JP2014123031A - Heating device, fixing device, and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heating device capable of providing uniformity in temperature in a longitudinal direction of a fixing member.SOLUTION: A heating device 45 employing an induction heating system includes: an excitation coil 61 that is arranged opposite to an outer peripheral surface of a fixing member 41 provided with a heating layer, and generates a magnetic flux; at least one type of magnetic body core 64 that forms a magnetic path to introduce the magnetic flux generated by the excitation coil to the fixing member; and a holding member 65 that holds the excitation coil and the magnetic body core. The magnetic body core 64 has a thickness in end parts formed smaller than that in the center part.

Description

  The present invention relates to a heating device used in an image forming apparatus such as a copying machine, a printer, a facsimile, or a complex machine thereof, a fixing device that fixes an unfixed toner image, and an image forming device. The present invention particularly relates to a heating device, a fixing device, and an image forming apparatus using an electromagnetic induction heating method.

  2. Description of the Related Art Conventionally, image forming apparatuses such as copying machines and printers that use an electromagnetic induction heating type fixing device are widely known for the purpose of reducing energy consumption by reducing the rise time of the apparatus.

  In Patent Document 1, an electromagnetic induction heating type fixing device includes a supporting roller (heating roller) as a heating element, a fixing auxiliary roller (fixing roller), a fixing belt stretched between the supporting roller and the fixing auxiliary roller, and a supporting roller. And an induction heating unit (induction heating means) opposed to each other via a fixing belt, a pressure roller that contacts the fixing auxiliary roller via the fixing belt, and the like. The induction heating unit includes a coil unit (coil) wound in the longitudinal direction, a core (coil core) disposed around the coil unit, and the like.

  The fixing belt is heated at a position facing the induction heating unit. The heated fixing belt heats and fixes the toner image on the recording medium conveyed to the positions of the auxiliary fixing roller and the pressure roller. Specifically, when a high-frequency alternating current is passed through the coil portion, an alternating magnetic field is formed around the coil portion, and an eddy current is generated near the surface of the support roller. When an eddy current is generated in the support roller, Joule heat is generated by the electrical resistance of the support roller itself. The fixing belt wound around the support roller is heated by the Joule heat.

  In such an electromagnetic induction heating type fixing device, since the heating element is directly heated by electromagnetic induction, the heat conversion efficiency is higher than that of the conventional halogen heater method, etc., and the startup time is short with less energy consumption. It is known that the surface temperature (fixing temperature) of the fixing belt can be raised to a desired temperature.

  In Patent Document 2, the core is insert-molded into the case for the purpose of further improving the heat generation efficiency. Thereby, the heating roller and the core can be brought close to each other, and the heat generation efficiency of the heating roller can be improved.

  FIG. 16 is a cross-sectional view of a fixing device used in Patent Document 2. The induction heating unit includes an exciting coil and a core for guiding an alternating magnetic field generated from the exciting coil to a heating element. By integrally forming the side core 52b and the center core 52c into the case 53, leakage of alternating magnetic flux is reduced, and improvement in heat generation efficiency is realized.

  Here, although the side core 52b has a rectangular parallelepiped shape, since the core is obtained by compression molding and sintering ferrite powder, the core contracts during the sintering, and the side core is likely to warp. When a warped side core is insert-molded into the case 53, the side core is pressed with a pin or the like and fixed to the mold, but at that time, the side core is easily cracked. When cracks occur in the side core, the contact state between the side core 52b and the arch core may vary, or the broken pieces may be molded away from the target position. Occurs. The heat generation efficiency is naturally good at a location where the magnetic path is well formed, but the leakage magnetic flux increases at a bad location and the heat generation efficiency is lowered. As a result, temperature uniformity cannot be obtained in the longitudinal direction of the heating roller.

  Therefore, an object of the present invention is to provide a heating device that can obtain temperature uniformity in the longitudinal direction of a fixing member.

