JP2001267050A - Heating device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To severely prevent firing or smoking from the heating device surely detecting abnormal rise in temperature of the heating member 10 and blocking power supply to it, even when temperature of a heat-emitting layer of the heating member 10 exceeds the Curie temperature of a conductive magnetic material constituting the heat-emitting layer, with a heating device of electromagnetic induction heating system and an image forming device using the heating device. SOLUTION: A temperature-detecting element 50 for detecting temperature of a heating member 10 to block power supply to excitation coil 18 is arranged at a place opposite to the excitation coil 18 across the heating member 10, and further, a leaking flux induction member 60 composed of a magnetic member inducing leak flux from the heat-emitting layer 10a which is generated when the temperature of the heat-emitting layer 10a of the heating member 10 exceeds the Curie temperature of the magnetic member of the heat-emitting layer 10a is arranged at or around the place where the temperature detecting element 50 is set.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an electromagnetic (magnetic) induction heating type heating apparatus and an image forming apparatus provided with the heating apparatus.

[0002]

2. Description of the Related Art In an image forming apparatus such as a copying machine, a printer or a facsimile, a toner (developing agent) made of a heat-meltable resin or the like is formed by an appropriate image forming process means such as electrophotography, electrostatic recording and magnetic recording. As a heating device (image heating device) for heating and fixing an unfixed toner image formed directly or indirectly on the surface of the recording material as a permanent fixed image on the surface of the recording material using Fixing devices are widely used.

In recent years, from the viewpoint of quick start and energy saving, a fixing device of a film heating system (Japanese Patent Application Laid-Open No. 63-313182, Japanese Patent Application Laid-Open No. 2-157878, Japanese Patent Application Laid-Open No. 4-44075, Japanese Patent Application Laid-Open No. −204
No. 980) has been put to practical use, but an electromagnetic induction heating type fixing device that generates heat from a metal film itself has been proposed as a more efficient device.

Japanese Utility Model Laid-Open Publication No. 51-109739 discloses an induction heating fixing device in which an eddy current is induced in a metal layer of a fixing film (heating roller) by an alternating magnetic field, and the metal layer is heated by Joule heat. ing. This is because the fixing film can be directly heated by utilizing the generation of eddy current, and the input power is more effectively used than the heat roller type fixing device using a halogen lamp as a heat source, thereby achieving low power consumption. The warm-up time can be reduced.

FIG. 16 shows a schematic configuration of an example of an electromagnetic induction heating type fixing device.

Reference numeral 10 denotes an electromagnetic induction heating layer (conductive magnetic member).
Is a cylindrical fixing film as a heating rotator having

Reference numeral 16 denotes a gutter-shaped film guide having a substantially semicircular cross section, and is made of a heat-resistant synthetic resin or the like.
The above-mentioned cylindrical fixing film 10 is a film guide 1
6 is loosely fitted outside.

Reference numeral 15 denotes a magnetic field generating means disposed inside the film guide 16, which comprises an exciting coil 18, an E-shaped magnetic core 17, and an exciting circuit (not shown).

Reference numeral 30 denotes a pressure roller. The fixing film 1 is fixed by the pressure roller 30 and the film guide 16.
By applying a predetermined pressing force from the pressure roller 30 to the film guide 16 with the pressure roller 30 interposed therebetween, the film guide 16 and the pressure roller 30 are formed into a fixing nip portion N having a predetermined width, and are pressed against each other. I have.

The magnetic core 17 of the magnetic field generating means 15 is disposed corresponding to the position where the fixing nip N is formed.

The pressure roller 30 is driven by a driving means M to an arrow a.
Is driven to rotate counterclockwise. Due to the rotational driving of the pressure roller 30, a frictional force is generated between the pressure roller 30 and the outer surface of the fixing film 10 in the fixing nip N, and the rotational force acts on the fixing film 10. The fixing film 10 slides in the fixing nip portion N in close contact with the lower surface of the film guide 16 and has a peripheral speed substantially corresponding to the peripheral speed of the pressure roller 30 in the clockwise direction of the arrow b. The outer periphery of the guide 16 is rotated (a pressure roller driving method).

The film guide 16 pressurizes the fixing nip N, supports the exciting coil 18 and the magnetic core 17 as the magnetic field generating means 15, supports the fixing film 10, and conveys the stability of the fixing film 10 during rotation. Plays a role. The film guide 16 is an insulating member that does not hinder the passage of magnetic flux, and is made of a material that can withstand a high load.

The exciting coil 18 generates an alternating magnetic flux by an alternating current supplied from an exciting circuit (not shown). Since the E-shaped magnetic core 17 is provided corresponding to the position of the fixing nip N, the alternating magnetic flux is intensively distributed in the fixing nip N, and the alternating magnetic flux is distributed in the fixing nip N by the fixing film. An eddy current is generated in the ten electromagnetic induction heating layers. This eddy current generates Joule heat in the heat generating layer due to the specific resistance of the heat generating layer.

The temperature of the fixing nip N is determined by a temperature sensor 26.
By controlling the current supply to the exciting coil 18 by a temperature control system (not shown) including the above, the amount of magnetic flux is controlled, and the temperature is adjusted so as to maintain a predetermined temperature.

As described above, the pressure roller 30 is driven to rotate, and accordingly, the cylindrical fixing film 10 rotates around the outer periphery of the film guide 16, and the fixing film 10 is supplied by the power supply from the excitation circuit to the excitation coil 18. The electromagnetic induction heating causes the fixing nip N to rise to a predetermined temperature. Then, in a state where the temperature is adjusted, the recording material P on which the unfixed toner image t is formed, which is transported from the image forming unit (not shown), has an image surface facing upward, that is, facing the fixing film 10 surface. It is introduced between the fixing film 10 and the pressure roller 30 in the fixing nip portion N.

At the fixing nip N, the image surface of the recording material P comes into close contact with the outer surface of the fixing film 10, and the fixing nip N
With the fixing film 10. In the process in which the recording material P is nipped and conveyed together with the fixing film 10, the fixing film 10 is heated in the fixing nip N, and the unfixed toner image t on the recording material P is heated and fixed, so that the permanently fixed image is formed. t 'is formed.

After passing through the fixing nip N, the recording material P is transported away from the outer peripheral surface of the fixing film 10.

In the fixing device having the above-described configuration, the alternating magnetic flux distribution from the exciting coil 18 as the magnetic field generating means 15 is concentrated in the fixing nip portion N. When the distribution of the alternating magnetic flux generated by the exciting coil 18 spreads over the entire fixing film 10, the energy of the alternating magnetic flux is used to raise the temperature of the entire fixing film 10, so that the heat loss is large. Therefore, there is a disadvantage that the ratio of the energy acting on the fixing to the input energy is low, and the efficiency is low. Therefore, in order to obtain energy that acts on the fixing process with high efficiency, the fixing device shown in FIG.
, And the distribution of the alternating magnetic flux of the exciting coil 18 is concentrated near the fixing nip portion N, thereby improving the efficiency.

[0019]

SUMMARY OF THE INVENTION Japanese Patent Application Laid-Open No. 7-31931
In the fixing device of the electromagnetic induction heating type disclosed in Japanese Patent Application Publication No. 2 (1993) -197, a temperature detecting element such as a thermostat is provided as a heat-sensitive safety device at a heat-facing portion of an electromagnetic induction heating member (heating member) to raise the temperature above a predetermined temperature. At the time of temperature detection, a method of preventing thermal runaway of the apparatus by shutting off power supply to an exciting coil has been adopted.

When the electromagnetic induction heating member is a magnetic member,
When the temperature of the electromagnetic induction heating member exceeds the Curie temperature of the electromagnetic induction heating member, the magnetic permeability of the magnetic member rapidly decreases. For this reason, magnetic flux leaks from the electromagnetic induction heating member,
This leakage magnetic flux is guided to the magnetic member around the heating member.
Then, in the portion of the heat generating member facing the magnetic member, the leakage magnetic flux is concentrated, so that high heat is locally generated due to the generation of eddy current.

If the local high heat is generated in a portion other than the heat-sensitive safety device facing portion of the electromagnetic induction heating member, the fixing device itself may be damaged before the heat-sensitive safety device operates, and furthermore, the electromagnetic induction heating member may be damaged. May cause ignition or smoking.

