Photosensitive diazo lithographic printing plate with oxalic acid as stabilizer

Claim 1

A pre-sensitized lithographic plate comprising an aluminum support anodized in sulfuric acid and thereafter treated with a silicate salt having thereon a layer of a photosensitive diazo composition comprising (a) a diazo resin, which is a salt of a condensate of p-diazodiphenylamine with formaldehyde, (b) an organic high molecular weight binder wherein said organic high molecular weight binder is selected from the group consisting of an organic high molecular weight binder which has an acid value of from about 10 to about 100 and contains both the recurring unit represented by the following general formula (I): ##STR5## wherein R 1 represents a hydrogen atom or a methyl group; R 2 represents a hydrogen atom, a methyl group, an ethyl group or a chloromethyl group; and n is an integer from 1 to 10; and the recurring unit represented by the following general formula (II): ##STR6## wherein R 3 represents a hydrogen atom or a methyl group; and (c) from about 0.1 to about 5% by weight of oxalic acid, based on the total amount of said composition, which provides lowered staining in background areas and extended shelf life to said pre-sensitized lithographic plate.