Fixing device and image forming apparatus

Abstract

To suppress the occurrence of a printing failure.SOLUTION: A fixing device comprises: a fixing belt; a belt support portion that supports an end in a first direction parallel to a rotation axis in the fixing belt; and a contact portion that is brought into contact with an outer peripheral surface of the fixing belt to form a nip portion. The belt support portion includes, in a nip exit portion, a first surface formed at a position away from the rotation axis of the fixing belt by a first distance, a second surface formed at a position closer than the first distance from the rotation axis of the fixing belt, and a first step surface formed between the first surface and the second surface. The first surface is provided between a center portion of the fixing belt and the first surface in the first direction, the first step surface has a first step portion and a second step portion which is located closer to downstream of the fixing belt in a rotation direction than the first step portion, and the second step portion is closer to the center portion of the fixing belt than the first step portion in the first direction.SELECTED DRAWING: Figure 9

Description

[Technical Field]

[0001] The present invention relates to a fixing device and an image forming apparatus. [Background technology]

[0002] In an electrophotographic image forming apparatus, an image (also called a developer image) formed using a developer such as toner is transferred onto a medium such as paper, and then the image (developer image) transferred onto the medium is fixed to the medium using a fixing device.

[0003] This fixing device rotates a cylindrical fixing belt and a pressure member while they are in contact with each other, and heats and presses the medium while sandwiching it in the nip formed between the fixing belt and the pressure member and transporting it, thereby heating and melting the image (developer image) formed on the medium and fixing it to the medium.

[0004] In conventional fixing devices, a contact member that contacts the inner peripheral surface of the fixing belt is provided on the inner peripheral side of the fixing belt, and since the fixing belt rotates while sliding against the contact member, a lubricant such as grease is applied between the fixing belt and the contact member. The contact member is, for example, a heat diffusion member that transfers heat from a heater to the fixing belt, or a guide member that guides the fixing belt (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-3642 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in conventional fixing devices, lubricant can leak from the end of the fixing belt in the direction of the rotation axis, and if the leaked lubricant adheres to the outer surface of the fixing belt, heat is not transferred sufficiently when fixing an image onto the medium, which can result in printing defects.

[0007] The present invention has been made in consideration of the above points, and aims to propose a fixing device and an image forming apparatus that can suppress the occurrence of printing defects. [Means for solving the problem]

[0008] The fixing device of the present invention includes a fixing belt rotatable about a predetermined rotation axis, the fixing belt having an inner peripheral surface coated with a lubricant and an outer peripheral surface opposite the inner peripheral surface, a belt support portion supporting an end of the fixing belt in a first direction parallel to the rotation axis, and a contact portion contacting the outer peripheral surface to form a nip portion and conveying a medium by sandwiching it between the fixing belt and the belt in the nip portion, the belt support portion facing the inner peripheral surface of the fixing belt at a nip outlet portion located downstream of the nip portion in a conveying direction of the medium, and a first surface formed at a distance from the inner circumferential surface of the fixing belt, a second surface formed opposite the inner circumferential surface of the fixing belt and at a position closer than the first distance from the rotation axis of the fixing belt in the second direction, and a first step surface formed between the first surface and the second surface, the second surface being provided between the center of the fixing belt and the first surface in the first direction, the first step surface having a first step portion and a second step portion located downstream of the first step portion in the rotation direction of the fixing belt, and the second step portion being closer to the center of the fixing belt in the first direction than the first step portion.

[0009] In the fixing device of the present invention, the lubricant that has migrated to the end of the inner surface of the fixing belt and entered between the inner surface of the fixing belt and the second surface of the belt support part is blocked by the first step surface, and as the fixing belt rotates, the lubricant can be moved along the first step surface toward the center of the fixing belt in the direction of the rotational axis, thereby suppressing leakage of the lubricant from the end of the fixing belt in the direction of the rotational axis.

[0010] a fixing device including a fixing belt having an inner peripheral surface coated with a lubricant and an outer peripheral surface opposite the inner peripheral surface, the fixing belt being rotatable around a predetermined rotation axis; a belt support portion supporting an end of the fixing belt in a first direction parallel to the rotation axis; and a contact member abutting the outer peripheral surface to form a nip portion and conveying a medium between the fixing belt and the belt at the nip portion, the belt support portion having a first surface facing the inner peripheral surface of the fixing belt at a nip exit portion located downstream of the nip portion in the conveying direction of the medium, the first surface being formed at a position a first distance away from the rotation axis of the fixing belt in a second direction perpendicular to the first direction; a second surface facing the inner peripheral surface of the fixing belt and formed at a position closer than the first distance from the rotation axis of the fixing belt in the second direction; and a first step surface formed between the first surface and the second surface, the second surface being located between a center of the fixing belt and the first surface in the first direction, and the second surface being formed at a position downstream of the nip portion in the conveying direction of the fixing belt.

[0011] In the fixing device of the present invention, the lubricant that has migrated to the end of the inner surface of the fixing belt and entered between the inner surface of the fixing belt and the second surface of the belt support part is blocked by the first step surface, and as the fixing belt rotates, the lubricant can be guided along the first step surface to the first hole and contained within the first hole, thereby preventing the lubricant from leaking from the end of the fixing belt in the direction of the rotational axis.

[0012] The image forming apparatus of the present invention includes the fixing device described above. [Effects of the Invention]

[0013] According to the present invention, it is possible to realize a fixing device and an image forming apparatus that can suppress the occurrence of printing defects. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a diagram showing a configuration of an image forming apparatus according to an embodiment; [Figure 2] FIG. 2 is a schematic diagram illustrating a configuration of a fixing unit according to an embodiment. [Figure 3] FIG. 2 is a cross-sectional view showing a configuration of a fixing unit according to an embodiment. [Figure 4] FIG. 2 is an external perspective view showing the configuration of a heating unit according to the embodiment. [Figure 5] FIG. 2 is an external perspective view showing the configuration of a plate support portion according to the embodiment. [Figure 6] FIG. 10 is an external perspective view showing the configuration of a left belt support portion according to the embodiment. [Figure 7] FIG. 10 is a plan view showing the configuration of the left belt support portion according to the embodiment. [Figure 8] FIG. 10 is an external perspective view showing the configuration of a right-side belt support portion according to the embodiment. [Figure 9] 10A and 10B are diagrams illustrating the movement of the lubricant in the heating section as viewed from the exit side of the nip section according to the embodiment. [Figure 10] 10A and 10B are diagrams illustrating the movement of a lubricant in a heating portion viewed from the entrance side of a nip portion according to an embodiment. [Figure 11] 10A and 10B are diagrams showing the shape of a first step surface according to another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, modes for carrying out the invention (hereinafter referred to as embodiments) will be described in detail with reference to the drawings.

[0016] [1. Configuration of image forming device] Fig. 1 shows an example of the configuration of an image forming apparatus 1 according to this embodiment. Fig. 1 is a side cross-sectional view showing the configuration of the image forming apparatus 1. This image forming apparatus 1 is a device that forms an image on paper P using toner as a developer, and is a so-called electrophotographic monochrome printer.

[0017] The image forming apparatus 1 has a substantially box-shaped device housing 2. Here, the right side of the device housing 2 in the drawing is the front side of the device housing 2, the left side of the drawing is the rear side of the device housing 2, the front side of the drawing is the left side of the device housing 2, and the back side of the drawing is the right side of the device housing 2. The direction from the left side to the right side of the device housing 2 in the drawing (i.e., the forward direction from the back side to the front side of the device housing 2) is the positive direction along the Y axis (+Y direction), the direction from the front side of the device housing 2 in the drawing to the back side of the device housing 2 in the drawing (i.e., the rightward direction from the left side to the right side of the device housing 2) is the positive direction along the X axis (+X direction), and the direction from the bottom side to the top side of the device housing 2 in the drawing (i.e., the upward direction from the bottom to the top of the device housing 2) is the positive direction along the Z axis (+Z direction).

