Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Radiation-sensitive composition or product
Reexamination Certificate
2002-03-22
2004-01-13
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
Reexamination Certificate
active
06677091
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
This application claims the priority benefit of Japanese application serial nos. 2001-083469, filed on Mar. 22, 2001, 2001-086532, filed on Mar. 26, 2001 and 2002-028623, filed on Feb. 5, 2002.
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a photoreceptor that has a surface layer with a specific structure and thereby has high sensitivity, high resolution and high durability. Moreover, the present invention relates to an electrophotographic method, an electrophotographic apparatus and a process cartridge used in electrophotography that use the photoreceptor of this invention.
2. Description of Related Art
In the prior art, the electrophotographic methods, which include the Carlson method and various modifications thereof, are widely used in copying machines and printers. In the photoreceptor used in such electrophotographic methods, organic photosensitive materials have been used recently since they are cheap, pollution-free, and suitable for mass production. The types of organic-type electrophotographic photoreceptor include the photoconductive resin type represented by polyvinylcarbazole, the charge-transfer complex type represented by 2,4,7-trinitrofluoreone (PVK-TNF), the pigment dispersion type represent by phthalocyanine binder, and the function separated type using a charge-generating material and a charge-transferring material in combination. Among them, the function separated type gets much attention.
The forming mechanism of an electrostatic latent mage on a photoreceptor of function separated type is explained below. The photoreceptor is firstly charged and then irradiated with light, which passes through a transparent charge-conducting layer to be absorbed by a charge-generating material in a charge-generating layer. Charges will be generated from the charge-generating material due to the light absorption and then injected into the charge-transferring layer and driven by the electric field established by charging to move in the charge-transferring layer. The charges induced by the light absorption will neutralize some charges on the surface of the photoreceptor to form an electrostatic latent mage thereon. A charge-transferring material mainly absorbing UV light and a charge-generating material mainly absorbing visible light can be used together in a photoreceptor of function separation type, and such a combination is particularly advantageous.
Recently, the miniaturization of the photoreceptor is desired and the photoreceptor and the machine using the same are both required having a high durability (long lifetime). Accordingly, the organic photosensitive bodies have been developed energetically and are actually progressive in the issue of high sensitivity and high electrostatic durability of the photoreceptor. However, the mechanical durability of the photoreceptor, especially the wear resistance of the photoreceptor, is always considered to be insufficient. In view of this, the photosensitive bodies that have surfaces having improved mechanical durability are proposed, wherein those using binder resin on their surfaces are frequently investigated. However, those methods are always not satisfactory.
In another point of view, the durability problem can be solved by forming a protective layer on the outmost surface of the photoreceptor. The effects of using a protective layer as the surface layer of a photoreceptor, as started from the cases of the inorganic photosensitive bodies, are discussed in Japan Patent Publication No. Hei 2-3171, Hei 2-7058 and Hei 3-43618. Where a protective layer is disposed on the surface of an inorganic photoreceptor, the protective layer preferably comprises fillers having low specific resistance. Thus when the surface of the photoreceptor is being charged, the bulk of the protective layer and the photoreceptor/protective layer interface can also be charged easily. Certainly, another merit lies on that the latent image is not formed on the surface of the photoreceptor but in the protective layer (including the interface with the photoreceptor), and the shape (defects or the like) of the surface of the photoreceptor therefore has little affect on the latent image. However, if the protective layer serving as a surface layer is intended to have the aforementioned functions, a large amount of electrically conductive metal oxide fillers have to be added into it. In this situation, since the bulk or the surface of the surface layer has a low resistance, the so-called “image blur” effect will occur as a drawback after repeated use even if the transparency of the surface layer is maintained. Japan Patent Publication No. Hei 2-7057 and JP-2675035 disclose a method for solving this problem, in which the concentration of the electrically conductive metal oxide in the surface layer varies along the vertical direction from the surface of the coating. By using this method, the drawbacks such as the image blur and the flowing defects can be prevented.
Moreover, as another method for solving the image blur problem with treatments during the process, an apparatus is used mounted with a drum heater for heating the photoreceptor. Though the image blur can be prevented from occurring by heating the photoreceptor, the incorporation of the drum heater will inevitably increase the size of the photoreceptor. Therefore, the method cannot be applied to miniaturized photosensitive bodies currently used in the mainstream accompanied with the miniaturization of electrophotographic apparatuses. In addition, high durability of a miniaturized photoreceptor is also hard to achieve by using this method. Moreover, the incorporation of the drum heater causes many problems in real use, such as the increased size of the photographic apparatus, the remarkably increased electricity consumption, and the increased time needed to setup the apparatus.
Because the transparency of the protective layer has to be maintained, it is important to assure that each component of the protective layer is transparent to the light used for writing the image. Particularly, the filler contained in the protective layer has a refractive index different from that of the binder resin used in the protective layer in most cases, so the protective layer tends to be opaque. To improve the problem for maintaining the transparency of the film, the filler can be made to have a size as small as possible. When the size of the filler is smaller than the wavelength of the light for writing the image, light scattering will not occur substantially and the protective layer becomes transparent. For example, a method is disclosed in which the mean size of the metal grains or the metal oxide grains contained in the filler is smaller than 0.3 &mgr;m (Japanese Patent Application Laid Open No. Sho 57-30846), so that the protective layer becomes substantially transparent and the residual voltage accumulation can also be inhibited. Though its effect on maintaining the transparency of the protective layer is recognized, the use of such fillers has little effect on increasing the wear resistance of the protective layer. In view of this, instead of increasing the wear resistance of the filler, increasing the wear resistance of the binder is a more effective way for improving the wear resistance of the protective layer. Specifically, when an inorganic protective layer with durable electrostatic properties and high wear resistance fabricated by using this method is incorporated with an inorganic photoreceptor represented by the saline photoconductive layer, a photoreceptor having a quite long lifetime can be obtained. Moreover, the transparency of the protective layer can also be obtained by using fillers with a mean grain size larger than 0.3 &mgr;m if only the dispersibility of the grain is high enough. On the other hand, if the fillers condense to a certain degree, the transparency of the protective layer will still be reduced even if the mean grain size is smaller than 0.3 &mgr;m.
On another aspect, the photoreceptor has shifted toward the polluti
Chapman Mark A.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Ricoh & Company, Ltd.
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