Ink set for ink-jet recording and ink-jet recording method

1. An ink set comprising plural inks for inkjet, each one of the plural inks having a maximum absorption wavelength of one of from 500 to 580 nm and from 580 to 680 nm in an aqueous medium and a different absorbance,

wherein based on an absorbance of a dye or a combination of dyes in an ink, which has a maximum dye concentration out of the plural inks, an absorbance of a dye or a combination of dyes in all another ink excepting the ink having a maximum dye concentration is from 1/20 to ½, and

wherein

when each one of the plural inks has a maximum absorption wavelength of from 500 to 580 nm in an aqueous medium, at least one of the plural inks having a maximum absorption wavelength of from 500 to 580 nm includes an azo dye having a chromophore represented by the following formula:

[(heterocyclic ring A)-N═N-(heterocyclic ring B)]

wherein the heterocyclic ring A and the heterocyclic ring B are the same or different, and the azo dye having a chromophore represented by the formula [(heterocyclic ring A)-N═N-(heterocyclic ring B)] is a colorant having an oxidation potential of more positive than 0.7 V (vs SCE); and

when each one of the plural inks has a maximum absorption wavelength of from 580 to 680 nm in the aqueous medium, at least one of the plural inks having a maximum absorption wavelength of from 580 nm to 680 nm includes a dye represented by the following formula (I) and the dye represented by formula (I) is a colorant having an oxidation potential of more positive than 1.0 V (vs SCE):

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 and at least one of X 1 , X 2 , X 3 and X 4 is —SO 2 -Z or —SO 2 NR 1 R 2 wherein 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 multiple Zs are present, these may be the same or different,

Y 1 , Y 2 , Y 3 and Y 4 each independently represents a monovalent substituent, provided that when multiple 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 the same or different,

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

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

2. The ink set for inkjet recording as claimed in claim 1 , wherein out of dyes contained in an ink having a maximum dye concentration in the plural inks constituting the ink set, a dye having a maximum absorbance is an azo dye having a chromophore represented by the following formula:

[(heterocyclic ring A)-N═N-(heterocyclic ring B)]

wherein the heterocyclic ring A and the heterocyclic B may have the same structure.

3. The ink set as claimed in claim 1 , wherein the azo dye having the chromophore represented by the formula [(heterocyclic ring A)-N═N-(heterocyclic ring B)] is a dye represented by the following 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, the 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 the hydrogen atom of each substituent may be substituted;

G, R 1 and R 2 each independently represents a hydrogen atom or a substituent, the 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 the 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.

4. The ink set as claimed in claim 3 , wherein the dye represented by formula (1) is a dye represented by formula (1a):

wherein R 1 , R 2 , R 5 and R 6 have the same meanings as in formula (1) in claim 3 ,

R 5 and R 4 each independently represents a hydrogen atom or a substituent and the substituent is an aliphatic group, an aromatic group, an heterocyclic group, an acyl group, an alkoxycarbonyl group, an aryloxycarbonyl group, a carbamoyl group, an alkylsulfonyl group, an arylsulfonyl group or a sulfamoyl group,

Z 1 represents an electron-withdrawing group having a Hammett's substituent constant σp value of 0.20 or more,

Z 2 represents a hydrogen atom or a substituent and the substituent is an aliphatic group, and aromatic group or a heterocyclic group, and

Q represents a hydrogen atom or a substituent and the substituent is an aliphatic group, an aromatic group or a heterocyclic group.

5. The ink set as claimed in claim 1 , wherein the dye represented by formula (I) is a dye represented by the following formula (II):

wherein X 11 to X 14 and M have the same meanings as X 1 to X 4 and M in formula (I), respectively, and when multiple X 11 s, X 12 s, X 13 s and X 14 s are present, these may be the same or different,

Y 11 to Y 18 each independently represents a hydrogen atom, a halogen atom, a cyano group, a carboxyl group or a sulfo group, and

a 11 to a 14 represents the number of substituents of X 11 to X 14 , respectively, and each independently represents an integer of 1 or 2.

6. The ink set as claimed in claim 5 , wherein Y 11 to Y 18 of formula (II) each is a hydrogen atom.

7. An inkjet recording method, which uses the ink set as claimed in claim 1 .

8. The inkjet recording method as claimed in claim 7 , wherein an image is recorded by ejecting ink droplets according to recording signals on an image-receiving material, which comprises a support and an image-receiving layer containing an inorganic white pigment particle on the support.

9. The inkjet recording method as claimed in claim 8 , wherein the image-receiving layer comprises the 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.

10. The ink set as claimed in claim 1 , wherein out of dyes contained in an ink having a maximum dye concentration in the plural inks constituting the ink set, a dye having a maximum absorbance is one of:

an azo dye having a chromophore represented by the formula:

[(heterocyclic ring A)-N═N-(heterocyclic ring B)]

wherein the heterocyclic ring A and the heterocyclic ring B may have the same structure; and a dye represented by the formula (I).

11. The ink set as claimed in claim 1 , wherein at least one of the azo dye having a chromophore represented by the formula:

[(heterocyclic ring A)-N═N-(heterocyclic ring B)]

wherein the heterocyclic ring A and the heterocyclic ring B may have the same structure; and the dye represented by the formula (I) is a water-soluble dye.