Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Radiation-sensitive composition or product
Reexamination Certificate
2000-08-04
2002-03-12
Goodrow, John (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Radiation-sensitive composition or product
C430S062000, C430S100000, C430S131000, C399S130000
Reexamination Certificate
active
06355390
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrophotographic photoconductor for use in a laser beam printer, facsimile machine, and digital copier, which photoconductor comprises an electroconductive support, and an undercoat layer and a photoconductive layer successively overlaid on the support in this order. In addition, the present invention relates to a production process of the above-mentioned photoconductor, an electrophotographic image forming method and apparatus using the above-mentioned photoconductor. Further, the present invention also relates to a process cartridge holding therein the above-mentioned photoconductor, which process cartridge is freely attachable to the image forming apparatus and detachable therefrom.
2. Discussion of Background
Basically, an electrophotographic photoconductor comprises an electroconductive support and a photoconductive layer formed thereon comprising a photoconductive material. Further, it is proposed to provide an undercoat layer between the electroconductive support and the photoconductive layer for the following purposes: improving the adhesion of the photoconductive layer to the support, the coating characteristics of the photoconductive layer, the charging characteristics of the photoconductive layer, inhibiting unnecessary charges from injecting from the support into the photoconductive layer, and compensating for any defects on the support.
Methoxymethylated polyamide is conventionally known as a well-balanced material for the undercoat layer as disclosed in Japanese Laid-Open Patent Application 6-202366. However, an N-alkoxymethylated polyamide represented by the above-mentioned methoxymethylated polyamide exhibits high water absorption properties because of the presence of an alkoxyl group in the structure. In the case where a photoconductor comprises an undercoat layer comprising such an N-alkoxymethylated polyamide, the photoconductor properties are largely changed in the repeated use under the circumstances of high temperature and humidity, or low temperature and humidity. Such a drawback results from the increase of water content in the undercoat layer. The above-mentioned photoconductor tends to produce abnormal images with toner deposition on the background and low image density.
In Japanese Laid-Open Patent Application Nos. 2-108064 and 10-268543, and Japanese Patent Nos. 2817421 and 2785282, an undercoat layer for use in the photoconductor consists of a crosslinked methoxymethylated polyamide. However, the photoconductor properties are still dependent on environmental conditions because of insufficient crosslinking in the methoxymethylated polyamide. Further, in this case, the problem of the increase in residual potential is caused when the undercoat layer is thickened. More specifically, the surface of the electrophotographic photoconductor is charged, and exposed to light images according to the electrophotographic process. The light-exposed portion of the photoconductor is made electroconductive, and electric charges can transfer in the photoconductor. Image data can be thus recorded in the form of latent electrostatic images. When the thickness of the undercoat layer exceeds 1.0 &mgr;m, the electric charge on the light-exposed portion unfavorably remains on the photoconductor, and the residual potential is increased in the repeated use of the photoconductor. The increase in residual potential, which means a deterioration of the photoconductor, will produce abnormal images.
To solve the above-mentioned problem, it is required that the thickness of the undercoat layer be decreased to 1.0 &mgr;m or less when the undercoat layer consists of methoxymethylated polyamide alone. However, a thin undercoat layer cannot effectively make up for the defects on the electroconductive support, such as scratches and surface roughness. To regulate the surface properties of the electroconductive support, the surface treatment steps of cutting and abrasion become necessary, thereby increasing the manufacturing cost of the photoconductor.
In addition, when a photoconductor with a thin undercoat layer is set in an electrophotographic image forming apparatus where a contact type charger is installed, discharge breakdown occurs in the photoconductor, with the result that abnormal images are easily produced. In particular, when the process of reversal development is adapted, the above-mentioned discharge breakdown produces a relatively large black spot image. This is conventionally regarded as a serious problem.
To eliminate the problem caused by the water absorption properties of methoxymethylated polyamide, it is proposed to add a thermosetting resin such as melamine resin to the methoxymethylated polyamide in Japanese Laid-Open Patent Application No. 3-337861 and Japanese Patent No. 2861557. The aforementioned undercoat layer comprising the methoxymethylated polyamide and the melamine resin can solve the problem resulting from the water absorption properties to some extent. However, there still remains the problem that the physical properties of the methoxymethylated polyamide are practically dependent upon temperature and humidity. Therefore, even though the photoconductive layer is provided on such an undercoat layer, the photoconductor properties are still susceptible to temperature and humidity. The result is that abnormal images such as black spots are produced and the image density is lowered when image formation is repeated under the circumstances of high temperature and humidity or low temperature and humidity.
According to Japanese Laid-Open Patent Application No. 5-150535 and Japanese Patent No. 2861557, an undercoat layer for use in the electrophotographic photoconductor comprises (i) a thermosetting resin and (ii) a thermoplastic resin such as a modified polyamide resin which comprises as the main component a copolymer polyamide comprising a modified polyamide 6 or polyamide 6. When such a photoconductor is operated under the circumstances of low temperature and humidity, the residual potential (VL) of a light-exposed portion tends to largely vary and produces abnormal images.
As disclosed in Japanese Laid-Open Patent Application Nos. 61-204642 and 62-280864, it is well known that an inorganic pigment such as titanium oxide is dispersed in the undercoat layer to effectively compensate for the defects on the surface of the electroconductive support and to enhance the light scattering effect of coherent light such as a laser beam and prevent the interference fringes. Such an undercoat layer comprising an inorganic pigment causes no problem in the initial stage. However, when the photoconductor is set in an electrophotographic image forming apparatus and repeatedly used for an extended period of time, defective images such as toner deposition on the background and non-printed white spots in a solid image become conspicuous with time.
To eliminate the defective images produced in the repeated use, there is proposed in Japanese Laid-Open. Patent Application Nos. 63-289554 and 64-031163 an electrophotographic photoconductor comprising an electroconductive support, and a first undercoat layer containing no filler, a second undercoat layer in which an inorganic pigment is dispersed, and a photoconductive layer which are successively overlaid on the electroconductive support. However, such a layered undercoat layer cannot solve the above-mentioned problem. Namely, occurrence of abnormal images cannot be prevented when the photoconductor is used for an extended period of time.
In Japanese Laid-Open Patent Application No. 6-202366 and Japanese Patent No. 2885609, it is proposed to provide an undercoat layer using a coating liquid prepared by dissolving and dispersing non-electroconductive titanium oxide particles and a polyamide resin in a mixed solvent of an alcohol and a particular organic solvent. However, the water absorption properties of the obtained undercoat layer are so high that the photoconductor properties are largely dependent upon environmental conditions. Therefore, b
Aruga Tamotsu
Yamanami Hirofumi
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Ricoh & Company, Ltd.
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