GB866358A - A method of and apparatus for obtaining smooth surfaces on films - Google Patents

Abstract

866,358. Cathode processing. SYLVANIA ELECTRIC PRODUCTS Inc. Dec. 1, 1959 [Dec. 30, 1958], No. 40862/59. Class 39(1). A method of forming a film, preferably the emissive film for the sleeve of a thermionic cathode, of even thickness and with smooth surfaces comprises the steps of flowing a suspension of solids preferably triple carbonates of Ca, Ba, Sr in-a binder dissolved in a volatile liquid on to a support, preferably a rotating wheel 22, Fig. 1, to form the film, heating the film by hot air from box 50 to partially set it removing the film from the support on to an Al conveyer 62 of mesh, and completing the drying of the film by an oven 66. The binder is of ethylcellulose and is dissolved in a mixture of toluene, ethanol and pentacetate as described in Specification 787,926 and the triple carbonate suspension is fed from metal hopper 10 to casting wheel 22 having a central drum 47 of Fe and a polished rim 48 of nickel steel, Ni or chrome. A water soaked sponge 26 sponges off dust or dirt from the wheel and rotating drum 34 applies a liquid film to the wheel 22 to promote stripping of the main film therefrom. The drum 34 has a shaft 31 on which are strung a large number of thin polyethylene discs 32 held between lucite end discs 34. The discs 32 dip into a tank of liquid e.g. 2, 2 aminoethylamino ethanol. The thickness of the liquid film is adjusted by adjusting the lucite end discs 34 on shaft 31 or by shifting shaft 31 towards or away from wheel 22 by differential screw 38. For this latter purpose, the tank is slidable on base 42. The speed of shaft 31 is variable. Two lamps 46 heat the polished surface of the wheel. The heater 50 and oven 66 have finned electrical resistance rods. An air stripper 64 blows air through nozzles on to the underside of the film. The tilting of hopper 10 is controlled by differential screw 148. The discharge tube may be grid controlled.