Radiation imagery chemistry: process – composition – or product th – Imaged product – Including resin or synthetic polymer
Reexamination Certificate
2000-05-23
2001-02-27
Martin, Roland (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Imaged product
Including resin or synthetic polymer
C428S141000, C428S447000
Reexamination Certificate
active
06194106
ABSTRACT:
FIELD OF INVENTION
The present invention relates to temporary image receptors for printing processes using liquid toner, and particularly electrostatic, electrophotographic, and ionographic imaging processes.
BACKGROUND OF INVENTION
Numerous temporary image receptors are known in the art of printing. For example, in offset printing intermediate transfer blankets are used to temporarily store a printed liquid toner image prior to transferring that image to a final receptor. Temporary image receptors are also used for electrographic imaging, which is known in the art to include electrophotographic, electrostatic and ionographic printing.
1) Electrophotography:
Electrophotography forms the technical basis for various well known processes, including photocopying and some forms of laser printing. The basic electrophotographic process involves placing a uniform electrostatic charge on a photoconductive element (also referred to as a photoconductor element or a photoreceptor), imagewise exposing the photoconductive element to activating electromagnetic radiation, also referred to herein as “light”, thereby dissipating the charge in the exposed areas, developing the resulting electrostatic latent image with a toner, and transferring the toner image from the photoconductor element to a final substrate, such as paper, either by direct transfer or via an intermediate transfer material. Liquid toners are often preferable because they are capable of giving higher resolution images.
In electrophotographic printing, particularly liquid electrophotographiic printing, the temporary receptor is a photoreceptor. The structure of a photoreceptive element may be a continuous belt, which is supported and circulated by rollers, or a rotatable drum. All pliotoreceptors have a photoconductive layer which conducts electric current when exposed to activating electromagnetic radiation. The photoconductive layer is generally affixed to an electroconductive support. The surface of the photoreceptor is either negatively or positively charged such that when activating electromagnetic radiation strikes the photoconductive layer, charge is conducted through the photoconductor in that region to nuetralize or reduce the surface potential in the illuminated region
Other layers, including surface release layers and interlayers, such as priming layers, charge injection blocking layers, barrier layers may also be used in some photoreceptive elements. These photoreceptors are typically multilayer constructions comprised of an underlying photoconductive layer sensitive to actinic radiation and various top coats which impart barrier and/or release properties to the photoreceptor. See R. M. Schaffert, “Electrophotography” (John Wiley: N.Y., 1975), pp. 260-396.
When multi-colored images are desired, one may apply each toner color to the photoconductor element and transfer each color image to the final substrate separately. Alternatively, all the colors may be first assembled in registration on the photoconductor element and then transferred to a final receptor, either directly or via an intermediate transfer element. This method is referred to herein as simplified color electrophotography (SCE). See e.g. WO97/12288, (incorporated herein by reference). Specifically, a photoreceptor is movably positioned to pass at least one exposure station and at least one developing station. If there is only one exposure station or one developing station, the photoreceptor will have to move past the stations several times to create a multicolor image on the photoreceptor, e.g. two or more rotations. If there are several exposure and developing stations the image may be created in a single pass of the photoreceptor. To begin creating a multi-color image, any previously accumulated charge is erased from the photoreceptor. The photoreceptor is charged to a predetermined charge level. The photoreceptor is first image-wise exposed to radiation modulated in accordance with the image data for one of a plurality of colors in order to partially discharge the photoreceptor to produce an image-wise distribution of charges on the photoreceptor corresponding to the image data for the one of the plurality of colors. A first color liquid toner is applied to the image-wise distribution of charges on the photoreceptor to form a first color image. The photoreceptor may then optionally be recharged by any known means, e.g. by corona charging, or the application of the first toner liquid may itself recharge the photoreceptor to a second predetermined charge level. The exposure, liquid toner application and optional recharging steps are repeated as necessary for each desired color.
A problem that may arise during electrophotographic imaging is poor transfer from the photoreceptor to the intermediate transfer member. Poor transfer may be manifested by images that are light, speckled, fuzzy, or smeared. These transfer problems may be reduced by the use of a surface release coating on the photoreceptor.
The release layer may be applied over the photoconductive layer or over an interlayer. The release layer should be durable and resistant to abrasion. The release layer should also resist chemical attack or excessive swelling by the toner carrier fluid. The release layer should also not significantly interfere with the charge dissipation characteristics of the photoconductor construction. Other desirable attributes of release surfaces include good adhesion to the underlying interlayer or photoconductor, excellent transparency to actinic radiation (i.e. laser scanning devices), and simple manufacturing processes and low cost.
Surface release layers are commonly low surface energy coatings such as silicones, fluorosilicones or fluoropolymers. Various silicone release layers useful as topcoats on photoreceptive elements are described in PCT Patent Publication No. WO96/34318 as well as U.S. Pat. No. 4,600,673, U.S. Pat. No. 5,320,923 and copending U.S. Pat. No. 5,733,698, all of which are incorporated herein by reference.
For liquid electrophotographic printing in particular, it may be desirable to avoid beading of toner excess carrier liquid on the surface of the release layer because the beads of carrier liquid can disturb the toner image. Specifically, the presence of the toner carrier liquid on the surface may allow the toned image to continue to flow with adverse effects on image resolution. Moreover, when a multi-color image is formed on the photoreceptor in a single pass without drying between imaging stages, such beading may cause diffraction of the exposing light during imaging resulting in lack of sharp lines or clarity in the final image.
Therefore, release layers which control the liquid on the surface of the photoreceptor are needed. However, the liquid toner should not cause smearing or diffusional broadening (i.e., blooming) of the image. Desirably, the surface release layers permit virtually 100% image transfer from the photoreceptor to an intermediate transfer member, thereby maintaining optimum image quality eliminating or reducing the need to clean the photoreceptor between images.
Color liquid electrophotography, particularly SCE, imposes a number of critical requirements on the release surface of the photoreceptor. The photoreceptor release surface must, in general, provide a low energy surface for transfer of the toner. Moreover, systems that rely on differential adhesive transfer rely on the relationship of the surface energies of the photoreceptor surface, the liquid toner, the toner film, and any rollers that contact the toner surface. See, for example, copending, coassigned U.S. Pat. No. 5,652,282 (Baker et al.) incorporated by reference herein. For some systems, the relative surface energies should be in the following hierarchy from the element with the lowest surface energy to the element with the highest surface energy: drying element, release layer of photoreceptor, intermediate transfer material, toner, final receptor.
Most references related to chemical modifiction of release surfaces for photoreceptors focus on specific combinations
Baker James A.
Berens Mark C.
Boardman Larry D.
Bretscher Kathryn R.
Butler Terri L.
Martin Roland
Minnesota Mining and Manufacturing Company
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