JP2008203455A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device designed so as to shorten a restoring time required for a fixing member to return to its fixing temperature, and to provide an image forming apparatus. <P>SOLUTION: A heating element 108 disposed in contact with the internal circumferential face of a fixing belt 102 extends to areas (A and C) where the heating element 108 does not face an excitation coil 120, in the moving direction of the fixing belt 102. An area (B) where the heating element 108 faces the excitation coil 120 generates heat by electromagnetic induction of a magnetic field H, and the heat is transmitted to the areas (A and C) where the heating element 108 does not face the excitation coil 120. In this case, if the operation of the excitation coil 120 is stopped and a standby state is required, the fixing belt 102 receives heat from the heating element 108 in a wide area, that is, in the area (B) where the heating element 108 faces the excitation coil 120 and the areas (A and C) where the heating element 108 does not face the excitation coil 120. This makes it possible to keep the temperature of the fixing belt 102 higher and shortens a restoring time required for the fixing belt 102 to return to its fixing temperature. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fixing device and an image forming apparatus.

  2. Description of the Related Art Conventionally, in an image forming apparatus such as a printer or a copying machine that forms an image using an electrophotographic method, a toner image transferred onto a recording sheet is pressed with a fixing roller or a fixing belt having a heat source such as a halogen heater. A fixing device that melts and fixes toner by the action of heat and pressure through a nip formed by a roller is used.

  On the other hand, as a heat source, there is an electromagnetic induction heating type fixing device using a coil that generates a magnetic field by energization and a heating element that generates heat by generating an eddy current by electromagnetic induction of the magnetic field.

As an example of a fixing device using an electromagnetic induction heating method, an exciting coil that generates magnetic flux, a fixing belt having a conductive layer that generates heat by the action of magnetic flux from the exciting coil, and a guide member that guides the conveyance of the fixing belt There is a fixing device (see, for example, Patent Document 1).
JP 2006-047988 A

  However, the fixing device of Patent Document 1 is a so-called local heating method in which only a part of the fixing belt in the circumferential direction is heated. Since only a part of the fixing belt is heated at the start of fixing, the fixing device can be fixed. It took a long time to return.

  An object of the present invention is to provide a fixing device and an image forming apparatus in which a return time until the fixing member reaches a fixing temperature is shortened.

  A fixing device according to a first aspect of the present invention includes a magnetic field generating unit that generates a magnetic field, a heating element that is disposed opposite to the magnetic field generating unit, and generates heat by electromagnetic induction of the magnetic field, and is wound around the heating element. Fixing having an endless fixing member that is rotatably supported at both ends, a support disposed inside the fixing member, and a pressure rotator that pressurizes the support through the fixing member. In the apparatus, the heating element extends in a moving direction of the fixing member to a region not facing the magnetic field generating unit.

  According to the above configuration, the region of the heating element that faces the magnetic field generating means generates heat due to electromagnetic induction of the magnetic field generated by the magnetic field generating means.

  Subsequently, the heat in the region facing the magnetic field generating means in the heating element is transferred to the region not facing the magnetic field generating means.

  Here, when the operation of the magnetic field generating means is stopped and the standby state is entered, the fixing member is given heat in a wide area of the heating element facing the magnetic field generating means and a non-facing area. Thereby, the temperature of the fixing member can be maintained at a higher temperature, and the return time until the fixing member reaches a temperature at which the fixing member can be fixed is shortened.

  Further, since heat is evenly applied to the fixing member, the fixing member does not buckle due to distortion due to a difference in thermal expansion.

  Further, since it is not necessary to adjust the temperature by rotating the fixing member during standby, the driving noise of the fixing device during standby can be reduced. Further, since it is not necessary to rotate the fixing member during standby, deterioration of slidability due to wear on the inner surface of the fixing member can be reduced.

  In the fixing device according to a second aspect of the present invention, the heating element is provided on a heat generating layer that generates heat by electromagnetic induction of the magnetic field and on the surface of the heat generating portion, and the friction force between the fixing member and the heat generating portion is obtained. And a heat release layer extending in a moving direction of the fixing member to a region not facing the magnetic field generating means.

  According to the above configuration, in order to improve the slidability between the fixing member and the heating element, the temperature of the fixing member can be maintained at a higher temperature even when a release layer is formed on the surface of the heating element to form a multilayer. The recovery time until the fixing member reaches a fixing temperature is shortened.

  According to a third aspect of the present invention, there is provided the fixing device according to the present invention, wherein the heating element includes a heating part that generates heat by electromagnetic induction of the magnetic field, and a heat conduction part that adjusts a temperature distribution of the heating part in contact with the heating part. It is characterized in that at least the heat conducting part extends in the moving direction to a region not facing the magnetic field generating means.

