Inkjet recording ink and inkjet recording method

1. An inkjet recording ink, comprising an aqueous medium having dissolved therein at least two water soluble coloring materials sharing one spectral absorption region selected from a region of 500 to 580 nm and a region of 580 to 680 nm as a main absorption region in the aqueous medium,

wherein at least one of said water soluble coloring materials sharing the region of 500 to 580 nm as a main absorption region is an azo dye having a chromophore represented by the formula: (heterocyclic ring A)-N═N-(heterocyclic ring B), provided that the heterocyclic ring A and the heterocyclic B may have the same structure.

2. The inkjet recording ink as claimed in claim 1 , wherein at least two of said water soluble coloring materials sharing one spectral absorption region selected from a region of 500 to 580 nm and a region of 580 to 680 nm as a main absorption region in the aqueous medium are dissolved in a single aqueous medium.

3. The inkjet recording ink as claimed in claim 1 , wherein at least two of said water soluble coloring materials sharing one spectral absorption region selected from a region of 500 to 580 nm and a region of 580 to 680 nm as a main absorption region in the aqueous medium are separately dissolved in multiple aqueous mediums.

4. The inkjet recording ink as claimed in claim 1 , wherein the main absorption region shared by at least two of said water soluble coloring materials in the aqueous medium is the region of 500 to 580 nm.

5. The inkjet recording ink as claimed in claim 1 , wherein the azo dye having a chromophore represented by the formula: (heterocyclic ring A)-N═N-(heterocyclic ring B), is a coloring material having an oxidation potential nobler than 0.7 V (vs SCE).

6. The inkjet recording ink as claimed in claim 1 , wherein said azo dye is a dye represented by the following formula (1):

Formula (1):

wherein A represents a 5-membered heterocyclic group;

B 1 and B 2 each represents ═CR 1 — or —CR 2 ═ or either one of B 1 and B 2 represents a nitrogen atom and other represents ═CR 1 — or —CR 2 ═;

R 5 and R 6 each independently represents a hydrogen atom or a substituent, said substituent is an aliphatic group, an aromatic group, a heterocyclic group, an acyl group, an alkoxycarbonyl group, an aryloxycarbonyl group, a carbamoyl group, an alkylsulfonyl group, an arylsulfonyl group or a sulfamoyl group, and hydrogen atom of each substituent may be substituted;

G, R 1 and R 2 each independently represents a hydrogen atom or a substituent, said substituent is a halogen atom, an aliphatic group, an aromatic group, a heterocyclic group, a cyano group, a carboxyl group, a carbamoyl group, an alkoxycarbonyl group, an aryloxycarbonyl group, a heterocyclic oxycarbonyl group, an acyl group, a hydroxy group, an alkoxy group, an aryloxy group, a heterocyclic oxy group, a silyloxy group, an acyloxy group, a carbamoyloxy group, an alkoxycarbonyloxy group, an aryloxycarbonyloxy group, an amino group, an acylamino group, a ureido group, a sulfamoylamino group, an alkoxycarbonylamino group, an aryloxycarbonylamino group, an alkylsulfonylamino group, an arylsulfonylamino group, a heterocyclic sulfonylamino group, a nitro group, an alkylthio group, an arylthio group, a heterocyclic thio group, an alkylsulfonyl group, an arylsulfonyl group, a heterocyclic sulfonyl group, an alkylsulfinyl group, an arylsulfinyl group, a heterocyclic sulfinyl group, a sulfamoyl group or a sulfo group, and hydrogen atom of each substituent may be substituted; and

R 1 and R 5, or R 5 and R 6 may combine to form a 5- or 6-membered ring.

7. The inkjet recording ink as claimed in claim 6 , wherein said at least two water soluble coloring materials sharing the main absorption region both are the dye represented by formula (1).

8. The inkjet recording ink as claimed in claim 1 , wherein the main absorption region shared by at least two of said water soluble coloring materials in the aqueous medium is the region of 580 to 680 nm.

