Particle-like water-absorbing agent composition production method, particle-like water-absorbing agent composition, and absorbent article

Abstract

This particle-like water-absorbing agent composition production method involves, in at least one step selected from among a step for preparing a monomer aqueous solution, a polymerization step, and a hydrous gel pulverization step which is an optional step, adding 0.01-0.25 mass% of a water-soluble polyalkylene glycol having a mass average molecular weight of 3000 or less with respect to the total mass of monomers contained in the monomer aqueous solution, and adding, after a surface crosslinking step, 0.02-0.40 mass% of a nonionic polymer having a polyalkylene glycol chain in the structure and having a mass average molecular weight of 300-15000, to a surface-crosslinked water-absorbing resin. By using said method, it is possible to produce a particle-like water-absorbing agent composition that has high anti-caking performance without deteriorating the pressure-applied water absorption performance.

Description

Particulate water-absorbing agent composition manufacturing method, particulate water-absorbing agent composition, and absorbent article

[0001] The present invention relates to a method for producing a particulate water-absorbing agent composition, a particulate water-absorbing agent composition, and an absorbent article.

[0002] A particulate water-absorbing agent composition (hereinafter, in this specification, may be simply referred to as a "water-absorbing agent") containing a water-absorbing resin as a main component is used in an absorbent body contained in an absorbent article such as a disposable diaper, a sanitary napkin, and an incontinence pad.

[0003] In the above-mentioned applications, the water-absorbing agent absorbs aqueous liquids such as urine and swells to seal in the aqueous liquid. Since absorbent articles are usually used in a state where the body weight is applied, the water-absorbing agent is required to have high water-absorbing performance under pressure in order to improve the absorption performance of the absorbent article. Examples of physical property values ​​that represent the water-absorbing performance under pressure of a water-absorbing agent include AAP (absorbency against pressure) and FHA (fixed height absorption value at a height of 20 cm).

[0004] Furthermore, from the viewpoint of ease of handling of the water-absorbing agent in the manufacture of absorbent articles, the water-absorbing agent is also required to have high anti-caking performance. One physical property that indicates the anti-caking performance is B.R. (moisture absorption blocking ratio). As a method for lowering the B.R., i.e., improving the anti-caking performance, a technique of adding inorganic fine particles such as silicon dioxide, kaolin, alumina, etc., as an anti-caking agent to the surface of the water-absorbent resin is known (Patent Documents 1 to 7). In addition, a technique of adding polyvalent metal salts of organic acids (Patent Document 8), various surfactants, hydrophobic polymers such as polysiloxane (Patent Documents 9 to 11), etc., as anti-caking agents other than inorganic fine particles, to the surface of the water-absorbent resin is also known.

[0005] It should be noted that water-absorbent resins are generally obtained through polymerization, drying, and surface cross-linking after drying, and it is known that various surface modifiers are added during or after surface cross-linking (Non-Patent Document 1). Among these surface modifiers, the inorganic fine particles are not only used as anti-caking agents, but are also widely used for the purpose of improving the physical properties of water-absorbent resins, such as liquid permeability and gel strength (Patent Documents 12 to 17).

[0006] Japanese published patent publication "JP-T-2002-523526A" Japanese published patent publication "JP-A-2001-137704A" Japanese published patent publication "JP-A-59-080459A" Japanese published patent publication "JP-T-2009-510177A" Japanese published patent publication "JP-A-2000-093792A" Japanese published patent publication "JP-A-11-286611A" Japanese published patent publication "JP-T-2017-509757A" Japanese published patent publication "JP-A-2004-261796A" Patent Publication "JP 2004-512165 A," International Publication No. 95 / 033558 Pamphlet, Japanese Patent Publication "JP 2003-082250 A," Japanese Patent Publication "JP H06-016822 A," International Publication No. 2002 / 005949 Pamphlet, Japanese Patent Publication "JP 2003-225565 A," Japanese Patent Publication "JP 2005-095759 A," International Publication No. 2008 / 015980 Pamphlet, Japanese Patent Publication "JP 2010-521577 A"

[0007] Modern Superabsorbent Polymer Technology (1998) pp. 69-103

[0008] However, the above-mentioned conventional surface modification techniques have room for improvement in terms of providing a water-absorbing agent having high anti-caking performance without deteriorating the water-absorbing performance under pressure.

[0009] An object of one aspect of the present invention is to provide a method for producing a water-absorbing agent having high anti-caking performance without deteriorating water-absorbing performance under pressure, a water-absorbing agent, and an absorbent article.

[0010] In order to solve the above problems, one aspect of the present invention includes the following configuration.

[0011] [1] A method for producing a particulate water-absorbing agent composition containing a poly(meth)acrylic acid (salt)-based water-absorbing resin, comprising: a monomer aqueous solution preparation step of preparing a (meth)acrylic acid (salt)-based monomer aqueous solution; a polymerization step of polymerizing the (meth)acrylic acid (salt)-based monomer aqueous solution; an optional hydrogel crushing step of gel-crushing a hydrogel-like crosslinked polymer produced during or after polymerization; a drying step of drying the particulate hydrogel; an optional crushing step and optional classification step of crushing and classifying the dried polymer; and a surface crosslinking step of surface-crosslinking a water-absorbing resin before surface crosslinking, wherein the particulate hydrogel is obtained through a polymerization step or both of the polymerization step and the hydrogel crushing step, the dried polymer is obtained through a drying step, and the water-absorbing resin before surface crosslinking is the dried polymer or a water-absorbing resin obtained by crushing and / or classifying the dried polymer, a method for producing a particulate water-absorbing agent composition containing a poly(meth)acrylic acid (salt)-based water-absorbing resin, the method comprising: adding a water-soluble polyalkylene glycol having a mass-average molecular weight of 3,000 or less in an amount of 0.01 mass % to 0.25 mass % relative to the total mass of the monomers contained in the (meth)acrylic acid (salt)-based monomer aqueous solution in at least any step selected from the monomer aqueous solution preparation step, the polymerization step, and an optional hydrous gel crushing step; and adding, after the surface cross-linking step, a nonionic polymer having a polyalkylene glycol chain in its structure and having a mass-average molecular weight of 300 to 15,000 in an amount of 0.02 mass % to 0.40 mass % relative to the surface-cross-linked water-absorbing resin.

[0012] [2] The method according to [1], wherein the particulate water-absorbing agent composition has a surface tension of 45 mN / m or more.

[0013] [3] The method according to [1], wherein the particulate water-absorbing agent composition has an absorbency against pressure (AAP) of 20 g / g or more under a pressure of 0.7 psi.

[0014] [4] The method according to [1], wherein the particulate water-absorbing agent composition has a fixed height absorption (FHA) of 20 g / g or more at a height of 20 cm.

[0015] [5] A particulate water-absorbing agent composition containing a poly(meth)acrylic acid (salt)-based water-absorbing resin as a main component and a nonionic polymer having a polyalkylene glycol chain in its structure, the mass ratio of particles having a particle size of 300 μm or more and less than 850 μm being 50 mass % or more, wherein: (a) the nonionic polymer contained in the particulate water-absorbing agent composition is designated as A1 and its content is designated as C1; (b) the particulate water-absorbing agent composition is subjected to a predetermined impact test; (c) the particulate water-absorbing agent composition subjected to the impact test is sieved using a JIS standard sieve into a particle group a having a particle size of 300 μm or more and a particle group b having a particle size of less than 300 μm; and (d) the nonionic polymer present in the particle group a is designated as A2 and its content is designated as C2, the particulate water-absorbing agent composition satisfies all of the following (1) to (4): (1) A1 is a water-soluble polyalkylene glycol having a mass average molecular weight of 3,000 or less, and a nonionic polymer having a polyalkylene glycol chain in its structure and a mass average molecular weight of 300 to 15,000; (2) A2 is a water-soluble polyalkylene glycol having a mass average molecular weight of 3,000 or less; (3) C2 is 0.005% by mass or more and 0.15% by mass or less; (4) C1-C2 is 0.02% by mass or more and 0.40% by mass or less.

[0016] [6] The particulate water-absorbing agent composition according to [5], wherein the particulate water-absorbing agent composition has a surface tension of 45 mN / m or more.

[0017] [7] The particulate water-absorbing agent composition according to [5], wherein the particulate water-absorbing agent composition has an absorbency against pressure (AAP) of 20 g / g or more under a pressure of 0.7 psi.

[0018] [8] The particulate water-absorbing agent composition according to [5], wherein the particulate water-absorbing agent composition has a fixed height absorption (FHA) of 20 g / g or more at a height of 20 cm.

[0019] [9] The particulate water-absorbing agent composition according to [5], wherein the particulate water-absorbing agent composition has a CRC of 25 g / g or more.

[0020]

[10] The particulate water-absorbing agent composition according to [5], wherein the particulate water-absorbing agent composition has a moisture absorption blocking ratio <1> (B.R.<1>) of 80 mass % or less.

[0021]

[11] The particulate water-absorbing agent composition according to [5], wherein the particulate water-absorbing agent composition has a mass average particle diameter (D50) of 300 μm or more and 600 μm or less.

[0022]

[12] A particulate water-absorbing agent composition according to [5], wherein the mass ratio of particles having a particle diameter of 850 μm or more in the particulate water-absorbing agent composition is 3 mass% or less, and the mass ratio of particles having a particle diameter of less than 150 μm is 5 mass% or less.

[0023]

[13] An absorbent article containing a particulate water-absorbing agent composition, the absorbent article comprising the particulate water-absorbing agent composition according to any one of [5] to

[12] as the particulate water-absorbing agent composition.

[0024] According to one aspect of the present invention, it is possible to provide a method for producing a particulate water-absorbing agent composition having high anti-caking performance without deteriorating the water-absorbing performance under pressure, a method for producing an absorbent article, and a particulate water-absorbing agent composition.

[0025] Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to these, and various modifications are possible within the scope of the description. Embodiments and examples obtained by appropriately combining the technical means described in different embodiments and examples are also included in the technical scope of the present invention. In this specification, unless otherwise specified, "A to B" representing a numerical range means "A or more and B or less." Furthermore, "(meth)acrylic" means "acrylic and / or methacrylic."

[0026] [1] Definition of Terms (1-1) Water-Absorbent Resin In this specification, the term "water-absorbent resin" refers to a water-swellable, water-insoluble crosslinked polymer. Here, "water-swellable" means that the absorption capacity under no load (also referred to as centrifuge retention capacity (CRC)) as defined in NWSP 241.0. R2(19) is 5 g / g or more, and "water-insoluble" means that the extractable content (Ext) as defined in NWSP 270.0. R2(19) is 50% by mass or less.

[0027] The "water-absorbent resin" is preferably a hydrophilic cross-linked polymer obtained by cross-linking a monomer composition containing (meth)acrylic acid (salt) as a main component. However, the entire amount, i.e., 100% by mass, does not need to be the hydrophilic cross-linked polymer, and it may contain additives added in one or more steps prior to the surface-cross-linking step, the surface-cross-linking step, and the step after the surface-cross-linking step, within a range that satisfies the required performance such as CRC and Ext. Furthermore, in this specification, the water-absorbent resin may refer to intermediates in the production process of the water-absorbent resin (e.g., a hydrogel-like cross-linked polymer after polymerization, a dried polymer after drying, a water-absorbent resin before surface-cross-linking, a water-absorbent resin after surface-cross-linking, a water-absorbent resin after granulation, etc.), and all of these are collectively referred to as "water-absorbent resin".

[0028] In addition, in this specification, the term "poly(meth)acrylic acid (salt)-based water-absorbing resin" means a hydrophilic crosslinked polymer obtained by crosslinking a monomer composition containing (meth)acrylic acid (salt) as a main component.

[0029] In addition, in this specification, the water-absorbent resin may refer to "a polymer crosslinked only internally, i.e., a polymer in which the crosslinking density in the interior and the surface is substantially the same" or "a polymer crosslinked internally and the surface, i.e., a polymer in which the crosslinking density in the surface is relatively high compared to the crosslinking density in the interior." In this specification, the "polymer crosslinked only internally" and the "polymer crosslinked internally and the surface" are not distinguished in principle, and both are referred to as "water-absorbent resin." However, when it is necessary to clearly distinguish between the presence or absence of surface crosslinking, the "polymer crosslinked only internally" is referred to as "a water-absorbent resin before surface crosslinking" because it is before surface crosslinking is performed, and the "polymer crosslinked internally and the surface" is referred to as "a water-absorbent resin after surface crosslinking" or "a surface-crosslinked water-absorbent resin" because it is after surface crosslinking is performed. Note that "before surface crosslinking" means "before adding a surface crosslinking agent" or "before starting the surface crosslinking reaction by heat treatment even after adding a surface crosslinking agent."

[0030] (1-2) Particulate Water-Absorbent Agent Composition In this specification, the term "particulate water-absorbent agent composition" refers to a composition containing the water-absorbent resin as a main component and various additives that are added after surface cross-linking as other components. Note that the term "containing a water-absorbent resin as a main component" means that the water-absorbent resin is contained in an amount of preferably 60% by mass or more and less than 100% by mass, more preferably 70% by mass or more and less than 100% by mass, even more preferably 80% by mass or more and less than 100% by mass, and particularly preferably 90% by mass or more and less than 100% by mass.

[0031] The "particulate water-absorbing agent composition" has a particulate shape (also known as a powder). The term "particulate" means having a particle form, and the term "particle" means a small solid or liquid granular body having a measurable size (JIS Industrial Terminology Dictionary, 4th edition, p. 2002).

[0032] In this specification, the "particulate water-absorbing agent composition" may be a single particle of the particulate water-absorbing agent composition or an aggregate of a plurality of particles of the particulate water-absorbing agent composition. In addition, in this specification, the "particulate water-absorbing agent", "water-absorbing agent composition" or "water-absorbing agent" may be referred to, but all of these are synonyms and mean the "particulate water-absorbing agent composition".

[0033] The particulate water-absorbing agent composition is an absorbent gelling agent for aqueous liquids, and is preferably used as a material for absorbing aqueous liquids in absorbent articles.

[0034] (1-3) "NWSP" "NWSP" is an abbreviation for Non-Woven Standard Procedures-Edition 2019, which is a standardized evaluation method for nonwoven fabrics and their products jointly published by EDANA (European Disposables and Nonwovens Associations) and INDA (Association of the Nonwoven Fabrics Industry) in Europe and the United States. The NWSP also specifies a standard measurement method for water-absorbent resins. In this specification, the physical properties of the water-absorbent resin and the particulate water-absorbing agent composition are measured in accordance with the original NWSP (2019). Unless otherwise specified in this specification, the measurement methods for various physical properties of the water-absorbent resin and the particulate water-absorbing agent composition follow the measurement methods in the following examples.

[0035] [2] Method for Producing Particulate Water-Absorbing Agent Compositions In conventional methods (Patent Documents 1 to 7) for adding inorganic fine particles to improve anti-caking performance during moisture absorption, adding inorganic fine particles such as silicon dioxide, kaolin, or alumina to the particle surfaces of water-absorbent resins improves the fluidity of the moisture-absorbed particles and reduces inter-particle adhesion, thereby improving anti-caking performance. However, this method has the problem of deteriorating the water-absorbent performance under pressure. In contrast, adding a surfactant or a nonionic polymer containing a polyalkylene glycol chain in its structure as an anti-caking agent to a surface-crosslinked water-absorbent resin to coat the particle surfaces improves the anti-caking performance of the resulting water-absorbent agent without substantially deteriorating the water-absorbent performance under pressure. However, this method has the problem of providing a smaller improvement in anti-caking performance than the inorganic fine particles.

[0036]

[0009] Furthermore, in the above-mentioned conventional methods, the addition of an anti-caking agent has been investigated by focusing solely on coating the particle surface of a water absorbent resin from the viewpoint of surface modification. That is, if the anti-caking agent is added in a step (e.g., polymerization step) that can uniformly distribute the anti-caking agent inside the water absorbent resin, the anti-caking agent will hardly be present on the particle surface of the water absorbent resin, and it was thought that the desired effect of improving the anti-caking performance would not be obtained, and therefore addition in the polymerization step or the like has not been investigated.

[0037] As described above, conventional techniques for improving anti-caking performance have been studied with a focus on coating on the particle surfaces of water absorbent resins, and various anti-caking agents have been proposed, but none of the obtained water absorbents have been able to achieve both high anti-caking performance and maintenance of water absorption performance under pressure.

[0038] In the course of investigations to solve such problems, the present inventors have focused for the first time on not only surface modification of a water-absorbent resin with an anti-caking agent, but also on additives added to the interior of a water-absorbent resin, which had previously been thought to be unrelated to anti-caking performance. Then, by adding a specific additive to the particle surfaces of the water-absorbent resin and also to the interior of the water-absorbent resin, they have succeeded in obtaining a water-absorbent agent composition that achieves both high anti-caking performance and maintenance of water-absorbency performance under pressure.

[0039] That is, the present invention has discovered that when a surface-crosslinked water-absorbent resin (i.e., a water-absorbent resin in which a specific additive exists inside the particles) obtained by polymerizing an ethylenically unsaturated monomer in the presence of a water-soluble polyalkylene glycol of a specific molecular weight and a specific amount is added to the nonionic polymer containing a polyalkylene glycol chain in its structure (i.e., a specific additive is added to the particle surface), the nonionic polymer surprisingly showed a significant improvement in the anti-caking performance compared to when the water-soluble polyalkylene glycol was not added.Furthermore, it was discovered that the water-absorbent agent obtained showed almost no deterioration in water-absorbency under pressure.

[0040] That is, a method for producing a particulate water-absorbing agent composition according to one embodiment of the present invention is a method for producing a particulate water-absorbing agent composition containing a poly(meth)acrylic acid (salt)-based water-absorbing resin, and includes a monomer aqueous solution preparation step of preparing a (meth)acrylic acid (salt)-based monomer aqueous solution, a polymerization step of polymerizing the (meth)acrylic acid (salt)-based monomer aqueous solution, a hydrogel crushing step which is an optional step of gel-crushing a hydrogel-like crosslinked polymer produced during or after the polymerization, a drying step of drying the particulate hydrogel, a crushing step which is an optional step of crushing and classifying the dried polymer, and an optional classification step, and a surface crosslinking step of surface-crosslinking a water-absorbing resin before surface crosslinking, a polymerization step, and an optional hydrogel crushing step, in which a water-soluble polyalkylene glycol having a mass average molecular weight of 3,000 or less is added in an amount of 0.01 mass % to 0.25 mass % relative to the total mass of monomers contained in the (meth)acrylic acid (salt)-based monomer aqueous solution (hereinafter, the "(meth)acrylic acid (salt)-based monomer aqueous solution" may be simply referred to as the "monomer aqueous solution"); and after the surface cross-linking step, a nonionic polymer having a polyalkylene glycol chain in its structure and a mass average molecular weight of 300 to 15,000 is added in an amount of 0.02 mass % to 0.40 mass % relative to the surface-cross-linked water-absorbent resin.

[0041] According to the above-mentioned production method, it is possible to obtain a water-absorbing agent having high anti-caking performance without deteriorating the water-absorbing performance under pressure.

[0042] That is, by using a surface-crosslinked water-absorbent resin produced by adding a water-soluble polyalkylene glycol having the mass-average molecular weight and in the amount described above in at least any one of the steps selected from the monomer aqueous solution preparation step, the polymerization step, and the hydrous gel crushing step, when a nonionic polymer containing a polyalkylene glycol chain having the mass-average molecular weight and in the structure thereof is added to the surface-crosslinked water-absorbent resin, the effect of improving the anti-caking performance by adding the nonionic polymer can be greatly improved compared to the case where the water-soluble polyalkylene glycol is not added.

[0043] Here, an example of a physical property value representing the anti-caking performance of a water-absorbing agent is the moisture-absorption blocking ratio (B.R.). In the present disclosure, the moisture-absorption blocking ratio is a value calculated by the method described in the Examples. The lower the moisture-absorption blocking ratio of the water-absorbing resin and the water-absorbing agent, the better the anti-caking performance of the water-absorbing resin and the water-absorbing agent. Furthermore, the greater the B.R. of the water-absorbing agent obtained by adding the nonionic polymer is reduced from the B.R. of the water-absorbing resin after surface cross-linking before the addition of the nonionic polymer, the greater the improvement in anti-caking performance. More specifically, the greater the value (ΔB.R. described below) obtained by subtracting the B.R. of the water-absorbing agent obtained by adding the nonionic polymer from the B.R. of the water-absorbing resin after surface cross-linking before the addition of the nonionic polymer, the greater the improvement in anti-caking performance.

[0044] Furthermore, examples of physical property values ​​that represent the water absorption performance under pressure of a water-absorbing agent and a water-absorbent resin include absorbency under pressure (AAP) and fixed height absorption at a height of 20 cm (FHA). In the present disclosure, AAP and FHA are values ​​calculated by the method described in the Examples.

[0045] [2-1] Monomer aqueous solution preparation step This step is a step of preparing an aqueous solution of a raw material (monomer composition; preferably containing (meth)acrylic acid (salt) as a main component and containing at least one type of internal crosslinking agent) that forms a water-absorbent resin (polymer). Although a slurry liquid of the monomer composition can also be used, for convenience, the present specification will explain about an aqueous solution of the monomer composition.

[0046] (Monomer) The monomer used in this step is a raw material component (monomer) forming a water-absorbent resin (polymer), and preferably includes (meth)acrylic acid (salt), a monomer other than (meth)acrylic acid (salt), and an internal crosslinking agent. In other words, the entire monomers forming the water-absorbent resin are a monomer composition.

[0047] In this specification, "(meth)acrylic acid (salt)" means (meth)acrylic acid and / or a salt thereof, and "a monomer composition containing (meth)acrylic acid (salt) as a main component" means a monomer composition containing (meth)acrylic acid (salt) in an amount of 50 mol % or more, more preferably 70 mol % or more, more preferably 90 mol % or more, and preferably 100 mol % or less, more preferably substantially 100 mol %, based on all monomers excluding the crosslinking agent.

[0048] In this specification, the term "aqueous (meth)acrylic acid (salt)-based monomer solution" refers to an aqueous solution of a monomer composition containing (meth)acrylic acid (salt) as a main component and at least one type of internal crosslinking agent.

