JP4969778B2 - Method for producing water-absorbent resin particles and sanitary material using the same - Google Patents

Description

  The present invention relates to a method for producing water absorbent resin particles. More specifically, a method for producing water-absorbent resin particles having high water retention capacity, high water absorption capacity under load, excellent water absorption speed, low water-soluble content, and suitable for use in sanitary materials, and obtained thereby. The present invention relates to water absorbent resin particles and sanitary materials using the same.

  Conventionally, water-absorbing resins have been widely used in industrial materials such as sanitary materials such as disposable diapers and sanitary napkins, and water-stopping materials for cables. Examples of water-absorbing resins include starch-acrylonitrile graft copolymer hydrolysates, starch-acrylic acid graft polymer neutralized products, vinyl acetate-acrylic ester copolymer saponified products, and polyacrylic acid moieties. Japanese products are known.

  In sanitary materials such as paper diapers and sanitary napkins, properties desired for the water-absorbent resin include high water retention capacity, excellent water absorption speed, high water absorption capacity under load, and low water-soluble content. However, it is difficult to sufficiently satisfy the balance of these characteristics.

  In particular, there is a contradictory relationship between water retention capacity, water absorption speed, and water absorption capacity under load. Generally, in order to obtain a high water retention capacity, it is necessary to lower the crosslink density of the water absorbent resin. However, when the crosslink density is lowered, the gel strength is lowered, and the water absorbability under the load of the water absorbent resin is lowered. As a result, when used as a sanitary material, the water-absorbent resins cause gel blocking, causing a decrease in diffusibility and an increase in the amount of reversion. In addition, when the crosslink density of the water absorbent resin is lowered, uncrosslinked components increase, and when it comes into contact with the liquid, the water absorption rate tends to decrease due to the Mamako state, and water-soluble components are likely to elute. Become. As a result, when it is used as a diaper, it causes a rash caused by water-soluble components and leakage of body fluids, and the wearer's comfort is impaired.

  As a technique for improving the performance of the above characteristics suitably used for sanitary materials, a method of performing reverse phase suspension polymerization using a specific amount of a specific polymer protective colloid and a surfactant (see Patent Document 1), A method in which reverse phase suspension polymerization is carried out in two or more stages (see Patent Document 2), and in the presence of β-1,3-glucans, reverse phase suspension polymerization is performed to obtain a water-absorbing resin. A cross-linking reaction by adding a cross-linking agent to a water-absorbent resin (see Patent Document 3), and a reverse-phase suspension polymerization using a specific amount of persulfate as a polymerization initiator (see Patent Document 4) A method of polymerizing an aqueous solution in the presence of phosphorous acid and / or a salt thereof to obtain a water-absorbent resin precursor, and then mixing and heating the water-absorbent resin precursor and a surface cross-linking agent (see Patent Document 5) Etc. are known. However, these water-absorbing resins do not fully satisfy all of the above-mentioned performances such as high water retention capacity, high water absorption capacity under load, excellent water absorption speed, and low water-soluble content, and there is still room for improvement. .

JP-A-6-345819 Japanese Patent Laid-Open No. 3-227301 JP-A-8-120013 JP-A-6-287233 JP-A-9-124710

  The present invention provides a method for producing water-absorbent resin particles that have high water retention capacity, high water absorption capacity under load, excellent water absorption speed and low water-soluble content, and can be suitably used for sanitary materials, and thereby obtained. It is an object of the present invention to provide water-absorbent resin particles and sanitary materials using the same.

That is, the present invention is a method for producing a water-absorbent resin by polymerizing a water-soluble ethylenically unsaturated monomer, and starts water-soluble azo radical polymerization in the presence of a polyvalent glycidyl compound as an internal crosslinking agent. after agent performing reverse phase suspension polymerization of 2-3 stages using a method for producing a water-absorbent resin particles, characterized by post-crosslinking the resultant water-absorbent resin in the post-crosslinking agent, and the method Water-absorbent resin particles that satisfy the following performance obtained in
Saline water absorption rate: within 60 seconds Saline retention capacity: 40-60 g / g
4. Saline water absorption capacity under a load of 14.14 kPa: 15 ml / g or more Water soluble content: 20% by mass or less Mass average particle size: 200 to 600 μm
In addition, the present invention relates to a sanitary material comprising the water-absorbent resin particles and hydrophilic fibers.

  ADVANTAGE OF THE INVENTION According to this invention, the water-absorbing resin particle which can be used suitably for a sanitary material which has a high water retention ability, a high water absorption ability under load, an excellent water absorption rate, and a small water-soluble content can be produced.

    Examples of the water-soluble ethylenically unsaturated monomer include (meth) acrylic acid [“(meth) acryl” means “acryl” or “methacryl”. The same shall apply hereinafter), 2- (meth) acrylamide-2-methylpropanesulfonic acid or alkali metal salts thereof; (meth) acrylamide, N, N-dimethylacrylamide, 2-hydroxyethyl (meth) acrylate, N-methylol (meth) Nonionic monomers such as acrylamide; amino group-containing unsaturated monomers such as diethylaminoethyl (meth) acrylate and diethylaminopropyl (meth) acrylate, or quaternized products thereof. These may be used alone or in combination of two or more. In addition, lithium, sodium, potassium etc. are mentioned as an alkali metal in an alkali metal salt.

  Among the water-soluble ethylenically unsaturated monomers, (meth) acrylic acid or an alkali metal salt thereof, acrylamide, methacrylamide and N, N-dimethylacrylamide are preferable from the viewpoint of easy industrial availability. Can be mentioned. More preferable is (meth) acrylic acid or an alkali metal salt thereof from an economical viewpoint.

  The water-soluble ethylenically unsaturated monomer can be usually used as an aqueous solution. The concentration of the water-soluble ethylenically unsaturated monomer in the aqueous solution of the water-soluble ethylenically unsaturated monomer is preferably 15% by mass to a saturated concentration.

  When the water-soluble ethylenic monomer used in the aqueous solution of the water-soluble ethylenically unsaturated monomer contains an acid group, the acid group may be neutralized with an alkali metal. The degree of neutralization with an alkali metal increases the osmotic pressure of the resulting water-absorbent resin particles, speeds up the water absorption rate, and prevents the presence of excess alkali metal from causing problems such as safety before neutralization. It is preferable that it exists in the range of 10-100 mol% of the acid group of the water-soluble ethylenically unsaturated monomer. Examples of the alkali metal include lithium, sodium, and potassium. Among these, sodium and potassium are preferable, and sodium is more preferable.

