JPH11327331A - Image heating device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the temperature of an exothermic part from rising and to make preventible an energizing member from being damaged by providing a movable belt, a pressure means for forming a nip on its surface side by being in press contact with the belt, an exothermic member having a specified Curie temperature and the energizing member for energizing the exothermic member. SOLUTION: A belt 21 moves while sliding to contact with the surface of a conductive plate 28 when it rotates and moves. When the temperature of the exothermic member 26 is equal to or under the Curie temperature, a current mostly flows through a magnetic plate 27, so that Joule heat is generated. When the temperature of the member 26 is near to the Curie temperature, the magnetism of the magnetic plate 27 is eliminated and magnetic flux diverges toward the conductive plate 28, and an induced current overwhelmingly flows in the conductive plate 28 whose electric resistance is low. At such a time, the electric resistance is low, so that generated heat is reduced. Since the member 26 has self temperature control characteristic, the exothermic part is prevented from getting to abnormally high temperature, and temperature control is automatically performed by setting the Curie temperature to the temperature near to the fixing temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image heating apparatus for shortening a warm-up time, and more particularly, to an image heating apparatus suitable for an image forming apparatus such as an electrophotographic apparatus and an electrostatic recording apparatus which is suitable for fixing an unfixed image. The present invention relates to an apparatus and an image forming apparatus using the same.

[0002]

2. Description of the Related Art As an image heating device represented by a heat fixing device, a contact heating system such as a heat roller system and a film heating system has been generally used.

In recent years, a film heating method with a small heat capacity has attracted attention due to demands for shortening a warm-up time and saving energy. Attempts have been made to use electromagnetic induction heating in this film heating method to further increase the efficiency of heat generation.

Japanese Patent Application Laid-Open No. 9-281821 is a typical example, and FIG. 9 shows its structure. An exciting coil 203 wound around a ferrite core 202 is installed inside an endless rotating film 201, and an alternating magnetic field penetrates the film 201 or the resistor 204. The toner image 207 on the recording material 206 that has passed through the pressure roller 205 is fixed by heat generated by the induced current generated in the film 201 or the resistor 204 as a heating element. In this example, the configuration of the exciting coil is devised in order to make the distribution of the amount of heat generated on the film 201 or the resistor 204 appropriate.

[0005]

Generally, in the film heating method including the above-mentioned conventional example, the heat capacity of the film is set to be small in order to shorten the warm-up time. There is a possibility that the heat generating part may be destroyed.

This causes a further problem when a recording material having a narrow width in the depth direction of the image heating apparatus in FIG. 9 is continuously passed. In other words, the portion through which the recording material passes must be heated accordingly in order for heat to be deprived by the recording material, but the portion through which the recording material does not pass is similarly heated, because the heat capacity of the heating element is small. The temperature rises. If the temperature rises excessively, the exciting coil and the like may be damaged.

On the other hand, Japanese Patent Application Laid-Open No. Hei 7-114276 discloses an attempt to obtain self-temperature controllability by using a film having a Curie temperature set. Therefore, the thickness of the film is set as small as possible, so that the material and thickness of the film cannot be freely set. This makes effective self-temperature control difficult.

[0008] In view of the above-mentioned conventional problems, an object of the present invention is to provide:
It is an object of the present invention to provide an image heating apparatus and an image forming apparatus that prevent an exciter member from being damaged by performing effective self-temperature control to prevent a temperature rise of a heat generating portion.

Another object of the present invention is to provide an image heating apparatus and an image forming apparatus which prevent the exciting member from being damaged by reducing the influence of the temperature of the heat generating portion on the exciting member. .

[0010]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a movable belt, and at least one pressing means for pressing the belt to form a nip on the surface side of the belt. An image heating device, comprising: a heating member formed of a magnetic material having a predetermined Curie temperature and adjacent to the back of the belt; and an excitation member for exciting the heating member, and an image forming apparatus using the heating device. Device.

