WO2024214752A1 - 吸水性樹脂粒子の製造方法、吸水性樹脂粒子、吸収体及び吸収性物品 - Google Patents

吸水性樹脂粒子の製造方法、吸水性樹脂粒子、吸収体及び吸収性物品 Download PDF

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WO2024214752A1
WO2024214752A1 PCT/JP2024/014596 JP2024014596W WO2024214752A1 WO 2024214752 A1 WO2024214752 A1 WO 2024214752A1 JP 2024014596 W JP2024014596 W JP 2024014596W WO 2024214752 A1 WO2024214752 A1 WO 2024214752A1
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Prior art keywords
water
resin particles
absorbent resin
polymerization
ethylenically unsaturated
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French (fr)
Japanese (ja)
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翠 飯島
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Sumitomo Seika Chemicals Co Ltd
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Sumitomo Seika Chemicals Co Ltd
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Priority to EP24788775.5A priority Critical patent/EP4696719A1/en
Priority to CN202480025393.3A priority patent/CN121002072A/zh
Priority to JP2025513989A priority patent/JPWO2024214752A1/ja
Priority to KR1020257036681A priority patent/KR20250172608A/ko
Publication of WO2024214752A1 publication Critical patent/WO2024214752A1/ja
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    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F2/00—Processes of polymerisation
    • C08F2/12—Polymerisation in non-solvents
    • C08F2/14—Organic medium
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F2/00—Processes of polymerisation
    • C08F2/12—Polymerisation in non-solvents
    • C08F2/16—Aqueous medium
    • C08F2/18—Suspension polymerisation
    • C08F2/20—Suspension polymerisation with the aid of macromolecular dispersing agents
    • 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
    • C08J3/24—Crosslinking, e.g. vulcanising, of macromolecules
    • 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
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L33/00—Compositions 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; Compositions of derivatives of such polymers
    • C08L33/02—Homopolymers or copolymers of acids; Metal 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
    • 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, water-absorbent resin particles, absorbents, and absorbent articles, and more specifically to a method for producing water-absorbent resin that constitutes an absorbent suitable for use in sanitary materials such as disposable diapers, sanitary napkins, and incontinence pads, water-absorbent resin particles, absorbents that use the water-absorbent resin particles, and absorbent articles.
  • water-absorbent resins have been widely used in sanitary materials such as disposable diapers, sanitary napkins, and incontinence pads.
  • cross-linked polymers of water-soluble ethylenically unsaturated monomers more specifically cross-linked polymers of partially neutralized polyacrylic acid
  • have excellent water absorption capabilities and since 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, and are therefore considered to be preferred water-absorbent resin particles (see, for example, Patent Document 1).
  • Absorbent articles such as disposable diapers, sanitary napkins, and incontinence pads are mainly composed of an absorbent body located in the center that absorbs and retains bodily fluids such as urine and menstrual blood excreted from the body, a liquid-permeable surface sheet (top sheet) located on the side that comes into contact with the body, and a liquid-impermeable back sheet (back sheet) located on the opposite side that comes into contact with the body.
  • the absorbent body is usually composed of hydrophilic fibers such as pulp and water-absorbent resin particles.
  • the water-absorbent resin particles contained in the absorbent are required to have a higher water retention capacity.
  • water-absorbent resin particles with a high water retention capacity in an absorbent article it is possible to reduce the amount of water-absorbent resin particles and the amount of hydrophilic fibers such as pulp used in the absorbent article from the viewpoint of maintaining the water retention capacity of the entire absorbent article, for example, but this may reduce other performance properties of the absorbent article (for example, permeation speed, backflow, liquid leakage). Therefore, by improving the absorption performance of the water-absorbent resin particles, it is possible to reduce the amount of water-absorbent resin particles and the amount of hydrophilic fibers such as pulp used in the absorbent article while maintaining the performance of the absorbent article.
  • the inventors of the present invention focused on the saline water retention capacity, saline water absorption capacity under a load of 4.14 kPa, and the 5-minute value of unpressurized Demand Wetability (hereinafter, unpressurized DW) from the viewpoint of improving the absorption performance of water-absorbent resin particles used in absorbent articles.
  • the main object of the present invention is to provide a new method for producing water-absorbent resin particles that can produce water-absorbent resin particles with excellent high absorption performance (particularly, saline water retention capacity, saline water absorption capacity under a load of 4.14 kPa, and 5-minute value of unpressurized DW). Furthermore, the present invention also aims to provide water-absorbent resin particles with excellent high absorption performance (particularly, saline water retention capacity, saline water absorption capacity under a load of 4.14 kPa, and 5-minute value of unpressurized DW), and absorbents and absorbent articles that utilize the water-absorbent resin particles.
  • the present inventors have conducted intensive research to solve the above problems. As a result, they have found that in a method for producing water-absorbent resin particles by reverse-phase suspension polymerization of a water-soluble ethylenically unsaturated monomer using a radical polymerization initiator, an azo-based compound is used as the radical polymerization initiator, reverse-phase suspension polymerization is performed in two or more stages, and the amount of the internal crosslinking agent used in the first stage polymerization, the amount of the internal crosslinking agent used in the second stage polymerization, and the amount of the azo-based compound used in the second stage polymerization are set within a predetermined range, and a surface crosslinking step is provided after polymerization, thereby obtaining water-absorbent resin particles with excellent absorption performance (particularly, saline water retention capacity, saline water absorption capacity under a load of 4.14 kPa, and 5-minute value of unpressurized DW).
  • the present invention is an invention that has
  • a method for producing water-absorbing resin particles by inverse suspension polymerization of a water-soluble ethylenically unsaturated monomer using a radical polymerization initiator comprising: At least one of the radical polymerization initiators is an azo compound,
  • the reverse phase suspension polymerization comprises two or more polymerization stages, In the first stage polymerization step, (a) using 0.01 mmol or more and 0.11 mmol or less of an internal crosslinking agent per 1 mole of the water-soluble ethylenically unsaturated monomer used in the first-stage polymerization, In the second stage polymerization step, (b) using 0 mmol or more and 0.042 mmol or less of an internal crosslinking agent per 1 mole of the water-soluble ethylenically unsaturated monomer used in the second-stage polymerization, (c) using 0.38 millimoles or less of an azo compound per mole of the water-soluble eth
  • the primary particles obtained in the first polymerization step have a storage modulus of a gel swollen 40 times with ion-exchanged water of 10 Pa or more and 200 Pa or less; Item 2.
  • a water-absorbing resin particle which is a crosslinked product of a polymer of a water-soluble ethylenically unsaturated monomer The water-absorbent resin particles have the following characteristics (A) to (C):
  • C) The 5-minute value of the unpressurized DW is 50 mL/g or more and 80 mL/g or less.
  • An absorbent body comprising the water-absorbent resin particles according to item 4.
  • An absorbent article comprising the absorbent body according to item 5.
  • the present invention provides a new method for producing water-absorbent resin particles that can produce water-absorbent resin particles with excellent absorption performance (particularly, saline water retention capacity, saline water absorption capacity under a load of 4.14 kPa, and 5-minute value of unpressurized DW). Furthermore, the present invention can also provide water-absorbent resin particles with excellent absorption performance (particularly, saline water retention capacity, saline water absorption capacity under a load of 4.14 kPa, and 5-minute value of unpressurized DW), as well as absorbents and absorbent articles that utilize the water-absorbent resin particles.
