Patent GB-1200931-A (GB)
Title: Improvements in and relating to magnetic information carriers
IPC: H01F10/00
Filed: 1967-08-01
Abstract: 1,200,931. Making magnetic records. HONEYWELL Inc. 1 Aug., 1967 [22 Aug., 1966], No. 35374/67. Heading G5R. An information carrier comprises a non- metallic substrate surmounted by a hydrophilic gel layer which is essentially free of metallic particles other than electroless-plating nuclei particles, wherein the gel layer bears at its exposed surface a discrete pattern of magnetic material having the form of two or more superimposed layers, which layers are respectively separated by a layer of non-magnetic material. Preferably the non-magnetic material separating the layers of magnetic material is copper. Preferably the, or each, layer of non-magnetic material has a thickness such that the associated magnetic layers are separated by a distance which effectively prevents any magnetic coupling between them. Preferably the pattern comprises one or more groups of parallel strips. The Figure is a cross-section of a card or tape. The substrate B is a polyethylene terephthalate film and may be translucent. Other substrate materials are: cellulose acetate, polyvinyl chloride, polyvinyl acetate, polyvinylidene chloride, polyacrylonitrile; and cloth or paper impregnated or coated with non-wetting resins. The complete starting material may consist of the substrate B, the gel layer IF and a photoemulsion coating e, and may comprise one of a small range of photographic films. Manufacture.-According to one method, an optical image of the pattern of magnetic strips required is projected or masked on to the photoemulsion coating e so that the areas intended for the magnetic strips are left unexposed. The film is then immersed in a solution which both develops and fixes it, to reduce the silver halide compounds to silver in the "void" areas and remove the unchanged silver compounds (and possibly also the emulsion) in the "strip" areas. Next, the film is drawn at about 10 inches per minute through a sensitizing bath containing stannous ions as acid (pH about 0À2) or as halide salts with, optionally, a wetting agent; alternatively, the bath may contain titanium ions. The immersion time may be adjusted by making the bottom rollers adjustable in height. Then the tape is drawn through an activating or seeding solution containing halide salts of palladium, preferably palladium chloride, or an acidic solution of palladium chloride; alternatively , halide salts of silver may be used; the immersion time is 30 seconds, at room temperature. Finally, a thin film of magnetic material is deposited on each of the strip areas by electroless plating using a bath containing, as the significant ingredients, cobalt chloride and nickel chloride, and sodium hypophosphite as a source of phosphorus and as a reducing agent. The resulting strips M2, as shown, consist of a nickel-cobalt-phosphorus compound. Superposed strips M1, of like magnetic material, are separated from the strips M2 by respective layers Cu of copper, having a thickness of about 10 micro-inches; the strips M1, M2, have a thickness of about 20 micro-inches. In a modified method of manufacture, a positive optical image of the required pattern is used so that the areas intended for the magnetic strips are, in this case, exposed.