above “main component”, the amount (content) of acrylic acid (salt) used is preferably with respect to the entire monomer (excluding internal crosslinking agent) subjected to the polymerization reaction of the water-absorbent resin Is 50 mol% or more, more preferably 70 mol% or more, still more preferably 90 mol% or more (upper limit is 100 mol%). Moreover, although the slurry liquid of a monomer can also be used in the range which the water absorption performance of the water-absorbing agent obtained does not fall, in this term, a monomer aqueous solution is demonstrated for convenience.

(Acrylic acid (salt))
In the present invention, acrylic acid and / or a salt thereof (hereinafter, referred to as “acrylic acid (salt)”) is used as a monomer from the viewpoint of physical properties and productivity of the water absorbing agent to be obtained. As said "acrylic acid", well-known acrylic acid containing trace components, such as a polymerization inhibitor and an impurity, can be used.

  The polymerization inhibitor is not particularly limited, but preferably includes phenols, more preferably methoxyphenols, and still more preferably p-methoxyphenols. The concentration of the polymerization inhibitor in acrylic acid is preferably 200 ppm or less, more preferably 10 to 160 ppm, and still more preferably 20 to 100 ppm, from the viewpoint of the polymerizability of acrylic acid and the color tone of the water absorbing resin.

  Examples of the impurities include carboxylic acids such as acetic acid, propionic acid and maleic acid, and aldehydes such as acrolein and furfural. Among them, among the above-mentioned impurities, it is necessary to control the total amount of acetic acid and propionic acid within a certain range from the viewpoint of the odor generated at the time of use of absorbent articles such as disposable diapers.

  The total amount of acetic acid and propionic acid is 200 to 2500 ppm, preferably 250 to 2000 ppm, more preferably 300 to 1500 ppm. The total amount is acrylic acid, that is, the amount contained in the monomer, or the amount contained in the polymer obtained by polymerizing the monomer. That is, it is the total amount of acetic acid and propionic acid contained in the monomer or its polymer.

  Since the odor at the time of use of the absorbent article produced using the obtained water absorbing agent can be suppressed by controlling the said total amount in the said range, it is preferable.

  Moreover, although the above-mentioned "acrylic acid salt" is what neutralized the above-mentioned acrylic acid by the following basic composition, it may be a commercially available acrylic acid salt (for example, sodium acrylate) as this acrylic acid salt. It may be obtained by neutralizing acrylic acid in a water-absorbent resin production plant.

(Basic composition)
In the present invention, the "basic composition" refers to a composition containing a basic compound, and corresponds to, for example, a commercially available aqueous sodium hydroxide solution and the like.

  Specific examples of the basic compound include carbonates and hydrogencarbonates of alkali metals, hydroxides of alkali metals, ammonia, and organic amines. Among them, from the viewpoint of the physical properties of the water absorbing agent to be obtained, it is preferable to be strongly basic. That is, hydroxides of alkali metals such as sodium hydroxide, potassium hydroxide and lithium hydroxide are more preferable, and sodium hydroxide is still more preferable.

(Neutralization)
In the present invention, acrylic acid can also be neutralized with a basic composition to obtain an acrylate salt. The neutralization is carried out by neutralization (before polymerization) with respect to acrylic acid or neutralization (after polymerization) with respect to a water-containing gel-like crosslinked polymer obtained by cross-linking polymerization of acrylic acid (hereinafter referred to as "post neutralization") Or one of them may be selected, or may be used in combination.

  The neutralization may be continuous or batch, and any of them may be employed, but is preferably continuous from the viewpoint of production efficiency and the like. The conditions described in WO 2009/123197 and U.S. Patent Application Publication No. 2008/0194863 apply to the present invention as to conditions for the apparatus for neutralization, neutralization temperature, residence time, etc. .

  The neutralization ratio in the present invention is preferably 10 to 90 mol%, more preferably 40 to 85 mol%, still more preferably 50 to 80 mol%, particularly preferably 60 to 80 mol%, based on the acid group of the monomer. It is 75 mol%.

  If the neutralization ratio is less than 10 mol%, the water absorption capacity may be significantly reduced, which is not preferable. On the other hand, when the said neutralization ratio exceeds 90 mol%, since a water absorbing resin with a high water absorption capacity under pressure may not be obtained, it is unpreferable.

  In addition, the said neutralization rate is the same also in the case of post-neutralization. The above-mentioned neutralization ratio is also applied to the neutralization ratio of the water absorbing agent as the final product.

(Other monomer)
In the present invention, a compound described in US Patent Application Publication No. 2005/0215734 as "the other monomer" (with the exception of acrylic acid) is used in combination with the above acrylic acid (salt) to produce a water absorbing agent. You may The water absorbing agent obtained by the manufacturing method according to the present invention also includes a water absorbing agent containing a hydrophilic or hydrophobic unsaturated monomer as a copolymer component.

(Internal crosslinking agent)
The compounds described in US Pat. No. 6,241,928 also apply to the present invention as an internal crosslinking agent used in the present invention. Among these, one or more compounds are selected in consideration of the reactivity.

  Further, from the viewpoint of water absorption performance of the water absorbing agent to be obtained, preferably a compound having two or more polymerizable unsaturated groups, more preferably a compound having thermal decomposition at the following drying temperature, still more preferably (poly) alkylene glycol A compound having two or more polymerizable unsaturated groups having a structural unit is used as an internal crosslinking agent.

  As said polymerizable unsaturated group, Preferably an allyl group, a (meth) acrylate group, More preferably, a (meth) acrylate group is mentioned. In addition, polyethylene glycol is preferable as the above (poly) alkylene glycol structural unit, and the n number is preferably 1 to 100, more preferably 6 to 50.

  Therefore, in the present invention, preferably (poly) alkylene glycol di (meth) acrylate or (poly) alkylene glycol tri (meth) acrylate, more preferably (poly) ethylene glycol di (meth) acrylate is used.

  The amount of the internal crosslinking agent to be used is preferably 0.0001 to 10 mol%, more preferably 0.001 to 1 mol%, based on the whole monomer. A desired water absorbing agent can be obtained by setting the amount to be in the above range. When the amount used is too small, the gel strength tends to decrease and the water soluble component tends to increase. When the amount used is too large, the water absorption capacity tends to decrease, which is not preferable.

  In the present invention, a method is preferably applied in which a predetermined amount of an internal crosslinking agent is previously added to the aqueous monomer solution, and a crosslinking reaction is performed simultaneously with the polymerization. On the other hand, other than the above method, a method of post-crosslinking by adding an internal crosslinking agent during or after polymerization, a method of radical crosslinking using a radical polymerization initiator, radiation using an active energy ray such as electron beam or ultraviolet ray A crosslinking method or the like can also be employed. Moreover, these methods can also be used together.

(Other substances added to the aqueous monomer solution)
In the present invention, from the viewpoint of improving the physical properties of the water-absorbing agent to be obtained, the following substances can be added at the time of preparation of the aqueous monomer solution.

