WO2024071258A1 - 吸水性樹脂粒子の製造方法 - Google Patents

吸水性樹脂粒子の製造方法 Download PDF

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Publication number
WO2024071258A1
WO2024071258A1 PCT/JP2023/035291 JP2023035291W WO2024071258A1 WO 2024071258 A1 WO2024071258 A1 WO 2024071258A1 JP 2023035291 W JP2023035291 W JP 2023035291W WO 2024071258 A1 WO2024071258 A1 WO 2024071258A1
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Prior art keywords
water
mass
absorbent resin
resin particles
added
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PCT/JP2023/035291
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English (en)
French (fr)
Japanese (ja)
Inventor
由伎 伍賀
直矢 淡路
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Sumitomo Seika Chemicals Co Ltd
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Sumitomo Seika Chemicals Co Ltd
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Priority to KR1020257003392A priority Critical patent/KR20250078427A/ko
Priority to JP2024550426A priority patent/JPWO2024071258A1/ja
Priority to US19/103,671 priority patent/US20260061393A1/en
Priority to CN202380058155.8A priority patent/CN119677785A/zh
Priority to EP23872480.1A priority patent/EP4600273A1/en
Publication of WO2024071258A1 publication Critical patent/WO2024071258A1/ja
Anticipated expiration legal-status Critical
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/22—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising organic material
    • B01J20/26—Synthetic macromolecular compounds
    • B01J20/265—Synthetic macromolecular compounds modified or post-treated polymers
    • 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
    • C08F2/04—Polymerisation in solution
    • C08F2/10—Aqueous solvent
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J3/00—Processes of treating or compounding macromolecular substances
    • C08J3/24—Crosslinking, e.g. vulcanising, of macromolecules
    • C08J3/245—Differential crosslinking of one polymer with one crosslinking type, e.g. surface crosslinking
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
    • A61F13/00—Bandages or dressings; Absorbent pads
    • A61F13/15—Absorbent pads, e.g. sanitary towels, swabs or tampons for external or internal application to the body; Supporting or fastening means therefor; Tampon applicators
    • A61F13/53—Absorbent pads, e.g. sanitary towels, swabs or tampons for external or internal application to the body; Supporting or fastening means therefor; Tampon applicators characterised by the absorbing medium
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61L—METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES
    • A61L15/00—Chemical aspects of, or use of materials for, bandages, dressings or absorbent pads
    • A61L15/16—Bandages, dressings or absorbent pads for physiological fluids such as urine or blood, e.g. sanitary towels, tampons
    • A61L15/42—Use of materials characterised by their function or physical properties
    • A61L15/60—Liquid-swellable gel-forming materials, e.g. super-absorbents
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/28—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties
    • B01J20/28014—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties characterised by their form
    • B01J20/28016—Particle form
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/28—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties
    • B01J20/28014—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties characterised by their form
    • B01J20/28047—Gels
    • 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
    • C08F120/00—Homopolymers 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
    • C08F120/02—Monocarboxylic acids having less than ten carbon atoms; Derivatives thereof
    • C08F120/04—Acids; Metal salts or ammonium salts thereof
    • C08F120/06—Acrylic acid; Methacrylic acid; Metal salts or ammonium salts thereof
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F20/00—Homopolymers and copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical or a salt, anhydride, ester, amide, imide or nitrile thereof
    • C08F20/02—Monocarboxylic acids having less than ten carbon atoms, Derivatives thereof
    • C08F20/04—Acids, Metal salts or ammonium salts thereof
    • C08F20/06—Acrylic acid; Methacrylic acid; Metal salts or ammonium salts thereof
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J3/00—Processes of treating or compounding macromolecular substances
    • C08J3/02—Making solutions, dispersions, lattices or gels by other methods than by solution, emulsion or suspension polymerisation techniques
    • C08J3/03—Making solutions, dispersions, lattices or gels by other methods than by solution, emulsion or suspension polymerisation techniques in aqueous media
    • C08J3/075—Macromolecular gels
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J3/00—Processes of treating or compounding macromolecular substances
    • C08J3/12—Powdering or granulating
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K3/00—Use of inorganic substances as compounding ingredients
    • C08K3/30—Sulfur-, selenium- or tellurium-containing compounds
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K5/00—Use of organic ingredients
    • C08K5/0008—Organic ingredients according to more than one of the "one dot" groups of C08K5/01 - C08K5/59
    • C08K5/005—Stabilisers against oxidation, heat, light, ozone
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L101/00—Compositions of unspecified macromolecular compounds
    • C08L101/12—Compositions of unspecified macromolecular compounds characterised by physical features, e.g. anisotropy, viscosity or electrical conductivity
    • C08L101/14—Compositions of unspecified macromolecular compounds characterised by physical features, e.g. anisotropy, viscosity or electrical conductivity the macromolecular compounds being water soluble or water swellable, e.g. aqueous gels
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
    • A61F13/00—Bandages or dressings; Absorbent pads
    • A61F13/15—Absorbent pads, e.g. sanitary towels, swabs or tampons for external or internal application to the body; Supporting or fastening means therefor; Tampon applicators
    • A61F13/53—Absorbent pads, e.g. sanitary towels, swabs or tampons for external or internal application to the body; Supporting or fastening means therefor; Tampon applicators characterised by the absorbing medium
    • A61F2013/530481—Absorbent pads, e.g. sanitary towels, swabs or tampons for external or internal application to the body; Supporting or fastening means therefor; Tampon applicators characterised by the absorbing medium having superabsorbent materials, i.e. highly absorbent polymer gel materials
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J2220/00—Aspects relating to sorbent materials
    • B01J2220/40—Aspects relating to the composition of sorbent or filter aid materials
    • B01J2220/44—Materials comprising a mixture of organic materials
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J2220/00—Aspects relating to sorbent materials
    • B01J2220/40—Aspects relating to the composition of sorbent or filter aid materials
    • B01J2220/48—Sorbents characterised by the starting material used for their preparation
    • B01J2220/4812—Sorbents characterised by the starting material used for their preparation the starting material being of organic character
    • 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
    • C08F2810/00—Chemical modification of a polymer
    • C08F2810/20—Chemical modification of a polymer leading to a crosslinking, either explicitly or inherently
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F8/00—Chemical modification by after-treatment
    • C08F8/14—Esterification
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2300/00—Characterised by the use of unspecified polymers
    • C08J2300/14—Water soluble or water swellable polymers, e.g. aqueous gels
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2333/00—Characterised by the use of homopolymers or 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 of salts, anhydrides, esters, amides, imides, or nitriles thereof; Derivatives of such polymers
    • C08J2333/02—Homopolymers or copolymers of acids; Metal or ammonium salts thereof

Definitions

  • the present invention relates to a method for producing water-absorbent resin particles, and more specifically, to a method for producing water-absorbent resin particles that constitute an absorbent material suitable for use in sanitary materials such as disposable diapers, sanitary napkins, and incontinence pads.
  • water-absorbent resins have been widely used in the field of sanitary materials such as disposable diapers, sanitary napkins, and incontinence pads.
  • cross-linked polymers of partially neutralized acrylic acid salts have excellent water-absorbing properties, 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 or deterioration, making them a preferred water-absorbent resin.
  • the gel that is produced when absorbent resins absorb bodily fluids such as human urine is affected by various components in the bodily fluids (e.g., vitamin C and iron in urine), and the gel deteriorates. For this reason, various additives (e.g., human urine stabilizers) are being added, and the manufacturing methods of absorbent resins are being improved.
  • various additives e.g., human urine stabilizers
  • sulfite compounds which are reducing agents, are effective as human urine stabilizers and are expected to increase the gel stability of water-absorbent resins.
  • the addition of sulfite compounds to water-absorbent resins can cause problems such as a deterioration in the general water-absorbency performance of the water-absorbent resin (e.g., the amount of saline water absorbed) and yellowing under high temperature and humidity conditions.
  • the main objective of the present invention is to provide a method for producing water-absorbent resin particles that have good general water-absorption performance (e.g., physiological saline water absorption capacity) required of water-absorbent resins, and further, that are inhibited from yellowing under high temperature and high humidity conditions and have high gel stability.
  • general water-absorption performance e.g., physiological saline water absorption capacity
  • the present inventors have conducted intensive research to solve the above problems. As a result, they have found that in a manufacturing method for obtaining water-absorbent resin particles by subjecting water-containing gel particles obtained by polymerizing a water-soluble ethylenically unsaturated monomer to a surface cross-linking treatment, a step of adding a chelating agent, a sulfite compound, and an organic antioxidant to the water-containing gel particles before the surface cross-linking treatment is performed, and further, when the water content of the water-containing gel particles when the sulfite compound is added in this step is within a predetermined range, water-absorbent resin particles having good general water absorption performance required for a water-absorbent resin, suppressed yellow coloring under high temperature and high humidity, and having high gel stability can be suitably manufactured.
