Fixing device and image forming apparatus

Abstract

To provide a fixing device that has reduced an image defect, and an image forming apparatus including the same.SOLUTION: A fixing device comprises: an endless first rotating body; a heating element that is arranged inside the first rotating body; a second rotating body that is in contact with an outer peripheral surface of the first rotating body and forms, together with the first rotating body, a nip part for fixing a toner image to a sheet; a nip member that is provided in slidable contact with an inner peripheral surface of the first rotating body so as to sandwich the first rotating body together with the second rotating body, and receives radiation heat from the heating element to heat the nip part; a support member that supports the nip member; and an elastic part that has a lower modulus of elasticity than those of the support member and the nip member, and is arranged between the support member and the nip member in a pressure direction orthogonal to the rotation axis direction of the second rotating body and a sheet conveyance direction.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a fixing device that fixes a toner image on a sheet, and an image forming apparatus that includes the fixing device. [Background technology]

[0002] Generally, an electrophotographic laser printer has a fixing device that applies heat and pressure to a toner image transferred onto a sheet to fix the toner image to the sheet. Conventionally, a fixing device has been proposed that has a cylindrical fixing belt, a heating unit that heats the fixing belt, and a pressure roller that forms a nip portion together with the fixing belt (see Patent Document 1).

[0003] The heating unit includes a halogen lamp that emits radiant heat, a nip plate that receives the radiant heat from the halogen lamp, a reflective member that reflects the radiant heat from the halogen lamp toward the nip plate, and a stay that supports the nip plate. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-66851 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the fixing device described in Patent Document 1, the stay supports the nip plate via the flange of the reflective member. The nip plate, reflective member, and stay are made of metal, and contact between rigid metals is prone to pressure unevenness because they cannot follow the unevenness of the metal surface. This causes unevenness in the nip pressure distribution in the nip, which can lead to image defects such as uneven gloss.

[0006] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a fixing device that reduces image defects and an image forming apparatus equipped with the same. [Means for solving the problem]

[0007] The present invention provides a fixing device comprising: an endless first rotating body; a heating body arranged inside the first rotating body; a second rotating body that contacts the outer circumferential surface of the first rotating body and forms, together with the first rotating body, a nip portion for fixing a toner image to a sheet; a nip member that is provided so as to be in sliding contact with the inner circumferential surface of the first rotating body so as to sandwich the first rotating body together with the second rotating body, and that receives radiant heat from the heating body to heat the nip portion; and a support member that supports the nip member and has a cross section perpendicular to the rotation axis direction of the second rotating body that is U-shaped so that the second rotating body side is open, the support member having one end that extends along the rotation axis direction and a second end that is arranged downstream of the one end in a sheet conveying direction and that is oriented in the rotation axis direction. a first elastic member having a modulus of elasticity lower than that of the support member and the nip member, the first elastic member being sandwiched in a state of contact between the one end of the support member and the nip member in a pressure direction perpendicular to both the rotation axis direction and the sheet conveying direction; and a second elastic member having a modulus of elasticity lower than that of the support member and the nip member, the second elastic member being sandwiched in a state of contact between the other end of the support member and the nip member in the pressure direction, the nip member having a heat-receiving surface that is not covered by the first elastic member and the second elastic member and that receives radiant heat from the heating element between the first elastic member and the second elastic member in the sheet conveying direction. death , each of the first elastic member and the second elastic member has a first portion and a second portion located at different positions in the rotational axis direction, the thickness of the first portion in the pressure direction being greater than the thickness of the second portion in the pressure direction, the first portion of the first elastic member being closer to a center of the first elastic member than the second portion of the first elastic member in the rotational axis direction, and the first portion of the second elastic member being closer to a center of the second elastic member than the second portion of the second elastic member in the rotational axis direction; It is characterized by: [Effects of the Invention]

