Laser-ablatable mask film

Abstract

The invention relates to a laser-ablatable mask film for the exposing 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, characterized in that 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.

Claims

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.

Description

EXAMPLE

(1) A PET sheet of the Melinex® OD type, 175 μm thick, was coated with an adhesion layer (primer layer). The composition of the primer layer is reproduced in table 1.

(2) TABLE-US-00001 TABLE 1 Solids fraction Component Chemistry/Function Manufacturer (wt %) Desmocoll ® 400/1 PUR/Binder Bayer 82 Desmodur ® RN Isocyanate/ Bayer 10 Crosslinker Syloid ® ED3 Silicate/Filler Degussa 8 Total 100

(3) The binder of the primer layer was dissolved in ethyl acetate. Then the filler was added and the dispersion was stirred for 2 hours. Shortly before coating, the crosslinker was added, and the solids content of the mixture was adjusted to 3 wt % by addition of ethyl acetate. The solution was applied in a metering roll application process on a coating line at a belt speed of 10 m/min. The layer was subsequently dried at 105° C. (drying tunnel length: 9 m). After drying, the coat weight was 1.2 g/m.sup.2. No free isocyanate was detectable in the layer.

(4) The PET sheet coated with the primer was subsequently top coated with the laser-ablatable mask layer. The composition of this layer is reproduced in table 2.

(5) TABLE-US-00002 TABLE 2 Chemistry/ Solids fraction Component Function Manufacturer (wt %) Alcotex ® 72.5 PVA/Binder Kuraray 65.2 Levanyl ® Schwarz Carbon black Lanxess 30.0 A-SF dispersion/IR absorber Syloid ® ED3 Silicate/Filler Degussa 2.0 Glyoxal Crosslinker BASF 2.8 Total 100

(6) To prepare the casting solution, the polyvinyl alcohol was dissolved in a mixture of water/n-propanol (3/1). Thereafter the carbon black dispersion and the filler were incorporated in portions with stirring and the mixture was run through a ball mill for 2 hours. Shortly before coating, the glyoxal was added, the solids content was adjusted to 8.2 wt % by dilution, and the pH was adjusted to 4 by addition of 7 wt % strength hydrochloric acid.

(7) The solution was applied in a metering roll application process on a coating line at a belt speed of 10 m/min. Subsequently, again, the layer was dried at 105° C. (drying tunnel length 9 m). After drying, the coat weight was 5.0+/−0.2 g/m.sup.2 (measured in each case at a distance of 10 cm over the whole coating width of 1.2 m). Glyoxal was no longer detectable in the dried layer. The coating was absolutely flawless. No pinholes or coating defects at all could be found. The optical density of the coating (again measured at a distance of 10 cm in each case over the whole coating width) was between 4.9 and 5.0.

(8) After a storage time of 2 weeks, the mask film produced was imaged on an Esko laser (CDI Spark 4835) at a resolution of 4000 dpi with a nyloflex test motive (Flint Group). The test motive included a halftone wedge with tonal values of 1% to 100% with a line width of 47 L/cm.

(9) The film was mounted onto the drum of the laser and ablated with an energy of 4.5 J/cm.sup.2. The film presented no handling problems. Even when handled without protective gloves, no prints or other damage could be found on the mask film. The solid area removed by lasering had an optical density of 0.1. The ablated elements of the mask film were all imaged with crisp edges.

(10) The ablated mask film was used to produce a flexographic printing plate (nyloflex ACE 114, Flint Group). The coversheet was removed from the printing plate. The ablated mask film was placed by the layer side onto the printing plate surface and was fixed with a vacuum sheet in a nyloflex FIII exposure unit (Flint Group). The printing plate was subsequently exposed through the mask film for 14 minutes using UVA radiation. Following exposure, the mask film was removed from the printing plate. The flexo plate was subsequently washed out by means of a commercial organic washout medium (Nylosoiv® A, Flint Group) in a nyloflex F III washout apparatus (Flint Group) in a transit time of 240 mm/min. After the washout operation, the printing plate was dried at 60° C. for 90 minutes and then aftertreated with UVA and UVC light. The cliché was examined by microscope. The half tone dots of the 1% tonal value were immaculately imaged on the cliché.

(11) Using the same mask film, 10 further flexographic printing plates were exposed and further-processed. The quality of cliché produced was identical. No deviations could be found in the dimensions of the typical test elements of a flexo cliché (1% positive half tone dot, in-between depth in the 200 μm negative dot, 50 μm positive lattice lines).