JPH0356502A - Production of water absorbing resin - Google Patents

Abstract

PURPOSE:To obtain the title resin having extremely low aggregation and adhesion to wall of polymerizer of particles, large particle diameters and a sharp particle size distribution in polymerizing a water-soluble polymerizable monomer by reversed-phase suspention polymerization by using a specific protective colloid. CONSTITUTION:A polymer [preferably acrylamide-2-mehylpropanesulfonic acid (Na)-styrene copolymer] containing sulfonic group and/or phsphate group is used as a protective colloid and a water-soluble polymerizable monimer (e.g. maleic acid) is polymerized in a hydrophobic organic solvent (preferably aliphat ic hydrocarbon) in the presence of a water-soluble radical polymerization cata lyst (e.g. azobisisobutyronitrile) by reversed-phase suspension polymerization. The polymerization is carried out preferably at 5-100 deg.C.

Description

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

[Conventional technology] A water-soluble polymerizable monomer aqueous solution is prepared in a hydrophobic organic solvent,
A method for obtaining a spherical polymer by polymerization using a reverse phase suspension polymerization method is described in Japanese Patent Publication No. 34-10844 and Japanese Unexamined Patent Application Publication No. 1987-10
It is publicly known from Publication No. 82 and the like.

What is important in this polymerization method is to stabilize the colloid of an aqueous solution of polymerizable monomers dispersed in an organic solvent. If the colloid is not sufficiently stabilized, agglomeration between particles or adhesion of particles to the walls of the polymerization tank may occur, and in some cases, the entire colloid may gel.

Therefore, in order to stabilize the colloid during polymerization, it is common to use a surfactant or a polymeric protective colloid as a dispersant.

This reverse-phase suspension polymerization technique is also used in the production of absorbent resins. For example, an example of using a surfactant as a dispersant is a method using sorbitan fatty acid ester (Japanese Patent Laid-Open No. 53 -552 [Publication i0, JP-A-56
Publication No.-76149, JP 511i-111i141
4), method using sorbitol monostearate (JP-A-58-28909, JP-A-5 [i-937]
16 Publications), methods using nonionic surfactants (JP-A-57-187302, JP-A-Sho flit-115)
! 104), method using sucrose fatty acid ester (JP-A-61-87702, JP-A-61-438)
Publication No. 08, JP-A-Shofi! -53308). Examples of using a protective colloid as a dispersant include a method using oil-soluble ethyl cellulose or cellulose ester (Japanese Patent Application Laid-open No. 158209/1982);
A method using a polymer having a carboxyl group (Unexamined Japanese Patent Publication No. 1983
-9401 No. 1), etc.

[Problems to be Solved by the Invention] However, with the method of using a surfactant as a dispersant, it is difficult to obtain particles with a large particle size, and the product may contain a large amount of fine powder, which requires a process to remove the fine powder from the product. There were problems such as the necessity of In addition, surfactants have strong permeability, so if surfactants remain in water-absorbing resin, they may penetrate into the skin when used in disposable diapers or sanitary products, etc., which is a safety concern. There is also a problem.

When a polymeric protective colloid is used as a dispersant, it is easier to obtain particles with a larger particle size than when a surfactant is used due to the viscosity effect and steric repulsion effect of the polymer, and the permeability is lower due to the larger molecular weight. However, when conventional polymeric protective colloids are used, their dispersion ability is lower than that of surfactants, so colloid stabilization is insufficient, resulting in aggregation between particles and particle formation. There were problems such as easy adhesion to the walls of the polymerization tank, and the particle size distribution of the obtained particles was not sharp.

[Means for solving the problem] The present inventors have discovered that when producing a water-absorbing resin using a reversed-phase suspension polymerization method, large particles can be obtained with a sharp particle size distribution, and a dispersing agent can be obtained. As a result of extensive research into a method for producing a water-absorbing resin using a dispersant, which has low permeability and very little agglomeration between particles and adhesion of particles to the walls of a polymerization tank, the present invention was discovered.

That is, the present invention utilizes a reverse-phase suspension polymerization method in which water-soluble polymerizable monomers are suspended and polymerized in a hydrophobic organic solvent using a water-soluble radical polymerization catalyst, and a water-soluble radical polymerization catalyst is used as a protective colloid. The present invention provides a method for producing a water-absorbing resin, which is characterized in that the water-absorbing resin is produced using a polymer containing a sulfonic acid group and/or a phosphoric acid group.

