Bleed alleviation in ink jet inks using acids containing a basic

Abstract

A pH adjusting organic compound having both at least one acid functional group and at least one basic functional group is employed along with an organic acid having no basic functional groups in a first ink-jet ink composition to reduce the pH differential required to render insoluble the pH-sensitive colorant of a second encroaching ink-jet ink composition. By inducing the precipitation of the pH-sensitive colorant, migration of the colorant is inhibited, thereby substantially reducing bleed between the pH-sensitive ink and the ink containing the organic acid (the 'target' ink). By employing an organic acid in the practice of the invention, a pH differential on the order of only 3 to 5 units may be required. Aside from increasing the pH of the ink to desirable levels, the pH adjusting organic compound enhances bleed control by increasing the concentration of acid functional groups beyond the amount provided by the organic acid component. The organic acid component is employed at a concentration ranging from about 0.1 to 20 wt % and may be represented by such acids as polyacrylic, acetic, glycolic, malonic, malic, maleic, ascorbic, succinic, glutaric, fumaric, citric, tartaric, lactic, sulfonic, and ortho-phosphoric acid and derivatives thereof. The pH adjusting organic compound is employed in sufficient amount (about 0.1 to 20 wt %) to achieve the desired pH differential and typically comprises an amino acid.