ABLATION-TYPE LITHOGRAPHIC PRINTING MEMBERS HAVING IMPROVED EXPOSURE SENSITIVITY AND RELATED METHODS
Ablation-type printing plates having improved exposure sensitivity are produced using an imaging layer—i.e., the plate layer that absorbs and ablates in response to imaging radiation—whose composition includes a large proportion of crosslinker.
1 . A method of imaging a printing member, the method comprising the steps of:
(a) providing a printing member comprising
(i) an oleophilic first layer;
(ii) disposed over the first layer, an oleophilic imaging layer having (A) a cured resin phase consisting essentially of a melamine resin and a resole resin, the resole resin being present in an amount ranging from 0% to 28% by weight of dry film, (B) dispersed within the cured resin phase, a near-IR absorber, and (C) a dry coating weight of at least 0.9 g/m 2 ; and
(iii) disposed over the imaging layer, an oleophobic third layer;
(b) exposing the printing member to imaging radiation in an imagewise pattern, the imaging radiation at least partially ablating the imaging layer where exposed; and
(c) subjecting the printing member to machine cleaning to remove the third layer and at least a portion of the imaging layer where the printing member received imaging radiation, thereby creating an imagewise pattern on the printing member.
2 . The method of claim 1 , wherein the imaging radiation has a fluence not exceeding 210 mJ/cm 2 .
3 . The method of claim 1 , wherein the machine cleaning is spray-on cleaning.
4 . The method of claim 1 , wherein the machine cleaning is carried out using oscillating brush rollers.
5 . The method of claim 1 , wherein the oleophilic first layer is an aluminum sheet.
6 . The method of claim 1 , wherein the imaging layer contains no resole resin.
7 . The method of claim 1 , wherein the near-IR absorber consists essentially of a dye.
8 . The method of claim 1 , wherein the near-IR absorber constitutes no more than 25% of the imaging layer by weight of dry film.
9 . The method of claim 1 , wherein the melamine resin constitutes no more than 88% of the imaging layer by weight.
10 . The method of claim 1 , wherein the melamine resin is a methylated, low-methylol, high-imino melamine.
11 . The method of claim 1 , wherein the melamine resin has a viscosity ranging from 7000 to 15,000 centipoises at 23° C.
12 . The method of claim 1 , wherein the melamine resin has a viscosity ranging from and 1000 to 1600 centipoises at 23° C.
13 . The method of claim 1 , wherein the imaging layer has a dry coating weight of approximately 1.1 g/m 2 .
14 . The method of claim 1 , wherein the imaging layer has a dry coating weight of approximately 1.3 g/m 2 .
15 . The method of claim 1 , wherein the imaging layer has a dry coating weight of approximately 1.5 g/m 2 .
16 . The method of claim 1 , wherein the machine cleaning comprises applying an aqueous liquid to the plate.
17 . The method of claim 16 , wherein the aqueous liquid is plain tap water.
18 . The method of claim 16 , wherein the aqueous liquid contains not more than 20% by weight of an organic solvent.
19 . The method of claim 18 wherein the organic solvent comprises at least one of a glycol, benzyl alcohol or phenoxyethanol.
20 . The method of claim 16 wherein the aqueous liquid comprises a surfactant.
21 . The method of claim 16 wherein the aqueous liquid is heated to a temperature greater than 80° F.