[0018] Inside the device housing 2, there are provided a tray unit 3, an image forming unit 4, a transfer unit 5, and a fixing unit 6. The tray unit 3 is provided in the lower part of the device housing 2, and stores (i.e., accumulates) a plurality of sheets of paper P in a stacked state. A stacker 7 to which the sheets of paper P are discharged is provided on the top surface of the device housing 2. Inside the device housing 2, there is provided a transport path R indicated by a solid arrow between the tray unit 3 and the stacker 7, and along this transport path R, there are provided the image forming unit 4, the transfer unit 5, and the fixing unit 6. Although not shown, the transport path R is provided with transport rollers and the like for transporting the sheets of paper P along the transport path R.

[0019] The image forming unit 4 and the transfer unit 5 are arranged facing each other in the vertical direction with the transport path R in between, with the image forming unit 4 on the upper side and the transfer unit 5 on the lower side. The image forming unit 4 has a photosensitive drum 10 and forms an image (toner image) on the surface of the photosensitive drum 10 using toner as a developer. The transfer unit 5 has a transfer roller 11 that abuts against the lower end of the photosensitive drum 10.

[0020] The image forming unit 4 rotates the photosensitive drum 10 and conveys a sheet of paper P sandwiched between the photosensitive drum 10 and a transfer roller 11. At this time, the transfer unit 5 charges the sheet of paper P to a polarity opposite to that of the toner via the transfer roller 11, thereby transferring the toner image formed on the surface of the photosensitive drum 10 onto the sheet of paper P.

[0021] The fixing unit 6 is provided downstream of the image forming unit 4 and the transfer unit 5 in the paper transport direction, and has a heating unit 12 and a pressure unit 13. The heating unit 12 and the pressure unit 13 are arranged opposite each other in the vertical direction across the transport path R, with the heating unit 12 on the upper side and the pressure unit 13 on the lower side, and the heating unit 12 is pressed against the pressure unit 13.

[0022] The fixing unit 6 fixes the toner image on the paper P to the paper P by heating and pressurizing the paper P while sandwiching the paper P between the heating unit 12 and the pressure unit 13 and transporting the paper P. The configuration of the fixing unit 6 will be described in detail later. After passing through the fixing unit 6, the paper P is transported to the stacker 7 and ejected onto the stacker 7.

[0023] The above is the configuration of the image forming apparatus 1. Here, the case where the image forming apparatus 1 has the configuration of a monochrome printer has been described, but the image forming apparatus 1 is not limited to this, and may have the configuration of a color printer provided with image forming units 4 and transfer units 5 for multiple colors.

[0024] [2. Configuration of the fixing unit] Next, the configuration of the fixing unit 6 will be described in detail. Fig. 2 is a schematic diagram of the heating unit 12 and the pressure applying unit 13, which are the main parts of the fixing unit 6, and Fig. 3 is a cross-sectional view of the heating unit 12 and the pressure applying unit 13. Fig. 2 is a perspective view of the heating unit 12 and the pressure applying unit 13 as seen from the front, and is a simplified view of the heating unit 12 and the pressure applying unit 13. Fig. 3 is a cross-sectional view of the heating unit 12 and the pressure applying unit 13 as seen from the -X direction (specifically, from the left side).

[0025] 2 and 3, the pressure unit 13 is a cylindrical pressure roller 30 extending in the X-axis direction, and is a covered roller in which an elastic layer or the like is cylindrically laminated on the surface of a rod-shaped core body 31. In this pressure roller 30, both ends of the core body 31 are rotatably supported by a frame (not shown), and the pressure roller 30 is rotationally driven by the driving force of a motor (not shown) or the like.

[0026] 2 and 3, the heating unit 12 includes a fixing belt 20, a plate unit 21, plate support units 23L and 23R, and belt support units 24L and 24R, as shown in Fig. 4(A) and (B), which are external perspective views seen from the front. Fig. 4(B) is a diagram in which the fixing belt 20 is omitted from Fig. 4(A).

[0027] The fixing belt 20 is a cylindrical belt extending in the X-axis direction, and a hollow rectangular prism-shaped plate member 21 extending in the X-axis direction is inserted inside the fixing belt 20. As shown in FIG. 4A, the plate member 21 is longer in the X-axis direction than the fixing belt 20, and both end portions in the X-axis direction extend beyond both ends of the fixing belt 20 in the X-axis direction. As shown in FIG. 2, the fixing belt 20 is longer in the X-axis direction than the pressure roller 30, and both end portions are located outside both ends of the pressure roller 30. In this embodiment, the total length (length in the X-axis direction) of the fixing belt 20 is 322 mm, and the center of the fixing belt 20 (also referred to as the center of the fixing belt 20 in the rotation axis direction) is located 161 mm from the end of the fixing belt 20 (position Pc shown in FIG. 4A).

[0028] 3, the plate portion 21 is provided with a heater 25 at the bottom on the side closer to the pressure roller 30, and further with a heat diffusion member 26 between the heater 25 and the fixing belt 20 (i.e., at the lower end of the plate portion 21). The heat diffusion member 26 is a member that comes into contact with the inner circumferential surface of the fixing belt 20 and transfers heat from the heater 25 to the fixing belt 20.

[0029] Plate support portions 23L and 23R are plate-shaped members that support plate portion 21. Plate support portion 23L supports one end portion (left end portion) of plate portion 21 in the X-axis direction, and plate support portion 23R supports the other end portion (right end portion) of plate portion 21 in the X-axis direction, and fixing belt 20 is positioned between plate support portion 23L and plate support portion 23R.

[0030] Furthermore, as shown in Figure 5(A), which is an enlarged oblique view of plate support part 23L in addition to Figure 3, plate support part 23L has belt support part 24L fixed to its inner surface facing plate support part 23R, and as shown in Figure 5(B), which is an enlarged view of plate support part 23R in addition to Figure 3, plate support part 23R has belt support part 24R fixed to its inner surface facing plate support part 23L.

[0031] The belt support portions 24L and 24R are flange-shaped members that support the fixing belt 20. The belt support portion 24L supports one end portion (left end portion) of the fixing belt 20 in the X-axis direction, and the belt support portion 24R supports the other end portion (right end portion) of the fixing belt 20 in the X-axis direction.

[0032] 3, 4, and 5A, as well as FIGS. 6A and 6B, which are enlarged perspective views of belt support portion 24L, and FIG. 7, which is an enlarged plan view of belt support portion 24L, left-side belt support portion 24L is composed of a base portion 40 that faces one end (left end) of fixing belt 20 in the X-axis direction, and a belt insertion portion 41 that extends from one surface of base portion 40 (the surface facing the left end of fixing belt 20) toward fixing belt 20 (i.e., extends rightward) and is inserted inside the left end portion of fixing belt 20. Note that FIG. 6A is an enlarged perspective view of belt support portion 24L as seen from the nip exit side (rear side), which is downstream of nip portion Np in the paper conveyance direction, and FIG. 6B is an enlarged perspective view of belt support portion 24L as seen from the nip entrance side (front side), which is upstream of nip portion Np in the paper conveyance direction. FIG. 7 is an enlarged plan view of the belt support portion 24L as viewed from the +X direction (specifically, the right side).

[0033] 6(A), (B), and 7, the base 40 is a generally disk-shaped member whose shape when viewed from the X-axis direction is a downward C-shape with the opening facing downward. An upward-protruding protrusion 42 is provided on the top of the base 40, and a downward U-shaped recess 43 is provided in the center of the lower side of the base 40. As shown in FIGS. 5(A) and (B), the belt support part 24L is attached to the plate support part 23L by fixing the protrusion 42 of the base 40 to the plate support part 23L with a flange fixing part 44, and the left end part of the plate part 21 (see FIG. 4(B)) is fitted into the recess 43 of the base 40.

[0034] 6(A), (B) and 7, the belt insertion portion 41 is a substantially cylindrical member with the lower part of the outer periphery cut off, and its shape when viewed from the X-axis direction is a downward C-shape that is slightly smaller than the base portion 40. The belt insertion portion 41 is provided so as to surround the recess 43 of the base portion 40, and as shown in FIG. 4(B), the inner periphery side is in contact with (or close to) the upper surface, front surface and rear surface of the left end portion of the plate portion 21.

[0035] As shown in Figure 9, which is a plan view of the heating section 12 and the pressure section 13 viewed from the entrance side of the nip section (the fixing belt 20 is visible through the view), the belt support section 24L has a belt insertion section 41 inserted inside the left end portion of the fixing belt 20 so as to abut against the inner surface of the fixing belt 20, thereby supporting the left end portion of the fixing belt 20 so as to be freely rotatable.