  • the present invention is an invention that was completed based on such knowledge and through further intensive research.
  • the present invention provides the following configuration.
  • Item 1 A process 1 for polymerizing a water-soluble ethylenically unsaturated monomer to obtain hydrogel particles;
  • the water content of the hydrous gel particles when the sulfite compound is added is 20% by mass or more and 75% by mass or less.
  • Item 2. The method for producing water-absorbent resin particles according to Item 1, wherein the step 2 further includes a step of adjusting the water content of the hydrous gel particles.
  • Item 4. The method for producing water-absorbent resin particles according to any one of Items 1 to 3, wherein in the step 2, a water content of the hydrous gel particles when the organic antioxidant is added is 20 mass% or more.
  • Item 5. The method for producing water-absorbent resin particles according to any one of Items 1 to 4, wherein in the step 2, an amount of the sulfite-based compound added is 0.001 parts by mass or more and 3.0 parts by mass or less with respect to 100 parts by mass of the water-soluble ethylenically unsaturated monomer.
  • Item 6 The method for producing water-absorbent resin particles according to any one of Items 1 to 5, wherein in the step 2, an amount of the chelating agent added is 0.001 parts by mass or more and 2.0 parts by mass or less with respect to 100 parts by mass of the water-soluble ethylenically unsaturated monomer.
  • Item 7. The method for producing water-absorbent resin particles according to any one of Items 1 to 6, wherein in the step 2, an amount of the organic antioxidant added is 0.1 parts by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the sulfite-based compound.
  • Item 8 The physiological saline water absorption is 40 to 70 g/g; The yellowness index after being left for 14 days in an environment of 70° C.
  • An absorbent body comprising the water-absorbent resin particles according to item 8.
  • An absorbent article comprising the absorbent body according to item 9.
  • the present invention can provide a method for producing water-absorbent resin particles that have good general water-absorption performance required of a water-absorbent resin (e.g., physiological saline water absorption capacity), and further have high gel stability with suppressed yellowing under high temperature and high humidity.
  • the present invention can also provide water-absorbent resin particles that have good physiological saline water absorption capacity, suppressed yellowing under high temperature and high humidity, and high gel stability, an absorbent body containing the water-absorbent resin particles, and an absorbent article containing the absorbent body.
  • FIG. 4 is a schematic diagram of a device for measuring the amount of physiological saline solution absorbed under a load of 4.14 kPa.
  • FIG. 2 is a schematic diagram of a measuring device used for measuring gel strength.
  • water-soluble refers to a solubility of 5% by mass or more in water at 25°C.
  • a numerical value connected with “ ⁇ ” means a numerical range that includes the numerical values before and after " ⁇ " as the lower and upper limits.
  • the manufacturing method of water-absorbent resin particles of the present invention comprises step 1 of polymerizing a water-soluble ethylenically unsaturated monomer to obtain hydrous gel particles, step 2 of adding a chelating agent, a sulfite compound and an organic antioxidant to the hydrous gel particles, and step 3 of performing a surface cross-linking treatment on the hydrous gel particles, in this order, and is characterized in that the water content of the hydrous gel particles when adding the sulfite compound in step 2 is 20% by mass or more and 75% by mass or less.
  • the water-absorbent resin particles manufactured by the manufacturing method of the present invention having such characteristics have good general water absorption performance required for water-absorbent resins (e.g., physiological saline water absorption amount, etc.), and further have high gel stability by suppressing yellow coloring under high temperature and high humidity.
  • the manufacturing method of water-absorbent resin particles of the present invention will be described in detail below.
  • Step 1 is a step of polymerizing a water-soluble ethylenically unsaturated monomer to obtain hydrogel particles.
  • 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.
  • aqueous solution polymerization polymerization is carried out by heating an aqueous solution of a water-soluble ethylenically unsaturated monomer while stirring as necessary.
  • reversed-phase suspension polymerization polymerization is carried out by heating a water-soluble ethylenically unsaturated monomer in a hydrocarbon dispersion medium while stirring.
  • Step 1 may further include a step of pulverizing the hydrous gel obtained by polymerizing the water-soluble ethylenically unsaturated monomer to obtain hydrous gel particles.
  • pulverization of the hydrous gel is usually not necessary since the hydrous gel particles are generated by polymerization.
  • step 1 for obtaining hydrous gel particles an example of reverse phase suspension polymerization is described below.
  • the polymerization is carried out in the presence of a radical polymerization initiator.
  • a radical polymerization initiator As described below, an internal crosslinking agent may be added to the water-soluble ethylenically unsaturated monomer as necessary to produce hydrogel particles having an internal crosslinked structure.
  • water-soluble ethylenically unsaturated monomers include (meth)acrylic acid (in the present specification, "acrylic” and “methacrylic” are collectively referred to as “(meth)acrylic", the same applies below) 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)
  • water-soluble ethylenically unsaturated monomers from the viewpoint of industrial ease of availability, etc., (meth)acrylic acid or a salt thereof, (meth)acrylamide, and N,N-dimethylacrylamide are preferred, and (meth)acrylic acid and a salt thereof are more preferred.
  • These water-soluble ethylenically unsaturated monomers may be used alone or in combination of two or more kinds.
  • 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 mentioned above.
  • 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 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 reversed-phase suspension polymerization.
  • a hydrocarbon dispersion medium in the form of an aqueous solution
  • 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.
  • 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 neutralizing agent, if necessary.
  • alkaline neutralizing agents include alkali metal salts such as sodium hydroxide, sodium carbonate, sodium hydrogencarbonate, potassium hydroxide, potassium carbonate, etc.; ammonia, etc.
  • alkaline neutralizing agents may be used in the form of an aqueous solution to simplify the neutralization operation.
  • the alkaline neutralizing agents described above may be used alone or in combination of two or more types.
  • the degree of neutralization of the water-soluble ethylenically unsaturated monomer by 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.
  • 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-butyl cumyl 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-phenylenediamine)-2-methylpropane].
  • persulfates such as potassium persulfate, ammonium persulfate, and sodium persulfate
  • peroxides such as methyl ethyl ketone peroxide, methyl isobutyl ketone per
  • azo compounds examples include 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).
  • radical polymerization initiators potassium persulfate, ammonium persulfate, sodium persulfate, and 2,2'-azobis(2-amidinopropane) dihydrochloride are preferred from the viewpoint of easy 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.
  • the amount of radical polymerization initiator used is, for example, 0.00005 to 0.01 mole per mole of water-soluble ethylenically unsaturated monomer. By using such an amount, it is possible to avoid a sudden polymerization reaction and to complete the polymerization reaction within an appropriate time.
  • the internal crosslinking agent may be one capable of crosslinking the polymer of the water-soluble ethylenically unsaturated monomer used, such as (poly)ethylene glycol (the term “(poly)” refers to the case where the "poly" prefix is used or not).
  • 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''-
  • a polyglycidyl compound more preferably a diglycidyl ether compound, and it is preferable to use (poly)ethylene glycol diglycidyl ether, (poly)propylene glycol diglycidyl ether, or (poly)glycerin diglycidyl ether.
  • These internal cross-linking agents may be used alone or in combination of two or more kinds.
  • 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 per mol of the water-soluble ethylenically unsaturated monomer.
  • hydrocarbon dispersion medium 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 they are easily available industrially, have stable quality, and are inexpensive.
  • These hydrocarbon dispersion media may be used alone or in combination of two or more types.
  • a commercially available product such as Exxol Heptane (manufactured by Exxon Mobil Corp.: contains 75 to 85% by mass of heptane and its isomers) can also be used to obtain favorable results.
  • the amount of the 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.
  • 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 in a multiple stage polymerization (the same applies below).
  • 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. As the dispersion stabilizer, a surfactant can be used.
  • Surfactants that can be used include, for example, 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, alkylarylformaldehyde 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 poly
  • surfactants it is particularly preferable to use sorbitan fatty acid esters, polyglycerin fatty acid esters, and sucrose fatty acid esters from the standpoint of dispersion stability of the monomer. These surfactants may be used alone or in combination of two or more.
  • the amount of surfactant used is preferably 0.1 to 30 parts by mass, and more preferably 0.3 to 20 parts by mass, per 100 parts by mass of the first stage water-soluble ethylenically unsaturated monomer.
