JP4979879B2 - Water-absorbing agent and sanitary material using the same - Google Patents

Description

  The present invention relates to a particulate water-absorbing agent mainly composed of a water-absorbing resin, and more particularly to a water-absorbing agent that exhibits excellent absorption performance for liquids such as urine and hygiene materials using the same. is there.

  In recent years, hygroscopic materials such as disposable diapers and sanitary napkins, so-called incontinence pads, have widely used water-absorbing resins for the purpose of absorbing bodily fluids as constituent materials. Examples of the water-absorbing resin include a crosslinked polyacrylic acid partially neutralized product, a hydrolyzate of starch-acrylic acid graft polymer, a saponified vinyl acetate-acrylic acid ester copolymer, an acrylonitrile copolymer or an acrylamide copolymer. A hydrolyzate of a polymer or a cross-linked product thereof, and a cross-linked polymer of a cationic monomer are known.

  For such water-absorbing resins, excellent water absorption and water absorption speed, gel strength, gel permeability, and water suction from a substrate containing aqueous liquid when in contact with aqueous liquids such as body fluids It is required to have excellent physical properties such as strength. Furthermore, in recent years, water-absorbing resin powders with a very narrow particle size distribution and water-absorbing resin powders with high absorption capacity and low water-soluble content have been demanded, and have high absorption capacity under pressure and liquid permeability under pressure. Being required is essential.

  For example, the following patent documents 1 to 24 disclose many parameter patents and measurement methods that define various properties of these water absorbent resins.

  That is, Patent Document 1 “US Reissue Patent 32649” proposes a water-absorbing resin excellent in gel strength, soluble content, and water absorption ratio. Patent Document 2 “British Patent No. 2,267,094B” proposes a water-absorbing resin excellent in pressureless liquid permeability, water absorption speed, and water absorption magnification. As a technique for defining a specific particle size distribution, Patent Document 3 “US Pat. No. 5,051,259”, Patent Document 4, “US Pat. No. 5,419,956”, Patent Document 5, “US Pat. No. 6,087,002”, Patent Document 6, “European Patent No. 629441”, etc. There are techniques described in.

  Also, many water-absorbing resins excellent in water absorption capacity under pressure under various loads and methods for measuring the same have been proposed. A water-absorbing resin alone or in combination with other physical properties is disclosed in Patent Document 7 “European Patent 0707603”. ”, Patent Document 8“ European Patent 0712659 ”, Patent Document 9“ European Patent 1029886 ”, Patent Document 10“ US Pat. No. 5,462,972 ”, Patent Document 11“ US Pat. No. 5,453,323 ”, Patent Document 12“ US Pat. No. 5,977,893 ”. ”, Patent Document 13“ US Patent 6127454 ”, Patent Document 14“ US Patent 6184433 ”, Patent Document 15“ US Patent 6297335 ”, Patent Document 16“ US Reissue Patent Re37021 ”, and the like. .

  Further, a water-absorbing resin excellent in impact resistance with reduced physical properties has been proposed in Patent Document 17 “US Pat. No. 5140076”, Patent Document 18 “US Pat. No. 6,414,214 B1”, and the like. A water-absorbing resin that defines the amount of dust is proposed in Patent Document 19 “US Pat. No. 5,994,440”, and a water-absorbing resin with little coloring is proposed in Patent Document 20 “US Pat. No. 6,444,744”. Regarding urine resistance, water-absorbing resins excellent in gel durability and water-absorbing ability to L-ascorbic acid aqueous solutions and the like have been proposed in Patent Document 21 “US Pat. No. 6,194,531” and Patent Document 22 “European Patent 0940148” A water-absorbing resin excellent in air permeability is proposed in Patent Document 23 “European Patent No. 1153656”. A water-absorbing resin with little residual monomer is proposed in Patent Document 24 “European Patent No. 0605215”.

Furthermore, the fact that a water-absorbing resin having specific physical properties is suitable for a water-absorbing article (diaper) having a specific physical property, a specific constitution or a specific polymer concentration is disclosed in Patent Document 25 “US Pat. No. 5,147,343” and Patent Document 26 “US Patent No. 5149335 ”, Patent Literature 27“ European Patent 532002 ”, Patent Literature 28“ U.S. Pat. No. 5,601,452 ”, Patent Literature 29“ U.S. Pat. No. 5,562,646 ”, Patent Literature 30“ U.S. Pat. No. 5,669,894 ”, Patent Literature 31“ U.S. Pat. Patent No. 6150582, Patent Document 32 “International Patent WO02 / 053198”, Patent Document 33 “US Patent No. 5843059”, Patent Document 34 “US Patent Publication No. 2001/4951”, and the like.
US Reissue Patent 32649 British Patent No. 2267094B US Pat. No. 5,051,259 US Pat. No. 5,419,956 US Pat. No. 6,087,002 European patent 629441 European Patent 0707603 European Patent 0712659 European Patent No. 1029886 US Pat. No. 5,462,972 US Pat. No. 5,453,323 US Pat. No. 5,797,893 US Pat. No. 6,127,454 US Pat. No. 6,184,433 US Pat. No. 6,297,335 US Reissue Patent Re37021 US Pat. No. 5140076 US Pat. No. 6,414,214 B1 US Pat. No. 5,994,440 US Pat. No. 6,444,744 US Pat. No. 6,194,531 European Patent 0940148 European Patent No. 1153656 European Patent 0605215 US Pat. No. 5,147,343 US Pat. No. 5,149,335 European Patent 532002 US Pat. No. 5,601,452 US Pat. No. 5,562,646 US Pat. No. 5,669,894 US Pat. No. 6,150,582 International patent WO02 / 053198 US Pat. No. 5,843,059 US Patent Publication 2001/4951

  However, the water-absorbent resin that has been developed with a focus on many of the above-mentioned physical properties has been manufactured and used as targets or specifications of the above-mentioned physical properties, but these specific physical properties (performance) are controlled. However, there is still a problem that it is difficult to say that it is sufficiently performing in actual use such as disposable diapers. In particular, sanitary materials with increased concentrations of water-absorbing resin and reduced fiber materials (high water-absorbing resin concentration) can not be said to exhibit sufficient performance for actual use.

  The purpose of the present invention has hitherto been focused on a number of physical properties (water absorption rate, no pressure (under no load) water absorption, under pressure (under load) water absorption, gel strength, durability, soluble content, particle size, etc.). Despite the fact that water-absorbing resins have been developed and used, the problem with conventional water-absorbing resins is that even if they are manufactured by these controls or designs, they do not exhibit sufficient performance for actual use. The problem is to provide a water-absorbing resin suitable for actual use.

  As a result of intensive studies in view of the above-mentioned problems, the present inventors have not paid any attention among many conventional physical properties, the difference in water absorption due to salt concentration, which is also the water absorption under pressure under a specific pressure. A water-absorbing agent that gives a constant absorbency (absorbency under pressure) and liquid permeability regardless of changes in salt concentration is the conventional model. The present inventors have found that it is an excellent water-absorbing agent as described above, and have completed the present invention.

That is, the particulate water-absorbing agent of the present invention is a particulate water-absorbing agent containing, as a main component, a water-absorbing resin that is a cross-linked polymer of a water-soluble unsaturated monomer, in order to solve the above-mentioned problem. The particulate water-absorbing resin having a particle diameter of less than 850 μm is contained in an amount of 90 to 100% by mass with respect to the total mass of the water-absorbing resin, and the following (formula 1)
(Salt concentration absorption index) = (absorption capacity under pressure at 4.83 kPa for a constant salt concentration aqueous solution) / (absorption capacity under no load for a constant salt concentration aqueous solution) (Equation 1)
(In the formula, the absorption capacity under pressure is an absorption capacity when immersed in a constant salt concentration aqueous solution for 60 minutes under a pressure of 4.83 kPa, and the absorption capacity under no load is under no pressure, The first salt concentration absorption index, which is the salt concentration absorption index when the above constant salt concentration aqueous solution is ion-exchanged water, is 0.60 or more. It is what is.

  The particulate water-absorbing agent of the present invention is a particulate water-absorbing agent containing, as a main component, a water-absorbing resin that is a cross-linked polymer of a water-soluble unsaturated monomer, in order to solve the above problems, The particulate water-absorbing resin having a particle diameter of less than 850 μm is contained in an amount of 90% by mass or more with respect to the total mass of the water-absorbing resin, and is immersed in ion-exchanged water for 60 minutes under a pressure of 4.83 kPa. The absorption capacity under pressure, which is the absorption capacity in the case of the above, is 50 g / g or more.

  Further, the particulate water-absorbing agent of the present invention is the above-mentioned particulate water-absorbing agent, which is a salt concentration absorption index when the constant salt concentration aqueous solution in (Formula 1) is a 0.10% by mass sodium chloride aqueous solution. The bi-salt concentration absorption index is preferably 0.80 or more.

  The particulate water-absorbing agent of the present invention is a salt concentration absorption index when the constant salt concentration aqueous solution in the above (formula 1) is a 0.30 mass% sodium chloride aqueous solution in the particulate water-absorbing agent. The trisalt concentration absorption index, the fourth salt concentration absorption index, which is the salt concentration absorption index when the constant salt concentration aqueous solution in (Equation 1) is a 0.50% by mass sodium chloride aqueous solution, The fifth salt concentration absorption index, which is the salt concentration absorption index when the constant salt concentration aqueous solution is 0.70% by mass sodium chloride aqueous solution, and the constant salt concentration aqueous solution in the above (formula 1) is 0.90% by mass sodium chloride aqueous solution It is preferable that at least one of the sixth salt concentration absorption index, which is the salt concentration absorption index, is 0.90 or more.

  Further, the particulate water-absorbing agent of the present invention is the above-mentioned particulate water-absorbing agent, wherein the first salt concentration absorption index, the second salt concentration absorption index, the third salt concentration absorption index, the fourth salt concentration absorption index, the fifth The average salt concentration absorption index, which is the average value of the salt concentration absorption index and the sixth salt concentration absorption index, is 0.90 or more, or the standard deviation of the average salt concentration absorption index is 0 to 0.100 It is preferable to be within the range.

Further, the particulate water-absorbing agent of the present invention is the above-mentioned particulate water-absorbing agent in the following (formula 2):
(Salt tolerance index) = (absorption capacity under no load with respect to a constant salt concentration aqueous solution) / (absorption capacity under no load with respect to ion-exchanged water) (Equation 2)
(In the formula, the absorption capacity under no load is the absorption capacity when immersed in a constant salt concentration aqueous solution or ion-exchanged water for 60 minutes), and the above-mentioned constant salt concentration is a 0.10% by mass sodium chloride aqueous solution. In this case, the first salt tolerance index, which is the salt tolerance index, is preferably 0.40 or more.

  Further, the particulate water-absorbing agent of the present invention has an absorption capacity under no load which is an absorption capacity when immersed in a 0.90 mass% sodium chloride aqueous solution for 60 minutes under no pressure in the particulate water-absorbing agent. 10 to 27 g / g.

  Further, the particulate water-absorbing agent of the present invention is the above-mentioned particulate water-absorbing agent, absorption under pressure which is an absorption capacity when immersed in a 0.90 mass% sodium chloride aqueous solution for 60 minutes under a pressure of 4.83 kPa. The magnification is preferably 10 to 27 g / g.

  The particulate water-absorbing agent of the present invention preferably further contains water-insoluble fine particles in the particulate water-absorbing agent.

  Moreover, it is preferable that the particulate water-absorbing agent of the present invention has a gel permeation index of 15 or more with respect to ion-exchanged water under the pressure of 2.07 kPa in the above-mentioned particulate water-absorbing agent.

  The particulate water-absorbing agent of the present invention preferably has a gel flow index of 50 or more with respect to a 0.30 mass% sodium chloride aqueous solution under the pressure of 2.07 kPa in the particulate water-absorbing agent.

  The particulate water-absorbing agent of the present invention preferably has a gel flow index of 15 or more with respect to a 0.70 mass% sodium chloride aqueous solution under the pressure of 4.83 kPa in the particulate water-absorbing agent.

