Conductive polymer compositions, and to devices comprising such compositions

• US 4,388,607 A
• Filed: 10/17/1979
• Issued: 06/14/1983
• Est. Priority Date: 12/16/1976
• Status: Expired due to Term

• Current Assignee: Raychem Limited (TE Connectivity Limited)
• Original Assignee: Raychem Limited (TE Connectivity Limited)
• Inventors: Lyons, Bernard J., Horsma, David A., Moyer, Wendell W., Toy, Lester T.
• Primary Examiner(s): Reynolds, B. A.
• Application Number:
  US06/085,679
• Time in Patent Office: 1,336 Days
• Field of Search: 338/22 R, 338/22 SD, 338/25, 219/553, 219/548, 219/549, 252/511
• US Class Current: 338/22.0SD
• CPC Class Codes: H01B 1/24 the conductive material comprising carbon-silicon compounds, carbon or silicon
• CPC Class Codes: H01C 7/027 consisting of conducting or semi-conducting material dispersed in a non-conductive organic material

Abstract

Conductive polymer compositions which have improved voltage stability and which preferably exhibit PTC behavior. The compositions comprise a carbon black dispersed in a crystalline copolymer of an olefin and at least 10% by weight of an olefinically unsaturated comonomer containing a polar group. The carbon black has a particle size greater than 18 millimicrons, preferably greater than 30 millimicrons, a d-spacing greater than 360 and a surface area which is less than

1.2S+e.sup.S/50

where S is the DBP absorption of the carbon black. The carbon black is preferably present in amount at least 15% by weight of the composition. Particularly useful devices including such compositions are self-regulating heaters.

Claims

1. An electrical device comprising an element composed of a conductive polymer and at least two electrodes adapted to be connected to an external source of electrical power so as to cause an electrical current to pass through the element, said element being composed of a cross-linked conductive polymer composition which exhibits PTC behavior with an R₁₄ value of at least 2.5 and which comprises

(a) conductive carbon black having a particle size greater than 18 millimicrons, a d-spacing greater than 360, and a surface area (A) which is less than

View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)

2. A device according to claim 1 wherein said carbon black has a particle size greater than 30 millimicrons.

3. A device according to claim 1 wherein said carbon black has a particle size of at most 75 millimicrons.

4. A device according to claim 1 wherein said composition has a gel fraction of at least 0.6.

5. A device according to claim 1 wherein said composition also comprises

(c) at least one crystalline polymer which is selected from polymers consisting essentially of units derived from at least one olefin, polymers comprising at least 50% by weight of --CH₂ CHCl-- units and polymers comprising at least 50% by weight of --CH₂ CF₂ -- units;

which has a softening point higher than said copolymer (b); and

which serves as a matrix for the carbon-black-containing copolymer (b).

6. A device according to claim 5 wherein said composition has a resistivity at 25°

C. of 80 to 10⁵ ohm.cm.

7. A device according to claim 6 which comprises a pair of laminar electrodes having a said element in the form of a lamina therebetween.

8. A device according to claim 7 which comprises

(1) an elongate element of a said composition;

(2) at least two longitudinally extending electrodes embedded in said composition parallel to each other; and

(3) an outer layer of a protective and insulating composition.

9. A device according to claim 1 wherein said composition also comprises

(c) at least one crystalline polymer which consists essentially of units derived from at least one olefin;

which has a softening point higher than said copolymer (b); and

which serves as a matrix for the carbon-black-containing copolymer (b).

10. A device according to claim 9 wherein said crystalline polymer (c) is polyethylene.

11. A device according to claim 10 wherein said crystalline copolymer (b) is a copolymer of ethylene and a polar comonomer selected from methyl acrylate, ethyl acrylate and vinyl acetate.

12. A device according to claim 9 wherein said crystalline copolymer (b) is a copolymer of ethylene and a polar comonomer selected from methyl acrylate, ethyl acrylate, vinyl acetate, acrylic acid and methacrylic acid.

