GB844077A - Improvements in or relating to a method of reproducing documents - Google Patents

Abstract

844,077. Photolithography. D'HAUTERIVE, G. M. G. June 7, 1957 [July 11, 1956], No. 18149/57. Class 98(2) Documents are copied onto a photosensitive surface which yields an imagewise change of acidity by light action, such surface is then pressed onto an inert support carrying a layer of aluminium compounds to cause a corresponding change of acidity therein and result, with or without application of a hygroscopic agent, in an imagewise variation of ink-accepting and inkrefusing portions, and the layer is inked up for lithographic printing. The zone for inkability of the aluminium compounds is centred on the neutrality value of pH7 but may extend between pH4 and pH11, thus change from pH4 to pH4À5 may allow inking and the reverse change cause this property to disappear. In Example 1 a tracing or a typewritten or printed text on a transparent support is exposed for 10 minutes onto an iron perchloride coated paper to release hydrochloric acid in the exposed areas, this is pressed for 4 or 5 minutes onto a glass plate coated with aluminium sulphocyanate and the latter is treated with a solution containing glycerin, lactic acid and sodium benzoate, and then with a specified fatty ink, to yield positive copies of the original. In Example 2 the initial material is a photographic negative and this is exposed to paper sensitised with ammoniacal ferrie oxalate and hydrochloric acid whereby exposed areas lose some of their acidity, and subsequent procedure is similar to that of Example 1 but of reversed effect whereby positive copies result from the negative original. Example 3 indicates that a water-steam treatment or a treatment employing the breath may be effected after the pressing of Examples 1, 2 and then inking may be effected directly. Photodissociation of diezonium chloride releasing hydrochloric acid may be used to operate the invention and numerous other variations are indicated.