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, and a slide layer 304c that covers the side including the plurality of projections 304b where the slide member 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 thickness of the slide layer 304c in the first areas is defined as a first slide layer thickness, and the thickness of the slide layer 304c in the second area as a second slide layer thickness, the first slide layer thickness is larger than the second slide layer thickness.SELECTED DRAWING: Figure 8

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] In a configuration in which unevenness is formed on the sliding member to reduce the frictional force between the sliding member and the inner peripheral surface of the belt, a sliding layer may be provided on the surface of the substrate layer of the sliding member to reduce the coefficient of friction. In this case, it is necessary to ensure a certain thickness (film thickness) during the manufacturing of the sliding member so that the sliding layer will remain in place throughout the life of the fixing device. While the sliding layer gradually wears out as the fixing device operates, the wear is usually gradual, allowing the fixing device to maintain sufficient functionality throughout its life. However, depending on the manner in which the sliding layer contacts the belt, the wear of parts of the sliding layer may progress more quickly than expected, potentially shortening the life of the fixing device.

[0007] SUMMARY OF THE INVENTION An object of the present invention is to provide a configuration that can prevent a shortened life of a fixing device. [Means for solving the problem]

[0008] 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 for nipping and conveying 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 having a plurality of protruding members provided on the side that slides against the belt and protruding toward the inner peripheral surface of the belt. and a sliding layer covering the surface that slides against the belt and includes the plurality of protrusions, wherein 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 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, and when the thickness of the sliding layer in the first region is defined as a first sliding layer thickness and the thickness of the sliding layer in the second region is defined as a second sliding layer thickness, the first sliding layer thickness is greater than the second sliding layer thickness. [Effects of the Invention]

[0009] According to the present invention, it is possible to prevent the life of the fixing device from being shortened. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a cross-sectional view showing a schematic configuration of an image forming apparatus according to an embodiment. [Figure 2] FIG. 2A is a cross-sectional view showing the schematic configuration of a fixing device according to an embodiment, and FIG. 2B is an enlarged schematic view showing a portion A of FIG. [Figure 3] 1A and 1B are a cross-sectional view and a plan view, respectively, schematically illustrating a sliding member according to an embodiment. [Figure 4] FIG. 2 is a schematic view of a sliding member, a belt, and a pressure roller according to the embodiment, cut along the width direction. [Figure 5] FIG. 3 is a cross-sectional view schematically showing the relationship between a sliding member and a belt according to the embodiment. [Figure 6] 1A and 1B are cross-sectional views schematically illustrating the relationship between the protrusions of the sliding member and the belt, showing a state in which the film thickness of the sliding layer of the protrusions is large, a state in which the film thickness has decreased, and a state in which the tip surfaces of the protrusions are exposed. [Figure 7] 1A and 1B are enlarged cross-sectional views schematically illustrating a protrusion of a sliding member according to an embodiment, in which (a) is a diagram illustrating a state in which a sliding layer is provided on the protrusion, (b) is a diagram illustrating a state in which the sliding layer at the tip of the protrusion has been removed, and (c) is a diagram for defining the thickness of the sliding layer. [Figure 8] 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 9] FIG. 4 is a schematic view showing a region where a part of the belt according to the embodiment is in strong contact with a sliding member, cut along the width direction. [Figure 10] 10 is a table showing the results of an experiment conducted to confirm the effects of the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] The embodiment will be described with reference to Figures 1 to 10. First, the schematic configuration of an image forming apparatus according to the present embodiment will be described with reference to Figure 1.

[0012] [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.

[0013] 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.

[0014] 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.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] [Fixing 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.

[0022] 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.

[0023] 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.

[0024] 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 on the outer periphery of the base layer 301a, and a release layer 301c formed on the outer periphery of 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 by a pad 303 and a heating roller 307. In this embodiment, the outer diameter of the belt 301 is 150 mm.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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).

[0031] 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.

[0032] 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.

[0033] [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.

[0034] 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 304e.

[0035] The base layer 304a only needs to have sufficient heat resistance and strength. Materials include stainless steel, copper, aluminum, engineering plastics (PI (polyimide), PEEK (polyether ether ketone), LCP (liquid crystal polymer), etc.), and in this embodiment, metal materials such as stainless steel, copper, and aluminum are preferred. In this embodiment, stainless steel with a thickness of 1.3 mm is used as the base layer 304a.

