JP2016212214A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress an excessive increase in temperature in a paper feed area of a temperature-sensitive magnetic member.SOLUTION: A fixing device comprises: a fixing belt that has a conductive layer heated by electromagnetic induction to fix a toner onto a recording material; an exciting coil that generates an AC magnetic field; and a temperature-sensitive magnetic member that faces the exciting coil across the fixing belt, has slits 640 blocking an eddy current from the AC magnetic field generated by the exciting coil, has a magnetic characteristic changing between ferromagnetism and paramagnetism according to temperature, and transmits the AC magnetic field when the magnetic characteristic is ferromagnetism. The slits 640 include a plurality of continuous slits 641 that are provided in an area corresponding to the ends in the width direction of a recording material orthogonal to the direction of movement of the fixing belt, where the temperature-sensitive magnetic member is continuously notched over the direction of movement, and a plurality of partial slits 642 that are provided between the continuous slits 641, where part of the temperature-sensitive magnetic member are notched in the direction of movement across a non-penetrating part 649 where the temperature-sensitive magnetic member is not notched.SELECTED DRAWING: Figure 10

Description

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

As a conventional technique, Patent Document 1 generates a heating element that generates heat by electromagnetic induction, a fixing belt that fixes heat on the recording material by receiving heat from the heating element, and an AC magnetic field that causes the heating element to generate heat by electromagnetic induction. There is disclosed a fixing device that includes a magnetic field generating unit that generates a magnetic path by inducing an alternating magnetic field generated by the magnetic field generating unit.
In this fixing device, the temperature-sensitive magnetic member is prevented from self-heating, and the end portion of the fixing belt that conducts heat to the recording material has a higher temperature than the average of the portion that conducts heat. In order to suppress this, the temperature-sensitive magnetic member is provided with a blocking portion that blocks eddy currents and a continuous portion that is provided in a direction along the axial direction of the fixing belt and allows continuous heat transfer. Yes.

JP 2011-2774 A

By the way, when the temperature-sensitive magnetic member is continuously provided with a non-penetrating portion through which the temperature-sensitive magnetic member is not penetrated along the axial direction of the fixing member, for example, continuous sheet passing is performed and the non-sheet-passing region of the temperature-sensitive magnetic member is provided. When the temperature rises, the heat moves from the non-sheet passing area to the sheet passing area through the non-penetrating portion. In this case, the temperature of the paper passing region of the temperature-sensitive magnetic member may be excessively increased.
The present invention suppresses an excessive temperature rise in the paper passing area of the temperature-sensitive magnetic member as compared to a case where heat transfer from the non-paper passing area of the temperature-sensitive magnetic member to the paper passing area is allowed. Objective.

The invention according to claim 1 includes a conductive member having a conductive layer, and a circulation member that can circulate and fix the toner onto a recording material conveyed by electromagnetic induction heating, and the conductive layer of the fixing member. A magnetic field generating member that generates an alternating magnetic field that intersects with the fixing member, and a magnetic shielding member that opposes the magnetic field generating member and blocks eddy current due to the alternating magnetic field generated by the magnetic field generating member, And a temperature-sensitive magnetic member that transmits the alternating magnetic field when the magnetic property changes between ferromagnetism and paramagnetism according to temperature and the magnetic property is ferromagnetic. A plurality of continuous notches provided in a region corresponding to an end in the width direction of the recording material orthogonal to the moving direction, and the temperature-sensitive magnetic member continuously cut out in the moving direction; The temperature-sensitive magnetic part provided between the notch parts Is a fixing device including a plurality of partial notch which is partially cut out of the temperature-sensitive magnetic member to the moving direction across the non-cut portion not cut away.
The invention according to claim 2 is the fixing device according to claim 1, wherein a width of the continuous notch is larger than a width of the partial notch.
According to a third aspect of the present invention, a plurality of types of recording materials having different sizes are conveyed to the fixing member, and the continuous notch is formed in an area corresponding to each end of the plurality of types of recording materials. The fixing device according to claim 1, wherein the fixing device is provided.
According to a fourth aspect of the present invention, there is provided a conductive member having a conductive layer, a fixing member capable of circulating movement for fixing toner onto a recording material conveyed by electromagnetic induction heating, and the conductive layer of the fixing member. A magnetic field generating member that generates an alternating magnetic field that intersects with the fixing member, and faces the magnetic field generating member across the fixing member, extends along a moving direction of the fixing member, blocks eddy currents due to the alternating magnetic field, and moves in the moving direction A heat transfer permitting portion that allows heat transfer in the width direction of the recording material orthogonal to the recording material, and an eddy current caused by the alternating magnetic field provided in a region corresponding to the end of the recording material in the width direction, and the heat Compared with the movement allowance part, it is equipped with a heat transfer suppression part that suppresses the movement of heat in the width direction, and the magnetic characteristic changes between ferromagnetism and paramagnetism according to temperature, and the magnetic characteristic becomes ferromagnetic Temperature-sensitive magnetic member that transmits the alternating magnetic field in the case of A fixing device comprising a.
The invention according to claim 5 is a toner image forming unit for forming a toner image, a transfer unit for transferring the toner image formed by the toner image forming unit onto a recording material, and any one of claims 1 to 4. An image forming apparatus comprising the fixing device according to item 1.

