Fixing device

Abstract

To provide a configuration capable of appropriately supplying oil between a fixing pad 303 and a fixing belt 301.SOLUTION: A heating roller 307 contacts an inner circumferential surface of a fixing belt 301 and stretches the fixing belt 301. A halogen heater 306 heats the fixing belt 301 by heating the heating roller 307. A steering roller 401 contacts the inner circumferential surface of the fixing belt 301 on a downstream side of the heating roller 307 and an upstream side of the fixing pad 303 with respect to a rotation direction of the fixing belt 301, and stretches the fixing belt 301. An oil application roller 501 contacts the inner circumferential surface of the fixing belt 301 on a downstream side of the heating roller 307 and an upstream side of the steering roller 401 with respect to the rotation direction of the fixing belt 301, and applies oil to the inner circumferential surface of the fixing belt 301.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a fixing device that heats a toner image carried on a recording material and fixes the toner image to the recording material. [Background technology]

[0002] Image forming devices such as copiers, printers, facsimiles, and multifunction devices having multiple functions of these include a fixing device that fixes a toner image carried on a recording material to the recording material. As a fixing device, a configuration in which a toner image on a recording material is heated and conveyed in a nip formed by an endless belt member and a rotating body has been conventionally known (Patent Document 1).

[0003] The fixing device described in Patent Document 1 forms a nip using a nip-forming member that sandwiches a belt member between itself and a rotating body. When a nip is formed using such a nip-forming member, it is known that the sliding resistance between the belt member and the nip-forming member at the nip increases, resulting in image defects and abrasion of the inner surface of the belt. For this reason, a configuration is widely adopted in which a lubricant is applied to the inner surface of the belt member to reduce the sliding resistance between the belt member and the nip-forming member.

[0004] The configuration described in Patent Document 1 has a lubricant applicator that applies lubricant to a heating roller that heats a belt member, and the lubricant is applied from the lubricant applicator to the inner circumferential surface of the belt member via the heating roller. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2023-77275 Summary of the Invention [Problem to be solved by the invention]

[0006] The lubricant application member is made of a material that has been impregnated with lubricant in advance, such as an organic or inorganic porous material such as a sponge or a porous ceramic body, or a woven or nonwoven fabric made of organic or inorganic fibers such as cloth or polyester fiber. In the configuration described in Patent Document 1, the lubricant application member is brought into contact with the heating roller, causing the lubricant to seep out little by little and apply the lubricant to the surface of the heating roller, and the lubricant is then applied from the heating roller to the inner circumferential surface of the belt member.

[0007] However, in the configuration described in Patent Document 1, although the direct application of heat from the heating roller maximizes the amount of lubricant dispensed from the lubricant applicator, excessive heat applied to the lubricant can result in the lubricant becoming too viscous. This can result in the lubricant applied to the inner circumferential surface of the belt member leaking from, for example, the longitudinal ends of the belt member. This results in the amount of lubricant delivered between the nip-forming member and the belt member, where lubricant is needed, being less than the amount dispensed from the lubricant applicator, resulting in inefficient use of the lubricant in the lubricant applicator. On the other hand, supplying a sufficient amount of lubricant between the nip-forming member and the belt member requires a larger lubricant applicator, which limits the installation space for the lubricant applicator. Furthermore, this can result in an increase in the size of the fixing device and image forming apparatus.

[0008] Alternatively, a lubricant applicator may be placed in contact with the inner circumferential surface of the belt member, and the lubricant may be applied directly to the inner circumferential surface of the belt member. However, the viscosity of the lubricant increases as the temperature drops, which reduces the amount of lubricant that can be dispensed from the lubricant applicator to the belt member.

[0009] SUMMARY OF THE INVENTION An object of the present invention is to provide a configuration that can appropriately supply a lubricant between a nip portion forming member and a belt member. [Means for solving the problem]

[0010] One aspect of the present invention is a fixing device that heats a toner image carried on a recording material and fixes it to the recording material, and is characterized by comprising: an endless belt member; a rotating body that rotates in contact with the outer surface of the belt member; a nip portion forming member that is arranged inside the belt member so as to sandwich the belt member between the rotating body and the rotating body, and forms a nip portion between the belt member and the rotating body to sandwich and transport the recording material; a first tension member that contacts the inner surface of the belt member and tensions the belt member; a second tension member that contacts the inner surface of the belt member downstream of the first tension member and upstream of the nip portion forming member in relation to the rotation direction of the belt member and tensions the belt member; a heating unit that heats the belt member by heating the first tension member; and a lubricant application member that contacts the inner surface of the belt member downstream of the first tension member and upstream of the second tension member in relation to the rotation direction of the belt member and applies lubricant to the inner surface of the belt member. [Effects of the Invention]

