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WO2025164340A1 - Particules de résine absorbante, et procédé de fabrication de celles-ci - Google Patents

Particules de résine absorbante, et procédé de fabrication de celles-ci

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Publication number
WO2025164340A1
WO2025164340A1 PCT/JP2025/001230 JP2025001230W WO2025164340A1 WO 2025164340 A1 WO2025164340 A1 WO 2025164340A1 JP 2025001230 W JP2025001230 W JP 2025001230W WO 2025164340 A1 WO2025164340 A1 WO 2025164340A1
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WO
WIPO (PCT)
Prior art keywords
mass
water
poly
parts
fatty acid
Prior art date
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Pending
Application number
PCT/JP2025/001230
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English (en)
Japanese (ja)
Inventor
秀之 西
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Sumitomo Seika Chemicals Co Ltd
Original Assignee
Sumitomo Seika Chemicals Co Ltd
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Filing date
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Publication of WO2025164340A1 publication Critical patent/WO2025164340A1/fr
Pending legal-status Critical Current
Anticipated expiration legal-status Critical

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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
    • C08F2/12—Polymerisation in non-solvents
    • C08F2/16—Aqueous medium
    • C08F2/18—Suspension polymerisation
    • 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

Definitions

  • the present invention relates to a method for producing water-absorbent resin particles, water-absorbent resin particles, absorbents, and absorbent articles. More specifically, the present invention relates to a method for producing water-absorbent resin particles that constitute absorbents suitable for use in hygienic materials such as disposable diapers, sanitary napkins, and incontinence pads, and to water-absorbent resin particles.
  • water-absorbent resin particles have been widely used in hygiene materials such as disposable diapers, sanitary napkins, and incontinence pads.
  • cross-linked polymers of water-soluble ethylenically unsaturated monomers more specifically cross-linked polymers of partially neutralized polyacrylic acid
  • have excellent water absorption capabilities and because the raw material, acrylic acid, is easily available industrially, they can be produced at low cost with consistent quality, and are less susceptible to spoilage and deterioration.
  • Absorbent articles such as disposable diapers, sanitary napkins, and incontinence pads are primarily composed of an absorbent core located in the center that absorbs and retains bodily 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 typically composed of hydrophilic fibers such as pulp and water-absorbent resin particles.
  • Water-absorbent resin particles can be produced, for example, by reverse-phase suspension polymerization of a water-soluble ethylenically unsaturated monomer in a hydrocarbon dispersion medium to obtain polymer particles.
  • the main object of the present invention is to provide a method for producing water-absorbent resin particles, which includes a step of obtaining polymer particles by reverse-phase suspension polymerization of a water-soluble ethylenically unsaturated monomer in a hydrocarbon dispersion medium, and which produces water-absorbent resin particles with a narrow particle size distribution.
  • a further object of the present invention is to provide water-absorbent resin particles with a narrow particle size distribution.
  • the present inventors conducted extensive research to solve the above-mentioned problems. As a result, they discovered that in a method for producing water-absorbent resin particles, which includes a step of obtaining polymer particles by reverse-phase suspension polymerization of a water-soluble ethylenically unsaturated monomer in a hydrocarbon dispersion medium, the method also includes a step of performing the reverse-phase suspension polymerization in two or more stages and aggregating the polymer particles in the presence of a dispersion stabilizer, and that water-absorbent resin particles having a narrow particle size distribution can be obtained by using, as the dispersion stabilizer, two or more types of (poly)glycerin fatty acid esters that have different precipitation temperatures when dissolved in a 0.46% by mass heptane solution.
  • the present invention was completed based on this finding and through further extensive research.
  • Item 1 A method for producing water-absorbent resin particles, comprising a step of obtaining polymer particles by reverse-phase suspension polymerization of a water-soluble ethylenically unsaturated monomer in a hydrocarbon dispersion medium, The reverse phase suspension polymerization is carried out in two or more stages, a step of aggregating the polymer particles in the presence of a dispersion stabilizer, A method for producing water-absorbent resin particles, wherein two or more types of (poly)glycerin fatty acid esters having different precipitation temperatures when dissolved in a 0.46% by mass heptane solution are used as the dispersion stabilizer.
  • Item 2 A method for producing water-absorbent resin particles, comprising a step of obtaining polymer particles by reverse-phase suspension polymerization of a water-soluble ethylenically unsaturated monomer in a hydrocarbon dispersion medium, The reverse phase suspension polymerization is carried out in two or more stages, a step of aggregat
  • Item 3 At least one of the (poly)glycerin fatty acid esters is hexaglyceryl tristearate, Item 3.
  • the dispersion stabilizer includes the hexaglyceryl tristearate and at least one of a (poly)glycerin fatty acid ester having a higher precipitation temperature than the hexaglyceryl tristearate and a (poly)glycerin fatty acid ester having a lower precipitation temperature than the hexaglyceryl tristearate, Item 4.
  • the dispersion stabilizer comprises the hexaglyceryl tristearate, a (poly)glycerin fatty acid ester having a higher precipitation temperature than the hexaglyceryl tristearate, and a (poly)glycerin fatty acid ester having a lower precipitation temperature than the hexaglyceryl tristearate, Item 5.
  • Water-absorbent resin particles containing polymer particles having a water-soluble ethylenically unsaturated monomer as a monomer unit, A water-absorbent resin particle having a particle size distribution uniformity of 2.5 or less and containing a (poly)glycerin fatty acid ester near the surface.
  • a method for producing water-absorbent resin particles which includes a step of obtaining polymer particles by reverse-phase suspension polymerization of a water-soluble ethylenically unsaturated monomer in a hydrocarbon dispersion medium, and which produces water-absorbent resin particles with a narrow particle size distribution. Furthermore, according to the present invention, it is also possible to provide water-absorbent resin particles with a narrow particle size distribution.
  • the vicinity of the surface of a water-absorbent resin particle refers to the outermost surface of the water-absorbent resin particle and the region extending from the outermost surface toward the center of the particle to a depth of approximately 30 ⁇ m.
  • the method for producing water-absorbent resin particles of the present invention is a method for producing water-absorbent resin particles, which comprises a step of obtaining polymer particles by reverse-phase suspension polymerization of a water-soluble ethylenically unsaturated monomer in a hydrocarbon dispersion medium (polymerization step).
  • reverse-phase suspension polymerization is carried out in two or more stages.
  • the production method of the present invention also includes a step of aggregating polymer particles in the presence of a dispersion stabilizer.
  • the production method of the present invention uses, as the dispersion stabilizer, two or more types of (poly)glycerin fatty acid esters that have different precipitation temperatures when dissolved in a 0.46% by mass heptane solution.
  • the method for producing water-absorbent resin particles of the present invention can suitably produce water-absorbent resin particles with a narrow particle size distribution.
  • the method for producing water-absorbent resin particles of the present invention is described in detail below.
