Electrophotography – Image formation – Combined or plural functions by single component
Reexamination Certificate
2000-08-01
2002-05-14
Braun, Fred L (Department: 2852)
Electrophotography
Image formation
Combined or plural functions by single component
C399S357000
Reexamination Certificate
active
06389253
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention related to an image forming apparatus based on electrophotography or electrophotographic recording used, for example, for printers or copiers. In particular, it relates to an image forming apparatus that utilizes a so-called cleaning process simultaneously with developing.
2. Related Background Art
FIG. 6
shows an example of a conventional image forming apparatus. This image forming apparatus is configured by developing images with a one-component developer placed in contact with an image bearing member bearing electrostatic latent images. It does not have any separate cleaning mechanism and it uses the developing device to clean the residual toner on the image bearing member by the so-called cleaning process simultaneous with developing. This conventional image forming apparatus will be described below briefly with reference to FIG.
6
.
This image forming apparatus comprises a photosensitive drum
101
which is an image bearing member for holding electrostatic latent images, exposing means
102
for recording electrostatic latent images on the photosensitive drum
101
, a developing device
103
for developing the electrostatic latent images on the photosensitive drum
101
as well as for collecting any residual toner that was not transferred to the transferring material and cleaning its history, a transfer roller
104
which is transfer means for transferring the toner images developed on the photosensitive drum
101
to the transferring material, a heat roller
105
which is fixing means for fixing the toner images transferred to the transferring material, etc.
On this image forming apparatus, images are formed as follows. First, image information is recorded as an electrostatic latent image on the photosensitive drum
101
by the exposing means
102
. The electrostatic latent image on the photosensitive drum
101
is visualized as a toner image, being developed by the developer supplied by the developing device
103
placed in abutment with the photosensitive drum
101
, under the action of the developing electric field generated by a power supply not shown. The toner image is transferred to the transferring material under the action of the transfer electric field generated between the photosensitive drum
101
and transfer roller
104
and is fixed on the transferring material under the heat and pressure applied by the heat roller
105
. The remainder of the toner image (residual toner) that was not transferred to the transferring material and left on the photosensitive drum
101
is brought into abutment with the developing device
103
again and collected to the developing device
103
for reuse under the action of the developing electric field described above.
At the time of developing electrostatic latent images in the image formation process described above, elastic bodies such as rubber rollers and sponge rollers are used for the developer carrying member
111
provided in the developing device
103
because the developer is brought into contact with the photosensitive drum
101
.
FIG. 7
shows an enlarged view of the developing device
103
.
The developing device
103
mainly comprises a developing roller
111
which is a developer carrying member for carrying a one-component developer on its surface and which rotates in the direction of the arrow in the figure, a regulating blade
112
which is a developer regulating member for regulating the developer, a feed roller
113
which serves both as developer supply means for supplying the developer to the developing roller
111
rotating in the direction of the arrow in the figure and as developer recovery means for collecting the developer not used for developing, an agitating paddle
114
for agitating and carrying the developer, a spout-proofing sheet
115
for preventing the developer from scattering from the lower part of the developing roller
111
, and a developer container
116
for housing the developer.
Now, the operation of the developer
103
will be described.
The developer housed in the developer container
116
is carried to the area R near the developing roller
111
and feed roller
113
by the agitating paddle
114
. The developer carried there is homogenized by being made denser once in the area R with the rotation of the feed roller
113
. Then it si given a charge by the frictional electrification resulting from rubbing with the developing roller
111
and feed
113
counterrotating in abutment with each other.
The developer given a charge in this way is supplied to the developing roller
111
by the reflection force received from the developing roller
111
through the acquired charge. Thin layers of the developer are applied to the developing roller
111
under the regulation of the regulating blade
112
pressed against the developing roller
111
. In this way, the charge for developing is given by the frictional electrification with respect to the surfaces of the developing roller
111
and blade
112
.
Through these actions, thin layers of charged developer are applied to the developing roller
111
for use in developing. The developer applied to the developing roller
111
but not used for developing is scraped off the developing roller
111
by the feed roller
113
. Part of it is supplied again to the developing roller
111
by the feed roller
113
together with fresh toner and the rest is returned to the developer container
116
.
On the other hand, the photosensitive drum
101
is placed in abutment with the developing roller
111
and thus the developer applied to the developing roller
111
is used for developing while being in contact with the photosensitive drum
101
. A power supply not shown is connected between the photosensitive drum
101
and developing roller
111
so as to form a developing electric field. The developer applied to the developing roller
111
is transferred to the electrostatic latent image borne on the photosensitive drum
101
under the action of this electric field to develop the image.
At the same time, in the abutment area between the photosensitive drum
101
and developing roller
111
, the residual toner produced as a result of the image formation is collected. The residual toner in the abutment area is transferred to the developing roller
111
by the developing electric field acting strongly between the very closely located photosensitive drum
101
and developing roller
111
. There the residual toner is collected.
The image formation process proceeds through the sequence of actions described above.
However, the image forming apparatus described above, where electrostatic latent images are developed with the one-component developer carried on the developing roller
111
kept in contact with the photosensitive drum
101
, is liable to produce image fog because toner that is contained in the developer carried by the developing roller
111
and that is charged insufficiently (uncharged toner) or charged oppositely (reverse toner) to the desired polarity will cling to the background and part of it will be transferred to the transferring material.
On the other hand, it is possible to reduce image fog by making the layers of developer applied to the developing roller
111
very thin and allowing sufficient frictional electrification, the history of previous image formation or so-called ghost may appear if the cleaning process simultaneous with developing is used. This will be described in detail below.
According to studies conducted by the inventors, if the layers of the developer carried on the developing roller
111
are made very thin, sufficient frictional electrification can decrease uncharged toner or reverse toner and thus reduce image fog. However, it was found that since very thin layers of developer are applied to the developing roller
111
, the history generated by the residual toner collected during the cleaning process simultaneously with developing would appear as local variations in the amount of developer carried on the developing roller
111
, resulting in a gh
Nonomura Makoto
Ozeki Yukihiro
Sakaizawa Katsuhiro
Sekiguchi Manami
Braun Fred L
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
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