Method for producing water-absorbent polymer particles with improved properties

Patent metadata

Field	Value
Publication number	US-9840598-B2
Application number	US-201314407490-A
Country	US
Kind code	B2
Filing date	Jun 21, 2013
Priority date	Jul 3, 2012
Publication date	Dec 12, 2017
Grant date	Dec 12, 2017

Abstract

The present invention relates to a process for producing water-absorbing polymer particles having an improved profile of properties, comprising thermal surface postcrosslinking in the presence of a salt of a polyvalent metal cation and a complexing anion and subsequent aftertreatment, the aftertreatment comprising coating with a salt of a polyvalent metal cation and a non-complexing anion, and remoisturization with further drying.

First claim

The invention claimed is:

1. A process for producing water-absorbing polymer particles comprising polymerizing a monomer solution or suspension comprising
a) at least one ethylenically unsaturated monomer which bears an acid group and may be at least partly neutralized,
b) at least one crosslinker,
c) at least one initiator,
d) optionally one or more ethylenically unsaturated monomer copolymerizable with the monomer mentioned under a) and
e) optionally one or more water-soluble polymer,
drying, grinding, and classifying a resulting polymer gel, and thermally surface postcrosslinking the classified polymer particles with
f) at least one covalent surface postcrosslinker, and
g) at least one salt of a polyvalent metal cation and a complexing acid anion selected from the group consisting of glycolate, glycinate, lactate, alanate, citrate, tartrate, tartronate, and glycerate,
which comprises subsequently aftertreating the surface postcrosslinked polymer particles, the aftertreatment comprising
i) coating with at least one salt of a polyvalent metal cation and a non-complexing acid anion selected from the group consisting of formate, acetate, propionate, methylsulfonate, sulfate, and chloride,
ii) increasing the moisture content by 1 to 150% by weight, and
iii) drying after the increase in the moisture content.

2. The process according to claim 1 , wherein step ii) is conducted before step i).

3. The process according to claim 1 , wherein the classified polymer particles are coated with 0.02 to 0.8% by weight of the polyvalent metal cation.

4. The process according to claim 1 , wherein the surface postcrosslinked polymer particles are coated with 0.02 to 0.8% by weight of the polyvalent metal cation.

5. The process according to claim 1 , wherein the polyvalent metal cation is selected from the group of Al 3+ , Ti 4+ , and Zr 4+ .

6. The process according to claim 1 , wherein the surface postcrosslinked polymer particles, after increasing the moisture content, are dried at a temperature of less than 150° C.

7. The process according to claim 1 , wherein the surface postcrosslinked polymer particles, after increasing the moisture content, are dried down to a moisture content of less than 10% by weight.

8. The process according to claim 1 , wherein the water-absorbing polymer particles have a centrifuge retention capacity of at least 15 g/g.

Assignees

• Basf Se

Inventors

• Bauduin Christophe
• Daniel Thomas
• Karim Asif

Classifications

• C08J2333/02

  Homopolymers or copolymers of acids; Metal or ammonium salts thereof · CPC title

• C08J3/245 Primary

  Differential crosslinking of one polymer with one crosslinking type, e.g. surface crosslinking · CPC title

• A61L15/60

  Liquid-swellable gel-forming materials, e.g. super-absorbents · CPC title

• A61L15/22

  containing macromolecular materials · CPC title

• A61L15/24

  Macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds; Derivatives thereof {(A61L15/225 takes precedence)} · CPC title