Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Radiation-sensitive composition or product
Reexamination Certificate
2001-11-02
2004-09-14
RoDee, Christopher D (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Radiation-sensitive composition or product
C430S066000, C430S067000, C430S058700, C399S159000
Reexamination Certificate
active
06790572
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrophotographic photoreceptor. In addition, the present invention relates to an electrophotographic image forming method and apparatus using the photoreceptor. Further, the present invention relates to a process cartridge for electrophotographic image forming apparatus, which includes the photoreceptor.
2. Discussion of the Background
Recently the growth of information processing system using electrophotography is remarkable. In particular, digital copiers capable of recording digital information using light after converting information to digital signals have been drastically improving in recording qualities and reliability. In addition, the technique has been applied to full color laser printers and copiers by being combined with a high speed recording technique. In the light of this background, a need exists for a photoreceptor which not only produces high quality images but also has high durability.
As the photoreceptor used for such laser printers and digital copiers, photoreceptors using an organic photosensitive material have been widely used because of having advantages such as good productivity and low pollution.
Specific examples of the organic photoreceptors include the photoreceptors including one of the following photosensitive layers:
(1) organic photoconductive resin layers typified by a poly-N-vinylcarbazole resin;
(2) charge transfer complex type photosensitive layers typified by a combination of poly-N-vinylcarbazole (PVK) with 2,4,7-trinitrofluorenon (TNF);
(3) pigment dispersion type photosensitive layers typified by a combination of phthalocyanine and a binder resin; and
(4) functionally-separated photosensitive layer typified by a combination of a charge generation material and a charge transport material.
Among these photoreceptors, the functionally-separated photoreceptors attract considerable attention now.
The electrophotographic image forming methods typically include the following processes:
(1) charging an electrophotographic photoreceptor in a dark place (charging process);
(2) irradiating the charged photoreceptor with imagewise light to form an electrostatic latent image thereon (light irradiating process);
(3) developing the latent image with a developer including a toner mainly constituted of a colorant and a binder to form a toner image thereon (developing process);
(4) optionally transferring the toner image onto an intermediate transfer medium (first transfer process);
(5) transferring the toner image onto a receiving material such as a receiving paper ((second) transfer process);
(6) heating the toner image to fix the toner image on the receiving material (fixing process); and
(7) cleaning the surface of the photoreceptor (cleaning process).
The mechanism of forming an electrostatic latent image in the functionally-separated photosensitive layer, which has a charge generation layer and a charge transport layer formed on the charge generation layer, is as follows:
(1) when the photosensitive layer is exposed to light after being charged, light passes through the transparent charge transport layer and then reaches the charge generation layer;
(2) the charge generation material included in the charge generation layer absorbs the light and generates a charge carrier such as electrons and positive holes;
(3) the charge carrier is injected into the charge transport layer and transported through the charge transport layer, which is caused by the electric field formed by the charge on the photosensitive layer;
(4) the charge carrier finally reaches the surface of the photosensitive layer and neutralizes the charge thereon, resulting in formation of an electrostatic latent image on the photosensitive layer.
However, photosensitive layers of organic photoreceptors are easily abraded when the photoreceptors are repeatedly used. When a photosensitive layer is largely abraded, various image quality problems such that the potential of the charged photoreceptor decreases; the photosensitivity thereof deteriorates; background fouling occurs in the resultant images; and image density decreases tend to occur. Therefore the abrasion of photoreceptors have been a big problem to be solved.
In addition, currently electrophotographic image forming apparatus become smaller and smaller in size. Therefore the diameter of photoreceptors used for such miniaturized image forming apparatus also becomes smaller and smaller. Accordingly a need exists for a photoreceptor having good durability.
In attempting to impart good durability to an organic photoreceptor, the following methods have been proposed:
(1) a protective layer having lubricating property is formed as an outermost layer of the photoreceptor;
(2) a crosslinked protective layer is formed as an outermost layer of the photoreceptor; and
(3) a protective layer including a filler is formed as an outermost layer of the photoreceptor.
In particular, the method (3) is effective. However, when an electrical insulating filler is included in a protective layer, the resistance of the protective layer increase, resulting in increase of residual potential of the resultant photoreceptor. The increase of residual potential is mainly caused by increase of the resistance of the protective layer and increase of the number of charge trap sites therein due to addition of the filler having high insulating property. In contrast, when an electroconductive filler is used, the resistance of the protective layer decreases, and thereby the residual potential of the protective layer hardly increase. However, a problem tends to occur such that the resultant images have unclear outlines, i.e., blurred images are produced.
In attempting to solve such a blurred image problem, a method is proposed in which a photoreceptor having a protective layer including an electroconductive filler is heated by a drum heater to decrease moisture in the photoreceptor. By heating the photoreceptor, the formation of blurred images can be avoided but the diameter of the photoreceptor becomes large because a drum heater has to be provided in the photoreceptor. Therefore, this technique cannot be used for small-size photoreceptors typically provided in current small image forming apparatus. In other words, a photoreceptor having a small-diameter and good durability has not yet been developed. In addition, when a drum heater is provided, the resultant image forming apparatus becomes large in size. Further, the image forming apparatus have other drawbacks such that it is needed for the image forming apparatus to continuously work the heater, resulting in increase of power consumption, and it takes a long warm-up time.
When a photoreceptor has a high residual potential due to use of a filler having high insulating property, the potential of a lighted area of the photoreceptor increases, resulting in deterioration of image density and half toner reproducibility of the resultant images. In order to avoid such problems, the potential of dark areas needs to be increased. However, when the dark-area potential is increased, the electric field strength is increased, and therefore not only undesired images such as background fouling are produced, but also the life of the photoreceptor is shortened.
In attempting to avoid increase of residual potential, methods in which a photoconductive protective layer is formed have been disclosed in Japanese Patent Publications Nos. (hereinafter JPPs) 44-834, 43-16198 and 49-10258. However, imagewise light is absorbed by the protective layer, and therefore the quantity of light which reaches the photosensitive layer decreases, resulting in decrease of the photosensitivity of the photoreceptor. Therefore, this method is of little effect.
Japanese Laid-Open Patent Publication No. (hereinafter JOP) 57-30846 discloses a method in which a metal or a metal oxide having an average particle diameter not greater than 0.3 &mgr;m is included as a filler in a protective layer to prepare a transparent protective layer, resulting in prevention of increase
Kami Hidetoshi
Kurimoto Eiji
Matsuyama Akihiko
Niimi Tatsuya
Suzuki Tetsuro
Ricoh Company Limited
RoDee Christopher D
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