  • a polymeric dispersant As the dispersion stabilizer used in the reversed phase suspension polymerization, a polymeric dispersant may be used in combination with the above-mentioned surfactant.
  • 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.
  • 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 kinds.
  • the amount of polymeric dispersant used is preferably 0.1 to 30 parts by mass, and more preferably 0.3 to 20 parts by mass, per 100 parts by mass of the first stage water-soluble ethylenically unsaturated monomer.
  • a thickener can be added to an aqueous solution containing a water-soluble ethylenically unsaturated monomer to carry out reverse suspension polymerization.
  • 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 suspension polymerization.
  • thickeners for example, 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. can be used. Note that, 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 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 a dispersion stabilizer.
  • the dispersion stabilizer surfactant or polymeric dispersant
  • the dispersion stabilizer may be added either before or after the addition of the aqueous monomer solution, so long as it is before the start of the polymerization reaction.
  • Such reverse phase suspension polymerization can be carried out in one stage or in multiple stages (two or more stages). From the viewpoint of increasing productivity, it is preferable to carry out the polymerization in two to three stages.
  • the water-soluble ethylenically unsaturated monomer is added to the reaction mixture obtained in the first stage of polymerization reaction and mixed, and the second and subsequent stages of reversed-phase suspension polymerization can be performed in the same manner as the first stage.
  • the reaction temperature for the polymerization reaction is preferably 20 to 110°C, and more preferably 40 to 90°C, from the viewpoints of promoting rapid polymerization and shortening the polymerization time, thereby improving economy, and of easily removing the heat of polymerization to allow the reaction to proceed smoothly.
  • Step 2 is a step of adding a chelating agent, a sulfite compound, and an organic antioxidant to the hydrogel particles obtained in step 1.
  • the water content of the hydrogel particles when the sulfite compound is added in step 2 is 20% by mass or more and 75% by mass or less.
  • the water content of the hydrous gel particles when a sulfite compound is added to the hydrous gel particles is preferably 20% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more, with preferred ranges being 20 to 75% by mass, 30 to 75% by mass, etc.
  • the water content of the hydrous gel particles when the chelating agent is added to the hydrous gel particles in step 2 is preferably 20% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more, and is preferably 150% by mass or less, more preferably 100% by mass or less, and even more preferably 75% by mass or less, with preferred ranges being 20-150% by mass, 20-75% by mass, 30-75% by mass, etc.
  • the water content of the hydrogel particles when the organic antioxidant is added to the hydrogel particles in step 2 is preferably 20% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more, and is preferably 150% by mass or less, more preferably 100% by mass or less, and even more preferably 75% by mass or less, with preferred ranges being 20 to 150% by mass, 20 to 75% by mass, 30 to 75% by mass, etc.
  • step 2 further includes a step of adjusting the moisture content of the hydrous gel particles obtained in step 1.
  • the moisture content of the hydrous gel particles produced in step 1 is less than 20% by mass, water can be added to the hydrous gel particles, and if the moisture content is more than 75% by mass, the hydrous gel particles can be heated to evaporate the water, thereby adjusting the moisture content to within the range of 20% to 75% by mass.
  • the moisture content of the obtained hydrous gel particles usually exceeds 75% by mass (for example, the moisture content is often within the range of 100 to 250% by mass), so it is effective to provide a step of adjusting the moisture content of the hydrous gel particles obtained in step 1.
  • the chelating agent, sulfite compound, and organic antioxidant are added to the hydrogel particles.
  • they can be added in the order of the chelating agent, sulfite compound, and organic antioxidant, or at least two of them can be added simultaneously.
  • the amount of sulfite compound added in step 2 is preferably 0.001 parts by mass or more, more preferably 0.01 parts by mass or more, even more preferably 0.05 parts by mass or more, and is preferably 3.0 parts by mass or less, more preferably 1.0 parts by mass or less, even more preferably 0.50 parts by mass or less, even more preferably 0.25 parts by mass or less, with preferred ranges being 0.001 to 3.0 parts by mass, 0.01 to 1.0 parts by mass, etc., relative to 100 parts by mass of the water-soluble ethylenically unsaturated monomer.
  • the amount of the chelating agent added in step 2 is preferably 0.001 parts by mass or more, more preferably 0.002 parts by mass or more, and even more preferably 0.003 parts by mass or more, relative to 100 parts by mass of the water-soluble ethylenically unsaturated monomer, and is preferably 2.0 parts by mass or less, more preferably 1.0 parts by mass or less, more preferably 0.50 parts by mass or less, even more preferably 0.10 parts by mass or less, and even more preferably 0.05 parts by mass or less, with preferred ranges being 0.001 to 2.0 parts by mass, 0.002 to 1.0 parts by mass, etc.
  • the amount of organic antioxidant added in step 2 is preferably 0.10 parts by mass or more, more preferably 0.30 parts by mass or more, and is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, with preferred ranges being 0.10 to 20 parts by mass, 0.30 to 10 parts by mass, etc., per 100 parts by mass of the sulfite compound.
  • the chelating agent, sulfite compound, and organic antioxidant are each added to the hydrogel particles in the form of an aqueous solution.
  • concentration of each component in the aqueous solution may be adjusted so as to obtain the above-mentioned addition amount.
  • the concentration of the aqueous solution of the chelating agent added to the hydrogel particles is preferably 0.1 to 50 mass%, more preferably 0.5 to 40 mass%.
  • the concentration of the aqueous solution of the sulfite compound added to the hydrogel particles is preferably 1 to 20 mass%, more preferably 5 to 20 mass%.
  • concentration of the aqueous solution of the organic antioxidant added to the hydrogel particles is preferably 0.01 to 10 mass%, more preferably 0.1 to 5 mass%.
  • sulfite compounds include sodium sulfite, potassium sulfite, calcium sulfite, sodium hydrogen sulfite, potassium hydrogen sulfite, ammonium hydrogen sulfite, sodium pyrosulfite, and potassium pyrosulfite. Only one type of sulfite compound may be used, or two or more types may be used.
  • the chelating agent is preferably ethylenediamine-N,N'-disuccinic acid, diethylenetriaminepentaacetic acid, glycol ether diaminetetraacetic acid, ethylenediaminetetramethylenephosphonic acid, diethylenetriaminepentamethylenephosphonic acid, etc.
  • the chelating agent may exist in the form of a salt. Examples of the salt include sodium salts and potassium salts. Only one type of chelating agent may be used, or two or more types may be used.
  • the organic antioxidants preferably include ascorbic acids, erythorbic acids, gallic acids, protocatechuic acids, benzimidazoles, and alkylhydroxyanisoles. Only one type of organic antioxidant may be used, or two or more types may be used.
  • Step 3 is a step of subjecting the hydrogel particles to surface cross-linking to which the chelating agent, the sulfite compound and the organic antioxidant have been added in step 2.
  • the surfaces of the hydrogel particles are cross-linked by the surface cross-linking (surface cross-linking reaction).
  • Examples of surface cross-linking agents include compounds having two or more reactive functional groups.
  • 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-to
  • polyols such as ethylene glycol, propylene glycol, 1,4-butanediol, diethylene glycol, triethylene glycol, trimethylolpropane, glycerin, polyoxyethylene glycol, polyoxypropylene glycol, and polyglycerin; (poly)ethylene glycol diglycidyl ether, (poly)glycerin diglycidyl ether, (poly)glycerin triglycidyl ether, trimethylolpropane triglycidyl ether, (poly)propylene glycol polyglycidyl ether, (poly)glycerin di ...
  • Polyglycidyl compounds such as roll polyglycidyl ether; ethylene carbonate, propylene carbonate, 4,5-dimethyl-1,3-dioxolane-2-one, 4,4-dimethyl-1,3-dioxolane-2-one, 4-ethyl-1,3-dioxolane-2-one, 4-hydroxymethyl-1,3-dioxolane-2-one, 1,3-dioxan-2-one, 4-methyl-1,3-dioxan-2-one, 4,6-dimethyl-1,3-dioxan-2-one, 1,3-dioxopan-2-one, and other carbonate compounds (e.g., alkylene carbonates) are preferred.
  • These surface crosslinking agents may be used alone or in combination of two or more.
  • the amount of the 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 it is or as an aqueous solution, but if necessary, it may be added as a solution using a hydrophilic organic solvent as a solvent.
  • hydrophilic organic solvents include lower alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, etc.; ketones such as acetone and methyl ethyl ketone; ethers such as diethyl ether, dioxane, tetrahydrofuran, etc.; amides such as N,N-dimethylformamide; sulfoxides such as dimethyl sulfoxide, etc.
  • These hydrophilic organic solvents may be used alone, in combination of two or more types, or as a mixed solvent with water.