[0008] According to the present invention, image defects can be reduced. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1A is a schematic diagram showing an entire printer according to a first embodiment, and FIG. 1B is a schematic diagram showing an image forming unit. [Figure 2] FIG. [Figure 3] FIG. 4A is an exploded perspective view showing a support member and a low-elasticity member, and FIG. 4B is a perspective view showing the support member and the low-elasticity member assembled together. [Figure 4] 10A is an exploded perspective view showing a support member and a low-elasticity member according to a modified example of the first embodiment, and FIG. 10B is a perspective view showing the support member and the low-elasticity member assembled together. [Figure 5] 10A is an exploded perspective view showing a support member and a low-elasticity member according to a second embodiment, and FIG. 10B is a perspective view showing the support member and the low-elasticity member assembled together. [Figure 6] 10A is an exploded perspective view showing a support member and a low-elasticity member according to a modified example of the second embodiment, and FIG. 10B is a perspective view showing the support member and the low-elasticity member assembled together. DETAILED DESCRIPTION OF THE INVENTION

[0010] First Embodiment [Overall configuration] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Fig. 1(a) is a diagram showing a printer 1 as an image forming apparatus according to a first embodiment. As shown in Fig. 1(a), the printer 1 includes a device main body 2 and an image reading device 3 provided on top of the device main body 2. Inside the device main body 2 is provided an image forming unit 10 that forms an image on a sheet.

[0011] As shown in FIG. 1(b), the image forming unit 10 includes an electrophotographic image forming section 100 and a fixing device 106. When a command to start an image forming operation is received in this image forming section 100, a photosensitive drum 101, which is a photosensitive member, rotates, and the drum surface is uniformly charged by a charging roller 102. Then, an exposure device 103 modulates and outputs laser light based on image data transmitted from the image reading device 3 or an external computer, and scans the surface of the photosensitive drum 101 to form an electrostatic latent image. This electrostatic latent image is visualized (developed) into a toner image T by toner supplied from a developing device 104.

[0012] In parallel with this image forming operation, a feeding operation is performed to feed sheets P stacked in a cassette or manual feed tray (not shown) toward the image forming unit 10. The fed sheets P are transported in accordance with the progress of the image forming operation by the image forming section 100.

[0013] The toner image T carried on the photosensitive drum 101 is then transferred onto the sheet P by a transfer roller 105. Any toner remaining on the photosensitive drum 101 after the toner image has been transferred is collected by a cleaning device 107. The sheet P onto which the unfixed toner image has been transferred is passed to a fixing device 106. The fixing device 106 applies heat and pressure to melt and fix the toner to the sheet P, thereby fixing the toner image T to the sheet P. The sheet P onto which the toner image T has been fixed is discharged outside the apparatus by a pair of discharge rollers or the like.

[0014] [Fixing device] Next, fixing device 106 according to the present embodiment will be described with reference to Fig. 2. As shown in Fig. 2, fixing device 106 includes an endless fixing belt 201, a heating unit 200 for heating fixing belt 201, and a pressure roller 202 for sandwiching fixing belt 201 between heating unit 200 and pressure roller 202. Fixing belt 201 includes a thin film-like belt.

[0015] The first rotating body, ie, fixing belt 201, is made of polyimide resin, which has high thermal conductivity and low heat capacity, and is a flexible endless belt. However, fixing belt 201 may be made of other resins or metals such as stainless steel.

[0016] Fixing belt 201 is rotatably provided, and a lubricant is applied to the inner peripheral surface of fixing belt 201 to ensure sliding properties with nip member 204 (described later). Guide members (not shown) are provided at both ends of fixing belt 201 in the direction of its rotation axis (hereinafter referred to as axial direction X) to guide the rotation of fixing belt 201 and restrict movement of fixing belt 201 in the direction of the rotation axis.

