Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F2/00—Processes of polymerisation
  • C08F2/44—Polymerisation in the presence of compounding ingredients, e.g. plasticisers, dyestuffs, fillers
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F20/00—Homopolymers and copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical or a salt, anhydride, ester, amide, imide or nitrile thereof
  • C08F20/02—Monocarboxylic acids having less than ten carbon atoms, Derivatives thereof
  • C08F20/04—Acids, Metal salts or ammonium salts thereof
  • C08F20/06—Acrylic acid; Methacrylic acid; Metal salts or ammonium salts thereof
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F8/00—Chemical modification by after-treatment
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J3/00—Processes of treating or compounding macromolecular substances
  • C08J3/12—Powdering or granulating

Definitions

• the present invention relates to a method for producing a particulate water-absorbing composition, a particulate water-absorbing composition, and an absorbent article.
• a particulate water-absorbing agent composition (hereinafter, sometimes simply referred to as "water-absorbing agent” in this specification) containing a water-absorbing resin as a main component is used in the absorbent body contained in absorbent articles such as disposable diapers, sanitary napkins, and incontinence pads.
• the water absorbent absorbs aqueous liquids such as urine and swells to seal in the aqueous liquid. Since absorbent articles are usually used with the weight of the user on them, the water absorbent is required to have high water absorption performance under pressure in order to improve the absorption performance of absorbent articles. Examples of physical values that indicate the water absorption performance of a water absorbent under pressure include AAP (absorption capacity under pressure) and FHA (fixed height absorption value at a height of 20 cm).
• the water absorbent is also required to have high caking resistance.
• One physical property that indicates the caking resistance is B.R. (moisture absorption blocking ratio).
• B.R. moisture absorption blocking ratio
• a technique for lowering this B.R., that is, for improving the caking resistance a technique is known in which inorganic fine particles such as silicon dioxide, kaolin, alumina, etc. are added as an anti-caking agent to the surface of the water absorbent resin (Patent Documents 1 to 7).
• Patent Document 8 polyvalent metal salts of organic acids (Patent Document 8) and various surfactants and hydrophobic polymers such as polysiloxane (Patent Documents 9 to 11) are added as anti-caking agents other than inorganic fine particles to the surface of the water absorbent resin.
• Non-Patent Document 1 water-absorbent resins are 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.
• 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).
• An aspect of the present invention aims to provide a method for producing a water-absorbing agent that has high caking resistance without deteriorating water-absorbing performance under pressure, and to provide a water-absorbing agent and an absorbent article.
• one aspect of the present invention includes the following configuration.
• 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: a monomer aqueous solution preparation step of preparing an aqueous (meth)acrylic acid (salt)-based monomer 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 the hydrogel-like crosslinked polymer produced during or after the polymerization; A drying step of drying the particulate hydrogel; an optional grinding step and an optional classification step of grinding and classifying the dried polymer; A surface cross-linking step of surface cross-linking the water absorbent resin before surface cross-linking, The particulate hydrogel is obtained through a polymerization step or through both a polymerization step and a hydrogel crushing step, The dried polymer is obtained through a drying step, The water absorbent resin before
• 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 particulate water-absorbing agent composition having a particle diameter of 300 ⁇ m or more and less than 850 ⁇ m in a mass ratio of 50 mass% or more, (a) The nonionic polymer contained in the particulate water-absorbing agent composition is designated as A1, and its content is designated as C1, (b) subjecting the particulate water-absorbing agent composition to a predetermined impact test; (c) The particulate water-absorbing agent composition that has been subjected to the impact test is sieved using a JIS standard sieve into a particle group a having a particle diameter of 300 ⁇ m or more and a particle group b having a particle diameter of less than 300 ⁇ m, (d) A particulate water-absorbing agent composition, which satisfies all of the following (1) to
• An absorbent article containing a particulate water-absorbing agent composition An absorbent article comprising the particulate water-absorbing agent composition according to any one of [5] to [12] as the particulate water-absorbing agent composition.
• Water-absorbent resin refers to a water-swellable, water-insoluble crosslinked polymer.
• water-swellable means that the absorption capacity under no load (also called centrifuge retention capacity (CRC)) defined in NWSP 241.0.
• R2 (19) is 5 g/g or more
• water-insoluble means that the soluble content (Ext) defined in NWSP 270.0.
• R2 (19) is 50 mass% or less.
• the "water-absorbent resin” is preferably a hydrophilic cross-linked polymer obtained by cross-linking polymerization of a monomer composition containing (meth)acrylic acid (salt) as a main component.
• 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 of the step before 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.
• the water-absorbent resin may refer to an intermediate in the manufacturing process of the water-absorbent resin (for example, a hydrous gel-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”.
• a hydrous gel-like cross-linked polymer after polymerization for example, a hydrous gel-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.
• poly(meth)acrylic acid (salt)-based water-absorbent resin means a hydrophilic cross-linked polymer obtained by cross-linking polymerization of a monomer composition containing (meth)acrylic acid (salt) as the main component.
• the water absorbent resin may refer to "a polymer crosslinked only inside, i.e., a polymer in which the crosslink density inside and the surface are substantially the same” or "a polymer crosslinked inside and the surface, i.e., a polymer in which the crosslink density at the surface is relatively high compared to the crosslink density inside".
• the "polymer crosslinked only inside” and the “polymer crosslinked inside and the surface” are not distinguished in principle, and both are expressed as “water absorbent resin”.
• the "polymer crosslinked only inside” is expressed as “water absorbent resin before surface crosslinking” since it is before surface crosslinking
• the "polymer crosslinked inside and the surface” is expressed as “water absorbent resin after surface crosslinking” or “surface crosslinked water absorbent resin” since it is after surface crosslinking.
• "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”.
• Particulate water-absorbent composition refers to a composition containing the water-absorbent resin as a main component and various additives added after surface cross-linking as other components.
• containing the water-absorbent resin as a main component refers to the composition containing the water-absorbent resin 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.
• the "particulate water-absorbing agent composition” is in a particulate form (also known as powder).
• the term “particulate” means having a particulate shape, and the term “particle” means a small solid or liquid granular object having a measurable size (JIS Industrial Terminology Dictionary, 4th Edition, p. 2002).
• the "particulate water-absorbing agent composition” in this specification may be a single particle of the particulate water-absorbing agent composition, or an aggregate of multiple particles of the particulate water-absorbing agent composition.
• it may be referred to as a "particulate water-absorbing agent,” “water-absorbing agent composition,” or “water-absorbing agent,” but all of these are synonymous and mean “particulate water-absorbing agent composition.”
• the particulate water-absorbing composition is an absorbent gelling agent for aqueous liquids, and is preferably used as a material for absorbing aqueous liquids in absorbent articles.
• NWSP Non-Woven Standard Procedures-Edition 2019, and is a joint effort between EDANA (European Disposables and Nonwovens Associations) and INDA (Association of the Nonwoven Fabrics Industry).
• the NWSP is a standardized method for evaluating nonwoven fabrics and their products that has been published in Europe and the United States.
• the NWSP also provides a standard method for measuring water-absorbent resins. In accordance with the "2019" standard, the physical properties of the water-absorbent resin and the particulate water-absorbing agent composition are measured. In addition, unless otherwise specified in this specification, the measurement of various physical properties of the water-absorbent resin and the particulate water-absorbing agent composition The measurement method used was the same as that described in the Examples below.
• the anti-caking performance of the obtained water-absorbing agent can be improved without almost deteriorating the water-absorbing performance under pressure.
• the surfactant or the nonionic polymer containing a polyalkylene glycol chain in its structure has a small effect of improving the anti-caking performance compared to the inorganic fine particles.
• the addition of anti-caking agents has been considered from the viewpoint of surface modification, focusing solely on coating the particle surface of the water-absorbent resin.
• the anti-caking agent is added in a process (e.g., a polymerization process) that can distribute it uniformly inside the water-absorbent resin, there will be almost no anti-caking agent on the particle surface of the water-absorbent resin, and it was thought that the desired improvement effect in anti-caking performance would not be obtained, so addition in the polymerization process, etc. has not been considered.
• the present inventors not only modified the surface of the water-absorbent resin with an anti-caking agent, but also focused for the first time on additives to the inside of the water-absorbent resin, which had previously been thought to be unrelated to caking resistance.
• a specific additive to the particle surface of the water-absorbent resin, as well as to the inside of the water-absorbent resin, they succeeded in obtaining a water-absorbent composition that achieves both high caking resistance and the maintenance of water absorption performance under pressure.
• the present invention has discovered that when a nonionic polymer having a predetermined molecular weight and a predetermined amount containing a polyalkylene glycol chain in its structure (i.e., a specific additive is added to the particle surface) is added to 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 having a predetermined molecular weight and a predetermined amount, it was surprisingly discovered that the effect of improving the anti-caking performance by the nonionic polymer was greatly improved compared to when the water-soluble polyalkylene glycol was not added. It was also discovered that there was almost no deterioration in the water-absorbent performance under pressure of the obtained water-absorbent.
• a surface-crosslinked water-absorbent resin i.e., a water-
• the method for producing a particulate water absorbent composition is a method for producing a particulate water absorbent composition containing a poly(meth)acrylic acid (salt)-based water absorbent 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, 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 of crushing and classifying the dried polymer, and an optional classification step, and a surface crosslinking step of surface-crosslinking a water absorbent resin before surface crosslinking, and the monomer aqueous solution preparation step In at least one step selected from the polymerization step and the optional hydrogel crushing step, a water
• 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% by mass to 0.40% by mass relative to the surface-cross-linked water-absorbent resin.
• the above manufacturing method makes it possible to obtain a water-absorbing agent with high caking resistance without compromising water-absorbing performance under pressure.
• a surface-crosslinked water-absorbent resin produced by adding a water-soluble polyalkylene glycol having the above-mentioned mass average molecular weight and amount 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 in its structure having the above-mentioned mass average molecular weight and amount is added to the surface-crosslinked water-absorbent resin, the effect of improving the anti-caking performance by adding the nonionic polymer can be significantly improved compared to the case where the water-soluble polyalkylene glycol is not added.
• the physical property value expressing the caking resistance of the water absorbent is, for example, the moisture absorption blocking ratio (B.R.).
• 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 absorbent resin and the water absorbent, the better the caking resistance of the water absorbent resin and the water absorbent.
• the greater the B.R. of the water absorbent obtained by adding the nonionic polymer is, the greater the reduction in the B.R. of the water absorbent obtained by adding the nonionic polymer from the B.R. of the water absorbent resin after surface crosslinking before the addition of the nonionic polymer. More specifically, the greater the value ( ⁇ B.R.
• physical properties that represent the water absorption performance under pressure of the water absorbent and water absorbent resin include, for example, the absorbency under pressure (AAP) and the fixed height absorption value (FHA) at a height of 20 cm.
• AAP and FHA are values calculated by the method described in the Examples.
• 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).
• a slurry liquid of the monomer composition can also be used, for convenience, the present specification will explain the aqueous solution of the monomer composition.
• 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.
• the entire monomer forming the water-absorbent resin is a monomer composition.
