Photopolymerizable composition

1. A photopolymer printing plate precursor comprising:

a photopolymerizable composition on a support, the photopolymerizable composition comprising:

a binder, a polymerizable compound, a sensitizer, a photoinitiator, and a polythiol compound, wherein the composition includes, with respect to its total solid weight, from about 0.01 wt. % to about 5 wt. % of the polythiol compound and the polythiol compound is selected from one of the following formulae (IIIa) or (IIIb):

wherein

R 8 mutually independent means H or a non-metal atom substituent;

A 1 , A 2 mutually independent mean a linear alkyl chain with at most 16 carbon atoms;

L 3 , L 4 mutually independent mean linking groups or single bonds;

s means an integer from 1 to 100;

r means 1, 2, 3 or 4;

the product of s times r is at least 2;

the thiol groups of formulae (IIIa) or (IIIb) may also be present in their tautomeric thione form;

the composition, when coated on a support, has a sensitivity of about 150 μJ/cm 2 or higher; and

for polythioles of formula (IIIa), R 8 means hydrogen, methyl, or ethyl; and r means 1, 2, or 3.

2. The photopolymer printing plate precursor according to claim 1 , wherein L 3 , L 4 mutually independent mean alkylene, alkyleneoxy or polyglycerol; or alkylene chain containing acyloxy, ether, carbonate, thioether, hydroxy, phenyl, heterocylic, amino, thiol, sulphonyl, amido, urethane, or urea functions.

3. The photopolymer printing plate precursor according to claim 1 , wherein R8 means hydrogen, methyl, or ethyl; s means 1; L 3 , L 4 mean alkylene; and r means 2.

4. The photopolymer printing plate precursor according to claim 1 , wherein the photoinitiator is a hexaaryl-bisimidazole compound.

5. The photopolymer printing plate precursor according to claim 3 , wherein the photoinitiator is a hexaaryl-bisimidazole compound.

6. The photopolymer printing plate precursor according to claim 1 , further comprising a further sulfur containing compound as a chain transfer agent.

7. The photopolymer printing plate precursor according to claim 3 , further comprising a further sulfur containing compound as a chain transfer agent.

8. The photopolymer printing plate precursor according to claim 5 , further comprising a further sulfur containing compound as a chain transfer agent.

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

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

providing the 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 600 nm;

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

processing the printing plate precursor in an aqueous alkaline developer.

11. The method according to claim 10 , wherein the printing plate precursor is exposed with a laser having an emission wavelength in a range from about 380 nm to about 600 nm.

12. The method according to claim 10 , wherein the exposure of the lithographic printing plate precursor is carried out at an energy density, measured on a surface of the plate, of about 100 μJ/cm 2 or less.