JP2006089525A - Method for producing water-absorbing resin particle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a water-absorbing resin particle comprising small amounts of fine powder and coarse powder and having a narrow particle size distribution. <P>SOLUTION: The method for producing a water-absorbing resin particle by subjecting a water-soluble ethylenic unsaturated monomer to reversed phase suspension polymerization comprises (A) subjecting an aqueous solution of a water-soluble ethylenic unsaturated monomer to first-stage reversed phase suspension polymerization in the presence of a surfactant and/or a polymer protective colloid and, if necessary, an internal crosslinking agent by using a water-soluble radical polymerization initiator in a hydrocarbon-based solvent, (B) adding an aqueous solution of a water-soluble ethylenic unsaturated monomer, which comprises a water-soluble radical polymerization initiator, 1.2-2.5 mols of a water-soluble ethylenic unsaturated monomer based on 1 mol of the water-soluble ethylenic unsaturated monomer subjected to the first-stage polymerization and optionally an internal crosslinking agent to the reaction mixture after the first-stage reversed phase suspension polymerization in a state in which the surfactant and/or the polymer protective colloid are dissolved in the hydrocarbon-based solvent and (C) then precipitating the surfactant and/or the polymer protective colloid and carrying out second-stage reversed phase suspension polymerization. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing water absorbent resin particles. More specifically, the present invention relates to a method for producing water-absorbing resin particles with a small amount of fine powder and coarse powder and a narrow particle size distribution.

  Water-absorbing resins are widely used in various fields such as sanitary materials such as disposable diapers and sanitary items, agricultural and horticultural materials such as water retention materials and soil improvement materials, water-proofing materials for cables, and industrial materials such as anti-condensation materials. .

  Examples of such a water-absorbing resin include a hydrolyzate of starch-acrylonitrile graft copolymer, a neutralized product of starch-acrylic acid graft copolymer, a saponified product of vinyl acetate-acrylic ester copolymer, A partially neutralized acrylic acid is known.

  In recent years, absorbent articles such as paper diapers are becoming thinner, and tend to reduce the content of hydrophilic fibers that are bulky and have a small amount of water absorption, and to increase the proportion of water-absorbing resin that has a large amount of water absorption. The water-absorbent resin in the absorber containing the water-absorbent resin at a high concentration is required to have high liquid diffusibility in addition to a high water absorption ratio, and further, the absorbent body itself has a good touch. There is also a need for flexibility.

  The liquid diffusibility generally tends to decrease as the proportion of fine powder in the water absorbent resin increases. That is, the fine powder in the water-absorbent resin particles tends to block the path for body fluid to diffuse when swollen, and so-called “gel blocking” is likely to occur. Since the absorber that has caused gel blocking has poor liquid diffusibility, the performance of the original absorber is not fully exhibited, and the amount of liquid reversion increases.

  On the other hand, the thinned absorbent body has a low content of hydrophilic fibers and a large proportion of water-absorbent resin particles. Therefore, when water-absorbent resin particles having a large proportion of large particle diameter are used, the absorbent body is very rugged. And its flexibility is greatly impaired. Such an absorber does not endure the use of a paper diaper or the like that places an emphasis on the feel of the touch. Therefore, the water-absorbing resin particles used in the thinned absorbent body excellent in water-absorbing performance and tactile sensation are preferably water-absorbing resin particles with few fine powders and coarse powders and a narrow particle size distribution.

  As a method for producing water-absorbing resin particles having a particle size suitable for such an absorbent article, a polymer after producing water-absorbing resin particles by the first-stage monomer in the production method by the reverse phase suspension polymerization method is used. By adding a polymerizable monomer to the polymerization reaction liquid in which the particles are suspended and polymerizing the monomer, the first stage particles are granulated (for example, refer to Patent Document 1), or by reverse phase suspension polymerization. After the first stage polymerization, a surfactant of HLB7 or higher is added to the polymerization reaction liquid in which the polymer particles are suspended, the second stage monomer is absorbed into the first stage polymer gel, polymerized, and granulated. Method (for example, refer to Patent Document 2), after the first stage polymerization, the second stage monomer is absorbed in the first stage polymer gel in the presence of the inorganic powder in the polymerization reaction liquid in which the polymer particles are suspended to polymerize. And granulating method (for example, Patent Document 3) Irradiation), and the like have been proposed.

  However, it is difficult to say that any of these water-absorbing resin particles is relatively satisfactory in fine powder or coarse powder and has a wide particle size distribution.

Japanese Patent Laid-Open No. 5-17509 JP-A-9-12613 JP-A-9-77810

  An object of the present invention is to provide a method for producing water-absorbing resin particles with a small amount of fine powder and coarse powder and a narrow particle size distribution.

That is, the present invention is a method for producing water-absorbent resin particles by reverse-phase suspension polymerization of a water-soluble ethylenically unsaturated monomer,
(A) A water-soluble ethylenically unsaturated monomer in a hydrocarbon solvent using a water-soluble radical polymerization initiator in the presence of a surfactant and / or polymer protective colloid and, if necessary, an internal crosslinking agent Subject the aqueous body solution to the first-stage reverse phase suspension polymerization,
(B) In the state where the surfactant and / or the polymer protective colloid is dissolved in the hydrocarbon solvent, a water-soluble radical polymerization initiator is added to the reaction mixture in which the first-stage reversed-phase suspension polymerization is completed, 1.2 to 2.5 moles of water-soluble ethylenically unsaturated monomer with respect to 1 mole of water-soluble ethylenically unsaturated monomer subjected to the first stage polymerization, and, if necessary, an internal crosslinking agent Add a water-soluble ethylenically unsaturated monomer aqueous solution containing
(C) Next, the present invention relates to a method for producing water-absorbing resin particles, characterized in that a surfactant and / or polymer protective colloid is deposited, and then second-phase reversed-phase suspension polymerization is performed.

  According to the present invention, water-absorbent resin particles with a small amount of fine powder and coarse powder and a narrow particle size distribution are provided.

  In the present invention, first, a water-soluble ethylenic acid is used in a hydrocarbon solvent using a water-soluble radical polymerization initiator in the presence of a surfactant and / or a polymer protective colloid and, if necessary, an internal crosslinking agent. The unsaturated monomer aqueous solution is subjected to the first-stage reverse phase suspension polymerization.

