JP2005084637A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the durability of a belt by preventing the occurrence of the residual deformation of a fixing belt or an intermediate transfer belt to prevent defects on the surface of the belt and also, to obtain a satisfactorily fixed image, in a fixing device and an image forming apparatus wherein an unfixed toner image on a recording medium or the intermediate transfer belt is heated and melted by an electromagnetic induction heating device and the toner image is transferred and fixed on the recording medium. <P>SOLUTION: In the fixing device and the image forming apparatus, after a heating operation by the electromagnetic induction heating device is stopped, the belts 21 and 55 are intermittently driven to run or continuously driven to run at a low speed until a temperature detected by a temperature detecting device lowers to a prescribed temperature. Thus, the residual deformation of the belt is prevented, the durability of the belt is improved, and the toner image is stably fixed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a fixing device or an image forming apparatus that fixes a visible image formed by attaching powder toner to a latent image due to a difference in electrostatic potential on a recording sheet.

  In general, the step of fixing a toner image in an image forming apparatus using powdered toner is to electrostatically transfer the toner image onto a recording medium, and then sandwich the recording medium between a heating member and a pressure member. A method in which a toner image is heated and melted and pressed onto a recording medium is widely used. Also known is an image forming apparatus that temporarily transfers a toner image to an intermediate transfer member, then heats the toner image on the intermediate transfer member, and presses the toner image against a recording medium to simultaneously perform secondary transfer and fixing. It has been.

  As means for heating the heating member or the intermediate transfer member, JP-A-10-254263 (Patent Document 1), JP-A-10-301415 (Patent Document 2), JP-A-11-352804 (Patent Document 3). ) And the like describe that a conductive layer is provided on a heating member or an intermediate transfer member and the conductive layer is heated by electromagnetic induction heating.

  In the electromagnetic induction heating, an exciting coil that generates a variable magnetic field is disposed close to a conductive layer, and heat is generated by an eddy current generated in the conductive layer. According to this electromagnetic induction heating, the heating member or the intermediate transfer member can be directly heated, and the range of the high temperature becomes a very limited range, and the heating member can be heated to a predetermined temperature in a short time. . For this reason, compared with the case where a heating element such as a halogen lamp is used as a heating source, the warm-up time of the apparatus can be shortened and the power consumption can be reduced.

  On the other hand, as the heating member (fixing member), an endless fixing belt is generally used in addition to the heating roll, and the endless belt has a type stretched by a plurality of support rolls and a pressing member inside. However, there is a type that is driven around in a non-tensioned state. The fixing belt has a thin heat resistant resin or the like as a base layer and has a smaller heat capacity than the heating roll, so that it can warm up in a shorter time than the heating roll. Furthermore, the non-stretching type fixing belt can reduce the contact area with other members, and heat transfer to the other members is reduced. For this reason, more efficient warming up can be performed.

  As described above, in an apparatus that uses an endless belt as a heating member and electromagnetically heats the belt, when the endless belt is stretched by a plurality of rolls, it is stretched as described in Patent Document 3. A high frequency coil (excitation coil) is disposed so as to face the inner surface or the outer surface of the belt. On the other hand, in the case where the endless belt is driven to circulate in a state where the endless belt is stretched, a high frequency coil having an axis in the width direction of the belt is arranged inside the endless belt as described in Patent Document 2. As described in Japanese Patent Application Laid-Open No. 2003-84591 (Patent Document 4) and Japanese Patent Application Laid-Open No. 2003-91185 (Patent Document 5), a high-frequency coil is disposed so as to be in close proximity to the outer peripheral surface of the endless belt. May be placed. The high frequency coil arranged so as to face the outer peripheral surface generates a variable magnetic field in a direction penetrating the belt. Further, in the case where the high-frequency coil is arranged inside the endless belt, an eddy current is generated in the circumferential direction of the endless belt.

  The endless belt has a base made of a heat-resistant resin film such as polyimide, and a metal layer (conductive layer) such as nickel, copper, chromium, aluminum, iron, cobalt, etc. is laminated on the base. An eddy current is generated in the metal layer due to the fluctuating magnetic field and heat is generated.

The endless belt can be provided with an elastic layer such as silicone rubber in order to improve the adhesion to the toner in addition to the heat-resistant substrate and the metal layer, and further improve the releasability from the melted toner. Therefore, a surface release layer can be provided.
Japanese Patent Laid-Open No. 10-254263 JP-A-10-301415 JP 11-352804 A JP 2003-84591 A JP 2003-91185 A

  However, the apparatus for electromagnetically heating the endless belt as described above has the following problems.

  In the belt having the conductive layer and the silicone rubber laminated on the polyimide base as described above, the heating is stopped in a state where the heated and heated belt is sandwiched between the pressure member and the heating member. When cooled as it is, the shape of the pressure contact portion remains in the sandwiched belt portion. Moreover, the shape of the surrounding surface of a roll may remain in the part wound by the roll etc. FIG. When the belt is deformed in this way, the belt bulges outward, and when the belt is re-driven, the belt comes into contact with the electromagnetic induction heating device or the like disposed outside, causing damage to the belt surface. As a result, the fixed image is affected and the durability of the fixing belt is significantly reduced.

