GB745814A - Improvements relating to luminescent screens - Google Patents

Abstract

745,814. Luminescent materials; cathode-ray tubes. EDISON SWAN ELECTRIC CO., Ltd. Nov. 28, 1951 [Nov. 30, 1950], No. 27929/51. Class 39 (1). A process of manufacturing a luminescent screen consists in forming a layer 2 of luminescent material on a base, such as a glass plate 1, covering the luminescent material with a sol 3 of colloidal inorganic hydrated clay-like material capable of forming a thin tough flexible film when deposited from a sol, drying the sol so as to leave on the base a film of the clay-like material in which is embedded the luminescent material and removing the film and embedded material from the base. The colloidal inorganic hydrated clay-like material includes hydrated aluminium oxide, magnesium oxide, aluminium silicate, magnesium silicate and aluminiummagnesium silicate, referred to generally as bentonite. The sol can comprise a suspension in water of from one to five, preferably two, per cent by weight of bentonite solids of particle sizes up to 1 micron, preferably 0.5 micron average particle size. With luminescent material particles averaging less than 0.6 microns a layer of sol about 150 microns deep and containing 2 per cent of bentonite can be used. The luminescent material layer is formed on the base by depositing mono-particle thick layers of the material on a water or other liquid surface and passing the base upward through the layer as described in Specification 686,259. Multiparticle thick layers may also be used. A thin aluminium film can be evaporated on to either surface of the bentonite film. Screens can be formed with more than one layer of luminescent material having different types of phosphor, for example one layer may be a blue phosphor activated by cathode rays and another layer a long after-glow layer activated by U.V. light from the first layer. Both layers may be in the same film or separate films may be formed. Fig. 4 shows the luminescent screen 7 mounted in a frame 8 in a C.R.T. 6. The frame 8 can be a split metal ring which clamps the edges of the screen and is cemented to the interior surface of the funnel portion 6a which can be of metal or glass and of circular or rectangular crosssection.