[0011] According to the present invention, it is possible to appropriately supply lubricant between the nip portion forming member and the belt member. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a cross-sectional view showing a schematic configuration of an image forming apparatus according to an embodiment. [Figure 2] FIG. 2 is a cross-sectional view showing a schematic configuration of a fixing device according to the embodiment. [Figure 3] FIG. 2 is a cross-sectional view showing a schematic configuration of the vicinity of the oil application roller according to the embodiment. [Figure 4] FIG. 3 is a schematic diagram showing the relationship between the oil application roller and the steering roller according to the embodiment. [Figure 5] Graph showing the relationship between oil temperature and viscosity. [Figure 6] Graph showing the relationship between oil viscosity and oil film thickness on a belt. [Figure 7] FIG. 4 is a diagram for explaining temperature measurement positions in the rotation direction of a fixing belt. [Figure 8]10 is a graph showing the relationship between the number of swings of the steering roller and the oil film thickness at each position in the longitudinal direction of the fixing belt. DETAILED DESCRIPTION OF THE INVENTION

[0013] The embodiment will be described with reference to Figures 1 to 8. First, the schematic configuration of an image forming apparatus according to the present embodiment will be described with reference to Figure 1.

[0014] [Image forming equipment] Image forming apparatus 1 is an electrophotographic full-color printer having four image forming units Pa, Pb, Pc, and Pd corresponding to the four colors of yellow, magenta, cyan, and black. In this embodiment, the image forming units Pa, Pb, Pc, and Pd are arranged in tandem along the rotation direction of an intermediate transfer belt 204 (described later). Image forming apparatus 1 forms a toner image (image) on a recording material in response to an image signal from an image reading unit (document reading device) 2 connected to image forming apparatus main body 3 or from a host device such as a personal computer connected to image forming apparatus main body 3 so as to be able to communicate with the image forming apparatus main body 3. Examples of recording materials include sheet materials such as paper, plastic film, and cloth.

[0015] The image forming apparatus 1 comprises an image reading unit 2 and an image forming apparatus main body 3. The image reading unit 2 reads an original placed on a platen glass 21. Light emitted from a light source 22 is reflected by the original and forms an image on a CCD sensor 24 via optical components 23 such as a lens. This optical unit scans in the direction of the arrow, converting the original into a line-by-line electrical signal data stream. The image signal obtained by the CCD sensor 24 is sent to the image forming apparatus main body 3, where it is subjected to image processing in accordance with each image forming unit (described later) by a control unit 30. The control unit 30 also receives external inputs as image signals from external host devices such as a print server.

[0016] The image forming apparatus main body 3 includes multiple image forming units Pa, Pb, Pc, and Pd, and each image forming unit forms an image based on the image signal. That is, the image signal is converted into a laser beam that is PWM (pulse width modulation) controlled by a control unit 30. A polygon scanner 31 serving as an exposure device scans the laser beam in accordance with the image signal. The laser beam is then irradiated onto photosensitive drums 200a to 200d serving as image carriers of each image forming unit Pa to Pd.

[0017] Note that Pa is a yellow (Y) image forming unit, Pb is a magenta (M) image forming unit, Pc is a cyan (C) image forming unit, and Pd is a black (Bk) image forming unit, each forming an image of the corresponding color. Since the image forming units Pa to Pd are substantially identical, the Y image forming unit Pa will be described in detail below, and descriptions of the other image forming units will be omitted. In the image forming unit Pa, a toner image is formed on the surface of the photosensitive drum 200a based on an image signal, as will be described below.

[0018] A charging roller 201a, which serves as a primary charger, charges the surface of the photosensitive drum 200a to a predetermined potential to prepare for the formation of an electrostatic latent image. A laser beam from a polygon scanner 31 forms an electrostatic latent image on the surface of the photosensitive drum 200a, which has been charged to a predetermined potential. A developing unit 202a develops the electrostatic latent image on the photosensitive drum 200a to form a toner image. A primary transfer roller 203a discharges electricity from the back surface of the intermediate transfer belt 204 and applies a primary transfer bias of opposite polarity to the toner, transferring the toner image on the photosensitive drum 200a onto the intermediate transfer belt 204. After transfer, the surface of the photosensitive drum 200a is cleaned by a cleaner 207a.

[0019] The toner image on intermediate transfer belt 204 is then conveyed to the next image forming station, where the toner images of each color formed at each image forming station are transferred in the order of Y, M, C, and Bk, forming a four-color image on the surface. The toner image that has passed through Bk image forming station Pd, which is located at the most downstream side in the rotation direction of intermediate transfer belt 204, is conveyed to a secondary transfer station made up of a pair of secondary transfer rollers 205 and 206. In the secondary transfer station, a secondary transfer electric field of opposite polarity to the toner image on intermediate transfer belt 204 is applied, thereby secondarily transferring the toner image onto the recording material.