According to the present invention, when producing an absorbent resin by a reverse phase suspension polymerization method, the aggregation between particles and adhesion of particles to the wall of a polymerization tank are extremely small, and the absorbent resin has a particle size of 50 to 2000 microns. can be obtained with a sharp particle size distribution.

As the protective colloid agent used in the present invention, a polymer containing a sulfonic acid group and/or a phosphoric acid group in the molecule and soluble in the organic solvent used in suspension polymerization can be used.

What is very important in this case is that the molecule contains a sulfonic acid group and/or a phosphoric acid group.

The reason for this is that sulfonic acid groups and phosphoric acid groups have a very strong affinity for water. It is strongly adsorbed to colloids and significantly stabilizes them.

More specifically, the weight average molecular weight of the protective colloid containing sulfonic acid groups and/or phosphoric acid groups is usually 5,000.
more than io, preferably more than io, ooo,
Most preferably, if it exceeds 20,000, the viscosity of the organic solvent in which the protective colloid is dissolved increases, and the adsorption amount of the protective colloid per unit area of micelles containing a water-soluble polymerizable monomer increases. This not only improves dispersion stability by preventing the processes of cleaning, agglomeration, and coalescence during and after polymerization, but also suppresses the coalescence and destruction of droplet particles during polymerization, resulting in large particle size and A water absorbent resin with a sharp particle size distribution can be obtained.

The composition of the polymer used as the protective colloid used in the present invention may be any polymer containing a sulfonic acid group and/or a phosphoric acid group in the molecule, but from the viewpoint of hydrophilic-hydrophobic balance, (A ) Sulfonic acid (salt) group and/or phosphoric acid (salt) group: 0. 001 to 50% (B) Hydrophobic group: 0 to 99.999% (C) Hydrophilic group other than sulfonic acid group and/or phosphoric acid group: 0 to 50%.

The content of sulfonic acid groups and/or phosphoric acid groups in the polymer is 0.
．． If it is less than 0.01%, the protective colloid agent will not be sufficiently adsorbed to the colloid of the polymerizable monomer aqueous solution dispersed in the organic solvent, resulting in insufficient dispersion stability of the colloid, resulting in aggregation of particles and polymerization of particles. Adhesion to the tank occurs. Furthermore, when the content of sulfonic acid groups and/or phosphoric acid groups exceeds 50%, the polymer no longer dissolves in the organic solvent, and even if it does, particles with a large particle size cannot be obtained.

The sulfonic acid group and/or phosphoric acid group contained in the polymer used as the protective colloid may be in an acid state or partially or completely in a salt state.

The hydrophobic group contained in the polymer used as the protective colloid may be any group as long as it is essentially hydrophobic and swells and dissolves in the organic solvent used, and its content is from 0 to 99. 999% is preferred. The amount of hydrophobic groups is 9
If it exceeds 9.999%, the hydrophobicity becomes too strong and the protective colloid agent is not sufficiently adsorbed to the colloid of the polymerizable monomer aqueous solution dispersed in the organic solvent, resulting in insufficient dispersion stability of the colloid and particles. Coagulation among particles and adhesion of particles to the polymerization tank occur.

Hydrophilic groups other than sulfonic acid groups and/or phosphoric acid groups are not necessarily required, but those containing 0 to 50% are preferred. If the content exceeds 50%, the hydrophilicity becomes too strong and large particles cannot be obtained. Examples of hydrophilic groups other than sulfonic acid groups and/or phosphoric acid groups include carboxylic acid esters, sulfuric esters, phosphoric esters, and hydroxyl groups. Preferred examples include carboxylic acid esters.