  Further, the particulate water-absorbing agent of the present invention is the particulate water-absorbing agent described above, wherein the water-soluble unsaturated monomer comprises acrylic acid and / or a salt thereof, and the particulate water-absorbing resin is: It is preferable that surface modification treatment is performed.

  Moreover, in order to solve the said subject, the sanitary material of this invention is a sanitary material for absorbing a bodily fluid, Comprising: One of said particulate water absorbing agents is included.

In addition, the sanitary material of the present invention includes the above sanitary material, and includes an absorption layer that absorbs the body fluid.
(Core concentration ratio) = (mass of particulate water-absorbing agent) / ((mass of particulate water-absorbing agent) + (mass of fiber material)) (Equation 3)
The core concentration defined by is good to be 0.3 or more and 1.0 or less.

  As described above, the particulate water-absorbing agent according to the present invention is a particulate water-absorbing agent mainly composed of a water-absorbing resin that is a cross-linked polymer of a water-soluble unsaturated monomer, and is less than 850 μm and 106 μm or more. The particulate water-absorbing resin having a particle size is contained in an amount of 90% by mass to 100% by mass with respect to the total mass of the water-absorbing resin contained in the particulate water-absorbing agent, and is defined by the above (formula 1). The first salt concentration absorption index, which is the salt concentration absorption index when the constant salt concentration aqueous solution is ion-exchanged water, is 0.60 or more.

  Therefore, the particulate water-absorbing agent has an effect that a certain amount of aqueous solution can be absorbed regardless of a change in salt concentration. In addition, the particulate water-absorbing agent has an excellent gel permeation index regardless of changes in salt concentration or pressure. Therefore, when the particulate water-absorbing agent is used in an absorbent article such as a sanitary material, the liquid can be sufficiently spread over the entire absorbent article, and the liquid absorption amount can be increased.

  Hereinafter, the particulate water-absorbing agent (water-absorbing agent) according to the present invention will be described in detail. However, the scope of the present invention is not limited to these descriptions, and the spirit of the present invention is not impaired except for the following examples. It can be implemented as appropriate within the range.

  In evaluating various physical properties of the water-absorbent resin, it has been proposed to use physiological saline (0.9 mass (mass%) sodium chloride aqueous solution) or various artificial urine as a urine model. However, the actual urine composition of human urine varies in each of the above-mentioned patent documents. As can be understood from this fact, the actual composition of urine is not constant, and the actual situation is that the living environment, diet, age, season, and even the same person varies greatly with time and physical condition. .

  Therefore, the present inventors have a problem that in the conventional evaluation of the water-absorbent resin, the physical properties are determined by evaluating using a certain water-absorbing solution (physiological saline, artificial urine, etc.) as a model. Since the conventional water-absorbent resin could not exhibit sufficient performance in actual use because it could not cope with the change in urine composition, the present invention focused on the difference in urine salt concentration.

  That is, in the case of adult urine, the ionic strength is almost equivalent to a 0.8 to 1.0 mass% sodium chloride aqueous solution, whereas in the case of infants, the ionic strength is 0.3 to 0.7 mass%. In particular, in the case of neonatal urine, the ionic strength is almost equivalent to 0.2 to 0.4 mass% sodium chloride aqueous solution, and conventional saline (0.9 In the evaluation of the properties of the water-absorbent resin using a mass% sodium chloride aqueous solution), the evaluation results of the water-absorbent resin with physiological saline do not necessarily correspond to actual use because the actual salt concentration of urine was not supported. I found that there was a problem.

  In addition, as the urine urinated from one point diffuses in the diaper, the salt concentration gradually changes (decreases) due to ion exchange with the water-absorbent resin. It has been found that the salt concentration change varies in each part of the diaper, so that it does not give sufficient physical properties in actual use.

  Therefore, in the present invention, a particulate water-absorbing agent mainly composed of a water-absorbing resin that is a crosslinked polymer of a water-soluble unsaturated monomer, having a particle diameter of less than 850 μm and 106 μm or more. The resin is contained in an amount of 90% by mass to 100% by mass with respect to the total mass of the water-absorbing resin contained in the particulate water-absorbing agent, and a constant salt concentration aqueous solution defined by (Equation 1) described later is provided. Since the particulate water-absorbing agent having a first salt concentration absorption index of 0.60 or more, which is a salt concentration absorption index in the case of ion-exchanged water, can absorb a certain amount regardless of changes in salt concentration, it is more than conventional. It was found to be an excellent particulate water-absorbing agent.

  Moreover, the particulate water-absorbing agent of the present invention has an excellent gel fluid permeability index regardless of changes in salt concentration or pressure. Therefore, when the water-absorbing agent of the present invention is used for the absorber, the liquid can be sufficiently distributed throughout the absorber and the amount of liquid absorption can be increased. Therefore, it has been found that the effect of preventing leakage of the liquid is remarkably improved.

  Hereinafter, the particulate water-absorbing agent of the present invention will be described in detail.

[Water-absorbing resin which is a cross-linked polymer of water-soluble unsaturated monomer]
The water-absorbing agent in the present invention includes a water-absorbing resin as a main component, and may optionally contain components other than the water-absorbing resin such as some additives and water, and is usually 50 to 100% by mass in the water-absorbing agent. Preferably it is 70-100 mass%, More preferably, it is 85-100 mass%, Most preferably, 95-100 mass% consists of the resin pure part of a water absorbing resin, The shape is the below-mentioned particle form. The water-absorbing agent is more than a specific physical property having a specific physical property parameter.

  In the present invention, the water-absorbing resin is a water-swellable and substantially water-insoluble crosslinked polymer, which is a conventionally known water-swellable crosslinked polymer that forms an anionic, nonionic or cationic substantially water-insoluble hydrogel. It is. The surface of these water-absorbing resins may be further cross-linked or treated in addition to the internal cross-linking of the polymer, and they are collectively referred to as a water-absorbing resin in the present invention. Furthermore, it may be called a crosslinked water absorbent resin.

  In the present invention, the water swellability means that it is essential to absorb 5 g / g or more of water in ion-exchanged water, and preferably absorbs a large amount of water of 50 to 1000 g / g. In the present invention, substantially water-insoluble means that the water-soluble component (water-soluble polymer) in the water-absorbent resin is 0 to 50 mass (weight)%, preferably 0 to 20 mass%, more preferably 0.01 to It is 15 mass%, More preferably, it is 0.1-10 mass%, Among these, Especially preferably, it is 0.1-5 mass%, Most preferably, it points out that it is 0.1-3 mass%. (In addition, the measuring method of the said absorption factor and a water-soluble component is prescribed | regulated by the below-mentioned Example).

  The water-absorbing resin is one or a mixture of two or more of them, and in particular, an acid group-containing water-absorbing resin, and further, one kind of a carboxyl group-containing water-absorbing resin that is a carboxylic acid or a salt thereof, or a mixture thereof. Preferably there is. More specifically, a cross-linked polymer obtained by polymerizing a water-soluble unsaturated monomer having acrylic acid and / or a salt thereof (neutralized product) as a main component, that is, a polymer containing a graft component as necessary. It is preferable that the acrylate cross-linked polymer is a main component.

  The above water-absorbent resin is preferably in the range of 0 to 50 mol% of acrylic acid and 100 to 50 mol% of acrylate (however, the total amount of both is 100 mol% or less). More preferred are those in the range of 10 to 40 mol% acrylic acid and 90 to 60 mol% acrylate (however, the total amount of both is 100 mol% or less). The molar ratio of acrylate to the total amount of acrylic acid and acrylate is called the neutralization rate.

  In order to form an acrylate as a structural unit of the water absorbent resin, neutralization of acrylic acid contained in the water absorbent resin is performed. It may be carried out in the form of a polymer, or may be carried out in the state of a polymer during or after polymerization, or these may be used in combination. Examples of the salt contained as a structural unit in the water absorbent resin include alkali metal salts such as sodium salt, potassium salt, lithium salt, ammonium salt, and amine salt of (poly) acrylic acid.

  Moreover, it is preferable that the acrylic acid used as a water-soluble unsaturated monomer by this invention contains p-methoxyphenol (other name, hydroquinone monomethyl ether) from the point of superposition | polymerization acceleration | stimulation and low coloring. It is preferable that content of this p-methoxyphenol is 200 mass ppm or less with respect to acrylic acid, More preferably, it is 10-160 mass ppm, More preferably, it is 20-140 mass ppm, More preferably Preferably it is 30-120 mass ppm, Among these, Most preferably, it is 40-100 mass ppm, and it is most preferable that it is 50-90 mass ppm. Further, the content of protoanemonin and / or furfural in acrylic acid is preferably 0 to 20 ppm by mass, more preferably 0 to 10 ppm by mass with respect to acrylic acid, It is particularly preferably 0 to 5 ppm by mass, and most preferably 0 to 1 ppm by mass.

  The water-soluble unsaturated monomer for obtaining the water-absorbent resin in the present invention may be substantially only acrylic acid (salt), or may be other water-soluble unsaturated monomer other than the acrylic acid (salt). Further, the other water-soluble unsaturated monomer and acrylic acid (salt) may be used in combination. The water-soluble unsaturated monomer other than acrylic acid (salt) is not particularly limited, and specific examples include methacrylic acid, maleic acid, vinyl sulfonic acid, styrene sulfonic acid, 2 Anionic unsaturated monomers such as (meth) acrylamide-2-methylpropanesulfonic acid, 2- (meth) acryloylethanesulfonic acid, 2- (meth) acryloylpropanesulfonic acid and salts thereof; acrylamide, methacrylamide, N-ethyl (meth) acrylamide, Nn-propyl (meth) acrylamide, N-isopropyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl ( (Meth) acrylate, methoxypolyethylene glycol (meth) a Nonionic hydrophilic group-containing unsaturated monomers such as relate, polyethylene glycol mono (meth) acrylate, vinylpyridine, N-vinylpyrrolidone, N-acryloylpiperidine, N-acryloylpyrrolidine, N-vinylacetamide; N, N- Dimethylaminoethyl (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylamide, and quaternary salts thereof And cationic unsaturated monomers. These unsaturated monomers may be used alone or in combination of two or more.

  In the present invention, in order to obtain good physical properties of the water-absorbent resin, acrylic acid and a salt thereof are used as a main component, and, if necessary, usually 0 to 30 mol%, preferably 0 to 20 mol%, More preferably, it is 0-10 mol%, and the other water-soluble unsaturated monomer may be used in combination.

  In the polymerization of each monomer described above to obtain the water-absorbent resin in the present invention, bulk polymerization and precipitation polymerization can be performed, but the performance of the water-absorbent resin and the ease of control of the polymerization, Furthermore, from the viewpoint of the absorption characteristics of the swollen gel, it is preferable to perform aqueous solution polymerization or reverse phase suspension polymerization by using the monomer as an aqueous solution. The concentration of the monomer in the aqueous solution (hereinafter referred to as the monomer aqueous solution) when each of the above monomers is an aqueous solution is determined by the temperature of the aqueous solution and the type of monomer and is particularly limited. Although not intended, it is preferably in the range of 10 to 70% by mass, more preferably in the range of 20 to 60% by mass. Moreover, when superposing | polymerizing using the said aqueous solution, you may use together solvents other than water as needed, and the kind of solvent used together is not specifically limited.

  As the method for the above aqueous solution polymerization, the water-containing gel-like cross-linked polymer from which the monomer aqueous solution can be obtained is polymerized while being crushed in a double-arm kneader, or the monomer aqueous solution is placed in a predetermined container or on a driving belt. Examples thereof include a method of pulverizing a gel obtained by supplying and polymerizing with a meat chopper or the like.

  When starting the above polymerization, for example, potassium persulfate, ammonium persulfate, sodium persulfate, t-butyl hydroperoxide, hydrogen peroxide, 2,2′-azobis (2-amidinopropane) dihydrochloride, etc. Photopolymerization initiators such as 2-hydroxy-2-methyl-1-phenyl-propan-1-one can be used. Furthermore, it is good also as a redox initiator which used the reducing agent which accelerates | stimulates decomposition | disassembly of these polymerization initiators together, and combined both. Examples of the reducing agent include (bi) sulfurous acid (salt) such as sodium sulfite and sodium bisulfite, L-ascorbic acid (salt), reducing metal (salt) such as ferrous salt, amines, and the like. Although it is mentioned, it is not particularly limited. The amount of these polymerization initiators used is usually from 0.001 to 2 mol% (based on monomers), preferably from 0.01 to 0.1 mol%, from the standpoint of physical properties such as residual monomer and water absorption characteristics.

