Preparation method of superabsorbent polymer

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, Na2CO3, and NaHCO3 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 %.