  • FIG. 2 is a schematic diagram of a measuring device used for measuring the pressureless DW of water-absorbent resin particles.
  • FIG. 2 is a schematic diagram of a measuring device used for measuring the amount of physiological saline solution absorbed by water-absorbent resin particles under a load of 4.14 kPa.
  • the term “comprising” includes “consisting essentially of” and “consisting of”.
  • (meth)acrylic means “acrylic or methacrylic”
  • (meth)acrylate means “acrylate or methacrylate”
  • (poly) means with or without the "poly” prefix.
  • water-soluble means exhibiting 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.
  • any lower limit and upper limit may be selected and connected with " ⁇ ".
  • the method for producing water-absorbent resin particles of the present invention is a method for producing water-absorbent resin particles by reverse-phase suspension polymerization of a water-soluble ethylenically unsaturated monomer using a radical polymerization initiator. At least one of the radical polymerization initiators is an azo compound.
  • the reverse-phase suspension polymerization comprises two or more polymerization stages.
  • the method for producing water-absorbent resin particles of the present invention includes a surface crosslinking step after the second and subsequent polymerization steps.
  • the method for producing water-absorbent resin particles of the present invention can suitably produce water-absorbent resin particles with excellent absorption performance (particularly saline water retention capacity, saline water absorption capacity under a load of 4.14 kPa, and 5-minute value of unpressurized DW).
  • the method for producing water-absorbent resin particles of the present invention will be described in detail below.
  • aqueous monomer solution containing a water-soluble ethylenically unsaturated monomer is dispersed in a dispersion medium in the presence of a dispersion stabilizer.
  • the dispersion medium is preferably, for example, a hydrocarbon dispersion medium.
  • the reversed-phase suspension polymerization can be performed in only one polymerization step, but the reversed-phase suspension polymerization in the present invention is performed in two or more polymerization steps. From the viewpoint of enhancing the productivity of water-absorbent resin particles while optimally exerting the effects of the present invention, it is preferable to perform the reversed-phase suspension polymerization in two to three polymerization steps.
  • reversed-phase suspension polymerization after the first polymerization step (first-stage reversed-phase suspension polymerization), a water-soluble ethylenically unsaturated monomer is added to the reaction mixture obtained in the first polymerization step and mixed, and the second and subsequent polymerization steps (first-stage reversed-phase suspension polymerization) can be carried out in the same manner as the first step.
  • reversed-phase suspension polymerization in each step from the second stage onwards it is preferable to carry out reversed-phase suspension polymerization by adding a predetermined amount of a polymerization initiator in addition to the water-soluble ethylenically unsaturated monomer, based on the amount of water-soluble ethylenically unsaturated monomer added during reversed-phase suspension polymerization in each step from the second stage onwards.
  • a polymerization initiator in addition to the water-soluble ethylenically unsaturated monomer, based on the amount of water-soluble ethylenically unsaturated monomer added during reversed-phase suspension polymerization in each step from the second stage onwards.
  • an internal crosslinking agent may be added to the water-soluble ethylenically unsaturated monomer as necessary.
  • a dispersion stabilizer surfactant or polymeric dispersant
  • the dispersion stabilizer can 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.
  • 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.
  • the water-soluble ethylenically unsaturated monomer is polymerized by reversed-phase suspension polymerization using a radical polymerization initiator. Specifically, an aqueous solution containing the water-soluble ethylenically unsaturated monomer, a hydrocarbon dispersion medium, a radical polymerization initiator, and an internal crosslinking agent are mixed to allow the polymerization reaction of the water-soluble ethylenically unsaturated monomer to proceed.
  • water-soluble ethylenically unsaturated monomer examples include (meth)acrylic acid and its salts; 2-(meth)acrylamido-2-methylpropanesulfonic acid and its salts; nonionic monomers such as (meth)acrylamide, N,N-dimethyl(meth)acrylamide, 2-hydroxyethyl(meth)acrylate, N-methylol(meth)acrylamide, and polyethylene glycol mono(meth)acrylate; and amino group-containing unsaturated monomers and quaternized products thereof such as N,N-diethylaminoethyl(meth)acrylate, N,N-diethylaminopropyl(meth)acrylate, and diethylaminopropyl(meth)acrylamide.
  • nonionic monomers such as (meth)acrylamide, N,N-dimethyl(meth)acrylamide, 2-hydroxyethyl(meth)acrylate, N-methylol(meth)acrylamide, and polyethylene
  • water-soluble ethylenically unsaturated monomers from the viewpoint of industrial ease of availability, etc., (meth)acrylic acid or its salts, (meth)acrylamide, and N,N-dimethylacrylamide are preferred, and (meth)acrylic acid and its salts are more preferred.
  • These water-soluble ethylenically unsaturated monomers may be used alone or in combination of two or more.
  • acrylic acid and its salts are widely used as raw materials for water-absorbent resin particles, and these acrylic acids and/or their salts may be copolymerized with the other water-soluble ethylenically unsaturated monomers described above.
  • the content of acrylic acid and its salts in the water-soluble ethylenically unsaturated monomers is 70 to 100 mol %.
  • the proportion of acrylic acid and its salts in the total water-soluble ethylenically unsaturated monomers is 70 to 100 mol %.
  • the water-soluble ethylenically unsaturated monomer is dispersed in a hydrocarbon dispersion medium in the form of an aqueous solution and subjected to reverse phase suspension polymerization.
  • a hydrocarbon dispersion medium in the form of an aqueous solution
  • the concentration of the water-soluble ethylenically unsaturated monomer in this aqueous solution is preferably in the range of 20% by mass to the saturated concentration.
  • the concentration of the water-soluble ethylenically unsaturated monomer during the first-stage polymerization is preferably 55% by mass or less, more preferably 50% by mass or less, and even more preferably 45% by mass or less, from the viewpoint of improving the saline water retention capacity, the saline water absorption capacity under a load of 4.14 kPa, and the 5-minute value of unpressurized DW.
  • the concentration of the water-soluble ethylenically unsaturated monomer is preferably 25% by mass or more, more preferably 30% by mass or more, and even more preferably 35% by mass or more, from the viewpoint of improving the saline water retention capacity, the saline water absorption capacity under a load of 4.14 kPa, and the 5-minute value of unpressurized DW.
  • the concentration of the water-soluble ethylenically unsaturated monomer during the second-stage polymerization is preferably 55% by mass or less, more preferably 50% by mass or less, and even more preferably 45% by mass or less, from the viewpoint of improving the saline water retention capacity, the saline water absorption capacity under a load of 4.14 kPa, and the 5-minute value of unpressurized DW.
  • the concentration of the water-soluble ethylenically unsaturated monomer is preferably 30% by mass or more, more preferably 35% by mass or more, and even more preferably 40% by mass or more, from the viewpoint of improving the saline water retention capacity, the saline water absorption capacity under a load of 4.14 kPa, and the 5-minute value of unpressurized DW.
  • the ratio of the amount of water-soluble ethylenically unsaturated monomer used in the second polymerization stage to the amount of water-soluble ethylenically unsaturated monomer used in the first polymerization stage is preferably 0.1 to 3.0, more preferably 0.5 to 2.5, even more preferably 1.0 to 2.0, and even more preferably 1.3 to 1.5, from the viewpoint of improving the saline water retention capacity, the saline water absorption capacity under a load of 4.14 kPa, and the 5-minute value of the unpressurized DW.
  • the water-soluble ethylenically unsaturated monomer may be used in which the acid group (the acid group of acrylic acid) has been neutralized in advance with an alkaline neutralizing agent, if necessary.