Accordingly, the present invention provides a method for controlling the temperature of a heating member of a heating member exceeding a Curie temperature of a conductive magnetic member constituting a heating layer due to a thermal runaway caused by a failure of a temperature control system of a heating device. Also provided a heating device that reliably detects abnormal heating of the heating member and shuts off power supply to the heating device, and an image forming apparatus equipped with the heating device, thereby strictly preventing ignition and smoke from the heating device. The purpose is to do.

[0023]

According to the present invention, there is provided a heating apparatus and an image forming apparatus having the following constitutions.

(1) A magnetic field generating means having an exciting coil, a heating member having a heating layer composed of a conductive magnetic member, and detecting the temperature of the heating member to shut off power supply to the exciting coil. And an electromagnetic induction heating method of heating a material to be heated by heat generated by the heat generating layer due to eddy current generated by applying an alternating magnetic field from the magnetic field generating means to the heat generating layer of the heating member. In the heating device, the temperature detection element is disposed at a position facing the excitation coil with the heating member interposed therebetween, and further when the temperature of the heating layer of the heating member exceeds the Curie temperature of the magnetic member of the heating layer. A heating device, wherein a leakage magnetic flux guiding member composed of a magnetic member for guiding the generated leakage magnetic flux from the heat generating layer is disposed at or near the position where the temperature detecting element is disposed.

(2) The distance from the leakage magnetic flux induction member to the excitation coil is the shortest among the magnetic members disposed at a position facing the excitation coil with the heating member interposed therebetween. The heating device according to (1).

(3) The magnetic permeability of the leakage magnetic flux guiding member is
The heating device according to (1) or (2), which is the largest of the magnetic members disposed at a position facing the excitation coil with the heating member interposed therebetween.

(4) The leakage magnetic flux guiding member and the temperature detecting element are arranged in a region of the heating member not in contact with the material to be heated, wherein any one of (1) to (3) is provided.
The heating device according to any one of the above.

(5) The leakage magnetic flux guiding member is a magnetic member having conductivity. (1) to (4)
The heating device according to any one of the above.

(6) The heating device according to (5), wherein the leakage magnetic flux guiding member is made of a ferromagnetic metal.

(7) The method according to any one of (1) to (6), wherein the heat-sensitive portion of the temperature detecting element is in direct or indirect contact with the leakage magnetic flux guiding member. Heating equipment.

(8) The heating device according to any one of (1) to (7), wherein the heat-sensitive portion of the temperature detecting element is in direct or indirect contact with the heating member. .

(9) The Curie temperature of the magnetic member constituting the leakage magnetic flux guiding member is higher than the Curie temperature of the magnetic member of the heating layer of the heating member.
The heating device according to any one of (1) to (8).

(10) The heating device according to any one of (1) to (9), wherein the temperature detecting element is a thermoswitch.

(11) The heating device according to any one of (1) to (10), wherein the heating member is a fixed member, a rotating body, or a moving end member.

(12) The heating device according to any one of (1) to (11), further including a pressing member for directly or indirectly bringing the material to be heated into close contact with the heating member.

(13) The heating device according to (12), wherein the pressure member is a pressure rotating body which is driven to rotate or driven to rotate.

(14) The material to be heated is a recording material carrying an image to be subjected to a heat treatment, and is an image heating device for heating the image on the recording material.
The heating device according to any one of (1) to (13).

(15) In an image forming apparatus having an image forming means for forming an unfixed toner image on a recording material and a heat fixing means for pressure fixing the unfixed toner image to the recording material, An image forming apparatus, wherein the means is the heating device according to any one of (1) to (14).

<Operation> If the temperature control system does not operate normally due to a device failure or the like and excessive power supply to the excitation coil of the magnetic field generating means continues, the temperature of the heating member rises. . At this time, if the temperature of the heating layer of the heating member exceeds the Curie temperature of the magnetic member used for the heating layer,
The magnetic permeability of the heat generating layer rapidly decreases, and the magnetic flux forming the magnetic path in the heat generating layer leaks. Most of this leakage flux
Since the magnetic flux is guided by the leakage magnetic flux guiding member, the magnetic flux in the heating layer of the heating member portion at the position facing the leakage magnetic flux guiding member becomes relatively larger than that of the other portions, and the temperature of the heating member is locally higher in that portion. Become. Therefore, it is possible to quickly operate the temperature detecting element, which is a heat-sensitive safety device provided at or near the same position as the leaked magnetic induction member.

As a result, the apparatus causes a thermal runaway due to the failure of the temperature control system, and the temperature of the heating layer of the heating member becomes abnormally high, exceeding the Curie temperature of the conductive magnetic member constituting the heating layer. Even so, it is possible to reliably operate the temperature detecting element, which is a heat-sensitive safety device, to cut off the power supply to the device, so that ignition and smoking from the device can be strictly prevented.

[0041]

Embodiments of the present invention will be described below.

<First Embodiment> (FIGS. 1 to 13) A first embodiment of the present invention will be described.

(1) Example of Image Forming Apparatus FIG. 1 is a schematic structural model diagram of an example of an image forming apparatus. The image forming apparatus of the present embodiment is a color laser printer using an electrophotographic process.

Reference numeral 101 denotes a photosensitive drum (image carrier) made of an organic photosensitive member or an amorphous silicon photosensitive member, and is rotated at a predetermined process speed (peripheral speed) in a counterclockwise direction indicated by an arrow A.

The photosensitive drum 101 is charged by a charging device 102 such as a charging roller at a predetermined polarity to a uniform potential during the rotation process.

Next, a laser beam 103 output from a laser optical box (laser scanner) 110 is placed on the charged surface.
As a result, scanning exposure processing of the target image information is performed. The laser optical box 110 outputs a laser beam 103 modulated (on / off) in accordance with a time-series electric digital pixel signal of image information from an image signal generator such as an image reader (not shown). An electrostatic latent image corresponding to image information is formed on the charging processing surface of the photosensitive drum 101 by this scanning exposure. Reference numeral 109 denotes a mirror that deflects the output laser light from the laser optical box 110 to the exposure position of the photosensitive drum 101. The electrostatic latent image thus formed on the photosensitive drum 101 is developed by the four color developing units 104.

In the case of forming a full-color image, scanning exposure and latent image formation are performed on a first color-separated component image of a target full-color image, for example, a yellow component image. When the yellow developing unit 104Y is operated, the toner is developed as a yellow toner image. The yellow toner image is transferred to the intermediate transfer drum 10 at a primary transfer portion T1, which is a contact portion (or a close portion) between the photosensitive drum 101 and the intermediate transfer drum 105.
5 is transferred to the surface. After the transfer of the yellow toner image to the surface of the intermediate transfer drum 105, the surface of the photosensitive drum 101 is cleaned by a cleaner 107 by removing the adhered residue such as untransferred toner.

The above-described process cycle of charging, scanning exposure, development, primary transfer, and cleaning is performed by a second color separation component image (eg, a magenta component image,
The magenta developing device 104M is activated), the third color-separated component image (for example, the cyan component image, the cyan developing device 104C is activated), and the fourth color-separated component image (for example, the black component image, the black developing device 104BK is activated). Each color separation component image is sequentially executed, and four color toner images of a yellow toner image, a magenta toner image, a cyan toner image, and a black toner image are sequentially transferred onto the surface of the intermediate transfer drum 105 so as to be transferred to a target full-color image. A corresponding color toner image is formed.

The intermediate transfer drum 105 is provided with a medium resistance elastic layer and a high resistance surface layer on a metal drum. The intermediate transfer drum 105 is driven to rotate in the clockwise direction indicated by the arrow B at substantially the same peripheral speed as the photosensitive drum 101 in contact with or close to the photosensitive drum 101. When a bias potential is applied to the metal drum of the intermediate transfer drum 105, a potential difference is generated between the intermediate transfer drum 105 and the photosensitive drum 101, and the toner image on the photosensitive drum 101 is transferred to the intermediate transfer drum 105 by the potential difference. 10
5 is transferred to the surface.