[0036] 4A and 5A, a sliding ring 50 is provided between one surface of the base 40 of the belt support portion 24L and the left end of the fixing belt 20. The sliding ring 50 is inserted into the belt insertion portion 41 of the belt support portion 24L and is rotatably held by the belt support portion 24L.

[0037] 3, 4, and 5(B), as well as Fig. 8(A) and (B), which are enlarged perspective views of belt support portion 24R, right-side belt support portion 24R has a shape symmetrical to left-side belt support portion 24L and has a similar configuration to left-side belt support portion 24L. Fig. 8(A) is an enlarged perspective view of belt support portion 24R as seen from the nip exit side (rear side), and Fig. 8(B) is an enlarged perspective view of belt support portion 24R as seen from the nip entrance side (front side).

[0038] That is, the right belt support portion 24R is also composed of a base portion 40 and a belt insertion portion 41, and the belt insertion portion 41 is inserted inside the right end portion of the fixing belt 20 and abuts against the inner circumferential surface of the fixing belt 20, thereby rotatably supporting the left end portion of the fixing belt 20. Furthermore, a sliding ring 50 is also provided between one surface of the base portion 40 of the right belt support portion 24R and the right end of the fixing belt 20.

[0039] Furthermore, in heating unit 12, left and right plate support members 23L, 23R are movable in the Z-axis direction (up and down direction) and are biased downward by a biasing member such as a spring (not shown), so that together with plate member 21, fixing belt 20 is pressed against pressure roller 30. As a result, as shown in Fig. 3, a nip portion Np is formed between fixing belt 20 and pressure roller 30, and as pressure roller 30 rotates in the direction indicated by arrow E, fixing belt 20 rotates in the direction indicated by arrow D.

[0040] The paper P passes through the nip Np thus formed in the direction indicated by the dotted arrow Ar, and is heated and pressed at this time so that the image is fixed.

[0041] 3, in the heating unit 12, a lubricant 51 is applied between the inner circumferential surface of the fixing belt 20 and the heat diffusion member 26. This lubricant 51 is a semi-solid lubricant oil that allows the fixing belt 20 to slide smoothly against the heat diffusion member 26 located at the lower end of the plate unit 21 while the fixing belt 20, together with the plate unit 21, is pressed against the pressure roller 30.

[0042] As the fixing belt 20 rotates in the direction of arrow D, the lubricant 51 moves in the directions indicated by arrows D1, D2, and D3, thereby spreading over the entire inner surface of the fixing belt 20.

[0043] In the fixing device 6, if the lubricant 51 leaks from one or both of the left and right ends of the fixing belt 20 and adheres to the outer peripheral surface of the fixing belt 20, heat is not transferred sufficiently when fixing an image on the paper P, resulting in printing defects. Therefore, in the fixing device 6 of this embodiment, the belt insertion portions 41 of the belt support portions 24L, 24R that support the left and right end portions of the fixing belt 20 are provided with a function to prevent leakage of the lubricant 51. The configuration of the belt insertion portion 41 will be described in detail below.

[0044] [3. Belt insertion section configuration] First, the configuration of the belt insertion section 41 provided in the left belt support section 24L will be described in detail with reference to Figures 6(A), (B), 7, 9, and 10. Note that Figure 10 is a plan view (with the fixing belt 20 visible) of the heating section 12 and the pressure section 13 as seen from the nip entrance side (front side).

[0045] As described above, the belt insertion portion 41 provided in the belt support portion 24L is an approximately cylindrical member with the lower part of the outer periphery of a cylinder cut off, and has a downward C-shape that is slightly smaller than the base portion 40 when viewed from the X-axis direction.

[0046] As shown in Figures 6(A), 7, and 9, this belt insertion section 41 has, on the outer periphery on the nip exit side (rear side), a first outer surface 60 that contacts the inner periphery of the fixing belt 20, a second outer surface 61 that is formed one step lower than the first outer surface 60 toward the inner periphery of the belt insertion section 41, and a first step surface 62 that forms a step connecting the first outer surface 60 and the second outer surface 61.

[0047] The first outer surface 60 is provided on the side closer to the base 40 (i.e., the side farther from the center of the fixing belt 20 in the direction of the rotation axis), and the second outer surface 61 is provided on the side farther from the base 40 (i.e., the side closer to the center of the fixing belt 20 in the direction of the rotation axis).

[0048] The first outer peripheral surface 60 is formed by a smoothly curved surface extending from the lower end to the upper end of the belt insertion portion 41 along the rotation direction of the fixing belt 20 indicated by arrow D, and the second outer peripheral surface 61 is formed by a smoothly curved surface extending from the lower end to near the upper end of the belt insertion portion 41 along the rotation direction of the fixing belt 20 indicated by arrow D. The rotation direction of the fixing belt 20 indicated by arrow D is the rotation direction during printing, and as will be described in detail later, the fixing belt 20 can also rotate in the direction opposite to arrow D. Hereinafter, the rotation direction opposite to arrow D will be referred to as the reverse rotation direction.

[0049] Furthermore, as shown in Figures 6(B), 7, and 10, this belt insertion portion 41 has, on the outer periphery on the nip entrance side, a third outer peripheral surface 63 that contacts the inner peripheral surface of the fixing belt 20, a fourth outer peripheral surface 64 that is formed one step lower than the third outer peripheral surface 63 toward the inner periphery of the belt insertion portion 41, and a second step surface 65 that forms a step connecting the third outer peripheral surface 63 and the fourth outer peripheral surface 64.

[0050] The third outer peripheral surface 63 is provided on the side closer to the base 40 (i.e., the side farther from the center of the rotation axis direction of the fixing belt 20), and the fourth outer peripheral surface 64 is provided on the side farther from the base 40 (i.e., the side closer to the center of the rotation axis direction of the fixing belt 20). The first outer peripheral surface 60 and the third outer peripheral surface 63 are connected at the upper end of the belt insertion portion 41.

[0051] The third outer peripheral surface 63 is formed as a smoothly curved surface extending from the lower end to the upper end of the belt insertion portion 41 along the reverse rotation direction of the fixing belt 20 indicated by the arrow D', and the fourth outer peripheral surface 64 is formed as a smoothly curved surface extending from the lower end to near the upper end of the belt insertion portion 41 along the reverse rotation direction of the fixing belt 20 indicated by the arrow D'. As shown in FIG. 7 , the rotation axis A of the fixing belt 20 is located at a distance L1 from the first outer peripheral surface 60 supporting the fixing belt 20 in the radial direction of the belt insertion portion 41, which is perpendicular to the rotation axis direction of the fixing belt 20. Here, the distance L2 between the rotation axis A and the second outer peripheral surface 61 in the radial direction of the belt insertion portion 41 is shorter than the distance L1. The distance L3 between the rotation axis A and the third outer peripheral surface 63 is equal to the distance L1, and the distance L4 between the rotation axis A and the fourth outer peripheral surface 64 is shorter than the distance L3. 7, in the first step surface 62, when the first step surface 62 is bisected in the extension direction, the upstream portion in the rotation direction of the fixing belt 20 indicated by the arrow D is defined as the first step surface upstream portion 62A, and the downstream portion is defined as the first step surface downstream portion 62B. In addition, in the second step surface 65, when the second step surface 65 is bisected in the extension direction, the upstream portion in the reverse rotation direction of the fixing belt 20 indicated by the arrow D' is defined as the second step surface upstream portion 65A, and the downstream portion is defined as the second step surface downstream portion 65B.

[0052] Furthermore, the belt insertion portion 41 has protrusions 66 at the upper end portions of the first outer peripheral surface 60 and the third outer peripheral surface 63, which protrude toward the center of the rotation axis direction of the fixing belt 20. The protrusions 66 are provided so that their lower surfaces come into contact with the upper surface of the plate portion 21.