Examples of polymers containing sulfonic acid groups used as protective colloid agents having the above composition include acrylamide-2-methylpropanesulfonic acid (Na)-styrene copolymer, acrylamide-2-methylpropanesulfone M(Na) monoethylene copolymer, acrylamide-2-methylpropanesulfonic acid (Na)-isobutylene copolymer, acrylamide-2-methylpropanesulfonic acid (Na)-styrene-alkyl (meth)acrylate copolymer, acrylamide -2-methylpropanesulfonic acid (Na) monostyrene-hydroxyalkyl (meth)acrylate copolymer, acrylamide 2-methylpropanesulfonic acid (Na) monoethylene-alkyl (meth)acrylate copolymer, acrylamide 2- Methylpropanesulfonic acid (Na) monoethylene-hydroxyalkyl (meth)acrylate copolymer, acrylamide 2-methylpropanesulfonic acid (Na) monostyrene-vinyl acetate copolymer or its saponified product, acrylamide 2-methylpropane Sulfonic acid (Na) monoethylene-vinyl acetate copolymer or its saponified product, Styrenesulfonic acid (Na) monostyrene copolymer, Styrenesulfonic acid (Na) monoethylene copolymer, Styrenesulfonic acid (Na) monostyrene copolymer,
Na) monoisobutylene copolymer, styrene sulfonic acid (
Na) monostyrene-(meth)alkyl acrylate copolymer, styrenesulfonic acid (Na) monostyrene-(meth)
Hydroxyalkyl acrylate copolymer, (Na) styrene sulfonate mono-dtyrene-(meth)alkyl acrylate copolymer, styrene snolephonate (Na) mono-ethylene=hydroxyalkyl (meth)acrylate copolymer, styrene sulfone Acid (Na) monostyrene-vinyl acetate copolymer or its saponified product, styrene sulfonic acid (Na)
monoethylene-vinyl acetate copolymer or its saponified product,
(Meth)allylsulfonic acid (Na) monostyrene copolymer, (meth)allylsulfonic acid (Na) monoethylene copolymer, (meth)allylsulfonic acid (Na) monobutylene copolymer, (meth)allyl Sulfonic acid (Na) monostyrene-alkyl (meth)acrylate copolymer, (
meth)allylsulfone M(Na)-styrene-(meth)
Hydroxyalkyl acrylate copolymer, (meth)allylsulfonic acid (Na) monoethylene-(meth)alkyl acrylate copolymer, (meth)allylsulfonic acid (N
a) monoethylene-hydroxyalkyl (meth)acrylate copolymer, (meth)allylsulfonic acid (Na) monostyrene-vinyl acetate copolymer or its saponified product, (
Meta)allylpropanesulfonic acid (Na) monoethylene-vinyl acetate copolymer or saponified product thereof, sulfonated polystyrene, sulfonated polybutadiene, condensation product of sulfonated naphthalene with formalin, sulfonic acid group on polyethylene by peroxide catalyst Examples include a graft polymer of a containing heptanomer, a graft polymer of a sulfonic acid group-containing monomer onto an ethylene-vinyl acetate copolymer using a peroxide catalyst, and the like.

Among these, those that can be preferably used include acrylamide-2-methylpropanesulfonic acid (Na)-styrene copolymer, acrylamide-2-methylpropanesulfonic acid (Na)-ethylene copolymer, and acrylamide-2-methylpropanesulfonic acid (Na)-ethylene copolymer. Methylpropanesulfonic acid (Na) monostyrene-alkyl (meth)acrylate copolymer, acrylamide 2-methylpropanesulfonic acid (Na) monoethylene-alkyl (meth)acrylate copolymer, styrenesulfonic acid (Na) monostyrene copolymer, styrene sulfonic acid (Na)-ethylene copolymer, styrene sulfonic acid (N
a) Monostyrene-alkyl (meth)acrylate copolymer, styrene sulfone af2(Na) monoethylene-alkyl (meth)acrylate copolymer, etc. can be exemplified.

More preferably used polymers include those having the compositions exemplified above and having a weight average molecular weight of more than 20,000.

Examples of polymers containing phosphoric acid groups used as protective colloid agents include vinyl phosphoric acid (Na)-styrene copolymer, vinyl phosphoric acid (Na)-one ethylene copolymer, and vinyl phosphoric acid (Na)-isobutylene copolymer. , vinyl phosphoric acid (Na
) monostyrene-(meth)alkyl acrylate copolymer,
Vinyl phosphate (Na) monostyrene-hydroxyalkyl (meth)acrylate copolymer, vinyl phosphate (Na) monoethylene-alkyl (meth)acrylate copolymer, vinyl phosphate (Na) monoethylene-hydroxyalkyl (meth)acrylate copolymer, vinyl phosphoric acid (Na) monostyrene-vinyl acetate copolymer or its saponified product, vinyl phosphoric acid (
Examples include Na) monoethylene-vinyl acetate copolymer or saponified products thereof.

