Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Radiation-sensitive composition or product
Reexamination Certificate
2000-01-19
2001-09-25
Dote, Janis L. (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Radiation-sensitive composition or product
C430S059100, C430S059400, C430S132000, C430S133000
Reexamination Certificate
active
06294300
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention is generally directed to imaging members for electrophotography. More specifically, this invention is directed to a process for preparing a charge generation layer for electrophotographic imaging members, and to electrophotographic imaging members produced thereby.
2. Description of Related Art
In electrophotography, an electrophotographic substrate containing a photoconductive insulating layer on a conductive layer is imaged by first uniformly electrostatically charging the surface. The plate is then exposed to a pattern of activating electromagnetic radiation, such as light. The light or other electromagnetic radiation selectively dissipates the charge in the illuminated areas of the photoconductive insulating layer while leaving behind an electrostatic latent image in the non-illuminated areas. This electrostatic latent image may then be developed to form a visible image by depositing finely divided electroscopic marking particles on the surface of the photoconductive insulating layer. The resulting visible image may then be transferred from the electrophotographic plate to a support such as paper. This image developing can be repeated as many times as necessary with reusable photoconductive insulating layers.
An electrophotographic imaging member may take one of many different forms. For example, layered photoresponsive imaging members are known in the art. U.S. Pat. No. 4,265,990, which is incorporated herein by reference in its entirety, describes a layered photoreceptor having separate photogenerating and charge transport layers. The photogenerating layer is capable of photogenerating holes and injecting the photogenerated holes into the charge transport layer. Thus, in photoreceptors of this type, the photogenerating material generates electrons and holes when subjected to light.
More advanced photoconductive receptors contain highly specialized component layers. For example, a multilayered photoreceptor that can be employed in electrophotographic imaging systems can include one or more of a substrate, an undercoating layer, an optional hole or charge blocking layer, a charge generating layer (including photogenerating material in a binder) over the undercoating and/or blocking layer, and a charge transport layer (including charge transport material in a binder). Additional layers such as an overcoating layer or layers can also be included. See, for example, U.S. Pat. Nos. 5,891,594 and 5,709,974.
The photogenerating layer utilized in multilayered photoreceptors can include, for example, inorganic photoconductive particles or organic photoconductive particles dispersed in a film forming polymeric binder. Inorganic or organic photoconductive material may be formed as a continuous, homogeneous photogenerating layer.
In photoreceptors of the above type, the photogenerating material generates electrons and holes when subjected to light. In the case of a photoreceptor that includes a hole blocking layer, the blocking layer prevents holes in the conductive ground plane from passing into the generator from which they would be conducted to the photoreceptor surface thus erasing any latent image formed thereon. The hole blocking layer does permit electrons generated in the generator to pass to the conductive ground plane, preventing an undesirably high electric field to build up across the generator upon cycling the photoreceptor. See, for example, U.S. Pat. No. 5,891,594.
U.S. Pat. No. 5,164,276 to Robinson et al., the disclosure of which is incorporated herein by reference in its entirety, and having a common assignee to the present application, discloses the addition of N,N′-diphenyl-N,N′-bis [3-methylpropyl]-[1,1′-biphenyl]-4,4′-diamine, a charge transport material that contains charge transport molecules, to a charge generating layer containing inorganic trigonal selenium in order to stabilize the variable cycle down that existed as a problem for inorganic photoconductive particles, such as trigonal selenium. Cycle down is defined as a decline in the Vddp with successive charge l erase cycles using constant current charging. For organic photoconductive particles, such as benzimadazole perylene, cycle down is generally not a problem since the organic pigments generally do not show cycle down.
U.S. Pat. No. 5,863,686 to Yuh et al., the disclosure of which is incorporated herein by reference in its entirety, and having a common assignee to the present application, discloses a photoreceptor including a charge generating layer containing a donor charge transport molecule selected from N,N′-diphenyl-N,N′-bis(3-hydroxyphenyl)-1,1′-biphenyl-4,4′-diamine and N,N′-di(3-methylphenyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine. Yuh also discloses a charge transport layer comprising N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine. A similar photoreceptor design is disclosed in U.S. Pat. No. 5,922,408 also to Yuh et al., the disclosure of which is also incorporated herein by reference in its entirety. Yuh does not use N,N′-diphenyl-N,N′-bis(3-methylpropyl)-1,1′-biphenyl-4,4′-diamine in the charge generating layer.
SUMMARY OF THE INVENTION
Generally, electrophotographic imaging members include a supporting substrate having an electrically conductive surface or coated with an electrically conductive layer, an optional charge blocking layer, an optional undercoat layer, a charge generating layer, a charge transport layer and an optional overcoating layer.
When the charge transport layer is coated over the charge generator layer, a problem that often occurs is that the hole transport molecule in this charge transport layer tends to migrate into the charge generator layer. This results in a disruption of the charge generator layer thickness and pigment loading uniformity. For example, such migration of the charge transport molecule causes the effective thickness of the charge generating layer to increase, and causes a gradient or blurring to occur at the interface of the charge transport layer and the charge generating layer. As the migration proceeds and increases, the photosensitivity of the photoreceptor, and particularly of organic photoreceptors (i.e., those using organic species as the charge generating material) decreases and becomes less predictable. As a result, the xerographic properties may be changed.
As a result of the altered properties of the photoreceptors resulting from migration of the charge generating material, production costs of the photoreceptors generally increases. For example, due to the variation in properties even from one photoreceptor to another, extra monitoring and inspection in the production processes is required. Furthermore, a significant number of photoreceptors are unsuitable for use based on the decreased sensitivity, and therefore are wasted. This results in a decrease in production efficiency as well as an increase in product cost.
Accordingly, a need exists in the art for ways to form photoreceptors, particularly organic photoreceptors, that exhibit predictable and reliable photogenerating properties, such as sensitivity. A need also exists for a means to eliminate or reduce migration of charge transport molecules from the charge transport layer into the photogenerating layer.
The present invention provides photoreceptors and methods of making such photoreceptors in which the hole transport molecule is intentionally added to the organic photoconductor containing charge generation layer to block migration from the charge transport layer. For example, many charge generating materials such as benzimidazole perylene (BzP) are extrinsic photoconductors which need contact with the hole transport molecule to photogenerate. The addition of the hole transport molecule to the charge generation layer can provide a more uniform contact with the charge generating material while not having to rely on the random distribution of the molecule in the
Carmichael Kathleen M.
Horgan Anthony M.
Mishra Satchidanand
Sullivan Donald P.
Dote Janis L.
Oliff & Berridg,e PLC
Palazzo Eugene O.
Xerox Corporation
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