  • the polymerization step is a step of polymerizing a water-soluble ethylenically unsaturated monomer by reversed-phase suspension polymerization to obtain polymer particles.
  • reversed-phase suspension polymerization the water-soluble ethylenically unsaturated monomer is polymerized by heating under stirring in a hydrocarbon dispersion medium.
  • an internal crosslinking agent may be added to the water-soluble ethylenically unsaturated monomer as needed to form crosslinked polymer particles having an internal crosslinked structure.
  • An example of the polymerization step is described below.
  • water-soluble ethylenically unsaturated monomers examples 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.
  • (meth)acrylic acid herein, "acrylic” and “methacryl
  • 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 ease of industrial availability.
  • These water-soluble ethylenically unsaturated monomers may be used alone or in combination of two or more.
  • acrylic acid and its salts are widely used as raw materials for water-absorbent resin particles, and these acrylic acids and/or their salts may be copolymerized with the other water-soluble ethylenically unsaturated monomers mentioned above.
  • acrylic acid and/or its salts be used as the main water-soluble ethylenically unsaturated monomer in an amount of 70 to 100 mol % relative to the total water-soluble ethylenically unsaturated monomers.
  • the water-soluble ethylenically unsaturated monomer may be dispersed in a hydrocarbon dispersion medium in the form of an aqueous solution and subjected to reverse-phase suspension polymerization.
  • a hydrocarbon dispersion medium in the form of an aqueous solution and subjected to reverse-phase suspension polymerization.
  • 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 or less.
  • 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.
  • the acid group may be neutralized in advance with an alkaline neutralizer, if necessary.
  • alkaline neutralizers include alkali metal salts such as sodium hydroxide, sodium carbonate, sodium bicarbonate, potassium hydroxide, and potassium carbonate; ammonia, etc. These alkaline neutralizers may also be used in the form of an aqueous solution to simplify the neutralization process.
  • the alkaline neutralizers mentioned above may be used alone or in combination of two or more types.
  • the degree of neutralization of the water-soluble ethylenically unsaturated monomer with the alkaline neutralizing agent is preferably 40 to 100 mol%, more preferably 50 to 90 mol%, even more preferably 60 to 85 mol%, and even more preferably 70 to 80 mol%, in terms of the degree of neutralization of all acid groups possessed by the water-soluble ethylenically unsaturated monomer.
  • radical polymerization initiator examples include persulfates such as potassium persulfate, ammonium persulfate, and sodium persulfate, peroxides such as methyl ethyl ketone peroxide, methyl isobutyl ketone peroxide, di-t-butyl peroxide, t-butylcumyl peroxide, t-butyl peroxyacetate, t-butylperoxyisobutyrate, t-butylperoxypivalate, and hydrogen peroxide, as well as 2,2'-azobis(2-amidinopropane) dihydrochloride and 2,2'-azobis[2-(N-phenyl)propane].
  • persulfates such as potassium persulfate, ammonium persulfate, and sodium persulfate
  • peroxides such as methyl ethyl ketone peroxide, methyl isobutyl ketone peroxide, di-t
  • radical polymerization initiator examples 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).
  • 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-
  • radical polymerization initiators potassium persulfate, ammonium persulfate, sodium persulfate, and 2,2'-azobis(2-amidinopropane) dihydrochloride are preferred from the viewpoints of ease of availability and 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.
  • the amount of radical polymerization initiator used is, for example, 0.00005 to 0.01 moles per mole of 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.
  • 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 both the presence and absence of the prefix "poly”).
  • unsaturated polyesters obtained by reacting polyols such as diols and triols, such as (poly)propylene glycol, 1,4-butanediol, 1,6-hexanediol, 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'
  • polyethylene glycol diacrylate, trimethylolpropane triacrylate, (poly)ethylene glycol diglycidyl ether, (poly)propylene glycol diglycidyl ether, and (poly)glycerin diglycidyl ether are preferably used.
  • These internal cross-linking agents may be used alone or in combination of two or more.
  • the amount of 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 per 1 mol of water-soluble ethylenically unsaturated monomer.
  • hydrocarbon dispersion media examples 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.
  • aliphatic hydrocarbons having 6 to 8 carbon atoms such as n-hexane, n-heptane, 2-methylhexane, 3-methylhexane, 2,3-dimethylp
  • hydrocarbon dispersion media n-hexane, n-heptane, and cyclohexane are particularly preferred because of 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 commercially available product, such as Exxol Heptane (manufactured by ExxonMobil Corporation; containing 75 to 85% by mass of hydrocarbons such as heptane and its isomers).
  • the amount of hydrocarbon dispersion medium used is preferably 100 to 1500 parts by mass, and 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 viewpoint of uniformly dispersing the water-soluble ethylenically unsaturated monomer and facilitating control of the polymerization temperature.
  • reverse-phase suspension polymerization is carried out in two or more stages, and the first-stage polymerization mentioned above refers to the first-stage polymerization reaction in the multi-stage polymerization (the same applies hereinafter).
  • the production method of the present invention includes a step of aggregating polymer particles in the presence of a dispersion stabilizer, and two or more types of (poly)glycerin fatty acid esters having different precipitation temperatures when dissolved in a 0.46% by mass heptane solution are used as the dispersion stabilizer.
  • the precipitation temperature (hereinafter sometimes simply referred to as "precipitation temperature") of a 0.46% by mass heptane solution of (poly)glycerin fatty acid ester was measured using the method described in the Examples.
  • the difference between the precipitation temperature of the (poly)glycerin fatty acid ester having the highest precipitation temperature and the precipitation temperature of the (poly)glycerin fatty acid ester having the lowest precipitation temperature among the two or more (poly)glycerin fatty acid esters is preferably 15°C or less, more preferably 10°C or less, even more preferably 6°C or less, and is preferably 1°C or more, more preferably 2°C or more, even more preferably 3°C or more.
  • Preferred ranges include 1 to 15°C, 1 to 10°C, 1 to 6°C, 2 to 15°C, 2 to 10°C, 2 to 6°C, 3 to 15°C, 3 to 10°C, and 3 to 6°C.
  • the precipitation temperature of the (poly)glycerin fatty acid ester is preferably 55°C or lower, more preferably 45°C or lower, even more preferably 40°C or lower, and even more preferably 35°C or lower, and is preferably 0°C or higher, more preferably 10°C or higher, even more preferably 15°C or higher, and even more preferably 20°C or higher.
  • Preferred ranges include 0-55°C, 0-45°C, 0-40°C, 0-35°C, 10-55°C, 10-45°C, 10-40°C, 10-35°C, 15-55°C, 15-45°C, 15-40°C, 15-35°C, 20-55°C, 20-45°C, 20-40°C, and 20-35°C.
  • (Poly)glycerin fatty acid esters can reduce discoloration of water-absorbent resin particles due to heating.
