Fixing device

Abstract

To provide a configuration that can prevent a reduction in the life of a fixing device.SOLUTION: A sliding member 304 has a plurality of projections 304b that is provided to project toward an inner peripheral surface of a belt 301 on a side where it slides with the belt 301. The plurality of projections 304b is distributed at a nip part N and on the outside of the nip part N with respect to a width direction. On the side of the slide member 304 where it slides with the belt 301, predetermined areas L on the outside in the width direction of the nip part are defined as first areas, and an area inside the first areas in the width direction as a second area (nip part N area). When the area ratio of the first area is defined as a first area ratio, and the area ratio of the second area as a second area ratio, the slide member 304 satisfies the following formula: first area ratio>second area ratio.SELECTED DRAWING: Figure 5

Description

[Technical Field]

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

[0002] A known fixing device has a nip formed between a belt and a nip-forming member such as a roller, which sandwiches and conveys the recording material, and heats and pressurizes the recording material as it passes through the nip. In this configuration, a sliding member slides on the inner circumferential surface of the belt in the nip, forming the nip between the belt and the nip-forming member.

[0003] In a fixing device, to ensure the quality of an image fixed to a recording material, it is necessary to suppress slippage between the recording material conveyed to the nip portion and the belt, and between the recording material and the nip-forming member. To achieve this, it is necessary to reduce the frictional force between the belt and the sliding member compared to the frictional force between the recording material and the belt and between the recording material and the nip-forming member. In particular, in a configuration having a wide nip in which the width of the nip is widened to increase heating efficiency, it is necessary to reduce the frictional force between the belt and the sliding member.

[0004] For example, Patent Document 1 discloses a configuration in which unevenness is formed on a sliding sheet that slides against the inner circumferential surface of the belt in the nip portion, thereby reducing the frictional force between the sliding sheet and the belt. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-52354 Summary of the Invention [Problem to be solved by the invention]

[0006] The surface of the sliding member is worn by rubbing against the belt, but the wear is usually gradual and the necessary and sufficient functionality can be maintained within the life of the fixing device. However, depending on the manner in which the belt and the sliding member contact, the wear of part of the sliding member may progress more quickly than expected, which may shorten the life of the fixing device.

[0007] In order to reduce wear on the sliding members in the nip area, a configuration has been proposed in which protrusions are provided on the sliding members to reduce wear. However, in some cases, the protrusions come into strong contact with the inner circumferential surface of the belt outside the nip area in the width direction. This can result in significant wear on the protrusions in the area outside the nip area, making it difficult to achieve the desired lifespan.

[0008] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a configuration that can prevent the shortening of the life of a fixing device. [Means for solving the problem]

[0009] One aspect of the present invention is a fixing device that fixes a toner image carried on a recording material to the recording material, the fixing device comprising: an endless rotatable belt; a nip portion forming member that contacts an outer peripheral surface of the belt to form a nip portion that sandwiches and conveys the recording material between the belt and the nip portion forming member; a sliding member that slides against an inner peripheral surface of the belt at the nip portion; and a backup member that is disposed inside the belt so as to sandwich the sliding member and the belt between the sliding member and the nip portion forming member and that backs up the sliding member, the sliding member being disposed on the side that slides against the belt. , the belt has a plurality of protrusions provided so as to protrude toward the inner peripheral surface thereof, the plurality of protrusions being distributed at the nip portion and outside the nip portion in a width direction of the recording material that intersects with the conveying direction of the recording material, and on the surface of the sliding member that slides against the belt, a predetermined region outside the nip portion in the width direction is defined as a first region, and a region inside the first region in the width direction is defined as a second region, where SFR is the area of ​​the region and Si is the sum of the areas of the tip surfaces of n of the protrusions present in the region, and Sa.r. defined by the following formula is an area ratio:

number

[0010] One aspect of the present invention is a fixing device that fixes a toner image carried on a recording material to the recording material, the fixing device comprising: an endless, rotatable belt; a nip portion forming member that contacts the outer peripheral surface of the belt to form a nip portion that sandwiches and conveys the recording material between the belt and the nip portion forming member; a sliding member that slides against the inner peripheral surface of the belt at the nip portion; and a backup member that is disposed inside the belt so as to sandwich the sliding member and the belt between the sliding member and the nip portion forming member and backs up the sliding member, the sliding member being disposed on the side that slides against the belt and protruding toward the inner peripheral surface of the belt. a fixing device having a plurality of protrusions, the plurality of protrusions being distributed in the nip portion and outside the nip portion in a width direction of the recording material that intersects with the conveying direction of the recording material; and wherein, on the surface of the sliding member that slides against the belt, a predetermined region outside the nip portion in the width direction is defined as a first region, and a region inside the first region in the width direction is defined as a second region; the average area of ​​the tip faces of the protrusions present in the first region is defined as a first average area, and the average area of ​​the tip faces of the protrusions present in the second region is defined as a second average area, the sliding member satisfies the condition that the first average area is greater than the second average area. [Effects of the Invention]