[0049] As the monomer other than (meth)acrylic acid (salt), a monomer containing an acid group is preferred among monomers having an unsaturated double bond (ethylenically unsaturated monomers). Specific examples of such monomers include anionic unsaturated monomers and / or salts thereof, such as maleic acid (anhydride), fumaric acid, crotonic acid, itaconic acid, cinnamic acid, vinyl sulfonic acid, allyl toluene sulfonic acid, vinyl toluene sulfonic acid, styrene sulfonic acid, 2-(meth)acrylamido-2-methylpropanesulfonic acid, 2-(meth)acryloylethanesulfonic acid, 2-(meth)acryloylpropanesulfonic acid, and 2-hydroxyethyl (meth)acryloyl phosphate. One or more of these monomers may be used as needed.

[0050] Examples of the salt include alkali metal salts, ammonium salts, and amine salts, with sodium salts, potassium salts, lithium salts, and ammonium salts being more preferred, and sodium salts being particularly preferred.

[0051] Furthermore, the monomer composition containing (meth)acrylic acid (salt) as a main component is preferably neutralized in the range of 10 to 90 mol %, more preferably neutralized in the range of 40 to 80 mol %, and particularly preferably neutralized in the range of 60 to 75 mol %.

[0052] Therefore, the monomer composition containing (meth)acrylic acid (salt) as a main component is preferably neutralized with a neutralizing solution containing a basic compound such as an alkali metal hydroxide, such as sodium hydroxide, potassium hydroxide, or lithium hydroxide, a (hydrogen)carbonate, such as sodium (hydrogen)carbonate or potassium (hydrogen)carbonate, or ammonia, and is particularly preferably neutralized with a neutralizing solution containing sodium hydroxide.

[0053] Furthermore, the monomer composition may contain, as necessary, a "hydrophilic or hydrophobic unsaturated monomer (hereinafter referred to as "other monomer")" in addition to the above-mentioned "(meth)acrylic acid (salt)" and "monomer other than (meth)acrylic acid (salt)." Examples of the other monomer include mercaptan group-containing unsaturated monomers; phenolic hydroxyl group-containing unsaturated monomers; amide group-containing unsaturated monomers such as N-vinyl-2-pyrrolidone, N-vinylacetamide, (meth)acrylamide, N-isopropyl(meth)acrylamide, N-ethyl(meth)acrylamide, and N,N-dimethyl(meth)acrylamide; and amino group-containing unsaturated monomers such as N,N-dimethylaminoethyl(meth)acrylate, N,N-dimethylaminopropyl(meth)acrylate, and N,N-dimethylaminopropyl(meth)acrylamide.

[0123] The amount of other monomers used may be such that the physical properties of the obtained water absorbent resin are not impaired, and specifically, the amount is 50 mol% or less, more preferably 20 mol% or less, based on the part of the monomer composition excluding the internal crosslinking agent.

[0054] (Neutralization with Basic Compound) In one embodiment of the present invention, it is preferable that the (meth)acrylic acid (salt) is partially neutralized with the above-mentioned basic compound. That is, in one embodiment of the present invention, it is preferable to obtain a water-absorbent resin in which the acid groups of the poly(meth)acrylic acid are partially neutralized.

[0055] The basic compound is preferably in the form of an aqueous solution from the viewpoint of ease of handling.

[0056] The timing of neutralization may be any of before, during, or after polymerization, and neutralization may be performed at multiple times or multiple times. From the viewpoint of production efficiency of the water absorbent resin, it is preferable to neutralize in a continuous manner.

[0057] In one embodiment of the present invention, the neutralization rate of (meth)acrylic acid (salt) is, as described above, preferably 10 mol% or more, more preferably 40 mol% or more, even more preferably 50 mol% or more, and particularly preferably 60 mol% or more, relative to the acid groups of the monomer composition, and is preferably 90 mol% or less, more preferably 85 mol% or less, even more preferably 80 mol% or less, and particularly preferably 75 mol% or less. By setting the neutralization rate within this range, it is possible to suppress a decrease in the water absorption performance of the water-absorbing resin and the water-absorbing agent. The neutralization rate is applicable to any of the neutralization before, during, and after the polymerization described above. The same is also applied to the water-absorbing resin and the water-absorbing agent.

[0058] (Internal crosslinking agent) Examples of the internal crosslinking agent used in this step include N,N'-methylenebis(meth)acrylamide, (poly)ethylene glycol di(meth)acrylate, (poly)propylene glycol di(meth)acrylate, trimethylolpropane di(meth)acrylate, trimethylolpropane tri(meth)acrylate, glycerin tri(meth)acrylate, glycerin acrylate methacrylate, ethylene oxide-modified trimethylolpropane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, triallyl cyanurate, triallyl isocyanurate, triallyl phosphate, triallylamine, poly(meth)allyloxyalkane, (poly)ethylene glycol diglycidyl ether, glycerol diglycidyl ether, ethylene glycol, polyethylene glycol, propylene glycol, glycerin, pentaerythritol, ethylenediamine, polyethyleneimine, and glycidyl (meth)acrylate. At least one type of internal crosslinking agent is selected from these internal crosslinking agents in consideration of reactivity and the like.

[0059] In one embodiment of the present invention, from the viewpoint of the water absorption performance of the water-absorbent resin and the water-absorbing agent, preferably an internal crosslinking agent having two or more polymerizable unsaturated groups is selected, and more preferably an internal crosslinking agent having two or more polymerizable unsaturated groups having a (poly)alkylene glycol structure. Specific examples of the polymerizable unsaturated group include an allyl group and a (meth)acrylate group. Of these, a (meth)acrylate group is preferred. Furthermore, an example of an internal crosslinking agent having two or more polymerizable unsaturated groups having a (poly)alkylene glycol structure is polyethylene glycol di(meth)acrylate. The number of alkylene glycol units (hereinafter referred to as "n") is preferably 1 or more, more preferably 2 or more, even more preferably 4 or more, and particularly preferably 6 or more, and is preferably 100 or less, more preferably 50 or less, even more preferably 20 or less, and particularly preferably 10 or less.

[0060] The amount of the internal crosslinking agent used is preferably 0.0001 mol% or more, more preferably 0.001 mol% or more, and even more preferably 0.01 mol% or more, relative to the monomer composition excluding the internal crosslinking agent, and is preferably 10 mol% or less, more preferably 5 mol% or less, and even more preferably 1 mol% or less. By using an amount within this range, a water-absorbent resin and a water-absorbing agent having desired water absorption performance can be obtained. On the other hand, if the amount used is outside this range, the gel strength may decrease, and the water-soluble content may increase, and / or the absorption capacity may decrease.

[0061] In one embodiment of the present invention, the timing of adding the internal crosslinking agent may be any timing as long as the polymer can be uniformly crosslinked, and examples thereof include a method of adding the internal crosslinking agent to an aqueous solution of the monomer composition before polymerization or to a hydrogel during or after polymerization. Among these, a method of adding a predetermined amount of the internal crosslinking agent in advance to an aqueous solution of the monomer composition is preferred.

[0062] (Other substances added to aqueous solution of monomer composition) In one embodiment of the present invention, from the viewpoint of improving physical properties of a water-absorbing resin and a water-absorbing agent, the following other substances can be added to the aqueous solution of the monomer composition, the solution during the reaction, or the solution after the reaction at one or more points selected from the preparation of the aqueous solution of the monomer composition, the period of the polymerization reaction and the crosslinking reaction, and the period after the polymerization reaction and the crosslinking reaction.

[0063] Examples of the other substances include hydrophilic polymers such as starch, starch derivatives, cellulose, cellulose derivatives, polyvinyl alcohol (PVA), polyacrylic acid (salts), and existing crosslinked products of polyacrylic acid (salts); carbonates, azo compounds, various foam-generating blowing agents, surfactants, chelating agents, and chain transfer agents.

[0064] By using the hydrophilic polymer, a water-absorbing resin to which the hydrophilic polymer is grafted can be obtained, for example, a polyacrylic acid (salt)-based water-absorbing resin to which starch is grafted, or a water-absorbing resin to which PVA is grafted can be obtained.

[0065] The amount of the other substances added is adjusted so as not to impair the effects of the present invention. For example, the total amount of the other substances added is preferably 50% by mass or less, more preferably 20% by mass or less, even more preferably 10% by mass or less, particularly preferably 5% by mass or less, and is preferably 0% by mass or more, more preferably more than 0% by mass, based on the aqueous solution of the monomer composition (aqueous monomer solution).

[0066] (Concentration of Monomer Component) The monomer composition, the polyalkylene glycol described below in "(2-4) Addition of Water-Soluble Polyalkylene Glycol," and the aforementioned substances and components (referred to as "monomer components" in this section) are selected in various amounts depending on the purpose, and the amounts are specified so as to satisfy the aforementioned ranges, and then mixed together to prepare an aqueous solution of the total monomer components (i.e., a mixture of the monomer composition, the substances and components described below in "(2-4) Addition of Water-Soluble Polyalkylene Glycol"). In one embodiment of the present invention, in addition to preparing an aqueous solution of the total monomer components, it is also possible to prepare a mixed solution of the aqueous solution of the total monomer components and a hydrophilic solvent.

[0067] From the viewpoint of the physical properties of the water-absorbing resin and the water-absorbing agent, the total concentration of the monomer components is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more, and is preferably 80% by mass or less, more preferably 75% by mass or less, and even more preferably 70% by mass or less. The total concentration of the monomer components can be determined by adding up the concentrations of each monomer component. The concentration of each monomer component is calculated using the following formula (A): Monomer component concentration (mass%) = [(mass of monomer component) / (mass of aqueous solution containing the total of the monomer components)] × 100 Formula (A) In the formula (A), the "mass of aqueous solution containing the total of the monomer components" does not include the mass of the hydrophobic organic solvent used in the reversed-phase suspension polymerization.

[0068] [2-2] Polymerization Step This step is a step of polymerizing the (meth)acrylic acid (salt)-based monomer aqueous solution to obtain a hydrogel-like crosslinked polymer (hereinafter simply referred to as "hydrogel"). That is, this step is a step of polymerizing the monomer aqueous solution obtained in the monomer aqueous solution preparation step, which contains a monomer containing (meth)acrylic acid (salt) as a main component and at least one internal crosslinking agent, to obtain a hydrogel.

[0069] (Polymerization initiator) As the polymerization initiator used in one embodiment of the present invention, one or more types can be selected and used from polymerization initiators used in the production of ordinary water-absorbent resins, depending on the type of monomer to be polymerized, polymerization conditions, etc. Examples of the polymerization initiator include a thermal decomposition type initiator and a photodecomposition type initiator.

[0070] Examples of the thermally decomposable initiator include persulfates such as sodium persulfate, potassium persulfate, and ammonium persulfate; peroxides such as hydrogen peroxide, t-butyl peroxide, and methyl ethyl ketone peroxide; and azo compounds such as azonitrile compounds, azoamidine compounds, cyclic azoamidine compounds, azoamide compounds, alkylazo compounds, 2,2'-azobis(2-amidinopropane)dihydrochloride, and 2,2'-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride.

[0071] Examples of the photodecomposition initiator include benzoin derivatives, benzil derivatives, acetophenone derivatives, benzophenone derivatives, and azo compounds.

[0072] Among these, persulfates are preferred in consideration of cost and the ability to reduce residual monomers. Furthermore, a reducing agent that promotes decomposition of the oxidative polymerization initiator, such as the persulfate or peroxide, can also be used in combination to form a redox initiator. Examples of the reducing agent include (bis)sulfite (salts) such as sodium sulfite and sodium hydrogensulfite, reducing metals (salts) such as L-ascorbic acid (salts) and ferrous salts, and amines.

[0073] The amount of the polymerization initiator used is preferably 0.001 mol% or more, more preferably 0.010 mol% or more, and preferably 1.000 mol% or less, more preferably 0.500 mol% or less, and even more preferably 0.100 mol% or less, based on the monomers excluding the internal crosslinking agent. The amount of the reducing agent used is preferably 0.0001 mol% or more, more preferably 0.0005 mol% or more, and preferably 0.0200 mol% or less, and more preferably 0.0150 mol% or less, based on the monomers excluding the internal crosslinking agent. By using an amount within this range, a water-absorbent resin and a water-absorbing agent having desired water absorption performance can be obtained.

[0074] In one embodiment of the present invention, the polymerization reaction may be initiated by irradiation with active energy rays such as radiation, electron beams, ultraviolet rays, etc. Alternatively, irradiation with active energy rays and the polymerization initiator may be used in combination.

[0075] (Polymerization form) Examples of polymerization forms applicable to one embodiment of the present invention include aqueous solution polymerization, reversed-phase suspension polymerization, spray polymerization, droplet polymerization, bulk polymerization, and precipitation polymerization. Among these, from the viewpoint of ease of polymerization control and the water absorption performance of the water-absorbing resin and water-absorbing agent, aqueous solution polymerization or reversed-phase suspension polymerization is preferably selected, and aqueous solution polymerization is more preferably selected. Aqueous solution polymerization is described in JP-A-4-255701, etc. Reverse-phase suspension polymerization is described in WO 2007 / 004529, WO 2012 / 023433, etc.

[0076] Preferred forms of the continuous aqueous solution polymerization include high-temperature initiation polymerization, high-concentration polymerization, and foam polymerization. "High-temperature initiation polymerization" refers to a polymerization form in which the temperature of the aqueous monomer solution at the start of polymerization is preferably 35°C or higher, more preferably 40°C or higher, even more preferably 45°C or higher, and particularly preferably 50°C or higher, and is preferably below the boiling point of the aqueous monomer solution. "High-concentration polymerization" refers to a polymerization form in which the monomer concentration at the start of polymerization is preferably 30% by mass or higher, more preferably 35% by mass or higher, even more preferably 40% by mass or higher, and particularly preferably 45% by mass or higher, and is preferably below the saturated concentration of the aqueous monomer solution. "Foam polymerization" refers to a polymerization form in which the aqueous monomer solution containing a foaming agent or bubbles is polymerized. These polymerization forms may be carried out alone or in combination of two or more. The aqueous solution polymerization may be either a batch system or a continuous system, with continuous being preferred from the viewpoint of production efficiency. A polymerization form applicable to one embodiment of the present invention is one in which the polymerization reaction is initiated quickly after the addition of a polymerization initiator. As the polymerization form, for example, a polymerization form in which the polymerization reaction starts within 1 minute after adding the polymerization initiator is preferred. Furthermore, as the polymerization form, a polymerization form in which the polymerization reaction is quickly completed is also preferred. As the polymerization form, for example, a polymerization form in which the polymerization reaction is completed within 1 minute after starting the polymerization reaction is preferred.

[0077] Further, examples of the continuous aqueous solution polymerization include continuous belt polymerization described in U.S. Pat. Nos. 4,893,999, 6,906,159, 7,091,253, 7,741,400, 8,519,212, and JP-A-2005-36100, and continuous kneader polymerization described in U.S. Pat. No. 6,987,151.

[0078] Examples of a method for dispersing bubbles in the foaming polymerization include a method for dispersing a gas dissolved in a monomer aqueous solution as bubbles by reducing the solubility, a method for introducing a gas from the outside and dispersing it as bubbles, a method for adding a foaming agent to a monomer aqueous solution to foam it, etc. Furthermore, the above-mentioned dispersion methods may be used in combination as appropriate depending on the physical properties of the target water-absorbent resin and water-absorbing agent.

[0079] When a gas is introduced from the outside, examples of the gas include oxygen, air, nitrogen, carbon dioxide, ozone, and a mixture of these gases. From the viewpoints of polymerizability and cost, an inert gas such as nitrogen or carbon dioxide is preferably used, and more preferably nitrogen is used.

[0080] Examples of usable foaming agents include azo compounds, organic or inorganic carbonate solutions, dispersions, and powders with particle sizes of 0.1 μm or more and 1000.0 μm or less. Among these, inorganic carbonates are preferred, and specifically, carbonates and hydrogencarbonates such as sodium carbonate, ammonium carbonate, and magnesium carbonate can be used.

[0081] Drying of the foamed hydrogel obtained by foaming polymerization is facilitated by gel pulverization. Furthermore, by forming a foamed water-absorbent resin, the water absorption rate of the water-absorbent resin and the water-absorbing agent can be improved, and furthermore, immobilization to an absorbent article becomes easier. The foamed shape can be determined by observing pores on the surface of the water-absorbent resin using an electron microscope, for example, pores with a diameter of 1 μm or more and 100 μm or less. The number of pores per water-absorbent resin particle is preferably 1 or more, more preferably 10 or more, and preferably 10,000 or less, more preferably 1,000 or less, and can be controlled by adjusting the conditions for the foaming polymerization.

[0082] [2-3] Hydrogel Crushing Step This step is an optional step performed during and / or after the polymerization step, in which the hydrogel is crushed to obtain a particulate hydrogel. Specifically, the hydrogel may be crushed during the polymerization step, or the hydrogel may be crushed after the polymerization step. That is, this step is a step in which the hydrogel is crushed to obtain a particulate hydrogel (hereinafter referred to as "particulate hydrogel"). Note that this step is referred to as "gel crushing" to distinguish it from the "crushing" in the crushing step described below. Furthermore, unless otherwise specified, the target of gel crushing is not only the hydrogel obtained in the polymerization step, but may also include a granulated gel obtained by mixing the fine powder recovered in the classification step described below with an aqueous liquid. Unless otherwise specified, other steps have the same purpose.

[0083] The gel crushing refers to adjusting the hydrogel to a predetermined size using a screw extruder such as a kneader or a meat chopper, or a gel crusher such as a cutter mill.

[0084] When pulverizing a hydrogel, it is preferable to add hot water and / or steam to the gel pulverizer. By adding hot water and / or steam, a particulate hydrogel with low viscosity and good breathability can be obtained, which is preferable because it is easy to dry. The temperature of the hot water is preferably 40°C or higher, more preferably 50°C or higher, and even more preferably 60°C or higher, and preferably 100°C or lower.

[0085] Regarding the embodiment and operating conditions of gel crushing, the aqueous solution polymerization employs a method described in a document describing continuous aqueous solution polymerization. The contents described in International Publication No. 2011 / 126079 are also preferably applied to one embodiment of the present invention. When the polymerization mode is kneader polymerization, the polymerization step and the gel crushing step are carried out simultaneously. Furthermore, by passing through the gel crushing step in one embodiment of the present invention, an amorphous crushed water-absorbent resin can be obtained.

[0086] Furthermore, a method for producing a particulate water-absorbing agent composition according to one embodiment of the present invention may include a granulation step in which a fine powder recovered in a classification step described below is mixed with an aqueous liquid to obtain a granulated gel, and at least one step from the end of the gel-crushing step to the completion of drying in a drying step, and / or a granulated gel adding step in which the granulated gel is added to a hydrogel between these steps. Additionally, in the gel-crushing step of the present invention, it is preferable to appropriately control the gel-crushing energy. The particulate hydrogel obtained by gel-crushing at the following predetermined gel-crushing energy improves the physical properties of the water-absorbent resin and water-absorbing agent obtained thereafter, such as the water absorption rate, as evaluated by the FSR method described in International Publication No. 2009 / 016055 and the Vortex method described in JIS K7224 (1996), "Testing Method for Water Absorption Rate of Super Absorbent Resins."

[0087] Here, "gel grinding energy" refers to the unit energy required by the gel grinding device when grinding the hydrogel, i.e., the mechanical energy per unit mass of the hydrogel, and does not include the energy required to heat and cool the jacket or the energy required for adding water and steam. Note that "gel grinding energy" is abbreviated as "GGE" from the English term "Gel Grinding Energy."

[0088] When the gel grinder is driven by three-phase AC power, GGE is calculated by the following formula (I): GGE [J / g] = {√3 × voltage × current × power factor × motor efficiency} / {mass of hydrogel fed into the gel grinder per second} ... formula (I). The "power factor" and "motor efficiency" are values ​​specific to the gel grinder that vary depending on the operating conditions, etc., and take values ​​of 0 or more and 1 or less. These values ​​can be obtained by contacting the device manufacturer, etc. In addition, when the gel grinder is driven by single-phase AC power, GGE can be calculated by changing "√3" in formula (I) to "1". The unit of voltage is [V], the unit of current is [A], and the unit of hydrogel mass is [g / s].

[0089] The "power factor" and "motor efficiency" in the GGE are values ​​used during gel crushing. The values ​​of the power factor and motor efficiency during idle operation are approximately defined as in the above formula (I), since the current value during idle operation is small. In the above formula (I), the "mass of hydrogel fed into the gel crusher per second" [g / s] refers to a value converted to [g / s], for example, when the hydrogel is continuously supplied by a metering feeder. However, as will be described later, the hydrogel may contain recycled granulated gel.

[0090] In one embodiment of the present invention, the gel-crushing energy (GGE) for crushing the gel is preferably 100 J / g or less, more preferably 80 J / g or less, and even more preferably 60 J / g or less, and is preferably 20 J / g or more, more preferably 25 J / g or more, and even more preferably 30 J / g or more. By controlling the gel-crushing energy within the above range, the gel can be crushed while applying appropriate shear and compression forces to the hydrogel.

[0091] In addition, when gel crushing is performed using multiple devices, such as using a screw extruder after kneader polymerization or using multiple screw extruders, the total energy consumed in each device is defined as the gel crushing energy (GGE).

[0092] Furthermore, when controlling the gel-crushing energy as described above, a more excellent effect can be obtained by combining this with the addition of hot water at the above temperature. Furthermore, gel crushing based on the above gel-crushing energy may be performed after normal gel crushing.

[0093] The particle diameter of the particulate hydrogel pulverized by the gel crushing step is preferably in the range of 0.100 mm or more and 10,000 mm or less from the viewpoint of ease of drying and the physical properties of the resulting water-absorbent resin and water-absorbing agent. The mass average particle diameter (D50) of the particulate hydrogel is preferably 0.100 mm to 5,000 mm, more preferably 0.100 mm to 2,000 mm. When the mass average particle diameter (D50) of the particulate hydrogel is within the above range, drying is performed sufficiently. In one embodiment of the present invention, the mass average particle diameter of the hydrogel subjected to the drying step is preferably within the above range, and more preferably satisfies both the above particle diameter and the above mass average particle diameter.

