Method for thermally processing photosensitive printing sleeves
View Patent ↗An improved method of manufacturing a photosensitive printing element that minimizes relief variation and improves image fidelity. The method involves a step of pre-curing the first (floor layer) of photocurable material prior to depositing an additional layer or layers of photocurable material that may be imaged and developed to produce a desired relief image on the surface of the photosensitive printing element. The photosensitive printing element is then thermally developed by contacting the photosensitive printing element with at least one roll that is capable of moving over at least a portion of the imaged surface of the flexographic printing element to remove the softened or melted non-crosslinked photopolymer. Non-crosslinked photopolymer on the imaged and exposed surface of the flexographic printing element can be softened or melted by positioning a heater adjacent to the imaged surface of the flexographic printing element and/or heating the at least one roll that contactable with the imaged surface of the flexographic printing element.
1. A method of manufacturing a photosensitive printing element comprising the steps of:
a) providing a photosensitive printing element on a rotatable cylindrical support, the photosensitive printing element comprising:
i) a support layer;
ii) a first layer of photocurable material on the support layer, the first layer of photocurable material being pre-cured;
iii) at least a second layer of photocurable material deposited on the first layer of pre-cured photocurable material; and
iv) a masking layer on top of the at least second layer of photocurable material that allows for the selective polymerization of the at least second layer of photocurable material;
b) imaging the at least second layer of photocurable material by ablating the masking layer to create a pattern of a desired image on the surface of the at least second layer of photocurable material;
c) exposing the second layer of photocurable material through the masking layer to one or more sources of actinic radiation to crosslink and cure portions of the second layer of photocurable material that are not covered by the masking layer;
d) melting or softening uncured portions of the second layer of photocurable material on the imaged and exposed surface of the photosensitive printing element;
e) causing contact between the imaged and exposed surface of the photosensitive printing element and at least one roll; and
f) rotating the at least one roll against at least a portion of the imaged and exposed surface of the photosensitive printing element to remove non-crosslinked photopolymer that has been melted or softened from the imaged and exposed surface of the photosensitive printing element.
2. The method according to claim 1 , wherein the first layer of photocurable material is pre-cured from the front of the photosensitive printing element.
3. The method according to claim 2 , further comprising the step of grinding, sanding, or machining the first layer of photocurable material to achieve a desired thickness before the at least second layer of photocurable material is deposited on the first layer of photocurable material.
4. The method according to claim 1 , wherein the masking layer is selectively exposed to a source of laser radiation at a selected wavelength and power to ablate portions of the masking layer that are contacted with the source of laser radiation without damage to the underlying second layer of photocurable material to create the desired image on a surface of the second layer of photocurable material.
5. The method according to claim 1 , further comprising a step of detacking and post-curing the photosensitive printing element.
6. The method according to claim 1 , wherein the one or more sources of actinic radiation comprise one or more ultraviolet lights.
7. The method according to claim 6 , wherein the one or more sources of actinic radiation traverse the length of the photosensitive printing element.
8. The method according to claim 1 , wherein the at least one roll traverses the length of the photosensitive printing element.
9. The method according to claim 8 , wherein the at least one roll traverses the length of the photosensitive printing element multiple times.
10. The method according to claim 8 , wherein the at least one roll traverses the length of the photosensitive printing element in a spiral or stepwise manner.
11. The method according to claim 1 , wherein the at least one roll rotates in a first direction and the cylindrical photosensitive printing element rotates in an opposite direction from the at least one roll.
12. The method according to claim 1 , wherein an air cylinder or a hydraulic cylinder is used to maintain contact between the at least one roll and the surface of the photosensitive printing element.
13. The method according to claim 1 , wherein at least the portion of the at least one roll that is in contact with the surface of the photosensitive printing element is covered with a blotting material and the blotting material removes the non-crosslinked polymer from the surface of the photosensitive printing element.
14. The method according to claim 13 , wherein the blotting material is looped under and around at the least the portion of the at least one roll that is in contact with the surface of the photosensitive printing element.
15. The method according to claim 13 , wherein the blotting material is continuously fed to the at least one roll from a remote source of the blotting material.
16. The method according to claim 13 , wherein the blotting material that contains the removed non-crosslinked photopolymer is rewound onto a rewind device.
17. The method according to claim 13 , wherein the blotting material comprises paper.
18. The method according to claim 1 , wherein the non-crosslinked polymer remaining on the at least one roll after removal from the imaged surface of the photosensitive printing element is removed from the at least one roll by positioning a doctor blade adjacent to the at least one roll to wipe the non-crosslinked polymer from the surface of the at least one roll.
19. The method according to claim 1 , wherein the at least one roll comprises two rolls that are positioned adjacent and apart from each other and are each maintained in contact with the imaged surface of the photosensitive printing element and wherein the two rolls are self-centering against the imaged surface of the flexographic printing element.
20. The method according to claim 19 , wherein the blotting material is continuously fed to the two rolls by wrapping blotting material around at least the portion of the first roll that is in contact wit the imaged surface of the photosensitive printing element, looping the blotting material around one or more track rolls positioned between the two rolls, and then wrapping the blotting material around at least the portion of the second roll that is in contact with the imaged surface of the flexographic printing element.
21. The method according to claim 19 , wherein one or more additional rolls are positioned in an opposing position on an opposite side of the cylindrical photosensitive printing element and maintained in contact with at least a portion of the imaged surface of the flexographic printing element.
22. The method according to claim 1 , wherein the non-crosslinked photopolymer on the imaged and exposed surface of the photosensitive printing element is melted or softened by heating the at least one roll that contacts the imaged and exposed surface of the flexographic printing element.
23. The method according to claim 22 , further comprising a heater positioned adjacent to the imaged and exposed surface of the photosensitive printing element to provide additional melting or softening of the non-crosslinked photopolymer.
24. The method according to claim 22 , wherein the at least one heated roll is maintained at a temperature of about 350° F. to about 450° F.
25. The method according to claim 1 , wherein the non-crosslinked photopolymer on the imaged and exposed surface of the photosensitive printing element is melted or softened by positioning a heater adjacent to the imaged and exposed surface of the flexographic printing element.