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, 304d that is provided to project toward an inner peripheral surface of a belt 301 on a side where it slides with the belt 301. In an image forming area (area A), the length of a first ridge of an apical surface of the projection 304b is defined as LA, and in a non-image forming area (area B), the length of a second ridge of an apical surface of the projection 304d located on the outermost side with respect to a width direction as LB. When the average length of LA of the plurality of projections 304b in the image forming area is defined as LAave, and the average length of LB of the plurality of projections 304d in the non-image forming area as LBave, LBave>LAave is satisfied.SELECTED DRAWING: Figure 9

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] Here, in a configuration in which unevenness is formed on the sliding member to reduce the frictional force with the inner peripheral surface of the belt, if multiple protrusions are provided on the sliding member, the friction between the outermost protrusion in the direction intersecting the conveyance direction of the recording material (hereinafter referred to as the width direction) and the inner peripheral surface of the belt increases, which may result in a shorter belt life than expected due to wear on the inner peripheral surface of the belt.

[0007] On the other hand, if the shape of the protrusions located on the outermost side in the width direction were made the same as that of the image forming area, the desired image quality would not be obtained. Therefore, the shape of the protrusions in the image forming area and the shape of the protrusions located on the outermost side in the width direction must be different to achieve the purpose.

[0008] An object of the present invention is to provide a configuration that can suppress a decrease in image quality while suppressing a shortened belt life. [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 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 having a plurality of protrusions on the side that slides against the belt so as to protrude toward the inner peripheral surface of the belt, the plurality of protrusions being spaced apart from the nip portion in a width direction of the recording material that intersects with the conveyance direction of the recording material. and the protrusions are distributed outside the nip portion and the nip portion, and on the surface of the sliding member that slides against the belt, an area where a recording material of a maximum size passes through the nip portion is defined as an image forming area, and an area outside the image forming area in a width direction of the recording material that intersects with the conveying direction of the recording material is defined as a non-image forming area, and in the image forming area, of both ends in the width direction of the tip surface of the protrusion, a line at an end that has a longer length in the conveying direction of the recording material is defined as a first ridge line, and the length of the first ridge line is defined as LA, and in the non-image forming area, a line at an outer end in the width direction of the tip surface of the protrusion that is positioned outermost in the width direction is defined as a second ridge line, and the length of the second ridge line is defined as LB, and the average length of the LA of the plurality of protrusions in the image forming area is defined as LA ave and the average length LB of the plurality of protrusions in the non-image forming region is LB ave In this case, LB ave >LA ave The fixing device is characterized by satisfying the above. [Effects of the Invention]

[0010] According to the present invention, it is possible to suppress a decrease in image quality and a shortened belt life. [Brief explanation of the drawings]

[0011] [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 cross-sectional view schematically showing the relationship between a sliding member and a belt according to the first embodiment. [Figure 5] FIG. 3 is a cross-sectional view schematically showing the relationship between the protrusions at the widthwise ends of the sliding member, the belt, and the pressure roller according to the first embodiment. [Figure 6] FIG. 4 is a plan view schematically showing the relationship between the projections of the sliding member and the image forming area and non-image forming area. [Figure 7] 1A is a schematic diagram illustrating a first example of ridge lines of a protrusion of a sliding member according to a first embodiment, FIG. 1B is a schematic diagram illustrating a second example, and FIG. 1C is a schematic diagram illustrating the first example. [Figure 8] Graph showing the relationship between the ridgeline of a protrusion and the coefficient of friction. [Figure 9] FIG. 2 is a plan view schematically showing the arrangement of protrusions of the sliding member according to the first embodiment. [Figure 10] 10 is a graph showing the relationship between the length of the ridge of the protrusion and the surface pressure on the surface of the protrusion. [Figure 11] 10 is a graph showing the relationship between the length of the ridge of a protrusion and the wear rate. [Figure 12] 10 is a graph showing the relationship between the length LB of the ridge of the protrusion in the non-image forming area and the thickness of the lubricant. [Figure 13] 10 is a graph showing the relationship between the length LA of the ridge line of the protrusion in the image forming area and the driving torque in the second embodiment. [Figure 14] 10A is a plan view schematically showing the arrangement of protrusions of a sliding member according to a third embodiment, and FIG. 10B is a schematic enlarged view showing protrusions at widthwise ends of a non-image forming area according to the third embodiment. [Figure 15] 10 is a graph showing the relationship between the angle of the ridge line of the protrusion at the end in the width direction of the non-image forming area with respect to the conveying direction and the wear rate. [Figure 16]FIG. 10A is a plan view schematically illustrating the arrangement of protrusions of a sliding member according to a fourth embodiment; FIG. 10B is a schematic enlarged view of protrusions at widthwise ends of a non-image forming area according to the fourth embodiment; and FIG. 10C is a schematic view illustrating the ridge lines of the protrusions at widthwise ends of a non-image forming area. DETAILED DESCRIPTION OF THE INVENTION