According to the first aspect of the present invention, as compared with the case where heat transfer from the non-sheet passing region of the temperature sensitive magnetic member to the sheet passing region is allowed, an excessive temperature in the sheet passing region of the temperature sensitive magnetic member is obtained. The rise can be suppressed.
According to the invention which concerns on Claim 2, the movement of the heat | fever from the non-sheet passing area | region of a temperature sensitive magnetic member to a sheet passing area | region can be suppressed more.
According to the third aspect of the present invention, an excessive temperature rise in the paper passing area can be suppressed even when recording materials having different sizes are used.
According to the invention of claim 4, an excessive temperature in the paper passing region of the temperature-sensitive magnetic member compared to the case where heat transfer from the non-paper passing region to the paper passing region of the temperature-sensitive magnetic member is allowed. The rise can be suppressed.
According to the fifth aspect of the present invention, as compared with a case where heat transfer from the non-sheet passing region of the temperature sensitive magnetic member to the sheet passing region is allowed, an excessive temperature in the sheet passing region of the temperature sensitive magnetic member is obtained. The rise can be suppressed.

1 is a diagram illustrating a configuration example of an image forming apparatus to which the exemplary embodiment is applied. 1 is a diagram illustrating a configuration of a fixing device according to an exemplary embodiment. 1 is a diagram illustrating a configuration of a fixing device according to an exemplary embodiment. FIG. 3 is a diagram illustrating a layer configuration of a fixing belt. It is the perspective view which showed the structure of the internal heating unit of this Embodiment. (A)-(b) is the figure which showed the state of the magnetic force line produced | generated by the IH heater. (A)-(b) is the figure which showed the slit formed in a temperature-sensitive magnetic member. It is the figure which showed the structure of the conventional temperature-sensitive magnetic member. FIG. 5 is a diagram illustrating temperatures of a fixing belt and a temperature-sensitive magnetic member when small-size paper is continuously fed. (A)-(c) is a figure for demonstrating the structure of the temperature-sensitive magnetic member of this Embodiment. It is an enlarged view of the XI part in Fig.10 (a). FIG. 6 is a diagram illustrating temperature changes of a temperature-sensitive magnetic member and a fixing belt in a paper passing area.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
<Description of Image Forming Apparatus>
FIG. 1 is a diagram illustrating a configuration example of an image forming apparatus to which the exemplary 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, and a control unit as an example of a control unit that controls the operation of the entire image forming apparatus 1. 30, a paper holding unit 40 that holds the paper P supplied to the image forming apparatus 1, and a paper stacking unit 45 that stacks the paper P on which an image is formed. Further, for example, a communication unit 41 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 41. An image processing unit 42 for performing processing is provided. Further, the image forming apparatus 1 includes a user interface (UI) 34 as an example of a display unit that is configured by a display panel and receives information from the user and displays information to the user.

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 device 60 as an example of fixing means (fixing device) for fixing each color-transferred toner image on 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 30, image forming processing is performed by the following process. That is, the image data from the PC 3 or the scanner 4 is received by the communication unit 41, subjected to predetermined image processing by the image processing unit 42, and then sent to each image forming unit 11 as image data of each color. . In the image forming unit 11K that forms, for example, 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 42. 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 paper P on which the superimposed toner image is electrostatically transferred is conveyed to the fixing device 60. The toner image on the paper P conveyed to the fixing device 60 receives heat and pressure by the fixing device 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.

  In the image forming apparatus 1 of the present embodiment, it is possible to form an image on paper P having different sizes such as B4 size, A4 size, and B5 size. Further, in the image forming apparatus 1, the paper P is transported by a so-called center registration method based on a central portion in a direction (width direction) intersecting the transport direction of the paper P.

<Description of Fixing Device Configuration>
Next, the fixing device 60 of the present embodiment will be described.
2 and 3 are diagrams showing the configuration of the fixing device 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, the fixing device 60 faces a fixing belt 61 as an example of a fixing member that fixes a toner image on a sheet P, and the fixing belt 61 on the outer peripheral side of the fixing belt 61. The pressure roll 62 is arranged on the inner peripheral side of the fixing belt 61 and is pressed from the pressure roll 62 via the fixing belt 61, and a nip portion N is formed between the pressure roll 62 and the pressure roll 62. A pressing pad 63 to be formed and a peeling assisting member 173 provided on the outer peripheral side of the fixing belt 61 and assisting the peeling of the paper P from the fixing belt 61 are provided. Further, the fixing device 60 is provided on the outer peripheral side of the fixing belt 61 and is provided on the inner peripheral side of the fixing belt 61 by heating the fixing belt 61 together with the IH heater 80 provided by electromagnetic induction heating of the fixing belt 61. An internal heating unit.

<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 comes into contact with a temperature-sensitive magnetic member 64 described later of the internal heating unit 70 on the inner peripheral side of the fixing belt 61, and the surface release layer 614 on the outer peripheral side of the fixing belt 61. Faces the pressure roll 62 and the IH 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 (see FIG. 3). 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.
Usually, a general-purpose power source that can be manufactured at low cost is used as a power source for the excitation circuit 88 (see FIG. 3) that supplies an alternating 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, as the conductive heating layer 612, a nonmagnetic metal such as Cu (a metal having a relative permeability of about 1) having a thickness of 2 μm to 20 μm and a specific resistance value of 2.7 × 10 ⁻⁸ Ω · m or less is used. Used.
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 μm 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 μm to 50 μm in consideration of the balance between wear resistance and heat capacity.

<Description of pressure roll>
The pressure roll 62 is disposed 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 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 is attached to the holder 65 at a position facing the pressure roll 62 as shown in FIG. Supported. 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.

