Plate for digitally-imaged offset printing

Abstract

A plateless process for offset lithographic printing using an inexpensive imaging system and using the surface of a lithographic printing cylinder itself as a plate substrate. The process enables production of a simple and inexpensive offset lithographic printing plate for use in an offset printing system, with the plate being produced by coating the substrate of the printing plate with a photosensitive liquid coating, and sealing the coated substrate with a release coating, coated on a protective film.

1 . An offset lithographic printing plate for use in an offset printing system, said plate being produced in accordance with a method comprising the steps of: 
 a) coating the substrate of said printing plate with a photosensitive liquid coating; and    b) sealing said coated substrate with a release coating, coated on a protective film.    
   
   
       2 . The printing plate of  claim 1  wherein said substrate is comprised of a hydrophilic surface.  
   
   
       3 . The printing plate of  claim 1  wherein said substrate is comprised of grained, anodized aluminum.  
   
   
       4 . The printing plate of  claim 1  wherein said liquid coating comprises a small amount of non-light-sensitive binder.  
   
   
       5 . The printing plate of  claim 1 , wherein said release coating is comprised of silicone.  
   
   
       6 . The printing plate of  claim 1  wherein said protective film is comprised of polypropelene.  
   
   
       7 . The printing plate of  claim 1  wherein said protective film is comprised of polyester.  
   
   
       8 . The printing plate of  claim 1  wherein, after said coating and sealing steps, said printing plate is readied for printing in an offset lithographic press in the further steps comprising: 
 a) mounting said printing plate into a CTP imaging system;    b) providing an actinic light source controlled by said CTP imaging system;    c) imaging said printing plate using actinic light from said actinic light source;    d) removing said protective film and said release coating from said printing plate after exposure to said actinic light; and    e) washing said printing plate with an aqueous solution to remove unpolymerized portions of said liquid coating.