[0012] First Embodiment The first embodiment will be described with reference to Figures 1 to 12. First, the schematic configuration of an image forming apparatus according to this embodiment will be described with reference to Figure 1.

[0013] [Image forming device] 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.

[0014] 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.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] [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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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).

[0032] 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.

[0033] 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 must be able to both apply heat and pressure and transport 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 326 mm.

[0034] [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.

[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 304b that protrude toward the inner circumferential surface of the belt 301 and protrusions 304d (described later) (see FIGS. 5 and 9, etc., omitted in FIGS. 2 to 4) are formed. 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, 304d). The convex portions formed by the protrusions 304b, 304d being covered by the sliding layer 304c are referred to as embossed portions 304e.

[0036] 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.

[0037] The plurality of protrusions 304b, 304d are provided from the base layer 304a toward the inner circumferential surface of the belt 301. The plurality of protrusions 304b, 304d are integrally formed from the same material as the base layer 304a and are arranged in the recording material conveyance direction (X direction) at the nip N and in the recording material width direction (Y direction) that intersects with the conveyance direction. The distance (interval) d between the centers of adjacent protrusions 304b, 304d in the conveyance direction and the distance (interval) d between the centers of adjacent protrusions 304b, 304d 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, 304d are the same in the conveyance direction and the width direction, and each interval d is 1.4 mm. Furthermore, the plurality of protrusions 304b, 304d are distributed at the nip portion N and outside the nip portion N in the width direction.

[0038] In this way, by providing multiple protrusions 304b, 304d on the surface (sliding surface) of sliding member 304 that slides against belt 301, the contact area between sliding member 304 and belt 301 is reduced, thereby reducing the sliding resistance between sliding member 304 and belt 301. Protrusions 304b, 304d have flat tip surfaces and are formed in a substantially cylindrical shape except for protrusions 304d at both ends in the width direction, as will be described later.

[0039] 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, including the plurality of protrusions 304b, with a 20 μm-thick PTFE. 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. In this embodiment, the sliding layer 304c is provided on the base layer 304a. However, an adhesive layer may be provided between the base layer 304a and the sliding layer 304c. The use of an adhesive layer can provide good adhesive strength between the base layer 304a and the sliding layer 304c when the base layer 304a is made of a metal material such as stainless steel, copper, or aluminum.

[0040] 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.

[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. 4, 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] FIG. 5 is a schematic diagram showing the relationship between the sliding member 304 and the belt 301 at the widthwise end. Focusing on the protrusion 304d at the outermost end in the width direction of the sliding member 304 (also referred to as the widthwise end), a gap is formed at the contact point with the belt 301 outside the protrusion 304d in the width direction, creating a step along which the belt 301 bends. Therefore, compared to the other protrusions 304b, the protrusion 304d at the widthwise end rotates in a state where the belt 301 is in strong contact with the outer end (in other words, the outer edge) of both widthwise end portions of the tip surface of the protrusion 304d. As a result, the sliding layer 304c covering the edge of the protrusion 304d at the widthwise end and the inner circumferential surface of the belt 301 that rubs against it are more likely to wear.

