JP2002116656A - Fixing device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an induction heat fixing-device which is capable of quick heating and provides high induction heat efficiency in an electrophotographic image forming device. SOLUTION: The induction heat type fixing device 10 has a heating rotational body 12 of an electromagnetic induction heat generation type, a magnetic field generating means 13 disposed near the heating rotational body 12, and a high frequency power source 18 which supplies an AC current to the magnetic field generating means 13. The fixing device 10 causes the heating rotational body 12 to generate heat by electromagnetic induction with a high frequency induction magnetic flux generated by the magnetic field generating means 13, thereby heating and fixing the toner image formed on the recording medium P. In the fixing device 10, the magnetic field generating means 13 has a magnetic core 131 and a magnetization coil 132 wound round the magnetic core 131, and a temperature detection element TS2 which detects a temperature of the magnetic core 131 is disposed near the magnetic core 131.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device used in an image forming apparatus such as an electrophotographic copying machine, a printer, and a facsimile, and more particularly, to a recording medium carrying a toner image using electromagnetic induction. The present invention relates to a fixing device that heats and fixes an object to be heated using electromagnetic induction, and an image forming apparatus provided with an induction heating type fixing device.

[0002]

2. Description of the Related Art A fixing device using electromagnetic induction is usually
A heating unit that utilizes electromagnetic induction; and a pressing unit that rotates while being in pressure contact with the heating unit. The heating unit and the pressing unit sandwich and convey the recording medium bearing the toner image to perform fixing. Will be The heating means has a spring-shaped coil or a vertically wound coil and, if necessary, a core inside a rotating heating element in the form of a roll or a belt.
A means for supplying an alternating current having a frequency of z or more to generate an alternating magnetic flux, inducing an eddy current in the heating element, and heating and fixing the generated heat due to the eddy current loss. Then, the toner image on the recording medium is heated and fixed.

A fixing device using the above-described electromagnetic induction is smaller and lighter than a fixing device using a conventional infrared heater, a nichrome wire heater, or the like. It has excellent characteristics such as being able to heat and fix at a rapid rise with the supply of a high-frequency alternating current. Recently, research and development on a fixing device using electromagnetic induction has been advanced.
000-29336, JP-A-2000-131981
And various publications propose various techniques relating to a fixing device using electromagnetic induction.

[0004]

In a conventional fixing device for heating and fixing using electromagnetic induction, a cooling device for cooling these members is arranged in order to suppress the temperature rise of the magnetic core and the exciting coil. I was However, these cooling devices continue to operate irrespective of the temperature of the magnetic core and the exciting coil, and thus consume unnecessary energy.

[0005] The present invention has been proposed in view of the above circumstances, and an object thereof is to control the operation of a cooling device such as a cooling fan or a blower so that unnecessary power is not wasted. An object of the present invention is to provide a fixing device that achieves power saving.

[0006]

The above object is achieved by the following constitution.

(1) a heating rotator made of a conductive member, and a magnetic field generating means arranged near the heating rotator;
A power supply for supplying an alternating current to the magnetic field generating means, and the high frequency induction magnetic flux generated from the magnetic field generating means causes the heating rotator to generate heat by electromagnetic induction, thereby heating the toner image formed on the recording medium. In the induction heating type fixing device, the magnetic field generating means has a magnetic core made of a magnetic material, and an exciting coil wound around the magnetic core, and the magnetic core is provided near the magnetic core. A temperature detecting element for detecting a temperature of the fixing device.

(2) a heating rotator made of a conductive member, and a magnetic field generating means arranged near the heating rotator;
A power supply for supplying an alternating current to the magnetic field generating means, and the high frequency induction magnetic flux generated from the magnetic field generating means causes the heating rotator to generate heat by electromagnetic induction, thereby heating the toner image formed on the recording medium. In the induction heating type fixing device, the magnetic field generating means has a magnetic core made of a magnetic material, and an exciting coil wound around the magnetic core, and the exciting coil is provided near the exciting coil. A temperature detecting element for detecting a temperature of the fixing device.

