Fixing device and image forming apparatus

Abstract

To provide a fixing device that can prevent lubricant from leaking to the outside of a belt as much as possible in a pad fixing system.SOLUTION: A fixing unit has a part to be pressed 322 at which a fixing pad 32 arranged inside an endless belt in a pad fixing system is pressed against a pressure roller arranged outside the belt with the belt therebetween, and an upstream side guide 321 that is extended to the upstream side in a belt revolving direction (arrow B) from the part to be pressed 322. The upstream side guide 321 is provided, on both ends in a belt width direction (arrow G), with convex surface parts 324, 325 that swell toward the belt, and the convex surface parts 324, 325 have a shape in which a length W in the belt revolving direction is gradually reduced from an end toward a center part in the belt width direction.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present disclosure relates to a fixing device that fixes an unfixed image on a recording sheet and an image forming apparatus. [Background technology]

[0002] Some image forming devices, such as printers, are equipped with a fixing device that uses a pad fixing method in which a fixed pad, which is a non-rotating body located on the inner side of a rotating endless belt, is pressed against the belt by a pressure roller located on the outer side of the belt, forming a fixing nip between the belt and the pressure roller, and a sheet is passed through the fixing nip to fix an unfixed image on the sheet (for example, Patent Documents 1 and 2).

[0003] In such a pad fixing method, the pressing force generated between the pressure roller and the fixed pad via the belt is large, so the frictional resistance between the belt and the fixed pad also increases, and the wear of the inner peripheral surface of the belt is likely to progress. Therefore, conventionally, a lubricant has been applied to the inner peripheral surface of the belt to reduce the frictional resistance between the belt and the fixed pad.

[0004] However, because the pressure of the fixing nip is quite high, when the lubricant applied to the inner peripheral surface of the belt passes through the fixing nip, it is easy for it to be divided into two parts: one that can get between the belt and the fixed pad, and one that cannot get in and flows to the end side of the belt in the width direction (corresponding to the axial direction of the pressure roller). The lubricant that flows to the end side eventually leaks out of the belt from the width direction edge of the belt. The lubricant on the inner peripheral surface of the belt is reduced by the amount that leaks out from the width direction edge of the belt, and the less the amount of lubricant on the inner peripheral surface of the belt, the greater the frictional resistance between the belt and the fixed pad. This increase in frictional resistance may accelerate the wear of the belt, or the increase in the torque driving the belt may hinder the smooth rotation of the belt and the pressure roller, resulting in poor sheet transport.

[0005] Patent document 1 discloses a configuration in which the end of the nip forming member (fixed pad) on the upstream side in the circumferential direction of the belt is formed into a comb-tooth shape over the entire area from one end of the belt in the width direction to the other end, and describes that lubricant can enter the comb-tooth recesses (grooves) and prevent it from leaking out from the width direction edge of the belt. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2017-90885 A [Patent Document 2] JP 2006-38990 A Summary of the Invention [Problem to be solved by the invention]

[0007] In the above configuration, the lubricant can be stored in the comb-tooth-shaped recesses formed in the nip forming member, but when a certain amount of lubricant is stored in the recesses and new lubricant applied to the inner peripheral surface of the belt as the belt rotates tries to enter the recesses, it is likely that the lubricant will not be able to enter the recesses and will overflow. If the overflowing lubricant flows into the adjacent recess in the belt width direction, and when that recess overflows, it flows into the adjacent recess again, and so on, the lubricant will gradually flow toward the end side in the belt width direction, and may eventually leak out from the edge of the belt in the belt width direction.

[0008] The present disclosure has been made in consideration of the above problems, and aims to provide a fixing device and an image forming apparatus that can prevent lubricant from leaking outside the belt as much as possible in a pad fixing method. [Means for solving the problem]

[0009] In order to achieve the above object, the fixing device according to the present disclosure is a fixing device that fixes an unfixed image on a sheet by passing the sheet through a fixing nip formed by pressing an endless belt having a lubricant applied to its inner surface with a pressure roller disposed on the outer periphery of the belt, the fixing device comprising: a non-rotating pad having a pressed portion that is pressed by the pressure roller via the belt on the inner periphery of the belt; and a guide that is disposed upstream of the pressed portion in the belt rotation direction and that guides the belt to the fixing nip; The position in the belt rotation direction is The upstream side of the fixing nip in the belt rotation direction is and a pressure applying section for applying a pressure between the end of the belt in the belt width direction and the guide at a position immediately before the guide, the pressure gradually decreasing from the end side toward the center side in the belt width direction. The guide has a convex surface portion that rises toward the inner peripheral surface of the belt at a position corresponding to the end of the belt, and the pressure applying portion is the convex surface portion. The convex surface portion is formed in a tapered shape in which the length of the convex surface portion in the belt circumferential direction gradually decreases from the end side toward the center side in the belt width direction so that the gradually decreasing pressure is applied, and the convex surface portion does not extend to the pressed portion located downstream of the guide in the belt circumferential direction. It is characterized by:

[0011] In another aspect of the present disclosure, a fixing device fixes an unfixed image on a sheet by passing the sheet through a fixing nip formed by pressing an endless belt having an inner peripheral surface coated with a lubricant with a pressure roller arranged on the outer peripheral side of the belt, the fixing device comprising: a non-rotating pad having a pressed portion pressed by the pressure roller via the belt on the inner peripheral side of the belt, and a guide provided upstream of the pressed portion in the belt rotation direction and guiding the belt to the fixing nip; and a pressure applying portion that applies a pressure between an end of the belt in the belt width direction and the guide at a position immediately before the fixing nip upstream of the fixing nip in the belt rotation direction, the pressure gradually decreasing from the end side toward the center in the belt width direction, The guide has a convex surface portion that rises toward the inner peripheral surface of the belt at a position corresponding to the end of the belt, the pressure applying portion is the convex surface portion, and the convex surface portion is formed in a shape in which the height of the convex surface portion gradually decreases from the end side toward the center side in the belt width direction so that the gradually decreasing pressure is applied. At the same time, the pressure-receiving portion is not extended to the pressed portion located downstream of the guide in the belt circumferential direction. .

[0012] Also, an end portion of the convex portion on the central side in the belt width direction may extend to a position closer to the axial center of the pressure roller in the belt width direction than an end portion of the pressure roller in the axial direction.

[0013] Furthermore, the tapered shape may be formed by a first side parallel to the belt width direction and a second side upstream of the first side in the belt circumferential direction and inclined with respect to the first side.

[0014] Further, a base end of the convex portion on an end side in the belt width direction may protrude to the outside of the belt in the belt width direction.

[0015] In yet another aspect of the present disclosure, a fixing device fixes an unfixed image on a sheet by passing the sheet through a fixing nip formed by pressing an endless belt having an inner peripheral surface coated with a lubricant with a pressure roller arranged on the outer peripheral side of the belt, the fixing device comprising: a non-rotating pad having a pressed portion pressed against the pressure roller via the belt on the inner peripheral side of the belt, and a guide provided upstream of the pressed portion in the belt rotation direction and guiding the belt to the fixing nip; and a pressure applying portion that applies a pressure between an end of the belt in the belt width direction and the guide at a position immediately before the fixing nip upstream of the fixing nip in the belt rotation direction, the pressure gradually decreasing from the end side toward the center side in the belt width direction,The pressure applying unit is a pressure roller having a truncated cone shape that presses the end of the belt against the guide from an outer circumferential side of the belt at the immediately preceding position, and the pressure roller is on the outer side of the belt, on the side where the end of the belt is located relative to the pressure roller in the belt width direction, and immediately before the pressure roller in the belt circumferential direction, The large diameter end is disposed so as to face the end side in the belt width direction, and the small diameter end is disposed so as to face the center side in the belt width direction. Characterized by .

[0016] Furthermore, the axial end of the pressure roller may be closer to the center of the belt in the belt width direction than the end edge of the belt in the belt width direction.