[0011] According to the present invention, it is possible to prevent the life of the fixing device from being shortened. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a cross-sectional view showing a schematic configuration of an image forming apparatus according to a first embodiment. [Figure 2] FIG. 2A is a cross-sectional view showing the schematic configuration of a fixing device according to the first embodiment, and FIG. 2B is an enlarged schematic view showing a portion A in FIG. [Figure 3]1A and 1B are a cross-sectional view and a plan view, respectively, schematically illustrating a sliding member according to a first embodiment. [Figure 4] FIG. 2 is a schematic view of a sliding member, a belt, and a pressure roller according to the first embodiment, cut along the width direction. [Figure 5] FIG. 10 is a graph showing the relationship between the amount of wear in the width direction of the sliding layer of the sliding member, together with a schematic diagram of the sliding member, the belt, and the pressure roller cut along the width direction. [Figure 6] 3 is a schematic view of a region where a part of the belt according to the first embodiment strongly contacts a sliding member, cut along the width direction. FIG. [Figure 7] 6 is a graph showing the relationship between the area ratio of the strong contact region and the amount of wear according to the first embodiment. [Figure 8] FIG. 2(a) is a schematic diagram showing each region on the surface of the sliding member according to the first embodiment, and FIG. 2(b) is a table showing the conditions of the sliding member used in the drive torque sensitivity experiment. [Figure 9] 10 is a graph showing the results of a drive torque sensitivity experiment. [Figure 10] FIG. 10(a) is a schematic diagram showing each region on the surface of a sliding member according to a second embodiment, (b) is a schematic diagram showing the shape of protrusions in three examples of area ratios, and (c) is a graph showing the relationship between the area ratio of strong contact regions according to the second embodiment and the amount of wear. DETAILED DESCRIPTION OF THE INVENTION

[0013] First Embodiment The first embodiment will be described with reference to Figures 1 to 9. First, the schematic configuration of an image forming apparatus according to this embodiment will be described with reference to Figure 1.

[0014] [Image forming equipment] Image forming apparatus 1 is an electrophotographic full-color printer having four image forming units Pa, Pb, Pc, and Pd corresponding to the four colors of yellow, magenta, cyan, and black. In this embodiment, the image forming units Pa, Pb, Pc, and Pd are arranged in tandem along the rotation direction of an intermediate transfer belt 204 (described later). Image forming apparatus 1 forms a toner image (image) on a recording material in response to an image signal from an image reading unit (document reading device) 2 connected to image forming apparatus main body 3 or from a host device such as a personal computer connected to image forming apparatus main body 3 so as to be able to communicate with the image forming apparatus main body 3. Examples of recording materials include sheet materials such as paper, plastic film, and cloth.

[0015] The image forming apparatus 1 comprises an image reading unit 2 and an image forming apparatus main body 3. The image reading unit 2 reads an original placed on a platen glass 21. Light emitted from a light source 22 is reflected by the original and forms an image on a CCD sensor 24 via optical components 23 such as a lens. This optical unit scans in the direction of the arrow, converting the original into a line-by-line electrical signal data stream. The image signal obtained by the CCD sensor 24 is sent to the image forming apparatus main body 3, where it is subjected to image processing in accordance with each image forming unit (described later) by a control unit 30. The control unit 30 also receives external inputs as image signals from external host devices such as a print server.

[0016] The image forming apparatus main body 3 includes multiple image forming units Pa, Pb, Pc, and Pd, and each image forming unit forms an image based on the image signal. That is, the image signal is converted into a laser beam that is PWM (pulse width modulation) controlled by a control unit 30. A polygon scanner 31 serving as an exposure device scans the laser beam in accordance with the image signal. The laser beam is then irradiated onto photosensitive drums 200a to 200d serving as image carriers of each image forming unit Pa to Pd.

[0017] Note that Pa is a yellow (Y) image forming unit, Pb is a magenta (M) image forming unit, Pc is a cyan (C) image forming unit, and Pd is a black (Bk) image forming unit, each forming an image of the corresponding color. Since the image forming units Pa to Pd are substantially identical, the Y image forming unit Pa will be described in detail below, and descriptions 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 an image signal, as will be described below.

[0018] A charging roller 201a, which serves as a primary charger, charges the surface of the photosensitive drum 200a to a predetermined potential to prepare for the formation of an electrostatic latent image. A laser beam from a polygon scanner 31 forms an electrostatic latent image on the surface of the photosensitive drum 200a, which has been charged to a predetermined potential. A developing unit 202a develops the electrostatic latent image on the photosensitive drum 200a to form a toner image. A primary transfer roller 203a discharges electricity from the back surface 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 onto the intermediate transfer belt 204. After transfer, the surface of the photosensitive drum 200a is cleaned by a cleaner 207a.

[0019] The toner image on intermediate transfer belt 204 is then conveyed to the next image forming station, where the toner images of each color formed at each image forming station are transferred in the order of Y, M, C, and Bk, forming a four-color image on the surface. The toner image that has passed through Bk image forming station Pd, which is located at the most downstream side in the rotation direction of intermediate transfer belt 204, is conveyed to a secondary transfer station made up of a pair of secondary transfer rollers 205 and 206. In the secondary transfer station, a secondary transfer electric field of opposite polarity to the toner image on intermediate transfer belt 204 is applied, thereby secondarily transferring the toner image onto the recording material.

