Particulate water-absorbent resin composition, its manufacturing method, absorbent material, and absorbent article

Abstract

A particulate water-absorbing resin composition having excellent flowability is provided.　The particulate water-absorbing resin composition comprises a hydrazide compound and a water-absorbing resin.

Description

[Technical Field]

[0001] The present invention relates to a particulate water-absorbent resin composition and a manufacturing method thereof, an absorbent body, and an absorbent article, and more particularly to a particulate water-absorbent resin composition constituting an absorbent body suitably used for hygiene materials such as disposable diapers, sanitary napkins, and incontinence pads, a manufacturing method thereof, and an absorbent article using the absorbent body. [Background technology]

[0002] BACKGROUND ART In recent years, water-absorbent resins have been widely used in the field of sanitary materials such as disposable diapers, sanitary napkins, and incontinence pads.

[0003] As such a water-absorbent resin, a crosslinked product of a polymer of a water-soluble ethylenically unsaturated monomer, more specifically a crosslinked product of a polymer of a partially neutralized polyacrylic acid, has excellent water-absorbing ability, and since its raw material, acrylic acid, is easily available industrially, it can be produced at low cost with consistent quality, and is less susceptible to decay or deterioration, and therefore, it is considered to be a preferred water-absorbent resin (see, for example, Patent Document 1).

[0004] On the other hand, absorbent articles such as disposable diapers, sanitary napkins, and incontinence pads are mainly composed of an absorbent core located in the center that absorbs and retains body fluids such as urine and menstrual blood excreted from the body, a liquid-permeable surface sheet (top sheet) located on the side that comes into contact with the body, and a liquid-impermeable back sheet (back sheet) located on the opposite side that comes into contact with the body. The absorbent core is usually composed of hydrophilic fibers such as pulp and a water-absorbent resin. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 3-227301 Summary of the Invention [Problem to be solved by the invention]

[0006] A main object of the present invention is to provide a particulate water-absorbing resin composition having excellent fluidity. [Means for solving the problem]

[0007] The present inventors have conducted extensive research to solve the above problems, and as a result have found that a particulate water-absorbent resin composition containing a hydrazide compound and a water-absorbent resin has excellent flowability. The present invention was completed based on these findings and through further intensive research.

[0008] That is, the present invention provides the following configuration. Item 1. A particulate water-absorbing resin composition comprising a hydrazide compound and a water-absorbing resin. Item 2. A particulate water-absorbing resin composition according to Item 1, wherein the hydrazide compound is present on at least one of the surface and the interior of the water-absorbing resin composition. Item 3. The particulate water-absorbing resin composition according to Item 1 or 2, wherein the hydrazide compound is in particulate form. Item 4. The particulate water-absorbing resin composition according to any one of Items 1 to 3, wherein the content of the hydrazide compound is 0.001 to 10% by mass. Item 5. The particulate water-absorbing resin composition according to any one of Items 1 to 4, wherein the particulate water-absorbing resin composition has a spatula angle of 20 to 38°. Item 6. The particulate water-absorbing resin composition according to any one of Items 1 to 5, wherein the particulate water-absorbing resin composition has a median particle size of 100 to 600 μm. Item 7. An absorbent material comprising the particulate water-absorbing resin composition according to any one of items 1 to 6. Item 8. An absorbent article comprising the absorbent body according to item 7 held between a liquid-permeable sheet and a liquid-impermeable sheet. Item 9. A method for producing a particulate water-absorbing resin composition, comprising a step of mixing a water-absorbing resin that is a polymer cross-linked product of a water-soluble ethylenically unsaturated monomer, an internal cross-linking agent, and a post-cross-linking agent, with a hydrazide compound at a temperature of 10 to 100°C. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a particulate water-absorbent resin composition having excellent fluidity. Furthermore, according to the present invention, it is also possible to provide a method for producing the water-absorbent resin composition, and an absorbent article and an absorbent body using the water-absorbent resin composition. DETAILED DESCRIPTION OF THE INVENTION

[0010] 1. Particulate water absorbent resin composition The particulate water-absorbent resin composition of the present invention contains a hydrazide compound and a water-absorbent resin. By having this constitution, the particulate water-absorbent resin composition of the present invention exhibits excellent fluidity. Hereinafter, the particulate water-absorbent resin composition of the present invention will be described in detail.

[0011] The particulate water-absorbing resin composition of the present invention has excellent fluidity. For example, the particulate water-absorbing resin composition of the present invention has a spatula angle measured by the following test method of preferably 20 to 38°, more preferably 25 to 35°, and even more preferably 28 to 34°.

[0012] <Fluidity test> The spatula angle is measured using a commercially available powder tester (for example, the Powder Tester PT-X model (manufactured by Hosokawa Micron Corporation)). The spatula angle is the inclination angle of the side of the resin powder deposited on the spatula, and is the angle required to move powder from a stationary state, and is one of the indicators of fluidity. The smaller the spatula angle value, the better the fluidity. The measurement procedure is carried out according to the instructions for the powder tester.

[0013] (hydrazide compounds) In order to more suitably exhibit the effects of the present invention, the hydrazide compound contained in the particulate water-absorbing resin composition of the present invention is preferably in particulate form.

[0014] The median particle diameter of the hydrazide compound is usually 5 to 350 μm, preferably 10 to 250 μm, and more preferably 15 to 150 μm. The median particle diameter of the hydrazide compound is measured in accordance with the sieving test method for chemical products (JIS K0069:1992), and the median value is calculated in accordance with the method of (median particle diameter of water-absorbent resin) in the Examples described later.