13. A device according to claim 1 wherein the copolymer (b) is a copolymer of ethylene and vinyl acetate and wherein the conductive polymer composition also comprises polyethylene.

14. A device according to claim 13 which is a self-limiting heater and which comprises

(1) an elongate element of a said composition;

(2) at least two longitudinally extending electrodes embedded in said composition parallel to each other; and

(3) an outer layer of a protective and insulating composition.

15. A device according to claim 1 wherein the copolymer (b) is a copolymer of ethylene and ethyl acrylate and wherein the conductive polymer composition also comprises polyethylene.

16. A device according to claim 15 which is a self-limiting heater and which comprises

(1) an elongate element of a said composition;

(2) at least two longitudinally extending electrodes embedded in said composition parallel to each other; and

(3) an outer layer of a protective and insulating composition.

17. An electrical device comprising an element composed of a conductive polymer and at least two electrodes adapted to be connected to an external source of electrical power so as to cause an electrical current to pass through the element, said element being composed of a cross-linked conductive polymer composition which has a gel fraction of at least 0.6 and which comprises

(a) a conductive carbon black having a particle size greater than 18 millimicrons, a d-spacing greater than 360, and a surface area (A) which is less than

View Dependent Claims (18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 33, 35, 36, 38, 40, 42, 45, 48, 49, 50)

18. A device according to claim 17 wherein said carbon black has a particle size greater than 30 millimicrons.

19. A device according to claim 17 wherein said carbon black has a particle size of at most 75 millimicrons.

20. A device according to claim 17 wherein said composition also comprises

(c) at least one crystalline polymer which is selected from polymers consisting essentially of units derived from at least one olefin, polymers comprising at least 50% by weight of --CH₂ CHCl-- units and polymers comprising at least 50% by weight of --CH₂ CF₂ units;

which has a softening point higher than said copolymer (b); and

which serves as a matrix for the carbon-black-containing copolymer (b).

21. A device according to claim 20 wherein said composition has a resistivity at 25°

C. of 80 to 10⁵ ohm.cm.

22. A device according to claim 21 which comprises a pair of laminar electrodes having a said element in the form of a lamina therebetween.

23. A device according to claim 21 which is a self-limiting heater and which comprises

(1) an elongate element of a said composition;

(2) at least two longitudinally extending electrodes embedded in said composition parallel to each other; and

(3) an outer layer of a protective and insulating composition.

24. A device according to claim 17 wherein said composition also comprises

(c) at least one crystalline polymer which consists essentially of units derived from at least one olefin;

which has a softening point higher than said copolymer (b); and

which serves as a matrix for the carbon-black-containing copolymer (b).

25. A device according to claim 24 wherein said crystalline polymer (c) is polyethylene.

26. A device according to claim 25 wherein said crystalline copolymer (b) is a copolymer of ethylene and a polar comonomer selected from methyl acrylate, ethyl acrylate and vinyl acetate.

27. A device according to claim 24 wherein said crystalline copolymer (b) is a copolymer of ethylene and a polar comonomer selected from methyl acrylate, ethyl acrylate, vinyl acetate, acrylic acid and methacrylic acid.

33. A device according to claim 27 wherein said composition also comprises

(c) at least one crystalline polymer which is selected from polymers consisting essentially of units derived from at least one olefin, polymers comprising at least 50% by weight of --CH₂ CHCl-- units and polymers comprising at least 50% by weight of --CH₂ CF₂ -- units;

which has a softening point higher than said copolymer (b); and

which serves as a matrix for the carbon-black-containing copolymer (b).

35. A device according to claim 33 which comprises a pair of laminar electrodes having a said element in the form of a lamina therebetween.

36. A device according to claim 33 which comprises

(1) an elongate element of a said composition;

(2) at least two longitudinally extending electrodes embedded in said composition parallel to each other; and

(3) an outer layer of a protective and insulating composition.

