Lithographic printing plate precursor and lithographic printing process

Abstract

A lithographic printing plate precursor, which comprises: a support; an image-recording layer; and a protective layer, in this order, wherein at least one of the image-recording layer and the protective layer comprises a phosphonium salt having a specific structure, and a lithographic printing process, which comprises: exposing a lithographic printing plate precursor; supplying an oil-based ink and a fountain solution comprising a phosphonium salt having a specific structure to the exposed lithographic printing plate precursor on a printing machine to remove an unexposed area of an image-recording layer; and conducting printing.

What is claimed is: 
     
         1 . A phosphonium salt represented by formula (2): 
       
         
           
           
               
               
           
         
         wherein Ar 1  to Ar 6  each independently represents a phenyl group; 
         L represents —(CH 2 ) 9 —; 
         R represents an alkyl group, an aryl group, a heterocyclic group, an alkoxy group, an alkylamino group or an arylamino group; 
         n represents an integer of from 1 to 3; and 
         m is a number satisfying n×m=2. 
       
     
     
         2 . The phosphonium salt according to  claim 1 ,
 wherein a sulfonate anion in the formula (2) is represented by one selected from the following structural formulae:   
       
         
           
           
               
               
           
         
       
     
     
         3 . The phosphonium salt according to  claim 1 ,
 wherein a sulfonate anion in the formula (2) is represented by one selected from the following structural formulae: