Fixing device

Abstract

A fixing device includes an endless belt, a rotating member, a pad disposed on an inner side of the belt to sandwich the belt between itself and the rotating member and form a nip portion, and a sliding member disposed between the pad and the belt. The pad includes a bent portion bent to directly contact the belt on a downstream side of the nip portion in a transport direction of the recording material. The curved portion includes a first portion located on a downstream side in a transport direction of a passing region at which a recording material having a maximum size passes through the nip portion, and a second portion located on a downstream side in a non-passing region located on an outer side of the passing region in a width direction. The curvature radius of the second part is larger than that of the first part.

Description

Technical Field

[0001] The present invention relates to a fixing device for fixing a toner image carried on a recording material onto the recording material. Background Art

[0002] Conventionally, a fixing device is known that forms a nip portion between a belt and a rotating member, such as a roller, to heat and pressurize recording material passing through the nip portion. Japanese Patent Application Laid-Open No. 2015-114394 discloses a configuration in which a pad member is provided inside the belt, facing the rotating member across the belt and forming the aforementioned nip portion. Furthermore, the pad member has a curved surface at its downstream end in the direction of conveyance of the recording material in the nip portion, and the belt is bent at the curvature of this curved surface, thereby separating the recording material passing through the nip portion from the belt. Summary of the Invention

[0003] According to one aspect of the present invention, there is provided a fixing device for fixing a colorant image carried on a recording material onto the recording material, the fixing device comprising: an endless rotatable belt; a rotating member configured to rotate in contact with the outer peripheral surface of the belt; a pad member disposed on the inner side of the belt so as to clamp the belt between itself and the rotating member, and forming a clamping portion for clamping and conveying the recording material between the belt and the rotating member; a sliding member disposed between the pad member and the belt and configured to contact and slide with the inner peripheral surface of the belt in the clamping portion; and a heating roller disposed on the inner side of the belt and configured The belt is heated, wherein the pad member includes a bent portion, the bent portion is bent to directly contact the belt on the downstream side of the clamping portion in the conveying direction of the recording material, and the belt is bent to separate the recording material passing through the clamping portion from the belt, and wherein the bent portion includes a first portion located on the downstream side of the conveying direction of a passing area, and a second portion located on the downstream side of the conveying direction of a non-passing area, where the recording material having a maximum size passes through the clamping portion, and the non-passing area is located outside the passing area in the width direction of the recording material intersecting the conveying direction, and wherein a curvature radius of the second portion is larger than a curvature radius of the first portion.

[0004] Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Figure 1 is a sectional view of the overall configuration of an image forming apparatus according to Embodiment 1.

[0006] Figure 2 Part (a) is a sectional view of the overall configuration of the fixing device according to Example 1, Figure 2 Part (b) is a schematic diagram showing an enlarged portion A in part (a).

[0007] Figure 3 Part (a) is a schematic diagram of the stay and the pad according to Example 1 viewed from above in the pressurizing direction, Figure 3 Part (b) is a cross-sectional view of the overall configuration of the stay and the pad cut along the width direction thereof and viewed from the downstream side in the conveying direction, and Figure 3 Part (c) is a cross-sectional view of the overall structure of the belt, the stay and the pad cut at the longitudinal center of the stay.

[0008] Figure 4 Part (a) is a graph showing a longitudinal distribution of peak pressure generated between the curved portion and the belt of the mat according to Example 1, Figure 4 Part (b) is a cross-sectional view of the overall configuration of the belt, strut, and pad at the A-np-Y1 position in part (a), and Figure 4 Part (c) is a cross-sectional view of the overall configuration of the belt, the stay, and the pad at the Ap-Yc position in part (a).

[0009] Figure 5 Part (a) is a cross-sectional view of the overall configuration of the belt, the stay and the pad according to Example 1, Figure 5 Part (b) is an enlarged view of part B in part (a), and Figure 5 Part (c) is a graph showing the relationship between the curvature radius of the bent portion of the strut and the bending strain.

[0010] Figure 6 Part (a) is a cross-sectional view of the overall configuration of the stay and the mat according to Example 1, cut along the width direction thereof and viewed from the downstream side in the conveying direction, Figure 6 Part (b) is a cross-sectional view of the overall configuration of the belt, the stay and the pad according to Example 1, Figure 6 Part (c) is an enlarged view of part C in part (b) at the A-np-Yn position in part (a), and Figure 6 Part (d) is an enlarged view of portion C in part (b) at the Ap-Yc position in part (a).

[0011] Figure 7 Part (a) is a schematic diagram of the brace and the mat according to Comparative Example 1 viewed from the downstream side in the conveying direction, Figure 7 Part (b) is a cross-sectional view of the overall configuration of the belt, stays and pads according to Comparative Example 1, Figure 7Part (c) is an enlarged view of part D in part (b) at the position of A-np-Yn in part (a), and Figure 7 Part (d) is an enlarged view of part D in part (b) at the Ap-Yc position in part (a).

[0012] Figure 8 Part (a) is a cross-sectional view of the overall configuration of the belt, the stay and the pad according to Example 2, Figure 8 Part (b) is an enlarged view of portion E in part (a), and Figure 8 Part (c) is a graph showing the relationship between ΔZ and bending strain.

[0013] Figure 9 Part (a) is a schematic diagram of the brace and the pad according to Example 2 as viewed from the downstream side in the conveying direction, Figure 9 Part (b) is a cross-sectional view of the overall configuration of the belt, the stay and the pad according to Example 2, Figure 9 Part (c) is an enlarged view of part F in part (b) at the position of A-np-Yn in part (a), and Figure 9 Part (d) is an enlarged view of portion F in part (b) at the Ap-Yc position in part (a).

[0014] Figure 10 Part (a) is a schematic diagram of the brace rod and the pad according to Comparative Example 2 viewed from the downstream side in the conveying direction, Figure 10 Part (b) is a cross-sectional view of the overall configuration of the belt, stays and pads according to Comparative Example 2, Figure 10 Part (c) is an enlarged view of part G in part (b) at the position of A-np-Yn in part (a), and Figure 10 Part (d) is an enlarged view of portion G in part (b) at the Ap-Yc position in part (a).

[0015] Figure 11 The table shows the verification results of Examples and Comparative Examples. DETAILED DESCRIPTION [Example 1]

[0016] Will use Figures 1 to 7 Part (d) describes Example 1. First, the Figure 1 The overall configuration of the imaging apparatus of this embodiment is described. [Imaging equipment]

[0017] Image forming apparatus 1 is an electrophotographic full-color printer equipped with four image forming sections Pa, Pb, Pc, and Pd, corresponding to the four colors of yellow, magenta, cyan, and black. In this embodiment, the printer is configured as a tandem type, with the image forming sections Pa, Pb, Pc, and Pd arranged along the rotational direction of an intermediate transfer belt 204, described below. Image forming apparatus 1 forms a toner image (image) on a recording material in response to an image signal from an image reading section (document reading device) 2 or a host device such as a personal computer. The image reading section is connected to the main assembly of image forming apparatus 3, and the host device is communicatively connected to the main assembly of image forming apparatus 3. Examples of recording materials include sheets such as paper, plastic film, and cloth.

[0018] The imaging device 1 includes an image reading section 2 and a main assembly of the imaging device 3. The image reading section 2 reads a document placed on a document table glass 21. Light emitted from a light source 22 is reflected by the document, and an image is formed on a CCD sensor 24 via an optical system component 23, such as a lens. This optical system component converts the document into a series of electrical signal data for each line by scanning in the direction indicated by the outlined arrow. The image signal obtained by the CCD sensor 24 is transmitted to the main assembly of the imaging device 3, where image processing appropriate to each imaging section is performed in the control section 30, as described below. The control section 30 also receives external input as image signals from an external host device, such as a print server.

[0019] The main assembly of the image forming apparatus 3 is provided with a plurality of image forming sections Pa, Pb, Pc, and Pd. In each of these sections, image formation is performed based on the aforementioned image signal. Specifically, the image signal is converted into a pulse-width modulated (PWM) laser beam by the control section 30. A polygon scanner 31, serving as an exposure device, scans the laser beam corresponding to the image signal. The laser beam then irradiates the photosensitive drums 200a to 200d, serving as image bearing members in each of the image forming sections Pa to Pd.

[0020] Incidentally, Pa is the image forming section for yellow (Y), Pb is the image forming section for magenta (M), Pc is the image forming section for cyan (C), and Pd is the image forming section for black (Bk), each forming an image of the corresponding color. Since the image forming sections Pa through Pd are essentially the same, the details of the image forming section Pa for Y will be described below, and descriptions of the other image forming sections will be omitted. As described below, in the image forming section Pa, a toner image is formed on the surface of the photosensitive drum 200a based on an image signal.