The present invention also provides a movable belt, pressing means for pressing the belt to form a nip on the surface side of the belt, and the nip portion from an upstream side of the nip portion in a belt moving direction. An image heating device, comprising: a heating member that is close to the belt rear surface in the vicinity; and an exciting member that generates an induced current in the heating member to generate heat, on the upstream side of the pressure contact portion with respect to the belt movement direction. Is an image forming apparatus using the image forming apparatus.

Still further, according to the present invention, there is provided a movable belt, pressurizing means for pressing the belt to form a nip on the front side of the belt, and contacting a part of the belt on the back side of the belt. An image heating apparatus comprising: a heating member; and an exciting member disposed at a position facing the heating member and on the surface side of the belt, and generating an induced current in the heating member to generate heat. Image forming apparatus.

[0013]

FIG. 6 is a sectional view of an image forming apparatus using an image heating device according to an embodiment of the present invention as a fixing device. The configuration and operation of this device will be described below.

Reference numeral 1 denotes an electrophotographic photosensitive member (hereinafter, photosensitive drum). The surface of the photosensitive drum 1 is uniformly charged to a predetermined negative dark potential V0 by the charger 2 while being rotationally driven at a predetermined peripheral speed in the direction of the arrow.

Reference numeral 3 denotes a laser beam scanner, which outputs a laser beam modulated according to a time-series electric digital pixel signal of image information input from a host device such as an image reading device or a computer (not shown). The surface of the photosensitive drum 1, which is uniformly charged as described above, is scanned and exposed by this laser beam, and the exposed portion has a small absolute value of potential and becomes a bright potential VL, and an electrostatic latent image is formed on the surface of the photosensitive drum 1. It is formed.

Next, the latent image is reversely developed with a negatively charged powder toner by a developing unit 4 to be visualized.

The developing device 4 includes a developing roller 4a which is driven to rotate.
A thin layer of toner having a negative charge is formed on the outer peripheral surface of the roller to oppose the surface of the photosensitive drum 1, and the absolute value of the developing roller 4a is
Is applied, the toner on the developing roller 4a transfers to only the portion of the photosensitive drum 1 where the light potential VL is applied, and the latent image is visualized. Is done.

On the other hand, a recording material 15 is fed one by one from a paper supply unit 10 and passes through registration roller pairs 11 and 12 to a nip portion between the photosensitive drum 1 and a transfer roller 13 abutting on the photosensitive drum 1. It is sent at an appropriate timing synchronized with the rotation of the photosensitive drum 1. The toner image on the photosensitive drum 1 is sequentially transferred to the recording material 15 by the action of the transfer roller 13 to which the transfer bias is applied. Recording material 1 that has passed through the transfer unit
5 is separated from the photosensitive drum 1 and introduced into the fixing device 16, where the transfer toner image is fixed. The recording material 15 to which the image has been fixed and fixed is output to the paper discharge tray 17.

After the recording material is separated, the surface of the photosensitive drum 1 is cleaned by the cleaning device 5 to remove the residual toner such as toner remaining after transfer, and is repeatedly used for the next image formation.

Next, an image heating apparatus according to an embodiment of the present invention will be described in detail. FIG. 1 is a sectional view of a fixing device as an image heating device according to a first embodiment of the present invention.

The thin belt 21 is made of Ni in the form of an endless belt by electroforming and has a diameter of 30 mm and a thickness of 50 μm.
As shown in FIG. 2, the surface of the endless belt is coated with a release layer 22 having a thickness of 30 μm made of a fluororesin in order to impart releasability. As the material of the belt 21, any metal such as Fe, Co, Cu, and Cr may be formed alone or in combination. In this embodiment, since heat is generated by a heat-generating member described later, the belt 21 may be made of a film made of a heat-resistant resin such as polyimide resin or fluororesin other than metal. The release layer 22 on the surface is made of PTFE, PFA,
A resin or rubber having good releasability, such as FEP, silicon rubber, or fluoro rubber, may be coated alone or in combination. For fixing a monochrome image, it is sufficient to secure only the releasability, but when used for fixing a color image, it is desirable to impart elasticity, in which case it is necessary to form a somewhat thick rubber layer .

