PTC compositions containing low molecular weight polymer molecules for reduced annealing
First Claim
1. An electrically conductive composite polymer material comprising a suitable finely divided electrically conductive carbon black in an amount of 4 to 25% by weight dispersed within an olefinic polymer wherein the polymer has a number average molecular weight in the range of about 15,000 to 40,000 to reduce the annealing time necessary to achieve an electrically conductive material exhibiting PTC behavior to less than one minute.
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Abstract
A revolutionary new semiconductive material having a sharp rise in electrical resistance at a predetermined maximum temperature with substantially no annealing necessary after extrusion to achieve an essentially constant resistance at room temperature. The PTC composition includes a finely divided conductive material, such as carbon black; a suitable semicrystalline polymer having a molecular weight distribution containing a sufficient number of relatively low molecular weight molecules to substantially eliminate annealing; and a suitable polymeric material providing a sufficient number of polar molecules for electrical conductivity. At least 9% by weight of the polymer molecules should be in the molecular weight range of 1,000 to 30,000, and particularly in the 5,000 to 23,000 range and the entire polymeric portion of the composite composition should have a number average molecular weight of 30,000 or less. Generally, the relatively low molecular weight molecules of the semicrystalline polymer (1,000 to 30,000 and particularly 5,000 to 23,000 M.S.) are included in an amount of 9% to 15% based on the total weight of polymer molecules in the composition.
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Citations
15 Claims
- 1. An electrically conductive composite polymer material comprising a suitable finely divided electrically conductive carbon black in an amount of 4 to 25% by weight dispersed within an olefinic polymer wherein the polymer has a number average molecular weight in the range of about 15,000 to 40,000 to reduce the annealing time necessary to achieve an electrically conductive material exhibiting PTC behavior to less than one minute.
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14. An electrically conductive composite polymer material comprising a suitable finely divided electrically conductive carbon black in an amount of 4 to 25% by weight dispersed within an olefinic polymer wherein the polymer has a number average molecular weight in the range of about 15,000 to about 40,000 to reduce the annealing time necessary to achieve an electrically conductive material exhibiting PTC behavior to less than one minute.
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15. An electrically conductive composite polymer material comprising a suitable finely divided electrically conductive carbon black in an amount of 4 to 25% by weight dispersed within a first, semicrystalline, olefinic polymer wherein the polymer has a number average molecular weight in the range of about 15,000 to 40,000;
- and a second polymer material having one or more polar groups in an amount of at least 2% by weight of the electrically conductive material to reduce the annealing time necessary to achieve an electrically conductive material exhibiting PTC behavior.
Specification