Printing ink, apparatus and method
The present invention provides an inkjet ink including at least 50% by weight of organic solvent based on the total weight of the ink, a radiation curable material, a photoinitiator and a colorant. The invention also provides an apparatus for printing the ink wherein the apparatus includes at least one printhead, a means for evaporating solvent from the printed ink and a source of actinic radiation. Furthermore, the invention provides a method of inkjet printing including i) inkjet printing the inkjet ink as defined above on to a substrate; ii) evaporating at least a portion of the solvent from the printed ink; and iii) exposing the printed ink to actinic radiation to cure the radiation curable material.
1. An inkjet ink comprising at least 50% by weight of organic solvent based on the total weight of the ink, a radiation curable material, a photoinitiator and a dispersible pigment , wherein the radiation curable material comprises a radiation curable oligomer having a viscosity of 0.5 to 20 Pa·s at 60° C., wherein the inkjet ink has a viscosity of 100 mPa·s or less, and wherein the radiation curable material is capable of polymerizing by free radical polymerisation.
2. The inkjet ink according to claim 1 wherein the organic solvent is present in an amount of at least 55% by weight based on the total weight of the ink.
3. The inkjet ink according to claim 1 wherein the solvent is selected from glycol ethers, organic carbonates, lactones or mixtures thereof; or propylene carbonate and mixtures of propylene carbonate with one or more glycol ethers; or mixtures of gamma butyrolactone with one or more glycol ethers and mixtures of gamma butyrolactone with one or more glycol ethers and propylene carbonate.
4. The inkjet ink according to claim 1 comprising less than 5% by weight of water based on the total weight of the ink.
5. The ink according to claim 1 wherein the radiation curable material is present in an amount of 2% to 45% by weight based on the total weight of the ink.
6. The ink according to claim 1 wherein the radiation curable material is present in an amount of 5% to 35% by weight based on the total weight of the ink.
7. The inkjet ink according to claim 1 wherein the radiation curable oligomer comprises a polyester, urethane, epoxy or polyether backbone.
8. The inkjet ink according to claim 7 wherein the radiation curable oligomer has a molecular weight of 500 to 4000.
9. The inkjet ink according to claim 7 wherein the radiation curable oligomer has a molecular weight of 600 to 4000.
10. The inkjet ink according to claim 1 wherein the radiation curable oligomer comprises an oligomer having (meth)acrylate groups or a mixture of two or more oligomers having (meth)acrylate groups.
11. The inkjet ink according to claim 10 wherein the radiation curable material comprises a urethane acrylate oligomer.
12. The inkjet ink according to claim 1 wherein the radiation curable material comprises 50 to 100% by weight of free radical curable monomer, based on the total weight of radiation curable material present in the ink, or wherein the radiation curable material is capable of polymerising by cationic polymerisation.
13. The inkjet ink according to claim 12 wherein the radiation curable material is selected from oxetanes, cycloaliphatic epoxides, bisphenol A epoxides, epoxy novolacs and mixtures thereof.
14. The inkjet ink according to claim 1 wherein the radiation curable material comprises a combination of free radical polymerisable and cationically polymerisable materials.
15. The inkjet ink according to claim 1 which comprises less than 20% by weight of (meth)acrylates with a molecular weight of less than 450 based on the total weight of the ink.
16. The inkjet ink according to claim 1 which comprises less than 20% by weight of (meth)acrylates with a molecular weight of less than 600 based on the total weight of the ink.
17. A substrate having printed thereon an ink obtained from the ink as claimed in claim 1 .
18. A method comprising:
i) inkjet printing the inkjet ink as defined in claim 1 on to a substrate;
ii) evaporating at least a portion of the solvent from the printed ink; and
iii) exposing the printed ink to actinic radiation to cure the radiation curable material.
19. The method according to claim 18 wherein the portion of solvent is evaporated from the printed ink before the ink is cured.
20. An inkjet printing apparatus for printing the inkjet ink of claim 1 onto a substrate comprising: a) at least one printhead, b) a source of the inkjet ink of claim 1 ; c) a means for evaporating solvent from the printed ink; and d) a source of actinic radiation, wherein the source of actinic radiation is positioned downstream from the means for evaporating solvent from the printed ink so that printed substrate is exposed to the means for evaporating solvent before it is exposed to radiation, allowing evaporation of the solvent before radiation curing of the ink.