GB1450597A - Cathode-ray tube with shadow mask - Google Patents

Abstract

1450597 Making shadow masks RCA CORPORATION 9 Nov 1973 [10 Nov 1972] 52076/73 Heading B3A [Also in Division H1] A cathode-ray tube for colour television has a shadow mask with rows of apertures parallel to the phosphor lines, elongated in the direction of the rows and separated by webs, wherein the apertures are randomly distributed along the rows. The formation of moirÚ patterns is thus avoided. In one form of mask, the webs between the apertures are all of the same length, but the distance between adjacent webs varies in random fashion, between a maximum and a minimun value. There is also a minimum distance between the centre lines of webs in adjacent rows. The pattern may cover the whole area of a mask, or it may form an element which is repeated to form a mask. In the latter case, rows in each element are displaced in random fashion up to a small maximum. The patterns may be generated by a computer, the output of which controls a plotter which produces masters for both sides of a plate which is photoetched to produce the mask. The masters may be of slightly different sizes so that the slot apertures have slanted sides. Also, the slot apertures may be graded on the final master to correct misregistration errors. The finished flat mask is given a curvature. In a second embodiment, the apertures are all of the same length, but the position along the row of corresponding apertures varies in random fashion, within limits similar to those mentioned above, and a mask may comprise a single or several pattern elements. The pattern may be reproduced by photolithography. The pattern may also be constructed by generating a single row and repeating it in random fashion, staggered or displaced with respect to each adjacent row, or by specifying a particular ratio for each web in its random spacing from a vertically adjacent web.