JP5900229B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

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

In a fixing device mounted on an image forming apparatus such as a copying machine or a printer using an electrophotographic method, a heating device is known which slides and conveys a heat-resistant film as a heating rotator in close contact with a heating rotator. (Patent Document 1).
There is also known an electromagnetic induction heating type fixing device in which a magnetic field generated by an induction coil is applied to a rotating body having a conductive layer, and the rotating body is directly heated by an eddy current generated in the conductive layer (patent). Reference 2).

In the heating device of Patent Document 1, a heating member and a material to be heated are pressed against each other by an applied pressure of an elastic body or a spring member.
The fixing device of Patent Document 2 is provided with a heating element that is disposed in contact with the fixing belt so as to face the magnetic field generating unit and generate heat by the action of the magnetic field.

JP 2003-086333 A JP 2008-129517 A

  SUMMARY OF THE INVENTION An object of the present invention is to provide a fixing device and an image forming apparatus that can prevent the occurrence of defective fixing and gloss unevenness.

In order to solve the above-mentioned problem, a fixing device according to claim 1,
A fixing member having a conductive layer and fixing the toner to the recording medium by electromagnetically heating the conductive layer;
A pressure roller that conveys the recording medium between the fixing member and the fixing member;
A magnetic field generating means disposed opposite to the fixing member to generate a magnetic field;
A temperature-sensitive heat storage member that is provided in contact with the inner peripheral surface of the fixing member while sliding, and generates heat by electromagnetic induction of the magnetic field to heat the fixing member;
A heating member provided in contact with the inside of the temperature-sensitive heat storage member and heating the temperature-sensitive heat storage member;
A heat storage member that is provided inside the heating member and stores heat;
An elastic member provided in contact with one surface of each of the heating member and the heat storage member;
With
It is characterized by that.

According to a second aspect of the present invention, in the fixing device according to the first aspect,
The elastic member has a hardness defined by JIS type A of 50 degrees or less.
It is characterized by that.

According to a third aspect of the present invention, in the fixing device according to the first aspect,
The elastic member has a thickness in the range of 100 μm to 1000 μm;
It is characterized by that.

According to a fourth aspect of the present invention, in the fixing device according to the first aspect,
The elastic member has a lower thermal conductivity than the temperature-sensitive heat storage member,
It is characterized by that.

According to a fifth aspect of the present invention, in the fixing device according to the first aspect,
The heating member heats the temperature-sensitive heat storage member by Joule heat generated by power supply;
It is characterized by that.

In order to solve the above problem, an image forming apparatus according to claim 6,
A photoreceptor on which an electrostatic latent image is formed;
Charging means for charging the photoreceptor;
Latent image forming means for forming a latent image by exposing the photoreceptor charged by the charging means;
A developing device for developing the latent image formed by the latent image forming means;
Transfer means for transferring an image obtained by development of the developing device to a recording medium;
The fixing device according to any one of claims 1 to 5, wherein an image transferred to a recording medium by the transfer unit is fixed.
With
It is characterized by that.

According to the first and sixth aspects of the invention, it is possible to prevent the occurrence of poor fixing and gloss unevenness.
According to invention of Claim 2, compared with the case where it does not have this structure, the adhesiveness of a temperature-sensitive heat storage member and a heating member can be raised.
According to the third aspect of the present invention, the temperature-sensitive heat storage member can be heated evenly as compared with the case where this configuration is not provided.
According to invention of Claim 4, compared with the case where it does not have this structure, the heat transfer from a heating member to an elastic member can be insulated.
According to invention of Claim 5, the temperature rise of a temperature-sensitive heat storage member can be accelerated compared with the case where this structure is not provided.

