JP2005123113A - Heating device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heating device of a low-cost means structure with generation of offset greatly reduced and an image forming apparatus having the heating device as a fixing device. <P>SOLUTION: In the heating device in which an induction heating coil L1 is set in opposition to and electromagnetically combined with a heating roller 100, a high-frequency power is impressed on the induction heating coil 1 to have a high-frequency magnetic field generated, an induction current is made to flow also in the heating roller 100 by having the high-frequency magnetic field act on the roller, and Joule heat of a roller resistance value multiplied by a square of the induction current is made generated to have the roller as a whole heated, the electromagnetic conversion coil L1 is held by a holding member 108 of a high dielectric constant molded from an insulation material with a dielectric constant of 2 or more. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a heating apparatus that pressurizes and heats a material to be heated such as paper, particularly a heating apparatus that uses induction heating as a heat source, and heat-melting powder such as toner formed and supported on a recording paper. The present invention relates to an image heating and fixing apparatus that applies heat-fixing processing to the recording paper by applying the apparatus, and to an image forming apparatus such as an electrophotographic / electrostatic recording type copying machine and facsimile equipped with the image heating and fixing apparatus.

  Conventionally, this type of image forming apparatus includes an image forming unit that forms a visible image (hereinafter referred to as a toner image) on a recording paper using a developing material (hereinafter referred to as a toner), and a recording paper on which the toner image is formed. When the recording paper P passes between the paper conveying means for conveying P and the fixing roller (heating roller) 100 and the pressure roller 101 that are opposed to each other as shown in FIG. 6, the heat of the fixing roller 100 is applied to the recording paper P. And a fixing means for applying a pressure of the pressure roller 101 to heat and fix the toner image on the recording paper.

  As a roller heating method for heating and fixing a toner image on the recording paper P using such a fixing unit, an induction heating method has recently attracted attention from the viewpoint of energy consumption efficiency.

  In the method using the induction heating method as a means for heating the fixing roller, an eddy current is applied to the conductive layer by applying a high frequency current to the exciting coil and causing the generated high frequency magnetic field to act on the conductive layer on the inner surface of the fixing roller. And the fixing roller self-heats by Joule heat due to the eddy current (see, for example, Patent Document 1).

In this heating method, since the conductive layer on the inner surface of the fixing roller is direct heating that becomes a heating element, the heat generation efficiency is high, and the fixing roller can be easily heated to the required fixing temperature in a short time, so It is possible to increase the power consumption and the power utilization rate is high, so that the power consumption can be greatly reduced.
JP-A-11-195477

  In the fixing device having the above heating method, in order to prevent the toner developed through the image forming process from being charged and electrostatically adhering when passing through the fixing roller (hereinafter, this phenomenon is referred to as offset). Conventionally, a cleaning member such as a fixing web that scrapes off the toner is used to clean the toner adhering to the fixing roller, or a fixing roller bias method in which a voltage having the same polarity as the charging potential of the toner is applied to the fixing roller core metal. ing.

  However, in the apparatus for applying a voltage to the fixing roller core, etc., there is a problem that a separate bias power source for generating the voltage has to be provided and the apparatus becomes complicated and the cost increases.

  Further, in the method of bringing the cleaning member into contact, the fixing device needs to have a maintenance interval for replacing the cleaning member every certain period due to exhaustion of the cleaning member.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to further improve an offset prevention technique in a contact heating type heating device and an image forming apparatus provided with the heating device as a fixing device. That is, it is an object of the present invention to provide a heating device with an inexpensive means configuration that greatly reduces the occurrence of offset, and an image forming apparatus provided with the heating device as a fixing device.

  The present invention is a heating apparatus and an image forming apparatus having the following configurations.

  (1) an induction heating coil disposed opposite to the heating roller and electromagnetically coupled thereto, and a power feeding means for generating a high frequency magnetic field by applying a high frequency power to the induction heating coil. In a heating device that causes an induced current to flow through the heating roller by causing it to act on the heating roller and generate heat by the Joule heat generated by the induced current and the resistance value of the heating roller, an insulating material having a dielectric constant of 2 or more A heating apparatus comprising a molded holding member for holding the induction heating coil.

