JP2007171318A - Fixing apparatus and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the occurrence of high-temperature offset and belt deterioration, to suppress the reduction of productivity and the enlargement and complexity of an apparatus and to remove useless energy. <P>SOLUTION: A fixing apparatus is constituted of winding an endless belt 23 around a heating member 21 and a supporting member 22, including a radiation heat source 24 in the cylindrical heating member 21 and pressing a pressure member 25 in contact with the belt 23. In the inner peripheral surface of the heating member 21, a high radiation rate area having a radiation rate required for heating a fixing nip part 27 up to a fixing temperature by the radiation heat of the radiation heat source 24, having a step-like or inclined shape and having different axial direction dimensions in the peripheral direction and a low radiation rate area having a radiation rate lower than that of the high radiation rate area are formed. The fixing apparatus is further provided with a rotary mechanism 28 for axially rotating the heating member 21 and a control means 29 for controlling the rotary mechanism 28 so that a part of the high radiation rate area having an axial direction dimension corresponding to the width dimension of a recording medium X is arranged on a position where the belt 23 is brought into contact with the heating member 21. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a belt fixing type fixing device and an electrophotographic image forming apparatus including the fixing device.

  For example, an electrophotographic image forming apparatus such as a laser printer, a copying machine, or a facsimile has a fixing device that heats and pressurizes a recording medium on which a toner image is electrostatically carried to fix the toner image on the recording medium. Is provided. As this fixing device, there is a belt fixing type fixing device. In this belt fixing type fixing device, a halogen lamp (radiant heat source) is included in a cylindrical heating roller (heating member), and the heating roller and a supporting roller (supporting member) arranged in parallel with the heating roller. A belt is wound between the belts, and a pressure roller (pressure member) is pressed against a part of the belt. The heating roller described above is made of a hollow metal tube, and the inner peripheral surface thereof is entirely coated with heat-resistant black paint in order to increase the radiation rate. In addition, in order to shorten the warm-up time and save energy, an extremely thin belt having a thickness of about several hundred μ is used for the belt, and the heat capacity of the belt is minimized. In the fixing device having the above-described configuration, the belt wound around the heating roller is heated by heating the entire heating roller with radiant heat from the halogen lamp. Then, by passing a sheet (recording medium) carrying a toner image through a fixing nip formed between the belt and the pressure roller, the toner image can be heated and pressed on the sheet to be fixed.

  However, if paper with a width smaller than the belt width (for example, postcards or envelopes) is continuously passed through the fixing device described above, the heat capacity of the belt is extremely small. ) Temperature rises excessively. Therefore, if belt-sized paper is passed immediately after passing small-size paper continuously through the fixing device, there is a problem that high-temperature offset occurs because both sides of the belt are higher than the fixing set temperature. . Further, there is a problem that the silicon rubber layer (elastic layer) on both sides of the belt (non-sheet passing portion), PFA (perfluoroalkoxy), PTFE (polytetrafluoroethylene), etc. on the surface release layer are deteriorated by high temperature.

As a conventional means to solve this problem,
(1) Reduce the number of prints per hour to avoid temperature rise,
(2) A plurality of halogen lamps having different heating patterns in the longitudinal direction are respectively included in the heating roller, and an optimum heating pattern is selected according to the paper size.
(3) When both sides of the belt (non-sheet passing portion) become excessively high in temperature, the temperature is lowered by bringing cooling rollers and blades into contact with both sides of the belt or the entire heating roller (for example, Patent Documents). 1).
(4) When both sides of the belt (non-sheet passing portion) become excessively high in temperature, the cooling air is applied to both sides of the belt or the entire heating roller to lower the temperature (see, for example, Patent Document 2).
Etc.
JP 2004-53674 A JP 2003-330298 A

  However, the conventional fixing device using the above-described means has the problem that (1) if the number of printed sheets per hour is reduced, productivity per hour is lowered. Further, (2) when a plurality of halogen lamps having different heating patterns are used, there is a problem that the fixing device is enlarged because a large-diameter heating roller capable of containing a plurality of halogen lamps is required. As the number of lamps increases, there is a problem that the apparatus becomes complicated and the cost increases. (3) When a cooling roller or blade is provided, a separation / contact mechanism for bringing the cooling roller into contact / separation with the heating roller is necessary, and there is a problem that the fixing device becomes complicated. In addition, since both sides of the belt (non-sheet passing portion) are cooled after being heated once, there is a problem that energy is wasted. (4) The means for applying the cooling air requires a blower that blows the cooling air, and there is a problem that the fixing device becomes complicated. In addition, both sides of the belt (non-sheet passing portion) are cooled after being heated once. Therefore, there is a problem that energy is wasted.

  The present invention takes the above-described conventional problems into consideration, prevents high-temperature offset and belt deterioration, suppresses productivity per hour, suppresses increase in size and complexity of the apparatus as much as possible, and An object of the present invention is to provide a fixing device and an image forming apparatus capable of eliminating waste of energy.

