GB1416753A - Methods of manufacture of colour picture tubes - Google Patents

Abstract

1416753 Colour television tubes RCA CORPORATION 15 Jan 1973 [14 Jan 1972] 1937/73 Heading H1D In a photographic method of fabricating the phosphor pattern of the screen of a shadow mask colour tube, in which a photosensitive coating is exposed to a small area light source through the shadow mask, misregister is reduced by exposing a central zone of the screen predominantly but not wholly to a light source positioned at a second order colour centre, and an outer zone of the screen, predominantly but not wholly to a light source positioned at a first order colour centre. Optical intensity filters are employed to permit the exposure of one or the other zone, and preferably for each exposure an appropriate correcting lens is employed further to reduce misregister throughout the relevant zone. Different lighthouses, or a simple, adjustable lighthouse may be employed for the two exposures, and preferably a longer light. source is used for the outer zone, to ensure adequate exposure at the edge of the screen despite a decrease in size of the mask apertures in that region. Exemplary calculations are provided for a case in which, for the exposure of the outer zone, the light source position and the shadow mask contour are chosen to eliminate degrouping error at the corners of the screen. The exposure is then carried out without the use of a correcting lens, whereafter the misregister at other points in the outer zone is determined by employing the screen in a colour tube, and the resulting data employed to design a correcting lens for minimizing misregister throughout the remainder of the outer zone. Reference is made to the possibility of exposing the whole screen to the second order source, but only the outer zone to the first order source, whereby distorted dots are produced in the outer zone to ensure full beam spot landing. The method may be employed for a dot or line screen, and for black-matrix and non-matrix screens.