Method of improving print performance in flexographic printing plates
View Patent ↗A method of tailoring the shape of a plurality of relief printing dots created in a photosensitive printing blank during a platemaking process is provided. The photocurable layer is exposed to actinic radiation using an array of UV LED light assemblies and the use of the array of UV LED light assemblies produces relief printing dots having at least one geometric characteristic selected from the group consisting of a desired planarity of a top surface of the relief printing dots, a desired shoulder angle of the relief printing dots and a desired edge sharpness of the relief printing dots.
1. A method of tailoring the shape of a plurality of relief printing dots created in a photosensitive printing blank during a platemaking process, said photosensitive printing blank comprising at least one photocurable layer disposed on a backing layer, the method comprising the steps of:
a) selectively exposing the at least one photocurable layer to a source of actinic radiation to selectively crosslink and cure the at least one photocurable layer; and
b) developing the exposed at least one photocurable layer of photosensitive printing blank to reveal a relief image therein, said relief image comprising the plurality of relief printing dots;
wherein the source of actinic radiation comprises an array of UV LED lights arranged in a pattern; wherein the pattern of UV LED lights comprises at least one of UV LED lights that operate at different wavelengths, UV LED lights that have different angles of light, and UV LED lights controlled to provide different light intensities;
wherein the array of UV LED lights produces relief printing dots having at least one geometric characteristic selected from the group consisting of a desired planarity of a top surface of the relief printing dots, a desired shoulder angle of the relief printing dots and a desired edge sharpness of the relief printing dots.
2. The method according to claim 1 , wherein the pattern of UV LED lights comprises UV LED lights arranged in at least four rows.
3. The method according to claim 2 , wherein alternate rows of UV LED lights have different peak wavelengths.
4. The method according to claim 3 , wherein the alternate rows of UV LED lights in the array of UV LED lights operate at wavelengths in the range of 360 nm to 420 nm.
5. The method according to claim 3 , wherein the alternate rows of UV LED lights operate at wavelengths of 365 nm and 395 nm.
6. The method according to claim 1 , wherein the at least one photocurable layer comprises a photoinitiator, wherein said photoinitiator has a UV-Vis absorption peak in the range of the operating wavelength of the UV LED light assembly.
7. The method according to claim 1 , wherein the pattern of UV LED lights comprises UV LED lights arranged to have different angles of light.
8. The method according to claim 7 , wherein the UV LED lights are arranged in rows and alternate rows of UV LED lights comprise collimated UV LED lights and non-collimated UV LED lights.
9. The method according to claim 1 , wherein the angle of the relief printing dot shoulder is greater than about 50°.
10. The method according to claim 1 , wherein the edge sharpness of the relief printing dots, defined as the ratio of the radius of curvature r e at the intersection of a shoulder and the top of the relief printing dot to the width of the dot's top printing surface p is less than about 5%.
11. The method according to claim 10 , wherein the ratio of r e :p is less than about 2%.
12. The method according to claim 1 , wherein a bump exposure is not performed.
13. A method according to claim 1 , wherein the array of UV LED lights comprises at least two LED lights which have peak wavelengths that are different from each other.
14. A method according to claim 1 wherein the relief printing dots comprise a planarity that is greater than a thickness of the at least one photocurable layer.