• (meth)acrylic acid (salt) means (meth)acrylic acid and/or its salt
• “monomer composition containing (meth)acrylic acid (salt) as a main component” means a monomer composition containing 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% of (meth)acrylic acid (salt) relative to the total monomers excluding the crosslinking agent.
• (meth)acrylic acid (salt)-based monomer aqueous solution refers to an aqueous solution of a monomer composition that contains (meth)acrylic acid (salt) as the main component and at least one type of internal crosslinking agent.
• a monomer containing an acid group is preferable among monomers having an unsaturated double bond (ethylenically unsaturated monomers).
• monomers having an unsaturated double bond include anionic unsaturated monomers and/or salts thereof, such as (anhydrous) maleic acid, 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.
• anionic unsaturated monomers and/or salts thereof such as (anhydrous) maleic acid, fumaric acid, crotonic
• the salts 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.
• the monomer composition containing (meth)acrylic acid (salt) as the main component is preferably neutralized in the range of 10 to 90 mol%, more preferably in the range of 40 to 80 mol%, and particularly preferably in the range of 60 to 75 mol%.
• the monomer composition containing (meth)acrylic acid (salt) as the main component is 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 carbonate (hydrogen) salt, such as sodium (hydrogen) carbonate or potassium (hydrogen) carbonate, or ammonia, and it is particularly preferable that it is neutralized with a neutralizing solution containing sodium hydroxide.
• a neutralizing solution containing a basic compound such as an alkali metal hydroxide, such as sodium hydroxide, potassium hydroxide, or lithium hydroxide
• a carbonate (hydrogen) salt such as sodium (hydrogen) carbonate or potassium (hydrogen) carbonate
• ammonia it is particularly preferable that it is neutralized with a neutralizing solution containing sodium hydroxide.
• 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)".
• other monomer a hydrophilic or hydrophobic unsaturated monomer
• 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.
• amide group-containing unsaturated monomers such as N-vinyl-2-pyrrolidone, N-vinylacetamide, (meth)acrylamide, N-isopropyl(meth)acrylamide, N-ethyl
• the amount of other monomers used may be such that the physical properties of the resulting water-absorbent resin are not impaired; specifically, the amount is 50 mol% or less, more preferably 20 mol% or less, relative to the portion of the monomer composition excluding the internal crosslinking agent.
• the (meth)acrylic acid (salt) is preferably partially neutralized with the above-mentioned basic compound. That is, in one embodiment of the present invention, it is preferable to obtain a water-absorbing resin in which the acid group of poly(meth)acrylic acid is partially neutralized.
• the basic compound is preferably in the form of an aqueous solution from the viewpoint of ease of handling.
• the neutralization may be carried out before, during, or after polymerization, and may be carried out at multiple times or multiple times. From the viewpoint of production efficiency of the water-absorbent resin, it is preferable to carry out the neutralization in a continuous manner.
• 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, 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, relative to the acid groups of the monomer composition.
• the neutralization rate is applied to any of the neutralizations before, during, and after the polymerization described above. The same is also applied to the water absorbent resin and water absorbent.
• 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
• an internal crosslinking agent having two or more polymerizable unsaturated groups is preferably selected, and an internal crosslinking agent having two or more polymerizable unsaturated groups having a (poly)alkylene glycol structure is more preferably selected.
• Specific examples of the polymerizable unsaturated groups include allyl groups and (meth)acrylate groups. Of these, (meth)acrylate groups are preferred.
• 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.
• 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, and is preferably 10 mol% or less, more preferably 5 mol% or less, and even more preferably 1 mol% or less, based on the monomer composition excluding the internal crosslinking agent.
• an amount within this range a water-absorbent resin and a water-absorbent agent having the desired water-absorbing performance can be obtained.
• the amount used is outside this range, the gel strength may decrease, the water-soluble content may increase, and/or the absorption capacity may decrease.
• the timing of adding the internal crosslinking agent may be such that the polymer can be uniformly crosslinked, and examples of such methods include adding the internal crosslinking agent to an aqueous solution of the monomer composition before polymerization or to a hydrogel during or after polymerization.
• a method in which a predetermined amount of the internal crosslinking agent is added in advance to an aqueous solution of the monomer composition is preferred.
• 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, foaming agents that generate various bubbles, surfactants, chelating agents, chain transfer agents, and other compounds.
• hydrophilic polymer By using the hydrophilic polymer, it is possible to obtain a water-absorbing resin to which the hydrophilic polymer is grafted, 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.
• a water-absorbing resin to which the hydrophilic polymer is grafted 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.
• the amount of the other substances added is adjusted so as not to impair the effects of the present invention.
• the amount added is preferably 50% by mass or less in total, more preferably 20% by mass or less, even more preferably 10% by mass or less, and particularly preferably 5% by mass or less, and is preferably 0% by mass or more, more preferably more than 0% by mass, relative to the aqueous solution of the monomer composition (aqueous monomer solution).
• the monomer composition, the polyalkylene glycol described in "[2-4] Addition of water-soluble polyalkylene glycol" below, and the above-mentioned respective substances and components (referred to as “monomer components” in this section) are selected in various amounts according to the purpose, and the amounts are specified so as to satisfy the above-mentioned ranges and mixed together to prepare an aqueous solution of the total monomer components (i.e., an aqueous solution of the monomer composition, the respective substances and components described in "[2-4] Addition of water-soluble polyalkylene glycol” below).
• an aqueous solution of the total monomer components i.e., an aqueous solution of the monomer composition, the respective substances and components described in "[2-4] Addition of water-soluble polyalkylene glycol” below.
• 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 the individual monomer components.
• 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 containing a monomer containing (meth)acrylic acid (salt) as a main component and at least one type of internal crosslinking agent obtained in the monomer aqueous solution preparation step to obtain a hydrogel.
• Polymerization initiator As the polymerization initiator used in one embodiment of the present invention, one or more types can be selected from polymerization initiators used in the production of ordinary water absorbent resins according to 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.
• thermally decomposable initiators 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.
• persulfates such as sodium persulfate, potassium persulfate, and ammonium persulfate
• peroxides such as hydrogen peroxide, t-butyl peroxide, and methyl ethyl ketone peroxide
• azo compounds such as azonitrile compounds, azoamidine
• photodegradable initiators examples include benzoin derivatives, benzyl derivatives, acetophenone derivatives, benzophenone derivatives, azo compounds, etc.
• persulfates are preferred in consideration of cost and ability to reduce residual monomers.
• a reducing agent that promotes decomposition of the oxidizing polymerization initiator such as the persulfates or peroxides, can be used in combination to form a redox initiator.
• the reducing agent include (bi)sulfite (salts) such as sodium sulfite and sodium hydrogensulfite, L-ascorbic acid (salts), reducing metals (salts) such as ferrous salts, and amines.
• 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.
• the polymerization reaction may be initiated by irradiation with active energy rays such as radiation, electron beams, or ultraviolet rays.
• active energy rays such as radiation, electron beams, or ultraviolet rays.
• irradiation with active energy rays may be used in combination with the polymerization initiator.
• 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.
• aqueous solution polymerization or reversed-phase suspension polymerization is selected, and more preferably aqueous solution polymerization is selected.
• Aqueous solution polymerization is described in JP-A-4-255701 and the like.
• Reverse-phase suspension polymerization is described in WO 2007/004529, WO 2012/023433 and the like.
• Preferred forms of the continuous aqueous solution polymerization include high-temperature initiation polymerization, high-concentration polymerization, and foaming 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.
• “Foaming 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 two or more of them may be used in combination.
• the aqueous solution polymerization may be either a batch type or a continuous type, and the continuous type is preferred from the viewpoint of production efficiency.
• a polymerization form in which the polymerization reaction is quickly initiated after the addition of a polymerization initiator is preferable.
• a polymerization form in which the polymerization reaction starts within 1 minute after the polymerization initiator is added is preferable.
• a polymerization form in which the polymerization reaction is also quickly completed is preferable.
• a polymerization form in which the polymerization reaction is completed within 1 minute after the polymerization reaction starts is preferable.
• examples of the above-mentioned continuous aqueous solution polymerization include the 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 the continuous kneader polymerization described in U.S. Pat. No. 6,987,151, etc.
• the method of dispersing bubbles in the foaming polymerization includes a method of dispersing the gas dissolved in the aqueous monomer solution as bubbles by reducing the solubility, a method of introducing gas from the outside and dispersing it as bubbles, and a method of adding a foaming agent to the aqueous monomer solution to cause foaming.
• the above dispersion methods may be used in combination as appropriate depending on the physical properties of the target water-absorbing resin and water-absorbing agent.
• examples of the gas include oxygen, air, nitrogen, carbon dioxide, ozone, and mixtures of these gases. From the viewpoints of polymerization property and cost, it is preferable to use an inert gas such as nitrogen or carbon dioxide, and more preferably nitrogen.
• Usable foaming agents include azo compounds, organic or inorganic carbonate solutions, dispersions, and powders with particle sizes of 0.1 ⁇ m or more and 1000.0 ⁇ m or less.
• inorganic carbonates are preferred, and specifically, carbonates and hydrogen carbonates such as sodium carbonate, ammonium carbonate, and magnesium carbonate can be used.
• the foamed hydrogel obtained by the foaming polymerization can be dried easily by gel crushing.
• the water absorption rate of the water-absorbent resin and the water-absorbing agent can be improved, and it also becomes easier to fix it to an absorbent article.
• the foamed shape can be determined by checking the pores on the surface of the water-absorbent resin with an electron microscope, for example, pores with a diameter of 1 ⁇ m or more and 100 ⁇ m or less.
• the number of pores is preferably 1 or more, more preferably 10 or more, and preferably 10,000 or less, more preferably 1,000 or less per particle of water-absorbent resin, and can be controlled by adjusting the conditions in the foaming polymerization.
• 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.
• the hydrogel may be crushed in the polymerization step, or may be crushed after the polymerization step. That is, this step is a step in which the hydrogel is gel-crushed to obtain a particulate hydrogel (hereinafter, referred to as "particulate hydrogel”).
• this step is referred to as "gel crushing” to distinguish it from the "crushing” in the crushing step described later.
• the subject 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 later with an aqueous liquid, unless otherwise specified. Other steps are of the same purpose unless otherwise specified.
• the gel crushing refers to adjusting the hydrogel to a specified size using a screw extruder such as a kneader or meat chopper, or a gel crusher such as a cutter mill.
• 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 is preferably 100°C or lower.
• the method described in the literature describing continuous aqueous solution polymerization is adopted for the aqueous solution polymerization.
• the contents described in the pamphlet of International Publication No. 2011/126079 are also preferably applied to one embodiment of the present invention. Note that, when the polymerization form is kneader polymerization, the polymerization step and the gel crushing step are carried out simultaneously. In addition, by passing through the gel crushing step in one embodiment of the present invention, an irregularly crushed water absorbent resin can be obtained.
• the method for producing a particulate water-absorbing agent composition may include a granulation step in which fine powder recovered in a classification step described below is mixed with an aqueous liquid to obtain a granulated gel, at least one step from the end of the gel crushing step until drying is completed in a drying step, and/or a granulated gel adding step in which the granulated gel is added to the hydrogel between the steps.
