Method for Producing Water-Absorbent Polymer Particles with a Higher Permeability by Polymerising Droplets of a Monomer Solution

• US 20100068520A1
• Filed: 07/11/2007
• Published: 03/18/2010
• Est. Priority Date: 07/19/2006
• Status: Active Grant

• Current Assignee: BASF SE
• Original Assignee: BASF SE
• Inventors: Stueven, Uwe
• Granted Patent: US 8,124,229 B2
• Time in Patent Office: Days
• US Class Current: 428/402
• CPC Class Codes: A61L 15/60 Liquid-swellable gel-forming materials, e.g. super-absorbents
• CPC Class Codes: C08F 2/00 Processes of polymerisation
• CPC Class Codes: C08F 2/10 Aqueous solvent
• CPC Class Codes: C08F 220/06 Acrylic acid; Methacrylic acid; Metal salts or ammonium salts thereof
• CPC Class Codes: C08F 222/103 of trialcohols, e.g. trimethylolpropane tri(meth)acrylate
• CPC Class Codes: Y10T 428/2982 Particulate matter [e.g., sphere, flake, etc.]

Abstract

A process for preparing water-absorbing polymer beads with high permeability by polymerizing droplets of a monomer solution in a gas phase surrounding the droplets, wherein the monomer solution comprises at least 0.5% by weight of a crosslinker, based on the monomer, the polymerization in the droplet takes place in homogeneous phase, and the polymer beads have a mean diameter of at least 150 μm.

Claims

1. A process for preparing water-absorbing polymer beads by polymerizing droplets of a monomer solution comprising

a) at least one ethylenically unsaturated monomer,

b) at least one crosslinker,

c) at least one initiator, and

d) water,

in a gas phase surrounding the droplets, the polymerization in the droplet taking place in a homogeneous phase, wherein the monomer solution comprises at least 0.5%, by weight, of the crosslinker b), based on the monomer a), and the polymer beads have a mean diameter of at least 150 μ

m.

2. The process according to claim 1, wherein the monomer a) has at least one acid group.

3. The process according to claim 2, wherein the acid groups of the monomer a) are at least partly neutralized.

4. The process according to claim 1, wherein the monomer a) is acrylic acid to an extent of at least 50 mol %.

5. The process according to claim 1, wherein the polymer beads have a mean diameter of at least 200 μ

m.

6. The process according to claim 1, wherein at least 90%, by weight of the polymer beads have a diameter of from 100 to 800 μ

m.

7. The process according to claim 1, wherein a carrier gas flows through a reaction chamber.

8. The process according to claim 7, wherein the carrier gas leaving the reaction chamber is recycled at least partly after one pass.

9. The process according to claim 7, wherein an oxygen content of the carrier gas is from 0.001 to 0.15% by volume.

10. The process according to claim 1, wherein the polymer beads are dried and/or postcrosslinked in at least one further process step.

11. Water-absorbing polymer beads prepared according to the method of claims 1.

22. A hygiene article comprising polymer beads prepared according to the process of claim 1.

12. Water-absorbing polymer beads having a mean sphericity of at least 0.84, a content of hydrophobic solvents of less than 0.005%, by weight, and a permeability of at least 5×

10<sup>−

7</sup> cm³ s/g.

13. Polymer beads according to claim 12, having a centrifuge retention capacity of at least 10 g/g.

14. Polymer beads according to claim 12, having a mean diameter of at least 200 μ

m.

15. Polymer beads according claim 12, wherein at least 90%, by weight, of the polymer beads have a diameter of from 100 to 800 μ

m.

16. Polymer beads according to claim 12, comprising at least partly of polymerized ethylenically unsaturated acid-bearing monomers.

17. Polymer beads according to claim 16, wherein the acid groups of the polymerized monomer are at least partly neutralized.

18. Polymer beads according to claim 16, wherein the ethylenically unsaturated monomer a) is acrylic acid to an extent of at least 50 mol %.

19. Polymer beads according to claim 12, which comprise at least 0.5%, by weight, of copolymerized crosslinker b).

21. A hygiene article comprising polymer beads according to claim 12.

20. (canceled)