Fixing device and image forming apparatus

Abstract

To provide a fixing device and an image forming device in which the warm-up time and the first print time are short, and no fixing failure occurs even when the device is operated at high speed, and a fixing member in a state where a reinforcing member is in pressure contact with the fixing member does not fall. [Solution] A fixed member 26 is provided, which is pressed against a pressure rotor 31 via a fixing belt 21 to form a nip portion, and a reinforcing member 23 is provided to abut against the fixed member 26 from the inside of the fixing belt 21 and reinforce the fixed member 26. The fixed member 26 has protrusions 26a, 26b formed in multiple rows along the conveyance direction, which protrude toward an opposing surface 23a of the reinforcing member 23 so as to abut against the reinforcing member 23.

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, or a combination machine thereof, and a fixing device installed therein. [Background technology]

[0002] Conventionally, in image forming devices such as copiers and printers, fixing devices have been known that have short warm-up times and first print times, and are less likely to cause fixing failures even when the device is operated at high speed (see, for example, Patent Document 1).

[0003] 2, 4, etc. of Patent Document 1 are composed of a fixing belt (reference number 21), a pipe-shaped heating member (reference number 22) fixedly disposed so as to face the inner peripheral surface of the fixing belt except for the nip portion, a heater (reference number 25) disposed inside the heating member for heating the heating member, a fixed member (reference number 26) disposed inside the fixing belt for forming the nip portion by pressing the fixing belt against a pressure roller (reference number 31) via the fixing belt, and a substantially plate-shaped reinforcing member (reference number 23) for reinforcing the fixed member by contacting it, etc. The substantially plate-shaped reinforcing member is formed with a relatively narrow width (length in the transport direction) so as to contact a part of the surface of the fixed member. The fixing belt is then heated by a pipe-shaped heating member heated by a heater, and the toner image on the recording medium transported toward the nip portion is fixed onto the recording medium by receiving heat and pressure at the nip portion. Summary of the Invention [Problem to be solved by the invention]

[0004] In the fixing device of Patent Document 1 mentioned above, the fixed member is installed so as to be fitted into the recess of the pipe-shaped heating member, so that the contact area (contact width) of the reinforcing member that comes into contact with the fixed member is narrow, and even if the balance of the forces that the fixed member receives from the reinforcing member becomes poor, the fixed member does not fall over.

[0005] On the other hand, in the fixing device of Patent Document 1 and the like, in order to further improve the heating efficiency of the fixing belt and reduce the cost and size of the device, it is conceivable to adopt a configuration in which the pipe-shaped heating member is removed and the fixing belt is heated directly by a heating means without going through the pipe-shaped heating member. In that case, however, there is no heating member (recess) to prevent the fixed member from falling over, and the reinforcing member cannot hold the fixed member in a balanced manner while it is pressed against the fixed member, which may result in the fixed member falling over. If the fixed member falls over in this way, the desired nip cannot be formed, which may result in poor fixing of the output image or poor transport of the recording medium.

[0006] The present invention has been made to solve the above-mentioned problems, and provides a fixing device and an image forming apparatus which have short warm-up times and first print times, and which do not cause fixing failures even when the device is operated at high speed, and which do not cause the fixed member to collapse when the reinforcing member is pressed against it. [Means for solving the problem]

[0007] The fixing device according to the invention described in claim 1 includes a flexible endless fixing belt, a nip forming member disposed inside the fixing belt and sandwiching the fixing belt with a pressure rotating body to form a nip portion where a recording medium is transported between the fixing belt and the pressure rotating body, a heat source facing the fixing belt and heating the fixing belt, a reinforcing member disposed inside the fixing belt and having an opposing surface that abuts against the nip forming member, and a pair of guide members that guide both ends of the fixing belt in the width direction, and the nip forming member has an upstream abutment portion that abuts against the opposing surface on the upstream side in a transport direction of a recording medium, a downstream abutment portion that abuts against the opposing surface on the downstream side in the transport direction, and a non-abutment portion that does not abut against the opposing surface between the upstream abutment portion and the downstream abutment portion. and a surface of the pressure rotating body with which the fixing belt slides is formed to be flat or curved so as to follow the curvature of the pressure rotating body,A sheet-like member is interposed between the nip forming member and the fixing belt.

[0008] In this application, the "fixed" state of the fixing member or the reinforcing member is defined as a state in which the fixing member or the reinforcing member is held in a non-rotating state without being rotationally driven. Therefore, for example, even if the fixing member is biased toward the nip portion by a biasing means such as a spring, the fixing member is in a "fixed" state as long as the fixing member is held in a non-rotating state.

[0009] In addition, in this application, the "transport direction" of the recording medium is defined as the same direction as the tangent direction of the nip portion when the fixing belt and the pressure rotor abut in an ideal arc without being deformed at the nip portion. In the present application, the "width direction" is defined as a direction perpendicular to the transport direction and the same direction as the rotation axis direction of the fixing belt and the pressure rotating body. Effect of the Invention

[0010] In the present invention, the fixed member has a plurality of rows of protruding portions formed along the transport direction, the protruding portions protruding toward the reinforcing member so as to come into contact with the reinforcing member. This makes it possible to provide a fixing device and an image forming apparatus that have a short warm-up time and a short first print time, do not cause fixing failures even when the device is operated at high speed, and do not cause the fixed member to fall when the reinforcing member is in pressure contact with it. [Brief description of the drawings]

[0011] [Figure 1] 1 is an overall configuration diagram showing an image forming apparatus according to a first embodiment of the present invention. [Diagram 2] FIG. 2 is a diagram illustrating a configuration of a fixing device. [Diagram 3] FIG. 2 is a side view of the fixing device as viewed in the width direction. [Figure 4] FIG. 4 is an enlarged view showing the vicinity of a nip portion. [Diagram 5]4 is a cross-sectional side view showing a state in which the fixing belt is held by a holding member. FIG. [Figure 6] 4 is a schematic front view showing a state in which the fixing belt and the reinforcing member are held by a holding member; FIG. [Figure 7] 1A and 1B are a side view and a bottom view, respectively, showing a fixing member covered with a sheet-like member. [Figure 8] 7A, (A) is a schematic cross-sectional view showing the X1-X1 cross section, (B) is a schematic cross-sectional view showing the X2-X2 cross section, and (C) is a schematic cross-sectional view showing the X3-X3 cross section. [Figure 9] 1A and 1B are a side view and a bottom view, respectively, showing a fixing member. [Figure 10] FIG. [Figure 11] FIG. [Figure 12] FIG. 11 is a configuration diagram showing a fixing device according to a second embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, the embodiments of the present invention will be described in detail with reference to the drawings. In each drawing, the same or corresponding parts are denoted by the same reference numerals, and the duplicated description will be appropriately simplified or omitted.

[0013] Embodiment 1 The first embodiment of the present invention will be described in detail with reference to Figs. 1 to 11. First, the overall configuration and operation of the image forming apparatus will be described with reference to FIG. 1, the image forming apparatus 1 in the present embodiment 1 is a tandem type color printer. In a bottle storage section 101 located at the top of the image forming apparatus main body 1, four toner bottles 102Y, 102M, 102C, and 102K corresponding to each color (yellow, magenta, cyan, and black) are detachably (replaceably) installed. An intermediate transfer unit 85 is disposed below the bottle storage unit 101. Opposite to the intermediate transfer belt 78 of the intermediate transfer unit 85, image forming units 4Y, 4M, 4C, and 4K corresponding to each color (yellow, magenta, cyan, and black) are arranged side by side.

