Electrical device

• US 6,111,234 A
• Filed: 11/06/1992
• Issued: 08/29/2000
• Est. Priority Date: 05/07/1991
• Status: Expired due to Term

• Current Assignee: Tyco Electronics Corporation (TE Connectivity Limited)
• Original Assignee: Tyco Electronics Corporation (TE Connectivity Limited)
• Inventors: Thompson, James C., Batliwalla, Neville S.
• Primary Examiner(s): PAIK, SANG YEOP
• Application Number:
  US08/211,829
• Time in Patent Office: 2,853 Days
• Field of Search: 219/552, 219/504, 219/549, 219/511, 219/528, 219/544, 219/553, 219/541, 338/20, 338/214, 338/22 R, 338/212
• US Class Current: 219/549
• CPC Class Codes: H05B 2203/02 Heaters using heating elements having a positive temperature coefficient
• CPC Class Codes: H05B 3/146 Conductive polymers, e.g. polyethylene, thermoplastics
• CPC Class Codes: H05B 3/56 Heating cables

Abstract

An elongate heater (1) in which a resistive heating element core is surrounded by a first insulating jacket (9) and a second insulating jacket (11). In a preferred embodiment the resistive heating element core comprises a conductive polymer composition (3) and the heater passes the VW-1 flame test. The second insulating jacket (11) may be made from the same material as the first insulating jacket (9). For some applications it is preferred that the second insulating jacket be a thin film, e.g. polyester film.

Claims

1. An elongate heater which passes the VW-1 flame test and which comprises

(1) a core which comprises a resistive heater element which comprises a conductive polymer composition which exhibits PTC behavior;

(2) a first insulating jacket which

(a) surrounds the core, and

(b) is composed of a first insulating material comprising an organic polymer; and

(3) a second insulating jacket which surrounds and contacts the first insulating jacket;

the components of the heater being such that (a) a heater which is substantially identical, except that it does not contain the second insulating jacket, fails the VW-1 flame test, and (b) a heater which is substantially identical, except that it does not contain the first insulating jacket, fails the VW-1 flame test.

2. A heater according to claim 1 wherein at least one of the following features is present:

(1) at least one of the first insulating jacket and the second insulating jacket is less than 0.015 inch (0.038 cm) thick;

(2) the second insulating jacket has been formed by wrapping a preformed tape around the first insulating jacket;

(3) the heater contains a metallic braid which surrounds the second insulating jacket;

(4) at least 75% by weight of the organic polymer in the first insulating material is a polymer which is not a polymer selected from one or more of a polyurethane, polyvinylidene fluoride, and polyethylene;

(5) the second insulating jacket is composed of a second insulating material which comprises an organic polymer, at least 75% by weight of the organic polymer being a polymer which is not a polymer selected from one or more of polyethylene, an ethylene/tetrafluoroethylene copolymer, and fluorinated ethylene propylene copolymer;

(6) the second insulating jacket is composed of a second insulating material which comprises an organic polymer, and at least 75% by weight of the organic polymer in the first insulating material is the same as at least 75% by weight of the organic polymer in the second insulating material;

(7) the second jacket has been formed by a tube-down extrusion process;

(8) the core of the heater comprises

(a) a resistive heating element which has a substantially constant cross-section along the length of the heater, and

(b) two elongate spaced-apart electrodes which are embedded in the resistive heating element,

the ratio of the maximum dimension of the cross-section of the heating element to the minimum dimension of the cross-section of the heating element being at most 7;

1, the maximum dimension of the cross-section preferably being less than 1 inch (2.54 cm), or the maximum area of the cross-section being less than 1.25 inch² (8.06 cm²);

(9) the core of the heater comprises

(a) two elongate spaced-apart electrodes, and

(b) a resistive heating element which is in the form of a continuous strip which makes intermittent contact alternately with each of the electrodes;

(10) the core of the heater comprises

(a) two elongate spaced-apart electrodes and

(b) a plurality of spaced-apart resistive heating elements each of which makes contact with each of the electrodes;

