Fixing device

Abstract

To extend the service life of a belt 301.SOLUTION: A slide member 304 slides with an inner peripheral surface of a belt 301 at a nip part N. The slide member 304 has, on a side sliding with the belt 301, a plurality of projections 304b, 304b1, 304b2 that project toward the inner peripheral surface of the belt 301. The plurality of projections 304b, 304b1, 304b2 are each arranged in plurality over a conveyance direction of a recording material and over a width direction of the recording material intersecting the conveyance direction at the nip part N. Of the plurality of projections 304b, 304b1, 304b2, the average height of the plurality of projections 304b1, 304b2 located at at least one end of an upstream end and a downstream end with respect to the conveyance direction is lower than the average height of the plurality of projections 304b located at a central area with respect to the conveyance direction.SELECTED DRAWING: Figure 6

Description

Technical Field

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[0005] ,

[0001] The present invention relates to a fixing device that fixes a toner image carried on a recording material to the recording material.

Background Art

[0002] As a fixing device, a configuration is conventionally known in which a nip portion is formed by nip portion forming members such as a belt and a roller, and the recording material passing through the nip portion is heated and pressurized. Further, in this configuration, a nip portion is formed between the belt and the nip portion forming member by sliding a sliding member on the inner peripheral surface of the belt in the nip portion.

[0003] In a fixing device, in order to guarantee the quality of an image to be fixed on a recording material, it is required to suppress slip between the recording material conveyed to the nip portion and the belt, and slip between the recording material and the nip portion forming member. For this purpose, it is required to make the frictional force between the belt and the sliding member smaller than the frictional forces between the recording material and the belt, and between the recording material and the nip portion forming member. In particular, in a configuration having a wide nip in which the width of the nip portion is widened to improve heating efficiency, it is required to make the frictional force between the belt and the sliding member smaller.

[0004] For example, Patent Document 1 discloses a configuration in which concavities and convexities are formed on a sliding sheet that slides on the inner peripheral surface of a belt in a nip portion to reduce the frictional force between the sliding sheet and the belt.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] In this configuration, where irregularities are formed on the sliding member to reduce frictional force between it and the inner circumferential surface of the belt, the belt bends when it comes into contact with a projection at the upstream or downstream end of the nip section in the direction of transporting the recording material. If the curvature of the bent portion of the belt is large, the belt may experience bending fatigue during rotation, potentially shortening its lifespan.

[0007] The present invention aims to extend the lifespan of belts. [Means for solving the problem]

[0008] The present invention relates to a fixing device for fixing a toner image supported on a recording material to the recording material, comprising: an endless, rotatable belt; a nip-forming member that contacts the outer circumferential surface of the belt and forms a nip portion that clamps and transports the recording material between itself and the belt; a sliding member that slides against the inner circumferential surface of the belt at the nip portion; and a backup member positioned inside the belt so as to clamp the sliding member and the belt between itself and the nip-forming member, and to back up the sliding member. A roller is provided downstream of the backup member and adjacent to the backup member in the rotational direction of the belt, and tensions the belt without forming the nip portion. The sliding member comprises a plurality of projections that protrude toward the inner circumferential surface of the belt on the side that slides with the belt, and the plurality of projections are arranged in the direction of transport of the recording material in the nip portion and in the width direction of the recording material intersecting the transport direction, and the plurality of projections teeth With respect to the aforementioned conveying direction The nip portion includes a plurality of first protrusions arranged in a first predetermined region within the nip portion, and a plurality of second protrusions arranged in a second predetermined region outside the nip portion, multiple Second The average height of the protrusions is, Record Number First It is characterized by being lower than the average height of the protrusions. Furthermore, the present invention relates to a fixing device for fixing a toner image supported on a recording material to the recording material, comprising: an endless, rotatable belt; a nip portion forming member that contacts the outer peripheral surface of the belt and forms a nip portion for clamping and transporting the recording material between itself and the belt; a sliding member that slides against the inner peripheral surface of the belt in the nip portion; and a backup member that is positioned inside the belt so as to clamp the sliding member and the belt between itself and the nip portion forming member, and backs up the sliding member, wherein the sliding member has a plurality of protrusions that project toward the inner peripheral surface of the belt on the side that slides with the belt, and the plurality of protrusions are arranged in the direction of transport of the recording material in the nip portion and in the width direction of the recording material intersecting the transport direction, and the average height of the plurality of protrusions located at at least one end of the upstream end and the downstream end with respect to the transport direction is 0.70 times or more and 0.99 times or less than the average height of the plurality of protrusions located in the central region with respect to the transport direction. Furthermore, the present invention relates to a fixing device for fixing a toner image supported on a recording material to the recording material, comprising: an endless, rotatable belt; a nip-forming member that contacts the outer circumferential surface of the belt and forms a nip portion that clamps and transports the recording material between itself and the belt; a sliding member that slides against the inner circumferential surface of the belt in the nip portion; and a backup member that is positioned inside the belt so as to clamp the sliding member and the belt between itself and the nip-forming member, and backs up the sliding member, wherein the sliding member has a plurality of projections that protrude toward the inner circumferential surface of the belt on the side that slides against the belt, and the transport of the recording material in the nip portion The sliding member has multiple protrusions arranged in the transport direction and in the width direction of the recording material intersecting the transport direction, and when a predetermined region upstream from the downstream end of the sliding member is defined as the downstream region, a predetermined region downstream from the upstream end of the sliding member is defined as the upstream region, and the region between the downstream region and the upstream region of the sliding member is defined as the central region, the average height of the multiple protrusions located in at least one of the downstream region and the upstream region is lower than the average height of the multiple protrusions located in the central region, and the predetermined region is a region of less than 33% of the length of the nip portion in the transport direction. [Effects of the Invention]