The color toner image formed on the surface of the intermediate transfer drum 105 as described above is
In a secondary transfer portion T2, which is a contact nip portion between the transfer roller 05 and the transfer roller 106, the toner image is transferred onto the surface of the recording material P sent to the secondary transfer portion T2 from a paper supply unit (not shown) at a predetermined timing. Go. The transfer roller 106 supplies a charge having a polarity opposite to that of the toner from the rear surface of the recording material P, thereby sequentially and collectively transferring the composite color toner images from the surface of the intermediate transfer drum 105 to the recording material P.

The recording material P that has passed through the secondary transfer portion T2 is separated from the surface of the intermediate transfer drum 105, introduced into a heating device (image heating device, fixing device) 100, and subjected to a heat fixing process for an unfixed toner image. Is discharged to a discharge tray (not shown) outside the apparatus.

The fixing device 100 will be described later in detail.

After the transfer of the color toner image to the recording material P, the intermediate transfer drum 105 is cleaned by a cleaner 108 to remove the transfer residual toner, paper dust, and other attached residues. The cleaner 108 is normally held in a non-contact state with the intermediate transfer drum 105, and is kept in contact with the intermediate transfer drum 105 during the secondary transfer of the color toner image from the intermediate transfer drum 105 to the recording material P. Is held.

Also, the transfer roller 106 is normally held in a non-contact state with the intermediate transfer drum 105, and during the secondary transfer of the color toner image from the intermediate transfer drum 105 to the recording material P, the intermediate transfer is performed. The recording medium P is held in contact with the drum 105 via the recording material P.

The image forming apparatus of the present embodiment can also execute a print mode of a mono-color image such as a monochrome image. Also, a double-sided image print mode can be executed. In the case of using the double-sided image print mode, the recording material P on which the first image has been printed discharged from the fixing device 100 is turned upside down via a recirculation transport mechanism (not shown), and is again returned to the secondary transfer unit T2.
And the toner image is transferred to the second surface, and is again introduced into the fixing device 100 to undergo a fixing process of the toner image on the second surface. In this way, double-sided image printing is performed.

In the present invention, in the image forming apparatus shown in FIG. 15, the structure excluding the fixing device 100 is used as the image forming means.

(2) Fixing Device (Heating Device) 100 Next, the fixing device 100 as a heating device used in the above-described image forming apparatus will be described. The fixing device 100 in this embodiment is an electromagnetic induction heating type device. 2 to 4 are views showing the configuration of the main part of the fixing device 100 of the present embodiment, FIG. 2 is a schematic cross-sectional view, FIG.
FIG. 4 is a longitudinal cross-sectional model along the line (4)-(4) in FIG. 2, and FIG. 5 is a perspective model diagram showing a cross section along the line (5)-(5) in FIG. (Illustration). In each of the drawings, constituent members common to the fixing device shown in FIG.
Parts are given the same reference numerals.

The fixing device 100 of this embodiment is the same as that of FIG.
6 is an electromagnetic induction heating type device using a cylindrical fixing film 10 like the fixing device of No. 6.

In FIG. 2, a film guide 16 is formed by joining two right and left trough-shaped trough-shaped members 16a and 16b with their opening portions facing each other to form a substantially cylindrical body as a whole. A cylindrical fixing film 10 is loosely fitted on the outer peripheral surface side of the cylindrical film guide 16.

The magnetic field generating means 15 includes the magnetic cores 17a and 17
b · 17c, the exciting coil 18 and the exciting circuit 27 (FIG. 5).

The magnetic cores 17a, 17b and 17c are arranged in a T-shape inside the right half 16a of the film guide 16. The exciting coil 18 includes the magnetic cores 17a and 17
c and the space surrounded by the film guide 16a and the magnetic cores 17a and 17b and the film guide 16a.
are held in a space surrounded by a.

The magnetic cores 17a, 17b, and 17c are members having high magnetic permeability, and are preferably made of a material such as ferrite or permalloy used for a transformer core.
Ferrite with less loss of magnetism even at z or more is more preferably used.

The exciting coil 18 has power supply portions 18a and 18b as shown in FIG.
Connected to the excitation circuit 27 by 18b; The excitation circuit 27 generates a high frequency of 20 kHz to 500 kHz by a switching power supply. The exciting coil 18 generates an alternating magnetic flux by an alternating current (high-frequency current) supplied from the exciting circuit 27.

A pressure roller 30 as a pressure member is pressed against a slide member 40 provided on the film guide 16 by a predetermined pressing force. As a result, the fixing film 10 is sandwiched between the pressure roller 30 and the sliding member 40, and a fixing nip portion N having a predetermined width is formed at a pressure contact portion between the fixing film 10 and the pressure roller 30.

The film guide 16 presses the fixing nip N, supports the exciting coil 18 as the magnetic field generating means 15 and the magnetic cores 17a, 17b, and 17c.
0 and the stability of conveyance of the fixing film 10 during rotation. The film guide 16 is made of a material that has an insulating property that does not hinder the passage of magnetic flux and that can withstand a high load. Examples of such a material include a polyimide resin, a polyamide resin, a polyamideimide resin, a polyether ketone resin, a polyether sulfone resin, a polyphenylene sulfide resin, and a liquid crystal polymer.

The right half 16a of the film guide 16 has a sliding member 4 having a longitudinal direction perpendicular to the paper surface as shown in FIG.
0 is the side of the fixing nip N facing the pressure roller 30;
It is provided inside the fixing film 10. That is,
The sliding member 40 is arranged at a position facing the pressure roller 30 via the fixing film 10 in the fixing nip portion N. The sliding member 40 is a member that supports the fixing film 10 from the inner peripheral surface thereof in the fixing nip N with respect to the pressing force of the pressure roller 30. As the sliding member 40, in order to reduce sliding resistance,
A member having lubricity is preferred. Such members include fluororesin, glass, boron nitride, graphite, and the like. The sliding member 40 is more preferably a member having high thermal conductivity in addition to lubricity. Such a sliding member 40 has an effect of making the temperature distribution in the longitudinal direction of the fixing nip N uniform. For example, when small-sized paper is passed, the amount of heat in the non-paper passing portion of the fixing film 10 is transferred to the sliding member 40, which is a good heat conducting member, and the heat conduction in the longitudinal direction of the member 40 causes The amount of heat in the paper passing section is transferred to the small-size paper passing section. As a result, an effect of reducing power consumption when passing small-sized paper is also obtained. Examples of such a sliding member 40 include a composite material such as a metal such as aluminum which has been mirror-polished, and a metal in which a lubricant such as fluororesin particles, boron nitride particles or graphite particles is dispersed. Further, a member having a two-layer structure in which a lubricating member is coated on a high heat conductive member, for example, a member in which glass is coated on aluminum nitride may be used. In this embodiment, a member coated with glass on an alumina substrate was used.

When the sliding member 40 has conductivity, the exciting coil 18 and the magnetic cores 17a
In order not to be affected by the magnetic field generated from b.17c,
Preferably, it is located outside this magnetic field. Specifically, the sliding member 40 is moved relative to the exciting coil 18 by the magnetic core 17b.
17c is disposed at a position separated from the magnetic path by the excitation coil 18.

In order to further reduce the sliding friction force between the sliding member 40 and the fixing film 10 in the fixing nip N, a heat-resistant grease or the like is provided between the sliding member 40 and the fixing film 10 in the fixing nip N. A lubricant may be interposed. By applying the lubricant, the sliding resistance can be further reduced and the life of the device can be prolonged.

On the inner flat surface of the film guide 16b,
A horizontally long pressing rigid stay 22 having a U-shaped cross section is abutted. An insulating member 19 is provided between the pressurizing rigid stay 22 and each of the magnetic cores 17a, 17b, 17c to insulate them.

As a material of the insulating member 19, a material having excellent insulating properties and good heat resistance is preferable. For example, phenolic resin, fluorine resin, polyimide resin, polyamide resin,
Polyamide imide resin, polyether ketone resin, polyether sulfone resin, polyphenylene sulfide resin, PFA resin, PTFE resin, FEP resin, LCP
It is better to select a resin or the like.

