Image forming apparatus

Abstract

To reduce the sliding resistance between a pad and a belt to extend the life of the belt.SOLUTION: A fixing device comprises: a belt 301 that heats a recording material; a pressure member 304; a pad 305; and an oil application member that applies oil to an inner peripheral surface of the belt. In a width direction of the belt, the length of the belt is larger than the length of the pad. The pad has a first surface 305a that forms a nip part, a second surface 305b that faces the first surface, and third surfaces 305c that connect the first surface and second surface to each other in the width direction. The third surfaces are formed at both ends in the width direction of the pad, and the boundary between the first surface and the third surface has a curved shape.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus for forming an image on a recording material. [Background technology]

[0002] In recent years, the on-demand printing market has expanded, where commercial printed materials such as catalogs, posters, and pamphlets are printed according to the required number of copies. There is a demand for faster printing times for electrophotographic image forming devices that handle on-demand printing. In order to achieve faster printing times, it is necessary to increase the heating efficiency of the recording material when fixing a toner image to the recording material. To this end, it has been proposed to widen the fixing nip in order to increase the heating efficiency. Furthermore, a fixing device has been proposed that suppresses the occurrence of paper wrinkles by making the fixing nip flat.

[0003] To make the fixing nip flat, an endless belt and a nip forming member that forms a flat nip on the inner peripheral surface of the belt are used. The belt conveys the recording material by rotating. The rotation of the belt causes the belt and the nip forming member to slide against each other. A configuration has been disclosed in which oil is applied to the inside of the belt to make this sliding smooth (Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2017-181948 A Summary of the Invention [Problem to be solved by the invention]

[0005] In order to prevent the oil applied to the inside of the belt from leaking out to the outside of the belt, the length of the belt is longer than that of the nip forming member in the width direction of the belt. However, since the belt is a suspended member, if the length of the belt in the width direction is longer than that of the nip forming member, stress will be concentrated at the end of the nip forming member that comes into contact with the belt.

[0006] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to reduce the sliding resistance between a nip forming member and a belt in a fixing device in which oil is applied to the inner peripheral surface of the belt. [Means for solving the problem]

[0007] In consideration of the above problems, the fixing device of the present invention is characterized in that it includes an endless belt for heating a recording material, a pressure member that contacts the outer peripheral surface of the belt to form a nip portion, a pad that is arranged on the inner peripheral surface of the belt and forms the nip portion together with the pressure member via the belt, the pressure member, together with the belt, applies heat and pressure to a recording material carrying a toner image at the nip portion to fix the toner image to the recording material, and an oil application member that applies oil to the inner peripheral surface of the belt, and in the width direction of the belt, a length of the belt is greater than a length of the pad, the pad has a first surface that forms the nip portion, a second surface opposite to the first surface, and a third surface that connects the first surface and the second surface in the width direction, the third surface is formed at each of both ends of the pad in the width direction, and the boundary between the first surface and the third surface has a curved shape. Effect of the Invention

[0008] According to the present invention, the sliding resistance between the nip forming member and the belt is reduced, thereby making it possible to improve the life of the belt. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram of an image forming apparatus. [Diagram 2] FIG. 2 is a schematic cross-sectional view of a fixing device according to the present embodiment. [Diagram 3] FIG. 4 is an enlarged view of a nip portion in the embodiment. [Figure 4] FIG. 4 is an enlarged view of a nip portion in the embodiment. [Diagram 5] 4 is a graph illustrating the durability of the belt of the present embodiment. [Figure 6] FIG. 4 is an enlarged view of a width direction end portion of the pad in the present embodiment. [Figure 7] FIG. 13 is a schematic diagram of a modified pad. [Figure 8] 4 is a graph illustrating the durability of the belt of the present embodiment. [Figure 9] 5 is a graph for explaining oil leakage from the belt of the present embodiment. [Figure 10] FIG. 11 is a diagram showing conditions for achieving both belt durability and oil leakage suppression. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] <Image forming device> The schematic configuration of the image forming apparatus of this embodiment will be described with reference to FIG.

[0011] FIG. 1 is a diagram showing a full-color image forming apparatus according to this embodiment. The image forming apparatus 1 includes an image reading unit 2 and an image forming apparatus main body 3. The image reading unit 2 reads an original placed on an original platen glass 21, and light emitted from a light source 22 is reflected by the original and an image is formed on a CCD sensor 24 via an optical system member 23 such as a lens. Such an optical system unit converts the original into an electric signal data string for each line by scanning in the direction of the arrow. The image signal obtained by the CCD sensor 24 is sent to the image forming apparatus main body 3, and image processing is performed in a control unit 30 according to each image forming unit described later. The control unit 30 also receives an external input from an external host device such as a print server as an image signal.

