Electrical resistors – Resistance value responsive to a condition – Current and/or voltage
Patent
1978-12-01
1980-12-02
Albritton, C. L.
Electrical resistors
Resistance value responsive to a condition
Current and/or voltage
29610, 252511, 338223, 338225, H01C 702
Patent
active
042374413
ABSTRACT:
Compositions which exhibit PTC behavior with a switching temperature (T.sub.s) above 0.degree. C., which have a resistivity at a temperature below T.sub.s of less than 7 ohm. cm, and which comprise a crystalline polymer and a particulate filler component which comprises carbon black having a particle size, D, which is from 20 to 150 millimicrons and a surface area S in m.sup.2 /gram such that S/D is not more than 10. The composition preferably has a peak resistivity of at least 1000 ohm. cm and is electrically stable when aged at elevated temperature. The quantity ##EQU1## is preferably less than 1, especially less than 0.5. Shaped articles of such compositions are prepared by a process in which the carbon black is dispersed in the molten polymer and the dispersion is then melt-shaped, the total energy used in preparing and melt-shaping the dispersion being 1 to 300 hp. hr. ft.sup.-3, preferably 1 to 100 hp. hr. ft.sup.-3, especially 1 to 50 hp. hr. ft.sup.-3. The compositions are particularly useful in circuit protection devices.
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Au Andrew
Gotcher Alan J.
Rauwendaal Chris
van Konynenburg Peter V.
Albritton C. L.
Raychem Corporation
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