  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 IH heater>
Next, the IH heater 80 will be described. The IH heater 80 of the present embodiment applies electromagnetic induction heating to the conductive heat generating layer 612 of the fixing belt 61 to perform electromagnetic induction heating.
As shown in FIG. 3, the IH heater 80 of the present embodiment includes a support 81 provided along the outer peripheral surface of the fixing belt 61, a support 81 supported by the support 81, and the fixing belt 61 via the support 81. And an excitation coil 82 as an example of a magnetic field generating member that generates an alternating magnetic field, and supported by the support 81 and provided opposite to the excitation coil 82, and generated by the excitation coil 82. And a magnetic core 84 that forms a magnetic path of an alternating magnetic field. In addition, the IH heater 80 of the present embodiment is provided on the excitation coil 82, and is attached to the support body 81 and the elastic support member 83 that fixes the excitation coil 82 on the support body 81. A shield 85 that surrounds the support member 83 and the magnetic core 84, shields the magnetic field, a pressure member 86 that is provided between the magnetic core 84 and the shield 85, and pressurizes the magnetic core 84 toward the support 81, and an excitation coil And an exciting circuit 88 for supplying an alternating current to 82.
Further, as shown in FIG. 3, the IH heater 80 of the present embodiment is opposed to a temperature-sensitive magnetic member 64 described later of an internal heating unit 70 provided on the inner peripheral side of the fixing belt 61 via the fixing belt 61. doing.

The support 81 is provided so as to face the fixing belt 61 over the entire width of the fixing belt 61 with the direction perpendicular to the moving direction of the fixing belt 61 (hereinafter referred to as the width direction of the fixing belt 61) as the longitudinal direction.
Further, as shown in FIG. 3, the support 81 is formed in a shape whose cross section is curved along the surface shape of the fixing belt 61, and the upper surface supporting the exciting coil 82 is predetermined as the surface of the fixing belt 61. The gap is set so as to maintain a gap (for example, 0.5 mm to 2 mm).
Examples of the material constituting the support 81 include heat-resistant resins such as polycarbonate, polyethersulfone, and PPS (polyphenylene sulfide), or heat-resistant resins obtained by mixing glass fibers with these materials, and heat-resistant glass. 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. 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 kHz 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 81.

A plurality of magnetic cores 84 are provided side by side in the width direction of the fixing belt 61 so that a plurality of magnetic cores 84 have a gap between adjacent magnetic cores 84. Each magnetic core 84 has a cross-sectional shape that is curved along the cross-sectional shape of the fixing belt 61, and has an arcuate shape in which the moving direction of the fixing belt 61 is a longitudinal direction. Each magnetic core 84 is positioned by a support body 81.
As shown in FIG. 3, the length of the magnetic core 84 along the moving direction of the fixing belt 61 is configured to be shorter than the length along the moving direction of the fixing belt 61 of the temperature-sensitive magnetic member 64 described later. Thereby, the leakage of the magnetic field lines H radiated from the magnetic core 84 (see FIGS. 6A to 6B described later) 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 device 60 is suppressed, and the heat generation efficiency of the fixing belt 61 (conductive heat generation layer 612) is increased.

  As a material for forming the magnetic core 84, for example, a ferromagnetic material composed of a high permeability oxide or alloy material such as soft ferrite, ferrite resin, amorphous alloy (amorphous alloy), permalloy, temperature-sensitive magnetic alloy, etc. Is used. The magnetic core 84 induces a magnetic force line H (magnetic flux) due to the alternating magnetic field generated by the exciting coil 82, travels from the magnetic core 84 to the direction of the temperature-sensitive magnetic member 64 across the fixing belt 61 via the support 81, A path (magnetic path) of magnetic lines of force H passing through the temperature-sensitive magnetic member 64 and returning to the magnetic core 84 via the support 81 is formed. That is, the AC magnetic field generated by the excitation coil 82 is configured to pass through the inside of the magnetic core 84 and the inside of the temperature-sensitive magnetic member 64, and the magnetic field line H wraps the fixing belt 61 and the excitation coil 82 inside. Such a closed magnetic circuit 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 84.

<Description of internal heating unit>
Next, the configuration of the internal heating unit 70 will be described. FIG. 5 is a perspective view showing the configuration of the internal heating unit 70 of the present embodiment.
As shown in FIGS. 3 and 5, the internal heating unit 70 of the present embodiment is disposed in a non-contact state with the fixing belt 61 on the inner peripheral side of the fixing belt 61, and is generated by the excitation coil 82 of the IH heater 80. A temperature-sensitive magnetic member 64 that induces an alternating magnetic field to form a magnetic path is provided. The internal heating unit 70 is provided in contact with the inner peripheral surface of the fixing belt 61, and includes temperature detection sensors 71 and 72 that detect the temperature of the fixing belt 61 and a hole 645 provided in the temperature-sensitive magnetic member 64. And a thermostat 73 that opposes the inner peripheral surface of the fixing belt 61 and interrupts energization from the general-purpose power supply to the excitation circuit 88 when the temperature-sensitive magnetic member 64 becomes hot. Furthermore, the internal heating unit 70 includes a holder 65 that supports the temperature-sensitive magnetic member 64, the temperature detection sensors 71 and 72, and the thermostat 73.

<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 the outer peripheral surface is a predetermined gap (for example, 0) from the inner peripheral surface of the fixing belt 61. .. 5 mm to 1.5 mm) and close to the fixing belt 61 without contact. By arranging the temperature-sensitive magnetic member 64 close to the fixing belt 61, the temperature of the temperature-sensitive magnetic member 64 changes in accordance with the temperature of the fixing belt 61. On the other hand, by disposing the temperature-sensitive magnetic member 64 on the fixing belt 61 in a non-contact manner, the main switch of the image forming apparatus 1 is turned on and the fixing belt 61 is heated when the fixing belt 61 is heated to the fixing set temperature. Can be prevented from flowing into the temperature-sensitive magnetic member 64, and the warm-up time can be shortened.

  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 and returns to the IH heater 80.

