Planographic printing original plate and method of plate-making a planographic printing plate

摘要

A positive type planographic printing original plate which enables direct plate-making using a solid or semiconductor laser emitting infrared rays by recording an image from digital data of computers, is highly sensitive to an infrared laser and has stability to developing treatment, and a method of plate-making a positive type planographic printing plate which is resistant to occurrence of flaw inferiors. The planographic printing original plate includes a first layer which contains a polymer that is insoluble in water and soluble in alkaline water, and a second layer which contains an infrared radiation absorber and a binder, which is not penetrative into an alkali developing solution containing an organic compound having a buffering effect and a base as principal components, and which is increased in solubility in an alkali developing solution by action of one of light and heat. The layers are sequentially provided on a support.