[0020] The recording material is stored in a cassette 9, and the recording material fed from the cassette 9 is transported to a registration unit 208, which is made up of, for example, a pair of registration rollers, and waits at the registration unit 208. Thereafter, the timing of the registration unit 208 is controlled to align the position of the toner image on the intermediate transfer belt 204 with the position of the paper, and the recording material is transported to a secondary transfer unit.

[0021] The recording material onto which the toner image has been transferred in the secondary transfer section is transported to a fixing device 8, where the toner image carried on the recording material is fixed to the recording material by heating and pressing. The recording material that has passed through the fixing device 8 is discharged onto a discharge tray 7. When forming images on both sides of the recording material, after the toner image has been transferred and fixed onto the first side (front side) of the recording material, the recording material is turned over via a reversing conveyance section 10, and the toner image is transferred and fixed onto the second side (rear side) of the recording material, and the recording material is then stacked on the discharge tray 7.

[0022] As described above, the control unit 30 controls the entire image forming apparatus 1. The control unit 30 can also perform various settings based on input from the operation unit 4 of the image forming apparatus 1. The control unit 30 has a CPU (Central Processing Unit), a ROM (Read Only Memory), and a RAM (Random Access Memory). The CPU controls each unit by reading a program corresponding to a control procedure stored in the ROM. The RAM stores working data and input data, and the CPU performs control by referring to the data stored in the RAM based on the aforementioned programs.

[0023] [Fusing device] Next, the configuration of the fixing device 8 in this embodiment will be described with reference to FIG. 2. FIG. 2 is a cross-sectional view that schematically shows the general configuration of the fixing device 8. In this embodiment, a belt heating type fixing device using an endless belt is adopted. In FIG. 2, the X direction indicates the conveyance direction of the recording material P, the Y direction indicates the width direction that intersects with the conveyance direction of the recording material P (orthogonal in this embodiment), and the Z direction indicates the pressure direction of the pressure roller 305, which will be described later. These directions are perpendicular to each other. Furthermore, one side of the width direction (Y direction) is the front side of the image forming apparatus 1, for example, the side where the operation unit 4 is located and operated by the user. On the other hand, the other side of the width direction is the rear side of the image forming apparatus 1.

[0024] The fixing device 8 includes a heating unit 300 having a fixing belt 301 as an endless rotatable belt member, and a pressure roller 305 as a rotating body that contacts the fixing belt 301 and forms a nip portion N together with the fixing belt 301.

[0025] The heating unit 300 includes the above-mentioned fixing belt 301, a fixing pad 303 serving as a nip forming member and a pad member, a stay 302, a heating roller 307 serving as a first tension member, a steering roller 401 serving as a second tension member, and an oil application roller 501 serving as a lubricant supply member. The pressure roller 305 rotates in contact with the outer circumferential surface of the fixing belt 301, and is also a driving rotor that applies a driving force to the fixing belt 301.

[0026] The fixing belt 301 has thermal conductivity, heat resistance, and the like, and is a thin cylindrical shape. In this embodiment, it has a three-layer structure consisting of a base layer, an elastic layer on the outer periphery of the base layer, and a release layer on the outer periphery of the elastic layer. The base layer is 80 μm thick and made of polyimide resin (PI), the elastic layer is 100 μm thick and made of silicone rubber, and the release layer is 30 μm thick and made of PFA (tetrafluoroethylene-perfluoroalkoxyethylene copolymer resin) as a fluororesin. The fixing belt 301 is stretched by the fixing pad 303, the heating roller 307, and the steering roller 401.

[0027] The fixing pad 303 is disposed non-rotatably inside the fixing belt 301 so as to sandwich the fixing belt 301 between itself and the pressure roller 305. The fixing pad 303 forms a nip portion N between the fixing belt 301 and the pressure roller 305, which sandwiches and conveys the recording material. In this embodiment, the fixing pad 303 is a substantially plate-shaped member that is long in the width direction of the fixing belt 301 (the longitudinal direction intersecting the rotation direction of the fixing belt 301, the direction of the rotation axis of the heating roller 307). The fixing pad 303 is pressed against the pressure roller 305 with the fixing belt 301 sandwiched therebetween, thereby forming the nip portion N. The fixing pad 303 is made of LCP (liquid crystal polymer) resin.

[0028] The fixing pad 303 is supported by a stay 302 serving as a support member disposed inside the fixing belt 301. That is, the stay 302 is disposed on the opposite side of the fixing pad 303 from the pressure roller 305, and supports the fixing pad 303. The stay 302 is a reinforcing member having long rigidity along the longitudinal direction of the fixing belt 301, and contacts the fixing pad 303 to back it up. That is, the stay 302 provides strength to the fixing pad 303 when the fixing pad 303 is pressed by the pressure roller 305, thereby ensuring the pressure force at the nip N.