• a granulation step in which fine powder recovered in a classification step described below is mixed with an aqueous liquid to obtain a granulated gel
• at least one step from the end of the gel crushing step until drying is completed in a drying step and/or a granulated gel adding step in which the granulated gel is added to the hydrogel between the steps.
• a granulated gel adding step in which the granulated gel is added to the hydrogel between the steps.
• the particulate hydrogel obtained by gel crushing with the below-mentioned predetermined gel crushing energy improves the water absorption speed of the water-absorbing resin and the water-absorbing agent obtained thereafter in terms of physical properties, for example, the FSR described in International Publication No. 2009/016055 and the Vortex described in JIS K7224 (1996) "Testing method for water absorption speed of superabsorbent resin".
• gel grinding energy refers to the unit energy required by the gel grinding device when grinding hydrous gel, i.e., the mechanical energy per unit mass of hydrous gel, and does not include the energy required to heat and cool the jacket or the energy of the water and steam added.
• GGE Gel Grinding Energy
• the "power factor” and “motor efficiency” are values specific to the device that change depending on the operating conditions of the gel grinding device, and take values of 0 to 1. These values can be obtained by contacting the device manufacturer, etc.
• GGE can be calculated by changing " ⁇ 3" in the above formula (I) to "1".
• the unit of voltage is [V]
• the unit of current is [A]
• the unit of mass of hydrous gel is [g/s].
• the "power factor” and “motor efficiency” of the GGE are the values used when gel is being crushed.
• the power factor and motor efficiency values during idle operation are approximately defined as in formula (I) above, since the current value during idle operation is small.
• the "mass of hydrous gel fed into the gel crusher per second" [g/s] refers to the value converted to [g/s], for example, when the hydrous gel is continuously fed by a fixed quantity feeder.
• the hydrous gel may contain recycled granulated gel, as described below.
• 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.
• GGE gel crushing energy
• GGE gel grinding energy
• gel crushing energy when controlling the gel crushing energy as described above, better effects can be obtained by combining it 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.
• the particle diameter of the particulate hydrogel finely granulated by the gel crushing step is preferably in the range of 0.100 mm or more and 10,000 mm or less.
• 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.
• drying is performed sufficiently.
• 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.
• the particle size of the particulate hydrogel is 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 ( ⁇ ) of the particle size distribution indicates the narrowness of the particle size distribution, and the smaller the value, the more uniform the particle size becomes, and the more uniform the drying can be.
• a special operation such as classification of the particulate hydrogel after gel crushing is required, which is practically difficult to implement from the viewpoints of productivity and cost.
• the mass average particle size (D50) and logarithmic standard deviation ( ⁇ ) of the particulate hydrogel are measured, for example, by the method described in WO2021/140905.
• the water content of the particulate hydrous gel 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.
• 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 % based on the total mass of the monomers contained in the aqueous monomer solution.
• the polyalkylene glycol may be one having a structure represented by the following general formula (1):
• R is an alkylene group having 2 to 4 carbon atoms, which may be linear or branched.
• n has an average value of 4 to 70, more preferably is 4 to 50, more preferably 6 to 15.
• the oxyalkylene groups (-OR-) in one molecule may be the same, or may contain two or more types of oxyalkylene groups.
• 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.
• the polyalkylene glycol is water-soluble.
• water-soluble means that 5 g or more, more preferably 10 g or more, dissolves in 100 g of water at 25°C.
• the polyalkylene glycol is water-soluble, so that it can be added more uniformly when added in at least one of the above-mentioned monomer aqueous solution preparation steps, polymerization steps, and hydrogel crushing steps. As a result, it is possible to obtain a water-absorbent resin and a water-absorbing agent in which the polyalkylene glycol is uniformly present.
• the polyalkylene glycol has a mass average molecular weight of 3000 or less.
• the effect of improving the anti-caking performance by adding a nonionic polymer having a polyalkylene glycol chain in its structure and having the mass average molecular weight and the amount of addition can be suitably improved when the nonionic polymer is added to the water absorbent resin after surface crosslinking.
• 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.
• the mass average molecular weight of the polyalkylene glycol is a value measured by gel permeation chromatography.
• the amount of the polyalkylene glycol added is 0.01% by mass to 0.25% by mass with respect to the total mass of the monomers contained in the aqueous monomer solution.
• 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. If the amount of the polyalkylene glycol added is 0.01% by mass or more, when a nonionic polymer containing a polyalkylene glycol chain in its structure with the mass average molecular weight and amount is added to a surface-crosslinked water-absorbent resin obtained by polymerization, the effect of improving the caking resistance due to the addition of the nonionic polymer can be improved.
• the amount of the polyalkylene glycol added exceeds 0.25% by mass, the caking resistance of the water-absorbent resin after surface crosslinking deteriorates, that is, the moisture absorption blocking rate (B.R.) increases, compared to when the polyalkylene glycol is not added, which is not preferable.
• 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, 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.
• polyalkylene glycol it is sufficient to add 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 that range. Furthermore, when one or multiple types of polyalkylene glycols are used, polyalkylene glycols having multiple types of mass average molecular weights may be used in combination.
• the water-soluble polyalkylene glycol having the mass average molecular weight and the amount is added in at least one of the steps selected from the above-mentioned monomer aqueous solution preparation step, polymerization step, and hydrous gel crushing step.
• the polyalkylene glycol may be added in any one of the above-mentioned aqueous monomer solution preparation process, polymerization process, and hydrous gel crushing process, or in any two or all of the processes.
• the polyalkylene glycol is added in multiple processes, the polyalkylene glycol added in each process may be the same or different.
• the amount added is such that the total amount of the polyalkylene glycol added in the multiple steps falls within the above-mentioned range.
• Drying step This step is a step of 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 is a step of drying the particulate hydrogel, or when a granulated gel is added, both the granulated gel and the particulate hydrogel to a 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 is preferably 99% by mass or less, even more preferably 98% by mass or less, particularly preferably 97% by mass or less.
• the dried polymer is in a block shape, and the water content may differ between the upper and lower parts, the center, and the ends of the block.
• the dried polymer is appropriately taken from various positions, crushed if necessary, and the moisture content is measured and averaged.
• a dried polymer below the specified solid content may be referred to as an undried material.
• the "material to be dried” or "particulate hydrous gel” in the drying process may include both particulate hydrous gel and granulated gel.
• the drying process of the present invention is particularly effective when it includes both particulate hydrous gel and granulated gel.
• the hydrous gel and its processed products may include granulated gel and its processed products.
• the drying method in the drying step includes, for example, 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.
• 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 ventilated band dryer that performs hot air drying on a ventilated belt. By using a ventilated band dryer, efficient drying can be performed while preventing physical damage to the material to be dried, such as the dried polymer or particulate hydrous gel during drying, and generation of fine powder due to friction.
• the drying temperature i.e., the temperature of the hot air
• 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.
• drying conditions may be set appropriately depending on the moisture content, total mass, and desired solid content of the particulate hydrous gel or granulated gel to be dried.
• band drying the conditions described in International Publication Nos. 2006/100300, 2011/025012, 2011/025013, 2011/111657, etc. are appropriately applied.
• the pulverization step is an optional step of pulverizing the dried polymer
• the classification step is an optional step of removing fine powder from the pulverized dried polymer.
• the pulverization step is a step of pulverizing the dried polymer obtained through the drying step.
• 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.
• the grinding device used in the grinding step includes high-speed rotary grinders such as roll mills, hammer mills, screw mills, and pin mills; vibration mills; knuckle-type grinders; cylindrical mixers, and the like.
• high-speed rotary grinders such as roll mills, hammer mills, screw mills, and pin mills; vibration mills; knuckle-type grinders; cylindrical mixers, and the like.
• a roll mill is preferably selected.
• a plurality of these grinders can be used in combination.
• the particle size can be adjusted in the classification step by sieve classification using a JIS standard sieve (JIS Z 8801-1 (2000)) or airflow classification.
• 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.
• the water-absorbent resin preferably has a mass average particle diameter (D50) of 300 ⁇ m or more and 600 ⁇ m or less.
• the water-absorbent resin preferably has a mass ratio of particles having a particle diameter of 850 ⁇ m or more of 3 mass% or less.
• the water-absorbent resin preferably has a mass ratio of particles having a particle diameter of 300 ⁇ m or more and less than 850 ⁇ m of 50 mass% or more ... less than 150 ⁇ m of 5 mass% or less.
• the upper limit of the mass average particle diameter (D50) is more preferably 500 ⁇ m or less, and even more preferably 450 ⁇ m or less.
• the mass ratio of particles having a particle diameter of 850 ⁇ m or more of the water-absorbent resin is more preferably 2 mass% or less, and even more preferably 1 mass% or less.
• the mass ratio of particles having a particle diameter of 300 ⁇ m or more and less than 850 ⁇ m of the water-absorbent resin is more preferably 55 mass% or more, and even more preferably 60 mass% or more.
• the mass ratio of the particles of the water absorbent resin having a particle diameter of less than 150 ⁇ m is more preferably 4 mass% or less, even more preferably 3 mass% or less, and particularly preferably 2 mass% or less.
• the logarithmic standard deviation ( ⁇ ) 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 ( ⁇ ) of the particle size distribution indicates the narrowness of the particle size distribution, and the smaller the value, the more uniform the particle diameter becomes, and there is an advantage that the segregation of the particles is reduced.
• 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 ⁇ m or more, the mass proportion of particles having a particle diameter of 300 ⁇ m or more and less than 850 ⁇ m, and the mass proportion of particles having a particle diameter of less than 150 ⁇ m, and more preferably satisfies the above-mentioned mass average particle diameter (D50), the mass proportion of particles having a particle diameter of 850 ⁇ m or more, the mass proportion of particles having a particle diameter of 300 ⁇ m or more and less than 850 ⁇ m, the mass proportion of particles having a particle diameter of less than 150 ⁇ m, and the logarithmic standard deviation, and can be appropriately combined within each of the above ranges.
• D50 mass average particle diameter
• the mass-average particle diameter (D50) and logarithmic standard deviation ( ⁇ ) are measured by the method described in U.S. Patent No. 7,638,570, “(3) Mass-Average Particle Diameter (D50) and Logarithmic Standard Deviation ( ⁇ ) of Particle Diameter Distribution.”
• the above-mentioned particle size is also applied to the water absorbent resin after the pulverization step and the classification step, and to the particulate water absorbent composition produced by the above-mentioned production method. Therefore, when surface cross-linking is performed, it is preferable to carry out surface cross-linking treatment in the surface cross-linking step so as to maintain the particle size in the above-mentioned range adjusted in 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.
• the water absorbent resin after the surface cross-linking step, the water absorbent resin and the particulate water absorbent composition to be subjected to the nonionic polymer addition step which are manufactured by the manufacturing method according to one embodiment of the present invention, preferably satisfy that the mass average particle diameter (D50), the mass ratio of particles having a particle diameter of 850 ⁇ m or more, the mass ratio of particles having a particle diameter of 300 ⁇ m or more and less than 850 ⁇ m, and the mass ratio of particles having a particle diameter of less than 150 ⁇ m are within the above-mentioned ranges, and it is more preferable that the mass average particle diameter (D50), the mass ratio of particles having a particle diameter of 850 ⁇ m or more, the mass ratio of particles having a particle diameter of 300 ⁇ m or more and less than 850 ⁇ m, the ratio of particles having a particle diameter of less than 150 ⁇ m, and the logarithmic standard deviation ( ⁇ ) of the particle size distribution are within the above-mentioned ranges.
