Method for manufacturing absorbent resin particles and absorbent resin particles

Abstract

A method for manufacturing absorbent resin particles comprising a process of reverse-phase suspension polymerization of a water-soluble ethylenically unsaturated monomer in a hydrocarbon dispersion medium to obtain polymer particles, wherein absorbent resin particles having a narrow particle size distribution are obtained. A method for manufacturing absorbent resin particles comprising a process of reverse-phase suspension polymerization of a water-soluble ethylenically unsaturated monomer in a hydrocarbon dispersion medium to obtain polymer particles, wherein the reverse-phase suspension polymerization is performed in two or more stages and the process of aggregating the polymer particles in the presence of a dispersion stabilizer is included, wherein two or more types of (poly)glycerin fatty acid esters having different precipitation temperatures when the dispersion stabilizer is a 0.46 mass% heptane solution are used as the dispersion stabilizer.

Description

Technology Field

[0001] The present invention relates to a method for manufacturing absorbent resin particles, absorbent resin particles, an absorbent body, and an absorbent article, and more specifically, to a method for manufacturing absorbent resin particles constituting an absorbent body suitable for use in sanitary materials such as paper diapers, sanitary pads, and incontinence pads, and to absorbent resin particles. Background Technology

[0002] Absorbent resin particles are recently being widely used in the field of hygiene materials, such as disposable diapers, sanitary pads, and incontinence pads.

[0003] As such, the crosslinked polymer of a water-soluble ethylenically unsaturated monomer, more specifically, the crosslinked polymer of a polyacrylic acid partial neutralization, is considered a desirable absorbent resin particle because it has excellent absorption capacity, and since the raw material acrylic acid is easily available industrially, it can be manufactured at a low cost with consistent quality, and furthermore, it is difficult for spoilage or deterioration to occur (see, for example, Patent Document 1).

[0004] Absorbent products such as disposable diapers, sanitary pads, and incontinence pads are composed of an absorbent core positioned mainly in the center to absorb and retain bodily fluids such as urine and menstrual blood excreted from the body, a liquid-permeable surface sheet (top sheet) positioned on the side in contact with the body, and a liquid-impermeable back sheet (back sheet) positioned on the opposite side in contact with the body. In addition, the absorbent core is typically composed of hydrophilic fibers such as pulp and absorbent resin particles. Prior art literature

[0005] Japanese Publication No. 3-227301 The problem to be solved

[0006] Absorbent resin particles can be manufactured, for example, by obtaining polymer particles through reverse-phase suspension polymerization of water-soluble ethylenically unsaturated monomers in a hydrocarbon dispersion medium.

[0007] The present invention has a primary objective of providing a method for manufacturing absorbent resin particles comprising a process of reverse-phase suspension polymerization of a water-soluble ethylenically unsaturated monomer in a hydrocarbon dispersion medium to obtain polymer particles, wherein absorbent resin particles having a narrow particle size distribution are obtained. Additionally, the present invention has an objective of providing absorbent resin particles having a narrow particle size distribution. means of solving the problem

[0008] The inventors of the present invention have conducted thorough investigations to solve the above problem. As a result, it was discovered that in a method for manufacturing absorbent resin particles comprising a process of obtaining polymer particles by reverse-phase suspension polymerization of a water-soluble ethylenically unsaturated monomer in a hydrocarbon dispersion medium, the reverse-phase suspension polymerization is performed in two or more stages, and the process of aggregating the polymer particles in the presence of a dispersion stabilizer is included, and by using two or more types of (poly)glycerin fatty acid esters with different precipitation temperatures when the dispersion stabilizer is a 0.46 mass% heptane solution, absorbent resin particles with a narrow particle size distribution are obtained. The present invention is an invention completed by conducting further thorough investigations based on such findings.

[0009] That is, the present invention provides an invention having the following configuration.

[0010] Claim 1. A method for manufacturing absorbent resin particles comprising a process of obtaining polymer particles by reverse-phase suspension polymerization of a water-soluble ethylenically unsaturated monomer in a hydrocarbon dispersion medium, wherein

[0011] The above reverse-phase suspension polymerization is carried out in two or more stages, and

[0012] The method includes a process of aggregating the polymer particles in the presence of a dispersion stabilizer, and

[0013] A method for manufacturing absorbent resin particles using two or more types of (poly)glycerin fatty acid esters with different precipitation temperatures when used as a dispersion stabilizer of 0.46 mass% heptane solution.

[0014] Claim 2. A method for manufacturing absorbent resin particles as described in Claim 1, wherein among two or more types of (poly)glycerin fatty acid esters, the difference between the precipitation temperature of the (poly)glycerin fatty acid ester with the highest precipitation temperature and the precipitation temperature of the (poly)glycerin fatty acid ester with the lowest precipitation temperature is 15°C or less.

[0015] Claim 3. At least one of the above (poly)glycerin fatty acid esters is tristearate hexaglyceryl, and

[0016] A method for manufacturing absorbent resin particles as described in claim 1 or claim 2, wherein the amount of hexaglyceryl tristearate used is in the range of 0.2 parts by mass or more and 4.0 parts by mass or less per 100 parts by mass of the water-soluble ethylenically unsaturated monomer used in the first stage polymerization.

[0017] Claim 4. The dispersion stabilizer comprises at least one of the tristearate hexaglyceryl, a (poly)glycerin fatty acid ester with a precipitation temperature higher than that of the tristearate hexaglyceryl, and a (poly)glycerin fatty acid ester with a precipitation temperature lower than that of the tristearate hexaglyceryl.

[0018] A method for manufacturing absorbent resin particles as described in claim 3, wherein the amount of (poly)glycerin fatty acid ester with a precipitation temperature higher than that of tristearate hexaglyceryl and the amount of (poly)glycerin fatty acid ester with a precipitation temperature lower than that of tristearate hexaglyceryl used is each in the range of more than 0 parts by mass and 3.0 parts by mass or less per 1 part by mass of tristearate hexaglyceryl.

[0019] Claim 5. The dispersion stabilizer comprises the tristearate hexaglyceryl, a (poly)glycerin fatty acid ester having a precipitation temperature higher than that of the tristearate hexaglyceryl, and a (poly)glycerin fatty acid ester having a precipitation temperature lower than that of the tristearate hexaglyceryl.

[0020] A method for manufacturing absorbent resin particles as described in claim 4, wherein the amount of (poly)glycerin fatty acid ester with a precipitation temperature higher than that of tristearate hexaglyceryl and the amount of (poly)glycerin fatty acid ester with a precipitation temperature lower than that of tristearate hexaglyceryl used is greater than 0 parts by mass and less than or equal to 2.0 parts by mass, respectively, per 1 part by mass of tristearate hexaglyceryl.

[0021] Claim 6. An absorbent resin particle comprising a polymer particle having a water-soluble ethylenically unsaturated monomer as a monomer unit,

[0022] Absorbent resin particles having a uniformity of particle size distribution of 2.5 or less and also containing (poly)glycerin fatty acid esters near the surface. Effects of the invention

[0023] According to the present invention, a method for manufacturing absorbent resin particles comprising a process of reverse-phase suspension polymerization of a water-soluble ethylenically unsaturated monomer in a hydrocarbon dispersion medium to obtain polymer particles can be provided, wherein absorbent resin particles having a narrow particle size distribution can be obtained. Furthermore, according to the present invention, absorbent resin particles having a narrow particle size distribution can also be provided. Specific details for implementing the invention

[0024] In this specification, the term "comprising" includes "consisting essentially of" and "consisting of". Also, in this specification, "(meth)acrylic" means "acrylic or methacrylic," "(meth)acrylate" means "acrylate or methacrylate," and "(poly)" means with or without the prefix "poly." Also, in this specification, "water-soluble" means exhibiting solubility of 5 mass% or more in water at 25°C.

[0025] In addition, in the present invention, the area near the surface of the absorbent resin particles refers to the outermost surface of the absorbent resin particles and the region extending from the outermost surface toward the center of the particles to a depth of approximately 30 μm.

[0026] In this specification, a numerical value connected by "~" refers to a numerical range that includes the values ​​before and after "~" as lower and upper limits. If multiple lower limits and multiple upper limits are listed separately, any lower and upper limits may be selected and connected by "~".

[0027] 1. Method for manufacturing absorbent resin particles

[0028] The method for manufacturing absorbent resin particles according to the present invention is a method for manufacturing absorbent resin particles comprising a process (polymerization process) of obtaining polymer particles by reverse-phase suspension polymerization of a water-soluble ethylenically unsaturated monomer in a hydrocarbon dispersion medium.

[0029] In the method for manufacturing absorbent resin particles of the present invention, reverse-phase suspension polymerization is performed in two or more stages. In addition, the manufacturing method of the present invention includes a process of aggregating polymer particles in the presence of a dispersion stabilizer. Furthermore, as a dispersion stabilizer, the manufacturing method of the present invention uses two or more types of (poly)glycerin fatty acid esters having different precipitation temperatures when using a 0.46 mass% heptane solution.

[0030] The method for manufacturing absorbent resin particles of the present invention can appropriately produce absorbent resin particles with a narrow particle size distribution by having these components. Hereinafter, the method for manufacturing absorbent resin particles of the present invention will be described in detail.

[0031] <Polymerization Process>

[0032] The polymerization process is a process of obtaining polymer particles by polymerizing water-soluble ethylenically unsaturated monomers using the reverse-phase suspension polymerization method. In the reverse-phase suspension polymerization method, polymerization is carried out by heating the water-soluble ethylenically unsaturated monomers under stirring in a hydrocarbon dispersion medium. In the polymerization process, if necessary, an internal crosslinking agent may be added to the water-soluble ethylenically unsaturated monomers to produce crosslinked polymer particles having an internal crosslinking structure. An example of the polymerization process is described below.

