Incremental printing of symbolic information – Ink jet – Medium and processing means
Reexamination Certificate
2003-01-03
2004-07-27
Meier, Stephen D. (Department: 2853)
Incremental printing of symbolic information
Ink jet
Medium and processing means
C347S102000, C347S105000
Reexamination Certificate
active
06767091
ABSTRACT:
BACKGROUND OF INVENTION
This invention relates generally to the treatment of the printed images from printing devices so as to improve their appearance. More particularly, it relates to the enhancement of color saturation, the protection of printed images from various types of damage and the extension of the lifetime of these images.
Digital printing involves the creation of graphical and textual material by means of depositing tiny spots of ink to a substrate. It differs from other forms of printing because the images are composed of well defined, uniformly placed spots of ink whose distribution and patterns are defined by the print engine rather than by photographic screens or monolithic type.
Ink jet printing is widely used for creating low cost, color printed output. Many aspects of the design, construction and operation of ink jet printers, and the chemical formulation of the inks used in these printers and also to the substrates upon which the printed image is created (e.g. coated papers, transparent materials for use in overhead projectors) have been taught in the prior art.
The quality of the output produced by ink Jet printers is limited by a number of factors related to the method used to produce it. There are a number of other printing technologies for producing color prints of higher perceived quality than ink jet, such as dye sublimation, thermal wax transfer and color xerography. Ink jet printed output is perceived to have reduced color intensity (a washed out appearance) because the ink must be carefully deposited so that adjacent pixels are distinct and separate. If not, then the inks will mix (“bleed”) and the resulting image will appear muddy and of low resolution.
FIG. 2
shows a series of the steps of an ink-jet printing process of the prior art. Element
202
is a drop of ink shown both in flight and upon contact with substrate—
204
. Element
206
is this drop of ink “impinging” onto the substrate. As depicted the droplet begins to lose its spherical shape as it encounters substrate
204
. Element
208
—is the same drop of ink, now being incorporated/absorbed into the substrate forming a wet drop of ink thus forming a spot. Element
210
depicts the spot somewhat later in time after the liquid vehicle of the ink has been completely absorbed into substrate
204
. Finally, element
212
represents the spot after the spot has dried and the colorant immobilized into and/or atop substrate
204
.
Jaeger et al.'s article entitled “The influence of Ink/Media interactions on Copy Quality in Ink-Jet Printing”, published in Proceedings of the SID, Vol. 25/1, 1984, provides a comprehensive overview of the influence of ink and paper choices on the color quality of ink-jet prints. They conclude that the quality of these prints is dependent on the rapid absorption of ink into the substrate and the ability of the colorant to be retained on or near the surface of the substrate. They observe that photographic quality images require high-resolution prints (higher number dots per inch-dpi) and that the ultimate resolution of these prints is dependent on minimizing the lateral migration of the ink drop in the substrate. Thus their effort and focus is to prevent, minimize and limit the ultimate size of each dot applied to the printed image.
A great deal of effort has been directed toward improvements in reducing ink drop size by specially treated substrates that quickly absorb the wet ink spots, fast drying inks as well as combinations of inks that employ a variety of physical and chemical phenomena to reduce or eliminate ink mixing.
Palmer et al.'s article entitled “ink and Media Development for the HP Paintjet Printer”, published in Hewlett-Packard Journal, August 1988, discusses the complex interactions between ink, print head design, properties of different substrates and the differing requirements of different forms of printing (text versus graphics). Their objective is to carefully control the resulting dot size to meet the requirements of each type of printing and each type of substrate (e.g. opaque versus transparent, coated versus non-coated). They clearly demonstrate that many factors must be considered (e.g. thermal tolerance of the ink, clogging of print heads, absorption of ambient moisture into coated papers thus making them tacky to the touch, etc.) when designing an Ink-jet printing system in which the dot size is carefully controlled to meet a variety of printing requirements.
Yoldas' article entitled “A dense transparent ink-jet receptive film that provides instantaneous print drying”, published in Journal of Material Research Vol. 14, No. 6, June 1999, focuses on the development of coatings for Ink-jet substrates that lead to a tighter containment of colorants resulting in higher edge acuity for deposited ink drops thus enabling high resolution images. Yoldas describes a family of Sol-Gel coatings that quickly absorb and immobilize the large volume of water used as the vehicle for colorant in ink-jet inks.
All of these teachings share the common objective of producing the smallest resulting ink dot on the printed substrate and the prevention of colorant migration and unintended mixing of different inks.
The undesired mixing of wet ink spots is generally called “bleeding”. One side effect of efforts to prevent bleeding is to deposit well-defined and separated ink spots. The substrate is not fully covered with ink and the underlying color of the substrate is seen. If that substrate is a white sheet of paper, then light scattered by the substrate itself increases the sense of the colors seeming to be “washed out”.
A variety of methods have been suggested to overcome these limitations. These include making multiple printing passes over the substrate and depositing ink in patterns that overlap. Such methods require that the ink deposited on the first pass is sufficiently dry such that subsequent deposition of inks of other colors does not mix with the ink spots already deposited. Or it requires that specialized inks are used that are mutually immiscible so that colorants do not mix. These methods also require that more pixels are printed. Such methods increase the resolution of the image, but require a substantial increase (e.g. quadratic) in the number pixels to be printed. This requires the use of more ink, requires significantly longer printing times and because of very heavy ink loading, can cause the substrate material to wrinkle because of excess moisture.
U.S. Pat. No. 6,090,749 for Kowalski issued on Jul. 18, 2000 discloses a method for creating vivid and water-fast printed images on a specially designed multi-layer substrate. Kowalski requires the substrate be composed of two transparent layers: a hydrophilic, ink absorbing front layer and a hydrophobic backing layer. Kowalski also requires that the surface of the substrate is not covered or coated with any additional materials or layers. An ink jet printer is used to apply a highly specialized set of inks. These require use of “sublimable dye diffusion thermal transfer coloring agent”. An ink jet printer is used to apply these inks onto an ink-absorbent hydrophilic front layer. The composite substrate is subsequently subjected to high temperature (and pressure) in order to vaporize the dye and to cause transference of colorant into a transparent hydrophobic backing layer. The transference of colorants into the interior of the backing layer is described as occurring by absorption, capillary action and alternatively termed diffused into the interior of the backing layer.
The objective of the Kowalski process is to produce a water-fast, vivid color image. These objectives impose a number of requirements and restrictions. For example, in order to assure that the resulting image is water-fast, all of the colorant initially deposited on the ink-absorbing layer must be transferred from the water absorbing front layer into the interior of the water resistant backing layer. Since all of the colorant must be removed from the first layer to the second layer, the transference of colorant cannot be c
Dudding Alfred
Meier Stephen D.
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