Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Radiation-sensitive composition or product
Reexamination Certificate
2001-03-09
2002-12-03
Goodrow, John (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Radiation-sensitive composition or product
C430S096000, C430S133000
Reexamination Certificate
active
06489070
ABSTRACT:
FIELD OF INVENTION
The present invention is directed toward photoconductors and compositions used to form photoconductors. More particularly, the invention is directed towards photoconductors comprising a substrate and a charge generation layer, wherein the charge generation layer comprises a cyclic carbonate polymer. The invention is further directed toward methods of improving electrical characteristics of photoconductors, and methods of improving the stability of photoconductors, as well as binder blends comprising a cyclic carbonate polymer.
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.
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, for example a squaraine pigment, a phthalocyanine, or an azo compound, alone or in combination with a binder. The 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.
Various polymers are known for use in charge generation and/or charge transport layers. For example, polycarbonate resins, including aromatic polycarbonate resins, are taught in U.S. Pat. Nos. 5,378,567, 5,942,363, and 6,066,428, for use in photoconductors. Miyamoto et al., U.S. Pat. No. 5,521,041, teach an electrophotographic photoreceptor comprising an electroconductive substrate and a photosensitive layer wherein the photosensitive layer comprises a polycarbonate. Miyamoto et al. teach the polycarbonate may be prepared by allowing a dihydric phenol to react with a carbonate precursor, such as phosgene, in the presence of an end terminator.
While the charge transport layers and charge generation layers of photoconductors generally comprise binders, the electrical sensitivity of a charge generation layer can be detrimentally affected by the polymer binders. For example, the use of polyvinylbutyral as a charge generation layer binder is advantageous in that it significantly improves adhesion of the charge generation layer to the substrate. Unfortunately, polyvinylbutyral can disadvantageously affect electrical characteristics of the resulting photoconductor in causing, inter alia, high dark decay and residual voltage properties. Polycarbonates have been known to improve the mechanical properties of a photoconductor, particularly impact resistance.
Thus, there is a need for binder and binder blends for use in charge generation layers which provide the photoconductors with good mechanical properties without significantly decreasing electrical sensitivity of photoreceptors.
SUMMARY OF THE INVENTION
Accordingly, it is an object of this invention to obviate various problems of the prior art. It is another object of this invention to provide photoconductors having good electrical characteristics, particularly good electrical sensitivity.
It is a further object of this invention to provide photoconductors which have reduced dark decay and/or improved print stability and fatigue characteristics, and/or which charge and discharge in a very short time. It is yet another object of this invention to provide binder blends which do not compromise the adhesion of coatings onto substrates.
In one embodiment, the invention is directed to photoconductors comprising a substrate and a charge generation layer comprising a cyclic carbonate polymer.
In accordance with another embodiment, the invention, is directed to methods of improving an electrical characteristic of a photoconductor. The methods comprise forming a photoconductor comprising a substrate and a charge generation layer comprising a charge generation molecular and a cyclic carbonate polymer.
In accordance with a further embodiment aspect of the invention there are provided methods of improving the stability of a photoconductor comprising a charge generation layer comprising a charge generation molecule and polyvinylbutyral, the method comprising the step of adding to the charge generation layer a cyclic carbonate polymer. In accordance with yet another embodiment of the invention there are provided charge generation layer-forming compositions comprising pigment, solvent and a binder blend, wherein the binder blend comprises polyvinylbutyral and a cyclic carbonate polymer.
In accordance with one embodiment of the invention, there are provided binder blends comprising a first binder selected from the group consist of cyclic carbonate polymers and mixtures thereof, and a second binder which is other than a cyclic carbonate polymer.
Photoconductors comprising charge generation layers in accordance with the present invention have good electrical characteristics, particularly good electrical sensitivity, low dark decay and/or stable fatigue through life. Further, in various embodiments, the photoconductors charge and discharge at a very short time interval, and thus are useful for high speed printing in the range of from about 30 to about 50 pages per minute.
These and additional objects and advantages will become more fully apparent in view of the following description.
DETAILED DESCRIPTION
The charge generation layers according to the present invention are suitable for use in dual layer photoconductors. Such photoconductors generally comprise a substrate, a charge generation layer (CGL) and a charge transport layer (CTL). The photoconductors may also comprise a sub-layer to assist in the adhesion of the charge generation and charge transport layers, or a protective coating to reinforce the durability of the charge generation and charge transport layers. Some substrates, such as aluminum, may be anodized. In one embodiment the substrate is anodized aluminum or aluminized MYLAR®. While various embodiments of the invention discussed herein refer to the charge generation layer as being formed on the substrate, with the charge transport layer formed on t
Goodrow John
Lexmark International Inc.
LandOfFree
Photoconductors comprising cyclic carbonate polymers does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Photoconductors comprising cyclic carbonate polymers, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Photoconductors comprising cyclic carbonate polymers will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2959422