  According to the above configuration, when the operation of the magnetic field generating unit is stopped and the standby state is entered, the heat of the heat generating part is transmitted to the heat conducting part, and the temperature distribution of the heat generating part is adjusted and equalized. The fixing member is supplied with heat from the heat conducting section in a wide area of the heating element facing the magnetic field generating means and a non-facing area.

  Thereby, the temperature of the fixing member can be maintained at a higher temperature, and the return time until the fixing member reaches a temperature at which the fixing member can be fixed is shortened.

  Further, since heat is evenly applied to the fixing member, the fixing member does not buckle due to distortion due to a difference in thermal expansion.

  Further, since it is not necessary to adjust the temperature by rotating the fixing member during standby, the driving noise of the fixing device during standby can be reduced. Further, since it is not necessary to rotate the fixing member during standby, deterioration of slidability due to wear on the inner surface of the fixing member can be reduced.

  The fixing device according to a fourth aspect of the present invention is characterized in that the thermal conductivity of the heat conducting portion is higher than the thermal conductivity of the heat generating portion.

  According to the above configuration, since the heat conductivity of the heat conducting part is larger than the heat conductivity of the heat generating part, the heat quantity of the heat generating part is easily transmitted to the heat conducting part, and the temperature of the heat generating part can be adjusted in a short time.

  In addition, when continuously fixing a small size recording medium, the temperature of the heat generating portion in the passage area of the recording medium is decreased due to the loss of heat in the recording medium, but the heat amount is not lost in the heat generating portion in the non-passing area. The temperature rises due to accumulation.

  Here, since the temperature difference (temperature distribution) between the pass area and the non-pass area of the recording medium in the heat generating part is adjusted by the heat conducting part, the temperature distribution of the heat generating part becomes uniform.

  The fixing device according to claim 5 of the present invention is characterized in that the heat conducting portion is in contact with the fixing member.

  According to the above configuration, since the heat conducting portion is in contact with the fixing member, the heat conduction efficiency to the fixing member is good, and the temperature distribution in the circumferential direction of the fixing member can be made uniform.

  The fixing device according to a sixth aspect of the present invention is characterized in that the heat conducting portion is in a non-contact state with the fixing member.

  According to the above configuration, since the fixing member and the heat conducting portion are in a non-contact state, the heat of the fixing member to be heated is difficult to escape, and the temperature of the fixing member can be increased in a short time when the power is turned on.

  An image forming apparatus according to a seventh aspect of the present invention is a fixing device according to any one of the first to fifth aspects, an exposure unit that emits exposure light, and a latent image formed by the exposure light. Is developed with a developer to form a developer image, a transfer unit that transfers the developer image made visible at the development unit onto a recording medium, and the developer image is transferred at the transfer unit. And a transport unit that transports the recorded recording medium to the fixing device.

  According to the above configuration, the return time to the fixing set temperature of the fixing member in the fixing device can be shortened, so that the processing time for image formation can be shortened.

  According to the first aspect of the present invention, the return time until the fixing member reaches a temperature at which the fixing member can be fixed is shorter than in the case where the present configuration is not provided.

  According to the second aspect of the present invention, even when the release layer is formed on the surface of the heating element to make it multilayer, the return time until the temperature at which the fixing member can be fixed becomes short.

  According to the third aspect of the present invention, the return time until the fixing member reaches a temperature at which the fixing member can be fixed is shorter than in the case where the present configuration is not provided.

  The invention according to claim 4 can adjust the temperature of the heat generating portion in a short time as compared with the case where the present configuration is not provided.

  According to the fifth aspect of the present invention, the temperature distribution in the circumferential direction of the fixing member can be made uniform as compared with the case where this configuration is not provided.

  According to the sixth aspect of the present invention, the temperature of the fixing member can be raised in a short time when the power is turned on, as compared with the case where this configuration is not provided.

  According to the seventh aspect of the present invention, the processing time for image formation can be shortened as compared with the case where the present configuration is not provided.

  A first embodiment of a fixing device and an image forming apparatus of the present invention will be described with reference to the drawings.

  FIG. 1 shows a printer 10 as an image forming apparatus.

  In the printer 10, the optical scanning device 54 is fixed to the housing 12 constituting the main body of the printer 10, and control for controlling the operation of each part of the optical scanning device 54 and the printer 10 at a position adjacent to the optical scanning device 54. A unit 50 is provided.

  The optical scanning device 54 scans a light beam emitted from a light source (not shown) with a rotating polygon mirror (polygon mirror), reflects it with a plurality of optical components such as a reflection mirror, and produces yellow (Y), magenta (M), Light beams 60Y, 60M, 60C, and 60K corresponding to cyan (C) and black (K) toners are emitted.

