PTC element and process for producing the same

Details PTC element and process for producing the same PTC element and process for producing the same

1996-02-27

1998-10-06

Zimmerman, John J.

Stock material or miscellaneous articles

Composite

Of metal

428500, 428457, 338 13, 4273742, 264241, 264340, 264345, 100 92, B32B 1508, H01C 700, B29C 6500, B30B 1100

Patent

active

058174230

ABSTRACT:
A PTC element comprising a conductive sheet of a crystalline polyolefin matrix and a conductive filler, having provided on both sides thereof an electrode of a metallic foil, the PTC element having a resistivity at 20.degree. C. (.rho..sub.20) of not more than 1.8 .OMEGA..multidot.cm, a peak resistivity (.rho..sub.p) of not less than 2.0.times.10.sup.6 (0.degree.C.)-T.sub.b (.degree.C.)! of not greater than 10.degree. C., wherein T.sub.a (.degree.C.) is a temperature at which the resistivity is 10.sup.6 times the resistivity at 20.degree. C. (.rho..sub.20) and T.sub.b (.degree.C.) is a temperature at which the resistivity is 10 times the resistivity at 20.degree. C. (.rho..sub.20). The PTC element is produced by a process comprising mixing a crystalline polyolefin and a conductive filler, molding the mixture into a conductive sheet, press bonding under heat a metallic foil to both sides of the conductive sheet, and repeatedly subjecting the conductive sheet to a heating and cooling cycle consisting of heating at a temperature of not lower than (the melting point of the crystalline polyolefin minus 5.degree. C.) and then cooling to a temperature lower than (the melting point of the crystalline polyolefin minus 5.degree. C.). The PTC elements exhibit an extremely low resistivity at 20.degree. C. and a high resistivity at a peak temperature, showing a very steep increase in resistance in a narrow temperature range.

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