[0094] The particle size of the particulate hydrogel has a logarithmic standard deviation (σζ) indicating the narrowness of its particle size distribution, preferably 0.20 to 1.50, more preferably 0.20 to 1.30, and even more preferably 0.20 to 1.20. The logarithmic standard deviation (σζ) of the particle size distribution indicates the narrowness of the particle size distribution, and the smaller its value, the more uniform the particle size becomes, which has the advantage of allowing for uniform drying. However, in order to make the logarithmic standard deviation (σζ) of the particle size distribution less than 0.20, special operations such as classification of the particulate hydrogel after gel pulverization are required, which is practically difficult to implement from the standpoint of productivity and cost. The mass average particle diameter (D50) and logarithmic standard deviation (σζ) of the particulate hydrogel are measured, for example, by the method described in WO2021 / 140905.

[0095] For uniform and efficient drying, the water content of the particulate hydrogel is preferably 30% by mass or more, more preferably 45% by mass or more, and is preferably 70% by mass or less, more preferably 55% by mass or less.

[0096] [2-4] Addition of Water-Soluble Polyalkylene Glycol In the method for producing a particulate water-absorbing agent composition according to one embodiment of the present invention, in at least any step selected from the above-mentioned aqueous monomer solution preparation step, polymerization step, and optional hydrogel crushing step, a water-soluble polyalkylene glycol having a mass average molecular weight of 3000 or less is added in an amount of 0.01 mass % to 0.25 mass % relative to the total mass of the monomers contained in the aqueous monomer solution.

[0097] The polyalkylene glycol may be a polyalkylene glycol having a structure represented by the following general formula (1):

[0098] H-(OR) ｎ In general formula (1), R is an alkylene group having 2 to 4 carbon atoms, which may be linear or branched. The average value of n is 4 to 70, more preferably 4 to 50, and even more preferably 6 to 15.

[0099] In general formula (1), the oxyalkylene groups (-OR-) in one molecule may be the same, or two or more types of oxyalkylene groups may be contained. More specifically, examples of the polyalkylene glycol include polyethylene glycol, polypropylene glycol, polyethylene glycol-polypropylene glycol copolymer, polyethylene glycol-polypropylene glycol-polybutylene glycol copolymer, etc. These polyalkylene glycols may be used alone or in combination of two or more types.

[0100] The polyalkylene glycol is water-soluble. In the present invention, "water-soluble" means that the polyalkylene glycol dissolves in 100 g of water at 25°C at a concentration of 5 g or more, more preferably 10 g or more. The water-soluble polyalkylene glycol can be added more uniformly in at least one step selected from the monomer aqueous solution preparation step, the polymerization step, and the hydrogel crushing step. As a result, a water-absorbent resin and a water-absorbing agent containing the polyalkylene glycol uniformly present therein can be obtained. Furthermore, as a result, when a nonionic polymer containing a polyalkylene glycol chain in its structure having the above-mentioned mass-average molecular weight and the above-mentioned amount is added to the surface-crosslinked water-absorbent resin, the effect of improving the anti-caking performance due to the addition of the nonionic polymer can be suitably improved.

[0101] Furthermore, the mass average molecular weight of the polyalkylene glycol is 3000 or less. By having the mass average molecular weight of the polyalkylene glycol be 3000 or less, when a nonionic polymer containing a polyalkylene glycol chain in its structure with the mass average molecular weight and the amount added is added to a surface-crosslinked water-absorbent resin, the effect of improving the anti-caking performance due to the addition of the nonionic polymer can be suitably improved. The mass average molecular weight of the polyalkylene glycol is preferably 200 or more, more preferably 300 or more, and even more preferably 400 or more. The mass average molecular weight is more preferably 2500 or less, even more preferably 2400 or less, and may be 2300 or less. Here, the mass average molecular weight of the polyalkylene glycol is a value measured by gel permeation chromatography.

[0102] The amount of the polyalkylene glycol added is 0.01% by mass to 0.25% by mass relative to the total mass of the monomers contained in the aqueous monomer solution. Here, the total mass of the monomers contained in the aqueous monomer solution refers to the total mass of the monomers excluding the internal crosslinking agent. When the amount of the polyalkylene glycol added is 0.01% by mass or more, the effect of improving the anti-caking performance of the nonionic polymer containing a polyalkylene glycol chain in its structure, with the weight average molecular weight and amount, can be improved when the nonionic polymer is added to a surface-crosslinked water-absorbent resin obtained by polymerization. On the other hand, when the amount of the polyalkylene glycol added exceeds 0.25% by mass, the anti-caking performance of the surface-crosslinked water-absorbent resin deteriorates compared to when the polyalkylene glycol is not added, i.e., the moisture absorption blocking ratio (B.R.) increases, which is undesirable. The amount of the polyalkylene glycol added is more preferably 0.02% by mass or more, even more preferably 0.03% by mass or more, and more preferably 0.23% by mass or less, even more preferably 0.20% by mass or less, and even more preferably 0.18% by mass or less.

[0103] The polyalkylene glycol may be a water-soluble polyalkylene glycol having the above-mentioned mass average molecular weight and amount, and multiple types of polyalkylene glycols may be used within these ranges. When one or multiple types of polyalkylene glycols are used, polyalkylene glycols having multiple mass average molecular weights may be used in combination.

[0104] In the method for producing a water-absorbing agent according to the present invention, the water-soluble polyalkylene glycol having the mass average molecular weight and the amount is added in at least any one of the steps selected from the above-mentioned aqueous monomer solution preparation step, polymerization step, and hydrous gel crushing step.

[0105] Therefore, the polyalkylene glycol may be added in any one of the above-mentioned aqueous monomer solution preparation step, polymerization step, and hydrogel crushing step, or in any two or all of the steps. When the polyalkylene glycol is added in a plurality of steps, the polyalkylene glycol added in each step may be the same or different.

[0106] When the polyalkylene glycol is added in a plurality of steps, the amount of the polyalkylene glycol added is such that the total amount of the polyalkylene glycol added in the plurality of steps falls within the above-mentioned range.

[0107] [2-5] Drying Step This step involves drying the particulate hydrogel obtained through the polymerization step or both the polymerization step and the hydrogel crushing step to obtain a dried polymer. Specifically, this step involves drying the particulate hydrogel, or, when a granulated gel is added, both the granulated gel and the particulate hydrogel, to the desired solid content to obtain a dried polymer. The solid content, i.e., the value obtained by subtracting the water content from 100% by mass of the gel, is preferably 80% by mass or more, more preferably 85% by mass or more, even more preferably 90% by mass or more, particularly preferably 92% by mass or more, and preferably 99% by mass or less, even more preferably 98% by mass or less, and particularly preferably 97% by mass or less. By keeping the solid content of the dried polymer within the above range, pulverization, classification, and surface crosslinking can be efficiently performed. In this specification, "drying is complete" refers to a state in which the solid content reaches 80% by mass. In this step, the dried polymer is in the form of a block, and the water content may differ between the upper and lower portions, the center, and the ends of the block. In this case, dried polymer may be appropriately collected from various locations, crushed if necessary, and the moisture content measured and averaged.

[0108] In this specification, a dried polymer having a solid content below the predetermined value may be referred to as an undried material. Furthermore, the "material to be dried" or "particulate hydrogel" in the drying process may include both particulate hydrogel and granulated gel. The drying process of the present invention is particularly effective when both particulate hydrogel and granulated gel are included. Similarly, in other processes, the hydrogel and its processed product may also include granulated gel and its processed product.

[0109] Examples of drying methods used in the drying step include heat drying, hot air drying, reduced-pressure drying, fluidized bed drying, infrared drying, microwave drying, drying by azeotropic dehydration with a hydrophobic organic solvent, high-humidity drying using high-temperature water vapor, and agitation drying. Among these, agitation drying or hot air drying is preferred from the viewpoint of drying efficiency. Agitation drying is preferably performed using an agitation dryer such as a paddle dryer or a rotary drum dryer. Hot air drying is preferably performed using a ventilation band dryer that performs hot air drying on a ventilation belt. Use of a ventilation band dryer allows for efficient drying while preventing physical damage to the material to be dried, such as the dried polymer or the particulate hydrogel during drying, and generation of fine powder due to friction.

[0110] In the case of hot air drying, the drying temperature, i.e., the temperature of the hot air, is preferably 120°C or higher, more preferably 130°C or higher, and even more preferably 150°C or higher, and is preferably 250°C or lower, more preferably 230°C or lower, and even more preferably 200°C or lower, in consideration of drying efficiency. The drying time is preferably 10 minutes to 120 minutes, more preferably 20 minutes to 90 minutes, and even more preferably 30 minutes to 60 minutes. By setting the drying temperature and drying time within the ranges, the physical properties of the obtained water-absorbent resin and water-absorbing agent can be set within desired ranges. Other drying conditions may be appropriately set depending on the moisture content, total mass, and target solid content of the particulate hydrogel or granulated gel to be dried, and when band drying is performed, the conditions described in WO 2006 / 100300, WO 2011 / 025012, WO 2011 / 025013, WO 2011 / 111657, etc. are appropriately applied.

[0111] [2-6] Pulverization step and classification step In the present invention, the pulverization step is an optional step of pulverizing the dried polymer, and the classification step is an optional step of removing fine powder from the pulverized dried polymer. Specifically, the pulverization step is a step of pulverizing the dried polymer obtained through the drying step. Furthermore, the classification step is a step of adjusting the particle size of the dried polymer or the dried polymer pulverized in the pulverization step to a desired range. By passing through the pulverization step after drying, an irregularly pulverized water absorbent resin can be obtained.

[0112] Examples of the grinding device used in the grinding step include high-speed rotary grinders such as roll mills, hammer mills, screw mills, and pin mills; vibration mills; knuckle-type grinders; and cylindrical mixers. Among these, a roll mill is preferably selected from the viewpoint of grinding efficiency. A plurality of these grinders can also be used in combination.

[0113] Methods for adjusting the particle size in the classification step include sieve classification using a JIS standard sieve (JIS Z 8801-1 (2000)) and air classification. Among these, sieve classification is preferably selected from the viewpoint of classification efficiency. Note that, from the viewpoint of ease of pulverization, classification may be additionally performed before the pulverization step.

[0114] In one embodiment of the present invention, the water-absorbent resin preferably has a mass average particle diameter (D50) of 300 μm or more and 600 μm or less. The mass percentage of particles having a particle diameter of 850 μm or more is preferably 3 mass% or less. The mass percentage of particles having a particle diameter of 300 μm or more and less than 850 μm is preferably 50 mass% or more. The mass percentage of particles having a particle diameter of 300 μm or more and less than 850 μm is preferably 5 mass% or less. The upper limit of the mass average particle diameter (D50) is more preferably 500 μm or less, and even more preferably 450 μm or less. Furthermore, the mass percentage of particles having a particle diameter of 850 μm or more in the water-absorbent resin is more preferably 2 mass% or less, and even more preferably 1 mass% or less. Furthermore, the mass percentage of particles having a particle diameter of 300 μm or more and less than 850 μm in the water-absorbent resin is more preferably 55 mass% or more, and even more preferably 60 mass% or more. Furthermore, the mass proportion of particles of the water-absorbent resin having a particle diameter of less than 150 μm is more preferably 4 mass% or less, even more preferably 3 mass% or less, and particularly preferably 2 mass% or less. Furthermore, in one embodiment of the present invention, the logarithmic standard deviation (σζ) of the particle size distribution of the water-absorbent resin is preferably 0.20 or more, more preferably 0.25 or more, even more preferably 0.27 or more, and preferably 0.50 or less, more preferably 0.45 or less, even more preferably 0.43 or less, particularly preferably 0.40 or less, and most preferably 0.35 or less. The logarithmic standard deviation (σζ) of the particle size distribution indicates the narrowness of the particle size distribution, and the smaller its value, the more uniform the particle diameter becomes, which has the advantage of reducing particle segregation. In one embodiment of the present invention, the particle size of the water-absorbent resin preferably satisfies the above-mentioned mass average particle diameter (D50), the mass proportion of particles having a particle diameter of 850 μm or more, the mass proportion of particles having a particle diameter of 300 μm or more and less than 850 μm, and the mass proportion of particles having a particle diameter of less than 150 μm, and more preferably satisfies the above-mentioned mass average particle diameter (D50), the mass proportion of particles having a particle diameter of 850 μm or more, the mass proportion of particles having a particle diameter of 300 μm or more and less than 850 μm, the mass proportion of particles having a particle diameter of less than 150 μm, and the logarithmic standard deviation, and can be appropriately combined within each of the above-mentioned ranges.

[0115] The mass-average particle diameter (D50) and logarithmic standard deviation (σζ) are measured by the measurement method described in U.S. Pat. No. 7,638,570, "(3) Mass-Average Particle Diameter (D50) and Logarithmic Standard Deviation (σζ) of Particle Diameter Distribution."

[0116] The above-mentioned particle size is also applied to the water absorbent resin after the pulverization step and the classification step, and the particulate water-absorbing agent composition produced by the above-mentioned production method. Therefore, when surface cross-linking is performed, it is preferable to perform surface cross-linking treatment in the surface cross-linking step so as to maintain the particle size adjusted in the above-mentioned range of the water absorbent resin before surface cross-linking, and it is more preferable to adjust the particle size by providing a sizing step after the surface cross-linking step. Therefore, it is preferable that the water-absorbent resin after the surface cross-linking step, the water-absorbent resin and the particulate water-absorbing agent composition to be subjected to the nonionic polymer adding step, which are produced by the production method according to one embodiment of the present invention, satisfy that the mass average particle diameter (D50), the mass proportion of particles having a particle diameter of 850 μm or more, the mass proportion of particles having a particle diameter of 300 μm or more and less than 850 μm, and the mass proportion of particles having a particle diameter of less than 150 μm are all within the above-mentioned ranges, and it is more preferable that the mass average particle diameter (D50), the mass proportion of particles having a particle diameter of 850 μm or more, the mass proportion of particles having a particle diameter of 300 μm or more and less than 850 μm, the proportion of particles having a particle diameter of less than 150 μm, and the logarithmic standard deviation (σζ) of the particle size distribution are all within the above-mentioned ranges. More preferably, the water-absorbent resin after the surface cross-linking step, the water-absorbent resin and the particulate water-absorbing agent composition to be subjected to the nonionic polymer adding step, which are produced by the production method according to one embodiment of the present invention, have a mass average particle diameter (D50) of 300 to 600 μm, a mass ratio of particles having a particle diameter of 850 μm or more is 3 mass% or less, a mass ratio of particles having a particle diameter of 300 μm or more and less than 850 μm is 50 mass% or more, a mass ratio of particles having a particle diameter of less than 150 μm is 5 mass% or less, and a logarithmic standard deviation (σζ) of the particle size distribution is 0.20 to 0.50.

[0117] [2-7] Surface cross-linking step This step is a step of providing a portion with a higher cross-linking density on the surface layer of the water-absorbent resin before surface cross-linking obtained through the above-mentioned steps, and is configured to include a mixing step, a heat treatment step, a cooling step, etc. In the surface cross-linking step, radical cross-linking, surface polymerization, a cross-linking reaction with a surface cross-linking agent, etc. occur on the surface of the water-absorbent resin before surface cross-linking, thereby obtaining a surface-cross-linked water-absorbent resin. Note that the water-absorbent resin before surface cross-linking obtained through the above-mentioned steps is the dried polymer, a water-absorbent resin obtained by pulverizing and / or classifying the dried polymer, etc.

[0118] [2-7-1] Mixing step

[0143] This step is a step of obtaining a mixture by mixing a solution containing a surface crosslinking agent (hereinafter referred to as "surface crosslinking agent solution") with a water absorbent resin before surface crosslinking in a mixing device.

[0119] (Surface Crosslinking Agent) Examples of the surface crosslinking agent used in the production method according to one embodiment of the present invention include the surface crosslinking agents described in U.S. Patent No. 7,183,456. At least one type of surface crosslinking agent is selected from these surface crosslinking agents in consideration of reactivity, etc. Furthermore, from the viewpoint of the handleability of the surface crosslinking agent and the water absorption performance of the water-absorbent resin and the water-absorbing agent, it is preferable to select an organic compound which is a surface crosslinking agent having two or more functional groups which react with a carboxyl group and which forms a covalent bond.

[0120] Specific examples of the surface cross-linking agent include ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 1,2-pentanediol, 1,3-pentanediol, 1,4-pentanediol, 1,5-pentanediol, 2,3-pentanediol, and 2,4-pentanediol. polyhydric alcohol compounds such as hexanediol, 1,2-hexanediol, 1,3-hexanediol, 1,4-hexanediol, 1,5-hexanediol, 1,6-hexanediol, 2,3-hexanediol, 2,4-hexanediol, glycerin, polyglycerin, diethanolamine, and triethanolamine; polyhydric amine compounds such as ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, polyallylamine, and polyethyleneimine; haloepoxy compounds, polyhydric amine compounds such as ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, polyallylamine, and polyethyleneimine; condensates of epoxy compounds with haloepoxy compounds; oxazoline compounds such as 1,2-ethylenebisoxazoline; oxazolidinone compounds; 1,3-dioxolan-2-one (ethylene carbonate), 4-methyl-1,3-dioxolan-2-one, 4,5-dimethyl-1,3-dioxolan-2-one, 4,4-dimethyl-1,3-dioxolan-2-one, 4-ethyl-1,3-dioxolan-2-one, 4-hydroxymethyl-1,3-dioxolan-2-one, 1,3-dioxan-2-one, 4-methyl-1,3-dioxan-2-one, 4, Examples of suitable alkylene carbonate compounds include 6-dimethyl-1,3-dioxan-2-one and 1,3-dioxopan-2-one; polyglycidyl compounds such as ethylene glycol diglycidyl ether, polyethylene diglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, glycerol polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, and glycidol; oxetane compounds; vinyl ether compounds; and cyclic urea compounds.These may be used alone or in combination of two or more.

[0121] The amount of the surface crosslinking agent used, or the total amount when a plurality of types are used, is preferably 0.01 to 10.00 parts by mass, more preferably 0.01 to 5.00 parts by mass, and even more preferably 0.01 to 2.00 parts by mass, relative to 100 parts by mass of the water absorbent resin before surface crosslinking. By setting the amount of the surface crosslinking agent used within this range, an optimal crosslinked structure can be formed in the surface layer of the crosslinked polymer, and a water absorbent resin and a water absorbent agent with high physical properties can be obtained.

[0122] The surface cross-linking agent is preferably added as an aqueous solution to a water absorbent resin before surface cross-linking. In this case, the amount of water used is preferably 0.1 parts by mass to 20.0 parts by mass, more preferably 0.3 parts by mass to 15.0 parts by mass, and even more preferably 0.5 parts by mass to 10 parts by mass, relative to 100 parts by mass of a water absorbent resin before surface cross-linking. By setting the amount of water used within this range, the handleability of the surface cross-linking agent solution is improved, and the surface cross-linking agent can be uniformly mixed with the water absorbent resin before surface cross-linking.

[0123] Furthermore, a hydrophilic organic solvent can be used in combination with the water as needed to prepare the surface cross-linking agent solution. In this case, the amount of the hydrophilic organic solvent used is preferably 5 parts by mass or less, more preferably 3 parts by mass or less, and even more preferably 1 part by mass or less, relative to 100 parts by mass of the water absorbent resin before surface cross-linking. Specific examples of the hydrophilic organic solvent include lower alcohols such as methyl alcohol; ketones such as acetone; ethers such as dioxane; amides such as N,N-dimethylformamide; sulfoxides such as dimethyl sulfoxide; and polyhydric alcohols such as ethylene glycol. However, it is preferable to limit the use of these hydrophilic organic solvents to as small an amount as possible.

[0124] Furthermore, various additives may be added to the surface cross-linking agent solution in an amount of 5 parts by mass or less, and / or may be added separately in the mixing step.

[0125] (Mixing method and mixing conditions) For mixing the water absorbent resin and the surface crosslinking agent solution, a method is selected in which a surface crosslinking agent solution is prepared in advance, and the solution is preferably sprayed or dropped onto a crosslinked polymer, more preferably sprayed and mixed.

[0126] It is preferable that a mixer for carrying out the mixing has a torque necessary for uniformly and reliably mixing the water absorbent resin and the surface crosslinking agent. The mixer is preferably a high-speed stirring mixer, more preferably a high-speed stirring continuous mixer. The rotation speed of the high-speed stirring mixer is preferably 100 rpm or more, more preferably 300 rpm or more, and is preferably 10,000 rpm or less, more preferably 2,000 rpm or less.

[0127] The temperature of the water absorbent resin to be supplied in this step is, from the viewpoint of mixability with a surface crosslinking agent solution and coagulation property of the humidified mixture, preferably 35° C. to 80° C., more preferably 35° C. to 70° C., and further preferably 35° C. to 60° C. In addition, the mixing time is preferably 1 second or more, more preferably 5 seconds or more, and preferably 1 hour or less, more preferably 10 minutes or less.

[0128] [2-7-2] Heat Treatment Step This step is a step of applying heat to the mixture obtained in the mixing step to cause a crosslinking reaction on the surface of the water-absorbent resin. The heat treatment of the water-absorbent resin may involve heating the water-absorbent resin in a stationary state, or heating it in a fluidized state using a power such as stirring. However, heating under stirring is preferred, as this allows the entire humidified mixture to be heated evenly. From this viewpoint, examples of the heat treatment device that performs the heat treatment include a paddle dryer, a multi-fin processor, and a tower dryer.

[0129] The so-called controlled temperature of the heat treatment device need only be able to heat the water-absorbent resin to the temperature described below, and does not need to be constant from the beginning to the end of the process. However, in order to prevent partial overheating, it is preferably 50°C to 300°C. When emphasis is placed on damage resistance as a physical property of the resulting water-absorbent resin, the temperature is more preferably 250°C or less, even more preferably 70°C to 230°C, and particularly preferably 90°C to 220°C. On the other hand, when emphasis is placed on water absorption performance, it is more preferably 120°C to 280°C, even more preferably 150°C to 250°C, and particularly preferably 170°C to 230°C.

[0130] The heating time is preferably 1 to 180 minutes, more preferably 5 to 120 minutes, even more preferably 10 to 120 minutes, and particularly preferably 15 to 60 minutes. If the heating time is shorter than 1 minute, the surface cross-linking treatment becomes insufficient, and the absorbency against load (AAP) decreases. On the other hand, if the heating time is longer, coloring may occur and / or the absorbency against load (CRC) may decrease too much.