The right and left ends of the assembly of the film guides 16a and 16b are respectively provided with flange members 23a.
23b (FIGS. 3 and 4) is rotatably mounted while the left and right positions are fixed by external fitting. This flange member 23
The reference numerals a and 23b receive the end of the fixing film 10 when the fixing film 10 rotates, and regulate the shift of the fixing film 10 along the longitudinal direction of the film guide 16.

The pressure roller 30 as a pressure member is made of a heat-resistant elastic material layer such as silicone rubber, fluorine rubber, or fluororesin, which is formed by concentrically forming a roller around the core metal 30a. 30b. The pressure roller 30 is disposed by holding both ends of a cored bar 30a in a freely rotatable manner between chassis side plates (not shown) of the fixing device.

In FIG. 3 and FIG.
Between the two end portions of the spring 2 and the spring receiving members 29a and 29b on the device chassis (not shown) side.
By contracting 5b, a pressing-down force is applied to the pressing rigid stay 22. This allows the film guide 16
The lower surface of the sliding member 40 and the upper surface of the pressure roller 30 are pressed against each other with the fixing film 10 interposed therebetween to form a fixing nip portion N having a predetermined width.

The pressure roller 30 is driven by the driving means M to rotate counterclockwise as indicated by an arrow a in the figure. The rotational driving of the pressure roller 30 generates a frictional force between the pressure roller 30 and the outer surface of the fixing film 10, and the rotational force acts on the fixing film 10. Then, the fixing film 10
The inner peripheral surface of the sliding member 40 at the fixing nip portion N.
While sliding in close contact with the lower surface of the film guide 16, the outer periphery of the film guide 16 is rotated clockwise as indicated by an arrow b in the drawing at a peripheral speed substantially corresponding to the peripheral speed of the pressure roller 30. That is, the fixing film 10 is rotated in conjunction with the pressure roller 30 by the surface frictional force with the pressure roller 30.

As shown in FIG. 5, a plurality of convex ribs 16e are formed on the peripheral surface of the right half 16a of the film guide 16.
They are formed at predetermined intervals in the longitudinal direction.
Thereby, the contact sliding resistance between the peripheral surface of the film guide 16a and the inner surface of the fixing film 10 is reduced, and the rotational load of the fixing film 10 is reduced. Such a convex rib portion can be similarly formed and provided on the left half 16 b of the film guide 16.

FIG. 6 schematically shows how the alternating magnetic flux generated by the magnetic field generating means 15 is generated. C represents a part of the generated alternating magnetic flux. Magnetic core 17
The alternating magnetic flux C guided to the magnetic cores 17a and 17c is transmitted between the magnetic core 17a and the magnetic core 17b.
An eddy current is generated in the electromagnetic induction heating layer 10a of the fixing film 10 between the magnetic core 17c and the magnetic core 17c. The eddy current generates Joule heat (eddy current loss) in the heat generating layer 10a due to the specific resistance of the heat generating layer 10a. The heating value Q here is determined by the density of the magnetic flux C passing through the heating layer 10a.
7 shows a distribution as shown in the graph of FIG. The graph shown in FIG.
The vertical axis indicates the position in the circumferential direction of the fixing film 10 represented by the angle θ with the center of the magnetic core 17a being 0, and the horizontal axis indicates the heat generation amount Q of the heat generating layer 10a of the fixing film 10. Here, the heating area H is defined as an area where the maximum heating value is Q and the heating value is Q / e or more (e is a natural logarithm base). This is an area where the amount of heat required for the fixing process can be obtained.

The temperature of the fixing nip portion N is controlled by a temperature control system including a temperature sensor 26 (FIG. 2) so that a predetermined temperature is maintained by controlling the current supply to the exciting coil 18. . The temperature sensor 26 is the fixing film 1
It is a temperature sensor such as a thermistor for detecting the temperature of 0. In this embodiment, the temperature of the fixing nip N is controlled based on the temperature information of the fixing film 10 measured by the temperature sensor 26.

As described above, when the fixing film 10 is rotated and the exciting coil 18 is supplied with power by the exciting circuit 27, the fixing film 10 is heated by electromagnetic induction as described above, and the fixing nip portion N The recording material P (corresponding to the material to be heated), on which the unfixed toner image t has been formed, conveyed from the image forming unit while the temperature has been raised to the predetermined temperature and controlled to the predetermined temperature, is transferred to the fixing nip portion N. It is introduced between the fixing film 10 and the pressure roller 30 such that the image surface faces upward, that is, faces the fixing film 10 surface. Then, the recording material P is nipped and conveyed together with the fixing film 10 so that the image surface thereof is in close contact with the outer surface of the fixing film 10 in the fixing nip portion N. In the process in which the recording material P is carried and conveyed through the fixing nip portion N, the fixing film 10 is heated by the electromagnetic induction heat, and the unfixed toner image t on the recording material P is heated and fixed. When the recording material P passes through the fixing nip portion N, it is separated from the outer surface of the fixing film 10 and is discharged and conveyed. After passing through the fixing nip N, the fixed toner image t on the recording material P is cooled and becomes a permanent fixed image t '.

In the present embodiment, since a toner containing a low softening substance is used in the toner t, the fixing device 100 is not provided with an oil coating mechanism for preventing offset (oil coating on the fixing film 10). When a toner containing no substance is used, an oil application mechanism may be provided. Also, when a toner containing a low softening substance is used, oil application or cooling separation may be performed.

In this embodiment, as shown in FIG.
A heat-sensitive safety device which is a temperature detecting element (temperature detecting means) for shutting off power supply to the exciting coil 18 at the time of thermal runaway of the fixing device 100, at a position facing the heat generation area H (see FIG. 6) of the fixing film 10. And a leakage flux guide member 60 are provided. These will be described later in detail.

Fixing device 100 of full-color image forming apparatus
When the width of the fixing nip portion N is 7.0 mm or more, the fixing property of a full-color image having a large amount of applied toner can be sufficiently secured, and therefore, it is preferable. If the width of the fixing nip portion N is smaller than the above range, a sufficient amount of heat for fixing the unfixed toner image t and the recording material P cannot be given.
This is not preferable because fixing failure occurs.

The surface pressure of the fixing nip N is 7.85 ×
A pressure of 10 ⁴ Pa (0.8 kgf / cm ² ) or more is preferable because when an OHP film is used as the recording material P, the light transmittance of a full-color image can be sufficiently ensured. If the surface pressure of the fixing nip N is smaller than the above range, the surface of the layer of the fixed toner image t 'cannot be sufficiently smoothed, so that irregularly reflected light increases and O
This is not preferable because the amount of transmitted light in the image area on the HP film is reduced.

From the above viewpoints, the fixing device 10 of this embodiment
0, the pressure roller 30 and the fixing film 10 are moved to 205.
94N (21 kgf), the width of the fixing nip N is about 8.0 mm, and the surface pressure of the fixing nip N is 11.77P.
a (1.2 kgf / cm ² ) (the length of the fixing nip portion N in the longitudinal direction is 220 mm).

Hereinafter, the above-described fixing device (heating device) 1
Each member used for 00 will be described.

A) Excitation Coil 18 The excitation coil 18 constituting the magnetic field generating means 15 is a bundle of a plurality of copper thin wires, each of which is insulated and coated, one by one as a conductor (electric wire) constituting a coil (wire ring). In this case, the excitation coil is formed by winding a plurality of bundles (bundled wires). In this example, the exciting coil 18 is formed by winding 10 turns.

It is preferable to use a coating having heat resistance in consideration of heat conduction due to heat generation of the fixing film 10 as the coating member for performing the insulating coating. For example, a coating of amide imide or polyimide may be used. The excitation coil 18 may improve the density by applying pressure from the outside.

The shape of the exciting coil 18 is formed along the curved surface of the fixing film 10 as shown in FIGS. The distance between the heat generating layer 10a of the fixing film 10 and the exciting coil 18 was set to be about 2 mm.

The closer the distance between the magnetic cores 17a, 17b, 17c and the exciting coil 18 and the heat generating layer 10a of the fixing film 10 is, the higher the magnetic flux absorption efficiency becomes. When the distance is 5 mm or less, it is preferable because the fixing film can efficiently absorb the magnetic flux.
If the distance is larger than the above range, the efficiency of absorbing magnetic flux is significantly reduced, which is not preferable. The heat generating layer 10a of the fixing film 10 and the exciting coil 18
This distance need not be constant as long as the distance is within 5 mm.