[0009] According to the present invention, the lifespan of the belt can be extended. [Brief explanation of the drawing]

[0010] [Figure 1]Schematic cross-sectional view of an image forming apparatus according to the first embodiment. [Figure 2] (a) Schematic cross-sectional view of a fixing device according to the first embodiment, (b) Schematic diagram showing an enlarged view of part A in (a). [Figure 3] Schematic diagrams showing a sliding member according to the first embodiment, (a) Cross-sectional view, (b) Planar view. [Figure 4] Schematic diagrams showing a sliding member according to Comparative Example 1, (a) Cross-sectional view, (b) Planar view. [Figure 5] Cross-sectional view schematically showing an enlarged nip portion of a fixing device according to Comparative Example 1. [Figure 6] Cross-sectional view schematically showing an enlarged nip portion of a fixing device according to the first embodiment. [Figure 7] Graph showing the relationship between the height of the protrusion and the axial torque of the pressure roller during belt rotation. [Figure 8] Cross-sectional view schematically showing an enlarged nip portion of a fixing device according to the second embodiment. [Figure 9] Cross-sectional view schematically showing an enlarged nip portion of a fixing device according to Comparative Example 2. [Figure 10] Schematic diagrams showing a sliding member according to the third embodiment, (a) Cross-sectional view, (b) Planar view. [Figure 11] Table showing the effects of each example. [Embodiments for Carrying Out the Invention]

[0011] [First Embodiment] The first embodiment will be described with reference to FIGS. 1 to 7. First, the schematic configuration of the image forming apparatus of the present embodiment will be described with reference to FIG. 1.

[0012] [Image Forming Apparatus] The image forming apparatus 1 is an electrophotographic full-color printer having four image forming units Pa, Pb, Pc, and Pd provided corresponding to four colors of yellow, magenta, cyan, and black. In the present embodiment, the image forming units Pa, Pb, Pc, and Pd are arranged in a tandem type along the rotation direction of an intermediate transfer belt 204 described later. The image forming apparatus 1 forms a toner image (image) on a recording material according to an image signal from an image reading unit (document reading apparatus) 2 connected to the image forming apparatus main body 3 or a host device such as a personal computer communicably connected to the image forming apparatus main body 3. Examples of the recording material include sheet materials such as paper, plastic film, and cloth.

[0013] The image forming apparatus 1 includes an image reading unit 2 and an image forming apparatus main body 3. The image reading unit 2 reads a document placed on a document table glass 21, and light irradiated from a light source 22 is reflected by the document and imaged on a CCD sensor 24 through an optical system member 23 such as a lens. Such an optical system unit scans in the direction of the arrow to convert the document into an electric signal data series for each line. The image signal obtained by the CCD sensor 24 is sent to the image forming apparatus main body 3, and image processing is performed by a control unit 30 according to each image forming unit described later. Further, the control unit 30 also receives an external input from an external host device such as a print server as an image signal.

[0014] The image forming apparatus main body 3 includes a plurality of image forming units Pa, Pb, Pc, and Pd. In each image forming unit, image formation is performed based on the above-described image signal. That is, the image signal is converted into a laser beam PWM (pulse width modulation control) by the control unit 30. A polygon scanner 31 as an exposure device scans a laser beam according to the image signal. Then, the laser beam is irradiated onto photosensitive drums 200a to 200d as image carriers of the respective image forming units Pa to Pd.

[0015] Pa is the image forming unit for yellow (Y), Pb is for magenta (M), Pc is for cyan (C), and Pd is for black (Bk), each forming an image of the corresponding color. Since the image forming units Pa to Pd are substantially the same, the details of the Y image forming unit Pa will be explained below, and the explanations of the other image forming units will be omitted. In the image forming unit Pa, a toner image is formed on the surface of the photosensitive drum 200a based on the image signal, as described below.

[0016] The charging roller 201a, acting as a primary charger, charges the surface of the photosensitive drum 200a to a predetermined potential, preparing it for electrostatic latent image formation. An electrostatic latent image is formed on the surface of the photosensitive drum 200a, which has been charged to the predetermined potential, by a laser beam from the polygon scanner 31. The developer 202a develops the electrostatic latent image on the photosensitive drum 200a to form a toner image. The primary transfer roller 203a discharges from the back of the intermediate transfer belt 204, applying a primary transfer bias with the opposite polarity to the toner, and transfers the toner image on the photosensitive drum 200a onto the intermediate transfer belt 204. After the transfer, the surface of the photosensitive drum 200a is cleaned by the cleaner 207a.

[0017] Furthermore, the toner image on the intermediate transfer belt 204 is transported to the next image forming section, and the toner images of each color formed in the respective image forming sections are transferred sequentially in the order of Y, M, C, and Bk, forming a four-color image on its surface. The toner image that has passed through the Bk image forming section Pd, which is the furthest downstream in the rotational direction of the intermediate transfer belt 204, is transported to a secondary transfer section consisting of a pair of secondary transfer rollers 205 and 206. In the secondary transfer section, a secondary transfer electric field with the opposite polarity to the toner image on the intermediate transfer belt 204 is applied, and the image is secondary transferred to the recording material.

[0018] The recording material is housed in a cassette 9. The recording material fed from the cassette 9 is transported to a registration unit 208, which consists of, for example, a pair of registration rollers, and waits in the registration unit 208. Subsequently, the registration unit 208 is controlled in timing to align the toner image on the intermediate transfer belt 204 with the position of the paper, and then transports the recording material to the secondary transfer unit.

[0019] The recording material onto which the toner image has been transferred in the secondary transfer unit is transported to the fuser unit 8, where it is heated and pressurized to fix the toner image onto the recording material. The recording material that has passed through the fuser unit 8 is discharged to the discharge tray 7. When image formation is performed on both sides of the recording material, once the transfer and fixing of the toner image to the first side (front) of the recording material is complete, the front and back sides of the recording material are reversed via the inversion transport unit 10, and the toner image is transferred and fixed to the second side (back) of the recording material, which is then loaded onto the discharge tray 7.

