Patent GB-1481314-A (GB)
Title: Screen gravure photoengraving
IPC: G03F5/20
Filed: 1974-07-08
Abstract: 1481314 Screen gravure photo-engraving TOPPAN PRINTING CO Ltd 8 July 1974 [9 July 1973 6 June 1974 14 June 1974 (2)] 30238/74 Heading G2M A method of screen gravure photo-engraving comprises exposing a photo-sensitive carbon tissue or photo-resist twice, once by contact printing with a planographic, relief or gravure screen positive, which carbon tissue or photo-resist has been exposed by contact printing with a white line gravure screen or which screen positive has been provided with gravure white lines, and once by exposing the carbon tissue or photo-resist (a) again to the screen positive in register with the first printing, a diffusion sheet being inserted  between the screen positive and the carbon tissue or photo-resist or (b) by contact printing a continuous tone positive or an approximately continuous tone positive corresponding to the screen positive already printed, in register with that printing and, after the double exposure, transferring the carbon tissue or photo-resist to a gravure cylinder and effecting engraving. Four embodiments of the method are described, the exposure steps being as follows:- (i) exposing the carbon tissue or photo-resist by contact printing in sequence with a white line gravure screen, the screen positive and again with the screen positive, a diffusion sheet being inserted between the positive and the carbon tissue or photo-resist Figs. 1- 4 (not shown); (ii) exposing the carbon tissue or photo-resist by contact printing with a screen positive provided with gravure white lines, and then again with the said screen positive in register with the first printing, a diffusion sheet being inserted between the positive and the carbon tissue or photo-resist Figs. 7 and 8 (not shown); (iii) exposing the carbon tissue or photo-resist by contact printing with a white line gravure screen and either a continuous tone negative corresponding to and having the same dimensions as the screen positive to be used, or a screen negative, corresponding to the screen positive, on top of a diffusion sheet as a spacer in place of the continuous tone negative, exposing the carbon tissue or photoresist by contacting printing the screen positive in register with the previous printing, and exposing the carbon tissue or photo-resist to the screen positive with a diffusion sheet between the screen positive and the carbon tissue or photo-resist Figs. 9 to 15 (not shown); and (iv) exposing the carbon tissue or photo-resist by contact printing with a white line gravure screen, then with the screen positive and with a continuous tone positive or approximately continuous tone positive corresponding to the screen positive already printed and in register with that printing Figs. 17 to 19 (not shown). The method gives a screen gravure printing plate having ink wells of differing sizes and depths. Moire patterns may be avoided by adjusting the angle between the lines of the white line gravure screen and the lines of dots in the screen positives. The screen positive having white gravure lines used in (ii) above is made by exposing photographic lith-type film to a continuous tone positive through a half-tone contact screen and then further exposing the film to a white line gravure screen. After development, the black line screen negative obtained is reversed by contact printing on to further film to obtain a white line screen positive Fig. 5 (not shown). Alternatively, a screen negative may be contact printed together with a black line screen to obtain a white line screen positive direct Fig. 6 (not shown). The approximately continuous tone positive used in (iv) above is made by contact printing a planographic screen positive on to film to form a screen negative and then further contact printing the screen negative through a diffusion sheet on to further film to produce the approximately continuous tone positive Fig. 16 (not shown). Alternatively, the screen negative, formed by contact printing the planographic screen positive, is projection printed out of focus using a plate making camera.