Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2002-03-15
2004-02-03
Goodrow, John (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C399S148000, C399S159000, C399S346000
Reexamination Certificate
active
06686114
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrophotographic image forming apparatus using a photoreceptor, and to an electrophotographic image forming method. In addition, the present invention also relates to a process cartridge for use in an electrophotographic image forming apparatus.
2. Discussion of the Background
Electrophotographic image forming methods are widely used for copiers, facsimile machines, laser printers, direct digital printing plate making machines, etc. The electrophotographic image forming methods typically include the following processes:
(1) charging a photoreceptor (charging process);
(2) irradiating the photoreceptor with imagewise light to form an electrostatic latent image thereon (imagewise light irradiation process);
(3) developing the electrostatic latent image with a developer including a toner to form a toner image on the photoreceptor (developing process);
(4) transferring the toner image onto a receiving material such as paper optionally via an intermediate transfer medium (transfer process);
(5) fixing the toner image on the receiving material, for example, upon application of heat and pressure thereto (fixing process); and
(6) cleaning the surface of the photoreceptor (cleaning process).
Recently, copiers, facsimile machines and laser printers tend to be personalized. Therefore, such image forming apparatus need to have high durability and stability (i.e., being maintenance-free) and to be small in size.
In addition, such image forming apparatus need to stably produce high quality images because recently the performance of image scanners and personal computers from which images are input to the image forming apparatus has been dramatically improved.
As the electrophotographic photoreceptor (hereinafter referred to as a photoreceptor) for use in such image forming apparatus, inorganic photoreceptors using a material such as selenium or amorphous silicon and organic photoreceptors are known. Among these photoreceptors, organic photoreceptors have been typically used because of having low costs, good designing flexibility and being non-polluting.
Specific examples of the organic photoreceptors include photoreceptors having the following photosensitive layers:
(1) photosensitive layers including a photoconductive resin typified by polyvinylcarbazole (PVK);
(2) photosensitive layers including a charge transfer complex typified by polyvinylcarbazole-2,4,7-trinitrofluorenon (PVK-TNF);
(3) photosensitive layers including a pigment dispersion typified by a phthalocyanine-binder system; and
(4) functionally-separated photosensitive layers using a combination of a charge generation material and a charge transport material.
Among these photoreceptors, the functionally-separated photoreceptors attract attention.
The mechanism of forming an electrostatic latent image on a functionally-separated photoreceptor is as follows:
(1) when imagewise light irradiates a charged photoreceptor, the imagewise light is absorbed by a charge generation material in a charge generation layer after passing through a transparent charge transport layer located overlying the charge generation layer;
(2) the charge generation material absorbing light generates a charge carrier;
(3) the charge carrier is injected into the charge transport layer and transported through the charge transport layer (or the photosensitive layer) along an electric field generated by the charge formed on the surface of the photoreceptor; and
(4) the charge carrier neutralizes the charge on the surface of the photoreceptor, resulting in formation of an electrostatic latent image.
In the functionally-separated photoreceptors, a combination of a charge transport material having an absorption in an ultraviolet region and a charge generation material having an absorption in a visible region is known. In addition, recently laser diodes emitting light having a relatively short wavelength have been developed and used, and therefore various constructions have been investigated for the functionally-separated photoreceptors.
Various organic photoreceptors have been developed. However, in order that the photoreceptors are practically used, the photoreceptors need to have good electrophotographic properties such as high sensitivity, high potential, high potential retainability, good potential stability, low residual potential and proper spectral properties; good mechanical durability such as high abrasion resistance; good chemical stability against heat, light and discharge-induced products (e.g. ozone and NOx), etc.
In particular, a need exists for a photoreceptor having a small diameter because downsizing of electrophotographic systems is strongly desired. Therefore, a need exists for a photoreceptor having good resistance to abrasion which increases in proportion to the number of produced copies.
Thus, mechanical durability which typically means abrasion resistance is strongly needed. However, conventional organic photoreceptors and electrophotographic apparatus using the photoreceptors do not have high durability because the organic materials used have low abrasion resistance. In addition, the need for a photoreceptor having good abrasion resistance has increased because the thickness of a photosensitive layer has to be decreased to produce high definition images. Thus the designing flexibility of the photosensitive layers becomes smaller and smaller.
The reason why the thickness of a photosensitive layer has a particularly big influence on producing high definition images is considered as follows.
Among positive and negative carriers formed in the charge generation layer of a negatively chargeable multilayer organic photoreceptor by light irradiation, the negative carrier (i.e., an electron) is absorbed in the substrate and the positive carrier (i.e., a hole) is transported through the charge transport layer to the surface of the photoreceptor to be re-combined with the electron thereat, resulting in pair-disappearance of the hole and electron.
Due to this pair-disappearance, the electric field moving the hole toward the surface of the photoreceptor gradually decreases, and the hole moves toward a non-lighted area.
This is called a carrier scattering phenomenon in a direction of the surface of the photoreceptor, and because of the carrier scatter phenomenon, formation of a latent image faithful to the irradiated light is prevented. This results in formation of a poor image having low resolution.
The thickness of the charge transport layer has a big influence on the carrier scattering phenomenon, and making the thickness smaller is very effective for producing high resolution images.
In addition, laser irradiation, which is typically used recently, is different from irradiation using a halogen lamp, etc. because the incident photon speed of a laser is about 10
7
times that of a halogen lamp. Therefore, the density of the formed carriers is extremely high, and the electric field strength of the charge generation layer decreases because charges flow into the charge transport layer. Thereby, the carrier transport speed is decreased, resulting in late arrival of the carrier, which is formed by irradiation of the center portion of the laser beam, at the surface of the photoreceptor. The thus formed space charge distribution tends to cause carrier scattering in a direction parallel to the surface of the photoreceptor, resulting in deterioration of the image resolution.
In attempting to improve the abrasion resistance of an organic photoreceptor, Japanese Laid-Open Patent Publication No. (hereinafter referred to as JOP) 57-30846 discloses a photoreceptor in which a protective layer including a filler such as a metal or a metal oxide is formed on the surface of the photoreceptor. The object of this method is to increase the transparency of the protective layer to prevent increase of residual potential by using a filler having an average particle diameter not greater than 0.3 &mgr;m. In addition, JOP 4-281461 discloses a photoreceptor, in which a charge transport mat
Ikuno Hiroshi
Kojima Narihito
Nagame Hiroshi
Sakon Yohta
Goodrow John
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Ricoh & Company, Ltd.
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