[0015] The hydrazide compounds are formohydrazide, acetohydrazide, propionic acid hydrazide, 4-methylbenzohydrazide, biphenyl-4-carboxylic acid hydrazide, 2-bromobenzohydrazide, 3-bromobenzohydrazide, 4-bromobenzohydrazide, 2-chlorobenzohydrazide, 3-chlorobenzohydrazide, 4-chlorobenzohydrazide, 3,4-dichlorobenzohydrazide, 2,4-dichlorobenzohydrazide, 2,4-dihydroxybenzohydrazide, 3-hydroxybenzohydrazide, 4-hydroxybenzohydrazide, isobutyric acid hydrazide, 3-methoxybenzohydrazide, 4-methoxybenzohydrazide, methylmaleic acid hydrazide, 1-naphthohydrazide, nicotinic acid hydrazide, 3-nitrophthalic acid hydrazide, 4-nitrophthalic acid hydrazide, and 4-nitrophthalic acid hydrazide. Examples of suitable hydrazide compounds include monohydrazide compounds such as phthalic acid hydrazide, n-octanohydrazide, palmitic acid hydrazide, 2-phenoxybenzohydrazide, phenylacetic acid hydrazide, 2-pyridinecarboxylic acid hydrazide, stearic acid hydrazide, 2-thiophenecarboxylic acid hydrazide, and L-tyrosine hydrazide; dihydrazide compounds such as malonic acid dihydrazide, succinic acid dihydrazide, adipic acid dihydrazide, carbohydrazide, isophthalic acid dihydrazide, phthalic acid dihydrazide, terephthalic acid dihydrazide, azelaic acid dihydrazide, sebacic acid dihydrazide, oxalic acid dihydrazide, dodecanedioic acid dihydrazide, oxalyl dihydrazide, and adipodihydrazide; and polyhydrazide compounds having tri-, tetra-, or higher hydrazide groups. Dihydrazide compounds are preferred, more preferably malonic acid dihydrazide, succinic acid dihydrazide, adipic acid dihydrazide, carbohydrazide, isophthalic acid dihydrazide, phthalic acid dihydrazide, terephthalic acid dihydrazide, azelaic acid dihydrazide, sebacic acid dihydrazide, oxalic acid dihydrazide, dodecanedioic acid dihydrazide, oxalyl dihydrazide, etc., and even more preferably malonic acid dihydrazide. The hydrazide compound contained in the particulate water-absorbing resin composition of the present invention may be one type or two or more types.

[0016] The hydrazide compound may be supported on a carrier. From the viewpoint of more suitably exhibiting the effects of the present invention, the carrier supporting the hydrazide compound is preferably a silicate or silicic acid, and more preferably a silicate. The silicate is preferably a layered silicate mineral (phyllosilicate mineral). The layered silicate mineral is preferably kaolin (for example, liesardite (Mg3SiO5(OH)4)), kaolinite (Al2SiO5(OH)4), berthierine (Fe 2.5 Al 0.5 )[Si 1.5 Al 0.5 O5(OH)4], mica clay minerals (e.g., fluorphlogopite (KMg3(AlSi3)O 10 F2), phlogopite (KMg3(AlSi3)O 10 (F,OH)2), polylithionite (KLi2AlSi4O 10 (F,OH)2), eastnite (KMg2Al(Al2Si2)O 10 (F,OH)2) and sucmetite (e.g., montmorillonite (Ca / 2,Na) 0.3 (Mg,Fe 2+ )3(Si,Al)4O 10 (OH)2 / 4H2O, etc.), mixed layer minerals, serpentine minerals (e.g., serpentine (Mg3Si2O5(OH)4), talc ((Mg3Si4O 10 (OH)2), chlorite (e.g., clinochlore ((Mg,Fe 2+ )5Al(Si3Al)O 10 (OH)8, chamosite ((Fe 2+ ,Mg,Fe 3+ )5Al(Si3Al)O 10 (OH)8), vermiculite, etc. The carrier for supporting the hydrazide compound may be one type or two or more types.

[0017] From the viewpoint of more suitably exhibiting the effects of the present invention, the content of the hydrazide compound in the particulate water-absorbing resin composition of the present invention is preferably 0.001 to 10 mass%, more preferably 0.005 to 5 mass%, and even more preferably 0.05 to 2 mass%.

[0018] From the viewpoint of more suitably exhibiting the effects of the present invention, in the particulate water-absorbent resin composition of the present invention, the hydrazide compound is preferably present on at least one of the surface and the interior of the particulate water-absorbent resin, and more preferably on the surface of the particulate water-absorbent resin. For example, by mixing the particulate water-absorbent resin and the hydrazide compound in a solid phase, the hydrazide compound can be present on the surface of the particulate water-absorbent resin to an extent that the effects of the present invention can be exhibited. Alternatively, the particulate water-absorbent resin composition of the present invention may be prepared by mixing the hydrazide compound dissolved or dispersed in a liquid medium such as an aqueous liquid with the particulate water-absorbent resin. Alternatively, the hydrazide compound may be contained inside the particulate water-absorbent resin.

[0019] (Water absorbent resin) The water-absorbing resin contained in the particulate water-absorbing resin composition of the present invention is constituted by a crosslinked polymer of a water-soluble ethylenically unsaturated monomer, i.e., a crosslinked polymer having a structural unit derived from a water-soluble ethylenically unsaturated monomer.

[0020] The water-absorbing resin is usually in a particulate form. The particulate water-absorbing resin preferably has a median particle diameter of 100 to 600 μm, more preferably 200 to 500 μm, and even more preferably 250 to 450 μm. That is, the particulate water-absorbing resin composition of the present invention also has a median particle diameter of preferably 100 to 600 μm, more preferably 200 to 500 μm, even more preferably 250 to 450 μm, and even more preferably 300 to 425 μm.

[0021] The particulate water-absorbing resin may be in a form consisting of a single particle, or in a form (secondary particles) in which fine particles (primary particles) are aggregated. Examples of the shape of the primary particles include an approximately spherical shape, an irregularly crushed shape, a plate shape, etc. In the case of primary particles produced by reverse-phase suspension polymerization, examples include approximately spherical single particle shapes having a smooth surface shape such as a perfect sphere or an oval sphere. Primary particles of such a shape have a smooth surface shape, which increases the fluidity as a powder, and the aggregated particles tend to be densely packed, which makes the water-absorbing resin less likely to be broken even when subjected to impact, resulting in a water-absorbing resin with high particle strength.

[0022] The median particle size of the particulate water-absorbent resin can be measured using a JIS standard sieve, and specifically, it is a value measured by the method described in the examples.

