Patent Application
20200133179
The present invention relates to an electrophotographic image forming apparatus such as a copying machine, a printing machine, a facsimileing machine, and a multifunctional image forming apparatus, which is capable of forming an image on a sheet of recording medium. It relates also to a fixing apparatus for an electrophotographic image forming apparatus.
A fixing apparatus for an image forming apparatus such as an electrophotographic copying machine, a printer, and so on, fixes a toner image to a sheet of recording medium after the transfer of the toner image onto the sheet. It is made up of a fixing member as a heating member, and a pressing member positioned in such a manner that it remains pressed upon the fixing member. As the sheet, on which the toner is present, is conveyed through the nip, which is formed by the fixing member and pressing member of the apparatus, the toner image becomes fixed to the sheet.
In the field of a fixing apparatus such as the one described above, there has been put into a practical usage, a fixing apparatus that is equipped with a fixing member which is in the form of a thin belt, being therefore smaller in thermal capacity, in order to reduce the fixing apparatus in the length of time (warm-up time) it takes for the fixing member to heat up to a preset temperature level which is necessary for the fixing member to fix a toner image, that is, from when the fixing apparatus is turned on to when it becomes ready for fixation.
There has been disclosed in Japanese Laid-open Patent Application No. H04-204980, a fixing apparatus which is equipped with a belt (which hereafter may be referred to as fixation belt), as a fixing member. This fixing apparatus comprises a fixation belt, a flat ceramic heater, a pressure roller as a pressing member, etc. It is structured so that the ceramic heater is disposed on the inward side of the loop which the belt forms, and a nip is formed between the heater and pressure roller, with the placement of the fixation belt between the ceramic heater and pressure roller. Further, it is structured so that the fixation belt is rotated by the rotation of the pressure roller. In the cases of this fixing apparatus, as a sheet of recording medium, on which an unfixed toner image is present is conveyed through the nip, an unfixed toner is heated while being pressed. Consequently, the unfixed toner image becomes fixed to the sheet.
Further, there is disclosed in Japanese Laid-open Patent Application No. H11-16667, a fixing apparatus which comprises a heater holding member, and a thermally conductive plate which is roughly in the form of a semicircular trough, in addition to the components which the aforementioned fixing apparatuses comprise. It is structured so that in order to prevent the problem that the inward surface of the fixation belt is damaged by being intensively rubbed by the heater and/or heater holding member, the heater is covered with the thermally conductive plate.
However, a fixing apparatus such as the one structured as disclosed in Japanese Laid-open Patent Application No. H11-16667, suffers from the following problem. That is, it was not reduced in the friction between the fixation belt and heater holding member, making it likely for the fixation belt to stick and slip as it slides on the heater holding member. Therefore, it is unsatisfactory in terms of the belt movement.
Thus, the present invention was made to improve a fixing apparatus having a heater and a heater holding member, not only in the manner in which the fixation belt slides on the combination of the heater and heater holding member, but also, the manner in which the fixation belt slides on the heater holding member alone, in order to prevent the fixation belt from sticking and slipping as it slides on the combination of the heater and heater holding member.
Thus, the primary object of the present invention is to provide a fixing apparatus which is structured to form a nip between its heater and fixation belt, and yet, is significantly superior to any similarly structured conventional fixing apparatus, in terms of the manner in which the fixation belt slides on the combination of the heater and heater holding member.
According to an aspect of the present invention, there is provided an image fixing device for fixing an image on a recording material, said fixing device comprising: a rotatable fixing film; a heater provided on an inner surface of said fixing belt; a rotatable pressing member provided in contact with an outer peripheral surface of said fixing film to press against said heater through said fixing film, thus forming a nip configured to nip and feed the recording material; a holding member including a guide portion configured to guide the rotation of said fixed in the field and to hold said heater; and a metal sheet which covers said heater and an area of guide portion slidable relative to said fixing film and which is slidable on an inner surface of said fixing film; wherein said metal sheet has a thermal conductivity ≥10 W/(m·° C.) and has a thickness more than 0 μm and not more than 50 μm.
Further features of the present invention will become apparent from the following description of exemplary embodiments (with reference to the attached drawings).
Hereinafter, preferred embodiments of the present invention are described with reference to appended drawings.
First, referring to
1. Image Forming Apparatus (Printer)
The printer shown in
Next, referring to
2. Fixing Apparatus
The fixation belt 111 in this embodiment is a fixing member which is in the form of an endless belt. It comprises: a cylindrical substrative layer which is formed of stainless steel (SUS) and is roughly 50 □m in thickness; an elastic layer which is formed of silicone rubber, on the outward surface of the substrative layer and is roughly 200 □m in thickness; and a piece of tube which is formed of tetrafluoroethylene-perfluoro-alkylvinyl-ether (PFA), in such a manner that it covers the outward surface of the elastic layer, and is roughly 30 □m in thickness. By the way, choice of the material for the substrative layer of the fixing member is not limited to the stainless steel. It may be nickel, heat resistant resinous material such as polyimide, or the like.
A referential code 114 stands for a holding member for holding a heater. The heater holding member 114 is formed of liquid polymer resin, which is heat resistant and rigid.