[0043] When the sliding layer 304c wears and wear debris accumulates in the gap between the sliding member 304 and the pad 303, the wear debris adhering to the gap may scratch the inner surface of the belt 301, potentially causing damage to the belt 301. Furthermore, increased sliding resistance may increase the driving torque, potentially shortening the life of the sliding member 304. Therefore, in order to improve the life of the sliding member 304, it is necessary to suppress wear of the sliding layer 304c of the protrusions 304d at the outermost ends in the width direction. Furthermore, if the inner circumferential surface of the belt 301 is prone to wear, the life of the belt 301 will be shorter than expected, so it is also necessary to suppress wear on the inner circumferential surface of the belt 301.

[0044] [Image forming area and non-image forming area] FIG. 6 is a schematic diagram showing the shape and arrangement of the protrusions of the sliding member 304. As shown in the figure, the surface of the sliding member 304 that slides against the belt 301 is composed of an image forming area, area A, and a non-image forming area, area B. The image forming area (area A) is the area on the surface of the sliding member 304 that slides against the belt 301 where a recording material of the maximum size that can be fixed by the fixing device 8 passes through the nip N. The non-image forming area (area B) is the area on the surface of the sliding member 304 that slides against the belt 301 that is outside the image forming area in the width direction. Note that in FIG. 6, the protrusion 304d at the outermost end in the width direction is shown as having a substantially cylindrical shape like the other protrusions 304b. However, in this embodiment, the protrusion 304d has a shape shown in FIG. 9, for example. The shape of the protrusion 304d may be different from that shown in FIG. 9, such as the shapes shown in FIG. 6 and FIGS. 7(b) and (c) described below, as long as the conditions described below are satisfied.

[0045] As shown in FIG. 9, the protrusions 304b in region A are circular. On the other hand, the protrusions 304d at the widthwise extreme end are polygonal. If polygonal protrusions were provided in region A, there is a risk of gloss streaks appearing as lines on the printed matter. Therefore, circular protrusions 304b are provided in region A, which is within the image forming region. On the other hand, the protrusions 304d at the widthwise extreme end are polygonal. Since the widthwise extreme end is not an image forming region, gloss streaks do not need to be considered. Therefore, the polygonal shape can reduce wear on the belt 301. The polygonal shape here includes a shape with chamfered corners, as shown on the left of FIG. 7(C). In this embodiment, a triangular or rectangular shape is used as the polygonal shape.

[0046] [Protrusion Edge] Regarding the shape of the protrusions 304b and 304d of the sliding member 304, as shown in Figures 7(a) to 7(c), the length of contact between the belt 301 and the edges of the protrusions 304b and 304d during rotational driving is defined as ridge line L. The ridge line L of the protrusion 304b located in region A is denoted as LA, and the ridge line L of the protrusion 304d located at the widthwise end of region B is denoted as LB. In this case, if one protrusion 304b (or 304d) has multiple ridge lines L of different lengths, for example, as shown in Figures 7(b) and 7(c), the longest ridge line L of the protrusion 304b located in region A is defined as LA, and the outermost ridge line L in the widthwise direction of the protrusion 304d at the widthwise end is defined as LB. That is, in the image forming area (area A), of the two widthwise ends of the tip surface of the protrusion 304b, the line of the end (hereinafter also referred to as the edge) that is longer in the recording material conveyance direction is defined as the first ridge line, and the length of the first ridge line is defined as LA. Also, in the non-image forming area (area B), the line of the outer widthwise end (hereinafter also referred to as the edge) of the tip surface of the protrusion 304d that is positioned outermost in the width direction is defined as the second ridge line, and the length of the second ridge line is defined as LB. In this embodiment, the second ridge line is a straight line that is approximately parallel to the recording material conveyance direction.

