Photosensitive lithographic printing plate and method for making a printing plate

Abstract

A photosensitive lithographic printing plate includes a photosensitive layer and a protective layer formed in this order on a support, wherein the photosensitive layer has a maximum peak of spectral sensitivity within a wavelength range ranging from 390 to 430 nm, the minimum exposure for the photosensitive lithographic printing plate for image formation at a wavelength of 410 nm (S410) is at most 100 μJ/cm 2 , and the relation between the minimum exposure for image formation at a wavelength of 450 nm (S450) and the minimum exposure for image formation at a wavelength of 410 nm (S410) is 0<S410/S450≦0.1.

1 . A photosensitive lithographic printing plate precursor comprising: 
 a support; and    a photosensitive layer; wherein    said photosensitive layer contains (A) an ethylenic monomer, (B) a sensitizing agent, and (C) a radical generator; and    said sensitizing agent is a dialkylaminobenzene compound including an aromatic heterocyclic group as a substituent on the carbon atom at the p-position relative to the amino group on the benzene ring.    
   
   
       2 . The photosensitive lithographic printing plate precursor of  claim 1 , wherein said radical generator (C) comprises a hexaarylbiimidazole compound or a titanocene compound.  
   
   
       3 . The photosensitive lithographic printing plate precursor of  claim 2 , wherein said hexaarylbiimidazole compound is present in an amount ranging from 15 to 40 parts by weight based on 100 parts by weight of said ethylenic monomer.  
   
   
       4 . The photosensitive lithographic printing plate precursor of  claim 2 , wherein said titanocene compound is present in an amount ranging from 5 to 20 parts by weight based on 100 parts by weight of said ethylenic monomer.  
   
   
       5 . The photosensitive lithographic printing plate precursor of  claim 1 , wherein said photosensitive layer comprises a coloring pigment in an amount from 0 to 20 wt. % based on the weight of said photosensitive layer.  
   
   
       6 . The photosensitive lithographic printing plate precursor of  claim 1 , wherein said photosensitive layer further comprises a polymer binder.  
   
   
       7 . The photosensitive lithographic printing plate according to  claim 6 , wherein the polymer binder contains a structural unit represented by the following formula (V):  
     
       
         
         
             
             
         
       
     
     wherein Re is a hydrogen atom or a methyl group.  
   
   
       8 . The photosensitive lithographic printing plate precursor of  claim 1 , wherein said photosensitive layer further comprises a hydrogen-donor compound.  
   
   
       9 . The photosensitive lithographic printing plate precursor of  claim 8 , wherein said hydrogen-donor compound comprises a mercapto group.  
   
   
       10 . The photosensitive lithographic printing plate precursor of  claim 1 , wherein said photosensitive layer further comprises an amine compound having a pKb of at most 7 at 25° C.  
   
   
       11 . The photosensitive lithographic printing plate precursor of  claim 1 , wherein said photosensitive layer further comprises an amine compound having a group of the formula [N—CH2].  
   
   
       12 . The photosensitive lithographic printing plate precursor of  claim 1 , wherein said photosensitive layer comprises, as the ethylenic monomer, a urethane compound (a3) having at least four urethane linkages and at least four addition-polymerizable double bonds in one molecule.  
   
   
       13 . The photosensitive lithographic printing plate precursor of  claim 12 , wherein said urethane compound (a3) has a molecular weight ranging from 600 to 200,000.  
   
   
       14 . The photosensitive lithographic printing plate precursor of  claim 12 , wherein said urethane compound (a3) is represented by formula (II):  
     
       
         
         
             
             
         
       
     
     wherein x is an integer ranging from 4 to 20, y is an integer ranging from 0 to 15, z is an integer ranging from 1 to 15, Ra is a group having a repeating unit derived from alkyleneoxy or aryleneoxy, and having from 4 to 20 oxy groups capable of combining with Rb, each of Rb and Rc, which are independent of each other, is a C 1-10  alkylene group, and Rd is an organic residue having from 1 to 10 (meth)acrylic group, provided that each of Ra, Rb, Rc and Rd which are independent of one another, may have a substituent.  
   
   
       15 . The photosensitive lithographic printing plate precursor of  claim 12 , wherein said urethane compound (a3) as the ethylenic monomer (A), is prepared by reacting a compound having at least four active isocyanate groups in one molecule (a1) with a compound having at least one hydroxyl group and at least two addition-polymerizable double bonds in one molecule (a2).  
   
   
       16 . The photosensitive lithographic printing plate precursor of  claim 15 , wherein the compound (a1) having at least four active isocyanate groups in one molecule has a molecular weight of at least 500.  
   
   
       17 . The photosensitive lithographic printing plate precursor of  claim 1 , wherein said photosensitive layer comprises, as the ethylenic monomer (A), a phosphate compound having an acryloyloxy group or a methacryloyloxy group.  
   
   
       18 . The photosensitive lithographic printing plate precursor of  claim 1 , wherein said photosensitive layer further comprises a surface active agent.  
   
   
       19 . The photosensitive lithographic printing plate precursor of  claim 1 , further comprising a protective layer including polyvinyl alcohol.  
   
   
       20 . The photosensitive lithographic printing plate precursor of  claim 1 , further comprising a protective layer including polyvinyl pyrrolidone.  
   
   
       21 . The photosensitive lithographic printing plate precursor of  claim 1 , wherein said support includes aluminum or an aluminum alloy having a roughened surface, and said support has a reflection density of at least 0.3.  
   
   
       22 . The photosensitive lithographic printing plate precursor of  claim 1 , wherein said support includes aluminum or an aluminum alloy having a roughened surface and an anodized layer.  
   
   
       23 . A method for making a printing plate, which comprises: 
 image-wise exposing the photosensitive lithographic printing plate precursor as defined in  claim 1  with laser light having a wavelength ranging from about 390 nm to about 430 nm; and    developing the exposed plate with an aqueous developer.    
   
   
       24 . The method for making a printing plate according to  claim 23 , wherein an exposure energy of the printing plate precursor in the image-wise exposing step at a wavelength of 410 nm is at most 100 μJ/cm 2 .  
   
   
       25 . The method for making a printing plate according to  claim 23 , wherein an exposure energy of the printing plate precursor in the image-wise exposing step at a wavelength of 410 nm is at most 50 μJ/cm 2 .  
   
   
       25 . The method for making a printing plate according to  claim 23 , wherein a relation between a minimum exposure energy for image formation of the printing plate precursor at a wavelength of 450 nm (S450) and a minimum exposure energy for image formation of the precursor at a wavelength of 410 nm (S410) is 0<S410/S450≦0.1.