JPH01103615A - Manufacture of water-absorptive resin - Google Patents

Abstract

PURPOSE:To obtain a water-absorptive resin which has high absorbency performance, and is high in gel strength after absorption of water, low in the amount of components which is dissolved in water, and high in safety, by using a specific copolymerizable crosslinking agent in the manufacture of a water- absorptive resin. CONSTITUTION:In the manufacture of a water-absorptive resin by polymerizing a water-soluble monomer, a copolymerizable crosslinking agent and, if desired, a polysaccharide, and then, if desired, neutralizing the product, a poly(meth) allyloxyalkane compound is used as a copolymerizable crosslinking agent. As the poly(meth)allyloxyalkane compound, tetraallyloxyethane is preferred. As the water-soluble monomer, a polymerizable monomer containing at least one acid group selected from among a carboxylic acid group, a sulfonic acid group and a phosphoric acid group can be used. The neutralization of the above polymer is carried out by adding an alkaline material to the polymer, thereby neutralizing about 50-90mol.% of acid groups in the polymer.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for producing a water absorbent resin.

[Prior Art] Conventionally, as a method for producing water-absorbent resins, there is a method of copolymerizing a water-soluble monomer (alkali metal acrylate, acrylic acid, etc.) and a copolymerizable crosslinking agent. For example, ethylene glycol diacrylate and trimethylolpropane triacrylate have been used as such (for example, Japanese Patent Publication No. 58-25500 and Japanese Patent Application Laid-Open No. 58-71907).

[Problems to be solved by the invention] However, water-absorbing resins using these copolymerizable crosslinking agents have low absorption capacity, weak gel strength after water absorption,
It has problems such as a large amount of water-eluted components and concerns about the safety of the crosslinking agent.

[Means for Solving the Problems] The present inventors have proposed a method for producing a water-absorbing resin that has high absorption capacity, strong gel strength after water absorption, low amount of water-eluted components, and high safety. As a result of intensive study, we have arrived at the present invention.

That is, the present invention involves polymerizing a water-soluble monomer, a copolymerizable crosslinking agent, and optionally a polysaccharide, and neutralizing the polysaccharide as necessary to produce a water absorbent resin. ) A method for producing a water-absorbing resin that specifically uses an allyloxyalkane compound (first invention) and a copolymerizable type with a water-soluble monomer (by polymerizing an n-agent and, if necessary, a polysaccharide, When neutralizing and producing water absorbent resin,
A polymerizable monomer containing at least one acid group selected from the group consisting of a carboxylic acid group, a sulfonic acid group, and an acid group is used as the water-soluble monomer, and poly(meth) is used as the copolymerizable crosslinking agent. ) An alkali metal compound is added to a polymer obtained by polymerization using an allyloxyalkane compound to neutralize 50 to 90 mol% of the acid groups in the polymer to partially form an alkali metal base. A method for producing a water-absorbing resin (second invention) characterized in that the combined neutralized product is further crosslinked with a compound having at least two groups capable of reacting with an acid group and/or an alkali metal base. .

Examples of the poly(meth)allyloxyalkane compounds used as a copolymerizable crosslinking agent in the present invention include diaryloxyethane, triaryloxyethane, tetraallyloxyethane, tetraallyloxypropane, tetraallyloxybutane, and tetramethallyloxy Examples include ethane. Preferred among these is tetraallyloxyethane.

Other copolymerizable crosslinking agents can be used together with the poly(meth)allyloxyalkane compound, if necessary. Other copolymerizable crosslinking agents used in combination if necessary include (1
) a compound having two polymerizable double bonds [excluding allyloxyalkane compounds]; and (2) a compound having at least one polymerizable double bond and at least one functional group reactive with a monomer. Examples include compounds that have

Examples of the compound (1) include the following.

(2) Bis(meth)acrylamide: N,N-alkylene (Cl-CG) bis(meth)acrylamide, such as N,N'-methylene-bisacrylamide.

■Di- or polyester of polyols and unsaturated mono- or polycarboxylic acids: Polyols [ethylene glycol, trimethylolpropane, serine, polyoxyethylene glycol,
Di- or tri-(meth)acrylic acid esters such as polyoxypropylene glycol: Unsaturated polyesters [obtained by reaction of the above polyols with unsaturated acids such as maleic acid] and di- or tri(meth)acrylic acid esters
Acrylic esters [obtained by the reaction of polyepoxide and (meth)acrylic acid, etc.].

