Dry lithographic imaging and printing with printing members having aluminum substrates
View Patent ↗Negative-working, IR-sensitive dry printing plates utilize an oleophobic topmost layer, a nitrocellulose-based imaging layer ablatable by laser discharge, and a grained metal substrate with no heat-insulating layer intervening between the imaging layer and the substrate.
1. A method of dry printing comprising the steps of:
providing a lithographic printing member consisting essentially of (i) an oleophobic topmost layer, (ii) disposed thereunder, a dried, crosslinked polymeric imaging layer consisting essentially of (a) a nitrocellulose composition, (b) a melamine binder and (c) dispersed therein, an infrared-absorbing dye or pigment, the melamine binder constituting at least 35% by weight of the polymeric imaging layer, and (iii) disposed under and in direct contact with the polymeric imaging layer, a metal sheet having a grained surface;
exposing the printing member to infrared imaging radiation in an imagewise pattern to cause ablation of the imaging layer;
cleaning the printing member by rubbing with plain tap water to reveal the grained metal surface; and
printing with the printing member by repeatedly applying only ink to the printing member, whereby the ink adheres to the grained metal surface where revealed and not to the oleophobic layer, and transferring the ink to a recording medium.
2. The method of claim 1 , wherein the metal is aluminum.
3. The method of claim 1 , wherein the nitrocellulose composition has a nitration level above 10.7% but less then 12.3%.
4. The method of claim 1 , wherein the nitrocellulose composition has a viscosity ranging from 1/16 second to 3 seconds.
5. The method of claim 4 , wherein the nitrocellulose composition has a viscosity ranging from ⅛ second to 1 second.
6. The method of claim 4 , wherein the nitrocellulose composition has a viscosity ranging from ⅛ second to ½ second.
7. The method of claim 1 , wherein the aluminum sheet has an Ra roughness of at least 0.20 μm.