  In order to solve the above-described problem, in the fixing device according to the first aspect of the present invention, an endless belt is wound around a cylindrical heating member and a support member including a radiant heat source, and the pressure member is pressed against the belt. Then, a fixing nip portion is formed between the belt and the pressure member, and a recording medium on which a toner image is electrostatically carried is passed through the fixing nip portion, whereby the toner image is transferred to the recording medium. In the fixing device for fixing the heating member, the inner peripheral surface of the heating member has a radiation rate required to heat the fixing nip portion to the fixing temperature by radiant heat of the radiant heat source, and has a stepped or inclined shape. A high emissivity region having different axial dimensions in the circumferential direction, and a low emissivity region having a lower emissivity than the high emissivity region, respectively, and a rotation mechanism for rotating the heating member about the axis, Control means for controlling the rotation mechanism so that a part of the high emissivity region having an axial dimension corresponding to the width dimension of the recording medium is disposed at a position where the recording belt and the heating member are in contact with each other. And is provided.

  According to a second aspect of the present invention, in the fixing device according to the first aspect, there is provided directing means for radiating heat only where the belt and the heating member are in contact with each other by providing directivity to the radiant heat source. It is characterized by being provided.

  According to a third aspect of the present invention, there is provided an image forming apparatus comprising: an image forming unit that electrostatically transfers a toner image onto a recording medium and carries the toner image on the recording medium. The fixing device according to claim 1 or 2, wherein the toner image is fixed on the recording medium.

  Due to the above-described features of the present invention, the rotation mechanism is controlled by the control means in accordance with the width of the recording medium, and the belt and the heating member are in contact with each other, and the high radiation of the axial dimension corresponding to the width dimension of the recording medium is obtained. The heating member is pivoted so that the rate region is reached. The heating member is heated by the radiant heat from the radiant heat source, and the heat of the heating member is transmitted to the belt when the belt and the heating member are in contact with each other. At this time, the heating by radiation is expressed by the following equation.

  As shown in the above equation, the higher the emissivity, the greater the heat flow rate. Therefore, the temperature increase is large in the high emissivity region of the heating member, and the temperature increase is small in the low emissivity region of the heating member. Of the belt wound around the heating member, the portion facing the high emissivity region is heated to a high temperature, while the portion of the belt wrapped around the heating member facing the low emissivity region is not so much. Without being heated, the belt is heated with a width corresponding to the axial dimension of the high emissivity region at the point where the belt and the heating member are in contact, that is, the width of the recording medium. In this way, the temperature distribution state of the belt is changed by rotating the heating member to change the axial dimension of the high emissivity region where the belt and the heating member are in contact with each other.

  In addition, by providing directing means that imparts directivity to the radiant heat source, the radiant heat of the radiant heat source is radiated only where the belt and the heating member are in contact with each other. Heated intensively.

  According to the fixing device and the image forming apparatus according to the present invention, a part of the high emissivity region having an axial dimension corresponding to the width dimension of the recording medium is disposed at a position where the belt and the heating member are in contact with each other. Since the belt is heated at a width corresponding to the width of the medium, for example, even if a belt width size paper is passed immediately after passing a paper with a width smaller than the belt width, The non-sheet-passing portion of the belt in the belt does not become high temperature, and it is possible to prevent the occurrence of high-temperature offset and to suppress the deterioration of the belt. Further, according to the fixing device and the image forming apparatus according to the present invention, since it is not necessary to leave a sheet passing interval (printing interval), productivity per hour is not lowered, and conventional productivity is maintained. Can do. Further, since only a rotation mechanism for rotating the heating member and a control means for controlling the rotation mechanism are added, the size can be reduced as compared with a fixing device provided with a plurality of heat sources in the heating member. In addition, the complexity of the apparatus can be suppressed as compared with a fixing device having a cooling roller and the like and a mechanism for separating and contacting the same, and a fixing device having a blower. In addition, the area of the high emissivity region is small compared to the fixing device in which the entire inner peripheral surface of the heating member is processed, so that the heating efficiency by the radiant heat source can be improved and energy waste can be eliminated. it can.

  Furthermore, since the directing means for providing directivity to the radiant heat source is provided, the portion of the heating member that contacts the belt is intensively heated, so that waste of energy can be further eliminated.

  Embodiments of a fixing device and an image forming apparatus according to the present invention will be described below with reference to the drawings.

  FIG. 1 is a schematic diagram illustrating a schematic configuration of a main part of the image forming apparatus 1. As shown in FIG. 1, the image forming apparatus 1 according to the present embodiment includes a transport unit 2 and a plurality of image forming units that are disposed on the transport unit 2 and electrostatically transfer a toner image onto a sheet X such as paper. Units 3M, 3Y, 3C, and 3BK, and a fixing device 4 that fixes and fixes (fixes) the toner image to the sheet X while nipping and conveying the sheet X that carries the toner image are provided.

