Inkjet printing system, ink, and process

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.

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.

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.