Electrophotography – Image formation – Charging
Reexamination Certificate
1998-06-08
2001-09-04
Grainger, Quana M. (Department: 2852)
Electrophotography
Image formation
Charging
C399S149000
Reexamination Certificate
active
06285848
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
The present invention relates to an electrophotographic apparatus including a charging means comprising a charging member formed of magnetic particles and a developing means also functioning as a substantial cleaning means. The present invention relates to an image forming method using such an electrophotographic apparatus and a process cartridge constituting a vital part of such an electrophotographic apparatus.
Hitherto, a large number of electrophotographic processes have been known. In these processes, an electrostatic latent image is formed on a photosensitive member, comprising a photoconductive material, by various means, then the latent image is developed and visualized with a toner, and the resultant toner image is, after being transferred onto a transfer-receiving material, such as paper, as desired, fixed by heating, pressing, heating and pressing, etc., to obtain a copy or a print. The residual toner remaining on the photosensitive member without being transferred is removed in a cleaning step. In such electrophotographic apparatus, corona discharge means, such as a so-called corotron or scorotron, have been conventionally used as charging means, but are accompanied by difficulties, such that a substantial amount of ozone occurs at the time of the corona discharge for forming a negative corona or a positive corona, and the electrophotographic apparatus is required to be equipped with a filter for removing the ozone, resulting in a size enlargement and an increase in the running cost of the apparatus.
As a technical solution of such difficulties, a charging method for minimizing the occurrence of ozone has been developed, wherein a charging means, such as a roller or a blade, is caused to contact the photosensitive member surface to form a narrow gap in the proximity of the contact portion where a discharge, appearing to follow the Paschen's law, occurs (contact charging scheme), e.g., as disclosed in Japanese Laid-Open Patent Application (JP-A) 57-178257, JP-A 56-104351, JP-A 58-40566, JP-A 58-139156 and JP-A 58-150975.
According to the contact charging scheme, however, there is liable to occur a difficulty, such as toner melt-sticking onto the photosensitive member. For this reason, there is also proposed a scheme of disposing a charging member in proximity to a photosensitive member so as to avoid a direct contact therebetween. The member for charging a photosensitive member may assume the form of a roller, a blade, a brush or an elongated plate member coated with a resistance layer. Any of such members still have difficulty in accurate proximity control, thus leaving a difficulty in practical application.
As another alternative, it has been also proposed to use magnetic particles held on an electroconductive sleeve enclosing a magnet as a charging member exerting a relatively small contacting lead onto the photosensitive member. For example, JP-A 59-133569 discloses a method wherein iron-coated particles are held on a magnet roll and supplied with a voltage to charge a photosensitive member; JP-A 4-116674 discloses a charging apparatus supplied with an AC-superposed DC voltage; and JP-A 7-72667 discloses magnetic particles coated with a styrene-acrylic resin so as to exhibit improved environmental stability.
On the other hand, in the cleaning step, a blade, a fur brush, a roller, etc., have been conventionally used as cleaning means. By cleaning means or member, the transfer residual toner is mechanically scraped off or held back, to be recovered into a waste toner vessel. Accordingly, some problems have been caused by pressing of such a cleaning member against the photosensitive member surface. For example, by strongly pressing the member, the photosensitive member can be worn out, resulting in a short life of the photosensitive member. Further, from an apparatus viewpoint, the entire apparatus is naturally enlarged because of the provision of such a cleaning device, thus providing an obstacle against a general demand for a smaller apparatus.
Further, from an ecological viewpoint and effective utilization of a toner, a system not resulting in a waste toner has been desired.
In order to solve the above-mentioned problems accompanying the provision of a separate cleaning system, a so-called simultaneous developing and cleaning system or cleaner-less system has been proposed wherein a separate cleaning means for recovering and storing residual toner remaining on the photosensitive member after the transfer step is not provided between the transfer position and the charging position or between the charging position and the developing position, but the cleaning is performed by the developing means. Examples of such a system are disclosed in JP-A 59-133573, JP-A 62-203182, JP-A 63-133179, JP-A 64-20587, JP-A 2-51168, JP-A 2-302772, JP-A 5-2287, JP-A 5-2289, JP-A 5-53482 and JP-A 5-61383. In these proposed systems, a corona charge, a fur brush charger and a roller charger are used as the charging means, and it has not been fully successful to solve problems, such as the soiling of the photosensitive member surface with discharge products, and charging non-uniformity.
For this reason, a cleaner-less system using a magnetic brush as a charging member has been proposed. For example, JP-A 4-21873 discloses an image forming apparatus using a magnetic brush supplied with an AC voltage having a peak-to-peak voltage exceeding a discharge threshold value for unnecessitating a cleaning apparatus. Further, JP-A 6-118855 discloses an image forming apparatus including a simultaneous magnetic brush charging and cleaning system without using an independent cleaning apparatus.
However, these prior art references fail to disclose specific forms of charging magnetic particles suitable for a cleaner-less system, thus leaving a technical problem in this respect.
More specifically, it is desired to provide a charging member capable of exhibiting a stable charging performance and treating a transfer residual toner in a form suitable form for recovery by a developing means, this being suitable for use in a cleaner-less system.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an electrophotographic apparatus including a magnetic brush and a cleaner-less system and capable of providing stable images continually for a long period.
Another object of the present invention is to provide an electrophotographic apparatus including a magnetic brush charger capable of effectively preventing toner scattering therefrom through the use of improved magnetic particles.
A further object of the present invention is to provide an image forming method using such an electrophotographic apparatus and a process cartridge forming a vital part of such an electrophotographic apparatus.
According to the present invention, there is provided an electrophotographic apparatus, comprising: an electrophotographic photosensitive member, and (i) charging means, (ii) imagewise exposure means, (iii) developing means and (iv) transfer means, disposed in this order opposite to the photosensitive member, wherein
said charging means includes a charging member comprising magnetic particles disposed in contact with the photosensitive member so as to charge the photosensitive member based on a voltage received thereby,
said magnetic particles are surface-coated with a coupling agent having a linear alkyl group having at least 6 carbon atoms, and
said developing means also functions to recover residual toner remaining on the photosensitive member after processing by the transfer means and the charging means.
According to another aspect of the present invention, there is provided an image forming method, comprising a cycle of:
a charging step of charging an electrophotographic photosensitive member by a charging means disposed in contact with the photosensitive member,
an exposure step of exposing the charged photosensitive member to image light to form an electrostatic image on the photosensitive member,
a developing step of developing the electrostatic image with
Aita Shuichi
Arahira Fumihiro
Fujita Ryoichi
Hano Yoshifumi
Mizoe Kiyoshi
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Grainger Quana M.
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