Conductive molding composition and discs therefrom

Claim 1

In a method of preparing a high density recording medium adapted for use with a playback stylus to effect recovery of signals occupying a band width of at least several megahertz when relative motion at a desired rate is established between the recording medium and the stylus, said medium having an information track constituted by a surface relief pattern in said track wherein the signals are recovered upon establishment of the relative motion at the desired rate, said method comprising: blending a composition comprising a resin consisting of a homopolymer or copolymer of vinyl chloride, stabilizers, lubricants, plasticizers and processing aids for such resins and a sufficient quantity of conductive carbon black particles so that said composition has a bulk resistivity below 500 ohm-cm at 900 megahertz; and compression molding high density recording medium therefrom, the improvement comprising the additional step of heating the conductive carbon black particles to a temperature above about 900° C. in an inert or reducing atmosphere so that the volatiles content of said particles at 950° C. is less than about 0.5 percent by weight, said heating step preceeding blending of said particles with the remaining ingredients.