The water-soluble ethylenically unsaturated monomer polymerization method is not particularly limited, and a typical polymerization method such as an aqueous solution polymerization method, an emulsion polymerization method, a reverse phase suspension polymerization method, or the like is used. In the aqueous solution polymerization method, polymerization is performed by heating a water-soluble ethylenically unsaturated monomer aqueous solution, an internal cross-linking agent, and a water-soluble radical polymerization initiator while stirring as necessary. In reverse phase suspension polymerization, a water-soluble ethylenically unsaturated monomer aqueous solution, a surfactant and / or polymer protective colloid, a water-soluble radical polymerization initiator and an internal crosslinking agent are stirred in a hydrocarbon solvent. Polymerization is carried out by heating at. In the present invention, the reverse phase suspension polymerization method is preferred from the viewpoint of precise polymerization reaction control and wide particle size control.

  Hereinafter, the reverse phase suspension polymerization method will be described in more detail as an example of an embodiment of the present invention.

  Examples of the surfactant used in the reverse phase suspension polymerization method include, for example, sorbitan fatty acid ester, polyglycerin fatty acid ester [“(poly)” means both with and without the prefix “poly”. . The same shall apply hereinafter), nonionic surfactants such as sucrose fatty acid ester, sorbitol fatty acid ester, polyoxyethylene alkylphenyl ether; fatty acid salt, alkylbenzene sulfonate, alkylmethyl taurate, polyoxyethylene alkylphenyl ether sulfate And anionic surfactants such as polyoxyethylene alkyl ether sulfonates. Among these, sorbitan fatty acid ester, polyglycerin fatty acid ester and sucrose fatty acid ester are preferable.

  Examples of the polymer protective colloid include ethyl cellulose, ethyl hydroxyethyl cellulose, polyethylene oxide, anhydrous maleated polyethylene, anhydrous maleated polybutadiene, and anhydrous maleated EPDM (ethylene / propylene / diene / terpolymer).

  The surfactant and the polymer protective colloid may be used alone or in combination.

  The amount of the surfactant and / or polymer protective colloid used is preferably 0.1 to 5 parts by mass, and 0.2 to 3 parts by mass with respect to 100 parts by mass of the aqueous solution of the water-soluble ethylenically unsaturated monomer. More preferred.

  Examples of the internal crosslinking agent include (poly) ethylene diglycidyl ether, glycerol polyglycidyl ether, diglycerol polyglycidyl ether, (poly) ethylene glycol diglycidyl ether, (poly) propylene glycol diglycidyl ether, and (poly) glycerin di Examples thereof include polyvalent glycidyl compounds such as glycidyl ether. These may be used alone or in combination of two or more. Among these, (poly) ethylene glycol diglycidyl ether, (poly) propylene glycol diglycidyl ether, and (poly) glycerin diglycidyl ether have high water absorption capacity under load, excellent water absorption speed, and water absorption of a small amount of water-soluble matter. From the viewpoint of obtaining conductive resin particles.

  The amount of the internal crosslinking agent used is from 1 mol of the water-soluble ethylenically unsaturated monomer from the viewpoint that the obtained polymer is suppressed in water-soluble properties by appropriate crosslinking and exhibits sufficient water absorption. 0.000001 to 0.001 mol, preferably 0.00001 to 0.01 mol.

  Examples of the water-soluble azo radical polymerization initiator include 1-{(1-cyano-1-methylethyl) azo} formamide, 2,2′-azobis [2- (N-phenylamidino) propane] dihydrochloride 2,2′-azobis {2- [N- (4-chlorophenyl) amidino] propane} dihydrochloride, 2,2′-azobis {2- [N- (4-hydroxyphenyl) amidino] propane} dihydrochloride Salt, 2,2′-azobis [2- (N-benzylamidino) propane] dihydrochloride, 2,2′-azobis [2- (N-allylamidino) propane] dihydrochloride, 2,2′-azobis (2-Amidinopropane) dihydrochloride, 2,2'-azobis {2- [N- (2-hydroxyethyl) amidino] propane} dihydrochloride, 2,2'-azobis [2- (5-methyl- 2-Imidazolin-2-yl) propane] dihydrochloride, 2,2'-azobis [2- (2-imidazolin-2-yl) propane] dihydrochloride, 2,2'-azobis [2- ( , 5,6,7-Tetrahydro-1H-1,3-diazepin-2-yl) dihydrochloride, 2.2'-azobis [2- (5-hydroxy-3,4,5,6-tetrahydropyrimidine- 2-yl) propane] dihydrochloride, 2,2′-azobis {2- [1- (2-hydroxyethyl) -2-imidazolin-2-yl] propane} dihydrochloride, 2,2′-azobis [ 2- (2-imidazolin-2-yl) propane], 2,2′-azobis {2-methyl-N- [1,1-bis (hydroxymethyl) -2-hydroxyethyl] propionamide}, 2,2 '-Azobis {2-methyl-N- [1,1-bis (hydroxymethyl) ethyl] propionamide}, 2,2'-azobis [2-methyl-N- (2-hydroxyethyl) -propionamide], 2,2′-azobis (2-methylpropionamide) dihydrate, 4,4′-azobis-4-cyanovaleric acid, 2,2′-azobis [2- (hydroxymethyl) propionitrile], 2,2 ' -Azobis [2- (2-imidazolin-2-yl) propane] disulfate, 2,2'-azobis [N- (2-carboxyethyl) -2-methylpropionamidine] tetrahydrate, 2,2 Examples include azo compounds such as' -azobis [2-methyl-N- (2-hydroxyethyl) propionamide]. These may be used alone or in combination of two or more. Among these, 2,2′-azobis (2-amidinopropane) dihydrochloride, 2,2′-azobis {2- [1- (2-hydroxyethyl) -2-imidazolin-2-yl] propane} Especially from the viewpoint of obtaining water-absorbing resin particles having high water retention ability and low water-soluble content with hydrochloride and 2,2′-azobis [N- (2-carboxyethyl) -2-methylpropionamidine] tetrahydrate. preferable.

  The amount of the water-soluble azo radical polymerization initiator used is preferably 0.00005 with respect to 1 mol of the water-soluble ethylenically unsaturated monomer, from the viewpoint of shortening the polymerization reaction time and preventing a rapid polymerization reaction. It is -0.001 mol, More preferably, it is 0.0001-0.001 mol.

