Superabsorbent polymers and method of manufacturing the same

• US 20050245393A1
• Filed: 07/24/2003
• Published: 11/03/2005
• Est. Priority Date: 08/23/2002
• Status: Abandoned Application

• Current Assignee: BASF AG (BASF SE)
• Original Assignee: BASF AG (BASF SE)
• Inventors: Herfert, Norbert, Woodrum, Guy T., Chiang, William G-J, Mitchell, Michael A., Azad, Michael M.
• Application Number:
  US10/523,086
• Publication Number:
  US 20050245393A1
• Time in Patent Office: Days
• US Class Current: 502/402
• CPC Class Codes: A61L 15/60 Liquid-swellable gel-forming materials, e.g. super-absorbents
• CPC Class Codes: B01J 20/12 Naturally occurring clays or bleaching earth
• 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 20/267 Cross-linked polymers
• CPC Class Codes: B01J 2220/46 Materials comprising a mixture of inorganic and organic materials materials coated or impregnated on a carrier B01J20/32
• CPC Class Codes: B01J 2220/68 Superabsorbents
• CPC Class Codes: C08J 2300/14 Water soluble or water swellable polymers, e.g. aqueous gels
• CPC Class Codes: C08J 2333/02 Homopolymers or copolymers of acids; Metal or ammonium salts thereof
• CPC Class Codes: C08J 3/245 Differential crosslinking of one polymer with one crosslinking type, e.g. surface crosslinking
• CPC Class Codes: C08K 3/346 Clay

Abstract

Surface-crosslinked superabsorbent polymer (SAP) particles having a clay in the vicinity of the surfaces of the SAP particles a clay are disclosed. The clay is added to SAP particles during surface crosslinking to substantially reduce the generation, and recycling, of SAP fines, and to provide SAP particles having an improved acquisition rate of fluids and an improved permeability of a fluid through the swollen SAP particles. Diaper cores and absorbent articles containing the surface crosslinked SAP particles also are disclosed.

Claims

1. Surface-crosslinked superabsorbent particles comprising:

(i) about 50% to about 88%, by weight, of a superabsorbent polymer, said superabsorbent polymer comprising about 0.001% to about 5%, by weight, of a surface crosslinking agent;

(ii) about 12% to about 35%, by weight, of a clay, said clay present in the vicinity of surfaces of the superabsorbent particles; and

(iii) 0% to about 25%, by weight, of an inorganic network builder,

said particles prepared by a method comprising the steps of;

(a) polymerizing one or more monomers capable of providing a superabsorbent absorbent polymer in the presence of an internal crosslinking monomer to form a superabsorbent polymer hydrogel;

(b) comminuting the superabsorbent polymer hydrogel to form superabsorbent polymer hydrogel particles;

(c) drying the superabsorbent polymer hydrogel particles of step (b) to provide dry superabsorbent particles;

(d) applying a mixture comprising a surface crosslinking agent and a clay to the surface of the superabsorbent particles of step (c) to provide surface-treated superabsorbent polymer particles; and

(e) then heating the surface-treated superabsorbent polymer particles for a sufficient time at a sufficient temperature to surface crosslink the surface-treated superabsorbent polymer particles and position the clay in the vicinity of the surfaces of the surface-crosslinked superabsorbent particles.

2. The particles of claim 1 wherein the superabsorbent polymer is present in an amount of about 55% to about 85%, by weight, and the clay is present in an amount of about 15% to about 25%, by weight.

3. The particles of claim 1 wherein the inorganic network builder is present in an amount of about 5% to about 20%, by weight.

4. The particles of claim 1 wherein the inorganic network builder is selected from the group consisting of a silicate, an aluminate, and an aluminosilicate.

5. The particles of claim 1 wherein the inorganic network builder comprises sodium silicate, sodium aluminate, or a mixture thereof.

6. The particles of claim 1 wherein less than 5%, by weight, of the particles have a diameter of 200 μ

M or less.

7. The particles of claim 1 wherein the superabsorbent polymer comprises a polymerized α

,β

-unsaturated carboxylic acid, or a salt or an anhydride thereof.

