Fixing apparatus and image forming apparatus

Abstract

To suppress push-in of a separation member to a surface of a rotor.SOLUTION: A fixation device comprises: a first rotor 21; a second rotor 22 which is brought into contact with an outer peripheral surface of the first rotor 21 and forms a nip part N that allows passage of a recording medium P that carries an unfixed image; a heating body 23 which has a resistance heating element 56 and heats the first rotor 21; a nip formation member 24 which is arranged in the first rotor 21 and forms the nip part N by holding the first rotor 21 between the second rotor 22 and itself; and a separation member 28 which separates the recording medium P passing through the nip part N from the first rotor 21. The separation member 28 comprises: a separation part 28a which is arranged in a non-contact manner with the outer peripheral surface of the first rotor 21 and separates the recording medium P from the first rotor 21; and a contact part 28b which is brought into contact with the outer peripheral surface of the first rotor 21. The contact part 28b is arranged at a position that can contact the nip formation member 24 via the first rotor 21.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a fixing device and an image forming apparatus.

Background Art

[0002] In electrophotographic image forming apparatuses such as copiers and printers, a fixing device for fixing a toner image on a recording medium such as paper is mounted.

[0003] Such a fixing device includes a pair of rotating bodies such as a belt or a roller, and heats and presses the recording medium by sandwiching and conveying the recording medium with these rotating bodies to fix the toner image on the recording medium. However, when the recording medium passes between the rotating bodies, the recording medium may stick to the rotating bodies. Therefore, some fixing devices include a separating member for separating the recording medium from the rotating body. The separating member is arranged such that the tip thereof approaches the surface of the rotating body, and when the recording medium passing between the rotating bodies contacts the tip of the separating member, the recording medium is separated from the rotating body.

[0004] In order for the separating member to exhibit a stable separating function, it is preferable that the distance between the tip of the separating member and the surface (outer peripheral surface) of the rotating body is maintained constant. Therefore, in conventional fixing devices, a part of the separating member is brought into contact with the surface of the rotating body so that the tip of the separating member can follow and displace with respect to the variation even when the surface position of the rotating body varies.

[0005] As described above, in the conventional configuration, the distance between the tip of the separating member and the surface of the rotating body is maintained constant by bringing a part of the separating member into contact with the surface of the rotating body. However, if an operator accidentally presses the separating member strongly during maintenance work and the separating member is pressed against the surface of the rotating body, the surface of the rotating body may be damaged.

[0006] Therefore, for example, Patent Document 1 (Japanese Patent Publication No. 2013-186394) proposes a configuration in which arm-shaped restricting parts are provided on the flanges that hold both ends of the belt as a rotating body, to restrict the pushing of the separating member against the belt. This prevents damage to the belt surface because, even if an operator accidentally pushes the separating member too hard, the restricting parts prevent the separating member from being pushed against the surface of the belt.

[0007] However, the configuration of providing an arm-shaped restricting portion on the flange presents challenges in ensuring sufficient strength of the restricting portion from the standpoint of the materials and costs used in the flange. Furthermore, if the restricting portion fails to withstand the load from the separating member and breaks, the separating member may be pressed against the surface of the rotating body, potentially damaging the surface of the rotating body. [Overview of the project] [Problems that the invention aims to solve]

[0008] For the reasons stated above, the objective of the present invention is to suppress the pressing of the separating member against the surface of the rotating body. [Means for solving the problem]

[0009] To solve the above problems, the present invention provides a first rotating body, a second rotating body that contacts the outer circumferential surface of the first rotating body and forms a nip portion through which a recording medium carrying an unfixed image passes, a heating body having a resistance heating element that heats the first rotating body, and a second rotating body disposed inside the first rotating body. of A fixing device comprising: a nip-forming member that forms the nip portion by sandwiching the first rotating body between itself and the rotating body; and a separating member that separates the recording medium passing through the nip portion from the first rotating body, The separating member is configured to be displaceable in a direction toward or toward the outer circumferential surface of the first rotating body, The separating member is the first of The recording medium has a separation portion that is positioned non-contact with the outer circumferential surface of the rotating body and separates the recording medium from the first rotating body, and a contact portion that contacts the outer circumferential surface of the first rotating body, wherein the contact portion is positioned to be able to contact the nip forming member via the first rotating body. When the separating member is pushed toward the first rotating body, the contact portion contacts the nip forming member via the first rotating body, and the separating member is supported by the nip forming member. It is characterized by the following: [Effects of the Invention]

[0010] According to the present invention, it is possible to suppress the pressing of the separating member against the surface of the rotating body. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic diagram of an image forming apparatus according to one embodiment of the present invention. [Figure 2] This is a side cross-sectional view of the fixing device according to this embodiment. [Figure 3] This is a perspective view of the fixing device according to this embodiment. [Figure 4] This is an exploded perspective view of the fixing device according to this embodiment. [Figure 5] This is a cross-sectional view of the fixing belt according to this embodiment. [Figure 6] This is a plan view of the heater according to this embodiment. [Figure 7] This is a perspective view showing the heater according to this embodiment with a connector, which serves as a power supply component, connected to it. [Figure 8] This is a diagram illustrating the deformation of the anchoring belt. [Figure 9] This figure shows a configuration for suppressing the pressing of the separation plate against the fixing belt. [Figure 10] This is a perspective view showing the configuration of the guide portion of the nip-forming member according to this embodiment. [Figure 11] This is a plan view showing the position of the contact portion of the separation plate according to this embodiment. [Figure 12] This figure shows an example where the guide portion of the nip-forming member has a continuous surface along the longitudinal direction of the fixing belt. [Figure 13] This figure shows an example where the tip of the separation plate is positioned closer to the fixing belt than the center, towards both ends. [Figure 14] This figure shows an example where the nip-forming member protrudes further towards the pressure roller than the heater. [Figure 15]It is a diagram showing an example in which the pressure roller is pressed toward the fixing belt. [Figure 16] It is a diagram showing a pressure release mechanism for releasing the pressure contact state between the fixing belt and the pressure roller. [Figure 17] It is a diagram showing an example of a fixing device including a nip forming member that does not hold a heater. [Figure 18] It is a diagram showing the configuration of a halogen heater. [Figure 19] It is a cross-sectional view of a fixing belt having no elastic layer. [Figure 20] It is a plan view of a heater having a plurality of resistance heating elements. [Figure 21] It is a diagram showing the configuration of a fixing device different from the above-described embodiment. [Figure 22] It is a diagram showing the configuration of a fixing device different from the above-described embodiment. [Figure 23] It is a diagram showing the configuration of a fixing device different from the above-described embodiment. [Figure 24] It is a diagram showing the configuration of an image forming apparatus different from the above-described embodiment. [Figure 25] It is a diagram showing the configuration of the fixing device shown in FIG. 24. [Figure 26] It is a plan view of the heater shown in FIG. 25. [Figure 27] It is a perspective view of the heater and the nip forming member shown in FIG. 25. [Figure 28] It is a diagram showing a method of attaching a connector to the heater shown in FIG. 25. [Figure 29] It is a diagram showing the arrangement of the temperature sensor and the thermostat provided in the fixing device shown in FIG. 24. [Figure 30] It is a diagram showing the groove portion of the flange shown in FIG. 28. [Figure 31] It is a diagram showing the configuration of a fixing device different from the above-described embodiment. [Figure 32] It is a perspective view of the heater, the first high heat conduction member, and the nip forming member shown in FIG. 31. [Figure 33] It is a plan view of the heater showing the arrangement of the first high heat conduction member. [Figure 34] This is a plan view of a heater showing another example of the arrangement of the first high-heat-conductivity member. [Figure 35] This is a plan view of a heater showing yet another example of the arrangement of the first high-heat-conductivity member. [Figure 36] This is a plan view of the heater showing the enlarged division area. [Figure 37] This figure shows a configuration of a fixing device that differs from the embodiment described above. [Figure 38] Figure 37 is a perspective view of the heater, first high heat conduction member, second high heat conduction member, and nip forming member shown. [Figure 39] This is a plan view of the heater showing the arrangement of the first high-heat-conducting member and the second high-heat-conducting member. [Figure 40] This is a plan view of a heater showing another example of the arrangement of the first and second high-heat-conductivity members. [Figure 41] This is a plan view of a heater showing yet another example of the arrangement of the second high-heat-conductivity member. [Figure 42] This figure shows a configuration of a fixing device that differs from the embodiment described above. [Figure 43] This is a diagram showing the atomic crystal structure of graphene. [Figure 44] Diagram showing the atomic crystal structure of graphite [Modes for carrying out the invention]

[0012] The present invention will be described below with reference to the attached drawings. In each drawing used to explain the present invention, components such as members and parts having the same function or shape will be given the same reference numerals to the extent possible so that they can be distinguished, and their description will be omitted after they have been described once.

[0013] Figure 1 is a schematic diagram of an image forming apparatus according to one embodiment of the present invention. Here, "image forming apparatus" in this specification includes printers, copiers, facsimile machines, printing presses, or multifunction devices that combine two or more of these. Furthermore, "image forming" as used in the following description means not only forming images that have meaning, such as characters and figures, but also forming images that do not have meaning, such as patterns. First, the overall configuration and operation of the image forming apparatus according to this embodiment will be described with reference to Figure 1.

[0014] As shown in Figure 1, the image forming apparatus 100 according to this embodiment includes an image forming unit 200 for forming an image on a sheet-like recording medium such as paper, a fixing unit 300 for fixing the image on the recording medium, a recording medium supply unit 400 for supplying the recording medium to the image forming unit 200, and a recording medium discharge unit 500 for discharging the recording medium outside the apparatus.

[0015] The image forming unit 200 includes four process units 1Y, 1M, 1C, and 1Bk as image forming units, an exposure apparatus 6 that forms an electrostatic latent image on the photoreceptor 2 provided in each process unit 1Y, 1M, 1C, and 1Bk, and a transfer apparatus 8 that transfers the image to a recording medium.

[0016] Each process unit 1Y, 1M, 1C, and 1Bk has essentially the same configuration, except that they contain toners (developers) of different colors: yellow, magenta, cyan, and black, which correspond to the color separation components of a color image. Specifically, each process unit 1Y, 1M, 1C, and 1Bk includes a photoreceptor 2 as an image carrier that carries an image on its surface, a charging member 3 that charges the surface of the photoreceptor 2, a developing device 4 that supplies toner as a developer to the surface of the photoreceptor 2 to form a toner image, and a cleaning member 5 that cleans the surface of the photoreceptor 2.

