PTC Devices and their preparation
First Claim
1. A flexible electrical device which comprises(a) an elongate flexible PTC element composed of a PTC conductive polymer composition which exhibits PTC behavior and which comprises(i) a polymer component which comprises a mixture of a first crystalline polymer having a first melting point T1 and a second melting point T2 which is at least (T1 +25)°
- C.; and
(ii) a particulate filler component which has been dispersed in said polymer component and which comprises a conductive filler;
(b) two elongate metal electrodes which are electrically connected to the PTC element so that, when the electrodes are connected to a source of electrical power, current flows through said PTC element; and
(c) surrounding said PTC element and melt-fused thereto, a layer of a second polymeric composition having substantially greater flexibility at 23°
C. than said PTC composition.
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Accused Products
Abstract
The flex life of devices comprising a relatively inflexible PTC conductive polymer element is improved by surrounding the PTC element with a layer of a relatively flexible polymeric composition which is melt-fused thereto. Particularly useful devices are self-limiting strip heaters in which the polymeric component of the PTC element comprises a mixture of two crystalline polymers having substantially different melting points, the higher melting polymer having a melting point of at least 160° C., preferably at least 200° C., for example a mixture of polyvinylidene fluoride and a copolymer of ethylene and tetrafluoroethylene. Such devices can be made by melt-extruding a layer of the relatively flexible polymeric composition around the PTC element, and heating to cause melt-fusion of the polymers at the interface of the layer and the PTC element.
37 Citations
14 Claims
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1. A flexible electrical device which comprises
(a) an elongate flexible PTC element composed of a PTC conductive polymer composition which exhibits PTC behavior and which comprises (i) a polymer component which comprises a mixture of a first crystalline polymer having a first melting point T1 and a second melting point T2 which is at least (T1 +25)° - C.; and
(ii) a particulate filler component which has been dispersed in said polymer component and which comprises a conductive filler; (b) two elongate metal electrodes which are electrically connected to the PTC element so that, when the electrodes are connected to a source of electrical power, current flows through said PTC element; and (c) surrounding said PTC element and melt-fused thereto, a layer of a second polymeric composition having substantially greater flexibility at 23°
C. than said PTC composition. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
- C.; and
Specification