Electrophotography – Machine operation
Reexamination Certificate
1999-12-01
2001-03-06
Chen, Sophia S. (Department: 2852)
Electrophotography
Machine operation
C399S162000
Reexamination Certificate
active
06198889
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates in general to electrostatography, and more specifically, to a process for preventing imaging member belt set in an imaging machine environment.
Flexible electrostatographic belt imaging members are well known in the art. Typical electrostatographic flexible belt imaging members include, for example, photoreceptors for electrophotographic imaging systems, electroreceptors such as ionographic imaging members for electrographic imaging systems, and intermediate image transfer belts for transferring toner images in electrophotographic and electrographic imaging systems. These belts are usually formed by cutting a rectangular sheet from a web containing at least one layer of thermoplastic polymeric material, overlapping opposite ends of the sheet, and welding the overlapped ends together to form a welded seam. The seam extends from one edge of the belt to the opposite edge. Generally, these belts comprise at least a supporting substrate layer and at least one imaging layer comprising thermoplastic polymeric matrix material. The “imaging layer” as employed herein is defined as the dielectric imaging layer of an electroreceptor belt, the transfer layer of an intermediate image transfer belt and, the charge transport layer of an electrophotographic belt. Thus, the thermoplastic polymeric matrix material in the imaging layer is located in the upper portion of a cross section of an electrostatographic imaging member belt, the substrate layer being in the lower portion of the cross section of the electrostatographic imaging member belt.
Flexible electrophotographic imaging member belts are usually multilayered photoreceptors that comprise a substrate, an electrically conductive layer, an optional hole blocking layer, an adhesive layer, a charge generating layer, and a charge transport layer and, in some embodiments, an anti-curl backing layer is desirable for imaging member flatness. Optionally, an overcoating layer may also be formed over the charge transport layer to provide wear protection. One type of multilayered photoreceptor comprises a layer of finely divided particles of a photoconductive inorganic compound dispersed in an electrically insulating organic resin binder. A typical layered photoreceptor having separate charge generating (photogenerating) and charge transport layers is described in U.S. Pat. No. 4,265,990, the entire disclosure thereof being incorporated herein by reference. In one embodiment, the charge transport layer is located at the top and over the charge generating layer of the imaging member. In an alternative embodiment, the charge generating layer is positioned on top of the charge transport layer. The charge generating layer is capable of photogenerating charge and injecting the photogenerated charge into the charge transport layer.
Although excellent toner images may be obtained utilizing multilayered seamed belt photoreceptors, it has been found that as more advanced, higher speed electrophotographic copiers, duplicators and printers were developed, fatigue induced cracking of the charge transport layer and cracking initiation at the welded seam area were frequently encountered during photoreceptor belt cycling. Seam cracking initiation has also been found to rapidly propagate into catastrophic seam delamination as a result of continuing imaging belt fatigue which shortens belt service life. Dynamic fatigue induced imaging layer cracking and seam cracking and delamination may also occur in ionographic imaging member belts and intermediate image transfer belts.
The seamed flexible electrostatographic imaging member belt is usually fabricated from a sheet cut from a web. The sheets are generally rectangular in shape. All edges may be of the same length or one pair of parallel edges may be longer than the other pair of parallel edges. The sheets are formed into a belt by joining overlapping opposite marginal end regions of the sheet. A seam is typically produced in the overlapping marginal end regions at the point of joining. Joining may be effected by any suitable means. Typical joining techniques include welding (including ultrasonic), gluing, taping, pressure heat fusing, and the like. Ultrasonic seam welding is generally the preferred method for joining imaging member belts because it is rapid, clean (no solvents) and produces a thin and narrow seam. Another reason that the ultrasonic seam welding process is preferred is because it causes generation of heat at the contiguous overlapping end marginal regions of the sheet to maximize melting of one or more layers in the contacting overlapped ends of the imaging member sheet, which facilitates direct substrate to substrate fusing at the overlapped ends to form a seam having strong bond strength. For reason of simplicity, the discussion hereinafter will focus primarily on electrophotographic imaging members as a representation of electrostatographic imaging members.
When the overlapped ends of the cut sheet are ultrasonically welded to form a belt, the seam of the flexible multilayered electrophotographic imaging member, due to material discontinuity and excess localized seam thickness, can initiate crack formation and eventually delaminate during extended bending and flexing over small diameter belt support rollers of an imaging machine or when subjected to lateral forces caused by rubbing contact with stationary web edge guides of a belt support module during cycling. Mechanical failure due to seam cracking and delamination is further aggravated when the belt is employed in an electrophotographic imaging system utilizing a cleaning device such as a cleaning blade. Alteration of materials in the various photoreceptor belt layers such as the conductive layer, hole blocking layer, adhesive layer, charge generating layer, and/or charge transport layer to suppress cracking and delamination problems is not easily accomplished because alteration may adversely affect the overall electrical, mechanical and other properties of the belt such as residual voltage, background, dark decay, flexibility, and the like.
For example, when a flexible imaging member in an electrophotographic machine is a photoreceptor belt fabricated by ultrasonic welding of overlapped opposite ends of a sheet, the ultrasonic energy transmitted to the overlapped ends melts the thermoplastic sheet components in the overlap region to form a seam. The ultrasonic welded seam of a multilayered photoreceptor belt is relatively brittle and low in strength and toughness. The joining techniques, particularly the welding process, can result in the formation of a splashing that projects out from each side of the seam in the overlap region of the belt. Because of the seam overlapping and the seam splashing, a typical flexible imaging member belt is about 1.6 times thicker in the seam region than that of the remainder of the belt for example, a typical belt thickness is about 116 micrometers, reference Example I, whereas the overlapping seam region can be about 186 micrometers.
The photoreceptor belt in an electrophotographic imaging apparatus undergoes bending strain as the belt is cycled over a plurality of support and drive rollers. The excessive thickness of the photoreceptor belt in the seam region due to the presence of the splashing results in a large induced bending strain as the seam travels over each roller. Generally, small diameter support rollers are highly desirable for simple, reliable copy paper stripping systems in electrophotographic imaging apparatus utilizing a photoreceptor belt system operating in a very confined space. Unfortunately, small diameter rollers, e.g., diameter less than about 0.75 inch (19 millimeters), raise the threshold of mechanical performance criteria to such a high level that photoreceptor belt seam failure can become unacceptable for seamed multilayered belt photoreceptors. For example, when bending over a 19 millimeter diameter roller, a typical photoreceptor belt seam splashing may develop a 0.96 percent tensile strain due to bending. This is 1.63 times greater
Mishra Satchidanand
Yu Robert C. U.
Chen Sophia S.
Haack John L.
Kondo Peter H.
Tran Hoan
Xerox Corporation
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