[0017] The transfer device 8 comprises an intermediate transfer belt 11, a primary transfer roller 12, and a secondary transfer roller 13. The intermediate transfer belt 11 is an endless belt member and is stretched by a plurality of support rollers. Four primary transfer rollers 12 are provided inside the intermediate transfer belt 11. Each primary transfer roller 12 contacts each photoreceptor 2 via the intermediate transfer belt 11, thereby forming a primary transfer nip between the intermediate transfer belt 11 and each photoreceptor 2. The secondary transfer rollers 13 contact the outer circumferential surface of the intermediate transfer belt 11, forming a secondary transfer nip.

[0018] In the fixing section 300, a fixing device 20 is provided. The fixing device 20 includes a fixing belt 21 made of an endless belt, and a pressure roller 22 as an opposing member facing the fixing belt 21. The fixing belt 21 and the pressure roller 22 contact each other on their respective outer surfaces, forming a nip section (fixing nip).

[0019] The recording medium supply unit 400 is provided with a paper feed cassette 14 for storing paper P as a recording medium, and a paper feed roller 15 for feeding paper P from the paper feed cassette 14. Hereinafter, "recording medium" will be described as "paper," but "recording medium" is not limited to paper. "Recording medium" includes not only paper but also OHP sheets or fabrics, metal sheets, plastic films, or prepreg sheets made by pre-impregnating carbon fibers with resin. Furthermore, "paper" includes not only plain paper but also cardboard, postcards, envelopes, thin paper, coated paper (such as coated paper and art paper), tracing paper, etc.

[0020] The recording medium discharge unit 500 is provided with a pair of paper discharge rollers 17 for discharging the paper P to the outside of the image forming apparatus, and a paper discharge tray 18 for placing the paper P discharged by the paper discharge rollers 17.

[0021] Next, the printing operation of the image forming apparatus 100 according to this embodiment will be described with reference to Figure 1.

[0022] When printing is started in the image forming apparatus 100, the photoreceptors 2 of each process unit 1Y, 1M, 1C, 1Bk and the intermediate transfer belt 11 of the transfer device 8 begin to rotate. At the same time, the paper feed roller 15 begins to rotate, and paper P is fed out from the paper feed cassette 14. The fed paper P comes to rest upon contact with a pair of timing rollers 16, and the transport of paper P is temporarily stopped until the image to be transferred to paper P is formed.

[0023] In each process unit 1Y, 1M, 1C, and 1Bk, first, the surface of the photoreceptor 2 is charged to a uniform high potential by the charging member 3. Next, based on the image information of the original document read by the document reader or the print image information instructed to print from the terminal, the exposure unit 6 exposes the surface (charged surface) of each photoreceptor 2. As a result, the potential of the exposed area decreases, and an electrostatic latent image is formed on the surface of each photoreceptor 2. Then, the developing unit 4 supplies toner to this electrostatic latent image, and a toner image is formed on each photoreceptor 2. As the toner image formed on each photoreceptor 2 reaches the primary transfer nip (position of the primary transfer roller 12) as the photoreceptor 2 rotates, it is transferred sequentially onto the rotating intermediate transfer belt 11. Thus, a full-color toner image is formed on the intermediate transfer belt 11. Furthermore, in the image forming apparatus 100, a monochrome image can be formed using any one of the process units 1Y, 1M, 1C, or 1Bk, or a two-color or three-color image can be formed using any two or three of the process units. After the toner image is transferred from the photoreceptor 2 to the intermediate transfer belt 11, residual toner and other contaminants on each photoreceptor 2 are removed by the cleaning member 5.

[0024] The toner image transferred onto the intermediate transfer belt 11 is transported to the secondary transfer nip (the position of the secondary transfer roller 13) as the intermediate transfer belt 11 rotates, and is transferred onto the paper P that has been transported by the timing roller 16. The paper P is then transported to the fuser unit 20, where the toner image on the paper P is heated and pressurized by the fuser belt 21 and the pressure roller 22, thereby fixing the toner image to the paper P. The paper P is then transported to the recording medium discharge unit 500 and discharged into the paper discharge tray 18 by the paper discharge roller 17. This completes the series of printing operations.

[0025] Next, the configuration of the fixing device according to this embodiment will be described in detail based on Figures 2 to 7.

[0026] As shown in Figure 2, the fixing device 20 according to this embodiment includes a fixing belt 21 and a pressure roller 22, as well as a heater 23, a nip forming member 24, a stay 25, a temperature sensor 27, a separation plate 28, and the like.

[0027] The fixing belt 21 is a rotating body (first rotating body or fixing member) that contacts the unfixed toner-carrying surface of the paper P to fix the unfixed toner (unfixed image) to the paper P, and is composed of a flexible, endless belt. The diameter of the fixing belt 21 is set to, for example, 15 to 120 mm. In this embodiment, the inner diameter of the fixing belt 21 is set to 25 mm.

[0028] As shown in Figure 5, the fixing belt 21 according to this embodiment has a base material 210, an elastic layer 211, and a release layer 212 laminated in order from the inner circumferential surface to the outer circumferential surface, and its overall thickness is set to 1 mm or less. The base material 210 has a layer thickness of 30 to 50 μm and is made of a metal material such as nickel or stainless steel, or a resin material such as polyimide. The elastic layer 211 has a layer thickness of 100 to 300 μm and is made of a rubber material such as silicone rubber, foamed silicone rubber, or fluororubber. Because the fixing belt 21 has an elastic layer 211, minute irregularities are not formed on the surface of the fixing belt 21 in the nip portion, so that heat is more easily transferred uniformly to the toner image on the paper P. The release layer 212 has a layer thickness of 10 to 50 μm and is made of a material such as PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer), PTFE (polytetrafluoroethylene), polyimide, polyetherimide, or PES (polyether sulfide). The fixing belt 21 has a release layer 212, which ensures release properties (peelability) from the toner (toner image).

[0029] As shown in Figure 2, the pressure roller 22 is a rotating body (second rotating body or opposing member) positioned opposite the outer circumferential surface of the fixing belt 21.

[0030] The pressure roller 22 is, for example, a roller with an outer diameter set to 25 mm, and has a hollow iron core material 220, an elastic layer 221 provided on the outer surface of the core material 220, and a release layer 222 provided on the outer surface of the elastic layer 221. The elastic layer 221 has a thickness of, for example, 3.5 mm and is made of silicone rubber or the like. The release layer 222 has a thickness of, for example, about 40 μm and is made of fluororesin or the like.

[0031] The heater 23 is a heating element that heats the fixing belt 21. As shown in Figure 2, the heater 23 is positioned inside the fixing belt 21 and is in contact with the inner circumferential surface of the fixing belt 21. Furthermore, the heater 23 in this embodiment is a planar or plate-shaped heater and extends longitudinally along the longitudinal direction of the fixing belt 21 (the paper width direction intersecting the paper transport direction).

[0032] As shown in Figure 6, the heater 23 has a plate-shaped base material 55 that extends in one direction (in the direction of arrow X in Figure 6). The base material 55 is positioned so that its longitudinal direction X is aligned with the longitudinal direction of the fixing belt 21 or the axial direction of the pressure roller 22. On the surface of the base material 55, two resistance heating elements 56 are arranged side by side in the longitudinal direction Y of the base material 55, extending in the longitudinal direction X of the base material 55. Here, "short direction" refers to the direction perpendicular to the longitudinal direction X along the surface of the base material 55 on which the resistance heating elements 56 are provided, and means the same direction as the longitudinal direction of the fixing belt 21, the axial direction of the pressure roller 22, and the paper transport direction in which the paper is transported.

[0033] As shown in Figure 6, a pair of electrode portions 58 are provided on one end of the base material 55 in the longitudinal direction X. Each electrode portion 58 is connected to each resistance heating element 56 via a power supply line 59. On the other hand, the ends of each resistance heating element 56 opposite to the ends connected to the electrode portions 58 are connected to each other via another power supply line 59. Each resistance heating element 56 and each power supply line 59 are covered with an insulating layer 57 to ensure insulation. In contrast, each electrode portion 58 is exposed and not covered by the insulating layer 57 so that a connector, which will be used as a power supply terminal as described later, can be connected to it.

[0034] The base material 55 is made of a material with excellent heat resistance and insulation properties, such as ceramics like alumina or aluminum nitride, glass, mica, or polyimide. Alternatively, the base material 55 may be a metal material (conductive material) such as stainless steel (SUS), iron, or aluminum, with an insulating layer formed on top. In particular, if the base material 55 is a highly thermally conductive material such as aluminum, copper, silver, graphite, or graphene, the uniformity of heating the heater 23 can be improved, enhancing image quality. The insulating layer 57 is made of a material with excellent heat resistance and insulation properties, such as ceramics like alumina or aluminum nitride, glass, mica, or polyimide. The resistive heating element 56 is formed, for example, by coating the surface of the base material 55 with a paste made of silver palladium (AgPd) and glass powder by screen printing, and then firing the base material 55. It is also possible to use a resistive material such as silver alloy (AgPt) or ruthenium oxide (RuO2) as the material for the resistive heating element 56. Furthermore, the electrode portion 58 and the power supply line 59 are formed by screen printing silver (Ag) or silver-palladium (AgPd).

[0035] Returning to Figure 2, in this embodiment, the resistance heating element 56 is provided on the surface of the base material 55 that faces the pressure roller 22. Alternatively, the resistance heating element 56 may be provided on the surface of the base material 55 opposite to the pressure roller 22. In that case, since the heat from each resistance heating element 56 is transferred to the fixing belt 21 via the base material 55, it is preferable that the base material 55 be made of a material with high thermal conductivity, such as aluminum nitride.

[0036] The nip-forming member 24 is positioned inside the fixing belt 21 and forms a nip portion N between itself and the pressure roller 22, sandwiching the fixing belt 21 between them. The nip-forming member 24 holds a heater 23 on the side facing the pressure roller 22, and the fixing belt 21 is pressurized between the heater 23 and the pressure roller 22, thereby forming a nip portion N between the fixing belt 21 and the pressure roller 22. Since the nip-forming member 24 is prone to becoming hot due to the heat from the heater 23, it is preferable that it be made of a heat-resistant material. For example, if the nip-forming member 24 is made of a heat-resistant resin with low thermal conductivity such as LCP or PEEK, the heat resistance of the nip-forming member 24 is ensured while heat transfer from the heater 23 to the nip-forming member 24 is suppressed, so the fixing belt 21 can be heated efficiently.

[0037] Furthermore, as shown in Figure 2, the nip-forming member 24 has a guide portion 24a that guides the fixing belt 21. The guide portion 24a has an arc-shaped cross-section that follows the inner circumferential surface of the fixing belt 21 and is positioned upstream and downstream of the center M of the nip portion N in the paper feeding direction (recording medium passing direction) A of the paper P passing through the nip portion N. In this embodiment, the guide portion 24a is integrally configured with the nip-forming member 24, but the guide portion 24a may be a separate component from the nip-forming member 24.