[0029] Between the fixing pad 303 and the fixing belt 301, a lubricating sheet 308 with a surface coated with PTFE (polytetrafluoroethylene) and silicone oil S (hereinafter referred to as oil S) are interposed, allowing the fixing belt 301 to slide smoothly against the fixing pad 303. Silicone oil is preferably used as the lubricant from the viewpoint of heat resistance, and oils of various viscosities are used depending on the conditions of use. In this embodiment, oil with a viscosity of 1000 cSt is used because oils with too high a viscosity have poor fluidity when applied. Specific examples of such oils include, but are not limited to, dimethyl silicone oil, amino-modified silicone oil, and fluorine-modified silicone oil.

[0030] Lubricating sheet 308 is formed by coating the surface of a 70 μm-thick polyimide base material with PTFE. Note that lubricating sheet 308 is arranged to improve the sliding properties between fixing pad 303 and fixing belt 301. Therefore, instead of lubricating sheet 308, it is possible to substitute a coating that improves sliding properties on the surface layer of fixing pad 303.

[0031] Heating roller 307 is disposed inside fixing belt 301, and stretches fixing belt 301 together with fixing pad 303 and steering roller 401. Heating roller 307 is formed into a cylindrical shape from a metal such as aluminum or stainless steel, and has a halogen heater 306 disposed inside as a heating unit for heating fixing belt 301. Heating roller 307 is heated to a predetermined temperature by halogen heater 306. Halogen heater 306 is heated by power supplied from power supply unit 601.

[0032] In this embodiment, the heating roller 307 is formed of, for example, a stainless steel pipe having a thickness of 1 mm. The halogen heater 306 may be provided in a single piece or in multiple pieces. In this embodiment, the power available to the fixing device 8, i.e., the power available to the halogen heater 306, is reduced to meet recent demands for power saving. Specifically, the power used by the halogen heater 306 is 1400 W or less. The heating unit that heats the heating roller 307 is not limited to a halogen heater, and may be another heater capable of heating the heating roller 307, such as a carbon heater. The fixing belt 301 is heated by the heating roller 307 heated by the halogen heater 306, and is controlled to a predetermined target temperature according to the type of recording material based on temperature detection by a thermistor (not shown).

[0033] The steering roller 401 is disposed inside the fixing belt 301, stretches the fixing belt 301 together with the fixing pad 303 and the heating roller 307, and is rotated by the fixing belt 301. In this embodiment, the steering roller 401 contacts the inner circumferential surface of the fixing belt 301 downstream of the heating roller 307 and upstream of the fixing pad 303 with respect to the rotation direction of the fixing belt 301, and stretches the fixing belt 301. The steering roller 401 is disposed so that its rotation axis can tilt in a direction parallel to the rotation axis direction (width direction, length direction) of the heating roller 307, and controls the position (offset position) of the fixing belt 301 with respect to the rotation axis direction of the heating roller 307 by tilting. In other words, the steering roller 401 is a roller for adjusting the position of the fixing belt 301 by tilting with respect to the heating roller 307 so that the fixing belt 301 is positioned within a predetermined range in the width direction of the fixing belt 301.

[0034] That is, the steering roller 401 has a rotation center at the center or one end of the rotation axis direction (longitudinal direction) of the steering roller 401, and tilts relative to the longitudinal direction of the heating roller 307 by swinging around this rotation center. This generates a tension difference between one side and the other side of the fixing belt 301 in the longitudinal direction, causing the fixing belt 301 to move in the longitudinal direction. The fixing belt 301 tends to shift to one end during rotation depending on the outer diameter accuracy of the rollers that tension it and the alignment accuracy between the rollers. For this reason, the steering roller 401 controls this shift. The steering roller 401 may be swung by a drive source such as a motor, or may be configured to swing by automatic centering.

[0035] The steering roller 401 of this embodiment will be described in more detail. The steering roller 401 is rotatably supported by a frame 410 of the heating unit 300 via a steering support part 411. The frame 410 supports the heating roller 307, the stay 302, and the fixing pad 303. The steering support part 411 is rotatably supported by the frame 410 around a rotation shaft 404. The steering support part 411 rotates relative to the frame 410 of the heating unit 300 with the rotation shaft 404 as a fulcrum, causing the steering roller 401 to tilt.

[0036] As shown in Figure 4, which will be described later, the steering support part 411 has a steering holding part 403 that holds the rotation shaft 401a of the steering roller 401 relative to the frame 410, and a swing arm 405 that is connected to the rotation shaft 401a of the steering roller 401 and supports the oil application roller 501, which will be described later, so that it can swing freely relative to the rotation shaft 401a of the steering roller 401.

[0037] In this embodiment, the steering roller 401 is urged toward the fixing belt 301 by a urging spring 402 serving as a steering urging portion, and also serves as a tension roller that applies a predetermined tension to the fixing belt 301. That is, the steering roller 401 is urged toward the fixing belt 301 by the urging spring 402 supported by a steering holding portion 403. The urging spring 402 is disposed between the steering roller 401 and the steering holding portion 403, and urges the steering roller 401 toward the inner circumferential surface of the fixing belt 301.

