Control of particulate magnetic coating properties using dispersion quality measurement

A description is given of the use of a rheomagnetic instrument which provides an indirect measurement of the dispersion quality of a magnetic ink suspension used for coating application in the manufacture of magnetic disks. The instrument was designed, tested, and put on a pilot line to characterize the relationships between the dispersion quality measurement and functional characteristics of the magnetic disks. The results of tests performed during pilot production suggest that it is possible to predict some of the disk coating properties based on the dispersion quality of the magnetic particle suspension measured prior to coating. The results 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 instrument then can be used in a feedforward process control scheme to monitor and control the dispersion quality of the coating suspension to maintain the uniformity of magnetic and wear properties of the magnetic disks