Printing ink

1. A radiation-curable ink-jet ink substantially free of water and volatile organic solvents, having a viscosity of 30 mPas or less at 25° C., the ink comprising:

at least two monofunctional (meth)acrylate monomers which comprise 10 to 25 wt% of a cyclic monofunctional (meth)acrylate monomer and 5 to 15 wt% of 2-(2-ethoxyethoxy)ethyl acrylate;

16 to 25 wt% of a monofunctional monomer selected from an N-vinyl amide, an N-acryloyl amine or a mixture thereof;

5 to 15 wt% of a multifunctional (meth)acrylate monomer;

5 to 35 wt% a polymerisable (meth)acrylate oligomer;

a radical photoinitiator; and

a colouring agent, wherein the percentages by weight are based on the total weight of the ink.

2. An ink-jet ink as claimed in claim 1 , wherein the total amount of the at least two monofunctional (meth)acrylate monomers and the at least one monofunctional monomer selected from an N-vinyl amide, an N-acryloyl amine or a mixture thereof is at least 25 wt% based on the total weight of the ink.

3. An ink-jet as claimed in claim 2 , wherein the cyclic monofunctional (meth)acrylate monomer is selected from phenoxyethyl acrylate (PEA), cyclic trimethylolpropane formal acrylate (CTFA), isobornyl acrylate (IBOA), tetrahydrofurfuryl acrylate (THFA) and mixtures thereof.

4. An ink-jet ink as claimed in 2 wherein the monomer selected from an N-vinyl amide, an N-acryloyl amine or a mixture thereof, is selected from N-vinyl caprolactam (NVC), N-vinyl pyrrblidone (NVP), N-acryloylmorpholine (ACMO) and mixtures thereof.

5. An ink-jet ink as claimed in claim 1 , wherein the cyclic monofunctional (meth)acrylate monomer is selected from phenoxyethyl acrylate (PEA), cyclic trimethylolpropane formal acrylate (CTFA), isobornyl acrylate (IBOA), tetrahydrofurfuryl acrylate (THFA) and mixtures thereof.

6. An ink-jet as claimed in claim 5 , wherein the monomer selected from an N-vinyl amide, an N-acryloyl amine or a mixture thereof, is selected from N- vinyl caprolactam (NVC), N-vinyl pyrrolidone (NVP), N-acryloylmorpholine (ACMO) and mixtures thereof.

7. An ink-jet ink as claimed in claim 5 , wherein the cyclic monofunctional (meth) acrylate monomer is phenoxyethyl acrylate (PEA).

8. An ink-jet ink as claimed in claim 1 , wherein the monomer selected from an N-vinyl amide, an N-acryloyl amine or a mixture thereof, is selected from N- vinyl caprolactam (NVC), N-vinyl pyrrolidone (NVP), N-acryloylomorpholine (ACMO) and mixtures thereof.

9. An ink-jet ink as claimed in claim 1 , wherein the multifunctional (meth)acrylate monomer is a difunctional monomer.

10. An ink-jet ink as claimed in claim 1 , wherein the polymerisable (meth)acrylate oligomer is has a molecular weight from 450 to 4,000.

11. An ink-jet ink as claimed in claim 1 , wherein the polymerisable (meth)acrylate oligomer has a degree of functionality from 2 to 6.

12. An ink-jet ink as claimed in claim 1 , wherein the ink is substantially free of acyclic-hydrocarbon monofunctional (meth)acrylate monomer.

13. A method of reel-to-reel ink-jet printing, comprising printing the ink-jet ink as claimed in claim 1 on to a substrate and curing the ink as the substrate is caused to move from a substrate reel to a receiving reel.

14. A method as claimed in claim 13 wherein the substrate is a polyolefin substrate.

15. A method of ink-jet printing, comprising providing an ink-jet printer with a plurality of substrates, printing the ink-jet ink as claimed in claim 1 on to a plurality of the substrates, curing the ink on each of the substrates to produce printed substrates, and stacking the printed substrates.

16. An method as claimed in claim 15 , wherein the printer contains a substrate-storage facility having a plurality of substrates held therein.