FIG. 2 is a schematic cross-sectional view illustrating an internal configuration of an image forming apparatus to which the fixing device according to the present embodiment is applied. FIG. 2 is a schematic cross-sectional view of a fixing device according to the present embodiment. FIG. 6 is a schematic front view of the fixing device according to the present embodiment as viewed from the paper carry-in side. FIG. 3 is a cross-sectional layer configuration diagram of a fixing belt constituting the fixing device according to the embodiment. (A) is a schematic diagram for explaining the operation of the temperature-sensitive magnetic member when the temperature of the fixing belt is equal to or lower than the magnetic permeability change start temperature, and (b) is a diagram illustrating the temperature of the fixing belt indicating the magnetic permeability change start temperature. It is a schematic diagram explaining the effect | action of the temperature-sensitive heat storage member in the state of exceeding. (A) is a figure which shows the transition after the energization start of the surface temperature of the heating member in the fixing device of a comparative example, (b) is the transition after the energization start of the surface temperature of the heating member of this embodiment. FIG. FIG. 3 is a schematic diagram illustrating a layer configuration of a heat transfer unit that configures the fixing device according to the exemplary embodiment. FIG. 3 is a schematic plan view illustrating an example of an appearance of a heating member of the fixing device according to the embodiment. It is a cross-sectional schematic diagram of a fixing device of a comparative example.

Next, the present invention will be described in more detail with reference to the drawings with reference to embodiments and specific examples. However, the present invention is not limited to these embodiments and specific examples.
Also, in the description using the following drawings, it should be noted that the drawings are schematic and the ratio of each dimension and the like are different from the actual ones, and are necessary for the description for easy understanding. Illustrations other than the members are omitted as appropriate.
In order to facilitate understanding of the following description, in the drawings, the front-rear direction is the X-axis direction, the left-right direction is the Y-axis direction, and the up-down direction is the Z-axis direction.

(1) Overall Configuration and Operation of Image Forming Apparatus FIG. 1 is a schematic cross-sectional view showing the internal configuration of the image forming apparatus 1 according to this embodiment.
Hereinafter, the overall configuration and operation of the image forming apparatus 1 will be described with reference to the drawings.

  The image forming apparatus 1 includes a control device 10, a paper feeding device 20, a photosensitive unit 30, a developing device 40, a transfer device 50, and a fixing device 60. On the upper surface (Z direction) of the image forming apparatus 1, a discharge tray 1a for discharging and storing a sheet on which an image is recorded is formed.

The control device 10 includes a controller 11 that controls the operation of the image forming apparatus 1, an image processing unit 12 that is controlled by the controller 11, a power supply device 13, and the like. The power supply device 13 applies a voltage to a charging roller 32, a developing roller 42, a primary transfer roller 52, a secondary transfer roller 53, and the like which will be described later.
The image processing unit 12 converts print information input from an external information transmission apparatus (for example, a personal computer) into image information for forming a latent image, and outputs a drive signal to the exposure apparatus LH at a preset timing. To do. The exposure apparatus LH of the present embodiment is configured by an LED head in which LEDs (Light Emitting Diodes) are arranged in a line.

  A paper feeding device 20 is provided at the bottom of the image forming apparatus 1. The sheet feeding device 20 includes a sheet stacking plate 21, and a plurality of sheets P as recording media are stacked on the upper surface of the sheet stacking plate 21. The paper P loaded on the paper stacking plate 21 and whose position in the width direction is determined by a regulating plate (not shown) is pulled out one by one from the top by the paper pulling unit 22 (−X direction), and then registered. It is conveyed to the nip portion of the pair 23.

  The photoconductor unit 30 includes a photoconductor drum 31 that is provided in parallel above the paper feeding device 20 (in the Z direction) and serves as an image carrier that is rotationally driven. A charging roller 32, an exposure device LH, a developing device 40, a primary transfer roller 52, and a cleaning blade 34 are arranged along the rotation direction of the photosensitive drum 31. A cleaning roller 33 for cleaning the surface of the charging roller 32 is disposed opposite to and in contact with the charging roller 32.

The developing device 40 includes a developing housing 41 in which a developer is accommodated. In the developing housing 41, a developing roller 42 disposed to face the photosensitive drum 31, and a pair of augers 44 that stir and convey the developer to the developing roller 42 side obliquely below the back side of the developing roller 42, 45 is arranged. A layer regulating member 46 that regulates the layer thickness of the developer is disposed in proximity to the developing roller 42.
Each of the developing devices 40 is configured in substantially the same manner except for the developer contained in the developing housing 41, and each forms a toner image of yellow (Y), magenta (M), cyan (C), and black (K). To do.