[0012] The image forming apparatus main body 3 includes a plurality of image forming sections Pa, Pb, Pc, and Pd, and each image forming section forms an image based on the image signal. That is, the image signal is converted into a laser beam that is PWM (pulse width modulation) controlled by a control section 30. In Fig. 1, 31 denotes a polygon scanner serving as an exposure device, which irradiates a laser beam according to the image signal. Then, the laser beam is irradiated onto photosensitive drums 200a to 200d serving as image carriers of the image forming sections Pa to Pd.

[0013] Note that Pa is a yellow (Y) image forming section, Pb is a magenta (M) image forming section, Pc is a cyan (C) image forming section, and Pd is a black (Bk) image forming section, which form images of the corresponding colors. Since the image forming sections Pa to Pd are substantially the same, the Y image forming section Pa will be described in detail below, and the description of the other image forming sections will be omitted. In the Y image forming section Pa, 200a is a photosensitive drum, and a toner image is formed on the surface based on an image signal, as described below.

[0014] A primary charger 201a charges the surface of the photosensitive drum 200a to a predetermined potential. An electrostatic latent image is formed on the surface of the photosensitive drum 200a, which is charged to a predetermined potential, by a laser beam from the polygon scanner 31. A developer 202a develops the electrostatic latent image on the photosensitive drum 200a to form a toner image. A transfer roller 203a discharges from the back of the intermediate transfer belt 204, applies a primary transfer bias of the opposite polarity to the toner, and transfers the toner image on the photosensitive drum 200a onto the intermediate transfer belt 204. The surface of the photosensitive drum 200a after transfer is cleaned by a cleaner 207a. The toner image on the intermediate transfer belt 204 is transported to the next image forming section, where the toner images of each color formed in each image forming section are transferred in the order of Y, M, C, and Bk, and a four-color image is formed on the surface. The toner image that has passed through the Bk image forming section is transported to a secondary transfer section composed of a pair of secondary transfer rollers 205 and 206. In the secondary transfer section, a secondary transfer electric field of the opposite polarity to the toner image on the intermediate transfer belt 204 is applied, so that the toner image is secondarily transferred to the recording material P. The recording material fed from the paper feed cassette 8 or 9 waits in the registration section 208, and then the timing is controlled to align the position of the toner image on the intermediate transfer belt with the recording material, and the recording material is conveyed from the registration section. The toner image on the recording material is then fixed to the recording material by the fixing device F, which serves as an image heating device. After passing through the fixing device, the recording material is discharged outside the machine. In the case of a double-sided JOB, when the transfer and fixing of the toner on the first side (first side) of the image formation is completed, the process proceeds to the step of image formation on the second side. The recording material on which the fixing of the first side has been completed passes through a reversing section provided inside the image forming device, where the front and back of the recording material are reversed. After that, a toner image is formed on the second side and fixed. The recording material on which the toner has been fixed on both sides is then discharged outside the machine and stacked on the discharge tray 7.

[0015] Next, the configuration of the fixing device F in this embodiment will be described with reference to FIG.

[0016] <Fixing device> A schematic diagram of the overall configuration of a belt heating fixing device F according to this embodiment is shown in Fig. 2. In the figure, the X direction indicates the recording material conveyance direction, the Y direction indicates the belt width direction, and the Z direction indicates the pressure direction in which the pressure roller 304 applies pressure against the pad.

[0017] The fixing device F has a fixing belt (hereinafter, "belt") 301 as an endless rotatable heating rotor. On the inner peripheral surface of the belt 301, a heating roller (heating member) 303, a pad 305 as a nip forming member, and a steering roller 307 are arranged. Furthermore, an oil application roller 306 as an oil application member that applies oil to the inner peripheral surface of the belt 301 is arranged. Inside the heating roller 303, a halogen heater 302 as a heat source is arranged. In addition, a pressure roller (pressure member) 304 that abuts against the outer peripheral surface of the belt 301 is arranged, and a fixing nip portion (hereinafter, nip) N is formed with the pad 305 as a nip forming member via the belt 301.