  The “permeability change start temperature” here is a temperature at which the magnetic permeability (for example, the magnetic permeability measured by JIS C2531) starts to decrease continuously. For example, a member such as the temperature-sensitive magnetic member 64 This is the temperature point at which the amount of magnetic flux that passes through (the number of lines of magnetic force) starts to change. Therefore, the permeability change start temperature is close to the Curie point, which is the temperature at which the substance loses magnetism, but has a different concept from the Curie point.

The material used for the temperature-sensitive magnetic member 64 is, for example, a binary system such as an Fe—Ni alloy (permalloy) in which a magnetic permeability change start temperature is set within a range of 140 ° C. to 240 ° C. used as a fixing set temperature. A ternary shunt steel such as magnetic steel or Fe—Ni—Cr alloy is used. For example, in the Fe-Ni binary magnetic shunt steel, the permeability change start temperature can be set around 225 ° C. by setting it to about Fe 64% and Ni 36% (atomic ratio). Such metal alloys such as permalloy and magnetic shunt steel 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 200 μm to 800 μm.

<Description of holder>
As shown in FIGS. 3 and 5, 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, the temperature detection sensors 71 and 72, and the thermostat 73. 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. Further, since the fixing device 60 of 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.

<Explanation of temperature detection sensor>
The temperature detection sensors 71 and 72 are provided in contact with the inner peripheral surface of the fixing belt 61 and detect the temperature of the fixing belt 61. In the present embodiment, one temperature detection sensor 71 is disposed at the center in the width direction of the fixing belt 61 (a position corresponding to the minimum sheet passing area in the nip portion N), and one end of the fixing belt 61 in the width direction. The other temperature detection sensor 72 is disposed (a position corresponding to the end side of the minimum sheet passing region in the nip portion N).
In addition, as shown in FIG. 5, each temperature detection sensor 71 and 72 is supported by the holder 65 via the spring members 71a and 72a. The temperature detection sensors 71 and 72 are pressed against the inner peripheral surface of the fixing belt 61 by spring members 71a and 72a.

  As the temperature detection sensors 71 and 72, for example, a thermistor type temperature detection sensor can be used. As the thermistor type temperature detection sensors used as the temperature detection sensors 71 and 72, for example, an NTC (Negative Temperature Coefficient) thermistor whose resistance decreases as the temperature rises, or a PTC ( Various thermistors such as a positive temperature coefficient (CTR) thermistor and a CTR (Critical Temperature Resistor) thermistor whose resistance decreases with an increase in temperature but has a good sensitivity in a specific temperature range can be used.

  Although details will be described later, in the present embodiment, the exciting coil 82 is normally connected via the exciting circuit 88 (see FIG. 3) according to the temperature of the fixing belt 61 detected by the temperature detecting sensors 71 and 72. The power supplied to (see FIG. 3) is determined.

<Explanation of thermostat>
The thermostat 73 faces the fixing belt 61 through a hole 645 provided in the temperature-sensitive magnetic member 64, and cuts off the power supply to the excitation circuit 88 when the temperature of the temperature-sensitive magnetic member 64 rises excessively. To be provided. In the present embodiment, the thermostat 73 is provided in an area corresponding to a small-size paper passing area Fs (see FIG. 9) described later in the temperature-sensitive magnetic member 64.
The thermostat 73 is made of, for example, a bimetal in which two types of metal plates having different thermal expansion coefficients are stacked. Specifically, the thermostat 73 is, for example, a first metal plate made of an alloy (invar) of iron and nickel, and a second metal obtained by adding a metal such as chromium or manganese to an alloy containing iron and nickel. It is composed of bimetal or the like on which plates are laminated.
The thermostat 73 deforms due to the difference in thermal expansion coefficient between the first metal plate and the second metal plate when the temperature-sensitive magnetic member 64 becomes excessively high in temperature, thereby supplying power to the excitation circuit 88. Shut off the supply.

<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 provided at both ends in the axial direction of the holder 65 (see FIG. 3) of the internal heating unit 70 while keeping the cross-sectional shape of both ends of the fixing belt 61 circular. An end cap member 67 that rotates and rotates in the circumferential direction 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.
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 device 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 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.

<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. FIGS. 6A and 6B are diagrams showing the state of the lines of magnetic force generated by the IH heater 80. FIG. 6A shows the temperature of the fixing belt 61 (temperature-sensitive magnetic member 64). FIG. 6B shows the state of the lines of magnetic force (H) in the temperature range below the magnetic permeability change start temperature, and FIG. 6B shows the temperature at which the temperature of the fixing belt 61 (temperature-sensitive magnetic member 64) exceeds the magnetic permeability change start temperature. The state of the lines of magnetic force (H) in the range is shown.

  First, as described above, the permeability change start temperature of the temperature-sensitive magnetic member 64 is within a temperature range that is equal to or higher than the set fixing temperature for fixing each color toner image and equal to or lower than the heat resistance temperature of the fixing belt 61 (for example, 220 ° C. ˜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.

  As shown in FIG. 6A, when the temperature of the fixing belt 61 is in a temperature range equal to or lower than the magnetic permeability change start temperature, the magnetic field lines H of the alternating magnetic field generated by the IH heater 80 cross the fixing belt 61. Thus, a magnetic path that passes through the inside of the temperature-sensitive magnetic member 64 along the spreading direction (direction orthogonal to the thickness direction) is formed. Therefore, the number of magnetic field lines H (magnetic flux density) per unit area in the region crossing the conductive heat generating layer 612 of the fixing belt 61 increases.

