Stock material or miscellaneous articles – Ink jet stock for printing – Particles present in ink receptive layer
Reexamination Certificate
2002-09-05
2004-09-28
Shewareged, B. (Department: 1774)
Stock material or miscellaneous articles
Ink jet stock for printing
Particles present in ink receptive layer
C428S032210, C428S032270, C428S032300
Reexamination Certificate
active
06797347
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method of ink-jet printing, and more particularly, to printing ink-jet inks onto a print medium where a coating on the medium contains an inorganic pigment that has been modified to have a positive charge.
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 connects to an ink storage reservoir. The arrangement of a plurality of such resistor elements forms 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 via a conductive trace to a microprocessor, where current-carrying signals cause one or more selected elements to heat. The heating creates a bubble of ink in the chamber, which jets 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-fill, and provides other print capabilities on the medium.
Recording media used in ink-jet printing include various papers such as plain papers and coated papers as well as synthetic papers, cloths and plastic films. The recording, or print, medium must absorb ink well and be free from bleed and feathering of the deposited image. The medium must be capable of accepting high resolution (i.e. small) dots with high image density (i.e. relatively large volumes of ink). Lateral diffusion of ink dots should be small. The medium should have high opacity and prevent show through to the non-printed side. The medium should promote the drying of the ink. Other aspects of the medium can affect the water- and light-fastness of the recorded images as well. As ink-jet printers have been designed with the ability to print at higher speeds and to place more precisely the dot of ink on the print medium, the demands on the print medium have increased. No print medium for use in modern ink-jet printers encompasses all the desired features.
Since an ink-jet recording paper was first sought, attempts have been made to satisfy the above-mentioned requirements. With the increased demands placed on the medium by more advanced printer capabilities, the performance of the paper necessary to satisfy the requirements has greatly increased. One method used in the past to satisfy the mentioned requirements provided a substrate with a coating layer (ink receptive layer) comprising a pigment and a binder that absorb ink well. As seen from the following patent citations, one method for improving the imaging output was to immobilize the ink on the paper coating by incorporating a cationic polymer or other additives in the paper coating. Metallic salts were used in the past for the same purpose. However, due to the water sensitivity of the metal salt, print quality varies depending of the printing environment.
U.S. Pat. No. 4,694,302, entitled “Reactive Ink-Jet Printing” and assigned to the same assignee as the present application, discloses a print method for increasing the water-fastness and print quality of an ink. In that invention, a reactive species that chemically links the ink dye to the paper substrate is applied to the print medium either before or after printing the ink.
U.S. Pat. No 4,419,388, entitled “Waterproofing Method for Ink-jet Records,” discloses an increase in waterfastness by applying a treatment of various mixed-metal sulfates or selenates to the surface of the paper after the image has been recorded. To improve ink-jet printing, U.S. Pat. No. 4,830,911, entitled “Recording Sheet for Ink-jet Printers,” employs a cationic water-soluble polymer coating applied after an aqueous ink has been printed to form the image. The preceding inventions suffer from the complexity of needing either two separate printheads or an additionally coating step after printing to achieve improvements in print quality.
U.S. Pat. No. 5,320,668, entitled “Bleed Alleviation Using pH-sensitive Agents” and assigned to the same assignee as the present application, uses a method of printing where contact with another ink of either higher or lower pH than the first forces the colorant/dispersant of the first ink out of solution. That patent specifically addresses the problem of color migration between inks of different colors and, while the invention effectively alleviates bleed between two ink colors, it cannot be used to improve the print quality when using a single ink.
U.S. Pat. No. 5,206,071, entitled “Archivable Ink-jet Recording Media,” uses a water insoluble high molecular weight quaternary ammonium salt to reduce bleed at high humidity. U.S. Pat. No. 4,740,420, entitled “Recording Medium for Ink-Jet Printing,” and U.S. Pat. No. 4,554,181, entitled “Inkjet Recording Sheet Having a Bicomponent Cationic Recording Surface,” disclose recording media which have been modified by surface treatments containing soluble metal salts to aid in insolubilization of the colorant in the ink. This latter reference suffers from the need for at least one extra step in the manufacturing of the medium to apply the soluble metal salt surface treatment. Also, when soluble salts are used, the print quality varies with humidity due to the interaction between the salts and air-borne water vapor. The references described above suffer from complex and expensive, post-manufacture, surface modification of the print medium or complicated multi-step processes to achieve the needed improvements in print quality. Furthermore, none of these methods simultaneously address all the needs of print media that are to be used with advanced ink-jet printers.
Although the above-described ink-jet printing methods and media treatments are suitable for their intended purposes, a need remains for a method of ink-jet printing that conveniently, economically, and simultaneously improves resolution, color retention, waterfastness, smear-fastness, image retention and image density while decreasing image bleed in ink-jet printing by improving the ink handling capabilities of the recording medium.
DISCLOSURE OF INVENTION
In accordance with the invention, a print method is provided which substantially improves resolution, color retention, waterfastness, smear-fastness, image retention and image density while decreasing image bleed in ink-jet printing by conveniently supplying a cation in the form of a metal-organic charge complex incorporated within the pigment of the print medium itself More specifically, the print method comprises the steps of:
(a) providing an ink-jet ink that contains a colorant that is either anionic or is a pigment, dispersed with an anion-sensitive dispersant;
(b) providing an ink-jet print medium containing:
(1) a base paper, and
(2) a coating on the base paper that contains an inorganic pigment, modified with a positively charged complex, and a binder; and
(c) printing the ink-jet ink onto the ink-jet print medium, thereby substantially improving resolution, color retention, waterfastness, smear-fastness, image retention and image density while decreasing image bleed between adjacently-printed inks.
The cationic metal-organic charge complex insolubilizes the anionic dyes in the ink-jet inks or destroys the dispersing ability of dispersants in the vehicle when the colorant is pigment-based. It serves to improve the waterfastness of the printed image more than the soluble metal salts used in the prior art. Also, the choice of a metal ion that is only very slightly soluble in water improves the performance of the paper when used in environments with adverse humidity conditions. When paper is used as the print medium in the present invention, no additional steps are required in the paper production process because common commercial paper already contains
Hewlett--Packard Development Company, L.P.
Shewareged B.
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