Method of Improving Print Performance in Flexographic Printing Plates
A method of making a relief image printing element from a photosensitive printing blank is provided. A photosensitive printing blank with a laser ablatable layer disposed on at least one photocurable layer is ablated with a laser to create an in situ mask. The printing blank is then exposed to at least one source of actinic radiation through the in situ mask to selectively cross link and cure portions of the photocurable layer. Diffusion of air into the at least one photocurable layer is limited during the exposing step and preferably at least one of the type, power and incident angle of illumination of the at least one source of actinic radiation is altered during the exposure step. The resulting relief image comprises a plurality of dots and a dot shape of the plurality of dots that provide optimal print performance on various substrates, including corrugated board.
1 . A flexographic relief image printing element comprising a plurality of dots in relief, and wherein said plurality of dots comprise at least one characteristic selected from the group consisting of:
a) a planarity of a top surface of the dot is such that the radius of curvature of the top surface of the dot, r t , is greater than the total thickness of the photopolymer layer;
b) a shoulder angle of the dot is such that either (i) the overall shoulder angle of the dot is greater than 50° or (ii) θ 1 is greater than 70° and θ 2 is less than 45°; and
c) an edge sharpness of the dots is such that the ratio of r e :p is less than 5%.
2 . The flexographic relief image printing element according to claim 1 , wherein shoulder angle of the dot is such that the overall shoulder angle is greater than about 50°.
3 . The flexographic relief image printing element according to claim 2 , wherein the shoulder angle of the dot is such that overall shoulder angle is greater than about 70°.
4 . The flexographic relief image printing element according to claim 1 , wherein the shoulder angle of the dot is such that θ 1 is greater than 70° and θ 2 is less than 45.
5 . The flexographic relief image printing element according to claim 1 , wherein the ratio of r e :p is less than 2%.
6 . The flexographic relief image printing element according to claim 1 wherein a dot relief of the printing element is greater than about 9% of the overall plate relief.
7 . The flexographic relief image printing element according to claim 6 , wherein the dot relief of the printing element is greater than about 12% of the overall plate relief.
8 . A plurality of relief dots created in a relief image printing element and forming a relief pattern, wherein said plurality of relief dots are created during a digital platemaking process, and
wherein said plurality of relief dots comprise at least one geometric characteristic selected from the group consisting of:
(a) a planarity of a top surface of the relief dots, measured as the radius of curvature of the top surface of the dot, r t , is greater than the total thickness of the photopolymer layer;
(b) a shoulder angle of the relief dots is such that (i) the overall shoulder angle is greater than 50°, or (ii) θ 1 is greater than 70° and θ 2 is less than 45°;
(c) a depth of relief between the relief dots, measured as a percentage of the overall plate relief, is greater than about 9%; and
(d) an edge sharpness of the relief dots, is such that the ratio of r e :p is less than 5%.
9 . The plurality of relief dots according to claim 8 , wherein said planarity of the top surface of the relief dots is such that the radius of curvature of the top surface of the dot, r t , is greater than the total thickness of the photopolymer layer.
10 . The plurality of relief dots according to claim 8 , wherein said shoulder angle of the relief dots is such that the overall shoulder angle is greater than 50°.
11 . The plurality of relief dots according to claim 10 , wherein the shoulder angle of the relief dots is such that the overall shoulder angle is greater than about 70°.
12 . The plurality of relief dots according to claim 8 , wherein the shoulder angle of the relief dots is such that θ 1 is greater than 70° and θ 2 is less than 45°.
13 . The plurality of relief dots according to claim 8 , wherein the depth of relief between the relief dots is greater than about 12% of the overall plate relief.
14 . The plurality of relief dots according to claim 8 wherein the edge sharpness of the relief dots is such that the ratio of r e :p is less than about 2 percent.
15 . The plurality of relief dots according to claim 8 , wherein said plurality of relief dots comprise the following geometric characteristics:
a) a planar top surface, such that the radius of curvature of the top surface to the dot, r t , is greater than the total thickness of the photopolymer layer;
b) an overall shoulder angle of the relief dots is greater than 50°;
c) a depth of relief between dots, measured as a percentage of the overall plate relief, is greater than about 9%; and
d) a ratio of r e :p is less than about 5%.
16 . The plurality of relief dots according to claim 8 , wherein said plurality of relief dots comprise the following geometric characteristics:
a) a planar top surface, such that the radius of curvature of the top surface to the dot, r t , is greater than the total thickness of the photopolymer layer;
b) a shoulder angle of the relief dots is such that θ 1 is greater than 70° and θ 2 is less than 45°;
c) a depth of relief between dots, measured as a percentage of the overall plate relief is greater than about 9%; and
d) a ratio of r e :p is less than about 5%.