Incremental printing of symbolic information – Ink jet – Medium and processing means
Reexamination Certificate
2000-08-03
2002-09-03
Gordon, Raquel Yvette (Department: 2853)
Incremental printing of symbolic information
Ink jet
Medium and processing means
Reexamination Certificate
active
06443571
ABSTRACT:
BACKGROUND OF THE INVENTION
Inkjet printing has been a major technology for bringing affordable color printing to the market. While there is a considerable variation in the products on offer and the specific technology employed, the basic method remains that of expelling a small droplet of ink-bearing liquid from a miniature nozzle onto the surface of the medium being printed on. Each droplet represents a pixel to be printed. A row or array of such nozzles is then scanned across the print page in order to address each pixel position by a wide range of interlacing and interleaving schemes. An electronic control unit directs the scanning process and sends the instructions to individual nozzles as to whether they should print at a given position or time. The method by which the droplets are expelled varies, as do the inks.
One of the most enduring shortcomings of the inkjet process has been the fact that the resulting print shows banding or striations. These may be traced back to one of three factors. Firstly, the lateral registration of the printing head, as it traverses laterally across the page in order to address all the columns being printed, may be less than perfect. Secondly, failed or clogged nozzles in the printing array head may cause missing or intermittent lines that are reproduced across the width of the page. Thirdly, droplets being emitted in either inconsistent trajectories or off-center lead to similar banding.
The first problem has been addressed via a variety of print head designs or interleaving printing arrangements driven by appropriate software. This includes page wide print head arrays. Examples of print head array designs addressing this issue are Furukawa in U.S. Pat. No. 4,272,771, Tsao in U.S. Pat. No. 4,232,324, Padalino in U.S. Pat. No. 4,809,016 and Lahut in U.S. Pat. No. 5,070,345.
The second problem has been addressed via various backup and redundancy schemes. Examples of such methods and head designs are given by Schantz in U.S. Pat. No. 5,124,720, Hirosawa in U.S. Pat. No. 5,398,053 and Silverbrook in U.S. Pat. No. 5,796,418.
The present invention addresses itself to the third issue, namely that of the ink droplets finally ending up on the print medium in a misaligned position. This issue has dogged the industry for some years now and is rather more fundamental to the basic process of inks expelled through a nozzle. Various techniques have been proposed and employed to address it.
One method of which variants are often proposed is that of using electrostatic fields to direct the droplet. Examples of this approach are given by Ruscitto in U.S. Pat. No. 4,054,882, Paranjpe in U.S. Pat. No. 4,219,822 and Crean U.S. Pat. No. 4,525,721.
One approach that has been followed in addressing the quality of inkjet printing is to introduce a roller between the nozzles and the final surface on which the printing is to take place. This offset roller approach is described in a number of inventions. Examples are given by Takita in U.S. Pat. No. 4,293,866 and Durkee in U.S. Pat. No. 4,538,156.
When an ink-bearing droplet is expelled from a nozzle onto a substrate surface the droplet will deform when it hits the surface and finally comes to rest. Depending on the particular combination of liquid and materials used for the solid surface, it will assume a spheroid shape of which the distortion away from a perfect sphere is determined by the surface energy of the substrate and the surface tension of the liquid of which the droplet is composed. All it requires is a single monolayer of surface material in order to change the behavior of a surface between hydrophilic and hydrophobic.
If, in particular, the substrate were hydrophobic, and the droplet were water-based, the droplet would tend more towards a perfect sphere than if the substrate were hydrophilic and wetted by water. A consequence of this particular former combination of substrate and ink is that the droplet would not adhere to the substrate very well for the very same reasons that caused it to be a near-perfect sphere. With the low attractive force between substrate and the droplet, there would then also be a much greater likelihood of independent neighboring drops coalescing.
This situation is of particular relevance to inkjet printing. In this technology a multiplicity of droplets is deposited and, depending on whether one is printing solid and shadow areas on the one hand, or highlighted areas on the other, the droplets may be very close together or far apart. If it is indeed solids and shadows to be printed, then there is a high likelihood of the droplets coalescing due to mutual proximity. The image being reproduced will therefore lose its integrity under these circumstances.
If the substrate surface were chosen to be hydrophilic, and the ink were water-based, then the droplet would deform considerably away from a sphere. Such a surface is said to be “wet” by water. The droplet would now much be more likely to adhere to the surface. Some prior art discusses a transfer via an intermediate roller, similar to offset printing.
In order to transfer the droplets to a final surface, such as paper, the droplets should however, not adhere too strongly to the intermediate surface otherwise droplets will partially remain on the transfer surface and transfer will be degraded.
While located on the transfer surface the droplets may ideally be made to undergo such change in their properties as will make them exhibit superior printing characteristics with respect to the final print surface. Finally, when printed, the droplets should absent themselves totally from the transfer surface and be committed totally to the final print surface, maintaining their registry in the process.
In a number of applications there is merit to the ink droplets being reduced in viscosity or in physical size while located on the transfer surface. This assists in avoiding the printed dot developing a misshapen form as the solvent spreads into the printing surface and assists in maintaining the color intensity and correctness of the reproduction and helps control dot gain. There are also applications in which it is useful to manage the ink in a water-based format for the purposes of ejection through a nozzle, but where it is more useful for the ink to change to non-water -soluble for the final transfer to the printing surface.
Sansone in U.S. Pat. No. 4,673,303 and Anderson in U.S. Pat. No. 5,099,256 describe apparatus that allow for the modification of the ink droplets while in residence on a transfer surface. None of this particular prior art addresses the problem of banding or striations. The transfer roller in the prior art improves the dot shape, but not the accuracy of the positioning of the dot. It is the object of the present invention to improve the dot positioning accuracy while incorporating all the advantages of the prior art.
BRIEF SUMMARY OF THE INVENTION
An inkjet printing method corrects for local error in position of droplets deposited by an inkjet nozzle. The method comprises inkjet droplets self-registering on a transferring surface that ensures that they are transferred to the correct pixel positions on the final printing surface.
REFERENCES:
patent: 4054882 (1977-10-01), Ruscitto
patent: 4219822 (1980-08-01), Paranjpe
patent: 4232324 (1980-11-01), Tsao
patent: 4272771 (1981-06-01), Furukawa
patent: 4293866 (1981-10-01), Takita
patent: 4525721 (1985-06-01), Crean
patent: 4538156 (1985-08-01), Durkee
patent: 4673303 (1987-06-01), Sansone
patent: 4809016 (1989-02-01), Padalino
patent: 5070345 (1991-12-01), Lahut
patent: 5099256 (1992-03-01), Anderson
patent: 5124720 (1992-06-01), Schantz
patent: 5398053 (1995-03-01), Hirosawa
patent: 5796418 (1998-08-01), Silverbrook
Gelbart Daniel
Shinkoda Ichiro
Creo Srl
Oyen Wiggs Green & Mutala
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