[0021] The charging roller 201a, acting as a primary charger, charges the surface of the photosensitive drum 200a to a predetermined potential, preparing to form an electrostatic latent image. A laser beam from the polygon scanner 31 forms an electrostatic latent image on the surface of the photosensitive drum 200a, which has been charged to the predetermined potential. The developing unit 202a develops the electrostatic latent image on the photosensitive drum 200a to form a toner image. The primary transfer roller 203a discharges the electrostatic latent image from the back of the intermediate transfer belt 204 and applies a primary transfer bias of opposite polarity to the toner, transferring the toner image on the photosensitive drum 200a to the intermediate transfer belt 204. After the transfer, the surface of the photosensitive drum 200a is cleaned by a cleaner 207a.

[0022] The toner images on the intermediate transfer belt 204 are then conveyed to the next image forming section in the order of Y, M, C, and Bk. The toner images of each color formed in each image forming section are sequentially transferred, forming a four-color image on its surface. The toner images that have passed through the image forming section Pd for Bk, located furthest downstream in the direction of rotation of the intermediate transfer belt 204, are then conveyed to the secondary transfer section comprised of the secondary transfer roller pair 205 and 206. In the secondary transfer section, the toner images are then secondarily transferred onto the recording material by applying a secondary transfer electric field having a polarity opposite to that of the toner images on the intermediate transfer belt 204.

[0023] The recording material is housed in the cassette 9, and the recording material fed from the cassette 9 is conveyed to a registration portion 208 constituted by, for example, a pair of registration rollers, and waits in the registration portion 208. Thereafter, timing is controlled to align the positions of the toner image on the intermediate transfer belt 204 and the sheet, and the registration portion 208 conveys the recording material to the secondary transfer portion.

[0024] The recording material to which the toner image has been transferred in the secondary transfer section is conveyed to the fixing device 8, where the toner image carried on the recording material is fixed to the recording material through heat and pressure. The recording material that has passed through the fixing device 8 is discharged onto the discharge tray 7. Incidentally, when duplex imaging is performed on the recording material, when the toner image is transferred and fixed to the first surface (front surface) of the recording material, the front and back surfaces of the recording material are reversed by the reverse conveying section 10, the toner image is transferred and fixed to the second surface (back surface) of the recording material, and the recording material is stacked on the discharge tray 7.

[0025] Incidentally, as described above, the control section 30 controls the entire imaging device 1. Furthermore, the control section 30 can perform various settings based on input from the operation section 4 provided in the imaging device 1. This control section 30 includes a CPU (Central Processing Unit), ROM (Read Only Memory), and RAM (Random Access Memory). The CPU controls each component while reading programs corresponding to control procedures stored in the ROM. Furthermore, the RAM stores working data and input data, and the CPU performs control based on the aforementioned programs and other information, referring to the data stored in the RAM. [Fixing unit]

[0026] Next, we will use Figure 2 Part (a) and part (b) of the drawings describe the configuration of the fixing device 8. In this embodiment, a fixing device of a belt heating method using an endless belt is employed. Figure 2 In part (a), the X direction indicates the conveyance direction of the recording material P (not shown in the figure), the Y direction indicates the width direction of the recording material that intersects (is perpendicular to, in this embodiment) the conveyance direction of the recording material, and the Z direction indicates the pressing direction, i.e., the direction in which the recording material is pressed in the nip portion N. In this embodiment, the X direction, the Y direction, and the Z direction are directions perpendicular to each other.

[0027] The fixing device 8 includes a fixing belt (hereinafter referred to as "belt") 301, a stay 302, a pressure pad (hereinafter referred to as "pad") 303, a sliding member 304, a pressure roller 305, a heating roller 307, and a steering roller 308. The belt 301 is a rotatable heating member that is an endless, rotatable member. The pressure roller 305, a rotating member, is a rotatable pressure member that contacts the outer peripheral surface of the belt 301 and forms a nip N between itself and the belt 301 for gripping and conveying the recording material.

[0028] The sliding member 304 slides with the inner peripheral surface of the belt 301 in the clamping portion N. The pad 303, which serves as a supporting member and a cushioning member, is provided on the inner side of the belt 301 to clamp the sliding member 304 and the belt 301 between itself and the pressure roller 305, and supports the sliding member 304. The sliding member 304 is provided to cover the outer peripheral surface of the pad 303 on the belt 301 side. The support rod 302 is provided on the inner side of the belt 301 on the opposite side of the clamping portion N and supports the pad 303, with the pad 303 being located between the support rod and the belt. The heating roller 307 is provided on the inner side of the belt 301 to stretch the belt 301 and heat the belt 301. As described below, the steering roller 308 is provided on the inner side of the belt 301 to stretch the belt 301, apply tension to the belt 301, and perform displacement control of the belt 301. Hereinafter, each structure will be described in detail.

[0029] The belt 301 has thermal conductivity and heat resistance, etc., and has a thin-walled cylindrical shape. In this embodiment, as Figure 2 As shown in part (b) of the figure, belt 301 has a three-layer structure comprising a base layer 301a, an elastic layer 301b formed on the periphery of base layer 301a, and a release layer 301c formed on the periphery of elastic layer 301b. Base layer 301a is, for example, 80 microns thick and made of polyimide resin (PI). Elastic layer 301b is, for example, 300 microns thick and made of silicone rubber. Release layer 301c is, for example, 30 microns thick and made of PFA (tetrafluoroethylene perfluoroalkoxyethylene copolymer), a fluororesin. Belt 301 is stretched by pad 303 and heated roller 307. In this embodiment, the outer diameter of belt 301 is 150 mm.

[0030] The pad 303 is positioned inside the belt 301, facing the pressure roller 305 across the belt 301. This position forms a nip N for sandwiching and conveying the recording material between the belt 301 and the pressure roller 305. In this embodiment, the pad 303 is a roughly plate-shaped member that is elongated along the width of the belt 301 (a longitudinal direction intersecting the belt 301's rotational direction and directed toward the rotational axis of the heating roller 307). The nip N is formed by pressing the pad 303 against the pressure roller 305 across the belt 301. LCP (liquid crystal polymer) resin is used as the material for the pad 303. A sliding member 304 is interposed between the pad 303 and the belt 301. Details of the sliding member 304 will be described below.

[0031] The pad 303 is supported by a support member, a stay 302, located inside the belt 301. Specifically, the stay 302 is located on the side of the pad 303 opposite the pressure roller 305 and supports the pad 303. The stay 302 is a reinforcing member that is long and rigid in the longitudinal direction of the belt 301 and contacts and supports the pad 303. Specifically, when the pad 303 is pressurized by the pressure roller 305, the stay 302 provides strength to the pad 303 and ensures the pressure applied in the nip portion N. The widthwise ends of the stay 302 are supported by a frame.

[0032] The strut 302 is made of a metal such as stainless steel, and its cross-section (intersecting surface) perpendicular to the longitudinal direction of the strut 302 (which intersects the rotational direction of the belt 301) is generally rectangular. For example, a pultruded SUS304 (stainless steel) member with a wall thickness of 3 mm is used for the strut 302. By forming the strut 302 into a hollow, approximately rectangular cross-section, its strength is ensured. Incidentally, the cross-section of the strut 302 can be formed into a substantially rectangular shape by combining multiple metal sheets and securing them together by welding or other means. Furthermore, the material of the strut 302 is not limited to stainless steel; any material can be used as long as its strength is ensured.

[0033] Heating roller 307 is disposed inside belt 301 and, together with pad 303 and steering roller 308, stretches belt 301. Heating roller 307 is formed into a cylindrical shape from a metal such as aluminum or stainless steel, and a halogen heater 306 is disposed inside heating roller 307 as a heat source for heating belt 301. Halogen heater 306 heats heating roller 307 to a predetermined temperature. Heating roller 307 is rotatably supported and urged by a frame and bearings (not shown) at its widthwise ends.

[0034] The steering roller 308 has a rotation center at one end or near its center in the longitudinal direction. By rotating relative to the belt 301, it creates a tension difference between the front and rear ends, thereby controlling the position (offset position) of the belt 301 in the main scanning direction (width direction). Furthermore, the steering roller 308 is biased by a spring supported by a frame (not shown) and also serves as a tension roller that applies a predetermined tension SF to the belt 301. Specifically, the steering roller 308, as a tension-applying member, is positioned inside the belt 301 and, together with the pad 303, stretches the belt 301 to apply a tension SF to the belt 301. The tension SF applied to the belt 301 is preferably approximately 40 N to 120 N.

