Patent ID: 8632937

Claim:
Lithographic printing plate precursor comprising (a) a lithographic substrate with a hydrophilic surface and (b) a radiation-sensitive coating on the hydrophilic surface comprising (i) one or more types of monomers and/or oligomers and/or polymers, each comprising at least one ethylenically unsaturated group accessible to a free-radical polymerization, (ii) at least one sensitizer, and (iii) at least one coinitiator capable of forming free radicals together with the sensitizer (ii), said coinitiator being other than metallocenes, characterized in that the at least one sensitizer comprises a compound of formula (Ia) or (Ib): wherein R 4 is selected from the group consisting of hydrogen, CN, halogen, unsubstituted and substituted alkyl, aralkyl, alkylaryl and aryl, —O-alkyl, —O-aryl, —S-alkyl, —COOR, —SOR, —SO 2 R, —SO 3 R, —NO 2 , N(R) 2 , N(R) 3 + , and —PO 3 (R) 2 , wherein each R is selected from H, alkyl, aryl, aralkyl and alkylaryl; R 5 and R 6 are independently selected from the group consisting of hydrogen, CN, halogen, unsubstituted and substituted alkyl, aralkyl, alkylaryl and aryl, —O-alkyl, —O-aryl, —S-alkyl, —COOR, —SOR, —SO 2 R, —SO 3 R, —NO 2 , N(R) 2 , N(R) 3 + , and —PO 3 (R) 2 , wherein each R is selected from the group consisting of H, alkyl, aryl, aralkyl; R 4 and R 6 can form a 5- or 6-membered fused aromatic ring; R 7 and R 8 are independently selected from the group consisting of hydrogen, CN, halogen, and unsubstituted and substituted alkyl, alkylaryl, aralkyl, and aryl; n is selected from 0, 1 and 2; Z represents O, S, Se or NR, wherein R is selected from the group consisting of hydrogen, alkyl, aryl, aralkyl and alkylaryl; R 9 to R 12 are independently selected from the group consisting of hydrogen, halogen, CN, unsubstituted and substituted alkyl, aralkyl, alkylaryl and aryl, —O-alkyl, —O-aryl, —S-alkyl, —COOR, —SOR, —SO 2 R, —SO 3 R, —NO 2 , N(R) 2 , N(R) 3 + , and —PO 3 (R) 2 , wherein each R is selected from the group consisting of H, alkyl, aryl, aralkyl and alkylaryl, provided that at least one of the groups R 9 to R 12 is a bulky group which has a van der Waals volume of at least 55 Å 3 ; each dotted line in Formula 1a represents an optionally present fused benzene ring; each R′ is independently selected from halogen, alkyl, alkoxy, CN, NO 2 , NR″ 2 , C(O)H, COOR″, OR″ and SR″; each R″ is independently selected from hydrogen, alkyl and aryl; and m is 0 or an integer from 1 to 4; and wherein: R 3 is selected from the group consisting of hydrogen, CN, halogen, unsubstituted and substituted alkyl, aralkyl, alkylaryl and aryl, —O-alkyl, —O-aryl, —S-alkyl, —COOR, —SOR, —SO 2 R, —SO 3 R, —NO 2 , N(R) 2 , N(R) 3 + and —PO 3 (R) 2 , wherein each R is selected from H, alkyl, aryl, aralkyl and alkylaryl; R 1 is selected from the group consisting of hydrogen, unsubstituted and substituted aryl, unsubstituted and substituted heteroaryl, and unsubstituted and substituted alkyl; and R 3 and R 5 can form a 5- or 6-membered fused aromatic ring.