[0038] The stay 25 is a support member that supports the nip-forming member 24. As shown in Figure 2, the stay 25 supports the side of the nip-forming member 24 opposite to the side facing the pressure roller 22 along the longitudinal direction of the fixing belt 21. This suppresses the bending of the nip-forming member 24 and the heater 23 due to the pressure applied by the pressure roller 22, and a nip portion N of uniform width is formed between the fixing belt 21 and the pressure roller 22. To ensure its rigidity, the stay 25 is preferably made of an iron-based metal material such as SUS or SECC.

[0039] The temperature sensor 27 is a temperature sensing member that detects the temperature of the heater 23. Known temperature sensors such as thermopiles, thermostats, thermistors, or NC sensors can be used as the temperature sensor 27. As shown in Figure 2, in this embodiment, the temperature sensor 27 is positioned to contact the side of the heater 23 opposite to the pressure roller 22 side. Furthermore, the temperature sensor 27 is not limited to a contact-type temperature sensor; it may also be a non-contact type temperature sensor that does not contact the heater 23 and detects the ambient temperature near the heater 23.

[0040] The separation plate 28 is positioned downstream of the nip N in the paper transport direction and is a separation member that separates the paper P after it has passed the nip N from the surface of the fixing belt 21. As shown in Figure 2, the separation plate 28 has a separation portion 28a that is not in contact with the outer circumferential surface of the fixing belt 21, a contact portion 28b that is in contact with the outer circumferential surface of the fixing belt 21, and a support shaft portion 28c that is attached to the side wall portion 33 of the fixing device (see Figure 4).

[0041] The separation portion 28a is a plate-shaped part positioned downstream of the nip portion N in the paper feeding direction, close to the surface (outer peripheral surface) of the fixing belt 21, and contacts the paper P after it has passed through the nip portion N, separating the paper P from the surface of the fixing belt 21. Furthermore, the separation portion 28a is positioned over a range larger than the maximum paper feeding area (maximum recording medium passing area) through which the widest paper passes, so that various widths of paper can be separated. On the other hand, the contact portion 28b is a part that contacts the outer peripheral surface of the fixing belt 21, downstream of the nip portion N in the paper feeding direction. The support shaft portion 28c is provided at both longitudinal ends of the separation plate 28 and is inserted into the holes 33c (see Figure 4) provided in the side wall portion 33. By rotatably inserting the support shaft portion 28c into the holes 33c of the side wall portion 33, the separation plate 28 (the tip portion of the separation portion 28a) is supported so as to be displaceable in the direction of approaching and moving away from the outer peripheral surface of the fixing belt 21. Furthermore, as shown in Figure 2, a spring 29, which acts as a biasing member such as a torsion spring, is attached to the support shaft portion 28c. This spring 29 biases the separation plate 28 toward the outer circumferential surface of the anchoring belt 21, so that the contact portion 28b is basically held in contact with the outer circumferential surface of the anchoring belt 21. Note that the biasing member that biases the separation plate 28 toward the anchoring belt 21 may be composed of other members such as a magnet or a weight, in addition to a spring such as a torsion spring.

[0042] As shown in Figures 3 and 4, the fixing device 20 according to this embodiment includes a rectangular frame-shaped device frame 30. The device frame 30 is composed of a first device frame 31 having a pair of side walls 33 and a front wall 34 integrally, and a second device frame 32 having a rear wall 35. The first device frame 31 and the second device frame 32 are assembled by the engagement of a plurality of engaging protrusions 33a provided on the pair of side walls 33 with a plurality of engaging holes 35a provided on the rear wall 35.

[0043] Various components, such as the fixing belt 21 and the pressure roller 22, are supported by a pair of side walls 33. Therefore, each side wall 33 is provided with a through groove 33b for inserting the rotation shaft of the pressure roller 22. The through groove 33b opens at one end (the rear wall 35 side) and has a non-opening abutment at the opposite end. A bearing 36 is provided in this abutment to rotatably support the rotation shaft of the pressure roller 22. When the pressure roller 22 is supported by each side wall 33, the drive transmission gear 37, which acts as a drive transmission member and is provided at one axial end of the pressure roller 22, is positioned so that it is exposed to the outside of the side wall 33. As a result, when the fixing device 20 is mounted on the image forming apparatus body, the drive transmission gear 37 is connected to a gear provided on the image forming apparatus body, enabling the transmission of driving force from the drive source. Alternatively, instead of the drive transmission gear 37, drive transmission members such as pulleys for tensioning the drive transmission belt or coupling mechanisms may be used.

[0044] A pair of belt holding members 26 (see Figure 4) are attached to both ends of the fixing belt 21 in the longitudinal direction, serving as rotatable holding members that rotatably hold the fixing belt 21. The pair of belt holding members 26 have cylindrical or C-shaped holding portions 26a that are inserted inside the fixing belt 21. By inserting these holding portions 26a inside both ends of the fixing belt 21, the fixing belt 21 is rotatably held. Guide grooves 26b are also formed in each belt holding member 26. As shown in Figure 4, with the pair of belt holding members 26, the fixing belt 21, the stay 25, the nip forming member 24, and the heater 23 assembled, each belt holding member 26 is assembled to each side wall portion 33 by inserting the guide groove 26b of each belt holding member 26 along the edge of the insertion groove 33b of each side wall portion 33. As a result, the fixing belt 21, stay 25, nip forming member 24, and heater 23 are supported by their respective side walls 33. Furthermore, each belt holding member 26 is biased by a pair of pressure springs 38, which act as pressurizing members provided between it and the rear wall 35, thereby pressurizing the fixing belt 21 against the pressure roller 22 and forming a nip portion.

[0045] Figure 7 is a perspective view showing the state in which the connector 40, which serves as a power supply component, is connected to the heater 23.

[0046] As shown in Figure 7, the connector 40 has a resin housing 41, a plurality of contact terminals 42 provided on the housing 41, and a power supply harness 43 connected to each contact terminal 42. Each contact terminal 42 is made of an elastically deformable member such as a leaf spring.

[0047] As shown in Figure 7, the connector 40 is attached so as to sandwich the heater 23 and the nip forming member 24 together. In this way, the heater 23 and the nip forming member 24 are held together by the connector 40. In this state, the tips (contact portions 42a) of each contact terminal 42 of the connector 40 elastically contact (pressure contact) with the corresponding electrode portion 58, thereby electrically connecting each contact terminal 42 and each electrode portion 58. This makes it possible to supply power to the heater 23 (each resistance heating element 56) from the power supply of the image forming apparatus via the connector 40.

[0048] The fixing device 20 according to this embodiment operates as follows.

[0049] When printing is started in the image forming apparatus, driving force is transmitted to the pressure roller 22 via the drive transmission gear 37, causing the pressure roller 22 to rotate. The driving force of the pressure roller 22 is then transmitted to the fixing belt 21, causing the fixing belt 21 to rotate in response. Power is also supplied to the heater 23, and the fixing belt 21 is heated by the heat generated by the heater 23. At this time, the temperature of the heater 23 is detected by the temperature sensor 27, and the amount of heat generated by the heater 23 is controlled based on the detected temperature, so that the temperature of the fixing belt 21 is maintained at a temperature at which the image can be fixed (fixing temperature). As shown in Figure 2, the paper P carrying the unfixed image (toner image) is transported between the fixing belt 21 and the pressure roller 22 (nip section N), so the paper P is heated and pressurized, and the toner image is fixed to the paper P.

[0050] Furthermore, when the paper P on which the toner image has been fixed passes between the fixing belt 21 and the pressure roller 22 (nip section N), it comes into contact with the separation plate 28, thereby separating it from the fixing belt 21 and being discharged. More specifically, after the leading edge of the paper P comes into contact with the leading edge of the separation section 28a of the separation plate 28, the paper P is transported along the separation section 28a, thereby separating the paper P from the outer surface of the fixing belt 21.

[0051] Here, since the fixing belt 21 is made of a flexible material, it is basically in a deformable state except at the nip portion N. Therefore, when the fixing belt 21 stops rotating and enters a stationary state, it deforms to spread out in the vertical direction of the figure, as shown by the solid line in Figure 8. On the other hand, when the fixing belt 21 is heated and sufficient time has elapsed since the fixing belt 21 started rotating, the fixing belt 21 takes on a shape close to a circle, as shown by the dashed line in Figure 8. In other words, when the fixing belt 21 starts rotating from its deformed state when stationary, it gradually becomes a stable circular shape as time passes.

[0052] As described above, the rotational trajectory of the anchoring belt 21 changes when it transitions from a stationary state to a normal rotational state. If the distance between the separating plate 28 and the anchoring belt 21 changes due to this change in rotational trajectory, the separating function of the separating plate 28 will not be able to be performed stably. Therefore, in this embodiment, a part of the separating plate 28 (contact portion 28b) is in contact with the outer surface of the anchoring belt 21. As a result, even if the rotational trajectory of the anchoring belt 21 changes, the separating plate 28 (contact portion 28b) displaces in accordance with that change, so that the distance between the separating plate 28 (tip of the separating portion 28a) and the anchoring belt 21 can be kept constant, and the separating function can be performed stably. In this embodiment, the contact portion 28b is provided only on both ends in the longitudinal direction of the separating plate 28 (see Figures 3 and 4), so the contact portion 28b displaces in accordance with the change in the rotational trajectory on both ends in the longitudinal direction of the anchoring belt 21. However, since the change in the rotational trajectory of the anchoring belt 21 occurs uniformly along the entire longitudinal direction of the anchoring belt 21, the separation plate 28 can follow the change in the rotational trajectory on the central side of the anchoring belt 21 by following the contact portion 28b, and the separation function of the separation plate 28 can be stably performed.

[0053] Incidentally, if paper jams and becomes stuck in the fuser unit during the fixing process, the operation of the image forming apparatus, including the fuser unit, may be stopped, and a service technician or user may perform a procedure to remove the jammed paper. If the operator accidentally presses the separator plate too hard during this removal procedure, the contact portion of the separator plate may be pressed against the surface of the fuser belt, potentially damaging the surface of the fuser belt.

[0054] Therefore, in the fixing device according to this embodiment, the following measures are taken to prevent damage to the fixing belt caused by the pressing of the separation plate as described above.

[0055] Figure 9 shows the configuration for suppressing the pressing of the separation plate 28 against the fixing belt 21 in this embodiment.

