Electrophotography – Control of electrophotography process – Control of fixing
Reexamination Certificate
2000-11-21
2002-06-25
Braun, Fred L. (Department: 2852)
Electrophotography
Control of electrophotography process
Control of fixing
C399S045000, C399S331000
Reexamination Certificate
active
06411785
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a fixing unit for use in an image forming apparatus such as a copying machine, a printer and a facsimile applying an electrophotographic or electrostatic recording scheme and to an image forming apparatus using the same. More specifically, present invention relates to a fixing unit capable of always performing a good fixing process regardless of the type of a transfer medium and an image forming mode and to an image forming apparatus using the same.
2. Related Art Statement
Hitherto, there has been a unit as shown in
FIG. 17
for example as a fixing unit for heating and fixing a non-fixed toner image which has been transferred to a copy sheet in an image forming apparatus such as a copying machine, a printer and a facsimile applying electrophotographic or electrostatic recording scheme. As shown in
FIG. 17
, the fixing unit is constructed so as to melt and fix a toner image
103
on a copy sheet
104
by heating and pressing it by passing the copy sheet
104
carrying the non-fixed toner image
103
through a pressure-contact area between a pair of rollers
101
and
102
wherein at least one roller has a heating source.
In
FIG. 17
, the reference numeral (
101
) denotes a fixing roller and (
102
) a pressure roller. The fixing roller
101
is structured by coating a relatively thick heat-resistant elastic layer
112
made of silicon rubber or the like and a top coat layer
113
made of fluorine rubber or the like on the surface of a metal hollow core
111
made of aluminum or the like whose thermal conductivity is high. A halogen lamp
114
is disposed as a heating source within the metal hollow core
111
and is turned on/off by a temperature control circuit not shown based on a signal from a temperature sensor
115
provided on the surface of the fixing roller
101
to control the surface at predetermined temperature. Further, an oil supply unit
105
for supplying a certain amount of silicon oil is provided on the surface of the fixing roller
101
to prevent a part of the non-fixed toner image
103
on the copy sheet
104
from being transferred to the fixing roller
101
(hereinafter referred to as “offset”) during fixing. A cleaning unit
106
for removing offset toner and the like is also provided on the surface of the fixing roller
101
.
Meanwhile, the pressure roller
102
is structured by coating a heat-resistant elastic layer
122
which is made of silicon rubber or the like and which is relatively thinner than the elastic layer
112
of the fixing roller
101
and a top coat layer
123
made of fluorine rubber or the like on the surface of a metal hollow core
121
made of aluminum or the like whose thermal conductivity is high. A halogen lamp
124
is disposed as a heating source within the metal hollow core
121
and is turned on/off by the temperature control circuit not shown based on a signal from a temperature sensor
125
provided on the surface of the pressure roller
102
to control the surface at predetermined temperature.
In the heating roller type fixing unit constructed as described above, a pressure-contact part (hereinafter referred to as a “nip”)
107
is created by elastic deformation of the elastic layer
112
of the fixing roller
101
. The non-fixed toner image
103
is melted and is fixed on the copy sheet
104
by thermal energy and pressure as the copy sheet
104
carrying the non-fixed toner image
103
passes through the nip
107
in such fixing unit.
However, the prior art technology described above has had the following problems. While the fixing roller
101
and the pressure roller
102
have the elastic layers
112
and
122
in the fixing unit constructed as described above, these elastic layers
112
and
122
are made of elastic member such as silicon rubber which has a certain thickness and whose thermal conductivity is relatively low. Therefore, when the surface temperature of the fixing roller
101
or of the pressure roller
102
drops below the predetermined temperature while feeding papers, there has been a possibility in the fixing unit described above that it takes time to transmit heat of the halogen lamps
114
and
124
to the surface via the elastic layers
112
and
122
, thus causing fixing failure, even if the temperature sensors
115
and
125
detect the drop of the temperature and power is fed to the halogen lamps
114
and
124
. The fixing failure is liable to occur when processing speed increases in particular and there has been a problem that continuous printing is limited in order to prevent the fixing failure from occurring.
Then, in order to solve such problems, there has been already proposed a technology for slowing down the drop of the temperature of the surface of the fixing roller by abutting an external heating roller whose temperature is kept high to the surface of the fixing roller as disclosed in Japanese Patent Laid-Open Nos. Hei. 10-149044 and Hei. 11-24489.
However, in case of the technology disclosed in Japanese Patent Laid-Open Nos. Hei. 10-149044 and Hei. 11-24489 described above, the external heating roller whose temperature is kept high is abutted to the surface of the fixing roller immediately when the sensor detects that the surface temperature of the fixing roller has dropped even though the optimum surface temperature of the fixing roller is different depending on the type of the copy sheet
104
and on image forming modes such as black-and-white mode and color mode. Therefore, there has been a case when the temperature of the fixing roller in fixing papers differs considerably from temperature suitable as conditions for fixing papers such as the copy sheet depending on the temperature of the external heating roller and the fixing roller. Accordingly, the technology disclosed in Japanese Patent Laid-Open Nos. Hei. 10-149044 and Hei. 11-24489 has had a possibility that it may cause new problems such as an increase of offset toner, a failure in peeling OHP sheets and insufficient fixing.
More specifically, in case of the technology disclosed in Japanese Patent Laid-Open Nos. Hei. 10-149044 and Hei. 11-24489, the surface temperature of the fixing roller
101
rises considerably above the predetermined temperature when the external heating roller not shown whose surface temperature is high abuts to the surface of the fixing roller
101
in the process when the surface temperature of the fixing roller
101
rises due to temporal delay of the increase of the surface temperature of the fixing roller
101
as shown in FIG.
18
. Then, because the surface temperature of the fixing roller
101
is considerably higher than the predetermined temperature, it has caused problems that the non-fixed toner image
103
to be fixed on the copy sheet
104
melts excessively, thus dropping the gross, an amount of toner transferred to the surface of the fixing roller
101
increases (called as hot offset), and the deterioration of the elastic layer
112
and the top coat layer
113
of the fixing roller
101
is accelerated. Still more, when the surface temperature of the fixing roller
101
is considerably higher than the predetermined temperature and when a transfer medium
104
made of a synthetic resin film called as an OHP sheet and a tack film is used, there has been a problem that those synthetic resin films such as the OHP sheet and the tack film are softened and are wrapped around the surface of the fixing roller
101
, thus making it impossible to perform the fixing process. Meanwhile, there has been a case when the surface temperature of the fixing roller
101
is lower than the predetermined temperature, thus causing insufficient fixing, depending on the surface temperature of the fixing roller
101
and the surface temperature of the external heating roller.
As a second problem, there has been a case when the surface temperature of the fixing roller
101
and the pressure roller
102
drops gradually as the heat of the fixing roller
101
and the pressure roller
102
is taken away gradually by the copy sh
Ogawahara Norio
Ohtsuka Hiroyuki
Okabayashi Yasuto
Braun Fred L.
Fuji 'Xerox Co., Ltd.
Morgan & Lewis & Bockius, LLP
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