Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Process of making radiation-sensitive product
Reexamination Certificate
2003-01-06
2004-02-24
Rodee, Christopher (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Process of making radiation-sensitive product
C430S133000, C430S134000, C430S135000, C430S059500
Reexamination Certificate
active
06696214
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrophotographic photoreceptor in which an undercoating layer and a photosensitive layer are formed in this order on a conductive support, and a method for producing the same. It also relates to a coating liquid for the photosensitive layer and a method for producing the same, and moreover, it relates to an image-forming apparatus using the electrophotographic photoreceptor.
2. Description of the Related Art
An electrophotographic process applicable to an image-forming apparatus such as copier and printer, is one of data-recording techniques utilizing photoconductive phenomena of a photoreceptor. In such an image-forming apparatus as digital-type copier, an image is formed by means of reversal development. That is, an image is formed by the steps of charging the surface of the photoreceptor uniformly by means of corona discharge in a dark place, then selectively discharging a certain region exposed to light to form a latent image, then depositing colored and charged particles (toner) on the latent image to form a visible image, and then transferring the toner onto a prefixed sheet of paper to fix and form an image thereon. The basic properties required for the photoreceptor are as follows. To be uniformly chargeable up to a desired level of the potential in a dark place, to have a high electric charge-holding capacity in a dark place with a lower electric discharge, and to have a high photosensitivity to rapidly discharge in response to photo-irradiation. It is also required for the photoreceptor that the electrostatic charge is easily removed and the residual potential is lower; that it is superior in mechanical strength and flexibility; that there is no fluctuation in the electric properties such as chargeability, photo-sensitivity, residual potential, and the like, even after repeated use; and that it is highly durable to heat, light, temperature, humidity, ozone deterioration, and the like. The photoreceptor for which such high stability and durability are required includes a monolayer type of which the photosensitive layer is composed of a charge-generating material and a charge-transporting material in a monolayer, and a multilayer type (function-separating type) which is made by laminating a charge-generating layer containing a charge-generating material and a charge-transferring layer containing a charge-transferring material.
On the other hand, in an image-forming apparatus in recent years, functional improvements such as improvement of image quality by image processing, maintaining high quality of image and image processing, and a combination with a facsimile apparatus, etc., have been attempted. Moreover, functional improvements for the photoreceptor has also been investigated. For example, improvement of image quality by reducing image defects has been investigated. Since toner deposits on a surface region of the photoreceptor on which the charges have been reduced by exposure to light, when the charge is reduced by other factor than exposure to light, image defects such as fogs, so-called black spots (very small dark spots), occur to decrease the image quality. In order to reduce such image defects, an undercoating layer is provided. In fact, an undercoating layer that works as a charge-blocking layer is provided between a conductive support and a photosensitive layer. Injection of a carrier from the conductive support microscopically erases or reduces the surface charge to produce image defects. However, the defects on the surface of the support are covered with the undercoating layer provided, which improves the chargeability, enhances adhering and coating properties of the photosensitive layer, and reduces the carrier injection from the support. Therefore, it is possible to prevent occurrence of image defects.
Moreover, an attempt to attain high sensitivity has been done. In fact, phthalocyanine pigments have been used as charge-generating materials contained in the photosensitive layer, particularly charge-generating layer. In an image-forming apparatus for digital-processing image data, a light source such as laser beams or LED (light emitting diode) is used for exposure to light, wherein the photoreceptor has to show high sensitivity at a relatively long wavelength range of approximately 620 nm-800 nm. Although there are phthalocyanine pigments and trisazo dyes as charge-generating materials therefor, a particularly highly sensitive and chemically stable phthalocyanine pigments are employed.
In the undercoating layer provided for improving the image quality by reducing the image defects, a variety of resin materials have been employed. For example, a polyamide resin is used in Japanese Unexamined Patent Publication JP-A 48-47344 (1973), but when the undercoating layer is constructed only with a resin material, accumulation of the residual potential becomes large to decrease sensitivity. This tendency is remarkable under an environment of lower temperature and lower humidity. Moreover, in Japanese Unexamined Patent Publication JP-A 56-52757 (1981), it contains titanium oxide, and in Japanese Unexamined Patent Publication JP-A 11-15184 (1999) it contains a coupling agent having an unsaturated linkage. Furthermore, in U.S. Pat. No. 5,489,496, an undercoating layer containing needle crystals with a particular resistance value is provided, and in U.S. Pat. No. 5,391,448 the content of titanium oxide and the film thickness in the undercoating layer are optimized. The so far known photoreceptor using such an undercoating layer, however, is insufficient in its characteristics, and further improvement is desired.
In order to attain high sensitivity, a phthalocyanine pigment is contained in the photosensitive layer, particularly charge-generating layer. The particle size of phthalocyanine pigments has an influence on the image quality, and in order to prevent image defects, it is necessary to make the particle size 1 &mgr;m or less in the prior art photoreceptor. The photosensitive layer and the charge-generating layer may be prepared by using a coating liquid which is prepared by dissolving a binder resin material and dispersing a phthalocyanine pigment therein, wherein the phthalocyanine pigment is dispersed into the coating liquid until particle size becomes 1 &mgr;m or less. In this connection, the phthalocyanine pigments exists in various crystal forms, and the dispersion time of the phthalocyanine pigment affects the crystal forms, so that when the crystal is dispersed to 1 &mgr;m or less in particle size the crystal form is changed to decrease the sensitivity. Moreover, when the dispersion time is prolonged, the sensitivity decreases due to contamination of impurities from the dispersing media. In Japanese Unexamined Patent Publication JP-A 3-221963 (1991), there is disclosed a charge-generating layer containing a phthalocyanine pigment, in which the content of large-sized particles with the average particle size of 1 &mgr;m or larger is made 10% by volume or lower in particle size distribution, using a technique for removing large-sized particles by centrifugation or filtration after dispersion of the phthalocyanine pigment. The content of large-sized particles with the average particle size of 1 &mgr;m or larger over 10% by volume or higher, is not preferable because image defects are produced.
SUMMARY
An object of the invention is to provide an electrophotographic photoreceptor capable of forming an image of high quality owing to its high sensitivity and reduced image defects, and a method for producing the same, to provide an coating liquid for a photosensitive layer and a method for producing the same, and moreover to provide an image-forming apparatus using such an electrophotographic photoreceptor.
The invention provides an electrophotographic photoreceptor comprising a conductive support, an undercoating layer formed on the conductive support, and a photosensitive layer formed on the undercoating layer, wherein
the undercoating layer contains titanium oxide par
Fujita Sayaka
Kakui Mikio
Katayama Satoshi
Morita Tatsuhiro
Nakamura Tadashi
Nixon & Vanderhye P.C.
Rodee Christopher
Sharp Kabushiki Kaisha
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