The present invention pertains to an inkjet ink with a self-dispersing pigment colorant and an aqueous vehicle comprising (a) 1,3-dimethyl urea and/or 1,1,3,3-tetramethyl urea and (b) diethylene glycol and/or triethylene glycol. The ink exhibits good print reliability and excellent latency.
1. An ink-jet ink comprising an aqueous vehicle and a colorant wherein the colorant comprises a self-dispersing pigment and the vehicle comprises water, a first humectant and a second humectant; and wherein said first humectant is selected from the group consisting of 1,3-dimethyl urea, 1,1,3,3-tetramethyl urea and a combination thereof, and is present in the ink in an amount of at least 2 weight percent based on the total weight of ink; and, said second humectant is diethylene glycol.
2. The ink of claim 1 wherein weight ratio of second humectant to first humectant present in the ink is equal to or greater than 0.7.
3. The ink of claim 1 wherein the first humectant is present in an amount of 3-15 weight % based on the total weight of ink.
4. The ink of claim 1 wherein the self-dispersing pigment has been surface modified with anionic dispersibility-imparting groups which anionic dispersibility-imparting groups consist essentially of carboxylate groups.
5. The ink of claim 4 wherein the self-dispersing pigment comprises less than 3.5 micromoles of carboxylate groups per square meter of surface area.
6. The ink of claims 1 , 4 or 5 wherein the self-dispersing pigment is a self-dispersing carbon black pigment.
7. The ink according to any of claims 1 - 5 wherein the first humectant consists of tetramethyl urea.
8. The ink according to any of claims 1 - 5 wherein the first humectant is 1,3-dimethyl urea.
9. The ink according to claim 8 wherein the second humectant is diethylene glycol.
10. An inkjet ink set comprising at least a cyan, magenta, yellow and black ink wherein the black ink is the ink according to claim 6 .