  • alkaline neutralizing agents include alkali metal salts such as sodium hydroxide, sodium carbonate, sodium bicarbonate, potassium hydroxide, and potassium carbonate; and ammonia. These 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 50 to 85 mol%, and even more preferably 70 to 80 mol%, as the degree of neutralization of all acid groups possessed by the water-soluble ethylenically unsaturated monomer, from the viewpoint of improving the saline water retention capacity, the saline water absorption capacity under a load of 4.14 kPa, and the 5-minute value of the unpressurized DW.
  • the polymerization initiator mixed in the polymerization step is a radical polymerization initiator, and at least one of them is an azo compound.
  • the radical polymerization initiator can be an azo compound alone. It is preferable to use an azo compound in combination with a peroxide in order to improve the saline water retention capacity, saline water absorption capacity under a load of 4.14 kPa, and the 5-minute value of unpressurized DW.
  • the azo compound and the peroxide do not necessarily need to coexist at the start of the polymerization reaction; this means that one compound is present while the monomer conversion rate due to radical cleavage of the other compound is less than 10%, but it is preferable that both of them coexist in an aqueous solution containing a water-soluble ethylenically unsaturated monomer before the start of the polymerization reaction.
  • the azo compound and the peroxide may be added to the polymerization reaction system through separate flow paths, or may be added to the polymerization reaction system sequentially through the same flow path.
  • the azo compound and peroxide used may be in the form of a powder or an aqueous solution.
  • peroxides examples include persulfates such as potassium persulfate, ammonium persulfate, and sodium persulfate, and 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.
  • potassium persulfate, ammonium persulfate, and sodium persulfate are preferred from the viewpoints of ease of availability and handling.
  • the amount of peroxide used in the first-stage polymerization is preferably 0.001 to 1.0 mmol per mole of water-soluble ethylenically unsaturated monomer used in the first-stage polymerization, from the viewpoint of improving the saline water retention capacity, saline water absorption capacity under a load of 4.14 kPa, and the 5-minute value of the unpressurized DW, and is more preferably 0.01 to 0.50 mmol, even more preferably 0.05 to 0.30 mmol, and even more preferably 0.075 to 0.15 mmol.
  • the amount of peroxide used in the second polymerization step is preferably 0.001 to 1.0 mmol per mole of water-soluble ethylenically unsaturated monomer used in the second polymerization step, from the viewpoint of improving the saline water retention capacity, saline water absorption capacity under a load of 4.14 kPa, and the 5-minute value of the unpressurized DW.
  • examples of azo compounds include 2,2'-azobis(2-amidinopropane) dihydrochloride, 2,2'-azobis[2-(N-phenylamidino)propane] dihydrochloride, 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).
  • 2,2'-azobis(2-amidinopropane) dihydrochloride is preferred because it is easily available and easy to handle.
  • the amount of the azo compound used in the first polymerization step is preferably 0 to 1.0 mmol per mole of the water-soluble ethylenically unsaturated monomer used in the first polymerization step, from the viewpoint of improving the saline water retention capacity, saline water absorption capacity under a load of 4.14 kPa, and the 5-minute value of the unpressurized DW.
  • the amount of the azo compound used in the second-stage polymerization is preferably 0 to 0.35 millimoles, more preferably 0.05 to 0.35 millimoles, and even more preferably 0.10 to 0.35 millimoles, per mole of the water-soluble ethylenically unsaturated monomer used in the second-stage polymerization.
  • the 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.
  • a reducing agent such as sodium sulfite, sodium hydrogen sulfite, ferrous sulfate, or L-ascorbic acid.
  • the molar ratio of peroxide to azo compound (peroxide/azo compound) during the first polymerization step is preferably in the range of 0.1 to 1.0, more preferably in the range of 0.2 to 0.5, and even more preferably in the range of 0.3 to 0.4.
  • the molar ratio of peroxide to azo compound (peroxide/azo compound) during the second polymerization step is preferably in the range of 0.1 to 1.5, more preferably in the range of 0.2 to 1.0, and even more preferably in the range of 0.3 to 0.7.
  • the internal crosslinking agent may be one capable of crosslinking a polymer of a water-soluble ethylenically unsaturated monomer used, and examples of the internal crosslinking agent include unsaturated polyesters obtained by reacting polyols such as diols and triols, such as (poly)ethylene glycol, (poly)propylene glycol, 1,4-butanediol, trimethylolpropane, and (poly)glycerin, with unsaturated acids, such as (meth)acrylic acid, maleic acid, and fumaric acid; bisacrylamides such as N,N-methylenebisacrylamide; di(meth)acrylic acid esters or tri(meth)acrylic acid esters obtained by reacting polyepoxides with (meth)acrylic acid; di(meth)acrylic acid carbamyl esters obtained by reacting polyisocyanates, such as tolylene diisocyanate and hexamethylene diiso
  • these internal crosslinking agents it is preferable to use unsaturated polyesters or polyglycidyl compounds, it is more preferable to use diglycidyl ether compounds, and it is preferable to use (poly)ethylene glycol diglycidyl ether, (poly)propylene glycol diglycidyl ether, or (poly)glycerin diglycidyl ether.
  • These internal crosslinking agents may be used alone or in combination of two or more kinds.
  • the amount of the internal crosslinking agent used in the first-stage polymerization is preferably 0.02 to 0.09 millimoles, more preferably 0.03 to 0.075 millimoles, and even more preferably 0.04 to 0.06 millimoles, per mole of the water-soluble ethylenically unsaturated monomer used in the first-stage polymerization.
  • an internal crosslinking agent is used in an amount of 0 to 0.042 millimoles per mole of the water-soluble ethylenically unsaturated monomer used in the second-stage polymerization.
  • the amount of the internal crosslinking agent used in the second-stage polymerization is preferably 0 to 0.038 millimoles, more preferably 0 to 0.032 millimoles, even more preferably 0 to 0.030 millimoles, and particularly preferably 0 to 0.025 millimoles, per mole of the water-soluble ethylenically unsaturated monomer used in the second-stage polymerization.
  • 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, more preferably 150 to 1000 parts by mass, even more preferably 200 to 500 parts by mass, and even more preferably 300 to 400 parts by mass, per 100 parts by mass of the first-stage water-soluble ethylenically unsaturated monomer, from the viewpoint of uniformly dispersing the water-soluble ethylenically unsaturated monomer and facilitating control of the polymerization temperature.
  • Dispersion stabilizer (Surfactant)
  • a dispersion stabilizer can be used as necessary to improve the dispersion stability of the water-soluble ethylenically unsaturated monomer in the hydrocarbon dispersion medium.
  • a surfactant can be used as the dispersion stabilizer.
  • Surfactants that can be used include, for example, sucrose fatty acid esters, 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, more preferably 0.3 to 10 parts by mass, even more preferably 0.5 to 1 part by mass, and even more preferably 0.6 to 0.9 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, and ethylhydroxyethyl cellulose.
  • 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, more preferably 0.3 to 10 parts by mass, even more preferably 0.5 to 1 part by mass, and even more preferably 0.6 to 0.9 parts by mass, per 100 parts by mass of the first stage water-soluble ethylenically unsaturated monomer.
  • a thickener may be added to an aqueous solution containing a water-soluble ethylenically unsaturated monomer before carrying out reverse suspension polymerization.