[0131] [2-7-3] Cooling step This step is an optional step that is provided as necessary after the heat treatment step and / or the drying step. This step is a step of forcibly cooling the high-temperature water absorbent resin that has been subjected to the heat treatment step to a predetermined temperature, thereby quickly completing the surface cross-linking reaction.

[0132] The cooling of the water-absorbent resin may be performed in a stationary state or in a fluidized state using a power such as stirring, but cooling under stirring is preferred in that the entire water-absorbent resin can be cooled uniformly. From the above viewpoint, examples of the cooling device for performing the cooling include a paddle dryer, a multi-fin processor, and a tower dryer. Note that these cooling devices can also have the same specifications as the heat treatment device used in the heat treatment step. This is because they can be used as cooling devices by changing the heat medium of the heat treatment device to a refrigerant.

[0133] The cooling temperature in this step may be appropriately set depending on the heating temperature in the heat treatment step, the water absorption performance of the water-absorbent resin, etc., and is preferably 40°C to 100°C, more preferably 50°C to 90°C, and even more preferably 50°C to 70°C.

[0134] [2-8] Nonionic Polymer Addition Step In a method for producing a particulate water-absorbing agent composition according to one embodiment of the present invention, after the surface-crosslinking step, a nonionic polymer containing a polyalkylene glycol chain in its structure and having a mass-average molecular weight of 300 to 15,000 is added to the surface-crosslinked water-absorbent resin in an amount of 0.02 mass % to 0.40 mass %. That is, a method for producing a particulate water-absorbing agent composition according to one embodiment of the present invention includes a nonionic polymer addition step. This step includes an adding step, a mixing step, a curing step, etc.

[0135] [2-8-1] Nonionic Polymer The nonionic polymer preferably contains a polyalkylene glycol chain represented by the following general formula (2) in its structure.

[0136] - (OR) ｍ In general formula (2), R is an alkylene group having 2 to 4 carbon atoms, which may be linear or branched, and m has an average value of 4 to 350, more preferably 5 to 250, and even more preferably 6 to 100.

[0137] In the general formula (2), the oxyalkylene groups (—OR—) in one molecule may be the same, or two or more types of oxyalkylene groups may be contained.

[0138] The nonionic polymer contains a polyalkylene glycol chain in its structure, and when the nonionic polymer is added to a surface-crosslinked water-absorbing resin produced by adding a water-soluble polyalkylene glycol having the mass average molecular weight and in the amount in at least any one of the steps selected from a monomer aqueous solution preparation step, a polymerization step, and a hydrous gel crushing step, the anti-caking performance of the resulting water-absorbing agent can be improved without deteriorating the water absorption performance under pressure.

[0139] Examples of the nonionic polymer containing a polyalkylene glycol chain in its structure include polyalkylene glycols such as polyethylene glycol, polypropylene glycol, polyethylene glycol-polypropylene glycol copolymer, and polyethylene glycol-polypropylene glycol-polybutylene glycol copolymer; polyoxyethylene alkyl ethers such as polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, polyoxyethylene oleyl ether, and polyoxyethylene higher alcohol ether; polyoxyethylene alkylaryl ethers such as polyoxyethylene nonylphenyl ether; polyoxyethylene sorbitan monolaurate; Examples of the nonionic polymer include polyoxyethylene sorbitan fatty acid esters such as urate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan tristearate, polyoxyethylene sorbitan monooleate, and polyoxyethylene sorbitan trioleate; polyoxyethylene sorbitol fatty acid esters such as polyoxyethylene sorbitan tetraoleate; polyoxyethylene fatty acid esters such as polyethylene glycol monolaurate, polyethylene glycol monostearate, polyethylene glycol distearate, and polyethylene glycol monooleate; polyoxyethylene alkylamines; and polyoxyethylene hydrogenated castor oil. These nonionic polymers may be used alone or in combination of two or more.

[0140] The nonionic polymer has a mass average molecular weight of 300 to 15,000. When the mass average molecular weight of the nonionic polymer is within this range, the anti-caking performance of the resulting water absorbent is significantly improved when the nonionic polymer is added to a surface-crosslinked water-absorbent resin produced by adding a water-soluble polyalkylene glycol of the mass average molecular weight and the amount in at least one step selected from the monomer aqueous solution preparation step, the polymerization step, and the hydrous gel crushing step. The mass average molecular weight of the nonionic polymer is preferably 350 or more, more preferably 400 or more, and even preferably 500 or more. The mass average molecular weight is more preferably 12,000 or less, even more preferably 10,000 or less, and may be 5,000 or less. The mass average molecular weight of the nonionic polymer is a value measured by gel permeation chromatography.

[0141] The HLB of the nonionic polymer is preferably not less than 5, more preferably not less than 10. When the HLB of the nonionic polymer is within the above range, when the nonionic polymer is added to a surface-crosslinked water-absorbent resin produced by adding a water-soluble polyalkylene glycol having the above mass-average molecular weight and in the above amount in at least any step selected from a monomer aqueous solution preparation step, a polymerization step, and a hydrous gel crushing step, the anti-caking performance of the obtained water-absorbing agent can be improved without deteriorating the water absorption performance under pressure.

[0142] Here, HLB is a value calculated by the Griffin method. The HLB of a nonionic polymer with an unknown HLB can be determined by the following method: A certain type of oil is emulsified with the nonionic polymer whose HLB is to be determined (adding a surfactant with a known HLB, if necessary), and the same oil is emulsified with a different surfactant with a known HLB (using surfactants with various HLB values). The HLB of the nonionic polymer when the emulsified states are identical is taken as the HLB of the nonionic polymer.

[0143] The amount of the nonionic polymer added is 0.02% to 0.40% by mass relative to the surface-crosslinked water-absorbent resin. When the amount of the nonionic polymer added is within this range, the anti-caking performance of the resulting water-absorbing agent is significantly improved when the nonionic polymer is added to a surface-crosslinked water-absorbent resin produced by adding a water-soluble polyalkylene glycol having the mass-average molecular weight and in the amount described above in at least one step selected from the monomer aqueous solution preparation step, the polymerization step, and the hydrogel crushing step. The amount of the nonionic polymer added is preferably 0.04% by mass or more, more preferably 0.06% by mass or more, even more preferably 0.08% by mass or more, and even more preferably 0.15% by mass or more relative to the surface-crosslinked water-absorbent resin. Furthermore, the amount added is more preferably 0.35% by mass or less.

[0144] The nonionic polymer may be added in the above-mentioned amount and weight average molecular weight range, and multiple types of nonionic polymers may be used within these ranges. When one or multiple types of nonionic polymers are used, multiple types of nonionic polymers having different weight average molecular weights may be used in combination.

[0145] [2-8-2] Addition step and mixing step In the manufacturing method of a water-absorbing agent according to the present invention, after the surface-crosslinking step, a nonionic polymer containing a polyalkylene glycol chain in its structure, having the mass-average molecular weight and the amount, may be added to a surface-crosslinked water-absorbent resin.

[0146] Furthermore, the method for adding the nonionic polymer to the surface-crosslinked water-absorbent resin is not particularly limited. The nonionic polymer may be added as is, as a solution diluted with an organic solvent, or as an aqueous solution, with addition as an aqueous solution being more preferred. In this case, the aqueous solution concentration is preferably 1% by mass to 70% by mass, more preferably 5% by mass to 60% by mass, and even more preferably 10% by mass to 50% by mass. By setting the aqueous solution concentration within this range, the handleability of the liquid containing the nonionic polymer is improved, and the nonionic polymer can be uniformly mixed with the surface-crosslinked water-absorbent resin.

[0147] The method of mixing the surface-crosslinked water-absorbent resin with the nonionic polymer or its aqueous solution is not particularly limited, and a method of dropping the nonionic polymer or its aqueous solution onto the surface-crosslinked water-absorbent resin under stirring using a straight pipe, or a method of spraying using a spray nozzle, etc. can be used. From the viewpoint of uniform mixing, the average droplet diameter of the nonionic polymer or its aqueous solution when dropped or sprayed is preferably 2.5 mm or less, more preferably 1.5 mm or less, even more preferably 1.0 mm or less, and particularly preferably 0.5 mm or less. On the other hand, since the cost required to make the droplets fine is too high compared to the effect obtained, the average droplet diameter is preferably 10 μm or more, more preferably 30 μm or more, and even more preferably 50 μm or more.

[0148] The mixing device used for the mixing preferably has a torque required to uniformly and reliably mix the surface-crosslinked water-absorbent resin and the nonionic polymer. Specific examples of the mixing device include cylindrical mixers, double-walled conical mixers, V-shaped mixers, ribbon mixers, screw mixers, rotary disk mixers, double-arm kneaders, internal mixers, grinding kneaders, rotary mixers, screw extruders, fluidized bed mixers, and airflow mixers. Devices capable of mixing by stirring are more preferred, including high-speed stirring mixers and vertical rotating disk mixers. Among these, high-speed stirring continuous mixers are preferred, with horizontal high-speed stirring continuous mixers and vertical high-speed stirring continuous mixers being more preferred. Specific examples of the high-speed stirring mixers include the Shugi Mixer (manufactured by Hosokawa Micron Corporation), Turbulizer (manufactured by Hosokawa Micron Corporation), Loedige Mixer (manufactured by Loedige Corporation), and Flow Jet Mixer (manufactured by Powder and Powtex Corporation). When a stirring type mixer is used, the rotation speed is preferably 5 rpm or more, more preferably 10 rpm or more, and is preferably 10,000 rpm or less, more preferably 2,000 rpm or less.

[0149] The temperature of the nonionic polymer or the aqueous solution thereof to be mixed is preferably 10° C. to 70° C., more preferably 20° C. to 60° C., from the viewpoint of mixability and coagulation property of the humidified mixture. The temperature range is a temperature measured before being affected by the temperature of a water absorbent resin and / or the temperature of an apparatus in which a water absorbent resin stays when the nonionic polymer or the aqueous solution thereof is added to a water absorbent resin.

[0150]

[0123] Moreover, the temperature of the water absorbent resin after surface cross-linking, which is subjected to mixing, is preferably 180°C or lower, more preferably 160°C or lower, still more preferably 150°C or lower, and is preferably 40°C or higher, more preferably 50°C or higher, still more preferably 60°C or higher, from the viewpoint of the time required for cooling after the surface cross-linking step, mixability, and coagulation property of the humidified mixture.

[0151] [2-8-3] Curing step The obtained mixture of the surface-crosslinked water-absorbent resin and the nonionic polymer or its aqueous solution is preferably subjected to a curing treatment. The "curing" refers to an operation of eliminating the wettability of the water-absorbent resin surface and powdering it. The "curing treatment" is a process of controlling the temperature of the object to a predetermined curing temperature and maintaining that temperature state for a predetermined curing time, thereby curing the object.

[0152] In one embodiment of the present invention, a heat medium such as hot air is preferably used for the curing treatment. The curing temperature, for example, the heat medium temperature or the material temperature, is preferably 40°C to 150°C, more preferably 50°C to 140°C. The curing time within this temperature range is preferably 1 minute or more, more preferably 5 minutes or more, and preferably 2 hours or less, more preferably 1.5 hours or less. If the curing temperature is too low and / or the curing time is too short, the surface of the resulting particulate water-absorbing agent composition will be in a wet state, resulting in strong adhesion and difficulty in handling the powder. If the curing temperature is too high and / or the curing time is too long, this is energy-inefficient.

[0153] The addition and mixing of the nonionic polymer or its aqueous solution and the subsequent curing treatment may be performed in the same apparatus or in different apparatuses. Furthermore, the timing of the above-mentioned series of treatments may be during the cooling step or after the cooling step. The apparatus used may be the above-mentioned mixing apparatus, and a heat medium such as gas or conductive heat may be adjusted so that the temperature inside the apparatus is maintained at the above-mentioned temperature. When curing, the mixture may be stirred or left to stand, i.e., unstirred, as long as the curing temperature and curing time can be controlled within a predetermined range. When the curing treatment is performed by standing, the water-absorbent resin may be layered to a thickness of preferably 1 cm or more, more preferably 5 cm or more, even more preferably 10 cm or more, and preferably 100 cm or less, more preferably 80 cm or less, and even more preferably 70 cm or less, before the curing treatment. The cured water-absorbent agent composition may be pulverized or classified as necessary to obtain a particulate water-absorbent agent composition having a desired particle size.

[0154] [3] Particulate Water-Absorbent Agent Composition One aspect of the present invention also includes a particulate water-absorbent agent composition manufactured by a method for manufacturing a particulate water-absorbent agent composition according to one embodiment of the present invention. That is, the particulate water-absorbent agent composition according to one embodiment of the present invention is a method for manufacturing a particulate water-absorbent agent composition containing a poly(meth)acrylic acid (salt)-based water-absorbent resin, comprising: a monomer aqueous solution preparation step of preparing a (meth)acrylic acid (salt)-based monomer aqueous solution; a polymerization step of polymerizing the (meth)acrylic acid (salt)-based monomer aqueous solution; a hydrogel crushing step which is an optional step of gel-crushing a hydrogel-like crosslinked polymer produced during or after the polymerization; a drying step of drying the particulate hydrogel; a crushing step which is an optional step of crushing and classifying the dried polymer; and a surface crosslinking step of surface-crosslinking the water-absorbent resin before surface crosslinking. and (iii) adding, to the surface-crosslinked water-absorbent resin, 0.02 to 0.40% by mass of a nonionic polymer having a polyalkylene glycol chain in its structure and a mass-average molecular weight of 300 to 15,000, in an amount of 0.02 to 0.40% by mass, in at least any one of the steps selected from the step of preparing an aqueous monomer solution, the step of polymerizing, and the step of crushing a hydrous gel, which is an optional step.

[0155] Furthermore, a particulate water-absorbing agent composition according to one embodiment of the present invention is a particulate water-absorbing agent composition containing a poly(meth)acrylic acid (salt)-based water-absorbing resin as a main component, including a nonionic polymer having a polyalkylene glycol chain in its structure, with a mass ratio of particles having a particle size of 300 μm or more and less than 850 μm being 50 mass % or more, wherein: (a) the nonionic polymer contained in the particulate water-absorbing agent composition is designated as A1 and its content is designated as C1; (b) the particulate water-absorbing agent composition is subjected to a predetermined impact test; (c) the particulate water-absorbing agent composition subjected to the impact test is sieved using a JIS standard sieve into a particle group a having a particle size of 300 μm or more and a particle group b having a particle size of less than 300 μm; and (d) the nonionic polymer present in the particle group a is designated as A2 and its content is designated as C2, the particulate water-absorbing agent composition satisfies all of the following (1) to (4): (1) A1 is a water-soluble polyalkylene glycol having a mass average molecular weight of 3,000 or less, and a nonionic polymer having a polyalkylene glycol chain in its structure and a mass average molecular weight of 300 to 15,000; (2) A2 is a water-soluble polyalkylene glycol having a mass average molecular weight of 3,000 or less; (3) C2 is 0.005% by mass or more and 0.15% by mass or less; (4) C1-C2 is 0.02% by mass or more and 0.40% by mass or less.

[0156] Here, the water-soluble polyalkylene glycol is a type of nonionic polymer having a polyalkylene glycol chain in its structure. Therefore, the nonionic polymer contained in the particulate water-absorbing agent composition satisfying all of the above A1, i.e., the above (1) to (4), specifically consists of polymers shown in the following (i) and (ii). (i) A water-soluble polyalkylene glycol having a mass average molecular weight of 3,000 or less, which is added in at least one step selected from the step of preparing an aqueous monomer solution, the step of polymerization, and an optional step of crushing a hydrous gel in the production method. (ii) A nonionic polymer having a polyalkylene glycol chain in its structure and having a mass average molecular weight of 300 to 15,000, which is added after the step of surface cross-linking in the production method.

[0157] The predetermined impact test is a test carried out by the following procedures (i) to (iii), and can be carried out, for example, by the method described in (Pretreatment 1: Impact Test) in the Examples. (i) 30 g of the particulate water-absorbing agent composition and 10 g of glass beads with a diameter of 6 mm are placed in a glass container with a diameter of 6 cm and a height of 11 cm. (ii) The glass container obtained in (i) is shaken using a paint shaker described in JP-A-9-235378 at a shaking speed of 800 rpm for a shaking time adjusted to satisfy the following formula (7), thereby pulverizing the particulate water-absorbing agent composition: 0.2<(mass of particle group a) / (total mass of particle group a and particle group b)<0.3 Formula (7) (iii) The glass beads are removed from the mixture of the pulverized particulate water-absorbing agent composition and the glass beads obtained in (ii). The removal method is not particularly limited, and examples thereof include sieving by passing the pulverized particulate water-absorbing agent composition through a sieve with a mesh size that does not allow the glass beads to pass through, for example, 2 mm mesh size. Furthermore, it is essential that the particulate water-absorbing agent composition that satisfies all of the above (1) to (4) can obtain both the particle group a and the particle group b by the sieving described in the above (c). Therefore, it is preferable that the particle size and particle size distribution of the particulate water-absorbing agent composition that satisfies all of the above (1) to (4) are in the same ranges as the preferred ranges of the particle size and particle size distribution of the water-absorbent resin after the surface cross-linking step and the water-absorbent resin that is subjected to the nonionic polymer adding step. The particle size and particle size distribution are specifically represented by, for example, the mass average particle diameter (D50), the mass proportion of particles having a particle diameter of 850 μm or more, the mass proportion of particles having a particle diameter of 300 μm or more and less than 850 μm, the mass proportion of particles having a particle diameter of less than 150 μm, and the logarithmic standard deviation (σζ) of the particle size distribution.

[0158] [3-1] Water-absorbent resin A particulate water-absorbent composition according to one embodiment of the present invention is a particulate water-absorbent composition containing a poly(meth)acrylic acid (salt)-based water-absorbent resin, and more preferably a particulate water-absorbent composition containing a poly(meth)acrylic acid (salt)-based water-absorbent resin as a main component (preferably 60% by mass or more but less than 100% by mass, 70% by mass or more but less than 100% by mass, 80% by mass or more but less than 100% by mass, or 90% by mass or more but less than 100% by mass). The water-absorbent resin may be a "surface-crosslinked water-absorbent resin". The shape of the water-absorbent resin is usually particulate. The particulate water-absorbent resin may be, for example, irregularly pulverized (irregular), spherical, fibrous, rod-like, approximately spherical, or flat. Among these, it is preferable that at least a portion of the water-absorbent resin is in an irregularly pulverized shape. When considering use in absorbent articles, it is more preferable that the water-absorbing resin has an irregular shape among the particle shapes mentioned above, in view of the liquid diffusibility and the difficulty of falling off from the pulp.

[0159] (AAP of water absorbent resin after surface cross-linking) In one embodiment of the present invention, the absorption capacity under pressure (AAP) of the water absorbent resin after surface cross-linking under a pressure of 0.7 psi is preferably 20.0 g / g or more, more preferably 21.0 g / g or more, even more preferably 24.0 g / g or more, particularly preferably 25.0 g / g or more, and most preferably 25.2 g / g or more. The upper limit is not particularly limited, and is preferably 30.0 g / g or less from the viewpoint of balance with other physical properties.

[0160] When the AAP is 20.0 g / g or more, the amount of liquid return when pressure is applied to the absorbent body is not too large, making it suitable for use as an absorbent body in absorbent articles such as disposable diapers. The AAP can be controlled by an internal crosslinking agent, particle size, and / or surface crosslinking agent, etc.

[0161] In this specification, the absorbency against pressure (AAP) at a pressure of 0.7 psi is a value determined by the method described in the Examples section below.

[0162] (FHA of water absorbent resin after surface cross-linking) In one embodiment of the present invention, the fixed height absorption (FHA) at a height of 20 cm of the water absorbent resin after surface cross-linking is preferably 20.0 g / g or more, more preferably 22.0 g / g or more, further preferably 25.0 g / g or more, particularly preferably 25.3 g / g or more. The upper limit is not particularly limited, and is preferably 30.0 g / g or less from the viewpoint of balance with other physical properties.

[0163] When the FHA is 20.0 g / g or more, the amount of liquid return when pressure is applied to the absorbent body is not too large, making it suitable for use as an absorbent body in absorbent articles such as disposable diapers. The FHA can be controlled by an internal crosslinking agent, particle size, and / or surface crosslinking agent, etc.

[0164] In this specification, FHA is a value determined by the method described in the Examples section below.

[0165] (B.R. of water-absorbent resin after surface-crosslinking) In one embodiment of the present invention, the moisture absorption blocking ratio <1> (B.R.<1>) of the water-absorbent resin after surface-crosslinking is preferably 99% by mass or less, and the lower limit is not particularly limited. From the viewpoint that the handleability of the water-absorbing agent or water-absorbent resin is poor in a humid environment, and that problems such as aggregation and clogging due to caking in the transfer piping of a manufacturing plant and inability to be uniformly mixed with hydrophilic fibers are unlikely to occur during the production of an absorbent body in an absorbent article, a low B.R.<1> is preferred. However, since it is possible to suitably lower B.R.<1> by adding, after the surface-crosslinking step, 0.02% by mass to 0.40% by mass of a nonionic polymer containing a polyalkylene glycol chain in its structure and having a mass-average molecular weight of 300 to 15,000 to the surface-crosslinked water-absorbent resin, it is possible to suitably lower B.R.<1> at the stage of the water-absorbent resin after surface-crosslinking. <1> may be 99% by mass or less.

[0166] In this specification, B.R.<1> is a value determined by the method described in the Examples section below.

[0167] (CRC of water absorbent resin after surface cross-linking) In one embodiment of the present invention, the water absorbent resin after surface cross-linking has an absorption capacity without load (CRC) of preferably 20.0 g / g or more, more preferably 25.0 g / g or more, even more preferably 28.0 g / g or more, and particularly preferably 28.5 g / g or more. The higher the upper limit of CRC, the better, but in view of the balance with other physical properties, it is preferably 45.0 g / g or less, more preferably 40.0 g / g or less, even more preferably 35.0 g / g or less, and particularly preferably 30.0 g / g or less.

