Zinc oxide varistor

摘要

A varistor of metal oxides, predominantly zinc oxide (ZnO), is provided on its lateral surface between two contact faces, with a coating consisting at least partially of an organic polymer. In order to prevent rapid degradation in oxygen-free surroundings, the coating contains at least one oxygen barrier layer or is formed entirely as such a layer, which contains filler particles in an organic matrix material. The filler is here taken from the group comprising the following substances or groups of substances: synthetic mica, natural mica, vermiculite, micaceous iron ore, glass and other non-metallic inorganic substances present in the form of platelets or flakes; metal oxides, active part material in a pulverulent form and other oxygen-releasing inorganic substances. The organic matrix material is selected from the group comprising epoxide resins, alkyd resins, polyurethanes, silicone resins, unsaturated polyester resins and acrylates. The oxygen barrier layer or layers can be formed by a coating consisting of a band with a carrier of paper, plastic or glass fabric, the band being wound once or several times around the active part.