Preparation method of superabsorbent polymer

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

forming a monomer composition including water-soluble ethylenic unsaturated monomers and a polymerization initiator;

polymerizing the monomer composition in a polymerization reactor so as to prepare a water-containing gel polymer;

drying, pulverizing and performing a first sorting step including sorting the water-containing gel polymer obtained from the polymerizing step to obtain a fine powder having a particle size of smaller than 150 μm;

obtaining a base-treated fine powder regranulated body by treating the sorted fine powder having the particle size of smaller than 150 μm from the first sorting step, followed by regranulation, wherein the alkaline solution is one or more solutions selected from the group consisting of NaOH, Na 2 CO 3 , and NaHCO 3 having a concentration of 1 to 10% by weight;

mixing the water-containing gel polymer and the base-treated fine powder regranulated body which are different from each other in degree of neutralization;

drying and pulverizing a mixture of the water-containing gel polymer and the base-treated fine powder regranulated body;

performing a second sorting step including sorting the pulverized mixture into two kinds of particles having different particle size distributions: (1) particles having a particle size of smaller than 150 μm and (2) particles having a particle size ranging from 150 μm to 850 μm;

preparing a base resin including the water-containing gel polymer and the particles having a particle size ranging from 150 μm to 850 μm from the second sorting step; and

surface-treating the base resin with a surface treatment solution to obtain a superabsorbent polymer having a particle size ranging from 150 μm to 850 μm,

wherein the water-containing gel polymer has a degree of neutralization of 70 to 80 mol %, and

the base-treated fine powder regranulated body has a degree of neutralization of 71 to 100 mol %.

2. The method of claim 1 , wherein the water-containing gel polymer and the base-treated fine powder regranulated body have a water content of 40 to 60% by weight.

3. The method of claim 1 , wherein the water-containing gel polymer and the base-treated fine powder regranulated body are mixed at a weight ratio of 95:5 to 70:30.

4. The method of claim 1 , wherein the surface treatment step solution in the step of surface-treating the base resin comprises: a surface-crosslinking agent,; a solvent, and water,

wherein the surface cross-linking agent is a diol or a glycol-based compound having 2 to 8 carbon atoms, and

the solvent is an alcohol or a glycol-based compound having 3 or more carbon atoms and a boiling point of 90° C. or higher.

5. The method of claim 4 , wherein the surface treatment solution includes the surface-cross linking agent at 0.1 to 20% by weight, the solvent at 10 to 70% by weight, and water at a residual amount.

6. The method of claim 1 , wherein the surface treatment step includes the step of surface-crosslinking the base resin at a temperature of 150 to 300 ° C. for 20 to 90 min.

7. The method of claim 4 , wherein the surface-crosslinking agent is one or more selected from the group consisting of 1,3-propanediol, 2,3,4-trimethyl-1,3-pentanediol, 2-butene-1,4-diol, 1,4-butanediol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-cyclohexanedimethanol, monoethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, glycerol, and polyglycerol.

8. The method of claim 4 , wherein the alcohol or glycol-based compound is one or more selected from the group consisting of normal-propanol, butanol, propylene glycol, and 1,3-propanediol.

9. The method of claim 1 , wherein the water-soluble ethylenic unsaturated monomer is one or more selected from a group consisting of: an anionic monomer such as acrylic acid, methacrylic acid, maleic anhydride, fumaric acid, crotonic acid, itaconic acid, 2-acryloylethane sulfonic acid, 2-methacryloylethane sulfonic acid, 2-acryloylpropane sulfonic acid, 2-methacryloylpropane sulfonic acid, 2-acrylamide-2-methyl propane sulfonic acid, 2-methacrylamide-2-methyl propane sulfonic acid and anionic monomer salts thereof; acrylamide, methacrylamide, N-substituted acrylate, N-substituted methacrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydropropyl methacrylate, methoxy polyethylene glycol acrylate, methoxy polyethylene glycol methacrylate, polyethylene glycol acrylate, polyethylene glycol methacrylate; and (N,N)-dimethylaminoethyl acrylate, (N,N)-dimethylaminoethyl methacrylate, (N,N)-dimethylaminopropylacrylamide, (N,N)-dimethylaminopropyl methacrylamide and quaternary compounds thereof.

10. The method of claim 1 , wherein the polymerization initiator is any one selected from the group consisting of an azo-based initiator, a peroxide-based initiator, a redox-based initiator, an organic halide-based initiator, a persulfate-based initiator, acetophenone, benzoin, benzophenone, a benzyl-based compound, and derivatives thereof.