The image forming units 3M, 3Y, 3C, and 3BK will be described in advance.
The image forming units 3M, 3Y, 3C, and 3BK are formed by exposure by charging a photosensitive drum (image carrier) 6 and scanning the surface of the charged photosensitive drum 6 with a laser beam 11 to perform exposure. The latent image is developed, and a developed image (toner image) formed by the development is transferred onto a sheet X conveyed by a transfer belt 10 described later. Here, the plurality of image forming units 3M, 3Y, 3C, and 3BK are sequentially arranged in the transfer direction along a transfer belt 10 to be described later, and the most upstream side based on the transfer direction of the transfer belt 10 To magenta, yellow, cyan, and black toner images. The image forming units 3M, 3Y, 3C, and 3BK are provided with a photosensitive drum 6, an exposure device (exposure unit) 7, a developing device (development unit) 8, a charging roller 9, and a cleaning unit 19, respectively.

The photosensitive drum 6 is an example of an image carrier, and rotates about the direction of the arrow shown in FIG. 1. The photosensitive drum 6 is irradiated with the laser beam 11 from the exposure device 7 to form a latent image on the surface.
The exposure device 7 scans the laser beam 11 focused on a minute spot in a fixed direction on a straight line parallel to the rotation axis of the photosensitive drum 6 at the exposure position on the photosensitive drum 6.

  The developing device 8 develops a latent image to form a visible image, and triboelectrically charges a powdered toner having a predetermined color to be negatively charged, and compares it with a non-exposed portion by exposure. The toner is supplied to the exposed portion of the photosensitive drum 6 that is set to a positive potential with respect to the developing potential, and the toner adheres to the surface of the photosensitive drum 6. In the developing device 8, toner, a stirrer 12d that stirs and charges the toner, a supply roller 12c that conveys the charged toner to the developing roller 12a side, and the toner supplied by the supply roller 12c are charged with the charge. A developing roller 12a that adheres to the surface by the Coulomb force generated by the toner and conveys it to the vicinity of the photosensitive drum 6 and a developing blade 12b for regulating the toner layer thickness to a constant thickness on the developing roller 12a are provided.

  The cleaning means 19 is in contact with the photosensitive drum 6 to remove the toner on the surface of the photosensitive drum 6 and the toner drum cleaning roller 19a disposed near the cleaning roller 19a and removed by the cleaning roller 19a. And a box (not shown) for collecting

  The charging roller 9 is for setting the surface potential of the photosensitive drum 6 to a predetermined potential at the time of image formation, and a roller portion is constituted by an elastic body imparted with conductivity to a metal shaft. It contacts the photosensitive drum 6 at the downstream charging position. The charging roller 9 is pressed against the photosensitive drum 6 with a predetermined pressure by pressing a bearing (not shown) by a biasing means such as a spring. As a result, the roller portion is deformed to form a nip portion that contacts the photosensitive drum 6 with a predetermined width in the circumferential direction, and when a DC voltage is applied to the charging roller 9, the surface of the photosensitive drum 6 is set to a predetermined potential. Can be charged. Further, a charging roller cleaning roller 20 is in contact with the charging roller 9 so as to remove dirt on the surface of the charging roller 9.

Next, the transport unit 2 will be described.
The transport unit 2 includes an endless transfer belt 10 that is circulated and moved in one direction by driven rollers 13 b and 13 c and a tension roller 14 disposed on the inner peripheral portion, a drive roller 13 a, and the transfer belt 10. A transfer roller 16a that is held in contact with the drum 6 at the transfer position, and a cleaning blade that contacts the transfer belt 10 to scrape off deposits on the surface of the transfer belt 10 and to collect the scraped deposits. A belt cleaning unit 17 is provided.

  The material of the transfer belt 10 is such that when the sheet X is opposed to the photosensitive drum 6 with the sheet X interposed therebetween, the toner on the photosensitive drum 6 can be attracted by the transfer voltage applied to the transfer roller 16a that contacts the back surface. A body sheet is used. Further, the transfer belt 10 has a light reflection characteristic for reflecting light.

The transfer roller 16a has a roller portion made of, for example, a conductive or semiconductive synthetic rubber on a metal rotation shaft, and a high voltage power supply for transfer (not shown) is connected to the rotation shaft. The surface potential of the part is controlled.
Here, the toner image formed by the image forming units 3M, 3Y, 3C, and 3BK is transferred by the transfer belt 10 by the transfer roller 16a and the control unit 16 that controls the surface potential of the roller unit. A transfer unit 18 for electrostatically transferring the toner image is configured.

