Photo-curable ink jet ink set and ink jet recording method using the same

1. An ink jet recording method using a photo-curable ink jet ink set comprising a first photo-curable ink jet ink and a second photo-curable ink jet ink, the method comprising:

ejecting the first photo-curable ink jet ink onto a recording medium, the first photo-curable ink jet ink comprising a white ink;

ejecting the second photo-curable ink jet ink onto the first photo-curable ink jet ink ejected onto the recording medium, wherein the second photo-curable ink jet ink comprises a non-white, color ink; and

curing the first photo-curable ink jet ink and the second photo-curable ink jet ink; the curing being conducted using a UV-LED having an emission peak at a wavelength in the range of 350 to 420 nm;

wherein the first photo-curable ink jet ink has a surface tension and contains a (meth) acrylic acid ester having a vinyl ether group expressed by general formula (I): CH 2 ═CR 1 —COOR 2 —O—CH═CH—R 3 , wherein R 1 represents a hydrogen atom or a methyl group, R 2 represents a divalent organic residue having a carbon number of 2 to 20, and R 3 represents a hydrogen atom or a monovalent organic residue having a carbon number of 1 to 11; and the second photo-curable ink jet ink has a surface tension,

wherein the surface tension of the first photo-curable ink jet ink is higher than the surface tension of the second photo-curable ink jet ink.

2. The ink jet recording method of claim 1 , wherein the first photo-curable ink jet ink and the second photo-curable ink jet ink contain a photopolymerization initiator comprising acylphosphine oxide compound.

3. The ink jet recording method of claim 1 , wherein a total content of a photopolymerization initiator in the first photo-curable ink jet ink and a photopolymerization initiator in the second photo-curable ink jet ink is 3% to 20% by mass relative to the total mass of the ink jet ink.

4. The ink jet recording method of claim 1 , wherein the first photo-curable ink jet ink and the second photo-curable ink jet ink contain a photopolymerization initiator comprising bis (2,4,6-trimethylbenzoyl)phenylphosphine oxide.

5. The ink jet recording method of claim 1 , wherein the surface tension of the first photo-curable ink jet ink is in the range of 20 to 40 mN/m and the surface tension of the second photo-curable ink jet ink in the range of 20 to 40 mN/m.

6. The ink jet recording method of claim 1 , wherein the first photo-curable ink jet ink further comprises a monofunctional (meth) acrylate other than the (meth) acrylic acid ester having a vinyl ether group as a polymerizable compound.

7. The ink jet recording method of claim 6 , wherein a content of the monofunctional (meth) acrylate is from 10% to 90% by mass relative to the total mass of the ink.

8. The ink jet recording method of claim 1 , wherein the first photo-curable ink jet ink further comprises a bifunctional or trifunctional or more (meth) acrylate.

9. The ink jet recording method of claim 1 , wherein a viscosity of the first photo-curable ink jet ink and a viscosity of the second photo-curable ink jet ink are 15 mPa·s or less at the ejecting.

10. The ink jet recording method of claim 1 , wherein the recording medium is transported to a position opposing a first head unit, the first head unit ejects the first photo-curable ink to the recording medium, the recording medium is transported to a portion opposing a second head unit, and the second head unit ejects the second photo-curable ink to the recording medium.

11. The ink jet recording method of claim 1 , wherein a difference in surface tension between the first photo-curable ink jet ink and the second photo-curable ink jet ink is 5 mN/m or more.

12. The ink jet recording method of claim 1 , wherein a content of the (meth) acrylic acid ester expressed by general formula (I) in the first photo-curable ink jet ink is 20% to 80% by mass relative to the total mass of the first photo-curable ink jet ink.

13. The ink jet recording method of claim 1 , wherein the second photo-curable ink jet ink contains a (meth) acrylic acid ester having a vinyl ether group expressed by general formula (I) in a lower content than the content of the (meth) acrylic acid ester in the first photo-curable ink jet ink.

14. The ink jet recording method of claim 1 , wherein the first photo-curable ink jet ink contains an acrylic surfactant.

15. The ink jet recording method of claim 1 , wherein the second photo-curable ink jet ink contains a silicone surfactant.

16. The ink jet recording method of claim 1 , wherein the second photo-curable ink jet ink is a nonwhite ink containing a nonwhite coloring material.

17. The ink jet recording method of claim 1 , wherein the second photo-curable ink jet ink contains a coloring material in a range from 0.5 to 20% by mass relative to the total mass of second ink jet ink.

18. The ink jet recording method of claim 5 , wherein the second photo-curable ink jet ink contains at least one of an organic pigment or an inorganic pigment as the coloring material.