  The surface of the rotating photosensitive drum 31 is charged by the charging roller 32, and an electrostatic latent image is formed by the latent image forming light emitted from the exposure device LH. The electrostatic latent image formed on the photosensitive drum 31 is developed as a toner image by the developing roller 42.

The transfer device 50 includes an intermediate transfer belt 51 to which each color toner image formed on the photoconductive drum 31 of each photoconductor unit 30 is transferred, and each color toner image formed on each photoconductor unit 30 to the intermediate transfer belt. A primary transfer roller 52 that sequentially transfers (primary transfer) to 51 is provided. Further, the image forming apparatus includes a secondary transfer roller 53 that collectively transfers (secondary transfer) each color toner image superimposed and transferred onto the intermediate transfer belt 51 onto a sheet P as a recording medium.

Each color toner image formed on the photosensitive drum 31 of each photosensitive unit 30 is sequentially transferred onto the intermediate transfer belt 51 by the primary transfer roller 52 to which a predetermined transfer voltage is applied from the power supply device 13 or the like controlled by the controller 11. Electrostatic transfer (primary transfer) is performed to form a superimposed toner image in which toners of respective colors are superimposed.
The superimposed toner image on the intermediate transfer belt 51 is conveyed to a region (secondary transfer portion T) where the secondary transfer roller 53 is disposed as the intermediate transfer belt 51 moves. When the superimposed toner image is conveyed to the secondary transfer unit T, the paper P is supplied from the paper feeding device 20 to the secondary transfer unit T in accordance with the timing. A predetermined transfer voltage is applied to the secondary transfer roller 53 from the power supply device 13 or the like controlled by the controller 11, and the intermediate transfer belt 51 is fed to the sheet P fed from the registration roller pair 23 and guided by the conveyance guide. The upper multiple toner images are collectively transferred.

Residual toner on the surface of the photosensitive drum 31 is removed by the cleaning blade 34 and collected in a waste toner container (not shown). The surface of the photosensitive drum 31 is recharged by the charging roller 32. Residues that cannot be completely removed by the cleaning blade 34 and adhere to the charging roller 32 are captured and accumulated on the surface of the cleaning roller 33 that rotates in contact with the charging roller 32.

The fixing device 60 includes an endless fixing belt 61 that rotates in one direction, and a pressure roller 62 that contacts the peripheral surface of the fixing belt 61 and rotates in one direction. A nip portion N (fixing region) is formed by the pressure contact region.
The sheet P on which the toner image is transferred in the transfer device 50 is conveyed to the fixing device 60 via the conveyance guide in a state where the toner image is not fixed. The toner image is fixed on the sheet P conveyed to the fixing device 60 by a pair of fixing belt 61 and pressure roller 62 by the action of pressure bonding and heating. The sheet P on which the fixed toner image is formed is guided by a conveyance guide and is discharged from a discharge roller pair 69 to a discharge tray 1 a on the upper surface of the image forming apparatus 1.

(2) Configuration of Fixing Device FIG. 2 is a schematic cross-sectional view of the fixing device 60 constituting the fixing unit of the image forming apparatus 1 according to the present embodiment. FIG. 3 is a schematic front view of the fixing device 60 as viewed from the paper carry-in side.
The fixing device 60 includes an IH (Induction Heating) heater 80 as an example of a magnetic field generation member that generates an alternating magnetic field, a fixing belt 61 as an example of a fixing member that is electromagnetically heated by the IH heater 80 and fixes a toner image, and fixing. And a pressure roller 62 as an example of a fixing member disposed so as to face the belt 61.

As an example of a support member that supports components such as a pressure pad 63 and a pressure pad 63 that are pressed from the pressure roller 62 via the fixing belt 61 to form the nip portion N on the inner peripheral side of the fixing belt 61. A heat transfer section 64 that generates heat by electromagnetic induction by the action of an alternating magnetic field generated by the holder 65 and the IH heater 80.

At both ends of the fixing belt 61, drive transmission members 67 for transmitting the rotational driving force are provided for rotationally driving the fixing belt 61.
Further, a separation assisting member 70 that assists the separation of the sheet P from the fixing belt 61 is provided on the downstream side in the conveyance direction of the sheet P of the nip portion N between the fixing belt 61 and the pressure roller 62.

