Method for producing water-absorbing polymer particles

Patent metadata

Field	Value
Publication number	US-10179185-B2
Application number	US-201515308383-A
Country	US
Kind code	B2
Filing date	May 7, 2015
Priority date	May 8, 2014
Publication date	Jan 15, 2019
Grant date	Jan 15, 2019

Abstract

A process for producing water-absorbing polymer particles is provided, comprising a) a polymerization step in which an aqueous monomer solution comprising at least one ethylenically unsaturated monomer M which bears acid groups and may have been at least partly neutralized and at least one crosslinker is polymerized to obtain an aqueous polymer gel; b) a pelletization step in which the aqueous polymer gel having a solids content of 35 to 70% by weight and a temperature of 75 to 125° C. is forced from a high-pressure zone through a die plate into a low-pressure zone and pellets are obtained, the pressure differential between the high-pressure zone and the low-pressure zone being 4 to less than 14 bar and the orifice ratio of the die plate being 30 to 80%; c) a drying step in which the pellets are dried to a moisture content of less than 10% by weight; d) a grinding step and a classifying step to obtain water-absorbing polymer particles; and e) surface crosslinking of the water-absorbing polymer particles. The water-absorbing polymer particles have a high swell rate and a high retention capacity combined with a favorable ratio of permeability of the swollen gel bed SFC to centrifuge retention capacity CRC.

First claim

The invention claimed is:

1. A process for producing water-absorbing polymer particles, comprising
a) a polymerization step in which an aqueous monomer solution comprising at least one ethylenically unsaturated monomer M which bears an acid group and optionally has been at least partly neutralized and at least one crosslinker are polymerized to obtain an aqueous polymer gel;
b) a pelletization step in which the aqueous polymer gel having a solids content of 35 to 70% by weight and a temperature of 75 to 125° C. is forced from a high-pressure zone through a die plate into a low-pressure zone and pellets are obtained, the pressure differential between the high-pressure zone and the low-pressure zone being 4 to less than 14 bar and the orifice ratio of the die plate being 30 to 80%;
c) a drying step in which the pellets are dried to a moisture content of less than 10% by weight;
d) a grinding step and a classifying step to obtain water-absorbing polymer particles; and
e) surface crosslinking of the water-absorbing polymer particles.

2. The process according to claim 1 , wherein the monomer M is acrylic acid.

3. The process according to claim 1 , wherein the monomer M has been neutralized to an extent of 25 to 85 mol %.

4. The process according to claim 1 , wherein at least 0.25% by weight of the crosslinker, based on the unneutralized monomer M, is used in step a).

5. The process according to claim 1 , wherein the monomer solution is polymerized in step a) in a polymerization reactor having at least two shafts that rotate in an axially parallel manner.

6. The process according to claim 1 , wherein a thickness of the die plate in step b) is 15 to 45 mm.

7. The process according to, wherein a diameter of holes in the die plate in step b) is 2 to 20 mm.

8. The process according to claim 1 , wherein the pelletization step b) is conducted in an extruder comprising an elongated extruder housing, an outlet orifice provided with the die plate, and at least one screw shaft which rotates within the extruder housing and which conveys the polymer gel in the direction of the outlet orifice while generating a backpressure.

9. The process according to claim 1 , wherein the dried pellets have a ratio of centrifuge retention capacity CRC to the water-soluble components of at least 2.5.

10. Water-absorbing polymer particles obtained by a process according to claim 1 , characterized by
a) a free swell rate FSR of at least 0.20 g/g·s,
b) a centrifuge retention capacity CRC of at least 26.0 g/g,
c) an absorption under a load of 49.2 g/cm 2 AUL 0.7psi of at least 20.0 g/g,
d) a permeability of the swollen gel bed SFC of at least 85×10 −7 cm 3 s/g, and
e) a ratio of the permeability of the swollen gel bed SFC to the centrifuge retention capacity CRC of at most 3.7.

11. A hygiene article comprising water-absorbing polymer particles obtained according to claim 1 and characterized by
a) a free swell rate FSR of at least 0.20 g/g·s,
b) a centrifuge retention capacity CRC of at least 26.0 g/g,
c) an absorption under a load of 49.2 g/cm 2 AUL0.7 psi of at least 20.0 g/g,
d) a permeability of the swollen gel bed SFC of at least 85×10−7 cm 3 s/g, and
e) a ratio of the permeability of the swollen gel bed SFC to the centrifuge retention capacity CRC of at most 3.7.

Assignees

• Basf Se

Inventors

• Braun Markus
• Haag Monica
• Deuerlein Stephan
• Klock Volker
• Krauss Roland

Classifications

• C08J2333/02

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

• C08F2/10

  Aqueous solvent · CPC title

• C08F2/001

  Multistage polymerisation processes characterised by a change in reactor conditions without deactivating the intermediate polymer (C08F295/00, C08F297/00 take precedence) · CPC title

• A61L15/60 Primary

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

• B01J20/267

  Cross-linked polymers · CPC title