  In addition, after the heating of the fixing belt is stopped, a method of suppressing the occurrence of residual deformation by continuing the running of the fixing belt until the temperature detected by the temperature detecting means reaches a predetermined temperature is also considered. If the belt is continuously driven until the speed decreases, the rotational speed of the belt increases remarkably, and the durability of the belt decreases.

  The present invention has been made in view of the above problems, and its purpose is as a fixing device or an intermediate transfer member that heats and melts an unfixed toner image carried on a recording medium and fixes it to the recording medium. In an image forming apparatus that heats and melts a toner image on a belt to be used, and transfers and fixes the toner image on a recording medium, the belt is prevented from being deformed, and the belt surface is prevented from being damaged. It is to improve.

  In order to solve the above-mentioned problems, an invention according to claim 1 includes an endless belt supported so as to be movable in the circumferential direction, and an endless circumferential surface, and the circumferential surface is formed on the outer circumferential surface of the belt. A pressure member to be pressed, an opposing member that is in contact with the inner peripheral surface of the belt and sandwiches the belt between the pressure member, and a heating device that heats the belt. As the endless peripheral surface of the pressure member is driven to circulate, a recording sheet is sandwiched between the pressure member and the belt, and the toner carried on the recording sheet is heated and pressed. A fixing device having temperature detecting means for detecting a temperature of the belt or a member that becomes high as the belt is heated by a heating device; and the belt stops heating by the heating device. After the temperature detection hand Temperature detected until reduced to a predetermined temperature, to provide a fixing device which is characterized in that intended to be intermittently driven by.

  In this fixing device, when the belt heated by the electromagnetic induction heating device becomes high temperature and is pressed against the recording medium, the toner carried on the recording medium is melted and fixed on the recording medium. Further, the heating device can be controlled so as to maintain the optimum temperature for melting and fixing the toner by detecting the temperature of the belt or a member in contact with the belt.

  After the heating is stopped, the belt is intermittently driven until the temperature detected by the temperature detecting means decreases to a predetermined temperature, so that the same position of the belt does not stop at the same position on the circulation path for a long time. The same position of the belt does not stay for a long time in a portion where a large deformation occurs such as a pressure contact portion with the pressure member. Since the temperature is lowered while moving intermittently in this way, it is possible to prevent the deformation following the shape of the press contact portion from remaining at a specific position of the belt.

  The predetermined temperature is a temperature at which the belt is not deformed or does not cause a problem even if the belt is deformed and the temperature drops from the temperature to room temperature. Can be determined.

  The belt of the fixing device according to claim 1 may be stretched by a plurality of members, or is sandwiched between the pressure member and the opposing member in a non-tensioned state. There may be.

  According to a second aspect of the present invention, in the fixing device according to the first aspect, the one-time driving distance of the belt that is intermittently driven is set to be greater than the length of the portion in pressure contact with the pressure member. And

  In this fixing device, since the driving distance for driving the belt intermittently is set larger than the length of the portion pressed against the pressure member, the portion pressed by the belt pressing portion is moved once. Escapes from the pressure contact portion, and deformation does not occur at the same position of the belt for a long time, and no deformation remains. As a result, the belt surface is not damaged by contacting the heating device or the like when the belt is re-driven, and the durability of the belt can be improved.

  According to a third aspect of the present invention, in the fixing device according to the first aspect, the interval of time during which the belt is intermittently driven is short when the temperature detected by the temperature detecting means is high, and the detected temperature is low. As it becomes, it is assumed that it is set longer.

  When the temperature detected by the temperature detecting means is high after the heating of the belt is stopped, the belt sandwiched between the press contact portions is likely to be deformed, but by shortening the time interval of intermittent belt driving, The time for which the belt is clamped at the press contact portion is shortened, and residual deformation can be prevented. Further, since the remaining deformation of the belt is reduced as the detected temperature is lowered, it is possible to prevent the remaining deformation of the belt even if the time interval of intermittent driving is set longer. Furthermore, if the interval of intermittent driving becomes longer, the number of times of belt rotation driving is reduced, the durability of the belt is improved, and power consumption is also reduced.

The invention according to claim 4 is an endless belt supported so as to be movable in the circumferential direction;
A heating device that heats the belt; an endless peripheral surface; and a pressing member that is pressed against the outer peripheral surface of the belt. The endless end of the belt or the pressing member A fixing device that sandwiches a recording sheet between the pressure member and the belt as the peripheral surface thereof is driven to rotate, heats the toner carried on the recording sheet, and press-bonds the toner. Alternatively, the belt includes temperature detecting means for detecting a temperature of a member that becomes a high temperature as the belt is heated by the heating device, and the belt detects the temperature by the temperature detecting means after the heating by the heating device is stopped. Provided is a fixing device which is driven at a lower speed than the time of fixing the toner until the detected temperature is lowered to a predetermined temperature.

  This fixing device has a temperature detecting means for detecting the temperature of the belt or a member in contact with the belt, and measures the temperature of the belt or the member in contact with the belt even after the heating is stopped. Thus, it is possible to detect that the temperature of the belt has been lowered to a temperature at which the belt is less likely to be deformed.

  As a result, the belt can be controlled to be driven at a lower speed than the speed during the toner fixing operation until the belt is lowered to a predetermined temperature. Can be prevented. Further, since the belt is driven at a low speed, heat radiation from the belt is promoted, and wear and the like associated with the rotational drive can be reduced, and durability can be improved.

