Ablation-type lithographic printing members having improved exposure sensitivity and related methods
View Patent ↗Ablation-type printing plates having improved exposure sensitivity are produced using a thin imaging layer—i.e., the plate layer that absorbs and ablates in response to imaging radiation—whose composition includes a large proportion of radiation absorber.
1. A method of imaging a printing member, the method comprising the steps of:
(a) providing a printing member comprising
(i) an oleophilic, polymeric first layer;
(ii) disposed over the first layer, an oleophilic imaging layer having (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 imaging layer, (B) dispersed within the imaging layer, a near-IR absorber present in an amount ranging from 20% to 30% by weight of dry film, and (C) a dry coating weight of not more than 0.5 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 195 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 polyester.
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 less than 25% of the imaging layer by weight of dry film.
9. The method of claim 1 , wherein the melamine component constitutes no more than 88% of the imaging layer by weight.
10. The method of claim 1 , wherein the melamine component is a methylated, low-methylol, high-imino melamine.
11. The method of claim 1 , wherein the melamine component has a viscosity ranging from 7000 to 15,000 centipoises at 23° C.
12. The method of claim 1 , wherein the melamine component 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 0.5 g/m 2 .
14. The method of claim 1 , wherein the machine cleaning comprises applying an aqueous liquid to the plate.
15. The method of claim 14 , wherein the aqueous liquid is plain tap water.
16. The method of claim 14 , wherein the aqueous liquid contains not more than 20% by weight of an organic solvent.
17. The method of claim 16 wherein the organic solvent comprises at least one of a glycol, benzyl alcohol or phenoxyethanol.
18. The method of claim 14 wherein the aqueous liquid comprises a surfactant.
19. The method of claim 14 wherein the aqueous liquid is heated to a temperature greater than 80° F.
20. A printing member comprising:
(a) an oleophilic, polymeric first layer;
(b) disposed over the first layer, an oleophilic imaging layer having (i) 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, (ii) dispersed within the crosslinked polymer network, a near-IR absorber present in an amount ranging from 20% to 30% by weight of dry film, and (iii) a dry coating weight of not more than 0.5 g/m 2 ; and
(c) disposed over the imaging layer, an oleophobic third layer.
21. The printing member of claim 20 , wherein the oleophilic first layer is polyester.
22. The printing member of claim 20 , wherein the imaging layer contains no resole resin.
23. The printing member of claim 20 , wherein the near-IR absorber consists essentially of a dye.
24. The printing member of claim 20 , wherein the near-IR absorber constitutes no less than 25% of the imaging layer by weight of dry film.
25. The printing member of claim 20 , wherein the melamine component constitutes no more than 88% of the imaging layer by weight.
26. The printing member of claim 20 , wherein the melamine component is a methylated, low-methylol, high-imino melamine.
27. The printing member of claim 20 , wherein the melamine component has a viscosity ranging from 7000 to 15,000 centipoises at 23° C.
28. The printing member of claim 20 , wherein the melamine component has a viscosity ranging from and 1000 to 1600 centipoises at 23° C.
29. The printing member of claim 20 , wherein the imaging layer has a dry coating weight of approximately 0.5 g/m 2 .
30. A method of making an ablation-type printing member, the method comprising the steps of:
(a) providing a precursor structure having a polymeric, oleophilic surface;
(b) coating, over the precursor structure, an oleophilic composition;
(c) curing the oleophilic composition to form a crosslinked polymer network;
(d) following step (c), coating, over the cured oleophilic composition, an oleophobic polymer composition; and
(e) curing the oleophobic polymer composition,
wherein the oleophilic composition 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 composition, (B) dispersed within the cured oleophilic composition, a near-IR absorber present in an amount ranging from 20% to 30% by weight of dry film, and (C) a dry coating weight of not more than 0.5 g/m 2 .
31. The method of claim 30 wherein the resin composition is cured at a temperature ranging from 220 to 320° F.
32. The method of claim 30 wherein the resin composition is cured at a temperature ranging from 240 to 280° F.