  Specifically, hydrophilic polymers such as starch, starch derivatives, cellulose, cellulose derivatives, polyvinyl alcohol, polyacrylic acid (salt), and polyacrylic acid (salt) cross-linked product are preferably 50% by weight or less, more preferably 20% by weight or less, more preferably 10% by weight or less, particularly preferably 5% by weight or less (the lower limit is 0% by weight), carbonates, azo compounds, foaming agents such as bubbles, surfactants, chelates The agent, chain transfer agent and the like can be added preferably at 5 wt% or less, more preferably at 1 wt% or less, still more preferably at 0.5 wt% or less (the lower limit is 0 wt%).

  In addition to the form added to the aqueous monomer solution, the above-mentioned substance may be added during the polymerization, or these forms may be used in combination.

  When a water-soluble resin or a water-absorbent resin is used as the hydrophilic polymer, a graft polymer or a water-absorbent resin composition (for example, a starch-acrylic acid polymer, a PVA-acrylic acid polymer, etc.) is obtained. Be These polymers and water-absorbent resin compositions are also within the scope of the present invention.

(Concentration of monomer component)
In the present invention, when preparing the aqueous monomer solution, the above-mentioned respective substances are added. The concentration of the monomer component in the aqueous monomer solution (hereinafter sometimes referred to as “monomer concentration”) is not particularly limited, but from the viewpoint of physical properties and productivity of the water absorbing agent, preferably 10 to 80 weight %, More preferably 20 to 75% by weight, still more preferably 30 to 70% by weight.

  Moreover, when employ | adopting aqueous solution polymerization or reverse phase suspension polymerization as a superposition | polymerization form, solvents other than water can also be used together as needed. In this case, the type of solvent used is not particularly limited.

  In addition, said "concentration of a monomer component" is a value calculated | required by the following (Formula 1), and it is a graft component, a water absorbing resin, hydrophobicity in reverse phase suspension polymerization in the weight of monomer aqueous solution. The weight of the solvent is not included.

(2-2) Polymerization step This step polymerizes the acrylic acid (salt) -based monomer aqueous solution obtained in the above-mentioned monomer aqueous solution preparation step to form a water-containing gel-like crosslinked polymer (hereinafter referred to as "water-containing gel Step))).

(Polymerization initiator)
The polymerization initiator used in the present invention is not particularly limited because it is appropriately selected depending on the polymerization form etc. For example, a thermally decomposable radical polymerization initiator, a photodegradable radical polymerization initiator, or a polymerization initiator thereof And redox type polymerization initiators in combination with a reducing agent that promotes the decomposition of Specifically, among the polymerization initiators described in US Pat. No. 7,265,190, one or more compounds are used. From the viewpoint of the handleability of the polymerization initiator and the physical properties of the water absorbing agent, a peroxide or an azo compound is preferably used, more preferably a peroxide, and still more preferably a persulfate.

  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 monomer. The amount of the reducing agent used is preferably 0.0001 to 0.02 mol% relative to the monomer. A desired water absorbing agent can be obtained by setting the amounts of the polymerization initiator and the reducing agent to be in the above ranges.

  The polymerization reaction may be carried out by irradiating an active energy ray such as radiation, electron beam or ultraviolet ray instead of the above-mentioned polymerization initiator, and these active energy ray and the polymerization initiator may be used in combination.

(Polymerization form)
The polymerization mode to be applied to the present invention is not particularly limited, but from the viewpoint of water absorption characteristics and ease of polymerization control, preferably spray polymerization, droplet polymerization, aqueous solution polymerization, reverse phase suspension polymerization, more preferably Aqueous solution polymerization, reverse phase suspension polymerization, more preferably aqueous solution polymerization may be mentioned. Among them, continuous aqueous solution polymerization is particularly preferable, and any of continuous belt polymerization and continuous kneader polymerization can be applied.

  As specific polymerization forms, continuous belt polymerization is disclosed in US Pat. Nos. 4,893,999 and 6,241,928, US Patent Application Publication No. 2005/0215734, etc., and continuous kneader polymerization is disclosed in US Pat. Nos. 6,987,151, 6710141, etc. , Each listed. By adopting these continuous aqueous solution polymerizations, the production efficiency of the water absorbing agent is improved.

  Moreover, "high temperature initiation polymerization" and "high concentration polymerization" are mentioned as a preferable form of the said continuous aqueous solution polymerization. The “high-temperature initiation polymerization” refers to polymerization at a temperature of the monomer aqueous solution of preferably 30 ° C. or more, more preferably 35 ° C. or more, still more preferably 40 ° C. or more, particularly preferably 50 ° C. or more (upper limit is boiling point) "High concentration polymerization" means that the monomer concentration is preferably 30% by weight or more, more preferably 35% by weight or more, still more preferably 40% by weight or more, particularly preferably 45% by weight or more (The upper limit is the saturation concentration). These polymerization forms can also be used in combination.

  In the present invention, polymerization can also be carried out in an air atmosphere, but polymerization is preferably carried out in an inert gas atmosphere such as nitrogen or argon from the viewpoint of the color tone of the water-absorbing agent obtained. In this case, for example, it is preferable to control the oxygen concentration to 1% by volume or less. The dissolved oxygen in the monomer aqueous solution is also preferably replaced with an inert gas (for example, dissolved oxygen; less than 1 mg / l).

  In the present invention, it is also possible to use foam polymerization in which bubbles (particularly the above-mentioned inert gas and the like) are dispersed in a monomer aqueous solution to carry out polymerization.

  In the present invention, the solid concentration may be increased during polymerization. The degree of increase in solid content is defined by the following (Expression 2) as an indicator of the increase in solid content concentration. The degree of increase in the solid content concentration is preferably 1% by weight or more, more preferably 2% by weight or more.

  However, the solid content concentration of the monomer aqueous solution is a value determined by the following (formula 3), and the components in the polymerization system are the monomer aqueous solution, the graft component, the water absorbing resin, and other solid substances (for example, water Insoluble particles etc.), and does not include hydrophobic solvents in reverse phase suspension polymerization.

(2-3) Gel-pulverizing step In this step, the water-containing gel obtained in the above-mentioned polymerization step is gel-pulverized by a gel crusher such as a screw extruder such as a kneader or a meat chopper, a cutter mill, etc. Hereinafter, it is the process of obtaining "a particulate water-containing gel". When the polymerization step is kneader polymerization, the polymerization step and the gel grinding step are simultaneously carried out. When the particulate water-containing gel can be directly obtained in the polymerization process, such as reverse phase suspension polymerization, the gel crushing process may not be carried out.

  The contents disclosed in WO 2011/126079 are preferably applied to the present invention as to gel grinding conditions and forms other than the above.

(2-4) Drying Step This step is a step of drying the particulate water-containing gel obtained in the above polymerization step and / or gel grinding step to a predetermined solid content to obtain a "dried polymer". The solid content after drying is a value determined from the loss on drying (weight change when 1 g of dry polymer is heated at 180 ° C. for 3 hours), preferably 80% by weight or more, more preferably 85 to 99%. %, More preferably 90 to 98% by weight, particularly preferably 92 to 97% by weight.