[0033] [Water-soluble ethylenically unsaturated monomer]

[0034] Examples of water-soluble ethylenically unsaturated monomers include (meth)acrylic acid (in this specification, "acryl" and "methacryl" are combined and denoted as "(meth)acryl"; the same applies hereinafter) and its salts; 2-(meth)acrylamide-2-methylpropanesulfonic acid and its salts; nonionic monomers such as (meth)acrylamide, N,N-dimethyl(meth)acrylamide, 2-hydroxyethyl(meth)acrylate, N-methylol(meth)acrylamide, polyethylene glycol mono(meth)acrylate; amino group-containing unsaturated monomers such as N,N-diethylaminoethyl(meth)acrylate, N,N-diethylaminopropyl(meth)acrylate, diethylaminopropyl(meth)acrylamide, and their quaternaries. Among these water-soluble ethylenically unsaturated monomers, (meth)acrylic acid or its salt, (meth)acrylamide, and N,N-dimethylacrylamide are preferred from the perspective of being industrially readily available, and (meth)acrylic acid and its salt are more preferred. In addition, these water-soluble ethylenically unsaturated monomers may be used alone or in combination of two or more types.

[0035] Among these, acrylic acid and its salts are widely used as raw materials for absorbent resin particles, and there are also cases where the aforementioned other water-soluble ethylenically unsaturated monomers are copolymerized with these acrylic acids and / or their salts and used. In this case, acrylic acid and / or its salts are preferred to be used as the main water-soluble ethylenically unsaturated monomers in an amount of 70 to 100 mol% relative to the total water-soluble ethylenically unsaturated monomers.

[0036] The water-soluble ethylenically unsaturated monomer may be dispersed in a hydrocarbon dispersion medium in an aqueous solution state and provided for reverse-phase suspension polymerization. By making the water-soluble ethylenically unsaturated monomer an aqueous solution, the dispersion efficiency in the hydrocarbon dispersion medium can be improved. In this aqueous solution, the concentration of the water-soluble ethylenically unsaturated monomer is preferably in the range of 20 mass% to the saturation concentration or lower. Furthermore, the concentration of the water-soluble ethylenically unsaturated monomer is more preferably 55 mass% or lower, even more preferably 50 mass% or lower, and even more preferably 45 mass% or lower. On the other hand, the concentration of the water-soluble ethylenically unsaturated monomer is more preferably 25 mass% or higher, even more preferably 28 mass% or higher, and even more preferably 30 mass% or higher.

[0037] If the water-soluble ethylenically unsaturated monomer has an acid group such as (meth)acrylic acid or 2-(meth)acrylamide-2-methylpropanesulfonic acid, the acid group may be neutralized in advance by an alkaline neutralizing agent as needed. Examples of such alkaline neutralizing agents include alkali metal salts such as sodium hydroxide, sodium carbonate, sodium bicarbonate, potassium hydroxide, and potassium carbonate; and ammonia. Furthermore, these alkaline neutralizing agents may be used in the form of aqueous solutions to simplify the neutralization operation. Additionally, the aforementioned alkaline neutralizing agents may be used alone or in combination of two or more types.

[0038] As for the degree of neutralization of a water-soluble ethylenically unsaturated monomer by an alkaline neutralizing agent, as the degree of neutralization for all acid groups of the water-soluble ethylenically unsaturated monomer, it is preferable that it be 40 to 100 mol%, more preferable that it be 50 to 90 mol%, even more preferable that it be 60 to 85 mol%, and even more preferable that it be 70 to 80 mol%.

[0039] [Radical Polymerization Initiator]

[0040] As radical polymerization initiators added to the polymerization process, examples include persulfates such as potassium persulfate, ammonium persulfate, and sodium persulfate; peroxides such as methyl ethyl ketone peroxide, methyl isobutyl ketone peroxide, di-t-butyl peroxide, t-butyl cumyl peroxide, t-butyl peroxyacetate, t-butyl peroxyisobutyrate, t-butyl peroxypivalate, and hydrogen peroxide; and 2,2'-azobis(2-amidinopropane)dihydrochloride, 2,2'-azobis[2-(N-phenylamidino)propane]dihydrochloride, and 2,2'-azobis[2-(N-allylamidino)propane]dihydrochloride. Examples of azo compounds include 2,2'-azobis{2-[1-(2-hydroxyethyl)-2-imidazoline-2-yl]propane}dihydrochloride, 2,2'-azobis{2-methyl-N-[1,1-bis(hydroxymethyl)-2-hydroxyethyl]propionamide}, 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)-propionamide], and 4,4'-azobis(4-cyanovaleric acid). Among these radical polymerization initiators, potassium persulfate, ammonium persulfate, sodium persulfate, and 2,2'-azobis(2-amidinopropane)dihydrochloride are preferably used from the perspective of being readily available and easy to handle. These radical polymerization initiators may be used alone or in combination of two or more types. In addition, the above radical polymerization initiator may also be used as a redox polymerization initiator in combination with reducing agents such as sodium sulfite, sodium bisulfite, ferrous sulfate, and L-ascorbic acid.

[0041] For example, the amount of radical polymerization initiator used can be 0.00005 to 0.01 mole per 1 mole of water-soluble ethylenically unsaturated monomer. By satisfying this amount, a rapid polymerization reaction can be avoided, and the polymerization reaction can also be completed within an appropriate time.

[0042] [Internal crosslinking agent]

[0043] Examples of internal crosslinking agents include those capable of crosslinking the polymer of the water-soluble ethylenically unsaturated monomer used, such as (poly)ethylene glycol [(poly) refers to cases with and without the prefix "poly". The same applies hereinafter], (poly)propylene glycol, 1,4-butanediol, 1,6-hexanediol, trimethylolpropane, (poly)glycerin, etc., polyols such as diols and triols, and unsaturated polyesters obtained by reacting them with unsaturated acids such as (meth)acrylic acid, maleic acid, and fumaric acid; bisacrylamides such as N,N-methylenebisacrylamide; and di(meth)acrylic acid esters or tri(meth)acrylic acid esters obtained by reacting polyepoxides with (meth)acrylic acid. Di(meth)acrylic acid carbamyl esters obtained by reacting polyisocyanates, such as tolylene diisocyanate and hexamethylene diisocyanate, with (meth)acrylic acid hydroxyethyl; compounds having two or more polymerizable unsaturated groups, such as allylated starch, allylated cellulose, diallyl phthalate, N,N',N''-triallyl isocyanurate, and divinylbenzene; polyglycidyl compounds, such as diglycidyl compounds and triglycidyl compounds, such as (poly)ethylene glycol diglycidyl ether, (poly)propylene glycol diglycidyl ether, and (poly)glycerin diglycidyl ether; epihalohydrin compounds, such as epichlorohydrin, epibromohydrin, and α-methyl epichlorohydrin; Examples include compounds having two or more reactive functional groups, such as isocyanate compounds like 2,4-tolylene diisocyanate and hexamethylene diisocyanate; and oxetane compounds such as 3-methyl-3-oxetanmethanol, 3-ethyl-3-oxetanmethanol, 3-butyl-3-oxetanmethanol, 3-methyl-3-oxetanethanol, 3-ethyl-3-oxetanethanol, and 3-butyl-3-oxetanethanol. Among these internal crosslinking agents, it is preferable to use polyethylene glycol diacrylate, trimethylolpropane triacrylate, (poly)ethylene glycol diglycidyl ether, (poly)propylene glycol diglycidyl ether, and (poly)glycerin diglycidyl ether.These internal crosslinking agents may be used alone or in combination of two or more types.

[0044] As for the amount of internal crosslinking agent used, it is preferable to have 0.000001 to 0.02 moles per 1 mole of water-soluble ethylenically unsaturated monomer, more preferable to have 0.00001 to 0.01 moles, even more preferable to have 0.00001 to 0.005 moles, and even more preferable to have 0.00005 to 0.002 moles.

[0045] [Hydrocarbon dispersion medium]

[0046] Examples of hydrocarbon dispersion media include aliphatic hydrocarbons having 6 to 8 carbon atoms, such as n-hexane, n-heptane, 2-methylhexane, 3-methylhexane, 2,3-dimethylpentane, 3-ethylpentane, and n-octane; alicyclic hydrocarbons, such as cyclohexane, methylcyclohexane, cyclopentane, methylcyclopentane, trans-1,2-dimethylcyclopentane, cis-1,3-dimethylcyclopentane, and trans-1,3-dimethylcyclopentane; and aromatic hydrocarbons, such as benzene, toluene, and xylene. Among these hydrocarbon dispersion media, n-hexane, n-heptane, and cyclohexane are particularly suitable for industrial use due to their ease of availability, stable quality, and low cost. These hydrocarbon dispersion media may be used individually or in combination of two or more types. In addition, as an example of a mixture of hydrocarbon dispersion media, commercial products such as exolheptane (ExxonMobil: containing 75-85 mass% of hydrocarbons of heptane and its isomers) can be used to obtain suitable results.

[0047] Regarding the amount of hydrocarbon dispersion medium used, from the perspective of uniformly dispersing the water-soluble ethylenically unsaturated monomer and facilitating the control of the polymerization temperature, it is preferable to use 100 to 1,500 parts by mass and more preferable to use 200 to 1,400 parts by mass per 100 parts by mass of the water-soluble ethylenically unsaturated monomer in the first stage. Furthermore, as will be described below, in the present invention, reverse-phase suspension polymerization is carried out in two or more stages, and the polymerization in the first stage described above refers to the polymerization reaction in the first stage of multi-stage polymerization (the same applies hereinafter).