In FIG. 5, the power supply portions 18a and 18b drawn from the excitation coil 18 are provided with insulating coating outside the bundle.

B) Fixing Film (Heating Member Having Heating Layer) 10 FIG. 7 is a schematic diagram of a layer structure of the fixing film 10 which generates heat by electromagnetic induction as a heating member in this embodiment.

The fixing film 10 of this embodiment has a heating layer (electromagnetic induction heating layer) 1 made of a metal film or the like serving as a base layer.
0a, an elastic layer 10b laminated on its outer surface, and a release layer 10c further laminated on its outer surface. A primer layer (not shown) may be provided between each layer for adhesion between the heat generating layer 10a and the elastic layer 10b and for adhesion between the elastic layer 10b and the release layer 10c. In the fixing film 10 having a substantially cylindrical shape, the heat generating layer 10a is on the inside in contact with the sliding member 40, and the release layer 10c is on the outside in contact with the pressure roller 30 or the recording material (heated material).

As described above, when the alternating magnetic flux acts on the heat generating layer 10a, an eddy current is generated in the heat generating layer 10a, and the heat generating layer 10a generates heat. Since the heat is transmitted to the elastic layer 10b and the release layer 10c, the entire fixing film is heated, and the recording material P as the heating material passed through the fixing nip N is heated to form a toner image. Heat fixing is performed.

A. Heating Layer 10a As the heating layer 10a, magnetic and non-magnetic metals can be used, but magnetic metals are preferably used. As such a magnetic metal, a ferromagnetic metal such as nickel, iron, ferromagnetic stainless steel, nickel-cobalt alloy, or permalloy is preferably used. Further, in order to prevent metal fatigue due to repeated bending stress received when the fixing film 10 rotates, a member obtained by adding manganese to nickel may be used.

The thickness of the heat generating layer 10a is preferably larger than the skin depth σ [m] represented by the following equation and not more than 200 μm. When the thickness of the heat generating layer 10a is within this range, the heat generating layer 10a can efficiently absorb electromagnetic waves, and can efficiently generate heat.

Σ = 503 × (ρ / fμ) ^1/2 where f is the frequency [Hz] of the excitation circuit, μ is the magnetic permeability,
ρ is the specific resistance [Ωm] of the heating layer 10a.

The skin depth indicates the depth of absorption of electromagnetic waves used for electromagnetic induction, and the depth of the skin is lower than 1 / e. Conversely, most energy is absorbed up to this depth. FIG.
The relationship between the depth of the heating layer and the electromagnetic wave intensity is shown in FIG.

The thickness of the heat generating layer 10a is more preferably 1
１００100 μm is preferred. If the thickness of the heat generating layer 10a is smaller than the above range, most of the electromagnetic energy cannot be absorbed, and the efficiency becomes poor. When the heat generating layer 10a is thicker than the above range, the rigidity of the heat generating layer 10a becomes too high, and the bending property deteriorates, which is not practical for use as a rotating body.

B. Elastic Layer 10b The elastic layer 10b is preferably made of a material having good heat resistance and thermal conductivity, such as silicone rubber, fluorine rubber, and fluorosilicone rubber.

The thickness of the elastic layer 10b is preferably from 10 to 500 μm in order to guarantee the quality of the fixed image.
When a color image is printed, particularly for a photographic image, a solid image is formed over a large area on the recording material P. In this case, if the heating surface (the release layer 10c) cannot follow the unevenness of the recording material P or the unevenness of the toner layer t, uneven heating will occur, and uneven gloss will occur on the image in the portion where the heat transfer amount is large and the portion where the heat transfer amount is small. . That is, a portion having a large amount of heat transfer has high gloss, and a portion having a small amount of heat transfer has low gloss.

If the thickness of the elastic layer 10b is smaller than the above range, the release layer 10c cannot follow the irregularities of the recording material P or the toner layer t, resulting in uneven image gloss. If the elastic layer 10b is too large, the thermal resistance of the elastic layer becomes too large, and it is difficult to realize a quick start. This elastic layer b
Is more preferably 50 to 500 μm.

If the hardness of the elastic layer 10b is too high, the elastic layer 10b cannot completely follow the irregularities of the recording material P or the toner layer t, resulting in uneven image gloss. Therefore, the hardness of the elastic layer 10b is preferably 60 ° or less (JIS-A; JIS-K (using an A-type measuring device)) or less, more preferably 45 ° or less.

The thermal conductivity λ of the elastic layer 10b is 2.52 ×
10^-1~ 8.4 × 10^-1W / m · ° C (6 × 10^-Four~ 2x
10^-3cal / cm · sec · deg. )That it is
preferable. When the thermal conductivity λ is smaller than the above range
Means that the thermal resistance is too large and the surface layer (separation) of the fixing film 10
The temperature rise in the mold layer 10c) becomes slow. Thermal conductivity λ
Is larger than the above range, the hardness of the elastic layer b is high.
It becomes too hard and compression set tends to occur. Yo
More preferably 3.35 × 10^-1~ 6.28 × 10 ^-1W /
m · ° C (8 × 10^-Four~ 1.5 × 10^-3cal / cm · s
ec.deg. ) Is good.

C. Release Layer 10c The release layer 10c is made of fluororesin, silicone resin, fluorosilicone rubber, fluororubber, silicone rubber, PF
It is preferable to use a material having good releasability and heat resistance such as A, PTFE, and FEP.

The thickness of the release layer 10c is preferably 1 to 100 μm. If the thickness of the release layer 10c is smaller than the above range, coating unevenness of the coating film occurs, and a problem such as formation of a part having poor releasability and insufficient durability occurs. Further, when the release layer is larger than the above range, heat conduction is deteriorated. In particular, when a resin-based material is used for the release layer 10c, the hardness of the release layer 10c becomes too high, and the effect of the elastic layer 10b is lost.

C) Temperature Detector 50 (Thermal Safety Device) As described above, in this embodiment, power is supplied to the exciting coil 18 at the position facing the heat generating area H of the fixing film 10 when the fixing device 100 runs away from heat. A thermo-switch 50 is disposed as a heat-sensitive safety device, which is a temperature detecting element (temperature detecting means) for shutting off.

FIG. 9 is a schematic cross-sectional view of the thermoswitch 50. Reference numerals 51a and 51b denote first and second fixed contacts, and reference numeral 52 denotes a movable contact which always connects the two fixed contacts 51a and 51b electrically (contact closed).

The movable contact 52 is disposed so as to be movable about a connection g with the first fixed contact 51a as an axis.
The moving pin 53 is pushed upward as shown by a two-dot chain line in the figure and separated from the second fixed contact 51b (contact open), thereby connecting to the first and second fixed contacts 51a and 51b. The electric circuit (power supply circuit for the exciting coil) that is being used can be opened.

The moving pin 53 is connected to the movable contact 52 and the heat sensitive portion 54.
It is arranged in contact with. The heat-sensitive portion 54 is formed of a member such as a bimetal that changes its shape with a rise in temperature. When the temperature of the heat-sensitive portion 54 becomes higher than a predetermined temperature, the heat-sensitive portion 54 is deformed into a convex shape in the figure. This predetermined temperature is the operating temperature at which the contacts are opened. With the deformation of the heat-sensitive portion 54, the moving pin 53 moves upward, pushes up the movable contact 52, and opens the contact.

Reference numeral 55 denotes the members 51a, 51b,
52, 53, and 54 are included.

The thermoswitch 50 is provided at a position facing the exciting coil 18 with the fixing film 10 interposed therebetween.
In this embodiment, the fixing film 10 is disposed on the outer surface of the fixing film 10 in a non-contact manner. More preferably, as shown in FIG. 6, the fixing film 10 is disposed so as to face the heat generating region H. The distance between the thermoswitch 50 and the fixing film 10 was about 2 mm. Accordingly, the fixing film 10 is not damaged by the contact of the thermoswitch 50, and the deterioration of the fixed image due to the durable use can be prevented.

The thermoswitch 50 may be provided with the heat-sensitive portion 54 in direct contact with the fixing film 10 or indirectly in contact with a lubricating layer or the like.