  (2) The heating roller is made of a conductor and includes a power supply member that is in sliding contact with the heating roller, and an electromotive voltage generation circuit that includes a capacitor, a diode, and a resistor and is connected to the power supply member. (1) The heating device according to (1).

  (3) An induction heating coil disposed opposite to the heating roller and electromagnetically coupled thereto, a power supply means for applying a high frequency power to the induction heating coil to generate a high frequency magnetic field, and a pressurizing pressure against the heating roller A heating roller, causing the high-frequency magnetic field to act on the heating roller, causing an induced current to flow through the roller, heating the entire heating roller with Joule heat generated by the induced current and the resistance value of the heating roller, and heating the heating roller. In a heating apparatus that heats and fixes the unfixed image on the recording paper by passing the recording paper having an unfixed image on the surface through the pressure contact portion between the roller and the pressure roller, the insulating member having a dielectric constant of 2 or more is formed. And a coil holder for holding the induction heating coil.

  (4) The heating apparatus according to (3), wherein a coil holder formed by an insulating material having a dielectric constant of 2 or more and holding an induction heating coil is disposed inside the heating roller.

  (5) The heating apparatus according to (3), wherein a coil holder that is formed of an insulating material having a dielectric constant of 2 or more and holds an induction heating coil is disposed outside the heating roller.

  (6) The heating roller is made of a conductor and includes a power supply member that is in sliding contact with the heat roller, and an electromotive voltage generation circuit that includes a capacitor, a diode, and a resistor and is connected to the power supply member. The heating device according to any one of (3) to (5), characterized in that:

  (7) Image forming means for directly or indirectly forming an unfixed image on recording paper, paper transport means for transporting the recording paper from a paper feed section to a paper discharge section, and the unfixed image on the recording paper An image forming apparatus having a fixing unit for heating and fixing the image forming apparatus, wherein the heating unit according to any one of (1) to (6) is used as the fixing unit.

  According to the configuration of (1), it is possible to efficiently apply high-frequency electric lines of force generated from the induction heating coil to the heating roller, and in the image heating and fixing apparatus, the heating bias potential that effectively reduces the offset. Can be generated efficiently.

  According to the configuration of (2), it is possible to take measures against offset of the image heating and fixing apparatus without preparing a high voltage power source for heating bias.

  According to the configuration of (3), it is possible to efficiently apply high-frequency electric lines of force generated from the induction heating coil to the heating roller, and in the image heating and fixing apparatus, a heating bias potential that effectively reduces the offset. Can be generated efficiently.

  According to the configuration of (4), it is possible to efficiently cause high-frequency electric lines of force generated from the induction heating coil to act on the heating roller, and it is possible to efficiently generate a heating bias potential that effectively reduces the offset. .

  According to the configuration of (5), it is possible to efficiently apply high-frequency electric lines of force generated from the induction heating coil to the heating roller, and in the image heating and fixing apparatus, a heating bias potential that effectively reduces the offset. Can be generated efficiently.

  According to the configuration of (6), it is possible to take measures against offset of the image heating and fixing apparatus without preparing a high voltage power source for the heating bias.

  According to the configuration of (7), it is possible to greatly reduce the occurrence of offset with an inexpensive means configuration.

  In short, according to the present invention, the induction heating coil holding member (coil holder) formed of an insulating material having a dielectric constant of 2 or more for holding the induction heating coil is provided, so that high-frequency electricity generated from the induction heating coil can be obtained. It is possible to cause the force lines to efficiently act on the heating roller, and in the image heating and fixing apparatus, there is an effect that the heating bias potential that effectively reduces the offset can be efficiently generated.