[0018] The belt 301 has thermal conductivity, heat resistance, etc., and is a thin-walled cylindrical shape. In this embodiment, it has a three-layer structure formed in the order of a base layer, an elastic layer, and a release layer from the inside. The base layer is 80 μm thick and made of polyimide resin (PI). The elastic layer is 300 μm thick and made of silicone rubber. The release layer is 30 μm thick and made of PFA (tetrafluoroethylene-perfluoroalkoxyethylene copolymer resin) as a fluororesin. In this embodiment, the belt 301 has a heating roller 303, a pad 305, an oil application roller 306, and a steering roller 307 in contact with the inner peripheral surface of the belt 301. The outer diameter of the belt 301 is 150 mm.

[0019] Heating roller 303 is a stainless steel pipe with a thickness of 1 mm, and has halogen heater 302 disposed therein as a heat source, capable of generating heat up to a predetermined temperature. Heating roller 303 is disposed downstream of pad 305 in the rotation direction of belt 301. Belt 301 is heated by heating roller 303. Heating roller 303 in this embodiment is configured to be rotated by a motor. As heating roller 303 is rotated, belt 301 is stretched between pad 305 and heating roller 303.

[0020] The pressure roller 304 is formed of a core metal layer which is a shaft, an elastic layer, and a release layer. The core metal layer is made of SUS material with a diameter of 72 mm. The elastic layer is formed on the outer peripheral surface of the core metal layer and is made of conductive silicone rubber with a thickness of 8 mm. The release layer is formed on the outer peripheral surface of the elastic layer and is made of PFA (tetrafluoroethylene-perfluoroalkoxyethylene copolymer resin) as a fluororesin with a thickness of 100 μm. The pressure roller 304 is axially supported by the frame of the fixing device F, and a gear is fixed to one end of the pressure roller 304, which is connected to a drive source via the gear and is driven to rotate.

[0021] Pad 305 forms a nip N with pressure roller 304 via belt 301. Pad 305 is made of LCP (liquid crystal polymer) resin. As shown in Fig. 3, pad 305 has a corner with R = 4 mm in the width direction. R is not limited to 4 mm, and may be in the range of 2.0 to 8.0 mm.

[0022] Oil application roller 306 applies oil as a lubricant to the inner peripheral surface of belt 301, enabling belt 301 to slide smoothly against pad 305. In this embodiment, a roller is used as the oil application member, but this is not limited to this. Any configuration that can apply oil to belt 301 may be used. For example, the oil application member may be a non-rotating body such as oil-impregnated felt that comes into contact with the inner peripheral surface of belt 301. Any oil application member that can apply oil to the inner peripheral surface of belt 301 may be used.

[0023] The steering roller 307 applies a predetermined tension to the belt 301 by pressing the belt 301 from the inside to the outside of the belt with a spring. The steering roller 307 also adjusts the position of the belt 301 in the Y direction by controlling the inclination in the Y direction. The steering roller 307 is disposed upstream of the pad 305 in the rotation direction of the belt 301.

[0024] Belt 301, stretched by multiple tension members, rotates in response to the rotation of pressure roller 304. As belt 301 rotates, steering roller 307 moves the belt 301 in the width direction, thereby shifting the position of the "edge" of the recording material. This makes it possible to prevent so-called edge scratches and improve image quality. Steering roller 307 has a swing center, and can move belt 301 in the width direction by swinging.

[0025] Heat and pressure are applied to the recording material carrying the toner image in the nip portion N formed between the belt 301 and the pressure roller 304. As a result, the unfixed toner image on the recording material is fixed to the recording material by passing through the nip portion N.

[0026] In this embodiment, the pressure in the nip N during printing is set to 1600 N, the width of the nip N in the X direction (transport direction) is set to 24.5 mm, and the width in the Y direction (paper width direction) is set to 326 mm. However, the present invention is not limited to this, and the pressure and the width of the nip N can be changed arbitrarily as long as the toner image on the recording material can be fixed.

[0027] In this embodiment, the use of oil improves the sliding property between the belt 301 and the pad 305. However, there is a risk that the oil will leak from the inner peripheral surface of the belt 301. This occurs due to the application of pressure to the nip portion N. A strong force is generated between the belt 301 and the pad at the nip portion N, which pushes the oil outward in the width direction. This causes the oil to leak outward from the belt 301. To prevent this, the length of the belt 301 in the width direction (Y direction) is made greater than the length of the pad 305 in the width direction.

[0028] However, on the other hand, if the length of the belt 301 in the width direction (Y direction) is made larger than the length of the pad 305 in the width direction, there is a risk that cracks will occur in the belt 301.