[0035] In this embodiment, the heating roller 307 is formed from a tube made of, for example, stainless steel and having a thickness of 1 mm. While a single halogen heater 306 may be provided, it is preferable to provide multiple halogen heaters 306 to control the temperature distribution in the longitudinal direction (direction of the rotational axis) of the heating roller 307. The multiple halogen heaters 306 provided have different illumination distributions in the longitudinal direction, and the illumination ratio is controlled according to the size of the recording material. In this embodiment, three halogen heaters 306 are provided. Incidentally, the heating source is not limited to a halogen heater; other heaters capable of heating the heating roller 307, such as a carbon heater, may also be used. The belt 301 is heated by the heating roller 307 heated by the halogen heater 306 and is controlled to a predetermined target temperature corresponding to the type of recording material based on temperature detection by a thermistor (temperature detection member) (not shown).

[0036] The pressure roller 305 is also a rotationally driven member that rotates while in contact with the outer peripheral surface of the belt 301 and applies a driving force to the belt 301. Incidentally, in this embodiment, the heating roller 307 is also rotationally driven by a drive source (e.g., a drive motor) and applies a driving force to the belt 301. However, the application of a driving force to the heating roller 307 can be omitted. The pressure roller 305 is a roller formed with a core metal (shaft) 305c, an elastic layer 305b on the outer periphery of the core metal 305c, and a release layer 305a on the outer periphery of the elastic layer 305b. For example, stainless steel with a diameter of 72 mm is used for the core metal 305c. For example, conductive silicone rubber with a thickness of 8 mm is used for the elastic layer 305b. For example, PFA (tetrafluoroethylene perfluoroalkoxyethylene copolymer), a fluororesin with a thickness of 100 microns, is used for the release layer 305a. The pressure roller 305 is rotatably supported by a frame (not shown) of the fixing device 8, with a gear fixed to one end thereof. The pressure roller 305 is connected to a drive source (e.g., an unillustrated drive motor) via a gear, and is rotationally driven. Furthermore, the pressure roller 305 is pressed by a pressure mechanism 309, thereby pressing the belt 301 against the pad 303. The pressure mechanism 309 includes a pressure arm 310 connected to a core metal 305c. The pressure arm 310 receives a force from an unillustrated drive mechanism and swings about a swing center 311, thereby pressing the pressure roller 305 against the pad 303 by a pressure force PF.

[0037] The fixing device 8 heats the toner image while holding and conveying the recording material P bearing the toner image in the nip N formed between the belt 301 and the pressure roller 305. In this way, the fixing device 8 fixes the toner image to the recording material P while holding and conveying it. Therefore, the fixing device 8 must perform effectively in both applying heat and pressure and conveying the recording material P. The pressure roller 305 is pressed against the sliding member 304 via the belt 301 by a drive source (not shown). In this embodiment, the pressing force (NF) in the nip N during image formation is 1600 N. The nip N is configured so that its width in the X direction (the direction in which the recording material is conveyed) is 24.5 mm and its width in the Y direction (the width of the recording material) is 326 mm. [Sliding member]

[0038] The sliding member 304 is fixed to the support rod 302 via the pad 303 by screws or the like. Incidentally, the sliding member 304 may be integral with the pad 303. In addition, a portion of the sliding member 304 may be fixed to the support rod 302 and / or the pad 303. For example, both ends of the sliding member 304 in the Y direction (width direction) may be fixed to the pad 303 by screws or the like. The sliding member 304 in this embodiment is configured to cover the pad 303 regardless of the inside and outside of the clamping portion N. However, hereinafter, it is not shown here, and it is acceptable as long as a portion of the clamping portion N is covered by the sliding member 304. In other words, a configuration in which the sliding member 304 is provided only in the clamping portion N is also acceptable.

[0039] Sliding member 304 is composed of a base layer 304a and a sliding layer 304c. On the side of base layer 304a that slides with belt 301, multiple protrusions 304b are formed, projecting toward the inner circumference of belt 301. Sliding layer 304c is provided to cover the surface of base layer 304a (including multiple protrusions 304b) that slides with belt 301. The protruding portion formed by protrusions 304b covered by sliding layer 304c is referred to as a raised portion 304d.

[0040] Base material layer 304a only needs to have sufficient heat resistance and strength. Examples of materials include stainless steel, copper, aluminum, and engineering plastics (such as PI (polyimide), PEEK (polyetheretherketone), and LCP (liquid crystal polymer). Metal materials such as stainless steel, copper, and aluminum are ideal in this embodiment. In this embodiment, PI with a thickness of 300 microns is used as base material layer 304a.

[0041] Multiple protrusions 304b are provided extending from the base material layer 304a toward the inner circumferential surface of the belt 301. Furthermore, the multiple protrusions 304b are integrally formed with the base material layer 304a from the same material and are arranged in the nip portion N in both the conveyance direction (X direction) and the width direction (Y direction) of the recording material intersecting the conveyance direction. The distance (interval) d between the centers of adjacent protrusions 304b in the conveyance direction and the distance (interval) d between the centers of adjacent protrusions 304b in the width direction are preferably at least 1.25 mm and at least 1.4 mm, respectively. In this embodiment, to ensure uniform sliding performance with the belt 301, the distances between the multiple protrusions 304b are configured to be the same in both the conveyance direction and the width direction, with each distance d being 1.4 mm. Furthermore, the multiple protrusions 304b are distributed in the width direction within the nip portion N and outside the nip portion N (the pass-through area and the non-pass-through area, described below).

[0042] In this manner, by providing a plurality of protrusions 304b on the surface (sliding surface) of the sliding member 304 on the side that slides with the belt 301, the contact area between the sliding member 304 and the belt 301 is reduced, and the sliding resistance between the sliding member 304 and the belt 301 is reduced. The protrusions 304b are formed so that the front side surface is flat and the protrusions 304b are approximately cylindrical.

[0043] The sliding layer 304c is preferably formed from a coating agent such as a fluororesin (PTFE (polytetrafluoroethylene), PFA, etc.) to achieve low friction. In this embodiment, the sliding member 304 is formed by coating the surface of the base layer 304a, which includes a plurality of protrusions 304b, with PTFE to a thickness of 20 microns. Furthermore, in this embodiment, a lubricant is applied to the inner surface of the belt 301. As a result, the belt 301 is configured to slide smoothly with the sliding member 304. Silicone oil is used as the lubricant. Incidentally, in this embodiment, the sliding layer 304c is provided on the base layer 304a. However, an adhesive layer can also be provided between the base layer 304a and the sliding layer 304c. The use of an adhesive layer can achieve good bonding strength between the base layer 304a and the sliding layer 304c, even when a metal material such as stainless steel, copper, or aluminum is used for the base layer 304a.

[0044] Furthermore, the sliding member 304 in this embodiment is configured to cover the pad 303 regardless of the inside or outside of the clamping portion N. Specifically, the entire surface of the pad 303 facing the belt 301 is covered by the sliding member 304, except for the surface of the pad 303 on the opposite side of the clamping portion N. Furthermore, a plurality of protrusions 304b are provided over the entire area of ​​the sliding member 304. However, as described below, and not illustrated here, a configuration in which the protrusions 304d are provided in a portion of the clamping portion N is also acceptable. In other words, a configuration in which the protrusions 304d are provided only in the clamping portion N is also acceptable. [Factors that shorten belt life]

[0045] Next, use Figure 3 Part (a) to Figure 4 Part (c) of the present invention will describe factors that cause fatigue failure (cracks) in the belt 301 and shorten the life of the belt 301. Figure 3 Part (a) of FIG. 3 is a schematic diagram showing the positions of the stay 302 and the pad 303 when viewed from above in the pressurizing direction. Figure 3 Part (b) of FIG. 3 is a view schematically showing a cross section viewed from downstream in the conveying direction, which shows the positions of the brace bar 302 and the pad 303 . Figure 3 Part (c) schematically shows Figure 3Part (b) is a view of a cross section at the Ap-Yc position (the center position in the longitudinal direction of the strut 302 ).

[0046] Figure 3 The Ap region (area) in the portion (a) is a region in the nip portion N through which a recording material of the maximum size that can be used for the imaging apparatus 1 passes (hereinafter referred to as a “passing region” or “Ap region”). Figure 3 The A-np area in portion (a) is an area where the recording material having the largest size in the nip portion N does not pass (hereinafter, referred to as a “non-passing area” or “A-np area”).

