Method for preparing a molding composition

Claim 2

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 performance properties have been prepared; (b) preparing at least two samples of conductive molding composition from carbon black to be utilized in a given batch, said samples containing varying weight percents of conductive carbon black, the total weight percent of carbon black and resin being constant in all compositions: (c) determining the melt viscosity of each of said samples; (d) plotting the log of the melt viscosity and the carbon black content of the samples and determining therefrom two empirical constants; and (e) determining the precise weight percent of conductive carbon black required to prepare said batch of molding composition according to the formula log n=A+B×W wherein n is said melt viscosity, A and B are the constants and W is the weight percent of conductive carbon black in said composition.

Claim 3

A method in accordance with claim 1, wherein the melt viscosity is determined in step (a) by direct measurement of said conductive molding composition.

Claim 4

A method in accordance with claim 1, wherein the melt viscosity is determined in step (a) according to the formula y=a+bx+cx.sup.2 +dx.sup.3 wherein x equals the log of the melt viscosity, y equals the log of one of said performance properties and a, b, c, and d are empirical constants.

Claim 5

A method in accordance with claim 1, wherein the performance property utilized for the determination in step (a) is video carrier signal to noise ratio.

Claim 6

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 a given batch of said molding composition by: (a) determining the melt viscosity of a conductive molding composition from which records having desired performance properties have been prepared; (b) providing at least two individual preblended molding compositions, at least one of which has a melt viscosity higher than the desired melt viscosity determined in step (a) and at least one of which has a melt viscosity lower than the desired melt viscosity determined in step (a); (c) determining the weight fraction of each of said individual preblended compositions to be combined with the others utilizing the formula ##EQU4## wherein n r is the desired viscosity, i is an individual conductive molding composition, n is the number of individual molding compositions, n 1 is the melt viscosity of an individual molding composition and f 1 is the weight fraction of an individual molding composition wherein the sum of F 1 is 1; and (d) mixing said individual conductive molding compositions to form said batch in accordance with said weight fraction determination.

Claim 7

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 a given batch of said molding composition by: (a) determining the melt viscosity of a conductive molding composition from which records having desired performance properties have been prepared; (b) providing at least two individual preblended molding compositions, at least one of which has a melt viscosity higher than the desired melt viscosity determined in step (a) and at least one of which has a melt viscosity lower than the desired melt viscosity determined in step (a); (c) determining the weight fraction of each of said individual preblended compositions to be combined with the others utilizing the formula ##EQU4## wherein n r is the desired viscosity, i is an individual conductive molding composition, n is the number of individual molding compositions, n 1 is the melt viscosity of an individual molding composition and f 1 is the weight fraction of an individual molding composition wherein the sum of F 1 is 1; and (d) mixing said individual conductive molding compositions to form said batch in accordance with said weight fraction determination.

Claim 8

A method in accordance with claim 5, wherein the melt viscosity is determined in step (a) by direct measurement of said conductive molding composition.

Claim 9

A method in accordance with claim 5, wherein the melt viscosity is determined in step (a) according to the formula y=a+bx+cx.sup.2 +dx.sup.3 wherein x equals the log of the melt viscosity, y equals the log of one of said performance properties and a, b, c, and d are empirical constants.

Claim 10

A method in accordance with claim 5, wherein the performance property utilized for the determination in step (a) is video carrier signal to noise ratio.