[0168] In this specification, the CRC is a value determined by the method described in the Examples section below.

[0169] (SFC of water-absorbent resin after surface cross-linking) In one embodiment of the present invention, the saline flow conductivity (SFC) of the water-absorbent resin after surface cross-linking is preferably 1×10 －７ cm ３ sec / g or more, more preferably 10×10 －７ cm ３ sec / g or more, more preferably 15×10 －７ cm ３ sec / g or more, and particularly preferably 20×10 －７ cm ３ sec / g or more. The upper limit of SFC is not particularly limited, but a higher value is preferable.

[0170] In this specification, the SFC is a value determined by the method described in the Examples section below.

[0171] (FSR of water absorbent resin after surface cross-linking) In one embodiment of the present invention, the free swelling rate (FSR) of the water absorbent resin after surface cross-linking is preferably 0.20 g / (g·s) or more, more preferably 0.25 g / (g·s) or more, more preferably 0.30 g / (g·s) or more, and further preferably 0.35 g / (g·s) or more.

[0172] In this specification, the FSR is a value determined by the method described in the Examples section below.

[0173] [3-2] Physical Properties of Particulate Water-Absorbing Agent Composition (AAP) In one embodiment of the present invention, the particulate water-absorbing agent composition has an absorption capacity against pressure (AAP) of preferably 20.0 g / g or more, more preferably 21.0 g / g or more, even more preferably 24.0 g / g or more, particularly preferably 25.0 g / g or more, and most preferably 25.2 g / g or more under a pressure of 0.7 psi. The upper limit is not particularly limited, and is preferably 30.0 g / g or less from the viewpoint of a balance with other physical properties.

[0174] When the AAP is 20.0 g / g or more, the amount of liquid return when pressure is applied to the absorbent body is not too large, making it suitable for use as an absorbent body in absorbent articles such as disposable diapers. The AAP can be controlled by an internal crosslinking agent, particle size, a surface crosslinking agent, and / or an additive added after the surface crosslinking step.

[0175] (FHA) In one embodiment of the present invention, the particulate water-absorbing agent composition has a fixed height absorption (FHA) at a height of 20 cm of preferably 20.0 g / g or more, more preferably 22.0 g / g or more, even more preferably 25.0 g / g or more, and particularly preferably 25.3 g / g or more. The upper limit is not particularly limited, and is preferably 30.0 g / g or less from the viewpoint of a balance with other physical properties.

[0176] When the FHA is 20.0 g / g or more, the absorbency when pressure is applied to the absorbent body is improved, making it suitable for use as an absorbent body in absorbent articles such as disposable diapers. The FHA can be controlled by an internal crosslinking agent, particle size, a surface crosslinking agent, and / or an additive added after the surface crosslinking step.

[0177] (B.R.) In one embodiment of the present invention, the moisture absorption blocking ratio <1> (B.R.<1>) of the particulate water-absorbing agent composition is preferably 90% by mass or less, more preferably 85% by mass or less, even more preferably 80% by mass or less, and particularly preferably 75% by mass or less. If the B.R.<1> exceeds 90% by mass, the particulate water-absorbing agent composition becomes difficult to handle in a humid environment, and there is a risk that problems such as aggregation and clogging due to caking in transfer piping in a manufacturing plant or inability to be uniformly mixed with hydrophilic fibers may occur during the production of an absorbent body in an absorbent article, etc.

[0178] (ΔB.R.) In one embodiment of the present invention, the value (ΔB.R.) obtained by subtracting the B.R. of the particulate water-absorbing agent composition obtained by adding the nonionic polymer from the B.R. of the water-absorbent resin after surface cross-linking is preferably 20% by mass or more, more preferably 25% by mass or more, even more preferably 30% by mass or more, and particularly preferably 35% by mass or more. When ΔB.R. is 20% by mass or more, the effect of improving the anti-caking performance by adding the nonionic polymer is large.

[0179] In this specification, ΔB.R. is a value determined by the method described in the Examples section below.

[0180] (CRC) In one embodiment of the present invention, the particulate water-absorbing agent composition has a non-load absorption capacity (CRC) of preferably 20.0 g / g or more, more preferably 25.0 g / g or more, even more preferably 28.0 g / g or more, and particularly preferably 28.5 g / g or more. The higher the upper limit of the CRC, the better, but in view of the balance with other physical properties, it is preferably 45.0 g / g or less, more preferably 40.0 g / g or less, even more preferably 35.0 g / g or less, and particularly preferably 30.0 g / g or less.

[0181] (SFC) In one embodiment of the present invention, the particulate water-absorbing agent composition preferably has a saline flow conductivity (SFC) of 1×10 －７ cm ３ sec / g or more, more preferably 10×10 －７ cm ３sec / g or more, more preferably 15×10 －７ cm ３ sec / g or more, and particularly preferably 20×10 －７ cm ３ sec / g or more. The upper limit of the SFC is not particularly limited, although a higher value is preferable.

[0182] (FSR) In one embodiment of the present invention, the particulate water-absorbing agent composition has a free swelling rate (FSR) of preferably 0.20 g / (g·s) or more, more preferably 0.25 g / (g·s) or more, more preferably 0.30 g / (g·s) or more, and even more preferably 0.35 g / (g·s) or more.

[0183] (Surface tension) In one embodiment of the present invention, the surface tension of the particulate water-absorbing agent composition is preferably 45 mN / m or more, more preferably 50 mN / m or more, even more preferably 55 mN / m or more, and particularly preferably 60 mN / m or more. The upper limit is not particularly limited, and is preferably 75 mN / m or less from the viewpoint of the balance with other physical properties.

[0184] When the surface tension is 45 mN / m or more, the amount of liquid returning when pressure is applied to the absorbent is not too large, making it suitable for use as an absorbent in absorbent articles such as disposable diapers. Note that the surface tension can be controlled by an additive or the like added after surface cross-linking.

[0185] (Mass Average Particle Diameter (D50)) In one embodiment of the present invention, the mass average particle diameter (D50) of the particulate water-absorbing agent composition is preferably 300 μm or more and 600 μm or less, more preferably 500 μm or less, and even more preferably 450 μm or less. As a result, the balance of the AAP, CRC, and SFC described above can be maintained.

[0186] (Mass Proportion of Particles with a Particle Diameter of 850 μm or More) In one embodiment of the present invention, the mass proportion of particles with a particle diameter of 850 μm or more in the particulate water-absorbing agent composition is preferably 3 mass % or less, more preferably 2 mass % or less, and even more preferably 1 mass % or less. This is preferable because when the particulate water-absorbing agent composition according to the present invention is used in sanitary goods such as thin disposable diapers, the rough feeling of the particulate water-absorbing agent composition is reduced and the wearing comfort is improved.

[0187] (Mass Proportion of Particles with a Particle Diameter of 300 μm or More and Less than 850 μm) In one embodiment of the present invention, the mass proportion of particles with a particle diameter of 300 μm or more and less than 850 μm in the particulate water-absorbing agent composition is 50 mass % or more, preferably 55 mass % or more, and more preferably 60 mass % or more. As a result, the balance of the AAP, CRC, and SFC described above can be maintained.

[0188] (Mass Proportion of Particles with a Particle Diameter of Less than 150 μm) In one embodiment of the present invention, the mass proportion of particles with a particle diameter of less than 150 μm in the particulate water-absorbing agent composition is preferably 5 mass% or less, more preferably 4 mass% or less, even more preferably 3 mass% or less, and particularly preferably 2 mass% or less. As a result, the balance (equivalent) of the AAP, CRC, and SFC described above can be maintained. In addition, it is preferable that the mass proportion of particles with a particle diameter of less than 150 μm is equal to or less than the upper limit described above from the viewpoint of preventing deterioration of the working environment due to scattering of dust in places where the particulate water-absorbing agent composition is handled.

[0189] [3-3. Content of Nonionic Polymer in Particulate Water-Absorbent Agent Composition] The impact test causes particles constituting the surface layer of the particulate water-absorbent agent composition to peel off. Particle group b is composed of the peeled particles and particles less than 300 μm that were present before the impact test, and particle group a is composed of particles that remain after the particles constituting the surface layer have peeled off. Thus, particle group a is composed of particles that constitute the part other than the surface layer of the particulate water-absorbent agent composition. Furthermore, the content represented by C2 means the content of the polyalkylene glycol contained in the part other than the surface layer of the particulate water-absorbent agent composition, i.e., the interior. Furthermore, the value represented by C1-C2 means the amount of nonionic polymer present in the surface layer of the particulate water-absorbent agent composition, i.e., the surface. In a particulate water-absorbing agent composition that satisfies all of the above (1) to (4), the content represented by C1, i.e., the total content of the polyalkylene glycol present inside the particulate water-absorbing agent composition and the content of the nonionic polymer present on the surface of the particulate water-absorbing agent composition, is preferably within a range that includes the preferred ranges of each content described below, and is preferably 0.025 mass% or more, more preferably 0.03 mass% or more, relative to the mass of the solid content in the particulate water-absorbing agent composition. Furthermore, the content represented by C1 is preferably 0.55 mass% or less, more preferably 0.50 mass% or less, relative to the mass of the solid content in the particulate water-absorbing agent composition. In a particulate water-absorbing agent composition that satisfies all of the above (1) to (4), the content represented by C2, i.e., the content of the polyalkylene glycol present inside the particulate water-absorbing agent composition, is 0.005 mass% or more, preferably 0.01 mass% or more, more preferably 0.015 mass% or more, relative to the mass of the solid content in the particle group a. Furthermore, the content represented by C2 is 0.15 mass % or less, preferably 0.14 mass % or less, and more preferably 0.12 mass % or less, relative to the mass of the solid content in the particle group a. It is preferable that the content represented by C2 is equal to or more than the above-mentioned lower limit value, because the effect of improving the anti-caking performance of the particulate water-absorbing agent composition can be sufficiently exhibited.It is preferable that the content represented by C2 is equal to or less than the above-mentioned upper limit, since this prevents deterioration of anti-caking performance due to excessive inclusion of the polyalkylene glycol. In a particulate water-absorbing agent composition that satisfies all of the above (1) to (4), the content represented by C1-C2, i.e., the content of the nonionic polymer present on the surface of the particulate water-absorbing agent composition, is 0.02 mass% or more, preferably 0.023 mass% or more, and more preferably 0.025 mass% or more. Furthermore, it is preferable that the content represented by C1-C2 is 0.40 mass% or less, and 0.35 mass% or less. It is preferable that the content represented by C1-C2 is equal to or greater than the above-mentioned lower limit, since this allows the particulate water-absorbing agent composition to fully exhibit its effect of improving the anti-caking performance. It is preferable that the content represented by C1-C2 is equal to or less than the above-mentioned upper limit, from the viewpoint of preventing cost increases due to excessive use of the nonionic polymer. C1 and C2 can be measured by the methods shown in (A) to (E) below, specifically, by the methods described in the Examples. (A) A nonionic polymer aqueous solution having a known concentration is subjected to mass spectrometry by chromatography in advance to prepare a calibration curve. (B) 1 g of the particle group a or the particulate water-absorbing agent composition is placed in an appropriate container to prepare a measurement sample. (C) 1000 g of ultrapure water is added to the container containing the measurement sample and stirred to swell the measurement sample. Here, the "ultrapure water" means water having a specific resistance of 15 MΩ cm or more. (D) After (C), the supernatant liquid in the container that does not contain the swollen measurement sample is recovered by filtration. (E) The supernatant liquid recovered in (D) is analyzed by a liquid chromatography mass spectrometer under the same conditions as when preparing the calibration curve, and the value of C1 or C2 is calculated taking into consideration the calibration curve prepared in (A), the dilution ratio of the measurement sample with ultrapure water, and the solid content of the measurement sample.

[0190] [4] Absorbent Article The particulate water-absorbing agent composition manufactured by the manufacturing method according to one embodiment of the present invention may be included in an absorbent article. Therefore, one aspect of the present invention also includes an absorbent article. An absorbent article according to one embodiment of the present invention is an absorbent article manufactured by a manufacturing method for an absorbent article including an absorbent body containing a particulate water-absorbing agent composition, and the particulate water-absorbing agent composition manufactured by the manufacturing method for a water-absorbing agent according to one embodiment of the present invention described above is used as the particulate water-absorbing agent composition. In other words, an absorbent article according to one embodiment of the present invention is an absorbent article including the particulate water-absorbing agent composition according to one embodiment of the present invention.

[0191] In the present disclosure, the term "absorbent article" refers to an article that is placed against or in close proximity to the body of a wearer to absorb and contain various bodily exudates, such as urine, feces, and blood. Specifically, the absorbent article includes diapers and pants worn by babies, toddlers, and / or adults; absorbent inserts for diapers and pants; and feminine care absorbent articles such as sanitary napkins and panty liners.

[0192] The absorbent article may comprise a topsheet, a backsheet, an absorbent core, and optionally an absorbent-diffusion system, the absorbent core being disposed between the backsheet and the topsheet, and the optional absorbent-diffusion system being generally disposed between the absorbent core and the topsheet.

[0193] The particulate water-absorbing agent composition produced by the production method according to one embodiment of the present invention may be contained in an absorbent core of an absorbent article. The absorbent core may or may not contain other water-absorbing materials such as uncrosslinked cellulose fibers (pulp fibers). The absorbent core may contain at least 60% by weight, or at least 75% by weight, or at least 85% by weight, or at least 95% by weight, or at least 98% by weight, or 100% by weight of the water-absorbing agent.

[0194] "Disposable diaper" and "pants" refer to absorbent articles worn by infants, toddlers, and incontinent (adult) individuals around the lower torso, encircling the waist and legs, and adapted, inter alia, to receive and contain urinary and fecal exudates. In pants, the longitudinal edges of the first and second waist regions (those corresponding to the front and back waist regions) are attached to one another to pre-form waist and leg openings. Pants are placed in position on a wearer by inserting the wearer's legs into the leg openings and sliding the pant absorbent article into position about the wearer's lower torso. Pants may be pre-formed by any suitable technique, including, but not limited to, joining portions of the absorbent article together using reattachable and / or non-reattachable attachments (e.g., stitching, welding, adhesives, adhesive bonds, fasteners, etc.). Pants can be pre-formed anywhere along the circumference of the article (e.g., side fastening, front waist fastening). In a disposable diaper, the waist opening and leg openings are formed only when the diaper is applied to a wearer by (releasably) attaching the longitudinal edges of the first and second waist regions to each other on both sides with a suitable fastening system. Suitable fastening systems may include, for example, tape tabs including hook material and cooperating landing areas (e.g., a nonwoven web providing the loops in a hook-and-loop fastening system).

[0195] Disposable diapers and pants may include elastic leg cuffs and barrier leg cuffs that improve containment of liquids and other body exudates, particularly in the area of ​​the leg openings. Typically, each leg cuff and barrier cuff includes one or more elastic strings.

[0196] "Feminine care absorbent articles" are personal care products used by women to absorb and contain menstrual blood, vaginal discharge, and other products resulting from the female bodily functions. Feminine care absorbent articles include panty liners and sanitary napkins.

[0197] One aspect of the present invention may also include a method for manufacturing an absorbent article. The method for manufacturing an absorbent article is a method for manufacturing an absorbent article including an absorbent body containing a particulate water-absorbing agent composition, and is a manufacturing method using, as the particulate water-absorbing agent composition, a particulate water-absorbing agent composition manufactured by the method for manufacturing a particulate water-absorbing agent composition according to one embodiment of the present invention described above.

[0198] The method for manufacturing the absorbent article is not particularly limited as long as it is a method using a particulate water-absorbing agent composition manufactured by the method for manufacturing a particulate water-absorbing agent composition according to one embodiment of the present invention described above, and may include, for example, a step of manufacturing an absorbent core containing the particulate water-absorbing agent composition, a step of arranging the absorbent core between a back sheet and a top sheet, etc.

[0199] The present invention includes the following aspects and embodiments 1 to 13.

[0200] 1. A method for producing a particulate water-absorbing agent composition containing a poly(meth)acrylic acid (salt)-based water-absorbing resin, comprising: a monomer aqueous solution preparation step of preparing a (meth)acrylic acid (salt)-based monomer aqueous solution; a polymerization step of polymerizing the (meth)acrylic acid (salt)-based monomer aqueous solution; an optional hydrogel crushing step of gel-crushing a hydrogel-like crosslinked polymer produced during or after polymerization; a drying step of drying the particulate hydrogel; an optional crushing step and optional classification step of crushing and classifying the dried polymer; and a surface crosslinking step of surface-crosslinking a water-absorbent resin before surface crosslinking, wherein the particulate hydrogel is obtained through a polymerization step or both of the polymerization step and the hydrogel crushing step, the dried polymer is obtained through a drying step, and the water-absorbent resin before surface crosslinking is the dried polymer or a water-absorbent resin obtained by crushing and / or classifying the dried polymer, a method for producing a particulate water-absorbing agent composition containing a poly(meth)acrylic acid (salt)-based water-absorbing resin, the method comprising: adding a water-soluble polyalkylene glycol having a mass-average molecular weight of 3,000 or less in an amount of 0.01 mass % to 0.25 mass % relative to the total mass of the monomers contained in the (meth)acrylic acid (salt)-based monomer aqueous solution in at least any step selected from the monomer aqueous solution preparation step, the polymerization step, and an optional hydrous gel crushing step; and adding, after the surface cross-linking step, a nonionic polymer having a polyalkylene glycol chain in its structure and having a mass-average molecular weight of 300 to 15,000 in an amount of 0.02 mass % to 0.40 mass % relative to the surface-cross-linked water-absorbing resin.

[0201] 2. The method according to 1., wherein the particulate water-absorbing agent composition has a surface tension of 45 mN / m or more.

[0202] 3. The manufacturing method according to 1. or 2., wherein the particulate water-absorbing agent composition has an absorbency against pressure (AAP) of 20 g / g or more under a pressure of 0.7 psi.

[0203] 4. The method according to any one of 1. to 3., wherein the particulate water-absorbing agent composition has a fixed height absorption (FHA) of 20 g / g or more at a height of 20 cm.

[0204] 5. A particulate water-absorbing agent composition containing a poly(meth)acrylic acid (salt)-based water-absorbing resin as a main component and a nonionic polymer having a polyalkylene glycol chain in its structure, with a mass ratio of particles having a particle size of 300 μm or more and less than 850 μm of 50 mass % or more, wherein: (a) the nonionic polymer contained in the particulate water-absorbing agent composition is designated as A1 and its content is designated as C1; (b) the particulate water-absorbing agent composition is subjected to a predetermined impact test; (c) the particulate water-absorbing agent composition subjected to the impact test is sieved using a JIS standard sieve into a particle group a having a particle size of 300 μm or more and a particle group b having a particle size of less than 300 μm; and (d) when the nonionic polymer present in the particle group a is designated as A2 and its content is designated as C2, the particulate water-absorbing agent composition satisfies all of the following (1) to (4): (1) A1 is a water-soluble polyalkylene glycol having a mass average molecular weight of 3,000 or less, and a nonionic polymer having a polyalkylene glycol chain in its structure and a mass average molecular weight of 300 to 15,000; (2) A2 is a water-soluble polyalkylene glycol having a mass average molecular weight of 3,000 or less; (3) C2 is 0.005% by mass or more and 0.15% by mass or less; (4) C1-C2 is 0.02% by mass or more and 0.40% by mass or less.

[0205] 6. The particulate water-absorbing agent composition according to 5., wherein the particulate water-absorbing agent composition has a surface tension of 45 mN / m or more.

[0206] 7. The particulate water-absorbing agent composition according to 5. or 6., wherein the particulate water-absorbing agent composition has an absorbency against pressure (AAP) of 20 g / g or more under a pressure of 0.7 psi.

[0207] 8. The particulate water-absorbing agent composition according to any one of 5. to 7., wherein the particulate water-absorbing agent composition has a fixed height absorption (FHA) of 20 g / g or more at a height of 20 cm.

[0208] 9. The particulate water-absorbing agent composition according to any one of 5. to 8., wherein the particulate water-absorbing agent composition has a CRC of 25 g / g or more.

[0209] 10. The particulate water-absorbing agent composition according to any one of 5. to 9., wherein the particulate water-absorbing agent composition has a moisture absorption blocking ratio <1> (B.R.<1>) of 80 mass % or less.

[0210] 11. The particulate water-absorbing agent composition according to any one of 5. to 10., wherein the particulate water-absorbing agent composition has a mass average particle diameter (D50) of 300 μm or more and 600 μm or less.

[0211] 12. A particulate water-absorbing agent composition according to any one of 5. to 11., wherein the mass ratio of particles having a particle diameter of 850 μm or more in the particulate water-absorbing agent composition is 3 mass% or less, and the mass ratio of particles having a particle diameter of less than 150 μm is 5 mass% or less.

[0212] 13. An absorbent article containing a particulate water-absorbing agent composition, the absorbent article comprising the particulate water-absorbing agent composition according to any one of 5. to 12. as the particulate water-absorbing agent composition.

[0213] The present invention will be described below with reference to examples and comparative examples, but the present invention should not be construed as being limited by these examples. The physical properties described in the claims and examples of the present invention are obtained by the measurements and evaluations described below. Unless otherwise specified regarding room temperature and humidity, measurements were taken under conditions of room temperature (23±2°C) and a relative humidity of 40±10% RH.

[0214] [Measurement and evaluation of physical properties of water-absorbent resin and particulate water-absorbing agent composition] Measurement and evaluation of physical properties of the water-absorbent resin obtained in the following production examples and / or the particulate water-absorbing agent composition obtained in the following examples and comparative examples were carried out by the following methods.

[0215] (D50 (mass average particle diameter) of particulate hydrogel) The mass average particle diameter (D50) of the pulverized particulate hydrogel in terms of solid content was measured by the following method.

[0216] 20 g of particulate hydrogel (solid content α% by mass) at a temperature of 20°C to 25°C was added to 500 g of a 20% by mass aqueous sodium chloride solution (hereinafter referred to as "aqueous EMAL solution") containing 0.08% by mass of EMAL 20C (surfactant, manufactured by Kao Corporation) to prepare a dispersion, which was stirred at 300 rpm for 1 hour using a cylindrical stirrer tip having a length of 50 mm and a cross-sectional diameter of 7 mm (a cylindrical polypropylene container (capacity approximately 1.14 L) having a height of 21 cm and a bottom diameter of 8 cm was used).

