An ink-jet printing ink composition which has high printing stability after long periods of time and at high temperatures is provided. The ink-jet printing ink composition is an aqueous ink having a nitrite ion concentration between about 0.2 to 10 parts per million (ppm) in order to lower the concentration of dissolved gas in the ink.
1. A aqueous ink-jet printing ink composition, comprising an effective amount as a colorant of a dye in water and having a nitrite ion concentration of between about 0.2 to 10 ppm and wherein the molecular structure of the dye includes at least one azo linkage.
2. The ink-jet printing ink composition of claim 1, wherein the dye is present in an amount from about 0.5 to 10 parts by weight, based on the total weight of the composition.
3. The ink-jet printing ink composition of claim 1, further including a wetting agent.
4. The ink-jet printing ink composition of claim 3, wherein the wetting agent is a water-soluble organic solvent.
5. The ink-jet printing inkcomposition of claim 4, wherein the viscosity of the ink is equal to or less than 50 mPa.
6. The ink-jet printing ink composition of claim 4, wherein the wetting agent is present in an amount between about 5 to 80 percent by weight.
7. The ink-jet printing ink composition of claim 1, wherein the water is ultrapure water.
8. The ink-jet printing ink composition of claim 4, the ink is between about 12 to 14.
9. The ink-jet printing ink composition of claim 4, wherein the wetting agent is selected from the group consisting of polyhydric alcohols, ether and ester derivatives of polyhydric alcohols, water-soluble amines, cyclic nitrogenous compounds and mixtures thereof.
10. An aqueous ink-jet printing ink composition, comprising:
an effective amount as a colorant of a dye including at least one azo linkage;
between about 5 to 80 weight percent of a water-soluble organic solvent wetting agent; and
the balance water;
the composition having between about 0.2 to 10 ppm nitrite ion concentration.
11. The aqueous ink-jet printing ink composition of claim 10, wherein the pH is between about 12 and 14.
12. A method of reducing the nitrite ion concentration in an ink-jet printing ink composition, comprising:
dissolving of a dye containing at least one azo linkage as a colorant in water;
dissolving between about 50 to 80 weight percent of a water-soluble organic solvent of a wetting agent in the dye and water heating the composition to remove dissolved gases; treating the composition to remove nitrous acid to reduce the nitrite ion concentration to between about 0.2 to 10 ppm; and
sealing in a container having- low gas permeability.
13. The method of claim 12, wherein the treating step is accomplished by passing the composition through an ion exchange resin.
14. The method of claim 12, wherein the treating step is accomplished by passing the composition through an ultrafiltration membrane.
15. An ink-jet printing ink container, comprising:
an hermetically sealed ink bag made of a material having low gas permeability; and
an ink-jet printing ink composition including an effective amount of a colorant of a dye including at least one azo linkage, between about 5 to 80 weight percent of an organic solvent wetting agent, and the balance water, the composition having between about 0.2 to 10 ppm nitrite ion concentration, sealed therein.