Next, the fixing device 4 will be described.
FIG. 2 is a schematic diagram illustrating the configuration of the fixing device 4. As shown in FIG. 2, the fixing device 4 is a device that fixes the toner image on the sheet X by passing the sheet X on which the toner image is electrostatically carried through the fixing nip portion 27. The fixing device 4 includes a cylindrical heating roller 21, a driving roller 22 disposed in parallel with the heating roller 21, and an endless wound around these rollers 21 and 22 so as to be movable in the circumferential direction. (Cylindrical) fixing belt 23, a radiant heat source 24 included in the heating roller 21, and a pressure roller 25 that is pressed against the fixing belt 23 and forms a fixing nip portion 27 between the fixing belt 23 and the fixing belt 23. A rotating mechanism 28 that rotates the heating roller 21 intermittently and a control unit 29 that controls the rotating mechanism 28 are provided. In the fixing device 4, the sheet X is passed through the center of the fixing belt 23.

  The fixing belt 23 is formed by laminating an elastic layer made of heat-resistant rubber such as heat-conductive silicon rubber having a thickness of about 50 to 500 microns on a base layer made of metal or heat-resistant resin film having a thickness of about several tens to 150 microns. Furthermore, a toner release layer made of a coating or film of fluororesin having a thickness of about 5 to 50 microns with excellent heat resistance and a modified fluororesin (polytetrafluoroethylene, etc.) is formed on the surface of the elastic layer. It is a laminated member, and is a thin member having a substantially cylindrical shape in a state in which the longitudinal direction is longer than the width of the sheet X and no external force is received. The fixing belt 23 includes a heating roller 21 and a driving roller 22 disposed therein, and the pressure roller 25 is pressed against the pressure roller 25, so that the fixing roller 23 is interposed between the driving roller 22 and the pressure roller 25 and between the heating roller 21 and the pressure roller 25. And are supported while being sandwiched respectively.

  The heating roller 21 and the driving roller 22 are respectively arranged inside the cylindrical fixing belt 23, and the fixing belt 23 is wound around the outer peripheral surface thereof. Further, the heating roller 21 and the driving roller 22 are in pressure contact with the pressure roller 25 via the fixing belt 23, respectively. The drive roller 22 is disposed on the upstream side (the left side in the drawing) in the conveyance direction of the sheet X (the rotation direction of the pressure roller 25). Has been.

  The drive roller 22 has a configuration in which a cylindrical silicon rubber made of a highly heat-insulating material is coated, or a structure in which the outer peripheral surface of a cylindrical member or a columnar member is coated with a highly heat-insulating material. The downstream drive roller 22 is a roller that rotates in one direction by a drive mechanism (not shown) provided in the fixing device 4, and the fixing belt 23 rotates around the drive roller 22 in the axial direction. It is rotated in the direction.

  The heating roller 21 is a cylindrical round tube member made of iron, aluminum, stainless steel, or the like, which is a good heat conductor, and is a roller that is fixed so as not to rotate on the axis when the fixing belt 23 is moved in the circumferential direction. Further, the frictional force of the upstream heating roller 21 with respect to the fixing belt 23 is lower than the frictional force of the downstream driving roller 22 with respect to the fixing belt. As a result, a resistance is given to the circumferential movement of the fixing belt 23, and the pressure roller 25 among the spanning portions 23 a and 23 b of the fixing belt 23 spanned between the heating roller 21 and the driving roller 22 is applied. The contact portion 23a on one side (on the fixing nip portion 27 side) in contact is stretched in a tension state, and the other stretch portion 23b (on the opposite side) is stretched in a tensionless state.

FIGS. 3A, 3 </ b> B, and 3 </ b> C are cross-sectional views of the heating roller 21 in the axial direction of the heating roller 21, and FIG. 4 illustrates the heating roller 21 that represents the inner peripheral surface of the heating roller 21. FIG. Note that the vertical direction in FIG. 4 is the circumferential direction (paper passing direction) of the heating roller 21, and the horizontal direction is the axial direction (width direction) of the heating roller 21.
As shown in FIG. 3A, FIG. 3B, FIG. 3C, and FIG. 4, the heating roller 21 has a difference in emissivity between its inner peripheral surfaces, and the inner peripheral surface of the heating roller 21. A high emissivity region A having a high emissivity and a low emissivity region B having a low emissivity are formed. Specifically, the high emissivity area A is an area of emissivity required for heating the fixing nip portion 27 to the fixing temperature by the radiant heat of the radiant heat source 24, and heat resistance is applied to a part of the inner peripheral surface of the heating roller 21. By applying black coating, a high emissivity region A having an emissivity of 0.98 or more is formed. Moreover, the low emissivity area | region B has a low emissivity compared with the high emissivity area | region A, and it exposes a raw tube, such as aluminum, about parts other than the high emissivity area | region A, and emissivity 0.03-0.3 A low emissivity region B having a low degree is formed.