[0036] 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 integrally formed from the same material as the base layer 304a and are arranged in the nip N along the recording material conveyance direction (X direction) and the width direction (Y direction) of the recording material, which intersects with the conveyance direction. The distance (interval) d between the centers of adjacent protrusions 304b in the conveyance direction and the distance (interval) d between the centers of adjacent protrusions 304b in the width direction are each 1.25 mm or more, preferably 1.4 mm or more. In this embodiment, to ensure uniform sliding performance with the belt 301, the intervals between the plurality of protrusions 304b are the same in the conveyance direction and the width direction, and each interval d is 1.4 mm. The plurality of protrusions 304b are distributed at the nip N and outside the nip N in the width direction.

[0037] 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.

[0038] The sliding layer 304c is preferably made of a coating agent such as a fluororesin (e.g., PTFE (polytetrafluoroethylene), PFA, etc.) to achieve low friction. Specifically, the sliding layer 304c is formed by spraying a coating agent such as a fluororesin (e.g., PTFE, PFA, etc.) dispersed in water or an organic solvent onto the surface of the base layer 304a that slides against the belt 301, i.e., the surface on which the protrusions 304b are formed, followed by high-temperature baking. In this embodiment, the viscosity of the coating agent when sprayed (liquid) is 10 Pa·sec or less at room temperature (25°C). In this embodiment, the sliding member 304 is formed by coating the surface of the base layer 304a, including the multiple protrusions 304b, with PTFE. In addition, 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.

[0039] 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.

[0040] 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.

[0041] [Relationship between the substrate layer and the sliding layer of the sliding member] As described above, sliding member 304 is covered with sliding layer 304c on the surface of base layer 304a on which multiple protrusions 304b are formed. Here, sliding layer 304c of sliding member 304 when fixing device 8 is driven will be described in detail. As shown in Fig. 5, when fixing device 8 is driven, belt 301 moves relative to sliding member 304 in direction D in the figure, causing sliding layer 304c to slide against base layer 301a of belt 301.

[0042] 6(a) to 6(c) show the change over time of the sliding layer 304c when the base layer 301a of the belt 301 slides on the sliding layer 304c and continues image formation for a long period of time. The sliding layer 304c of a certain protrusion 304b is used when it is thick, as shown in FIG. 6(a). As the image formation operation of the image forming apparatus progresses, the sliding layer 304c gradually wears away, and the thickness of the sliding layer 304c at the tip of the protrusion 304b decreases, as shown in FIG. 6(b). As the image formation operation of the image forming apparatus continues, the tip surface 304d (base layer 304a) of the protrusion 304b becomes exposed, as shown in FIG. 6(c), and the base layer 304a, which has a higher coefficient of friction than the sliding layer 304c, comes into direct contact with the base layer 301a of the belt 301. As a result, the driving torque increases due to an increase in the frictional force between belt 301 and sliding member 304, and image defects occur due to abrasion of base layer (substrate) 301a of belt 301 that rubs against it, and cracks occur in base layer 301a of belt 301. At this point, fixing device 8 reaches the end of its life, so it is required that sliding layer 304c have a certain thickness or more.

[0043] [Thickness of the sliding layer of the protrusions] Next, the thickness Tbc of the sliding layer 304c at the protrusion 304b of the sliding member 304 (hereinafter also referred to as the protrusion sliding layer thickness Tbc) will be described with reference to FIGS. 7(a) to 7(d). FIG. 7(a) is an enlarged cross-sectional view of one of the multiple protrusions 304b on the sliding member 304, and is shown upside down from FIGS. 3(a), 5, and 6(a) to 6(c), with the protrusion 304b facing upward. FIG. 7(b) is a schematic diagram showing the state after the sliding layer 304c at the tip of the protrusion 304b has been removed using a metal blade or the like. The protrusion sliding layer thickness Tbc is defined as the difference between the height (Z direction) of the sliding layer 304c before removal and the height (Z direction) of the protrusion 304b, as shown in FIG. 7(c). That is, the protrusion slide layer thickness Tbc is the height in the Z direction from the tip surface 304d of the protrusion 304b to the highest point of the slide layer 304c. As an example of an actual measurement, there is a measurement method in which the thickness is calculated from the difference in two-dimensional height profiles measured at a set magnification of 40 times using a three-dimensional shape measuring instrument, VR-3200 manufactured by Keyence Corporation.

[0044] [Regarding the early wear region of the sliding layer] The graph in Fig. 8 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. 8 also shows the positional relationship between the sliding member 304, belt 301, and pressure roller 305 shown in Fig. 4 along with the graph.

[0045] The results in FIG. 8 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 (a predetermined region L surrounded by a dashed line in FIG. 8), 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 FIG. 8 was calculated by averaging the embossed portions 304e in the conveyance direction for each row.

