Processes and apparatus for producing photopolymerizable, cylindrical, continuous, seamless flexographic printing elements

1. A process comprising providing a layer composite comprising a layer of photopolymerizable material and a removable substrate film disposed on one side of the layer of photopolymerizable material, wherein the photopolymerizable material comprises an elastomeric binder, an ethylenically unsaturated monomer and a photoinitiator; and

(a) miter-cutting two edges of the layer composite to be joined, to form two miter-cut ends;

(b) providing a hollow cylinder on a rotatably mounted support cylinder, wherein the hollow cylinder has an outer surface and is in a temporarily locked position relative to the support cylinder;

(c) applying an adhesion-promoting layer to the outer surface of the hollow cylinder wherein said adhesion-promoting layer comprises a double-sided adhesive film which has two miter-cutting edges, is sized to the dimensions of the hollow cylinder and is joined at the two miter-cut edges;

(d) applying the layer composite to the hollow cylinder bearing the adhesive-promoting layer, wherein the layer composite is disposed on the hollow cylinder such that the removable substrate film faces away from the hollow cylinder and the two miter-cut ends lie substantially one on top of the other, but not overlapping;

(e) removing the substrate film from the layer of photopolymerizable material to provide an exposed surface of the layer of photopolymerizable material;

(f) contacting the exposed surface of the layer of photopolymerizable material with a rotating calender roll with heating to join the two miter-cut edges and form a processed hollow cylinder, wherein heating comprises a locally-acting heat source moved in an axial direction relative to the hollow cylinder along the entire width of the layer of photopolymerizable material such that the exposed surface is heated; and

(g) removing the processed hollow cylinder from the support cylinder.

2. The process according to claim 1 , wherein the locally-acting heat source comprises a warm gas stream.

3. The process according to claim 2 , wherein the adhesive film has a static shear strength of at least 3 h at 70° C.

4. The process according to claim 1 , wherein the adhesive film has a static shear strength of at least 3 h at 70° C.

5. The process according to claim 1 , wherein the layer composite further comprises a second removable film disposed on a surface of the layer of photopolymerizable material opposing the surface bearing the removable substrate film.

6. The process according to claim 1 , wherein the layer of photopolymerizable material is preexposed to actinic light from a side of the layer not bearing the removable substrate film.

7. The process according to claim 6 , wherein the layer is preexposed to actinic light prior to miter-cutting.

8. The process according to claim 1 , wherein the rotating calender roll is rotated such that the hollow cylinder rotates in a direction of increasing photopolymerizable material thickness at the miter-cut edge lying substantially on top of the other miter-cut edge.

9. The process according to claim 1 , wherein a temperature of the exposed surface of the layer of photopolymerizable material during contacting with the rotatable calender roll is 80 to 100° C.

10. The process according to claim 1 , wherein the support cylinder comprises an air cylinder.

11. The process according to claim 1 , further comprising applying a digitally imageable layer to the exposed surface of the layer of photopolymerizable material.

12. The process according to claim 11 , wherein the digitally imageable layer comprises at least one selected from the group consisting of IR-ablative layers, inkjet layers, thermographically inscribable layers, and combinations thereof.