[0023] As a method for polymerizing a water-soluble ethylenically unsaturated monomer, typical polymerization methods such as aqueous solution polymerization, emulsion polymerization, and reversed-phase suspension polymerization are used. In the aqueous solution polymerization, polymerization is carried out by heating an aqueous solution of a water-soluble ethylenically unsaturated monomer while stirring as necessary. In the reversed-phase suspension polymerization, polymerization is carried out by heating a water-soluble ethylenically unsaturated monomer in a hydrocarbon dispersion medium while stirring, and the reversed-phase suspension polymerization is preferably used from the viewpoints of precise polymerization reaction control and wide range of particle size control.

[0024] An example of a method for producing the water-absorbent resin will be described below.

[0025] A specific example of the method for producing a water-absorbent resin is a method for producing a water-absorbent resin by reversed-phase suspension polymerization of a water-soluble ethylenically unsaturated monomer in a hydrocarbon dispersion medium, which method comprises a step of carrying out polymerization in the presence of a radical polymerization initiator and a step of post-crosslinking the hydrogel-like material obtained by the polymerization in the presence of a post-crosslinking agent. Note that in the method for producing a water-absorbent resin, an internal crosslinking agent may be added to the water-soluble ethylenically unsaturated monomer, if necessary, to form a hydrogel-like material having an internal crosslinked structure.

[0026] <Polymerization process> [Water-soluble ethylenically unsaturated monomers] Examples of water-soluble ethylenically unsaturated monomers include (meth)acrylic acid (herein, "acrylic" and "methacrylic" are collectively referred to as "(meth)acrylic"; the same applies hereinafter) and salts thereof; 2-(meth)acrylamido-2-methylpropanesulfonic acid and salts thereof; nonionic monomers such as (meth)acrylamide, N,N-dimethyl(meth)acrylamide, 2-hydroxyethyl(meth)acrylate, N-methylol(meth)acrylamide, and polyethylene glycol mono(meth)acrylate; and amino group-containing unsaturated monomers and quaternized products thereof such as N,N-diethylaminoethyl(meth)acrylate, N,N-diethylaminopropyl(meth)acrylate, and diethylaminopropyl(meth)acrylamide. Among these water-soluble ethylenically unsaturated monomers, (meth)acrylic acid or salts thereof, (meth)acrylamide, and N,N-dimethylacrylamide are preferred, and (meth)acrylic acid and salts thereof are more preferred, from the viewpoint of industrial availability. These water-soluble ethylenically unsaturated monomers may be used alone or in combination of two or more.

[0027] Among these, acrylic acid and its salts are widely used as raw materials for water-absorbent resins, and these acrylic acid and / or its salts may be copolymerized with the other water-soluble ethylenically unsaturated monomers described above. In this case, it is preferable that acrylic acid and / or its salts are used as the main water-soluble ethylenically unsaturated monomer in an amount of 70 to 100 mol % based on the total amount of water-soluble ethylenically unsaturated monomers.

[0028] The water-soluble ethylenically unsaturated monomer is preferably dispersed in a hydrocarbon dispersion medium in the form of an aqueous solution and subjected to reversed-phase suspension polymerization. By forming the water-soluble ethylenically unsaturated monomer into an aqueous solution, the dispersion efficiency in the hydrocarbon dispersion medium can be increased. The concentration of the water-soluble ethylenically unsaturated monomer in this aqueous solution is preferably in the range of 20% by mass to the saturated concentration. The concentration of the water-soluble ethylenically unsaturated monomer is more preferably 55% by mass or less, even more preferably 50% by mass or less, and even more preferably 45% by mass or less. Meanwhile, the concentration of the water-soluble ethylenically unsaturated monomer is more preferably 25% by mass or more, even more preferably 28% by mass or more, and even more preferably 30% by mass or more.

[0029] When the water-soluble ethylenically unsaturated monomer has an acid group, such as (meth)acrylic acid or 2-(meth)acrylamido-2-methylpropanesulfonic acid, the acid group may be neutralized in advance with an alkaline neutralizer, if necessary. Examples of such alkaline neutralizers include alkali metal salts such as sodium hydroxide, sodium carbonate, sodium bicarbonate, potassium hydroxide, and potassium carbonate; and ammonia. These alkaline neutralizers may be used in the form of an aqueous solution to simplify the neutralization process. The alkaline neutralizers described above may be used alone or in combination of two or more.

[0030] The degree of neutralization of the water-soluble ethylenically unsaturated monomer with the alkaline neutralizing agent is preferably 10 to 100 mol%, more preferably 30 to 90 mol%, even more preferably 40 to 85 mol%, and even more preferably 50 to 80 mol%, in terms of the degree of neutralization of all acid groups possessed by the water-soluble ethylenically unsaturated monomer.

[0031] [Radical polymerization initiator] Examples of the radical polymerization initiator added to the polymerization step include persulfates such as potassium persulfate, ammonium persulfate, and sodium persulfate, peroxides such as methyl ethyl ketone peroxide, methyl isobutyl ketone peroxide, di-t-butyl peroxide, t-butylcumyl peroxide, t-butyl peroxyacetate, t-butyl peroxyisobutyrate, t-butyl peroxypivalate, and hydrogen peroxide, as well as 2,2'-azobis(2-amidinopropane) dihydrochloride and 2,2'-azobis[2-(N-phenyl)propane]. Examples of suitable radical polymerization initiators include azo compounds such as 2,2'-azobis[2-(N-allylamidino)propane] dihydrochloride, 2,2'-azobis{2-[1-(2-hydroxyethyl)-2-imidazolin-2-yl]propane} dihydrochloride, 2,2'-azobis{2-methyl-N-[1,1-bis(hydroxymethyl)-2-hydroxyethyl]propionamide}, 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)-propionamide], and 4,4'-azobis(4-cyanovaleric acid). Among these radical polymerization initiators, potassium persulfate, ammonium persulfate, sodium persulfate, and 2,2'-azobis(2-amidinopropane) dihydrochloride are preferred due to their ease of availability and ease of handling. These radical polymerization initiators may be used alone or in combination of two or more. The radical polymerization initiator can also be used as a redox polymerization initiator in combination with a reducing agent such as sodium sulfite, sodium hydrogen sulfite, ferrous sulfate, or L-ascorbic acid.

[0032] The amount of radical polymerization initiator used is, for example, 0.00005 to 0.01 mole per mole of the water-soluble ethylenically unsaturated monomer. By using such an amount, it is possible to avoid a rapid polymerization reaction and complete the polymerization reaction within an appropriate time.