Among these, vinyl phosphoric acid (
Na) monostyrene copolymer, vinyl phosphoric acid (Na) monoethylene copolymer, vinyl phosphoric acid (Na) monostyrene-alkyl (meth)acrylate copolymer, vinyl phosphoric acid (Na)
Examples include monoethylene-alkyl (meth)acrylate copolymer.

The amount of the polymer containing a sulfonic acid group and/or phosphoric acid group used as the protective colloid agent is usually 0.01% to 30.0% based on the hydrophobic organic solvent. Preferably 0.05% to ls. It is 0%.

If it is less than 0.01X, the protective colloid agent will not be sufficiently adsorbed to the colloid of the polymerizable monomer aqueous solution dispersed in the organic solvent,
The dispersion stability of the colloid becomes insufficient, resulting in agglomeration of particles and adhesion of particles to the polymerization tank. Also, 30
If it exceeds %, the viscosity of the system will increase too much and cleaning will be troublesome.

The polymerizable monomer used in the present invention includes (1) a water-soluble polymerizable monomer containing at least one acid group and/or a salt thereof in the molecule; (2) a water-soluble polymerizable monomer containing at least one acid group and/or a salt thereof in the molecule;
water-soluble heavy weight monomer (3) containing at least one amine or quaternary ammonium salt; or a combination of two or more water-soluble polymerizable monomers containing at least one hydroxyl group in the molecule. Can be mentioned.

The water-soluble polymerizable monomer (1) containing at least one acid group and/or its salt in the molecule is a monomer having a carboxyl group, specifically, an unsaturated mono- or polycarboxylic acid group. Acids [(meth)acrylic acid, ethacrylic acid,
Crotonic acid, sorbic acid, maleic acid, itaconic acid, cinnamic acid, etc.], their anhydrides [maleic anhydride, etc.; monomers having sulfonic acid groups, specifically aliphatic or aromatic vinyl sulfones. Acids [vinylsulfonic acid, allylsulfonic acid, vinyltoluenesulfonic acid, styrenesulfonic acid, etc., (meth)acrylicsulfonic acid [sulfoethyl (meth)acrylate, sulfopropyl (meth)acrylate, etc.], (meth)acrylamide sulfone Examples include acids such as 2-acrylamido-2-methylpropanesulfonic acid.

These polymerizable monomers having acid groups such as carboxylic acid groups and/or sulfonic acid groups may be used as water-soluble salts. 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 noethanolamine) and two or more thereof. Preferred among these are sodium and potassium salts.

Usually, the degree of neutralization of monomers containing acid groups is 30 mol% or less, preferably 50 to 80 mol%. If the degree of neutralization exceeds 30 mol%, the resulting resin will have a high Pll, which poses a problem in terms of safety for human skin.

The acid group-containing polymerizable monomers (1) above may be used alone or in combination of two or more. Among these, monomers having a carboxylic acid group are preferred.

The water-soluble polymerizable monomer (2) containing at least one amine or quaternary ammonium salt in the molecule may be a reaction product of dialkylaminoalkyl (meth)acrylate and alkyl halide or dialkyl sulfuric acid [for example (
(meth)acryloyloxyethyltrimethylammonium chloride or bromide, (meth)acryloyloxyethyltrimethynoleammonium sanolephate, (meth)acryloyloxyethyltrimethylammonium chloride, (meth)acryloyloxyethyldiethylmethyl Ammonium chloride, (meth)acryloinoleoxyethinoledimethylbenzyl ammonium chloride, (meth)acryloinoleoxyprovinoletrimethynoleammonium chloride, (meth)acryloyloxypyltrimethylammonium sulfate, etc.; dialkylaminohydroxy Reactants of alkyl (meth)acrylates and alkyl halides or dialkyl sulfates [e.g. (meth)acryloyloxyhydroxyethyltrimethylammonium chloride or bromide, (meth)acryloyloxyhydroxyethyltrimethylammonium sulfate, (meth)acryloyloxyhydroxypropyltrimethyl ammonium chloride, etc.]; Reactants of dialkylaminoalkyl (meth)acrylamide and alkyl halide or dialkyl sulfate [e.g., chloride or bromide of trimethylaminoethyl (meth)acrylamide, chloride of trimethylaminopropyl (meth)acrylamide, Diethylmethylaminoprobyl (meth)acrylamide chloride, etc.; dialkylaminohydroxyalkyl (meth)
Reactants of acrylamide and alkyl halides or dialkyl sulfates [e.g. chloride of trimethylaminohydroxyethyl (meth)acrylamide, chloride of trimethylaminohydroxypropyl (meth)acrylamide, diethylmethylaminohydroxypropyl (meth)
Acrylamide chloride, etc.; N-alkylvinylpyridinium chloride [e.g. N-methyl-2-vinylpyridinium chloride or bromide, N-methyl-4-vinylpyridinium chloride, etc.; trianolequinolearylinoleammonium halide] [For example, trimethylallylammonium chloride or bromide, triethylallylammonium chloride, etc.]
Examples include (meth)acrylamide and vinylpyrrolidone. These water-soluble heavy weight monomers containing at least one amine or quaternary ammonium salt in the molecule may be used alone or in combination of two or more.

