Lithographic imaging and printing with printing members having fusible polymeric particles
View Patent ↗Embodiments of the present invention involve printing members that utilize a particle-fusion imaging mechanism but avoid susceptibility to handling damage. In particular, printing plates in accordance with the invention may utilize two phases, and these may originate, during manufacture, as two particle systems. Both systems are initially dispersed in a single coating applied as a layer, or in multiple coatings applied as adjacent layers, on a substrate. The second particle system exhibits a glass-transition or thermal coalescing temperature well above room temperature and also above the temperature at which the coating is dried. The coalescing temperature of the first particle system is below the drying temperature. As a result, when the coating is dried, the first particle system coalesces and forms a binder that entrains the second particle system, which has not coalesced. The binder formed by the first particle system is preferably insoluble in aqueous liquids, but is swellable or softened by such liquids, whereas the binder formed by the second particle system is preferably insoluble in and not swellable by aqueous liquids. Aqueous insolubility allows the dried (and ready-to-image) coating to resist handling damage, while swellability facilitates development.
1. A method of imaging a lithographic printing member, the method comprising the steps of:
(a) providing a lithographic printing member comprising (i) an imaging layer that itself comprises a first polymer binder and, dispersed therein, particles coalesceable into a second polymer binder at a thermal coalescing temperature substantially above room temperature, (ii) a material that absorbs imaging radiation and is heatable thereby to a temperature of at least the thermal coalescing temperature, and (iii) a substrate disposed below the imaging layer, wherein: (1) the first polymer binder is insoluble in but swellable by an aqueous liquid and comprises at least one of butyl methacrylate or butyl acrylate; (2) the second polymer binder is insoluble in and not swellable by the aqueous liquid and comprises at least one of styrene and butyl acrylate; (3) the first and second polymer binders collectively exhibit a first lithographic affinity for ink or a liquid to which ink will not adhere and the substrate exhibits a second lithographic affinity opposite to the first lithographic affinity; and (4) the particles comprise at least one of butyl(meth)acrylate, methyl(meth)acrylate, ethyl(meth)acrylate, styrene, (meth)acrylonitrile, N-phenyl maleimide, vinyl carbazole, or vinyl chloride,
(b) exposing the printing member to imaging radiation in an imagewise pattern so as to heat the polymer particles to the thermal coalescing temperature to form the second polymer binder; and
(c) after the second polymer binder has cooled to a solid form, subjecting the printing member to an aqueous liquid to remove unimaged portions of the imaging layer, thereby creating an imagewise lithographic pattern on the printing member.
2. The method of claim 1 wherein the material that absorbs imaging radiation is contained within the imaging layer.
3. The method of claim 2 wherein the imaging radiation is applied by at least one IR laser having a beam energy of at least 100 mJ/cm 2 .
4. The method of claim 1 wherein the aqueous liquid has a pH of at least 7.
5. The method of claim 4 wherein the second polymer binder is not swellable by an aqueous liquid having a pH below 7.
6. The method of claim 1 wherein the material that absorbs imaging radiation comprises a pigment.
7. The method of claim 1 wherein the material that absorbs imaging radiation comprises a dye.
8. The method of claim 1 wherein the thermal coalescing temperature is at least 60° C.
9. The method of claim 8 wherein the thermal coalescing temperature is at least 80° C.
10. The method of claim 1 wherein the first lithographic affinity is oleophilicity and the second lithographic affinity is hydrophilicity.
11. The method of claim 10 wherein the substrate is a metal sheet having a hydrophilic surface texture.
12. The method of claim 1 wherein the imaging layer has a latex content consisting of the first polymer binder and the particles, the first polymer binder representing at least 15% of the latex content.
13. The method of claim 12 wherein the first polymer binder represents no more than 35% of the latex content.
14. The method of claim 1 wherein the particles have a mean diameter of at least 175 nm.
15. The method of claim 14 wherein the particles have a mean diameter no greater than 800 nm.
16. A method of imaging a lithographic printing member, the method comprising the steps of:
(a) providing a lithographic printing member comprising (i) an imaging layer that itself comprises a first polymer binder and, dispersed therein, particles coalesceable into a second polymer binder at a thermal coalescing temperature substantially above room temperature, (ii) a material that absorbs imaging radiation and is heatable thereby to a temperature of at least the thermal coalescing temperature, and (iii) a substrate disposed below the imaging layer, wherein: (1) the first polymer binder is insoluble in but swellable by an aqueous liquid and consists essentially of butyl methacrylate, butyl acrylate and acrylic acid; (2) the second polymer binder is insoluble in and not swellable by the aqueous liquid and comprises at least one of styrene and butyl acrylate; and (3) the first and second polymer binders collectively exhibit a first lithographic affinity for ink or a liquid to which ink will not adhere and the substrate exhibits a second lithographic affinity opposite to the first lithographic affinity,
(b) exposing the printing member to imaging radiation in an imagewise pattern so as to heat the polymer particles to the thermal coalescing temperature to form the second polymer binder; and
(c) after the second polymer binder has cooled to a solid form, subjecting the printing member to an aqueous liquid to remove unimaged portions of the imaging layer, thereby creating an imagewise lithographic pattern on the printing member.
17. The method of claim 16 wherein the material that absorbs imaging radiation is contained within the imaging layer.
18. The method of claim 16 wherein the first lithographic affinity is oleophilicity and the second lithographic affinity is hydrophilicity.