[0014] Photoconductor drums 5Y, 5M, 5C, and 5K are disposed in the image forming units 4Y, 4M, 4C, and 4K, respectively. A charging unit 75, a developing unit 76, a cleaning unit 77, a discharging unit (not shown), and the like are disposed around each of the photoconductor drums 5Y, 5M, 5C, and 5K. An image forming process (charging process, exposure process, developing process, transfer process, and cleaning process) is performed on each of the photoconductor drums 5Y, 5M, 5C, and 5K, and an image of each color is formed on each of the photoconductor drums 5Y, 5M, 5C, and 5K.

[0015] The photoconductor drums 5Y, 5M, 5C, and 5K are rotated clockwise in Fig. 1 by a drive motor (not shown). Then, at the position of the charging unit 75, the surfaces of the photoconductor drums 5Y, 5M, 5C, and 5K are uniformly charged (charging process). Thereafter, the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K reach the irradiation position of the laser light L emitted from the exposure unit 3, and an electrostatic latent image corresponding to each color is formed by exposure scanning at this position (this is the exposure process).

[0016] Thereafter, the surfaces of the photoconductor drums 5Y, 5M, 5C, and 5K reach positions facing the developing devices 76, where the electrostatic latent images are developed to form toner images of the respective colors (developing process). Thereafter, the surfaces of the photoconductor drums 5Y, 5M, 5C, and 5K reach positions facing the intermediate transfer belt 78 and the first transfer bias rollers 79Y, 79M, 79C, and 79K, and at these positions the toner images on the photoconductor drums 5Y, 5M, 5C, and 5K are transferred onto the intermediate transfer belt 78 (this is the first transfer step). At this time, a small amount of untransferred toner remains on the photoconductor drums 5Y, 5M, 5C, and 5K.

[0017] Thereafter, the surfaces of the photoconductor drums 5Y, 5M, 5C, and 5K reach a position facing the cleaning unit 77, at which point the untransferred toner remaining on the photoconductor drums 5Y, 5M, 5C, and 5K is mechanically collected by the cleaning blade of the cleaning unit 77 (this is the cleaning process). Finally, the surfaces of the photoconductor drums 5Y, 5M, 5C, and 5K reach a position facing a charge removing unit (not shown), where the residual potential on the photoconductor drums 5Y, 5M, 5C, and 5K is removed. Thus, a series of image forming processes carried out on the photoconductor drums 5Y, 5M, 5C, and 5K is completed.

[0018] Thereafter, the toner images of the respective colors formed on the respective photosensitive drums through a developing process are transferred in a superimposed manner onto the intermediate transfer belt 78. In this way, a color image is formed on the intermediate transfer belt 78. Here, the intermediate transfer unit 85 is composed of the intermediate transfer belt 78, four primary transfer bias rollers 79Y, 79M, 79C, 79K, a secondary transfer backup roller 82, a cleaning backup roller 83, a tension roller 84, an intermediate transfer cleaning section 80, etc. The intermediate transfer belt 78 is stretched and supported by three rollers 82 to 84, and is moved endlessly in the direction of the arrow in FIG.

[0019] The four primary transfer bias rollers 79Y, 79M, 79C, and 79K form primary transfer nips by sandwiching the intermediate transfer belt 78 between the photoconductor drums 5Y, 5M, 5C, and 5K, respectively. A transfer bias opposite to the polarity of the toner is applied to the primary transfer bias rollers 79Y, 79M, 79C, and 79K. Then, the intermediate transfer belt 78 travels in the direction of the arrow and passes sequentially through the primary transfer nips of the primary transfer bias rollers 79Y, 79M, 79C, and 79K. In this way, the toner images of each color on the photoconductor drums 5Y, 5M, 5C, and 5K are primarily transferred onto the intermediate transfer belt 78 in a superimposed manner.

[0020] Thereafter, the intermediate transfer belt 78 onto which the toner images of each color have been transferred and superimposed reaches a position facing the secondary transfer roller 89. At this position, the secondary transfer backup roller 82 pinches the intermediate transfer belt 78 between itself and the secondary transfer roller 89 to form a secondary transfer nip. The four-color toner images formed on the intermediate transfer belt 78 are then transferred onto the recording medium P that has been conveyed to the position of this secondary transfer nip. At this time, untransferred toner that has not been transferred to the recording medium P remains on the intermediate transfer belt 78. Thereafter, the intermediate transfer belt 78 reaches the position of the intermediate transfer cleaning unit 80. At this position, the untransferred toner on the intermediate transfer belt 78 is collected. Thus, a series of transfer processes carried out on the intermediate transfer belt 78 is completed.

[0021] Here, the recording medium P transported to the position of the secondary transfer nip is transported from the paper feed section 12 arranged below the device main body 1 via a paper feed roller 97, a pair of registration rollers 98 (a pair of timing rollers), etc. More specifically, a plurality of recording media P, such as transfer paper, are stored in a stack in the paper feed section 12. When the paper feed roller 97 is rotated counterclockwise in FIG. 1, the topmost recording medium P is fed toward between the pair of registration rollers 98.

[0022] The recording medium P conveyed to the registration roller pair 98 stops temporarily at the roller nip of the registration roller pair 98, which has stopped rotating. Then, in synchronization with the color image on the intermediate transfer belt 78, the registration roller pair 98 is rotated and the recording medium P is conveyed toward the secondary transfer nip. In this way, the desired color image is transferred onto the recording medium P.

[0023] Thereafter, the recording medium P onto which the color image has been transferred at the secondary transfer nip position is transported to the position of the fixing unit 20. Then, at this position, the color image transferred onto the surface is fixed onto the recording medium P by heat and pressure from the fixing belt 21 and the pressure roller 31. Thereafter, the recording medium P is discharged to the outside of the apparatus through a pair of discharge rollers 99. The recording medium P discharged to the outside of the apparatus by the pair of discharge rollers 99 is sequentially stacked on a stack unit 100 as an output image. In this manner, a series of image forming processes in the image forming apparatus is completed.

[0024] Next, the configuration and operation of the fixing device 20 installed in the image forming apparatus main body 1 will be described in detail with reference to FIGS. 2 to 4, the fixing device 20 is composed of a fixing belt 21 (belt member) as a fixing member, a fixed member 26 (nip portion forming member), a reinforcing member 23, a heater 25 (heat source) as a heating means, a pressure roller 31 as a pressure rotating body, a temperature sensor 40, a sheet-like member 22, a screw 24, a plate-like member 28 (fixed plate), a reflecting member 27, etc.

[0025] Here, the fixing belt 21 is a thin, flexible endless belt that rotates (runs) in the direction of the arrow (counterclockwise) in Fig. 2. The fixing belt 21 has a base layer, an elastic layer, and a release layer laminated in this order from the inner peripheral surface 21a (the surface that comes into contact with the fixed member 26) side, and the overall thickness is set to 1 mm or less. The base layer of the fixing belt 21 has a thickness of 30 to 50 μm, and is made of a metal material such as nickel or stainless steel, or a resin material such as polyimide. The elastic layer of the fixing belt 21 has a thickness of 100 to 300 μm and is made of a rubber material such as silicone rubber, foamed silicone rubber, fluororubber, etc. By providing the elastic layer, minute irregularities are not formed on the surface of the fixing belt 21 at the nip portion, and heat is uniformly transferred to the toner image T on the recording medium P, preventing the occurrence of an orange peel image. The release layer of the fixing belt 21 has a layer thickness of 10 to 50 μm, and is made of materials such as PFA (tetrafluoroethylene-perfluoroalkylvinylether copolymer), PTFE (polytetrafluoroethylene), polyimide, polyetherimide, PES (polyether sulfide), etc. By providing the release layer, releasability (peelability) for the toner T (toner image) is ensured.