[0038] The oil application roller 501 comes into contact with the inner circumferential surface of the fixing belt 301 and applies a lubricant to the inner circumferential surface of the fixing belt 301. In this embodiment, as will be described in detail later, the oil application roller 501 is disposed downstream of the heating roller 307 and upstream of the steering roller 401 in the rotation direction of the fixing belt 301.

[0039] The pressure roller 305 rotates in contact with the outer peripheral surface of the fixing belt 301, applying a driving force to the fixing belt 301. In this embodiment, the pressure roller 305 is a roller having an elastic layer formed on the outer periphery of its shaft and a release layer formed on the outer periphery of the elastic layer. The shaft is made of stainless steel with a diameter of 72 mm, the elastic layer is made of conductive silicone rubber with a thickness of 8 mm, and the release layer is made of PFA (tetrafluoroethylene-perfluoroalkoxyethylene copolymer resin) as a fluororesin with a thickness of 100 μm. The pressure roller 305 is rotatably supported by a pressure arm that is movable relative to the fixing frame (not shown) of the fixing device 8, and has a gear fixed to one end thereof. The pressure roller 305 is connected to a motor M, which serves as a pressure roller drive source, via the gear, and is driven to rotate.

[0040] In the fixing device 8 configured as above, the toner image is heated in the nip portion N formed between the fixing belt 301 and the pressure roller 305 while the recording material P carrying the toner image is sandwiched and conveyed. The toner image is then fixed to the recording material P. Therefore, the fixing device 8 needs to have both the function of applying heat and pressure and the function of conveying the recording material P. The pressure roller 305 is pressed against the fixing pad 303 via the fixing belt 301 by a drive source (not shown). In this embodiment, the pressure force (NF) at the nip portion N during image formation is set to 1600 N, and the length of the nip portion N in the X direction (conveyance direction) is set to 24.5 mm, and the length in the Y direction (width direction) is set to 326 mm.

[0041] Further, downstream of the nip portion N in the conveying direction of the recording material P, there are arranged a pair of discharge rollers 310 for discharging the recording material P that has passed through the nip portion N out of the fixing device 8, a separation plate 309a, and a lower separation guide 309b. The separation plate 309a is arranged downstream of the nip portion N in the conveying direction of the recording material and vertically above the nip portion N, with its leading edge closely facing the vicinity of the nip portion N of the fixing belt 301. Then, the recording material P that has passed through the nip portion N is peeled off from the fixing belt 301.

[0042] The lower separation guide 309b is disposed downstream of the nip portion N in the recording material conveyance direction and vertically below the nip portion N, with its tip closely facing the pressure roller 305 near the nip portion N. When the recording material P sticks to the pressure roller 305, the lower separation guide 309b separates the recording material P from the pressure roller 305. The lower separation guide 309b also supports the lower surface of the recording material P discharged from the nip portion N and guides the recording material P to the discharge roller pair 310. The discharge roller pair 310 discharges the recording material P discharged from the nip portion N to the outside of the fixing device 8.

[0043] [Oil application roller] FIG. 3 is a schematic diagram of the oil application roller 501 and its surroundings. The oil application roller 501, which serves as a lubricant application roller, is composed of a core 501a serving as a shaft and an oil-impregnated layer 501b serving as a lubricant-impregnated layer provided around the core 501a. The core 501a is a roller shaft made of a material such as aluminum, iron, or stainless steel. The oil-impregnated layer 501b is formed by winding a nonwoven fabric impregnated with the same silicone oil as that previously applied to the inner surface of the fixing belt 301 around the core 501a. However, the oil-impregnated layer 501b is not limited to this and may also be made of, for example, an organic or inorganic porous material such as a sponge or porous ceramic body, or a woven fabric of organic or inorganic fibers such as polyester fiber. That is, oil-impregnated layer 501b may be any of a nonwoven fabric impregnated with a lubricant, a porous material impregnated with a lubricant, and a woven fabric of fibers impregnated with a lubricant. Oil application roller 501 is biased toward the inner circumferential surface of fixing belt 301 (in the direction of arrow A) by spring 502 as a biasing portion.

[0044] 4 is a diagram showing the relationship between the oil application roller 501 and the steering roller 401. The oil application roller 501 is supported by a steering support part 411 that supports the steering roller 401. As described above, the steering support part 411 has a steering holder part 403 that holds the rotation shaft 401a of the steering roller 401, and a swing arm 405. One end of the swing arm 405 is connected to the rotation shaft 401a of the steering roller 401, and the other end is connected to the core part 501a that is the shaft part of the oil application roller 501. As a result, the swing arm 405 supports the oil application roller 501 so that it can swing freely around the rotation shaft 401a of the steering roller 401.