• the water absorbent resin after the surface cross-linking step, the water absorbent resin to be subjected to the nonionic polymer addition step, and the particulate water absorbent composition which are manufactured by the manufacturing method according to one embodiment of the present invention, have a mass average particle diameter (D50) of 300 to 600 ⁇ m, a mass ratio of particles having a particle diameter of 850 ⁇ m or more is 3 mass% or less, a mass ratio of particles having a particle diameter of 300 ⁇ m or more and less than 850 ⁇ m is 50 mass% or more, a mass ratio of particles having a particle diameter of less than 150 ⁇ m is 5 mass% or less, and a logarithmic standard deviation ( ⁇ ) of the particle size distribution is 0.20 to 0.50.
• D50 mass average particle diameter
• 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 each of the steps described above, and is configured to include a mixing step, a heat treatment step, a cooling step, etc.
• 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, and a surface-cross-linked water-absorbent resin is obtained.
• the water-absorbent resin before surface cross-linking obtained through each of the steps described above is the dried polymer, the water-absorbent resin obtained by pulverizing and/or classifying the dried polymer, etc.
• Mixing step This step is a step of obtaining a mixture by mixing a solution containing a surface crosslinking agent (hereinafter, referred to as a "surface crosslinking agent solution”) with a water absorbent resin before surface crosslinking in a mixing device.
• a surface crosslinking agent solution a solution containing a surface crosslinking agent
• water absorbent resin a water absorbent resin
• Examples of the surface cross-linking agent used in the production method according to one embodiment of the present invention include the surface cross-linking agents described in U.S. Patent No. 7,183,456. At least one type of surface cross-linking agent is selected from these surface cross-linking agents in consideration of reactivity, etc. In addition, from the viewpoint of the handleability of the surface cross-linking agent and the water absorption performance of the water-absorbing resin and the water-absorbing agent, it is preferable to select an organic compound that is a surface cross-linking agent having two or more functional groups that react with a carboxyl group and that forms a covalent bond.
• the surface cross-linking agent examples 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, 2,4 polyhydric alcohol compounds such as 1,2-pentanediol, 1,3-hexanediol, 1,4-hexanediol, 1,5-hexanediol, 1,6-hexanediol, 2,3-hexanediol, 2,4-hex
• the amount of the surface cross-linking agent 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 cross-linking.
• the surface cross-linking agent is preferably added as an aqueous solution to the water absorbent resin before surface cross-linking.
• 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 the water absorbent resin before surface cross-linking.
• the surface cross-linking agent solution can be prepared by using a hydrophilic organic solvent together with the water as necessary.
• 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.
• various additives can be added to the surface cross-linking agent solution in an amount of 5 parts by mass or less, and/or can be added separately in the mixing step.
• the water absorbent resin and the surface crosslinking agent solution are mixed by preparing a surface crosslinking agent solution in advance, and then spraying or dropping the solution onto the crosslinked polymer, preferably by spraying or dropping the solution onto the crosslinked polymer.
• a method of mixing is selected.
• the mixing device for carrying out the mixing preferably has a torque required for uniformly and reliably mixing the water absorbent resin and the surface cross-linking agent.
• the mixing device is preferably a high-speed stirring type mixer, and more preferably a high-speed stirring type continuous mixer.
• the rotation speed of the high-speed stirring type 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.
• the temperature of the water-absorbent resin supplied to this step is preferably 35°C to 80°C, more preferably 35°C to 70°C, and even more preferably 35°C to 60°C, from the viewpoint of mixability with the surface cross-linking agent solution and coagulation of the humidified mixture.
• the mixing time is preferably 1 second or more, more preferably 5 seconds or more, and is preferably 1 hour or less, more preferably 10 minutes or less.
• Heat Treatment 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 be performed by heating the water-absorbent resin in a stationary state or by heating the water-absorbent resin in a fluidized state using a power such as stirring, but heating under stirring is preferable in that the entire humidified mixture can be heated evenly.
• examples of the heat treatment device include a paddle dryer, a multi-fin processor, and a tower dryer.
• the so-called controlled temperature of the heat treatment device is sufficient if it can 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 preferable that the temperature is 50°C to 300°C. When emphasis is placed on damage resistance as a physical property of the obtained water-absorbent resin, it is more preferable that the temperature is 250°C or lower, even more preferable that the temperature is 70°C to 230°C, and especially preferable that the temperature is 90°C to 220°C.
• the temperature is 120°C to 280°C, even more preferable that the temperature is 150°C to 250°C, and especially preferable that the temperature is 170°C to 230°C.
• 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 process will be insufficient and the absorbency under pressure (AAP) will decrease. On the other hand, if the heating time is longer, discoloration may occur and/or the absorbency under no pressure (CRC) may decrease too much.
• AAP absorbency under pressure
• CRC absorbency under no pressure
• 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, and quickly completing the surface cross-linking reaction.
• the water-absorbent resin may be cooled in a stationary state or in a fluidized state using a power such as stirring, but it is preferable to cool the water-absorbent resin under stirring, since the entire water-absorbent resin can be cooled evenly.
• cooling devices that perform the cooling include paddle dryers, multi-fin processors, tower dryers, etc. Note that these cooling devices can also be of the same specifications as the heat treatment devices used in the heat treatment process. This is because they can be used as cooling devices by changing the heat medium of the heat treatment device to a refrigerant.
• the cooling temperature in this step may be set appropriately 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 or less.
• Nonionic polymer addition step In the manufacturing method of the particulate water-absorbing agent composition according to one embodiment of the present invention, after the surface cross-linking step, a nonionic polymer containing a polyalkylene glycol chain in its structure and having a mass average molecular weight of 300 to 15000 is added to the surface-cross-linked water-absorbing resin in an amount of 0.02 mass % to 0.40 mass %. That is, the manufacturing method of the particulate water-absorbing agent composition according to one embodiment of the present invention includes a nonionic polymer addition step. This step includes an addition step, a mixing step, and a curing step.
• Nonionic Polymer preferably contains a polyalkylene glycol chain represented by the following general formula (2) in its structure.
• R is an alkylene group having 2 to 4 carbon atoms, which may be linear or branched.
• m has an average value of 4 to 350, more preferably is preferably 5 to 250, more preferably 6 to 100.
• the oxyalkylene groups (-OR-) in one molecule may be the same, or two or more types of oxyalkylene groups may be included.
• the nonionic polymer contains a polyalkylene glycol chain in its structure, and when 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 one process selected from the monomer aqueous solution preparation process, the polymerization process, and the hydrous gel crushing process, the caking resistance can be improved without deteriorating the water absorption performance under pressure of the resulting water absorbent.
• Nonionic polymers containing the polyalkylene glycol chain in their structure include, for example, 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 alkyl aryl ethers such as polyoxyethylene nonylphenyl ether; polyoxyethylene sorbitan monooxyethylene ether; Examples of the nonionic polymers include polyoxyethylene sorbitan fatty acid esters such as polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan tristearate, polyoxyethylene sorbitan monooleate,
• the mass average molecular weight of the nonionic polymer is 300 to 15,000.
• the anti-caking performance of the obtained water absorbent is greatly improved 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 the above amount in at least one process selected from the monomer aqueous solution preparation process, the polymerization process, and the hydrous gel crushing process.
• the mass average molecular weight of the nonionic polymer is more preferably 350 or more, even more preferably 400 or more, and also 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.
• the HLB of the nonionic polymer is preferably 5 or more, more preferably 10 or more. If the HLB of the nonionic polymer is within the above range, when the nonionic polymer is added to a surface-crosslinked water-absorbing 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 one of the steps selected from the monomer aqueous solution preparation step, the polymerization step, and the hydrous gel crushing step, the caking resistance can be improved without deteriorating the water absorption performance under pressure of the resulting water absorbent.
• 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. Emulsify a certain type of oil with the nonionic polymer whose HLB you wish to determine (add a surfactant with a known HLB if necessary), and emulsify the same oil with a different surfactant with a known HLB (use one with the appropriate HLB value). The HLB of the nonionic polymer when the emulsified states are the same is taken as the HLB of the nonionic polymer.
• the amount of the nonionic polymer added is 0.02% by mass to 0.40% by mass relative to the surface-crosslinked water-absorbent resin.
• the anti-caking performance of the obtained water absorbent is greatly improved when the nonionic polymer is added to the surface-crosslinked water-absorbent resin produced by adding the water-soluble polyalkylene glycol having the above mass average molecular weight and the above amount 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.
• the amount of the nonionic polymer added is more preferably 0.04% by mass or more, even 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. Moreover, the amount added is more preferably 0.35% by mass or less.
• nonionic polymer it is sufficient to add a nonionic polymer with the above-mentioned mass average molecular weight and amount, and multiple types of nonionic polymers may be used within that range. Furthermore, when using one or multiple types of nonionic polymers, each nonionic polymer may be used in combination with multiple types of mass average molecular weight.
• 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-cross-linked water absorbent resin.
• the method of adding the nonionic polymer to the surface-crosslinked water-absorbent resin is not particularly limited.
• the nonionic polymer may be added as it is, or may be added as a solution diluted with an organic solvent, or may be added as an aqueous solution, and it is more preferable to add it as an aqueous solution.
• 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.
• the method of mixing the surface-crosslinked water-absorbent resin with the nonionic polymer or its aqueous solution is not particularly limited, and may be 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.
• 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.
• the cost required to make the droplets fine is too expensive for the effect obtained, so the average droplet diameter is preferably 10 ⁇ m or more, more preferably 30 ⁇ m or more, and even more preferably 50 ⁇ m or more.
• the mixing device for carrying out the mixing preferably has a torque necessary for uniformly and reliably mixing the water-absorbent resin after surface cross-linking with the nonionic polymer.
• the mixing device include a cylindrical mixer, a double-walled cone mixer, a V-shaped mixer, a ribbon mixer, a screw mixer, a rotary disk mixer, a double-arm kneader, an internal mixer, a grinding kneader, a rotary mixer, a screw extruder, a fluidized bed mixer, and an airflow mixer.
• Devices capable of mixing by stirring are more preferable, and examples of such devices include a high-speed stirring mixer and a vertical rotating disk mixer.
• a high-speed stirring continuous mixer is preferable, and a horizontal high-speed stirring continuous mixer and a vertical high-speed stirring continuous mixer are more preferable.
• the high-speed stirring mixer include a Shugi mixer (manufactured by Hosokawa Micron Corporation), a Turbulizer (manufactured by Hosokawa Micron Corporation), a Redidge mixer (manufactured by Redidge Corporation), and a Flow Jet Mixer (manufactured by Powder and Powder Powtex Corporation).
• the rotation speed is preferably 5 rpm or more, more preferably 10 rpm or more, and preferably 10,000 rpm or less, more preferably 2,000 rpm or less.
• the temperature of the nonionic polymer or its aqueous solution to be mixed is preferably 10°C to 70°C, more preferably 20°C to 60°C, from the viewpoint of mixability and coagulation of the humidified mixture.