[0026] The diameter of the fixing belt 21 is set to be 15 to 120 mm. In the first embodiment, the inner diameter of the fixing belt 21 is set to be 30 mm. Fixed inside (on the inner circumferential surface side) of fixing belt 21 are a fixing member 26, a heater (heating means), a reinforcing member 23, a reflecting member 27, a sheet-like member 22, screws 24, a plate-like member 28 (fixing plate), and the like. Here, the fixed member 26 is fixed so as to be in sliding contact with the inner circumferential surface 21a of the fixing belt 21. The fixed member 26 is pressed against the pressure roller 31 via the fixing belt 21, thereby forming a nip portion through which the recording medium P is transported. With reference to Figs. 3 and 5, both ends of the fixed member 26 in the width direction are held by flanges 29 (holding members) fixedly supported by the side plates 43 of the fixing device 20. Also, both ends of the fixing belt 21 in the width direction are rotatably held by the flanges 29. The configurations of the fixed member 26 and the flanges 29 will be described in more detail later. The fixing belt 21 is directly heated by radiant heat from a heater 25 (heating means) installed inside the fixing belt 21.

[0027] Heater 25 as heating means is a halogen heater (or a carbon heater), and both ends thereof are fixed to side plates 43 of fixing device 20 (see FIG. 3). Then, the fixing belt 21 is heated mainly except for the nip portion by radiant heat from heater 25 (heating means) whose output is controlled by the power supply unit of the apparatus main body 1. Furthermore, heat is applied to the toner image T on recording medium P from the heated surface of fixing belt 21. The output control of heater 25 is performed based on the detection result of the belt surface temperature by temperature sensor 40 such as a thermistor facing the surface of fixing belt 21. Also, by such output control of heater 25, the temperature of fixing belt 21 (fixing temperature) can be set to a desired temperature. In the first embodiment, one heater 25 is provided on the inner circumferential surface side of the fixing belt 21, but a plurality of heaters may be provided on the inner circumferential surface side of the fixing belt 21.

[0028] In this way, in the fixing device 20 in the present embodiment 1, since only a part of the fixing belt 21 is heated locally, but the fixing belt 21 is heated over a relatively wide range in the circumferential direction, the fixing belt 21 is heated sufficiently and the occurrence of fixing defects can be suppressed even when the device is operated at high speed. In other words, since the fixing belt 21 can be heated efficiently with a relatively simple configuration, the warm-up time and the first print time are shortened, and the device can be made compact. In particular, the fixing device 20 in the present embodiment 1 is configured so that the fixing belt 21 is directly heated by the heater 25 (heating means), thereby further improving the heating efficiency of the fixing belt 21 and enabling the fixing device 21 to be further reduced in cost and size.

[0029] 5 and 6, the two flanges 29 serving as holding members are made of a heat-resistant resin material or the like, and are fitted into the side plates 43 at both ends in the width direction of the fixing device 20. The flanges 29 are provided with a guide portion 29a for holding the fixing belt 21 while maintaining the circular posture of the fixing belt 21, a stopper portion 29b for restricting the movement of the fixing belt 21 in the width direction (toward the belt), and the like. Further, low-friction portions 21a1 are formed on both ends of the inner peripheral surface 21a of the fixing belt 21 in the width direction (left-right direction in FIG. 5) to reduce sliding resistance at the sliding portion (encircled by the dashed line in FIG. 5) with the guide portion 29a of the flange 29. Specifically, the low-friction portions 21a1 are formed by coating the surface of the base layer with a low-friction material such as fluororesin. With this configuration, even if the fixing belt 21 and the flange 29 (guide portion 29a) come into sliding contact with each other as the fixing belt 21 rotates (runs), the fixing belt 21 and the flange 29 (guide portion 29a) are less likely to wear out and deteriorate. In this embodiment 1, the only members that come into contact with the inner circumferential surface 21a of the fixing belt 21 are the flanges 29 at both ends in the width direction and the fixed member 26, and there are no other members (belt guides) that come into contact with the inner circumferential surface 21a to guide the rotation of the fixing belt 21.

[0030] Here, in the present embodiment 1, the reinforcing member 23 for reinforcing the strength of the fixed member 26 forming the nip portion is fixed on the inner peripheral surface side of the fixing belt 21. Referring to FIG. 3, the reinforcing member 23 is formed so that its widthwise length is equal to that of the fixed member 26, and both ends in the widthwise direction are held by the flange 29 (holding member) of the fixing device 20. In detail, the position of the reinforcing member 23 is determined by being sandwiched between the flange 29 and the fixed member 26. Note that, in the present embodiment 1, as shown in FIG. 6, the end faces (reference surfaces 23b) of the two standing portions 23c (portions standing in a direction away from the opposing surface 23a) of the reinforcing member 23 abut against the holding portions 29c (see FIG. 6) of the flange 29 to hold the reinforcing member 23. In contrast, the reinforcing member 23 can be held by abutting against the side plate 43 instead of the holding portions 29c of the flange 29. Reinforcing member 23 abuts against pressure roller 31 via fixed member 26 and fixing belt 21, thereby preventing a problem in which fixed member 26 is significantly deformed by the pressure of pressure roller 31 at the nip portion. In the present embodiment 1, reinforcing member 23 is a plate-like member having a substantially U-shape with a recess facing the side where heater 25 is located. In order to satisfy the above-mentioned functions, reinforcing member 23 is preferably formed from a metal material having high mechanical strength, such as stainless steel or iron. The configuration of the reinforcing member 23 will be described in more detail later.

[0031] In the first embodiment, a reflecting member 27 (reflecting plate) is fixed to the side of the reinforcing member 23 that faces the heater 25. This allows the heat (heat that heats the reinforcing member 23) from the heater 25 to be reflected by the reflecting member 27 and used to heat the fixing belt 21, thereby further improving the heating efficiency of the fixing belt 21. The same effect can be obtained even if a part or the whole of the surface of the reinforcing member 23 facing the heater 25 is subjected to a mirror finish or provided with a heat insulating material.

[0032] 2, the pressure roller 31 as a pressure rotating body that contacts the outer circumferential surface of the fixing belt 21 at the nip portion has a diameter of 30 mm, and is formed by forming an elastic layer 33 on a hollow core metal 32. The elastic layer 33 of the pressure roller 31 (pressure rotating body) is made of a material such as foamed silicone rubber, silicone rubber, or fluororubber. A thin release layer made of PFA, PTFE, or the like may be provided on the surface of the elastic layer 33. The pressure roller 31 is pressed against the fixing belt 21 to form a desired nip portion between the two members. Also, referring to FIG. 3, the pressure roller 31 is provided with a gear 45 that meshes with a drive gear of a drive mechanism (not shown), and the pressure roller 31 is driven to rotate in the direction of the arrow in FIG. 2 (clockwise direction). Also, both ends of the pressure roller 31 in the width direction are rotatably supported by side plates 43 of the fixing device 20 via bearings 42. A heat source such as a halogen heater may be provided inside the pressure roller 31.