[0053] 6(A), 6(B), and 7, a first hole 67 is provided between the upper end of the second outer peripheral surface 61 and the protrusion 66 (i.e., on the downstream side of the second outer peripheral surface 61 in the rotation direction of the fixing belt 20), which penetrates the second outer peripheral surface 61 in the thickness direction of the belt insertion portion 41 and reaches the upper surface of the plate portion 21, and a second hole 68 is provided between the upper end of the fourth outer peripheral surface 64 and the protrusion 66 (i.e., on the upstream side of the fourth outer peripheral surface 64 in the rotation direction of the fixing belt 20), which penetrates the fourth outer peripheral surface 64 in the thickness direction of the belt insertion portion 41 and reaches the upper surface of the plate portion 21. In this way, the first hole 67 is provided on the nip outlet side, and the second hole 68 is provided on the nip entrance side, with the protrusion 66 sandwiched therebetween.

[0054] 9, the first step surface 62 is inclined by a predetermined inclination angle θ1 with respect to the rotation direction of the fixing belt 20 (the circumferential direction of the belt insertion portion 41) so as to approach the center of the rotation axis (X-axis) of the fixing belt 20 from the upstream side to the downstream side in the rotation direction of the fixing belt 20 indicated by arrow D. In other words, the downstream portion 62B of the first step surface 62 is closer to the center of the rotation axis (X-axis) of the fixing belt 20 than the upstream portion 62A of the first step surface in the rotation axis direction of the fixing belt 20. It is desirable that the lower end of the first step surface 62 (i.e., the upstream end in the rotation direction of the fixing belt 20) is located outside the nip portion Np and the upper end (i.e., the downstream end in the rotation direction of the fixing belt 20) is located inside the nip portion Np in the rotation axis direction of the fixing belt 20. The first step surface 62 forms a step of approximately constant height from the upstream side to the downstream side in the rotation direction of the fixing belt 20. Furthermore, the length L6 of the first step surface 62 in the direction of the rotation axis of the fixing belt 20 indicated by the arrow D is shorter than the length L5 of the first step surface 62 in the direction of the rotation of the fixing belt 20.

[0055] 10 , the second step surface 65 is inclined by a predetermined inclination angle θ2 with respect to the rotation direction of the fixing belt 20 (the circumferential direction of the belt insertion portion 41) so as to approach the center of the rotation axis direction (X-axis direction) of the fixing belt 20 from the upstream side to the downstream side in the reverse rotation direction indicated by arrow D′, which is the opposite direction to the rotation direction of the fixing belt 20 indicated by arrow D. In other words, the second step surface 65 has the downstream portion 65B of the second step surface closer to the center of the rotation axis direction of the fixing belt 20 than the upstream portion 65A of the second step surface in the rotation axis direction of the fixing belt 20. It is desirable that the lower end of the second step surface 65 (i.e., the upstream end in the reverse rotation direction of the fixing belt 20) is located outside the nip portion Np and the upper end (i.e., the downstream end in the rotation direction of the fixing belt 20) is located inside the nip portion Np in the rotation axis direction of the fixing belt 20. The second step surface 65 forms a step of approximately constant height from the upstream side to the downstream side in the reverse rotation direction of the fixing belt 20. The inclination angles (θ1 and θ2) of the first step surface 62 and the second step surface 65 are approximately the same. Furthermore, the length L8 of the second step surface 65 in the rotation axis direction is shorter than the length L7 in the direction along the reverse rotation direction of the fixing belt 20 indicated by the arrow D'.

[0056] 9 and 10, the first outer peripheral surface 60 and the third outer peripheral surface 63 each have approximately the same length (width) from top to bottom in the direction of the rotation axis (left-right direction) of the fixing belt 20, and also have approximately the same overall area. Furthermore, the first outer peripheral surface 60 and the third outer peripheral surface 63 have the smallest width at their bottom ends and the largest width at their top ends. Note that the bottom end of the first outer peripheral surface 60 is located slightly above the bottom end of the second outer peripheral surface 61, but it may extend to the bottom end of the second outer peripheral surface 61.

[0057] The second outer peripheral surface 61 and the fourth outer peripheral surface 64 each have a maximum width at their lower ends and a minimum width at their upper ends. That is, the width of the second outer peripheral surface 61 narrows from the upstream side to the downstream side in the rotation direction of the fixing belt 20. On the other hand, the width of the fourth outer peripheral surface 64 narrows from the downstream side to the upstream side in the rotation direction of the fixing belt 20 (from the upstream side to the downstream side in the reverse rotation direction). Furthermore, the width of the fourth outer peripheral surface 64, which is the length in the rotational axis direction of the fixing belt 20, is longer than that of the second outer peripheral surface 61 from the lower end to the upper end, and the overall area is also larger than that of the second outer peripheral surface 61. Specifically, one end (right end) of the fourth outer peripheral surface 64 closer to the center in the rotational axis direction of the fixing belt 20 is located at approximately the same position as the tip of the protrusion 66, and one end (right end) of the second outer peripheral surface 61 is located closer to the base 40 than the tip of the protrusion 66.

[0058] The first outer peripheral surface 60, the second outer peripheral surface 61, and the third outer peripheral surface 63 are parallel to the rotational axis direction of the fixing belt 20. In contrast, the fourth outer peripheral surface 64 has a portion closer to the base 40 that is parallel to the rotational axis direction of the fixing belt 20, and a portion farther from the base 40 that is inclined toward the inner periphery of the belt insertion portion 41 (the rotational axis A of the fixing belt 20) as it approaches the center in the rotational axis direction. The belt insertion portion 41 provided in the left belt support portion 24L has the above-described configuration. In this embodiment, "parallel" does not only mean completely parallel, but also includes substantial parallelism within a certain tolerance range. For example, the fourth outer peripheral surface 64 may be considered parallel if the acute angle at which the rotational axis direction of the fixing belt 20 intersects with the first outer peripheral surface 60 is 5 degrees or less.

[0059] 8(A), (B), 9, and 10, the belt insertion portion 41 provided on the right belt support portion 24R is symmetrical in shape to the belt insertion portion 41 provided on the left belt support portion 24L, and has the same configuration as the belt insertion portion 41 provided on the left belt support portion 24L. That is, the belt insertion portion 41 provided on the right belt support portion 24L also has a first outer peripheral surface 60, a second outer peripheral surface 61, a first stepped surface 62, a third outer peripheral surface 63, a fourth outer peripheral surface 64, a second stepped surface 65, and a protrusion 66.

[0060] [4. Operation of the belt insertion part] Next, we will explain in detail the operation of belt insertion unit 41, that is, how belt insertion unit 41 suppresses leakage of lubricant 51. First, we will explain the operation of belt insertion unit 41 when fixing belt 20 is rotating in the direction indicated by arrow D (i.e., during printing) using Figure 9.

[0061] At this time, the lubricant 51 (omitted in Figure 9, see Figure 3) adhering to the inner surface of the fixing belt 20 moves in the direction of the rotation axis of the fixing belt 20, as shown by the dotted arrow in the figure, escaping from the inside of the nip portion Np to the outside of the nip portion Np where no pressure is applied (i.e., one end side and the other end side of the rotation axis direction of the fixing belt 20).

[0062] Here, for example, lubricant 51 that has moved to one end (left end) of the rotational axis direction of fixing belt 20 enters the gap formed between second outer peripheral surface 61 provided on the nip portion exit side of left belt insertion portion 41 and the inner peripheral surface of fixing belt 20. At this time, since there is no gap between first outer peripheral surface 60 of belt insertion portion 41 and the inner peripheral surface of fixing belt 20, lubricant 51 is blocked by first step surface 62 between first outer peripheral surface 60 and second outer peripheral surface 61.

[0063] In this way, the belt insertion portion 41 can block the lubricant 51 by the first step surface 62 between the first outer peripheral surface 60 and the second outer peripheral surface 61, thereby preventing the lubricant 51 from leaking out from one end side of the fixing belt 20 in the rotational axis direction.

[0064] Furthermore, if the fixing belt 20 continues to rotate in the direction of arrow D from this state, the lubricant 51 that has entered the gap between the second outer surface 61 and the inner surface of the fixing belt 20 moves upward along the second outer surface 61 as the fixing belt 20 rotates.

[0065] At this time, since the first step surface 62 is inclined so as to approach the center in the rotational axis direction of the fixing belt 20 as it moves from the upstream side to the downstream side in the rotation direction of the fixing belt 20 (i.e., as it moves upward), the lubricant 51 moves upward along the first step surface 62 and approaches the center in the rotational axis direction of the fixing belt 20. In other words, since the first step surface downstream portion 62B of the first step surface 62 is closer to the center in the rotational axis direction of the fixing belt 20 than the first step surface upstream portion 62A, the lubricant 51 moves upward along the first step surface 62 and approaches the center in the rotational axis direction of the fixing belt 20.