FIG. 10 is a circuit diagram of a thermal runaway prevention circuit used in this embodiment. The thermoswitch 50 is incorporated in the thermal runaway prevention circuit. The thermo switch 50 which is a temperature detecting element has a DC power supply of 24 V and a relay switch 70.
And are connected in series. When the thermoswitch 50 is turned off, the power supply to the relay switch 70 is cut off, and the relay switch 70 operates to cut off the power supply to the excitation circuit 27, thereby cutting off the power supply to the excitation coil 18 (a, b). It has a configuration to do. In this embodiment, the operating temperature of the contact opening of the thermoswitch 50 is set to 220 ° C.

According to the present embodiment, when the fixing device 100 goes out of control due to a failure in the temperature control system or the like, the fixing device 100 stops while the recording material P is sandwiched in the fixing nip N, and the exciting coil 18 Even when the power is supplied to the fixing film 10 and the fixing film 10 continues to generate heat, unlike the configuration in which heat is generated in the fixing nip N as shown in FIG. 16, no heat is generated in the fixing nip N where the recording material P is sandwiched. Therefore, the recording material P is not directly heated. Further, since the thermoswitch 50 is provided in the heat generation region H where the amount of generated heat is large, the thermoswitch 50 senses a temperature of 220 ° C. or more, and when the thermoswitch is turned off, is excited by the relay switch 70. Power supply to the coil 18 is cut off.

According to the present embodiment, since the ignition temperature of the paper as the recording material P is around 400 ° C., the heat generation of the fixing film 10 can be stopped without the paper igniting.

As the temperature detecting element 50, a temperature fuse may be used instead of the thermoswitch. Further, in this embodiment, a non-contact type thermoswitch is used, but a contact type thermoswitch may be used in contact with the fixing film 10.

D) Leakage Flux Induction Member 60 In this embodiment, as shown in FIGS. 2 and 6, the leakage flux induction member 60 is disposed at or near the position where the thermoswitch 50 is disposed.

The leakage magnetic flux guiding member 60 is for inducing a leakage magnetic flux generated when the temperature of the heat generating layer 10a of the fixing film 10 exceeds the Curie temperature of the members constituting the heat generating layer 10a.

The Curie temperature is a temperature at which a magnetic material such as a ferromagnetic material undergoes a magnetic transition to paramagnetism. The permeability of a ferromagnetic material gradually decreases at first as the temperature rises,
When the temperature reaches the Curie temperature, the temperature suddenly decreases, and becomes paramagnetic.

The leakage magnetic flux guiding member 60 may be a plate-like member, or, as shown in FIG. 11, a through hole 6 may be provided at a position corresponding to the heat sensitive portion 54 of the thermoswitch 50 of the leakage magnetic flux guiding member 60.
0a is provided to fix the thermoswitch 50 from the fixing film 10.
It is also effective to make the shape so as not to block the radiant heat to the heat-sensitive portion 54. That is, since the radiation heat from the fixing film 10 is not blocked by having such a shape, when the heat capacity of the leakage magnetic flux guiding member 60 is large or when the thermal conductivity is small, that is, when the leakage magnetic flux guiding member 60 This is effective when a member having poor thermal response is used.

Since the leakage magnetic flux guiding member 60 induces the magnetic flux C, it needs to be a member having magnetism such as a ferromagnetic material. Such magnetic members include iron, ferrite, nickel, permalloy, and the like.

Further, the leakage magnetic flux guiding member 60 may be a conductive magnetic member. In this case, the leakage flux guiding member 6
0 is an eddy current caused by the leakage magnetic flux, and the leakage magnetic flux guiding member 6
0 can generate heat, and the ambient temperature around the thermoswitch 50 can be further increased. Therefore, the ambient temperature around the heat sensitive part 54 of the thermoswitch 50 can be increased. Such members include iron,
Metals having magnetism such as nickel, cobalt, permalloy, and magnetic stainless steel may be used. In this embodiment, iron is used for the leakage magnetic flux guiding member 60.

The magnetic member forming the leakage magnetic flux guiding member 60 may have a Curie temperature higher than the Curie temperature of the member forming the heat generating layer 10a. in this case,
Since the magnetism of the leakage magnetic flux guide member 60 can be ensured up to a temperature range higher than that of the heat generating layer 10a, the leakage magnetic flux can be reliably induced. For example, when nickel (Curie temperature: 358 ° C.) is used for the heat generating layer 10a, iron (Curie temperature: 770 ° C.) may be used for the leakage magnetic flux induction member 60.

In the fixing device 100, the fixing film 1
In the case where a magnetic member other than the leakage magnetic flux guiding member 60 is provided in a region facing the excitation coil 18 with respect to 0, the shortest distance from the leakage magnetic flux guiding member 60 to the excitation coil 18 is opposite to the excitation coil 18. It is necessary to make it the shortest among the magnetic members arranged at the positions where the magnetic members are located. As a result, the leakage magnetic flux generated when the heat generating layer 10a exceeds the Curie temperature is guided toward the leakage magnetic flux guiding member 60.

Further, the shape of the sheet metal member of the fixing device 100 made of a magnetic member (for example, iron) is changed only at the position where the thermoswitch 50 is provided.
A member having such a shape that the distance of 8 is shorter than other portions can be used as the leakage magnetic flux guiding member 60.

E) Safe Operation Next, an outline of the safe operation of the fixing device 100 during a thermal runaway due to a failure in the temperature control system will be described.

When the temperature control system does not operate normally due to a device failure or the like and excessive power supply to the exciting coil 18 continues, the temperature of the fixing film 10 rises to the control temperature or higher. In particular, when the fixing film 10 is in the rotation stopped state, the temperature (heat generation area H in FIG. 6) of the fixing film 10 where the eddy current is generated does not change, and the temperature rises instantaneously.

FIG. 12 shows the heating layer 10 of the fixing film 10.
a shows the state of the magnetic path when the temperature is raised to the Curie temperature or higher of the magnetic member constituting the layer. When the temperature of the heat generating layer 10a exceeds the Curie temperature (for example, 358 ° C. when the heat generating layer 10a is made of nickel), the magnetic permeability of the heat generating layer 10a rapidly decreases, and a magnetic path in the heat generating layer 10a is formed. The magnetic flux C leaks from the heating layer 10a. The magnetic flux leaked from the heat generating layer 10a makes a part of the magnetic path in the air.

In the state where the heat generating layer 10a is heated to the Curie temperature or higher, the difference in the temperature of the fixing film 10 due to the presence or absence of the leakage magnetic flux guiding member 60 can be verified by considering the magnetic circuit described below. It is possible.

Consider the magnetic resistance in the magnetic path shown in FIG. 12 and use this as the magnetic resistance per unit length in the longitudinal direction. It is considered that each magnetic resistance at each position in the longitudinal direction is distributed in the longitudinal direction from end to end of the exciting coil with respect to the exciting coil generating the magnetomotive force. Therefore, in the magnetic circuit of the fixing device 100 of the present embodiment, the magnetic resistance at each position in the longitudinal direction can be replaced by an equivalent circuit model connected in parallel. This is shown in FIG.

Among the magnetic resistances shown in FIG.
The magnetic resistance at the position where the conductive member 60 is provided is represented by R_M , Leakage flux induction
The magnetic resistance at the position where the body 60 is not provided is reduced by the magnetic resistance.
Anti-R _N And The magnetic resistance depends on the magnitude of the magnetic permeability in the magnetic path.
Inversely proportional. When the temperature of the heating layer 10a is above the Curie point
Is composed of a magnetic member in which the magnetic flux C leaks from the heat generating layer 10a.
The leaked magnetic flux guiding member 60 to be a part of the magnetic path
And the magnetic resistance R at the position where the leakage magnetic flux guiding member 60 is disposed._M 
Is R_M <R_N Becomes the relationship.