[0047] By lengthening the ridgeline L, the pressure acting on the edges of the protrusions 304b and 304d is dispersed, thereby reducing the amount of wear on the sliding layer 304c at the edges of the protrusions 304b and 304d. Wear on the inner circumferential surface of the belt 301 can also be suppressed. On the other hand, as shown in FIG. 8, when the ridgeline L is lengthened, the contact area between the protrusions 304b and 304d and the belt 301 increases, which increases the viscous resistance of the lubricant applied to the inner surface of the belt 301, thereby increasing the friction coefficient μ. Continuing rotation with μ high may accelerate wear on the sliding layer 304c, shortening the life of the sliding member 304. Therefore, by shortening the length LA of the first ridge of protrusion 304b located in region A, which occupies a wide area in the region where protrusions 304b, 304d of sliding member 304 are arranged, and lengthening the length LB of the second ridge of protrusion 304d located at the widthwise extreme end of region B, it is possible to suppress wear of sliding layer 304c of protrusion 304d at the widthwise extreme end while maintaining a low friction coefficient μ of protrusion 304b, thereby suppressing the impact on the rotational operation of belt 301.

[0048] Therefore, in this embodiment, the average length of LA of the plurality of protrusions 304b in the region A (image forming region) is LA ave The average length of LB of the plurality of protrusions 304d in the region B (non-image forming region) is LB ave In this case, LB ave >LA ave In this way, the average ridge length LB of the projections 304d at the widthwise outermost ends of the region B is ave The average ridge length LA of the protrusions 304b located in the region A ave By making it longer than this, the life of the sliding member 304 can be improved.

[0049] At this time, the average edge length LB ave and L.A. ave is calculated as follows: LA ave is the average length LA of all the protrusions 304b in the image forming area (area A). ave is the average length LB of all the protrusions 304d in the non-image forming area (area B). ave The LB may be the longest average length of the LA of the plurality of protrusions 304b in one row along the conveying direction among the plurality of protrusions 304b in the image forming area. ave may be the average length of LB of the plurality of protrusions 304b that have LB greater than the median value among the plurality of protrusions 304d in the non-image forming region.

[0050] 9 shows an example of a sliding member 304 having protrusions 304b, 304d shaped to satisfy the above-mentioned conditions. In the example shown in FIG. 9, the multiple protrusions 304b in region A have a generally cylindrical shape with a circular tip surface, and the protrusion 304d at the widthwise end of region B has a generally triangular prism shape with a triangular tip surface. The protrusion 304d at the widthwise end of region B is formed so that one side of the triangle is located at the outer end in the width direction and is generally parallel to the conveyance direction. The protrusions 304b other than the protrusion 304d in region B are formed in the same manner as the protrusions 304b in region A.

[0051] 10 shows the change in the surface pressure applied to the surfaces of protrusions 304b and 304d when the ridge lengths LA and LB are changed. The surface pressure of protrusion 304d with ridge length LB is greater than the surface pressure of protrusion 304b with ridge length LA because protrusion 304d is located only at the outermost end in the width direction and therefore experiences a greater contact pressure with belt 301 than protrusion 304b.

[0052] Fig. 11 shows the change in the wear rate when the ridge length L is changed. The value of the wear rate (µm / 100K sheets) was calculated as the amount of wear (µm) of the sliding layer 304c per 100K sheets (100 x 1000 sheets) of recording material passed through the nip portion N from the relationship between the ridge length L and the surface pressure in Fig. 10.

