Ink set and ink jet recording method

1. An ink set comprising:

at least two kinds of inks, each of the at least two kinds of inks comprising triethyleneglycol and having a common hue and different densities, and containing an aqueous medium and a dye,

wherein each of the at least two kinds of inks has a corresponding discoloration velocity constant (k) for an image printed with each one of the at least two kinds of inks,

a ratio defined by a minimum value (k min ) selected from among said corresponding constants divided by a maximum value (k max ) selected from among the corresponding constants, is within a range of 0.7 to 1.0,

and in inks having the same hue, the content of a specific water-soluble organic solvent in the ink having a low concentration of dye is less than the content of the specific water-soluble organic solvent in the ink having a high concentration of dye.

2. The ink set as claimed in claim 1 , wherein each of the inks having a common hue and different densities includes at least one kind of dye having an oxidation potential nobler than 1.0 V (Vs SCE).

3. The ink set as claimed in claim 1 , wherein the dye is at least one of an azo dye and a phthalocyanine dye each having a heterocyclic group.

4. The ink set as claimed in claim 1 , wherein the aqueous medium contains at least a water-soluble glycol derivative.

5. The ink set as claimed in claim 1 is an ink set for ink jet recording.

6. An ink jet recording method of performing image-recording by an ink jet printer with the ink set as claimed in claim 1 .

7. The ink set as claimed in claim 1 , wherein the specific water-soluble organic solvent is a water-soluble glycol derivative organic solvent.

8. The ink set as claimed in claim 1 , wherein the dye is selected from the group consisting of dyes represented by formula (1), formula (2), formula (3) and formula (4):

(A-N═N—B) n -L  (1)

wherein A and B each represents a heterocyclic group which may be substituted; L represents a hydrogen atom, a single bond, or a divalent linking group; and n represents 1 or 2, provided that when n represents 1, L represents a hydrogen atom, and A and B both represent a monovalent heterocyclic group; and when n represents 2, L represents a single bond or a divalent linking group, and either A or B represents a monovalent heterocyclic group and the other represents a divalent heterocyclic group; and further provided that when n represents 2, the two A groups may be the same or different and the two B groups may also be the same or different;

wherein X 21 , X 22 , X 23 and X 24 each represents —SO-Z 2 , —SO 2 -Z 2 , —SO 2 NR 21 R 22 , a sulfo group, —CONR 21 R 22 or —COOR 21 ;

Z 2 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;

R 21 and R 22 each 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;

Y 21 , Y 22 , Y 23 and Y 24 each represents a monovalent substituent;

a 21 to a 24 , and b 21 to b 24 respectively represent the number of the substituents of X 21 to X 24 and Y 21 to Y 24 ; a 21 to a 24 each represents a number of from 0 to 4, provided that a 21 to a 24 do not represent 0 at the same time; b 21 to b 24 each represents a number of from 0 to 4; when a 21 to a 24 and b 21 to b 24 represent a number of 2 or higher, a plurality of X 21 to X 24 and Y 21 to Y 24 may be the same or different;

and M represents a hydrogen atom, a metal atom, oxide or hydroxide of the metal atom, or halide;

wherein A 31 represents a residue of 5-membered heterocyclic diazo component A 31 -N 2 —;

B 31 and B 32 each represents ═CR 31 — or —CR 32 ═, or either B 31 or B 32 represents a nitrogen atom and the other represents ═CR 31 — or —CR 32 ═; R 35 and R 36 each represents a hydrogen atom, an aliphatic group, an aromatic group, a heterocyclic group, an acyl group, an alkoxycarbonyl group, an aryloxycarbonyl group, a carbamoyl group, an alkyl- or arylsulfonyl group, or a sulfamoyl group, and each group may further have a substituent;

G 3 , R 31 and R 32 each represents a hydrogen atom, 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 hydroxyl group, an alkoxyl 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 (including an arylamino group and a heterocyclic amino group), an acylamino group, a ureido group, a sulfamoyl-amino group, an alkoxycarbonylamino group, an aryloxycarbonylamino group, an alkyl- or arylsulfonylamino group, a heterocyclic sulfonylamino group, a nitro group, an alkyl- or arylthio group, an alkyl- or arylsulfonyl group, a heterocyclic sulfonyl group, an alkyl- or arylsulfinyl group, a heterocyclic sulfinyl group, a sulfamoyl group, a sulfo group, or a heterocyclic thio group, and each group may further be substituted; and

R 31 and R 35 , or R 35 and R 36 may be bonded to each other to form a 5- or 6-membered ring;

A 41 -N═N—B 41 —N═N—C 41   (4)

wherein A 41 , B 41 and C 41 each represents an aromatic group which may be substituted or a heterocyclic group which may be substituted.

