Electrophotography – Control of electrophotography process – Control of charging
Reexamination Certificate
2001-02-21
2002-12-17
Braun, Fred L. (Department: 2852)
Electrophotography
Control of electrophotography process
Control of charging
C399S176000
Reexamination Certificate
active
06496663
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates an image forming apparatus such as an electrophotographic apparatus, an electrographic recording apparatus or the like having an electrification device for charging an image bearing member such as a photosensitive member or a dielectric member.
2. Related Background Art
An image forming apparatus such as an electrophotographic apparatus conventionally requires an electrification step of uniformly electrifying an image bearing member for forming an electrostatic latent image on the image bearing member and used as electrifying means is a corona electrification device or the like which is not brought into contact with the image bearing member. However, the corona electrification device poses problems in that it produces a large amount of ozone, and that is requires applying a high voltage on the order of 10 kV between the electrification device and the image bearing member.
As an electrification device which solves these problems, there has recently been proposed and put to practical use the so-called contact electrification device which electrifies an image bearing member uniformly by applying a voltage to an electrifying member which is in direct contact with the image bearing member.
A) Roller Charging Device
A representative of the above described contact electrification device is a roller electrification device
2
-X shown in FIG.
9
.
An electrification member
2
-X-
a
of the roller electrification device is a roller (electrification roller) having a layer of medium resistance disposed on an electrically conductive base roller which is kept in contact with an image bearing member
1
under a predetermined pressure, rotatably held by a bearing and rotated in a direction indicated by an arrow b while following a rotation of the image bearing member
1
which is rotatingly driven in a direction indicated by an arrow a. A predetermined bias voltage is applied from a power supply S
1
between the above described roller
2
-X-
a
and the image bearing member
1
, whereby the above described image bearing member
1
is uniformly electrified at a uniform potential.
Applied as the above described voltage is (1) only a DC voltage or (2) a DC voltage overlapped with an AC voltage. In case of (1), a voltage on the order of −1300 V must be applied to obtain a potential of −600V on the image bearing member
1
or in case of (2), a potential on the image bearing member
1
can be set similarly at −600 V by applying a DC voltage of −600 V overlapped with an AC voltage not lower than 1500 Vpp.
In either case of (1) or (2), an electrification mechanism is governed by Paschen's law and the image bearing member
1
is electrified owing to a discharge phenomenon which takes place in an area such as an area H shown in
FIG. 9
where Paschen's law is satisfied at a specific distance between the above described electrification roller
2
-X-
a
and the image bearing member
1
.
As understood from the electrification mechanism described above, however, such a contact electrification device causes discharge which is the same as that caused by the initially described corona electrification device in the minute spatial area H and also produces ozone though in an amount remarkably smaller than that produced by the corona electrification device. This ozone produces nitric oxide which has low resistance and a defective image is formed due to improper electrification when the nitric acid adheres to the image bearing member
1
.
B) Injection Electrification Device
Japanese Patent Application Laid-Open No. 6-3921 or the like proposes an injection electrification process which is free from a problem of ozone production and therefore permits lowering a voltage to be applied to an electrification device.
This electrification process is characterized by being capable of setting a surface potential of an image bearing member nearly at a voltage applied to an electrification device without using a discharge phenomenon but by injecting electric charges to the image bearing member through direct electric charge transfer from the electrification device to a surface of the image bearing member which is brought into contact with the electrification device.
(1) Magnetic Brush Electrification Device
Several types of injection electrification devices are proposed as electrification device for realizing the above described injection electrification process.
As a representative one of the injection electrification devices, a magnetic brush type electrification device
2
-Y is shown in FIG.
10
. This electrification device is configured by a magnet
2
-Y-
a
, a nonmagnetic electrification sleeve
2
-Y-
b
which comprises the magnet
2
-Y-
a
, a magnet carrier (magnetic carrier, magnetic powder)
2
-Y-
c
, electrically conductive regulating blade
2
-Y-
d
, a housing
2
-Y-
e
and the like. The magnet carrier
2
-Y-
c
is a substance which is magnetic and electrically conductive.
The electrification sleeve
2
-Y-
b
is rotatably disposed in the housing
2
-Y-
e
and a portion of a circumferential surface of the electrification sleeve
2
-Y-
b
is exposed outside through an opening of the housing. The electrification device
2
-Y is disposed in a condition where the portion of the electrification sleeve
2
-Y-
b
exposed outside is opposed to the image bearing member
1
with a predetermined slight gap reserved. The magnet
2
-Y-
a
is fixed so as not to rotate. The magnet carrier
2
-Y-
c
is reserved in the housing
2
-Y-
e
. The regulating blade
2
-Y-
d
is disposed in the opening of the housing
2
-Y-
e
so as to reserve a predetermined gap from the electrification sleeve
2
-Y-
b.
The magnet carrier
2
-Y-
c
in the housing
2
-Y-
e
is magnetically adsorbed and held as a magnetic brush to the circumferential surface of the electrification sleeve
2
-Y-
b
by a magnetic field of the magnet
2
-Y-
a
, conveyed as the electrification sleeve
2
-Y-
b
rotates, regulated to a predetermined layer thickness by the regulating blade
2
-Y-
d
, conveyed outside through the opening of the housing
2
-Y-
e
, brought into contact with a surface of the image bearing member
1
, frictionally slides on the surface of the image bearing member, and is returned and conveyed into the housing
2
-Y-
e
as the electrification sleeve
2
-Y-
b
rotates successively.
The image bearing member
1
is rotatingly driven in a direction indicated by an arrow a and the electrification sleeve
2
-Y-
b
is rotatingly driven in a direction indicated by an arrow s reverse to a rotating direction of the image bearing member
1
in a contact portion (electrification portion) between the image bearing member
1
and the magnetic brush of the magnet carrier
2
-y-
c
. In other words, the magnetic brush of the magnet carrier
2
-Y-
c
rotates at a peripheral speed different from that of the image bearing member
1
as the electrification sleeve
2
-Y-
b
rotates, thereby frictionally slides on the surface of the image bearing member
1
.
In the magnetic brush electrification device
2
-Y taken as this example, a DC voltage, for example, of −600 V is applied as an electrification bias voltage from a power supply S
1
to the regulating blade
2
-Y-
d
. Accordingly, a portion of the image bearing member
1
which is in contact with the magnetic brush of the magnet carrier
2
-Y-
c
tends to be at the same potential. The image bearing member
1
is electrified at this time when electric charges are injected from the magnet carrier
2
-Y-
c
to the image bearing member
1
beyond an energy barrier or electrification does not take place when electric charges move again from the image bearing member
1
to the magnet carrier
2
-Y-
c
at a step the magnet carrier
2
-Y-
c
separates from the image bearing member
1
. This phenomenon is largely dependent on a surface energy barrier and electric charge holding capability of the image bearing member
1
, whereas a frequency of occasions of contact between the magnet carrier
2
-Y-
c
and the i
Kato Jun-ichi
Ohba Hiroyuki
Sato Hiroshi
Shimizu Yasushi
Yoshida Masahiro
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
LandOfFree
Image forming apparatus including image bearing member and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Image forming apparatus including image bearing member and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Image forming apparatus including image bearing member and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2917781