Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Radiation-sensitive composition or product
Reexamination Certificate
2001-07-13
2003-05-13
Goodrow, John (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Radiation-sensitive composition or product
C430S059600, C430S126200, C399S159000
Reexamination Certificate
active
06562531
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 a photoreceptor. Further, the present invention relates to a process cartridge for electrophotographic image forming apparatus, which includes a photoreceptor.
2. Discussion of the Background
As electrophotographic image forming methods, various methods using a photoreceptor such as the Carlson process and its modified processes are known and have been used for image forming apparatus such as copiers and printers. Among photoreceptors used for such image forming methods, photoreceptors using an organic photosensitive material have been currently used because of having advantages such as low manufacturing cost, 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 poly-N-vinylcarbazole;
(2) charge transfer complex type photosensitive layers as 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 having 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.
For such functionally-separated photoreceptors, a combination of a charge transport material mainly absorbing ultraviolet light and a charge generation material mainly absorbing visible light is known to be useful.
Currently, a need exists for a photoreceptor having a long life. In particular, investigation of improving mechanical durability (i.e., abrasion resistance) of photoreceptors has been mainly made. For example, new binder resins have been proposed in Japanese Patent Publication No. (hereinafter referred to as JPP) 8-20739, etc. and various photoreceptors having new construction have also been disclosed. This is because the life of a photoreceptor substantially depends on the abrasion of the photosensitive layer and does not depend on the deterioration of the electrostatic properties of the photoreceptor.
However, when the abrasion resistance of photoreceptors is improved by various methods, it is considered that there will be severe demands for improving the deterioration of electrostatic properties such as decrease of charge potential (i.e., the potential of a dark area of a photoreceptor V
D
, hereinafter sometimes referred to as a dark area potential) and increase of residual potential (i.e., the potential of a lighted area of the photoreceptor V
L
, hereinafter sometimes referred to as a lighted area potential) In attempting to improve the deterioration of electrostatic properties, main materials constituting organic photoreceptors, such as charge generation materials and charge transport materials, have been improved. In addition, methods such that various additives such as antioxidants are added to photoreceptors have also been proposed. However, there is a trade-off between the deteriorated electrostatic properties, i.e., the decrease of charge potential and the increase of residual potential. Therefore, there is no method for improving both the decrease of charge potential and the increase of residual potential. Therefore, a photoreceptor having good combination of high dark area potential and low residual potential is earnestly desired.
As one of measures against abrasion of photoreceptors, methods in which a protective layer is formed on a surface of a photoreceptor have been proposed. Investigation of forming a protective layer is at first made for inorganic photoreceptors and has been disclosed in, for example, JPP 2-3171, 2-7058 and 3-43618. In these cases in which a protective layer is formed on inorganic photoreceptors, a filler having a relatively low resistance is preferably used for the protective layer. Therefore, when such photoreceptors are charged, the entire protective layer or the interface between the protective layer and the inorganic photosensitive layer is typically charged rather than the surface of the photoreceptor.
When a latent image is not formed on a surface of a photoreceptor but is formed on the inside of the protective layer, the photoreceptor has an advantage such that the resultant electrostatic latent image is hardly influenced by deficiencies of the surface of the photoreceptor, such as scratches. However, in order to impart a protection function to the protective layer, a large amount of an electroconductive filler such as metal oxides has to be added to the protective layer. In such a case, even if the protective layer is made so as to be transparent by using a suitable metal oxide, the resistance of the entire protective layer or the surface resistance of the protective layer decreases, resulting in occurrence of blurred images in repeated use. In attempting to solve the blurred image problem, JPP 2-7057 and Japanese Patent No. 2,675,035 have disclosed methods in which the concentration of an electroconductive metal oxide is changed in the depth direction of the protective layer.
In addition, in attempting to solve the blurred-image problem on the process side, a device including a heater heating a photoreceptor is proposed. By heating a photoreceptor, occurrence of blurred images can be avoided. However, when a drum heater is set in the photoreceptor, the diameter of the photoreceptor has to be widened.
Currently electrophotographic image forming apparatus are miniaturized more and more and therefore photoreceptors having a small diameter are mainly used. Since this heating technique cannot be used for such photoreceptors having a small diameter, it is hard to provide small-diameter photoreceptor having good durability. In addition, when a drum heater is provided in an image forming apparatus, the apparatus has many drawbacks such that the apparatus becomes large-sized; electric power consumption seriously increases; and it takes a long time until the apparatus is warmed
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