Fixation device and image forming apparatus

Abstract

To suppress occurrence of a printing failure.SOLUTION: A fixation device includes: a rotatable belt; a pressurizing member which is rotatable and makes contact with a portion of an outer peripheral surface of the belt; a contact member which makes contact with an inner peripheral surface of the belt across a lubricant and forms a nip part between the pressurizing member and itself via the belt; and a projection member provided on the inner peripheral surface of the belt outside the nip part in a contactable manner and projecting to the pressure member side relative to the contact member. The belt and the pressurizing member rotate to convey a medium nipped in the nip part. The projection member is provided such that it can contact the inner peripheral surface of an end part in a rotation axis direction of the belt on a downstream side of the nip part in a medium conveyance direction.SELECTED DRAWING: Figure 15

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] The fixing device rotates a cylindrical belt heated by a heater or the like in contact with a cylindrical pressure member, and heats and presses the medium while sandwiching it in a nip formed at the point where the belt and pressure member contact, thereby heating and melting the image (developer image) transferred to the medium and fixing it on the medium.

[0004] In addition, the fixing unit is provided with a contact member on the inner circumferential side of the belt that contacts the pressure member side of the inner circumferential surface of the belt to form a nip between the belt and the pressure member, and since the belt rotates while sliding against the contact member, a lubricant such as grease is applied between the belt and the contact member.

[0005] In a fixing device with this configuration, if the lubricant leaks from the end of the belt in the direction of the rotation axis and adheres to the outer surface of the belt, heat may not be transferred sufficiently when fixing an image to the medium, which may result in printing defects.

[0006] Therefore, in conventional fixing devices, a cylindrical low-friction member is provided between the belt and the contact member, and a step that increases in height toward the inner circumferential surface of the belt is provided at the axial end of the low-friction member, which is also within the nip portion.In this fixing device, the lubricant that has migrated to the end of the belt in the rotational axis direction is blocked by the step provided in the low-friction member, preventing the lubricant from leaking out from the end of the belt in the rotational axis direction (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-72218 Summary of the Invention [Problem to be solved by the invention]

[0008] However, in conventional fixing devices, the step of the low-friction member is provided within the nip portion, which can prevent leakage of the lubricant, but the nip pressure when fixing the image to the medium can be insufficient, resulting in printing defects. In other words, if the fixing device can prevent leakage of the lubricant and obtain sufficient nip pressure, it is thought that the occurrence of printing defects can be further suppressed.

[0009] 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 further reduce the occurrence of printing defects. [Means for solving the problem]

[0010] The fixing device of the present invention comprises a rotatable belt, a rotatable pressure member that is in contact with a portion of the outer surface of the belt, a contact member that is in contact with the inner surface of the belt via a lubricant and forms a nip portion between the belt and the pressure member, and a protruding member that is arranged outside the nip portion and can be in contact with the inner surface of the belt and protrudes toward the pressure member beyond the contact member, and the belt and the pressure member rotate to sandwich and transport a medium in the nip portion, and the protruding member is arranged downstream of the nip portion in the media transport direction and can be in contact with the inner surface of the end of the belt in the rotational axis direction.

[0011] The fixing device of the present invention also includes a rotatable belt, a pressure member that is rotatable and abuts against a portion of the outer surface of the belt, a contact member that abuts against the inner surface of the belt via a lubricant and forms a nip portion between the belt and the pressure member, and an edge portion that can abut against the inner surface of the belt, wherein the belt and the pressure member rotate to sandwich and transport a medium in the nip portion, and the edge portion has a contact portion that can contact the inner surface of the belt downstream of the nip portion in the media transport direction, and a recess that is spaced apart from the inner surface of the belt, and wherein the recess is recessed in a direction away from the inner surface of the belt at a portion located between one end and the other end of the belt in the direction of the rotation axis.

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

[0013] In the fixing device of the present invention, a protruding member (or contact portion) that can contact the inner peripheral surface of the end of the belt in the direction of the rotation axis downstream of the nip portion in the medium conveying direction prevents the lubricant from leaking out from the end of the belt in the direction of the rotation axis. In addition, since the protruding member (or contact portion) is provided outside the nip portion, sufficient nip pressure can be obtained. [Effects of the Invention]

[0014] According to the present invention, it is possible to realize a fixing device and an image forming apparatus that can further reduce the occurrence of printing defects. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a diagram showing a configuration of an image forming apparatus according to an embodiment; [Figure 2] 2A and 2B are diagrams illustrating an external configuration of a fixing unit according to an embodiment. [Figure 3] 3A and 3B are diagrams illustrating the configuration of a heating unit and a pressure unit according to an embodiment. [Figure 4] FIG. 4 is an enlarged view of a part of the heating unit in FIG. 3. [Figure 5]4 is an enlarged view of a part of the heating unit in FIG. 3 (a part different from that in FIG. 4). [Figure 6] 3A and 3B are diagrams illustrating a configuration of a heating unit according to an embodiment. [Figure 7] 3A and 3B are diagrams illustrating a configuration of a heating belt according to an embodiment. [Figure 8] 10A and 10B are diagrams illustrating a configuration of a support according to an embodiment. [Figure 9] 3A and 3B are diagrams illustrating a configuration of a pressure belt according to an embodiment. [Figure 10] FIG. 10 is a diagram showing an example of an angle (90°) formed between the side surface of the convex portion on the upstream side in the belt rotation direction and the lower surface of the heat diffusion member according to the embodiment. [Figure 11] FIG. 10 is a diagram showing an example of an angle (70°) formed between the side surface of the convex portion on the upstream side in the belt rotation direction and the lower surface of the heat diffusion member according to the embodiment. [Figure 12] FIG. 10 is a diagram showing an example of an angle (110°) formed between the side surface of the convex portion on the upstream side in the belt rotation direction and the lower surface of the heat diffusion member according to the embodiment. [Figure 13] 10A and 10B are diagrams illustrating examples of shapes of convex portions according to an embodiment. [Figure 14] 10A and 10B are diagrams illustrating the movement of a lubricant at a central portion in the rotation axis direction of a fixing belt according to an embodiment. [Figure 15] 10A and 10B are diagrams illustrating the movement of a lubricant at both ends of a fixing belt in the direction of the rotation axis according to an embodiment. [Figure 16] 10A and 10B are diagrams showing a structure in which an edge portion and a protrusion portion are integrated according to another embodiment. [Figure 17] FIG. 10 is a diagram showing a configuration (1) in which a convex portion is provided in a belt insertion portion according to another embodiment. [Figure 18] FIG. 10 is a diagram showing a configuration (2) in which a convex portion is provided in a belt insertion portion according to another embodiment. [Figure 19] 10A and 10B are diagrams showing a configuration in which a heat diffusion member is omitted according to another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, modes for carrying out the invention (hereinafter referred to as embodiments) will be described in detail with reference to the drawings.

[0017] [1. Configuration of image forming device] FIG. 1 shows an example of the configuration of an image forming apparatus 200 according to this embodiment. Note that FIG. 1 is a side cross-sectional view showing the configuration of the image forming apparatus 200. This image forming apparatus 200 is an apparatus that forms an image on a medium M using toner as a developer, and is a so-called electrophotographic color printer. Note that the type of medium M that can be used with the image forming apparatus 200 is not particularly limited, but may be one or more types of paper, film, etc., for example.

