JP2015041092A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent deviation of a fixing belt to prevent damage to the ends of the fixing belt.SOLUTION: A fixing device 20 includes a rotatable, endless fixing belt 21, a pressure roller 22 that contacts the outer peripheral surface of the fixing belt 21, a nip forming member 24 that is provided inside the fixing belt 21 and contacts the pressure roller 22 with the fixing belt 21 therebetween to form a nip part between the fixing belt 21 and pressure roller 22, and holding flanges 31 and 32 that hold the end sides of the fixing belt 21 so that the fixing belt 21 can be rotated. The fixing device 20 further has strip areas 21a and 21b having the coefficient of friction higher than that of another area 21c on at least a part of a surface layer of the fixing belt 21, which is in contact with the pressure roller 22 in the longitudinal direction; in a strip area contact range 22e of the pressure roller 22 that can be in contact with the strip areas 21a and 21b, the outer diameter of the pressure roller 22 is larger at end sides r2 than at the center sides r1 in the longitudinal direction.

Description

  The present invention relates to a fixing device and an image forming apparatus. More specifically, the present invention relates to a fixing device and an image forming apparatus that are mounted on an electrophotographic image forming apparatus such as a copying machine, a facsimile machine, a printer, or a complex machine thereof.

  Various image forming apparatuses using an electrophotographic system have been devised as image forming apparatuses such as copying machines, facsimiles, and printers, and are well-known techniques. In the image forming process, an electrostatic latent image is formed on the surface of the photosensitive drum as an image carrier, and the electrostatic latent image on the photosensitive drum is developed with a toner as a developer to be visualized and developed. The image is transferred to a recording medium (also referred to as paper, recording paper, or recording material) by a transfer device to carry the image, and the unfixed toner image on the recording medium is fixed by a fixing device using pressure, heat, or the like. It is established.

  Various types of fixing devices have been proposed. The fixing device includes a fixing roller maintained at a predetermined temperature, and a pressure roller as a pressure member in pressure contact with the fixing roller. The pressure roller and the fixing roller There is known a roller fixing method in which a recording medium carrying an unfixed toner image is heated while being nipped and conveyed by a nip portion (fixing nip portion) formed by pressure contact with the toner.

  A nip formed by a pressure contact between the pressure roller and the fixing belt is provided with a fixing roller disposed opposite the pressure roller and an endless fixing belt stretched between the fixing roller and the heating roller. A belt fixing method is known in which the heat of a heating roller is applied to a transfer material through a fixing belt to press an unfixed toner image onto a recording medium and fix it (for example, Patent Document 1). A contact heating type fixing method such as an electromagnetic induction heating method is also known.

  In recent years, belt-fixing type fixing devices have further increased warm-up time (referred to as the time required from a normal temperature state such as when the power is turned on to a predetermined temperature at which printing is possible) and first print time (after receiving a print request, preparation for printing) It is desired to shorten the time until the paper discharge is completed after performing the printing operation (Problem (1)).

  In addition, as the speed of image forming apparatuses increases, the number of sheets to be passed per unit time increases and the required amount of heat increases, so that there is a problem that the amount of heat is insufficient particularly at the beginning of continuous printing (temperature drop). (Problem (2)).

  In order to solve the above problem (1), for example, a heating device (fixing device) of a film heating method as in Patent Document 2 has been proposed. With this film heating method, it is possible to reduce the heat capacity and reduce the size compared to the belt fixing type fixing device, but only the nip part is locally heated, so other parts are not heated, and the nip part The film is in the coldest state on the inlet side of the recording medium, and there is a problem that fixing defects are likely to occur. In particular, in a high-speed machine, there is a problem that fixing failure is more likely to occur because the film rotates quickly and the heat radiation of the film at the portion other than the nip portion increases (problem (3)).

  In order to solve the problems (1) to (3) as described above, Patent Document 3 discloses that in the configuration using an endless belt, the entire belt can be heated, and the first print time from the heating standby time is set. There has been proposed a fixing device that can be shortened and that can solve the shortage of heat at the time of high-speed rotation so that good fixability can be obtained even when mounted on a high-production image forming apparatus. .

  FIG. 6 is a cross-sectional view illustrating a schematic configuration of the fixing device disclosed in Patent Document 3. In this fixing device, a pipe-shaped metal heat conductor 92 is fixed inside the endless belt 91 so that the movement of the endless belt 91 can be guided, and the heat source 93 in the metal heat conductor 92 is used to heat the metal heat conductor. The endless belt 91 is heated via 92. Furthermore, a pressure roller 94 that forms a nip portion N in contact with the metal heat conductor 92 via the endless belt 91 is provided, and the endless belt 91 is moved in the circumferential direction so as to rotate as the pressure roller 94 rotates. Let With this configuration, it is possible to warm the entire endless belt constituting the fixing device, to shorten the first print time from the heating standby time, and to solve the shortage of heat during high-speed rotation. Yes.

  In addition, it is necessary to further improve the thermal efficiency in order to further improve energy saving and first print time. As a fixing device that further improves the thermal efficiency, for example, Patent Document 4 discloses that the endless belt is not indirectly heated via a metal heat conductor, but not via a metal heat conductor or the like. In addition, a fixing device that directly heats an endless belt has been proposed.

  FIG. 7 is a cross-sectional view illustrating a schematic configuration of the fixing device disclosed in Patent Document 4. In this fixing device, the pipe-shaped metal heat conductor is removed from the inside of the endless belt 91, and instead, a plate-shaped nip forming member 95 is provided at a position facing the pressure roller 94. In the case of this configuration, the endless belt 91 can be directly heated by the heat source 93 at a place other than the place where the nip forming member 95 is disposed, so that heat transfer efficiency is improved and power consumption is reduced. This makes it possible to shorten the first print time from the heating standby time.

