Rapid Determination of Coating Percent Pigment from Magnetic Recording Ink Density and Volume Fraction

Abstract

A magnetic recording ink formulation consists of mixed solvents, a polymeric binder, 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. Conventionally, this is done by an off-line method of Thermo Gravimetric Analysis (TGA), in which the solvent is first evaporated and then the binder is pyrolized, leaving behind the magnetic pigment. The TGA method is time-consuming, and often too slow for process control. The advantage of the new method described here is that it can be used on-line, as well as for rapid measurements, therefore it can be applied to process control. The ink volume fraction and density are related to the percent pigment by a mass and volume balance, and the method is illustrated with data from a typical recording disk ink.