Black-to-color bleed alleviation using non-specific ionic, pH and colloidal effects

• Main Authors: TSANG, JOSEPH W, MOFFAT, JOHN R
• Format: Patent
• Language: English; French; German
• Published: 19.04.2000
• Edition: 7
• Subjects: ADHESIVES; CHEMICAL PAINT OR INK REMOVERS; CHEMISTRY; COATING COMPOSITIONS, e.g. PAINTS, VARNISHES ORLACQUERS; COLOUR PRINTING; CORRECTING FLUIDS; CORRECTION OF TYPOGRAPHICAL ERRORS; DYES; FILLING PASTES; i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; INKS; LINING MACHINES; METALLURGY; MISCELLANEOUS APPLICATIONS OF MATERIALS; MISCELLANEOUS COMPOSITIONS; NATURAL RESINS; PAINTS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; PERFORMING OPERATIONS; POLISHES; PRINTING; PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; SELECTIVE PRINTING MECHANISMS; STAMPS; TRANSPORTING; TYPEWRITERS; USE OF MATERIALS THEREFOR; WOODSTAINS

An ink-jet ink set comprises (a) a microemulsion-based black ink in which the colorant is a water-insoluble black pigment has been chemically modified to impart water solubility by addition of functional groups to form a macromolecular chromophore and (b) at least one non-black (cyan, yellow, or magenta) ink that is a typical aqueous dye-based ink with an agent that increases the ionic strength of the no-black ink and comprises either an inorganic salt or an organic acid; the organic acid is used to adjust the pH of the non-black ink to a value of less than 5. The non-black ink may alternatively comprise a water-insoluble non-black pigment that has also been chemically modified. The macromolecular chromophore-containing ink, or pigment-based ink, of the ink-jet ink set is a microemulsion that contains a substantially water-insoluble organic oil, an organic co-solvent, and water and, optionally, an amphiphile and a high molecular weight colloid. By employing an ink set in which some of the members of the set have a higher ionic strength than the black, microemulsion-based ink, then bleed alleviation can be achieved. When the higher ionic strength ink comes in contact with the lower ionic strength microemulsion ink, the rapid change in ionic strength of the microemulsion causes flocculation of the dissolved modified pigment. The result of the flocculation is that the colorant is precipitated on the print medium. It is no longer capable of diffusion into the other ink, thereby alleviating bleed, nor is it capable of penetration into the medium, thereby resulting in improved color density and edge acuity. The inks described herein also exhibit fast drying times, high waterfastness, and high smearfastness. They also show reduced problems with inter-color bleed and show no halo effect.