■ Calphemyl ester: Reaction of polyisocyanate [such as tolylene diisocyanate phenylmethane diisocyanate and NCO group-containing prepolymer (obtained by reaction of the above polyisocyanate with a compound containing an active hydrogen atom) and hydroxyethyl (meth)acrylate. Carbamyl ester obtained by.

■Di- or polyvinyl compounds such as divinylbenzene, divinyltoluene, divinylxylene, divinyl ether, divinyl ketone, trivinylbenzene, etc.

■ Di- or poly(meth)allyl ether of polyols: Polyols [alkylene gelate kohl, glycerin, polyalkylene kohl, polyalkylene polyol,
carbohydrates, etc.) or poly(meth)allyl ethers such as polyethylene cold diallyl ether, allylated starch, allylated cellulose.

■ Di- or poly-allyl ester of polycarboxylic acid: diallyl phthale-1, diallyl adipate, etc.

■Ester of unsaturated mono- or poly-carboxylic acid and mono(meth)allyl ether of polyol: (meth)allyl ether of polyethylene glycol monoallyl ether
acrylic esters, etc.

Examples of compounds in (2) include groups reactive with (meth)acrylic acid and/or other copolymerizable monomers, such as carboxyl groups, groups reactive with carboxylic acid anhydride groups (hydroxyl groups, epoxy groups, etc.). , cationic groups, etc.). Specifically, unsaturated compounds containing nonionic groups, such as unsaturated compounds containing hydroxyl groups.

compounds [N-methylol (meth)acrylamide, etc. and epoxy group-containing unsaturated compounds [glycidyl (meth)
acrylate, etc.] and cationic group-containing unsaturated compounds, such as quaternary ammonium base-containing unsaturated compounds [N, N, N-1-limethyl-N-(meth)acryloyloxyethyltrimethylammonium chloride,
N, N, N-1-diethyl-N-(meth)acryloyloxyethylammonium chloride, etc.], and tertiary amino group-containing unsaturated compounds [dimethylaminoethyl (meth)acrylate, (meth)acrylic acid, diethylaminoethyl acid, etc.].

Among other copolymerizable crosslinking agents, preferred are bis(meth)acrylamide and di- or polyesters of polyols and unsaturated mono- or polycarboxylic acids; particularly preferred are N,N'-methylene- Bisacrylamide, ethylene glycol diacrylate, and trimethylolpropane triacrylate In the present invention, water-soluble monomers include polymerizable monomers that are water-soluble or become water-soluble upon neutralization, such as monomers containing a carboxylic acid group. Examples include acid group-containing polymerizable monomers such as sulfonic acid group-containing monomers, sulfonic acid group-containing monomers, and phosphoric acid group-containing monomers, and salts thereof.

Examples of the polymerizable monomer containing a carboxylic acid group include unsaturated mono- or polycarboxylic acids [(meth)acrylic acid (referring to acrylic acid and/or methacrylic acid. The same description will be used hereinafter), (meth) acrylic acid, crotonic acid,
Examples include sorbic acid, maleic acid, itaconic acid, cinnamic acid, and their anhydrides [maleic anhydride, etc.].

Examples of polymerizable monomers containing sulfonic acid groups include aliphatic or aromatic vinylsulfonic acids (vinylsulfonic acid, allylsulfonic acid, vinyltoluenesulfonic acid, styrenesulfonic acid, etc.), (meth)acrylsulfonic acid [( Sulfoethyl (meth)acrylate, sulbopropyl (meth)acrylate, etc.], (meth)acrylamide sulfonic acid [2-acrylamido-2-methylpropanesulfonic acid, etc.].

As the polymerizable monomer containing a phosphoric acid group, (meth)acrylic acid hydroxyalkyl phosphate monoester [2-
Hydroxyethyl acryloyl phosphate-1., 2-hydroxyethyl methacryloyl phosphate, phenyl-2-acryloyloxyethyl phosphate, etc.].

Among these, preferred are polymerizable monomers containing a carboxylic acid group or a sulfonic acid group, and particularly preferred are polymerizable monomers containing a carboxylic acid group. These acid group-containing polymerizable monomers may be used alone or in combination of two or more.

