Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Radiation-sensitive composition or product
Reexamination Certificate
2002-01-07
2003-12-09
Chapman, Mark A. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Radiation-sensitive composition or product
Reexamination Certificate
active
06660441
ABSTRACT:
BACKGROUND OF INFORMATION
1. Field of the Invention
The present invention relates to imaging members and to the preparation of a structurally simplified imaging member which does not exhibit curling of the multilayered imaging member webstock after coating and drying of the charge transport layer.
An advantage of the present invention is to provide improved methodology for fabricating multiple layered imaging member webstocks which overcomes curling of the multiple layers.
The present invention provides an improved process for imaging member webstock fabrication having a simplified material configuration.
2. Description of Related Art
Electrostatographic flexible imaging members are well known in the art. Typical flexible electrostatographic imaging members include, for example, (1) photosensitive members (photoreceptors) commonly utilized in electrophotographic processes and (2) electroreceptors such as ionographic imaging members for electrographic imaging systems. The flexible electrostatographic imaging members may be seamless or seamed belts. Electrophotographic imaging member belts comprise a charge transport layer and a charge generating layer on one side of a supporting substrate layer and an anticurl backing layer coated on the opposite side of the substrate layer. Some electrographic imaging member belts have a more simple material structure comprising a dielectric imaging layer on one side of a supporting substrate and an anticurl backing layer on the opposite side of the substrate.
Electrophotographic flexible imaging members may comprise a photoconductive layer comprising a single layer or composite layers. Typical electrophotographic imaging members exhibit undesirable imaging member curling and require an anticurl backing layer. The anticurl backing layer is provided to prevent the multiple layers of an imaging member from curling and thereby keeping the member flat. One type of composite photoconductive layer used in electrophotography is illustrated in U.S. Pat. No. 4,265,990, which describes a photosensitive member having at least two electrically operative layers. One layer comprises a photoconductive layer which is capable of photogenerating holes and injecting the photogenerated holes into a contiguous charge transport layer. Generally, where the two electrically operative layers are supported on a conductive layer with the photoconductive layer sandwiched between the contiguous charge transport layer and the conductive layer, the outer surface of the charge transport layer is charged with a uniform charge of a negative polarity and the supporting electrode is utilized as an anode. The supporting electrode may still function as an anode when the charge transport layer is sandwiched between the supporting electrode and the photoconductive layer. The charge transport layer in this latter embodiment is capable of supporting the injection of photogenerated electrons from the photoconductive layer and transporting the electrons through the charge transport layer. Photosensitive members having at least two electrically operative layers, as discussed above, provide excellent electrostatic latent images when charged with a uniform negative electrostatic charge, exposed to a light image and thereafter developed with finely divided electroscopic marking particles. The resulting image is transferable to a receiving member such as paper.
As more advanced, higher speed electrophotographic copiers, duplicators and printers were developed, degradation of image quality was encountered during extended cycling. Moreover, complex, highly sophisticated duplicating and printing systems operating at very high speeds have placed stringent requirements including narrow operating limits on photoreceptors. For flexible electrophotographic imaging members having a belt configuration, the numerous layers found in modern photoconductive imaging members are highly flexible, adhere well to adjacent layers, and exhibit predictable electrical characteristics within narrow operating limits to provide excellent toner images over many thousands of cycles. One type of multilayered photoreceptor that has been employed as a belt in negatively charging electrophotographic imaging systems consists of a substrate, a conductive layer, a blocking layer, an adhesive layer, a charge generating layer, a charge transport layer, and a conductive ground strip layer adjacent to one edge of the imaging layers. This photoreceptor belt may also comprise an additional layer such as an anticurl backing layer to achieve the desired imaging member belt flatness.
In a service environment, a flexible imaging member belt, mounted on a belt supporting module, is exposed to repetitive electrophotographic image cycling which subjects the outer-most charge transport layer to mechanical fatigue as the imaging member belt bends and flexes over the belt drive roller and all other belt module support rollers, as well as sliding bend contact above each backer bar's curving surface. This repetitive imaging member belt cycling leads to a gradual deterioration in the physical and mechanical integrity of the exposed outer charge transport layer leading to premature onset of fatigue charge transport layer cracking. The cracks developed in the charge transport layer as a result of dynamic belt fatiguing are found to manifest themselves into copy print out defects which thereby adversely affect the image quality on the receiving paper. In essence, the appearance of charge transport cracking cuts short the imaging member belt's intended functional life.
When a production web stock of several thousand feet of coated multilayered photoreceptor material is obtained after finishing the charge transport layer coating and drying process, curling of the multilayered photoreceptor is observed and requires an anticurl backing layer applied to the backside of the substrate support, opposite to the side having the charge transport layer, to offset the curl and render the photoreceptor web stock flat. The exhibition of photoreceptor curling after completion of charge transport layer coating has been determined to be the consequent of thermal contraction mismatch between the applied charge transport layer and the substrate support under the conditions of elevated temperature, heating and drying the wet coating and the eventual cooling down to room temperature. Since the charge transport layer in a typical prior art photoreceptor device has a coefficient of thermal contraction approximately 3½ times larger than the substrate support, the charge transport layer, upon cooling down to room ambient, results in greater dimensional contraction than that of the substrate support causing photoreceptor curling.
Although it has been desirable to have the anticurl backing layer to complete a photoreceptor web stock material package, an anticurl backing layer application represents an additional coating step increasing labor and material cost, which can result in a decrease of daily photoreceptor production through-put of about 25%. Moreover, sending the photoreceptor web stock back to the coater immediately after coating the charge transport layer for anticurl backing layer application has frequently resulted in photoreceptor production yield lost due to web stock scratching caused by handling. Photoreceptors with an anticurl backing layer have a built-in internal strain of about 0.28% in the charge transport layer. This strain is cumulatively added to each photoreceptor bending induced strain as the photoreceptor belt flexes over a variety of belt module support rollers during cycling within a machine. This internal built-in strain exacerbates the fatigue charge transport layer failure and promotes the onset of charge transport layer cracking.
Imaging members having an anticurl backing layer not only require one addition coating step to complete the finish production, but also create an environmental issue involving solvent emission release to the atmoshere.
Seamed flexible photoreceptor belts are fabricated from sheets cut from a electro
Chapman Mark A.
Palazzo E. D.
Thompson R.
Xerox Corporation
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