  Examples of the hydrocarbon solvent include aliphatic hydrocarbons such as n-hexane, n-heptane, and ligroin; alicyclic hydrocarbons such as cyclopentane, methylcyclopentane, cyclohexane, and methylcyclohexane; benzene, toluene, xylene, and the like And aromatic hydrocarbons. These may be used alone or in combination of two or more. Among these, n-hexane, n-heptane, and cyclohexane are preferable from the viewpoint of industrial availability, stable quality, and low cost.

  The amount of the hydrocarbon solvent used is usually preferably 50 to 600 parts by mass with respect to 100 parts by mass of the water-soluble ethylenically unsaturated monomer, from the viewpoint of easily removing the heat of polymerization and controlling the polymerization temperature. -550 mass parts is more preferable.

  The reaction temperature of the polymerization reaction is preferably 20 to 110 ° C. from the viewpoint of increasing the economic efficiency by rapidly advancing the polymerization and shortening the polymerization time, and from the viewpoint of easily removing the heat of polymerization and performing the reaction smoothly. 40 to 90 ° C. is more preferable. The reaction time is usually 0.5 to 4 hours.

  In the present invention, the reverse phase suspension polymerization is carried out in one or more stages, but the number of stages is preferably 2 to 3 in order to increase productivity.

  In the present invention, the water-absorbent resin obtained by the polymerization is post-crosslinked with a post-crosslinking agent. Any post-crosslinking agent may be used as long as it can react with the carboxyl group of the water-absorbent resin. For example, (poly) ethylene glycol, (poly) propylene glycol, 1,4-butanediol, trimethylolpropane, polyoxyethylene Diols such as glycol, polyoxypropylene glycol, (poly) glycerin, triols or polyols; diglycidyl ethers such as (poly) ethylene glycol diglycidyl ether, (poly) propylene glycol diglycidyl ether, (poly) glycerin diglycidyl ether Compounds; epihalohydrin compounds such as epichlorohydrin, epibromohydrin, α-methylepichlorohydrin; isocyanate compounds such as 2,4-tolylene diisocyanate and hexamethylene diisocyanate Compounds having a reactive functional group 2 or more thereof. These may be used alone or in combination of two or more.

  Among these, (poly) ethylene diglycidyl ether, glycerol polyglycidyl ether, diglycerol polyglycidyl ether, (poly) ethylene glycol diglycidyl ether, (poly) propylene glycol diglycidyl ether, (poly) glycerin diglycidyl ether, etc. A polyvalent glycidyl compound is preferable from the viewpoint of obtaining water-absorbing resin particles having a high water absorption capacity under load, an excellent water absorption rate, and a small water-soluble content.

  The amount of the post-crosslinking agent used varies depending on the type of the post-crosslinking agent, but is usually 0.00001 to 0.01 mol with respect to 1 mol of the total amount of the water-soluble ethylenically unsaturated monomer subjected to the polymerization. Preferably it is 0.00005-0.005 mol, More preferably, it is 0.0001-0.002 mol. When the amount of the post-crosslinking agent used is less than 0.00001 mol, the crosslink density of the water-absorbent resin cannot be sufficiently increased, so that the water-soluble component may increase or the water absorption capacity under load may be reduced. is there. Moreover, when the usage-amount of post-crosslinking agent exceeds 0.01 mol, since a crosslinking reaction advances remarkably, there exists a possibility that water retention ability may fall.

  The timing for adding the post-crosslinking agent is not particularly limited as long as it is after the completion of the polymerization reaction of almost all the monomers.

  The mixing of the water absorbent resin and the postcrosslinking agent is preferably performed in the presence of water. The amount of water when mixing the water-absorbent resin and the post-crosslinking agent varies depending on the type, particle size and water content of the water-absorbent resin, but usually the total amount of water-soluble ethylenically unsaturated monomers subjected to polymerization Preferably it is 5-300 mass parts with respect to 100 mass parts, More preferably, it is 10-100 mass parts, More preferably, it is 10-50 mass parts. When the amount of water with respect to 100 parts by mass of the total amount of water-soluble ethylenically unsaturated monomers subjected to polymerization is less than 5 parts by mass, the water absorption capacity under load tends to decrease, and when it exceeds 300 parts by mass The crosslinking reaction is excessively promoted, and the water-retaining ability of the resulting water-absorbent resin tends to be too low. The amount of water means the total amount of water contained in the polymerization reaction system and water used as necessary when the post-crosslinking agent is added.

  After completion of the post-crosslinking treatment, the water-absorbing resin particles of the present invention are obtained by distilling off water and the hydrocarbon solvent.

  Such water-absorbing resin particles have a physiological saline water absorption rate of 60 seconds or less, a physiological saline water retention capacity of 40 to 60 g / g, a physiological saline water absorption capacity under a load of 4.14 kPa of 15 ml / g or more, Since the dissolved content is 20% by mass or less and the mass average particle size is 200 to 600 μm, the water-soluble content is small, the water retention capability is high, the water absorption capability under load is high, and the water absorption rate is excellent. And can be suitably used for sanitary materials.

  The physiological saline water absorption rate is preferably within 60 seconds, more preferably within 55 seconds, more preferably within 55 seconds, from the viewpoint of having the advantage that the faster one is used as a sanitary material, the amount of reversion is small and the diffusibility is good. Preferably, it is within 50 seconds. The water retention capacity of physiological saline is preferably 40 to 60 g / g, more preferably 40 to 50 g / g.

  4. Saline water absorption capacity under a load of 14.14 kPa is preferably 15 ml / g from the viewpoint of having the advantage that when the higher one is used as a sanitary material, the amount of reversal when pressure is applied to the sanitary material is reduced, More preferably, it is 20 ml / g.

  When the water-soluble component is used as a sanitary material, the lower one has less “rash” and “slimming” due to the water-soluble component, and the comfort when the sanitary material is worn is improved. % Or less, more preferably 15% by mass or less.

  The mass average particle diameter is preferably 200 to 600 μm, more preferably 250 to 500 μm, and still more preferably 300 to 400 μm. When the mass average particle diameter of the water-absorbent resin particles is less than 200 μm, the existing ratio of small particles increases, and the handleability of the powder may deteriorate due to powdering or the like. Moreover, when used as a sanitary material, gel blocking is likely to occur, and as a result, there is a risk that the diffusibility is lowered and the amount of reversion is increased. When the mass average particle diameter of the water-absorbent resin particles exceeds 600 μm, the water absorption rate is slow, and when used as a sanitary material, it tends to cause leakage from the sanitary material, and the wearer may not be able to use the sanitary material comfortably. is there.

