Photopolymerizable composition

Abstract

A composition that is photopolymerizable upon absorption of light and/or heat, the composition including a binder, a polymerizable compound, a sensitizer, and a photoinitiator, characterized in that the composition includes, with respect to its non-volatile compounds, at least about 0.01 wt. % of a polythiol compound and has a very high sensitivity and hardness.

What is claimed is: 
     
         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 (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 alkylene 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 2 or an integer greater than 4; 
         for polythioles of formula (IIIa), R 8  means methyl or ethyl; and 
         the thiol groups of formulae (IIIa) and (IIIb) may also be present in their tautomeric thione form. 
       
     
     
         2 . The lithographic printing plate precursor according to  claim 1 , wherein
 L 3 , L 4  mutually independent mean alkylene, alkyleneoxy, or polyglycerol; or an alkylene chain containing acyloxy, ether, carbonate, thioether, hydroxy, phenyl, heterocylic, amino, thiol, sulphonyl, amido, urethane, or urea functions.   
     
     
         3 . The lithographic printing plate precursor according to  claim 1 , wherein
 R 8  means hydrogen, methyl, or ethyl;   s means 1;   L 3 , L 4  mean alkylene; and   r means 2.   
     
     
         4 . The lithographic printing plate precursor according to  claim 1 , further comprising an additional sulfur containing compound as a chain transfer agent. 
     
     
         5 . 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. 
     
     
         6 . 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.