Patent GB-776665-A (GB)
Title: Improvements in or relating to the formation of tensioned films for use in cathode-ray tubes and the like
IPC: H01J29/02
Filed: 1954-05-17
Abstract: 776,665. Cathode ray tubes. SOC. GENERALE D'ELECTRONIQUE. May 17, 1954 [May 19, 1953], No. 14471/54. Class 39(1). A light modulating screen for a cathode ray tube comprising a deformable metal film supported by a plurality of spacers from a base member is made by placing the base member and a grid in an evacuated chamber, evaporating a first substance through the grid, then a second substance on top of the first substance, removing the grid and evaporating a third substance to form a continuous layer, evaporating a fourth or more substances in succession to form the deformable metal film and finally heating the assembly to a temperature of less than 450‹C. to remove by sublimation those of the deposits of the third substance which have not reacted chemically with the second substance to form a stable compound, the first, fourth substances and the compound being stable at the sublimation temperature of the third substance. The first substance 6, Figs. 4, 6 may be aluminium and the fourth substance 10 of beryllium. Suitable pairs for the second and third substances are (a) a metal, e.g. Cd and iodine, (b) an alkali metal, e.g. Na and a salt, e.g., ferric chloride or mercuric iodide, (c) an oxide or hydroxide of an alkali or alkaline earth metal, e.g. NaOH, and an acidic oxide, e.g., As2O3. The first and second substances 6, 7 are evaporated through a masking grid (not shown) which may consist of a single set of parallel wires or two sets of crossed wires. The grid is now removed by opening the chamber or by a remote control arrangement operated by electromagnets. The third substance 8 now evaporated on reacts with the second substance 7 to give compound 9, Fig. 6, and finally one or more layers 10 are evaporated on top. One layer 10 may be a reflecting layer. The screen is now removed from the chamber and sealed in to the cathode ray tube. The heat generated in degassing or by heating in a special oven, causes the third substance 8 to evaporate so allowing layer 10 to stretch flat as shown in Fig. 6. In a modification, layer 6 is dispensed with. In another modification, Figs. 7-9 (not shown) a set of parallel opaque metal strips are evaporated on a glass base through a first masking grid and then a second grid whose wires run perpendicular to the wires of the first grid is placed against the first grid and a further evaporation carried out to form spacer strips which serve as strips 6 in Figs. 4, 6. The opaque and spacer strips may be of the same metal. In another modification, Fig. 10, masking grids 12, 13 have their wires at right angles and metal is evaporated from two or more crucibles so positioned that metal from one deposits between metal areas deposited by the other so as to form long continuous parallel strips. Evaporation is then continued with a single crucible so as to obtain the spacer strips. The base may have a pre-coating. In another modification, layer 7 is formed by evaporation through a grid whose wires extend at right angles to those of the grid used for evaporating layer 6. In another modification further metal is deposited through a masking grid on to layer 10 so that the resulting layer is of variable thickness. In all forms, the base plate may be made slightly spherical. Specification 684,706 is referred to.