[0017] Also, the belt may be in contact with the guide over an entire area from one end to the other end in the belt width direction at the immediately preceding position.

[0018] Furthermore, a low friction sheet may be provided between the belt and the pad.

[0019] Here, the belt may be in contact with the guide over an entire area from one end to the other end in the belt width direction at the immediately preceding position via the low friction sheet.

[0020] Furthermore, a lubricant supplying member for supplying a lubricant to the inner peripheral surface of the belt may be provided.

[0021] The pressure applied by the pressure applying portion may be within a range of 1 to 200 kPa, and the height of the convex portion may be within a range of 0.1 to 0.5 mm.

[0022] The image forming apparatus according to the present disclosure is an image forming apparatus equipped with a fixing section that fixes an unfixed image formed on a recording sheet being transported, and is characterized in that the fixing section is equipped with the above-mentioned fixing device. Effect of the Invention

[0023] According to the above configuration, when the lubricant applied to the inner peripheral surface of the belt reaches the guide as the belt runs around, the pressure generated between the guide and the belt edge in the belt width direction is high, so that even if the lubricant tries to flow into the gap between the belt and the guide, only a small amount of the lubricant can enter, and the rest tends to flow into the central part where the pressure is lower than the belt edge. In other words, by applying the above pressure, the lubricant near the belt edge tends to move toward the center, and the lubricant can be prevented from leaking out from the belt edge. [Brief description of the drawings]

[0024] [Figure 1] FIG. 1 is a schematic diagram illustrating the overall configuration of a printer. [Diagram 2] FIG. 2 is a cross-sectional view illustrating a schematic configuration of a fixing unit of the printer. [Diagram 3] 2 is a schematic exploded perspective view of a support member, a fixed pad, a guide member, a sliding member, and a lubricant supplying member in the fixing unit. FIG. [Figure 4] FIG. 2 is a schematic diagram showing a configuration of a fixed pad. [Diagram 5] 5 is a schematic perspective view of the upstream guide of the fixed pad as viewed from the direction indicated by the arrow E in FIG. 4. [Figure 6] FIG. 2 is a schematic plan view of the belt, the fixed pad, and the pressure roller as viewed from above. [Figure 7] 3 is a schematic side view of a belt and a fixed pad seen through the pressure roller from the direction of the arrow Xa in FIG. 2. [Figure 8] 5A to 5C are schematic diagrams showing the magnitude relationship of pressure generated between the belt and fixed pads at three different positions in the belt width direction in an embodiment. [Figure 9] FIG. 13 is a graph showing pressure distribution between an upstream guide and a belt. [Figure 10] 5A and 5B are schematic diagrams showing the magnitude relationship of pressure generated between a belt and a fixed pad at three different positions in the belt width direction in a comparative example. [Figure 11]FIG. 1A is a schematic diagram for explaining how the lubricant flows as the belt rotates in an embodiment, and FIG. 1B is a schematic diagram for explaining the flow of the lubricant in a comparative example. [Figure 12] 13A and 13B are diagrams showing a configuration of a convex portion according to a modified example. [Figure 13] 13(a) and 13(b) are diagrams showing the configuration of another convex portion according to a modified example. [Figure 14] 13A and 13B are diagrams showing the configuration of still another convex portion according to a modified example. [Figure 15] 13(a) and 13(b) are diagrams illustrating the configuration of a pressure applying portion according to a modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] A fixing device and an image forming apparatus according to an embodiment of the present disclosure will be described below with reference to the drawings, using a tandem color printer (hereinafter simply referred to as a "printer") as an example.

[0026] (1) Overall configuration of the printer FIG. 1 is a schematic cross-sectional view showing the overall configuration of a printer 1.

[0027] As shown in the figure, the printer 1 includes an image forming unit 10, a paper feeding unit 20, and a fixing unit 30.

[0028] The image forming section 10 includes imaging units 11Y, 11M, 11C, and 11K corresponding to the respective colors of Y (yellow), M (magenta), C (cyan), and K (black), and an intermediate transfer belt 13.

[0029] The imaging unit 11K includes a photoconductor drum 12, a charging unit 16, an exposure unit 17, a developing unit 18, and a cleaner 19, which are arranged along the circumferential direction of the photoconductor drum 12.

[0030] The exposure unit 17 includes a light emitting element such as a laser diode, a lens, and the like, and modulates the laser light in response to a drive signal from a control unit (not shown) to expose and scan the photosensitive drum 12 .

[0031] The photosensitive drum 12 is rotated by a drive source (not shown), and before being exposed to the light, any remaining toner on the surface is removed by a cleaner 19, and then the photosensitive drum 12 is uniformly charged by a charging unit 16. When the photosensitive drum 12 is exposed to the laser light in this uniformly charged state, an electrostatic latent image is formed on the surface of the photosensitive drum 12.

[0032] The electrostatic latent image formed on the photoreceptor drum 12 is developed by the developing unit 18, whereby a K-color toner image is formed on the surface of the photoreceptor drum 12. This K-color toner is primarily transferred from the photoreceptor drum 12 onto the intermediate transfer belt 13 by a primary transfer roller 14 disposed on the opposite side of the photoreceptor drum 12, via the circulating intermediate transfer belt 13.

[0033] Imaging units 11Y, 11M, and 11C have a similar configuration to imaging unit 11K, and for each imaging unit, a toner image of the corresponding color (Y, M, or C) is formed on photosensitive drum 12 and then primarily transferred onto intermediate transfer belt 13 by primary transfer roller 14.

[0034] The image forming operations in the image forming units 11Y to 11K are performed with different timing so that the toner images are primarily transferred in a superimposed manner at the same position on the intermediate transfer belt 13. As a result, color toner images of Y to K colors are formed on the intermediate transfer belt 13.

[0035] The paper feed section 20 includes a paper feed cassette 21 that stores recording sheets S, a feed roller 22, a transport roller 23, and a timing roller 24.

[0036] The delivery roller 22 comes into contact with the topmost recording sheet S in the paper feed cassette 21 and delivers it to a transport path 25. The transport roller 23 transports the recording sheet S delivered by the delivery roller 22 toward a timing roller 24. The timing roller 24 sends the recording sheet S downstream at a timing instructed by a control unit (not shown).

[0037] The color toner images transferred in multiple layers onto the intermediate transfer belt 13 in the image forming unit 10 move to a secondary transfer position 15a, which is a contact position between the intermediate transfer belt 13 and the secondary transfer roller 15, as the intermediate transfer belt 13 rotates.

[0038] In synchronization with the movement of the toner image on the circulating intermediate transfer belt 13, the recording sheet S is fed on the conveying path 25 from the timing roller 24 of the paper feed unit 20, and when the recording sheet S passes through the secondary transfer position 15a, the color toner image on the intermediate transfer belt 13 is secondarily transferred onto the recording sheet S by the secondary transfer roller 15. The recording sheet S that has passed the secondary transfer position 15a is sent to the fixing unit 30.

[0039] The fixing section 30 passes the recording sheet S, which is transported from the secondary transfer roller 15 in the direction indicated by the arrow D (sheet transport direction), through the fixing nip 3, and fixes the color toner image (unfixed image) on the recording sheet S to the recording sheet S by applying heat and pressure.

[0040] The recording sheet S that has passed through the fixing unit 30 is discharged outside the apparatus by a discharge roller 26 and stored in a discharge tray 27 .

[0041] (2) Configuration of the fixing unit 2 is a schematic cross-sectional view showing the configuration of the fixing unit 30. Here, in the figure, the X-axis direction and the Y-axis direction represent the left-right direction and the up-down direction when the printer 1 is viewed from the front side, and the Z-axis direction is a direction perpendicular to both the X-axis and the Y-axis and corresponds to the depth direction of the printer 1. The figure is a cross-sectional view of the fixing unit 30 cut along an XY plane perpendicular to the Z-axis.

