# US 4,400,614 A · PTC Devices and their preparation > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 4,400,614 A - Document ID: US4400614A - Status: Granted - Kind: A - Application number: 06/322,647 - Filed: 1981-11-18 - Granted: 1983-08-23 - Earliest claimed: 1980-05-19 - Assignees: Raychem Corporation - Inventors: Umesh K. Sopory - Web page: https://patentgrep.com/patent/US4400614A ## CPC - H01C 7/027: {consisting of conducting or semi-conducting material dispersed in a non-conductive organic material} - B29C 48/08: flexible, e.g. films - B29C 48/12: Articles with an irregular circumference when viewed in cross-section, e.g. window profiles - B29C 48/156: Coating two or more articles simultaneously - H05B 3/146: {Conductive polymers, e.g. polyethylene, thermoplastics} - Y10T 29/49083: Heater type - H01C: RESISTORS - B29C: SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING (making preforms B29B11/00; making laminated products by combining previously unconnected layers which become one product whose layers will remain together B32B37/00 - B32B41/00) - H05B: ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL - Y10T: TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION ## 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.degree. C., preferably at least 200.degree. 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. ## Claims ### 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 T.sub.1 and a second melting point T.sub.2 which is at least (T.sub.1 +25).degree. 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.degree. C. than said PTC composition. ### Claim 2 (depends on 1) A device according to claim 1 wherein said electrodes are surrounded by and in physical contact with said PTC element. ### Claim 3 (depends on 1) A device according to claim 1 wherein T.sub.2 is at least (T.sub.1 +70).degree. C. ### Claim 4 (depends on 1) A device according to claim 1 wherein the second polymeric composition has a melting point of (T.sub.1 -10).degree. C. to (T.sub.1 +50).degree. C. ### Claim 5 (depends on 1) A device according to claim 1 wherein the second polymeric composition comprises said first crystalline polymer. ### Claim 6 (depends on 5) A device according to claim 5 wherein the second polymeric composition consists essentially of said first crystalline polymer. ### Claim 7 (depends on 1) A device according to claim 1 wherein said PTC composition has a resistivity of 10.sup.2 to 10.sup.5 ohm.cm. ### Claim 8 (depends on 1) A device according to claim 1 wherein T.sub.2 is at least 160.degree. C. ### Claim 9 (depends on 8) A device according to claim 8 wherein T.sub.2 is at least 200.degree. C. ### Claim 10 (depends on 9) A device according to claim 9 wherein T.sub.1 is 100.degree. to 175.degree. C. ### Claim 11 (depends on 1) A device according to claim 1 wherein each of the crystalline polymers in the PTC composition is a fluorinated polymer. ### Claim 12 (depends on 1) A device according to claim 1 wherein the first crystalline polymer is polyvinylidene fluoride and the second crystalline polymer is an ethylene/tetrafluoroethylene copolymer. ### Claim 13 (depends on 1) A device according to claim 1 wherein said second polymeric composition has substantially greater flexibility than said PTC composition at all temperatures between 0.degree. C. and 100.degree. C. ### Claim 14 (depends on 1) A device according to claim 1 wherein said second polymeric composition has substantially greater flexibility than said PTC composition at all temperatures between 0.degree. C. and the switching temperature of the composition.