  Further, the polymerization reaction may be initiated by irradiating the reaction system with active energy rays such as radiation, electron beam, and ultraviolet rays, and the above polymerization initiator may be used in combination. In addition, although the reaction temperature in the said polymerization reaction is not specifically limited, The inside of the range of 15-130 degreeC is preferable, and the inside of the range of 20-120 degreeC is more preferable. Further, the reaction time and the polymerization pressure are not particularly limited, and may be appropriately set according to the type of monomer or polymerization initiator, the reaction temperature, and the like.

  The water-absorbent resin in the present invention has a crosslinked structure inside (so-called internal crosslinking). The internal cross-linking is not particularly limited as long as the resulting water-absorbent resin is water-insoluble, and may be one formed without using a cross-linking agent (self-crosslinking type). It is more preferable that the polymer is formed by copolymerizing or reacting a crosslinking agent (internal crosslinking agent) having two or more polymerizable unsaturated groups or two or more reactive groups in the molecule.

  Specific examples of these internal crosslinking agents include, for example, N, N′-methylenebis (meth) acrylamide, (poly) ethylene glycol di (meth) acrylate, (poly) propylene glycol di (meth) acrylate, trimethylolpropane tri ( (Meth) acrylate, glycerin tri (meth) acrylate, glycerin acrylate methacrylate, ethylene oxide modified trimethylolpropane tri (meth) acrylate, pentaerythritol hexa (meth) acrylate, triallyl cyanurate, triallyl isocyanurate, triallyl phosphate, tri Allylamine, poly (meth) allyloxyalkane, (poly) ethylene glycol diglycidyl ether, glycerol diglycidyl ether, ethylene glycol, polyethylene Glycol, propylene glycol, glycerol, pentaerythritol, ethylenediamine, ethylene carbonate, propylene carbonate, polyethylenimine, and glycidyl (meth) acrylate.

  These internal cross-linking agents may be used alone or in combination of two or more. Moreover, these internal crosslinking agents may be added to the reaction system all at once, or may be added separately. When using one or two or more types of internal cross-linking agents, a compound having two or more polymerizable unsaturated groups must be used during the polymerization in consideration of the absorption characteristics of the finally obtained water-absorbing agent. It is preferable.

  The amount of these internal cross-linking agents used is preferably 0.001 to 2 with respect to the water-soluble unsaturated monomer (excluding the internal cross-linking agent) from the viewpoint of obtaining good physical properties of the water-absorbing resin or water-absorbing agent. Mol%, more preferably 0.005 to 1 mol%, still more preferably 0.005 to 0.7 mol%, still more preferably 0.01 to 0.5 mol%. Among these, it is particularly preferably 0.01 to 0.2 mol%, and most preferably within the range of 0.03 to 0.15 mol%.

  When the crosslinked structure is introduced into the water-absorbent resin using the internal crosslinking agent, the internal crosslinking agent may be added before or during the polymerization of the water-soluble unsaturated monomer, after the polymerization, or after the neutralization. It may be added to the reaction system.

  In the above polymerization, the reaction system includes starch / cellulose, starch / cellulose derivatives, polyvinyl alcohol, polyacrylic acid (salt), polyacrylic acid (salt) cross-linked hydrophilic polymer 0 to 50% by mass. (Mass of water-soluble unsaturated monomer) and other 0-10% by mass (mass of water-soluble unsaturated monomer), carbonic acid (hydrogen) salt, carbon dioxide, azo compound, inert organic solvent Various foaming agents such as: various surfactants; chelating agents; chain transfer agents such as hypophosphorous acid (salt) may be added.

  The hydrogel crosslinked polymer obtained in the polymerization step is dried simultaneously with or separately from the polymerization, and the drying is usually 60 to 250 ° C, preferably 100 to 220 ° C, more preferably 120 to 200 ° C. Performed in the temperature range. The drying time depends on the surface area of the polymer, the moisture content, the type of dryer, etc., and is usually selected in the range of 1 minute to 3 hours, preferably 10 minutes to 2 hours, so that the desired moisture content is obtained. The Moisture content of the water-absorbent resin in the present invention (specified by the amount of water contained in the water-absorbent resin / Measured weight loss when 1 g of the water-absorbent resin was dried at 180 ° C. for 3 hours, What is represented by the ratio to the mass of the resin) is not particularly limited, but is a powder showing fluidity even at room temperature from the physical properties of the resulting water-absorbent resin product, more preferably a water content of 0.2 to 30% by mass, More preferably, it is 0.3-15 mass%, Most preferably, it is a 0.5-10 mass% powder state. (In the present invention, a small amount of water such as 30% by mass or less is also collectively referred to as a water-absorbing resin).

  The production method according to the present invention includes a pulverizing step in which the hydrogel crosslinked polymer obtained in the polymerization step is dried in the drying step and then pulverized by a pulverizer to form a particulate water-absorbing resin. The particle shape of the water-absorbent resin thus obtained is not particularly limited to a spherical shape, a crushed shape, an indeterminate shape or the like, but an indeterminate crushed shape obtained through a pulverization step can be preferably used.

  The particulate water-absorbing agent or water-absorbing resin in the present invention preferably has a smaller proportion of fine powder (preferably less than 106 μm, more preferably less than 150 μm), specifically less than 10% by mass, preferably less than 5% by mass. More preferably, it is less than 3 mass%, More preferably, it is less than 2 mass%, Especially less than 1 mass%. The water-absorbent resin in the present invention preferably has a smaller proportion of coarse particles (preferably 850 μm sieve or more, more preferably 500 μm sieve or more). Therefore, the water-absorbent resin of the present invention is a particulate water-absorbent resin having a particle size of 850 to 106 μm (preferably 850 to 150 μm) of 90 to 100% by mass, preferably 97 to 100% by mass, and more preferably 98 to 100% by mass. Especially preferably, it is made into the range of 99-100 mass%.

  The particulate water-absorbing resin thus obtained is usually further surface-modified to obtain the particulate water-absorbing agent of the present invention. Surface modification in the present invention means that the surface of the particle or the vicinity thereof (surface layer of 0.001 μm to several tens of μm) is further crosslinked or coated with an inert additive such as inorganic powder.

  Considering the physical properties of the water-absorbent resin, the amount of the surface modifier (inactive additive such as surface cross-linking agent and water-insoluble fine particles) used is 0.001 to 10 parts by mass with respect to 100 parts by mass of the water-absorbent resin. The range is preferably 0.01 to 8 parts by mass, more preferably 0.05 to 5 parts by mass, and most preferably 0.1 to 2 parts by mass.

  Surface cross-linking is an operation for improving various physical properties of the water-absorbent resin by increasing the cross-link density in the vicinity of the surface of the water-absorbent resin from inside the particles. A second cross-linking agent different from the cross-linking agent) is added to the water absorbent resin to cross-link only the surface.

  As such a surface crosslinking agent, a dehydration-reactive crosslinking agent is used. Specifically, for example, when the water-absorbent resin contains a carboxyl group, a hydroxyl group-containing crosslinking agent such as a polyhydric alcohol; An amino group-containing crosslinking agent such as a polyvalent amine; a cyclic crosslinking agent such as an alkylene carbonate, a monooxazolidinone compound, a dioxazolidinone compound or a polyoxazolidinone compound, or an oxetane compound such as 3-methyl-3-oxetanemethanol, Examples thereof include a cyclic cross-linking agent that generates a hydroxyl group or an amino group in association with the ring-opening reaction of the cyclic cross-linking agent, and the hydroxyl group or amino group undergoes a cross-linking reaction.

  More specifically, the dehydration-reactive cross-linking agent is described, for example, propylene glycol, 1,3-propanediol, 2-methyl-1,3-propanediol, glycerin, 1,4-butanediol, 1,5- Polyhydric alcohol compounds such as pentanediol; alkylene carbonate compounds of 1,3-dioxolan-2-one and 4-methyl-1,3-dioxolan-2-one; oxetane compounds such as 3-methyl-3-oxetanemethanol and many others Oxetane compounds and the like. Among these, in order to maximize the effects of the present invention, one or more dehydration reactive crosslinking agents selected from polyhydric alcohols, alkylene carbonates, oxazolidinone compounds, and (polyhydric) oxetane compounds are preferable, and polyhydric alcohols are essential. It is particularly preferable to use for the above.

  As the surface cross-linking agent, in addition to the above dehydration-reactive cross-linking agent, epoxy compounds such as ethylene glycol diglycidyl ether and γ-glycidoxypropyltrimethoxysilane; polyvalent isocyanate compounds such as 2,4-tolylene diisocyanate Polyvalent oxazoline compounds such as 1,2-ethylenebisoxazoline; silane coupling agents such as γ-aminopropyltrimethoxysilane; 2,2-bishydroxymethylbutanol-tris [3- (1-aziridinyl) propionate], etc. And non-dehydrating reactive crosslinking agents for polyvalent metals such as beryllium, magnesium, calcium, strontium, zinc, aluminum, iron, chromium, manganese, titanium, and zirconium.

  When mixing the surface cross-linking agent with the water-absorbent resin, the surface-crosslinking agent may be mixed using water and / or a solvent such as a hydrophilic organic solvent.

  The amount of water used as a solvent is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 8 parts by mass, and further preferably 1 to 5 parts per 100 parts by mass of the water-absorbent resin. It is the range of mass parts.

  Examples of the hydrophilic organic solvent include alcohols such as ethyl alcohol, propyl alcohol, and isopropyl alcohol; ketones such as acetone; ethers such as dioxane, alkoxy (poly) ethylene glycol, and tetrahydrofuran; amides of ε-caprolactam; Sulfoxides such as dimethyl sulfoxide; and the like. The amount of the hydrophilic organic solvent used is preferably in the range of 0 to 10 parts by mass, more preferably in the range of 0 to 5 parts by mass, and still more preferably 0 to 3 parts by mass with respect to 100 parts by mass of the water absorbent resin. It is a range.

  The method for mixing the surface cross-linking agent is not particularly limited. Therefore, the above-mentioned surface cross-linking agent and a solvent such as water or a hydrophilic organic solvent may be mixed separately with respect to the water-absorbent resin, may be mixed together, or mixed in several times. However, it is more preferable to mix the surface cross-linking agent and the solvent in advance and then add the mixture to the water-absorbent resin to form an aqueous solution.

  In mixing the surface cross-linking agent, an inorganic powder, a water-insoluble fine particle powder, a surfactant, and a hydrophilic or hydrophobic polymer compound may coexist within a range that does not interfere with the effect of the particulate water-absorbing agent of the present invention. .

  Among the above-mentioned various mixing methods, a method in which a surface cross-linking agent and, if necessary, water and / or a hydrophilic organic solvent are dropped and mixed in a water-absorbent resin is preferable, and a spraying method is more preferable. The size of the droplets to be sprayed is preferably 0.01 to 300 μm, more preferably 0.1 to 200 μm. The temperature of the solution sprayed at this time is preferably 0 ° C. to boiling point, more preferably 5 to 50 ° C., and further preferably 10 to 30 ° C. from the viewpoints of mixing property and stability. The temperature of the water absorbent resin powder before mixing is preferably 0 to 80 ° C., more preferably 40 to 70 ° C., from the viewpoint of mixing properties.

  A suitable mixing device used for the mixing may be a device capable of generating a large mixing force to ensure uniform mixing. Examples of such a mixing apparatus include a cylindrical mixer, a double wall conical mixer, a high-speed stirring mixer, a V-shaped mixer, a ribbon mixer, a screw mixer, and a fluidized furnace rotary disk. Examples thereof include a type mixer, an airflow type mixer, a double arm type kneader, an internal mixer, a pulverizing type kneader, a rotary mixer, and a screw type extruder.