(2.1) Fixing Belt FIG. 4 is a cross-sectional layer configuration diagram of the fixing belt 61 constituting the fixing device 60 according to the present embodiment. Hereinafter, the fixing belt 61 will be described with reference to FIGS.
The fixing belt 61 is formed of an endless belt member having an original cylindrical shape, and has a diameter of 20 mm to 50 mm and a length in the width direction of 370 mm when the original shape (cylindrical shape) is used, for example. The fixing belt 61 includes a base material layer 611, a conductive heat generating layer 612 laminated on the base material layer 611, an elastic layer 613 for improving the fixability of the toner image, and a surface release layer 614 coated on the uppermost layer. A belt member having a multilayer structure.

The base material layer 611 is composed of a heat-resistant sheet-like member that supports the thin conductive heat generating layer 612 and forms the mechanical strength of the fixing belt 61 as a whole. 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 up to the temperature-sensitive heat storage member 641 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 μm to 200 μm (preferably 50 μm to 150 μm), a resin material having a thickness of 50 μm to 200 μm, or the like (for example, polyimide resin) ) Is used.

The conductive heating layer 612 is an example of a conductive layer, and is an electromagnetic induction heating element layer that is electromagnetically heated by an AC magnetic field generated by the IH heater 80. The AC magnetic field from the IH heater 80 is increased in the thickness direction. It is a layer that generates eddy current by passing through.
The frequency of the alternating magnetic field generated by the IH heater 80 is, for example, the frequency of the alternating current generated by a general general-purpose power source, that is, 20 kHz to 100 kHz. Therefore, the conductive heating layer 612 has an alternating magnetic field having a frequency of 20 kHz to 100 kHz. Is configured to penetrate and pass.

The region where the alternating magnetic field can enter the conductive heating 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). In the equation (1), f is the frequency of the alternating magnetic field (for example, 20 kHz), ρ is the specific resistance (Ω · m), and μr is the relative permeability.
δ = 503 (ρ / (f × μr)) ^1/2 (1)
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) such that an alternating magnetic field having a frequency of 20 k to 100 kHz penetrates and passes through the conductive heat generating layer 612. It is configured in a thinner layer. 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 relative permeability of about 1) having a thickness of 2 μm to 20 μm and a specific resistance of 2.7 × 10 ⁻⁸ Ω · m or less 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 preferably configured as a thin layer. .

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 50 ° (JIS-A) is suitable for the elastic layer 613.

The surface release layer 614 is provided to weaken the adhesive force with the toner melted on the paper P so that the paper P can be easily peeled from the fixing belt 61. For example, PFA (tetrafluoroethylene perfluoroalkyl vinyl ether polymer), PTFE (polytetrafluoroethylene), silicone copolymer, or a composite layer thereof is used. The thickness of the surface release layer 614 is preferably 1 μm to 50 μm in consideration of the balance between wear resistance and heat capacity.

(2.2) Pressure roller The pressure roller 62 includes, for example, a metal cylindrical core material 621 and a heat-resistant elastic body layer 622 (for example, a silicone rubber layer or the like) coated on the outer peripheral surface of the core material 621. And a release layer 623 made of a heat-resistant resin coating such as PFA or a heat-resistant rubber coating, if necessary.
The pressure roller 62 is arranged to be pressed against the pressing pad 63 via the fixing belt 61 by the moving mechanism 200 to form the nip portion N. Further, the moving mechanism 200 supports the outer peripheral surface of the fixing belt 61 so as to be able to contact and separate. During the fixing operation, the sheet P rotates in the direction of arrow B in FIG. 2 and passes the paper P holding the unfixed toner image through the nip portion N, so that the unfixed toner image is fixed on the paper P by applying heat and pressure.

(2.3) The pressing pad and the holder pressing pad 63 are arranged in a state of being pressed from the pressure roller 62 via the fixing belt 61, and form a nip portion N with the pressure roller 62.
If the pressing pad 63 is a material in which the bending amount when combined with the holder 65 when receiving the pressing force from the pressure roller 62 is less than an allowable value, specifically, the bending amount is 1.0 mm or less. There is no restriction | limiting, For example, heat resistant resins, such as elastic bodies, such as a silicone rubber etc. and fluororubber, glass fiber reinforcement | strengthened PPS (polyphenylene sulfide), a phenol, a polyimide, a liquid crystal polymer, etc. can be used.

