Cross-linkable fluoroelastomer, its composition and cross-linked rubber molded product

1. A cross-linkable fluoroelastomer having a Mooney viscosity of from 20 to 300, obtained by heat treating a mixture of a fluoroelastomer (A) and an organic peroxide (B) at a temperature of from 110 to 380° C. for from 10 seconds to 3 hours,

wherein the cross-linkable fluoroelastomer has an absorption peak at from 1,640 to 1,700 cm −1 , wherein the intensity of the absorption peak at from 1,640 to 1,700 cm −1 of the infrared absorption spectrum as represented by absorbance of a hot pressed sample having a thickness of 0.2 mm is from 0.05 to 1.5, and

wherein after the heat treating the cross-linkable fluoroelastomer has more unsaturated carbon-carbon bonds than the fluoroelastomer (A),

wherein the fluoroelastomer (A) is a tetrafluoroethylene/propylene copolymer.

2. The cross-linkable fluoroelastomer according to claim 1 , wherein the intensity of the absorption peak at from 1,640 to 1,700 cm −1 of the infrared absorption spectrum as represented by absorbance of a hot pressed sample having a thickness of 0.2 mm is from 0.01 to 5.0.

3. The cross-linkable fluoroelastomer according to claim 1 , of which the infrared absorption spectrum as represented by absorbance has no absorption peak at from 1,740 to 1,800 cm −1 or has an absorption peak at from 1,740 to 1,800 cm −1 with an absorption peak intensity of a hot pressed sample having a thickness of 0.2 mm of at most 2.0.

4. The cross-linkable fluoroelastomer according to claim 1 , wherein the blend ratio of the organic peroxide (B) is from 0.1 to 10 parts by mass per 100 parts by mass of the fluoroelastomer (A).

5. The cross-linkable fluoroelastomer according to claim 1 , wherein the temperature for half life of one minute of the organic peroxide (B) is from 110 to 300° C.

6. A fluoroelastomer composition comprising the cross-linkable fluoroelastomer as defined in claim 1 , a cross-linking agent (C) and a cross-linking assistant (D).

7. A cross-linked rubber molded product obtained by cross-linking the fluoroelastomer composition as defined in claim 6 .

8. The cross-linkable fluoroelastomer of claim 1 , wherein the fluoroelastomer has one or more unsaturated carbon-carbon groups.

9. The cross-linkable fluoroelastomer according to claim 1 , having no hydroxycarbonyl group.

10. The cross-linkable fluoroelastomer according to claim 1 , which has a cross-linking density of from 34 to 44 when subjected to primary cross-linking conditions of 170° C. for 20 minutes and secondary cross-linking at 200° C. for 4 hours.

11. The cross-linkable fluoroelastomer according to claim 1 , having a Mooney viscosity of from 20 to 105.

12. The cross-linkable fluoroelastomer of claim 1 , wherein the organic peroxide is dicumyl peroxide, tertiary butyl cumyl peroxide, 1,3-bis(tert-butyl peroxy isopropyl) benzene or ditertiary butyl peroxide.

13. The cross-linkable fluoroelastomer according to claim 1 , wherein the heat treating includes extruding the fluoroelastomer in the presence of the organic peroxide.

14. The cross-linkable fluoroelastomer according to claim 1 , wherein the only halogen atoms in the fluoroelastomer (A) are F atoms.

15. The cross-linkable fluoroelastomer according to claim 1 , wherein the fluoroelastomer (A) consists of polymerized monomer units of tetrafluoroethylene and propylene.

16. The cross-linkable fluoroelastomer according to claim 1 , wherein the fluoroelastomer (A) consists of atoms of carbon, hydrogen and fluorine.

17. The cross-linkable fluoroelastomer according to claim 1 , wherein the intensity of the absorption peak at from 1,640 to 1,700 cm −1 , of a hot pressed sample having a thickness of 0.2 mm, is from 0.239 to 2.0.

18. A cross-linked rubber molded product obtained by cross-linking the cross-linkable fluoroelastomer as defined in claim 1 by applying an ionizing radiation thereto.

19. A method for producing a cross-linkable fluoroelastomer, which comprises

heat-treating a mixture of a fluoroelastomer (A) and an organic peroxide (B) at a temperature of from 110 to 380° C. for from 10 seconds to 3 hours to form the cross-linkable fluoroelastomer,

wherein the cross-linkable fluoroelastomer formed by the heat-treating has an absorption peak at from 1,640 to 1,700 cm −1 , wherein the intensity of the absorption peak at from 1,640 to 1,700 cm −1 of the infrared absorption spectrum as represented by absorbance of a hot pressed sample having a thickness of 0.2 mm is from 0.05 to 1.5, and

wherein after the heat treating the cross-linkable fluoroelastomer has more unsaturated carbon-carbon bonds than the fluoroelastomer (A),

wherein the fluoroelastomer (A) is a tetrafluoroethylene/propylene copolymer.

20. The method for producing a cross-linkable fluoroelastomer according to claim 19 , wherein the fluoroelastomer (A) and the organic peroxide (B) are kneaded by means of an extruder.

21. The method for producing a cross-linkable fluoroelastomer according to claim 19 , wherein the only halogen atoms in the fluoroelastomer (A) are F atoms.