  The light beams 60Y, 60M, 60C, and 60K are guided to the corresponding photoreceptors 20Y, 20M, 20C, and 20K, respectively.

  A paper tray 14 for storing the recording paper P is provided below the printer 10. A pair of registration rollers 16 for adjusting the position of the leading end of the recording paper P is provided above the paper tray 14.

  An image forming unit 18 is provided at the center of the printer 10. The image forming unit 18 includes the above-described four photoconductors 20Y, 20M, 20C, and 20K, which are arranged in a vertical line.

  Charging rollers 22Y, 22M, 22C, and 22K that charge the surfaces of the photoreceptors 20Y, 20M, 20C, and 20K are provided on the upstream side in the rotation direction of the photoreceptors 20Y, 20M, 20C, and 20K.

  Further, on the downstream side in the rotation direction of the photoconductors 20Y, 20M, 20C, and 20K, developing units 24Y, 24M that develop the Y, M, C, and K toners on the photoconductors 20Y, 20M, 20C, and 20K, respectively. 24C and 24K are provided.

  On the other hand, the first intermediate transfer member 26 is in contact with the photoconductors 20Y and 20M, and the second intermediate transfer member 28 is in contact with the photoconductors 20C and 20K. The third intermediate transfer member 30 is in contact with the first intermediate transfer member 26 and the second intermediate transfer member 28.

  A transfer roll 32 is provided at a position facing the third intermediate transfer member 30. The recording paper P is conveyed between the transfer roll 32 and the third intermediate transfer body 30, and the toner image on the third intermediate transfer body 30 is transferred to the recording paper P.

  A fixing device 100 is provided downstream of the paper conveyance path 34 through which the recording paper P is conveyed. The fixing device 100 includes a fixing belt 102 and a pressure roll 104, and heats and presses the recording paper P to fix the toner image on the recording paper P.

  The recording paper P on which the toner image is fixed is discharged to a tray 38 provided on the upper portion of the printer 10 by a paper transport roll 36.

  Here, image formation of the printer 10 will be described.

  When image formation is started, the surfaces of the photoreceptors 20Y to 20K are uniformly charged by the charging rollers 22Y to 22K.

  Light beams 60Y to 60K corresponding to the output image are irradiated from the optical scanning device 54 onto the surfaces of the charged photoreceptors 20Y to 20K, and electrostatic latent images corresponding to the respective color separation images are formed on the photoreceptors 20Y to 20K. Is done.

  The developing devices 24Y to 24K selectively apply toners of respective colors, that is, Y to K, to the electrostatic latent images, and Y to K toner images are formed on the photoreceptors 20Y to 20K.

  Thereafter, the magenta toner image is primarily transferred from the magenta photosensitive member 20M to the first intermediate transfer member 26. Further, a yellow toner image is primarily transferred from the yellow photoreceptor 20Y to the first intermediate transfer member 26, and is superimposed on the magenta toner image on the first intermediate transfer member 26.

  On the other hand, similarly, a black toner image is primarily transferred from the black photosensitive member 20K to the second intermediate transfer member 28. Further, a cyan toner image is primarily transferred from the cyan photoconductor 20 </ b> C to the second intermediate transfer member 28, and is superimposed on the black toner image on the second intermediate transfer member 28.

  The magenta and yellow toner images primarily transferred to the first intermediate transfer member 26 are secondarily transferred to the third intermediate transfer member 30. On the other hand, the black and cyan toner images primarily transferred to the second intermediate transfer member 28 are also secondarily transferred to the third intermediate transfer member 30.

  Here, the magenta and yellow toner images that have been secondarily transferred first, and the cyan and black toner images are superimposed, and a color (three colors) and black full-color toner images are formed on the third intermediate transfer member 30. Is done.

  The secondary color transferred full-color toner image reaches the nip portion between the third intermediate transfer body 30 and the transfer roll 32. In synchronization with the timing, the recording paper P is conveyed from the registration roll 16 to the nip portion, and a full-color toner image is thirdarily transferred (final transfer) onto the recording paper P.

  Thereafter, the recording paper P is sent to the fixing device 100 and passes through a nip portion between the fixing belt 102 and the pressure roll 104. At that time, the full color toner image is fixed on the recording paper P by the action of heat and pressure applied from the fixing belt 102 and the pressure roll 104. After fixing, the recording paper P is discharged to the tray 38 by the paper transport roll 36, and the formation of the full color image on the recording paper P is completed.

  Next, the fixing device 100 according to the present embodiment will be described.

  As shown in FIG. 2, the fixing device 100 includes a housing 106 in which an opening for entering or discharging the recording paper P is formed.