8. The particles of claim 1 wherein the monomer is selected from the group consisting of acrylic acid, methacrylic acid, ethacrylic acid, α

-chloroacrylic acid, α

-cyanoacrylic acid, β

-methylacrylic acid, α

-phenylacrylic acid, β

-acryloxypropionic acid, sorbic acid, α

-chlorosorbic acid, angelic acid, cinnamic acid, p-chlorocinnamic acid, β

-stearylacrylic acid, itaconic acid, citraconic acid, mesaconic acid, glutaconic acid, aconitic acid, maleic acid, fumaric acid, tricarboxyethylene, maleic anhydride, vinyl sulfonic acid, allyl sulfonic acid, vinyl toluene sulfonic acid, styrene sulfonic acid, sulfoethyl acrylate, sulfoethyl methacrylate, sulfopropyl acrylate, sulfopropyl methacrylate, sulfopropyl acrylate, sulfopropyl methacrylate, 2-hydroxy-3-methacryloxypropyl sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, methacryloxy ethyl phosphate, and mixtures thereof.

9. The particles of claim 1 wherein the superabsorbent polymer is selected from the group consisting of poly(acrylic acid), a hydrolyzed starch-acrylonitrile graft copolymer, a starch-acrylic acid graft copolymer, a saponified vinyl acetate-acrylic ester copolymer, a hydrolyzed acrylonitrile copolymer, a hydrolyzed acrylamide copolymer, an ethylene-maleic anhydride copolymer, an isobutylene-maleic anhydride copolymer, a poly(vinylsulfonic acid), a poly(vinylphosphonic acid), a poly(vinylphosphoric acid), a poly(vinylsulfuric acid), a sulfonated polystyrene, and salts and mixtures thereof.

10. The particles of claim 1 wherein the superabsorbent polymer is selected from the group consisting of a poly(vinylamine), a poly(dialkylaminoalkyl (meth)acrylamide), a polyethylenimine, a poly(allylamine), a poly(allylguanidine), a poly(dimethyldiallylammonium hydroxide), a quaternized polystyrene derivative, a guanidine-modified polystyrene, a quaternized poly((meth)acrylamide) or ester analog, a poly(vinylguanidine), and salts and mixtures thereof.

11. The particles of claim 1 wherein the superabsorbent polymer comprises polyacrylic acid neutralized about 25% to 100%.

12. The particles of claim 1 wherein the clay is a swelling clay selected from the group consisting of montmorillonite, saponite, nontronite, laponite, beidelite, hectorite, sauconite, stevensite, vermiculite, volkonskoite, magadite, medmontite, kenyaite, and mixtures thereof.

13. The particles of claim 1 wherein the clay is a nonswelling clay selected from the group consisting of a kaolin mineral, a serpentine mineral, a mica mineral, a chlorite mineral, sepolite, palygorskite, bauxite, and mixtures thereof.

14. The particles of claim 13 wherein the nonswelling clay comprises a kaolinite.

15. The particles of claim 1 wherein the clay is an organophilic clay having an organic component and an inorganic component.

16. The particles of claim 15 wherein the inorganic component of the organophilic clay comprises smectite, bentonite, hectorite, montmorillonite, beidelite, saponite, stevensite, nontronite, illite, attapulgite, a zeolite, fuller'"'"'s earth, and mixtures thereof.

17. The particles of claim 15 wherein the inorganic component of the organophilic clay comprises montmorillonite.

18. The particles of claim 15 wherein the organic component of the organophilic clay comprises

19. The particles of claim 15 wherein the organophilic clay is selected from the group consisting of dimethyl benzyl (hydrogenated tallow) ammonium bentonite, methyl benzyl di(hydrogenated tallow) ammonium bentonite, dimethyl di(hydrogenated tallow) ammonium bentonite, methyl bis(2-hydroxyethyl) octadecyl ammonium bentonite, a bentonite clay treated with an amine containing three to eight carbon atoms, and mixtures thereof.

