Compositions: coating or plastic – Coating or plastic compositions – Marking
Reexamination Certificate
2000-03-14
2002-11-12
Klemanski, Helene (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Marking
C106S031860, C106S031750, C106S031760, C106S031780, C106S031870
Reexamination Certificate
active
06478862
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION(S)
NONE
BACKGROUND OF THE INVENTION
The present invention generally relates to a thermal ink jet printer ink. More specifically, the present invention relates to a thermal ink jet printer ink that may incorporate a pigment dispersion. The present invention further relates to a pigmented, thermal ink jet printer ink with a long shelf life.
Thermal ink jet printing is a commonly used method of recording images on recording material, such as paper or cloth, by discharging discrete droplets of ink from nozzles of a print head and allowing these droplets to be absorbed by the recording material. Thermal ink jet recording offers opportunities for quiet, high speed, full color printing. Also, images printed with thermal ink jet printers seldom need to be fixed or treated after the ink droplets are absorbed on the recording material.
Thermal ink-jet printing is a non-impact printing process in which ink droplets are formed and thereafter deposited on a print medium in a particular order to form an image on the print medium. The low cost and high quality of the printed output in combination with the relatively noise-free operation of ink jet printers have made ink jet printing a popular and economical alternative to other types of printing in consumer, office, and industrial settings.
Thermal ink-jet printing is one example of a drop-on-demand form of non-impact printing. Other examples of drop-on-demand systems, besides thermal ink jet, are piezoelectric ink jet, acoustic ink jet, and vibrating ink jet systems. Besides drop-on-demand systems, there are also continuous stream ink jet printing systems. In continuous stream ink jet systems, ink is emitted in a continuous stream under pressure through at least one orifice or nozzle. The steam of ink is then broken up into droplets at a fixed distance from the orifice, and the ink droplets are thereafter directed toward the recording medium or recycled into the printing ink supply.
In drop-on-demand systems, an ink droplet is not formed or expelled from the print head unless the droplet is to be placed on the recording medium. Therefore, since drop-on-demand systems require no ink recovery or post-ejection treatment, drop-on-demand systems are typically somewhat simpler in construction and operation than continuous stream ink jet printing systems. Thermal ink jet (sometimes referred to as “bubble jet”) systems are one of the most common types of drop-on-demand ink jet printing systems.
In thermal ink jet printing, the energy for drop formation and ejection is generated by electrically heated resistor elements. The resistor elements heat up rapidly in response to electrical signals from a microprocessor to create a vapor bubble. Superheating of the ink far above the normal boiling point of the ink causes the bubble formation. The expansion of the bubble forces a droplet of ink out of a nozzle at a high rate of speed toward the recording medium. After the collapse of the bubble, the ink channel proximate the resistor element refills by capillary action.
Colorants for inks printed by thermal ink jet printing may be generally classified as dyes or pigments. Accordingly, thermal ink jet printer inks may incorporate dye(s), pigment(s), or a combination of dye(s) and pigment(s) to print images on the recording media. Of these three, dye-based thermal ink jet printer ink compositions are most widely available commercially.
One reason that dyes are sometimes selected over pigments concerns the expansive color gamuts and color vibrancy that combinations of different, separately-applied, dye-based thermal ink jet inks typically achieve via process printing, as compared to combinations of conventional pigment-based inks that are separately applied via process printing. Also, the mechanics of printing dye-based inks via thermal ink jet are often simpler than those of printing pigment-based inks since pigments often constitute relatively large particles, as opposed to the molecules of dyes. These particles of pigment may influence the mechanism of drop formation and consequently may enhance the difficulty of achieving good printing performance, such as optimum drop size (drop volume), velocity, and trajectory, as compared to thermal ink jet inks that are based upon molecule-size dyes. Finally, owing to the particle form of pigments, there is a tendency for the pigments of pigmented inks, such as thermal ink jet ink, to sediment, agglomerate, and/or flocculate if the pigments are not properly dispersed in the suspension medium of the ink over the long term. Dyes, as compared to pigments, do not typically exhibit this tendency toward sedimentation, agglomeration, and/or flocculation since dyes are typically in the form of molecules, as opposed to particles.
However, despite these advantages of dye-based inks, there is motivation to use pigments instead of dyes in printing inks. For example, pigments typically exhibit enhanced light fastness characteristics, as compared to dyes. More specifically, printed images formed from thermal ink jet printing inks are often more resistant to color degradation and fading upon exposure to various types of light, such as ultraviolet light, as compared to dyes. Also, pigment-based inks are typically more water resistant than dye-based inks, since many dyes are water soluble to some extent. Furthermore, in many potential new markets for thermal ink jet printing, pigment has traditionally been used as the colorant in printing inks. For example, in the graphic arts industry, the printing systems that are predominantly relied upon, such as lithographic printing, screen printing, gravure printing, flexographic printing, and offset printing, typically employ pigmented inks, as opposed to dye-based inks. Consequently, due to the familiarity of these potential new markets with pigmented inks, any attempt to penetrate these new markets with thermal ink jet printing would benefit from incorporating pigmented ink.
Much development work has focused on pigmented thermal ink jet inks over the past decade or so. Many approaches have focused on preparation of thermal ink jet inks using increasingly sophisticated proprietary pigments. Other attempts have been made to enhance dispersion of pigments in ink using increasingly sophisticated compounds. Though these attempts have added to the store of knowledge concerning pigmented thermal ink jet inks, problems still remain. For example, despite these attempts to enhance dispersion of pigments in ink, no one has found an inexpensive way to maintain uniform dispersion of pigments in thermal ink jet inks over longer periods of time, such as about a month, about six months, about one year, or even about two years or longer. Indeed, pigment particle settling, agglomeration, and/or flocculation, within as little as a few hours or days of manufacture, are prevalent among commercially available pigmented thermal ink jet inks, including even expensive pigmented thermal ink jet inks that are based upon sophisticated proprietary pigments and/or sophisticated dispersion agents.
Corresponding to the increasingly sophisticated and propriety nature of pigments and pigment dispersants, the cost of preparing pigment-based thermal ink jet printer ink has skyrocketed. These sophisticated pigments and pigment dispersants are only available at a high cost, due to the research and development costs that led to creation of these sophisticated pigments and pigment dispersants and/or due to the costly processing and/or mechanical equipment required to prepare these sophisticated pigments and pigment dispersants. Consequently, retail purchase prices for pigmented thermal ink jet inks are often as high as about $300 per pound, or more, depending upon the sophistication of the pigment and pigment dispersant.
On the other hand, in the graphic arts industry, retail purchase prices for inks used in lithographic printing, screen printing, gravure printing, flexographic printing, and offset printing typically are as low as about $5 per pound, or less. Thus, retail purchase prices for
Carmody & Torrance LLP
Faison Veronica F.
Klemanski Helene
MacDermid Acumen, Inc.
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