Electrophotography – Image formation – Fixing
Reexamination Certificate
2001-09-04
2003-06-17
Grainger, Quana M. (Department: 2852)
Electrophotography
Image formation
Fixing
Reexamination Certificate
active
06580893
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
The present invention relates to a fixing device for an image forming apparatus for fixing an image formed on a recording material surface and an image forming apparatus using the fixing device. More specifically, the present invention relates to a fixing device for heat-fixing a yet unfixed image formed on a recording material by passing and conveying the recording material between a pair of a fixation roller and a pressure roller under pressure, and an image forming apparatus using the fixing device, particularly a color image forming apparatus comprising a heat fixing device and a plurality of image forming means.
Heat fixing devices have been widely used as means for fixing a yet unfixed image formed through an electrophotographic process, i.e., a yet unfixed toner image formed on a surface of a recording material such as paper.
Image forming apparatus using such fixing devices includes color image forming apparatus as shown in
FIGS. 3 and 4
wherein image formation is performed by using four color toners.
Referring to
FIG. 3
, the color image forming apparatus comprises a color laser beam printer M using four drums provided with four independent light scanning means for four colors, respectively. More specifically, the laser beam printer M includes four image forming means (image forming stations) Pa, Pb, Pc and Pd for four colors disposed in succession. Each image forming station includes a drum-shaped electrophotographic photosensitive member as a latent image-bearing member (hereinafter, referred to as “photosensitive drum”), and a developing device using a prescribed color toner and a transfer device integrally disposed around a peripheral surface of the photosensitive drum.
In each of the (four) image forming stations, an image formed on the photosensitive drum is transferred onto a recording material such as paper carried on a conveyance means. The conveyance means is disposed along the respective (four) image forming stations, so that the respective color toner images formed on the corresponding photosensitive drums are successively transferred on the recording material carried on the conveyance means to the fixing device where the respective color toner images (yet unfixed images) are heat-fixed at the same time.
FIG. 4
is an enlarged sectional view of the four image forming stations described above.
Referring to
FIG. 4
, the four image forming stations Pa, Pb, Pc and Pd are used for forming toner images of magenta, cyan, yellow and black, respectively.
Each image forming station Pa (Pb, Pc, Pd) includes a rotatable photosensitive drum
1
a
(
1
b
,
1
c
,
1
d
), and other members including a charger
12
a
(
12
b
,
12
c
,
12
d
), a developing device
2
a
(
2
b
,
2
c
,
2
d
) for supplying a corresponding color toner, and a cleaner
4
a
(
4
b
,
4
c
,
4
d
) successively disposed along the rotation direction of the photosensitive drum
1
a
(
1
b
,
1
c
,
1
c
). On a downstream side of the respective developing devices
2
a
-
2
d
, i.e., below the photosensitive drums
1
a
-
1
d
on
FIG. 4
, a transfer unit
3
is disposed. The transfer unit
3
includes a transfer belt
31
carrying thereon the recording material used common to the respective image forming stations Pa-Pd and four transfer chargers
3
a
,
3
b
,
3
c
and
3
d
disposed opposite to the photosensitive drums
1
a
,
1
b
and
1
d
, respectively.
In the above-mentioned color laser beam printer, paper P (as the recording material) supplied from a paper supply cassette
61
is conveyed to the respective image forming stations Pa-Pd while being supported on the transfer belt
31
. Thereafter, the respective color toner images formed on the respective photosensitive drums
1
a
-
1
d
are successively transferred onto the paper P carried on the transfer belt
31
. After the succession of transfer steps for the respective color toner images is completed, the paper P having thereon yet unfixed color toner images is separated from the transfer belt
31
to be conveyed to the fixing device (fixing unit)
5
by a conveyance belt
62
(shown in
FIG. 3
) as a recording material-guiding means.
FIG. 5
is a schematic sectional view of an embodiment of a conventional heat fixing device (as described, e.g., in Japanese Laid-Open Application (JP-A) No. 7-219378) as the fixing device (unit)
5
shown in FIG.
3
.
Referring to
FIG. 5
, the heat fixing device includes a pair of rotatably disposed rollers, i.e., a fixation roller
51
and a pressure roller
52
pressing the fixation roller
51
via the paper P (recording material) carrying thereon a yet unfixed image, and further includes a release agent application means
53
as a means for supplying and applying a release agent onto the surface of the fixation roller
51
and roller cleaning means
54
and
55
. Inside the fixation roller
51
and the pressure roller
52
, heaters
56
and
57
(e.g., halogen lamps) are disposed, respectively. Further, thermistors
58
and
59
are disposed in contact with the surfaces of the fixation roller
51
and the pressure roller
52
, respectively, whereby voltages supplied to the heaters
56
are controlled through a temperature control circuit to adjust surface temperatures of the fixing roller
51
and the pressure roller
52
to desired temperatures.
The roller cleaning means
54
provided to the fixation roller
51
has a cleaning function of removing, e.g., toner particles detached from the surface of the paper P and attached to the fixation roller surface at the time of fixation. On the downstream side of the cleaning means
54
with respect to the rotation direction (indicated by an arrow) of fixation roller
51
, the release agent application means
53
is provided to the fixation roller
51
. After the cleaning (removal of toner particles), a release agent such as a silicone oil is applied onto the surface of the fixation roller
51
by the release agent application means
53
. The release agent is used for facilitating the separation of the paper P (recording material) from the fixation roller
51
after the fixing step and preventing an occurrence of offset phenomenon of toner particles during the fixation.
The cleaning means
54
includes a cleaning web
54
a
comprising an elongated heat-resistant nonwoven fabric, a pressing roller
54
b
for pressing the cleaning web
54
a
against the fixation roller
51
, a feeding roller
54
c
for feeding a fresh cleaning web
54
a
, and a take-up roller for gradually winding up the cleaning web
54
a
lowered in cleaning performance due to the attachment of toner particles. Particularly, in order to prevent an occurrence of detection failure of the thermistor
58
caused by the attachment of toner particles detached from the paper surface to the thermistor used for monitoring the surface temperature of the fixation roller
51
, the cleaning means
54
is disposed on the upstream side of the fixation roller
51
with respect to the rotation direction thereof.
In the cleaning means
54
shown in
FIG. 5
, the cleaning web is wound up in such a manner that a prescribed amount of the cleaning web
54
a
is wound up in a direction opposite to the rotation direction of the fixation roller
51
by energizing a solenoid (not shown) to actuate a one-way clutch when a prescribed number of sheets of paper P is counted by a counting means (counter) provided to the image forming apparatus (laser beam printer). The take-up operation in the direction opposite to the fixation roller rotation direction prevents the cleaning web
54
a
from being wound up towards the fixation roller side by the rotation of the fixation roller
51
.
On the other hand, the release agent application means
53
includes an oil tank (container)
53
a
containing therein an release agent such as a silicone oil, conveyance rollers
53
b
and
53
c
for carrying and supplying the release agent from the oil tank
53
a
, an application roller
53
d
for applying the release agent supplied via the conveyance rollers
53
b
and
53
c
onto the surface of the fixation
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Grainger Quana M.
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