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 first photo-curable ink jet ink and second photo-curable ink jet ink, the method comprising:

ejecting first photo-curable ink jet ink onto a recording medium; and

ejecting second photo-curable ink jet ink onto the first photo-curable ink jet ink ejected onto the recording medium;

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, and

the first photo-curable ink jet ink and the second photo-curable ink jet ink each contain a coloring material.

2. The ink jet recording method of claim 1 , wherein the surface tension of the second photo-curable ink jet ink is in the range of 20 to 30 mN/m, and the surface tension of the first photo-curable ink jet ink is in the range of 25 to 40 mN/m.

3. The ink jet recording method of claim 1 , wherein the first photo-curable ink jet ink contains at least one of a pigment as the color material, the pigment having average particle size is from 50 to 300 nm.

4. 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.

5. The ink jet recording method of claim 1 , further comprising:

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.

6. 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.

7. The ink jet recording method of claim 1 , wherein the first photo-curable ink jet ink is a white ink containing a white coloring material or a metallic ink, and the second photo-curable ink jet ink is a nonwhite ink containing a nonwhite coloring material.

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

9. The ink jet recording method of claim 1 , wherein the second photo-curable ink jet ink contains at least one of an organic pigment or an inorganic pigment as the coloring material.

10. 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.

11. The ink jet recording method of claim 1 , wherein the content of the (meth) acrylic acid ester 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.

12. 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.

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

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