Fixing device and image forming apparatus

Abstract

To provide a fixing device capable of suppressing the occurrence of abnormal noise due to stick slip without providing a sliding sheet, and an image forming apparatus equipped with the fixing device.SOLUTION: The fixing device 40 includes the pressure pad 105 including the first curved portion 105R3 having the curve following the shape of the pressure roller 101, the second curved portion 105R3 having the curve in the direction opposite to the curve of the first curved portion 105R1, the third curved portion 105R2 having the curve including the inflection point, the fourth curved portion 105R3 having the curve in the direction opposite to the curve of the first curved portion 105R5, and the fifth curved portion 105R4 having the curve including the inflection point. The curvature radii at the inflection points of the third curved portion 105R2 and the fifth curved portion 105R4 are equal to or larger than 1mm.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to an image forming apparatus such as a copier, printer, facsimile machine, or a multifunction machine having a plurality of these functions, and a fixing device used in the image forming apparatus. [Background technology]

[0002] Some image forming apparatuses are equipped with a pad-fixing type fixing device in which a pressure pad, which is a non-rotating body located on the inner side of a heated, endless belt that runs in a circular motion, is pressed against the belt by a pressure roller located on the outer side of the belt to form a fixing nip between the belt and the pressure roller, and a recording material is passed through the fixing nip to fix an unfixed image on the recording material.

[0003] In this type of pad fixing method, the pressure applied from the pressure roller to the pressure pad via the belt is large, which increases the frictional resistance between the belt and the pressure pad, and this tends to accelerate wear on the inner peripheral surface of the belt. Therefore, it has been customary to apply a lubricant to the inner peripheral surface of the belt to reduce the frictional resistance between the belt and the pressure pad.

[0004] Furthermore, Patent Document 1 discloses a pressure pad that has a curved shape facing the pressure roller in the fixing nip portion, and a curved shape following the belt outside the fixing nip portion. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2020-190628 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the past, when the belt temperature rose or the belt rotation speed slowed, the thickness of the lubricant between the belt and the pressure pad became thinner, resulting in a mixed lubrication state in which fluid lubrication (fluid-mediated lubrication) and boundary lubrication (solid-solid contact) were mixed, causing stick-slip noise.

[0007] As a measure to prevent the generation of such noise, a method has been proposed in which a sliding sheet with fine irregularities is sandwiched between the belt and the pressure pad, but sliding sheets are expensive, which leads to an increase in costs.

[0008] The present disclosure has been made in consideration of the above circumstances, and aims to provide a fixing device that can suppress the generation of abnormal noise caused by stick-slip without providing a sliding sheet, and an image forming apparatus equipped with the fixing device. [Means for solving the problem]

[0009] In order to achieve the above object, the present disclosure provides a fixing device including an endless fixing belt, a heating member for heating the fixing belt, a nip forming member for supporting the fixing belt from an inner peripheral side, and a pressure rotating member for forming a fixing nip portion by pressing the fixing belt against the nip forming member, the nip forming member having a first curved portion having a curve following the shape of the pressure rotating member at the fixing nip portion, and a second curved portion having a curve in a direction opposite to the curve of the first curved portion on the upstream side of the first curved portion in the rotation direction of the fixing belt. a third curved-shaped portion disposed between the first curved-shaped portion and the second curved-shaped portion and having a curve including an inflection point; a fourth curved-shaped portion disposed downstream of the first curved-shaped portion in the rotation direction of the fixing belt and having a curve in the opposite direction to the curve of the first curved-shaped portion; and a fifth curved-shaped portion disposed between the first curved-shaped portion and the fourth curved-shaped portion and having a curve including an inflection point, wherein the radius of curvature at the inflection points of the third curved-shaped portion and the fifth curved-shaped portion is 1 mm or more. [Effects of the Invention]

