JP5765135B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a fixing device and an image forming apparatus.

As a fixing device mounted on an image forming apparatus such as a copying machine or a printer using an electrophotographic system, an apparatus using an electromagnetic induction heating system is known.
For example, Patent Document 1 discloses that a magnetic field generating unit configured by winding an excitation coil around a plurality of core members made of a material having high magnetic permeability such as ferrite and arranged in at least one direction is an endless as a conductive member. The endless film is placed directly in the endless film by arranging multiple cores in the width direction of the endless film and generating an eddy current in the endless film by the induced magnetic field generated by the exciting coil. An electromagnetic induction heating type fixing device is described which heats automatically.

JP-A-8-16005

  An object of the present invention is to suppress the occurrence of temperature unevenness in a fixing member used in an electromagnetic induction heating type fixing device.

The invention according to claim 1 has an endless belt-like shape and a conductive layer, is provided rotatably, and the conductive layer is heated by electromagnetic induction to fix the toner on the recording material;
A magnetic field generating member that is provided facing the fixing member and generates an alternating magnetic field that intersects the conductive layer of the fixing member by being supplied with an alternating current;
A plurality of first magnetic path forming members provided opposite to the fixing member via the magnetic field generating member and forming a magnetic path of an alternating magnetic field generated by the magnetic field generating member;
A second magnetic path formed so as to face the magnetic field generating member via the fixing member and forms a magnetic path of an alternating magnetic field generated by the magnetic field generating member together with the plurality of first magnetic path forming members. With members,
The plurality of first magnetic path forming members extend in the rotation direction of the fixing member, and each of the first magnetic path forming members has a rotation direction of the fixing member so as to have an interval between the adjacent first magnetic path forming members. Arranged side by side in the width direction of the fixing member intersecting with
The fixing member is provided adjacent to the first region passing through a portion facing the first magnetic path forming member through the magnetic field generating member, and the first member through the magnetic field generating member. A second region that passes through a portion that does not face the first magnetic path forming member,
The second magnetic path forming member includes a first portion facing the first region of the fixing member, and a second portion facing the second region of the fixing member and having a heat capacity lower than that of the first portion. The fixing device is characterized by comprising:

The invention according to claim 2 is the fixing device according to claim 1, wherein the second magnetic path forming member has a volume at the first portion larger than a volume at the second portion.
According to a third aspect of the present invention, in the second magnetic path forming member, the length along the rotation direction of the fixing member at the first portion is along the rotation direction of the fixing member at the second portion. The fixing device according to claim 1, wherein the fixing device is longer than the length.
According to a fourth aspect of the present invention, the second magnetic path forming member is disposed such that an outer peripheral surface thereof is in contact with an inner peripheral surface of the fixing member, and the magnetic property is between ferromagnetism and paramagnetism depending on temperature. When the magnetic characteristic is ferromagnetic, the magnetic field of the alternating magnetic field generated by the magnetic field generating member is formed, and when the magnetic characteristic is paramagnetic, the alternating current generated by the magnetic field generating member is formed. When the temperature-sensitive magnetic member that transmits a magnetic field and the outer peripheral surface are arranged in contact with the inner peripheral surface of the temperature-sensitive magnetic member and the magnetic property of the temperature-sensitive magnetic member is paramagnetic, the temperature-sensitive magnetic member is An induction member for inducing a transmitted alternating magnetic field,
3. The fixing device according to claim 1, wherein the temperature-sensitive magnetic member and the guide member have a notch along the rotation direction of the fixing member in the second portion. 4.
According to a fifth aspect of the present invention, in the fixing device according to the first or second aspect, the second magnetic path forming member has a thickness at the first portion larger than a thickness at the second portion. It is.
According to a sixth aspect of the present invention, the second magnetic path forming member is disposed such that an outer peripheral surface thereof is in contact with an inner peripheral surface of the fixing member, and the magnetic property is between ferromagnetism and paramagnetism depending on temperature. When the magnetic characteristic is ferromagnetic, the magnetic field of the alternating magnetic field generated by the magnetic field generating member is formed, and when the magnetic characteristic is paramagnetic, the alternating current generated by the magnetic field generating member is formed. When the temperature-sensitive magnetic member that transmits a magnetic field and the outer peripheral surface are arranged in contact with the inner peripheral surface of the temperature-sensitive magnetic member and the magnetic property of the temperature-sensitive magnetic member is paramagnetic, the temperature-sensitive magnetic member is An induction member for inducing a transmitted alternating magnetic field,
The said induction | guidance | derivation member has a convex part which protrudes rather than the said 2nd site | part on the opposite side to the surface which contact | connects the inner peripheral surface of the said temperature-sensitive magnetic member in the said 1st site | part. 2. The fixing device according to 2.

The invention according to claim 7 is a toner image forming means for forming a toner image;
Transfer means for transferring the toner image formed by the toner image forming means onto a recording material;
Fixing means for fixing the toner image transferred onto the recording material to the recording material;
The fixing means is
A fixing member having an endless belt-like shape, having a conductive layer, rotatably provided, and fixing the toner on the recording material by electromagnetically heating the conductive layer;
A magnetic field generating member that is provided facing the fixing member and generates an alternating magnetic field that intersects the conductive layer of the fixing member by being supplied with an alternating current;
A plurality of first magnetic path forming members provided opposite to the fixing member via the magnetic field generating member and forming a magnetic path of an alternating magnetic field generated by the magnetic field generating member;
A second magnetic path formed so as to face the magnetic field generating member via the fixing member and forms a magnetic path of an alternating magnetic field generated by the magnetic field generating member together with the plurality of first magnetic path forming members. With members,
Each of the plurality of first magnetic path forming members extends along the rotation direction of the fixing member, and has a rotation direction of the fixing member so as to have an interval between the adjacent first magnetic path forming members. Provided side by side in the width direction of the fixing members that intersect,
The fixing member is provided adjacent to the first region passing through a portion facing the first magnetic path forming member through the magnetic field generating member, and the first member through the magnetic field generating member. A second region that passes through a portion that does not face the first magnetic path forming member,
The second magnetic path forming member includes a first portion facing the first region of the fixing member, and a second portion facing the second region of the fixing member and having a heat capacity lower than that of the first portion. An image forming apparatus comprising:

The invention according to claim 8 is the image forming apparatus according to claim 7, wherein the second magnetic path forming member has a volume in the first part larger than a volume in the second part. .
According to a ninth aspect of the present invention, in the second magnetic path forming member, a length along the rotation direction of the fixing member at the first portion is along the rotation direction of the fixing member at the second portion. 9. The image forming apparatus according to claim 7, wherein the image forming apparatus is longer than the length.
According to a tenth aspect of the present invention, in the second magnetic path forming member, the thickness at the first portion is thicker than the thickness at the second portion. Device.

According to the first aspect of the present invention, it is possible to suppress the occurrence of temperature unevenness in the fixing member as compared with the case where this configuration is not provided.
According to the second aspect of the present invention, the heat capacity of the first part of the second magnetic path forming member is made larger than the heat capacity of the second part with a simpler structure as compared with the case without this structure. Can do.
According to the third aspect of the present invention, the heat capacity distribution in the second magnetic path forming member can be realized with a simpler configuration as compared with the case without this configuration.
According to the fourth aspect of the present invention, it is possible to suppress an excessive temperature rise in the fixing member as compared with the case where this configuration is not provided.
According to the fifth aspect of the present invention, the heat capacity distribution in the second magnetic path forming member can be realized with a simpler configuration as compared with the case where this configuration is not provided.
According to the sixth aspect of the present invention, it is possible to suppress an excessive temperature rise in the fixing member as compared with the case where this configuration is not provided.

According to the seventh aspect of the present invention, it is possible to suppress the occurrence of temperature unevenness in the fixing member as compared with the case where this configuration is not provided.
According to the eighth aspect of the present invention, the heat capacity of the first part of the second magnetic path forming member is made larger than the heat capacity of the second part with a simpler structure as compared with the case without this structure. Can do.
According to the ninth aspect of the present invention, the heat capacity distribution in the second magnetic path forming member can be realized with a simpler configuration than in the case where the present configuration is not provided.
According to the tenth aspect of the present invention, the heat capacity distribution in the second magnetic path forming member can be realized with a simpler configuration than in the case where the present configuration is not provided.

1 is a diagram illustrating a configuration example of an image forming apparatus to which a fixing device according to an exemplary embodiment is applied. FIG. 2 is a front view illustrating a configuration of a fixing unit of the present embodiment. FIG. 3 is a sectional view of the fixing unit in FIG. 2 taken along the line III-III. FIG. 3 is a diagram illustrating a layer configuration of a fixing belt. (A) is a side view of an end cap member, (b) is a top view of the end cap member seen from the VB direction. It is sectional drawing explaining the structure of the IH heater of this Embodiment. It is a figure explaining the laminated structure of the IH heater in this Embodiment, a fixing belt, a temperature-sensitive magnetic member, and an induction member. It is a figure explaining the relationship between the magnetic core, temperature-sensitive magnetic member, and induction | guidance | derivation member in the IH heater of this Embodiment. It is a figure explaining the state of a line of magnetic force in case the temperature of a fixing belt exists in the temperature range below the magnetic permeability change start temperature. It is a perspective view explaining the laminated structure of an IH heater, a fixing belt, a temperature-sensitive magnetic member, and an induction member in the present embodiment. It is sectional drawing explaining the laminated structure of the IH heater in this Embodiment, a fixing belt, a temperature-sensitive magnetic member, and an induction member.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
[Embodiment 1]
<Description of Image Forming Apparatus>
FIG. 1 is a diagram illustrating a configuration example of an image forming apparatus to which the fixing device of the present embodiment is applied. An image forming apparatus 1 illustrated in FIG. 1 is a so-called tandem color printer, and includes an image forming unit 10 that forms an image based on image data, a control unit 31 that controls the operation of the entire image forming apparatus 1, and the image forming apparatus 1. Are provided with a paper holding unit 40 for holding the paper P supplied thereto, and a paper stacking unit 45 for loading the paper P on which an image is formed. Further, for example, a communication unit 32 that receives image data by communicating with a personal computer (PC) 3 or an image reading device (scanner) 4, and a predetermined image for the image data received by the communication unit 32. An image processing unit 33 that performs processing is provided.

