Printing method

1. A method comprising:

applying a UV-curable ink to a substrate;

partially curing the ink by exposing the ink to UV radiation from an LED source; and

exposing the partially cured ink to UV radiation from a flash lamp, wherein said UV-curable link cures by free radical polymerization.

2. The method of claim 1 wherein the flash lamp is a xenon or krypton flash lamp.

3. The method of claim 1 wherein the LED source emits peak radiation between 250 and 450 nm.

4. The method of claim 1 wherein the UV dose provided to the ink during the partial cure step is 10 to 300 mJ/cm 2 .

5. The method of claim 1 wherein the LED source emits UV radiation at 90% or less of the maximum power output.

6. The method of claim 1 wherein the ink is an ink-jet ink that is applied to the substrate using an ink-jet printer.

7. The method of claim 1 wherein no inert environment is provided during the curing steps.

8. The method of claim 1 wherein the UV-curable ink comprises a UV-curable monomer or oligomer or a mixture thereof; a photoinitiator and a colorant.

9. The method of claim 8 wherein the UV-curable ink is an ink-jet ink.

10. The method of claim 8 wherein the ink comprises a monofunctional (meth)acrylate monomer, a multifunctional (meth)acrylate monomer or a combination thereof.

11. The method of claim 10 wherein the ink comprises 1-90% by weight of said monofunctional (meth)acrylate monomer, based on the total weight of the ink.

12. The method of claim 10 wherein the ink comprises 1-90% by weight of said multifunctional (meth)acrylate monomer, based on the total weight of the ink.

13. The method of claim 8 wherein the ink comprises an N-vinyl amide and/or an N-acryloyl amine.

14. The method of claim 13 wherein the ink comprises 3-50% by weight of said N-vinyl amide and/or said N-acryloyl amine, based on the total weight of the ink.

15. The method of claim 8 wherein the ink comprises 1-30% by weight of oligomer, based on the total weight of the ink.

16. The method of claim 8 wherein the ink comprises a monofunctional (meth)acrylate monomer, an N-vinyl amide and/or an N(meth)acryloyl amine, at least one multifunctional (meth)acrylate and a UV curable oligomer.

17. The method of claim 8 wherein the ink comprises THFA/NVC, IBOA/NVC, PEA/NVC, CTFA/NVC, IBOA/ACMO or IBOA/NVP; together with at least one multifunctional acrylate monomer.

18. The method of claim 8 wherein the ink comprises phenoxyethyl acrylate, NVC and at least one multifunctional acrylate monomer.

19. The method of claim 8 wherein the photoinitiator produces free radicals on irradiation with UV.

20. The method of claim 8 wherein the photoinitiator is selected from one or more of: 2-methyl-1[4-(methylthio)phenyl]-2-morpholinopropan-1-one (Irgacure 907), 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1 (Irgacure 369), 2-(dimethylamino)-2-[(4-methylphenyl)methyl]-1-[4-(4-morpholinyl)phenyl]-1 butanone; (Irgacure 379), isopropyl thioxanthone, diethyl thioxanthone, 2-chlorothioxanthone, bis(2,6-dimethylbenzoyl)-2,4,4-trimethylpentylphosphine oxide, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, ethyl(2,4,6-trimethylbenzoyl)-phenylphosphinate, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, camphorquinone, 1-phenyl-1,2-propanedione and 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propane-1-one (Irgacure 2959).

21. The method of claim 8 wherein the photoinitiator comprises one or more of 2-methyl-1[4-(methylthio)phenyl]-2-morpholinopropan-1-one, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1,2-(dimethylamino)-2-[(4-methylphenyl)methyl]-1-[4-(4-morpholinyl)phenyl]-1 butanone, isopropyl thioxanthone, diethyl thioxanthone or 2-chlorothioxanthone; and

one of bis(2,6-dimethylbenzoyl)-2,4,4 trimethylpentylphosphine oxide, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, ethyl(2,4,6-trimethylbenzoyl)-phenylphosphinate or 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-l-propane-l-one;

and wherein the peak in the wavelength distribution of the LED source is 365 nm.

22. The method of claim 8 wherein the photoinitiator comprises one or more of bis(2,6-dimethylbenzoyl)-2,4,4-trimethylpentylphosphine oxide, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, ethyl(2,4,6-trimethylbenzoyl)-phenylphosphinate, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide or isopropyl thioxanthone; and

1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propane-1-one;

and wherein the peak in the wavelength distribution of the LED source is 395 nm or 400 nm.

23. The method of claim 8 wherein the photoinitiator comprises one or more of bis(2,6-dimethylbenzoyl)-2,4,4-trimethylpentylphosphine oxide, camphorquinone or 1-phenyl-1,2-propanedione; and

1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propane-1-one;

and wherein the peak in the wavelength distribution of the LED source is 405 nm.

24. The method of claim 8 wherein the photoinitiator comprises bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, isopropyl thioxanthone and 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propane-l-one and the peak in the wavelength distribution of the LED source is 395 nm or 400 nm.

25. A printing apparatus comprising:

means for applying a UV-curable ink to a substrate;

an LED source that is capable of emitting UV radiation and partially curing the ink; and

a flash lamp that emits UV radiation, wherein said UV-curable link cures by free radical polymerization.

26. The printing apparatus of claim 25 wherein the flash lamp is a xenon or krypton flash lamp.

27. The printing apparatus of claim 26 wherein the flash lamp is positioned such that ink that has been applied to the substrate is exposed to UV radiation from the flash lamp after it has been exposed to UV radiation from the LED source.

28. The printing apparatus of claim 26 wherein the means for applying a UV-curable ink to a substrate is an ink-jet printer.

29. The printing apparatus of claim 28 wherein the ink-jet printer comprises a printhead and the LED source is positioned so that the LED source moves with the printhead during ink-jet printing.

30. The printing apparatus of claim 28 wherein the printhead and LED source are positioned on a printer carriage that is capable of moving across the substrate during printing.

31. The printing apparatus of claim 29 comprising one LED source that is positioned adjacent to the printhead, or two LED sources that are located on either side of the printhead.

32. The printing apparatus of claim 29 wherein the flash lamp is static and is positioned downstream of the printhead.

33. The printing apparatus of claim 26 comprising two or more flash lamps.