[0033] When the elastic layer 33 of the pressure roller 31 is made of a sponge-like material such as foamed silicone rubber, the pressure acting on the nip portion can be reduced, thereby reducing the load on the fixed member 16. Furthermore, the heat insulation of the pressure roller 31 is improved, and the heat of the fixing belt 21 is less likely to transfer to the pressure roller 31 side, thereby improving the heating efficiency of the fixing belt 21. In the first embodiment, the diameter of the fixing belt 21 is approximately equal to the diameter of the pressure roller 31, but the diameter of the fixing belt 21 can also be smaller than the diameter of the pressure roller 31. In that case, the curvature of the fixing belt 21 at the nip portion is smaller than the curvature of the pressure roller 31, so that the recording medium P sent out from the nip portion is easily separated from the fixing belt 21.

[0034] 4, fixed member 26, which is in sliding contact with inner circumferential surface 21a of fixing belt 21, has a surface (sliding surface) facing pressure roller 31 formed in a concave shape so as to conform to the curvature of pressure roller 31. As a result, recording medium P is sent out from the nip portion so as to conform to the curvature of pressure roller 31, and therefore it is possible to prevent a problem in which recording medium P is attracted to fixing belt 21 after the fixing process and is not separated. In the first embodiment, the fixed member 26 forming the nip portion is formed in a concave shape, but the fixed member 26 forming the nip portion can also be formed in a flat shape. That is, the sliding surface of the fixed member 26 (the surface facing the pressure roller 31) can be formed in a flat shape. This makes the shape of the nip portion approximately parallel to the image surface of the recording medium P, and the adhesion between the fixing belt 21 and the recording medium P is increased, thereby improving the fixing performance. Furthermore, the curvature of the fixing belt 21 at the exit side of the nip portion is large, so that the recording medium P sent out from the nip portion can be easily separated from the fixing belt 21.

[0035] Furthermore, the material for forming the fixing member 26 may be a resin material or a metal material, but a resin material (such as a liquid crystal polymer or polyamideimide) that has a degree of rigidity such that it does not bend significantly even when subjected to the pressure of the pressure roller 31, and has heat resistance and heat insulation properties is preferable. In the present embodiment 1, the material for the fixing member 26 is a liquid crystal polymer (LCP).

[0036] Moreover, the fixed member 26 is covered with a sheet-like member 22 made of a low-friction material such as PTFE in order to reduce the sliding resistance with the fixing belt 21. More specifically, the sheet-like member 22 is disposed so as to cover the periphery of the fixed member 26 (the periphery of the fixed member 26 as viewed in cross section as shown in FIG. 4) so ​​as to be interposed between the fixed member 26 and the fixing belt 21 in the width direction at the position of the nip portion. Moreover, the sheet-like member 22 in the present embodiment 1 is formed of a fiber material (a cloth member made of PTFE) impregnated with a lubricant such as silicone oil. This results in a state in which the lubricant is held on the surface where the fixed member 26 and the fixing belt 21 come into contact with each other. Therefore, the problem of both members 21 and 26 being worn due to the sliding contact between the fixed member 26 and the fixing belt 21 is reduced. The configurations of the sheet-like member 22 and the fixing member 26 will be described in more detail later.

[0037] In the first embodiment, the reinforcing member 23 (and the reflecting member 27) is disposed so as to isolate the space between the fixing member 26 and the heater 25 (heating means). In the first embodiment, the heater 25 is installed so as to face a relatively wide range of the circumferential direction of the fixing belt 21 (inner peripheral surface 21a), so that the fixing belt 21 can be heated without temperature unevenness in the circumferential direction even during heating standby (print operation standby). Therefore, after receiving a print request, the print operation can be performed promptly. In this case, in a conventional on-demand fixing device (see, for example, Japanese Patent No. 2884714), if the pressure roller is deformed during heating standby at the nip portion and heat is applied, depending on the material of the rubber of the pressure roller, thermal deterioration may occur, shortening the life of the pressure roller, or compression set may occur in the pressure roller (compression set of rubber increases when heat is applied to the deformation of the rubber). If compression set occurs in the pressure roller, a part of the pressure roller becomes concave, and the desired nip width cannot be obtained, causing poor fixing or abnormal noise during rotation. In contrast, in the present embodiment 1, the reinforcing member 23 (and the reflecting member 27) is provided between the fixed member 26 and the heater 25 so as to block the heat of the heater 25, so that the heat is less likely to reach the fixed member 26 during heating standby. Therefore, the problem of the pressure roller 31 being heated to a high temperature in a deformed state during heating standby is reduced, and the occurrence of the above-mentioned problems can be prevented.

[0038] Furthermore, the lubricant applied between the fixed member 26 and the fixing belt 21 to reduce the frictional resistance between the two members may deteriorate when used under high temperature conditions in addition to the high pressure conditions in the nip area, which may cause problems such as slippage of the fixing belt 21. In contrast, in the present embodiment 1, reinforcing member 23 (and reflecting member 27) is provided between fixed member 26 and heater 25 to block the heat of heater 25, so that the heat of heater 25 is less likely to reach the lubricant in the nip portion. This reduces deterioration of the lubricant due to high temperatures, and makes it possible to prevent the above-mentioned problems from occurring.

[0039] In addition, in the present embodiment 1, the reinforcing member 23 (and the reflecting member 27) is provided between the fixed member 26 and the heater 25 so as to block the heat of the heater 25, so that the fixed member 26 is insulated and the fixing belt 21 is not actively heated in the nip portion. Therefore, the temperature of the recording medium P fed into the nip portion is lowered when it is sent out of the nip portion. That is, at the exit of the nip portion, the temperature of the toner image fixed on the recording medium P is lowered, the viscosity of the toner is reduced, and the toner adhesive force to the fixing belt 21 is reduced when the recording medium P is separated from the fixing belt 21. Therefore, the recording medium P immediately after the fixing process is prevented from wrapping around the fixing belt 21 and causing a jam, and the toner is prevented from sticking to the fixing belt 21.

[0040] Hereinafter, a brief description will be given of the normal operation of the fixing device 20 configured as above. When the power switch of the device main body 1 is turned on, power is supplied to the heater 25, and the pressure roller 31 starts to rotate in the direction of the arrow in Fig. 2. As a result, the fixing belt 21 also rotates in the direction of the arrow in Fig. 2 due to the frictional force with the pressure roller 31 at the nip portion. Thereafter, the recording medium P is fed from the paper feed unit 12, and an unfixed color image is carried (transferred) on the recording medium P at the position of the secondary transfer roller 89. The recording medium P carrying the unfixed image T (toner image) is transported in the direction of the arrow Y10 in FIG. 2 while being guided by a guide plate (not shown), and is sent into the nip portion between the fixing belt 21 and the pressure roller 31, which are in a pressure-contact state. Then, the toner image T is fixed onto the surface of the recording medium P by the heating of the fixing belt 21 heated by the heater 25 and the pressing force of the fixed member 26 reinforced by the reinforcing member 23 and the pressure roller 31. Thereafter, the recording medium P sent out from the nip portion is transported in the direction of the arrow Y11.