[0018] The image forming apparatus 200 has a substantially box-shaped device housing 1. Here, the right side of the device housing 1 in the drawing is the front side of the device housing 1, the left side of the drawing is the rear side of the device housing 1, the front side of the drawing is the left side of the device housing 1, and the back side of the drawing is the right side of the device housing 1. The direction from the left side to the right side of the device housing 1 in the drawing (i.e., the direction from the back side to the front side of the device housing 1) is the positive direction of the X-axis, the direction from the front side of the device housing 1 in the drawing to the back side of the device housing 1 in the drawing (i.e., the direction from the left side to the right side of the device housing 1) is the positive direction of the Y-axis, and the direction from the bottom side to the top side of the device housing 1 in the drawing (i.e., the direction from the bottom side to the top side of the device housing 1) is the positive direction of the Z-axis.

[0019] Inside the device housing 1, there are provided a tray T, a developing unit 10, a transfer unit 20, a fixing unit 30, various rollers, and a switching guide 60. The various rollers include, for example, a pickup roller 41, a paper feed roller 42, a separation roller 43, a registration roller 44, a pressure roller 45, and conveyance rollers 46 to 53. These various rollers, as well as various rollers described below, are cylindrical members extending in the Y-axis direction (left-right direction) and are rotatable around a rotation axis extending in the Y-axis direction.

[0020] Tray T is provided at the bottom of device housing 1, and stores (i.e., accumulates) a plurality of media M in a stacked state, for example. A stacker 2 onto which media M having images formed thereon is provided on the top surface of device housing 1. Inside device housing 1, transport paths R1 to R4 indicated by dotted arrows in the drawing are provided between tray T and stacker 2, and along these transport paths R1 to R4, a development unit 10, a transfer unit 20, a fixing unit 30, various rollers, and a switching guide 60 are provided.

[0021] The image forming apparatus 200 is capable of forming an image on one side (front side) of the medium M and also on both sides (front and back sides) of the medium M by switching the transport direction of the medium M using the switching guide 60. In other words, the image forming apparatus 200 has both a single-sided printing function and a double-sided printing function.

[0022] In this image forming apparatus 200, the medium M is transported in the medium transport direction indicated by the arrow H on each of the transport paths R1 to R4 (that is, the direction of the dotted arrow indicating each of the transport paths R1 to R4).

[0023] Transport path R1 is a path for transporting medium M from tray T to developing unit 10 and transfer unit 20 provided at the top of device housing 1. Transport path R2 is a path for transporting medium M from developing unit 10 and transfer unit 20 to fixing unit 30 provided behind them when an image is formed on one side of medium M. Transport path R3 is a path for transporting medium M from fixing unit 30 to stacker 2. Transport path R4 is a path for transporting (bypassing) medium M from fixing unit 30 back to developing unit 10 and transfer unit 20 to form an image on the back side of medium M after an image has been formed on the front side of medium M when images are formed on both sides of medium M.

[0024] [1-1. Development unit] The developing unit 10 and the transfer unit 20 are arranged facing each other in the vertical direction with the transport path R2 in between. Specifically, the developing unit 10 is arranged on the upper side of the transport path R2 and the transfer unit 20 is arranged on the lower side. The developing unit 10 is a unit that performs development using toner. Specifically, the developing unit 10 forms an electrostatic latent image by exposure to light and develops it by adhering toner to the electrostatic latent image using Coulomb force.

[0025] The developing unit 10 includes a developing unit 11 that performs a developing process and an exposure unit 12 that performs an exposure process. The developing unit 11 is detachable from the device housing 1 and includes a photosensitive drum 13 on which an electrostatic latent image is formed. The photosensitive drum 13 is a cylindrical member extending in the Y-axis direction and is rotatable about a rotation axis that also extends in the Y-axis direction. The exposure unit 12 is attached to the developing unit 11 and exposes the surface of the photosensitive drum 13 to light to form an electrostatic latent image on the surface. The exposure unit 12 includes, for example, a light-emitting diode (LED) element as exposure means. The developing unit 11 forms a toner image as a developer image on the surface of the photosensitive drum 13 by attaching toner to the electrostatic latent image formed on the surface of the photosensitive drum 13 and developing it.

[0026] The developing unit 10 has, for example, four developing processing units 11 (11K, 11Y, 11M, 11C) and four exposure processing units 12 (12K, 12Y, 12M, 12C). The four developing processing units 11K, 11Y, 11M, 11C are arranged in this order, for example, from the upstream side in the medium transport direction indicated by arrow H. The four exposure processing units 12K, 12Y, 12M, 12C are also arranged in the same order as the four developing processing units 11K, 11Y, 11M, 11C.

[0027] The four development processing units 11K, 11Y, 11M, and 11C have the same configuration except for the type (color) of toner used in the development processing. Specifically, the four development processing units 11K, 11Y, 11M, and 11C perform development processing using black (K) toner, yellow (Y) toner, magenta (M) toner, and cyan (C) toner, respectively.

[0028] [1-2. Transcription unit] Transfer unit 20 is a unit that transfers the toner image developed by development unit 10 onto medium M. Specifically, transfer unit 20 transfers the toner image formed on the surface of photosensitive drum 13 by development unit 10 onto medium M being transported in the medium transport direction indicated by arrow H.

[0029] The transfer unit 20 has a drive roller 21, an idle roller 22, a transfer belt 23, and a transfer roller 24. The drive roller 21 is rotatable by a drive source such as a motor. The idle roller 22 is rotatable in response to the rotation of the drive roller 21. The transfer belt 23 is stretched by the drive roller 21, the idle roller 22, and the transfer roller 24, and is movable in response to the rotation of the drive roller 21. The transfer roller 24 is pressed against the photosensitive drum 13 via the transfer belt 23, and when the medium M passes between the photosensitive drum 13 and the transfer belt 23, the transfer roller 24 charges the medium M to a polarity opposite to that of the toner, thereby transferring the toner image formed on the photosensitive drum 13 to the medium M.

[0030] The transfer unit 20 has, for example, four transfer rollers 24 (24K, 24Y, 24M, and 24C). The four transfer rollers 24K, 24Y, 24M, and 24C are arranged in the same order as the four development processing units 11K, 11Y, 11M, and 11C.

[0031] [1-3. Fusing unit] The fixing unit 30 is a unit that fixes the toner image transferred onto the medium M by the transfer unit 20. Specifically, the fixing unit 30 fixes the toner image onto the medium M by applying heat and pressure to the medium M onto which the toner image has been transferred by the transfer unit 20. The configuration of the fixing unit 30 will be described in detail later.

[0032] [1-4. Various rollers and switching guides] The pickup roller 41 is a roller that feeds the medium M from the tray T along the transport path R1. The paper feed roller 42 is a roller that guides (i.e., feeds) the medium M that has been fed from the tray T by the pickup roller 41 from the transport path R1 to the transport path R2. The separation roller 43 is a roller that separates the uppermost medium M from the other media M when multiple media M are fed from the tray T, so that only the uppermost medium M is fed.

[0033] The registration roller 44 and the pressure roller 45 are rollers that correct skew of the medium M while transporting the medium M along the transport path R2. The transport rollers 46 to 53 are pairs of rollers that face each other across the transport paths R2 to R4, and transport the medium M along the transport paths R2 to R4. The transport roller 48 is a roller that discharges the medium M with the fixed toner image into the stacker 2.

[0034] The switching guide 60 is disposed downstream of the fixing unit 30 in the medium transport direction indicated by the arrow H, and is a guide that switches the transport direction of the medium M depending on the image formation format (double-sided image formation or single-sided image formation). Specifically, when an image is to be formed on only one side (the front side) of the medium M, the switching guide 60 transports the medium M from transport path R2 to transport path R3. On the other hand, when an image is to be formed on both sides (the front and back sides) of the medium M, the switching guide 60 transports the medium M from transport path R2 to transport path R4.