[0033] [Internal crosslinking agent] The internal crosslinking agent can be one that can crosslink the polymer of the water-soluble ethylenically unsaturated monomer used, such as (poly)ethylene glycol ("(poly)" refers to the presence or absence of the prefix "poly"). the same applies hereinafter)], unsaturated polyesters obtained by reacting polyols such as diols and triols, such as (poly)propylene glycol, 1,4-butanediol, trimethylolpropane, and (poly)glycerin, with unsaturated acids, such as (meth)acrylic acid, maleic acid, and fumaric acid; bisacrylamides such as N,N-methylenebisacrylamide; di(meth)acrylic acid esters or tri(meth)acrylic acid esters obtained by reacting polyepoxides with (meth)acrylic acid; di(meth)acrylic acid carbamyl esters obtained by reacting polyisocyanates, such as tolylene diisocyanate and hexamethylene diisocyanate, with hydroxyethyl (meth)acrylate; allylated starch, allylated cellulose, diallyl phthalate, N,N',N''-triallyl isocyanurate, and divinylbenzene. Examples of the compound include compounds having two or more polymerizable unsaturated groups; diglycidyl compounds such as (poly)ethylene glycol diglycidyl ether, (poly)propylene glycol diglycidyl ether, and (poly)glycerin diglycidyl ether, and polyglycidyl compounds such as triglycidyl compounds; epihalohydrin compounds such as epichlorohydrin, epibromohydrin, and α-methylepichlorohydrin; compounds having two or more reactive functional groups, such as isocyanate compounds such as 2,4-tolylene diisocyanate and hexamethylene diisocyanate; and oxetane compounds such as 3-methyl-3-oxetanemethanol, 3-ethyl-3-oxetanemethanol, 3-butyl-3-oxetanemethanol, 3-methyl-3-oxetaneethanol, 3-ethyl-3-oxetaneethanol, and 3-butyl-3-oxetaneethanol. Among these internal cross-linking agents, it is preferable to use unsaturated polyesters or polyglycidyl compounds, it is more preferable to use diglycidyl ether compounds, and it is preferable to use (poly)ethylene glycol diglycidyl ether, (poly)propylene glycol diglycidyl ether, or (poly)glycerin diglycidyl ether.These internal crosslinking agents may be used alone or in combination of two or more.

[0034] The amount of the internal crosslinking agent used is preferably 0.000001 to 0.02 mol, more preferably 0.00001 to 0.01 mol, even more preferably 0.00001 to 0.005 mol, and even more preferably 0.00005 to 0.002 mol, relative to 1 mol of the water-soluble ethylenically unsaturated monomer.

[0035] [Hydrocarbon dispersion medium] Examples of hydrocarbon dispersion media include aliphatic hydrocarbons having 6 to 8 carbon atoms, such as n-hexane, n-heptane, 2-methylhexane, 3-methylhexane, 2,3-dimethylpentane, 3-ethylpentane, and n-octane; alicyclic hydrocarbons, such as cyclohexane, methylcyclohexane, cyclopentane, methylcyclopentane, trans-1,2-dimethylcyclopentane, cis-1,3-dimethylcyclopentane, and trans-1,3-dimethylcyclopentane; and aromatic hydrocarbons, such as benzene, toluene, and xylene. Among these hydrocarbon dispersion media, n-hexane, n-heptane, and cyclohexane are particularly preferred due to their industrial availability, stable quality, and low cost. These hydrocarbon dispersion media may be used alone or in combination of two or more. Suitable results can also be obtained using a mixture of hydrocarbon dispersion media, such as commercially available Exxol Heptane (manufactured by ExxonMobil Corporation; containing 75 to 85% by mass of heptane and its isomeric hydrocarbons).

[0036] The amount of hydrocarbon dispersion medium used is preferably 100 to 1500 parts by mass, more preferably 200 to 1400 parts by mass, per 100 parts by mass of the water-soluble ethylenically unsaturated monomer in the first stage, from the viewpoints of uniformly dispersing the water-soluble ethylenically unsaturated monomer and facilitating control of the polymerization temperature. As will be described later, the reversed-phase suspension polymerization is carried out in one stage (single stage) or in multiple stages of two or more stages, and the above-mentioned first stage polymerization refers to the polymerization reaction in a single stage or a first stage in a multistage polymerization (the same applies hereinafter).

[0037] [Dispersion stabilizer] (surfactant) In the reversed-phase suspension polymerization, a dispersion stabilizer can be used to improve the dispersion stability of the water-soluble ethylenically unsaturated monomer in the hydrocarbon dispersion medium. A surfactant can be used as the dispersion stabilizer.

[0038] Examples of surfactants that can be used include sucrose fatty acid esters, polyglycerin fatty acid esters, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene glycerin fatty acid esters, sorbitol fatty acid esters, polyoxyethylene sorbitol fatty acid esters, polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene castor oil, polyoxyethylene hydrogenated castor oil, alkylaryl formaldehyde condensed polyoxyethylene ethers, polyoxyethylene polyoxypropylene block copolymers, polyoxyethylene polyoxypropyl alkyl ethers, polyethylene glycol fatty acid esters, alkyl glucosides, N-alkyl gluconamides, polyoxyethylene fatty acid amides, polyoxyethylene alkylamines, polyoxyethylene alkyl ether phosphate esters, and polyoxyethylene alkyl allyl ether phosphate esters. Among these surfactants, sorbitan fatty acid esters, polyglycerin fatty acid esters, and sucrose fatty acid esters are particularly preferred in terms of dispersion stability of the monomer. These surfactants may be used alone or in combination of two or more.

[0039] The amount of surfactant used is preferably 0.1 to 30 parts by mass, more preferably 0.3 to 20 parts by mass, per 100 parts by mass of the first stage water-soluble ethylenically unsaturated monomer.

[0040] (polymer dispersant) As a dispersion stabilizer used in the reversed phase suspension polymerization, a polymeric dispersant may be used in combination with the surfactant described above.