  Moreover, as shown in FIG. 4, the high emissivity area | region A is formed in steps (step shape) toward the circumferential direction, and the width dimension (axial direction dimension) L1-L3 of the high emissivity area | region A is shown. Are different in the circumferential direction. Specifically, the high-emissivity region A is formed in a plurality of steps (three steps in the present embodiment) in the shape of a chevron centered around a virtual center line O extending in the circumferential direction. The inner peripheral surface of the roller 21 is in a state of being divided into a plurality (three) of areas E1 to E3 having different width dimensions L1 to L3 of the high emissivity region A. The width dimensions L1, L2, and L3 of the areas E1 to E3 are gradually increased in the order of L1 (E1), L2 (E2), and L3 (E3), and the relationship of L1 <L2 <L3 is established. ing.

As shown in FIGS. 3A and 4, the first area E1 in which the width of the high emissivity region A is the narrowest is an area that is applied when passing a small-sized sheet X such as a postcard or an envelope. The width dimension L1 of the first area E1 is equal to or slightly larger than the width dimension of the small size sheet X, that is, the width dimension of the small size sheet X.
As shown in FIGS. 3B and 4, the second area E2 in which the width of the high emissivity region A is the second narrowest is a sheet of medium size X such as B5 size or A4 size. The width dimension L2 of the second area E2 is a size corresponding to the width dimension of the medium size sheet X, that is, equal to or slightly larger than the width dimension of the medium size sheet X. ing.
Further, as shown in FIGS. 3C and 4, the third area E3 where the width of the high emissivity region A is the widest is, for example, when passing a large sheet X such as B4 size or A3 size. The width dimension L3 of the third area E3 is a size corresponding to the width dimension of the large size sheet X, that is, the same as or slightly larger than the width dimension of the large size sheet X. .

  As shown in FIG. 2, the radiant heat source 24 is, for example, a halogen lamp or the like, and is a member in which a main body that emits heat is disposed inside the heating roller 21 and heats the heating roller 21 by radiant heat from the main body. . The heat of the heated heating roller 21 is transmitted to the winding portion 23c of the fixing belt 23 where the fixing belt 23 and the heating roller 21 are in contact with each other (belt winding portion M), whereby the fixing belt 23 is heated. Is done. The radiant heat source 24 is covered with a directional cover 30 made of a reflector or the like that imparts directivity to the radiant heat source 24. The directional cover 30 is a cylindrical member having a C-shaped cross section with the belt winding portion M side open, and radiates the radiant heat of the radiant heat source 24 only in the direction of the belt winding portion M.

  5 and 6 are perspective views showing the rotation mechanism 28. FIG. As shown in FIG. 5 and FIG. 6, the rotating mechanism 28 is attached to the stepping motor 31, the motor gear 32 attached to the rotating shaft 31 a of the stepping motor 31, the motor gear 32 and the end of the heating roller 21. And a transmission type optical sensor 34 (position detecting means) for detecting the rotation initial position of the heating roller 21 by detecting the detected roller gear 33 and the detected plate 33a attached to the roller gear 33 (or the end of the heating roller 21). It consists of and. The rotation mechanism 28 detects the initial rotation position of the heating roller 21 with the optical sensor 34, and then controls the rotation angle with the stepping motor 31, so that the heating roller 21 is controlled at a predetermined angle (120 degrees in this embodiment). The shaft is rotated intermittently.

  FIG. 7 is a block diagram showing the control means 29. As shown in FIG. 7, in the control unit 29, a high emissivity region A having widths L <b> 1 to L <b> 3 corresponding to the width dimension of the sheet X passed through the fixing nip portion 27 is arranged at the belt winding portion M. Thus, the rotation mechanism 28 is controlled. Specifically, the control board 40 is connected to the operation panel 41 for setting the size of the sheet X and connected to the stepping motor 31 of the rotating mechanism 28. The control board 40 is connected to the sheet X from the operation panel 41. A signal relating to the size (width dimension) of the sheet is received, and on the basis of the received signal, an area corresponding to the width of the sheet X to be passed is one of the first to third areas E1 to E3. A drive signal is transmitted to the stepping motor 31 so as to be arranged at M.

  As shown in FIG. 2, the pressure roller 25 is a cylindrical member that can rotate in one direction. A heat resistant elastic layer such as silicon rubber is wound around a metal core, and a fluororesin is formed on the surface thereof. And the like. The pressure roller 25 is provided in a state in which the central portion in the length direction of the spanning portion 23a in the tension state is always mechanically pressed, and fixing between the pressure roller 25 and the spanning portion 23a has an arc shape in cross section. A nip portion 27 is formed. A force in the normal direction acts on the fixing nip portion 27 in accordance with the tension acting on the stretched portion 23a. Further, the pressure roller 25 is in frictional contact with the outer peripheral surface of the fixing belt 23, so that the pressure roller 25 is axially rotated following the fixing belt 23 moving in the circumferential direction.

  Next, the operation of the image forming apparatus 1 having the above configuration will be described. Note that the overall operation of the image forming apparatus 1 is the same as that of a known color printer or the like, so that the description thereof will be omitted as appropriate and the operation of the fixing device 4 will be mainly described.