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

  Preferred among the water-soluble ethylenically unsaturated monomers are (meth) acrylic acid or alkali metal salts thereof, (meth) acrylamide and N, N-dimethylacrylamide, because they are easily available industrially. .

  The water-soluble ethylenically unsaturated monomer is used as an aqueous solution. The concentration of the water-soluble ethylenically unsaturated monomer in the water-soluble ethylenically unsaturated monomer aqueous solution is preferably 25% by weight to the saturated concentration.

  When the water-soluble ethylenically unsaturated monomer contains an acid group, the acid group may be neutralized with an alkali metal. The degree of neutralization with alkali metal is neutralized from the viewpoint of increasing the osmotic pressure of the resulting water-absorbent resin particles, increasing the water absorption rate, and preventing problems such as safety due to the presence of excess alkali metal. It is preferable that it exists in the range of 10-100 mol% of the acid group of the previous water-soluble ethylenically unsaturated monomer. Examples of the alkali metal include lithium, sodium, and potassium. Of these, sodium and potassium are preferred.

  As the surfactant, for example, sorbitan fatty acid ester, (poly) glycerin fatty acid ester [“(poly)” means both with and without the prefix “poly”. The same shall apply hereinafter), nonionic surfactants such as sucrose fatty acid ester, sorbitol fatty acid ester, polyoxyethylene alkylphenyl ether, hexaglyceryl monobeherate; fatty acid salt, alkylbenzene sulfonate, alkylmethyl taurate, polyoxyethylene Anionic surfactants such as alkylphenyl ether sulfates and polyoxyethylene alkyl ether sulfonates can be mentioned, and these may be used alone or in combination of two or more. Good. Among these, at least one selected from the group consisting of sorbitan fatty acid ester, polyglycerin fatty acid ester and sucrose fatty acid ester is preferable from the viewpoint of ease of particle size distribution control.

  Examples of the polymer protective colloid include, for example, ethyl cellulose, ethyl hydroxyethyl cellulose, polyethylene oxide, polyethylene-polyacrylic acid copolymer, anhydrous maleated polyethylene, anhydrous maleated polybutadiene, and anhydrous maleated EPDM (ethylene-propylene-diene-methylene copolymer). Polymer) and anhydrous maleated polypropylene. These may be used alone or in combination of two or more.

  The amount of the surfactant and / or the polymer protective colloid is determined in the first-stage reversed-phase suspension polymerization from the viewpoint of easy control of the particle size of the water-absorbent resin particles and suspension stability during polymerization. Preferably it is 0.05-5 weight part with respect to 100 weight part of water-soluble ethylenically unsaturated monomer aqueous solution made, More preferably, it is 0.1-3 weight part. When the amount of the surfactant and / or polymer protective colloid is less than 0.05 parts by weight, the suspension stability during polymerization tends to be low, and when it is more than 5 parts by weight, the amount is only commensurate with the amount. However, there is a tendency that it is economically disadvantageous.

  Examples of the internal crosslinking agent include di- or tri (meth) acrylic esters of polyols such as ethylene glycol, propylene glycol, trimethylolpropane, glycerin, polyoxyethylene glycol, polyoxypropylene glycol, polyglycerin; Polyesters obtained by reacting alcohols with unsaturated acids such as maleic acid and fumaric acid; bisacrylamides such as N, N′-methylenebisacrylamide; and reacting polyepoxides with (meth) acrylic acid Di- or tri (meth) acrylic acid esters obtained; carbamyl ester of di (meth) acrylic acid obtained by reacting polyisocyanate such as tolylene diisocyanate or hexamethylene diisocyanate with hydroxyethyl (meth) acrylate Tels; compounds having two or more polymerizable unsaturated groups such as diallylized starch, diallylized cellulose, diallyl phthalate, N, N ′, N ″ -triallyl isocyanate, and divinylbenzene; (poly) ethylene glycol diglycidyl Diglycidyl ether compounds such as ether, (poly) propylene glycol diglycidyl ether, (poly) glycerin diglycidyl ether; haloepoxy compounds such as epichlorohydrin, epibromhydrin, α-methylepichlorohydrin; 2,4-tolylene diisocyanate, hexa Compounds having two or more reactive functional groups such as isocyanate compounds such as methylene diisocyanate; 3-methyl-3-oxetanemethanol, 3-ethyl-3-oxetanemethanol, 3-butyl-3-oxetanemethanol, Examples include oxetane compounds such as 3-methyl-3-oxetaneethanol, 3-ethyl-3-oxetaneethanol, and 3-butyl-3-oxetaneethanol, and these may be used alone or in combination of two kinds. You may mix and use the above. Among them, ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, glycerin diglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, polyglycerin diglycidyl ether and N, N′-methylenebisacrylamide are It is preferable because of its excellent reactivity at low temperatures.

  The amount of the internal cross-linking agent is selected for the first-stage reverse phase suspension polymerization from the viewpoint that the water solubility of the resulting polymer is suppressed by appropriate cross-linking and that the polymer exhibits sufficient water absorption. The amount is preferably 3 parts by weight or less, more preferably 0.001 to 1 part by weight based on 100 parts by weight of the water-soluble ethylenically unsaturated monomer.

  Examples of the water-soluble radical polymerization initiator include persulfates such as potassium persulfate, ammonium persulfate, and sodium persulfate; 2,2′-azobis (2-amidinopropane) dihydrochloride, azobis (cyanovaleric acid), and the like. These azo compounds may be used, and these may be used alone or in admixture of two or more. Among these, potassium persulfate, ammonium persulfate, and sodium persulfate are preferable from the viewpoint of easy availability and good storage stability. In addition, a radical polymerization initiator can be used as a redox-type polymerization initiator by using together with nitrite etc.

  The amount of the water-soluble radical polymerization initiator is usually determined from the viewpoint of shortening the polymerization reaction time and preventing a rapid polymerization reaction. Preferably it is 0.00001-0.02 mol, More preferably, it is 0.0001-0.01 mol per mol of a monomer.

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

  The amount of the hydrocarbon-based solvent is usually the water-soluble ethylenically unsaturated monomer 100 that is subjected to the first-stage reversed-phase suspension polymerization from the viewpoint of removing the heat of polymerization and easily controlling the polymerization temperature. Preferably it is 50-600 weight part with respect to a weight part, More preferably, it is 100-550 weight part.

