| 摘要 |
<p>Prodn. of a photogravure half-tone printing plate involves (a) printing a contact screen (A) of very small dark dots on a light-sensitive carbon tissue; (b) printing a half-tone positive (B) on it in the contact process; (c) laminating a light-diffusion sheet (C) and then a half-tone positive (D) on the tissue and printing the combination onto the tissue in the contact printing process, using any sequence in these stages; (d) placing the tissue on a printing plate to develop the tissue; and (e) etching the printing plate. Dots are square with rounded corners and vignetted margins and thicknesses which vary from a max. of 3.0 in the middle to a min. of 0.1 at the margin. Esp. good tone reprodn. is possible. A photomask (E), in the form of a vignetted negative, is applied to the tissue before or between (C) and (D) and all 3 are printed onto the tissue, so that areas of (E) corresp. to the region of (D) with a half-tone dot area of 5-8% have a continuously varying tone shading below a density of 0.6.</p> |
