Support For Lithographic Printing Plate and Presensitized Plate

Abstract

Disclosed is a support for a lithographic printing plate which, when measured over a 400 μm×400 μm surface region thereon using a three-dimensional non-contact roughness tester, has at most 5.0 convex portions of a height from centerline of at least 0.70 μm and an equivalent circle diameter of at least 20 μm, and has at least 800 concave portions of a depth from centerline of at least 0.50 μm and an equivalent circle diameter of at least 2.0 μm. Presensitized plates which are obtainable by using the support for a lithographic printing plate according to the present invention have an excellent scumming resistance and an extremely long press life.

1 . A support for a lithographic printing plate which, when measured over a 400 μm×400 μm surface region thereon using a three-dimensional non-contact roughness tester, has at most 5.0 convex portions of a height from centerline of at least 0.70 μm and an equivalent circle diameter of at least 20 μm, and has at least 800 concave portions of a depth from centerline of at least 0.50 μm and an equivalent circle diameter of at least 2.0 μm. 
   
   
       2 . The support for a lithographic printing plate according to  claim 1  which has a surface area ratio ΔS 50  defined by formula (1) below
   Δ S   50 =( S   x   50   −S   0   50 )/ S   0   50 ×100(%)  (1),   
     wherein S x   50  is a true surface area of a 50 μm×50 μm surface region as determined by three-point approximation from three-dimensional data obtained by measurement with an atomic force microscope at 512×512 points over the surface region and S 0   50  is a geometrically measured surface area of the surface region, of 30 to 80%. 
   
   
       3 . A presensitized plate, which comprises the support for a lithographic printing plate according to  claim 1  and an image recording layer thereon. 
   
   
       4 . A presensitized plate, which comprises the support for a lithographic printing plate according to  claim 2  and an image recording layer thereon. 
   
   
       5 . A method of preparing a support for a lithographic printing plate which, when measured over a 400 μm×400 μm surface region thereon using a three-dimensional non-contact roughness tester, has at most 5.0 convex portions of a height from centerline of at least 0.70 μm and an equivalent circle diameter of at least 20 μm, and has at least 800 concave portions of a depth from centerline of at least 0.50 μm and an equivalent circle diameter of at least 2.0 μm comprising the steps of;
 cold rolling an aluminum sheet with a metal-rolling roll having on the surface convex portions to form concave portions on the aluminum surface and   electrochemical graining.   
   
   
       6 . The method of preparing a support for a lithographic printing plate according to  claim 5  wherein the obtained support has a surface area ratio ΔS 50  defined by formula (1) below
   Δ S   50 =( S   x   50   −S   0   50 )/ S   0   50 ×100(%)  (1),   
     wherein S x   50  is a true surface area of a 50 μm×50 μm surface region as determined by three-point approximation from three-dimensional data obtained by measurement with an atomic force microscope at 512×512 points over the surface region and S 050  is a geometrically measured surface area of the surface region, of 30 to 80%. 
   
   
       7 . The method of preparing a support for a lithographic printing plate according to  claim 5  wherein the electrochemical graining process is conducted in hydrochloric acid electrolysis.