[0056] As shown in Figure 9, in this embodiment, the contact portion 28b of the separation plate 28 is positioned to be able to contact the nip-forming member 24 via the fixing belt 21. Here, "position where contact is possible" means a position where, when the separation plate 28 is displaced in a direction approaching the fixing belt 21 (in the inner diameter direction of the fixing belt 21), the contact portion 28b of the separation plate 28 can contact the nip-forming member 24 via the fixing belt 21. Therefore, the contact portion 28b does not always have to be in contact with the nip-forming member 24 via the fixing belt 21. For example, if a gap is created between the inner circumferential surface of the fixing belt 21 and the nip-forming member 24 during the rotation of the fixing belt 21, the contact portion 28b does not have to be in contact with the nip-forming member 24 via the fixing belt 21 (see Figure 8).

[0057] Furthermore, in this embodiment, the guide portion 24a of the nip-forming member 24 is positioned opposite the contact portion 28b of the separation plate 28 via the fixing belt 21. Therefore, when the separation plate 28 is displaced in a direction approaching the fixing belt 21, the contact portion 28b of the separation plate 28 comes into contact with the guide portion 24a of the nip-forming member 24 via the fixing belt 21.

[0058] Furthermore, as shown in Figure 10, in this embodiment, multiple guide portions 24a of the nip-forming member 24 are arranged at equal intervals along the longitudinal direction (arrow X direction) of the fixing belt 21. Therefore, the contact portion 28b is positioned to be able to contact at least one of these guide portions 24a (see Figure 11). The contact portion 28b may be formed to be larger than the spacing D between adjacent guide portions 24a (see Figure 11), so that the contact portion 28b contacts two or more guide portions 24a.

[0059] Thus, in this embodiment, the contact portion 28b of the separation plate 28 is positioned to be able to contact the nip forming member 24 via the fixing belt 21. Therefore, even if an operator accidentally pushes the separation plate 28 too hard toward the fixing belt 21 during the jammed paper removal process, the contact portion 28b will contact the nip forming member 24, and the separation plate 28 will be supported by the nip forming member 24. This suppresses the pushing of the separation plate 28 toward the fixing belt 21, thereby preventing damage to the fixing belt 21 caused by the pushing of the separation plate 28.

[0060] Furthermore, in this embodiment, compared to the configuration described in Patent Document 1, in which an arm-shaped restricting portion is formed by extending from the flange, it is easier to ensure the strength of the portion that supports the separation plate 28 (guide portion 24a). That is, in this embodiment, when the guide portion 24a receives a load from the separation plate 28, the load is received by the main body portion of the nip forming member 24 (the portion that holds the heater 23), so damage and deformation of the guide portion 24a are less likely to occur. For this reason, according to the configuration of this embodiment, it is possible to more reliably prevent the separation plate 28 from being pressed against the fixing belt 21.

[0061] Furthermore, according to the configuration of this embodiment, since the pushing of the separation plate 28 can be suppressed using the existing nip-forming member 24, there is no need to add any new members, and damage to the fixing belt 21 due to the pushing of the separation plate 28 can be prevented at low cost.

[0062] The material constituting the separation plate 28 is not particularly limited, and for example, resin materials or metal materials can be used. However, since the contact portion 28b of the separation plate 28 contacts the outer surface of the fixing belt 21, it is preferable that it be made of an elastic material. When the contact portion 28b (especially the contact surface) is made of an elastic material, wear of the outer surface of the fixing belt 21 due to contact by the contact portion 28b can be suppressed, and its lifespan can be extended. In addition, when the contact portion 28b is pressed against the nip forming member 24, the pressing load can be distributed, and the occurrence of indentation in the fixing belt 21 can be prevented. Examples of elastic materials used for the contact portion 28b include foamed materials such as resin or nonwoven fabrics, and an elastic material with a low coefficient of friction is preferred.

[0063] Furthermore, in Figure 11, if W is the paper feeding area (recording medium passing area) through which the paper passes through the fixing device 20, it is preferable that the contact portion 28b contacts the outer surface of the fixing belt 21 outside the paper feeding area W, i.e., in the non-paper feeding area (non-passing area where the recording medium does not pass). By the contact portion 28b contacting the outer surface of the fixing belt 21 in the non-paper feeding area, wear and damage to the outer surface of the fixing belt 21 in the paper feeding area can be avoided, and fixing defects such as image unevenness can be prevented. If the fixing device 20 is configured to be able to feed paper of different width sizes, it is preferable that the contact portion 28b is positioned to contact the outer surface of the fixing belt 21 in areas other than the maximum paper feeding area (non-paper feeding area).

[0064] Furthermore, it is preferable that the contact portion 28b is positioned so that the inner circumferential surface of the fixing belt 21 does not come into contact with the nip forming member 24 during rotation. This suppresses wear of the fixing belt 21 caused by the inner circumferential surface of the fixing belt 21 coming into contact with the nip forming member 24, thereby extending the lifespan of the fixing belt 21 and preventing image defects caused by uneven fixing between worn areas and other areas of the fixing belt 21.

[0065] Furthermore, if the region where the resistance heating element 56 of the heater 23 is located in the longitudinal direction of the fixing belt 21 is denoted as Z (see Figure 10), then, as shown in Figure 11, it is preferable that the contact portion 28b contacts the outer circumferential surface of the fixing belt 21 in regions other than region Z where the resistance heating element 56 of the heater 23 is located. This prevents heat from being lost from the region (region Z) where the fixing belt 21 is heated by the resistance heating element 56 to the separation plate 28 via the contact portion 28b, thereby preventing fixing failure due to a localized temperature drop of the fixing belt 21.

[0066] In this embodiment, the contact portion 28b of the separation plate 28 is brought into contact with at least one of the multiple guide portions 24a of the nip forming member 24. However, as shown in the example in Figure 12, the multiple guide portions 24a may be made continuous along the longitudinal direction (arrow X direction) of the fixing belt 21 to form a smooth curved surface portion 240. The contact portion 28b may then be brought into contact with this smooth curved surface portion 240 along the longitudinal direction. In this case, since the inner circumferential surface of the fixing belt 21 does not come into contact with the edge of the guide portion 24a at the point where the contact portion 28b makes contact, wear and damage to the fixing belt 21 due to contact with the edge can be suppressed.

[0067] Furthermore, the distance between the tip of the separation plate 28 (separation section 28a) and the outer surface of the fixing belt 21 may be constant along the longitudinal direction of the fixing belt 21 (see Figure 11), or it may vary as shown in the example in Figure 13. In the example shown in Figure 13, the tip 280 of the separation section 28a is formed in a concave curve shape so as to be closer to the outer surface of the fixing belt 21 at both ends than at the center in the longitudinal direction (arrow X direction) of the fixing belt 21. In this case, the distance between the tip 280 of the separation section 28a and the outer surface of the fixing belt 21 is smaller at both ends than at the center in the longitudinal direction of the fixing belt 21 (e1>e2). Generally, paper tends to be more difficult to separate at both ends than at the center in the longitudinal direction of the fixing belt 21. Therefore, as shown in the example in Figure 13, by bringing the tip 280 of the separation section 28a closer to the fixing belt 21 at both ends (reducing the distance), separation performance at both ends can be improved.

[0068] Furthermore, to improve separation, the nip-forming member 24 (particularly the part enclosed by the circle in the figure) may be made to protrude further toward the pressure roller 22 than the heater 23, as shown in the example in Figure 14. In this example, the recess 241 of the nip-forming member 24 that houses the heater 23 is formed to be deeper than the thickness of the heater 23, and the opening edge of the recess 241 (the part enclosed by the circle) protrudes further toward the pressure roller 22 than the heater 23. With this configuration, downstream of the center M of the nip portion N in the paper feeding direction A, the trajectory of the fixing belt 21 deforms so as to bulge toward the pressure roller 22 (the curvature increases), making it easier for the paper to separate from the fixing belt 21.

[0069] In this embodiment, the fixing belt 21 is pressed against the pressure roller 22 by the pressure spring 38 shown in Figure 4, but conversely, the pressure roller 22 may be pressed against the fixing belt 21. For example, as shown in the example in Figure 15, the pressure roller 22 may be pressed against the fixing belt 21 by the pressure spring 39 and pressure lever 45, which act as pressurizing members. In the case where the pressure roller 22 is pressed against the fixing belt 21, the positions of the nip forming member 24 and the heater 23 are fixed, so the position of the fixing belt 21 is stabilized. As a result, the relative positional relationship between the fixing belt 21 and the separation plate 28 is also stabilized, and the separation function of the separation plate 28 is also more stable.

[0070] Furthermore, as shown in the example in Figure 16, the fixing device 20 may also be equipped with a depressurization mechanism 44 for releasing the pressure contact between the fixing belt 21 and the pressure roller 22. In this case, the pressure lever 45 is pushed in the opposite direction to the pressure direction by rotating the cam member 46, thereby releasing the pressure contact between the fixing belt 21 and the pressure roller 22. The presence of such a depressurization mechanism 44 prevents plastic deformation of the fixing belt 21 and compression set of the elastic layer of the pressure roller 22 due to the fixing belt 21 and the pressure roller 22 being left in a pressure contact state. In addition, during jamming, releasing the pressure contact between the fixing belt 21 and the pressure roller 22 makes it easier to remove paper stuck in the nip section N.

[0071] In the above embodiment, a configuration in which the separating plate 28 is in contact with the nip forming member 24 that holds the heater 23 was described as an example. However, the present invention is also applicable to a fixing device 60 that has a nip forming member 24 that does not hold a heater, as shown in Figure 17.

[0072] The fixing device 60 shown in Figure 17 includes a fixing belt 21, a pressure roller 22, a nip forming member 24, a stay 25, a separation plate 28, and a halogen heater 51 as a heating element that is not held by the nip forming member 24.

[0073] As shown in Figure 18, the halogen heater 51 is a filament lamp having a glass tube 48 made of quartz glass or the like, and a filament 47 housed inside the glass tube 48. The filament 47 has a straight section 47a and a tightly wound section 47b, which is tightly wound in a coil shape, and this tightly wound section 47b becomes a resistance heating element that generates heat when power is supplied. The halogen heater 51 is positioned inside the fixing belt 21 and not in contact with the fixing belt 21 (see Figure 17), and when the halogen heater 51 generates heat, the fixing belt 21 is heated by the radiant heat emitted from the halogen heater 51.

[0074] In a fixing device 60 equipped with a nip-forming member 24 that does not hold such a heater, similar to the embodiment described above, by positioning the separation plate 28 in a position where it can contact the nip-forming member 24 (via the fixing belt 21), the pressing of the separation plate 28 against the fixing belt 21 can be suppressed using existing components, thereby preventing damage to the fixing belt 21. Furthermore, the present invention is also applicable to fixing devices using other non-contact heating elements, such as electromagnetic induction heating.

