Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Radiation-sensitive composition or product
Reexamination Certificate
2001-09-26
2003-04-01
Goodrow, John L (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Radiation-sensitive composition or product
C430S069000, C399S174000
Reexamination Certificate
active
06541172
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrophotographic photosensitive member, a process cartridge containing the electrophotographic photosensitive member, and an electrophotographic apparatus containing the process cartridge. In more detail, this invention relates to an electrophotographic photosensitive member comprising a specific charge generation layer, a charge transport layer having a specific thickness, a support portion having a specific surface roughness, and possessing a specific electrostatic capacity. This invention also relates to a process cartridge containing the electrophotographic photosensitive member, as well as an electrophotographic apparatus containing the process cartridge.
2. Description of the Related Art
As an electrophotographic photosensitive member for use in an electrophotographic apparatus, there has been commonly used an organic electrophotographic photosensitive member formed by an organic photoconductive material serving as a charge generation substance. This is because the use of an organic electrophotographic photosensitive member can ensure a low production cost, as well as a high freedom in designing an electrophotographic photosensitive member. Another advantage of using an organic electrophotographic photosensitive member is that it does not cause an industrial pollution.
In fact, using an organic photoconductive material as a charge generation substance can make it possible to freely select a wavelength range of a light sensible by an electrophotographic photosensitive member. For example, a series of azo pigments disclosed in Japanese Unexamined Patent Laid-Open No. 61-272754 as well as in Japanese Patent Laid-Open No. 56-167759 have exhibited a high sensitivity in the visible light region. Further, the substances disclosed in Japanese Patent Laid-Open No. 57-19576 as well as in Japanese Patent Laid-Open No. 61-228453 have shown a high sensibility even in the infrared region.
Among the charge generation substances disclosed in the aforementioned patent publications, those exhibiting a high sensitivity in the infrared region have been used in a laser beam printer (which will sometimes be referred to as LBP in the following description) and in a LED printer, each of which is adapted to digitally form electrostatic latent images. In fact, the needs for using such charge generation substances has become more and more frequent.
Recently, laser beam printer and LED printer have become a main trend printer in the commercial market. As a result, conventional printers having resolutions of 240, 300 dpi have become those having resolutions of 400, 600, 1200 dpi.
On the other hand, various copy machines have been improved in order to be equipped with more and more functions, and this has formed a rapid development in the direction of digitalization. In particular, digital machine involves the use of a method for forming electrostatic latent images using a laser beam, and this has become a main trend in this technical field. Similarly, recent printer also involves the use of a laser beam for forming electrostatic latent images, thereby obtaining an improvement in its resolution.
Usually, an electrophotographic photosensitive member for use in digitally forming electrostatic latent images is required to have the following properties.
(1) Capable of charging in dark position to a certain potential.
(2) Dispersing amount of charges in dark position is small.
(3) Capable of rapidly dispersing charges by virtue of a light irradiation.
In particular, with regard to the above (3), an electrophotographic photosensitive member is required to have a high sensitivity in the infrared region.
On the other hand, most phthalocyanine compounds have a high sensitivity in the infrared region and thus have been widely used as a charge generation substance contained in an electrophotographic photosensitive member. Particularly, in recent years, there has been widely used an oxytitanium phthalocyanine as a material having a high sensitivity in the infrared region. In addition, Japanese Patent Laid-Open No. 5-188615 has disclosed an electrophotographic photosensitive member formed by using a chlorogallium phthalocyanine, and Japanese Patent Laid-Open No. 5-249716 has disclosed an electrophotographic photosensitive member formed by using a hydroxygallium phthalocyanine.
In this way, each of the aforementioned conventional electrophotographic photosensitive members is formed by using a phthalocyanine compound as a charge generation substance and is found to have an extremely high sensitivity not only in the visible light region but also in the infrared region. This is because a phthalocyanine compound usually has a relatively high quantum efficiency and is capable of generating a great number of carriers. Although, at the present time it is still not quite clear as to why a phthalocyanine compound can generate a great number of carriers, a possible reason for this phenomenon is supposed to be the presence of oxygen and some other impurities.
However, in the case where a great number of carriers have been generated, if the electrons having the same amount as the holes (injected into the charge transport layer) can not quickly move towards a support portion, the electrons remaining in the charge generation layer will become excessive, forming a kind of memory easy to effect a potential change.
In principle, it is allowed to consider that the electrons remaining in the charge generation layer will usually proceed (due to a certain possible reason) to an interface between the charge generation layer and the charge transport layer, thus reducing a barrier efficiency of the holes injected in the vicinity of the interface.
In fact, when an electrophotographic photosensitive member is formed by using a phthalocyanine compound as a charge generation substance, the barrier efficiency will be reduced and this fact can be confirmed by finding a reduced bright position potential and a reduced residual potential during a continuous printing process. For example, in a development process (or a so-called reversal development process) where a dark position potential portion often used in a conventional printer serves as a non-developing portion and a bright position potential portion serves as a developing portion, positions which have received a light during a former printing process will offer a quick sensitivity. Accordingly, once an entire black image is removed during a next printing process, there will occur a so-called ghost phenomenon in which a formerly printed portion will be floated out.
The above phenomenon is particularly remarkable when an electrophotographic photosensitive member contains an intermediate layer serving as an adhesive layer for supporting the charge generation layer. In particular, under an environment of a low temperature and a low humidity, since a volume resistivity against the electrons in the charge generation layer as well as in the intermediate layer will be increased, the electrons will easily fill the charge generation layer, resulting in a problem that the aforesaid ghost phenomenon is more likely to occur.
Similarly, if a reversal developing electrophotographic process employs a laminated type of a electrophotographic photosensitive member whose charge generation layer contains a phthalocyanine compound, the aforesaid ghost phenomenon will also occur. In order to solve the above problem, a commonly used method requires that an electrophotographic photosensitive member's first rotation involving a charging voltage drop is not used to form image (i.e., forming an idle rotation), but only the processes from a second rotation onward are used to form image, since each of these later processes has a stable charging voltage. Alternatively, a charge removal process is carried out by virtue of a light exposure conducted prior to a charging process, thereby avoiding the aforementioned problem. In fact, the above-described method is found to be useful in a reversal development type printer which i
Nagasaka Hideaki
Nakamura Kazushige
Takagi Noriyuki
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Goodrow John L
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