  In this mixing step, when heat treatment is performed, the treatment time is preferably 1 to 180 minutes, more preferably 3 to 120 minutes, and particularly preferably 5 to 100 minutes. The heat treatment temperature (specified by heat medium temperature or material temperature) is preferably in the range of 100 to 250 ° C, more preferably in the range of 140 to 220 ° C, further preferably in the range of 150 to 230 ° C, and in the range of 160 to 220 ° C. Is particularly preferred.

  The heat treatment can be performed using a normal dryer or a heating furnace, and examples include a grooved mixed dryer, a rotary dryer, a disk dryer, a fluidized bed dryer, an airflow dryer, and an infrared dryer. The

  In the surface modification performed by the method for producing a water-absorbent resin of the present invention, inactive surface activity in the sense that it does not substantially react with the water-absorbent resin in addition to surface crosslinking or without causing surface crosslinking. An additive such as an agent, an inert deodorant, or an inert inorganic fine particle powder may be added. As the surfactant and inert inorganic fine particle powder used at this time, preferably, inorganic or organic fine particles described later, fatty acids (for example, long chain fatty acids or salts), and the like are used. Are preferably performed simultaneously or separately.

  In the present invention, the cationic polymer compound as an additive used for surface modification of the water-absorbent resin can improve the fixability to hygiene materials, and preferably has a mass average molecular weight of 2,000 to 1,000,000. 000, more preferably 5,000 to 500,000, and most preferably 10,000 to 500,000. The organic compound as an additive used for surface modification of the water absorbent resin is a fatty acid or a salt thereof, preferably a long chain fatty acid or a salt thereof.

  The mixture of the cationic polymer compound is added alone or in solution (aqueous solution). Preferably, specific examples of the cationic polymer compound include polyethyleneimine, polyvinylamine, polyallylamine, polyamidoamine and epichlorohydrin condensate. , Polyamidine, a partial hydrolyzate of poly (N-vinylformaldehyde) or a salt thereof.

  When water-insoluble fine particles are used as the additive, it is possible to improve the liquid permeability of the water-absorbent resin, the blocking resistance at the time of moisture absorption, and the like. The water-insoluble fine particles are, on average, preferably 0.0001 to 10 μm, more preferably 0.001 to 1 μm, and particularly 0.001 to 0.1 μm (particle diameter is measured by, for example, Coulter counter method) Inorganic or organic water-insoluble fine particles are used. Specifically, silicon oxide (trade name, Aerosil, manufactured by Nippon Aerosil Co., Ltd.), titanium oxide, aluminum oxide, or the like is used. Mixing may be performed by powder mixing (Dry-Blend) or slurry mixing.

  The amount of these additives used is preferably 10 parts by mass or less, more preferably 0.001 to 5 parts by mass, and still more preferably 0.01 to 2 parts by mass with respect to 100 parts by mass of the water absorbent resin. Part.

[Method for producing particulate water-absorbing agent]
Preferred examples of the method for producing the particulate water-absorbing agent in the present invention include the following 1-3.

(Production method 1)
A polyacrylic acid (salt) -based crosslinked polymer (water-absorbing resin) polymerized using a water-soluble unsaturated monomer that has been polymerized as described above, preferably with reduced protoanemonene in the presence of methoxyphenol. In addition to controlling to the specific particle diameter described above, the unloaded absorption capacity (60-minute value) with respect to the 0.90 mass% sodium chloride aqueous solution is controlled to be 15 to 27 g / g. Thereafter, the water absorption capacity of the resulting water-absorbing agent is usually 10 to 27 g / g, preferably 12 to 27 g / g, more preferably at an absorption capacity under load with respect to a 0.90% by mass sodium chloride aqueous solution (60-minute value). The surface of the water-absorbing resin is modified, preferably surface-crosslinked, so that the water-absorbent resin is in the range of 15 to 27 g / g, more preferably 17 to 25 g / g, and particularly preferably 18 to 22 g / g. A particulate water-absorbing agent is produced.

(Manufacturing method 2)
A polyacrylic acid (salt) -based crosslinked polymer (water-absorbent resin) polymerized using water-soluble unsaturation in which protoanemonene is reduced in the presence of methoxyphenol, preferably in the presence of methoxyphenol, as described above. In addition, the absorption capacity under load with respect to a 0.90% by mass sodium chloride aqueous solution (60 minute value) is usually 10 to 27 g / g, preferably 12 to 27 g / g, more preferably 15 to 27 g. / G, more preferably 17 to 25 g / g, particularly preferably 18 to 22 g / g. Thereafter, the particulate water-absorbing agent of the present invention is produced by coating the surface of the water-absorbing resin, the particle system and the absorption capacity under no load (60-minute value), with the inorganic fine powder within the aforementioned range.

(Manufacturing method 3)
A polyacrylic acid (salt) -based crosslinked polymer (water-absorbent resin) polymerized using water-soluble unsaturation in which protoanemonene is reduced in the presence of methoxyphenol, preferably in the presence of methoxyphenol, as described above. In addition, the absorption capacity under no load (60 minutes value) with respect to the 0.90 mass% sodium chloride aqueous solution is controlled to 17 to 25 g / g, preferably 18 to 22 g / g. Then, the particulate water-absorbing agent of the present invention is produced by coating the surface of the water-absorbent resin, the particle system and the absorption capacity under no load (60-minute value), with a fatty acid or a salt thereof.

  Furthermore, the water absorption capacity of the particulate water-absorbing agent obtained by surface-coating the water-absorbing resin obtained by the above-described production methods 2 and 3 is the absorption capacity (60 minutes value) under no load with respect to a 0.90% by mass sodium chloride aqueous solution. In general, 10 to 27 g / g, preferably 12 to 27 g / g, more preferably 15 to 27 g / g, still more preferably 17 to 25 g / g, and particularly preferably 18 to 22 g / g. It is preferably crosslinked.

  Here, the absorption capacity without load (60 minutes value) with respect to the 0.90% by mass sodium chloride aqueous solution is a large excess of 0. 0 which is not absorbed by the particulate water-absorbing agent under no pressure. The absorption capacity when a particulate water-absorbing agent (water-absorbing resin) is immersed in a 90% by mass sodium chloride aqueous solution for 60 minutes.

  In addition, it is natural that the absorption rate of the water-absorbing agent (water-absorbing resin) is high, and it is usually 30 g / g or more in a commercial product, preferably 35 g / g or more, and more preferably 40 g / g or more. However, in the present invention, it is seen that the novel particulate water-absorbing agent of the present invention can be provided by controlling the absorption capacity under no load to a narrow range lower than the conventional water-absorbent resin. It was issued.

  Further, as in the conventional case, the absorption capacity (60 minutes value) of the water-absorbing agent after the surface treatment with respect to the 0.90 mass% sodium chloride aqueous solution is 15 to 27 g / g, preferably 17 to 25 g / g. It is preferable to be controlled as described above. Here, the absorption capacity under load (60-minute value) with respect to a 0.90 mass% sodium chloride aqueous solution is a particulate water-absorbing agent (water-absorbent) into a 0.90 mass% sodium chloride aqueous solution under a pressure of 4.83 kPa. Resin) refers to the absorption capacity when immersed (contacted) for 60 minutes.

  Since the control of the water absorption ratio of the particulate water-absorbing agent is achieved by appropriately controlling the amount of the surface treatment agent, reaction conditions, etc., preferably 0.9 mass under no pressure of the water-absorbing resin before the surface treatment. Polymerization is carried out by adjusting the crosslink density so that the water absorption capacity under no load with respect to an aqueous solution of sodium chloride is 40 to 15 g / g, further 35 to 16 g / g, and 30 to 17 g / g, and before surface treatment. The particle diameter of the water-absorbent resin may be controlled within the above range.

[Particulate water-absorbing agent of the present invention]
The particulate water-absorbing agent of the present invention obtained as described above is affected by the salt concentration of the liquid to be absorbed at a water absorption capacity under pressure (Absorbency against pressure / abbreviated as AAP) of 4.83 kPa. It is an excellent water-absorbing agent that is hardly affected. That is, in practical use, it exhibits a constant water absorption performance regardless of the urine salt concentration. Therefore, it always has high physical properties such as a constant water absorption regardless of the salt concentration fluctuation during use or the change in the salt concentration in the diaper. I have.

The particulate water-absorbing agent of the present invention is a particulate water-absorbing agent mainly composed of a water-absorbing resin that is a crosslinked polymer of a water-soluble unsaturated monomer, and is less than 850 μm and 106 μm or more (preferably 150 μm or more). The particulate water-absorbing resin having a particle diameter is 90 to 100% by mass with respect to the total mass of the water-absorbing resin contained in the particulate water-absorbing agent, more ^preferably less than 850 μm and 150 μm or more in particulate form. The water-absorbing resin (hereinafter sometimes referred to as particles) is 95% by mass or more, further 98% by mass or more of the entire water-absorbing resin. The mass average particle diameter of the particulate water-absorbing resin is preferably 200 to 700 μm, more preferably 300 to 600 μm, and particularly preferably 350 to 550 μm, and most preferably 400 to 500 μm. .

  When the particle size of less than 150 μm exceeds 10% by mass, the diffusibility of body fluids such as blood and urine to the absorber is inhibited during water absorption, and the contact area with air increases when used as an absorber. It is not preferable because the particulate water-absorbing agent is easily solubilized. When the particle size exceeding 850 μm exceeds 10% by mass, the water absorption rate of the water absorbing agent becomes slow, which is not preferable.

  Furthermore, in addition to the above specific particle diameter, the particulate water-absorbing agent of the present invention exhibits a constant absorption capacity under pressure regardless of the salt concentration. The absorption capacity under pressure is evaluated as an absorption capacity after a predetermined time when a load of 4.83 kPa is applied with an absorption solution having various salt concentrations (0 to 0.90 mass% sodium chloride aqueous solution). In the particulate water-absorbing agent of the present invention, it has been found that this specific absorption capacity under pressure corresponds most to changes in the concentration of body fluids such as urine in actual use.

That is, the water-absorbing agent of the present invention, in addition to the specific particle size described above, further essentially includes the following (formula 1)
(Salt concentration absorption index) = (absorption capacity under pressure at 4.83 kPa for a constant salt concentration aqueous solution) / (absorption capacity under no load for a constant salt concentration aqueous solution) (Equation 1)
(In the formula, the absorption capacity under pressure is the absorption capacity when immersed (contacted) in a constant salt concentration aqueous solution for 60 minutes under a pressure of 4.83 kPa, and the absorption capacity under no load is under no pressure. Is a salt concentration absorption index when the constant salt concentration aqueous solution is ion-exchanged water. A water-absorbing agent having a certain first salt concentration absorption index of 0.60 or more.

  The first salt concentration absorption index is preferably 0.70 or more, more preferably 0.80 or more, more preferably 0.90 or more, and particularly preferably 0.95 or more. When the first salt concentration absorption index is less than 0.60, the water-absorbing resin (added by the water-absorbing salt concentration) is accompanied by changes in the salt concentration of urine and changes (decrease) in salt concentration accompanying urine diffusion in diapers. The change in rolling reduction ratio (freight) is large and it is not preferable because sufficient performance in actual use cannot be exhibited.Since the upper limit of the first salt concentration absorption index is too high, the same phenomenon can be seen, so the upper limit is Usually, it is preferably 1.20 or less, more preferably 1.10 or less (note that the above index 0.60 is synonymous with 0.600, and hereinafter, the salt concentration absorption index or the salt tolerance index has two decimal places. The digits smaller than the eyes are omitted).

  Furthermore, preferably, the particulate water-absorbing agent of the present invention further exhibits the following physical properties in addition to the specific particle diameter and the first salt concentration absorption index, thereby further changing the salt concentration of urine and in diapers. Stable urine absorption is exhibited even when the salt concentration changes (decreases) due to urine diffusion.

  That is, the particulate water-absorbing agent of the present invention is preferably a second salt concentration absorption index (salt concentration absorption index when the constant salt concentration aqueous solution is a 0.1% by mass sodium chloride aqueous solution in the above (formula 1)). Is 0.80 or more. The secondary salt concentration absorption index is more preferably 0.90 or more, particularly preferably 0.95 or more, and the upper limit is usually 1.20 or less, and further 1.10 or less.