  The first-stage reversed-phase suspension polymerization involves carbonizing a water-soluble ethylenically unsaturated monomer aqueous solution, a surfactant and / or polymer protective colloid, a water-soluble radical polymerization initiator, and an internal crosslinking agent as necessary. It can carry out by heating under stirring in a hydrogen-based solvent.

  The reaction temperature during reverse-phase suspension polymerization varies depending on the water-soluble radical polymerization initiator used, so it cannot be determined unconditionally, but the polymerization proceeds rapidly and the polymerization time is shortened, resulting in excellent economic efficiency. From the viewpoint of easily removing the heat of polymerization and performing the reaction smoothly, it is preferably 20 to 110 ° C, more preferably 40 to 80 ° C. The reaction time is usually 0.5 to 4 hours.

  The completion of the first-stage reversed-phase suspension polymerization can be confirmed by the polymerization reaction temperature reaching the highest point and the reaction temperature starting to decrease.

  Thus, the reaction mixture in which the first-stage reversed-phase suspension polymerization is completed is subjected to the second-stage reversed-phase suspension polymerization.

  In the present invention, the reverse phase suspension polymerization may be performed in two or more stages, but the number of stages is from the viewpoint of easily controlling the particle diameter of the water-absorbent resin particles and further increasing the productivity. Usually, it is preferably two stages.

  The feature of the present invention is that the surfactant and / or polymer protective colloid contained in the reaction mixture obtained in the first stage is dissolved in the hydrocarbon solvent, and the first stage. A water-soluble ethylenically unsaturated monomer containing a water-soluble radical polymerization initiator, a specific amount of a water-soluble ethylenically unsaturated monomer, and, if necessary, an internal crosslinking agent, in the reaction mixture after the reverse phase suspension polymerization is completed The body aqueous solution is added, and then the surfactant and / or polymer protective colloid is once precipitated, and then the second-stage reversed-phase suspension polymerization reaction is performed.

  In order to keep the surfactant and / or polymer protective colloid dissolved in the hydrocarbon solvent, or to deposit the surfactant and / or polymer protective colloid, the reaction mixture is used. What is necessary is just to control the temperature.

  The temperature of the reaction mixture when adding the water-soluble ethylenically unsaturated monomer aqueous solution in the second stage to the reaction mixture may be any temperature at which the surfactant and / or the polymer protective colloid are dissolved, For example, it is desirable that the temperature is higher than 30 ° C and lower than 60 ° C, preferably 35-60 ° C, more preferably 40-60 ° C. When the temperature when adding the water-soluble ethylenically unsaturated monomer aqueous solution to the reaction mixture is 30 ° C. or less, the surfactant and / or the polymer protective colloid tends to precipitate in the hydrocarbon solvent, Moreover, when it exceeds 60 degreeC, there exists a tendency for a polymerization reaction to advance before water-soluble ethylenically unsaturated monomer aqueous solution is fully mixed in a hydrocarbon-type solvent.

  After adding the water-soluble ethylenically unsaturated monomer aqueous solution to the reaction mixture, the temperature of the reaction mixture when depositing the surfactant and / or polymer protective colloid is, for example, 30 ° C. or less, preferably 10-30. It is desirable that the temperature be When the temperature of the reaction mixture exceeds 30 ° C., the surfactant and / or polymer protective colloid is dissolved in the hydrocarbon solvent, or the water-soluble ethylenically unsaturated monomer aqueous solution is sufficient in the hydrocarbon solvent. The polymerization reaction tends to proceed before being mixed.

  Thus, a water-soluble ethylenically unsaturated monomer aqueous solution was added to the reaction mixture after the reverse phase suspension polymerization in the first stage was completed, and a surfactant and / or polymer protective colloid was precipitated from the reaction mixture. Thereafter, by performing reverse-phase suspension polymerization in the second stage, water-absorbent resin particles with a small amount of fine powder and coarse powder and a narrow particle size distribution are obtained. Thus, although the reason why the water-absorbent resin particles having a small amount of fine powder and coarse powder and a narrow particle size distribution are obtained is not clear, it is presumed to be based on the following reason.

  That is, the second-stage water-soluble ethylenically unsaturated monomer aqueous solution added to the reaction mixture in a state where the surfactant and / or the polymer protective colloid are dissolved is the first-stage polymerization reaction. In the reaction mixture, it is dispersed in the form of droplets without being absorbed by the water-containing gel produced in (1). Next, the reaction mixture is cooled while maintaining this dispersed state, and the surfactant and / or polymer protective colloid is precipitated, so that the water-soluble ethylenically unsaturated monomer aqueous solution in the second stage is in a dispersed state. As it is, it is uniformly absorbed in the hydrogel produced in the first stage, and the first stage particles agglomerate. By polymerizing this, water-absorbent resin particles with less fine powder and coarse powder and narrow particle size distribution are generated. Presumed to be.

  The water-soluble radical polymerization initiator, the internal cross-linking agent, and the water-soluble ethylenically unsaturated monomer aqueous solution added to the reaction mixture after completion of the first-stage reversed-phase suspension polymerization are the first-stage reversed-phase suspension. It may be the same as that used in the polymerization, or may be different.

  The amount of the water-soluble radical polymerization initiator in the water-soluble ethylenically unsaturated monomer aqueous solution is usually the polymerization of each stage after the second stage from the viewpoint of shortening the polymerization reaction time and preventing a rapid polymerization reaction. The amount is preferably 0.00001 to 0.02 mol, and more preferably 0.0001 to 0.01 mol, per 1 mol of the water-soluble ethylenically unsaturated monomer to be attached.

  Further, the amount of the internal crosslinking agent in the water-soluble ethylenically unsaturated monomer aqueous solution is from the viewpoint that the water solubility of the obtained polymer is suppressed by appropriate crosslinking, and that the polymer exhibits sufficient water absorption. , Preferably 3 parts by weight or less, more preferably 0.001 to 1 part by weight with respect to 100 parts by weight of the water-soluble ethylenically unsaturated monomer to be subjected to polymerization in each stage after the second stage. .