[0035] [2. Configuration of the fixing unit] The configuration of the fixing unit 30 will now be described in more detail with reference to FIGS. 2 to 6. FIG. 2 is a perspective view showing the exterior configuration of the fixing unit 30. FIG. 3 is a side cross-sectional view showing the configuration of the heating section 120 and the pressure section 130 included in the fixing unit 30, as seen from one end side (left side) in the Y-axis direction. FIGS. 4 and 5 are partially enlarged cross-sectional views of a portion of FIG. 3. FIG. 6 is a cross-sectional view of the heating section 120, as seen from one end side (bottom side) in the Z-axis direction. As shown in FIG. 1, the fixing unit 30 is slightly tilted so that the front side is positioned lower than the rear side, but for ease of explanation, this tilt is omitted in FIGS. 2 to 5.

[0036] 2, the fixing unit 30 has a housing 110 that is long in the Y-axis direction, and has a heating section 120 and a pressure section 130 inside the housing 110. The housing 110 has a connector 140 on one side surface (left side surface) that is one end side in the Y-axis direction.

[0037] [2-1. Heating section] 2, 3, and 6, the heating section 120 includes, for example, a heater 121, a fixing belt 122, a temperature sensor 123, a heat conduction plate 124, a heat diffusion member 125, a lubricant 126, supports 127, 128, 161, and 162, and a pair of compression springs 129. Of these, a unit consisting of the heater 121, the fixing belt 122, the temperature sensor 123, the heat conduction plate 124, the heat diffusion member 125, and the supports 127 and 128 is referred to as a heater unit 180. Note that, as will be described in detail later, the fixing belt 122 has a cylindrical shape extending in the Y-axis direction, and the heater 121, the temperature sensor 123, the heat conduction plate 124, the heat diffusion member 125, and the supports 127 and 128 are disposed inside the fixing belt 122.

[0038] 2 and 6, the heating unit 120 extends in the Y-axis direction (i.e., the direction of the rotation axis of the fixing belt 122), and each part of the heating unit 120, such as the heater 121, also extends in the Y-axis direction. The pair of compression springs 129 (FIG. 2) is an elastic member that is flexible and expandable in, for example, the Z-axis direction. One of the pair of compression springs 129 is attached, for example, to one end side (left end side) of the housing 110 in the Y-axis direction and one end side (left end side) of the heating unit 120 in the Y-axis direction, and the other is attached, for example, to the other end side (right end side) of the housing 110 in the Y-axis direction and the other end side (right end side) of the heating unit 120 in the Y-axis direction.

[0039] Heating unit 120 is movable in the Z-axis direction and is biased by a pair of compression springs 129 in a direction approaching pressure unit 130 (specifically, downward), so that heating unit 120 is pressed against pressure unit 130 when heating medium M. As a result, nip 150 is formed between heating unit 120 and pressure unit 130 (specifically, between fixing belt 122 and pressure roller 131), as shown in FIG.

[0040] [2-2. Heater] 3 generates heat for heating the fixing belt 122. The heater 121 is supplied with power from outside the fixing unit 30 via a connector 140 (FIG. 2). The type of heater 121 is not particularly limited, but may be, for example, a planar heater.

[0041] [2-3. Fixing belt] The fixing belt 122 is a generally cylindrical (ring-shaped cross section) belt that is heated by heat generated by the heater 121. As shown in Fig. 3, the fixing belt 122 rotates in the belt rotation direction indicated by the arrow D in the figure while being heated by the heater 121.

[0042] Specifically, as shown in a cross section viewed from one end side in the longitudinal direction in Figure 7, this fixing belt 122 is a laminate in which a base material 201 such as a metal such as stainless steel (SUS) or a heat-resistant resin (polyimide), an elastic layer 202 such as silicone rubber, and a surface layer 203 such as a PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer) tube are layered in this order.

[0043] In this embodiment, the base material 201 is made of a polyimide material, which is a heat-resistant resin, and is formed into a cylindrical shape with a thickness of 60 to 80 μm and an inner diameter of φ30 mm.

[0044] [2-4. Temperature sensor] The temperature sensor 123 is a sensor that detects the temperature (heating temperature) of the heater 121 located below the temperature sensor 123. A heat conduction plate 124 is interposed between the heater 121 and the temperature sensor 123, so the temperature sensor 123 detects the temperature of the heater 121 via the heat conduction plate 124.

[0045] [2-5. Heat Conduction Plate] The heat conduction plate 124 is a plate-like member that is disposed between the heater 121 and the temperature sensor 123 and conducts the heat generated from the heater 121 to the temperature sensor 123. The heat conduction plate 124 is a metal plate made of, for example, stainless steel (SUS), and is in contact with the upper surface of the heater 121 and the lower surface of the temperature sensor 123, respectively.

[0046] [2-6. Heat diffusion materials] The heat diffusion member 125 is a plate-shaped member that is disposed between the heater 121 and the fixing belt 122 and separates the fixing belt 122 from the heater 121. The heat diffusion member 125 is in contact with the lower surface of the heater 121 and the inner circumferential surface of the fixing belt 122. In other words, the heat diffusion member 125 is in contact with the lower portion (the portion on the pressure unit 130 side) of the entire inner circumferential surface of the fixing belt 122. In other words, the heater 121 and the pressure unit 130 face each other with the heat diffusion member 125 and the fixing belt 122 sandwiched therebetween.

[0047] The heat diffusion member 125 is a member having thermal conductivity and is configured to conduct the heat generated from the heater 121 to the fixing belt 122. Specifically, the heat diffusion member 125 is, for example, a metal plate made of glass-coated stainless steel (SUS) or the like, and has high thermal conductivity. The heat diffusion member 125 functions as a heat diffusion plate that diffuses the heat generated by the heater 121 when the heat is conducted to the fixing belt 122. As a result, the heat generated by the heater 121 is dispersed and conducted to the fixing belt 122, so the fixing belt 122 is heated uniformly and temperature unevenness in the fixing belt 122 is less likely to occur.

[0048] As described above, the heat diffusion member 125 contacts the pressure section 130 side of the inner circumferential surface of the fixing belt 122, thereby forming a nip portion 150 between the heat diffusion member 125 and the pressure section 130 via the fixing belt 122. When the fixing belt 122 rotates, the surface (lower surface) of the heat diffusion member 125 on the pressure section 130 side and the inner circumferential surface of the fixing belt 122 slide against each other.

[0049] [2-7. Lubricants] The lubricant 126 is a liquid lubricant that allows the fixing belt 122 to slide smoothly relative to the heat diffusion member 125 when the heating unit 120 is pressed against the pressure unit 130. The lubricant 126 is interposed between the fixing belt 122 and the heat diffusion member 125. Specifically, the lubricant 126 is applied to the lower surface of the heat diffusion member 125 (i.e., the surface that contacts the fixing belt 122). The lubricant 126 is supplied to the gap between the fixing belt 122 and the heat diffusion member 125 as the fixing belt 122 rotates when the image forming apparatus 200 starts printing. As a result, the lubricant 126 reduces the frictional resistance between the fixing belt 122 and the heat diffusion member 125 when the fixing belt 122 slides relative to the heat diffusion member 125.

[0050] The lubricant 126 may contain, for example, one or more additives in addition to the liquid lubricant oil described above. As shown in FIG. 6, the length W1 of the application area 141 when the lubricant 126 is applied to the heat diffusion member 125 in the Y-axis direction (the longitudinal direction, i.e., the left-right direction, of the heat diffusion member 125) is approximately the same as the width of the medium M (i.e., the paper passing width). Note that the width in this case refers to the width of the largest medium M (i.e., the maximum paper passing width) among the media M handled by the image forming apparatus 200. The length W2 of the application area 141 in the X-axis direction (the short-side direction, i.e., the front-rear direction, of the heat diffusion member 125) is approximately the same as the length W of the nip portion 150 in the X-axis direction (the belt rotation direction of the fixing belt 122) shown in FIG. 3. In this embodiment, the length W of the nip portion 150 in the X-axis direction is 10 mm.