[0041] The characteristic configuration and operation of fixing device 20 in the first embodiment will be described in detail below. As described above, the fixing device 20 in the present embodiment 1 is provided with a fixed member 26 that is fixed to the inner circumferential surface side of the fixing belt 21 and presses against the pressure roller 31 via the fixing belt 21 to form a nip portion, and a reinforcing member 23 that is fixed to the inner circumferential surface side of the fixing belt 21 and abuts against the fixed member 26 from the inside of the fixing belt 21 to reinforce the fixed member 26. 4, in the present embodiment 1, protrusions 26a, 26b that protrude toward the opposing surface 23a of the reinforcing member 23 so as to come into contact with the reinforcing member 23 are provided in a plurality of rows on the fixed member 26 along the conveying direction of the recording medium P (or the rotation direction of the fixing belt 21). Specifically, as the plurality of rows of protrusions, an upstream protrusion 26a that protrudes toward the opposing surface 23a of the reinforcing member 23 so as to come into contact with the reinforcing member 23 on the upstream side with respect to the conveying direction of the recording medium P, and a downstream protrusion 26b that protrudes toward the opposing surface 23a of the reinforcing member 23 so as to come into contact with the reinforcing member 23 on the downstream side with respect to the conveying direction of the recording medium P are formed. That is, the fixed member 26 has two rows of protrusions 26a, 26b (the distance between the upstream end and the downstream end is set to B) spaced apart in the conveying direction on the side facing the reinforcing member 23, and these two rows of protrusions 26a, 26b each come into surface contact with the opposing surface 23a of the reinforcing member 23.

[0042] With this configuration, even if no pipe-shaped heating member is provided to fit and fix the fixed member 26, the fixed member 26 with the reinforcing member 23 pressed against it is held in a well-balanced state, preventing the fixed member 26 from falling over. The desired nip is then formed with high precision, preventing problems such as poor fixing of the output image and poor transport of the recording medium. That is, when the fixed member 26 contacts the reinforcing member 23 biased toward the upstream side or downstream side in the conveying direction, or when the contact width (distance B) of the fixed member 26 contacting the reinforcing member 23 is narrow, the fixed member 26 receiving the pressure force at the nip portion is likely to rotate (tip over) in the clockwise or counterclockwise direction in Fig. 4 with the contact portion with the reinforcing member 23 as a fulcrum. In contrast, in the present embodiment, the fixed member 26 does not contact the reinforcing member 23 biased toward the upstream side or downstream side in the conveying direction, and the contact width (distance B) of the fixed member 26 contacting the reinforcing member 23 is set sufficiently large, so that the fixed member 26 receiving the pressure force at the nip portion is supported in a well-balanced manner by the reinforcing member 23, and the fixed member 26 is less likely to tip over with the contact portion with the reinforcing member 23 as a fulcrum.

[0043] Furthermore, in the present embodiment 1, only the portion of the fixed member 26 divided into the upstream protrusion 26a and the downstream protrusion 26b is configured to abut against the reinforcing member 23. Therefore, compared to a case where one flat surface formed over a wide area from the upstream side to the downstream side of the fixed member 26 abuts against the reinforcing member 23, the contact area between the reinforcing member 23 and the fixed member 26 can be reduced, making it difficult for heat to be transferred to the fixed member 26. That is, the amount of heat transferred from the fixing belt 21 through the fixed member 26 to the reinforcing member 26 at the nip portion can be reduced (the amount of heat escaping from the fixing belt 21 to the reinforcing member 23 through the fixed member 26 can be reduced). In particular, when the thickness of the fixing belt 21 is made thin (for example, when the thickness is set to 160 μm or less) or when the nip width is set wide, the amount of heat is easily transferred from the fixing belt 21 to the fixed member 26, so the configuration of reducing the contact area between the reinforcing member 23 and the fixed member 26 as in the present embodiment 1 is useful.

[0044] 7 and 9, the fixing member 26 in the present embodiment 1 has multiple rows of protrusions (upstream protrusions 26a and downstream protrusions 26b) each divided into multiple parts spaced apart in the width direction (left-right direction in Figs. 7 and 9). More specifically, in the present embodiment 1, eight upstream protrusions 26a and eight downstream protrusions 26b are each formed at approximately equal intervals in the width direction. With this configuration, the contact area between the reinforcing member 23 and the fixing member 26 can be further reduced, so that the above-mentioned effects are more reliably achieved. In the first embodiment, the multiple rows of protrusions 26a, 26b are configured to be in surface contact with the opposing surface 23a of the reinforcing member 23, but in order to further ensure the above-mentioned effects, the multiple rows of protrusions 26a, 26b can also be configured to be in line contact or point contact (or contact in a state close to it) with the opposing surface 23a of the reinforcing member 23. In the first embodiment, two rows of protrusions, the upstream protrusions 26a and the downstream protrusions 26b, are provided as the multiple rows of protrusions, but three or more rows of protrusions can also be provided as the multiple rows of protrusions.

[0045] Also, in this embodiment 1, referring to Figure 4, the fixed member 26 is formed so that, when viewed in a cross section perpendicular to the width direction, it is linearly symmetrical with respect to a virtual straight line (shown by a dotted line in Figure 4) that passes through the center of the conveying direction in the nip portion and is perpendicular to the conveying direction. With this configuration, the fixing member 26 receiving the pressure force at the nip portion can be supported by the reinforcing member 23 in a more balanced manner, and the fixing member 26 is more unlikely to fall over.

[0046] Furthermore, in the first embodiment, as shown in FIG. 4, when the length of the nip portion (nip width) in the transport direction of the recording medium is A, the length from the upstream contact portion where fixed member 26 and reinforcing member 23 contact each other on the upstream side in the transport direction to the downstream contact portion where fixed member 26 and reinforcing member 23 contact each other on the downstream side in the transport direction is B, and the length of opposing surface 23a of reinforcing member 23 facing fixed member 26 in the transport direction is C, A <B<C The above relationship is established. Furthermore, with respect to the conveying direction, the range of the nip portion (range A in Figure 4) is included in the range from the upstream abutment portion to the downstream abutment portion (range B in Figure 4), and the range from the upstream abutment portion to the downstream abutment portion (range B in Figure 4) is included in the range of the opposing surface 23a of the reinforcing member 23 (range C in Figure 4). In other words, the range of the nip width is included within the range of the transport direction (the vertical direction in FIG. 4) of the fixed member 26 that contacts the reinforcing member 23. Furthermore, the range of the transport direction of the opposing surface 23a of the reinforcing member 23 includes the range of the transport direction of the fixed member 26 that contacts the reinforcing member 23. With this configuration, the fixing member 26 receiving the pressure force at the nip portion can be supported by the reinforcing member 23 in a more balanced manner, and the fixing member 26 is more unlikely to fall over.

[0047] 7 to 11, a plurality of holes 22b that fit with the plurality of rows of protrusions (the upstream protrusions 26a and the downstream protrusions 26b) are formed in the sheet-like member 22. The sheet-like member 22 is installed so as to be in close contact with the fixing member 26 along the circumferential direction at positions excluding the plurality of rows of protrusions 26a, 26b. 10, the sheet-like member 22 has a rectangular shape when developed as an independent part. A plurality of holes 22a, 22b (holes that fit with the protrusions 26a, 26b) and a screw hole 22c (holes through which the threaded portions of the screws 24 are inserted) are formed on both ends of the rectangular sheet-like member 22. When the sheet-like member 22 is covered by the fixing member 26, both ends of the rectangle are folded between the upstream protruding portion 26a and the downstream protruding portion 26b (between the protruding portions in the multiple rows) to form an overlapping portion (the area surrounded by a dashed line in FIG. 8 and the hatched area in FIG. 10). Then, as shown in FIG. 8, a plate-like member 28 (fixing plate) is fixed to the fixing member 26 by a plurality of screws 24 so as to sandwich the overlapping portion of the sheet-like member 22. In detail, the plate-like member 28 is placed on the fixing member 26 via the overlapping portion so as to sandwich the overlapping portion of the sheet-like member 22, and the screw hole portion 28c of the plate-like member 28 (see FIG. 11) and the screw hole portion 22c of the sheet-like member 22 are inserted, and the screw portion of the screw 24 is screwed into the female screw portion 26c of the fixing member 26 (see FIG. 9(B)). Here, the multiple screws 24 are formed so that the height of the screw heads does not exceed the height of the protrusions 26a, 26b and does not come into contact with the reinforcing member 23.