  • Specific examples of (poly)glycerin fatty acid esters include monoglyceryl monostearate, tetraglyceryl monostearate, tetraglyceryl tristearate, tetrapolyglyceryl pentastearate, hexaglyceryl tristearate, decaglyceryl tristearate, decaglyceryl decastearate, decaglyceryl pentastearate, decaglyceryl dodecabehenate, decaglyceryl pentaisostearate, decaglyceryl pentaoleate, decaglyceryl pentapalmitate, decaglyceryl pentalaurate, decaglyceryl pentahydroxystearate, and hexaglyceryl condensed ricinoleate.
  • the present invention it is preferable to use two or more types of (poly)glycerin fatty acid esters from among these (poly)glycerin fatty acid esters. Furthermore, it is more preferable that one of the two or more (poly)glycerin fatty acid esters be hexaglyceryl tristearate.
  • the total amount of two or more (poly)glycerin fatty acid esters used is preferably 0.2 parts by mass or more, more preferably 0.9 parts by mass or more, even more preferably 1.3 parts by mass or more, and even more preferably 1.4 parts by mass or more, relative to 100 parts by mass of the water-soluble ethylenically unsaturated monomer used in the first stage of reversed-phase suspension polymerization, and is preferably 12.0 parts by mass or less, more preferably 4.0 parts by mass or less, even more preferably 2.0 parts by mass or less, and even more preferably 1.7 parts by mass or less.
  • parts or less and preferred ranges include 0.2 to 12.0 parts by mass, 0.2 to 4.0 parts by mass, 0.2 to 2.0 parts by mass, 0.2 to 1.7 parts by mass, 0.9 to 12.0 parts by mass, 0.9 to 4.0 parts by mass, 0.9 to 2.0 parts by mass, 0.9 to 1.7 parts by mass, 1.3 to 12.0 parts by mass, 1.3 to 4.0 parts by mass, 1.3 to 2.0 parts by mass, 1.3 to 1.7 parts by mass, 1.4 to 12.0 parts by mass, 1.4 to 4.0 parts by mass, 1.4 to 2.0 parts by mass, and 1.4 to 1.7 parts by mass.
  • the amount of the (poly)glycerin fatty acid ester having the highest precipitation temperature among two or more types of (poly)glycerin fatty acid esters is preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, and even more preferably 0.3 parts by mass or more, relative to 100 parts by mass of the water-soluble ethylenically unsaturated monomer used in the first stage of reversed-phase suspension polymerization, and is preferably 12.0 parts by mass or less, more preferably 6.0 parts by mass or less, even more preferably 4.0 parts by mass or less, even more preferably 1.2 parts by mass or less, and even more preferably 1.0 part by mass or less. and more preferably 0.5 parts by mass or less.
  • Preferred ranges include 0.1 to 12.0 parts by mass, 0.1 to 6.0 parts by mass, 0.1 to 4.0 parts by mass, 0.1 to 1.2 parts by mass, 0.1 to 1.0 parts by mass, 0.1 to 0.5 parts by mass, 0.2 to 12.0 parts by mass, 0.2 to 6.0 parts by mass, 0.2 to 4.0 parts by mass, 0.2 to 1.2 parts by mass, 0.2 to 1.0 parts by mass, 0.2 to 0.5 parts by mass, 0.3 to 12.0 parts by mass, 0.3 to 6.0 parts by mass, 0.3 to 4.0 parts by mass, 0.3 to 1.2 parts by mass, 0.3 to 1.0 parts by mass, and 0.3 to 0.5 parts by mass.
  • the amount of the (poly)glycerin fatty acid ester having the lowest precipitation temperature, among two or more types of (poly)glycerin fatty acid esters, used relative to 100 parts by mass of the water-soluble ethylenically unsaturated monomer used in the first-stage polymerization of the reversed-phase suspension polymerization is preferably 0.2 parts by mass or more, more preferably 0.4 parts by mass or more, and is preferably 12.0 parts by mass or less, more preferably 4.0 parts by mass or less, even more preferably 1.2 parts by mass or less, and even more preferably 0.8 parts by mass or less.
  • Preferred ranges include 0.2 to 12.0 parts by mass, 0.2 to 4.0 parts by mass, 0.2 to 1.2 parts by mass, 0.2 to 0.8 parts by mass, 0.4 to 12.0 parts by mass, 0.4 to 4.0 parts by mass, 0.4 to 1.2 parts by mass, and 0.4 to 0.8 parts by mass.
  • the amount of hexaglyceryl tristearate used is preferably 0.2 parts by mass or more, more preferably 0.5 parts by mass or more, and preferably 9.0 parts by mass or less, more preferably 4.0 parts by mass or less, more preferably 0.9 parts by mass or less, and even more preferably 0.7 parts by mass or less, per 100 parts by mass of the water-soluble ethylenically unsaturated monomer used in the first stage of the reverse suspension polymerization.
  • Preferred ranges include 0.2 to 9.0 parts by mass, 0.2 to 4.0 parts by mass, 0.2 to 0.9 parts by mass, 0.2 to 0.7 parts by mass, 0.5 to 9.0 parts by mass, 0.5 to 4.0 parts by mass, 0.5 to 0.9 parts by mass, and 0.5 to 0.7 parts by mass.
  • the composition contains hexaglyceryl tristearate and at least one of a (poly)glycerin fatty acid ester having a higher precipitation temperature than hexaglyceryl tristearate and a (poly)glycerin fatty acid ester having a lower precipitation temperature
  • one or more types of (poly)glycerin fatty acid esters having a higher precipitation temperature than hexaglyceryl tristearate may be used.
  • one or more types of (poly)glycerin fatty acid esters having a lower precipitation temperature than hexaglyceryl tristearate may be used.
  • the composition contains hexaglyceryl tristearate and at least one of a (poly)glycerin fatty acid ester having a higher precipitation temperature than hexaglyceryl tristearate and a (poly)glycerin fatty acid ester having a lower precipitation temperature, and the amount of the (poly)glycerin fatty acid ester having a higher precipitation temperature than hexaglyceryl tristearate and the (poly)glycerin fatty acid ester having a lower precipitation temperature are used in an amount of 1:1 of hexaglyceryl tristearate, respectively.
  • parts by mass it is preferably 0.0 part by mass or more, more preferably 0.3 part by mass or more, even more preferably 0.5 part by mass or more, and preferably 3 parts by mass or less, more preferably 2.0 parts by mass or less, even more preferably 1.3 parts by mass or less, and even more preferably 1.0 part by mass or less.
  • Preferred ranges include 0.0 to 3.0 parts by mass, 0.0 to 2.0 parts by mass, 0.0 to 1.3 parts by mass, 0.3 to 3.0 parts by mass, 0.3 to 2.0 parts by mass, 0.3 to 1.3 parts by mass, 0.5 to 3.0 parts by mass, 0.5 to 2.0 parts by mass, and 0.5 to 1.3 parts by mass.