  According to a fifth aspect of the invention, the speed at which the belt is driven after the heating device is stopped is fast when the temperature detected by the temperature detecting means is high, and is slow as the detected temperature becomes low. It is assumed that it is set.

  In this fixing device, the speed at which the belt is driven after the heating device is stopped is set to be fast when the temperature detected by the temperature detecting means is high, and to rotate slowly as the detected temperature decreases. In addition, the remaining deformation of the belt is appropriately prevented according to the temperature decrease of the belt. Further, as the temperature is lowered, the circumferential driving is slowed down, so that the number of times of circumferential driving of the belt is reduced, the belt is prevented from being worn and the durability is improved.

  The invention according to claim 6 is the fixing device according to claim 1 or 4, wherein the pressure member is a roll-shaped member, and the temperature detection means detects a temperature of the pressure member. Shall.

  In this fixing device, since the pressure member is in a roll shape, when the belt is heated by the heating means and becomes high temperature, the heat is conducted almost uniformly to the peripheral surface of the pressure member in the roll shape. Changes in temperature occur. For this reason, heat may be stored in the roll-shaped pressure member even after heating is stopped, and the temperature of the pressure member may be higher than the temperature of the belt. Thus, the belt can be controlled to be intermittently driven or driven at a low speed.

According to a seventh aspect of the present invention, there is provided an image forming portion that selectively transfers toner to a latent image due to a difference in electrostatic potential to form a toner image, and an endless intermediate transfer to which the formed toner image is once transferred A belt, and a heating device for heating and melting the toner image carried on the intermediate transfer belt,
An image forming apparatus comprising: a secondary transfer unit that presses a toner image on the intermediate transfer belt onto a recording sheet and simultaneously performs transfer and fixing, the intermediate transfer belt or a member that stretches the intermediate transfer belt Temperature detecting means for detecting the temperature of the intermediate transfer belt, and the intermediate transfer belt is intermittently driven or toner until the temperature detected by the temperature detecting means decreases to a predetermined temperature after the heating by the heating device is stopped. Provided is an image forming apparatus that is driven at a lower speed than during image formation.

  In this image forming apparatus, the intermediate transfer belt is heated in order to melt the toner image on the intermediate transfer belt and perform secondary transfer onto the recording sheet. Then, after the secondary transfer is completed and the heating is stopped, it is driven intermittently or at a low speed, so that a portion bent with a large curvature by a member such as a roll moves intermittently or slowly. The temperature gradually decreases. For this reason, deformation following the peripheral surface of a roll or the like is prevented from remaining on the intermediate transfer belt.

  In addition, since the intermediate transfer belt is driven intermittently or at a low speed, the number of revolutions of the intermediate transfer belt does not increase significantly within the service life of the apparatus, and a situation where the durability of the intermediate transfer belt is insufficient is avoided. it can.

  As described above, in the fixing device and the image forming apparatus according to the present invention, after the heating by the heating device is stopped, the belt or the fixing belt is fixed until the temperature detected by the temperature detecting means decreases to a predetermined temperature. Since the running of the intermediate transfer belt is intermittently driven or continuously driven at a low speed, the belt can be prevented from being deformed and a secondary failure can be prevented. As a result, the durability of the belt is improved and stable toner fixing can be achieved.

  Hereinafter, embodiments of the invention according to the present application will be described with reference to the drawings.

  FIG. 1 is a schematic configuration diagram of an image forming apparatus using a fixing device or a belt according to an embodiment of the present invention. FIG. 2 is a schematic configuration diagram of a fixing device used in the image forming apparatus. It is.

  The image forming apparatus shown in FIG. 1 includes a cylindrical photosensitive drum 1 on which a latent image due to a difference in electrostatic potential is formed by irradiating image light after uniform charging, and this photosensitive drum. 1, a charging device 2 for uniformly charging the surface of the photosensitive drum 1, an exposure device 3 for irradiating the photosensitive drum 1 with image light to form a latent image on the surface, and a photosensitive drum A developing unit 4 that selectively transfers toner to the latent image to form a toner image, an endless belt-like intermediate transfer member 5 that is opposed to the photosensitive drum 1 and is supported so that the circumferential surface can circulate, and a toner image A cleaning device 6 that removes toner remaining on the photosensitive drum 1 after the transfer of the toner, and a static elimination exposure device 7 that neutralizes the surface of the photosensitive drum 1.

  Further, inside the intermediate transfer member 5, a transfer charger 8 for primary transfer of the toner image formed on the photosensitive drum to the intermediate transfer member 5, two support rolls 9a and 9b, and secondary transfer are performed. A transfer counter roll 10 for carrying out is disposed, and the intermediate transfer body 5 is stretched around these rolls so as to be able to go around. A transfer roll 11 for transferring a toner image on the intermediate transfer body onto a recording sheet is disposed at a position facing the transfer opposing roll 10 via the intermediate transfer body 5. The transfer opposing roll 10 and the transfer roll The recording paper P is fed from a paper tray (not shown) into the pressure contact portion with the paper 11. Further, on the downstream side of the press contact portion, a fixing device 12 that heats and melts the toner image on the recording paper and press-bonds it to the recording paper, and removes the toner remaining on the intermediate transfer member at a position along the intermediate transfer member 5. A cleaning device 13 is provided.

  Next, details of the configuration of the fixing device 12 will be described with reference to FIG.