  In the fixing device using the endless belt as described above, generally, a regulating member is provided for regulating the movement of the endless belt in the axial direction. For example, in the fixing device described in Patent Document 5, as shown in FIG. 8, both ends of the endless belt 91 are rotatably held and a fixed flange for restricting the endless belt 91 from moving in the axial direction. 96 is provided. Further, in this fixing device, a driven ring 97 as a protective member for protecting the end of the endless belt 91 is provided between the fixing flange 96 and the end of the endless belt 91. When the endless belt 91 receives an axial force and moves toward one side, the end of the endless belt 91 abuts against the driven ring 97, so that the driven ring 97 rotates together with the endless belt 91. This prevents the end of the endless belt 91 from rubbing.

  By using a thin endless belt (fixing belt) as a fixing member in the fixing device and rotating along with the rotation of the pressure roller that is a counter-rotating body, as described above, energy saving and first printing are achieved. Although the time can be improved, on the other hand, the strength of the endless belt decreases, the endless belt moves in the axial direction, hits the holding member at the end, and the load applied to the end causes its end There exists a subject that a part will be damaged.

  Factors that cause the endless belt to approach the end may be a deviation in the outer diameter of the opposing rotating body that drives the endless belt, or the parallelism between the endless belt and the opposing rotating body. It is difficult to do.

  As described above, in Patent Document 5, a driven ring is provided as a protective member for protecting the end of the endless belt in order to prevent the endless belt from moving in the axial direction and being damaged. In the configuration in which the protective member is provided as in Document 5, it is considered that the protective member is worn when the endless belt is strongly displaced due to variations in parts or the like. Further, there are problems such as separately providing a protective member, increasing the number of parts and increasing the cost.

  Therefore, the present invention suppresses the endless belt from moving in the axial direction and prevents the endless belt from being damaged in the fixing device configured to rotate the endless belt following the rotation of the counter rotating body. An object of the present invention is to provide a fixing device that can be used.

  In order to achieve such an object, a fixing device according to the present invention includes a rotatable endless fixing belt, an opposing rotating body that contacts an outer peripheral surface of the fixing belt, and the fixing belt provided inside the fixing belt. A nip forming member that forms a nip portion between the fixing belt and the counter rotating body by contacting the counter rotating body via the fixing belt, and the fixing belt rotatably holds the end side of the fixing belt. And a holding member that has a belt-like region whose friction coefficient is higher than other regions on at least a part of the surface layer of the region in contact with the counter rotating body in the longitudinal direction of the fixing belt. In the longitudinal width of the counter-rotating body that can come into contact with the belt-like region, the outer diameter of the counter-rotating body is larger on the end side than on the center side in the longitudinal direction.

  ADVANTAGE OF THE INVENTION According to this invention, it can suppress that an endless belt moves toward an axial direction, and can prevent the endless belt edge part from being damaged.

1 is a cross-sectional view illustrating an embodiment of an image forming apparatus according to the present invention. 1 is a side cross-sectional view illustrating a configuration of an embodiment of a fixing device according to the present invention. FIG. 3 is a schematic configuration diagram illustrating a configuration of a main part of the fixing device. FIG. 4 is an explanatory diagram illustrating a state in which the fixing belt is deviated on the left side in the drawing. FIG. 6 is a side cross-sectional view illustrating a configuration of another embodiment of the fixing device. It is a schematic block diagram of the fixing apparatus using the conventional endless belt. It is a schematic block diagram of the conventional fixing device of the direct heating system. It is a figure which shows the holding structure of the conventional belt edge part.

  Hereinafter, the configuration according to the present invention will be described in detail based on the embodiment shown in FIGS.

(Image forming device)
[Constitution]
FIG. 1 is a schematic configuration diagram illustrating the overall configuration of a tandem type color copier that is an embodiment of an image forming apparatus according to the present invention. The outline and operation of the internal configuration of the image forming apparatus will be described with reference to FIG.

  As shown in FIG. 1, an image forming apparatus 1 in the present embodiment is configured by a tandem color printer. The image forming apparatus 1 has a bottle accommodating portion 101 above the main body, and four toner bottles 102Y, 102M, 102C, and 102K are detachably installed in the bottle accommodating portion 101. The toner bottles 102Y, 102M, 102C, and 102K contain toners of corresponding colors (yellow, magenta, cyan, and black).

  An intermediate transfer unit 85 is disposed below the bottle storage unit 101. The intermediate transfer unit 85 includes an intermediate transfer belt 78, four primary transfer bias rollers 79Y, 79M, 79C, and 79K, a secondary transfer backup roller 82, a cleaning backup roller 83, a tension roller 84, and an intermediate transfer cleaning unit 80. ing. The intermediate transfer unit 85 has image forming units 4Y, 4M, 4C, and 4K that face the intermediate transfer belt 78 and correspond to the respective colors (yellow, magenta, cyan, and black).

  Photosensitive drums 5Y, 5M, 5C, and 5K are disposed in the image forming units 4Y, 4M, 4C, and 4K, respectively. Further, around each of the photosensitive drums 5Y, 5M, 5C, and 5K, a charging unit 75, a developing unit 76, a cleaning unit 77, and a charge eliminating unit (not shown) are disposed.

  The photosensitive drums 5Y, 5M, 5C, and 5K are formed in a cylindrical shape and are driven to rotate by a driving source (not shown). The photosensitive drums 5Y, 5M, 5C, and 5K are provided with photosensitive layers on the outer peripheral surface portions, and the light beams indicated by broken lines emitted from the exposure apparatus are spotted on the outer peripheral surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K. By irradiation, electrostatic latent images corresponding to image information read by the document reading unit or image information acquired from the terminal via the network are written on the outer peripheral surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K. .