[0010] According to the present disclosure, it is possible to provide a fixing device that can suppress the generation of noise due to stick-slip without providing a sliding sheet, and an image forming apparatus equipped with the fixing device. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a front cross-sectional view of an image forming apparatus according to a first embodiment of the present disclosure. [Figure 2] 2 is an enlarged cross-sectional view of the fixing device according to the first embodiment of the present disclosure. FIG. [Figure 3] FIG. 2 is a detailed cross-sectional view of the pressure pad according to the first embodiment of the present disclosure. [Figure 4] FIG. 10 is a detailed cross-sectional view of a conventional pressure pad. [Figure 5] 4 is a graph showing the results of a comparative experiment using a pressure pad configuration according to the first embodiment of the present disclosure and a conventional pressure pad configuration. [Figure 6] FIG. 10 is a detailed cross-sectional view of a fixing device provided with a conventional sliding sheet. [Figure 7] FIG. 6 is an enlarged cross-sectional view of a fixing device according to a second embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0012] Preferred embodiments of the present disclosure will be described in detail below with reference to the drawings. Note that the components described in the following embodiments are merely examples, and various conditions such as the configuration, function, dimensions, materials, shape, and relative arrangement of the device to which the present disclosure is applied can be appropriately modified or changed without departing from the spirit of the present disclosure, and are not limited to the following embodiments.

[0013] [First embodiment] FIG. 1 is a front cross-sectional view of an image forming apparatus according to a first embodiment of the present disclosure.

[0014] 1, a printer 500 serving as an image forming apparatus has four cartridges 7Y, 7M, 7C, and 7K arranged diagonally in a vertical direction as image forming units that sequentially form toner images of four colors: yellow (Y), magenta (M), cyan (C), and black (K). The four cartridges 7Y, 7M, 7C, and 7K each include photosensitive drum units 26Y, 26M, 26C, and 26K, each having photosensitive drum 1Y, 1M, 1C, and 1K as an electrophotographic photosensitive member, and developing units 4Y, 4M, 4C, and 4K.

[0015] Photosensitive drums 1Y, 1M, 1C, and 1K are each driven to rotate in a clockwise direction (direction Q) in Fig. 1 by a driving member (not shown). Additionally, cleaning members 6Y, 6M, 6C, and 6K, charging rollers 2Y, 2M, 2C, and 2K, and developing units 4Y, 4M, 4C, and 4K are arranged around photosensitive drums 1Y, 1M, 1C, and 1K in this order in the direction of rotation.

[0016] Cleaning members 6Y, 6M, 6C, and 6K remove toner remaining on photosensitive drums 1Y, 1M, 1C, and 1K, respectively, after the toner images formed on photosensitive drums 1Y, 1M, 1C, and 1K are transferred onto intermediate transfer film 5. The toner removed by cleaning members 6Y, 6M, 6C, and 6K is collected in removed toner chambers in photosensitive drum units 26Y, 26M, 26C, and 26K.

[0017] Furthermore, charging rollers 2Y, 2M, 2C, and 2K uniformly charge the surfaces of photoreceptor drums 1Y, 1M, 1C, and 1K, respectively. After the surfaces of photoreceptor drums 1Y, 1M, 1C, and 1K are charged by charging rollers 2Y, 2M, 2C, and 2K, the surfaces of photoreceptor drums 1Y, 1M, 1C, and 1K are exposed to laser light from scanner unit (exposure means) 3 through unit openings 32Y, 32M, 32C, and 32K. As a result, electrostatic latent images are formed on the surfaces of photoreceptor drums 1Y, 1M, 1C, and 1K. In this embodiment, scanner unit 3 is disposed below cartridges 7Y, 7M, 7C, and 7K.

[0018] Furthermore, developing units 4Y, 4M, 4C, and 4K are configured to supply toner to the electrostatic latent images formed on photosensitive drums 1Y, 1M, 1C, and 1K, respectively, to develop the electrostatic latent images into toner images. Developing units 4Y, 4M, 4C, and 4K are provided with developing rollers 25Y, 25M, 25C, and 25K that come into contact with photosensitive drums 1Y, 1M, 1C, and 1K, respectively, to supply toner to the surfaces of photosensitive drums 1Y, 1M, 1C, and 1K, and supply rollers 34Y, 34M, 34C, and 34K that come into contact with developing rollers 25Y, 25M, 25C, and 25K, respectively, to supply toner to developing rollers 25Y, 25M, 25C, and 25K.

