US-12624135-B2 - Method for preparing super absorbent polymer

Abstract

This invention relates to a method for preparing super absorbent polymer, and more specifically, a method for preparing super absorbent polymer that can more productively prepare super absorbent polymer having excellent absorption properties and optimum gel strength at the same time, by using a specific polymerization initiator and chelating agent in combination during a crosslinking polymerization step.

Inventors

• Serin LEE
• Seung Hun Yang
• Ju Eun Kim
• Joonil Cho
• Hoyong Lee
• Jungmin Lee

Assignees

• LG CHEM, LTD.

Dates

Publication Date

20260512

Application Date

20220128

Priority Date

20210203

Claims (7)

1. 1 . A method for preparing a super absorbent polymer comprising: conducting crosslinking polymerization of water soluble ethylenically unsaturated monomers having acid groups at least a part of which are neutralized with an internal crosslinking agent, in the presence of an azo-based polymerization initiator and diethylenetriamine pentaacetic acid, to obtain a hydrogel polymer; and drying, grinding and classifying the hydrogel polymer to form base resin powder, wherein the azo-based polymerization initiator and the diethylenetriamine pentaacetic acid are included at a weight ratio of 1:2 to 1:10, wherein the base resin powder has a centrifuge retention capacity (CRC) measured according to EDENA method WSP 241.2, of 45.0 g/g or more and wherein gel strength measured using tension and compression tester is 0.30 N or more, said gel strength being measured by dipping 2.5 g of the base resin powder in 50 g of a saline solution of ascorbic acid and swelling the base resin powder in a 40° C. oven for 24 hours, and then, measuring the swollen base resin powder.
2. 2 . The method for preparing super absorbent polymer according to claim 1 , wherein the azo-based polymerization initiator and the diethylenetriamine pentaacetic acid are included at the weight ratio of 1:3 to 1:7.
3. 3 . The method for preparing super absorbent polymer according to claim 1 , wherein the azo-based polymerization initiator is included in a content of 500 ppmw to 1,500 ppmw based on a total weight of the water soluble ethylenically unsaturated monomers.
4. 4 . The method for preparing super absorbent polymer according to claim 1 , wherein the diethylenetriamine pentaacetic acid is included in a content of 1,000 ppmw to 5,000 ppmw based on a total weight of the water soluble ethylenically unsaturated monomers.
5. 5 . The method for preparing super absorbent polymer according to claim 1 , wherein the azo-based polymerization initiator comprises one or more selected from the group consisting of 2,2-azobis(2-amidinopropane) dihydrochloride, 2,2-azobis-(N,N-dimethylene)isobutyramidine dihydrochloride, 2-(carbamoylazo)isobutyronitrile, 2,2-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride and 4,4-azobis-(4-cyanovaleric acid).
6. 6 . The method for preparing super absorbent polymer according to claim 1 , wherein the internal crosslinking agent comprises one or more selected from the group consisting of N,N′-methylenebisacrylamide, trimethylolpropane tri(meth)acrylate, ethyleneglycol di(meth)acrylate, polyethyleneglycol (meth)acrylate, polyethyleneglycol di(meth)acrylate, propyleneglycol di(meth)acrylate, polypropyleneglycol(meth)acrylate, butanediol di(meth)acrylate, butyleneglycol di(meth)acrylate, diethyleneglycol di(meth)acrylate, hexanediol di(meth)acrylate, triethyleneglycol di(meth)acrylate, tripropyleneglycol di(meth)acrylate, tetraethyleneglycol di(meth)acrylate, dipentaerythritol pentaacrylate, glycerin tri(meth)acrylate, pentaerythritol tetraacrylate, triarylamine, ethyleneglycol diglycidyl ether, propyleneglycol, glycerin, and ethylene carbonate.
7. 7 . The method for preparing super absorbent polymer according to claim 1 , wherein the internal crosslinking agent is included in a content of 500 ppmw to 1,500 ppmw based on a total weight of the water soluble ethylenically unsaturated monomers.

