Method for producing a printing plate

Claim 1

IN A METHOD FOR FORMING A PRINTING PLATE WHICH INCLUDES COATING A METAL BASE PLATE WITH POLYVINYL ALCOHOL SENSITIZED TO LIGHT BY A DICHROMATE, EXPOSING THE COATING TO LIGHT IN A DESIRED DESIGN, WASHING FROM THE METAL BASE PLATE PORTIONS OF THE COATING NOT AFFECTED BY THE LIGHT, SUBJECTING THE LIGHT-AFFECTED DESIGN OF THE COATING TO AN AQUEOUS CHROMIC ACID SOLUTION, WASHING THE PLATE TO REMOVE THE ACID SOLUTION, DRYING AND HEAT HARDENING THE COATING ON THE METAL BASE PLATE, AND ETCHING THE EXPOSED PORTIONS OF THE PLATE, THE IMPROVEMENT COMPRISING USING AN AQUEOUS DISPERSION CONTAINING FROM ABOUT 0.1 PERCENT TO ABOUT 6 PERCENT OF A DEVELOPING AGENT FOR THE LIGHTAFFECTED POLYVINYL ALCOHOL COATING FOR WASHING FROM THE METAL BASE PLATE PORTIONS OF THE COATING NOT AFFECTED BY THE LIGHT, SAID DEVELOPING AGENT BEING A DYE HAVING A POLYHYDROXY AROMATIC RING IN ITS MOLECULAR STRUCTURE, AND BEING SELECTED FROM THE GROUP CONSISTING OF HEMATINE, HEMATOXYLIN, A MIXTURE OF HEMATINE AND HEMATOXYLIN, CATECHIN. FUSTIN, QUERCITRIN AND HYPERNIC.