[0066] In this way, the lubricant 51 that has moved upward along the first step surface 62 drops from the upper end of the second outer peripheral surface 61 into the first hole 67 and accumulates on the upper surface of the plate portion 21 located at the bottom of the first hole 67. In other words, the first hole 67, together with the upper surface of the plate portion 21, forms a storage portion for the lubricant 51, and the lubricant 51 accumulates inside this first hole 67 (i.e., inside the storage portion). Here, the width of the second outer peripheral surface 61 narrows from the lower end to the upper end, making it easier to guide the lubricant 51 to the first hole 67 on the upper end side.

[0067] 9, the first hole 67 is located inside the nip portion Np (specifically, above the nip portion Np) in the rotational axis direction (X-axis direction) of the fixing belt 20. Therefore, the lubricant 51 moves upward along the first step surface 62 and approaches the center of the rotational axis direction of the fixing belt 20, and when it reaches at least the first hole 67, it has returned to a position inside the nip portion Np.

[0068] The lubricant 51 that has fallen into the first hole 67 softens and becomes more fluid as the temperature inside the fixing device 6 rises. As a result, the lubricant 51 is supplied again by gravity from the upper surface of the plate portion 21 down the rear surface to the inner circumferential surface of the fixing belt 20 below (specifically, the inner circumferential surface of the fixing belt 20 on the nip exit side). In other words, the bottom of the first hole 67 is connected to the inner circumferential surface of the fixing belt 20 via the plate portion 21, so that the lubricant 51 that has fallen into the first hole 67 can be returned to the inner circumferential surface of the fixing belt 20. Note that the protrusion 66 blocks the passage between the first hole 67 and the second hole 68, so that the lubricant 51 that has reached the first hole 67 on the exit side of the nip Np does not move toward the entrance side of the nip Np.

[0069] In this way, the belt insertion section 41 can return the lubricant 51 that has moved to the outside of the nip portion Np in the direction of the rotation axis of the fixing belt 20 along the first step surface 62 to a position inside the nip portion Np, and can also drop the lubricant 51 that has been returned to a position inside the nip portion Np into the first hole 67 and re-supply it to the inner surface of the fixing belt 20 along the plate section 21.

[0070] Here, the operation of the left belt insertion portion 41 when the fixing belt 20 is rotating in the direction indicated by the arrow D (i.e., during printing) has been described, but the right belt insertion portion 41 also operates in the same manner.

[0071] Thus, in the fixing device 6, when the fixing belt 20 rotates in the rotation direction indicated by arrow D (i.e., during printing), leakage of the lubricant 51 from both ends of the fixing belt 20 in the rotational axis direction can be suppressed. Furthermore, in the fixing device 6, the lubricant 51 that has migrated to the outside of the nip portion Np is accommodated in the space (accommodation portion) formed between the first hole 67 and the upper surface of the plate portion 21. This effectively prevents leakage of the lubricant 51 even when the gap formed between the second outer peripheral surface 61 and the inner peripheral surface of the fixing belt 20 is not large enough to accommodate the lubricant 51. Furthermore, in the fixing device 6, the lubricant 51 that has migrated to the outside of the nip portion Np can be returned to the inside of the nip portion Np and resupplied to the inner peripheral surface of the fixing belt 20. In this case, it is preferable to provide the first hole 67 at the downstream portion 62B of the first stepped surface, which is closer to the center of the fixing belt 20 in the rotational axis direction than the upstream portion 62A of the first stepped surface. This facilitates returning the lubricant 51 to a position inside the nip portion Np.

[0072] Next, the operation of the belt insertion unit 41 when the fixing belt 20 is rotating in the reverse direction indicated by the arrow D' will be described with reference to Fig. 10. The fixing belt 20 rotates in the reverse direction indicated by the arrow D' when, for example, a jam (paper jam) occurs on the conveying path R.

[0073] In this case, lubricant 51 (omitted from FIG. 10, see FIG. 3) that had accumulated on the nip exit side is carried to the nip entrance side, and it is assumed that the amount of lubricant 51 that escapes to the outside of nip Np will be greater than during printing. In particular, when fixing belt 20 is once separated from pressure roller 30, and then pressed against pressure roller 30 again, and then fixing belt 20 is rotated in the reverse direction, the amount of lubricant 51 that escapes to the outside of nip Np will be greater.

[0074] Here, for example, the lubricant 51 that has moved to one end (left end) of the fixing belt 20 in the rotational axis direction enters the gap formed between the fourth outer peripheral surface 64 provided on the nip entrance side of the left belt insertion portion 41 and the inner peripheral surface of the fixing belt 20. At this time, since there is no gap between the third outer peripheral surface 63 of the belt insertion portion 41 and the inner peripheral surface of the fixing belt 20, the lubricant 51 is blocked by the second step surface 65 between the third outer peripheral surface 63 and the fourth outer peripheral surface 64.

[0075] In this way, the belt insertion portion 41 can block the lubricant 51 by the second step surface 65 between the third outer peripheral surface 63 and the fourth outer peripheral surface 64, thereby preventing the lubricant 51 from leaking out from one end side of the fixing belt 20 in the rotational axis direction.

[0076] Furthermore, if the fixing belt 20 continues to rotate in the direction of arrow D' from this state, the lubricant 51 that has entered the gap between the fourth outer surface 64 and the inner surface of the fixing belt 20 moves upward along the fourth outer surface 64 as the fixing belt 20 rotates.

[0077] At this time, since the second step surface 65 is inclined so as to approach the center in the rotational axis direction of the fixing belt 20 as it moves from the upstream side to the downstream side in the reverse rotation direction of the fixing belt 20 (i.e., as it moves upward), the lubricant 51 moves upward along the second step surface 65 and approaches the center in the rotational axis direction of the fixing belt 20. In other words, since the second step surface downstream portion 65B of the second step surface 65 is closer to the center in the rotational axis direction of the fixing belt 20 than the second step surface upstream portion 65A, the lubricant 51 moves upward along the second step surface 65 and approaches the center in the rotational axis direction of the fixing belt 20.

[0078] In this way, the lubricant 51 that has moved upward along the second step surface 65 drops from the upper end of the fourth outer peripheral surface 64 into the second hole 68 and accumulates on the upper surface of the plate portion 21 located at the bottom of the second hole 68. In other words, the second hole 68, together with the upper surface of the plate portion 21, forms a storage portion for the lubricant 51, and the lubricant 51 accumulates inside this second hole 68 (i.e., inside the storage portion). Here, the width of the fourth outer peripheral surface 64 narrows from the lower end to the upper end, making it easier to guide the lubricant 51 to the second hole 68 on the upper end side.

[0079] 10 , the second hole 68 is located inside the nip portion Np (specifically, above the nip portion Np) in the rotational axis direction (X-axis direction) of the fixing belt 20, similar to the first hole 67. Therefore, the lubricant 51 moves upward along the second step surface 65 and approaches the center of the rotational axis direction of the fixing belt 20, and when it reaches at least the second hole 68, it has returned to a position inside the nip portion Np.

[0080] The lubricant 51 that has fallen into the second hole 68 softens and becomes more fluid as the temperature inside the fixing device 6 rises. As a result, the lubricant 51 is supplied again by gravity from the upper surface of the plate portion 21 down along the front surface to the inner circumferential surface of the fixing belt 20 below (specifically, the inner circumferential surface of the fixing belt 20 on the nip entrance side). In other words, the bottom of the second hole 68 is connected to the inner circumferential surface of the fixing belt 20 via the plate portion 21, so that the lubricant 51 that has fallen into the second hole 68 can be returned to the inner circumferential surface of the fixing belt 20. Note that the protrusion 66 blocks the passage between the first hole 67 and the second hole 68, so that the lubricant 51 that has reached the second hole 68 on the entrance side of the nip Np does not move to the exit side of the nip Np.

