Stock material or miscellaneous articles – Structurally defined web or sheet – Discontinuous or differential coating – impregnation or bond
Reexamination Certificate
1993-07-21
2001-03-20
Krynski, William (Department: 1774)
Stock material or miscellaneous articles
Structurally defined web or sheet
Discontinuous or differential coating, impregnation or bond
C428S343000, C428S411100, C428S480000, C428S483000, C428S488410
Reexamination Certificate
active
06203887
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to a method and apparatus for producing continuous tone images with near photographic print qualities using xerography.
In the practice of conventional xerography, it is the general procedure to form electrostatic latent images on a xerographic surface by first uniformly charging a charge retentive surface such as a photoreceptor. The charged area is selectively dissipated in accordance with a pattern of activating radiation corresponding to original images. The selective dissipation of the charge leaves a latent charge pattern on the imaging surface corresponding to the areas not exposed by radiation.
This charge pattern is made visible by developing it with toner by passing the photoreceptor past one or more developer housings. In monochromatic imaging, the toner is generally comprises black thermoplastic powder particles which adhere to the charge pattern by electrostatic attraction. The developed image is then fixed to the imaging surface or is transferred to a receiving substrate such as plain paper to which it is fixed by suitable fusing techniques.
Recently, there has been a great deal of effort directed to the development of color copiers/printers which utilize the xerographic process. Such efforts have resulted in the recent introduction of the Xerox™ 5775™ copier/printer and the Fuji XeroxA-Color 635 machine.
The quality of color xerographic images on paper has approached the quality of color photographic prints. However, color xerographic prints fall short because they do not have the uniform gloss, dynamic range or brilliance typical of photographic prints. Nor do xerographic prints have the feel of photographic prints because the paper usually used is too lightweight and too limp.
Typically the surface of color toner images is irregular, therefore, rather rough or lumpy. The behavior of incident white light vis-a-vis such color images is believed to be as follows:
Some of the white light incident on the substrate carrying the color toner images specularly reflects off the substrate.
Some of the light goes down into the paper, scatters around and comes back out in various directions, some through the toner and some not.
Because the toner surface is rough or irregular some of the light incident thereon is reflected off the toner in various directions.
Some of the light incident on the irregular toner surfaces passes through the toner into the paper and comes back out in various directions.
White light becomes colored due to selective absorption as it passes through toner. The light then goes down into the paper and back out through the toner whereby it becomes more colored through more absorption. As will be appreciated, any white light which does not pass through the toner diminishes the appearance of the final print.
Attempts to make up this deficiency in conventionally formed color toner images have led to the lamination of xerographic images on paper using a transparent substrate. This procedure has been only partially successful because the lamination process tends to reduce the density range of the print resulting in a print that has less shadow detail. The lamination process also adds significant weight and thickness to the print.
Additionally, it is believed that the aforementioned lamination process does not produce good results because typically the color toner images at the interface between the laminate and the toner do not make suitable optical contact. That is to say, the initially irregular toner image at the interface, is still irregular (i.e. contains voids) enough after lamination that light is reflected from at least some of those surfaces and is precluded from passing through the toner. In other words, when there are voids between the transparency and toner image, light gets scattered and reflected back without passing through the colored toner. Loss of image contrast results when any white light is scattered, either from the bottom surface of the transparent substrate or from the irregular toner surfaces and doesn't pass through the toner.
A known method of improving the gloss of color xerographic images on a transparent substrate comprises refusing the color images. Such a process was observed at a NOMDA trade show in 1985 at a Panasonic exhibit. The process exhibited was carried out using an off-line transparency fuser, available from Panasonic as model FA-F100, in connection with a color printer which was utilized for creating multi-color toner images on a transparent substrate for the purpose of producing colored slides. Since the finished image from the color printer was not really suitable for projection, it was refused using the aforementioned off-line refuser. To implement the process, the transparency is placed in a holder intermediate a clear relatively thin sheet of plastic and a more sturdy support. The holder is used for transporting the imaged transparency through the off-line refuser. After passing out of the refuser, the transparency is removed from the holder. This process resulted in an attractive high gloss image useful in image projectors. The refuser was also used during the exhibit for refusing color images on paper. However, the gloss is image-dependent. Thus, the gloss is high in areas of high toner density because the toner refuses in contact with the clear plastic sheet and becomes very smooth. In areas where there is little or no toner the gloss is only that of the substrate.
The following is a discussion of prior art which may be relevant to the patentability of the present invention:
U.S. Pat. Nos. 4,686,163 and 4,600,669 describe an electrophotographic imaging method that uses an element comprising a photoconductive layer on an electrically conducting substrate capable of transmitting actinic radiation to which the photoconductive layer is responsive, and a dielectric support, releasably adhered to the substrate, comprising the photoconductive layer or an overcoat thereof forming a surface of the element capable of holding an applied electrostatic charge. To use the element, the surface of the dielectric support is charged, and the photoconductive layer is imagewise-exposed to actinic radiation, thereby forming a developable electrostatic image on the dielectric surface. The electrostatic image, in turn, is developed with toner to form a first color image. A composite color image is formed on the element by repeating the sequence one or more times with imagewise exposure of the photoconductive layer to actinic radiation transmitted through the substrate, and developing over each preceding image with a different color toner. The composite toner image is transferred with the dielectric support to a receiving element to form a color copy such as a three-color filter array or a color proof closely simulating the color print expected from a full press run.
The dielectric support on the photoconductive layer comprised a transparent blend of poly(vinylacetate-co-crotonic acid, 95/5 mole ratio) and cellulose acetate butyrate. The resulting multicolor proof presented a multicolor toner image against a white paper background and protected by the overlying dielectric support, thus accurately resembling a multicolor print from a full press run.
The receiver element to which the dielectric support and composite toner image are transferred can be any suitable material against or through which the toner image is desired to be viewed. The receiver can be print stock, such as paper, upon which a press run will be conducted. The receiver can also be of transparent material such as a polymeric film. With respect to the latter, the invention also contemplates, as an embodiment, transfer of the composite toner image and dielectric support to image-bearing elements such as microfilm or microfiche so that the composite color image forms information in addition to image information already present on such image-bearing elements. In addition, the invention contemplates the use of transparent glass or nonbirefringent translucent polymeric materials such as cellulose esters fo
Krynski William
Xerox Corporation
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