Dry printing with simplified plate cleaning
View Patent ↗The blanket cylinder of a printing press is used to remove oleophobic debris from an imaged dry printing member. Following imaging—e.g., imagewise exposure of the printing member to radiation that ablates the layer below the oleophobic layer, or de-anchors it from the oleophobic layer without ablation—the printing member is brought into rolling contact with the blanket cylinder, and the press is operated “on impression.” This rolling contact may remove not only the oleophobic top layer but ablation debris of the underlying imaging layer as well.
1. A method of printing with an ablation-type printing member comprising (i) an oleophilic substrate, (ii) over and in contact with the substrate, an ablatable imaging layer, and (iii) over and in contact with the imaging layer, a cured oleophobic polymer layer, the method comprising the steps of:
a) exposing the printing member to imaging radiation in an imagewise pattern, the imaging radiation at least partially ablating the imaging layer where exposed;
b) with the printing member on a printing press comprising (i) a plate cylinder for retaining the printing member, (ii) an inking system for transferring ink to the printing member on the plate cylinder, (iii) an impression cylinder for retaining a recording medium, and (iv) a blanket cylinder engageable to rolling contact with the plate cylinder and the impression cylinder for transferring ink from the plate to the recording medium, operating the press in an on impression mode to engage the blanket cylinder but not engage the inking system, whereby the blanket cylinder is brought into rolling contact with the uninked printing member so as to remove ablation debris therefrom and thereby create an imagewise lithographic pattern thereon, rendering the printing member suitable for printing; and
c) thereafter, engaging the inking system to cause transfer of ink to the printing member and thereafter from the printing member to a recording medium, via the blanket cylinder, in the imagewise pattern.
2. The method of claim 1 , wherein the blanket cylinder has a rubber surface.
3. The method of claim 1 , wherein the cured oleophobic substrate is a silicone.
4. The method of claim 1 , wherein the cured oleophobic substrate is a fluoropolymer.
5. The method of claim 1 , further comprising the step of cleaning the blanket cylinder following step (b) but prior to step (c), followed by air drying.
6. The method of claim 1 , wherein the ablatable imaging layer has (A) a single crosslinked polymer network consisting essentially of a melamine component and a resole component, the resole component being present in an amount ranging from 0% to 28% by weight of dry film, wherein the single crosslinked polymer network is the only crosslinked polymer network in the oleophilic resin composition, (B) dispersed within the crosslinked polymer network, a near-IR absorber, and (C) a dry coating weight in the range of 1.0 to 2.5 g/m 2 .
7. The method of claim 6 , wherein the imaging layer contains no resole component.
8. The method of claim 6 , wherein the near-IR absorber consists essentially of a dye.
9. The method of claim 6 , wherein the near-IR absorber constitutes at least 20% of the imaging layer by weight of dry film.
10. The method of claim 9 , wherein the near-IR absorber constitutes at least 30% of the imaging layer by weight of dry film.
11. The method of claim 6 , wherein the melamine component constitutes no more than 88% of the imaging layer by weight.
12. The method of claim 6 , wherein the oleophobic layer has a dry coating weight of less than 2.0 g/m 2 .
13. The method of claim 12 , wherein the oleophobic layer has a dry coating weight of less than 0.5 g/m 2 .
14. The method of claim 1 , wherein the oleophilic substrate is an aluminum sheet.
15. The method of claim 14 , wherein the aluminum is grained and anodized.