[0051] 3, as the fixing belt 122 rotates in the direction of arrow D, the lubricant 126 moves in the directions indicated by arrows D1, D2, and D3 in that order, thereby spreading over the entire circumference of the inner circumferential surface of the fixing belt 122. As the lubricant 126 spreads over the entire circumference of the inner circumferential surface of the fixing belt 122, it also moves in the directions indicated by arrows D4 and D5, which extend from the center Ct of the fixing belt 122 in the direction of the rotation axis to both ends in the direction of the rotation axis (i.e., in the directions from the inside to the outside of the nip portion 150), as shown in FIG.

[0052] In this embodiment, the lubricant 126 has a complex viscosity of 800 Pa·s to 1200 Pa·s at room temperature and 2000 Pa·s to 2500 Pa·s when the fixing unit 30 is heated.

[0053] [2-8.Support] 3, the support 127 is a member that supports the heater 121, the heat conduction plate 124, and the heat diffusion member 125. The support 128 is a member that holds the support 127, and is fixed to the housing 110. The supports 127, 128 are each a member that extends in the Y-axis direction and has a substantially U-shaped cross section, and are combined so that the support 128 is on the upper side and the support 127 is on the lower side (i.e., on the pressure unit 130 side), forming a rectangular cylindrical shape as a whole.

[0054] A temperature sensor 123 is attached to the support 127. The support 127 has a recess extending in the Y-axis direction on its lower surface facing the fixing belt 122, and the heater 121, the heat conduction plate 124, and the heat diffusion member 125 are disposed in this recess. For this reason, as shown in FIGS. 4 and 5, both ends of the support 127 in the X-axis direction (short side direction, i.e., front-to-back direction) are located outside both ends of the heat diffusion member 125 in the X-axis direction (short side direction, i.e., front-to-back direction). Note that, as shown in FIG. 3, the lower surfaces of both ends of the support 127 in the X-axis direction are located upstream and downstream of the nip portion 150 in the belt rotation direction (direction of arrow D) of the fixing belt 122.

[0055] 6 and 8 showing supports 161 and 162 from the Y-axis direction, supports 161 and 162 are flange-shaped members that support fixing belt 122, and are provided at both ends in the Y-axis direction (longitudinal direction, i.e., left-right direction) of heating unit 120. In other words, supports 161 and 162 are provided at one end side and the other end side of fixing belt 122 in the rotational axis direction, and are configured to rotatably support both ends of fixing belt 122 in the rotational axis direction.

[0056] As shown in Figure 6, the support 161 is composed of a base 163 that is provided at the other end (right end) of the fixing belt 122 in the rotational axis direction (Y axis direction) and faces the belt end surface of the fixing belt 122 in the rotational axis direction, and a belt insertion portion 164 that extends from one surface 163s of the base 163 (the surface that faces the belt end surface, called the belt facing surface) toward the fixing belt 122 and is inserted inside the fixing belt 122.

[0057] As shown in Figure 8, the base 163 is a roughly disk-shaped member that has a C-shape with the opening facing downward when viewed from the Y-axis direction, and has a recess in the center of the bottom side into which the other end (right end) of the supports 127 and 128 in the longitudinal direction (i.e., extension direction) is fitted.

[0058] The belt insertion portion 164 is a substantially cylindrical member with a C-shape, slightly smaller than the base portion 163, when viewed from the Y-axis direction, with part of the outer periphery of the cylinder cut away, and is provided so as to surround the recess of the base portion 163. The belt insertion portion 164 is inserted inside the other end of the fixing belt 122 and comes into contact with the inner circumferential surface of the fixing belt 122.

[0059] The support 162 has the same configuration as the support 161, and is provided at one end (left end) of the fixing belt 122 in the direction of the rotation axis, and the belt insertion portion 164 is inserted inside the other end of the fixing belt 122 and abuts against the inner surface of the fixing belt 122, and one longitudinal end (left end) of the supports 127 and 128 is fitted into the recess of the base 163.

[0060] In this way, the supports 161 and 162 are configured to rotatably support both ends of the fixing belt 122 in the rotational axis direction by means of belt insertion portions 164 that are inserted inside both ends of the fixing belt 122 in the rotational axis direction. The supports 161 and 162 are also configured to fixedly support both ends of the supports 127 and 128 in the longitudinal direction (extension direction) by means of base portions 163 that fit into both ends of the supports 127 and 128 in the longitudinal direction (extension direction).

[0061] Furthermore, as shown in Figure 6, even if the fixing belt 122 tries to shift in the Y-axis direction, the supports 161 and 162 prevent the fixing belt 122 from shifting too far in the Y-axis direction by having the belt-facing surface 163s of the base 163 abut against the belt end surface of the fixing belt 122.

[0062] 3 to 6, both ends of support 127 in the X-axis direction are defined as edge portions 151 and 152. Of these, edge portion 151 is an edge portion located on the upstream side when fixing belt 122 rotates in the belt rotation direction (i.e., the upstream side in the belt rotation direction), and edge portion 152 is an edge portion located on the downstream side in the belt rotation direction. These edge portions 151 and 152 are provided so as to stand upright relative to the inner circumferential surface of fixing belt 122.

[0063] 5 and 6, the support 127 has protrusions 153 and 154 at both ends in the Y-axis direction (the direction of the rotation axis of the fixing belt 122) of an edge portion 152 on the downstream side in the belt rotation direction, which protrude from the undersurface of the both ends in the Z-axis direction (towards the inner peripheral surface of the fixing belt 122) and can come into contact with the inner peripheral surface of the fixing belt 122. These protrusions 153 and 154 are provided to scrape off and clean the lubricant 126 adhering to the inner peripheral surface of the fixing belt 122.

[0064] The protrusions 153 and 154 are required to be heat resistant because they are provided on the support 127 that supports the heater 121. In this embodiment, a polyimide film with excellent heat resistance is used as the material for the protrusions 153 and 154. Note that the polyimide film is just one example, and other materials may also be used, such as a material that absorbs the lubricant 126.

[0065] 6, the protrusion 153 located on the other end side (right end side) of the edge portion 152 in the Y axis direction is provided more inward in the Y axis direction than the belt-facing surface 163s of the base portion 163 of the support body 161 (i.e., closer to the center Ct in the rotation axis direction of the fixing belt 112). On the other hand, the protrusion 154 located on one end side (left end side) of the edge portion 152 in the Y axis direction is also provided more inward in the Y axis direction than the belt-facing surface 163s of the base portion 163 of the support body 162 (i.e., closer to the center Ct in the rotation axis direction of the fixing belt 112).

[0066] Furthermore, the positions at which the protrusions 153 and 154 are provided are outside the application area 141 where the lubricant 126 is applied in the Y-axis direction (the direction of the rotation axis of the fixing belt 122). Furthermore, the positions at which the protrusions 153 and 154 are provided are outside the maximum paper passing width (not shown), which is the width of the medium passing area through which the medium M passes when the medium M is sandwiched and transported in the nip portion 150, in the Y-axis direction. The position and size of the maximum paper passing width in the Y-axis direction are approximately the same as the position and size of the application area 141 in the Y-axis direction. Furthermore, the positions at which the protrusions 153 and 154 are provided are preferably outside the nip portion 150 in the Y-axis direction. In other words, the positions at which the protrusions 153 and 154 are provided are between the medium passing area (application area 141) and the bases 163 of the supports 161 and 162 in the Y-axis direction.