  The drying method employed in this step is not particularly limited. For example, heat drying, hot air drying, reduced pressure drying, fluidized bed drying, infrared radiation drying, microwave drying, drum dryer drying, co-treatment with a hydrophobic organic solvent Drying by boiling dehydration, high humidity drying using high temperature steam, and the like can be mentioned. Among them, hot air drying is preferable from the viewpoint of drying efficiency, and band drying in which hot air drying is performed on a ventilated belt is more preferable.

  The drying temperature in this step (in the case of hot air drying, defined by the temperature of hot air) is preferably 100 to 300 ° C., more preferably 120 to 250 ° C., further preferably from the viewpoint of the color tone of the water absorbing agent obtained and drying efficiency. Is 150 to 200 ° C. The drying time is appropriately determined in accordance with the physical properties of the desired water-absorbing agent, but is preferably 1 minute to 10 hours, more preferably 5 minutes to 3 hours, and still more preferably 10 minutes to 1 hour. Furthermore, in the case of hot air drying, the wind speed of the hot air is preferably 3.0 m / s or less, more preferably 0.5 to 2.0 m / s. The other drying conditions may be appropriately set according to the moisture content and the total weight of the particulate water-containing gel to be dried, the target solid content, and the like.

  By controlling the drying conditions within the above range, unevenness in the physical properties of the dried polymer is unlikely to occur, and the solid content can be controlled within a predetermined range, and the color tone deterioration and water absorption performance of the water absorbing agent obtained further Can reduce the In the case of band drying, the conditions described in WO2006 / 100300, WO2011 / 025012, 2011/025013, 2011/111657, etc. are applied as appropriate.

(2-5) Pulverization step, classification step In this step, the dried polymer obtained in the above-mentioned drying step is pulverized (pulverization step), adjusted to a particle size of a predetermined range (classification step), water absorbent resin powder ( This is a step of obtaining a powdery water-absorbent resin before surface crosslinking, for convenience, referred to as "water-absorbent resin powder".

  The equipment used in the pulverizing step of the present invention is not particularly limited, but, for example, high-speed rotary pulverizers such as roll mills, hammer mills, screw mills and pin mills, vibration mills, knuckle type pulverizers, cylindrical mixers etc. It is mentioned and used together as needed.

  Further, the particle size adjustment method in the classification step of the present invention is not particularly limited, and examples thereof include sieve classification and air flow classification using a JIS standard sieve (JIS Z8801-1 (2000)). In addition, particle size adjustment is not limited to the said crushing process and classification process, A polymerization process (especially reverse phase suspension polymerization, spray polymerization, droplet polymerization), and other processes (for example, granulation process, fine powder recovery process etc.) Can be implemented as appropriate.

(Physical properties of water-absorbent resin powder)
(Solid content)
The solid content of the water-absorbent resin powder obtained in this step is preferably 90% by weight or more, more preferably 93% by weight or more, and still more preferably 95% by weight or more. The upper limit of the solid content is preferably 98% by weight or less, more preferably 97% by weight or less, from the viewpoint of grinding efficiency.

(Grain size)
The water-absorbent resin powder obtained in this step preferably has a D50 (weight average particle diameter) of 200 to 600 μm, more preferably 200 to 550 μm, still more preferably 250 to 500 μm, and particularly preferably 250 to 450 μm. The proportion of particles having a particle size of less than 150 μm is preferably 10% by weight or less, more preferably 5% by weight or less, still more preferably 1% by weight or less, and the proportion of particles having a particle size of 850 μm or more is preferably Is 5% by weight or less, more preferably 3% by weight or less, still more preferably 1% by weight or less. The lower limit of the proportion of these particles is preferably as low as possible in any case, and 0% by weight is desired, but it may be about 0.1% by weight. Furthermore, σζ (logarithmic standard deviation of particle size distribution) is preferably 0 to 0.50, more preferably 0.20 to 0.50, still more preferably 0.25 to 0.45, particularly preferably 0.30 to It is 0.40. In addition, these particle sizes are measured using a standard sieve according to the measuring method described in US Patent No. 7638570 or ERT 420.2-02.

  The above particle size is applied not only to the water absorbent resin after surface crosslinking (hereinafter referred to as “water absorbent resin particles” for convenience), but also to a water absorbent as a final product. Therefore, it is preferable to be surface-crosslinked so as to maintain the particle size in the above-mentioned range, and it is more preferable to provide a particle size adjustment step after the surface cross-linking step to adjust the particle size.

(2-6) Surface Crosslinking Step This step is a step carried out for the purpose of improving the liquid permeability and the water absorption rate of the water absorbent resin powder after drying and classification, and is obtained through the above steps. In the surface layer of the water-absorbent resin powder (a part of several tens of μm from the surface of the water-absorbent resin powder), this is a step of providing a portion with a high crosslinking density.

  This process comprises a mixing process, a heat treatment process and a cooling process (optional). When particle size control is performed at the time of polymerization, such as reverse phase suspension polymerization, gas phase polymerization, spray polymerization, and droplet polymerization, a grinding process and a classification process before the surface crosslinking process are unnecessary. The following heat treatment step may be performed simultaneously with the drying step.

  In the surface crosslinking step, water-absorbing resin particles are obtained which are surface-crosslinked by radical crosslinking or surface polymerization on the surface of the water-absorbent resin powder, a crosslinking reaction with a surface crosslinking agent, or the like.

(Surface crosslinking agent)
Although it does not specifically limit as a surface crosslinking agent used by this invention, An organic or inorganic surface crosslinking agent is mentioned. Among them, an organic surface crosslinking agent that reacts with a carboxyl group is preferable from the viewpoint of the physical properties of the water absorbing agent to be obtained and the handleability of the surface crosslinking agent. For example, one or more surface crosslinkers described in US Pat. No. 7,183,456 may be mentioned. More specifically, polyhydric alcohol compounds, epoxy compounds, haloepoxy compounds, polyvalent amine compounds or their condensates with haloepoxy compounds, oxazoline compounds, oxazolidinone compounds, polyvalent metal salts, alkylene carbonate compounds, cyclic urea compounds, etc. It can be mentioned.

  The amount of the surface crosslinking agent used (the total amount used in the case of multiple use) is preferably 0.01 to 10 parts by weight, more preferably 0.01 to 5 parts by weight, based on 100 parts by weight of the water absorbent resin powder It is. The surface crosslinking agent is preferably added as an aqueous solution. In this case, the amount of water used is preferably 0.1 to 20 parts by weight, more preferably 0. 0 to 100 parts by weight of the water-absorbent resin powder. 5 to 10 parts by weight. Furthermore, when a hydrophilic organic solvent is used, the amount thereof used is preferably 10 parts by weight or less, more preferably 5 parts by weight or less, based on 100 parts by weight of the water-absorbent resin powder.