(3) a heating rotator made of a conductive member, and a magnetic field generating means arranged near the heating rotator;
A power supply for supplying an alternating current to the magnetic field generating means, and the high frequency induction magnetic flux generated from the magnetic field generating means causes the heating rotator to generate heat by electromagnetic induction, thereby heating the toner image formed on the recording medium. In the induction heating type fixing device, the magnetic field generating means has a magnetic core made of a magnetic material, and an exciting coil wound around the magnetic core, and detects a temperature of the magnetic core. A fixing device comprising: a detecting element; a temperature detecting element for detecting a temperature of the exciting coil; and a temperature detecting element for detecting a surface temperature of the heating rotator.

(4) a heating rotator made of a conductive member, and a magnetic field generating means disposed inside the heating rotator;
A power supply for supplying an alternating current to the magnetic field generating means, and the high frequency induction magnetic flux generated from the magnetic field generating means causes the heating rotator to generate heat by electromagnetic induction, thereby heating the toner image formed on the recording medium. In the induction heating type fixing device, the magnetic field generating means has a magnetic core made of a magnetic material, and an exciting coil wound around the magnetic core, and detects a temperature of the magnetic core. A sensing element, a temperature sensing element for sensing a temperature of the exciting coil, a temperature sensing element for sensing a surface temperature of the heating rotator, a cooling device for cooling the magnetic field generating means, and controlling operation of the cooling device. And a control unit for performing the fixing.

(5) An image forming means for forming an image on a recording medium, and a fixing device for heating and fixing the image, wherein the fixing device is any one of (1) to (4).
An image forming apparatus comprising: the induction heating type fixing device according to any one of the preceding items.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a fixing device and an image forming apparatus according to the present invention will be described below with reference to the drawings.

(1) Overall Configuration of Fixing Device FIG. 1 is a front sectional view showing an embodiment of the fixing device of the present invention, FIG. 2 is a side sectional view of the fixing device, and FIG. 3 is a perspective view of the fixing device. It is.

The fixing device 10 includes a fixing roller 11 and a pressure roller 14. Around the fixing roller 11, a cleaning roller 15, an oil application roller 16, and a temperature detecting element TS2 are arranged.

The fixing roller 11 has a heating rotator 12 of electromagnetic induction heating and a magnetic field generating means 13 disposed inside the heating rotator 12. A surface layer (release layer) 121 is formed on the outer peripheral surface of the heating rotator 12. The magnetic field generating means 13 includes a magnetic core 131 and an exciting coil 132.

The pressure roller 14 is provided around the core 141.
An elastic layer 142 of silicone rubber or the like is further formed by coating the outermost layer with a fluororesin. N is a fixing nip portion where the pressure roller 14 and the fixing roller 11 are pressed against each other.

The temperature detecting element TS2 detects the surface temperature of the heating rotator 12, and controls the amount of current applied from the excitation circuit (not shown) to the magnetic field generating means 13 based on the detection signal.

When the fixing roller 11 is driven to rotate and a magnetic field is generated from the magnetic field generating means 13, the magnetic field acts on the heating rotator 12 in the fixing nip portion N, and the heating rotator 12 Electromagnetically induced heat is generated by the high-frequency induction magnetic flux generated from the electromagnetic wave 13. In this state,
A recording medium (hereinafter, referred to as a sheet) P is introduced into a fixing nip portion N where the heating rotator 12 and the pressure roller 14 are pressed against each other.
The heat of the heating rotator 12 is applied to the sheet P, and the toner image on the sheet P is heated and fixed.

(2) Heating Rotator The heating rotator 12 is mainly formed of an iron core cylinder having a thickness of 0.5 to 5 mm, transmitting magnetic flux, and having good heat conductivity. In order to improve the releasability from the toner, the surface of the heating rotator 12 is coated with a perfluoroacrylate (PFA) tube or a polytetrafluoroethylene (PTFE) tube having a thickness of 20 to 100 μm, Fluorine resin (PFA or PTFE) paint 20
Surface layer 1 having a thermal conductivity of (3 to 10) × 10 ⁻³ J / cm · s · K which is formed by coating silicone rubber or fluoro rubber having a thickness of 20 to 500 μm or a layer having a thickness of 20 to 500 μm.
21 may be provided.

(3) Magnetic field generating means The magnetic field generating means 13 includes a magnetic core 131 and the magnetic core 1.
And an excitation coil 132 wound around the motor 31. The excitation coil 132 is connected to the high frequency power supply 18 via the conductor 17.