[0047] The A-np region (non-passing region) is located outside the Ap region (passing region) in the width direction. Furthermore, the raised portion 304d may be provided in the A-np region. In this embodiment, the width of the Ap region is 340 mm, and the width of the A-np region is 15 mm. Figure 3 The curved portion 303a in section (c) is an area where the belt 301 is bent to a specific curvature by being stretched from its inner circumference by the steering roller 308 (not shown). Specifically, the pad 303 includes the curved portion 303a on the downstream side of the nip N relative to the recording material conveyance direction. This curved portion is continuous with the downstream end of the nip N and is curved to bring the sliding member 304 into contact with the belt 301, thereby bending the belt 301 and separating the recording material passing through the nip N from the belt 301. Incidentally, if the sliding member 304 is not provided in the curved portion 303a, the belt 301 is bent by the curved portion 303a directly contacting the belt 301. To stably secure the Ap region for recording material passing through the nip N, the pad 303 is configured to have a width greater than that of the pressure roller 305. In other words, to stably secure the Ap region, the pad 303 is configured to form an A-np region outside the Ap region in the width direction.

[0048] As described above, to improve the separation performance between the recording material and the belt 301, the belt 301 is stretched by the steering roller 308 and bent to a specific radius of curvature at the curved portion 303a downstream of the nip portion N. By reducing the radius of curvature of the belt 301 downstream of the nip portion N, separation energy is imparted to the recording material during conveyance, making the separation energy greater than the adhesion energy between the toner and the belt 301. This allows the recording material, after the toner has been fixed, to be separated from the belt 301 and conveyed. On the other hand, bending the belt 301 with a radius of curvature exceeding the necessary value generates unnecessary strain in the belt 301. As a result, the belt 301 is repeatedly subjected to significant strain during rotation. This can lead to fatigue failure in the belt 301, such as cracks in the base layer 301a of the belt 301, shortening the life of the belt 301.

[0049] Figure 4 Part (a) is a graph showing a longitudinal (width direction) distribution of peak pressure generated between the curved portion 303 a and the belt, which is bent to a specific curvature by stretching the belt 301 from the inner peripheral surface using the steering roller 308 and the pad 303 . Figure 4 Part (b) and Figure 4 Part (c) is shown in Figure 4 Part (a) is a cross-sectional view of the overall configuration of the observation result near the clamping portion N at the positions of A-np-Y1 and Ap-Yc.

[0050] from Figure 4 The results in part (a) show that in the Ap region, the pressure applied to the curved portion 303a of the pad 303 due to the tension SF applied to the belt 301 by the steering roller 308 is low. In contrast, in the A-np region, the pressure applied to the curved portion 303a of the pad 303 due to the tension SF applied to the belt 301 by the steering roller 308 is high. When the tension SF applied to the belt 301 by the steering roller 308 changes, the belt 301's ability to follow the curved portion 303a changes. The tension SF applied to the belt 301 by the steering roller 308 becomes locally higher, and the peak pressure applied to the curved portion 303a becomes higher. In other words, it can be assumed that as the belt 301's ability to follow the curved portion 303a increases, the radius of curvature of the belt 301 in that portion of the curved portion 303a decreases.

[0051] In addition, from Figure 4 Part (b) and Figure 4The results observed in part (c) of FIG. 3 confirm that, in the A-np-Y1 cross section, the peak pressure of the bent portion 303a due to the tension SF is large, and the curvature radius of the belt 301 in the bent portion 303a downstream of the nip portion N is small, while in the Ap-Yc cross section, the peak pressure of the bent portion 303a due to the tension SF is small, and the curvature radius of the belt 301 in the bent portion 303a downstream of the nip portion N is large. Therefore, although the curvature radius of the belt 301 bent by the bent portion 303a (which is originally necessary for improving the separation performance of the recording material) is sufficiently small in the Ap-Yc cross section, the curvature radius of the belt 301 bent by the bent portion 303a becomes even smaller in the A-np-Y1 cross section where the recording material does not pass.

[0052] Therefore, it was discovered that, without any countermeasures, excessive strain occurred in the belt 301, the belt being bent by the curved portion 303a in the A-np region where recording material does not pass, and fatigue failure occurred when the belt 301 rotated. The cause of this is presumed to be deformation of the pad 303, the heating roller 307, and the steering roller 308 when the belt 301 was stretched by providing a spring at the end of the steering roller 308. In other words, it is presumed that this is because when tension is applied to the belt 301 by the steering roller 308, the inner side of the fixing device 8 deforms, and the tension applied in the A-np region becomes stronger than the tension applied in the Ap region. [Structure of the curved portion of the pad]

[0053] As described above, it was discovered that, without any countermeasures being taken for the curved portion 303a of the pad 303, although the radius of curvature of the belt 301 bent by the curved portion 303a (which is necessary for improving the recording material separation performance) is sufficiently small in the Ap-Yc cross section, the radius of curvature of the belt 301 bent by the curved portion 303a is even smaller in the A-np-Y1 cross section, where the recording material does not pass. To address the above issues, in this embodiment, the shape of the pad 303 is configured so that the bending strain in the A-np region, where the recording material separation performance does not need to be improved, is smaller than the bending strain in the Ap region, where the recording material separation performance does need to be improved.

[0054] Next, use Figure 5 From Part (a) to Part (c) of FIG. 1 , a method for calculating the strain generated in the belt 301 when the belt 301 is bent to a specific radius of curvature in the bent portion downstream of the clamping portion N will be described step by step. First, the bent portion 303a is measured with pressure-sensitive paper to identify the area of ​​the bent portion 303a where the pad 303 and the belt 301 contact each other to bend the belt 301. Next, based on the shape of the area, the size of each portion is measured. Finally, the measured values ​​are substituted into the theoretical formula to calculate the strain of each portion. Figure 5 In part (a) of FIG. 3 , a cross-sectional view of the belt 301 , the stay 302 , and the pad 303 near the clamping portion N is shown. Figure 5 Part (B) is Figure 5 An enlarged view of portion B surrounded by a dotted line in part (a).

[0055] As described above, first, the area of ​​the curved portion 303a where the pad 303 and the belt 301 come into contact with each other to bend the belt 301 is measured and identified using pressure-sensitive paper. In the measurement, a three-dimensional shape measuring instrument VR-3200 manufactured by Keyence and pressure-sensitive paper Prescale manufactured by Fujifilm were used. For Prescale manufactured by Fujifilm, in order to match the pressure range of measurement (0.2 MPa or more and 0.6 MPa or less), Prescale for ultra-low pressure (LLLW) was used. Figure 2 In the fixing device 8 shown in part (a), the spring pressing the steering roller 308 is removed, and the belt 301 is removed in its longitudinal direction. Next, the Prescale is set and fixed in the entire longitudinal direction of the pad 303 so that Figure 5 , shown in part (a) and part (b), from the clamping portion N to the bent portion 303a is covered. After setting the Prescale, the belt 301 is inserted into the fixing device 8, and further, the pressure on the steering roller 308 by the spring is released, and pressure is applied to the belt 301 through the steering roller 308. After the pressure is applied, the pressure on the steering roller 308 by the spring is removed again, and the belt 301 is removed. When observing the collected Prescale, by the pad 303 and the belt 301 being in contact with each other and pressure being applied to the bent portion 303a of the bent belt 301, only the contact area turns red. The contact area in the Prescale after the color change is measured in two dimensions using a three-dimensional shape measuring instrument VR-3200 manufactured by Keyence Corporation, and the contact area is calculated as the bent portion 303a. When measuring, it is preferable to set the magnification to 10 times or more. At this time, as Figure 5 As shown in part (b), when the curved portion 303a exists continuously from the most downstream of the clamping portion, the starting point (the most downstream position of the clamping portion N) is defined as R-1, and the end point of the curved portion 303a is defined as RE.

[0056] Next, we will describe methods for measuring the dimensions of various parts of the curved portion 303a and calculating the bending strain generated in the belt 301. To calculate the strain generated in the belt 301, the radius of curvature R at the curved portion of the belt 301 is calculated from the shape of the pad 303 at the curved portion 303a. First, the shape of the pad 303 is measured using a three-dimensional shape measuring instrument VR-3200 manufactured by Keyence. During measurement, the magnification is preferably set to 10x or higher. During measurement, the pad 303 is mounted on the measuring instrument with its surface on the side of the clamping portion N facing upward, and its three-dimensional shape is obtained. The longitudinal position (width position) to be measured is determined, and a shape profile in the pressurized direction is output at that longitudinal position along the conveying direction. Based on this shape profile, the center position of the interval between R-1 and RE in the curved portion 303a, calculated using the pressure-sensitive paper measurement described above, is defined as RC. A circle is drawn through the three points R-1, RC, and RE, and its radius is defined as r. At three or more positions in each region (Ap region and A-np region), r is measured, and the average value thereof is defined as the curvature radius R of the curved portion 303 a .