[0048] [Dispersion Stabilizer]

[0049] The manufacturing method of the present invention includes a process of aggregating polymer particles in the presence of a dispersion stabilizer, and uses two or more types of (poly)glycerin fatty acid esters with different precipitation temperatures when a 0.46 mass% heptane solution is used as the dispersion stabilizer.

[0050] The method for measuring the precipitation temperature (hereinafter simply referred to as "precipitation temperature") when the (poly)glycerin fatty acid ester is used as a 0.46 mass% heptane solution follows the measurement method described in the example.

[0051] In order to further appropriately demonstrate the effects of the present invention, among two or more types of (poly)glycerin fatty acid esters, the difference between the precipitation temperature of the (poly)glycerin fatty acid ester with the highest precipitation temperature and the precipitation temperature of the (poly)glycerin fatty acid ester with the lowest precipitation temperature is preferably 15°C or less, more preferably 10°C or less, even more preferably 6°C or less, and also preferably 1°C or more, more preferably 2°C or more, even more preferably 3°C or more, and preferred ranges include 1 to 15°C, 1 to 10°C, 1 to 6°C, 2 to 15°C, 2 to 10°C, 2 to 6°C, 3 to 15°C, 3 to 10°C, and 3 to 6°C.

[0052] In addition, the precipitation temperature of the (poly)glycerin fatty acid ester is preferably 55°C or lower, more preferably 45°C or lower, even more preferably 40°C or lower, and even more preferably 35°C or lower, and is also preferably 0°C or higher, more preferably 10°C or higher, even more preferably 15°C or higher, and even more preferably 20°C or higher, and preferred ranges include 0 to 55°C, 0 to 45°C, 0 to 40°C, 0 to 35°C, 10 to 55°C, 10 to 45°C, 10 to 40°C, 10 to 35°C, 15 to 55°C, 15 to 45°C, 15 to 40°C, 15 to 35°C, 20 to 55°C, 20 to 45°C, 20 to 40°C, and 20 to 35°C.

[0053] (Poly)glycerin fatty acid esters can reduce the discoloration of absorbent resin particles caused by heating. Specific examples of (poly)glycerin fatty acid esters include monostearate monoglyceryl, monostearate tetraglyceryl, tristearate tetraglyceryl, pentastearate tetrapolyglyceryl, tristearate hexaglyceryl, tristearate decaglyceryl, decastearate decaglyceryl, pentastearate decaglyceryl, dodecabehenate decaglyceryl, pentaisosterate decaglyceryl, pentaoleate decaglyceryl, pentapalmitate decaglyceryl, pentalaurate decaglyceryl, pentahydroxystearate decaglyceryl, condensed ricinoleate hexaglyceryl, etc. In the present invention, it is preferable to use two or more types of (poly)glycerin fatty acid esters among these (poly)glycerin fatty acid esters. Furthermore, among the two or more types of (poly)glycerin fatty acid esters, it is more preferable to use hexaglyceryl tristearate as one type.

[0054] The total amount of two or more types of (poly)glycerin fatty acid esters used is preferably 0.2 parts by mass or more, more preferably 0.9 parts by mass or more, even more preferably 1.3 parts by mass or more, and even more preferably 1.4 parts by mass or more, based on 100 parts by mass of a water-soluble ethylenically unsaturated monomer used in the first-step polymerization of reverse-phase suspension polymerization, and is also preferably 12.0 parts by mass or less, more preferably 4.0 parts by mass or less, even more preferably 2.0 parts by mass or less, and even more preferably 1.7 parts by mass or less, and the preferred range is 0.2 to 12.0 parts by mass, 0.2 to 4.0 parts by mass, 0.2 to 2.0 parts by mass, 0.2 to 1.7 parts by mass, 0.9 to 12.0 parts by mass, 0.9 to 4.0 parts by mass, 0.9 to 2.0 parts by mass, and 0.9 to 1.7 parts by mass. Examples include 1.3 to 12.0 parts by mass, 1.3 to 4.0 parts by mass, 1.3 to 2.0 parts by mass, 1.3 to 1.7 parts by mass, 1.4 to 12.0 parts by mass, 1.4 to 4.0 parts by mass, 1.4 to 2.0 parts by mass, 1.4 to 1.7 parts by mass.

[0055] In addition, among two or more types of (poly)glycerin fatty acid esters, the amount of the (poly)glycerin fatty acid ester with the highest precipitation temperature used is preferably 0.1 parts by weight or more, more preferably 0.2 parts by weight or more, and even more preferably 0.3 parts by weight or more, based on 100 parts by weight of the water-soluble ethylenically unsaturated monomer used in the first-stage polymerization of reverse-phase suspension polymerization, and is also preferably 12.0 parts by weight or less, more preferably 6.0 parts by weight or less, even more preferably 4.0 parts by weight or less, even more preferably 1.2 parts by weight or less, even more preferably 1.0 parts by weight or less, and even more preferably 0.5 parts by weight or less, and as a preferred range, 0.1 to 12.0 parts by weight, 0.1 to 6.0 parts by weight, 0.1 to 4.0 parts by weight, 0.1 to 1.2 parts by weight, 0.1 to 1.0 parts by weight, Examples include 0.1 to 0.5 parts by mass, 0.2 to 12.0 parts by mass, 0.2 to 6.0 parts by mass, 0.2 to 4.0 parts by mass, 0.2 to 1.2 parts by mass, 0.2 to 1.0 parts by mass, 0.2 to 0.5 parts by mass, 0.3 to 12.0 parts by mass, 0.3 to 6.0 parts by mass, 0.3 to 4.0 parts by mass, 0.3 to 1.2 parts by mass, 0.3 to 1.0 parts by mass, 0.3 to 0.5 parts by mass.

[0056] In addition, among two or more types of (poly)glycerin fatty acid esters, the amount of (poly)glycerin fatty acid ester having the lowest precipitation temperature used is preferably 0.2 parts by mass or more, more preferably 0.4 parts by mass or more, and also preferably 12.0 parts by mass or less, more preferably 4.0 parts by mass or less, even more preferably 1.2 parts by mass or less, and even more preferably 0.8 parts by mass or less, with preferred ranges including 0.2 to 12.0 parts by mass, 0.2 to 4.0 parts by mass, 0.2 to 1.2 parts by mass, 0.2 to 0.8 parts by mass, 0.4 to 12.0 parts by mass, 0.4 to 4.0 parts by mass, 0.4 to 1.2 parts by mass, 0.4 to 0.8 parts by mass, etc.

[0057] When at least one of the (poly)glycerin fatty acid esters is tristearate hexaglyceryl, the amount of tristearate hexaglyceryl used is preferably 0.2 parts by weight or more, more preferably 0.5 parts by weight or more, and also preferably 9.0 parts by weight or less, more preferably 4.0 parts by weight or less, more preferably 0.9 parts by weight or less, and even more preferably 0.7 parts by weight or less, with preferred ranges including 0.2 to 9.0 parts by weight, 0.2 to 4.0 parts by weight, 0.2 to 0.9 parts by weight, 0.2 to 0.7 parts by weight, 0.5 to 9.0 parts by weight, 0.5 to 4.0 parts by weight, 0.5 to 0.9 parts by weight, 0.5 to 0.7 parts by weight, etc.

[0058] In the case where at least one of the (poly)glycerin fatty acid esters is tristearate hexaglyceryl, and at least one of tristearate hexaglyceryl, a (poly)glycerin fatty acid ester with a precipitation temperature higher than that of tristearate hexaglyceryl, and a (poly)glycerin fatty acid ester with a precipitation temperature lower than that of tristearate hexaglyceryl is included, the (poly)glycerin fatty acid ester with a precipitation temperature higher than that of tristearate hexaglyceryl may be one type or two or more types may be used. In addition, the (poly)glycerin fatty acid ester with a precipitation temperature lower than that of tristearate hexaglyceryl may be one type or two or more types may be used.

[0059] In addition, when at least one of the (poly)glycerin fatty acid esters is tristearate hexaglyceryl, the composition comprises at least one of tristearate hexaglyceryl, a (poly)glycerin fatty acid ester with a precipitation temperature higher than that of tristearate hexaglyceryl, and a (poly)glycerin fatty acid ester with a precipitation temperature lower than that of tristearate hexaglyceryl, wherein the amounts of the (poly)glycerin fatty acid ester with a precipitation temperature higher than that of tristearate hexaglyceryl and the (poly)glycerin fatty acid ester with a precipitation temperature lower than that of tristearate are each preferably 0.0 parts by mass or more, more preferably 0.3 parts by mass or more, and even more preferably 0.5 parts by mass or more per 1 part by mass of tristearate hexaglyceryl, and also preferably 3 parts by mass or less, more preferably 2.0 parts by mass or less, even more preferably 1.3 parts by mass or less, and even more preferably 1.0 parts by mass or less, and as a preferred range, 0.0 to 3.0 parts by mass. Examples include 0.0 to 2.0 parts by mass, 0.0 to 1.3 parts by mass, 0.3 to 3.0 parts by mass, 0.3 to 2.0 parts by mass, 0.3 to 1.3 parts by mass, 0.5 to 3.0 parts by mass, 0.5 to 2.0 parts by mass, and 0.5 to 1.3 parts by mass.

[0060] In the case where at least one of the (poly)glycerin fatty acid esters is tristearate hexaglyceryl, and the (poly)glycerin fatty acid ester has a precipitation temperature higher than that of tristearate hexaglyceryl and a (poly)glycerin fatty acid ester has a precipitation temperature lower than that of tristearate hexaglyceryl, there may be one type of (poly)glycerin fatty acid ester with a precipitation temperature higher than that of tristearate hexaglyceryl, or two or more types may be used. Additionally, there may be one type of (poly)glycerin fatty acid ester with a precipitation temperature lower than that of tristearate hexaglyceryl, or two or more types may be used.