  • a thickener By adjusting the viscosity of the aqueous solution by adding a thickener in this manner, it is possible to control the median particle size obtained in the 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.
  • the polymerization of a water-soluble ethylenically unsaturated monomer may be carried out in the presence of a chain transfer agent.
  • chain transfer agents include thiols such as ethanethiol, propanethiol, and dodecanethiol; thiolic acids such as thioglycolic acid, thiomalic acid, dimethyldithiocarbamic acid, diethyldithiocarbamic acid, and salts thereof; secondary alcohols such as isopropanol; phosphite compounds such as phosphorous acid, normal salts of phosphorous acid such as disodium phosphite, dipotassium phosphite, and diammonium phosphite, and acidic salts of phosphorous acid such as sodium hydrogen phosphite, potassium hydrogen phosphite, and ammonium hydrogen phosphite; phosphate compounds such as normal salts of phosphoric acid such as phosphoric acid, sodium phosphate, potassium phosphate, and ammonium phosphate, and acidic salts of phosphoric acid such as sodium dihydrogen phosphat
  • the amount of chain transfer agent used in the second polymerization step is preferably 0 to 0.0005 mol, more preferably 0 to 0.0003 mol, even more preferably 0 to 0.0002 mol, and even more preferably 0 to 0.0001 mol per mol of water-soluble ethylenically unsaturated monomer, from the viewpoint of improving the saline water retention capacity, saline water absorption capacity under a load of 4.14 kPa, and the 5-minute value of the unpressurized DW.
  • the inventor of the present invention focused on the saline water retention capacity, saline water absorption capacity under a load of 4.14 kPa, and the 5-minute value of the non-pressurized DW from the viewpoint of improving the absorption performance of the water-absorbent resin particles used in absorbent articles.
  • the 5-minute value of the non-pressurized DW it is necessary to increase the surface area of the water-absorbent resin particles.
  • the inventor of the present invention has found that in a method of manufacturing water-absorbent resin particles by inverse suspension polymerization of a water-soluble ethylenically unsaturated monomer, the inverse suspension polymerization is carried out in two or more polymerization steps, the storage modulus of the primary particles obtained in the first polymerization step is increased, and the aggregation of the secondary particles obtained in the second and subsequent polymerization steps is suppressed, thereby increasing the surface area of the water-absorbent resin particles obtained by surface-crosslinking the secondary particles, and increasing the 5-minute value of the non-pressurized DW.
  • the storage modulus of the gel swollen 40 times with ion-exchanged water of the primary particles obtained in the first polymerization step is preferably set to a range of 10 Pa or more and 200 Pa or less.
  • the storage modulus is preferably 10 Pa or more, more preferably 15 Pa or more, and even more preferably 20 Pa or more.
  • the storage modulus is preferably 200 Pa or less, more preferably 150 Pa or less, and even more preferably 100 Pa or less.
  • the storage modulus is preferably in the range of 15 to 150 Pa, and more preferably in the range of about 20 to 100 Pa.
  • the storage modulus can be adjusted, for example, in the first polymerization step by adjusting the amount of the internal crosslinking agent used, the concentration of the water-soluble ethylenically unsaturated monomer, the degree of neutralization of the water-soluble ethylenically unsaturated monomer, the amount of the polymerization initiator used, etc.
  • the storage modulus is the storage modulus measured in a 25°C environment using a stress-controlled rheometer for the primary particles obtained in the first polymerization step, which are dried and then swollen 40 times with ion-exchanged water to form a 40-fold swollen gel.
  • the specific measurement of the storage modulus is performed by the measurement method described in the Examples.
  • the secondary particles obtained in the second or subsequent polymerization steps preferably have a storage modulus of a gel swollen 40 times with ion-exchanged water set to a range of 5 Pa or more and 200 Pa or less.
  • the storage modulus is preferably 5 Pa or more, more preferably 20 Pa or more, even more preferably 30 Pa or more, and is preferably 200 Pa or less, more preferably 190 Pa or less, even more preferably 170 Pa or less, even more preferably 150 Pa or less, and particularly preferably 100 Pa or less, with preferred ranges being 20 to 190 Pa, more preferably 20 to 170 Pa, even more preferably 30 to 150 Pa, and even more preferably about 30 to 100 Pa.
  • the storage modulus can be adjusted, for example, in the second and subsequent polymerization steps by adjusting the amount of the internal crosslinking agent used, the concentration of the water-soluble ethylenically unsaturated monomer, the ratio of the amount of the water-soluble ethylenically unsaturated monomer used in the second polymerization step to the amount of the water-soluble ethylenically unsaturated monomer used in the first polymerization step, the degree of neutralization of the water-soluble ethylenically unsaturated monomer, the amount of the polymerization initiator used, the amount of the chain transfer agent used, etc.
  • the storage modulus is the storage modulus measured in a 25°C environment using a stress-controlled rheometer for the secondary particles obtained in the second polymerization step, which are dried and then swollen 40 times with ion-exchanged water to form a 40-fold swollen gel.
  • the specific measurement of the storage modulus is performed by the measurement method described in the Examples.
  • the ratio of the storage modulus of the secondary particles to the storage modulus of the primary particles is preferably 10 times or less, more preferably 5 times or less, and even more preferably 3 times or less, with a preferred range being 0.1 to 5 times, and a more preferred range being 0.5 to 3 times, etc.
  • the inventor of the present invention has found that in a method for producing water-absorbent resin particles by inverse suspension polymerization of a water-soluble ethylenically unsaturated monomer, the inverse suspension polymerization is carried out in two or more polymerization steps, the storage modulus of the primary particles obtained in the first polymerization step is increased, and the aggregation of the secondary particles obtained in the second and subsequent polymerization steps is suppressed, thereby increasing the surface area of the water-absorbent resin particles obtained by surface-crosslinking the secondary particles, and increasing the 5-minute value of the non-pressurized DW.
  • the degree of internal crosslinking formed during the second and subsequent polymerization stages is lowered, thereby lowering the storage modulus of the secondary particles before being subjected to surface crosslinking, and increasing the contribution of surface crosslinking, which is considered to result in water-absorbent resin particles that are excellent in the properties of saline water retention capacity, saline water absorption capacity under a load of 4.14 kPa, and 5-minute value of unpressurized DW.
  • the surface crosslinking process is a process for polymerizing a water-soluble ethylenically unsaturated monomer in the second or subsequent polymerization steps of reversed-phase suspension polymerization to form secondary particles (a hydrogel-like substance having an internal crosslinking structure).
  • the water-absorbent resin particles of the present invention are produced by mixing the secondary particles obtained in the polymerization step with a surface cross-linking agent and cross-linking the secondary particles (surface cross-linking reaction). This surface crosslinking reaction is preferably carried out in the presence of a surface crosslinking agent after the polymerization of the water-soluble ethylenically unsaturated monomer.
  • the molar ratio of the surface cross-linking agent to the water-soluble ethylenically unsaturated monomer is preferably in the range of 0.00001 to 0.001, more preferably in the range of 0.00005 to 0.00080, even more preferably in the range of 0.00010 to 0.00060, and even more preferably in the range of 0.00020 to 0.00040.
  • 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, 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
  • polyglycidyl compounds such as (poly)ethylene glycol diglycidyl ether, (poly)glycerin diglycidyl ether, (poly)glycerin triglycidyl ether, trimethylolpropane triglycidyl ether, (poly)propylene glycol polyglycidyl ether, and (poly)glycerol polyglycidyl ether are preferred.