9. The ink set as claimed in claim 8 , wherein the dye of formula (1) is selected from the group consisting of dyes represented by formulae (1-A), (1-B) and (1-C), the dye of formula (2) is represented by formula (5), the dye of formula (3) is represented by formula (3-A), and the dye of formula (4) is limited to formula (4-A) or (4-B):

wherein R 1 and R 3 each represents a hydrogen atom, a cyano group, an alkyl group, a cycloalkyl group, an aralkyl group, an alkoxyl group, an alkylthio group, an arylthio group, an aryl group, or an ionic hydrophilic group; R2 represents a hydrogen atom, an alkyl group, a cycloalkyl group, an aralkyl group, a carbamoyl group, an acyl group, an aryl group or a heterocyclic group; and R4 represents a heterocyclic group;

wherein R5 represents a hydrogen atom, a cyano group, an alkyl group, a cycloalkyl group, an aralkyl group, an alkoxyl group, an alkylthio group, an arylthio group, an aryl group or an ionic hydrophilic group; Za represents —N═, —NH— or —C(R11)═; Zb and Zc each represents —N═ or —C(R11)═; R11 represents a hydrogen atom or a nonmetallic substituent; and R6 represents a heterocyclic group;

wherein R7 and R9 each represents a hydrogen atom, a cyano group, an alkyl group, a cycloalkyl group, an aralkyl group, an aryl group, an alkylthio group, an arylthio group, an alkoxycarbonyl group, a carbamoyl group or an ionic hydrophilic group; R8 represents a hydrogen atom, a halogen atom, an alkyl group, an alkoxyl group, an aryl group, an aryloxy group, a cyano group, an acylamino group, a sulfonyl-amino group, an alkoxycarbonylamino group, a ureido group, an alkylthio group, an arylthio group, an alkoxycarbonyl group, a carbamoyl group a sulfamoyl group, a sulfonyl group, an acyl group, an alkylamino group, an arylamino group, a hydroxyl group or an ionic hydrophilic group; and R10 represents a heterocyclic group;

wherein, X 51 to X 54 , Y 51 to Y 58 and M 1 have the same meaning as X 21 to X 24 , Y 21 to Y 24 and M in formula (2) in claim 8 , respectively; a 51 to a 54 each represents an integer of 1 or 2;

wherein R 31 , R 32 , R 35 and R 36 have the same meaning as in formula (3) in claim 8 , respectively; R 33 and R 34 each represents a hydrogen atom or a substituent; Z 31 represents an electron attractive group having a σp value of Hammett's substitution constant of 0.20 or more; Z 32 represents a hydrogen atom or a substituent; and Q represents a hydrogen atom or a substituent;

wherein A 41 and B 41 have the same meaning as in formula (4) in claim 8 , respectively; B 1 and B 2 each represents ═CR 41 — or —CR 42 ═, or either B 1 or B 2 represents a nitrogen atom and the other represents ═CR 41 — or —CR 42 ═;

G 4 , R 41 and R 42 each represents a hydrogen atom, 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 hydroxyl group, an alkoxyl 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 (including an alkylamino group, an arylamino group and a heterocyclic 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 allcylthio group, an arylthio group, a heterocyclic thio group, an alkylsulfonyl group, an aryl-sulfonyl group, a heterocyclic sulfonyl group, an alkyl-sulfinyl group, an arylsulfinyl group, a heterocyclic sulfinyl group, a sulfamoyl group, or a sulfo group, and each group may further be substituted;

R 45 and R 46 each represents a hydrogen atom, 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 each group may further have a substituent; provided however that R 45 and R 46 do not represent a hydrogen atom at the same time; and

R 41 and R 45 , or R 45 and R 46 may be bonded to each other to form a 5- or 6-membered ring;

wherein A 41 has the same meaning as A 41 in formula (4) in claim 8 ; B 1 , B 2 , G 4 , R 45 and R 46 have the same meaning as B 1 , B 2 , G 4 , R 45 and R 46 in formula (4-A), respectively; and R 47 and R 48 have the same meaning as R 41 in formula (4-A).