Laser-engravable pad printing plate

1. A laser-engravable pad printing plate comprising:

(a) a metal support,

(b) an adhesion layer,

(c) a laser-engravable recording layer having a layer thickness of 20 μm to 200 μm obtained from a mixture comprising

(c1) 40 to 95 wt % of a polyvinyl alcohol,

(c2) 5 to 50 wt % of an IR absorber,

(c3) 0 to 30 wt % of an inorganic filler,

(c4) 0.1 to 20 wt % of a crosslinker, and

(c5) 0 to 10 wt % of further additives,

(d) a cover film,

wherein the crosslinker (c4) is selected from the group consisting of polyfunctional isocyanates, mono- or polyfunctional aldehydes, polyfunctional epoxides, polyfunctional carboxylic acids and polyfunctional carboxylic anhydrides; and

wherein the laser-engravable recording layer is obtained in a process comprising chemically crosslinking the crosslinker with the polyvinyl alcohol.

2. The laser-engravable pad printing plate as claimed in claim 1 , wherein the laser-engravable recording layer (c) comprises as polyvinyl alcohol (c1) a partially hydrolyzed polyvinyl alcohol ester having a degree of hydrolysis of 50 to 98 mol %.

3. The laser-engravable pad printing plate as claimed in claim 1 , wherein the recording layer (c) comprises as IR absorber (c2) carbon black, graphite or carbon nanoparticles.

4. The laser-engravable pad printing plate as claimed in claim 1 , wherein the recording layer (c) comprises 5 to 30 wt % of an inorganic filler.

5. The laser-engravable pad printing plate as claimed in claim 1 , wherein the recording layer (c) comprises an inorganic filler (c3) having a hardness of >4 Mohs.

6. The laser-engravable pad printing plate as claimed in claim 1 , wherein the recording layer (c) comprises as inorganic filler (c3) a finely ground quartz whose surface has been modified with silanes.

7. The laser-engravable pad printing plate as claimed in claim 1 , wherein the sum total of IR absorber (c2) and inorganic filler (c3) in the recording layer is <50 wt %.

8. The laser-engravable pad printing plate as claimed in claim 7 , wherein the crosslinker is glyoxal or glutaraldehyde.

9. The laser-engravable pad printing plate as claimed in claim 1 , wherein the adhesion layer is a 2-component polyurethane adhesion varnish.

10. The laser-engravable pad printing plate as claimed in claim 1 , wherein the metal support (a) is a steel plate having a thickness of 50 to 300 μm.

11. The laser-engravable pad printing plate as claimed in claim 1 , wherein the cover film is a PET film having a mean roughness depth Rz of 0.3 to 3 μm.

12. A method for producing a pad printing plate comprising:

(a) a metal support,

(b) an adhesion layer,

(c) a laser-engravable recording layer having a layer thickness of 20 μm to 200 μm,

(d) a PET cover film,

wherein the laser-engravable recording layer (c) is made from a mixture which comprises

(c1) 40 to 95 wt % of a polyvinyl alcohol,

(c2) 5 to 50 wt % of an IR absorber,

(c3) 0 to 30 wt % of an inorganic filler,

(c4) 0.1 to 20 wt % of a crosslinker, and

(c5) 0 to 10 wt % of further additives,

wherein the laser-engravable recording layer is obtained by a process comprising chemically crosslinking the crosslinker with the polyvinyl alcohol;

the method comprising steps (i) to (iii):

(i) coating the metal support with the adhesion layer,

(ii) applying the laser-engravable recording layer to the PET cover film and drying the recording layer in one or more steps,

(iii) laminating the coated PET cover film onto the metal support coated with the adhesion layer;

wherein the crosslinker (c4) is selected from the group consisting of polyfunctional isocyanates, mono- or polyfunctional aldehydes, polyfunctional epoxides, polyfunctional carboxylic acids and polyfunctional carboxylic anhydrides.

13. A method for producing a pad printing cliché from a laser-engravable pad printing plate as defined in claim 12 , further comprising steps (iv) to (vi):

(iv) removing the PET cover film from the pad printing plate,

(v) engraving the depressions into the laser-engravable recording layer by means of an IR laser,

(vi) cleaning the laser-engraved pad printing cliché by rinsing with a solvent.

14. A method for printing a substrate by the pad printing process with a pad printing cliché obtainable by the method of claim 13 , further comprising steps (vii) to (x):

(vii) fastening the pad printing cliché in the pad printing machine,

(viii) inking the pad printing cliché with a solvent-based pad printing ink,

(ix) stripping off the excess printing ink by means of a doctor blade,

(x) transferring the printing ink by means of a rubber pad onto the substrate to be printed.

15. A laser-engravable pad printing plate comprising:

(e) a metal support,

(f) an adhesion layer,

(g) a laser-engravable recording layer having a layer thickness of 20 μm to 200 μm obtained from a mixture comprising

(c6) 40 to 95 wt % of a polyvinyl alcohol,

(c7) 5 to 50 wt % of an IR absorber,

(c8) 0 to 30 wt % of an inorganic filler,

(c9) 0.1 to 20 wt % of a crosslinker, and

(c10) 0 to 10 wt % of further additives,

(h) a cover film,

wherein the crosslinker (c4) is selected from the group consisting of mono- or polyfunctional aldehydes, polyfunctional epoxides, and polyfunctional carboxylic anhydrides;

wherein the laser-engravable recording layer is obtained by a process comprising chemically crosslinking the crosslinker with the polyvinyl alcohol.