Laminated flexographic printing sleeves and methods of making the same
View Patent ↗A method of tailoring the shape of a plurality of relief dots created in a photosensitive printing blank during a digital platemaking process is provided. The photosensitive printing blank comprises a laser ablatable mask layer disposed on at least one photocurable layer which is mountable on a printing sleeve. The method comprises the steps of (1) laser ablating the laser ablatable mask layer to create an in situ negative in the laser ablatable layer; (2) placing a barrier layer on top of the laser ablatable mask layer; (3) exposing the at least one photocurable layer to actinic radiation through the barrier layer and the in situ negative; (4) removing the barrier layer; and (5) developing the imaged and exposed photosensitive printing blank to reveal the relief image therein, the relief image comprising the plurality of relief dots. The presence of the barrier layer produces printing dots having desired geometric characteristics.
1. A method of creating a plurality of relief dots in a cylindrical photosensitive printing blank during a digital platemaking process, said cylindrical photosensitive printing blank comprising a laser ablatable mask layer disposed on at least one photocurable layer, said cylindrical photosensitive printing blank being mountable on a printing cylinder, the method comprising the steps of:
a. laser ablating the laser ablatable mask layer to create an in situ negative in the laser ablatable mask layer;
b. placing a barrier layer on top of the laser ablatable mask layer;
c. exposing the at least one photocurable layer to actinic radiation through the barrier layer and the in situ negative;
d. removing the barrier layer; and
e. developing the imaged and exposed photosensitive printing blank to reveal the relief image therein, said relief image comprising the plurality of relief dots.
2. The method according to claim 1 , wherein the barrier layer is laminated to the top of the laser ablatable mask layer.
3. The method according to claim 1 , wherein the barrier layer is shrink wrapped over the laser ablatable mask layer.
4. The method according to claim 1 , wherein the shoulder angle of the relief dots is greater than 50°.
5. The method according to claim 4 , wherein the shoulder angle of the relief dots is greater than about 70°.
6. The method according to claim 1 , wherein an edge sharpness of the relief dots is such that a ratio of radius of curvature at the intersection of the shoulder and the top surface of the dot, r e , to the width of the top of the dot, p, is less than 5%.
7. The method according to claim 6 , wherein an edge sharpness of the relief dots is such that the ratio of radius of curvature at the intersection of the shoulder and the top surface of the dot, r e , to the width of the top of the dot, p, is less than 2%.
8. The method according to claim 1 , wherein the barrier layer is an oxygen barrier membrane.
9. The method according to claim 8 , wherein the oxygen barrier membrane comprises a material selected from the group consisting of polyamides, polyvinyl alcohol, hydroxyalkyl cellulose, polyvinyl pyrrolidone, copolymers of ethylene and vinyl acetate, amphoteric interpolymers, cellulose acetate butyrate, alkyl cellulose, butyral, cyclic rubbers, and combinations of one or more of the foregoing.
10. The method according to claim 8 , wherein the oxygen barrier membrane comprises a film that is optically transparent to the actinic radiation used to expose the at least one photocurable layer, said film selected from the group consisting of polypropylene, polyethylene, polyvinyl chloride, polyester and combinations of one or more of the foregoing.
11. The method according to claim 10 , where the oxygen barrier membrane comprises a polypropylene film or a polyethylene terephthalate film.
12. The method according to claim 1 , wherein the barrier layer is a liquid layer that is optically transparent to the actinic radiation used to expose the at least one photocurable layer.
13. The method according to claim 12 , wherein the liquid layer comprises a paraffinic or naphthenic hydrocarbon oil, silicone oil or a vegetable-based oil.
14. The method according to claim 1 , wherein the cylindrical photosensitive printing blank is seamless.
15. The method according to claim 14 , wherein the cylindrical photosensitive printing blank is subjected to a blanket pre-curing through the front to establish a floor layer.
16. The method according to claim 1 , wherein step (e) comprises thermal development.
17. The method according to claim 1 , wherein the cylindrical photosensitive printing blank comprises a photopolymer printing blank wrapped around a printing sleeve.