  In order to solve this problem, the present invention provides an exciting coil that is arranged opposite to the outer peripheral surface of a fixing member having a heat generating layer and generates a magnetic flux, and a magnetic flux that guides the magnetic flux generated by the exciting coil to the fixing member. In an induction heating type heating apparatus having a magnetic core that forms a path, and a holding member that holds the exciting coil and the magnetic core, the thickness of the end of the magnetic core is thinner than the central portion. A heating device characterized by being formed is proposed.

  According to the present invention, since the variation in the contact state between the magnetic cores in the longitudinal direction of the heating device is reduced, the temperature in the longitudinal direction of the fixing member can be made uniform.

1 is a schematic configuration diagram for explaining an image forming apparatus. FIG. 2 is a schematic cross-sectional view of a fixing device. 2 is a schematic sectional view of a fixing belt. FIG. It is a schematic side sectional view of an induction heating part. It is a perspective view of an induction heating part. It is a perspective view of a metal mold | die. It is a perspective view of a movable side metal mold | die. It is a perspective view of a movable side metal mold | die. It is a perspective view of a fixed side mold. It is a perspective view of the metal mold | die at the time of insert integral molding. It is a figure which shows the shape of the side core before and behind sintering as 1st Embodiment. It is state explanatory drawing when fixing a side core to a metal mold | die. It is the perspective view, side view, and top view of a side core as 2nd Embodiment. It is a schematic side view which shows the contact state of a side core and an arch core. It is explanatory drawing about how to cover a side core. It is a figure of the prior art which shows insert integration of a side core and a center core and a case.

Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings.
First, the configuration and operation of the entire image forming apparatus will be described with reference to FIG.
This printer forms four color toner images of yellow, magenta, cyan, and black on the surfaces of the photosensitive drums 1Y, 1M, 1C, and 1Bk as corresponding image carriers, respectively. Four sets of electrophotographic image forming units 10Y, 10M, 10C, and 10Bk are provided.

  Below these image forming units 10Y, 10M, 10C, and 10Bk, a conveying belt 20 is stretched for conveying a sheet 46 as a recording medium through each image forming unit. The photoconductive drums 1Y, 1M, 1C, and 1Bk of the image forming units 10Y, 10M, 10C, and 10Bk are arranged in rolling contact with the conveyance belt 20, and the sheet is electrostatically attracted to the surface of the conveyance belt 20.

  The four sets of image forming units 10Y, 10M, 10C, and 10Bk have substantially the same structure. Therefore, here, the yellow image forming unit 10Y disposed on the most upstream side in the sheet conveyance direction will be described as a representative, and the other color image forming units 10M, 10C, and 10Bk are denoted by the same reference numerals. Detailed description is omitted.

  The image forming unit 10Y includes a photosensitive drum 1Y that is in rotational contact with the transport belt 20 at a substantially central position. Around the photosensitive drum 1Y, a charging device 2Y for charging the surface of the photosensitive drum 1Y to a predetermined potential, the charged drum surface is exposed based on the color-separated image signal, and the surface of the drum is electrostatically charged. An exposure device 3Y that forms a latent image, a developing device 4Y that supplies yellow toner to the electrostatic latent image formed on the drum surface and develops it, and a developed toner image on a sheet that is conveyed via a conveyance belt 20 A transfer roller 5Y as a transfer device for transferring, a cleaner 6Y for removing residual toner remaining on the drum surface without being transferred, and a charge eliminating lamp for removing electric charge remaining on the drum surface (not shown) are provided in the rotational direction of the photosensitive drum 1Y. Are disposed in order.

A paper feed mechanism 30 for feeding paper onto the transport belt 20 is disposed on the lower right side of the transport belt 20 in the drawing.
A fixing device 40 according to an embodiment of the present invention, which will be described later, is disposed on the left side of the conveyance belt 20 in the figure (excitation coils and the like are omitted in this figure). The paper transported by the transport belt 20 is transported through a transport path continuously extending from the transport belt 20 through the fixing device 40 and passes through the fixing device 40.

