Conductive polymer compositions

• US 4,935,156 A
• Filed: 09/27/1982
• Issued: 06/19/1990
• Est. Priority Date: 09/09/1981
• Status: Expired due to Term

• Current Assignee: Littelfuse Incorporated
• Original Assignee: Raychem Limited (TE Connectivity Limited)
• Inventors: Au, Andrew, van Konynenburg, Peter H.
• Primary Examiner(s): Barr, Josephine
• Application Number:
  US06/423,589
• Time in Patent Office: 2,822 Days
• Field of Search: 219/528, 219/549, 219/553, 219/548, 338/22 R, 338/22SD, 524/545, 524/495, 524/496, 524/300, 524/709, 252/511
• US Class Current: 219/553
• CPC Class Codes: F02B 3/06 with compression ignition compression ignition engines using air or gas for blowing fuel into compressed air in cylinder F02B13/02
• 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
• CPC Class Codes: H05B 3/146 Conductive polymers, e.g. polyethylene, thermoplastics

Abstract

Conductive polymer compositions based on polyvinylidene fluoride have improved properties when the polyvinylidene fluoride has a very regular structure which can be characterized by a low head-to-head content in the repeating units. The improved properties include electrical stability when contacted by organic fluids and/or when maintained at elevated temperatures in air. Such compositions which exhibit PTC behavior are particularly useful in the form of self-limiting heaters which are immersed in organic fluids, especially flexible strip heaters for heating diesel fuel before it passes through a fuel filter.

Claims

1. A conductive polymer composition which comprises carbon black dispersed in a polymeric component which consists essentially of 65 to 100% by weight of a crystalline polyvinylidene fluoride which has a head-to-head content of less than 5.0%, and 0 to 35% by weight of at least one elastomeric polymer.

2. A composition according to claim 1 wherein the polyvinylidene fluoride has a head-to-head content of less than 4.5%.

3. A composition according to claim 2 wherein the polyvinylidene fluoride has a head-to-head content of less than 4.0%.

4. A composition according to claim 1 which contains an amount of carbon black such that the composition exhibits PTC behavior.

12. A composition according to claim 1 where the polyvinylidene fluoride is a homopolymer of vinylidene fluoride.

13. A composition according to claim 1 wherein the polyvinylidene fluoride is a copolymer of vinylidene fluoride and a comonomer which is present in amount up to 15% by weight and which is selected from tetrafluoroethylene, hexafluoropropylene and ethylene.

14. A composition according to claim 1 in which the polymeric ingredients consist essentially of the polyvinylidene fluoride and 0 to 20% by weight of at least one elastomeric polymer.

15. A composition according to claim 1 which contains 16 to 25% by weight of carbon black.

16. A composition according to claim 1 which has been cross-linked.

5. A device which comprises

(i) a conductive polymer element comprising carbon black dispersed in a polymeric component which consists essentially of 65 to 100% by weight of a crystalline polyvinylidene fluoride which has a head-to-head content of less than 5%, and 0 to 35% by weight of at least one elastomeric polymer;

and

(ii) at least one electrode which is in electrical contact with the conductive polymer element.

6. A device according to claim 5 wherein the polyvinylidene fluoride has a head-to-head content of less than 4.5%.

7. A device according to claim 6 wherein the polyvinylidene fluoride has a head-to-head content of less than 4.0%.

8. A device according to claim 5 which is a self-regulating heater in which the conductive polymer composition comprises an amount of carbon black such that the composition exhibits PTC behavior.

9. A device according to claim 6 which comprises at least two electrodes which can be connected to a source of electrical power to cause current to flow through the conductive polymer element.

10. A device according to claim 6 wherein the polyvinylidene fluoride is a homopolymer of vinylidene fluoride.

11. A device according to claim 6 which contains 16 to 25% by weight of carbon black.