GB1300238A - Improvements relating to coloured cathode ray tubes - Google Patents

Abstract

1300238 Making shadow masks ZENITH RADIO CORP 4 Sept 1970 [15 Oct 1969] 42509/70 Heading B3A [Also in Division B6] A process of fabricating a colour c.r.t. shadow mask, comprises etching apertures in a blank in a pattern defined by etch resistant material on the outer surfaces, lining the aperture walls with material 13, relatively oxidation resistant compared with the blank material and of thickness small (e.g. 0À2 mm.) compared with the smallest dimension of the apertures, removing the etch resistant material, oxidizing the blank on the outer surfaces 14, 14a, removing the lining material on the aperture walls and re-etching the walls to increase the smallest dimension of the apertures which in use determines the electron beam cross-section, so that the mask can be used for photographic printing of a colour c.r.t. after the oxidation step and before re-etching, and as a shadow mask for the c.r.t. after the re-etching. The process is applicable to phosphor deposits, red, green or blue dot triads, and circular or hexagonal shapes for instance, with black surrounds, and rectangular or circular screens. The mask may be spherical section to be nearly parallel to the screen surface. The intermediate mask mountings may be by leaf springs on the faceplate flange mounting studs. The blank may be a ferrous metal, cold rolled steel, aluminium clad steel, (e.g. 6 to 7 mm. thickness), or Cu-Ni alloy, the photosensitive resist of dichromated polyvinyl alcohol, fish glue or shellac, normally soluble in a solvent such as water and insoluble on exposure to U.V. radiation. The etchant may be ferric chloride providing differently sized holes (D1) (D2) (Fig. 2, not shown), and concentration 45‹ Baume at 130‹ F. The apertures may be graded radially from the mask centre, 7 and 8 mm. diameters at centre and edge respectively. Lining (13) may be flashed, electroplated or electroless plated, processes being described, and preferably etched by the etchant as used in the first etching step. Layers (11) (11a) are removed and oxide layers (14) (14a) provided which also increase heat losses in use as a mask, being provided by heating at 1040‹ F. in an oxidizing atmosphere, applied chemically in a salt bath, or by heating in steam. The photographic printing process may use pva. with ammonium bichromate. After phosphor depositions, the mask is re-etched to enlarge the aperture (D 2 ) to (D 3 ) (Fig. 5, not shown) of size larger than the individual phosphor deposits and remove liner (13). If liner (13) is not removed by the above etchant, the liner may be first etched separately or electrode-plating. An Al conductive backing layer may also be added.