  FIG. 1 is a block diagram showing an outline of a temperature control circuit of a heating device of the present invention according to Example 1, FIG. 2 is a schematic diagram of a structure in which the heating device of the present invention incorporating the temperature control circuit is applied as a fixing device, and FIG. 3 is a detailed cross-sectional view of a coil structure showing a relationship between a fixing roller (heating roller) and an induction heating coil (electromagnetic conversion coil) in Embodiment 1. FIG.

  In FIG. 1, TR1 is a MOS-FET of a power switching element that is a component of the power supply means, C1 is a resonance capacitor for making a high-frequency alternating current applied to a dielectric heating coil L1 as a load a resonance waveform, D5 is a flywheel diode that regenerates the electric power stored in the dielectric heating coil L1.

  TH1 is a temperature detection element, which is thermally coupled to the fixing roller 100 by the structure shown in FIG. 2, and its output is input to the temperature detection comparison circuit IC2. The temperature detection comparison circuit IC2 compares the temperature adjustment input signal and the output of the temperature detection element, and inputs the difference as a control signal to the pulse modulation (hereinafter referred to as PFM) control circuit IC1.

  The temperature adjustment input signal is sent as a signal from the main body controller in consideration of the fixing temperature necessary for the image forming process, and the target temperature is set according to the signal, and the error with the temperature detection means is PFM. Supplied to the control circuit.

  This pulse modulation oscillation circuit IC1 outputs a PFM pulse corresponding to the control signal value to the gate of the MOS-FET of the power switching element TR1 to drive the power switching element. D1 to D4 are diodes that rectify input power from the AC power supply AC, and supply a pulsating flow obtained by rectifying the AC power to the power control circuit unit.

  The noise filter formed by the input noise filter NF1 and the capacitor C1 is set to a constant that ensures a sufficient amount of attenuation for the switching frequency of the power switching element TR1 and passes through the power supply frequency without attenuation. To do.

  The current collecting member 103 is in electrical contact with the fixing roller 100 to maintain conductivity, and a capacitor C10 and a resistor R10 are connected to the current collecting member 103. The capacitor C10 is connected to the diodes D10 and D11 and the capacitor C12, and the diodes D10 and D11 are connected to both ends of the capacitor C11 to constitute a so-called voltage doubler rectifier circuit. In the illustrated example, this voltage doubler rectifier circuit is configured by stacking four stages by capacitors C1 to C17 and diodes D1 to D17.

  Next, the operation will be described.

  When an AC input voltage is applied to the input terminal in of FIG. 1, this AC input voltage is rectified by the rectifying elements of the diodes D1 to D4 to become a pulsating current, and this pulsating voltage passes through the input noise filter NF1 and is applied to the capacitor C1. Applied to both ends. The voltage across the capacitor C1 has a waveform obtained by rectifying the AC input voltage. When the temperature adjustment input signal VC is input to the temperature detection comparison circuit IC2, the temperature detection comparison circuit IC2 compares the output of the temperature detection element TH1 with the temperature setting value of the temperature adjustment input signal VC.

  The comparison result is applied to the pulse modulation oscillation circuit IC1 as a control signal. This pulse modulation oscillation circuit IC1 compares the output of the one-shot pulse generation circuit IC1-1 with the control signal value by the comparison circuit IC1-2, and generates a PFM signal having a pulse corresponding to the control signal value. And applied between the gates of the power switching element TR1. Thereby, the power switching element TR1 is switched by the output pulse of the pulse modulation oscillation circuit IC1, and the drain current ID flows to energize the induction heating coil L1.

  Since the electric current that flows when the power switching element TR1 is turned on is stored in the dielectric heating coil L1, a counter electromotive voltage is generated when the power switching element TR1 is turned off, and the coil accumulated current is charged in the resonance capacitor C2. . The resonant capacitor voltage rises due to the flowing coil accumulated current.

  The current flowing out of the dielectric heating coil L1 is attenuated in inverse proportion to the rise of the voltage of the resonance capacitor C2, and when passing through the moment when the coil current does not flow at a certain point, this time, the current is accumulated in the resonance capacitor C2 on the contrary. Current flows out toward the induction heating coil L1.