[0017] Heating unit 200 is disposed on the inner circumferential side of fixing belt 201 and includes a halogen lamp 203, a nip member 204, a reflector 205, and a support member 206. Halogen lamp 203, which serves as a heating element, is disposed at a distance from fixing belt 201 and nip member 204 and is provided to emit radiant heat to heat fixing belt 201. The temperature of the radiant heat emitted by halogen lamp 203 changes depending on the amount of power supplied by a power source (not shown). In this embodiment, the temperature of the radiant heat emitted by halogen lamp 203 is adjusted by a control unit (not shown) controlling the amount of power supplied to halogen lamp 203 so that the temperature of nip portion N detected by a temperature sensor (not shown) is maintained at a predetermined target temperature. It should be noted that other heating elements may be used in place of a halogen lamp.

[0018] Nip member 204 is a long member that is provided so as not to rotate relative to rotating fixing belt 201 and that extends in axial direction X so as to be able to slide on the inner circumferential surface of fixing belt 201. As described above, halogen lamp 203 emits radiant heat to heat fixing belt 201, and at that time, nip member 204 receives the radiant heat from halogen lamp 203. In other words, nip member 204 has heat-receiving surface 204a that faces halogen lamp 203 and receives the radiant heat from halogen lamp 203.

[0019] The reflector 205 is a member for reflecting radiant heat emitted from the halogen lamp 203 toward the nip member 204, and is disposed at a predetermined distance from the halogen lamp 203 so as to cover the halogen lamp 203. For this reason, the reflector 205 is formed by curving an aluminum plate, for example, which has a high reflectivity for infrared and far-infrared rays, so that the cross section is substantially U-shaped. The reflector 205 collects the radiant heat from the halogen lamp 203 toward the nip member 204, so that the radiant heat from the halogen lamp 203 can be efficiently used to quickly heat the nip portion N via the nip member 204. The reflector 205 may be omitted.

[0020] Support member 206 is a structure having a predetermined rigidity for supporting nip member 204, and is formed in a shape that conforms to the outer surface of reflector 205 using a metal with excellent strength, such as stainless steel or spring steel. More specifically, support member 206 supports both ends of nip member 204 in sheet conveying direction Y, which is the widthwise direction of nip member 204. In the present embodiment, nip member 204 supported by support member 206 presses fixing belt 201 from the inside toward pressure roller 202, thereby more reliably forming nip portion N.

[0021] Pressure roller 202, which serves as a second rotating body, contacts the outer peripheral surface of fixing belt 201 and is rotatably supported. In this embodiment, pressure roller 202 is rotated in the direction of the arrow at a predetermined peripheral speed by a drive motor (not shown). Then, frictional force generated at nip portion N transmits the rotational force of pressure roller 202 to fixing belt 201. In this manner, fixing belt 201 is rotated by pressure roller 202 (a so-called pressure roller drive system). Pressure roller 202 has, for example, a metal core 202A serving as a rotating shaft, on the outer periphery of which elastic layer 202B is formed, and release layer 202C made of a fluororesin such as PTFE, PFA, or FEP is further formed on the outer periphery of elastic layer 202B. Elastic layer 202B has voids therein.

[0022] Both ends of core metal 202A in axial direction X are rotatably supported by bearings (not shown). Support member 206 presses nip member 204 in pressure direction Z, pressing fixing belt 201 against pressure roller 202. This causes the surface of pressure roller 202 to elastically deform, and a nip portion N of a predetermined width in the sheet conveying direction is formed between the surfaces of pressure roller 202 and fixing belt 201.

[0023] The pressure direction Z is a direction perpendicular to the axial direction X and the sheet conveying direction Y. Alternatively, the nip member 204 may not be pressed in the pressure direction Z, but the pressure roller 202 may be pressed toward the nip member 204. The nip member 204 is not limited to being in direct contact with the fixing belt 201, and may be in contact with the fixing belt 201 via a sheet material with high thermal conductivity, such as an iron alloy or aluminum.