[0019] When forming an image on recording paper S as a recording material, first, an electrostatic latent image formed on the surface of photosensitive drums 1Y, 1M, 1C, and 1K by scanner unit 3 is developed into a toner image by cartridges 7Y, 7M, 7C, and 7K, and then transferred to intermediate transfer film 5.

[0020] The intermediate transfer film 5 is stretched over a drive roller 10 and a tension roller 11, and is driven in the direction of arrow R in Fig. 1. Furthermore, primary transfer rollers 12Y, 12M, 12C, and 12K are disposed inside the intermediate transfer film 5, facing the respective photosensitive drums 1Y, 1M, 1C, and 1K, and a transfer bias is applied to them by a bias application means (not shown).

[0021] For example, when a negatively charged toner agent is used, a positive bias is applied to the primary transfer rollers 12Y, 12M, 12C, and 12K, whereby the toner images are sequentially transferred onto the intermediate transfer film 5. Then, the intermediate transfer film 5 is transported to the secondary transfer unit 15 with the four color toner images superimposed on it.

[0022] Meanwhile, in synchronization with the image forming operation described above, the recording paper S is fed toward the secondary transfer section 15 by a conveying mechanism including the feeding device 13, the pair of registration rollers 17, and the like.

[0023] The feeding device 13 has a feeding cassette 24 that stores a plurality of recording sheets S, a feeding roller 8 that feeds the recording sheets S, and a pair of conveying rollers 16 that convey the fed recording sheets S.

[0024] The feed cassette 24 is configured to be detachable from the printer 500. The user pulls out the feed cassette 24, removes it from the printer 500, sets the recording paper S, and inserts it into the printer 500 to complete the supply of recording paper S. The feed roller 8 presses against the topmost recording paper S stored in the feed cassette 24, and as the feed roller 8 rotates, the separation pad 9 separates the recording paper S one by one (friction piece separation method) and transports the recording paper S.

[0025] Then, the recording paper S transported from the feeding device 13 is transported to the secondary transfer unit 15 by a pair of registration rollers 17. In the secondary transfer unit 15, a positive bias is applied to a secondary transfer roller 18, thereby secondarily transferring the four-color toner image on the intermediate transfer film 5 onto the transported recording paper S. At this time, any toner remaining on the intermediate transfer film 5 after the secondary transfer onto the recording paper S is removed by a transfer film cleaning device 23, and the removed toner passes through a waste toner transport path (not shown) and is collected in a waste toner collection container (not shown).

[0026] The recording paper S onto which the toner image has been secondarily transferred in the secondary transfer section 15 is transported from the secondary transfer section 15 to the fixing device 40, which applies heat and pressure to the image transferred onto the recording paper S to fix the image onto the recording paper S.

[0027] Thereafter, the recording paper S on which the toner image has been fixed is discharged onto a discharge tray 20 by a pair of discharge rollers 19.

[0028] Figure 2 is an enlarged cross-sectional view of the fixing device 40 in Figure 1. Here, in Figure 2, the X-axis direction and the Y-axis direction represent the left-right direction and the up-down direction when the printer 500 is viewed from the front side, and the Z-axis direction is a direction perpendicular to both the X-axis and the Y-axis and corresponds to the depth direction of the printer 500. Furthermore, the X-axis direction is the positive direction of the X-axis (the right direction in Figure 2), and the direction opposite to the X-axis direction is the negative direction of the X-axis (the left direction in Figure 2). Figure 2 is a cross-sectional view of the fixing device 40 cut along an XY plane perpendicular to the Z-axis.

[0029] In Figure 2, the fixing device 40 is composed of an endless fixing belt 102, a heating roller 104 as a heating member that heats the fixing belt 102, a heater 107 as a heat source, a pressure pad 105 as a nip forming member that is a sliding member that supports the fixing belt 102 from the inner side, a pad stay 103 that supports the pressure pad 105, a pressure roller 101 as a pressure rotating member that presses the pressure pad 105 from the outer side of the fixing belt 102 to form a nip, and a regulating member (not shown) that regulates the movement of the fixing belt 102 in the rotational axis direction (Z direction), and the fixing belt 102 is driven to rotate by receiving drive from the pressure roller 101, thereby conveying the recording paper S while pressing and heating it.