  The amount of the water-soluble ethylenically unsaturated monomer added to the reaction mixture obtained by the reverse phase suspension polymerization in the first stage is the same as that of the water-soluble ethylenically unsaturated monomer 1 used in the first stage. Preferably it is 1.2-2.5 mol with respect to mol, More preferably, it is 1.3-2.3 mol, More preferably, it is 1.4-2.2 mol. When the amount of the water-soluble ethylenically unsaturated monomer relative to 1 mol of the water-soluble ethylenically unsaturated monomer used in the first stage is less than 1.2 mol, it was generated by the polymerization reaction in the first stage. If the amount of water-soluble ethylenically unsaturated monomer required to agglomerate resin particles is insufficient and the amount of fine powder tends to increase and exceeds 2.5 mol, the amount of water-soluble ethylenically unsaturated monomer Therefore, the agglomeration proceeds too much and the coarse powder tends to increase.

  Reverse reaction after adding a water-soluble ethylenically unsaturated monomer aqueous solution containing a water-soluble radical polymerization initiator and, if necessary, an internal crosslinking agent, to the reaction mixture obtained by the first-stage reversed-phase suspension polymerization. The phase suspension polymerization can be carried out under the same conditions as in the first-stage reverse phase suspension polymerization. As described above, the operation is performed in one or more stages.

  The water absorbent resin particles thus obtained may be post-crosslinked with a post-crosslinking agent after polymerization, if necessary.

  Examples of the post-crosslinking agent include ethylene glycol, propylene glycol, trimethylol propane, glycerin, polyoxyethylene glycol, polyoxypropylene glycol, polyglycerin and other diols, triols and polyols; (poly) ethylene glycol diglycidyl ether, Diglycidyl ether compounds such as (poly) propylene glycol diglycidyl ether and (poly) glycerin diglycidyl ether; epihalohydrin compounds such as epichlorohydrin, epibromhydrin and α-methylepichlorohydrin; 2,4-tolylene diisocyanate, hexamethylene diisocyanate And compounds having two or more reactive functional groups, such as isocyanate compounds, and the like. May be used, it may be used as a mixture of two or more. Among these, from the viewpoint of excellent reactivity at low temperatures, ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, glycerin diglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether and polyglycerin diglycidyl. Ether is preferred.

  The amount of the post-crosslinking agent added is controlled from the viewpoint of controlling the amount of water absorption and further maintaining the gel strength at the time of water absorption, with respect to 100 parts by weight of the total amount of the water-soluble ethylenically unsaturated monomer subjected to polymerization. Preferably it is 0.01-5 weight part, More preferably, it is 0.02-4 weight part, More preferably, it is 0.03-3 weight part. When the added amount of the post-crosslinking agent is less than 0.01 parts by weight, the water-absorbing resin particles obtained have a tendency to weaken the gel strength and the water-absorbing resin particles have a tendency to weaken the gel strength. Since the particles are excessively crosslinked, the water-absorbent resin particles tend not to exhibit sufficient water absorption.

  The post-crosslinking of the water-absorbing resin particles with the post-crosslinking agent is preferably performed after the end of the reverse phase suspension polymerization in the final stage.

  The mixing of the water absorbent resin particles and the postcrosslinking agent is preferably performed in the presence of water. The amount of water when mixing the water-absorbent resin particles and the post-crosslinking agent varies depending on the type, particle size and water content of the water-absorbent resin particles, but is usually a water-soluble ethylenically unsaturated monomer subjected to polymerization. The total amount is preferably 10 to 30 parts by weight with respect to 100 parts by weight. The amount of water means the total amount of water contained in the polymerization reaction and water used as necessary when adding the post-crosslinking agent.

  Thus, the post-crosslinking reaction in the vicinity of the surface of the water-absorbent resin particles can be more suitably advanced by controlling the amount of water during mixing of the water-absorbent resin particles and the post-crosslinker.

  When mixing the water-absorbent resin particles and the post-crosslinking agent, a hydrophilic organic solvent may be used as a solvent, if necessary.

  Examples of the hydrophilic organic solvent include lower alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol and isopropyl alcohol, ketones such as acetone and methyl ethyl ketone, ethers such as diethyl ether, dioxane and tetrahydrofuran, N, N -Amides such as dimethylformamide, sulfoxides such as dimethyl sulfoxide, and the like. These hydrophilic organic solvents may be used alone or in combination of two or more.

  The reaction temperature when the water-absorbing resin particles are subjected to a crosslinking reaction with a post-crosslinking agent is preferably 30 to 170 ° C, more preferably 40 to 150 ° C. When the reaction temperature is less than 30 ° C., the crosslinking reaction is difficult to proceed and the crosslinking reaction tends to take an excessive amount of time. When the reaction temperature exceeds 170 ° C., the resulting water-absorbent resin particles tend to decompose. .

  The reaction time varies depending on the reaction temperature, the type and amount of the crosslinking agent, the type of solvent and the like, and thus cannot be determined unconditionally, but is usually 1 to 300 minutes, preferably 5 to 200 minutes.

  Thus, the water absorbent resin particles of the present invention are obtained. Such water-absorbent resin particles have a weight average particle size of 200 to 500 μm, a small content of fine powder and coarse powder, and a narrow particle size distribution. The weight average particle diameter of the water-absorbent resin particles is a value when measured by the measurement method described in Examples described later.

  In addition, you may add additives, such as a lubricant, a deodorant, and an antibacterial agent, to the water absorbing resin particle of this invention further according to the objective.

  The amount of the additive varies depending on the use of the water-absorbent resin particles, the kind of the additive, etc., but is preferably 0.001 with respect to 100 parts by weight of the total amount of the water-soluble ethylenically unsaturated monomer subjected to polymerization. -10 parts by weight, more preferably 0.01-5 parts by weight.

  Next, the present invention will be described in more detail based on examples, but the present invention is not limited to such examples.

Example 1
Into a 500 mL Erlenmeyer flask, 92 g (1.02 mol) of 80 wt% aqueous acrylic acid solution was added, and 146.1 g of 21.0 wt% aqueous sodium hydroxide solution was added dropwise with ice cooling to add 75 mol acrylic resin. Acid neutralization was performed to prepare a partially neutralized acrylic acid salt solution with a monomer concentration of 38% by weight. To the resulting aqueous solution of partially neutralized acrylic acid, 18.4 mg (119 μmol) of N, N′-methylenebisacrylamide as an internal crosslinking agent and 92 mg (0.34 mmol) of potassium persulfate as a water-soluble radical polymerization initiator were added. This was added to obtain a monomer aqueous solution (a1) for reverse phase suspension polymerization in the first stage.

