Electric heating – Inductive heating – With heat exchange
Reexamination Certificate
1999-10-12
2001-06-12
Hoang, Tu Ba (Department: 3742)
Electric heating
Inductive heating
With heat exchange
C219S216000, C219S634000, C399S330000, C399S332000
Reexamination Certificate
active
06246035
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
The present invention relates to a heating device for imparting heat energy to a member to be heated, such as a recording sheet, an image forming apparatus using the heating device as a fixing means, and an induction heating member included in such a heating device.
Hitherto, as a fixing device for an image forming apparatus, such as a copying machine, a printer, an image-outputting apparatus for a facsimile apparatus, a hot roller-type fixing device has been popularly used. This type of fixing device basically comprises a metallic heating roller containing therein an internal heater, and an elastic pressure roller pressed against the heating roller so as to form a fixing nip therebetween, whereby a recording material carrying a toner image is passed through the fixing nip to fix the toner image under heating and pressure onto the recording material. In the hot roller-type device, the fixing roller generally has a large heat capacity, so that a very long time is required for raising the roller surface temperature up to the fixing temperature. For this reason, in order to quickly perform an image forming operation at a desired time, it is necessary to keep the roller surface temperature at a certain temperature even in the absence of the image forming operation.
A fixing system solving the above-mentioned problems of the hot roller fixing system has been proposed by our research and development group (Japanese Laid-Open Patent Application (JP-A) 63-313182 and JP-A 2-157878). The fixing device of this type (film heating-type fixing device) generally includes a thin heat-resistant film, a heater fixedly supported on one surface-side of the film, and a pressing film disposed on the other surface-side of the film and opposite to the heater so as to press a recording material subjected to image fixation against the heater via the film.
A fixing operation by the film heating-type fixing device is performed by passing a recording material through a fixing nip formed by pressing the pressing member against the heater via the film and heating the surface of the recording material carrying the toner image via the film to heat-melt and fix the toner image onto the recording medium. The fixing film used in the film heating-type fixing deice has comprised a 20 to 50 &mgr;m-thick film of a heat-resistant resin, such as polyimide, coated on its outer surface with a 5 to 20 &mgr;m-thick release layer of PTFE (polytetrafluoroethylene) or PFA (tetrafluoroethylene perfluoroalkyl vinyl ether copolymer).
In such a fixing device of the film heating-type, a heater of small heat capacity can be used so that it is possible to shorten the waiting time (i.e., effect a quick start), compared with the conventional hot roller scheme. Further, as the quick start is possible, preheating during a non-image forming operation period becomes unnecessary, so that overall power economization can be realized.
In the fixing system using such a fixing film, the occurrence of image irregularities, such as image aberration or blurring has been encountered in some cases. Particularly, in the case of fixing plural layers of different color toners in superposition, the overall toner layer becomes thick, so that the reproduced objective image is liable to be accompanied with image blurring of respective toner colors.
For obviating the problem, it has been proposed to coat the film surface with an elastic layer by our research and development group (JP-A 10-48868). This is effective for preventing image aberration or blurring by covering or wrapping the toner image with such a deformable elastic layer. On the other hand, the resultant thicker fixing film is liable to exhibit a worse fixing performance and is also liable to cause offsetting.
SUMMARY OF THE INVENTION
A generic object of the present invention is to solve the above-mentioned problems involved in the film heating-type fixing device.
A more specific object of the present invention is to provide a film heating device suitable for use as a fixing device for an image forming apparatus using a powdery toner, capable of obviating fixing failure and fixed image aberration or blurring.
Another object of the present invention is to provide a film heating device suitable for use as a fixing device for an image forming apparatus using a powdery toner, capable of exhibiting good fixing performance free from offsetting.
A further object of the present invention is to provide an image forming apparatus including such a heating device, and also an induction heating member included in such a heating device.
According to my further study, the difficulties, such as inferior fixing performance or offsetting, caused by the provision of an elastic layer effective for preventing image aberration or blurring are principally attributable to an increase in thickness of the fixing film due to provision of the elastic layer.
For example, the increased film thickness leads to a smaller capacitance, so that even an identical charge can result in an increased surface potential liable to cause offset phenomenon. According to my study, it has been found that these difficulties can be effectively obviated by inclusion of appropriate fillers in the elastic layer.
Thus, according to the present invention, there is provided a heating device, comprising: a heating member, and a heat-resistant film having a first surface to be moved relative to and in contact with the heating member and a second surface to be in contact with a member to be heated, so that the member to be heated and the heat-resistant film are moved together over the heating member to heat the member to be heated; wherein the heat-resistant film comprises at least a base layer for providing the first surface and an elastic layer on the other side of the heat-resistant film, the elastic layer containing a filler exhibiting a thermal conductivity of at least 0.04 cal/cm.sec. °C.
According to the present invention, there is also provided a heating device, comprising: an excitation coil, an induction heating member, and a pressing member pressed against the induction heating member to form a nip, so that a member to be heated is passed through the nip between the induction heating member and the pressing member to be heated, wherein the induction heating member comprises at least a heat-generating layer comprising a magnetic metal, and an elastic layer; the elastic layer containing a filler having a thermal conductivity of at least 0.04 cal/cm.sec. °C.
According to another aspect of the present invention, there is also provided an image forming apparatus including the above-mentioned heating device as a fixing device.
According to still another aspect of the present invention, there is provided an induction heating member, comprising a heat-generating layer comprising a magnetic metal, and an elastic layer; the elastic layer containing a filler having a thermal conductivity of at least 0.04 cal/cm.sec. °C.
Thus, in the heating device of the present invention, the elastic layer of the heat-resistant film is caused to contain filler particles exhibiting a high thermal conductivity, whereby heat for fixation is effectively conducted to the member to be heated, particularly a toner image on a recording member, thereby effectively fixing the toner image without causing image aberration or blurring. Further, by using thermally conductive particles also exhibiting a good electroconductivity or additionally including electroconductive particles, the electric charge accumulation on the elastic layer is effectively suppressed, and further an increased capacitance by inclusion of the electroconductive filler is effective for suppressing a surface potential caused by the surface charge on the heat-resistant film, whereby an electrostatic offset of the toner image on the member to be heated can be effectively prevented.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Hoang Tu Ba
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