[0020] The control unit 30 controls the entire image forming apparatus 1 as described above. The control unit 30 can also perform various settings based on input from the operation unit 4 of the image forming apparatus 1. This control unit 30 includes a CPU (Central Processing Unit), ROM (Read Only Memory), and RAM (Random Access Memory). The CPU controls each part while reading programs corresponding to control procedures stored in the ROM. The RAM stores working data and input data, and the CPU controls the apparatus by referring to the data stored in the RAM based on the aforementioned programs.

[0021] [Fusing device] Next, the configuration of the fixing device 8 in this embodiment will be described using Figures 2(a) and 2(b). In this embodiment, a belt heating type fixing device using an endless belt is employed. In Figure 2(a), the X direction is the transport direction of the recording material P (not shown in the figure), the Y direction is the width direction of the recording material which intersects (orthogonal in this embodiment) the transport direction of the recording material, and the Z direction is the pressurizing direction in which the recording material is pressurized at the nip portion N. In this embodiment, the X, Y, and Z directions are all orthogonal to each other.

[0022] The fixing device 8 includes a fixing belt (hereinafter referred to as the belt) 301, a stay 302, a pressure pad (hereinafter referred to as the pad) 303, a sliding member 304, a pressure roller 305, a heating roller 307, a thermistor 308, and the like. The belt 301 is an endless, rotatable heating rotating body. The pressure roller 305, as a nip-forming member, is a pressure rotating body that contacts the outer circumferential surface of the belt 301 and forms a nip portion N that grips and conveys the recording material between itself and the belt 301.

[0023] The sliding member 304 slides against the inner circumferential surface of the belt 301 at the nip portion N. The pad 303, acting as a backup member, is positioned inside the belt 301 so as to sandwich the sliding member 304 and the belt 301 between itself and the pressure roller 305, thereby backing up the sliding member 304. The sliding member 304 is positioned so as to cover the outer circumferential surface of the pad 303 on the belt 301 side. The stay 302 is positioned inside the belt 301, on the opposite side of the nip portion N, sandwiching the pad 303, and supports the pad 303. The heating roller 307 is positioned inside the belt 301 so as to tension the belt 301 and heats the belt 301. The thermistor 308, acting as a temperature sensing member, detects the temperature of the belt 301. Each component will be described in detail below.

[0024] The belt 301 has thermal conductivity and heat resistance, and is a thin-walled cylindrical shape. In this embodiment, as shown in Figure 2(b), the belt 301 has a three-layer structure with a base layer 301a, an elastic layer 301b on the outer circumference of the base layer 301a, and a release layer 301c on the outer circumference of the release layer. The base layer 301a is, for example, 80 μm thick and made of polyimide resin (PI). The elastic layer 301b is, for example, 300 μm thick and made of silicone rubber. The release layer 301c is, for example, 30 μm thick and made of PFA (tetrafluoroethylene-perfluoroalkoxyethylene copolymer resin) as a fluororesin. The belt 301 is stretched by a pad 303 and a heating roller 307. The outer diameter of the belt 301 is 150 mm in this embodiment.

[0025] The pad 303 is positioned inside the belt 301, facing the pressure roller 305 with the belt 301 in between, and forms a nip portion N that grips and conveys 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 long along the width direction of the belt 301 (the longitudinal direction intersecting the rotation direction of the belt 301, and the rotation axis direction of the heating roller 307). The nip portion N is formed when the pad 303 is pressed against the pressure roller 305 with the belt 301 in between. The material of the pad 303 is LCP (liquid crystal polymer) resin. A sliding member 304 is interposed between the pad 303 and the belt 301. Details of the sliding member 304 will be described later.

[0026] The pad 303 is supported by a stay 302, which acts as a support member positioned inside the belt 301. That is, the stay 302 is positioned on the opposite side of the pad 303 from the pressure roller 305 and supports the pad 303. Such a stay 302 is a rigid reinforcing member that is long along the longitudinal direction of the belt 301, and it contacts the pad 303 to back it up. In other words, when the pad 303 is pressed by the pressure roller 305, the stay 302 provides strength to the pad 303 and ensures the applied pressure at the nip portion N.

[0027] The stay 302 is made of metal such as stainless steel, and its cross-section (transverse plane), perpendicular to the longitudinal direction of the stay 302 and intersecting the rotational direction of the belt 301, is approximately rectangular. For example, the stay 302 is made of 3mm thick extruded SUS304 (stainless steel), and its strength is ensured by forming the cross-section into a roughly square hollow shape. The stay 302 may also be formed into a roughly rectangular cross-section by combining multiple sheet metal pieces and fixing them to each other by welding or other means. Furthermore, the material of the stay 302 is not limited to stainless steel as long as strength can be ensured.

[0028] The heating roller 307 is positioned inside the belt 301 and, together with the pad 303, tensions the belt 301. The heating roller 307 is formed in a cylindrical shape from a metal such as aluminum or stainless steel, and a halogen heater 306 is disposed inside it as a heat source for heating the belt 301. The heating roller 307 is then heated to a predetermined temperature by the halogen heater 306.

[0029] The heating roller 307 has a pivot point at one end or near the center in the longitudinal direction, and rotates relative to the belt 301 to generate a tension difference in the front and rear directions, thereby controlling the position of the belt 301 in the main scanning direction, and also functions as a steering roller. Furthermore, the heating roller 307 is biased by a spring supported by a frame (not shown), and also functions as a tension roller that applies a predetermined tension to the belt 301.

