JP2009074025A - Method for producing water-absorbing resin - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a water-absorbing resin with high water absorption speed, in view of the fact that water-absorbing resins produced by conventional production methods are insufficient with respect to water-absorbing capacity, particularly to water absorption speed. <P>SOLUTION: The method for producing a water-absorbing resin consisting of a crosslinked polymer (A) obtained from a (meth)acrylic acid (salt) and a crosslinking agent (b) is provided, being characterized by that the reaction of forming (A) the crosslinked polymer is conducted in the presence of at least one foaming agent (B), which generates a gas under heating, selected from the group consisting of a sulfonyl hydrazide compound (B1) and/or a nitroso compound (B2). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing a water absorbent resin.

Conventionally, in order to improve the water absorption capacity of water-absorbent resin, especially to improve the water-absorption rate, a production method that increases the cross-linking density of the particle surface has been proposed to prevent gel blocking between water-absorbent resin particles and increase liquid permeability. (Patent Document 1). Moreover, in order to enlarge the surface area of a water-absorbent resin particle, the manufacturing method to granulate is proposed (patent document 2). Furthermore, a production method in which water-absorbent resin particles are foamed and made porous has been proposed (Patent Documents 3 and 4).
JP 57-44627 A International Publication No. 93/24153 Pamphlet International Publication No. 96/17884 Pamphlet JP-T 9-507085

  However, the water-absorbing resin obtained by these production methods cannot satisfy the absorptivity, particularly the absorption rate. An object of this invention is to provide the manufacturing method of the water absorbing resin excellent in the absorption rate.

  The method for producing a water-absorbent resin of the present invention is a method for producing a water-absorbent resin comprising a crosslinked polymer (A) formed from (meth) acrylic acid (salt) and a crosslinking agent (b). The gist is that the formation reaction is performed in the presence of at least one blowing agent (B) that generates gas by heating, selected from the group consisting of the sulfonyl hydrazide compound (B1) and / or the nitroso compound (B2). .

  The production method of the present invention can produce a water-absorbent resin that is extremely excellent in the absorption rate of water, saline, and the like.

In the present invention, (meth) acrylic acid means acrylic acid and / or methacrylic acid, and "... acid (salt)" means "... acid" and / or "... acid salt". Means. Examples of the salt include alkali metal salts such as potassium, sodium and lithium, alkaline earth metal salts such as calcium, and onium salts.
As the onium salt, those described in JP-A Nos. 2003-251178 and 2005-95357 can be used, and examples of the onium cation include a quaternary ammonium cation (I) and a tertiary phosphonium cation ( II), quaternary phosphonium cation (III), tertiary oxonium cation (IV), alkylpyridinium cation (V), ammonium cation (VI) excluding quaternary ammonium cation (hereinafter referred to as cation) Is omitted).

  The quaternary ammonium (I) includes an aliphatic quaternary ammonium (I1) having 4 to 30 or more carbon atoms having an alkyl and / or alkenyl group, an aromatic quaternary having 9 to 30 or more carbon atoms. Quaternary ammonium (I2), alicyclic quaternary ammonium (I3) having 6 to 30 or more carbon atoms, imidazolinium (I4) having 6 to 30 or more carbon atoms, 5 to 30 or more carbon atoms Of imidazolium (I5), tetrahydropyrimidinium having 6 to 30 or more carbon atoms (substituents may be combined to form a bicyclo ring), (I6), 6 to 30 or more carbon atoms Dihydropyrimidinium (I7) and guanidinium (I8) having an imidazolinium skeleton having 8 to 30 or more carbon atoms.

  Examples of the aliphatic quaternary ammonium (I1) having 4 to 30 or more carbon atoms having an alkyl and / or alkenyl group include tetramethylammonium, tetraethylammonium, trimethylpropylammonium, dimethylpropylammonium and the like.

  Examples of the aromatic quaternary ammonium (I2) having 9 to 30 or more carbon atoms include trimethylphenylammonium, triethylphenylammonium, benzyltrimethylammonium and the like.

  Examples of the alicyclic quaternary ammonium (I3) having 6 to 30 or more carbon atoms include N, N-dimethylpyrrolidinium, N, N-diethylpyrrolidinium, N, N dimethylmorpholinium and the like. It is done.

  Examples of the imidazolinium (I4) having 6 to 30 or more carbon atoms include 1,2,3-trimethylimidazolinium, 1,2,3,4-tetramethylimidazolinium and the like.

  Examples of the imidazolium (I5) having 5 to 30 or more carbon atoms include 1,3-dimethylimidazolium, 1,2,3-trimethylimidazolium, 1,2,3,4-tetramethylimidazolium and the like. It is done.

  Tetrahydropyrimidinium having 6 to 30 or more carbon atoms (a substituent may be bonded to form a bicyclo ring) (I6) includes 1,3-dimethyltetrahydropyridinium, 1,2,3- Examples thereof include trimethyltetrahydropyridinium, 1,2,3,4-tetramethyltetrahydropyridinium and the like.

  As dihydropyrimidinium (I7) having 6 to 30 or more carbon atoms, 1,3-dimethyl-2,4- or -2,6-dihydropyrimidinium [these are 1,3-dimethyl-2, This is expressed as 4, (6) -dihydropyrimidinium, and the same expression is used hereinafter. 1,2,3-trimethyl-2,4, (6) -dihydropyrimidinium, 1,2,3,4-tetramethyl-2,4, (6) -dihydropyrimidinium and the like. .

  Examples of guanidinium (I8) having an imidazolinium skeleton having 8 to 30 or more carbon atoms include 2-dimethylamino-1,3,4-trimethylimidazolinium and 2-diethylamino-1,3,4-trimethylimidazole. Examples include linium.

Examples of the ammonium cation (VI) excluding the quaternary ammonium cation include tertiary ammonium (VI1), secondary ammonium (VI2), primary ammonium (VI3), and ammonium cation (VI4).
Examples of tertiary ammonium (VI1) include alkylammonium (trimethylammonium, triethylammonium, etc.), alkanol ammonium (trimethanolammonium, triethanolammonium, etc.), pyridinium, and the like.
Secondary ammonium (VI2) includes alkylammonium (dimethylammonium, diethylammonium, etc.) and alkanolammonium (dimethanolammonium, diethanolammonium, etc.).
Examples of the primary ammonium (VI3) include alkyl ammonium (monomethyl ammonium, monoethyl ammonium, etc.) and alkanol ammonium (monomethanol ammonium, monoethanol ammonium, etc.).