  First, the operation panel 41 is operated, and the size of the sheet X to be printed by the user is appropriately selected. At this time, a signal related to the size of the sheet X is transmitted from the operation panel 41 to the control board 40. The control board 40 that receives the signal transmits a drive signal to the stepping motor 31 based on the signal. On the other hand, the signal of the rotation initial position of the heating roller 21 detected by the optical sensor 34 is transmitted to the stepping motor 31. The stepping motor 31 is driven from the rotation initial position by a predetermined angle based on the drive signal, and the heating roller 21 is rotated to a predetermined angle. Thus, any one of the first to third areas E1 to E3 on the inner peripheral surface of the heating roller 21 corresponding to the width of the sheet X to be passed is arranged at the belt winding portion M. For example, when a small-sized sheet X is selected, the heating roller 21 rotates and the first area E1 is aligned with the belt winding portion M. Similarly, when the medium size sheet X is selected, the heating roller 21 is rotated to align the second area E2 with the belt winding portion M, and when the large size sheet X is selected. Then, the heating roller 21 rotates and the third area E3 is aligned with the belt winding portion M.

  Further, when the operation panel 41 is operated, a warm-up process is performed in which the radiant heat source 24 of the fixing device 4 is operated to start heating. Specifically, heating is performed until the temperature of the fixing nip portion 27 reaches a predetermined fixing temperature. At this time, since the temperature in the image forming apparatus 1 rises due to heat radiation from the fixing device 4, forced convection is generated around the fixing device 4 by a fan (not shown) to cool the inside of the image forming apparatus 1. In addition, during the warm-up process, the driving roller 22 on the downstream side is rotated by a driving mechanism (not shown), and the fixing belt 23 is moved in the circumferential direction by the rotation of the driving roller 22. When the fixing belt 23 moves, the heating roller 21 and the pressure roller 25 on the upstream side are driven to rotate.

  Next, when the temperature of the fixing device 4 reaches a predetermined fixing temperature, a process of forming an image on the sheet X conveyed by the transfer belt 10 is performed by the image forming units 3M, 3Y, 3C, and 3BK. Specifically, the deflected laser beam 11 is irradiated, the laser beam 11 is scanned on the surface of the photosensitive drum 6 charged by the charging roller 9 to form a latent image, and the latent image is developed by the developing device 8. Thus, a toner image is formed, and the toner image formed on the surface of the photosensitive drum 6 is transferred to the sheet X conveyed by the transfer belt 10.

  Next, the sheet X carrying the toner image is conveyed to the fixing device 4, and the toner image is melted and fixed on the sheet X while the sheet X is nipped and conveyed by the fixing belt 23 and the pressure roller 25. Specifically, the sheet X carrying the toner image is carried into the fixing nip portion 27 from the carry-in side (right side in FIG. 2). In the fixing nip portion 27, the toner image carried on the sheet X is melted by the heat of the heated fixing belt 23 and pressed by the pressure roller 25 to be fixed on the sheet X. Then, the sheet X on which the toner image is fixed is carried out from the carry-out side (left side in FIG. 2).

  According to the fixing device 4 and the image forming apparatus 1 having the above-described configuration, the rotation mechanism 28 is controlled by the control unit 29, and the high emissivity region A having the widths L1 to L3 corresponding to the width dimension of the sheet X to be passed. Is disposed at the belt winding portion M, and the higher the emissivity of the inner peripheral surface of the heating roller 21, the higher the heat flow rate and the greater the temperature rise, and the higher the emissivity by the radiant heat from the radiant heat source 24. While the area A is heated to a high temperature, the low emissivity area B is not heated so much, so that the fixing belt 23 has the widths L1 to L3 of the high emissivity area A at the belt winding position M, that is, the width of the sheet X. Heated with a width corresponding to the dimensions. As described above, the temperature distribution state of the fixing belt 23 is changed by changing the width of the high emissivity region A of the belt winding portion M. Thereby, for example, even if a small size sheet X is continuously passed, both sides of the fixing belt 23 (non-sheet passing portions of the fixing belt 23 when the small size sheet X is passed) do not become high temperature. Even if the large-size sheet X is passed immediately after the small-size sheet X is continuously fed, a high-temperature offset does not occur on both sides of the fixing belt 23, and the toner image on the sheet X is properly fixed. Can do. Further, even if the small-sized sheet X is continuously fed, both sides of the fixing belt 23 do not become high temperature, and therefore, deterioration of the elastic layer and the toner release layer of the fixing belt 23 can be suppressed.

  Further, according to the fixing device 4 and the image forming apparatus 1 described above, both sides of the fixing belt 23 do not become high temperature even if the small-sized sheet X is continuously passed, so it is necessary to leave a paper passing interval (printing interval). Therefore, the productivity per hour is not lowered and the conventional productivity can be maintained.

