Search

EP-4424291-B1 - MONOMER COMPOSITION FOR PREPARING SUPERABSORBENT POLYMER COMPRISED IN AN ABSORBENT ARTICLE

EP4424291B1EP 4424291 B1EP4424291 B1EP 4424291B1EP-4424291-B1

Inventors

  • SIMONYAN, ARSEN
  • BORGMANN, CAROLIN
  • WON, TaeYoung
  • SOHN, JUNG-MIN
  • RYU, JIHYE
  • HAN, CHANG HUN
  • KIM, YUN SOO

Dates

Publication Date
20260506
Application Date
20230303

Claims (17)

  1. Method of making an absorbent article comprising superabsorbent polymer, wherein the superabsorbent polymer is prepared by using a monomer composition, the monomer composition comprising: acrylic acid-based monomers having acid groups, at least a part of said acid groups being neutralized; a crosslinking agent; clay; a carbonate-based blowing agent; and a polymerization initiator, wherein the crosslinking agent is used in the content of 0.01 to 5 parts by weight, based on 100 parts by weight of the acrylic acid-based monomers; and wherein the content of the clays is 0.1 parts by weight or more, and 10 parts by weight or less, based on 100 parts by weight of the acrylic acid-based monomers; and wherein the carbonate-based blowing agent is used in the content of 0.005 to 1 part by weight, based on 100 parts by weight of the acrylic acid-based monomers; wherein, when irradiating heat and/or light to the monomer composition for preparing superabsorbent polymer to progress a polymerization reaction, a normalized gel point represented by the following Formula 1 is 0.01 to 0.1: Normalized gel point = gel point second / total polymerization time second in the Formula 1, a gel point is a polymerization time at the intersection point of a storage modulus graph of the monomer composition for preparing superabsorbent polymer according to a polymerization time, and a loss modulus graph of the monomer composition for preparing superabsorbent polymer according to a polymerization time.
  2. The method of claim 1, wherein, when irradiating heat and/or light to the monomer composition for preparing superabsorbent polymer to progress a polymerization reaction, increase speed of gel strength from the gel point to the time of completion of polymerization is 210 Pa/s or more.
  3. The method of claim 1 or 2,, wherein the clay is included in the monomer composition in the content of 0.1 to 5 parts by weight, based on 100 parts by weight of the acrylic acid-based monomers.
  4. The method of any of the preceding claims, wherein, in the monomer composition for preparing the superabsorbent polymer, the clay has an average particle diameter of 0.025 µm to 10 µm.
  5. The method of any of the preceding claims, wherein, in the monomer composition for preparing the superabsorbent polymer, the surface of the clay is modified with a polymer dispersant comprising 2 or more functional groups selected from the group consisting of an amine group, a carbonyl group and a hydroxyl group.
  6. The method of any of the preceding claims, wherein, in the monomer composition for preparing the superabsorbent polymer, the polymer dispersant is one or more selected from the group consisting of polyvinyl pyrrolidone, polyacrylamide, and polyacrylic acid.
  7. The method of any of the preceding claims, wherein the method comprises the further step of incorporating the superabsorbent polymer in the absorbent article.
  8. A method for making an absorbent article, the method comprising the step of making the monomer composition of claim 1 for preparing superabsorbent polymer, the method comprising the steps of: mixing the acrylic acid-based monomers having acid groups, at least a part of said acid groups being neutralized; the crosslinking agent; the carbonate-based blowing agent; and the polymerization initiator; and adding the clay to the mixture, and shear mixing at a stirring speed of 6,500 rpm or more, wherein the method comprises the further step of incorporating the superabsorbent polymer prepared by the monomer composition in an absorbent article.
  9. Method of making the absorbent article of claim 8, wherein a polymer is prepared from the monomer composition for preparing the superabsorbent polymer, wherein, the polymer has a gel strength of from 35,000 Pa to 60,000 Pa when the moisture content is 40 wt% to 80 wt%.
  10. Absorbent article comprising the superabsorbent polymer prepared from the monomer composition of any of claims 1 to 7, wherein The Performance Index (PI) of the superabsorbent polymer, represented by the following Calculation Formula 1, is 2.35 or more, and T20 is less than 190 seconds: Performance Index PI = CRC / 27 + AUP / 24 + SFC / 30 − T 20 / 140 in the Calculation Formula 1, CRC is centrifuge retention capacity(g/g) of superabsorbent polymer to 0.9 wt% sodium chloride aqueous solution for 30 seconds, AUP is absorbency under 4826.33 Pa (0.7 psi) pressure(g/g) of the superabsorbent polymer to 0.9 wt% sodium chloride aqueous solution for 1 hour, SFC of the superabsorbent polymer is saline flow conductivity(·10-7cm3·s/g) of 0.685 wt% sodium chloride aqueous solution, and T20 is a time(seconds) taken for 1g of the superabsorbent polymer to absorb 20g of C12-14 alcohol ethoxylate aqueous solution under 0.3 psi.
  11. A method for making an absorbent article, the absorbent article comprising superabsorbent polymer, the method comprising the steps of: irradiating heat and/or light to a monomer composition of claim 1 for preparing superabsorbent polymer to polymerize, thus preparing hydrogel polymer, drying, grinding and classifying the hydrogel polymer to form base resin; and forming a surface crosslink layer on the surface of the base resin, in the presence of a surface crosslinking solution comprising a surface crosslinking agent and a solvent, wherein the method further comprises the step of incorporating the superabsorbent polymer in an absorbent article.
  12. The method of claim 11, wherein the absorbent article is a diaper or a pant.
  13. The method of claim 11 or 12, wherein, the superabsorbent polymer is incorporated into an absorbent core, the absorbent core being comprised by the absorbent article.
  14. The method of claim 13, wherein the absorbent core is made by providing two nonwoven webs and incorporating the surface-crosslinked particulate water-absorbing resin between the two nonwoven webs.
  15. The method of claim 14, wherein the absorbent core, in between the two nonwoven webs, comprises less than 20 weight-% of cellulose fibers, preferably less than 10 weight-% of cellulose fibers, and more preferably less than 5 weight-% of cellulose fibers.
  16. The method of claim 14 or 15, wherein the method comprises the further step of adhesively immobilizing the superabsorbent polymer in between the two nonwoven webs.
  17. The method of any of claims 13 to 16, wherein the method comprises the further steps of: - providing a topsheet - providing a backsheet - providing the absorbent core in between the topsheet and the backsheet.

