Fixing device

Abstract

To provide a configuration that can efficiently reduce a temperature difference with respect to a width direction of a surface of a fixing belt.SOLUTION: Heaters A1, A2, A3 constituting a heating halogen heater heat a heating roller that stretches a fixing belt. A heater B constituting a stay halogen heater heats a fixing pad that forms a nip part where a recording material is sandwiched and conveyed between the fixing belt and a pressure roller. When a length of an area where the heaters A generate heat is defined as a first heat generation width L1, and a length of an area where the heater B generates heat as a second heat generation width L2, with respect to a width direction of the recording material intersecting a conveyance direction of the recording material, the second heat generation width L2 is longer than the first heat generation width L1.SELECTED DRAWING: Figure 3

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. A fixing device that includes an endless belt member, a heater that heats the belt member, and a rotating body that forms a nip between the belt member and the rotating body, and that heats and conveys the toner image on the recording material at the nip has been known in the art (Patent Document 1).

[0003] Also, in order to reduce the temperature difference in the width direction of the surface of the belt member, a configuration has been proposed that includes a heat diffusion roller that comes into contact with the belt member to diffuse the temperature of the surface of the belt member (Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-79036 [Patent Document 2] Japanese Patent Application Laid-Open No. 2011-158662 Summary of the Invention [Problem to be solved by the invention]

[0005] As described in Patent Document 2, in the case of a configuration in which a thermal diffusion roller is in contact with a belt member, the heat capacity of the belt member increases by the amount of the thermal diffusion roller, which results in wasted power consumption by the heater, resulting in inefficiency.

[0006] An object of the present invention is to provide a configuration that can efficiently reduce the temperature difference in the width direction of the surface of a belt member. [Means for solving the problem]

[0007] 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, 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 face the rotating body via the belt member and forms a nip portion between the belt member and the rotating body to sandwich and transport the recording material; a tension roller that contacts the inner surface of the belt member and tensions the belt member; a first heater that heats the tension roller; and a second heater that heats the nip portion forming member, wherein, in the width direction of the recording material that intersects the transport direction of the recording material, when the length of the area heated by the first heater is defined as a first heating width and the length of the area heated by the second heater is defined as a second heating width, the second heating width is longer than the first heating width. [Effects of the Invention]

[0008] According to the present invention, the temperature difference in the width direction of the surface of the belt member can be efficiently reduced. [Brief explanation of the drawings]

[0009] [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. 2A is a diagram showing the light emission characteristics of a heating halogen heater according to the embodiment, and FIG. 2B is a diagram showing the light emission characteristics of a stay halogen heater according to the embodiment. [Figure 4] (a) A diagram showing the temperature distribution of the fixing belt when the heating halogen heater and the stay halogen heater have the same heating width, and (b) A diagram showing the temperature distribution of the fixing belt when the heating width of the stay halogen heater is longer than that of the heating halogen heater. [Figure 5] 10 is a schematic diagram of a cross-sectional configuration of a fixing device in which the heat generating width of a stay halogen heater is longer than the length of a fixing pad in the width direction. [Figure 6] FIG. 10 is a diagram showing another example of the light emission characteristics of the halogen heater according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] The embodiment will be described with reference to Figures 1 to 6. First, the schematic configuration of an image forming apparatus according to the present embodiment will be described with reference to Figure 1.

[0011] [Image forming device] 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.

[0012] 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.

[0013] 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.

[0014] 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.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] [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.

[0021] 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.

[0022] The heating unit 300 includes the above-mentioned fixing belt 301, a fixing pad 303 serving as a nip portion forming member and a pad member, a stay 302 serving as a support member and a stay member, a heating roller 307 serving as a tension roller, and a steering roller 308. 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.

[0023] 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 300 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 a fixing pad 303, a heating roller 307, and a steering roller 308.

[0024] The fixing pad 303 is disposed non-rotatably inside the fixing belt 301, facing the pressure roller 305 with the fixing belt 301 sandwiched therebetween. The fixing pad 303 forms a nip 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 generally plate-shaped member that is long along 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 N. The fixing pad 303 is made of LCP (liquid crystal polymer) resin. That is, in this embodiment, the fixing pad 303 is made of resin. Note that the material of the fixing pad 303 is not limited to LCP, and other resins or metals may also be used.

