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Orienting CrO(2) Particles on the Surface of a Recording Disk

IP.com Disclosure Number: IPCOM000076039D
Original Publication Date: 1971-Dec-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 13K

Publishing Venue

IBM

Related People

Comstock, RL: AUTHOR [+2]

Abstract

To utilize the magnetic properties of chromium dioxide and, in particular, to orient magnetically the particles of material on a disk for memory access files, it is necessary to apply the pigment in an organic binder.

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Orienting CrO(2) Particles on the Surface of a Recording Disk

To utilize the magnetic properties of chromium dioxide and, in particular, to orient magnetically the particles of material on a disk for memory access files, it is necessary to apply the pigment in an organic binder.

Chromium dioxide is a vigorous oxidizing agent and will destroy many organic binders; resins containing reactive groups susceptible to free radicle polymerization are rapidly catalyzed by chromium dioxide and pose very considerable manufacturing problems. Such resins include acrylics, epoxies and polyesters. As an example, mixing 5% chromium dioxide with an epoxy- acrylic resin leads to a vigorous reaction in which the resin becomes completely polymerized (i.e. gelled) in 7 minutes and the temperature rises from 65 degrees F to 387 degrees F in 6 1/2 minutes.

However, polymers of methyl methacrylate are inert to chromium dioxide and can be used as excellent binders for the pigment. To allow for later orientation of the particles, the viscosity of the medium must be low so that the applied magnetic field will furnish enough torque to pull the particles into an oriented form and high enough to keep them in this form until the film loses its liquid character.

A solution of polymethyl methacrylate that dries by solvent evaporation at a controlled rate forms an ideal binder for orientation purposes. The preferred solvent is a mixture of cyclohexanone and isophorone falling within the range of 10-30% of cyclohexanone and 90-70% isophorone by weight. The preferred solvent composition is 15% cyclohexanone and 85% isophorone.

The polymer itself must be soluble in the solvent at a sufficient concentration to be usable and of a suitable character. The...