  Thereafter, the charge accumulated in the resonant capacitor C2 returns to the induction heating coil L1, and at the same time, the voltage of the resonant capacitor C2 decreases, the drain voltage of the power switching element TR1 decreases below the source voltage, and the flywheel diode D5 Turns on and forward current flows.

  Thereafter, when the power switching element TR1 is turned on again, a current flows through the induction heating coil L1 and the current is repeatedly accumulated in the induction heating coil. Therefore, the load is coupled electromagnetically with respect to the induction heating coil L1. An induced current also flows through a certain fixing roller 100, and the fixing roller 100 made of a conductive material generates Joule heat obtained by multiplying its own roller resistance value by the square of the induced current, so that the inner surface of the fixing roller 100 is efficiently formed. The entire fixing roller that generates heat and rotates is heated.

  Here, the capacitor C1 charges and discharges the high-frequency component of the current flowing through the power switching element TR1 and the induction heating coil L1 to smooth it. Therefore, only high-frequency current does not flow through the input noise filter NF1, but only AC input current rectified waveform flows.

  The current flowing through the rectifier diodes D1 to D4 is the AC input current waveform before rectification in order to make the current waveform flowing through the power switching element TR1 and the induction heating coil L1 into a current waveform filtered by the capacitor C1 and the input noise filter NF1. Becomes an input current waveform having a shape close to an AC input voltage waveform, the harmonic component contained in the input current can be greatly reduced, and the power factor of the input current of the temperature control circuit in the fixing heating circuit can be greatly improved.

  Further, the input noise filter NF1 and the capacitor C1 used in this circuit may be any one that can exhibit a filter effect with respect to the high frequency oscillation frequency by the pulse modulation oscillation circuit IC1, and the capacitance of the capacitor C1 and the input noise filter NF1. Since the inductance value can be reduced, the size and weight can be reduced. When a temperature adjustment signal is input to this dielectric heating drive power supply circuit, a high-frequency AC voltage having a frequency of about 20 KHz to 1 MHz is generated at the output terminal of the induction heating power supply.

  Here, the output of the temperature measuring element composed of the temperature detecting element TH1 for measuring the temperature of the fixing roller surface is input to the temperature detection comparison circuit IC2 at any time and compared with the temperature adjustment input signal VC, and the difference from the target value is a pulse. It is fed back to the modulation oscillation circuit IC1.

  The temperature detection comparison circuit IC2 uses a control method called proportional control or so-called PID control to reduce the applied high-frequency power when the detection temperature of the temperature detection element TH1 approaches the set target temperature, and the fixing roller surface temperature is kept constant. Generate a feedback signal that keeps

  The pulse modulation oscillation circuit IC1 receives the temperature setting target value error detected by the temperature detection comparison circuit IC2, the gate ON signal time of the power switching element TR1 is determined according to the value, and the energization power of the power switching element TR1 is The toner fixing temperature is stabilized by adjusting the electric power input to the fixing roller 100 and controlling the amount of heat generated by the fixing roller.

  In order to perform such a heating operation, a resonance voltage of about 100 to 600 V is applied to both ends of the induction heating coil L1 arranged inside the fixing roller as shown in a detailed structural diagram of FIG. In order to mechanically hold the induction heating coil L1 and to electrically insulate the fixing roller 100 made of a conductive material, a high dielectric constant holding member (coil holder) made of an insulating member resin or the like ) 108.

  In the present invention, an induction heating coil holding member (coil holder) 108 formed of an insulating material having a dielectric constant of 2 or more (hereinafter referred to as a high dielectric constant insulating material) is disposed between the induction heating coil L1 and the fixing roller 100. Thus, the clearance between the induction heating coil L1 and the fixing roller 100 can be appropriately maintained, and the induction electric field lines from the induction heating coil L1 are allowed to pass through the resin layer having a high induction rate as shown in FIG. Thus, it is possible to effectively apply electric lines of force to the fixing roller 100 and generate a high-frequency induced voltage in the fixing roller 100.