[0041] Examples of polymeric dispersants include maleic anhydride-modified polyethylene, maleic anhydride-modified polypropylene, maleic anhydride-modified ethylene-propylene copolymer, maleic anhydride-modified EPDM (ethylene-propylene-diene terpolymer), maleic anhydride-modified polybutadiene, maleic anhydride-ethylene copolymer, maleic anhydride-propylene copolymer, maleic anhydride-ethylene-propylene copolymer, maleic anhydride-butadiene copolymer, polyethylene, polypropylene, ethylene-propylene copolymer, oxidized polyethylene, oxidized polypropylene, oxidized ethylene-propylene copolymer, ethylene-acrylic acid copolymer, ethyl cellulose, and ethylhydroxyethyl cellulose. Among these polymeric dispersants, it is particularly preferable to use maleic anhydride-modified polyethylene, maleic anhydride-modified polypropylene, maleic anhydride-modified ethylene-propylene copolymer, maleic anhydride-ethylene copolymer, maleic anhydride-propylene copolymer, maleic anhydride-ethylene-propylene copolymer, polyethylene, polypropylene, ethylene-propylene copolymer, oxidized polyethylene, oxidized polypropylene, and oxidized ethylene-propylene copolymer from the viewpoint of dispersion stability of the monomer. These polymeric dispersants may be used alone or in combination of two or more.

[0042] The amount of polymeric dispersant used is preferably 0.1 to 30 parts by mass, more preferably 0.3 to 20 parts by mass, per 100 parts by mass of the first stage water-soluble ethylenically unsaturated monomer.

[0043] [Other ingredients] In the method for producing a water-absorbent resin, if desired, other components may be added to an aqueous solution containing a water-soluble ethylenically unsaturated monomer to carry out reverse phase suspension polymerization. As other components, various additives such as a thickener and a chain transfer agent can be added.

[0044] For example, a thickener can be added to an aqueous solution containing a water-soluble ethylenically unsaturated monomer to carry out reversed-phase suspension polymerization. By adjusting the viscosity of the aqueous solution by adding a thickener in this way, it is possible to control the median particle size obtained in the reversed-phase suspension polymerization.

[0045] Examples of thickeners that can be used include hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, carboxymethyl cellulose, polyacrylic acid, (partially) neutralized polyacrylic acid, polyethylene glycol, polyacrylamide, polyethyleneimine, dextrin, sodium alginate, polyvinyl alcohol, polyvinylpyrrolidone, polyethylene oxide, etc. If the stirring speed during polymerization is the same, the higher the viscosity of the water-soluble ethylenically unsaturated monomer aqueous solution, the larger the primary particles and / or secondary particles of the resulting particles tend to be.

[0046] [Reverse Phase Suspension Polymerization] In performing reversed-phase suspension polymerization, for example, an aqueous monomer solution containing a water-soluble ethylenically unsaturated monomer is dispersed in a hydrocarbon dispersion medium in the presence of a dispersion stabilizer. In this case, the dispersion stabilizer (surfactant or polymeric dispersant) may be added either before or after the addition of the aqueous monomer solution, as long as it is before the start of the polymerization reaction.

[0047] Among these, from the viewpoint of easily reducing the amount of hydrocarbon dispersion medium remaining in an obtained water absorbent resin, it is preferable to disperse an aqueous monomer solution in a hydrocarbon dispersion medium having a polymeric dispersant dispersed therein, and then further disperse a surfactant therein, and then carry out polymerization.

[0048] Such reversed-phase suspension polymerization can be carried out in one stage or in multiple stages of two or more stages, and is preferably carried out in two to three stages from the viewpoint of increasing productivity.

[0049] When performing reversed-phase suspension polymerization in two or more stages, after performing the first-stage reversed-phase suspension polymerization, a water-soluble ethylenically unsaturated monomer is added to and mixed with the reaction mixture obtained in the first-stage polymerization reaction, and reversed-phase suspension polymerization in the second and subsequent stages can be performed in the same manner as in the first stage. In the reversed-phase suspension polymerization in each stage from the second stage onwards, it is preferable to perform the reversed-phase suspension polymerization by adding, in addition to the water-soluble ethylenically unsaturated monomer, a radical polymerization initiator within the molar ratio of each component to the water-soluble ethylenically unsaturated monomer as described above, based on the amount of water-soluble ethylenically unsaturated monomer added during the reversed-phase suspension polymerization in each stage from the second stage onwards. Note that, in the second and subsequent polymerization stages, an internal crosslinking agent may also be added to the water-soluble ethylenically unsaturated monomer, if necessary.

[0050] The reaction temperature of the polymerization reaction is preferably 20 to 110°C, more preferably 40 to 90°C, from the viewpoints of rapidly progressing the polymerization, shortening the polymerization time, thereby improving economic efficiency, and easily removing the heat of polymerization to allow the reaction to proceed smoothly.

[0051] <Post-crosslinking process> Next, the water-absorbent resin is obtained by adding a post-crosslinking agent to a hydrogel-like substance having an internal crosslinked structure obtained by polymerizing a water-soluble ethylenically unsaturated monomer to crosslink it (post-crosslinking reaction). This post-crosslinking reaction is preferably carried out in the presence of a post-crosslinking agent after the polymerization of the water-soluble ethylenically unsaturated monomer. In this way, by subjecting a hydrogel-like substance having an internal crosslinked structure to a post-crosslinking reaction after polymerization, the crosslink density near the surface of the water-absorbent resin can be increased, and a water-absorbent resin with improved performance such as water absorption capacity under load can be obtained.

[0052] Examples of the post-crosslinking agent include compounds having two or more reactive functional groups. For example, polyols such as ethylene glycol, propylene glycol, 1,4-butanediol, trimethylolpropane, glycerin, polyoxyethylene glycol, polyoxypropylene glycol, and polyglycerin; polyglycidyl compounds such as (poly)ethylene glycol diglycidyl ether, (poly)glycerin diglycidyl ether, (poly)glycerin triglycidyl ether, trimethylolpropane triglycidyl ether, (poly)propylene glycol polyglycidyl ether, and (poly)glycerol polyglycidyl ether; epichlorohydrin, epibromohydrin, α-methylepichlorohydrin, isocyanate compounds such as 2,4-tolylene diisocyanate and hexamethylene diisocyanate; oxetane compounds such as 3-methyl-3-oxetanemethanol, 3-ethyl-3-oxetanemethanol, 3-butyl-3-oxetanemethanol, 3-methyl-3-oxetaneethanol, 3-ethyl-3-oxetaneethanol, and 3-butyl-3-oxetaneethanol; oxazoline compounds such as 1,2-ethylenebisoxazoline; carbonate compounds such as ethylene carbonate; and hydroxyalkylamide compounds such as bis[N,N-di(β-hydroxyethyl)]adipamide. Among these post-crosslinking agents, preferred are polyglycidyl compounds such as (poly)ethylene glycol diglycidyl ether, (poly)glycerin diglycidyl ether, (poly)glycerin triglycidyl ether, trimethylolpropane triglycidyl ether, (poly)propylene glycol polyglycidyl ether, (poly)glycerol polyglycidyl ether, etc. These post-crosslinking agents may be used alone or in combination of two or more.

