Method for developing positive acting light-sensitive planographic printing plate

摘要

A development method which comprises imagewise exposing a positive acting light-sensitive planographic printing plate comprising an aluminum support and a light-sensitive layer of an o-quinonediazide compound formed thereon, and then developing the exposed plate with a developer, comprising an aqueous solution of an alkali metal silicate, adding a supplementary solution comprising an aqueous solution of an alkali metal silicate to the developer to compensate for the degradation of the developer brought about by development and/or by carbon dioxide in the air; wherein the developer comprises an aqueous solution of an alkali metal salt having an [SiO2]/[M] ratio of from 0.5 to 0.75 and an SiO2 concentration of from 1 to 4% by weight based on the total weight of the developer, where [SiO2] represents the concentration of SiO2 per unit volume expressed as gram-molecules, and [M] represents the concentration of the alkali metal per unit volume expressed as gram-atoms, and the supplementary solution comprises an aqueous solution of an alkali metal silicate having an [SiO2]/[M] ratio of from 0.25 to 0.75.