  Among these, the preferred onium cation is (I), and more preferably (I1), (I4) and (I5). These onium cations may be used alone or in combination of two or more.

Content of (meth) acrylic acid (salt) is 99.0-99 with respect to the total weight of (meth) acrylic acid (salt) and a crosslinking agent (b) from a viewpoint of the absorptivity of a water absorbing resin. It is preferably 0.95% by weight, more preferably 99.2 to 99.90% by weight, and particularly preferably 99.4 to 99.85% by weight.
The molar ratio ((meth) acrylic acid: (meth) acrylate) of (meth) acrylic acid to (meth) acrylate is 70:30 to 0: 100 from the viewpoint of the absorption capacity of the water absorbent resin. It is preferably 60:40 to 5:95, more preferably 50:50 to 10: 90% by weight.

  The crosslinking agent (b) includes at least two polymerizable double bonds and a crosslinking agent (b1) having no functional group having reactivity with a carboxyl group, at least one polymerizable double bond, A crosslinking agent (b2) having a functional group reactive with at least one carboxyl group and a crosslinking agent having a functional group reactive with at least two carboxyl groups without having a polymerizable double bond ( b3).

  Examples of the polymerizable double bond include an acryloyl group, an allyl ether group, and a vinyl ether group. The functional group having reactivity with a carboxyl group is a functional group that reacts with a carboxyl group to form an ester bond or an amide bond, and examples thereof include a hydroxyl group, an epoxy group, and an amino group.

  As the crosslinking agent (b1), a crosslinking agent (b11) having two or more (meth) acryloyl groups, a crosslinking agent (b12) having two or more vinyl ether groups, and a crosslinking agent having two or more allyl ether groups (B13) etc. are mentioned. These crosslinking agents may be used alone or in combination of two or more.

Examples of the crosslinking agent (b11) include N, N′-methylenebisacrylamide, ethylene glycol di (meth) acrylate, trimethylolpropane di (meth) acrylate, trimethylolpropane tri (meth) acrylate, and pentaerythritol di (meth). ) Copolymerizable cross-linking agents having 2 to 10 acryloyl groups in the molecule such as acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate and polyglycerin (degree of polymerization 3 to 13) polyacrylate Can be mentioned.
Among the crosslinking agents (b11), N, N′-methylenebisacrylamide, ethylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, and pentaerythritol tri (meth) are used from the viewpoint of the absorbability of the water absorbent resin. Acrylates are preferred, more preferably N, N′-methylenebisacrylamide, ethylene glycol di (meth) acrylate and trimethylolpropane tri (meth) acrylate, particularly preferably N, N′-methylenebisacrylamide and trimethylolpropane tri ( (Meth) acrylate.

  Examples of the crosslinking agent (b12) include ethylene glycol divinyl ether, 1,4-butanediol divinyl ether, 1,4-cyclohexanedimethanol divinyl ether, 1,6-hexanediol divinyl ether, polyethylene glycol divinyl ether (degree of polymerization of 2 5), bisphenol A divinyl ether, pentaerythritol trivinyl ether, sorbitol trivinyl ether, polyglycerol (degree of polymerization 3 to 13) polyvinyl ether and the like.

  As the crosslinking agent (b13), there are two allyl ether groups in the molecule and no hydroxyl group, and 3-10 allyl ether groups in the molecule and no hydroxyl group. A crosslinking agent (b132) etc. are mentioned.

As the crosslinking agent (b131) having two allyl ether groups in the molecule and having no hydroxyl group, diallyl ether, 1,4-cyclohexanedimethanol diallyl ether, alkylene (2 to 5 carbon atoms) glycol diallyl ether, And polyethylene glycol (weight average molecular weight: 100 to 4000) diallyl ether and the like.
Examples of the cross-linking agent (b132) having 3 to 10 allyl groups in the molecule and having no hydroxyl group include trimethylolpropane triallyl ether, glyceryl triallyl ether, pentaerythritol tetraallyl ether, and tetraallyloxyethane. Can be mentioned.

Examples of the crosslinking agent (b2) having at least one polymerizable double bond and at least one functional group having reactivity with a carboxyl group include JP-A-1-103615 and JP-A-2000-26510. Can be used, and examples thereof include a crosslinking agent (b21) having a nonionic group and a crosslinking agent (b22) having a cationic group. These crosslinking agents may be used alone or in combination of two or more.
As the crosslinking agent (b21), a crosslinking agent (b211) having 2 allyl groups and 1 to 5 hydroxyl groups in the molecule, 3 to 10 allyl groups in the molecule and 1 to 3 hydroxyl groups. Cross-linking agent (b212) having one, cross-linking agent (b213) having no allyl group in the molecule and having a hydroxyl group {N-methylol (meth) acrylamide, etc.} and hydroxyethyl (meth) acrylate, and allyl group in the molecule And a crosslinking agent (b214) having no epoxy and having an epoxy group, such as {glycidyl (meth) acrylate}.

As a crosslinking agent (b211) having two allyl groups and 1 to 5 hydroxyl groups in the molecule, glycerin diallyl ether, trimethylolpropane diallyl ether, pentaerythritol diallyl ether, polyglycerin (degree of polymerization: 2 to 5) Examples include diallyl ether.
As the crosslinking agent (b212) having 3 to 10 allyl groups and 1 to 3 hydroxyl groups in the molecule, pentaerythritol triallyl ether and diglyceryl triallyl ether, sorbitol triallyl ether, polyglycerol (degree of polymerization) 3-13) and polyallyl ether.
Examples of the crosslinking agent (b213) having no allyl group in the molecule and having a hydroxyl group include N-methylol (meth) acrylamide and hydroxyethyl (meth) acrylate.
A glycidyl (meth) acrylate etc. are mentioned as a crosslinking agent (b214) which does not have an allyl group in a molecule | numerator and has an epoxy group.

  As the crosslinking agent (b22), a crosslinking agent having a quaternary ammonium salt {N, N, N-trimethyl-N- (meth) acryloyloxyethylammonium salt (carbonate, carboxylate, etc.) and N, N , N-triethyl-N- (meth) acryloyloxyethylammonium salt (carbonate, carboxylate, etc.)} and a cross-linking agent having a tertiary amino group {dimethylaminoethyl (meth) acrylate and (meth) And diethylaminoethyl acrylate}.