• the temperature range is the temperature measured before being affected by the temperature of the water-absorbent resin and/or the temperature of the device in which the water-absorbent resin is retained when the nonionic polymer or its aqueous solution is added to the water-absorbent resin.
• the temperature of the water absorbent resin after surface cross-linking that is used for mixing is preferably 180°C or lower, more preferably 160°C or lower, and even more preferably 150°C or lower, from the viewpoints of the time required for cooling after the surface cross-linking step, the mixability, and the coagulation property of the humidified mixture, and is preferably 40°C or higher, more preferably 50°C or higher, and even more preferably 60°C or higher.
• the mixture of the obtained water-absorbent resin after surface cross-linking and the nonionic polymer or its aqueous solution is preferably subjected to a curing process.
• the "curing” refers to an operation of removing the wettability of the water-absorbent resin surface and powdering it.
• the “curing process” is a process of controlling the temperature of the object to a predetermined curing temperature and maintaining the temperature state for a predetermined curing time to cure the object.
• 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 is in a wet state, which may result in strong adhesion and difficulty in handling the powder. If the curing temperature is too high and/or the curing time is too long, it is energy uneconomical.
• the addition and mixing of the nonionic polymer or its aqueous solution and the subsequent curing treatment may be performed in the same device or in different devices.
• the above-mentioned series of treatments may be performed during the cooling process or after the cooling process.
• the device to be used may be the above-mentioned mixing device, and a heat medium such as gas or conductive heat may be adjusted so that the temperature inside the device is the above-mentioned temperature.
• 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.
• the water absorbent resin When the curing treatment is performed by leaving the mixture to stand, the water absorbent resin may be layered to a thickness of preferably 1 cm or more, more preferably 5 cm or more, and 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, and then cured.
• the cured water absorbent composition may be crushed or classified as necessary to obtain a particulate water absorbent composition having a desired particle size.
• the particulate water absorbent composition according to one embodiment of the present invention is a method for manufacturing a particulate water absorbent composition containing a poly(meth)acrylic acid (salt)-based water absorbent resin, comprising a monomer aqueous solution preparation step for preparing a (meth)acrylic acid (salt)-based monomer aqueous solution, a polymerization step for polymerizing the (meth)acrylic acid (salt)-based monomer aqueous solution, a hydrogel crushing step which is an optional step for gel-crushing a hydrogel-like crosslinked polymer generated during or after polymerization, a drying step for drying the particulate hydrogel, a crushing step which is an optional step for crushing and classifying the dried polymer, and a classification step which is an optional step
• a particulate water-absorbing agent composition is a particulate water-absorbing agent composition containing a poly(meth)acrylic acid (salt)-based water-absorbing resin as a main component, a nonionic polymer having a polyalkylene glycol chain in its structure, and a mass ratio of particles having a particle diameter of 300 ⁇ m or more and less than 850 ⁇ m of 50 mass % or more, (a) The nonionic polymer contained in the particulate water-absorbing agent composition is designated as A1, and its content is designated as C1, (b) subjecting the particulate water-absorbing agent composition to a predetermined impact test; (c) The particulate water-absorbing agent composition that has been subjected to the impact test is sieved using a JIS standard sieve into a particle group a having a particle diameter of 300 ⁇ m or more and a particle group b having a particle diameter of less than 300 ⁇ m, (d) When the nonionic polymer present in the particle group
• the water-soluble polyalkylene glycol is a kind of nonionic polymer having a polyalkylene glycol chain in its structure. Therefore, the nonionic polymer contained in the particulate water-absorbing agent composition satisfying A1, i.e., all of (1) to (4), is specifically composed of the polymers shown in (i) and (ii) below.
• the predetermined impact test is a test carried out by the following operations (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 having a diameter of 6 mm are placed in a glass container having 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.
• the glass beads are removed from the mixture of the pulverized particulate water-absorbing agent composition obtained in (ii) and the glass beads.
• the method of removing the glass beads is not particularly limited, and examples thereof include sieving the pulverized particulate water-absorbing agent composition through a sieve having a mesh size that does not allow the glass beads to pass through, for example, a sieve having a mesh size of 2 mm.
• the particle size and particle size distribution of the particulate water-absorbing agent composition satisfying all of the above (1) to (4) are preferably in the same range as the preferred ranges of the particle size and particle size distribution of the water-absorbing resin after the above-mentioned surface cross-linking step and the water-absorbing resin to be subjected to the nonionic polymer addition step.
• the particle size and particle size distribution are represented, for example, by the mass average particle size (D50), the mass ratio of particles having a particle size of 850 ⁇ m or more, the mass ratio of particles having a particle size of 300 ⁇ m or more and less than 850 ⁇ m, the mass ratio of particles having a particle size of less than 150 ⁇ m, and the logarithmic standard deviation ( ⁇ ) of the particle size distribution.
• D50 mass average particle size
• ⁇ logarithmic standard deviation
• the 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-absorbent resin, and more preferably, a particulate water-absorbing agent composition containing a poly(meth)acrylic acid (salt)-based water-absorbent resin as a main component (preferably, 60% by mass or more and less than 100% by mass, 70% by mass or more and less than 100% by mass, 80% by mass or more and less than 100% by mass, or 90% by mass or more and 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 crushed (irregular), spherical, fibrous, rod-like, approximately spherical, or flat. Among them, it is preferable that at least a part of the resin is irregularly crushed.
• the water-absorbent resin has an irregular shape.
• the absorbency under pressure (AAP) of the water absorbent resin after surface crosslinking 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.
• the AAP When the AAP is 20.0 g/g 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.
• the AAP can be controlled by an internal cross-linking agent, particle size, and/or a surface cross-linking agent, etc.
• the absorbency under pressure (AAP) at a pressure of 0.7 psi is a value determined by the method described in the Examples section below.
• the fixed height absorption value (FHA) at a height of 20 cm of the water absorbent resin after surface crosslinking 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.
• the FHA When the FHA is 20.0 g/g 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.
• the FHA can be controlled by an internal cross-linking agent, particle size, and/or a surface cross-linking agent, etc.
• FHA is a value determined by the method described in the Examples section below.
• the moisture absorption blocking rate ⁇ 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.
• the water absorbent or water absorbent resin is difficult to handle, and during the production of the absorbent in the absorbent article, the problem of coagulation and clogging in the transfer piping of the production plant due to caking, and the problem of not being able to be mixed uniformly with the hydrophilic fiber are unlikely to occur.
• the B.R. ⁇ 1> is low from the viewpoint that the B.R. ⁇ 1> can be suitably reduced by adding 0.02% by mass to 0.40% by mass of a nonionic polymer having a mass average molecular weight of 300 to 15,000, which contains a polyalkylene glycol chain in its structure, to the surface crosslinked water absorbent resin after the surface crosslinking step. Therefore, at the stage of the water absorbent resin after surface crosslinking, the B.R. ⁇ 1> may be 99% by mass or less.
• B.R. ⁇ 1> is a value determined by the method described in the Examples section below.
• the water absorbent resin after surface crosslinking has a non-loaded 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.
• CRC non-loaded absorption capacity
• CRC is a value determined by the method described in the Examples section below.
• 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, further 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, and a higher value is more preferable.
• SFC is a value determined by the method described in the Examples section below.
• the free swelling rate (FSR) of the water absorbent resin after surface crosslinking 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.
• FSR is a value determined by the method described in the Examples section below.
• the particulate water-absorbing agent composition has an absorbency 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.
• AAP absorbency against pressure
• 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.
• the AAP When the AAP is 20.0 g/g 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.
• the AAP can be controlled by the internal cross-linking agent, particle size, surface cross-linking agent, and/or additives added after the surface cross-linking process.
• 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, further preferably 25.0 g/g or more, and particularly preferably 25.3 g/g or more.
• FHA fixed height absorption
• the absorbency improves when pressure is applied to the absorbent, making it suitable for use as an absorbent in absorbent articles such as disposable diapers.
• the FHA can be controlled by the internal cross-linking agent, particle size, surface cross-linking agent, and/or additives added after the surface cross-linking process.
• 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.
• the B.R. ⁇ 1> exceeds 90% by mass, the particulate water-absorbing agent composition is difficult to handle in a humid environment, and there is a risk of problems occurring during the production of an absorbent body in an absorbent article, such as the occurrence of aggregation and clogging in a transfer pipe in a production plant due to caking, or the inability to be uniformly mixed with hydrophilic fibers.
• the value ( ⁇ B.R.) obtained by subtracting the B.R. of the particulate water absorbent composition obtained by adding the nonionic polymer from the B.R. of the water absorbent resin after surface crosslinking is preferably 20 mass% or more, more preferably 25 mass% or more, even more preferably 30 mass% or more, and particularly preferably 35 mass% or more. If ⁇ B.R. is 20 mass% or more, the effect of improving the caking resistance by adding the nonionic polymer is large.
• ⁇ B.R. is a value determined by the method described in the Examples section below.
• the particulate water-absorbing agent composition has a non-loaded 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.
• CRC non-loaded absorption capacity
• the particulate water-absorbing agent composition has a saline flow conductivity (SFC) of preferably 1 ⁇ 10 ⁇ 7 cm 3 sec/g or more, more preferably 10 ⁇ 10 ⁇ 7 cm 3 sec/g or more, further preferably 15 ⁇ 10 ⁇ 7 cm 3 sec/g or more, and particularly preferably 20 ⁇ 10 ⁇ 7 cm 3 sec/g or more.
• SFC saline flow conductivity
• the upper limit of the SFC is not particularly limited, although a higher value is more preferable.
• the free swelling rate (FSR) of the particulate water-absorbing agent composition 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 even more preferably 0.35 g/(g ⁇ s) or more.
• the surface tension of the particulate water-absorbing agent composition is preferably 45 mN/m or more, more preferably 50 mN/m or more, further 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.
• the surface tension is 45 mN/m or more, the amount of liquid that returns to the absorbent when pressure is applied to it is not too large, making it suitable for use as an absorbent in absorbent products such as disposable diapers.
• the surface tension can be controlled by additives added after surface cross-linking.
• the particulate water-absorbing agent composition has a mass average particle diameter (D50) of preferably 300 ⁇ m or more and 600 ⁇ m or less, more preferably 500 ⁇ m or less, and more preferably 450 ⁇ m or less.
• the mass ratio of particles having a particle diameter of 850 ⁇ m 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 paper diapers, the rough feeling of the particulate water-absorbing agent composition is reduced and the wearing comfort is improved.
• the mass ratio of particles having a particle diameter of 300 ⁇ m or more and less than 850 ⁇ m in the particulate water-absorbing agent composition is 50 mass% or more, preferably 55 mass% or more, and more preferably 60 mass% or more.
• the mass ratio of particles having a particle diameter of less than 150 ⁇ m 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.
• the mass ratio of particles having a particle diameter of less than 150 ⁇ m is equal to or less than the above-mentioned upper limit value from the viewpoint of preventing deterioration of the working environment due to scattering of dust in the place where the particulate water-absorbing agent composition is handled.
• the impact test causes the particles constituting the surface layer of the particulate water absorbent composition to peel off.
• the particles that have peeled off and the particles smaller than 300 ⁇ m that existed before the impact test constitute a particle group b, and the particles remaining after the particles constituting the surface layer have peeled off constitute a particle group a.