A heater 113 is the heat source of the fixing apparatus 100. It has: a long, narrow, and flat ceramic substrate; an electrically resistive member which is formed on the ceramic substrate, in a manner to extend in the direction parallel to the lengthwise direction of the substrate, and quickly generates heat as electric current is flowed through it; a protective layer which is formed of glass, in a manner to protect the electrically resistive member; and a pair of electrodes which are formed on the lengthwise ends of the resistive member to apply voltage to the resistive member.
The heater holding member 114 is provided with a groove which extends in the direction parallel to the rotational axis of the fixation belt 111 (which hereafter may be referred to simply as lengthwise direction). The heater 113 is placed in this groove, and is glued to the heater holding member 114 with heat resistant adhesive. The fixation belt 111 is loosely fitted around the heater holding member 114.
A stay 115 is a highly rigid supporting member. It is formed of a sheet of stainless steel. It is U-shaped in cross-section. The heater holding member 114 is fixed to the stay 115, being reinforced by the stay 115.
A referential code 119 stands for a pressure roller as a pressing member. It is made up of a metallic core formed of stainless steel, a roughly 3 mm thick silicone rubber layer formed on the peripheral surface of the metallic core by injection molding, and a piece of roughly 40 μm thick PFA resin tube, which covers the silicone rubber layer. A fixation nip N, which is necessary for fixation and has a preset width, is formed by pressing the combination of the heater holding member 114 and heater 113 against the pressure roller 119 by an unshown pressing mechanism 211, with the positioning of the fixation belt 111 between the combination and pressure roller 119.
The pressure roller 119 is rotationally driven by an unshown driving mechanism 212 in the direction indicated by an arrow mark A at a preset peripheral velocity. Thus, the fixation belt 111, which is remaining pressed upon the peripheral surface of the pressure roller 119, is rotated by the friction which the pressure roller 119 generates between itself and fixation belt 111 as it rotates. The inward surface of the fixation belt 111 is coated with heat-resistant grease, as lubricant, which contains fluorinated resin, in order to ensure that the fixation belt 111 smoothly slides on a thermally conductive sheet 116, which is described later.
A referential code 118 stands for a thermistor as a temperature detecting means. The thermistor 118 is positioned so that it will be at roughly the center of a sheet of recording medium, in terms of the widthwise direction of the fixation belt 111, regardless of sheet size. It detects the temperature of the heater 113. The electrical power to be supplied to the heater 113 is controlled so that the temperature detected by the central thermistor reaches, and remains at, a target level.
While the pressure roller 119 and belt 111 are rotationally driven, and the heater 113 is controlled so that it temperature remains at the target level, a sheet P of recording medium, which is bearing an unfixed toner image, is conveyed to the nip N, and then, is conveyed through the nip N. As the sheet P and the toner image thereon are conveyed through the nip N, remaining pinched between the fixation belt 111 and pressure roller 119, they are heated by the heat which they receive from the heater 113 through the fixation belt 111. Consequently, the toner image becomes fixed to the surface of the sheet P. After being conveyed through the nip N, the sheet P separates from the fixation belt 111 at the exit side of the nip N, because the fixation belt 111 curves diagonally upward at the exit, whereas the sheet P remains straight because of its resiliency.
Next, referring to
In this embodiment, the fixing apparatus 100 is provided with the thermally conductive sheet 116, which is configured and position so that it positioned between the fixation belt 111 and the combination of the heater 113 and holding member 114, in such a manner that, were it not for the thermally conductive sheet 116, the fixation belt 111 would come into contact with the combination, at least while the fixation belt 111 is rotated. While the fixation belt 111 rotates under the pressure, it does not always remain stable in its path. That is, it possibly comes into contact with the heater holding member 114, within ranges F shown in
The thermally conductive sheet 116 is roughly semicircular in cross-section. It is held to the holding member 114 by its widthwise edge portions 116a and 116b (end portions in terms of circumferential direction of fixation belt 111) which are fixed to the holding member 114. Its length is roughly the same as the width of the fixation belt 111.
The material for the thermally conductive sheet 116 is desired not to impede heat transmission from the heater 113 to fixation belt 111. It is desired to be no less than 10 W/(m·° C.) in thermal conductivity λ. Further, it is desired to be no less than 0 μm, and no more than 50 μm, in thickness t.
Further, it is desired that while the fixation belt 111 is sliding on the thermally conductive sheet 116 by its inward surface, it is lower in coefficient of friction, and greater in wear resistance, than the heater holding member 114. In a case where the material for the thermally conductive sheet 116 is metallic, the material is desired to be no less than 60 in Vicker's hardness scale HV as an index for wear resistance. In this embodiment, a sheet of stainless steel (SUS) which is 16 W/(m·° C.) in thermal conductivity λ, 200 in HV, and 20 μm in thickness was used as the material for the thermally conductive sheet 116.
The thermal conductivity of the thermally conductive sheet 116 was measured through the following procedure.