  The water absorption rate, water retention capacity, water absorption capacity for physiological saline under a load of 4.14 kPa, water-soluble content, and mass average particle diameter are all values measured by the measurement methods described in the examples described later. It is.

  The sanitary material of the present invention includes a liquid permeable sheet (top sheet) that allows an aqueous liquid to pass through an absorber that absorbs and retains an aqueous liquid, and a liquid impermeable sheet that does not allow an aqueous liquid to pass through (top sheet). (Back sheet). The liquid permeable sheet is disposed on the side that contacts the body, and the liquid impermeable sheet is disposed on the side that does not contact the body.

  Examples of the liquid permeable sheet include a nonwoven fabric made of polyethylene, polypropylene, polyester, polyamide, and the like, and a porous synthetic resin sheet. However, the present invention is not limited to these.

  Examples of the liquid-impermeable sheet include films made of synthetic resins such as polyethylene, polypropylene, and polyvinyl chloride, and sheets made of composite materials of these synthetic resins and nonwoven fabrics, but the present invention is not limited thereto. It is not something.

  The absorber used for the sanitary material is composed of hydrophilic fibers and water-absorbing resin particles. Examples of hydrophilic fibers include, but are not limited to, cellulose fibers such as cotton pulp, mechanical pulp, chemical pulp, and semi-chemical pulp obtained from wood, and artificial cellulose fibers such as rayon and acetate. It is done. The hydrophilic fiber may contain synthetic fibers such as polyamide, polyester, and polyolefin.

  EXAMPLES The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to these examples and the like.

Example 1
A 1000 mL five-necked cylindrical round bottom flask equipped with a stirrer, reflux condenser, dropping funnel, thermometer and nitrogen gas inlet tube is 340 g of n-heptane and sucrose fatty acid ester having an HLB of 3.0 (Mitsubishi Chemical) Trade name: S-370) 0.92 g was added, dispersed, heated and dissolved, and then cooled to 55 ° C.

  Separately, a 500 mL Erlenmeyer flask was charged with 92 g (1.02 mol) of an 80% by weight aqueous acrylic acid solution, and 102.2 g (0.77%) of a 30% by weight aqueous sodium hydroxide solution was cooled from the outside. Mol) was added dropwise to neutralize 75 mol% of acrylic acid. Further, 36.9 g of water, 0.11 g (0.00041 mol) of 2,2′-azobis (2-amidinopropane) dihydrochloride as a water-soluble azo polymerization initiator, and ethylene glycol diglycidyl ether 8 as an internal crosslinking agent .3 mg (0.000048 mol) was added to prepare an aqueous monomer solution for the first stage polymerization.

  The monomer aqueous solution for the first stage polymerization is added to and dispersed in the five-necked cylindrical round bottom flask with stirring, and the system is sufficiently replaced with nitrogen. Was kept at 70 ° C. and the polymerization reaction was carried out for 1 hour, and then the polymerization slurry was cooled to room temperature.

  Into another 500 mL Erlenmeyer flask, 119.1 g (1.32 mol) of 80 mass% acrylic acid aqueous solution was charged, and 132.2 g (0.99 mol) of 30 mass% sodium hydroxide aqueous solution was dropped while cooling this. 75 mol% of acrylic acid was neutralized, and further 5.8 g of water, 2,4′-azobis (2-amidinopropane) dihydrochloride 0.14 g (0.00052 mol) and ethylene glycol diglycidyl ether 10.7 mg (0.000061 mol) was added to prepare a monomer aqueous solution for the second stage polymerization, and cooled using an ice water bath.

  After adding the entire amount of the monomer aqueous solution for the second stage polymerization to the polymerization slurry liquid, the system was again sufficiently replaced with nitrogen, and then the temperature was raised and the bath temperature was maintained at 70 ° C. The eye polymerization reaction was carried out for 2 hours. After completion of the polymerization, the mixture was heated in an oil bath at 120 ° C., and only water was removed from the system by azeotropic distillation to obtain a gel-like product. Next, 7.81 g (0.00089 mol) of a 2% by weight ethylene glycol diglycidyl ether aqueous solution as a post-crosslinking agent was added and mixed to carry out a post-crosslinking reaction, and water and n-heptane were removed by distillation and dried. 215.5 g of water-absorbing resin particles having a mass average particle diameter of 380 μm were obtained.

Example 2
In Example 1, the amount of 2,2′-azobis (2-amidinopropane) dihydrochloride used in the first stage monomer aqueous solution was changed from 0.11 g to 0.17 g (0.00063 mol). Except for changing the amount of 2,2′-azobis (2-amidinopropane) dihydrochloride used in the second-stage monomer aqueous solution from 0.14 g to 0.21 g (0.00077 mol) In the same manner as in Example 1, 214.7 g of water absorbent resin particles having a mass average particle diameter of 325 μm were obtained.

Example 3
In Example 1, the amount of 2,2′-azobis (2-amidinopropane) dihydrochloride used in the first-stage polymerization monomer aqueous solution was changed from 0.11 g to 0.06 g (0.00022 mol). Implementation was performed except that the amount of 2,2′-azobis (2-amidinopropane) dihydrochloride used in the second-stage monomer aqueous solution was changed from 0.14 g to 0.07 g (0.00026 mol). In the same manner as in Example 1, 215.1 g of water absorbent resin particles having a mass average particle diameter of 372 μm was obtained.

Example 4
In Example 1, the same method as in Example 1 except that the amount of the 2 mass% ethylene glycol diglycidyl ether aqueous solution used as the post-crosslinking agent was changed from 7.81 g to 15.83 g (0.00180 mol). As a result, 216.9 g of water-absorbing resin particles having a mass average particle diameter of 320 μm were obtained.

Example 5
In Example 1, the amount of ethylene glycol diglycidyl ether used in the first-stage polymerization monomer aqueous solution was changed from 8.3 mg to 18.4 mg (0.00011 mol) to the second-stage polymerization monomer aqueous solution. A water-absorbing agent having a mass average particle diameter of 313 μm was obtained in the same manner as in Example 1 except that the amount of ethylene glycol diglycidyl ether used in 1 was changed from 10.7 mg to 23.8 mg (0.00014 mol). 212.2 g of resin particles were obtained.

Example 6
In Example 1, 2,2′-azobis (2-amidinopropane) dihydrochloride used for the first and second stage polymerization initiators was converted to 2,2′-azobis [N- (2-carboxyethyl), respectively. ) -2-Methylpropionamidine] 219.3 g of water-absorbing resin particles having a mass average particle diameter of 390 μm were obtained in the same manner as in Example 1 except that the tetrahydrate was changed.

