GB458421A - A process and a light-sensitive layer for producing pictures with the aid of screens - Google Patents

Abstract

458,421. Photo-mechanical printing- surfaces. REDDIE, L. N., 6, Bream's Buildings, Fetter Lane, London.-(Naamlooze Vennootschap Nederlandsche Laboratorium de Spaarnestad; 51, Nassaulaan, Haarlem, Holland) June 18, 1935, No. 17572. [Class 98 (ii)] In producing screened images, a halftone original is copied through a screen onto a light-sensitive layer which is highly light diffusing so that the sizes of the images of the elements of the screen pattern formed in the layer are determined by the brightness of corresponding parts of the original owing to the diffusion. The sensitive layer may be of bichromated gelatin in which pigment is incorporated or of silver halide with or without pigment. Suitable pigments are titanium dioxide or barium sulphate. The screens used are adapted to the nature of the printing forme to be produced, e.g. for intaglio formes a screen of transparent lines and opaque squares is used. The screens may be used in contact with the sensitive layer or the original or both. Alternatively the screen may be spaced from the sensitive layer by interposing a transparent film. A screen having slightly translucent elements in place of the opaque elements may also be used. Such a screen is prepared by copying a negative intaglio screen on a gelatined plate sensitized with ammonium ferri citrate and potassium ferricyanide. The diffusion effect may also be enhanced by copying with diffused or oblique light or by the use of a screen having refracting elements.