Method and system for thermal processing of flexo printing elements
The present disclosure is directed to a system and method configured for curing non-reactive photopolymer collected by an absorbent blotting material during thermal processing of flexographic printing elements. Uncured non-reacted portions of the photopolymer are removed by contacting the one or more layers of photopolymer with the web of absorbent blotting material at an elevated temperature to soften or liquefy the uncured non-reacted portions of the one or more layers of photopolymer and absorb the softened or liquefied uncured non-reacted portions into the absorbent web of absorbent blotting material. The web of absorbent blotter material containing the absorbed softened or liquefied non-reacted portions of the photopolymer is exposed to actinic radiation from the one or more UV light sources to crosslink and cure the softened or liquefied non-reacted portions of the photopolymer.
1. A method of curing non-reacted photopolymer absorbed into a web of absorbent blotter material during thermal processing of a flexographic printing elements in a thermal developing assembly, wherein the thermal developing assembly receives an imaged and exposed flexographic printing element, the imaged and exposed flexographic printing element comprising one or more layers of photopolymer, the one or more layers of photopolymer comprising crosslinked cured portions of photopolymer that form a cured relief image and uncured non-reacted portions of photopolymer that are removed during thermal processing to reveal the cured relief image,
wherein the uncured non-reacted portions of the photopolymer are removed by contacting the one or more layers of photopolymer with the web of absorbent blotting material at an elevated temperature to soften or liquefy the uncured non-reacted portions of the one or more layers of photopolymer and absorb the softened or liquefied uncured non-reacted portions into the absorbent web of absorbent blotting material,
the method comprising the steps of:
a) arranging one or more UV light sources in the thermal processor at a distance from a width of the absorbent blotter material containing the absorbed softened or liquefied non-reacted portions of the photopolymer, wherein the absorbent web of blotter material containing the absorbed softened or liquefied non-reacted portions of the photopolymer moves relative to the one or more UV light sources; and
b) exposing the web of absorbent blotter material to actinic radiation from the one or more UV light sources to crosslink and cure the softened or liquefied non-reacted portions of the photopolymer as the absorbent web of blotter material moves relative to the one or more UV light sources.
2. The method according to claim 1 , further comprising the step of winding the web of absorbent blotter material containing the crosslinked and cured non-reacted portions onto a rewind roller.
3. The method according to claim 1 , wherein the one or more UV light sources comprise one or more UV-LEDs, one or more fluorescent UV exposure tubes or combinations thereof.
4. The method according to claim 3 , wherein the one or more UV light sources comprise a plurality of UV-LEDs, wherein an intensity of each of the one or more UV-LEDs is at least 10 mW/cm 2 .
5. The method according to claim 4 , wherein the intensity of each of the one or more UV-LEDs is at least 13 mW/cm 2 .
6. The method according to claim 3 , wherein the one or more UV light sources comprise a one or more fluorescent UV exposure tubes, wherein an intensity of each of the one or more fluorescent UV exposure tubes is at least 20 mW/cm 2 .
7. The method according to claim 1 wherein the one or more UV light sources comprise a plurality of UV light sources arranged approximately equidistantly from each other across the width of the web of absorbent blotter material, wherein the width of the web of absorbent blotter material is uniformly exposed to actinic radiation from the one or more UV light sources.
8. The method according to claim 1 , wherein the one or more UV light sources operate at a wavelength within the range of 365 to 405 nm.
9. The method according to claim 1 , wherein the intensity of each of the one or more UV light sources is 13 to 15 mW/cm 2 when the one or more UV light sources are arranged at a distance of about 0.5 inches from the surface of the web of absorbent blotter material.
10. The method according to claim 9 , wherein the one or more UV light sources comprise a one or more fluorescent UV exposure tubes, wherein an intensity of each of the one or more fluorescent UV exposure tubes is at least 30 mW/cm 2 .
11. The method according to claim 10 , wherein the Dose of the one or more UV light sources is at least 150 mJ/cm 2 .
12. The method according to claim 1 , wherein the Dose of the one or more UV light sources, defined as the intensity of the light sources times the dwell time of exposure, is at least 130 mJ/cm 2 .
13. The method according to claim 12 , wherein the Dose of the one or more UV light sources is at least 160 mJ/cm 2 .
14. The method according to claim 1 , further comprising one or more heaters positionable either before or after the one or more UV light sources, wherein the one or more heaters aid in curing the uncured un-reacted photopolymer in the web of absorbent blotter material.
15. The method according to claim 1 , wherein a Dose of the one or more UV light sources, defined as the intensity of the light sources times the dwell time of exposure, is reduced by using a lower intensity UV light source, fewer UV light sources, or a decreased dwell time of exposure.