  The charging unit 75 is configured to uniformly charge the outer peripheral surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K, and is a contact type that charges the photosensitive drums 5Y, 5M, 5C, and 5K by contact. The thing is adopted.

  The developing unit 76 supplies toner to the photosensitive drums 5Y, 5M, 5C, and 5K, and the supplied toner adheres to the electrostatic latent image written on the outer peripheral surface of the photosensitive drums 5Y, 5M, 5C, and 5K. As a result, the electrostatic latent images on the photosensitive drums 5Y, 5M, 5C, and 5K are visualized as toner images, and the toner is not brought into contact with the photosensitive drums 5Y, 5M, 5C, and 5K. A non-contact type is used.

  The cleaning unit 77 is configured to remove residual toner adhering to the outer peripheral surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K, and a brush is applied to the outer peripheral surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K. A brush contact method is used.

  The intermediate transfer belt 78 is stretched and supported by the secondary transfer backup roller 82, the cleaning backup roller 83, and the tension roller 84, and is endlessly moved in the direction of the arrow shown in FIG. The

  The intermediate transfer belt 78 is constituted by an endless belt formed using a resin film or rubber as a base, and a toner image formed on the photosensitive drums 5Y, 5M, 5C, and 5K is transferred. It has become. Further, the toner image transferred to the intermediate transfer belt 78 is transferred to the recording medium P as an unfixed image.

  Each of the photosensitive drums 5Y, 5M, 5C, and 5K is subjected to an image forming process including a charging process, an exposure process, a developing process, a primary transfer process, and a cleaning process. Images of each color are formed on 5M, 5C, and 5K.

  The primary transfer bias rollers 79Y, 79M, 79C, and 79K respectively sandwich the intermediate transfer belt 78 with the photosensitive drums 5Y, 5M, 5C, and 5K to form primary transfer nips. Further, a transfer bias having a polarity opposite to the polarity of the toner is applied to the primary transfer bias rollers 79Y, 79M, 79C, and 79K.

[Image creation process]
Next, the image forming process will be described. First, in the charging step, the photosensitive drums 5Y, 5M, 5C, and 5K are rotationally driven clockwise in FIG. 1 by a drive motor (not shown). The surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K are uniformly charged at the position of the charging unit 75.

  In the exposure process, the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K reach the irradiation position of the laser beam emitted from the exposure unit 3, and the electrostatic latent images corresponding to the respective colors by the exposure scanning at this position. Is formed.

  Next, in the development process, the surfaces of the photoconductor drums 5Y, 5M, 5C, and 5K reach a position facing the developing unit 76, and the electrostatic latent image is developed at this position to form toner images of each color. The

  Next, in the primary transfer process, the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K reach the positions facing the intermediate transfer belt 78 and the first transfer bias rollers 79Y, 79M, 79C, and 79K, and this position is reached. Thus, the toner images on the photosensitive drums 5Y, 5M, 5C, and 5K are transferred onto the intermediate transfer belt 78. At this time, a small amount of untransferred toner remains on the photosensitive drums 5Y, 5M, 5C, and 5K.

  Next, in the cleaning process, the surfaces of the photoconductor drums 5Y, 5M, 5C, and 5K reach a position facing the cleaning unit 77, and the unremained portions on the photoconductor drums 5Y, 5M, 5C, and 5K at this position. The transferred toner is mechanically collected by the cleaning blade of the cleaning unit 77.

  Then, the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K reach a position facing a neutralization unit (not shown), and the residual potential on the photosensitive drums 5Y, 5M, 5C, and 5K is removed at this position. . Thereby, the image forming process in the photosensitive drums 5Y, 5M, 5C, and 5K is completed.

  The toner images of the respective colors formed on the respective photosensitive drums through the above development process are transferred onto the intermediate transfer belt 78 in an overlapping manner. As a result, a color image is formed on the intermediate transfer belt 78.

[Transfer process]
Next, the transfer process will be described. The intermediate transfer belt 78 travels in the direction of the arrow in FIG. 1 and sequentially passes through the primary transfer nips of the primary transfer bias rollers 79Y, 79M, 79C, and 79K. As a result, the toner images of the respective colors on the photosensitive drums 5Y, 5M, 5C, and 5K are primarily transferred while being superimposed on the intermediate transfer belt 78.

  The intermediate transfer belt 78 reaches a position facing the secondary transfer roller 89 in a state where the toner images of the respective colors are transferred in an overlapping manner. At this position, the secondary transfer backup roller 82 sandwiches the intermediate transfer belt 78 between the secondary transfer roller 89 and forms a secondary transfer nip. The four color toner images formed on the intermediate transfer belt 78 are transferred onto the recording medium P conveyed to the position of the secondary transfer nip. At this time, untransferred toner that has not been transferred to the recording medium P remains on the intermediate transfer belt 78.

  Thereafter, the intermediate transfer belt 78 reaches the position of the intermediate transfer cleaning unit 80. At this position, the untransferred toner on the intermediate transfer belt 78 is collected. Thereby, the transfer process in the intermediate transfer belt 78 is completed.

[Image formation process]
Next, the image forming process will be described. The recording medium P is conveyed from the paper supply unit 12 disposed below the image forming apparatus 1 to the position of the secondary transfer nip via the paper supply roller 97, the registration roller pair 98, and the like. A plurality of recording media P such as transfer paper are stored in the paper supply unit 12 in an overlapping manner. When the paper feed roller 97 is rotationally driven in the counterclockwise direction in FIG. 1, the uppermost recording medium P is fed between the rollers of the registration roller pair 98.

