Process for producing negative and positive original images on a bilevel printing plate utilizing non-silver halide layer and silver halide overlayer

摘要

A lithographic printing plate precursor and process for its utilization have been discovered through which negative and positive original images can be printably reproduced on the plate precursor in substantially fewer development steps. The precursor plate is exposed sequentially to either the negative or positive original with the resultant image subsequently developable in a single process or step. The process is achieved by using a precursor plate having two coatings of significantly different photographic sensitivity to light, i.e., speed as characterized by "camera speed" or "contact speed" and imagewise exposing the originals in sequence to alternative speeds. The contact speed coating may be negative-working or positive working while the camera speed coating is negative-working. The camera speed coating is developed followed by exposure of the contact speed coating. Images produced at camera speed are removed and non-image bearing portions of the contact speed coating are removed. The remaining image areas corresponding to the negative and positive originals are treated to provide positive printable images.