  • the water content of the hydrogel particles is preferably in the range of 1 to 75% by mass, more preferably in the range of 5 to 60% by mass, even more preferably in the range of 10 to 50% by mass, and even more preferably in the range of 15 to 40% by mass.
  • the reaction temperature in 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.
  • the reaction time in the surface cross-linking reaction is preferably 1 to 300 minutes, and more preferably 5 to 200 minutes.
  • the step 3 preferably further includes a drying step of the water-absorbent resin particles obtained by surface-treating the hydrous gel particles.
  • a drying step may be included in which water, the hydrocarbon dispersion medium, and the like are removed by distillation by applying energy such as heat from the outside.
  • the system in which the hydrous gel particles are dispersed in the hydrocarbon dispersion medium is heated to once distill off the water and the hydrocarbon dispersion medium from the system by azeotropic distillation. At this time, if only the distilled hydrocarbon dispersion medium is returned to the system, continuous azeotropic distillation is possible.
  • 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 the resin being less likely to deteriorate.
  • the water and the hydrocarbon dispersion medium are distilled off to obtain dried water-absorbent resin particles.
  • the drying process by distillation may be performed under normal pressure or under reduced pressure. From the viewpoint of increasing the drying efficiency, it may also be performed under a stream of nitrogen or the like.
  • 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.
  • the loss on drying of the water-absorbent resin particles obtained by the manufacturing method of the present invention is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less, with a preferred range being 1 to 10% by mass, etc.
  • a surface cross-linking step using a surface cross-linking agent is carried out after polymerization of monomers by reversed-phase suspension polymerization
  • the above-mentioned drying step by distillation 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, radical chain inhibitors, 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 an inorganic powder to 100 parts by mass of the water-absorbent resin particles.
  • the additives are preferably hydrophilic or water-soluble.
  • the additives are preferably added to the water-absorbent resin particles obtained after the surface cross-linking step.
  • the content of the water-absorbent resin (excluding additives) including moisture (loss on drying) is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more.
  • the water-absorbent resin particles obtained by the manufacturing method of the present invention have good water-absorption performance (e.g., physiological saline water absorption capacity) generally required of water-absorbent resins, and furthermore, yellowing under high temperature and high humidity conditions is suppressed, and the particles have high gel stability.
  • good water-absorption performance e.g., physiological saline water absorption capacity
  • the water-absorbent resin particles of the present invention have, for example, a saline water absorption of 40 to 70 g/g, a yellowness index of less than 40 after being left for 14 days in an environment of 70° C. and 90% relative humidity, and a gel strength of 5500 N/m 2 or more after being left for 14 hours in an environment of 37° C. and 60% relative humidity.
  • the water-absorbent resin particles of the present invention are suitably produced by the production method of the present invention, but are not limited to water-absorbent resin particles produced by the production method, and may be any particles that satisfy the above-mentioned saline water absorption, yellowness index after being left for 14 days in an environment of 70° C. and 90% relative humidity, and gel strength after being left for 14 hours in an environment of 37° C. and 60% relative humidity.
  • the physiological saline water absorption capacity of the water-absorbent resin particles of the present invention is preferably 40 g/g or more, more preferably 45 g/g or more, and even more preferably 50 g/g or more.
  • the upper limit is preferably 70 g/g or less, and the preferred range is 40 to 70 g/g, 45 to 70 g/g, etc.
  • the physiological saline water retention capacity of the water-absorbent resin particles of the present invention is preferably 25 g/g or more, more preferably 30 g/g or more, and is preferably 60 g/g or less, more preferably 55 g/g or less, and even more preferably 50 g/g or less, with preferred ranges being 25 to 60 g/g, 30 to 55 g/g, etc.
  • the physiological saline water absorption capacity of the water-absorbent resin particles obtained by the manufacturing method of the present invention under a load of 4.14 kPa is preferably 5 mL/g or more, more preferably 10 mL/g or more, and is preferably 40 mL/g or less, more preferably 35 mL/g or less, and even more preferably 30 mL/g or less, with preferred ranges being 5 to 40 mL/g, 10 to 30 mL/g, etc.
  • the saline water absorption capacity, saline water retention capacity, and saline water absorption capacity under a load of 4.14 kPa of the water-absorbent resin particles were each measured using the method described in the Examples.
  • the water-absorbent resin particles of the present invention have an "initial yellowness value" evaluated by the method described in the Examples, which is preferably less than 20, more preferably less than 15, and even more preferably less than 10.
  • the lower limit of the yellowness value is, for example, 0.
  • the water-absorbent resin particles of the present invention preferably have a yellowness index after being left for 7 days in an environment of 70°C and 90% relative humidity, as evaluated by the method described in the Examples, of less than 40, more preferably less than 38, and even more preferably less than 30.
  • the lower limit of the yellowness index is, for example, 5.
  • the water-absorbent resin particles of the present invention preferably have a yellowness index after being left for 14 days in an environment of 70°C and 90% relative humidity, as evaluated by the method described in the Examples, of less than 40, and more preferably less than 38.
  • the lower limit of the yellowness index is, for example, 10.
  • the water absorbent resin particles of the present invention have an "initial gel strength" of preferably 5500 N/ m2 or more, more preferably 6200 N/ m2 or more, as evaluated by the method described in the Examples.
  • the upper limit of the initial gel strength is, for example, 20000 N/ m2 .
  • the water absorbent resin particles of the present invention have a "gel strength after standing at 37°C for 14 hours" evaluated by the method described in the Examples of preferably 5500 N/ m2 or more, more preferably 6200 N/ m2 or more.
  • the upper limit of the gel strength is, for example, 20000 N/ m2 .
  • the water-absorbing resin particles of the present invention constitute an absorbent body used in sanitary materials such as sanitary products and disposable diapers, and are suitably used in absorbent articles containing the absorbent body.
  • the absorbent using the water-absorbent resin particles of the present invention contains the water-absorbent resin particles of the present invention.
  • the absorbent may further contain hydrophilic fibers.
  • the absorbent configuration 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 obtain a uniform composition, a sandwich structure in which water-absorbent resin particles are sandwiched between layered hydrophilic fibers, and a structure in which water-absorbent resin particles and hydrophilic fibers are wrapped in tissue.
  • the absorbent may 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 content of water-absorbent resin particles in the absorbent 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.
  • 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 polyamide, polyester, and polyolefin that have been hydrophilically treated.
  • the average fiber length of hydrophilic fibers is usually 0.1 to 10 mm, or may be 0.5 to 5 mm.
  • the absorbent article of the present invention can be made 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-punch types made of fibers such as polyethylene, polypropylene, and polyester, as well as porous synthetic resin sheets.
  • Liquid-impermeable sheets include synthetic resin films made of resins such as polyethylene, polypropylene, and polyvinyl chloride.
  • the water-absorbent resin particles obtained in the following manufacturing examples and the water-absorbent resin particles obtained in the examples and comparative examples were evaluated by the following various tests. Unless otherwise specified, the measurements were performed in an environment of a temperature of 25 ⁇ 2°C and a relative humidity of 50 ⁇ 10%.
  • Example 1 [Production process of hydrogel particles (step 1)] A round-bottomed cylindrical separable flask with an inner diameter of 11 cm and a volume of 2 L was prepared, which was equipped with a reflux condenser, a dropping funnel, a nitrogen gas inlet tube, and a stirring blade having two stages of four inclined paddle blades with a blade diameter of 5 cm. 293 g of n-heptane was added to this flask as a hydrocarbon dispersion medium, and 0.736 g of maleic anhydride-modified ethylene-propylene copolymer (Mitsui Chemicals, Inc., Hiwax 1105A) was added as a polymeric dispersant.
  • step 1 A round-bottomed cylindrical separable flask with an inner diameter of 11 cm and a volume of 2 L was prepared, which was equipped with a reflux condenser, a dropping funnel, a nitrogen gas inlet tube, and a stirring blade having two stages of four inclined paddle blades with a blade diameter
  • the aqueous liquid 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 an HLB of 3 (Ryoto Sugar Ester S-370, Mitsubishi Chemical Foods Corporation) in 6.62 g of n-heptane as a surfactant in a 20 mL vial was then added.
  • the system was thoroughly purged with nitrogen while stirring at a stirrer speed of 500 rpm, and the flask was immersed in a water bath at 70° C. to raise the temperature, and polymerization was carried out for 60 minutes to obtain a first-stage polymerization slurry.