  In addition, each additive added in the below-mentioned "re-wetting step" is mixed and added to the surface cross-linking agent (aqueous solution) within 5 parts by weight or less, or separately added in the mixing step It can also be done.

(Mixing process)
This step is a step of mixing the water-absorbent resin powder and the surface crosslinking agent. The method of mixing the surface crosslinking agent is not particularly limited, but a surface crosslinking agent solution is previously prepared, and the solution is preferably sprayed or dropped onto the water-absorbent resin powder, and more preferably sprayed. And mixing methods.

  Although it does not specifically limit as an apparatus which performs the said mixing, Preferably a high speed stirring type mixer, More preferably, a high speed stirring type continuous mixer is mentioned.

(Heating process)
This step is a step of applying heat to the mixture discharged from the mixing step to cause a crosslinking reaction on the surface of the water absorbent resin powder.

  Although it does not specifically limit as an apparatus which performs the said crosslinking reaction, Preferably a paddle dryer is mentioned. The reaction temperature in the crosslinking reaction is appropriately set depending on the type of surface crosslinking agent used, but is preferably 50 to 300 ° C., more preferably 100 to 200 ° C.

(Cooling process)
This step is an optional step which is installed as necessary after the heat treatment step.

  Although it does not specifically limit as an apparatus which performs the said cooling, Preferably it is an apparatus of the same specification as the apparatus used by a heat treatment process, More preferably, it is a paddle dryer. By changing the heat medium to a refrigerant, it can be used as a cooling device. In the cooling step, the water-absorbent resin particles obtained in the heat treatment step are preferably cooled to preferably 40 to 80 ° C., more preferably 50 to 70 ° C., if necessary.

(2-7) Re-wetting step (curing step)
This step is a step of adding an aqueous liquid containing a bactericidal component to the water absorbent resin particles obtained in the surface crosslinking step. Further, in this step, at least simultaneously selected from the group consisting of polyvalent metal salts, cationic polymers, chelating agents, inorganic reducing agents, α-hydroxycarboxylic acid compounds and deodorants simultaneously with the addition of the aqueous liquid containing the bactericidal component. One additive can also be added.

  In addition, in this process, in order to add an aqueous liquid to the surface-crosslinked water-absorbent resin particles, the water-absorbent resin particles will swell again in water. Therefore, this process is referred to as a "re-humidifying process". On the other hand, since the water existing on the surface of the water-absorbent resin particles is also made to penetrate to the inside, the operation may be referred to as "curing". In this case, it is called a "curing step".

  Moreover, addition of the said additive can also be performed simultaneously with the said cooling process, and as long as the surface-crosslinked water-absorbent resin particles can be re-humidified, any timing may be used.

(Aqueous liquid containing germicidal ingredients)
About the absorbent article (especially paper diapers) manufactured using the water absorbing agent obtained by the present invention, the surface cross-linked water-absorbent resin particles from the viewpoint of hygiene at the time of disposal and stable operation of the device in the rewetting process. On the other hand, an aqueous liquid containing a bactericidal component is essentially added.

  The above-mentioned bactericidal component is not particularly limited, but is preferably at least one selected from the group consisting of sodium hypochlorite, chlorine dioxide, iodine tincture and povidone-iodine, more preferably sodium hypochlorite.

  Further, as the concentration of the germicidal component, the amount of free residual chlorine contained in the aqueous liquid containing the germicidal component is preferably 0.1 to 5.0 mg / l, more preferably 0.2 to 3.0 mg / l, More preferably, it is 0.5 to 1.5 mg / l.

  By making the said amount of free residual chlorine into the said range, since the odor at the time of use of an absorbent article can be suppressed, it is preferable. Furthermore, from the viewpoint of stable operation of the manufacturing apparatus, it is possible to reduce equipment troubles associated with product number switching, which is preferable. That is, in the product type in which the aqueous liquid is not added, the re-humidifying step (curing step) may not be carried out. Therefore, conventionally, the aqueous liquid stagnates in piping or the like when the stop period of the device becomes long. Although clogging may occur, it is preferable because it can be solved by adding an aqueous liquid containing a bactericidal component.

  The amount of the aqueous liquid containing the sterilizing component is preferably 1 to 10% by weight, more preferably 2 to 8% by weight, still more preferably 3 to 7% by weight, based on the water absorbent resin particles.

  Although it does not specifically limit about the addition method of the aqueous liquid containing the said sterilizing component, Preferably it is spray addition.

  Moreover, when adding the aqueous liquid containing the said sterilizing component, the temperature of a water absorbing resin particle becomes like this. Preferably it is 30-70 degreeC, More preferably, it is 35-65 degreeC, More preferably, it is 40-60 degreeC. When the temperature of the water-absorbent resin particles is less than 30 ° C., the permeation rate of the aqueous liquid to the water-absorbent resin particles is slowed. Conversely, when the temperature exceeds 70 ° C., the permeation rate is too fast. It is not preferable because the appropriate permeability to the water-absorbent resin particles and the uniform dispersibility deteriorate.

  After stopping the step of adding the aqueous liquid containing the bactericidal component for one day or more, it is preferable to operate the step of adding the aqueous liquid containing the bactericidal component again.

  Hereinafter, a polyvalent metal salt, a cationic polymer, a chelating agent, an inorganic reducing agent, an alpha-hydroxy carboxylic acid compound and a deodorant will be described as an example of the additive added in this step.

(Polyvalent metal salt and / or cationic polymer)
In the present invention, it is preferable to add a polyvalent metal salt and / or a cationic polymer from the viewpoint of the water absorption rate, liquid permeability, hygroscopicity and flowability of the water absorbing agent to be obtained.

  Specifically as the above-mentioned polyvalent metal salt and / or cationic polymer, the compound described in "[7] polyvalent metal salt and / or cationic polymer" of WO 2011/040530 and the amount thereof used Applies to the present invention.

(Chelating agent)
In the present invention, it is preferable to add a chelating agent from the viewpoint of color tone (coloring prevention), deterioration prevention, etc. of the water-absorbing agent to be obtained.

  As the above-mentioned chelating agent, specifically, the compound described in "[2] chelating agent" of WO 2011/040530 and the amount thereof used are applied to the present invention.

(Inorganic reductant)
In the present invention, it is preferable to add an inorganic reducing agent from the viewpoints of color tone (coloring prevention), deterioration prevention, reduction of residual monomers, etc. of the water absorbing agent to be obtained.

  As the inorganic reducing agent, specifically, the compound described in "[3] inorganic reducing agent" of WO 2011/040530 and the amount thereof used are applied to the present invention.

(Α-hydroxycarboxylic acid compound)
In the present invention, it is preferable to add an α-hydroxycarboxylic acid compound from the viewpoint of the color tone (coloring prevention) of the water absorbing agent to be obtained. In addition, "(alpha) -hydroxy carboxylic acid compound" is carboxylic acid which has a hydroxyl group in a molecule | numerator, or its salt, and is hydroxycarboxylic acid which has a hydroxyl group in alpha-position.