  • These surface cross-linking agents may be used alone or in combination of two or more.
  • the 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 timing of adding the surface cross-linking agent may be after the polymerization reaction of the water-soluble ethylenically unsaturated monomer has been almost completely completed. It is preferable to add the agent in the presence of moisture in the range of 1 to 400 parts by mass, more preferably in the range of 5 to 100 parts by mass, even more preferably in the range of 10 to 50 parts by mass, and even more preferably in the range of 15 to 35 parts by mass, relative to 100 parts by mass of the water-soluble ethylenically unsaturated monomer.
  • the amount of moisture means the total amount of moisture contained in the reaction system and the moisture used as necessary when adding the surface cross-linking agent.
  • 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.
  • a drying step may be included in which water, the hydrocarbon dispersion medium, and the like are removed by distillation by adding energy such as heat from the outside.
  • the system in which the hydrogel is dispersed in the hydrocarbon dispersion medium is heated, and the water and the hydrocarbon dispersion medium are once distilled out of 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 water-absorbent resin particles.
  • 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 obtained by the manufacturing method of the present invention may contain additives according to the purpose.
  • additives include inorganic powders, surfactants, oxidizing agents, reducing agents, metal chelating agents, radical chain inhibitors, antioxidants, antibacterial agents, and the like.
  • inorganic powders may be used to further improve the fluidity of the water-absorbent resin particles.
  • the amount of inorganic powder used is preferably in the range of 0.01 to 5 parts by mass, more preferably 0.1 to 1 part by mass, per 100 parts by mass of the water-absorbent resin particles.
  • Water-absorbent resin particles Among the above-mentioned methods for producing water-absorbent resin particles of the present invention, by adopting preferable conditions from the viewpoint of improving the physiological saline water retention capacity, the physiological saline water absorption capacity under a load of 4.14 kPa, and the 5-minute value of non-pressurized DW, it becomes possible to suitably produce water-absorbent resin particles having, for example, the following properties (A) to (C). For example, in the method for producing water-absorbent resin particles, it is preferable to satisfy the preferable storage moduli in the first and second stages described above.
  • the saline water retention capacity is 50 g/g or more and 80 g/g or less.
  • the physiological saline water absorption amount under a load of 4.14 kPa is 15 g/g or more and 40 g/g or less.
  • the 5-minute value of the unpressurized DW is 50 mL/g or more and 80 mL/g or less.
  • the saline water retention capacity (A) of the water-absorbent resin particles of the present invention is preferably 50 g/g or more, and is preferably 80 g/g or less, more preferably 70 g/g or less, and even more preferably 60 g/g or less, with a preferred range being 50 to 70 g/g, and a more preferred range being 50 to 60 g/g, etc.
  • the physiological saline water absorption amount of the water-absorbent resin particles of the present invention under a load of 4.14 kPa is preferably 15 g/g or more, more preferably 17 g/g or more, even more preferably 19 g/g or more, and is preferably 29 g/g or less, more preferably 27 g/g or less, even more preferably 25 g/g or less, and even more preferably 23 g/g or less, with a preferred range being 15 to 29 g/g, and a more preferred range being 17 to 25 g/g, etc.
  • the 5-minute value of the non-pressurized DW of (C) of the present invention is preferably 50 mL/g or more, more preferably 53 mL/g or more, even more preferably 55 mL/g or more, and particularly preferably 58 mL/g or more, and is preferably 78 mL/g or less, more preferably 73 mL/g or less, and even more preferably 68 mL/g or less, with a preferred range being 50 to 78 mL/g, and a more preferred range being 58 to 68 mL/g, etc.
  • the saline water retention capacity of the water-absorbent resin particles, the saline water absorption capacity under a load of 4.14 kPa, and the 5-minute value of the unpressurized DW were measured using the measurement methods described in the Examples.
  • the saline water absorption of the water-absorbent resin particles is preferably in the following ranges.
  • the saline water absorption is, for example, preferably 30 g/g or more, 35 g/g or more, 40 g/g or more, 45 g/g or more, 50 g/g or more, 55 g/g or more, or 60 g/g or more.
  • the saline water absorption is, for example, preferably 90 g/g or less, 85 g/g or less, 80 g/g or less, or 75 g/g or less.
  • the saline water absorption is preferably 30 to 90 g/g, more preferably 40 to 80 g/g, and even more preferably 60 to 75 g/g. The method for measuring the saline water absorption will be described in detail in the examples below.
  • the water absorption rate of the water-absorbent resin particles for physiological saline is preferably in the following ranges.
  • the water absorption rate is preferably 70 seconds or less, 60 seconds or less, 50 seconds or less, 45 seconds or less, or 40 seconds or less.
  • the water absorption rate is preferably 20 seconds or more, 25 seconds or more, or 30 seconds or more.
  • the water absorption rate is preferably 20 to 70 seconds, more preferably 25 to 60 seconds, and even more preferably 30 to 50 seconds.
  • the water absorption rate can be measured at room temperature (25 ⁇ 2°C). The method for measuring the water absorption rate will be described in detail in the examples below.
  • the water-absorbent resin particles of the present invention are composed of a crosslinked polymer of a water-soluble ethylenically unsaturated monomer, i.e., a crosslinked polymer having structural units derived from a water-soluble ethylenically unsaturated monomer.
  • the water-absorbent resin particles of the present invention are in the form of an aggregate (secondary particles) of fine particles (primary particles).
  • Examples of the shape of the primary particles include substantially spherical, irregularly crushed, and plate-like shapes.
  • the water-absorbent resin particles of the present invention, which are secondary particles may have various shapes. Examples of the shape of the water-absorbent resin particles include granular, substantially spherical, irregularly crushed, plate-like, fibrous, flake-like shapes, and shapes in which these resins are aggregated.
  • the water-absorbent resin particles are preferably granular, substantially spherical, irregularly crushed, fibrous, and shapes in which these resins are aggregated.
  • the median particle diameter of the water-absorbent resin particles is preferably 200 ⁇ m or more, 250 ⁇ m or more, 280 ⁇ m or more, 300 ⁇ m or more, or 320 ⁇ m or more. From the same viewpoint, the median particle diameter is preferably 700 ⁇ m or less, 600 ⁇ m or less, 550 ⁇ m or less, 500 ⁇ m or less, 450 ⁇ m or less, or 400 ⁇ m or less. In other words, the median particle diameter is preferably 200 to 700 ⁇ m, preferably 200 to 600 ⁇ m, more preferably 250 to 500 ⁇ m, even more preferably 300 to 450 ⁇ m, and even more preferably 320 to 400 ⁇ m.
  • the median particle diameter of the water-absorbent resin particles can be measured using a JIS standard sieve, and specifically, is a value measured by the method described in the examples.
  • 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 of the present invention includes the water-absorbent resin particles of the present invention.
  • the absorbent may further include hydrophilic fibers.
  • Examples of 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 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 also contain other components, such as adhesive binders such as heat-fusible synthetic fibers, hot melt adhesives, and adhesive emulsions to improve the shape retention of the absorbent.
  • the basis weight of the water-absorbent resin particles in the absorbent body of the present invention is 50 g/ m2 or more and 400 g/m2 or less.
  • the basis weight is preferably 100 g/ m2 or more, more preferably 120 g/ m2 or more, even more preferably 140 g/m2 or more , and is preferably 300 g/m2 or less , more preferably 250 g/m2 or less , even more preferably 200 g/m2 or less .