  That is, after the magnetic field lines H are radiated from the magnetic core 84 of the IH heater 80 and pass through the regions R1 and R2 across the conductive heat generating layer 612 of the fixing belt 61, the magnetic field lines H enter the inside of the temperature-sensitive magnetic member 64 which is a ferromagnetic material. Be guided. 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 increases. Further, even when the magnetic field lines H that have passed through the inside of the temperature-sensitive magnetic member 64 along the spreading direction return to the magnetic core 84 again, in the region R3 that crosses the conductive heating layer 612 in the thickness direction, the magnetic field in the temperature-sensitive magnetic member 64 is increased. It is concentrated toward the magnetic core 84 from the lower part. Therefore, the magnetic force lines H that cross 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 84, and the magnetic flux density in the region R3 is also increased.

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. Accordingly, as shown in FIG. 6A, a large eddy current I is generated in the regions R1, R2 and R3 where the amount of change in magnetic flux density is large. 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. Thereby, a large Joule heat W is generated in the conductive heat generating layer 612 where the large eddy current I is generated.
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, large heat is generated in the regions R1 and R2 and the region R3 where the magnetic lines H cross the conductive heat generating layer 612. Thereby, the fixing belt 61 is heated.

  By the way, in the fixing device 60 of the present embodiment, the temperature-sensitive magnetic member 64 is disposed in the vicinity of the fixing belt 61 on the inner peripheral surface side of the fixing belt 61. As a result, the magnetic core 84 that guides the magnetic lines of force H generated by the exciting coil 82 and the temperature-sensitive magnetic member 64 that guides the magnetic lines of force H that have passed through the fixing belt 61 in the thickness direction are close to each other. The configuration is realized. For this reason, since the alternating magnetic field generated by the IH heater 80 (excitation coil 82) forms a loop with a short magnetic path, 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.

<Description of function for suppressing temperature rise of fixing belt>
On the other hand, the temperature of the fixing belt 61 rises due to induction heating. For example, in the region corresponding to the non-sheet passing portion where the sheet is not conveyed in the nip portion N (see FIG. 3), the temperature of the fixing belt 61 becomes the magnetic permeability change start temperature. If it exceeds, the temperature of the temperature-sensitive magnetic member 64 adjacent to the fixing belt 61 also exceeds the permeability change start temperature corresponding to the temperature of the fixing belt 61. In this case, the temperature-sensitive magnetic member 64 has a relative magnetic permeability close to 1, and the properties as a ferromagnetic material disappear. When the relative permeability of the temperature-sensitive magnetic member 64 decreases and approaches 1, the magnetic field lines H of the alternating magnetic field generated by the IH heater 80 are not induced inside the temperature-sensitive magnetic member 64, and the temperature-sensitive magnetic member 64. Will become transparent. For this reason, the magnetic field lines H after passing through the conductive heat generating layer 612 of the fixing belt 61 are diffused, and the magnetic flux density of the magnetic field lines H crossing the conductive heat generating layer 612 is reduced. As a result, the eddy current I generated in the conductive heat generation layer 612 is reduced, and the heat generation amount (Joule heat W) in the fixing belt 61 is reduced. As a result, an excessive temperature rise of the fixing belt 61 is suppressed, and damage to the fixing belt 61 is suppressed.

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

  As shown in FIG. 6B, when the temperature of the fixing belt 61 is in a temperature range that rises in the non-sheet passing region and exceeds the magnetic permeability change start temperature, for example, the relative magnetic permeability of the temperature-sensitive magnetic member 64. Decreases. For this reason, the magnetic field line H of the alternating magnetic field generated by the IH heater 80 changes so as to easily pass through the temperature-sensitive magnetic member 64. Accordingly, the magnetic field lines H of the alternating magnetic field generated by the IH heater 80 (excitation coil 82) are radiated so as to diffuse from the magnetic core 84 toward the fixing belt 61 side.

That is, in the regions R1 and R2 where the magnetic force lines H are radiated from the magnetic core 84 of the IH heater 80 and cross the conductive heat generating layer 612 of the fixing belt 61, the magnetic force lines H are difficult to be guided to the temperature-sensitive magnetic member 64 and thus diffuse radially. As a result, the magnetic flux density (number of magnetic force lines H per unit area) of the magnetic field lines H crossing the conductive heat generating layer 612 of the fixing belt 61 in the thickness direction decreases. Further, even in the region R3 that crosses the conductive heat generating layer 612 in the thickness direction when the magnetic force line H returns to the magnetic core 84 again, the magnetic force line H returns to the magnetic core 84 from the diffused wide region. The magnetic flux density of the magnetic field lines H crossing 612 in the thickness direction decreases.
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 that cross the conductive heating layer 612 in the thickness direction decreases in the regions R1, R2, and R3. It becomes. 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. As a result, the temperature of the fixing belt 61 decreases.

<Configuration for suppressing temperature rise of temperature-sensitive magnetic member>
Here, in order to perform the function of suppressing the excessive temperature rise of the temperature-sensitive magnetic member 64, the temperature of each region in the longitudinal direction of the temperature-sensitive magnetic member 64 is the temperature of each region in the longitudinal direction of the fixing belt 61 facing it. It is necessary to fulfill a function as a detection unit for detecting the temperature of the fixing belt 61 described above.
Therefore, regarding the temperature-sensitive magnetic member 64 itself, a configuration that is difficult to be induction-heated by the magnetic field lines H is adopted. 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 that crosses in the thickness direction. As a result, a weak eddy current I is generated inside the temperature-sensitive magnetic member 64, and a slight amount of heat is generated in the temperature-sensitive magnetic member 64 itself. Therefore, for example, when a large amount of image formation is continuously performed, heat is accumulated in the temperature-sensitive magnetic member 64, and the temperature of the temperature-sensitive magnetic member tends to increase even in the paper passing region. Thereby, in the temperature-sensitive magnetic member 64 that has large eddy current loss and hysteresis loss and easily generates heat due to the passage of the magnetic lines of force H, depending on the situation, even if the temperature of the fixing belt 61 does not exceed the permeability change start temperature, The member 64 may function to suppress the temperature increase of the fixing belt 61 in the paper passing area. Therefore, the correspondence between the temperature of the temperature-sensitive magnetic member 64 and the temperature of the fixing belt 61 is maintained, and the temperature-sensitive magnetic member 64 functions as a detection unit that detects the temperature of the fixing belt 61 with high accuracy. It is necessary to suppress the Joule heat W generated in the member 64 itself.

