Lexmark Granted Patent for Yellow Pigment Inkjet Ink

U.S. patent No. 8,431,631 was awarded to Lexmark International, Inc. on April 30, 2013 for an ink jet ink containing an insoluble yellow pigment.

Inks used in inkjet printers typically consist of deionized water, a water-soluble, or water-miscible, organic solvent, and a colorant. Generally, the colorant is a soluble dye. Unfortunately, inks comprising soluble dyes can cause such problems as poor water-fastness, poor light-fastness, nozzle clogging as a result of solvent evaporation and changes in the dye’s solubility, dye crystallization, poor print quality, including: ink bleeding and feathering, poor thermal stability, chemical instability, and ease of oxidation.

These problems can be overcome by replacing the soluble dyes used in ink formulations with insoluble pigments. An ink formulation which optimizes all of these desired ink printing properties had not been achieved prior to this invention, the Lexmark patent claims.

Many solvents help kogation but they negatively increase the viscosity of the ink which can lead to jetting failure in the printhead. Kogation is an undesirable effect in thermal inkjet printers whereby the ink decomposes leaving behind a deposit on the heating element that renders it useless. Cosolvents can be added to the ink composition to help maintain the colorant in the ink composition and to enhance ink performance. However, often the addition of particular cosolvents can negatively impact the print quality of the ink. But high quantities of cosolvent have negative effects on the yellow ink in terms of viscosity, dry time and smudging. Consequently, there is a need to balance these competing factors when deciding which components to include and at what percentage each component should be used in a yellow ink formulation. Lexmark’s yellow inkjet ink balances these many trade-offs to formulate an optimized yellow inkjet ink formulation.

The inventors also claim that their novel yellow ink uses a unique group of cosolvents. It produces an optimal ink formulation which minimizes kogation and paper curl while still providing acceptable print quality.

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