Fixing device

Abstract

To provide a configuration that ensures the adhesive strength between a base material layer 304a and a slide layer 304c of a slide member 304, and even when the base material layer 304a is exposed, can prevent damage to an inner peripheral surface of a belt 301.SOLUTION: A slide member 304 slides with an inner peripheral surface of a belt 301 at a nip part. The slide member 304 has a base material layer 304a that is formed with a plurality of projections 304b projecting toward the inner peripheral surface of the belt 301 on a side sliding with the belt 301, and a slide layer 304c that is provided to cover a surface of a side of the base material layer 304a sliding with the belt 301. The arithmetic average roughness Ra of apical surfaces 304d1 of the plurality of projections 304b satisfies 0.13 μm≤Ra≤1.67 μm.SELECTED DRAWING: Figure 7

Description

Technical Field

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

Background Art

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

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

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

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] In a configuration where irregularities are formed on the sliding member to reduce frictional force between it and the inner circumferential surface of the belt, a sliding layer is sometimes provided on the surface of the base layer to reduce the coefficient of friction. In this case, it is necessary to ensure appropriate adhesive strength between the base layer and the sliding layer. One factor affecting adhesive strength is the surface roughness of the base layer. If the surface of the base layer is smooth, the adhesive strength will decrease. On the other hand, if the surface roughness of the base layer is high, the inner circumferential surface of the belt is more likely to be damaged when the sliding layer wears down and the base layer is exposed, which may shorten the lifespan of the belt. In addition, belt dust may accumulate in the sliding part, which may lead to image defects or an increase in the belt's driving torque.

[0007] The present invention aims to provide a configuration that ensures the adhesive strength between the base material layer and the sliding layer of the sliding member, while also suppressing damage to the inner circumferential surface of the belt even when the base material layer is exposed. [Means for solving the problem]

[0008] The present invention relates to a fixing device for fixing a toner image supported on a recording material to the recording material, comprising: an endless, rotatable belt; a nip-forming member that contacts the outer circumferential surface of the belt and forms a nip portion for gripping and transporting the recording material between itself and the belt; a sliding member that slides against the inner circumferential surface of the belt at the nip portion; and a backup member positioned inside the belt so as to sandwich the sliding member and the belt between itself and the nip-forming member, and to back up the sliding member, wherein the sliding member has a plurality of protrusions that project toward the inner circumferential surface of the belt on the side that slides against the belt. , made of metal A base material layer and a provision provided to cover the surface of the base material layer on the side that slides with the belt. , composed of resin The device has a sliding layer, and the arithmetic mean roughness Ra of the tip surfaces of the plurality of protrusions satisfies 0.13 μm ≤ Ra ≤ 1.67 μm. [Effects of the Invention]

[0009] According to the present invention, it is possible to ensure the adhesive strength between the base material layer and the sliding layer of the sliding member, while suppressing damage to the inner circumferential surface of the belt even when the base material layer is exposed. [Brief explanation of the drawing]

[0010] [Figure 1] A schematic cross-sectional view of the image forming apparatus according to the embodiment. [Figure 2] (a) A schematic cross-sectional view of the fixing device according to the embodiment, and (b) A schematic diagram showing an enlarged view of part A in (a). [Figure 3] (a) a cross-sectional view and (b) a plan view schematically showing a sliding member according to the embodiment. [Figure 4] A schematic cross-sectional view showing the relationship between the sliding member and the belt according to this embodiment. [Figure 5] A schematic cross-sectional view showing the relationship between the projection of the sliding member and the belt in Comparative Example 1, (a) showing the relationship of forces generated in the sliding layer of the projection, and (b) showing the state in which the sliding layer has peeled off from the base layer. [Figure 6] A schematic cross-sectional view showing the relationship between the projection of the sliding member and the belt according to Comparative Example 2, (a) showing the projection with a sliding layer, and (b) showing the projection with the sliding layer exposed. [Figure 7] A schematic cross-sectional view showing the relationship between the projection of the sliding member according to the embodiment and the belt, (a) showing the projection with a sliding layer, and (b) showing the projection with the sliding layer exposed. [Figure 8] A table showing the results of experiments conducted to confirm the effectiveness of the embodiment. [Figure 9] A schematic cross-sectional view showing a projection of a sliding member according to another embodiment. [Modes for carrying out the invention]

[0011] Embodiments will be described using Figures 1 to 8. First, the schematic configuration of the image forming apparatus of this embodiment will be described using Figure 1.

