Patent GB-865394-A (GB)
Title: Improvements in and relating to recording material
IPC: B41M5/24
Filed: 1957-04-12
Abstract: 865,394. Telegraphic &c. recording paper;  coated fabrics. RENKER-BELIPA G.m.b.H. April 12, 1957 [April 14, 1956; Dec. 1, 1956], No. 12113/57. Drawings to Specification. Classes 96 and 140. [Also in Groups XIX and XL (b)] A recording material for use, e.g., in echosounding and for transmitting signs by wireless telegraphy, and comprising a carrier layer and an external marking layer which changes its appearance when electrical energy is applied, e.g. by the penetration of an electric spark, is prepared by coating or impregnating the carrier layer with a solution comprising an acetal of polyvinyl alcohol and precipitating the acetal in the form of a white layer. The reaction products of polyvinyl alcohol with formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, benzaldehyde or mixtures thereof are preferred acetals. It is stated that marking layers formed from such acetals respond to spark penetration at voltages as low as 50 to 70 volts. Marking layers can consist of 2 to 100 parts of acetal and 0 to 98 parts of pigment. The acetals are applied as solutions or suspensions in aqueous alcohol, e.g. methanol or ethanol, precipitation being effected by gentle warming in air or in a vacuum, or by a current of air. Instead of using aqueous alcohol, alcohol alone may be used and the water applied in the form of water vapour contained in a current of air, or aqueous alcohol may be used in conjunction with moist air. In all cases the water assists in the precipitation of the acetal. Air temperatures of 20‹ to 70‹ C. and a relative humidity of 20 to 90% are preferred. Precipitation is further assisted by the incorporation of diluents in the solvent, e.g. benzene, toluene, xylene, tetralin, petrols or ethers. Pigments, which may be ground into the solution of the acetal, include metal compounds which change colour due to decomposition on the passage of a spark, e.g. lead thiosulphate, cuprous thiocyanate, complex mercury compounds and salts of aromatic acids such as lead or zinc salts of benzoic, mono- and dinitrobenzoic, salicylic, nitrosalicylic, anthranilic, phthalic, terephthalic and nitrophthalic acids, and compounds which increase the hardness of the layer, e.g. titanium dioxide, zinc oxide, lead sulphate, basic lead sulphate and basic lead carbonate. Other pigments, e.g. chromium oxide, lead chromate, ultramarine or organic dyestuffs, may also be used. The carrier layer can consist of foils of paper, metal, natural materials, e.g. transparent cellulose foils, and/or synthetic materials, e.g. synthetic resins. Where the carrier layer is non-conductive, e.g. paper, conductivity is ensured by, e.g., condensing metal vapours thereon, or by the use of soot or graphite or metal powder incorporated in the paper pulp or in or on the carrier layer itself. Response to low voltages is also enhanced by the presence of an intermediate layer of, e.g., soot, graphite, metal powder or metal foil between carrier and marking layer. The soot, for example, can be coated on the carrier layer using as binding agent a solution or dispersion of a synthetic resin, e.g. polymers derived from styrene, cumarone and vinyl chloride, or cellulose ethers and esters and their alkali metal salts, or the alkali metal salts of polyuronic acids. Fluorescent substances may also be coated on the marking layer. Adherence between marking layers, especially where both sides of the carrier layer are coated, is prevented if the marking layer is coated with an aqueous solution containing 0.2 to 5% of methyl cellulose, the alkali metal salts of cellulose-glycollic acid, polyuronic acids, polymethacrylic or polyacrylic acid or their partial amides, alkali metal or ammonium alginates or pectinates, the reaction products of alkali metal, ammonium, or amine salts of alginic acid with ethylene oxide or propylene oxide, starch ethers, or the reaction products of cellulose-glycollic acid, polyuronic acids, cellulose and starch with ethylene oxide, propylene oxide, or epichlorhydrin. Other compounds which may be used in the protective layer are ethyl cellulose; the ammonium salts of cellulose-glycollic acid, carboxymethyl cellulose, or polyuronic acids; tragacanth or agar-agar; salts of polymethacrylic or polyacrylic acid; and proteins.