[0046] FIG. 9 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. 8. 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 direction of pressure 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.

[0047] Therefore, it was found that the embossed portion 304e 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.

[0048] In the following explanation, we will discuss the thickness of the sliding layer 304c of the protrusion 304b arranged in the strong contact area in response to the above-mentioned problem. 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 tolerance (play) of each part related to the formation of 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 about 1 mm. Therefore, when defining the strong contact area, it is assumed that this assembly tolerance is taken into consideration.

[0049] [Thickness of the sliding layer in the strong contact area and non-strong contact area] In this embodiment, by increasing the thickness of the sliding layer at the strong contact points where wear progresses quickly, early wear of the sliding layer is suppressed, and the life of the fixing device 8 is suppressed from being shortened. Specifically, on the surface of sliding member 304 that slides against belt 301, a predetermined region on the widthwise outer side of nip portion N is designated as a first region (strong contact region), and a region on the widthwise inner side of the first region is designated as a second region (nip portion N region, non-strong contact region). The first region includes a region from the widthwise end of nip portion N to a position 2 mm outward. The second region includes a widthwise region through which a maximum-size recording material passes through nip portion N.

[0050] The thickness Tbc of the slide layer 304c in the first region is referred to as the first slide layer thickness Tbc1, and the thickness Tbc of the slide layer 304c in the second region is referred to as the second slide layer thickness Tbc2. In this case, the first slide layer thickness Tbc1 is made thicker than the second slide layer thickness Tbc2. In this embodiment, the first slide layer thickness Tbc1 is made 1.5 times or more the second slide layer thickness Tbc (Tbc1≧1.5×Tbc2). It is preferable that the first slide layer thickness Tbc1 is made 2.0 times or less the second slide layer thickness Tbc2 (Tbc1≦2.0×Tbc2).

[0051] In this embodiment, the thickness including the base layer 304a and the protrusions 304b is the same in the first region and the second region. In this embodiment, the base layer 304a and the protrusions 304b are made of metal. Changing the thickness for each widthwise region requires separate processing, which increases costs. Furthermore, changing the thickness of the metal base layer 304a and the protrusions 304b results in uneven pressure on the inner circumferential surface of the belt. Specifically, for example, if the protrusions 304b (embossed portions 304e) in the thicker sliding layer are made thinner, the pressure on the protrusions 304b around the lowered protrusions 304b increases. This increases the pressure on the inner circumferential surface of the belt 301 and shortens its lifespan. Therefore, it is preferable to have the same thickness for the metal portions.

[0052] [Experiment] An investigation experiment conducted to confirm the effects of this embodiment will be described. In the investigation experiment, a plurality of sliding members A to I were prepared, each having a sliding layer 304c formed thereon with a plurality of levels of protrusion sliding layer thickness Tbc in the strong contact region (first region) and other regions (non-strong contact region, second region). These sliding members A to I were then sequentially replaced in the fixing device 8, and a drive durability test was conducted. The drive durability test was conducted in a mode in which the pressure roller 305 alternately contacted and did not contact the belt 301. The design target time in this mode was 240 hours. The drive durability test was terminated when the drive torque exceeded a preset upper limit within the design target time, or when a crack occurred in the belt 301.

[0053] To check the image, a sheet of paper on which a solid black (Bk) image was formed was passed through the nip N of the fixing device 8 with the sliding members A to I in the initial state, and it was checked whether glossy streaks occurred. The paper used was OK Topcoat (basis weight 128 g / m) manufactured by Oji Paper Co., Ltd. 2 ) paper was used.

[0054] Next, the results of the experimental study will be described using the table in FIG. 10. FIG. 10 shows the results of a drive durability test and image confirmation conducted using sliding members A to I in which the slide layer thickness in the strong contact region (first slide layer thickness Tbc1) and the slide layer thickness in the non-strong contact region (second slide layer thickness Tbc2) were changed. The "durability" evaluation in the table is given as "Good" if the drive torque does not exceed the upper limit even after the design target time (240 hours) is reached and no cracks occur in the belt 301. The evaluation is given as "Poor" if the drive torque exceeds the upper limit or cracks occur in the belt 301 within the design target time (240 hours). The evaluation of "Image Defect" is given as "Good" if no gloss streaks occur, "Good" if gloss streaks occur but are minor, and "Poor" if gloss streaks occur.