  Inside the housing 106, an endless fixing belt 102 having both ends (not shown) supported so as to be rotatable in the direction of the arrow X is provided.

  As shown in FIG. 3b, the fixing belt 102 is composed of a base layer 134, an elastic layer 136, and a release layer 138 from the inside to the outside, and these are laminated and integrated.

  The base layer 134 only needs to maintain the mechanical strength of the fixing belt 102. In the present embodiment, polyimide is used, but nonmagnetic SUS may be used. The thickness is 50 μm.

  Further, the fixing belt may have a heat generating layer made of, for example, copper or aluminum that is electromagnetically heated by an exciting coil described later.

  The elastic layer 136 is preferably silicon rubber or fluorine rubber from the viewpoint of obtaining excellent elasticity and heat resistance. In this embodiment, silicon rubber is used. In the present embodiment, the thickness of the elastic layer 136 is 200 μm.

  The release layer 138 is provided to weaken the adhesive force with the toner T (see FIG. 2) melted on the recording paper P so that the recording paper P can be easily separated from the fixing belt 102. In order to obtain excellent surface releasability, it is preferable to use a fluororesin, a silicon resin, or a polyimide resin as the release layer 138. In this embodiment, PFA (tetrafluoroethylene / perfluoroalkoxyethylene copolymer) is used. Resin). The thickness of the release layer 138 is 10 μm.

  As shown in FIG. 2, a bobbin 116 made of an insulating material is disposed at a position facing the outer peripheral surface of the fixing belt 102. The distance between the bobbin 116 and the fixing belt 102 is about 1 to 3 mm. The bobbin 116 is formed in a substantially arc shape that follows the outer peripheral surface of the fixing belt 102, and is provided with a protruding portion 118.

  An excitation coil 120 is wound around the bobbin 116 a plurality of times in the axial direction (the depth direction in FIG. 2) around the convex portion 118. The exciting coil 120 is energized by an energizing circuit 134 (see FIG. 4) described later to generate a magnetic field H.

  A magnetic core 122 formed in a substantially arc shape following the arc shape of the bobbin 116 is disposed at a position facing the exciting coil 120 and supported by the bobbin 116.

  On the other hand, on the inner side of the fixing belt 102, a heating element 108 is provided that comes into surface contact with the inner peripheral surface of the fixing belt 102 and generates heat to raise the temperature of the fixing belt 102 to a preset fixing temperature.

  The heating element 108 is wider than the region (B) facing the exciting coil 120 and is in contact with the inner peripheral surface of the fixing belt 102 in a region (A + B + C) excluding the nip portion between the fixing belt 102 and the pressure roll 104. is doing.

  As shown in FIG. 3A, the heating element 108 is composed of a heating part 130 and a release part 132 from the inside to the outside.

  The heating element 108 is fixed to the housing 106 (see FIG. 2).

  The heat generating part 130 is a metal material that generates heat by electromagnetic induction action in which eddy current flows so as to generate a magnetic field that cancels the magnetic field H (see FIG. 2). For example, gold, silver, copper, aluminum, zinc, tin, lead , Bismuth, beryllium, antimony, or metal materials of these alloys can be used. In the present embodiment, iron having a thickness of 1 mm is used as the heat generating layer 130.

  The release part 132 is provided to reduce the frictional force when the fixing belt 102 (see FIG. 2) slides on the surface of the heating element 108. In this embodiment, PTFE (polytetrafluoroethylene) is used. It is applied.

  A support member 110 is provided inside the fixing belt 102. The support member 110 is made of aluminum which is a nonmagnetic material, and both ends thereof are fixed to the housing 106.

  A pressing pad 112 for pressing the fixing belt 102 outward at a predetermined pressure is fixed to the end surface of the support member 110.

  The pressure pad 112 is made of an elastic member such as urethane rubber or sponge, or a heat resistant resin such as PES (polyether sulfone) or PPS (polyphenylene sulfide), and one end surface is in contact with the inner peripheral surface of the fixing belt 102. Thus, the fixing belt 102 is pressed.

  On the other hand, at a position facing the outer peripheral surface of the fixing belt 102, the fixing belt 102 is pressed with a pressing force F toward the pressing pad 112 and is rotated in the arrow Y direction by a driving mechanism including a motor and a gear (not shown). A pressure roll 104 is disposed.

  The pressure roll 104 has a configuration in which silicon rubber and PFA are coated around a cored bar 114 made of a metal such as aluminum.

  Here, when the pressure roll 104 is rotated by a drive mechanism (not shown), the fixing belt 102 is driven to rotate.

