JP2009042615A - Fixing device and electrophotographic apparatus equipped with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device capable of easily obtaining uniform temperature distribution in an axial direction regardless of paper passing width, securing rigidity and realizing the shortening of a rise time accompanying thinning simultaneously and improving processability and versatility, and also, without bring about an increase in the number of components and a complicated constitution. <P>SOLUTION: The fixing device 20 is configured to fix an unfixed toner carried on a recording medium 11 onto the recording medium 11 at a nip part 38. A first heat roller 23 incorporates a first heat source 29 in a position corresponding to one of the center part and each end part of the paper passing area L. A second heat roller 24 incorporating a second heat source 30 in a position corresponding to the other of the center part and each end part of the paper passing area L is brought in contact with the fixing belt 25, and the fixing belt 25 is stretched on a small-diameter roller 26 disposed on the downstream side of the nip part 38, in addition to the first heat roller 23 and the fixing roller 21. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a heat fixing used to heat and fix an image made of heat-meltable unfixed toner formed on a recording medium surface in an electrophotographic recording apparatus such as a copying machine, a facsimile, and an electrophotographic printer. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a type fixing device and an electrophotographic apparatus including the fixing device.

  For example, in an image forming apparatus of an electrophotographic recording apparatus, as a method for fixing an unfixed toner image formed on a recording medium such as paper or film, there is a heat fixing method in which toner is welded by heat and fixed on the recording medium. It is used. Various methods are known as the heat fixing method. Among them, the belt fixing method is most widely used because of its high thermal efficiency and safety. A fixing device 60 using this belt fixing method is shown in FIG.

  As shown in FIG. 6, the fixing device 60 includes a fixing roller 61, a pressure roller 62, a heating roller 63, a fixing belt 64, a tension roller 65, and a separation mechanism (separation claw) 66. In the fixing device 60, an endless fixing belt 64 is mounted so as to go around the fixing roller 61 and the heating roller 63, and a tension roller 65 is provided to apply tension to the fixing belt 64. In the fixing belt 64, a release layer made of a fluororesin or the like is formed on the surface 64a (a surface that comes into contact with a recording medium S described later and adheres toner s). In order to heat the fixing belt 64, the heating roller 63 is provided with a heat source 67.

  The heat source 67 heats the heating roller 63 so as to heat the toner s attached to the recording medium S described later to a temperature necessary for fixing. As the heat source 67, a halogen lamp or a ceramic heater provided along the axis of the heating roller 63 is used. In order to fix the heated toner s to the recording medium S, the pressure roller 62 is pressed against the fixing roller 61 with the fixing belt 64 interposed.

  The pressure roller 62 is provided with a biasing force toward the fixing roller 61 by a biasing means (not shown), thereby forming a nip portion 68 with the fixing roller 61. A recording medium S on which an unfixed toner image (s) is formed by attaching unfixed toner s in a desired shape on one side surface is inserted into the nip portion 68. In this nip portion 68, the fixing belt 64 heated via the heating roller 63 and the pressure roller 62 are rotated so that the recording medium S is conveyed, and accordingly, an unfixed toner image (s) on the recording medium S is conveyed. ) Is pressed while being heated, and the toner is fixed on the recording medium S as a desired image. Since the recording medium S may stick to the fixing belt 64 due to the adhesion force of the toner fixed thereon, the recording medium S is peeled from the fixing belt 64 on the downstream side in the circulation direction of the fixing belt 64. A separation mechanism (separation claw) 66 is provided.

  In the fixing device 60, a temperature sensor 69 is in contact with the surface 64 a of the fixing belt 64 at a position corresponding to the heating roller 63, and the temperature of the nip portion 68 is appropriately determined based on the detection result of the temperature sensor 69. The amount of power supplied to the heat source 67 is controlled so as to be maintained at a temperature at which the toner s can be fixed to the toner.

  For the heating roller 63 of the fixing device 60, an aluminum alloy having good thermal conductivity and rigidity is used as the core metal in consideration of appropriately stretching the fixing belt 64 while ensuring the heating efficiency of the heat source 67. Used. As shown in FIG. 7 (a), this mandrel is formed by drawing a cylindrical long cylindrical tube extruded from an aluminum alloy material (by drawing) to form a long cylindrical tube, The long cylindrical tube is cut into a predetermined length to form a metal cylindrical tube (roller core) 70 having a uniform outer shape and inner diameter. The cylindrical metal tube (roller core) 70 is made thin by reducing the outer peripheral surface by cutting or grinding the outer peripheral surface using a diamond tool, for example, and making the surface uniform. It becomes. Further, as shown in FIG. 7B, a coating made of a fluororesin or the like is applied to the outer peripheral surface of the metal cylindrical tube (roller core metal) 70 in order to suppress slippage with the fixing belt 64. A finishing process is performed in which the resin layer 70a is formed by firing later. Further, in place of the coating with the resin layer 70a, the outer peripheral surface of the metal cylindrical tube (roller core) may be subjected to a finishing process such as an alumite process or a sand blast process (roughening). The heating roller 63 formed in this way has a detent member (not shown) for suppressing twisting of the circulating fixing belt 64 and meandering of the fixing belt 64 as necessary. Provided.

  By the way, due to recent demands for energy saving and cost reduction, the heating roller 63 is required to be further thinned in order to improve thermal conductivity. That is, it is desired to reduce the time required to reach a fixing temperature by thinning the roller core (also referred to as the fixing roller rising time or warm-up time), and to promote power saving in copying machines and the like. It is rare.

  However, when the roller core metal is made thinner, the rigidity of the roller core metal is reduced, which causes a conveyance failure such as empty slip, twist or meandering in the fixing belt 64. Further, if the roller metal core is thinned, the heat capacity of the heating roller 63 itself is reduced, so that it is difficult to store heat in the heating roller 63. For this reason, the axis line of the sheet passing area set along the axial direction of the roller core bar, for example, when an A4 size sheet is continuously passed vertically by a device capable of handling A3 size sheets. When paper having a width smaller than the width in the direction is continuously passed, the fixing belt 64 loses heat at the central portion, which is the paper passing portion, and the temperature at the central portion decreases. For this reason, when the heating roller 63 is heated by the heat source 67 so as to raise the temperature of the central portion of the fixing belt 64 to a temperature at which the toner s can be fixed, both end portions which are outer portions of the sheet that are not deprived of heat by the sheet passing. Temperature rises higher than the temperature of the paper passing portion (center portion), resulting in a temperature difference, and both ends thereof are overheated.

  Therefore, as shown in FIG. 6, a halogen heater (67 a) for heating the central portion of the heating roller 63 and a halogen heater for heating both ends of the heating roller 63 in the roller core of the heating roller 63. (67b) and a method of controlling the temperature of each halogen heater independently has been proposed (see, for example, Patent Documents 1 to 17).

  According to this method, the heating roller 63 is used when the temperature of the central portion of the fixing belt 64, which has been lowered by continuously passing paper having a width smaller than the width of the paper passing area, is raised to the toner fixing temperature. The temperature at the center can be increased without increasing the temperature at both ends. Thereby, it is possible to suppress the temperature at both ends of the fixing belt 64 from rising above the temperature at the center.

  However, in a system in which two heat sources, a halogen heater (heat source) for heating the central portion of the heating roller and a halogen heater (heat source) for heating both ends of the heating roller, are arranged in the roller metal core. Since the inner diameter of the roller core becomes larger than when one halogen heater (heat source) is disposed in the roller core, the heat capacity of the heating roller itself increases, and the temperature of the heating roller rises to a predetermined temperature. It takes a long time to complete. For this reason, the time until the heat of the heating roller is transmitted to the fixing roller via the fixing belt becomes long, and it becomes difficult to shorten the time until the temperature of the fixing roller rises to the toner fixing temperature, that is, the rise time.

  In addition to the above-described method, although not shown, a method has been proposed in which a preheating chamber is provided at the inlet of the fixing device and the recording medium is preheated before the toner is fixed to the recording medium (for example, Patent Document 18). reference).