Reference numeral 23 denotes an exciting coil as an exciting member, which is wound around a core material 24 made of ferrite.
The core member 24 is fixedly supported by the image forming apparatus main body at the end in the depth direction of the paper. The core 24 may be made of a material having a high magnetic permeability such as iron or permalloy. FIG. 3 is a perspective view of the configuration of the core material 24 and the exciting coil 23. An alternating current of 30 kHz is applied to the exciting coil 23 from the exciting circuit 25, whereby a magnetic flux indicated by an arrow H is generated around the exciting coil 23. Repeat generation and extinction.

Returning to FIG. 1, the exciting coil 23 and the core 24
A heat-generating member 26 is provided at a position opposed to the belt 21 with a small gap therebetween. The heat-generating member 26 is biased by a spring so that the lower surface thereof is in contact with the inner surface of the belt 21, and is supported by the image forming apparatus main body.
The magnetic flux generated by the exciting coil is mainly
The shape of the core material 24 is configured and arranged so as to penetrate in a concentrated manner. In this embodiment, the core material 24 has an E-shaped cross section. In the present embodiment, a gap is provided between the exciting coil 23, the core member 24 and the heat generating member 26, but a heat insulating material may be filled in place of the gap.

The heat generating member 26 has a structure in which two metal plates are brought into close contact with each other, and FIG. 4 shows a cross section thereof. The side facing the exciting coil is a magnetic plate 27 as a first layer made of an alloy of iron, nickel and chromium having a thickness of 0.4 mm, and its Curie point is set to 200 degrees depending on the amount of chromium mixed into the material. It is manufactured to be adjusted to. The side of the heat generating member that contacts the belt is formed of a conductive plate 28 as a second layer made of aluminum having a thickness of 0.3 mm. The belt moves while sliding in contact with the surface of the conductive plate 27 of the heat generating member 26 during rotational movement described below. The heat generating member 26 has an arc shape as a whole, but has a flat portion 29 at the center thereof.

In the present embodiment, the above-described heat generating member has a self-temperature control characteristic. The operation will be described below.

Referring again to FIG. 1, when the temperature of the magnetic plate 27 is lower than the Curie point, most of the magnetic flux generated by the exciting coil 23 is due to the magnetism of the magnetic plate 27.
It penetrates the inside and repeats generation and extinction, whereby an induced current is mainly generated in the magnetic plate 27. The induced current generated in the heating member 26 by the high-frequency magnetic field flows almost only to the magnetic plate 27 on the surface due to the skin effect. FIG. 5 is a diagram illustrating this skin effect. FIGS. 5 (a) and 5 (b) show, by hatching, a portion where current mainly flows when the temperature of the heat generating member is lower than or equal to the Curie point. When the temperature is below the Curie temperature, most of the current flows through the portion 30 in the magnetic plate 27 as shown in (a), thereby generating Joule heat. When the heat generating member approaches the Curie temperature, the magnetic plate 27 loses its magnetism, so that the magnetic flux diverges toward the outer conductive plate 28, and the induced current is reduced as shown in FIG. At this point, the flow of the heat flows overwhelmingly. At this time, the electric resistance is low, so that the generation of heat is significantly reduced. According to the calculation, the depth of the portion where the current due to the skin effect flows is, for example, 0.3 mm or more when the frequency of the exciting current is 30 kHz.
A thickness of about 0.4 mm is desirable. If the thickness of the magnetic plate 27 is equal to or greater than the skin depth, almost all current is generated in the magnetic plate 27 at low temperatures. As the current frequency is increased, the skin depth becomes smaller, and a thinner magnetic plate can be used. However, if the frequency of the exciting current is too high, the cost increases and the noise emitted to the outside increases.

In this embodiment, the heating element is set at the above-mentioned setting, and about 18
Stable temperature control of 0 degrees was realized.

Since the heat-generating member itself has the self-temperature control characteristic in this manner, the heat-generating portion does not become abnormally high, and the Curie temperature is set to a temperature almost close to the fixing temperature. Temperature control can be performed automatically. This also solves the above-described problem of the partial temperature rise due to the width of the recording material, because a partial difference in the heat generation action occurs even with respect to the partial temperature difference in the depth direction in FIG. .