These salts include alkali metal salts (salts of sodium, potassium, lithium, etc.), alkaline earth metal salts (salts of calcium, magnesium, etc.), ammonium salts and amine salts (salts of alkylamines such as methylamine, trimethylamine, etc.). ; salts of alkanolamines such as triethanolamine and jetanolamine), and two or more thereof. Preferred among these are sodium and potassium salts.

Other polymerizable monomers may be used together with the acid group-containing monomer or its salt, for example, unsaturated carboxylic acids [monocarboxylic acids such as (meth)acrylic acid; maleic acid, fumaric acid, etc. Alkyl (C+ to C1θ) esters of polycarboxylic acids, aromatic vinyl hydrocarbons [such as styrene], aliphatic vinyl hydrocarbons [ethylene, propylene, butene, etc.], unsaturated nitriles [such as acrylonitrile], (meth) Examples include acrylamide.

Examples of optional polysaccharides include starch and cellulose. Examples of starches include raw starches such as sweet potato starch, potato starch, wheat starch, corn starch, rice starch, oxidized starch, dialdehyde starch, alkyl etherified starch, oxyalkylated starch, aminoethyl etherified starch, etc. modified starch.

Examples of cellulose include cellulose obtained from wood, leaves, stems, gin bark, seed hair, etc.; processed cellulose such as alkyl etherified cellulose, organic acid esterified cellulose, oxidized cellulose, and hydrocellulose.

The amount of the poly(meth)allyloxyalkane compound, which is a copolymerizable crosslinking agent, is usually 0.001 to 10%, preferably 0.01%, based on the total weight of all polymerizable monomers and copolymerizable crosslinking agent. ~5%. The amount of copolymerizable crosslinking agent is 0.0
If it is less than 0.01%, the resulting resin will have a low gel strength upon water absorption, will be in the form of a sol, and will have a large amount of water-eluted components. On the other hand, 10
%, on the contrary, the gel strength becomes too excessive and the absorption capacity decreases.

・The amount of other copolymerizable crosslinking agents used in combination if necessary is usually 40% or less of the amount of poly(meth)allyloxyalkane,
Preferably it is 20% or less.

The amount of other polymerizable monomers used if necessary is usually 30% or less, preferably 10% or less, based on the total weight of all polymerizable monomers and copolymerizable crosslinking agent.

The amounts of each component are as follows. However, % is weight % based on the total weight of all polymerizable monomers, copolymerizable crosslinking agents, and polysaccharides.

Usually preferably total polymerizable monomers = 56-99.999 73-09. Ri9 water-soluble monomer: 26-99.999 63-9.9
9 Other polymerizable monomers: 0-30 0-10 Polysaccharide: 0-30 0-20 Copolymerizable crosslinking agent: 0.001-14 0.01-7
Boaryloxyalkane: o, oot~10 0.0
1 to 5 Other copolymerizable crosslinking agents: 0 to 4 0 to 2 The method of polymerizing the water-soluble monomer, copolymerizable crosslinking agent, and optionally polysaccharide may be any conventionally known method, such as radical Examples include a method of polymerization using a polymerization catalyst and a conventional method of irradiating with radiation, electron beams, ultraviolet rays, etc.

In the method using a radical polymerization catalyst, the catalyst may be an azo compound [such as azobisisobutyronitrile, azobiscyanovaleric acid, 2,2'-azobis(2-amidinopropane) hydrochloride, etc.] or a non-TM peroxide [
hydrogen peroxide, ammonium persulfate, persulfate power, lium,
Organic peroxides such as sodium persulfate, organic peroxides [benzoyl peroxide, di-t-butyl peroxide, cumene hydroperoxide, succinic peroxide, di(2-ethoxyethyl) peroxydicarbonate, etc.] and radox catalysts [ Alkali metal sulfites or bisulfites, ammonium sulfite, ammonium bisulfite, reducing agents such as ascorbic acid and alkali metal persulfates,
ammonium persulfate, peroxide, etc.] and two or more of these.

The method of polymerization using this catalyst is not particularly limited. For example, the temperature can be varied depending on the type of catalyst used, but is usually 0 to 150°C, preferably 10 to 150°C.
00°C.

The amount of catalyst may also be the same as usual, for example, usually o, oo based on the total weight of all polymerizable monomers and copolymerizable crosslinking agent.
o5-5%, preferably 0.001-1%.