[0067] 5, the protrusions 153 and 154 are provided at positions spaced a distance L downstream in the belt rotation direction from the nip portion 150. In other words, the distance L is from the downstream end of the nip portion 150 in the belt rotation direction to the upstream ends of the protrusions 153 and 154 in the belt rotation direction. In this embodiment, the protrusions 153 and 154 are provided at positions spaced a distance L of 5 mm from the nip portion 150.

[0068] 6, the side surfaces of the convex portions 153 and 154, which are edges on the inside in the Y-axis direction (i.e., the side closer to the center Ct in the rotation axis direction of the fixing belt 112), are shaped to be perpendicular to the Y-axis direction. In other words, the left side surface of the convex portion 153 located on the right side in FIG. 6, which faces the convex portion 154, is perpendicular to the Y-axis direction, and the right side surface of the convex portion 154 located on the left side in FIG. 6, which faces the convex portion 153, is perpendicular to the Y-axis direction.

[0069] 5, the length of the protrusions 153, 154 in the Z axis direction (i.e., the amount of protrusion from the bottom surface of the edge portion 152) is defined as the thickness N of the protrusions 153, 154. If the thickness N of the protrusions 153, 154 is too thin, the cleaning performance when scraping off the lubricant 126 will be insufficient, and if it is too thick, the force pressing against the fixing belt 122 from the inner periphery will be strong, increasing the load torque when the fixing belt 122 rotates. If the load torque when the fixing belt 122 rotates increases, unevenness will occur in the rotation speed of the fixing belt 122, which may cause problems such as jams (media clogging) due to poor transport of the medium M or image misalignment, where part of the toner is misaligned during fixing.

[0070] In this embodiment, the thickness N of the protrusions 153 and 154 is preferably set within a range of 150 μm (micrometers) or more and 1 mm (millimeters) or less. This allows for sufficient cleaning performance without increasing the load torque during rotation of the fixing belt 122. Furthermore, in this embodiment, by setting the thickness N of the protrusions 153 and 154 to 150 μm or more, when the fixing belt 122 rotates with the pressure roller 131 pressed against the fixing belt 122 to form the nip 150, as shown in FIG. 5 , at least a portion of the protrusions 153 and 154 (the upstream end in the belt rotation direction) always contacts the inner circumferential surface of the end of the fixing belt 122 in the rotational axis direction. In other words, for example, when the pressure roller 131 and the fixing belt 122 are spaced apart, the protrusions 153 and 154 may be spaced apart from the inner circumferential surface of the fixing belt 122.

[0071] 6, if the length K of the convex portions 153 and 154 in the Y-axis direction is too short, the scraped lubricant 126 will leak beyond the convex portions 153 and 154 and onto the belt end surface of the fixing belt 122. On the other hand, if the length K of the convex portions 153 and 154 in the Y-axis direction is too long, the portion outside the printing area will increase, and the heating portion 120 will become larger. In this embodiment, the length K of the convex portions 153 and 154 in the Y-axis direction is preferably set within a range of 5 mm (millimeters) or more and 20 mm (millimeters) or less, which makes it possible to prevent the leakage of the lubricant 126 without increasing the size of the heating portion 120.

[0072] 5, in this embodiment, the angle θ formed between the side surfaces 153s, 154s of the protrusions 153, 154 on the upstream side in the belt rotation direction and the lower surface 125b of the heat diffusion member 125 (the surface facing the inner circumferential surface of the fixing belt 122) is set to a range of 70° to 110°. Note that Fig. 10 shows an example in which the angle θ is 90°, Fig. 11 shows an example in which the angle θ is 70°, and Fig. 12 shows an example in which the angle θ is 110°.

[0073] If the angle θ is too small, the contact pressure between the convex portions 153, 154 and the fixing belt 122 becomes strong, increasing the load torque when the fixing belt 122 rotates. On the other hand, if the angle θ is too large, the contact pressure between the convex portions 153, 154 and the fixing belt 122 becomes weak, reducing the cleaning performance when the convex portions 153, 154 scrape off the lubricant 126. For this reason, in the present embodiment, it is preferable to set the angle θ within a range of 70° (degrees) or more and 110° (degrees) or less, which makes it possible to obtain sufficient cleaning performance without increasing the load torque when the fixing belt 122 rotates.

[0074] 10 to 12, the side surfaces 153t, 154t of the protrusions 153, 154 on the downstream side in the belt rotation direction are shaped to intersect at right angles with the lower surface 125b of the heat diffusion member 125. As shown in Fig. 13, the corners between the side surfaces 153t, 154t of the protrusions 153, 154 on the downstream side in the belt rotation direction and the lower surfaces 153b, 154b of the protrusions 153, 154 may be chamfered to have, for example, an R-shape.

[0075] [2-9. Pressurizing section] As shown in FIG. 3, the pressure unit 130 is specifically a pressure roller 131. The pressure roller 131 is a roller extending in the Y-axis direction. The pressure roller 131 is a cylindrical member that can rotate about a rotation axis J extending in the Y-axis direction by a driving source such as a motor (not shown). As described above, the pressure roller 131 is pressed against the heater 121 with the heat diffusion member 125 and the fixing belt 122 sandwiched therebetween, thereby forming the nip portion 150. In this embodiment, the load when the pressure roller 131 is pressed against the heater 121 with the heat diffusion member 125 and the fixing belt 122 sandwiched therebetween is set to 20 kgf to 49 kgf. Note that the dotted arrow P in FIG. 3 indicates the transport path of the medium M within the fixing unit 30.

[0076] As shown in Figure 9, the cross section of the pressure roller 131 viewed from one end in the longitudinal direction, is a coated roller in which an elastic layer 133 of silicone rubber, a primer layer 134, and a surface layer 135 such as a PFA tube are layered in this order on the surface of a cylindrical core metal 132 such as free-cutting steel (SUM).

[0077] Non-conductive RTV silicone rubber with a thickness of 5 μm or less was used for the primer layer 134. Non-conductive PFA tubing with a thickness of 15 μm to 25 μm was used for the surface layer 135. Furthermore, the elastic layer 133 was set to a thickness of 3 mm, and the pressure roller 131 used had an overall outer diameter of φ30.

[0078] When this pressure roller 131 is pressed against the fixing belt 122, the surface layer 135, the primer layer 134, and the elastic layer 133 are each pressed against the fixing belt 122, causing them to contract and deform, forming a nip portion 150 at the point of contact with the fixing belt 122.

[0079] [2-10.Other] The fixing unit 30 may include one or more other components in addition to the components described above. The other components referred to here include, for example, a control unit that controls the operation of the fixing unit 30. This control unit includes, for example, a temperature adjustment circuit that controls the temperature of the heater 121 via the temperature sensor 123, and a power supply circuit that supplies current to the heater 121. This completes the description of the configuration of the fixing unit 30.

[0080] [3. Operation of image forming device] Next, the operation of the image forming apparatus 200 will be described in order, including the operation of the entire image forming apparatus 200, the operation of the fixing unit 30, and the movement of the lubricant 126. First, the operation of the entire image forming apparatus 200 will be described.

[0081] When forming an image on a medium M, the image forming apparatus 200 sequentially performs a developing process, a transfer process, and a fixing process. That is, the image forming apparatus 200 first sends out the medium M stored in the tray T using the pickup roller 41, and then guides the medium M from the transport path R1 to the transport path R2.

[0082] Here, as a development process, the image forming apparatus 200 forms an electrostatic latent image on the surface of the photosensitive drum 13 of the development unit 10, and then forms a toner image by developing the electrostatic latent image with toner attached thereto.