[0053] The amount of the post-crosslinking agent used is preferably 0.00001 to 0.01 mol, more preferably 0.00005 to 0.005 mol, and even more preferably 0.0001 to 0.002 mol, per mol of the total amount of water-soluble ethylenically unsaturated monomers used in the polymerization.

[0054] The post-crosslinking agent may be added as it is or as an aqueous solution, or may be added as a solution using a hydrophilic organic solvent as a solvent, if necessary. Examples of hydrophilic organic solvents include lower alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol, and isopropyl alcohol; ketones such as acetone and methyl ethyl ketone; ethers such as diethyl ether, dioxane, and tetrahydrofuran; amides such as N,N-dimethylformamide; and sulfoxides such as dimethyl sulfoxide. These hydrophilic organic solvents may be used alone, in combination with two or more, or as a mixed solvent with water.

[0055] The timing of adding the post-crosslinking agent may be after the polymerization reaction of the water-soluble ethylenically unsaturated monomer has almost completely finished, and it is preferably added in the presence of water in the range of 1 to 400 parts by mass, more preferably in the range of 5 to 200 parts by mass, even more preferably in the range of 10 to 100 parts by mass, and even more preferably in the range of 20 to 60 parts by mass, relative to 100 parts by mass of the water-soluble ethylenically unsaturated monomer. Note that the amount of water means the total amount of water contained in the reaction system and water used as needed when adding the post-crosslinking agent.

[0056] The reaction temperature in the post-crosslinking reaction is preferably 50 to 250° C., more preferably 60 to 180° C., even more preferably 60 to 140° C., and even more preferably 70 to 120° C. The reaction time in the post-crosslinking reaction is preferably 1 to 300 minutes, and more preferably 5 to 200 minutes.

[0057] <Drying process> After the above-mentioned reversed-phase suspension polymerization, a drying step may be included in which water, hydrocarbon dispersion medium, etc. are removed by distillation by applying energy such as heat from the outside. When dehydrating the hydrogel after reversed-phase suspension polymerization, the system in which the hydrogel is dispersed in the hydrocarbon dispersion medium is heated, and the water and hydrocarbon dispersion medium are temporarily distilled out of the system by azeotropic distillation. In this case, if only the distilled hydrocarbon dispersion medium is returned to the system, continuous azeotropic distillation is possible. In this case, the temperature in the system during drying is maintained below the azeotropic temperature with the hydrocarbon dispersion medium, which is preferable from the viewpoint of preventing deterioration of the resin. Subsequently, water and hydrocarbon dispersion medium are distilled off to obtain water-absorbent resin particles. By controlling the processing conditions of this drying step after polymerization to adjust the amount of dehydration, it is possible to control the various properties of the obtained water-absorbent resin.

[0058] In the drying step, the drying treatment by distillation may be carried out under normal pressure or under reduced pressure. Furthermore, from the viewpoint of increasing the drying efficiency, the drying treatment may be carried out under a stream of gas such as nitrogen. When the drying treatment is carried out under normal pressure, the drying temperature is preferably 70 to 250°C, more preferably 80 to 180°C, even more preferably 80 to 140°C, and even more preferably 90 to 130°C. When the drying treatment is carried out under reduced pressure, the drying temperature is preferably 40 to 160°C, and more preferably 50 to 110°C.

[0059] In addition, when a post-crosslinking step using a post-crosslinking agent is carried out after the polymerization of the monomer by reversed-phase suspension polymerization, the drying step by distillation described above is carried out after the post-crosslinking step is completed. Alternatively, the post-crosslinking step and the drying step may be carried out simultaneously.

[0060] The particulate water-absorbing resin composition of the present invention may contain additives according to the purpose in addition to the hydrazide compound. Examples of such additives include inorganic powders, surfactants, oxidizing agents, reducing agents, metal chelating agents, radical chain inhibitors, antioxidants, antibacterial agents, etc. For example, by adding 0.05 to 5 parts by mass of amorphous silica as inorganic powder to 100 parts by mass of the water-absorbing resin, the fluidity of the particulate water-absorbing resin composition can be further improved.

[0061] In the particulate water-absorbing resin composition of the present invention, the content of the water-absorbing resin (excluding additives) is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 98% by mass or more.

[0062] The particulate water-absorbent resin composition of the present invention can be suitably produced, for example, by a method including a step of mixing a water-absorbent resin, which is a crosslinked polymer of the water-soluble ethylenically unsaturated monomer, an internal crosslinking agent, and a post-crosslinking agent, with a hydrazide compound at a temperature of 10 to 100°C. The temperature of the mixing step may be 20 to 90°C. As described above, for example, by mixing the particulate water-absorbent resin and the hydrazide compound in a solid phase, the hydrazide compound can be present on the surface of the particulate water-absorbent resin to an extent that the effects of the present invention can be exhibited. Alternatively, the particulate water-absorbent resin composition of the present invention may be prepared by mixing the hydrazide compound dissolved or dispersed in a liquid medium such as an aqueous liquid with the particulate water-absorbent resin. Alternatively, the hydrazide compound may be incorporated into the particulate water-absorbent resin.

[0063] 2. Absorbent materials and absorbent articles The particulate water-absorbing resin composition of the present invention constitutes an absorbent material used in hygiene materials such as sanitary products and disposable diapers, and is suitably used in absorbent articles containing the absorbent material.