The image forming unit 10 includes four image forming units 11Y, 11M, 11C, and 11K (also collectively referred to as “image forming unit 11”), which are examples of toner image forming units that are arranged in parallel at regular intervals. I have. Each image forming unit 11 is charged by a photosensitive drum 12 that forms an electrostatic latent image and holds a toner image, a charger 13 that charges the surface of the photosensitive drum 12 at a predetermined potential, and a charger 13. An LED (Light Emitting Diode) print head 14 that exposes the photosensitive drum 12 based on each color image data, a developing device 15 that develops an electrostatic latent image formed on the photosensitive drum 12, and the surface of the photosensitive drum 12 after transfer A drum cleaner 16 is provided.
Each of the image forming units 11 is configured in the same manner except for the toner stored in the developing device 15, and each forms a toner image of yellow (Y), magenta (M), cyan (C), and black (K). .

  The image forming unit 10 also receives the intermediate transfer belt 20 onto which the color toner images formed on the photosensitive drums 12 of the image forming units 11 are transferred, and the color toner images formed on the image forming units 11. A primary transfer roll 21 that sequentially transfers (primary transfer) to the intermediate transfer belt 20 is provided. Further, a secondary transfer roll 22 that batch-transfers (secondary transfer) each color toner image transferred onto the intermediate transfer belt 20 onto a sheet P that is a recording material (recording paper), and intermediate transfer after the secondary transfer. A belt cleaner 25 for cleaning the surface of the belt 20 and a fixing unit 60 as an example of fixing means (fixing device) for fixing each color toner image that has been secondarily transferred onto the paper P are provided. In the image forming apparatus 1 of the present embodiment, the intermediate transfer belt 20, the primary transfer roll 21, and the secondary transfer roll 22 constitute a transfer unit.

  In the image forming apparatus 1 of the present embodiment, under the operation control by the control unit 31, image forming processing is performed by the following process. That is, image data from the PC 3 or the scanner 4 is received by the communication unit 32, subjected to predetermined image processing by the image processing unit 33, and then sent to each image forming unit 11 as image data of each color. . For example, in the image forming unit 11K that forms a black (K) toner image, the photosensitive drum 12 is charged at a predetermined potential by the charger 13 while rotating in the direction of arrow A, and is transmitted from the image processing unit 33. The LED print head 14 scans and exposes the photosensitive drum 12 based on the black (K) color image data. As a result, an electrostatic latent image relating to a black (K) color image is formed on the photosensitive drum 12. The black (K) electrostatic latent image formed on the photosensitive drum 12 is developed by the developing device 15, and a black (K) toner image is formed on the photosensitive drum 12. Similarly, yellow (Y), magenta (M), and cyan (C) toner images are formed in the image forming units 11Y, 11M, and 11C, respectively.

  Each color toner image formed on the photosensitive drum 12 of each image forming unit 11 is sequentially electrostatically transferred (primary transfer) onto the intermediate transfer belt 20 that moves in the direction of arrow B by the primary transfer roll 21, and each color toner is superimposed. A superimposed toner image is formed. The superimposed toner image on the intermediate transfer belt 20 is conveyed to a region (secondary transfer portion T) where the secondary transfer roll 22 is disposed as the intermediate transfer belt 20 moves. When the superimposed toner image is conveyed to the secondary transfer unit T, the paper P is supplied from the paper holding unit 40 to the secondary transfer unit T in accordance with the timing. The superimposed toner image is collectively electrostatically transferred (secondary transfer) onto the conveyed paper P by the transfer electric field formed by the secondary transfer roll 22 in the secondary transfer portion T.

Thereafter, the sheet P on which the superimposed toner image is electrostatically transferred is conveyed to the fixing unit 60. The toner image on the paper P conveyed to the fixing unit 60 receives heat and pressure by the fixing unit 60 and is fixed on the paper P. Then, the paper P on which the fixed image is formed is conveyed to a paper stacking unit 45 provided in the discharge unit of the image forming apparatus 1.
On the other hand, the toner (primary transfer residual toner) adhering to the photosensitive drum 12 after the primary transfer and the toner (secondary transfer residual toner) adhering to the intermediate transfer belt 20 after the secondary transfer are respectively drum cleaner 16. , And the belt cleaner 25.
In this way, the image forming process in the image forming apparatus 1 is repeatedly executed for the number of printed sheets.

<Description of fixing unit configuration>
Next, the fixing unit 60 of this embodiment will be described.
2 and 3 are views showing a configuration of the fixing unit 60 of the present embodiment, FIG. 2 is a front view, and FIG. 3 is a sectional view taken along line III-III in FIG.
First, as shown in FIG. 3 which is a cross-sectional view, a fixing unit 60 includes an IH (Induction Heating) heater 80, a fixing belt 61 as an example of a fixing member that is heated by electromagnetic induction by the IH heater 80 and fixes a toner image. On the outer peripheral side of the fixing belt 61, a pressure roll 62 disposed so as to face the fixing belt 61, provided on the inner peripheral side of the fixing belt 61, and pressed from the pressure roll 62 via the fixing belt 61, A pressure pad 63 that forms a nip portion N is provided between the pressure roll 62 and the pressure roll 62. In the present embodiment, the IH heater 80 is provided on the outer peripheral side of the fixing belt 61.
Furthermore, the fixing unit 60 is provided in contact with the fixing belt 61 on the inner peripheral side of the fixing belt 61, and a temperature-sensitive magnetic member 64 that induces an alternating magnetic field generated by the IH heater 80 to form a magnetic path. Provided on the inner peripheral side of the fixing belt 61 and provided in contact with the temperature-sensitive magnetic member 64, and provided on the inner peripheral side of the fixing belt 61, an induction member 66 that guides the magnetic field lines that have passed through the temperature-sensitive magnetic member 64, A pressing pad 63, a holder 65 that supports the temperature-sensitive magnetic member 64 and the guiding member 66, and a separation assisting member 173 that is provided on the outer peripheral side of the fixing belt 61 and assists the separation of the paper P from the fixing belt 61. In the fixing unit 60 of the present embodiment, the temperature-sensitive magnetic member 64 and the guide member 66 constitute a second magnetic path forming member.

<Description of fixing belt>
FIG. 4 is a diagram illustrating the layer configuration of the fixing belt 61. The fixing belt 61 is formed of an endless belt member having an original cylindrical shape, and has a diameter of 30 mm and a length in the width direction of 370 mm in the original shape (cylindrical shape), for example. As shown in FIG. 4, the fixing belt 61 includes a base material layer 611, a conductive heat generating layer 612 as an example of a conductive layer laminated on the base material layer 611, and a toner image fixing from the inner peripheral side. It is a belt member having a multilayer structure in which an elastic layer 613 for improving the property and a surface release layer 614 coated on the uppermost layer are laminated. Therefore, in the present embodiment, the base material layer 611 is in contact with the temperature-sensitive magnetic member 64 on the inner peripheral side of the fixing belt 61, and the surface release layer 614 is connected to the pressure roll 62 and the IH on the outer peripheral side of the fixing belt 61. Opposite the heater 80.

The base material layer 611 is composed of a heat-resistant sheet-like member that supports the conductive heat generating layer 612 and forms the mechanical strength of the entire fixing belt 61. In addition, the base material layer 611 is made of a material having a physical property (relative magnetic permeability, specific resistance) that allows the magnetic field to pass therethrough so that the AC magnetic field generated by the IH heater 80 acts to the temperature-sensitive magnetic member 64, and the thickness. Formed with. On the other hand, the base material layer 611 itself is configured not to generate heat or hardly generate heat due to the action of a magnetic field.
Specifically, as the base material layer 611, for example, a nonmagnetic metal such as nonmagnetic stainless steel having a thickness of 30 to 200 μm (preferably 50 to 150 μm), a resin material having a thickness of 60 to 200 μm, or the like is used.

The conductive heating layer 612 is an electromagnetic induction heating element layer that is electromagnetically heated by an alternating magnetic field generated by the IH heater 80. That is, the conductive heat generating layer 612 is a layer that generates an eddy current when the AC magnetic field from the IH heater 80 passes in the thickness direction.
In general, a general-purpose power source that can be manufactured at low cost is used as a power source for an excitation circuit 88 (see also FIG. 6 below) that supplies an AC current to the IH heater 80. Therefore, the frequency of the alternating magnetic field generated by the IH heater 80 is generally 20 kHz to 100 kHz by a general-purpose power source. Thereby, the conductive heat generating layer 612 is configured such that an alternating magnetic field having a frequency of 20 kHz to 100 kHz enters and passes therethrough.

The region where the alternating magnetic field can enter the conductive heat generating layer 612 is defined as “skin depth (δ)”, which is a region where the alternating magnetic field attenuates to 1 / e, and is derived from the following equation (1). (1) In the equation, f is the AC magnetic field frequency (e.g., 20 kHz), [rho is resistivity (Omega · m), the mu _r is the relative permeability.
Therefore, the thickness of the conductive heat generating layer 612 is determined by the skin depth (δ) of the conductive heat generating layer 612 defined by the equation (1) so that an AC magnetic field having a frequency of 20 kHz to 100 kHz penetrates and passes through the conductive heat generating layer 612. It is configured to be thinner. Further, as a material constituting the conductive heat generating layer 612, for example, metals such as Au, Ag, Al, Cu, Zn, Sn, Pb, Bi, Be, and Sb, and metal alloys thereof are used.

Specifically, a nonmagnetic metal such as Cu having a thickness of 2 to 20 μm and a specific resistance value of 2.7 × 10 ⁻⁸ Ω · m or less (relative permeability is approximately 1) is used as the conductive heat generating layer 612. .
Also, from the viewpoint of shortening the time required for the fixing belt 61 to be heated to the fixing set temperature (hereinafter referred to as “warm-up time”), the conductive heat generating layer 612 is configured as a thin layer.

