Microencapsulated rubber additives and method for production thereof

1. Microcapsules having a polymer capsule wall and a core which comprises at least one rubber additive, wherein the polymer capsule wall comprises an interpenetrating or semi-interpenetrating network formed between at least one reactive resin component and at least one anionically substituted polymer selected from the group consisting of homo- and copolymers of vinyl phosphorous acid, homopolymers of vinyl sulphonic acid, and homo- and copolymers of styrene phosphonic acid, the reactive resin component being a melamine formaldehyde resin, a polyurea resin, or both.

2. The microcapsules according to claim 1 , wherein the polyurea resin is formed from a diisocyanate and polyfunctional amine.

3. The microcapsules according to claim 1 , wherein the anionically substituted polymer is selected from the group consisting of the homo- and copolymers of vinyl phosphorous acid and homo- and copolymers of styrene phosphonic acid.

4. The microcapsules according to claim 1 , wherein the capsule wall is formed from a melamine formaldehyde resin which is soluble in water and the anionically substituted polymer.

5. The microcapsules according to claim 1 , wherein the capsule wall is formed from a melamine formaldehyde resin which is soluble in an organic solvent and the anionically substituted polymer.

6. The microcapsules according to claim 1 , wherein the core consists of sulphur.

7. The microcapsules according to claim 6 , wherein the sulphur is present in liquid or solid form.

8. The microcapsules according to claim 6 , wherein the sulphur content of the microcapsules is at least 70% by weight.

9. The microcapsules according to claim 1 , wherein the microcapsules have a further outer capsule wall or coating.

10. The microcapsules according to claim 9 , wherein the outer capsule wall or coating consists of at least one straight-chain polymer.

11. The microcapsules according to claim 9 , wherein the outer capsule wall or coating consists of at least one low-molecular organic or inorganic substance.

12. The microcapsules according to claim 1 , wherein the microcapsules have an average particle diameter of 1 to 30 μm.

13. The microcapsules according to claim 1 , wherein the wall thickness of the capsule wall is from 30 to 100 nm.

14. The microcapsules according to claim 1 , wherein the microcapsules are thermally and mechanically stable under formulation and processing conditions in kneaders, calenders or twin-screw extruders at temperatures up to 140° C.

15. The microcapsules according to claim 1 , wherein the capsule wall dissolves under vulcanisation conditions with release of the rubber additive.

16. A method for the production of microcapsules having a core comprising at least one rubber additive, comprising:

a) dispersing the at least one rubber additive with shearing in a solution comprising at least one compound which forms a reactive resin and at least one anionically substituted polymer selected from the group consisting of homo- and copolymers of vinyl phosphorous acid, homopolymers of vinyl sulphonic acid, and homo- and copolymers of styrene phosphonic acid, and

b) forming a capsule wall which encloses the rubber additive by the addition of a catalyst and/or by the effect of temperature, wherein the polymer capsule wall

comprises an interpenetrating or semi-interpenetrating network formed between the at least one compound which forms a reactive resin and the at least one anionically substituted polymer,

wherein in step a), the compound which forms the reactive resin is a prepolymer.

17. The method according to claim 16 , wherein the reactive resin in step a) is formed in situ from the compounds which form the reactive resin.

18. The method according to claim 16 , wherein the reactive resin is a melamine formaldehyde resin, a polyurea resin, or both.

19. The method according to claim 18 , wherein the polyurea resin is formed from a diisocyanate and a polyfunctional amine.

20. The method according to claim 16 , wherein the anionically substituted polymer is selected from the group consisting of the homo- and copolymers of vinyl phosphorous acid and homo- and copolymers of styrene phosphonic acid.

21. The method according to claim 16 , wherein in step a), a melamine formaldehyde resin and the anionically substituted polymer are dissolved in an aqueous solution.

22. The method according to claim 16 , wherein in step a), a melamine formaldehyde resin and the anionically substituted polymer are dissolved in an organic solvent.

23. The method according to claim 16 , wherein the rubber additive is sulphur in liquid or solid form.

24. The method according to claim 16 , wherein following the formation of the capsule wall, the latter is cured thermally and/or chemically.

25. The method according to claim 16 , wherein a further outer capsule wall or coating is deposited on the microcapsules.

26. The method according to claim 25 , wherein the outer capsule wall or coating consists of at least one straight-chain polymer or at least one low-molecular organic or inorganic substance.

27. Microcapsules having a polymer capsule wall and a core which comprises at least one rubber additive, wherein the capsule wall comprises an interpenetrating or semi-interpenetrating network formed between at least one reactive resin component and at least one polyelectrolyte component or ionomer component, the reactive resin component being a polyurea resin;

wherein the polyelectrolyte component or ionomer component is an anionically substituted polymer selected from the group consisting of homo- and copolymers of vinyl phosphorous acid, homopolymers of vinyl sulphonic acid, and homo- and copolymers of styrene phosphonic acid.

28. A method of vulcanizing natural or synthetic rubber comprising utilizing the microcapsules according to claim 1 during the vulcanization.

29. A method of vulcanizing natural or synthetic rubber comprising utilizing the microcapsules according to claim 27 during the vulcanization.

30. The microcapsules according to claim 1 , wherein the interpenetrating or semi-interpenetrating network is present in the polymer capsule wall throughout its thickness.

31. Microcapsules having a polymer capsule wall and a core which comprises at least one rubber additive, wherein the polymer capsule wall comprises an interpenetrating or semi-interpenetrating network formed between at least one reactive resin component and an anionically substituted polymer which is poly(styrene-co-sodium maleate), the reactive resin component being a melamine formaldehyde resin, a polyurea resin, or both.

32. The microcapsules according to claim 31 , wherein the capsule wall is formed from a melamine formaldehyde resin which is soluble in water and the anionically substituted polymer.

33. The microcapsules according to claim 31 , wherein the capsule wall is formed from a melamine formaldehyde resin which is soluble in an organic solvent and the anionically substituted polymer.

34. The microcapsules according to claim 31 , wherein the core consists of sulphur.

35. The microcapsules according to claim 34 , wherein the sulphur is present in liquid or solid form.

36. A method of vulcanizing natural or synthetic rubber comprising utilizing the microcapsules according to claim 31 during the vulcanization.

37. A method for the production of microcapsules according to claim 31 , comprising:

a) dispersing the at least one rubber additive with strong shearing in a solution comprising at least one compound which forms a reactive resin and the anionically substituted polymer, and

b) forming a capsule wall which encloses the rubber additive by the addition of a catalyst and/or by the effect of temperature, wherein the polymer capsule wall comprises an interpenetrating or semi-interpenetrating network formed between the reactive resin component and the anionically substituted polymer.