  In a 2 L five-necked cylindrical round bottom flask equipped with a stirrer, two-stage paddle blade, reflux condenser, dropping funnel and nitrogen gas introduction tube, 340 g (500 mL) of n-heptane and poly (surfactant) as a surfactant 0.92 g of glycerin fatty acid ester [manufactured by Taiyo Kagaku Co., Ltd., trade name: Sunsoft Q-185S] was added and dissolved in n-heptane, and the internal temperature was adjusted to 35 ° C. Thereafter, while maintaining the internal temperature at 35 ° C., the monomer aqueous solution (a1) for the first stage polymerization was added and suspended under stirring, and the system was replaced with nitrogen gas. Subsequently, the temperature was raised to 70 ° C., and the first-stage reversed-phase suspension polymerization was performed.

  Separately, 147.2 g (1.64 mol) of 80 wt% aqueous acrylic acid solution was placed in a 500 mL Erlenmeyer flask, and 181.8 g of 27.0 wt% sodium hydroxide aqueous solution was added dropwise while cooling with ice. Then, 75 mol% of acrylic acid was neutralized to prepare a partially neutralized aqueous solution of acrylic acid having a monomer concentration of 44% by weight. To the resulting partially neutralized acrylic acid aqueous solution, 29.4 mg (191 μmol) of N, N′-methylenebisacrylamide as an internal crosslinking agent and 147 mg (0.54 mmol) of potassium persulfate as a water-soluble radical polymerization initiator were added. This was added to obtain a monomer aqueous solution (b1) for the second-phase reversed phase suspension polymerization.

  After the completion of the first-stage reversed-phase suspension polymerization, the second-stage polymerization is performed while controlling the temperature of the reaction mixture so as not to be 40 ° C. or lower in order to keep the surfactant dissolved. A monomer aqueous solution (b1) was added to the system. Subsequently, the reaction mixture was cooled to 13 ° C. to precipitate a surfactant, and the system was stirred for 30 minutes in that state, and at the same time, the system was replaced with nitrogen gas. Thereafter, the temperature was raised to 70 ° C., and the second-stage reversed-phase suspension polymerization was performed.

  After completion of the reverse phase suspension polymerization, 280 g of water was extracted from the azeotrope of n-heptane and water by heating again, and then 120 mg (0.69 mmol) of ethylene glycol diglycidyl ether as a post-crosslinking agent. And a post-crosslinking reaction was carried out at 80 ° C. for 2 hours in the presence of 52 g of water. After the crosslinking reaction, n-heptane and water in the system were distilled off with heating to obtain 248 g of water-absorbing resin particles.

Example 2
In a 2 L five-neck cylindrical round bottom flask equipped with a stirrer, two-stage paddle blade, reflux condenser, dropping funnel and nitrogen gas introduction tube, 340 g (500 mL) of n-heptane and sorbitan as a surfactant After adding 0.92 g of fatty acid ester (Nippon Yushi Co., Ltd., trade name: Nonion SP-60R) and dissolving it in n-heptane, the internal temperature was set to 35 ° C. Thereafter, while maintaining the internal temperature at 35 ° C., the monomer aqueous solution (a1) for the first stage polymerization prepared in the same manner as in Example 1 was added, suspended under stirring, and the system was filled with nitrogen gas. Replaced. Subsequently, the temperature was raised to 70 ° C., and the first-stage reversed-phase suspension polymerization was performed.

After the completion of the first-stage reversed-phase suspension polymerization, the second-stage polymerization is performed while controlling the temperature of the reaction mixture so as not to be 40 ° C. or lower in order to keep the surfactant dissolved. A monomer aqueous solution (b1) was added to the system. Subsequently, the reaction mixture was cooled to 15 ° C. to precipitate a surfactant, and the system was stirred for 30 minutes in that state, and at the same time, the system was replaced with nitrogen gas. Thereafter, the temperature was raised to 70 ° C., and the second-stage reversed-phase suspension polymerization was performed.
After completion of the reverse phase suspension polymerization, the same treatment as in Example 1 was performed to obtain 249 g of water absorbent resin particles.

Example 3
In a 2 L five-necked cylindrical round bottom flask equipped with a stirrer, two-stage paddle blade, reflux condenser, dropping funnel, and nitrogen gas inlet tube, 340 g (500 mL) of n-heptane and a surfactant as a surfactant were added. 0.92 g of sugar fatty acid ester [Mitsubishi Chemical Foods, trade name: S-370] was added and dissolved in n-heptane, and the internal temperature was adjusted to 35 ° C. Thereafter, while maintaining the internal temperature at 35 ° C., the monomer aqueous solution (a1) for the first stage polymerization prepared in the same manner as in Example 1 was added, suspended under stirring, and the system was filled with nitrogen gas. Replaced. Subsequently, the temperature was raised to 70 ° C., and the first-stage reversed-phase suspension polymerization was performed.

  Separately, 128.8 g (1.43 mol) of 80 wt% aqueous acrylic acid solution was placed in a 500 mL Erlenmeyer flask, and 159.0 g of 27.0 wt% aqueous sodium hydroxide solution was added dropwise while cooling with ice. Then, 75 mol% of acrylic acid was neutralized to prepare a partially neutralized aqueous solution of acrylic acid having a monomer concentration of 44% by weight. To the obtained partially neutralized acrylic acid aqueous solution, 25.8 mg (167 μmol) of N, N′-methylenebisacrylamide as an internal crosslinking agent and 129 mg (0.48 mmol) of potassium persulfate as a water-soluble radical polymerization initiator were added. This was added to obtain a monomer aqueous solution (b2) for reverse phase suspension polymerization in the second stage.

  After the completion of the first-stage reversed-phase suspension polymerization, the second-stage polymerization is performed while controlling the temperature of the reaction mixture so as not to be 40 ° C. or lower in order to keep the surfactant dissolved. A monomer aqueous solution (b2) was added to the system. Subsequently, the reaction mixture was cooled to 24 ° C. to precipitate a surfactant, and the system was stirred for 30 minutes in that state, and at the same time, the system was replaced with nitrogen gas. Thereafter, the temperature was raised to 70 ° C., and the second-stage reversed-phase suspension polymerization was performed.

