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EP-4737507-A1 - METHOD FOR PRODUCING WATER-ABSORBING RESIN PARTICLES, WATER-ABSORBING RESIN PARTICLES, ABSORBER, AND ABSORBENT ARTICLE

EP4737507A1EP 4737507 A1EP4737507 A1EP 4737507A1EP-4737507-A1

Abstract

There is provided a novel method for producing water-absorbent resin particles having gel stability against artificial urine containing iron, long-term gel stability against artificial urine, and yellowing resistance. A method for producing water-absorbent resin particles, comprising the steps of polymerizing a water-soluble ethylenically unsaturated monomer to obtain polymer particles; and subjecting the polymer particles to surface-crosslinking, wherein before and/or after the step of surface-crosslinking, a phosphonic acid-based chelating agent is added to the polymer particles having a water content of 5% by mass or more and 100% by mass or less, and wherein an amount of the phosphonic acid-based chelating agent added is 0.055 parts by mass or more and 0.6 parts by mass or less per 100 parts by mass of the water-soluble ethylenically unsaturated monomer.

Inventors

  • AWAJI, Yuki
  • HIRANO, Saho

Assignees

  • Sumitomo Seika Chemicals Co., Ltd.

Dates

Publication Date
20260506
Application Date
20240620

Claims (6)

  1. A method for producing water-absorbent resin particles, comprising the steps of: polymerizing a water-soluble ethylenically unsaturated monomer to obtain polymer particles; and subjecting the polymer particles to surface-crosslinking, wherein before and/or after the step of surface-crosslinking, a phosphonic acid-based chelating agent is added to the polymer particles having a water content of 5% by mass or more and 100% by mass or less, and wherein an amount of the phosphonic acid-based chelating agent added is 0.055 parts by mass or more and 0.6 parts by mass or less per 100 parts by mass of the water-soluble ethylenically unsaturated monomer.
  2. The method according to claim 1, wherein the water content in the polymer particles is 20% by mass or more and 80% by mass or less.
  3. The method according to claim 1 or 2, wherein the water-absorbent resin particles have the following properties (A) to (E): (A) a physiological saline retention capacity of 20 g/g or more and 70 g/g or less; (B) a physiological saline absorption capacity under a load of 4.14 kPa of 5 mL/g or more and 40 mL/g or less; (C) a yellowness index of less than 25 after allowing the water-absorbent resin particles to stand for 7 days in an environment of 70°C and 90% relative humidity; (D) a gel strength of 6000 N/m 2 or more after allowing a gel swollen 40-fold with artificial urine to stand for 14 hours in an environment of 37°C and 60% relative humidity; and (E) a gel strength of 4000 N/m 2 or more after allowing a gel swollen 40-fold with artificial urine containing iron at an iron concentration of 10 ppm to stand for 2.5 hours in an environment of 25°C and 50% relative humidity.
  4. Water-absorbent resin particles, the water-absorbent resin particles being a crosslinked product of a polymer of a water-soluble ethylenically unsaturated monomer, wherein the water-absorbent resin particles have the following properties (A) to (E): (A) a physiological saline retention capacity of 20 g/g or more and 70 g/g or less; (B) a physiological saline absorption capacity under a load of 4.14 kPa of 5 mL/g or more and 40 mL/g or less; (C) a yellowness index of less than 25 after allowing the water-absorbent resin particles to stand for 7 days in an environment of 70°C and 90% relative humidity; (D) a gel strength of 6000 N/m 2 or more after allowing a gel swollen 40-fold with artificial urine to stand for 14 hours in an environment of 37°C and 60% relative humidity; and (E) a gel strength of 4000 N/m 2 or more after allowing a gel swollen 40-fold with artificial urine containing iron at an iron concentration of 10 ppm to stand for 2.5 hours in an environment of 25°C and 50% relative humidity.
  5. An absorbent material comprising the water-absorbent resin particles according to claim 4.
  6. An absorbent article comprising the absorbent material according to claim 5.

