Photopolymerizable composition

1. A lithographic printing plate precursor comprising:

a photopolymerizable composition, the composition including a binder, a polymerizable compound, a sensitizer, a photoinitiator, and a polythiol compound; wherein

the composition includes, with respect to its total solid weight, at least about 0.01 wt. % of the polythiol compound and the polythiol compound is selected from one of the following formulae (I) or (II):

wherein

X 1 means O, S, Se, or NR 5 ;

L 1 means a linking group or a single bond;

R 1 to R 5 mutually independent mean H, a non-metal atom substituent, or L 1 ;

m is an integer from 1 to 100; and

for the case that m is 1, L 1 includes at least one additional thiol group;

wherein

X 2 represents O, S, Se, or NR 6 ;

Y 1 , Y 2 mutually independent mean N or CR 7 ;

L 2 means a linking group or a single bond;

R 6 , R 7 mutually independent mean H, a non-metal atom substituent, or L 2 ;

n is an integer from 2 to 100;

the thiol groups of formulae (I) or (II) may also be present in their tautomeric thione form; and

L 1 , L 2 mutually independent mean alkylene, alkyleneoxy, alkylenethio, oxygen, sulfur, amino, alkylamino, amido, alkylamido, sulphonyl, acyloxy, or alkylsiloxane; or an alkylene chain containing acyloxy, ether, carbonate, thioether, hydroxy, phenyl, heterocylic, amino, thiol sulphonyl, amido, glycerol monoether, urethane, or urea functions.

2. The lithographic printing plate precursor according to claim 1 , wherein

n and m mean 2.

3. The lithographic printing plate precursor according to claim 2 , comprising at least one polythiol compound of formula (I).

4. The lithographic printing plate precursor according to claim 2 , comprising at least one polythiol compound of formula (II).

5. The lithographic printing plate precursor according to claim 3 , wherein

L 1 means -X 3 -A 3 -X 4 - or divalent phenylene;

R 1 and R 4 mean H;

X 1 means O, S, NH, or N—R 5 ;

R 2 , R 3 , and R 5 mutually independent mean L 1 , H, or methyl;

A 3 means a linear, branched, or cyclic alkylene chain or divalent phenylene;

X 3 , X 4 mutually independent mean CH 2 , O, S, NH, or N-methyl; and

m means 2.

6. The lithographic printing plate precursor according to claim 4 , wherein

X 2 means S, O, NH, or N—R 6 ;

Y 1 , Y 2 mutually independent mean CR 7 or N;

L 2 means -X 5 -A 4 -X 6 - or divalent phenylene;

R 6 , R 7 mutually independent mean L 2 , H, or methyl;

A 4 means a linear, branched, or cyclic alkylene chain or divalent phenylene;

X 5 , X 6 mutually independent mean CH 2 , O, S, NH, or N-methyl; and

n means 2.

7. The lithographic printing plate precursor according to claim 1 , further comprising an additional sulfur containing compound as a chain transfer agent.

8. The lithographic printing plate precursor according to claim 2 , further comprising an additional sulfur containing compound as a chain transfer agent.

9. The lithographic printing plate precursor according to claim 3 , further comprising an additional sulfur containing compound as a chain transfer agent.

10. The lithographic printing plate precursor according to claim 4 , further comprising an additional sulfur containing compound as a chain transfer agent.

11. The lithographic printing plate precursor according to claim 1 , wherein a minimum exposure for image formation, measured on a surface of the plate, is about 100 μJ/cm 2 or less.

12. A method of making a lithographic printing plate comprising the steps of:

providing a photopolymer printing plate precursor as defined in claim 1 ;

exposing the printing plate precursor with a laser having an emission wavelength in the range from about 300 nm to about 600 nm;

heating the plate to a temperature, when measured at a rear surface of the plate, of about 90° C. to about 150° C., for a time between 10 seconds and 1 minute; and

processing the printing plate precursor in an aqueous alkaline developer.