[0025] The fixing pad 303 is supported by a stay 302, which serves as a support member and is 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 a long rigidity along the longitudinal direction of the fixing belt 301, and contacts the fixing pad 303 to back it up. That is, when the fixing pad 303 is pressed by the pressure roller 305, the stay 302 provides strength to the fixing pad 303, thereby ensuring the pressure force at the nip N. The stay 302 is made of stainless steel and has a thickness of 3 mm. That is, in this embodiment, the stay 302 is made of metal. However, other metals such as iron or aluminum, or resin, may also be used.

[0026] Between the fixing pad 303 and the fixing belt 301, a sliding member (not shown), such as a lubricating sheet whose surface is coated with PTFE (polytetrafluoroethylene), and silicone oil (hereinafter referred to as oil) as a lubricant, are interposed, allowing the fixing belt 301 to slide smoothly against the fixing pad 303. The sliding member is formed, for example, by coating the surface of a 70 μm-thick polyimide substrate with PTFE. Note that the sliding member is arranged to improve the sliding properties between the fixing pad 303 and the fixing belt 301, and therefore, it is possible to substitute a coating that improves sliding properties for the surface layer of the fixing pad 303 instead of the sliding member.

[0027] Heating roller 307 is disposed inside fixing belt 301, contacts the inner circumferential surface of fixing belt 301, and stretches fixing belt 301 together with fixing pad 303 and steering roller 308. Heating roller 307 is formed into a cylindrical shape from a metal such as aluminum or stainless steel, and is provided therein with a halogen heater 306 as a heating unit for heating fixing belt 301. That is, inside hollow cylindrical heating roller 307, halogen heater 306 is disposed along the width direction. Heating roller 307 is heated to a predetermined temperature by halogen heater 306.

[0028] In this embodiment, the heating roller 307 is formed, for example, from a 2 mm thick aluminum alloy pipe. Considering the temperature rise at the end of the recording material as it passes through the nip, the material for the heating roller 307 is preferably one with high thermal conductivity, and other metals such as stainless steel alloys may be used in addition to aluminum alloys. The halogen heater 306 may be one or more. The heating unit for heating 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. In this embodiment, a stay halogen heater 309 is disposed inside the stay 302 as a second heater, as will be described in detail later.

[0029] The steering roller 308 is disposed inside the fixing belt 301, contacts the inner circumferential surface of 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. The steering roller 308 is disposed so as to be tiltable in a direction parallel to the rotation axis direction (width direction, longitudinal direction) of the heating roller 307, and controls the position (offset position) of the fixing belt 301 with respect to this rotation axis direction by tilting. That is, the steering roller 308 has a rotation center at the center or one end of the rotation axis direction (longitudinal direction) of the steering roller 308, and tilts with respect 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, moving the fixing belt 301 in the longitudinal direction.

[0030] 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, such shifting is controlled by steering roller 308. Note that steering roller 308 may be oscillated by a drive source such as a motor, or may be configured to oscillate by automatic centering.

[0031] In this embodiment, the steering roller 308 is biased by a spring supported by the frame of the heating unit 300, and also serves as a tension roller that applies a predetermined tension to the fixing belt 301. The steering roller 308 is formed into a cylindrical shape from a metal such as aluminum or stainless steel. In this embodiment, the steering roller 308 is formed from a stainless steel pipe with an outer diameter of 20 mm. The steering roller 308 may be provided with a rubber material or the like on its surface to increase its grip on the fixing belt 301.

[0032] 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 a shaft (core metal), 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 is connected to a motor M1, which serves as a pressure roller drive source, via the gear, and is driven to rotate.

[0033] 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.

[0034] Further, downstream of the nip N in the conveyance direction of the recording material P, a discharge unit 350 is disposed for discharging the recording material P that has passed through the nip N to the outside of the fixing device 8. The discharge unit 350 includes an air nozzle 401, a pair of discharge rollers 400a, and a lower separation guide 400b. The air nozzle 401 blows out air (compressed air) to separate the recording material P from the fixing belt 301. Specifically, the air nozzle 401 is disposed downstream of the nip N in the conveyance direction of the recording material (hereinafter sometimes simply referred to as the "conveyance direction") and vertically above the nip N, and blows out air upstream in the conveyance direction and vertically downward. The air is then blown toward the leading edge of the recording material P after it has passed through the nip N, thereby separating the recording material P from the fixing belt 301.