[0024] As described above, the temperature of the fixing belt 201 increases as the nip member 204 is heated by the radiant heat from the halogen lamp 203 and the radiant heat reflected by the reflector 205. The sheet P on which the unfixed toner image is formed is heated and pressurized at the nip portion N while being nipped and conveyed between the rotating fixing belt 201 and the pressure roller 202, whereby the toner image is fixed to the sheet S.

[0025] [Low elasticity material] 2 to 3(b), the low-elasticity member 207 disposed between the support member 206 and the nip member 204 will be described. The support member 206 presses the nip member 204 in the pressure direction Z, forming a nip portion N between the fixing belt 201 and the pressure roller 202. For this reason, the support member 206 and the nip member 204 must have a predetermined rigidity, and metal is often used as the material for them.

[0026] In this case, the support member 206 and the nip member 204 come into contact with each other as metals. Contact between rigid metals is prone to pressure unevenness because they cannot follow each other's unevenness on the metal surfaces. If contact becomes uneven, the support member 206 applies pressure unevenly to the nip member 204, which in turn causes unevenness in the pressure distribution between the nip member 204 and the pressure roller 202, resulting in uneven gloss on the toner image.

[0027] Therefore, in this embodiment, low-elasticity member 207 made of polyimide resin is disposed between support member 206 and nip member 204 in pressure direction Z. Low-elasticity member 207 has a lower modulus of elasticity than support member 206 and nip member 204. Therefore, low-elasticity member 207 is sandwiched between support member 206 and nip member 204 with a predetermined pressure in pressure direction Z, and conforms to the shapes of support member 206 and nip member 204. This allows the pressure from support member 206 to nip member 204 to be smoothed.

[0028] More specifically, the support member 206 extends in the axial direction X over the entire length of the sheet passing area and has a U-shaped cross section. The support member 206 has side walls 206b and 206c extending in the pressure direction Z, and a connecting portion 206a extending in the sheet conveying direction Y to connect the side walls 206b and 206c.

[0029] The low-elasticity member 207 extends in the axial direction X over the entire length of the sheet passing area, and is formed with a U-shaped cross section so that its opening is on the opposite side from the support member 206. The low-elasticity members 207 are attached to the tip portions of the side walls 206b and 206c of the support member 206. The low-elasticity members 207 attached to the tip portions of the side walls 206b and 206c are made of the same material, and the following description will mainly focus on the side wall 206b and the low-elasticity member 207 attached to the side wall 206b.

[0030] The low-elasticity member 207 has side walls 207b, 207c extending in the pressure direction Z, and a connecting portion 207a as an elastic portion extending in the sheet conveying direction Y so as to connect these side walls 207b, 207c. The side wall 206b of the support member 206 has a contact surface 206d that comes into contact with the connecting portion 207a of the low-elasticity member 207. By sandwiching the side wall 206b of the support member 206 between the side walls 207b, 207c of the low-elasticity member 207, it is possible to reduce positional deviation of the low-elasticity member 207 in the sheet conveying direction Y. The contact surface 206d of the support member 206 has a uniform height in the pressure direction Z over the entire length in the axial direction X.

[0031] Incidentally, for example, if a low-elasticity member with a uniform cross-sectional shape in the axial direction X is used, the shape of the nip portion N in a pressurized state will be uniform in the axial direction X. When a toner image is fixed to a sheet P in the nip portion N, preventing paper wrinkles becomes an issue. Paper wrinkles occur when pressure is applied to overlapping sheets P in the nip portion N. Therefore, to prevent paper wrinkles, it is necessary to generate a force in the nip portion N that spreads the paper from the center toward the edges in the axial direction X.

[0032] Therefore, in this embodiment, the thickness of the connection portion 207a of the low-elasticity member 207 is made different between the center and the end portions in the axial direction X, so that the sheet conveying speed at the nip portion N is faster at the end portions than at the center portion in the axial direction X.

