GB713908A - Cathode-ray tubes and methods of manufacturing the same - Google Patents

Abstract

713,908. Photographic processes. PHILCO CORPORATION. Aug. 6, 1952 [Sept. 26, 1951], No. 19795/52. Drawings to Specification. Class 98(2) [Also in Group XL(a)] A photographic method of making a three-colour screen for use in colour television consists in forming a photographically sensitive layer containing one of the colour phosphors, exposing it to light through a mask in accordance with a desired pattern and removing the unexposed portions, the other complementary phosphor patterns being then formed successively in a similar way. A glass plate which may be the end face of a cathode-ray tube is subjected to a series of cleaning steps which may be physical or chemical, and which may involve as a final step a slight etching of the surface. The phosphor patterns which may make up stripe or dot triplets are then formed. Each photographically sensitive layer containing the appropriate phosphor is laid down as a succession of thin layers by spraying. The unexposed portions are dissolved in water; preferably an initial damping is provided by a fine mist spray. Each layer may be subjected to a baking step prior to the deposition of the succeeding layer. The whole structure is then baked to remove the photographically sensitive material and to bond the phosphors to the glass. To enhance the bonding, the structure may be immersed in a binder such as potassium or sodium silicate prior to the baking treatment. The photographically sensitive material may consist of a polyvinyl alcohol or an animal gelatin, an animal glue, egg albumen or a natural gum such as gum acacia, and ammonium or potassium dichromate together with a suitable diluent such as ethyl or methyl alcohol. For the phosphor materials the usual silicates, phosphates or tungstates may be' used. Index coatings for synchronizing the excitation of the colour patterns may be formed by a similar photographic process. An index stripe may be formed, for example, on each stripe of one of the colour. patterns. The " index" material may consist of gold, platinum or tungsten or of magnesium oxide and may be applied as a suspension in the photographically sensitive material, or it may be sprayed on an initially formed photographically sensitive layer. In the former case an initial photographically sensitive layer is also preferably provided.