[0030] The fixing belt 102 is wound around a pressure pad 105 and a heating roller 104, and tension acts on the heating roller 104 in a direction away from the pressure pad 105 by an elastic member such as a spring (not shown).

[0031] The fixing belt 102 is a cylindrical heat-resistant fixing belt that serves as a heating member for transferring heat to the recording paper S. From the inside, the fixing belt 102 is made up of a base layer made of polyimide, SUS (stainless steel), Ni (nickel) electroforming, or the like, on which an elastic layer made of a highly heat-resistant material such as silicone rubber or fluororubber, and a release layer provided with release properties such as a fluorine tube or fluorine coating are laminated in this order.

[0032] The pressure roller 101, which serves as a pressure member, is composed of a metal core and a heat-resistant, elastic material layer such as silicone rubber, fluororubber, or fluororesin that is concentrically molded and coated around the core into a roller shape, with a release layer provided on the surface. For example, the release layer can be made of a material with good release and heat resistance, such as fluororesin, silicone resin, fluorosilicone rubber, fluororubber, silicone rubber, PFA, PTFE, or FEP. The pressure roller 101 receives drive from a fuser motor (not shown) installed in the printer 500, causing the fuser belt 102 to rotate in tandem with the pressure roller 101. In this embodiment, the pressure roller 101 has a diameter of 35 mm.

[0033] The heating roller 104 is a cylindrical roller made of a metal such as aluminum or SUS, and its rotation axis is parallel to the Z-axis direction in Fig. 2, with both axial ends of the heating roller 104 rotatably supported by a frame (not shown). The outer diameter of the heating roller 104 is arbitrary, but since a heater 107 as a heat source is inserted into the space within the heating roller 104, it is desirable to paint the inner surface of the heating roller 104 black so that heat is efficiently transferred from the heater 107 to the heating roller 104.

[0034] Heater 107 (a halogen heater in this embodiment) is a heating means (heat source). Heater 107 is a long halogen heater that is inserted along the axial direction of heating roller 104 and is supported within the interior space of cylindrical heating roller 104. Heater 107 applies heat generated by power supply from a power source (not shown) to heating roller 104. Note that heater 107 is not limited to a type that uses heat from a halogen heater. For example, other types of heaters, such as an infrared heater or an electric heating wire, may also be used.

[0035] A lubricant is interposed between the fixing belt 102 and the pressure pad 105 to reduce the sliding friction resistance on the sliding surfaces of the fixing belt 102 and the pressure pad 105. In this embodiment, fluorine oil (viscosity 1000 cSt at 23°C) is used. Other lubricants include, but are not limited to, silicone oil or PEPE (perfluoropolyether) grease thickened with the fluororesin PTFE.

[0036] The lubricant is applied to the sliding surface of the pressure pad 105 or the fixing belt 102. When the fixing belt 102 and the pressure roller 101 rotate while being pressed against each other and forming a nip, the lubricant spreads evenly over the sliding surface, thereby reducing the sliding torque.

[0037] The pressure pad 105 is a heat-resistant and heat-insulating member whose length is in a direction that intersects with the conveyance direction of the recording paper S, and is made of a material with good insulating and heat-resistant properties, such as phenolic resin, polyimide resin, polyamide resin, polyamideimide resin, PEEK resin, PES resin, PPS resin, PFA resin, PTFE resin, or LCP resin, and serves to back up the fixing belt 102, apply pressure to the fixing nip formed by pressing the pressure roller 101 against the fixing belt 102, and ensure stable conveyance when the fixing belt 102 rotates.

[0038] 3 shows a detailed cross-sectional view of the pressure pad 105. In this embodiment, the radius of curvature is measured using, for example, a shape measuring machine (VR3000 or VR6000 manufactured by KEYENCE Corporation).

[0039] In FIG. 3, the sliding surface of the pressure pad 105 is made up of a combination of curved shapes.