17. A method as claimed in claim 15 , wherein the printer is a flat-bed ink-jet printer.

18. A substrate having the ink-jet ink as claimed in claim 1 printed thereon.

19. A substrate as claimed in claim 18 , wherein the substrate is a polyolefin substrate.

20. A radiation-curable ink-jet ink substantially free of water and volatile organic solvents, having a viscosity of 30 mPas or less at 25° C., the ink comprising:

at least two monofunctional (meth)acrylate monomers which comprise 10 to 25 wt% of a cyclic monofunctional (meth)acrylate monomer selected from phenoxyethyl acrylate (PEA), cyclic trimethylolpropane formal acrylate (CTFA),tetrahydrofurfuryl acrylate (THFA) and mixtures thereof and 5 to 15 wt% of 2-(2-ethoxyethoxy)ethyl acrylate;

10 to 25 wt% of a monofunctional monomer selected from an N-vinyl amide, an N-acryloyl amine or a mixture thereof;

5 to 15 wt% of a multifunctional (meth)acrylate monomer;

5 to 35 wt% a polymerisable (meth)acrylate oligomer;

a radical photoinitiator; and

a coloring agent, wherein the percentages by weight are based on the total weight of the ink.

21. An ink-jet ink as claimed in claim 20 , wherein the total amount of the at least two monofunctional (meth)acrylate monomers and the at least one monofunctional monomer selected from an N-vinyl amide, an N-acryloyl amine or a mixture thereof is at least 25 wt% based on the total weight of the ink.

22. An ink-jet ink as claimed in claim 20 , wherein the monomer selected from an N-vinyl amide, an N-acryloyl amine or a mixture thereof, is selected from N- vinyl caprolactam (NVC), N-vinyl pyrrolidone (NVP), N-acryloylomorpholine (ACMO) and mixtures thereof.

23. An ink-jet ink as claimed in claim 21 wherein the monomer selected from an N-vinyl amide, an N-acryloyl amine or a mixture thereof, is selected from N- vinyl caprolactam (NVC), N-vinyl pyrrolidone (NVP), N-acryloylmorpholine (ACMO) and mixtures thereof.

24. An ink-jet ink as claimed in claim 20 , wherein the multifunctional (meth)acrylate monomer is a difunctional monomer.

25. An ink-jet ink as claimed in claim 20 , wherein the polymerisable (meth)acrylate oligomer is has a molecular weight from 450 to 4,000.

26. An ink-jet ink as claimed in claim 20 , wherein the polymerisable (meth)acrylate oligomer has a degree of functionality from 2 to 6.

27. An ink-jet ink as claimed in claim 20 , wherein the ink is substantially free of acyclic-hydrocarbon monofunctional (meth)acrylate monomer.

28. A radiation-curable ink-jet ink substantially free of water and volatile organic solvents, having a viscosity of 30 mPas or less at 25° C., the ink comprising:

at least two monofunctional (meth)acrylate monomers which comprise about 17 wt% of a phenoxyethyl acrylate (PEA), and about 10 wt% of 2-(2-ethoxyethoxy)ethyl acrylate;

about 16 wt% of an N-vinyl caprolactam (NVC);

about 10% wt% of dipropylene glycol diacrylate DPGDA;

about 29 wt% a polymerisable (meth)acrylate oligomer;

a radical photoinitiator; and

a coloring agent, wherein the percentages by weight are based on the total weight of the ink.

29. A method of reel-to-reel ink-jet printing, comprising printing the ink-jet ink as claimed in claim 20 onto a substrate and curing the ink as the substrate is caused to move from a substrate reel to a receiving reel.

30. A method as claimed in claim 29 wherein the substrate is a polyolefin substrate.

31. A method of ink-jet printing, comprising providing an ink-jet printer with a plurality of substrates, printing the ink-jet in as claimed in claim 20 onto a plurality of substrates, curing the ink on each of the substrates to produce printed substrates and stacking the printed substrates.

32. A method as claimed in claim 31 , wherein the printer contains a substrate-storage facility having a plurality of substrates held therein.

33. A method as claimed in claim 31 , wherein the printer is a flat-bed ink-jet printer.

34. A substrate having the ink-jet ink as claimed in claim 20 printed thereon.

35. A substrate as claimed in claim 34 , wherein the substrate is a polyolefin substrate.