Electrophotography – Supplemental electrophotographic process – Exposure or charging
Reexamination Certificate
1999-12-27
2001-05-15
Braun, Fred L (Department: 2852)
Electrophotography
Supplemental electrophotographic process
Exposure or charging
C399S153000, C399S175000
Reexamination Certificate
active
06233416
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrophotographic image-forming apparatus and an electrophotographic image-forming method utilizing an electrophotographic photosensitive member of high gamma, in particular, an electrophotographic photosensitive member for digital photo-input. More precisely, the present invention relates to an electrophotographic image-forming apparatus and an electrophotographic image-forming method utilizing a novel charge erasing method.
2. Background Art
As shown in
FIG. 5
, conventional electrophotographic image-forming apparatuses have, for example, a structure comprising, around a rotatably maintained cylindrical photosensitive member
1
, a main electrifier
2
, light exposure means
3
, image development means
4
, image transfer means
5
, cleaning means
6
, and charge erasing (eliminating) light source
7
in this order, and charge erasing of the photosensitive member is attained by light-exposing the surface of the photosensitive member
1
by means of the charge erasing light source
7
.
On the other hand, photosensitive members of high gamma have been developed in recent years in order to form static latent images with high resolution in electrophotographic image formation, in particular, by digital photo-input. For example, Japanese Patent Publication (Kokoku) No. 5-19140 discloses an electrophotographic photosensitive member for digital photo-input having a gamma for latent image of 6 or more, which comprises a photosensitive layer consisting of intrinsic semiconductor fine powder contained in a binder having a high volume resistivity. Japanese Patent Unexamined Publication (Kokai) No. 8-286396 also discloses a photosensitive member having a gamma value of 2 to less than 6.
However, because such photosensitive layers of high gamma utilize a highly resistive binder, charge transfer therein is strongly prevented, and after electrification, a part of charge flowing in the photosensitive members by the light exposure remains throughout the whole photosensitive layer. Therefore, it is difficult to completely erase the charge after the image formation only by the light exposure as in the conventional electrophotographic image-forming apparatuses. As a result, the high-gamma photosensitive members suffer a problem of so-called hysteresis, i.e., electrification potential may be different among light-exposed areas and unexposed areas in a former image formation process, and thus images of high resolution cannot be stably formed.
Moreover, there is also the problem of sensitivity shift, i.e., shift of the sensitivity curve of the photosensitive member in the higher sensitivity direction due to the residual charge in the photosensitive member caused by repetition of image formation.
A larger light exposure amount for charge erasing may excite a deeper portion of the photosensitive member by its photocurrent, thereby providing uniform charge distribution. However, the light energy may accelerate yield of the binder of the photosensitive member, and hence dark decay may become faster. This may make sequential image-forming operations impossible.
Furthermore, reversal development is usually used in printers, in which a transfer electrifier is applied with a voltage of opposite polarity to that applied to the main electrifier, and may invite another problem. That is, such voltage of reverse polarity provides a field of opposite polarity to that of the main electrification inside the photosensitive member, and this may cause sensitivity variation due to higher internal field during the main electrification. Thus, images cannot be stably formed.
Therefore, various techniques have been proposed in order to solve such problems as mentioned above. For example, Japanese Patent Unexamined Publication (Kokai) No. 4-337762 proposes a method comprising controlling light exposure amounts for image formation and charge erasing to be in a particular relationship in order to solve the aforementioned problem of hysteresis. This method may achieve the desired effect for a photosensitive member of a gamma for latent image of less than 3. However, when the gamma for latent image is 3 or higher, completely stable operation cannot be performed even with this technique, because of sensitivity variation due to ununiform electrification after repeated image formation and the like.
Therefore, the object of the present invention is to provide an image-forming apparatus and an image-forming method that can solve the aforementioned problems, specifically an apparatus and a method enabling effective uniform charge erasing (eliminating), hence not causing the so-called hysteresis or sensitivity shift even in continuous image formation, and capable of stably forming images of high quality and high resolution without residual images in electrophotographic image formation utilizing a high-gamma photosensitive member.
SUMMARY OF THE INVENTION
The image-forming apparatus of the present invention comprises a photosensitive member having a gamma for latent image of 3 or more, electrification means, light exposure means, image development means, image transfer means, cleaning means, and a charge erasing (eliminating) light source, wherein the image-forming apparatus further comprises electric field applying means for applying an alternating current electric field at a frequency of 50 Hz to 1 kHz to a portion of the photosensitive member which is excited through light exposure by the charge erasing light source.
One embodiment of the image-forming apparatus of the present invention is an image-forming apparatus comprising, around a rotatably maintained cylindrical photosensitive member
1
having a gamma for latent image of 3 or more, a main electrifier
2
, a light exposure means
3
, an image development means
4
, an image transfer means
5
, and a cleaning means
6
in this order, wherein the image-forming apparatus comprises a charge erasing light source
7
for light exposure of photosensitive member surface and the electric field applying means
9
for applying an alternating current electric field at a frequency of 50 Hz to 1 kHz to a portion of the photosensitive member which is excited through light exposure by the charge erasing light source between the cleaning means
6
and the main electrifier
2
(FIG.
1
).
In the aforementioned image-forming apparatus of the present invention, an alternating current electrifier, which is the electric field applying means
9
, may be provided between the charge erasing light source
7
and the photosensitive member surface which is light-exposed by the charge erasing light source, and applies an alternating current electric field at a frequency of 50 Hz to 1 kHz to a portion of the photosensitive member excited through light exposure by the charge erasing light source (FIG.
1
).
Alternatively, in the aforementioned image-forming apparatus of the present invention, an alternating current electrifier, which is the electric field applying means
9
, may be provided immediately after the charge erasing light source
7
with respect to the photosensitive member surface, and applies an alternating current electric field at a frequency of 50 Hz to 1 kHz to a portion of the photosensitive member which is excited through light exposure by the charge erasing light source (FIG.
2
).
In the aforementioned image-forming apparatus of the present invention, the electric field applying means may be a contact electrifier
9
a
generating an alternating current electric field at a frequency of 50 Hz to 1 kHz, which is provided immediately after the charge erasing light source
7
a
with respect to the photosensitive member surface so that a portion of the photosensitive member which is excited through light exposure by the charge erasing light source
7
a
is contacted by the contact electrifier
9
a,
and applied with an alternating current electric field at a frequency of 50 Hz to 1 kHz (FIG.
3
).
In a preferred embodiment of the image-forming apparatus of the present invention, the charge erasing
Abe Masanori
Kinosita Koichi
Konuma Takaaki
Sato Masahiro
Braun Fred L
Kimoto & Co., Ltd.
Lorusso & Loud
LandOfFree
Electrophotography with AC erasing of latent image does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electrophotography with AC erasing of latent image, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electrophotography with AC erasing of latent image will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2461771