[0061] In addition, when at least one of the (poly)glycerin fatty acid esters is tristearate hexaglyceryl, the composition comprises tristearate hexaglyceryl, a (poly)glycerin fatty acid ester with a precipitation temperature higher than that of tristearate hexaglyceryl, and a (poly)glycerin fatty acid ester with a precipitation temperature lower than that of tristearate hexaglyceryl, wherein the amounts of the (poly)glycerin fatty acid ester with a precipitation temperature higher than that of tristearate hexaglyceryl and the (poly)glycerin fatty acid ester with a precipitation temperature lower than that of tristearate are each preferably greater than 0.0 parts by mass, more preferably 0.3 parts by mass or more, and even more preferably 0.5 parts by mass or more per 1 part by mass of tristearate hexaglyceryl, and also preferably 2.0 parts by mass or less, more preferably 1.3 parts by mass or less, and even more preferably 1.0 parts by mass or less, and as a preferred range, greater than 0.0 parts by mass and 2.0 parts by mass or less, greater than 0.0 parts by mass Examples include 1.3 parts by mass or less, more than 0.0 parts by mass and 2.0 parts by mass or less, 0.3 to 2.0 parts by mass, 0.3 to 1.3 parts by mass, 0.3 to 1.0 parts by mass, 0.5 to 2.0 parts by mass, 0.5 to 1.3 parts by mass, and 0.5 to 1.0 parts by mass.

[0062] In addition, when at least one of the (poly)glycerin fatty acid esters is tristearate hexaglyceryl, and comprises tristearate hexaglyceryl, a (poly)glycerin fatty acid ester with a precipitation temperature higher than that of tristearate hexaglyceryl, and a (poly)glycerin fatty acid ester with a precipitation temperature lower than that of tristearate hexaglyceryl, the amount of the (poly)glycerin fatty acid ester with a precipitation temperature higher than that of tristearate hexaglyceryl used is preferably greater than 0.0 parts by weight, more preferably 0.2 parts by weight or more, and even more preferably 0.4 parts by weight or more per 1 part by weight of tristearate hexaglyceryl, and also preferably 2.0 parts by weight or less, more preferably 1.0 parts by weight or less, and even more preferably 0.8 parts by weight or less, and as a preferred range is greater than 0.0 parts by weight and less than or equal to 2.0 parts by weight, greater than 0.0 parts by weight and less than or equal to 1.0 parts by weight, and greater than 0.0 parts by weight Examples include 0.8 parts by mass or less, 0.2 to 2.0 parts by mass, 0.2 to 1.0 parts by mass, 0.2 to 0.8 parts by mass, 0.4 to 2.0 parts by mass, 0.4 to 1.0 parts by mass, and 0.4 to 0.8 parts by mass.

[0063] In addition, when at least one of the (poly)glycerin fatty acid esters is tristearate hexaglyceryl, and comprises tristearate hexaglyceryl, a (poly)glycerin fatty acid ester with a precipitation temperature higher than that of tristearate hexaglyceryl, and a (poly)glycerin fatty acid ester with a precipitation temperature lower than that of tristearate hexaglyceryl, the amount of the (poly)glycerin fatty acid ester with a precipitation temperature lower than that of tristearate hexaglyceryl used is preferably greater than 0.0 parts by weight, more preferably 0.2 parts by weight or more, and even more preferably 0.5 parts by weight or more per 1 part by weight of tristearate hexaglyceryl, and also preferably 2.0 parts by weight or less, more preferably 1.5 parts by weight or less, and even more preferably 0.9 parts by weight or less, and as a preferred range is greater than 0.0 parts by weight and less than or equal to 2.0 parts by weight, greater than 0 parts by weight and less than or equal to 1.5 parts by weight, and greater than 0 parts by weight and less than or equal to 0.9 parts by weight Examples include 0.2 to 2.0 parts by mass, 0.2 to 1.5 parts by mass, 0.2 to 0.9 parts by mass, 0.5 to 2.0 parts by mass, 0.5 to 1.5 parts by mass, and 0.5 to 0.9 parts by mass.

[0064] When using a 0.46 mass% heptane solution, two or more types of (poly)glycerin fatty acid esters with different precipitation temperatures may be used, but preferably 2 to 5 types, more preferably 2 to 4 types, even more preferably 2 to 3 types, and particularly preferably 3 types.

[0065] In the coagulation process of the manufacturing method of the present invention, in addition to the two or more types of (poly)glycerin fatty acid esters described above, a dispersion stabilizer different from the (poly)glycerin fatty acid esters may be further present, and as the other dispersion stabilizer, a polymeric dispersant is preferred from the perspective of narrowing the particle size distribution. In the coagulation process, the total ratio of two or more types of (poly)glycerin fatty acid esters among the total dispersion stabilizers is preferably 50 mass% or more, more preferably 60 mass% or more, and even more preferably 80 mass% or more, and may be 90 mass% or more, 95 mass% or more, 99 mass%, etc.

[0066] Surfactants and polymeric dispersants may be used as dispersion stabilizers in the process of aggregating polymer particles in the presence of a dispersion stabilizer, and (poly)glycerin fatty acid esters are surfactants. Examples of dispersion stabilizers different from (poly)glycerin fatty acid esters include the following surfactants and polymeric dispersants.

[0067] (Surfactant)

[0068] In reverse-phase suspension polymerization, a dispersion stabilizer may be used to improve the dispersion stability of a water-soluble ethylenically unsaturated monomer in a hydrocarbon dispersion medium. A surfactant may be used as the dispersion stabilizer.

[0069] Examples of surfactants that may be used include sucrose fatty acid esters, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene glycerin fatty acid esters, sorbitol fatty acid esters, polyoxyethylene sorbitol fatty acid esters, polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene castor oil, polyoxyethylene hydrogenated castor oil, alkylallyl formaldehyde condensation polyoxyethylene ethers, polyoxyethylene polyoxypropylene block copolymers, polyoxyethylene polyoxypropyl alkyl ethers, polyethylene glycol fatty acid esters, alkyl glucosides, N-alkylgluconamides, polyoxyethylene fatty acid amides, polyoxyethylene alkylamines, phosphate esters of polyoxyethylene alkyl ethers, and phosphate esters of polyoxyethylene alkylallyl ethers. These surfactants may be used individually or in combination of two or more types.

[0070] (Polymer-based dispersant)

[0071] In addition, as a dispersion stabilizer used in reverse-phase suspension polymerization, a polymer-based dispersant may be used in combination with the surfactant described above.

[0072] Examples of polymer-based dispersants include maleic anhydride-modified polyethylene, maleic anhydride-modified polypropylene, maleic anhydride-modified ethylene-propylene copolymer, maleic anhydride-modified EPDM (ethylene-propylene-diene-terpolymer), maleic anhydride-modified polybutadiene, maleic anhydride-ethylene copolymer, maleic anhydride-propylene copolymer, maleic anhydride-ethylene-propylene copolymer, maleic anhydride-butadiene copolymer, polyethylene, polypropylene, ethylene-propylene copolymer, oxidized polyethylene, oxidized polypropylene, oxidized ethylene-propylene copolymer, ethylene-acrylic acid copolymer, ethylcellulose, ethylhydroxyethylcellulose, etc. Among these polymer-based dispersants, it is preferable to use maleic anhydride-modified polyethylene, maleic anhydride-modified polypropylene, maleic anhydride-modified ethylene-propylene copolymer, maleic anhydride-ethylene copolymer, maleic anhydride-propylene copolymer, maleic anhydride-ethylene-propylene copolymer, polyethylene, polypropylene, ethylene-propylene copolymer, oxidized polyethylene, oxidized polypropylene, and oxidized ethylene-propylene copolymer, particularly in terms of monomer dispersion stability. These polymer-based dispersants may be used alone or in combination of two or more types.

[0073] [Other ingredients]

[0074] In a method for manufacturing absorbent resin particles, other components may be added to an aqueous solution containing a water-soluble ethylenically unsaturated monomer and reverse-phase suspension polymerization may be performed as desired. Various additives such as thickeners and chain transfer agents may be added as other components.

[0075] As an example, reverse-phase suspension polymerization can be performed by adding a thickening agent to an aqueous solution containing a water-soluble ethylenically unsaturated monomer. By adjusting the viscosity of the aqueous solution by adding a thickening agent in this way, it is possible to control the intermediate particle diameter obtained from reverse-phase suspension polymerization.

[0076] Examples of thickeners that may be used include hydroxyethylcellulose, hydroxypropylcellulose, methylcellulose, carboxymethylcellulose, polyacrylic acid, polyacrylic acid (partially) neutralized product, polyethylene glycol, polyacrylamide, polyethyleneimine, dextrin, sodium alginate, polyvinyl alcohol, polyvinylpyrrolidone, polyethylene oxide, etc. In addition, if the stirring speed during polymerization is the same, the higher the viscosity of the aqueous solution of the water-soluble ethylenically unsaturated monomer, the larger the primary particles and / or secondary particles of the obtained particles tend to be.

[0077] [Reverse Phase Suspension Polymerization]

[0078] In carrying out reverse-phase suspension polymerization, for example, an aqueous monomer solution containing a water-soluble ethylenically unsaturated monomer is dispersed in a hydrocarbon dispersion medium in the presence of two or more types of (poly)glycerin fatty acid esters (or, if necessary, another dispersion stabilizer) as dispersion stabilizers. At this time, if the polymerization reaction is not yet started, the timing of adding the dispersion stabilizers may be either before or after the addition of the aqueous monomer solution.