  According to this method, since the recording medium is heated by passing through the preheating chamber before being conveyed to the fixing device, the amount of heat taken by the recording medium from the central portion of the fixing belt is reduced when the recording medium is passed. Therefore, it is possible to suppress a temperature drop at the center of the fixing belt. As a result, the amount of heating by the heat source for raising the temperature at the center of the fixing belt, the temperature of which has been lowered due to paper passing, to the toner fixing temperature is reduced, so that the temperature rise at both ends of the fixing belt can be suppressed.

  However, in this method, the temperature of the preheating chamber cannot be controlled, and the temperature depends on the atmosphere, and the fixing device is increased in size. In addition, the rise time cannot be shortened.

  In addition to the above-described methods, although not shown, in order to suppress a temperature rise at both ends of the fixing belt, a heat transfer member is brought into contact with the fixing roller to contact both ends of the fixing belt passing through the fixing roller. There has been proposed a method of absorbing heat or releasing heat at both ends of the fixing belt passing through the fixing roller by providing an electrode member on the fixing roller (see, for example, Patent Documents 19 to 21).

  However, in these methods, the rise time cannot be shortened and the rigidity of the roller core cannot be enhanced.

  Thus, there is a contradictory relationship between the suppression of the temperature rise at the end of the fixing belt and the shortening of the rise time of the fixing roller, and a technique that satisfies both is desired.

  In addition, even if the heat source extending in the axial direction inside the long heating roller emits non-uniform radiant energy when viewed in the long direction, the surface temperature of the heating roller is centered. In order to make uniform the entire area from the two ends to the both ends, the inner wall surface of the heating roller should be arranged with a member having a different absorption rate according to the density of the radiant energy, and a thickness different according to the density of the radiant energy. (For example, refer to Patent Document 22). However, even with this method, the rise time cannot be shortened.

From this, it is possible to easily obtain a uniform temperature distribution in the axial direction regardless of the sheet passing width, to ensure rigidity, and at the same time, to shorten the rise time due to the thinning, and in addition to workability and general purpose The invention which can improve property is proposed (refer patent document 23).
Japanese Patent No. 3151551 JP-A-4-3377781 JP-A-4-337778 JP-A-4-337778 JP-A-4-337784 JP-A-4-337785 Japanese Patent No. 3184489 JP 2001-201978 A JP 2001-318557 A JP-A-11-202673 Japanese Patent No. 3446828 JP 2006-215143 A JP-A-11-24469 JP-A-2005-258108 JP 2005-258109 A JP 2005-258110 A JP 2005-258111 A JP-A-9-34283 JP-A-9-127811 JP-A-10-123873 JP-A-10-115993 JP 2006-337521 A JP 2006-11061 A

  However, in the invention of Patent Document 23, since the recording medium on which the toner is fixed in the nip portion may stick to the fixing belt so as to surround the fixing roller due to the adhesion force of the toner, the fixing belt is circulated. Although it is desirable to provide a separation claw (see the separation mechanism 66 in FIG. 6) on the downstream side of the nip portion as viewed in the direction, the number of components increases, the configuration becomes complicated, and the fixing device increases in size.

  In addition, it is desirable to realize further energy saving and cost reduction as compared with the invention of Patent Document 23.

  The present invention has been made in view of the above problems, and can easily obtain a uniform temperature distribution in the axial direction regardless of the sheet passing width, and can ensure rigidity and at the same time shorten the rise time due to thinning. And a fixing device that can improve processability and versatility, and that does not increase the number of components and complicate the configuration, and an electrophotographic apparatus including the fixing device. There is.

  In order to solve the above-mentioned problem, in the invention according to claim 1, an endless fixing belt is laid around the first heating roller and the fixing roller, and the fixing roller is pressed through the fixing belt. A fixing device in which a roller is pressed and a nip portion is formed at the pressing portion, and unfixed toner carried on the recording medium conveyed to the nip portion as the fixing belt circulates is fixed on the recording medium. The first heating roller includes a first heat source at a position corresponding to either the central portion or both end portions of the sheet passing region set along the axial direction, and the fixing belt includes A second heating roller containing a second heat source is brought into contact with a position corresponding to the other of the central portion or the both end portions in the sheet passing area, and is downstream of the nip portion as viewed in the circulation direction of the fixing belt. The small-diameter rollers are provided, the fixing belt is characterized in that in addition to the first heating roller and the fixing roller are bridged to around the small diameter roller.

  A second aspect of the present invention is the fixing device according to the first aspect, wherein the small-diameter roller has a smaller outer diameter than the fixing roller.

  A third aspect of the present invention is the fixing device according to the first or second aspect, wherein the small-diameter roller is a tension roller that is movable to apply tension to the fixing belt. Features.

  A fourth aspect of the present invention is the fixing device according to any one of the first to third aspects, wherein the second heating roller contacts the first heating roller with the fixing belt interposed therebetween. It is contacted.

  The invention according to claim 5 is the fixing device according to claim 4, wherein each of the first heating roller and the second heating roller has a cylindrical roller core, The first roller cored bar is a thin part in which the central part in the sheet passing region is thinner than the thickness of the both end parts. In the first heating roller, the first roller cored bar The first heat source is provided in the first roller core corresponding to the thin-walled portion, and the second roller core of the second heating roller is configured such that the both end portions in the sheet passing region are the central portion of the wall. In the second heating roller, the second heat source is provided in the second roller metal core corresponding to the two thin wall parts of the second roller metal core. It is characterized by.

  The invention according to claim 6 is the fixing device according to claim 5, wherein each of the first roller core metal and the second roller core metal is made of a manganese-based aluminum alloy.

  The invention according to claim 7 is the fixing device according to any one of claims 1 to 6, wherein the small-diameter roller is provided with a heat insulating layer on an outer surface. .

  According to an eighth aspect of the present invention, an endless fixing belt is looped around the heating roller and the fixing roller, and the pressure roller is pressed against the fixing roller with the fixing belt interposed therebetween. A fixing device in which a nip portion is formed and unfixed toner carried on a recording medium conveyed to the nip portion as the fixing belt circulates is fixed on the recording medium. In order to peel off the recording medium on which the toner is fixed in the nip portion from the fixing belt by using a restoring force to return to the state, the fixing belt is located downstream of the nip portion in the circulation direction. In addition to the heating roller and the fixing roller, the roller is stretched over the small-diameter roller so as to go around a small-diameter roller having a smaller outer diameter than the fixing roller. To.

  According to the ninth aspect of the present invention, an endless fixing belt is looped around the first heating roller and the fixing roller, and the pressure roller is pressed against the fixing roller with the fixing belt interposed therebetween. A fixing device in which a nip portion is formed at a location and unfixed toner carried on a recording medium conveyed to the nip portion as the fixing belt circulates is fixed on the recording medium. The roller incorporates a first heat source at a position corresponding to either the central portion or both ends of the sheet passing region set along the axial direction, and the fixing belt includes the first heat source in the sheet passing region. A second heating roller containing a second heat source is in contact with the center portion or a position corresponding to the other of the both end portions with the fixing belt interposed therebetween.

  The invention according to claim 10 is the fixing device according to claim 9, wherein each of the first heating roller and the second heating roller has a cylindrical roller core, The first roller cored bar is a thin part in which the central part in the sheet passing region is thinner than the thickness of the both end parts. In the first heating roller, the first roller cored bar The first heat source is provided in the first roller core corresponding to the thin-walled portion, and the second roller core of the second heating roller is configured such that the both end portions in the sheet passing region are the central portion of the wall. In the second heating roller, the second heat source is provided in the second roller metal core corresponding to the two thin wall parts of the second roller metal core. It is characterized by.

  An eleventh aspect of the present invention is an electrophotographic apparatus comprising the fixing device according to any one of the first to tenth aspects.

