| 摘要 |
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. |