[0217] After stirring, the dispersion was poured into the center of a JIS standard sieve (diameter 21 cm, sieve openings: 8 mm / 4 mm / 2 mm / 1 mm / 0.60 mm / 0.30 mm / 0.15 mm / 0.075 mm) stacked on a rotating plate. After washing out all the particulate hydrogel onto the sieve using 100 g of an aqueous emasculated ammonium nitrate solution, 6,000 g of the aqueous emasculated ammonium nitrate solution was poured from above into the water injection range (50 cm) using a shower (72 holes, liquid volume: 6.0 L / min) from a height of 30 cm while rotating the sieve by hand (20 rpm). ２ The particulate hydrous gel was then evenly poured onto the sieve so that it was distributed over the entire surface, and the particulate hydrous gel was classified. The particulate hydrous gel on the first sieve was drained for about 2 minutes and then weighed. The second and subsequent sieves were also classified in the same manner, and the particulate hydrous gel remaining on each sieve after draining was weighed.

[0218] From the mass of the particulate hydrogel remaining on each sieve, the mass proportion X (unit: mass%) relative to the total particulate hydrogel was calculated using the following formula (1). The mesh size R(α) (unit: mm) of the sieve used for the particulate hydrogel with a solids content of α% by mass remaining on the sieve was calculated according to the following formula (2). X and R(α) of the particulate hydrogel remaining on each sieve were plotted on logarithmic probability paper to create a graph (particle size distribution) showing the relationship between the cumulative mass ratio of X and R(α). From this graph, the particle size corresponding to a residual percentage of 50% by mass was read as the mass average particle size (D50) of the particulate hydrogel.

[0219] X=(w / W)×100 Formula (1) R(α)=(20 / W) １／３×r Formula (2) Here, X, w, W, R(α), and r mean the following values: X: mass % (unit: mass %) of the particulate hydrogel remaining on each sieve after classification and draining; w: each mass (unit: g) of the particulate hydrogel remaining on each sieve after classification and draining; W: total mass (unit: g) of the particulate hydrogel remaining on each sieve after classification and draining; R(α): sieve opening when the particulate hydrogel converted into a solid content α% by mass is classified (unit: mm: calculated value); r: JIS standard sieve opening (unit: mm: measured value) when the particulate hydrogel swollen in a 20% by mass sodium chloride aqueous solution containing 0.08% by mass Emar 20C (surfactant, manufactured by Kao Corporation) is classified.

[0220] (σζ (logarithmic standard deviation of particle size distribution) of particulate hydrogel) The mass% of the particulate hydrogel remaining on each sieve was calculated using the same method as for D50 (mass average particle size) of the particulate hydrogel, and the particle size distribution of the particulate hydrogel was plotted on logarithmic probability paper. From the plot, the particle sizes of cumulative on-sieve %R = 84.1 mass% (referred to as X1) and cumulative on-sieve %R = 15.9 mass% (referred to as X2) were determined, and σζ (logarithmic standard deviation of particle size distribution) was calculated based on the following formula (3).

[0221] σζ=0.5×ln(X2 / X1) Equation (3) A smaller value of σζ means a narrower particle size distribution.

[0222] (Blocking Ratio after Moisture Absorption <1> (B.R.<1>)) The blocking ratio after moisture absorption <1> (B.R.<1>) of the water-absorbing resin and the particulate water-absorbing agent composition was measured by the following method.

[0223] Specifically, 2.0 g of a water-absorbent resin or a particulate water-absorbing agent composition was uniformly spread in a cylindrical aluminum cup having a bottom diameter of 52 mm, and then allowed to stand for 40 minutes in a thermo-hygrostat (manufactured by Espec Corporation; Model: SH-641) at a temperature of 40°C and a relative humidity of 75±5%RH. After 40 minutes had elapsed, the water-absorbent resin or the particulate water-absorbing agent composition in the aluminum cup was gently transferred onto a JIS standard sieve (The IIDA Testing Sieve: inner diameter 80 mm) with an opening of 2000 μm (JIS 8.6 mesh), and classified for 40 seconds under the conditions of room temperature (20 to 25°C) and a relative humidity of 50%RH using a low-tap type sieve shaker (manufactured by Iida Seisakusho Co., Ltd., Model ES-65 sieve shaker; rotation speed 230 rpm, impact number 130 rpm). The mass W1 (g) of the water-absorbent resin or particulate water-absorbing agent composition remaining on the JIS standard sieve and the mass W2 (g) of the water-absorbent resin or particulate water-absorbing agent composition that passed through the JIS standard sieve were measured, and the moisture absorption blocking ratio <1> was calculated by the following formula (4): Moisture absorption blocking ratio <1> (mass %) = {W1 / (W1+W2)} × 100 Formula (4) The lower the value of the moisture absorption blocking ratio <1>, the more excellent the anti-caking performance of the water-absorbent resin or particulate water-absorbing agent composition.

[0224] (Moisture absorption blocking ratio <2> (B.R. <2>)) The moisture absorption blocking ratio <2> (B.R. <2>) of the water-absorbent resin and the particulate water-absorbing agent composition was measured by the same procedure as in the moisture absorption blocking ratio <1>, except that the standing time in the thermo-hygrostat was changed from 40 minutes to 1 hour.

[0225] (ΔB.R.) obtained by subtracting the B.R. of the particulate water-absorbing agent composition from the B.R. of the water-absorbent resin after surface cross-linking) The ΔB.R. of the particulate water-absorbing agent composition was calculated by the following formula (5).

[0226] ΔB.R. (mass%)=W5−W6 Formula (5) Here, W5 and W6 have the following values.

[0227] W5: B.R. (unit: mass%) of the surface-crosslinked water-absorbent resin used in producing the particulate water-absorbing agent composition W6: B.R. (unit: mass%) of the particulate water-absorbing agent composition

[0228] It should be noted that the larger the ΔB.R., the higher the effect of improving the anti-caking performance due to the additive added to the water absorbent resin after surface cross-linking. Furthermore, in order to calculate an appropriate ΔB.R., W5 and W6 are preferably 1 to 99% by mass. For example, when W5 is 0% by mass, even if the anti-caking performance is improved by the additive added to the water absorbent resin after surface cross-linking, W6 is 0% by mass, and as a result, ΔB.R. is calculated to be 0% by mass. That is, the effect of improving the anti-caking performance due to the additive added to the water absorbent resin after surface cross-linking cannot be appropriately expressed by ΔB.R., which is not preferable. Furthermore, for example, when W5 is 20% by mass and W6 is 0% by mass, ΔB.R. is calculated to be 20% by mass, but it is not preferable because it is not possible to determine whether the original effect of improving the anti-caking performance due to the additive added to the water absorbent resin after surface cross-linking is 20% by mass or more. Therefore, when calculating the B.R. by the method of B.R. <1>, When measuring W5 and W6, if either or both of W5 and W6 are not 1 to 99% by mass, it is preferable to measure B.R. by the method of B.R. <2>. Furthermore, when measuring B.R. by either method of B.R. <1> or B.R. <2>, if either or both of W5 and W6 are not 1 to 99% by mass, it is preferable to find a method that makes W5 and W6 1 to 99% by mass, measure B.R. by that method, and calculate ΔB.R. Note that when comparing the improving effect of an additive on anti-caking performance by ΔB.R., the ΔB.R. is calculated using B.R. obtained by the same measurement method.

[0229] (Absorption Capacity Under Load (AAP)) The AAP of the water-absorbent resin and the particulate water-absorbing agent composition was measured in accordance with NWSP 242.0. R2(19). Specifically, a large excess of a 0.9% by mass aqueous solution of sodium chloride was used, and 0.9 g of the water-absorbent resin or the particulate water-absorbing agent composition was subjected to pressure of 4.83 kPa (49 g / cm) for 1 hour. ２ After swelling under a pressure of 0.7 psi, the absorbency against pressure (AAP) (unit: g / g) was measured.

[0230] (Fixed Height Absorption Value (FHA) at a Height of 20 cm) The FHA of the water-absorbent resin and the particulate water-absorbing agent composition was measured in accordance with the measurement method described in US Patent Application Publication No. 2005 / 0003191.

[0231] (Surface Tension) The surface tension of the particulate water-absorbing agent composition was measured by the following method.

[0232] First, 40 ml of a 0.9% by mass sodium chloride aqueous solution adjusted to 23°C to 24°C was placed in a thoroughly washed 50 ml beaker, and the surface tension of the 0.9% by mass sodium chloride aqueous solution was measured using a surface tensiometer (K11 automatic surface tensiometer, manufactured by KRUSS). In this measurement, the surface tension value must be in the range of 72 mN / m to 74 mN / m. Next, a thoroughly washed cylindrical stirring bar with a length of 25 mm and a cross-sectional diameter of 7 mm and 0.5 g of the particulate water-absorbing agent composition were placed in the beaker containing 40 ml of the 0.9% by mass sodium chloride aqueous solution adjusted to 23°C to 24°C after the surface tension measurement, and the mixture was stirred at 350 rpm for 3 minutes. After 3 minutes, the stirring was stopped, and the mixture was allowed to stand for 2 minutes to allow the water-absorbed particulate water-absorbing agent composition to settle. The surface tension of the supernatant was then measured again by the same procedure. In this measurement, a plate method using a platinum plate was adopted, and the plate was thoroughly washed with deionized water and heated and washed with a gas burner before each measurement.

[0233] (Cell absorption capacity (CRC)) The CRC of the water-absorbent resin and the particulate water-absorbing agent composition was measured in accordance with NWSP 241.0. R2 (19). Specifically, 0.2 g of the water-absorbent resin or the particulate water-absorbing agent composition was placed in a nonwoven fabric bag, and then immersed in a large excess of a 0.9 mass % sodium chloride aqueous solution for 30 minutes to allow the water-absorbent resin or the particulate water-absorbing agent composition to freely swell. Thereafter, the water-absorbent resin or the particulate water-absorbing agent composition was dehydrated for 3 minutes using a centrifuge (250 G), and then the cell absorption capacity (CRC) (unit: g / g) was measured.

[0234] (Saline Flow Conductivity (SFC)) The saline flow conductivity (SFC) of the water-absorbent resin and the particulate water-absorbing agent composition (unit: × 10 －７ cm ３ The viscosity (sec / g) was measured in accordance with the measurement method described in US Pat. No. 5,669,894.

[0235] Specifically, 1.500 g of a water-absorbent resin or a particulate water-absorbing agent composition was uniformly placed in a container, and then the water-absorbent resin or the particulate water-absorbing agent composition was immersed in artificial urine and pressurized at a pressure of 2.07 kPa to cause the water-absorbent resin or the particulate water-absorbing agent composition to swell. The artificial urine was prepared by mixing 0.25 g of calcium chloride dihydrate, 2.0 g of potassium chloride, 0.50 g of magnesium chloride hexahydrate, 2.0 g of sodium sulfate, 0.85 g of ammonium dihydrogen phosphate, 0.15 g of diammonium hydrogen phosphate, and 994.25 g of pure water.

[0236] Sixty minutes after applying pressure, the height (cm) of the gel layer, which was the swollen water-absorbent resin or particulate water-absorbing agent composition, was recorded. Next, 0.69% by mass saline solution was passed through the gel layer while the gel layer was pressurized at a pressure of 2.07 kPa. The room temperature during this process was adjusted to 20-25°C. Using a balance and a computer, the amount of saline solution passing through the gel layer was recorded at 20-second intervals, and the flow rate Fs (T) of the passing saline solution was measured. The flow rate Fs (T) was calculated by dividing the mass (g) of the passing saline solution, which increased every 20 seconds, by the passage time (s). The time Ts was defined as the time at which the hydrostatic pressure of the saline solution became constant and a stable flow rate was obtained. Using data measured over a 10-minute period starting from this Ts, the flow rate Fs (T = 0) was calculated. That is, Fs (T) was plotted against time, and Fs (T = 0) was calculated based on the results obtained by the least squares method. Fs (T=0) is the initial flow rate (g / s) of saline solution passing through the gel layer, and the saline flow conductivity (SFC) was calculated by the following equation (6):

[0237] SFC={Fs(T=0)×L ０} / (ρ×A×ΔP) Equation (6) Here, L ０ , ρ, A, and ΔP have the following values.

[0238] L ０ : height of gel layer (unit: cm) ρ: density of saline solution (unit: g / cm ３ ) A: Cross-sectional area of ​​the gel layer (unit: cm ２ ) ΔP: Hydrostatic pressure applied to the gel layer (unit: dyne / cm ２ ).

[0239] (Free Swelling Rate (FSR)) The free swelling rate (FSR) of the water-absorbent resin and the particulate water-absorbing agent composition is the rate (g / (g·s)) at which 1.0 g of the water-absorbent resin or the particulate water-absorbing agent composition absorbs 20 g of a 0.9 mass % sodium chloride aqueous solution, and was measured in accordance with the measurement method described in WO 2009 / 016055.

[0240] (Quantitative Analysis of Nonionic Polymers by LC-MS) (Pretreatment 1: Impact Test) 30 g of the particulate water-absorbing agent composition obtained in each Example and 10 g of glass beads with a diameter of 6 mm (soda-lime glass beads for precision fractional distillation filling) were placed in a glass container (Mayonnaise 225, manufactured by Nippon Yamamura Glass Co., Ltd.) with a diameter of 6 cm and a height of 11 cm. The container was then sealed using a resin inner and outer lids for the container (for example, the inner and outer lids included in the Mayonnaise Bottle PP Cap Set, manufactured by TOP Co., Ltd., product code: 604-003). The particulate water-absorbing agent composition was then pulverized using a paint shaker (Toyo Seiki Seisakusho Co., Ltd., test disperser: product No. 488). The pulverization was performed by shaking the paint shaker at 800 rpm. Details of the paint shaker are described in JP-A-9-235378. The shaking time was adjusted for each particulate water-absorbing agent composition to be used so as to satisfy the following formula (7).

[0241] 0.2<(mass of particle group a) / (total mass of particle group a and particle group b)<0.3 Equation (7) Subsequently, after the shaking, the glass beads were removed using a JIS standard sieve with 2 mm openings.

[0242] (Pretreatment 2: Sieving) The particulate water-absorbing agent composition after pulverization obtained in the impact test of Pretreatment 1 was sieved using a JIS standard sieve with a mesh size of 300 μm into a particle group a having a particle size of 300 μm or more and a particle group b having a particle size of less than 300 μm.

[0243] (Qualitative and Quantitative Analysis: Nonionic Polymer) 1 g of the particle group a obtained by the sieving and 1,000 g of ultrapure water were placed in a cylindrical polypropylene container (volume approximately 1.14 L) with a height of 21 cm and a bottom diameter of 8 cm, and the mixture was stirred at 500 rpm for 1 hour using a cylindrical stirrer tip with a length of 50 mm and a cross-sectional diameter of 7 mm. After the stirring, the supernatant liquid, which did not contain the swollen particulate water-absorbing agent composition, was filtered using a sample pretreatment filter (GL Chromatodisc, 25A, 0.2 μm, Cat. No. 5040-28502), and then the nonionic polymer contained in the particle group a was qualitatively and quantitatively analyzed using a liquid chromatography mass spectrometer (LC-MS).

[0244] In addition, when qualitatively and quantitatively determining the nonionic polymer contained in the particulate water-absorbing agent composition before the impact test, the pre-treatment 1: impact test and pre-treatment 2: sieving were not performed, and the procedure described in "Qualitative and quantitative determination: nonionic polymer" was performed, except that particle group a was replaced with the particulate water-absorbing agent composition.

[0245] LC-MS was performed under the following measurement conditions. Eluent: A solution obtained by mixing an ultrapure aqueous solution containing 0.1% by mass of formic acid and 0.01 mol / L of ammonium formate with an acetonitrile solution containing 0.1% by mass of formic acid at a volume ratio of 6:4. Column: InertSustain C18 (particle size: 2 μm, inner diameter: 2.1 mm, length: 100 mm, Cat. No. 5020-14354 / GL Sciences Inc.). Column temperature: 40°C. Flow rate: 0.35 ml / min. Detector: RI, UV, QDa.

[0246] The contents of the nonionic polymer in the particle group a and in the particulate water-absorbing agent composition before the impact test were determined in consideration of the dilution ratio of the particle group a or the particulate water-absorbing agent composition with ultrapure water, using a calibration curve obtained by measuring a nonionic polymer standard solution of a known concentration as an external standard.

[0247] The content of the nonionic polymer in the particle group a and in the particulate water-absorbing agent composition before the impact test was a value corrected for moisture content, i.e., a value converted to the solid content in the particle group a or the particulate water-absorbing agent composition before the impact test, which is calculated from the solid content amount described below.

[0248] (Solid Content) The solid content of the particulate water-absorbing agent composition was measured by the following method.

[0249] Approximately 1 g of the particulate water-absorbing agent composition was weighed out (mass: W7 (g)) and uniformly dispersed in a cylindrical aluminum cup (mass: W8 (g)) with a bottom diameter of 52 mm. The cup was then left to stand in a windless dryer at 180°C for 3 hours to dry. After drying, the total mass (mass: W9 (g)) of the particulate water-absorbing agent composition and the aluminum cup was measured. The solid content of the particulate water-absorbing agent composition was calculated using the following formula (8).

[0250] Solid content (mass%) = {(W9-W8) / W7}×100 Formula (8)

[0251] The relationship between the solid content and the moisture content is as shown in the following formula (9): Solid content (mass%)=100−Moisture content (mass%) Formula (9)

[0252] [Production Example 1] (Aqueous Monomer Solution Preparation Step) 422.0 parts by mass of acrylic acid, 173.9 parts by mass of a 48.5% by mass aqueous sodium hydroxide solution, 2.5 parts by mass of polyethylene glycol diacrylate (average molecular weight: 523), 1.3 parts by mass of a 2.0% by mass aqueous solution of diethylenetriaminepentaacetic acid trisodium, and 403.3 parts by mass of deionized water were charged into a 2 L polypropylene container and mixed to prepare an aqueous monomer solution (1'). The liquid temperature of the aqueous monomer solution (1') exceeded 40°C due to the heat of neutralization and heat of dissolution generated during the mixing process.

[0253] (Polymerization Step) Next, the aqueous monomer solution (1') was cooled with stirring, and when the liquid temperature reached 40°C, 178.7 parts by mass of a 48.5% by mass aqueous sodium hydroxide solution adjusted to 40°C was added to the aqueous monomer solution (1') over approximately 20 seconds in an open-to-air state and mixed (starting the second-stage neutralization). Thus, the aqueous monomer solution (1) was prepared. At this time, the liquid temperature of the aqueous monomer solution (1) rose to approximately 78°C due to the heat of neutralization and heat of dissolution generated during the mixing process. Although precipitates were observed immediately after starting to mix the aqueous sodium hydroxide solution with the aqueous monomer solution (1'), they gradually dissolved, and the prepared aqueous monomer solution (1) became a transparent, homogeneous solution.

[0254] Next, under stirring, nitrogen gas was introduced into the aqueous monomer solution (1) using a gas filter tube (manufactured by TOP Corporation, particle number #4) under conditions of a pressure of 0.1 MPa and a flow rate of 0.1 L / min for 5 seconds. Subsequently, 18.4 parts by mass of a 4.5 mass% aqueous sodium persulfate solution was added to the aqueous monomer solution (1) into which nitrogen gas had been introduced. Thereafter, the aqueous monomer solution (1) was immediately poured into a stainless steel bat-shaped container (bottom 340 mm x 340 mm, height 25 mm, inner surface: Teflon (registered trademark) coated) in an open-to-air state. The time from the start of the second-stage neutralization to the pouring of the aqueous monomer solution (1) into the bat-shaped container was 65 seconds. The bat-shaped container was preheated to a surface temperature of 50°C using a hot plate (NEO HOTPLATE HI-1000 / manufactured by Iuchi Seieido Co., Ltd.) before pouring the aqueous monomer solution (1).

[0255] The polymerization reaction started within 1 minute after the aqueous monomer solution (1) was poured into the batt-shaped container. During the polymerization reaction, the polymerization of the aqueous monomer solution (1) proceeded while expanding and foaming in all directions and generating steam. The resulting polymer then shrunk to a size slightly larger than the bottom of the batt-shaped container. Two minutes after the start of the polymerization reaction, the resulting polymer, a hydrogel (1), was removed from the batt-shaped container. This series of operations was carried out in an open-to-air state.

[0256] (Hydrogel Crushing Step) Next, the hydrogel (1) obtained by the polymerization reaction was cut into pieces each having a mass of about 60 g, and then the gel was crushed using a meat chopper (HL-G22SN, plate hole diameter 6.0 mm / manufactured by Remacom Co., Ltd.) to obtain a particulate hydrogel (1). The amount of the hydrogel (1) added was approximately 360 g / min, and in parallel with the addition of the hydrogel (1), deionized water adjusted to 90 ° C. was added to the meat chopper at a rate of 50 g / min to crush the gel.

[0257] The particulate hydrogel (1) had a D50 (mass average particle diameter) of 400 μm and a σζ (logarithmic standard deviation of particle size distribution) of 0.93.

[0258] (Drying step) Next, the particulate hydrogel (1) was spread on a wire mesh with a mesh size of 300 μm and placed in a hot air dryer. Thereafter, the particulate hydrogel (1) was dried by passing hot air at 190° C. for 30 minutes to obtain a dried polymer (1). There was no undried material in the dried polymer (1).

[0259] (Classification step) Next, the dried polymer (1) was put into a roll mill (WML type roll crusher, manufactured by Inokuchi Giken Co., Ltd.) and crushed, and then classified using two types of JIS standard sieves with mesh sizes of 710 μm and 150 μm. By this operation, an irregularly crushed water absorbent resin (1) before surface crosslinking, which passed through the sieve with mesh size of 710 μm and remained on the sieve with mesh size of 150 μm, was obtained.