An alternating magnetic field H is formed inside the heating rotator 12 by the magnetic flux generated from the magnetic field generating means 13, and the heating rotator 12 is heated. The heating rotator 12 is rapidly heated by an AC magnetic field H formed inside by a magnetic flux generated from the magnetic field generating means 13. That is, the heating rotator 12
Supplies a current to the exciting coil 132 to
The inside of the heating rotator 12 is formed by magnetic flux generated from
An AC magnetic field H of about 5 to 50 kHz is formed, and the heating rotator 12 is heated by an eddy current inside the heating rotator 12 generated by the AC magnetic field H.

Although iron is used for the magnetic core 131, in order to increase heat generation of the heating rotator 12, a material having high magnetic permeability and low residual magnetic flux density, such as ferrite or permalloy, is used. To increase the magnetic flux. Alternatively, the current flowing through the heating rotator 12 is increased by increasing the change in the magnetic flux.

The magnetic field generating means 13 has various structures. Magnetic core 1 of magnetic field generating means 13 shown in FIG.
Reference numeral 31 denotes an I-shape having one central wall, but a U-shape having two side walls and an E-shape having one center wall and two side walls are also applicable.

FIG. 4A is a sectional view showing another arrangement example of the magnetic field generating means 13, and FIG. 4B is a partially enlarged sectional view of the magnetic field generating means 13 and the heating rotator 12.

As shown in FIG.
The magnetic field generating means 13 may be provided. Magnetic field generating means 13
An alternating magnetic field H is formed inside the heating rotator 12 by the magnetic flux generated from the heating rotator 12, and is rapidly heated. , Heating rotator 1
2 is heated. The shape of the illustrated magnetic core 131 is an E-shape.

FIG. 5A is a sectional view showing still another example of the arrangement of the magnetic field generating means 13, and FIG. 5B is a partially enlarged sectional view of the heating rotator 12.

The first magnetic field generating means 13A is arranged inside the heating rotator 12, and the second magnetic field generating means 13B is arranged outside the heating rotator 12. First magnetic field generating means 13A
To form an alternating magnetic field H1, and the second magnetic field generating means 1
An AC magnetic field H2 is formed by 3B. AC magnetic field H1,
Due to the combined magnetic field of H2, the current flowing in the heating rotator 12 is increased, and the heat generation effect is improved.

(4) Pressure Roller The pressure roller 14 serving as a lower cylindrical fixing member that is paired with the upper fixing roller 11 is, for example, a core 141 made of an aluminum material, and On the outer peripheral surface, for example, a silicone rubber layer or a fluorine rubber layer, or a sponge-like material using a silicone rubber foam material, having a thickness (thickness) of 5 to 2
0mm thickness, rubber hardness 10Hs-40Hs (JIS,
It is configured as a soft roller having an outer diameter of about 25 to 50 mm on which an elastic layer 142 formed of a thick rubber layer having a (A rubber hardness) is formed. On the outer side (outer peripheral surface) of the elastic layer 142, a coating layer 143 which covers a tube (not shown) of a heat-resistant fluororesin such as PFA or PTFA having releasability is formed. An elastic rubber roller having a high heat insulating property is used for the lower pressure roller 14 to prevent diffusion of heat from the upper heating rotator 12 to the lower pressure roller 14 and to secure a wide nip width. Upper heating rotator 12 and lower pressure roller 14
A flat fixing nip portion N is formed between the two and the fixing of the toner image is performed.

(5) Temperature Detector As shown in FIGS. 1 to 3, a plurality of temperature detectors TS1 for detecting the surface temperature of the heating rotator 12 are arranged near the outer peripheral surface of the heating rotator 12. The temperature detecting elements TS1 are arranged near the outer peripheral surfaces at the center and both ends in the axial direction of the heating rotator 12.

Further, a temperature detecting element TS2 for detecting the temperature of the magnetic core 131 is arranged near the magnetic core 131 of the magnetic field generating means 13 fixedly arranged inside the heating rotator 12. Further, a temperature detecting element TS3 for detecting the temperature of the exciting coil 132 is arranged near the exciting coil 132 of the magnetic field generating means 13. Both of the temperature detecting elements TS2 and TS3 are arranged inside the heating rotator 12 at the center and both ends in the axial direction.

