Electrophotography – Image formation – Transfer
Reexamination Certificate
2002-08-28
2004-12-21
Brase, Sandra L. (Department: 2852)
Electrophotography
Image formation
Transfer
C399S302000
Reexamination Certificate
active
06834177
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
The present invention relates to an electrophotographic image forming apparatus such as a copying machine, a printer, and the like.
An image forming apparatus which employs an intermediary transfer belt has long been known. An image forming method employing an intermediary transfer belt is effective for full-color image forming apparatuses or multicolor image forming apparatuses for synthetically obtaining full-color images or multicolor images through an image formation process, in which a plurality of temporary images different in color formed sequentially in accordance with full-color image formation data or multicolor image formation data are sequentially transferred in layers onto an intermediary transfer medium to synthesize full-color images or multicolor images, respectively.
FIG. 5
shows the general structure of a typical image forming apparatus employing an intermediary transfer belt in accordance with conventional arts. This image forming apparatus is a color image forming apparatus (copying machine, laser beam printer, or the like) having an intermediary transfer belt
120
. The material for this intermediary transfer belt
120
is an elastic substance, the electrical resistance of which is in the mid range.
This image forming apparatus comprises an electrophotographic photoconductive member
101
(which hereinafter will be referred to as photoconductive drum) in the form of a drum. This photoconductive drum
101
is rotationally driven in the direction indicated by an arrow mark at a predetermined peripheral velocity (process speed).
As the photoconductive drum
101
is rotationally driven, it is uniformly charged by a primary charging device
102
to predetermined polarity and potential level, and is exposed to a beam of light
103
projected by an exposing means while being modulated with image formation data. As a result, an electrostatic latent image corresponding to one of the color components (for example, yellow color component) of an intended color image is formed on the photoconductive drum
101
.
Next, the electrostatic latent image is developed into a visual image, that is, a yellow toner image, by first developing device
141
(yellow color component developing device), in the developing station. During this process of developing the electrostatic latent image corresponding to the yellow color component, second to fourth developing devices
2
-
4
, that is, a magenta color component developing device
142
, a cyan color component developing device
143
, and a black color component developing device
144
, are kept inactive; they do not act on the photoconductive drum
101
. Therefore, the yellow toner image is not affected by the second to fourth developing devices
142
-
144
. The first to fourth developing devices
141
-
144
are mounted in a supporting member
140
rotatable about its center axle, being enabled to be sequentially moved to the development station, in which they oppose the photoconductive drum
101
as they are moved into the development station.
The intermediary transfer belt
120
is stretched around rollers
161
and
162
, and a primary transfer roller
125
, being positioned so that it is placed in contact with the peripheral surface of the photoconductive drum
101
at a predetermined contact location. It is rotationally driven at the same peripheral velocity as that of the photoconductive drum
101
in such a direction that its peripheral surface moves in the same direction as that of the photoconductive drum
101
, at the contact location. At the contact location, a primary transfer roller
125
is disposed on the inward side of the loop of the intermediary transfer belt
120
, so that a primary transfer bias can be applied to the intermediary transfer belt
120
from a bias power source
129
through the primary transfer roller
125
. The primary transfer bias is opposite in polarity to the toner, and its potential level is within the range of +100 V-2 kV.
While the yellow toner image on the photoconductive drum
101
is passed through the contact area, or recording paper nipping portion (which hereinafter will be simply referred to as nip), between the photoconductive drum
101
and intermediary transfer belt
120
, it is continually transferred onto the outwardly facing surface of the intermediary transfer belt
120
, with reference to the belt loop, by the primary transfer electric field formed by the primary transfer bias applied to the intermediary transfer belt
120
through the primary transfer roller
125
.
After the transfer of the yellow toner image, that is, the toner image corresponding to the first color component, onto the intermediary transfer belt
120
, the primary transfer residual toner particles, that is, the toner particles remaining on the peripheral surface of the photoconductive drum
101
after the primary transfer of the yellow toner image, are removed by a cleaning apparatus
113
; the peripheral surface of the photoconductive drum
101
is cleaned by the cleaning apparatus
113
. Thereafter, the cleaned portion of the peripheral surface of the photoconductive drum
101
is again subjected to the above described image forming process which begins with the primary charging of the photoconductive drum
101
, to form a magenta toner image, or the toner image corresponding to the second color component, on the photoconductive drum
101
, and transfer the magenta toner image onto the intermediary transfer belt
120
in such a manner that the magenta image is placed in layers on the yellow toner image. This process is repeated two more times, to sequentially form a cyan toner image, or the toner image corresponding to the third color component, and a black toner image, or the toner image corresponding to the fourth color component, on the photoconductive drum
101
, and sequentially transfer them in layers onto the preceding two toner images on the intermediary transfer belt
120
. As a result, a synthetic full-color image reflecting the intended color image is effected on the intermediary transfer belt
120
.
The roller
164
, which supports the intermediary transfer belt
120
, doubles as a roller which opposes a secondary transfer roller
163
located outside the loop of the intermediary transfer belt
120
. The secondary transfer roller
163
is enabled to be moved so that it can be pressed against the roller
164
with the interposition of the intermediary transfer belt
120
, or can be moved away from the intermediary transfer belt
120
and roller
164
. To the secondary transfer roller
163
, a secondary transfer bias is applied from a bias power source
128
. Further, the secondary transfer roller
163
is enabled to be kept away from the intermediary transfer belt
120
during the primary transfer of the toner images corresponding to the first-fourth color components of the intended image.
Immediately before the four color toner images transferred in layers on the intermediary transfer belt
120
reach the secondary transfer station due to the rotation of the intermediary transfer belt
120
, the application of the secondary transfer bias to the secondary transfer roller
163
from the bias power source
128
is started, and at the same time, the secondary transfer roller
163
is placed in contact with the intermediary transfer belt
120
. Meanwhile a transfer medium P as recording medium (paper, resinous sheet, and the like) is sent into the recording medium path by a sheet feeding roller pair
111
with a predetermined timing, and is delivered, being guided by a guide
110
, to the contact area between the secondary transfer roller
163
and intermediary transfer belt
120
.
While the transfer medium P is passed through the contact area, or the recording paper nipping portion, between the transfer roller
163
and intermediary transfer belt
120
, the four color toner images, different in color, on the intermediary transfer belt
120
are continually transferred together onto the transfer medium P by the secondary transfer electric field formed b
Iida Kenichi
Saito Hisahiro
Yoda Yasuo
LandOfFree
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