38. A device according to claim 36 wherein said crystalline polymer (c) is polyethylene.

40. A device according to claim 36 wherein said crystalline copolymer (b) is a copolymer of ethylene and a polar comonomer selected from methyl acrylate, ethyl acrylate, vinyl acetate, acrylic acid and methacrylic acid.

42. A heater according to claim 40 wherein the copolymer (b) is an ethylene/vinyl acetate copolymer and the polymer (c) is polyethylene.

45. A heater according to claim 40 wherein the copolymer (b) is an ethylene/ethyl acrylate copolymer and the polymer (c) is polyethylene.

48. A heater according to claim 40 wherein the carbon black is a furnace black.

49. A heater according to claim 40 wherein the carbon black is a thermal black.

50. A heater according to claim 40 wherein the carbon black is a channel black.

28. An electrical device comprising an element composed of a conductive polymer and at least two electrodes adapted to be connected to an external source of electrical power so as to cause an electrical current to pass through the element, said element being composed of a cross-linked conductive polymer composition which exhibits PTC behavior with an R₁₀₀ value at least 10 and which comprises

(a) conductive carbon black having a particle size greater than 18 millimicrons, a d-spacing greater than 360, and a surface area (A) which is less than

30. A device according to claim 28 wherein said carbon black has a particle size greater than 30 millimicrons.

31. A device according to claim 28 wherein said carbon black has a particle size of at most 75 millimicrons.

37. A device according to claim 28 wherein said composition also comprises

(c) at least one crystalline polymer which consists essentially of units derived from at least one olefin;

which has a softening point higher than said copolymer (b); and

which serves as a matrix for the carbon-black-containing copolymer (b).

39. A device according to claim 37 wherein said crystalline copolymer (b) is a copolymer of ethylene and a polar comonomer selected from methyl acrylate, ethyl acrylate and vinyl acetate.

29. 2S+e^S/50

where S is the DBP absorption of the carbon black, said carbon black being present in amount at least 15% by weight of the composition and being dispersed in

(b) at least one crystalline copolymer which consists essentially of units derived from at least one olefin and at least 10 weight %, based on the copolymer, of units derived from at least one olefinically unsaturated comonomer containing a polar group;

subject to the proviso that when

(i) said crystalline copolymer (b) has a melt index of more than 20 and

(ii) 2L+5 log₁₀ R≦

45, where L is the content of carbon black in percent by weight based on the weight of the composition and R is the resistivity of the composition at 25°

C. in ohm.cm,

said composition has a gel fraction of at least 0.6.

32. A device according to claim 29 wherein said composition has a gel fraction of at least 0.6.

34. A device according to claim 32 wherein said composition has a resistivity at 25°

C. of 80 to 10⁵ ohm.cm.

41. A self-limiting heater which comprises

(1) an elongate element composed of a cross-linked conductive polymer composition which has a gel fraction of at least 0.6, which exhibits PTC behavior, which has a resistivity at 25°

C. of 80 to 50,000 ohm.cm, and which comprises

(a) a conductive carbon black having a particle size greater than 18 millimicrons, a d-spacing greater than 360, and a surface area (A) which is less than

space="preserve" listing-type="equation">1.2S+e.sup.S/50

where S is the DBP absorption of the carbon black, said carbon black being present in amount at least 15% by weight of the composition and being dispersed in

(b) at least one crystalline copolymer which consists essentially of units derived from at least one olefin and at least 10 weight %, based on the copolymer, of units derived from at least one olefinically unsaturated comonomer containing a polar group and

(c) at least one crystalline polymer which consists essentially of units derived from at least one olefin and which has a softening point higher than said co-polymer (b);

(2) at least two longitudinally extending electrodes embedded in said composition parallel to each other; and

(3) an outer layer of a protective and insulating composition.

43. A heater according to claim 41 wherein the copolymer (b) has a melt index less than 20.

44. A heater according to claim 41 wherein the copolymer (b) has a melt index less than 10.

46. A heater according to claim 44 wherein the copolymer (b) has a melt index less than 20.

47. A heater according to claim 44 wherein the copolymer (b) has a melt index less than 10.