Treatment soln. for bimetallic lithographic printing plates - contg. potassium permanganate nitric acid and phosphoric acid or sulphuric acid

摘要

Treatment soln. for polymetallic lithographic plates to give hydrophilic and ink-receptive areas, comprises an aq. soln. contg. 0.5-100 (0.5-3) g/l potassium permanganate; 5-100 (10-30) g/l H3PO4 and/or H2SO4, and 1-20 (2-5) g/l HNO3. The solns. are esp. useful for treatment of polymetallic lithographic plates with a sensitised polyvinyl alcohol (PVA) coating. After exposure, the plates are developed, fixed and etched in the usual way, then the remainder of the PVA layer is removed in a soln. contg. e.g. 5-100 (10-50) g/l Na paraperiodate. The plate is treated with the soln. to form the hydrophilic and ink receptive areas. The treatment solns. give rapid one-stage pretreatment of bimetallic copper-chrome printing plates and simultaneously remove the remainder of the resist layer whilst rendering the copper ink- receptive and the chromium hydrophilic.