  • the hydrophilic fiber may be at least one selected from the group consisting of finely ground wood pulp, cotton, cotton linters, rayon, cellulose acetate, polyamide, polyester, and polyolefin.
  • Examples include cellulose fibers such as cotton-like pulp obtained from wood, mechanical pulp, chemical pulp, and semi-chemical pulp, artificial cellulose fibers such as rayon and acetate, and fibers made of synthetic resins such as polyamide, polyester, and polyolefin that have been hydrophilically treated.
  • the average fiber length of the hydrophilic fiber is usually 0.1 to 10 mm, or may be 0.5 to 5 mm.
  • the basis weight of the hydrophilic fibers in the absorbent of the present invention is 50 g/m2 or more and 800 g/m2 or less.
  • the basis weight is preferably 100 g/m2 or more , more preferably 120 g/m2 or more , even more preferably 140 g/m2 or more , and is preferably 700 g/ m2 or less, more preferably 600 g/m2 or less , even more preferably 500 g/m2 or less.
  • the content of water-absorbent resin particles in the absorbent is preferably 5 to 100% by mass, more preferably 10 to 95% by mass, even more preferably 20 to 90% by mass, and even more preferably 30 to 80% by mass.
  • the absorbent article of the present invention can be 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 of the air-through type, spunbond type, chemical bond type, needle punch type, etc., made of fibers such as polyethylene, polypropylene, polyester, etc., and porous synthetic resin sheets.
  • Liquid-impermeable sheets include synthetic resin films made of resins such as polyethylene, polypropylene, polyvinyl chloride, etc.
  • the liquid-permeable sheet is preferably at least one type selected from the group consisting of thermal-bonded nonwoven fabrics, air-through nonwoven fabrics, spunbonded nonwoven fabrics, and spunbonded/meltblown/spunbonded nonwoven fabrics.
  • the basis weight of the liquid-permeable sheet is preferably 5 g/m2 or more and 100 g/m2 or less, and more preferably 10 g/m2 or more and 60 g/m2 or less .
  • the liquid-permeable sheet may be embossed or perforated on the surface in order to improve the liquid diffusibility.
  • the embossing or perforation can be performed by a known method.
  • liquid-impermeable sheet examples include sheets made of synthetic resins such as polyethylene, polypropylene, and polyvinyl chloride, sheets made of nonwoven fabrics such as spunbond/meltblown/spunbond (SMS) nonwoven fabrics in which a water-resistant meltblown nonwoven fabric is sandwiched between high-strength spunbond nonwoven fabrics, and sheets made of composite materials of these synthetic resins and nonwoven fabrics (e.g., spunbond nonwoven fabrics, spunlace nonwoven fabrics).
  • SMS spunbond/meltblown/spunbond
  • composite materials of these synthetic resins and nonwoven fabrics e.g., spunbond nonwoven fabrics, spunlace nonwoven fabrics.
  • LDPE low-density polyethylene
  • the liquid-impermeable sheet may be, for example, a sheet made of a synthetic resin having a basis weight of 10 to 50 g/m 2 .
  • the absorbent article preferably has a laminate having an absorbent body containing water-absorbent resin particles and core wraps sandwiching the absorbent body from above and below, a liquid-permeable sheet disposed on the upper surface of the laminate, and a liquid-impermeable sheet disposed on the surface of the laminate opposite the liquid-permeable sheet side.
  • a method for producing water-absorbent resin particles by inverse suspension polymerization of a water-soluble ethylenically unsaturated monomer using a radical polymerization initiator comprising the steps of: At least one of the radical polymerization initiators is an azo compound,
  • the reverse phase suspension polymerization comprises two or more polymerization stages, In the first stage polymerization step, (a) using 0.01 mmol or more and 0.11 mmol or less of an internal crosslinking agent per 1 mole of the water-soluble ethylenically unsaturated monomer used in the first-stage polymerization, In the second stage polymerization step, (b) using 0 mmol or more and 0.042 mmol or less of an internal crosslinking agent per 1 mole of the water-soluble ethylenically unsaturated monomer used in the second-stage polymerization, (c) using 0.38 millimoles or less of an
  • the amount of the internal crosslinking agent used is 0.01 to 0.11 mmol, 0.02 to 0.09 mmol, 0.03 to 0.075 mmol, or 0.04 to 0.06 mmol, relative to 1 mol of the water-soluble ethylenically unsaturated monomer used in the first-stage polymerization.
  • the primary particles obtained in the first polymerization step have a storage modulus of a gel swollen 40 times with ion-exchanged water of 10 Pa or more and 200 Pa or less;
  • a water-absorbent resin particle which is a crosslinked product of a polymer of a water-soluble ethylenically unsaturated monomer,
  • the water-absorbent resin particles have the following characteristics (A) to (C):
  • (A) The saline water retention capacity is 50 g/g or more and 80 g/g or less.
  • the physiological saline water absorption amount under a load of 4.14 kPa is 15 g/g or more and 40 g/g or less.
  • C The 5-minute value of the unpressurized DW is 50 mL/g or more and 80 mL/g or less.
  • Example 1 [First stage polymerization step] 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 0.782 g of maleic anhydride-modified ethylene-propylene copolymer (Mitsui Chemicals, Inc., Hiwax 1105A) was added as a polymeric dispersant. The mixture was heated to 80°C while stirring to dissolve the dispersant, and then cooled to 50°C.
  • n-heptane was added to this flask as a hydrocarbon dispersion medium
  • maleic anhydride-modified ethylene-propylene copolymer Mitsubishi Chemicals, Inc., Hiwax
  • aqueous solution prepared above was added to a separable flask and stirred for 10 minutes, after which a surfactant solution prepared by heating and dissolving 0.828 g of sucrose stearate with an HLB of 3 (Ryoto Sugar Ester S-370, Mitsubishi Chemical Foods Corporation) in 7.45 g of n-heptane was further added, and the system was thoroughly replaced with nitrogen while stirring at a stirrer speed of 500 rpm.
  • the flask was then 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 liquid containing primary particles.
  • the contents of the separable flask were cooled to 25°C while stirring at a stirrer speed of 1000 rpm, and the entire amount of the second-stage aqueous solution was added to the first-stage polymerization slurry liquid.
  • the system was replaced with nitrogen for 30 minutes, and the flask was then immersed again in a 70°C water bath to raise the temperature and carry out the polymerization reaction for 60 minutes.
  • a hydrous gel was obtained after the second-stage polymerization.
  • the flask was again immersed in an oil bath set at 125°C, and an additional 80.5 g (total 257.1 g) of water was extracted from the system by azeotropic distillation of n-heptane and water while refluxing n-heptane. Then, 5.52 g (0.634 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 flask was kept at 83°C for 2 hours.
  • n-heptane was evaporated at 125°C to dry the product, yielding a dried product.
  • This dried product was passed through a sieve with an opening of 850 ⁇ m, and 0.2% by mass of amorphous silica (Toxil NP-S, Oriental Silicas Corporation) was mixed with the dried product, yielding 235.2 g of water-absorbent resin particles.
  • the median particle size of the water-absorbent resin particles was 347 ⁇ m.
  • the saline water absorption capacity of the water-absorbent resin particles of Example 1 was 64 g/g, and the water absorption speed of the water-absorbent resin particles was 35 seconds.
  • Example 2 Except for changing the amount of water extracted from the system by the second azeotropic distillation to 90.2 g (total 266.8 g), the same procedure as in Example 1 was repeated to obtain 223.4 g of water-absorbent resin particles.
