Preparation method of super absorbent polymer

1. A preparation method of a super absorbent polymer, comprising:

preparing a monomer mixture comprising a water-soluble ethylene-based unsaturated monomer having at least partially neutralized acidic groups and an internal cross-linking agent;

transferring the monomer mixture to a polymerization reactor;

during the transferring the monomer mixture to the polymerization reactor, adjusting a dynamic pressure applied to the monomer mixture being transferred calculated by the following Equation 1 to 0.140 kPa or more by controlling a transfer rate;

cross-linking and polymerizing the monomer mixture transferred to the polymerization reactor to form a hydrogel polymer;

drying, pulverizing and classifying the hydrogel polymer to form a base resin powder; and

further cross-linking a surface of the base resin powder in the presence of a surface cross-linking agent to form a surface cross-linked layer:

Dynamic pressure=½* p*V 2   [Equation 1]

in Equation 1, p denotes a density (g/cm 3 ) of the monomer mixture being transferred, and V denotes a transfer rate (m/s) of the monomer mixture.

2. The preparation method of a super absorbent polymer of claim 1 ,

wherein the monomer mixture is transferred along a transfer pipe having a diameter that varies from section to section, the monomer mixture has a maximum transfer rate in a minimum diameter section of the transfer pipe, and the dynamic pressure applied to the monomer mixture in the maximum transfer rate section is adjusted to 0.140 kPa or more.

3. The preparation method of a super absorbent polymer of claim 2 ,

wherein the transfer pipe has a diameter of 0.002 to 0.01 m in the minimum diameter section, and has a diameter of 0.011 to 0.020 m in a maximum diameter section before the minimum diameter section.

4. The preparation method of a super absorbent polymer of claim 3 ,

wherein the monomer mixture is transferred through the transfer pipe at a flow rate of 100 to 15000 kg/hr.

5. The preparation method of a super absorbent polymer of claim 2 ,

wherein the monomer mixture is transferred in the minimum diameter section of the transfer pipe at a rate of 0.45 to 2.5 m/s, and is transferred in a maximum diameter section of the transfer pipe at a rate of 0.1 to 0.4 m/s.

6. The preparation method of a super absorbent polymer of claim 1 ,

wherein the monomer mixture further comprises a blowing agent in an amount of 0.01 to 0.3 wt % based on a total mixture weight.

7. The preparation method of a super absorbent polymer of claim 1 ,

wherein oxygen bubbles are generated in the monomer mixture during the dynamic pressure adjustment, and a foaming polymerization proceeds by the generated bubbles in the cross-linking polymerization.

8. The preparation method of a super absorbent polymer of claim 1 ,

wherein the super absorbent polymer has T-20 of 170 seconds or less, wherein T-20 represents a time required for 1 g of the super absorbent polymer to absorb 20 g of an aqueous solution of sodium chloride and C12 to C14 alcohol ethoxylate under a pressure of 0.3 psi.

9. The preparation method of a super absorbent polymer of claim 1 ,

wherein the super absorbent polymer has a centrifuge retention capacity (CRC) of saline (0.9 wt % aqueous solution of sodium chloride) for 30 min of 28 g/g or more.

10. The preparation method of a super absorbent polymer of claim 1 ,

wherein the super absorbent polymer has an absorbency under pressure (AUP) at 0.7 psi of 23 to 27 g/g, measured according to EDANA method WSP 242.3-10.

11. The preparation method of a super absorbent polymer of claim 1 ,

wherein the super absorbent polymer has a saline (0.685 wt % aqueous solution of sodium chloride) flow conductivity (SFC; ·10 −7 cm 3 ·s/g) of 30 (·10 −7 cm 3 ·s/g) or more.

12. The preparation method of a super absorbent polymer of claim 1 ,

wherein the super absorbent polymer has a vortex time of 5 to 50 seconds by a vortex method, and

wherein the vortex method comprises:

adding an amount of the super absorbent polymer to a saline solution at a temperature of 23° C. to 24° C.,

stirring the super absorbent polymer in the saline solution using a magnetic bar at 600 rpm to produce a vortex, and

measuring a time until the vortex disappears.

13. The preparation method of a super absorbent polymer of claim 1 , wherein the super absorbent polymer has a centrifuge retention capacity (CRC) of saline (0.9 wt % aqueous solution of sodium chloride) for 30 min of 40 g/g or less.

14. The preparation method of a super absorbent polymer of claim 1 , wherein the super absorbent polymer has a saline (0.685 wt % aqueous solution of sodium chloride) flow conductivity (SFC; ·10 −7 cm 3 ·s/g) of 70 (·10 −7 cm 3 ·s/g) or less.

15. The preparation method of a super absorbent polymer of claim 1 , wherein the dynamic pressure applied to the monomer mixture is adjusted to be within the range of 0.150 to 1,000 kPa.