Electrophotography – Image formation – Development
Reexamination Certificate
2000-10-06
2002-03-05
Pendegrass, Joan (Department: 2852)
Electrophotography
Image formation
Development
C399S235000, C399S281000, C399S283000
Reexamination Certificate
active
06353720
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to an developing device which performs development of the static latent image formed on the static latent image bearer with a toner as the coloring agent, and in particular, relates to a developing device using a developer as the toner composed of a single component.
(2) Description of the Prior Art
An image forming apparatus using electrophotographic technology, such as a copier, printer, etc. has a developing device which, in order to visualize the static latent image formed on the photoreceptor surface as a latent image bearer, etc., supplies a developer, such as toner or other coloring agents, to the photoreceptor and allows the toner to selectively adhere to the latent image.
In this developing device, the static latent image formed on the photoreceptor is developed and then the developed toner image is transferred to a sheet of paper as the printing material. On passing the transfer step, part of the toner which could not transfer to the sheet remains on the photoreceptor surface. This unnecessary leftover toner is removed from the photoreceptor surface in order to perform a subsequent image forming operation. Therefore, a cleaning device for removal of the leftover toner from the photoreceptor surface is arranged downstream of the transfer station, and the unnecessary toner removed by this cleaning device is collected into the collecting portion in the cleaning device.
With a trend of image forming apparatuses having a developing device of the above type toward being compact, the space for arrangement of the processing devices for image formation around the photoreceptor needs to be reduced. So there has been also a strong demand for a compact developing device.
Instead of using a dual component developer made up of a toner and a magnetic carrier, developing devices which use a mono component developer have been proposed and come into practice. In such a developing device using a mono component toner, there is no longer any necessity to control the toner concentration, and the volume of the developer hopper can be markedly reduced because of the absence of carrier, making it possible to make the developing device compact. In addition, the mono component toner developing device is simple and excellent in maintenance. Specifically, there is no need to replace the developer because of degradation of the developer, especially degradation of the carrier, so that maintenance for its replacement is unnecessary.
Control as to the toner also can be simplified because only the toner needs to be re-supplied while neither toner concentration detection and hence nor its control will be needed. Particularly, in a developing device using a mono component toner, the only thing to be done is to re-supply the toner when it is needed.
For example, as shown in
FIG. 4
, opposed to a photoreceptor
1
as an image bearer is a developing device
4
for visualizing the static latent image formed on photoreceptor
1
. In this developing device
4
, a rotatable developing roller
41
is arranged so as to oppose the opening of a developer hopper
40
holding a toner
10
, the mono component developer. This developing roller
41
is exposed in part to the opening of developer hopper
40
and arranged in such a manner as to be in contact with photoreceptor
1
, for example. This contact area will be the developing area.
Developing roller
41
supports the mono component toner on the surface thereof and conveys it to the developing area opposing photoreceptor
1
. After development, the toner which has not been used for development is conveyed into developer hopper
40
and collected therein. The collected toner is once removed from the developing roller
41
surface. For this purpose, a supplying roller
42
is provided in pressing contact with developing roller
41
so as to scrape the toner supported on the developing roller
41
surface. This supplying roller
42
also functions to newly supply the toner to the developing roller
41
surface.
The mono component toner is supplied by supplying roller
42
and adheres to the developing roller
41
surface. In order to regulate the amount of adherence, a regulating means
43
is arranged in pressing contact with the developing roller
41
surface. The toner after having passed through regulating means
43
is regulated as to its amount and reaches the developing area where the toner opposes and is in contact with photoreceptor
1
as stated above. In this area, the toner selectively adheres to the static latent image formed on the photoreceptor
1
surface, thus development is carried out. The developing device having this configuration is disclosed in, for example, Japanese Patent Application Laid-Open Hei 3 No.33776.
In this disclosure, as the above regulating element
43
, a plate-like element, instead of a roller configuration shown in
FIG. 4
, is provided so as to abut developing roller
41
. In such a configuration, the life of a plate-like regulating element
43
is determined dependent on the degree of abrasion at the contact portion at which the element abuts developing roller
41
. This contact portion comes in sliding contact with developing roller
41
while developing roller
41
rotates, and it is abraded by this contact. When the contact portion has become unusable because of the progress of abrasion, it is understood as the end of life of the regulating element
43
. Since in a plate-like regulating element
43
, the element is in contact with, and abraded by, the peripheral surface of developing roller, continuously at the unchanged, contact portion, the element becomes badly worn out.
Use of a plate-like element as regulating element
43
makes it possible to provide a simple configuration and reduce the cost, however suffers from marked abrasion at the contact portion with developing roller
41
as stated above. This further leads to liability to cause toner sticking at the contact portion of regulating element
43
with developing roller
41
. When the toner sticks to an area, the amount of adherence on developing roller
41
at that area, differing from that in the other areas, becomes extremely low or becomes locally high, bringing about imbalance in the distribution of the toner layer thickness. This results in white stripes or black stripes attributed to the development.
Accordingly, the problem is the shortening of the life of regulating element
43
due to deficiencies of abrasion and toner sticking. This problem has been conventionally solved by providing a roller type regulating element
43
disclosed in Japanese Patent Application Laid-Open Hei 2 No.116872 and shown in FIG.
4
. That is, the regulating element is avoided from abutting developing roller
41
at a fixed contact so as to reduce toner sticking and realize a longer life.
The use of regulating element
43
having a roller configuration consequentially stabilizes the amount of toner adherence on developing roller
41
and beneficially prevents unevenness in the amount of charge on the toner, providing the effect of stabilizing the development. However, the problem of toner sticking still occurs even using such regulating element
43
of a roller configuration. For example, when the development with the developing roller has been completed, the toner deposited on the developing roller is pressed by the regulating roller that is pressed against the developing roller as the toner moves together with the developer roller. During this period this, i.e., during development, the developing roller has a bias voltage applied thereto which causes the toner to be attracted toward the developing roller surface. Thus, any combination of these may cause toner to stick on the developing roller.
In the developing roller configured as in
FIG. 4
, the same phenomenon as in the position of regulating element will occur at the position of supplying roller
42
. Actually, supplying roller
42
also is rotated with it also being abutted against developing roller
41
so as to supply the toner to
Inoue Atsushi
Masuda Jitsuo
Sakai Takashi
Yamanaka Takayuki
Pendegrass Joan
Sharp Kabushiki Kaisha
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