Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Radiation-sensitive composition or product
Reexamination Certificate
2002-01-31
2003-07-01
Goodrow, John (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Radiation-sensitive composition or product
C430S058800, C430S059500
Reexamination Certificate
active
06586148
ABSTRACT:
The appropriate components and processes of the above copending applications may be selected for the invention of the present application in embodiments thereof.
BACKGROUND
This invention relates in general to imaging members and, more specifically, to negatively charged electrophotographic imaging members having an electrophotographic photoconductive insulating bilayer and processes for forming images on the member. More specifically, the present invention relates to a bilayered photoconductive imaging member containing a charge generation layer or photogenerating layer comprised of a photogenerating component, such as a photogenerating pigment, dispersed in a resin binder containing hole transporting and electron transporting molecule(s), and thereover as the second or top layer a charge transporting layer, especially a hole transport layer. The photogenerating layer, which can be dispersed in various suitable resin binders, can be of various thicknesses, however, in embodiments a thick photogenerating layer, such as from about 3 to about 50 microns, and more specifically, from about 5 to about 20 microns is selected. This first layer can be considered a dual functioning layer since it can generate charge and transport charge over a wide distance, such as a distance of at least about 20 microns. Also, the presence of the electron transport components in the photogenerating layer can enhance electron mobility and thus enable a thicker photogenerating layer, and which thick layers can be more easily coated than a thin layer, such as about 1 to about 2 microns thick.
Many imaging members are multilayered imaging members comprising a substrate and a plurality of other layers such as a charge generating layer and a charge transport layer. These multilayered imaging members often also contain a charge blocking layer and an adhesive layer between the substrate and the charge generating layer, and an antiplywooding layer may be selected. “Plywooding” refers, for example, in embodiments to the formation of unwanted patterns in electrostatic latent images caused by multiple reflections during laser exposure of a charged imaging member. When developed, these patterns resemble plywood. Multilayered imaging members are costly and time consuming to fabricate primarily because of the many layers that need to be formed. Further, complex equipment and valuable factory floor space are needed to manufacture multilayered imaging members. In addition to presenting plywooding problems, the multilayered imaging members often encounter charge spreading which degrades image resolution.
Another problem encountered with multilayered photoreceptors comprising a charge generating layer and a charge transport layer is that the thickness of the charge transport layer, which is normally the outermost layer, tends to become thinner due to wear during image cycling. This change in thickness causes changes in the electrical properties of the photoreceptor. Thus, to maintain image quality, complex and sophisticated electronic equipment is needed in the imaging machine to compensate for electrical changes, thereby increasing the complexity, cost, and size of the footprint occupied by the machine. Without proper compensation of the changing electrical properties of the photoreceptor during cycling, the quality of the images formed degrades due to spreading of the charge pattern on the surface of the imaging member causing a decline in image resolution. High quality images are important for digital copiers, duplicators, printers, and facsimile machines, particularly laser exposure machines that demand high resolution images. Moreover, the use of lasers to expose conventional multilayered photoreceptors can lead to the formation of undesirable plywood patterns that are visible in the final images.
Attempts have been made to fabricate suitable high resolution electrophotographic imaging members comprised of substrate and a single electrophotographic photoconductive insulating layer in place of a plurality of layers such as a charge generating layer and a charge transport layer. However, in formulating single electrophotographic photoconductive insulating layer photoreceptors, a number of problems need to be overcome including charge acceptance for hole and/or electron transporters. In addition to electrical compatibility and performance, a material mix for forming a single layer photoreceptor should possess the proper rheology and resistance to agglomeration to enable acceptable coatings. Also, compatibility among pigment, hole and electron transport molecules, and film forming binder is important.
Single electrophotographic photoconductive insulating layer refers in embodiments to, for example, a single electrophotographically active photogenerating layer capable of retaining an electrostatic charge in the dark during electrostatic charging, imagewise exposure and image development. Thus, unlike a single electrophotographic photoconductive insulating layer photoreceptor, a multilayered photoreceptor has at least two electrophotographically active layers, namely at least one charge generating layer and at least one separate charge transport layer.
REFERENCES
U.S. Pat. No. 4,265,990 a photosensitive member having at least two electrically operative layers is disclosed. The first layer comprises a photoconductive layer which is capable of photogenerating holes and injecting photogenerated holes into a contiguous charge transport layer. The charge transport second layer comprises a polycarbonate resin containing from about 25 to about 75 percent by weight of one or more of a compound having a specified general formula.
U.S. Pat. No. 5,336,577 discloses a thick organic ambipolar layer on a photoresponsive device which is simultaneously capable of charge generation and charge transport. In particular, the organic photoresponsive layer contains an electron transport material, such as a fluorenylidene malonitrile derivative, and a hole transport material, such as a dihydroxy tetraphenyl benzadine containing polymer. These may be complexed to provide photoresponsivity, and/or a photoresponsive pigment or dye may also be included.
The entire disclosures of these patents are incorporated herein by reference.
With respect to the prior art, only a small part thereof has been selected and this part may or may not be fully representative of the prior art teachings or disclosures.
SUMMARY
It is, therefore, a feature of the present invention to provide electrophotographic imaging members comprising an electrophotographic photoconductive member layer having two layers of a thick charge generating layer overcoated with a charge transporting layer.
It is another feature of the present invention to provide an improved electrophotographic imaging member with two layers that avoids plywooding problems wherein the bottom or first layer contains a photogenerating pigment, an electron transport component and a hole transport component.
It is still another feature of the present invention to provide an improved electrophotographic imaging member comprising an electrophotographic photoconductive insulating member with two layers that eliminate the need for a charge blocking layer between a supporting substrate and the electrophotographic photoconductive insulating layer.
It is still another feature of the present invention to provide a photogenerating mixture layer of a thickness of, for example, from about 5 to about 20 microns overcoated with charge transporting molecules dispersed in a resin binder.
It is still another feature of the present invention to provide an electrophotographic single layer imaging member having two layers which can be fabricated with fewer coating steps at reduced cost compared to a multilayer imaging member.
It is yet another feature of the present invention to provide an improved electrophotographic imaging member with two layers, and which member possesses cycling and stability.
It yet another feature of the present invention there is provided an improved electrophotographic imaging member with two layers and
Bender Timothy P.
Graham John F.
Ioannidis Andronique
Lin Liang-Bih
Goodrow John
Palazoo E. D.
Xerox Corporation
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