Patent ID: 6139139
Filing Date: 2000-10-31
Classification: B41J,C09D

Abstract:
A method of inkjet printing whereby black ink and color inks from an ink set comprising cyan ink, yellow ink, and magenta ink are dispensed by a color ink-jet printer, comprising the steps of:(a) providing a black ink;(b) providing a color ink set comprising a cyan ink, a yellow ink, and a magenta ink, each color ink in said color ink set containing at least one vehicle component and at least one colorant and further formulated such that when said carriage moves said at least one printhead across a print zone and deposits drops of said black ink and drops of said color ink adjacent and in contact with one another on media in said print zone, then either (1) said black ink has a pH within a selected range and each of said color inks includes a pH sensitive component selected from the group consisting of a pH sensitive colorant and a pH sensitive vehicle, said pH of said black ink being such that said pH sensitive component precipitates upon contact with said black ink, thereby substantially reducing bleed between said black ink and each of said color inks; or (2) said black ink includes a polymer having a charge and each of said color inks includes a pigment and a pigment dispersant, said pigment dispersant having an opposite charge of said polymer, such that said pigment is substantially insoluble in the presence of said polymer, thereby substantially reducing bleed between said black ink and each of said color inks; or (3) said black ink includes a pigment and a pigment dispersant and each of said color inks includes a polymer, said pigment dispersant and said polymer being oppositely charged, such that said pigment is substantially insoluble in the presence of said polymer, thereby substantially reducing bleed between said black ink and each of said color inks;(c) associating said black ink and each of said color inks in said color ink set each with a separate group of nozzles, each group of nozzles contained in a printhead;(d) positioning each said printhead on a carriage of said color inkjet printer; and(e) moving said carriage across said print zone of said print medium and depositing drops of said black ink and drops of at least one of said color inks such that said black ink and said color ink are deposited onto said print medium adjacent and in contact with one another, whereupon said chemical reaction occurs between said black ink and said color ink or said pH change occurs between adjacently-printed inks such that bleed is substantially reduced therebetween.