PHOTOPOLYMERIZATION INITIATOR, PHOTOPOLYMERIZABLE COMPOSITION, METHOD FOR GENERATING RADICAL, PHOTOSENSITIVE MATERIAL FOR LITHOGRAPHIC PRINTING PLATE AND METHOD FOR MAKING LITHOGRAPHIC PRINTING PLATE

摘要

PROBLEM TO BE SOLVED: To obtain a photopolymerization initiator which can give a photopolymerizable composition which can form images capable of being written with light having a specified wavelength and having good resolution and sensitivity by combining a specified pyrazoloazole-methine or dimethine dye with a radical generator. SOLUTION: This initiator is obtained by combining a pyrazoloazole-methine or dimethine sensitizing dye (A) represented by formula I or II (wherein Z1 , Z2 and Z3 are each -N= or -C(R2 )=; R1 and R2 are each H or a monovalent substituent; L1 and L2 are each a methine group; and B1 and B2 are each a five- or six-membered aromatic or heterocyclic residue) with a radical generator (B) (selected among organic peroxides, onium salts, halotriazines, iron arene complexes, bisimidazole and titanocene compounds). Dye A absorbs visible light at 488nm or 532nm and exhibits the capability of generating radicals by itself, and when it is combined with a conventional radical generator, the combination exhibits high sensitivity and an excellent shelf life and is useful for a photosensitive material used to make lithographic printing plates.