  In addition to the specific particle size and the first salt concentration absorption index, the particulate water-absorbing agent of the present invention is more preferably a third salt concentration absorption index (the above (Formula 1) above). Salt concentration absorption index when is a 0.3% by mass sodium chloride aqueous solution), the fourth salt concentration absorption index (in the above (Formula 1), the salt when the constant salt concentration aqueous solution is a 0.5% by mass sodium chloride aqueous solution) Concentration absorption index), fifth salt concentration absorption index (salt concentration absorption index when the constant salt concentration aqueous solution is 0.7 mass% sodium chloride aqueous solution in the above (formula 1)), sixth salt concentration absorption index (above ( In Formula 1), at least one of the salt concentration absorption index when the constant salt concentration aqueous solution is a 0.9 mass% sodium chloride aqueous solution is a water absorbing agent of 0.90 or more. In these third to sixth salt concentration absorption indexes, the value is particularly preferably 0.95 or more, and the upper limit is usually 1.20 or less, and further 1.10 or less.

  The particulate water-absorbing agent of the present invention is more preferably an average value from the first salt concentration absorption index to the sixth salt concentration absorption index in addition to the specific particle diameter and the first salt concentration absorption index. The average salt concentration absorption index index is 0.90 or more, the value is particularly preferably 0.95 or more, and the upper limit is usually 1.20 or less, and further 1.10 or less. Further, the standard deviation of the average salt concentration absorption index is preferably in the range of 0 to 0.100, more preferably in the range of 0 to 0.50.

In addition to the specific particle size and the first salt concentration absorption index, the particulate water-absorbing agent of the present invention is more preferably the following (formula 2).
(Salt tolerance index) = (absorption capacity under no load with respect to a constant salt concentration aqueous solution) / (absorption capacity under no load with respect to ion-exchanged water) (Equation 2)
(In the formula, the absorption capacity under no load is the absorption capacity when immersed in a large excess of constant salt concentration aqueous solution or ion-exchanged water for 60 minutes), and the constant salt concentration is 0.10 mass% sodium chloride aqueous solution. The first salt tolerance index, which is the salt tolerance index in the case of, is 0.40 or more. The lower limit of the first salt tolerance index is preferably 0.50 or more, and the upper limit thereof is usually 1.20 or less, and more preferably 1.10 or less.

  The absorption capacity under load of the particulate water-absorbing agent of the present invention is adjusted to the above-mentioned range (15 to 27 g / g). Moreover, the unloading absorption capacity | capacitance (60 minute value) with respect to 0.90 mass% sodium chloride aqueous solution is 10-27 g / g normally, Preferably it is 12-27 g / g, More preferably, it is 15-27 g / g, More preferably It is 17 to 25 g / g, particularly preferably 18 to 22 g / g.

Further, the particulate water-absorbing agent of the present invention has a gel permeability index (Gel Permeability Index / abbreviation GPI, unit: 10 ⁻⁷ × cm ³ × s × g ⁻¹ , hereinafter omitted units) of 10 or more. Is preferred. As a result of earnestly examining the problem of the conventional water-absorbing agent, the present inventor has found that the gel water permeability index (GPI) in the conventional water-absorbing agent is related to salt concentration (living movement and ion exchange in the living environment and the absorbent body). It has been found that it greatly decreases with the increase in salt concentration) and pressure (change in load due to body weight and posture), and has a great influence on the fluid permeability to absorption liquid such as urine after swelling. However, in the particulate water-absorbing agent of the present invention, the liquid permeability between the gels is stably good regardless of changes in salt concentration or pressure (presence / absence). When used, it is possible to sufficiently spread the liquid to the absorber (improvement of the liquid diffusion area), further increase the liquid absorption amount of the absorber, and prevent leakage of the liquid. GPI is more preferably 15 or more, and still more preferably 20 or more. GPI will be described later in the embodiment.

  The particulate water-absorbing agent of the present invention has a GPI of 2.07 kPa and 10 or more, preferably 15 or more, more preferably 20 or more with respect to ion-exchanged water. Compared to the GPI value, it is much lower than the increase in pressure. Also, the GPI is 10 or more, preferably 20 or more, more preferably 50 or more, even more preferably 100 with respect to a sodium chloride aqueous solution of 0.3 to 0.9 mass% at 2.07 kPa. Above, particularly preferably 150 or more, a GPI value much higher than the conventional GPI value of 0 to several tens, and a decrease with respect to the increase in the salt concentration is small. Furthermore, GPI is 10 or more, preferably 15 or more, and more preferably 20 or more with respect to a 0.7% by mass sodium chloride aqueous solution at 4.83 kPa. The GPI value is remarkably high compared to the above, and the decrease with respect to the increase in the salt concentration is small. In particular, the GPI value for a 0.3-0.9 mass% sodium chloride aqueous solution at 2.07 kPa is stable with little change and shows a high value of 150 or more. As described above, the particulate water-absorbing agent of the present invention stably exhibits high GPI regardless of changes in pressure and salt concentration, and has excellent absorption performance even when actually used as an absorbent (high diffusion area and high absorption amount). ).

  Furthermore, the particulate water-absorbing agent of the present invention preferably has an absorption capacity (60-minute value) under pressure at 4.83 kPa against ion-exchanged water of 50 g / g or more, more preferably 60 g / g or more, and still more preferably 70 g / g. Excellent water absorption capacity of g or more. The upper limit of the absorption capacity under pressure is not particularly limited and is preferably a high value. However, the upper limit is preferably 200 g / g and 150 g / g from the balance with economics such as manufacturing costs. More preferably.

  That is, the present invention also provides the following novel particulate water-absorbing agent. A particulate water-absorbing agent mainly composed of a water-absorbing resin that is a crosslinked polymer of a water-soluble unsaturated monomer, wherein the particulate water-absorbing resin having a particle diameter of less than 850 μm and 106 μm or more is the above particulate Absorption capacity under pressure, which is an absorption capacity when immersed in ion-exchanged water for 60 minutes under a pressure of 4.83 kPa, with respect to the total weight of the water-absorbent resin contained in the water-absorbing agent. , 50 g / g or more of the particulate water-absorbing agent. Such a particulate water-absorbing agent has an unprecedented high water-absorbing ability with respect to ion-exchanged water, and exhibits particularly excellent water-absorbing ability at a low salt concentration. Such a particulate water-absorbing agent preferably exhibits the above-described salt concentration absorption index, salt resistance index, average salt concentration absorption index and its standard deviation, and gel permeation index.

[Other additives]
In the present invention, in addition to the surface cross-linking as the surface treatment, other additives (hereinafter referred to as other additives) may be added as necessary. That is, the other additives include deodorants, antibacterial agents, fragrances, foaming agents, pigments, dyes, hydrophilic short fibers, plasticizers, adhesives, surfactants, fertilizers, oxidizing agents, reducing agents, water , Salts, chelating agents, bactericides, hydrophilic polymers such as polyethylene glycol and polyethyleneimine, hydrophobic polymers such as paraffin, thermoplastic resins such as polyethylene and polypropylene, thermosetting resins such as polyester resins and urea resins, etc. An addition step for imparting various functions to the water-absorbent resin, preferably an addition step to the surface, may be included.

  The usage-amount of these additives is 0-30 mass parts normally with respect to 100 mass parts of water absorbing resin, Preferably it is the range of 0-10 mass parts, More preferably, it is the range of 0-1 mass part.

[Use of particulate water-absorbing agent]
The particulate water-absorbing agent of the present invention stably absorbs regardless of the salt concentration. Therefore, it is widely used in agricultural and horticultural water retention agents, industrial water retention agents, hygroscopic agents, dehumidifying agents, building materials, etc., but particularly preferably, hygiene for absorption of feces, urine or blood, represented by paper diapers, sanitary napkins, etc. Material used.

  That is, since the particulate water-absorbing agent of the present invention is balanced and excellent in various physical properties, the hygienic material for absorption is a concentration of the particulate water-absorbing agent defined by the core concentration ratio (Equation 3 below) ( The weight ratio of the water-absorbent resin to the total of the water-absorbent resin and the fiber substrate is high, preferably 30 to 100% by mass, more preferably 40 to 100% by mass, and still more preferably 50 to 95% by mass. Is possible.

(Core concentration ratio) = (mass of particulate water-absorbing agent) / ((mass of particulate water-absorbing agent) + (mass of fiber material)) (Equation 3)
Further, the structure of the absorbent body in hygienic materials (referred to a composite molded of absorbent core / water absorbent) is not particularly limited. For example, a water absorbent is disposed between hydrophilic fiber materials molded into a sheet shape. There are so-called sandwich structure absorbers and so-called blend structure absorbers formed by mixing a hydrophilic fiber material and a water-absorbing agent.

  The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope shown in the claims. That is, embodiments obtained by combining technical means appropriately modified within the scope of the claims are also included in the technical scope of the present invention.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further in detail, this invention is not limited to these Examples etc., unless the summary is exceeded. Unless otherwise specified, “parts” means parts by mass (parts by weight).

  Unless otherwise specified, the measurement was performed at an air temperature and a liquid temperature of 25 ° C. ± 1 ° C., and the room atmosphere was measured at normal pressure and a relative humidity of less than 50%.

  Furthermore, when measuring the above-described parameters of the water-absorbing agent or water-absorbing resin described later, the measurement was usually performed using the water-absorbing agent or water-absorbing resin as it was. However, when the water-absorbing agent or the water-absorbing resin is excessively hygroscopic, that is, for example, the water-absorbing agent or the water-absorbing resin collected from an absorbent article such as a diaper is dried under reduced pressure at, for example, 60 ° C. The water content was adjusted to 7 ± 1% by mass or less, preferably 5 ± 1% by mass or less.

<Preparation of absorption solution>
In the present invention, in order to evaluate the absorption characteristics of the water-absorbent resin or water-absorbing agent (particulate water-absorbing agent), ion-exchanged water or sodium chloride aqueous solution having the following concentrations and different salt concentrations were used.

Absorbing solution S0: ion-exchanged water Absorbing solution S1: 0.10 mass (wt)% sodium chloride aqueous solution Absorbing solution S2: 0.20 mass (wt)% sodium chloride aqueous solution Absorbing solution S3: 0.30 mass (wt)% chloride Sodium aqueous solution Absorbing solution S4: 0.40 mass (wt)% sodium chloride aqueous solution Absorbing solution S5: 0.50 mass (wt)% sodium chloride aqueous solution Absorbing solution S6: 0.70 mass (wt)% sodium chloride aqueous solution Absorbing solution S7 : 0.90 mass (weight)% sodium chloride aqueous solution <absorption capacity (absorption capacity (GV, Gel Volume) for 60 minutes under no pressure)>
0.20 g of water-absorbing resin (or water-absorbing agent) was evenly placed in a non-woven bag (60 mm × 60 mm) and immersed in a large excess (100 g or more) of the S0 to S7 absorbing solution. And after 60 minutes, the bag was pulled up, drained at 250 G for 3 minutes using a centrifuge, and the weight W2 (g) of the bag was measured.

  In addition, when the swelling ratio of the water absorbent resin (or water absorbent) is high such that the weight W2 (g) of the bag exceeds 15 (g), the water absorbent resin (or water absorbent) put into the non-woven bag. The amount of the agent) was adjusted appropriately so that it was 0.20 g or less. That is, when the absorbent solutions S0 to S3 are used, the amount of the water-absorbing resin (or water absorbent) to be added to the bag is 0.01 to 0.05 g, and when the absorbent solutions S4 and S5 are used. When the amount of water-absorbing resin (or water-absorbing agent) introduced into the bag is 0.05 to 0.15 g and the absorbing solutions S6 and S7 are used, the water-absorbing resin (or water-absorbing agent) into the bag is used. Was adjusted so that the weight W2 (g) of the bag was 5 to 15 (g).

  Further, the same operation was performed without using a water absorbent resin (water absorbent), and the weight W1 (g) at that time was measured. And from these weights W1 and W2, the absorption capacity (g / g) was calculated according to the following (formula 4).

