Electrophotography – Image formation – Fixing
Reexamination Certificate
2001-01-18
2002-06-18
Chen, Sophia S. (Department: 2852)
Electrophotography
Image formation
Fixing
C118SDIG001, C219S216000, C399S067000
Reexamination Certificate
active
06408159
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a fixing apparatus applicable to an image forming apparatus such as a copying machine or a printer, and more particularly to an apparatus for coating a fixing member with a releasing agent.
2. Related Background Art
As an example of such image forming apparatus, there is conventionally known an apparatus equipped with a fixing apparatus
150
as shown in FIG.
12
.
As detailedly shown in
FIG. 12
, the fixing apparatus
150
is provided with a fixing roller
151
constituting a rotatably provided fixing member, a pressure roller
152
constituting another fixing member (pressurizing member) rotated in pressurized contact with the fixing roller
151
, a releasing agent applying (coating) apparatus
153
, and roller cleaning apparatuses
154
,
155
. The fixing roller
151
and the pressure roller
152
are respectively provided therein with heaters
156
,
157
constituting heating means an composed for example of halogen lamps. Thermistors
158
,
159
are so positioned as to be respectively in contact with the fixing roller
151
and the pressure roller
152
and control the voltages supplied to the heaters
156
,
157
through temperature adjusting circuits thereby executing adjustment of the surface temperature of the fixing roller
151
and the pressure roller
152
.
On the fixing roller
151
there are mounted the cleaning apparatus
154
and the releasing agent coating apparatus
153
. The cleaning apparatus
154
cleans the fixing roller
151
by removing the toner etc. deposited thereon by offsetting, and the releasing agent coating apparatus
153
coats a releasing agent such as silicone oil onto the fixing roller
151
thereby facilitating the separation of a transfer paper P, constituting the recording material, from the fixing roller
151
and prevents the toner deposition by offsetting.
The cleaning apparatus
154
is composed of a cleaning web
154
a
consisting of a heat-resistant web-shaped non-woven cloth, a pressure roller
154
b
for pressing the cleaning web
154
a
to the fixing roller
151
, an unwinding roller
154
c
for feeding the new cleaning web
154
a
, and a winding roller
154
d
for gradually winding the cleaning web
154
a
which is deteriorated in the cleaning ability for example by deposition of toner. The cleaning apparatus
154
is provided upstream of the thermistor
158
in the rotating direction of the fixing roller
151
, in order to protect the thermistor
158
from detection error resulting from the sticking thereto of the offset toner.
When a predetermined number of copying operations is judged by a counter, a solenoid (not shown) is energized to activate a one-way clutch to wind the cleaning web
154
a
by a predetermined amount, in a direction opposite to the rotating direction of the roller. Such winding in the opposite direction avoids dragging of the cleaning web
154
a
in the rotating direction of the roller.
The releasing agent coating apparatus
153
is composed of an oil tank
153
a
or a releasing agent container for containing the releasing agent such as silicone oil, and a coating roller
153
d
constituting releasing agent supply means which bears the releasing agent on oil, picked up by pickup rollers
153
b
,
153
c
from the oil tank
153
a
, for supply onto the surface of the fixing roller
151
, and a regulating blade
153
e
consisting of an elastic member is so provided as to abut on the coating roller
153
d
for maintaining a constant oil amount thereon, thereby attaining uniform oil coating onto the fixing roller
151
. The releasing agent coating apparatus
153
is positioned downstream of the thermistor
158
in the rotating direction of the fixing roller
151
.
Also the pressure roller
152
is provided with a cleaning apparatus
155
composed, similarly to the cleaning apparatus
154
, of a cleaning web
155
a
, a pressure roller
155
b
, an unwinding roller
155
c
and a winding roller
155
d
, in order to remove the toner on the pressure roller
152
transferred from the fixing roller
151
.
On the pressure roller
152
, there abuts an oil removing blade
160
consisting of an elastic member for removing the excessive releasing agent remaining on the pressure roller
152
. Without such oil removing blade
160
, the excessive releasing agent is accumulated in the nip of the fixing roller
151
and the pressure roller
152
, eventually causing a stain on the recording material or failure in the entry into the nip in certain recording material such as a transparent laminate OHP film. The oil removing blade
160
is composed for example of silicone rubber or fluorinated rubber, and abuts on the pressure roller
152
with an appropriate amount of intrusion in the opposite (or forward) direction with respect to the rotating direction of the pressure roller
152
.
When a transfer paper P is conveyed in such configuration, the fixing roller
151
and the pressure roller
152
are rotated and silicone oil as the releasing agent is coated on the surface of the fixing roller
151
. Thus, while passing between the fixing roller
151
and the pressure roller
152
, the transfer paper P is pressed and heated by substantially constant pressure and temperature from both surfaces, whereby the unfixed toner image on the paper is fused and fixed to form a full-color image thereon. The transfer paper P bearing the fixed image is separated by an under separation claw
168
from the pressure roller
152
and is discharged from the apparatus.
However, such conventional image forming apparatus has been associated with the following drawbacks.
Firstly, the heat fixing apparatus in the ordinary copying machine waits for a predetermined period, after the power supply is turned on, until the fixing roller reaches a predetermined temperature, and the copying operation is enabled after such predetermined temperature is reached. However the fixing ability is different between immediately after the copying operation is enabled (“first run in the morning”) and after the lapse of a certain time in the copy-enabled stand-by state (“standing state”). Such phenomenon arises from the difference, between the first run in the morning and the standing state, not only in the surface temperature of the fixing roller but also the temperature of the entire fixing apparatus and that of the releasing agent to be coated on the surface of the fixing roller.
More specifically, in the standing state, the heat of the fixing roller is transferred to the releasing agent through the coating roller and the pickup rollers thereby elevating the temperature of the releasing agent. In such state, the temperature loss of the fixing roller is limited when the releasing agent is coated thereon, and the releasing agent present between the fixing roller and the toner is also heated, whereby satisfactory fixing ability is secured. On the other hand, in the first run in the morning, the releasing agent is still cold and the fixing roller shows an abrupt temperature loss when such releasing agent is coated thereon, and the releasing agent of a low temperature is present between the fixing roller and the toner, whereby the fixing ability is deteriorated. Such phenomenon becomes more conspicuous in an environment of low temperature.
In order to avoid such drawback, the present applicant already proposed a fixing apparatus, provided, as shown in
FIG. 13
, with a releasing agent heating member
180
composed of a heat generating member or a heater
182
, a heat conductive member
181
composed for example of a metal, a temperature of the heater
182
, a safety element
184
for preventing excessive temperature of the heater
182
etc., setting to heat the releasing agent in the oil tank
153
a.
In such fixing apparatus, the temperature detecting element
183
detects the temperature of the heater
182
, and, if the detected temperature is lower than a desired temperature, the heater
182
of the releasing agent heating member
180
is powered to elevate the temperature of the heater
18
Ishizuka Jiro
Kodama Hirokazu
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