Ink set and printing method

1. An ink set comprising:

an ink composition; and

a treatment liquid composition,

wherein

each of the ink composition and the treatment liquid composition is used for printing by being applied onto a printing medium by an ink jet method,

the ink composition is a water-based composition containing a coloring material and a surfactant,

the treatment liquid composition is a water-based composition containing a flocculant and a surfactant,

each of the surfactant contained in the ink composition and the surfactant contained in the treatment liquid composition includes a silicone surfactant whose 0.1 mass % aqueous solution has a surface tension of 32 mN/m or less,

any one of the surfactant contained in the ink composition and the surfactant contained in the treatment liquid composition includes a silicone surfactant whose 0.1 mass % solution in a nitrogen-containing solvent has a surface tension of 32 mN/m or less,

any one of the ink composition and the treatment liquid composition contains any one of a nitrogen-containing solvent, a sulfur-containing solvent, and a cyclic ester, and

any one of the ink composition and the treatment liquid composition contains a nitrogen-containing solvent represented by any one of following formulas (1), (3) and (4):

wherein R 1 and R 2 each independently represent one selected from the group consisting of a hydrogen atom and alkyl groups with 1 to 5 carbon atoms, and R 3 represents an alkyl group with 1 to 5 carbon atoms;

wherein R 1 and R 2 each independently represent one selected from the group consisting of a hydrogen atom and alkyl groups with 1 to 5 carbon atoms, and R 3 represents an alkyl group with 1 to 5 carbon atoms;

wherein R 1 represents one selected from the group consisting of a hydrogen atom and an alkyl or alkenyl group with 1 to 6 carbon atoms, and R 2 represents an alkylene group with 1 to 6 carbon atoms that is a part of a cyclic amide ring.

2. The ink set according to claim 1 , wherein

the surfactant contained in the treatment liquid composition includes the silicone surfactant whose 0.1 mass % solution in the nitrogen-containing solvent has a surface tension of 32 mN/m or less.

3. The ink set according to claim 1 , wherein

each of the ink composition and the treatment liquid composition contains any one of a nitrogen-containing solvent, a sulfur-containing solvent, and a cyclic ester.

4. The ink set according to claim 1 , wherein

any one of the surfactant contained in the ink composition and the surfactant contained in the treatment liquid composition includes a silicone surfactant whose 0.1 mass % aqueous solution and 0.1 mass % solution in the nitrogen-containing solvent have surface tensions of 32 mN/m or less.

5. The ink set according to claim 1 , wherein

the silicone surfactant whose 0.1 mass % solution in the nitrogen-containing solvent has a surface tension of 32 mN/m or less is a silicone surfactant that has a surface tension of 32 mN/m or less when the nitrogen-containing solvent is 2-pyrrolidone.

6. The ink set according to claim 1 , wherein

a total content, in each of the ink composition and the treatment liquid composition, of the silicone surfactant whose 0.1 mass % aqueous solution has a surface tension of 32 N/m or less and the silicone surfactant whose 0.1 mass % solution in the nitrogen-containing solvent has a surface tension of 32 mN/m or less is 0.1% to 4% relative to a total mass of the composition.

7. The ink set according to claim 1 , wherein

the flocculant includes any one of a multivalent metal salt, a cationic polymer, and an organic acid.

8. The ink set according to claim 1 , wherein

any one of the ink composition and the treatment liquid composition contains a nitrogen-containing solvent.

9. The ink set according to claim 1 , wherein

any one of the ink composition and the treatment liquid composition contains a nitrogen-containing solvent represented by the formula (4).

10. The ink set according to claim 1 , wherein

any one of the ink composition and the treatment liquid composition contains a solvent selected from a nitrogen-containing solvent, a sulfur-containing solvent, and a cyclic ester in a proportion of 40% or more relative to a total mass of an organic solvent contained in the composition.

11. The ink set according to claim 1 , wherein

the ink set is used for printing on a poorly absorbent or non-absorbent printing medium.

12. A printing method using the ink set as set forth in claim 1 , the method comprising:

applying the ink composition onto a printing medium by an ink jet method; and

applying the treatment liquid composition onto the printing medium by an ink jet method.

13. The printing method according to claim 12 , wherein

the ink composition with a temperature of 20° C. to 45° C. is applied onto a printing medium with a temperature higher than the temperature of the ink composition by 0° C. to 5° C., and the treatment liquid composition with a temperature of 20° C. to 45° C. is applied onto the printing medium with a temperature higher than the temperature of the treatment liquid composition by 0° C. to 5° C.

14. The printing method according to claim 12 , wherein

printing is performed by repeating main scans and sub-scans, and

the ink composition and the treatment liquid composition are applied onto a same region of the printing medium by being ejected in an identical main scan.