Ink-jet ink formulations containing imidazole

1. An ink for use in combination with an ink-jet printer, comprising a mixture comprising:

a colorant;

a liquid vehicle containing 5.0-7.0 wt % 1,6-hexanediol and 2.0-5.0 wt % 1,5-pentanediol, together providing 7.0-12.0 wt % of said mixture, in a ratio in the rang of 1:1 (wt/wt) to 3:1 (wt/wt);

at least one multivalent salt dissolved in said vehicle in a total amount of from about 1.0 wt % to about 5 wt % by weight of the ink; and

an amount of imidazole, in the range of about 0.5-2.5 wt % of the ink, the mixture providing at least one of the following enhancements to said ink: improved print quality, increased decap time, pen reliability, environmental robustness of ink in pen, environmental robustness of printed ink on media, and aid in maintaining the pH of the ink in a desired range.

2. An ink for use in combination with an ink-jet printer, comprising a mixture comprising:

a colorant;

a liquid vehicle comprising 1,6-hexanediol and 1,5-pentanediol in a ratio in the range of 1:4 (wt/wt) to 4:1 (wt/wt); and

an amount of imidazole, in the range of about 0.1 wt % -6 wt % of the ink, the mixture providing one or more of the following enhancements to the ink: improved print quality, increased decap time, pen reliability, environmental robustness of ink in pen, environmental robustness of printed ink on media, and aid in maintaining the pH of the ink in a desired range.

3. The ink according to claim 2 , wherein said mixture comprises: 5-15 wt % 1,6-hexanediol and 3-8 wt % 1,5-pentanediol.

4. The ink according to claim 1 wherein said colorant comprises:

(a) a magenta dye having the structure:

and salts thereof, wherein

R 21 , R 23 , R 25 , R 27 , R 29 and R 31 , are independently a hydrogen atom or a sulfonate group;

R 22 is a hydrogen atom or a nitro group;

R 26 and R 28 are independently a hydrogen atom or a methyl group;

R 24 and R 30 are independently a methyl or sulfonate group; and

R 32 is a methyl or a methoxy group; and

(b) a second magenta dye having the structure:

and salts thereof, wherein Q is lithium, potassium, sodium, ammonium, tetramethylammonium, or a mixture thereof.

5. The ink of claim 1 , wherein said colorant comprises a cyan dye having the structure:

wherein

M is a hydrogen atom; a metal atom; or an oxide, hydroxide, or halide of the metal atom;

P c is a phthalocyanine nucleus;

R 1 and R 2 are independently a substituent selected from the group consisting of —SOX 1 , —SO 2 X 1 , SO 2 NX 2 X 3 , —SO 3 X 4 ; where X 1 , X 2 , X 3 , and X 4 are independently a hydrogen atom, a substituted or unsubstituted C 1 to C 7 alkyl group, a substituted or unsubstituted aryl group, or a substituted or unsubstituted heterocyclic group; wherein at least one of R 1 or R 2 has an ionic hydrophilic group as a substituent; and

k and I are independently an integer ranging from 1 to 3, where the sum of k and I is 4.

6. The ink of claim 5 , wherein, with respect to the cyan dye:

R 1 is —SO—(CH 2 ) 3 —SO 3 Z, or —SO 2 —(CH 2 ) 3 —SO 3 Z;

R 2 is —SO 2 —(CH 2 ) 3 —SO 2 NH—C 2 H 4 OC 2 H 4 OH, or

—SO 2 —(CH 2 ) 3 —SO 2 NH—CH 2 CH(OH)CH 3 ;

k is from 2 to 3; and

Z is lithium, sodium, potassium, ammonium, tetramethylammonium, or a mixture thereof.

7. The ink of claim 5 , wherein, with respect to the cyan dye:

R 1 is —SO 2 —(CH 2 ) 3 —SO 3 Z;

R 2 is —SO 2 —(CH 2 ) 3 —SO 2 NH—CH 2 CH(OH)CH 3 ;

k is 3; and

Z is lithium.

8. The ink according to claim 1 wherein said colorant comprises a yellow dye having the structure:

9. The ink according to claim 1 further comprises a phenylenediamine compound having the structure:

and salts thereof, wherein M is a monovalent cation.