[0053] The threshold wear rate for maintaining the sliding layer 304c within the design life of the fixing device 8 is 3 μm / 100,000 sheets. If this threshold is exceeded, the sliding layer 304c will be worn away by the rotation of the belt 301 before the fixing device 8 reaches its lifespan of 1,000,000 sheets (1,000 x 1,000 sheets of recording material passing through the nip portion N), which may increase friction and shorten the lifespan of the fixing device 8. As shown in FIG. 11, in order to suppress wear of the sliding layer 304c and prevent the sliding member 304 from having a short lifespan, it is preferable that the length LB of the second ridgeline be 2 mm or more (LB≧2 mm).

[0054] Furthermore, to confirm possible adverse effects of increasing LB, the lubrication state of the belt 301 and the surface of the protrusions 304d was investigated. In this embodiment, a lubricant is applied to the inner surface of the belt 301 to reduce the sliding resistance between the belt 301 and the surface of the protrusions 304d. When the thickness of the lubricant (oil film) approaches the surface roughness of the sliding layer 304c, the belt 301 and the protrusions 304d come into solid contact with each other, increasing the coefficient of friction.

[0055] Here, the oil film parameter Λ is the minimum oil film thickness h min and the composite roughness σ, and is expressed by the following formula: σ1 and σ2 are the root mean square roughness of each surface.

number

[0056] When Λ>3, a fluid lubrication state occurs with almost no solid contact. In other words, to maintain fluid lubrication with a low friction coefficient and allow belt 301 to continue rotating without any problems, it is necessary to ensure a lubricant thickness that is at least three times the surface roughness of sliding layer 304c. Since the surface roughness of sliding layer 304c after 1000K sheets of recording material, which is the lifespan of fixing device 8, have passed through nip portion N is approximately 0.8 μm, it is sufficient to ensure a lubricant thickness of at least 2.4 μm, which is three times that amount.

[0057] To investigate the effect on the lubricant thickness when the length LB of the second ridge line is changed, several levels of sliding member 304 with LB of 0.5 to 8 mm were prepared, and the thickness (μm) of the lubricant flowing into protrusion 304d during the rotation of belt 301 was measured. Figure 12 shows the measurement results.

[0058] As is clear from FIG. 12, the lubricant thickness decreases as LB increases. When LB exceeds 5 mm, the lubricant thickness falls below 2.4 μm, which is the threshold lubricant thickness for maintaining a low coefficient of friction. The reason for this is as follows: The lubricant that flows into the protrusions 304d is scraped off at the contact area between the tips of the protrusions 304d and the belt 301 as the protrusions 304d pass by. As LB increases, the contact area in the conveyance direction becomes longer, and the amount of scraped lubricant increases, making it more likely that the lubricant on the surface of the protrusions 304d will be depleted. Therefore, when LB exceeds 5 mm, a large amount of lubricant is scraped off as the protrusions 304d pass by, making it impossible to ensure the lubricant thickness necessary to maintain a low coefficient of friction. For this reason, it is preferable that the length LB of the second ridge be 5 mm or less (LB≦5 mm).

[0059] For the above reasons, it is preferable that the length LB of the second ridgeline satisfy the condition 2 mm≦LB≦5 mm. Satisfying this condition effectively suppresses wear of the sliding layer 304c at the edge of the widthwise end protrusions 304d, thereby improving the lifespan of the sliding member 304 and the belt 301. As a result, it is possible to prevent the sliding member 304 and the belt 301 from reaching the end of their lifespan within the lifespan of the fixing device 8, thereby preventing a shortened lifespan of the fixing device 8. Furthermore, it is possible to prevent gloss streaks from occurring in the image forming area and to prevent wear of the belt 301 due to friction between the widthwise end protrusions 304d and the inner circumferential surface of the belt 301, thereby preventing a deterioration in image quality and preventing a shortened lifespan of the belt 301.

[0060] <Second embodiment> The second embodiment will be described with reference to Figure 13. In the first embodiment described above, the range of LB was specified to suppress wear at the edge of the widthwise outermost protrusion 304d. In contrast, in this embodiment, the length of LA is also specified to further improve the life of the sliding member. Since the other configurations and functions are the same as those of the first embodiment described above, the same configurations are assigned the same reference numerals and explanations and illustrations are omitted. The following description will focus on the points that are different from the first embodiment.

