Electrophotography – Image formation – Fixing
Reexamination Certificate
2001-08-01
2002-12-03
Ngo, Hoang (Department: 2852)
Electrophotography
Image formation
Fixing
C399S330000, C399S331000, C399S333000
Reexamination Certificate
active
06490429
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a heat fixing member which applies heat and pressure to a recording material, and is disposed in a fixing apparatus which uses a heat and pressure fixing method, the fixing apparatus being used in an image formation apparatus using electro-photography such as a copier, a printer, facsimile machine and the like. The invention also relates to a heat and pressure fixing apparatus and an image formation apparatus which use said heat fixing member.
2. Description of the Related Art
Conventionally, in a copier, printer, etc. that utilizes an electro-photography, it is necessary to perform fixing of a unfixed toner image formed on a recording material, thereby making that unfixed toner image a permanent image. As a method for performing such fixing, there are known a solvent fixing method, a pressure fixing method, and a heat and pressure fixing method.
However, the solvent fixing method has the drawback that the solvent gives off vapor, and this causes problems in terms of odor and sanitation. On the other hand, the pressure fixing method has the drawback that the fixability is inferior to that obtained with the use of other mixing methods and that the pressure-sensitive toner is expensive. For those reasons, the solvent fixing method and pressure fixing method have not been put to practical use. The actual situation is that the heat and pressure fixing method has instead been generally widely used.
In the heat and pressure fixing method, the following technique is the most widely used. Namely, of a heating roll that is a heat fixing member and a pressure roll that is a pressure applying member, at least inside the heating roll, there is disposed a heat source. The both rolls are pressure-contacted with each other to thereby form a nip portion. And, while they are being rotated, a recording material having formed thereon a unfixed toner image is inserted through the nip portion. By doing so, the toner is molten and pressurized and is fixed onto the recording material. In this type of heating roll, on the surface of a hollow-cylindrical core metal, a heat-resisting release layer is provided as at least a surface layer. By doing so, the toner is prevented from adhering onto the heating roll. Particularly, if only color fixing apparatus are considered, there are many cases where, for the purpose of evenly conducting heat to the toner of each color, an elastic layer is provided between the core metal and the release layer. And this elastic layer may function to cover the laminated toners therein. On the other hand, the pressure roll is generally of a type wherein a heat-resisting elastic layer and, according to the necessity, a heat-resisting release layer are sequentially applied to the surface of the hollow-cylindrical or solid core metal.
In general, the thickness of the elastic layer is made greater than a certain value to thereby cause the deformation of the elastic layer of each of the rolls through the use of the nip pressure. The nip width is ensured by that deformation. Conventionally, the elastic layer is generally constructed of a heat-resisting rubber such as silicone rubber or fluorine rubber since these have large heat capacity. A time period of 3 to 8 minutes or so was needed for it to rise from room temperature. Thus in order to minimize the waiting period when a print job was received (or when there was an attempt to make a copy), even when the device was in a standby state, the temperature was kept at high temperature which was gather room temperature, but less than the temperature at which fixing is carried out. Because of this, most of the power consumed in the electro-photographic image formation apparatus was attributable to the operation of the fixing apparatus.
In order to solve this problem, decreasing the thickness of the heat fixing member as a whole is the most effective means. In order to obtain an excellent quality of fixed image,the thickness of the elastic layer must exceed a certain level. Especially, in a color copier/printer, toner images that correspond to 4 colors of yellow, magenta, cyan, and monochrome black are superposed one upon the other. Therefore, in order to equally conduct heat to the toner in a state in which all four color layers are superimposed and prevent the toner images from being mechanically brought out of their original shape, the the elastic layer must be used. An attempt has been made to realize reaching a temperature at which fixing is possible in a short period of time by making the hollow-cylindrical metal core which becomes the core metal thin.
However, if the core metal is simply made thin, the rigidity of the core metal decreases. For this reason, there occurs the inconvenience that the core metal flexes initially due to the nip pressure occurring between itself and the pressure member, or that the metal core undergoes permanent deformation of the core metal due to long use or being left unused. As a result, the nip pressure is unevenly applied in the circumferential direction of the heat fixing member. Thus, there defects of the fixed image quality such as gloss unevenness or fixation defects at the area where the nip pressure is low are caused.
In contrast, Japanese Patent Application Laid-Open Publications (JP-A) Nos. 59-155875 and 11-149226 each propose the following. Namely, on the inner surface of the core metal are rib is formed in parallel with the axial direction, or formed spirally, to thereby increase the mechanical strength of the heating roll. However, in this method, unevenness is substantially created in the thickness of the core metal. Consequently unevenness occurs in the direction of heat conduction from the heater (the heat source). Thus, there occurs a temperature difference between the rib-containing portion and the no-rib portion on the surface of the heating roll. This is considered to cause defects in the fixed image. In addition, ordinarily, the core metal can achieve a required precision by being made into a pipe by extrusion of metal such as aluminum or iron and thereafter being drawn off. However, in this case when a rib is formed in the inner surface of the core metal, it becomes necessary to perform a complex step in terms of the working. Consequently, the processing cost is also increased.
Also, JP-A No. 10-240059 has proposed a method of increasing the mechanical strength by making a composite from an aluminum core metal and a resin layer. In this method, though, it is certainly possible to decrease the thickness of the aluminum core metal, because a resin such as epoxy constituting the resin layer is inferior in the conduction of heat to metal, there occurs the drawback that the period needed to reach to a temperature at which fixing is possible becomes large. Also, the adherence at the interface between the aluminum and the resin layer, or the durability thereof, is not sufficient. Therefore, when consideration is given to the fact that the core metal when used as a fixing member is used in an environment of high temperature, and that peeling occurs at the interface due to use for a long period, the core metal does not have sufficient mechanical strength.
Further, JP-A No. 2-149628 has proposed an invention that concerns an aluminum alloy having 1.0 to 5.0% Mn as an additive that is added to the aluminum itself. However, it cannot be said that that alloy having that composition ratio exhibits a sufficiently high level of extrusion workability. This leads to an increase in the working cost. Furthermore, bends that occurs due to use for a long period at a high temperature are likely to be formed.
SUMMARY OF THE INVENTION
Accordingly, the present invention has been made in order to solve the problems inherent in the above-described conventional techniques and has an object to provide a heat fixing member which while maintaining an image that is has a high image quality, enables shortening of the length of time needed until a temperature at which fixing is possible is reached, and a heat and pressure fixing
Fujihara Issei
Okayasu Takahiro
Tamemasa Hiroshi
Fuji 'Xerox Co., Ltd.
Ngo Hoang
Oliff & Berridg,e PLC
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