[0083] Next, in a transfer process, the image forming apparatus 200 transfers the toner image formed on the surface of the photosensitive drum 13 onto the medium M using the transfer unit 20. Finally, in a fixing process, the image forming apparatus 200 fixes the toner image transferred onto the medium M to the medium M by applying heat and pressure using the fixing unit 30. This results in an image being formed (i.e., printed) on the medium M. The medium M on which the image has been formed in this way is discharged into stacker 2 of the image forming apparatus 200. The overall operation of the image forming apparatus 200 is as described above.

[0084] Next, the operation of the fixing unit 30 will be described in detail. When heating the medium M, the fixing unit 30 moves the heating section 120 so as to approach the pressure section 130. At this time, the pressure roller 131 is pressed against the fixing belt 122, thereby forming a nip section 150. Also, at this time, as shown in FIG. 5, protrusions 153 and 154 provided on an edge section 152 of the support body 127 abut against the inner circumferential surface of the fixing belt 122. Here, in the fixing unit 30, the medium M is supplied to the upstream side of the nip section 150 in the belt rotation direction (the right side in the figure) along the transport path indicated by the dotted arrow P in FIG. 3. At this time, the fixing unit 30 transports the medium M supplied to the upstream side of the nip section 150 in the belt rotation direction to the downstream side of the nip section 150 in the belt rotation direction by rotating the fixing belt 122 in the belt rotation direction indicated by the arrow D in conjunction with the rotation of the pressure roller 131. At this time, in the fixing unit 30, the heat generated from the heater 121 is conducted to the fixing belt 122 via the heat diffusion member 125, thereby heating the fixing belt 122. As a result, the medium M passing through the nip portion 150 (i.e., between the fixing belt 122 and the pressure roller 131) is heated while being pressed, and at this time the toner image is fixed to the medium M. The details of the operation of the fixing unit 30 are as described above.

[0085] Finally, the movement of lubricant 126 in fixing unit 30 will be described with reference to FIGS. 3, 6, 14, and 15. FIG. 14 is a partial cross-sectional view showing a portion of a cross section (the peripheral portion of edge portion 152 on the downstream side in the belt rotation direction) of the center portion of heating unit 120 in the Y-axis direction as viewed from one end side (left side) in the Y-axis direction. FIG. 15 is a partial cross-sectional view showing a portion of a cross section (the peripheral portion of edge portion 152 on the downstream side in the belt rotation direction) of one end side (left end) of heating unit 120 in the Y-axis direction as viewed from one end side (right side) in the Y-axis direction. In other words, FIG. 14 is a partial cross-sectional view showing a center portion of edge portion 152 in the Y-axis direction (i.e., a portion where convex portions 153 and 154 are not provided), and FIG. 15 is a partial cross-sectional view showing one end side of edge portion 152 in the Y-axis direction (i.e., a portion where convex portion 154 is provided).

[0086] When assembling the heating unit 120, a lubricant 126 is applied to an application area 141 (FIG. 6) of the heat diffusion member 125. The lubricant 126 applied to the application area 141 is sandwiched and crushed between the heat diffusion member 125 and the fixing belt 122. Thereafter, when the power of the image forming apparatus 200 is turned on, the pressure roller 131 is rotated in the roller rotation direction indicated by arrow E in FIG. 3 by a driving source (not shown). At this time, the fixing belt 122 is pressed against the pressure roller 131, and therefore rotates together with the pressure roller 131 in the belt rotation direction indicated by arrow D.

[0087] 3, the lubricant 126 adhering to the inner circumferential surface of the fixing belt 122 is carried and applied to the inner circumferential surface of the fixing belt 122 in the directions of arrows D1, D2, and D3 in this order. As the fixing belt 122 continues to rotate, the lubricant 126 is supplied thinly and uniformly in the circumferential direction of the inner circumferential surface of the fixing belt 122.

[0088] As the rotation of the fixing belt 122 continues, the lubricant 126 is pushed out in the directions of arrows D4 and D5 from the center Ct of the fixing belt 122 in the direction of the rotation axis toward both ends of the rotation axis, as shown in FIG. 6.

[0089] 14, the movement of the lubricant 126 near the center Ct (FIG. 6) of the fixing belt 122 in the direction of the rotation axis when the fixing belt 122 rotates will be described. Near the center Ct of the fixing belt 122 in the direction of the rotation axis, the lubricant 126 applied to the heat diffusion member 125 is supplied to the inner circumferential surface of the fixing belt 122. The fixing belt 122 rotates in the direction of arrow D. Here, the portion of the fixing belt 122 that has passed through the nip portion 150 is no longer pressurized by the pressure roller 131 (not shown in FIG. 14), and therefore, while retaining the lubricant 126 on its inner circumferential surface, moves away from the heat diffusion member 125, passes below the edge portion 152 while also moving away from the edge portion 152, and then follows an upward trajectory.

[0090] In this way, since there are no convex portions 153, 154 near the center Ct of the fixing belt 122 in the rotation axis direction (i.e., near the center of the edge portion 152 in the Y axis direction), the fixing belt 122 rotates after passing through the nip portion 150 while retaining the lubricant 126 on its inner circumferential surface without coming into contact with the edge portion 152. By repeating this operation, the lubricant 126 is supplied thinly and uniformly in the circumferential direction on the inner circumferential surface of the fixing belt 122.

[0091] Next, using Figure 15, we will explain the movement of lubricant 126 at both ends of fixing belt 122 in the rotational axis direction when fixing belt 122 rotates. At both ends of fixing belt 122 in the rotational axis direction, lubricant 126 applied to heat diffusion member 125 is supplied to the inner circumferential surface of fixing belt 122. Fixing belt 122 rotates in the direction of arrow D. Here, the portion of fixing belt 122 that has passed through nip portion 150 is no longer pressurized by pressure roller 131 (not shown in Figure 15), so it separates from heat diffusion member 125 while retaining lubricant 126 on its inner circumferential surface, passes below edge portion 152 while abutting convex portions 153 and 154 of edge portion 152, and then follows an upward trajectory.

[0092] At this time, the lubricant 126 adhering to the inner circumferential surface of the fixing belt 122 is scraped off and cleaned by the protrusions 153 and 154 that are in contact with the inner circumferential surface of the fixing belt 122 .

[0093] Specifically, the lubricant 126 adhering to the inner surface of the fixing belt 122 moves from the nip portion 150 toward the downstream side in the belt rotation direction along with the fixing belt 122, and when it reaches the upstream side surfaces 153s, 154s of the protrusions 153, 154 located a distance L downstream in the belt rotation direction from the nip portion 150, it is scraped off by the corners between the side surfaces 153s, 154s and the lower surfaces 153b, 154b of the protrusions 153, 154 (i.e., the parts abutting the inner surface of the fixing belt 122).

[0094] In other words, the lubricant 126 adhering to the inner surface of the fixing belt 122 moves from the nip portion 150 to the downstream side in the belt rotation direction together with the fixing belt 122, and when it reaches the side surfaces 153s, 154s of the protrusions 153, 154 on the upstream side in the belt rotation direction, it is blocked by the side surfaces 153s, 154s of the protrusions 153, 154.

[0095] In this way, the lubricant 126 scraped off (blocked) by the convex portions 153 and 154 remains between the lower surface of the heat diffusion member 125 and the inner surface of the fixing belt 122, and does not move downstream of the convex portions 153 and 154 in the belt rotation direction.