9. The inkjet recording ink as claimed in claim 8 , wherein at least one of said water soluble coloring materials sharing the region of 580 to 680 nm as a main absorption region is a dye represented by the following formula (I):

wherein X 1, X 2, X 3 and X 4 each independently represents —SO-Z, —SO 2 -Z, —SO 2 NR 1 R 2 , a sulfo group, —CONR 1 R 2 or —CO 2 R 1 , in which Z represents a substituted or unsubstituted alkyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted aralkyl group, a substituted or unsubstituted aryl group, or a substituted or unsubstituted heterocyclic group, and R 1 and R 2 each independently represents a hydrogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted aralkyl group, a substituted or unsubstituted aryl group, or a substituted or unsubstituted heterocyclic group, provided that when a plurality of Zs are present, these may be same or different,

Y 1, Y 2, Y 3 and Y 4 each independently represents a monovalent substituent,

provided that when a plurality of X 1 s, X 2 s, X 3 s, X 4 s, Y 1 s, Y 2 s, Y 3 s or Y 4 s are present, these may be same or different,

a 1 to a 4 and b 1 to b 4 represent a number of substituents X 1 to X 4 and Y 1 to Y 4, respectively, a 1 to a 4 each independently represents an integer of 0 to 4 but all are not 0 at a same time, b 1 to b 4 each independently represents an integer of 0 to 4, and

M represents a hydrogen atom, a metal atom or an oxide, hydroxide or halide thereof.

10. The inkjet recording ink as claimed in claim 9 , wherein the dye represented by formula (I) is a dye represented by the following formula (II):

wherein X 11 to X 14, Y 11 to Y 18 and M have same meanings as X 1 to X 4, Y 1 to Y 4 and M in formula (I), respectively, and

a 11 to a 14 each independently represents an integer of 1 or 2.

11. The inkjet recording ink as claimed in claim 9 , wherein the dye represented by formula (I) is a coloring material having an oxidation potential nobler than 0.7 V (vs SCE).

12. The inkjet recording ink as claimed in any one of claims 8 to 10 , wherein at least one dye represented by formula (I) and at least one dye having a structure different from said dye are dissolved in an aqueous medium.

13. The inkiet recording ink as claimed in claim 8 , wherein at least two dyes represented by formula (I) are dissolved in an aqueous medium.

14. An inkjet recording method comprising using the ink claimed in claim 1 .

15. The inkjet recording method as claimed in claim 14 , which uses an ink set comprising multiple aqueous mediums having separately dissolved therein at least two water soluble coloring materials sharing one spectral absorption region selected from a region of 500 to 580 nm and a region of 580 to 680 nm as a main absorption region in the aqueous medium, wherein an inkjet recording ink comprising an aqueous medium having dissolved therein at least one dye represented by formula (I) and an inkiet recording ink comprising an aqueous medium having dissolved therein at least one coloring material differing in a structure from said dye and sharing the main absorption region with said dye are used as a combined set.

16. The inkjet recording method as claimed in claim 14 , which uses an ink comprising an aqueous medium having dissolved therein at least two water soluble coloring materials sharing one spectral absorption region selected from a region of 500 to 580 nm and a region of 580 to 680 nm as a main absorption region in the aqueous medium, wherein in the inkjet recording ink used, at least one dye represented by formula (1) and at least one dye differing in structure from said dye and sharing the main absorption region with said dye are dissolved in the same aqueous medium.

17. The inkjet recording method as claimed in any one of claims 14 to 16 , wherein an image is recorded by ejecting ink droplets according to recording signals on an image-receiving material comprising a support having thereon an image-receiving layer containing an inorganic white pigment particle.

18. The inkiet recording method as claimed in claim 17 , wherein the image-receiving layer comprises an inorganic white pigment particle and at least one aqueous binder selected from polyvinyl alcohol, silanol-modified polyvinyl alcohol, starch, cationized starch, gelatin, carboxyalkyl cellulose, casein and polyvinylpyrrolidone.