[0033] More specifically, the connecting portion 207a of the low-elasticity member 207 has a central portion 207f in the axial direction X and an end portion 207g in the axial direction X. The central portion 207f as a first portion and the end portion 207g as a second portion are located at different positions in the axial direction X. The central portion 207f is closer to the center of the connecting portion 207a than the end portion 207g in the axial direction X. The thickness h1 of the central portion 207f in the pressure direction Z is configured to be thicker than the thickness h2 of the end portion 207g in the pressure direction Z.

[0034] In the present embodiment, when the pressure roller 202 is a balloon roller having an elastic layer 202B with an internal void, the more the pressure roller 202 is compressed, the closer the distance between the roller surface and the core 202A becomes, and the sheet conveying speed slows. That is, because the thickness h1 of the center portion 207f of the low-elasticity member 207 is thicker than the thickness h2 of the end portion 207g, the nip member 204 conforms to the shape of the low-elasticity member 207. Then, when the pressure roller 202 is pressed by the nip member 204 whose center portion is convex downward, the center portion of the pressure roller 202 in the axial direction X is compressed more than the end portions in the axial direction X. Therefore, the sheet conveying speed at the nip portion N becomes faster at both ends in the axial direction X than at the center, thereby suppressing paper wrinkles.

[0035] Here, to compare the occurrence of paper wrinkles and gloss unevenness, low-elasticity members made of two different materials were prepared to be placed between the support member 206 and the nip member 204. These low-elasticity members made of two different materials are designated as Comparative Example and Example 1, respectively, and their configurations are shown in Table 1.

[0036] [Table 1]

[0037] The comparative example is made of aluminum, while Example 1 is made of polyimide resin, which is the same as the configuration of this example. The longitudinal shape, i.e., the shape in the axial direction X, is configured as shown in Figure 3, with the longitudinal center being thicker than the longitudinal ends in both the comparative example and Example 1. Specifically, the thickness of the longitudinal center of the connecting portion 207a in the sheet thickness direction is 2.3 mm, and the thickness at the longitudinal ends is 2.0 mm.

[0038] The evaluation of paper wrinkles is carried out under the following conditions. Environment: High temperature and humidity environment (30°C / 80%RH, hereinafter referred to as H / H environment) Main unit: Throughput 27 ppm (A4), process speed 148 mm / sec Sheet (plain paper): Oce A4 size Red Label paper (basis weight 80 g / m 2) left in a H / H environment for more than 48 hours Sheet (thin paper): Canon A4 size paper CS-060F (basis weight 60 g / m 2 ) left in a H / H environment for more than 48 hours Print image: Full white image How to determine whether paper wrinkles have occurred: Check by touching the entire sheet of paper with your hand. If even one of the 30 sheets has wrinkles, mark it as "X", otherwise mark it as "O".

[0039] The evaluation of gloss unevenness was carried out under the following conditions. Environment: High temperature and high humidity environment (30℃ / 80%RH) Main unit: Throughput 27 ppm (A4), process speed 148 mm / sec Sheet (plain paper): HP LTR size paper, HP Brochure Paper 200 Glossy (basis weight 200 g / m 2 ) left in a H / H environment for more than 48 hours Print image: Full black image Gloss unevenness occurrence judgment: If gloss unevenness can be visually recognized on a uniform solid black image, it is marked as "X", and if it cannot be visually recognized, it is marked as "O".

[0040] Table 2 shows the relationship between the occurrence of paper wrinkles and gloss unevenness in the comparative example and Example 1. [Table 2]

[0041] In both the comparative example and Example 1, the center is thicker than the longitudinal ends, so the amount of compression by the pressure roller 202 is less at the longitudinal ends than at the longitudinal center, resulting in a faster sheet conveyance speed. Therefore, the force pushing the sheet toward the longitudinal ends is strong, so no paper wrinkles occurred, whether on plain paper or thin paper. In the comparative example, aluminum was used, and because of its low contact with rigid metals, the pressure force from the support member 206 could not be uniformly transmitted to the nip member 204, resulting in uneven gloss.