  The fixing device 40 heats and presses the conveyed paper, that is, the paper on which the toner images of the respective colors are transferred, melts the toner images of the respective colors, and permeates the paper to fix them. Then, the sheet is discharged to the downstream side of the conveyance path of the fixing device 40 via a discharge roller, and a series of image forming processes is completed.

Next, the fixing device 40 according to the present invention will be described with reference to FIG.
The fixing device 40 is configured as a belt fixing device, and includes a heating roller (supporting roller) 41 as a fixing member having a heat generating layer, a fixing roller 43, a fixing belt 44 stretched between the heating roller and the fixing roller, and fixing. It comprises an induction heating unit 45 that faces the heating roller via a belt, and a pressure roller 42 as a pressure member that contacts the fixing roller 43 via a fixing belt 44. The fixing belt 44 rotates in the rotation direction A, and the paper 46 carrying the toner image T is pressurized and heated at the fixing nip N to fix the toner image T.

  The heating roller 41 is made of nonmagnetic stainless steel (SUS) and has a core metal layer thickness of about 0.2 to 1 mm. Copper (Cu) as a heat generation layer is formed on the surface of the core metal to a thickness of about 3 to 15 μm to enhance the heat generation efficiency. In this case, it is also suitable to apply Ni plating to the Cu surface layer for the purpose of rust prevention. As another example, a magnetic shunt alloy having a Curie point of about 160 to 220 ° C. can be used. At this time, the magnetic shunt alloy may be used as a heat generating layer, or copper as a heat generating layer may be formed on the surface of the magnetic shunt alloy about 3 to 15 μm thick. An aluminum member is disposed inside the magnetic shunt alloy, which makes it possible to stop the temperature increase near the Curie point without a special control mechanism.

  The fixing roller 43 includes a metal core 43a made of, for example, stainless steel or carbon steel, and an elastic member 43b covered with a core made of heat-resistant silicone rubber or the like in a solid or foamed form. Then, a contact portion (fixing nip portion N) having a predetermined width is formed between the pressure roller 42 and the fixing roller 43 by the pressing force from the pressure roller 42. Its outer diameter is about 30 to 40 mm, and the elastic member has a thickness of about 3 to 10 mm and a hardness of about 10 to 50 ° (JIS-A).

Next, the fixing belt 44 will be described in detail with reference to FIG. 3 which is a sectional view of the fixing belt 44. As shown in the figure, an elastic layer 44b and a release layer 44c are laminated on the base material 44a.
Properties required for the substrate 44a include mechanical strength when the belt is stretched, flexibility, and heat resistance that can withstand use at a fixing temperature. In the present invention, in order to inductively heat the heating roller 41, an insulating heat-resistant resin material, polyimide, polyimide amide, PEEK, PES, PPS, fluorine resin, or the like is suitable as the substrate 44a. The thickness of the base material 44a is preferably about 30 to 200 μm from the viewpoint of heat capacity and strength.

  The elastic layer 44b is formed for the purpose of giving flexibility to the belt surface in order to obtain a uniform image without uneven glossiness, and is made of an elastomer material having a rubber hardness of 5 to 50 ° (JIS-A), and has a thickness. Is preferably 50 to 500 μm. From the viewpoint of heat resistance at the fixing temperature, silicone rubber, fluorosilicone rubber or the like is used as the material.

  Materials used for the release layer 44c include tetrafluoroethylene resin (PTFE), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer resin (PFA), and tetrafluoroethylene / hexafluoropropylene copolymer ( FEP) and the like, or a mixture of these resins, or a heat resistant resin in which these fluorine resins are dispersed.