[0045] Furthermore, spring 502 is provided between steering holder 403 and oil application roller 501, and urges oil application roller 501 toward the inner circumferential surface of fixing belt 301. Oil application roller 501 is urged by spring 502 with a force of approximately 800 to 1500 gf against fixing belt 301. With this configuration, oil application roller 501 can be made to follow the movement of fixing belt 301 that accompanies deviation control of steering roller 401.

[0046] [Oil application roller location] 2, oil application roller 501 is disposed downstream of heating roller 307 and upstream of steering roller 401 in the rotation direction of fixing belt 301, and is biased toward the inner circumferential surface of fixing belt 301 by spring 502, so as to be in contact with the inner circumferential surface of fixing belt 301. There are two reasons for disposing oil application roller 501 in this position:

[0047] The first reason is the amount of heat imparted to the oil impregnated in the oil application roller 501. The temperature of the fixing belt 301 required to melt and fix the toner on the recording material at the nip N is 140°C, which requires the temperature of the heating roller 307 to be 200°C. If the oil application roller 501 were to be in contact with the heating roller 307 and apply oil to the heating roller 307, a heat of 200°C would be imparted to the oil. In this case, the amount of heat imparted to the oil would be excessive, causing the oil to become too low in viscosity. As a result, there is a risk of oil leaking from the longitudinal ends of the heating roller 307 or the fixing belt 301.

[0048] The second reason is in terms of the amount of oil applied from the oil application roller 501 to the fixing belt 301. To prevent the above-mentioned oil leakage, it is conceivable to place the oil application roller 501 on the fixing belt 301, which has a relatively low temperature, but the temperature of the fixing belt 301 varies depending on the position in the rotational direction. The temperature of the fixing belt 301 heated by the heating roller 307 gradually decreases as heat is released into the atmosphere as the fixing belt 301 rotates. Furthermore, at the position of the fixing pad 303, heat is absorbed by the toner and the recording material P, so the temperature of the fixing belt 301 drops significantly.

[0049] Here, the higher the temperature of the oil impregnated in the oil application roller 501, the lower the viscosity and the more fluid it becomes, allowing a larger amount of oil to be applied to the fixing belt 301. Therefore, if the oil application roller 501 is brought into contact with the fixing belt 301 at a position where the temperature of the fixing belt 301 is low, the viscosity of the oil increases and the fluidity decreases, resulting in a decrease in the amount of oil applied to the fixing belt 301. If the amount of oil applied to the fixing belt 301 decreases, less oil is supplied to the sliding portion between the fixing belt 301 and the fixing pad 303, and the sliding resistance between the fixing belt 301 and the fixing pad 303 increases. If the sliding resistance increases, there is a risk of image defects occurring when the toner image is fixed or the inner circumferential surface of the fixing belt 301 being worn away, shortening the life of the fixing belt 301.

[0050] Therefore, in this embodiment, the oil application roller 501 is disposed in a position on the fixing belt 301 immediately downstream of the heating roller 307 in the direction of rotation of the fixing belt 301, where the temperature of the fixing belt 301 is high. This improves the fluidity of the oil, allowing the oil application roller 501 to apply a larger amount of oil to the fixing belt 301. Increasing the amount of oil applied to the fixing belt 301 allows a sufficient amount of oil to be supplied to the sliding portion between the fixing belt 301 and the fixing pad 303. Furthermore, the temperature of the fixing belt 301 at the position where the oil application roller 501 contacts is sufficiently lower than the temperature of the fixing belt 301 at the position where the heating roller 307 contacts, thereby preventing excessive heat from being supplied to the oil. As a result, the viscosity of the oil is reduced too much, preventing oil from leaking from the longitudinal ends of the fixing belt 301.

[0051] Fig. 5 is a graph showing the relationship between the oil temperature and oil viscosity used in this embodiment. Generally, as shown in Fig. 5, as the oil temperature increases, the oil viscosity decreases. Because the oil application roller 501 is in contact with the fixing belt 301, it can be considered that the temperature of the oil impregnated in the oil application roller 501 and the temperature of the fixing belt 301 are proportional to each other. In other words, as the temperature of the fixing belt 301 increases, the oil viscosity decreases.