[0075] Thus, the present invention is also applicable to configurations in which the nip-forming member 24 does not hold a heating element. However, in configurations such as the above embodiment in which the nip-forming member 24 holds a heater 23 and the heater 23 heats the nip portion N, deformation of the fixing belt is generally more likely to occur, thus increasing the need to apply the present invention. When deformation of the fixing belt occurs, the rotational trajectory of the fixing belt fluctuates, so it is necessary to bring a part of the separating plate into contact with the fixing belt in order to maintain a constant distance between the tip of the separating plate and the surface of the fixing belt. However, when a part of the separating plate is brought into contact with the fixing belt, there is a risk that a part of the separating plate will be strongly pressed into the surface of the fixing belt.

[0076] The following are some of the reasons why deformation of the fixing belt is likely to occur in the fixing device according to the above embodiment.

[0077] First, in the above embodiment, as shown in Figure 2, the heater 23 held by the nip forming member 24 is configured to heat the nip portion N. Therefore, when the fixing operation is completed and the heater 23 stops generating heat, variations occur in the rate of temperature decrease (cooling rate) of the fixing belt 21 between the nip portion N and the rest of the belt. That is, when the rotation of the fixing belt 21 stops, the temperature decrease of the fixing belt 21 slows down in the nip portion N due to the influence of the heat remaining in the heater 23, while in areas other than the nip portion N, the fixing belt 21 is not affected by the heat remaining in the heater 23, so the temperature decrease of the fixing belt 21 is faster. Thus, in the above embodiment, because the heater 23 is located in the nip portion N, variations occur in the rate of temperature decrease of the fixing belt 21 after the fixing operation is completed, and these variations make plastic deformation of the fixing belt 21 more likely to occur.

[0078] Furthermore, in the above embodiment, since the contact surface of the heater 23 with respect to the fixing belt 21 is flat, deformation of the fixing belt 21 is likely to occur if the fixing belt 21 is left sandwiched between the heater 23 and the pressure roller 22. In other words, since the flat heater 23 contacts the fixing belt 21, which is basically circular or cylindrical, the deformation of the fixing belt 21 at the nip portion N becomes large, and plastic deformation of the fixing belt 21 is likely to occur. Moreover, if the base material of the fixing belt 21 is made of resin, its rigidity is lower compared to when the base material is made of metal, so plastic deformation of the fixing belt 21 is even more likely to occur.

[0079] Furthermore, as in the above embodiment, the configuration in which the fixing belt 21 rotates in a manner driven by the pressure roller 22 also contributes to the increased likelihood of deformation of the fixing belt 21. When the fixing belt 21 rotates in a manner driven by the pressure roller, it is necessary to ensure a large gap between the fixing belt 21 and the member positioned inside it. However, ensuring a large gap leads to increased deformation (variation of the rotational trajectory) of the fixing belt 21.

[0080] Furthermore, if the outer diameter of the fixing belt 21 is larger than the outer diameter of the pressure roller 22, this can also cause deformation of the fixing belt 21. Making the outer diameter of the fixing belt 21 larger than the outer diameter of the pressure roller 22 widens the width of the nip section N, which in turn widens the width of the heater 23 located in the nip section N, thereby improving productivity (number of prints per unit time). However, widening the width of the nip section N increases the deformation of the fixing belt 21 in the nip section N, making plastic deformation of the fixing belt 21 more likely.

[0081] Furthermore, although different from the above embodiment, if the fixing belt 21 is made of a belt member without an elastic layer, deformation of the fixing belt 21 is more likely to occur. As shown in Figure 19, if the fixing belt 21 consists of a base material 210 and a surface layer (release layer) 212 provided on the outer periphery of the base material 210, and there is no elastic layer such as a rubber layer between the surface layer 212 and the base material 210, the thermal insulation performance is lower and the thermal conductivity from the heater to the fixing belt surface (outer surface) is better compared to a fixing belt with an elastic layer. However, on the other hand, the rigidity of the fixing belt 21 is lower, so plastic deformation of the fixing belt 21 is more likely to occur.

[0082] As described above, there are various reasons why the fixing belt is prone to deformation, but in particular, the present invention can be expected to have a significant effect in configurations with such reasons. Specifically, even in configurations where the gap between the separation plate and the fixing belt is prone to fluctuation due to the deformation of the fixing belt, the present invention can be applied to maintain a constant gap between the tip of the separation plate and the surface of the fixing belt, and the pressing of the separation plate against the surface of the fixing belt can be suppressed using existing components, thereby preventing damage to the fixing belt.

[0083] Furthermore, in the present invention, the heating element is not limited to a heater 23 having resistance heating elements 56 continuously arranged along the longitudinal direction X of the base material 55 as shown in Figure 6, but may also be a heater 23 having a plurality of resistance heating elements 56 arranged along the longitudinal direction X of the base material 55 as shown in Figure 20. In the example shown in Figure 20, each resistance heating element 56 is electrically connected in parallel to the electrode portion 58 via a power supply line 59.

[0084] A heater 23 having multiple resistance heating elements 56 like this is suitable for a configuration that widens the nip width in order to improve productivity. However, widening the width of the nip portion N makes plastic deformation of the fixing belt more likely, so it is preferable to apply the present invention. This makes it possible to maintain a constant distance between the tip of the separation plate and the surface of the fixing belt, and also suppresses the pressing of the separation plate against the surface of the fixing belt.

[0085] Furthermore, the present invention is also applicable to fixing devices with configurations as shown in Figures 21 to 23. The configurations of each fixing device shown in Figures 21 to 23 will be described below. In the configurations shown in Figures 21 to 23, parts of the configuration that are common with the fixing device 20 of the above embodiment shown in Figure 2 will be denoted by the same reference numerals, and their descriptions will be omitted.

[0086] The fuser 20 shown in Figure 21 differs from the fuser 20 shown in Figure 2 in the position of the temperature sensor 27 that detects the temperature of the heater 23. Other than that, the configuration is the same. In the fuser 20 shown in Figure 21, the temperature sensor 27 is positioned upstream of the center M of the nip section N in the paper feeding direction (nip inlet side). On the other hand, in the fuser 20 shown in Figure 2, the temperature sensor 27 is positioned at the center M of the nip section N. As shown in Figure 21, when the temperature sensor 27 is positioned upstream of the center M of the nip section N in the paper feeding direction, the temperature sensor 27 can accurately detect the temperature on the nip inlet side. Since the nip inlet side is a region where heat from the fuser belt 21 is particularly easily lost by the paper P entering the nip section N, accurately detecting the temperature on the nip inlet side with the temperature sensor 27 ensures image fixation and effectively suppresses the occurrence of fixation offset (a state where the toner image cannot be sufficiently heated).

[0087] Next, in the embodiment shown in Figure 22, a heating nip section N1 that heats the fixing belt 21 with a heater 23 and a fixing nip section N2 that allows the paper P to pass through are formed at separate locations. Specifically, in this embodiment, the heater 23 and the nip forming member 68 are arranged at separate locations inside the fixing belt 21, and separate pressure rollers 69 and 70 are pressed against the heater 23 and the nip forming member 68 via the fixing belt 21, thereby forming the heating nip section N1 and the fixing nip section N2. In this case, the fixing belt 21 is heated at the heating nip section N1, and the heat from the fixing belt 21 is applied to the paper P at the fixing nip section N2, thereby fixing the unfixed image to the paper P.

[0088] Next, the fixing device 20 shown in Figure 23 is an example in which the pressure roller 69 on the heater 23 side is omitted from the fixing device shown in Figure 22, and the heater 23 is formed in an arc shape to match the curvature of the fixing belt 21. Otherwise, the configuration is the same as shown in Figure 22. In this case, because the heater 23 is formed in an arc shape, the contact length between the fixing belt 21 and the heater 23 in the belt rotation direction is secured, and the fixing belt 21 can be heated efficiently.

[0089] Furthermore, the image forming apparatus according to the present invention is not limited to the color image forming apparatus shown in Figure 1, but is also applicable to image forming apparatuses with configurations such as those shown in Figure 24. The configurations of other image forming apparatuses to which the present invention can be applied will be described below.

[0090] The image forming apparatus 100 shown in Figure 24 comprises an image forming means 80 consisting of a photosensitive drum and the like, a paper transport unit consisting of a pair of timing rollers 81 and the like, a paper feeder 82, a fuser 83, a paper discharger 84, and a reading unit 85. The paper feeder 82 has multiple paper trays, each of which accommodates paper of a different size.

[0091] The reading unit 85 reads the image of the original document Q. The reading unit 85 generates image data from the read image. The paper feeder 82 receives multiple sheets of paper P and feeds the paper P to the transport path. The timing roller 81 transports the paper P on the transport path to the image forming means 80.

[0092] The image forming means 80 forms a toner image on the paper P. Specifically, the image forming means 80 includes a photoreceptor drum, a charging roller, an exposure device, a developing device, a replenishment device, a transfer roller, a cleaning device, and a static elimination device. The fixing device 83 heats and pressurizes the toner image to fix it to the paper P. The paper P with the fixed toner image is transported to the paper discharge device 84 by a transport roller or the like. The paper discharge device 84 discharges the paper P to the outside of the image forming device 100.

[0093] Next, the fixing device 83 according to this embodiment will be described with reference to Figure 25. In the configuration shown in Figure 25, parts that are common with the fixing device 20 of the above embodiment shown in Figure 2 are denoted by the same reference numerals, and their descriptions are omitted.

[0094] As shown in Figure 25, the fixing device 83 includes a fixing belt 21, a pressure roller 22, a heater 23, a nip forming member 24, a stay 25, a temperature sensor 27, a separation plate 28, and the like.

[0095] A nip section N is formed between the fixing belt 21 and the pressure roller 22. The nip width of the nip section N is 10 mm, and the linear speed of the fixing device 83 is 240 mm / s.

[0096] The fixing belt 21 comprises a polyimide substrate and a release layer, and does not have an elastic layer. The release layer is formed from a heat-resistant film material, for example, a fluororesin. The outer diameter of the fixing belt 21 is approximately 24 mm.

[0097] The pressure roller 22 includes a core metal, an elastic layer, and a release layer. The outer diameter of the pressure roller 22 is 24-30 mm, and the thickness of the elastic layer is 3-4 mm.

[0098] The heater 23 includes a base material, an insulating layer, a conductor layer containing a resistive heating element, and an insulating layer, with an overall thickness set to 1 mm. The width of the heater 23 in the paper transport direction is 13 mm.