[0020] The recording material is stored in a cassette 9, and the recording material fed from the cassette 9 is transported to a registration unit 208, which is made up of, for example, a pair of registration rollers, and waits at the registration unit 208. Thereafter, the timing of the registration unit 208 is controlled to align the position of the toner image on the intermediate transfer belt 204 with the position of the paper, and the recording material is transported to a secondary transfer unit.

[0021] The recording material onto which the toner image has been transferred in the secondary transfer section is transported to a fixing device 8, where the toner image carried on the recording material is fixed to the recording material by heating and pressing. The recording material that has passed through the fixing device 8 is discharged onto a discharge tray 7. When forming images on both sides of the recording material, after the toner image has been transferred and fixed onto the first side (front side) of the recording material, the recording material is turned over via a reversing conveyance section 10, and the toner image is transferred and fixed onto the second side (rear side) of the recording material, and the recording material is then stacked on the discharge tray 7.

[0022] As described above, the control unit 30 controls the entire image forming apparatus 1. The control unit 30 can also perform various settings based on input from the operation unit 4 of the image forming apparatus 1. The control unit 30 has a CPU (Central Processing Unit), a ROM (Read Only Memory), and a RAM (Random Access Memory). The CPU controls each unit by reading a program corresponding to a control procedure stored in the ROM. The RAM stores working data and input data, and the CPU performs control by referring to the data stored in the RAM based on the aforementioned programs.

[0023] [Fusing device] Next, the configuration of the fixing device 8 in this embodiment will be described with reference to Figures 2(a) and (b). In this embodiment, a fixing device of a belt heating type using an endless belt is adopted. In Figure 2(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 with the conveyance direction of the recording material (orthogonal in this embodiment), and the Z direction indicates the pressure direction in which the recording material is pressed at the nip portion N. In this embodiment, the X direction, Y direction, and Z direction are each orthogonal to each other.

[0024] 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, and a heating roller 307. The belt 301 is an endless, rotatable heating rotor. The pressure roller 305, which serves as a nip portion forming member, is a pressure rotor that contacts the outer circumferential surface of the belt 301 to form a nip portion N between the belt 301 and the pressure roller 305, which sandwiches and conveys the recording material.

[0025] Sliding member 304 slides against the inner circumferential surface of belt 301 at nip portion N. Pad 303, which serves as a backup member, is disposed inside belt 301 so as to sandwich sliding member 304 and belt 301 between it and pressure roller 305, and backs up sliding member 304. Sliding member 304 is disposed so as to cover the outer circumferential surface of pad 303 facing belt 301. Stay 302 is disposed inside belt 301, on the opposite side of nip portion N with pad 303 in between, and supports pad 303. Heating roller 307 is disposed inside belt 301 so as to stretch belt 301, and heats belt 301. Each component will be described in detail below.

[0026] The belt 301 has thermal conductivity, heat resistance, and the like, and is a thin-walled cylindrical shape. In this embodiment, as shown in FIG. 2(b), the belt 301 has a three-layer structure including a base layer 301a, an elastic layer 301b formed around the outer periphery of the base layer 301a, and a release layer 301c formed around the elastic layer 301b. 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 between a pad 303 and a heating roller 307, and the tension applied to the belt 301 is 80 N in this embodiment. The outer diameter of the belt 301 is 150 mm in this embodiment.

[0027] The pad 303 is disposed inside the belt 301 so as to face the pressure roller 305 with the belt 301 sandwiched therebetween, and forms a nip portion N between the belt 301 and the pressure roller 305 for sandwiching and conveying the recording material. In this embodiment, the pad 303 is a substantially plate-shaped member that is long in the width direction of the belt 301 (the longitudinal direction intersecting the rotation direction of the belt 301, the direction of the rotation axis of the heating roller 307). The pad 303 is pressed against the pressure roller 305 with the belt 301 sandwiched therebetween, thereby forming the nip portion N. The pad 303 is made of 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.

[0028] Pad 303 is supported by stay 302, which serves as a support member and is disposed inside belt 301. That is, stay 302 is disposed on the opposite side of pad 303 from pressure roller 305, and supports pad 303. Such stay 302 is a reinforcing member having long rigidity along the longitudinal direction of belt 301, and contacts pad 303 to back up pad 303. That is, stay 302 provides strength to pad 303 when pad 303 is pressed by pressure roller 305, thereby ensuring the pressure at nip portion N.

[0029] The stay 302 is made of a metal such as stainless steel, and has a substantially rectangular cross section (transverse cross section) perpendicular to the longitudinal direction of the stay 302, which intersects with the rotation direction of the belt 301. For example, the stay 302 is made of a 3 mm thick drawn material of SUS304 (stainless steel), and the transverse cross section is formed into a hollow, substantially square shape to ensure strength. Note that the stay 302 may also be formed into a substantially rectangular cross section by combining multiple metal plates and fixing them together by welding or the like. The material of the stay 302 is not limited to stainless steel as long as strength can be ensured.