[0030] In this embodiment, the heating roller 307 is formed from, for example, a stainless steel pipe with a thickness of 1 mm. While one halogen heater 306 may suffice, it is desirable to have multiple halogen heaters to control the temperature distribution along the longitudinal direction (rotation axis direction) of the heating roller 307. Multiple halogen heaters 306 have different light distributions along their longitudinal direction, and the lighting ratio is controlled according to the size of the recording material. In this embodiment, three halogen heaters 306 are arranged. Note that the heating source is not limited to halogen heaters; other heaters capable of heating the heating roller 307, such as carbon heaters, may also be used.

[0031] The belt 301 is heated by a heating roller 307 heated by a halogen heater 306, and controlled to a predetermined target temperature according to the type of recording material based on temperature detection by a thermistor 308. The thermistor 308 is positioned opposite the outer circumferential surface of the belt 301 near the center, where recording materials of all sizes that can be fixed by the fixing device 8 pass, in the width direction of the belt 301. The thermistor 308 detects the temperature of the belt 301, and the control unit 30 controls the power supplied to the halogen heater 306 so that the temperature detected by the thermistor 308 becomes the target temperature. The thermistor 308 may be a non-contact type sensor positioned close to the outer circumferential surface of the belt 301, or a contact type sensor positioned in contact with the outer circumferential surface of the belt 301.

[0032] The pressure roller 305 is a rotating drive body that rotates in contact with the outer surface of the belt 301 and imparts driving force to the belt 301. In this embodiment, the heating roller 307 is also rotationally driven by a drive source (e.g., a drive motor) and imparts driving force to the belt 301. However, the provision of driving force to the heating roller 307 may be omitted. The pressure roller 305 is a roller with a core metal (shaft) 305c, an elastic layer 305b formed on the outer circumference of the core metal 305c, and a release layer 305a formed on the outer circumference of the release layer. For example, the core metal 305c is made of stainless steel with a diameter of 72 mm. For example, the elastic layer 305b is made of conductive silicone rubber with a thickness of 8 mm. For example, the release layer 305a is made of PFA (tetrafluoroethylene-perfluoroalkoxyethylene copolymer resin) as a fluororesin with a thickness of 100 μm. The pressure roller 305 is rotatably supported by the frame (not shown) of the fixing device 8, and a gear is fixed to one end of it. The pressure roller is rotated by being connected to a drive source (e.g., a drive motor, not shown) via the gear.

[0033] The fixing device 8 grips the recording material P, which carries the toner image, in a nip section N formed between the belt 301 and the pressure roller 305, and heats the toner image while transporting it. In this way, the fixing device 8 fixes the toner image to the recording material P while gripping and transporting it. Therefore, it is necessary to balance the function of applying heat and pressure with the function of transporting 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 applied pressure (NF) in the nip section N during image formation is 1600N, and the width of the nip section N in the X direction (direction of transport of the recording material) is set to 24.5 mm, and the width in the Y direction (width direction of the recording material) is set to 326 mm.

[0034] [Sliding member] The detailed configuration of the sliding member 304 is shown in Figures 3(a) and 3(b). Figure 3(a) is a cross-sectional view of the sliding member 304 when cut in the conveying direction, and Figure 3(b) is a plan view of the sliding member 304 as seen from the contact surface side between the belt 301 and the sliding member 304. The sliding member 304 is fixed to the stay 302 with screws or the like via the pad 303. The sliding member 304 may be integrated with the pad 303. Alternatively, the sliding member 304 may be partially fixed to the stay 302 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 with screws or the like.

[0035] The sliding member 304 is composed of a base layer 304a and a sliding layer 304c. On the side of the base layer 304a that slides against the belt 301, there are a number of protrusions (embossed portions) 304b, 304b1, and 304b2 that project toward the inner circumferential surface of the belt 301. The sliding layer 304c is provided so as to cover the surface of the base layer 304a that slides against the belt 301 (including the number of protrusions 304b, 304b1, and 304b2).

[0036] The base layer 304a only needs to have sufficient heat resistance and strength. The material is preferably stainless steel, copper, aluminum, or engineering plastic (such as PI (polyimide), PEEK (polyetheretherketone), LCP (liquid crystal polymer)). In this embodiment, a 300 μm thick PI was used as the base layer 304a.

[0037] The multiple protrusions 304b, 304b1, and 304b2 are integrally formed from the same material as the base layer 304a, and are arranged in multiples along the transport direction (X direction) of the recording material in the nip portion N, and along the width direction (Y direction) of the recording material that intersects the transport direction. The multiple protrusions 304b, 304b1, and 304b2 are arranged such that the sum of the area of ​​the tip surfaces of all the multiple protrusions 304b is 90% or more of the total area of ​​the surface of the sliding member 304 that slides against the inner circumferential surface of the belt 301.

[0038] The distance (spacing) d between the centers of adjacent protrusions 304b, 304b1, and 304b2 in the conveying direction, and the distance (spacing) d between the centers of adjacent protrusions 304b, 304b1, and 304b2 in the width direction, are 1.25 mm or more, preferably 1.4 mm or more. In this embodiment, in order to ensure uniform sliding performance with the belt 301, the spacing between the multiple protrusions 304b, 304b1, and 304b2 is the same in the conveying direction and the width direction, with each spacing d being 1.4 mm. However, if the pressure distribution differs between the width direction and the conveying direction, the spacing between the protrusions in each direction may be changed according to the pressure distribution. Furthermore, the height of the protrusions 304b, 304b1, and 304b2 in the Z direction (pressure direction) is 250 μm in the central region in the conveying direction, as will be described in detail later.

[0039] By providing multiple protrusions 304b, 304b1, and 304b2 on the side of the sliding member 304 that slides against the belt 301, the contact area between the sliding member 304 and the belt 301 is reduced, thereby reducing the sliding resistance between the sliding member 304 and the belt 301.