  This high frequency induced voltage is collected from the fixing roller 100 by the current collecting member 103 and guided to the bias circuit 104. In the bias circuit 104, the high-frequency AC voltage injected from the capacitor C10 is rectified by the diode D10, whereby the peak value of the AC voltage waveform is charged in the capacitor C10.

  The charge accumulated in the capacitor C10 charges the capacitor C11 when the diode D12 conducts in the next cycle, and a DC voltage corresponding to the peak value of the AC voltage input to the capacitor C10 is generated in the capacitor C11. . The capacitors C10 and D10 to the diode D12 and the capacitor C11 constitute a so-called voltage doubler rectifier circuit, which is a circuit for one stage. Here, since the combinations are stacked in four stages, a 4-fold pressure rectifier circuit is configured.

  As an example, if the potential induced from the induction heating coil L1 to the fixing roller 100 is 150 Vp-p, a DC potential of −150 V is generated in the first-stage capacitor C11, and the fourth-stage diode D17 and the capacitor C17 A DC potential of −600 V is generated at the connection point. By supplying this DC potential to the current collecting member 103 via the resistor R10, the fixing roller 100 can be applied with a DC potential of −600 V with respect to the ground level.

  FIG. 2 is a block diagram when the present invention is actually incorporated into a fixing device. As shown in the figure, in the present invention, the bias circuit 104 can be configured as a circuit block disposed on a printed circuit board or a ceramic substrate, so that the wiring to the current collecting member 103 and the bias circuit 104 are grounded for mounting on the fixing device. Since there are only two and the circuit configuration itself is simple, it can be directly attached to the exterior portion of the fixing device, and the fixing roller bias can be mounted with a very simple configuration.

  FIG. 3 is a detailed cross-sectional view of the configuration of the fixing roller 100 and the induction heating coil L1, and the fixing roller 100 is a surface layer for ensuring releasability while pressing the roller core metal 109, which is a heating element, and the toner against the paper. The rubber layer 110 is. The rubber layer 110 is characterized in that it has appropriate conductivity in order to effectively apply the bias potential applied to the roller mandrel 109 to the roller surface.

  In order to further improve the releasability from the paper, a conductive Teflon coat or tube may be used instead of the rubber layer 110 (Teflon is a trade name of tetrafluoroethylene resin).

  An induction heating coil L1 is arranged inside the roller so as to face the roller, and a ferrite core 106 is arranged inside the coil in order to cause the magnetic flux generated in the induction heating coil L1 to act on the fixing roller 100 effectively. .

Here, when a high frequency current from the dielectric heating drive power supply circuit is applied to the induction heating coil L1, both ends of the induction heating coil L1 are
E (L) = ω ・ L ・ i
L = induction coil inductance
i = the potential of the applied current is generated.

  The electric potential causes the electric force lines 107 in the drawing to the fixing roller mandrel 109 from the surface of the induction heating coil L1 via the holding member 108 having a high dielectric constant. As an action of the electric force lines 107, the potential of the fixing roller core 109 generates a potential proportional to the voltage applied to the induction heating coil L1.

Further, as the effect of the high dielectric constant holding member 108, the resin thickness is t, the distance from the high dielectric constant holding member 108 to the inner surface of the fixing roller is g, and the dielectric constant of the high dielectric constant holding member 108 is 4. When the resin thickness t is equal to the fixing roller distance g, the capacitance ratio between the induction heating coil L1 and the fixing roller 100 is Cgap.
∴ Cgap = 1.6
Thus, the electric force lines 107 can be applied to the fixing roller 100 with efficiency about 1.6 times that of the conventional example.

