Electrophotography – Control of electrophotography process – Control of fixing
Reexamination Certificate
2000-05-08
2004-01-06
Grainger, Quana M. (Department: 2852)
Electrophotography
Control of electrophotography process
Control of fixing
C399S328000
Reexamination Certificate
active
06674978
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
The present invention relates to an image heating device.
The image heating device includes a fixing device for heating and fixing an unfixed image on a recording material into a permanent fixed image thereon, an apparatus for temporarily fixing by heating an unfixed image, an apparatus for heating an image to improve a surface property such as gloss, or the like.
a) Heat roller type fixing device
Heretofore, in an image forming apparatus such as a copying machine, a facsimile machine, a laser beam printer or the like using an electrophotographic process, electrostatic recording process or the like, the use is made with a fixing device of a heat roller type which is one of a fixing devices an in which an unfixed toner image formed on a recording material (transfer material, photosensitive paper, electrostatic recording paper, print sheet OHP (OHT) film or the like) is heated and fixed thereon into a permanent fixed image.
FIG. 14
is a schematic cross-sectional view of an example of a heat roller type fixing device.
The fixing device comprises a pair of pressing rollers
201
,
202
, one of or both of which contain heat sources
201
a,
202
a
such as halogen lamp or the like. The rollers constitute a nip N therebetween, and the recording material P is nipped and fed by the nip while being subjected to heat and pressure, so that unfixed toner image t is fixed on the recording material P.
The fixing roller
201
and the pressing roller
202
comprise hollow core shafts
201
b,
202
b
of aluminum or the like, elastic layers
201
c,
202
c
of silicone rubber on the outer surfaces of the core shafts, and parting layers
201
d,
202
d
of fluorine resin material or the like on the outer surfaces, respectively.
Generally, the roller contactable to the unfixed toner image t is “fixing roller”, and the roller not contactable to the unfixed toner image t is “pressing roller”. The temperatures of the fixing and pressing rollers
201
,
202
are detected by temperature detecting means
26
such as thermister means contacted to the roller surface, and the detected temperature is fed back to an ON/OFF control circuit (unshown) for activating and deactivating heat sources
201
a,
202
a
so as to maintain a predetermined temperature.
The heat quantity applied to the recording material P per unit time is determined mainly on the basis of the width of the nip, the roller temperature and the recording material feeding speed. Among these factors, the roller temperature and the recording material feeding speed can be relatively easily exchanged in accordance with a desired fixing process and the recording material so as to supply proper heat quantity.
For example, the glossiness (gloss) of the fixed image is significantly influenced by the recording material feeding speed and the roller control temperature of the fixing device. The gloss tends to be higher if the roller control temperature is higher and if the recording material feeding speed is slower, within a certain range. In other words, the gloss rises with increase of the heat quantity.
By adjusting the parameters, the gloss of the image can be controlled. For example, in an image forming apparatus producing low gloss images, high gloss images can be provided by controlling the fixing condition.
As for the recording material used with the image forming apparatus, there are OHP (overhead projector) film, gloss film or the like in addition to the sheet of paper. The former is a transparent resin film through which light from a projector is transmitted, and the latter is a white resin film having a glossiness. They are made of synthetic resin material film such as PET having a thickness of 4-5 microns so that thermal capacity is very large as compared with that of usually paper. Therefore, a larger amount of heat supply is required to properly fix the unfixed toner image. Furthermore, the OHP film requires good permeability, and gloss film requires high glossiness. In order to accomplish this, it is desirable that toner is sufficiently fused and deformed to smooth the surface of the toner image. Therefore, it is necessary to increase the amount of the heat supply by decreasing the recording material feeding speed or by rising the roller control temperature.
Thus, in order to control the glossiness of the image or to improve the permeability or the glossiness of the image on the film, the recording material feeding speed and/or the roller control temperature is instantaneously switched to provide an optimum amount of the heat supply. If the roller control temperature is constant irrespective of the recording material feeding speed, the amount of the heat tends to be insufficient or too much at the time of changing the recording material feeding speed with the result of fixing defect or unintended image quality. Therefore, it is desirable that roller control temperature is changed in accordance with the recording material feeding speed.
However, in the case of the heat roller type fixing device, the surface temperature of the fixing roller
201
(heating portion material) does not become the set control temperature instantaneously after the roller control temperature is switched. Such a poor thermal responsivity results mainly from the following two factors.
The first is that heat source
201
a
is away from the surface of the roller in the case of the fixing roller
201
. For example, the heat from the heat source
201
a
in the fixing roller
201
is transferred to the surface of the roller from the heat source
201
a
(halogen lamp or the like) via air layer, core shaft
201
b
(A1 or the like), elastic layer
201
c
the magnetic field for heating an image on a recording material; a temperature detecting element for detecting a temperature of said heating portion material; control means for controlling said magnetic field generating means to maintain a temperature detected by said temperature detecting means at a target temperature; heating condition setting means for setting a feeding speed of the target temperature.
The second cause is that thermal capacity of the entire fixing roller
101
is relatively large. This leads to larger amount of heat quantity required to rise the temperature of the roller so that in the thermal responsivity is worsened. This is also a cause of the fact that roller temperature does not easily lower.
For these reasons, the temperature of the roller surface does not linearly follow the switching of the control temperature.
In such a fixing device, when the recording material feeding speed is switched from a normal speed to a slower speed, excessive supply of the heat results, so that problem of hot offset or OHPpermeability decrease arises. Additionally, there arises a problem that high gloss image is not provided even under a high gloss fixing condition.
Moreover, the next printing operation is required to be interrupted until the surface temperature of the fixing roller
201
reaches the control temperature to avoid the image defects described above.
b) Fixing device of a film heating type using a ceramic heater
The inventors have investigated the possibility of improving the thermal responsivity of a fixing device of a film heating type using a ceramic heater.
Such a fixing device has been proposed in Japanese Laid-open Patent Application No. SHO 63-313182, Japanese Laid-open Patent Application No. HEI 2-157878, Japanese Laid-open Patent Application No. HEI 4-44075, Japanese Laid-open Patent Application No. HEI 4-204980, for example.
FIG. 15
is a schematic view of an example of such a fixing device.
The rotatable member
10
constituting the nip N is a cylindrical fixing film. From the standpoint of reducing the thermal capacity an improve the quick start feature, the fixing film
10
preferably has a film thickness of not more than 100 &mgr;m, preferably not more than 50 &mgr;m and not less than 20 &mgr;m and is a heat resistive film of a monolayer of PTFE, PFA, FEP resin material or a complex layer film comprising a PI, PAI, PSEK, PES, PPS resin material, a coating
Abe Atsuyoshi
Suzuki Masahiro
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