Incremental printing of symbolic information – Ink jet – Fluid or fluid source handling means
Reexamination Certificate
2000-09-11
2002-05-14
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Fluid or fluid source handling means
C347S101000, C347S096000
Reexamination Certificate
active
06386695
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to ink-jet inks, and, more particularly, to improving various aspects of the resulting print by an underprinting process.
BACKGROUND ART
Thermal ink-jet printers offer a low cost, high quality, and comparatively noise-free option to other types of printers commonly used with computers. Such printers employ a resistor element in a chamber provided with an egress for ink to enter from a plenum. The plenum is connected to a reservoir for storing the ink. A plurality of such resistor elements are arranged in a particular pattern, called a primitive, in a printhead. Each resistor element is associated with a nozzle in a nozzle plate, through which ink is expelled toward a print medium. The entire assembly of printhead and reservoir comprise an ink-jet pen.
In operation, each resistor element is connected through a conductive trace to a microprocessor, where current-carrying signals cause one or more selected elements to heat up. The heating creates a bubble of ink in the chamber, which is expelled through the nozzle toward the print medium. In this way, firing a plurality of such resistor elements in a particular order in a given primitive forms alphanumeric characters, performs area-fills, and provides other print capabilities on the medium.
Ink-jet inks used in thermal ink-jet printing typically comprise a colorant and a vehicle, with the vehicle often containing water and other relatively low surface tension liquids.
The tight tolerances of the nozzles (typically less than 30 &mgr;m diameter) require that the ink not clog the nozzles. Further, repeated firings of the resistor elements, which must withstand about 100 million firings over the life of the ink cartridge, can result in fouling of the resistor element. Finally, the ink composition must be capable of interacting with the print medium, especially paper, to penetrate the paper without undue spreading, and the ink composition should be smear and water resistant on the paper.
Inks are known which possess one or more of the foregoing properties. However, few ink compositions are known that posses all of those properties, since an improvement in one property often results in the degradation of another. Thus, inks used commercially represent a compromise in an attempt to achieve an ink evidencing at least an adequate performance in each of the aforementioned properties.
In commercially-available thermal ink-jet color printers, such as the DeskJet® printer available from Hewlett-Packard Company, a color spectrum is achieved by combining yellow, magenta, and cyan inks in various proportions. Typically, water-soluble dyes are employed. Black ink is either provided separately or by composite printing all three color inks. In the former case, a water-soluble black dye may be used or, more recently, a pigment-based black colorant may be used.
Water-soluble dyes are commonly used in dye-based inks. However, many dye-based inks, after being printed, exhibit poor water-fastness. There is an increased demand by consumers on the permanence or durability of ink-jet print, including water-fastness, light-fastness, smear-fastness, smudge-fastness, etc. Pigment-based black inks typically evidence the desired water-fastness, but exhibit other undesirable properties, such as slow dry time.
Color ink underprinting has recently received a lot of attention, given the benefits of color bleed, halo, dry time, media independence, and enhanced optical density (OD); see, e.g., application Ser. No. 09/659,666, filed Sep. 11, 2000. As used herein, color bleed refers to the lateral migration of inks which would otherwise lead to mixing at the color interfaces. The halo-effect occurs when two inks of different chemical potentials including surface tension are printed adjacent each other. At the interface between the two inks, there is an apparent depletion of optical density, resulting in the appearance of a “halo”.
However, there are two main disadvantages associated with color underprinting: (1) poor waterfastness associated with non-waterfast colors used in the color ink, and (2) the writing system using anionic black inks has required the color inks (anionic dyes) to use highly reactive additives to control bleed at black and color boundaries. While the reactive component is required, in order to create the precipitating or gellation mechanism, these materials have severely limited the dye choices for color inks.
Thus, a printing method is required that provides a printed product having improved properties such as low bleed, high edge acuity, high optical density, fast drying times, good waterfastness, good lightfastness, and good smearfastness without sacrificing performance in other necessary properties.
DISCLOSURE OF INVENTION
In accordance with the present invention, a method of printing an ink onto a print medium is provided. In the method, two inks are employed, a first ink that includes at least one water-soluble, color dye having a first charge and a second ink that includes at least one black pigment having a second and opposite charge. The method comprises:
(a) providing the first ink, which contains at least one water-soluble, color dye having one charge (anionic or cationic) and at least one surfactant;
(b) providing the second ink, which contains at least one black pigment, which has an opposite charge (cationic or anionic);
(c) printing in a first pass across the print medium the first ink; and
(d) printing the second ink over the first ink, totally covering and overlapping the first ink,
whereby the black pigment(s) reacts with the color dye(s) to form an insoluble complex on the print medium due to the use of opposite charges, thereby improving print speed, print quality, bleed, and waterfastness of the ink.
An ink set for an ink-jet printer is also provided for printing black ink on a print medium to form a printed ink set. The ink set comprises (a) the first ink, above, and (b) the second ink, above. The printed ink set comprises the second ink totally covering and overlapping the first ink.
BEST MODES FOR CARRYING OUT THE INVENTION
The present invention uses cationic black pigment inks and underprinting to give advantages in waterfastness for the black ink. Specifically, the present invention defines an ink system that yields waterfast black prints, even when underprinting with non-waterfast color inks. The present invention defines an ink system that yields waterfast black prints, even if the particular black colorant is not very waterfast shortly after printing.
In accordance with the present invention, two different inks are printed onto a print medium: a first ink that includes at least one water-soluble color dye having a first charge and a second ink that includes at least one black pigment having a second and opposite charge. The method comprises:
(a) providing the first ink, which contains at least one water-soluble color dye having one charge (anionic or cationic) and at least one surfactant;
(b) providing the second ink, which contains at least one black pigment, which has an opposite charge (cationic or anionic);
(c) printing in a first pass across the print medium the first ink; and
(d) printing the second ink over the first ink, totally covering and overlapping the first ink,
whereby the black pigment(s) reacts with the color dye(s) to form an insoluble complex on the print medium due to opposite charges, thereby improving print speed, print quality, bleed, and waterfastness of the ink.
The net result of using the above black pigment ink, the above color ink, and underprinting with the color ink is a simpler ink system that optimizes the chemistry of each colorant and allows the colorants to complex each other, to yield good waterfastness. This allows much greater latitude in dye choice.
For example and preferably, an anionic color ink may comprise any of the dye-based inks used in ink-jet printing wherein at least one anionic color dye is employed. Many of these inks are well-known and have been disclosed elsewhere; see, e.g., U.S. Pat. Nos. 5,091,005; 5,098,476
Barlow John
Shah Manish S.
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