[0057] Finally, the measured curvature radius R is substituted into the following theoretical formula to calculate the bending strain E. In the calculation, the thickness of the base layer 301a of the belt 301 is defined as t, t is uniformly set to a fixed value of 0.095, and substituted into the following formula. [Formula 1]

[0058] Figure 5 Part (c) shows the change in bending strain E when the curvature radius R is changed using the above formula. Figure 5 From part (c), it can be confirmed that as the curvature radius R decreases, the bending strain E increases.

[0059] Figure 6 Parts (a) to (d) are cross-sectional views of the nip portion N of the fixing device 8 equipped with the pad 303 in this embodiment, respectively. Figure 6 Part (a) is a cross-sectional view of the overall configuration in which the stay 302 and the pad 303 are cut along the width direction and viewed from the downstream side in the conveying direction. Figure 6 Part (b) is in Figure 6 Cross-sectional view at the Ap-Yc position in part (a). Figure 6 Part (c) is in Figure 6 The A-np-Yn position in part (a) is magnified Figure 6 Part (b) is a cross-sectional view of a portion C surrounded by a dotted square portion. Figure 6 Part (d) is in Figure 6The Ap-Yc position in part (a) is magnified Figure 6 Part (b) is a cross-sectional view of part C.

[0060] like Figure 6 As shown in parts (c) and (d) of FIG. , in this embodiment, the shape of the pad 303 is configured so that the bending strain E at the A-np-Yn position is smaller than the bending strain E at the Ap-Yc position. Here, in the curved portion 303a, the area located on the downstream side of the transport direction of the AP region is defined as the first portion 303a1, which is the pass-through area for the recording material having the largest size passing through the clamping portion N. In addition, in the curved portion 303a, the area located on the downstream side of the transport direction of the A-np region is defined as the second portion 303a2, which is the non-pass-through area outside the pass-through area in the width direction (longitudinal direction). That is, as Figure 6 As shown in part (c) of FIG. 1 , the area on the downstream side of the conveying direction of the clamping portion N at the position A-np-Yn is defined as the second portion 303a2, and as shown in FIG. Figure 6 As shown in part (d) of the diagram, the area downstream of the nip portion N at the Ap-Yc position in the conveying direction is defined as the first portion 303a1. Furthermore, the radius of curvature R of the first portion 303a1 of the curved portion 303a is defined as R1, and the radius of curvature R of the second portion 303a2 of the curved portion 303a is defined as R2. Furthermore, in this embodiment, the radius of curvature R2 of the second portion 303a2 is configured to be greater than the radius of curvature R1 of the first portion 303a1 (R2 > R1).

[0061] Specifically, the curvature radius R2 of the second portion 303a2 (A-np-Yn position) is set to 8 mm, and its bending strain E is set to 1.2%. In addition, the curvature radius R1 of the first portion 303a1 (Ap-Yc position) is set to 4 mm, and the bending strain E is set to 2.4% (Example 1). The shape of the boundary area between the Ap region and the A-np region is defined so that ... Figure 6 As the curved portion 303a extends outward (in the direction of the hollow arrow in section (a)), the radius of curvature R, measured in a cross section taken along the pressurizing direction, gradually and continuously increases. Specifically, the curved portion 303a is formed so that the radius of curvature R increases continuously from the first portion 303a1 to the second portion 303a2. Incidentally, while the above description has been of one side in the longitudinal direction, the same shape is also provided for the A-np region on the opposite side in the longitudinal direction. [Comparative Example 1]

[0062] Figure 7Parts (a) to (d) are cross-sectional views of the nip portion N of the fixing device 8 , which is equipped with the pad 3030 of Comparative Example 1, for verifying the effect of this embodiment. Figure 7 Part (a) is a cross-sectional view of the overall configuration, in which the stay 302 and the pad 3030 are cut along the width direction and viewed from the downstream side in the conveying direction.

[0063] Figure 7 Part (b) is Figure 7 Cross-sectional view of the Ap-Yc position in part (a). Figure 7 Part (c) is in Figure 7 The A-np-Yn position in part (a) is magnified Figure 7 Part (b) is a cross-sectional view of portion D surrounded by a dotted square portion. Figure 7 Part (d) is in Figure 7 Part (a) of the Ap-Yc position is enlarged Figure 7 (b) is a cross-sectional view of portion D.

[0064] In Comparative Example 1, Figure 7 As shown in parts (c) and (d) of FIG. , the shape of the pad 3030 is set so that the bending strain E at the A-np-Yn position and the bending strain E at the Ap-Yc position due to the shape of the pad 3030 are the same. Incidentally, in Comparative Example 1, also in the curved portion 3030a, the region located on the downstream side of the AP region in the conveying direction is defined as the first portion 3030a1 ( Figure 7 d). Furthermore, in the curved portion 3030a, the region downstream of the A-np region in the conveying direction is defined as a second portion 3030a2. In Comparative Example 1, the curvature radius R2 of the second portion 3030a2 is set to be the same as the curvature radius R1 of the first portion 3030a1 (R2 = R1).

[0065] Specifically, the curvature radius R2 of the second portion 3030a2 (A-np-Yn position) is set to 4 mm, and its bending strain E is set to 2.4%. In addition, the curvature radius R1 of the first portion 3030a1 (Ap-Yc position) is set to 4 mm, and its bending strain E is set to 2.4%. In this specification, one side in the longitudinal direction has been described, however, the same shape is also provided for the A-np region on the opposite side in the longitudinal direction. If used Figure 4As described above, in reality, the tension SF from the steering roller 308 is higher at the A-np-Yn position than at the Ap-Yc position. Therefore, in calculation, the bending strain E is the same at the Ap-Yc position and the A-np-Yn position. However, in reality, it is assumed that the bending strain generated at the A-np-Yn position becomes larger than the bending strain generated at the Ap-Yc position.

[0066] In this manner, in this embodiment, the curvature radius R2 of the second portion 303a2 of the curved portion 303a is configured to be larger than the curvature radius R1 of the first portion 303a1. Therefore, compared to Comparative Example 1, in which R2 and R1 are the same, the bending strain E of the second portion 303a2 can be made smaller. As described above, in the ribbon 301 bent by the curved portion 303a (i.e., the second portion 303a2) in the A-np region, excessive strain may be generated, and fatigue failure may occur as the ribbon 301 rotates.

[0067] In contrast, in this embodiment, by making the curvature radius of the second portion 303a2 larger, the bending strain E generated in the belt 301 bent by the second portion 303a2 can be made smaller, and fatigue failure can be suppressed in the belt 301. As a result, shortening of the life of the belt 301 can be suppressed. [Example 2]

[0068] Will use Figure 8 Part (a) to Figure 10 Part (d) of the embodiment 2 describes the embodiment 2. In the above embodiment 1, the configuration is described in which, in the pad 303 , the curved portion 303 a for separating the recording material from the belt 301 exists continuously from the most downstream side of the nip portion N.

[0069] In contrast, in the present embodiment, in the pad 303A, the separation portion 303b for separating the recording material from the belt 301 includes a contact portion 303d provided discontinuously from the downstream end 303c, which is the most downstream position of the nip portion N. Since other configurations and effects are the same as those in the above-described embodiment 1, the same reference numerals will be assigned to the same configuration to omit or simplify description and illustration, and hereinafter, description will focus on points different from embodiment 1.

[0070] In this embodiment, the pad 303A, serving as a pad member, includes a contact portion 303d, located downstream of the nip portion N in the conveying direction of the recording material, discontinuous with the downstream end 303c of the nip portion N. This contact portion allows the sliding member 304 to contact or directly contact the belt 301. In other words, the pad 303A in this embodiment has a step structured downstream of the nip portion N. The downstream end 303c of the nip portion N and the contact portion 303d constitute a separating portion 303b, which bends the belt 301 and separates the recording material passing through the nip portion N from the belt 301. Incidentally, the downstream end 303c of the nip portion N can be the downstream end of the protrusion 304b furthest downstream in the conveying direction among the multiple protrusions 304b. Alternatively, if the sliding member 304 is not present in the separating portion 303b, the contact portion 303d directly contacts the belt 301, bending the belt 301.

