Water-absorbing polymers with improved properties, process for the preparation and use thereof

• US 6,143,821 A
• Filed: 05/20/1998
• Issued: 11/07/2000
• Est. Priority Date: 11/21/1995
• Status: Expired due to Term

• Current Assignee: Evonik Degussa GmbH
• Original Assignee: Stockhausen GmbH & Company Kg (Stockhausen Incorporated)
• Inventors: Houben, Jochen
• Primary Examiner(s): BOYKIN, TERRESSA M
• Application Number:
  US09/068,560
• Time in Patent Office: 902 Days
• Field of Search: 524/557
• US Class Current: 524/557
• CPC Class Codes: A61L 15/60 Liquid-swellable gel-forming materials, e.g. super-absorbents
• CPC Class Codes: C08F 220/04 Acids; Metal salts or ammonium salts thereof
• CPC Class Codes: C08F 251/00 Macromolecular compounds obtained by polymerising monomers on to polysaccharides or derivatives thereof
• CPC Class Codes: C08F 261/04 on to polymers of vinyl alcohol
• CPC Class Codes: C08F 290/062 Polyethers
• CPC Class Codes: H01B 3/30 plastics; resins; waxes

Abstract

The present invention relates to powdery absorbents for water and aqueous liquids, which are based on water-swellable, but not water-soluble, polymers, are cross-linked, and are built up of partially neutralized, monoethylenically unsaturated, acid groups-containing monomers, optional further monomers copolymerizable with these, and optional polymers suitable as a graft basis. These polymers are produced by using a cross-linker combination consisting of

CH.sub.2 ═CR.sup.5 --CO--(OCHR.sup.3 --CHR.sup.3).sub.z O--CH.sub.2

--CR⁵ ═CH₂ I.

R.sup.1 --[O(CHR.sup.3 --CHR.sup.3 O).sub.u --CO--R.sup.2 ].sub.x II.

with

R¹ : multivalent C_2-10 -alkyl,

R² : linear or branched C_2-10 -alkenyl,

R³ : H, CH₃, C₂ H₅,

R⁵ : H, CH₃,

x: 2-6,

u: 0-15,

z: 3-20

and a secondary cross-linker. Superficial secondary cross-linkage achieves a property combination of high retention, high absorption under pressure, low soluble contents, and a rapid liquid absorption. The polymers are used in constructions, such as diapers, for the absorption of body fluids, in current-conducting or light-transmitting cables, and in the cultivation of plants.

Claims

1. A cross-linked polymer which absorbs aqueous liquids prepared by:

(co)polymerizing (i) at least one partially neutralized, monoethylenically unsaturated, acid group-containing monomer or (ii) at least one partially neutralized, monoethylenically unsaturated, acid-group-containing monomer with a copolymerizable monomer or (iii) graft (co)polymerizing monomer(s) (i) or monomer combination (ii) onto a graft base in the presence of a cross-linking agent combination consisting of;

space="preserve" listing-type="equation">40-90 mol. % of CH.sub.2 ═

CR.sup.5 --CO--(OCHR.sup.3 --CHR.sup.3).sub.z O--CH.sub.2 --CR.sup.5 ═

CH.sub.2 (I)

and

space="preserve" listing-type="equation">10-60 mol. % of R.sup.1 --[O(CHR.sup.3 --CHR.sup.3 O).sub.u --CO--R.sup.2 ].sub.x (II)

wherein R¹ is a multivalent C_2-10 -alkyl group, R² is a linear or branched C_2-10 -alkenyl group, R³ is H, CH₃ or C₂ H₅, R⁵ is H or CH₃, x is 2-6, u is 0-15 and z is 3-20, and a surface cross-linking agent.

2. The polymer according to claim 1 wherein 50-80 mol-% of cross-linking agent I is used and 20-50 mol-% of cross-linking agent II is used, relative to the cross-linker mixture.

3. The polymer according to claim 1 wherein 60-80 mol-% of cross-linking agent I is used and 20-40 mol-% of cross-linking agent II is used, relative to the cross-linker mixture.

