Patent GB-623386-A (GB)
Title: Improvements in or relating to fluorescent screens
IPC: G03C5/17
Filed: 1946-03-29
Abstract: 623,386. Luminescent materials. DU PONT DE NEMOURS & CO., E. I. March 29, 1946, No. 9843. Convention date, April 26, 1945. [Class 39 (i)] A fluorescent screen has a fluorescent surface coated with a thin, separate, substantially non- fluorescent film of a resinous water-insoluble film-forming material having dispersed therethrough fine discrete particles of wax. The coating may be applied to the screen surface by brushing, beading, transfer rollers, dipping, spraying or coating from a hopper provided with a doctor knife, or by flowing the solution across the surface of the fluorescent layer which may be in a horizontal or inclined position. In one example, a fluorescent sheet composed of calcium tungstate crystals dispersed in cellulose nitrate and adhesively secured to a sheet of cardboard is coated with a solution of cellulose acetate in dioxane which has dispersed therein in the form of fine particles about three parts of carnauba wax per hundred parts of water-insoluble cellulose acetate to form a layer about 0.01 to 0.02 inches in thickness. The latter constitutes 8.0 per cent by weight of the dioxane. In a modification, the fluorescent surface is coated with a dispersion of 2.5 parts of the synthetic wax with the trade name " Albacer," having a melting point of 95‹ to 97‹ C., in 85 parts of cellulose acetate which is dissolved in 1000 parts of a solvent composed of 90 per cent dioxane and 10 per cent methyl lactate. In another example, a fluorescent sheet composed of calcium tungstate crystals dispersed in cellulose nitrate and adhesively secured to a paper base is coated with a solution of cellulose nitrate in a mixture of amyl acetate and acetone of about equal proportions which has dispersed therethrough about three parts of carnauba wax in the form of fine particles per hundred parts of waterinsoluble cellulose nitrate. The latter constitutes about 6 per cent by weight of the solvents. In a modification, tetrachlorethane can be used as the solvent. The wax used should have a melting point at or above 65‹ C. Suitable additional waxes include Chinese insect wax, candelilla wax, raphia wax, pisang wax and hard synthetic waxes. Water-insoluble, resinous, film-forming materials which can be used as the binding medium for the wax dispersion include cellulose derivatives, synthetic resins, natural resins, and super-polymers such as cellulose acetate-propionate, cellulose nitroacetate, benzyl cellulose, polyvinyl-formal, polyvinylacetal, polyvinylisobutyral, polystrene, polyvinylacetate, polyvinylchloride, methylmethacrylate and nylons, e.g. polyhexamethyleneadipamide. Additional fluorescent materials are lead and/or barium sulphate, zinc sulphide, zinc cadmium sulphide and barium chlorofluoride. The fluorescent materials can be used in conjunction with binders such as (1) water-soluble gelatin, starch, gum tragacanth, casein, albumen, dextrin, gum arabic and methyl cellulose, and (2) waterinsoluble nitrocellulose, cellulose acetate, methyl methacrylate and alkyd resins. Additional types of supports for the fluorescent screens are glass, synthetic resin films and cellulose derivative films. Fluorescent screens without supports can be used. Methods of testing the coated fluorescent screen for scratch, speed, detail and static are described. Specification 190,201, [Class 98 (i)], is referred to.