[0040] The pressure pad 105 has a first curved portion 105R3 in the fixing nip region 105H3, which has a curve that is convex in the opposite direction of the X-axis direction and follows the shape of the pressure roller 101. The radius of curvature of the first curved portion 105R3 is larger than the radius of curvature of the pressure roller 101. The center of the radius of curvature of the first curved portion 105R3 is located on the X-axis side of the first curved portion 105R3. By providing the first curved portion 105R3 configured as described above, the pressure gradually increases from the entrance side to the exit side. In this embodiment, the radius of curvature of the first curved portion 105R3 is 30 mm.

[0041] The second curved portion 105R1 in the region 105H1 on the fixing entrance side (the upstream side of the first curved portion 105R3 in the rotation direction of the fixing belt 102) has a curve that is convex in the X-axis direction, opposite to the curve of the first curved portion 105R3, so as to prevent unnecessary stress from being applied to the fixing belt 102 when it is pulled by the fixing belt 102. In other words, the center of the radius of curvature of the second curved portion 105R1 is located on the opposite side of the X-axis direction from the second curved portion 105R1. In this embodiment, the radius of curvature of the second curved portion 105R1 is 15 mm.

[0042] The fourth curved portion 105R5 in the region 105H5 on the fixing exit side (downstream of the first curved portion 105R3 in the rotation direction of the fixing belt 102) has a curve that is convex in the X-axis direction opposite to the curve of the first curved portion 105R3, and functions to separate the recording paper S so that it does not wrap around the fixing belt 102. In other words, the center of the curvature radius of the fourth curved portion 105R5 is located on the opposite side of the X-axis direction from the fourth curved portion 105R5. In this embodiment, the radius of curvature of the fourth curved portion 105R5 is 40 mm.

[0043] In region 105H2 between fixing entrance region 105H1 and fixing nip region 105H3, there is a third curved portion 105R2, which forms the junction between second curved portion 105R1 and first curved portion 105R3. The third curved portion 105R2 has a curve that is convex in the X-axis direction, including an inflection point where the slope of the third curved portion 105R2 relative to the Y-axis changes from increasing to decreasing. More specifically, the radius of curvature at the inflection point of the third curved portion 105R2 in FIG. 3 is 1 mm. The center of the radius of curvature at the inflection point of the third curved portion 105R2 is located on the opposite side of the X-axis from the third curved portion 105R2. As a result, the center of the radius of curvature of first curved portion 105R3 and the center of the radius of curvature at the inflection point of third curved portion 105R2 are located on opposite sides of third curved portion 105R2. The radius of curvature at the inflection point of third curved portion 105R2 is calculated by taking the inflection point of third curved portion 105R2 in the X-axis direction relative to the Y-axis as one point and choosing two arbitrary points a predetermined distance (e.g., 0.1 mm) on either side of the inflection point. The radius of curvature at the inflection point of third curved portion 105R2 is not limited to 1 mm, but may be 1 mm or greater.

[0044] Additionally, a fifth curved portion 105R4 is located in a region 105H4 between the fixing exit region 105H5 and the fixing nip region 105H3, where the fourth curved portion 105R5 and the first curved portion 105R3 join. The fourth curved portion 105R5 has a curve that is convex in the X-axis direction and includes an inflection point where the slope of the fifth curved portion 105R4 relative to the Y-axis changes from increasing to decreasing. In this embodiment, the radius of curvature at the inflection point of the fifth curved portion 105R4 is 1 mm. The center of the radius of curvature at the inflection point of the fifth curved portion 105R4 is located on the opposite side of the X-axis from the fifth curved portion 105R4. As a result, the center of the radius of curvature of first curved portion 105R3 and the center of the radius of curvature at the inflection point of fifth curved portion 105R4 are located on opposite sides of fifth curved portion 105R4. The radius of curvature at the inflection point of fifth curved portion 105R4 is calculated by taking the inflection point of fifth curved portion 105R4 in the X-axis direction relative to the Y-axis as one point and choosing two arbitrary points a predetermined distance (e.g., 0.1 mm) on either side of the inflection point. The radius of curvature at the inflection point of fifth curved portion 105R4 is not limited to 1 mm, but may be 1 mm or greater.

[0045] Here, for comparison, the difference in shape between the pressure pad 105 of this embodiment and a conventional pressure pad will be described.

[0046] FIG. 4 is a detailed cross-sectional view of a pressure pad in a conventional example.

