Pigment-based ink formulations having improved printhead lifetime

An inkjet printing system comprising:

• a printhead comprising a plurality of inkjet nozzle devices, each nozzle device comprising:
• a nozzle chamber and a heater element disposed on a subjacent silicon oxide pedestal;
• and
• an aqueous-based inkjet ink contained in the nozzle chamber, the inkjet ink comprising a pigment;
• 2 to 90 ppm ammonium ions;
• and an ink vehicle,
• wherein the ink has a pH in the range of 8 to 9.5.

A method of printing from a thermal inkjet printhead, said printhead comprising a plurality of inkjet nozzle devices, each nozzle device comprising a nozzle chamber and a heater element disposed on a subjacent silicon oxide pedestal, said method comprising the steps of:

• supplying an aqueous-based inkjet ink from an ink reservoir to the nozzle chamber;
• and
• actuating the heater element so as to eject ink droplets from the nozzle chamber,
• wherein the ink comprises a pigment, 2 to 90 ppm ammonium ions and an ink vehicle, the ink having a pH in the range of 8 to 9.5.

An ink set for an inkjet printer having one or more printheads, each ink in the ink set having an associated printhead lifetime, wherein:

• a first ink contains a first pigment and 2 to 90 ppm ammonium ions;
• and a second ink contains a second pigment and a lower amount of ammonium ions than the first ink, and wherein:
• the first and second inks each have a pH in the range of 8 to 9.5;
• and
• the first and second inks each have an associated printhead lifetime of greater than a minimum threshold number of ejections.