  In this way, the fixing roller 100 is effectively obtained by interposing the electric lines of force from the induction heating coil L1 with the holding member 108 having a high dielectric constant without changing the arrangement relationship between the induction heating coil L1 and the fixing roller 100. It is possible to efficiently generate a fixing bias potential that effectively reduces the fixing offset by guiding this high-frequency potential fluctuation to the rectifier circuit.

  FIG. 4 is a schematic diagram showing the second embodiment of the present invention, in which the induction heating coil L1 is arranged outside the fixing roller 100. Insulation of ceramics, resin, or the like so as to follow the outer curvature of the fixing roller 100 By disposing the induction heating coil L1 outside the high dielectric constant holding member 108 made of a material, the arrangement gap between the induction heating coil L1 and the fixing roller 100 can be optimized, and the high dielectric Because of the high dielectric constant of the holding member 108, the electric lines of force 107 generated by the induction heating coil L1 can be efficiently applied to the fixing roller 100.

  By supplying the high-frequency pulsation generated in the fixing roller 100 to the bias circuit 104 through the current collecting member 103, the bias potential can be efficiently supplied to the fixing roller 100. Further, by using this configuration, the induction heating coil L1 can be arranged outside the fixing roller 100.

  In general, the insulating material has a high heat insulating property, and therefore, a kind of heat insulating layer by the holding member 108 having a high dielectric constant is disposed in the gap with the fixing roller 100, and the operating temperature of the induction heating coil L1 can be lowered. Therefore, the power loss of the induction heating coil L1 can be reduced.

  In the embodiment explanatory diagram, the number of stages of the voltage doubler rectifier circuit constituting the bias circuit 104 is described as four stages. However, as a matter of course, the number of voltage doubler rectifier stages is adjusted according to the required bias potential. .

  Further, the holding member 108 having a high dielectric constant is a material having both insulating properties and heat resistance, such as heat-resistant PPS, LCP, phenol resin, ceramics, etc., and a material having a dielectric constant of 2 or more. There is no limit.

  FIG. 5 is a cross-sectional view showing an outline of a laser beam printer as an image forming apparatus to which the fixing device of the present invention shown in FIG. 2 is applied as a third embodiment. Components of the laser beam printer of FIG. 5 will be described below. . In the printer main body (image forming apparatus main body), there are a laser scanner 10, a printing process unit 15, a transfer roller 16, a fixing device 30, a conveying roller pair 18, a paper feeding cassette 20, a paper feeding roller (including a pickup roller) 21, and the like. Is installed. In the printing process unit 15, a photosensitive drum 11, a primary charger 12, and a developing roller 13 are integrally assembled, and are detachably attached to the printer main body.

  The sheet-like recording paper P stacked and stored in the paper feed cassette 20 is fed by a paper feed roller 21 that rotates counterclockwise, guided to a transport guide 22, and sent to the nip portion of the transport roller pair 18. . Next, the recording paper P is fed between the photosensitive drum 11 and the transfer roller 16 by the conveying roller pair 18.

  The photosensitive drum 11 rotates in the clockwise direction, and the outer peripheral surface thereof is uniformly charged by the primary charger 12. Then, an electrostatic latent image is sequentially formed on the outer peripheral surface by the laser light L of the laser scanner 10, and then the electrostatic latent image is developed by the developing roller 13 to form a toner image. The toner images on the photosensitive drum 11 are sequentially transferred from the transfer roller 16 to the recording paper P sent between the photosensitive drum 11 and the transfer roller 16.

  The recording paper P onto which the toner image has been transferred in this way is sent to the fixing device 30 where it is heated and pressurized to fix the toner image on the recording paper P. Thereafter, the recording paper P is sent to a paper discharge roller 81 by a fixing paper discharge roller pair 70, and then discharged onto a paper discharge tray 80 on the upper surface of the printer main body by the paper discharge roller 81. As the fixing device described above, the fixing device of the present invention shown in FIG. 2 is used.