  The recording medium P conveyed to the registration roller pair 98 is temporarily stopped at the position of the roller nip of the registration roller pair 98 that has stopped rotating. Then, the registration roller pair 98 is rotationally driven in synchronization with the color image on the intermediate transfer belt 78, and the recording medium P is conveyed toward the secondary transfer nip. In this way, a desired color image is transferred onto the recording medium P.

  Thereafter, the recording medium P on which the color image is transferred at the position of the secondary transfer nip is conveyed to the position of the fixing device 20. At this position, the color image transferred to the surface is fixed on the recording medium P by heat and pressure generated by the fixing belt 21 and the pressure roller 22.

  Thereafter, the recording medium P is discharged out of the apparatus through a pair of paper discharge rollers 99. The recording medium P discharged out of the apparatus by the discharge roller pair 99 is sequentially stacked on the stack unit 100 as an output image. Thereby, the image forming process is completed. Further, a sheet reversing device 90 is provided that reverses the recording medium P so as to record images on both sides of the recording medium P, and again conveys the recording medium P toward the secondary transfer nip.

[Control unit]
The image forming apparatus 1 includes a main body control unit and an operation input unit (not shown). The main body control unit is constituted by a microcomputer including a CPU, ROM, RAM, I / O interface, and the like, and a program stored in advance in the ROM is executed by the CPU.

  The main body control unit is connected to the operation input unit and various sensors and motors provided in the image forming apparatus 1. The main body control unit includes a drive motor for driving the above-described photosensitive drums 5Y, 5M, 5C, and 5K, a drive mechanism for rotationally driving the pressure roller 22 and the like based on detection signals input from various sensors. While controlling each motor, the electricity supply control with respect to a heat source is performed.

  The operation input unit is provided in the main body of the image forming apparatus 1 and has various keys such as a numeric keypad and a print start key and various displays, and outputs input signals input through the various keys to the main body control unit. It is supposed to be.

(Fixing device)
Next, the fixing device 20 installed in the image forming apparatus 1 will be described. The fixing device according to the present embodiment is provided inside a rotatable endless fixing belt (fixing belt 21), an opposing rotating body (pressure roller 22) that contacts an outer peripheral surface of the fixing belt, and the fixing belt. A nip forming member (nip forming member 24) that abuts against the counter rotator via the fixing belt to form a nip portion between the fixing belt and the counter rotator, and the fixing belt is connected to the end of the fixing belt. In a fixing device (fixing device 20) including a holding member (holding flanges 31 and 32) that is rotatably held, friction is applied to at least a part of a surface layer of a region that is in contact with the counter rotating body in the longitudinal direction of the fixing belt. The longitudinal width of the counter-rotating body that has a band-like region (band-like region 21a, 21b) whose coefficient is higher than that of the other region (other region 21c) and can come into contact with the band-like region (band-like region contact range 22e) Then The outer diameter of the opposite rotational member is of greater in the end side (r2) than the longitudinal center side (r1). In addition, the code | symbol in embodiment and the example of application are shown in a parenthesis.

[Basic configuration]
FIG. 2 is a side cross-sectional view illustrating a configuration of an embodiment of the fixing device. The basic configuration of the fixing device 20 will be described with reference to FIG. The fixing device 20 includes a rotatable fixing belt 21, a pressure roller 22 rotatably provided facing the fixing belt 21, a halogen heater 23 as a heating source for heating the fixing belt 21, and the fixing belt 21. A nip forming member 24 disposed inside, a stay 25 as a support member for supporting the nip forming member 24, a reflecting member 26 for reflecting light emitted from the halogen heater 23 to the fixing belt 21, and a fixing belt A temperature sensor 27 as temperature detecting means for detecting the temperature of 21; a separating member 28 for separating the paper from the fixing belt 21; a pressure means (not shown) for pressing the pressure roller 22 to the fixing belt 21; .

  The fixing belt 21 is composed of an endless belt member (including a film) that is thin and flexible. Specifically, the fixing belt 21 includes a base material on the inner peripheral side formed of a metal material such as nickel or SUS or a resin material such as polyimide (PI), and a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA). Or it is comprised by the release layer of the outer peripheral side formed with polytetrafluoroethylene (PTFE) etc. Further, an elastic layer formed of a rubber material such as silicone rubber, foamable silicone rubber, or fluorine rubber may be interposed between the base material and the release layer.

  The pressure roller 22 includes a cored bar 22a, an elastic layer 22b made of foamable silicone rubber, silicone rubber, or fluororubber provided on the surface of the cored bar 22a, and PFA provided on the surface of the elastic layer 22b. It is constituted by a release layer 22c made of PTFE or the like. The pressure roller 22 is pressed toward the fixing belt 21 by a pressure unit (not shown) and is in contact with the nip forming member 24 via the fixing belt 21. At the place where the pressure roller 22 and the fixing belt 21 are in pressure contact, the elastic layer 22b of the pressure roller 22 is crushed to form a nip portion N having a predetermined width. The pressure roller 22 is configured to be rotationally driven by a drive source such as a motor (not shown) provided in the image forming apparatus main body. When the pressure roller 22 is rotationally driven, the driving force is transmitted to the fixing belt 21 at the nip portion N, and the fixing belt 21 is driven to rotate.