[0040] The sliding layer 304c is preferably a coating agent such as a fluororesin (PTFE (polytetrafluoroethylene), PFA, etc.) to achieve low friction. In this embodiment, the sliding member 304 was formed by coating the surface of a base layer 304a containing a plurality of protrusions 304b, 304b1, and 304b2 with PTFE with a thickness of 20 μm. 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 against the sliding member 304. Silicone oil was used as the lubricant.

[0041] Furthermore, the sliding member 304 in this embodiment is configured to cover the pad 303 both inside and outside the nip portion N. That is, the entire surface of the pad 303 facing the belt 301 is covered by the sliding member 304, except for the surface opposite to the nip portion N. The sliding member 304 may also be placed only on the nip portion N of the surface of the pad 303. In addition, although the multiple protrusions 304b, 304b1, and 304b2 are placed over the entire surface of the sliding member 304, if the sliding member 304 is larger than the nip portion N, the multiple protrusions 304b, 304b1, and 304b2 may be placed only on the nip portion N.

[0042] In this embodiment, as shown in Figure 6 later, the tip surface 304u of projection 304b2 located at the upstream end and the tip surface 304d of projection 304b1 located at the downstream end are located within the range of the nip section N with respect to the conveying direction. Therefore, the positions where projections 304b1 and 304b2 contact the inner circumferential surface of the belt 301 are within the range of the nip section N. In particular, with respect to the conveying direction, the upstream end of the tip surface 304u of projection 304b2 at the upstream end is located at approximately the same position as the upstream end of the nip section N, and the downstream end of the tip surface 304d of projection 304b1 at the downstream end is located at approximately the same position as the downstream end of the nip section N. It should be noted that a portion of at least one of the tip surfaces 304u of projection 304b2 and 304d of projection 304b1 located at the downstream end may protrude outside the nip section N.

[0043] [Regarding the height of the protrusions] The heights of the multiple protrusions 304b, 304b1, and 304b2 of the sliding member 304 in this embodiment will be explained using Figures 3(a) to 7. First, Comparative Example 1 shown in Figures 4(a), (b) and 5 will be explained. The sliding member 304A of Comparative Example 1 is configured such that the heights of all the multiple protrusions 304b are the same. In the case of this configuration of Comparative Example 1, as shown in Figure 5, the tip surfaces 304u and 304d of the protrusions 304b come into contact with the inner circumferential surface of the belt 301 at the upstream and downstream ends with respect to the transport direction of the recording material in the nip section N, thereby forming a bent portion of the belt 301.

[0044] In the configuration of Comparative Example 1, the curvature of this bent portion is large, which may cause bending fatigue in the belt 301 when it rotates, potentially shortening the lifespan of the belt 301. Therefore, in this embodiment, the sliding member 304 is configured as follows to reduce the bending stress on the belt 301 and extend the lifespan of the belt 301.

[0045] First, of the multiple protrusions 304b, 304b1, and 304b2 mentioned above, multiple protrusions (First projection) 304b is the central region with respect to the transport direction of the recording material. (First predetermined area) It is located at multiple protrusions. (Second projection) 304b1 is the downstream end with respect to the transport direction of the recording material. (Second predetermined area) It is located at multiple protrusions. (Second projection) 304b2 is the upstream end with respect to the transport direction of the recording material. (Second predetermined area) They are arranged as follows: The multiple projections 304b1 at the downstream end include at least one row of projections located at the downstream end in the conveying direction, and the multiple projections 304b2 at the upstream end include at least one row of projections located at the upstream end in the conveying direction. A row of projections here refers to multiple projections that are aligned along the width direction at approximately the same position with respect to the conveying direction. The multiple projections 304b in the central region are projections located between projections 304b1 and 304b2 with respect to the conveying direction.

[0046] In the case of the sliding member 304 of this embodiment, the average height of the multiple protrusions 304b1 or 304b2 located at at least one end between the upstream end and the downstream end with respect to the transport direction of the recording material is lower than the average height of the multiple protrusions 304b located in the central region in the transport direction. Here, the height h of the protrusions 304b, 304b1, and 304b2 is the height in the Z direction (pressure direction), and as shown in Figure 3(a), it is the difference in the Z direction between the portion of the surface of the sliding member 304 that slides with the belt 301 where no protrusions are formed (protrusion-free region) and the tip of the protrusions 304b, 304b1, and 304b2.

[0047] Furthermore, the reason for comparing the average heights is to take into account the variations in the heights of the multiple protrusions 304b, 304b1, and 304b2. Therefore, for example, even if any of the multiple protrusions 304b1 are lower than any of the protrusions 304b in the central region, the requirements of this embodiment are satisfied if the overall average height of the multiple protrusions 304b1 is lower than the overall average height of the protrusions 304b in the central region. The same applies to the multiple protrusions 304b2. However, it is preferable that the height of all the protrusions 304b1 at the downstream end is lower than the height of all the protrusions 304b in the central region, or that the height of all the protrusions 304b2 at the upstream end is lower than the height of all the protrusions 304b in the central region.

[0048] In this embodiment, the average height of the protrusions 304b1 and 304b2 at both the downstream and upstream ends in the conveying direction is lower than the average height of the protrusion 304b in the central region. Specifically, the height of the protrusion 304b in the central region is 250 μm, while the height of the protrusions at the downstream and upstream ends in the conveying direction, and the downstream 304b1 and 304b2, are 225 μm. Furthermore, the protrusion 304b1 at the downstream end and the protrusion 304b2 at the upstream end are the single row of protrusions at the furthest downstream and furthest upstream ends, respectively.