  The fixing device 12 includes an endless fixing belt 21, an electromagnetic induction heating device 22 supported at a position facing the peripheral surface of the fixing belt 21, a pressure roll 23 pressed against the fixing belt 21, and fixing. A pressure opposing member 24 that is supported inside the belt 21 and sandwiches the fixing belt 21 between the pressure roll 23 and a downstream side of a pressure contact portion between the pressure roll 23 and the pressure opposing member 24. And a peeling member 25. Further, a temperature detection device 26 that measures the temperature of the inner peripheral surface of the fixing belt 21 is provided upstream of the pressure contact portion between the pressure roll 23 and the pressure facing member 24.

  As shown in FIG. 3, the fixing belt 21 includes a base layer 21a made of a sheet member having high heat resistance, represented by polyimide, polyimide amide, etc., a conductive layer 21b thereon, and an elastic layer 21c thereon. The surface release layer 21d is laminated.

  The conductive layer 21b is made of, for example, a magnetic metal such as iron, magnetic stainless steel, nickel or the like, or a main alloy thereof, a nonmagnetic metal such as nonmagnetic stainless steel, aluminum, or copper, or a main alloy thereof having a thickness of 5 μm to 50 μm. The material is selected so that the specific resistance value is such that sufficient heat can be obtained by electromagnetic induction. The elastic layer 21c adheres the surface of the fixing belt 21 to the toner image on the recording paper, and has heat resistance, high thermal conductivity such as silicone rubber, fluorine rubber, fluorosilicone rubber, etc., and has a thickness. Is preferably 10 μm to 500 μm and the hardness is 600 (JIS-KA type tester) or less. The surface release layer 21d has a thickness of 1 μm to 100 μm and has a fluororesin, silicone resin, fluorosilicone rubber, fluororubber, silicone rubber, PFA (tetrafluoroethylene-perfluoroalkoxyvinyl ether copolymer), PTFE (polytetra Fluoroethylene), FEP (tetrafluoroethylene-hexafluoropropylene copolymer) and the like having high mold release properties and heat resistance can be used.

  The pressure roll 23 has a metal cylindrical cored bar 23a as a core material, and includes an elastic layer 23b such as sponge or rubber on the surface of the cored bar 23a. The pressure roll 23 is rotationally driven by a drive motor (not shown), and the fixing belt 21 is driven to rotate accordingly.

  The electromagnetic induction heating device 22 is arranged so that the gap with the outer peripheral surface is 1 to 3 mm along the outer peripheral surface of the fixing belt 21 and heats the conductive layer of the fixing belt 21. The electromagnetic induction heating device 22 includes a magnetic core 22b made of ferrite or the like supported by a pedestal 22a, an excitation coil 22c wound around the magnetic core 22b, and supplies an alternating current to the excitation coil 22c. The main part is composed of the excitation circuit 22d.

  The pressure opposing member 24 includes an elastic member 24a having a contact surface curved in a shape along the peripheral surface of the pressure roll 23, and a support member 24b that supports the elastic member 24a and is fixedly supported at both ends. The main portion is constituted by a belt traveling guide (not shown) that is supported by the support member 24b, abuts against the inner peripheral surface at both ends in the width direction of the fixing belt 21, and regulates the position of the fixing belt 21. Yes. A magnetic body 24 d that collects the magnetic flux that has passed through the conductive layer 21 a of the fixing belt 21 is provided at a portion of the pressure facing member 24 that faces the electromagnetic induction heating device 22. For the magnetic body 24d, iron, cobalt, nickel, ferrite, or the like is used.

  The elastic member 24 a is in pressure contact with the pressure roll 23 and has a concave shape following the circumferential surface of the pressure roll 23, so that a sufficient pressure contact width is provided between the elastic member 24 a and the pressure roll 23 via the fixing belt 21. Can be obtained. Further, a low friction layer 24e is provided on the surface of the elastic member 24a to reduce friction with the inner peripheral surface of the fixing belt 21.

  The release member 25 includes a support portion 25a having one end fixedly supported and a release sheet 25b supported by the support portion 25a. The release member 25b is disposed so that the front end of the release sheet 25b approaches or contacts the fixing belt 21. . As a result, the release sheet 25 b enters between the recording paper P that has passed through the press contact portion and the fixing belt 21, and the recording paper P is released from the fixing belt 21.

  The temperature detection device 26 is in contact with the fixing belt 21 to detect the temperature of the fixing belt 21, supports the temperature sensor 31, and presses the temperature sensor 31 against the inner peripheral surface of the fixing belt 21. An elastic support member 32 and a restraining member 33 for restraining the elastic support member 32 so that a part of the elastic support member 32 is curved are configured. The amount of power supplied from the excitation circuit 22d to the excitation coil 22c is controlled by the detected value of the temperature sensor 31, so that the surface temperature of the fixing belt 21 maintains a desired temperature.

  The temperature sensor 31 measures the temperature in contact with the object to be measured, and a thermocouple using the Seebeck effect, a thermistor using an element having a large temperature coefficient of resistance, or the like is used. Since these contact-type temperature sensors are inexpensive, the cost of the apparatus can be reduced.

