EP0040537A2
Expired / Lapsed
EP
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PTC conductive polymer compositions and devices comprising them and a method of making them
Assignee: Raychem Corp
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Filing: 1981-05-18
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Granted: —
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Expires: 2001-05-18
Abstract
Abstract The inventon relates to PTC conductive polymer compositions and devices containing them. The novel compositions contain a conductive filler, e.g. carbon black, which is dispersed a mixture of two crystalline polymers of different melting points. The higher melting of the two polymers has a melting point which is at least 160°C and at least 25°C higher than the melting point of the other polymer. A preferred mixture of polymers is poly(vinylidene fluoride) and an ethylene/tetrafluoroethylene copolymer. The compositions do not increase in resistivity by a factor more than 2 when maintained at 150°C for 1000 hours, and are therefore particularly suitable for self-limiting heaters which can be used on apparatus which is periodically subjected to high temperature, e.g. during steam-cleaning thereof. The compositions are preferably annealed at a temperature between the melting points of the two polymers. The novel compositions are relatively brittle and preferred devices are rendered more flex- resistant by the presence of a layer of a relatively flexible composition which is melt-fused to a PTC element composed of the novel composition. A preferred heater is illustrated in Figure 1.
Inventors
- 👤 Umesh Kumar Sopory
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-10-31 05:23
CPC Classifications
H; H05; H05B; H05B3/00; H05B3/10; H05B3/12; H05B3/14; H05B3/146; B; B29; B29C; B29C48/00; B29C48/15; B29C48/156; H01; H01C; H01C7/00; H01C7/02; H01C7/027; B29C48/03; B29C48/12
Claims Analysis
Total Claims: 11
Claim 1
Independent Claim
143 words
A conductive polymer composition (1) which exhibits PTC behavior; (2) which comprises (a) a polymer component which comprises a mixture of a first crystalline polymer having a first melting point, T 1 , and a second crystalline polymer having a second melting point, T 2 , which is at least 160°C and at least (T 1 + 25)°C, preferably at least (T 1 + 70)°C, and (b) a particulate filler component which has been dispersed in said polymer component and which comprises a conductive filler; and (3) which, after being subjected to a heat treatment in which the composition is maintained at a temperature of 150°C for 1000 hours, has a resistivity at 25° C, ℓ 1000 , which is less than 2 x ℓ o , where ℓ o is the resistivity of the composition at 25°C prior to said heat treatment.
Claim 2
Dependent Claim
143 words
A conductive polymer composition (1) which exhibits PTC behavior; (2) which comprises (a) a polymer component which comprises a mixture of a first crystalline polymer having a first melting point, T 1 , and a second crystalline polymer having a second melting point, T 2 , which is at least 160°C and at least (T 1 + 25)°C, preferably at least (T 1 + 70)°C, and (b) a particulate filler component which has been dispersed in said polymer component and which comprises a conductive filler; and (3) which, after being subjected to a heat treatment in which the composition is maintained at a temperature of 150°C for 1000 hours, has a resistivity at 25° C, ℓ 1000 , which is less than 2 x ℓ o , where ℓ o is the resistivity of the composition at 25°C prior to said heat treatment.
Claim 3
Dependent Claim
54 words
A composition according to Claim 1 wherein said first and second crystalline polymers constitute at least 75% by weight of the polymer component, the ratio by weight of the first polymer to the second polymer is from 1:3 to 3:1, preferably from 1:2 to 2:1, and the conductive filler consists essentially of carbon black.
Claim 4
Dependent Claim
26 words
A composition according to Claim 1 or 2 wherein T 2 is at least 200°C., preferably at least 230°C., and T 1 is 100°C to 175°C.
Claim 5
Dependent Claim
35 words
A composition according to Claim 1, 2 or 3 wherein the first crystalline polymer is a fluorinated polymer, preferably polyvinylidene fluoride, and the second crystalline polymer is a fluorinated polymer, preferably an ethylene/ tetrafluoroethylene copolymer.
Claim 6
Dependent Claim
56 words
An electrical device, especially a flexible self-limiting heater, which comprises a PTC element composed of a PTC conductive polymer composition as claimed in any one of claims 1 to 4 and two electrodes which can be connected to a source of electrical power and which when so connected cause current to flow through the PTC element.
Claim 7
Dependent Claim
136 words
A device according to Claim 5 which is a flexible self-limiting electrical heating strip and in which the PTC conductive polymer composition has a resistivity at 25°C of 10 2 to 10 5 ohm.cm and comprises (i) 50 to 85%, by weight of the composition, of a polymer component which comprises a mixture of a first crystalline polymer having a first melting point, T 1 , which is from 100°C to 175°C and a second crystalline polymer having a second melting point, T 2 , which is at least 200°C, the ratio by weight of said first polymer to said second polymer being from 0.5:1 to 1:1, and (ii) a particulate filler component which has been dispersed in said polymer component and which comprises carbon black in amount 8 to 40% by weight of the composition.
Claim 8
Dependent Claim
92 words
A method of making an electrical device according to Claim 5 or 6 which comprises annealing the device at a temperature T A which is between (T 1 + 5)°C and (T 2 - 40)°C, especially between (T 1 + 10)°C and (T 2 - 75)°C, for a time which is sufficient to reduce the resistivity at 25°C of the PTC composition from a first value ℓ x prior to said annealing to a second value ℓ o after said annealing, where ℓ o is less than 0.8 x e x .
Claim 9
Dependent Claim
49 words
An electrical device according to Claim 5 or 6 which further comprises a layer of a second polymeric composition having substantially greater flexibility at 25°C than said PTC composition, said layer (1) being adjacent to, and preferably surrounding, said PTC element and (2) being melt-fused to said PTC element.
Claim 10
Dependent Claim
48 words
An electrical device according to Claim 8 wherein the second polymeric composition comprises a polymeric component which consists essentially of at least one polymer having a melting point of (T 1 - 10)°C to (T 1 + 50)°C and which preferably consists essentially of said first crystalline polymer.
Claim 11
Dependent Claim
108 words
A method of making an electrical device according to Claim 8 or 9 which comprises (1) melt-extruding the second polymeric composition in contact with said PTC element, and (2) heating the device to effect melt fusion of the PTC element and the layer, the PTC element preferably being heated to a temperature between (T 1 + 5)°C and (T 2 - 40)°C. for a time which is sufficient to reduce the resistivity at 25°C of the PTC composition from a first value ℓ x prior to said annealing to a second value ℓ o after said annealing, where e o is less than 0.8 x ℓ x .
References Cited (Backward Citations)
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