GB479356A - Improvements in or relating to cathode ray tubes - Google Patents

Abstract

479,356. Cathode-ray tubes. STRANGE, J. W., and CONNELL, W. H. Aug. 1, 1936, No. 21330. [Class 39 (i)] In cathode-ray tubes for television of the projection type employing a fluorescent screen, the mask is formed on the same surface as that on which the screen is formed and on the same side thereof. The material forming the mask must be such as to withstand. the evacuating temperatures of 300-550‹ C. When the end of the tube is formed of a sheet of optical glass sealed to the conical portion of the envelope, the fluorescent surface and the mask of heat resisting material such as vitreous enamel or metallic suspensions may be applied before sealing the parts of the envelope together. Alternatively the mask may be applied after the end plate is sealed in position and may be constituted by the metallic coating which is employed as one of the anodes. The coating may be applied by the use of a chemical silvering solution, or a conducting coating of lead sulphide or copper, or by evaporation of metals in vacuum. The coating may be removed from the area to be covered with fluorescent material or this area may be protected during the coating operation by a sheet or plate which is readily removable, e.g. a sheet of flexible material with a thin layer of low melting point wax or a coating of material soluble in a suitable solvent such as nitrocellulose or other lacquer. Where the conducting coating is applied in liquid form, the limits of the coating forming the edges of the mask may be determined by tilting the tube. The fluorescent surface may be raised or lowered slightly above or below the rest of the surface of the end plate. In a modification the fluorescent surface and mask may be formed on a plate of transparent material such as mica or opaque material such as aluminium and suspended in the tube. Specifications 383,889 and 457,951 are referred to.