[0030] Heating roller 307 is disposed inside belt 301 and stretches belt 301 together with pad 303. Heating roller 307 is formed into a cylindrical shape from a metal such as aluminum or stainless steel, and has a halogen heater 306 disposed inside as a heat source for heating belt 301. Heating roller 307 is heated to a predetermined temperature by halogen heater 306.

[0031] The heating roller 307 has a rotation center at one end or near the center in the longitudinal direction, and rotates relative to the belt 301 to generate a tension difference between the front and rear, thereby also serving as a steering roller that controls the position of the belt 301 in the main scanning direction. The heating roller 307 is also biased by a spring supported by a frame (not shown), and serves as a tension roller that applies a predetermined tension to the belt 301.

[0032] In this embodiment, the heating roller 307 is formed, for example, from a stainless steel pipe having a thickness of 1 mm. While a single halogen heater 306 is sufficient, it is preferable to have multiple heaters in consideration of temperature distribution control in the longitudinal direction (rotation axis direction) of the heating roller 307. The multiple halogen heaters 306 have different light distributions in the longitudinal direction, and the lighting ratio is controlled according to the size of the recording material. In this embodiment, three halogen heaters 306 are provided. The heat source is not limited to a halogen heater, and 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 according to the type of recording material based on temperature detection by a thermistor (temperature detection member) (not shown).

[0033] The pressure roller 305 rotates in contact with the outer circumferential surface of the belt 301 and also serves as a driving rotor that applies a driving force to the belt 301. In this embodiment, the heat roller 307 is also 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 heat roller 307 may be omitted. The pressure roller 305 is a roller comprising a core (shaft) 305c, an elastic layer 305b on the outer periphery of the core 305c, and a release layer 305a on the outer periphery of the elastic layer 305b. The core 305c is made of stainless steel, for example, with a diameter of 72 mm. The elastic layer 305b is made of conductive silicone rubber, for example, with a thickness of 8 mm. The release layer 305a is made of a fluororesin, such as PFA (tetrafluoroethylene-perfluoroalkoxyethylene copolymer resin), with a thickness of 100 μm. The pressure roller 305 is rotatably supported by a frame (not shown) of the fixing device 8, has a gear fixed to one end, and is connected to a drive source (e.g., a drive motor, not shown) via the gear to be rotated.

[0034] The fixing device 8 sandwiches the recording material P carrying a toner image in a nip portion N formed between the belt 301 and the pressure roller 305, and heats the toner image while transporting the recording material P. In this way, the fixing device 8 fixes the toner image to the recording material P while sandwiching and transporting the recording material P. Therefore, the fixing device 8 needs to have both the function of applying heat and pressure and the function of transporting the recording material P. A driving source (not shown) presses the pressure roller 305 against the sliding member 304 via the belt 301. In this embodiment, the pressure force (NF) at the nip portion N during image formation is set to 1600 N, and the width of the nip portion N in the X direction (the transport direction of the recording material) is set to 24.5 mm, and the width in the Y direction (the width direction of the recording material) is set to 350 mm.

[0035] [Sliding member] The detailed configuration of the sliding member 304 is shown in Figures 3(a) and (b). Figure 3(a) is a cross-sectional view of the sliding member 304 cut in the conveyance direction, and Figure 3(b) is a plan view of the sliding member 304 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 via the pad 303 with screws or the like. The sliding member 304 may be integral with the pad 303. Alternatively, a portion of the sliding member 304 may be 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.

[0036] The sliding member 304 is composed of a base material layer 304a and a sliding layer 304c. A plurality of protrusions 304b protruding toward the inner peripheral surface of the belt 301 are formed on the side of the base material layer 304a that slides against the belt 301. The sliding layer 304c is provided so as to cover the surface of the base material layer 304a that slides against the belt 301 (including the plurality of protrusions 304b). The convex portions formed by the protrusions 304b being covered with the sliding layer 304c are referred to as embossed portions 304d.

[0037] The base layer 304a only needs to have sufficient heat resistance and strength. Materials such as stainless steel, copper, aluminum, and engineering plastics (PI (polyimide), PEEK (polyether ether ketone), LCP (liquid crystal polymer), etc.) are desirable. In this embodiment, stainless steel with a thickness of 300 μm is used as the base layer 304a.

[0038] The plurality of protrusions 304b are provided from the base layer 304a toward the inner circumferential surface of the belt 301. The plurality of protrusions 304b are formed integrally with the base layer 304a using the same material, and are arranged in the conveying direction (X direction) of the recording material at the nip portion N, and in the width direction (Y direction) of the recording material that intersects with the conveying direction. The distance (interval) d between the centers of adjacent protrusions 304b in the conveying direction and the distance (interval) d between the centers of adjacent protrusions 304b in the width direction are each 1.4 mm or more. The area S of the tip surface of the protrusions 304b (embossed tip shape area) is 0.031 mm2 The plurality of protrusions 304b are distributed in the nip portion N and outside the nip portion N in the width direction.