  The crosslinking agent (b2) is preferably (b21), more preferably (b211) and (b212), more preferably (b212), particularly preferably an allyl group of 3 to 3, from the viewpoint of the absorbability of the water absorbent resin. A crosslinking agent having 5 and 1 to 3 hydroxyl groups, most preferably pentaerythritol triallyl ether and sorbitol triallyl ether.

Examples of the crosslinking agent (b3) having no polymerizable double bond and having a functional group reactive with at least two carboxyl groups are described in JP-A-1-103615 and JP-A-2000-26510. Can be used. Examples thereof include a polyvalent glycidyl compound (b31), a polyvalent isocyanate compound (b32), a polyvalent amine compound (b33), and a polyhydric alcohol compound (b34). These crosslinking agents may be used alone or in combination of two or more.
Examples of the polyvalent glycidyl compound (b31) include ethylene glycol diglycidyl ether, glycerin diglycidyl ether, and sorbitol polyglycidyl ether.
Examples of the polyvalent isocyanate compound (b32) include 4,4′-diphenylmethane diisocyanate.
Examples of the polyvalent amine compound (b33) include ethylenediamine.
Examples of the polyhydric alcohol compound (b34) include (poly) alkylene glycol, glycerin and sorbitol.
Of the crosslinking agent (b3), the polyvalent glycidyl compound (b31) is preferable, and ethylene glycol diglycidyl ether is more preferable.
When the cross-linking agent (b3) is used, it is general that the cross-linking reaction proceeds by heating at 100 to 230 ° C., more preferably 120 to 160 ° C. at any stage after the addition of the cross-linking agent. Further, the crosslinking agent (b3) may be used in combination of two or more in a predetermined amount range, and further in combination with (b1) and (b2).

  (B) is preferably (b1) and (b3), more preferably (b11), (b13) and (b3) from the viewpoint of the absorbability of the water absorbent resin. These crosslinking agents may be used alone or in combination of two or more.

  The ratio of the crosslinking agent (b) constituting the crosslinked polymer (A) is from the viewpoint of the absorbent capacity of the water-absorbent resin to a value of 0. 0 to the total weight of (meth) acrylic acid (salt) and (b). The content is preferably 0.5 to 1% by weight, more preferably 0.1 to 0.8% by weight, and particularly preferably 0.1 to 0.6% by weight.

In the present invention, other ethylenically unsaturated monomers (a) can be used as long as they can be copolymerized with (meth) acrylic acid (salt). The other ethylenically unsaturated monomer (a) is not particularly limited as long as it is copolymerizable with (meth) acrylic acid (salt), but is preferably water-soluble.
Other unsaturated monomers (a) include carboxylic acid (salt) monomers such as maleic acid (salt), fumaric acid (salt) and itaconic acid (salt); 2-acrylamido-2-methylpropanesulfone Sulfonic acid (salt) monomers such as acid (salt), sulfoalkyl (meth) acrylate and 4-vinylbenzenesulfonic acid (salt); (meth) acrylamide, N-alkyl (carbon number 1 to 3) substitution (meta ) Amide monomers such as acrylamide [N-methylacrylamide, N, N-dimethylacrylamide, etc.] and N-vinylacetamide; alcohol monomers such as monohydroxyalkyl (1 to 3 carbon atoms) mono (meth) acrylate; Polyethylene glycol (polymerization degree: 2 to 100) mono (meth) acrylate, polypropylene glycol (polymerization degree: 2 to 100) mono (meth) acrylate Examples include relate, ether monomers such as methoxypolyethylene glycol (polymerization degree: 2 to 100) mono (meth) acrylate; ester monomers such as alkyl (1 to 5 carbon atoms) (meth) acrylate and vinyl acetate. be able to. These (a) may use 2 or more types together.
The content of (a) is preferably 0.1 to 50% by weight based on the total weight of (meth) acrylic acid (salt) and (b) from the viewpoint of the absorbability of the water absorbent resin of the present invention. More preferably, it is 0.5 to 40% by weight, particularly preferably 1 to 30% by weight.

(B) which generates gas by heating, when (B) is heated to a temperature of 70 to 210 ° C., for 1 to 300 minutes, (B) 1 to 1 g of (B) 50 to 300 ml amount (0 ° C., 1 atm) ) Means a gas generating compound.
From the viewpoint of the absorbability of the water-absorbent resin of the present invention, the temperature at which (B) generates the gas is preferably 80 to 190 ° C, more preferably 90 to 170 ° C. Moreover, it is preferable that (B) generate | occur | produces the said gas by the heating for 2-120 minutes from a viewpoint of the absorptivity of this water absorbing resin. Moreover, from the viewpoint of the absorbability of the water absorbent resin, the amount of gas generated is preferably 60 to 290 ml / g, more preferably 70 to 280 ml / g, and particularly preferably 80 to 250 ml / g.

As the foaming agent (B), a sulfonyl hydrazide compound (B1) and a nitroso compound (B2) can be used. These foaming agents may be used alone or in combination of two or more.
Examples of the sulfonyl hydrazide compound (B1) include p-toluenesulfonyl hydrazine and p, p′-oxybis (benzenesulfohydrazide).
Examples of the nitroso compound (B2) include N, N′-dinitrosopentamethylenetetramine.
Among (B), (B1) is preferable from the viewpoint of the absorbability of the water-absorbent resin, and more preferably p, p′-oxybis (benzenesulfohydrazide).

  The amount of the foaming agent (B) used is preferably 0.1 to 10% by weight with respect to the total weight of the (meth) acrylic acid (salt) and (b) from the viewpoint of the absorbability of the water absorbent resin. More preferably, it is 0.2 to 8% by weight, particularly preferably 0.5 to 5.0% by weight, and most preferably 1.0 to 3.0% by weight.