[0035] The lower separation guide 400b 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 400b separates the recording material P from the pressure roller 305. The lower separation guide 400b also supports the underside of the recording material P discharged from the nip portion N and guides the recording material P to the discharge roller 40a. The discharge roller pair 400a discharges the recording material P discharged from the nip portion N to the outside of the fixing device 8. In this embodiment, the discharge roller pair 400a is disposed approximately 40 mm downstream of the nip portion N in the conveyance direction.

[0036] Furthermore, upstream of the nip portion N of the fixing device 8 in the conveying direction, there are arranged a guide portion 94 for guiding the recording material P to the nip portion N, and a detection sensor 95 for detecting the recording material P immediately before the nip portion N. The control portion 30 detects the timing at which the recording material P enters the nip portion N using the detection sensor 95.

[0037] [Halogen heater] As described above, the halogen heater 306 is disposed inside the heating roller 307. The halogen heater 306 heats the heating roller 307. The halogen heater 306 heats the heating roller 307, thereby heating the fixing belt 301 stretched by the heating roller 307. That is, the halogen heater 306 heats the fixing belt 301 via the heating roller 307. Although not disposed in this embodiment, a halogen heater may be disposed inside the steering roller 308.

[0038] A thermistor Th1 serving as a first temperature detector for detecting the surface temperature of the heating roller 307 is in contact with the outer peripheral surface of the heating roller 307. Based on the temperature detected by thermistor Th1, the control unit 30 controls (temperature control) the power supply to the halogen heater 306 so that the first temperature is reached. Thermistor Th1 is disposed at the center position in the width direction of the recording material P, which intersects with the conveyance direction of the recording material P. In addition, in order to control the temperature distribution in the width direction of the heating roller 307, thermistor Th2 is disposed at a position shifted 150 mm in the width direction from the center position in the width direction. The position in the width direction is not limited to 150 mm and may be changed depending on the size of the corresponding recording material, or multiple thermistors may be used.

[0039] The number of heaters in the halogen heater 306 is determined based on the amount of power required, etc. In this embodiment, three halogen heaters capable of inputting 500 W of power are used as the halogen heater 306. These halogen heaters are designated as heaters A1, A2, and A3, respectively. That is, multiple heaters A1, A2, and A3 are arranged inside the heating roller 307, and the halogen heater 306 is composed of these heaters A1, A2, and A3.

[0040] As shown in FIG. 3A, the heaters A1, A2, and A3 have different widthwise light-emission distribution characteristics, and the temperature distribution in the widthwise direction of the heating roller 307 is controlled by controlling the turn-on ratios of these heaters. That is, the heaters A1, A2, and A3 have different heat-generating widths, which are the lengths of the heater-generated areas in the widthwise direction. In this embodiment, the heaters A1, A2, and A3 have the same widthwise length (340 mm in the illustrated example). The heater A1 has a uniform light-emission distribution characteristic across the entire widthwise direction. The heater A2 emits more light at the widthwise ends than at the widthwise center. The heater A3 emits more light at the widthwise center than at the widthwise ends. For example, if the temperature of the widthwise ends of the fixing belt 301 rises excessively (i.e., if an excessive temperature rise occurs at the ends) due to, for example, passing a recording material through the nip, the turn-on ratio of the heater A2 is reduced and the turn-on ratio of the heater A3 is increased.

[0041] [Stay halogen heater] In this embodiment, in addition to the above-described heating halogen heater 306, a stay halogen heater 309 is disposed inside the stay 302. A space is formed inside the stay 302 along the width direction, and the stay halogen heater 309 is disposed in the space inside the stay 302 along the width direction. The stay halogen heater 309 heats the fixing pad 303. The stay halogen heater 309 heats the fixing pad 303, thereby heating the fixing belt 301 stretched by the fixing pad 303. In other words, the stay halogen heater 309 heats the fixing belt 301 via the fixing pad 303. In this way, in this embodiment, the fixing belt 301 is heated by the heating halogen heater 306 and the stay halogen heater 309.

[0042] A thermistor Th3 serving as a second temperature detector that detects the surface temperature of the stay 302 is in contact with the outer surface of the stay 302. Based on the temperature detected by thermistor Th3, the control unit 30 controls the power supply to the stay halogen heater 309 (temperature control) so that the second temperature is reached. Thermistor Th3 is disposed at the center position in the width direction of the recording material P. Although not disposed in this embodiment, additional thermistors may be disposed at end positions in the width direction in order to control the temperature distribution in the width direction of the stay 302.