The magnetomotive force F is determined by the product of the number of turns N of the exciting coil 18 and the current I flowing therethrough. The magnetoresistances at the respective longitudinally connected positions connected in parallel have the same magnitude. work. That is, the magnetoresistance R _M and R _N working in magnetomotive force F is equal in magnitude. Leakage flux guide member 6
_Assuming that the magnetic flux at the zero disposition position is φ _M and the magnetic flux at the position where the leakage flux guide member 60 is not disposed is φ _N , the magnetomotive force F
Since equal regardless of the longitudinal position, and _{φ M = F / R M φ} N = F / R N. Since the magnetic resistance has a relationship of R _M <R _N , the magnetic flux becomes φ _M > φ _N , and the magnetic flux at the position where the leakage magnetic flux guiding member 60 is disposed is larger than the position where the leakage magnetic flux guiding member 60 is not disposed. You can see that. The total magnetic flux generated from the exciting coil 18 is given by φ _M + φ _N + φ _N + φ _N.
In view of the above, it can be seen that concentration of the magnetic flux distribution occurs in the longitudinal direction.

As described above, when the temperature of the heat generating layer 10a is equal to or higher than the Curie temperature, the magnetic flux generated from the exciting coil 18 concentrates on the portion where the leakage magnetic flux guiding member 60 is disposed, where the magnetic resistance is small. Of the fixing film 10 locally increases.

The leakage magnetic flux guiding member 60 of the fixing film 10
In the vicinity of the opposing portion, the calorific value locally becomes relatively larger than in the other portions, so that the temperature of the fixing film 10 locally increases. Therefore, the thermoswitch 5 provided at the same position as or near the leakage magnetic flux guiding member 60
0 can be activated earlier.

As described above, in the fixing device of this embodiment,
Even if the temperature of the heat generating layer 10a of the fixing film 10 as the heating member exceeds the Curie temperature of the magnetic member of the heat generating layer 10a due to thermal runaway due to the failure of the temperature control control system, the thermosensitive type Since it is possible to operate the safety device 50, it is possible to prevent ignition and smoke from the device.

<Second Embodiment> Next, a second embodiment will be described.

The image forming apparatus according to the present embodiment includes a fixing device 10
Except for 0, the image forming apparatus is the same as the image forming apparatus described in the first embodiment. The configuration of the fixing device 100 of the first embodiment is the same as that of the fixing device 10 of the first embodiment except for the leakage magnetic flux guiding member 60.
Same as 0.

In this embodiment, the leakage magnetic flux guiding member 60 is
It is characterized by comprising a magnetic member having a maximum magnetic permeability among magnetic members disposed at a position facing the exciting coil 18 with the fixing film 10 interposed therebetween.

For example, iron (permeability:
In the case of using 10 ² ), permalloy (permeability: 10 ³ order) can be used for the leakage magnetic flux guiding member 60.

According to the structure of this embodiment, the fixing film 10
Even if another magnetic member is provided in the vicinity of the heat generating region H, the leakage magnetic flux generated when the heat generation layer 10a exceeds the Curie point is moved to the vicinity of the leakage magnetic flux guiding member 60 more reliably than in the first embodiment. Can be guided to. Therefore, the temperature of the fixing film 10 at the position where the leakage magnetic flux guiding member 60 is disposed is
Because it can be relatively hotter than other positions,
The thermoswitch 50 provided at the same position as or near the leakage magnetic flux guiding member 60 can be operated more quickly and reliably.

As described above, also in the fixing device of this embodiment, as in the first embodiment, the device causes thermal runaway due to the failure of the temperature control system, and the heat generation layer 10 of the fixing film 10 is formed.
Even in the state where the temperature a exceeds the Curie temperature of the magnetic member of the heat generating layer 10a, the thermal safety device 50 can be reliably operated, so that ignition and smoke from the device can be prevented. .

<Third Embodiment> (FIG. 14) Next, a third embodiment will be described.

The image forming apparatus according to the present embodiment includes a fixing device 10
Except for 0, the image forming apparatus is the same as the image forming apparatus described in the first embodiment. The configuration of the fixing device 100 of the present embodiment is the same as that of the fixing device 100 of the first embodiment, except for the positions at which the thermoswitch 50 and the leakage magnetic flux guiding member 60 are provided.

FIG. 14 shows a fixing device 100 according to this embodiment.
FIG. The fixing device 100 of this embodiment is characterized in that the thermoswitch 50 and the leakage magnetic flux guiding member 60 as the temperature detecting elements are disposed in the non-sheet passing area of the fixing film 10.

In the configuration of this embodiment, the thermoswitch 50
Is provided in the non-paper passing area of the fixing film 10, even if the surface of the fixing film 10 is damaged by contact with the thermoswitch 50, there is no possibility that the quality of the fixed image is deteriorated. Therefore, the thermoswitch 50 can be arranged in contact with the fixing film 10.

Further, even when a material to be heated such as paper or an OHP film is wrapped around the fixing film 10, the thermoswitch 50 disposed in the non-sheet passing area reliably detects the surface temperature of the fixing film 10. Therefore, the reliability of the operation of the thermoswitch 50 can be improved.

Further, since the high heat generating area of the fixing film 10 due to the leakage magnetic flux guiding member 60 when the heat generating layer 10a exceeds the Curie point is in the non-paper passing area of the fixing film 10,
Since the material to be heated P wound around the fixing film 10 is not locally concentrated and heated, ignition from the material to be heated P can be prevented.

As described above, also in the fixing device of this embodiment, as in the first embodiment, the device causes thermal runaway due to the failure of the temperature control system, and the heat generating layer 10 of the fixing film 10 is heated.
Even in the state where the temperature a exceeds the Curie temperature of the magnetic member of the heat generating layer 10a, the thermal safety device 50 can be reliably operated, so that ignition and smoke from the device can be prevented. .

<Fourth Embodiment> (FIG. 15) Next, a fourth embodiment will be described.

The image forming apparatus according to the present embodiment includes a fixing device 10
Except for 0, the image forming apparatus is the same as the image forming apparatus described in the first embodiment. The configuration of the fixing device 100 is the same as that of the fixing device 100 described in the first embodiment, except for the thermoswitch 50 and the leakage magnetic flux guiding member 60.

FIG. 15 shows the fixing device 10 in this embodiment.
FIG. 5 is a cross-sectional model diagram showing a positional relationship between a thermo switch of No. 0 and a leakage magnetic flux guiding member 60. Fixing device 1 of the present embodiment
00 is characterized in that the heat sensing portion 54 of the thermoswitch 50 and the leakage magnetic flux guiding member 60 are in contact with each other. In this embodiment, the leakage magnetic flux guiding member 60 is further incorporated in the thermoswitch 50.

Thermoswitch 50 as a temperature detecting element
Is disposed at a position 2 mm away from the surface of the fixing film 10 as in the first embodiment. Thermo switch 50
Is incorporated in the thermal runaway prevention circuit (FIG. 10) as in the first embodiment, so that the excitation coil 1
8 can be cut off.

The leakage magnetic flux guiding member 60 is preferably a magnetic member having conductivity. In this case, the eddy current can be generated in the leakage magnetic flux inducing member 60 itself by the leakage magnetic flux to generate Joule heat, so that the temperature of the heat sensitive portion 54 of the thermoswitch 50 can be increased more quickly.

The leakage magnetic flux guiding member 60 is preferably a member having a high thermal conductivity. In this case, the radiant heat received by the leakage magnetic flux guiding member 60 from the fixing film 10 can be quickly transmitted to the heat-sensitive portion 54 of the thermoswitch 50, so that the temperature of the heat-sensitive portion 54 can be similarly quickly raised.

The leakage magnetic flux guiding member 60 may be brought into direct contact with the heat sensitive part 54 of the thermoswitch 50, or may be brought into indirect contact with another member through another member.

According to the configuration of the present embodiment, the Joule heat generated by the eddy current of the leakage magnetic flux
0 by the radiant heat from the fixing film 10
The temperature of the heat sensitive portion 54 of the thermoswitch 50 can be raised more quickly. Therefore, even if the thermoswitch 50 is disposed in non-contact with the fixing film 10, it is possible to reduce the delay in the response of the temperature detected by the thermoswitch 50 from the temperature of the fixing film 10.

As described above, also in the fixing device of this embodiment, as in the first embodiment, the device causes thermal runaway due to the failure of the temperature control system, and the heating layer 10
Even in the state where the temperature a exceeds the Curie temperature of the magnetic member of the heat generating layer 10a, the thermal safety device 50 can be reliably operated, so that ignition and smoke from the device can be prevented. .