The method for producing the water-absorbent resin of the present invention comprises a crosslinking weight obtained by a formation reaction (polymerization and crosslinking reaction) of (meth) acrylic acid (salt) and a crosslinking agent (b) in the presence of the foaming agent (B). A combination (A) is obtained.
As the polymerization and crosslinking reaction methods, known polymerization methods can be applied, and examples thereof include aqueous solution polymerization, suspension polymerization, bulk polymerization, reverse phase suspension polymerization, and emulsion polymerization.
Among these polymerization methods, aqueous solution polymerization, suspension polymerization, reverse phase suspension polymerization and emulsion polymerization are preferable from the viewpoint of the absorbability of the water absorbent resin of the present invention, and more preferably aqueous solution polymerization, reverse phase suspension polymerization and emulsion. Polymerization, particularly preferably aqueous solution polymerization and reverse phase suspension polymerization. For these polymerizations, known polymerization initiators, chain transfer agents and / or solvents can be used.
With these polymerization methods, a water-absorbing resin excellent in absorbability can be obtained.
The method of polymerizing (meth) acrylic acid (salt) by an aqueous solution polymerization method may be a normal method, for example, a method of polymerizing using a radical polymerization initiator, a method of irradiating with radiation, ultraviolet rays, electron beams or the like. .
When a radical polymerization initiator is used, the initiator includes an azo compound [azobisisovaleronitrile, azobisisobutyronitrile, 4,4'-azobis (4-cyanovaleric acid), 2,2'- Azobis [2-methyl-N- (2-hydroxyethyl) propionamide, 2,2′-azobis (2-amidinopropane) hydrochloride, etc.], inorganic peroxides [hydrogen peroxide, potassium persulfate, ammonium persulfate, Sodium persulfate, etc.], organic peroxides [di-t-butyl peroxide, cumene hydroperoxide, etc.], redox initiators [alkali metal sulfites or bisulfites, ammonium sulfites, ammonium bisulfites, L- Reducing agents such as ascorbic acid, alkali metal persulfate, ammonium persulfate, hydrogen peroxide, etc. Combination etc. peroxides. Two or more of these may be used in combination.

The polymerization temperature varies depending on the type of initiator used, but is preferably −10 ° C. to 100 ° C., more preferably −10 ° C. to 80 ° C. from the viewpoint of the degree of polymerization.
The amount of the initiator is not particularly limited, but from the viewpoint of the degree of polymerization with respect to the total weight of the unsaturated monomer {ie, (meth) acrylic acid (salt), (b) and (a)}. , Preferably 0.000001-3.0%, more preferably 0.000001-0.5%.

  In the case of aqueous solution polymerization, the polymerization concentration (% by weight) of the unsaturated monomer {ie, (meth) acrylic acid (salt), (b) and (a)} varies depending on the polymerization conditions, but the water absorption From the viewpoint of the resin absorbability and ease of adjusting the polymerization temperature, 10 to 40% by weight is preferable, and 10 to 30% by weight is more preferable. Moreover, about -10-100 degreeC regarding polymerization temperature, -10-80 degreeC is more preferable. The amount of dissolved oxygen during polymerization depends on the amount of radical initiator added and the like, but is preferably 0 to 2 ppm, more preferably 0 to 0.5 ppm from the viewpoint of the degree of polymerization.

The degree of neutralization of (meth) acrylic acid at the time of polymerization is not particularly limited as long as a predetermined amount of (b) can be completely dissolved in the monomer aqueous solution, but the water solubility of (b) is particularly poor. ) Since the solubility in acrylic acid (salt) aqueous solution is very low and (b) may be separated from the aqueous monomer solution even if a predetermined amount of (b) is added, the predetermined cross-linking may not be performed. The degree of neutralization of the acid is 0 to 30 mol%, and the polymerization is preferably carried out after the polymerization if necessary, and more preferably after the polymerization in an unneutralized state and after the polymerization if necessary.
In addition, (meth) acrylic acid is polymerized under the same conditions. Since the degree of polymerization tends to increase when the degree of neutralization is low, in order to increase the degree of polymerization of the polymer, the degree of neutralization is low. It is preferable to perform polymerization.

  Regarding the reverse phase suspension polymerization method, an aqueous solution of (meth) acrylic acid (salt) is suspended and dispersed in a hydrophobic organic solvent typified by hexane, toluene, xylene, etc. in the presence of a dispersant. In this polymerization method, the monomer concentration in the monomer aqueous solution is preferably 10 to 40% by weight, and more preferably 10 to 30% by weight. Within this range, a crosslinked polymer (A) having a high degree of polymerization can be produced.

  In addition, regarding this reverse phase suspension polymerization method, you may use a dispersing agent at the time of superposition | polymerization. Examples of the dispersant include sorbitan fatty acid esters such as sorbitan monostearate having 3 to 8 HLB (Hydrophile-Lipophile Balance), glycerin fatty acid esters such as glycerol monostearate, and sucrose fatty acid esters such as sucrose distearate. Surfactant such as ethylene / acrylic acid copolymer maleated, ethylene / vinyl acetate copolymer maleated, styrene sulfonic acid (salt) / styrene copolymer has hydrophilic groups in the molecule In addition, a polymer dispersant (hydrophilic group; 0.1 to 20% by weight, weight average molecular weight; 1,000 to 1,000,000) soluble in a solvent for dispersing the monomer aqueous solution can be exemplified. It is better to use a polymer dispersant as the dispersant. Easy to adjust the size of the suspended particles, preferred because it creates a hydrogel crosslinked polymer particle size that requires (A).

0.1-20 weight% is preferable with respect to the weight of a hydrophobic organic solvent, and, as for the addition amount of surfactant and / or polymer dispersing agent, 0.5-10 weight% is more preferable.
0.1-2.0 are preferable and, as for the weight ratio (W / O ratio) of the monomer aqueous solution and hydrophobic organic solvent in reverse phase suspension polymerization, 0.3-1.0 are more preferable. Within these ranges, the weight average particle diameter of the crosslinked polymer (A) can be further easily adjusted.

When neutralizing (meth) acrylic acid, an alkali (C) is mixed to obtain a neutralized product. Alkali (C) includes alkali metal hydroxide, alkali metal carbonate, onium cation hydroxide and onium cation carbonate.
Examples of the alkali metal hydroxide include potassium hydroxide, sodium hydroxide, lithium hydroxide and the like. Examples of the alkali metal carbonate include sodium carbonate and sodium bicarbonate. Examples of the onium cation hydroxide include tetraethylammonium hydroxide. Examples of the onium cation carbonate include 1,2,3,4-tetramethylimidazolinium monomethyl carbonate.

In the production of the crosslinked polymer (A), the average degree of polymerization of the polymer when the polymer is produced under exactly the same polymerization conditions except that no crosslinking agent is used, is preferably 5,000 to 1,000,000. It is more preferred to polymerize under polymerization conditions (type of initiator, amount of initiator, polymerization concentration of unsaturated monomer, polymerization temperature, dissolved oxygen amount, etc.) that are preferably 10,000 to 1,000,000.
When the polymerization is carried out under the condition that the average degree of polymerization is 5,000 or more, the absorbability of the water absorbent resin is further improved by using an appropriate amount of the crosslinking agent. The average degree of polymerization can be measured by gel permeation chromatography (GPC).