  In the present embodiment, the pressure roller 22 is a solid roller, but may be a hollow roller. In that case, a heating source such as a halogen heater may be disposed inside the pressure roller 22. If the elastic layer 22b is not provided, the heat capacity is reduced and the fixability is improved. However, when the unfixed toner is crushed and fixed, minute irregularities on the belt surface are transferred to the image and uneven glossiness is formed on the solid portion of the image. May occur. In order to prevent this, it is desirable to provide an elastic layer having a thickness of 100 μm or more. By providing the elastic layer 22b having a thickness of 100 μm or more, minute irregularities can be absorbed by elastic deformation of the elastic layer, so that occurrence of uneven gloss can be avoided. The elastic layer 22b may be solid rubber, but if there is no heat source inside the pressure roller 22, sponge rubber may be used. Sponge rubber is more preferable because heat insulation is enhanced and heat of the fixing belt 21 is less likely to be taken away. In addition, the fixing member and the pressure member are not limited to being in pressure contact with each other, and may be configured to simply contact without pressing.

  Both ends of the halogen heater 23 are fixed to a side plate (not shown) of the fixing device 20. The halogen heater 23 is configured to generate heat by being output controlled by a power supply unit provided in the main body of the image forming apparatus. The output control is based on the detection result of the surface temperature of the fixing belt 21 by the temperature sensor 27. Done. By such output control of the heater 23, the temperature of the fixing belt 21 (fixing temperature) can be set to a desired temperature. In addition to the halogen heater, an IH, a resistance heating element, a carbon heater, or the like may be used as a heating source for heating the fixing belt 21.

  The nip forming member 24 includes a base pad 241 and a sliding sheet (low friction sheet) 240 provided on the surface of the base pad 241. The base pad 241 is continuously disposed in the longitudinal direction over the axial direction of the fixing belt 21 or the axial direction of the pressure roller 22, and receives the pressure from the pressure roller 22 to change the shape of the nip portion N. It is a decision. The base pad 241 is fixedly supported by the stay 25. Thus, the nip forming member 24 is prevented from being bent by the pressure of the pressure roller 22, and a uniform nip width is obtained in the axial direction of the pressure roller 22. The stay 25 is preferably formed of a metal material having high mechanical strength such as stainless steel or iron in order to satisfy the function of preventing the nip forming member 24 from bending. The base pad 241 is also preferably made of a material that is hard to some extent to ensure strength. As a material for the base pad 241, a resin such as a liquid crystal polymer (LCP), a metal, a ceramic, or the like can be used.

  The base pad 241 is made of a heat resistant member having a heat resistant temperature of 200 ° C. or higher. This prevents the nip forming member 24 from being deformed by heat in the toner fixing temperature range and ensures a stable state of the nip portion N, thereby stabilizing the output image quality. For the base pad 241, general materials such as polyethersulfone (PES), polyphenylene sulfide (PPS), liquid crystal polymer (LCP), polyethernitrile (PEN), polyamideimide (PAI), polyetheretherketone (PEEK), etc. It is possible to use a heat resistant resin.

  The sliding sheet 240 may be disposed on at least the surface of the base pad 241 that faces the fixing belt 21. As a result, when the fixing belt 21 rotates, the fixing belt 21 slides with respect to the low friction sheet, so that the driving torque generated in the fixing belt 21 is reduced, and the load due to the frictional force on the fixing belt 21 is reduced. The It is also possible to adopt a configuration without the sliding sheet 240.

  In FIG. 2, the shape of the nip portion (nip forming member 24) is flat, but may be a concave shape or other shapes. For example, by making the shape of the nip portion concave on the fixing belt 21 side, the discharge direction of the leading edge of the paper P becomes closer to the pressure roller and the separation property is improved, so that the occurrence of jam is suppressed.

  The reflection member 26 is disposed between the stay 25 and the halogen heater 23. In the present embodiment, the reflecting member 26 is fixed to the stay 25. Examples of the material of the reflecting member 26 include aluminum and stainless steel. By arranging the reflection member 26 in this way, the light emitted from the halogen heater 23 toward the stay 25 is reflected to the fixing belt 21. As a result, the amount of light applied to the fixing belt 21 can be increased, and the fixing belt 21 can be efficiently heated. Further, since it is possible to suppress the radiant heat from the halogen heater 23 from being transmitted to the stay 25 and the like, energy saving can be achieved. Note that the same effect can be obtained by performing heat insulation or mirror surface treatment on the surface of the stay 25 instead of providing the reflecting member 26.

  In addition, the fixing device 20 according to the present embodiment is devised in various configurations in order to further improve energy saving and first print time.

  Specifically, the fixing belt 21 can be directly heated at a place other than the nip portion N by the halogen heater 23 (direct heating method). In the present embodiment, nothing is interposed between the halogen heater 23 and the left portion of the fixing belt 21 in FIG. 2, and the radiant heat from the halogen heater 23 is directly applied to the fixing belt 21 in that portion.

  Further, in order to reduce the heat capacity of the fixing belt 21, the fixing belt 21 is made thinner and smaller in diameter. Specifically, the thicknesses of the base material, the elastic layer, and the release layer constituting the fixing belt 21 are set in a range of 20 to 50 μm, 100 to 300 μm, and 10 to 50 μm, and the overall thickness is set. It is set to 1 mm or less. The diameter of the fixing belt 21 is set to 20 to 40 mm. In order to further reduce the heat capacity, the thickness of the entire fixing belt 21 is desirably 0.2 mm or less, and more desirably 0.16 mm or less. The diameter of the fixing belt 21 is desirably 30 mm or less.

  In this embodiment, the diameter of the pressure roller 22 is set to 20 to 40 mm, and the diameter of the fixing belt 21 and the diameter of the pressure roller 22 are configured to be equal. However, it is not limited to this configuration. For example, the fixing belt 21 may be formed so that the diameter thereof is smaller than the diameter of the pressure roller 22. In that case, since the curvature of the fixing belt 21 at the nip portion N is smaller than the curvature of the pressure roller 22, the recording medium discharged from the nip portion N is easily separated from the fixing belt 21.