  • the contents of the separable flask system were cooled to 27°C while stirring at a stirrer speed of 1000 rpm, and then the entire amount of the second-stage aqueous liquid was added to the first-stage polymerization slurry liquid, and the system was replaced with nitrogen for 30 minutes. After that, the flask was again immersed in a 70°C water bath to raise the temperature, and the polymerization reaction was carried out for 60 minutes to obtain hydrous gel particles.
  • Step 2 After obtaining the hydrous gel particles, the flask was immersed in an oil bath set at 125°C, and 175.1 g of water was extracted from the system by azeotropic distillation of n-heptane and water while refluxing n-heptane (first water content adjustment step). Then, 4.42 g of a 0.5% by mass aqueous solution of trisodium ethylenediamine-N,N'-disuccinic acid was added under stirring. At this time, the water content of the hydrous gel particles when the aqueous solution of trisodium ethylenediamine-N,N'-disuccinic acid was added was 62% by mass.
  • step 3 [Surface cross-linking step (step 3)] Then, 84.7 g of water was extracted from the system by azeotropic distillation of n-heptane and water again while refluxing n-heptane. Then, 4.42 g (0.507 mmol) of a 2% by mass aqueous solution of ethylene glycol diglycidyl ether was added to the flask as a surface crosslinking agent, and the mixture was kept at 83° C. for 2 hours. Then, n-heptane was evaporated at 125° C. to dry the mixture, and the mixture was passed through a sieve with an opening of 850 ⁇ m to obtain 225.7 g of water-absorbent resin particles.
  • Step of adding additives to water-absorbent resin particles 0.5 parts by mass of amorphous silica (Toxil NP-S, Oriental Silicas Corporation) was mixed with 100 parts by mass of the obtained water absorbent resin particles to obtain 226.8 g of water absorbent resin particles (1).
  • the physiological saline water absorption capacity of the water absorbent resin particles (1) was 65 g/g
  • the physiological saline water retention capacity was 43 g/g
  • the physiological saline water absorption capacity under a load of 4.14 kPa was 14 mL/g.
  • Example 1 The same operation as in Example 1 was performed except that 4.42 g of 0.5 mass% ethylenediamine-N,N'-disuccinic acid trisodium aqueous solution was not used, and the amount of water extracted from the system by azeotropic distillation of n-heptane and water in the [surface cross-linking step] was changed from 84.7 g to 80.3 g, to obtain 224.0 g of water-absorbent resin particles (2).
  • the water content of the hydrous gel particles when the sodium sulfite aqueous solution was added was 62 mass%, and the water content of the hydrous gel particles when the L(+)-ascorbic acid aqueous solution was added was 63 mass%.
  • the physiological saline water absorption amount of the water-absorbent resin particles (2) was 62 g/g, the physiological saline water retention amount was 42 g/g, and the physiological saline water absorption amount under a load of 4.14 kPa was 18 mL/g.
  • Example 2 The same operation as in Example 1 was performed except that the 20% by mass aqueous sodium sulfite solution was not used, and the amount of water extracted from the system by azeotropic distillation of n-heptane and water in the [Surface cross-linking step] was changed from 84.7 g to 83.0 g, to obtain 225.5 g of water-absorbent resin particles (3).
  • the water content of the hydrous gel particles when the aqueous solution of ethylenediamine-N,N'-disuccinic acid trisodium was added was 62% by mass, and the water content of the hydrous gel particles when the aqueous solution of L(+)-ascorbic acid was added was 64% by mass.
  • the physiological saline water absorption amount of the water-absorbent resin particles (3) was 61 g/g, the physiological saline water retention amount was 37 g/g, and the physiological saline water absorption amount under a load of 4.14 kPa was 18 mL/g.
  • Example 3 The same operation as in Example 1 was performed except that the 0.1% by mass L(+)-ascorbic acid aqueous solution was not used, and the amount of water extracted from the system by azeotropic distillation of n-heptane and water in the [Surface cross-linking step] was changed from 84.7 g to 82.5 g, to obtain 224.8 g of water-absorbent resin particles (4).
  • the water content of the hydrogel particles when the ethylenediamine-N,N'-disuccinic acid trisodium aqueous solution was added was 62% by mass, and the water content of the hydrogel particles when the sodium sulfite aqueous solution was added was 64% by mass.
  • the physiological saline water absorption amount of the water-absorbent resin particles (4) was 73 g/g, the physiological saline water retention amount was 42 g/g, and the physiological saline water absorption amount under a load of 4.14 kPa was 16 mL/g.
  • Example 2 The same operation as in Example 1 was performed except that the amount of water extracted from the system by azeotropic distillation of n-heptane and water in the first water content adjustment step was changed from 175.1 g to 253.8 g, and the amount of water extracted from the system by azeotropic distillation of n-heptane and water in the [surface cross-linking step] was changed from 84.7 g to 6.1 g, to obtain 221.4 g of water-absorbent resin particles (5).
  • the water content of the hydrous gel particles when the ethylenediamine-N,N'-disuccinic acid trisodium aqueous solution was added was 26 mass%
  • the water content of the hydrous gel particles when the sodium sulfite aqueous solution was added was 28 mass%
  • the water content of the hydrous gel particles when the L(+)-ascorbic acid aqueous solution was added was 29 mass%.
  • the physiological saline water absorption capacity of the water-absorbent resin particles (5) was 59 g/g
  • the physiological saline water retention capacity was 36 g/g
  • the physiological saline water absorption capacity under a load of 4.14 kPa was 23 mL/g.
  • Example 3 The same operation as in Example 1 was performed except that the amount of water extracted from the system by azeotropic distillation of n-heptane and water in the first water content adjustment step was changed from 175.1 g to 223.2 g, and the amount of water extracted from the system by azeotropic distillation of n-heptane and water in the [surface cross-linking step] was changed from 84.7 g to 36.7 g, to obtain 223.8 g of water-absorbent resin particles (6).
  • the water content of the hydrous gel particles when the ethylenediamine-N,N'-disuccinic acid trisodium aqueous solution was added was 40 mass%
  • the water content of the hydrous gel particles when the sodium sulfite aqueous solution was added was 42 mass%
  • the water content of the hydrous gel particles when the L(+)-ascorbic acid aqueous solution was added was 43 mass%.
  • the physiological saline water absorption capacity of the water-absorbent resin particles (6) was 66 g/g
  • the physiological saline water retention capacity was 43 g/g
  • the physiological saline water absorption capacity under a load of 4.14 kPa was 12 mL/g.
  • Example 4 The same operation as in Example 1 was performed except that the amount of water extracted from the system by azeotropic distillation of n-heptane and water in the first water content adjustment step was changed from 175.1 g to 157.6 g, and the amount of water extracted from the system by azeotropic distillation of n-heptane and water in the [surface crosslinking step] was changed from 84.7 g to 102.2 g, to obtain 225.1 g of water-absorbent resin particles (7).
  • the water content of the hydrous gel particles when the ethylenediamine-N,N'-disuccinic acid trisodium aqueous solution was added was 70 mass%
  • the water content of the hydrous gel particles when the sodium sulfite aqueous solution was added was 72 mass%
  • the water content of the hydrous gel particles when the L(+)-ascorbic acid aqueous solution was added was 73 mass%.
  • the physiological saline water absorption capacity of the water-absorbent resin particles (7) was 64 g/g
  • the physiological saline water retention capacity was 42 g/g
  • the physiological saline water absorption capacity under a load of 4.14 kPa was 12 mL/g.
  • Example 4 The same operation as in Example 1 was performed except that the amount of water extracted from the system by azeotropic distillation of n-heptane and water in the first water content adjustment step was changed from 175.1 g to 135.8 g, and the amount of water extracted from the system by azeotropic distillation of n-heptane and water in the [surface cross-linking step] was changed from 84.7 g to 124.1 g, to obtain 223.8 g of water-absorbent resin particles (8).
  • the water content of the hydrous gel particles when the ethylenediamine-N,N'-disuccinic acid trisodium aqueous solution was added was 80 mass%
  • the water content of the hydrous gel particles when the sodium sulfite aqueous solution was added was 82 mass%
  • the water content of the hydrous gel particles when the L(+)-ascorbic acid aqueous solution was added was 83 mass%.
  • the physiological saline water absorption capacity of the water-absorbent resin particles (8) was 67 g/g
  • the physiological saline water retention capacity was 46 g/g
  • the physiological saline water absorption capacity under a load of 4.14 kPa was 12 mL/g.
  • Step 2 After obtaining the hydrous gel particles, the flask was immersed in an oil bath set at 125°C, and 135.8 g of water was extracted from the system by azeotropic distillation of n-heptane and water while refluxing n-heptane (first water content adjustment step). Then, 2.21 g of a 20% by mass aqueous sodium sulfite solution was added under stirring. At this time, the water content of the hydrous gel particles when the aqueous sodium sulfite solution was added was 80% by mass.
