GB1169455A - Electrostatic Coating Methods and Apparatus. - Google Patents

Abstract

1,169,455. Electrostatic coating; coated cathode ray tubes. RANSBURG ELECTROCOATING CORP. 11 Jan., 1967 [28 Feb., 1966], No. 1439/67. Heading B2J. [Also in Divisions C4 and H1] Charged phosphor particles are electrostatically applied. under the influence of an electric field, to a face of a Cathode ray tube which has first been coated with a sensitized binder. The apparatus comprises a deposition chamber 11 a gas-permeable plate 28, to support powder particles, mounted in the chamber, an electrode assembly including annuli 39 and points 42, on a charging head 38 and pins 43 on the plate, an earthed support 22 for the C.R.T. face 10 above the electrode assembly, means 34 to force air or other gas through the plate to form a fluidized bed of particles with a cloud of particles above it, and means 44 to establish an electric field, charge the particles and deposit them on the face. Phosphor particles flowing over the chamber edges are caught by a jacket 14 and pumped to a reservoir 19. The support 22 is rotated by a motor 21. Alternatively the plate 28 may be rotated, or both support and plate may be fixed. A colour television tube face is prepared by applying to the uncoated face a light-sensitive binder e.g. comprising 3% polyvinyl alcohol (P.V.A.) 0.5% ammonium dichromate in 1:1 isospropylalcohol/water. After drying the tube face is coated with a first phosphor and a dotted image-producing screen layed over the phosphor screen which is then exposed to light. The light polymerizes the P.V.A. Unpolymerized P.V.A. and phosphor not within the dotted areas is removed by rinsing with water. Second and third offset phosphor dot patterns are similarly applied to second and third polymerizable binder coatings. A monochrome tube is prepared by light exposure without the image-producing screen.