Inkjet printing system, ink, and process
View Patent ↗An inkjet printing system comprises an inkjet printer and an inkjet ink comprising water, a self-dispersing carbon black pigment, and a water soluble polymer containing carboxylate groups, wherein: the carbon black pigment comprises greater than 11 weight % volatile surface functional groups; and the ink also contains an organic base having a pKa>7.5 and an optional inorganic base in combined amounts sufficient to provide alkaline equivalents of at least 150% of the acid equivalents of the water soluble polymer; provided the equivalents of the organic base are greater than or equal to the equivalents of the inorganic base.
1. An inkjet printing system comprising an inkjet printer and an inkjet ink comprising water, a self-dispersing carbon black pigment, and a water soluble polymer containing carboxylate groups; wherein:
the carbon black pigment comprises greater than 11 weight % volatile surface functional groups, and
the ink also contains an organic base having a pKa>7.5 and an optional inorganic base in combined amounts sufficient to provide alkaline equivalents of at least 150% of the acid equivalents of the water soluble polymer;
provided the equivalents of the organic base are greater than or equal to the equivalents of the inorganic base, such that the ratio of equivalents of organic base to inorganic base is greater than or equal to 1:1.
2. The inkjet printing system of claim 1 wherein the self-dispersing carbon black pigment comprises greater than 15 weight % volatile surface functional groups.
3. The inkjet printing system of claim 1 wherein the self-dispersing carbon black pigment comprises greater than 18 weight % volatile surface functional group.
4. The inkjet printing system of claim 1 wherein the self-dispersing carbon black pigment is anionically charged.
5. The inkjet printing system of claim 4 wherein the self-dispersing carbon black pigment is neutralized by sodium, potassium, lithium, or rubidium cation.
6. The inkjet printing system of claim 4 wherein the self-dispersing carbon black pigment comprises greater than 5 weight % volatile lactonic surface functional group content.
7. The inkjet printing system of claim 4 wherein the water-soluble polymer has an acid number of from 100 to 270.
8. The inkjet printing system of claim 7 wherein the water-soluble polymer has an acid number of from 100 to 250.
9. The inkjet printing system of claim 4 wherein the pKa of the organic base is less than 9.5.
10. The inkjet printing system of claim 1 wherein 50 weight % of the pigment particles have a particle size of less than 500 nm.
11. The inkjet printing system of claim 10 wherein 50 weight % of the pigment particles have a particle size of less than 200 nm.
12. The inkjet printing system of claim 1 wherein the total amount of pigment is 0.1 weight % to 6.0 weight % of the ink.
13. The inkjet printing system of claim 1 wherein the water-soluble polymer has a weight average molecular weight of from 4,000 to 40,000 Daltons.
14. The inkjet printing system of claim 1 wherein 75 to 100% of the acid groups on the polymer are neutralized by alkaline metal hydroxide.
15. The inkjet printing system of claim 14 wherein the alkaline metal hydroxide is lithium hydroxide, sodium hydroxide, or potassium hydroxide, or a mixture thereof.
16. The inkjet printing system of claim 1 wherein the organic base is selected from a primary, secondary, or tertiary amine.
17. The inkjet printing system of claim 16 wherein the organic base is an amino acid.
18. The inkjet printing system of claim 1 wherein the organic base contains a sulfonic acid group.
19. An inkjet ink according to claim 1 wherein the organic base is a metal salt of a carbonate or bicarbonate.
20. The inkjet printing system of claim 1 wherein the organic base and the optional inorganic base are present in combined amounts sufficient to provide alkaline equivalents of at least 200% of the acid equivalents of the water soluble polymer.
21. The inkjet printing system of claim 1 wherein the ratio of organic base to inorganic base is greater than or equal to 1.5:1.
22. An inkjet ink comprising water, a self-dispersing carbon black pigment, and a water soluble polymer containing carboxylate groups, wherein
the carbon black pigment comprises greater than 7 weight % volatile surface functional groups; and
the ink also contains an organic base having a pKa>7.5 and an optional inorganic base in combined amounts sufficient to provide alkaline equivalents of at least 150% of the acid equivalents of the water soluble polymer;
provided the equivalents of the organic base are greater than or equal to the equivalents of the inorganic base, such that the ratio of equivalents of organic base to inorganic base is greater than or equal to 1:1.
23. The inkjet ink of claim 22 wherein the organic base and the optional inorganic base are present in combined amounts sufficient to provide alkaline equivalents of at least 200% of the acid equivalents of the water soluble polymer.
24. The inkjet ink of claim 22 wherein the ratio of organic base to inorganic base is greater than or equal to 1.5:1.
25. A method for printing an inkjet image comprising:
I) providing an aqueous inkjet ink comprising: water, a self-dispersing carbon black pigment, and a water soluble polymer containing carboxylate groups;
wherein the carbon black pigment comprises greater than 11 weight % volatile surface functional groups; and
wherein the ink contains an organic base having a pKa>7.5 and an optional inorganic base in combined amounts sufficient to provide alkaline equivalents of at least 150% of the acid equivalents of the water soluble polymer;
provided the equivalents of the organic base are greater than or equal to the equivalents of the inorganic base, such that the ratio of equivalents of organic base to inorganic base isgreater than or equal to 1:1; and
II) jetting the inkjet ink in the form of ink drops onto a recording element to form a printed image.
26. An inkjet printing system, comprising an inkjet printer responsive to digital signals and containing an ink composition comprising: water, a self-dispersing carbon black pigment, and a water soluble polymer containing carboxylate groups:
wherein the carbon black pigment comprises greater than 11 weight % volatile surface functional groups; and
wherein the ink contains an organic base having a pKa>7.5 and an optional inorganic base in combined amounts sufficient to provide alkaline equivalents of at least 150% of the acid equivalents of the water soluble polymer, and
provided the equivalents of the organic base are greater than or equal to the equivalents of the inorganic base, such that the ratio of equivalents of organic base to inorganic base is greater than or equal to 1:1.