Therefore, first, the temperature-sensitive magnetic member 64 is selected from a material having physical properties (specific resistance value and magnetic permeability) that are difficult to be induction-heated by the magnetic field lines H.
Second, the thickness of the temperature-sensitive magnetic member 64 exhibits ferromagnetism so that the magnetic field lines H are difficult to cross in the thickness direction of the temperature-sensitive magnetic member 64 at least in the temperature range below the permeability change start temperature. It is formed thicker than the skin depth δ in the state.

  Third, the temperature-sensitive magnetic member 64 is formed with a plurality of slits 640 that divide the flow of the eddy current I generated by the lines of magnetic force H. Even if the material and thickness of the temperature-sensitive magnetic member 64 are selected so that induction heating is difficult, it is difficult to set the eddy current I generated in the temperature-sensitive magnetic member 64 to zero. Therefore, by dividing the flow of the eddy current I generated in the temperature-sensitive magnetic member 64 by the plurality of slits 640, the eddy current I is reduced and the Joule heat W generated in the temperature-sensitive magnetic member 64 is kept low. .

  FIGS. 7A and 7B are views showing a slit 640 formed in the temperature-sensitive magnetic member 64. FIG. 7A is a side view showing a state in which the temperature-sensitive magnetic member 64 is installed in the holder 65, and FIG. 7B is a plan view seen from above (z direction) in FIG. 7A. is there. As shown in FIGS. 7A to 7B, in the temperature-sensitive magnetic member 64, a plurality of slits 640 are formed orthogonal to the direction in which the eddy current I generated by the lines of magnetic force H flows. Therefore, when there is no slit 640, the eddy current I (broken line in FIG. 7B) that flows as a large eddy over the entire longitudinal direction of the temperature-sensitive magnetic member 64 is divided by the slit 640. Thereby, when the slit 640 is formed, the eddy current I flowing through the temperature-sensitive magnetic member 64 (solid line in FIG. 7A) becomes a small eddy in the region between the slit 640 and the slit 640, The amount of eddy current I as a whole is reduced. As a result, the amount of heat generated by the temperature-sensitive magnetic member 64 (Joule heat W) is reduced, and a configuration that hardly generates heat is realized. Therefore, the plurality of slits 640 function as a blocking unit that blocks the eddy current I.

Further, as shown in FIGS. 7A to 7B, the slit 640 formed in the temperature-sensitive magnetic member 64 of the present embodiment is formed in the short direction of the temperature-sensitive magnetic member 64 (the fixing belt 61 (FIG. 3)). A continuous slit 641 as an example of a continuous notch portion in which the temperature-sensitive magnetic member 64 is continuously cut out over the moving direction) of the reference), and a non-cut which performs heat transfer without passing through the temperature-sensitive magnetic member 64 It has a partial slit 642 as an example of a partial notch part in which a part in the short direction of the temperature-sensitive magnetic member 64 is cut across a non-penetrating part 649 as an example of a notch part.
The configuration of the slit 640 formed in the temperature-sensitive magnetic member 64 of the present embodiment will be described in detail later.

<About problems that may occur in conventional temperature-sensitive magnetic members>
By the way, when the partial slit 642 having the non-penetrating portion 649 is provided over the entire longitudinal direction of the temperature-sensitive magnetic member 64, for example, when the continuous paper is passed, the temperature-sensitive magnetic member 64 excessively increases in temperature. May happen. FIGS. 8A and 8B are diagrams showing the structure of a conventional temperature-sensitive magnetic member 64. FIG.
In the conventional temperature-sensitive magnetic member 64 shown in FIGS. 8A to 8B, the partial slits 642 are provided at equal intervals from one end in the longitudinal direction of the temperature-sensitive magnetic member 64 to the entire region of the other end. . Thereby, as shown in FIG. 8B, a non-penetrating portion 649 through which the temperature-sensitive magnetic member 64 does not penetrate is continuously formed from one end to the other end of the temperature-sensitive magnetic member 64 in the longitudinal direction. ing.

  FIG. 9 shows the temperature of the temperature-sensitive magnetic member 64 when small-size paper is continuously fed in the fixing device 60 using the conventional temperature-sensitive magnetic member 64 shown in FIGS. It is a figure. Specifically, FIG. 9 is a diagram showing an outline of the temperature distribution in the longitudinal direction (width direction) of the temperature-sensitive magnetic member 64 when the small-size paper P1 is continuously fed. In FIG. 9, the maximum sheet passing area which is the maximum size width (for example, A3 width) of the sheet P used in the image forming apparatus 1 is Ff, and the small size sheet P1 (for example, smaller than the maximum size sheet P) (for example, , A4 (vertical feed) passes through the area (small size paper passing area) as Fs, and the non-sheet passing area through which the small size paper P1 does not pass is Fb. In the image forming apparatus 1, it is assumed that the sheet is passed based on the center position.