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

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

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

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

[0016] The charging roller 201a as the primary charger charges the surface of the photosensitive drum 200a to a predetermined potential to prepare for electrostatic latent image formation. An electrostatic latent image is formed on the surface of the photosensitive drum 200a charged to a predetermined potential by the laser beam from the polygon scanner 31. The developing device 202a develops the electrostatic latent image on the photosensitive drum 200a to form a toner image. The primary transfer roller 203a discharges from the back of the intermediate transfer belt 204 and applies a primary transfer bias of the 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 the cleaner 207a.

[0017] Also, the toner image on the intermediate transfer belt 204 is conveyed to the next image forming unit, and in the order of Y, M, C, Bk, the toner images of each color formed in each image forming unit are sequentially transferred, and a four-color image is formed on its surface. Then, the toner image that has passed through the Bk image forming unit Pd, which is the most downstream in the rotation direction of the intermediate transfer belt 204, is conveyed to the secondary transfer unit composed of the secondary transfer roller pair 205 and 206. And in the secondary transfer unit, a secondary transfer electric field of the opposite polarity to the toner image on the intermediate transfer belt 204 is applied, and secondary transfer is performed onto the recording material.

[0018] The recording material is housed in the cassette 9, and the recording material fed from the cassette 9 is conveyed to the registration unit 208 composed of, for example, a pair of registration rollers and waits in the registration unit 208. Then, 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 paper, and the recording material is conveyed to the secondary transfer unit.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

[0033] The fixing device 8 grips the recording material P, which carries the toner image, in a nip section N formed between the belt 301 and the pressure roller 305, and heats the toner image while transporting it. In this way, the fixing device 8 fixes the toner image to the recording material P while gripping and transporting it. Therefore, it is necessary to balance the function of applying heat and pressure with the function of transporting the recording material P. The pressure roller 305 is pressed against the sliding member 304 via the belt 301 by a drive source (not shown). In this embodiment, the applied pressure (NF) in the nip section N during image formation is 1600N, and the width of the nip section N in the X direction (direction of transport of the recording material) is set to 24.5 mm, and the width in the Y direction (width direction of the recording material) is set to 326 mm.

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

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

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

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

[0038] The distance (spacing) d between the centers of adjacent protrusions 304b in the conveying direction, and the distance (spacing) d between the centers of adjacent protrusions 304b in the width direction, are 1.25 mm or more, preferably 1.4 mm or more. In this embodiment, in order to ensure uniform sliding performance with the belt 301, the spacing between the multiple protrusions 304b is the same in the conveying direction and the width direction, and the respective spacing d is set to 1.4 mm. However, if the pressure distribution differs in the width direction and the conveying direction, the spacing between the protrusions in each direction may be changed according to the pressure distribution.

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

[0040] The sliding layer 304c is preferably a coating agent such as a fluororesin (PTFE (polytetrafluoroethylene), PFA, etc.) to achieve low friction. In this embodiment, the sliding member 304 was formed by coating the surface of a base layer 304a containing a plurality of protrusions 304b with PTFE that is 20 μm thick. In this embodiment, a lubricant is applied to the inner surface of the belt 301. As a result, the belt 301 slides smoothly against the sliding member 304. Silicone oil was used as the lubricant.

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

[0042] [Relationship between the base layer and the sliding layer of the sliding member] As described above, the sliding member 304 has a sliding layer 304c covering the side of the base layer 304a where multiple protrusions 304b are formed. Here, we will describe in detail the sliding layer 304c of the sliding member 304 when the fixing device 8 is driven. As shown in Figure 4, when the fixing device 8 is driven, the belt 301 moves relative to the sliding member 304 in the direction D in the figure, and this causes a force F in the conveying direction to be applied to the sliding layer 304c. D This will occur.