In this embodiment, the magnetic plate 27 and the conductive plate 28
However, by using a single-layer structure of a magnetic plate having a thickness of about 2 to 4 times the skin depth, current flows when the temperature is below the Curie temperature. Since the portion is thin, a large amount of heat is generated. When the Curie point is exceeded, a current flows through almost the entire thickness of the magnetic plate, thereby lowering the resistance.

Further, a one-layer structure of a magnetic plate having a skin depth is used, a highly conductive material is used for the belt, and when the temperature is below the Curie point, an electric current is applied to this portion to reduce heat generation. It is possible.

Further, one of the magnetic plates having a skin depth of about 1
Using a layered structure, high-conductivity material such as aluminum is used for the part of the pressure roller side opposite to this, which will be described later. When the temperature is below the Curie point, current can flow through this part to almost eliminate heat generation It is. As described above, if the thickness of the magnetic plate is equal to or greater than the skin depth corresponding to the frequency applied to the exciting coil, the effect of the self-temperature control is increased.

In this embodiment, aluminum is used as the conductive plate. However, other highly conductive metals such as copper can be used. Similar effects can be obtained with other alloys that can set the Curie temperature of the magnetic plate. Further, the surface of the conductive plate 28 which slides on the belt 21 has a thickness of several μm of a fluororesin or the like which does not greatly affect the thermal conductivity.
A very thin lubricant layer may be provided.

Reference numeral 32 denotes a pressing roller as pressing means, which has a low hardness (J) of 35 mm in diameter molded integrally with the metal shaft 33.
ISA 40 degrees) elastic silicone rubber,
As shown in FIG. 1, the image forming apparatus main body is formed such that the nip 34 is formed by being pressed against the heat generating member 26 via the belt 21 while deforming the surface along the flat portion 29 of the heat generating member, and rotating at that position. It is supported rotatably. The belt is rotated by friction by rotating the pressure roller in the direction of arrow A by a driving unit (not shown).

The material of the pressure roller 28 is other fluorine rubber,
It may be made of heat-resistant resin such as fluororesin or rubber. The surface of the pressure roller 28 may be coated with a resin or rubber such as PFA, PTFE, FEP, or the like, alone or as a mixture, in order to enhance abrasion resistance and releasability. In order to prevent heat from dissipating, it is desirable that the pressure roller be made of a material having low thermal conductivity.

The recording material 15 onto which the toner image has been transferred by the image forming apparatus shown in FIG.
As shown in FIG. 1, the toner 35 was rushed in the direction of the arrow with the surface with the toner 35 facing upward, and the toner on the recording material 15 was fixed.

According to the above-described embodiment, since the heat-generating member itself has the self-temperature control characteristic, the heat-generating portion does not become abnormally high, and the temperature control at a temperature almost close to the fixing temperature is automatically performed. You can do it. This also acts on a partial temperature difference in the depth direction in FIG. 1, and a partial difference in the heat generation action occurs. The portion that does not pass through is not abnormally high in temperature, and there is no hot offset afterwards through a wide recording material.

Further, since the material and thickness of the heating element can be set independently of the belt, an optimum material, thickness and shape can be selected for self-temperature control, and the heat capacity of the belt can be selected accordingly. Can be set separately.

Next, as an image heating apparatus of the second embodiment, a fixing apparatus particularly suitable for fixing a color image will be described with reference to FIG.

In the second embodiment, a detailed description of portions having the same configuration and the same function as those of the fixing device of the first embodiment will be omitted.