  As shown in FIG. 9, when small-size paper P1 is continuously passed, heat for fixing is consumed in the small-size paper passing area Fs through which the small-size paper P1 passes. Therefore, the temperature adjustment control at the fixing setting temperature Tf is performed by the control unit 30 (see FIG. 1), and the temperature of the fixing belt 61 in the small size paper passing area Fs is maintained within the vicinity of the fixing setting temperature Tf. The On the other hand, temperature adjustment control similar to that of the small-size paper passing area Fs is performed also in the non-paper passing area Fb. However, heat for fixing is not consumed in the non-sheet passing area Fb. For this reason, the temperature of the fixing belt 61 in the non-sheet passing region Fb is likely to rise to a temperature higher than the fixing set temperature Tf.

As described above, when the temperature of the fixing belt 61 rises due to induction heating and the temperature of the fixing belt 61 in the non-sheet passing region Fb exceeds the magnetic permeability change start temperature Tcu, the temperature sensitivity close to the fixing belt 61 is detected. The temperature in the non-sheet passing region Fb of the magnetic member 64 also exceeds the magnetic permeability change start temperature Tcu.
When the non-penetrating part 49 is continuously provided in the longitudinal direction in the temperature-sensitive magnetic member 64, as shown in FIG. 9, the non-sheet passing area Fb through the non-sheet passing area Fb are passed through the non-penetrating part 49. The heat moves to. In this case, as indicated by a broken line in FIG. 9, the temperature of the temperature-sensitive magnetic member 64 may exceed the permeability change start temperature Tcu not only in the non-sheet passing area Fb but also in the small size sheet passing area Fs.

  When the temperature of the temperature-sensitive magnetic member 64 exceeds the magnetic permeability change start temperature Tcu in the small-size paper passing area Fs, the relative magnetic permeability of the temperature-sensitive magnetic member 64 approaches 1, and the AC generated by the IH heater 80 Magnetic field lines of the magnetic field are transmitted through the temperature-sensitive magnetic member 64. When the magnetic lines of force pass through the temperature-sensitive magnetic member 64, the magnetic flux density of the magnetic lines of force crossing the conductive heat generating layer 612 of the fixing belt 61 is reduced, so that the amount of heat generated by the fixing belt 61 is reduced. In this case, the temperature of the fixing belt 61 is unlikely to rise, and the temperature of the fixing belt 61 in the small-size paper passing area Fs does not easily reach the target fixing setting temperature Tf.

  Furthermore, as described above, in the present embodiment, since the thermostat 73 is provided so as to contact the inner peripheral surface of the temperature-sensitive magnetic member 64, the lines of magnetic force are transmitted through the temperature-sensitive magnetic member 64. Thus, the lines of magnetic force that have passed through the temperature-sensitive magnetic member 64 are induced inside the thermostat 73. As a result, the thermostat 73 is directly induction-heated, the temperature of the thermostat 73 becomes high, the thermostat 73 is deformed, and the power supply to the IH heater 80 may be interrupted.

<Description of slit in this embodiment>
In contrast, in the temperature-sensitive magnetic member 64 of the present embodiment, in addition to the partial slit 642, the continuous slit 641 formed continuously in the short direction of the temperature-sensitive magnetic member 64 is provided, whereby the above-described feeling. Occurrence of a temperature rise in the sheet passing region of the warm magnetic member 64 is suppressed.
FIGS. 10A to 10C are diagrams for explaining the configuration of the temperature-sensitive magnetic member 64 of the present embodiment. FIG. 10A is a perspective view of the temperature-sensitive magnetic member 64 attached to the holder 65, and FIG. 10B shows the temperature-sensitive magnetic member 64 viewed from the XB direction of FIG. 10A. FIG. 10C is a view of the temperature-sensitive magnetic member 64 as viewed from the XC direction of FIG. 10B. FIG. 11 is an enlarged view of the XI portion in FIG.

As shown in FIGS. 10A to 10C, the temperature-sensitive magnetic member 64 according to the present embodiment has an end position in the width direction of each size of paper to be image-formed in the image forming apparatus 1. A continuous slit 641 is provided in a region corresponding to. In this example, a continuous slit 641 is provided in a region corresponding to an end position in the width direction of each of the B4 size, A4 size, and B5 size sheets.
Thereby, in the temperature-sensitive magnetic member 64 of the present embodiment, the sheet passing area and the non-sheet passing area when the respective size sheets are conveyed are divided by the continuous slit 641. In other words, in the temperature-sensitive magnetic member 64 of the present embodiment, the non-penetrating portion 649 through which the temperature-sensitive magnetic member 64 does not penetrate is divided into a plurality of portions in the longitudinal direction of the temperature-sensitive magnetic member 64 by the continuous slit 641. Yes.
Further, as shown in FIGS. 10A to 10C, a part of the temperature-sensitive magnetic member 64 is notched in the region between the continuous slits 641 of the temperature-sensitive magnetic member 64 with the non-penetrating portion 649 interposed therebetween. A partial slit 642 is provided.

  Furthermore, in the temperature-sensitive magnetic member 64 of the present embodiment, as shown in FIG. 11, the width of the continuous slit 641 along the longitudinal direction of the temperature-sensitive magnetic member 64 is aligned with the longitudinal direction of the temperature-sensitive magnetic member 64. It is wider than the width of the partial slit 642. In this example, the width of the continuous slit 641 is 0.5 mm, and the width of the partial slit 642 is 0.2 mm.

In the present embodiment, since the temperature-sensitive magnetic member 64 has the above-described configuration, for example, the temperature of the fixing belt 61 in the non-sheet passing region exceeds the magnetic permeability change start temperature by performing continuous sheet passing. Even when the temperature of the temperature-sensitive magnetic member 64 exceeds the magnetic permeability change start temperature, the continuous slit 641 prevents heat from being transferred from the non-sheet passing region to the sheet passing region of the temperature-sensitive magnetic member 64. Is done.
Thereby, it is suppressed that the temperature of the temperature-sensitive magnetic member 64 exceeds the permeability change start temperature in the paper passing area. As a result, a decrease in the relative magnetic permeability of the temperature-sensitive magnetic member 64 in the sheet passing area is suppressed, and the temperature of the fixing belt 61 easily reaches the target fixing set temperature in the sheet passing area.