  After completion of the reverse phase suspension polymerization, 261 g of water was extracted from the azeotrope of n-heptane and water by heating again, and then 111 mg (0.63 mmol) of ethylene glycol diglycidyl ether as a post-crosslinking agent. And a post-crosslinking reaction was carried out at 80 ° C. for 2 hours in the presence of 48 g of water. After the crosslinking reaction, n-heptane and water in the system were distilled off by heating to obtain 228 g of water absorbent resin particles.

Example 4
In the same manner as in Example 3, reverse phase suspension polymerization of the first stage was performed.
After the completion of the first-stage reversed-phase suspension polymerization, the second-stage polymerization is performed while controlling the temperature of the reaction mixture so as not to be 40 ° C. or lower in order to keep the surfactant dissolved. A monomer aqueous solution (b1) was added to the system. Subsequently, the reaction mixture was cooled to 26 ° C. to precipitate a surfactant, and the system was stirred for 30 minutes in that state, and at the same time, the system was replaced with nitrogen gas. Thereafter, the temperature was raised to 70 ° C., and the second-stage reversed-phase suspension polymerization was performed. After the completion of the reverse phase suspension polymerization, the same treatment as in Example 1 was performed to obtain 250 g of water absorbent resin particles.

Example 5
In the same manner as in Example 3, reverse phase suspension polymerization of the first stage was performed.
Separately, 165.6 g (1.84 mol) of 80 wt% aqueous acrylic acid solution was placed in a 500 mL Erlenmeyer flask, and 204.5 g of 27.0 wt% sodium hydroxide aqueous solution was added dropwise while cooling with ice. Then, 75 mol% of acrylic acid was neutralized to prepare a partially neutralized aqueous solution of acrylic acid having a monomer concentration of 44% by weight. The resulting aqueous solution of partially neutralized acrylic acid salt was charged with 33.1 mg (215 μmol) of N, N′-methylenebisacrylamide as an internal cross-linking agent and 166 mg (0.61 mmol) of potassium persulfate as a water-soluble radical polymerization initiator. This was added to obtain a monomer aqueous solution (b3) for the second-phase reversed phase suspension polymerization.

  After completion of the first-stage reversed-phase suspension polymerization, the second-stage polymerization is performed while controlling the temperature of the reaction mixture so as not to be 40 ° C. or lower in order to keep the surfactant dissolved. A monomer aqueous solution (b3) was added to the system. Subsequently, the reaction mixture was cooled to 26 ° C. to precipitate a surfactant, and the system was stirred for 30 minutes in that state, and at the same time, the system was replaced with nitrogen gas. Thereafter, the temperature was raised to 70 ° C., and the second-stage reversed-phase suspension polymerization was performed.

  After completion of the reverse phase suspension polymerization, 299 g of water was extracted from the azeotropic mixture of n-heptane and water by heating again, and then 129 mg (0.74 mmol) of ethylene glycol diglycidyl ether as a post-crosslinking agent. And a post-crosslinking reaction was performed in the presence of 56 g of water at 80 ° C. for 2 hours. After the crosslinking reaction, n-heptane and water in the system were distilled off with heating to obtain 267 g of water absorbent resin particles.

Example 6
In the same manner as in Example 3, reverse phase suspension polymerization of the first stage was performed.
Separately, 184.0 g (2.04 mol) of 80% by weight acrylic acid aqueous solution was placed in a 500 mL Erlenmeyer flask, and 227.2 g of 27.0% by weight sodium hydroxide aqueous solution was dropped while cooling with ice. Then, 75 mol% of acrylic acid was neutralized to prepare a partially neutralized aqueous solution of acrylic acid having a monomer concentration of 44% by weight. To the resulting aqueous solution of partially neutralized acrylic acid salt, 36.8 mg (211 μmol) of ethylene glycol diglycidyl ether as an internal crosslinking agent and 184 mg (0.68 mmol) of potassium persulfate as a water-soluble radical polymerization initiator were added, This was designated as a monomer aqueous solution (b4) for the reverse phase suspension polymerization in the second stage.

  After completion of the first-stage reversed-phase suspension polymerization, the second-stage polymerization is performed while controlling the temperature of the reaction mixture so as not to be 40 ° C. or lower in order to keep the surfactant dissolved. A monomer aqueous solution (b4) was added to the system. Next, the reaction mixture is cooled to 27 ° C., a surfactant is precipitated, and the mixture is stirred for 30 minutes, and at the same time, the system is replaced with nitrogen gas. Reverse phase suspension polymerization was performed.

  After the reverse-phase suspension polymerization was completed, 318 g of water was extracted from the azeotropic mixture of n-heptane and water by heating again, and then 138 mg (0.79 mmol) of ethylene glycol diglycidyl ether as a post-crosslinking agent. And a post-crosslinking reaction was carried out at 80 ° C. for 2 hours in the presence of 60 g of water. After the crosslinking reaction, n-heptane and water in the system were distilled off with heating to obtain 291 g of water-absorbing resin particles.

Example 7
In an Erlenmeyer flask with an internal volume of 500 mL, 89 g (0.99 mol) of an 80 wt% acrylic acid aqueous solution was added, and 141.3 g of a 21.0 wt% aqueous sodium hydroxide solution was added dropwise with ice cooling to add 75 mol acrylic. Acid neutralization was performed to prepare a partially neutralized acrylic acid salt solution with a monomer concentration of 38% by weight. In the obtained aqueous solution of partially neutralized acrylic acid, 17.8 mg (115 μmol) of N, N′-methylenebisacrylamide as an internal crosslinking agent and 89 mg (0.33 mmol) of potassium persulfate as a water-soluble radical polymerization initiator were added. This was added to prepare a monomer aqueous solution (a2) for reverse phase suspension polymerization in the first stage.

  In a 2 L five-necked cylindrical round bottom flask equipped with a stirrer, two-stage paddle blade, reflux condenser, dropping funnel and nitrogen gas introduction tube, 340 g (500 mL) of n-heptane and sucrose fatty acid ester [ Mitsubishi Chemical Foods, Inc., trade name: S-370] 0.89 g was added and dissolved in n-heptane, and the internal temperature was adjusted to 35 ° C. Thereafter, the monomer aqueous solution (a2) for the first stage polymerization was added while maintaining the internal temperature at 35 ° C., suspended under stirring, and the system was replaced with nitrogen gas. Subsequently, the temperature was raised to 70 ° C., and the first-stage reversed-phase suspension polymerization was performed.