Example 7 (However, it is a reference example.)
A 2000 mL 5-neck cylindrical round bottom flask equipped with a stirrer, reflux condenser, dropping funnel, thermometer and nitrogen gas inlet tube was charged with 92 g (1.02 mol) of an 80% by weight acrylic acid aqueous solution, and this was externally added. Then, 102.2 g (0.77 mol) of a 30% by mass aqueous sodium hydroxide solution was added dropwise while cooling to neutralize 75 mol% of acrylic acid. Further, after 36.9 g of water and 0.11 g (0.00041 mol) of 2,2′-azobis (2-amidinopropane) dihydrochloride were added and dissolved under stirring, and the system was sufficiently substituted with nitrogen. The temperature was raised and the bath temperature was kept at 65 ° C., and the polymerization reaction was carried out for 1 hour. After completion of the polymerization, the mixture was heated in an oil bath at 120 ° C. to remove moisture from the system, and a gel-like product was obtained. Subsequently, 2.40 g (0.00039 mol) of a 2% by weight ethylene glycol diglycidyl ether aqueous solution was added and mixed to carry out a post-crosslinking reaction, and water was removed by distillation, followed by drying to obtain a massive water absorbent resin. It was. This was pulverized with a desktop mixer and then classified using a JIS standard sieve having an opening of 850 μm to obtain 112.8 g of water-absorbing resin particles having a mass average particle diameter of 356 μm.

Comparative Example 1
A 1000 mL five-necked cylindrical round bottom flask equipped with a stirrer, reflux condenser, dropping funnel, thermometer and nitrogen gas inlet tube is 340 g of n-heptane and sucrose fatty acid ester having an HLB of 3.0 (Mitsubishi Chemical) Trade name: S-370) 0.92 g was added, dispersed, heated and dissolved, and then cooled to 55 ° C.

  Separately, a 500 mL Erlenmeyer flask was charged with 92 g (1.02 mol) of an 80% by weight aqueous acrylic acid solution, and 102.2 g (0.77%) of a 30% by weight aqueous sodium hydroxide solution was cooled from the outside. Mol) was added dropwise to neutralize 75 mol% of acrylic acid. Furthermore, 36.9 g of water, 0.11 g (0.00041 mol) of potassium persulfate as a water-soluble radical polymerization initiator and 8.3 mg (0.000048 mol) of ethylene glycol diglycidyl ether as an internal cross-linking agent were added. A monomer aqueous solution for stage polymerization was prepared.

  The monomer aqueous solution for the first stage polymerization is added to and dispersed in the five-necked cylindrical round bottom flask with stirring, and the system is sufficiently replaced with nitrogen. Was kept at 70 ° C. and the polymerization reaction was carried out for 1 hour, and then the polymerization slurry was cooled to room temperature.

  Into another 500 mL Erlenmeyer flask, 119.1 g (1.32 mol) of 80 mass% acrylic acid aqueous solution was charged, and 132.2 g (0.99 mol) of 30 mass% sodium hydroxide aqueous solution was dropped while cooling this. Then, 75 mol% of acrylic acid was neutralized, and 5.8 g of water, 0.14 g (0.00052 mol) of potassium persulfate and 10.7 mg (0.000061 mol) of ethylene glycol diglycidyl ether were added. A monomer aqueous solution for the second stage polymerization was prepared and cooled using an ice water bath.

  After adding the entire amount of the monomer aqueous solution for the second stage polymerization to the polymerization slurry liquid, the system was again sufficiently replaced with nitrogen, and then the temperature was raised and the bath temperature was maintained at 70 ° C. The eye polymerization reaction was carried out for 2 hours. After completion of the polymerization, the mixture was heated in an oil bath at 120 ° C., and only water was removed from the system by azeotropic distillation to obtain a gel-like product. Subsequently, 7.81 g (0.00089 mol) of a 2% by weight ethylene glycol diglycidyl ether aqueous solution was added and mixed as a post-crosslinking agent, followed by post-crosslinking treatment, and further, moisture and n-heptane were removed by distillation and dried. 214.5 g of water-absorbing resin particles having a mass average particle diameter of 345 μm were obtained.

Comparative Example 2
A 1000 mL five-necked cylindrical round bottom flask equipped with a stirrer, reflux condenser, dropping funnel, thermometer and nitrogen gas inlet tube is 340 g of n-heptane and sucrose fatty acid ester having an HLB of 3.0 (Mitsubishi Chemical) Trade name: S-370) 0.92 g was added, dispersed, heated and dissolved, and then cooled to 55 ° C.

  Separately, a 500 mL Erlenmeyer flask was charged with 92 g (1.02 mol) of an 80% by weight aqueous acrylic acid solution, and 102.2 g (0.77%) of a 30% by weight aqueous sodium hydroxide solution was cooled from the outside. Mol) was added dropwise to neutralize 75 mol% of acrylic acid. Further, 36.9 g of water and 0.11 g (0.00041 mol) of 2,2′-azobis (2-amidinopropane) dihydrochloride as a water-soluble azo polymerization initiator were added, and a single unit for the first stage polymerization was added. A meter aqueous solution was prepared.

  The monomer aqueous solution for the first stage polymerization is added to and dispersed in the five-necked cylindrical round bottom flask with stirring, and the system is sufficiently replaced with nitrogen. Was kept at 70 ° C. and the polymerization reaction was carried out for 1 hour, and then the polymerization slurry was cooled to room temperature.

  Into another 500 mL Erlenmeyer flask, 119.1 g (1.32 mol) of 80 mass% acrylic acid aqueous solution was charged, and 132.2 g (0.99 mol) of 30 mass% sodium hydroxide aqueous solution was dropped while cooling this. Then, 75 mol% of acrylic acid was neutralized, and further 5.8 g of water and 0.14 g (0.00052 mol) of 2,2′-azobis (2-amidinopropane) dihydrochloride were added. A monomer aqueous solution for eye polymerization was prepared and cooled using an ice water bath.

  After adding the entire amount of the monomer aqueous solution for the second stage polymerization to the polymerization slurry liquid, the system was again sufficiently replaced with nitrogen, and then the temperature was raised and the bath temperature was maintained at 70 ° C. The eye polymerization reaction was carried out for 2 hours. After completion of the polymerization, the mixture was heated in an oil bath at 120 ° C., and only water was removed from the system by azeotropic distillation to obtain a gel-like product. Next, 7.81 g (0.00089 mol) of a 2% by weight ethylene glycol diglycidyl ether aqueous solution as a post-crosslinking agent was added and mixed to carry out a post-crosslinking reaction, and water and n-heptane were removed by distillation and dried. Thus, 213.7 g of water-absorbing resin particles having a mass average particle diameter of 367 μm were obtained.

