Super absorbent polymer and preparation method thereof
The present disclosure relates to a super absorbent polymer and a preparation method of the same, which not only has excellent basic absorption performance, but also exhibits an improved absorption rate, and the like. The super absorbent polymer includes a base resin powder containing a first cross-linked polymer of a water-soluble ethylene-based unsaturated monomer having at least partially neutralized acidic groups; and a surface cross-linked layer containing a second cross-linked polymer in which the first cross-linked polymer is additionally cross-linked by a surface cross-linking agent on the base resin powder, wherein the super absorbent polymer contains less than 9.9% by number of super absorbent polymer particles having an aspect ratio, which is defined as shortest diameter/longest diameter of each super absorbent polymer particle, of less than 0.5, a vortex time is 5 to 55 seconds by a vortex method, and a surface tension is 50 to 80 mN/m.
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 along a transfer pipe having a diameter that varies from section to section;
cross-linking and polymerizing the monomer mixture transferred to the polymerization reactor to form a hydrogel polymer containing a first cross-linked polymer;
gel-pulverizing, drying, pulverizing and classifying the hydrogel polymer to form a base resin powder containing less than 9.9% by number of base resin powder having an aspect ratio, which is defined as shortest diameter/longest diameter of each base resin powder, of less than 0.5; 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;
wherein during the transferring of the monomer mixture, the monomer mixture has a maximum transfer rate in a minimum diameter section of the transfer pipe and a minimum transfer rate in a maximum diameter section of the transfer pipe, and the maximum transfer rate is 2.5 times or more compared to the minimum transfer rate.
2. The preparation method of a super absorbent polymer of claim 1 ,
wherein the monomer mixture further comprises a surfactant.
3. The preparation method of a super absorbent polymer of claim 1 ,
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 the maximum diameter section of the transfer pipe at a rate of 0.1 to 0.4 m/s.
4. The preparation method of a super absorbent polymer of claim 1 ,
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 the maximum diameter section before the minimum diameter section.
5. The preparation method of a super absorbent polymer of claim 1 ,
wherein the monomer mixture is transferred through the transfer pipe at a flow rate of 100 to 15000 kg/hr.
6. The preparation method of a super absorbent polymer of claim 1 ,
wherein bubbles are generated in the monomer by the change in the transfer rate during the transfer of the monomer mixture, and a foaming polymerization proceeds by the generated bubbles during the cross-linking polymerization.
7. The preparation method of a super absorbent polymer of claim 1 ,
wherein the surface cross-linking agent comprises at least one of polyalcohol-based compounds, polyepoxy-based compounds, polyamine compounds, haloepoxy compounds, condensates of haloepoxy compounds, oxazoline-based compounds, or alkylene carbonate-based compounds.
8. The preparation method of a super absorbent polymer of claim 1 ,
wherein the surface cross-linking is carried out by increasing an initial temperature of 20° C. to 130° C. to a highest temperature of 140° C. to 200° C. over 10 minutes to 30 minutes, and maintaining at the highest temperature for 5 to 60 minutes for heat-treatment.