Method of preparing superabsorbent polymer sheet

1. A method of preparing a superabsorbent polymer sheet, comprising:

preparing a monomer composition by mixing an acrylic acid-based monomer having acidic groups, of which at least a part is neutralized, an internal crosslinking agent comprising a polyol, an encapsulated foaming agent, an inorganic foaming agent, and a polymerization initiator;

forming a water-containing gel polymer by performing thermal polymerization or photopolymerization of the monomer composition; and

drying the water-containing gel polymer.

2. The method of claim 1 , wherein the polyol comprises one or more of ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, 1,2-hexanediol, 1,3-hexanediol, 2-methyl-1,3-propanediol, 2,5-hexanediol, 2-methyl-1,3-pentanediol, 2-methyl-2,4-pentanediol, tripropylene glycol, or glycerol.

3. The method of claim 1 , wherein the polyol is included in an amount of 10 parts by weight to 80 parts by weight with respect to 100 parts by weight of the acrylic acid-based monomer.

4. The method of claim 1 , wherein the encapsulated foaming agent has a mean diameter of 2 μm to 50 μm.

5. The method of claim 1 , wherein the encapsulated foaming agent has an expansion ratio of 3 times to 15 times in air.

6. The method of claim 1 , wherein the encapsulated foaming agent has a structure including a core which contains hydrocarbon and a shell which surrounds the core and is formed using a thermoplastic resin.

7. The method of claim 6 , wherein the hydrocarbon is one or more selected from the group consisting of n-propane, n-butane, iso-butane, cyclobutane, n-pentane, iso-pentane, cyclopentane, n-hexane, iso-hexane, cyclohexane, n-heptane, iso-heptane, cycloheptane, n-octane, iso-octane, and cyclooctane.

8. The method of claim 6 , wherein the thermoplastic resin is a polymer formed from one or more monomers selected from the group consisting of (meth)acrylate, (meth)acrylonitrile, aromatic vinyl, vinyl acetate, vinyl halide, and vinylidene halide.

9. The method of claim 1 , wherein the inorganic foaming agent is one or more selected from calcium carbonate (CaCO 3 ), sodium bicarbonate (NaHCO 3 ), ammonium bicarbonate (NH 4 HCO 3 ), ammonium carbonate ((NH 4 ) 2 CO 3 ), ammonium nitrite (NH 4 NO 2 ), sodium borohydride (NaBH 4 ), and sodium carbonate (Na 2 CO 3 ).

10. The method of claim 1 , wherein the encapsulated foaming agent and the inorganic foaming agent are included in a weight ratio of 3:1 to 1:1.

11. The method of claim 1 , wherein the encapsulated foaming agent is included in an amount of 0.3 parts by weight to 20 parts by weight with respect to 100 parts by weight of the acrylic acid-based monomer.

12. The method of claim 1 , wherein the inorganic foaming agent is included in an amount of 0.2 parts by weight to 10 parts by weight with respect to 100 parts by weight of the acrylic acid-based monomer.

13. A superabsorbent polymer sheet comprising a crosslinked polymer which is prepared by crosslinking polymerization of an acrylic acid-based monomer having acidic groups, of which at least a part is neutralized, in the presence of an internal crosslinking agent including polyol, an encapsulated foaming agent, and an inorganic foaming agent.

14. The superabsorbent polymer sheet of claim 13 , wherein centrifuge retention capacity (CRC) is 10 g/g to 40 g/g, as measured in accordance with EDANA method WSP 241.2.

15. The superabsorbent polymer sheet of claim 13 , wherein absorbency under pressure (AUP) of 0.7 psi is 5 g/g to 20 g/g, as measured in accordance with EDANA method WSP 242.2.

16. The superabsorbent polymer sheet of claim 13 , wherein an expansion ratio is 200% or more, the expansion ratio defined by an area of width*length of the superabsorbent polymer sheet which is cut to a size of width*length*thickness=50 mm*50 mm*2 mm and an area of width*length of the superabsorbent polymer sheet after being dried at a temperature of 180° C. for 5 minutes.