[0079] In particular, from the perspective of easily reducing the amount of residual hydrocarbon dispersion medium in the obtained absorbent resin particles, it is preferable to disperse an aqueous monomer solution in a hydrocarbon dispersion medium in which a polymeric dispersant is dispersed, and then further disperse a surfactant before performing polymerization.

[0080] It is possible to perform such reverse-phase suspension polymerization in two or more stages. In addition, it is desirable to perform it in two to three stages to increase productivity.

[0081] In reverse-phase suspension polymerization performed in two or more stages, after performing the first stage of reverse-phase suspension polymerization, a water-soluble ethylenically unsaturated monomer is added to and mixed with the reaction mixture obtained from the first stage of polymerization reaction, and the subsequent stages of reverse-phase suspension polymerization are performed in the same manner as the first stage. In the reverse-phase suspension polymerization at each subsequent stage, in addition to the water-soluble ethylenically unsaturated monomer, it is preferable to perform the reverse-phase suspension polymerization by adding a radical polymerization initiator within the range of the molar ratio of each component to the water-soluble ethylenically unsaturated monomer described above, based on the amount of water-soluble ethylenically unsaturated monomer added during the reverse-phase suspension polymerization at each subsequent stage. Furthermore, in the subsequent stages of polymerization, an internal crosslinking agent may be added to the water-soluble ethylenically unsaturated monomer if necessary.

[0082] As for the reaction temperature of the polymerization reaction, it is preferable to have a temperature of 20 to 110°C, and more preferable to have a temperature of 40 to 90°C, from the perspective of increasing economic efficiency by rapidly proceeding with the polymerization and shortening the polymerization time, and easily removing the heat of polymerization to carry out the reaction smoothly.

[0083] The aggregation process of polymer particles may be performed after the first stage of reverse-phase suspension polymerization, or it may be performed between the first stage of reverse-phase suspension polymerization and the second stage of reverse-phase suspension polymerization, or it may be performed after the second stage of reverse-phase suspension polymerization. From the perspective of more appropriately exhibiting the effects of the present invention, it is preferable to perform the aggregation process of polymer particles between the first stage of reverse-phase suspension polymerization and the second stage of reverse-phase suspension polymerization. Furthermore, in the aggregation process of polymer particles, the polymerization reaction of the water-soluble ethylenically unsaturated monomer may or may not be in progress.

[0084] In the present invention, when polymer particles obtained from a first-stage reverse-phase suspension polymerization are aggregated in an aggregation process, it is possible to control the degree of aggregation of polymer particles by adjusting the temperature of the slurry solution and sequentially precipitating two or more types of (poly)glycerin fatty acid esters with different precipitation temperatures. For example, before adding an aqueous solution of a water-soluble ethylenedimethyl unsaturated monomer in a second-stage reverse-phase suspension polymerization, the temperature of the slurry solution is lowered to precipitate at least one of two or more types of (poly)glycerin fatty acid esters. Then, the droplets of the water-soluble ethylenedimethyl unsaturated monomer added thereafter are not stabilized in the hydrocarbon dispersion medium but are absorbed into the polymer particles (gel-like primary particles), thereby promoting aggregation among the polymer particles. Meanwhile, when the temperature of the slurry is increased, the (poly)glycerin fatty acid ester dissolves, the droplets of water-soluble ethylenically unsaturated monomers are stabilized in the hydrocarbon dispersion medium, and the aggregation between polymer particles is suppressed. In the present invention, absorbent resin particles with a narrow particle size distribution can be appropriately produced by adjusting the promotion and suppression of aggregation between polymer particles.

[0085] The temperature range in the aggregation process is not particularly limited as long as it is a temperature range that can control the aggregation of polymer particles, for example, a range of 5 to 50°C, preferably 10 to 40°C, more preferably 15 to 30°C.

[0086] Dehydration Process

[0087] After performing the reverse-phase suspension polymerization described above, a dehydration treatment may be included to remove water, hydrocarbon dispersion medium, etc. by distillation by applying energy from an external source, such as heat. When performing dehydration from the aqueous gel material after reverse-phase suspension polymerization, the system in which the aqueous gel material is dispersed in the hydrocarbon dispersion medium is heated to remove water and the hydrocarbon dispersion medium by distillation from the system by azeotropic distillation. At this time, if only the hydrocarbon dispersion medium removed by distillation is returned into the system, continuous azeotropic distillation becomes possible. In this case, since the temperature within the system being dried is maintained below the azeotropic temperature with the hydrocarbon dispersion medium, it is desirable from the perspective that the resin is less likely to deteriorate. By controlling the dehydration treatment conditions after this polymerization and adjusting the amount of dehydration (i.e., adjusting the moisture content of the polymer particles), it is possible to control the overall performance of the obtained absorbent resin particles.

[0088] In the dehydration process, dehydration treatment by distillation may be performed under atmospheric pressure. When dehydration treatment is performed under atmospheric pressure, the dehydration temperature is preferably 70 to 250°C, more preferably 80 to 180°C, even more preferably 80 to 140°C, and even more preferably 90 to 130°C.

[0089] Surface Crosslinking Process

[0090] The surface crosslinking process is a process of performing surface crosslinking on polymer particles obtained from a polymerization process. When the polymer particles are crosslinked polymer particles (hydrated gel-like material), the process involves adding a surface crosslinking agent to a hydrated gel-like material having an internal crosslinked structure obtained by polymerizing a water-soluble ethylenically unsaturated monomer to perform crosslinking (surface crosslinking reaction). It is preferable to perform this surface crosslinking reaction in the presence of a surface crosslinking agent after the polymerization of the water-soluble ethylenically unsaturated monomer. In this way, by performing a surface crosslinking reaction on a hydrated gel-like material having an internal crosslinked structure after polymerization, the crosslinking density near the surface of the absorbent resin particles is increased, thereby obtaining absorbent resin particles with improved overall performance, such as load-bearing capacity.

[0091] Examples of surface crosslinking agents include compounds having two or more reactive functional groups. Examples include polyols such as ethylene glycol, propylene glycol, 1,4-butanediol, diethylene glycol, triethylene glycol, trimethylolpropane, glycerin, polyoxyethylene glycol, polyoxypropylene glycol, and polyglycerin; polyglycidyl compounds such as (poly)ethylene glycol diglycidyl ether, (poly)glycerin diglycidyl ether, (poly)glycerin triglycidyl ether, trimethylolpropane triglycidyl ether, (poly)propylene glycol polyglycidyl ether, and (poly)glycerol polyglycidyl ether; haloepoxy compounds such as epichlorohydrin, epibromohydrin, and α-methyl epichlorohydrin; and isocyanate compounds such as 2,4-tolylene diisocyanate and hexamethylene diisocyanate. Oxetane compounds such as 3-methyl-3-oxetanmethanol, 3-ethyl-3-oxetanmethanol, 3-butyl-3-oxetanmethanol, 3-methyl-3-oxetaneethanol, 3-ethyl-3-oxetaneethanol, 3-butyl-3-oxetaneethanol; oxazoline compounds such as 1,2-ethylenebisoxazoline; Examples include carbonate compounds such as ethylene carbonate, propylene carbonate, 4,5-dimethyl-1,3-dioxolanam-2-one, 4,4-dimethyl-1,3-dioxolanam-2-one, 4-ethyl-1,3-dioxolanam-2-one, 4-hydroxymethyl-1,3-dioxolanam-2-one, 1,3-dioxan-2-one, 4-methyl-1,3-dioxan-2-one, 4,6-dimethyl-1,3-dioxan-2-one, and 1,3-dioxolanam-2-one (e.g., alkylene carbonates); and hydroxyalkylamide compounds such as bis[N,N-di(β-hydroxyethyl)]adipamide. Among these surface crosslinking agents, polyglycidyl compounds such as (poly)ethylene glycol diglycidyl ether, (poly)glycerin diglycidyl ether, (poly)glycerin triglycidyl ether, trimethylolpropane triglycidyl ether, (poly)propylene glycol polyglycidyl ether, and (poly)glycerol polyglycidyl ether are preferred. These surface crosslinking agents may be used alone or in combination of two or more types.

[0092] As for the amount of surface crosslinking agent used, it is preferable to have 0.00001 to 0.01 moles per 1 mole of the total amount of water-soluble ethylenically unsaturated monomer used in polymerization, more preferable to have 0.00005 to 0.005 moles, and even more preferable to have 0.0001 to 0.002 moles.

[0093] As for the method of adding a surface crosslinking agent, the surface crosslinking agent may be added as is or as an aqueous solution, but if necessary, it may also be added as a solution using a hydrophilic organic solvent as a solvent. Examples of hydrophilic organic solvents 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; amides such as N,N-dimethylformamide; and sulfoxides such as dimethyl sulfoxide. These hydrophilic organic solvents may be used alone, in combination of two or more types, or as a mixed solvent with water.

[0094] The timing for adding the surface crosslinking agent is after the polymerization reaction of the water-soluble ethylenically unsaturated monomer has been almost completely finished. It is preferable to add it in the presence of moisture in the range of 1 to 400 parts by mass per 100 parts by mass of the water-soluble ethylenically unsaturated monomer, more preferable to add it in the presence of moisture in the range of 5 to 200 parts by mass, even more preferable to add it in the presence of moisture in the range of 10 to 100 parts by mass, and even more preferable to add it in the presence of moisture in the range of 20 to 60 parts by mass. In addition, the amount of moisture refers to the total amount of moisture included in the reaction system and moisture used as necessary when adding the surface crosslinking agent.

