Magnetic recording medium having a magnetic layer prepared from

Details Magnetic recording medium having a magnetic layer prepared from Magnetic recording medium having a magnetic layer prepared from

1993-04-29

1995-05-16

Resan, Stevan A.

Stock material or miscellaneous articles

Web or sheet containing structurally defined element or...

Including a second component containing structurally defined...

428403, 428407, 428694BA, 428900, G11B 500

Patent

active

054159296

ABSTRACT:
In the preparation of dispersions of magnetic pigments in organic solvents, dispersants which have a sterically stabilizing effect are used. Milling results in division of the pigment aggregates, which combine again as a result of attractive forces to give secondary agglomerates in the event of poor stabilization. These flocculating materials must be removed from the dispersion by expensive filtration. If an increase in the fineness or pigment batch fluctuations lead to an increase in the secondary agglomerates, filter breakthroughs may occur, resulting in a dramatic reduction in the yield of magnetic recording medium. It was found that excellent dispersion stability is achieved when the magnetic pigments are first precoated with a long-chain dispersant. Subsequently, the use of charge-generating, low molecular weight codispersants, a charge build-up on the pigment is specifically induced by means of bases or acids. The electrostatic repulsion which additionally becomes effective leads to an increase in the dispersion stability. The charges on the pigment are monitored by means of ESA measurements (electrokinetic sound amplitude). These ESA measurements make it possible to establish the order of addition of the dispersants and the optimum amount of codispersant.

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Fowkes et al., "Mechanism of Electric Charging . . . ", Am. Chem. Soc. 1982, pp. 307-324.
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Fowkes , Adv. in Ceramics, vol. 21, 1987, "Dispersions of Ceramic . . . ".
Fowkes, J. Adhesion Sci. Tech., vol. 1, No. 1, pp. 7-27, 1987.

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