Electrophotography – Control of electrophotography process – Control of charging
Reexamination Certificate
2000-12-21
2002-08-20
Grimley, Arthur T. (Department: 2852)
Electrophotography
Control of electrophotography process
Control of charging
C399S149000
Reexamination Certificate
active
06438331
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus of a copier, a printer or the like, using an electrophotographic method or an electrostatic recording method.
2. Related Background Art
In recent years, attention has been attracted to an image forming apparatus of a cleaning simultaneous with developing type, free from waste toner.
FIG. 6
shows a schematic configuration of one example of image forming apparatus of the cleaning simultaneous with developing type in the contact development using nonmagnetic unicomponent toner.
As shown in
FIG. 6
, this type of image forming apparatus conventionally comprises a photosensitive drum (image bearing body)
101
rotating along an arrow X as well as a charging roller (primary charger)
102
, an exposing tool
103
, a developing device
104
and a transferring roller (transferring charger)
105
disposed around the photosensitive drum
101
. Besides, downstream of the transferring roller
105
along the conveying direction (along the arrow Kp) of the transferring material P, a fixing device
107
is disposed.
The developing device
104
comprises a developing roller
108
provided in contact with the photosensitive drum
101
for performing the development while rotating along the arrow Y, a supply roller (developer supply means)
109
for supplying a nonmagnetic toner T to the developing roller
108
by the rotation along the arrow Z, a regulating blade (developer regulation means)
110
for regulating the applied amount and the charged amount of the toner T on the developing roller
108
and a agitating member
111
for supplying a toner T to the supply roller
109
and simultaneously agitating the nonmagnetic unicomponent toner. The toner T is a negative polarity toner and a process of sticking this toner T to the exposed portion or a so-called reversal development is performed.
The image forming operation of the above-constructed image forming apparatus will be described below.
In response to an external print signal (image forming signal), the photosensitive drum
101
begins to rotate along the arrow X. First, the surface of the photosensitive drum
101
is charged uniformly by the charging roller
102
. The charging roller
102
has the shape of a roller and is rotated by driving means (unillustrated) along the arrow W. Next, an exposure L by means of the exposing tool
103
causes an electrostatic latent image on the photosensitive drum
101
and the electrostatic latent image arrives at the contact part of the developing device
104
by the rotation of the photosensitive drum
101
.
In linkage with the above operation, the developing device
104
performs the following operation.
By the sliding friction of the supply roller
109
rotating along an arrow Z and the developing roller
108
rotating along the arrow Y, the toner T agitated by means of the agitating member
111
is supplied onto the developing roller
108
. The toner on the developing roller
108
, which is given a desired charging amount while the quantity (layer thickness) of the toner is regulated, is carried on the developing roller
108
. Besides, the toner in the developing device
104
is agitated by means of the agitating member
111
and carried to the supply roller
109
.
When the toner T carried on the developing roller
108
reaches the location in contact with the photosensitive drum
101
, a DC development bias is applied to the developing roller
108
by a power supply (unillustrated). Thereby, the toner T carried on the surface of the developing roller
108
is stuck thereto, so that the electrostatic latent image formed on the surface of the developing drum
101
is developed (visualized) as a toner image. At this time, the toner remaining on the surface of the developing roller
108
without contribution to the development is collected into the developing device
104
via the supply roller
109
.
In a contact developing unit using a rigid photosensitive drum
101
to perform the cleaning simultaneously with the development under contact with the developing roller
108
, the developing roller
108
is desirably a roller made by forming an elastic body into the shape of a roller. Used as this elastic body are those subjected to the resin coating on a solid rubber monolayer or a solid rubber in view of the toner charging property.
Besides, to execute a contact development, a method of using a rigid developing roller to a belt-shaped photosensitive belt is also available in addition to a method of abutting an elastic developing roller
108
against a rigid photosensitive drum
108
.
The toner on a photosensitive roller
101
reaches the opposed part of a transferring roller
105
by the rotation of the photosensitive drum
101
and is transferred to a transferring material P by the transferring roller
105
. The transferring material P after the transfer of a toner image is conveyed in a direction of the arrow Kp and discharged outside the image forming apparatus after the thermal melting and fixation of the surface toner image by means of the fixing device
107
.
On the other hand, the toner remaining (transfer residual toner) on the photosensitive drum
101
without being transferred onto the transferring material P at the time of transfer, passes through the charging roller
102
and reaches the abutting part against the developing roller
108
. At this time, the residual toner is collected onto the developing roller
108
under action of a DC developing bias applied to the developing roller
108
and this collected toner is to be supplied to the development at the next image forming.
By repeating the above operation, the image forming of the cleaning simultaneous with developing type is repeated.
In the image forming apparatus of the cleaning simultaneous with developing type shown in the above conventional example, however, there was a problem that a toner had been stuck to the charging roller
102
by long-term use, thus resulting in poor charging. The cause of this is considered as follows.
The image forming apparatus of the cleaning simultaneous with developing type collects the transfer residual toner remaining on the photosensitive drum
101
without being transferred to the transferring material P by means of the developing device
104
.
Accordingly, the transfer residual toner has to pass through the charging roller
102
. The transfer residual toner at the moment of having passed through the transferring roller
105
, however, is a toner comprising the mixing of positive and negative polarities or a broad distribution of rather positive polarity under the influence of a positive polarity transferring bias. Thus, it cannot pass through the charging roller
102
and ends in being stuck thereto for the following reason.
FIGS. 7A and 7B
are illustrations of the behavior of the toner near the charging roller
102
. As shown in
FIGS. 7A and 7B
, the transfer residual toner at the moment of having passed through the transferring roller
105
arrives near the charging roller
102
with the mixing of positive and negative polarities or a broad distribution of rather positive polarity, under influence of a positive polarity transferring bias. Here, applied to the charging roller
102
from a charging bias power supply
112
is a negative polarity DC charging bias. And, near the nip part between the charging roller
102
and the photosensitive drum
101
, a discharge area is formed by this DC charging bias (B area in FIG.
7
A).
Because of mostly comprising a positive polarity toner charged oppositely to the normal polarity, or a so-called reverse toner, the toner having arrived near the charging roller
102
(A area of
FIG. 7A
) ends in being attracted to the charging roller
102
by the electric field acting between the charging roller
102
and the photosensitive drum
101
.
The transfer residual toner stuck to the charging roller
102
enters the B area of a discharge area with the rotation of the charging roller
102
. There, as shown in
FIG. 7B
of an enlarged view of the B ar
Sakaizawa Katsuhiro
Sekiguchi Manami
Canon Kabushiki Kaisha
Grimley Arthur T.
Ngo Hoang
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