GB802908A - Improvements in and relating to the manufacture of masks of varying opacity and to screen structures for cathode ray tubes - Google Patents

Abstract

802,908. Colour television tube processes. PHILCO CORPORATION. Jan. 31, 1955 [Feb. 4, 1954], No. 2827/55. Class 39(1). Correcting masks for use in photographic methods for depositing phosphors and other materials on the concave side of a curved cathode-ray tube face are prepared photographically. Correction for depositing lines of different colour phosphors and indexing strips is obtained by photographing on a sensitized surface shaped like the C.R.T. an opaque mask with parallel transparent lines formed therein ; the printing light being projected from a point source. The exposed lines have pin-cushion distortions and are developed to form a mask, Fig. 1 (not shown). Flooding light from lamps 21 is then passed through the mask 10 with its opaque lines to print a pre-distorted mask on a plane photographic plate 19. The formation of the intermediate mask 10 may be avoided by forming the first image on a light-diffusing screen and projecting it direct onto a flat photographic plate. Separate masks are prepared for the materials to be deposited on the tube screens, to print from the concave side the lines on which the materials are left deposited as in the process described in Specification 788,661. A mask to correct for the non-uniformity of light illumination across the screen 10 when printed from the parallel-lined screen, is prepared by exposing a photo-sensitive surface of the curvature of the C.R.T. to light without interposition of the parallel-lined mask and developing it to a negative transparency, to be applied over the surface 10 when being printed. Four masks may be mounted into a rotatable frame with clamp catches determining the registering position of each mask, Fig. 4 (not shown).