To provide a planographic printing original plate with a water- insoluble photosensitive layer containing a photosensitive composition containing a hydrophilic polymer, a specified cyanine compound as a light absorbent and a crosslinker formed on a substrate directly or by way of another layer.
Since the specified cyanine compound excellent in thermal decomposability is used as a light absorbent, when the printing plate is irradiated with light, the hydrophilic functional groups of the hydrophilic polymer in the photosensitive layer are partially decomposed to impart an affinity for ink to the layer. The printing plate can be handled in a light room, does not require operations such as development and wiping and is excellent in sensitivity, resolution and printing resistance. Since the light absorbent has a sulfonic acid group or its salt, it is excellent also in compatibility with the highly hydrophilic polymer.
MATSUMOTO TAKATSURU
SANADA TAKAYUKI
HIROSE SUMIO