[0055] In the case of sliding member A, that is, when the first sliding layer thickness Tbc1 and the second sliding layer thickness Tbc2 are each 1 μm or less, the initial driving torque exceeds a predetermined value, and the inner surface of the belt 301 rubs against the inner surface of the belt 301 with almost no sliding layer 304c present, causing abrasion of the inner surface of the belt 301 and resulting in image defects. Also, in sliding members B, C, and D, the exposure of the sliding layer 304c in the strong contact area caused the inner surface of the belt 301 to be worn away, resulting in cracks in the belt 301 in the strong contact area.

[0056] In sliding members E and F, the thickness of the sliding layer 304c in the strong contact region increased, so cracks did not occur in the belt 301 with use, and the drive torque was below the upper limit at the design target time. In sliding member G, the sliding layer 304c was exposed at the boundary between the strong contact region and the non-strong contact region, causing cracks in the belt 301 with use. The reason for this is as follows. First, when the difference in thickness between adjacent sliding layers 304c becomes too large, the belt 301 makes contact with the thicker protrusions 302b of the sliding layer 304c at the stepped portion at the boundary. Then, pressure concentrates on the edge of the thicker protrusions 304b, which causes the belt 301 to receive a large contact pressure, accelerating wear and causing cracks in the belt 301.

[0057] In sliding members H and I, the increased thickness of the sliding layer 304c in the strong contact region prevented cracks from occurring in the belt 301 during use, and the drive torque was below the upper limit for the designed target time. However, in the case of sliding members H and I, image defects (glossy streaks) occurred. The reason for this is as follows: When attempting to increase the thickness of the sliding layer 304c, the absolute value of the thickness increases, and the thickness unevenness of the entire sliding member also increases. Furthermore, by increasing the thickness of the sliding layer 304c in the image area outside the strong contact region, specifically by setting the thickness of the sliding layer 304c in the non-strong contact region to 30 μm or more, the difference in thickness between adjacent sliding layers 304c increased, and it is thought that this difference in contact pressure caused the image defects (glossy streaks).

[0058] For these reasons, it is preferable to make the thickness of the sliding layer in the strong contact region thicker than that of the sliding layer in the image region outside the strong contact region. In particular, regarding the relationship between the thickness of the sliding layer 304c in the strong contact region and the thickness of the sliding layer 304c in the image region outside the strong contact region, by making the thickness of the sliding layer 304c in the strong contact region (first sliding layer thickness Tbc1) 1.5 times or more the thickness of the sliding layer in the image region outside the strong contact region (second sliding layer thickness Tbc2), durability can be improved and the occurrence of image defects can be suppressed. This can also prevent a shortened lifespan of the fixing device 8. Furthermore, by making the thickness of the sliding layer 304c in the strong contact region (first sliding layer thickness Tbc1) 2.0 times or less the thickness of the sliding layer in the image region outside the strong contact region (second sliding layer thickness Tbc2), durability can be further improved. Furthermore, by setting the thickness of the sliding layer in the image area of ​​the strong contact outer area (second sliding layer thickness Tbc2) to less than 30 μm, the occurrence of image defects can be further suppressed.

[0059] [Other embodiments] In the above-described embodiment, the strong contact region is a region extending 2.0 mm from the end of pressure roller 305 toward the region outside nip portion N. Here, protrusions 304b at the end of the strong contact region on the nip portion N side experience strong contact pressure where they make contact with belt 301, causing rapid wear of sliding layer 304c. Therefore, the sliding layer thickness of protrusions 304b at the end of the strong contact region on the nip portion N side may be made thicker than the sliding layer thickness in other parts of the strong contact region. In the above-described embodiment, the area of ​​the tip surface of protrusions 304b is uniform across the entire region, but the area of ​​the tip surface of protrusions 304b may be changed depending on the contact pressure with belt 301. [Explanation of symbols]

[0060] 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 a side that slides against the belt so as to protrude toward an inner peripheral surface of the belt, and a sliding layer that covers the surface that slides against the belt and includes the plurality of protrusions, 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 thickness of the slide layer in the first region is defined as a first slide layer thickness and the thickness of the slide layer in the second region is defined as a second slide layer thickness, the first slide layer thickness is larger than the second slide layer thickness. A fixing device characterized by:

2. The thickness of the first sliding layer is 1.5 times or more the thickness of the second sliding layer.

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 thickness of the first sliding layer is 2.0 times or less the thickness of the second sliding layer.

3. The fixing device according to claim 2, wherein the fixing device is a fixing device.

4. The thickness of the second sliding layer is less than 30 μm.

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 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.

7. 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.

8. 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.

9. 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.

10. 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.

10. The fixing device according to claim 9.

11. The thickness of the base material layer and the protrusion in the first region is the same as the thickness of the base material layer and the protrusion in the second region. The fixing device according to claim 10 .

Images