  The elastic support member 32 includes an elastic support portion 32a supported so as to be elastically curved with a curvature larger than that of the fixing belt 21, and a bent portion 32b which is continuous with the elastic support portion 32a and is bent. And a locking portion 32c formed by bending the tip of the bent portion 32b. One end of the elastic support portion 32a is fixed to the restraining member 33, and the temperature sensor 31 attached to the distal end side of the elastic support portion 32a is pressed against the inner peripheral surface of the fixing belt 21 by the elastic repulsion force of the curved elastic support portion 32a. Has been.

  Due to the restriction of the bent portion 32b, the elastic support portion 32a is deformed so as to be curved, and the contact pressure when the temperature sensor 31 attached to the outside of the curved surface is pressed against the fixing belt 21 can be reduced. it can. Since the bent portion 32b is movable in the axial direction, the temperature sensor 31 can advance and retreat by the elastic repulsive force of the elastic support portion 32a, and follows the displacement of the fixing belt 21. .

  The temperature sensor 31 of the temperature detection device 26 is in contact with the fixing belt 21 so as to detect the temperature of the fixing belt. Instead of or in addition to the temperature detection device 26, A temperature detection device 27 that detects the surface temperature of the pressure roll 23 may be provided.

  Next, operations of the image forming apparatus and the fixing device 12 will be described.

  First, the surface of the photosensitive drum 1 is charged almost uniformly by the charging device 2, and then image light is irradiated from the exposure device 3 to form a latent image on the surface of the photosensitive drum 1 due to the difference in electrostatic potential. . Then, the photosensitive drum 1 rotates to move to a position facing one developing device 4a of the developing unit 4, and the first color toner is transferred from the developing device 4a to form a toner image. This toner image is conveyed to a position facing the intermediate transfer member 5 by the circumferential movement of the photosensitive drum 1, and is electrostatically primary-transferred onto the intermediate transfer member.

  On the other hand, the toner remaining on the photosensitive drum 1 after the primary transfer is removed by the cleaning device 6, and the surface of the photosensitive drum 1 is potentialally initialized by the static elimination exposure device 7, and again at a position facing the charging device 2. Moving.

  Thereafter, the three developing devices 4b, 4c, and 4d of the developing unit 4 sequentially move to positions facing the photosensitive drum 1, and similarly, toner images of the second, third, and fourth colors are sequentially formed, and the intermediate transfer member is formed. 5 is superimposed and transferred.

  The toner image T superimposed on the intermediate transfer member is conveyed to a position where the transfer roller 11 and the transfer counter roller 10 face each other by the circumferential movement of the intermediate transfer member 5, and comes into contact with the recording paper P fed from the paper tray. Is done. A transfer bias voltage is applied between the transfer roll 11 and the intermediate transfer member 5, and the toner image T is secondarily transferred onto the recording paper.

  The recording paper P carrying the unfixed toner image T is conveyed to the fixing device 12 and sent between the fixing belt 21 and the pressure roll 23 of the fixing device 12.

  In the fixing device 12, the excitation coil 22 c from the excitation circuit 22 d of the electromagnetic induction heating device 22 is almost simultaneously with or immediately after the pressing roll 23 starts driving and the fixing belt 21 is driven to start the circulation. Is supplied with an alternating current. When an alternating current is supplied to the exciting coil 22c, the magnetic flux indicated by the arrow H around the exciting coil 22c repeats generation and disappearance. When the magnetic flux H crosses the conductive layer 21b of the fixing belt 21, an eddy current is generated in the conductive layer 21b so as to generate a magnetic field that hinders the change in the magnetic field, and the skin of the conductive layer 21b is generated. Heat is generated in proportion to the magnitude of the current flowing through the resistance and conductive layer 21b. On the other hand, the magnetic flux penetrating through the conductive layer 21b forms a closed path toward the magnetic body 24d included in the pressure facing member 24.

  The recording paper P sent to the fixing device is heated and pressed by the fixing belt 21 heated to a predetermined temperature by the electromagnetic induction heating device 22 and the pressure roll 23, and the toner image T is melt-pressed on the recording paper P. Is done. When the recording paper P is fed out from the pressure contact portion between the pressure roll 23 and the elastic member 24a, the recording paper P tends to move straight in the fed-out direction due to its rigidity, and is easily peeled off from the bent fixing belt 21. Further, it is peeled off from the fixing belt 21 by the peeling member 25.

  During the fixing operation as described above, the output of the excitation circuit 22d is controlled based on the detection value of the temperature detection device 32. That is, when the temperature detecting device 32 detects that the fixing belt 21 or a member that contacts the fixing belt is heated to a predetermined temperature or more, the voltage value applied to the exciting coil 22c, the supplied current value, or the frequency is determined. It is changed and adjusted so as to reduce the amount of heat generated in the conductive layer 21b. Further, when the detected value decreases to a predetermined lower limit value, the heat generation amount of the conductive layer 21b is adjusted to increase.

  Further, after the fixing operation as described above is finished, the heating is stopped, but the fixing belt 21 is controlled to be intermittently driven until the temperature of the fixing belt is lowered to a temperature at which no residual deformation occurs. . In this control, as shown in FIG. 7, the temperature of the fixing belt 21 is detected at predetermined time intervals, and if this temperature is equal to or higher than a preset temperature, intermittent driving is continuously performed, and the detected value When the temperature becomes equal to or lower than the set temperature, the driving of the fixing belt 21 is completely stopped. The set temperature is determined in advance by experiments or the like, and is a temperature at which no residual deformation occurs in the fixing belt even when the temperature is lowered from the temperature to the normal temperature while the fixing belt is deformed.