[0081] In this way, the belt insertion portion 41 can return the lubricant 51 that has moved to the outside of the nip portion Np in the rotational axis direction of the fixing belt 20 along the second step surface 65 to a position inside the nip portion Np, and can also drop the lubricant 51 that has returned to the position inside the nip portion Np into the second hole 68 and resupply it to the inner circumferential surface of the fixing belt 20 along the plate portion 21. In this case, it is preferable to provide the second hole 68 at a position in the second step surface downstream portion 65B that is closer to the center of the rotational axis direction of the fixing belt 20 than at the second step surface upstream portion 65A, because this makes it easier to return the lubricant 51 to a position inside the nip portion Np.

[0082] Although the operation of the left belt insertion portion 41 when the fixing belt 20 is rotating in the reverse direction indicated by the arrow D' has been described above, the right belt insertion portion 41 also operates in the same manner.

[0083] Thus, in the fixing device 6, even when the fixing belt 20 is rotating in the reverse rotation direction indicated by the arrow D', the lubricant 51 can be prevented from leaking out from both ends of the fixing belt 20 in the rotation axis direction.

[0084] Furthermore, when the fixing belt 20 rotates in the reverse direction indicated by arrow D', it is expected that a greater amount of lubricant 51 will escape to the outside of the nip portion Np compared to when the fixing belt 20 rotates in the direction indicated by arrow D. Therefore, the area of the fourth outer peripheral surface 64 on the nip entrance side is made larger than the area of the second outer peripheral surface 61, thereby increasing the amount of lubricant 51 that can be accommodated in the gap formed between the fourth outer peripheral surface 64 and the inner peripheral surface of the fixing belt 20.

[0085] Furthermore, in the fixing device 6, the lubricant 51 that has migrated to the outside of the nip portion Np is contained in the space (container) formed between the second hole 68 and the upper surface of the plate portion 21, thereby sufficiently suppressing leakage of the lubricant 51 even when the gap formed between the fourth outer peripheral surface 64 and the inner peripheral surface of the fixing belt 20 cannot contain all of the lubricant 51. Furthermore, in the fixing device 6, the lubricant 51 that has migrated to the outside of the nip portion Np can be returned to the inside of the nip portion Np and resupplied to the inner peripheral surface of the fixing belt 20. The operation of the belt insertion portion 41, that is, how the belt insertion portion 41 suppresses leakage of the lubricant 51, has been described above.

[0086] [5. Summary and Effects] As described above, in this embodiment, the fixing device 6 is provided with a fixing belt 20 that has an inner surface coated with lubricant 51 and an outer surface opposite to the inner surface and is rotatable around a predetermined rotation axis A, belt support portions 24L and 24R that support the ends of the fixing belt 20 in the rotation axis direction, which is a first direction parallel to the rotation axis A, and a pressure roller 30 that is an example of a contact portion that contacts the outer surface of the fixing belt 20 to form a nip portion Np and clamps and transports paper P, an example of a medium, between the fixing belt 20 and the pressure roller 30 at the nip portion Np.

[0087] Furthermore, at the nip exit portion located downstream of the nip portion Np in the paper conveying direction, the belt support portions 24L and 24R have a first outer surface 60 which is an example of a first surface that faces the inner surface of the fixing belt 20 and is formed at a position a distance L1 as a first distance from the rotation axis A of the fixing belt 20 in the radial direction of the belt insertion portion 41 which is a second direction perpendicular to the rotation axis direction of the fixing belt 20, a second outer surface 61 which is an example of a second surface that faces the inner surface of the fixing belt 20 and is formed at a position closer than the first distance from the rotation axis A of the fixing belt 20 in the radial direction of the belt insertion portion 41, and a first step surface 62 formed between the first outer surface 60 and the second outer surface 61.

[0088] Furthermore, the second outer peripheral surface 61 is provided between the center of the fixing belt 20 and the first outer peripheral surface 60 in the direction of the rotation axis of the fixing belt 20. Furthermore, the first step surface 62 has a first step surface upstream portion 62A which is an example of a first step portion, and a first step surface downstream portion 62B which is an example of a second step portion located downstream of the first step surface upstream portion 62A in the direction of the rotation axis of the fixing belt 20, and the first step surface downstream portion 62B is closer to the center of the fixing belt 20 in the direction of the rotation axis of the fixing belt 20 than the first step surface upstream portion 62A.

[0089] By doing so, in the fuser 6 of the present embodiment, when the fuser belt 20 is rotated in the rotation direction, the lubricant 51 that has moved to the end of the inner peripheral surface of the fuser belt 20 and entered between the inner peripheral surface of the fuser belt 20 and the second outer peripheral surfaces 61 of the belt support portions 24L, 24R is blocked by the first step surface 62, and as the fuser belt 20 rotates, the lubricant 51 can be moved along the first step surface 62 in a direction approaching the center of the fuser belt 20 in the rotation axis direction, thereby preventing the leakage of the lubricant 51 from the end of the fuser belt 20 in the rotation axis direction. Thus, the fuser 6 of the present embodiment can prevent the occurrence of printing defects.

[0090] In addition, in the fixing device 6 of the present embodiment, the first hole 67 penetrating the second outer peripheral surface 61 is provided on the downstream side of the second outer peripheral surface 61 in the rotation direction of the fixing belt 20 .

[0091] In this manner, in the fuser 6 of the present embodiment, the first step surface 62 blocks the lubricant 51 that has migrated to the end of the inner circumferential surface of the fuser belt 20 and entered between the inner circumferential surface of the fuser belt 20 and the second outer circumferential surface 61 of the belt support members 24L and 24R. As the fuser belt 20 rotates, the lubricant 51 is guided along the first step surface 62 to the first hole 67 and accommodated in the first hole 67. Furthermore, because the first hole 67 is connected to the inner circumferential surface of the fuser belt 20 via the plate portion 21 located at the bottom of the first hole 67, the lubricant 51 accommodated in the first hole 67 can flow along the plate portion 21 and return to the inner circumferential surface of the fuser belt 20, thereby preventing leakage of the lubricant 51 from the end of the fuser belt 20 in the direction of the rotation axis. Thus, the fuser 6 of the present embodiment can prevent printing defects from occurring.

[0092] Furthermore, in the fixing device 6 of this embodiment, the belt support portions 24L, 24R have a third outer surface 63, which is an example of a third surface, facing the inner surface of the fixing belt 20 at the nip entrance portion located downstream in the paper transport direction of the nip portion Np and formed at a distance L3, which is a third distance, from the rotation axis A of the fixing belt 20 in the radial direction of the belt insertion portion 41; a fourth outer surface 64, which is an example of a fourth surface, facing the inner surface of the fixing belt 20 and formed at a position closer than the distance L3 from the rotation axis A of the fixing belt 20 in the radial direction of the belt insertion portion 41; and a second step surface 65 formed between the third outer surface 63 and the fourth outer surface 64.

[0093] Furthermore, the fourth outer peripheral surface 64 is provided between the center of the fixing belt 20 and the third outer peripheral surface 63 in the direction of the rotation axis of the fixing belt 20. Furthermore, the second step surface 65 has a second step surface upstream portion 65A which is an example of a third step portion, and a second step surface downstream portion 65B which is an example of a fourth step portion located upstream of the second step surface upstream portion 65A in the direction of the rotation axis of the fixing belt 20 (i.e., downstream of the direction of the reverse rotation of the fixing belt 20), and the second step surface downstream portion 65B is closer to the center of the fixing belt 20 in the direction of the rotation axis of the fixing belt 20 than the second step surface upstream portion 65A.

[0094] By doing so, in the fuser 6 of the present embodiment, when the fuser belt 20 is rotated in the reverse direction, the lubricant 51 that has moved to the end of the inner peripheral surface of the fuser belt 20 and entered between the inner peripheral surface of the fuser belt 20 and the fourth outer peripheral surface 64 of the belt support portions 24L, 24R is blocked by the second step surface 65, and as the fuser belt 20 rotates, the lubricant 51 can be moved along the second step surface 65 in a direction approaching the center of the fuser belt 20 in the rotational axis direction, thereby preventing the leakage of the lubricant 51 from the end of the fuser belt 20 in the rotational axis direction. Thus, the fuser 6 of the present embodiment can prevent the occurrence of printing defects.

