Positive-working lithographic printing plate precursor

Abstract

A positive-working lithographic printing plate precursor is disclosed which comprises (i) a grained and anodized aluminum support having a hydrophilic surface and (ii) a heat-sensitive oleophilic coating provided on the hydrophilic surface, wherein said coating is capable of dissolving in an aqueous alkaline developer at a higher dissolution rate in areas of said coating which are exposed to heat or infrared light than in unexposed areas, characterized in that the hydrophilic surface has a surface roughness, expressed as arithmetical mean center-line roughness Ra, which is less than 0.40 μm. The use of a low surface roughness as defined above provides an improved shelf life of the coating.

1 . A positive-working lithographic printing plate precursor comprising (i) a grained and anodized aluminum support having a hydrophilic surface and (ii) a heat-sensitive oleophilic coating provided on the hydrophilic surface, wherein said coating is capable of dissolving in an aqueous alkaline developer at a higher dissolution rate in areas of said coating which are exposed to heat or infrared light than in unexposed areas, characterized in that the hydrophilic surface has a surface roughness, expressed as arithmetical mean center-line roughness Ra, which is less than 0.40 μm and comprises more than 3.0 g/m 2  of aluminum oxide.  
   
   
       2 . A plate precursor according to  claim 1  wherein the hydrophilic surface has a surface roughness, expressed as arithmetical mean center-line roughness Ra, which is less than 0.3 μm.  
   
   
       3 . A plate precursor according to  claim 1  wherein the aluminum support comprises more than 4.0 g/m 2  of aluminum oxide at the hydrophilic surface.  
   
   
       4 . A plate precursor according to  claim 1  wherein the coating comprises (a) a hydrophobic polymer which is soluble in the developer and (b) a dissolution inhibitor.  
   
   
       5 . A plate precursor according to  claim 4  wherein the dissolution inhibitor is a water-repellent polymer.  
   
   
       6 . A plate precursor according to  claim 5  wherein the water-repellent polymer is (a) a polymer comprising siloxane and/or perfluoroalkyl units or (b) a block- or graft-copolymer of a poly(alkylene oxide) block and a block comprising siloxane and/or perfluoroalkyl units.  
   
   
       7 . A plate precursor according to  claim 4  wherein the dissolution inhibitor is an organic compound comprising an aromatic group and a hydrogen bonding site.  
   
   
       8 . A plate precursor according to  claim 1  wherein the coating further comprises a dissolution accelerator.  
   
   
       9 . The plate precursor according to  claim 2  wherein the aluminum support comprises more than 4.0 g/m 2  of aluminum oxide at the hydrophilic surface.  
   
   
       10 . The plate precursor according to  claim 2  wherein the coating comprises (a) a hydrophobic polymer which is soluble in the developer and (b) a dissolution inhibitor.  
   
   
       11 . The plate precursor according to  claim 4  wherein the coating further comprises a dissolution accelerator.  
   
   
       12 . The plate precursor according to  claim 3  wherein the coating comprises (a) a hydrophobic polymer which is soluble in the developer and (b) a dissolution inhibitor.  
   
   
       13 . The plate precursor according to  claim 6  wherein the coating further comprises a dissolution accelerator.  
   
   
       14 . The plate precursor according to  claim 7  wherein the coating further comprises a dissolution accelerator.