  In the fixing device according to the present invention, since the small-diameter roller is provided on the downstream side of the nip portion as viewed in the circulation direction of the fixing belt, the recording medium on which the toner is fixed in the nip portion is fixed by the adhesion force of the toner. Even when the recording medium is stuck to the belt, when the recording medium tries to surround the small-diameter roller, a restoring force is applied to the recording medium to return to the original flat state. Since the recording medium is peeled off from the fixing belt at the bent portion, it is possible to prevent the recording medium from sticking to the fixing belt so as to surround the small-diameter roller. For this reason, it is not necessary to provide a separation mechanism such as a separation claw, and it is possible to prevent an increase in the number of components and to prevent the configuration from being complicated, and to reduce the size of the fixing device.

  In addition, the first heating roller and the second heating roller are individually arranged, and both the heating roller can individually heat the center portion and both end portions in the sheet passing region. Compared to a heating roller provided with two types of heat sources, the inner diameter of each heating roller can be reduced, and the heat capacity of each heating roller can be reduced. For this reason, the time required for the temperature of each heating roller to rise to a predetermined temperature is shorter than before, and the time required for heat to be transferred from the respective heating roller heated by each heat source to the fixing roller via the fixing belt. Is shortened. Therefore, the rise time of the fixing roller can be surely shortened, and the power consumption can be reduced.

  Furthermore, if it is necessary to raise the temperature of the center of the fixing belt, which has been lowered by continuously passing paper having a width smaller than the width of the paper passing area, to the toner fixing temperature, both ends of the fixing belt The temperature of the center portion of the fixing belt can be increased by the first heating roller or the second heating roller without increasing the temperature of the portion.

  In addition to the above-described configuration, if the small-diameter roller has a smaller outer diameter than the fixing roller, the small-diameter roller has a smaller outer diameter than the fixing roller. Even in the case where the recording medium is attached to the fixing belt so as to be wound around the fixing roller by the adhesion force of the toner in the apparatus, the small-diameter roller has a smaller radius of curvature than the fixing roller. Since a large restoring force acts, the recording medium can be peeled from the fixing belt.

  In addition to the above-described configuration, if the small-diameter roller is a tension roller that can be moved to apply tension to the fixing belt, the small-diameter roller also has a function as a tension roller. Can be further reduced in size.

  In addition to the above-described configuration, if the second heating roller is in contact with the first heating roller with the fixing belt interposed, the first heating roller and the second heating roller may Since they are arranged so as to be sandwiched, the heat of each heat source can be more efficiently transmitted to the fixing belt.

  In addition, since the second heating roller is disposed outside the fixing belt around the first heating roller, the fixing roller, and the small-diameter roller, the belt length of the fixing belt can be shortened and the fixing device can be further reduced. It can be downsized.

  In addition to the above-described configuration, each of the first heating roller and the second heating roller has a cylindrical roller core, and the first roller core of the first heating roller is in the sheet passing area. The central portion is a thin portion that is thinner than the thickness of the both end portions. In the first heating roller, the first heat source corresponds to the thin portion of the first roller core. Provided in one roller cored bar, the second roller cored bar of the second heating roller is a thin part in which the both end portions in the sheet passing region are thinner than the thickness of the central part, In the second heating roller, if the second heat source is provided in the second roller core corresponding to the both thin portions of the second roller core, The first heat source corresponding to the thin part at the center of the sheet passing area of one roller cored bar In the second heating roller, since the second heat source is provided corresponding to the thin portion at the center of the sheet passing area of the second roller core metal, the heat absorption of each roller core metal from each heat source Efficiency can be increased. For this reason, the time required for the temperature of each roller core to rise to a predetermined temperature can be further shortened, and heat is transmitted from each roller core heated by each heat source to the fixing roller via the fixing roller. Can be shortened.

  Further, portions other than the thin portion of the roller cored bar of the first heating roller, that is, both end portions in the sheet passing region of the roller cored bar, and portions other than the thinned portion of the roller cored bar of the second heating roller, that is, The central part in the paper passing area can be formed thick. Thereby, the fall of the rigidity of each heating roller by thinning of each roller core metal can be suppressed reliably.

  In addition to the above-described configuration, if the first roller cored bar and the second roller cored bar are each made of a manganese-based aluminum alloy, the first roller cored bar and the second roller cored bar have a thermal conductivity. It can be made higher than other aluminum alloys and the creep property can be increased. Thereby, the process of a 1st roller core metal and a 2nd roller core metal can be made easy.

  In addition to the above-described configuration, if the small diameter roller is provided with a heat insulating layer on the outer surface, the heat of the fixing belt is conducted to the small diameter roller because the small diameter roller is provided with a heat insulating layer. That is, it is possible to prevent the heat of the fixing belt from being taken away.

  An endless fixing belt is stretched around the heating roller and the fixing roller, and a pressure roller is pressed against the fixing roller with the fixing belt interposed therebetween, so that a nip portion is formed at the pressing position, and the fixing A fixing device for fixing unfixed toner carried on a recording medium conveyed to the nip portion as the belt circulates on the recording medium, and having a restoring force for returning the recording medium to an original state. In order to peel off the recording medium on which toner is fixed in the nip portion from the fixing belt, the fixing belt is provided by a fixing roller provided on the downstream side of the nip portion as viewed in the circulation direction. In addition to the heating roller and the fixing roller, the small-diameter roller spans the small-diameter roller having a small outer diameter. Even if the recording medium on which the toner is fixed in the nip portion is stuck to the fixing belt by the adhesion force of the toner by the small-diameter roller provided on the downstream side of the nip portion, the fixing belt follows the small-diameter roller. Since the recording medium is peeled off from the fixing belt by the restoring force acting on the recording medium at the bent portion, it is possible to prevent the recording medium from sticking to the fixing belt. For this reason, it is not necessary to provide a separation mechanism such as a separation claw, and it is possible to prevent an increase in the number of components and to prevent the configuration from being complicated, and to reduce the size of the fixing device.

  An endless fixing belt is stretched around the first heating roller and the fixing roller, a pressure roller is pressed against the fixing roller with the fixing belt interposed, and a nip portion is formed at the pressure contact point. A fixing device that fixes unfixed toner carried on a recording medium conveyed to the nip portion as the fixing belt circulates on the recording medium, wherein the first heating roller extends along an axial direction thereof. A first heat source is incorporated at a position corresponding to either the central portion or both end portions of the sheet passing region set in the above, and the fixing belt has the central portion of the sheet passing region or both end portions thereof. Assuming that the second heating roller containing the second heat source is in contact with the fixing belt through a position corresponding to the other, the first heating roller and the second heating roller sandwich the fixing belt. Since it was urchin disposed, it is possible to transfer heat of each heat source to more efficiently fixing belt.

  In addition, since the second heating roller is disposed outside the fixing belt around the first heating roller, the fixing roller, and the small-diameter roller, the belt length of the fixing belt can be shortened and the fixing device can be further reduced. It can be downsized.

  In addition to the above-described configuration, each of the first heating roller and the second heating roller has a cylindrical roller core, and the first roller core of the first heating roller is in the sheet passing area. The central portion is a thin portion that is thinner than the thickness of the both end portions. In the first heating roller, the first heat source corresponds to the thin portion of the first roller core. Provided in one roller cored bar, the second roller cored bar of the second heating roller is a thin part in which the both end portions in the sheet passing region are thinner than the thickness of the central part, In the second heating roller, if the second heat source is provided in the second roller core corresponding to the both thin portions of the second roller core, The first heat source corresponding to the thin part at the center of the sheet passing area of one roller cored bar In the second heating roller, since the second heat source is provided corresponding to the thin portion at the center of the sheet passing area of the second roller core metal, the heat absorption of each roller core metal from each heat source Efficiency can be increased. For this reason, the time required for the temperature of each roller core to rise to a predetermined temperature can be further shortened, and heat is transmitted from each roller core heated by each heat source to the fixing roller via the fixing roller. Can be shortened.