[0061] To investigate the effect of varying the length LA of the first ridge of the protrusion 304b in region A on the drive torque of the belt 301, we prepared several levels of the sliding member 304 with LA ranging from 0.2 to 1.2 mm and conducted a drive durability test. A sliding member with LB of 4 mm was used. These sliding members 304 were sequentially inserted into the fixing device 8 and the drive durability test was conducted. The drive durability test was conducted in a mode in which the pressure roller 305, which rotates the belt 301, alternated between contacting and non-contacting with the belt 301. The design target time in this mode was 240 hours. If the drive torque exceeded a preset upper limit within the design target time, the drive durability test was terminated. 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 upper limit (threshold) of the drive torque was set at 300 mNm, at which point slippage could cause image defects or damage to the drive gear. The viscosity η of the lubricant was 1000 mm. 2 The test was carried out with the recording material conveying speed v set to 435 mm / s.

[0062] The results of the drive durability test described above are shown in Figure 13. Figure 13 shows the change in drive torque (mNm) versus LA. The longer the LA, the greater the drive torque. When LA exceeded 1 mm, the drive torque exceeded the threshold value of 300 mNm. When the state of the sliding member was checked, no disappearance of the sliding layer 304c at the tip of the protrusion 304b was observed. This suggests that as the LA length increased, the contact area between the protrusion 304b and the belt 301 increased, increasing the viscous resistance of the lubricant applied to the belt 301, which led to an increase in drive torque. Continued use with the drive torque exceeding the threshold value could result in the rotation stopping and a shortened lifespan. For this reason, in this embodiment, it is preferable that LA be 1 mm or less (LA ≦ 1 mm).

[0063] Furthermore, when LA is 0.1 mm or less, the tips of the protrusions 304b are very small and sharp, and it was confirmed that the sliding layers 304c of the multiple protrusions 304b are lost during the manufacturing stage. For this reason, it was determined that a durability test was not necessary. For this reason, in this embodiment, LA is preferably 0.2 mm or more (LA≧0.2 mm).

[0064] From the above, it is preferable that the length LA of the first ridge line satisfies 0.2 mm≦LA≦1 mm. By satisfying this condition, an increase in the driving torque of the belt 301 can be suppressed, and the life of the fixing device 8 can be further improved.

[0065] <Third embodiment> The third embodiment will be described with reference to Figures 14(a) to 15. In the first and second embodiments described above, the edge (second ridge) of the protrusion 304d at the widthwise extreme end of region B is formed substantially parallel to the conveying direction of the recording material. In contrast, in this embodiment, the edge (second ridge) of the protrusion 304d1 at the widthwise extreme end of region B is inclined with respect to the conveying direction. Since the other configurations and functions are the same as those of the first or second embodiment described above, the same reference numerals are used for the similar configurations and descriptions and illustrations are omitted, and the following description will focus on the differences from the first and second embodiments.

[0066] FIG. 14(a) shows a sliding member similar to that shown in FIG. 9, but in this embodiment, the protrusion 304d1 at the widthwise outermost end of region B has the shape shown in FIG. 14(b). That is, the protrusion 304d1 has a substantially triangular prism shape with a triangular tip surface. The protrusion 304d1 is formed so that one side of the triangle is located at the outer end in the width direction and is inclined at an angle θ with respect to the conveying direction. Note that the shape of the protrusion 304d1 is not limited to a triangular shape, and may be any shape with a straight portion, such as the shapes shown in FIGS. 7(b) and (c), as long as this straight portion is located at the outer end in the width direction.