Next, the elastic layer 613 is composed of a heat-resistant elastic body such as silicone rubber. The toner image held on the sheet P to be fixed is formed by laminating each color toner as powder. Therefore, in order to supply heat uniformly to the entire toner image at the nip portion N, it is preferable that the surface of the fixing belt 61 is deformed following the unevenness of the toner image on the paper P. Therefore, for example, a silicone rubber having a thickness of 100 to 600 μm and a hardness of 10 ° to 30 ° (JIS-A) is used for the elastic layer 613.
Since the surface release layer 614 is in direct contact with the unfixed toner image held on the paper P, a material having a high release property is used. For example, PFA (tetrafluoroethylene perfluoroalkyl vinyl ether polymer), PTFE (polytetrafluoroethylene), silicone copolymer, or a composite layer thereof is used. If the thickness of the surface release layer 614 is too thin, it is not sufficient in terms of wear resistance, and the life of the fixing belt 61 is shortened. On the other hand, if it is too thick, the heat capacity of the fixing belt 61 becomes too large and the warm-up time becomes long. Therefore, the thickness of the surface release layer 614 is 1 to 50 μm in consideration of the balance between wear resistance and heat capacity.

<Description of pressing pad>
The pressing pad 63 is made of an elastic body such as silicone rubber or fluorine rubber, or a heat resistant resin such as LCP or PPS (polyphenylene sulfide), and has a holder 65 at a position facing the pressure roll 62 as shown in FIG. Supported by The pressing pad 63 is disposed in a state of being pressed from the pressure roll 62 via the fixing belt 61, and forms a nip portion N with the pressure roll 62.
The pressing pad 63 includes a pre-nip region 63a on the inlet side of the nip portion N (upstream side in the conveyance direction of the paper P) and a peeling nip region 63b on the outlet side of the nip portion N (downstream side in the conveyance direction of the paper P). Different nip pressures are set. That is, the press pad 63 is formed in an arc shape in which the surface on the pressure roll 62 side substantially follows the outer peripheral surface of the pressure roll 62 in the pre-nip region 63a, and forms a uniform and wide nip portion N. In addition, the pressing pad 63 is locally pressed from the surface of the pressure roll 62 with a large nip pressure so that the radius of curvature of the fixing belt 61 passing through the peeling nip region 63b becomes small in the peeling nip region 63b. It is formed. Accordingly, the pressing pad 63 forms a curl (down curl) in a direction away from the surface of the fixing belt 61 on the paper P passing through the peeling nip region 63b, and promotes peeling from the surface of the fixing belt 61 with respect to the paper P. Yes.

  In the present embodiment, a peeling assisting member 173 is arranged on the downstream side of the nip portion N as a peeling assisting means by the pressing pad 63. The peeling assisting member 173 includes a peeling baffle 171 that extends toward the fixing belt 61 and a holder 172 that supports the peeling baffle 171 on the downstream side of the nip portion N in the sheet conveyance direction. Then, the curled portion formed on the paper P by the pressing pad 63 at the exit of the nip portion N is supported by the peeling baffle 171, thereby suppressing the paper P from moving toward the fixing belt 61.

<Description of temperature-sensitive magnetic member>
Next, the temperature-sensitive magnetic member 64 will be described. As shown in FIG. 3, the temperature-sensitive magnetic member 64 is formed in an arc shape that follows the inner peripheral surface of the fixing belt 61, and is arranged so that the outer peripheral surface is in contact with the inner peripheral surface of the fixing belt 61. Thereby, the temperature of the temperature-sensitive magnetic member 64 changes corresponding to the temperature of the fixing belt 61, and the temperature-sensitive magnetic member 64 functions as a detection unit that detects the temperature of the fixing belt 61.
The temperature-sensitive magnetic member 64 has a “permeability change start temperature”, which is a temperature at which the magnetic permeability of the magnetic characteristics changes suddenly, equal to or higher than a fixing set temperature at which each color toner image melts, and the elastic layer of the fixing belt 61. It is comprised with the material set in the temperature range lower than the heat-resistant temperature of 613 and the surface release layer 614. FIG. That is, the temperature-sensitive magnetic member 64 is made of a material having a characteristic (“temperature-sensitive magnetism”) that reversibly changes between ferromagnetic and non-magnetic (paramagnetic) in a temperature range including the fixing set temperature. . As a result, the temperature-sensitive magnetic member 64 functions as a magnetic path forming member in a temperature range that is equal to or lower than the permeability change start temperature exhibiting ferromagnetism, and induces the magnetic field lines generated by the IH heater 80 and transmitted through the fixing belt 61 to the inside. Thus, a magnetic path passing through the inside of the temperature-sensitive magnetic member 64 is formed. The temperature-sensitive magnetic member 64 forms a closed magnetic path that encloses the fixing belt 61 and the exciting coil 82 of the IH heater 80 (see FIG. 6 at a later stage). On the other hand, in the temperature range exceeding the permeability change start temperature, the temperature-sensitive magnetic member 64 crosses the magnetic field lines generated by the IH heater 80 and transmitted through the fixing belt 61 in the thickness direction of the temperature-sensitive magnetic member 64. Make it transparent. Thereby, the magnetic lines of force generated by the IH heater 80 and transmitted through the fixing belt 61 form a magnetic path that passes through the temperature-sensitive magnetic member 64, passes through the inside of the guide member 66, and returns to the IH heater 80.

As a material used for the temperature-sensitive magnetic member 64, a binary system such as an Fe—Ni alloy (permalloy), for example, in which a magnetic permeability change start temperature is set in a range of 140 ° C. to 240 ° C. used as a fixing set temperature, for example A ternary temperature-sensitive magnetic alloy such as a temperature-sensitive magnetic alloy or an Fe—Ni—Cr alloy is used. For example, in a Fe-Ni binary temperature-sensitive magnetic alloy, the permeability change start temperature can be set around 220 ° C. to 225 ° C. by using about 64% Fe and 36% Ni (atomic ratio). Such metal alloys such as permalloy and temperature-sensitive magnetic alloy are suitable for the temperature-sensitive magnetic member 64 because they are excellent in moldability and workability, have high heat conductivity, and are inexpensive. As other materials, a metal alloy made of Fe, Ni, Si, B, Nb, Cu, Zr, Co, Cr, V, Mn, Mo or the like is used.
Further, the temperature-sensitive magnetic member 64 is formed with a thickness greater than the skin depth δ (see the above formula (1)) with respect to the AC magnetic field (lines of magnetic force) generated by the IH heater 80. Specifically, for example, when an Fe—Ni alloy is used, the thickness is set to about 50 to 300 μm.

Further, the temperature-sensitive magnetic member 64 of the present embodiment also functions as a heating element, and supplies heat to the fixing belt 61 disposed in contact therewith. Accordingly, the temperature-sensitive magnetic member 64 assists heat generation of the fixing belt 61 that functions as a fixing member for fixing the toner image, and maintains the temperature of the fixing belt 61 during image formation within the range of the fixing set temperature. For example, the temperature-sensitive magnetic member 64 itself generates heat and supplies heat to the fixing belt 61, so that the temperature of the fixing belt 61 that is likely to occur at the start of the fixing operation temporarily drops (so-called “temperature droop phenomenon”). Is suppressed so that the temperature of the fixing belt 61 is stably maintained within the range of the fixing set temperature.
Note that the structure of the temperature-sensitive magnetic member 64 in the present embodiment will be described in detail later.

<Description of holder>
As shown in FIG. 3, the holder 65 is provided on the inner peripheral side of the fixing belt 61 and supports the pressing pad 63, the temperature-sensitive magnetic member 64, and the guide member 66. The holder 65 is made of a material having high rigidity so that the bending amount of the pressing pad 63 becomes a certain amount or less in a state where the pressing pad 63 receives the pressing force from the pressing roll 62. Thereby, the uniformity of the pressure (nip pressure) in the width direction of the fixing belt 61 at the nip portion N is maintained. Furthermore, since the fixing unit 60 according to the present embodiment employs a configuration in which the fixing belt 61 is heated using electromagnetic induction, the holder 65 is made of a material that does not affect or hardly gives influence to the induced magnetic field. It is made of a material that is not affected or hardly affected by the induced magnetic field. For example, a heat-resistant resin such as glass-mixed PPS (polyphenylene sulfide) or a nonmagnetic metal material such as Al, Cu, or Ag is used.

<Description of induction member>
As shown in FIG. 3, the guide member 66 is formed in an arc shape that follows the inner peripheral surface of the temperature-sensitive magnetic member 64, and is disposed in contact with the inner peripheral surface of the temperature-sensitive magnetic member 64. The induction member 66 is made of a nonmagnetic metal having a relatively small specific resistance value, such as Ag, Cu, or Al. Then, when the temperature-sensitive magnetic member 64 rises to a temperature equal to or higher than the permeability change start temperature, an alternating magnetic field (line of magnetic force) generated by the IH heater 80 is induced, and the vortex is more vortexed than the conductive heating layer 612 of the fixing belt 61. A state in which the current I is easily generated is formed. Thereby, the thickness of the induction member 66 is formed with a thickness (for example, 1.0 mm) sufficiently thicker than the skin depth δ (see the above formula (1)) so that the eddy current I flows easily. . In this embodiment, the guide member 66 is formed thicker than the temperature-sensitive magnetic member 64 over the entire width direction of the fixing belt 61.

Furthermore, the induction member 66 functions as a heat storage body that stores heat generated in the temperature-sensitive magnetic member 64 by being disposed in contact with the temperature-sensitive magnetic member 64. The induction member 66 supplies the stored heat to the fixing belt 61 via the temperature-sensitive magnetic member 64, thereby maintaining the temperature of the fixing belt 61 during image formation within the range of the fixing set temperature. That is, the induction member 66 of the present embodiment stores the heat generated by the temperature-sensitive magnetic member 64 and supplies the heat to the fixing belt 61 whose temperature has dropped via the temperature-sensitive magnetic member 64. As a result, for example, the temperature of the fixing belt 61 is stabilized within the range of the fixing set temperature by assisting in suppressing the occurrence of a temporary drop (temperature droop phenomenon) of the fixing belt 61 that is likely to occur at the start of the fixing operation. Function to be maintained.
Note that the structure of the guide member 66 in the present embodiment will be described in detail later.

