Photopolymerisable layered composite for producing flexo printing elements

1. A laminate comprising

a) a photopolymerizable relief-forming layer comprising an elastomeric binder, ethylenically unsaturated monomers, a photoinitiator, and optionally further additives;

b) an elastomeric substrate layer which is optionally photopolymerizable comprising an elastomeric binder, optionally ethylenically unsaturated monomers, a photoinitiator, and optionally further additives;

wherein said photopolymerizable relief-forming layer a) has a hardness of 30 to 70° Shore A and said elastomeric substrate layer b) has a hardness of from 75° Shore A to 70° Shore D in the photopolymerized state, and wherein said elastomeric substrate layer b) has a hardness of at least 5° Shore A greater than that of said photopolymerizable relief-forming layer a), and wherein the photopolymerizable relief-forming layer a) is present on the elastomeric substrate layer b).

2. The laminate of claim 1 , wherein said laminate comprises the sequence of layers (1) to (6):

(1) a substrate film;

(2) optionally a release layer;

(3) the elastomeric substrate layer b);

(4) the photopolymerizable relief-forming layer a);

(5) optionally a release layer; and

(6) a cover sheet.

3. A hollow cylinder comprising the laminate of claim 1 .

4. A process for producing a photopolymerizable, cylindrical, continuous, seamless, flexographic printing element from a laminate comprising

a) a photopolymerizable relief-forming layer comprising an elastomeric binder, ethylenically unsaturated monomers, a photoinitiator, and optionally further additives;

b) an elastomeric substrate layer which is optionally photopolymerizable comprising an elastomeric binder, optionally ethylenically unsaturated monomers, a photoinitiator, and optionally further additives;

wherein said photopolymerizable relief-forming layer a) has a hardness of 30 to 70° Shore A and said elastomeric substrate layer b) has a hardness of from 75° Shore A to 70° Shore D in the photopolymerized state, and wherein said elastomeric substrate layer b) has a hardness of at least 50 Shore A greater than that of said photopolymerizable relief-forming layer a),

said process comprising:

(i) cutting the edges of the laminate to be joined to size by means of mitre cuts;

(ii) pushing on and locking a hollow cylinder on a rotatably mounted support cylinder;

(iii) applying an adhesion-promoting layer to the outer surface of the hollow cylinder;

(iv) mounting the laminate cut to size, with the elastomeric substrate layer b), on the hollow cylinder provided with the adhesion-promoting layer, the ends provided with the mitre cut resting substantially one on top of the other but not overlapping;

(v) optionally peeling off a cover sheet from said photopolymerizable relief-forming layer a);

(vi) joining the cut edges by bringing the surface of the photopolymerizable layer on the hollow cylinder into contact with a rotating calender roll with heating until the cut edges are joined to one another; and

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

5. The process of claim 4 , wherein the elastomeric substrate layer is photopolymerizable and preexposed to actinic light from the side facing away from the cover sheet, directly or through the substrate film, prior to (iii).

6. The process of claim 4 , wherein said adhesion-promoting layer is a double-sided adhesive tape.

7. The laminate of claim 1 , wherein the elastomeric substrate layer is photopolymerizable.