[0095] In order to further appropriately demonstrate the effects of the present invention, the moisture content of the polymer particles when a surface crosslinking agent is added is preferably 1 mass% or more, more preferably 10 mass% or more, even more preferably 20 mass% or more, and also preferably 60 mass% or less, more preferably 40 mass% or less, even more preferably 35 mass% or less, and preferred ranges include 1 to 60 mass%, 1 to 40 mass%, 1 to 35 mass%, 10 to 60 mass%, 10 to 40 mass%, 10 to 35 mass%, 20 to 60 mass%, 20 to 40 mass%, 20 to 35 mass%, etc.

[0096] As for the reaction temperature in the surface crosslinking reaction, it is preferable to have a temperature of 50 to 250°C, more preferable to have a temperature of 60 to 180°C, even more preferable to have a temperature of 60 to 140°C, and even more preferable to have a temperature of 70 to 120°C. In addition, as for the reaction time of the surface crosslinking reaction, it is preferable to have a reaction time of 1 to 300 minutes, and more preferable to have a reaction time of 5 to 200 minutes.

[0097] <Drying Process>

[0098] After performing the surface crosslinking described above, a drying treatment may be included to remove water, hydrocarbon dispersion medium, etc. by distillation by applying energy such as heat from the outside. Absorbent resin particles are obtained by drying the polymer particles after surface crosslinking and removing water and hydrocarbon dispersion medium by distillation.

[0099] In the drying process, drying treatment by distillation may be performed under atmospheric pressure or under reduced pressure. Additionally, from the perspective of increasing drying efficiency, it may be performed under a stream of air such as nitrogen. When the drying treatment is performed under atmospheric pressure, the drying temperature is preferably 70 to 250°C, more preferably 80 to 180°C, even more preferably 80 to 140°C, and even more preferably 90 to 130°C. Furthermore, when the drying treatment is performed under reduced pressure, the drying temperature is preferably 40 to 160°C, and more preferably 50 to 110°C.

[0100] In addition, if a surface crosslinking process using a surface crosslinking agent is performed after polymerizing the monomer by reverse-phase suspension polymerization, the drying process by distillation described above is performed after the completion of the surface crosslinking process. Alternatively, the surface crosslinking process and the drying process may be performed simultaneously.

[0101] The absorbent resin particles of the present invention may include additives according to the purpose. Examples of such additives include inorganic powders, surfactants, oxidizing agents, reducing agents, metal chelating agents, radical chain inhibitors, antioxidants, antibacterial agents, etc. For example, the fluidity of the absorbent resin particles can be further improved by adding 0.05 to 5 parts by mass of amorphous silica as an inorganic powder per 100 parts by mass of the absorbent resin particles. In addition, it is preferable that the above additive be hydrophilic or water-soluble.

[0102] 2. Absorbent resin particles

[0103] By employing the method for manufacturing absorbent resin particles of the present invention described above, absorbent resin particles with a narrow particle size distribution can be appropriately manufactured. More specifically, by employing the method for manufacturing absorbent resin particles of the present invention, it becomes possible to appropriately manufacture absorbent resin particles having, for example, a uniformity of particle size distribution of 2.5 or less and containing (poly)glycerin fatty acid esters near the surface.

[0104] The uniformity of the particle size distribution of the absorbent resin particles of the present invention may be 2.5 or less, preferably 2.3 or less, more preferably 1.8 or less, and even more preferably 1.6 or less, and the lower limit is, for example, 1.

[0105] The uniformity of the particle size distribution of absorbent resin particles is measured according to the measurement method described in the example.

[0106] In addition, the absorbent resin particles of the present invention comprise (poly)glycerin fatty acid esters near the surface. In the method for manufacturing the absorbent resin particles of the present invention, (poly)glycerin fatty acid esters are used as described above. Accordingly, (poly)glycerin fatty acid esters are included near the surface of the absorbent resin particles. Specific examples of (poly)glycerin fatty acid esters are exemplified as those exemplified in the method for manufacturing the absorbent resin particles of the present invention. It is preferable that two or more types of (poly)glycerin fatty acid esters are included near the surface of the absorbent resin particles, and it is preferable that tristearate hexaglyceryl be included.

[0107] The amount of (poly)glycerin fatty acid ester contained near the surface of the absorbent resin particles of the present invention is preferably 1 part by mass or less, more preferably 0.65 parts by mass or less, and even more preferably 0.55 parts by mass or less, per 100 parts by mass of the absorbent resin particles. In addition, the lower limit is preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, and even more preferably 0.3 parts by mass or more.

[0108] In addition, the absorbent resin particles of the present invention have a yellowness of preferably 20 or less, more preferably 15 or less, and even more preferably 12 or less after being heated at 200°C for 2 hours. In addition, the lower limit of said yellowness is, for example, 0.

[0109] In addition, the initial value of the yellowness of the absorbent resin particles of the present invention (yellowness before heating at 200°C for 2 hours) is preferably 15 or less, more preferably 12 or less, and even more preferably 10 or less. In addition, the lower limit of the said yellowness is, for example, 0.

[0110] The measurement of the yellowness of absorbent resin particles before and after heating at 200°C for 2 hours follows the measurement method described in each example.

[0111] The absorbent resin particles of the present invention are preferably composed of a polymer of water-soluble ethylenically unsaturated monomers, that is, a cross-linked polymer having structural units derived from water-soluble ethylenically unsaturated monomers.

[0112] The absorbent resin particles of the present invention are in the form of aggregated fine particles (primary particles) (secondary particles). Examples of the shapes of the primary particles include approximately spherical, irregularly fragmented, and plate-like forms. The absorbent resin particles of the present invention, which are secondary particles, may have various shapes. Examples of the shapes of the absorbent resin particles include granular, approximately spherical, irregularly fragmented, plate-like, fibrous, flake-like forms, or forms in which these resins are aggregated. It is preferable that the absorbent resin particles be granular, approximately spherical, irregularly fragmented, fibrous, or forms in which these resins are aggregated.

[0113] The median particle diameter of the absorbent resin particles is preferably 100 µm or more, 150 µm or more, 200 µm or more, 250 µm or more, 280 µm or more, 300 µm or more, or 320 µm or more. In addition, from the same perspective, the median particle diameter is preferably 700 µm or less, 600 µm or less, 550 µm or less, 500 µm or less, 450 µm or less, or 400 µm or less. That is, it is preferable for the median particle diameter to be 150 to 700 µm, 200 to 600 µm, more preferable for 250 to 500 µm, even more preferable for 250 to 450 µm, and even more preferable for 250 to 400 µm.

[0114] The median particle diameter of the absorbent resin particles can be measured using a JIS standard sieve, specifically the value measured by the method described in the example.

[0115] The absorption rate of physiological saline by the absorbent resin particles is preferably 20 seconds or more, more preferably 25 seconds or more, even more preferably 30 seconds or more, and also preferably 65 seconds or less, more preferably 60 seconds or less, even more preferably 55 seconds or less, and more preferably 20 to 65 seconds, 25 to 60 seconds, etc. as a more preferred range.

[0116] The physiological saline retention capacity of the absorbent resin particles of the present invention is preferably 20 g / g or more, more preferably 30 g / g or more, and also preferably 80 g / g or less, more preferably 60 g / g or less, even more preferably 55 g / g or less, and even more preferably 53 g / g or less. Preferred ranges include 20 to 80 g / g, 20 to 60 g / g, 20 to 55 g / g, 20 to 53 g / g, 30 to 80 g / g, 30 to 60 g / g, 30 to 55 g / g, 30 to 53 g / g, etc.

[0117] 3. Absorbent material, absorbent article

[0118] The absorbent resin particles of the present invention constitute an absorbent body used in sanitary materials, such as sanitary products and paper diapers, for example, and are suitably used in absorbent articles containing said absorbent body.

[0119] The absorbent of the present invention comprises the absorbent resin particles of the present invention. The absorbent may further comprise hydrophilic fibers. Examples of the composition of the absorbent include a sheet-like structure in which absorbent resin particles are fixed on a nonwoven fabric or between multiple nonwoven fabrics, a mixed dispersion obtained by mixing absorbent resin particles and hydrophilic fibers to obtain a uniform composition, a sandwich structure in which absorbent resin particles are sandwiched between layered hydrophilic fibers, and a structure in which absorbent resin particles and hydrophilic fibers are wrapped in tissue. In addition, other components may be incorporated into the absorbent, such as adhesive binders like heat-sealable synthetic fibers, hot-melt adhesives, and adhesive emulsions to enhance the shape retention of the absorbent.

[0120] The mass per unit area of ​​the absorbent resin particles in the absorbent of the present invention is 50 g / m² or more and 400 g / m² or less. The mass per unit area is preferably 100 g / m² or more, more preferably 120 g / m² or more, and even more preferably 140 g / m² or more, and is also preferably 300 g / m² or less, more preferably 250 g / m² or less, and even more preferably 200 g / m² or less.

[0121] As hydrophilic fibers, at least one type selected from the group consisting of finely ground wood pulp, cotton, cotton lint, rayon, cellulose acetate, polyamide, polyester, and polyolefin may be used. Examples include cellulose fibers such as cotton pulp, mechanical pulp, chemical pulp, and semi-chemical pulp obtained from wood, artificial cellulose fibers such as rayon and acetate, and fibers made of synthetic resins such as hydrophilized polyamide, polyester, and polyolefin. The average fiber length of the hydrophilic fiber is typically 0.1 to 10 mm, or it may be 0.5 to 5 mm.

[0122] The mass per unit area of ​​the hydrophilic fiber in the absorbent of the present invention is 50 g / m² or more and 800 g / m² or less. The mass per unit area is preferably 100 g / m² or more, more preferably 120 g / m² or more, and even more preferably 140 g / m² or more, and also preferably 700 g / m² or less, more preferably 600 g / m² or less, and even more preferably 500 g / m² or less.