  While various examples and embodiments of the present invention have been shown and described, those skilled in the art will recognize that the spirit and scope of the present invention are not limited to the specific descriptions and figures within this specification, It will be understood that various modifications and changes are set forth in all the claims. For example, in the illustrated example, the fixing device that heat-fixes an unfixed image formed on the recording paper is described as an example. However, the sheet paper other than the recording paper is simply heated to polish and remove the sheet paper. It is also effective as a heating device for performing the above.

1 is a block diagram showing an outline of a temperature control circuit of a heating device of the present invention according to Embodiment 1. FIG. FIG. 2 is a schematic diagram of a structure in which the heating device of the present invention incorporating the temperature control circuit of FIG. 1 is applied as a fixing device. 2 is a detailed cross-sectional view of a coil structure showing a relationship between a roller and an induction heating coil in Embodiment 1. FIG. The detailed sectional view of the coil structure which shows the relation between the roller and induction heating coil in Example 2. 1 is a cross-sectional view showing an outline of a laser beam printer as an image forming apparatus to which a fixing device of the present invention is applied. Schematic diagram of a conventional fixing device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Laser scanner 11 Photosensitive drum 12 Primary charger 13 Developing roller 15 Printing process unit 16 Transfer roller 30 Fixing device L1: Induction heating coil 100 Fixing roller (heating roller)
DESCRIPTION OF SYMBOLS 101: Pressure roller C10-C17: Voltage doubler smoothing capacitor 102: Fixing device D10-D17: Rectifier diode 103: Sliding current collection member R10: Bias application resistance 104: Fixing bias circuit block TH1: Temperature detection element 108: Insulation Coil support member (high dielectric constant holding member)

Claims (7)

An induction heating coil disposed opposite to the heating roller and electromagnetically coupled thereto; and a power feeding means for generating a high frequency magnetic field by applying a high frequency power to the induction heating coil, wherein the high frequency magnetic field is applied to the heating roller. In a heating apparatus that causes an induced current to flow through the heating roller and causes the heating roller to generate heat by Joule heat generated by the induced current and the resistance value of the heating roller, the dielectric was molded from an insulating material having a dielectric constant of 2 or more. A heating apparatus comprising a holding member for holding the induction heating coil. A heating member is formed of a conductor and includes a power supply member that is in sliding contact with the heating roller, and an electromotive voltage generation circuit that includes a capacitor, a diode, and a resistor and is connected to the power supply member. The heating apparatus according to claim 1. An induction heating coil disposed opposite to the heating roller and electromagnetically coupled thereto, a power feeding means for applying a high frequency power to the induction heating coil to generate a high frequency magnetic field, and a pressure roller pressed against the heating roller The high frequency magnetic field is applied to the heating roller to cause an induction current to flow through the roller, the entire heating roller is heated by Joule heat generated by the induction current and the resistance value of the heating roller, and the heating roller is heated. In a heating device for passing a recording paper having an unfixed image on its surface through a pressure contact portion with a pressure roller and heating and fixing the unfixed image on the recording paper, the induction is performed by molding with an insulating material having a dielectric constant of 2 or more. A heating apparatus comprising a coil holder for holding a heating coil. The heating apparatus according to claim 3, wherein a coil holder that is formed of an insulating material having a dielectric constant of 2 or more and holds an induction heating coil is disposed inside the heating roller. The heating apparatus according to claim 3, wherein a coil holder that is formed of an insulating material having a dielectric constant of 2 or more and holds an induction heating coil is disposed outside the heating roller. A heating member is formed of a conductor and includes a power supply member that is in sliding contact with the heating roller, and an electromotive voltage generation circuit that includes a capacitor, a diode, and a resistor and is connected to the power supply member. The heating apparatus according to any one of Examples 3 to 5. Image forming means for directly or indirectly forming an unfixed image on recording paper, paper transport means for transporting the recording paper from a paper feed section to a paper discharge section, and heating and fixing the unfixed image on the recording paper An image forming apparatus having a fixing unit to be used, wherein the heating device according to any one of claims 1 to 6 is used as the fixing unit.