<Other Embodiments> 1) The fixing device 1 in each of the above-described first to fourth embodiments.
00 is a configuration in which an endless belt-shaped fixing film 10 as a heating member is stretched between a plurality of members and rotated by throwing with a driving hand, or a rolled endless long fixing film is fed out. It is also possible to adopt a device configuration for traveling. It is also possible to adopt a device configuration in which the heating member is fixedly disposed as a fixing member.

2) The fixing film 10 may have a configuration in which the elastic layer 10b is omitted in the case of fixing by heating a monochrome or one-pass multicolor image or the like.
The release layer 10c may be omitted. A layer configuration in which another desired functional layer is added may be employed.

3) The pressing member 30 is not limited to a roller, but may be another type of pressing member such as a rotating belt type. Further, in order to supply thermal energy to the recording material P also from the pressing member side, a heating device such as electromagnetic induction heating is also provided on the pressing member side to heat and control the temperature to a predetermined temperature. You can also.

When the pressing member 30 is a rotating body, it can be configured to be driven to rotate as in the embodiment, or to a device configured to be driven and rotated by frictional contact with a heating member or the like. You can also.

4) The heating device of the present invention is not limited to the image heating and fixing device of the embodiment, but may be an image heating device for heating a recording material carrying an image to improve the surface properties such as gloss and the like. The present invention can be widely used as an image heating device that performs heat treatment, a device that heats a material to be heated, such as drying or laminating.

[0162]

As described above in detail, according to the present invention, in a heating device of an electromagnetic (magnetic) induction heating type and an image forming apparatus equipped with the heating device, the device causes thermal runaway, and the heating member generates heat. Even in a state where the temperature of the layer exceeds the Curie temperature of the conductive magnetic member constituting the heat generating layer, it is possible to reliably detect the abnormal temperature rise of the heating member and cut off the power supply to the heating device. It is possible to prevent the ignition and smoking of the gas.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment.

FIG. 2 is a schematic cross-sectional view of a main part of the fixing device.

FIG. 3 is a front view of the same main part.

FIG. 4 is a longitudinal sectional model diagram along line (4)-(4) in FIG. 2;

FIG. 5 is a perspective model diagram along a line (5)-(5) in FIG. 2 (a fixing film is not shown).

FIG. 6 is a diagram showing a relationship between a magnetic field generating means and a heating value Q;

FIG. 7 is a schematic diagram of a layer structure of a fixing film.

FIG. 8 is a diagram showing a relationship between a heating layer depth and electromagnetic wave intensity.

FIG. 9 is a schematic longitudinal sectional view of the thermoswitch of the first embodiment.

FIG. 10 is a circuit diagram for preventing thermal runaway

FIG. 11 is a perspective view showing an example of the shape of a leakage magnetic flux guide member 60;

FIG. 12 is a diagram showing a magnetic path when the heat generation layer of the fixing film exceeds the Curie temperature.

FIG. 13 is a diagram showing an equivalent circuit model of a magnetic circuit in the fixing device.

FIG. 14 is a schematic front view of a fixing device according to a third embodiment.

FIG. 15 is a schematic longitudinal sectional view of a thermoswitch according to a fourth embodiment.

FIG. 16 is a schematic cross-sectional view of a main part of a conventional fixing device.

[Explanation of symbols]

10 fixing film, 10a heating layer, 10b elastic layer, 10c release layer, 15 magnetic field generating means, 16 (a
b) Film guide, 17 (abc) magnetic core, 18 excitation coil, 22 rigid stay for pressing, 23
(A / b): Flange member, 25 (ab): Pressure spring, 26: Temperature sensor, 27: Excitation circuit, 30: Pressure roller, 40: Sliding member, 50: Thermoswitch (Temperature detection element , Heat-sensitive safety device) 54: heat-sensitive portion, 60: leakage magnetic flux guiding member, 70: relay switch, 100: fixing device (heating device), 101: photosensitive drum, 102: charging device, 103: laser beam, 104: development , 105 ... intermediate transfer drum, 106 ... transfer roller, 107/108 ...
Cleaner, C: alternating magnetic flux, H: heat generating position, M: driving means, N: fixing nip portion, P: recording material, t: unfixed toner image, t ': fixed toner image, T1: primary transfer portion, T
2: Secondary transfer unit

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G05F 1/10 G05F 1/10 G H05B 6/14 H05B 6/14 (72) Inventor Akihiko Takeuchi Ota, Tokyo 3-30-2 Shimomaruko-ku, Canon Inc. (72) Inventor Hitoshi Sato 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. F-term (reference) 2H033 AA24 AA41 AA42 BA26 BA32 BA35 BE03 BE06 CA04 CA06 CA07 CA30 CA34 CA44 3K059 AB00 AB19 AB20 AB23 AB28 AC10 AC34 AC65 AC73 AD04 AD10 AD26 AD34 BD21 CD10 CD37 CD72 CD77 5H323 AA36 BB17 CA08 CB06 DA01 DB06 DB24 FF01 GG04 GG23 KK05 MM02 QQ06 RR04 SS01 TT04 TT04 TT04 TT04 TT04 FF26 LL09 LL20

Claims (15)

[Claims] 1. A magnetic field generating means having an exciting coil, a heating member having a heating layer formed of a conductive magnetic member,
An eddy current generated by applying an alternating magnetic field from the magnetic field generating means to a heating layer of the heating member, the temperature detection element detecting a temperature of the heating member and interrupting power supply to the excitation coil. In the heating device of the electromagnetic induction heating system for heating the material to be heated by the heat generated by the heat generating layer, the temperature detecting element is disposed at a position facing the exciting coil with the heating member interposed therebetween, and A position where the temperature sensing element is disposed or a leakage magnetic flux guiding member formed of a magnetic member that induces a leakage magnetic flux from the heating layer that is generated when the temperature of the heating layer exceeds the Curie temperature of the magnetic member of the heating layer or A heating device disposed near the heating device. 2. A magnetic head according to claim 1, wherein a distance from said leakage magnetic flux guiding member to said exciting coil is the shortest among magnetic members disposed at a position facing said exciting coil with said heating member interposed therebetween. The heating device according to claim 1. 3. The magnetic flux member according to claim 1, wherein the magnetic permeability of the leakage magnetic flux guiding member is the largest among the magnetic members disposed at a position facing the exciting coil with the heating member interposed therebetween. Or the heating device according to 2. 4. The device according to claim 1, wherein the leakage magnetic flux guiding member and the temperature detecting element are arranged in a region of the heating member not in contact with the material to be heated. Heating equipment. 5. The heating device according to claim 1, wherein the leakage magnetic flux guiding member is a magnetic member having conductivity. 6. The heating device according to claim 5, wherein the leakage magnetic flux guiding member is made of a ferromagnetic metal. 7. The heating device according to claim 1, wherein the heat-sensitive portion of the temperature detecting element is in direct or indirect contact with the leakage magnetic flux guiding member. 8. The heating device according to claim 1, wherein the heat-sensitive portion of the temperature detecting element is in direct or indirect contact with the heating member. 9. The method according to claim 1, wherein the Curie temperature of the magnetic member constituting the leakage magnetic flux guiding member is higher than the Curie temperature of the magnetic member of the heating layer of the heating member. A heating device according to claim 1. 10. The heating device according to claim 1, wherein the temperature detecting element is a thermo switch. 11. The heating device according to claim 1, wherein the heating member is a fixed member, a rotating body, or a moving end member. 12. The heating apparatus according to claim 1, further comprising a pressing member for directly or indirectly bringing the material to be heated into close contact with the heating member. 13. The heating apparatus according to claim 12, wherein the pressing member is a pressing rotary member that is driven to rotate or driven to rotate. 14. The apparatus according to claim 1, wherein said material to be heated is a recording material carrying an image to be heat-treated, and is an image heating apparatus for heating said image to said recording material. The heating device according to any one of the above. 15. An image forming apparatus comprising: an image forming means for forming an unfixed toner image on a recording material; and a heat fixing means for pressure-fixing the unfixed toner image to the recording material. An image forming apparatus, comprising: the heating device according to claim 1.