Effect of dispersion quality on particulate magnetic recording disk properties

Abstract

Theproduction ofparticulate magnetic disks or tapes requires consistent and uniform magnetic characteristics over the entire disk or tape to have as few defects aspossihie. 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 floes, the on-disk orientation ratio, and the signal to noise ratio. The current results are the first demonstration of the dispersion quality measurement in apractical manufacturing environment.

Microrheological Study of Magnetic Particle Suspensions

“…The coil was located immediately downstream from the contraction formed at the junction of the large and small tube (Jhon and Karis, 1989). The Reynolds number was in the range 1-10 3 , which is well below the critical Reynolds number for transition to turbulence in pipe flow (Shah et al, 1991).…”

“…The magnetic particle suspension, which is inherently unstable to flocculation due to strong interparticle magnetic forces, is usually prepared by dispersing particulate powder into a suspending fluid (a mixture of binder polymer and solvent). The amount of the flocs that appear in the coating, whose size and distribution is commonly referred to as the "dispersion quality," is directly related to the quality of the media (Karis, 1989;Shah et al, 1991). Therefore, characterizing and stabilizing the magnetic particle dispersion is an important engineering consideration in advanced particulate media production.…”