Comparative Example 3
A 1000 mL five-necked cylindrical round bottom flask equipped with a stirrer, reflux condenser, dropping funnel, thermometer and nitrogen gas inlet tube is 340 g of n-heptane and sucrose fatty acid ester having an HLB of 3.0 (Mitsubishi Chemical) Trade name: S-370) 0.92 g was added, dispersed, heated and dissolved, and then cooled to 55 ° C.

  Separately, a 500 mL Erlenmeyer flask was charged with 92 g (1.02 mol) of an 80% by weight aqueous acrylic acid solution, and 102.2 g (0.77%) of a 30% by weight aqueous sodium hydroxide solution was cooled from the outside. Mol) was added dropwise to neutralize 75 mol% of acrylic acid. Further, 36.9 g of water, 0.11 g (0.00041 mol) of 2,2′-azobis (2-amidinopropane) dihydrochloride as a water-soluble azo polymerization initiator, and ethylene glycol diglycidyl ether 8 as an internal crosslinking agent .3 mg (0.000048 mol) was added to prepare an aqueous monomer solution for the first stage polymerization.

  The monomer aqueous solution for the first stage polymerization is added to and dispersed in the five-necked cylindrical round bottom flask with stirring, and the system is sufficiently replaced with nitrogen. Was kept at 70 ° C. and the polymerization reaction was carried out for 1 hour, and then the polymerization slurry was cooled to room temperature.

  Into another 500 mL Erlenmeyer flask, 119.1 g (1.32 mol) of 80 mass% acrylic acid aqueous solution was charged, and 132.2 g (0.99 mol) of 30 mass% sodium hydroxide aqueous solution was dropped while cooling this. 75 mol% of acrylic acid was neutralized, and further 5.8 g of water, 2,4′-azobis (2-amidinopropane) dihydrochloride 0.14 g (0.00052 mol) and ethylene glycol diglycidyl ether 10.7 mg (0.000061 mol) was added to prepare a monomer aqueous solution for the second stage polymerization, and cooled using an ice water bath.

  After adding the entire amount of the monomer aqueous solution for the second stage polymerization to the polymerization slurry liquid, the system was again sufficiently replaced with nitrogen, and then the temperature was raised and the bath temperature was maintained at 70 ° C. The eye polymerization reaction was carried out for 2 hours. After completion of the polymerization, the mixture was heated in an oil bath at 120 ° C., and only water was removed from the system by azeotropic distillation to obtain a gel-like product. Subsequently, moisture and n-heptane were removed by distillation and dried to obtain 213.8 g of water absorbent resin particles having a mass average particle diameter of 383 μm.

Comparative Example 4
A 1000 mL five-necked cylindrical round bottom flask equipped with a stirrer, reflux condenser, dropping funnel, thermometer and nitrogen gas inlet tube is 340 g of n-heptane and sucrose fatty acid ester having an HLB of 3.0 (Mitsubishi Chemical) Trade name: S-370) 0.92 g was added, dispersed, heated and dissolved, and then cooled to 55 ° C.

  Separately, a 500 mL Erlenmeyer flask was charged with 92 g (1.02 mol) of an 80% by weight aqueous acrylic acid solution, and 102.2 g (0.77%) of a 30% by weight aqueous sodium hydroxide solution was cooled from the outside. Mol) was added dropwise to neutralize 75 mol% of acrylic acid. Further, 36.9 g of water, 0.12 g (0.00041 mol) of 2,2′-azobis (2-amidinopropane) dihydrochloride as a water-soluble azo polymerization initiator, and N, N ′ as a copolymerizable crosslinking agent -8.3 mg (0.000054 mol) of methylenebisacrylamide was added to prepare a monomer aqueous solution for the first stage polymerization.

  The monomer aqueous solution for the first stage polymerization is added to and dispersed in the five-necked cylindrical round bottom flask with stirring, and the system is sufficiently replaced with nitrogen. Was kept at 70 ° C. and the polymerization reaction was carried out for 1 hour, and then the polymerization slurry was cooled to room temperature.

  Into another 500 mL Erlenmeyer flask, 119.1 g (1.32 mol) of 80 mass% acrylic acid aqueous solution was charged, and 132.2 g (0.99 mol) of 30 mass% sodium hydroxide aqueous solution was dropped while cooling this. Then, 75 mol% of acrylic acid was neutralized, and further 5.8 g of water, 0.14 g (0.00052 mol) of 2,2′-azobis (2-amidinopropane) dihydrochloride and N, N′— 10.7 mg (0.000069 mol) of methylenebisacrylamide was added to prepare a monomer aqueous solution for the second stage polymerization, and the mixture was cooled using an ice water bath.

  After adding the entire amount of the monomer aqueous solution for the second stage polymerization to the polymerization slurry liquid, the system was again sufficiently replaced with nitrogen, and then the temperature was raised and the bath temperature was maintained at 70 ° C. The eye polymerization reaction was carried out for 2 hours. After completion of the polymerization, the mixture was heated in an oil bath at 120 ° C., and only water was removed from the system by azeotropic distillation to obtain a gel-like product. Next, 7.81 g (0.00101 mol) of a 2% by weight N, N′-methylenebisacrylamide aqueous solution as a post-crosslinking agent was added and mixed to carry out a post-crosslinking reaction, and water and n-heptane were removed by distillation. And dried to obtain 214.5 g of water absorbent resin particles having a mass average particle diameter of 350 μm.

  Next, the water-absorbent resin particles obtained in Examples 1 to 7 and Comparative Examples 1 to 4 were subjected to various tests shown below. The results are shown in Table 1.

(1) Mass average particle diameter 100 g of water-absorbent resin particles were weighed, and this was replaced with eight standard sieves corresponding to JIS-Z8801-1982 (openings 850 μm, 500 μm, 355 μm, 300 μm, 250 μm, 180 μm, 106 μm, and the order of the bottom container) Particles that are accumulated in the uppermost sieve), vibrated for 10 minutes using a low-tap type sieve vibrator, sieved, and weighed for each sieve. Based on the result, the total mass was 50% by mass. The diameter was calculated by the following formula.