An infrared non-contact temperature sensor, a thermistor, a thermocouple, or the like is used as the temperature detecting elements TS1, TS2, and TS3.

FIG. 6 is a sectional view of the temperature detecting elements TS2 and TS3 and the electromagnetic shield member TSa.

Each of the temperature detecting elements TS2 and TS3 is covered with an electromagnetic shield member TSa. The electromagnetic shield member TSa is formed of a conductive member. The electromagnetic shield member TSa is any of ferrite, nickel fiber, and permalloy. The temperature sensing elements TS2 and TS3 arranged in the magnetic field of the magnetic field generating means 13 are covered with the electromagnetic shield member TSa, so that the magnetic core 131
The temperature can be accurately detected without being affected by the magnetic flux generated from the magnetic field.

(6) Cooling device Magnetic field generating means 13 arranged inside heating rotator 12
Is cooled by the cooling device 20. As the cooling device 20, a fan 20A having a pressure ratio of less than 1.1 (JIS standard) for continuously pumping air by rotation of the impeller (see FIG. 2)
Or a blower such as a blower 20B (see FIG. 3) having a pressure ratio of 1.1 to less than 2 (JIS standard) for continuously pumping air by rotation of the rotor (above, JIS standard). . Note that a cooling device 20 configured to connect cooling means to the fan 20A or the blower 20B to send out cool air is also applicable.

Air or cold air sent by the fan 20A or the blower 20B is sent into one opening of the heating rotator 12, passes through the inside of the heating rotator 12, and is discharged from the other opening. To form a flow.

The magnetic field generating means 13 arranged in the heating rotator 12 is cooled by air or cold air blown by the fan 20A or the blower 20B, and
1. The surface temperature of the exciting coil 132 is reduced. Also,
A rise in temperature due to radiant heat from the heating rotator 12 can be prevented.

In the above embodiment, the magnetic field generating means 13 is cooled by blowing air from the fan 20A or the blower 20B. However, the present invention is not limited to this.
The cooling device 20 may be a device that actively cools the magnetic field generating means 13 using a Peltier element or the like.

(7) Control of Cooling Device FIG. 7 is a block diagram showing control means of the fixing device 10 according to the present invention, and FIG. 8 is a flowchart showing control of the cooling device 20.

The fixing device 10 of the present invention comprises
By detecting the temperatures of the magnetic core 131, the exciting coil 132, and the heating rotator 12, the operation of the cooling device 20, such as the fan 20A or the blower 20B, is controlled to perform the cooling efficiently, and the cooling time is reduced. It is possible to shorten the time.

Magnetic core 1 made of ferromagnetic material such as ferrite
When the temperature T2 of FIG. 31 becomes close to the Curie temperature Tc, the magnetic permeability sharply decreases, and the heat generation efficiency decreases. Further, since the inductance of the magnetic core 131 changes greatly, the output of the high-frequency power supply decreases.

To prevent these problems, the magnetic core 1
When the temperature T2 of 31 approaches the Curie temperature Tc, the magnetic core 131 is forcibly cooled. However, the Curie temperature Tc is different depending on the material of the magnetic core 131 such as ferrite. Even if the same product is used, the Curie temperature Tc of the magnetic core 131 and the temperature T2 of the magnetic core 131 vary. When it is detected that the temperature difference (Tc−T2) with respect to 35 ° C. has reached 35 ° C., the driving of the cooling device 20 is started, and the magnetic core 131 and the exciting coil 132
To cool. When the magnetic core 131 is cooled, the temperature difference (T
When it is detected that c-T2) is 35 ° C. or more,
The control means 19 stops driving the cooling device 20. The temperature difference (Tc−T2) of 35 ° C. is about 2 times the Curie temperature Tc.
It corresponds to 0%.

Alternatively, when the relationship between the temperature T2 of the magnetic core 131 detected by the temperature detecting element TS2 and the surface temperature T1 of the heating rotator 12 satisfies T2> T1, the controller 19 controls the cooling device 20 The operation is started, and the magnetic field generating means 13 is cooled.

Alternatively, when the relationship between the temperature T3 of the exciting coil and the surface temperature T1 of the heating rotator 12 satisfies T3> T1, the operation of the cooling device 20 is started by the control means 19, and the magnetic field generation means 13 is cooled.