Description

Technical Field This invention relates to a monomer composition for preparing superabsorbent polymer, the superabsorbent polymer being comprised in an absorbent article. Background of the Invention Superabsorbent polymers (SAPs) are synthetic polymer materials that can absorb moisture of 500 to 1000 times of self-weight, began to be commercialized in absorbent articles, and currently, it is being widely used as water-holding material for soil, water stop material for civil engineering and architecture, sheets for raising seedling, freshness preservatives in the field of food circulation, fomentation material, and the like, besides hygienic goods such as paper diapers for children or sanitary pads, and the like. Superabsorbent polymer is generally prepared by neutralizing water soluble unsaturated ethylene-based monomers with an alkali metal salt such as sodium salt, or a basic compound such as caustic soda, and then, adding a crosslinking agent, a polymerization initiator, and the like to polymerize the prepared monomer composition. As a method for improving the absorption speed of superabsorbent polymer, a method of adding a blowing agent to conduct polymerization while bubbles are formed in the monomer composition, thereby forming a porous structure in superabsorbent polymer to increase the surface area, is known. However, in the case of a preparation method of superabsorbent polymer using the existing blowing agent, bubbles generated by the blowing agent are lost before monomers are polymerized, and thus, sufficient pores cannot be formed in superabsorbent polymer. Thus, a method of reducing loss of bubbles using a bubble stabilizer together with a blowing agent has been suggested, but it has a problem with deterioration of surface tension of superabsorbent polymer due to the bubble stabilizer. Therefore, there is a demand for development of superabsorbent polymer exhibiting rapid absorption speed without deterioration of properties such as surface tension, and the like. EP3391960 relates to superabsorbent polymer particles which comprise clay platelets with edge modification and/or surface modification. EP3342787 discloses a process to make continuous strand polymer comprising the following steps: a) providing a monomer mixture comprising water, a monomer, a crosslinker and an initiator; b) transporting the monomer mixture of step a) into a confining means; c) initiating polymerization of the monomer mixture in the confining means to make a continuous strand polymer; and d) emitting the continuous strand polymer from the confining means. Technical Problem It is an object of the invention to provide a monomer composition for preparing superabsorbent polymer that can prepare superabsorbent polymer having rapid absorption speed and excellent gel strength and wherein the superabsorbent polymer is subsequently incorporated in an absorbent article. Technical Solution There is provided a monomer composition for preparing superabsorbent polymer for incorporation in an absorbent article, the monomer composition comprising: acrylic acid-based monomers having acid groups, at least a part of said acid groups being neutralized; a crosslinking agent; clay; a carbonate-based blowing agent; and a polymerization initiator, wherein the crosslinking agent, the clays and the carbonate-based blowing agent are usedin the amounts as specified by claim 1,wherein, when irradiating heat and/or light to the monomer composition for preparing superabsorbent polymer to progress a polymerization reaction, a normalized gel point represented to by the following Formula 1 is 0.01 0.1: Normalizedgelpoint=gelpointsecond/totalpolymerizationtimesecondin the Formula 1, a gel point is a polymerization time at the intersection point of a storage modulus graph of the monomer composition for preparing superabsorbent polymer according to a polymerization time, and a loss modulus graph of the monomer composition for preparing superabsorbent polymer according to a polymerization time. The absorbent article comprising the superabsorbent polymer made by using the monomer composition, may be a diaper or a pant. The superabsorbent polymer may be incorporated into an absorbent core, the absorbent core being comprised by the absorbent article. The absorbent core may be made by providing two nonwoven webs and incorporating the surface-crosslinked particulate water-absorbing resin between the two nonwoven webs. The absorbent core, in between the two nonwoven webs, may comprise less than 20 weight-% of cellulose fibers, preferably less than 10 weight-% of cellulose fibers, and more preferably less than 5 weight-% of cellulose fibers. In the absorbent core, the superabsorbent polymer may be adhesively immobilized in between the two nonwoven webs. The absorbent article may comprise a topsheet, a backsheet and the absorbent core in between the topsheet and the backsheet. There is also provided a method for preparing the monomer composition for preparing supera