[0029] <Cracks occurring in the fixing belt> The cracks in the belt 301 will now be described. The fixing belt crack is a phenomenon in which the belt 301 breaks due to bending fatigue. In the configuration of this embodiment, the belt 301 bends at the end of the nip N in the width direction when passing through the nip N as shown in FIG. 4. This bending occurs every time the belt 301 passes through the nip N. There is a limit to the number of times the belt 301 can bend, and when the limit is reached, a crack occurs in the belt 301.

[0030] Therefore, the fixing device of this embodiment suppresses the occurrence of cracks in the belt 301 while suppressing oil leakage. The detailed method thereof will be described below.

[0031] <Pad shape> The pad 305 of this embodiment has a curved shape. The curved shape is formed at the boundary between the first surface 305a and the third surface 305c of the pad 305.

[0032] The pad 305 has a first surface 305a, a second surface 305b, and a third surface 305c. The pad 305a is a surface that forms the nip portion N, and indicates the range up to the dashed line in FIG. 3. The second surface 305b is a surface that is located opposite the first surface 305a. More specifically, it is a surface that faces the first surface 305a in the direction from the pressure roller 304 toward the pad 305. The third surface 305c is a surface that connects the first surface 305a and the second surface 305b. The third surface is formed at both ends of the pad 305 in the width direction.

[0033] In this embodiment, the starting point of the curved shape is the boundary between the first surface 305a and the third surface 305c. The belt moves away from the pressure roller 304 from the point where the curved shape starts.

[0034] In addition, the boundary between the second surface and the third surface is shaped as a right angle. It may be shaped as a curved surface. In this embodiment, the boundary between the second surface and the third surface is shaped as a right angle for ease of processing.

[0035] In the width direction, the length of belt 301 is longer than that of pad 305, so that belt 301 is wound around the end of pad 305. Furthermore, the tension applied to belt 301 is increased by the driving of heating roller 303. Therefore, the stress on the end of pad 305, that is, the boundary between first surface 305a and third surface 305c, becomes strong. In order to reduce this, the boundary is provided with a curved shape. By providing a curved shape on the boundary between first surface 305a and third surface 305c, the stress is reduced.

[0036] During the fixing of the recording material, the belt 301 reciprocates by a predetermined width due to the steering roller 307. Even during this reciprocating movement, the first surface 305a of the pad 305 of this embodiment is covered by the belt 301. By setting the length relationship as described above, the first surface 305a is not exposed from the belt 301, and the configuration is such that oil leakage can be suppressed.

[0037] The number of times that the belt 301 can be bent varies depending on the Young's modulus and strain ε, which are determined by the material of the belt 301. In the configuration of this embodiment, polyimide (PI) is used as the material of the belt 301, and the bending strain is 1.0×10 6 The target is to endure bending times of 1.0×10 6 In order to withstand bending, the stress on the belt 301 must be 156 MPa or less, as shown in Figure 5. In general, when a beam with a thickness t [mm] bends along an arc with a radius of curvature R, the strain ε is expressed by the following equation.

[0038]

number

[0039] In addition, the stress σ, Young's modulus E, and strain ε are related by the following equations. σ=Eε Combining the above two equations gives the following equation:

[0040]

number

[0041] Therefore, in order to keep the stress on the belt 301 at 156 MPa or less, the following relationship must be satisfied.

[0042]

number

[0043] This formula can be transformed into the following formula:

[0044]

number

[0045] <Oil leak> Next, oil leakage will be described. Oil leakage is a phenomenon in which oil applied to the inner surface of the belt 301 runs down the pad and drips. The dripping oil stains the outer surface of the belt 301 and the recording material P, causing image defects. As shown in FIG. 6, when the belt is wrapped around the third surface 305c of the pad 305, oil leakage occurs when the length L [mm] of the pad 305 that contacts the belt 301 on the third surface 305c is shorter than the arc length πR / 2 of the end of the pad. To prevent oil leakage, the curvature radius R [mm] and L [mm] of the end of the pad 305 must satisfy the following relationship.

[0046]

number

[0047] It is preferable that L is 30 mm or less due to spatial restrictions of belt 301 and pad 305 inside the image forming apparatus.

[0048] From the above, the condition for suppressing the fixing belt crack and preventing the oil leakage at the same time can be expressed by the following formula.

[0049]

number

[0050] In the following, while changing the Young's modulus E in the configuration of the embodiment, t [mm], L, and the radius of curvature R of the end of the pad 305 are plotted to verify whether the above-mentioned formula is valid. Before the verification, the parameters used in the verification will be explained.