  On the other hand, the time interval for starting the intermittent drive is shorter as the detected temperature is higher, and is set longer as the temperature is lower, so that residual deformation does not occur during stoppage during the intermittent drive. In addition, the driving distance for this intermittent driving is set to be longer than the length of the portion that is in pressure contact with the pressure roll, and the portion that has been deformed in the pressure contact portion during the stop is completely from the pressure contact portion. The distance to escape is moved by one drive.

  FIG. 8 is a flowchart showing an example of another control method, and heating is performed using both the temperature detection device 26 that detects the temperature of the fixing belt and the temperature detection device 27 that detects the temperature of the pressure roll 23. The driving of the fixing belt after the stop is controlled. In this method, the temperature of the fixing belt is detected at predetermined time intervals, and intermittent driving is continued when the detected value is larger than a preset value. When the detected value is smaller than the set value, the temperature of the pressure roll 23 is detected, and when the detected value is larger than a preset value, intermittent driving is further continued. When the detected values of both temperature sensors are smaller than the set value, the driving of the fixing belt is completely stopped.

  In the above embodiment, the fixing belt is intermittently driven after the heating is stopped. However, the fixing belt may be continuously driven at a lower driving speed than the fixing operation. Then, the driving of the fixing belt is stopped when the temperature detected by the temperature sensor becomes equal to or lower than a value set as a temperature at which no residual deformation occurs.

  Next, an experiment for confirming the effect of performing the intermittent drive will be described.

  In the experiment, the temperature of the fixing unit belt during the fixing operation is set to 180 ° C., heating is stopped, and then intermittent driving is performed until the temperature of the fixing belt reaches room temperature (25 ° C.). Then, the deflection in the direction perpendicular to the peripheral surface of the fixing belt when the fixing belt is driven is measured. This shake is based on the position of the peripheral surface in the steady state during the fixing operation, and the amount of displacement from the reference position to the outside during driving is the shake amount.

  The intermittent driving is performed every 5 seconds, and the distance corresponding to 30 ° of the central angle of the fixing belt is moved by one driving.

  On the other hand, as an experiment for comparing with the result of the above experiment, when the fixing belt is driven at 180 ° C. and the heating is stopped and the circular driving is immediately stopped, the fixing belt is moved to 90 ° after the heating is stopped. When the driving was repeated at the same speed until the temperature became 0 ° C., and then stopped, the temperature was lowered to room temperature for each case where the driving was repeated until the temperature reached 45 ° C., and then the driving was performed again and the vibration was measured. The results of these experiments are shown in Table 1.

本実験において、定着ベルトの温度が１８０℃から２５℃（室温）になるまでの時間は加熱を停止してから１８０秒であり、その１８０秒間にベルトの間欠駆動を５秒ごとに行った場合、常温となった後の駆動時における定着ベルトの外へ向けての変形（振れ）は0.18mmであった。定着ベルトの外周面と加熱装置のギャップを1mmから３mmに設定している上記実施例の定着装置では、定着ベルトの振れによって電磁誘導加熱装置と接触することはない。

In this experiment, the time until the temperature of the fixing belt is changed from 180 ° C. to 25 ° C. (room temperature) is 180 seconds after the heating is stopped, and the belt is intermittently driven every 5 seconds during the 180 seconds. The deformation (runout) toward the outside of the fixing belt during driving after reaching room temperature was 0.18 mm. In the fixing device according to the above embodiment in which the gap between the outer peripheral surface of the fixing belt and the heating device is set to 1 mm to 3 mm, the electromagnetic induction heating device does not come into contact with the fixing belt due to vibration.

  On the other hand, when intermittent driving is performed every 5 seconds for 180 seconds, the rotation speed of the fixing belt is about 3 times and the moving distance is 282 mm (when the peripheral length of the fixing belt is 95.25 mm and the process speed is 140 mm / s). ).

  The shake in the above experiment is almost the same as that in the comparative example when the circuit is driven at the same speed until the temperature reaches room temperature after stopping the heating (Table 1: bottom row in the right column), and almost no residual deformation occurs. However, in the comparative example, the driving is performed at the same speed as that for heating for 180 seconds, the rotation speed of the fixing belt is 267 times, and the moving distance is as extremely large as 25,200 mm.

  Further, when the driving of the fixing belt is stopped immediately after the heating is stopped (Table 1: right column, first row), the rotation speed of the fixing belt does not increase, but a large fluctuation is caused by driving after the temperature reaches normal temperature. Has occurred. Further, when the fixing belt is stopped after being driven until the temperature is lowered to 90 ° C., and when it is stopped after being driven until it is lowered to 45 ° C., a large shake occurs and the rotation speed of the fixing belt is greatly increased.

  Therefore, by intermittently driving the fixing belt, it is possible to prevent the remaining amount of the fixing belt from being deformed, and it is possible to suppress the occurrence of shake during re-driving. In addition, the rotation speed and moving distance of the fixing belt can be significantly reduced as compared with the case where the driving at the same speed as the fixing operation is continued to prevent residual deformation, and the durability of the fixing belt is remarkably improved. be able to.

    Next, another example of a fixing belt that can be used in the fixing device shown in FIG. 2 will be described.

