ORIGINAL FORM FOR LITHOGRAPHIC PLATE AND PROCESS FOR PREPARING LITHOGRAPHIC PLATE

摘要

Object: A method for preparing a lithographic printing plate directly from digital image signals with the use of a presensitized lithographic printing plate comprising a support having thereon a photosensitive layer and a light-shielding layer which can be removed imagewise with laser light is provided, wherein the light-shielding layer, which can be industrially produced readily at a moderate price can be removed sufficiently during a process of development without the need of removing a masking layer at an unexposed portion and adverse effect on a photosensitive layer. Constitution: A lithographic printing plate can be obtained by making use of a presensitized lithographic printing plate comprising a support having thereon a photosensitive layer containing o-quinonediazide compound, photo-degradable or photo-polymerizable resin and water-soluble resin and a light-shielding layer containing an infrared absorbing material and a material capable of absorbing the photosensitive wavelength of the photosensitive layer and by a process comprising ablating imagewise the light-shielding layer with laser light, overall-exposing with a ray active to the photosensitive layer to cause photochemical change of the photosensitive layer in which the light-shielding layer has been removed by ablation (e.g., making alkali-soluble) and dissolving out the photosensitive layer at a non-imaging area.