[0042] As shown in the figure, the fixing section 30 includes an endless belt 31, a fixed pad 32 that contacts the inner surface 311 of the belt 31 via a sliding member 37, a guide member 33 that contacts the inner surface 311 of the belt 31 immediately after it passes through the fixing nip 3 and guides the belt 31, a support member 34 that supports the fixed pad 32 and the guide member 33, a heating roller 35 that heats the belt 31, a heater 36 that applies heat to the heating roller 35, a lubricant supply member 38 that applies lubricant to the inner surface 311 of the belt 31, and a pressure roller 39 that presses the outer surface 312 of the belt 31.

[0043] The belt 31 is wound around a fixed pad 32, a heating roller 35, and a guide member 33, and tension is applied to the belt 31 by biasing the heating roller 35 in a direction away from the fixed pad 32 by an elastic member such as a spring (not shown).

[0044] The belt 31 is formed by laminating, in this order, an elastic layer made of a highly heat-resistant material such as silicone rubber or fluororubber, and a release layer provided with releasability such as a fluorine tube or fluorine coating on a base layer made of polyimide, SUS (stainless steel), Ni (nickel) electroforming, etc. The outer diameter of the belt 31 is arbitrary, but is preferably within the range of 10 to 100 mm. The thickness of the base layer is preferably within the range of 5 to 100 μm, for example, the thickness of the elastic layer is preferably within the range of 10 to 300 μm, and the thickness of the release layer is preferably within the range of 5 to 100 μm, for example. The inner diameter of the belt 31 is constant and the same at any position in the Z-axis direction (belt width direction).

[0045] The pressure roller 39 is formed by laminating, in this order, an elastic layer 39b made of a heat-resistant material such as silicone rubber or fluororubber, and a release layer 39c provided with releasability such as a fluorine tube or fluorine-based coating on a solid core metal 39a made of aluminum, iron, or the like. The outer diameter of the pressure roller 39 is arbitrary, but is preferably within the range of 20 to 100 mm. The core metal 39a may be, for example, a pipe-shaped one having a thickness within the range of 0.1 to 10 mm, or a non-circular cross-sectional shape such as a three-arrow shape. The thickness of the elastic layer 39b is preferably within the range of 1 to 20 mm, and the thickness of the release layer 39c is preferably within the range of 5 to 100 μm.

[0046] The pressure roller 39 has an axis 395 of its rotation shaft parallel to the Z axis, and both axial ends of the pressure roller 39 are rotatably supported by a fixed frame (not shown: hereinafter simply referred to as the "frame") that constitutes the housing of the fixing unit 30, and the outer peripheral surface 391 of the pressure roller 39 is pressed against the belt 31 by the biasing force from an elastic member (not shown) such as a spring.

[0047] The pressure roller 39 is driven to rotate at a predetermined rotation speed in the direction indicated by the arrow A by the rotational drive force of the fixing and conveying motor 40. Due to the rotation of the pressure roller 39, the belt 31 is rotated (runs) in the direction indicated by the arrow B (belt circumferential direction).

[0048] The fixed pad 32 and the guide member 33 are arranged in line along the belt rotation direction, are non-rotating bodies that do not rotate with the rotating belt 31, and have a Z-axis length that is slightly longer than the Z-axis length (belt width) of the belt 31.

[0049] The fixed pad 32 is disposed on the inner peripheral side of the belt 31, on the opposite side to the pressure roller 39 located on the outer side of the belt 31, with the belt 31 sandwiched therebetween, and an upstream guide 321, a pressed portion 322, and a downstream guide 323 are provided adjacent to each other in this order along the belt circulation direction.

[0050] The upstream guide 321 is provided upstream of the pressed portion 322 in the belt rotation direction, and guides a belt portion 315 of the belt 31, which is upstream of the fixing nip 3 in the belt rotation direction and immediately before entering the fixing nip 3, to the fixing nip 3. The upstream guide 321 is located upstream of the fixing nip 3 in the belt rotation direction, and does not contribute to the formation of the fixing nip 3.

[0051] Here, the fixed pad 32 is a single molded product, and the upstream guide 321 extends from the pressed portion 322 upstream in the belt rotation direction, but if possible, it is also possible to use a fixed pad 32 in which the upstream guide 321 and the pressed portion 322 are formed from separate members.

[0052] Between the upstream guide 321 and the belt 31, pressure application sections 324, 325 (FIG. 5) are provided. The pressure application sections 324, 325 apply pressure that gradually decreases from the edge toward the center in the width direction (corresponding to the Z-axis direction) of the belt 31. The pressure application sections 324, 325 will be described later. Hereinafter, the width direction of the belt 31 is referred to as the belt width direction.

[0053] The pressed portion 322 receives the pressing force from the pressure roller 39 via the sliding member 37 present between the pressure roller 39 and the inner peripheral surface 311 of the belt 31. The pressure roller 39 located on the outer peripheral side of the belt 31 presses the pressed portion 322 of the fixed pad 32 located on the inner peripheral side of the belt 31 via the belt 31, whereby the outer peripheral surface 391 of the pressure roller 39 and the outer peripheral surface 312 of the belt 31 are in pressure contact with each other, forming the fixing nip 3 between the belt 31 and the pressure roller 39. The upstream end of the fixing nip 3 in the belt rotation direction is 3b, and the downstream end in the belt rotation direction is 3c.

[0054] The downstream guide 323 guides a belt portion 317 of the belt 31 immediately after it has passed through the fixing nip 3 to a guide member 33 located downstream of the belt portion 317 in the belt rotation direction.

[0055] The fixing pad 32 is preferably made of a resin such as polyphenylene sulfide, polyimide, or liquid crystal polymer, which has excellent heat resistance. It may also be made of metal such as aluminum or iron, or ceramic, or may be a composite of these with silicone rubber or fluororubber.

[0056] The guide member 33 is disposed downstream of the fixed pad 32 in the belt rotation direction and upstream of the heating roller 35 in the belt rotation direction, and is closer to the fixed pad 32 than the heating roller 35, in this case, in a position adjacent to the fixed pad 32 with a space 45 interposed therebetween, and guides the belt portion 317 of the belt 31 guided by the downstream guide 323 further downstream in the belt rotation direction. Note that the guide member 33 is located at a position away from the fixing nip 3 in the belt rotation direction, and does not contribute to the formation of the fixing nip 3. The material of the guide member 33 may be the same as that of the fixed pad 32, or may be a different resin or metal.

[0057] The support member 34 is a U-shaped cross-section member made of metal such as aluminum, iron, or SUS, and supports the fixed pad 32, the guide member 33, and the sliding member 37 in a fixed manner.

[0058] FIG. 3 is a schematic exploded perspective view of the support member 34, the fixed pad 32, the guide member 33, the sliding member 37, and the lubricant supplying member 38, and the belt 31 is not shown.

[0059] As shown in the same figure, the support member 34 is elongated in the Z-axis direction, and both longitudinal ends thereof are fixedly supported by the frame. The support member 34 has a central portion 341 extending in the vertical direction, an upper horizontal portion 342 extending in the left direction from the upper end of the central portion 341, and a lower horizontal portion 343 extending in the left direction from the lower end of the central portion 341.

[0060] The fixed pad 32 is fixedly supported by adhesive or the like on the right side surface 345 of the central portion 341 of the support member 34 via a sliding member 37, and the guide member 33 is fixedly supported by adhesive or the like on the upper surface 346 of the upper horizontal portion 342 of the support member 34.

[0061] The lubricant supplying member 38 is long in the Z-axis direction and has a length substantially equal to the belt width of the belt 31. The lubricant supplying member 38 is fitted into a groove 339 along the Z-axis direction, which is provided in the belt guide surface 335 of the guide member 33. The lubricant supplying member 38 contains a lubricant J, and an upper surface 381 of the lubricant supplying member 38 contacts the inner circumferential surface 311 of the belt 31 to apply the lubricant J to the inner circumferential surface 311 of the belt 31. The lubricant supplying member 38 also has a function of collecting and retaining the lubricant J applied to the inner circumferential surface 311 of the belt 31 during rotational travel of the belt 31, and reapplying the retained lubricant J to the inner circumferential surface 311 of the belt 31.