The crosslinked polymer (A) obtained by aqueous solution polymerization or reverse phase suspension polymerization is obtained as a gel containing water (hydrous gel). The hydrogel is neutralized and broken if necessary, and is usually dried and then used as a water absorbent resin.
When neutralizing the hydrogel, alkali (C) is mixed into the hydrogel of (A) to obtain a neutralized product of the hydrogel. The neutralization degree of the water-containing gel obtained in this step is preferably 60 to 80 mol% of the carboxyl group in (A) from the viewpoint of the adhesiveness of the water-containing gel and the safety of the water-absorbent resin to the human skin, Preferably it is 65-78 mol%.
As a method of neutralizing the hydrogel of (A) with alkali (C), an aqueous solution of alkali (C) or (C) is added while chopping the hydrogel of (A) into small pieces of about 1 cm ³ or less. The method of mixing is mentioned.

As a mixing device with (C), a vertical slitting machine equipped with a cutter blade conventionally used in this step, a horizontal slitting machine equipped with a cutter blade, a cutter type crusher equipped with a rotary blade, a predetermined diameter A meat chopper equipped with an eye plate and a rotating blade can be used.
The temperature at the time of mixing may be a range conventionally used in this step, and is preferably 10 to 80 ° C. Moreover, the shearing to mix may be a conventionally well-known method, and the rotation speed of an apparatus becomes like this. Preferably it is 20-100 rpm.

When breaking the hydrous gel, a vertical slitting machine equipped with a cutter blade conventionally used in this process, a horizontal slitting slitter equipped with a cutter blade, a cutter type crusher equipped with a rotary blade, a predetermined diameter A meat chopper equipped with an eye plate and a rotating blade can be used.
The temperature at the time of fracture may be in the range conventionally used in this step, and is preferably 10 to 80 ° C. Moreover, the shearing to mix may be a conventionally well-known method, and the rotation speed of an apparatus becomes like this. Preferably it is 20-100 rpm.

Regarding the drying method of hydrous gel, in the case of aqueous solution polymerization, the hydrogel is subdivided to some extent with a meat chopper or cutter type crusher (the level of subdivision is about 0.5 to 20 mm square) or noodles, if necessary After neutralizing the hydrous gel by adding an alkali metal hydroxide or the like, air-permeable drying (lamination of the hydrogel on a punching metal or a screen and forcing a hot air of 80 to 210 ° C. to dry it) Etc.) and ventilation drying (water gel is put in a container, hot air is aerated and circulated and dried, and the gel is further subdivided with a machine such as a rotary kiln). Among these, air drying is preferable because efficient drying can be performed in a short time.
On the other hand, the drying method of the hydrogel in the case of reverse phase suspension polymerization is carried out by solid-liquid separation of the polymerized hydrogel and the organic solvent by a method such as decantation, followed by drying under reduced pressure (degree of vacuum; about 100 to 50,000 Pa) Or it is common to perform ventilation drying.

  As another drying method of the hydrogel in aqueous solution polymerization, for example, there is a contact drying method in which the hydrogel is compressed and stretched on a drum dryer and the like. It is necessary to create a thin film of hydrogel on the drum or the like.

In the present invention, the drying temperature at the time of drying the hydrogel varies depending on the dryer used, the drying time, and the like, but is preferably 80 to 210 ° C, more preferably 100 to 180 ° C. When the drying temperature is 210 ° C. or lower, the polymer is difficult to crosslink due to heat at the time of drying, the degree of cross-linking does not increase excessively due to thermal cross-linking, and the amount of absorption does not decrease. When the temperature is 80 ° C. or higher, drying does not take a long time and it is efficient. The drying time also varies depending on the model of the dryer to be used, the drying temperature, and the like, but is preferably 5 to 300 minutes, more preferably 5 to 120 minutes.
The dried product of the crosslinked polymer (A) thus obtained is pulverized and powdered as necessary. The pulverization method may be a normal method, and can be performed by, for example, an impact pulverizer (pin mill, cutter mill, skiller mill, ACM pulverizer, etc.) or an air pulverizer (jet pulverizer, etc.).
The weight average particle diameter of the resin particles (A1) obtained by pulverization is 10 to 1000 μm, preferably 20 to 800 μm, and 90% by weight or more of the particles is preferably in the range of 10 to 850 μm.

  The resin particles (A1) obtained by pulverization can be further crosslinked with a compound (D) having at least two groups capable of reacting with a carboxyl group and / or a carboxylate salt. In this method, compound (D) is added to A1), mixed, heated, subjected to a crosslinking reaction, and pulverized to obtain a particulate water-absorbing resin.

  As the compound (D), those described in JP-A-1-103615 can be used. Examples thereof include a compound (D1) having at least two functional groups selected from an epoxy group, a hydroxyl group, an amino group or an isocyanate group, and a polyvalent metal compound (D2) capable of forming an ionic bridge.

As the compound (D1) having at least two functional groups selected from an epoxy group, a hydroxyl group, an amino group or an isocyanate group, a polyepoxy or polyglycidyl ether compound (D11), a polyol compound (D12), a (poly) alkylene polyamine A compound (D13) etc. are mentioned.
Examples of the polyepoxy or polyglycidyl ether compound (D11) include ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, glycerin-1,3-diglycidyl ether, polyethylene glycol diglycidyl ether, and bisphenol A-epichlorohydrin type epoxy resin. Can be mentioned.
Examples of the polyol compound (D12) include glycerin, ethylene glycol, and propylene glycol.
Examples of the (poly) alkylene polyamine compound (D13) include ethylenediamine.

Examples of the polyvalent metal compound (D2) capable of forming ionic crosslinking include hydroxides, salts (halides, sulfates, carbonates) of alkaline earth metals (calcium, magnesium, etc.), zinc, aluminum, titanium, etc. Salt, acetate, etc.).
Specific examples include calcium chloride, zinc diacetate, and aluminum sulfate.

  Of these, polyglycidyl ether compounds and polyvalent metal compounds capable of forming ionic crosslinks are preferred.

  The addition amount of the compound (D) is preferably 0.005 to 3% by weight, more preferably 0.01 to 2% by weight, particularly preferably from the weight of (A1), from the viewpoint of the absorbability of the water absorbent resin. Is 0.05 to 1% by weight.