  • step 3 [Surface cross-linking step (step 3)] Then, 34.9 g of water was extracted from the system by azeotropic distillation of n-heptane and water again while refluxing n-heptane. Then, 4.42 g (0.507 mmol) of a 2% by mass aqueous solution of ethylene glycol diglycidyl ether was added to the flask as a surface crosslinking agent, and the mixture was kept at 83° C. for 2 hours. Then, n-heptane was evaporated at 125° C. to dry the mixture, and the mixture was passed through a sieve with an opening of 850 ⁇ m to obtain 221.1 g of water-absorbent resin particles.
  • Example 5 [Production process of hydrogel particles (step 1)] The same procedure as in the [Production process of hydrogel particles] of Example 1 was carried out to obtain hydrogel particles.
  • Step 2 After obtaining the hydrous gel particles, the flask was immersed in an oil bath set at 125°C, and 135.8 g of water was extracted from the system by azeotropic distillation of n-heptane and water while refluxing n-heptane (first water content adjustment step). Then, 4.42 g of a 0.5% by mass aqueous solution of trisodium ethylenediamine-N,N'-disuccinic acid was added under stirring. At this time, the water content of the hydrous gel particles when the aqueous solution of trisodium ethylenediamine-N,N'-disuccinic acid was added was 80% by mass.
  • step 3 [Surface cross-linking step (step 3)] Then, 32.3 g of water was extracted from the system by azeotropic distillation of n-heptane and water again while refluxing n-heptane. Then, 4.42 g (0.507 mmol) of a 2 mass% aqueous solution of ethylene glycol diglycidyl ether was added to the flask as a surface crosslinking agent, and the mixture was kept at 83 ° C. for 2 hours. Then, n-heptane was evaporated at 125 ° C. to dry the mixture, and the mixture was passed through a sieve with an opening of 850 ⁇ m to obtain 222.7 g of water-absorbent resin particles.
  • Example 6 [Production process of hydrogel particles (step 1)] The same procedure as in the [Production process of hydrogel particles] of Example 1 was carried out to obtain hydrogel particles.
  • Step 2 After obtaining the hydrous gel particles, the flask was immersed in an oil bath set at 125°C, and 135.8 g of water was extracted from the system by azeotropic distillation of n-heptane and water while refluxing n-heptane (first water content adjustment step). Then, 2.21 g of a 0.2 mass% L(+)-ascorbic acid aqueous solution was added under stirring. At this time, the water content of the hydrous gel particles when the L(+)-ascorbic acid aqueous solution was added was 80 mass%.
  • step 3 [Surface cross-linking step (step 3)] Then, 34.5 g of water was extracted from the system by azeotropic distillation of n-heptane and water again while refluxing n-heptane. Then, 4.42 g (0.507 mmol) of a 2 mass% aqueous solution of ethylene glycol diglycidyl ether was added to the flask as a surface crosslinking agent, and the mixture was kept at 83 ° C. for 2 hours. Then, n-heptane was evaporated at 125 ° C. to dry the mixture, and the mixture was passed through a sieve with an opening of 850 ⁇ m to obtain 223.7 g of water-absorbent resin particles.
  • step 3 After obtaining the hydrous gel particles, the flask was immersed in an oil bath set at 125°C, and 251.5 g of water was extracted from the system by azeotropic distillation of n-heptane and water while refluxing n-heptane. Then, 4.42 g (0.507 mmol) of a 2% by mass aqueous solution of ethylene glycol diglycidyl ether was added to the flask as a surface crosslinking agent, and the mixture was kept at 83°C for 2 hours. Then, n-heptane was evaporated at 125°C to dry, and the mixture was passed through a sieve with an opening of 850 ⁇ m to obtain 217.6 g of water-absorbing resin particles.
  • amorphous silica (Toxil NP-S, Oriental Silicas Corporation) was mixed to 100 parts by mass of the obtained mixture to obtain water-absorbent resin particles (12).
  • the physiological saline water absorption of the water-absorbent resin particles (12) was 60 g/g, the physiological saline water retention was 42 g/g, and the physiological saline water absorption under a load of 4.14 kPa was 14 mL/g.
  • step 3 After obtaining the hydrous gel particles, the flask was immersed in an oil bath set at 125°C, and 251.5 g of water was extracted from the system by azeotropic distillation of n-heptane and water while refluxing n-heptane. Then, 4.42 g (0.507 mmol) of a 2% by mass aqueous solution of ethylene glycol diglycidyl ether was added to the flask as a surface crosslinking agent, and the mixture was kept at 83°C for 2 hours. Then, n-heptane was evaporated at 125°C to dry, and the mixture was passed through a sieve with an opening of 850 ⁇ m to obtain 226.8 g of water-absorbent resin particles.
  • Step of adding additives to water-absorbent resin particles 20 g of the water-absorbent resin particles obtained in the [Surface cross-linking step] was weighed into a round-bottomed cylindrical separable flask with an inner diameter of 11 cm equipped with an anchor-shaped stirring blade made of fluororesin. Next, while stirring at 300 rpm, 0.2 g of a 1.0 mass% aqueous solution of diethylenetriaminepentaacetic acid.pentasodium (DTPA.5Na) was dropped into the separable flask with a Pasteur pipette, and a mixture was obtained by stirring for 10 minutes.
  • DTPA.5Na diethylenetriaminepentaacetic acid.pentasodium
  • the physiological saline water absorption capacity of the water-absorbent resin particles was 58 g/g, the physiological saline water retention capacity was 40 g/g, and the physiological saline water absorption capacity under a load of 4.14 kPa was 21 mL/g.
  • Comparative Example 8 The same operation as in Comparative Example 7 was carried out except that 0.2 g of a 1.0 mass% aqueous solution of ethylenediamine-N,N'-disuccinic acid.trisodium (EDDS.3Na) was used instead of 0.2 g of a 1.0 mass% aqueous solution of diethylenetriaminepentaacetic acid.pentasodium (DTPA.5Na) in Comparative Example 7, to obtain 218.8 g of water absorbent resin particles (14).
  • EDDS.3Na ethylenediamine-N,N'-disuccinic acid.trisodium
  • DTPA.5Na diethylenetriaminepentaacetic acid.pentasodium
  • the physiological saline water absorption of the water absorbent resin particles (14) was 56 g/g, the physiological saline water retention was 39 g/g, and the physiological saline water absorption under a load of 4.14 kPa was 23 mL/g.
  • Example 7 The same operation as in Example 1 was carried out except that 4.42 g of 0.5 mass% diethylenetriaminepentaacetic acid.pentasodium (DTPA.5Na) aqueous solution was used instead of 4.42 g of 0.5 mass% ethylenediamine-N,N'-disuccinic acid.trisodium aqueous solution in Example 1, to obtain 225.6 g of water-absorbent resin particles (15).
  • DTPA.5Na diethylenetriaminepentaacetic acid.pentasodium
  • the water content of the hydrous gel particles when the diethylenetriaminepentaacetic acid.pentasodium aqueous solution was added was 62 mass%
  • the water content of the hydrous gel particles when the sodium sulfite aqueous solution was added was 64 mass%
  • the water content of the hydrous gel particles when the L(+)-ascorbic acid aqueous solution was added was 65 mass%.
  • the physiological saline water absorption of the water-absorbent resin particles (15) was 58 g/g
  • the physiological saline water retention was 39 g/g
  • the physiological saline water absorption under a load of 4.14 kPa was 14 mL/g.
  • Example 8 The same operation as in Example 1 was carried out except that 4.42 g of 0.5 mass% ethylenediamine-N,N'-disuccinic acid ⁇ trisodium aqueous solution was replaced with 4.42 g of 0.5 mass% ethylenediaminetetramethylenephosphonic acid (EDTMP ⁇ 8H) aqueous solution, and 224.6 g of water-absorbent resin particles (16) were obtained.
  • ETMP ⁇ 8H ethylenediaminetetramethylenephosphonic acid
  • the water content of the hydrous gel particles when the ethylenediaminetetramethylenephosphonic acid aqueous solution was added was 62 mass%
  • the water content of the hydrous gel particles when the sodium sulfite aqueous solution was added was 64 mass%
  • the water content of the hydrous gel particles when the L(+)-ascorbic acid aqueous solution was added was 65 mass%.
  • the physiological saline water absorption of the water-absorbent resin particles (16) was 61 g/g
  • the physiological saline water retention was 37 g/g
  • the physiological saline water absorption under a load of 4.14 kPa was 18 mL/g.