Absorption capacity (g / g) = (weight W2 (g) −weight W1 (g)) / weight of water-absorbing resin (or water-absorbing agent) (g) (Formula 4)
<Absorption capacity under pressure (AAP)>
A stainless steel 400 mesh standard sieve (aperture 38 μm) was fused to the bottom of a plastic support cylinder having an inner diameter of 60 mm, and 0.9000 g of a water absorbent resin or a water absorbent was uniformly sprayed on the sieve. Adjusted so that a load of 4.83 kPa (0.7 psi) can be uniformly applied to the water-absorbing resin or water-absorbing agent, the outer diameter is slightly smaller than 60 mm, and there is no gap in the support cylinder, In addition, a piston and a load that are not hindered from moving up and down were placed in this order on a water absorbent resin or a water absorbent, and the mass Wa (g) of this measurement set was measured. Place a glass filter with a diameter of 90 mm (manufactured by Mutual Riken Glass Co., Ltd., pore diameter: 100 to 120 μm) inside a petri dish with a diameter of 150 mm, and add the absorbing solution so as to be at the same level as the upper surface of the glass filter. It was.

  On top of that, a sheet of 90 mm diameter filter paper (ADVANTAEC Toyo Co., Ltd., product name: quantitative filter paper Qualitative Filter Papers (JIS P 3801, No. 2), thickness 0.26 mm, retained particle diameter 5 μm) is placed. All were wetted and excess liquid was removed.

  The set of measuring devices was placed on the wet filter paper, and the contacted liquid was absorbed under load. After 1 hour, the measuring device set was lifted and its mass Wb (g) was measured. Then, the absorption capacity under load (g / g) was calculated from Wa and Wb according to the following (formula 5).

Absorption capacity under pressure (g / g) = (Wb (g) -Wa (g)) / mass of water absorbent resin or water absorbent (0.9000) g) (Equation 5)
<Salt concentration absorption index>
The salt concentration absorption index of the present invention is based on the absorption capacity under load and the absorption capacity under no load of each absorption solution (S0, S1 to S7) obtained by the above-described method. Absorption capacity under pressure at a constant salt concentration aqueous solution at 4.83 kPa) / (absorption capacity under no load for a constant salt concentration aqueous solution) (Equation 1)
Calculated according to In the above (Formula 1), the absorption capacity under pressure is the absorption capacity when immersed (contacted) in a constant salt concentration aqueous solution for 60 minutes under a pressure of 4.83 kPa, and the absorption capacity under no load is The absorption ratio when immersed in a large excess of a constant salt concentration aqueous solution for 60 minutes under no pressure.

  Here, the first salt concentration absorption index is a salt concentration absorption index when the constant salt concentration aqueous solution is ion-exchanged water in the above (Equation 1). Hereinafter, similarly, when the constant salt concentration aqueous solution is a 0.10% by mass sodium chloride aqueous solution in (Formula 1), the third salt concentration absorption index is (Formula 1). When the constant salt concentration aqueous solution is 0.30% by mass sodium chloride aqueous solution, the fourth salt concentration absorption index is (Formula 1) when the constant salt concentration aqueous solution is 0.50% by mass sodium chloride aqueous solution. The fifth salt concentration absorption index is (Expression 1), and when the constant salt concentration aqueous solution is a 0.70 mass% sodium chloride aqueous solution, the sixth salt concentration absorption index is (constant salt) When the concentration aqueous solution is a 0.90% by mass sodium chloride aqueous solution, the salt concentration absorption index is as follows.

<Salt tolerance index>
Based on the measurement result of the absorption capacity under no load by the method described above, the following (Formula 2)
(Salt tolerance index) = (absorption capacity under no load with respect to a constant salt concentration aqueous solution) / (absorption capacity under no load with respect to ion-exchanged water) (Equation 2)
(In the formula, the absorption capacity under no load is the absorption capacity when immersed in a large excess of a constant salt concentration aqueous solution or ion-exchanged water for 60 minutes), and the salt tolerance index was determined. Here, the first salt tolerance index is a salt tolerance index when the constant salt concentration is a 0.10% by mass sodium chloride aqueous solution in the above (Equation 2).

<Weight (mass) average particle size>
The water-absorbing resin or water-absorbing agent was sieved with JIS standard sieves such as 850 μm, 710 μm, 600 μm, 500 μm, 425 μm, 300 μm, 212 μm, 150 μm, 106 μm, and 75 μm, and the residual percentage was plotted on logarithmic probability paper. Thereby, the weight average particle diameter (D50) was read.

  For screening, a water-absorbing resin powder or a water-absorbing agent 10.00 g is applied to a JIS standard sieve having a mesh size of 850 μm, 710 μm, 600 μm, 500 μm, 425 μm, 300 μm, 212 μm, 150 μm, 106 μm, 75 μm, etc. (The IIDA TESTING SIVE: inner diameter 80 mm ) And classified for 10 minutes using a low-tap type sieve shaker (ES-65 type sieve shaker manufactured by Iida Seisakusho Co., Ltd.). The weight average particle diameter (D50) is used when 50% by weight of the whole particles are classified when classified for 10 minutes by the above-mentioned sieve shaker as described in US Pat. No. 5,051,259. It is the particle size of the standard sieve.

<Water-soluble component amount (soluble component)>
Weigh out 184.3 g of 0.900 mass% sodium chloride aqueous solution in a 250 mL capacity plastic container with a lid, add 1.00 g of a water-absorbing resin or water-absorbing agent to the aqueous solution, and have a total length of 40 mm × diameter of 8 mm. By using a stirrer (for example, a stirrer A manufactured by Mutual Chemical Glass Co., Ltd.) so that the vortex depth is about 2 cm (for example, 250 to 350 rpm), the water absorbent resin is stirred for 16 hours with a magnetic stirrer. The soluble content in the water-absorbing agent was extracted. This extract is obtained by filtering using one filter paper (ADVANTEC Toyo Co., Ltd., product name: quantitative filter paper Qualitative Filter Papers (JIS P 3801, No. 2), thickness 0.26 mm, retention particle diameter 5 μm). 50.0 g of the obtained filtrate was measured and used as a measurement solution.

  Subsequently, the physiological saline to which the water-absorbing resin or water-absorbing agent is not added is first titrated to pH 10 using 0.1N NaOH aqueous solution, and then titrated to pH 2.7 with 0.1N HCl aqueous solution. To obtain an empty titer ([bNaOH] mL, [bHCl] mL).

  Titrations ([NaOH] mL, [HCl] mL) were determined by performing the same titration operation as described above for the measurement solution.

  Thereafter, the amount of soluble components in the water-absorbent resin or the water-absorbing agent was calculated based on the above-described empty titration amount and the titration amount of the measurement solution. That is, for example, in the case of a water-absorbing resin or water-absorbing agent comprising a known amount of acrylic acid and its sodium salt, based on the average molecular weight of the monomer and the titration amount obtained by the above operation, The amount of soluble component can be calculated by the following (formula 6.1).

Soluble content (% by weight) = 0.1 × (average molecular weight) × 184.3 × 100 × ([HCl] − [bHCl]) / 1000 / 1.0 / 50.0 (formula 6.1)
When a water-absorbing resin or water-absorbing agent comprising an unknown amount of component is used, the average molecular weight of the monomer is calculated using the neutralization rate obtained from the above titration based on (Equation 6.2) below. Then, the soluble content in the water-absorbing resin or water-absorbing agent is calculated by the above (formula 6.1).

Neutralization rate (mol%) = (1 − ([NaOH] − [bNaOH]) / ([HCl] − [bHCl])) × 100 (Equation 6.2)
<Performance evaluation of absorbent articles (Cuppy doll test)>
An absorbent article for performance evaluation was prepared by the following method. That is, first, 50 parts by weight of the water-absorbent resin (water-absorbing agent) obtained in Examples and Comparative Examples described later and 50 parts by weight of pulverized wood pulp were dry-mixed using a mixer. Next, the resulting mixture is formed into a 120 mm × 400 mm web by air-making on a wire screen formed to 400 mesh (mesh size: 38 μm) using a batch type air-making machine. did. Further, this web was pressed at a pressure of 2 kg / cm ² (196.14 kPa) for 5 seconds to obtain an absorbent having a basis weight of about 0.047 g / cm ² .

  Subsequently, a back sheet (liquid impermeable sheet) made of liquid impervious polypropylene and having a so-called leg gather, the above-described absorber, and a top sheet (liquid permeable sheet) made of liquid permeable polypropylene. Then, while adhering to each other in this order using a double-sided tape, two so-called tape fasteners were attached to the adhered product to obtain an absorbent article (paper diaper).

  The above absorbent article is attached to a so-called cupie doll (Kewpie Doll, body length 55 cm, weight 5 kg). After the cupy doll is turned down, a tube is inserted between the absorbent article and the cupie doll and urination is performed by the human body. One of the absorbing solutions selected from S0 to S7 was heated to 37 ° C. at a position corresponding to the position for performing the step, and then poured into 20 mL at 20 minute intervals. Then, when the injected absorbent solution was not absorbed by the absorbent article and leaked to the outside, the above injection operation was terminated, and the amount of the absorbed solution injected up to this time was measured.

  For each of the absorbing solutions of S0 to S7, the above measurement is repeated four times, an average value of the four measured values obtained is obtained, and this average value is the amount of absorption of the absorbing solution with respect to the absorbing solution of S0 to S7. (Hereinafter, QP absorption (g)) was calculated. And it evaluated that the performance of an absorbent article was so favorable that there was much said QP absorption amount in a cupy doll test.

  Furthermore, after injection of the absorbent solution, the four corners of the absorbent article are fixed with adhesive tape, and only the top sheet of the absorbent article is cut out and removed, so that the absorbent after use can be observed from the liquid injection side. did. Subsequently, as viewed from the liquid injection side, the size of the absorber portion used for absorption in the absorber was measured, and the diffusivity (%) was obtained. The diffusivity (%) was calculated by dividing the area of the portion used in the absorber by the total area of the absorber.

  As described above, since the measurement of the amount of the absorbing solution is repeated four times for the calculation of the QP absorption amount, the diffusivity (%) is obtained for each measurement, and the obtained four diffusivities are obtained. The average value of (%) was calculated as the QP diffusion rate (%) for the absorbing solutions of S0 to S7. And it evaluated that the performance of an absorbent article was so favorable that QP spreading | diffusion rate (%) was high.

<Gel Permeability Index / GPI>
Using the physiological saline flow-inductive test apparatus described in International Patent WO952356 (corresponding to Japanese Published Patent Publication “Special Table No. 9-509591”), the above-mentioned ion-exchanged water is used as a swelling solution and a solution-flowing solution. And the gel flow index (GPI) was calculated using sodium chloride aqueous solution S0-S7.

  That is, as shown in FIG. 1, the measuring device for GPI measurement includes a tank 31 that stores a liquid passing solution 33, and a cell 41 that passes through a gel layer 44 formed by swelling a water absorbing resin or a water absorbing agent. , A collecting container 48 for collecting the liquid passing solution that has passed through the gel, and an upper pan balance 49 for measuring the weight of the collected liquid flowing solution.

  A glass tube 32 is inserted into the tank 31, and the liquid passing solution supplied into the cell 41 is maintained at a height of 5 cm above the bottom of the gel layer 44 at the lower end of the glass tube 32. Arranged. Further, the liquid passing solution 33 in the tank 31 is supplied to the cell 41 through an L-shaped tube 34 provided with a cock 35.

  The cell 41 is a container for allowing the liquid passing solution to pass through the gel layer 44 obtained by swelling the water absorbent resin or the water absorbent. The cell 41 has an inner diameter of 6 cm. A 400 stainless steel wire mesh (mesh opening 38 μm) 42 is installed. The cell 41 is provided with a piston 46 that is pressed against the surface of the gel layer 44. The piston 46 is provided with a hole 47 in the lower part thereof through which the liquid passing solution passes, and a water-absorbing resin or a water-absorbing agent or a swelling gel thereof is prevented from entering the hole 47 at the bottom part. A glass filter 45 with good permeability is attached. The cell 41 is placed on a table on which the cell 41 is placed, and the surface of the table in contact with the cell is a stainless steel wire mesh 43 that does not prevent the permeation of the liquid solution.

