GB1319433A - Screening a black-surround colour cathode ray tube - Google Patents

Abstract

1319433 Luminescent screens ZENITH RADIO CORP 27 Oct 1971 [21 Dec 1970] 49891/71 Heading H1D A method of fabricating a tricolor phosphor dor (e.g. R.G.B.) c.r.t. comprising exposing a photosensitive resist (e.g. water based solution of p.v.a. with ammonium bichromate) to radiation from a source located at each of three exposure positions displaced in a first direction from three reference exposure positions corresponding to the deflection centres of the three electron beams, removing unexposed portions with a solvent, depositing on the unexposed areas a light absorbing material, stripping exposed resist from the screen, and repeating the steps at at least one more time but with the source located at three exposure positions displaced in a different direction from the reference exposure positions, the light absorbing material defining openings in which phosphor material is to be provided. The method permits the provision of phosphor dots of smaller area than the mask holes. The light source may project a linear rather than circular light pattern having a length dimension greater than a width dimension and the length directed along toward the centre of the triangle defined by the reference exposure positions. The displacements in the respective directions may control the horizontal and vertical dimensions of the openings in the coating pattern. In Fig. 2A, S may be 0À190 inch, and + #S need not equal - #S but is usually the same, and in the range 0À030 to 0À065 inch. The sequence of steps may for example be performed twice or three times, in the latter case the displacements defining a triangular pattern about each of the three reference positions, the apices pointing inwards or outwards for example. (Figs. 6A and 7, not shown). The recesses in the coating at each step of a two sequence process are generally approximately semicircular arcs while the geometry for a three sequence may be as in Fig. 6B (not shown). For exposure at the respective positions in each sequence, the faceplate or light source may be indexed or separate tables used for each colour centre. A light source with collimator having circular tip may produce ellipitcal distortion as in Fig. 5A (not shown), and the major axis may be controlled by the light pattern and the minor axis by control of #S. The former may be by suitable shaping and/or masking the collimator tip (e.g. Fig. 5B, not shown). A slot 0À030 x 0À1 inch may be used with #S of 0À030 to 0À035 inch. The light absorber may be applied as colloidal graphite slurry, and dried to fix, and p.v.a. residue stripped with hydrogen peroxide. The light source (Fig. 8, not shown) may have three tips energized individually at each sequence. The resist may contain the phosphor material during the processing or preferably the matrix is formed prior to phosphor deposition. The phosphor dots may overlap the opaque masking material. Round or rectangular faceplates of spherical sections are instanced. Graphite, manganese dioxide, pigment, and ceramic black are light absorbers mentioned.