Method for producing laser-engravable flexographic printing elements on flexible metallic supports

1. A process for the production of laser-engravable flexographic printing elements, at least comprising a flexible metallic support and a crosslinked elastomeric layer which comprises at least one absorber for laser radiation, which comprises the following steps:

(a) preparation of a thermally crosslinked mixture by intimate mixing of at least one elastomeric binder, 0.5 to 20% by weight of at least one absorber for laser radiation and at least one polymerization initiator whose 10 h-t 1/2 10 hour half-life temperature is at least 60° C., in a suitable solvent,

(b) application of the mixture to a temporary support,

(c) evaporation of the solvent at a temperature T 1 ,

(d) lamination of the dried layer by means of the side facing away from the support onto a flexible metallic support,

(e) optionally removal of the temporary support, and

(f) thermal crosslinking of the polymerizable layer by warming to a temperature T 2 where T 2 is at least 80° C. and T 2 is greater than T 1 , the thickness of the crosslinked elastomeric layer being from 0.5 to 5 mm.

2. A process as claimed in claim 1 , wherein the thermally crosslinkable mixture furthermore comprises at least one ethylenically unsaturated monomer.

3. A process as claimed in claim 1 , wherein the thermally crosslinkable, mixture comprises further additives and auxiliaries.

4. A process as claimed in claim 1 , wherein the flexible, metallic support is a support made from aluminum, steel or magnetizable spring steel.

5. A process as claimed in claim 1 , wherein the flexible metallic support is provided with an adhesive layer.

6. A process as claimed in claim 1 , wherein the amount of the absorber for laser radiation is from 0.5 to 10% by weight, based on the amount of all constituents of the crosslinked, elastomeric layer.

7. A process as claimed in claim 1 , wherein the absorber for laser radiation is carbon black and/or an iron-containing, inorganic solid.

8. A process for the production of flexographic printing plates, which comprises engraving a relief into a laser-engravable flexographic printing element produced by a process as claimed in claim 1 , by means of a laser.

9. A flexographic printing plate produced by a process as claimed in claim 8 .

10. The process of claim 1 wherein the metallic support is made from magnetizable spring steel.

11. The process of claim 1 , wherein from 1-10% by weight of the polymerization initiator is used.

12. A process for the production of laser-engravable flexographic printing elements, at least comprising a flexible metallic support and a crosslinked elastomeric layer which comprises at least one absorber for laser radiation, which comprises the following steps:

(a) preparation of a thermally crosslinkable mixture by intimate mixing of at least one elastomeric binder, 0.5 to 20% by weight of at least one absorber for laser radiation and at least one polymerization initiator whose 10 h-t 1/2 10 hour half-life temperature is at least 60° C., in a suitable solvent,

(b) application of the mixture to a flexible, metallic support,

(c) evaporation of the solvent at a temperature T 1 ,

(d) thermal crosslinking of the dried, polymerizable layer by warming to a temperature T 2 , where T 2 is at least 80° C. and T 2 is greater than T 1 , the thickness of the crosslinked elastomeric layer being from 0.5 to 7 mm.

13. A process as claimed in claim 12 , wherein the thermally crosslinkable mixture furthermore comprises at least one ethylenically unsaturated monomer.

14. A process as claimed in claim 12 , wherein the thermally crosslinkable mixture comprises further additives and auxiliaries.

15. A process as claimed in claim 12 , wherein the flexible, metallic support is a support made from aluminum, steel or magnetizable spring steel.

16. A process as claimed in claim 12 , wherein the flexible, metallic support is provided with an adhesive layer.

17. A process as claimed in claim 12 , wherein the amount of the absorber for laser radiation is from 0.5 to 10% by weight, based on the amount of all constituents of the crosslinked, elastomeric layer.

18. A process as claimed in claim 12 , wherein the absorber for laser radiation is carbon black and/or an iron-containing, inorganic solid.

19. A process for the production of flexographic printing plates, which comprises engraving a relief into a laser-engravable flexographic printing element produced by a process as claimed in claim 12 , by means of a laser.

20. A flexographic printing plate produced by a process as claimed in claim 19 .

21. The process of claim 12 , wherein the metallic support is made from magnetizable spring steel.

22. The process of claim 12 , wherein from 1-10% by weight of the polymerization initiator is used.