  As an example of a method of further crosslinking with the compound (D) having at least two functional groups, for example, the compound (D) is added to and mixed with the resin particles (A1), and the crosslinking reaction is performed by heating as necessary. If necessary, it is pulverized to obtain a particulate water-absorbing resin.

  Compound (D) is added and mixed as an aqueous solution if necessary, and is usually carried out in a kneader such as a kneader or a universal mixer. The heating method may be a normal method such as a method of heating with hot air at a temperature of 100 to 230 ° C., a thin film drying method using a drum dryer heated to 100 to 230 ° C., a reduced pressure drying method, a freeze drying method, or the like. Further, the water-absorbent resin obtained by surface cross-linking is sieved and pulverized to adjust the particle size as necessary. The pulverization method is not particularly limited, and is the same as that described above.

  The weight average particle diameter of the obtained water-absorbent resin is preferably 10 to 1000 μm, more preferably 20 to 800 μm, and more preferably 90 to 90% by weight of particles in the range of 10 to 850 μm, from the viewpoint of the water absorption capacity of the water absorbent resin. Preferably there is.

The crosslinked polymer (A) may be heated as necessary, and the process may be performed at any timing as long as it is after the polymerization process. The heating device is not particularly limited, and a normal heating dryer such as a hot air dryer, a fluidized bed dryer, a nauter dryer, or a rotary kiln can be used. The heating temperature varies depending on the model to be used, the heating time, etc., but is 70 to 210 ° C., and preferably 80 to 190 ° C. from the viewpoint of the efficiency of generating gas from (B) and the absorbent capacity of the water absorbent resin. More preferably, it is 90-170 degreeC. The heating time also varies depending on the model used and the drying temperature, but is preferably 1 to 300 minutes, more preferably 2 to 120 minutes.
In the case of performing the heating step, it is preferable to carry out between the step of neutralizing the hydrogel of (A) and the step of drying the hydrogel of (A) from the viewpoint of absorbability.

  The water-absorbent resin obtained by the production method of the present invention preferably has a 0.9M / vol% saline absorption rate of 0.83 to 3.5 g / g / s, more preferably 0.83 to 2.5 g. / G / s, next more preferably 0.89 to 2.0 g / g / s, most preferably 1.0 to 1.7 g / g / s. Within this range, when used in a paper diaper or sanitary napkin, dry feeling and leakage prevention are further improved.

The 0.9M / vol% saline absorption rate is measured by the following method.
<Measurement method of 0.9M / vol% saline absorption rate>
The 0.9M / vol% saline absorption rate is measured according to JIS K7224-1996.

  The water absorbent resin obtained by the production method of the present invention is preferably porous. When used as a porous diaper or sanitary napkin, it is more excellent in dryness and leakage prevention.

  The water-absorbent resin composition obtained by the production method of the present invention preferably has an apparent density of 0.55 to 0.64 g / ml, more preferably 0.56 to 0, from the viewpoints of dry feeling and leakage prevention. .64 g / ml, particularly preferably 0.57 to 0.61 g / ml.

The apparent density is measured by the following method.
<Measurement method of apparent density>
The apparent density is measured according to JIS K3362-1998.

  The water-absorbent resin composition obtained by the production method of the present invention preferably has a fractal order of 1.87 to 1.91, more preferably 1.90 to 1.91, from the viewpoint of dry feeling and leakage prevention. It is.

  In the present invention, the fractal order is one of indices indicating the shape of particles, that is, the irregularities of the particle surface. A small fractal order means that the external surface area of the particles is large. The fractal order is 2 if the resin particles are truly spherical with no irregularities on the surface.

In addition, said fractal order can be measured with the following method described in Unexamined-Japanese-Patent No. 2001-2935.
<Fractal order measurement method>
Using a scanning electron microscope (for example, JSM-7000F manufactured by JEOL Datum), a photograph of one water-absorbent resin particle is taken at each magnification of 25, 30, 50, and 100 times. For each of these photographs, the particle contour length and the particle projected area are determined using image analysis software (WinROOF manufactured by Mitani Corporation). Next, the common logarithm of the particle contour length and the particle projected area of each photograph is obtained. The obtained values are plotted in an XY coordinate diagram with the common logarithm of the particle contour length as the X axis and the common logarithm of the particle projection area as the Y axis, and a straight line is drawn by the method of least squares. The above straight line is drawn for each of the five water-absorbing resin particles taken out at random, and the average value of the slopes is taken as the fractal order.

  Since the water-absorbent resin obtained by the production method of the present invention has an excellent absorption rate, it can be suitably used for applications such as disposable diapers, sanitary napkins, freshness-keeping materials, and water-stopping materials. When the water-absorbent resin obtained by the production method of the present invention is used for these applications, the method of use is the same as the method of using a conventionally known water-absorbent resin.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further, this invention is not limited to this.

