Electrophotography – Internal machine environment – Particle or contaminant control
Reexamination Certificate
1998-04-02
2001-01-16
Royer, William J. (Department: 2852)
Electrophotography
Internal machine environment
Particle or contaminant control
C399S297000, C399S302000
Reexamination Certificate
active
06175702
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an image forming apparatus of a type which transfers a toner image formed on an image bearing member to a transfer material through an intermediate transferring member.
2. Related Background Art
In a color image forming apparatus of the electrophotographic type (for example, a copying apparatus or a laser beam printer), so-called primary transferring in which a toner image formed on a photosensitive drum as an image bearing member is once transferred onto an intermediate transferring member and is repeated a plurality of times to thereby superpose toner images of plural colors on the intermediate transferring member, and these toner images of plural colors are collectively secondary-transferred onto a transfer material such as paper.
FIG. 13
of the accompanying drawings shows an example of a color image forming apparatus using an intermediate transferring belt as the intermediate transferring member.
The image forming apparatus shown in
FIG. 13
is provided with a photosensitive drum
101
, and around the photosensitive drum
101
supported for rotation in the direction of arrow R
1
, there are disposed four developing devices
105
,
106
,
107
and
108
in which black (Bk) toner, cyan (C) toner, magenta (M) toner and yellow (Y) toner are contained respectively. One of these developing devices which is used for the development of an electrostatic latent image on the photosensitive drum
101
is designed to abut against the photosensitive drum
101
by means (not shown) for moving it toward and away from the photosensitive drum.
The photosensitive drum
101
is uniformly charged by a charger
102
, and an electrostatic latent image is formed thereon by a laser beam (scanning light)
104
from a laser exposure optical system
103
. Next, the electrostatic latent image is developed as toner images with the toners caused to adhere thereto by the developing devices
105
-
108
, and in a primary transfer nip portion N
1
, the toner images are primary-transferred onto an intermediate transferring belt
109
by a primary transferring roller
110
. The formation, development and primary transferring of the electrostatic latent image are successively effected in the order of Y, M, C and Bk with respect to the four colors by the developing devices
108
,
107
,
106
and
105
, whereby toner images of four colors superposed one upon another are formed on the intermediate transferring belt
109
. These toner images are then collectively secondary-transferred onto a transfer material
118
conveyed while being held by and between a secondary transferring roller
111
and the intermediate transferring belt
109
.
The primary transfer and the secondary transfer will further be described in detail. First, when the photosensitive drum
101
is, for example, an OPC (organic photo-semiconductive) photosensitive member having a negative charged characteristic, toners of negative polarity are used to develop the exposed portion to which the laser beam
104
has been applied by the developing devices
108
,
107
,
106
and
105
. Accordingly, a primary transfer bias of positive polarity is applied to the primary transferring roller
110
by a primary bias voltage source
120
.
Here, as the intermediate transferring belt
109
, use can be made, for example, an endless resin belt having a thickness of the order of 100 to 300 &mgr;m and resistance-adjusted to volume resistivity of the order of 10
11
to 10
16
&OHgr;.cm. In this case, as the material of the resin belt, use can be made of resin film (resistance-adjusted as required) such as PVdF (polyvinylidene fluoride), nylon, PET (polyethylene terephthalate) or polycarbonate. Also, as another example, there is a case where the above-described resin belt is adjusted to a volume resistance value of the order of 10
7
to 10
11
&OHgr;.cm by carbon, ZnO
2
, SnO
2
, TiO
2
or other electrically conductive filler and used. By achieving medium to low resistance like the latter, it is possible to prevent the formation of a bad image by charges being accumulated in the intermediate transferring belt
109
.
As still another example, a rubber material (such as chloroprene rubber, EPDM, NBR or urethane rubber) having lower hardness than resin and having a thickness of the order of 0.5 to 2 mm and adjusted to volume resistivity of the order of 10
6
to 10
11
&OHgr;.cm can be used as the material of the intermediate transferring belt
109
.
The intermediate transferring belt
109
is passed over a back roller
112
, a drive roller
115
, and a tension roller
116
. As the primary transferring roller
110
, use is usually made of a low resistance roller having volume resistivity of 10
5
&OHgr;.cm or less. In the foregoing, the primary transferring roller
110
and the primary bias voltage source
120
together constitute primary transferring means.
Next, the secondary transferring of the toner images to the transfer material
118
is effected by secondary transferring means constituted by the secondary transferring roller
111
, the back roller
112
, the secondary bias voltage source
121
. The secondary transfer is effected by disposing the back roller
112
of low resistance grounded or having a suitable bias applied thereto as an opposing electrode inside the intermediate transferring belt
109
, holding the intermediate transferring belt
109
between the back roller and the secondary transferring roller
111
of low resistance disposed outside the intermediate transferring belt to thereby constitute a secondary transferring region N
2
, applying a secondary transfer bias of positive polarity to the secondary transferring roller
111
by the secondary bias voltage source
121
, and causing the secondary transferring roller
111
to bear against the transfer material
118
from the back side thereof.
After the above-described primary transferring has been completed, the photosensitive drum
101
has any residual toner of primary transferring remaining on its surface removed by a cleaner
119
, and has any residual charges thereon removed by an exposure device
117
, and is used for the formation of the next toner images.
On the other hand, after the above-described secondary transferring has been completed, the intermediate transferring belt
109
has any residual toner of secondary transferring remaining thereon removed by a cleaner
113
, whereafter it has its charges removed by a charge removing charger (charge removing means)
114
. AC corona charging is often used as the charge removing charger
114
.
The charge removing charger
114
can be omitted when the intermediate transferring belt of low to medium resistance as previously described is used.
As the above-described intermediate transferring member, there is available an intermediate transferring drum besides the intermediate transferring belt
109
, but generally the intermediate transferring belt
109
is excellent in the height of the degree of freedom of the disposition of the intermediate transferring member and the good separability of the transfer material
118
after the secondary transferring (the possibility of the separation of curvature in the bent portion of the belt), as compared with the intermediate transferring drum. In contrast, the intermediate transferring drum can be simplified in structure, as compared with a case where the belt is driven. Even in the case of the intermediate transferring drum, the electrical characteristic of a resin or rubber layer provided on the surface of an electrically conductive cylindrical member can be considered as in the case of the intermediate transferring belt
109
and therefore, detailed description will be omitted.
In the above-described image forming apparatus, the order of formation of the toner images of four colors (Y, M, C and Bk) (the order of primary transfer) has heretofore been such that toner images are formed in suitable order by the toners of three colors, i.e., Y toner, M toner and C toner, and finally a toner image is formed by Bk toner.
Also,
Enomoto Naoki
Funatani Kazuhiro
Kobayashi Tatsuya
Miyashiro Toshiaki
Takeuchi Akihiko
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Royer William J.
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