  • the composition includes hexaglyceryl tristearate, (poly)glycerin fatty acid esters with a higher precipitation temperature than hexaglyceryl tristearate, and (poly)glycerin fatty acid esters with a lower precipitation temperature
  • one or more types of (poly)glycerin fatty acid esters with a higher precipitation temperature than hexaglyceryl tristearate may be used.
  • one or more types of (poly)glycerin fatty acid esters with a lower precipitation temperature than hexaglyceryl tristearate may be used.
  • the composition contains hexaglyceryl tristearate, (poly)glycerin fatty acid esters with a higher precipitation temperature than hexaglyceryl tristearate, and (poly)glycerin fatty acid esters with a lower precipitation temperature, and the amount of the (poly)glycerin fatty acid esters with a higher precipitation temperature than hexaglyceryl tristearate and (poly)glycerin fatty acid esters with a lower precipitation temperature is, respectively, 1 mass of hexaglyceryl tristearate.
  • parts it is preferably greater than 0.0 part by mass, more preferably at least 0.3 part by mass, even more preferably at least 0.5 part by mass, and preferably not greater than 2.0 parts by mass, more preferably not greater than 1.3 parts by mass, and even more preferably not greater than 1.0 part by mass.
  • Preferred ranges include greater than 0.0 part by mass and not greater than 2.0 parts by mass, greater than 0.0 part by mass and not greater than 1.3 parts by mass, greater than 0.0 part by mass and not greater than 2.0 parts by mass, 0.3 to 2.0 parts by mass, 0.3 to 1.3 parts by mass, 0.3 to 1.0 parts by mass, 0.5 to 2.0 parts by mass, 0.5 to 1.3 parts by mass, and 0.5 to 1.0 part by mass.
  • the amount of the (poly)glycerin fatty acid ester with a higher precipitation temperature than hexaglyceryl tristearate used is preferably 0.0 mass parts per 1 mass part of hexaglyceryl tristearate.
  • Preferred ranges include more than 0.0 part by mass and not more than 2.0 parts by mass, more than 0.0 part by mass and not more than 1.0 part by mass, more than 0.0 part by mass and not more than 0.8 parts by mass, 0.2 to 2.0 parts by mass, 0.2 to 1.0 parts by mass, 0.2 to 0.8 parts by mass, 0.4 to 2.0 parts by mass, 0.4 to 1.0 parts by mass, and 0.4 to 0.8 parts by mass.
  • the amount of the (poly)glycerin fatty acid ester having a lower precipitation temperature than hexaglyceryl tristearate used is preferably 0.
  • Preferred ranges include greater than 0.0 parts by mass and 2.0 parts by mass or less, greater than 0 parts by mass and 1.5 parts by mass or less, greater than 0 parts by mass and 0.9 parts by mass or less, 0.2 to 2.0 parts by mass, 0.2 to 1.5 parts by mass, 0.2 to 0.9 parts by mass, 0.5 to 2.0 parts by mass, 0.5 to 1.5 parts by mass, and 0.5 to 0.9 parts by mass.
  • two or more (poly)glycerin fatty acid esters are used, each having a different precipitation temperature when dissolved in a 0.46% by mass heptane solution, two or more types may be used, but preferably two to five types, more preferably two to four types, even more preferably two to three types, and particularly preferably three types.
  • the total proportion of the two or more types of (poly)glycerin fatty acid esters in all dispersion stabilizers is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 80% by mass or more, and may be 90% by mass or more, 95% by mass or more, 99% by mass or more, etc.
  • the dispersion stabilizer used in the process of aggregating polymer particles in the presence of a dispersion stabilizer can be a surfactant or a polymeric dispersant, and (poly)glycerin fatty acid esters are surfactants.
  • Examples of dispersion stabilizers other than (poly)glycerin fatty acid esters include the following surfactants and polymeric dispersants:
  • a dispersion stabilizer 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.
  • Surfactants that can be used include, for example, sucrose fatty acid esters, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene glycerin fatty acid esters, sorbitol fatty acid esters, polyoxyethylene sorbitol fatty acid esters, polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene castor oil, polyoxyethylene hydrogenated castor oil, 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, phosphate esters of polyoxyethylene alkyl ethers, and phosphate esters of polyoxyethylene alkyl allyl ethers.
  • polymeric 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.
  • 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, ethylhydroxyethyl cellulose, etc.
  • These polymeric dispersants may be used alone or in combination of two or more.
  • reverse-phase suspension polymerization can be carried out by adding a thickener to an aqueous solution containing a water-soluble ethylenically unsaturated monomer.
  • a thickener By adding a thickener in this way to adjust the viscosity of the aqueous solution, it is possible to control the median particle size obtained in reverse-phase suspension polymerization.
  • thickeners examples 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, and polyethylene oxide. Furthermore, if the stirring speed during polymerization is the same, the higher the viscosity of the aqueous solution of the water-soluble ethylenically unsaturated monomer, the larger the primary and/or secondary particles that are obtained tend to be.
  • aqueous monomer solution containing a water-soluble ethylenically unsaturated monomer is dispersed in a hydrocarbon dispersion medium in the presence of two or more types of (poly)glycerin fatty acid esters as dispersion stabilizers (and, if necessary, other dispersion stabilizers).
  • the dispersion stabilizer 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.
  • Such reverse phase suspension polymerization can be carried out in two or more stages. From the standpoint of increasing productivity, it is preferable to carry it out in two to three stages.
  • reversed-phase suspension polymerization carried out in two or more stages, after the first stage of reversed-phase suspension polymerization, a water-soluble ethylenically unsaturated monomer is added to and mixed with the reaction mixture obtained in the first polymerization reaction, and the second and subsequent stages of reversed-phase suspension polymerization are carried out in the same manner as the first stage.
  • reversed-phase suspension polymerization in each stage from the second stage onwards it is preferable to carry out 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.
  • an internal crosslinking agent may also be added to the water-soluble ethylenically unsaturated monomer, if necessary.
  • the reaction temperature for the polymerization reaction is preferably 20 to 110°C, and more preferably 40 to 90°C, from the perspective of improving economic efficiency by rapidly progressing the polymerization and shortening the polymerization time, as well as easily removing the heat of polymerization to ensure a smooth reaction.
  • the aggregation step may be carried out between the first-stage reverse phase suspension polymerization and the second-stage reverse phase suspension polymerization, or may be carried out after the second-stage or subsequent reverse phase suspension polymerizations. From the perspective of more optimally achieving the effects of the present invention, it is preferable that the polymer particle aggregation step be carried out between the first-stage reverse phase suspension polymerization and the second-stage reverse phase suspension polymerization. Furthermore, during the polymer particle aggregation step, the polymerization reaction of the water-soluble ethylenically unsaturated monomer may or may not be in progress.
