Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Radiation-sensitive composition or product
Reexamination Certificate
2001-03-27
2002-12-10
Goodrow, John (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Radiation-sensitive composition or product
C399S220000
Reexamination Certificate
active
06492079
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrophotographic photoconductor in which a charge generation layer and a charge transport layer are successively provided on an electroconductive support. In addition, the present invention relates to an electrophotographic image forming apparatus using the above-mentioned photoconductor and a light source with a wavelength in the range of 400 to 450 nm as a light exposure means for data recording. The present invention also relates to a process cartridge including the photoconductor, which process cartridge is freely attachable to the image forming apparatus and detachable therefrom.
2. Discussion of Background
It is well known that a photoconductor for use with an electrophotographic process employs a photoconductive material, which is divided into an inorgnaic photoconductive material and an organic photoconductive material.
According to the above-mentioned electrophotographic process, image formation is usually achieved by following the procedures shown below. The surface of a photoconductor is uniformly charged in the dark, for example, by corona charging, and exposed to light images to selectively dissipate electric charge of a light-exposed portion, thereby forming latent electrostatic images on the surface of the photoconductor. The latent electrostatic images are developed as visible toner images with a toner that is made up of a coloring agent, such as a dye or pigment, and a polymeric material. Image formation can thus be repeated, using the photoconductor, by the so-called Carlson process, for an extended period of time.
Most of the currently available photoconductors employ organic photoconductive materials. This is because an organic photoconductive material is superior to an inorganic material in terms of the degree of freedom in selection of wavelength of light to which the photoconductive material is sensitive, the filming forming properties, flexibility, transparency of the obtained film, mass productivity, toxicity, and cost.
The photoconductor repeatedly used in the electrophotographic process or the like is required to have basic electrostatic properties such as good sensitivity, sufficient charging potential, charge retention properties, stable charging characteristics, minimal residual potential, and excellent spectral sensitivity.
In recent years, data processors employing the electrophotographic process have exhibited remarkable development. The image quality and printing reliability have noticeably improved, in particular, in the field of a printer that adapts a digital recording system by which information is converted into a digital signal and recorded by means of light. Such a digital recording system is applied to not only printers, but also to copying machines. Namely, a digital copying machine has been actively developed. Further, there is a tendency for the digital copying machine to be provided with various data processing functions, so that demand for the digital copying machine is expected to rise sharply.
A function-separation layered photoconductor has become the mainstream in the field of electrophotographic photoconductors for the above-mentioned digital copying machine. The function-separation layered photoconductor is constructed in such a manner that a charge generation layer and a charge transport layer are successively overlaid on an electroconductive support. To improve the durability of the photoconductor from the mechanical and chemical viewpoints, a surface protection layer may be overlaid on the top surface of the photoconductor.
When the surface of the function-separation layered photoconductor is charged and thereafter exposed to light images, the light passes through the charge transport layer and is absorbed by a charge generation material in the charge generation layer. Upon absorbing light, the charge generation material produces a charge carrier. The charge carrier is injected into the charge transport layer and travels along an electric field generated by the charging step to neutralize the surface charge of the photoconductor. As a result, latent electrostatic images are formed on the surface of the photoconductor.
In view of the above-mentioned mechanism of the function-separation layered photoconductor, a charge generation material which exhibits absorption peaks within the range from the near infrared region to the visible light region is often used in combination with a charge transport material that does not hinder the charge generation material from absorbing light, in other words, exhibiting absorption within the range from the visible light region (yellow light region) to the ultraviolet region.
As a light source capable of coping with the above-mentioned digital recording system, a semiconductor laser diode (LD) and a light emitting diode (LED), which are compact, inexpensive, and highly reliabler are widely employed. The LD most commonly used these days has an oscillation wavelength range in the near infrared region of around 780 to 800 nm. The emitting wavelength of the typical LED is located at 740 nm.
Recently, an LD or LED with oscillation wavelengths of 400 to 450 nm to emit a violet or blue light has been developed and finally put on the market as a light source for writing information so as to cope with the digital recording system. This kind of LD or LED is hereinafter referred to as “shorter wavelength LD or LED.” In the case where a shorter wavelength LD, of which the oscillation wavelength is as short as nearly half the conventional one located in the near infrared light region, is used as the light source for writing, it is theoretically possible to decrease the spot size of a laser beam projected on the surface of a photoconductor, in accordance with the following formula (A):
d
=(&pgr;/4)(&lgr;
f/D
) (
A
)
wherein d is the spot size projected on the surface of the photoconductor, &lgr; is the wavelength of the laser beam, f is the focal length of a f&thgr; lens, and D is the lens diameter.
In other words, the use of the shorter wavelength LD or LED can enormously contribute to improvement of the recording density, that is, resolution, of a latent electrostatic image formed on the photoconductor.
Further, for the use of such a shorter wavelength LD or LED, it will be possible to make the electrophotographic image forming apparatus compact as a whole, and to speed up the electrophotographic image forming method. Accordingly, there is an increasing demand for high sensitivity and high stability of the electrophotographic photoconductor so as to cope with the light source of the LD or LED having wavelengths of about 400 to 450 nm.
As previously mentioned, the function-separation layered photoconductor has been the mainstream of the electrophotographic photoconductors. With such a layered structure, the charge transport layer is usually overlaid on the charge generation layer. High sensitivity can be obtained if light emitted from the shorter wavelength LD or LED can efficiently reach the charge generation layer after passing through the charge transport layer. Namely, it becomes important that the charge transport layer not absorb the light from the LD or LED.
The charge transport layer is generally a film with a thickness of about 10 to 30 &mgr;m made from a solid solution in which a low-molecular weight charge transport material is dispersed in a binder resin. Most of the currently available photoconductors employ as a binder resin for the charge transport layer a bisphenol polycarbonate resin or a copolymer consisting of a monomer of the above-mentioned polycarbonate resin and any other monomers. The bisphenol polycarbonate resin has the characteristics that no absorption appears in the wavelength range from 390 to 460 nm. Therefore, the bisphenol polycarbonate resin does not severely hinder the light for a recording operation from passing through the charge transport layer.
The following are commercially available charge transport materials that are conventionally known: 1,1-bis(p-di
Kawamura Shin'ichi
Nagai Kazukiyo
Namba Michihiko
Shimada Tomoyuki
Tanaka Chiaki
Goodrow John
Ricoh & Company, Ltd.
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