Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Radiation-sensitive composition or product
Reexamination Certificate
2002-07-02
2003-12-02
Goodrow, John (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Radiation-sensitive composition or product
C430S059400, C430S900000
Reexamination Certificate
active
06656650
ABSTRACT:
BACKGROUND
This invention relates in general to electrophotographic imaging members and, more specifically, to electrophotographic imaging members having a low surface energy and a single photogenerating layer dispersed with submicron size polytetrafluroethylene, and to processes for forming images on the member.
A low surface energy single layer photoreceptor refers, for example, to a device wherein a photoelectroactive pigment, hole transport and electron transport materials, polytetrafluroethylene particles and a polymeric binder are dissolved or dispersed within a single layer. In embodiments, a typical low surface energy single layer device is composed of from about 1 to about 3 percent of a photoelectroactive pigment of a polymer, from about 1 to about 20 percent polytetrafluroethylene particles, from about 40 to about 60 percent of bisphenol-Z polycarbonate, from about 25 to about 40 percent of a hole transport molecule, and from about 10 to about 25 percent of an electron transport molecule. Single layer devices are fabricated with dispersions containing all the functional materials in a solvent mixture of tetrahydrofuran and toluene or tetrahydrofuran and monochlorobenzene.
A number of current electrophotographic imaging members are multi-layered imaging members comprising a substrate and a plurality of other layers such as a charge generating layer and a charge transport layer. These multi-layered imaging members also often contain a charge blocking layer and an adhesive layer between the substrate and the charge generating layer.
One problem encountered with multilayered photoreceptors comprising a charge generating layer and the charge transport layer is that the thickness of the charge transport layer, which is normally the outermost layer, tends to become thinner during image cycling. This change in thickness causes changes in the electrical properties of the photoreceptor. Thus, in order to maintain image quality, complex and sophisticated electronic equipment is necessary in the imaging machine to compensate for the electrical changes. This increases the complexity of the machine, cost of the machine, size of the footprint occupied by the machine, and the like. 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 and a decline in image resolution. High quality images are essential for digital copiers, duplicators, printers, and facsimile machines, particularly laser exposure machines that demand high resolution images.
To achieve long-life in conventional multi-layer photoreceptors, several advanced concepts such as protective overcoat and wear resistant fillers in the charge transport layer (charge transport layer) have been pursued. Alternatively, owing to their top-photogeneration mechanism, a long operating life is also feasible using single layer organic photoreceptors, with thicknesses of, for example, in the range of from about 25 micrometers to about 40 micrometers. Another method of extending photoreceptor life is by using a thick one layer device, typically based on organic materials. Single layer organic photoreceptors have many advantages over multi-layer photoreceptors in manufacturing costs, total cost of ownership, environmental friendliness, and print quality. The photogeneration mechanism is at the top or near-the-top of the photoreceptor surface, and therefore the photoreceptor is less prone to problems or variants associated with substrate-related and thickness-dependent photoelectrical properties. Top photogeneration also allows thick devices to be implemented as dictated by constraints of photoinduced discharge properties.
One aspect of this invention is to provide submicrometer size polytetrafluroethylene particles in single layer organic photoreceptors to, for example, lower the surface energy of the resulting devices and to improve toner cleaning and transfer efficiency. The particles may also in embodiments enhance light scattering efficiency and further alleviate the need for substrate treatments.
However, similar to conventional charge transport layer, single layer organic photoreceptors containing only photoelectroactive pigments, transport molecules, and, for example, nominal polymeric binder may not be toner compatible, especially for toners generated by emulsion aggregation processes because they are susceptible to low toner transfer efficiency and cleaning failures. Proposals to disperse submicrometer size polytetrafluroethylene (polytetrafluroethylene ) particles in single layer organic photoreceptors to lower the surface energy of the devices and therefore to improve print quality and print life have been advanced. Long-life photoreceptors compatible with chemical toners are of value to high speed, high image quality color machines.
Photoreceptors with small polytetrafluroethylene and silicate particles and doped charge transport layer are believed to be emulsion aggregate toner compatible and have up to two times better wear life in imaging systems employing bias charge roller charging unit and a polyurethane based cleaning blade than conventional charge transport layer. Nylon-based overcoats, containing charge transport molecules with optional inorganic pigment additives, have also shown some wear resistant properties.
Attempts have been made to fabricate electrophotographic imaging members comprising a substrate and a single photogenerating layer in place of a plurality of layers. However, in formulating single photogenerating layer photoreceptors, many problems must be overcome including charge acceptance for hole and/or electron transporters from photoelectroactive pigments. In addition to electrical compatibility and performance, the formulation for forming a single layer photoreceptor must have 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. As employed herein, the expression “single photogenerating layer” is defined as a single electrophotographically active layer capable of retaining an electrostatic charge in the dark during electrostatic charging, imagewise exposure and image development
REFERENCES
U.S. Pat. No. 4,265,990 to Stolka et al, issued May 5, 1981 illustrates 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 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. This structure may be imaged in the conventional imaging mode which usually includes charging, exposure to light and development.
U.S. Pat. No. 5,336,577 to Spiewak et al, issued Aug. 9, 1994, discloses a thick organic ambipolar layer on a photoresponsive device 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.
BRIEF SUMMARY
Disclosed is an electrophotographic imaging member comprising a single electrophotographic photoconductive insulating layer that eliminates the need for a charge blocking layer between a supporting substrate and an electrophotographic photoconductive insulating layer.
Also disclosed is an electrophotographic imaging member comprising a single photogenerating layer which can be fabricated with fewer coating steps at reduced cost, and which eliminates charge sprea
Bender Timothy P.
Chambers John S.
Chen Cindy C.
Cherniack Helen R.
Duff James M.
Goodrow John
Palazzo E. O.
Thompson R.
Xerox Corporation
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