  As described above, as a result of reducing the diameter of the fixing belt 21, the space inside the fixing belt 21 is reduced. However, the stay 25 is formed in a concave shape bent at both ends, and the inside of the portion formed in the concave shape. By accommodating the halogen heater 23, the stay 25 and the halogen heater 23 can be arranged even in a small space.

  Further, in order to dispose the stay 25 as large as possible even in a small space, the nip forming member 24 is formed compact on the contrary. Specifically, the width of the base pad 241 in the sheet conveyance direction is formed to be smaller than the width of the stay 25 in the sheet conveyance direction. Further, in FIG. 2, the heights of the base pad 241 at the upstream end 24a and the downstream end 24b in the sheet conveyance direction with respect to the nip portion N or its virtual extension line E are h1 and h2, respectively, and the upstream end 24a. When the maximum height with respect to the nip portion N or the virtual extension line E in the portion of the base pad 241 other than the downstream side end portion 24b is h3, h1 ≦ h3 and h2 ≦ h3 are satisfied. With this configuration, the upstream end 24 a and the downstream end 24 b of the base pad 241 are not interposed between the bent portions on the upstream and downstream sides of the stay 25 in the sheet conveying direction and the fixing belt 21. Therefore, each bent portion can be disposed close to the inner peripheral surface of the fixing belt 21. As a result, the stay 25 can be disposed as large as possible in a limited space in the fixing belt 21, and the strength of the stay 25 can be ensured. As a result, it is possible to prevent the nip forming member 24 from being bent by the pressure roller 22 and to improve the fixing property.

  Further, in order to ensure the strength of the stay 25, in this embodiment, the stay 25 comes into contact with the nip forming member 24 and extends in the paper transport direction (vertical direction in FIG. 2), and the base portion 25a. And a rising portion 25b extending in the contact direction of the pressure roller 22 (left side in FIG. 2) from the upstream and downstream ends of the sheet conveyance direction. That is, by providing the stay 25 with the rising portion 25b, the stay 25 has a horizontally long cross section extending in the pressure direction of the pressure roller 22, and the section modulus is increased, so that the mechanical strength of the stay 25 is increased. Can be improved.

  In addition, the strength of the stay 25 is improved by forming the rising portion 25b longer in the contact direction of the pressure roller 22. Therefore, it is desirable that the leading end of the rising portion 25 b is as close as possible to the inner peripheral surface of the fixing belt 21. However, during rotation, the fixing belt 21 may be shaken (disturbance in behavior) regardless of whether it is large or small. Therefore, if the leading end of the rising portion 25b is too close to the inner peripheral surface of the fixing belt 21, the fixing belt 21 is moved to the leading end of the rising portion 25b. There is a risk of contact. In particular, in the configuration using the thin fixing belt 21 as in the present embodiment, since the swinging width of the fixing belt 21 is large, care must be taken in setting the position of the leading end of the rising portion 25b.

  Specifically, in the case of this embodiment, the distance d in the contact direction of the pressure roller 22 between the tip of the rising portion 25b and the inner peripheral surface of the fixing belt 21 is at least 2.0 mm, preferably 3.0 mm or more. It is preferable to set. On the other hand, when the fixing belt 21 has a certain thickness and almost no vibration, the distance d can be set to 0.02 mm. When the reflecting member 26 is attached to the tip of the rising portion 25b as in the present embodiment, it is necessary to set the distance d so that the reflecting member 26 does not contact the fixing belt 21.

  In this way, the rising portion 25b is disposed long in the contact direction of the pressure roller 22 by disposing the leading end of the rising portion 25b as close as possible to the inner peripheral surface of the fixing belt 21. Can do. Accordingly, the mechanical strength of the stay 25 can be improved even in the configuration using the small-diameter fixing belt 21.

[basic action]
Hereinafter, the basic operation of the fixing device according to the present embodiment will be described with reference to FIG. When the power switch of the main body of the image forming apparatus is turned on, power is supplied to the halogen heater 23 and the pressure roller 22 starts to rotate clockwise in FIG. As a result, the fixing belt 21 is driven to rotate counterclockwise in FIG. 2 by the frictional force with the pressure roller 22. The fixing belt 21 is sandwiched and rotated at the nip portion N, and travels while being guided by belt holding members (holding flanges 31 and 32, see FIG. 3) at both ends other than the nip portion N.

  Thereafter, the paper P carrying the unfixed toner image T in the above-described image forming process is conveyed in the direction of the arrow A1 in FIG. 2 while being guided by a guide plate (not shown), and the fixing belt 21 in the pressure contact state and It is fed into the nip N of the pressure roller 22. Then, the toner image T is fixed on the surface of the paper P by heat from the fixing belt 21 heated by the halogen heater 23 and pressure applied between the fixing belt 21 and the pressure roller 22.

  The paper P on which the toner image T is fixed is carried out from the nip portion N in the direction of the arrow A2 in FIG. At this time, the paper P is separated from the fixing belt 21 by the leading edge of the paper P coming into contact with the leading edge of the separation member 28. Thereafter, the separated paper P is discharged out of the apparatus by the paper discharge roller as described above, and stocked on the paper discharge tray.

[Main part configuration]
Hereinafter, characteristic portions of the fixing device according to the present invention will be described. FIG. 3 is a schematic configuration diagram illustrating a configuration of a main part of the fixing device 20, and is a front view of the fixing belt 21 and the pressure roller 22. 3 and 4, there is a space between the fixing belt 21 and the pressure roller 22, but in reality both members are in pressure contact and the shaft 22 d of the pressure roller 22 is not illustrated. The fixing belt 21 is driven to rotate by being rotated by the means.