[0095] 6. Other Embodiments [6-1. Other embodiment 1] In the above-described embodiment, the first step surface 62 connecting the first outer peripheral surface 60 and the second outer peripheral surface 61 is provided so as to approach the center of the rotational axis direction of the fixing belt 20 from the upstream side to the downstream side in the rotation direction (the rotation direction indicated by the arrow D) of the fixing belt 20. In other words, the first step surface downstream portion 62B of the first step surface 62 is closer to the center of the rotational axis direction of the fixing belt 20 than the first step surface upstream portion 62A.

[0096] Here, first step surface 62 may have a linear shape inclined at a predetermined inclination angle θ1 with respect to the rotation direction of fixing belt 20 indicated by arrow D when viewed from the nip exit side, as shown in Fig. 9, or may have a curved shape when viewed from the nip exit side, as shown in the simplified diagram of Fig. 11(A). In the case of a curved shape, first step surface 62 may have an arc shape bulging toward first outer peripheral surface 60, as shown in Fig. 11(A), or may have an arc shape bulging toward second outer peripheral surface 61, although not shown.

[0097] Furthermore, without being limited to this, as shown in Figure 11 (B), the first step surface 62 may be formed into an approximately sawtooth shape by connecting multiple triangles each consisting of a part parallel to the rotation direction of the fixing belt 20 and a part perpendicular to the rotation direction of the fixing belt 20, when viewed from the exit side of the nip portion.

[0098] Furthermore, without being limited to this, as shown in Figure 11 (C), the upstream portion 62A of the first step surface 62 may be made into a linear shape parallel to the rotation direction of the fixing belt 20, and the downstream portion 62B of the first step surface may be made into a linear shape inclined at a predetermined angle relative to the rotation direction of the fixing belt 20, so that the overall shape is approximately L-shaped.

[0099] 11(C), the first step surface upstream portion 62A of the first step surface 62 may be linearly shaped inclined at a predetermined angle with respect to the rotation direction of the fixing belt 20, and the first step surface downstream portion 62B may be linearly shaped parallel to the rotation direction of the fixing belt 20, thereby forming a generally V-shaped surface overall. In other words, the inclination angle of the first step surface upstream portion 62A and the inclination angle of the first step surface downstream portion 62B of the first step surface 62 may be different. Note that with respect to the first step surface 62 described here as well, the length L6 in the rotation axis direction is shorter than the length L5 in the direction along the rotation direction of the fixing belt 20 indicated by the arrow D.

[0100] Although not shown in the drawings, the second step surface 65 may also have a shape different from that of the embodiment described above.

[0101] [6-2. Other embodiment 2] Furthermore, in the above-described embodiment, a first hole 67 is provided on the second outer surface 61 of the belt insertion portion 41 on the upstream side of the rotation direction of the fixing belt 20, which penetrates the belt insertion portion 41 in a thickness direction perpendicular to the rotation axis direction of the fixing belt 20 and reaches the upper surface of the plate portion 21.

[0102] This is not limiting, and the first holes 67 may be omitted. Even in this case, the lubricant 51 that has moved to the end of the inner circumferential surface of the fixing belt 20 and entered between the inner circumferential surface of the fixing belt 20 and the second outer circumferential surfaces 61 of the belt support portions 24L and 24R can be moved along the first step surface 62 in a direction approaching the center of the fixing belt 20 in the rotational axis direction.

[0103] In this case, if the upper end of the first step surface 62 is positioned at the end of the belt insertion portion 41 that is closer to the center of the rotational axis direction of the fixing belt 20, the lubricant 51 that has moved to the upper end of the first step surface 62 can be released from the end of the belt insertion portion 41 toward the center of the rotational axis direction of the fixing belt 20 and re-supplied to the nip portion Np via the plate portion 21. Like the first hole 67, the second hole 68 may also be omitted.

[0104] [6-3. Other embodiment 3] Furthermore, in the above-described embodiment, the area of the fourth outer peripheral surface 64 provided on the nip entrance side is made larger than the area of the second outer peripheral surface 61 provided on the nip exit side of the belt insertion portion 41. Specifically, the length of the fourth outer peripheral surface 64 in the rotation axis direction (X-axis direction) of the fixing belt 20 is made longer than that of the second outer peripheral surface 61, so that the area of the fourth outer peripheral surface 64 is made larger than that of the second outer peripheral surface 61.

[0105] Without being limited to this, for example, the area of fourth outer peripheral surface 64 may be made larger than that of second outer peripheral surface 61 by making inclination angle θ2 of second step surface 65 smaller than inclination angle θ1 of first step surface 62. This makes it easier to move lubricant 51 accumulated on the nip exit side to the center in the rotational axis direction of fixing belt 20, and makes it possible to increase the amount of lubricant 51 stored on the nip entrance side compared to the amount of lubricant 51 stored on the nip exit side.

[0106] Furthermore, without being limited to this, if there is not much difference in the amount of lubricant 51 escaping to the outside of the nip portion Np between the nip portion exit side and the nip portion entrance side, the area of the second outer peripheral surface 61 and the area of the fourth outer peripheral surface 64 may be made approximately the same.

[0107] [6-4. Other embodiment 4] 7, distance L2 from rotation axis A of fixing belt 20 to second outer peripheral surface 61 on the nip exit side and distance L4 from rotation axis A to fourth outer peripheral surface 64 on the nip entrance side are set to be approximately the same, but either distance L2 or distance L4 may be shortened. For example, by shortening distance L4 from rotation axis A to fourth outer peripheral surface 64 on the nip entrance side, the gap formed between the inner peripheral surface of fixing belt 20 and fourth outer peripheral surface 64 can be widened, thereby increasing the amount of lubricant 51 that tends to accumulate on the nip entrance side more than on the nip exit side.

[0108] [6-5. Other embodiment 5] Furthermore, in the above-described embodiment, the present invention is applied to the image forming apparatus 1, but is not limited to this, and can be applied to various image forming apparatuses that include a fixing device such as the fixing unit 6 (i.e., that employ an electrophotographic method). For example, the present invention can also be applied to image forming apparatuses such as copiers, multifunction machines, and fax machines that include a fixing device.

[0109] [6-6. Other Embodiments 6] Furthermore, the present invention is not limited to the above-described embodiments, and the scope of application of the present invention extends to embodiments in which some or all of the above-described embodiments are arbitrarily combined, or embodiments in which some of the embodiments are extracted.

[0110] [7. Notes] The following aspects are further disclosed as supplementary notes regarding the above-described embodiment. [7-1. Appendix 1] a fixing belt having an inner circumferential surface coated with a lubricant and an outer circumferential surface opposite to the inner circumferential surface, the fixing belt being rotatable around a predetermined rotation axis; a belt support portion that supports an end portion of the fixing belt in a first direction parallel to the rotation axis; a contact portion that contacts the outer peripheral surface to form a nip portion, and that conveys the medium while sandwiching it between the contact portion and the fixing belt at the nip portion; Equipped with The belt support portion is a first surface formed at a nip exit portion located downstream of the nip portion in the medium transport direction, the first surface facing the inner circumferential surface of the fixing belt and positioned a first distance away from the rotation axis of the fixing belt in a second direction perpendicular to the first direction; a second surface facing the inner circumferential surface of the fixing belt and formed at a position closer to the rotation axis of the fixing belt in the second direction than the first distance; a first step surface formed between the first surface and the second surface; and the second surface is provided between a center portion of the fixing belt and the first surface in the first direction, The first step surface includes a first step portion and a second step portion located downstream of the first step portion in the rotation direction of the fixing belt. and The second step portion is closer to the center of the fixing belt in the first direction than the first step portion. A fixing device characterized by:

[0111] [7-2. Appendix 2] The belt support portion is a third surface formed at a nip entrance portion located upstream of the nip portion in the medium transport direction, the third surface facing the inner circumferential surface of the fixing belt and positioned a third distance away from the rotation axis of the fixing belt in the second direction; a fourth surface facing the inner circumferential surface of the fixing belt and formed at a position closer than the third distance from the rotation axis of the fixing belt in the second direction; a second step surface formed between the third surface and the fourth surface; and the fourth surface is provided between a center portion of the fixing belt and the third surface in the first direction, The second step surface includes a third step portion and a fourth step portion located upstream of the third step portion in the rotation direction of the fixing belt. and The fourth step portion is closer to the center of the fixing belt than the third step portion in the first direction. 2. The fixing device according to claim 1.