The holder 65 that supports the pressing pad 63 includes a holder body 65 a and a spring member 65 b that supports a temperature-sensitive heat storage member 641, a heating member 642, an elastic member 643, and a heat storage member 644 that form the heat transfer section 64. Thus, the uniformity of the pressure in the longitudinal direction (nip pressure) at the nip portion N is maintained. Further, since the fixing device 60 according to the present embodiment employs a configuration in which the fixing belt 61 is heated using electromagnetic induction, the holder main body 65a uses an Fe-based member. Since the magnetic shielding plate 65c made of Al of 0 mm shields the induction magnetic field with respect to the holder main body 65a, the holder main body 65a is not affected by the induction magnetic field.

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, in the pre-nip region 63a, the surface on the pressure roller 62 side is formed in an arc shape that substantially follows the outer peripheral surface of the pressure roller 62, thereby forming a uniform and wide nip portion N. Further, the peeling nip region 63b is formed so as to be locally pressed from the surface of the pressure roller 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.
As a result, a curl in a direction away from the surface of the fixing belt 61 is formed on the paper P passing through the peeling nip region 63b to promote the peeling of the paper P from the surface of the fixing belt 61.

(2.4) Peeling Auxiliary Means In this embodiment, the peeling auxiliary member 70 is disposed on the downstream side of the nip portion N as a peeling auxiliary means by the pressing pad 63. The peeling assisting member 70 is supported by the support plate 72 in a state where the peeling baffle 71 is close to the fixing belt 61 in a direction opposite to the rotational movement direction of the fixing belt 61. The curled portion formed on the paper P at the outlet of the pressing pad 63 is supported by the peeling baffle 71, thereby suppressing the paper P from moving toward the fixing belt 61.

(2.5) Driving Device of Fixing Device Next, the driving mechanism of the pressure roller 62 and the fixing belt 61 in the fixing device 60 of the present embodiment will be described with reference to FIG.
The pressure roller 62 is supported by a moving mechanism 200 that moves to move away from the fixing belt 61 when the fixing roller 61 is not pressed, thereby forming a nip portion N by pressing against the outer peripheral surface of the fixing belt 61. Yes.

During standby before the fixing operation, the pressure roller 62 is placed at a warm-up position separated from the fixing belt 61 by the moving mechanism 200, and the pressure roller 62 is not in physical contact with the fixing belt 61 (latch OFF). become.

As shown in FIG. 3, in the fixing device 60, a rotational driving force from a drive motor 90 as an example of a drive unit is transmitted between a transmission gear 92 fixed to a rotary shaft 91 and transmission gears 93, 94, 95, and 96. And the pressure roller 62 is driven to rotate.
Further, the rotational driving force from the drive motor 90 is transmitted to the shaft 103 via a transmission gear 101 fixed coaxially to the transmission gear 92 on the rotation shaft 91 and a one-way clutch 102 as an example of a rotation transmission limiting member, The transmission gears 104 and 105 coupled to the shaft 103 are transmitted to the gear portions 67b of the drive transmission members 67 disposed at both axial ends of the fixing belt 61, and the fixing belt 61 is rotationally driven.

Next, during the fixing operation, the fixing device 60 is placed in a state where the pressure roller 62 is in pressure contact with the fixing belt 61 (latch ON) by the moving mechanism 200. At this time, the one-way clutch 102 is operated, and the fixing belt 61 is rotated by being driven by the pressure roller 62.

(2.6) IH Heater Next, an 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 with reference to FIG.
As shown in FIG. 2, the IH heater 80 is configured to follow the outer peripheral surface of the fixing belt 61, and is disposed so as to face the heat transfer section 64 with the fixing belt 61 interposed therebetween.