22. The method according to claim 19 , wherein the fluoroelastomer (A) consists of polymerized monomer units of tetrafluoroethylene and propylene.

23. The method according to claim 19 , wherein the fluoroelastomer (A) consists of atoms of carbon, hydrogen and fluorine.

24. The method according to claim 19 , wherein the intensity of the absorption peak at from 1,740 to 1,800 cm −1 is from 0.239 to 2.0.

25. The method according to claim 19 , further comprising:

isolating the cross-linkable fluoroelastomer after the heat treating.

26. A cross-linkable fluoroelastomer obtained by a heat-treatment of a mixture of a fluoroelastomer (A) which does not have an absorption peak at from 1,640 to 1,700 cm −1 of the infrared absorption spectrum, and an organic peroxide (B) at a temperature of from 110 to 380° C. for from 10 seconds to 3 hours, wherein the cross-linkable fluoroelastomer has a Mooney viscosity of from 20 to 300, of which the absorption peak is at from 1,640 to 1,700 cm −1 of the infrared absorption spectrum; the intensity of the absorption peak at from 1,640 to 1,700 cm −1 of the infrared absorption spectrum as represented by absorbance of a hot pressed sample having a thickness of 0.2 mm is from 0.05 to 1.5; and the infrared absorption spectrum as represented by absorbance has no absorption peak at from 1,740 to 1,800 cm −1 or has an absorption peak at from 1,740 to 1,800 cm −1 with an absorption peak intensity of at most 0.2, and

wherein after the heat treating the cross-linkable fluoroelastomer has more unsaturated carbon-carbon bonds than the fluoroelastomer (A),

wherein the fluoroelastomer (A) is a tetrafluoroethylene/propylene copolymer.

27. The cross-linkable fluoroelastomer according to claim 26 , wherein the blend ratio of the organic peroxide (B) is from 0.1 to 10 parts by mass per 100 parts by mass of the fluoroelastomer (A).

28. The cross-linkable fluoroelastomer according to claim 26 , wherein the temperature for half life of one minute of the organic peroxide (B) is from 110 to 300° C.

29. A cross-linked rubber molded product obtainable by cross-linking the cross-linkable fluoroelastomer as defined in claim 26 , by applying an ionizing radiation thereto.

30. The cross-linkable fluoroelastomer according to claim 26 , wherein the only halogen atoms in the fluoroelastomer (A) are F atoms.

31. The cross-linkable fluoroelastomer according to claim 26 , wherein the fluoroelastomer (A) consists of polymerized monomer units of tetrafluoroethylene and propylene.

32. The cross-linkable fluoroelastomer according to claim 26 , wherein the fluoroelastomer (A) consists of atoms of carbon, hydrogen and fluorine.

33. The cross-linkable fluoroelastomer according to claim 26 , wherein the intensity of the absorption peak at from 1,640 to 1,700 cm −1 is from 0.239 to 1.5.

34. A process for producing a cross-linkable fluoroelastomer comprising a heat-treatment of a mixture of a fluoroelastomer (A) which does not have an absorption peak at from 1,640 to 1,700 cm −1 of the infrared absorption spectrum, and an organic peroxide (B) at a temperature of from 110 to 380° C. for from 10 seconds to 3 hours,

wherein the cross-linkable fluoroelastomer has a Mooney viscosity of from 20 to 300, of which the absorption peak is at from 1,640 to 1,700 cm −1 of the infrared absorption spectrum; the intensity of the absorption peak at from 1,640 to 1,700 cm −1 of the infrared absorption spectrum as represented by absorbance of a hot pressed sample having a thickness of 0.2 mm is from 0.05 to 1.5; and the infrared absorption spectrum as represented by absorbance has no absorption peak at from 1,740 to 1,800 cm −1 or has an absorption peak, at from 1,740 to 1,800 cm −1 with an absorption peak intensity of at most 0.2, and

wherein after the heat treating the cross-linkable fluoroelastomer has more unsaturated carbon-carbon bonds than the fluoroelastomer (A),

wherein the fluoroelastomer (A) is a tetrafluoroethylene/propylene copolymer.

35. The process for producing a cross-linkable fluoroelastomer according to claim 34 , wherein the heat-treatment is carried out by kneading a mixture of the fluoroelastomer (A) and the organic peroxide (B) by means of an extruder.

36. A fluoroelastomer composition comprising the cross-linkable fluoroelastomer produced by the process as defined in claim 34 , a cross-linking agent (C) and a cross-linking assistant (D).

37. A cross-linked rubber molded product obtainable by cross-linking the fluoroelastomer composition as defined in claim 36 .

38. The process for producing a cross-linkable fluoroelastomer according to claim 34 , wherein the only halogen atoms in the fluoroelastomer (A) are F atoms.

39. The process for producing a cross-linkable fluoroelastomer according to claim 34 , wherein the fluoroelastomer (A) consists of polymerized monomer units of a perfluoro olefin and a hydrocarbon.

40. The process for producing a cross-linkable fluoroelastomer according to claim 34 , wherein the fluoroelastomer (A) consists of atoms of carbon, hydrogen and fluorine.

41. The process according to claim 34 , wherein the intensity of the absorption peak at from 1,640 to 1,700 cm −1 is from 0.239 to 1.5.

42. The process according to claim 34 , further comprising:

isolating the cross-linkable fluoroelastomer after the heat treating.