[0260] (Surface Cross-Linking Step) Next, an aqueous solution of a surface cross-linking agent consisting of 0.2 parts by mass of 1,6-hexanediol, 0.4 parts by mass of triethylene glycol, and 3.0 parts by mass of deionized water was sprayed and added to 100 parts by mass of the water absorbent resin (1) before surface cross-linking, and mixed uniformly. Thereafter, the obtained mixture was heat-treated at 210°C for 40 minutes, thereby carrying out surface cross-linking. Next, the heat-treated mixture was classified using two types of JIS standard sieves with mesh sizes of 710 μm and 150 μm. By this operation, a surface-cross-linked water absorbent resin (1) was obtained, which passed through a sieve with a mesh size of 710 μm and remained on a sieve with a mesh size of 150 μm. The physical properties of the obtained surface-cross-linked water absorbent resin (1) are shown in Table 1.

[0261] [Production Example 2] A surface-crosslinked water-absorbent resin (2) was obtained by performing the same operation as in Production Example 1, except that the amount of a 2.0 mass% diethylenetriaminepentaacetic acid trisodium aqueous solution and the amount of deionized water were changed to 2.6 parts by mass and 400.5 parts by mass, and 1.6 parts by mass of a 50 mass% malic acid aqueous solution was additionally added in the monomer aqueous solution preparation step of Production Example 1. Various physical properties of the obtained surface-crosslinked water-absorbent resin (2) are shown in Table 1.

[0262] The particulate hydrogel (2) obtained in the hydrogel crushing step had a D50 (mass average particle diameter) of 405 μm and a σζ (logarithmic standard deviation of particle size distribution) of 0.95.

[0263] [Production Example 3] A surface-crosslinked water absorbent resin (3) was obtained by performing the same operation as in Production Example 1, except that the surface crosslinking agent aqueous solution to be used in the surface crosslinking step of Production Example 1 was changed to a surface crosslinking agent aqueous solution containing 0.4 part by mass of ethylene carbonate, 0.7 part by mass of propylene glycol, and 2.9 parts by mass of deionized water. Various physical properties of the obtained surface-crosslinked water absorbent resin (3) are shown in Table 1.

[0264] The particulate hydrogel (3) obtained in the hydrogel crushing step had a D50 (mass average particle diameter) of 400 μm and a σζ (logarithmic standard deviation of particle size distribution) of 0.93.

[0265] [Production Example 4] The same operation as in Production Example 1 was carried out, except that in the monomer aqueous solution preparation step in Production Example 1, deionized water was changed to 403.1 parts by mass and 0.2 parts by mass of polyethylene glycol 600 (mass average molecular weight 600, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was additionally added, to obtain a surface-crosslinked water-absorbent resin (4). The proportion of polyethylene glycol 600 added relative to the total mass of the monomers contained in the aqueous monomer solution was 0.04% by mass. The physical properties of the obtained surface-crosslinked water-absorbent resin (4) are shown in Table 1.

[0266] The particulate hydrogel (4) obtained in the hydrogel crushing step had a D50 (mass average particle diameter) of 390 μm and a σζ (logarithmic standard deviation of particle size distribution) of 0.92.

[0267] [Production Example 5] The same operation as in Production Example 1 was carried out, except that in the monomer aqueous solution preparation step in Production Example 1, deionized water was changed to 402.6 parts by mass and 0.7 parts by mass of polyethylene glycol 600 (mass average molecular weight 600, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was additionally added, to obtain a surface-crosslinked water-absorbent resin (5). The proportion of polyethylene glycol 600 added relative to the total mass of the monomers contained in the aqueous monomer solution was 0.14% by mass. The physical properties of the obtained surface-crosslinked water-absorbent resin (5) are shown in Table 1.

[0268] The particulate hydrogel (5) obtained in the hydrogel crushing step had a D50 (mass average particle diameter) of 395 μm and a σζ (logarithmic standard deviation of particle size distribution) of 0.91.

[0269] [Production Example 6] The same operation as in Production Example 4 was performed, except that the polyethylene glycol used in the monomer aqueous solution preparation step in Production Example 4 was changed to 0.2 part by mass of polyethylene glycol 400 (mass average molecular weight 400, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and the surface cross-linking agent aqueous solution used in the surface cross-linking step was changed to the surface cross-linking agent aqueous solution containing 0.4 part by mass of ethylene carbonate, 0.7 part by mass of propylene glycol, and 2.9 parts by mass of deionized water, which was used in Production Example 3, to obtain a surface-cross-linked water absorbent resin (6). The addition ratio of polyethylene glycol 400 to the total mass of the monomers contained in the aqueous monomer solution was 0.04% by mass. The physical properties of the obtained surface-cross-linked water absorbent resin (6) are shown in Table 1.

[0270] The particulate hydrogel (6) obtained in the hydrogel crushing step had a D50 (mass average particle diameter) of 393 μm and a σζ (logarithmic standard deviation of particle size distribution) of 0.95.

[0271] [Production Example 7] The same operation as in Production Example 6 was carried out, except that in the step of preparing an aqueous monomer solution in Production Example 6, the polyethylene glycol used was changed to 0.2 parts by mass of polyethylene glycol 1000 (mass average molecular weight 1000, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), to obtain a surface-crosslinked water-absorbent resin (7). The proportion of polyethylene glycol 1000 added relative to the total mass of the monomers contained in the aqueous monomer solution was 0.04% by mass. The physical properties of the obtained surface-crosslinked water-absorbent resin (7) are shown in Table 1.

[0272] The particulate hydrogel (7) obtained in the hydrogel crushing step had a D50 (mass average particle diameter) of 398 μm and a σζ (logarithmic standard deviation of particle size distribution) of 0.92.

[0273] [Production Example 8] The same operation as in Production Example 6 was carried out, except that in the monomer aqueous solution preparation step in Production Example 6, the polyethylene glycol used was changed to 0.2 parts by mass of polyethylene glycol 2000 (mass average molecular weight 2000, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), to obtain a surface-crosslinked water-absorbent resin (8). The proportion of polyethylene glycol 2000 added relative to the total mass of the monomers contained in the aqueous monomer solution was 0.04% by mass. The physical properties of the obtained surface-crosslinked water-absorbent resin (8) are shown in Table 1.

[0274] The particulate hydrogel (8) obtained in the hydrogel crushing step had a D50 (mass average particle diameter) of 396 μm and a σζ (logarithmic standard deviation of particle size distribution) of 0.94.

[0275] [Production Example 9] In the preparation step of the aqueous monomer solution of Production Example 4, the amount of 2.0 mass% diethylenetriaminepentaacetic acid trisodium aqueous solution was changed to 2.6 parts by mass, and deionized water was changed to 400.2 parts by mass, and 1.6 parts by mass of 50 mass% malic acid aqueous solution was additionally added, so as to obtain a surface-crosslinked water-absorbent resin (9) by the same operation as in Production Example 4. The proportion of polyethylene glycol 600 added relative to the total mass of the monomers contained in the aqueous monomer solution was 0.04 mass%. The physical properties of the obtained surface-crosslinked water-absorbent resin (9) are shown in Table 1.

[0276] The particulate hydrogel (9) obtained in the hydrogel crushing step had a D50 (mass average particle diameter) of 389 μm and a σζ (logarithmic standard deviation of particle size distribution) of 0.90.

[0277] [Production Example 10] (Aqueous Monomer Solution Preparation Step) 422.0 parts by mass of acrylic acid, 173.9 parts by mass of a 48.5% by mass aqueous sodium hydroxide solution, 1.2 parts by mass of polyethylene glycol diacrylate (average molecular weight: 523), 1.3 parts by mass of a 2.0% by mass aqueous solution of diethylenetriaminepentaacetic acid trisodium, and 404.5 parts by mass of deionized water were charged into a 2 L polypropylene container and mixed to prepare an aqueous monomer solution (10'). The liquid temperature of the aqueous monomer solution (10') exceeded 40°C due to the heat of neutralization and heat of dissolution generated during the mixing process.

[0278] (Polymerization Step) Next, the aqueous monomer solution (10') was cooled with stirring, and when the liquid temperature reached 40°C, 178.7 parts by mass of a 48.5% by mass aqueous sodium hydroxide solution adjusted to 40°C was added to the aqueous monomer solution (10') over approximately 20 seconds in an open-to-air state and mixed (starting the second-stage neutralization). This prepared the aqueous monomer solution (10). At this time, the liquid temperature of the aqueous monomer solution (10) rose to approximately 77°C due to the heat of neutralization and heat of dissolution generated during the mixing process. Although precipitates were observed immediately after starting to mix the aqueous sodium hydroxide solution with the aqueous monomer solution (10'), they gradually dissolved, and the prepared aqueous monomer solution (10) became a transparent, homogeneous solution.

[0279] Next, under stirring, nitrogen gas was introduced into the aqueous monomer solution (10) using a gas filter tube (manufactured by TOP Corporation, particle number #4) under conditions of a pressure of 0.1 MPa and a flow rate of 0.1 L / min for 5 seconds. Subsequently, 18.4 parts by mass of a 4.5 mass% aqueous sodium persulfate solution was added to the aqueous monomer solution (10) into which nitrogen gas had been introduced. Thereafter, the aqueous monomer solution (10) was immediately poured into a stainless steel batt-type container (bottom 340 mm x 340 mm, height 25 mm, inner surface: Teflon (registered trademark) coated) in an open-to-air state. The time from the start of the second-stage neutralization to the pouring of the aqueous monomer solution (10) into the batt-type container was 65 seconds. The vat-shaped container was heated in advance to a surface temperature of 50° C. using a hot plate (NEO HOTPLATE HI-1000 / manufactured by Iuchi Seieido Co., Ltd.) before pouring the aqueous monomer solution (10).

[0280] The polymerization reaction started within 1 minute after the aqueous monomer solution (10) was poured into the bat-shaped container. During the polymerization reaction, the polymerization of the aqueous monomer solution (10) proceeded while expanding and foaming in all directions and generating steam. The resulting polymer then shrunk to a size slightly larger than the bottom of the bat-shaped container. Two minutes after the start of the polymerization reaction, the resulting polymer, a hydrogel (10), was removed from the bat-shaped container. This series of operations was carried out in an open-to-air state.

[0281] (Hydrogel Crushing Step) Next, the hydrogel (10) obtained by the polymerization reaction was cut into pieces each having a mass of about 60 g, and then the gel was crushed using a meat chopper (HL-G22SN, plate hole diameter 8.0 mm / manufactured by Remacom Co., Ltd.) to obtain a particulate hydrogel (10). The amount of the hydrogel (10) added was approximately 360 g / min, and in parallel with the addition of the hydrogel (10), deionized water adjusted to 90°C was added to the meat chopper at a rate of 50 g / min to crush the gel.

[0282] The particulate hydrogel (10) had a D50 (mass average particle diameter) of 915 μm and a σζ (logarithmic standard deviation of particle size distribution) of 1.04.

[0283] (Drying step) Next, the particulate hydrogel (10) was spread on a wire mesh with a mesh size of 300 μm and placed in a hot air dryer. Thereafter, the particulate hydrogel (10) was dried by passing hot air at 190° C. for 30 minutes to obtain a dried polymer (10). No undried matter was present in the dried polymer (10).

[0284] (Classification step) Next, the dried polymer (10) was put into a roll mill (WML type roll crusher, manufactured by Inokuchi Giken Co., Ltd.) and crushed, and then classified using two types of JIS standard sieves with mesh sizes of 710 μm and 150 μm. By this operation, an irregularly crushed water absorbent resin (10) before surface crosslinking, which passed through the sieve with mesh size of 710 μm and remained on the sieve with mesh size of 150 μm, was obtained.

[0285] (Surface Cross-Linking Step) Next, an aqueous solution of the surface cross-linking agent used in Production Example 3, which consisted of 0.4 parts by mass of ethylene carbonate, 0.7 parts by mass of propylene glycol, and 2.9 parts by mass of deionized water, was sprayed and added to 100 parts by mass of the water absorbent resin (10) before surface cross-linking, and the mixture was uniformly mixed. Thereafter, the obtained mixture was heat-treated at 210°C for 40 minutes, thereby carrying out surface cross-linking. Next, the mixture after the heat treatment was classified using two types of JIS standard sieves with mesh sizes of 710 μm and 150 μm. By this operation, a surface-cross-linked water absorbent resin (10) was obtained, which passed through a sieve with a mesh size of 710 μm and remained on a sieve with a mesh size of 150 μm. The physical properties of the obtained surface-cross-linked water absorbent resin (10) are shown in Table 1.

[0286] [Production Example 11] The same operation as in Production Example 10 was carried out, except that in the monomer aqueous solution preparation step in Production Example 10, deionized water was changed to 404.3 parts by mass and 0.2 parts by mass of polyethylene glycol 600 (mass average molecular weight 600, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was additionally added, to obtain a surface-crosslinked water-absorbent resin (11). The proportion of polyethylene glycol 600 added relative to the total mass of the monomers contained in the aqueous monomer solution was 0.04% by mass. The physical properties of the obtained surface-crosslinked water-absorbent resin (11) are shown in Table 1.

[0287] The particulate hydrogel (11) obtained in the hydrogel crushing step had a D50 (mass average particle diameter) of 905 μm and a σζ (logarithmic standard deviation of particle size distribution) of 1.02.

[0288] [Production Example 12] The same operation as in Production Example 10 was carried out, except that in the monomer aqueous solution preparation step in Production Example 10, deionized water was changed to 403.0 parts by mass and 1.6 parts by mass of polyethylene glycol 600 (mass average molecular weight 600, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was additionally added, to obtain a surface-crosslinked water-absorbent resin (12). The proportion of polyethylene glycol 600 added relative to the total mass of the monomers contained in the aqueous monomer solution was 0.30% by mass. The physical properties of the obtained surface-crosslinked water-absorbent resin (12) are shown in Table 1.

[0289] The particulate hydrogel (12) obtained in the hydrogel crushing step had a D50 (mass average particle diameter) of 908 μm and a σζ (logarithmic standard deviation of particle size distribution) of 1.03.

[0290] [Production Example 13] The same operation as in Production Example 1 was performed, except that in the monomer aqueous solution preparation step in Production Example 1, deionized water was changed to 403.2 parts by mass and 0.1 parts by mass of polyethylene glycol 600 (mass average molecular weight 600, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was additionally added, to obtain a surface-crosslinked water-absorbent resin (13). The proportion of polyethylene glycol 600 added relative to the total mass of the monomers contained in the aqueous monomer solution was 0.02% by mass. The physical properties of the obtained surface-crosslinked water-absorbent resin (13) are shown in Table 1.

[0291] The particulate hydrogel (13) obtained in the hydrogel crushing step had a D50 (mass average particle diameter) of 388 μm and a σζ (logarithmic standard deviation of particle size distribution) of 0.90.

[0292] [Production Example 14] The same operation as in Production Example 1 was carried out, except that in the monomer aqueous solution preparation step in Production Example 1, deionized water was changed to 402.3 parts by mass and 1.03 parts by mass of polyethylene glycol 600 (mass average molecular weight 600, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was additionally added, to obtain a surface-crosslinked water-absorbent resin (14). The proportion of polyethylene glycol 600 added relative to the total mass of the monomers contained in the aqueous monomer solution was 0.20% by mass. The physical properties of the obtained surface-crosslinked water-absorbent resin (14) are shown in Table 1.

[0293] The particulate hydrogel (14) obtained in the hydrogel crushing step had a D50 (mass average particle diameter) of 380 μm and a σζ (logarithmic standard deviation of particle size distribution) of 0.89.

[0294]

[0295] [Comparative Example 1] 40 g of the surface-crosslinked water-absorbent resin (1) obtained in Production Example 1 was placed in a plastic container with a capacity of 200 mL (inner diameter: 70 mm, depth: 140 mm) after adjusting the temperature to 24 ° C. Subsequently, using a three-one motor equipped with an anchor-type stirring blade (diameter: 57 mm, height: 70 mm) made of a metal rod with a diameter of 3 mm, the surface-crosslinked water-absorbent resin (1) in the plastic container was stirred at a rotation speed of 450 rpm, and an aqueous solution at a liquid temperature of 25 ° C. consisting of 0.17 parts by mass of deionized water and 0.08 parts by mass of polyethylene glycol 600 (mass average molecular weight 600, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added using a straight pipe with an inner diameter of 0.5 mm to 100 parts by mass of the surface-crosslinked water-absorbent resin (1). The resulting mixture was laminated into layers with a thickness of 5 cm and allowed to stand for 30 minutes in a ventilated hot air dryer with an atmospheric temperature set to 60 ° C. to harden. The cured mixture was passed through a wire mesh with an opening of 850 μm to obtain a particulate water-absorbing agent composition (C1). The amount of polyethylene glycol 600 added was 0.08 mass % relative to the surface-crosslinked water-absorbing resin (1). The physical properties of the obtained particulate water-absorbing agent composition (C1) are shown in Table 2.

[0296] [Comparative Example 2] A particulate water-absorbing agent composition (C2) was obtained by the same operation as in Comparative Example 1, except that the aqueous solution to be added in Comparative Example 1 was changed to an aqueous solution containing 0.34 parts by mass of deionized water and 0.16 parts by mass of polyethylene glycol 600 (mass average molecular weight 600, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) at a liquid temperature of 25°C. The amount of polyethylene glycol 600 added was 0.16% by mass with respect to the water-absorbent resin (1) after surface cross-linking. The physical properties of the obtained particulate water-absorbing agent composition (C2) are shown in Table 2.

[0297] [Comparative Example 3] A particulate water-absorbing agent composition (C3) was obtained by carrying out the same operation as in Comparative Example 1, except that the aqueous solution to be added in Comparative Example 1 was changed to a mixed solution of 0.604 parts by mass of a 27% by mass aqueous solution of aluminum sulfate (8% by mass in terms of aluminum oxide), 0.181 parts by mass of a 60% by mass aqueous solution of sodium lactate, and 0.015 parts by mass of propylene glycol, with a liquid temperature of 25°C. Various physical properties of the obtained particulate water-absorbing agent composition (C3) are shown in Table 2.

[0298] [Comparative Example 4] A particulate water-absorbing agent composition (C4) was obtained by carrying out the same operation as in Comparative Example 2, except that the surface-crosslinked water-absorbent resin used in Comparative Example 2 was changed to the surface-crosslinked water-absorbent resin (2) obtained in Production Example 2. The amount of polyethylene glycol 600 added was 0.16% by mass relative to the surface-crosslinked water-absorbent resin (2). The physical properties of the obtained particulate water-absorbing agent composition (C4) are shown in Table 2.

[0299] [Comparative Example 5] A particulate water-absorbing agent composition (C5) was obtained by carrying out the same operation as in Comparative Example 2, except that the surface-crosslinked water-absorbent resin used in Comparative Example 2 was changed to the surface-crosslinked water-absorbent resin (3) obtained in Production Example 3. The amount of polyethylene glycol 600 added was 0.16% by mass relative to the surface-crosslinked water-absorbent resin (3). The physical properties of the obtained particulate water-absorbing agent composition (C5) are shown in Table 2.

[0300] [Comparative Example 6] A particulate water-absorbing agent composition (C6) was obtained by the same procedure as in Comparative Example 1, except that the surface-crosslinked water-absorbent resin used in Comparative Example 1 was changed to the surface-crosslinked water-absorbent resin (4) obtained in Production Example 4, and the aqueous solution to be added was changed to an aqueous solution containing 0.34 parts by mass of deionized water and 0.16 parts by mass of polyethylene glycol 200 (mass-average molecular weight 200, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) at a liquid temperature of 25°C. The amount of polyethylene glycol 200 added was 0.16% by mass relative to the surface-crosslinked water-absorbent resin (4). The physical properties of the obtained particulate water-absorbing agent composition (C6) are shown in Table 2.

[0301] [Example 1] A particulate water-absorbing agent composition (1) was obtained by the same operation as in Comparative Example 6, except that the aqueous solution to be added in Comparative Example 6 was changed to an aqueous solution containing 0.70 parts by mass of deionized water and 0.30 parts by mass of polyethylene glycol 400 (mass average molecular weight 400, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) at a liquid temperature of 25°C. The amount of polyethylene glycol 400 added was 0.30% by mass with respect to the surface-crosslinked water-absorbent resin (4). The physical properties of the obtained particulate water-absorbing agent composition (1) are shown in Tables 2 and 3.

[0302] [Example 2] A particulate water-absorbing agent composition (2) was obtained by the same operation as in Example 1, except that the aqueous solution to be added in Example 1 was changed to an aqueous solution containing 0.17 parts by mass of deionized water and 0.08 parts by mass of polyethylene glycol 600 (mass average molecular weight 600, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) at a liquid temperature of 25°C, which was used in Comparative Example 1. The amount of polyethylene glycol 600 added was 0.08% by mass with respect to the water-absorbent resin (4) after surface cross-linking. The physical properties of the obtained particulate water-absorbing agent composition (2) are shown in Tables 2 and 3.

[0303] [Example 3] A particulate water-absorbing agent composition (3) was obtained by the same operation as in Example 1, except that the aqueous solution to be added in Example 1 was changed to an aqueous solution containing 0.34 parts by mass of deionized water and 0.16 parts by mass of polyethylene glycol 600 (mass average molecular weight 600, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) used in Comparative Example 2 and having a liquid temperature of 25°C. The amount of polyethylene glycol 600 added was 0.16% by mass with respect to the surface-crosslinked water-absorbent resin (4). The physical properties of the obtained particulate water-absorbing agent composition (3) are shown in Tables 2 and 3.

[0304] [Example 4] A particulate water-absorbing agent composition (4) was obtained by the same operation as in Example 1, except that the polyethylene glycol used in the aqueous solution to be added in Example 1 was changed to polyethylene glycol 600 (mass average molecular weight 600, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.). The amount of polyethylene glycol 600 added was 0.30 mass% with respect to the water-absorbing resin (4) after surface cross-linking. The physical properties of the obtained particulate water-absorbing agent composition (4) are shown in Tables 2 and 3.

[0305] [Example 5] A particulate water-absorbing agent composition (5) was obtained by the same operation as in Example 1, except that the polyethylene glycol used in the aqueous solution to be added in Example 1 was changed to polyethylene glycol 1000 (mass average molecular weight 1000, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.). The amount of the added polyethylene glycol 1000 was 0.30 mass % with respect to the surface-crosslinked water-absorbent resin (4). The physical properties of the obtained particulate water-absorbing agent composition (5) are shown in Tables 2 and 3.

