Polyvinyl chloride (PVC) homopolymers and copolymers are useful in a wide variety of applications, such as in making pipe, phonograph records or video discs. For use in records or video discs the PVC polymers are molded in the form of a disc and are grooved to carry a signal. Carbon black is distributed throughout to impart conductivity. The carbon black must be well dispersed to achieve good conductivity, and the blend may have to be held for extended periods of time under high shear during mixing for good dispersion. During the high shear, the blend temperature rises. This can cause decomposition of the blend ingredients.
Moreover, PVC polymers which contain carbon black can be difficult to mold. The high melt viscosity of PVC polymers renders compression molding difficult and the carbon black tends to embrittle the molded articles.
Components which reduce high melt viscosity can be added, but such components usually result in either lack of compatibility, embrittlement, reduced thermal stability or partial loss of conductivity in the final PVC product. In addition, such components are often fugitive or volatile and can result in mold deposits.
USPTO Backgrounds
USPTO Backgrounds