[0123] The content of absorbent resin particles in the absorbent material is preferably 5 to 100 mass%, more preferably 10 to 95 mass%, even more preferably 20 to 90 mass%, and even more preferably 30 to 80 mass%.

[0124] An absorbent body using the absorbent resin particles of the present invention can be made into an absorbent article of the present invention by maintaining it between a liquid-permeable sheet (top sheet) through which liquid can pass and a liquid-impermeable sheet (back sheet) through which liquid cannot pass. The liquid-permeable sheet is positioned on the side in contact with the body, and the liquid-impermeable sheet is positioned on the opposite side from the body.

[0125] Examples of liquid-permeable sheets include nonwoven fabrics such as air-through, spunbond, chemical bond, and needle-punch types made of fibers such as polyethylene, polypropylene, and polyester, as well as porous synthetic resin sheets. Additionally, examples of liquid-impermeable sheets include synthetic resin films made of resins such as polyethylene, polypropylene, and polyvinyl chloride. It is preferable that the liquid-permeable sheet be at least one type selected from the group consisting of thermal bond nonwoven fabric, air-through nonwoven fabric, spunbond nonwoven fabric, and spunbond / meltblown / spunbond nonwoven fabric.

[0126] The mass per unit area of ​​the liquid permeable sheet is preferably 5 g / m² or more and 100 g / m² or less, and more preferably 10 g / m² or more and 60 g / m² or less. In addition, the surface of the liquid permeable sheet may be embossed or perforated to improve the diffusivity of the liquid. The embossing or perforating process may be performed using known methods.

[0127] Examples of liquid impermeable sheets include sheets made of synthetic resins such as polyethylene, polypropylene, and polyvinyl chloride; sheets made of nonwoven fabrics such as spunbond / meltblown / spunbond (SMS) nonwoven fabrics in which water-resistant meltblown nonwoven fabric is sandwiched between high-strength spunbond nonwoven fabrics; and sheets made of composite materials of these synthetic resins and nonwoven fabrics (e.g., spunbond nonwoven fabric, spunlace nonwoven fabric). As a liquid impermeable sheet, a sheet made of a synthetic resin mainly consisting of low-density polyethylene (LDPE) resin may also be used. The liquid impermeable sheet may be a sheet made of a synthetic resin having, for example, a mass per unit area of ​​10 to 50 g / m².

[0128] It is preferable that the absorbent article comprises an absorbent body containing absorbent resin particles, a laminate having a core wrap positioned between the upper and lower parts of the absorbent body, a liquid permeable sheet disposed on the upper surface of the laminate, and a liquid impermeable sheet disposed on the side of the laminate opposite to the liquid permeable sheet.

[0129] (Example)

[0130] The present invention will be described in detail below by presenting examples and comparative examples. However, the present invention is not limited to the examples.

[0131] In addition, the absorbent resin particles obtained in the following examples and comparative examples were evaluated by the following various tests. Also, unless otherwise noted, measurements were performed under conditions of a temperature of 25±2℃ and a humidity of 50±10%.

[0132] [Manufacture of absorbent resin particles]

[0133] (Example 1)

[0134] A round-bottom cylindrical separable flask with an inner diameter of 11 cm and a volume of 2 L was prepared, equipped with a reflux condenser, a dropping funnel, a nitrogen gas inlet tube, and a stirrer (a stirring blade having two stages of four inclined paddle blades with a blade diameter of 5 cm). 300 g of n-heptane (hydrocarbon dispersion medium) was placed in this separable flask, 0.737 g of tetraglyceryl tristearate (dispersion stabilizer, manufactured by Sakamoto Yakuhin Kogyo Co., Ltd., SY Glister TS-3S) and 0.737 g of hexaglyceryl tristearate (dispersion stabilizer, manufactured by Sakamoto Yakuhin Kogyo Co., Ltd., SY Glister TS-5S) were added, and the mixture was dissolved by raising the temperature to 80°C while stirring, and then cooled to 55°C.

[0135] Next, 92.0 g of an 80.5 mass% aqueous acrylic acid solution (acrylic acid: 1.03 mol) was placed in a 500 ml volume Erlenmeyer flask. Subsequently, while cooling from the outside, 102.78 g of a 30 mass% aqueous sodium hydroxide solution was added dropwise to achieve 75 mol% neutralization, and then 0.0736 g (0.272 mmol) of potassium persulfate (water-soluble radical polymerization initiator), 0.0101 g (0.0580 mmol) of ethylene glycol diglycidyl ether (internal crosslinking agent), and 44.62 g of ion-exchanged water were added and dissolved to prepare the aqueous solution of the first stage.

[0136] The aqueous solution of the first step described above was added to the separable flask described above, and the inside of the separable flask system was sufficiently purged with nitrogen while stirring at a rotational speed of 400 rpm. Afterwards, the separable flask was immersed in a water bath at 70°C to raise the temperature of the reaction solution, and the polymerization of the first step was carried out for 60 minutes to obtain the slurry of the first step.

[0137] Next, 128.8 g of an 80.5 mass% aqueous acrylic acid solution (acrylic acid: 1.44 mol) was placed in a separate Erlenmeyer flask with a capacity of 500 ml. Subsequently, while cooling from the outside, 75 mol% neutralization was performed by adding 143.89 g of a 30 mass% aqueous sodium hydroxide solution dropwise, and then 0.1030 g (0.3810 mmol) of potassium persulfate, 0.0116 g (0.0666 mmol) of ethylene glycol diglycidyl ether (internal crosslinking agent), and 16.75 g of ion-exchanged water were added and dissolved to prepare the aqueous solution of the second stage.

[0138] While stirring the slurry of the first stage at a rotational speed of 1000 rpm, the separable flask system was cooled to 20°C, and then the entire amount of the aqueous solution of the second stage was added to the slurry of the first stage to perform a coagulation process. After purging the system with nitrogen for 30 minutes, the separable flask was again immersed in a water bath at 70°C to raise the temperature, and a polymerization reaction was carried out for 60 minutes to obtain the slurry of the second stage.

[0139] After the second stage of polymerization, the second stage slurry was heated in an oil bath at 125°C, and 248g of water was removed from the system while refluxing n-heptane by azeotropic distillation of n-heptane and water. Subsequently, a dried product was obtained by evaporating and drying the n-heptane. By passing this dried product through a sieve with a mesh size of 850 μm, 203.8g of absorbent resin particles in the form of aggregated, approximately spherical particles were obtained.

[0140] (Example 2)

[0141] 200.3 g of absorbent resin particles were obtained by performing the same operation as in Example 1, except that decaglyceril pentastearate (dispersion stabilizer, manufactured by Nihon S.Factant Co., Ltd., NIKKOL Decaglyn 5-SV) was used instead of tetraglyceril tristearate in Example 1.

[0142] (Example 3)

[0143] 194.5 g of absorbent resin particles were obtained by performing the same operation as in Example 1, except that 0.552 g of tristearate tetraglyceryl, 0.552 g of tristearate hexaglyceryl, and 0.184 g of pentastearate decaglyceryl were used instead of 0.737 g of tristearate tetraglyceryl and 0.737 g of tristearate hexaglyceryl in Example 1.

[0144] (Example 4)

[0145] 215.5 g of absorbent resin particles were obtained by performing the same operation as in Example 1, except that 0.276 g of tristearate tetraglyceryl, 0.460 g of tristearate hexaglyceryl, and 0.368 g of pentastearate decaglyceryl were used instead of 0.737 g of tristearate tetraglyceryl and 0.737 g of tristearate hexaglyceryl in Example 1.

[0146] (Example 5)

[0147] A round-bottom cylindrical separable flask with an inner diameter of 11 cm and a volume of 2 L was prepared, equipped with a reflux condenser, a dropping funnel, a nitrogen gas inlet tube, and a stirrer (a stirring blade having two stages of four inclined paddle blades with a blade diameter of 5 cm). 293 g of n-heptane (hydrocarbon dispersion medium) was placed in this separable flask, and 0.276 g of maleic anhydride-modified ethylene-propylene copolymer (polymer-based dispersant, Mitsui & Co., Ltd., Hi-Wax 1105A) was added. The mixture was dissolved by raising the temperature to 80°C while stirring, and then cooled to 55°C.

[0148] Next, 92.0 g of an 80.5 mass% aqueous acrylic acid solution (acrylic acid: 1.03 mol) was added to a 500 ml volume Erlenmeyer flask. Subsequently, while cooling from the outside, 102.78 g of a 30 mass% aqueous sodium hydroxide solution was added dropwise to achieve 75 mol% neutralization, after which 0.0736 g (0.272 mmol) of potassium persulfate (water-soluble radical polymerization initiator), 0.0558 g of tetra(ethylene glycol) diacrylate (internal crosslinking agent), and 44.62 g of ion-exchanged water were added and dissolved to prepare the aqueous solution of the first stage.

[0149] The aqueous solution of the first step described above was added to the separable flask described above and stirred for 10 minutes. Then, a dispersion stabilizer solution was obtained by heating and dissolving 0.276 g of tristearate tetraglyceryl, 0.460 g of tristearate hexaglyceryl, and 0.368 g of pentastearate decaglyceryl in 6.62 g of n-heptane. 7.724 g of the obtained dispersion stabilizer solution was added to the separable flask, and the inside of the separable flask system was sufficiently purged with nitrogen while stirring at a rotational speed of 400 rpm. Subsequently, the separable flask was immersed in a water bath at 70°C to raise the temperature of the reaction solution, and the polymerization of the first step was carried out for 60 minutes to obtain the slurry of the first step.