  When the release layer 44c covers the elastic layer 44b, toner release properties and prevention of paper powder adhesion can be achieved without using silicone oil (oilless). However, since these resins having releasability generally do not have elasticity like a rubber material, if the release layer 44c is formed thick on the elastic layer 44b, the flexibility of the belt surface is impaired and uneven gloss is generated. End up. In order to achieve both releasability and flexibility, the thickness of the release layer 44c is 5 to 50 μm, desirably 10 to 30 μm.

Moreover, a primer layer may be provided between each layer as needed, and a layer for improving durability during sliding may be provided on the inner surface of the substrate.
It is also preferable to provide the base material 44a with a heat generating layer. For example, a Cu layer of 3 to 15 μm may be formed on a base layer made of polyimide or the like and used as a heat generating layer.

  The pressure roller 42 includes a metal core 42a made of a metal cylindrical member, an elastic layer 42b having high heat resistance, and a release layer 42c. The pressure roller 42 presses the fixing roller 43 via the fixing belt 44 to fix the fixing nip. Part N is formed. The outer diameter of the pressure roller is about 30 to 40 mm, the thickness of the elastic layer is about 0.3 to 5 mm, and the hardness is about 20 to 50 ° (Asker hardness). Since heat resistance is required, silicone rubber may be used as the material for the elastic layer. Further, in order to improve the releasability at the time of double-sided printing, a release layer 42c using a fluororesin is formed on the elastic layer 42b by about 10 to 100 μm.

  By making the hardness of the pressure roller 42 larger than that of the fixing roller 43, the pressure roller bites into the fixing roller (and the fixing belt). By this biting in, the sheet has a curvature that cannot follow the surface of the fixing belt at the exit of the nip portion, and the releasability of the sheet can be improved.

Next, the induction heating unit 45 will be described with reference to FIGS.
The induction heating unit 45 serving as a heating device is an excitation coil 61 that generates a magnetic flux linked to the heating roller so as to face the outer peripheral surface of the heating roller 41, and a continuous magnetic flux that is generated by the excitation coil 61 to the heating roller 41. And a case 65 as a holding member for holding the exciting coil and the magnetic core.

  As shown in the figure, the magnetic core includes an arch core 62 disposed so as to sandwich the excitation coil 61 with respect to the outer peripheral surface of the heating roller 41, and the heating roller 41 without contacting the arch core 62 and via the excitation coil. It consists of a side core 64 facing the outer peripheral surface, and a center core 63 disposed at the center of the wound exciting coil 61. Since the magnetic core surrounds the excitation coil 61 and forms a closed magnetic path for guiding the magnetic flux from the excitation coil 61 to the heating roller 41 and the fixing belt 44, the magnetic circuit is reliably formed as a closed magnetic circuit. The heat generation efficiency of the heating roller and the fixing belt can be improved. Further, the side core 64 is integrally formed with the case 65 by an insert.

  As shown in FIG. 5, ten arch cores 62 are arranged at equal intervals in the case 65 so that the temperature distribution in the longitudinal direction of the heating roller 41 is uniform, and both ends thereof are in contact with the side core 64. ing. The exciting coil 61 is surrounded by an arch core 62, a center core 63, and a side core 64. In FIG. 5, the center core 63 is not shown.

  The exciting coil 61 is formed by winding a litz wire obtained by twisting about 50 to 500 conductor wires having a diameter of about 0.05 to 0.2 with an insulating coating, and is wound in the case 65 within the heating roller 41. A magnetic flux extending over the entire maximum heating region and interlinking with the heating roller 41 is generated. The surface of the litz wire is provided with a fusing layer, and the fusing layer is solidified by heating in an electric heating or thermostatic bath, and the shape of the wound coil can be maintained. Instead of this, it is also possible to give a shape by winding a coil using a litz wire that does not hold the fusion layer and press-molding it. Since the litz wire needs to have a heat resistance equal to or higher than the fixing temperature, a resin having both heat resistance and insulation properties, such as polyamideimide and polyimide, is used for the insulation coating material of the strand.