[0099] As shown in Figure 26, the conductor layer of the heater 23 comprises a plurality of resistive heating elements 56, a power supply line 59, and electrode sections 58A to 58C. The plurality of resistive heating elements 56 are arranged at intervals from each other in the longitudinal direction (arrow X direction) of the heater 23. Here, the portion between each resistive heating element 56 is called a "divided region," and as shown in the enlarged view of Figure 26, a divided region B is formed between each resistive heating element 56 (in Figure 26, divided region B is only shown in the enlarged view, but in reality, divided region B is provided between all resistive heating elements 56). Also, in Figure 26, the direction of arrow Y is a direction that intersects or is perpendicular to the longitudinal direction X of the heater 23 (longitudinal intersection direction), and is a different direction from the thickness direction of the base material 55. Furthermore, the direction of arrow Y is the same as the direction that intersects the arrangement direction of the multiple resistance heating elements 56 (arrangement intersection direction), or the direction that follows the surface of the base material 55 on which the resistance heating elements 56 are provided, which is the short-side direction of the heater 23, or the same direction as the transport direction of the paper fed through the fixing device.

[0100] Furthermore, multiple resistive heating elements 56 constitute a central heating element 50B and heating elements 50A and 35C at both ends that can generate heat independently of it. For example, when current is applied to the leftmost electrode 58A and the central electrode 58B of the three electrode elements 58A to 58C in Figure 26, the heating elements 50A and 35C at both ends will generate heat. Also, when current is applied to the electrode elements 58A and 58C at both ends, the central heating element 50B will generate heat. For example, when performing a fixing operation on small-sized paper, only the central heating element 50B will be heated, and when performing a fixing operation on large-sized paper, all heating elements 50A to 35C will be heated, allowing for heating according to the size of the paper.

[0101] Furthermore, as shown in Figure 27, the nip-forming member 24 according to this embodiment has a recess 241 for housing and holding the heater 23. The recess 241 is formed on the heater 23 side of the nip-forming member 24. The recess 241 is composed of a rectangular surface (bottom surface) 24f formed in the shape of approximately the same size as the heater 23, and four wall portions (sides) 24b, 24c, 24d, and 24e provided along the four edges forming the outer perimeter of the surface 24f so as to intersect with the surface 24f. Note that in Figure 27, the right-side wall portion 24e is omitted from the illustration. Alternatively, one of the pair of wall portions 24d and 24e that intersect with the longitudinal direction X of the heater 23 (the arrangement direction of the resistance heating elements 56) may be omitted, and the recess 241 may be configured to open at one end of the heater 23 in the longitudinal direction.

[0102] As shown in Figure 28, the heater 23 and nip-forming member 24 according to this embodiment are held by a connector 86. The connector 86 has a housing made of resin (e.g., LCP) and a plurality of contact terminals provided inside the housing.

[0103] The connector 86 is attached to the heater 23 and the nip forming member 24 in a direction intersecting the longitudinal direction X of the heater 23 (the arrangement direction of the resistance heating elements 56) (see the direction of the arrow from the connector 86 in Figure 28). The connector 86 is attached to the heater 23 and the nip forming member 24 on one end side of the heater 23 in the longitudinal direction X (the arrangement direction of the resistance heating elements 56), on the side opposite to the side where the drive motor for the pressure roller 22 is provided. When attaching the connector 86 to the nip forming member 24, a protrusion provided on one of the connector 86 or the nip forming member 24 may engage with a recess provided on the other, and the protrusion may move relative to the other within the recess.

[0104] With the connector 86 attached, the heater 23 and the nip forming member 24 are held in place by the connector 86 from both their front and back sides. In this state, each contact terminal makes contact (pressure contact) with each electrode portion of the heater 23, thereby electrically connecting each resistive heating element 56 to the power supply provided in the image forming apparatus via the connector 86. This makes it possible to supply power from the power supply to each resistive heating element 56.

[0105] Furthermore, the flanges 87 shown in Figure 28 are belt retaining members provided at both ends in the longitudinal direction of the anchoring belt 21, and hold both ends of the anchoring belt 21 from the inside. The flanges 87 are inserted into both ends of the stay 25 and fixed to a pair of side plates which are frame members of the anchoring device.

[0106] Figure 29 shows the arrangement of the temperature sensor 27 and the thermostat 88, which is an electrical cutoff member, according to this embodiment.

[0107] As shown in Figure 29, the temperature sensor 27 according to this embodiment is positioned to face the inner circumferential surfaces of the central Xm side and the end side of the fixing belt 21 in the longitudinal direction (direction of arrow X). In addition, one of these temperature sensors 27 is positioned in a location corresponding to the divided region B (see Figure 26) between the resistance heating elements of the heater 23.

[0108] Furthermore, thermostats 88, which act as power-cutting members, are positioned at the central Xm side and the end side of the fixing belt 21 so as to face the inner circumferential surface of the fixing belt 21. Each thermostat 88 detects the temperature of the inner circumferential surface of the fixing belt 21 or the ambient temperature near the inner circumferential surface. If the temperature detected by the thermostat 88 exceeds a preset threshold, the power supply to the heater 23 is cut off.

[0109] Furthermore, as shown in Figures 29 and 30, the flanges 87 that hold both ends of the fixing belt 21 are provided with slide grooves 87a. The slide grooves 87a extend in the direction in which the fixing belt 21 moves toward and toward the pressure roller 22. The engaging portion of the fixing device housing engages with the slide grooves 87a. By the relative movement of these engaging portions within the slide grooves 87a, the fixing belt 21 is configured to move toward and toward the pressure roller 22.

[0110] Furthermore, the present invention is also applicable to fixing devices having the following configuration.

[0111] Figure 31 is a schematic diagram of a fixing device according to another embodiment to which the present invention can be applied.

[0112] The fixing device 20 shown in Figure 31 comprises a fixing belt 21 as a rotating body or fixing member, a pressure roller 22 as an opposing rotating body or pressure member, a heater 23 as a heating body, a nip forming member 24 which also functions as a heating body holding member, a stay 25 as a support member, a temperature sensor (thermistor) 27 as a temperature sensing member, a first high thermal conductivity member 89, and a separation plate 28. The fixing belt 21 consists of an endless belt. The pressure roller 22 contacts the outer circumferential surface of the fixing belt 21 to form a nip portion N between itself and the fixing belt 21. The heater 23 heats the fixing belt 21. The nip forming member 24 holds the heater 23. The stay 25 supports the nip forming member 24. The temperature sensor 27 detects the temperature of the first high thermal conductivity member 89. The separation plate 28 separates the paper P that has passed through the nip portion N from the fixing belt 21. In other words, the fixing device 20 according to this embodiment has basically the same configuration as the fixing device shown in Figure 2, except that it is equipped with a first high-heat-conducting member 89. The direction perpendicular to the plane of the paper in Figure 31 is the longitudinal direction of the fixing belt 21, pressure roller 22, heater 23, nip forming member 24, stay 25, first high-heat-conducting member 89, and separation plate 28, and this direction will be simply referred to as the longitudinal direction below. This longitudinal direction is also the width direction of the paper being conveyed, the belt width direction of the fixing belt 21, and the axial direction of the pressure roller 22.

[0113] In this embodiment, the heater 23, like the heater shown in Figure 26, has a plurality of resistance heating elements 56 arranged at intervals from each other in the longitudinal direction of the heater 23. However, in a configuration where a plurality of resistance heating elements 56 are arranged at intervals from each other, the temperature of the heater 23 in the divided region B, which is the space between the resistance heating elements 56, tends to be lower than in the part where the resistance heating elements 56 are arranged. As a result, the temperature of the fixing belt 21 also becomes lower in the divided region B, and there is a risk that the temperature of the fixing belt 21 will become uneven over the longitudinal direction.

[0114] Therefore, in this embodiment, the first high thermal conductivity member 89 is provided to suppress temperature drops in the divided region B and to suppress temperature unevenness in the longitudinal direction of the fixing belt 21. The first high thermal conductivity member 89 will be described in more detail below.

[0115] As shown in Figure 31, the first high-heat-conductivity member 89 is positioned between the heater 23 and the stay 25 in the left-right direction of the figure, and is particularly sandwiched between the heater 23 and the nip-forming member 24. That is, one side of the first high-heat-conductivity member 89 is in contact with the back surface of the base material 55 of the heater 23, and the other side of the first high-heat-conductivity member 89 (the side opposite to the other side) is in contact with the nip-forming member 24.

[0116] The stay 25 supports the nip forming member 24, the first high heat conductive member 89, and the heater 23 by bringing the contact surfaces 25a1 of two vertical portions 25a extending in the thickness direction of the heater 23 and the like into contact with the nip forming member 24. In the longitudinal intersection direction (up and down direction in Figure 31), the contact surfaces 25a1 are located outside the area where the resistance heating element 56 is provided. This suppresses heat transfer from the heater 23 to the stay 25, allowing the heater 23 to efficiently heat the fixing belt 21.

[0117] As shown in Figure 32, the first high-heat-conductivity member 89 is a plate-shaped member having a certain thickness, for example, its thickness is set to 0.3 mm, its length in the longitudinal direction to 222 mm, and its width in the longitudinal intersection direction to 10 mm. In this embodiment, the first high-heat-conductivity member 89 is made of a single plate material, but it may be made of multiple members. Note that in Figure 32, the guide portion 24a shown in Figure 31 is omitted.

[0118] The first high-heat-conductivity member 89 is fitted into the recess 241 of the nip-forming member 24, and the heater 23 is attached on top of it, so that it is sandwiched and held between the nip-forming member 24 and the heater 23. In this embodiment, the longitudinal width of the first high-heat-conductivity member 89 is set to be approximately the same as the longitudinal width of the heater 23. The longitudinal movement of the first high-heat-conductivity member 89 and the heater 23 is restricted by side walls (longitudinal direction restricting parts) 24d, 24e, which are arranged in a direction intersecting the longitudinal direction of the recess 241. In this way, the longitudinal displacement of the first high-heat-conductivity member 89 within the fixing device is restricted, thereby improving the heat conduction efficiency over the target range in the longitudinal direction. Furthermore, the longitudinal movement of the first high-heat-conductivity member 89 and the heater 23 is restricted by side walls (arrangement crossing direction restricting parts) 24b, 24c, which are arranged in the longitudinal direction of the recess 241.

[0119] The range in the longitudinal direction (arrow X direction) in which the first high heat conductive member 89 is placed is not limited to the range shown in Figure 32. For example, as shown in Figure 33, the first high heat conductive member 89 may be placed only in the longitudinal range in which the resistance heating element 56 is placed (see hatched area in Figure 33). Also, as shown in the example in Figure 34, the first high heat conductive member 89 may be placed only in the entire area at a position corresponding to the interval (divided region) B in the longitudinal direction (arrow X direction). Note that in Figure 34, for convenience, the resistance heating element 56 and the first high heat conductive member 89 are shown offset vertically in Figure 34, but they are placed at approximately the same position in the longitudinal intersection direction (arrow Y direction). Furthermore, the first high-heat-conductivity member 89 may be positioned over a portion of the longitudinal direction (arrow Y direction) of the resistance heating element 56, or, as shown in the example in Figure 35, the first high-heat-conductivity member 89 may be positioned over the entire longitudinal direction (arrow Y direction) of the resistance heating element 56. Moreover, as shown in Figure 35, the first high-heat-conductivity member 89 may be positioned not only at a position corresponding to the longitudinal spacing B, but also across the resistance heating elements 56 on both sides that straddle the spacing B. "Positioning the first high-heat-conductivity member 89 across the resistance heating elements 56 on both sides" means that the longitudinal position of the first high-heat-conductivity member 89 overlaps with the resistance heating elements 56 on both sides in at least a portion of the way. Furthermore, the first high-heat-conductivity member 89 may be positioned at a position corresponding to all of the spacing B of the heater 23, or, as shown in the example in Figure 35, it may be positioned at a position corresponding to only a portion of the spacing B (in this case, one location). Here, "the first high heat-conducting member 89 is positioned at a location corresponding to the interval B" means that at least a portion of the interval B and the first high heat-conducting member 89 overlap in the longitudinal direction.