20. A method of absorbing an aqueous medium comprising contacting the medium with the superabsorbent particles of claim 1.

21. The method of claim 20 wherein the aqueous medium contains electrolytes.

22. The method of claim 21 wherein the electrolyte-containing aqueous medium is selected from the group consisting of urine, saline, menses, and blood.

23. An absorbent article comprising the superabsorbent particles of claim 1.

24. The article of claim 23 wherein the article is a diaper or a catamenial device.

25. A diaper having a core, said core comprising at least 10% by weight of the superabsorbent polymer of claim 1.

26. The diaper of claim 25 further comprising a topsheet in contact with a first surface of the core, and a backsheet in contact with a second surface of the core, said second core surface opposite from said first core surface.

27. The diaper of claim 26 further comprising an acquisition layer disposed between the topsheet and the core.

28. A method of manufacturing surface-crosslinked superabsorbent polymer particles having a clay positioned in a vicinity of surfaces of the particles comprising the steps of:

(a) forming an aqueous monomer mixture comprising (i) at least one monomer capable of forming a superabsorbent polymer, (ii) an internal crosslinking agent, and (iii) a polymerization catalyst;

(b) polymerizing the monomer in the aqueous mixture to form a superabsorbent polymer hydrogel;

(c) comminuting the superabsorbent polymer hydrogel to provide superabsorbent polymer hydrogel particles;

(d) drying the superabsorbent polymer hydrogel particles for a sufficient time at a sufficient temperature to provide dry superabsorbent polymer particles;

(e) applying a mixture of a clay and a surface crosslinking agent to surfaces of the dry superabsorbent polymer particles to provide surface-treated superabsorbent polymer particles; and

(f) heating the surface treated superabsorbent polymer particles for a sufficient time at a sufficient temperature to surface crosslink the surface treated superabsorbent polymer particles and position the clay in the vicinity of the surfaces of the particles.

29. The method of claim 28 wherein the monomer capable of forming the superabsorbent polymer is selected from the group consisting of acrylic acid, methacrylic acid, ethacrylic acid, α

-chloroacrylic acid, α

-cyanoacrylic acid, β

-methylacrylic acid, α

-phenylacrylic acid, β

-acryloxypropionic acid, sorbic acid, α

-chlorosorbic acid, angelic acid, cinnamic acid, p-chlorocinnamic acid, β

-stearylacrylic acid, itaconic acid, citraconic acid, mesaconic acid, glutaconic acid, aconitic acid, maleic acid, fumaric acid, tricarboxyethylene, maleic anhydride, vinyl sulfonic acid, allyl sulfonic acid, vinyl toluene sulfonic acid, styrene sulfonic acid, sulfoethyl acrylate, sulfoethyl methacrylate, sulfopropyl acrylate, sulfopropyl methacrylate, sulfopropyl acrylate, sulfopropyl methacrylate, 2-hydroxy-3-methacryloxypropyl sulfonic acid, 2-acrylamide-2-methylpropane sulfonic acid, methacryloxy ethyl phosphate, and mixtures thereof.

30. The method of claim 28 wherein the superabsorbent polymer is selected from the group consisting of poly(acrylic acid), a hydrolyzed starch-acrylonitrile graft copolymers, a starch-acrylic acid graft copolymer, a saponified vinyl acetateacrylic ester copolymer, a hydrolyzed acrylonitrile copolymer, a hydrolyzed acrylamide copolymer, an ethylene-maleic anhydride copolymer, an isobutylenemaleic anhydride copolymer, poly(vinylsulfonic acid), poly(vinylphosphonic acid), poly(vinylphosphoric acid), poly(vinylsulfuric acid), sulfonated polystyrene, a poly(vinylamine), a poly(dialkylaminoalkyl (meth)acrylamide), a lightly crosslinked polyethylenimine, a poly(allylamine), a poly(allylguanidine), a poly(dimethyldiallylammonium hydroxide), a quaternized polystyrene derivative, a guanidine-modified polystyrene, a quaternized poly((meth)acrylamide) or ester analog, and mixtures thereof.