[0096] In this way, at both ends of the fixing belt 122 in the rotational axis direction (i.e., both ends of the edge portion 152 in the Y-axis direction), convex portions 153 and 154 that abut against the inner surface of the fixing belt 122 are provided, so that when the fixing belt 122 passes under the edge portion 152 after passing through the nip portion 150, the lubricant 126 adhering to the inner surface is scraped off and cleaned by the convex portions 153 and 154.

[0097] In other words, as the fixing belt 122 rotates, the lubricant 126 that moves from the center Ct of the fixing belt 122 in the direction of the rotation axis (Y-axis) toward both ends is scraped off and cleaned by the convex portions 153 and 154 provided at both ends of the edge portion 152 in the Y-axis direction.

[0098] As a result, at both ends of the fixing belt 122 in the direction of the rotation axis, the lubricant 126 is not attached to the inner surface (cleaned state), and the lubricant 126 can be prevented from leaking from both ends of the fixing belt 122 in the direction of the rotation axis.

[0099] Furthermore, on the upstream side of the protrusions 153 and 154 in the medium conveyance direction (i.e., upstream side in the belt rotation direction), the fixing belt 122 moves away from the heat diffusion member 125 during rotation of the fixing belt 122, increasing the gap Sp between the heat diffusion member 125 and the fixing belt 122. At least a portion of the lubricant 126 scraped off (blocked) by the protrusions 153 and 154 is retained in this gap Sp. Because this gap Sp is located outside the nip portion 150 and is not subjected to nip pressure, it is easy to retain the lubricant 126 scraped off (blocked) by the protrusions 153 and 154, and this more reliably prevents the lubricant 126 from leaking beyond the protrusions 153 and 154 and out of both ends in the rotational axis direction of the fixing belt 122.

[0100] The protrusions 153 and 154 are provided so as to come into contact with a portion of the entire fixing belt 122 downstream of the nip portion 150 in the belt rotation direction, away from the heat diffusion member 125, passing below the edge portion 152, and then tracing an upward trajectory. This allows the protrusions 153 and 154 to smoothly and reliably bring the side surfaces 153s and 154s on the upstream side in the belt rotation direction into contact with the inner circumferential surface of the fixing belt 122.

[0101] [4. Summary and Effects] As described above, in this embodiment, the fixing unit 30 as a fixing device comprises a fixing belt 122 which is an example of a rotatable cylindrical belt, a pressure roller 131 which is an example of a pressure member that is rotatable and abuts against a portion of the outer surface of the fixing belt 122, a heat diffusion member 125 which is an example of an abutting member that abuts against the inner surface of the fixing belt 122 on the pressure roller 131 side via a lubricant 126 and forms a nip portion 150 between the fixing belt 122 and the pressure roller 131 via the fixing belt 122, and convex portions 153 and 154 which are an example of a protruding member that is arranged so as to be able to abut against the inner surface of the fixing belt 122 outside the nip portion 150 and protrudes toward the pressure roller 131 side more than the heat diffusion member 125.

[0102] In this fixing unit 30, the fixing belt 122 and the pressure roller 131 rotate to sandwich and transport the medium M in the nip portion 150, and the convex portions 153 and 154 are arranged so as to be able to abut against the inner surface of the end portion of the fixing belt 122 in the rotational axis direction downstream of the nip portion 150 in the medium transport direction.

[0103] Specifically, in the fixing unit 30, convex portions 153 and 154 are provided at both ends in the Y-axis direction (the direction of the rotation axis of the fixing belt 122) of an edge portion 152 located downstream in the media conveying direction of a support body 127, which is an example of a support member that supports the heat diffusion member 125, so that when the fixing belt 122 rotates with the pressure roller 131 pressed against the fixing belt 122 to form a nip portion 150, at least a portion of the convex portions 153 and 154 always abuts against the inner surface of the fixing belt 122.

[0104] In this way, in the fixing unit 30, the protrusions 153, 154 that can come into contact with the inner circumferential surface of both ends in the rotational axis direction of the fixing belt 122 are provided, and thereby the lubricant 126 can be scraped off and cleaned by the protrusions 153, 154 at both ends in the rotational axis direction of the fixing belt 122. In this way, in the fixing unit 30 of the present embodiment, it is possible to prevent the lubricant 126 that has moved from the center Ct of the fixing belt 122 in the rotational axis direction toward both ends from leaking out from both ends in the rotational axis direction of the fixing belt 122.

[0105] Furthermore, in the fixing unit 30 of this embodiment, the convex portions 153 and 154 are provided outside the nip portion 150, so that the effect of the convex portions 153 and 154 on the nip pressure of the nip portion 150 can be minimized, and sufficient nip pressure can be obtained.

[0106] Thus, the fixing unit 30 of this embodiment can further reduce the occurrence of printing defects.

[0107] Furthermore, in the fixing unit 30 of this embodiment, the convex portions 153 and 154 are provided outside the maximum paper passing width, which is an example of a medium passing area, in the rotation axis direction of the fixing belt 122. By doing so, in the fixing unit 30 of this embodiment, the influence of the convex portions 153 and 154 on the transport of the medium M can be minimized, and poor transport and fixing of the medium M can be suppressed.

[0108] Furthermore, in the fixing unit 30 of this embodiment, it is possible to prevent the lubricant 126 from leaking out of the fixing belt 122, thereby reducing loss of the lubricant 126. This has the advantage that it is not necessary to increase the amount of lubricant 126 applied to the heat diffusion member 125 in consideration of loss of the lubricant 126.

[0109] From another perspective, in this embodiment, the fixing unit 30 can be considered to include a fixing belt 122 which is an example of a rotatable cylindrical belt, a pressure roller 131 which is an example of a pressure member that is rotatable and abuts against a portion of the outer surface of the fixing belt 122, a heat diffusion member 125 which is an example of an abutting member that abuts against the inner surface of the fixing belt 122 on the pressure roller 131 side via a lubricant 126 and forms a nip portion 150 between the fixing belt 122 and the pressure roller 131 via the fixing belt 122, and an edge portion 152 (including convex portions 153, 154) which is an example of an edge portion that can abut against the inner surface of the fixing belt 122.

[0110] Furthermore, the edge portion 152 has convex portions 153 and 154, which are an example of a contact portion that can contact the inner surface of the end portion in the rotational axis direction of the fixing belt 122 downstream of the nip portion 150 in the media conveying direction, and a concave portion 170 (see Figure 6), which is an example of a recess that is spaced apart from the inner surface of the fixing belt 122, and the portion of the concave portion 170 located between one end and the other end in the rotational axis direction of the fixing belt 122 (i.e., the portion between the convex portion 153 and the convex portion 154) can be considered to be recessed in a direction away from the inner surface of the fixing belt 122.

[0111] From this perspective, in the recess 170 located between one end and the other end of the fixing belt 122 in the direction of the rotation axis, the lubricant 126 can be scraped off and cleaned by the protrusions 153 and 154 of the edge portion 152 at both ends of the fixing belt 122 in the direction of the rotation axis without interfering with the movement of the lubricant 126 in the circumferential direction of the fixing belt 122, thereby preventing the lubricant 126 from leaking from both ends of the fixing belt 122 in the direction of the rotation axis.

[0112] Furthermore, since the convex portions 153 and 154 of the edge portion 152 are provided outside the nip portion 150, the effect of the convex portions 153 and 154 on the nip pressure of the nip portion 150 can be minimized, and sufficient nip pressure can be obtained.

[0113] 5. Other Embodiments [5-1. Other embodiment 1] In the above-described embodiment, the convex portions 153 and 154 protruding from the lower surface of the edge portion 152 located downstream in the belt rotation direction of the support body 127 are provided. However, as shown in FIG. 16, for example, the convex portions 153 and 154 may be integral with the edge portion 152.