[0150] Next, 128.8 g of an 80.5 mass% aqueous acrylic acid solution (acrylic acid: 1.44 mol) was placed in a separate Erlenmeyer flask with a capacity of 500 ml. Subsequently, while cooling from the outside, 75 mol% neutralization was performed by adding 143.89 g of a 30 mass% aqueous sodium hydroxide solution dropwise, and then 0.1030 g of potassium persulfate (0.3810 millimol), 0.0447 g of tetra(ethylene glycol) diacrylate (internal crosslinking agent), and 16.75 g of ion-exchanged water were added and dissolved to prepare the aqueous solution of the second stage.

[0151] While stirring the slurry of the first stage at a rotational speed of 1000 rpm, the separable flask system was cooled to 20°C, and then the entire amount of the aqueous liquid of the second stage was added to the slurry of the first stage to perform a coagulation process. After purging the system with nitrogen for 30 minutes, the flask was again immersed in a water bath at 70°C to raise the temperature, and a polymerization reaction was carried out for 60 minutes to obtain the slurry of the second stage.

[0152] After the second stage of polymerization, the second stage slurry was heated in an oil bath at 125°C, and 248g of water was removed from the system while refluxing n-heptane by azeotropic distillation of n-heptane and water. Subsequently, a dried product was obtained by evaporating and drying the n-heptane. By passing this dried product through a sieve with a mesh size of 850 μm, 205.4g of absorbent resin particles in the form of aggregated, approximately spherical particles were obtained.

[0153] (Comparative Example 1)

[0154] 103.1 g of absorbent resin particles were obtained by performing the same operation as in Example 1, except that 1.289 g of tristearate tetraglyceryl was used instead of 0.737 g of tristearate tetraglyceryl and 0.737 g of tristearate hexaglyceryl in Example 1.

[0155] <Evaluation of Absorbent Resin Particles>

[0156] (Median particle diameter)

[0157] An absorbent resin composition was prepared by mixing 0.5 g of amorphous silica (Tokusil NP-S, manufactured by Oriental Silicas Corporation) as a lubricant with 100 g of absorbent resin particles. For this measurement, seven types of JIS standard sieves (mesh sizes 600 µm, 500 µm, 425 µm, 300 µm, 250 µm, 150 µm, and 75 µm) were used. The absorbent resin composition was placed on the top of a sieve formed by combining the selected JIS standard sieve and a tray in sequence, and shaken for 20 minutes using a rotary shaker. Next, the mass of the absorbent resin composition remaining on each sieve was calculated as a mass percentage relative to the total amount, and the relationship between the sieve mesh size and the accumulated mass percentage remaining on the sieve was plotted on a logarithmic probability sheet by accumulating the values ​​in order from smallest particle diameter. By connecting the plots on the probability sheet with a straight line, the particle diameter corresponding to an accumulated mass percentage of 50 mass% was defined as the median particle diameter. The results are shown in Table 3.

[0158] (Uniformity)

[0159] In the above measurement of the intermediate particle diameter, the particle diameter (A1) corresponding to an accumulated mass percentage passing through a sieve of 10 mass% and the particle diameter (A2) corresponding to 60 mass% were determined, and the uniformity was calculated according to the following formula. The results are shown in Table 3.

[0160] Uniformity = A2 / A1

[0161] In other words, when the particle diameter distribution is narrow, the uniformity approaches 1, and when the particle diameter distribution is wide, the uniformity becomes greater than 1.

[0162] (Precipitation temperature of dispersion stabilizer)

[0163] The precipitation temperature of the dispersion stabilizer was determined by cooling a mixed solution in which the dispersion stabilizer was dissolved in a solvent by heating, and measuring the turbidity of the mixed solution at each temperature. Specifically, 100 g of n-heptane (hydrocarbon dispersion medium) and 0.46 g of dispersion stabilizer were added to a branched flask. This solution was heated to 80°C under stirring with a stirrer tip to obtain a mixed solution in which the dispersion stabilizer was dissolved. Subsequently, the mixed solution was cooled, and turbidity was measured at 1°C intervals using an integrating sphere turbidity meter SEP-PT-706D (manufactured by Nitto Seiko Analytics Co., Ltd., optical path length 10 mm) based on a calibration curve prepared with a turbidity standard solution (kaolin 1000°C). The precipitation temperature of the dispersion stabilizer was defined as the temperature at which the turbidity increased by 10 ppm or more compared to the turbidity at a temperature 1°C higher. The results are shown in Table 1.

[0164] <Yellow Coloration Test (Measurement of Yellowness) Before and After Heating at 200℃ for 2 Hours>

[0165] 2.0 g of absorbent resin particles were uniformly placed in a glass measuring container with an inner diameter of 3 cm. The yellowness of the absorbent resin particles was measured using a colorimeter (Color Meter ZE6000, manufactured by Nippon Tenshoku Kogyo Co., Ltd.) that corrected the three stimulus values ​​X, Y, and Z of the colorimeter using a standard white plate. From the X, Y, and Z (three stimulus values) of the absorbent resin particles obtained, the yellowness was calculated according to the following formula and used as the yellowness before heating. The results are shown in Table 3.

[0166] Yellowness = 100(1.28X - 1.06Z) / Y

[0167] In addition, a test on the yellowness of the absorbent resin particles after heating was performed as follows. Specifically, 2.0 g of absorbent resin particles were uniformly placed in a glass petri dish with an inner diameter of 3 cm and a depth of 1 cm. Nitrogen was blown at the outlet to achieve a flow rate of 400 ml / min, and a vacuum dryer (manufactured by Azwon Co., Ltd., AVO-310N) preheated to 200 ± 5°C was prepared, and a glass wool insulation material with a thickness of 3 cm was placed on the inner bottom. A stainless steel tray was placed on the insulation material inside the vacuum dryer, and the glass petri dish containing the absorbent resin particles and a surface thermometer were installed on the stainless steel tray. Heating was carried out for 2 hours starting from the point when the surface thermometer reached 200 ± 5°C. Afterward, the glass petri dish containing the absorbent resin particles was removed from the vacuum dryer along with the stainless steel tray, and cooled to room temperature by leaving it in a desiccator for 30 minutes. The entire amount of absorbent resin particles in a glass petri dish was placed into a glass measuring container with an inner diameter of 3 cm, and the yellowness of the absorbent resin particles was measured using a colorimeter (Color Meter ZE6000, manufactured by Nippon Tenshoku Kogyo Co., Ltd.). The yellowness was calculated according to the above formula from the X, Y, and Z (three stimulus values) of the obtained absorbent resin particles and was used as the yellowness after heating. The results are shown in Table 3.

[0168] [Table 1]

[0169]

[0170] [Table 2]

[0171]

[0172] In Table 2, the amount of dispersion stabilizer added is based on 100 parts by mass of acrylic acid, a water-soluble ethylenically unsaturated monomer used in the first stage of polymerization.

[0173] [Table 3]

[0174]

Claims

Claim 1 A method for manufacturing absorbent resin particles comprising a process of obtaining polymer particles by reverse-phase suspension polymerization of a water-soluble ethylenically unsaturated monomer in a hydrocarbon dispersion medium, wherein the reverse-phase suspension polymerization is performed in two or more stages and the process of aggregating the polymer particles in the presence of a dispersion stabilizer is included, wherein two or more types of (poly)glycerin fatty acid esters having different precipitation temperatures when the dispersion stabilizer is a 0.46 mass% heptane solution are used. Claim 2 A method for manufacturing absorbent resin particles according to claim 1, wherein among two or more types of (poly)glycerin fatty acid esters, the difference between the precipitation temperature of the (poly)glycerin fatty acid ester with the highest precipitation temperature and the precipitation temperature of the (poly)glycerin fatty acid ester with the lowest precipitation temperature is 15°C or less. Claim 3 A method for manufacturing absorbent resin particles according to claim 1 or 2, wherein at least one of the (poly)glycerin fatty acid esters is tristearate hexaglyceryl, and the amount of tristearate hexaglyceryl used is in the range of 0.2 parts by mass or more and 4.0 parts by mass or less per 100 parts by mass of the water-soluble ethylenically unsaturated monomer used in the first stage polymerization. Claim 4 A method for manufacturing absorbent resin particles according to claim 3, wherein the dispersion stabilizer comprises at least one of the tristearate hexaglyceryl, a (poly)glycerin fatty acid ester having a precipitation temperature higher than that of the tristearate hexaglyceryl, and a (poly)glycerin fatty acid ester having a precipitation temperature lower than that of the tristearate hexaglyceryl, and the amounts of the (poly)glycerin fatty acid ester having a precipitation temperature higher than that of the tristearate hexaglyceryl and the (poly)glycerin fatty acid ester having a precipitation temperature lower than that of the tristearate are each in the range of more than 0 parts by mass and 3.0 parts by mass or less per 1 part by mass of the tristearate hexaglyceryl. Claim 5 A method for manufacturing absorbent resin particles according to claim 4, wherein the dispersion stabilizer comprises the tristearate hexaglyceryl, a (poly)glycerin fatty acid ester with a precipitation temperature higher than that of the tristearate hexaglyceryl, and a (poly)glycerin fatty acid ester with a precipitation temperature lower than that of the tristearate hexaglyceryl, wherein the amount of the (poly)glycerin fatty acid ester with a precipitation temperature higher than that of the tristearate hexaglyceryl and the (poly)glycerin fatty acid ester with a precipitation temperature lower than that of the tristearate is each greater than 0 parts by mass and less than or equal to 2.0 parts by mass per 1 part by mass of the tristearate hexaglyceryl. Claim 6 Absorbent resin particles comprising polymer particles having water-soluble ethylenically unsaturated monomers as monomer units, wherein the uniformity of the particle size distribution is 2.5 or less, and further comprising (poly)glycerin fatty acid esters near the surface.

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