Effect of dispersion quality on particulate magnetic recording disk properties

The production of particulate magnetic disks or tapes requires consistent and uniform magnetic characteristics over the entire disk or tape to have as few defects as possible. To achieve this goal, the magnetic particle suspension used to coat the disk must be well dispersed. This article describes the use of a rheomagnetic instrument that provides an indirect measurement of the dispersion quality prior to coating application. The instrument was designed, tested, and put on a manufacturing scale line to characterize the relationships between the measured dispersion quality and functional characteristics of the magnetic coating. The results of tests done during scaleup for production yielded a qualitative correlation between the in‐situ measurements made on the magnetic particle suspension at the coater with the surface roughness due to flocs, the on‐disk orientation ratio, and the signal to noise ratio. The current results are the first demonstration of the dispersion quality measurement in a practical manufacturing environment. Copyright © 1991 American Institute of Chemical Engineers