Inkjet ink set and inkjet recording method

1. An inkjet ink set comprising at least two inks, wherein at least one ink contains a betaine compound and at least one other ink contains a nonionic surfactant, and

(A) the betaine compound is a compound represented by one of formulae (5) and (7),

R—N-(L-COOM 1 ) 2   (7)

wherein M 1 is an alkali metal cation or a hydrogen atom, at least one of R 1B to R 3B and L in the formula (5) contains a group

having 8 or more carbon atoms, and at least one of R and L in the formula (7) contains a group having 8 or more carbon atoms; and

(B) the at least two inks contains a dye represented by one of formulae (C1), (M1), (Y1) and (BK2),

wherein Y 1 , Y 2 , Y 3 and Y 4 each independently represents a hydrogen atom, a halogen atom, an alkyl group, a cycloalkyl group, an alkenyl group, an aralkyl group, an aryl group, a heterocyclic group, a cyano group, a hydroxyl group, a nitro group, an amino group, an alkylamino group, an alkoxy group, an aryloxy group, an acylamino group, an arylamino group, a ureido group, a sulfamoylamino group, an alkylthio group, an arylthio group, an alkoxycarbonylamino group, a sulfonamido group, a carbamoyl group, a sulfamoyl group, a sulfonyl group, an alkoxycarbonyl group, a heterocyclic group, an azo group, an acyloxy group, a carbamoyloxy group, a silyloxy group, an aryloxycarbonyl group, an aryloxycarbonylamino group, an imido group, a heterocyclic thio group, a phosphoryl group, an acyl group, a carboxyl group or a sulfo group, and

wherein X 1 , X 2 , X 3 and X 4 in the formula (CI) each independently represents —SO-Z c , —SO 2 -Z c , —SO 2 NR 1c R 2c or —CONR 1c R 2c

wherein each Z c independently represents an alkyl group, a cycloalkyl group, an alkenyl group, an aralkyl group, an aryl group, or a heterocyclic group; and R 1c and R 2c each independently represents a hydrogen atom, an alkyl group, a cycloalkyl group, an alkenyl group, an aralkyl group, an aryl group, or a heterocyclic a 1 +b 1 =4 group.

2. The inkjet ink set according to claim 1 , wherein at least one of the betaine compound is a compound represented by the following formula (1):

(R) p —N-[L-(COOM) q ] r   (1)

wherein R represents a hydrogen atom, an alkyl group, an aryl group or a heterocyclic group; L represents a di- or more valent linking group; M represents a hydrogen atom, an alkali metal atom, an ammonium group, a protonated organic amine or nitrogen-containing heterocyclic group or a quaternary ammonium ion group, provided that when p+r is 4, one of Ms is not present; q represents an integer of 1 or more; r represents an integer of 1 to 4; p represents an integer of 0 to 4; p+r is 3 or 4 and when p+r is 4, the N atom becomes an ammonium atom; when q is 2 or more, COOMs may be the same or different; when r is 2 or more, L-(COOM) q s may be the same or different; and when p is 2 or more, Rs may be the same or different.

3. The inkjet ink set according to claim 1 , wherein the nonionic surfactant is a compound represented by the following formula (2), (3) or (4):

R 21 O CH 2 CH 2 O m 1 H  Formula (2):

wherein R 21 represents an alkyl group having from 5 to 40 carbon atoms and m 1 represents an average addition molar number of ethylene oxide and is a number of 2 to 40;

R 22 COO CH 2 CH 2 O m 2 H  Formula (3):

wherein R 22 represents an alkyl group having from 5 to 40 carbon atoms and m 2 represents an average addition molar number of ethylene oxide and is a number of 2 to 40;

wherein R 31 and R 32 each independently represents an alkyl group having from 1 to 18 carbon atoms, R 33 represents a hydrogen atom, an alkyl group having from 1 to 6 carbon atoms or a phenyl group and X represents a hydrogen atom or

wherein R 34 and R 35 each independently represents an alkyl group having from 1 to 18 carbon atoms, R 36 represents a hydrogen atom, an alkyl group having from 1 to 6 carbon atoms or a phenyl group, m 3 and m 4 each independently represents an average addition molar number of ethylene oxide, and m 3 +m 4 is from 0 to 100, provided that when m 3 is 0, R 33 represents a hydrogen atom, when m 4 is 0, R 36 represents a hydrogen atom, and when X is a hydrogen atom, m 3 is from 1 to 100.

4. The inkjet ink set according to claim 1 , wherein at least one ink contains the betaine compound and at least one other ink contains a betaine compound and the nonionic surfactant.

5. The inkjet ink set according to claim 2 , wherein at least one ink contains the betaine compound and at least one other ink contains a betaine compound and the nonionic surfactant.

6. The inkjet ink set according to claim 3 , wherein at least one ink contains the betaine compound and at least one other ink contains a betaine compound and the nonionic surfactant.

7. The inkjet ink set according to claim 1 , wherein the betaine compound is a compound which has both of a cationic site and an anionic site in its molecule.

8. The inkjet ink set according to claim 7 , wherein the cationic site is selected from the group consisting of an aminic nitrogen atom, a nitrogen atom of a heterogromatic ring, and a phosphoric atom, and the anionic site is selected from the group consisting of a hydroxyl group, a thio group, a sulfonamido group, a sulfo group, a carboxyl group, an imido group, a phosphate group, and a phosphonate group.

9. The inkjet ink set according to claim 1 , wherein the dye has an oxidation potential nobler than 1.0 V (vs. SCE).

10. The inkjet ink set according to claim 1 , wherein the dye has at least two heterocyclic groups.

11. The inkjet ink set according to claim 10 , wherein the heterocyclic group is a 5-membered heterocyclic group or a 6-membered heterocyclic group in which hetero atom is at least one of N, O and S.

12. The inkjet ink according to claim 10 , wherein the heterocyclic group contains at least one of pyridine, thiophene, thiazole, benzothiazole, benzoxazole and furan rings.

13. The inkjet ink set according to claim 1 , wherein at least one of the inks contains a phthalocyanine dye containing at least one of —SO—, —SO 2 —, —CO— and —CO 2 —.

14. An inkjet recording method, comprising recording an image in an inkjet printer comprising the inkjet ink set according to claim 1 .

15. An inkjet recording method, comprising recording an image in an inkjet printer comprising the inkjet ink set according to claim 2 .

16. An inkjet recording method, comprising recording an image in an inkjet printer comprising the inkjet ink set according to claim 3 .