[0043] Using Comparative Example 1 shown in Figures 5(a) and (b), the force F acting on the sliding layer 304c in the transport direction is D The influence of on the sliding layer 304c and the influence of the surface properties of the base layer 304a on this will be explained. Figure 5(a) shows a simplified relationship of the forces generated on the sliding layer 304c of a certain projection 304b. On the sliding layer 304c, F is applied from the base layer 301a of the belt 301 in the conveying direction. DThe force acts upon it. Furthermore, the sliding layer 304c is bonded to the base layer 304a which includes a plurality of protrusions 304b, and F from the bonded portion. D A force F that opposes A That is at work.

[0044] Here, F D If the adhesive strength between the base layer 304a and the sliding layer 304c becomes too high, the sliding layer 304c will peel off from the projection 304b of the base layer 304a, as shown in Figure 5(b). Then, the tip surface 304d1 of the projection 304b will be exposed and come into contact with the base layer 301a of the belt 301. This may increase the frictional force between the belt 301 and the sliding member 304, potentially increasing the driving torque of the belt 301 or causing image defects due to uneven height of the projection 304b.

[0045] F acts between the base layer 304a and the sliding layer 304c A This depends on the adhesive strength between the base layer 304a and the sliding layer 304c, and the greater the adhesive strength, the higher F A The adhesive strength increases. It has been found that the adhesive strength is sensitive to the surface properties of the substrate layer 304a. This point will be discussed later.

[0046] Next, using Comparative Example 2 shown in Figures 6(a) and (b), we will explain the effect of the surface properties of the base layer 304a when the sliding layer 304c is worn. Figure 6(a) shows the case when the surface roughness of the surface 304d of the base layer 304a, including the tip surface 304d1 of a certain protrusion 304b, is rough. When the surface 304d of the base layer 304a is rough, the adhesive strength increases because the adhesive area between the base layer 304a and the sliding layer 304c expands.

[0047] Figure 6(b) shows the condition when the sliding layer 304c wears down with use of the fixing device 8. When the thickness of the sliding layer 304c decreases due to wear, the tip surface 394d1 of the projection 304b is exposed and comes into contact with the base layer 301a of the belt 301. In this case, if the surface of the tip surface 304d1 of the projection 304b is rough, and the hardness of the projection 304b is equal to or harder than the hardness of the base layer 301a of the belt 301, the projection 304b will damage the base layer 301a.

[0048] This can lead to a reduced lifespan for the belt 301, and the generation of metal shavings due to the grinding of the inner surface of the base layer 301a of the belt 301, which can accumulate in the nip section N, resulting in image defects and increased driving torque. The relationship between the projection 304b and damage to the base layer 301a of the belt 301 will be described later.

[0049] When the surface roughness of the base layer 304a, which includes multiple protrusions 304b, is small, the adhesive strength between the base layer 304a and the sliding layer 304c decreases. When the surface roughness of the base layer 304a is large, the sliding layer 304c wears down and the base layer 304a is exposed, making it easier to damage the inner surface of the belt 301. Therefore, in this embodiment, the surface roughness of the surface 304d of the base layer 304a, which includes multiple protrusions 304b, is set to an appropriate range, as described below.

[0050] [Surface roughness of the base material layer] The surface roughness of the base layer 304a in the sliding member 304 of this embodiment will be explained using Figures 7(a) and 7(b). Figures 7(a) and 7(b) show the case where the surface roughness of the base layer 304a, which includes a plurality of protrusions 304b, is appropriate. That is, in this embodiment, the arithmetic mean roughness Ra of the tip surfaces 304d1 of the plurality of protrusions 304b satisfies 0.13 μm ≤ Ra ≤ 1.67 μm. As a result, as shown in Figure 7(a), the adhesive strength between the tip surfaces 304d1 of the plurality of protrusions 304b and the sliding layer 304c is ensured. At the same time, as shown in Figure 7(b), even if the sliding member 304 wears down and the tip surfaces 304d1 of the protrusions 304b are exposed, damage to the inner circumferential surface of the belt 301 can be suppressed.