In this embodiment, the material of the belt 41 is the same as the material and material except that the diameter is set to 60 mm.
The thickness and the like are the same as in the first embodiment. The surface 42 was coated with 100 μm silicone rubber for fixing a color image. Also in this embodiment, since heat is generated by a heat generating member described later, the belt 21 may be formed of a film made of a heat-resistant resin such as a polyimide resin or a fluorine resin other than metal. The belt 41 has a diameter of 20 as a low heat conductive roller whose surface is made of a resilient foamed silicone rubber having a low hardness (JISA 30 degrees).
roller 43 having a diameter of 30 mm, and a first roller 43 having a diameter of 30 mm.
4 is suspended with a predetermined tension, and is rotatable in the direction of arrow B. First roller 43, second roller 44
Are formed by integrally molding rubbers on metal shafts 45 and 46, respectively. The metal shaft 45 is driven by a driving means of an apparatus main body (not shown) so as to rotate the belt. The pressure roller 47 is made of silicone rubber having a hardness of JISA 60 degrees, and is pressed against the first roller 43 via the belt 41 as shown in FIG.
It is made rotatable by following around.

A heat generating member 49 is provided between the first roller 43 and the second roller 44 so as to lightly contact the back surface of the belt 41.
Is biased and supported by the image forming apparatus main body toward the lower side in FIG. As in the first embodiment, the heat generating member 49 is composed of two layers, a magnetic plate 50 as an inner first layer and a conductive plate 51 as a second layer on the belt side.
The setting is the same as that of the embodiment. In addition, the front end portion 49a of the conductive plate 51 in the belt moving direction extends to a nip 52 formed between the belt 41 and the pressure roller 47 so as to lightly push a part of the nip 52 from the back of the belt. . In this embodiment, the Curie point of the magnetic plate 50 was set to 210 degrees, and a self-temperature control characteristic stabilized at about 190 degrees was obtained.

A small gap is provided on the opposite side of the belt 41 from the heat generating member 49, and an exciting coil 53 as a heat generating means and a core material 54 made of ferrite are fixed to the image forming apparatus main body. It has been installed.

In the fixing device constructed as described above, a sharp melt color toner 55 made of polyester is used.
The recording material 56 on which the color image formed by the above is placed is pushed in from the direction of the arrow in FIG. 6, and the color toner on the recording material 56 is fixed.

In this embodiment, the heat-generating portion extends to the vicinity of the nip, so that necessary heat can be obtained at the nip portion. On the other hand, the exciting coil and the core material can be installed upstream of the nip portion. There is no danger of being affected, and it is difficult to raise the temperature, and the calorific value can be kept stable.

Further, in this embodiment, since the nip 52 requiring a high pressure is formed by pressing between the first roller 43 and the pressing roller 47, the nip 52 slides while receiving a strong frictional force. It is suitable for high-speed and long-time operation because there is no part to do. The pressure contact between the belt 41 and the heat generating member 49 has nothing to do with the nip formation for fixing the toner.
Since it is only necessary to conduct heat, a light pressing force is sufficient.

Also, in this embodiment, since the heat capacity of the belt is small, when the belt starts to contact the recording material, the recording material begins to lose heat, and the leading end portion 49a of the heat generating member 49 starts.
, The temperature rapidly decreases, and the toner does not hot offset when leaving the nip. Therefore, hot offset does not occur even if the temperature at the time of entering the nip is set to be considerably high. In this embodiment, the temperature in the first half of the nip can be finely controlled since the tip of the heat generating member 49 extends to the vicinity of the nip. Therefore, even a sharp melt color toner can be fixed without hot offset while being sufficiently melted once. Even if the heat capacity of the belt is small, the self-temperature control characteristic similar to that of the first embodiment can be obtained by the configuration of the heat generating member, and an excellent fixing device for fixing a color image without excessive temperature rise or hot offset can be obtained. can get.

On the other hand, since the elastic roller 23 inside the belt 21 has a low thermal conductivity and is made of a foam, the heat generated in the belt 21 is hardly dissipated due to the presence of the internal voids. Has become.

Next, a fixing device as an image heating device according to a third embodiment will be described with reference to FIG. In the third embodiment, a detailed description of portions having the same configuration and the same role as those of the fixing device of the first embodiment will be omitted.