Examples of the water-soluble polymerizable monomer (3) containing at least one hydroxyl group in the molecule include hydroxyethyl (meth)acrylate and hydroxybutypyr (meth)acrylate.

In producing the water absorbent resin according to the present invention, a crosslinking agent can be used if necessary.

The crosslinking agent to be added to the aqueous solution containing the polymerizable monomer is (1) a compound having at least two polymerizable double bonds and (2>! compounds having polymerizable double bonds and polymerizable). Examples include compounds having at least x groups capable of reacting with the functional groups of the functional monomers.

Examples of the compound (1) include the following.

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

■ Di- or polyesters of polyols and unsaturated mono- or polycarboxylic acids: Di- or tri-(meth) of polyols [ethylene glycol, trimethylonolebroban, glycerin, polyoxyethylene glycol, polyoxypropylene glycol, etc.] ) Acrylic acid ester: Unsaturated polyester [co- and di- or tri-(
meth)acrylic acid ester [polyepoxide and (meth)
Obtained by reaction with acrylic acid, etc.

■Carbamyl ester: Polyisocyanate [tolylene diisocyanate, hexamethylene diisocyanate, 4.4'-/phenylmethane diisocyanate, NCO group-containing prepolymer (obtained by reaction of the above polyisocyanate with an active hydrogen atom-containing compound), etc. ] and hydroxyethyl (meth)acrylate.

■Di- or polyvinyl compounds: divinylbenzene, divinyltoluene, divinylxylene, divinyl ether, divinyl ketone, trivinylbenzenate.

■G- or poly(meth)allyl ethers of polyols: Polyols [alkylene glycol, glycerin, polyalkylene glycol, polyalkylene polyol,
carbohydrates, etc.] or poly(meth)allyl ethers, such as polyethylene glycol, allylated starch, allylated cellulose.

■G- or polyallylic esters of polycarboxylic acids: diallyl phthalate, diallyl adipate, etc.

■Esters of unsaturated mono- or polycarboxylic acids and polyol mono(meth)allyl ethers: (meth)acrylic acid esters of polyethylene glycol monoallyl ether, etc.

■Polyaryloxyalkanes: Tetraallyloxyethane etc.

Examples of compounds (2) include ethylenically unsaturated compounds containing carboxyl groups, sulfonic acid groups and/or groups reactive with quaternary ammonium bases, such as hydroxyl groups, epoxy groups, tertiary amino groups, etc. Specifically, unsaturated compounds containing hydroxyl groups [such as N-methylol (meth)acrylamide], unsaturated compounds containing epoxy groups [such as glycidyl (meth)acrylate], and unsaturated compounds containing tertiary amino groups [such as (meth)acrylic dimethylaminoethyl acid, diethylaminoethyl (meth)acrylate, etc.).

Among the copolymerizable crosslinking agents, the compound (1) is preferred, and particularly preferred are N,N-methylenebisacrylamide, ethylene glycol diacrylate,
trimethylolbroban triacrylate and tetraallyloxyethane.

In the present invention, the amount of crosslinking agent added to the aqueous solution containing the polymerizable monomer is usually 0.01 to I (1% by weight, preferably O.1% by weight) based on the total weight of the polymerizable monomer. -5% by weight, more preferably 0.6-3% by weight.

If the amount of the crosslinking agent is less than 0.01% by weight, the resulting resin will have a low gel strength upon water absorption and will be in the form of a sol. On the other hand, lO wt%
On the contrary, if it exceeds this, the gel strength becomes excessive and the water absorption capacity decreases.