• the particle group a is composed of particles constituting the part other than the surface layer of the particulate water absorbent composition.
• 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 composition, i.e., the inside.
• the value represented by C1-C2 means the amount of nonionic polymer present in the surface layer of the particulate water absorbent composition, i.e., the surface.
• the content represented by C1 i.e., the total value of the 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 including the preferred range of each content described later, and is preferably 0.025 mass% or more, more preferably 0.03 mass% or more, based on the mass of the solid content in the particulate water-absorbing agent composition.
• the content represented by C1 is preferably 0.55 mass% or less, more preferably 0.50 mass% or less, based on the mass of the solid content in the particulate water-absorbing agent composition.
• 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, and more preferably 0.015 mass% or more, relative to the mass of the solid content in the particle group a.
• 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, since the effect of improving the caking resistance 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 value, since it is possible to prevent deterioration of the caking resistance due to excessive inclusion of the polyalkylene glycol.
• 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. Also, the content represented by C1-C2 is preferably 0.40 mass% or less, and more preferably 0.35 mass% or less. It is preferable that the content represented by C1-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.
• the content represented by C1-C2 is equal to or less than the above-mentioned upper limit value, from the viewpoint of preventing an increase in cost due to an excessive amount of the nonionic polymer used.
• the C1 and C2 can be measured by the following methods (A) to (E), specifically, by the method described in the Examples.
• (A) In advance, mass spectrometry is performed by chromatography on aqueous solutions of nonionic polymers having known concentrations, and a calibration curve is prepared.
• B) 1 g of the particle group a or the particulate water-absorbing agent composition is placed in an appropriate container and used as a measurement sample.
• the "ultrapure water” refers to water having a specific resistance of 15 M ⁇ cm or more.
• the particulate water-absorbing agent composition produced by the production 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.
• the absorbent article according to one embodiment of the present invention is an absorbent article that is a production method for an absorbent article having an absorbent body containing a particulate water-absorbing agent composition, and uses, as the particulate water-absorbing agent composition, a particulate water-absorbing agent composition produced by the production method for a water-absorbing agent according to one embodiment of the present invention described above.
• the absorbent article according to one embodiment of the present invention is an absorbent article that includes the particulate water-absorbing agent composition according to one embodiment of the present invention.
• 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 exudates, such as urine, feces, and blood, discharged from the body.
• absorbent articles include diapers and pants worn by infants, toddlers, and/or adults; absorbent inserts for diapers and pants; feminine care absorbent articles such as sanitary napkins and panty liners.
• the absorbent article may include a topsheet, a backsheet, an absorbent core, and optionally an absorbent-diffusion system.
• the absorbent core is disposed between the backsheet and the topsheet, and the optional absorbent-diffusion system is typically disposed between the absorbent core and the topsheet.
• the particulate water-absorbing agent composition produced by the production method according to one embodiment of the present invention may be included in an absorbent core of an absorbent article.
• the absorbent core may or may not include 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.
• Diaper and “Pants” refer to absorbent articles worn by infants, toddlers, and incontinent (adults) about the lower torso to encircle the waist and legs of the wearer, and are specifically adapted to receive and contain urinary and fecal exudates.
• the longitudinal edges of the first and second waist regions (those corresponding to the waist region at the front of the body and the waist region at the back of the body) are attached to one another to preform waist and leg openings. The pant is placed in position on the 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.
• the pant may be preformed by any suitable technique, including, but not limited to, joining portions of the absorbent article together using reattachable and/or non-reattachable joints (e.g., stitching, welding, adhesives, adhesive joints, fasteners, etc.). Pants can be preformed anywhere along the circumference of the article (e.g., side fastened, front waist fastened).
• a suitable fastening system 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).
• the diapers and pants may include elastic leg cuffs and barrier leg cuffs that improve containment of liquids and other body exudates, especially in the area of the leg openings.
• each leg cuff and barrier cuff includes one or more elastic strings.
• Feminine care absorbent articles are personal care products used by women to absorb and contain menstrual blood, vaginal discharges, and other products resulting from the female bodily functions. Feminine care absorbent articles include panty liners and sanitary napkins.
• An 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 having an absorbent body containing a particulate water-absorbing agent composition, and uses, 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.
• the method for producing the absorbent article is not particularly limited as long as it uses a particulate water-absorbing agent composition produced by the method for producing a particulate water-absorbing agent composition according to one embodiment of the present invention described above, and may include, for example, a step of producing an absorbent core containing the particulate water-absorbing agent composition, a step of disposing the absorbent core between a back sheet and a top sheet, etc.
• the present invention encompasses the following aspects and configurations 1 to 13.
• 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 an aqueous (meth)acrylic acid (salt)-based monomer 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 the hydrogel-like crosslinked polymer produced during or after the polymerization; A drying step of drying the particulate hydrogel; an optional grinding step and an optional classification step of grinding and classifying the dried polymer; A surface cross-linking step of surface cross-linking the water absorbent resin before surface cross-linking, The particulate hydrogel is obtained through a polymerization step or through both a polymerization step and a hydrogel crushing step, The dried polymer is obtained through a drying step, The water absorbent resin before surface crosslinking is
• 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 particulate water-absorbing agent composition having a mass ratio of particles having a particle diameter of 300 ⁇ m or more and less than 850 ⁇ m of 50 mass % or more, (a) The nonionic polymer contained in the particulate water-absorbing agent composition is designated as A1, and its content is designated as C1, (b) subjecting the particulate water-absorbing agent composition to a predetermined impact test; (c) The particulate water-absorbing agent composition that has been subjected to the impact test is sieved using a JIS standard sieve into a particle group a having a particle diameter of 300 ⁇ m or more and a particle group b having a particle diameter of less than 300 ⁇ m, (d) A particulate water-absorbing agent composition, which satisfies all of the following (1)
• AAP absorbency under pressure
• FHA fixed height absorption value
• the particulate water-absorbing composition according to any one of 5. to 8., wherein the CRC of the particulate water-absorbing composition is 25 g/g or more.
• the particulate water absorbent composition according to any one of 5. to 9., wherein the particulate water absorbent composition has a moisture absorption blocking ratio ⁇ 1> (B.R. ⁇ 1>) of 80 mass% or less.
• 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 ⁇ m or more and 600 ⁇ m or less.
• D50 mass average particle diameter
• An absorbent article containing a particulate water-absorbing agent composition An absorbent article comprising the particulate water-absorbing agent composition according to any one of 5. to 12. as the particulate water-absorbing agent composition.
• the mass average particle diameter (D50) of the pulverized particulate hydrogel in terms of solid content was measured by the following method.
• 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.
• 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.
• 6000 g of EMAL aqueous solution was poured evenly from the top while rotating the sieve by hand (20 rpm) using a shower (72 holes, liquid volume: 6.0 L/min) from a height of 30 cm so that the water injection range (50 cm 2 ) spreads over the entire sieve, and the particulate hydrous gel was classified.
• the particulate hydrous gel on the first sieve that was classified was drained for about 2 minutes and then weighed.
• the mass ratio X (unit: mass%) of the particulate hydrogel remaining on each sieve to the entire particulate hydrogel was calculated from the mass of the particulate hydrogel remaining on each sieve using the following formula (1).
• the mesh size R( ⁇ ) (unit: mm) of the sieve used for the particulate hydrogel with a solid content of ⁇ mass% remaining on the sieve was calculated according to the following formula (2).
• X and R( ⁇ ) 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( ⁇ ). From this graph, the particle size corresponding to a residual percentage of 50 mass% was read as the mass average particle size (D50) of the particulate hydrogel.
• X (w/W) ⁇ 100 Formula (1)
• R( ⁇ ) (20/W) 1/3 ⁇ r Formula (2)
• X, w, W, R( ⁇ ) and r have the following values.
• r the mesh size (unit: mm) of a JIS standard sieve used to classify a particulate hydrogel swollen in a 20% by mass sodium chloride aqueous solution containing 0.08% by mass EMAL 20C (surfactant, manufactured by Kao Corporation) Actual value).
• ⁇ 0.5 ⁇ ln(X2/X1) Formula (3)
• a smaller ⁇ value means a narrower particle size distribution.
• thermohygrostat manufactured by Espec Corporation; Model: SH-641
• the water-absorbent resin or 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 ⁇ m (JIS 8.6 mesh), and classified for 40 seconds under the conditions of room temperature (20 to 25° C.) and relative humidity of 50% RH using a low-tap type sieve shaker (ES-65 type sieve shaker manufactured by Iida Seisakusho Co., Ltd.; rotation speed 230 rpm, impact speed 130 rpm).
• a JIS standard sieve TAE IIDA TESTING SIEVE: inner diameter 80 mm
• 2000 ⁇ m JIS 8.6 mesh
• the mass W1 (g) of the water absorbent resin or the particulate water absorbent composition remaining on the JIS standard sieve and the mass W2 (g) of the water absorbent resin or the particulate water absorbent composition passing through the JIS standard sieve were measured, and the moisture absorption blocking ratio ⁇ 1> was calculated by the following formula (4).
• Moisture absorption blocking rate ⁇ 1> (mass%) ⁇ W1/(W1+W2) ⁇ ⁇ 100 Formula (4)
• ⁇ B.R. ( ⁇ B.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 ⁇ B.R. of the particulate water-absorbing agent composition was calculated by the following formula (5).
• W5 and W6 have the following values.
• W5 B.R. (unit: mass%) of the surface-crosslinked water-absorbent resin used in the preparation of the particulate water-absorbing agent composition
• W6 B.R. (unit: mass%) of the particulate water-absorbing agent composition.
• W5 and W6 are 1 to 99% by mass.
• W5 is 0% by mass
• W6 is 0% by mass
• ⁇ B.R. is calculated to be 0% by mass. That is, the effect of improving the caking resistance due to the additive added to the water absorbent resin after surface cross-linking cannot be appropriately expressed by ⁇ B.R., which is not preferable.
• ⁇ B.R. is calculated to be 20% by mass, but it is not preferable because it is not possible to distinguish whether the original improvement effect of the caking resistance due to the additive added to the water absorbent resin after surface cross-linking is 20% by mass or more by mass. Therefore, when B.R. is calculated by the method of B.R. ⁇ 1>, When measuring B.R., 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 ⁇ B.R. Note that when comparing the improvement effect of anti-caking performance by additives by ⁇ B.R., the ⁇ B.R. is calculated by using the B.R. obtained by the same measurement method.
• AAP Absorption Capacity Under Pressure
• FHA Fiberd Height Absorption
• the surface tension of the particulate water-absorbing agent composition was measured by the following method.
• a thoroughly washed cylindrical stirrer with a length of 25 mm and a cross-sectional diameter of 7 mm and 0.5 g of the particulate water absorbent composition were placed in a 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 for 3 minutes at 350 rpm. After 3 minutes, the stirring was stopped, and the mixture was left to stand for 2 minutes to allow the particulate water absorbent composition to settle, and the surface tension of the supernatant liquid was measured again by the same operation.
• a plate method using a platinum plate was used, and the plate was thoroughly washed with deionized water and heated and cleaned with a gas burner before each measurement.