FIG. 12 is a diagram showing temperature changes of the temperature-sensitive magnetic member 64 and the fixing belt 61 in the paper passing area. FIG. 12 shows the temperature-sensitive magnetic member 64 of the present embodiment and the conventional feeling shown in FIG. 8 when A4 size paper is continuously passed as the temperature change of the temperature-sensitive magnetic member 64 in the paper passing area. The temperature change of the temperature magnetic member 64 is shown.
As shown in FIG. 12, when the temperature-sensitive magnetic member 64 according to the present embodiment provided with the continuous slit 641 is used, the conventional temperature-sensitive magnetic member 64 that does not have the continuous slit 641 is used. In contrast, even when continuous paper feeding is performed, it can be confirmed that the temperature of the temperature-sensitive magnetic member 64 in the paper feeding region does not exceed the permeability change start temperature Tcu.

  Further, it is possible that the line of magnetic force transmitted through the temperature-sensitive magnetic member 64 is induced inside the thermostat 73 by suppressing the temperature of the temperature-sensitive magnetic member 64 in the paper passing region from exceeding the permeability change start temperature. It is suppressed. Thereby, it is suppressed that the thermostat 73 deform | transforms and the supply of the electric power to the IH heater 80 is interrupted | blocked.

  Moreover, the area | region pinched | interposed into each continuous slit 641 of the temperature-sensitive magnetic member 64 is connected via the non-penetrating part 649, and heat can be transferred via the non-penetrating part 649. For this reason, when the temperature of the fixing belt 61 in the non-sheet-passing region exceeds the magnetic permeability change start temperature, heat is transferred through the non-penetrating portion 649, so that the temperature-sensitive magnetic member 64 does not pass the sheet. The entire region exceeds the permeability change start temperature in the longitudinal direction. As a result, the relative magnetic permeability of the temperature-sensitive magnetic member 64 decreases in the non-sheet-passing region, and an excessive temperature rise of the temperature-sensitive magnetic member 64 in the non-sheet-passing region is suppressed.

Furthermore, in the temperature-sensitive magnetic member 64 of the present embodiment, when the width of the continuous slit 641 is made larger than the width of the partial slit 642, for example, the width of the continuous slit 641 is the same as the width of the partial slit 642. In contrast, the continuous slit 641 suppresses heat transfer from the non-sheet passing region to the sheet passing region. As a result, an excessive temperature rise in the sheet passing region of the temperature-sensitive magnetic member 64 is suppressed.
Further, by making the width of the continuous slit 641 larger than the width of the partial slit 642, air movement easily occurs in the continuous slit 641. Thereby, the heat radiation from the temperature-sensitive magnetic member 64 is promoted in the continuous slit 641, and the temperature rise of the temperature-sensitive magnetic member 64 is further suppressed.

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 10 ... Image forming part, 60 ... Fixing apparatus, 61 ... Fixing belt, 64 ... Temperature-sensitive magnetic member, 640 ... Slit, 641 ... Continuous slit, 642 ... Partial slit, 649 ... Non-penetrating part

Claims (5)

A fixing member having a conductive layer and capable of circulating movement for fixing toner on a recording material conveyed by electromagnetic induction heating of the conductive layer;
A magnetic field generating member that generates an alternating magnetic field that intersects the conductive layer of the fixing member;
A blocking portion is formed that opposes the magnetic field generation member across the fixing member and blocks eddy currents generated by the alternating magnetic field generated by the magnetic field generation member. The magnetic characteristics are ferromagnetic and paramagnetic depending on the temperature. And a temperature-sensitive magnetic member that transmits the alternating magnetic field when the magnetic property is ferromagnetic and changes between
The blocking part is
A plurality of continuous notches provided in a region corresponding to an end portion of the recording material in the width direction perpendicular to the moving direction of the fixing member, and the temperature-sensitive magnetic member continuously cut out in the moving direction; ,
A plurality of partial cutouts provided between the continuous cutout portions, wherein a part of the temperature-sensitive magnetic member is cut in the moving direction across a non-cutout portion in which the temperature-sensitive magnetic member is not cutout. A fixing device.   The fixing device according to claim 1, wherein a width of the continuous notch is larger than a width of the partial notch. A plurality of types of recording materials having different sizes are conveyed to the fixing member,
The fixing device according to claim 1, wherein the continuous notch is provided in a region corresponding to each end of the plurality of types of recording materials. A fixing member having a conductive layer and capable of circulating movement for fixing toner on a recording material conveyed by electromagnetic induction heating of the conductive layer;
A magnetic field generating member that generates an alternating magnetic field that intersects the conductive layer of the fixing member;
Heat transfer in the width direction of the recording material that faces the magnetic field generating member across the fixing member, extends along the moving direction of the fixing member, blocks eddy currents due to the alternating magnetic field, and is orthogonal to the moving direction And a heat transfer allowance portion that allows heat transfer in the width direction as compared with the heat transfer allowance portion that is provided in a region corresponding to the end portion in the width direction of the recording material and blocks eddy current due to the AC magnetic field. A temperature-sensitive magnetic member that includes a heat transfer suppressing portion that suppresses the movement of the magnetic field, and transmits the alternating magnetic field when the magnetic characteristic changes between ferromagnetism and paramagnetism according to temperature and the magnetic characteristic is ferromagnetic. A fixing device. 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;
An image forming apparatus comprising: the fixing device according to claim 1.

Images