  The pressing pad 112 presses the fixing belt 102 toward the pressure roll 104 and bends along the inner peripheral surface of the fixing belt 102 to widen the area of the nip portion between the fixing belt 102 and the pressure roll 104. ing.

  A temperature sensor 124 that measures the temperature of the surface of the fixing belt 102 is provided in a non-contact manner in an area on the outer peripheral surface side of the fixing belt 102 that is not opposed to the excitation coil 120 and on the discharge side of the recording paper P.

  The temperature sensor 124 is configured by an infrared sensor (thermopile) that receives infrared rays emitted from the surface of the fixing belt 102 and generates a thermoelectromotive force according to the amount of energy.

  As shown in FIG. 4, the temperature sensor 124 is connected to a control circuit 130 provided in the control unit 50 (see FIG. 1) via a wiring 128. The control circuit 130 is connected to the energizing circuit 134 via the wiring 132, and the energizing circuit 134 is connected to the above-described exciting coil 120 via the wirings 136 and 138.

  Here, the control circuit 130 measures the temperature of the surface of the fixing belt 102 based on the amount of electricity sent from the temperature sensor 124, and this measured temperature and a preset fixing temperature (170 ° C. in the present embodiment) stored in advance. Compare with When the measured temperature is lower than the fixing set temperature, the energizing circuit 134 is driven to energize the exciting coil 120, and a magnetic field H (see FIG. 2) as a magnetic circuit is generated. On the other hand, when the measured temperature is higher than the fixing set temperature, the energization circuit 134 is stopped.

  The energization circuit 134 is driven or stopped based on an electrical signal sent from the control circuit 130, and supplies or stops supplying an alternating current having a predetermined frequency to the exciting coil 120 via the wires 136 and 138. .

  Next, the operation of the first embodiment of the present invention will be described.

  As shown in FIGS. 1 and 2, the recording paper P onto which the toner T has been transferred is sent to the fixing device 100 through the image forming process of the printer 10 described above.

  In the fixing device 100, the pressure roll 104 starts to rotate in the arrow Y direction, and the fixing belt 102 is driven to rotate in the arrow X direction. At this time, the energizing circuit 134 (see FIG. 4) is driven based on the electrical signal from the control circuit 130 (see FIG. 4), and an alternating current is supplied to the exciting coil 120.

  When an alternating current is supplied to the exciting coil 120, the magnetic field H as a magnetic circuit repeats generation and disappearance around the exciting coil 120.

  When the magnetic field H enters the heat generating part 130 of the heat generating element 108, an eddy current (not shown) is generated in the heat generating part 130 so that a magnetic field that prevents the change of the magnetic field H is generated.

  The heat generating part 130 generates heat in proportion to the skin resistance of the heat generating part 130 and the magnitude of the eddy current flowing through the heat generating part 130, thereby heating the fixing belt 102.

  The temperature of the surface of the fixing belt 102 is detected by the temperature sensor 124, and when the fixing temperature has not reached 170 ° C., the control circuit 130 drives and controls the energizing circuit 134 so that the excitation coil 120 has a predetermined frequency (from 20 kHz to 20 kHz). 100 kHz). When the fixing set temperature is reached, the control circuit 130 stops the control of the energization circuit 134.

  Subsequently, the recording paper P sent to the fixing device 100 is heated and pressed by the fixing belt 102 having a predetermined fixing set temperature (170 ° C.) and the pressure roll 104, and the toner image is recorded on the surface of the recording paper P. To be established.

  When the recording paper P is fed from the nip portion between the fixing belt 102 and the pressure roll 104, the recording paper P is peeled off from the fixing belt 102 because the recording paper P tends to advance straight in the direction along the nip portion due to its own rigidity.

  The recording paper P discharged from the fixing device 100 is discharged to the tray 44 by the paper transport roll 42.

  In this way, the fixing device 100 that has been fixed on the recording paper P is in a standby state until the next image forming process is performed.

  Here, as a comparative example with the present invention, FIG. 5a shows a graph of the heating element temperature (T3) and the fixing belt temperature (T4) at the exit of the nip portion in a conventional electromagnetic induction heating type fixing device. In the conventional electromagnetic induction heating type fixing device, the heating element is provided only in a region facing the magnetic field generating means.

  In the conventional fixing device, the heating element itself that has been heated once by the fixing operation is held in a state close to the fixing set temperature during the standby (graph T3).

  However, since the heat is not supplied to the fixing belt in a region that is not in contact with the heating element, the temperature of the fixing belt is greatly reduced in comparison with the heating element during standby. For this reason, when the fixing operation is resumed, the fixing belt has a long temperature rise time (recovery time) to a predetermined fixing set temperature (graph T4), and thus a long recovery time as the fixing device. .

