Patent GB-857451-A (GB)
Title: Improvements in and relating to image-reproducing cathode ray tube apparatus
IPC: H01J29/34
Filed: 1956-12-07
Abstract: 857,451. Cathode-ray tubes. PHILCO CORPORATION. Dec. 7, 1956 [Dec. 7, 1955], No. 37472/56. Class 39(1). In a colour receiver the fluorescent areas such as strips or dots or white areas in a monochrome receiver are spaced apart and the intervening spaces are filled with similarly shaped areas of substantially non light reflecting material, such as ferric oxide, graphite, or unactivated Willemite and the whole of the screen is covered by a heat reflecting layer. The non reflective areas are also opaque to light. The substantially non reflecting material may however, reflect light of low visibility, e.g. the dark red of ferric oxide. It prevents the beam from striking two adjacent phosphor strips ; and if also opaque reduces colour dilution and halation due to ambient light and screen light being multiply reflected in the glass end wall of the tube since it will absorb such light. In a modification, Fig. 3, non-light reflecting strips have different widths and mask off part of the fluorescent light from the observer since the fluorescent material overlaps the rear edges of the opaque strips so compensating for the different light emission efficiencies of the phosphors and achieving colour balance, the red usually having less luminous efficiency than the blue or green phosphors. Alternatively the opaque strips are of uniform width but the phosphor strips of different widths to equalise the light intensities or to over emphasise a particular component colour, or both sets of strips can be of different widths ; in the latter case, the centre to centre spacing of the adjacent phosphor strips is preferably the same so that the beam can be intensity modulated at a single frequency. If the centre to centre spacing is not constant as may be necessary for other reasons a complex modulating frequency is used. In manufacture, the opaque strips 27, Fig. 2 are always deposited first, through a grill, then the phosphor strips also through a grill. A photographic deposition process can be used as in Specification 788,661, or in which each strip is deposited in two layers. A detailed procedure is given involving coating the inner surface of the face plate with photosensitive material, comprising water, polyvinyl alcohol and denatured alcohol known as "Solox" (Registered Trade Mark) and photo-sensitive material, drying, projecting an image of a grill on to the coating to form water soluble and insoluble areas, flowing on a slurry of unactivated Willemite with " Solox " and water, drying, washing with water to remove tmexposed areas, drying, depositing a second layer of photo-sensitive material dry, projecting an image of a grill as before, flowing on a slurry of ferric oxide, water and " Solox " (the slurry of Willemite can also be replaced by ferric oxide), drying washing with water to remove unexposed areas, drying to get the discrete strips of opaque material. To get the phosphor strips the faceplate is again coated with photo-sensitive material, dried, the image of a grill is projected on to it to form soluble and insoluble areas, flowing on a slurry of water, " Solox " and phosphor of first colour, washing to remove the unexposed areas and repeating the process (as with the opaque strips) to get two layered phosphor strips. This is repeated to get the phosphor strips of the two other colours. Then the light reflecting electron permeable and ion stopping Al layer is deposited on the rear surfaces of all the strips, and finally the indexing strips are deposited on the rear surface of the Al layer by a process similar to that for the non light reflecting and phosphor strips. The invention is also applicable to shadow mask receivers with three guns and phosphor dots ; in this case in manufacture the opaque and non- reflecting material is deposited first in a pattern corresponding to the spaces oetween the phosphor dots after which the phosphor dots are deposited in the vacant spaces. The non reflecting material pattern can be formed by projecting the image of the tube mask or of an apertured master plate on to a photo-sensitive layer, the parts exposed to light being subsequently removable by washing. Ferrous oxide is now flowed on and dried and the exposed areas removed by washing. Alternatively the image of a negative mask opaque at the areas to be occupied by the phosphor dots is projected on to the photo-sentitive layer which has opposite characteristics, i.e. the parts not exposed to light being removable by washing, the ferrous oxide being deposited and the said parts being removed by washing. The phosphor dots are now deposited by a conventional method such as silk screening or purely photographic. The silk screen mask or a photographic equivalent thereof is rotated by 120 degrees clockwise for the second phosphor deposit and 240 degrees anticlockwise for the third phosphor deposit. In all embodiments an aluminium layer 26 can be deposited on the rear of the screen and indexing strips 28 of distinctive secondary emission ratio, e.g. MgO, or of light emitting phosphor are deposited on the aluminium layer 26. The particle size of the material of the non light reflecting strips is less than that of the phosphors. The invention can be applied to colour receivers termed " Chromatron " (Registered Trade Mark) having a colour switching and focusing grid near the screen as described in PIRE, January, 1954, page 304, and to post deflection focusing colour tubes with three guns as described in Radio Electronics, December, 1955, page 90, and also to monochromatic tubes having a screen of white phosphor areas backed by an aluminium layer.