[0067] With this configuration, the effect of suppressing wear at the edge of the protrusion 304d1 at the endmost position in the width direction was verified. In the verification, multiple levels of the sliding member 304 were prepared with θ changed in the range of -20 to 20°, and the driving durability test described in Fig. 13 of the second embodiment was performed, and verification similar to that in Fig. 11 of the first embodiment was performed. In this case, sliding members with LA of 0.5 mm and LB of 4 mm were used.

[0068] The results of the above verification are shown in Figure 15. Figure 15 shows the change in the wear rate versus the angle θ (°) of the edge of the protrusion 304d1. The wear rate was calculated by measuring the thickness of the sliding layer 304c at the start and end of the drive durability test, and converting the difference between the measured values ​​into the amount of wear equivalent to when 100,000 sheets of recording material were passed through the nip N.

[0069] As is clear from Figure 15, when θ is -15°≦θ≦15°, the wear rate is below 3 μm / 100K, which is the threshold value for maintaining the sliding layer 304c within the design life. When the condition of the edge of the widthwise outermost protrusion 304d1 was confirmed, the sliding layer 304c was found to be sufficiently intact. On the other hand, when θ is less than -15° or greater than 15°, the wear rate exceeds the threshold value of 3 μm / 100K, and it was confirmed that the sliding layer 304c at the edge of the widthwise outermost protrusion 304d1 has disappeared. This is thought to be because the edge of the protrusion 304d1, which had followed the rotation of the belt 301 and made line contact with the entire second ridgeline until θ became a certain value from 0°, no longer followed the rotation as θ increased. In other words, it is believed that as θ increased, the edge of the protrusion 304d1 came into partial point contact with the belt 301, resulting in a large local pressure, which accelerated wear of the sliding layer 304c.

[0070] As described above, as long as the angle θ of the second ridge line with respect to the conveying direction is in the range of -15°≦θ≦15°, regardless of the arrangement of the protrusions 304d1 at the widthwise end, the wear of the sliding layer 304c at the edge of the protrusions 304d1 can be effectively suppressed, thereby improving the life of the sliding member. Furthermore, as in the first embodiment, the wear of the belt 301 can also be suppressed.

[0071] <Fourth embodiment> The fourth embodiment will be described with reference to Figures 16(a) to 16(c). In the above-described embodiments, the edge portions (second ridge lines) of the protrusions 304d, 304d1 at the widthwise extreme ends of region B are straight. In contrast, in this embodiment, the edge portion (second ridge line) of the protrusion 304d2 at the widthwise extreme end of region B is curved. Since the other configurations and functions are the same as those of the first or second embodiment described above, the same reference numerals are used for the similar configurations, and description and illustration thereof will be omitted. The following description will focus on the differences from the first and second embodiments.

[0072] In this embodiment, the second ridge line (shown by the thick line) of the protrusion 304d2 at the widthwise end of region B is curved, as shown in Figures 16(a) to 16(c). In the illustrated example, the shape of the tip end surface of the protrusion 304d2 is elliptical, but the same applies to other shapes having a curve, such as a sector shape.

[0073] With this configuration, the effect of suppressing wear at the edge of the protrusion 304d2 at the endmost position in the width direction was verified. In the verification, multiple levels of the sliding member 304 were prepared with θ changed in the range of -20 to 20°, and the drive durability test described in FIG. 13 of the second embodiment was performed, and verification similar to that in FIG. 11 of the first embodiment was performed. Note that when the edge of the protrusion 304d2 is curved, the angle at which the tangent to the second ridgeline is inclined with respect to the conveyance direction was defined as θ, as shown in FIG. 16(b).

[0074] 16(c), it was confirmed that when θ is within the range of -15°≦θ≦15°, the sliding layer 304c at the edge of the protrusion 304d2 at the outermost end in the width direction remains after the durability test, and the wear rate value is also within the threshold range. This is thought to be because, as in the third embodiment, until θ reaches a certain value, the edge of the protrusion 304d2 follows the movement of the belt 301 during rotation, and the edge comes into line contact, thereby dispersing pressure.