  • the temperature of the slurry liquid is adjusted to gradually precipitate two or more types of (poly)glycerin fatty acid esters with different precipitation temperatures, thereby controlling the degree of aggregation of the polymer particles. For example, before adding the aqueous solution of water-soluble ethylenically unsaturated monomer in the second-stage reversed-phase suspension polymerization, the temperature of the slurry liquid is lowered to precipitate at least one of the two or more types of (poly)glycerin fatty acid esters.
  • the droplets of the water-soluble ethylenically unsaturated monomer added subsequently are not stabilized in the hydrocarbon dispersion medium and are absorbed by the polymer particles (gel-like primary particles), promoting aggregation between the polymer particles.
  • the temperature of the slurry liquid is increased, the (poly)glycerin fatty acid ester dissolves, and the droplets of the water-soluble ethylenically unsaturated monomer are stabilized in the hydrocarbon dispersion medium, suppressing aggregation between the polymer particles.
  • water-absorbent resin particles with a narrow particle size distribution can be suitably produced.
  • the temperature range for the aggregation step is not particularly limited as long as it is within a temperature range that allows for controlled aggregation of polymer particles. Examples include a range of 5 to 50°C, preferably 10 to 40°C, and more preferably 15 to 30°C.
  • the process may include a dehydration treatment in which water, hydrocarbon dispersion medium, etc. are removed by distillation by applying energy such as heat from the outside.
  • a dehydration treatment in which water, hydrocarbon dispersion medium, etc. are removed by distillation by applying energy such as heat from the outside.
  • 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.
  • dehydration by distillation may be carried out under normal pressure.
  • the dehydration temperature is preferably 70 to 250°C, more preferably 80 to 180°C, even more preferably 80 to 140°C, and even more preferably 90 to 130°C.
  • the surface cross-linking step is a step of subjecting the polymer particles obtained in the polymerization step to surface cross-linking.
  • the polymer particles are cross-linked polymer particles (hydrogel-like material)
  • it is a step of adding a surface cross-linking agent to a hydrogel-like material having an internal cross-linked structure obtained by polymerizing a water-soluble ethylenically unsaturated monomer to perform cross-linking (surface cross-linking reaction).
  • This surface cross-linking reaction is preferably carried out in the presence of a surface cross-linking agent after the polymerization of the water-soluble ethylenically unsaturated monomer.
  • the cross-linking density near the surface of the water-absorbent resin particles can be increased, and water-absorbent resin particles with improved performance such as water absorption capacity under load can be obtained.
  • Surface cross-linking agents include compounds with two or more reactive functional groups.
  • Examples include polyols such as ethylene glycol, propylene glycol, 1,4-butanediol, diethylene glycol, triethylene glycol, trimethylolpropane, glycerin, polyoxyethylene glycol, polyoxypropylene glycol, and polyglycerin; polyglycidyl compounds such as (poly)ethylene glycol diglycidyl ether, (poly)glycerin diglycidyl ether, (poly)glycerin triglycidyl ether, trimethylolpropane triglycidyl ether, (poly)propylene glycol polyglycidyl ether, and (poly)glycerol polyglycidyl ether; haloepoxy compounds such as epichlorohydrin, epibromohydrin, and ⁇ -methylepichlorohydrin; isocyanate compounds such as 2,4-tolylene di
  • polyglycidyl compounds such as (poly)ethylene glycol diglycidyl ether, (poly)glycerin diglycidyl ether, (poly)glycerin triglycidyl ether, trimethylolpropane triglycidyl ether, (poly)propylene glycol polyglycidyl ether, and (poly)glycerol polyglycidyl ether are preferred.
  • These surface cross-linking agents may be used alone or in combination of two or more.
  • the amount of surface cross-linking 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.
  • the surface cross-linking agent may be added as is or as an aqueous solution, but if necessary, it may be added as a solution using a hydrophilic organic solvent as the solvent.
  • 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 types, or as a mixed solvent with water.
  • the timing of adding the surface cross-linking 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.
  • the amount of water refers to the total amount of water contained in the reaction system and water used as needed when adding the surface cross-linking agent.
  • the water content of the polymer particles when the surface cross-linking agent is added is preferably 1% by mass or more, more preferably 10% by mass or more, and even more preferably 20% by mass or more, and is preferably 60% by mass or less, more preferably 40% by mass or less, and even more preferably 35% by mass or less.
  • Preferred ranges include 1 to 60% by mass, 1 to 40% by mass, 1 to 35% by mass, 10 to 60% by mass, 10 to 40% by mass, 10 to 35% by mass, 20 to 60% by mass, 20 to 40% by mass, and 20 to 35% by mass.
  • the reaction temperature for the surface cross-linking 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. Furthermore, the reaction time for the surface cross-linking reaction is preferably 1 to 300 minutes, and more preferably 5 to 200 minutes.
  • a drying treatment may be included in which water, a hydrocarbon dispersion medium, etc. are removed by distillation by applying energy such as heat from the outside.
  • the polymer particles after surface cross-linking are dried and the water and the hydrocarbon dispersion medium are distilled off, thereby obtaining water-absorbent resin particles.
  • the drying process by distillation may be carried out under normal pressure or under reduced pressure. Furthermore, from the viewpoint of increasing drying efficiency, it may also be carried out under a stream of gas such as nitrogen.
  • 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.
  • the drying temperature is preferably 40 to 160°C, and more preferably 50 to 110°C.
  • a surface cross-linking step using a surface cross-linking agent is carried out after the polymerization of monomers by reverse phase suspension polymerization
  • the drying step by distillation described above is carried out after the surface cross-linking step is completed.
  • the surface cross-linking step and the drying step may be carried out simultaneously.
  • the water-absorbent resin particles of the present invention may contain additives according to the purpose.
  • additives include inorganic powders, surfactants, oxidizing agents, reducing agents, metal chelating agents, radical chain inhibitors, antioxidants, and antibacterial agents.
  • the fluidity of the water-absorbent resin particles can be further improved by adding 0.05 to 5 parts by mass of amorphous silica as inorganic powder per 100 parts by mass of the water-absorbent resin particles.
  • the additives are preferably hydrophilic or water-soluble.
  • Water-absorbent resin particles By employing the method for producing water-absorbent resin particles of the present invention described above, it is possible to suitably produce water-absorbent resin particles having a narrow particle size distribution. More specifically, by employing the method for producing water-absorbent resin particles of the present invention, it is possible to suitably produce water-absorbent resin particles having, for example, a uniformity of particle size distribution of 2.5 or less and containing a (poly)glycerin fatty acid ester in the vicinity of the surface.
  • the uniformity of the particle size distribution of the water-absorbent resin particles of the present invention may be 2.5 or less, but is preferably 2.3 or less, more preferably 1.8 or less, and even more preferably 1.6 or less, with the lower limit being, for example, 1.