[0062] The lubricant supplying member 38 is made of a material suitable for holding the lubricant J, such as a fibrous material such as aramid fiber or fluorine fiber, or a porous material such as silicon sponge. Here, an elastically deformable material is used, but is not limited to this. As the lubricant J, a silicon-based or fluorine-based lubricant having high heat resistance is preferable, but other materials such as fluorine grease may also be used. By using grease that is highly viscous and contains solid components, the lubricant is more likely to remain between the belt 31 and the sliding member 37 in the fixing nip 3, and wear can be suppressed for a longer period of time.

[0063] The sliding member 37 is a low-friction sheet, and in this case, is wrapped around the fixed pad 32 so as to surround the periphery of the fixed pad 32 for approximately one revolution. For example, a sheet having a sliding surface (outer surface) based on glass cloth and coated with a fluorine-based resin is used.

[0064] A surface 371 of the sliding member 37 facing the belt 31 is formed with minute projections and recesses, and these projections and recesses reduce the contact area with the belt 31, thereby reducing frictional force. The size of the projections and recesses is arbitrary, but from the viewpoint of the function of retaining the lubricant J and suppressing image unevenness caused by the projections and recesses, it is desirable that the surface roughness Ra of the surface 371 is within a range of, for example, 1 to 50 μm. The sliding member 37 may be any member made of a material that can reduce the sliding resistance with the belt 31, and may be, for example, a fluorofiber fabric, a fluororesin sheet, or a glass coating.

[0065] By interposing a sliding member 37 between the belt 31 and the fixed pad 32, the lubricant J applied to the inner surface 311 of the belt 31 by the lubricant supply member 38 is supplied to the surface 371 of the sliding member 37 via the belt 31, thereby reducing the sliding resistance when the belt 31 passes through the fixing nip 3, ensuring stability of the circulating movement of the belt 31 over a long period of time, and reducing wear of the belt 31.

[0066] Returning to Fig. 2, heating roller 35 is made of a cylinder made of metal such as aluminum or SUS, with axis 359 of its rotation axis parallel to the Z-axis direction, and both axial ends of heating roller 35 are rotatably supported by a frame. The outer diameter of heating roller 35 is arbitrary, but is preferably within the range of 10 to 100 mm, and the thickness is preferably within the range of 0.1 to 5 mm.

[0067] The heater 36 as a heat source is a halogen heater that is long along the axial direction of the heating roller 35, and is inserted into the inner space of the cylindrical heating roller 35, and applies heat generated by power supply from a power source (not shown) to the heating roller 35. It is desirable to color the inner circumferential surface of the heating roller 35 black so that heat is efficiently transferred from the halogen heater to the heating roller 35.

[0068] Note that the method is not limited to heating belt 31 with heat from a halogen heater. For example, heater 36 may be another type of heater, such as an infrared heater or an electric heating wire. Any configuration may be used as long as belt 31 is heated, and for example, a resistance heating method may be used in which belt 31 is formed by a resistance heating element that generates heat when supplied with power. In this configuration, belt 31 is heated by passing electricity through the resistance heating element. Also, a so-called electromagnetic induction heating (IH: Induction Heating) method in which belt 31 generates heat through electromagnetic induction may be used.

[0069] In the above configuration, when the pressure roller 39 is rotationally driven in the direction of arrow A, the belt 31 receives the rotational drive force and travels in the direction of arrow B. This travel direction is the belt rotation direction. When the heater 36 is energized while the pressure roller 39 is rotationally driven, heat generated by the heater 36 is transferred from the heating roller 35 to the belt 31, and reaches the fixing nip 3 as the belt 31 travels around. This supplies heat from the heater 36 to the fixing nip 3.

[0070] In this embodiment, a sensor (not shown) is disposed in the fixing unit 30 to detect the surface temperature of the belt 31 and send the detection result to a control unit (not shown). The control unit performs temperature control to switch the heater 36 on and off so that the temperature of the fixing nip 3 is maintained at a fixing temperature (e.g., 170° C.) required for fixing based on the temperature detected by the sensor.

[0071] This temperature control stabilizes the temperature of the fixing nip 3 at the fixing temperature, and when the recording sheet S transported along the transport path 25 passes through the fixing nip 3, the unfixed image on the recording sheet S is heated, melted, and pressurized to be fixed onto the recording sheet S.

[0072] (3) Configuration of the fixed pad Figure 4 is a schematic diagram showing the configuration of fixed pad 32, Figure 5 is a schematic oblique view of the upstream guide 321 of fixed pad 32 as viewed from the direction indicated by arrow E in Figure 4, and Figure 6 is a schematic plan view of belt 31, fixed pad 32, and pressure roller 39 as viewed from above, with components other than belt 31, fixed pad 32, and pressure roller 39 being omitted from the illustration.

[0073] As shown in Figures 4 and 5, the upstream guide 321 of the fixed pad 32 has a guide surface 320 that contacts the inner surface 311 of the belt 31 via the sliding member 37, and is provided with convex portions (pressure application portions) 324, 325 that rise by a predetermined amount H toward the inner surface 311 of the belt 31 at the downstream end in the belt circulation direction (arrow B direction) and both ends in the belt width direction (arrow G direction).

[0074] Here, the upstream guide 321 and the pressed portion 322 for forming the fixing nip 3 are adjacent to each other in this order in the belt rotation direction, so the position in the belt rotation direction of the convex portions 324 and 325 provided on the upstream guide 321 can be said to be the position of the area just before the fixing nip 3 (reference numeral 333 in FIGS. 4 and 7). Hereinafter, this position will be referred to as the position just before the fixing nip 3.

[0075] If the portion 326 (dashed line) toward the center of the belt width direction, sandwiched between the convex portions 324, 325 located on both ends of the belt width direction, is defined as the central portion, the central portion 326 is an area other than the convex portions 324, 325 on the guide surface 320 of the upstream guide 321, and is recessed relative to the convex portions 324, 325.

[0076] Therefore, it can be said that the guide surface 320 of the convex portions 324, 325 is a surface whose height (height in the thickness direction) in the direction approaching the inner circumferential surface 311 of the belt 31 is higher by a predetermined amount H than the guide surface 320 of the central portion 326. The predetermined amount H is a value in the range of 0.1 to 0.5 mm here. The thickness of the convex portions 324, 325 is thicker than that of the central portion 326 so that the height of the convex portions 324, 325 is higher than that of the central portion 326 by the predetermined amount H. Note that, depending on the device configuration, the predetermined amount H may be set to a value within a range different from the above.

[0077] 5, the convex surface portion 324 has a right-angled triangular shape in a plan view, and has a side 241 (first side) parallel to the belt width direction, a hypotenuse 242 (second side), and a side 243 along the belt circumferential direction. The angle between the side 241 and the side 243 is 90°, and the angle θ between the side 241 and the hypotenuse 242 is 30° in this case.

[0078] The convex portion 324 is formed with a side 243 facing the end side in the belt width direction, and a vertex 244 of a 30° angle facing the center side in the belt width direction. In other words, the side 243 is the outermost end in the belt width direction (the base end on the end side in the belt width direction), and the vertex 244 is the side farthest from the end in the belt width direction, that is, the end on the center side in the belt width direction. The side 243 is called the base end of the convex portion 324 in the belt width direction, and the vertex 244 is called the tip end of the convex portion 324 in the belt width direction.

[0079] The length (width) W of the convex portion 324 in the belt circumferential direction corresponds to the distance between the side 241 and the oblique side 242, and has a tapered shape that gradually decreases from the belt width direction base end 243, which is the end side in the belt width direction, toward the belt width direction tip end 244, which is the central side in the belt width direction.

[0080] The convex portion 325 has a right-angled triangular shape in a plan view, which has basically the same shape and height as the convex portion 324, and has a tapered shape in which the length W in the belt circumferential direction gradually decreases from the base end 253 in the belt width direction to the tip 254 in the belt width direction, as shown in FIG. 5.

