GB789613A - Improvements in or relating to magnetic recording media - Google Patents

Abstract

789,613. Magnetic dust structures. ELECTRIC & MUSICAL INDUSTRIES, Ltd. June 1, 1956 [June 2, 1955], No. 15829/55. Class 38 (2). A magnetic recording medium is made by discharging on to a thin film 1 of material such as polyvinyl chloride, cellulose-acetate or polyester resin, a coating of magnetically anisotropic magnetic particles in a binder rendered fluid by a solvent. After forming a free loop 8 the coated support 1 travels with its uncoated face adjacent a magnetic pole 11 having a knife edge form to concentrate the flux. This magnetically orientates the particles which are fixed in position when, after being driven by belt 12 over rollers 13, 14, the tape passes through drying chamber 16, where hot air passes in and out at ports 17, 18, respectively. The film 1 is held against the knife edge, and belt 12 by vacuum boxes 9, 10 and 15. The support 1 which may be 14 inches wide and 0.001 inch thick and coated with a layer 0.0005 inch thick, of acicular gamma, ferric oxide particles 0.5 Á by 0.08 Á in size, is then cut into strips of suitable width such as “ inch. The knife-edge of the pole may be rounded and not. sharp and longer than the support is wide. It may be formed by chamfering the pole of a permanent or electromagnet, or on a separate polepiece attached to the pole. A number of spaced knife-edged poles may be employed, e.g. two at the ends of a horse-shoe magnet.