[0048] In this way, the end of the sheet-like member 22 corresponding to the upstream side in the conveying direction and the end of the sheet-like member 22 corresponding to the downstream side in the conveying direction when unfolded are fixed and held on the fixed member 26. Therefore, even when the sheet-like member 22 receives a frictional force between the sheet-like member 22 and the fixing belt 21 traveling toward the downstream side (such as during a normal fixing process), and even when the sheet-like member 22 receives a frictional force between the sheet-like member 22 and the fixing belt 21 traveling toward the upstream side (such as when the fixing belt 21 or the pressure roller 31 is manually rotated in reverse during jam clearance), defects such as the sheet-like member 22 shifting and creating a gap between the sheet-like member 22 and the fixed member 26 or wrinkles are prevented. In particular, in this embodiment, the overlapping portion of sheet-like member 22 is sandwiched between plate-like member 28 and plate-like member 28 is fastened to fixing member 26 with a plurality of screws 24 arranged approximately evenly in the width direction, so that sheet-like member 22 can be fixed more stably and firmly to fixing member 26 than with other fixing and holding methods (for example, when the overlapping portion is adhered with an adhesive, or when the overlapping portion is made into a hook shape and hooked onto protrusions 26a, 26b, etc.).

[0049] In addition, the holes 22a, 22b of the sheet-like member 22 are fitted into the protrusions 26a, 26b of the fixing member 26, and the plate-like member 28 and the screws 24 are placed between the protrusions 26a, 26b (the center in the conveying direction), so that the fixing member 26 with the sheet-like member 22 installed is made compact. Furthermore, since the fixing member 26 with the sheet-like member 22 installed can be managed as a single sub-assembled part, it is possible to improve parts management and assembly during manufacturing and maintenance. In addition, since the sheet-like member 22 is held in place by fitting into multiple protrusions 26a, 26b that are divided at approximately equal intervals in the width direction, even if the sheet-like member 22 is subjected to a sliding force, the force is likely to be applied evenly to the multiple holes 22a, 22b, thereby reducing the problem of the sheet-like member 22 being damaged by localized stress concentration.

[0050] As described above, in the present embodiment 1, the fixed member 26 has a plurality of rows of protrusions 26a, 26b formed along the transport direction, which protrude toward the reinforcing member 23 so as to come into contact with the reinforcing member 23. This makes it possible to reduce the problem of the fixed member 26 collapsing when the reinforcing member 23 is in pressure contact with it, without causing fixing failures or the like, even when the warm-up time or first print time is short and the device is operated at high speed.

[0051] In the first embodiment, the fixing belt 21 having a multi-layer structure is used as the fixing belt, but an endless fixing film made of polyimide, polyamide, fluororesin, metal, etc. can also be used as the fixing belt. In that case, the same effect as in the first embodiment can be obtained.

[0052] Embodiment 2 The second embodiment of the present invention will be described in detail with reference to FIG. Fig. 12 is a configuration diagram showing a fixing device in embodiment 2, and corresponds to Fig. 2 in embodiment 1. The fixing device in embodiment 2 differs from that in embodiment 1 in that fixing belt 21 is heated by electromagnetic induction.

[0053] As shown in FIG. 12, the fixing device 20 in the present embodiment 2 is similar to that in the embodiment 1 and is composed of a fixing belt 21 (belt member), a fixed member 26, a reinforcing member 23, a pressure roller 31 (heating rotor), a temperature sensor 40, a sheet-like member 22, a screw 24, a plate-like member 28 (fixed plate), etc. Also in this embodiment 2, as in the above-described embodiment 1, the fixing member 26 is formed with multiple rows of protrusions (upstream protrusions 26a and downstream protrusions 26b) that protrude toward the opposing surface 23a of the reinforcing member 23 so as to abut against the reinforcing member 23.

[0054] Here, in the fixing device 20 of the present embodiment 2, an induction heating unit 50 is installed as a heating means instead of the heater 25. The fixing belt 21 of the present embodiment 2 is heated by electromagnetic induction by the induction heating unit 50, unlike that of the fixing belt 21 of the first embodiment, which is heated by radiant heat from the heater 25.

[0055] The induction heating unit 50 is composed of an excitation coil, a core, a coil guide, and the like. The excitation coil is a Litz wire made of bundled thin wires that is extended in the width direction (the direction perpendicular to the paper surface of FIG. 12) so as to cover a part of the fixing belt 21. The coil guide is made of a highly heat-resistant resin material or the like, and holds the excitation coil and the core. The core is a semi-cylindrical member made of a ferromagnetic material such as ferrite (relative magnetic permeability is about 1000 to 3000), and is provided with a center core and a side core to form an efficient magnetic flux toward the fixing belt 21. The core is disposed so as to face the excitation coil that is extended in the width direction. Meanwhile, in addition to the base layer, elastic layer, and release layer described in the first embodiment, fixing belt 21 is formed with a heat generating layer (for example, it can be formed between the elastic layer and the release layer, or the base layer can be used as the heat generating layer) that is electromagnetically induction heated by induction heating unit 50. Materials that can be used for the heat generating layer include nickel, stainless steel, iron, copper, cobalt, chromium, aluminum, gold, platinum, silver, tin, palladium, and alloys made of a plurality of these metals.

[0056] The fixing device 20 configured in this manner operates as follows. When the fixing belt 21 is driven to rotate in the direction of the arrow in Fig. 12, the fixing belt 21 is heated at a position facing the induction heating unit 50. More specifically, by passing a high-frequency alternating current through the excitation coil, magnetic lines of force are formed around the fixing belt 21 so that they alternate in both directions. At this time, eddy currents are generated on the surface of the heat generating layer of the fixing belt 21, and Joule heat is generated due to the electrical resistance of the heat generating layer itself. This Joule heat causes electromagnetic induction heating of the heat generating layer, and the fixing belt 21 is heated. In order to efficiently heat the fixing belt 21 by electromagnetic induction, it is preferable to configure the induction heating section 50 so as to face the entire area of ​​the fixing belt 21 in the circumferential direction.

[0057] As described above, in the second embodiment as well, similarly to the above-described embodiments, the fixed member 26 has a plurality of rows of protrusions 26a, 26b formed in the transport direction, which protrude toward the reinforcing member 23 so as to come into contact with the reinforcing member 23. This makes it possible to reduce the problem of the fixed member 26 falling over with the reinforcing member 23 pressed against it, without causing fixing failures, even when the warm-up time or first print time is short and the device is operated at high speed.

