Ink for ink jet-recording curable through irradiation with a radioactive ray and method for preparing lithographic printing plates using the same

An ink jet-recording ink capable of being cured through the irradiation with a radioactive ray, comprising a coloring material, a polymerizable compound and a polymerization initiator system, wherein said polymerization initiator system comprises a polymerization initiator and at least one co-sensitizing agent selected from the group consisting of compounds represented by the following general formulas (i) to (iv) and (vii) to (ix):

• General Formula (i):
• (R1)(R2)C═N—O—R3 (i)
• wherein R1, R2 and R3 may be the same or different and each represents a monovalent organic group;
• General Formula (ii):
• wherein A1 to A4 each independently represents an aromatic group or a heterocyclic group and M+ represents a monovalent cationic atom or atomic group;
• General Formula (iii):
• wherein A represents a monovalent non-metallic atomic group, —X— represents a divalent connecting group selected from the group consisting of —O—, —S—, —SO2—, —NH—, —N(R3)—, —CO—, —CH2—, —CH(R4)— and —C(R4)(R5)—, wherein R3, R4 and R5 each independently represents a hydrogen atom or a monovalent substituent and R1 and R2 each independently represents a hydrogen atom or a monovalent substituent;
• General Formula (iv):
• wherein Ar represents an aromatic group or a heterocyclic group, —X— represents —O—, —S—, —SO2—, or —N(R3)—, R1, R2 and R3 each independently represents a hydrogen atom or a monovalent substituent comprising non-metallic atoms, and —Y represents —OR4 or —NR5R6, wherein R4 represents a monovalent substituent comprising non-metallic atoms, other than a hydroxyl group, and R5 and R6 each independently represents a hydrogen atom or a monovalent substituent comprising non-metallic atoms;
• General Formula (vii):
• wherein X, Y and Z each independently represents a monovalent substituent;
• General Formula (viii):
• wherein X and Y each independently represents a monovalent substituent, and n represents an integer ranging from 0 to 4, provided that, when n is not less than 2, a plurality of Ys present in the formula may be the same or different or may form a ring structure;
• General Formula (ix):
• wherein X and Y each independently represents a monovalent substituent, and n represents an integer ranging from 1 to 5, provided that, when n is not less than 2, a plurality of Ys present in the formula may be the same or different or may form a ring structure.