1. Field of the Invention
The present invention relates to a method for manufacturing pigmented inks of consistent quality and producing limited or no waste.
2. Description of the Related Art
Pigment dispersions are used in inks for producing monochrome or multicolored images. In the printing business, it is important that the inks are of consistent quality in order to obtain accurate reproduction of the image on paper or polymeric media. Color images are often produced with a CMYK ink set consisting of a cyan, a magenta, a yellow and a black ink each including one or more dispersed pigments.
Pigment dispersions are made using a dispersant. A dispersant is a substance for promoting the formation and stabilization of a dispersion of pigment particles in a dispersion medium. Dispersants are generally surface-active materials having an anionic, cationic or non-ionic structure. The presence of a dispersant substantially reduces the required dispersing energy. Dispersed pigment particles may have a tendency to re-agglomerate after the dispersing operation due to mutual attraction forces. The use of dispersants also counteracts the re-agglomeration tendency of the pigment particles.
Generally, the pigment dispersions are manufactured in a batch process and different pigment dispersions often use the same dispersing installation. In between two batches of pigment dispersions employing different pigments, dispersants and/or dispersion media, the dispersion installation has to be cleaned to avoid hue shifts leading to inconsistent quality of inks.
U.S. Pat. No. 6,863,386 (RICOH) discloses a method for washing the ink manufacturing apparatus including charging the mixing vessel with a washing liquid, circulating the washing liquid through the ink manufacturing apparatus, and then discharging the washing liquid from the ink manufacturing apparatus. The discharged washing liquid is treated as waste.
EP 753552 A (TOYO INK) and JP 09-227810 (TOYO INK) disclose salt milling an organic pigment in the presence of a water-soluble inorganic salt, followed by washing the pigment in water to remove the inorganic salt to produce a processed pigment, and dispersing the obtained pigment in an aqueous liquid to obtain an inkjet ink. In this process, a determination of concentration is required to obtain consistent inkjet ink.
U.S. 2002/0088375 (SEIKO EPSON) discloses a method for manufacturing a pigment dispersed liquid, including at least: Step A of introducing a hydrophilic dispersibility-imparting group directly and/or via another atomic group to the surface of pigment particles; Step B of dispersing the pigment obtained in Step A in an aqueous medium; and Step C of conducting a refining treatment of the dispersed liquid obtained in Step B. Ultrafiltration is used in Step C wherein the pigment concentration is adjusted by adding ion exchange water.
U.S. Pat. No. 5,714,993 (XEROX) discloses a method of imaging including: jetting with a liquid jet an ink jettable toner composition including a liquid carrier vehicle and stabilized core particles including resin, colorant, and a stabilizer component which is covalently bonded to the core particles, in a predetermined pattern onto a receiving member to form an image; and fixing the image to a receiver by heating or irradiating the image and/or the receiver at from about 40° C. to about 150° C. The preparation of stabilized carbon black suspensions involves rinsing with water. The pigment concentration in the stock suspension for preparing ink formulations is reduced by approximately 25%.
Along with the discharged washing liquid, certain amounts of pigments are wasted. Correction of the amounts of the components to complete the ink composition is then necessary to obtain consistent quality, leading to extra measurements and manipulations. Measurement of the color strength of an ink is cumbersome and very time consuming and the accuracy of the measurement is also dependent on the color and strength stability of the standard ink. Even with careful control, these standard inks can vary from batch to batch and tend to flocculate or settle in time, leading to poor test repeatability and difficulty in accurately matching the ink being made to a standard ink.
The in-between cleaning of the pigment dispersing apparatus results in large amounts of washing liquids, representing financial penalties not only due to the cost of the raw materials wasted, but also due to the cost for treating these waste solutions and the loss in production time and efficiency. Therefore, it would be desirable to have a simple and fast method for manufacturing pigmented inks of consistent quality and producing limited or no waste.