In this embodiment, the belt 61 is set to have a diameter of 30 mm using a polyimide film as a base material. The surface layer 62 covered a 100 μm silicon rubber layer. The belt 61 is integrally formed on a metal shaft 64 and is wound around an upper roller 63 as a rotatable low heat conductive roller having a diameter of 25 mm and made of low-hardness (JIS 30 degrees) elastic silicone rubber. I have. The pressure roller 65 has a higher hardness than the upper roller 63 (JISA).
(60 degrees) It is made of silicone rubber and is integrally molded with the metal shaft 66. The pressure roller 65 is pressed against the upper roller 63 via the belt 61, and the upper roller 63 is deformed as shown in FIG. In this state, the pressing roller 65 was rotated in the direction of arrow C by driving means (not shown). As a result, the belt 61 and the upper roller 63 rotate in the direction indicated by the arrow in FIG. A heat generating member 68 is supported by the image forming apparatus in the belt 61 on the upstream side of the nip 67 by being spring-biased leftward in FIG. 8 so as to slightly apply tension to the belt 61.
The configuration of the heat generating member 68 is different from that of the first embodiment, and the magnetic plate 69 as the outer first layer that slides in contact with the belt.
And a conductive plate 70 as an inner second layer. The respective materials and thicknesses are the same as in the first embodiment. Belt 61
The excitation coil 71 and the core material 72 are provided at a position opposed to this with a small gap therebetween.

The recording material 74 on which the toner image has been placed on the fixing device constructed as described above is transferred to the toner 7 as shown in FIG.
The recording material 74 was fixed by pressing the recording material 74 in the direction indicated by the arrow, with the surface 3 facing upward.

In this embodiment, the nip 6 requiring a strong pressure is used.
7 is formed by pressing between the upper roller 63 and the pressure roller 65, so that there is no part that slides while receiving a strong frictional force for forming the nip, so that it can be operated at high speed for a long time. Suitable. The pressure contact between the belt 61 and the heat generating member 68 is irrelevant to the nip formation, and it suffices to apply a light tension to the belt 61 and perform heat conduction.

In the present embodiment, the heat generating portion is located inside the belt, while the exciting coil and the core member can be installed outside the belt. The calorific value can be kept stable.

Also in this embodiment, as in the first embodiment,
The self-temperature control characteristic similar to that of the first embodiment can be obtained by the configuration of the heat generating member, and an excellent fixing device free from excessive temperature rise and hot offset of the belt can be obtained. In this embodiment, the magnetic plate 69 and the conductive plate 70 are configured to be in close contact with each other. However, even if a gap is provided between the magnetic plate 69 and the conductive plate 70, the self-temperature control characteristic can be similarly obtained. In this case, the heat capacity as the heat generating member can be further reduced.

Further, in the nip portion 67, the belt 61
Is deformed along the outer peripheral surface of the pressure roller 65, and when the recording material comes out through the nip portion, the recording material is pushed out in a direction away from the belt 61, so that the peeling property is increased. Is very good.

Further, the upper roller 6 inside the belt 61
Since the material 3 itself has a low thermal conductivity and is made of a foam, the presence of internal voids makes it extremely difficult for the heat of the belt 61 to escape, resulting in high efficiency.

In the above embodiment, the self-temperature control of the heat generating member is set to the fixing temperature. However, as another configuration, the control of the fixing temperature is performed by a control using a normal thermistor or the like. It can also be used at higher settings to prevent abnormal temperature rise to ensure safety against damage due to high temperature of the device.

In the first to third embodiments, the heating member is in contact with the inner surface of the belt.
It may be arranged in the vicinity of the inner surface of the belt at a distance.

In the first to third embodiments, the exciting coil is used as the exciting member. However, the present invention is not limited to this, and any structure that generates a magnetic field may be used.

[0059]

As described above, according to the present invention, the belt to be heated has a very small heat capacity, so that it can be quickly warmed, and the warm-up time until the fixing temperature is reached can be extremely reduced.

Further, according to the present invention, even when the heat capacity of the belt is set to be small, the self-temperature control is effectively performed, so that the temperature of the heat generating portion can be prevented from rising. Therefore, even when a narrow recording material is continuously passed,
Excessive temperature rise in a portion through which the recording material does not pass is prevented, and as a result, the exciting member is not likely to be damaged by heat. In addition,
By preventing the excessive temperature rise, the occurrence of hot offset is prevented, and there is no possibility that the calorific value becomes unstable.

