JP7764153B2 - Fixing device and image forming apparatus - Google Patents

Description

The present invention relates to a fixing device that fixes a toner image to a sheet, and an image forming apparatus equipped with the fixing device.

Electrophotographic laser printers generally have a fixing device that applies heat and pressure to a toner image transferred to a sheet to fix the toner image to the sheet. A fixing device that has been proposed to date includes a cylindrical fixing belt, a heating unit that heats the fixing belt, and a pressure roller that forms a nip with the fixing belt (see Patent Document 1).

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.

JP 2014-66851 A

However, in the fixing device described in Patent Document 1, the stay supports the nip plate via the flange portion 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 each other's unevenness on the metal surface. This causes unevenness in the nip pressure distribution in the nip, which can lead to image defects such as uneven gloss.

The present invention therefore aims to provide a fixing device that reduces image defects and an image forming apparatus equipped with the same.

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 where a toner image is fixed to a sheet; a nip member that is provided 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; 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 extending along the rotation axis direction and another end disposed downstream of the one end in a sheet conveying direction and extending along the rotation axis direction; and a first elastic member that has a lower elastic modulus than the support member and the nip member and is sandwiched 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 lower elastic modulus than the support member and the nip member, and being clamped in contact with the other end of the support member and the nip member in the pressure application direction, wherein the nip member has a heat receiving surface between the first elastic member and the second elastic member in the sheet conveying direction that receives radiant heat from the heating element without being covered by the first elastic member and the second elastic member, wherein the first elastic member and the second elastic member each have a first portion and a second portion located at different positions from each other in the rotation axis direction, wherein the thickness of the first portion in the pressure application direction is thicker than the thickness of the second portion in the pressure application direction, the first portion of the first elastic member is closer to the center of the first elastic member in the rotation axis direction than the second portion of the first elastic member, and the first portion of the second elastic member is closer to the center of the second elastic member in the rotation axis direction than the second portion of the second elastic member .

This invention can reduce image defects.

1A is a schematic diagram showing an overall configuration of a printer according to a first embodiment, and FIG. 1B is a schematic diagram showing an image forming unit. 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. 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. 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. 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.

First Embodiment
[Overall configuration]
[0023] Hereinafter, an embodiment 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 main body 2 and an image reading device 3 provided on top of the main body 2. Inside the main body 2, an image forming unit 10 is provided that forms an image on a sheet.

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 image formation is received in this image forming section 100, the photosensitive drum 101, which is a photosensitive member, rotates and the drum surface is uniformly charged by the charging roller 102. The exposure device 103 then modulates and outputs laser light based on image data sent from the image reading device 3 or an external computer, scanning 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 using toner supplied from the developing device 104.

In parallel with this image forming operation, a feeding operation is performed to feed sheets P loaded 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.

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

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

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

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

The heating unit 200 is disposed on the inner periphery of the fixing belt 201 and includes a halogen lamp 203, a nip member 204, a reflector 205, and a support member 206. The halogen lamp 203, which serves as a heating element, is disposed at a distance from the fixing belt 201 and the nip member 204 and is provided to emit radiant heat to heat the fixing belt 201. The temperature of the radiant heat emitted by the 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 the halogen lamp 203 is adjusted according to the control of the amount of power supplied to the halogen lamp 203 by a control unit (not shown) so that the temperature of the nip portion N detected by a temperature sensor (not shown) is maintained at a predetermined target temperature. Note that other heating elements may be used in addition to halogen lamps.

Nip member 204 is a long, non-rotating member that extends in axial direction X and is capable of sliding contact with the inner circumferential surface of fixing belt 201. As described above, halogen lamp 203 emits radiant heat to heat fixing belt 201, and 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.

The reflector 205 is a component that reflects the radiant heat emitted from the halogen lamp 203 toward the nip member 204, and is positioned a predetermined distance from the halogen lamp 203 so as to cover it. For this reason, the reflector 205 is made of a material that has a high reflectivity for infrared and far-infrared rays, such as an aluminum plate, and is curved so that its cross section is roughly U-shaped. This reflector 205 collects the radiant heat from the halogen lamp 203 toward the nip member 204, allowing the radiant heat from the halogen lamp 203 to be efficiently used to quickly heat the nip portion N via the nip member 204. The reflector 205 may also be omitted.