[0039] By providing multiple protrusions 304b on the surface (sliding surface) of the sliding member 304 that slides against the belt 301 in this way, 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.

[0040] The sliding layer 304c is preferably made of 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 having a thickness of 20 μm. In this embodiment, a lubricant is applied to the inner surface of the belt 301. This allows the belt 301 to slide smoothly against the sliding member 304. Silicone oil is used as the lubricant.

[0041] Furthermore, the sliding member 304 of this embodiment is configured to cover the pad 303 regardless of whether it is inside or outside the nip portion N. That is, the entire surface of the pad 303 that faces the belt 301 is covered by the sliding member 304, except for the surface opposite the nip portion N. Furthermore, the multiple protrusions 304b are arranged over the entire area of ​​the sliding member 304.

[0042] 4 shows the positional relationship in the width direction between sliding member 304, belt 301, and pressure roller 305. In this embodiment, the length in the width direction of sliding member 304 is 370 mm, the belt 301 is similarly 365 mm, the pressure roller 305 is similarly 350 mm, and the length in the width direction (maximum width, paper-passable area) of the maximum size recording material P that can be fixed by fixing device 8 is 329 mm. As described above, nip portion N (nip portion N area) is formed by the pressure of pressure roller 305, and therefore the length in the width direction matches the length in the width direction of pressure roller 305.

[0043] [Early wear region of the sliding layer] The graph in Fig. 5 shows the wear sensitivity of the sliding layer 304c in the width direction. The vertical axis of the graph shows the height (µm) lost by wear of the sliding layer 304c when 1000K (1,000,000) sheets of A4-sized recording material, which is the lifespan of the fixing device 8 in this embodiment, are passed through the nip portion. The horizontal axis shows the position in the width direction. Note that Fig. 5 also shows the positional relationship between the sliding member 304, belt 301, and pressure roller 305 shown in Fig. 4 along with the graph.

[0044] The results in Figure 5 show that the sliding layer 304c in the nip N region remains in place until the end of the fixing device 8's lifespan, but that the sliding layer 304c has been lost in a portion of the outside nip N region (the area of ​​a predetermined region L surrounded by a dashed line in Figure 5), which is the region outside the nip N in the width direction. In other words, it can be seen that the amount of wear has reached 20 µm, which is the thickness of the sliding layer 304c. The amount of wear shown in the results in Figure 5 was calculated by averaging the embossed portions 304d in the conveyance direction for each row.

[0045] FIG. 6 is an enlarged view of a portion of the area outside the nip N where the sliding layer 304c has been lost, as described in FIG. 5. As shown in this figure, when the belt 301 is pushed up by the pressure roller 305 pressing against the belt 301 and released from the area sandwiched in the nip N, it bends in the pressure direction of the pressure roller 305 and comes into strong local contact with the sliding layer 304c. This area is called the "strong contact area." Note that this strong contact with the sliding layer 304c occurs due to the relationship between the pressure of the pressure roller 305 and the belt 301. Therefore, even if the belt 301 rotates in the direction of conveying the recording material, as long as the pressure roller 305 continues to press against it, the strong contact continues in the same area in the width direction.

[0046] Therefore, it was found that the embossed portion 304d arranged in this region continues to receive a strong contact force (hereinafter referred to as strong contact) from the belt 301, and wears out earlier than other regions. Also, in the configuration of the fixing device of this embodiment, it was found that the strong contact is prominent in the region between the end of the pressure roller 305 and the region outside the nip portion N, which is 2.0 mm.

[0047] In the following explanation, we will discuss the arrangement and shape of the protrusions 304b arranged in the strong contact area in response to the above-mentioned issues. The strong contact area is defined by the widthwise position of the pressure roller 305 and the sliding member 304 via the belt 301. Therefore, the strong contact area cannot be uniquely determined due to the widthwise assembly tolerances (play) of the various parts involved in forming the strong contact area. For example, the pressure roller 305 is joined to the fixing device 8 in the widthwise direction by being attached to the frame of the fixing device 8 (not shown), but the pressure roller 305 is allowed to move widthwise relative to the frame of the fixing device 8 by up to approximately 1 mm. Therefore, when defining the strong contact area, it is assumed that this assembly tolerance is taken into consideration.

[0048] [Area ratio] In this embodiment, a countermeasure for the strong contact area of ​​the belt 301 will be described. As shown in Fig. 6, the strong contact area occurs when the belt 301 strongly contacts the sliding member 304 due to bending of the belt 301. For this reason, it is considered effective to reduce the contact pressure between the belt 301 and the embossed portion 304d by increasing the area ratio of the embossed surface (the tip surface of the protrusions 304b) of the sliding member 304 that receives the force applied to the strong contact area.

