GB786353A - Improvements in or relating to cathode ray tubes - Google Patents

Abstract

786,353. Colour television tubes. ELECTRIC & MUSICAL INDUSTRIES, Ltd. July 25, 1955 [Aug. 10, 1954], No. 23156/54. Class 39(1). The phosphor screen of a C.R.T. is coated on the beam side with a series of electron permeable metal strips formed by sub-dividing a continuous layer of metal deposited on the screen. A monochrome screen, Fig. 2 (not shown) is made by depositing a layer of aluminium, magnesium or beryllium on the phosphor layer using an intermediate layer of nitro-cellulose which is afterwards dispersed, and dividing the layer by means of a reciprocating cutter. The strips are interconnected in two groups and potentials applied to the respective group to ensure interlaced scanning. For colour tubes, the phosphors are applied in lines by printing wheels either successively or simultaneously, the metal layer evaporated on and subdivided by a cutter as before. In Fig. 4, two plates 6 are placed together and coated with an adhesive e.g. phosphoric acid or sodium silicate. Three phosphor coated glass threads R, G, B, carrying red, green, and blue phosphors respectively and separated individually by glass threads 21 of slightly larger diameter are wound round the plates 6 from spools 17, 20, and the assembly is dried to set the adhesive. A conducting layer is evaporated onto both sides, and a light buffing or cutting action is applied to remove the coating over the spacer threads. The two plates are separated by cutting the wires and the individual conductors of the same colour phosphor are joined together. Alternatively the threads are laid across one or a series of plates in the same plane and secured by adhesive. The glass spacer threads may be replaced by threads of organic material dispersed by heat. In another modification, the phosphors are printed into straight grooves in a glass plate, metal evaporated on and the layer buffed to expose the glass ridges, Figs. 6-8 (not shown). In a further modification, Fig. 9, the grooves are laid down in a pattern with straight grooves 31, 32 for red and green and a zig-zag groove 33 for blue extending between the other sets of grooves as shown. The electrical connections between like metal strips may be tungsten wire helices extending over the strips and sealed to the glass plate at the sides ; short pins of chrome iron are sealed in the glass in positions occupied by the conductive lines and are afterwards connected together electrically. A screen may form the end wall of a C.R.T. being sealed in with glass frit or enamel or formed at its peripheral edge with a chrome iron ring which is seam welded to a similar ring on the conical portion of the tube. With a glass-glass seal, the mating edges are optically polished and the conductors are taken out at the sealed junction by using platinum paste strips burnt in the glass. The metal strips may be used to control and correct the scanning of the beam.