[0051] Furthermore, in this embodiment, the arithmetic mean roughness Ra of the side surfaces 304d2 of the multiple protrusions 304b is also set to satisfy 0.13 μm ≤ Ra ≤ 1.67 μm. By appropriately adjusting the surface roughness of the side surfaces 304d2 in addition to the tip surfaces 304d1 of the protrusions 304b in this way, the adhesive strength between the base layer 304a and the sliding layer 304c can be further increased. Moreover, even if the side surfaces 304d2 are exposed and come into contact with the inner surface of the belt 301, damage to the inner surface of the belt 301 can be suppressed.

[0052] Furthermore, in this embodiment, the bottom surface 304d3 of the recess 304f between adjacent protrusions 304b on the front surface 304d of the base layer 304a on the side where the sliding layer 304c is provided is also made to satisfy the arithmetic mean roughness Ra of 0.13 μm ≤ Ra ≤ 1.67 μm. That is, in this embodiment, the entire surface 304d of the base layer 304a is made to satisfy the arithmetic mean roughness Ra of 0.13 μm ≤ Ra ≤ 1.67 μm. By appropriately adjusting the surface roughness of the bottom surface 304d3 in addition to the tip surface 304d1 and side surface 304d2 of the protrusions 304b, the adhesive strength between the base layer 304a and the sliding layer 304c can be further increased. Also, even if the bottom surface 304d3 is exposed and comes into contact with the inner surface of the belt 301, damage to the inner surface of the belt 301 can be suppressed.

[0053] In this embodiment, the base layer 304a is subjected to a surface treatment to achieve a predetermined surface roughness. In this case, as described above, if the tip surface 304d1 of the projection 304b, the side surface 304d2, and the bottom surface 304d3 of the recess 304f have the same range of surface roughness, the surface treatment can be easily performed.

[0054] [Experimental study] Next, we will describe the experimental tests conducted to confirm the effects of this embodiment. For the experimental tests, we prepared several sliding members A to E, each with a different surface roughness level for the surface 304d of the base layer 304a. These sliding members A to E were then sequentially replaced in the fixing device 8, and a drive durability test was conducted. The drive durability test was performed in a mode in which the pressure roller 305 alternately contacted the belt 301 and then became non-contacted. The design target time for this mode was 240 hours. If the drive torque (the drive torque of the drive motor that drives the pressure roller 305 (initial torque)) exceeded a preset upper limit within the design target time, the drive durability test was terminated, the sliding member was removed from the fixing device 8, and the condition of the sliding layer 304c of the sliding member was observed. If the drive torque did not exceed the upper limit within the design target time, the drive durability test was terminated after the design target time had elapsed, the sliding member was removed from the fixing device 8, and the condition of the sliding layer 304c of the sliding member was observed.

[0055] In this study, we used base layer 304a of sliding members A to E, whose surface properties were altered by various treatments. Surface roughness was measured using a surface roughness measuring instrument at a cutoff frequency of 0.08 mm, and the measurement was taken at the end of the base layer 304a of the sliding member where no protrusions 304b were present. The samples used in this study had surface roughness Ra values ​​of 0.04 μm (sliding member A), 0.13 μm (sliding member B), 0.52 μm (sliding member C), 1.67 μm (sliding member D), and 2.09 μm (sliding member E). After measuring the surface roughness, the sliding members were completed by applying a sliding layer 304c to the base layer 304a of each sliding member A to E.

[0056] Next, the results of the experimental design will be explained using the table in Figure 8. As shown in the table in Figure 8, when the surface roughness Ra of the surface 304d of the base layer 304a was 0.04 μm or less, the driving torque exceeded the threshold within the durability design target time. Furthermore, upon removing and inspecting the sliding member, it was observed that the sliding layer 304c had peeled off from the base layer 304a in many places, indicating insufficient adhesive strength. In addition, the presence of abrasive particles from the belt 301 was minimal, suggesting that the increase in driving torque was due to an increase in frictional force caused by direct contact between the base layer 304a and the base layer 301a of the belt 301.