[0049] Furthermore, in order to separate the recording material from the belt 301 when the recording material is discharged from the nip section N, the curvature of the belt 301 is usually increased at the exit side of the nip section N, i.e., the downstream end in the conveying direction. As a result, the bending stress of the belt 301 tends to increase at the exit side of the nip section N. For this reason, it is preferable to make the average height of the projections 304b1 at least the downstream end in the conveying direction lower than the average height of the projections 304b in the central region.

[0050] Furthermore, the average height of the projection 304b1 at the downstream end and the projection 304b2 at the upstream end in the conveying direction may be the same or different. When the heights of projections 304b1 and 304b2 are different, it is preferable to lower the height of the projection on the side with a larger curvature of the belt 301 on the inlet side and the outlet side of the nip section N. For example, if the curvature of the belt 301 on the outlet side of the nip section N is greater than the curvature of the belt 301 on the inlet side, it is preferable to lower the height of the projection 304b1 at the downstream end on the outlet side compared to the projection 304b2 at the upstream end on the inlet side.

[0051] In this embodiment, by making the average height of the protrusions 304b1 and 304b2 lower than the average height of the protrusion 304b in the central region at both the downstream and upstream ends in the conveying direction, the curvature of the belt 301 that bends when it comes into contact with the tip surfaces 304d and 304u of the protrusions 304b1 and 304b2 near the exit and entrance of the nip section N can be reduced, as shown in Figure 6. This reduces the bending stress on the belt 301, thereby suppressing bending fatigue and extending the lifespan of the belt 301.

[0052] Furthermore, this effect can also be achieved by making the average height of the multiple protrusions 304b1 or 304b2 located at at least one end of the upstream and downstream ends with respect to the conveying direction lower than the average height of the multiple protrusions 304b located in the central region. That is, if the height of the protrusion 304b1 at the downstream end is lowered, the curvature of the belt 301 that bends when it comes into contact with the tip surface 304d of the protrusion 304b1 near the exit of the nip section N can be reduced. Similarly, if the average height of the protrusion 304b2 at the upstream end is lowered, the curvature of the belt 301 that bends when it comes into contact with the tip surface 304u of the protrusion 304b2 near the entrance of the nip section N can be reduced. As a result, the bending stress on the belt 301 can be reduced near the exit or entrance of the nip section N, respectively, thereby suppressing bending fatigue and extending the lifespan of the belt 301.

[0053] Here, the average height of the multiple protrusions 304b1 or 304b2 located at at least one end of the upstream end and the downstream end with respect to the conveying direction is set to be between 0.70 and 0.99 times the average height of the multiple protrusions 304b located in the central region. This is because if the height of the downstream end protrusion 304b1 or the upstream end protrusion 304b2 is sufficiently low, bending fatigue of the belt 301 can be suppressed. However, if the height is too low, the inner surface of the belt 301 may slide not only with the protrusions 304b1 or 304b2 but also with the area without protrusions adjacent to the protrusions 304b1 or 304b2. If the inner surface of the belt 301 comes into contact with the area without protrusions, the coefficient of friction between the inner surface of the belt 301 and the sliding member 304 will increase, which may cause problems such as poor conveying of the belt 301 or an increase in driving torque. Therefore, the average height of the projection 304b1 at the downstream end or the projection 304b2 at the upstream end is set to be 0.70 times or more, preferably 0.75 times or more, and more preferably 0.80 times or more, than the average height of the projection 304b in the central region.

[0054] On the other hand, if the average height of the projection 304b1 at the downstream end or the projection 304b2 at the upstream end is lower than the average height of the projection 304b in the central region, the bending fatigue of the belt 301 can be reduced. However, if the difference is small, the effect of reducing the bending fatigue of the belt 301 cannot be sufficiently obtained. For this reason, the average height of the projection 304b1 at the downstream end or the projection 304b2 at the upstream end is set to 0.99 times or less, preferably 0.95 times or less, and more preferably 0.90 times or less, the average height of the projection 304b in the central region.

[0055] Figure 7 shows the results of measuring the on-axial torque of the pressure roller 305 during the rotation of the belt 301 by varying the heights of the projections 304b1 at the downstream end and 304b2 at the upstream end. The height of the projection 304b in the central region was set to 250 μm. A significant increase in torque was observed in the region where the heights of projections 304b1 and 304b2 were less than 175 μm. That is, if the average height of the projection 304b1 at the downstream end or the projection 304b2 at the upstream end is less than 0.70 times the average height of the projection 304b in the central region, the driving torque of the belt 301 increases significantly. Therefore, from the viewpoint of reducing bending fatigue life and friction coefficient, it is desirable that the average height of the projection 304b1 at the downstream end or the projection 304b2 at the upstream end be in the range of 0.70 times to 0.99 times the average height of the projection 304b in the central region, as described above.

[0056] <Second Embodiment> A second embodiment will be described with reference to Figures 8 and 9. In the first embodiment described above, the tip surface 304u of projection 304b2 located at the upstream end and the tip surface 304d of projection 304b1 located at the downstream end were described as being located within the range of the nip portion N with respect to the conveying direction. In contrast, in this embodiment, of the multiple projections 304b, 304b1, and 304b2, projection 304b1 or projection 304b2 located at at least one end between the upstream end and the downstream end with respect to the conveying direction are located outside the range of the nip portion N with respect to the conveying direction. The other configurations and operations are the same as in the first embodiment described above, so the same reference numerals are used for similar configurations, and their description and illustration are omitted or simplified. The following description will focus on the differences from the first embodiment.

[0057] In the case of the sliding member 304B of this embodiment, as in the first embodiment, the average height of the multiple protrusions 304b1 or 304b2 located at at least one end of the upstream end and the downstream end with respect to the transport direction of the recording material is lower than the average height of the multiple protrusions 304b located in the central region in the transport direction. In this embodiment as well, the average height of the protrusions 304b1 and 304b2 at both the downstream and upstream ends in the transport direction is lower than the average height of the protrusion 304b in the central region.

