| abstract |
The present invention relates to a positive-type planographic printing plate precursor comprising: a hydrophilic substrate; an image recording layer including a novolak resin (A) and a light-to-heat conversion agent (B), disposed on the substrate, the image recording layer increasing in solubility in an aqueous alkali solution when exposed to light emitted from an infrared laser, wherein the weight average molecular weight (Mw) of the novolak resin (A) is in a range of 500 to 10000 based on polystyrene, the molecular weight being found by a gel permeation chromatographic (GPC) method using monodispersion polystyrene as a standard, and the degree of dispersion (Mw/Mn) is 1.7 or less when the weight average molecular weight (Mw) is 500 to 3000, the degree of dispersion (Mw/Mn) is 2.0 or less when the weight average molecular weight (Mw) is 3000 to 4500, and the degree of dispersion (Mw/Mn) of the novolak resin (A) fulfills the following equation: (Mw/Mn)≦{(4·Mw−1500)/5500}, when the weight average molecular weight (Mw) is 4500 to 10000. |