method of producing a hydrophilic glue in pre sensitized flachdruckplatten zinc, aluminium or copper

摘要

A lithographic plate comprising a plate of Zn, Al or Cu having a surface consisting of the phosphomolybdate of the metal is formed by treating the plate with a aqueous solution containing phospho - molybdate ions. The aqueous solution has a pH of 4-6 and contains either molybdic acid (85%) and tribasic sodium phosphate; or sodium phosphomolybdate and caustic soda; or ammonium molybdate phosphoric acid and sulphuric acid. The preferred solution contains 12-16 mols of molybdic oxide to 1 mol of phosphate and preferably 9.1-37.7 gms. of 85% molybdic acid and 1.8-7.5 gms. of tribasic sodium phosphate in 1 litre of water, the solution temperature being 155-180 DEG F. The metal plate is cleaned and etched in an aqueous solution containing tribasic sodium phosphate, NaOH and a wetting agent such as an alkyl phenyl ether of polyethylene glycol, rinsed in water and desmutted in a solution of HNO3 and HF. After treating with the phosphomolybdate solution the plate is sealed by immersion in an aqueous 1% solution of one of the following at 200-212 DEG F.: an acetate of sodium, potassium, magnesium, barium or calcium, or a carbonate of ammonium, lithium, barium, calcium, magnesium or zinc, or dibasic sodium phosphate, or NH4OH or urea. Alternatively the plate may first be cleaned in an aqueous solution containing ethylene glycol monoethyl ether, Na2Co3 and Na3Po4 and then mechanically grained with pumice powder. The treated phosphomolybdate surface is finally treated with a superpolyamide nylon diazo sensitizer or a bichromated gum arabic solution or a bichromated casein, exposed to light and the required pattern is then produced by developing.