Polymerization may be carried out in the presence of a solvent if necessary. Examples of this solvent include water, methanol, ethanol,
Mention may be made of acetone, N,N-dimethylborumamide, dimethyl sulfoxide, methyl ethyl ketone, and mixtures of two or more thereof. The concentration of the copolymerizable monomer when a solvent is used is not particularly limited, but it is usually 10% or more, preferably 15 to 80% by weight. If the concentration is less than 10%, the resulting resin will have a low absorption capacity and will also have a large amount of water-eluted components.

In the present invention, a salt type monomer may be polymerized, or an alkali metal compound may be added to the polymer obtained by polymerizing an acid type monomer to partially neutralize the acid groups in the polymer. It can also be used as a base. Examples of alkali metal compounds used for neutralization include alkali metal hydroxides (thorium hydroxide, potassium hydroxide, lithium hydroxide, etc.), alkali metal carbonates (thorium carbonate, thorium bicarbonate, etc.). ), etc.

In the present invention, 50 to 90 mol% of acid groups in the polymer,
Preferably 60 to 80 mol% is converted into an alkali metal salt by neutralization reaction with an alkali metal compound. When the conversion rate, that is, the degree of neutralization, is less than 50 mol%, the resulting gel-like hydropolymer has high stickiness, making it difficult to produce a water-absorbing resin with good workability. If it exceeds 90 mol%, the pH of the resulting resin increases, which poses a problem in terms of safety for human skin.

As a method for neutralizing a polymer with an alkali metal compound, when polymerization is performed using a solvent, an aqueous solution of an alkali metal compound is added while cutting the obtained gel-like polymer into pieces of about 1 cm3 or less, and then There is a method of kneading. In addition, when polymerizing without using a solvent, there is a method of adding an alkali metal compound or adding an aqueous solution of an alkali metal compound to the polymer after adding a solvent such as water to the fixed-type polymer to swell it. .

Next, the neutralized salt-type polymer or acid-type polymer as a reaction product can be dried and pulverized by the method described below to obtain the water-absorbing resin of the present invention.

In the present invention, by further crosslinking with a compound having at least two groups that react with acid groups and/or alkali metal bases in the polymer or neutralized polymer, even higher gel strength and water-eluting components can be obtained. It is possible to produce a small amount of water absorbent resin.

Examples of compounds having at least two groups that can react with acid groups and/or alkali metal bases include functional groups that can react with acid groups and/or alkali metal bases (e.g., epoxy groups, hydroxyl groups, amino groups, isocyanate groups, etc.) and polyvalent metal compounds capable of forming ionic crosslinks.

Examples of compounds having functional groups that can react with acid groups and/or alkali metal bases include polyepoxy or polyglycidyl ether compounds (ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, glycidyl serine-1,3- diglycidyl ether,
polyethylene glycol digcasidyl ether, bisphenol-epichlorohydrin type epoxy resin, etc.)
, polyols (glycerin, ethylene glycol, propylene glycol, etc.), and (poly)alkylene polyamines (ethylene diamine, etc.).

Examples of polyvalent metal compounds include compounds that can form ionic crosslinks, such as alkaline earth metals (calcium, magnesium, etc.), hydroxides, halides, salts (sulfates, carbonates, etc.) of zinc, aluminum, titanium, etc. acetate, etc.), specific examples include calcium chloride, zinc diacetate, aluminum sulfate, etc.

Among these, preferred are polyglycidyl ether compounds and polyvalent metal compounds.

The amount of these compounds added can be varied depending on the degree of crosslinking of the polymer by the copolymerizable crosslinking agent, but it is usually 10% or less, preferably 0.001 to 5%, based on the total weight of acid groups and alkali metal bases. be.

This compound having at least two functional groups is added to a polymer or a neutralized product of the polymer, kneaded, dried, and pulverized.

Addition and kneading are carried out, if necessary, in the form of an aqueous solution, and usually in a kneader such as a kneader-1 universal mixer.

Drying methods include drying by heating with hot air at a temperature of 100 to 230°C, thin film drying using a drum dryer heated to 100 to 230°C, vacuum drying, freeze drying, etc. This method is fine.

There are no particular limitations on the pulverization method, and conventional equipment such as a hammer-type pulverizer, impact-type pulverizer, roll-type pulverizer, or shed air-flow pulverizer can be used.