[0071] Next, use Figure 8 Parts (a) to (c) of the present invention will describe a method for calculating the strain generated in the belt 301 when the belt 301 is bent to a specific radius of curvature by the separation portion 303b downstream of the clamping portion N. The calculation method for the strain in this embodiment is the same as the calculation method described in Example 1. That is, first, the separation portion 303b (where the pad 303A and the belt 301 are in contact with each other and the belt 301 is bent) is measured with pressure-sensitive paper, and the area of ​​the separation portion 303b is identified. Next, based on the shape of the area, the size of each portion is measured. Finally, the measured values ​​are substituted into the theoretical formula to calculate the strain at each portion. Figure 8 In part (a) of FIG. 3 , a cross-sectional view of the belt 301 , the stay 302 , and the pad 303A near the clamping portion N is shown. Figure 8 Part (b) is Figure 8 An enlarged view of portion E surrounded by a dotted line in part (a).

[0072] As described in Example 1, the separation portion 303b was measured using a three-dimensional shape measuring instrument VR-3200 manufactured by Keyence and pressure-sensitive paper Prescale manufactured by Fujifilm. The measurement method was the same as in Example 1. The contact area (the area where the color changed) of the collected Prescale was then two-dimensionally measured using the three-dimensional shape measuring instrument VR-3200 manufactured by Keyence, and this contact area was calculated as the separation portion 303b. During the measurement, the magnification is preferably set to 10x or greater.

[0073] At this time, if Figure 8As shown in part (b), in the case where one or more contact portions 303d of the separation portion 303b are discontinuously and separately arranged from the downstream end 303c of the clamping portion N, the starting point (the most downstream position of the clamping portion N) is defined as R-1, and multiple regions where the Prescale color changes (multiple contact portions 303d) are defined in order from the most downstream of the clamping portion N as 303b-2, 303b-3, ... 303b-E, and the center position in the rotation direction of each region is defined as R-2, R-3, ... RE. Incidentally, in the raised portion 304d in the clamping portion N, the position of R-1 may be the downstream end of the raised portion 304d set at the most downstream in the conveying direction. Figure 8 In the example shown in part (b), the separation portion 303b is configured at two positions, R-1 of the downstream end 303c of the clamping portion N and RE of the contact portion 303d. However, the same applies to the case where one or more contact portions are provided between R-1 and RE.

[0074] Next, we will describe a method for measuring the dimensions of each portion of the separation section 303b and a method for calculating the bending strain generated in the belt 301. The conveying direction distance ΔX and the pressure direction distance ΔZ of the portion of the bent belt 301 are calculated based on the shape of the pad 303A in the separation section 303b. Here, the conveying direction distance ΔX is the distance between the downstream end 303c of the clamping section N and the contact portion 303d in the conveying direction. The pressure direction distance ΔZ is the distance between the downstream end of the clamping section N and the contact portion 303d in the pressure direction. Incidentally, as described above, the pressure direction is the direction in which the recording material is pressurized in the clamping section N and is perpendicular to both the conveying direction and the width direction.

[0075] The pressurizing direction distance ΔZ is defined as the distance in the pressurizing direction between the downstream end of the clamping portion N and the contact portion 303d. However, the clamping portion is coated with a sliding layer 304c to improve the sliding characteristics with the belt. The pressurizing direction distance ΔZ can be from the contact belt 301 (see Figure 2 The distance from the front end of the sliding layer 304c of the portion (b) to the contact portion 303d, or the distance excluding the sliding layer 304c.

[0076] Sliding layer 304c wears due to sliding with the belt. Therefore, the distance from the front side of protrusion 304b is preferably such that the pressure direction distance ΔZ is maintained even after the fixing device has been used a certain number of times. On the other hand, it is also preferable to use the distance including sliding layer 304c as the pressure direction distance ΔZ so that the pressure direction distance ΔZ is maintained even from the start of use of the fixing device.

[0077] When calculating the conveying direction distance ΔX and the pressurizing direction distance ΔZ, first, the shape of the pad 303A is measured using a three-dimensional shape measuring instrument VR-3200 manufactured by Keyence Corporation. When measuring, it is preferable to set the magnification to 10 times or more. When measuring, the pad 303A is mounted to the measuring instrument so that its surface on the side of the clamping portion N faces upward, and a three-dimensional shape is obtained. The position in the longitudinal direction to be measured (the position in the width direction) is determined, and the shape profile in the pressurizing direction is output along the conveying direction at this position in the longitudinal direction. Based on this shape profile, the coordinates of R-1 and RE in the separation portion 303b are confirmed, and the coordinates are calculated by the above-mentioned pressure-sensitive paper measurement. Based on these coordinates, calculation Figure 8 The conveying direction distance ΔX and the pressurizing direction distance ΔZ are shown in part (b). Three or more positions are measured in each area (Ap area, A-np area), and their average values ​​are defined as the conveying direction distance ΔX and the pressurizing direction distance ΔZ, respectively.

[0078] Finally, by substituting the measured conveying direction distance ΔX and pressing direction distance ΔZ into the following theoretical formula, the bending strain E is calculated. In the calculation, the thickness of the base layer 301a of the belt 301 is defined as t, which is uniformly set to a fixed value of 0.095 and substituted into the following formula. [Formula 2]

[0079] Figure 8 Part (c) shows the change in bending strain E when the pressurizing direction distance ΔZ is changed using the above formula. Here, the calculation is performed with the conveying direction distance ΔX fixed to a constant value of 1.2 mm. Figure 8 It can be confirmed from part (c) that the bending strain E increases as the distance ΔZ in the pressurizing direction increases.

[0080] Figure 9 Parts (a) to (d) are cross-sectional views of the nip portion N of the fixing device 8 equipped with the pad 303A in this embodiment, respectively. Figure 9 Part (a) is a cross-sectional view of the overall configuration in which the stay 302 and the pad 303A are cut along the width direction and viewed from the downstream side in the conveying direction. Figure 9 Part (b) is in Figure 9 Cross-sectional view at the Ap-Yc position in part (a). Figure 9 Part (c) is in Figure 9 A-np-Yn position in part (a) is enlarged Figure 9 Part (b) is a cross-sectional view of part F surrounded by a dotted square portion. Figure 9 Part (d) is in Figure 9Part (a) of the Ap-Yc position is enlarged Figure 9 (b) is a cross-sectional view of part F.

[0081] like Figure 9 As shown in parts (c) and (d) of FIG. , in this embodiment, the shape of the pad 303A is configured so that the bending strain E at the A-np-Yn position is smaller than the bending strain E at the Ap-Yc position. Here, in the separation portion 303b, the area located on the downstream side of the conveying direction of the AP region is defined as the first portion 303b1, which is the passing area where the recording material having the largest size passes through the clamping portion N. In addition, in the separation portion 303b, the area located on the downstream side of the conveying direction of the A-np region is defined as the second portion 303b2, which is the non-passing area outside the passing area in the width direction (longitudinal direction). That is, as Figure 9 As shown in part (c) of FIG. 1 , the area on the downstream side of the conveying direction of the clamping portion N at the position A-np-Yn is defined as the second portion 303b2, and as shown in FIG. Figure 9 As shown in part (d) of the figure, the area downstream of the nip portion N in the conveying direction at the Ap-Yc position is defined as the first portion 303b1. Furthermore, the pressurizing distance ΔZ of the first portion 303b1 of the separation portion 303b is defined as ΔZ1, and the pressurizing distance ΔZ of the second portion 303b2 of the separation portion 303b is defined as ΔZ2. Furthermore, in this embodiment, the pressurizing distance ΔZ2 of the second portion 303b2 is shorter than the pressurizing distance ΔZ1 of the first portion 303b1 (ΔZ2 < ΔZ1). The pressurizing distance ΔZ is preferably greater than 0 mm and less than or equal to 1.5 mm.