  The exciting coil 61 that has been wound is adhered to the case 65 using a silicone adhesive or the like. Since the case 65 requires heat resistance equal to or higher than the fixing temperature, a resin material having high heat resistance (for example, resin polyethylene terephthalate (PET), polyphenylene sulfide (PPS), liquid crystal polymer (LCP), or the like) is used. .

Next, the operation of the fixing device 40 configured as described above will be described.
The fixing belt 44 is rotated in the direction of arrow A in FIG. 2 by a drive motor (not shown). The heating roller 41 is induction-heated by the induction heating unit 45 to heat the fixing belt 44.
Specifically, the high-frequency alternating current of 10 kHz to 1 MHz is passed through the induction heating unit 45 so that the magnetic lines of force are alternately switched in both directions in the coil loop. By forming the alternating magnetic field in this way, an eddy current is generated in the heating roller 41, Joule heat is generated, and the heating roller 41 is induction-heated. The fixing belt 44 is heated by the heat generated from the heating roller 41 in this way, the conveyed paper 46 and the fixing belt 44 come into contact with each other at the fixing nip N, and the toner image T on the paper 46 is heated, melted and fixed. The

Next, a method for integrally forming the insert of the case and the side core will be described with reference to FIGS.
FIG. 6 is an overall perspective view of the mold 71 and the case 65. The case 65 is molded as illustrated by pouring molten resin into the mold 71 and cooling and solidifying the resin. The mold 71 has a fixed portion 71a and a movable portion 71b on the side where the resin is poured. Further, between the fixed portion 71a and the movable portion 71b, there are a portion 71c for forming the end portion in the longitudinal direction and a portion 71d for forming the side surface in the direction orthogonal to the longitudinal direction.

  FIG. 7 is a partially enlarged view of the mold movable portion 71b. The mold movable part 71b has a magnet 72 and a core fixing pin 73 for fixing the side core 64, which is integrally formed with the case, to the mold. As shown in FIG. 8, the side core 64 is disposed between the core fixing pins 73. On the other hand, as shown in FIG. 9, the mold fixing portion 71 a also has a core fixing pin 73. As shown in FIG. 10, when the complementary shaped mold fixing part 71a and the mold movable part 71b are combined, the side core 64 is completely fixed, and a gap corresponding to the shape of the case is formed. In this state, the molten resin is poured and hardened from the direction indicated by the arrow m, whereby the case 65 in which the resin and the side core 64 are integrally formed with the insert is molded.

  As the material of the core, it is preferable to use a soft magnetic material such as Mn—Zn-based ferrite or Ni—Zn-based ferrite having a high electric resistivity. Ferrite cores are processed by compressing and sintering powder. However, the core contracts during the sintering process, and the side core 64 is warped.

  As described above, when the case 65 and the side core 64 are integrally formed by insert, the side core 64 is fixed to the mold 71 of the case 65 by the magnet 72, the pin 73, or the like. At this time, if the side core 64 is warped, the side core 64 is bent by three-point bending, and the side core is easily cracked by the pressing force. Since there are variations in the amount of warpage and the presence or absence of cracks, the contact state between the side core 64 and the arch core 62 also varies between individuals.

  As the contact area between the side core 64 and the arch core 62 is larger, the leakage magnetic flux is reduced, the heat generation efficiency is improved, and the temperature of the heating element is likely to rise. Therefore, when the side core 64 and the arch core 62 having different contact states are mixed, the temperature uniformity in the longitudinal direction of the heating roller 41 is impaired.

  Therefore, as shown in FIGS. 11 and 12, in the present invention, the thickness of both end portions of the side core having a rectangular parallelepiped shape is formed thin. FIG. 11 is a schematic diagram showing the shape of the side core 64 before and after sintering as the first embodiment. FIG. 12 is a schematic diagram showing the side core 64 fixed to the mold 71.