  • the median particle diameter of the water-absorbent resin particles was 339 ⁇ m.
  • the saline water absorption capacity of the water-absorbent resin particles of Example 2 was 72 g/g, and the water absorption speed of the water-absorbent resin particles was 33 seconds.
  • Example 3 The amount of 2,2'-azobis(2-amidinopropane) dihydrochloride added to the second-stage aqueous monomer solution was changed to 0.129 g (0.475 mmol), the amount of ion-exchanged water added was changed to 6.42 g, and the amount of water extracted from the system by the second azeotropic distillation was changed to 80.3 g (total 256.9 g) in the same manner as in Example 1, and 226.0 g of water-absorbent resin particles were obtained.
  • the median particle diameter of the water-absorbent resin particles was 353 ⁇ m.
  • the saline water absorption capacity of the water-absorbent resin particles of Example 3 was 71 g/g, and the water absorption speed of the water-absorbent resin particles was 39 seconds.
  • Example 4 The same procedure as in Example 1 was repeated except that 0.0052 g (0.030 mmol) of ethylene glycol diglycidyl ether was added as an internal crosslinking agent to the second-stage aqueous monomer solution, the amount of ion-exchanged water added to the second-stage aqueous monomer solution was changed to 6.48 g, and the amount of water extracted from the system by the second azeotropic distillation was changed to 83.9 g (total 260.6 g), to obtain 224.3 g of water-absorbent resin particles.
  • the median particle diameter of the water-absorbent resin particles was 361 ⁇ m.
  • the saline water absorption capacity of the water-absorbent resin particles of Example 4 was 68 g/g, and the water absorption speed of the water-absorbent resin particles was 39 seconds.
  • Example 5 The amount of water extracted from the system by the second azeotropic distillation was changed to 89.9 g (total 266.5 g), and the amount of 2 mass% ethylene glycol diglycidyl ether aqueous solution was changed to 8.28 g (0.951 mmol) in the same manner as in Example 1, and 225.7 g of water absorbent resin particles were obtained.
  • the median particle diameter of the water absorbent resin particles was 360 ⁇ m.
  • the saline water absorption capacity of the water-absorbent resin particles of Example 5 was 72 g/g, and the water absorption speed of the water-absorbent resin particles was 40 seconds.
  • Example 6 The same procedure as in Example 1 was repeated except that 0.0129 g (0.122 mmol) of sodium hypophosphite was added as a chain transfer agent to the second-stage aqueous monomer solution, the amount of ion-exchanged water added to the second-stage aqueous monomer solution was changed to 6.47 g, and the amount of water extracted from the system by the second azeotropic distillation was changed to 82.9 g (total 259.5 g), to obtain 221.5 g of water-absorbent resin particles. The median particle diameter of the water-absorbent resin particles was 369 ⁇ m.
  • the saline water absorption capacity of the water-absorbent resin particles of Example 6 was 64 g/g, and the water absorption speed of the water-absorbent resin particles was 37 seconds.
  • Example 7 Except for changing the amount of ethylene glycol diglycidyl ether added to the first-stage aqueous monomer solution to 0.0184 g (0.106 mmol), and changing the amount of water extracted from the system by the second azeotropic distillation to 84.7 g (total 261.4 g), the same procedure as in Example 1 was carried out to obtain 220.1 g of water-absorbent resin particles.
  • the median particle diameter of the water-absorbent resin particles was 423 ⁇ m.
  • the saline water absorption capacity of the water-absorbent resin particles of Example 7 was 67 g/g, and the water absorption speed of the water-absorbent resin particles was 48 seconds.
  • Example 8 [First stage polymerization step] 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 introduction tube, and a stirring blade having two stages of four inclined paddle blades with a blade diameter of 5 cm. 294 g of n-heptane was added to this flask as a hydrocarbon dispersion medium, and 0.644 g of maleic anhydride-modified ethylene-propylene copolymer (Mitsui Chemicals, Inc., Hiwax 1105A) was added as a polymeric dispersant. The mixture was heated to 80°C with stirring to dissolve the dispersant, and then cooled to 50°C.
  • aqueous solution prepared above was added to a separable flask and stirred for 10 minutes, after which a surfactant solution prepared by heating and dissolving 0.644 g of sucrose stearate with an HLB of 3 (Ryoto Sugar Ester S-370, Mitsubishi Chemical Foods Corporation) in 5.8 g of n-heptane was further added, and the system was thoroughly replaced with nitrogen while stirring at a stirrer speed of 500 rpm.
  • the flask was then 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 liquid containing primary particles.
  • the contents of the separable flask were cooled to 25°C while stirring at a stirrer speed of 1000 rpm, and the entire amount of the second-stage aqueous solution was added to the first-stage polymerization slurry liquid.
  • the system was replaced with nitrogen for 30 minutes, and the flask was then immersed again in a 70°C water bath to raise the temperature and carry out the polymerization reaction for 60 minutes.
  • a hydrous gel was obtained after the second-stage polymerization.
  • the flask was again immersed in an oil bath set at 125°C, and an additional 79.7 g of water (total 256.4 g) was extracted from the system by azeotropic distillation of n-heptane and water while refluxing n-heptane. Then, 5.52 g (0.634 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 flask was kept at 83°C for 2 hours.
  • n-heptane was evaporated at 125°C to dry the product, yielding a dried product.
  • This dried product was passed through a sieve with an opening of 850 ⁇ m, and 0.2% by mass of amorphous silica (Toxil NP-S, Oriental Silicas Corporation) was mixed with the dried product, yielding 214.9 g of water-absorbent resin particles.
  • the median particle size of the water-absorbent resin particles was 372 ⁇ m.
  • the saline water absorption capacity of the water-absorbent resin particles of Example 8 was 73 g/g, and the water absorption speed of the water-absorbent resin particles was 41 seconds.
  • the saline water absorption capacity of the water-absorbent resin particles of Comparative Example 1 was 67 g/g, and the water absorption speed of the water-absorbent resin particles was 39 seconds.
  • aqueous solution prepared above was added to a separable flask and stirred for 10 minutes, after which 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 was further added, and the system was thoroughly replaced with nitrogen while stirring at a stirrer speed of 600 rpm.
  • the flask was then 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 liquid containing primary particles.
  • the contents of the separable flask were cooled to 25°C while stirring at a stirrer speed of 1000 rpm, and the entire amount of the second-stage aqueous solution was added to the first-stage polymerization slurry liquid.
  • the system was replaced with nitrogen for 30 minutes, and the flask was then immersed again in a 70°C water bath to raise the temperature and carry out the polymerization reaction for 60 minutes.
  • a hydrous gel was obtained after the second-stage polymerization.
  • the flask was again immersed in an oil bath set at 125°C, and an additional 49.3 g of water (total 226.0 g) 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 flask was kept at 83°C for 2 hours.
  • n-heptane was evaporated at 125°C to dry the product, yielding a dried product.
  • This dried product was passed through a sieve with an opening of 850 ⁇ m, and 0.2% by mass of amorphous silica (Toxil NP-S, Oriental Silicas Corporation) was mixed with the dried product, yielding 229.4 g of water-absorbent resin particles.
  • the median particle size of the water-absorbent resin particles was 352 ⁇ m.
  • the saline water absorption capacity of the water-absorbent resin particles of Comparative Example 2 was 66 g/g, and the water absorption speed of the water-absorbent resin particles was 36 seconds.
