Patent GB-595301-A (GB)
Title: Method of manufacturing electrode foundation structures for cathode ray tubes
IPC: H01J29/41
Filed: 1944-06-13
Abstract: 595,301. Electron beam apparatus. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. June 13, 1944, No. 11328. Convention date, April 29, 1943. [Class 39 (i)] [Also in Groups XX, XXIII and XXXVI] A foundation plate for use in the production of a mosaic target electrode of an electron beam tube is prepared as follows. A thin glass plate of thickness, e.g. 0.001-0.005 inch, is coated with a layer 3 of a tacky substance such as rubber cement and then with a layer 4 of photographic emulsion such as gelatine containing potassium bichromate preferably also containing a small quantity of a wetting agent such as aerosol. It is then exposed to light through a screen 5 comprising crossed transparent lines 7 with intervening opaque areas 6. The plate 1 is then developed in water at about 50‹ C. to remove the unexposed areas of the emulsion, this also hardening and contracting the exposed areas. Refractory powder such as silicon carbide is then dusted over the plate and excess removed by an air blast leaving piles adhering only to the exposed areas of the tacky substance. The plate is then heated sufficiently to soften the glass slightly during which bubbles or recesses are formed beneath the piles of refractory powder and remaining parts of the emulsion are evaporated. The plate is then immersed in dilute hydrofluoric acid to remove the refractory powder. The glass foundation is also attacked ; the etching may be allowed to proceed until the bubbles are opened at the lower surface of the glass plate or may be stopped short of this point according to the type of target electrode required.. In a modification, the foundation plate is covered with a single layer of a tacky photographic emulsion and the whole surface covered with refractory powder and the emulsion is exposed to light from the opposite side of the glass plate through a screen having opaque crossed lines and transparent intermediate areas, subsequent treatment being as in the previous case. In one method of preparing a mosaic electrode from a plate having perforations extending through it, one side of the plate is first covered with a film of lacquer closing the apertures in that side and the recesses so formed are filled with gelatine by repeated immersion of the plate in a gelatine solution and drying. The lacquer film is then removed and a conducting film of graphite or aluminium applied in its place, the gelatine then being removed from the recesses by immersion in hot water. The recesses are then filled with metal, e.g. silver, by electro-deposition, the conducting film serving as cathode. In an alternative method, graphite is applied directly to the lacquer film by a suspension in wood alcohol which partially dissolves the lacquer so as to form conductive paths therethrough. The graphite layer is placed in contact with mercury in the electro-depositing operation. In one form of mosaic electrode employing a foundation plate in which the recesses do not extend right through it, the lower parts of the recesses are provided with a photo-electric coating sensitive to red light, the remainder of the upper surface round the recesses being provided with a photo-electric coating sensitive to blue light. The softening point of the glass foundation is preferably below 800‹ C. ; Corning 705 glass is suitable. Specifications 542,332 and 595,330 are referred to.