  • the uniformity of the particle size distribution of water-absorbent resin particles is measured using the measurement method described in the Examples.
  • the water-absorbent resin particles of the present invention contain a (poly)glycerin fatty acid ester near the surface.
  • a (poly)glycerin fatty acid ester is used in the method for producing water-absorbent resin particles of the present invention. Therefore, a (poly)glycerin fatty acid ester is contained near the surface of the water-absorbent resin particles.
  • Specific examples of the (poly)glycerin fatty acid ester are the same as those exemplified in the method for producing water-absorbent resin particles of the present invention. It is preferable that two or more types of (poly)glycerin fatty acid esters are contained near the surface of the water-absorbent resin particles, and it is preferable that hexaglyceryl tristearate is contained.
  • the amount of (poly)glycerin fatty acid ester contained near the surface of the water-absorbent resin particles of the present invention is preferably 1 part by mass or less, more preferably 0.65 parts by mass or less, and even more preferably 0.55 parts by mass or less, per 100 parts by mass of the water-absorbent resin particles.
  • the lower limit is preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, and even more preferably 0.3 parts by mass or more.
  • the water-absorbent resin particles of the present invention preferably have a yellowness index of 20 or less, more preferably 15 or less, and even more preferably 12 or less, after being heated at 200°C for 2 hours.
  • the lower limit of the yellowness index is, for example, 0.
  • the initial yellowness value of the water-absorbent resin particles of the present invention is preferably 15 or less, more preferably 12 or less, and even more preferably 10 or less.
  • the lower limit of the yellowness value is, for example, 0.
  • the yellowness of the water-absorbent resin particles was measured before and after heating at 200°C for 2 hours using the measurement method described in the Examples.
  • the water-absorbent resin particles of the present invention are preferably composed of a crosslinked polymer of a water-soluble ethylenically unsaturated monomer, i.e., a crosslinked polymer having structural units derived from a water-soluble ethylenically unsaturated monomer.
  • the water-absorbent resin particles of the present invention are in the form of aggregates (secondary particles) of fine particles (primary particles). Examples of the shape of the primary particles include roughly spherical, irregularly crushed, and plate-like.
  • the water-absorbent resin particles of the present invention, which are secondary particles, may have a variety of shapes. Examples of the shape of the water-absorbent resin particles include granular, roughly spherical, irregularly crushed, plate-like, fibrous, flake-like, and shapes formed by agglomeration of these resins.
  • the water-absorbent resin particles are preferably granular, roughly spherical, irregularly crushed, fibrous, or shapes formed by agglomeration of these resins.
  • the median particle diameter of the water-absorbent resin particles is preferably 100 ⁇ m or more, 150 ⁇ m or more, 200 ⁇ m or more, 250 ⁇ m or more, 280 ⁇ m or more, 300 ⁇ m or more, or 320 ⁇ m or more. From the same perspective, the median particle diameter is preferably 700 ⁇ m or less, 600 ⁇ m or less, 550 ⁇ m or less, 500 ⁇ m or less, 450 ⁇ m or less, or 400 ⁇ m or less. In other words, the median particle diameter is preferably 150 to 700 ⁇ m, preferably 200 to 600 ⁇ m, more preferably 250 to 500 ⁇ m, even more preferably 250 to 450 ⁇ m, and even more preferably 250 to 400 ⁇ m.
  • the median particle diameter of the water-absorbent resin particles can be measured using a JIS standard sieve, and specifically, is the value measured using the method described in the Examples.
  • the saline absorption rate of the water-absorbent resin particles is preferably 20 seconds or more, more preferably 25 seconds or more, and even more preferably 30 seconds or more, and is preferably 65 seconds or less, more preferably 60 seconds or less, and even more preferably 55 seconds or less, with more preferred ranges including 20 to 65 seconds and 25 to 60 seconds.
  • the saline water retention capacity of the water-absorbent resin particles of the present invention is preferably 20 g/g or more, more preferably 30 g/g or more, and is preferably 80 g/g or less, more preferably 60 g/g or less, even more preferably 55 g/g or less, and even more preferably 53 g/g or less.
  • Preferred ranges include 20 to 80 g/g, 20 to 60 g/g, 20 to 55 g/g, 20 to 53 g/g, 30 to 80 g/g, 30 to 60 g/g, 30 to 55 g/g, and 30 to 53 g/g.
  • the water-absorbing resin particles of the present invention constitute an absorbent material used in hygiene materials such as sanitary products and disposable diapers, and are suitably used in absorbent articles containing the absorbent material.
  • the absorbent of the present invention contains the water-absorbent resin particles of the present invention.
  • the absorbent may further contain hydrophilic fibers.
  • Examples of absorbent configurations include a sheet-like structure in which water-absorbent resin particles are fixed on a nonwoven fabric or between multiple nonwoven fabrics, a mixed dispersion obtained by mixing water-absorbent resin particles and hydrophilic fibers to form a uniform composition, a sandwich structure in which water-absorbent resin particles are sandwiched between layers of hydrophilic fibers, and a structure in which water-absorbent resin particles 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.
  • the basis weight of the water-absorbent resin particles in the absorbent body of the present invention is 50 g/ m2 or more and 400 g/ m2 or less.
  • the basis weight is preferably 100 g/ m2 or more, more preferably 120 g/ m2 or more, even more preferably 140 g/ m2 or more, and is preferably 300 g/ m2 or less, more preferably 250 g/m2 or less , even more preferably 200 g/ m2 or less.
  • Hydrophilic fibers include at least one selected from the group consisting of finely ground wood pulp, cotton, cotton linters, rayon, cellulose acetate, polyamide, polyester, and polyolefin.
  • Examples 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 from synthetic resins such as hydrophilically treated polyamide, polyester, and polyolefin.
  • the average fiber length of the hydrophilic fibers is typically 0.1 to 10 mm, or may be 0.5 to 5 mm.
  • the basis weight of the hydrophilic fibers in the absorbent body of the present invention is 50 g/ m2 or more and 800 g/ m2 or less.
  • the basis weight is preferably 100 g/ m2 or more, more preferably 120 g/ m2 or more, even more preferably 140 g/m2 or more , and is preferably 700 g/m2 or less , more preferably 600 g/m2 or less , even more preferably 500 g/ m2 or less.
  • the content of water-absorbent resin particles 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.
  • the absorbent article of the present invention can be produced by holding an absorbent body using the water-absorbent resin particles 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 placed on the side that comes into contact with the body, and the liquid-impermeable sheet is placed on the opposite side that comes into contact with the body.
  • Liquid-permeable sheets include nonwoven fabrics such as air-through, spunbond, chemical-bond, and needle-punched types made from fibers such as polyethylene, polypropylene, and polyester, as well as porous synthetic resin sheets.
  • Liquid-impermeable sheets include synthetic resin films made from resins such as polyethylene, polypropylene, and polyvinyl chloride.
