Formulation of electrically conductive plastics

Claim 1

In a method of mass-producing conductive plastic capacitive information records by compression molding a composition comprising conductive carbon black particles, a molding resin comprising a homopolymer or copolymer of vinyl chloride and suitable additives compatible therewith, the improvement wherein the records are produced without batch-to-batch nonuniformity in predetermined performance properties resulting from variation in the physical properties of the carbon black by preparing each batch of said molding composition with a precise weight of carbon black determined by: (a) determining the melt viscosity of a conductive molding composition from which records having the desired preformance properties have been prepared, wherein the total weight percent of carbon black and resin in said composition and said batch is constant; (b) measuring the surface area of samples of carbon black to be utilized in a given batch of molding composition and determining the average surface area thereof; and (c) determining the precise weight percent of conductive carbon black required for said batch of molding composition according to a relationship selected from log n=k.sub.1 +k.sub.2 ×W+k.sub.3 ×W×SA, log n=k.sub.4 +k.sub.5 ×W×k.sub.6 ×SA, and log n=k.sub.8 ×W×SA wherein n is the melt viscosity provided in step (a), W is the weight percent of the carbon black present in said composition, SA is the average surface area of the carbon black particles and each of k 1 through k 7 is an empirical constant, wherein said constants correlate with the method utilized in step (b) to determine surface area.