| 摘要 |
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 DEG C. ( rho 20) of not more than 1.8 OMEGA xcm, a peak resistivity ( rho p) of not less than 2.0x106 OMEGA xcm, and a temperature difference [Ta(0 DEG C.)-Tb( DEG C.)] of not greater than 10 DEG C., wherein Ta( DEG C.) is a temperature at which the resistivity is 106 times the resistivity at 20 DEG C. ( rho 20) and Tb ( DEG C.) is a temperature at which the resistivity is 10 times the resistivity at 20 DEG C. ( rho 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 DEG C.) and then cooling to a temperature lower than (the melting point of the crystalline polyolefin minus 5 DEG C.). The PTC elements exhibit an extremely low resistivity at 20 DEG 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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