  As shown in FIG. 4, in the fixing belt 41, a metal layer 41b is formed outside the polyimide layer 41a, a second polyimide layer 41c is formed outside the polyimide layer 41a, and the metal layer 41b is formed by the polyimide layers 41a and 41c. It is intended to be sandwiched. And the elastic layer 41d and the surface release layer 41e are formed in the outer side. Such a fixing belt 41 can be formed by the following process.

  A polyimide film having a thickness of 60 μm formed into a tube shape having an outer shape of 30 mm (manufactured by Nitto Denko) is used as the first polyimide layer 41a, and electroless nickel plating is performed on the outer surface thereof. In this step, the polyimide film is immersed in an electroless nickel plating solution to form a nickel plating layer having a thickness of about 1 μm on the outer peripheral surface. Next, copper is laminated to a thickness of 10 μm by electrolytic plating as the metal layer 41b that generates heat by electromagnetic induction. Next, using a polyimide varnish, a polyimide layer 41c having a thickness of 40 μm is formed on the metal layer 41b by a conventional method, and the electromagnetic induction heating layer is sandwiched between the polyimide layers 41a and 41b. Next, a silane coupling agent primer (not shown) of about 1 μm is applied on the outer surface layer of the second polyimide layer 41c, dried, and then coated with silicone rubber as the elastic layer 41d. The coated rubber layer is ground to adjust the thickness from 200 μm to 500 μm, and then a silicone primer (not shown) is applied to the thickness of about 1 μm, and the entire outer peripheral surface of the belt is toner releasable. A surface release layer 41e having a thickness of 30 μm is formed by using a PFA tube or the like having

  In such a fixing belt, since the metal layer 41b that generates heat by electromagnetic induction is sandwiched between the polyimide layers 41a and 41c, the bending strain generated even when it is repeatedly bent is small, and deterioration of the metal layer can be prevented.

  FIG. 5 is a schematic configuration diagram illustrating an image forming apparatus according to an embodiment of the present invention.

  This image forming apparatus includes a cylindrical photosensitive drum 51 on which a latent image due to a difference in electrostatic potential is formed, a charging device 52, an exposure device 53, and a developing unit 54 around the photosensitive drum 51. , An endless intermediate transfer belt 55, a cleaning device 56, and a static elimination exposure device 57. Further, inside the intermediate transfer belt 55, the transfer charger 58 that primarily transfers the toner image formed on the photosensitive drum to the intermediate transfer belt 55, and the two support rolls 59a and 59b are subjected to secondary transfer. The intermediate transfer belt 55 is stretched around the intermediate transfer belt 55 so as to be able to rotate. Further, a pressure roll 61 is disposed at a position facing the transfer roll 60 via the intermediate transfer belt 55. Further, along the inner peripheral surface of the intermediate transfer belt 55, an electromagnetic induction heating device 62 that heats the toner image on the intermediate transfer belt 55 and the intermediate transfer belt 55, and a temperature detection device that measures the temperature of the intermediate transfer belt 55. 63, and a cleaning device 64 for removing residual toner on the intermediate transfer belt 55.

  The photosensitive drum 51, the charging device 52, the exposure device 53, the developing unit 54, the cleaning device 56, the static elimination exposure device 57, and the transfer charging device 58 can be the same as the image forming apparatus shown in FIG. .

  As shown in FIG. 6, the intermediate transfer belt 55 includes a base layer 55a made of a sheet member having high heat resistance, a conductive layer 55b laminated thereon, and a surface release layer 55c as the uppermost layer. For the conductive layer 55b, a material having a specific resistance value is selected so that sufficient heat generation can be obtained by electromagnetic induction. Further, the surface release layer 55c is preferably a sheet or coat layer having high release properties, and is preferably a light-transmitting material, particularly a transparent material, such as PFA.

  The temperature detection device 63 can be the same as the temperature detection device 26 included in the fixing device shown in FIG. 2, and the temperature sensor is pressed against the inner peripheral surface of the intermediate transfer member 55 by the elastic repulsion force of the elastic support portion. Thus, the temperature is detected. Since the elastic repulsion force of the elastic support portion is suppressed, the temperature sensor is strongly pressed against the intermediate transfer belt 55 so that the intermediate transfer belt 55 is not excessively deformed or damaged.

  In this image forming apparatus, the toner image T transferred from the photosensitive drum 51 onto the intermediate transfer belt 55 and overlaid with a plurality of colors is heated in a heating region facing the electromagnetic induction heating device 62 by the circular movement of the intermediate transfer belt 55. Pass through. The toner image T is heated and melted on the intermediate transfer belt, and is conveyed to a pressure contact portion between the transfer roll 60 and the pressure roll 61. In synchronization with this conveyance, the recording paper P is fed from a paper tray (not shown) between the intermediate transfer belt 55 and the pressure roll 61, and the toner image T is pressure-bonded to the recording paper P to transfer and fix. Are performed simultaneously.

  At this time, the power supplied to the electromagnetic induction heating device 62 is controlled by the detection value of the temperature detection device 63 so that the surface temperature of the intermediate transfer belt 55 maintains a desired temperature. Further, when an abnormal temperature is detected, the supply of power is cut off immediately.

  Also in this image forming apparatus, the rotation driving of the intermediate transfer belt 55 is controlled in the same manner as the rotation driving of the fixing belt 21 in the fixing device shown in FIG.