According to another aspect of the present invention, the heat generation amount required at the nip portion is obtained by extending to the vicinity of the nip between the belt and the pressurizing portion, while the exciting member can be installed upstream of the nip portion. This eliminates the risk of being affected by the temperature of the magnet, and prevents the excitation member from being damaged. Further, since there is no possibility that the exciting member is affected by the temperature of the nip portion, the temperature does not easily rise, and the calorific value can be stably maintained.

In still another invention, since the exciting member can be installed outside the belt, there is no possibility that the exciting member is affected by the temperature of the nip portion, and damage to the exciting member is prevented. In addition, since there is no possibility that the exciting member is affected by the temperature of the nip portion, a stable heat generation amount can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view of an image heating apparatus according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view of a belt used in the image heating apparatus according to the first embodiment of the present invention.

FIG. 3 is a perspective view of an excitation coil and a core material used in the image heating apparatus according to the first embodiment of the present invention.

FIG. 4 is a sectional view of a heating member used in the image heating apparatus according to the first embodiment of the present invention.

FIG. 5 is an explanatory diagram for explaining self-temperature control characteristics of a heating member used in the image heating apparatus according to the first embodiment of the present invention.

FIG. 6 is a sectional view of an image forming apparatus according to an embodiment of the present invention.

FIG. 7 is a sectional view of an image heating apparatus according to a second embodiment of the present invention.

FIG. 8 is a sectional view of an image heating apparatus according to a third embodiment of the present invention.

FIG. 9 is a sectional view of a conventional image heating apparatus.

[Explanation of symbols]

 Reference Signs List 1 photosensitive drum 16 fixing device 21, 41, 61 belt 23, 53, 71 excitation coil 24, 54, 72 core material 26, 49, 68 heating member 32, 47, 65 pressure roller 15, 56, 74 recording material

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Nobuo Motoji 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd.

Claims (10)

[Claims] 1. A movable belt, and pressing means for pressing the belt to form a nip on the surface side of the belt,
An image heating apparatus comprising at least a part made of a magnetic material having a predetermined Curie temperature and having a heating member close to a back surface of a belt, and an exciting member for exciting the heating member. 2. The image heating apparatus according to claim 1, wherein the thickness of the magnetic body is equal to or greater than the skin depth when excited. 3. The heat generating member has a first layer of the magnetic material and a second layer of a conductive layer having higher conductivity than the magnetic material.
Or the image heating device according to 2. 4. A movable belt, and pressurizing means for pressing the belt to form a nip on the surface side of the belt;
A heating member that is close to the belt back surface from the upstream side of the nip portion to the vicinity of the nip portion with respect to the belt moving direction;
An image heating apparatus, comprising: an excitation member that generates an induced current in the heat-generating member to generate heat, on the upstream side of the pressure contact portion with respect to a belt moving direction. 5. A movable belt, and pressurizing means for pressing the belt to form a nip on the front side of the belt;
A heating member that is close to a part of the belt on the back side of the belt, and an exciting member that is disposed at a position facing the belt and on the front surface side of the belt and generates an induced current to the heating member to generate heat. An image heating device comprising: 6. The heat generating member according to claim 4, wherein at least a part of the heat generating member is made of a magnetic material having a predetermined Curie temperature, and a thickness of the magnetic material is equal to or greater than a skin depth when excited. 6. The image heating device according to 5. 7. The heating member according to claim 4, wherein the heat generating member has a first layer having magnetism and a second layer having high conductivity, and the magnetic material of the first layer has a predetermined Curie temperature. The image heating device according to any one of the above. 8. An image heating apparatus according to claim 1, wherein the pressing means comprises a low heat conductive roller on the back side of the belt and a pressing roller on the front side of the belt. 9. The image heating apparatus according to claim 1, wherein the belt is formed in a thin endless shape. 10. An image forming apparatus comprising: an image forming means for forming and carrying an unfixed image on a recording material; and a heat fixing device for thermally fixing the unfixed image to the recording material. An image forming apparatus, which is the image heating apparatus according to any one of 1 to 9.