Ink set for forming multiple layers, ink jet recording method, and printed material

1. An ink set for forming multiple layers comprising:

a colored ink composition comprising a yellow ink composition, a magenta ink composition, a cyan ink composition, and a black ink composition, and a white ink composition,

each ink composition comprising

(Component A) a radically polymerizable compound and

(Component B) a radical polymerization initiator,

Component A above comprising

(Component A-1) an N-vinyl compound and

(Component A-2) a compound represented by Formula (a-2) below, and

when the content of the radical polymerization initiator in the white ink composition is X and the content of the radical polymerization initiator in the magenta ink composition is Y, Expression (1) below being satisfied

wherein R 1 , R 2 , and R 3 independently denote a hydrogen atom, a methyl group, or an ethyl group, and X 2 denotes a single bond or a divalent linking group

0.1

≤

Y

X

<

1.

(

1

)

2. The ink set for forming multiple layers according to claim 1 , wherein when the content of the radical polymerization initiator in the white ink composition is X and the content of the radical polymerization initiator in the magenta ink composition is Y, Expression (2) below is satisfied

0.3

≤

Y

X

<

1.

(

2

)

3. The ink set for forming multiple layers according to claim 1 , wherein Component A above further comprises (Component A-3) trimethylolpropane triacrylate.

4. The ink set for forming multiple layers according to claim 1 , wherein Component A-1 above is an N-vinyllactam.

5. The ink set for forming multiple layers according to claim 1 , wherein Component A-1 above comprises N-vinylcaprolactam.

6. The ink set for forming multiple layers according to claim 1 , wherein the content of the radical polymerization initiator in the magenta ink composition is at least 3 wt % but less than 12 wt %, and the content of the radical polymerization initiator in the white ink composition is at least 12 wt % but no greater than 20 wt %.

7. The ink set for forming multiple layers according to claim 1 , wherein Component A above comprises a monofunctional radically polymerizable compound in an amount of at least 50 wt % but no greater than 90 wt % relative to the total amount of Component A.

8. The ink set for forming multiple layers according to claim 1 , wherein the magenta ink composition comprises as Component B a bisacylphosphine oxide compound and/or a monoacylphosphine oxide compound, and the white ink composition comprises as Component B a monoacylphosphine oxide compound.

9. The ink set for forming multiple layers according to claim 1 , wherein all the ink compositions have a surface tension of 32 to 40 mN/m.

10. The ink set for forming multiple layers according to claim 2 , wherein Component A above further comprises (Component A-3) trimethylolpropane triacrylate.

11. The ink set for forming multiple layers according to claim 10 , wherein Component A-1 above comprises N-vinylcaprolactam.

12. The ink set for forming multiple layers according to claim 11 , wherein the content of the radical polymerization initiator in the magenta ink composition is at least 3 wt % but less than 12 wt %, and the content of the radical polymerization initiator in the white ink composition is at least 12 wt % but no greater than 20 wt %.

13. The ink set for forming multiple layers according to claim 11 , wherein Component A above comprises a monofunctional radically polymerizable compound in an amount of at least 50 wt % but no greater than 90 wt % relative to the total amount of Component A.

14. The ink set for forming multiple layers according to claim 11 , wherein the magenta ink composition comprises as Component B a bisacylphosphine oxide compound and/or a monoacylphosphine oxide compound, and the white ink composition comprises as Component B a monoacylphosphine oxide compound.

15. An ink jet recording method employing the ink set for forming multiple layers according to claim 1 , the method comprising:

an image formation step of carrying out image formation by discharging the colored ink composition, and

a white ink layer application step of applying the white ink composition to thus form a white ink layer.

16. The ink jet recording method according to claim 15 , wherein the method comprises in sequence

an image formation step of carrying out image formation by discharging the colored ink composition onto a recording medium, and

a white ink layer application step of applying the white ink composition onto the image that is formed to thus form a white ink layer.

17. The ink jet recording method according to claim 15 , wherein the method comprises in sequence

a white ink layer application step of applying the white ink composition onto a recording medium to thus form a white ink layer, and

an image formation step of carrying out image formation by applying the colored ink composition onto the white ink layer.

18. The ink jet recording method according to claim 15 , wherein the method comprises

a scanning step of reciprocatingly moving in a first direction relative to a recording medium an ink jet head comprising a plurality of nozzle arrays comprising a first nozzle array having a plurality of nozzles arranged for discharging the colored ink composition and a second nozzle array having a plurality of nozzles arranged for discharging the white ink composition,

a relative movement step of moving the recording medium relative to the ink jet head in a second direction that is not parallel to the first direction,

a discharge control step of dividing the nozzle array into a plurality of regions in the second direction and controlling ink discharge of the ink jet head for each of the divided nozzle region, and

an actinic radiation irradiation step of carrying out irradiation with actinic radiation of ink that has been discharged from the ink jet head in the discharge control step and is attached to the recording medium,

the actinic radiation irradiation step being a step of carrying out said irradiation with actinic radiation by dividing an area that is to be irradiated with actinic radiation into a plurality of regions corresponding to the divided nozzle regions, and controlling the amount of light for each of the divided irradiation regions individually for each region.

19. The ink jet recording method according to claim 18 , wherein the nozzles for discharging the colored ink composition have a minimum droplet volume of at least 5 pL but less than 20 pL, and the nozzles for discharging the white ink composition have a minimum droplet volume of at least 20 pL but no greater than 60 pL.

20. A printed material obtained by the method according to claim 15 .