[0075] From the above, even if the edge of the protrusion 304d2 is curved, as long as θ is within the range of −15°≦θ≦15°, the edge of the widthwise outermost protrusion 304d2 in region B can be regarded as the second ridgeline, as in the case where the edges (second ridgelines) of the protrusions 304d and 304d1 described in the above embodiments are straight. In other words, even if the second ridgeline is curved, if it is a line similar to a straight line, by setting the angle θ within the range of −15°≦θ≦15°, it is possible to obtain the effect of suppressing wear of the sliding layer 304c at the edge of the widthwise outermost protrusion 304d2. Furthermore, as in the first embodiment, wear of the belt 301 can also be suppressed. Note that, even if the first ridgeline is curved, a line at the edge of the protrusion 304b, at which the angle θ of the tangent to the conveyance direction is in the range of −15°≦θ≦15°, can be regarded as the first ridgeline. [Explanation of symbols]

[0076] 8. Fixing device 301···Belt 303 Pad (backup member) 304...Sliding member 304b, 304d, 304d1, 304d2...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, an area on the surface of the sliding member that slides against the belt, where a recording material of a maximum size passes through the nip portion, is defined as an image forming area, and an area outside the image forming area in a width direction of the recording material that intersects with the conveying direction of the recording material is defined as a non-image forming area; In the image forming area, a line at an end of the tip surface of the protrusion that is longer in the conveying direction of the recording material than the other end in the width direction is defined as a first ridge line, and a length of the first ridge line is defined as LA, In the non-image forming region, a line of an outer end portion in the width direction of a tip surface of the protrusion positioned outermost in the width direction is defined as a second ridge line, and a length of the second ridge line is defined as LB, The average length of the LA of the plurality of protrusions in the image forming area is LA ａｖｅ year, The average length of the LB of the plurality of protrusions in the non-image forming area is LB ａｖｅ In this case, <h2 style=";text-align:left;direction:ltr">LB<h2 style=";text-align:left;direction:ltr"> ａｖｅ <h2 style=";text-align:left;direction:ltr"> >LA<h2 style=";text-align:left;direction:ltr"> ａｖｅ A fixing device characterized by satisfying the above.

2. LB≧2mm 2. The fixing device according to claim 1, wherein the above formula (1) is satisfied.

3. LB≦5mm 2. The fixing device according to claim 1, wherein the above formula (1) is satisfied.

4. LA≧0.2 mm 2. The fixing device according to claim 1, wherein the above formula (1) is satisfied.

5. LA≦1 mm 2. The fixing device according to claim 1, wherein the above formula (1) is satisfied.

6. The second ridge line is a straight line substantially parallel to the conveying direction.

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 second ridge line is a straight line inclined with respect to the conveying direction.

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. When the angle of the second ridge line with respect to the conveying direction is θ, -15°≦θ≦15° 8. The fixing device according to claim 7, wherein the above expression is satisfied.

9. the second ridge is a curve, When the angle at which the tangent to the second ridge line is inclined with respect to the conveying direction is θ, -15°≦θ≦15° 2. The fixing device according to claim 1, wherein the above formula (1) is satisfied.

10. The LA ａｖｅ is the average length of the LA of all protrusions in the image forming area 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. Said LB ａｖｅ is the average length of the LB of all protrusions in the non-image forming area 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. The LA ａｖｅ is the longest average length of the LA of the plurality of protrusions in one row along the conveying direction among the plurality of protrusions in the image forming area.

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. Said LB ａｖｅ is the average length of the LB of the plurality of protrusions in the non-image forming area that are larger than the median value.

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.

14. 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.

15. 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.

15. The fixing device according to claim 14.

16. 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.

17. 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.

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

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.

19. The tip surface of the protrusion positioned outermost in the width direction is polygonal.

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.

20. The tip surface of the protrusion in the image forming area is circular.

20. The fixing device according to claim 19.

Images