  Holding flanges 31 and 32 as holding members are provided at both ends of the fixing belt 21 in the longitudinal direction (rotating axis direction). The holding flanges 31 and 32 have a diameter smaller than the inner diameter of the fixing belt 21 and can be inserted inward from the end of the fixing belt 21 to a predetermined range, and the insertion portions 31a and 32a and the fixing belt. The end portions of the fixing belt 21 are rotatably held by the holding flanges 31 and 32. The restricting portions 31b and 32b are formed to have an outer diameter larger than 21.

  Further, the restricting portions 31 b and 32 b of the holding flanges 31 and 32 are fixed to the side plate 29 of the fixing device 20. Further, the rotation shaft 22 d of the pressure roller 22 is pivotally supported on the side plate 29 of the fixing device 20 via a bearing 30.

  Between the end portion of the fixing belt 21 and the restricting portions 31b and 32b of the holding flanges 31 and 32, predetermined gaps c1 and c2 are provided in a normal state where the fixing belt 21 is not displaced. ing. The gaps c1 and c2 are preferably equidistant. In this embodiment, c1 and c2 are each A / 2 [mm], and A = 5 mm, and the gaps c1 and c2 are formed by 2.5 mm. To be.

  The rotational driving force of the fixing belt 21 is the frictional force between the fixing belt 21 and the pressure roller 22 as described above. Therefore, the fixing device 20 according to the present embodiment has a friction coefficient other than that of the fixing belt 21 along the circumferential direction on the surface layer of the fixing belt 21 in a range where the fixing belt 20 contacts the pressure roller 22 in the longitudinal direction. Band-shaped regions 21a and 21b that are higher than the region 21c are provided. The longitudinal widths of the belt-like regions 21a and 21b are B [mm], respectively, and in this embodiment, B = 5 mm.

  Thus, by providing the belt-like regions 21 a and 21 b, the rotational driving force of the fixing belt 21 is transmitted from the pressure roller 22 to the fixing belt 21 mainly in the range of the belt-like regions 21 a and 21 b of the fixing belt 21. To be.

  Further, as shown in FIG. 3, the pressure roller 22 has a drum shape whose outer diameter is larger on the end side than on the center side in the longitudinal direction. The outer diameter of the pressure roller 22 is larger on the end side than on the center side in the longitudinal direction, as shown in FIG. In the longitudinal direction of the pressure roller 22, the pressure roller 22 is preferably provided in a range that may come into contact with the belt-like regions 21a and 21b (referred to as a belt-like region contact range 22e). The belt-shaped region contact range 22e is a range in which the fixing belt 21 contacts the belt-shaped regions 21a and 21b even when the fixing belt 21 is shifted from side to side because the movement may occur by gaps c1 and c2. is there.

  Therefore, it is preferable that the longitudinal width of the belt-shaped region contact range 22e is at least A + B [mm]. In this embodiment, it is 10 mm. As a result, even when the fixing belt 21 is deviated, the belt-like regions 21a and 21b are formed in the belt-like regions in which the outer diameter of the pressure roller 22 is larger on the end side than on the center side in the longitudinal direction. The contact range 22e can be contacted.

  In addition, it is preferable that the shape of the pressure roller 22 in the belt-shaped region contact range 22e on both sides is symmetrical, and the outer diameter difference r2 when the outer diameter on the center side is r1 and the outer diameter on the end side is r2. -R1 is preferably 0.1 mm to 0.3 mm. In this embodiment, the outer diameter difference is 0.2 mm.

  In the configuration described above, as shown in FIG. 3, when the fixing belt 21 is driven in the center in the axial direction, the pressure applied to the portion that contacts the belt-like regions 21a and 21b and drives the belt-like regions 21a and 21b. The diameter of the roller 22 is equal. Here, when the linear velocity of the fixing belt 21 in the belt-like region 21a is V1, and the linear velocity of the fixing belt 21 in the belt-like region 21b is V2, in the example of FIG. No longitudinal force is applied.

  Here, a case where the fixing device 20 is driven and the fixing belt 21 is displaced in the axial direction for some reason will be described. For example, as shown in FIG. 4, when the fixing belt 21 is moved to the left side in the drawing, the diameter of the pressure roller 22 in the portion facing the belt-like region 21a is the pressure roller 22 in the portion facing the belt-like region 21b. Therefore, the linear velocity is relatively V1> V2. When the speed difference occurs in this way, a force in the right direction in the figure is generated with respect to the fixing belt 21, and the fixing belt 21 can be moved to the right side.

  On the contrary, when the fixing belt 21 is shifted to the right side, the linear velocity is V1 <V2, so that a force in the left direction in FIG. Can be moved to the left. As described above, the belt-shaped region contact range 22e is formed with a width of at least A + B, so that a force that moves the fixing belt 21 to the center can be generated regardless of the amount of deviation of the fixing belt 21. it can.

  As described above, when a deviation occurs in the fixing belt 21, a force in a direction to always eliminate the deviation can be applied, and the deviation of the fixing belt 21 can be suppressed. Therefore, it is possible to prevent the end portion of the fixing belt 21 from coming into contact with the flanges 31 and 32, and it is possible to prevent the fixing belt end portion from being damaged by the contact.

  The belt-like regions are preferably provided on both end portions of the fixing belt 21 as in the example shown in FIG. As a result, the fixing belt 21 can be driven and rotated stably on the center side.

  Further, it is preferable that the belt-like region is provided outside the image forming width. As described above, since the belt-like region is a region having a different surface layer property, it is possible to eliminate the influence on the fixed image by being outside the image forming range.

