Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2002-01-11
2003-12-30
Goodrow, John (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S066000, C430S122520, C399S159000
Reexamination Certificate
active
06670089
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
The present invention relates to an electrophotographic image forming system (method and apparatus) including a specific system) using non-single crystal silicon-based electrophotographic photosensitive member, a contact charging means and a spherical toner and including no cleaning step between the transfer and charging system, and more particularly to such an electrophotographic image forming system using a non-single crystalline silicon photosensitive member provided with a surface layer having a silicon content (percentage of silicon versus total of silicon and carbon).
A conventional electrophotographic image forming method generally includes a cycle of charging-exposure-development-transfer-cleaning of transfer residual toner-residual charge removal of the photosensitive member-charging (in a subsequent cycle). According to this, transfer residual toner remaining on the photosensitive member (image-bearing member) after the transfer step is removed from the photosensitive member surface and recovered as waste toner by a cleaner (cleaning device). It is desired that such waste toner does not occur from a viewpoint of environmental protection. Accordingly, there has been proposed an electrophotographic apparatus of a toner-recycle type having removed such a cleaner and including a developing device for simultaneous developing and cleaning for removing transfer residual toner on the photosensitive member and recover it in the developing device for reuse. Such an electrophotographic apparatus is disclosed in, e.g., Japanese Laid-Open Patent Application (JP-A) 10-307455.
Simultaneous developing and cleaning is an operation of removing the transfer residual toner on the photosensitive member in a developing step of a subsequent cycle, i.e., after charging and exposing the photosensitive member to form a latent image, under the action of a fog-removing bias voltage difference Vback (i.e., a potential difference between a DC voltage applied to the developing device and the surface potential on the photosensitive member). According to this method, the transfer residual toner is recovered in the developing device and re-used in a subsequent image forming cycle or later, thus removing the waste toner and reducing the troublesome maintenance operation. The cleanerless system is advantageous for space economization, thus providing an electrophotographic apparatus remarkably reduced in size.
Hereinbelow, such a toner recycle process including a simultaneous developing and cleaning step will be briefly described with reference to FIG.
3
.
(1) A photosensitive member
201
is supplied with a voltage by a contact charging member
202
to be uniformly charged to, e.g., a negative polarity in this case.
(2) The uniformly negatively charged photosensitive member
201
is exposed to light
203
carrying image data (e.g., laser light) for the reversal development scheme, to form a latent image thereon.
(3) A charged toner
205
comprising colored powder is supplied from a developing device
204
in a form corresponding to the latent image onto the photosensitive member
201
surface to form a visible toner image thereon. The toner in this case is a negatively charged one.
(4) By applying a voltage from a transfer roller
206
or by the action of a member exerting an electrostatic attraction force, the toner image is transferred onto a recording material (or transfer (-receiving) material)
207
to be fixed thereon by a fixing device
209
. In this instance, a portion of the toner is caused to remain as a transfer residual toner without being transferred, and a portion of the residual toner is liable to be charged in a polarity opposite to the polarity to which the toner is normally charged by a voltage of an opposite polarity (e.g., positive) applied to the transfer roller
206
. The portion of the transfer residual toner charged to the opposite polarity may be referred to as an inverted toner
208
.
(5) The transfer residual toner remaining on the photosensitive member surface including the above-mentioned inverted toner
208
is re-charged to the normal toner charge polarity by rubbing between the contact charging member
202
and the photosensitive member
202
in the step (1) of a subsequent cycle and then discharged onto the photosensitive member. The charging of the invented toner to the normal polarity may be referred to a normalization of toner polarity.
(6) The residual toner re-charged to the normal polarity is recovered to the developing device
204
together with excessive toner supplied at the time of development under the action of a developing bias voltage.
By repeating the above-mentioned cycle, a system yielding no waste toner is realized. The above explanation is a summary and not an exhaustive description of such a cleanerless system.
Incidentally, JP-A 10-307455 discloses a toner recycle process using a non-single crystalline silicon photosensitive member. Further, JP-A 2000-98846 contains a disclosure regarding contact charging of a non-single crystal material having a surface layer comprising non-single crystalline carbon.
Further, Japanese Patent (JP-B) 2811312, etc., discloses a composition represented by a formula of Si
1−x
C
x
with a value x of 0.5<x<0.9, and JP-A 10-20663 discloses a composition represented by a formula of Si
1−x
C
x
with a value x of 0.95≦x<1.
On the other hand, JP-A 10-213946 discloses a cleanerless process wherein a voltage lower than a saturation potential of a photosensitive member is applied to a charging means to improve the toner discharge. JP-A 10-2774884 contains a disclosure to the effect that it is desirable to normalize the toner charge in a toner recycle process. Further, JP-A 9-325578 discloses an auxiliary charging mean for charging the residual toner to an opposite polarity before the ordinary charging step.
A non-single crystalline silicon photo-sensitive member has a superior potential stability not comparable to any other photosensitive members and has been frequently used in high-speed copying machines and high-speed printers. Particularly, a photosensitive member comprising a photoconductor layer comprising a silicon-based non-single crystal material and a surface layer comprising a carbon-based non-single crystal material successively formed on an electroconductive support has excellent properties of sticking prevention, long life and environmental stability because of the characteristics of the non-single crystalline carbon film, such as lubricity, high hardness and oxidation resistance.
The potential stability is also desired in small-size machines and popular machines, but these machines are disposed after printing on at most one million sheets. This is not matched with a durability on several million sheets of a non-single crystalline silicon photosensitive member, thus posing an obstacle to wide popularization of the non-single crystalline silicone photosensitive member.
Further, when used in the above-mentioned cleanerless system, some among a variety of non-single crystal material silicon photosensitive members is liable to convert the inverted to a polarity distribution not readily recovered by the fog-prevention voltage, more specifically, to an average polarity opposite to the normal charge polarity, thus posing a difficulty for realizing a cleanerless system capable of fully enjoying the advantages of a non-single crystalline silicon photosensitive member.
Particularly, compared with a surface layer comprising an organic material such as a resin, a surface layer comprising a carbon-based non-single crystal material is liable to make difficult the normalization of inverted toner, thus causing image defects, such as image fog and lower image density due to deterioration of the developer.
It is particularly important that the toner and the photosensitive member have an identical charge polarity so as to ensure an IAE (image area exposure) scheme wherein an image forming part or region on the photosensitive member is exposed to have a part of lower poten
Aoike Tatsuyuki
Ehara Toshiyuki
Hashizume Junichiro
Miura Masaharu
Canon Kabushiki Kaisha
Goodrow John
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