Method for preparing lithographic printing plate.

摘要

A method for preparing a lithographic printing plate comprises imagewise exposing a PS plate comprising an aluminum substrate having an anodized layer and a light-sensitive layer applied on one side of the substrate and then developing the PS plate with a developer comprising an aqueous solution of an alkali metal silicate, while compensating changes in the developer due to the development of the PS plate by supplementing, to the developer, a replenisher comprising an aqueous solution of an alkali metal silicate, wherein the PS plate is provided with a coating layer containing an organic polymeric compound on the back face and the replenisher is an aqueous solution of an alkali metal silicate having a ratio: [SiO2] / [M2O] (wherein [SiO2] means molar concentration (mol/l) of SiO2 and [M2O] is molar concentration (mol/l) of oxide M2O of an alkali metal (M)) ranging from 0.3 to 1.0 and an SiO2 content ranging from 0.5 to 4.0% by weight. The method makes it possible to substantially reduce the amount of the developer to be replenished, does not cause any formation of insolubles even if a great deal of PS plates are processed over a long time period and thus stable developing treatment can be carried out.