GB735633A - Improvements in or relating to the manufacture of luminescent screens - Google Patents

Abstract

Apparatus for use in the manufacture of a luminescent screen for a cathode-ray tube by a process of the type involving the deposition of a luminescent powder or powders on to the screen support from a suspension in a liquid, comprises a plurality of closed vessels for containing, in the form of liquids or suspensions, the ingredients for forming the deposition suspension, a sprinkler insertable within the cathode ray tube envelope for applying the ingredients to the surface of the luminescent screen support, and a closed feed system for conveying the ingredients to the sprinkler, the feed system including means for <PICT:0735633/III/1> controlling the quantity of each of the ingredients to be delivered to the sprinkler. The four reservoirs 1, 2, 3 4 contain respectively demineralized water, an aqueous solution of the binder (such as potassium silicate), an aqueous solution of an electrolyte (such as sodium sulphate) and a concentrated suspension of the luminescent powder in water or in an aqueous solution of the binder, the reservoirs being all connected through a closed system of pipes and vessels to a sprinkler 5 disposed within the cathode ray tube envelope 6. The reservoirs 1, 2 and 3 are each connected through a stopcock to graduated cylinders 7, 8 and 9 respectively, and the outlets from the three graduated cylinders are connected through stopcocks to a single pipe 10 which passes to a Buchner-type vacuum filter 11. The outlet from the filter 11 is connected to a reservoir 12 for the mixed diluents, the reservoir 12 being connected to a vacuum pump. The reservoir 4 is fitted with a rotatable stirring paddle 13 attached to the flanged detachable top 14 which is separated from the top and side of the reservoir by small gaps. A tube 16 passes through an aperture in the reservoir wall and filtered air is blown therethrough. The outlet from the reservoir is connected through a stopcock to a graduated cylinder 17 connected to a vacuum pump. The outlet from the combination of the reservoir 4 and graduated cylinder 17 and the outlet from the reservoir 12 are connected through stopcocks 18 and 19 respectively to the sprinkler 5. For preventing the entry of air from the atmosphere into the envelope 6 there is provided a cylindrical cover 21 attached to the hollow cylindrical stem 22 of the sprinkler 5. Filtered air can be blown through the envelope 6 through the tube 23. The whole system can be washed out by passing demineralized water from the reservoir 1 through each of the cylinders 8 and 9 and by drawing water from the reservoir 1 through the remainder of the closed system via the cylinders 7, 8 and 9 and the stopcock 20.