LITHOGRAPHIC IMAGING AND PRINTING WITH NEGATIVE-WORKING PHOTORESPONSIVE PRINTING MEMBERS
Negative-working, IR-sensitive printing plates utilize a radiation-sensitive composition having a component polymerizable by a free-radical mechanism, at least part of which comprises or consists essentially of a non-particulate, aliphatic urethane acrylic oligomer that is infinitely water-dilutable but not water-soluble.
1 . A method of preparing and printing with a lithographic printing member, the method comprising the steps of:
providing a lithographic printing member comprising:
(a) a hydrophilic first layer; and
(b) disposed over the first layer, an oleophilic imaging layer comprising (i) a component polymerizable by a free-radical polymerization mechanism, (ii) an initiator for generating, upon exposure to imaging radiation, free radicals to initiate polymerization of the polymerizable component, (iii) a near-IR absorber, and (iv) a polymeric binder, wherein the polymerizable component comprises a non-particulate, aliphatic urethane acrylic oligomer that is infinitely water-dilutable but not water-soluble;
exposing the printing member to infrared imaging radiation in an imagewise pattern to cause polymerization of the polymerizable component; and
printing with the printing member to remove only unexposed portions of the imaging layer without a developer during a make-ready phase, and thereafter to produce printed copy.
2 . The method of claim 1 , wherein a percentage by weight of acrylate groups in the urethane acrylic oligomer is in the range of 5 to 30 wt %.
3 . The method of claim 2 , wherein a percentage by weight of acrylate groups in the urethane acrylic oligomer is in the range of 10 to 30 wt %.
4 . The method of claim 1 , wherein the polymerizable component consists essentially of the non-particulate, aliphatic urethane acrylic oligomer that is infinitely water-dilutable but not water-soluble.
5 . The method of claim 1 , wherein the aliphatic urethane acrylic oligomer constitutes more than 10 wt % but less than 40 wt % of the oleophilic imaging layer after drying.
6 . The method of claim 5 , wherein urethane acrylic oligomer constitutes more than 10 wt % but less than 25 wt % of the oleophilic imaging layer after drying.
7 . The method of claim 1 , wherein the polymerizable component further comprises a non-urethane monomer.
8 . The method of claim 7 , wherein a weight ratio of the aliphatic urethane acrylic oligomer to the non-urethane monomer in the polymerizable component is in the range of 1:1.5 to 1:6.
9 . The method of claim 7 , wherein the weight ratio is in the range of 1:1.5 to 1:4.
10 . The method of claim 7 , wherein the weight ratio is 1:3.
11 . The method of claim 7 , wherein the aliphatic urethane acrylic oligomer and the monomer collectively constitute about 60 to 80 wt % of the oleophilic imaging layer after drying.
12 . The method of claim 1 , further comprising the step of applying the oleophilic imaging layer to the hydrophilic first layer using no water.
13 . The method of claim 1 , wherein the hydrophilic first layer is grained, anodized and post-anodically treated with sodium silicate.
14 . The method of claim 1 , wherein the imaging layer has a dry coating weight less than 1 g/m 2 .
15 . The method of claim 1 , wherein the initiator is an onium salt.
16 . The method of claim 1 , wherein the lithographic printing member further comprises a water-soluble or water-dispersible topcoat.
17 . The method of claim 16 , wherein the topcoat has a dry coating weight no greater than 0.4 g/m 2 .
18 . The method of claim 16 , wherein the topcoat comprises a dispersion of particles of a poly(urethane-acrylic) hybrid.
19 . A lithographic printing member comprising:
a hydrophilic first layer; and
disposed over the first layer, an oleophilic imaging layer comprising (i) a component polymerizable by a free-radical polymerization mechanism, (ii) an initiator responsive to imaging radiation for generating free radicals to initiate polymerization of the polymerizable component, (iii) a near-IR absorber, and (iv) a polymeric binder, wherein
the polymerizable component comprises a non-particulate, aliphatic urethane acrylic oligomer that is infinitely water-dilutable but not water-soluble.
20 . The printing member of claim 19 , wherein a percentage by weight of acrylate groups in the urethane acrylic oligomer is in the range of 5 to 30 wt %.
21 . The printing member of claim 20 , wherein a percentage by weight of acrylate groups in the urethane acrylic oligomer is in the range of 10 to 30 wt %.
22 . The printing member of claim 19 , wherein the polymerizable component consists essentially of the non-particulate, aliphatic urethane acrylic oligomer that is infinitely water-dilutable but not water-soluble.
23 . The printing member of claim 19 , wherein the aliphatic urethane acrylic oligomer constitutes more than 10 wt % but less than 40 wt % of the oleophilic imaging layer after drying.
24 . The printing member of claim 23 , wherein urethane acrylic oligomer constitutes more than 10 wt % but less than 25 wt % of the oleophilic imaging layer after drying.
25 . The printing member of claim 21 , wherein the polymerizable component further comprises a non-urethane monomer.
26 . The printing member of claim 25 , wherein a weight ratio of the aliphatic urethane acrylic oligomer to the non-urethane monomer in the polymerizable component is in the range of 1:1.5 to 1:6.
27 . The printing member of claim 26 , wherein the weight ratio is in the range of 1:1.5 to 1:4.
28 . The printing member of claim 26 , wherein the weight ratio is 1:3.
29 . The printing member of claim 25 , wherein the aliphatic urethane acrylic oligomer and the monomer collectively constitute about 60 to 80 wt % of the oleophilic imaging layer after drying.
30 . The printing member of claim 19 , wherein the hydrophilic first layer is grained, anodized and post-anodically treated with sodium silicate.
31 . The printing member of claim 19 , wherein the imaging layer has a dry coating weight less than 1 g/m 2 .
32 . The printing member of claim 19 , wherein the initiator is an onium salt.
33 . The printing member of claim 19 , further comprising a water-soluble or water-dispersible topcoat over the oleophilic imaging layer.
34 . The printing member of claim 33 , wherein the topcoat has a dry coating weight no greater than 0.4 g/m 2 .
35 . The printing member of claim 34 , wherein the topcoat comprises a dispersion of particles of a poly(urethane-acrylic) hybrid.