[0057] It was found that adhesive strength could be ensured for the duration of the durability design target time when the surface roughness Ra of the surface 304d of the base layer 304a was 0.13 μm or more. On the other hand, when the surface roughness Ra of the surface 304d of the base layer 304a was 2.09 μm or more, the driving torque exceeded the threshold within the durability time. Upon removing and inspecting the sliding member, it was observed that a large amount of shavings from the base layer 301a of the belt 301 were attached to it. Therefore, it was confirmed that if the surface roughness Ra of the surface 304d of the base layer 304a satisfies 0.13 μm ≤ Ra ≤ 1.67 μm, adhesive strength can be ensured and the increase in driving torque due to damage to the inner surface of the belt 301 can be suppressed.

[0058] Furthermore, it is more preferable that the surface roughness Ra of the surface 304d of the substrate layer 304a satisfies the condition 0.13 μm ≤ Ra ≤ 0.52 μm. In the above experiment, the best results were obtained when the surface roughness Ra was 0.13 μm.

[0059] [Another example of an embodiment] In the above-described embodiment, a configuration in which the sliding layer 304c is directly provided on the base layer 304a was explained. However, as shown in Figure 9, an adhesive layer 304e may be provided between the base layer 304a and the sliding layer 304c. That is, an adhesive layer 304e that adheres the base layer 304a and the sliding layer 304c may be provided between the base layer 304a, which includes a plurality of protrusions 304b, and the sliding layer 304c. By using the adhesive layer 304e, when the material of the base layer 304a is a metal material such as stainless steel, copper, or aluminum, it is possible to achieve good adhesive strength between the base layer 304a and the sliding layer 304c. [Explanation of Symbols]

[0060] 8. Fixing device 301... belt 303... Pad (backup component) 304...Sliding member 304a...Base material layer 304b...Protrusion 304c...Sliding layer 304d...Surface 304d1...Tip surface 304d2...side 304d3...Bottom 304e...adhesive layer 304f...recess 305... Pressure roller (nip forming member)

Claims

1. A fixing device for fixing a toner image supported on a recording material to the recording material, An endless, rotatable belt, A nip-forming member that contacts the outer surface of the belt and forms a nip portion that grips and transports the recording material between itself and the belt, A sliding member that slides against the inner circumferential surface of the belt in the nip portion, The belt comprises a backup member positioned on the inside of the belt so as to sandwich the sliding member and the belt between the nip portion forming member, and which backs up the sliding member, The sliding member has a base layer made of metal, with a plurality of protrusions formed on the side that slides with the belt, projecting toward the inner circumferential surface of the belt, and a sliding layer made of resin that covers the surface of the base layer on the side that slides with the belt. The arithmetic mean roughness Ra of the tip surfaces of the plurality of protrusions satisfies 0.13 μm ≤ Ra ≤ 1.67 μm. A fixing device characterized by the following features.

2. The arithmetic mean roughness Ra of the sides of the plurality of protrusions satisfies 0.13 μm ≤ Ra ≤ 1.67 μm. The fixing device according to feature 1.

3. The arithmetic mean roughness Ra of the bottom surface of the recess between adjacent protrusions on the side of the substrate layer where the sliding layer is provided satisfies 0.13 μm ≤ Ra ≤ 1.67 μm. The fixing device according to claim 1 or 2.

4. An adhesive layer is provided between the base layer and the sliding layer to bond the base layer and the sliding layer together. A fixing device according to any one of claims 1 to 3.

5. The arithmetic mean roughness Ra of the tip surfaces of the plurality of protrusions satisfies 0.13 μm ≤ Ra ≤ 0.52 μm. A fixing device according to any one of claims 1 to 4.

6. The sliding layer is a fluororesin. A fixing device according to any one of claims 1 to 5, characterized by the features described herein.

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