  Further, portions other than the thin portion of the roller cored bar of the first heating roller, that is, both end portions in the sheet passing region of the roller cored bar, and portions other than the thinned portion of the roller cored bar of the second heating roller, that is, The central part in the paper passing area can be formed thick. Thereby, the fall of the rigidity of each heating roller by thinning of each roller core metal can be suppressed reliably.

  An electrophotographic apparatus including the fixing device having the above-described configuration can be a downsized electrophotographic apparatus while reducing power consumption.

  According to the present invention, it is possible to easily obtain a uniform temperature distribution in the axial direction regardless of the sheet passing width, to secure rigidity and at the same time to shorten the rise time due to the thinning, and the workability In addition, it is possible to provide a fixing device and an electrophotographic apparatus that can improve versatility and that do not increase the number of components and make the configuration complicated.

  Hereinafter, embodiments of a fixing device according to the present invention, an electrophotographic apparatus including the fixing device, and a method of manufacturing a heating roller used in the apparatus will be described with reference to the drawings.

<Embodiment 1>
FIG. 1 schematically shows an image forming apparatus 10 as an electrophotographic apparatus including the fixing device 20 according to the first embodiment of the present invention. As shown in FIG. 1, the image forming apparatus 10 according to the first embodiment includes four image forming apparatuses 10 along the conveying path defined by the endless conveying belt 12 that surrounds the driving roller 12a and the driven roller 12b. This is a so-called tandem type full-color image forming apparatus in which image forming units 13M, 13C, 13Y and 13Bk (hereinafter also referred to as each image forming unit 13 when colors are not distinguished) are sequentially arranged. The image forming unit 13 is an image forming unit that forms a toner image. The image forming unit 13M is magenta, the image forming unit 13C is cyan, the image forming unit 13Y is yellow, and the image forming unit 13Bk is black. Each color toner image is formed. Each image forming unit 13 is arranged in alignment with the above-described conveyance path, and forms each toner image on a recording sheet 11 as a recording medium conveyed on the conveyance belt 12 from the paper feeding mechanism 14. A full color image is formed.

  Each image forming unit 13 has the same basic configuration as each other, and each includes photosensitive drums 1M, 1C, 1Y and 1Bk as image carriers, and charging rollers 2M, 2C, 2Y and 2Bk as charging means, Scanning image forming devices 3M, 3C, 3Y and 3Bk as latent image forming means comprising a beam scanning system, developing devices 4M, 4C, 4Y and 4Bk as developing means, and transfer rollers 5M, 5C and 5Y as transferring means And 5Bk and cleaning devices 6M, 6C, 6Y and 6Bk as cleaning means. The charging rollers 2M, 2C, 2Y and 2Bk are sequentially arranged around each photosensitive drum (image carrier) along the rotation direction.

  In each image forming unit 13, the surfaces (peripheral surfaces) of the photosensitive drums 1M, 1C, 1Y, and 1Bk are neutralized by a neutralizing unit (not shown), and then positive or negative from the charging rollers 2M, 2C, 2Y, and 2Bk. These are uniformly charged by one of the charges. On the photosensitive drums 1M, 1C, 1Y and 1Bk, electrostatic latent images are formed by optical scanning of the scanning imaging devices 3M, 3C, 3Y and 3Bk. The electrostatic latent images on the photosensitive drums 1M, 1C, 1Y, and 1Bk are visualized by adhesion of the respective color toners supplied from the developing devices 4M, 4C, 4Y, and 4Bk. The visualized images of the toners of the respective colors together with the conveying belt 12 between the respective photosensitive drums 1M, 1C, 1Y and 1Bk on which the image is formed and the corresponding transfer rollers 5M, 5C, 5Y and 5Bk. The images are sequentially transferred onto the recording paper 11 that passes there.

  After the transfer, the color toner remaining on the photosensitive drums 1M, 1C, 1Y and 1Bk is removed by the cleaning devices 6M, 6C, 6Y and 6Bk. Thereafter, in order to repeat a new image forming cycle, each image forming unit 13 can prepare for the next image formation, that is, be able to shift to the above operation again.

  On the other hand, the recording paper 11 on which the multiple color images are transferred, that is, the recording paper 11 on which the unfixed toner image s (see FIG. 2) is formed by passing through the image forming units 13 along the above-described conveyance path. Is sent to the fixing device 20 for fixing the color image.

  FIG. 2 is an explanatory diagram schematically showing the configuration of the fixing device 20 according to the present invention. The fixing device 20 is a heat fixing method, and includes a fixing roller 21, a pressure roller 22, a first heating roller 23, a second heating roller 24, a fixing belt 25, and a small diameter roller 26. In the fixing device 20, an endless fixing belt 25 is attached so as to go around the fixing roller 21, the first heating roller 23, and the small diameter roller 26.

  The fixing belt 25 is circulated in the clockwise direction when the front view of FIG. 2 is viewed. A release layer made of a fluororesin or the like is formed on the surface 25a of the fixing belt 25, although not shown. In order to heat the fixing belt 25, a first heating roller 23 and a second heating roller 24 are provided.

  The first heating roller 23 is configured by providing a resin layer 27 a on a cylindrical first roller core 27, and the second heating roller 24 is provided by a resin layer 28 a on a cylindrical second roller core 28. Is configured. The first heating roller 23 and the second heating roller 24 are provided with support portions (see reference numerals 27b and 28b in FIG. 3) at both ends, and both the support portions are provided on a support frame body of the fixing device 20 ( 3) (see reference numerals 27c and 28c in FIG. 3). Thereby, the first heating roller 23 and the second heating roller 24 rotate according to the circulation of the fixing belt 25, respectively. In the first embodiment, each of the first roller core metal 27 and the second roller metal core 28 is made of a manganese-based aluminum alloy. The schematic shape is an outer diameter φ10 mm of each support portion at both ends. Other than the above, the outer diameter is 20 mm, the length is 350 mm, and the wall thickness is 0.6 mm.

  In the first heating roller 23 and the second heating roller 24 (the first roller core metal 27 and the second roller core metal 28), a sheet passing region L (see FIG. 3) is set along each axis. . In the first embodiment, the sheet passing area L is equal to or greater than the A3 size recording paper in the horizontal width direction (see the recording paper 113 indicated by the two-dot chain line in FIG. 5) (the A3 size recording paper is the vertical direction). The width is such that it can be passed through.) The first roller core 27 of the first heating roller 23 includes a first heat source 29 corresponding to the central portion of the sheet passing region L (at the same position in the axial direction). A second heat source 30 is incorporated in the second roller core 28 so as to correspond to both end portions adjacent to the central portion of the sheet passing region L. Each of the first heat source 29 and the second heat source 30 uses a halogen heater. Further, in the fixing device 20, temperature sensors 31 for detecting the respective outer surface temperatures are arranged so as to be in contact with the fixing belt 25 in the vicinity of the first heating roller 23 and the second heating roller 24 (FIG. 2). In FIG. 2, only one is shown, but two are arranged in parallel in the width direction of the fixing belt 25 corresponding to each of the first heating roller 23 and the second heating roller 24).

  The fixing roller 21 around which the fixing belt 25 is wound is configured by providing an elastic layer 33 on an iron-based cored bar 32. In the first embodiment, the iron-based cored bar 32 has a body outer diameter φ30 mm, a wall thickness 1 mm, and a body length 346 mm. The elastic layer 33 is generally formed of a resin material made of silicone rubber. In the first embodiment, the rubber thickness is 1 mm. An auxiliary heat source (halogen heater) 34 is provided inside the fixing roller 21. Further, the fixing roller 21 is provided with a temperature sensor 35 for detecting the outer surface temperature, and the electric power to the auxiliary heat source 34 is maintained by the detection signal from the temperature sensor 35 in order to maintain the outer surface temperature appropriately. Supply is controlled. A pressure roller 22 is provided so as to be juxtaposed in the vicinity of the fixing roller 21.