  Specifically, the compound described in "[6] α-hydroxycarboxylic acid compound" in WO 2011/040530 and the amount thereof used as the above α-hydroxycarboxylic acid compound are applied to the present invention .

(Deodorants)
In the present invention, it is preferable to add a deodorant from the viewpoint of deodorizing when using the obtained absorbent article (especially paper diaper).

  As the above-mentioned deodorant, a natural product-derived deodorant is preferable, and specifically, the compound described in JP-A-2001-285021 and the amount thereof used are applied to the present invention.

(2-8) Other Additives Addition Step In the present invention, additives other than the above-described additives can be added in order to add various functions to the water absorbent resin. Specific examples of the additive include surfactants, compounds having a phosphorus atom, oxidizing agents, organic reducing agents, water-insoluble inorganic fine particles, organic powders such as metal soaps, pulp and thermoplastic fibers. The surfactant is a compound described in WO 2005/075070, and the water-insoluble inorganic fine particle is described in "[5] water-insoluble inorganic fine particle" in WO 2011/040530. The respective compounds apply to the present invention.

  The use amount (addition amount) of the additive is not particularly limited because it is appropriately determined according to the application of the water absorbing agent to be obtained, but preferably 3 parts by weight or less with respect to 100 parts by weight of the water absorbing resin powder. More preferably, it is 1 part by weight or less. Further, the additive can be added in any of the production steps of the polyacrylic acid (salt) -based water absorbing agent.

(2-9) Other Steps In the present invention, in addition to the above-described steps, a particle sizing step, a fine powder removing step, a fine powder recycling step, and the like can be provided as necessary. Moreover, you may further include 1 type, or 2 or more types of processes, such as a transportation process, a storage process, a packing process, a storage process. The “particle sizing step” includes the fine powder removing step after the surface crosslinking step and the step of classification and crushing when the water-absorbent resin is aggregated and exceeds a desired size. Further, the "reuse step of fine powder" includes a step of adding fine powder as it is as in the present invention, or adding it to a large water-containing gel and any of the production steps of a water absorbing agent.

[3] Physical Properties of Polyacrylic Acid (Salt) -Based Water Absorbent The polyacrylic acid (salt) -based water absorbent obtained by the production method according to the present invention is desired to satisfy the following physical properties. When the water-absorbing agent is used for absorbent articles such as paper diapers, at least one or more, and preferably two, of the physical properties listed in the following (3-1) to (3-6): Or more, more preferably three or more including AAP, still more preferably four or more including AAP, particularly preferably five or more including AAP, most preferably all six physical properties within a desired range It is desirable to do. When these physical properties do not satisfy the following range, the effects of the present invention can not be sufficiently obtained, and there is a possibility that sufficient performance can not be exhibited in absorbent articles (particularly high-density paper diapers).

  The water absorbing agent of the present invention is not particularly limited as to its shape, but is preferably particulate. The physical properties of the particulate water-absorbing agent, which is a preferred embodiment, will be described herein. The following physical properties were measured according to the EDANA method unless otherwise noted.

(3-1) CRC (centrifuge holding capacity)
The CRC (centrifuge holding capacity) of the water-absorbing agent of the present invention is usually 5 g / g or more, preferably 20 g / g or more, more preferably 25 g / g or more, still more preferably 30 g / g or more. The upper limit is not particularly limited and is preferably as high as possible, but it is preferably 70 g / g or less, more preferably 50 g / g or less, still more preferably 40 g / g or less from the viewpoint of balance with other physical properties.

  Therefore, as a typical range of the above-mentioned CRC (centrifuge retention capacity), it can choose suitably within the limits of the upper limit and the lower limit which were mentioned above. For example, arbitrary ranges, such as 5-70 g / g, 20-50 g / g, 25-40 g / g, etc. can be selected.

  When the above-mentioned CRC is less than 5 g / g, the water absorption amount of the water absorbing agent is so small that it is not suitable as an absorbent for absorbent articles such as disposable diapers. In addition, when the above-mentioned CRC exceeds 70 g / g, the rate of absorbing body fluid such as urine and blood decreases, so that it is not suitable for use in high water absorption type paper diapers and the like. The CRC can be controlled by an internal crosslinking agent, a surface crosslinking agent or the like.

(3-2) AAP (water absorption capacity under pressure)
The AAP (water absorption capacity under pressure) of the water-absorbing agent of the present invention is preferably 18 g / g or more, more preferably 20 g / g or more, still more preferably 23 g / g or more, particularly preferably 24 g / g or more, most preferably 25 g / g It is more than / g. The upper limit value is not particularly limited, but preferably 30 g / g or less.

  Therefore, as a typical range of the above-mentioned AAP (water absorption capacity under pressure), it can be suitably chosen within the limits of the upper limit and the lower limit which were mentioned above. For example, arbitrary ranges, such as 18-30 g / g, 22-30 g / g, 25-30 g / g, etc. can be selected.

  When the AAP is less than 20 g / g, when used in paper diapers and the like, the amount of absorption when the pressure is applied to the absorbent decreases, so it is suitable as an absorbent for absorbent articles such as paper diapers. Absent. In addition, AAP can be controlled by particle size, surface crosslinking agent and the like.

(3-3) Particle size (PSD (particle size distribution), D50 (weight average particle size), σζ (log standard deviation of particle size distribution))
The particle size (PSD (particle size distribution), D50 (weight-average particle size), σζ (log standard deviation of particle size distribution)) of the water-absorbing agent of the present invention is the same as the particle size of the water-absorbent resin powder before surface crosslinking. So, it is controlled.

(3-4) Ext (water soluble matter)
The Ext (water-soluble component) of the water-absorbing agent of the present invention is usually 50% by weight or less, preferably 35% by weight or less, more preferably 25% by weight or less, and still more preferably 15% by weight or less. The lower limit value is not particularly limited, but is preferably about 0% by weight, more preferably about 0.1% by weight.

  Therefore, as a typical range of the above-mentioned Ext (water-soluble matter), it can be suitably chosen within the limits of the upper limit and the lower limit which were mentioned above. For example, any range such as 0 to 50% by weight, 0.1 to 50% by weight, 0.1 to 35% by weight, and the like can be selected.

  When the above Ext exceeds 50% by weight, the gel strength is weak, and there is a possibility that the water absorbing agent becomes inferior in liquid permeability. Furthermore, since the amount of return is large, it is not suitable as an absorbent for absorbent articles such as disposable diapers. In addition, Ext can be controlled by an internal crosslinking agent or the like.

(3-5) Water Content The water content of the water-absorbing agent of the present invention is preferably more than 1% by weight and 15% by weight or less, more preferably 2 to 15% by weight, still more preferably 2 to 12% by weight, particularly preferably Is 2 to 10% by weight.

  By controlling the water content to the above range, a water absorbing agent excellent in powder properties (for example, flowability, transportability, damage resistance, etc.) can be obtained. The water content can be controlled by heat treatment at surface crosslinking.