  The belt-like region and other regions in the fixing belt 21 only need to satisfy the above friction coefficient relationship. For example, PFA is used for the surface layer other than the belt-like region of the fixing belt 21 and the belt-like region is used. It is preferable to use a rubber material. Thereby, the difference of a friction coefficient is realizable. This can be formed, for example, by not providing a release layer (PFA) in the belt-like region but by making the elastic layer (rubber material) the outermost layer. Further, since the fixing device is at a high temperature, it is preferable to use, for example, silicone rubber, fluorine rubber, or the like as the rubber material of the belt-like region.

  According to the fixing device according to the present embodiment described above, a belt-like region having a friction coefficient larger than that of other regions is provided on both ends of the surface of the fixing belt, and pressure is applied at a position facing the belt-like region. By increasing the diameter of the roller from the axial center toward the end, when the fixing belt is deviated, a force to return to the center in the axial direction is applied to suppress the deviating movement of the fixing belt in the axial direction. It is possible to prevent the fixing belt end from being damaged.

  In addition, since the fixing belt is prevented from being damaged by suppressing the deviation of the fixing belt itself, it is not necessary to separately provide a protective member such as a driven ring for protecting the end portion of the fixing belt. There is no increase in parts. Therefore, realization at a low cost is possible.

  Further, by using the image forming apparatus (FIG. 1) provided with the fixing device 20, it is possible to realize an image forming apparatus having the above effect and a highly reliable fixing device.

  The above-described embodiment is a preferred embodiment of the present invention, but is not limited thereto, and various modifications can be made without departing from the gist of the present invention.

  For example, the fixing device to which the present invention can be applied is not limited to the fixing device of the above embodiment, and the present invention can also be applied to a fixing device having a plurality of halogen heaters 23 as shown in FIG. . In this case, the fixing belt 21 can be heated in a range corresponding to various widths of the paper by varying the heat generation area for each halogen heater 23.

  Although not shown, the fixing belt 21 is provided with a shielding member that shields heat from the halogen heater 23 between the fixing belt 21 and the halogen heater 23 at both axial ends of the fixing belt 21. It is also preferable. Thereby, in particular, an excessive temperature rise in the non-sheet passing region of the fixing belt during continuous sheet feeding can be suppressed, and deterioration and damage of the fixing belt due to heat can be prevented.

In addition, the fixing device according to the present invention is not limited to the color laser printer shown in FIG. 1, and can be mounted on a monochrome image forming apparatus, other printers, copiers, facsimiles, or complex machines thereof. .

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 3 Exposure part 4Y, 4M, 4C, 4K Image forming part 5Y, 5M, 5C, 5K Photosensitive drum 12 Paper feed part 20 Fixing device 21 Fixing belt 21a, 21b Belt-like area | region 21c Other area | region 22 Pressure roller 22a Metal core 22b Elastic layer 22c Release layer 22d Shaft 22e Band-shaped region contact range 23 Halogen heater 24 Nip forming member 240 Sliding sheet (low friction sheet)
241 Base pad 25 Stay 25a Base portion 25b Standing portion 26 Reflecting member 27 Temperature sensor 28 Separating member 29 Side plate 30 Bearings 31 and 32 Holding flanges 31a and 32a Inserting portions 31b and 32b Restricting portion 75 Charging portion 76 Developing portion 77 Cleaning portion 78 Intermediate Transfer belt 79Y, 79M, 79C, 79K Primary transfer bias roller 80 Intermediate transfer cleaning unit 82 Secondary transfer backup roller 83 Cleaning backup roller 84 Tension roller 85 Intermediate transfer unit 89 Secondary transfer roller 90 Sheet reversing device 97 Paper feed roller 98 Registration roller pair 99 Paper discharge roller pair 100 Stack unit 101 Bottle storage unit 102Y, 102M, 102C, 102K Toner bottle P Paper T Toner image

JP 2004-286922 A Japanese Patent No. 2861280 JP 2007-334205 A Japanese Patent Laid-Open No. 2007-233011 JP 2009-288284 A

Claims (8)

A rotatable endless fixing belt;
An opposing rotating body that contacts the outer peripheral surface of the fixing belt;
A nip forming member provided inside the fixing belt and forming a nip portion between the fixing belt and the counter rotating body by contacting the counter rotating body via the fixing belt;
A fixing device comprising: a holding member that rotatably holds the fixing belt at an end side thereof;
In a surface layer of at least a part of a region in contact with the counter rotating body in the longitudinal direction of the fixing belt, a belt-like region having a higher friction coefficient than other regions is provided.
The fixing device according to claim 1, wherein an outer diameter of the counter-rotating body is larger on an end side than a center side in the longitudinal direction with respect to a longitudinal width of the counter-rotating body capable of contacting the belt-shaped region.   The fixing device according to claim 1, wherein the belt-like regions are provided on both ends in the longitudinal direction. The holding member includes an insertion portion that is inserted inward from an end side of the fixing belt to a predetermined range, and a restriction portion that is formed to have an outer diameter larger than the insertion portion.
When the gap between the fixing belt and the restricting portion at both ends is A / 2 [mm] and the width of the belt-like region is B [mm],
The fixing device according to claim 2, wherein a longitudinal width of the counter rotating body capable of contacting the belt-shaped region is at least A + B [mm].   The fixing device according to claim 1, wherein the belt-like region is provided outside an image forming width in a longitudinal direction.   The longitudinal width of the counter-rotating body that can abut on the belt-like region has an outer diameter that is 0.1 to 0.3 mm larger on the end side than on the center side. The fixing device according to any one of the above.   6. The fixing device according to claim 1, wherein the outermost layer of the belt-shaped region is made of a rubber material, and the outermost layer of the other region is a release layer.   The fixing device according to claim 6, wherein silicone rubber or fluororubber is used as the rubber material of the belt-shaped region.   An image forming apparatus comprising the fixing device according to claim 1.

Images