  The pressure roller 22 is configured by providing an iron cored bar 36 with an elastic layer 37. In the first embodiment, the iron-based cored bar 36 has a body outer diameter φ24 mm, a wall thickness 2 mm, and a body length 354 mm. In addition, the elastic layer 37 is generally formed of a foamable silicone rubber and a heat-insulating resin material having a lower thermal conductivity than the elastic layer 33 of the fixing roller 21. In the first embodiment, the rubber thickness is 6 mm. Has been. The pressure roller 22 is pressed toward the fixing roller 21 via the fixing belt 25 by an urging force from an urging means (not shown) (see a circle indicated by a one-dot chain line). As a result, a nip portion 38 is formed at a contact portion between the pressure roller 22 and the fixing roller 21. A small-diameter roller 26 is provided on the downstream side in the circulation direction of the fixing belt 25 as viewed from the nip portion 38.

  The small-diameter roller 26 is configured by providing a heat insulating layer 26b on a metal core 26a made of stainless steel. In the first embodiment, the small-diameter roller 26 is configured such that the core metal 26a has a barrel outer diameter φ8 mm and a barrel length 350 mm, and the heat insulating layer 26b is bonded to a 1 mm thick nonwoven fabric. The small-diameter roller 26 can be moved by an urging mechanism 39 so that a desired tension force can be applied to the fixing belt 25 including the fixing roller 21 and the first heating roller 23 including itself. . In the first embodiment, the small-diameter roller 26 urges the fixing belt 25 by the urging mechanism 39 so that the belt tension of the fixing belt 25 is 10N. In the first embodiment, the urging mechanism 39 is provided on the support frame of the fixing device 20 and is configured to urge the fixing belt 25 with the shaft portion 39a as a fulcrum. The fixing belt 25 is circulated while maintaining an appropriate belt tension. When viewed in the circulation direction, the fixing belt 25 is bent so as to surround the small-diameter roller 26 and heads toward the upper end portion of the fixing roller 21. It is bent so as to surround the first heating roller 23, is bent so as to surround the first heating roller 23, and is directed to the nip portion 38 (lower end portion of the fixing roller 21). Will head to. Although illustration is omitted, a cleaning roller for removing the toner (s) attached to the surface 25a of the fixing belt 25 by offset may be provided as appropriate.

  As described above, the fixing device 20 according to the first embodiment uses a belt fixing method. In this fixing device 20, an unfixed toner image s (unfixed toner s is attached to one side in a desired shape is formed together with the fixing belt 25 heated by the first heating roller 23 and the second heating roller 24. The recording paper 11 (recording medium carrying unfixed toner) formed thereon is conveyed to the nip portion 38, and the unfixed toner image s on the recording paper 11 is pressurized while being heated. Then, it is fixed on the recording paper 11 as a desired color image.

  The recording paper 11 on which the unfixed toner image s is fixed as a desired color image in the nip portion 38 is carried out to the outside of the fixing device 20 (image forming apparatus 10) as the fixing belt 25 circulates. . At this time, in the fixing device 20, since the fixing belt 25 that has passed through the nip portion 38 is bent so as to surround the small-diameter roller 26, the recording paper 11 is prevented from sticking due to the adhesive force of the toner (s). Yes. This is due to the following.

  The recording paper 11 is flat before being transported by the paper feed mechanism 14 (see FIG. 1), and is a force for returning to the original flat state (the so-called stiffness of the recording paper 11). Hereinafter, it is also referred to as a restoring force. For this reason, in the fixing device 20, the restoring force of the recording paper 11 itself overcomes the adhesion force of the toner (s) that tries to stick the recording paper 11 to the fixing belt 25 bent so as to surround the small diameter roller 26. The recording paper 11 is peeled from the fixing belt 25. Therefore, in the fixing device 20 of the first embodiment, the fixing roller 21 is configured by providing an elastic core 33 having a rubber thickness of 1 mm on an iron-based core metal 32 having an outer diameter φ30 mm, and a small-diameter roller 26. However, a non-woven fabric having a thickness of 1 mm is bonded to a cored bar 9a having a barrel outer diameter of 8 mm, but a recording medium (recording paper in the above example) is conveyed to the nip portion 38 to fix unfixed toner. 11) If the outer diameter dimension of the small diameter roller 26 is set in consideration of the restoring force of the recording medium, the adhesive force of the toner, etc., which change according to the material of 11) and the curvature thereof (that is, the outer diameter dimension of the small diameter roller 26) Well, it is not limited to the first embodiment described above.

  In the fixing device 20 according to the first embodiment, the fixing belt 25 is bent from the nip portion 38 so as to surround the small-diameter roller 26 and heads toward the upper end portion of the fixing roller 21, so that it is bent along the small-diameter roller 26. Gravity acts on the upstream side of the recording paper 11 stuck to the fixing belt 25 at the location. The gravity acting on the upstream side of the recording paper 11 assists a restoring force that acts to separate the recording paper 11 from the fixing belt 25. Therefore, in the fixing device 20, the recording paper 11 can be peeled off from the fixing belt 25 more reliably.

  In contrast, in the conventional fixing device 60 shown in FIG. 6, the fixing belt 64 that has passed through the nip portion 68 is bent so as to surround the fixing roller 61, so that the fixing along the curvature of the outer peripheral surface of the fixing roller 61 is performed. The restoring force that acts on the curved recording medium S by sticking to the belt 64 cannot overcome the adhesion force of the toner, and the recording medium S does not peel from the fixing belt 64. Here, the fixing roller (including the fixing roller 21 of the first embodiment) is the length dimension of the nip portion as viewed in the recording medium conveyance direction in order to obtain a good fixing property of unfixed toner to the recording medium. From the viewpoint of securing the toner, it is required to have an outer diameter of a certain degree or more. Therefore, it is difficult to obtain a curvature that provides a restoring force that peels the recording medium from the fixing belt against the adhesion force of the toner. is there. For this reason, in the conventional fixing device 60, a separation mechanism (separation claw in the example of FIG. 6) is provided downstream of the nip portion 68 because the recording medium S sticks to the fixing belt 64 due to the adhesion force of the toner. 66) must be provided.

  Thus, in the fixing device 20 according to the present invention, the recording paper 11 can be separated from the fixing belt 25 without providing the separation mechanism (separation claw) 66 as in the conventional fixing device 60, and this fixing belt Thus, it is possible to reliably prevent the occurrence of a jam due to the sticking (wrapping) of the recording paper 11 to 25.

  In addition, since the fixing device 20 does not require the separation claw 66 as in the conventional fixing device 60, the configuration can be simplified and the size can be reduced.

  Further, in the fixing device 20, since the fixing belt 25 spans the fixing roller 21, the first heating roller 23, and the small diameter roller 26, the peripheral length (belt length) of the fixing belt 25 can be shortened. Therefore, the overall heat capacity can be reduced and the rise time can be shortened.

  In the fixing device 20, the pressure roller 22 around which the fixing belt 25 is stretched is provided with an elastic layer 37, and the small-diameter roller 26 is provided with a heat insulating layer 26b. Heat can be used more efficiently for fixing from the heat source 30 and the auxiliary heat source 34.

  In the fixing device 20, since a predetermined pressure from the small-diameter roller 26 is applied to the fixing belt 25 (functions as a tension roller), the fixing belt 25 may be twisted, shifted, or lifted by its driving. It is possible to reliably prevent the conveyance unevenness from occurring.

  In the fixing device 20, since the small-diameter roller 26 also functions as a tension roller, it is not necessary to separately provide the tension roller and the separation mechanism, and the configuration can be simplified and the size can be reduced.