[0058] However, as shown in Figure 8, the projections 304b1 and 304b2 at the downstream and upstream ends are located outside the range of the nip section N with respect to the conveying direction. In this embodiment, the downstream row of projections 304b1 and the upstream row of projections 304b2 in the conveying direction are located outside the range of the nip section N. Therefore, the position where the projections 304b1 and 304b2 contact the inner circumferential surface of the belt 301 is outside the range of the nip section N. Even though the projections 304b1 and 304b2 at the downstream and upstream ends are outside the range of the nip section N, compared to Comparative Example 1 shown in Figure 5, the curvature of the belt 301 that bends due to contact with the tip surfaces 304d and 304u of the projections 304b1 and 304b2 can be reduced, thereby reducing bending stress and thus reducing bending fatigue and extending the lifespan of the belt 301.

[0059] As an alternative, it is conceivable to eliminate the outer protrusion of the nip portion N, as shown in Comparative Example 2 in Figure 9, for the sliding member 304C. However, due to positional variations in the direction of transport of the recording material between the pad 303 and the pressure roller 305 caused by part shape tolerances, there is a possibility that the area without protrusions on the sliding member 304C may slide against the inner surface of the belt 301, raising concerns about increased torque and wear on the inner surface of the belt 301. Therefore, as in this embodiment, by ensuring sufficient area where the protrusions of the sliding member 304B are formed, while lowering the height of the protrusions 304b1 and 304b2 at both ends in the transport direction, it is possible to achieve both good sliding performance and suppression of bending fatigue.

[0060] Furthermore, the projection located outside the range of the nip portion N may be either the projection at the upstream end or the projection at the downstream end. That is, the projection 304b1 at the downstream end may be located outside the range of the nip portion N, and the projection 304b2 at the upstream end may be located within the range of the nip portion N, as in the first embodiment. Similarly, the projection 304b2 at the upstream end may be located outside the range of the nip portion N, and the projection 304b1 at the downstream end may be located within the range of the nip portion N, as in the first embodiment.

[0061] <Third Embodiment> A third embodiment will be described using Figure 10. In the first and second embodiments described above, a configuration was described in which the height of the uppermost row of protrusions 304b2 and the lowermost row of protrusions 304b1 in the transport direction was lower than the height of the protrusion 304b in the central region. In contrast, in this embodiment, the height of multiple rows of protrusions 304b2 at the upstream end and multiple rows of protrusions 304b1 at the downstream end in the transport direction is lower than the height of the protrusion 304b in the central region. The other configurations and operations are the same as in the first embodiment described above, so the same reference numerals are used for similar configurations, and their description and illustration are omitted or simplified. The following description will focus on the differences from the first embodiment.

[0062] First, with respect to the conveying direction, the predetermined area upstream from the downstream end of the sliding member 304D is defined as the downstream region S1, the predetermined area downstream from the upstream end of the sliding member 304D is defined as the upstream region S2, and the area between the downstream region and the upstream region of the sliding member 304D is defined as the central region. In this case, the average height of the multiple protrusions 304b1 or 304b2 located in at least one of the regions between the downstream region S1 and the upstream region S2 is set to be lower than the average height of the multiple protrusions 304b located in the central region.

[0063] The predetermined regions defining the downstream region S1 and the upstream region S2 are preferably regions less than 33% of the length of the nip section N in the conveying direction. In this embodiment, the projections 304b1 or 304b2 of the downstream region S1 and the upstream region S2 are set to three rows, but any region less than 33% of the length of the nip section N in the conveying direction may be set to two rows or four or more rows.

[0064] If the downstream region S1 and upstream region S2, which reduce the height of the protrusions, are too wide, pressure will concentrate in the central region of the nip section N in the conveying direction where the taller protrusion 304b is located, which may cause the inner surface of the belt 301 to wear down. The inventors investigated the ease with which the inner surface of the belt 301 wears down by varying the conveying direction lengths of the downstream region S1 and upstream region S2. As a result, it was confirmed that in this embodiment, the conveying direction length of the nip section N is 24.5 mm, and when the conveying direction lengths of the downstream region S1 and upstream region S2 are 8 mm or more, the inner surface of the belt 301 becomes more susceptible to wear. Therefore, the conveying direction lengths of the downstream region S1 and upstream region S2, which reduce the height of the protrusions compared to the central region, are preferably less than 33% of the length of the nip section N in the conveying direction, and more preferably 30% or less, considering the relationship between bending fatigue life and prevention of damage to the inner surface of the belt.

[0065] Furthermore, in this embodiment, the height of the multiple protrusions 304b1 and 304b2 located in the downstream region S1 and the upstream region S2 decreases in stages as they move away from the central region in the conveying direction. That is, the height of the protrusions decreases in stages as they move closer to the entrance and exit of the nip section N. By arranging the protrusions 304b1 and 304b2 in this way, it is possible to prevent the formation of sharp bends in the belt 301 near the entrance and exit of the nip section N, compared to the first and second embodiments, and to further extend the lifespan of the belt 301.

[0066] Furthermore, the region in which the height of the protrusions is gradually reduced may be limited to only one of the downstream region S1 and the upstream region S2. In other words, it is sufficient that the height of multiple protrusions located in at least one of the downstream region S1 and the upstream region S2 decreases gradually as they move away from the central region in the transport direction.

[0067] Furthermore, the lengths of the downstream region S1 and the upstream region S2 in the conveying direction may be different from each other. That is, the number of rows of low-height protrusions may be different. In short, the lengths of the downstream region S1 and the upstream region S2 in the conveying direction can be appropriately set according to the belt trajectory at the entrance and exit of the nip section N. For example, the protrusions in either the downstream region S1 or the upstream region S2 may be in one row, while the protrusions in the other region may be in multiple rows.

