Electrophotography – Image formation – Development
Reexamination Certificate
2001-02-15
2002-09-24
Ngo, Hoang (Department: 2852)
Electrophotography
Image formation
Development
C399S272000, C399S260000, C399S254000, C399S256000
Reexamination Certificate
active
06456814
ABSTRACT:
CROSS-REFERENCE TO RELATED DOCUMENTS
The present document claims priority and contains subject matter related to Japanese Patent Application No. 2000-041135 filed in the Japanese Patent Office on February 18, 2000, and the entire contents of which is hereby incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image developing device for use in image forming apparatuses, such as electrophotographic copying machines, facsimile machines, printers, etc., and more particularly to an image developing device and an image forming apparatus using the developing device to prevent toner from adhering to a developing sleeve of the developing device.
2. Discussion of the Background
In an image forming apparatus using electrophotography, it is well known to use two-component developer including carrier and toner for development.
FIG. 5
schematically illustrates an image forming apparatus including a developing device using a two-component developer.
FIG. 6
is a diagram for explaining an operation of the developing device.
In
FIG. 5
, a drum-like shaped photoconductor
101
is rotated in a counterclockwise direction indicated by an arrow by a driving device (not shown). Around the photoconductor
101
are arranged, a charging roller
102
, an exposure device
103
, a developing device
104
, a transfer device
105
, a cleaning device
106
, and a discharging device
107
.
The charging roller
102
uniformly charges the surface of the photoconductor
101
. The exposure device
103
irradiates a laser light on the surface of the photoconductor
101
, which has been uniformly charged by the charging roller
102
, to form a latent image thereupon. The developing device
104
applies toner to the latent image on the surface of the photoconductor
101
to form a toner image. The transfer device
105
transfers the toner image to a transfer sheet. The cleaning device
106
removes residual toner remaining on the surface of the photoconductor
101
after transfer of the toner image to the transfer sheet. Thereafter, the discharging device
107
discharges the surface of the photoconductor
101
, which has been cleaned by the cleaning device
106
. The image forming apparatus then repeats each of the above-noted operations by the charging roller
102
, the exposure device
103
, the developing device
104
, the transfer device
105
, the cleaning device
106
, and the discharging device
107
(i.e., a charging process, an exposure process, a developing process, a transfer process, a cleaning process, and a discharging process).
The developing device
104
includes a developer container
108
having an opening formed facing the photoconductor
101
, a developing sleeve
109
arranged so as to face the photoconductor
101
in the developer container
108
, and a two-component developer
110
accommodated in the developer container
108
. The developing device
104
further includes a stirring member
111
configured to stir and to supply the developer
110
to the surface of the developing sleeve
109
, and a doctor blade
112
configured to regulate the thickness of the developer
110
carried on the surface of the developing sleeve
109
.
The developer
110
includes magnetic carrier and non-magnetic toner, which are mixed with each other. When the developer
110
is stirred by the stirring member
111
, the toner of the developer
110
is charged by friction between the toner and the carrier. A magnet (not shown) is arranged within the developing sleeve
109
. The developer
110
is held on the surface of the developing sleeve
109
by a magnetic force of the magnet. The developing sleeve
109
is rotated in a direction indicated by an arrow in
FIG. 5
, and the developer
110
held on the surface of the developing sleeve
109
is moved, after having its thickness regulated by the doctor blade
112
, to a space between the photoconductor
101
and the developing sleeve
109
. Toner adhered to the carrier held on the surface of the developing sleeve
109
is moved toward a latent image on the photoconductor
101
by an electric field formed between the developing sleeve
109
and the latent image on the photoconductor
101
, so as to adhere to the latent image.
Generally, in digital image forming apparatuses using electrophotography, such as laser beam printers or digital copying machines, the photoconductor
101
is charged to the same polarity as that of the toner. When the toner has a negative charge, the electric potential of the photoconductor
101
is set, for example, to −950V, and an electric field is formed as illustrated in
FIG. 6. A
voltage of the same polarity as that of the toner (e.g., −600V) is applied to the developing sleeve
109
. In this case, when the exposure device
103
irradiates a laser beam light to the surface of the photoconductor
101
which has been uniformly charged, the electric potential of non-image (background) parts of the surface of the photoconductor
101
is kept at −950V and the electric potential of image parts thereof is changed to about −100V. Therefore, the electric field between the developing sleeve
109
and the image parts of the photoconductor
101
is directed from the image parts of −100V to the developing sleeve
109
of −600V, and thereby the toner having a negative charge adheres to the image parts of the photoconductor
101
. On the other hand, the electric field between the developing sleeve
109
and the non-image parts of the photoconductor
101
is directed from the developing sleeve
109
of −600V to the non-image parts of −950V. Therefore, the toner having a negative charge does not adhere to the non-image parts of the photoconductor
101
.
The transfer device
105
transfers a toner image on the surface of the photoconductor
101
to a transfer sheet. The transfer sheet carrying the transferred toner image thereupon is conveyed to a fixing device (not shown). The fixing device fixes the toner image onto the transfer sheet by heating the toner image so as to be melted and by then applying a pressure to the toner image. The electric power consumed by the fixing device when heating and melting a toner image generally occupies a major part of the necessary power of an image forming apparatus.
Recently, from a view point of energy saving, it is desired to reduce power consumption in image forming apparatuses. For meeting such a demand for energy saving it is desired to reduce the temperature at a fixing device when heating and melting a toner image at the fixing device. For reducing the temperature at a fixing device when heating a toner image, the toner must be a type of toner capable of being fixed onto a transfer sheet at a relatively low temperature.
In image forming apparatuses, generally the electric potential difference between the developing sleeve
109
and the non-image parts of the photoconductor
101
is configured such that charged toner of the developer
110
carried on the developing sleeve
109
does not move to non-image (background) parts of the surface of the photoconductor
101
. Rather, the electric field having a direction toward the developing sleeve
109
causes the toner to adhere to the developing sleeve
109
. When the toner of the type that can be fixed onto a transfer sheet at a relatively high temperature, because of its relatively weak adhering force, even when the toner has once adhered to the developing sleeve
109
, the adhered toner is easily removed from the developing sleeve
109
when the adhered toner is rubbed by the developer
110
in the developer container
108
.
However, when toner of the type that can be fixed to a transfer sheet at a relatively low temperature is used in the developing device
104
, because of its relatively strong adhering force, the toner adhered to the developing sleeve
109
is gradually fixed to the developing sleeve
109
, and thereby an insulating layer is formed by the toner on the developing sleeve
109
. Such an insulating layer of toner on the dev
Ngo Hoang
Ricoh & Company, Ltd.
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