EP0038718A1
Expired / Lapsed
EP
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Conductive polymer compositions containing fillers
Assignee: Raychem Corp
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Filing: 1981-04-21
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Granted: —
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Expires: 2001-04-21
Abstract
Abstract The invention relates to conductive polymer compositions. The compositions of the invention have improved electrical stability when exposed to thermal cycling. They comprise a polymer component and a filler component which has a total surface area of at least 1800 m 2 per cc. of composition and which comprises carbon black and non-conductive particulate filler, each present in amount at least 4% by volume of the composition, In one preferred class of compositions, the polymer component is crystalline. In another preferred class the polymer is amorphous and the amount of filler is such that the composition has an elongation of at most 10% at 23°C. The compositions may have PTC, ZTC or NTC resistivity/temperature characteristics. Figure 2 shows the resistivity/temperature characteristics of a PTC composition of the invention. The new compositions are useful in a variety of electrical devices, including heaters, circuit control devices and temperature sensors.
Inventors
- 👤 Robert W. J.R. Fouts
- 👤 David W. Whitney
- 👤 Robert Wasley
- 👤 Robert Walty
- 👤 Alan Jeffrey Gotcher
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-10-30 11:34
CPC Classifications
C; C08; C08K; C08K3/00; C08K3/02; C08K3/04; H; H01; H01B; H01B1/00; H01B1/20; H01B1/24; H01C; H01C7/00; H01C7/008
Claims Analysis
Total Claims: 11
Claim 1
Independent Claim
188 words
A conductive polymer composition comprising a polymer component and a particulate filler component which has been dispersed in the polymer component and which comprises carbon black and a non-conductive particulate filler, said composition having a resistivity of 1 0 2 to 10 6 ohm.cm at 23°C after having been subjected to a thermal cycle which consists of heating the composition from 23°C to T test and cooling the composition from T test to 23°C, where T test is 100°C when the polymer is substantially free from crystallinity and is 20°C above the crystalline melting point of the polymer when the polymer is crystalline, characterised in that the particulate filler component has a total surface area of at least 1800 m 2 per cc. of composition and comprises at least 4°o by volume of the composition of carbon black and at least. 4% by volume of the composition of at least one non-conductive particulate filler, subject to the proviso that if the polymer component is substantially free from crystallinity, the quantity of particulate filler component is such that the composition has an elongation at 23°C of at most 10%.
Claim 2
Dependent Claim
188 words
A conductive polymer composition comprising a polymer component and a particulate filler component which has been dispersed in the polymer component and which comprises carbon black and a non-conductive particulate filler, said composition having a resistivity of 1 0 2 to 10 6 ohm.cm at 23°C after having been subjected to a thermal cycle which consists of heating the composition from 23°C to T test and cooling the composition from T test to 23°C, where T test is 100°C when the polymer is substantially free from crystallinity and is 20°C above the crystalline melting point of the polymer when the polymer is crystalline, characterised in that the particulate filler component has a total surface area of at least 1800 m 2 per cc. of composition and comprises at least 4°o by volume of the composition of carbon black and at least. 4% by volume of the composition of at least one non-conductive particulate filler, subject to the proviso that if the polymer component is substantially free from crystallinity, the quantity of particulate filler component is such that the composition has an elongation at 23°C of at most 10%.
Claim 3
Dependent Claim
75 words
A composition according to Claim 1 characterised in that the polymer component has a crystallinity of at least 10% and constitutes up to 60°o by weight of the composition; the carbon black has a particle size (D) of 20 to 150 millimicrons and a surface area (S) in m 2 /gram such that S/D is not more than 10; and the volume of non-conductive filler is 0.3 to 0.8 times the volume of. carbon black.
Claim 4
Dependent Claim
15 words
A composition according to Claim 2 characterised in that the quantity is less than 1.
Claim 5
Dependent Claim
71 words
A composition according to Claim 1 characterised in that the polymer component has a crystallinity of at least 10% and constitutes up to 60% by weight of the composition; the carbon black has a particle size (D) which is less than 27 millimicrons and a surface area (S) such that S/D is at least 12; and the volume of non-conductive filler is 2 to 12 times the volume of carbon black.
Claim 6
Dependent Claim
122 words
A composition according to Claim 1 characterised in that the polymer component has a crystallinity of at least 10% and is substantially free from cross-linking, and the carbon black (a) is present in amount 4 to 20% by volume of the composition and (b) has a particle size, D, which is less than 18 millimicrons and a surface area, S, in m 2 /gram such that S/D is greater than 12, whereby the composition, when heated, has a resistivity which reaches a maximum at a temperature T p eak and then decreases rapidly in the temperature range T peak to (T peak + 25)°C to a value, e min , which is less than 10 ohm.cm and less than 0.35 x .
Claim 7
Dependent Claim
21 words
A composition according to Claim 5 characterised in that S/D is at least 18 and D is less than 15 millimicrons.
Claim 8
Dependent Claim
29 words
A composition according to Claim 4, 5 or 6 characterised in that volume of the non-conductive filler is from 2 to 12 times the volume of the carbon black.
Claim 9
Dependent Claim
42 words
A composition according to Claim 1 characterised in that the polymer component is substantially free of crystallinity and consists essentially of one or more cross-linked elastomers having a carbon-containing backbone, and the composition has an elongation at 23°C of at most 2%.
Claim 10
Dependent Claim
42 words
A composition according to any one of the preceding claims characterised in that the particulate filler component has a total surface area of at least 4,000 m 2 per cc. of composition and provides at least 20% by volume of the composition.
Claim 11
Dependent Claim
51 words
An electrical device which comprises a conductive polymer element and at least two electrodes which can be connected to a power source so that current flows through the element, characterised in that the element is composed of a conductive polymer composition as claimed in any one of claims 1 to 9.
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