Example 1
In a 2-liter beaker, 300 g of acrylic acid, 1.0 g of pentaerythritol triallyl ether and 660 g of ion-exchanged water were mixed with stirring to prepare an aqueous acrylic acid solution, and the temperature was adjusted to 8 ° C.
Acrylic acid aqueous solution and p, p′-oxybis (benzenesulfohydrazide) (manufactured by Eiwa Kasei Kogyo, trade name: N # 1000M / cell paste 101) 7.34 g {based on the total weight of acrylic acid (salt) and crosslinking agent 2.0 wt%} was placed in a 1.5 liter adiabatic polymerization tank, and the amount of dissolved oxygen in the aqueous acrylic acid solution was adjusted to 0.1 ppm or less by passing nitrogen through the aqueous solution from the bottom of the adiabatic polymerization tank. To this heat insulation polymerization layer, 2.0 wt% 2,2′-azobis {2-methyl-N- (2-hydroxyethyl) -propionamide} (manufactured by Wako Pure Chemical Industries, Ltd., trade name: VA-086) 4.65 g of aqueous solution, 1.23 g of 1.0 wt% aqueous hydrogen peroxide, 4.65 g of 1.0 wt% L-ascorbic acid aqueous solution and 0.45 g of 0.1 wt% iron (II) sulfate heptahydrate aqueous solution And nitrogen bubbling into the aqueous solution was continued until polymerization started. After confirming that the polymerization started and the viscosity of the acrylic acid aqueous solution started to rise, the nitrogen aeration was stopped and the polymerization was carried out for 6 hours. When the temperature of the aqueous acrylic acid solution was measured with a hot spot thermometer, the highest temperature reached 98 ° C.
After taking out the block-like crosslinked hydrous gel from the adiabatic polymerization tank and using a small meat chopper (Royal) to subdivide the gel into noodles with a thickness of 3 to 10 mm at 60 rpm at room temperature. Then, 250 g of a 48 wt% sodium hydroxide (reagent special grade) aqueous solution (neutralization degree 72 mol%) was added, and the carboxyl group of the polyacrylic acid in the crosslinked polymer was neutralized under the same conditions as in the above apparatus.
This hydrogel was laminated on a SUS screen having an opening of 850 μm with a thickness of 5 cm, and a small air-permeable dryer (manufactured by Yako Electric Manufacturing Co., Ltd.) was used to supply a supply air temperature of 160 ° C. and a wind speed of 1 Under a condition of 0.5 m / sec, the water-containing gel was passed through for 40 minutes, and the water-containing gel was dried by heating to obtain a dried product having a water content of about 4%.
The dried product was pulverized using a home mixer, and a particle having a particle size of 32 to 710 μm (400 to 22 mesh) was collected using a sieve to obtain resin particles.
While stirring 100 g of the obtained resin particles, a solution consisting of 0.01 g of ethylene glycol diglycidyl ether, 0.9 g of water, and 0.46 g of propylene glycol was used at room temperature using a Nauter mixer (manufactured by Hosokawa Micron Corporation). And mixing at 50 rpm. The obtained resin particles were subjected to a heating reaction at 140 ° C. for 40 minutes using a smooth air dryer (manufactured by Tabai Espec Co., Ltd.) to obtain a water absorbent resin (1).

Example 2
Example 1 is different from Example 1 except that p, p′-oxybis (benzenesulfohydrazide) is 0.37 g {0.1% by weight based on the total weight of acrylic acid (salt) and the crosslinking agent}. In the same manner, a water absorbent resin (2) was obtained.

Example 3
Example 1 is different from Example 1 except that p, p′-oxybis (benzenesulfohydrazide) is 0.73 g {0.2% by weight based on the total weight of acrylic acid (salt) and the crosslinking agent}. In the same manner, a water absorbent resin (3) was obtained.

Example 4
Example 1 is different from Example 1 except that p, p′-oxybis (benzenesulfohydrazide) is 1.84 g {0.5% by weight based on the total weight of acrylic acid (salt) and the crosslinking agent}. In the same manner, a water absorbent resin (4) was obtained.

Example 5
Example 1 is the same as Example 1 except that p, p′-oxybis (benzenesulfohydrazide) is 3.67 g {1.0% by weight based on the total weight of acrylic acid (salt) and the crosslinking agent}. In the same manner, a water absorbent resin (5) was obtained.

Example 6
In a 2-liter beaker, 200 g of acrylic acid, 0.16 g of pentaerythritol triallyl ether, 0.72 g of trimethylolpropane triacrylate, and 880 g of ion-exchanged water are mixed with stirring to prepare an aqueous acrylic acid solution, and the temperature is kept at 8 ° C. Adjusted.
Acrylic acid aqueous solution and p, p′-oxybis (benzenesulfohydrazide) (manufactured by Eiwa Kasei Kogyo, trade name: Neocerbon N # 5000) 7.36 g {3 based on the total weight of acrylic acid (salt) and the crosslinking agent. 0 wt%} was put into a 1.5 liter adiabatic polymerization tank, and the amount of dissolved oxygen in the aqueous acrylic acid solution was adjusted to 0.1 ppm or less by passing nitrogen through the aqueous solution from the bottom of the adiabatic polymerization tank. To this heat insulation polymerization layer, 0.62 g of 1.0 wt% aqueous hydrogen peroxide, 0.62 g of 1.0 wt% L-ascorbic acid aqueous solution, 10 wt% 2,2′-azobis (2-amidinopropane) hydrochloride (Product name: V-50, manufactured by Wako Pure Chemical Industries, Ltd.) 6.2 g of aqueous solution and 0.32 g of 0.1 wt% iron (II) sulfate heptahydrate aqueous solution were added, and the solution was in the aqueous solution until polymerization started. Continued nitrogen aeration. After confirming that the polymerization started and the viscosity of the acrylic acid aqueous solution started to rise, the nitrogen aeration was stopped and the polymerization was carried out for 6 hours. When the temperature of the aqueous acrylic acid solution was measured with a hot spot thermometer, the maximum temperature reached was 63 ° C.
After taking out the block-like crosslinked hydrous gel from the adiabatic polymerization tank and using a small meat chopper (Royal) to subdivide the gel into noodles with a thickness of 3 to 10 mm at 60 rpm at room temperature. , 167 g of a 48% by weight aqueous solution of sodium hydroxide (special grade reagent) (neutralization degree 72 mol%) was added to neutralize the carboxyl group of the polyacrylic acid in the cross-linked polymer under the same conditions as above. A hydrogel was obtained.
This water-containing gel was laminated on a SUS screen having an opening of 850 μm with a thickness of 5 cm, and using a small air-permeable dryer (manufactured by Yako Electric Manufacturing Co., Ltd.), the supply air temperature was 150 ° C. and the air speed was 1. Under a condition of 0.5 m / sec, air was passed through the hydrogel for 45 minutes, and the hydrogel was dried by heating to obtain a dried product having a water content of about 4%.
The obtained dried product was pulverized using a household mixer, and a particle having a particle size of 32 to 710 μm (400 mesh to 22 mesh) was collected using a sieve to obtain a water absorbent resin (6).

Example 7
In Example 6, except that p, p′-oxybis (benzenesulfohydrazide) is 12.3 g {5.0% by weight based on the total weight of acrylic acid (salt) and the crosslinking agent} In the same manner, a water absorbent resin (7) was obtained.

Example 8
Example 1 is the same as Example 1 except that p, p′-oxybis (benzenesulfohydrazide) is 19.6 g {8.0% by weight based on the total weight of acrylic acid (salt) and the crosslinking agent}. In the same manner, a water absorbent resin (8) was obtained.

Example 9
In Example 6, p, p′-oxybis (benzenesulfohydrazide) was changed to 24.5 g {10% by weight based on the total weight of acrylic acid (salt) and the cross-linking agent}. Thus, a water absorbent resin (9) was obtained.

