Electrophotography – Control of electrophotography process – Control of developing
Reexamination Certificate
2000-09-08
2001-08-14
Grimley, Arthur T. (Department: 2852)
Electrophotography
Control of electrophotography process
Control of developing
Reexamination Certificate
active
06275666
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to developing devices used in image formation apparatus, such as copiers, printers and the like, and particularly to those using a one-component developer.
2. Description of the Background Art
FIG. 16
shows a conventional electrophotography image formation apparatus with a developing device applied to a one-component development system using a one-component developer only of toner. As shown in
FIG. 16
, opposite to a photoreceptor
1
corresponding an image carrier, there is arranged a developing device
4
which visualizes an electrostatic latent image formed on photoreceptor
1
. In general, developing device
4
supports developing roller
41
rotatably opposite in particular to an opening of a development tank
40
housing insulative toner
10
. Developing roller
41
is partially exposed at the opening of development tank
40
and thus arranged for example in contact with photoreceptor
1
. This contact area serves as a developing area.
One-component toner
10
is fed to a feed roller
42
and adsorbed on a surface of developing roller
41
and to control the amount of toner adsorbed there is provided a control member
43
pressed into contact with the surface of developing roller
41
. Toner
10
passes under control member
43
and is thus controlled to have a predetermined amount and thus transported to the developing area borne on a surface of developing roller
41
opposite to photoreceptor
1
. In accordance with the electrostatic latent image on the photoreceptor
1
surface the toner is selectively adsorbed and thus developed.
Toner
10
which has not been used in the development is transported to development tank
40
and thus recovered. To remove recovered toner
10
from the developing roller
41
surface, feed roller
42
is arranged, pressed against developing roller
41
to scrape toner
10
off the developing roller
41
surface. Then, feed roller
42
receives new toner
10
and feeds it onto the developing roller
41
surface.
Furthermore, to develop the toner satisfactorily, developing roller
41
normally receives a developing bias voltage which is set to have a voltage value allowing toner
10
to adhere to an electrostatic latent image borne on photoreceptor
1
while preventing toner
10
from adhering to an background of the image borne on photoreceptor
1
.
Furthermore, to provide toner
10
adsorbed on developing roller
41
with a predetermined amount of electric charge of a predetermined polarity, the aforementioned control member
43
receives a control voltage to charge toner
10
to have the predetermined polarity. As such, toner
10
past control member
43
is provided by a fixed amount and after it is charged it is transported to the developing area.
Thus, the toner corresponding to a one-components developer can be adsorbed on the developing roller and thus transported to the developing area to allow the toner to adhere to an electrostatic latent image on the photoreceptor to form an image.
In the developing device employing triboelectricity as described above, however, the toner is rubbed against the control member only for a short period of time. As such, the toner is not charged to reach a sufficiently saturated range and each toner particle thus has a different level of electric charge. Furthermore, there are also provided toner uncharged because it has missed the chance to contact the control member, and toner inevitably charged to have a polarity opposite to a desired polarity when it is charged with triboelectricity (hereinafter referred to as “toner charged opposite in polarity”), which results in the developer having different levels of electric charge widely distributed. As such the toner cannot be developed reliably and in particular the toner charged opposite in polarity is developed at a portion other than an image. Thus the image is degraded in quality.
Furthermore, the level of electric charge has its average value significantly varying with the material(s) of the control member and that of the toner, the grain size of the toner, the environment in which the toner is used, and the like. To allow them to have their respective desired values, the material/materials added to the toner is/are adjusted extremely subtly.
Such disadvantages as above can be alleviated by using a corona charger to charge toner, as disclosed for example in Japanese Patent Laying-Open No. 10-148999.
FIG. 17
shows a developing device with a corona charger applied thereto. Toner
10
, accommodated in a toner tank
40
, is agitated by the rotation of an agitator
47
and transported to a developing roller
41
by the rotation of a feed roller
42
. The transported toner
10
is rubbed against and thus adhered to developing roller
41
rotating in the same direction as feed roller
42
and it is rubbed against a control member
43
and thus charged and also formed in a uniform layer. The toner layer formed is more reliably charged by a charger
45
and thus develops an electrostatic latent image formed on photoreceptor
1
rotating in the same direction as developing roller
41
. In this method the level of electric charge can have an average value relatively readily controlled and it can be also be provided in a narrow distribution.
The above developing device, however, also inevitably suffers toner charged opposite in polarity for the following reason: toner
10
is rubbed against control member
43
and feed roller
42
as well as each other. As such, when the toner is formed in a layer, it has a surface having a portion negatively charged and another portion positively charged. As such, when the charge level of one toner particle is noted, toner
10
is considered as being partially charged opposite in polarity.
When corona charger
45
charges the toner layer containing the toner charged opposite in polarity, toner
10
with each individual particle charged with a regular polarity as a whole but in effect partially charged with the opposite polarity, and the like, the electric charge generated by corona-discharging moves along a line of electric force, as shown in
FIG. 18
, and eventually adheres to toner
10
. If toner
10
has a portion charged with the opposite polarity along a side thereof allowing the electric charge to adhere thereto (upwards in the figure) then toner
10
has the electric charge of the opposite polarity canceled and is eventually charged with the regular polarity. If toner
10
has a portion charged with the opposite polarity along a side thereof not allowing the electric charge to adhere thereto (downwards in the figure), however, even with a corona charger providing electric charge of a single polarity the electric charge of the opposite polarity is not canceled.
In other words, toner
10
opposite to corona charger
45
can have a desired level of electric charge through corona-charging and toner
10
not present in a surface of a toner particle, i.e., in the toner layer cannot effectively receive electric charge. Furthermore, toner
10
in a particle surface internal to the toner layer also cannot receive the electric charge provided through corona-charging. As such, the electric charge present therein and having the opposite polarity cannot be canceled and as a result only the toner surface facing the charger can have an electric charge as desired.
To overcome this disadvantage its phenomena were studied in detail and as a result there has been found a charging condition capable of canceling the electric charge of the opposite polarity existing in toner.
SUMMARY OF THE INVENTION
An object of the present invention is to achieve stable development and improve image quality by providing a level of electric charge in a reduced distribution range and particularly reducing toner charged opposite in polarity, without using a developer having its components subtly adjusted.
The present invention in one aspect provides a developing device including a developer carrier having a surface carrying a one-component developer thereon, a dev
Furukawa Kazuhiko
Hirakawa Hiroyuki
Nishio Shigeru
Conlin David G.
Dike Bronstein Roberts & Cushman IP Group
Grimley Arthur T.
Ngo Hoang
Sharp Kabushiki Kaisha
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