  • the primary particles were swollen 40 times with ion-exchanged water to prepare a 40-fold swollen gel.
  • 195.0 g of ion-exchanged water was weighed into a 500 mL beaker.
  • the beaker containing ion-exchanged water was placed in a MIYAMOTO CORPORATION jar tester (MJS-8S), and a stirring blade with a stainless steel flat blade (horizontal length 7 cm x vertical length 2.5 cm x thickness 0.1 cm) was connected and placed at a height of 0.5 cm from the bottom of the beaker and rotated at 500 rpm.
  • the storage modulus was measured by creep measurement using a stress-controlled rheometer (TA Instruments Ltd, model number AR2000ex). The measurement temperature was 25°C, and the jig used was an aluminum parallel plate with a diameter of 60 mm (TA Instruments Ltd, model number 513600.901). The shear stress was measured at 0.7 Pa.
  • the measurement sample was weighed out using a 15 mL spoon and placed on the sample stage, taking care not to introduce air bubbles.
  • the jig was then lowered so that the bottom of the jig was filled with the measurement sample, leaving a gap of 4000 ⁇ m between the jig and the sample stage. Any measurement sample that protruded outside the jig was removed. Creep measurements were performed, and the storage modulus was calculated using Jeffreys underdamped ringing analysis. The results are shown in Table 1.
  • This dried product was passed through a sieve with an opening of 850 ⁇ m, and 0.2% by mass of amorphous silica (Toxil NP-S, Oriental Silicas Corporation) was mixed with the dried product to obtain secondary particles.
  • amorphous silica Toxil NP-S, Oriental Silicas Corporation
  • the measuring device has a burette section 1, a conduit 5, a measuring stand 13, a nylon mesh sheet 15, a stand 11, and a clamp 3.
  • the burette section 1 has a burette tube 21 with a scale, a rubber plug 23 that seals the upper opening of the burette tube 21, a cock 22 connected to the lower tip of the burette tube 21, and an air introduction tube 25 and a cock 24 connected to the lower part of the burette tube 21.
  • the burette section 1 is fixed with a clamp 3.
  • the flat measuring stand 13 has a through hole 13a with a diameter of 2 mm formed in its center, and is supported by a stand 11 whose height is adjustable.
  • the through hole 13a of the measuring stand 13 and the cock 22 of the burette section 1 are connected by a conduit 5.
  • the inner diameter of the conduit 5 is 6 mm.
  • the cocks 22 and 24 of the burette part 1 were closed, and 0.9% by mass saline solution 50 adjusted to 25°C was poured into the burette tube 21 through the opening at the top of the burette tube 21.
  • the concentration of saline solution 0.9% by mass is based on the mass of the saline solution.
  • the cocks 22 and 24 were opened.
  • the inside of the conduit 5 was filled with 0.9% by mass saline solution 50 so as 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 nylon mesh sheet 15 (100 mm x 100 mm, 250 mesh, approximately 50 ⁇ m thick) was laid near the through-hole 13a on the measurement table 13, and a cylinder with an inner diameter of 30 mm and a height of 20 mm was placed in the center of the sheet. 1.00 g of water-absorbent resin particles 10a was evenly dispersed in the cylinder. The cylinder was then carefully removed, and a sample was obtained in which the water-absorbent resin particles 10a were dispersed in a circular shape in the center of the nylon mesh sheet 15.
  • the nylon mesh sheet 15 on which the water-absorbent resin particles 10a were placed was moved quickly so that its center was at the position of the through-hole 13a, without dissipating the water-absorbent resin particles 10a, and the measurement was started.
  • the point at which air bubbles were first introduced into the burette tube 21 from the air introduction tube 25 was defined as the start of water absorption (0 seconds).
  • the water absorption amount of the water-absorbent resin particles in physiological saline under a load of 4.14 kPa was measured using an apparatus whose outline is shown in FIG. The water absorption under load was measured twice for each sample, and the average of the measured values was calculated.
  • the burette section 1 is provided with a measuring section 4 having a scale marking, a rubber plug 23 for sealing the upper opening of the burette tube 21, and a
  • the burette part 1 has a cock 22 connected to the bottom of the burette tube 21, and an air inlet tube 25 and a cock 24 connected to the bottom of the burette tube 21.
  • the burette part 1 is fixed by a clamp 3.
  • the flat measuring table 13 has a
  • the sensor 1 has a through hole 13a with a diameter of 2 mm and is supported by a stand 11 whose height is adjustable.
  • the through hole 13a of the measuring 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 cylinder 31 made of acrylic resin, 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 to the water-absorbent resin particles 10a 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).
  • the mass of the water-absorbent resin particles remaining on each sieve was calculated as a mass percentage relative to the total amount to obtain a particle size distribution.
  • the relationship between the sieve opening and the accumulated value of the mass percentage of the water-absorbent resin particles remaining on the sieve was plotted on logarithmic probability paper. The plots on the probability paper were connected with a straight line to determine the particle size corresponding to a cumulative mass percentage of 50% by mass as the median particle size.

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PCT/JP2024/014596 2023-04-13 2024-04-10 吸水性樹脂粒子の製造方法、吸水性樹脂粒子、吸収体及び吸収性物品 Ceased WO2024214752A1 (ja)

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CN202480025393.3A CN121002072A (zh) 2023-04-13 2024-04-10 吸水性树脂颗粒的制造方法、吸水性树脂颗粒、吸收体及吸收性物品
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WO2025164342A1 (ja) * 2024-01-29 2025-08-07 住友精化株式会社 吸水性樹脂粒子、吸収体及び吸収性物品

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JPH03227301A (ja) 1990-01-31 1991-10-08 Sumitomo Seika Chem Co Ltd 吸水性樹脂の製造方法
WO2015163438A1 (ja) * 2014-04-25 2015-10-29 株式会社日本触媒 ポリアクリル酸（塩）系吸水性樹脂の製造方法
WO2016006134A1 (ja) * 2014-07-11 2016-01-14 住友精化株式会社 吸水性樹脂及び吸収性物品
JP2020121297A (ja) * 2019-01-30 2020-08-13 住友精化株式会社 吸水性樹脂粒子、吸収体及び吸収性物品
WO2020184393A1 (ja) * 2019-03-08 2020-09-17 住友精化株式会社 吸水性樹脂粒子、吸収体及び吸収性物品
JP7129490B2 (ja) * 2018-12-12 2022-09-01 住友精化株式会社 吸水性樹脂粒子、吸収体、吸収性物品、及び液吸引力測定方法

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JPH03227301A (ja) 1990-01-31 1991-10-08 Sumitomo Seika Chem Co Ltd 吸水性樹脂の製造方法
WO2015163438A1 (ja) * 2014-04-25 2015-10-29 株式会社日本触媒 ポリアクリル酸（塩）系吸水性樹脂の製造方法
WO2016006134A1 (ja) * 2014-07-11 2016-01-14 住友精化株式会社 吸水性樹脂及び吸収性物品
JP7129490B2 (ja) * 2018-12-12 2022-09-01 住友精化株式会社 吸水性樹脂粒子、吸収体、吸収性物品、及び液吸引力測定方法
JP2020121297A (ja) * 2019-01-30 2020-08-13 住友精化株式会社 吸水性樹脂粒子、吸収体及び吸収性物品
WO2020184393A1 (ja) * 2019-03-08 2020-09-17 住友精化株式会社 吸水性樹脂粒子、吸収体及び吸収性物品

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