(11) the second jacket is composed of a second insulating material comprising an organic polymer which has been oriented so that, under the conditions of the VW-1 test, the second jacket shrinks before it burns;

(12) the second jacket is not bonded to the first jacket;

(13) the sum of the thickness of the first jacket and the thickness of the second jacket is less than 0.040 inch (0.10 cm);

(14) if the core of the heater comprises

(a) a resistive heating element which is composed of a conductive polymer composition exhibiting PTC behavior and

(b) two elongate spaced-apart electrodes which are embedded in the resistive heating element,

the heater has not been made by a process which comprises heating the heating element, after the first insulating jacket has been placed around the heating element, to a temperature above the crystalline melting point of any polymer in the heating element;

(15) the first insulating material is such that a heater which is substantially identical, except that the first and second insulating jackets are replaced by a single insulating jacket which is composed of the first insulating material and which has the same thickness as the sum of the thickness of the first and second jackets, fails the VW-1 test;

(16) the second insulating material is such that a heater which is substantially identical, except that the first and second insulating jackets are replaced by a single insulating jacket which is composed of the second insulating material and which has the same thickness as the sum of the thickness of the first and second jackets, fails the VW-1 test;

(17) the heater contains a metallic braid which surrounds the second insulating jacket; and

(18) at least one of the resistive heating element, the first insulating jacket, and the second insulating jacket is free from bromine-containing ingredients.

3. A heater according to claim 1 wherein the conductive polymer is in the form of a continuous strip, and (b) the resistive heating element comprises two elongate electrodes which are embedded in the conductive polymer.

4. A heater according to claim 3 wherein the second insulating jacket contacts the first insulating jacket and is composed of a second insulating material which comprises an organic polymer.

5. A heater according to claim 3 wherein the second insulating material is the same as the first insulating material.

6. A heater according to claim 1 wherein the second insulating jacket contacts the first insulating jacket and is composed of a second insulating material which comprises an organic polymer.

7. A heater according to claim 6 wherein the the second insulating material is the same as the first insulating material.

8. An elongate heater which comprises

(1) a core which comprises a resistive heating element which comprises a conductive polymer composition which exhibits PTC behavior;

(2) a first insulating jacket which surrounds the core, and which is composed of a first insulating material comprising an organic polymer; and

(3) a second insulating jacket which has been formed by wrapping a preformed tape of a second insulating material around the first insulating jacket so that the edges of the tape overlap.

9. A heater according to claim 8 wherein the tape is less than 0.005 inch (0.013 cm).

10. A heater according to claim 9 wherein the tape comprises a polyester.

11. A heater according to claim 9 wherein the tape is less than 0.002 inch (0.005 cm) thick.

12. A heater according to claim 10 which further comprises:

(4) a metallic braid which surrounds and contacts the second insulating jacket.

13. A heater according to claim 10 wherein the tape consists essentially of polyethylene terephthalate.

14. A heater according to claim 8 wherein the heater is not suitable for use as a water bed heater because the edges of the tape overlap without sealing.

15. A heater assembly for heating a substrate, said assembly comprising

(1) a heater which comprises

(a) a core which comprises a resistive heating element which comprises a continuous strip of a conductive polymer which exhibits PTC behavior;

(b) a first insulating jacket which surrounds the core, and which is composed of a first insulating material comprising an organic polymer; and

(c) a second insulating jacket which has been formed by wrapping a preformed tape of a second insulating material or a metallized polymer tape around the first insulating jacket so that the edges of the tape overlap; and

(2) an insulation layer which comprises PVC,

said heater being positioned in contact with the substrate and being surrounded by the insulation layer.

16. An assembly according to claim 15 wherein the insulating layer comprises PVC foam.

17. An assembly according to claim 15 wherein two elongate electrodes are embedded in the continuous strip of conductive polymer.

18. An assembly according to claim 15 wherein the preformed tape of a second insulating material or the metallized polymer tape comprises a polyester.

19. An assembly according to claim 18 wherein the polyester consists essentially of polyester terephthalate.