  On the other hand, as shown in FIG. 5b, in the fixing device 100 of the present invention, the heating element 108 that has been once heated by the fixing operation is held in a state close to the fixing set temperature during the standby (graph T1). ).

  In addition, since heat is conducted inside the heating element 108, heat is given to the fixing belt 102 in a region in contact with the heating element 108, so that a decrease in the temperature of the fixing belt 102 is suppressed, and the fixing belt 102 is almost entirely removed. It is held at a temperature close to the temperature of the heating element 108 over the circumference. For this reason, when the fixing operation is resumed, the temperature rise time (recovery time) of the fixing belt 102 to the predetermined fixing set temperature is shortened (graph T2), and the restoration time of the entire fixing device is shortened.

  Next, a second embodiment of the fixing device and the image forming apparatus of the present invention will be described with reference to the drawings.

  Note that components that are basically the same as those in the first embodiment described above are given the same reference numerals as those in the first embodiment, and descriptions thereof are omitted.

  As shown in FIG. 6, the fixing device 140 is obtained by replacing the heating element 108 of the fixing device 100 (see FIG. 2) with a heating element 141.

  The heating element 141 includes a heat generating portion 142 that is in surface contact with the inner peripheral surface of the fixing belt 102, and a heat conducting portion 144 that is disposed on the back side of the heat generating portion 142 (on the opposite side to the fixing belt 102). Are united.

  The heat generating portion 142 is a metal material that generates heat due to electromagnetic induction action in which eddy current flows so as to generate a magnetic field that cancels the magnetic field H. For example, a metal material of iron, nickel, cobalt, SUS, or an alloy thereof is used. Can do. In this embodiment, iron is used. Further, the heat generating portion 142 is disposed only in the region (B) facing the exciting coil 120.

  On the other hand, the heat conducting portion 144 is made of a metal such as silver, copper, gold, aluminum, or an alloy thereof, and in this embodiment, copper having a thickness of 1 mm is used. As a result, the thermal conductivity of the heat conducting unit 144 is greater than that of the heat generating unit 142.

  In addition to the region (B) facing the exciting coil 120, the heat conducting unit 144 extends to the vicinity of the nip between the fixing belt 102 and the pressure roll 104 (A + B + C). In regions (A and C) that do not face the exciting coil 120, the heat conducting unit 144 is in contact with the fixing belt 102.

  The heat generating part 142 and the heat conducting part 144 are attached and integrated with an adhesive.

  Next, the operation of the second embodiment of the present invention will be described.

  As shown in FIGS. 6 and 7, in the fixing belt 102, an area through which the small recording paper P passes is L3, an area through which the large recording paper P passes is L2 + L3 + L4, and the recording paper P does not pass through the exciting coil. The areas where 120 is not arranged are assumed to be L1 and L5. In addition, the temperature graph of the fixing belt 102 without the heat conducting unit 144 is T1, and the temperature graph of the fixing belt 102 of the present embodiment is T2.

  First, when the small size recording paper P is continuously passed and fixed, the recording paper P is deprived of heat in the passage region L3 of the recording paper P in the fixing belt 102, and the temperature of the fixing belt 102 is fixed. It falls below the set temperature (170 ° C).

  Based on the difference between the temperature detected by the temperature sensor 124 and the preset fixing temperature, the control circuit 130 (see FIG. 4) sets the energizing circuit 134 (see FIG. 4) so that the temperature of the fixing belt 102 approaches the preset fixing temperature. And the heat generating part 142 generates heat. As a result, the temperature of the fixing belt 102 increases.

  In the non-passing areas L2 and L4 (including L1 and L5) of the recording paper P on the fixing belt 102, the recording paper P does not lose heat, and the temperature further rises due to the heat generation of the heat generating layer 120.

  Here, in the absence of the heat conducting portion 144, since there is no means for reducing the temperature rise in the non-passage areas L2 and L4 of the recording paper P, the recording paper P of the fixing belt 102 as shown in the graph T1. The temperature difference between the passing region L3 and the non-passing regions L2, L4 increases.

  If the temperature difference between the passing area L3 and the non-passing areas L2 and L4 of the recording paper P becomes large, when the large recording paper P is fixed after the small recording paper P, an excessive amount is formed at the end of the recording paper P. An amount of heat is applied, and a part of the toner T remains on the fixing belt 102 side, which is a so-called hot offset phenomenon.

  On the other hand, in the fixing device 140 of the present embodiment, the heat generation amount per unit length of the heat generating portion 142 does not change in the regions L2, L3, and L4, but heat is generated in the non-passing regions L2 and L4 of the recording paper P in the fixing belt 102. The temperature of the part 142 rises and a temperature gradient is generated between the part 142 and the heat conducting part 144.

