Radiation-curable ink-jet printing

1. A radiation-curable ink-jet ink set comprising only one radiation-curable ink-jet black ink and at least three radiation-curable ink-jet color inks wherein the radiation-curable ink-jet black ink includes at least one black pigment, at least one color pigment, at least one surfactant, at least one photoinitiator and at least one radiation-curable compound,

wherein the wavelength of the absorption maximum of the color pigment is located between 500 and 700 nm;

wherein the at least one radiation-curable compound is a monofunctional or polyfunctional acrylate monomer;

wherein the photoinitiator is present in an amount of 1-6 weight % of the total ink weight;

wherein the ink-jet black ink is free of a fluorinated surfactant;

wherein the ink-jet ink has a viscosity of less than 30 mPa·s at a shear rate of 100 s −1 and at 25° C.; and

wherein the radiation-curable ink-jet black ink has a chroma C* of less than 1.5.

2. The radiation-curable ink jet ink set according to claim 1 , wherein at least one of said radiation-curable ink jet inks comprises a polyether modified poly-dimethyl-siloxane.

3. The radiation-curable ink-jet ink set according to claim 1 , wherein the at least one color pigment is C.I. Pigment Blue 15:3.

4. The radiation-curable ink-jet ink set according to claim 1 , wherein the radiation-curable ink jet black ink further comprises a copolymerizable monomer having surface-active effects.

5. The radiation-curable ink-jet ink set according to claim 4 , wherein the copolymerizable monomer having surface-active effects is a silicone-modified acrylate or a silicone-modified methacrylate.

6. The radiation-curable ink jet ink set according to claim 1 , the ink set further comprising a light magenta ink and a light cyan ink.

7. The radiation-curable ink-jet ink set according to claim 1 , the ink set further comprising a white ink.

8. The radiation-curable ink-jet ink set according to claim 1 , the ink set further comprising an ink for a spot color.

9. The radiation-curable ink jet ink set according to claim 8 , wherein the spot color is orange, green, red or blue.

10. The radiation-curable ink jet ink set according to claim 1 , wherein said at least one pigment comprises a cyan pigment and a magenta pigment.

11. The radiation-curable ink jet ink set according to claim 1 , wherein said at least one radiation-curable compound is a difunctional monomer.

12. The radiation-curable ink jet ink set according to claim 1 , wherein the radiation-curable ink-jet black ink comprises a second difunctional monomer.

13. The radiation-curable ink jet ink set according to claim 1 , wherein the radiation-curable ink-jet black ink has a solvent content of less than 5 wt % based on the total weight of the radiation-curable ink-jet black ink.

14. The radiation-curable ink-jet ink set according to claim 1 , wherein the at least one photoinitiator consists of one or more photoinitiators that initiate free radical curing.

15. A process for ink-jet printing comprising the steps of:

a) providing a radiation-curable ink jet ink set comprising only one radiation-curable ink-jet black ink and at least three radiation-curable ink-jet color inks wherein the radiation-curable ink-jet black ink comprises at least one black pigment, at least one surfactant, at least one color pigment, at least one photoinitiator, and at least one radiation-curable compound,

wherein the wavelength of the absorption maximum of the color pigment is located between 500 and 700 nm,

wherein the at least one radiation-curable compound is a monofunctional or polyfunctional acrylate monomer,

wherein the ink-jet black ink is free of a fluorinated surfactant,

wherein the radiation-curable ink has a viscosity of less than 30 mPa·s at a shear rate of 100 s −1 at 25° C., and

wherein the radiation-curable ink-jet black ink has a chroma C* of less than 1.5; and

b) jetting said radiation-curable ink-jet black ink on a substantially non-absorbing ink-jet ink receiver.

16. The process for ink-jet printing according to claim 15 , further comprising the step of:

c) curing said jetted radiation-curable ink-jet black ink on said substantially non-absorbing ink-jet ink receiver with UV radiation or electron beam exposure.

17. The process for ink-jet printing according to claim 15 , wherein the areal throughput printing speed is at least 50 m 2 /hour at a resolution of at least 180 dpi.

18. The process for ink-jet printing according to claim 15 , wherein the at least one photoinitiator consists of one or more photoinitiators that initiate free radical curing.

19. A process of forming an imaged article having neutral black tone comprising the steps of:

a) providing a radiation-curable ink-jet ink set comprising only one radiation-curable ink-jet black ink and at least three radiation-curable ink-jet color inks wherein the radiation-curable ink-jet black ink comprises at least one black pigment, at least one surfactant, at least one color pigment, at least one photoinitiator, and at least one radiation-curable compound,

wherein the wavelength of the absorption maximum of the color pigment is located between 500 and 700 nm,

wherein the at least one radiation-curable compound is a monofunctional or polyfunctional acrylate monomer,

wherein the ink-jet black ink is free of a fluorinated surfactant,

wherein the radiation-curable ink has a viscosity of less than 30 mPa·s at a shear rate of 100 s −1 at 25° C.; and

wherein the radiation-curable ink-jet black ink has a chroma C* of less than 1.5;

b) jetting said radiation-curable ink jet black ink on a substantially non-absorbing ink-jet ink receiver, and

c) curing said jetted radiation-curable ink-jet black ink on said substantially non-absorbing ink-jet ink receiver with UV radiation or electron beam exposure.

20. The process of forming an imaged article having neutral black tone according to claim 19 , wherein the at least one photoinitiator consists of one or more photoinitiators that initiate free radical curing.