Rapid determination of coating per cent pigment from ink density and volume fraction

Abstract

A magnetic recording ink formulation consists of mixed solvents, a polymer binder system, and magnetic pigment. This is coated onto a disk or tape substrate and cured. In the process, the solvent evaporates, and the binders polymerize, embedding the pigment to form the magnetic film. For quality control of the process, it is important to maintain the composition of the film. A method is described in which the per cent pigment to expect in the cured film can be determined from the volume fraction of pigment in the ink and the ink density. A rapid electromagnetic method for measuring the volume fraction of pigment in the ink is described. The ink volume fraction and density are related to the per cent pigment by a mass and volume balance, and the method is illustrated with data from a typical recording disk ink.