[0043] The number of stay halogen heaters 309 is determined according to the amount of power required, etc. In this embodiment, one halogen heater that inputs 500 W of power is used as stay halogen heater 309. This halogen heater is referred to as heater B. As shown in FIG. 3(b), heater B has a uniform light emission distribution characteristic across the entire width direction. However, the light emission distribution characteristic of heater B is not limited to this. For example, the light emission amount at the ends in the width direction may be greater or smaller than the light emission amount in the center in the width direction, in accordance with the light emission distribution characteristic of heat halogen heater 306.

[0044] [Heater heating width] Here, the length of the region where heaters A1, A2, and A3 constituting the heating halogen heater 306 generate heat is referred to as the first heating width, and the length of the region where heater B constituting the stay halogen heater 309 generates heat is referred to as the second heating width. Heaters A1, A2, and A3 have different light emission distributions in the width direction, but have the same heating width. Stay halogen heater 309 is composed of a single heater B. Therefore, hereinafter, heaters A1, A2, and A3 may be simply referred to as heating halogen heater 306, and heater B may be simply referred to as stay halogen heater 309. In this embodiment, heaters A1, A2, and A3 all correspond to the first heater, but the following description will mainly focus on heater A1 as the first heater. In this embodiment, heater B corresponds to the second heater.

[0045] The heating width of the halogen heater is determined by the width direction length (filament length) of the filament of the halogen heater. The filament lengths (first heating width and second heating width) of the heating halogen heater 306 and the stay halogen heater 309 must be determined according to the relationship between the amount of heat transfer in the width direction (the product of thermal conductivity and cross-sectional area) and the amount of heat transfer to the fixing belt 301.

[0046] FIG. 4(a) shows the temperature distribution in the width direction of the fixing belt 301 when the hot halogen heater 306 and the stay-halogen heater 309, both of which have a heating width (filament length) of 340 mm and heaters A1 and B, each of which has a uniform light emission distribution characteristic in the width direction, are used. The solid line in FIG. 4(a) shows the temperature distribution of the fixing belt 301 when only heater A1 is turned on, and the dashed line shows the temperature distribution of the fixing belt 301 when only heater B is turned on. The range within the solid line frame in the figure is the allowable temperature range for fixing a toner image on a recording material. Looking at the temperature distribution in FIG. 4(a), it is clear that the temperature at the end of the fixing belt 301 in the width direction drops significantly when only heater B (i.e., stay-halogen heater 309) is turned on.

[0047] This is because the stay 302 is heated by the stay halogen heater 309, but the heat is dissipated to the width direction end of the stay 302. For example, if the heat conductivity of the heating roller 307 is 220 W / m·K and the cross-sectional area is 207 mm 2 The thermal conductivity of stay 302 is 50 W / m K, and the cross-sectional area is 264 mm 2 Since the amount of heat transferred in the width direction is greater for the heating roller 307 than for the stay 302, the temperature drop at the end of the heating roller 307 in the width direction should be greater than that of the stay 302.

[0048] However, because the stay 302 has the fixing pad 303 between it and the fixing belt 301, heat first diffuses toward the widthwise edges of the stay 302 and then transfers to the fixing belt 301 via the fixing pad 303. Because the temperature at the edges of the stay 302 is lowered due to heat dissipation toward the edges, the heat is transferred to the fixing belt 301 in a state where the temperature at the edges of the stay 302 is lower. Therefore, the temperature distribution of the fixing belt 301 when only the stay halogen heater 309 is turned on is more likely to be lower than the temperature distribution of the fixing belt 301 when only the heating halogen heater 306 is turned on. As a result, the temperature distribution of the fixing belt 301 when only the stay halogen heater 309 is turned on falls below the frame (allowable temperature range) shown in the figure within the width range of the maximum-size recording material (maximum recording material width). In this case, it may be difficult to ensure sufficient fixation of the toner image on the recording material.

[0049] Therefore, it is necessary to increase the heat generation width of stay-halogen heater 309 to suppress a temperature drop at the widthwise ends of fixing belt 301. For this reason, in this embodiment, the second heat generation width of stay-halogen heater 309 is made longer than the first heat generation width of hot-halogen heater 306. That is, the second heat generation width L2 (350 mm in this embodiment) of heater B as the second heater is made longer than the first heat generation width L1 (340 mm in this embodiment) of heater A as the first heater (see FIGS. 3(a) and 3(b)).

