Oliophilic Coating On Underside Of Printing Plate
In a stack of lithographic printing plate precursors, each plate has an aluminum substrate, a photo-polymerizable (PS) layer carried on the upper surface of the substrate, a water soluble topcoat oxidation inhibitor carried on the PS layer, and a water insoluble bottom coat on the lower surface of the substrate, wherein the bottom coat of each intermediate plate is in direct covering contact with the topcoat of an immediately adjacent plate. The associated process includes cutting through multiple sections of the finished web without interleaving to produce stacks of finally sized precursor plates, and without interleafing, packaging together at least 25 stacked and confronting precursor plates.
1 . A stack of lithographic printing plate precursors comprising:
a multiplicity of said plates, including a top plate, a bottom plate and a plurality of intermediate plates, wherein each plate comprises
an aluminum sheet with upper and lower surfaces;
a photopolymerizable layer carried directly or indirectly on the upper surface of the sheet;
a water-soluble top coat oxidation inhibitor carried directly or indirectly on the photopolymerizable layer; and
a water-insoluble bottom coat on the lower surface of the aluminum sheet;
wherein the bottom coat of each intermediate plate is in direct covering contact with the top coat of an immediately adjacent plate.
2 . The stack of plates according to claim 1 , wherein the stack of plates is contained in a sealed package.
3 . The stack of plates according to claim 1 , wherein said stack includes at least 25 plates.
4 . The stack of plates according to claim 2 , wherein said stack contains at least 25 plates.
5 . The stack of plates according to claim 4 , wherein a plurality of said packages are stacked on a floor or pallet.
6 . The stack of plates according to claim 1 , wherein said bottom coat is oliophilic.
7 . The stack of plates according to claim 6 , wherein said bottom coat is laminated to the lower surface of the sheet.
8 . The stack of plates according to claim 6 , wherein the bottom coat is electrically non-conductive.
9 . The stack of plates according to claim 8 , wherein the entire upper surface of the sheet is grained and anodized and none of the lower surface of the sheet is grained or anodized.
10 . The stack of plates according to claim 1 , wherein
the top coat is polyvinyl alcohol;
the bottom coat is an electrically non-conductive and oliophilic polymer laminated to the lower surface of the sheet; and
said stack consists of at least 25 plates contained in a sealed package.
11 . The stack of claim 1 , wherein the aluminum sheet and bottom coat form a substrate and the bottom coating has a thickness in the range of 25%-75% of the thickness of the substrate.
12 . A method for manufacturing lithographic printing plate precursors, comprising the step sequence of:
a. selecting a source consisting essentially of an aluminum sheet with an electrically nonconductive, oliophilic polymer material laminated on one side of the sheet;
b. graining and anodizing only the other side of the sheet to form a substrate web with a grained and anodized top surface and a polymeric, oliophilic bottom surface;
c. applying and drying a photopolymerizable resin layer to the top surface of the substrate web;
d. applying and drying a water soluble oxygen inhibition layer as a top coat to the resin layer to form a fully coated, a final web;
e. cutting the final web into a multiplicity of sections;
f. without interleafing, placing the multiplicity of sections one on top the other whereby the top coat of one section directly confronts the polymer laminate of a next higher section; and
g. without interleafing, cutting entirely through the multiplicity of sections to produce a plurality of stacks of finally sized precursor plates.
13 . The method of claim 12 , including the further step of packaging together at least 25 stacked and confronting precursor plates.
14 . The method of claim 12 , wherein the step of anodizing is performed with a liquid contact cell.
15 . The method of claim 12 , wherein the finally sized precursor plates are rectangular with the same length and width dimensions from plate to, and in step g, the cut sections are rectangular with said precursor plate length and width dimensions.
16 . The method of claim 12 , wherein the substrate web is continuously conveyed through steps c. and d. and step e. comprises cutting sections off the final web as the final web is continuously discharged from drying in step d.
17 . The method of claim 14 , wherein
the finally sized precursor plates are rectangular with the same length and width dimensions from plate to plate;
the aluminum sheet has a width dimension that is the same as one of said length or width dimensions of the finally sized precursor plates; and
in step g, the cut sections are rectangular with said precursor plate length and width dimensions.