(8) Embodiment of Image Forming Apparatus FIG. 9 is a sectional view showing an embodiment of an image forming apparatus provided with a fixing device 10 according to the present invention.

The image forming apparatus shown in FIG.
, A charging unit 2, an exposing unit 3, a developing unit 4, a transferring unit 5, a discharging unit 5A, a separating unit 6, and a cleaning unit 7 are provided around the unit. After uniformly charging the surface of the photoreceptor 1 by the charging unit 2, a latent image is formed by irradiating the laser of the exposure unit 3 with light based on image data read from a document. The toner image is formed on the surface of the photoconductor 1 by reversal development by the developing unit 4 to which a bias is applied.

On the other hand, the paper P fed from the paper storage means 8 is sent to the transfer position, where the transfer means 5
As a result, the toner image is transferred onto the sheet P. Thereafter, the charge on the back surface of the paper P is erased by the charge removing means 5A, separated from the photoreceptor 1 by the separation means 6, conveyed by the intermediate conveyance section 9, subsequently heated and fixed by the fixing device 10, and discharged to the paper discharge tray. Paper. On the other hand, the developer remaining on the surface of the photoreceptor 1 is removed by the cleaning unit 7 downstream of the separation unit 6 to prepare for the next image formation.

In the fixing device of the present invention, a color image is formed on a photoreceptor or an intermediate transfer member by an image forming means, a color toner image is transferred to a sheet by a transfer means, and then the color toner image is formed by the fixing device. The present invention is also applicable to a color image forming apparatus that performs a fixing process.

[0048]

According to the present invention, in a fixing device of an electromagnetic induction heating type in which a magnetic field generating means is disposed in a heating rotator, heat generated by the magnetic field generating means is cooled by temperature detection by a temperature detecting element and control means. By controlling the operation of cooling devices such as fans and blowers, a fixing device that can reduce the warm-up time (quick start) due to instantaneous heating, save energy, and prevent temperature fluctuation inside the heating rotator. Provided.

In particular, in a color image forming apparatus, when the fixing temperature is set high for fixing a color image and the viscosity of the toner is reduced to obtain sufficient color reproducibility by mixing a plurality of color toners, It is possible to perform a heat fixing process without causing bleeding.

[Brief description of the drawings]

FIG. 1 is a front sectional view showing an embodiment of a fixing device according to the present invention.

FIG. 2 is a side sectional view of the fixing device.

FIG. 3 is a perspective view of the fixing device.

FIG. 4 is a sectional view showing another arrangement example of the magnetic field generating means, and a partially enlarged sectional view of the magnetic field generating means and the heating rotator.

FIG. 5 is a sectional view showing still another arrangement example of the magnetic field generating means.
And a partial enlarged sectional view of the heating rotator.

FIG. 6 is a sectional view of a temperature detecting element and an electromagnetic shield member.

FIG. 7 is a block diagram showing control means of the fixing device according to the present invention.

FIG. 8 is a flowchart illustrating control of the cooling device.

FIG. 9 is a cross-sectional configuration diagram illustrating an embodiment of an image forming apparatus including a fixing device according to the invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 fixing device 11 fixing roller 12 heating rotator 13, 13A, 13B magnetic field generating means 14 pressure roller 18 high frequency power supply 19 control means 20 cooling device 20A fan 20B blower 121 surface layer (release layer) 131 magnetic core 132 exciting coil H , H1, H2 AC magnetic field N Fixing nip P Recording medium (paper) T1 Surface temperature of heating rotating body T2 Temperature of magnetic core T3 Temperature of exciting coil TS1, TS2, TS3 Temperature detecting element TSa Electromagnetic shield member

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H05B 6/42 H05B 6/42 F term (Reference) 2H033 AA30 BA25 BA29 BA31 BA32 BB02 BB18 BB21 BB22 BE06 CA02 CA07 CA23 CA27 CA44 CA53 3K059 AA08 AA10 AB10 AB19 AB28 AC33 AD03 AD05 AD15 BD01 BD23 CD09 CD48 CD73 CD75 CD77 5H323 AA36 BB04 BB12 CA08 CB06 CB25 CB33 CB44 DA01 DA04 DB01 DB11 EE01 FF01 FF03 GG02 GG04 GG16 KK16

