Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Radiation-sensitive composition or product
Reexamination Certificate
2000-04-12
2001-06-12
Rodee, Christopher (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Radiation-sensitive composition or product
C430S059400, C430S059500, C430S059100, C430S058800, C252S501100
Reexamination Certificate
active
06245471
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to charge generation layers which comprise a charge generation compound and at least one titanate. The invention is also directed to photoconductors including such charge generation layers.
BACKGROUND OF THE INVENTION
In electrophotography, a latent image is created on the surface of an imaging member such as a photoconducting material by first uniformly charging the surface and then selectively exposing areas of the surface to light. A difference in electrostatic charge density is created between those areas on the surface which are exposed to light and those areas on the surface which are not exposed to light. The latent electrostatic image is developed into a visible image by electrostatic toners. The toners are selectively attracted to either the exposed or unexposed portions of the photoconductor surface, depending on the relative electrostatic charges on the photoconductor surface, the development electrode and the toner. Electrophotographic photoconductors may be a single layer or a laminate formed from two or more layers (multi-layer type and configuration).
Typically, a dual layer electrophotographic photoconductor comprises a substrate such as a metal ground plane member on which a charge generation layer (CGL) and a charge transport layer (CTL) are coated. The charge transport layer contains a charge transport material which comprises a hole transport material or an electron transport material. For simplicity, the following discussions herein are directed to use of a charge transport layer which comprises a hole transport material as the charge transport compound. One skilled in the art will appreciate that if the charge transport layer contains an electron transport material rather than a hole transport material, the charge placed on a photoconductor surface will be opposite that described herein.
When the charge transport layer containing a hole transport material is formed on the charge generation layer, a negative charge is typically placed on the photoconductor surface. Conversely, when the charge generation layer is formed on the charge transport layer, a positive charge is typically placed on the photoconductor surface. Conventionally, the charge generation layer comprises the charge generation compound or molecule alone and/or in combination with a binder. A charge transport layer typically comprises a polymeric binder containing the charge transport compound or molecule. The charge generation compounds within the charge generation layer are sensitive to image-forming radiation and photogenerate electron hole pairs therein as a result of absorbing such radiation. The charge transport layer is usually non-absorbent of the image-forming radiation and the charge transport compounds serve to transport holes to the surface of a negatively charged photoconductor. Photoconductors of this type are disclosed in the Adley et al U.S. Pat. No. 5,130,215 and the Balthis et al U.S. Pat. No. 5,545,499.
Typically, the charge generation layer comprises a charge generating pigment or dye (phthalocyanines, azo compounds, squaraines, etc.), with or without a polymeric binder. Since the pigment or dye in the charge generation layer typically does not have the capability of binding or adhering effectively to a metal substrate, the polymer binder is usually inert to the electrophotographic process, but forms a stable dispersion with the pigment/dye and has good adhesive properties to the metal substrate. The electrical sensitivity associated with the charge generation layer can be affected by the nature of polymeric binder used. The polymeric binder, while forming a good dispersion with the pigment should also adhere to the metal substrate.
The laser printer industry requires a tremendous range of photosensitivities which are dictated by performance constraints of a printer. For example, printers that produce an increased number of prints per minute are continually being developed. In order to produce more prints per minute, such printers operate at higher process speeds. If laser output power remains fixed, then the higher process speed means that there will be less laser energy per square centimeter available to discharge the photoconductor. As a result, photoconductors with increased sensitivities are required. Similarly, color laser printers that use a number of photoconductors in a serial arrangement typically have low output speeds because the electrophotographic process must be repeated on each drum. In order to provide color output at acceptable speeds, process speeds are increased and, in turn, increased photoconductor sensitivity is required.
Furthermore, in order to insure faithful color reproduction over the useful life of a photoconductor, the drums cannot fatigue at different rates. This is best achieved by minimizing photoconductor fatigue. As such, there is a continuing need for photoconductors exhibiting increased photoconductor sensitivity and reduced photoconductor fatigue.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide novel photoconductors and/or novel charge generation layers which overcome disadvantages of the prior art. It is a more specific object of the invention to provide charge generation layers which improve electrical sensitivity of photoconductors. It is a further object of the invention to provide charge generation layers which minimize photoconductor fatigue. These and additional objects and advantages are provided by charge generation layers and photoconductors of the present invention. In one aspect of the present invention, the charge generation layer comprises a charge generation compound and at least one titanate. Preferably, the titanate comprises a metal titanate. Another embodiment of the present invention is directed to a photoconductor comprising a conductive substrate, a charge generation layer and a charge transport layer, wherein the charge generation layer comprises a charge generation compound and at least one titanate.
Another embodiment of the present invention is directed to a photoconductor comprising a conductive substrate, a charge generation layer and a charge transport layer, wherein the charge generation layer comprises a phthalocyanine charge generation compound, a polyvinylbutyral binder and at least one titanate.
The charge generation layers of the present invention improve electrical characteristics of photoconductors in which they are employed, for example, by reducing dark decay and/or improving sensitivity, as compared with photoconductors which contain a charge generation layer in which the charge generation layer comprises a charge generation compound in the absence of at least one titanate.
These and additional objects and advantages will be more readily apparent in view of the following detailed description.
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Levin Ronald Harold
Mosier Scott Thomas
Brady John A.
Lexmark International Inc.
Rodee Christopher
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