[0306] [Example 6] A particulate water-absorbing agent composition (6) was obtained by the same operation as in Example 1, except that the polyethylene glycol used in the aqueous solution to be added in Example 1 was changed to polyethylene glycol 2000 (mass average molecular weight 2000, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.). The amount of polyethylene glycol 2000 added was 0.30 mass% with respect to the surface-crosslinked water-absorbent resin (4). The physical properties of the obtained particulate water-absorbing agent composition (6) are shown in Tables 2 and 3.

[0307] [Example 7] A particulate water-absorbing agent composition (7) was obtained by carrying out the same operation as in Example 1, except that the polyethylene glycol used in the aqueous solution to be added in Example 1 was changed to polyethylene glycol 10000 (mass average molecular weight 10000, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.). The amount of the added polyethylene glycol 10000 was 0.30 mass% with respect to the surface-crosslinked water-absorbent resin (4). The physical properties of the obtained particulate water-absorbing agent composition (7) are shown in Tables 2 and 3.

[0308] [Comparative Example 7] A particulate water-absorbing agent composition (C7) was obtained by the same operation as in Comparative Example 6, except that the polyethylene glycol used in the aqueous solution to be added in Comparative Example 6 was changed to polyethylene glycol 20000 (mass average molecular weight 20000, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.). The amount of polyethylene glycol 20000 added was 0.16 mass% with respect to the surface-crosslinked water-absorbent resin (4). The physical properties of the obtained particulate water-absorbing agent composition (C7) are shown in Table 2.

[0309] [Example 8] A particulate water-absorbing agent composition (8) was obtained by the same operation as in Example 1, except that the aqueous solution to be added in Example 1 was changed to a mixed solution of 0.70 parts by mass of isopropyl alcohol and 0.30 parts by mass of polypropylene glycol 700 (mass average molecular weight 700, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) at a liquid temperature of 25°C. The amount of polypropylene glycol 700 added was 0.30% by mass with respect to the water-absorbent resin (4) after surface cross-linking. The physical properties of the obtained particulate water-absorbing agent composition (8) are shown in Tables 2 and 3.

[0310] [Example 9] A particulate water-absorbing agent composition (9) was obtained by the same operation as in Example 8, except that the polypropylene glycol used in the aqueous solution to be added in Example 8 was changed to polypropylene glycol 1000 (mass average molecular weight 1000, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.). The amount of the added polypropylene glycol 1000 was 0.30 mass% with respect to the surface-crosslinked water-absorbing resin (4). The physical properties of the obtained particulate water-absorbing agent composition (9) are shown in Tables 2 and 3.

[0311] [Example 10] A particulate water-absorbing agent composition (10) was obtained by the same operation as in Example 1, except that the aqueous solution added in Example 1 was changed to a mixed solution of 0.76 parts by mass of isopropyl alcohol and 0.04 parts by mass of polyoxyethylene (20) sorbitan monostearate (manufactured by Kao Corporation) at a liquid temperature of 25°C. The amount of polyoxyethylene (20) sorbitan monostearate added was 0.04% by mass with respect to the surface-crosslinked water-absorbent resin (4). The physical properties of the obtained particulate water-absorbing agent composition (10) are shown in Tables 2 and 3.

[0312] [Example 11] A particulate water-absorbing agent composition (11) was obtained by the same operation as in Example 10, except that the nonionic polymer used in the aqueous solution to be added in Example 10 was changed to polyoxyethylene (20) sorbitan tristearate (manufactured by Kao Corporation). The amount of the added polyoxyethylene (20) sorbitan tristearate was 0.04 mass% with respect to the surface-crosslinked water-absorbent resin (4). The physical properties of the obtained particulate water-absorbing agent composition (11) are shown in Tables 2 and 3.

[0313] [Comparative Example 8] A particulate water-absorbing agent composition (C8) was obtained by the same operation as in Example 10, except that the nonionic polymer used in the aqueous solution to be added in Example 10 was changed to sorbitan monooleate (manufactured by Kao Corporation). Various physical properties of the obtained particulate water-absorbing agent composition (C8) are shown in Table 2.

[0314] [Comparative Example 9] A particulate water-absorbing agent composition (C9) was obtained by the same operation as in Example 1, except that the aqueous solution to be added in Example 1 was changed to a mixed solution having a liquid temperature of 25°C, which was composed of 0.604 parts by mass of a 27% by mass aqueous aluminum sulfate solution (8% by mass in terms of aluminum oxide), 0.181 parts by mass of a 60% by mass aqueous sodium lactate solution, and 0.015 parts by mass of propylene glycol, which was used in Comparative Example 3. The physical properties of the obtained particulate water-absorbing agent composition (C9) are shown in Table 2.

[0315] [Comparative Example 10] 0.10 parts by mass of fumed silica (Aerosil 200, manufactured by Nippon Aerosil Co., Ltd.) was mixed with 100 parts by mass of the surface-crosslinked water-absorbent resin (4) obtained in Production Example 4 to obtain a particulate water-absorbing agent composition (C10). The mixing was carried out by adjusting the temperature of 30 g of the surface-crosslinked water-absorbent resin (4) to 24°C, and then placing the mixture together with the fumed silica in a 225 mL mayonnaise bottle, followed by shaking for 3 minutes using a paint shaker. The physical properties of the obtained particulate water-absorbing agent composition (C10) are shown in Table 2.

[0316] [Comparative Example 11] A particulate water-absorbing agent composition (C11) was obtained by carrying out the same operation as in Comparative Example 10, except that the amount of fumed silica (Aerosil 200, manufactured by Nippon Aerosil Co., Ltd.) used in Comparative Example 10 was changed to 0.20 parts by mass. Various physical properties of the obtained particulate water-absorbing agent composition (C11) are shown in Table 2.

[0317] [Example 12] A particulate water-absorbing agent composition (12) was obtained by carrying out the same operation as in Comparative Example 2, except that the surface-crosslinked water-absorbent resin used in Comparative Example 2 was changed to the surface-crosslinked water-absorbent resin (5) obtained in Production Example 5. The amount of polyethylene glycol 600 added was 0.16 mass % relative to the surface-crosslinked water-absorbent resin (5). The physical properties of the obtained particulate water-absorbing agent composition (12) are shown in Tables 2 and 3.

[0318] [Example 13] A particulate water-absorbing agent composition (13) was obtained by carrying out the same operation as in Comparative Example 2, except that the surface-crosslinked water-absorbent resin used in Comparative Example 2 was changed to the surface-crosslinked water-absorbent resin (6) obtained in Production Example 6. The amount of polyethylene glycol 600 added was 0.16 mass % relative to the surface-crosslinked water-absorbent resin (6). The physical properties of the obtained particulate water-absorbing agent composition (13) are shown in Tables 2 and 3.

[0319] [Example 14] A particulate water-absorbing agent composition (14) was obtained by carrying out the same operation as in Comparative Example 2, except that the surface-crosslinked water-absorbent resin used in Comparative Example 2 was changed to the surface-crosslinked water-absorbent resin (7) obtained in Production Example 7. The amount of polyethylene glycol 600 added was 0.16% by mass relative to the surface-crosslinked water-absorbent resin (7). The physical properties of the obtained particulate water-absorbing agent composition (14) are shown in Tables 2 and 3.

[0320] [Example 15] A particulate water-absorbing agent composition (15) was obtained by carrying out the same operation as in Comparative Example 2, except that the surface-crosslinked water-absorbent resin used in Comparative Example 2 was changed to the surface-crosslinked water-absorbent resin (8) obtained in Production Example 8. The amount of polyethylene glycol 600 added was 0.16% by mass relative to the surface-crosslinked water-absorbent resin (8). The physical properties of the obtained particulate water-absorbing agent composition (15) are shown in Tables 2 and 3.

[0321] [Example 16] A particulate water-absorbing agent composition (16) was obtained by carrying out the same operation as in Comparative Example 2, except that the surface-crosslinked water-absorbent resin used in Comparative Example 2 was changed to the surface-crosslinked water-absorbent resin (9) obtained in Production Example 9. The amount of polyethylene glycol 600 added was 0.16% by mass relative to the surface-crosslinked water-absorbent resin (9). The physical properties of the obtained particulate water-absorbing agent composition (16) are shown in Tables 2 and 3.

[0322] [Comparative Example 12] The same operation as in Comparative Example 1 was carried out to obtain a particulate water-absorbing agent composition (C12), except that the surface-crosslinked water-absorbent resin used in Comparative Example 1 was changed to the surface-crosslinked water-absorbent resin (10) obtained in Production Example 10, and the aqueous solution to be added was changed to an aqueous solution containing 0.35 parts by mass of deionized water and 0.15 parts by mass of polyethylene glycol 600 (mass-average molecular weight 600, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) at a liquid temperature of 25°C. The amount of polyethylene glycol 600 added was 0.15% by mass relative to the surface-crosslinked water-absorbent resin (10). The physical properties of the obtained particulate water-absorbing agent composition (C12) are shown in Table 2.

[0323] [Example 17] A particulate water-absorbing agent composition (17) was obtained by carrying out the same operation as in Comparative Example 12, except that the surface-crosslinked water-absorbent resin used in Comparative Example 12 was changed to the surface-crosslinked water-absorbent resin (11) obtained in Production Example 11. The amount of polyethylene glycol 600 added was 0.15% by mass relative to the surface-crosslinked water-absorbent resin (11). The physical properties of the obtained particulate water-absorbing agent composition (17) are shown in Tables 2 and 3.

[0324] [Example 18] A particulate water-absorbing agent composition (18) was obtained by the same operation as in Example 1, except that the surface-crosslinked water-absorbent resin used in Example 1 was changed to the surface-crosslinked water-absorbent resin (13) obtained in Production Example 13, and the aqueous solution to be added was changed to a mixed solution of 0.48 parts by mass of isopropyl alcohol and 0.025 parts by mass of polyoxyethylene (20) sorbitan monostearate (manufactured by Kao Corporation) at a liquid temperature of 25°C. The amount of polyoxyethylene (20) sorbitan monostearate added was 0.025% by mass relative to the surface-crosslinked water-absorbent resin (13). The physical properties of the obtained particulate water-absorbing agent composition (18) are shown in Tables 2 and 3.

[0325] [Example 19] In Example 1, the surface-crosslinked water-absorbent resin used was changed to the surface-crosslinked water-absorbent resin (14) obtained in Production Example 14, and the aqueous solution to be added was changed to an aqueous solution containing 0.82 parts by mass of deionized water and 0.35 parts by mass of polyethylene glycol 600 (mass-average molecular weight 600, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) at a liquid temperature of 25°C, and the same operation as in Example 1 was performed to obtain a particulate water-absorbing agent composition (19). The amount of polyethylene glycol 600 added was 0.35% by mass with respect to the surface-crosslinked water-absorbent resin (14). The physical properties of the obtained particulate water-absorbing agent composition (19) are shown in Tables 2 and 3.

[0326]

[0327]

[0328] [Summary] Comparative Examples 1 to 5 are examples in which water-absorbent resins (surface-crosslinked water-absorbent resins (1) to (3)) produced without adding water-soluble polyalkylene glycol were used in any of the aqueous monomer solution preparation step, the polymerization step, and the hydrous gel crushing step.

[0329] Comparing Comparative Example 1 and Example 2, in which the same 0.08% by mass of polyethylene glycol 600 was added to the surface-crosslinked water-absorbent resins (1) and (4), it is found that the particulate water-absorbent composition (2) of Example 2, which uses the surface-crosslinked water-absorbent resin (4) produced by adding a water-soluble polyalkylene glycol before the hydrous gel crushing step, has a larger ΔB.R. than the particulate water-absorbent composition (C1) of Comparative Example 1, and is significantly improved in terms of improving the anti-caking performance. Furthermore, the particulate water-absorbent composition (2) also shows almost no deterioration in AAP or FHA.

[0330] Similarly, when comparing Comparative Examples 2, 4, and 5 with Example 3 and Example 16, in which the same 0.16 mass% polyethylene glycol 600 was added to the surface-crosslinked water-absorbent resins (1), (2), (3), (4), and (9), the particulate water-absorbent agent compositions (3) and (16) of Examples 3 and 16, which used the surface-crosslinked water-absorbent resins (4) and (9) produced by adding water-soluble polyalkylene glycol before the hydrogel crushing step, showed a larger ΔB.R. than the particulate water-absorbent agent compositions (C2), (C4), and (C5) of Comparative Examples 2, 4, and 5, and it can be seen that the improvement in anti-caking performance was significantly improved. Furthermore, the particulate water-absorbent agent compositions (3) and (16) did not exhibit a deterioration in AAP or FHA.

[0331] On the other hand, the particulate water-absorbing agent composition (C3) of Comparative Example 3, in which aluminum sulfate was added to the same surface-crosslinked water-absorbent resin (1) as in Comparative Examples 1 and 2, had a large ΔB.R. and a good effect of improving the anti-caking performance, but the AAP0.7 and FHA were deteriorated, indicating that the water-absorbing performance under pressure was poor.

[0332] Furthermore, by comparing Examples 1 to 7 with Comparative Examples 6 and 7, in which the same surface-crosslinked water-absorbent resin (4) was used and the molecular weight (mass-average molecular weight) of the added nonionic polymer polyethylene glycol was changed, it is found that the particulate water-absorbing agent compositions (C6) and (C7) of Comparative Examples 6 and 7, in which the mass-average molecular weight of the nonionic polymer was 200 and 20,000, respectively, had small ΔB.R. and a low effect of improving anti-caking performance.

[0333] From Examples 1 to 11 and Comparative Example 8, in which the same surface-crosslinked water-absorbent resin (4) was used and the added nonionic polymer was changed, it is found that the particulate water-absorbing agent composition (C8) of Comparative Example 8, in which a nonionic polymer not containing a polyalkylene glycol chain in its structure was added, exhibited a greatly deteriorated FHA.

[0334] From Comparative Examples 9 to 11, it can be seen that even in the case of using a surface-crosslinked water-absorbent resin (4) produced by adding a water-soluble polyalkylene glycol before the hydrogel crushing step, when silica or an aluminum salt is added, AAP and FHA deteriorate.

[0335] The particulate water-absorbing agent composition (12) of Example 12, which was produced by using a surface-crosslinked water-absorbent resin (5) produced by changing the amount of water-soluble polyalkylene glycol added before the hydrogel crushing step to 0.14 mass% relative to the total mass of the monomers, and to which 0.16 mass% of polyethylene glycol 600 was added in the same manner as in Example 3, also showed a large ΔB.R., indicating a remarkable improvement in the anti-caking performance. Furthermore, the particulate water-absorbing agent composition (12) did not show any deterioration in AAP or FHA.

[0336] The particulate water-absorbing agent compositions (13), (14), and (15) of Examples 13, 14, and 15, which were produced by changing the molecular weight (mass average molecular weight) of the water-soluble polyalkylene glycol added before the hydrogel crushing step to 400, 1000, and 2000, respectively, and to which 0.16 mass% of polyethylene glycol 600 was added in the same manner as in Example 3, also showed large ΔB.R. values, indicating a significant improvement in the anti-caking performance. Furthermore, the particulate water-absorbing agent compositions (13), (14), and (15) also showed no deterioration in AAP or FHA.

[0337]

[0222] Comparative Example 12 and Example 17 are examples in which the amount of polyethylene glycol diacrylate (average molecular weight: 523) added in the aqueous monomer solution preparation step was reduced compared with other Examples and Comparative Examples, and CRC of the water absorbent resin after surface cross-linking was increased.

[0338] Comparing Comparative Example 12, in which 0.15% by mass of polyethylene glycol 600 was added to the surface-crosslinked water-absorbent resin (10), and Example 17, in which the same 0.15% by mass of polyethylene glycol 600 was added to the surface-crosslinked water-absorbent resin (11), the particulate water-absorbent composition (17) of Example 17 using the surface-crosslinked water-absorbent resin (11) produced by adding water-soluble polyalkylene glycol before the hydrous gel crushing step, compared to the particulate water-absorbent composition (C12) of Comparative Example 12, it can be seen that the ΔB.R. is large and the improvement effect of anti-caking performance is significantly improved. In other words, even in the example in which the CRC of the water-absorbent resin after surface crosslinking is increased, by adding water-soluble polyalkylene glycol before the hydrous gel crushing step, it can be seen that the improvement effect of anti-caking performance by the nonionic polymer added to the water-absorbent resin after surface crosslinking is significantly improved. Furthermore, the particulate water-absorbing agent composition (17) shows almost no deterioration in AAP or FHA compared to the surface-crosslinked water-absorbing resin (11) before the addition of polyethylene glycol 600.

[0339] On the other hand, the surface-crosslinked water-absorbent resin (12) in which the amount of water-soluble polyalkylene glycol added before the hydrogel-crushing step was 0.30% by mass relative to the total mass of the monomers contained in the aqueous monomer solution had a larger B.R., i.e., worsened anti-caking performance, than the surface-crosslinked water-absorbent resin (10) in which no water-soluble polyalkylene glycol was added before the hydrogel-crushing step. In other words, it can be seen that when the amount of water-soluble polyalkylene glycol added before the hydrogel-crushing step is 0.30% by mass or more, the B.R. deteriorates and is not preferable from the viewpoint of improving anti-caking performance.

[0340] According to the method for producing a particulate water-absorbing agent composition of the present invention, it is possible to provide a particulate water-absorbing agent composition having high anti-caking performance without deteriorating its water-absorbing performance under pressure. Therefore, the particulate water-absorbing agent composition obtained by the present invention can be suitably used in absorbent articles such as disposable diapers, sanitary napkins, and incontinence pads.

Claims

1. A method for producing a particulate water-absorbing agent composition containing a poly(meth)acrylic acid (salt)-based water-absorbing resin, comprising: a monomer aqueous solution preparation step of preparing a (meth)acrylic acid (salt)-based monomer aqueous solution; a polymerization step of polymerizing the (meth)acrylic acid (salt)-based monomer aqueous solution; an optional hydrogel crushing step of gel-crushing a hydrogel-like crosslinked polymer produced during or after polymerization; a drying step of drying the particulate hydrogel; an optional crushing step and an optional classification step of crushing and classifying the dried polymer; and a surface crosslinking step of surface-crosslinking a water-absorbing resin before surface crosslinking, wherein the particulate hydrogel is obtained through a polymerization step or both of a polymerization step and a hydrogel crushing step, the dried polymer is obtained through a drying step, and the water-absorbing resin before surface crosslinking is the dried polymer or a water-absorbing resin obtained by crushing and / or classifying the dried polymer, A method for producing a particulate water-absorbing agent composition containing a poly(meth)acrylic acid (salt)-based water-absorbing resin, comprising the steps of: adding 0.01% by mass to 0.25% by mass of a water-soluble polyalkylene glycol having a mass average molecular weight of 3000 or less to the total mass of the monomers contained in the (meth)acrylic acid (salt)-based monomer aqueous solution in at least any step selected from the monomer aqueous solution preparation step, the polymerization step, and an optional hydrous gel crushing step; and adding 0.02% by mass to 0.40% by mass of a nonionic polymer having a polyalkylene glycol chain in its structure and having a mass average molecular weight of 300 to 15000 to the surface-crosslinked water-absorbing resin after the surface-crosslinking step.

2. The method according to claim 1, wherein the particulate water-absorbing agent composition has a surface tension of 45 mN / m or more.

3. The method according to claim 1, wherein the particulate water-absorbing agent composition has an absorbency against pressure (AAP) of 20 g / g or more under a pressure of 0.7 psi.

4. The method according to claim 1, wherein the particulate water-absorbing agent composition has a fixed height absorption (FHA) of 20 g / g or more at a height of 20 cm.

5. A particulate water-absorbing agent composition comprising a poly(meth)acrylic acid (salt)-based water-absorbing resin as a main component and a nonionic polymer having a polyalkylene glycol chain in its structure, with a mass ratio of particles having a particle diameter of 300 μm or more and less than 850 μm being 50 mass % or more, wherein: (a) the nonionic polymer contained in the particulate water-absorbing agent composition is designated as A1 and its content as C1; (b) the particulate water-absorbing agent composition is subjected to a prescribed impact test; (c) the particulate water-absorbing agent composition subjected to the impact test is sieved with a JIS standard sieve into a particle group a having a particle diameter of 300 μm or more and a particle group b having a particle diameter of less than 300 μm; and (d) the particulate water-absorbing agent composition satisfies all of the following (1) to (4) when the nonionic polymer present in the particle group a is designated as A2 and its content as C2: (1) A1 is a water-soluble polyalkylene glycol having a mass average molecular weight of 3,000 or less, and a nonionic polymer having a polyalkylene glycol chain in its structure and a mass average molecular weight of 300 to 15,000; (2) A2 is a water-soluble polyalkylene glycol having a mass average molecular weight of 3,000 or less; (3) C2 is 0.005% by mass or more and 0.15% by mass or less; and (4) C1-C2 is 0.02% by mass or more and 0.40% by mass or less.

6. The particulate water-absorbing agent composition according to claim 5, wherein the particulate water-absorbing agent composition has a surface tension of 45 mN / m or more.

7. The particulate water-absorbing agent composition according to claim 5, wherein the particulate water-absorbing agent composition has an absorbency against pressure (AAP) of 20 g / g or more under a pressure of 0.7 psi.

8. The particulate water-absorbing agent composition according to claim 5, wherein the particulate water-absorbing agent composition has a fixed height absorption value (FHA) at a height of 20 cm of 20 g / g or more.

9. The particulate water-absorbing composition according to claim 5, wherein the particulate water-absorbing composition has a CRC of 25 g / g or more.

10. The particulate water-absorbing agent composition according to claim 5, wherein the particulate water-absorbing agent composition has a moisture absorption blocking ratio <1> (B.R.<1>) of 80 mass % or less.

11. The particulate water-absorbing agent composition according to claim 5, wherein the particulate water-absorbing agent composition has a mass median particle diameter (D50) of 300 μm or more and 600 μm or less.

12. A particulate water-absorbing agent composition according to claim 5, wherein the mass ratio of particles having a particle diameter of 850 μm or more in the particulate water-absorbing agent composition is 3 mass% or less, and the mass ratio of particles having a particle diameter of less than 150 μm is 5 mass% or less.

13. An absorbent article containing a particulate water-absorbing agent composition, comprising, as the particulate water-absorbing agent composition, the particulate water-absorbing agent composition according to any one of claims 5 to 12.