Patent GB-1187264-A (GB)
Title: Method and Apparatus for Depositing a Phosphor or Phosphors on a Cathode Ray Tube Faceplate
IPC: H01J9/227
Filed: 1967-07-14
Abstract: 1,187,264. Coating cathode-ray tubes. HUGHES AIRCRAFT CO. 14 July, 1967 [25 Aug., 1966], No. 32590/67. Heading B2J. [Also in Division H1] The luminescent coating of a cathode ray tube screen is applied to the tube faceplate by directing a stream of electrically charged phosphor particles along a predetermined path 0toward the faceplate, effecting relative movement between the. stream and the faceplate in a direction transverse to the path, and permanently depositing the phosphor particles on the faceplate in a predetermined pattern. For a colour television tube, the faceplate, a portion of the tube envelope, and a colour-switching wire grid or a shadow mask electrode may be permanently assembled together prior to deposition of the phosphor, during which the particles follow trajectories in the evacuated tube portion identical to those followed by electrons in the completed and functioning tube. In the apparatus shown, in which the tube envelope 26 is maintained temporarily hermetically sealedto the evacuable cabinet 21 by a sealing ring 25, phosphor particles from an appropriate one of the three different colour phosphor containers 56, 57, 58 are charged by falling through the box 66 in which a hot wire cathode 71 is mounted, accelerated by plates 74 and 75, and scanned over the faceplate, which is coated with tacky polyvinyl alcohol, by electrostatic deflection plates 78. If the tube is of single gun type, the apparatus is maintained in the condition shown, and a colour switching signal appropriate to the colour of the phosphor being deposited on the faceplate is applied to the colour switching grid 29; if of three-gun type, employing either, as shown, a grid of parallel wires 29 with colour stripes, or a shadow mask electrode with colour dot triods, each stream of phosphor particles is, according to its colour caused to pass through the correspondnig deflection centre 79, 80, or 81 of the completed tube by transverse movement of the panel 44, to which the charging box 66 and accelerating and deflecting electrodes are secured, the positions for the flanking deflection centres 79 and 81 being defined by the stops 48 and 49. The phosphor particles, which are preferably 10 to 20 microns in diameter, are fed by the moving belt 51 from the appropriate container to the charging box, where they are chargedpreferably positively-by second emission consequent upon bombardment by electrons from cathode 71, the rate of deposition being exhibited by the ammeter 41. The phosphor layer may thereafter be provided with an evaporated aluminium layer, which may or may not be connected to the aluminium coating 37 on the envelope cone, the tacky poly vinyl alcohol finally being removed by baking. In alternative arrangements, different colour phosphor streams may be caused to pass through their appropriate deflection centre by transverse adjustment of the cathode ray tube assembly with respect to the phosphor particle charging, accelerating, and scanning assembly which remains stationary (Fig. 13, not shown); and instead of electrostatic scanning of the particles over the faceplate, the particle supply, charging, and accelerating assembly may be supported within the cathode ray tube neck by a gimbal mounting and maintained by a pendulum weight in a vertical orientation While the cathode ray tube assembly is swivelled about the appropriate deflection centre by means of a further gimbal mounting arrangement (Figs. 14 to 18, not shown).