[Examples] Hereinafter, the present invention will be further explained with reference to Examples, but the present invention is not limited thereto. Parts in the examples are parts by weight.

Example 1 Contents 98 parts of sodium acrylate, 25 parts of acrylic acid, 0.1 part of t)-lalyloxyethane, and 350 parts of water were placed in a stainless steel separable flask with a size of 1 1 to 1 liters, and while stirring, the mixture was poured from the outside of the flask. The temperature of the contents was maintained at 40°C. After replacing the system with nitrogen, 2.2'
-0.1 part of azobis(2-amidinopropane) hydrochloride was added to initiate polymerization. Polymerization was completed in about 1 hour to obtain a gel-like polymer. The gel polymer was taken out from the flask and stirred for about 2 minutes using a kneader. After stretching and drying the obtained gel-like polymer on a drum dryer heated to a surface temperature of 150°C,
A water absorbent resin was obtained by pulverizing the powder to a particle size of 45 mesh.

The absorption capacity, gel strength, and amount of water-eluted components of the obtained water-absorbent resin were measured. The results are shown in Table 1. here,
The absorption capacity was measured by the T-Bac method using 1% saline (under normal pressure), the gel strength was measured by the card meter method, and the amount of water-eluted components was measured by evaporating the filtrate extracted with excess physiological saline to dryness.

Example 2 In Example 1, the amount of tetraallyloxyethane was changed to 0.5
A water-absorbing resin was obtained in exactly the same manner except that The performance measurement results of this product are shown in Table 1.

Example 3 100 parts of acrylic acid, 0.1 part of tetraallyloxyethane, and 350 parts of water were placed in a closed container that could be opened and closed, and the liquid temperature was brought to 10°C under a nitrogen atmosphere, followed by a 0.5% ammonium persulfate aqueous solution. When 1 part and 1 part of a 0.5% sodium bisulfite aqueous solution were added and polymerized, it became gel-like with heat generation. Eight hours after the start of polymerization, the closed reaction vessel was opened, and the produced gel-like hydrous crosslinked polymer was taken out. After 400 parts of this gel was shredded, 73.5 parts of 1 volume of 50% sodium hydroxide solution was added to neutralize it, and the mixture was further uniformly kneaded to make approximately 75 mol% of the polyacrylic acid in the polymer.
was converted to thorium polyacrylate.

This neutralized gel was dried with a drum dryer heated to 150°C, and then pulverized to a particle size of 32 to 145 mesh to obtain a water absorbent resin.

The performance measurement results of this product are shown in Table 1.

Example 4 A water absorbent resin was obtained in exactly the same manner as in Example 3 except that 60 parts of acrylic acid and 115 parts of 2-acrylamido-2-methylpropanesulfonic acid were used instead of 100 parts of acrylic acid.

The performance measurement results of this product are shown in Table 1.

Example 5 To a neutralized gel prepared in the same manner as in Example 3, 6 parts of a 5% aqueous solution of ethylene glycol sidyl ether was added to a colander, kneaded uniformly, and then heated to 150°C. It was dried with a drum dryer and pulverized to a particle size of 32 to 145 mesh to obtain a water absorbent resin. The performance measurement results of this product are shown in Table 1.

Example 6 In Example 1, instead of 350 parts of water, 80 parts of water was added in advance.
Using 350 parts of a 2.5% aqueous solution of corn starch gelatinized at °C, 0.1 part of 2,2'-azobis(2-amidinopropane) hydrochloride was replaced with 1 part of 1% hydrogen peroxide solution. A water absorbent resin was obtained in the same manner as in Example 1, except that 1 part of a 0.5% ascorbic acid aqueous solution was used and polymerization was started at 15°C. The performance measurement results of this product are shown in Table 1.

Comparative Example 1 A water absorbent resin was obtained in the same manner as in Example 1 except that 0.1 part of trimethylolpropane triacrylate was used in place of 0.1 part of tetraallyloxyethane. The performance measurement results of this product are also listed in Table 1.

Comparative Example 2 A water absorbent resin was obtained in the same manner as in Example 1 except that 0.1 part of N,N'-methylenebisacrylamide was used in place of 0.1 part of tetraallyloxyethane. The performance measurement results of this product are also listed in Table 1.