4. The polymer according to claim 1 wherein the cross-linker combination is used in an amount of 0.1-2.0%-wt., relative to the monomers.

5. The polymer according to claim 1 wherein the cross-linker combination is used in an amount of 0.3-1.0%-wt., relative to the monomers.

6. The polymer according to claim 1 wherein cross-linker I in the polyglycol chain consists in weight average of at least 3 glycol units.

7. The polymer according to claim 1 wherein the unsaturated acid groups-containing monomers are selected from the group consisting of acrylic acid, methacrylic acid, vinyl acetic acid, vinyl sulfonic acid, methallyl sulfonic acid, and 2-acrylamido-2-methylpropane sulfonic acid.

8. The polymer according to claim 1 wherein it comprises incorporated by polymerization 0 to 40%-wt., relative to the acid groups-containing monomers, of further comonomers of the group consisting of (meth)acrylamide, (meth)acrylonitrile, vinyl pyrrolidone, hydroxyethyl acrylate, and vinyl acetamide.

9. The polymer according to claim 1 wherein it comprises 0 to 30%-wt., relative to the sum of all monomers, of water-soluble polymers suitable as a graft basis.

10. The polymer according to claim 1 wherein the secondary cross-linkage is optionally repeated several times.

11. The polymer according to claim 10 wherein it has been cross-linked at the surface with a secondary cross-linker belonging to the group of polyols, polyepoxides, polyamines, or alkylene carbonates.

12. The polymer according to claim 10 wherein has a retention of at least 30 g/g, a liquid absorption under pressure (49 g/cm2) of at least 20 g/g, a maximum of soluble constituents after 16 hours of 12%, and a swell rate of below 40 sec.

13. The polymer according to claim 1 wherein it has a liquid absorption under pressure (49 g/cm2) of at least 22 g/g.

14. The polymer according to claim 1 wherein it has a swell rate of below 35 sec.

15. The polymer according to claim 1 wherein the maximum of soluble constituents after 16 hours amounts to 10%.

16. The process according to claim 1 characterized in that surface treatment and cross-linkage are carried out several times.

17. A process for the production of a cross-linked polymer which absorbs aqueous liquids according to claim 1, comprising:

(co)polymerizing at least one unsaturated, acid group-containing, partially neutralized monomer and a cross-linking agent mixture of;

space="preserve" listing-type="equation">40-90 mol. % CH.sub.2 ═

CR.sup.5 --CO--(OCHR.sup.3 --CHR.sup.3).sub.z O--CH.sub.2 --CR.sup.5 ═

CH.sub.2 (I)

and

space="preserve" listing-type="equation">10-60 mol. % of R.sup.1 --[O(CHR.sup.3 --CHR.sup.3 O).sub.u --CO--R.sup.2 ].sub.x (II)

wherein R¹ is a multivalent C_2-10 -alkyl group, R² is a linear or branched C_2-10 -alkenyl group, R³ is H, CH₃ or C₂ H₅, R⁵ is H or CH₃, x is 2-6, u is 0-15 and z is 3-20 in the presence of a radical generating agent in solution or in suspension thereby forming a hydrogel;

comminuting, drying, grinding and screening the polymer material obtained; and

treating the polymer with a surface cross-linking agent at an elevated temperature.

18. The polymer according to claim 6, wherein the weight average of said cross-linker I in the polyglycol chain ranges from 5-20.

19. The polymer according to claim 18, wherein said range is from 8-12.

20. The polymer according to claim 9, wherein said graft base is a polysaccharide.

21. The polymer according to claim 9, wherein said graft base is polyvinyl alcohol.

22. A method of absorption, comprising:

contacting water, an aqueous liquid or body fluid with the cross-linked polymer of claim 1 which is a component of a device which comes into contact with water, an aqueous liquid or body fluid.

23. A method of supporting fertilizer or an active substance which is released in the environment, comprising:

supporting certain fertilizer or other active substance on the cross-linked polymer of claim 1, thereby providing for the prolonged release of said fertilizer or other active substance over a period of time.