Disclosed is a positive-type photosensitive composition that has high sensitivity, good latitude in development, and good storage stability and is for use in a direct plate production process using an infrared laser and a novel anionic infrared-ray absorbing agent suitable therefor. This composition comprises (a) an anionic, infrared-ray absorbing agent and (b) a polymeric compound that is insoluble in water but soluble in an aqueous alkaline solution so that the composition becomes soluble in the aqueous alkaline solution when irradiated with the infrared laser. Preferably, (a) the anionic, infrared-ray absorbing agent is (a-1) an anionic metal complex, (a-2) an anionic carbon black, (a-3) an anionic phthalocyanine, or (a-4) a compound represented by the general formula (I) given below. More preferably, from the standpoint of sensitivity, a counter cation of (a) the anionic, infrared-ray absorbing agent has a construction of a thermally decomposable onium salt. In the general formula (I) given below, M represents a conjugated chain, Ga- represents an anionic substituent group, Gb represents a neutral substituent group, and X m+ represents a cation including a portion, the cation having a valence of from 1 to m, wherein m represents an integer ranging from 1 to 6.
Ga- - M - Gb}m X m+ (I)
本发明公开了一种具有高灵敏度、良好的显影宽容度和良好的储存稳定性,可用于使用红外激光的直接制版工艺的正型感光组合物,以及适用于该工艺的新型阴离子红外线吸收剂。这种组合物包括:(a) 一种阴离子红外线吸收剂;(b) 一种不溶于
水但可溶于碱性
水溶液的高分子化合物,这样,当用红外线激光照射时,组合物就可溶于碱性
水溶液中。优选地,(a) 阴离子红外线吸收剂是 (a-1) 阴离子
金属络合物,(a-2) 阴离子
炭黑,(a-3) 阴离子
酞菁,或 (a-4) 下文通式 (I) 所代表的化合物。从灵敏度的角度来看,阴离子红外线吸收剂(a)的阳离子最好具有可热分解的鎓盐结构。在下面给出的通式(I)中,M 代表共轭链,Ga- 代表阴离子取代基,Gb 代表中性取代基,X m+ 代表包括一部分的阳离子,阳离子的价数为 1 至 m,其中 m 代表 1 至 6 的整数。
Ga- - M - Gb}m X m+ (I)