Comparative Example 3 A water-absorbing resin was obtained in the same manner as in Example 3, except that 0.1 part of N,N'-methylene-bisacrylamide was used in place of 0.1 part of tetraallyloxyethane. The performance measurement results of this product are also listed in Table 1.

Comparative Example 4 A water absorbent resin was obtained in the same manner as in Example 6 except that 0.1 part of trimethylolpropane triacrylate was used in place of 0.1 part of tetraallyloxyethane. The performance measurement results of this product are also listed in Table 1.

Table 1 [Effects of invention The present invention has the following effects.

(1) A water-absorbing resin with strong gel strength and excellent absorption capacity can be produced.

Conventional copolymerizable crosslinking agents generally have poor water solubility, so in order to increase gel strength, a large amount of crosslinking agent must be used or an activator must be added to emulsify and disperse the crosslinking agent.1. As a result, absorption capacity decreased due to the use of a large amount of crosslinking agent, or gel strength decreased due to addition of an activator.

However, according to the present invention, since it is possible to produce a resin with a large molecular weight, a water-absorbing resin with strong gel strength and excellent absorption capacity can be obtained.

(2) The amount of water-eluted components is small.

Since the crosslinking agent of the present invention has high water solubility and excellent copolymerizability with water-soluble monomers, the amount of water-eluted components in the obtained water-absorbing resin is small. Therefore, it is safe to the skin and is excellent in terms of hygiene.

(3) A highly safe water absorbent resin can be obtained.

Conventional copolymerizable crosslinking agents generally have low safety, and there have been concerns about the safety of the resulting water absorbent resins. However, the crosslinking agent of the present invention is highly safe, and the resulting water absorbent resin is also highly safe.

As an effect of the second invention, after crosslinking a polymerizable monomer containing at least one acid group selected from the group consisting of a carboxylic acid group, a sulfonic acid group, and a phosphoric acid group with a poly(meth)allyloxyalkane compound. Neutralize, carboxylic acid and/or
Alternatively, by reacting with a compound having a group reactive with a carboxylic acid group, the gel strength can be further improved and a resin with a small amount of water-eluted components can be produced.

Since the water-absorbing resin obtained by the present invention exhibits the above-mentioned effects, it can be used as absorbent materials, sanitary materials (disposable diapers for children and adults, sanitary napkins, sanitary cotton, bandages, incontinence pads, paper towels, etc.) It is particularly useful for applications that come into contact with the human body, such as freshness-preserving agents for fresh vegetables, drip absorbers from fish and shellfish, and livestock meat, and applications that may come into contact with food, such as ice packs. In addition, water separating agents in oil and other dehydrating or drying agents; water retention agents such as plants and soil; sludge coagulating agents;
It is also useful for industrial applications such as anti-condensation agents used in interior building materials.

Claims (1)

[Claims] 1. When producing a water-absorbent resin by polymerizing a water-soluble monomer, a copolymerizable crosslinking agent, and if necessary a polysaccharide, and neutralizing if necessary, poly( A method for producing a water-absorbing resin, characterized by using a meta)allyloxyalkane compound. 2. The water-soluble monomer according to claim 1, wherein the water-soluble monomer is a polymerizable monomer containing at least one acid group selected from the group consisting of a carboxylic acid group, a sulfonic acid group, and a phosphoric acid group. Manufacturing method. 3. The production method according to claim 2, wherein the neutralization involves adding an alkaline substance to the polymer to neutralize 50 to 90 mol% of the acid groups in the polymer. 3. The manufacturing method according to claim 1 or 2, wherein the poly(meth)allyloxyalkane compound is tetraallyloxyethane. 4. When producing a water-absorbing resin by polymerizing a water-soluble monomer, a copolymerizable crosslinking agent, and if necessary a polysaccharide, and neutralizing the water-soluble monomer, a carboxylic acid group, a sulfonic acid group, and a phosphorus group are used as water-soluble monomers. A polymer obtained by polymerizing a polymerizable monomer containing at least one acid group selected from the group consisting of acid groups and using a poly(meth)allyloxyalkane compound as a copolymerizable crosslinking agent. Add an alkali metal compound to neutralize 50 to 90 mol% of the acid groups in the polymer to partially form an alkali metal base, and react the neutralized polymer with the acid group and/or the alkali metal base. 1. A method for producing a water-absorbing resin, which further comprises crosslinking with a compound having at least two functional groups.