(3-6) Residual Monomer The residual monomer contained in the water absorbing agent of the present invention is preferably 500 ppm or less, more preferably 400 ppm or less, still more preferably 300 ppm or less from the viewpoint of safety. The lower limit value is not particularly limited, but is preferably about 0 ppm, more preferably about 10 ppm.

  Therefore, as a representative range of the said residual monomer, it can select suitably within the range of the upper limit and lower limit which were mentioned above. For example, arbitrary ranges, such as 0-500 ppm, 0-300 ppm, 10-400 ppm, etc. can be selected.

  By controlling the residual monomer to the above-mentioned range, a water-absorbing agent in which the stimulation on the skin or the like of the human body is reduced can be obtained.

[4] Applications of Polyacrylic Acid (Salt) -Based Water Absorbent The application of the water absorbent of the present invention is not particularly limited, but preferably the absorbent application of absorbent articles such as paper diapers, sanitary napkins, incontinence pads etc. is mentioned Be In particular, it can be used as an absorbent for high-density paper diapers (with a large amount of water-absorbing agent used per paper diaper) in which the odor, coloring and the like derived from raw materials have become a problem. Furthermore, a remarkable effect can be expected when it is used for the upper layer part of the said absorber.

  Moreover, absorbent materials, such as a pulp fiber, can also be used as said absorbent body other than a water absorption agent. In this case, the content (core concentration) of the water absorbing agent in the absorbent is preferably 30 to 100% by weight, more preferably 40 to 100% by weight, still more preferably 50 to 100% by weight, still more preferably 60 100 to 100% by weight, particularly preferably 70 to 100% by weight, and most preferably 75 to 95% by weight.

  When the core concentration is in the above range, when the absorbent is used in the upper layer portion of the absorbent article, the absorbent article can maintain a clean white state. Furthermore, since it is excellent in the diffusibility of body fluids such as urine and blood, it is possible to improve the absorption amount by efficient liquid distribution.

  The present invention will be more specifically described according to the following Examples and Comparative Examples, but the present invention is not construed as being limited thereto, and Examples obtained by appropriately combining the technical means disclosed in each Example. Are also included in the scope of the present invention.

  In addition, the electric equipment (a physical-property measurement of a water absorbing resin is also included) used by the Example and the comparative example used the power supply of 200V or 100V unless there is a note in particular. Moreover, various physical properties of the water absorbing agent of the present invention were measured under the conditions of room temperature (20 to 25 ° C.) and relative humidity 50% RH unless otherwise noted.

  Moreover, for convenience, "liter" may be described as "l" or "L", and "weight%" may be described as "wt%". Furthermore, in the measurement of trace components, the lower limit of detection is expressed as "ND (Non Detected)".

[Measurement of physical properties of water absorbing agent]
Hereinafter, measurement of physical properties of the water absorbing agent obtained by the manufacturing method according to the present invention will be described. In the case where the measurement target is, for example, a water-absorbent resin powder other than the water-absorbent agent, the “water-absorbent agent” is read as “water-absorbent resin powder” and applied.

(A) CRC (centrifuge holding capacity)
The CRC (centrifuge holding capacity) of the water-absorbing agent of the present invention was measured according to the EDANA method (ERT 441.2-02).

(B) AAP (water absorption capacity under pressure)
AAP (water absorption capacity under pressure) of the water absorbing agent of the present invention was measured in accordance with the EDANA method (ERT 442.2-02).

(C) Particle size (PSD (particle size distribution), D50 (weight average particle size), σζ (log standard deviation of particle size distribution))
The particle size (PSD (particle size distribution), D50 (weight average particle size), σζ (log standard deviation of particle size distribution)) of the water-absorbing agent of the present invention is described in US Pat. No. 7,638,570 “(3) Mass-Average It measured based on "Particle Diameter (D50) and Logarithmic Standard Deviation ((sigma) (perp)) of Particle Diameter Distribution".

(D) Ext (water soluble matter)
The Ext (water-soluble matter) of the water-absorbing agent of the present invention was measured according to the EDANA method (ERT 470.2-02).

(E) Water content, resin solid content The water content of the water-absorbing agent of the present invention was measured in accordance with the EDANA method (ERT 430.2-02). In the present invention, the measurement was carried out by changing the amount of sample to 1.0 g and the drying temperature to 180 ° C.

  In addition, resin solid content (weight%) was prescribed | regulated by (100-moisture content) (weight%).

(F) Residual Monomer The residual monomer of the water-absorbing agent of the present invention was measured according to the EDANA method (ERT 410.2-02).

(G) Odor test and mold generation test First, human urine for the odor test and the mold generation test was prepared. The human urine was collected from 10 adults within 2 hours after excretion and used as a human urine mixture. Subsequently, 10 ml of the human urine mixture was collected and placed in a lidded polypropylene container (trade name: Pac Ace, manufactured by Teraoka Co., Ltd./size; caliber 58 mm × bottom diameter 54 mm × height 74 mm) having a volume of 120 ml. .

  Next, 1 g of a water absorbing agent was added to a container containing 10 ml of the above human urine mixture to form a swollen gel which absorbed human urine, and after 1 minute, its odor was confirmed (odor when using paper diapers ).

  Subsequently, the container was sealed and stored at room temperature (25 ° C.) in a cold and dark place. After 10 days, the appearance of the above-mentioned swollen gel was confirmed (confirmation of mold generation at the time of paper diaper disposal).

  Confirmation of the said odor was performed by the monitor (20 adults) chosen arbitrarily. In addition, if the odor at the time of adding a water absorbing agent is made into an acceptable range by making the odor at the time of testing a human urine mixture alone without adding a water absorbing agent into “Level 5”, “Level 3” If it is odorless, it was evaluated as "Level 1".

  The evaluation points of all the above monitors were averaged (rounded off), and if the level was 3 or less, it was judged as "no odor".

Example 1
As a continuous production device of water absorbing agent, a production device is prepared which performs each step of polymerization, gel grinding, drying, grinding, classification, surface crosslinking (mixing of surface crosslinking agent, heat treatment, cooling), addition of aqueous liquid and particle sizing. did. The manufacturing devices were configured in this order, and the devices were connected by a transport device. The water absorbing agent was continuously produced at 1500 kg / hr using the continuous production apparatus. The continuous production apparatus of the water absorbing agent also includes a step of filling the shipping container with the water absorbing agent obtained as a product.

  First, as a monomer aqueous solution (1), an acrylic acid partial sodium salt aqueous solution having a neutralization rate of 75 mol% and a monomer concentration of 38 wt% was prepared. At that time, polyethylene glycol diacrylate (average n number; 9) as an internal crosslinking agent was added so as to be 0.03 mol% with respect to the number of moles of all monomers. The "average n number" means the average number of degrees of polymerization of methylene chains in the polyethylene glycol chain.