[0042] In Example 1, polyimide resin, which has a lower elastic modulus than metal, is used, so it has good contact with metal and can smoothly transmit the pressure force from the support member 206 to the nip member 204, so there is no uneven gloss.

[0043] As described above, by disposing the low-elasticity member 207 between the metal support member 206 and the nip member 204 in the pressure direction Z, it is possible to reduce uneven gloss. Also, the thickness h1 of the center portion 207f of the low-elasticity member 207 in the axial direction X is configured to be thicker than the thickness h2 of the end portion 207g. In other words, the low-elasticity member 207 as an elastic member gradually becomes thinner in the pressure direction Z from the center portion to both end portions in the axial direction X. This makes it possible to suppress paper wrinkles. As a result, it is possible to reduce image defects such as uneven gloss and paper wrinkles.

[0044] In this embodiment, the low-elasticity member 207 used has a thickness of 2.3 mm at the longitudinal center and 2.0 mm at the longitudinal ends, but the low-elasticity member 207 needs to have a certain level of strength in order to reduce pressure unevenness in the nip portion N. For this reason, it is desirable that the low-elasticity member 207 has a thickness of 1.0 mm or more even at the thinnest longitudinal portion.

[0045] [Variations] 4(a) and 4(b) show modified examples of the first embodiment. The connecting portion 307a serving as the elastic portion of the low-elasticity member 307 shown in FIGS. 4(a) and 4(b) has a central portion 307f in the axial direction X and an end portion 307g in the axial direction X. The central portion 307f serving as the second portion and the end portion 307g serving as the first portion are located at different positions in the axial direction X. Furthermore, the central portion 307f is closer to the center of the connecting portion 307a than the end portion 307g in the axial direction X.

[0046] The connecting portion 307a is configured so that the thickness h11 of the central portion 307f in the axial direction X is smaller than the thickness h12 of the end portion 307g. In other words, the connecting portion 307a of the low-elasticity member 307 gradually becomes thicker in the pressure direction Z from the central portion to both end portions in the axial direction X. This allows the nip width at both end portions of the nip portion N in the axial direction X to be larger than that at the central portion, thereby improving the fixability at both end portions of the nip portion N.

[0047] <Second embodiment> Next, a second embodiment of the present invention will be described, which is configured by modifying the support member and low-elasticity member of the first embodiment. Therefore, the same components as those of the first embodiment will be omitted from the illustrations or will be described by using the same reference numerals in the drawings.

[0048] 5(a) and 5(b), the support member 406 extends in the axial direction X over the entire length of the sheet passing area and has a U-shaped cross section. The support member 406 has side walls 406b and 406c extending in the pressure direction Z, and a connecting portion 406a extending in the sheet conveying direction Y to connect the side walls 406b and 406c.

[0049] The low-elasticity member 407 made of polyimide resin extends in the axial direction X over the entire length of the sheet passing region, and is formed with a U-shaped cross section so that its opening is on the opposite side from the support member 406. The low-elasticity members 407 are attached to the tip portions of the side walls 406b and 406c of the support member 406. The low-elasticity members 407 attached to the tip portions of the side walls 406b and 406c are made of the same material, and the following description will mainly focus on the side wall 406b and the low-elasticity member 407 attached to the side wall 406b.

[0050] The low-elasticity member 407 has side walls 407b, 407c extending in the pressure direction Z, and a connecting portion 407a as an elastic portion extending in the sheet conveying direction Y to connect these side walls 407b, 407c. The side wall 406b of the support member 406 has a contact surface 406d that comes into contact with the connecting portion 407a of the low-elasticity member 407. By sandwiching the side wall 406b of the support member 406 between the side walls 407b, 407c of the low-elasticity member 407, it is possible to reduce positional deviation of the low-elasticity member 407 in the sheet conveying direction Y.