10. The ink according to claim 2 wherein said colorant comprises:

(a) a magenta dye having the structure:

and salts thereof, wherein

R 21 , R 23 , R 25 , R 27 , R 29 and R 31 , are independently a hydrogen atom or a sulfonate group;

R 22 is a hydrogen atom or a nitro group;

R 26 and R 28 are independently a hydrogen atom or a methyl group;

R 24 and R 30 are independently a methyl or sulfonate group; and

R 32 is a methyl or a methoxy group; and

(b) a second magenta dye having the structure:

and salts thereof, wherein Q is lithium, potassium, sodium, ammonium, tetramethylammonium, or a mixture thereof.

11. The ink of claim 2 , wherein said colorant comprises a cyan dye having the structure:

wherein

M is a hydrogen atom; a metal atom; or an oxide, hydroxide, or halide of the metal atom;

P c is a phthalocyanine nucleus;

R 1 and R 2 are independently a substituent selected from the group consisting of —SOX 1 , —SO 2 X 1 , SO 2 NX 2 X 3 , —SO 3 X 4 ; where X 1 , X 2 , X 3 , and X 4 are independently a hydrogen atom, a substituted or unsubstituted C 1 to C 7 alkyl group, a substituted or unsubstituted aryl group, or a substituted or unsubstituted heterocyclic group; wherein at least one of R 1 or R 2 has an ionic hydrophilic group as a substituent; and

k and I are independently an integer ranging from 1 to 3, where the sum of k and I is 4.

12. The ink of claim 11 , wherein, with respect to the cyan dye:

R 1 is —SO—(CH 2 ) 3 —SO 3 Z, or —SO 2 —(CH 2 ) 3 -SO 3 Z;

R 2 is —SO 2 —(CH 2 ) 3 —SO 2 NH—C 2 H 4 OC 2 H 4 OH, or

—SO 2 —(CH 2 ) 3 —SO 2 NH—CH 2 CH(OH)CH 3 ;

k is from 2 to 3; and

Z is lithium, sodium, potassium, ammonium, tetramethylammonium, or a mixture thereof.

13. The ink of claim 11 , wherein, with respect to the cyan dye:

R 1 is —SO 2 —(CH 2 ) 3 —SO 3 Z;

R 2 is —SO 2 —(CH 2 ) 3 —SO 2 NH—CH 2 CH(OH)CH 3 ;

k is 3; and

Z is lithium.

14. The ink according to claim 2 wherein said colorant comprises a yellow dye having the structure:

15. The ink according to claim 2 further comprises a phenylenediamine compound having the structure:

and salts thereof, wherein M is a monovalent cation.

16. The ink according to claim 1 wherein the amount of imidazole is in the range of about 0.5 to 2 wt %.

17. The ink according to claim 2 comprising at least one multivalent salt dissolved in said vehicle in a total amount of from about 1.0 wt % to about 5 wt % by weight of the ink.

18. A method of improving print quality of an ink-jet printed medium, comprising applying to a swellable medium, porous medium or plain paper medium, by way of an ink-jet printer, the ink according to claim 1 , to enhance at least one quality selected from the group consisting of bronzing reduction, humid hue shift reduction, bleeding reduction, and environmental robustness in the resulting ink-jet ink printed medium.

19. A method of improving print quality of an ink-jet printed medium, comprising applying to a swellable medium, porous medium or plain paper medium, by way of an ink-jet printer, the ink according to claim 2 , to enhance at least one quality selected from the group consisting of bronzing reduction, humid hue shift reduction, bleeding reduction, and environmental robustness in the resulting ink-jet ink printed medium.

20. A method of increasing pen reliability or decap time in an ink-jet printer, comprising employing the ink according to claim 1 in said ink-jet printer.

21. A method of increasing pen reliability or decap time in an ink-jet printer, comprising employing the ink according to claim 2 in said ink-jet printer.

22. A printed product comprising an ink-jet ink-receptive medium on which the ink of claim 1 has been deposited by an ink-jet printer.

23. A printed product comprising an ink-jet ink-receptive medium on which the ink of claim 2 has been deposited by an ink-jet printer.

24. The ink according to claim 2 , wherein the amount of imidazole is in the range of about 0.5 to 2 wt%.

25. The ink according to claim 2 , wherein the 1,6-hexanediol and the 1,5-pentanediol together comprise 8 to 25 wt % of said mixture.

26. The ink according to claim 2 , wherein the 1,6-hexanediol and 1,5-pentanediol are in a ratio in the range of 1:4 (wt/wt) to 2:3 (wt/wt).