[0081] The positional relationship in the belt width direction among the convex surface portions 324 and 325, the belt 31, and the pressure roller 39 is shown in Fig. 6. That is, on one end side in the belt width direction (the left end side in the same figure), the base end 243 in the belt width direction of the convex surface portion 324, one end (edge) 318 in the belt width direction of the belt 31, one end 398 in the axial direction of the pressure roller 39, and the tip 244 in the belt width direction of the convex surface portion 324 are aligned in this order in the direction from one end in the belt width direction toward the center (the direction of the arrow Z).

[0082] Similarly, on the other end side in the belt width direction (the right end side in the same figure), the belt width direction base end 253 of the convex portion 325, the other end (edge) 319 in the belt width direction of the belt 31, the other axial end 399 of the pressure roller 39, and the belt width direction tip 254 of the convex portion 325 are arranged in this order in the direction from the other end in the belt width direction toward the center (the opposite direction of arrow Z).

[0083] Here, the region 3d where the pressure roller 39 and the belt 31 are in contact indicates the nip formation region of the fixing nip 3, and the axial ends 398 and 399 of the pressure roller 39 are equal to the edges in the belt width direction of the nip formation region 3d.

[0084] From FIG. 6, the base ends 243 and 253 in the belt width direction of the convex portions 324 and 325 protrude outside the belt 31 in the belt width direction.

[0085] Also, the tip 244 in the belt width direction of the convex portion 324 extends to a position closer to the center in the nip formation region 3d (the axial center of the pressure roller 39) than the edge (one end of the pressure roller 39) 398 of one edge of the nip formation region 3d in the belt width direction.

[0086] Similarly, the tip 254 in the belt width direction of the convex portion 325 extends to a position closer to the center in the nip formation region 3d (the axial center of the pressure roller 39) than the edge (the other end of the pressure roller 39) 399 of the other edge of the nip formation region 3d in the belt width direction.

[0087] FIG. 7 is a schematic side view when the belt 31 and the fixing pad 32 are viewed in a state of seeing through the pressure roller 39 in the direction of arrow Xa in FIG. 2, and the rectangular region indicated by the solid line 3d shows the nip formation region.

[0088] As shown in FIG. 7, when the belt width direction length of the nip formation region 3d is L1, the belt width direction length of the belt 31 is L2, and the belt width direction length of the fixing pad 32 is L3, they have the magnitude relationship of L1 < L2 < L3. The belt width direction length L1 of the nip formation region 3d is equal to the axial length of the pressure roller 39.

[0089] In the normal state where the pressure roller 39 presses the fixing pad 32 via the belt 31 with a normal pressure during printing, the magnitude relationship of the pressures generated between the belt 31 and the fixing pad 32 at three different positions α, β, and γ in the belt width direction is shown in the schematic diagram of FIG. 8. This pressure corresponds to the value obtained by dividing the pressing force acting in the direction perpendicular to the inner peripheral surface 311 of the belt 31 by the unit area.

[0090] Here, the position α is a position outside the nip formation region 3d in the belt width direction.

[0091] Position β is a position within the nip formation region 3d in the belt width direction and within the area between one end 398 of the nip formation region 3d and the belt width direction tip 244 of the convex portion 324, or a position within the area between the other end 399 of the nip formation region 3d and the belt width direction tip 254 of the convex portion 325.

[0092] The position γ is located within the nip formation region 3d in the belt width direction and is closer to the center than the leading ends 244 and 254 of the convex portion 324 in the belt width direction.

[0093] As shown in FIG. 8, at position α, pressure P between belt 31 and upstream guide 321 is Pa, and pressure P between belt 31 and pressed portion 322 is Pe.

[0094] Since position α is outside the nip formation area 3d, the pressures Pa and Pe are generated not by the pressing force of the pressure roller 39, but by the tension acting on the belt 31 which is stretched between the fixed pad 32, the heating roller 35 and the guide member 33.

[0095] As described above, the inner diameter of the belt 31 is the same at any position in the belt width direction. Therefore, when comparing the portion where the convex surface portions 324, 325 are provided on the upstream guide 321 (end portion in the belt width direction: position α) with the portion where they are not provided (center portion in the belt width direction: position γ), the force with which the convex surface portions 324, 325 press the belt 31 from the inner peripheral surface side to the outer peripheral surface side is greater at the end portion where the convex surface portions 324, 325 are provided than at the center portion where the convex surface portions 324, 325 are not provided, by the thickness of the convex surface portions 324, 325. The tension acting on the belt 31 as a reaction to the increased pushing force is greater than that at the center portion where the convex surface portions 324, 325 are not provided, and the increased tension is expressed as a pressure P with a magnitude Pa.

[0096] The pressed portion 322 is not provided with convex portions 324 and 325. Unlike the guide 321 which is a convex curved surface, the pressed portion 322 is a concave curved surface, so the pressure Pe is much smaller than the pressure Pa of the guide 321.

[0097] At position β, the pressure P is Pb (<Pa), and the pressure P between the belt 31 and the pressed portion 322 is Pc (>Pb). Since position β is within the nip formation region 3d, the nip pressure Pc is considerably increased by the pressing force of the pressure roller 39. In the figure, for the sake of illustration, the magnitude Pc of the pressure P is shown to be about twice that of Pb, but actually it is about 10 times or more. If the nip pressure is too high, the lubricant J may not enter between the belt 31 and the fixed pad 32 at all. Therefore, within the range where the required amount of lubricant J can enter between the belt 31 and the fixed pad 32, a nip pressure suitable for fixing is set in advance by experiments or the like.

[0098] On the other hand, the pressure Pb at position β is smaller than the pressure Pa at position α. This is because the length Wb of the convex portions 324 and 325 in the belt circumferential direction at position β is shorter than the length Wa of the convex portions 324 and 325 in the belt circumferential direction at position α. That is, also at position β, similar to position α, since the pressing force of the pressure roller 39 does not act at the position immediately before the fixing nip 3, the magnitude of the tension acting on the belt 31 affects the magnitude of the pressure Pb. The thickness of the convex portions 324 and 325 is the same at any position in the belt width direction as described above. However, the shorter the length W in the belt circumferential direction, the shorter the length in the belt circumferential direction of the region where the belt 31 is pushed from the inner circumferential surface side to the outer circumferential surface side, and accordingly, the force with which the convex portions 324 and 325 push the belt 31 from the inner circumferential surface side to the outer circumferential surface side decreases. Due to the decrease in this pushing force, the tension acting on the belt 31 decreases, and due to the decrease in the tension, the pressure Pb at position β becomes smaller than the pressure Pa at position α.

[0099] Although the pressure P is not illustrated between the position α and the position β, as shown in FIG. 7, the convex portions 324 and 325 are in the shape of a right triangle in plan view, and the convex portions 324 and 325 are formed in a shape in which the belt circumferential direction length W of the convex portions 324 and 325 gradually decreases from the end side in the belt width direction toward the center side. Due to the gradual decrease in the length W of the convex portions 324 and 325, the pressure P between the upstream guide 321 and the belt 31 becomes a pressure distribution that gradually decreases as it goes from the edge in the belt width direction of the belt 31 toward the center (from the end side to the center side in the belt width direction), as shown in the solid line graph of FIG. 9. This pressure distribution is equivalent to having a relationship in which, in the region where the belt 31 is pressed by the convex portions 324 and 325, at any two positions at different positions in the belt width direction, the pressure P is higher on the end side (outer side) than on the center side (inner side).

[0100] The magnitude of this pressure P is desirably in the range of, for example, 1 to 200 kPa. If the pressure P is less than 1 kPa, the contact state between the belt 31 and the upstream guide 321 is likely to become unstable, and if there are strong and weak pressing force portions between one end and the other end in the belt width direction, temperature unevenness in the belt width direction may occur, and image unevenness after fixing may occur. On the other hand, if the pressure P exceeds 200 kPa, the pressure becomes too high and it becomes difficult for the lubricant J to enter between the belt 31 and the upstream guide 321, and wear of the belt 31 and the sliding member 37 is promoted, and the durability may decrease. Note that depending on the device configuration, the magnitude of the pressure P may be set to a value within a range different from the above.

