Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1999-03-22
2001-06-12
Le, N. (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S015000
Reexamination Certificate
active
06244687
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to inkjet printers and, in particular, to a printing technique for reducing the dry time of black ink in a color printer.
BACKGROUND
Inkjet printers are well known and extremely popular. Details of a particular inkjet printer are described in U.S. Pat. No. 5,648,806, entitled Stable Substrate Structure for a Wide Swath Nozzle Array in a High Resolution Inkjet Printer, by Steven Steinfeld et al., assigned to the present assignee and incorporated herein by reference.
An inkjet printer ejects fine droplets of ink onto a print medium, typically paper, in response to electrical signals generated by a microprocessor. A typical inkjet printhead has an array of precisely formed nozzles overlying a printhead substrate. The substrate incorporates an array of firing chambers (or drop ejection chambers) that receive liquid ink through ink channels connected to one or more ink reservoirs. Each firing chamber typically has a thin-film resistor or a piezoelectric element which, when energized, causes a droplet of ink to ejected through an associated nozzle onto the medium as the printhead scans across the medium. Energizing a thin-film resistor heats the resistor to vaporize a portion of ink in the firing chamber to cause a droplet of ink to be ejected from its associated nozzle. Energizing a piezoelectric crystal causes the crystal to expand to propel a droplet of ink from a nozzle.
High quality color inkjet printers include printheads for the three primary color inks, cyan, magenta, and yellow, and a separate printhead for black ink. One type of color inkjet printer incorporates a separate replaceable print cartridge for each of the four colors of ink installed in a scanning carriage. Another type of color inkjet printer incorporates two, three, or four different color printheads in the same print cartridge. Still another type of color inkjet printer uses a single printhead (having a single substrate), having multiple sets of nozzles, that ejects a different color ink (e.g., CMY) through each set of nozzles. Some color printers use more than four colors of ink, with a separate printhead for each color. The order of printheads in the carriage is typically black on the left side or right side of the primary color cartridges, with the order of the primary color cartridges being arbitrary.
A common black ink is a pigment-based ink where undissolved particles are suspended in a clear solution. Such pigment-based ink creates the darkest black with a minimum of bleed into the paper. Since the paper is typically white, any significant bleeding of the black ink into the paper will noticeably reduce the sharpness of the edges of black text or other black print.
For color inks, dye-based inks are very popular. Dye-based inks do not have color particles suspended in solution and thus tend to bleed into the paper more than pigment-based inks. This bleeding is not noticeable due to the relatively low contrast between the white paper and the color ink. Since the dye-based ink wicks or bleeds into the paper, the dye-based inks dry faster than the pigment-based black inks, which effectively pool on the paper surface. Color inks may also be pigment-based.
Examples of such black inks and color inks are described in U.S. Pat. Nos. 5,695,820 and 5,626,655 assigned to the present assignee and incorporated herein by reference.
As inkjet printers evolve to print faster, there is less time for the ink to dry. In some cases, after printing on a page is complete, the printer needs to hold onto the page for a predetermined time in order to let the ink dry before depositing the page in an output tray. The drying of the black ink is likely to be the bottleneck for drying time of a page.
What is needed is a technique for reducing the drying time of inks deposited by an inkjet printer.
SUMMARY
In accordance with one embodiment of the present invention, a black printhead is installed in a scanning carriage with at least one primary color ink printhead on both sides of the black ink printhead. In one embodiment, the color inks are the type which wick into a standard sheet of paper faster than the black ink. These types of color inks contain surfactants. The color inks will typically be dye-based (but may also be pigment-based) and the black ink will typically be pigment-based. In another embodiment, the color inks are either dye-based or pigment-based and react with the black ink to precipitate out the black ink pigment so as to dramatically speed the drying time of the black ink. These types of color inks contain reactants. Useful color inks may also contain both surfactants and reactants.
In one embodiment of the invention, to reduce the drying time of black ink, an amount of one of the primary color inks is deposited on the paper where the black ink is intended to be subsequently deposited during the same pass across the paper. This is referred to as underprinting. During the same pass of the carriage across the paper, the black ink is then deposited over the primary color ink. Since primary color printheads are located on both sides of the black printhead, this printing technique may be accomplished whether the carriage scans from left to right or from right to left. The wicking of the small amount of primary color ink into the paper (“wetting” the paper) also causes some wicking of the black ink solution into the paper while the black pigment remains on the surface of the paper. There is no noticeable bleeding of the black ink. The dispersion of the black ink solution into the paper causes the black ink to dry faster than had the black ink been the only ink printed.
In the embodiment where the color inks react with the black ink to precipitate out the black pigment, wicking of the color ink into the paper is not necessary (although wicking may occur if the ink contains reactants and surfactants). The underprinted color ink reacts with the black ink to reduce drying time.
The primary color ink beneath the black ink will be different for the two carriage scan directions. Changing the underprinted color from, for example, cyan to magenta during consecutive scans will cause a shift in the hue of the black ink from one swath to another.
In one embodiment of the invention, to avoid this hue shift, after the black ink is printed over the primary color ink (e.g., magenta), another primary color ink is then printed over the black ink during the same scan, such that three layers of ink form the black printed image. This is referred to as overprinting.
In the example above, black is printed using a combination of underprinted cyan, black, and overprinted magenta when the carriage scans from left to right, and black is printed using a combination of underprinted magenta, black, and overprinted cyan when the carriage scans from right to left so that no hue shift will occur when the carriage prints in both directions. If the color effect of the underprinted color ink is less then the color effect of the overprinted color ink, the optimum amount of overprinted color ink will be less than the underprinted color ink. The proper amounts of underprinted and overprinted inks should be determined empirically. In one embodiment, the amounts of underprinted and overprinted inks are symmetrical, but the amounts of underprinted and overprinted inks when scanning from left-to-right may be different from the amounts going from right-to-left.
In one embodiment, the order of print cartridges in the scanning carriage, as viewed from the front of the printer, is cyan, black, magenta, and yellow. In another embodiment, the order is cyan, black, yellow, and magenta. All other orders where black is not located at the ends are envisioned. If a single printhead using multiple sets of nozzles, one set per color, is used, then the black set of nozzles is to be located between two primary color sets.
In another embodiment, the color printer uses a two-pass technique, or other multiple pass technique, where multiple passes over the same area are needed to complete the printing across a page. In such multiple pa
Gast Paul David
Looman Steven D
Prasad Keshava A
Riou Michel A.
Smith Brooke E
Hewlett--Packard Company
Le N.
Nguyen Lamson D.
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