Patent Grant
10859953
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.
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, that 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 copier, 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 formed by the fixing member and pressing member of the apparatus the toner image becomes fixed to the sheet.
In the field of fixing apparatus, such as the one described above, a fixing apparatus that is equipped with a fixing member in the form of a thin belt has been put into practical usage. The belt is relatively small in thermal capacity in order to reduce the length of time (warm-up time) the fixing apparatus takes for the fixing member to heat up to a preset temperature level necessary for the fixing member to fix a toner image, that is, the time from when the fixing apparatus is turned on to the time when it becomes ready for fixation.
Japanese Laid-open Patent Application No. H04-204980 discloses a fixing apparatus that 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, and a pressure roller, as a pressing member. The fixing apparatus 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, the fixing apparatus is structured so that rotation of the pressure roller rotates the fixation belt. As a sheet of recording medium is conveyed through the nip, unfixed toner of an unfixed toner image on the sheet is heated while being pressed. Consequently, the unfixed toner image becomes fixed to the sheet.
Further, Japanese Laid-open Patent Application No. H11-16667 discloses a fixing apparatus that 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 comprising the aforementioned fixing apparatus. This fixing apparatus is structured so that the heater is covered with the thermally conductive plate 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.
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, the friction between the fixation belt and heater holding member was not reduced, making it likely for the fixation belt to stick and slip as it slides on the heater holding member. Therefore, the belt movement of this fixing apparatus is unsatisfactory.
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 one aspect the present invention provides an image fixing device for fixing an image on a recording material. The fixing device includes a rotatable fixing film, a heater, a holding member, and a metal sheet. The heater is provided on an inner surface of the fixing belt. The rotatable pressing member is provided in contact with an outer peripheral surface of the fixing film to press against the heater through the fixing film, thus forming a nip configured to nip and feed the recording material. The holding member includes a guide portion configured to guide the rotation of the fixing film and to hold the heater. The metal sheet covers the heater and an area of guide portion slidable relative to an inner surface of the fixing film. The 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).
Hereafter, 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. The fixation belt 111 comprises a cylindrical substrative layer, an eleastic layer, and a piece of tube. The cylindrial substative layer is formed of stainless steel (SUS) and is roughly 50 μm in thickness. The elastic layer is formed of silicone rubber on the outward surface of the substrative layer and is roughly 200 μm in thickness. The piece of tube 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 μm 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 holding member 114 holds 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. The heater 113 has a long, narrow, and flat ceramic substrate, an electrically resistive member, a protective layer, and a pair of electrodes. The electrically resistive member 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 the electrically resistive member. The protective layer is formed of glass in a manner to protect the electrically resistive member. The pair of electrodes 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. The stay 115 is formed of a sheet of stainless steel. The stay 115 is U-shaped in cross-section. The heater holding member 114 is fixed to the stay 115 and reinforced by the stay 115.
A pressure roller 119, as a pressing member, 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 remains 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 thermistor 118, as a temperature detecting means, 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. The thermistor 118 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 and remain 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 2. 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 when 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 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 using 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, the fixation belt 111 comes into contact with the protrusion, being thereby prevented from deviating further and 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 when the heater holding member 114 has a protrusive portion such as the one in this embodiment, the thermally conductive sheet 116 is desired to follow the contour of the protrusive portion 114a to satisfactorily release. 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 a force that works on the thermally conductive sheet 116 in a bending 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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2018-204732 | Oct 2018 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 20140086651 | Otsu | Mar 2014 | A1 |
| 20160274514 | Ishii | Sep 2016 | A1 |
| 20170097598 | Kudo | Apr 2017 | A1 |
| Number | Date | Country |
|---|---|---|
| H04204980 | Jul 1992 | JP |
| H05119648 | May 1993 | JP |
| H1116667 | Jan 1999 | JP |
| H1116667 | Jan 1999 | JP |
| 2016114743 | Jun 2016 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20200133179 A1 | Apr 2020 | US |