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

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

The core metal 202A is rotatably supported at both ends in the axial direction X by bearings (not shown). The support member 206 presses the nip member 204 in the pressure direction Z, pressing the fixing belt 201 against the pressure roller 202. This causes the surface of the pressure roller 202 to elastically deform, and a nip portion N of a predetermined width in the sheet conveyance direction is formed between the surface of the pressure roller 202 and the surface of the fixing belt 201.

Note that 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 configured to press toward the nip member 204. Furthermore, 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.

As described above, the nip member 204 is heated by radiant heat from the halogen lamp 203 and radiant heat reflected by the reflector 205, causing the temperature of the fixing belt 201 to rise. The sheet P on which an unfixed toner image has been formed is heated and pressurized at the nip portion N as it is nipped and conveyed between the rotating fixing belt 201 and pressure roller 202, thereby fixing the toner image to the sheet S.

[Low elasticity member]
2 to 3B, 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.

In this case, the support member 206 and 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 is uneven, the support member 206 will apply pressure unevenly to the nip member 204, which will cause unevenness in the pressure distribution between the nip member 204 and the pressure roller 202, resulting in uneven gloss on the toner image.

In this embodiment, therefore, a low-elasticity member 207 made of polyimide resin is placed between the support member 206 and the nip member 204 in the pressure direction Z. The low-elasticity member 207 has a lower modulus of elasticity than the support member 206 and the nip member 204. As a result, the low-elasticity member 207 is sandwiched between the support member 206 and the nip member 204 in the pressure direction Z with a predetermined pressure, and conforms to the shapes of the support member 206 and the nip member 204. This allows for a smooth pressure from the support member 206 to the nip member 204.

More specifically, the support member 206 extends in the axial direction X over the entire length of the sheet passage 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 these side walls 206b and 206c.

The low-elasticity member 207 extends in the axial direction X over the entire length of the sheet passage area and has a U-shaped cross section with its opening facing away from the support member 206. The low-elasticity members 207 are attached to the tip ends of the side walls 206b and 206c of the support member 206. The low-elasticity members 207 attached to the tip ends of the side walls 206b and 206c are made of the same material, and the following description will mainly focus on the low-elasticity members 207 attached to the side walls 206b and 206c.

The low-elasticity member 207 has side walls 207b and 207c extending in the pressure direction Z and a connecting portion 207a, which serves as an elastic portion, extending in the sheet conveying direction Y to connect these side walls 207b and 207c. The side wall 206b of the support member 206 has a contact surface 206d that contacts 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 and 207c of the low-elasticity member 207, misalignment of the low-elasticity member 207 in the sheet conveying direction Y can be reduced. The contact surface 206d of the support member 206 has a uniform height in the pressure direction Z over its entire length in the axial direction X.

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 N when pressed will be uniform in the axial direction X. When fixing a toner image to a sheet P in the nip N, preventing paper wrinkles becomes an issue. Paper wrinkles occur when pressure is applied to overlapping sheets P in the nip N, so to prevent paper wrinkles, it is necessary to generate a force in the nip N that spreads the paper from the center toward the edges in the axial direction X.

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

More specifically, the connection 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, which serves as the first portion, and the end portion 207g, which serves as the second portion, are located at different positions in the axial direction X. Furthermore, the central portion 207f is closer to the center of the connection portion 207a in the axial direction X than the end portion 207g. 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.

In this embodiment, when the pressure roller 202 is a balloon roller equipped with an elastic layer 202B having an internal void, the more the pressure roller 202 is compressed, the closer the distance between the roller surface and the core metal 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. Furthermore, 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 is faster at both ends in the axial direction X than at the center, thereby suppressing paper wrinkles.

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

The comparative example is made of aluminum, while Example 1 is made of polyimide resin, which is the same configuration as this example. Furthermore, 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.

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/ ^m2 ) left in a H/H environment for 48 hours or more. Sheet (thin paper): Canon A4 size CS-060F paper (basis weight 60 g/ ^m2 ) left in a H/H environment for 48 hours or more. Printed image: Full white image. Method for determining whether paper wrinkles have occurred: Check by touching the entire paper with your hand. If wrinkles have occurred on even one of the 30 sheets passed, mark it as "X", otherwise mark it as "O".

