Disclosed are a photosensitive composition characterized by high sensitivity and good latitude in development, and a positive-type planographic printing plate precursor that uses the composition in a direct plate production process and enables an image to be formed with high sensitivity with an infrared laser. Namely, the photosensitive composition is disclosed comprising components (a) and (b) as follows and becoming soluble in an aqueous alkaline solution when irradiated with an infrared laser:
(a) an infrared-ray absorbing agent represented by formula (I) as follows; and
(b) a polymeric compound insoluble in water but soluble in an aqueous alkaline solution
                            本发明公开了一种感光组合物,其特点是感光度高、显影宽容度好;还公开了一种正片型平面印刷版原版,该原版在直接制版工艺中使用该组合物,并能用红外激光以高感光度形成图像。也就是说,所公开的感光组合物由以下成分(a)和(b)组成,在红外激光照射下可溶于碱性
水溶液:
(a) 由下式(I)表示的红外线吸收剂;和
(b) 不溶于
水但可溶于碱性
水溶液的聚合化合物