  Under the wire mesh 43 where the cell 41 is disposed, a collection container 48 for collecting the passed liquid solution is disposed. The collection container 48 is installed on an upper pan balance 49. Yes. The weight of the liquid solution collected in the collection container 48 is measured by an upper pan balance 49.

  When GPI is measured using the above measuring apparatus, it is performed as follows. That is, the water-absorbing resin or water-absorbing agent (0.900 g) put in the cell 41 so as to have a uniform height is placed in the swelling solution under a predetermined pressure (0.3 psi (2.07 kPa) or 0.7 psi). (4.83 kPa)) for 60 minutes, and the height of the gel layer 44 formed by gelation of the water-absorbing resin or water-absorbing agent by the swelling was recorded. Subsequently, the liquid solution is supplied from the tank 31 at a constant hydrostatic pressure under the same pressure as the pressure at the time of swelling, and the gel layer 44 is allowed to flow. In addition, the same solution (ion exchange water or sodium chloride aqueous solution of the same density | concentration) as the swelling solution used at the time of swelling was used for the liquid passing solution to be used. For example, when the S0 solution was used at the time of swelling, the S0 solution was used as the liquid passing solution.

Next, using a computer and a balance, the amount (g) of the solution passing through the gel layer 44 (FIG. 1) is recorded for 10 minutes at intervals of 20 seconds as a function of time. The flow rate F _s (t) of the solution passing through the swollen gel layer 44 (mainly between the gel particles) is an increased weight that is the weight of the solution passing through the gel layer 44 within a predetermined time. (G) is divided by the increase time (s), which is the predetermined time, and the unit is g / s.

Gel liquid passing Index (GPI) is the time when the constant hydrostatic pressure and the stable flow rate are obtained and t _s, t _s and the data obtained (flow rate F between the 10 minutes the amount of passed through the solution was recorded _s (t)) is used to calculate based on (Equation 7) below. Incidentally, the first flow rate _F s (t = 0) through the value, i.e. the gel layer 44 of _F s (Equation 7) in (t = 0) is the aforementioned velocity _F s (t) versus time t _{(t s} The value at t = 0 obtained by extrapolating the plot of (time between the above 10 minutes) by the least square method is used.

GPI = (F _s (t = 0) × L ₀ ) / (ρ × A × ΔP)
= (F _s (t = 0) × L ₀ ) / 139506 (Equation 7)
Here, the unit of the GPI value is 10 ⁻⁷ × cm ³ × s × g ⁻¹ ,
L ₀ : height of the gel layer (cm)
ρ: Density of NaCl solution (g / cm ³ )
A: Area above the gel layer in the cell 41 (28.27 cm ² )
ΔP: hydrostatic pressure applied to the gel layer (4920 dyne / cm ² )
Represents.

<Reference Example 1>
71. Obtained by neutralizing acrylic acid containing protoanemonene and furfural with ND (non-Detactable / 1 ppm and less than 50 ppm p-methoxyphenol (weight of acrylic acid) with caustic soda, In 4500 g of an aqueous solution of sodium acrylate having a neutralization rate of 3 mol% (monomer concentration: 39% by weight), 14.6 g of polyethylene glycol diacrylate (average number of moles of ethylene oxide added 8) was dissolved, and the reaction solution (1 ).

  Next, this reaction liquid (1) was deaerated for 30 minutes in a nitrogen gas atmosphere. Subsequently, the degassed reaction liquid (1) was supplied to a reactor formed by attaching a lid to a stainless steel double-armed kneader with an internal volume of 10 L having two sigma blades, and the reaction liquid ( While maintaining 1) at 30 ° C., nitrogen gas substitution was performed. Thereafter, 2.46 g of sodium persulfate and 0.10 g of L-ascorbic acid were added as an aqueous solution while stirring the reaction liquid (1) purged with nitrogen gas, and polymerization was started after about 1 minute. Then, polymerization was carried out at 30 ° C. to 90 ° C., and after 60 minutes from the start of polymerization, a hydrogel crosslinked polymer (1) was obtained.

  The obtained hydrogel crosslinked polymer (1) had a diameter of about 5 mm. This finely divided hydrogel crosslinked polymer (1) was spread on a 50 mesh (mesh opening 300 μm) wire net and dried with hot air at 150 ° C. for 90 minutes. The obtained dried polymer (1) is pulverized using a vibration mill, and further classified and prepared with a 20 mesh (mesh 850 μm) wire mesh, whereby the irregularly crushed water-absorbent resin particles (a) are obtained. Obtained.

<Reference Example 2>
A neutralization rate of 60.0 mol% obtained by neutralizing acrylic acid containing protoanemonene and furfural ND and p-methoxyphenol 50 ppm (weight of acrylic acid) with caustic soda was obtained. 11.7 g of polyethylene glycol diacrylate (average number of moles of ethylene oxide added 8) was dissolved in 5200 g of an aqueous solution of sodium acrylate having a monomer concentration of 39% by weight to obtain a reaction solution (2).

  Next, this reaction liquid (2) was degassed in the same manner as in Reference Example 1, and then kept at 30 ° C. in a reactor formed by attaching a lid to the stainless steel double-arm kneader described in Reference Example 1. While replacing with nitrogen gas. Thereafter, 2.88 g of sodium persulfate and 0.10 g of L-ascorbic acid were added as an aqueous solution while stirring the reaction liquid (2) purged with nitrogen gas, and polymerization was started after about 1 minute. Then, polymerization was carried out at 30 ° C. to 90 ° C., and after 60 minutes from the start of polymerization, a hydrogel crosslinked polymer (2) (subdivided into about 5 mm) was obtained, and then dried in the same manner as in Reference Example 1.

  The obtained dried polymer (2) was pulverized with a vibration mill, and further classified and prepared with a 20 mesh (mesh 850 μm) wire mesh to obtain amorphous crushed water-absorbent resin particles (b).

<Reference Example 3>
A neutralization ratio of 75.0 mol% obtained by neutralizing acrylic acid containing protoanemonene and furfural with ND and p-methoxyphenol 50 ppm (weight of acrylic acid) with caustic soda was obtained. 58.5 g of polyethylene glycol diacrylate (average added mole number of ethylene oxide 8) was dissolved in 5650 g of an aqueous solution of sodium acrylate having a monomer concentration of 37% by weight to obtain a reaction solution (3).

  Next, after this reaction liquid (3) was degassed in the same manner as in Reference Examples 1 and 2, the reactor was formed by attaching a lid to the stainless steel double arm kneader described in Reference Examples 1 and 2. While maintaining at 30 ° C., nitrogen gas substitution was performed. Thereafter, 2.88 g of sodium persulfate and 0.10 g of L-ascorbic acid were added as an aqueous solution while stirring the reaction solution (3) purged with nitrogen gas, and polymerization was started after about 1 minute. Then, polymerization was performed at 30 ° C. to 90 ° C., and after 60 minutes from the start of polymerization, a hydrogel crosslinked polymer (3) (subdivided into about 5 mm) was obtained, and then dried in the same manner as in Reference Examples 1 and 2. .

  The obtained dried polymer (3) was pulverized with a vibration mill, and further classified and prepared with a 20 mesh (mesh 850 μm) wire mesh to obtain irregularly crushed water-absorbent resin particles (c).

<Reference Example 4>
A neutralization ratio of 75.0 mol% obtained by neutralizing acrylic acid containing protoanemonene and furfural with ND and p-methoxyphenol 50 ppm (weight of acrylic acid) with caustic soda was obtained. 4.4 g of polyethylene glycol diacrylate (average number of moles of ethylene oxide added 8) was dissolved in 5330 g of an aqueous solution of sodium acrylate having a monomer concentration of 33% by weight to obtain a reaction solution (4).

  Next, this reaction liquid (4) was degassed in the same manner as in Reference Examples 1 to 3, and then the reactor was formed by attaching a lid to the stainless steel double-arm kneader described in Reference Examples 1 to 3. While maintaining the temperature, the nitrogen gas was replaced. Thereafter, 2.88 g of sodium persulfate and 0.10 g of L-ascorbic acid were added as an aqueous solution while stirring the reaction liquid (4) purged with nitrogen gas, and polymerization was started after about 1 minute. Then, polymerization was performed at 30 ° C. to 90 ° C., and after 60 minutes from the start of polymerization, a hydrogel crosslinked polymer (4) (subdivided into about 5 mm) was obtained, and then dried in the same manner as in Reference Examples 1 to 3. .

  The obtained dried polymer (4) was pulverized with a vibration mill and further classified and prepared with a 20 mesh (mesh 850 μm) wire mesh to obtain irregularly crushed water-absorbent resin particles (d).

<Reference Example 5>
A neutralization rate of 60.0 mol% obtained by neutralizing acrylic acid containing protoanemonene and furfural ND and p-methoxyphenol 50 ppm (weight of acrylic acid) with caustic soda was obtained. 63.0 g of polyethylene glycol diacrylate (average added mole number of ethylene oxide 8) was dissolved in 5650 g of an aqueous solution of sodium acrylate having a monomer concentration of 37% by weight to obtain a reaction solution (5).

  Next, after this reaction liquid (5) was degassed in the same manner as in Reference Examples 1 to 4, the reactor was formed by attaching a lid to the stainless steel double arm kneader described in Reference Examples 1 to 4. While maintaining at 30 ° C., nitrogen gas substitution was performed. Thereafter, 2.88 g of sodium persulfate and 0.10 g of L-ascorbic acid were added as an aqueous solution while stirring the reaction solution (3) purged with nitrogen gas, and polymerization was started after about 1 minute. Then, polymerization was carried out at 30 ° C. to 90 ° C., and after 60 minutes from the start of polymerization, a hydrogel crosslinked polymer (5) (subdivided into about 5 mm) was obtained, and then dried in the same manner as in Reference Examples 1 to 4. .

  The obtained dried polymer (5) was pulverized with a vibration mill, and further classified and prepared with a 20 mesh (mesh 850 μm) wire mesh to obtain irregularly crushed water-absorbent resin particles (e).

<Reference Example 6>
The same procedure as in Reference Example 5 was performed, except that the polyethylene glycol diacrylate (average number of moles of ethylene oxide added 8) used to obtain the reaction liquid (5) was 88.2 g, and the irregularly crushed water absorption Resin particles (f) were obtained.

<Example 1>
A surface cross-linking agent composed of 0.5 part of propylene glycol, 0.3 part of 1,4-butanediol and 3 parts of water was mixed with 100 parts of the water absorbent resin (a) obtained in Reference Example 1. The mixture was heat-treated at 220 ° C. for 90 minutes to obtain a water-absorbing agent (1) made of a surface-treated water-absorbing resin.

<Example 2>
Instead of using the water-absorbent resin (a), the same procedure as in Example 1 was carried out except that the water-absorbent resin (b) obtained in Reference Example 2 was used. Agent (2) was obtained.

<Example 3>
For 100 parts of the water-absorbent resin (c) obtained in Reference Example 3, 0.3 part of hydrophilic silicon dioxide (trade name Aerosil 200; manufactured by Nippon Aerosil Co., Ltd.) M5R) and stirred at 330 rpm for 15 seconds to obtain a water-absorbing agent (3) made of a surface-treated water-absorbing resin.

<Example 4>
Except for using calcium stearate instead of hydrophilic silicon dioxide, the same operation as in Example 3 was performed to obtain a water-absorbing agent (4) comprising a surface-treated water-absorbing resin.

<Example 5>
A surface cross-linking agent composed of 0.5 part of propylene glycol, 0.3 part of 1,4-butanediol and 3 parts of water was mixed with 100 parts of the water absorbent resin (e) obtained in Reference Example 5. The mixture was heat treated at 220 ° C. for 40 minutes to obtain a water absorbing agent (5) composed of a surface treated water absorbent resin.

<Example 6>
Instead of using the water-absorbent resin (e), the same procedure as in Example 5 was performed, except that the water-absorbent resin (f) obtained in Reference Example 6 was used. Agent (6) was obtained.