In the present invention, a resin having higher gel strength and excellent water absorption gel stability is produced by crosslinking with a compound having at least two groups that can react with the functional group of the polymerizable monomer. be able to.

Examples of this compound include compounds having at least two epoxy groups, hydroxyl groups, incyanato groups, etc., and polyvalent metal compounds capable of forming ionic crosslinks.

Specific examples of compounds include polyepoxy or polyglycidyl ether compounds (ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, glycerin to 1,3-diglycidyl ether, polyethylene glycol diglycidyl ether, bisphenol A-shrimp chlorohydrin) epoxy resins, etc.), polyols (glycerin, ethylene glycol, propylene glycol, etc.).

Examples of polyvalent metal compounds include alkaline earth metals (calcium, magnesium, etc.), hydroxides of zinc, aluminum, titanium, etc., their halides, and salts (sulfates, carbonates, acetates, etc.). Specifically, calcium hydroxide, magnesium chloride, zinc diacetate,
Examples include aluminum sulfate.

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 crosslinking agent added to the aqueous solution containing the polymerizable monomer, the water absorption capacity required of the resin, and the gel strength. It is usually 5% or less, preferably 0.001 to 3% of the total body weight. This compound may be added to the polymer at any point during polymerization, after polymerization, or after drying into powder.

In the present invention, the method of polymerizing the dispersion containing the water-soluble polymerizable monomer and the crosslinking agent may be a conventionally known method, such as a method of polymerizing using a radical polymerization catalyst, a method of polymerizing with a radical polymerization catalyst, a method of polymerizing with a radiation, an electron Examples include conventional methods such as irradiation with radiation, ultraviolet rays, etc.

In the method using a radical polymerization catalyst, the catalyst is an azo compound C azobisisobutyanitrile (AI
BN), azobiscyanovaleric acid, 22'-azobis(
(2-amidinopropane) hydrochloride, inorganic peroxides [hydrogen peroxide, ammonium persulfate, potassium persulfate, sodium persulfate, etc.], organic peroxides [benzoyl peroxide, di-t-butyl peroxide, cumene hydro peroxide, succinic acid peroxide, di(2-ethoxyethyl) peroxydicarbonate, etc.] and rednox catalysts [alkali metal sulfite or bisulfite, ammonium sulfite, ammonium bisulfite, ascorbic acid, and other reducing agents and alkalis] Examples include combinations of oxidizing agents such as metal persulfates, ammonium persulfates, and peroxides, 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 it is usually 0-150'C, preferably 5
~100'C.

The amount of catalyst may be the same as usual, for example, it is usually 0 based on the total weight of all polymerizable vinyl monomers and copolymerizable crosslinking agent.
．． 0.0005 to 5%, preferably 0.001 to 2%.

In principle, any liquid can be used as the hydrophobic organic solvent used in the present invention, as long as it does not participate in polymerization and does not mix with water. Preferred are aliphatic, aromatic and halogenated hydrocarbons, or a mixed solvent thereof.

In the present invention, the ratio of the aqueous solution containing the polymerizable monomer to the organic solvent serving as the dispersion medium can be varied over a wide range. Generally, if the proportion of the organic solvent as a dispersion medium is small, the amount of polymerizable monomer charged per batch in the reactor can be increased, but it becomes difficult to control heat generation.

Therefore, a volume ratio of 1=4 to 4:1 is usually appropriate.

[Example] Hereinafter, the present invention will be explained in detail with reference to Examples and Comparative Examples. The protective colloid agents used in the examples are listed below.

Protective colloid A: Acrylamide 2-methylpropanesulfonic acid 10g1 Styrene 200g1
100 g of methyl acrylate was dissolved in 300 g of ethanol and polymerized using AIBNIg at 78° C. under a nitrogen stream. After polymerization, ethanol was distilled off to obtain a polymer. The weight average molecular weight of this polymer was soo, and the content of sulfonic acid groups in the polymer was 1.0%.

Protective colloid B: styrene sulfonate soflog styrene 300 g, vinyl acetate to og,
Sodium dodecylbenzenesulfonate Ig in distilled water 5Q
The mixture was dispersed in Qg, and emulsion polymerization was carried out using 0.5 g of potassium persulfate at 85° C. under a nitrogen stream. After polymerization, the emulsion was separated using a centrifuge, washed with distilled water, and dried to obtain a polymer. The weight average molecular weight of this polymer was 300,000, and the content of sulfonic acid groups in the polymer was 0.
．． It was 9%.

