Process for the production of offset printing plates

Claim 1

A PROCESS FOR REVERSING THE PRINTING AND NON-PRINTING AREAS OF AN OFF-SET PRINTING PLATE COMPRISING A HYDROPHILIC LAYER CONSISTING ESSENTIALLY OF AT LEAST ONE METAL OF THE GROUP CONSISTING OF ALUMINUM AND ZINC AND A LAYER OF SILVER METAL SUPERIMPOSED ON SELECTED AREAS OF SAID HYDROPHILIC LAYER CORRESPONDING TO AN IMAGE, WHICH PROCESS COMPRISES THE STEPS OF: (1) TREATING SAID PLATE WITH AN ORGANIC COMPOUND ADAPTED TO IONIZE IN SOLUTION TO FORM A GROUP REACTIVE WITH IONS OF THE METAL OF SAID HYDROPHILIC LAYER TO PRODUCE IN SITU AT THE SURFACE OF SAID HYDROPHILIC LAYER A WATER-INSOLUBLE COMPOUND REPELLING WATER FROM SAID LAYER SURFACE, SAID REACTIVE GROUP CONTAINING OLEOPHILIC AND ACID HYDROPHILIC MOIETIES AND REACTING THROUGH THE LATTER, SAID ORGANIC COMPOUND BEING APPLIED TO SAID PLATE IN SOLUTION IN A SOLVEN PERMITTING IONIZATION THEREOF, AND (2) THEREAFTER, REMOVING THE SILVER IMAGE LAYER BY TREATING SAID PLATE WITH AN OXIDIZING AGENT FOR SILVER AND DISSOLVING THE RESULTANT OXIDATION PRODUCTS IN A SOLVENT THEREFOR.