  • Example 9 [Production process of hydrogel particles (step 1)] The same procedure as in the [Production process of hydrogel particles] of Example 1 was carried out to obtain hydrogel particles.
  • Step 2 After obtaining the hydrous gel particles, the flask was immersed in an oil bath set at 125°C, and 175.1 g of water was extracted from the system by azeotropic distillation of n-heptane and water while refluxing n-heptane (first water content adjustment step). Then, 4.42 g of a 0.5% by mass aqueous solution of trisodium ethylenediamine-N,N'-disuccinic acid was added under stirring. At this time, the water content of the hydrous gel particles when the aqueous solution of trisodium ethylenediamine-N,N'-disuccinic acid was added was 62% by mass.
  • step 3 [Surface cross-linking step (step 3)] Then, 56.7 g of water was extracted from the system by azeotropic distillation of n-heptane and water again while refluxing n-heptane. Then, 4.42 g (0.507 mmol) of a 2% by mass aqueous solution of ethylene glycol diglycidyl ether was added to the flask as a surface crosslinking agent, and the mixture was kept at 83° C. for 2 hours. Then, n-heptane was evaporated at 125° C. to dry the mixture, and the mixture was passed through a sieve with an opening of 850 ⁇ m to obtain 219.7 g of water-absorbent resin particles.
  • Example 10 In Example 9, 8.83 g of 0.5 mass% ethylenediamine-N,N'-disuccinic acid trisodium aqueous solution was used instead of 4.42 g of 0.5 mass% ethylenediamine-N,N'-disuccinic acid trisodium aqueous solution, and the amount of water extracted from the system by azeotropic distillation of n-heptane and water in the second water content adjustment step was changed from 15.3 g to 19.7 g, and the same operation as in Example 9 was performed to obtain 225.7 g of water-absorbent resin particles (18).
  • the water content of the hydrous gel particles when the ethylenediamine-N,N'-disuccinic acid trisodium aqueous solution was added was 62 mass%
  • the water content of the hydrous gel particles when the sodium sulfite aqueous solution was added was 57 mass%
  • the water content of the hydrous gel particles when the L(+)-ascorbic acid aqueous solution was added was 52 mass%.
  • the physiological saline water absorption capacity of the water-absorbent resin particles (18) was 64 g/g
  • the physiological saline water retention capacity was 40 g/g
  • the physiological saline water absorption capacity under a load of 4.14 kPa was 11 mL/g.
  • Example 11 In Example 9, 2.21 g of 0.5% by mass ethylenediamine-N,N'-disuccinic acid trisodium aqueous solution was used instead of 4.42 g of 0.5% by mass ethylenediamine-N,N'-disuccinic acid trisodium aqueous solution, and the amount of water extracted from the system by azeotropic distillation of n-heptane and water in the second water content adjustment step was changed from 15.3 g to 13.1 g, and the same operation as in Example 9 was performed to obtain 223.4 g of water-absorbent resin particles (19).
  • the water content of the hydrous gel particles when the ethylenediamine-N,N'-disuccinic acid trisodium aqueous solution was added was 62% by mass
  • the water content of the hydrous gel particles when the sodium sulfite aqueous solution was added was 57% by mass
  • the water content of the hydrous gel particles when the L(+)-ascorbic acid aqueous solution was added was 52% by mass.
  • the physiological saline water absorption capacity of the water-absorbent resin particles (19) was 62 g/g
  • the physiological saline water retention capacity was 46 g/g
  • the physiological saline water absorption capacity under a load of 4.14 kPa was 10 mL/g.
  • Example 12 The same operation as in Example 9 was performed except that 3.31 g of a 20% by mass aqueous sodium sulfite solution was used instead of 2.21 g of a 20% by mass aqueous sodium sulfite solution in Example 9, and the amount of water extracted from the system by azeotropic distillation of n-heptane and water in the third water content adjustment step was changed from 12.7 g to 13.6 g, to obtain 223.8 g of water-absorbent resin particles (20).
  • the water content of the hydrous gel particles when the aqueous ethylenediamine-N,N'-disuccinic acid trisodium solution was added was 62% by mass
  • the water content of the hydrous gel particles when the aqueous sodium sulfite solution was added was 57% by mass
  • the water content of the hydrous gel particles when the aqueous L(+)-ascorbic acid solution was added was 52% by mass.
  • the physiological saline water absorption of the water-absorbent resin particles (20) was 67 g/g
  • the physiological saline water retention was 50 g/g
  • the physiological saline water absorption under a load of 4.14 kPa was 8 mL/g.
  • Example 13 The same operation as in Example 9 was performed except that 1.10 g of a 20% by mass aqueous sodium sulfite solution was used instead of 2.21 g of a 20% by mass aqueous sodium sulfite solution in Example 9, and the amount of water extracted from the system by azeotropic distillation of n-heptane and water in the third water content adjustment step was changed from 12.7 g to 11.8 g, to obtain 224.6 g of water-absorbent resin particles (21).
  • the water content of the hydrous gel particles when the aqueous solution of ethylenediamine-N,N'-disuccinic acid trisodium was added was 62% by mass
  • the water content of the hydrous gel particles when the aqueous solution of sodium sulfite was added was 57% by mass
  • the water content of the hydrous gel particles when the aqueous solution of L(+)-ascorbic acid was added was 52% by mass.
  • the physiological saline water absorption amount of the water-absorbent resin particles (21) was 65 g/g
  • the physiological saline water retention amount was 45 g/g
  • the physiological saline water absorption amount under a load of 4.14 kPa was 11 mL/g.
  • Example 14 The same operation as in Example 9 was performed except that 11.0 g of a 0.2 mass% L(+)-ascorbic acid aqueous solution was used instead of 2.21 g of a 0.2 mass% L(+)-ascorbic acid aqueous solution in Example 9, and the amount of water extracted from the system by azeotropic distillation of n-heptane and water in the [Surface crosslinking step] was changed from 56.7 g to 65.5 g, to obtain 226.8 g of water-absorbent resin particles (22).
  • the water content of the hydrous gel particles when the ethylenediamine-N,N'-disuccinic acid trisodium aqueous solution was added was 62 mass%
  • the water content of the hydrous gel particles when the sodium sulfite aqueous solution was added was 57 mass%
  • the water content of the hydrous gel particles when the L(+)-ascorbic acid aqueous solution was added was 52 mass%.
  • the saline water absorption capacity of the water-absorbent resin particles (22) was 62 g/g
  • the saline water retention capacity was 45 g/g
  • the saline water absorption capacity under a load of 4.14 kPa was 22 mL/g.
  • Example 15 The same operation as in Example 9 was performed except that 1.10 g of a 0.2 mass% L(+)-ascorbic acid aqueous solution was used instead of 2.21 g of a 0.2 mass% L(+)-ascorbic acid aqueous solution in Example 9, and the amount of water extracted from the system by azeotropic distillation of n-heptane and water in the [Surface crosslinking step] was changed from 56.7 g to 55.6 g, to obtain 224.0 g of water-absorbent resin particles (23).
  • the water content of the hydrous gel particles when the ethylenediamine-N,N'-disuccinic acid trisodium aqueous solution was added was 62 mass%
  • the water content of the hydrous gel particles when the sodium sulfite aqueous solution was added was 57 mass%
  • the water content of the hydrous gel particles when the L(+)-ascorbic acid aqueous solution was added was 52 mass%.
  • the physiological saline water absorption capacity of the water-absorbent resin particles (23) was 66 g/g
  • the physiological saline water retention capacity was 46 g/g
  • the physiological saline water absorption capacity under a load of 4.14 kPa was 10 mL/g.
  • the water content of the hydrous gel particles was calculated as follows: It was calculated by the following formula using the amount of water W1 (g) contained in the aqueous liquid used in the production of hydrous gel particles in the [hydrous gel particle production step (step 1)], the amount of water W2 (g) contained in the aqueous additive solution added to the system in the [additive addition step (step 2)], the amount of water W3 (g) extracted from the system by azeotropic distillation of n-heptane and water in the [additive addition step (step 2)], the amount of water W4 (g) extracted from the system by azeotropic distillation of n-heptane and water in the [surface crosslinking step (step 3)], and the amount of water-soluble ethylenically unsaturated monomer M1 (g) contained in the aqueous liquid used in the production of hydrous gel particles in the [hydrous gel particle production step (step 1)].
  • the sieve was tilted at an angle of about 30 degrees to the horizontal and left for 30 minutes to filter out excess water.