  • the liquid-permeable sheet is preferably at least one type selected from the group consisting of thermal-bonded nonwoven fabrics, air-through nonwoven fabrics, spunbonded nonwoven fabrics, and spunbonded/meltblown/spunbonded nonwoven fabrics.
  • the basis weight of the liquid-permeable sheet is preferably 5 g/m or more and 100 g/m or less , and more preferably 10 g/m or more and 60 g/m or less .
  • the liquid-permeable sheet may be embossed or perforated on its surface to improve liquid diffusibility. The embossing or perforation can be carried out by a known method.
  • 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 (e.g., 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 may be, for example, a sheet made of a synthetic resin with a basis weight of 10 to 50 g/m 2 .
  • the absorbent article preferably comprises a laminate having an absorbent body containing water-absorbent resin particles and core wraps sandwiching the absorbent body from above and below, a liquid-permeable sheet disposed on the upper surface of the laminate, and a liquid-impermeable sheet disposed on the surface of the laminate opposite the liquid-permeable sheet side.
  • the water-absorbent resin particles obtained in the following examples and comparative examples were evaluated by the following various tests. Unless otherwise specified, measurements were carried out in an environment of a temperature of 25 ⁇ 2°C and a humidity of 50 ⁇ 10%.
  • Example 1 A round-bottomed, cylindrical, separable flask with an inner diameter of 11 cm and a volume of 2 L was prepared, equipped with a reflux condenser, a dropping funnel, a nitrogen gas inlet tube, and a stirrer (a stirring blade with two stages of four inclined paddle blades, each 5 cm in blade diameter).
  • n-heptane hydrocarbon dispersion medium
  • 0.737 g of tetraglyceryl tristearate 0.737 g
  • 0.737 g of hexaglyceryl tristearate 0.737 g
  • the above-mentioned first-stage aqueous liquid was added to the above-mentioned separable flask, and the atmosphere inside the separable flask was thoroughly replaced with nitrogen while stirring at a rotation speed of 400 rpm.
  • the separable flask was then immersed in a 70°C water bath to raise the temperature of the reaction liquid, and first-stage polymerization was carried out for 60 minutes, yielding a first-stage slurry liquid.
  • the separable flask system While stirring the first-stage slurry at 1000 rpm, the separable flask system was cooled to 20°C, and then the entire amount of the second-stage aqueous liquid was added to the first-stage slurry to carry out the aggregation process. After purging the system with nitrogen for 30 minutes, the separable flask was again immersed in a 70°C water bath to raise the temperature, and a polymerization reaction was carried out for 60 minutes to obtain the second-stage slurry.
  • the second-stage slurry liquid was heated in an oil bath at 125°C, and 248 g of water was extracted from the system by azeotropic distillation of n-heptane and water while refluxing n-heptane. The n-heptane was then evaporated and dried to obtain a dried product. 203.8 g of water-absorbent resin particles in the form of agglomerates of approximately spherical particles were obtained by passing this dried product through a sieve with 850 ⁇ m openings.
  • Example 2 The same operation as in Example 1 was performed except that decaglyceryl pentastearate (dispersion stabilizer, manufactured by Nippon Surfactant Industry Co., Ltd., NIKKOL Decaglyn 5-SV) was used instead of tetraglyceryl tristearate in Example 1, to obtain 200.3 g of water absorbent resin particles.
  • decaglyceryl pentastearate dispenser stabilizer, manufactured by Nippon Surfactant Industry Co., Ltd., NIKKOL Decaglyn 5-SV
  • tetraglyceryl tristearate was used instead of tetraglyceryl tristearate in Example 1, to obtain 200.3 g of water absorbent resin particles.
  • Example 3 The same operation as in Example 1 was carried out except that 0.737 g of tetraglyceryl tristearate and 0.737 g of hexaglyceryl tristearate in Example 1 were used, and 194.5 g of water absorbent resin particles were obtained.
  • Example 4 [0123] The same operation as in Example 1 was carried out except that 0.276 g of tetraglyceryl tristearate, 0.460 g of hexaglyceryl tristearate, and 0.368 g of decaglyceryl pentastearate were used instead of 0.737 g of tetraglyceryl tristearate and 0.737 g of hexaglyceryl tristearate in Example 1, thereby obtaining 215.5 g of water absorbent resin particles.
  • Example 5 A round-bottomed cylindrical separable flask with an inner diameter of 11 cm and a volume of 2 L was prepared, equipped with a reflux condenser, a dropping funnel, a nitrogen gas inlet tube, and a stirrer (a stirring blade with two stages of four inclined paddle blades with a blade diameter of 5 cm). 293 g of n-heptane (hydrocarbon dispersion medium) was placed in this separable flask, and 0.276 g of maleic anhydride-modified ethylene-propylene copolymer (polymer dispersant, Mitsui Chemicals, Inc., Hiwax 1105A) was added. The mixture was dissolved by heating to 80 ° C with stirring, and then cooled to 55 ° C.
  • n-heptane hydrocarbon dispersion medium
  • the above-mentioned first-stage aqueous liquid was added to the above-mentioned separable flask and stirred for 10 minutes, after which 0.276 g of tetraglyceryl tristearate, 0.460 g of hexaglyceryl tristearate, and 0.368 g of decaglyceryl pentastearate were heated and dissolved in 6.62 g of n-heptane to obtain a dispersion stabilizer solution. 7.724 g of the resulting dispersion stabilizer solution was added to the separable flask, and the atmosphere inside the separable flask was thoroughly purged with nitrogen while stirring at 400 rpm. The separable flask was then immersed in a 70°C water bath to raise the temperature of the reaction liquid, and first-stage polymerization was carried out for 60 minutes to obtain a first-stage slurry.
  • the separable flask system While stirring the first-stage slurry at 1000 rpm, the separable flask system was cooled to 20°C, and then the entire amount of the second-stage aqueous liquid was added to the first-stage slurry to carry out an aggregation step. After the system was purged with nitrogen for 30 minutes, the flask was again immersed in a 70°C water bath to raise the temperature, and a polymerization reaction was carried out for 60 minutes to obtain a second-stage slurry.
  • the second-stage slurry liquid was heated in an oil bath at 125°C, and 248 g of water was extracted from the system by azeotropic distillation of n-heptane and water while refluxing n-heptane. The n-heptane was then evaporated and dried to obtain a dried product. 205.4 g of water-absorbent resin particles in the form of agglomerates of approximately spherical particles were obtained by passing this dried product through a sieve with 850 ⁇ m openings.
  • Example 1 The same procedure as in Example 1 was carried out except that 1.289 g of tetraglyceryl tristearate was used instead of 0.737 g of tetraglyceryl tristearate and 0.737 g of hexaglyceryl tristearate in Example 1, to obtain 103.1 g of water-absorbent resin particles.