  In the fixing device 20, the first heating roller 23 having the first heat source 29 and the second heating roller 24 having the second heat source 30 are individually arranged. Since the inner diameters of the first heating roller 23 (first roller core metal 27) and the second heating roller 24 (second roller core metal 28) can be reduced compared to the case where they are inserted together in the core metal, these The heat capacity can be reduced. For this reason, the time required to raise the first roller core 27 and the second roller core 28 to a predetermined temperature can be shortened as compared with the prior art, and the first roller core heated by each first heat source 29. It is possible to shorten the time until heat is transferred from the gold 27 and the second roller core 28 heated by the second heat source 30 to the fixing roller 21 via the fixing belt 25. Therefore, the rise time of the fixing roller 21 can be surely shortened, and the power consumption can be reduced.

  In the fixing device 20, the first heating roller 23 incorporates a first heat source 29 at the center of the sheet passing area L, and the second heating roller 24 includes a second heat source 30 at both ends of the sheet passing area L. Therefore, when it becomes necessary to raise the temperature of the central portion of the fixing belt 25, which has been lowered by continuously passing paper having a width narrower than the width of the paper passing area L, to the toner fixing temperature, The temperature of the center portion of the fixing belt 25 in the width direction can be increased by the first heating roller 23 without increasing the temperature of both ends of the fixing belt 25 in the width direction. Accordingly, since the necessary portions of the fixing belt 25 can be appropriately heated by the first heating roller 23 and the second heating roller 24, the temperature distribution in the width direction of the fixing belt 25 can be kept uniform.

  In the fixing device 20, the auxiliary heat source 34 is provided on the fixing roller 21, and the pressure roller 22 is provided with the low-hardness elastic layer 37, so that the toner is fixed on the recording medium (recording paper 11 in the above example). Therefore, the heat energy from the first heat source 29, the second heat source, and the auxiliary heat source 34 provided for the purpose can be efficiently used.

  In the fixing device 20, since the first heating roller 23 and the second heating roller 24 are arranged so as to sandwich the fixing belt 25, the heat of the respective heat sources 29 and 30 can be more efficiently transmitted to the fixing belt. Can do.

  In the fixing device 20, the second heating roller 24 is disposed outside the fixing belt 25 around the first heating roller 23, the fixing roller 21, and the small-diameter roller 26, that is, the second heating roller 24 is disposed on the fixing belt 25. Since it is located outside the circulation path, the belt length of the fixing belt 25 can be shortened, and the fixing device 20 can be further downsized.

  In the fixing device 20, since the heat insulating layer 26 b is provided on the small diameter roller 26, the heat of the fixing belt 25 is transmitted to the small diameter roller 26, that is, the heat of the fixing belt 25 can be prevented from being taken away. .

In the fixing device 20, the auxiliary heat source 34 is provided on the fixing roller 21, but the unfixed toner on the recording medium in the nip portion 38 is excellently heated by the first heating roller 23 and the second heating roller 24. If the fixing property can be obtained, the auxiliary heat source 34 can be eliminated.
(Embodiment 2)
Next, the fixing device of Embodiment 2 will be described. The fixing device of the second embodiment is an example in which the first heating roller 23 and the second heating roller 24 are different from the fixing device 20 of the first embodiment. Since the basic configuration of the fixing device is the same as that of the fixing device 20 of the first embodiment, the same functional parts are denoted by the same reference numerals as those of the first embodiment, and illustrated (partially incorporated disclosure). Detailed description will be omitted. FIG. 3 schematically shows the configuration of the first roller metal core 27 ′ of the first heating roller 23 ′ and the second roller metal core 28 ′ of the second heating roller 24 ′ used in the fixing device of the second embodiment. (A) shows the first roller mandrel 27 ', (b) shows the second roller mandrel 28', and the positional relationship of the first roller mandrel 27 'with respect thereto is two points. Shown with a chain line. FIG. 4 is an explanatory view using the second heating roller 24 ′ as an example for explaining the method of manufacturing the heating roller, (a) shows the second roller core 28 ′ before processing, b) shows a state in which the drawing step is being performed, (c) shows the second roller metal core 28 'that has been subjected to the drawing step, and (d) shows a state in which the grinding step is being performed. (E) shows a second roller cored bar 28 'subjected to a grinding process.

  As shown in FIG. 3A, the first heating roller 23 ′ is rotatably supported by a support frame body (not shown) via bearings 27 c provided at both ends of the support portions 27 b on the support frame body of the fixing device. The first roller mandrel 27 'is provided with a resin layer (not shown) (see reference numeral 27a in FIG. 2). The first roller core metal 27 'has a thin-walled portion in which the central portion (23a) is thinner than the thickness of both sides (both ends (23b)) in the sheet passing region L set along the axis. 23a.

  Further, as shown in FIG. 3B, the second heating roller 24 ′ is configured such that the support portions 28b at both ends can rotate to a support frame (not shown) via a bearing 28c provided on the support frame of the fixing device. The second roller mandrel 28 'supported is provided with a resin layer (not shown) (see reference numeral 28a in FIG. 2). The second roller metal core 28 'has a thin-walled portion having a thickness that is thinner at the both end portions (24a) than at the inner side (center portion (24b)) in the sheet passing region L set along the axis. 24a.

  The first roller core metal 27 'and the second roller core metal 28' are configured symmetrically with respect to the cross section orthogonal to the axis of each paper passing region L at the center position, and the thin portion 23a and the both thin portions 24a pass therethrough. In the paper region L, the left and right portions are equally distributed. In the second embodiment, the thin portion 23a of the first roller core metal 27 'is thicker than the thick portion 24b of the second roller core metal 28' (region excluding both thin portions 24a from the sheet passing region L). It has a large length when viewed in the axial direction.

  Specifically, the first roller core metal 27 ′ and the second roller core metal 28 ′ are each made of a manganese-based aluminum alloy, and both support portions 27b and 28b have an outer diameter φ10. Both the support portions 27b and 28b The outline shape except for the outer diameter is 18 mm, the length is 350 mm, the thickness t1 of the thin portions 23a and 24a is 0.3 mm, and the thickness t2 of the thick portions 23b and 24b is 0.6 mm. Further, when viewed in the axial direction of the roller cores 27 'and 28', the sheet passing area L of each of the first heating roller 23 'and the second heating roller 24' is set to about 320 mm (general area). The width of the thin portions 23a, 24a is set within 200 mm.

  The first roller core metal 27 ′ is provided with a first heat source 29 corresponding to the thin portion 23 a, and the thin portion 23 a is heated by radiation from the first heat source 29. The second roller metal core 28 ′ is provided with a second heat source 30 corresponding to the both thin portions 24 a, and both thin portions 24 a are heated by radiation from the second heat source 30.

  Next, a method for forming the first roller core metal 27 'and the second roller core metal 28' will be described with reference to FIGS. In the example of FIG. 4, a method for forming the second roller cored bar 28 ′ is shown, but the same applies to the first roller cored bar 27 ′ except that the processing location in the drawing process is changed.

  First, as shown in FIG. 4A, a metal cylindrical body 40 having a uniform inner diameter and outer diameter in the axial direction and having support portions 28b at both ends is formed from a manganese-based aluminum alloy. The thickness T of the metal cylinder 40 forms a thickness t1 (thick part 24b) of the second roller core 28 'and a circumferential convex part 40c described later on the inner peripheral surface 40a of the metal cylinder 40. In consideration of the pushing amount H (see FIG. 4B), the thickness is at least equal to the thickness obtained by adding the thickness t1 and the pushing amount H. In the present embodiment, the metal cylindrical body 40 has a wall thickness T of 1.2 mm.

  Next, as shown in FIG. 4B, while the metal cylindrical body 40 is fixed to an NC lathe (not shown), the drawing tool 41 (roller tool) fixed to the turret of the NC lathe is rotated. The squeezing tool 41 is pressed against the center of the sheet passing region L (the region corresponding to the thick portion 24b) on the outer peripheral surface of the metal cylindrical body 40. At this time, in the metal cylindrical body 40, the peripheral wall of the area where the squeezing tool 41 is pressed is displaced (indented) inward, the outer peripheral surface is recessed, and the inner peripheral surface is protruded inward. The Thus, a circumferential recess 40b is formed on the outer peripheral surface side of the metal cylindrical body 40, and a circumferential convex portion 40c is formed on the inner peripheral surface side of the metal cylindrical body 40 corresponding to the circumferential recess 40b (FIG. 4 (c)). Drawing the desired region is a drawing step for the metal cylindrical body 40.

