Electrophotography – Control of electrophotography process – Control of fixing
Reexamination Certificate
1999-07-28
2001-01-30
Chen, Sophia S. (Department: 2852)
Electrophotography
Control of electrophotography process
Control of fixing
C399S043000, C399S071000
Reexamination Certificate
active
06181890
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus, such as a copying machine, a printer, which forms images utilizing the electrophotographic method. More particularly, the invention relates to an image forming apparatus provided with a fixing device that thermally fixes the unfixed toner images transferred to a recording material.
2. Related Background Art
To form images, the image forming apparatus that utilizes the electrophotographic method is arranged to charge the surface of the electrophotographic photosensitive body uniformly by use of the charging device, and to expose the charged surface of the electrophotographic photosensitive body by use of the exposing device, thus forming the electrostatic latent images. Then, the electrostatic latent images are developed by use of the developing device to form toner images. The toner images are transferred to a recording material, such as a recording sheet, by use of the transferring device. The toner images are then fixed on the recording material by use of the fixing device as permanently fixed images for output.
As shown in
FIG. 8
, the aforesaid fixing device is, for example, arranged to be able to pinch and convey by use of the guiding member
18
a recording material P which is provided with the unfixed toner transferred to it on the fixing nip unit N between the fixing roller
100
and the pressure roller
110
, and then, to heat and press the toner T by the heater
13
that serves as the heating body arranged in the fixing roller
100
in order to fix the unfixed toner (unfixed toner images) T on the recording material P as the permanently fixed images.
The fixing roller
100
is structured with the releasing layer
10
b
formed by PFA, PTFE, or some other fluororesin on the core metal
10
a
formed by aluminum, iron, or the like. In the releasing layer
10
b
, the heater
13
is arranged as heating means to heat the fixing roller
100
from its inside.
The releasing layer
10
b
is provided for the prevention of the “offset phenomenon” which tends to stain the images to follow after the transfer of the unfixed toner images to the fixing roller
100
. Here, further, by the utilization of the electrostatic charge given characteristically to the toner (that is, the negative polarity in the specification hereof), the electric potential of the negative polarity is generated on the surface of the fixing roller
100
when the bias of the negative polarity is applied to the core metal
10
a
from the fixing bias supply source
12
. Thus, by the utilization of the force of repulsion of the negatively charged toner, the toner is allowed to adhere to the surface of the fixing roller
100
so as to prevent the occurrence of the offset phenomenon that may result in defects on the images to follow.
On the fixing roller
100
, there are arranged the separating claws
14
, and the thermistor
15
which serves as temperature detecting sensor.
The separating claws
14
are in contact with the surface of the fixing roller
100
to prevent the recording material P from being wound around the fixing roller
100
when it passes the fixing nip unit N. It is generally practiced to use the separating claws
14
which are coated with PFA, PTFE, or some other fluororesin having an excellent releasability for the prevention of the adhesion or accumulation of toner to or on the surface of the separating claws
14
.
The thermistor
15
is in contact with the surface of the fixing roller
100
under a specific pressure to detect the surface temperature of the fixing roller
100
. On the basis of the information of the surface temperature of the fixing roller
100
thus detected by the thermistor
15
, the current to the heater
13
is turned on and off by use of a controller (not shown) so that the surface temperature of the fixing roller
100
is kept at a constant level.
The pressure roller
110
is pressed to the fixing roller
100
by use of pressure means (not shown) to form the fixing nip unit N. The pressure roller
110
is provided with the elastic layer
11
b
which is formed by the heat resistive silicon sponge rubber or the like on the core metal
11
a
formed by aluminum, iron, or the like, and on the elastic layer
11
b
, there is further provided the releasing layer
11
c
which is formed by the PFA, PTFE, or some other fluororesin having a minute quantity of conductive particles, such as carbon, dispersed in it.
With the minute quantity of the conductive particles, such as carbon, which is dispersed in the fluororesin, the releasing layer
11
c
is provided with the resistive value so that it can ground the releasing discharge generated between the trailing end of the recording material P and the surface of the fixing roller
100
to the GND of the apparatus main body through the surface of the pressure roller
110
the moment the trailing end of the recording material P is parted from the fixing roller
100
.
The diode element
17
is arranged to connect the core metal
11
a
of the pressure roller
110
and the GND of the apparatus main body. The cathode of the diode element
17
is connected with the core metal
11
a,
and the anode thereof is connected with the GND of the apparatus main body so as not to allow the potential of the core metal
11
a
to present the negative polarity. Then, the potential difference is provided between the surface of the fixing roller
100
and the core metal
11
a
of the pressure roller
110
so that with the electric field thereof, it is arranged to prevent the offset phenomenon from taking place between the recording material P and the fixing roller
100
.
Now, as shown in
FIGS. 9A
to
9
D, the aforesaid fixing device allows the unfixed toner or the offset toner described above to adhere to its fixing roller
100
when the image formation is carried out on a specific number of recording sheets. As a result, the toner T
1
is accumulated on the surface where the separating claws
14
and the fixing roller
100
are in contact (FIG.
9
A).
Then, when the toner T
1
is accumulated to a certain extent, it is transferred from the separating claws
14
to the fixing roller
100
, and transferred further to the pressure roller
110
, hence adhering to the recording material P again as the stained toner T
1
(
FIGS. 9B
,
9
C, and
9
C).
The transfer of the toner T
1
from the separating claws
14
to the fixing roller
100
is a phenomenon that tends to occur more often when the fixing roller
100
begins to rotate, that is, the first run in the morning with the fixing device being in the state of the room temperature or at the actuation in the state on standby. The toner T
1
transferred to the fixing roller
100
or the pressure roller
110
is again transferred to the recording material P when the recording material P passes the fixing nip unit N.
The separating claws
14
are aimed at separating the recording material P from the fixing roller
100
exactly. Therefore, it is necessary to arrange a plurality of the separating claws to be in contact with the recording material P in the longitudinal direction of the image area thereof. Also, the contact surface of the separating claws
14
on the fixing roller
100
should be provided with some measures to make the adhesion or accumulation of toner difficult. As such means, the surface layer of each separation claw
14
is coated with PFA, PTFE, or some other fluororesin having an excellent releasability.
Nevertheless, with the excellent releasability which is given to the separating claws
14
alone, it is insufficient to reduce the toner stains that may be allowed to adhere to the recording material P, although there is an effect that the adhesion of toner to or the accumulation thereof on the leading end portion of each separation claw can be reduced.
Also, this phenomenon may lead to the repetition of the cycle of the adhesion of the offset toner to or the accumulation thereof on the separating claws
14
, which is peeled off to fall when the fixing roller
100
is actuated, and agai
Fukuhara Taro
Kataoka Hiroshi
Canon Kabushiki Kaisha
Chen Sophia S.
Fitzpatrick ,Cella, Harper & Scinto
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