[0120] The pressure applied by the pressure roller 22 causes the first high-heat-conductivity member 89 to be sandwiched between the heater 23 and the nip-forming member 24, causing it to adhere closely to these members. The contact of the first high-heat-conductivity member 89 with the heater 23 improves the thermal conductivity of the heater 23 in the longitudinal direction. Furthermore, by positioning the first high-heat-conductivity member 89 at a position corresponding to the gap B of the heater 23 in the longitudinal direction, the thermal conductivity at gap B can be improved, increasing the amount of heat transferred to gap B and raising the temperature at gap B. This suppresses temperature unevenness in the longitudinal direction of the heater 23 and suppresses temperature unevenness in the longitudinal direction of the fixing belt 21. As a result, uneven fixing and gloss unevenness of the image fixed to the paper can be suppressed. In addition, it becomes unnecessary to increase the heat output of the heater 23 to ensure sufficient fixing performance at gap B, thereby achieving energy savings in the fixing device. In particular, when the first high heat conductive member 89 is arranged over the entire longitudinal area where the resistance heating element 56 is located, the heat transfer efficiency of the heater 23 can be improved over the entire main heating area of ​​the heater 23 (i.e., the image forming area of ​​the paper being fed through), and temperature unevenness in the longitudinal direction of the heater 23 and, consequently, the fixing belt 21 can be suppressed.

[0121] Furthermore, the combination of the first high thermal conductivity member 89 and the resistance heating element 56 having PTC characteristics can more effectively suppress overheating in the non-paper-feeding area when small-sized paper is fed. PTC characteristics refer to the characteristic that the resistance value increases as the temperature rises (when a constant voltage is applied, the heater output decreases). In other words, because the resistance heating element 56 has PTC characteristics, the amount of heat generated by the resistance heating element 56 in the non-paper-feeding area can be effectively suppressed, and the first high thermal conductivity member 89 can efficiently transfer the heat from the non-paper-feeding area, where the temperature has risen, to the paper-feeding area. As a result of these synergistic effects, overheating in the non-paper-feeding area can be effectively suppressed.

[0122] Furthermore, in the vicinity of interval B, the temperature of the heater 23 is lower due to the small amount of heat generated by interval B, so it is preferable to place the first high heat conductive member 89. For example, by placing the first high heat conductive member 89 at a position corresponding to the enlarged division region C, which includes the area around interval B shown in Figure 36, the longitudinal heat transfer efficiency in and around interval B can be improved, and longitudinal temperature unevenness of the heater 23 can be suppressed more effectively. In addition, if the first high heat conductive member 89 is placed over the entire longitudinal direction of the region where all resistance heating elements 56 are placed, longitudinal temperature unevenness of the heater 23 (fixing belt 21) can be suppressed more reliably.

[0123] Next, we will describe yet another embodiment of the fixing device.

[0124] The fixing device 20 shown in Figure 37 has a second high-thermal-conductivity member 90 between the nip-forming member 24 and the first high-thermal-conductivity member 89. The second high-thermal-conductivity member 90 is provided at a different position from the first high-thermal-conductivity member 89 in the stacking direction (left-right direction in Figure 37) of the members such as the nip-forming member 24, the stay 25, and the first high-thermal-conductivity member 89. More specifically, the second high-thermal-conductivity member 90 is provided superimposed on the first high-thermal-conductivity member 89. In this embodiment, a temperature sensor (thermistor) 27 is provided, as in the embodiment shown in Figure 31, but Figure 37 shows a cross-section where the temperature sensor 27 is not located.

[0125] The second high thermal conductivity member 90 is made of a material with a higher thermal conductivity than the base material 55, such as graphene or graphite. In this embodiment, the second high thermal conductivity member 90 is made of a graphite sheet with a thickness of 1 mm. Alternatively, the second high thermal conductivity member 90 may be made of a plate material such as aluminum, copper, or silver.

[0126] As shown in Figure 38, multiple second high-heat-conductivity members 90 are arranged in the recesses 241 of the nip-forming member 24, with longitudinal spacing between each second high-heat-conductivity member 90. The portion of the nip-forming member 24 where the second high-heat-conductivity members 90 are provided has a recess that is deeper than the rest of the nip-forming member. The second high-heat-conductivity members 90 have gaps between them and the nip-forming member 24 on both longitudinal sides. This suppresses heat transfer from the second high-heat-conductivity members 90 to the nip-forming member 24, allowing the heater 23 to efficiently heat the fixing belt 21. Note that in Figure 38, the guide portion 24a shown in Figure 37 is omitted.

[0127] As shown in Figure 39, the second high-heat-conductivity member 90 (see hatched area) is positioned in the longitudinal direction (arrow X direction) at a location corresponding to the interval B, overlapping at least a portion of the adjacent resistance heating elements 56. In particular, in this embodiment, the second high-heat-conductivity member 90 is positioned over the entire interval B. Note that Figure 39 (and Figure 41 described later) shows the case where the first high-heat-conductivity member 89 is positioned over the entire longitudinal direction of the area where all the resistance heating elements 56 are arranged, but the arrangement range of the first high-heat-conductivity member 89 is not limited to this.

[0128] As in this embodiment, in addition to the first high heat conductive member 89, the second high heat conductive member 90 is positioned at a location corresponding to the longitudinal spacing B, overlapping at least a portion of the adjacent resistance heating elements 56. This further improves the longitudinal heat transfer efficiency at spacing B, and more effectively suppresses longitudinal temperature unevenness of the heater 23. Most preferably, as shown in Figure 40, the first high heat conductive member 89 and the second high heat conductive member 90 are provided only over the entire area at the location corresponding to spacing B. This makes it possible to particularly improve the heat transfer efficiency at the location corresponding to spacing B compared to other areas. Note that in Figure 40, for convenience, the resistance heating elements 56, the first high heat conductive member 89, and the second high heat conductive member 90 are shown offset in the vertical direction of the figure, but they are actually positioned at approximately the same location in the longitudinal intersection direction (arrow Y direction). However, the first high thermal conductivity member 89 and the second high thermal conductivity member 90 may be arranged in a part of the longitudinal direction of the resistance heating element 56, or they may be arranged to cover the entire longitudinal direction.

[0129] Furthermore, both the first high thermal conductivity member 89 and the second high thermal conductivity member 90 may be made of the graphene sheet. In this case, the first high thermal conductivity member 89 and the second high thermal conductivity member 90 can be formed in a predetermined direction along the surface of the graphene, that is, in the longitudinal direction rather than the thickness direction. This effectively suppresses temperature unevenness in the longitudinal direction of the heater 23 and the fixing belt 21.

[0130] Graphene is a flaky powder. As shown in Figure 43, graphene consists of a planar hexagonal lattice structure of carbon atoms. A graphene sheet is a sheet of graphene, usually a single layer. A graphene sheet may also contain impurities in the single layer of carbon, or it may have a fullerene structure. A fullerene structure is generally recognized as a compound in which an equal number of carbon atoms form a polycyclic structure fused in a cage-like manner with 5-membered and 6-membered rings, such as C60, C70, and C80 fullerenes, or other closed cage-like structures having 3-coordinate carbon atoms.

[0131] Graphene sheets are artificial materials and can be fabricated, for example, by chemical vapor deposition (CVD).

[0132] Commercially available graphene sheets can be used. The size and thickness of the graphene sheet, as well as the number of layers of the graphite sheet described later, can be measured, for example, by a transmission electron microscope (TEM).

[0133] Furthermore, graphite with multiple layers of graphene exhibits high thermal conductivity anisotropy. As shown in Figure 44, graphite has a crystalline structure in which layers of condensed six-membered rings of carbon atoms are spread out in a planar manner, and these layers are stacked multiple times. In this crystalline structure, adjacent carbon atoms within a layer form covalent bonds, while carbon atoms between layers form van der Waals bonds. The covalent bonds have a stronger bonding force than van der Waals bonds, and there is a large anisotropy between the bonds within a layer and the bonds between layers. In other words, by constructing the first high thermal conductivity member 89 or the second high thermal conductivity member 90 from graphite, the heat transfer efficiency in the longitudinal direction of the first high thermal conductivity member 89 or the second high thermal conductivity member 90 becomes larger than in the thickness direction (i.e., the stacking direction of the members), and heat transfer to the nip-forming member 24 can be suppressed. Therefore, temperature unevenness in the longitudinal direction of the heater 23 can be efficiently suppressed, and the heat flowing out to the nip-forming member 24 can be minimized. Furthermore, by constructing the first high-temperature conductive member 89 or the second high-temperature conductive member 90 from graphite, the first high-temperature conductive member 89 or the second high-temperature conductive member 90 can be given excellent heat resistance, such as not oxidizing up to about 700 degrees Celsius.

[0134] The physical properties and dimensions of the graphite sheet can be appropriately changed according to the function required of the first high-thermal-conductivity member 89 or the second high-thermal-conductivity member 90. For example, the anisotropy of its thermal conductivity can be increased by using high-purity graphite or single-crystal graphite, or by increasing the thickness of the graphite sheet. In addition, to increase the speed of the fixing device, a thinner graphite sheet may be used to reduce the heat capacity of the fixing device. Furthermore, if the width of the nip portion N and the heater 23 is large, the longitudinal width of the first high-thermal-conductivity member 89 or the second high-thermal-conductivity member 90 may be increased accordingly.

[0135] From the viewpoint of increasing mechanical strength, it is preferable that the graphite sheet has 11 or more layers. Furthermore, the graphite sheet may partially consist of single-layer and multi-layer sections.

[0136] The second high-heat-conductivity member 90 may be provided in the longitudinal direction at a position corresponding to the interval B (further expanded division region C) and overlapping with at least a portion of the adjacent resistance heating element 56, and is not limited to the arrangement shown in Figure 39. For example, as shown in the example in Figure 41, the second high-heat-conductivity member 90A may be provided extending outwards on both sides of the base material 55 in the longitudinal intersection direction (arrow Y direction). The second high-heat-conductivity member 90B may be provided in the longitudinal intersection direction within the range where the resistance heating element 56 is provided. The second high-heat-conductivity member 90C may be provided in a portion of the interval B.