  In the second embodiment, in this drawing step, a drawing tool 41 having a rotating mechanism by a bearing provided with a roller-shaped tool on the shank is used, and the rotation speed of the spindle of this drawing tool 41 is set to 1000 rpm. The indentation speed was set to φ0.1 mm / rev. In the second embodiment, by setting the indentation amount H by pressing to 0.4 mm, the protrusion amount of the circumferential convex portion 40c from the inner peripheral surface 40a (height dimension h of the circumferential convex portion 40c viewed in the radial direction). Can be set to 0.3 mm, and as described above, the thick portion 24b (thickness t1 is 0.6 mm) and the thin portion 24a (thickness t2 is 0.2 mm) which are set values of the second roller core 28 '. A difference of 0.3 mm, which is a difference in thickness from 3 mm), was obtained.

  After this drawing step, as shown in FIG. 4 (d), the cutting tool 42 is moved along the axial direction of the metal cylinder 40 so as to grind the outer surface of the metal cylinder 40 with a cutting tool (diamond tool) 42. It is moved to remove the recess, that is, the circumferential recess 40b, so that the outer surface of the metal cylindrical body 40 has a uniform columnar shape (the outer shape has a hollow portion inside). In the second embodiment, the cutting tool 42 is moved along the axial direction of the metal cylindrical body 40 so as to peel the thin skin on the outer peripheral surface of the metal cylindrical body 40 to grind the outer peripheral surface of the metal cylindrical body 40. By repeating the process over and over, the outer recess 40b is removed and the outer surface has a desired outer diameter and no irregularities (see FIG. 4E). Grinding to the metal cylindrical body 40 is performed by removing the circumferential recess 40b and performing grinding until the outer surface has a uniform cylindrical shape.

  By this grinding process, as shown in FIG. 4 (e), the outer wall has a uniform outer diameter in the axial direction, and the central portion (24b) in the paper passing region L on the inner peripheral surface is a thick wall having a predetermined thickness t2. It is possible to form the second roller cored bar 28 'which is the portion 24b and whose both end portions (24a) are thin portions 24a having a predetermined thickness t1.

  Thus, in forming the second roller core metal 28 '(the same applies to the first roller core metal 27') from the metal cylindrical body 40, an NC lathe which is a general-purpose processing machine is used as a roller tool. Since it can be machined, it is not necessary to introduce a dedicated machine, and it has excellent repeatability, that is, even when a plurality of roller metal cores are processed, the desired roller metal core (cylindrical shape) can be obtained with stable accuracy. It is possible to easily manufacture an outer shape whose wall thickness is different at a desired position.

In the fixing device according to the second embodiment, the roller metal cores (first roller metal core 27 ′ and second roller metal core 28 ′ in the second embodiment) are made of a manganese-based aluminum alloy.
Since this manganese-based aluminum alloy has a higher creep resistance than other aluminum alloys, it is suitable for plastic processing (spinning processing) when forming a desired roller metal core using the above-described method.

  Furthermore, in the fixing device according to the second embodiment, the central portion (23a) of the sheet passing region L of the first roller core 27 'of the first heating roller 23' and the second roller core of the second heating roller 24 '. Both end portions (24a) of the paper passing region L of 28 'are formed as thin portions 23a and 24a, respectively, and a first heat source 29' is provided on the first roller cored bar 27 'corresponding to the thin portion 23a, In addition, since the second roller metal core 28 'is provided with the second heat source 30' corresponding to the thin portion 24a, the first roller of the heat energy from each of the first heat source 29 'and the second heat source 30'. The heat absorption efficiency of the core metal 27 'and the second roller core metal 28' can be increased.

  In the fixing device of the second embodiment, a portion other than the thin portion 23a of the first roller core metal 27 'of the first heating roller 23', that is, the thick portion 23b of the first roller core metal 27 ', or the second heating roller 24. Since the portion other than the thin portion 24a of the second roller core metal 28 ', that is, the thick portion 24b of the second roller core metal 28 can be formed thick, the first roller core metal 27' and the second roller The reduction in rigidity of the first heating roller 23 ′ and the second heating roller 24 ′ due to the thinning of the metal core 28 ′ can be reliably suppressed.

In the fixing device according to the second embodiment, the first roller core metal 27 ′ and the second roller core metal 28 ′ are formed symmetrically with respect to the central longitudinal section orthogonal to the center position of the axis, and thus the recording paper 11 When the fixing belt 25 is heated in order to replenish the heat taken away by the sheet passing, a necessary portion can be appropriately heated without causing a deviation in the temperature distribution in the width direction of the fixing belt 25. The temperature distribution of 25 can be reliably kept uniform.
(Embodiment 3)
Next, a fixing device according to Embodiment 3 will be described. The fixing device according to the third embodiment is the same as the fixing device according to the second embodiment, except for the materials of the first roller core metal 27 'of the first heating roller 23' and the second roller core metal 28 'of the second heating roller 24'. Is a different example. Since the fixing device of the third embodiment has the same configuration as that of the fixing device of the second embodiment, the same functional parts are denoted by the same reference numerals as those of the second embodiment, and the illustration and detailed description thereof are omitted. To do.

  The first roller core metal of the first heating roller and the second roller core metal of the second heating roller of the fixing device according to the third embodiment are manufactured by Sumitomo Light Metal Co., Ltd. as a manganese-based aluminum alloy material. The material is used. This manganese-based aluminum alloy is a material rich in creep resistance at high temperatures, and can improve the strength of the first roller metal core and the second roller metal core.

  Table 1 shows the results of evaluating the temperature characteristics of the fixing devices described in Embodiments 1 to 3 using the examples of the present invention. In the present embodiment, the rising time under the fixing condition of the medium speed machine class where the linear velocity is 162 mm / s and the fixing temperature is 150 ° C., and the A4 size recording paper 114 (see FIG. 5) is set to 100 in the vertical direction. The end temperature of the fixing belt 25 when the sheet was passed and the end temperature of the fixing belt 25 when 100 sheets of A5 size recording paper 115 (see FIG. 5) were passed in the vertical direction were evaluated. In this evaluation, the total power of the halogen heater as the heat source of the first heating roller and the second heating roller of each fixing device is 1200 W, and the center side (first heat source) and the end side (second heat source) are evenly distributed. Allocating power. In addition, FIG. 5 is explanatory drawing for demonstrating the evaluation method of a present Example. Table 1 shows the results of evaluating the temperature characteristics of the fixing device described in Embodiments 1 to 3 and the fixing device as a comparative example using this example.

  In this evaluation, a temperature sensor 43 is provided to measure the temperature of the fixing belt 25 on the upstream side of the nip portion 38 when viewed in the circulation direction of the fixing belt 25 (see FIGS. 2 and 6). As shown in FIG. 5, the temperature sensor 43 is provided at a total of five locations along the width direction of the fixing belt 25, that is, a central position 1, a central position 2, a central position 3 and an end position 4, and an end position 5. The temperature of each part of the fixing belt 25 was measured by appropriately moving. In this embodiment, a contact temperature sensor (E-type thermocouple) is used as the temperature sensor 43.

  The edge temperature shown in Table 1 is the maximum value of the measured temperature at the center position 2, the center position 3, the edge position 4 or the edge position 5 when the A5 size recording paper 115 is passed. When the recording paper 114 is passed, the measured temperature is the maximum value at the end position 4 or the end position 5. The end temperature is desirably 200 ° C. or less in the hot offset region of the fixing temperature, and the smaller the difference from the fixing temperature (150 ° C.) that is the control value, the better.

