High resolution pigment ink for impulse ink jet printing

#This invention is directed to ink compositions for use in impulse or drop on demand (DOD) inkjet printers, and more specifically, to solvent-based, pigment and dye inks formulated for high resolution and low spread bar code and graphics printing applications on porous substrates such as Kraft paper or corrugated cardboard and other porous materials like web off-set paper. The inks of this invention are also for printing on non-porous substrates.

#Ink jet printing is performed by discharging ink droplets from a print head to a substrate. The droplets are ejected through orifices or nozzles in the print head and are directed to the substrate to form an image thereon. In contrast to many other types of printing, there is no contact between the printer and the substrate in ink jet techniques.

#Most of the ink jet printers known in the art may be characterized as either continuous, thermal, or impulse devices, depending upon the mechanism by which the ink droplets are directed to the substrate. In continuous ink jet systems, an essentially uninterrupted stream of ink is ejected from a nozzle and breaks up into droplets. The droplets bear an electric charge so that they can be deflected by an applied electric field which is modulated according to the particular image to be recorded. The electric field directs the droplets toward either the substrate or an ink re-circulating reservoir. The inks employed in conjunction with continuous ink jet systems typically comprise a colorant such as a dye or pigment, an electrolyte to facilitate droplet deflection, and a liquid vehicle to dissolve or disperse the colorant and the electrolyte. While the vehicle in many continuous-type inks comprises water, U.S. Pat. No. 4,142,905, in the name of Cooke, disclosed a water-free ink composition consisting essentially of a low molecular weight glycol, an inorganic salt electrolyte, and a dye which is soluble in the glycol.

#FIGS. 1A–1E are diagrams of a device according to the present invention showing a firing signal applied to a piezoelectric print head chamber and the movement of ink within the chamber in response to the signal.

#FIG. 2 illustrates the effect of an antioxidant on the ink compositions according to the present invention.

#FIG. 3 depicts an impulse ink jet printing apparatus operated by a method in accordance with the present invention.

#The present invention provides improved dispersion ink compositions for use with drop-on-demand or impulse ink jet systems. The invention further provides ink jet ink compositions capable of printing clear, well-defined alphanumeric text and narrow bar width bar codes on porous and non-porous substrates. Throughout the description, the invention is described in connection with a solvent based pigment dispersion wherein the dispersed pigment is carbon black. However, the particular pigment, and its associated color described herein, only illustrate the present invention and are not intended to be limitations. The invention is equally applicable to other pigments as long as the performance characteristics as herein described are not adversely affected. Accordingly, the invention should not be limited to the particular pigment described as the invention contemplates the application of other pigments.

#As used herein, numerical ranges preceded by the term “about” should not be considered to be limited to the recited range. Rather, numerical ranges preceded by the term “about” should be understood to include a range accepted by those skilled in the art for any given element in impulse ink jet ink formulations according to the present invention.

#The dispersion ink compositions of the present invention contain a pigment dispersion. The pigment dispersion contains at least a pigment, a polymeric dispersant, and a dispersion medium. According to some embodiments, the dispersion medium is an ester, however other dispersion mediums are recognized by those skilled in the art, such as, for example, a glycol alkyl ether, a diol, or a diol ether are also suitable.