[0051] <Methods for measuring various parameters> The parameter measuring method of this embodiment will be described below with reference to FIG.

[0052] The method for measuring the Young's modulus E of the belt 301 will be described. When measuring the Young's modulus, a tensile tester AG-X manufactured by Shimadzu Corporation is used. The attachment of the tensile tester AG-X is a load cell for 500N, and the chuck is a mechanical parallel clamping grip for 500N. When performing the tensile test, the thermostatic chamber temperature is set to 180 degrees, the pulling speed is set to 5mm / min, and the result of the thickness measurement in advance is input. The thickness measurement value used above is the thickness value of the belt base layer, which has the greatest strength among the layers of the belt 301. The elastic modulus is calculated in the range of the load cell test force from 10N to 15N. This measurement is started after confirming that the thermostatic chamber setting temperature for the tensile test has reached 180 degrees. The dumbbell shape used in the tensile test is that specified by JIS K7139-A24. After performing 10 measurements in each of the circumferential direction and the width direction, the average value of each is taken to determine the elastic modulus in the circumferential direction and the width direction. The belt's longitudinal elastic modulus E [MPa] in this measurement was the average value in the circumferential and width directions. If the belt has multiple types and layers, they should all be treated as one layer and the above procedure should be followed.

[0053] The method of measuring the thickness t of the belt 301 will be described. When measuring the thickness, the belt 301 is cut into four equal parts in the Y direction (paper width direction) to create samples. The belt thickness was measured using a digital length measuring device CT6001 manufactured by HEIDENHAIN. The temperature and humidity conditions during the measurement were 23 degrees and 30%. The thickness of each of the four equal parts was measured in the X direction (paper feed direction) at four points, and the average value of the four equal parts was taken as the belt thickness t [mm]. In this measurement, if the belt has multiple types and layers like the belt 301 in Figure 1, the thickness of the base layer excluding the belt elastic layer and surface layer is measured. If the belt has layers other than the elastic layer, surface layer, and base layer, the thickness of the other layers and the base layer is defined as the belt thickness, and the measurement is performed.

[0054] A method for measuring the radius of curvature R of the width direction end of pad 305 will be described. A three-dimensional shape measuring machine, VR-3200, manufactured by Keyence Corporation, was used to measure R. Pad 305 was placed with the surface in contact with belt 301 facing up, and the shape of the width direction end was measured. After measurement, the cross-sectional shape profile was confirmed, and its radius of curvature was recorded as R [mm]. When the width direction end of pad 305 has corners with multiple radii of curvature as in FIG. 7, the smallest value is taken as R. In the case of FIG. 7, R=R1.

[0055] L can be measured directly at the relevant location using a ruler, scale, etc. In this embodiment, the position of belt 301 in the Y direction is controlled by steering roller 307, so the value at which this distance is shortest is adopted as L [mm].

[0056] <How to check for cracks in the fixing belt> Cracks occurring on the belt 301 can be visually confirmed. Therefore, the inner surface of the belt was observed once, and if no cracks were found on the belt, it was determined that there was no abnormality.

[0057] <How to check for oil leaks in the fixing belt> A method for checking for oil leakage from belt 301 will now be described. For the check, plain paper of the maximum width that can be used by the image forming apparatus is used. In this embodiment, plain paper measuring 330 mm x 483 mm is used. The plain paper for checking for oil leakage is passed through using the same settings as when the image forming apparatus is normally used. At this time, no image is formed on the plain paper. After the plain paper has been passed through, if a liquid-like substance is observed on the paper, it is determined that oil leakage has occurred from the inner surface of belt 301. If no substance is observed on the paper, it is determined that no oil leakage has occurred.

[0058] <Verification procedure and results> Using the configuration of this embodiment, an investigation was carried out into cracks in the fixing belt and oil leakage from the fixing belt, and the procedure and results will be described.