Protective colloid C: Vinyl phosphoric acid 151h n-butyl vinyl ether 200g methyl ethyl ketone 200g
and polymerized using 1 g of AIBN at 85° C. under a nitrogen stream. After polymerization, methyl ethyl ketone was distilled off to obtain a polymer. The molecular weight of this polymer was 70,000, and the content of phosphoric acid groups was 1.5%.

Example 1 500 g of xylene was placed in a separable flask equipped with a stirrer, a reflux condenser, a dropping funnel, and a nitrogen introduction tube, and 5 g of protective colloid A was added and dissolved by stirring. After blowing nitrogen through the nitrogen inlet tube to drive out dissolved oxygen, the humidity was raised to 65°C.

Separately, take 144 g of acrylic acid in a beaker, add 80 g of sodium hydroxide to neutralize it, and then add 80 g of sodium hydroxide to neutralize it.
．． 1 g was added and mixed uniformly. This aqueous sodium acrylate solution was placed in a dropping funnel attached to a separable flask. Nitrogen was again introduced into the separable flask from the nitrogen introduction tube, and an aqueous sodium acrylate solution was added dropwise under a nitrogen stream, and polymerization was carried out while maintaining the inside of the flask at 80-65°C. After polymerization, 0.1 g of ethylene glycol diglycidyl ether was added and the temperature was raised to 90°C to effect crosslinking. Thereafter, xylene was distilled off under reduced pressure, and the remaining swollen polymer was dried under reduced pressure at 80°C. The particle size distribution and center particle diameter of this absorbent resin were measured and are listed in Table-1.

Example 2 The same operation as in Example 1 was performed except that protective colloid agent B was used.

Example 3 The same operation as in Example 1 was performed except that the adhesive colloid agent C was used.

Comparative Example 1 The same operation as in Example 1 was performed except that sorbitol monostearate was used as the dispersant.

Comparative Example 2 The same operation as in Example 1 was performed except that ethyl cellulose was used as the dispersant.

[Effects of the Invention] As is clear from Table 1, when the present invention is used to produce absorbent resin using the reverse phase suspension polymerization method, agglomeration between particles and adhesion of particles to the walls of the polymerization tank can be prevented. It is possible to produce a water-absorbing resin with a sharp particle size distribution, which is extremely small and has a large particle size.

Claims (1)

[Claims] 1. In the reverse phase suspension polymerization method in which a water-soluble polymerizable monomer is polymerized by suspending it in a hydrophobic organic solvent using a water-soluble radical polymerization catalyst, a protective colloid is used. A method for producing a water-absorbing resin, which comprises producing the water-absorbing resin using a polymer containing a sulfonic acid group and/or a phosphoric acid group. 2. The polymerizable monomer is (1) a water-soluble polymerizable monomer containing at least one acid group and/or a salt thereof in the molecule (2) at least one amine or Water-soluble polymerizable monomer containing quaternary ammonium salt (3) Any one or a combination of two or more water-soluble polymerizable monomers containing at least one or more hydroxyl group in the molecule. 1. The method for producing a water-absorbing resin according to 1. 3. The method for producing a water-absorbing resin according to claim 1 or 2, wherein a crosslinking agent is used in producing the water-absorbing resin in the reverse phase suspension polymerization method. 4. The method for producing a water-absorbing resin according to any one of claims 1 to 3, wherein the weight average molecular weight of the polymer used as the protective colloid exceeds 10,000. 5. The method for producing a water-absorbing resin according to any one of claims 1 to 3, wherein the weight average molecular weight of the polymer used as the protective colloid exceeds 20,000. 6. Sulfonic acid groups and/or used as protective colloids
Or, the composition of the polymer containing phosphoric acid groups is based on the total weight of the polymer: (A) Sulfonic acid (salt) group and/or phosphoric acid (salt) group: 0.001 to 50% (B) Hydrophobicity The method for producing a water-absorbing resin according to any one of claims 1 to 5, comprising groups: 0 to 99.999% (C) hydrophilic groups other than sulfonic acid groups and/or phosphoric acid groups: 0 to 50%.