  Separately, 195.8 g (2.18 mol) of 80 wt% acrylic acid aqueous solution was placed in a 500 mL Erlenmeyer flask, and 241.8 g of 27.0 wt% sodium hydroxide aqueous solution was dropped while cooling with ice. Then, 75 mol% of acrylic acid was neutralized to prepare a partially neutralized aqueous solution of acrylic acid having a monomer concentration of 44% by weight. To the resulting aqueous solution of partially neutralized acrylic acid salt, 39.2 mg (225 μmol) of ethylene glycol diglycidyl ether as an internal crosslinking agent and 196 mg (0.73 mmol) of potassium persulfate as a water-soluble radical polymerization initiator were added, This was designated as a monomer aqueous solution (b5) for reverse phase suspension polymerization in the second stage.

  After completion of the first-stage reversed-phase suspension polymerization, the second-stage polymerization is performed while controlling the temperature of the reaction mixture so as not to be 40 ° C. or lower in order to keep the surfactant dissolved. A monomer aqueous solution (b5) was added to the system. Subsequently, the reaction mixture was cooled to 27 ° C. to precipitate a surfactant, and the system was stirred for 30 minutes in that state, and at the same time, the system was replaced with nitrogen gas. Thereafter, the temperature was raised to 70 ° C., and the second-stage reversed-phase suspension polymerization was performed.

  After completion of the reverse phase suspension polymerization, 326 g of water was extracted from the azeotropic mixture of n-heptane and water by heating again, and then 142 mg (0.82 mmol) of ethylene glycol diglycidyl ether as a post-crosslinking agent. And a post-crosslinking reaction was carried out at 80 ° C. for 2 hours in the presence of 62 g of water. After the crosslinking reaction, 301 g of water-absorbent resin particles were obtained by heating and distilling off n-heptane and water in the system.

Comparative Example 1
In the same manner as in Example 3, reverse phase suspension polymerization of the first stage was performed.
After completion of the first-stage reversed-phase suspension polymerization, the reaction mixture was cooled to 24 ° C. to precipitate the surfactant. While maintaining the temperature of the reaction mixture at 24 ° C., the aqueous monomer solution (b1) for the second stage polymerization prepared in the same manner as in Example 1 was added to the system while the surfactant was precipitated. In this state, stirring was performed for 30 minutes, and at the same time, the system was replaced with nitrogen gas. Thereafter, the temperature was raised to 70 ° C., and the second-stage reversed-phase suspension polymerization was performed.
After completion of the reverse phase suspension polymerization, the same treatment as in Example 1 was performed to obtain 255 g of water absorbent resin particles.

Comparative Example 2
In the same manner as in Example 3, reverse phase suspension polymerization of the first stage was performed.
After completion of the reverse phase suspension polymerization in the first stage, the temperature of the reaction mixture was controlled so as not to be 50 ° C. or lower in order to keep the surfactant dissolved, as in Example 1. The prepared monomer aqueous solution (b1) for the second stage polymerization was added to the system, and the system was stirred for 30 minutes in that state, and at the same time, the system was replaced with nitrogen gas. Thereafter, the temperature was raised to 70 ° C., and the second-stage reversed-phase suspension polymerization was performed.
After completion of the reverse phase suspension polymerization, the same treatment as in Example 1 was performed to obtain 249 g of water absorbent resin particles.

Comparative Example 3
In the same manner as in Example 3, reverse phase suspension polymerization of the first stage was performed.
Separately, 92.0 g (1.02 mol) of 80 wt% aqueous acrylic acid solution was placed in a 500 mL Erlenmeyer flask, and 113.6 g of 27.0 wt% sodium hydroxide aqueous solution was added dropwise while cooling with ice. Then, 75 mol% of acrylic acid was neutralized to prepare a partially neutralized aqueous solution of acrylic acid having a monomer concentration of 44% by weight. 18.4 mg (119 μmol of N, N′-methylenebisacrylamide as an internal cross-linking agent and 92 mg (0.34 mmol) of potassium persulfate as a water-soluble radical polymerization initiator were added to the resulting partially neutralized acrylic acid aqueous solution. This was used as the monomer aqueous solution (b6) for the reverse phase suspension polymerization in the second stage.

  After completion of the first-stage reversed-phase suspension polymerization, the second-stage polymerization is performed while controlling the temperature of the reaction mixture so as not to be 40 ° C. or lower in order to keep the surfactant dissolved. A monomer aqueous solution (b6) was added to the system. Subsequently, the reaction mixture was cooled to 19 ° C. to precipitate a surfactant, and the system was stirred for 30 minutes in that state, and at the same time, the system was replaced with nitrogen gas. Thereafter, the temperature was raised to 70 ° C., and the second-stage reversed-phase suspension polymerization was performed.

  After completion of the reverse phase suspension polymerization, 223 g of water was extracted from the azeotropic mixture of n-heptane and water by heating again, and then 92 mg (0.53 mmol) of ethylene glycol diglycidyl ether as a post-crosslinking agent. And a post-crosslinking reaction was performed in the presence of 40 g of water at 80 ° C. for 2 hours. After the crosslinking reaction, 194 g of water-absorbent resin particles were obtained by heating and distilling off n-heptane and water in the system.

Comparative Example 4
Into a 500 mL Erlenmeyer flask, 79 g (0.88 mol) of 80 wt% acrylic acid aqueous solution was added, and 125.7 g of 21.0 wt% aqueous sodium hydroxide solution was added dropwise with ice cooling to add 75 mol acrylic acid. Acid neutralization was performed to prepare a partially neutralized acrylic acid salt solution with a monomer concentration of 38% by weight. To the obtained partially neutralized acrylic acid aqueous solution, 15.8 mg (102 μmol) of N, N′-methylenebisacrylamide as an internal crosslinking agent and 79.2 mg (0.29 mmol) of potassium persulfate as a water-soluble radical polymerization initiator. This was used as the monomer aqueous solution (a3) for reverse phase suspension polymerization in the first stage.