[0047] 4, the conventional pressure pad 205 differs from the pressure pad 105 of this embodiment in the curved shape 205R2 of the region 205H2 at the junction between the curved shape of the fixing nip portion and the curved shape of the fixing inlet, and the curved shape 205R4 of the region 205H4 at the junction between the curved shape of the fixing nip portion and the curved shape of the fixing outlet. The pressure pad 105 of this embodiment has a curvature radius of 1 mm (third curved shape portion 105R2, fifth curved shape portion 105R4), while the conventional pressure pad 205 has a curvature radius of 0.5 mm (curved shapes 205R2, 205R4).

[0048] Next, as a comparative experiment to determine whether the lubricant is effectively used in the pressure pad configuration of this embodiment and the pressure pad configuration of a conventional example, data comparing the film thickness of the lubricant passing through the fixing nip is shown in the graph of FIG.

[0049] The conveying conditions were a pressure of 350 N in the fixing nip, a conveying speed of 300 mm / sec, and a temperature of the fixing belt of 180° C. The horizontal axis in Figure 5 represents the radius of curvature of the curved shape of the joints between the fixing nip and the fixing entrance and exit sections.

[0050] The pressure pad 105 of this embodiment has a curvature radius of 1 mm (third curved portion 105R2, fifth curved portion 105R4), whereas the pressure pad 205 of the conventional example has a curvature radius of 0.5 mm (curved shapes 205R2, 205R4). Cases with curvature radii of 2 mm and 3 mm are also shown.

[0051] The vertical axis represents the thickness of the lubricant film that passes through the fixing nip. This shows that the thickness of the lubricant film is more than double when the curvature radius is 1 mm or more (third curved portion 105R2, fifth curved portion 105R4) compared to when the curvature radius is 0.5 mm (curved portions 205R2, 205R4). This shows that by increasing the curvature radius of the curved portion at the joint, the contact area between the curved portion at the joint and the fixing belt increases, reducing the peak pressure, and increasing the film thickness that allows the lubricant to pass through the fixing nip.

[0052] When the lubricant film thickness becomes too thin, a mixed lubrication state occurs in which fluid lubrication (fluid-mediated lubrication) and boundary lubrication (solid-solid contact) are mixed, causing noise due to stick-slip. However, by increasing the lubricant film thickness, stable fluid lubrication can be maintained and noise due to stick-slip does not occur. Experiments have shown that the boundary must be 1.5 μm or more, so the conventional example's curvature radius of 0.5 mm (curved shapes 205R2, 205R4) cannot maintain fluid lubrication, and the present embodiment's curvature radius of 1 mm or more (third curved shape portion 105R2, fifth curved shape portion 105R4) is required.

[0053] FIG. 6 shows a detailed cross-sectional view of a conventional fixing device provided with a sliding sheet.

[0054] In conventional fixing devices, the conventional pressure pad shape shown in FIG. 4 causes noise due to stick-slip, so as shown in FIG. 6, a sliding sheet 206 is arranged so as to be wrapped around the pressure pad 205, and the sliding sheet 206 is interposed between the fixing belt 102 and the pressure pad 205.

[0055] Sliding sheet 206 is fixed to pad stay 103307 with screws (not shown). Sliding sheet 206 is made of a heat-resistant resin sheet such as PEEK (polyether ether ketone) or a glass fiber substrate, on which a fluororesin layer is formed to reduce sliding resistance with fixing belt 102. This suppresses noise caused by stick-slip in conventional fixing devices.

[0056] In contrast to this, in this embodiment, it is possible to suppress noise due to stick-slip without providing the sliding sheet 206 that was necessary in the conventional fixing device.

[0057] Second Embodiment Next, a second embodiment of the present disclosure will be described with reference to FIG.

[0058] 7 is an enlarged cross-sectional view of a fixing device according to a second embodiment of the present disclosure. Note that the basic configuration and operation of this embodiment are the same as those of the first embodiment, and therefore, by way of reference, the same components as those of the first embodiment are denoted by the same reference numerals and their description will be omitted.

