Electrophotography – Image formation – Transfer
Reexamination Certificate
2000-07-14
2002-05-07
Grimley, Arthur T. (Department: 2852)
Electrophotography
Image formation
Transfer
C399S306000, C399S309000
Reexamination Certificate
active
06385426
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus using an electrophotographic process such as, for example, a copying machine, a printer, a facsimile or other image forming apparatus.
2. Related Background Art
Conventionally there are various color image forming apparatuses having a plurality of image forming sections, each of which forms a toner image having a color different from colors of other sections and transferring the toner images on an identical recording material with being sequentially superimposed to obtain a color image. Among these image forming apparatuses, a color copying machine with a polychromatic electrophotographic process is frequently used.
An example of this type of color electrophotographic copying machine is briefly described below by referring to FIG.
14
. As shown in
FIG. 14
, the color electrophotographic copying machine includes a conveying belt
108
suspended between a pair of rollers
111
and caused to travel in a direction indicated by an arrow c by a driving source which is not shown and is provided with four image forming sections Pa, Pb, Pc, and Pd arranged above the conveying belt
108
. The image forming sections have the same configuration and therefore the configuration will be outlined below by giving an example of the image forming section Pa of a first color.
The image forming section Pa has a drum-shaped image bearing member, that is, a photosensitive drum
101
a
rotating in a direction indicated by an arrow A and arranged in the vicinity of the conveying belt
108
. After a photoconductive layer of a surface of the photosensitive drum
101
a
is uniformly charged by a primary charge
115
a
, a light image
116
a
of an yellow component of an original image is exposed to form an electrostatic latent image on the photosensitive drum
101
a
. The latent image shifts to a position of a developing device
103
a
by a rotation of the photosensitive drum
101
a
and developed by yellow toner supplied by the developing device
103
a
at the position, so that the latent image is visualized as a yellow toner image.
With a rotation of the photosensitive drum
101
a
, the yellow toner image reaches a transfer position where a blade-shaped transfer charger
104
a
having a conductive blade is disposed. At the same timing, a recording material, which is not shown, is supplied from the conveying path
112
onto the conveying belt
108
and then conveyed to a transfer position by the conveying belt
108
. In addition a transfer bias is applied to the transfer charger
104
a
, by which the yellow toner image on the photosensitive drum
110
a
is transferred to the recording material.
Subsequently, a cleaning blade
130
of a cleaning unit cleans residual toner on the photosensitive drum
101
a
, by which the photosensitive drum
101
a
is prepared to enter the next image forming process. On the other hand, the recording material to which the yellow toner image is transferred advances to the next second-color image forming section Pb by conveyance with the conveying belt
108
.
The second color image forming section Pb has the same configuration as the first color image forming section Pa, and therefore in the same manner as the above a latent image is formed on a photosensitive drum
101
b
, the latent image is developed by magenta toner, the obtained magenta toner image is transferred and superimposed on the yellow toner image on the recording material in its transfer portion. In the same manner, a cyan toner image and a black toner image are formed on the photosensitive drums
101
c
and
101
d
in the image forming sections Pc and Pd, respectively, and they are sequentially transferred and superimposed on the recording material by transfer chargers
104
c
and
104
d
, thereby achieving a color image having 4-color toner images superimposed on the recording material.
The recording material to which the 4-color toner images have been transferred is submitted to charge elimination and then separated from the conveying belt
8
by a separation charge-eliminator
161
, conveyed to a fixing device
107
having a pair of a fixing roller
107
a
and a pressure roller
107
b
, and pressed and heated in a nip portion of the rollers
107
a
and
107
b
normally heated at a predetermined temperature for fixing. This mixes the colors of the toner images and fixes them to the recording material, by which a full-color permanent image is obtained and then the recording material is ejected to the outside of the copying machine.
After the recording material is separated from the conveying belt
106
, an inside charge-eliminator
113
and an outside charge-eliminator
114
eliminate charges on the conveying belt received at the transfer and further a cleaning blade
120
and a backup roller
121
arranged in the downstream in a traveling direction remove rubbish or the like such as fog toner, scattered toner, or paper dust adhered to the surface of the conveying belt so as to clean the surface in preparation for the next image formation.
Additionally, in the image forming apparatus for forming a color image in the multi-transfer process, there has been used a single-layer resin belt made of polyethylene terephthalate resin, polycarbonate resin, or the like having a high resistance, specifically a volume resistivity of 10
15
&OHgr;·cm or greater for a purpose of attracting the recording material tightly for the transfer belt. For a transfer charging member, a transfer blade is recently used which enables a transfer electric field to be narrow in the transfer area in order to reduce a poor image such as a scatter at the transfer.
The transfer belt
108
used here is required to have various performances in order to convey the recording material stably and to achieve the multi-transfer of the 4-color toner image without any poor image.
It is a first reason for wide use of the transfer belt in the polychromatic image forming apparatus as described in this embodiment that the recording material is stably conveyed. In other words, in an image forming apparatus in which a recording material passes a plurality of image forming sections during the multi-transfer of respective colors, the image forming sections form images of their own colors in accordance with a timing when the recording material is conveyed and the images are sequentially transferred to the conveyed recording material. Unless the recording material is electrostatically attracted to the transfer belt nor fixed by any means during conveyance, the recording material is not stably conveyed between the plurality of image forming sections, leading to misregistered images of the respective colors at the transfer or to any recording material jammed in the worst case. In this embodiment, the recording material supplied from the registration roller is integrated with the transfer belt to pass the transfer nip in the first image forming section, by which the toner image in the first image forming section is transferred, and electric charges are supplied to the both sides of the recording material and those of the transfer belt, by which the recording material and the transfer belt are electrostatically attracted to each other. At this point, electric resistance conditions of the transfer belt relate to the electrostatic attraction. In general, the electrostatic attracting force is generated by an electric field given to substances having different permittivities. If a transfer belt having a low electric resistance is used, however, electric charges given to the transfer belt surface are easily eliminated, by which the attracting force may be reduced.
Therefore, to obtain a conveyance effect of a stable electrostatic attracting force, it is preferable to use a transfer belt having a volume resistivity of about 10
10
&OHgr;·cm or higher and there is an example of a use of an insulating substance. The use of the insulating substance or a material having a high resistivity for the transfer belt in this manner, however, easily causes a separation e
Inoue Masahiro
Kimura Yoichi
Omata Haruhiko
Suzuki Shinya
Grimley Arthur T.
Tran Hoan
LandOfFree
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