Laser-ablatable mask film

1. A laser-ablatable mask film for the exposure of relief printing plates and screen printing stencils, comprising at least

(i) a dimensionally stable base sheet,

(ii) a UV-transparent adhesion layer, and

(iii) a laser-ablatable mask layer which has a thickness from 1 μm to 10 μm,

wherein the laser-ablatable mask layer (iii) comprises

a) a binder comprising a crosslinked polyvinyl alcohol,

b) a material which absorbs UV/VIS light and IR light, and

c) optionally an inorganic filler and wherein the crosslinked polyvinyl alcohol is crosslinked with 2 to 40 parts by weight of crosslinker per 100 parts by weight of polyvinyl alcohol.

2. The laser-ablatable mask film as claimed in claim 1 , wherein the polyvinyl alcohol of the binder a) is a partially hydrolyzed polyvinyl acetate having a degree of hydrolysis of 50 to 99 mol %.

3. The laser-ablatable mask film as claimed in claim 1 , wherein the polyvinyl alcohol of the binder a) is crosslinked with glyoxal or glutaraldehyde.

4. The laser-ablatable mask film as claimed in claim 1 , wherein the laser-ablatable mask layer (iii) has an optical density of >2.5.

5. The laser-ablatable mask film as claimed in claim 1 , wherein the material b) which absorbs UV/VIS light and IR light is selected from the group consisting of carbon black, graphite, carbon nanotubes, and carbon nanoparticles.

6. The laser-ablatable mask film as claimed in claim 1 , wherein the laser-ablatable mask layer (iii) comprises

a) 21 to 70 wt % of the binder comprising a crosslinked polyvinyl alcohol,

b) 5 to 70 wt % of the material which absorbs UV/VIS light and IR light, and

c) 0 to 30 wt % of the inorganic filler.

7. The laser-ablatable mask film as claimed in claim 1 , wherein the laser-ablatable mask layer (iii) comprises

c) 5 to 30 wt % of the inorganic filler.

8. The laser-ablatable mask film as claimed in claim 1 , wherein the adhesion layer (ii) comprises

d) 70 to 100 wt % of a polymeric binder,

e) 0 to 30 wt % of a crosslinker,

f) 0 to 30 wt % of an inorganic filler.

9. The laser-ablatable mask film as claimed in claim 8 , wherein the polymeric binder d) is selected from the group consisting of polyesters, polyetheresters, polyurethanes, and polyesterurethanes.

10. The laser-ablatable mask film as claimed in claim 8 , wherein the polymeric binder d) is a polymer which contains OH groups and which is crosslinked with a polyfunctional isocyanate as crosslinker e).

11. A method for producing a flexographic cliché, comprising the steps of

(i) digital imaging by laser ablation of the mask film as defined in claim 1 ,

(ii) placing or laminating the digitally imaged mask film onto a flexographic printing plate that is to be exposed,

(iii) exposing a relief-forming layer of the printing plate with UVA light through the digitally imaged mask film,

(iv) removing of the mask film,

(v) developing a relief by removal of the unpolymerized portions of the relief-forming layer with a washout medium or by thermal development,

(vi) optionally, drying of the resulting flexographic cliché,

optionally, aftertreatment of the flexographic cliché with UVA or UVC light.

12. The laser-ablatable mask film as claimed in claim 1 , wherein the laser-ablatable mask layer (iii) has a thickness from 2 μm to 6 μm.

13. The laser-ablatable mask film as claimed in claim 1 , wherein the stable base sheet (i) is a polyester film.

14. The laser-ablatable mask film as claimed in claim 1 , wherein the polyester film is a polyethylene terephthalate (PET) film.

15. The laser-ablatable mask film as claimed in claim 1 , wherein the crosslinked polyvinyl alcohol is crosslinked with 2 to 20 parts by weight of crosslinker per 100 parts by weight of polyvinyl alcohol.

16. A laser-ablatable mask film for the exposure of relief printing plates and screen printing stencils, comprising at least

(i) a dimensionally stable base sheet,

(ii) a UV-transparent adhesion layer, and

(iii) a laser-ablatable mask layer which has a thickness from 1 μm to 10 μm,

wherein the laser-ablatable mask layer (iii) comprises

a) a binder comprising a crosslinked polyvinyl alcohol,

b) a material which absorbs UV/VIS light and IR light, and

c) optionally an inorganic filler and

the adhesion layer (ii) comprises

d) 70 to 100 wt % of a polymeric binder,

e) 0 to 30 wt % of a crosslinker,

f) 0 to 30 wt % of an inorganic filler and

wherein the polymeric binder d) is a polymer which contains OH groups and which is crosslinked with a polyfunctional isocyanate as crosslinker e).

17. The laser-ablatable mask film as claimed in claim 16 , wherein the crosslinked polyvinyl alcohol is crosslinked with 2 to 40 parts by weight of crosslinker per 100 parts by weight of polyvinyl alcohol.

18. The laser-ablatable mask film as claimed in claim 16 , wherein the polyvinyl alcohol of the binder a) is a partially hydrolyzed polyvinyl acetate having a degree of hydrolysis of 50 to 99 mol %.

19. The laser-ablatable mask film as claimed in claim 16 , wherein the polyvinyl alcohol of the binder a) is crosslinked with glyoxal or glutaraldehyde.

20. The laser-ablatable mask film as claimed in claim 16 , wherein the laser-ablatable mask layer (iii) has an optical density of >2.5.

21. The laser-ablatable mask film as claimed in claim 16 , wherein the material b) which absorbs UV/VIS light and IR light is selected from the group consisting of carbon black, graphite, carbon nanotubes, and carbon nanoparticles.

22. The laser-ablatable mask film as claimed in claim 16 , wherein the laser-ablatable mask layer (iii) comprises

a) 21 to 70 wt % of the binder comprising a crosslinked polyvinyl alcohol,

b) 5 to 70 wt % of the material which absorbs UV/VIS light and IR light, and

c) 0 to 30 wt % of the inorganic filler.

23. The laser-ablatable mask film as claimed in claim 22 , wherein the laser-ablatable mask layer (iii) comprises

c) 5 to 30 wt % of the inorganic filler.

24. The laser-ablatable mask film as claimed in claim 22 , wherein the polymeric binder d) is selected from the group consisting of polyesters, polyetheresters, polyurethanes, and polyesterurethanes.

25. A method for producing a flexographic cliché, comprising the steps of

(i) digital imaging by laser ablation of the mask film as defined in claim 16 ,

(ii) placing or laminating the digitally imaged mask film onto a flexographic printing plate that is to be exposed,

(iii) exposing a relief-forming layer of the printing plate with UVA light through the digitally imaged mask film,

(iv) removing of the mask film,

(v) developing a relief by removal of the unpolymerized portions of the relief-forming layer with a washout medium or by thermal development,

(vi) optionally, drying of the resulting flexographic cliché,

optionally, aftertreatment of the flexographic cliché with UVA or UVC light.

26. The laser-ablatable mask film as claimed in claim 16 , wherein the laser-ablatable mask layer (iii) has a thickness from 2 μm to 6 μm.

27. The laser-ablatable mask film as claimed in claim 16 , wherein the stable base sheet (i) is a polyester film.

28. The laser-ablatable mask film as claimed in claim 16 , wherein the polyester film is a polyethylene terephthalate (PET) film.

29. The laser-ablatable mask film as claimed in claim 16 , wherein the crosslinked polyvinyl alcohol is crosslinked with 2 to 20 parts by weight of crosslinker per 100 parts by weight of polyvinyl alcohol.