[0112] [7-3. Appendix 3] The area of the fourth surface is larger than the area of the second surface. 3. The fixing device according to claim 1 or 2.

[0113] [7-4. Appendix 4] The second surface has a width, which is a length in the first direction, that narrows from the upstream side to the downstream side in the rotation direction of the fixing belt. 4. The fixing device according to claim 1, wherein:

[0114] [7-5. Appendix 5] a first hole penetrating the second surface, the first hole being provided on the downstream side of the second surface in the rotation direction of the fixing belt; 5. The fixing device according to claim 1, wherein:

[0115] [7-6. Appendix 6] The bottom of the first hole is connected to the inner circumferential surface of the fixing belt. 6. The fixing device according to claim 5,

[0116] [7-7. Appendix 7] The fourth surface has a width, which is the length in the first direction, that narrows from the downstream side to the upstream side in the rotation direction of the fixing belt. 7. The fixing device according to claim 2, wherein:

[0117] [7-8. Appendix 8] a second hole penetrating the fourth surface, the second hole being provided on the upstream side of the fourth surface in the rotation direction of the fixing belt; 8. The fixing device according to claim 2, wherein:

[0118] [7-9. Appendix 9] The bottom of the second hole is connected to the inner circumferential surface of the fixing belt. 9. The fixing device according to claim 8,

[0119] [7-10. Appendix 10] The first step surface is The length in the first direction is shorter than the length in the direction along the rotation direction of the fixing belt. 10. The fixing device according to any one of claims 1 to 9.

[0120] [7-11. Appendix 11] a fixing belt having an inner circumferential surface coated with a lubricant and an outer circumferential surface opposite to the inner circumferential surface, the fixing belt being rotatable around a predetermined rotation axis; a belt support portion that supports an end portion of the fixing belt in a first direction parallel to the rotation axis; a contact portion that contacts the outer peripheral surface to form a nip portion, and that conveys the medium while sandwiching it between the contact portion and the fixing belt at the nip portion; Equipped with The belt support portion is a first surface formed at a nip exit portion located downstream of the nip portion in the medium transport direction, the first surface facing the inner circumferential surface of the fixing belt and positioned a first distance away from the rotation axis of the fixing belt in a second direction perpendicular to the first direction; a second surface facing the inner circumferential surface of the fixing belt and formed at a position closer than the first distance from the rotation axis of the fixing belt in the second direction; a first step surface formed between the first surface and the second surface; and the second surface is provided between a center portion of the fixing belt and the first surface in the first direction, The second surface has a first hole penetrating the second surface on the downstream side in the rotation direction of the fixing belt. A fixing device characterized by:

[0121] [7-12. Appendix 12] The bottom of the first hole is connected to the inner circumferential surface of the fixing belt. 12. The fixing device according to claim 11,

[0122] [7-13. Appendix 13] The fixing device according to any one of claims 1 to 12 is included. An image forming apparatus characterized by: [Industrial Applicability]

[0123] The present invention can be widely used in, for example, electrophotographic printers. [Explanation of symbols]

[0124] 1...image forming apparatus, 6...fixing unit, 12...heating section, 13...pressure section, 20...fixing belt, 21...plate section, 23L, 23R...plate support section, 24L, 24R...belt support section, 30...pressure roller, 40...base section, 41...belt insertion section, 51...lubricant, 60...first outer peripheral surface, 61...second outer peripheral surface, 62...first step surface, 62A...upstream portion of first step surface, 62B...downstream portion of first step surface, 63...third outer peripheral surface, 64...fourth outer peripheral surface, 65...second step surface, 65A...upstream portion of second step surface, 65B...downstream portion of second step surface, 66...protrusion, 67...first hole, 68...second hole, P...paper.

Claims

1. a fixing belt having an inner circumferential surface coated with a lubricant and an outer circumferential surface opposite to the inner circumferential surface, the fixing belt being rotatable around a predetermined rotation axis; a belt support portion that supports an end portion of the fixing belt in a first direction parallel to the rotation axis; a contact portion that contacts the outer peripheral surface to form a nip portion, and that conveys the medium while sandwiching it between the contact portion and the fixing belt at the nip portion; Equipped with The belt support portion is a first surface formed at a nip exit portion located downstream of the nip portion in the medium transport direction, the first surface facing the inner circumferential surface of the fixing belt and positioned a first distance away from the rotation axis of the fixing belt in a second direction perpendicular to the first direction; a second surface facing the inner circumferential surface of the fixing belt and formed at a position closer to the rotation axis of the fixing belt in the second direction than the first distance; a first step surface formed between the first surface and the second surface; and the second surface is provided between a center portion of the fixing belt and the first surface in the first direction, The first step surface includes a first step portion and a second step portion located downstream of the first step portion in the rotation direction of the fixing belt. and The second step portion is closer to the center of the fixing belt in the first direction than the first step portion. A fixing device characterized by:

2. The belt support portion is a third surface formed at a nip entrance portion located upstream of the nip portion in the medium transport direction, the third surface facing the inner circumferential surface of the fixing belt and positioned a third distance away from the rotation axis of the fixing belt in the second direction; a fourth surface facing the inner circumferential surface of the fixing belt and formed at a position closer than the third distance from the rotation axis of the fixing belt in the second direction; a second step surface formed between the third surface and the fourth surface; and the fourth surface is provided between a center portion of the fixing belt and the third surface in the first direction, The second step surface includes a third step portion and a fourth step portion located upstream of the third step portion in the rotation direction of the fixing belt. and The fourth step portion is closer to the center of the fixing belt than the third step portion in the first direction.

2. The fixing device according to claim 1, wherein the fixing device is a fixing device for fixing a toner image onto a recording medium.

3. The area of the fourth surface is larger than the area of the second surface.

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

4. The second surface has a width, which is a length in the first direction, that narrows from the upstream side to the downstream side in the rotation direction of the fixing belt.

2. The fixing device according to claim 1, wherein the fixing device is a fixing device for fixing a toner image onto a recording medium.

5. a first hole penetrating the second surface, the first hole being provided on the downstream side of the second surface in the rotation direction of the fixing belt; 5. The fixing device according to claim 1, wherein the fixing member is a fixing member.

6. The bottom of the first hole is connected to the inner circumferential surface of the fixing belt.

6. The fixing device according to claim 5,

7. The fourth surface has a width, which is the length in the first direction, that narrows from the downstream side to the upstream side in the rotation direction of the fixing belt.

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

8. a second hole penetrating the fourth surface, the second hole being provided on the upstream side of the fourth surface in the rotation direction of the fixing belt; 8. The fixing device according to claim 2 or 7.

9. The bottom of the second hole is connected to the inner circumferential surface of the fixing belt.

9. The fixing device according to claim 8, wherein the fixing member is a fixing member.

10. The first step surface is The length in the first direction is shorter than the length in the direction along the rotation direction of the fixing belt.

2. The fixing device according to claim 1, wherein the fixing device is a fixing device for fixing a toner image onto a recording medium.

11. a fixing belt having an inner circumferential surface coated with a lubricant and an outer circumferential surface opposite to the inner circumferential surface, the fixing belt being rotatable around a predetermined rotation axis; a belt support portion that supports an end portion of the fixing belt in a first direction parallel to the rotation axis; a contact portion that contacts the outer peripheral surface to form a nip portion, and that conveys the medium while sandwiching it between the contact portion and the fixing belt at the nip portion; Equipped with The belt support portion is a first surface formed at a nip exit portion located downstream of the nip portion in the medium transport direction, the first surface facing the inner circumferential surface of the fixing belt and positioned a first distance away from the rotation axis of the fixing belt in a second direction perpendicular to the first direction; a second surface facing the inner circumferential surface of the fixing belt and formed at a position closer than the first distance from the rotation axis of the fixing belt in the second direction; a first step surface formed between the first surface and the second surface; and the second surface is provided between a center portion of the fixing belt and the first surface in the first direction, The second surface has a first hole penetrating the second surface on the downstream side in the rotation direction of the fixing belt. A fixing device characterized by:

12. The bottom of the first hole is connected to the inner circumferential surface of the fixing belt. The fixing device according to claim 11 .

13. The fixing device according to claim 1 or 11 is provided. An image forming apparatus characterized by:

Images