<Description of Fixing Belt Drive Mechanism>
Next, a driving mechanism for the fixing belt 61 will be described.
As shown in FIG. 2 which is a front view, the fixing belt 61 is rotated in the circumferential direction while maintaining the cross-sectional shape of both ends of the fixing belt 61 in a circular shape at both axial ends of the holder 65 (see FIG. 3). An end cap member 67 to be driven is fixed. The fixing belt 61 directly receives the rotational driving force from both ends via the end cap member 67, and rotates and moves in the direction of arrow C in FIG. 3 at a process speed of 140 mm / s, for example.
5A is a side view of the end cap member 67, and FIG. 5B is a plan view of the end cap member 67 viewed from the VB direction. As shown in FIG. 5, the end cap member 67 has a fixing portion 67 a that is fitted inside the both ends of the fixing belt 61 and has an outer diameter larger than that of the fixing portion 67 a, and is fixed when attached to the fixing belt 61. Rotates through a flange portion 67d formed so as to project radially outward from the belt 61, a gear portion 67b to which rotational driving force is transmitted, a support portion 65a formed at both ends of the holder 65, and a coupling member 166. A bearing bearing portion 67c that is freely coupled is provided. That is, the end cap member 67 has a structure in which the fixing portion 67a, the flange portion 67d, and the gear portion 67b are sequentially arranged from the axial center of the fixing belt 61 to the outside. As shown in FIG. 2, the end cap member 67 is supported by fixing the support portions 65a at both ends of the holder 65 (see FIG. 3) to both ends of the casing 70 of the fixing unit 60. It is rotatably supported via a bearing bearing portion 67c coupled to the portion 65a.
As a material constituting the end cap member 67, so-called engineering plastics having high mechanical strength and heat resistance are used. For example, as a material constituting the end cap member 67, phenol resin, polyimide resin, polyamide resin, polyamideimide resin, PEEK resin, PES resin, PPS resin, LCP resin, or the like is used.

As shown in FIG. 2, in the fixing unit 60, the rotational driving force from the drive motor 90 is transmitted to the shaft 93 via the transmission gears 91 and 92, and both are transmitted from the transmission gears 94 and 95 coupled to the shaft 93. It is transmitted to the gear portion 67b (see FIG. 5) of the end cap member 67. As a result, a rotational driving force is transmitted from the end cap member 67 to the fixing belt 61, and the end cap member 67 and the fixing belt 61 are integrally rotated.
Thus, the fixing belt 61 rotates by receiving the driving force directly from both ends of the fixing belt 61, so that the fixing belt 61 rotates stably.

Here, when the fixing belt 61 rotates by receiving a driving force directly from the end cap members 67 at both ends, a torque of about 0.1 to 0.5 N · m is generally applied. However, in the fixing belt 61 of the present embodiment, the base material layer 611 is made of, for example, nonmagnetic stainless steel having high mechanical strength. For this reason, even when a torsional torque of about 0.1 to 0.5 N · m acts on the entire fixing belt 61, buckling or the like hardly occurs in the fixing belt 61.
Further, the flange portion 67d of the end cap member 67 suppresses the deviation of the fixing belt 61. In general, the fixing belt 61 at that time is generally 1 to 5 in the axial direction from the end portion (flange portion 67d) side. A compressive force of about 5N works. However, even when the fixing belt 61 receives such a compressive force, since the base material layer 611 of the fixing belt 61 is made of nonmagnetic stainless steel or the like, occurrence of buckling or the like is suppressed.
As described above, the fixing belt 61 according to the present embodiment rotates by receiving the driving force directly from both ends of the fixing belt 61, so that stable rotation is performed. At that time, the base material layer 611 of the fixing belt 61 is made of, for example, non-magnetic stainless steel having high mechanical strength, thereby realizing a structure in which buckling or the like hardly occurs against torsion torque or compression force. doing. Furthermore, since the base material layer 611 and the conductive heat generating layer 612 are formed as thin layers to ensure the flexibility / flexibility of the fixing belt 61 as a whole, deformation and shape restoration following the nip portion N are prevented. Done.

<Description of pressure roll>
Returning to FIG. 3, the pressure roll 62 is arranged so as to face the fixing belt 61, and rotates in the direction of arrow D in FIG. 3 at a process speed of 140 mm / s, for example, following the fixing belt 61. Then, a nip portion N is formed in a state where the fixing belt 61 is sandwiched between the pressure roll 62 and the pressing pad 63, and the sheet P holding the unfixed toner image is passed through the nip portion N, so that the heat and pressure To fix the unfixed toner image on the paper P.
The pressure roll 62 includes, for example, a solid aluminum core (cylindrical metal core) 621 having a diameter of 18 mm, and a heat-resistant elastic body layer 622 such as a silicone sponge having a thickness of 5 mm, which is coated on the outer peripheral surface of the core 621. Further, for example, a release layer 623 made of a heat-resistant resin coating such as PFA containing carbon having a thickness of 50 μm or a heat-resistant rubber coating is laminated. The pressure roll 62 presses the pressing pad 63 via the fixing belt 61 with a load of 25 kgf, for example, by a pressing spring 68 (see FIG. 2).

<Description of IH heater>
Next, the IH heater 80 that performs electromagnetic induction heating by applying an AC magnetic field to the conductive heat generating layer 612 of the fixing belt 61 will be described.
FIG. 6 is a cross-sectional view illustrating the configuration of the IH heater 80 of the present embodiment, and FIG. 7 is a stack of the IH heater 80, the fixing belt 61, the temperature-sensitive magnetic member 64, and the induction member 66 in the present embodiment. It is a figure explaining a structure. In FIG. 7, the description of the shield 85 (see FIG. 6) is omitted. FIG. 8 is a diagram for explaining the relationship between the magnetic core 84 (see FIG. 6), the temperature-sensitive magnetic member 64, and the induction member 66 in the IH heater 80. 8 corresponds to the view from the shield 85 side, assuming that the laminated structure of the magnetic core 84, the temperature-sensitive magnetic member 64, and the guide member 66 curved along the outer peripheral shape of the fixing belt 61 is flat. .

As shown in FIG. 6, the IH heater 80 according to the present embodiment is supported by the support 81 provided along the outer peripheral surface of the fixing belt 61, the support 81, and the fixing belt 61 via the support 81. The excitation coil 82 is an example of a magnetic field generating member that generates an alternating magnetic field and is supported by the support 81 and is opposed to the excitation coil 82, and is generated by the excitation coil 82. The magnetic core 84 which forms the magnetic path of a magnetic field is provided. In addition, the IH heater 80 of the present embodiment is provided on the excitation coil 82 and is attached to the elastic support member 83 and the support body 81 for fixing the excitation coil 82 on the support body 81. A shield 85 provided to surround the member 83 and the magnetic core 84, shields the magnetic field, is provided between the magnetic core 84 and the shield 85, pressurizes the magnetic core 84 toward the support 81, and an alternating current to the excitation coil 82 An excitation circuit 88 for supplying current is provided.
Further, the IH heater 80 of the present embodiment is opposed to the temperature-sensitive magnetic member 64 and the guide member 66 provided on the inner peripheral side of the fixing belt 61 via the fixing belt 61 (see FIG. 3).

As shown in FIG. 7, the support 81 of the IH heater 80 in this embodiment has a longitudinal direction in the direction perpendicular to the moving direction of the fixing belt 61 (hereinafter referred to as the width direction of the fixing belt 61). The belt 61 is provided to face the fixing belt 61 over the entire width of the belt 61.
Further, the support 81 is formed in a shape whose cross section is curved along the surface shape of the fixing belt 61, and an upper surface (support surface) 81 a (see FIG. 6) for supporting the exciting coil 82 is in advance with the surface of the fixing belt 61. It is set so as to maintain a predetermined gap (for example, 0.5 to 2 mm).
Further, as shown in FIG. 6, the support 81 has a pair of magnetic core support portions arranged in parallel along the width direction of the fixing belt 61 at the center portion in the moving direction of the fixing belt 61 on the support surface 81a. 81b and a magnetic core restricting portion 81c that is disposed at both ends of the support surface 81a in the moving direction of the fixing belt 61 and contacts the magnetic core 84 to restrict the position of the magnetic core 84 in the moving direction of the fixing belt 61. ing. The pair of magnetic core support portions 81b can move the magnetic core 84 forward and backward in the moving direction of the fixing belt 61 between the two magnetic core regulating portions 81c provided at both ends of the supporting surface 81a in the moving direction of the fixing belt 61. To support. As a result, the support 81 has a gap between the magnetic core 84 and the support surface 81a, the shape of which tends to vary due to heat treatment during manufacturing, in the upstream region and the downstream region centering on the central portion in the moving direction of the fixing belt 61. The magnetic core 84 is supported so as to be substantially symmetric.
Examples of the material constituting the support 81 include heat-resistant resins such as heat-resistant glass, polycarbonate, polyethersulfone, and PPS (polyphenylene sulfide), or heat-resistant resins obtained by mixing glass fibers with these materials. A non-magnetic material is used.

The exciting coil 82 is composed of, for example, 90 litz wires that are bundled with, for example, 90 copper wires having a diameter of 0.17 mm and are formed in an oval shape, an elliptical shape, or a rectangular shape in which the width direction of the fixing belt 61 is the longitudinal direction. It is configured to be wound in a closed loop with a hollow space. The excitation coil 82 is disposed on the support surface 81a of the support 81 so that the magnetic core support portion 81b of the support 81 protrudes from the empty portion of the excitation coil 82. Then, when an alternating current having a predetermined frequency is supplied to the exciting coil 82 from the exciting circuit 88, an alternating magnetic field centered around a litz wire wound in a closed loop is generated around the exciting coil 82. . Generally, the frequency of the alternating current supplied from the excitation circuit 88 to the excitation coil 82 is 20 to 100 kHz generated by the general-purpose power source.
The elastic support member 83 is a sheet-like member made of an elastic body such as silicone rubber or fluorine rubber. The elastic support member 83 is set to press the excitation coil 82 against the support 81 so that the excitation coil 82 is fixed in close contact with the support surface 81a of the support 81.

