GB761451A - Improvements in or relating to magnetic recording media - Google Patents

Abstract

761,451. Magnetic dust structures. GENERAL ELECTRIC CO., Ltd., DENNIS, H. M., and POLGREEN, G. R. June 22, 1954 [June 26, 1953], No. 17825/53. Class 38 (2). A magnetic recording medium comprises a thin flexible sheet or strip of non-magnetizable material, e.g. of paper or plastic, in or on which is a substantially evenly distributed layer or dispersion of permanently magnetizable powder consisting wholly or mainly of iron and composed of crystallites having a smallest dimension less than 0.1 micron, preferably between 0.01 and 0.1 micron. The particles of the powder may comprise single or aggregate of crystallites which are the ultra-microscopic crystals constituting the ultimate constituent units, and may be produced by the methods referred to in Specification 590,392. The powder may include cobalt and/or nickel, an iron-cobalt powder containing 5-30 per cent by weight of cobalt being produced by decomposition and reduction of mixed formates, or by the method described in Specification 743,792. To accelerate the reduction process a little zinc, magnesium or aluminium dust may be mixed with the iron compound and some iron oxide may be left unreduced. The iron powder being pyrophoric must be collected in a protective liquid such as acetone or benzene, or an inert atmosphere as described in Specification 761,459. When the powder is dispersed in a plastic carrier material or mixed with an insulating material these materials may provide the protection. A suitable coating may comprise 65-80 per cent of magnetic powder mixed with 20 to 35 per cent of binder such as cellulose acetate or nitrate ball-milled in acetone. To make a sheet in which the powder is distributed, the powder optionally coated with insulating material, is dispersed in polyvinyl chloride plasticised with tricresyl phosphate, to the extent of 25-10 per cent by weight. Specification 743,791, [Group II], also is referred to.