  As shown in FIG. 11A, when the thickness of the side core 64 before sintering is constant, the side core 64 warps after sintering. Therefore, as shown in FIG. 12 (a), when the side core 64 is fixed to the mold 71 as it is, the center portion of the warped side core 64 is pushed downward by the force 73 by the pin 73, so that the side core is bent at three points. 64 will crack. As the warp amount h of the side core 64 increases, the force f generated by the pin 73 increases and cracking is likely to occur.

  In contrast, in the present embodiment, as shown in FIG. 11B, the thickness of the end of the side core 64 before sintering is in the center in the direction in which the side core 64 is pressed against the mold during molding. Compared to thin. Preferably, as shown in the cross-sectional view, the central portion of the side core 64 before sintering has a flat portion, and the upper surface and the lower surface of the end portion are inclined from the flat portion, in other words, the end portion has a cone shape. have. Thereby, as shown in FIG. 12B, the warp amount h after sintering becomes small, and even if the center portion is pushed by the pin 73, the side core 64 can be prevented from cracking. Since the side core 64 can be prevented from cracking, there is no variation in the contact state between the side core 64 and the arch core 62, and the temperature uniformity in the longitudinal direction of the heating roller 41 is not impaired. In addition, since the side core 64 has a flat portion, the flat portion can be pressed for integral molding with the case, and the side core can be easily fixed to the mold. If the side core is arranged so that the magnet 72 and the pin 73 are in the flat portion, the degree of adhesion between the magnet 72 and the side core is increased.

  Such a side core 64 can be manufactured at low cost. That is, the tolerance of the side core must be set strictly in order to reduce the amount of warpage of the side core and make the contact state between the individuals uniform. However, this leads to an increase in costs due to additional processes such as yield reduction and side core cutting after sintering. On the other hand, in the side core according to the present embodiment in which the wall thickness of the end portion is reduced, the warpage amount h is reduced, so that uniform exothermicity can be obtained without losing heat generation efficiency without selecting a core by setting a tight tolerance. It is done.

Next, a side core cracking experiment of the present embodiment will be described.
The side core 64 as Example 1 used in this experiment is formed so that the thickness of the end portion shown in FIG. 11B is thinner than that of the central portion. The side core had a longitudinal length of 26 mm, a width of 10 mm, a thickness of 3 mm near the center, and a thickness of 2.6 mm near the end. The flat portion near the center was 13 mm, and the wall thickness became thinner with an inclination of R250 from there toward the end.

  As Comparative Example 1, a side core having a constant thickness shown in FIG. In Example 1 and Comparative Example 1, the conditions other than the side core were the same.

  In Example 1 and Comparative Example 1, the number of side cores that were broken when the side core was set in the mold 71b and clamped with the mold 71a was confirmed. In order to compare the degree of cracking when set in the mold, only the mold was opened and closed, and no resin was poured. As shown in Table 1, in Example 1, out of the 25 side cores, the number of cracks was one at the first time, one at the second time, and two at the third time. On the other hand, in Comparative Example 1, the number of cracks was 21 at the first time, 23 at the second time, and 22 at the third time. From the above, according to the present embodiment, it was confirmed that the cracks of the side core can be greatly reduced and the temperature uniformity in the longitudinal direction of the heating roller 41 can be easily obtained.

Next, a side core 64 as a second embodiment will be described with reference to FIG. In the present embodiment, only the shape of the side core is different from that of the first embodiment, and the configurations of the other cores and the induction heating unit are the same.
As shown in FIG. 13A, which is a perspective view of the side core 64, the thickness near the end is near the center in both the direction in which the side core 64 is pressed against the mold during molding and the direction perpendicular thereto. It is thinner than That is, in both FIG. 13 (b) which is a side view and FIG. 13 (c) which is a plan view, the thickness of both end portions of the side core having a rectangular parallelepiped shape is formed thinner than the central portion. Thereby, generation | occurrence | production of the curvature of the direction in which the side core 64 is pressed at the time of insert integral molding and the direction perpendicular | vertical to it is suppressed, and even when a pressing force is applied from two directions at the time of shaping | molding, it can prevent a core crack.