Description

Technical Field The present invention relates to a method for producing water-absorbent resin particles, water-absorbent resin particles, an absorbent material, and an absorbent article; and more particularly relates to a method for producing water-absorbent resin particles that constitute an absorbent material suitably used for hygienic materials, such as disposable diapers, sanitary napkins, and incontinence pads, water-absorbent resin particles, an absorbent material including the water-absorbent resin particles, and an absorbent article. Background Art In recent years, water-absorbent resin particles have been widely used in the field of hygienic materials, such as disposable diapers, sanitary napkins, and incontinence pads. As such water-absorbent resin particles, crosslinked products of polymers of a water-soluble ethylenically unsaturated monomer, more specifically, crosslinked products of polymers of partially neutralized polyacrylic acid, have been proposed as preferable water-absorbent resin particles, because of many advantages: for example, they have good water absorption capacity; acrylic acid used as a raw material thereof is readily industrially available, and thus, they can be produced at low cost with uniform quality; additionally, they are resistant to decomposition or degradation (see, for example, Patent Literature 1). An absorbent article, such as a disposable diaper, a sanitary napkin, or an incontinence pad, is mainly composed of an absorbent material that is positioned in a central portion, and absorbs and retains a body liquid, such as urine or menses excreted from the body; a liquid-permeable front sheet (top sheet) positioned on the side of the absorbent article that is brought into contact with the body; and a liquid-impermeable rear sheet (back sheet) positioned opposite to the side that is brought into contact with the body. The absorbent material is typically composed of hydrophilic fibers, such as pulp, and water-absorbent resin particles. Citation List Patent Literature Patent Literature 1: JP-A-H3-227301 Summary of Invention Technical Problem In such an absorbent article, the water-absorbent resin particles contained in the absorbent material may be affected by vitamin C in urine and iron contained in urine or in the water-absorbent resin particles, which may cause a phenomenon in which the gel deteriorates. A method for inhibiting the gel deterioration of the water-absorbent resin particles as described above is known, in which a metal chelating agent is added in the production process of the water-absorbent resin particles. For example, an aminocarboxylic acid-based chelating agent coordinates to iron or the like, and exhibits the effect of inhibiting the deterioration of the water-absorbent resin particles due to vitamin C and iron. Furthermore, the aminocarboxylic acid-based chelating agent not only inhibits the gel deterioration of the water-absorbent resin particles, but also exhibits the effect of inhibiting yellowing of the water-absorbent resin particles. However, the inventors of the present invention have found that when urine has a high iron concentration, the effect of inhibiting the gel deterioration by the aminocarboxylic acid-based chelating agent is not sufficient. Under such circumstances, it is a main object of the present invention to provide a novel method for producing water-absorbent resin particles having gel stability against artificial urine containing iron, long-term gel stability against artificial urine, and yellowing resistance. It is also an object of the present invention to provide water-absorbent resin particles having high absorption performance (particularly in terms of physiological saline retention capacity and physiological saline absorption capacity under a load of 4.14 kPa) and also having gel stability against artificial urine containing iron, long-term gel stability against artificial urine, and yellowing resistance, an absorbent material including the water-absorbent resin particles, and an absorbent article. Solution to Problem The present inventors have conducted extensive research to solve the aforementioned problem. As a result, the inventors have found that water-absorbent resin particles having gel stability against artificial urine containing iron, long-term gel stability against artificial urine, and yellowing resistance can be obtained using a method for producing water-absorbent resin particles, comprising the steps of polymerizing a water-soluble ethylenically unsaturated monomer to obtain polymer particles; and subjecting the polymer particles to surface-crosslinking, wherein at at least one timing from before and after the step of surface-crosslinking, a predetermined amount of a phosphonic acid-based chelating agent is added to the polymer particles adjusted to a predetermined water content. The present invention has been accomplished as a result of further research based on this finding. In summary, the present inve