Ablation-type lithographic printing members having improved exposure sensitivity and related methods
View Patent ↗Dry, ablation-type, nitrocellulose-containing lithographic printing members include dual adjacent imaging layers, both including an absorber and at least one containing a binder (which may include or consist essentially of a melamine resin). The absorber of the nitrocellulose-containing layer is a pigment and this layer contains no absorbing dye, while the absorber of the other imaging layer includes or consists essentially of a dye.
1. A method of imaging a printing member, the method comprising the steps of:
(a) providing a printing member comprising
(i) a substrate having an oleophilic surface;
(ii) first and second imaging layers disposed over the substrate, the first imaging layer comprising a binder and a near-IR absorber including a dye, the second imaging layer comprising a polymer and a near-IR absorber that does not include a dye; and
(iii) disposed over the imaging layers, 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 layers where exposed; and
(c) cleaning the printing member to remove the third layer and at least a portion of the imaging layers where the printing member received imaging radiation, thereby creating an imagewise pattern on the printing member.
2. The method of claim 1 , wherein (i) the first imaging layer has a first side in contact with the third layer and a second side, opposed to the first side, in contact with the second imaging layer, and (ii) the second imaging layer has a first side in contact with the first imaging layer and a second side, opposed to the first side, in contact with the substrate.
3. The method of claim 1 , wherein the substrate is a metal sheet having a surface in contact with one of the imaging layers.
4. The method of claim 3 , wherein the metal is aluminum.
5. The method of claim 1 , wherein the binder of the first imaging layer is a melamine resin.
6. The method of claim 1 , wherein the second imaging layer further comprises a resole resin.
7. The method of claim 1 , wherein the second imaging layer comprises a melamine resin.
8. The method of claim 1 , wherein the near-IR absorber of the first imaging layer further comprises carbon black.
9. The method of claim 1 , wherein the near-IR absorber of the first imaging layer consists of a dye.
10. The method of claim 9 , wherein the near-IR absorber of the second imaging layer consists of carbon black.
11. The method of claim 1 , wherein a loading level of the near-IR absorber of the second imaging layer is no greater than 25%.
12. A lithographic printing member comprising:
(a) a substrate having an oleophilic surface;
(b) first and second imaging layers disposed over the substrate, wherein (i) the first imaging layer comprises a binder and a near-IR absorber including a dye, (ii) the second imaging layer comprises a polymer and a near-IR absorber that does not include a dye, and (iii) the first and second imaging layers are at least partially ablatable by exposure to near-IR radiation at a fluence level no greater than 210 mJ/cm 2 ; and
(c) disposed over the imaging layers, an oleophobic third layer.
13. The printing member of claim 12 , wherein (i) the first imaging layer has a first side in contact with the third layer and a second side, opposed to the first side, in contact with the second imaging layer, and (ii) the second imaging layer has a first side in contact with the first imaging layer and a second side, opposed to the first side, in contact with the substrate.
14. The printing member of claim 12 , wherein the substrate is a metal sheet having a surface in contact with one of the imaging layers.
15. The printing member of claim 14 , wherein the metal is aluminum.
16. The printing member of claim 12 , wherein the binder of the first imaging layer is a melamine resin.
17. The printing member of claim 12 , wherein the second imaging layer further comprises a resole resin.
18. The printing member of claim 12 , wherein the second imaging layer comprises a melamine resin.
19. The printing member of claim 12 , wherein the near-IR absorber of the first imaging layer further comprises carbon black.
20. The printing member of claim 12 , wherein the near-IR absorber of the first imaging layer consists of a dye.
21. The printing member of claim 20 , wherein the near-IR absorber of the second imaging layer consists of carbon black.
22. The printing member of claim 12 , wherein a loading level of the near-IR absorber of the second imaging layer is no greater than 25%.
23. The printing member of claim 12 , wherein the first and second imaging layers are at least partially ablatable by exposure to near-IR radiation at a fluence level no greater than 150 mJ/cm 2 .