[0049] 7 is a graph showing the amount of wear when the area ratio (first area ratio, described later) of the surface of the sliding layer 304c in contact with the belt 301 near the strong contact region of the belt 301 is varied in the width direction. The amount of wear is a graph showing the height lost by wear of the sliding layer 304c when 1000K sheets of A4-sized recording material, as described above, are passed through the nip portion N. The area ratio is calculated from the area of ​​a certain region of the sliding surface and the sum of the areas of the tip surfaces of all the protrusions 304b included in that region, and is defined by the following equation:

number

[0050] where S a.r. is the area ratio of the region, SFR is the area of ​​the region, S iindicates the total area of ​​the tip surfaces of n protrusions 304b present in that region (embossed tip shape area). Furthermore, on the surface of the sliding member 304 that slides against the belt 301, a predetermined region on the widthwise outer side of the nip portion N is defined as a first region (strong contact region), and a region on the widthwise inner side of the first region is defined as a second region (nip portion N region). The first region includes a region extending from the widthwise end of the nip portion N to a position 2 mm outward. The second region includes a widthwise region through which the maximum-sized recording material passes through the nip portion N. Furthermore, Sa.r. of the first region is defined as a first area ratio, and Sa.r. of the second region is defined as a second area ratio. In this case, the sliding member 304 of this embodiment is configured so that the first area ratio is greater than the second area ratio. This reduces the contact pressure between the belt 301 and the embossed portions 304d in the strong contact region, thereby preventing the sliding layer 304c from wearing out faster than expected in the strong contact region.

[0051] In the experiment shown in Figure 7, the area ratio was varied by decreasing the distance d between the centers of adjacent protrusions 304b (the distance between embossed shapes) and increasing the number of protrusions 304b in the strong contact region, and the wear amount for each was examined. In this embodiment, the protrusions 304b constituting the embossed portion 304d were manufactured using chemical etching. When the distance d between embossed shapes was narrower than 0.35 mm, adjacent protrusions 304b were too close, leading to adhesion between the protrusions 304b during manufacturing. Adhesion between adjacent protrusions 304b leads to problems due to the lack of gaps between the protrusions 304b. For example, debris such as wear particles from the sliding layer 304c worn during use can become trapped and accumulate in the relevant areas, absorbing lubricant and blocking the flow path, resulting in partial depletion of the lubricant. Furthermore, the accumulated and enlarged foreign matter itself applies strain stress to the belt 301, potentially causing the belt 304b to break during the life of the fixing device 8.

[0052] Therefore, under the condition that the embossed tip shape area S is constant and the embossed shape distance d is 0.35 mm, an area ratio of 50% is set as the upper limit of this condition. As is clear from FIG. 7, when the first area ratio is less than 30%, the amount of wear remains constant at 20 μm / 1000 K. This means that the sliding layer 304c will wear and be lost within the life of the fixing device 8. On the other hand, when the first area ratio is 30% or more, the amount of wear decreases, confirming that the sliding layer 304c remains. This is because an increase in the area ratio increases the area of ​​the embossed portions 304d that support the belt 301, and the contact pressure applied to each embossed portion 304d when the belt 301 contacts each embossed portion 304d decreases. Therefore, in this embodiment, it was found that by setting the first area ratio to 30% or more, the sliding layer 304c can be prevented from being lost within the life of the fixing device 8.

[0053] From the above, it is possible to suppress the amount of wear of the sliding layer 304c by increasing the first area ratio, and it is preferable to set the first area ratio to 30% or more. Therefore, it would be desirable to increase the area ratio not only in the strong contact area but also in all areas, but the experimental results described below have shown that there is an upper limit to the area ratio in terms of the increase in drive torque caused by sliding between the belt 301 and the embossed portion 304d.

[0054] Next, the driving torque sensitivity experiment will be described. The experiment was conducted under the following conditions. Fig. 8(a) is a schematic diagram showing each area on the sliding surface of the sliding member 304 used in this experiment. Fig. 8(b) is a table showing the conditions of the sliding member 304 used in the driving torque sensitivity experiment. In this experiment, the embossed tip shape area S was set to 0.031 mm 2 The area ratio of the strong contact region (first area ratio) was set to two levels, 3.2% and 30%, by keeping the distance d between the embossed shapes constant and varying it from 1.4 mm to 0.45 mm, and sliding members 304 were created in which the area ratio of the nip portion N region (second area ratio) was varied from 3.2% to 30% at each level of the area ratio of the strong contact region.

[0055] The drive torque sensitivity experiment was conducted in a mode in which pressure roller 305 alternately contacted and did not contact belt 301, with the design target time being 240 hours. If the drive torque exceeded 300 mNm, the preset upper limit for the experiment, within the design target time, the experiment was terminated even if it was partway through, and if the drive torque did not exceed the upper limit for the experiment within the design target time, the experiment was terminated after the design target time had elapsed.

[0056] The upper limit of the driving torque mentioned above is set at 300 mNm as a threshold value at which a defective image due to slippage or damage to the driving gear may occur. 2 The experiment was carried out with the recording material conveying speed v set to 435 mm / s.