• CRC Crystal Cell Charcoal Absorption Capacity
• NWSP 241.0. R2 (19) 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 bag, and then immersed in a large excess of 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, and then dehydrated for 3 minutes using a centrifuge (250G), and the absorbency under no load (CRC) (unit: g/g) was measured.
• CRC absorbency under no load
• Saline Flow Conductivity The saline flow conductivity (SFC) (unit: ⁇ 10 ⁇ 7 cm 3 ⁇ sec/g) of the water-absorbent resin and the particulate water-absorbing agent composition was measured in accordance with the measurement method described in US Pat. No. 5,669,894.
• 1,500 g of the water-absorbent resin or particulate water-absorbing agent composition was uniformly placed in a container, and then the water-absorbent resin or 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 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.
• the height (cm) of the gel layer which was the swollen water absorbent resin or particulate water absorbent composition, was recorded.
• 0.69% by mass saline was passed through the gel layer while the gel layer was pressurized at a pressure of 2.07 kPa.
• the room temperature at this time was adjusted to 20-25°C.
• the amount of saline passing through the gel layer was recorded at 20-second intervals, and the flow rate Fs (T) of the passing saline was measured.
• the flow rate Fs (T) is measured by dividing the mass (g) of the passing saline, which increases every 20 seconds, by the passing time (s).
• the saline flow conductivity (SFC) was calculated using the following formula (6):
• L 0 Height of gel layer (unit: cm) ⁇ : density of salt water (unit: g/cm 3 ) A: Cross-sectional area of the gel layer (unit: cm 2 ) ⁇ P: hydrostatic pressure acting on the gel layer (unit: dyne/cm 2 ).
• 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 International Publication No. 2009/016055.
• the particulate water-absorbing agent composition was pulverized using a paint shaker (manufactured by Toyo Seiki Seisakusho Co., Ltd./Test disperser: Product No. 488).
• the pulverization was performed by shaking the paint shaker at 800 times/min. 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).
• 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 ⁇ m into a particle group a having a particle size of 300 ⁇ m or more and a particle group b having a particle size of less than 300 ⁇ m.
• the pretreatment 1 impact test and pretreatment 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 absorbent composition.
• 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 in a volume ratio of 6:4.
• the content of the nonionic polymer in the particle group a and in the particulate water absorbent composition before the impact test was determined by taking into consideration the dilution rate of the particle group a or the particulate water absorbent composition with ultrapure water, using a calibration curve obtained by measuring a nonionic polymer standard solution of known concentration as an external standard.
• the content of the nonionic polymer in the particle group a and in the particulate water absorbent composition before the impact test was a value corrected for the water content. In other words, it was a value converted to the solid content in the particle group a or the particulate water absorbent composition before the impact test, which was calculated from the solid content amount described below.
• Solid content The solid content of the particulate water-absorbing agent composition was measured by the following method.
• Solid content (mass%) 100-moisture content (mass%) Formula (9)
• the time from the start of the second stage neutralization to the pouring of the monomer aqueous solution (1) into the bat-shaped container was 65 seconds.
• the vat-shaped container was heated in advance using a hot plate (NEO HOTPLATE HI-1000/Iuchi Seieido Co., Ltd.) until the surface temperature reached 50°C before pouring in the aqueous monomer solution (1).
• the polymerization reaction started within one minute.
• the polymerization of the monomer aqueous solution (1) proceeded while expanding and foaming in all directions while generating water vapor.
• the resulting polymer then shrunk to a size slightly larger than the bottom of the vat-shaped container.
• the resulting polymer, hydrous gel (1) was removed from the vat-shaped container. This series of operations was carried out in an open-to-air state.
• 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 about 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.
• the particulate hydrogel (1) had a D50 (mass average particle diameter) of 400 ⁇ m and a ⁇ (logarithmic standard deviation of particle size distribution) of 0.93.
• the particulate hydrogel (1) was spread on a wire mesh with an opening of 300 ⁇ m and placed in a hot air dryer. After that, 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 matter in the dried polymer (1).
• the dried polymer (1) was put into a roll mill (WML type roll grinder, manufactured by Inokuchi Giken Co., Ltd.) and ground, and then classified using two types of JIS standard sieves with openings of 710 ⁇ m and 150 ⁇ m. By this operation, an irregularly crushed water absorbent resin (1) before surface crosslinking, which passed through the sieve with openings of 710 ⁇ m and remained on the sieve with openings of 150 ⁇ m, was obtained.
• WML type roll grinder manufactured by Inokuchi Giken Co., Ltd.
• the particulate hydrogel (2) obtained in the hydrogel crushing step had a D50 (mass average particle size) of 405 ⁇ m and a ⁇ (logarithmic standard deviation of particle size distribution) of 0.95.
• the particulate hydrogel (3) obtained in the hydrogel crushing step had a D50 (mass average particle size) of 400 ⁇ m and a ⁇ (logarithmic standard deviation of particle size distribution) of 0.93.
• the particulate hydrogel (4) obtained in the hydrogel crushing step had a D50 (mass average particle size) of 390 ⁇ m and a ⁇ (logarithmic standard deviation of particle size distribution) of 0.92.
• the particulate hydrogel (5) obtained in the hydrogel crushing step had a D50 (mass average particle size) of 395 ⁇ m and a ⁇ (logarithmic standard deviation of particle size distribution) of 0.91.
• the particulate hydrogel (6) obtained in the hydrogel crushing step had a D50 (mass average particle size) of 393 ⁇ m and a ⁇ (logarithmic standard deviation of particle size distribution) of 0.95.
• the particulate hydrogel (7) obtained in the hydrogel crushing step had a D50 (mass average particle size) of 398 ⁇ m and a ⁇ (logarithmic standard deviation of particle size distribution) of 0.92.
• the particulate hydrogel (8) obtained in the hydrogel crushing step had a D50 (mass average particle size) of 396 ⁇ m and a ⁇ (logarithmic standard deviation of particle size distribution) of 0.94.
• the particulate hydrogel (9) obtained in the hydrogel crushing step had a D50 (mass average particle size) of 389 ⁇ m and a ⁇ (logarithmic standard deviation of particle size distribution) of 0.90.
• the time from the start of the second stage neutralization to the pouring of the monomer aqueous solution (10) into the bat-shaped container was 65 seconds.
• the vat-shaped container was heated in advance using a hot plate (NEO HOTPLATE HI-1000/Iuchi Seieido Co., Ltd.) until the surface temperature reached 50°C before pouring in the aqueous monomer solution (10).
• the polymerization reaction started within one minute.
• the monomer aqueous solution (10) progressed while expanding and foaming in all directions while generating water vapor.
• the resulting polymer then shrunk to a size slightly larger than the bottom of the vat-shaped container.
• the resulting polymer a hydrous gel (10) was removed from the vat-shaped container. This series of operations was carried out in an open-to-air state.
• 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) fed was about 360 g/min, and in parallel with the feeding 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.
• the particulate hydrogel (10) had a D50 (mass average particle diameter) of 915 ⁇ m and a ⁇ (logarithmic standard deviation of particle size distribution) of 1.04.
• the particulate hydrogel (10) was spread on a wire mesh with an opening of 300 ⁇ m and placed in a hot air dryer. After that, the particulate hydrogel (10) was dried by passing hot air at 190° C. for 30 minutes to obtain a dried polymer (10). There was no undried matter in the dried polymer (10).
• the particulate hydrogel (11) obtained in the hydrogel crushing step had a D50 (mass average particle size) of 905 ⁇ m and a ⁇ (logarithmic standard deviation of particle size distribution) of 1.02.
• the particulate hydrogel (12) obtained in the hydrogel crushing step had a D50 (mass average particle size) of 908 ⁇ m and a ⁇ (logarithmic standard deviation of particle size distribution) of 1.03.
• the particulate hydrogel (13) obtained in the hydrogel crushing step had a D50 (mass average particle size) of 388 ⁇ m and a ⁇ (logarithmic standard deviation of particle size distribution) of 0.90.
• the particulate hydrogel (14) obtained in the hydrogel crushing step had a D50 (mass average particle size) of 380 ⁇ m and a ⁇ (logarithmic standard deviation of particle size distribution) of 0.89.
• Comparative Example 2 In Comparative Example 1, the aqueous solution to be added was changed to an aqueous solution having a liquid temperature of 25° C., which was composed of 0.34 parts by mass of deionized water and 0.16 parts by mass of polyethylene glycol 600 (weight average molecular weight 600, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and the same operation as in Comparative Example 1 was performed to obtain a particulate water-absorbing agent composition (C2). The amount of the added polyethylene glycol 600 was 0.16% by mass relative to the water-absorbing resin (1) after surface cross-linking. The physical properties of the obtained particulate water-absorbing agent composition (C2) are shown in Table 2.
• a particulate water-absorbing agent composition (C3) was obtained by the same operation as in Comparative Example 1, except that the aqueous solution added in Comparative Example 1 was changed to a mixed solution of 0.604 parts by mass of 27% by mass aluminum sulfate aqueous solution (8% by mass in terms of aluminum oxide), 0.181 parts by mass of 60% by mass sodium lactate aqueous solution, and 0.015 parts by mass of propylene glycol, the solution having a liquid temperature of 25° C.
• the various physical properties of the obtained particulate water-absorbing agent composition (C3) are shown in Table 2.
• Comparative Example 4 In Comparative Example 2, except that the surface-crosslinked water absorbent resin used was changed to the surface-crosslinked water absorbent resin (2) obtained in Production Example 2, the same operation as in Comparative Example 2 was performed to obtain a particulate water absorbent composition (C4).
• the amount of the added polyethylene glycol 600 was 0.16% by mass relative to the surface-crosslinked water absorbent resin (2).
• the physical properties of the obtained particulate water absorbent composition (C4) are shown in Table 2.
• a particulate water-absorbing agent composition (C5) was obtained by the same operation as in Comparative Example 2, except that the surface-crosslinked water-absorbing resin used in Comparative Example 2 was changed to the surface-crosslinked water-absorbing 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-absorbing resin (3).
• the physical properties of the obtained particulate water-absorbing agent composition (C5) are shown in Table 2.
• Comparative Example 6 In Comparative Example 1, the surface-crosslinked water absorbent resin used was changed to the surface-crosslinked water absorbent resin (4) obtained in Production Example 4, and the aqueous solution added was changed to an aqueous solution having a liquid temperature of 25°C consisting of 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.), and the same operation as in Comparative Example 1 was performed to obtain a particulate water absorbent composition (C6). 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 absorbent composition (C6) are shown in Table 2.
• Example 1 In Comparative Example 6, except that the aqueous solution to be added was changed to an aqueous solution having a liquid temperature of 25° C., which was composed of 0.70 parts by mass of deionized water and 0.30 parts by mass of polyethylene glycol 400 (weight average molecular weight 400, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), a particulate water-absorbing agent composition (1) was obtained by the same operation as in Comparative Example 6. The amount of polyethylene glycol 400 added was 0.30% by mass relative to the water-absorbing resin (4) after surface cross-linking. The physical properties of the obtained particulate water-absorbing agent composition (1) are shown in Tables 2 and 3.
