Ink formulations for improving printhead lifetime

1. An inkjet ink comprising:

(i) a disazo dye of formula (I):

wherein:

A is a C 6-14 aryl group having 0, 1, 2, 3, 4 or 5 substituents selected from the group consisting of: —SO 3 M, nitro, carboxyl, halogen, hydroxyl, amino, C 1-4 alkylamino, C 1-4 alkoxy, C 1-4 alkyl, C 1-4 haloalkyl, cyano, sulfonamide, carbamoyl, C 1-4 alkylamido and C 1-4 alkoxycarbonyl;

B is a C 6-14 aryl group having 0, 1, 2, 3, 4 or 5 substituents selected from the group consisting of: —SO 3 M, nitro, carboxyl, halogen, hydroxyl, amino, C 1-4 alkylamino, C 1-4 alkoxy, C 1-4 alkyl, C 1-4 haloalkyl, cyano, sulfonamide, carbamoyl, C 1-4 alkylamido and C 1-4 alkoxycarbonyl;

each M is independently selected from the group consisting of: hydrogen, lithium, sodium, potassium, ammonium and quaternary ammonium; and

the dye of formula (I) comprises at least 3 groups of formula —SO 3 M;

(ii) sulfolane;

(iii) a glycol compound selected from the group consisting of: ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol and pentaethylene glycol; and

(iv) water.

2. The inkjet ink of claim 1 , wherein an amount of sulfolane is greater than an amount of the glycol compound.

3. The inkjet ink of claim 1 , wherein a ratio of sulfolane to the glycol compound is in the range of 10:1 to 2:1.

4. The inkjet ink of claim 1 , wherein sulfolane is present in an amount ranging from 5 to 40 wt. %.

5. The inkjet ink of claim 1 , wherein the glycol compound is present in an amount ranging from 1 to 20 wt. %.

6. The inkjet ink of claim 1 , wherein the glycol compound is a higher order glycol selected from the group consisting of: triethylene glycol, tetraethylene glycol and pentaethylene glycol.

7. The inkjet ink of claim 1 , further comprising glycerol.

8. The inkjet ink of claim 1 , further comprising a non-ionic surfactant.

9. The inkjet ink of claim 1 , wherein M is sodium.

10. The inkjet ink of claim 1 , wherein A is a phenyl or naphthyl group having 1, 2 or 3 substituents selected from the group consisting of: —SO 3 M, nitro, carboxyl, halogen, hydroxyl, amino, C 1-4 alkoxy and C 1-4 alkyl; and B is a phenyl or naphthyl group having 1, 2 or 3 substituents selected from the group consisting of: —SO 3 M, nitro, carboxyl, halogen, hydroxyl, amino, C 1-4 alkoxy and C 1-4 alkyl.

11. A method of improving a lifetime of an inkjet printhead, the method comprising the steps of:

supplying an ink according to claim 1 to nozzle chambers of the printhead, each nozzle chamber having an associated actuator in contact with the ink; and

actuating one or more of the actuators to eject ink from the printhead.

12. The method of claim 11 , wherein each actuator comprises a resistive heater element.

13. The method of claim 12 , wherein the heater element is uncoated.

14. The method of claim 13 , wherein the heater element is comprised of a material selected from the group consisting of:

a titanium alloy;

titanium nitride; and

a nitride of a titanium alloy.

15. The method of claim 14 , wherein the printhead has a lifetime of at least 100 million ejections.