Electrophotography – Cleaning of imaging surface – Blade
Reexamination Certificate
2001-12-20
2004-04-13
Braun, Fred L. (Department: 2852)
Electrophotography
Cleaning of imaging surface
Blade
C399S351000
Reexamination Certificate
active
06721533
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a toner cleaning device employed in electrophotographic copiers and printers, an image forming method using the toner cleaning device, and an image forming apparatus using the toner cleaning device.
In recent years, as image holding bodies, employed in electrophotographic image forming apparatus, organic photoreceptors (hereinafter referred simply to as photoreceptors) comprising organic photoconductive materials have been most widely employed. Organic photoreceptors are superior to other photoreceptors since it is easier to develop materials in response to various types of exposure light sources ranging from visible light to infrared light; it is possible to select materials which result in no environmental pollution; the production cost is lower; and the like. However, organic photoreceptors are mechanically weak. Due to that, problems occur in which, during copying or printing a large number of sheets, the photoreceptor surface tends to result in degradation as well as abrasion.
Further, the organic photoreceptors exhibit a large contact energy toward the toner, which visualizes electrostatic latent images formed on the photoreceptor. As a result, after transferring the toner image to a transfer material in the transfer process, it is difficult to completely remove the residual toner which remains on the photoreceptor. Accordingly, during cleaning of the photoreceptor surface, various problems tend to occur.
On the other hand, in the image forming process utilizing the electrophotographic system, image formation, utilizing a digital system, has been playing a main role due to the recent progress of digital technology. In the image formation utilizing the digital system, an image of minute dots comprised of pixels such as 400 dpi (dots per inch) is basically visualized. Accordingly, a high quality image technology is demanded to faithfully reproduce such minute-dot images.
On the other hand, in order to minimize degradation of the organic photoreceptor surface due to cleaning, proposed have been various techniques to enhance the mechanical strength of the photoreceptor surface. Japanese Patent Publication Open to Public Inspection No. 9-258460 proposes a photoreceptor comprising a polycarbonate resin of high hardness on the surface layer. The photoreceptor comprising the polycarbonate resin is different from conventional ones and results in less surface abrasion due to cleaning. As a result, the frictional force against a cleaning blade (hereinafter occasionally referred to as a blade) increases. Thus, when a conventional cleaning blade is employed for cleaning, cleaning problems tend to occur, in which the blade is subjected to curl-under, whereby a toner is not completely removed due to vibrational fluctuation of the blade.
On the other hand, Japanese Patent Publication Open to Public Inspection No. 5-341701 proposes a technique in which, as a means to damp blade vibration, a toner cleaning device is provided with a vibration damping means. However, in the vibration damping technique described herein, vibration is damped employing a vibration damping means which is also employed as the blade holding member linearly joined to the blade. Accordingly, the vibration of the blade itself is not sufficiently damped. At the same time, it is difficult to achieve a stable enough connection due to the small joined area between the blade and the holding member. Therefore, blade vibration tends to become unstable.
Further, one other technique to achieve high image quality is a toner production technique. Heretofore, a so-called pulverized toner has been mainly employed to form electrophotographic images. The pulverized toner is prepared as follows: after blending and kneading resins and pigments, the resulting mixture is pulverized, and the resulting toner powder is classified employing a classifying process. However, the toner so prepared, employing the production processes, exhibits a limit in make the particle size distribution uniform. Accordingly, the toner results in insufficient particle size distribution as well as insufficient uniformity of particle shape. As a result, in the electrophotographic images prepared employing the pulverized toner, it is difficult to sufficiently achieve high image quality.
In recent years, as a means to make the particle size distribution as well as the shape of toner particles more uniform, an electrophotographic developer or an image forming method utilizing a polymerization toner has been proposed. The polymerization toner is prepared by dispersing monomers as the raw material into a water-based medium and subsequently subjecting then the monomers to polymerization. As a result, a toner is prepared which has a uniform particle size distribution as well as uniform particle shape.
When the polymerization toner is used in an image forming apparatus, employing the organic photoreceptor, new technical problems occur. Namely, as noted above, the shape of the polymerization toner particles is formed during the polymerization process of monomers, whereby the resulting shape is nearly spherical. As is well known, spherically shaped toner particles, which remain on the organic photoreceptor, tend to result in insufficient cleaning. Specifically, the surface of the organic photoreceptor tends to result in abrasion. When toner particles are adhered onto roughened surfaces formed through the abrasion, fine toner particles, which do not affect image formation, are not removed over an extended period of time and stain charging members (such as a charging wire and a charging roller), so that halftone images result in image unevenness.
In order to overcome cleaning problems such as blade curl-under as well as insufficient residual toner removal due to its passing under the blade with curl-under which result in the image forming method employing the polymerization toner, heretofore various proposals have been made. Of these, it has been proposed that the shape of polymerization toner particles be varied from a sphere to a spheroid, and the surface of polymerization toner particles be formed so as to exhibit roughness. However, these proposals have not sufficiently overcome the problems.
On the other hand, as the image forming apparatus utilizing the electrophotographic system, Japanese Patent Publication Open to Public Inspection No. 2001-109212 proposes an image forming apparatus which is constituted in such a manner that a toner cleaning device is provided just above the cylindrical photoreceptor. The image forming apparatus, which is constituted employing such an arrangement of the toner cleaning device as above, exhibits the advantage of being capable of being constituted in small dimensions. However, the image forming apparatus tends to result in insufficient cleaning due to the following reason. The toner cleaning device is provided above the photoreceptor and the cleaning blade is brought into pressure contact with the moving photoreceptor in a nearly horizontal direction from the upper side. As a result, toner particles scraped by the cleaning blade tend not to leave the photoreceptor surface resulting often in cleaning failure.
Specifically, when the polymerization toner is applied to an image forming apparatus which is constituted in a manner such that the toner cleaning device is provided just above the cylindrical organic photoreceptor, fine toner particles, which do not affect image formation, are not removed over an extended period of time and therefore stain charging members (such as the charging wire and the charging roller), whereby halftone images result in image unevenness.
SUMMARY OF THE INVENTION
A first object of the present invention is to provide a toner cleaning device which solves the aforesaid problems, is capable of maintaining excellent cleaning performance, resulting in no image defects, and forming excellent electrophotographic images for an extended period of time, when an organic photoreceptor as well as a polymerization toner is employed; an image forming method using
Endo Isao
Mochizuki Fumitaka
Sato Kazuhiko
Uchino Satoshi
Braun Fred L.
Squire Sanders & Dempsey L.L.P.
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