Electrophotography – Image formation – Combined or plural functions by single component
Reexamination Certificate
2001-03-26
2003-01-07
Brase, Sandra (Department: 2852)
Electrophotography
Image formation
Combined or plural functions by single component
C399S174000
Reexamination Certificate
active
06505021
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus such as a copier and a printer and a process cartridge detachably attachable thereto, and more particularly, to an apparatus for recovering residual toner on an image bearing member by developing means after transfer.
2. Related Background Art
Recently, miniaturization of an image forming apparatus, such as an electrophotographic copier and a printer, has been proceeding. There have been limits to the miniaturization effected merely by miniaturizing each means in a process of forming an image such as electrifying, exposing, developing, transferring, fixing and cleaning.
In an image forming apparatus of the transferring type, some transfer residual toner on a photosensitive member (hereinafter referred to a photosensitive drum) as an image bearing member after transfer is collected by a cleaner as waste toner, which is preferably not produced due to its environmental impact.
This has caused the development of an image forming apparatus of a cleaner-less system, where a cleaner is removed to carry out cleaning simultaneous with developing of the transfer residual toner by a developing apparatus (developing device). The cleaning simultaneous with developing is a method of recovering some transfer residual toner on the photosensitive drum after the transfer by a fog clearing bias (a potential difference of the fog clearing bias “V back,” which is the potential difference between a direct voltage applied on developing means and a surface potential of the photosensitive drum) at the time of developing in and after a next process.
According to this method, the transfer residual toner is recovered by the developing means to be used in and after the next process, which produces no waste toner and reduces trouble in maintenance. Such a cleaner-less system has a great space advantage to permit the considerable miniaturization of the image forming apparatus. Further, an electrifying apparatus (electrifying device) of the contact-electrifying type permits recovering of the transfer residual toner by an electrifying member, which makes contact with the photosensitive drum and discharging the same again onto the photosensitive drum to be recovered by the developing means.
Moreover, the contact electrifying apparatus, namely an apparatus of a type that effects electrification by causing a voltage-applied electrifying member to abut against the photosensitive drum, has been in practical use as the electrifying means of the photosensitive drum because of its advantage of low power or the like.
As such a contact electrifying apparatus, a magnetic brush electrifying apparatus has been preferably used in terms of stability of an electrifying contact. In the magnetic brush electrifying apparatus, the electrification is started by magnetically attracting conductive magnetic particles, functioning as a magnetic brush, directly on a magnet or a sleeve containing the magnet, stopping or rotating the magnetic brush to be contacted with the photosensitive drum, and applying the voltage thereon.
Conductive fibers in the form of a brush (a fur brush) and a conductive rubber roller, which is a rolled conductive rubber have been preferably used as a contact electrifying member.
The electrifying apparatus of the magnetic brush type and, as the photosensitive drum, a normal organic photosensitive drum having a surface on which the conductive fine particles are dispersed or an amorphous silicon photosensitive drum, are used to make it possible to obtain, on the surface of the photosensitive drum, an electrifying potential substantially the same as a direct component of the bias applied on the magnetic brush as the contact electrifying member. Such an electrifying method is called injecting electrification. This injecting electrification utilizes, in the electrification to the photosensitive drum, no electric discharging phenomenon as in the case of using a corona electrifying device, these by permitting the electrification without ozone and by consuming a small amount of power, and attention has been paid thereto.
In the image forming apparatus using such an injection electrifying method, use of a spherical carrier granulated by polymerizing as the conductive magnetic particle (hereinafter referred to as an injection carrier) narrows an area in contact with the photosensitive drum and prevents reaching a desired potential to cause a defective image, such as fog or a ghost, when passing-sheet enduring is continued.
This brings the use of a carrier granulated by grinding (hereinafter referred to a ground carrier) instead of the spherical injection carrier. The ground carrier produces a finely powdered carrier, which enlarges the area in contact with the photosensitive drum and thereby increases an electrifying property of the photosensitive drum. Further, the ground carrier is easy to convey and produces large friction against the photosensitive drum, which facilitates recovering the transfer residual toner and increases the cleaning property.
When such injection electrification is used as the electrifying method, the injection carrier is preferably of grounded shape in order to prevent degradation of the image resulting from the poor electrification.
In the injection electrifying method, the photosensitive drum passes an electrifying portion (electrifying area or electrifying nip) which is a contacting portion with the magnetic brush as the contact electrifying member. If the electrification is carried out merely by applying a DC (direct current) bias, the potential difference between a carrying member for the magnetic brush (hereinafter referred to as an injection sleeve) and the photosensitive drum is wide when the photosensitive drum starts contact with the magnetic brush at the electrifying portion so that the resistance of the injection carrier is low to facilitate the flow of the current.
Just before the photosensitive drum is separated from the electrifying portion, however, the potential is on the surface of the photosensitive drum to decrease the potential difference between the injection sleeve and the photosensitive drum and to thereby increase the resistance of the injection carrier. It is known that this causes difficulty in the flow of the current and reduces the electrifying property of the photosensitive drum (FIG.
5
).
For this reason, in the injection electrifying method, an AC (alternate bias) is often applied at the same time as applying the DC (direct bias applying) as the electrifying bias. Applying the AC decreases the resistance of the injection carrier to facilitate the flow of the current and to increase the electrifying property to the photosensitive drum, which permits the electrification to a desired potential.
However, the electrification by simultaneously applying the AC causes a micro potential difference between the photosensitive drum and the injection sleeve corresponding to a waveform of the AC. An example of this is shown in FIG.
6
. For example, when the electrification is carried out at −500 V by applying the DC and simultaneously by applying the AC at 700 Vpp, there exist locally a potential differences of −150 V at the injection sleeve and −850V at the photosensitive drum. The potentials of the injection sleeve and the photosensitive drum are the same during the time when the photosensitive drum passes the electrifying portion, which is the contacting portion with the magnetic brush, and just after the photosensitive drum has passed the electrifying portion, phases of the potentials are shifted between the injection sleeve and the photosensitive drum. The shift of the phase occurs such that the injection sleeve at −150 V and the photosensitive drum at −850 V causes a potential difference at 700 V between the injection sleeve and the photosensitive drum. At this time, between the injection sleeve and the photosensitive drum, a voltage drop between the injection carrier and the photosensitive drum is the largest, so that the inje
Gomi Fumiteru
Hashimoto Kouichi
Kadota Shuichi
Komiya Yoshiyuki
Shibuya Ken-ichi
Brase Sandra
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
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