[0058] In the second embodiment, the fixing belt 21 is heated by electromagnetic induction heating, but the fixing belt 21 can also be heated by heat from a resistance heating element. Specifically, a resistance heating element is brought into contact with a part or the whole of the inner or outer circumferential surface of the fixing belt 21. The resistance heating element is a planar heating element such as a ceramic heater, and a power supply is connected to both ends of the resistance heating element. When a current is passed through the resistance heating element, the temperature of the resistance heating element rises due to the electrical resistance of the resistance heating element itself, and the fixing belt 21 in contact with the resistance heating element is heated. Even in such a case, by providing the fixing member 26 with the upstream protrusion 26a and the downstream protrusion 26b, the same effect as in the second embodiment can be obtained.

[0059] It is clear that the present invention is not limited to the above-described embodiments, and that the above-described embodiments may be modified as appropriate within the scope of the technical concept of the present invention in addition to the modifications suggested in the above-described embodiments. Furthermore, the number, position, shape, etc. of the components are not limited to the above-described embodiments, and may be any number, position, shape, etc. suitable for implementing the present invention.

[0060] (Additional Note) (Appendix 1) a fixing belt that runs in a predetermined direction to heat and melt the toner image and has flexibility; a fixed member fixed to an inner peripheral surface side of the fixing belt, the fixed member being pressed against a pressure rotating body via the fixing belt to form a nip portion through which a recording medium is conveyed; a reinforcing member fixed to an inner peripheral surface of the fixing belt and contacting the fixed member from the inside of the fixing belt to reinforce the fixed member; Equipped with The fixing device according to claim 1, wherein the fixing member has a plurality of rows of protruding portions protruding toward an opposing surface of the reinforcing member so as to come into contact with the reinforcing member along a transport direction of the recording medium. (Appendix 2) The fixing device described in Appendix 1, characterized in that the multiple rows of protrusions include upstream protrusions that protrude toward the opposing surface of the reinforcing member so as to abut against the reinforcing member on the upstream side with respect to the transport direction, and downstream protrusions that protrude toward the opposing surface of the reinforcing member so as to abut against the reinforcing member on the downstream side with respect to the transport direction. (Appendix 3) 3. The fixing device according to claim 1, wherein each of the rows of protrusions is divided into a plurality of parts spaced apart from each other in the width direction. (Appendix 4) a sheet-like member made of a low-friction material and provided to cover the fixed member along a circumferential direction so as to be interposed between the fixed member and the fixing belt in a width direction at the nip portion; The fixing device described in Supplementary Note 1 to Supplementary Note 3, characterized in that the sheet-like member has a plurality of holes that fit into the plurality of rows of protrusions, and is installed so as to be in close contact with the fixed member along a circumferential direction at positions excluding the plurality of rows of protrusions. (Appendix 5) the sheet-like member has a rectangular shape when unfolded as a single component, and when the sheet-like member is covered by the fixing member, both ends of the rectangle are folded between the multiple rows of protruding portions to form overlapping portions; 5. The fixing device according to claim 4, wherein a plate-shaped member is fixed to the fixed member by a plurality of screws so as to sandwich the overlapping portion of the sheet-shaped member. (Appendix 6) 6. The fixing device according to claim 4, wherein the sheet-like member is made of a fibrous material impregnated with a lubricant. (Appendix 7) The fixing device according to any one of claims 1 to 6, characterized in that, when viewed in a cross section perpendicular to the width direction, the fixed member is formed so as to be linearly symmetrical with respect to a virtual line that passes through the center of the nip portion in the transport direction and is perpendicular to the transport direction. (Appendix 8) a holding member for holding both ends of the fixing belt in a width direction; a heating means for heating the fixing belt by facing or contacting the fixing belt; 8. The fixing device according to claim 1, further comprising: (Appendix 9) An image forming apparatus comprising the fixing device according to any one of claims 1 to 8.

[0061] (Additional Note) (Appendix 11) a flexible endless fixing belt; a fixed member disposed on an inner peripheral surface side of the fixing belt and pressed against a pressure rotating body via the fixing belt to form a nip portion through which a recording medium is conveyed; a heater that directly faces at least a portion of the fixing belt other than the nip portion and heats the fixing belt; a reinforcing member disposed between the fixed member and the heater on the inner circumferential surface side of the fixing belt and in contact with the fixed member to reinforce the fixed member; a holding member for holding both ends of the fixing belt in a width direction; Equipped with the reinforcing member is not in contact with the fixing belt when the fixing belt rotates, The fixing member has multiple rows of protrusions that protrude toward the opposing surface of the reinforcing member so as to abut against the reinforcing member along the transport direction of the recording medium, and contacts the fixing belt across the width direction via a low-friction sheet-like member. (Appendix 12) The fixing device described in Appendix 11, characterized in that the multiple rows of protrusions include upstream protrusions that abut against the opposing surface on the upstream side of the transport direction, and downstream protrusions that abut against the opposing surface on the downstream side of the transport direction. (Appendix 13) 13. The fixing device according to claim 11, wherein each of the plurality of rows of protrusions is divided into a plurality of portions spaced apart from each other in the width direction. (Appendix 14) The low friction sheet member has a plurality of holes, 14. The fixing device according to claim 11, wherein the plurality of holes are fitted into the plurality of rows of protrusions. (Appendix 15) the low-friction sheet-like member has a rectangular shape when unfolded as a single component, and when the low-friction sheet-like member is covered by the fixing member, both ends of the rectangle are folded between the multiple rows of protruding portions to form overlapping portions; 15. The fixing device according to claim 14, further comprising a contact member between the rows of protruding portions, the contact member contacting the fixed member via the overlapping portion. (Appendix 16) 16. The fixing device according to claim 14, wherein the low-friction sheet member is made of a fibrous material impregnated with a lubricant. (Appendix 17) The fixing device according to any one of claims 11 to 16, characterized in that, when viewed in a cross section perpendicular to the width direction, the fixed member is formed so as to be linearly symmetrical with respect to a virtual line that passes through the center of the nip portion in the transport direction and is perpendicular to the transport direction. (Appendix 18) The fixing device described in any one of Appendix 11 to Appendix 17, characterized in that the reinforcing member has an upstream wall portion that is provided on the upstream side of the opposing surface and approximately perpendicular to the direction opposite to the fixed member, and a downstream wall portion that is provided on the downstream side of the opposing surface and approximately perpendicular to the direction opposite to the fixed member and faces the upstream wall portion. (Appendix 19) When the length of the nip portion in the conveying direction of the recording medium is A, and the length from an upstream contact portion where the fixed member and the reinforcing member contact each other on the upstream side in the conveying direction to a downstream contact portion where the fixed member and the reinforcing member contact each other on the downstream side in the conveying direction is B, A As a relationship like this is established, The fixing device according to any one of claims 11 to 18, wherein the range of the nip portion with respect to the transport direction is included in the range from the upstream contact portion to the downstream contact portion. (Appendix 20) 20. The fixing device according to claim 11, wherein each of the rows of protrusions is formed so as to come into line contact or point contact with the opposing surface of the reinforcing member. (Appendix 21) The reinforcing member has a heat insulating member provided on a part or the whole of a surface facing the heater, 21. The fixing device according to claim 11, wherein the fixing member is made of a material having heat insulation properties. (Appendix 22) 22. An image forming apparatus comprising the fixing device according to claim 11.