  Into a 2 L five-necked cylindrical round bottom flask equipped with a stirrer, two-stage paddle blade, reflux condenser, dropping funnel and nitrogen gas introduction tube, 340 g (500 mL) of n-heptane and a surfactant as a surfactant were added. After adding 0.79g of sugar fatty acid ester [Mitsubishi Chemical Foods Co., Ltd., brand name: S-370] and making it melt | dissolve in n-heptane, internal temperature was 35 degreeC. Thereafter, while maintaining the internal temperature at 35 ° C., the monomer aqueous solution (a3) for the first stage polymerization was added and suspended under stirring, and the system was replaced with nitrogen gas. Subsequently, the temperature was raised to 70 ° C., and the first-stage reversed-phase suspension polymerization was performed.

  Separately, 205.9 g (2.29 mol) of 80 wt% aqueous acrylic acid solution was placed in a 500 mL Erlenmeyer flask, and 254.3 g of 27.0 wt% aqueous sodium hydroxide solution was added dropwise while cooling with ice. Then, 75 mol% of acrylic acid was neutralized to prepare a partially neutralized aqueous solution of acrylic acid having a monomer concentration of 44% by weight. In the obtained aqueous solution of partially neutralized acrylic acid, 41.2 mg (267 μmol) of N, N′-methylenebisacrylamide as an internal crosslinking agent and 206 mg (0.76 mmol) of potassium persulfate as a water-soluble radical polymerization initiator were added. This was added to obtain a monomer aqueous solution (b7) for the reverse phase suspension polymerization in the second stage.

  After completion of the first-stage reversed-phase suspension polymerization, the second-stage polymerization is performed while controlling the temperature of the reaction mixture so as not to be 40 ° C. or lower in order to keep the surfactant dissolved. A monomer aqueous solution (b7) was added to the system. Subsequently, the reaction mixture was cooled to 30 ° C. to precipitate a surfactant, and the system was stirred for 30 minutes in this state, and at the same time, the system was replaced with nitrogen gas. Thereafter, the temperature was raised to 70 ° C., and the second-stage reversed-phase suspension polymerization was performed.

  After the reverse phase suspension polymerization was completed, 323 g of water was extracted from the azeotropic mixture of n-heptane and water by heating again, and then 143 mg (0.82 mmol) of ethylene glycol diglycidyl ether as a post-crosslinking agent. And a post-crosslinking reaction was carried out at 80 ° C. for 2 hours in the presence of 62 g of water. After the crosslinking reaction, 300 g of water-absorbent resin particles were obtained by heating and distilling off n-heptane and water in the system.

  In addition, the water absorption amount, average particle diameter, and particle size distribution of the water absorbent resin particles obtained in each Example and each Comparative Example were measured by the following methods. The performance results of the water absorbent resin particles are shown in Table 1.

(1) Water absorption amount In a 500 mL beaker, 2 g of water-absorbent resin particles were dispersed in 500 g of 0.9 wt% physiological saline, and stirred for 60 minutes to swell sufficiently. A 0.9% by weight physiological saline solution containing a swollen gel was filtered with a standard sieve having a mesh size of 75 μm and the weight Wa (g) was measured in advance. The inclination angle of the sieve was about 30 degrees with respect to the horizontal. And left for 30 minutes in an inclined state to remove excess water from the swollen gel. Thereafter, the weight Wb (g) of the sieve containing the swollen gel was measured, and the formula:
[Water absorption (g / g)] = (Wb−Wa) / 2
Thus, the amount of water absorption (g / g) was determined.

(2) Weight average particle diameter and particle size distribution From the top, a JIS standard sieve is sieved with an opening of 850 μm, a sieve with an opening of 600 μm, a sieve with an opening of 425 μm, a sieve with an opening of 300 μm, a sieve with an opening of 150 μm, and an opening of 75 μm. In this order, about 100 g of the water-absorbent resin particles were put in the uppermost sieve and shaken for 20 minutes using a low-tap shaker.

  Next, the weight of the water-absorbent resin particles remaining on each sieve is calculated as a percentage by weight with respect to the total amount, and by integrating in order from the smaller particle size, the sieve weight and the weight percentage remaining on the sieve are integrated. The relationship with values was plotted on a logarithmic probability paper. By connecting the plots on the probability paper with a straight line, the particle size corresponding to an integrated weight percentage of 50% by weight was taken as the weight average particle size.

  In addition, the weight of the water-absorbent resin particles remaining on each sieve having a sieve with a mesh opening of 75 μm, a mesh opening of 150 μm, a mesh opening of 300 μm and a mesh opening of 425 μm, and a mesh opening of 600 μm and a mesh opening of 850 μm is calculated as a percentage by weight. The particle size distribution was determined from the value.

  As is clear from the results shown in Table 1, it can be seen that all of the water-absorbent resin particles obtained in each Example had few fine and coarse powders and a narrow particle size distribution. On the other hand, it can be seen that the water-absorbent resin particles obtained in the respective comparative examples are rich in fine powder or coarse powder.

  Since the water-absorbent resin particles obtained by the production method of the present invention have few fine powders and coarse powders and have a narrow particle size distribution, they can be suitably used particularly for sanitary materials such as sanitary products and paper diapers that have been made thinner.

Claims (3)

A method for producing water-absorbent resin particles by reverse-phase suspension polymerization of a water-soluble ethylenically unsaturated monomer,
(A) A water-soluble ethylenically unsaturated monomer in a hydrocarbon solvent using a water-soluble radical polymerization initiator in the presence of a surfactant and / or polymer protective colloid and, if necessary, an internal crosslinking agent Subject the aqueous body solution to the first-stage reverse phase suspension polymerization,
(B) In the state where the surfactant and / or the polymer protective colloid is dissolved in the hydrocarbon solvent, a water-soluble radical polymerization initiator is added to the reaction mixture in which the first-stage reversed-phase suspension polymerization is completed, 1.2 to 2.5 moles of water-soluble ethylenically unsaturated monomer with respect to 1 mole of water-soluble ethylenically unsaturated monomer subjected to the first stage polymerization, and, if necessary, an internal crosslinking agent Add a water-soluble ethylenically unsaturated monomer aqueous solution containing
(C) Next, after depositing a surfactant and / or polymer protective colloid, the second-stage reversed-phase suspension polymerization is performed, and the method for producing water-absorbing resin particles is characterized in that   The method for producing water-absorbent resin particles according to claim 1, wherein the surfactant is at least one surfactant selected from sorbitan fatty acid ester, polyglycerin fatty acid ester and sucrose fatty acid ester.   The water-absorbent resin particles obtained by the production method according to claim 1 or 2, wherein the weight average particle diameter is 200 to 500 µm.