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 Brochure Paper 200 Glossy LTR size paper (basis weight 200 g/ ^m2 ) left in a H/H environment for 48 hours or more. Printed image: Full black image. Gloss unevenness occurrence judgment: If gloss unevenness can be seen on the uniform solid black image, it is marked as "X", and if it cannot be seen, it is marked as "O".

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

In both the comparative example and example 1, the center is thicker than the longitudinal ends, so the pressure roller 202 compresses the longitudinal ends less than the longitudinal center, resulting in a faster sheet conveyance speed. This results in a stronger force spreading the sheet in the longitudinal end direction, and no paper wrinkles occurred with either plain paper or thin paper. In the comparative example, aluminum was used, which has poor contact with rigid metals, so the pressure force from the support member 206 could not be transmitted uniformly to the nip member 204, resulting in uneven gloss.

In Example 1, polyimide resin, which has a lower modulus of elasticity than metal, is used, which provides good contact with metal and allows the pressure from the support member 206 to be smoothly transmitted to the nip member 204, eliminating uneven gloss.

As explained 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. Furthermore, the thickness h1 of the central 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 central portion to both ends in the axial direction X. This makes it possible to suppress paper wrinkles. This in turn makes it possible to reduce image defects such as uneven gloss and paper wrinkles.

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

[Modification]
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.

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 ends in the axial direction X. This allows the nip width at both ends of the nip portion N in the axial direction X to be larger than at the central portion, improving the fixation at both ends of the nip portion N.

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.

As shown in Figures 5(a) and 5(b), the support member 406 extends in the axial direction X over the entire length of the sheet passage 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 these side walls 406b and 406c.

The low-elasticity member 407, made of polyimide resin, extends in the axial direction X over the entire length of the sheet passage area and has a U-shaped cross section with its opening facing away from the support member 406. The low-elasticity member 407 is attached to the tip of each of the side walls 406b and 406c of the support member 406. The low-elasticity members 407, 407 attached to the tip of each 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.

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 contacts 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.

In this embodiment, the contact surface 406d of the support member 406 does not have a uniform height in the pressure direction Z 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.

The central portion 407f is located closer to the rotation axis 202R (see Figure 2) of the pressure roller 202 in the pressure direction Z than the end portions 407g. In other words, 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 ends.

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

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

In addition, because the connection portion 407a of the low-elasticity member 407 has a uniform thickness, the heat dissipating to the support member 406 via the nip member 204 can be made uniform in the axial direction X, reducing variations in fixation performance at each position in the axial direction X of the nip portion N. On the other hand, if the height of the contact surface 406d of the support member 406 changes significantly, the low-elasticity member 407 will no longer be able to follow that shape, so the shape of the contact surface 406d must be optimized in consideration of the flexibility of the low-elasticity member 407.

[Modification]
6A and 6B 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 ends.

<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.

Furthermore, in all of the above-described embodiments, the low-elasticity member is configured to easily contact the support member and nip member, but this is not limited to this. 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.

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 this is not limited to this. For example, the low-elasticity member may omit the two side walls.

In addition, 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, but this is not limited to this. For example, the connecting portion 207a may be configured so that its thickness decreases in multiple stages from the center toward both ends.

1: Image forming apparatus (printer) / 100: Image forming unit / 106: Fuser / 201: First rotating body (fuser 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 portion) / 207g, 307f: Second portion (end portion, center portion) / 407f: Third portion (center portion) / 407g: Fourth portion (end portion) / h1, h2: Thickness / X: Rotation axis direction (axial direction) / Y: Sheet conveyance direction / Z: Pressure direction

Claims (12)

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 rotor so as to sandwich the first rotor together with the second rotor, and that receives radiant heat from the heating element 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: 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. 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 . 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. 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 . 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. 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. 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. 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. 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. 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;
The fixing device according to any one of claims 1 to 10 . an image forming unit that forms a toner image on a sheet;
and a fixing device according to claim 1 , which fixes a toner image formed by the image forming unit onto a sheet.
An image forming apparatus characterized by: