Electrophotography – Image formation – Fixing
Reexamination Certificate
1999-02-12
2001-11-20
Grimley, Arthur T. (Department: 2852)
Electrophotography
Image formation
Fixing
C399S328000, C399S330000, C399S333000, C219S216000
Reexamination Certificate
active
06321061
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a belt type fixing apparatus used in, for example, a copying machine, a printer, and a facsimile, particularly, to a belt type fixing apparatus for fixing an unfixed toner layer on a recording medium.
As known well, an electrophotographic image formation in, for example, a copying machine is performed by thermally fusing a powdery toner on a recording medium such as a paper sheet or a plastic sheet with a heat roll so as to fix the toner image on the recording medium.
In general, a recording medium bearing a toner image is passed through a clearance between a fixing roll comprising a mandrel and a halogen lamp arranged within the mandrel and a pressing roll so as to fuse and fix the toner under heat and pressure. Since the roll temperature is set at 200 to 250° C. and it is necessary to ensure a nip width of several millimeters, a heat resistant silicone rubber layer is formed on the circumferential surface of the mandrel of the fixing roll, and the silicone rubber layer is coated with a fluoroplastic resin layer so as to ensure release properties from the toner image.
In the conventional fixing roll of the particular construction, however, the mandrel is covered with a silicone rubber layer having a hardness of about 30° (Shore A) in a thickness of about 3 mm, leading to a poor heat conductivity and, thus, to a low fixing rate. Particularly, when it comes to a color copying machine or a color printer, it is necessary to develop color by completely fusing the toner in terms of the color reproduction, leading to requirement of the contact time and heating time about 3 times as long. as those for the fixing of a black toner image. Naturally, it is strongly required to shorten the fixing time.
Some proposals have been made in an attempt to shorten the fixing time, as follows:
(1) Decrease in Rubber Layer Thickness
If the thickness of the rubber layer is decreased, it is certainly possible to increase the heat conductivity. If the rubber layer thickness is decreased, however, the elasticity i.e. resiliency of the rubber layer is lowered, with the result that the rubber layer fails to be deformed to conform with the irregularity of the toner layer on the recording medium. It follows that a uniform fixing cannot be achieved. The low resiliency of the rubber layer gives rise to a serious problem in the case of fixing, particularly, a toner image having a large difference in thickness between the thick portion and the thin portion like a color image, or in the case of fixing a toner image on a hard medium such as an OHP film.
(2) Increase in Diameter of Fixing Roll to Increase Nip Width with Pressing Roll with the Rubber Layer Thickness Left Unchanged
The contact area between the recording medium and the fixing roll can be increased in this method. If the diameter of the roll is increased, however, the heat efficiency is lowered and the apparatus is rendered bulky. To overcome these problems, proposed nowadays is a system of using a belt stretched among supporting rolls in place of the pressing roll so as to increase the nip width and, thus, to shorten the fixing time.
Japanese Patent Disclosure (Kokai) No. 5-150679 discloses a fixing apparatus comprising a thermal fixing roll prepared by forming an elastic i.e. resilient layer having a thickness of at least 0.5 mm to cover an outer circumferential surface of a mandrel and a heat resistant endless belt stretched via a plurality of supporting rolls. It is taught that the heat resistant endless belt is wound at a predetermined angle about the fixing roll so as to form a nipping portion between the heat resistant belt and the thermal fixing roll. In this prior art, the resilient layer is formed to cover the circumferential surface of the mandrel to form the thermal fixing roll because the endless belt is formed of a plastic film which is not resilient and, thus, is not deformed. Therefore, in this prior art, a pressing roll is pressed against the thermal fixing roll with the endless belt interposed therebetween so as to deform the thermal fixing roll and, thus, to form a nipping portion between the roll and the belt. In this fashion, the toner is melted and fixed. It is taught that the heat resistant endless belt is made of a polyimide film or a Teflon film sized at, for example, 75 &mgr;m in thickness, 300 mm in width and 288 mm in length.
Japanese Patent Disclosure No. 61-132972 discloses a belt type fixing apparatus, comprising a heating roll having a fluoroplastic surface layer made of, for example, Teflon and a heat resistant belt formed of polyimide. Further, Japanese Patent No. 2650863 discloses an apparatus comprising a pressing roll and a seamless belt made of polyimide.
As described above, in the conventional technique, the surface of a fixing roll is covered with a resilient material and pressed by a pressing roll so as to generate strain within the fixing roll and, thus, to fix uniformly the toner layer. In the conventional technique, however, the elastic layer inhibits the heat conduction required for the fixing, making it difficult to shorten the warming up time to heat the roll or belt to temperatures required for the fixing.
BRIEF SUMMARY OF THE INVENTION
An object of the present invention is to provide a belt type fixing apparatus comprising a heating roll and a resilient endless belt stretched by a plurality of supporting rolls such that the endless belt is partly pressed against a part on the circumferential outer surface of the heating roll to form a nipping portion, the heating roll consisting of a mandrel, a heating means arranged inside the mandrel and a release coating layer formed on the outer circumferential surface of the mandrel, and the endless belt being deformed at the nipping portion between the endless belt and the heating roll to conform with the irregularity of the toner layer so as to melt and fix uniformly the toner layer.
Another object is to provide a belt type fixing apparatus, in which some of the plural supporting rolls supporting the resilient endless belt are made movable so as to adjust the tension of the elastic endless belt and, thus, to deform the belt at the nipping portion with the heating roll.
Another object is to provide a belt type fixing apparatus, in which the resilient endless belt consists of a spiral reinforcing layer made of a continuous heat resistant string, a heat resistant elastic layer formed on the reinforcing layer, and a release coating layer formed on the heat resistant resilient layer. The particular construction of the resilient endless belt permits improving the heat conductivity, compared with the conventional heating roll using a rubber layer low in heat conductivity, so as to promptly transmit the heat generated from the heating means arranged within the heating roll to the toner layer. As a result, the toner layer is melted promptly so as to improve the fixing speed and shorten markedly the warming up time.
Another object is to provide a belt type fixing apparatus for thermally fixing an unfixed toner layer on a recording medium, comprising a heating roll and a resilient endless belt stretched by a plurality of supporting rolls such that the endless belt is partly pressed against a part on the circumferential outer surface of the heating roll to form a nipping portion, the heating roll consisting of a mandrel, a heating means arranged inside the mandrel and a release coating layer formed on the outer circumferential surface of the mandrel.
Another object is to provide a belt type;fixing apparatus, in which some of the plural supporting rolls supporting the resilient endless belt are made movable so as to adjust the tension of the elastic endless belt and, thus, to deform the belt at the nipping portion with the heating roll.
Further, a still another object of the present invention is to provide a belt type fixing apparatus, in which the resilient endless belt consists of a spiral reinforcing layer made of a continuous heat resistant string, a heat resistant resilient layer formed on the reinforcing lay
Onuki Akio
Sonobe Saburo
Grimley Arthur T.
Kinyosha Co., Ltd.
Ngo Hoang
Volpe and Koenig P.C.
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