  • a water-absorbent resin composition was prepared by mixing 100 g of water-absorbent resin particles with 0.5 g of amorphous silica (Toxil NP-S, manufactured by Oriental Silicas Corporation) as a lubricant. Seven types of JIS standard sieves (mesh openings: 600 ⁇ m, 500 ⁇ m, 425 ⁇ m, 300 ⁇ m, 250 ⁇ m, 150 ⁇ m, and 75 ⁇ m) were used in this measurement.
  • the water-absorbent resin composition was placed on top of a sieve in which the selected JIS standard sieve and a tray were combined in order, and the mixture was shaken for 20 minutes using a Rotap shaker. Next, 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 values were integrated in order from the smallest particle diameter, and the relationship between the sieve opening and the integrated value of the mass percentage remaining on the sieve was plotted on logarithmic probability paper. The plots on the probability paper were connected with a straight line to determine the particle size corresponding to a cumulative mass percentage of 50% by mass as the median particle size. The results are shown in Table 3.
  • the precipitation temperature of the dispersion stabilizer was determined by cooling a mixed solution in which the dispersion stabilizer was dissolved in a solvent by heating, and measuring the turbidity of the mixed solution at each temperature. That is, 100 g of n-heptane (hydrocarbon dispersion medium) and 0.46 g of dispersion stabilizer were added to an eggplant-shaped flask. This solution was heated to 80 ° C while stirring with a stirrer tip, thereby obtaining a mixed solution in which the dispersion stabilizer was dissolved.
  • the mixed solution was then cooled, and the turbidity was measured every 1 ° C using an integrating sphere turbidimeter SEP-PT-706D (manufactured by Nitto Seiko Analytech Co., Ltd., optical path length 10 mm) using a calibration curve created with a turbidity standard solution (kaolin 1000 ° C).
  • the precipitation temperature of the dispersion stabilizer was compared with the turbidity at a temperature 1 ° C higher, and the temperature at which the turbidity rose by 10 ppm or more was taken as the precipitation temperature. The results are shown in Table 1.
  • a test for the yellowness of water-absorbent resin particles after heating was performed as follows. Specifically, 2.0 g of water-absorbent resin particles were uniformly placed in a glass petri dish with an inner diameter of 3 cm and a depth of 1 cm. Nitrogen was passed through the dish so that the flow rate at the outlet was 400 mL/min. A vacuum dryer (AVO-310N, manufactured by AS ONE Corporation) preheated to 200 ⁇ 5°C was prepared, and a 3 cm thick glass wool insulation material was laid on the inner bottom. A stainless steel tray was placed on top of the insulation material inside the vacuum dryer, and the glass petri dish containing the water-absorbent resin particles and a surface thermometer were further placed on the stainless steel tray.
  • a vacuum dryer AVO-310N, manufactured by AS ONE Corporation
  • the amount of dispersion stabilizer added is based on 100 parts by mass of acrylic acid, the water-soluble ethylenically unsaturated monomer used in the first-stage polymerization.

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  • Polymerisation Methods In General (AREA)

Abstract

L'invention fournit un procédé de fabrication de particules de résine absorbante qui inclut une étape au cours de laquelle un monomère hydrosoluble éthyléniquement insaturé, est soumis à une polymérisation en suspension en phase inversée dans un milieu de dispersion d'hydrocarbure, et des particules de polymère sont obtenues. En outre, le procédé de fabrication de l'invention permet d'obtenir des particules de résine absorbante de distribution granulométrique étroite.　Ainsi, l'invention concerne un procédé de fabrication de particules de résine absorbante qui inclut une étape au cours de laquelle un monomère hydrosoluble éthyléniquement insaturé, est soumis à une polymérisation en suspension en phase inversée dans un milieu de dispersion d'hydrocarbure, et des particules de polymère sont obtenues. Plus précisément, le procédé de fabrication de particules de résine absorbante de l'invention inclut une étape au cours de laquelle la polymérisation en suspension en phase inversée est effectuée en au moins deux temps, et lesdites particules de polymère sont agglomérées en présence d'un agent de stabilisation de dispersion. Au moins deux sortes d'ester d'acide gras de (poly)glycérine présentant une température de précipitation différente dans le cas d'une solution d'heptane à ０,４６% en masse, sont mises en œuvre en tant qu'agent de stabilisation de dispersion.
PCT/JP2025/001230 2024-01-29 2025-01-16 Particules de résine absorbante, et procédé de fabrication de celles-ci Pending WO2025164340A1 (fr)

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Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2007123188A1 (fr) * 2006-04-24 2007-11-01 Sumitomo Seika Chemicals Co., Ltd. Particule de resine hydroabsorbable et son procede de production
WO2007126002A1 (fr) * 2006-04-27 2007-11-08 Sumitomo Seika Chemicals Co., Ltd. Procédé de production de résine hydro-absorbable
WO2009025235A1 (fr) * 2007-08-23 2009-02-26 Sumitomo Seika Chemicals Co., Ltd. Résine absorbant l'eau appropriée pour être utilisée dans des produits sanitaires
WO2012066888A1 (fr) * 2010-11-15 2012-05-24 住友精化株式会社 Procédé de production d'une résine absorbant l'eau
JP2013100543A (ja) * 2013-02-13 2013-05-23 Sumitomo Seika Chem Co Ltd 吸水性樹脂粒子の製造方法
WO2015016075A1 (fr) * 2013-07-29 2015-02-05 住友精化株式会社 Procédé de production de particule de résine absorbant l'eau
CN114149529A (zh) * 2021-12-31 2022-03-08 南京紫鸿生物科技有限公司 部分中和的聚丙烯酸钠及其制备方法和应用

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2007123188A1 (fr) * 2006-04-24 2007-11-01 Sumitomo Seika Chemicals Co., Ltd. Particule de resine hydroabsorbable et son procede de production
WO2007126002A1 (fr) * 2006-04-27 2007-11-08 Sumitomo Seika Chemicals Co., Ltd. Procédé de production de résine hydro-absorbable
WO2009025235A1 (fr) * 2007-08-23 2009-02-26 Sumitomo Seika Chemicals Co., Ltd. Résine absorbant l'eau appropriée pour être utilisée dans des produits sanitaires
WO2012066888A1 (fr) * 2010-11-15 2012-05-24 住友精化株式会社 Procédé de production d'une résine absorbant l'eau
JP2013100543A (ja) * 2013-02-13 2013-05-23 Sumitomo Seika Chem Co Ltd 吸水性樹脂粒子の製造方法
WO2015016075A1 (fr) * 2013-07-29 2015-02-05 住友精化株式会社 Procédé de production de particule de résine absorbant l'eau
CN114149529A (zh) * 2021-12-31 2022-03-08 南京紫鸿生物科技有限公司 部分中和的聚丙烯酸钠及其制备方法和应用

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