[0052] FIG. 6 is a graph showing the results of an experiment that investigated the relationship between oil viscosity and the oil film thickness on the fixing belt 301 after oil is discharged from the oil application roller 501 onto the fixing belt 301 (film thickness on the belt after discharge). The thicker the oil film thickness on the fixing belt 301, the greater the amount of oil discharged from the oil application roller 501. This experiment was conducted at a viscosity of 1000 mm at room temperature of 25°C. 2 / S, 3000mm 2 / S, 5000mm 2Three types of oil, 1 / S, were used. In the experiment, these three types of oil were discharged from oil application roller 501 onto fixing belt 301, the temperature of heating roller 307 was set to 160°C, and fixing belt 301 was rotated for 60 minutes. Figure 6 shows the oil film thickness on fixing belt 301 at this time. From the relationship between Figures 5 and 6, it can be seen that the higher the temperature of fixing belt 301, the lower the oil viscosity, and the lower the oil viscosity, the thicker the oil film on fixing belt 301. In other words, it can be seen that as the temperature of fixing belt 301 increases, the amount of oil discharged from oil application roller 501 onto fixing belt 301 increases.

[0053] Next, an experiment to examine the temperature difference depending on the position on the fixing belt 301 will be described with reference to FIG. 7. In the experiment, the temperature of the fixing belt 301 was measured at multiple points in the rotation direction of the fixing belt 301 while the fixing device 8 was in operation. FIG. 7 shows the positions where the temperature of the fixing belt 301 was measured in the experiment. The temperature measurements at each position were carried out using a sheet of paper with a density of 81 g / m 2 The experiment was carried out while an image was being formed on the recording material P. At this time, the temperature of the fixing device 8 was controlled by controlling the heating of the halogen heater 306 so that a thermistor (not shown) placed in contact with the heating roller 307 reached a predetermined temperature. The predetermined temperature was a temperature determined in advance, and was set to 200°C in this experiment.

[0054] The temperature of fixing belt 301 was measured at position P1, which is downstream of heating roller 307 and upstream of steering roller 401, position P2, which is downstream of steering roller 401 and upstream of fixing pad 303, and position P3, which is downstream of fixing pad 303 and upstream of heating roller 307, in relation to the rotation direction of fixing belt 301. Table 1 shows the results of temperature measurement at each position. [Table 1]

[0055] As can be seen from Table 1, with respect to the rotation direction of the fixing belt 301, the temperature is highest at 155°C at position P1, immediately downstream of the heating roller 307, but drops to 147°C at position P2 due to heat dissipation into the atmosphere. At position P3, the temperature drops further to 140°C due to heat loss by the toner and recording material P at the nip N and heat dissipation into the atmosphere.

[0056] Next, the reason for placing the oil application roller 501 in the position of this embodiment will be explained in relation to the steering roller 401. Fig. 8 is a graph showing the results of measuring the oil film thickness on the fixing belt 301 (oil film thickness on the belt) at the rear, center, and front sides in the longitudinal direction of the fixing belt 301 when the oil application roller 501 is placed in the position of this embodiment and the number of oscillations per unit time (times / 60 minutes) of the steering roller 401 is varied. Fig. 8 indicates that the more the number of oscillations of the steering roller 401, the more uniform the oil distribution in the longitudinal direction of the fixing belt 301 can be.

[0057] In other words, by placing the oil application roller 501 upstream of the steering roller 401 in the rotation direction of the fixing belt 301, it is possible to supply oil uniformly in the longitudinal direction of the nip portion N formed between the fixing belt 301 and the pressure roller 305.

[0058] Table 2 shows the results of measuring the oil film thickness on the fixing belt 301 when the oil application roller 501 was installed at the P1 position, P2 position, and P3 position shown in FIG. [Table 2]

[0059] As is clear from Table 2, the oil film thickness increases as the temperature of the fixing belt 301 increases. The P1 position, which is the position of this embodiment, results in an approximately 10% increase in the discharge amount compared to the P2 position, and an approximately 27% increase in the discharge amount compared to the P3 position.

[0060] As described above, in this embodiment, the oil application roller 501 is disposed downstream of the heating roller 307 and upstream of the steering roller 401 in relation to the rotational direction of the fixing belt 301, so as to contact the inner circumferential surface of the fixing belt 301. This allows for an appropriate supply of oil between the fixing pad 303 and the fixing belt 301. That is, the oil application roller 501 is not in contact with the heating roller 307, but is in contact with the inner circumferential surface of the fixing belt 301 downstream of the heating roller 307. This prevents excessive heat from being applied to the oil, and reduces the viscosity of the oil. As a result, oil leakage along the longitudinal direction of the fixing belt 301 is prevented, and an appropriate amount of oil can be supplied between the fixing pad 303 and the fixing belt 301 without increasing the size of the oil application roller 501 to increase the amount of oil impregnated into the oil application roller 501.

[0061] Furthermore, by positioning the oil application roller 501 downstream of the heating roller 307 and upstream of the steering roller 401 in the rotation direction of the fixing belt 301, the oil application roller 501 can apply oil to the fixing belt 301 at a position where the temperature of the fixing belt 301 is relatively high. As described above, if the temperature of the oil is too low, the fluidity of the oil decreases, and the amount of oil applied to the fixing belt 301 decreases. For this reason, in this embodiment, by positioning the oil application roller 501 downstream of the heating roller 307 and upstream of the steering roller 401, the decrease in oil temperature is suppressed and the amount of oil applied to the fixing belt 301 is ensured. In this way, if the amount of oil applied can be ensured, an appropriate amount of oil can be supplied between the fixing pad 303 and the fixing belt 301.