[0051] In this embodiment, the height of the contact surface 406d of the support member 406 in the pressure direction Z is not uniform over the entire length in the axial direction X. More specifically, the contact surface 406d has a central portion 407f in the axial direction X and an end portion 407g in the axial direction X. The central portion 407f as the third portion and the end portion 407g as the fourth portion are located at different positions in the axial direction X. Furthermore, the central portion 407f is closer to the center of the support member 406 than the end portion 407g in the axial direction X.

[0052] The central portion 407f is located closer to the rotation axis 202R (see FIG. 2) of the pressure roller 202 than the end portions 407g in the pressure direction Z. That is, the contact surface 406d is located gradually farther from the rotation axis 202R of the pressure roller 202 in the axial direction X from the central portion 407f to both end portions.

[0053] On the other hand, the connection portion 407a of the low-elasticity member 407 has a uniform thickness in the pressure direction Z over the entire length in the axial direction X. That is, the thickness of the connection portion 407a is uniform over the entire length in the axial direction X.

[0054] In this embodiment, contact surface 406d of support member 406 is configured so that center portion 407f bulges out more than end portion 407g, and connection portion 407a of low-elasticity member 407 has a uniform thickness. This allows nip member 204 to conform to the shape of contact surface 406d of support member 406 and low-elasticity member 407. Then, nip member 204, whose center portion is convex downward, presses pressure roller 202, thereby preventing paper wrinkles.

[0055] Furthermore, since the thickness of connection portion 407a of low-elasticity member 407 is made uniform, heat dissipating to support member 406 via nip member 204 can be made uniform in axial direction X, reducing variations in fixability at each position in axial direction X of nip portion N. On the other hand, if the change in height of contact surface 406d of support member 406 is large, low-elasticity member 407 will not be able to follow that shape, so the shape of contact surface 406d needs to be optimized in consideration of the flexibility of low-elasticity member 407.

[0056] [Variations] 6(a) and 6(b) show a modified example of the second embodiment. The support member 506 has a contact surface 506d with multiple steps. As described above, the contact surface 506d is not limited to a shape curved at a constant curvature, but may be configured so that the center portion is closer to the rotation axis 202R of the pressure roller 202 than the two end portions.

[0057] <Other embodiments> In all of the above-described embodiments, the low-elasticity member is made of a highly heat-resistant polyimide resin, but this is not limiting. For example, the low-elasticity member may be made of a highly insulating material, such as a resin containing glass bubbles. Using a highly insulating material can prevent radiant heat from the halogen lamp 203 from escaping from the nip member 204 to the support member when the temperature of the fixing device is increased. This allows the radiant heat to be efficiently transferred to the nip portion N, thereby speeding up the start-up of the fixing device.

[0058] In addition, in all of the above-described embodiments, the low-elasticity member is configured to easily contact the support member and the nip member, but this is not limiting. For example, the reflector 205 may have a flange portion facing the contact surface of the support member, and the low-elasticity member may be disposed between the flange portion and the support member in the pressure direction Z.

[0059] In addition, in all of the above-described embodiments, the low-elasticity member has a U-shaped cross section with two side walls and a connecting portion, but is not limited to this. For example, the low-elasticity member may omit the two side walls.

[0060] In the first embodiment, the connecting portion 207a of the low-elasticity member 207 is formed so that its thickness gradually decreases from the center toward both ends in the axial direction X. However, this is not limiting. For example, the connecting portion 207a may be configured so that its thickness decreases in multiple stages from the center toward both ends. [Explanation of symbols]

[0061] 1: image forming apparatus (printer) / 100: image forming unit / 106: fixing device / 201: first rotating body (fixing belt) / 202: second rotating body (pressure roller) / 202R: rotating shaft / 203: heating element (halogen lamp) / 204: nip member / 206: support member / 206d, 406d: contact surface / 207a, 307a, 407a: elastic portion (connection portion) / 207f, 307g: first portion (center, end) / 207g, 307f: second portion (end, center) / 407f: third portion (center) / 407g: fourth portion (end) / h1, h2: thickness / X: rotation axis direction (axial direction) / Y: sheet conveyance direction / Z: pressure direction