As shown in FIG. 7, the magnetic core 84 (see FIG. 6) has a plurality of magnetic core pieces 84 a as an example of a plurality of first magnetic path forming members such that there are spaces between adjacent magnetic core pieces 84 a. The fixing belt 61 is arranged side by side in the width direction. Each of the plurality of magnetic core pieces 84 a constituting the magnetic core 84 has a cross-sectional shape that is curved along the cross-sectional shape of the fixing belt 61 and an arcuate shape in which the moving direction of the fixing belt 61 is a longitudinal direction. Yes. The plurality of magnetic core pieces 84a are positioned by a magnetic core support portion 81b and a magnetic core restricting portion 81c provided on the support body 81, respectively.
8, the length of the magnetic core piece 84a along the moving direction of the fixing belt 61 is smaller than the length of the temperature-sensitive magnetic member 64 and the guiding member 66 along the moving direction of the fixing belt 61. Is done. As a result, leakage of magnetic lines of force H (see FIG. 9 described later) radiated from the magnetic core piece 84a constituting the magnetic core 84 to the periphery of the IH heater 80 is reduced, and the power factor is improved. Furthermore, electromagnetic induction to the metal member constituting the fixing unit 60 is suppressed, and the heat generation efficiency of the fixing belt 61 (conductive heat generation layer 612) is increased.

  Examples of the material for forming the magnetic core piece 84a constituting the magnetic core 84 include oxides or alloy materials having high magnetic permeability such as soft ferrite, ferrite resin, amorphous alloy (amorphous alloy), permalloy, and temperature-sensitive magnetic alloy. A composed ferromagnetic material is used. The magnetic core piece 84a induces a magnetic force line H (magnetic flux) due to the alternating magnetic field generated by the exciting coil 82, and crosses the fixing belt 61 from the magnetic core piece 84a via the support 81 in the direction of the temperature-sensitive magnetic member 64. A path (magnetic path) of lines of magnetic force H is formed so as to pass through the temperature-sensitive magnetic member 64 and return to the magnetic core piece 84a via the support 81. That is, the AC magnetic field generated by the exciting coil 82 is configured to pass through the inside of the magnetic core piece 84a and the inside of the temperature-sensitive magnetic member 64, and the magnetic field line H brings the fixing belt 61 and the exciting coil 82 into the inside. A closed magnetic circuit that wraps around is formed. As a result, the magnetic field lines H of the alternating magnetic field generated by the exciting coil 82 are concentrated on the region of the fixing belt 61 facing the magnetic core piece 84a.

<Description of the state in which the fixing belt generates heat>
Subsequently, a state in which the fixing belt 61 generates heat by the alternating magnetic field generated by the IH heater 80 will be described.
First, as described above, the permeability change start temperature of the temperature-sensitive magnetic member 64 is within a temperature range that is not less than the set fixing temperature for fixing each color toner image and not more than the heat resistance temperature of the fixing belt 61 (for example, 140 to 240 ° C.). When the temperature of the fixing belt 61 is equal to or lower than the magnetic permeability change start temperature, the temperature of the temperature-sensitive magnetic member 64 adjacent to the fixing belt 61 is also started corresponding to the temperature of the fixing belt 61. Below temperature. Therefore, since the temperature-sensitive magnetic member 64 exhibits ferromagnetism, the magnetic field lines H of the alternating magnetic field generated by the IH heater 80 pass through the fixing belt 61 and then pass through the inside of the temperature-sensitive magnetic member 64 along the spreading direction. To form a magnetic path. Here, the “spreading direction” means a direction orthogonal to the thickness direction of the temperature-sensitive magnetic member 64.

  FIG. 9 is a diagram for explaining the state of the lines of magnetic force H when the temperature of the fixing belt 61 is in the temperature range equal to or lower than the permeability change start temperature. As shown in FIG. 9, when the temperature of the fixing belt 61 is in a temperature range equal to or lower than the permeability change start temperature, the magnetic field lines H of the alternating magnetic field generated by the IH heater 80 pass through the fixing belt 61, A magnetic path passing through the inside of the temperature-sensitive magnetic member 64 along the spreading direction (direction orthogonal to the thickness direction) is formed. Therefore, as compared with the case where the temperature of the fixing belt 61 is in a temperature range higher than the permeability change start temperature, the number of magnetic field lines H per unit area (magnetic flux density) in the region crossing the conductive heating layer 612 of the fixing belt 61. ) Will increase.

  That is, after the magnetic force line H is radiated from the magnetic core piece 84a of the magnetic core 84 in the IH heater 80 and passes through the regions R1 and R2 crossing the conductive heating layer 612 of the fixing belt 61, the magnetic force line H is a ferromagnetic temperature sensitive magnetic member. 64 is guided inside. Therefore, the magnetic field lines H crossing the conductive heat generating layer 612 of the fixing belt 61 in the thickness direction are concentrated so as to enter the inside of the temperature-sensitive magnetic member 64, and the magnetic flux density in the regions R1 and R2 is the same as the magnetic flux density in other regions. It becomes high compared. Further, when the magnetic lines H that have passed through the inside of the temperature-sensitive magnetic member 64 along the spreading direction return to the magnetic core piece 84a again, the magnetic lines of force H are generated in the region R3 that crosses the conductive heating layer 612 in the thickness direction. The magnetic flux is generated from a portion having a low magnetic potential in 64 toward the magnetic core piece 84a. Therefore, the magnetic field lines H crossing the conductive heat generating layer 612 of the fixing belt 61 in the thickness direction are concentrated from the temperature-sensitive magnetic member 64 toward the magnetic core piece 84a, and the magnetic flux density in the region R3 is also the magnetic flux density of other regions. Higher than

In the conductive heating layer 612 of the fixing belt 61 where the magnetic lines H cross in the thickness direction, an eddy current I proportional to the amount of change in the number of magnetic lines H per unit area (magnetic flux density) is generated. As a result, as shown in FIG. 9, an eddy current I larger than the other regions is generated in the regions R1, R2 and R3 where the amount of change in the magnetic flux density is larger than the other regions. The eddy current I generated in the conductive heat generation layer 612 generates Joule heat W (W = I ² R), which is the product of the specific resistance value R of the conductive heat generation layer 612 and the square of the eddy current I. As a result, in the regions R1, R2, and R3 of the conductive heating layer 612 where the eddy current I larger than that in the other region is generated, a Joule heat W that is larger than that in the other region is generated.
As described above, when the temperature of the fixing belt 61 is in the temperature range equal to or lower than the magnetic permeability change start temperature, the region R1, R2 and the region R3 where the magnetic lines of force H cross the conductive heat generating layer 612 have a larger heat than the other regions. Occur. Thereby, the fixing belt 61 is heated.

  In the fixing unit 60 of the present embodiment, the temperature-sensitive magnetic member 64 is disposed in contact with the inner peripheral surface of the fixing belt 61. Accordingly, a magnetic core 84 (magnetic core piece 84a) for guiding the magnetic force lines H generated by the exciting coil 82 to the inside, and a temperature-sensitive magnetic member for guiding the magnetic force lines H transmitted through the fixing belt 61 in the thickness direction to the inside. 64 realizes a configuration close to 64. For this reason, the AC magnetic field generated by the IH heater 80 (excitation coil 82) forms a loop with a short magnetic path, so that the magnetic flux density and the magnetic coupling degree in the magnetic path increase. Accordingly, when the temperature of the fixing belt 61 is in a temperature range equal to or lower than the magnetic permeability change start temperature, heat is more efficiently generated in the fixing belt 61.

  Further, when the temperature of the fixing belt 61 is in a temperature range higher than the magnetic permeability change start temperature, the temperature of the temperature-sensitive magnetic member 64 is also higher than the magnetic permeability change start temperature. Magnetic susceptibility decreases. Therefore, the magnetic field line H of the alternating magnetic field generated by the exciting coil 82 of the IH heater 80 changes so as to easily pass through the temperature-sensitive magnetic member 64. Thereby, the magnetic field lines H of the alternating magnetic field generated by the exciting coil 82 are radiated so as to diffuse toward the fixing belt 61 from the magnetic core 84 (magnetic core piece 84a), pass through the temperature-sensitive magnetic member 64, and pass through the induction member 66. To come to reach.

On the other hand, in the induction member 66 to which the magnetic force line H that has passed through the temperature-sensitive magnetic member 64 has reached, an eddy current that generates a magnetic force line in a direction that cancels the magnetic force line H is generated. Then, the magnetic lines of force generated by the eddy current generated in the induction member 66 and the magnetic lines of force H transmitted through the temperature-sensitive magnetic member 64 and reaching the induction member 66 cancel each other.
Therefore, when the temperature of the fixing belt 61 is in a temperature range exceeding the permeability change start temperature, the magnetic flux density of the magnetic field lines H crossing the conductive heat generating layer 612 in the thickness direction decreases. As a result, the eddy current I generated in the conductive heating layer 612 where the magnetic field lines H cross in the thickness direction is reduced, and the Joule heat W generated in the fixing belt 61 is reduced. Thereby, the temperature rise of the fixing belt 61 is suppressed.

  Further, part of the magnetic force lines H that have passed through the temperature-sensitive magnetic member 64 and reached the guide member 66 are guided into the guide member 66. When the magnetic field lines H are induced inside the induction member 66, more eddy current I flows through the induction member 66 where the eddy current I flows more easily than the conductive heating layer 612 of the fixing belt 61. Therefore, the amount of eddy current I flowing in the conductive heat generating layer 612 is further suppressed, and the temperature rise of the fixing belt 61 is further suppressed.

  Thereafter, when the temperature of the fixing belt 61 becomes lower than the magnetic permeability change start temperature, the temperature of the temperature-sensitive magnetic member 64 also becomes lower than the magnetic permeability change start temperature, so that the temperature-sensitive magnetic member 64 changes to ferromagnetic again. As a result, the lines of magnetic force H are again induced inside the temperature-sensitive magnetic member 64, so that a large amount of eddy current I flows through the conductive heat generating layer 612 of the fixing belt 61. Therefore, the fixing belt 61 is heated again.