[0064] Here, an absorbent using the particulate water-absorbent resin composition of the present invention contains the particulate water-absorbent resin composition of the present invention. The absorbent may further contain hydrophilic fibers. Examples of the configuration of the absorbent include a sheet-like structure in which a water-absorbent resin is fixed on a nonwoven fabric or between multiple nonwoven fabrics, a mixed dispersion obtained by mixing the water-absorbent resin composition and hydrophilic fibers to form a uniform composition, a sandwich structure in which the particulate water-absorbent resin composition is sandwiched between layered hydrophilic fibers, and a structure in which the particulate water-absorbent resin composition and hydrophilic fibers are wrapped in tissue. The absorbent may also contain other components, such as adhesive binders such as heat-fusible synthetic fibers, hot-melt adhesives, and adhesive emulsions, to improve the shape retention of the absorbent.

[0065] The content of the water-absorbent resin in the absorbent body is preferably 5 to 100% by mass, more preferably 10 to 95% by mass, even more preferably 20 to 90% by mass, and even more preferably 30 to 80% by mass.

[0066] Examples of hydrophilic fibers include cellulose fibers such as cotton-like pulp obtained from wood, mechanical pulp, chemical pulp, and semi-chemical pulp, artificial cellulose fibers such as rayon and acetate, and fibers made of synthetic resins such as hydrophilically treated polyamide, polyester, and polyolefin. The average fiber length of the hydrophilic fibers is usually 0.1 to 10 mm, or may be 0.5 to 5 mm.

[0067] The absorbent article of the present invention can be produced by holding an absorbent body using the particulate water-absorbing resin composition of the present invention between a liquid-permeable sheet (top sheet) through which liquid can pass and a liquid-impermeable sheet (back sheet) through which liquid cannot pass. The liquid-permeable sheet is arranged on the side that comes into contact with the body, and the liquid-impermeable sheet is arranged on the opposite side that comes into contact with the body.

[0068] Examples of liquid-permeable sheets include air-through, spunbond, chemical-bond, and needle-punched nonwoven fabrics made of fibers such as polyethylene, polypropylene, and polyester, as well as porous synthetic resin sheets. Examples of liquid-impermeable sheets include synthetic resin films made of resins such as polyethylene, polypropylene, and polyvinyl chloride. The liquid-permeable sheet is preferably at least one selected from the group consisting of thermal-bonded nonwoven fabrics, air-through nonwoven fabrics, spunbonded nonwoven fabrics, and spunbonded / meltblown / spunbonded nonwoven fabrics.

[0069] The weight of the liquid-permeable sheet is 5g / m 2 More than 100g / m 2 Preferably, it is 10 g / m or less. 2 More than 60g / m 2 It is more preferable that the liquid-permeable sheet has a surface embossed or perforated to improve the liquid diffusibility. The embossing or perforation can be carried out by a known method.

[0070] Examples of liquid-impermeable sheets include sheets made of synthetic resins such as polyethylene, polypropylene, and polyvinyl chloride; sheets made of nonwoven fabrics such as spunbond / meltblown / spunbond (SMS) nonwoven fabrics in which a water-resistant meltblown nonwoven fabric is sandwiched between high-strength spunbond nonwoven fabrics; and sheets made of composite materials of these synthetic resins and nonwoven fabrics (for example, spunbond nonwoven fabrics, spunlace nonwoven fabrics). A sheet made of a synthetic resin primarily composed of low-density polyethylene (LDPE) resin can also be used as the liquid-impermeable sheet. The liquid-impermeable sheet has, for example, a basis weight of 10 to 50 g / m. 2 The sheet may be made of a synthetic resin. [Example]

[0071] The present invention will be described in detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0072] The particulate water-absorbing resin compositions obtained in the following Examples and Comparative Examples were evaluated by the following various tests, each of which will be described below.

[0073] <Median particle size> The measurements were carried out in an environment with a temperature of 25±2°C and a humidity of 50±10%. JIS standard sieves were arranged in the following order from top to bottom: a sieve with an opening of 850 μm, a sieve with an opening of 600 μm, a sieve with an opening of 500 μm, a sieve with an opening of 425 μm, a sieve with an opening of 300 μm, a sieve with an opening of 250 μm, a sieve with an opening of 150 μm, and a tray.

[0074] 50 g of the water-absorbent resin composition was placed on the top sieve of the combination, and the composition was shaken for 10 minutes using a rotary shaker to classify it. After classification, the mass of the water-absorbent resin composition remaining on each sieve was calculated as a mass percentage relative to the total amount, and the particle size distribution was determined. The particles on the sieves were integrated in descending order of particle size in this particle size distribution, and the relationship between the sieve openings and the integrated value of the mass percentage of the water-absorbent resin remaining on the sieves was plotted on a logarithmic probability paper. The particle size corresponding to an integrated mass percentage of 50% by mass was determined as the median particle size by connecting the plots on the probability paper with a straight line.

[0075] <Fluidity test> The spatula angle was measured using a powder tester PT-X type (manufactured by Hosokawa Micron Corporation) under an environment of a temperature of 25±2°C and a humidity of 50±10%, and the fluidity of the particulate water-absorbent resin compositions of the Examples and Comparative Examples was evaluated. The spatula angle is the inclination angle of the side surface of the resin powder deposited on the spatula, and is the angle required to move powder in a stationary state, and is one of the indicators of fluidity. The smaller the spatula angle value, the better the fluidity. The measurement procedure was carried out according to the instruction manual of the powder tester. The measured spatula angle values ​​are shown in Table 1.

[0076] <Production of water-absorbent resin> (Production Example 1) A 2-L round-bottom cylindrical separable flask with an inner diameter of 11 cm and equipped with a reflux condenser, a dropping funnel, a nitrogen gas inlet, and a stirrer with a two-stage, four-paddle blade arrangement with a blade diameter of 5 cm was prepared. 293 g of n-heptane was added to the flask as a hydrocarbon dispersion medium, and 0.736 g of maleic anhydride-modified ethylene-propylene copolymer (Hiwax 1105A, Mitsui Chemicals, Inc.) was added as a polymeric dispersant. The flask was heated to 80°C with stirring to dissolve the dispersant, and then cooled to 50°C.