[0114] [5-2. Other embodiment 2] In the above-described embodiment, convex portions 153 and 154, which are an example of protruding members protruding downward from the lower surface, are provided on the lower surface of edge portion 152 located downstream in the belt rotation direction of support body 127. However, this is not limiting, and for example, as shown in Figures 17 and 18, convex portions 301 and 302 protruding downward from the lower end surface may be provided on the lower end surface of belt insertion portion 164 of supports 161 and 162 on the edge portion 152 side, rather than on edge portion 152 of support body 127. Note that fixing belt 122 is omitted in Figure 17.

[0115] In this case, the size of the protrusions 301 and 302 may be approximately the same as that of the protrusions 153 and 154. The positions where the protrusions 301 and 302 are provided may be downstream of the positions where the protrusions 153 and 154 are provided in the belt rotation direction.

[0116] Alternatively, a protruding member that protrudes downward from the lower surfaces 153b and 154b of the edge portion 152 may be provided on the side surfaces 153t and 154t on the downstream side in the belt rotation direction of the edge portion 152. Alternatively, a protruding member that protrudes downward from the lower surface of the heat diffusion member 125 may be provided on the end portion of the heat diffusion member 125 on the downstream side in the belt rotation direction.

[0117] [5-3. Other embodiment 3] Furthermore, in the above-described embodiment, the heating unit 120 is configured such that the heat diffusion member 125 is interposed between the heater 121 and the fixing belt 122. However, this is not limiting, and as shown in Fig. 19, the heat diffusion member 125 may be omitted and the heater 121 may be configured to contact the fixing belt 122. In this case, when the fixing belt 122 rotates, the surface (lower surface) of the heater 121 facing the pressure unit 130 slides against the inner circumferential surface of the fixing belt 122. The lower surface of the heater 121 (the surface that slides against the fixing belt 122) may be coated.

[0118] [5-4. Other embodiment 4] Furthermore, in the above-described embodiment, the convex portions 153 and 154 are provided at both ends in the Y-axis direction of the edge portion 152 of the support body 127, but this is not limiting, and a configuration may be adopted in which one of the convex portions 153 and 154 is omitted. In other words, a configuration may be adopted in which the convex portion 153 (or the convex portion 154) is provided at only one end of the both ends in the Y-axis direction of the edge portion 152 of the support body 127.

[0119] Incidentally, a case where the convex portion 153 (or the convex portion 154) is provided only at one of the two ends in the Y-axis direction of the edge portion 152 of the support body 127 is considered, for example, when the fixing belt 122 is pre-positioned toward the support body 162 (or the support body 161), and there is no gap between the fixing belt 122 and the support body 162 (or the support body 161), but a gap is formed between the fixing belt 122 and the support body 161 (or the support body 162).

[0120] [5-5. Other Embodiment 5] Furthermore, in the above-described embodiment, the present invention is applied to the image forming apparatus 200, but is not limited to this, and can be applied to various image forming apparatuses (i.e., electrophotographic type) that include a fixing device such as the fixing unit 30, and an image forming section such as the developing unit 10 and transfer unit 20 that form a developer image on the medium M. For example, this type of image forming apparatus can also be applied to image forming apparatuses such as copiers, multifunction machines, and fax machines.

[0121] [5-6. Other Embodiment 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. [Industrial Applicability]

[0122] The present invention can be widely used in, for example, electrophotographic printers. [Explanation of symbols]

[0123] 200...image forming apparatus, 10...developing unit, 20...transfer unit, 30...fixing unit, 110...casing, 120...heating section, 130...pressure section, 140...connector, 121...heater, 122...heating belt, 123...temperature sensor, 124...heat conduction plate, 125...heat diffusion member, 126...lubricant, 127, 128, 161, 162...support, 129...compression spring, 150...nip portion, 151, 152...edge portion, 153, 154, 201, 202...convex portion, 163...base portion, 164...belt insertion portion, M...medium.

Claims

1. A rotatable belt, a rotatable pressure member that abuts against a portion of the outer circumferential surface of the belt; a contact member that contacts the inner circumferential surface of the belt via a lubricant and forms a nip portion between the contact member and the pressure member via the belt; a protruding member that is provided outside the nip portion and can contact the inner circumferential surface of the belt, and that protrudes toward the pressure member beyond the contact member; Equipped with The belt and the pressure member are By rotating, the medium is sandwiched in the nip portion and conveyed, The protruding member is The nip portion is provided downstream in the medium conveyance direction and is capable of contacting the inner circumferential surface of the end portion of the belt in the rotation axis direction. A fixing device characterized by:

2. The protruding member is In the direction of the rotation axis of the belt, the nip is provided outside a medium passing area through which the medium passes when the medium is sandwiched and transported in the nip.

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 belt is During rotation, the contact member is separated from the nip portion downstream in the medium transport direction, The protruding member is The belt is provided so as to be able to abut against an inner circumferential surface of a portion of the belt that is downstream of the nip portion in the medium transport direction and that is spaced apart from the abutting member. The fixing device according to claim 1 or 2.

4. A gap is formed between the contact member and the belt spaced apart from the contact member on the upstream side of the protruding member in the medium transport direction, and at least a portion of the lubricant scraped off from the inner circumferential surface of the belt by the protruding member is held in the gap when the belt rotates.

4. The fixing device according to claim 3.

5. a support member provided on an inner circumferential side of the belt and supporting the contact member; The protruding member is The support member is provided with 3. The fixing device according to claim 2.

6. a belt insertion portion inserted into the inner peripheral side of each end of the belt in the rotation axis direction; The protruding member is The belt insertion portion is provided 3. The fixing device according to claim 2, wherein the fixing device is a fixing device.

7. The protruding amount of the protruding member is set to 150 μm or more and 1 mm or less.

3. The fixing device according to claim 1, wherein the fixing member is a fixing member.

8. The protruding member is The length of the belt in the direction of the rotation axis is 5 mm or more and 20 mm or less.

3. The fixing device according to claim 1, wherein the fixing member is a fixing member.

9. The angle formed between the upstream side of the protruding member in the medium transport direction and the surface of the contact member that contacts the belt is set to be equal to or greater than 70° and equal to or less than 110°.

3. The fixing device according to claim 1, wherein the fixing member is a fixing member.

10. The abutment member is A heat diffusion member that diffuses heat from a heater, When the belt rotates, the surface of the heat diffusion member facing the pressure member slides against the inner circumferential surface of the belt.

3. The fixing device according to claim 1, wherein the fixing member is a fixing member.

11. The abutment member is It is a heater, When the belt rotates, the surface of the heater facing the pressure member slides against the inner circumferential surface of the belt.

3. The fixing device according to claim 1, wherein the fixing member is a fixing member.

12. The fixing device according to claim 1 or 2; an image forming unit that forms a developer image on the medium; An image forming apparatus comprising:

13. A rotatable belt, a rotatable pressure member that abuts against a portion of the outer circumferential surface of the belt; a contact member that contacts the inner circumferential surface of the belt via a lubricant and forms a nip portion between the contact member and the pressure member via the belt; an edge portion that can come into contact with the inner circumferential surface of the belt; Equipped with The belt and the pressure member are By rotating, the medium is sandwiched in the nip portion and conveyed, The edge portion is a contact portion that can contact an inner circumferential surface of an end portion of the belt in a rotation axis direction downstream of the nip portion in a medium conveying direction, and a recess that is spaced apart from the inner circumferential surface of the belt; The recessed portion is A portion of the belt located between one end and the other end in the rotation axis direction is recessed in a direction away from the inner circumferential surface of the belt. A fixing device characterized by:

Images