[0050] Figure 4(b) shows the temperature distribution of fixing belt 301 when the heat generation width of stay-halogen heater 309 is changed. The dashed line in Figure 4(b) shows the temperature distribution of fixing belt 301 when only heater B1 with a heat generation width of 340 mm is turned on, the dashed line shows the temperature distribution of fixing belt 301 when only heater B2 with a heat generation width of 360 mm is turned on, and the solid line shows the temperature distribution of fixing belt 301 when only heater B3 with a heat generation width of 400 mm is turned on.

[0051] In this embodiment, as shown in FIG. 5 , which will be described later, the width of the fixing pad 303 is 380 mm, the width of the stay 302 is 440 mm, and the width of the pressure roller 305 is 360 mm. A nip portion N is formed between the pressure roller 305 and the fixing belt 301, and the width of the nip portion N is also 360 mm. Therefore, in the fixing device 8 of this embodiment, the width of the fixing pad 303 is longer than the width of the nip portion N, and the width of the stay 302 is longer than the width of the fixing pad 303.

[0052] 4(b) shows that by widening the heat generation width of stay halogen heater 309 from 340 mm (dashed line) to 360 mm (chain line), the temperature drop at the widthwise ends of fixing belt 301 is alleviated, and the temperature is within the frame (tolerable temperature range) shown in the figure within the range of the maximum recording material width. However, if the heat generation width of stay halogen heater 309 is widened too much, such as to 400 mm (solid line), the heater will heat up even areas where there is nothing facing stay 302.

[0053] 5 is a schematic diagram showing the cross sections of stay 302, stay halogen heater 309, fixing pad 303, and pressure roller 305 when stay halogen heater 309 has a heat generation width of 400 mm, which exceeds 380 mm, the length L3 of fixing pad 303. As can be seen from FIG. 5, when the heat generation width exceeds fixing pad 303, there is no opposing member between stay 302 and fixing belt 301, and therefore an area is generated at the end of fixing belt 301 in the width direction that is directly heated by stay halogen heater 309. As a result, the temperature at the end of fixing belt 301 in the width direction reaches the overheating area (FIG. 4(b)).

[0054] Therefore, if the heat generation width of stay halogen heater 309 is made too long, it can lead to durability issues due to excessive temperature rise at the widthwise ends of fixing belt 301 and increased power consumption due to unnecessary heat generation. Therefore, the heat generation width of stay halogen heater 309 needs to be contained within the area where stay 302 and the opposing member on the fixing belt 301 side, i.e., fixing pad 303, are present. For this reason, in this embodiment, the second heat generation width of stay halogen heater 309 (heater B) is made shorter than the widthwise length of fixing pad 303. Furthermore, it is preferable that the second heat generation width of stay halogen heater 309 (heater B) be contained within the widthwise range of nip portion N. That is, the second heat generation width is preferably equal to or shorter than the widthwise length of nip portion N, and more preferably shorter than the widthwise length of nip portion N.

[0055] From the above, in this embodiment, when the first heat generation width of heater A1 of heating halogen heater 306 is L1, the second heat generation width of heater B of stay halogen heater 309 is L2, and the width direction length of fixing pad 303 is L3, the relationship of the following formula (1) is satisfied. L1 <L2<L3 ···(1) Furthermore, when the length of the nip portion N in the width direction is L4, it is preferable that the relationship of the following formula (2) be satisfied. L1 <L2<L4<L3 ···(2)

[0056] In this embodiment, the second heat generation width of heater B of stay-halogen heater 309 is longer than the first heat generation width of heater A1 of hot-halogen heater 306. This prevents temperature drops at the widthwise ends of fixing belt 301 without increasing the thermal capacity of fixing belt 301, thereby reducing the temperature difference across the width of fixing belt 301. That is, as described in Patent Document 2, a configuration in which a thermal diffusion roller is in contact with the belt can reduce the temperature difference across the width of the belt, but the thermal capacity of the belt increases due to the thermal diffusion roller. This increased thermal capacity results in wasted power consumption by the heater, resulting in inefficiency. In contrast, in this embodiment, the second heat generation width of heater B of stay-halogen heater 309 is simply longer than the first heat generation width of heater A1 of hot-halogen heater 306; a component such as a thermal diffusion roller is not in contact with fixing belt 301. This effectively reduces the temperature difference across the width of fixing belt 301.

