POSITIVE PHOTOSENSITIVE COMPOSITION AND POSITIVE LITHOGRAPHIC PRINTING PLATE

摘要

PROBLEM TO BE SOLVED: To provide a positive photosensitive composition high in sensitivity to light in a near infrared region and excellent in contrast between an image part and a nonimage part and to widen the width of development conditions by incorporating a near infrared ray absorbing dye having a structure formed by combining hetero rings through specified polymethine chains. SOLUTION: This positive photosensitive composition contains a photothermoconverting material for absorbing light from an image exposure light source and converting it into heat and an alkali-soluble resin and as this converting material, contains a near infrared ray absorbing dye having a structure formed by combining hetero rings through polymethine chains having at least barbituric acid or thiobarbituric acid groups as a substituted group. The photothermoconverting material for absorbing the light from the image exposure light source and converting it into heat means a compound capable of converting the absorbed light into heat and the dye having an absorption band in a part or all of the near infrared wavelength region of 700-1300 nm is especially effective.