<Comparative Example 1>
A surface cross-linking agent composed of 0.5 part of propylene glycol, 0.3 part of 1,4-butanediol and 3 parts of water was mixed with 100 parts of the water absorbent resin (a) obtained in Reference Example 1. The above mixture was heat-treated at 210 ° C. for 40 minutes to obtain a comparative water-absorbing agent (1) made of a surface-treated water-absorbing resin.

<Comparative example 2>
To 100 parts of the water absorbent resin (d) obtained in Reference Example 4, 0.02 part of ethylene glycol diglycidyl ether, 0.3 part of 1,4-butanediol, 0.4 part of propylene glycol and 2 parts of water And mixed. The said mixture was heat-processed at 195 degreeC for 50 minutes, and the comparative water absorbing agent (2) which consists of surface-treated water-absorbing resin was obtained.

<Comparative Example 3>
Except for heat treatment at 210 ° C. for 40 minutes, the same operation as in Comparative Example 2 was performed to obtain a comparative water-absorbing agent (3) made of a surface-treated water-absorbing resin.

<Comparative example 4>
The water-absorbent resin (c) obtained in Reference Example 3 was heat-treated at 220 ° C. for 90 minutes without mixing the surface cross-linking agent to obtain a comparative water-absorbing agent (4).

<Result>
Table 1 shows the absorption capacity, the soluble content (weight (wt)%), and the particle size (weight (wt)%) of 0.90 mass% sodium chloride aqueous solution of the water absorbent resins (a) to (f). Shown in

  Further, the water-absorbing agents (1) to (6) made of the surface-treated water-absorbing resin, the comparative water-absorbing agents (1) to (4), and the water-absorbing resin (c) as a comparison with respect to the absorbing solutions S0 to S7. The absorption capacity under load is shown in Tables 2 and 3, and the absorption capacity under load (AAP), the salt concentration absorption index, the average value and the standard deviation of the salt concentration absorption index are shown in Tables 4-7.

  Table 8 shows the results of performance evaluation (QP absorption amount) of absorbent articles using the water-absorbing agent (1) (2) and the comparative water-absorbing agent (1) (2) (3). Pressure (0.3 psi (2.07 kPa) and 0.7 psi) of the water absorbing agent (1) and the comparative water absorbing agent (3) when the absorbing solution S6 (0.7 mass (weight)% sodium chloride aqueous solution) is used. The gel permeation index at 4.83 kPa)) is shown in Table 9. Table 10 shows the gel permeation index at a pressure of 0.3 psi (2.07 kPa) when the absorbing solutions S0, S3, S6, and S7 of the water absorbing agent (1) and the comparative water absorbing agent (3) are used. Table 11 shows the results of performance evaluation (QP diffusion rate) of absorbent articles using the water-absorbing agent (1) and the comparative water-absorbing agent (1) (3).

  Furthermore, the water-absorbing agents (1) to (6) made of the surface-treated water-absorbing resin, the comparative water-absorbing agents (1) to (4), and the salt-tolerant index of the water-absorbing resin (c) as a comparison are shown in Tables 12 and 13. Shown in

  It should be noted that the specific embodiments or examples made in the best mode for carrying out the invention are merely to clarify the technical contents of the present invention, and are limited to such specific examples. The present invention should not be construed as narrowly defined but can be implemented with various modifications within the spirit of the present invention and the scope of the following claims.

  Since the particulate water-absorbing agent of the present invention exhibits high performance regardless of use conditions, it is widely used in agricultural and horticultural water-retaining agents, industrial water-retaining agents, moisture-absorbing agents, dehumidifying agents, building materials and the like. Of these, particularly preferably used are sanitary materials for absorbing feces, urine or blood, such as disposable diapers and sanitary napkins.

It is a schematic sectional drawing which shows the measuring apparatus used for the measurement of a gel flow index.

Explanation of symbols

31 Tank 32 Glass tube 33 Liquid solution 34 L-shaped tube 35 Cock 41 Cell 42 Stainless steel wire mesh 43 Wire mesh 44 Gel layer 45 Glass filter 46 Piston 47 Hole 48 Collection container 49 Upper plate balance

Claims (16)

A particulate water-absorbing agent for urine absorption containing 85 to 100% by mass of a particulate water-absorbing resin whose main component is a polyacrylate cross-linked polymer,
(1) The surface is modified with 0.001 to 10 parts by mass of a surface modifier with respect to 100 parts by mass of the water absorbent resin,
The surface modifier is selected from the group consisting of a surface cross-linking agent and an inert additive,
(2) The particulate water-absorbing resin having a particle diameter of 106 μm or more and less than 850 μm is contained in an amount of 90% by mass or more based on the total mass of the water-absorbing resin,
(3) The absorption capacity under no load (60 minutes value) of the particulate water-absorbing agent with respect to a 0.9% by mass sodium chloride aqueous solution is 10 to 27 g / g,
(4) The following (Formula 1)
(Salt concentration absorption index) = (absorption capacity under pressure at 4.83 kPa for a constant salt concentration aqueous solution) / (absorption capacity under no load for a constant salt concentration aqueous solution) (Equation 1)
(In the formula, the absorption capacity under pressure is an absorption capacity when immersed in a constant salt concentration aqueous solution for 60 minutes under a pressure of 4.83 kPa, and the absorption capacity under no load is under no pressure, The first salt concentration absorption index, which is the salt concentration absorption index when the above constant salt concentration aqueous solution is ion-exchanged water, is 0.60 or more. 1.20 or less ,
The second salt concentration absorption index, which is the salt concentration absorption index when the constant salt concentration aqueous solution in (Formula 1) is a 0.10% by mass sodium chloride aqueous solution, is 0.80 or more and 1.20 or less,
A third salt concentration absorption index which is a salt concentration absorption index when the constant salt concentration aqueous solution in the above (formula 1) is a 0.30 mass% sodium chloride aqueous solution;
A fourth salt concentration absorption index, which is a salt concentration absorption index when the constant salt concentration aqueous solution in the above (formula 1) is a 0.50 mass% sodium chloride aqueous solution,
A fifth salt concentration absorption index, which is a salt concentration absorption index when the constant salt concentration aqueous solution in (Formula 1) is a 0.70 mass% sodium chloride aqueous solution,
A sixth salt concentration absorption index which is a salt concentration absorption index when the constant salt concentration aqueous solution in the above (formula 1) is a 0.90 mass% sodium chloride aqueous solution;
A particulate water-absorbing agent for urine absorption , wherein at least one of them is 0.90 or more and 1.20 or less .   The particulate water-absorbing agent for urine absorption according to claim 1, wherein the surface modifier is a dehydration-reactive surface cross-linking agent.   The particulate water-absorbing agent for urine absorption according to claim 1 or 2, wherein the surface modifier is inert inorganic fine particles.   The particulate water-absorbing agent for urine absorption according to any one of claims 1 to 3, wherein the surface modifier is a fatty acid or a salt thereof.   The particulate water-absorbing agent for urine absorption according to any one of claims 1 to 4, wherein the urine is urine of an infant or a newborn. Average salt concentration which is the average value of the above-mentioned first salt concentration absorption index, second salt concentration absorption index, third salt concentration absorption index, fourth salt concentration absorption index, fifth salt concentration absorption index, and sixth salt concentration absorption index The absorption index index is 0.90 or more and 1.10 or less, and
The particulate water-absorbing agent for urine absorption according to any one of claims 1 to 5 , wherein a standard deviation of the average salt concentration absorption index index is in a range of 0 to 0.100. Below (Formula 2)
(Salt tolerance index) = (absorption capacity under no load with respect to a constant salt concentration aqueous solution) / (absorption capacity under no load with respect to ion-exchanged water) (Equation 2)
(In the formula, the absorption capacity under no load is the absorption capacity when immersed in a constant salt concentration aqueous solution or ion-exchanged water for 60 minutes), and the above-mentioned constant salt concentration is a 0.10% by mass sodium chloride aqueous solution. The particulate salt water-absorbing agent for urine absorption according to any one of claims 1 to 6 , wherein a first salt-tolerance index, which is a salt-tolerance index in the case, is 0.40 or more and 1.20 or less. . The particulate water-absorbing agent for urine absorption according to any one of claims 1 to 7, wherein a gel permeation index with respect to ion-exchanged water is 15 or more under a pressure of 2.07 kPa. The particulate form for urine absorption according to any one of claims 1 to 8, wherein a gel permeation index with respect to a 0.30 mass% sodium chloride aqueous solution is 50 or more under a pressure of 2.07 kPa. Water absorbent. The urine absorption particulate form according to any one of claims 1 to 9, wherein a gel permeation index with respect to a 0.70 mass% sodium chloride aqueous solution is 15 or more under a pressure of 4.83 kPa. Water absorbent. A urine-absorbing sanitary material comprising the urine-absorbing particulate water-absorbing agent according to any one of claims 1 to 10 . The sanitary material for absorption of urine according to claim 11, which is a disposable diaper. An absorption layer for absorbing the urine,
The absorption layer is represented by the following (formula 3)
(Core concentration ratio) = (mass of the particulate water-absorbing agent) / ((mass of the particulate water-absorbing agent) + (mass of the fiber material)) (Equation 3)
The sanitary material for absorption of urine according to claim 11 or 12, wherein the core concentration defined by the above is 0.3 or more and 1.0 or less. It is a manufacturing method of the particulate water-absorbing agent for urine absorption according to any one of claims 1 to 5,
Using acrylic acid with protoanemonene and / or furfural reduced to 20 ppm or less in the presence of 200 ppm or less of p-methoxyphenol, 0 to 50 mol% of acrylic acid and 100 to 50 mol% of acrylate (with the exception of , And the total amount of both is 100 mol% or less), and polyacrylic acid (salt) -based cross-linked polymer obtained by polymerizing 0 to 30 mol% of other water-soluble unsaturated monomers with an internal cross-linking agent. The ratio of the particle diameter of 106 μm or more and less than 850 μm is 90 to 100% by mass, and the absorption capacity without load (60 minutes value) with respect to 0.90% by mass sodium chloride aqueous solution is 15 to 27 g / 100 parts by weight of the water-absorbing resin g is an absorption capacity under no load with respect to a 0.90 mass% sodium chloride aqueous solution (6 (0 minute value) The manufacturing method characterized by carrying out surface crosslinking by 0.001-10 mass parts of surface crosslinking agents so that it may become the range of 10-27 g / g. It is a manufacturing method of the particulate water-absorbing agent for urine absorption according to any one of claims 1 to 5,
Using acrylic acid with protoanemonene and / or furfural reduced to 20 ppm or less in the presence of 200 ppm or less of p-methoxyphenol, 0 to 50 mol% of acrylic acid and 100 to 50 mol% of acrylate (with the exception of , And the total amount of both is 100 mol% or less), and polyacrylic acid (salt) -based cross-linked polymer obtained by polymerizing 0 to 30 mol% of other water-soluble unsaturated monomers with an internal cross-linking agent. The ratio of the particle diameter of 106 μm or more and less than 850 μm is 90 to 100% by mass, and the absorption capacity without load (60 minutes value) with respect to 0.90% by mass sodium chloride aqueous solution is 15 to 27 g / The manufacturing method characterized by surface-treating 100 mass parts of water-absorbent resin which is g with 0.001-10 mass parts of inorganic fine powder. It is a manufacturing method of the particulate water-absorbing agent for urine absorption according to any one of claims 1 to 5,
Using acrylic acid with protoanemonene and / or furfural reduced to 20 ppm or less in the presence of 200 ppm or less of p-methoxyphenol, 0 to 50 mol% of acrylic acid and 100 to 50 mol% of acrylate (with the exception of , And the total amount of both is 100 mol% or less), and polyacrylic acid (salt) -based cross-linked polymer obtained by polymerizing 0 to 30 mol% of other water-soluble unsaturated monomers with an internal cross-linking agent. The ratio of the particle diameter of 106 μm or more and less than 850 μm is 90 to 100% by mass, and the absorption capacity without load (60 minutes value) with respect to 0.90% by mass sodium chloride aqueous solution is 15 to 27 g / The manufacturing method characterized by surface-coating 100 mass parts of water-absorbing resin which is g with a fatty acid or its salt 0.001-10 mass parts.

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