  Further, the fixing device 4 and the image forming apparatus 1 described above have a configuration in which a rotation mechanism 28 that rotates the heating roller 21 and a control unit 29 that controls the rotation mechanism 28 are added to the conventional fixing device. Therefore, for example, it is possible to reduce the size as compared with other fixing devices (not shown) in which a plurality of radiant heat sources are provided in the heating roller, and a cooling roller and the separation / contact mechanism thereof are provided. Compared with other fixing devices (not shown) and other fixing devices (not shown) provided with a blower, the complexity of the device can be suppressed.

  Further, according to the fixing device 4 and the image forming apparatus 1 described above, the area of the high emissivity region A is larger than that of another fixing device (not shown) in which the entire inner peripheral surface of the heating roller is processed with high emissivity. Therefore, the heating efficiency by the radiant heat source 24 is improved, and waste of energy can be eliminated.

  In addition, by providing the directivity cover 30 that imparts directivity to the radiant heat source 24, the radiant heat of the radiant heat source 24 is radiated only in the direction of the belt winding portion M and contacts the fixing belt 23 of the heating roller 21. The belt winding portion M is heated intensively. This can further eliminate energy waste.

  Further, the radiant heat is concentrated in the direction of the belt winding portion M by the directional cover 30, so that the toner image carried on the sheet X is heated at a high temperature when passing near the entrance of the fixing nip portion 27. Thus, it is melted to a viscosity that does not adhere to the fixing belt 23, and cold offset can be prevented. Further, the toner image carried on the sheet X has a cohesive force that is heated at a low temperature and does not break when passing near the exit of the fixing nip portion 27, thereby preventing hot offset. it can.

Further, in the fixing belt 23, the extending portion 23 a on the fixing nip portion 27 side is stretched in a tension state, so that a normal force corresponding to the belt tension is applied to the pressure roller 25 in the fixing nip portion 27. It acts and a stable fixing pressure can be obtained.
Further, since the extending portion 23b opposite to the fixing nip portion 27 is stretched in a tensionless state, the fixing belt 23 is deformed by the distortion of the fixing belt 23 itself, the distortion of the sectional shape of the heating roller 21 or the driving roller 22, or the like. The movement can be absorbed by the tension portion 23b, and the displacement of the fixing belt 23 in the axial direction of the heating roller 21 and the driving roller 22 can be reduced.

  Although the embodiments of the fixing device and the image forming apparatus according to the present invention have been described above, the present invention is not limited to the above-described embodiments, and can be appropriately changed without departing from the spirit of the present invention. For example, in the above-described embodiment, heat radiation black coating is applied to the inner peripheral surface of the heating roller 21 to form the high emissivity region A, and the raw tube of the heating roller 21 made of aluminum or the like is exposed to reduce low radiation. Although the rate region B is formed, in the present invention, the high emissivity region may be formed by applying another coating having a high emissivity. Moreover, you may form a high emissivity area | region by performing a chemical process on the internal peripheral surface of a heating roller (heating member), for example, by oxidizing the internal peripheral surface of an iron heating roller (heating member) The inner peripheral surface of the heating roller may be discolored to form a high emissivity region. Further, a low emissivity region may be formed by applying a coating having a low emissivity or coating a low emissivity material on the inner peripheral surface of the heating roller, for example, a heating roller made of a black material having a high emissivity. The low emissivity region may be formed by coating a reflective film on the inner peripheral surface of the film.

In the above-described embodiment, the sheet X is configured to pass through the center of the fixing belt 23, and as illustrated in FIG. 4, the high emissivity region A formed on the inner peripheral surface of the heating roller 21. However, in the present invention, as shown in FIG. 8A, the sheet X is passed through in a state where the sheet X is brought close to one side of the belt, and the high emissivity is obtained. The region A may have a stepped shape with one side approached.
In the above-described embodiment, as shown in FIG. 4, the high emissivity region A is formed in a step shape, and its width dimensions L1 to L3 are changed stepwise in the circumferential direction. However, in the present invention, as shown in FIG. 8B, the high emissivity region A is formed in an inclined shape, and the width dimension of the high emissivity region A is continuously changed in the circumferential direction. May be.

  In the above-described embodiment, the rotation mechanism 28 that intermittently rotates the heating roller 21 includes a combination of the stepping motor 31 and the optical sensor 34 that detects the initial rotation position of the heating roller 21. In the present invention, the heating roller may be intermittently rotated by a rotating mechanism including a solenoid plunger, a cam gear, an initial position detection switch, and the like. In addition, power is guided to the heating roller from another power source (for example, the driving source of the driving roller 22) via a gear, a belt, and the like, and a clutch is interposed in the middle, and heating is performed by switching the clutch. The roller may be intermittently rotated.

  In the above-described embodiment, the radiant heat source 24 is provided with directivity by covering the radiant heat source 24 with the directional cover 30 formed of a cylindrical member having a C-shaped cross section. A reflection film may be coated on the surface of the main body portion with the belt winding portion side opened so that the radiation heat source has directivity.