[0057] FIG. 9 shows the results of the drive torque sensitivity experiment described above, with the horizontal axis representing the area ratio of the nip N region (second area ratio) and the vertical axis representing the drive torque value. The two profiles represent the results when the area ratio of the strong contact region (first area ratio) is 3.2% and 30%, respectively. In the configuration of this embodiment, the lubricating layer of the lubricant formed between the belt 301 and the embossed portion 304d is a mixed lubrication layer. As the contact area increases, the sliding resistance increases, resulting in an increase in drive torque. Furthermore, with continued use of the device, the sliding layer 304c of the embossed portion 304d wears, increasing the area of ​​the sliding surface between the belt 301 and each embossed portion 304d. Based on these findings, the results confirmed that when the area ratio of the nip N region exceeds 5%, the drive torque exceeds the threshold value of 300 mNm.

[0058] Regarding the difference in the area ratio of the strong contact area, it was also found that the influence on the drive torque is negligible because the area is outside the nip portion N and therefore there is no pressure from the pressure roller 305, and the area ratio of the area to the entire sliding member 304 is small.

[0059] From the above, it was found that the area ratio in the nip portion N region desirably does not exceed 5% from the viewpoint of drive torque, and the area ratio in the strong contact region desirably is 30% or more from the viewpoint of maintaining the sliding layer 304c of the embossed portion 304d within the life of the fixing device 8. In other words, it was found that the first area ratio is preferably 30% or more, and the second area ratio is preferably 5% or less. This makes it possible to maintain the sliding layer 304c in the strong contact region within the life of the fixing device 8 while suppressing an increase in drive torque, and to prevent the life of the fixing device 8 from being shortened.

[0060] In the above description, the area ratios of the first region (strong contact region) and the second region (nip region N) are used, but the same applies when the average area is used as follows. That is, when the average area of ​​the tip faces of the protrusions 304b present in the first region is defined as the first average area and the average area of ​​the tip faces of the protrusions 304b present in the second region is defined as the second average area, the sliding member 304 is configured to satisfy the relation: first average area > second average area. Even in this case, as in the case described above using the area ratio, the contact pressure between the belt 301 and the embossed portion 304d can be reduced in the strong contact region, and wear of the sliding layer 304c in the strong contact region can be prevented from progressing faster than expected.

[0061] <Second embodiment> The second embodiment will be described with reference to FIGS. 10(a) to 10(c). In the first embodiment described above, the number of embossed portions 304d (i.e., the number of protrusions 304b) arranged in the strong contact region was increased to increase the area ratio, thereby improving the lifespan. However, as described above, increasing the number of embossed portions 304d (in other words, increasing the density in the embossed portion 304d region) results in an upper limit of an area ratio of approximately 50%. Therefore, in this embodiment, to further improve the lifespan, the shape of each protrusion 304b is changed and optimal placement is implemented, aiming for an area ratio of 50% or more in the strong contact region. Since the other configurations and functions are the same as those of the first embodiment described above, the same components are designated by the same reference numerals, and their description and illustration will be omitted or simplified. The following description will focus on the differences from the first embodiment.

[0062] FIG. 10(a) is a schematic diagram showing each region on the sliding surface of the sliding member 304A according to this embodiment. In FIG. 10(a), the shape of the protrusions 304b in the region (including the nip N region) other than the strong contact region (first region) is shown as a circle. However, as shown in FIG. 10(b), the shape of the protrusions 304b in the strong contact region may be, for example, a diamond. The shape of the protrusions 304b in the region other than the strong contact region may be the same as the shape of the protrusions 304b in the strong contact region. However, whether the shape of the protrusions 304b in the strong contact region and the shape of the protrusions 304b in the region other than the strong contact region are the same or different, the first area ratio must be greater than the second area ratio.

[0063] FIG. 10(b) is a schematic diagram showing an example in which the arrangement and shape of the protrusions 304b in the strong contact region are optimized from the perspective of area ratio. The shape of the protrusions 304b in this embodiment is, for example, an "area ratio of 50%" or "area ratio of 70%." For reference, FIG. 10(b) also shows an "area ratio of 100%." ​​The maximum area ratio of 100% means that the distance d between the embossed shapes is 0, i.e., a flat shape. FIG. 10(c) is a graph in which the results of an experiment similar to FIG. 7 were additionally plotted, using the arrangement and shape of the protrusions 304b in the strong contact region as shown in FIG. 10(b).

[0064] As shown in Figure 10(c), when the area ratio is 100%, the wear amount is minimized to 5 μm / 1000 K. However, when the area ratio is extremely large, such as when the embossment distance d is zero or very small, the gaps between the embossments disappear. As a result, foreign matter such as wear particles that would normally flow through the gaps between the embossments with the lubricant are blocked at the entrance or embossed area. The accumulation of blocked foreign matter causes the absorption of lubricant and obstruction of the flow path, resulting in partial depletion of the lubricant. Furthermore, the accumulated and enlarged foreign matter itself applies strain stress to the belt 301, potentially causing the belt 301 to break during the life of the fixing device 8.

[0065] In this experiment, when the area ratio was 50%, no deposits occurred and no lubricant depletion occurred.When the area ratio was 70%, deposits were slight and no lubricant depletion occurred.When the area ratio was 100%, large deposits occurred and lubricant depletion occurred.