Here, as shown in FIGS. 7 and 8, in the IH heater 80 of the present embodiment, the magnetic core 84 (see FIG. 6) is arranged along the longitudinal direction of the exciting coil 82 (width direction of the fixing belt 61). Is formed of a plurality of magnetic core pieces 84a.
In the present embodiment, a region of the rotating fixing belt 61 that passes through a portion facing the magnetic core piece 84a via the exciting coil 82 is referred to as a first region S1, and among the rotating fixing belt 61, A region that is provided adjacent to the region S1 and passes through a portion that does not face the magnetic core piece 84a via the exciting coil 82 is referred to as a second region S2. Therefore, as shown in FIG. 7, in the fixing belt 61 of the present embodiment, the first regions S1 and the second regions S2 are alternately arranged in the width direction of the fixing belt 61. FIG. 8 shows an area corresponding to the first area S <b> 1 and an area corresponding to the second area S <b> 2 set on the fixing belt 61.

As described above, when the temperature of the fixing belt 61 is in the temperature range equal to or lower than the permeability change start temperature, the magnetic lines of force H are emitted from the magnetic core 84 (magnetic core piece 84a), and the conductive heating layer 612 of the fixing belt 61 is passed through. After passing the crossing temperature-sensitive magnetic member 64, the magnetic head 84 (magnetic core piece 84a) is again directed. Therefore, in the fixing belt 61, the first region S1 that passes through the portion facing the magnetic core piece 84a via the exciting coil 82 is the second region that passes through the portion that does not face the magnetic piece 84a via the exciting coil 82. Compared with the region S2, the lines of magnetic force H concentrate on the conductive heat generating layer 612, and the magnetic flux density tends to be high. In the conductive heat generating layer 612 of the fixing belt 61, the eddy current I is more likely to occur in the first region S1 than the second region S2, and the Joule heat W is likely to occur.
As a result, in the fixing belt 61, the temperature in the first region S1 is more likely to rise than in the second region S2, and thus the temperature unevenness occurs between the first region S1 and the second region S2 in the fixing belt 61. It tends to be easier.

<Description of Configuration for Preventing Temperature Unevenness in Fixing Belt>
In this case, in order to suppress the occurrence of temperature unevenness in the fixing belt 61, the interval between the adjacent magnetic core pieces 84a is made narrow so that the magnetic core pieces 84a are spread over the longitudinal direction of the exciting coil 82. For example, a configuration in which the magnetic core 84 is formed or a configuration in which the magnetic core 84 is integrally formed over the longitudinal direction of the exciting coil 82 may be employed. However, with such a configuration, the weight of the entire IH heater 80 is increased, and the manufacturing cost is also expensive. Further, when the magnetic core 84 is formed of ferrite, the shape of the magnetic core 84 is likely to vary due to the heat treatment after molding, and it is difficult to increase the dimensional accuracy of the magnetic core 84. Therefore, when the magnetic core 84 is formed by spreading the magnetic core pieces 84 a over the longitudinal direction of the excitation coil 82, or when the magnetic core 84 is integrated with the longitudinal direction of the excitation coil 82, Variation in the distance between the magnetic core 84 and the exciting coil 82 tends to increase along the longitudinal direction. As a result, the lines of magnetic force supplied to the fixing belt 61 become non-uniform, and the amount of heat generated by the fixing belt 61 also varies in the width direction of the fixing belt 61, which may cause uneven temperature in the fixing belt 61.

  Therefore, in the fixing unit 60 of the present embodiment, in the guide member 66 provided on the inner peripheral side of the fixing belt 61, the heat capacity of the portion through which the first region S1 of the fixing belt 61 passes is determined as the second region of the fixing belt 61. By making it larger than the heat capacity of the portion through which S2 passes, the occurrence of temperature unevenness in the fixing belt 61 is suppressed.

As described above, the temperature-sensitive magnetic member 64 also functions as a heating element, and supplies heat to the fixing belt 61 arranged in contact with it to assist the amount of heat generated by the fixing belt 61.
That is, even if the temperature of the fixing belt 61 is equal to or lower than the permeability change start temperature and the temperature-sensitive magnetic member 64 exhibits ferromagnetism, the temperature-sensitive magnetic member 64 is included in the magnetic force lines H from the IH heater 80. There is a magnetic field line H crossing in the thickness direction. Thereby, a weak eddy current I is generated inside the temperature-sensitive magnetic member 64, and the temperature-sensitive magnetic member 64 itself also generates heat. In that case, the temperature-sensitive magnetic member 64 of the present embodiment is configured such that the temperature-sensitive magnetic member 64 actively generates heat without providing a mechanism for suppressing the eddy current I such as a slit. Then, the arc-shaped temperature-sensitive magnetic member 64 is arranged so as to be in contact with the fixing belt 61 having an arc-shaped inner peripheral surface in a large area region, and the heat generated in the temperature-sensitive magnetic member 64 is fixed. The belt 61 is configured to transfer heat. Thereby, the temperature-sensitive magnetic member 64 supplies heat to the fixing belt 61.
At that time, the heat generated in the temperature-sensitive magnetic member 64 is conducted to the induction member 66 arranged in contact with the temperature-sensitive magnetic member 64, and the induction member 66 serves as a heat storage material for storing the heat. It has a function. Further, the induction member 66 supplies the heat stored from the temperature-sensitive magnetic member 64 to the fixing belt 61 via the temperature-sensitive magnetic member 64.

The amount of heat supplied from the induction member 66 to the fixing belt 61 via the temperature-sensitive magnetic member 64 depends on the heat capacity of the induction member 66 provided in contact with the temperature-sensitive magnetic member 64. That is, as the heat capacity of the induction member 66 increases, the amount of heat stored in the induction member 66 out of the heat generated in the temperature-sensitive magnetic member 64 increases, and accordingly, the heat generated in the temperature-sensitive magnetic member 64 increases. Of this, the amount of heat supplied to the fixing belt 61 is reduced. Conversely, the smaller the heat capacity of the induction member 66, the smaller the amount of heat stored in the induction member 66 out of the heat generated in the temperature-sensitive magnetic member 64. The amount of heat supplied to the belt 61 increases.
Therefore, in the fixing unit 60 of the present embodiment, Joule heat W is generated in the conductive heat generation layer 612 in the guide member 66 provided on the inner peripheral side of the fixing belt 61 as compared with the second region S2 of the fixing belt 61. By making the heat capacity of the portion of the fixing belt 61 through which the first region S1 of the fixing belt 61 easily passes the temperature larger than the portion of the fixing belt 61 through which the second region S2 of the fixing belt 61 passes, Occurrence is suppressed.

Here, the guide member 66 of the present embodiment is integrally formed over the width direction of the fixing belt 61 and is formed of the same nonmagnetic metal material over the width direction of the fixing belt 61. Yes. Therefore, by fixing the volume of the guide member 66 in the portion through which the first region S1 of the fixing belt 61 passes is larger than the volume of the guide member 66 in the portion of the fixing belt 61 through which the second region S2 passes. The heat capacity of the part through which the first region S1 passes can be made larger than the heat capacity of the part through which the second region S2 of the fixing belt 61 passes.
In the description of the present embodiment, “volume” refers to the volume per unit length of the guide member 66 along the width direction of the fixing belt 61. Similarly, “heat capacity” refers to the heat capacity per unit length of the guide member 66 along the width direction of the fixing belt 61.

Subsequently, in the present embodiment, the heat capacity of the portion through which the first region S1 of the fixing belt 61 passes is made larger than the heat capacity of the portion of the guide member 66 through which the second region S2 of the fixing belt 61 passes. The configuration will be described.
As shown in FIG. 7, the guide member 66 of the present embodiment is formed in a shape that follows the inner peripheral surface of the temperature-sensitive magnetic member 64. The outer peripheral surface of the guide member 66 is disposed in contact with the inner peripheral surface of the temperature-sensitive magnetic member 64. In the present embodiment, the guide member 66 is integrally formed across the width direction of the fixing belt 61.
Furthermore, the guide member 66 of the present embodiment is configured such that the thickness of the portion through which the first region S1 of the fixing belt 61 passes and the portion through which the second region S2 pass are equal.
Furthermore, as shown in FIGS. 7 and 8, the guide member 66 of the present embodiment has a notch formed upstream in the movement direction of the fixing belt 61 at a portion through which the second region S <b> 2 of the fixing belt 61 passes. Has been. As a result, the guide member 66 of the present embodiment has a long diameter portion 66a whose length along the moving direction of the fixing belt 61 is the first length at a portion through which the first region S1 of the fixing belt 61 passes. In addition, a portion of the fixing belt 61 through which the second region S2 passes has a short diameter portion 66b having a second length shorter than the first length along the moving direction of the fixing belt 61. .

Since the guide member 66 of the present embodiment has the above-described configuration, the long diameter portion 66a through which the first region S1 of the fixing belt 61 passes is more than the short diameter portion 66b through which the second region S2 of the fixing belt 61 passes. Also increases in volume.
As a result, in the present embodiment, in the guide member 66, the long diameter portion 66a through which the first region S1 of the fixing belt 61 passes has a heat capacity greater than the short diameter portion 66b through which the second region S2 of the fixing belt 61 passes. growing. Therefore, as compared with the case where this configuration is not provided, the amount of heat supplied from the long diameter portion 66a of the guide member 66 to the first region S1 of the fixing belt 61 is greater than the short diameter portion 66b of the guide member 66. The amount of heat supplied to the second region S2 of 61 becomes smaller.
As described above, in the present embodiment, it is possible to suppress the occurrence of temperature unevenness in the first region S1 and the second region S2 of the fixing belt 61 as compared with the case where this configuration is not provided. .

  Further, as shown in FIGS. 7 and 8, the temperature-sensitive magnetic member 64 of the present embodiment has a notch on the upstream side in the moving direction of the fixing belt 61 at a portion where the second region S2 of the fixing belt 61 passes. Is formed. As a result, the temperature-sensitive magnetic member 64 of the present embodiment has a long-diameter portion 64a in which the length along the moving direction of the fixing belt 61 is the third length at the portion through which the first region S1 of the fixing belt 61 passes. And a short diameter portion 64b having a length along the moving direction of the fixing belt 61 that is a fourth length shorter than the third length at a portion through which the second region S2 of the fixing belt 61 passes. ing.