[0062] (Additional Note) (Appendix 31) a flexible endless fixing belt; a fixed member disposed on an inner peripheral surface side of the fixing belt and pressed against a pressure rotating body via the fixing belt to form a nip portion through which a recording medium is conveyed; a heater that directly faces at least a portion of the fixing belt other than the nip portion and heats the fixing belt; a reinforcing member disposed on an inner circumferential surface side of the fixing belt between the fixed member and the heater and in contact with the fixed member; a holding member for holding both ends of the fixing belt in a width direction; Equipped with the reinforcing member is not in contact with the fixing belt when the fixing belt rotates,​ the fixing member has a plurality of rows of protruding portions protruding toward the opposing surface of the reinforcing member along a conveying direction of the recording medium, and contacts the fixing belt via a sheet-like member across the width of the fixing belt; The fixing device, wherein the protruding portion has a length in the width direction that is longer than a length in the transport direction. (Appendix 32) The fixing device described in Appendix 1, characterized in that the multiple rows of protrusions include upstream protrusions that abut against the opposing surface on the upstream side of the transport direction, and downstream protrusions that abut against the opposing surface on the downstream side of the transport direction. (Appendix 33) 33. The fixing device according to claim 31, wherein each of the plurality of rows of protrusions is divided into a plurality of portions spaced apart from each other in the width direction. (Appendix 34) 34. The fixing device according to claim 33, wherein the protrusions are provided in a plurality of positions at equal intervals in the width direction. (Appendix 35) The sheet-like member has a plurality of holes, 35. The fixing device according to claim 31, wherein the plurality of holes are fitted into the plurality of rows of protrusions. (Appendix 36) the sheet-like member has a rectangular shape when unfolded as a single component, and when the sheet-like member is covered by the fixing member, both ends of the rectangle are folded between the multiple rows of protruding portions to form overlapping portions; 6. The fixing device according to claim 5, further comprising a contact member between the rows of protruding portions, the contact member contacting the fixed member via the overlapping portion. (Appendix 37) 37. The fixing device according to claim 35, wherein the sheet-like member is formed of a fibrous material impregnated with a lubricant. (Appendix 38) The fixing device according to any one of claims 31 to 37, characterized in that, when viewed in a cross section perpendicular to the width direction, the fixed member is formed so as to be linearly symmetrical with respect to a virtual line that passes through the center of the nip portion in the transport direction and is perpendicular to the transport direction. (Appendix 39) The fixing device described in any one of Appendix 31 to Appendix 38, characterized in that the reinforcing member has an upstream wall portion that is provided upstream of the opposing surface and approximately perpendicular to the direction opposite the fixed member, and a downstream wall portion that is provided downstream of the opposing surface and approximately perpendicular to the direction opposite the fixed member and faces the upstream wall portion. (Appendix 40) When the length of the nip portion in the conveying direction of the recording medium is A, and the length from an upstream contact portion where the fixed member and the reinforcing member contact each other on the upstream side in the conveying direction to a downstream contact portion where the fixed member and the reinforcing member contact each other on the downstream side in the conveying direction is B, A As a relationship like this is established, The fixing device according to any one of claims 31 to 39, wherein the range of the nip portion with respect to the transport direction is included in the range from the upstream contact portion to the downstream contact portion. (Appendix 41) 41. An image forming apparatus comprising the fixing device according to any one of claims 31 to 40. [Explanation of symbols]

[0063] 1 Image forming apparatus main body (apparatus main body), 20 Fixing device, 21 Fixing belt (fixing member), 22 sheet-like member, 23 Reinforcing member, 24 screws (fixing screws), 25 heater (heating means), 26 Fixing member, 26a upstream protrusion, 26b downstream protrusion, 28 Plate-shaped member (fixed plate), 29 Flange (retaining member), 31 Pressure roller (pressure rotating body). [Prior art documents] [Patent documents]

[0064] ​ [Patent Document 1] Patent Gazette No. 2010-96782

Claims

1. a flexible endless fixing belt; a nip forming member disposed inside the fixing belt and sandwiching the fixing belt between the fixing belt and a pressure rotating body to form a nip portion through which a recording medium is conveyed between the fixing belt and the pressure rotating body; a heat source facing the fixing belt and configured to heat the fixing belt; a reinforcing member disposed inside the fixing belt and having a facing surface that comes into contact with the nip forming member; a pair of guide members for guiding both ends of the fixing belt in a width direction; Equipped with the nip forming member has an upstream contact portion that contacts the opposing surface on the upstream side in the transport direction of the recording medium, a downstream contact portion that contacts the opposing surface on the downstream side in the transport direction, and a non-contact portion that does not contact the opposing surface between the upstream contact portion and the downstream contact portion, and the surface that faces the pressure rotating body and with which the fixing belt slides is formed to be flat or curved so as to follow the curvature of the pressure rotating body, A fixing device comprising: a sheet-like member interposed between the nip forming member and the fixing belt.

2. 2. The fixing device according to claim 1, wherein the sliding surface is a surface with which the fixing belt indirectly slides via the sheet-like member.

3. 3. The fixing device according to claim 1, wherein the heat source is a radiant heat source.

4. 4. The fixing device according to claim 3, wherein the radiant heat source is a halogen heater.

5. the reinforcing member is disposed between the nip forming member and the heating source on the inner side of the fixing belt, 5. The fixing device according to claim 1, further comprising a reflecting member provided between the reinforcing member and the heat source.

6. The fixing device described in any one of claims 1 to 5, characterized in that the reinforcing member has an upstream wall portion that is arranged upstream of the opposing surface and approximately perpendicular to the direction opposite the nip forming member, and a downstream wall portion that is arranged downstream of the opposing surface and approximately perpendicular to the direction opposite the nip forming member and faces the upstream wall portion.

7. The fixing device according to claim 6 , wherein the upstream contact portion and the downstream contact portion are provided between the upstream wall portion and the downstream wall portion in the transport direction.

8. 8. The fixing device according to claim 1, wherein the facing surface faces the nip forming member and extends downstream of the downstream contact portion in the transport direction.

9. the nip forming member has an upstream side protruding portion protruding toward the opposing surface and a downstream side protruding portion protruding toward the opposing surface, the upstream protrusion has the upstream contact portion, 9. The fixing device according to claim 1, wherein the downstream protrusion has the downstream contact portion.

10. The upstream abutment portion is a surface of the upstream protrusion that faces the opposing surface, The fixing device according to claim 9 , wherein a surface of the downstream protrusion that faces the opposing surface is the downstream contact portion.

11. The upstream protrusion is disposed in a plurality of portions in a longitudinal direction of the nip forming member, 11. The fixing device according to claim 9, wherein a plurality of the downstream protruding portions are arranged in the longitudinal direction of the nip forming member.

12. 12. The fixing device according to claim 1, wherein the nip forming member is covered with the sheet-like member.

13. the sheet-like member covering the nip forming member has a plurality of holes; 12. The fixing device according to claim 9, wherein the upstream protrusion or the downstream protrusion is fitted into the plurality of holes.

14. 14. The fixing device according to claim 1, wherein the sheet-like member is made of a low-friction material.

15. 15. The fixing device according to claim 1, further comprising a member for fixing the sheet-like member to the nip forming member so as to sandwich an overlapping portion where one end and the other end of the sheet-like member are folded over.

16. 16. The fixing device according to claim 1, wherein the nip forming member has a plurality of contact points with the opposing surface in a direction perpendicular to the transport direction.

17. An image forming apparatus comprising the fixing device according to any one of claims 1 to 16.

Images