Preparation method of superabsorbent polymer
Provided is a method of preparing a superabsorbent polymer. According to the method of preparing the superabsorbent polymer of the present invention, provided is a superabsorbent polymer having improved physical properties, in which the superabsorbent polymer has improved absorption rate and liquid permeability without reduction in centrifuge retention capacity or absorbency under load.
1. A method of preparing a superabsorbent polymer, the method comprising the steps of:
performing thermal polymerization or photo-polymerization of a monomer composition comprising a water-soluble ethylene-based unsaturated monomer, an internal crosslinking agent, and a polymerization initiator to prepare a hydrogel polymer having a gel strength of 10,000 Pa to 13,000 Pa,
wherein the internal crosslinking agent includes polyethyleneglycol diacrylate, and hexanediol diacrylate at a concentration of 4,000 ppm to 7,500 ppm, based on the total weight of the water-soluble ethylene-based unsaturated monomer comprised in the monomer composition;
coarsely pulverizing the hydrogel polymer by extruding the hydrogel polymer through an outlet having holes;
drying the coarsely pulverized hydrogel polymer;
pulverizing the dried polymer; and
mixing the pulverized polymer and a surface crosslinking agent to perform a surface crosslinking reaction of the mixture.
2. The method of claim 1 , wherein the diameter of the holes and the gel strength of the hydrogel polymer satisfy the following Formula 1:
1140* x+ 730< y< 600* x+ 8400 [Formula 1]
wherein x is the diameter of the hole (unit: mm) and y is the gel strength (unit: Pa) of the hydrogel polymer before coarse pulverization.
3. The method of claim 1 , wherein the internal crosslinking agent is a compound having a cure dose of 80% to 200%, relative to a cure dose of the water-soluble ethylene-based unsaturated monomer.
4. The method of claim 1 , wherein the internal crosslinking agent is a compound having a cure dose of 160 to 400 mJ/cm 2 .
5. The method of claim 1 , further comprising the step of classifying the pulverized polymer according to a particle size of 150 to 850 μm, before the step of performing surface crosslinking reaction of the pulverized polymer.
6. The method of claim 1 , wherein the superabsorbent polymer has centrifuge retention capacity (CRC) of 25 g/g or more, absorbency under load (AUL) of 20 g/g or more, absorption rate (FSR) of 0.25 g/g/s or more, and liquid permeability (SFC) of 70*10 −7 cm 3 *sec/g or more.