  Due to this temperature gradient, an excessive amount of heat of the heat generating portion 142 in the non-passing regions L2 and L4 is conducted to the heat conducting portion 144, and the temperatures of the heat generating portion 142 and the fixing belt 102 in the non-passing regions L2 and L4 are lowered (arrows). D).

  In the heat conducting unit 144, the temperature of the non-passing regions L2 and L4 is higher than the temperature of the passing region L3 due to the amount of heat conducted from the heat generating unit 142, and a temperature gradient is generated in the heat conducting unit 144. For this reason, the amount of heat transferred from the heat generating portion 142 to the heat conducting portion 144 moves within the heat conducting portion 144.

  In the passing region L3 of the recording paper P on the fixing belt 102, the temperature of the heat generating portion 142 is reduced by the temperature of the heat conducting portion 144 because the heat amount of the fixing belt 102 and the heat generating portion 142 is deprived by the recording paper P. Lower than the temperature gradient. As a result, the heat quantity of the heat conducting unit 144 is conducted to the heat generating unit 142 and the fixing belt 102 in the passage region L3 of the recording paper P.

  As described above, the excessive amount of heat moves from the heat generating portion 142 of the non-passing regions L2 and L4 to the heat generating portion 142 of the passing region L3 via the heat conducting portion 144, whereby the temperature distribution in the heat generating portion 142 is adjusted and uniform. become. Further, the temperature increase in the non-passage areas L2 and L4 of the recording paper P on the fixing belt 102 is reduced, and the temperature of the passage area L3 where the temperature is lowered rises, so the temperature distribution graph is as shown in T2.

  Thus, when the temperature difference between the non-passing areas L2, L4 and the passing area L3 is reduced and the temperature of the fixing belt 102 becomes substantially uniform in each area, the large-size recording paper P is fixed after the small-size recording paper P is fixed. Even so, the above-described hot offset phenomenon is unlikely to occur at the end of the large-size recording paper P, and uneven fixing is unlikely to occur.

  Further, the amount of heat transferred to the heat conducting unit 144 is diffused and moved in the heat conducting unit 144, and the entire surface of the heat conducting unit 144 is warmed. For this reason, the fixing belt 102 is warmed in the regions (A, C) of the heat conducting unit 144 that do not face the exciting coil 120, and the temperature difference in the circumferential direction of the fixing belt 102 is reduced.

  Further, since the entire fixing belt 102 is warmed uniformly, the temperature rise time of the fixing belt 102 at the time of the next fixing is shortened.

  Next, a third embodiment of the fixing device and the image forming apparatus of the present invention will be described with reference to the drawings.

  Note that components that are basically the same as those in the first embodiment described above are given the same reference numerals as those in the first embodiment, and descriptions thereof are omitted.

  As illustrated in FIG. 8, the fixing device 150 is obtained by replacing the heating element 108 of the fixing device 100 (see FIG. 2) with a heating element 151.

  The heating element 151 includes a heat generating portion 152 that is in surface contact with the inner peripheral surface of the fixing belt 102, and a heat conducting portion 154 that is disposed on the back side of the heat generating portion 152 (on the side opposite to the fixing belt 102). Are united.

  The heat generating part 152 is a metal material that generates heat by an electromagnetic induction effect in which an eddy current flows so as to generate a magnetic field that cancels the magnetic field H. For example, a metal material of iron, nickel, cobalt, SUS, or an alloy thereof is used. Can do. In this embodiment, iron is used. Further, the heat generating part 152 is disposed only in the region (B) facing the exciting coil 120.

  On the other hand, the heat conducting portion 154 is made of a metal such as silver, copper, gold, or aluminum, or an alloy thereof, and in this embodiment, aluminum having a thickness of 1.2 mm is used. As a result, the thermal conductivity of the heat conducting unit 154 is greater than that of the heat generating unit 152.

  In addition to the region (B) facing the exciting coil 120, the heat conducting unit 154 extends to the vicinity of the nip portion between the fixing belt 102 and the pressure roll 104 (A + B + C). In the regions (A and C) that do not face the exciting coil 120, the heat conducting unit 154 is not in contact with the fixing belt 102.

  The heat generating part 152 and the heat conducting part 154 are bonded and integrated with an adhesive.

  Next, the operation of the third embodiment of the present invention will be described.

  When a predetermined image is formed in the printer 10 (see FIG. 1) and the fixing of the toner image T onto the recording paper P is completed, the fixing device 150 enters a standby state.

  Here, the fixing belt 102 is warmed by the heat of the heat generating portion 152 in the region (B) facing the exciting coil 120. Further, in the regions (A, C) that do not face the exciting coil 120, the fixing belt 102 is warmed by the amount of heat radiated from the non-contact heat conducting portion 154.