  That is, when the fixing operation is completed, the heating of the intermediate transfer belt is also stopped. At this time, the intermediate transfer belt 55 does not immediately stop rotating, but the surface temperature of the intermediate transfer belt 55 detected by the temperature detection device 63 is set to a temperature set in advance as a temperature at which no residual deformation occurs in the belt. It is controlled to intermittently drive until The time interval of intermittent driving, the driving distance once, and the like are determined so that no residual deformation occurs in the intermediate transfer belt 55 as in the fixing belt shown in FIG. In addition, after the heating is stopped, it may be controlled to rotate at low speed instead of intermittent driving, and when the detected temperature becomes equal to or higher than a preset value, the belt is driven completely. Stopped.

1 is a schematic configuration diagram illustrating an image forming apparatus using a fixing device according to an embodiment of the present invention. FIG. 2 is a schematic configuration diagram illustrating a fixing device used in the image forming apparatus illustrated in FIG. 1. FIG. 3 is an enlarged cross-sectional view of a fixing belt that can be used in the fixing device shown in FIG. 2. FIG. 4 is an enlarged cross-sectional view illustrating another example of a fixing belt that can be used in the fixing device illustrated in FIG. 2. 1 is a schematic configuration diagram illustrating an image forming apparatus according to an embodiment of the present invention. FIG. 6 is an enlarged cross-sectional view of an intermediate transfer belt that can be used in the image forming apparatus shown in FIG. 5. 6 is a flowchart showing control of driving of the fixing belt after heating of the fixing belt is stopped. 6 is a flowchart showing control of driving of the fixing belt after heating of the fixing belt is stopped.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,51 Photoconductor drum 2,52 Charging device 3,53 Exposure device 4,54 Development unit 5 Intermediate transfer body 6,56 Cleaning device 7,57 Static elimination exposure device 8,58 Transfer charger 9, 59 Support roll 10 Transfer facing Roll 11, 60 Transfer roll 12 Fixing device 13, 64 Cleaning device 21, Fixing belt 21a Base layer 21b Conductive layer 21c Elastic layer 21d Surface release layer 22, 62 Electromagnetic induction heating device 23 Pressure roll (pressure member)
24 pressure facing member 25 peeling member 26, 27, 63 temperature detecting device 28 control device 31 temperature sensor 32 elastic support member 33 restraining member 41 fixing belt 41a first polyimide layer 41b metal layer 41c second polyimide layer 41d elastic layer 41e Surface release layer 55 Intermediate transfer belt 55a Base layer 55b Conductive layer 55c Surface release layer 61 Pressure roll

Claims (7)

An endless belt supported movably in the circumferential direction;
An opposing end surface having an endless peripheral surface, the peripheral surface being in contact with the outer peripheral surface of the belt and the inner peripheral surface of the belt and sandwiching the belt between the pressurizing member Members,
A heating device for heating the belt;
Have
As the endless peripheral surface of the belt or the pressure member is driven to circulate, a recording sheet is sandwiched between the pressure member and the belt, and the toner carried on the recording sheet is heated. A fixing device for pressure bonding,
Temperature detecting means for detecting the temperature of the belt or a member that becomes high as the belt is heated by a heating device;
The fixing device is characterized in that the belt is intermittently driven after the heating by the heating device is stopped until the temperature detected by the temperature detecting means decreases to a predetermined temperature.   The fixing device according to claim 1, wherein a driving distance of the belt that is intermittently driven is set to be greater than a length of a portion that is in pressure contact with the pressure member.   2. The interval of time during which the belt is intermittently driven is set short when the temperature detected by the temperature detecting means is high, and is set longer as the detected temperature becomes lower. The fixing device according to 1. An endless belt supported movably in the circumferential direction;
A heating device for heating the belt;
An endless peripheral surface, the peripheral surface having a pressure member pressed against the outer peripheral surface of the belt,
As the endless peripheral surface of the belt or the pressure member is driven to circulate, a recording sheet is sandwiched between the pressure member and the belt, and the toner carried on the recording sheet is heated. A fixing device for pressure bonding,
Temperature detecting means for detecting the temperature of the belt or a member that becomes high as the belt is heated by a heating device;
The belt is driven at a lower speed than that at the time of fixing the toner until the temperature detected by the temperature detecting means is lowered to a predetermined temperature after the heating by the heating device is stopped. Fixing device to do.   The speed at which the belt is driven after the heating device is stopped is set to be fast when the temperature detected by the temperature detecting means is high, and is set to be slow as the detected temperature becomes low. The fixing device according to claim 4. The pressure member is a roll-shaped member,
The fixing device according to claim 1, wherein the temperature detecting unit detects a temperature of the pressure member. An image forming unit that selectively transfers toner to a latent image due to a difference in electrostatic potential to form a toner image;
An endless intermediate transfer belt on which the formed toner image is once transferred;
A heating device for heating and melting the toner image carried on the intermediate transfer belt;
An image forming apparatus having a secondary transfer unit that presses the toner image on the intermediate transfer belt to a recording sheet and performs transfer and fixing simultaneously;
Temperature detection means for detecting the temperature of the intermediate transfer belt or a member that stretches the intermediate transfer belt;
The intermediate transfer belt is driven at a lower speed than that at the time of intermittent drive or toner image formation until the temperature detected by the temperature detecting means is lowered to a predetermined temperature after heating by the heating device is stopped. An image forming apparatus.

Images