  Next, the above monomer aqueous solution (1) was continuously supplied (sent to liquid) to the polymerization apparatus using a metering pump. At that time, nitrogen gas was continuously blown from the middle of the liquid delivery piping, and the concentration of dissolved oxygen in the monomer aqueous solution (1) was adjusted to 0.5 mg / l or less.

  Subsequently, sodium persulfate and L-ascorbic acid as polymerization initiators were continuously mixed (line mixing) into the aqueous monomer solution (1) using separate feed pipes. The amounts of sodium persulfate and L-ascorbic acid added were 0.12 g and 0.005 g, respectively, per mole of the monomer.

  The polymerization apparatus in the continuous production apparatus used in Example 1 was a flat steel belt polymerization apparatus having a weir at both ends, and using the polymerization apparatus, stationary aqueous solution polymerization was continuously performed. The liquid supplied to the polymerization apparatus had a thickness of about 30 mm on a flat steel belt. The polymerization time was 30 minutes. By the operation, a band-like water-containing gel-like crosslinked polymer (water-containing gel) (1) was obtained.

  Next, the strip-shaped water-containing gel (1) is cut at regular intervals perpendicular to the traveling direction of the flat steel belt, and then continuously supplied to a meat chopper having a hole diameter of 7 mm to obtain particles of about 2 mm. Gel crushed. By the operation, a particulate water-containing gel (1) was obtained.

  Subsequently, the particulate water-containing gel (1) was continuously loaded on the perforated plate of the ventilated belt type drying apparatus so as to have a thickness of 50 mm, and dried at 185 ° C. for 30 minutes. By this operation, a block-like dry polymer (1) was obtained. The time required for the water-containing gel (1) discharged from the polymerization apparatus to be introduced into the aeration belt type drying apparatus was about 1 minute.

  Subsequently, the whole amount of the block-like dry polymer (1) was continuously supplied to a three-stage roll mill (roll gap; 1.0 mm / 0.55 mm / 0.32 mm in order from the top) and pulverized. This operation gave a ground polymer (1). The temperature of the dry polymer (1) supplied to the three-stage roll mill was about 60.degree. Moreover, the pressure reduction degree in the crushing process was adjusted to 0.29 kPa.

  Subsequently, the whole of the pulverized polymer (1) was continuously supplied to a classifier (sieving device consisting of a total of two metal sieves; 850 μm / 150 μm in order from the top) and classified. . Water-absorbent resin powder (1) was obtained by the above operation. The temperature of the pulverized polymer (1) supplied to the classifier was about 60.degree. In addition, the frame on which the classifier was installed was grounded (static charge) having a ground resistance value of 5Ω.

  By the above-described series of procedures, a water-absorbent resin powder (1) having a proportion of particles with a particle diameter of 150 μm to less than 850 μm of 98% by weight and a CRC (centrifuge holding capacity) of 43 g / g was obtained.

  Next, a surface cross-linking agent solution consisting of 0.3 parts by weight of 1,4-butanediol, 0.5 parts by weight of propylene glycol and 3 parts by weight of deionized water with respect to 100 parts by weight of the heavy aqueous resin powder (1) (1) was prepared. The electric conductivity of the ion-exchanged water was 0.5 μS / cm.

  The water-absorbent resin powder (1) was continuously supplied from the above-mentioned classifier at 1500 kg / hr to a high-speed mixer (turbulizer / 1000 rpm) using pneumatic transportation. At that time, the surface crosslinker solution (1) was uniformly mixed by spraying it into the high-speed mixer.

  Next, the mixture (1) obtained by the above operation was continuously supplied to a horizontal stirring apparatus (paddle dryer) for heat treatment. The temperature during the heat treatment was 198 ° C., and the average residence time was 45 minutes. In addition, the temperature at the time of the heat treatment uses pressurized steam of 2.5 MPa as a heating source, and uses a thermometer installed near the discharge part of the horizontal stirring device to obtain the mixture (1) in the device. The temperature was measured and the flow of pressurized steam was controlled so that the temperature was 198 ° C. In addition, the position of the exhaust weir was adjusted so that the average filling rate was 75% by volume.

  Subsequently, using the horizontal stirring apparatus of the same type and a slightly smaller capacity as the horizontal stirring apparatus (paddle dryer) used in the heat treatment, the temperature of the heat treated mixture (1) is forced to 60 ° C. It cooled down. Water-absorbent resin particles (1) were obtained by this operation. The total amount of acetic acid and propionic acid contained in the water-absorbent resin particles (1) obtained was 200 mg / kg.

  Next, 10 parts by weight of water (free residual chlorine amount; 0.8 mg / l (chlorine conversion)) to which sodium hypochlorite as a bactericidal component is added with respect to 100 parts by weight of the water absorbent resin particles (1) Were sprayed and mixed using a high speed mixer. In addition, the mixing is also performed by permeating water existing on the surface of the water absorbent resin particles to the inside, and the operation may be referred to as “curing”.

  Subsequently, the water-absorbent resin particles (1) were crushed until the whole amount of the water-absorbent resin particles (1) passed through the sieve mesh, using a sieving device having a JIS standard sieve having an opening of 850 μm. In addition, said "crushing" means the operation of grind | pulverizing the water absorbent resin particle (1) aggregated at the time of said hardening until it passes the mesh screen of 850 micrometers of mesh openings. Therefore, coarse particles (non-passable / on product) which do not pass through the screen are crushed again. By the operation, a water absorbing agent (1) as a sized product was obtained. The CRC of the obtained water-absorbing agent (1) was 34.0 g / g, and the AAP was 24.0 g / g. Further, an odor test and a mold generation test were conducted on the obtained water-absorbing agent (1). The results are shown in Table 1.

  Next, after the production of the water absorbing agent (1) is continuously performed for 5 days, the water absorbing agent of the type not requiring the curing operation (state in which the water addition process is stopped) is continuously generated for 10 days Then, the production of the water absorbing agent (1) was started. Table 2 shows the operating conditions after resumption of production of the water absorbing agent (1).

Comparative Example 1
Comparative water-absorbing agent (Example 1) in the same manner as Example 1, except that ion-exchanged water containing no bactericidal component was used instead of water to which sodium hypochlorite as the bactericidal component was added. I got 1). Furthermore, an odor test and a mold generation test were conducted on the obtained comparative water-absorbing agent (1). The results are shown in Table 1.

  Next, as in Example 1, after the production of the comparative water absorbing agent (1) is continuously performed for 5 days, a water absorbing agent of a type not requiring the curing operation is continuously produced for 10 days, and Production of the water absorbing agent (1) was started. The operating conditions at the start of production of the water absorbing agent (1) are shown in Table 2.

Comparative Example 2
A comparative water-absorbing agent (2) was obtained in the same manner as in Comparative Example 1 except that acetic acid was added at 2800 mg / kg in combination when mixing ion-exchanged water containing no bactericidal component in Comparative Example 1. . Furthermore, an odor test and a mold generation test were conducted on the obtained comparative water-absorbing agent (2). The results are shown in Table 1.