[0068] Furthermore, the tip surfaces of the downstreammost row of protrusions 304b1 in the downstream region S1 and the tip surfaces of the downstreammost row of protrusions 304b2 in the upstream region S2 may be located within the range of the nip portion N, as in the first embodiment. Alternatively, some of the protrusions in the downstream region S1 and the upstream region S2 may be located outside the range of the nip portion N, as in the second embodiment. For example, at least one of the downstreammost row of protrusions 304b1 in the downstream region S1 and the downstreammost row of protrusions 304b2 in the upstream region S2 may be located outside the range of the nip portion N, as in the second embodiment.

[0069] <Examples> Here, we will describe the experimental results of investigating the curvature of the bent portion of the belt 301 and the lifespan of the belt 301 using Example 1, Example 2, Example 3, and Comparative Example 1, which satisfy the configuration of the first embodiment described above. In the experiment, image formation was performed in each example and Comparative Example 1 until the belt 301 broke. The results are shown in Figure 11. In Comparative Example 1, the curvature of the bent portion of the belt, which is formed by contact with the tip surface 304d of the downstream projection 304b in the transport direction of the recording material, was 1.0. As a result, bending fatigue occurred easily, and the belt broke after 400,000 (400k) belts.

[0070] On the other hand, as in Examples 1 to 3, by lowering the height of the projection 304b1 at the downstream end in the conveying direction, the curvature of the bent portion of the belt 301 formed by the contact between the tip surface 304d of the downstream projection 304b1 and the inner circumferential surface of the belt 301 was reduced compared to Comparative Example 1. As a result, the belt life was improved to 800,000 (800k) to 1,000,000 (1,000k) belts. [Explanation of symbols]

[0071] 8. Fixing device 301... belt 303... Pad (backup component) 304, 304B, 304D... Sliding members 304b, 304b1, 304b2...Protrusion 305... Pressure roller (nip forming member)

Claims

1. A fixing device for fixing a toner image supported on a recording material to the recording material, An endless, rotatable belt, A nip-forming member that contacts the outer surface of the belt and forms a nip portion that grips and transports the recording material between itself and the belt, A sliding member that slides against the inner circumferential surface of the belt in the nip portion, Inside the belt, a backup member is positioned to sandwich the sliding member and the belt between the nip portion forming member and to back up the sliding member, The belt comprises a roller provided downstream of the backup member and adjacent to the backup member in the rotational direction of the belt, which tensions the belt without forming the nip portion, The sliding member has a plurality of projections that protrude toward the inner circumferential surface of the belt on the side that slides with the belt, and the plurality of projections are arranged in the direction of transport of the recording material in the nip portion and in the width direction of the recording material intersecting the transport direction. The plurality of protrusions include a plurality of first protrusions arranged in a first predetermined region within the nip portion with respect to the transport direction, and a plurality of second protrusions arranged in a second predetermined region outside the nip portion. The average height of the plurality of second protrusions is lower than the average height of the plurality of first protrusions. A fixing device characterized by the following features.

2. The plurality of second protrusions are located downstream of the nip portion. The fixing device according to feature 1.

3. A fixing device for fixing a toner image supported on a recording material to the recording material, An endless, rotatable belt, A nip-forming member that contacts the outer surface of the belt and forms a nip portion that grips and transports the recording material between itself and the belt, A sliding member that slides against the inner circumferential surface of the belt in the nip portion, The belt comprises a backup member positioned on the inside of the belt so as to sandwich the sliding member and the belt between the nip portion forming member, and which backs up the sliding member, The sliding member has a plurality of projections that protrude toward the inner circumferential surface of the belt on the side that slides with the belt, and the plurality of projections are arranged in the direction of transport of the recording material in the nip portion and in the width direction of the recording material intersecting the transport direction. Of the plurality of protrusions, the average height of the plurality of protrusions located at at least one end of the upstream end and the downstream end with respect to the conveying direction is 0.70 times or more and 0.99 times or less than the average height of the plurality of protrusions located in the central region with respect to the conveying direction. A fixing device characterized by the following features.

4. The tip surfaces of the projections located at the upstream end and the projections located at the downstream end are located within the range of the nip portion with respect to the conveying direction. The fixing device according to feature 3.

5. Of the plurality of protrusions, the protrusion located at at least one end between the upstream end and the downstream end with respect to the conveying direction is located outside the range of the nip portion with respect to the conveying direction. The fixing device according to feature 3.

6. A fixing device for fixing a toner image supported on a recording material to the recording material, An endless, rotatable belt, A nip-forming member that contacts the outer surface of the belt and forms a nip portion that grips and transports the recording material between itself and the belt, A sliding member that slides against the inner circumferential surface of the belt in the nip portion, The belt comprises a backup member positioned on the inside of the belt so as to sandwich the sliding member and the belt between the nip portion forming member, and which backs up the sliding member, The sliding member has a plurality of projections that protrude toward the inner circumferential surface of the belt on the side that slides with the belt, and the plurality of projections are arranged in the direction of transport of the recording material in the nip portion and in the width direction of the recording material intersecting the transport direction. With respect to the conveying direction, if a predetermined region upstream from the downstream end of the sliding member is defined as the downstream region, a predetermined region downstream from the upstream end of the sliding member is defined as the upstream region, and the region between the downstream region and the upstream region of the sliding member is defined as the central region, Of the plurality of protrusions, the average height of the plurality of protrusions located in at least one of the downstream region and the upstream region is lower than the average height of the plurality of protrusions located in the central region. The predetermined region is an area less than 33% of the length of the nip portion in the conveying direction. A fixing device characterized by the following features.

7. The multiple protrusions located in at least one of the downstream and upstream regions have a gradual decrease in height as they move away from the central region in the transport direction. The fixing device according to feature 6.

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