Patent GB-1006061-A (GB)
Title: Luminescent screens
IPC: H01J9/22
Filed: 1962-05-07
Abstract: Luminescent screens for cathode-ray tubes are formed by adhering phosphor particles of colloidal size to a support by an adsorptive film of material, e.g. gelatin, polyvinyl alcohol or a starch, having protective colloid properties and, if necessary, building up the thickness by further depositions.  The screen may be of the monochrome or multicolour type; in the latter case it may comprise a plurality of superimposed different colour producing phosphor layers with or without inert separating layers. The front facing layer may comprise particles of sedimentary size. In one type of screen, multicolour layers togeth r with inert separating layers are built up on either glass or phosphor base particles.  A final inert protective layer may also be provided. Two methods of making extended layer screens, or forming multiple-coated-particles, described: (1) the filmed substrate method, in which the support is coated with particle adsorbent films to which the phosphor particles adhere, and (2) the filmed particle method in which the adsorbent films are formed on the particles themselves. In method (1), the support is first bathed in an aqueous gelatin solution adjusted to a pH value of about 4 with the addition of glacial acetic acid.  Alternatively, or in addition, an acid bath may be given after the gelatin solution bath.  A water bath step is then used and the adsorbent film may then be dried. Next a monoparticle thick phosphor layer is deposited from a dispersion of phosphor particles in water, the particles being up to three microns in diameter.  The dispersion may be agitated during the deposition. Denser or thicker layers may be formed by a series of alternate acid and phosphor dispersion washes or by acidifying the original phoshor dispersion. Thicker layers still may be built up by alternately repeating the gelatin and phosphor dispersion washes or by repeating the above procedures to superimpose a number of phosphor layers.  To improve the adhesion of the phosphor particles there may be a final wash with potassium silicate solution, with a gelatin hardener solution such as a solution of chrome alum or formaldehyde, or with a dispersion of extremely fine particles, e.g. colloidal silica. In a specific example of making a multicolour superimposed phosphor layer screen the blue phosphor is silver activated zinc sulphide, the green phosphor manganese activated zinc orthosilicate, and the red phosphor manganese activated zinc - magnesium - cadmium - silicate, inert separator layers of vermiculite being provided. The phosphors are prepared by ball-milling. Finally, the screen is aluminized.  In method (2), the phosphor particles are provided with adsorbent films by bathing in a gelatin water solution and after washing are deposited in a water dispersion.  In a modification of either of the above methods, two phosphor dispersions may be used, the second containing particles of smaller size than the first.  With multiple-coated particles, i.e. layers built up on glass or phosphor base particles, either of the above methods may be used and the separator layers may comprise silica or mica colloidal particles. Other specific separator materials mentioned as suitable are bentonite, kaolin, vanadium pentoxide and talc.  The base particles are about 40 microns in diameter. Finally, the particles may be deposited on the screen using a slurry or settling technique.ALSO:Luminescent screens for cathode-ray tubes are formed by adhering phosphor particles of colloidal size to a support by an adsorptive film of material, e.g. gelatin, polyvinyl alcohol or a starch, having protective colloid properties and, if necessary, building up the thickness by further depositions.  The screen may be of the monochrome or multicolour type; in the latter case it may comprise a plurality of superimposed different colour producing phosphor layers with or without inert separating layers. The front facing layer may comprise particles of sedimentary size. In one type of screen, multicolour layers together with inert separating layers are built up on either glass or phosphor base particles.  A final inert protective layer may also be provided. Two methods of making extended layer screens, or forming multiple-coated-particles, described: (1) the filmed substrate method, in which the support is coated with particle adsorbent films to which the phosphor particles adhere, and (2) the filmed particle method in which the adsorbent films are formed on the particles themselves.  In method (1), the support is first bathed in an aqueous gelatin solution adjusted to a pH value of about 4 with the addition of glacial acetic acid. Alternatively, or in addition, an acid bath may be given after the gelatin solution bath.  A water bath step is then used and the adsorbent film may then be dried.  Next a monoparticle thick phosphor layer is deposited from a dispersion of phosphor particles in water, the particles being up to 3 microns in diameter.  The dispersion may be agitated during the deposition.  Denser or thicker layers may be formed by a series of alternate acid and phosphor dispersion washes or by acidifying the original phosphor dispersion.  Thicker layers still may be built up by alternately repeating the gelatin and phosphor dispersion washes or by repeating the above procedures to superimpose a number of phosphor layers.  To improve the adhesion of the phosphor particles there may be a final wash with potassium silicate solution, with a gelatin hardener solution such as a solution of chrome alum or formaldehyde, or with a dispersion of extremely fine particles, e.g. colloidal silica.  In a specific example of making a multicolour superimposed phosphor layer screen the blue phosphor is silver activated zinc sulphide, the green phosphor manganese activated zinc orthosilicate, and the red phosphor manganese activated zinc-magnesium-cadmium-silicate, inert separator layers of vermiculite being provided.  The phosphors are prepared by ball-milling.  Finally the screen is aluminized.  In method (2), the phosphor particles are provided with adsorbent films by bathing in a gelatin water solution and after washing are deposited in a water dispersion.  In a modification of either of the above methods, two phosphor dispersions may be used, the second containing particles of smaller size than the first.  With multiple-coated-particles, i.e. layers built up on glass or phosphor base particles, either of the above methods may be used and the separator layers may comprise silica or mica colloidal particles.  Other specific separator materials mentioned as suitable are bentonite, kaolin, vanadium pentoxide and talc.  The base particles are about 40 microns in diameter.  Finally the particles may be deposited on the screen using a slurry or settling technique.