# US 8,541,528 B2 · Process for producing water-absorbing particles

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- Number: US 8,541,528 B2
- Document ID: US8541528B2
- Status: Granted
- Kind: B2
- Application number: 13/032,410
- Filed: 2011-02-22
- Published: 2011-08-25
- Granted: 2013-09-24
- Earliest claimed: 2010-02-24
- Assignees: BASF SE
- Applicants: Rüdiger Funk; Thomas Pfeiffer; Matthias Weismantel; Stefan Blei; Wilfried Heide; Volker Braig; Thomas Gieger; Andreas Brockmeyer
- Inventors: Rüdiger Funk; Thomas Pfeiffer; Matthias Weismantel; Stefan Blei; Wilfried Heide; Volker Braig; Thomas Gieger; Andreas Brockmeyer
- Web page: https://patentgrep.com/patent/US8541528B2

## CPC

- C08F 6/008: {Treatment of solid polymer wetted by water or organic solvents, e.g. coagulum, filter cakes}
- C08F 220/06: Acrylic acid; Methacrylic acid; Metal salts or ammonium salts thereof
- C08F 222/102: {of dialcohols, e.g. ethylene glycol di(meth)acrylate or 1,4-butanediol dimethacrylate}
- F26B 17/02: with movement performed by belts carrying the materials; with movement performed by belts propelling the materials over stationary surfaces {(F26B17/003, F26B17/263 take precedence)}
- C08F: MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- F26B: DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM (drying devices for combines A01D41/133; racks for drying fruit or vegetables A01F25/12; drying foodstuffs A23; drying hair A45D20/00; body-drying implements A47K10/00; drying household articles A47L; drying gases or vapours B01D; chemical or physical processes for dewatering or like separating liquids from solids B01D43/00; centrifugal apparatus B04; drying ceramics C04B33/30; drying yarns or fabrics in association with some other form of treatment D06C; drying frames for laundry without heating or positive air circulation, domestic laundry-or spin-driers, wringing or hot pressing laundry D06F; furnaces, kilns, ovens F27)

## Abstract

A process for producing water-absorbing polymer particles, wherein an aqueous polymer gel is dried in a forced-air belt drier on a circulating conveyor belt and the surface of the conveyor belt has a multitude of elevations or depressions which are suitable for restricting the mobility of the aqueous polymer gel in transverse direction.

## Claims

### Claim 1

A process for producing water-absorbing polymer particles by polymerizing an aqueous monomer solution or suspension comprising
a) at least one ethylenically unsaturated monomer which bears an acid group and optionally 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,
comprising drying a resulting aqueous polymer gel in a forced-air belt drier by means of a circulating conveyor belt, grinding, classifying and optional thermal surface postcrosslinking, wherein the surface of a conveyor belt has a multitude of elevations or depressions for restricting mobility of the aqueous polymer gel in a transverse direction, wherein the surface of the conveyor belt has a multitude of spikes with a height of 0.01 to 5 cm.

### Claim 2 (depends on 1)

The process according to claim 1, wherein the circulating conveyor belt is made from austenitic steel.

### Claim 3 (depends on 1)

The process according to claim 1, wherein the circulating conveyor belt has a multitude of orifices.

### Claim 4 (depends on 1)

The process according to claim 1, wherein the circulating conveyor belt has, transverse to a direction of transport, a multitude of slots arranged in offset rows and having a length of 5 to 50 mm, a width of 0.5 to 5 mm, and a ratio of length to width of 2 to 20.

### Claim 5 (depends on 1)

The process according to claim 1, wherein the circulating conveyor belt is a width of at least 1 m.

### Claim 6 (depends on 1)

The process according to claim 1, wherein a conveyor belt speed is from 0.005 to 0.05 m/s.

### Claim 7 (depends on 1)

The process according to claim 1, wherein a water content of the polymer gel before the drying in the forced-air belt drier is from 30 to 70% by weight.

### Claim 8 (depends on 1)

The process according to claim 1, wherein a water content of the polymer gel after the drying in the forced-air belt drier is from 0.5 to 15% by weight.

### Claim 9 (depends on 1)

The process according to claim 1, wherein a height of the polymer gel bed on the circulating conveyor belt is from 2 to 20 cm.

### Claim 10 (depends on 1)

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