Polyethylene terephthalate capacitor dielectric

Saran (Dow polyvinylidene dichloride) is a tough, chemically resistant plastic available in a variety of forms that are useful in the laboratory. Saran pipe or tubing can easily be welded to itself or sealed to glass and is useful for handling corrosive solutions. Thin Saran film, available commercially as a packaging material, is useful for windows, support films, etc. Mylar (du Pont polyethylene terephthalate) film and other polyester films are also useful for these purposes. Mylar is chemically inert and has excellent electrical properties for electrical insulation and for use as a dielectric medium in capacitors. Much thinner than these are films that can be made in the laboratory by allowing a dilute ethylene dichloride solution of Formvar (polyvinyl acetal) to spread on a water surface and dry. 

Figure 12.12 Percentage change in capacitance with temperature for capacitors with polystyrene and polyethylene terephthalate dielectric (from Bruins, R, Ed., Plastics for Electrical Insulation, Wiley Interscience, 1968).

The high impact strength, dimensional stability and optical clarity (low crystallinity) of bisphenol-A polycarbonate (PC) together with its low dielectric loss have led to a range of applications embracing optical components, CD-ROMs, film capacitors and safety-related products Subsequent market demands for enhanced physical properties has stimulated the development of a range of commercial blends of which rubber-modified bisphenol-A polycarbonate (PC) with polybutylene terephthalate (PBT) or polyethylene terephthalate (PET) are amongst the more successful ... 

Dielectric materials vary by cost and the capacitance needed for a specific application. Glass, ceramic, and mica papers are high quality, low capacitance dielectrics with extremely high breakdown resistance. Conversely, metal-ized polymer foils such as polystyrene, polyethylene terephthalate (PET), and Teflon (PTFE) are single-piece dielectric films that offer better capacitor performance. In recent years, polymer foils have come to dominate the static capacitor market because they have better stability at high temperatures, can be manufactured at lower cost, and age better than dielectric papers. 

Many polymer films have been examined as capacitor dielectrics but those principally used are polyethylene terephthalate, polystyrene, polycarbonate, polytetrafluoroethylene, polyimides and polypara-xylylene. A number of these materials are more familiar by their trade names ... 

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