A test piece was cut out of the material for the thermally conductive sheet 116. Then, the thermal diffusivity of the test piece in terms of its thickness direction is measured with the use of a thermal diffusiveness measuring apparatus (Model FTC-1; product of AlVAC Riko Co., Ltd.). Then, the thermal diffusivity of each material in terms of its thickness direction is obtained from the following formula.
Thermal conductivity=thermal diffusivity×specific gravity×specific heat.
The specific gravity of the material is obtained by measuring the specific gravity of the test piece by an electronic gravimeter (model SD-200L; product of Alphamirage Co., Ltd.).
Further, the specific heat of the material was obtained by measuring the specific heat of the test piece by a differential scanning calorimeters (Model DSC8240; product of Rigaku Co., Ltd.).
By the way, choice of the material for the thermally conductive sheet 116 is not limited to the abovementioned ones. It may be metal such as stainless steel, and nickel, or alloys. Further, it may be a sheet of heat-resistant resin such as polyimide (PI), poly phenylene-sulfide (PPS), polyether-ether-keton (PEEK), which is highly wear-resistant.
The fixation belt 111 is supported by a pair of supporting members 112a and 112b fitted in the hollow of the widthwise ends of the fixation belt 111. The holding member 114 is disposed in the hollow of the fixation belt 111 in such a manner that it bridges between the supporting members 112a and 112b. The heater 113 is fixed to the holding member 114 with adhesive. Each of the pair of supporting members 112a and 112b is provided with an unshown semicircular protrusion, which protrudes outward of the supporting member 112 in the direction which is perpendicular to its axial line. Thus, as the fixation belt 111 deviates in position in its widthwise direction, it comes into contact with the protrusion, being thereby prevented from deviating further; it is regulated in position in terms of its widthwise direction. The supporting members are supported by a pair of frames 131a and 131b, respectively, of the fixing apparatus 100, in such a manner that they are allowed to slide relative to the frames 113a and 113b, respectively. It is also by these frames 113a and 113b that the pressure roller 119 is supported. Further, the supporting members 112a and 112b are under the pressure generated toward the pressure roller 119 by a pair of compression springs 132a and 132b, respectively. Thus, the combination of the holding member 114 and heater 113 remains pressed against the pressure roller 119 with the presence of the fixation belt 111 between the combination and pressure roller 119.
As described above, by configuring and positioning the thermally conductive sheet 116 so that it is between the fixation belt 111 and the combination of the heater and heater holding member, and in the area in which the fixation belt will possibly come into contact with the combination if the sheet is not present, it is possible to prevent the occurrence of the problem that the fixation belt unsatisfactorily rotates because the fixation belt 111 “sticks and slips” as it slides on the combination of the heater and heater holding member.
In this embodiment, the fixation belt 111 is suspended and tension by a pair of suspending-tensioning rollers 120a and 120b. In comparison to the fixing apparatus in the first embodiment, the fixing apparatus 100 in this embodiment is kept more stable in the path of the fixation belt 111, by the suspending-tensioning rollers 120. Therefore, while the fixation belt 111 is rotationally driven, the fixation belt 111 always remains in contact with the holding member 114 in the area F. Although
In this embodiment, the holding member 114 is provided with a protrusive portion 114a, which is in the form of roughly half the cylindrical column, and protrudes toward the pressure roller 119 from the downstream edge of the main structure of the holding member 114. The protrusive portion 114a increases in curvature, the portion of the fixation belt 111, which is in contact with the protrusive portion 114a, making it easier for the recording medium to separate from the fixation belt 111.
In a case where the heater holding member 114 has a protrusive portion such as the one in this embodiment, the thermally conductive sheet 116 is desired to be enabled to follow the contour of the protrusive portion 114a, in order to be satisfactory in releasing properties. Further, for the purpose of ensuring that the thermally conductive sheet 116 remains airtightly in contact with the surface of the heater 113 so that heat is efficiently conducted from the heater 113 to the fixation belt 111 through the thermally conductive sheet 116, it is desired that the thermally conductive sheet 116 can follow the contour of the surface of the heater 113. Therefore, it is desired that the thermally conductive sheet 116 is less resistant than the fixation belt 111, to such force that works on the thermally conductive sheet 116 in the direction to bend in the direction perpendicular to the circumferential direction of the fixation belt 111.
In the first to third embodiments, the substrative layer of the fixation belt 111 was formed of stainless steel, and 50 μm in thickness. The other layers (rubber layer and PFA layer) of the fixation belt 111 than the substrative layer are less resistant to bending than the substrative layer. Therefore, the overall resistance of the fixation belt 111 to bending is determined by the resistance of the substrative layer to bending. Further, the thermally conductive sheet 116 was formed of stainless steel, and was 20 μm in thickness, which is less than the thickness of the substrative layer. Therefore, the thermally conductive sheet 116 was less resistant to bending than the fixation belt 111. Therefore, the thermally conductive sheet 116 conformed to the contour of the combination of the heater 113 and heater holding member 114 as described above.
As described above, even if the fixation belt unit is structured so that the portion of the downwardly facing portion of the surface of the holding member 114, which is in the area S in
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2018-204732 filed on Oct. 31, 2018, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2018-204732 | Oct 2018 | JP | national |