[0062] In this embodiment, the oil application roller 501 is supported by a steering support portion 411 that also supports the steering roller 401. This causes the oil application roller 501 to oscillate together with the steering roller 401, allowing the oil application roller 501 to apply oil to the fixing belt 301 uniformly in the longitudinal direction of the fixing belt 301. As a result, oil can be supplied between the fixing pad 303 and the fixing belt 301 that is uniformly applied in the longitudinal direction.

[0063] As described above, in this embodiment, an appropriate amount of oil can be supplied between the fixing pad 303 and the fixing belt 301, and the amount of oil applied can be uniform in the longitudinal direction. This prevents the sliding resistance between the fixing pad 303 and the fixing belt 301 from increasing, and prevents image defects and wear on the inner circumferential surface of the fixing belt 301.

[0064] [Other embodiments] In the above-described embodiment, a configuration using a pressure roller as the driving rotor has been described. However, the driving rotor may be an endless belt that is tensioned by a plurality of tension rollers and driven by one of the tension rollers. Furthermore, in the above-described embodiment, the pressure roller as the driving rotor presses against the belt to form a nip, but the belt may also be pressed against the driving rotor. Furthermore, in the above-described embodiment, a configuration using a fixing pad as the nip-forming member has been described, but the nip-forming member may also be a roller. [Explanation of symbols]

[0065] 8. Fixing device 301 Fixing belt (belt member) 303 Fixing pad (nip forming member, pad member) 305 Pressure roller (rotating body) 306 Halogen heater (heating part) 307 Heating roller (first tension member) 401: Steering roller (second tension member) 401a Rotating shaft 402.... Spring (steering spring) 403 Steering retaining part 405···Swing arm 410···Frame 411 Steering support 501 Oil application roller (lubricant application member, lubricant application roller) 501a...Core part (shaft part) 501b Oil-impregnated layer (lubricant-impregnated layer) 502 Spring (urging part)

Claims

1. A fixing device that heats a toner image carried on a recording material and fixes the toner image to the recording material, an endless belt member; a rotating body that rotates in contact with the outer peripheral surface of the belt member; a nip portion forming member that is disposed inside the belt member so as to sandwich the belt member between the rotating body and the nip portion forming member, and that forms a nip portion between the belt member and the rotating body to sandwich and convey a recording material; a first tension member that contacts an inner peripheral surface of the belt member and tensions the belt member; a second tension member that contacts an inner peripheral surface of the belt member downstream of the first tension member and upstream of the nip portion forming member in relation to a rotation direction of the belt member and tensions the belt member; a heating unit that heats the first tension member to heat the belt member; a lubricant application member that contacts the inner circumferential surface of the belt member downstream of the first tension member and upstream of the second tension member in relation to the rotation direction of the belt member, and applies a lubricant to the inner circumferential surface of the belt member. A fixing device characterized by:

2. The lubricant application member is further provided with a biasing portion that biases the lubricant application member toward the inner circumferential surface of the belt member.

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

3. The lubricant application member is a lubricant application roller having a shaft portion and a lubricant-impregnated layer provided around the shaft portion.

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.

4. The lubricant-impregnated layer is any one of a nonwoven fabric impregnated with a lubricant, a porous material impregnated with a lubricant, and a woven fabric of fibers impregnated with a lubricant.

4. The fixing device according to claim 3.

5. The first tension member is a heating roller having the heating portion therein.

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.

6. The second tension member is a steering roller whose rotation axis is tiltable relative to a direction parallel to the rotation axis of the heating roller, and whose tilting motion controls the position of the belt member relative to the rotation axis of the heating roller.

6. The fixing device according to claim 5,

7. a frame supporting the heating roller and the nip portion forming member; a steering support portion that is rotatably supported by the frame and supports the steering roller, 7. The fixing device according to claim 6, wherein the lubricant application member is supported by the steering support portion.

8. the steering support portion includes a steering holding portion that holds a rotation shaft of the steering roller relative to the frame, and a swing arm that is connected to the rotation shaft of the steering roller and supports the lubricant application member so as to be swingable relative to the rotation shaft of the steering roller, The lubricant application member is provided with a biasing portion disposed between the steering holding portion and the lubricant application member, and biases the lubricant application member toward the inner circumferential surface of the belt member.

8. The fixing device according to claim 7,

9. a steering biasing section that biases the steering roller toward the belt member; 7. The fixing device according to claim 6, wherein the steering roller applies tension to the belt member.

10. 2. The fixing device according to claim 1, wherein the nip portion forming member is a pad member.

Images