Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Process of making radiation-sensitive product
Reexamination Certificate
2000-01-19
2001-04-24
Chapman, Mark (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Process of making radiation-sensitive product
C430S136000, C283S093000, C283S100000, C428S916000
Reexamination Certificate
active
06221552
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates in general to electrophotography and, in particular, to a process for permanently marking electrophotographic imaging members or photoreceptors with fiducial or registration marks, as well as photoreceptors produced thereby. The present invention provides a process for forning fiducial or registration marks on a photoreceptor such that the marks may or may not readily appear, at least to the naked eye, on a print made from such a photoreceptor.
2. Description of Related Art
In electrophotography, also known as Xerography, electrophotographic imaging or electrostatographic imaging, the surface of an electrophotographic plate, drum, belt or the like (imaging member or photoreceptor) containing a photoconductive insulating layer on a conductive layer is first uniformly electrostatically charged. The imaging member is then exposed to a pattern of activating electromagnetic radiation, such as light. The radiation selectively dissipates the charge on the illuminated areas of the photoconductive insulating layer while leaving behind an electrostatic latent image on the non-illuminated areas. This electrostatic latent image may then be developed to form a visible image by depositing finely divided electroscopic marking particles on the surface of the photoconductive insulating layer. The resulting visible image may then be transferred from the imaging member directly or indirectly (such as by a transfer or other member) to a print substrate, such as transparency or paper. The imaging process may be repeated many times with reusable imaging members.
An electrophotographic imaging member may be provided in a number of forms. For example, the imaging member may be a homogeneous layer of a single material such as vitreous selenium or it may be a composite layer containing a photoconductor and another material. In addition, the imaging member may be layered. Current layered organic imaging members generally have at least a substrate layer and two active layers. These active layers generally include (1) a charge generating layer containing a light-absorbing material, and (2) a charge transport layer containing electron donor molecules. These layers can be in any order, and sometimes can be combined in a single or mixed layer. The substrate layer may be formed from a conductive material. In addition, a conductive layer can be formed on a nonconductive substrate.
The charge generating layer is capable of photogenerating charge and injecting the photogenerated charge into the charge transport layer. For example, U.S. Pat. No. 4,855,203 to Miyaka teaches charge generating layers comprising a resin dispersed pigment. Suitable pigments include photoconductive zinc oxide or cadmium sulfide and organic pigments such as phthalocyanine type pigment, a polycyclic quinone type pigment, a perylene pigment, an azo type pigment and a quinacridone type pigment Imaging members with perylene charge generating pigments, particularly benzimidazole perylene, show superior performance with extended life.
In the charge transport layer, the electron donor molecules may be in a polymer binder. In this case, the electron donor molecules provide hole or charge transport properties, while the electrically inactive polymer binder provides mechanical properties. Alternatively, the charge transport layer can be made from a charge transporting polymer such as poly(N-vinylcarbazole), polysilylene or polyether carbonate, wherein the charge transport properties are incorporated into the mechanically strong polymer.
Imaging members may also include a charge blocking layer and/or an adhesive layer between the charge generating and the conductive layer. In addition, imaging members may contain protective overcoatings. Further, imaging members may include layers to provide special functions such as incoherent reflection of laser light, dot patterns and/or pictorial imaging or subbing layers to provide chemical sealing and/or a smooth coating surface.
Although excellent toner images may be obtained with multilayered belt or drum photoreceptors, it has been found that as more advanced, higher speed electrophotographic copiers, duplicators and printers are developed, there is a greater demand on copy quality. A delicate balance in charging image and bias potentials, and characteristics of the toner and/or developer, must be maintained. This places additional constraints on the quality of photoreceptor manufacturing, and thus, on the manufacturing yield. In certain combinations of materials for photoreceptors, or in certain production batches of photoreceptor materials involved in the same kind of materials, localized microdefect sites (which may vary in size from about 50 to about 200 microns) can occur, using photoreceptors fabricated from these materials, where the dark decay is high compared to spatially uniform dark decay present in the sample. These sites appear as print defects (microdefects) in the final imaged copy. In charged area development, where the charged areas are printed as dark areas, the sites print out as white spots. These microdefects are called microwhite spots. Likewise, in discharged area development systems, where the exposed area (discharged area) is printed as dark areas, these sites print out as dark spots in a white background. All of these microdefects, which exhibit inordinately large dark decay, are called charge deficient spots (or CDS).
Since the microdefect sites are fixed in the photoreceptor, the spots are registered from one cycle of belt revolution to the next. Charge deficient spots have been a serious problem for a very long time in many organic photoreceptors. Little progress has been made in developing photoreceptors that resist formation of such charge deficient spots because of a lack of rapid techniques suitable for quickly assessing research laboratory samples. Charge deficient spots are also a source of major yield losses in the production of photoreceptors. The only techniques known in the past for evaluation of the charge deficiency spots in a photoreceptor were through the formation of actual imaging machine prints or the use of a stylus scanner. Both of these techniques have serious flaws. Evaluation through machine testing cannot be accomplished on hand made samples because it is difficult to coat laboratory samples that are large enough to make a belt size sample usable to run in an imaging machine. Also, contributions or “noise” from non-charge deficient spot related defects can overwhelm print quality during testing on imaging machines. Thus, any investigation of the charge deficient spots characteristics on imaging machines is very expensive because belts of a suitable size for testing on such imaging machines must be fabricated on production equipment. The stylus scanner can be used for hand made devices, but it is very slow (e.g. a 1 cm
2
area on a sample requires an hour or two to scan). Further, the stylus scanner test can be too sensitive and present serious problems in extrapolating the test results for large area performance (such as full page) from a realistically feasible measurement (e.g. 1 cm
2
). In response to these problems, an improved method for assessing the occurrence of microdefects is disclosed, for example, in U.S. Pat. No. 5,703,487.
Whether these localized microdefect or charge deficient spot sites will show up as print defects in the final document will depend on the development system utilized and, thus, on the machine design selected. For example, some of the variables governing the final print quality include the surface potential of the photoreceptor, the image potential of the photoreceptor, the photoreceptor to development roller spacing, toner characteristics (such as size, charge and the like), the bias applied to the development rollers, and the like. The image potential depends on the light level selected for exposure. The defect sites are discharged, however, by the dark discharge rather than by the light The copy quality from generation to generation is maint
Grabowski Edward F
Street Terry L
Chapman Mark
Oliff & Berridg,e PLC
Palazzo Eugene O.
Xerox Corporation
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