[0059] 7, the base material of fixing belt 302 is made of Ni (nickel), and is a metal layer that generates heat by induction due to the action of magnetic flux generated by IH coils 307a and 307b (described later). The elastic layer and the release layer are the same as those in the first embodiment, so their description will be omitted.

[0060] Next, a description will be given of the IH unit 306. The IH unit 306 is made up of IH coils 307a and 307b and magnetic cores 308a and 308b, and is encased in an IH case (not shown) made of heat-resistant resin.

[0061] IH coils 307a and 307b are made by winding copper wire around a horizontally long, flat sheet-like spiral coil and forming it into a predetermined cross-sectional shape. The copper wire is a Litz wire, and it is desirable to use a coating with a high heat resistance temperature. IH coils 307a and 307b are formed so as to fit the outer surface of fixing belt 302, which is the heated object. A high-frequency current is applied to IH coils 307a and 307b to generate a magnetic field, which inductively heats fixing belt 302.

[0062] Magnetic cores 308a and 308b are formed to cover IH coils 307a and 307b so that the magnetic field generated by IH coils 307a and 307b does not leak outside the metal layer of fixing belt 302. Magnetic cores 308a and 308b are preferably made of a material with high magnetic permeability and low self-loss, such as ferrite.

[0063] In this embodiment, as in the first embodiment, noise due to stick-slip can be suppressed without providing a sliding sheet. [Explanation of symbols]

[0064] 40...Fusing device 101...Pressure roller 102, 302...Fuser belt 103...Pad stay 104...heating roller 105...Pressure pad 105R1...Second curved section 105R2...Third curved section 105R3...First curved section 105R4...5th curved section 105R5...Fourth curved section 107...Heater 205...Pressure pad in the conventional example 206... Conventional sliding sheet 306...IH unit 307a, 307b...IH coil 308a, 308b...Magnetic core 500...Printer S...Recording paper

Claims

1. an endless fixing belt; a heating member that heats the fixing belt; a nip forming member that supports the fixing belt from the inner peripheral side; a pressure rotating member that presses against the nip forming member via the fixing belt to form a fixing nip portion; and The nip forming member is a first curved portion having a curve that follows the shape of the pressure rotating member in the fixing nip portion; a second curved portion having a curve that is opposite to the curve of the first curved portion on the upstream side of the first curved portion in the rotation direction of the fixing belt; a third curved portion provided between the first curved portion and the second curved portion and having a curve that includes an inflection point; a fourth curved portion having a curve that is opposite to the curve of the first curved portion on the downstream side of the first curved portion in the rotation direction of the fixing belt; and a fifth curved portion provided between the first curved portion and the fourth curved portion and having a curve that includes an inflection point, The radius of curvature at the inflection points of the third curved portion and the fifth curved portion is 1 mm or more. A fixing device characterized by:

2. A lubricant is applied to the inner circumferential surface of the belt.

2. The fixing device according to claim 1, wherein the fixing device is a fixing device for fixing a toner image onto a recording medium.

3. The nip forming member is made of resin.

2. The fixing device according to claim 1, wherein the fixing device is a fixing device for fixing a toner image onto a recording medium.

4. the heating member contacts the inner circumferential surface of the fixing belt and heats the belt; 2. The fixing device according to claim 1, wherein the fixing device is a fixing device for fixing a toner image onto a recording medium.

5. the heating member is disposed opposite to the outer peripheral surface of the fixing belt and heats the belt; 2. The fixing device according to claim 1, wherein the fixing device is a fixing device for fixing a toner image onto a recording medium.

6. a center of the radius of curvature of the first curved portion and a center of the radius of curvature at the inflection point of the third curved portion are located on opposite sides of the third curved portion; 2. The fixing device according to claim 1, wherein the fixing device is a fixing device for fixing a toner image onto a recording medium.

7. a center of the radius of curvature of the first curved portion and a center of the radius of curvature at the inflection point of the fifth curved portion are located on opposite sides of the fifth curved portion; 2. The fixing device according to claim 1, wherein the fixing device is a fixing device for fixing a toner image onto a recording medium.

8. an image forming unit that forms a toner image; a fixing device according to claim 1 , which fixes a toner image formed by the image forming unit onto a recording material; An image forming apparatus comprising:

Images