Description

CROSS-REFERENCE TO RELATED APPLICATION This application claims the benefit of Korean Patent Application No. 10-2021-0015453 filed on Feb. 3, 2021 and Korean Patent Application No. 10-2022-0012653 filed on Jan. 27, 2022 with the Korean Intellectual Property Office, the disclosures of which are herein incorporated by reference in their entirety. Technical Field This invention relates to a method for preparing super absorbent polymer, and more specifically, a method for preparing super absorbent polymer that can more productively prepare super absorbent polymer having excellent absorption performance and optimum gel strength at the same time, by using a specific polymerization initiator and chelating agent in combination during a crosslinking polymerization step. Background Art Super absorbent polymer (SAP) is synthetic polymer material that can absorb moisture of 500 to 1000 times of self-weight, and is also named differently as super absorbency material (SAM), absorbent gel material (AGM), etc. according to developing companies. The superabsorbent polymer began to be commercialized as sanitary items, and currently, it is being widely used as water-holding material for soil, water stop material for civil engineering and architecture, sheets for raising seedling, freshness preservatives in the field of food circulation, fomentation material, and the like, besides paper diapers for children. In most cases, such super absorbent polymer is widely used in the field of hygienic products such as diapers or sanitary pads, and the like, and for such purpose, it should exhibit high absorption force for moisture, and the like, and it should exhibit excellent absorption under pressure such that moisture may not be discharged even under external pressure, and excellent permeability such that a shape may be maintained even if swollen by absorption of water. In addition, when the super absorbent polymer is included in hygienic products such as a diaper, it should diffuse urine, and the like as widely as possible, even under pressure by body weight of a user. Thereby, super absorbent polymer particles included in the entire area of an absorption layer of a hygienic product may be wholly applied, thus further improving absorption performance and absorption speed of the hygienic product. And, due to such diffusion under pressure, rewet property of a diaper may be further improved such that rewet of urine, and the like once absorbed in super absorbent polymer may be prevented, and furthermore, leakage inhibition property of a diaper may be improved. Previously, there have been attempts to widely diffuse urine, and the like, by modifying the design of a hygienic product such as a diaper. For example, there have been attempts to improve diffusion property of urine, and the like, by introducing an ADL (Acquisition Distribution Layer) in a hygienic product, or applying an absorption channel. However, improvement in diffusion property by such design change of hygienic products was not sufficient. Meanwhile, in order to improve absorption-related properties such as absorption power or absorption speed of super absorbent polymer, various post-treatment processes such as surface crosslinking, foaming, and the like are conducted, or various additives are used, but in such a process, crosslinking density of polymer may be lowered, and thus, sufficient gel strength may not be realized, and additives may be detached, and thus, when applied for a product, wearing comfort of a user may be degraded such as occurrence of skin rash. Therefore, there is a demand for studies on the preparation of super absorbent polymer that not only maintains excellent absorption properties, but also realizes optimum gel strength. DISCLOSURE Technical Problem It is an object of the invention to provide a method for preparing super absorbent polymer that can more productively prepare super absorbent polymer having excellent absorption performance and optimum gel strength at the same time, by using a specific polymerization initiator and chelating agent in combination in the crosslinking polymerization step during the preparation process. Technical Solution In order to achieve the object, there is provided a method for preparing super absorbent polymer comprising steps of: conducting crosslinking polymerization of water soluble ethylenically unsaturated monomers having acid groups of which at least a part are neutralized and an internal crosslinking agent, in the presence of an azo-based polymerization initiator and diethylenetriamine pentaacetic acid, to obtain hydrogel polymer; anddrying, grinding and classifying the hydrogel polymer to form base resin powder,wherein the azo-based polymerization initiator and diethylenetriamine pentaacetic acid are included at the weight ratio of 1:2 to 1:10. Effect of the Invention According to the invention, there is provided a method for preparing super absorbent polymer that can more productively prepare super absorbent poly