Low resistivity PTC compositions

A conductive polymer composition which exhibits PTC behavior with a switching temperature T.sub.s above 0.degree. C., which has a resistivity of less than 7 ohm. cm at at least one temperature between T.sub.s and -40.degree. C., and which, after having been subjected to a thermal aging treatment which consists of maintaining the composition, by external heating thereof, for 25 hours at a temperature at which the resistivity of the composition is between 100 ohm. cm and the peak resistivity,

• (a) exhibits PTC behavior, and
• (b) has a resistivity at at least one temperature between T.sub.s and -40.degree. C. which is between 0.5 times and 2 times the resistivity of the composition at the same temperature before said thermal aging treatment,
• and which composition comprises
• (1) a polymer component having at least 10% crystallinity and
• (2) a particulate filler component which has been dispersed in said polymer component and 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.

An electrical device which comprises a melt-shaped PTC element and at least two electrodes which can be connected to a source of electrical power and which, when so connected, causes current to flow through said PTC element, said PTC element being composed of a PTC conductive polymer composition which comprises a polymer component having at least 10% crystallinity, and, dispersed in said polymer, a particular filler component which comprises a 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;

• which composition
• (a) exhibits PTC behavior with a switching temperature T.sub.s and a peak resitivity of at least 1000 ohm. cm;
• and
• (b) has a resistivity of less than 7 ohm. cm in a temperature range which is between T.sub.s and the lower of 0.degree. C. and (T.sub.s -50).degree. C.

A process for the preparation of shaped article of a conductive polymer composition, which process comprises

• (1) providing
• (a) a polymer component having at least 10% crystallinity;
• and
• (b) a filler component which comprises a carbon black having a particle size, D, which is from 20 to 150 millimicronsand a surface area, S, in m.sup.2 /gram such that S/D is not more than 10, and
• (2) preparing a composition which comprises a dispersion of said carbon black in said polymer component by a process which comprises dispersing said carbon black in said polymer component while said polymer component is molten;
• and
• (3) melt-shaping said dispersion;
• the total energy used in preparing and melt-shaping said dispersion being from 1 to 300 hp. hr. ft..sup.-3 and being selected so that the product
• (a) exhibits PTC behavior with a switching temperature T.sub.s above 0.degree. C. and a peak resistivity of at least 1000 ohm. cm;
• and
• (b) has a resistivity of less that 7 ohm. cm at at least one temperature between T.sub.s and -40.degree. C.

A conductive polymer composition which exhibits PTC behavior with a switching temperature T.sub.s above 0.degree. C., which has a resistivity of less than 7 ohm. cm at at least one temperature between T.sub.s and -40.degree. C.;

• and which comprises
• (1) a polymer component having at least 10% crystallinity;
• and
• (2) a particulate filler component which has been dispersed in said polymer component and 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 /grams such that S/D is not more than 10.