[0082] Specifically, the conveying direction distance ΔX of the second portion 303b2 (A-np-Yn position) is set to 1.2 mm, the pressurizing direction distance ΔZ2 is set to 0.2 mm, and the bending strain E is set to 1.3%. In addition, the conveying direction distance ΔX of the first portion 303b1 (Ap-Yc position) is set to 1.2 mm, the pressurizing direction distance ΔZ2 is set to 0.9 mm, and the bending strain E is set to 4.8% (Example 2). That is, the conveying direction distance ΔX of the second portion 303b2 is configured to be the same as the conveying direction distance ΔX of the first portion 303b1. In addition, for the boundary area of ​​the Ap region and the A-np region, the shape is defined so that from the outer end side of the Ap region to the A-np region, as it moves toward the outside in the longitudinal direction ( Figure 9As the pressure-direction distance ΔZ (measured in a cross section taken along the pressure direction) of the first portion 303b1 (in the direction of the hollow arrow in section (a)) decreases as it advances outward, the pressure-direction distance ΔZ continuously decreases. Specifically, the separation portion 303b is formed so that the pressure-direction distance ΔZ continuously decreases from the first portion 303b1 toward the second portion 303b2. Incidentally, while the above description has been of one side in the longitudinal direction, the same shape is also provided for the A-np region on the opposite side in the longitudinal direction. [Comparative Example 2]

[0083] Figure 10 Parts (a) to (d) are cross-sectional views of the nip portion N of the fixing device 8 , which is equipped with the pad 3031 of Comparative Example 2, for verifying the effect of this embodiment. Figure 10 Part (a) is a cross-sectional view of the overall configuration in which the stay 302 and the pad 3031 are cut along the width direction and viewed from the downstream side in the conveying direction. Figure 10 Part (b) is in Figure 10 Cross-sectional view at the Ap-Yc position in part (a). Figure 10 Part (c) is in Figure 10 The A-np-Yn position in part (a) is magnified Figure 10 Part (b) is a cross-sectional view of portion G surrounded by a dotted square portion. Figure 10 Part (d) is in Figure 10 Part (a) of the Ap-Yc position is enlarged Figure 10 (b) is a cross-sectional view of part G.

[0084] In Comparative Example 2, Figure 10 As shown in parts (c) and (d) of FIG. , the shape of the pad 3031 is constructed so that the bending strain E at the A-np-Yn position and the bending strain E at the Ap-Yc position caused by the shape of the pad 3031 are the same. Incidentally, in Comparative Example 2, also in the separation portion 3031b, the region located on the downstream side of the AP region in the conveying direction is defined as the first portion 3031b1 ( Figure 10 (d)). Furthermore, in the separation section 3031b, the area downstream of the A-np region in the conveying direction is defined as the second section 3031b2. In Comparative Example 2, the pressurizing direction distance ΔZ2 of the second section 3031b2 is the same as the pressurizing direction distance ΔZ1 of the first section 3031b1 (ΔZ2 = ΔZ1).

[0085] Specifically, the conveying direction distance ΔX of the second portion 3031b2 (A-np-Yn position) is set to 1.2 mm, the pressurizing direction distance ΔZ2 is set to 0.9 mm, and the bending strain E is set to 4.8%. In addition, the conveying direction distance ΔX of the first portion 3031b1 (Ap-Yc position) is set to 1.2 mm, the pressurizing direction distance ΔZ1 is set to 0.9 mm, and the bending strain E is set to 4.8%. In this specification, one side in the longitudinal direction is described, however, the same shape is also provided for the A-np region on the opposite side in the longitudinal direction. As used Figure 4 As described above, in reality, the tension SF from the steering roller 308 is higher at the A-np-Yn position than at the Ap-Yc position. Therefore, in the calculation, the bending strain E is the same at the Ap-Yc position and the A-np-Yn position. However, it is actually assumed that the bending strain generated at the A-np-Yn position becomes larger than the bending strain generated at the Ap-Yc position.

[0086] In this manner, the pressurizing direction distance ΔZ2 of the second portion 303b2 of the separation portion 303b is configured to be shorter than the pressurizing direction distance ΔZ1 of the first portion 303b1. Therefore, the bending strain E of the second portion 303b2 can be made smaller than that of Comparative Example 2 in which ΔZ2 and ΔZ1 are the same.

[0087] As described above, excessive strain may occur in the belt 301 bent by the separation portion 303b (i.e., the second portion 303b2) in the A-np region, leading to fatigue failure as the belt 301 rotates. In contrast, in this embodiment, by shortening the pressurizing direction distance Δz2 of the second portion 303b2, the bending strain E generated in the belt 301 bent by the second portion 303b2 can be reduced, and fatigue failure in the belt 301 can be suppressed. As a result, shortening the life of the belt 301 can be suppressed. [verify]

[0088] For Examples 1 and 2 and Comparative Examples 1 and 2 described above, belt durability evaluation tests and sheet (recording material) separation performance evaluation tests were conducted, respectively, to verify their effectiveness. Below, after describing the procedures for each verification test, the verification results using Examples 1 and 2 and Comparative Examples 1 and 2 will be described. [Process of belt durability evaluation test]

[0089] In the belt durability evaluation test, the fixing device 8 was mounted on a printer (trade name: Canon imagePRESS V1000), the pads of Examples 1 and 2 and Comparative Examples 1 and 2 were respectively attached to the fixing device 8, and the life of the belt 301 was evaluated. The peripheral speed of the pressure roller 305 mounted in the fixing device 8 was set to 450 mm / s, and the adjustment temperature of the halogen heater 306 was set to 190°C.

[0090] In the belt durability evaluation test, after continuously printing 10,000 sheets of paper and forming a designated image on them, the printer was stopped to inspect the belt 301. The process of continuously printing 10,000 sheets of paper and forming the designated image on them was then repeated. The number of sheets printed before cracks appeared in the belt 301 was defined as the lifespan (number of durable sheets) of the belt 301. Visual inspection was performed at the width ends of the belt 301 to determine damage. A configuration with a lifespan exceeding 3000K (3000 × 1000) sheets was defined as achieving the target. The temperature and humidity conditions during the measurement were set at 23°C and 30%. The base layer 301a of the belt 301 used in this verification was made of polyimide with a thickness of 95μm. An A4-sized CS-680 (manufactured by Canon Inc.) was used as the sheet material. [Process of Sheet Material Separation Performance Evaluation Test]

[0091] In the sheet separation performance evaluation test, the fixing device 8 was installed on a printer (trade name: Canon imagePRESS V1000), and the pads in Examples 1 and 2 and Comparative Examples 1 and 2 were respectively assembled on the fixing device 8, and the sheet separation performance of the fixing device 8 in each case was evaluated. The peripheral speed of the pressure roller 305 installed in the fixing device 8 was set to 450 mm / sec, and the adjustment temperature of the halogen heater 306 was set to 190°C. In the sheet separation performance evaluation test, 20 sheets on which images with the maximum amount of toner stacked were formed passed through the clamping portion N continuously, and it was confirmed that no conveying defects or the like occurred. The case where no conveying defects occurred was defined as the case where the target was achieved. The temperature and humidity conditions during the measurement were set to 30°C and 80%. For the base layer 301a of the belt 301 used for this verification, the material was set to polyimide, and the thickness was set to 95μm. For the sheet, a base weight of 73 g / m 2 A4 size OK Top Coat + (Oji Paper Co. Ltd.). [Verification Result 1]

[0092] exist Figure 11, the results of the belt durability evaluation test and the sheet separation performance evaluation test performed on Example 1 and Comparative Example 1 are shown. Incidentally, Figure 11 "◯" determined in the sheet separation performance evaluation test indicates that the lifespan exceeds 3000K (3000 × 1000) sheets, while "×" indicates that the lifespan is less than 3000K (3000 × 1000) sheets. In addition, "◯" in the sheet separation performance evaluation test indicates that no conveyance failure occurred.

[0093] The results of the belt durability evaluation test showed that Example 1 lasted 10 million sheets, while Comparative Example 1 lasted 3 million sheets. This difference can be attributed to the fact that the bending strain in the second portion 303a2 downstream of the A-np region in Example 1 was smaller than that in Comparative Example 1. Furthermore, while cracks appeared at the widthwise ends of the belt 301 in Comparative Example 1, cracks appeared in the widthwise center of the belt 301 in Example 1. This is presumably because the bending strain at the widthwise ends (A-np region) of the belt 301 was reduced in Example 1, while the strain at the widthwise center increased relatively, leading to cracks in the center. Furthermore, in the sheet separation performance evaluation test, all sheets met the requirements, confirming that even changes in the shape of the second portion of the pad had no effect on the recording material separation performance. [Verification Result 2]

[0094] exist Figure 11 Figure 2 shows the results of belt durability evaluation tests and sheet separation performance evaluation tests conducted on Example 2 and Comparative Example 2. The results of the belt durability evaluation test showed that the belt lasted 8 million sheets in Example 2, while the belt lasted 1.2 million sheets in Comparative Example 2. This difference can be attributed to the fact that the bending strain in the second portion 303b2 downstream of the A-np region in Example 2 was smaller than that in Comparative Example 2. Furthermore, while cracks appeared in the belt 301 at the widthwise ends (A-np region) in Comparative Example 2, cracks appeared in the widthwise center of the belt 301 in Example 2. This is presumably because the bending strain at the widthwise ends (A-np region) of the belt 301 was reduced in Example 2, while the strain at the widthwise center increased relatively, leading to cracks in the center. Furthermore, in the sheet separation performance evaluation test, all sheets met the requirements, confirming that even changes in the shape of the second portion of the pad had no effect on the recording material separation performance.