[0059] First, the conditions under which cracks do not occur in the fixing belt were verified. The procedure is described below. The fixing device having the configuration of the embodiment was operated, and the belt 301 was rotated at a speed of 1.0×10 6 After the rotation, the belt 301 was removed from the fixing device and examined for cracks using the method described above. The results of the examination are shown in FIG. 8. In the graph of FIG. 8, ◯ indicates conditions under which no cracks occurred, and × indicates conditions under which cracks occurred. In the graph of FIG. 8a) where E=3500 MPa,

[0060]

number

[0061] In the graph of Figure 8b) where E = 5000 MPa in the region

[0062]

number

[0063] It was therefore possible to confirm that the conditions under which no cracks occur when the Young's modulus E of the belt 301 is in the range of 3500 to 5000 MPa can be expressed as follows:

[0064]

number

[0065] Next, the conditions under which oil leakage from the fixing belt does not occur were verified. First, the procedure is described. The fixing device having the configuration of the embodiment was operated, and the belt 301 was rotated at 1.0×10 4The fixing belt was rotated (at a rotation speed at which there is no risk of cracking and no effect). After that, the presence or absence of oil adhesion to plain paper was checked using the above-mentioned fixing belt oil leakage confirmation method. The verification results are shown in Figure 9. In the graph of Figure 9, ◯ indicates conditions under which no oil leakage occurred, and × indicates conditions under which oil leakage occurred. Comparing Figures 9a) and b) shows that the conditions for oil leakage do not change within the range of Young's modulus E in this embodiment, but change depending on L,

[0066]

number

[0067] Therefore, it was confirmed that the condition for no oil leakage to occur can be expressed as follows using L and the radius of curvature R of the width direction end of the pad 305.

[0068]

number

[0069] From the verification results of fixing belt cracks and oil leakage, it has become possible to determine the range of the curvature radius R of the width direction end of pad 305 that does not cause either of these problems as follows.

[0070]

number

[0071] In order to verify the validity of this range, the fixing device having the configuration of this embodiment is operated under the conditions shown in FIGS. 10a) to 10d), and the belt 301 is rotated at a speed of 1.0×10 6 After rotation, the fixing belt was checked for cracks and oil leakage. As shown in Figures 10a) to 10d), no cracks or oil leakage occurred in the fixing belt under the condition that the radius of curvature R of the width direction end of the pad 305 was within the range of the above formula. Therefore, the validity of this formula was demonstrated.

[0072] As shown in Fig. 10, the Young's modulus E of the belt is preferably in the range of 500 MPa to 5000 MPa. Furthermore, the thickness of the belt is preferably in the range of 0.08 to 0.1 mm. Also, L is preferably in the range of 5 to 10 mm. [Explanation of symbols]

[0073] Fusing unit F Image forming device 1 Image forming device body 3 Belt 301 Halogen heater 302 Heating roller 303 Pressure roller 304 Pad 305 Front page 305a Second side 305b Third side 305c Oil application roller 306 Steering roller 307

Claims

1. an endless belt for heating a recording material; a pressure member that contacts the outer peripheral surface of the belt to form a nip portion; a pad disposed on an inner circumferential surface of the belt and forming the nip portion together with the pressure member via the belt; The pressure member, together with the belt, applies heat and pressure to the recording material carrying the toner image at the nip portion, thereby fixing the toner image to the recording material, an oil application member that applies oil to the inner circumferential surface of the belt; a length of the belt in a width direction of the belt perpendicular to the conveying direction of the recording material is greater than a length of the pad, and a length of the pad is greater than a length of the pressure member in a width direction of the belt perpendicular to the conveying direction of the recording material, the pad has a first surface that forms the nip portion, a second surface that faces the first surface, and a third surface that connects the first surface and the second surface in the width direction, the third surfaces being formed at both end portions of the pad in the width direction, and the boundary between the first surface and the third surface being curved; A fixing device characterized by:

2. a steering roller that contacts the inner circumferential surface of the belt; The steering roller moves the belt in the width direction by swinging, the first surface of the recording material is covered by the belt in the width direction during fixing; 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 radius of curvature of the curved surface is in the range of 2.0 to 8.0 mm.

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 Young's modulus of the belt is in the range of 3500 MPa to 5000 MPa.

4. The fixing device according to claim 3.

5. The thickness of the belt is in the range of 0.08 to 0.1 mm.

5. The fixing device according to claim 4.

6. The length of the second surface that contacts the belt is L, and L is in the range of 5 to 10 mm.

6. The fixing device according to claim 5,

7. 2. The fixing device according to claim 1, wherein the following formula is satisfied, where L [mm] is the length of contact between the second surface and the belt, E [MPa] is the Young's modulus of the belt, t [mm] is the thickness of the belt, and R [mm] is the radius of curvature of the curved surface shape. [Equation 1]

8. The oil application member is a roller 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.

9. a heating roller in contact with the inner circumferential surface of the belt; the heating roller is disposed downstream of the pad in the direction of rotation of the belt and heats the belt; The heating roller is driven to rotate.

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.

Images