Example 10
In Example 6, 7.36 g of p, p′-oxybis (benzenesulfohydrazide) was added to 4.91 g of N, N′-dinitrosopentamethylenetetramine (manufactured by Eiwa Kasei Kogyo, trade name: Cellular GX) {acrylic acid (salt) ) And 2.0% by weight with respect to the total weight of the crosslinking agent} in the same manner as in Example 6 to obtain a water absorbent resin (10).

Example 11
To the water absorbent resin (1) obtained in Example 1, 2.0% by weight of silicon dioxide {made by Nippon Aerosil Co., Ltd., trade name: Aerosil 200PE} is uniformly added to the water absorbent resin (1). Mixing was performed to obtain a water absorbent resin (11).

Example 12
The same operation as in Example 1 was performed, and the resulting water-absorbent resin (1) was pulverized using a household mixer, and samples having a particle size of 106 to 300 μm (145 mesh to 48 mesh) were collected using a sieve. Thus, a water absorbent resin (12) was obtained.

Example 13
To the water-absorbent resin (12) obtained in Example 12, 2.0% by weight of silicon dioxide {manufactured by Nippon Aerosil Co., Ltd., trade name: Aerosil 200PE} is uniformly added to the water-absorbent resin (12). By mixing, a water absorbent resin (13) of the present invention was obtained.

Example 14
In a 1 liter beaker, 100 g of acrylic acid, 272.2 g of ion-exchanged water and 0.13 g of ethylene glycol diglycidyl ether were added and mixed to obtain a uniform solution. While cooling the beaker with an ice bath, 100 g of 40% sodium hydroxide aqueous solution was added to neutralize a part (72 mol%) of acrylic acid. After the neutralized monomer solution was cooled to 5 ° C., 0.2 g of potassium persulfate was added as a polymerization initiator to prepare a monomer aqueous solution.
In a 2 liter separable flask equipped with a stirrer and a condenser (cooler), 1000 ml of cyclohexane and polyoxyethylene octyl phenyl ether phosphate as a dispersant (Daiichi Kogyo Seiyaku Co., Ltd., trade name: Prisurf A210G) 2 0.5 g was added and stirred while adjusting the temperature to 60 ° C. using a hot water bath to dissolve the dispersant in cyclohexane.
P, p'-oxybis (benzenesulfohydrazide) (manufactured by Eiwa Kasei Kogyo Co., Ltd., trade name: Neocerbon N # 5000) 2.07 g {based on the total weight of acrylic acid (salt) and crosslinking agent in cyclohexane in a separable flask 2.0 wt%}, and the dissolved oxygen of cyclohexane is reduced to 0.1 ppm or less through nitrogen in the cyclohexane liquid, and 400 g of the monomer aqueous solution is added using a dropping funnel while stirring the cyclohexane using a stirrer. Dropped at 6.6 g / min over 1 hour, reverse phase suspension polymerization was performed at a polymerization temperature of 60 ° C., and after completion of dropping of the monomer aqueous solution, the temperature was further adjusted to 60 ° C. for 2 hours to complete the suspension polymerization. After cooling to 30 ° C., a spherical hydrous gel was obtained in cyclohexane.
After the rotation of the stirrer was stopped and the produced hydrogel was allowed to settle, cyclohexane was removed by decantation, and the remaining hydrogel was washed twice with cyclohexane to remove the dispersant adhering to the hydrogel.
The obtained spherical water-containing gel was spread on a release paper, and dried for 2 hours with a 80 ° C. vacuum dryer (degree of vacuum: 10,000 to 20,000 Pa).
100 g of the obtained dried product was pulverized using a household mixer, and a particle having a particle size of 32 to 710 μm (400 to 22 mesh) was collected using a sieve to obtain a water absorbent resin (15).

Comparative Example 1
A water absorbent resin (H1) was obtained in the same manner as in Example 1, except that 7.34 g of p, p′-oxybis (benzenesulfohydrazide) was not added.

Comparative Example 2
In Example 1, 7.34 g of p, p′-oxybis (benzenesulfohydrazide) was changed to 73.4 g {20% by weight based on the total weight of acrylic acid (salt) and the cross-linking agent}. Water-absorbing resin (H2) was obtained.

Comparative Example 3
A water absorbent resin (H3) was obtained in the same manner as in Example 6 except that 7.36 g of p, p′-oxybis (benzenesulfohydrazide) was not added.

Comparative Example 4
In Example 6, the same except that 7.36 g of p, p′-oxybis (benzenesulfohydrazide) was changed to 0.0368 g {0.01 wt% based on the total weight of acrylic acid (salt) and the crosslinking agent}. Thus, a water absorbent resin (H4) was obtained.

  Table 1 summarizes the measurement results of 0.9M / vol% saline solution absorption rate, apparent density, and fractal order of the water-absorbent resins prepared in the above Examples and Comparative Examples.

  From the result of Table 1, the water absorption resin of Examples 1-14 obtained by the manufacturing method of this invention is excellent in absorption rate compared with Comparative Examples 1-4.

By the method for producing a water-absorbent resin of the present invention, a water-absorbent resin excellent in absorption rate can be obtained. Therefore, when the water-absorbent resin obtained by the production method of the present invention is used as a sanitary material such as a paper diaper or a sanitary napkin, a sanitary material excellent in absorption capacity such as absorption rate and diffusibility can be created. In addition, when the water-absorbent resin obtained by the production method of the present invention is used for a freshness-keeping material, a water-stopping agent, or the like, a freshness-holding material, a water-stopping agent, etc. excellent in absorbability such as an absorption rate can be created.

Claims (5)

  In the method for producing a water-absorbent resin comprising the crosslinked polymer (A) formed from (meth) acrylic acid (salt) and the crosslinking agent (b), the formation reaction of (A) is carried out with the sulfonyl hydrazide compound (B1) and / or Or the manufacturing method of the water absorbing resin characterized by performing in presence of the foaming agent (B) which generate | occur | produces gas by heating at least 1 sort (s) chosen from the group which consists of a nitroso compound (B2).   The production method according to claim 1, wherein the amount (% by weight) of (B) used is 0.1 to 10 based on the weight of (A).   The production method according to claim 1 or 2, wherein the water-absorbent resin is porous.   The production method according to any one of claims 1 to 3, wherein the water absorbent resin has a 0.9 M / vol% saline absorption rate of 0.80 to 3.5 g / g / s.   The apparent density of the water-absorbent resin is 0.55 to 0.64 g / ml, and the fractal order is 1.87 to 1.91. The production method according to any one of claims 1 to 4.