[0095] As described above, it was found that in Examples 1 and 2, the shortening of the life of the belt 301 could be suppressed without deteriorating the sheet separation performance, as compared with Comparative Examples 1 and 2. In other words, according to Examples 1 and 2, the shortening of the life of the belt 301 could be suppressed without deteriorating the recording material separation performance. <Other embodiments>

[0096] In the above embodiments, the respective pads 303 and 303A are integrally formed. However, the pads 303 and 303A may be formed from multiple components. For example, the pads 303 and 303A may be separated into two main bodies. Furthermore, in the above embodiments, the configuration of the pad 303 downstream of the nip portion N in the conveying direction is described. However, the configuration of the pad 303 upstream of the nip portion N in the conveying direction may be similar to that of the downstream portion.

[0097] Furthermore, in each of the above-described embodiments, a configuration has been described in which tension is applied to the belt 301 by the deflection roller 308 as a tension applying member. However, a configuration may be employed in which pads and rollers are provided to apply tension to the belt even without such a tension applying member. For example, the present invention can be applied to a configuration in which the belt 301 is stretched only by the heating roller 307 and the pads 303 and 303A.

[0098] While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

Claims

1. A fixing device for fixing a toner image carried on a recording material to the recording material, the fixing device comprising: an endless rotatable belt; a rotating member configured to rotate in contact with an outer peripheral surface of the belt; a pad member provided inside the belt so as to sandwich the belt between the pad member itself and the rotating member and forming a sandwich portion for sandwiching and conveying the recording material between the belt and the rotating member; a sliding member provided between the pad member and the belt and configured to contact and slide with the inner peripheral surface of the belt in the clamping portion; as well as a heating roller disposed inside the belt and configured to heat the belt, wherein the pad member includes a bent portion that is bent to directly contact the belt on a downstream side of the nip portion in the conveying direction of the recording material and bends the belt to separate the recording material passing through the nip portion from the belt, and wherein the curved portion includes a first portion located on the downstream side in the conveying direction of a passing region where the recording material having the largest size passes through the clamping portion, and a second portion located on the downstream side in the conveying direction of a non-passing region located on the outside of the passing region in a width direction of the recording material intersecting the conveying direction, and The curvature radius of the second portion is greater than the curvature radius of the first portion. 2 . The fixing device according to claim 1 , wherein the curved portion is formed such that a radius of curvature continuously increases from the first portion toward the second portion.

3. The fixing device according to claim 1, wherein The belt includes a base layer, and Wherein, when the thickness of the base layer is defined as t, the curvature radius of the curved portion is defined as R, and the bending strain represented by the following formula is defined as E, The bending strain E of the second portion is smaller than the bending strain E of the first portion.

4. The fixing device according to claim 1 , wherein the sliding member includes a plurality of protrusions provided on a side sliding with the belt so as to protrude toward the inner peripheral surface of the belt, and The plurality of protrusions are distributed in the width direction. 5 . The fixing device according to claim 4 , wherein the plurality of protrusions are distributed in the passage area and the non-passage area in the width direction. 6 . The fixing device according to claim 1 , further comprising a tension applying member configured to apply tension to the belt. 7 . The fixing device according to claim 6 , wherein the tension applying member is a steering roller provided inside the belt and configured to stretch the belt and control a position of the belt in the width direction.

8. A fixing device for fixing a toner image carried on a recording material to the recording material, the fixing device comprising: an endless rotatable belt; a rotating member configured to rotate in contact with an outer peripheral surface of the belt; a pad member provided inside the belt to sandwich the belt between the pad member itself and the rotating member, and forming a sandwich portion for sandwiching and conveying the recording material between the belt and the rotating member; as well as a sliding member provided between the pad member and the belt and configured to contact and slide with the inner peripheral surface of the belt in the clamping portion; as well as a heating roller disposed inside the belt and configured to heat the belt, wherein the pad member includes a bent portion that is bent so as to directly contact the belt on a downstream side of the nip portion in the conveying direction of the recording material and bends the belt so as to separate the recording material passing through the nip portion from the belt, wherein the curved portion includes a first portion located on the downstream side in the conveying direction of a passing region where the recording material having the largest size passes through the clamping portion, and a second portion located on the downstream side in the conveying direction of a non-passing region, wherein the non-passing region is located outside the passing region in a width direction of the recording material intersecting the conveying direction. wherein the pad member includes a contact portion that is provided on the downstream side of the nip portion in the conveying direction of the recording material so as to be discontinuous with the downstream end of the nip portion, and In which, when a direction perpendicular to each of the conveying direction and the width direction is defined as a pressing direction, the recording material is pressed by the clamping portion along the pressing direction, and the distance from the downstream end of the clamping portion to the contact portion is defined as the distance in the pressing direction, the distance of the second portion in the pressing direction is shorter than the distance of the first portion in the pressing direction.

9. A fixing device for fixing a toner image carried on a recording material to the recording material, the fixing device comprising: an endless rotatable belt; a rotating member configured to rotate in contact with an outer peripheral surface of the belt; a pad member provided inside the belt to sandwich the belt between the pad member itself and the rotating member, and forming a sandwich portion for sandwiching and conveying the recording material between the belt and the rotating member; as well as a sliding member provided between the pad member and the belt and configured to contact and slide with the inner peripheral surface of the belt in the clamping portion; as well as a heating roller disposed inside the belt and configured to heat the belt, wherein the pad member includes a contact portion that is provided on a downstream side of the nip portion in the conveying direction of the recording material so as to be discontinuous with a downstream end of the nip portion and that brings the sliding member into contact with or directly into contact with the belt, wherein a separation portion that bends the belt to separate the recording material passing through the nip portion from the belt is constituted by the downstream end of the nip portion and the contact portion, wherein the separation portion includes a first portion located on the downstream side in the conveying direction of a passing region where the recording material having the largest size passes through the clamping portion, and a second portion located on the downstream side in the conveying direction of a non-passing region located on the outside of the passing region in a width direction of the recording material intersecting the conveying direction, and In which, when a direction perpendicular to each of the conveying direction and the width direction is defined as a pressing direction, the recording material is pressed by the clamping portion along the pressing direction, and the distance from the downstream end of the clamping portion to the contact portion is defined as the distance in the pressing direction, the distance of the second portion in the pressing direction is shorter than the distance of the first portion in the pressing direction.

10. The fixing device according to claim 9, wherein when a distance from a downstream end of the nip portion to the contact portion in a conveying direction is defined as a distance in the conveying direction, a distance of the second portion in the conveying direction is the same as a distance of the first portion in the conveying direction. 11 . The fixing device according to claim 9 , wherein the separation portion is formed such that a distance in the pressing direction continuously shortens from the first portion toward the second portion.

12. The fixing device according to claim 9, wherein The belt includes a base layer, and Wherein, when the thickness of the base layer is defined as t, the distance in the pressing direction is defined as ΔZ, the conveying direction distance from the downstream end of the clamping portion to the contact portion in the conveying direction is defined as ΔX, and the bending strain expressed by the following formula is defined as E, The bending strain E of the second portion is smaller than the bending strain E of the first portion.

13. The fixing device according to claim 12, wherein the sliding member includes a plurality of protrusions provided on a side sliding with the belt so as to protrude toward the inner peripheral surface of the belt, and Among the plurality of protrusions, the downstream end of the gripping portion is the downstream end of the protrusion that is most downstream in the conveying direction.

14. The fixing device according to claim 9, wherein the sliding member includes a plurality of protrusions provided on a side sliding with the belt so as to protrude toward the inner peripheral surface of the belt, and The plurality of protrusions are distributed in the width direction. 15 . The fixing device according to claim 14 , wherein the plurality of protrusions are distributed in the passage area and the non-passage area in the width direction.

16. A fixing device according to claim 14, wherein the sliding member includes a sliding layer, the sliding layer is configured to cover a surface on the side sliding with the belt, the surface including the plurality of protrusions, and the distance in the pressing direction is the distance from the sliding layer covering the protrusions located at the downstream end of the clamping portion to the contact portion.

17. A fixing device according to claim 14, wherein the sliding member includes a sliding layer, the sliding layer is configured to cover a surface on the side sliding with the belt, the surface includes the plurality of protrusions, and the distance in the pressing direction is the distance from the protrusion located at the downstream end of the clamping portion to the contact portion.

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