  Mass average particle diameter = [(50−A) / (D−A)] × (C−B) + B

  In the formula, A is the cumulative value (g) in the case where the mass is sequentially accumulated from the coarser particle size distribution, and the cumulative mass is less than 50 mass% and the integral value at the point closest to 50 mass% is obtained. In addition, B is a sieve opening (μm) when the integrated value is obtained. D is the integrated value (g) in the case where the integrated mass is sequentially calculated from the coarser particle size distribution and the integrated mass is 50% by mass or more and the integrated value at the point closest to 50% by mass is obtained. Yes, and C is the sieve opening (μm) when the integrated value is obtained.

(2) Saline water absorption rate In a 100 mL beaker, weigh 50 ± 0.01 g of 25 ± 0.2 ° C. physiological saline, and put a magnetic stirrer bar (no ring of 8 mmφ × 30 mm). It placed on a magnetic stirrer (manufactured by uchi, product number: HS-30D). Subsequently, the magnetic stirrer bar was adjusted to rotate at 600 ppm, and the bottom of the vortex generated by the rotation of the magnetic stirrer bar was adjusted to be close to the top of the magnetic stirrer bar.

  Next, 2.0 ± 0.002 g of water-absorbing resin particles classified to 300 to 500 μm using a JIS standard sieve was quickly poured between the center of the vortex in the beaker and the side surface of the beaker, and the vortex converged from the time of pouring. The time (seconds) until the time point was measured using a stopwatch and was defined as the water absorption rate.

(3) Water retention ability of physiological saline 2.0 g of water-absorbing resin particles were weighed into a cotton bag (Membroroad No. 60, width 100 mm × length 200 mm) and placed in a 500 mL beaker. Pour 500 g of physiological saline into a cotton bag at a time and disperse the saline so that no water-absorbent resin particles are generated. Then, bind the upper part of the cotton bag with a rubber band and let it stand for 1 hour. Was sufficiently swollen. The weight Wa of the cotton bag containing the swollen gel after dehydration by dehydrating the cotton bag for 1 minute using a dehydrator (manufactured by Kokusan Centrifuge Co., Ltd., product number: H-122) set to have a centrifugal force of 167G (G) was measured. The same operation was performed without adding water-absorbent resin particles, the wet hourly space mass Wb (g) of the cotton bag was measured, and the water retention capacity was calculated from the following equation.

  Water retention capacity of physiological saline (g / g) = [Wa-Wb] (g) / mass of water-absorbent resin particles (g)

(4) Saline water absorption capacity under 4.14 kPa load The physiological water absorption capacity 60 minutes after the start of water absorption of the water-absorbent resin particles under a load of 4.14 kPa is shown in FIG. X was used.

  The measuring apparatus X shown in FIG. 1 includes a burette unit 1, a conduit 2, a measuring table 3, and a measuring unit 4 placed on the measuring table 3. The burette unit 1 has a rubber stopper 14 connected to the upper part of the burette 10, an intake introduction pipe 11 and a cock 12 connected to the lower part, and an upper part of the intake introduction pipe 11 has a cock 13. A conduit 2 is attached from the burette part 1 to the measuring table 3, and the diameter of the conduit 2 is 6 mm. A hole with a diameter of 2 mm is formed at the center of the measuring table 3 and the conduit 2 is connected thereto. The measuring unit 4 includes a cylinder 40, a nylon mesh 41 attached to the bottom of the cylinder 40, and a weight 42. The inner diameter of the cylinder 40 is 2.0 cm. The nylon mesh 41 is formed to 200 mesh (aperture 75 μm). A predetermined amount of the water-absorbing resin particles 5 is uniformly distributed on the nylon mesh 41. The weight 42 has a diameter of 1.9 cm and a mass of 119.6 g. The weight is placed on the water absorbent resin particles 5 so that a load of 4.14 kPa can be applied to the water absorbent resin particles 5.

  In the measuring apparatus X having such a configuration, the cock 12 of the burette 10 and the cock 13 of the air introduction pipe 11 are first closed, and a predetermined amount of physiological saline adjusted to 25 ° C. is introduced from the upper part of the burette 10, and the rubber plug 14 is used. After plugging the top of the burette, the cock 12 of the burette 10 and the cock 13 of the air introduction pipe 11 are opened. Next, the height of the measurement table 3 is adjusted so that the upper surface of the measurement table 3 and the surface of the physiological saline solution coming out from the conduit port at the center of the measurement table 3 have the same height.

  On the other hand, 0.1 g of water absorbent resin 5 particles are uniformly spread on the nylon mesh 41 of the cylinder 40, and a weight 42 is placed on the water absorbent resin particle 5. The measuring part 4 is placed so that the center part thereof coincides with the conduit port of the central part of the measuring table 3.

  From the time when the water-absorbing resin particles 5 start to absorb water, the decrease amount of physiological saline in the burette 10 (the amount of physiological saline absorbed by the water-absorbing resin 5) Wc (ml) is read. The water absorption capacity under the load of the water absorbent resin particles 5 after 60 minutes from the start of water absorption was determined by the following equation.

  4. Saline water absorption capacity under load of 14 kPa (ml / g) = Wc ÷ 0.10

(5) Water-soluble matter In a 500 mL beaker, 500 ± 0.01 g of physiological saline is weighed, and a magnetic stirrer bar (without 8 mmφ × 30 mm ring) is put in. A magnetic stirrer (manufactured by Iuchi: HS) -30D). Subsequently, the magnetic stirrer bar was adjusted to rotate at 600 rpm, and the bottom of the vortex generated by the rotation of the magnetic stirrer bar was adjusted to be close to the top of the magnetic stirrer bar.

  Next, 2.0 ± 0.002 g of water-absorbing resin particles classified to 300 to 500 μm using a JIS standard sieve was quickly poured and dispersed between the center of the vortex in the beaker and the side of the beaker, and stirred for 3 hours. The water-absorbent resin particle-dispersed water after stirring for 3 hours was filtered with a JIS standard sieve (aperture 75 μm), and the obtained filtrate was further filtered with suction using a Kiriyama funnel (filter paper No. 6).

  80 ± 0.01 g of the filtrate obtained in a 100 mL beaker previously dried at 140 ° C. and cooled to room temperature was weighed and constant in a hot air dryer (ADVANTEC) with the internal temperature set at 140 ° C. And the mass Wd (g) of the solid content of the filtrate was measured.

  On the other hand, it carried out similarly to the said operation, without using a water-absorbent resin particle | grain, measured blank mass We (g), and computed the water-soluble content from following Formula.

