Process for preparing water-absorbing polymer particles

• US 7,682,702 B2
• Filed: 11/10/2006
• Issued: 03/23/2010
• Est. Priority Date: 11/16/2005
• Status: Active Grant

• Current Assignee: BASF SE
• Original Assignee: BASF SE
• Inventors: Nitschke, Meinhard
• Primary Examiner(s): Boykin; Terressa M
• Application Number:
  US12/092,754
• Publication Number:
  US 20080287631A1
• Time in Patent Office: 1,229 Days
• Field of Search: 241/24.28, 241/29, 264/2.6, 264/140, 424/445, 424/486, 424/487, 428/327, 428/500, 428/503, 514/55, 514/57, 560/209, 560/222, 562/545, 562/547, 604/367, 604/368
• US Class Current: 428/503
• CPC Class Codes: B01J 20/26 Synthetic macromolecular compounds
• CPC Class Codes: B01J 20/261 obtained by reactions only involving carbon to carbon unsaturated bonds macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds per se C08F
• CPC Class Codes: B01J 20/28047 Gels
• CPC Class Codes: B01J 20/30 Processes for preparing, regenerating, or reactivating
• CPC Class Codes: B01J 20/3021 Milling, crushing or grinding
• CPC Class Codes: B01J 2220/68 Superabsorbents
• CPC Class Codes: C08F 6/008 Treatment of solid polymer wetted by water or organic solvents, e.g. coagulum, filter cakes
• CPC Class Codes: C08J 2333/00 Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical, or of salts, anhydrides, esters, amides, imides, or nitriles thereof; Derivatives of such polymers
• CPC Class Codes: C08J 3/12 Powdering or granulating
• CPC Class Codes: F26B 1/005 by means of disintegrating, e.g. crushing, shredding, milling the materials to be dried F26B17/102, F26B17/103 take precedence
• CPC Class Codes: Y10T 428/254 Polymeric or resinous material
• CPC Class Codes: Y10T 428/31855 Of addition polymer from unsaturated monomers
• CPC Class Codes: Y10T 428/31866 Impregnated or coated cellulosic material

Abstract

A process for producing water-absorbing polymeric particles comprises the steps of

• i) drying a hydrogel to produce a dried hydrogel,
• ii) separating incompletely dried polymeric particles from the dried hydrogel, and
• iii) drying the separated-off incompletely dried polymeric particles,
  wherein the separated incompletely dried polymeric particles are comminuted before said drying iii).

Claims

1. A process for producing water-absorbing polymeric particles comprising the steps of

i) drying a hydrogel to produce a dried hydrogel,

ii) separating incompletely dried polymeric particles from the dried hydrogel, wherein the incompletely dried polymeric particles have a water content of at least 10% by weight, and

iii) drying the separated incompletely dried polymeric particles,

wherein the separated incompletely dried polymeric particles are comminuted before said drying iii).

2. The process according to claim 1 wherein said drying i) is carried on to such an extent that a fraction of incompletely dried polymeric particles amounts to less than 50% by weight of the dried hydrogel.

3. The process according to claim 1 wherein said separating ii) is carried out such that incompletely dried polymeric particles at least 5 mm in diameter are separated.

4. The process according to claim 1 wherein the incompletely dried polymeric particles are comminuted using a roll mill.

5. The process according to claim 1 wherein the comminuted incompletely dried polymeric particles are classified before said drying iii) and only coarse size is transferred into said drying iii) step.

6. The process according to claim 5 wherein said separated coarse size is comminuted before said drying iii).

7. The process according to claim 6 wherein said separated coarse size is comminuted by means of a mill having sharp beaters or blades and further a sieve as grinding space bound.

8. The process according to claim 6 wherein comminuted coarse size is classified before said drying iii), oversize is combined with coarse size, undersize is combined with the dried hydrogel, and only midsize is transferred into said drying iii) step.

9. The process according to claim 1 wherein said drying i) and said drying iii) are carried out in the same dryer.

10. The process according to claim 1 wherein further comminution is effected during said drying iii).

11. The process according to claim 10 wherein a shovel dryer is used for comminuting and drying.

12. The process according to claim 1 wherein the comminuted dried polymeric particles obtained after said drying iii) are further comminuted.

13. The process according to claim 12 wherein the comminuted dried polymeric particles are further comminuted using a roll mill.

14. The process according to claim 1 wherein the separated incompletely dried polymeric particles, after comminution, drying, and optional further comminution, are recycled into said separating ii) step.

15. The process according to claim 1 wherein the water-absorbing polymer is formed by a solution polymerization, and a polymerized monomer solution comprises acrylic acid and at least one crosslinker copolymerizable with acrylic acid.

16. The process according to claim 15 wherein at least 50 mol % of the monomers of said monomer solution are acrylic acid and/or salts thereof.

17. The process according to claim 1 wherein polymeric particles not separated off in said separating ii) step are ground and classified.

18. The process according to claim 17 wherein the classified polymeric particles are postcrosslinked.

19. A hygiene article comprising water-absorbing polymeric particles prepared by the method of claim 1.