  Further, the temperature difference shown in Table 1 indicates that the temperature at the center position 1 and the end temperature (the center position 2, the center position 3, the end position 4 or the end position 5 when the A5 size recording paper 115 is passed. When the A4 size recording paper 114 is passed through, the minimum value of the measured temperature at the center position 1, the center position 2 or the center position 3 and the end temperature (the end position 4). Or the maximum value of the end position 5).

In this evaluation, as a fixing device of Comparative Example 1 and Comparative Example 2, a conventional configuration (see FIG. 6) in which two heat sources are incorporated in a single heating roller is used. The outer diameter is 30 mm and the wall thickness is 0.6 mm. In Comparative Example 1, a heating roller formed of the same material (A6063) as the first heating roller and the second heating roller in the first and second embodiments of the fixing device according to the present invention is used. In Comparative Example 2, a heating roller formed of the same material (CM10 (R)) as the first heating roller and the second heating roller in Embodiment 3 of the fixing device according to the present invention is used.

  As can be seen from the evaluation results (Table 1), the fixing device according to the present invention is in any embodiment compared to a conventional fixing device in which two heat sources of a single heating roller are incorporated. Thus, the temperature difference generated in the fixing belt 25 when a recording medium having a smaller size compared to the set sheet passing area L is continuously passed can be reduced, and the end temperature of the fixing belt 25 can be suppressed. In addition, the rise time can be shortened. Specifically, in the conventional fixing devices (Comparative Example 1 and Comparative Example 2), when an A5 size recording paper 115 (see FIG. 5) is passed, the end temperature exceeds 200 ° C., and A4 When the recording paper 114 of the size (see FIG. 5) was passed, the end temperature increased to around 200 ° C., whereas in each of the embodiments, the end temperature increased. Could be suppressed. In addition, in all the conventional fixing devices, the rise time required 90 seconds or more, whereas in each of the embodiments, the rise time can be reduced to less than half compared to the conventional fixing device. It was.

  Therefore, in the fixing device according to the present invention, it is possible to easily obtain a uniform temperature distribution in the axial direction regardless of the sheet passing width, and it is possible to ensure the rigidity and reduce the rise time due to the thinning. In addition, workability and versatility can be improved, and an increase in the number of components and a complicated configuration can be prevented.

  The present invention has been described in detail based on the embodiments. However, the present invention is not limited to this specific configuration, and design changes that do not depart from the spirit of the present invention are included in the technical scope of the present invention.

1 is a schematic diagram illustrating an image forming apparatus according to the present invention. 1 is a schematic diagram illustrating a fixing device according to a first embodiment of the present invention. It is sectional drawing which shows typically the structure of the 1st heating roller of Embodiment 2, and a 2nd heating roller, (a) shows a 1st roller core metal, (b) shows a 2nd roller core metal, The positional relationship of the first roller mandrel relative thereto is indicated by a two-dot chain line. It is explanatory drawing which uses a 2nd heating roller as an example in order to demonstrate the manufacturing method of a heating roller, (a) shows the 2nd roller core metal before a process, (b) is a drawing process performed (C) shows the second roller mandrel subjected to the drawing process, (d) shows the grinding process, and (e) shows the grinding process. The second roller cored bar is shown. It is explanatory drawing for demonstrating the evaluation method of a present Example. FIG. 10 is a schematic diagram illustrating a conventional fixing device. It is explanatory drawing for demonstrating the heating roller of the conventional fixing device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Image forming device 11 Recording paper (as recording medium) 20 Fixing device 21 Fixing roller 22 Pressure roller 23 First heating roller 23a Thin portion 25 Fixing belt 24 Second heating roller 24a Thin portion 26 Small diameter roller 26b Heat insulation layer 27 First Single roller core 28 Second roller core 29 First heat source 30 Second heat source 38 Nip portion 40b Circumferential recess 40c Circumferential convex portion L Paper passing area

Claims (11)

An endless fixing belt is stretched around the first heating roller and the fixing roller, a pressure roller is pressed against the fixing roller with the fixing belt interposed, and a nip portion is formed at the pressure contact point. A fixing device that fixes unfixed toner carried on a recording medium conveyed to the nip portion as the fixing belt circulates on the recording medium;
The first heating roller incorporates a first heat source at a position corresponding to either the central portion or both end portions in the sheet passing region set along the axial direction,
A second heating roller containing a second heat source is brought into contact with the fixing belt at a position corresponding to the other one of the center portion or the both end portions in the sheet passing region,
A small-diameter roller is provided on the downstream side of the nip portion as seen in the circulation direction of the fixing belt,
The fixing device, wherein the fixing belt is looped around the small-diameter roller in addition to the first heating roller and the fixing roller.   The fixing device according to claim 1, wherein the small-diameter roller has a smaller outer diameter than the fixing roller.   The fixing device according to claim 1, wherein the small-diameter roller is a tension roller that is movable to apply tension to the fixing belt.   4. The fixing device according to claim 1, wherein the second heating roller is in contact with the first heating roller with the fixing belt interposed therebetween. Each of the first heating roller and the second heating roller has a cylindrical roller cored bar,
The first roller cored bar of the first heating roller is a thin portion in which the central portion in the sheet passing region is thinner than the thickness of the both end portions,
In the first heating roller, the first heat source is provided in the first roller core corresponding to the thin portion of the first roller core,
The second roller cored bar of the second heating roller is a thin portion where the both end portions in the sheet passing region are thinner than the thickness of the central portion,
The said 2nd heat roller WHEREIN: Said 2nd heat source is provided in the said 2nd roller core metal corresponding to the both said thin part of said 2nd roller core metal, The Claim 4 characterized by the above-mentioned. Fixing device.   The fixing device according to claim 5, wherein each of the first roller core metal and the second roller core metal is made of a manganese-based aluminum alloy.   The fixing device according to claim 1, wherein the small-diameter roller is provided with a heat insulating layer on an outer surface. An endless fixing belt is stretched around the heating roller and the fixing roller, and a pressure roller is pressed against the fixing roller with the fixing belt interposed therebetween, so that a nip portion is formed at the pressing position, and the fixing A fixing device for fixing unfixed toner carried on a recording medium conveyed to the nip portion as the belt circulates on the recording medium;
In order to peel off the recording medium on which the toner has been fixed at the nip portion from the fixing belt using a restoring force for returning to the original state of the recording medium, the fixing belt is viewed in its circulation direction. In addition to the heating roller and the fixing roller, it is stretched over the small-diameter roller so as to go around a small-diameter roller having a smaller outer diameter than the fixing roller provided on the downstream side of the nip portion. Fixing device to do. An endless fixing belt is stretched around the first heating roller and the fixing roller, a pressure roller is pressed against the fixing roller with the fixing belt interposed, and a nip portion is formed at the pressure contact point. A fixing device that fixes unfixed toner carried on a recording medium conveyed to the nip portion as the fixing belt circulates on the recording medium;
The first heating roller incorporates a first heat source at a position corresponding to either the central portion or both end portions in the sheet passing region set along the axial direction,
A second heating roller containing a second heat source is in contact with the fixing belt via the fixing belt at a position corresponding to the other one of the center portion or the both end portions in the sheet passing area. A fixing device characterized by the above. Each of the first heating roller and the second heating roller has a cylindrical roller cored bar,
The first roller cored bar of the first heating roller is a thin portion in which the central portion in the sheet passing region is thinner than the thickness of the both end portions,
In the first heating roller, the first heat source is provided in the first roller core corresponding to the thin portion of the first roller core,
The second roller cored bar of the second heating roller is a thin portion where the both end portions in the sheet passing region are thinner than the thickness of the central portion,
The said 2nd heat roller WHEREIN: Said 2nd heat source is provided in the said 2nd roller core metal corresponding to the both said thin part of said 2nd roller core metal, The said 9th roller core metal is characterized by the above-mentioned. Fixing device. An electrophotographic apparatus comprising the fixing device according to claim 1.

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