[0137] In another embodiment shown in Figure 42, a gap in the thickness direction (left-right direction in Figure 42) is provided between the first high-heat-conducting member 89 and the nip-forming member 24. In other words, a relief portion 24g acting as an insulating layer is provided in a part of the recess 241 (see Figure 38) of the nip-forming member 24 where the heater 23, the first high-heat-conducting member 89, and the second high-heat-conducting member 90 are arranged. The relief portion 24g is provided in a part of the longitudinal direction other than the part where the second high-heat-conducting member 90 (not shown in Figure 42) is provided. Furthermore, the relief portion 24g is formed by making the depth of the recess 241 of the nip-forming member 24 deeper than the other parts. As a result, the contact area between the nip-forming member 24 and the first high-heat-conducting member 89 can be minimized, so that heat transfer from the first high-heat-conducting member 89 to the nip-forming member 24 is suppressed, and the heater 23 can efficiently heat the fixing belt 21. In the cross-section where the second high-thermal-conductivity member 90 in the longitudinal direction is provided, the second high-thermal-conductivity member 90 contacts the nip-forming member 24, as shown in the embodiment in Figure 37.

[0138] Furthermore, in this embodiment, the relief portion 24g is provided over the entire area where the resistance heating element 56 is installed in the longitudinal direction (vertical direction in Figure 42). This effectively suppresses heat transfer from the first high thermal conductivity member 89 to the nip forming member 24, improving the heating efficiency of the fixing belt 21 by the heater 23. In addition to the configuration that provides a space as in the relief portion 24g, the insulating layer may also be configured with an insulating material having a lower thermal conductivity than the nip forming member 24.

[0139] Furthermore, in this embodiment, the second high-temperature conductive member 90 is provided as a different member from the first high-temperature conductive member 89, but this is not limited to this. For example, the portion of the first high-temperature conductive member 89 corresponding to the gap B may be made thicker than the other portions so that the first high-temperature conductive member 89 also functions as the second high-temperature conductive member 90.

[0140] Although the configurations of other fixing devices and image forming devices to which the present invention can be applied have been described above, the same effects as in the above embodiments can be obtained by applying the present invention to fixing devices and image forming devices with such configurations. That is, by applying the present invention, it is possible to maintain a constant distance between the tip of the separation plate and the surface of the fixing belt, and to suppress the pressing of the separation plate against the surface of the fixing belt using existing components.

[0141] To summarize the embodiments of the present invention described above, the present invention includes a heating device, a fixing device, and an image forming apparatus having at least the following configurations.

[0142] [First Structure] The first configuration is a fixing device comprising: a first rotating body; a second rotating body that contacts the outer circumferential surface of the first rotating body and forms a nip portion through which a recording medium carrying an unfixed image passes; a heating element having a resistance heating element for heating the first rotating body; a nip forming member disposed inside the first rotating body and sandwiching the first rotating body between itself and the second rotating body to form the nip portion; and a separation member for separating the recording medium passing through the nip portion from the first rotating body, wherein the separation member has a separation portion disposed non-contacting the outer circumferential surface of the first rotating body for separating the recording medium from the first rotating body, and a contact portion that contacts the outer circumferential surface of the first rotating body, and the contact portion is positioned to be able to contact the nip forming member via the first rotating body.

[0143] [Second Structure] The second configuration is a fixing device in which, in the first configuration, the contact portion contacts the outer circumferential surface of the first rotating body in a non-pass region through which the recording medium does not pass.

[0144] [The third structure] The third configuration is a fixing device in which, in the first or second configuration, the nip forming member holds the heating element in the nip portion so as to be in contact with the inner circumferential surface of the first rotating body.

[0145] [Fourth component] The fourth configuration is a fixing device in which, in the third configuration, the surface of the heating element that contacts the inner circumferential surface of the first rotating body is a flat surface.

[0146] [Fifth Structure] The fifth configuration is a fixing device in which, in the third or fourth configuration, the nip forming member protrudes downstream of the center of the nip portion in the recording medium passage direction, and toward the second rotating body side from the heating body.

[0147] [The sixth component] The sixth configuration is a fixing device in which, in any one of the first to fifth configurations, the contact surface of the nip-forming member that the contact portion contacts via the first rotating body is free of irregularities along the longitudinal direction of the first rotating body.

[0148] [The seventh component] The seventh configuration is a fixing device in which, in any one of the first to sixth configurations, the contact portion contacts the outer circumferential surface of the first rotating body in a region other than the region in the longitudinal direction of the first rotating body where the resistance heating element is located.

[0149] [The eighth component] The eighth configuration is a fixing device in which, in any one of the first to seventh configurations, the first rotating body rotates in association with the rotation of the second rotating body.

[0150] [The ninth structure] The ninth configuration is one of the first to eighth configurations, wherein the first rotating body is a fixing device having a resin substrate.

[0151] [The 10th component] The tenth configuration is a fixing device comprising, in any one of the first to ninth configurations, a pressurizing member that presses the first rotating body and the second rotating body against each other, and a depressurizing mechanism that releases the pressurized state between the first rotating body and the second rotating body caused by the pressurizing member.

[0152] [Structure of the 11th] The eleventh configuration is a fixing device in which the contact portion is made of an elastic material, in any one of the first to tenth configurations.

[0153] [Structure 12] The twelfth configuration is a fixing device in which, in any one of the first to eleventh configurations, the outer diameter of the first rotating body is larger than the outer diameter of the second rotating body.

[0154] [Structure 13] The thirteenth configuration is a fixing device that, in any one of the first to twelfth configurations, includes a pressurizing member that presses the first rotating body and the second rotating body against each other, wherein the pressurizing member pressurizes the second rotating body against the first rotating body.

[0155] [Structure 14] The 14th configuration is a fixing device in which, in any one of the first to 13 configurations, the distance between the tip of the separation portion and the outer surface of the first rotating body is smaller towards the end of the first rotating body than towards the center in the longitudinal direction.

[0156] [Structure of the 15th] The 15th configuration is a fixing device in which, in any one of the first to 14 configurations, the first rotating body comprises a base material and a surface layer provided on the outer circumference side of the base material, and there is no elastic layer between the surface layer and the base material.

[0157] [Structure of the 16th] The 16th configuration is a fixing device in which, in any one of the first to 15 configurations, the heating element has a plurality of resistance heating elements arranged along the longitudinal direction of the first rotating body.

[0158] [Structure of the 17th] The seventeenth configuration is an image forming apparatus comprising a fixing device of any one of the first to sixteenth configurations. [Explanation of Symbols]

[0159] 20 Fixing device 21 Fixing belt (first rotating body) 22 Pressure roller (second rotating body) 23 Heater (heating element) 24 Nip forming member 28 Separation plate (separation member) 28a Separation part 28b Contact part 56 Resistive heating element 38. Compression spring (compression component) 39. Compression spring (compression component) 44 Pressure relief mechanism 100 Image forming apparatus N Nip section P Paper (recording medium) [Prior art documents] [Patent Documents]

[0160] [Patent Document 1] Japanese Patent Publication No. 2013-186394

Claims

1. The first solid of revolution and, A second rotating body that contacts the outer circumferential surface of the first rotating body and forms a nip portion through which a recording medium carrying an unfixed image passes; A heating element having a resistance heating element, which heats the first rotating body, A nip-forming member is positioned inside the first rotating body and sandwiches the first rotating body between itself and the second rotating body to form the nip portion, A fixing device comprising: a separating member for separating the recording medium passing through the nip portion from the first rotating body, The separating member is configured to be displaceable in a direction toward or toward the outer circumferential surface of the first rotating body, The separation member has a separation portion that is positioned non-contact with the outer circumferential surface of the first rotating body and separates the recording medium from the first rotating body, and a contact portion that contacts the outer circumferential surface of the first rotating body. The contact portion is positioned to be able to contact the nip forming member via the first rotating body. A fixing device characterized in that when the separating member is pushed toward the first rotating body, the contact portion contacts the nip forming member via the first rotating body, and the separating member is supported by the nip forming member.

2. The fixing device according to claim 1, wherein the contact portion contacts the outer circumferential surface of the first rotating body in a non-pass region through which the recording medium does not pass.

3. The fixing device according to claim 1 or 2, wherein the nip-forming member holds the heating element in the nip portion so as to be in contact with the inner circumferential surface of the first rotating body.

4. The fixing device according to claim 3, wherein the surface of the heating element that contacts the inner circumferential surface of the first rotating body is a flat surface.

5. The fixing device according to claim 3, wherein the nip-forming member protrudes downstream of the center of the nip portion in the recording medium passage direction, and toward the second rotating body side from the heating body.

6. The fixing device according to claim 1 or 2, wherein the contact surface of the nip-forming member that the contact portion contacts via the first rotating body is a surface without irregularities in the longitudinal direction of the first rotating body.

7. The fixing device according to claim 1 or 2, wherein the contact portion contacts the outer circumferential surface of the first rotating body in a region other than the region in the longitudinal direction of the first rotating body where the resistance heating element is arranged.

8. The fixing device according to claim 1 or 2, wherein the first rotating body rotates in association with the rotation of the second rotating body.

9. The fixing device according to claim 1 or 2, wherein the first rotating body has a resin base material.

10. A pressing member that presses the first rotating body and the second rotating body against each other, A depressurization mechanism for releasing the pressure contact between the first rotating body and the second rotating body by the pressurizing member, The fixing device according to claim 1 or 2, comprising:

11. The fixing device according to claim 1 or 2, wherein the contact portion is made of an elastic material.

12. The fixing device according to claim 1 or 2, wherein the outer diameter of the first rotating body is larger than the outer diameter of the second rotating body.

13. The system includes a pressurizing member that presses the first rotating body and the second rotating body against each other. The fixing device according to claim 1 or 2, wherein the pressurizing member pressurizes the second rotating body onto the first rotating body.

14. The fixing device according to claim 1 or 2, wherein the distance between the tip of the separation portion and the outer circumferential surface of the first rotating body is smaller towards the end of the first rotating body than towards the center in the longitudinal direction.

15. The fixing device according to claim 1 or 2, wherein the first rotating body comprises a base material and a surface layer provided on the outer circumference side of the base material, and there is no elastic layer between the surface layer and the base material.

16. The fixing device according to claim 1 or 2, wherein the heating element has a plurality of resistance heating elements arranged along the longitudinal direction of the first rotating body.

17. An image forming apparatus characterized by comprising the fixing device described in claim 1.

Images