[0101] Returning to FIG. 8, at the position γ (center portion in the belt width direction), the pressure P between the belt 31 and the upstream guide 321 in the upstream guide 321 is Pd (<Pb), and the pressure P between the belt 31 and the pressed portion 322 in the pressed portion 322 is Pc. Since the position γ is within the nip formation region 3d similarly to the position β, the pressure Pc of the pressed portion 322 is the same nip pressure Pc as that of the position β.

[0102] The pressure Pd between the belt 31 and the upstream guide 321 is quite small. The position γ is within the central region where the convex portions 324 and 325 are not provided, so the tension acting on the belt 31 is lower than that in the end regions where the convex portions 324 and 325 are provided.

[0103] On the guide surface 320 of the upstream guide 321, the pressure P in the central region (region 326 in FIG. 5: the region where the convex portions 324 and 325 are not provided) intervening between the convex portions 324 and 325 is substantially the same as Pd (>0) at any position in the belt width direction.

[0104] That is, immediately before the fixing nip 3, due to the tension of the belt 31, a predetermined pressing force acts between the entire area from one end to the other end of the belt 31 in the belt width direction and the guide surface 320 of the upstream guide 321. Due to the action of this pressing force, immediately before the fixing nip 3, the entire area from one end 318 to the other end 319 of the belt 31 in the belt width direction is in contact with the upstream guide 321 via the sliding member 37.

[0105] Thereby, for example, in a configuration where there are alternately portions in contact with and not in contact with the inner peripheral surface 311 of the belt 31 like a comb-shaped guide, temperature unevenness in the belt width direction caused by heat escaping from the belt 31 at the contacting portions and not escaping at the non-contacting portions is prevented. Note that the magnitude relationship between the pressures Pe and Pd can be arbitrary, and there may be cases where Pe < Pd or they are substantially the same.

[0106] Here, when a configuration without the convex portions 324 and 325 is taken as a conventional equivalent configuration (comparative example), the magnitudes of the pressure P at the positions α, β, and γ are shown in the schematic diagram of FIG. 10. The upstream guide without the convex portions 324 and 325 is denoted by 921, and the pressed portion 922 and the downstream guide 923 correspond basically to the above-mentioned pressed portion 322 and downstream guide 323.

[0107] As shown in Fig. 10, in the comparative example, the magnitude of pressure P between pressed portion 922 and downstream guide 923 is approximately the same as the magnitude of pressure P shown in Fig. 8. On the other hand, upstream guide 921 does not have convex portions 324, 325, and therefore pressure P with belt 31 is the same magnitude Pd at all positions α, β, and γ. The same is true for positions other than positions α and β, and pressure P is approximately constant at Pd at all positions in the entire region from one end to the other end in the belt width direction (graph of wavy line in Fig. 9).

[0108] Using Figures 11(a) and (b), we will explain how the lubricant J flows as the belt 31 rotates in a configuration (embodiment) having a pressure distribution in which the pressure gradually decreases from the edge to the center in the belt width direction of the belt 31 as shown in Figures 7 and 8, and a conventional configuration (comparison example) having a pressure distribution in which the pressure is constant in the belt width direction as shown in Figure 10.

[0109] Here, the embodiment in Figure 11(a) is a schematic side view of the fixed pad 32 when viewed from the direction of arrow Xa in Figure 2, through the pressure roller 39, belt 31, and sliding member 37, and shows diagrammatically how the lubricant J, indicated by a circle, applied to the inner surface 311 of the belt 31 has entered between the upstream guide 321 of the fixed pad 32 and the belt 31 as the belt 31 rotates, and in this figure, the direction from bottom to top corresponds to the belt rotation direction.

[0110] As shown in the embodiment, when the lubricant J reaches the convex portion 324 of the upstream guide 321 at position 328 in the belt width direction, a portion Ja of the lubricant J passes directly between the convex portion 324 and the belt 31 along the belt circulation direction (bottom to top) and enters the nip formation region 3d, while the remaining portion Jb proceeds in a direction slightly inclined toward the center of the belt width direction with respect to the belt circulation direction, passes between the convex portion 324 and the belt 31, and enters the nip formation region 3d at position 329, which is closer to the center of the belt width direction than position 328.

[0111] This is due to the pressure distribution shown in FIG. 9, and the lubricant J passes between the belt 31 and the convex surface portion 324 more easily at the position 329 where the pressure P between the belt 31 and the convex surface portion 324 is lower than at the position 328 where the pressure P between the belt 31 and the convex surface portion 324 is higher. Due to the pressure distribution shown in FIG. 9, that is, the pressure distribution in which the pressure P between the belt 31 and the convex surface portion 324 gradually decreases from the edge 318 in the belt width direction of the belt 31 toward the center, the lubricant J present at the end of the belt width direction immediately before the fixing nip 3 is transported toward the center in the belt width direction and enters the nip formation region 3d. Note that the flow of the lubricant J is not shown for the convex surface portion 325, but the lubricant J is transported from the edge 319 in the belt width direction toward the center in the same manner as the convex surface portion 324. The lubricant J present at the center in the belt width direction is also not shown, but this lubricant J enters the nip formation region 3d as it is.

[0112] In contrast, in the comparative example, the upstream guide 921 does not have the convex portions 324, 325, and the pressure P between the belt 31 and the upstream guide 921 at a position immediately before the fixing nip 3 is the same across the entire area from one end to the other end in the belt width direction.

[0113] As a result, a portion of the lubricant J Jc that reaches the high-pressure nip formation region 3d at the end of the belt width direction is unable to pass through the nip formation region 3d and escapes in the direction toward the edge of the belt width direction (to the left in the same figure), eventually leaking out of the belt 31 from the edge of the belt 31.

[0114] In the embodiment, the lubricant J present at the end in the belt width direction is transported toward the center in the belt width direction and then passes through the nip formation area 3d by the convex portions 324, 325 provided at both ends in the belt width direction of the upstream guide 321 just before the fixing nip 3, so that the lubricant J present at the end in the belt width direction can be prevented from leaking out of the belt 31 as in the comparative example.

[0115] Since the lubricant J does not leak out of the belt 31, the amount of lubricant J on the inner peripheral surface 311 of the belt 31 can be stably maintained, and an increase in the frictional resistance between the belt 31 and the fixed pad 32 via the sliding member 37 can be prevented. By preventing this increase in frictional resistance, it is possible to prevent the belt 31 from wearing more quickly and to prevent an increase in the torque driving the belt 31, so that the belt 31 and the pressure roller 39 can be maintained in smooth rotation for a long period of time, and a decrease in the conveyance of the recording sheet S can be prevented.

[0116] In addition, since the convex surface portions 324, 325 are provided only on both ends in the belt width direction, the lubricant J can be returned from the ends in the belt width direction to the center while suppressing the sliding resistance with the inner peripheral surface 311 of the belt 31. The length J in the belt circumferential direction of the convex surface portions 324, 325 is gradually decreased from the ends in the belt width direction toward the center of the belt 31. As a result, the area where the convex surface portions 324, 325 contact the inner peripheral surface 311 of the belt 31 becomes smaller toward the center in the belt width direction, and the sliding resistance with the inner peripheral surface 311 of the belt 31 can be suppressed accordingly.

[0117] <Modification> While the present disclosure has been described above based on the embodiments, it goes without saying that the present disclosure is not limited to the above-described embodiments, and the following modified examples are possible.

