Abstract: A method for preparinq a lithographic printing plate comprising the steps of imagewise exposing, to light, a negative-working presensitized plate for use in making a lithographic printing plate which comprises a substrate provided thereon with a light-sensitive layer comprising an aromatic diazonium compound having at least one member selected from the group consisting of carboxyl groups, phenolic hydroxyl groups, sulfonic acid residues, sulfinic acid residues and phosphorus atom-containing oxyacid residues and developing the imagewise exposed presensitized plate with a developer which comprises an aqueous solution of an alkali metal or ammonium silicate having a ratio: [SiO.sub.2 ]/[M], wherein [SiO.sub.2 ] and [M] represent the molar concentrations of SiO.sub.2 and the alkali metal or ammonia in the developer respectively, ranging from 0.15 to 0.75 and an SiO.sub.2 content ranging from 1.0 to 4.

Abstract: Disclosed is a novel diazo resin which has at least one repeating unit represented by the following general formula (I): ##STR1## wherein R.sup.2 represents a hydrogen atom, an alkyl group or an alkoxy group, a hydroxyl group, a carboxy ester group or a carboxyl group: R.sup.1 represents a carboxyl group or a group having at least one carboxyl group; R.sup.3 and R.sup.4 each represents a hydrogen atom or an alkyl group or an alkoxy group; X.sup.31 represents an anion; and Y represents --NH--, --O-- or --S--. The diazo resin is useful for a presensitized plate for use in making a lithographic printing plate when it is incorporated into a light-sensitive layer or an underlayer on a substrate. According to the present invention, a presensitized plate using the diazo resin has excellent properties such as high sensitivity, good adhesion between the substrate and the light-sensitive layer and can thus provide a lithographic printing plate having a high printing durability and free of background contamination.

Abstract: A light-sensitive composition is herein disclosed, which comprises at least one free radical generator represented by the following general formula: ##STR1## and at least one discoloring agent which interacts with products generated through the photolytic degradation of the free radical generator to change the color tone of the composition. The composition has a high stability with time and a good printing out property and therefore it can be used in making light-sensitive layer of PS plates, photoresists, proof plates for printing and films for overhead projector, intermediate print and photomask having high sensitivity long shelf life.

Abstract: A photosensitive recording material comprising (a) a substrate having a hydrophilic surface, (b) an undercoating layer comprising at least one compound having at least one functional group selected from the group consisting of thiol, thioether and disulfide groups, and (c) a photosensitive layer comprising at least one diazonium compound and a high molecular weight binder compound which is insoluble in water and soluble in aqueous alkaline solution. The resulting developed plate yields no background contamination in printing process.

Abstract: A light-sensitive composition for use with lithographic printing plates is described which comprises (1) a light-sensitive, organic solvent soluble and substantially water-insoluble diazo resin which is the reaction product of a water-soluble, light-sensitive condensate of an aromatic diazonium compound and an organic condensing agent with a halogenated Lewis acid or a salt thereof, (2) a substantially water-insoluble, film forming organic high-molecular weight compound having an acid value of from 10 to 200, (3) a polynuclear aromatic sulfonic acid or a salt thereof, and (4) a salt-forming organic dye compound.

Abstract: A presensitized lithographic printing plate precursor is described, comprising an aluminum support that has been rendered hydrophilic having provided thereon a light-sensitive layer composed of a light-sensitive composition comprising (1) an organic solvent-soluble and substantially water-insoluble diazo resin, (2) a substantially water-insoluble, film-forming polymeric compound, and at least one of (3a) an organic solvent-soluble polymeric compound having a sulfonic acid group or a sulfonic acid salt group in its side chain and (3b) a substituted or unsubstituted dipicolinic acid or a salt thereof, the total amount of (3a) and (3b) components being about 1 to about 100% by weight, based on the weight of the diazo resin.

Abstract: A light-sensitive lithographic printing plate comprising a support having on at least one surface thereof a light-sensitive layer, said light-sensitive layer exhibiting a higher oleophilicity (high affinity to grease) at the outermost surface thereof than in the balance of the light-sensitive layer. This light-sensitive lithographic printing plate is capable of beginning the printing operation with a relatively small number of spoilages and exhibits not only excellent press life but also high developability and excellent storage stability.