Next, a contact surface between the arch core 62 and the side core 64 will be described with reference to FIG.
As shown in FIG. 14A, when the arch core 62 contacts the inclined portion of the side core 64, there is a portion where the arch core 62 and the side core 64 do not contact as shown in the region g. Therefore, as shown in FIG. 14B, the arch core 62 is preferably in contact with the flat portion of the side core. Thereby, the contact surface of the arch core 62 and the side core 64 becomes larger, and the heat generation efficiency is improved.

Next, how to cover the side core 64 will be described with reference to FIG.
As illustrated, the side core 64 is covered with the resin of the case 65 except for the contact surface of the side core 64 with which the arch core 62 contacts. During the operation of the induction heating unit 45, the coil case and the side core are at a high temperature of 100 ° C or higher. On the other hand, the temperature becomes room temperature while the vehicle is stopped, and it is cooled to about 5 ° C. in winter, for example. Therefore, the side core 64 may repeat thermal expansion and contraction, and may crack. Therefore, by covering the side core 64 with resin as much as possible, it is possible to prevent the fragments from scattering outside the coil case even if the core is broken.

  Note that the present invention is not limited to the above-described embodiment, and it is obvious that the configuration of the above-described embodiment can be appropriately changed within the scope of the technical idea of the present invention. For example, the fixing device is not limited to the belt fixing method, and may be a roller fixing method including an induction heating unit, a fixing roller as a fixing member, and a pressure roller. In addition, the number, position, etc. of the side cores and arch cores can be set to a suitable number, position, etc. for carrying out the present invention.

40 fixing device 41 heating roller (fixing member)
45 Induction heating unit (heating device)
61 Excitation coil 62 Arch core (magnetic core)
63 Center core (magnetic core)
64 Side core (magnetic core)
65 Case (holding member)

JP 2006-350054 A JP 2012-159829 A

Claims (10)

An exciting coil that is arranged opposite to the outer peripheral surface of the fixing member having a heat generating layer and generates a magnetic flux, a magnetic core that forms a magnetic path that guides the magnetic flux generated by the exciting coil to the fixing member, and the excitation In an induction heating type heating apparatus having a coil and a holding member for holding the magnetic core,
A heating device, wherein the end of the magnetic core is formed thinner than the central portion. The magnetic core has at least one arch core disposed to face the outer peripheral surface of the fixing member and sandwich the excitation coil, and at least one arch core disposed to contact the arch core and face the fixing member. Has two side cores,
The heating apparatus according to claim 1, wherein a thickness of an end portion of the side core is formed thinner than a central portion.   The heating apparatus according to claim 2, wherein the side core includes a flat portion, and the flat portion is pressed against the mold.   The heating device according to claim 3, wherein the arch core is in contact with the flat portion of the side core.   The heating apparatus according to any one of claims 2 to 4, wherein the side core is covered with the holding member except for a contact surface of the side core with which the arch core contacts.   A thickness of an end portion of the magnetic core is formed thinner than a central portion in a direction in which the magnetic core is pressed against a mold when the magnetic core is integrally formed with the holding member. The heating apparatus as described in any one of Claims 1-5. The magnetic core has a rectangular parallelepiped shape,
In a direction in which the magnetic core is pressed against the mold when integrally formed with the holding member, the end of the magnetic core is formed thinner than the center before sintering. The heating apparatus according to any one of claims 1 to 6, wherein   Also in the direction perpendicular to the direction pressed against the mold when the magnetic core is integrally formed with the holding member, the thickness of the end of the magnetic core is made thinner than the central portion. The heating apparatus according to claim 6 or 7, wherein   A fixing device comprising the heating device according to claim 1.   An image forming apparatus comprising the heating device according to claim 1 or the fixing device according to claim 9.

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