[0118] (1) In the above embodiment, the angle θ of the belt width direction tip 244 of the convex surface portions 324, 325 is 30°, but is not limited to this. Any angle may be used as long as it can form the above-mentioned pressure distribution required to return the lubricant J from the end portion in the belt width direction to the center. If the angle θ is made too large, the area of ​​the convex surface portions 324, 325 becomes large, and the sliding resistance with the belt 31 increases. Conversely, if the angle θ is made too small, it becomes difficult to ensure the above-mentioned pressure distribution. An angle within an appropriate range from the viewpoints of both the sliding resistance with the belt 31 and ensuring the above-mentioned pressure distribution is determined in advance through experiments, etc.

[0119] (2) In the above embodiment, the shape of the convex surfaces 324, 325 of the upstream guide 321 in a plan view is a right-angled triangle, but this is not limited to this. Any shape can be used as long as it can form the above pressure distribution.

[0120] For example, a convex surface portion 424 having a planar shape as shown in Fig. 12 may be provided. The convex surface portion 424 has a tapered shape in which an edge 442 connecting a leading end 444 in the belt width direction and an upstream end 445 in the belt circumferential direction forms a convex arc shape (solid line) in the belt circumferential direction.

[0121] If the above pressure distribution can be formed, such an arc-shaped edge 442 can also be used. It may also be possible to form the edge 442 in an arc shape that protrudes in the opposite direction to the belt rotation direction, as shown by the dashed line.

[0122] Furthermore, the convex surface portion 524 may have the configuration shown in Fig. 13(a) and (b). Fig. 13(a) is a schematic diagram of the convex surface portion 524 in a plan view, and Fig. 13(b) is a diagram showing a QQ cross section of Fig. 13(a). As shown in Fig. 13(a), the convex surface portion 524 is rectangular in a plan view, and as shown in Fig. 13(b), the convex surface portion 524 has a shape in which the height I in the thickness direction (the direction approaching the belt 31) gradually decreases from the base end 545 in the belt width direction (arrow G direction) toward the tip 544 in the belt width direction. This gradual decrease in the height I forms the above pressure distribution. In the above, only the convex surface portion on one end side in the belt width direction is shown, but the convex surface portion on the other end side in the belt width direction can also have the same shape.

[0123] (3) In the above embodiment, as shown in FIG. 7, a configuration example has been described in which the belt width direction leading ends 244, 254 of the convex portions 324, 325 of the upstream guide 321 are positioned closer to the center in the belt width direction than one end (edge) 398 and the other end (edge) 399 of the nip formation area 3d. However, this is not limited to this.

[0124] 14, the belt width direction tips 244, 254 of the convex portions 324, 325 may be positioned closer to the belt width direction edges 318, 319 of the belt 31 than to the edges 398, 399 of the nip formation region 3d, that is, may not extend to the belt width direction positions of the edges 398, 399 of the nip formation region 3d. If the pressure at the belt width direction edge of the belt 31 immediately before the fixing nip 3 has the above pressure distribution, it is possible to prevent the lubricant J from leaking out from the edge of the belt 31.

[0125] (4) In the above embodiment, a configuration example has been described in which the convex portions 324, 325 as pressure-applying portions for forming the above pressure distribution are provided at both ends of the upstream guide 321 of the fixed pad 32 in the belt width direction. However, this is not limited to this.

[0126] In a configuration in which the fixed pad 32 does not have the convex portions 324, 325, it is also possible to adopt a configuration in which a pressure applying section 100 having truncated cone-shaped pressure rollers 111, 112 as shown in FIG. 15(a) is provided on the outer periphery of the belt 31.

[0127] FIG. 15(a) is a schematic plan view of the belt 31, fixed pad 32, pressure roller 39, and pressure applying section 100 according to this modified example, as viewed from above.

[0128] As shown in the figure, pressure applying section 100 has pressure rollers 111, 112 in a truncated cone shape, and rotation shafts 113, 114 that support pressure rollers 111, 112 rotatably about an axis that passes through the center of the truncated cone.

[0129] The truncated cone shaped pressure rollers 111, 112 press the end of the belt 31 in the belt width direction against the upstream guide 321 of the fixed pad 32 via the belt 31 immediately before the fixing nip 3, and are disposed in the belt width direction closer to the edges 318, 319 of the belt 31 than the axial ends 398, 399 of the pressure roller 39, and slightly upstream in the belt rotation direction (upstream in the sheet conveying direction) than the pressure roller 39. With this arrangement, when viewed from the axial direction of the pressure roller 39, the end of the pressure roller 39 and the end of the pressure roller 111 (or 112) partially overlap each other.

[0130] The rotating shaft 113 is parallel to the belt width direction, has a tip end side 115 into which the pressure roller 111 is rotatably fitted, and has a base end side 116 fixed to the frame. The rotating shaft 114 is also parallel to the belt width direction like the rotating shaft 113, has a tip end side 115 into which the pressure roller 112 is rotatably fitted, and has a base end side 116 fixed to the frame.

[0131] 15(b) is an enlarged view of the pressing roller 111, which has a truncated cone shape in which the diameter Da of one end 118 in the belt width direction is larger than the diameter Db of the other end 119. The other pressing roller 112 is also in a truncated cone shape in which the diameter Da of the end 118 is larger than the diameter Db of the end 119. The pressing rollers 111 and 112 are fitted into the rotating shafts 113 and 114 with the large diameter end 118 facing the end side in the belt width direction and the small diameter end 119 facing the center side in the belt width direction.

[0132] Since the pressure rollers 111, 112 have a truncated cone shape, the pressure in the belt width direction of the pressure when the pressure rollers 111, 112 press the upstream guide 321 of the fixed pad 32 through the belt 31 has a pressure distribution as shown by the solid line in Fig. 7. This makes it possible to prevent the lubricant J from leaking out from the edge of the belt 31, as in the embodiment.

[0133] (5) In the above embodiment, the convex surface portions 324, 325 are provided at one and the other ends in the belt width direction, but this is not limited to the above. For example, a configuration in which a convex surface portion is provided only at one end in the belt width direction may be adopted. Specifically, there is a configuration in which the belt 31 gradually moves toward one end or the other end in the belt width direction while traveling in a circular motion.

[0134] In such a configuration, the lubricant J applied to the inner peripheral surface of the belt 31 also tends to flow in the same direction as the belt 31 shifts just before the fixing nip 3, and the lubricant J tends to leak out of the belt 31. On the other hand, the lubricant J hardly leaks out of the belt 31 in the direction opposite to the direction in which the belt 31 shifts.

[0135] Therefore, by providing a convex portion only on the end portion in the direction in which the belt 31 shifts, the lubricant J can be prevented from leaking out from the belt 31.

[0136] (6) In the above embodiment, the heating roller 35 and the guide member 33 are used as tension members for tensioning the belt 31 together with the fixed pad 32, but the present invention is not limited to this. For example, there is a configuration that does not include the guide member 33, and in this configuration, the heating roller 35 is the tension member. In addition, in the electromagnetic induction type or the resistance heating type, in a configuration that does not include the heater 36, a configuration in which another driven roller is arranged as the tension member instead of the heating roller 35 can be adopted. In addition, in the configuration according to the modified example shown in FIG. 15(a), if the belt 31 is an elastic self-shape-retaining belt that can independently maintain a substantially cylindrical shape, a configuration in which a member for tensioning the belt 31 is not provided can be adopted. In addition, when a self-shape-retaining belt is used in the above embodiment, if the same pressure distribution as the above can be formed without providing a tension member, the embodiment can also be configured without providing a tension member.

[0137] (7) In the above embodiment, a configuration example in which the lubricant supplying member 38 that applies the lubricant J to the inner circumferential surface 311 of the belt 31 is provided has been described, but the present invention is not limited to this, and for example, a configuration is also possible in which the lubricant supplying member 38 is not provided. In this configuration, the lubricant J is applied to the inner circumferential surface 311 of the belt 31 by an operator during the manufacturing stage of the fixing unit 30 or during maintenance.

[0138] Also, while a configuration example in which the sliding member 37 is provided has been described, the present invention is not limited thereto, and as long as stable rotation of the belt 31 can be maintained, a configuration without the sliding member 37 may be adopted. In this configuration, the entire area of ​​the belt 31 in the belt width direction from one end 318 to the other end 319 in the belt width direction immediately before the fixing nip 3 comes into direct contact with the upstream guide 321 of the fixed pad 32.