[0066] The above results demonstrate that increasing the area ratio suppresses wear of the sliding layer 304c and improves the lifespan of the fixing device 8. For example, an area ratio of 50% or more is preferable. However, as described above, taking into consideration unexpected damage to the belt 301 due to partial depletion of the lubricant or accumulation of foreign matter such as wear particles, an area ratio of 70% or less is preferable. In this embodiment, by optimizing the arrangement and shape of the protrusions 304b, the area ratio in the strong contact region can be set to, for example, 50% or more, thereby further improving the lifespan of the fixing device 8. Note that the shape of the protrusions 304b in the strong contact region is not limited to the diamond shape shown in FIG. 10(b), and various shapes such as triangles and hexagons can be used as long as the area ratio can be increased. [Explanation of symbols]

[0067] 8. Fixing device 301 Belt 303 Pad (backup member) 304, 304A... Sliding member 304b...Protrusion 304c···Sliding layer 305 Pressure roller (nip forming member)

Claims

1. A fixing device that fixes a toner image carried on a recording material to the recording material, an endless rotatable belt; a nip portion forming member that contacts the outer peripheral surface of the belt to form a nip portion between the belt and the nip portion, for nipping and conveying a recording material; a sliding member that slides against the inner circumferential surface of the belt in the nip portion; a backup member that is disposed inside the belt so as to sandwich the sliding member and the belt between the nip portion forming member and the backup member, and that backs up the sliding member; the sliding member has a plurality of protrusions provided on the side that slides against the belt so as to protrude toward the inner circumferential surface of the belt, the plurality of protrusions are distributed at the nip portion and outside the nip portion in a width direction of the recording material that intersects with a conveyance direction of the recording material, a first region is a predetermined region on the outer side of the nip portion in the width direction, and a second region is a region on the inner side of the first region in the width direction, on a surface of the sliding member that slides against the belt; When SFR is the area of ​​a region and Si is the total area of ​​the tip surfaces of the n projections present in the region, Sa.r. defined by the following formula is the area ratio: [Equation 1] When Sa.r. of the first region is a first area ratio and Sa.r. of the second region is a second area ratio, The sliding member is First area ratio>Second area ratio A fixing device characterized by satisfying the above.

2. The first area ratio is 30% or more.

2. The fixing device according to claim 1, wherein the fixing device is a fixing device for fixing a toner image onto a recording medium.

3. The second area ratio is 5% or less.

2. The fixing device according to claim 1, wherein the fixing device is a fixing device for fixing a toner image onto a recording medium.

4. The first area ratio is 70% or less.

2. The fixing device according to claim 1, wherein the fixing device is a fixing device for fixing a toner image onto a recording medium.

5. The second region includes a region in the width direction through which the recording material of the maximum size passes through the nip portion.

2. The fixing device according to claim 1, wherein the fixing device is a fixing device for fixing a toner image onto a recording medium.

6. The sliding member has a substrate layer made of metal.

2. The fixing device according to claim 1, wherein the fixing device is a fixing device for fixing a toner image onto a recording medium.

7. The plurality of protrusions are provided from the base layer toward the inner circumferential surface of the belt, and the plurality of protrusions and the base layer are integrally formed.

7. The fixing device according to claim 6, wherein the fixing member is a fixing member.

8. The sliding member has a sliding layer that covers the belt including the plurality of protrusions and a surface on the sliding side.

8. The fixing device according to claim 7,

9. The sliding layer is made of a fluororesin.

9. The fixing device according to claim 8, wherein the fixing member is a fixing member.

10. The first region includes a region extending from an end of the nip portion in the width direction to a position 2 mm outward.

2. The fixing device according to claim 1, wherein the fixing device is a fixing device for fixing a toner image onto a recording medium.

11. The nip portion forming member is a pressure roller that presses the belt toward the sliding member.

2. The fixing device according to claim 1, wherein the fixing device is a fixing device for fixing a toner image onto a recording medium.

12. a heating roller in contact with the inner circumferential surface of the belt; a heat source for heating the heating roller.

2. The fixing device according to claim 1, wherein the fixing device is a fixing device for fixing a toner image onto a recording medium.

13. A fixing device that fixes a toner image carried on a recording material to the recording material, an endless rotatable belt; a nip portion forming member that contacts the outer peripheral surface of the belt to form a nip portion between the belt and the nip portion, for nipping and conveying a recording material; a sliding member that slides against the inner circumferential surface of the belt in the nip portion; a backup member that is disposed inside the belt so as to sandwich the sliding member and the belt between the nip portion forming member and the backup member, and that backs up the sliding member; the sliding member has a plurality of protrusions provided on the side that slides against the belt so as to protrude toward the inner circumferential surface of the belt, the plurality of protrusions are distributed at the nip portion and outside the nip portion in a width direction of the recording material that intersects with a conveyance direction of the recording material, a first region is a predetermined region on the outer side of the nip portion in the width direction, and a second region is a region on the inner side of the first region in the width direction, on a surface of the sliding member that slides against the belt; When the average area of ​​the tip surfaces of the protrusions present in the first region is defined as a first average area, and the average area of ​​the tip surfaces of the protrusions present in the second region is defined as a second average area, The sliding member is First average area>Second average area A fixing device characterized by satisfying the above.

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