Image recording method, treatment liquid and ink set

1. An image recording method comprising the steps of:

applying an ink comprising a pigment to a recording medium; and

applying a treatment liquid comprising an organic acid and water to the recording medium, so as to overlap at least a part of a region to which the ink is applied,

wherein the treatment liquid comprises at least one organic compound:

(a) having (i) an anionic group, and (ii) an amino group or quaternary ammonium in its molecular structure, and

(b) having a surface-activating capability, wherein the static surface tension of water is changed to 60 mN/m or less when added in an amount of 0.1% by mass into the water.

2. The image recording method according to claim 1 , wherein the anionic group of the organic compound is —COO − or —COOM 1 , in which M 1 is a hydrogen atom, an alkali metal, ammonium, or organic ammonium.

3. The image recording method according to claim 1 , wherein the treatment liquid has a pH of 0.5 to 5.

4. The image recording method according to claim 1 , wherein the organic acid has a first pKa of 0.5 to 4.5.

5. The image recording method according to claim 1 , wherein a concentration of the organic compound in the treatment liquid is 0.1% to 10% by mass.

6. The image recording method according to claim 1 , wherein the organic compound is at least one compound selected from 2-alkyl-N-carboxyalkyl-N-hydroxyalkyl-imidazolinium betaines represented by the following general formula (1) and an alkali metal salt of β-alkylaminocarboxylic acids represented by the following general formula (2):

wherein R 1 is an alkyl, alkenyl, or alkynyl group that has 1 to 20 carbon atoms and may be branched, an aryl group having 6 to 20 carbon atoms, a benzyl group, or a heterocyclic group; and R 2 and R 3 are, independently of each other, an alkylene group having 1 to 3 carbon atoms; and

wherein R 4 is an alkyl, alkenyl, or alkynyl group that has 1 to 20 carbon atoms and may be branched, an aryl group having 6 to 20 carbon atoms, a benzyl group, or a heterocyclic group; R 5 is an alkylene group having 1 to 3 carbon atoms; and M is an alkali metal.

7. The image recording method according to claim 1 , wherein the ink is applied to the recording medium from a recording head of an ink jet system, and the treatment liquid is applied to the recording medium by a roller.

8. The image recording method according to claim 1 , wherein the recording medium is an intermediate transfer member, and an image formed on the intermediate transfer member is transferred to another recording medium than the intermediate transfer member.

9. The image recording method according to claim 1 , wherein the amount of the organic compound in the treatment liquid is in a range of 0.1% by mass to 10% by mass.

10. The image recording method according to claim 1 , wherein a content of the organic acid is 10% to 99% by mass based on the total mass of the treatment liquid.

11. The image recording method according to claim 1 , wherein the organic acid is oxalic acid, formic acid, acetic acid, propionic acid, glycolic acid, malonic acid, malic acid, maleic acid, ascorbic acid, levulinic acid, succinic acid, glutaric acid, glutamic acid, fumaric acid, citric acid, 1,2,3-propanetricarboxylic acid, tartaric acid, lactic acid, pyridonecarboxylic acid, pyronecarboxylic acid, pyrrolcarboxylic acid, furancarboxylic acid, pyridinecarboxylic acid, coumalic acid, thiophenecarboxylic acid, nicotinic acid, hydroxysuccinic acid, or dihydroxysuccinic acid.

12. The image recording method according to claim 1 , wherein the anionic group of the organic compound is —COO − , —SO 3 − , —PO 3 2− , —COOM 1 , —SO 3 M 1 , —PO 3 HM 1 , or —PO 3 M 1 2 , in which M 1 is a hydrogen atom, an alkali metal, ammonium, or organic ammonium.

13. A treatment liquid to be used for aggregating a pigment-containing ink that is applied to a recording medium, the treatment liquid comprising water and at least one organic compound:

(a) having (i) an anionic group, and (ii) an amino group or quaternary ammonium in its molecular structure, and

(b) having a surface-activating capability, wherein the static surface tension of water is changed to 60 mN/m or less when added in an amount of 0.1% by mass into the water.

14. An ink set comprising:

a pigment-containing ink; and

a treatment liquid to be used for aggregating the pigment-containing ink that is applied to a recording medium, wherein the treatment liquid comprises water and at least one organic compound:

(a) having (i) an anionic group, and (ii) an amino group or quaternary ammonium in its molecular structure, and

(b) having a surface-activating capability, wherein the static surface tension of water is changed to 60 mN/m or less when added in an amount of 0.1% by mass into the water.