Claims

1. an endless first rotor; a heating element disposed inside the first rotating body; a second rotating body that contacts an outer peripheral surface of the first rotating body and forms a nip portion together with the first rotating body to fix a toner image onto a sheet; a nip member that is provided to be in sliding contact with an inner circumferential surface of the first rotating body so as to sandwich the first rotating body together with the second rotating body, and that receives radiant heat from the heating body to heat the nip portion; a support member for supporting the nip member, the cross section of which orthogonal to the rotation axis direction of the second rotating body is formed in a U-shape so as to be open on the second rotating body side, the support member having one end extending along the rotation axis direction and another end disposed downstream of the one end in the sheet conveying direction and extending along the rotation axis direction; a first elastic member having a lower elastic modulus than the support member and the nip member, the first elastic member being sandwiched in a state of contact with the one end of the support member and the nip member in a pressure direction perpendicular to both the rotation axis direction and the sheet conveying direction; a second elastic member having a lower elastic modulus than the support member and the nip member, the second elastic member being sandwiched in a state of contact with the other end of the support member and the nip member in the pressure direction; the nip member has a heat-receiving surface that is not covered by the first elastic member and the second elastic member and receives radiant heat from the heat generating element between the first elastic member and the second elastic member in the sheet conveying direction, each of the first elastic member and the second elastic member has a first portion and a second portion located at different positions in the rotation axis direction; a thickness of the first portion in the pressure applying direction is greater than a thickness of the second portion in the pressure applying direction; the first portion of the first elastic member is closer to a center portion of the first elastic member in the rotation axis direction than the second portion of the first elastic member, the first portion of the second elastic member is closer to a center portion of the second elastic member than the second portion of the second elastic member in the rotation axis direction; A fixing device characterized by:

2. The thickness of each of the first elastic member and the second elastic member in the pressure direction gradually decreases from a central portion to both end portions in the rotation axis direction.

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 one end and the other end of the support member each have a uniform height in the pressure direction over the entire length in the rotation axis direction.

3. The fixing device according to claim 1, wherein the fixing member is a fixing member.

4. the one end and the other end of the support member each have a third portion and a fourth portion located at different positions in the rotation axis direction, the third portion is located at a position closer to the rotation axis of the second rotating body than the fourth portion in the pressure application direction.

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 third portion is closer to a center portion of the support member than the fourth portion in the rotation axis direction; 5. The fixing device according to claim 4.

6. the one end and the other end of the support member are located at positions that are gradually farther from the rotation axis of the second rotating body from a central portion to both end portions in the rotation axis direction, 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. Each of the first elastic member and the second elastic member is made of polyimide resin.

7. The fixing device according to claim 1, wherein the fixing member is a fixing member having a fixing surface.

8. Each of the first elastic member and the second elastic member is made of a resin containing glass bubbles.

7. The fixing device according to claim 1, wherein the fixing member is a fixing member having a fixing surface.

9. The nip member and the support member are made of metal.

9. The fixing device according to claim 1, wherein the fixing member is a fixing member having a fixing surface.

10. a reflector disposed inside the support member and reflecting radiant heat emitted from the heating element toward the heat-receiving surface of the nip member; the reflecting plate is not interposed between the one end of the support member and the nip member and between the other end of the support member and the nip member in the pressure direction; 10. The fixing device according to claim 1, wherein the fixing member is a fixing member having a fixing surface.

11. each of the first elastic member and the second elastic member uniformly distributes nip pressure in the nip portion to suppress uneven gloss on the sheet; 11. The fixing device according to claim 1, wherein the fixing member is a fixing member having a fixing surface.

12. an image forming unit that forms a toner image on a sheet; and a fixing device according to claim 1 , which fixes the toner image formed by the image forming unit onto a sheet. An image forming apparatus characterized by:

Images