POSITIVE TYPE PHOTOSENSITIVE COMPOSITION, POSITIVE TYPE PHOTOSENSITIVE PLANOGRAPHIC PRINTING PLATE AND POSITIVE IMAGE FORMING METHOD

摘要

PROBLEM TO BE SOLVED: To obtain a positive type photosensitive composition and a positive type photosensitive planographic printing plate having high sensitivity to light in the near IR region and high visible distinction of an exposed part, excellent in contrast between unexposed and exposed parts, therefore excellent in plate making efficiency and having a wide development latitude and to provide a positive mage forming method. SOLUTION: The positive type photosensitive composition contains a photothermal conversion material that absorbs light of a light source for exposure and converts it into heat and an alkali-soluble resin. At least a near IR absorbing dye of the formula is contained as the photothermal conversion material. A layer of the photosensitive composition is formed on the surface of a substrate to obtain the objective positive type photosensitive planographic printing plate. This planographic printing plate is imagewise exposed with laser beams in the wavelength region of 700-1,300 m and developed. In the formula, each of the rings A and B is an N-containing heterocycle and the ring C is an N- containing heterocycle or a hydrocarbon ring.