  As described above, since the fixing belt 102 is warmed by the heating element 151 in the areas A, B, and C, even if the fixing operation is resumed, the temperature raising time (return time) to the predetermined fixing set temperature is shortened.

  In addition, since the fixing belt 102 and the heat conducting unit 154 are in a non-contact state, the heat capacity of the fixing belt 102 and the heating element 151 is reduced. Thus, the temperature of the fixing belt 102 is raised in a short time when the fixing belt 102 is heated for the first time.

  In addition, this invention is not limited to said embodiment.

  The printer 10 may use a liquid developer as well as a dry electrophotographic system using a solid developer.

  As a means for detecting the temperature of the fixing belt 102, a thermistor may be used instead of the non-contact type temperature sensor 124. Further, the temperature sensor 124 may be attached at a position facing the pressure roll 104.

  The area and circumferential length of the region B facing the exciting coil 120 and the areas and circumferential lengths of the regions A and C not facing each other may be appropriately changed according to the region where the exciting coil 120 is disposed.

1 is an overall view of an image forming apparatus according to a first embodiment of the present invention. 1 is a cross-sectional view of a fixing device according to a first embodiment of the present invention. (A) It is sectional drawing of the heat generating body which concerns on 1st Embodiment of this invention. (B) It is sectional drawing of the fixing belt which concerns on 1st Embodiment of this invention. FIG. 3 is a connection diagram of a control circuit and an energization circuit according to the first embodiment of the present invention. (A) It is a temperature graph of the fixing belt and heat generating body of a prior art example. (B) It is a temperature graph of the fixing belt and heat generating body which concern on 1st Embodiment of this invention. FIG. 6 is a cross-sectional view of a fixing device according to a second embodiment of the present invention. 6 is a temperature graph of a fixing belt according to a second embodiment of the present invention and a conventional sheet passing area and a non-sheet passing area. FIG. 6 is a cross-sectional view of a fixing device according to a third embodiment of the present invention.

Explanation of symbols

10 Printer (image forming device)
18 Image forming unit (developing part)
32 Transfer roll (transfer section)
34 Paper transport path (transport section)
54 Optical scanning device (exposure unit)
100 Fixing device (fixing device)
102 Fixing belt (fixing member)
104 Pressurizing roll (Pressurizing rotating body)
108 Heating element (heating element)
112 Press pad (support)
120 exciting coil (magnetic field generating means)
130 Heat generation part (heat generation layer)
132 Release part (release layer)
141 Heating element (heating element)
142 Heating part (heating part)
144 Heat conduction part (heat conduction part)
151 Heating element (heating element)
H Magnetic field (magnetic field)
T Toner (Developer)
P Recording paper (recording medium)

Claims (7)

Magnetic field generating means for generating a magnetic field;
A heating element disposed opposite to the magnetic field generating means and generating heat by electromagnetic induction of the magnetic field;
An endless fixing member wound around the heating element and rotatably supported at both ends;
A support disposed inside the fixing member;
A pressure rotator that pressurizes the support through the fixing member;
In a fixing device having
The fixing device, wherein the heating element extends in a moving direction of the fixing member to a region not facing the magnetic field generating means. The heating element is
A heat generating layer that generates heat by electromagnetic induction of the magnetic field;
A release layer that is provided on the surface of the heat generating portion and reduces a frictional force between the fixing member and the heat generating portion;
Have
The fixing device according to claim 1, wherein the heat generating layer extends in a moving direction of the fixing member to a region not facing the magnetic field generating unit. The heating element is
A heat generating portion that generates heat by electromagnetic induction of the magnetic field;
A heat conducting part that adjusts a temperature distribution of the heat generating part in contact with the heat generating part;
Including at least
The fixing device according to claim 1, wherein the heat conducting portion extends in the moving direction to a region not facing the magnetic field generating unit.   The fixing device according to claim 3, wherein a thermal conductivity of the heat conducting unit is higher than a thermal conductivity of the heat generating unit.   The fixing device according to claim 3, wherein the heat conducting unit is in contact with the fixing member.   The fixing device according to claim 3, wherein the heat conducting portion is in a non-contact state with the fixing member. A fixing device according to any one of claims 1 to 5,
An exposure unit that emits exposure light; and
A developing unit that exposes the latent image formed by the exposure light with a developer to form a developer image; and
A transfer unit that transfers the developer image made visible in the developing unit onto a recording medium;
A transport unit that transports the recording medium onto which the developer image has been transferred in the transfer unit to the fixing device;
An image forming apparatus comprising:

Images