• Example 2 In Example 1, the aqueous solution to be added was changed to an aqueous solution having a liquid temperature of 25°C, which was composed of 0.17 parts by mass of deionized water and 0.08 parts by mass of polyethylene glycol 600 (weight average molecular weight 600, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), which was used in Comparative Example 1, and the same operation as in Example 1 was performed to obtain a particulate water-absorbing agent composition (2).
• the amount of polyethylene glycol 600 added was 0.08% by mass relative to the water-absorbing 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.
• Example 3 In Example 1, the aqueous solution to be added was changed to an aqueous solution having a liquid temperature of 25°C, which was composed of 0.34 parts by mass of deionized water and 0.16 parts by mass of polyethylene glycol 600 (weight average molecular weight 600, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), which was used in Comparative Example 2, and the same operation as in Example 1 was performed to obtain a particulate water-absorbing agent composition (3).
• the amount of polyethylene glycol 600 added was 0.16% by mass relative to the water-absorbing resin (4) after surface cross-linking.
• the physical properties of the obtained particulate water-absorbing agent composition (3) are shown in Tables 2 and 3.
• 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 the added polyethylene glycol 600 was 0.30 mass% relative to the surface-crosslinked water-absorbing resin (4).
• the physical properties of the obtained particulate water-absorbing agent composition (4) are shown in Tables 2 and 3.
• 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% relative to the surface-crosslinked water-absorbing resin (4).
• the physical properties of the obtained particulate water-absorbing agent composition (5) are shown in Tables 2 and 3.
• 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 the added polyethylene glycol 2000 was 0.30 mass% relative to the surface-crosslinked water-absorbing resin (4).
• the physical properties of the obtained particulate water-absorbing agent composition (6) are shown in Tables 2 and 3.
• Example 7 A particulate water-absorbing agent composition (7) 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 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% relative to the surface-crosslinked water-absorbing resin (4).
• the physical properties of the obtained particulate water-absorbing agent composition (7) are shown in Tables 2 and 3.
• Comparative Example 7 In Comparative Example 6, the polyethylene glycol used in the aqueous solution to be added was changed to polyethylene glycol 20000 (weight average molecular weight 20000, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and the same operation as in Comparative Example 6 was performed to obtain a particulate water-absorbing agent composition (C7).
• the amount of the added polyethylene glycol 20000 was 0.16% by mass relative to the surface-crosslinked water-absorbing resin (4).
• the physical properties of the obtained particulate water-absorbing agent composition (C7) are shown in Table 2.
• Example 8 In Example 1, the aqueous solution to be added 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, and the same operation as in Example 1 was performed to obtain a particulate water-absorbing agent composition (8).
• the amount of polypropylene glycol 700 added was 0.30% by mass relative to the water-absorbing 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.
• 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% relative 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.
• 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 the added polyoxyethylene (20) sorbitan monostearate was 0.04% by mass relative to the surface-crosslinked water-absorbing resin (4).
• the physical properties of the obtained particulate water-absorbing agent composition (10) are shown in Tables 2 and 3.
• 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 was changed to polyoxyethylene (20) sorbitan tristearate (manufactured by Kao Corporation). The amount of the added polyoxyethylene (20) sorbitan tristearate was 0.04% by mass relative to the surface-crosslinked water-absorbing resin (4).
• the physical properties of the obtained particulate water-absorbing agent composition (11) are shown in Tables 2 and 3.
• 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 particulate water-absorbing agent composition (C8) obtained are shown in Table 2.
• a particulate water-absorbing agent composition (C9) 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 having a liquid temperature of 25° C., which was composed of 0.604 parts by mass of an aqueous 27% by mass aluminum sulfate solution (8% by mass in terms of aluminum oxide), 0.181 parts by mass of an aqueous 60% by mass 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.
• a particulate water-absorbing agent composition (C11) was obtained by the same operation as in Comparative Example 10, except that the amount of fumed silica (Aerosil 200, manufactured by Nippon Aerosil Co., Ltd.) added in Comparative Example 10 was changed to 0.20 parts by mass.
• Various physical properties of the particulate water-absorbing agent composition (C11) obtained are shown in Table 2.
• Example 12 In Comparative Example 2, except that the surface-crosslinked water absorbent resin used was changed to the surface-crosslinked water absorbent resin (5) obtained in Production Example 5, the same operation as in Comparative Example 2 was carried out to obtain a particulate water absorbent composition (12). The amount of the added polyethylene glycol 600 was 0.16% by mass relative to the surface-crosslinked water absorbent resin (5). The physical properties of the obtained particulate water absorbent composition (12) are shown in Tables 2 and 3.
• Example 13 In Comparative Example 2, except that the surface-crosslinked water absorbent resin used was changed to the surface-crosslinked water absorbent resin (6) obtained in Production Example 6, the same operation as in Comparative Example 2 was carried out to obtain a particulate water absorbent composition (13). The amount of the added polyethylene glycol 600 was 0.16% by mass relative to the surface-crosslinked water absorbent resin (6). The physical properties of the obtained particulate water absorbent composition (13) are shown in Tables 2 and 3.
• Example 14 In Comparative Example 2, except that the surface-crosslinked water absorbent resin used was changed to the surface-crosslinked water absorbent resin (7) obtained in Production Example 7, the same operation as in Comparative Example 2 was carried out to obtain a particulate water absorbent composition (14). The amount of the added polyethylene glycol 600 was 0.16% by mass relative to the surface-crosslinked water absorbent resin (7). The physical properties of the obtained particulate water absorbent composition (14) are shown in Tables 2 and 3.
• Example 15 In Comparative Example 2, except that the surface-crosslinked water absorbent resin used was changed to the surface-crosslinked water absorbent resin (8) obtained in Production Example 8, the same operation as in Comparative Example 2 was carried out to obtain a particulate water absorbent composition (15).
• the amount of polyethylene glycol 600 added was 0.16 mass % relative to the surface-crosslinked water absorbent resin (8).
• the physical properties of the obtained particulate water absorbent composition (15) are shown in Tables 2 and 3.
• Example 16 In Comparative Example 2, except that the surface-crosslinked water absorbent resin used was changed to the surface-crosslinked water absorbent resin (9) obtained in Production Example 9, the same operation as in Comparative Example 2 was carried out to obtain a particulate water absorbent composition (16). The amount of the added polyethylene glycol 600 was 0.16% by mass relative to the surface-crosslinked water absorbent resin (9). The physical properties of the obtained particulate water absorbent composition (16) are shown in Tables 2 and 3.
• Comparative Example 12 In Comparative Example 1, the surface-crosslinked water absorbent resin used was changed to the surface-crosslinked water absorbent resin (10) obtained in Production Example 10, and the aqueous solution added was changed to an aqueous solution having a liquid temperature of 25°C consisting of 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.). The same operation as in Comparative Example 1 was performed to obtain a particulate water absorbent composition (C12). 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 absorbent composition (C12) are shown in Table 2.
• Example 17 In Comparative Example 12, except that the surface-crosslinked water absorbent resin used was changed to the surface-crosslinked water absorbent resin (11) obtained in Production Example 11, the same operation as in Comparative Example 12 was performed to obtain a particulate water absorbent composition (17). The amount of the added polyethylene glycol 600 was 0.15% by mass relative to the surface-crosslinked water absorbent resin (11). The physical properties of the obtained particulate water absorbent composition (17) are shown in Tables 2 and 3.
• Example 18 In Example 1, the surface-crosslinked water absorbent resin used was changed to the surface-crosslinked water absorbent resin (13) obtained in Production Example 13, and the aqueous solution 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 same operation as in Example 1 was performed to obtain a particulate water absorbent composition (18). The amount of the added polyoxyethylene (20) sorbitan monostearate was 0.025% by mass relative to the surface-crosslinked water absorbent resin (13). The physical properties of the obtained particulate water absorbent composition (18) are shown in Tables 2 and 3.
• 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 added was changed to an aqueous solution having a liquid temperature of 25°C consisting of 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.), and the same operation as in Example 1 was performed to obtain a particulate water absorbent composition (19). The amount of polyethylene glycol 600 added was 0.35% by mass relative to the surface-crosslinked water absorbent resin (14). The physical properties of the obtained particulate water absorbent composition (19) are shown in Tables 2 and 3.
• 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 monomer aqueous solution preparation step, the polymerization step, and the hydrous gel crushing step.
• the particulate water-absorbent compositions (3) and (16) of Examples 3 and 16 which use the surface-crosslinked water-absorbent resins (4) and (9) produced by adding water-soluble polyalkylene glycol before the hydrous gel crushing step, have a larger ⁇ B.R. than the particulate water-absorbent compositions (C2), (C4), and (C5) of Comparative Examples 2, 4, and 5, and show a significantly improved effect in improving the caking resistance.
• the particulate water-absorbent compositions (3) and (16) do not show a deterioration in AAP or FHA.
• the particulate water absorbent composition (C3) of Comparative Example 3 which was prepared by adding aluminum sulfate to the same surface-crosslinked water absorbent resin (1) as in Comparative Examples 1 and 2, had a large ⁇ B.R. and a good improvement effect on the anti-caking performance, but the AAP0.7 and FHA were deteriorated, indicating that the water absorption performance under pressure was poor.
• Comparative examples 1 to 11 and comparative example 8 were used in which the same surface-crosslinked water-absorbent resin (4) was used but the added nonionic polymer was changed, and it was found that the particulate water-absorbent composition (C8) of comparative example 8, to which a nonionic polymer not containing a polyalkylene glycol chain in its structure was added, exhibited a significant deterioration in FHA.
• Comparative Examples 9 to 11 show that even when using a surface-crosslinked water-absorbent resin (4) produced by adding a water-soluble polyalkylene glycol before the hydrous gel crushing process, the AAP and FHA deteriorate when silica or an aluminum salt is added.
• the particulate water absorbent composition (12) of Example 12 which was produced by changing the amount of water-soluble polyalkylene glycol added before the hydrous gel crushing step to 0.14 mass% relative to the total mass of the monomers, and added 0.16 mass% of polyethylene glycol 600 as in Example 3, also had a large ⁇ B.R., and it was found that the improvement effect of the anti-caking performance was significantly improved. In addition, the particulate water absorbent composition (12) did not deteriorate in AAP or FHA.
• Comparative Example 12 and Example 17 are examples in which the amount of polyethylene glycol diacrylate (average molecular weight: 523) added in the monomer aqueous solution preparation step was reduced compared to the other examples and comparative examples, and the CRC of the water absorbent resin after surface cross-linking was increased.
• the effect of improving the caking resistance by the nonionic polymer added to the surface-crosslinked water-absorbent resin is significantly improved by adding water-soluble polyalkylene glycol before the hydrous gel crushing step.
• 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.
• the surface-crosslinked water-absorbent resin (12) in which the amount of water-soluble polyalkylene glycol added before the hydrous gel crushing step was 0.30 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 hydrous gel crushing step.
• B.R. i.e., worsened anti-caking performance
• the method for producing the particulate water-absorbing agent composition of the present invention it is possible to provide a particulate water-absorbing agent composition having high caking resistance without deteriorating the water-absorbing performance under pressure. Therefore, the particulate water-absorbing agent composition obtained by the present invention can be suitably used for absorbent articles such as paper diapers, sanitary napkins, and incontinence pads.

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