Comparative Example 3
A comparative water-absorbing agent (3) is obtained in the same manner as in Comparative Example 1 except that 2800 mg / kg of propionic acid is added in combination with ion-exchanged water containing no bactericidal component in Comparative Example 1. The Furthermore, an odor test and a mold generation test were conducted on the obtained comparative water-absorbing agent (3). The results are shown in Table 1.

Comparative Example 4
Comparative water-absorbing agent (4) was carried out in the same manner as in Example 1, except that, when mixing water to which sodium hypochlorite as a bactericidal component was added in Example 1, 2800 mg / kg of acetic acid was additionally added. Got). Furthermore, an odor test and a mold generation test were conducted on the obtained comparative water-absorbing agent (4). The results are shown in Table 1.

(Summary)
As shown in Table 1, the water-absorbing agent (1) had no odor after absorption of human urine (when using paper diapers) and no generation of mold was observed after 10 days (when discarding paper diapers). On the other hand, in the comparative water-absorbing agent (1) cured with ion-exchanged water containing no bactericidal component, there was no odor after absorbing human urine (when using paper diapers), but after 10 days (when paper diapers are discarded) Occurrence of mold was observed. From these facts, it is understood that it is possible to suppress the generation of mold at the time of paper diaper disposal by containing a sterilizing component in water used at the time of curing.

  In addition, based on the results of the comparative water absorbing agents (2) to (4), by setting the total amount of acetic acid and propionic acid in the water absorbing agent to 2500 mg / kg or more, odor is absorbed after absorbing human urine (when using paper diapers). Admitted. On the other hand, in the water absorbing agent (1) and the comparative water absorbing agent (1) in which the total amount of the acetic acid and propionic acid is 200 mg / kg, no odor occurs after absorbing human urine (when using paper diapers). The odor of is presumed to be due to acetic acid and propionic acid in the water-absorbing agent.

  On the other hand, with respect to mold generation after 10 days (when disposable diapers are discarded), no generation of mold is observed even with the comparative water absorbents (2) and (3) cured with ion-exchanged water containing no bactericidal component The From this, it is presumed that not only the bactericidal component but also the acetic acid and propionic acid in the water-absorbing agent are affecting the generation of mold after 10 days (when disposable diapers are discarded).

  From the above results, the total of acetic acid and propionic acid in the water-absorbing agent to suppress the generation of odor and mold both when absorbing human urine (when using paper diapers) and after 10 days (when discarding paper diapers) It can be seen that it is necessary to keep the amount low and to add an aqueous liquid containing traces of germicidal components.

  Further, as shown in Table 2, it can be seen that, by including a sterilizing component in the water used at the time of curing, it is possible to prevent clogging in the water addition spray nozzle and piping.

  From the above results, in the step of adding the aqueous liquid to the water-absorbent resin particles after surface crosslinking, if ion exchange water containing a predetermined amount or more of the bactericidal component is used, the device trouble at the product type switching can be prevented. It has become clear that stable operation with reduced production loss can be achieved.

  The method for producing a polyacrylic acid (salt) -based water absorbing agent according to the present invention can be applied to the production of a water absorbing agent, particularly for mass production. Moreover, the polyacrylic acid (salt) -based water absorbing agent obtained by the present invention is suitable for use as an absorbent for sanitary goods such as paper diapers.

Claims (11)

A method for producing a polyacrylic acid (salt) -based water absorbing agent, comprising a polymerization step of a monomer aqueous solution, a drying step, and a surface crosslinking step,
The total amount of acetic acid and propionic acid contained in the polymer obtained by polymerizing monomer and 200～2500Ppm,
The amount of free residual chlorine contained in the aqueous liquid containing no bactericidal component relative to the surface cross-linked water-absorbent resin particles is 0.1 to 5.0 mg / l, and sodium hypochlorite And a method of producing a polyacrylic acid (salt) -based water absorbing agent, further comprising the step of adding 1 to 10% by weight of an aqueous liquid containing a bactericidal component selected from the group consisting of After stopping the step of adding the aqueous liquid to the surface-crosslinked water-absorbent resin particles, including the polymerization step of the monomer aqueous solution, the drying step, and the surface crosslinking step, for one day or more, the aqueous liquid is added again A process for producing a polyacrylic acid (salt) -based water-absorbing agent,
The total amount of acetic acid and propionic acid contained in the polymer obtained by polymerizing the monomer is 200 to 2500 ppm,
The step of adding the aqueous liquid is such that the amount of free residual chlorine contained in the aqueous liquid containing the bactericidal component is 0.1 to 5.0 mg / l, and is selected from the group consisting of sodium hypochlorite and chlorine dioxide A method for producing a polyacrylic acid (salt) -based water absorbing agent, further comprising the step of adding 1 to 10% by weight of an aqueous liquid containing a sterilizing component to the water absorbent resin particles. The method according to claim 1 or 2 , wherein the addition of the aqueous liquid containing the bactericidal component is spray addition. The manufacturing method according to any one of claims 1 to 3 , wherein heat treatment is performed so that the water content of the water absorbing agent becomes 1 to 15% by weight. The process according to any one of claims 1 to 4 , wherein in the step of adding an aqueous liquid containing the sterilizing component, the temperature of the water absorbent resin particles to which the aqueous liquid is added is 30 to 70 ° C. . A step of adding an aqueous solution containing the bactericidal component after stopping least 1 day, again, to run the step of adding an aqueous solution containing a bactericidal component, as described in any one of claims 1, 3-5 Production method. In the step of adding an aqueous solution containing the bactericidal component, a polyvalent metal salt simultaneously with the addition of an aqueous solution containing the bactericidal component, a cationic polymer, a chelating agent, non-machine reducing agents, alpha-hydroxy carboxylic acid compound, and deodorant adding at least one additive selected from the group consisting of the method according to any one of 請 Motomeko 1-6. The above water absorbing agent has a CRC (centrifuge holding capacity) of 30 g / g or more, an AAP (water absorption capacity under pressure) of 18 g / g or more, a D50 (weight average particle diameter) of 250 to 600 μm, The manufacturing method according to any one of claims 1 to 7 , wherein the logarithmic standard deviation) is 0 to 0.50. The manufacturing method in any one of Claims 1-8 whose drying temperature in a drying process is 120-250 degreeC, and whose heating temperature in a surface bridge | crosslinking process is 50-300 degreeC. A bactericidal component selected from the group consisting of sodium hypochlorite and chlorine dioxide in which the amount of free residual chlorine contained in the aqueous liquid containing no bactericidal component is 0.1 to 5.0 mg / l; Containing 1 to 10% by weight of a water-containing liquid to water-absorbent resin particles, CRC (centrifuge holding capacity) is 30 g / g or more, AAP (water absorption capacity under pressure) is 18 g / g or more, D50 (weight-average particle A water absorbing agent having a diameter of 250 to 600 μm and σζ (logarithmic standard deviation of particle size distribution) of 0 to 0.50. An absorbent article comprising the water absorbing agent according to claim 10 .