Claims (13)

[Claims] 1. A heating rotator made of a conductive member, a magnetic field generating means arranged near the heating rotator, and a power supply for supplying an alternating current to the magnetic field generating means, In the induction heating type fixing device for heating and fixing the toner image formed on the recording medium by causing the heating rotator to generate heat by electromagnetic induction by the high frequency induction magnetic flux generated from the magnetic material, the magnetic field generating means includes a magnetic material. A magnetic core comprising:
A fixing device comprising: an excitation coil wound around the magnetic core; and a temperature detecting element for detecting a temperature of the magnetic core, disposed near the magnetic core. 2. A magnetic rotator comprising: a heating rotator made of a conductive member; magnetic field generating means disposed near the heating rotator; and a power supply for supplying an alternating current to the magnetic field generating means. In the induction heating type fixing device for heating and fixing the toner image formed on the recording medium by causing the heating rotator to generate heat by electromagnetic induction by the high frequency induction magnetic flux generated from the magnetic material, the magnetic field generating means includes a magnetic material. A magnetic core comprising:
A fixing device, comprising: an exciting coil wound around the magnetic core; and a temperature detecting element for detecting a temperature of the exciting coil disposed near the exciting coil. 3. A heating rotator comprising a conductive member, a magnetic field generating means disposed near the heating rotator, and a power supply for supplying an alternating current to the magnetic field generating means. In the induction heating type fixing device for heating and fixing the toner image formed on the recording medium by causing the heating rotator to generate heat by electromagnetic induction by the high frequency induction magnetic flux generated from the magnetic material, the magnetic field generating means includes a magnetic material. A magnetic core comprising:
A temperature detection element for detecting a temperature of the magnetic core, a temperature detection element for detecting a temperature of the excitation coil, and a surface temperature of the heating rotator, the excitation coil being wound around the magnetic core; And a temperature detecting element. 4. The fixing device according to claim 1, wherein the temperature detecting element is one of a thermistor, an infrared non-contact temperature sensor, and a thermocouple. 5. A heating rotator made of a conductive member, a magnetic field generating means disposed inside the heating rotator, and a power supply for supplying an alternating current to the magnetic field generating means, In the induction heating type fixing device for heating and fixing the toner image formed on the recording medium by causing the heating rotator to generate heat by electromagnetic induction by the high frequency induction magnetic flux generated from the magnetic material, the magnetic field generating means includes a magnetic material. A magnetic core comprising:
A temperature detection element for detecting a temperature of the magnetic core, a temperature detection element for detecting a temperature of the excitation coil, and a surface temperature of the heating rotator, the excitation coil being wound around the magnetic core; A temperature detecting element, a cooling device for cooling the magnetic field generating means, and a control means for controlling the operation of the cooling device. 6. The cooling device is activated when a temperature difference between the Curie temperature of the magnetic core and the temperature of the magnetic core detected by the temperature detecting element is 35 ° C. or less. 6. The fixing device according to 5. 7. When the relationship between the temperature T2 of the magnetic core and the surface temperature T1 of the heating rotator satisfies T2> T1, the control device activates the cooling device. The fixing device according to claim 5. 8. The cooling device is operated by the control means when the relationship between the temperature T3 of the exciting coil and the surface temperature T1 of the heating rotator satisfies T3> T1. The fixing device according to claim 5. 9. The fixing device according to claim 5, wherein the cooling device is a blower that forms a flow of air into the heating rotator through an opening at an end of the heating rotator. 10. At least one of a temperature detecting element for detecting a temperature of the magnetic core, a temperature detecting element for detecting a temperature of the exciting coil, and a temperature detecting element for detecting a surface temperature of the heating rotator, The fixing device according to claim 1, wherein the fixing device is covered with a shield member. 11. The fixing device according to claim 10, wherein the electromagnetic shield member is a conductive member. 12. The fixing device according to claim 10, wherein the electromagnetic shield member is at least one of ferrite, nickel fiber, and permalloy. 13. An induction heating apparatus according to claim 1, further comprising: an image forming unit for forming an image on a recording medium; and a fixing device for heating and fixing the image. An image forming apparatus comprising a mold-type fixing device.