PTC Devices comprising oxygen barrier layers

摘要

Electrical devices comprising PTC elements have improved electrical stability when they comprise an oxygen barrier which restricts access of air to the element so that the PTC element absorbs oxygen at a rate less than 10-6 cc/sec/gram. The devices are for example circuit control devices or self-limiting heaters. Preferred PTC elements comprise a polymer having dispersed therein carbon black and an additive which stabilizes the polymer against degradation, especially an organic antioxidant. The oxygen barrier may for example be a layer of a polymeric composition or a self-supporting container principally made of metal and filled with an inert gas.