  In the above-described embodiment, the fixing belt 23 is supported by the heating roller 21 and the driving roller 22. However, in the present invention, in addition to the driving roller (supporting roller) driven by the driving mechanism, the fixing belt (belt). ) May be provided.

  In the above-described embodiment, the heating roller 21 and the driving roller 22 are in contact with the pressure roller 25 via the fixing belt 23. However, the present invention includes a heating roller (heating member) and a driving roller (supporting member). Aside from the pressure roller (pressure member), a pinch roller is provided on each side of the heating roller and the driving roller, and the fixing belt (belt) wound around the heating roller is heated. It is good also as a structure pinched with the roller and the pinch roller. Also, either the heating roller or the driving roller (for example, the downstream roller) is disposed away from the pressure roller, and the other (for example, the upstream roller) is brought into contact with the pressure roller via the fixing belt. Furthermore, a configuration may be adopted in which a pinch roller is disposed on the side of one roller separated from the pressure roller. Accordingly, a pressure gradient can be applied to the fixing nip portion, and the toner image can be more reliably fixed to the sheet. Further, according to the present invention, the heating roller and the driving roller may be pressed against the pressure roller via the fixing belt with different pressing forces, respectively, whereby a pressure gradient can be applied to the fixing nip portion, The toner image can be fixed more reliably.

  In the present invention, a cleaning mechanism that removes and cleans toner adhering to the surface of the fixing belt may be appropriately installed. As the cleaning mechanism, for example, fixing to a heating roller on the upstream side containing a heat source is possible. There are some which consist of a pinch roller pressed by a belt and a pad-like or rotary brush-like removing member pressed against the pinch roller.

  In addition, the configurations of the modified examples of the above-described embodiments may be combined as appropriate, and the configurations in the above-described embodiments may be appropriately changed from known configurations without departing from the gist of the present invention. It is.

  The image forming units 3M, 3Y, 3C, and 3BK in the above-described embodiment correspond to the image forming unit according to the present invention, and the heating roller 21 in the above-described embodiment corresponds to the heating member according to the present invention. The driving roller 22 in the above embodiment corresponds to a support member according to the present invention, the fixing belt 23 in the above embodiment corresponds to a belt according to the present invention, and the pressure roller 25 in the above embodiment corresponds to the present invention. Corresponding to the pressure member, the directional cover 30 in the above embodiment corresponds to the directional means according to the present invention, the sheet X in the above embodiment corresponds to the recording medium according to the present invention, and in the above embodiment. The width dimensions L1 to L3 of the high emissivity region A correspond to the axial dimensions of the high emissivity region according to the present invention.

1 is a diagram illustrating a schematic configuration of a main part of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a diagram illustrating a schematic configuration of a main part of a fixing device according to an embodiment of the present invention. It is sectional drawing showing the heating member in embodiment which concerns on this invention. It is an expanded view showing the internal peripheral surface of the heating member in embodiment which concerns on this invention. It is a perspective view showing the rotation mechanism in embodiment concerning this invention. It is a perspective view showing the rotation mechanism in embodiment concerning this invention. It is a block diagram showing the control means in embodiment which concerns on this invention. It is an expanded view showing the internal peripheral surface of the heating member in other embodiment which concerns on this invention.

Explanation of symbols

1 Image forming apparatus 3M, 3Y, 3C, 3BK Image forming unit (image forming means)
4 Fixing device 21 Heating roller (heating member)
22 Drive roller (support member)
23 Fixing Belt (Belt)
24 Radiant heat source 25 Pressure roller (Pressure member)
27 Fixing nip portion 28 Rotating mechanism 29 Control means 30 Direction cover (Direction means)
A High emissivity area B Low emissivity area X Sheet (recording medium)

Claims (3)

An endless belt is wound around a cylindrical heating member and a support member that contain a radiant heat source, and a pressure member is pressed against the belt to form a fixing nip portion between the belt and the pressure member. In the fixing device for fixing the toner image to the recording medium by passing a recording medium on which the toner image is electrostatically carried through the fixing nip portion,
The inner peripheral surface of the heating member has a radiation rate required to heat the fixing nip portion to the fixing temperature by radiant heat of the radiant heat source, and has a stepped or inclined shape and has an axial dimension in the circumferential direction. A different high emissivity region and a low emissivity region having a lower emissivity than the high emissivity region, respectively,
A portion of the high emissivity region having an axial dimension corresponding to the width dimension of the recording medium is disposed at a position where the rotation mechanism for rotating the heating member and the belt and the heating member are in contact with each other. As described above, the fixing device is provided with control means for controlling the rotation mechanism. The fixing device according to claim 1.
A fixing device comprising a directivity unit that radiates heat only where the belt and the heating member are in contact with each other so that the radiation heat source has directivity. In an image forming apparatus provided with image forming means for electrostatically transferring a toner image to a recording medium and supporting the toner image on the recording medium,
3. An image forming apparatus comprising the fixing device according to claim 1, wherein the toner image on the recording medium is fixed to the recording medium.

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