In the present embodiment, the outer periphery of the induction member 66 is disposed in contact with the inner peripheral side of the temperature-sensitive magnetic member 64, and the short-diameter portion 64 b of the temperature-sensitive magnetic member 64 and the short-diameter portion of the induction member 66 are arranged. 66b overlap, and the long diameter portion 64a of the temperature-sensitive magnetic member 64 and the long diameter portion 66a of the guide member 66 overlap each other. As a result, a notched portion 69 in which both the temperature-sensitive magnetic member 64 and the guiding member 66 are notched is formed at a portion through which the second region S2 of the fixing belt 61 passes.
In the fixing unit 60 of the present embodiment, the long diameter portion 66a of the guide member 66 and the long diameter portion 64a of the temperature-sensitive magnetic member 64 constitute a first portion of the second magnetic path forming member. The short diameter portion 66b and the short diameter portion 64b of the temperature-sensitive magnetic member 64 constitute a second part of the second magnetic path forming member.

  In the present embodiment, the notch 69 is formed by notching both the temperature-sensitive magnetic member 64 and the guide member 66 at the portion through which the second region S2 of the fixing belt 61 passes. The unit 69 includes a thermistor (not shown) that detects the temperature of the fixing belt 61 and a thermoswitch (not shown) that cuts off the supply of power to the fixing unit 60 when the temperature of the fixing belt 61 rises abnormally. Can be provided. Accordingly, it is possible to save the space of the fixing unit 60 as compared with the case where a thermistor or a thermo switch is installed in addition to the notch portion 69. Further, in this embodiment, in order to install the thermistor and the thermo switch, it is not necessary to further cut out the temperature-sensitive magnetic member 64 and the induction member 66 in addition to the notch portion 69, and in order to install the thermistor and the thermo switch. It is possible to suppress the occurrence of temperature unevenness in the fixing belt 61 due to the cutout of the temperature-sensitive magnetic member 64 and the guide member 66.

Further, in the present embodiment, the length along the moving direction of the fixing belt 61 in the magnetic core piece 84a is the moving direction of the fixing belt 61 in the long diameter portion 64a of the temperature-sensitive magnetic member 64 and the long diameter portion 66a of the guide member 66. Shorter than the length along. Both end portions of the magnetic core piece 84a along the moving direction of the fixing belt 61 are both end portions of the long diameter portion 64a of the temperature-sensitive magnetic member 64 and the long diameter portion 66a of the guiding member 66 along the moving direction of the fixing belt 61. It is provided inside.
Thereby, it can suppress that the magnetic force line H (refer FIG. 9) radiated | emitted from the magnetic core piece 84a leaks around IH heater 80, and a power factor improves. Furthermore, electromagnetic induction to the metal member constituting the fixing unit 60 can be suppressed, and the heat generation efficiency of the fixing belt 61 (conductive heat generation layer 612) can be increased.

In the present embodiment, the long diameter portion 64 a and the short diameter portion 64 b are formed in the temperature-sensitive magnetic member 64, and the long diameter portion 66 a and the short diameter portion 66 b are formed in the guide member 66. However, for example, in the temperature-sensitive magnetic member 64, the long diameter portion 66a and the short diameter portion 66b may be formed only in the guide member 66 without forming the long diameter portion 64a and the short diameter portion 64b.
In the present embodiment, the guide member 66 has a long diameter portion 66a and a short diameter at the portion of the guide member 66 through which the second region S2 of the fixing belt 61 passes by notching the upstream side in the moving direction of the fixing belt 61. Part 66b was formed. However, the location where the guide member 66 is not cut is not limited to this, and the downstream side in the moving direction of the fixing belt 61 may be cut out at a portion of the guide member 66 where the second region S2 of the fixing belt 61 passes. The long diameter portion 66a and the short diameter portion 66b may be formed by cutting out both the upstream side and the downstream side in the moving direction.

Further, in the present embodiment, the guide member 66 is cut into a rectangular shape at a portion through which the second region S2 of the fixing belt 61 passes, so that the guide member 66 has a rectangular long diameter portion 66a and a rectangular short diameter portion. 66b was formed. However, the shape of the long diameter portion 66a and the shape of the short diameter portion 66b of the guide member 66 are not limited to a rectangle, and any shape such as a triangular shape or a semicircular shape can be adopted.
Further, in the present embodiment, the width along the width direction of the fixing belt 61 in the long diameter portion 66a of the guide member 66, and the width along the width direction of the fixing belt 61 in the first region S1 of the fixing belt 61 And the width along the width direction of the fixing belt 61 in the short diameter portion 66b of the guide member 66 is made equal to the width along the width direction of the fixing belt 61 in the second region S2 of the fixing belt 61. . However, the width of the long diameter portion 66a and the short diameter portion 66b in the guide member 66 is not limited to this. For example, in the guide member 66, it is sufficient if the short diameter portion 66b is formed at least at a part of the part through which the second region S2 of the fixing belt 61 passes.

  In the present embodiment, the guide member 66 is notched at the portion through which the second region S2 of the fixing belt 61 passes, so that the guide member 66 has the long diameter portion 66a and the short diameter portion 66b. However, the method of forming the long diameter portion 66a and the short diameter portion 66b in the guide member 66 is not limited to this. For example, in the guide member 66, the long diameter portion 66a and the short diameter portion 66b may be formed in the guide member 66 by a method such as stretching the material of the portion through which the first region S1 of the fixing belt 61 passes.

  Furthermore, in the present embodiment, the first region of the fixing belt 61 has a lower capacity in the portion of the guide member 66 that faces the second region S2 than the portion of the fixing belt 61 that faces the first region S1. A long diameter portion 66a is formed at a portion facing S1, and a short diameter portion 66b is formed at a portion facing the second region S2 of the fixing belt 61. However, for example, in the guide member 66, by providing a hole in a portion facing the second region S2 of the fixing belt 61, a portion facing the second region S2 rather than a portion facing the first region S1 of the fixing belt 61. And the heat capacity of the portion facing the second region S2 may be made smaller than the portion facing the first region S1 of the fixing belt 61.

[Embodiment 2]
Next, a second embodiment of the present invention will be described.
In the first embodiment, in the guide member 66, the long diameter portion 66a is formed at a portion facing the first region S1 of the fixing belt 61, and the short diameter portion 66b is formed at a portion facing the second region S2 of the fixing belt 61. Then, by making the volume of the portion through which the first region S1 of the fixing belt 61 passes is larger than the volume of the portion through which the second region S2 passes, the heat capacity of the portion through which the first region S1 of the fixing belt 61 passes is obtained. The configuration has been described in which the heat capacity of the portion where the second region S2 of the fixing belt 61 passes is made larger and the occurrence of temperature unevenness in the fixing belt 61 is suppressed.
In the present embodiment, the length of the guide member 66 along the moving direction of the fixing belt 61 is equal between the portion through which the first region S1 passes and the portion through which the second region S2 passes. In addition, the unevenness of temperature in the fixing belt 61 is suppressed by making the thickness of the guide member 66 different between the portion through which the first region S1 of the fixing belt 61 passes and the portion through which the second region S2 passes. The structure to perform is demonstrated.
In addition, the same code | symbol is used about the structure similar to Embodiment 1, and the detailed description is abbreviate | omitted here.

  FIG. 10 is a perspective view for explaining a laminated structure of the IH heater 80 (see FIG. 7), the fixing belt 61, the temperature-sensitive magnetic member 64, and the induction member 66 in the present embodiment, and FIG. 11 shows the present embodiment. 8 is a cross-sectional view illustrating a laminated structure of an IH heater 80 (see FIG. 7), a fixing belt 61, a temperature-sensitive magnetic member 64, and an induction member 66 in FIG. 11 corresponds to the XI-XI cross section of FIG. In FIG. 10, the description of the shield 85 is omitted, and in FIG. 11, the description of the support 81, the elastic support member 83, and the shield 85 is omitted.

As shown in FIG. 10, the temperature-sensitive magnetic member 64 of the present embodiment is formed in an arc shape that follows the inner peripheral surface of the fixing belt 61, and the outer peripheral surface of the temperature-sensitive magnetic member 64 is the inner surface of the fixing belt 61. It is provided in contact with the peripheral surface.
Further, as shown in FIG. 10, the guide member 66 of the present embodiment is formed in a shape that follows the inner peripheral surface of the temperature-sensitive magnetic member 64. The outer peripheral surface of the guide member 66 is provided in contact with the inner peripheral surface of the temperature-sensitive magnetic member 64. Further, the guide member 66 of the present embodiment is integrally configured across the width direction of the fixing belt 61 and is formed of the same nonmagnetic metal across the width direction of the fixing belt 61.

In the guide member 66 of the present embodiment, the length along the moving direction of the fixing belt 61 is equal between the portion through which the first region S1 of the fixing belt 61 passes and the portion through which the second region S2 passes. Composed.
Further, as shown in FIG. 11, the guide member 66 of the present embodiment is in contact with the temperature-sensitive magnetic member 64 along the moving direction of the fixing belt 61 at a portion through which the first region S1 of the fixing belt 61 passes. By projecting to the opposite side to the side, a thick portion 66c having a thickness of the first thickness is provided, and along the moving direction of the fixing belt 61 at a portion through which the second region S2 of the fixing belt 61 passes. And a thin portion 66d having a second thickness that is smaller than the first thickness.
In the fixing unit 60 of the present embodiment, the first portion is configured by the thick portion 66 c of the guide member 66 and the portion of the temperature-sensitive magnetic member 64 that contacts the thick portion 66 c of the guide member 66. The second portion is configured by the thin portion 66d and the portion of the temperature-sensitive magnetic member 64 that contacts the thin portion 66d of the guide member 66.

In the guide member 66 of the present embodiment, the thick portion 66c and the thin portion 66d are formed so that the lengths along the moving direction of the fixing belt 61 are equal, and therefore the guide member 66 of the present embodiment. With the above configuration, the thick portion 66c has a larger volume than the thin portion 66d.
Thereby, in this Embodiment, since the heat capacity of the thick part 66c becomes larger than the thin part 66d in the guide member 66, compared with the case where this structure is not provided, the thick part of the guide member 66 The amount of heat supplied from 66c to the first region S1 of the fixing belt 61 is smaller than the amount of heat supplied from the thin portion 66d of the guide member 66 to the second region S2 of the fixing belt 61.
Accordingly, it is possible to suppress the occurrence of temperature unevenness in the first region S1 and the second region S2 of the fixing belt 61.

