Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Radiation-sensitive composition or product
Reexamination Certificate
2002-06-20
2004-09-07
Rodee, Christopher (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Radiation-sensitive composition or product
C430S058350, C430S059600, C430S059500, C430S059400, C430S096000, C524S502000, C524S513000, C524S537000, C524S539000, C524S543000
Reexamination Certificate
active
06787276
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to dual layer photoconductors which comprise a charge transport layer and a charge generation layer formed on a substrate. More particularly, the invention is directed to such dual layer photoconductors wherein the charge transport layer comprises binder including styrene-acrylic resin which provides the photoconductor with improved resistance to non-uniform wear, including scratching and gouging.
BACKGROUND OF THE INVENTION
In electrophotography, a latent image is created on the surface of an imaging member such as a photoconducting material by 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.
Although organic electrophotographic photoconductors may be of single layer construction, many organic photoconductors have a dual layer construction. Dual layer photoconductors typically comprise a substrate such as a metal ground plane member on which a charge generation layer and a charge transport layer are coated. When the charge transport layer is formed on the charge generation layer, the photoconductor exhibits a negative charge on its surface. Conversely, when the charge generation layer is formed on the charge transport layer, the photoconductor exhibits a positive charge on the surface. Conventionally, the charge generation layer comprises a polymeric binder containing a charge generating compound or molecule while the charge transport layer comprises a polymeric binder containing a charge transport compound or molecule. The charge generating compounds within the charge generation layer are sensitive to image-forming radiation and photogenerate free electron-hole pairs within the charge generation layer as a result of 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 the 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.
One problem associated with some organic photoconductors is that their wear performance is generally inferior to that of inorganic photoconductors, such as amorphous silicon. Photoreceptor wear in the print area is either roughly uniform or non-uniform in nature. This latter wear mechanism often appears as gouges or scratches on the photoreceptor surface, which may manifest themselves as defects in the printed product. Even thin scratches can result in a general print lightning when present in a sufficient density, or they can result in thicker printed areas when printing in duplex mode. Photoreceptor surface scratches may appear due to several factors which include: (1) interaction of an abrasive toner with the cleaning blade and the organic photoconductor surface; and/or (2) interaction of paper with the organic photoconductor surface. The abrasive components of the toner are key contributors to the level of scratching: common toner additives such as silicon carbide are extremely hard, and thus more prone to scratch the photoconductor surface.
A known approach to decreasing the wear and scratching of an organic photoconductor is to provide an additional hardened overcoating which is designed to make the organic photoconductor harder and thus more wear resistant. This additional layer, however, adds additional expense and an additional manufacturing step. Consequently, a need exists for providing organic photoconductors that exhibit improved wear characteristics without adversely affecting the electrical properties of the photoconductor or significantly increasing cost or manufacturing complexity of the photoconductors.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide improved photoconductors and improved charge transport layers for use in photoconductors. More particularly, it is an object of the present invention to provide charge transport layers and dual layer photoconductors which exhibit improved resistance to non-uniform wear, for example scratching and gouging, which may detract from printed images, while maintaining good electrical performance and acceptable durability.
These and additional objects and advantages are provided by the charge transport layers and the dual layer photoconductors according to the present invention. The charge transport layers according to the invention comprise charge transport compound and binder including styrene-acrylic resin. The photoconductors according to the present invention comprise a substrate, a charge generation layer and a charge transport layer, wherein the charge transport layer comprises charge transport compound and binder including styrene-acrylic resin. In another embodiment, photoconductors according to the present invention comprise a substrate; a charge generation layer formed on the substrate and comprising charge generation compound and charge generation layer binder, wherein the charge generation compound comprises titanylphthalocyanine; and c) a charge transport layer formed on the charge generation layer and comprising charge transport compound and binder including polycarbonate and styrene-acrylic resin, wherein the charge transport compound comprises a hydrazone compound, and wherein the styrene-acrylic resin is present in an amount sufficient to improve non-uniform wear resistance of the charge transport layer.
Styrene-acrylic resins, especially those containing a high percentage of styrene, are well known as soft polymers. Surprisingly, the addition of such a soft polymer resin to the charge transport layer of an organic photoconductor decreases or eliminates non-uniform wear such as scratching or gouging on the photoconductor surface. Furthermore, the dual layer photoconductors according to the present invention are advantageous in that they exhibit good electrical performance, including good sensitivity and/or good residual voltage.
These and additional objects and advantages will be further apparent in view of the following detailed description.
DETAILED DESCRIPTION
The charge transport layers according to the present invention comprise charge transport compound and binder including styrene-acrylic resin. The dual layer photoconductors according to the present invention comprise a substrate, a charge generation layer and a charge transport layer. The charge transport layer comprises charge transport compound and binder including styrene-acrylic resin. The charge generation layer typically comprises charge generating compound and binder.
The photoconductor substrate may be flexible, for example in the form of a flexible web or a belt, or inflexible, for example in the form of a drum. Typically, the photoconductor substrate is uniformly coated with a thin layer of a metal, which functions as an electrical ground plate. In one embodiment, this metal layer is aluminum. In a further embodiment, the aluminum is anodized to convert the aluminum surface into a thicker aluminum oxide surface. Alternatively, the ground plane member may comprise a metallic plate, such as aluminum or nickel, a metallic drum or foil, or a plastic film on which aluminum, tin oxide or indium oxide or the like is vacuum evaporated.
Typically the charge generation layer may be formed on the photoconductor substrate, followed by formation of the charge transport layer, whereby the photoconductor surface exhibits a negative charge and the non-uniform wear resistance benefits of the charge transport layer are maximized.
The charge transport layer included in the dual layer photoconductors according to the prese
Black David Glenn
Levin Ronald Harold
Nguyen Dat Quoc
Taylor Bradford Lee
Ting Vincent Wen-Hwa
Brady John A.
Lexmark International Inc.
Rodee Christopher
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