  • ⁇ Saline water retention capacity> A cotton bag (membrane broad 60, 100 mm wide x 200 mm long) containing 2.0 g of water-absorbent resin particles was placed in a 500 mL beaker. 500 g of 0.9% by mass sodium chloride aqueous solution (physiological saline) was poured into the cotton bag containing the water-absorbent resin particles at once so as not to cause any lumps, the top of the cotton bag was tied with a rubber band, and the bag was left to stand for 30 minutes to swell the water-absorbent resin particles.
  • the cotton bag was dehydrated for 1 minute using a dehydrator (manufactured by Kokusan Co., Ltd., product number: H-122) set to a centrifugal force of 167 G, and the mass Wd (g) of the cotton bag containing the swollen gel after dehydration was measured.
  • the same operation was performed without adding the water-absorbent resin particles, the empty mass We (g) of the cotton bag when wet was measured, and the physiological saline water retention was calculated from the following formula.
  • Saline water retention capacity (g/g) [Wd-We]/2.0
  • the measuring device includes a burette part 1, a clamp 3, a conduit 5, a stand 11, a measurement table 13, and a measurement part 4 placed on the measurement table 13.
  • the burette part 1 has a burette tube 21 with a scale, a rubber stopper 23 that seals the opening at the top of the burette tube 21, a cock 22 connected to the tip of the bottom of the burette tube 21, and an air introduction tube 25 and a cock 24 connected to the bottom of the burette tube 21.
  • the burette part 1 is fixed with a clamp 3.
  • the flat measurement table 13 has a through hole 13a with a diameter of 2 mm formed in its center, and is supported by a height-variable stand 11.
  • the through hole 13a of the measurement table 13 and the cock 22 of the burette part 1 are connected by a conduit 5.
  • the inside diameter of the conduit 5 is 6 mm.
  • the measuring section 4 has a Plexiglas cylinder 31, a polyamide mesh 32 adhered to one opening of the cylinder 31, and a weight 33 that can move up and down within the cylinder 31.
  • the cylinder 31 is placed on the measuring table 13 via the polyamide mesh 32.
  • the inner diameter of the cylinder 31 is 20 mm.
  • the opening of the polyamide mesh 32 is 75 ⁇ m (200 mesh).
  • the weight 33 has a diameter of 19 mm and a mass of 119.6 g, and can apply a load of 4.14 kPa (0.6 psi) to the water-absorbent resin particles 10a that are uniformly arranged on the polyamide mesh 32 as described below.
  • the stopcocks 22 and 24 of the burette part 1 were closed, and 0.9% by mass physiological saline adjusted to 25°C was poured into the burette tube 21 through the opening at the top of the burette tube 21.
  • the top opening of the burette tube 21 was sealed with a rubber stopper 23, and then the stopcocks 22 and 24 were opened.
  • the inside of the conduit 5 was filled with 0.9% by mass saline 50 to prevent air bubbles from entering.
  • the height of the measurement table 13 was adjusted so that the height of the water surface of the 0.9% by mass saline solution 50 that reached the through hole 13a was the same as the height of the upper surface of the measurement table 13. After the adjustment, the height of the water surface of the 0.9% by mass saline solution 50 in the burette tube 21 was read on the scale of the burette tube 21, and this position was set as the zero point (the reading at 0 seconds).
  • a test for coloring of the water-absorbent resin particles over time was carried out as follows. That is, 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, and the container was stored for a specified number of days (7 days or 14 days) in a thermostatic chamber (Espec Corp., LHU-113) set at a temperature of 70 ⁇ 2°C and a relative humidity of 90 ⁇ 2%. Thereafter, the container was removed from the thermostatic chamber and left to cool to room temperature for a while.
  • a thermostatic chamber Espec Corp., LHU-113
  • the entire amount of water-absorbent resin particles in a glass measuring container with an inner diameter of 3 cm was placed in the container, and the yellowness of the water-absorbent resin particles was measured with a color difference meter (Color Meter ZE6000, Nippon Denshoku Industries Co., Ltd.). The yellowness was calculated from the X, Y, and Z (tristimulus values) of the obtained water-absorbent resin particles using the following formula.
  • the gel strength at each temperature and after the rest time was measured using an apparatus having the measurement principle shown in FIG. 2.
  • the apparatus shown in FIG. 2 is composed of a support part 50a, a movable base plate 60, a drive part 70 for driving the movable base plate 60, and a measurement part 80.
  • a stand 53 is fixed to the upper part of a support 52 erected on a support stand 51.
  • the movable base plate 60 is attached to the support 52 so as to move up and down.
  • the movable base plate 60 can be loaded with a measurement sample (gel) 61.
  • a pulse motor 71 is mounted on the stand 53, and the movable base plate 60 is moved up and down via a wire 73 by rotating a pulley 72.
  • a pressure-sensitive shaft 84 with a disk is attached to a load cell 81 for measuring the strain caused by deformation via a precision spring 82 and a connecting shaft 83.
  • the pressure-sensitive shaft 84 with a disk has a disk at its tip. The diameter of the disk can be changed depending on the measurement conditions.
  • a weight 90 can be mounted on the top of the pressure-sensitive shaft 84 with a disk.
  • the operating principle of the device for measuring gel strength is as follows.
  • a precision spring 82 is fixed to a load cell 81 (stress detector) above, and the pressure-sensitive shaft 84 with a disk is connected to the bottom and suspended vertically with a predetermined weight 90 placed on it.
  • the movable base plate 60 with the measurement sample 61 placed on it rises at a constant speed due to the rotation of the pulse motor 71.
  • a constant-speed load is applied to the measurement sample 61 via the precision spring 82, and the strain caused by deformation is measured by the load cell 81, and the hardness is measured and calculated.
  • the gel strength value (N/ m2 ) was measured using a Curdmeter-MAX (Asuka Kikai, product number: ME-500) with a disk of 16 mm diameter for the pressure-sensitive shaft 84 with a disk, a load of 400 g, a speed of 7 seconds/inch, and viscous mode settings under the following temperature and standing time conditions: (initial gel strength) and (gel strength after standing at 37°C for 14 hours).
  • thermohygrostat Espec Corp., LHU-113 set at a temperature of 37 ⁇ 2°C and a relative humidity of 60 ⁇ 10%, after which the plastic wrap was removed from the beaker containing the swollen gel, and the gel strength was measured by the method described above. The gel strength value at this time was taken as the gel strength (14-hour value).

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PCT/JP2023/035291 2022-09-29 2023-09-27 吸水性樹脂粒子の製造方法 Ceased WO2024071258A1 (ja)

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US19/103,671 US20260061393A1 (en) 2022-09-29 2023-09-27 Method for producing water-absorbent resin particles
CN202380058155.8A CN119677785A (zh) 2022-09-29 2023-09-27 吸水性树脂颗粒的制造方法
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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2026028880A1 (ja) * 2024-08-02 2026-02-05 住友精化株式会社 吸水性樹脂粒子の製造方法
WO2026034250A1 (ja) * 2024-08-09 2026-02-12 住友精化株式会社 吸水性樹脂粒子の製造方法

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2005029751A (ja) 2003-07-11 2005-02-03 Sumitomo Seika Chem Co Ltd 吸水性樹脂組成物
WO2011040530A1 (ja) * 2009-09-30 2011-04-07 株式会社日本触媒 粒子状吸水剤及びその製造方法
JP2018131558A (ja) * 2017-02-16 2018-08-23 Ｓｄｐグローバル株式会社 吸水性樹脂粒子及びその製造方法
WO2021006178A1 (ja) * 2019-07-05 2021-01-14 住友精化株式会社 粒子状吸水性樹脂組成物

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2005029751A (ja) 2003-07-11 2005-02-03 Sumitomo Seika Chem Co Ltd 吸水性樹脂組成物
WO2011040530A1 (ja) * 2009-09-30 2011-04-07 株式会社日本触媒 粒子状吸水剤及びその製造方法
JP2018131558A (ja) * 2017-02-16 2018-08-23 Ｓｄｐグローバル株式会社 吸水性樹脂粒子及びその製造方法
WO2021006178A1 (ja) * 2019-07-05 2021-01-14 住友精化株式会社 粒子状吸水性樹脂組成物

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2026028880A1 (ja) * 2024-08-02 2026-02-05 住友精化株式会社 吸水性樹脂粒子の製造方法
WO2026034250A1 (ja) * 2024-08-09 2026-02-12 住友精化株式会社 吸水性樹脂粒子の製造方法

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CN119677785A (zh) 2025-03-21
JPWO2024071258A1 (https=) 2024-04-04
US20260061393A1 (en) 2026-03-05
EP4600273A1 (en) 2025-08-13
TW202424065A (zh) 2024-06-16
KR20250078427A (ko) 2025-06-02

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