[0077] Separately, 92.0 g (1.03 mol) of an 80.5 mass% aqueous acrylic acid solution was placed in a 300 mL beaker as a water-soluble ethylenically unsaturated monomer, and while cooling with ice water, 147.7 g of a 20.9 mass% aqueous sodium hydroxide solution was added dropwise to neutralize the solution to 75 mol%, followed by adding and dissolving 0.092 g of hydroxyethyl cellulose (Sumitomo Seika Chemicals Co., Ltd., HECAW-15F) as a thickener, 0.0736 g (0.272 mmol) of potassium persulfate as a water-soluble radical polymerization agent, and 0.010 g (0.057 mmol) of ethylene glycol diglycidyl ether as an internal crosslinking agent to prepare a first-stage aqueous monomer solution.

[0078] The aqueous monomer solution prepared above was added to a separable flask and stirred for 10 minutes. A surfactant solution prepared by heating and dissolving 0.736 g of sucrose stearate with HLB3 (Ryoto Sugar Ester S-370, Mitsubishi Chemical Foods Corporation) as a surfactant in 6.62 g of n-heptane in a 20 mL vial was then added. The system was thoroughly purged with nitrogen while stirring at a stirrer speed of 550 rpm, and the flask was then immersed in a water bath at 70°C for 60 minutes to obtain a first-stage polymerization slurry.

[0079] Meanwhile, 128.8 g (1.43 mol) of an 80.5 mass% aqueous acrylic acid solution was placed in a separate 500 mL beaker as a water-soluble ethylenically unsaturated monomer, and while cooling with ice water, 159.0 g of a 27 mass% aqueous sodium hydroxide solution was added dropwise to carry out 75 mol% neutralization. Thereafter, 0.103 g (0.381 mmol) of potassium persulfate as a water-soluble radical polymerization initiator and 0.0116 g (0.067 mmol) of ethylene glycol diglycidyl ether as an internal crosslinking agent were added and dissolved to prepare a second-stage aqueous monomer solution.

[0080] The contents of the separable flask system were cooled to 25°C while stirring at a stirrer speed of 1000 rpm, and then the entire amount of the second-stage aqueous monomer solution was added to the first-stage polymerization slurry. The atmosphere in the system was replaced with nitrogen for 30 minutes, and the flask was again immersed in a water bath at 70°C for 60 minutes to obtain a second-stage hydrogel polymer. After the second-stage polymerization, 0.589 g of a 45% by weight aqueous solution of pentasodium diethylenetriamine pentacetate was added to the hydrogel polymer under stirring. The flask was then immersed in an oil bath set at 125°C, and 257.7 g of water was extracted from the system by azeotropic distillation of n-heptane and water while refluxing the n-heptane. 4.42 g (0.507 mmol) of a 2% by weight aqueous solution of ethylene glycol diglycidyl ether was then added to the flask as a post-crosslinking agent, and the mixture was maintained at 83°C for 2 hours.

[0081] Thereafter, n-heptane was evaporated at 125°C to dry the mixture, thereby obtaining a particulate crosslinked polymer (dried product). The particulate crosslinked polymer was passed through a sieve with an opening of 850µm to obtain 228.0g of a particulate water absorbent resin. The median particle diameter of the particulate water absorbent resin was 352µm.

[0082] <Production of Water-Absorbent Resin Composition> Example 1 A particulate water-absorbent resin composition was obtained by powder-mixing 0.07 parts by mass of malonic acid dihydrazide as a hydrazide compound with 100 parts by mass of the particulate water-absorbent resin obtained in Production Example 1 under an environment of 25°C. The spatula angle of this particulate water-absorbent resin composition was 33.9°.

[0083] Example 2 A particulate water-absorbing resin composition was obtained in the same manner as in Example 1, except that the amount of malonic acid dihydrazide was changed to 0.35 parts by mass relative to 100 parts by mass of the particulate water-absorbing resin in Example 1. The spatula angle of this particulate water-absorbing resin composition was 32.3°.

[0084] Example 3 A particulate water-absorbing resin composition was obtained in the same manner as in Example 1, except that the amount of malonic acid dihydrazide was changed to 0.7 parts by mass relative to 100 parts by mass of the particulate water-absorbing resin in Example 1. The spatula angle of this particulate water-absorbing resin composition was 31.9°.

[0085] Example 4 A particulate water-absorbing resin composition was obtained in the same manner as in Example 1, except that malonic acid dihydrazide was changed to adipic acid dihydrazide as the hydrazide compound in Example 3. The spatula angle of this particulate water-absorbing resin composition was 31.8°.

[0086] (Comparative Example 1) The particulate water-absorbent resin obtained in Production Example 1 was used as it was as the particulate water-absorbent resin of Comparative Example 1. The spatula angle of this particulate water-absorbent resin was 40.4°.

[0087] [Table 1]

Claims

1. A particulate water-absorbent resin composition comprising a hydrazide compound and a particulate water-absorbent resin, a particulate hydrazide compound is present on a surface of the particulate water absorbent resin, the hydrazide compound has a median particle size of 5 to 350 μm; The particulate water absorbent resin has a median particle diameter of 100 to 600 μm, the content of the hydrazide compound in the particulate water-absorbing resin composition is 0.001 to 10 mass %, The particulate water-absorbing resin composition has a spatula angle of 20 to 38°.

2. 2. The particulate water-absorbing resin composition according to claim 1, wherein the hydrazide compound is further present inside the particulate water-absorbing resin.

3. 3. The particulate water-absorbing resin composition according to claim 1, wherein the content of the hydrazide compound is 0.005 to 5% by mass.

4. 4. The particulate water-absorbing resin composition according to claim 1, wherein the particulate water-absorbing resin composition has a spatula angle of 20 to 35 degrees.

5. 5. The particulate water-absorbing resin composition according to claim 1, wherein the particulate water-absorbing resin composition has a median particle size of 200 to 500 μm.

6. An absorbent material comprising the particulate water-absorbing resin composition according to any one of claims 1 to 5.

7. An absorbent article comprising the absorbent body according to claim 6 held between a liquid-permeable sheet and a liquid-impermeable sheet.

8. 6. A method for producing a particulate water-absorbing resin composition according to claim 1, comprising a step of mixing a water-absorbing resin that is a polymer cross-linked product of a water-soluble ethylenically unsaturated monomer, an internal cross-linking agent, and a post-cross-linking agent, with a hydrazide compound at a temperature of 10 to 100°C.

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