[0057] Furthermore, in this embodiment, the second heat generation width of heater B constituting stay-halogen heater 309 is shorter than the widthwise length of fixing pad 303. This prevents a decrease in durability of fixing belt 301 due to excessive temperature rise at the widthwise ends of fixing belt 301, and also prevents an increase in power consumption due to unnecessary heat generation. Therefore, in this embodiment, power consumption can be reduced while preventing a decrease in durability of fixing belt 301, and temperature differences in the widthwise direction on the surface of fixing belt 301 can be reduced. Furthermore, by reducing temperature differences in the widthwise direction on the surface of fixing belt 301, the image quality of the toner image fixed to the recording material by fixing device 8 is made uniform in the widthwise direction, thereby preventing a decrease in image quality.

[0058] As shown in FIG. 3A, the halogen heater 306 includes multiple heaters A1, A2, and A3 with different light emission distributions. However, the halogen heater 306 may also include heater A2', which emits 0% light at the center of the width, or heater A3', which emits 0% light at the end of the width, as shown in FIG. 6. In such cases, heaters A1 and A2' are considered to contribute to the maximum heat generation width in the width direction. Therefore, the above equations (1) and (2) are compared using the heater with the maximum heat generation width of the halogen heater 306. In other words, in the example of FIG. 6, the first heater is heater A1, which has the longest heat generation width among the multiple heaters A1, A2', and A3', and the heat generation width of heater A1, 340 mm, is the first heat generation width. The same applies when the halogen heater 309 includes multiple heaters.

[0059] <Other embodiments> In the above-described embodiment, a configuration has been described in which a halogen heater is provided on the heating roller as a first heater for heating the fixing belt. However, the first heater may not be provided on the heating roller, but may be provided on another tension roller such as a steering roller. Also, in the above-described embodiment, a fixing device has been described in which the fixing belt is stretched by a fixing pad, a heating roller, and a steering roller. However, fixing devices to which the present invention can be applied are not limited to this, and may have a configuration in which the fixing belt is stretched by only one tension roller and a fixing pad, for example. The key is to have at least one tension roller that stretches the fixing belt together with the fixing pad.

[0060] In the above-described embodiments, a pressure roller is used as the rotating body. However, the rotating body may be an endless belt that is tensioned by a plurality of tension rollers and driven by one of the tension rollers. In the above-described embodiments, the pressure roller as the rotating body presses against the belt to form the nip, but the belt may also be pressed against the rotating body. [Explanation of symbols]

[0061] 8. Fixing device 301 Fixing belt (belt member) 302... Stay (support member, stay member) 303 Fixing pad (nip forming member, pad member) 305 Pressure roller (rotating body) 306 Halogen heater 307 Heating roller (tension roller) 308···Steering roller 309···Stay halogen heater A1 heater (first heater) B···Heater (second heater)

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 disposed inside the belt member so as to face the rotating body with the belt member interposed therebetween, and forming a nip portion between the belt member and the rotating body for nipping and conveying a recording material; a tension roller that contacts the inner peripheral surface of the belt member and tensions the belt member; a first heater for heating the tension roller; a second heater that heats the nip portion forming member, A fixing device characterized in that, in a width direction of a recording material that intersects with the conveying direction of the recording material, when the length of the area where the first heater generates heat is defined as a first heat generation width and the length of the area where the second heater generates heat is defined as a second heat generation width, the second heat generation width is longer than the first heat generation width.

2. a support member disposed on the opposite side of the rotating body from the nip portion forming member, supporting the nip portion forming member, and having a space formed therein along the width direction; 2. The fixing device according to claim 1, wherein the second heater is disposed inside the support member.

3. 3. The fixing device according to claim 2, wherein the second heat generation width is shorter than the length of the nip portion forming member in the width direction.

4. the nip portion forming member is a pad member made of resin, 3. The fixing device according to claim 2, wherein the support member is a metal stay member.

5. the first heater and the second heater are halogen heaters each having a filament, 2. The fixing device according to claim 1, wherein the first heat generation width and the second heat generation width are lengths of the filament in the width direction.

6. 2. The fixing device according to claim 1, wherein the first heater is disposed inside the tension roller.

7. A plurality of heaters including the first heater are disposed inside the tension roller, The plurality of heaters have different heating widths, which are lengths of regions in the width direction where the heaters generate heat, 7. The fixing device according to claim 6, wherein the first heater is a heater having the longest heat generating width among the plurality of heaters.

8. 2. The fixing device according to claim 1, further comprising a steering roller that contacts the inner peripheral surface of the belt member, has a rotation axis that is tiltable relative to a direction parallel to the rotation axis of the tension roller, and tilts to control the position of the belt member relative to the rotation axis of the tension roller.

Images