  Water-soluble content (mass%) = [(Wd−We) × (500/80)] / 2 × 100

Example 8
A mixture obtained by dry-mixing 10 g of the water-absorbent resin particles obtained in Example 1 and 10 g of pulverized pulp using a mixer onto a tissue having a size of 40 cm × 12 cm and a weight of 0.6 g, is the same size. And hygiene material was obtained by putting the tissue of the weight into a sheet shape, applying a load of 196 kPa to the whole for 30 seconds and pressing it. By sandwiching the obtained sanitary material between a polyethylene air-through porous liquid permeable sheet having a size of 40 cm × 12 cm and a basis weight of 22 g / cm ^{2 and} a polyethylene impermeable sheet having the same size and a weight of 1 g. A sanitary material having a water absorbent resin concentration of 50% by mass was obtained.

Examples 9-14 and Comparative Examples 5-8
In Example 8, it replaced with the water absorbing resin obtained in Example 1, and replaced with the water absorbing resin particle obtained in Examples 2-7 and Comparative Examples 1-4, respectively, and was the same as that of Example 8. Operation was performed to obtain a sanitary material. The obtained sanitary materials were used as sanitary materials in Examples 9 to 14 and Comparative Examples 5 to 8, respectively.

  Next, the sanitary materials obtained in Examples 8 to 14 and Comparative Examples 5 to 8 were evaluated according to the following methods. The results are shown in Table 2.

(A) Preparation of artificial urine In a 10 L container, 60 g of sodium chloride, 1.8 g of calcium chloride dihydrate, 3.6 g of magnesium chloride hexahydrate and an appropriate amount of distilled water were added and completely dissolved. Next, 0.02 g of polyoxyethylene nonylphenyl ether was added, and distilled water was further added to adjust the total mass of the aqueous solution to 6000 g. Furthermore, it was colored with a small amount of blue No. 1 to obtain artificial urine.

(B) Penetration rate Penetration rate is measured by using a cylinder with a diameter of 3 cm in the vicinity of the center of the sanitary material and pouring 50 ml of artificial urine and simultaneously starting a stopwatch so that the artificial urine completely penetrates the sanitary material. This was done by measuring the time until (first time). Next, remove the cylinder and store the sanitary material as it is, and after 30 minutes from the start of the first artificial urine injection, place the cylinder in the same position again, pour 50 ml of artificial urine and start the stopwatch. The time (second) until the artificial urine completely penetrates the sanitary material was measured (second time). Furthermore, the penetration rate was measured up to the third time in the same manner.

(C) Reversal amount 60 minutes after the completion of the measurement of the permeation rate, filter paper (Toyo filter paper No. 2) cut to 10 cm × 10 cm was overlapped to obtain about 80 g, and the dry mass (g) was measured. Place the filter paper in the center of the sanitary material, place a 5 kg weight (bottom area = 10 cm x 10 cm) on top of the filter paper, apply a load for 5 minutes, remove the weight, and absorb the return liquid mass (g) Was measured. The return amount (g) was calculated by subtracting the dry weight (g) of the filter paper from the weight (g) of the filter paper that absorbed the return solution.

(D) Diffusion length The longitudinal dimension (cm) of the sanitary material into which the artificial urine penetrated was measured within 5 minutes after the measurement of the amount of reversion. The numbers after the decimal point are rounded off.

  From Table 1, it can be seen that the water-absorbent resin particles obtained in each Example have a high water-retaining ability, a high water-absorbing ability under load, an excellent water-absorbing speed, and a small amount of water-soluble matter. Furthermore, as shown in Table 2, it can be seen that the use of such water-absorbing resin particles makes it possible to provide a sanitary material that has excellent liquid diffusibility and a small amount of reversion.

It is a schematic block diagram which shows schematic structure of the apparatus for measuring the water absorption ability under load.

Explanation of symbols

X measuring device Bullet section 10. Bullet (of the bullet part)
11. Air inlet pipe (for burette)
12 Cook (burette 10)
13. Cock (for air inlet tube 11)
14 Rubber stopper (for burette 10)
2. 2. Conduit Measuring table 4. Measurement unit 40. Cylindrical (measurement part)
41. Nylon mesh (for measuring part)
42. Weight (measurement part)
5. Water absorbent resin particles

Claims (9)

A method for producing a water-absorbent resin by polymerizing a water-soluble ethylenically unsaturated monomer, wherein a water-soluble azo radical polymerization initiator is used in the presence of a polyvalent glycidyl compound as an internal cross-linking agent. A method for producing water-absorbent resin particles, wherein the obtained water-absorbent resin is post-crosslinked with a post-crosslinking agent after three-stage reversed-phase suspension polymerization (polymerization in the presence of alkoxy titanium) Except in cases) .   The production method according to claim 1, wherein the polyvalent glycidyl compound is at least one selected from (poly) ethylene glycol diglycidyl ether, (poly) propylene glycol diglycidyl ether and (poly) glycerin diglycidyl ether.   The production method according to claim 1 or 2, wherein the amount of the polyvalent glycidyl compound used is 0.000001 to 0.001 mol per mol of the water-soluble ethylenically unsaturated monomer.   Water-soluble azo radical polymerization initiator is 2,2′-azobis (2-amidinopropane) dihydrochloride, 2,2′-azobis (N- (2-carboxyethyl) -2-methylpropionamidine) tetrahydrate The compound is at least one selected from a hydrate and 2,2′-azobis {2- [1- (2-hydroxyethyl) -2-imidazolin-2-yl] propane} dihydrochloride. The manufacturing method of any one of these.   The production according to any one of claims 1 to 4, wherein the amount of the water-soluble azo radical polymerization initiator used is 0.00005 to 0.001 mol per mol of the water-soluble ethylenically unsaturated monomer. Method.   The manufacturing method of any one of Claims 1-5 whose post-crosslinking agent is a polyvalent glycidyl compound.   The usage-amount of a post-crosslinking agent is 0.00001-0.01 mol per 1 mol total amount of the water-soluble ethylenically unsaturated monomer attached | subjected to superposition | polymerization, It is any one of Claims 1-6. Manufacturing method. Water-absorbent resin particles satisfying the following performance obtained by the production method according to claim 1.
Saline water absorption rate: within 60 seconds Saline retention capacity: 40-60 g / g
4. Saline water absorption capacity under 14 kPa load: 15 ml / g or more Water soluble content: 20 mass% or less Mass average particle size: 200-600 μm   A sanitary material comprising the water-absorbent resin particles according to claim 8 and hydrophilic fibers.

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