Conductive polymer compositions, and to devices comprising such compositions
First Claim
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
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<
45where 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.
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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.
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Citations
50 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 - 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; 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<
45where 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. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)
- 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 - 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 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;
the content of carbon black in said composition being L% by weight and the resistivity of said composition at 25°
C. being R ohm.cm, and R and L being such that
space="preserve" listing-type="equation">2L+5 log.sub.10 R>
45.- View Dependent Claims (18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 33, 35, 36, 38, 40, 42, 45, 48, 49, 50)
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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
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29. 2S+eS/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. - View Dependent Claims (32, 34)
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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/50where 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. - View Dependent Claims (43, 44, 46, 47)
- C. of 80 to 50,000 ohm.cm, and which comprises
Specification