[0139] (8) In the above embodiment, the fixed pad 32 is fixedly supported by the support member 34, and the pressure roller 39 presses the fixed pad 32 via the belt 31, but this is not limited to the above. The fixed pad 32 may be a non-rotating body that does not rotate as the belt 31 travels around, and may be configured, for example, so that the fixed pad 32 presses the pressure roller 39 via the belt 31 by the biasing force of a biasing member such as a spring. In either case, a pressing force acts between the pressure roller 39 and the fixed pad 32, and therefore this is included in the configuration in which the pressure roller 39 presses the fixed pad 32.

[0140] (9) In the above embodiment, an example in which the image forming apparatus according to the present disclosure is applied to a tandem color printer has been described, but the present disclosure is not limited to this. The present disclosure can be applied to a fixing device having an endless belt and an image forming apparatus including the fixing device. The image forming apparatus can be one capable of forming color images or one capable of forming monochrome images only, and is not limited to printers, but can be applied to image forming apparatuses such as copiers, facsimile machines, and MFPs (Multiple Function Peripherals).

[0141] The size, shape, material, number and each value of each of the above-mentioned members are merely examples, and the size, shape, material, number and each value of each member are determined in advance according to the device configuration.

[0142] In addition, the contents of the above-described embodiment and the above-described modified examples may be combined as much as possible. The mechanisms and members of each unit, such as the fixing unit, may be replaced with other mechanisms or members of other shapes within the scope of the present disclosure. [Industrial Applicability]

[0143] The present disclosure can be widely applied to fixing devices having an endless belt. [Explanation of symbols]

[0144] 1. Printer 3 Fixing nip 30 Fixing section 31 Belt 32 Fixed pad 34 Support member 35 Heating roller 36 Heater 37 Sliding members 38 Lubricant supply member 39 Pressure Roller 111, 112: Cone-shaped pressure roller (pressure applying part) 241 First Side 242 Second Side 243 Base end of the convex part on the belt width direction end side 244, 254 The tip of the convex part on the center side in the belt width direction 311 Inner surface of belt 320 Guide surface 318 One end of the belt in the width direction (edge) 319 The other end (edge) of the belt in the belt width direction 321 Upstream guide of fixed pad 324, 325, 424, 524 Convex surface portion (pressure applying portion) on the upstream guide 326 Area other than the convex part on the guide surface of the upstream guide 333 Immediately before the fixing nip 398, 399 Edges in the belt width direction of the nip forming area (axial ends of the pressure roller) B Belt rotation direction G Belt width direction J Lubricants P Pressure between belt and upstream guide S Record Sheet W: Length (width) of the convex part in the belt circumferential direction

Claims

1. A fixing device for fixing an unfixed image on a sheet by passing the sheet through a fixing nip formed by pressing an endless belt having an inner peripheral surface coated with a lubricant with a pressure roller disposed on an outer peripheral side of the belt, the fixing device comprising: a non-rotating pad including a pressure receiving portion that is pressed against a pressure roller via the belt on an inner peripheral side of the belt, and a guide that is provided upstream of the pressure receiving portion in a belt rotation direction and guides the belt to the fixing nip; a pressure applying section that applies a pressure between an end of the belt in a belt width direction and the guide at a position immediately upstream of the fixing nip in the belt rotation direction, the pressure gradually decreasing from the end side toward a center side in the belt width direction; Equipped with the guide has a convex portion that rises toward an inner circumferential surface of the belt at a position corresponding to the end of the belt, the pressure applying portion is the convex portion, The convex surface portion is formed in a tapered shape in which the length of the convex surface portion in the belt circumferential direction gradually decreases from the end side toward the center side in the belt width direction so that the gradually decreasing pressure is applied, and the convex surface portion does not extend to the pressed portion located downstream of the guide in the belt circumferential direction. A fixing device comprising:

2. A fixing device for fixing an unfixed image on a sheet by passing the sheet through a fixing nip formed by pressing an endless belt having an inner peripheral surface coated with a lubricant with a pressure roller disposed on an outer peripheral side of the belt, the fixing device comprising: a non-rotating pad including a pressure receiving portion that is pressed against a pressure roller via the belt on an inner peripheral side of the belt, and a guide that is provided upstream of the pressure receiving portion in a belt rotation direction and guides the belt to the fixing nip; a pressure applying section that applies a pressure between an end of the belt in a belt width direction and the guide at a position immediately upstream of the fixing nip in the belt rotation direction, the pressure gradually decreasing from the end side toward a center side in the belt width direction; Equipped with the guide has a convex portion that rises toward an inner circumferential surface of the belt at a position corresponding to the end of the belt, the pressure applying portion is the convex portion, The convex surface portion is formed in a shape in which the height of the convex surface portion gradually decreases from the end side toward the center side in the belt width direction so that the gradually decreasing pressure is applied, and is not extended to the pressed portion located downstream of the guide in the belt circumferential direction. A fixing device comprising:

3. 3. The fixing device according to claim 1, wherein the end of the convex portion on the center side in the belt width direction extends to a position closer to the axial center of the pressure roller in the belt width direction than the axial end of the pressure roller.

4. 2. The fixing device according to claim 1, wherein the tapered shape is formed by a first side parallel to the belt width direction and a second side upstream of the first side in the belt rotation direction and inclined with respect to the first side.

5. 5. The fixing device according to claim 1, wherein a base end of the convex portion on an end side in the belt width direction protrudes to an outside of the belt in the belt width direction.

6. A fixing device for fixing an unfixed image on a sheet by passing the sheet through a fixing nip formed by pressing an endless belt having an inner peripheral surface coated with a lubricant with a pressure roller disposed on an outer peripheral side of the belt, the fixing device comprising: a non-rotating pad including a pressure receiving portion that is pressed against a pressure roller via the belt on an inner peripheral side of the belt, and a guide that is provided upstream of the pressure receiving portion in a belt rotation direction and guides the belt to the fixing nip; a pressure applying section that applies a pressure between an end of the belt in a belt width direction and the guide at a position immediately upstream of the fixing nip in the belt rotation direction, the pressure gradually decreasing from the end side toward a center side in the belt width direction; Equipped with the pressure applying portion is a pressure roller having a truncated cone shape that presses the end portion of the belt against the guide from an outer circumferential side of the belt at the immediately preceding position, The fixing device is characterized in that the pressure roller is arranged on the outside of the belt, on the side of the pressure roller in the belt width direction where the end of the belt is located, and just before the pressure roller in the belt rotation direction, with the large diameter end facing the end side in the belt width direction and the small diameter end facing the center side in the belt width direction.

7. 7. The fixing device according to claim 1, wherein an end portion in the axial direction of the pressure roller is closer to a center of the belt in the belt width direction than an end edge of the belt in the belt width direction.

8. 8. The fixing device according to claim 1, wherein the belt is in contact with the guide over an entire area from one end to the other end in the belt width direction at the immediately preceding position.

9. 8. The fixing device according to claim 1, further comprising a low-friction sheet interposed between the belt and the pad.

10. 10. The fixing device according to claim 9, wherein the belt is in contact with the guide via the low friction sheet over an entire area from one end to the other end in the belt width direction at the immediately preceding position.

11. 11. The fixing device according to claim 1, further comprising a lubricant supplying member for supplying a lubricant to an inner peripheral surface of the belt.

12. 12. The fixing device according to claim 1, wherein the pressure applied by the pressure applying section is within a range of 1 to 200 kPa.

13. 5. The fixing device according to claim 1, wherein the height of the convex portion is within a range of 0.1 to 0.5 mm.

14. An image forming apparatus including a fixing unit that fixes an unfixed image formed on a conveyed recording sheet, 14. An image forming apparatus comprising the fixing device according to claim 1 as the fixing section.

Images