Lithographic printing plate and method of making the same

Abstract

In a lithographic printing plate comprising a base and a lithographic printing surface thereon, said printing surface comprising colloidal silica and an insolubilized hydrophilic polymer, the improvement which comprises providing a positively charged colloidal silica as said colloidal silica component and, as said hydrophilic polymer, a nonionic or cationic polymer or a mixture of the same.

What is claimed is: 
     
       1. In a lithographic printing plate comprising a base and a lithographic printing surface thereon, said printing surface comprising colloidal silica and insolubilized hydrophilic polymer, the improvement comprising; providing a positively charged colloidal silica as said colloidal silica component, wherein said silica and hydrophilic polymer are present in the weight ratio of at least about four parts silica to one part polymer.Iadd., the hydrophilic polymer being cationic, nonionic, or a mixture of the same. .Iaddend. .[.2. The printing plate of claim 1 wherein said hydrophilic polymer is anionic, nonionic, or a mixture of the 
     
     
        same..]. 3. The printing plate of claim .[.2.]. .Iadd.1 .Iaddend.wherein said hydrophilic polymer is polyvinyl alcohol and wherein the silica and polyvinyl alcohol are present in the silica:polymer ratio of about 4:1- 15:1, said polyvinyl alcohol being at least 88% hydrolyzed and of medium 
     
     
        or high viscosity grade. 4. The printing plate of claim 3 wherein the silica and the hydrophilic polymer are present in the ratio of about 10:1, 
     
     
        said polyvinyl alcohol being essentially fully hydrolyzed. 5. The printing 
     
     
        plate of claim 1 wherein said base is cellulosic. 6. The printing plate of claim 1 wherein said base has hydrophilic or basic chemical groups 
     
     
        reactive with the cationic silica. 7. A process for preparing a lithographic printing plate comprising a base and a lithographic printing surface thereon, said printing surface comprising colloidal silica and an insolubilized hydrophilic polymer, said process comprising the steps of applying to said base said colloidal silica and an insolubilizable hydrophilic polymer wherein said colloidal silica is a positively charged colloidal silica, the silica and hydrophilic polymer being present in the weight ratio of at least about four parts silica to one part polymer, and then drying said surface.Iadd., the hydrophilic polymer being cationic, nonionic, or a mixture of the same. .Iaddend. .[.8. The process of claim 7 wherein said hydrophilic polymer is anionic, nonionic, or a mixture of the 
     
     
        same..]. 9. The process of claim .[.8.]. .Iadd.7 .Iaddend.wherein said hydrophilic polymer is polyvinyl alcohol and wherein the silica and polyvinyl alcohol are present in the silica:polymer ratio of about 4:1- 15:1, said polyvinyl alcohol being at least 88% hydrolyzed and of medium 
     
     
        or high viscosity grade. 10. The process of claim 9 wherein the silica and the hydrophilic polymer are present in the ratio of about 10:1, said 
     
     
        polyvinyl alcohol being essentially fully hydrolyzed. 11. The process of 
     
     
        claim 7 wherein said base is cellulosic. 12. The process of claim 7 wherein said base has hydrophilic or basic chemical groups reactive with the cationic silica.