Patent GB-844301-A (GB)
Title: Improvements in or relating to the manufacture of luminescent screens for cathode ray tubes
Inventor: DAVIES BRIAN LEONARD
IPC: H01J9/22
Filed: 1955-10-07
Abstract: The process in which a luminescent screen in a cathode ray tube is settled from a liquid suspension comprises the steps of introducing a predetermined volume of each ingredient of the suspension (namely one or more fluorescent suspensions and one or more diluent liquids) into a separate measuring vessel, and transferring the ingredients from the measuring vessels into the cathode ray tube bulb by predetermined amounts in a desired sequence, the introduction and transfer of at least one ingredient each being effected either by applying pressure to a vessel to cause a predetermined amount of liquid to flow out or by evacuating a vessel to cause a predetermined volume of liquid to flow in.  The diluent liquids are preferably fed from respective stainless steel storage tanks 4, 5, Fig. 1, through diaphragm valves 441 to stainless steel tanks 2, 3 controlled by ball valves 42, 43. Tanks 2, 3 are connected by pipes to glass measuring vessels 7, 8 connected by further pipes to the cathode ray tube 75.  The luminescent powder suspension is contained in a glass vessel 1 and is continuously agitated by a stirrer 21; it proceeds to glass measuring vessel 6 and thence to the cathode ray tube by gravity feed.  The electrolyte in vessel 7 and the luminescent powder suspension in measuring vessel 6 are sprayed into the cathode ray tube through roses 45, 46 to ensure thorough mixing with the binder from measuring vessel 8.  The dispensing head 9 is of transparent plastic and terminates in a sponge rubber ring 10 to give a vacuum tight connection to the cathode ray tube. The flow of liquid from 2 to 7 and 3 to 8 is effected by compressed air introduced via valves 16, 18 and continues until the liquid level in 7, 8 reaches the lower ends of upper probes 37, 35 whereupon valves <PICT:0844301/III/1> <PICT:0844301/III/2> 16, 18 close and valves 17, 19 open to the atmosphere, so terminating the liquid flow.  The cathode ray tube is now evacuated by vacuum pump through valve 12 so that the diluent liquids in 7, 8 are forced into the cathode ray tube until the liquid level in 7, 8 reaches the lower ends of lower probes 36, 33 whereupon valve 12 closes and valve 13 open to the atmosphere opens so restoring the pressure inside the cathode ray tube to atmospheric and stopping the entry of diluent liquid thereto. After the electrolyte and binder doses have simultaneously entered the cathode ray tube, valve 26 is opened so the fluorescent suspension runs into measuring vessel 6 until it touches the lower end of probe 41, Fig. 2; this closes 26 and opens 27 so the suspension can run by gravity feed into the cathode ray tube through sprinkler 46.  When the level of the suspension falls to the lower end of probe 40, valve 28 opens to fill 6 with demineralised water more quickly than the suspension emerges through 27 to flush out any remaining powder in 6 and in the pipe to the cathode ray tube, the water level then falling to the level of the lower end of probe 39.  The electrolyte may be a weak water solution e.g. M/750 of barium nitrate and the binder is a weak water solution of potassium silicate e.g. 8% of a 1.1 N solution of 1 K2O. 3.5 SiO2.  The volume of barium nitrate used may be three times the volume of the silicate so a constriction is introduced into the potassium silicate pipe to get the same length of time for each to enter (simultaneously) the cathode ray tube. If the volumes are the same so are the rates of flow.  A numerical example of quantities of diluent liquids and luminescent suspension is given.  Magnetically operated spring clips 26, 27, 28 control the fluorescent suspension (see Group XXIX).  Apertures 30, 31, Fig. 1 prevent back siphoning and filters 32 remove undesired particles from the air and liquid pipes.  In modifications there may be more than one mixing vessel.  A small quantity of dispersing agent may if desired be added to the luminescent suspension.  The probes are preferably of platinum. The whole dispensing system can be controlled by electromagnetic means. Suitable operating circuits are described with reference to Fig. 5 (not shown) for automatic operation and Fig. 6 (not shown) for manual operation by switches.  The coating process may be a continuous one, cathode ray tubes passing by the apparatus on a moving belt. Specification 735,633 is referred to.