Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Radiation-sensitive composition or product
Reexamination Certificate
2002-10-08
2004-08-10
Chapman, Mark A. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Radiation-sensitive composition or product
C399S159000
Reexamination Certificate
active
06773857
ABSTRACT:
The present disclosure relates to the subject matter contained in Japanese Patent Application No. 2001-311869 filed on Oct. 9, 2001, Japanese Patent Application No. 2002-064162 filed on Mar. 8, 2002, and Japanese Patent Application No. 2002-220100 filed on Jul. 29, 2002, which are incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrophotographic photoreceptor, processes for producing the same, a process cartridge, and an electrophotographic apparatus.
2. Description of the Related Art
Electrophotography is utilized in electrophotographic apparatus such as copy duplicator and laser beam printers because it is capable of high-speed high-quality printing. Recently, organic photoreceptors employing a photoconductive organic material have come to be mainly used as photoreceptors for such electrophotographic apparatus. In addition, the constitution of photoreceptors is shifting to the function-separated type in which a charge-generating material and a charge-transporting material are dispersed in separate layers (a charge-generating layer and a charge transport layer).
Many photoreceptors of such function-separated type have an undercoat layer interposed between the substrate and the photosensitive layer so as to prevent charge injection from the substrate into the photosensitive layer or for another purpose. Since properties of the photoreceptor, such as stability to cycling and environmental stability, depend not only on the charge-generating layer and charge transport layer but also on the properties of the undercoat layer, there is a desire for an undercoat layer which attains reduced charge accumulation during repetitions of use. An undercoat layer further plays an important role in preventing image quality defects. It is highly effective to form an undercoat layer in order to diminish image quality defects attributable to defects or fouling of the substrate or to coating film defects or unevenness of an overlying layer, e.g., the charge-generating layer.
In recent years, contact electrification type charging units reduced in ozone generation have come to be used in place of corotrons as the charging units of electrophotographic apparatus. However, when a contact charging unit is used, the photoreceptor is apt to be charged unevenly. Furthermore, in case where the photoreceptor has a local deteriorated area, a local high electric field is applied to the deteriorated area during contact charging to cause an electrostatic pinhole, which tends to result in an image quality defect. Although this pinhole leakage can occur due to coating film defects of the photosensitive layer, it may also occur because electrically conducting paths are apt to be formed by electroconductive foreign particles (e.g., carbon fibers or carrier particles) which have generated within the electrophotographic apparatus and are in contact with the photoreceptor or have penetrated into the photoreceptor.
Under these circumstances, investigations have been made on constituent materials for undercoat layers and properties of the layers so as to avoid those phenomena accompanying the use of a contact charging unit, and electrophotographic photoreceptors having various undercoat layers have been proposed. For example, Japanese Patent Laid-Open No. 204641/1986 discloses an electrophotographic photoreceptor having an undercoat layer which contains a permittivity regulator and thereby has a volume resistivity and a permittivity in respective given ranges. Japanese Patent Laid-Open No. 113758/1989 discloses an organic photoreceptor having an undercoat layer comprising a binder resin, a charge-transporting material, and electroconductive fine particles. Furthermore, Japanese Patent Laid-Open No. 84393/1995 discloses an electrophotographic photoreceptor having an undercoat layer which contains compact particles of fine cicular titanium oxide particles and has a given value of volume resistivity.
However, even with any of those electrophotographic photoreceptors of the related art, it has been extremely difficult to obtain sufficient image quality when they are used together with a contact charging unit. The reasons for this are as follows. From the standpoint of the property of preventing charge leakage due to pinhole generation or the like (hereinafter referred to as “leakage preventive properties”), it is desirable that the thickness of the undercoat layer be large (e.g., about from 10 to 30 &mgr;m). For obtaining sufficient electrical properties, it is necessary to reduce the resistance of the undercoat layer having such an increased thickness. As a result, however, that blocking properties of the undercoat layer by which charge injection from the substrate into the photosensitive layer is prevented become insufficient and fogging is hence apt to occur.
On the other hand, investigations are being made on processes for forming a photoreceptor which comprises an electroconductive support layer (substrate) and formed thereon a layer containing electroconductive fine particles in order to attain stable electrical properties by diminishing the increase in residual potential while hiding the defects of the electroconductive support layer.
An example of such processes is proposed, for example, in Japanese Patent Laid-Open No. 45961/1991. In this process, a photoreceptor having an undercoat layer with a two-layer structure is produced. This process comprises forming a layer containing electroconductive fine particles on an electroconductive support layer, e.g., an aluminum substrate, and further forming a layer having the same constitution as usual undercoat layers on the layer containing electroconductive fine particles. In this process, the layer containing electroconductive fine particles is intended to hide defects, such as surface irregularities and fouling, of the electroconductive support layer and to regulate electrical resistance, while the layer having the same constitution as usual undercoat layers is intended to have a blocking function (inhibition of charge injection).
In another process is produced a photoreceptor having a constitution comprising an electroconductive support layer and formed thereon an undercoat layer which consists only of a layer containing electroconductive fine particles and combines the blocking function and resistance-regulating function. This type of photoreceptor and processes for producing the same are disclosed, for example, in Japanese Patent Laid-Open Nos. 258469/1997, 96916/1997, and 2001-75296.
However, the above-described electrophotographic photoreceptors of the related art are still insufficient in having electrical properties sufficient to enable the photoreceptors to withstand repetitions of use. These electrophotographic photoreceptors have had a problem that when they are repeatedly used, the residual potential increases and this results in fogging such as black spots on the image.
Specifically, the electrophotographic photoreceptor having an undercoat layer of a two-layer structure disclosed in Japanese Patent Laid-Open No. 45961/1991 has had the following problems. It has poor leakage preventive properties and is hence apt to suffer the pinhole leakage described above. Because of this, the photoreceptor comes to have reduced electrification characteristics and causes a decrease in image density with repetitions of use. Another drawback of this photoreceptor is that due to the two-layer structure, the photoreceptor production is troublesome and costly.
The electrophotographic photoreceptors disclosed in Japanese Patent Laid-Open Nos. 258469/1997, 96916/1997, and 2001-75296 are advantageous in that because the undercoat layer has a single-layer structure, the photoreceptor production processes can be simplified and the cost of the photoreceptors can be reduced. However, the necessity of forming a single layer combining a resistance-regulating function and a charge injection-inhibiting function imposes limitations in selecting constituent materials for the undercoat layer.
From th
Aida Michiko
Bando Koji
Ezumi Tetsuya
Hoshizaki Taketoshi
Iwasaki Masahiro
Chapman Mark A.
Fuji 'Xerox Co., Ltd.
Oliff & Berridg,e PLC
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