  In the guide member 66 of the present embodiment, the thickness of the thick portion 66c is, for example, 0.8 to 1.2 mm, and the thickness of the thin portion 66d is, for example, 0.4 to 0.6 mm. . Further, the guide member 66 of the present embodiment is formed thicker than the temperature-sensitive magnetic member 64 over the entire width direction of the fixing belt 61.

Here, as a method of forming the thick portion 66 c and the thin portion 66 d in the guide member 66, for example, a drawing press method, or the thickness becomes the first thickness in the width direction of the fixing belt 61. For example, a method of forming the thick portion 66c and the thin portion 66d by cutting a portion through which the second region S2 of the fixing belt 61 passes is formed with respect to the base portion formed as described above.
In addition, another member is bonded to a portion where the first region S1 of the fixing belt 61 passes through a base portion having a thickness of the second thickness over the width direction of the fixing belt 61. The thick part 66c and the thin part 66d may be formed. In this case, from the viewpoint of adhesion and the like, it is preferable that the base portion of the guide member 66 and the other members bonded to the base portion are made of the same material.

  Further, in the present embodiment, the width along the width direction of the fixing belt 61 in the thick portion 66c of the guide member 66 and the width along the width direction of the fixing belt 61 in the first region S1 of the fixing belt 61. And the width along the width direction of the fixing belt 61 in the thin portion 66d of the guide member 66 and the width along the width direction of the fixing belt 61 in the second region S2 of the fixing belt 61 are equalized. . However, the width of the thick portion 66c and the thin portion 66d in the guide member 66 is not limited to this. For example, in the guiding member 66, it is sufficient if the thick portion 66c is formed in at least a portion of the portion through which the first region S1 of the fixing belt 61 passes.

In the first embodiment, in the guide member 66, the length along the traveling direction of the fixing belt 61 in the portion through which the first region S1 of the fixing belt 61 passes is larger than the portion through which the second region S2 of the fixing belt 61 passes. The configuration that suppresses the occurrence of temperature unevenness in the first region S1 and the second region S2 of the fixing belt 61 by increasing the length has been described. Further, in the second embodiment, the guide member 66 is fixed by increasing the thickness of the portion of the fixing belt 61 through which the first region S1 passes rather than the portion of the fixing belt 61 through which the second region S2 passes. The configuration for suppressing the occurrence of temperature unevenness in the first region S1 and the second region S2 of the belt 61 has been described.
However, the method of making the portion of the guide member 66 through which the first region S1 of the fixing belt 61 passes larger than the heat capacity of the portion of the fixing belt 61 through which the second region S2 passes is not limited to these forms. For example, the configuration of the first embodiment and the configuration of the second embodiment may be used in combination. Specifically, in the guide member 66, a portion through which the second region S <b> 2 of the fixing belt 61 passes is cut out, and the thickness of the portion through which the first region S <b> 1 of the fixing belt 61 passes is set to the second region S <b> 2 of the fixing belt 61. It is also possible to suppress the occurrence of uneven temperature in the fixing belt 61 by forming it thicker than the portion through which the toner passes.

  In the first embodiment and the second embodiment, in the guide member 66, the volume of the part of the fixing belt 61 through which the first region S1 passes is made larger than the volume of the part of the guide belt 66 through which the second region S2 passes. The configuration for suppressing the occurrence of temperature unevenness in the first region S1 and the second region S2 of the fixing belt 61 has been described. However, for example, in the guide member 66, the part through which the first region S1 of the fixing belt 61 passes is formed of the first material, and the part through which the second region S2 passes is more heat capacity per unit volume than the first material. By using the second material having a small size, the heat capacity of the portion through which the first region S1 of the fixing belt 61 passes is made larger than the heat capacity of the portion through which the second region S2 passes, and the first region S1 of the fixing belt 61 is obtained. It is also possible to suppress the occurrence of temperature unevenness in the second region S2. When such a configuration is employed, the volume of the portion of the guide member 66 through which the first region S1 of the fixing belt 61 passes may be equal to the volume of the portion of the guide belt 66 through which the second region S2 passes. The volume of the part through which the region S1 passes may be smaller than the volume of the part through which the second region S2 passes.

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 60 ... Fixing unit, 61 ... Fixing belt, 62 ... Pressure roll, 64 ... Temperature-sensitive magnetic member, 66 ... Induction member, 69 ... Notch part, 80 ... IH heater, 82 ... Excitation coil, 84 ... Magnetic core

Claims (10)

A fixing member having an endless belt-like shape, having a conductive layer, rotatably provided, and fixing the toner on the recording material by electromagnetically heating the conductive layer;
A magnetic field generating member that is provided facing the fixing member and generates an alternating magnetic field that intersects the conductive layer of the fixing member by being supplied with an alternating current;
A plurality of first magnetic path forming members provided opposite to the fixing member via the magnetic field generating member and forming a magnetic path of an alternating magnetic field generated by the magnetic field generating member;
A second magnetic path formed so as to face the magnetic field generating member via the fixing member and forms a magnetic path of an alternating magnetic field generated by the magnetic field generating member together with the plurality of first magnetic path forming members. With members,
The plurality of first magnetic path forming members extend in the rotation direction of the fixing member, and each of the first magnetic path forming members has a rotation direction of the fixing member so as to have an interval between the adjacent first magnetic path forming members. Arranged side by side in the width direction of the fixing member intersecting with
The fixing member is provided adjacent to the first region passing through a portion facing the first magnetic path forming member through the magnetic field generating member, and the first member through the magnetic field generating member. A second region that passes through a portion that does not face the first magnetic path forming member,
The second magnetic path forming member includes a first portion facing the first region of the fixing member, and a second portion facing the second region of the fixing member and having a heat capacity lower than that of the first portion. A fixing device.   The fixing device according to claim 1, wherein the second magnetic path forming member has a volume at the first portion larger than a volume at the second portion.   The length of the second magnetic path forming member along the rotation direction of the fixing member at the first portion is longer than the length along the rotation direction of the fixing member at the second portion. The fixing device according to claim 1. The second magnetic path forming member is disposed so that an outer peripheral surface thereof is in contact with an inner peripheral surface of the fixing member, and the magnetic characteristics change between ferromagnetism and paramagnetism according to temperature, and the magnetic characteristics are ferromagnetic. A temperature-sensitive magnetic member that forms a magnetic path of the alternating magnetic field generated by the magnetic field generating member and transmits the alternating magnetic field generated by the magnetic field generating member when the magnetic characteristic is paramagnetic; An induction member that induces an alternating magnetic field that is transmitted through the temperature-sensitive magnetic member when the outer circumferential surface is disposed in contact with the inner surface of the temperature-sensitive magnetic member and the magnetic property of the temperature-sensitive magnetic member is paramagnetic. And
3. The fixing device according to claim 1, wherein the temperature-sensitive magnetic member and the guide member have a notch along the rotation direction of the fixing member at the second portion.   3. The fixing device according to claim 1, wherein the second magnetic path forming member has a thickness at the first portion larger than a thickness at the second portion. The second magnetic path forming member is disposed so that an outer peripheral surface thereof is in contact with an inner peripheral surface of the fixing member, and the magnetic characteristics change between ferromagnetism and paramagnetism according to temperature, and the magnetic characteristics are ferromagnetic. A temperature-sensitive magnetic member that forms a magnetic path of the alternating magnetic field generated by the magnetic field generating member and transmits the alternating magnetic field generated by the magnetic field generating member when the magnetic characteristic is paramagnetic; An induction member that induces an alternating magnetic field that is transmitted through the temperature-sensitive magnetic member when the outer circumferential surface is disposed in contact with the inner surface of the temperature-sensitive magnetic member and the magnetic property of the temperature-sensitive magnetic member is paramagnetic. And
The said induction | guidance | derivation member has a convex part which protrudes rather than the said 2nd site | part on the opposite side to the surface which contact | connects the inner peripheral surface of the said temperature-sensitive magnetic member in the said 1st site | part. 3. The fixing device according to 2. Toner image forming means for forming a toner image;
Transfer means for transferring the toner image formed by the toner image forming means onto a recording material;
Fixing means for fixing the toner image transferred onto the recording material to the recording material;
The fixing means is
A fixing member having an endless belt-like shape, having a conductive layer, rotatably provided, and fixing the toner on the recording material by electromagnetically heating the conductive layer;
A magnetic field generating member that is provided facing the fixing member and generates an alternating magnetic field that intersects the conductive layer of the fixing member by being supplied with an alternating current;
A plurality of first magnetic path forming members provided opposite to the fixing member via the magnetic field generating member and forming a magnetic path of an alternating magnetic field generated by the magnetic field generating member;
A second magnetic path formed so as to face the magnetic field generating member via the fixing member and forms a magnetic path of an alternating magnetic field generated by the magnetic field generating member together with the plurality of first magnetic path forming members. With members,
Each of the plurality of first magnetic path forming members extends along the rotation direction of the fixing member, and has a rotation direction of the fixing member so as to have an interval between the adjacent first magnetic path forming members. Provided side by side in the width direction of the fixing members that intersect,
The fixing member is provided adjacent to the first region passing through a portion facing the first magnetic path forming member through the magnetic field generating member, and the first member through the magnetic field generating member. A second region that passes through a portion that does not face the first magnetic path forming member,
The second magnetic path forming member includes a first portion facing the first region of the fixing member, and a second portion facing the second region of the fixing member and having a heat capacity lower than that of the first portion. An image forming apparatus comprising:   The image forming apparatus according to claim 7, wherein the second magnetic path forming member has a volume at the first portion larger than a volume at the second portion.   The length of the second magnetic path forming member along the rotation direction of the fixing member at the first portion is longer than the length along the rotation direction of the fixing member at the second portion. The image forming apparatus according to claim 7 or 8.   The image forming apparatus according to claim 7, wherein the second magnetic path forming member has a thickness at the first portion larger than a thickness at the second portion.

Images