Process for preparing positive or negative lithographic printing plates using a developer having at least one alkali-soluble mercapto compound and/or thioether compound

摘要

A developer composition comprises an aqueous alkaline solution which contains at least one alkali-soluble mercapto compound and/or thioether compound. The developer composition is excellent in developing properties and provides lithographic printing plates which do not cause background contamination of non-image areas during printing, when it is used in developing PS plates. It can be stored for a long time. The developer composition further makes it possible to develop both negative and positive working PS plates if its pH value is not less than 12.