The IH heater 80 includes, for example, a support 81 made of a nonmagnetic material such as a heat resistant resin, an excitation coil 82 that generates an alternating magnetic field, an elastic support member 83 that fixes the excitation coil 82 on the support 81, and a fixing belt 61. And a magnetic core 84 that forms a magnetic path of an alternating magnetic field generated by the exciting coil 82.
Furthermore, a shield 85 that shields the magnetic field, a pressure member 86 that pressurizes the magnetic core 84 toward the support 81, and an excitation circuit 88 that supplies an alternating current (electric power) to the excitation coil 82 are provided.

The support 81 is formed so that the cross section thereof follows the outer peripheral surface of the fixing belt 61 and maintains a predetermined gap (for example, 0.5 mm to 2 mm) with the outer peripheral surface of the fixing belt 61.
As a material constituting the support 81, for example, liquid crystal polymer, heat resistant glass, heat resistant resin such as PC (polycarbonate), PES (polyethersulfone), PPS (polyphenylene sulfide), or glass fiber is mixed with these. A heat-resistant nonmagnetic material such as a heat-resistant resin is used.

The exciting coil 82 is configured by winding, for example, 90 litz wires, which are bundled with, for example, 90 copper wires having a diameter of 0.17 mm and wound in a closed loop with a hollow shape such as an ellipse, an ellipse, or a rectangle. . Then, when an alternating current of 20 k to 100 kHz generated by a general-purpose power supply is supplied from the excitation circuit 88 to the excitation coil 82, an alternating magnetic field is generated around the excitation coil 82.

The elastic support member 83 is a sheet-like member made of an elastic material such as silicone rubber or fluorine rubber, for example, and presses the excitation coil 82 against the support 81, and the excitation coil 82 supports the support surface of the support 81. It is set to be fixed in close contact with 81a.

The magnetic core 84 induces a magnetic field line (magnetic flux) generated by the alternating magnetic field generated by the exciting coil 82, crosses the fixing belt 61 from the magnetic core 84 toward the temperature-sensitive heat storage member 641, and moves inside the temperature-sensitive heat storage member 641. A path of magnetic lines of force (magnetic path) is formed so as to pass through and return to the magnetic core 84. As a result, the magnetic field lines of the alternating magnetic field generated by the exciting coil 82 are concentrated in a region facing the magnetic core 84 of the fixing belt 61.

The magnetic core 84 is desirably used in a form that reduces eddy current loss (current path interruption or division by slits, thin plate bundling, etc.), and is preferably formed of a material having low hysteresis loss. Specifically, for example, an arc-shaped ferromagnetic material composed of a high permeability oxide or alloy material such as sintered ferrite, ferrite resin, amorphous alloy (amorphous alloy), permalloy, temperature-sensitive magnetic alloy, etc. Used.

The length of the magnetic core 84 along the rotation direction of the fixing belt 61 is configured to be smaller than the length of the temperature heat storage member 641 along the rotation direction of the fixing belt 61. Thereby, the leakage of magnetic lines of force 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 is suppressed, and the heat generation efficiency in the fixing belt 61 (conductive heat generation layer 612) is increased.

(2.7) Heat Transfer Part The heat transfer part 64 includes the temperature-sensitive heat storage member 641, the heating member 642, the elastic member 643, and the heat storage member 644 from the inner peripheral surface side of the fixing belt 61 to the central axis O1 of the fixing belt 61. It is laminated in this order toward. The heat transfer section 64 is disposed in contact with the inner peripheral surface of the fixing belt 61 without being pressed while the fixing belt 61 is maintained in a cylindrical shape without contact with the holder main body 65a by the spring member 65b of the holder 65. .

The temperature-sensitive heat storage member 641 is formed in an arc shape (arc-shaped portion) that follows the inner peripheral surface of the fixing belt 61, contacts the inner peripheral surface of the fixing belt 61, and faces the IH heater 80 via the fixing belt 61. Arranged.

Further, the temperature-sensitive heat storage member 641 has a “permeability change start temperature” (see later), which is a temperature at which the magnetic permeability of the magnetic characteristics changes suddenly, is equal to or higher than the fixing set temperature, and the elastic layer 613 and the surface of the fixing belt 61. It is made of a material set within a temperature range lower than the heat resistant temperature of the release layer 614.
Therefore, in the temperature range below the magnetic permeability change start temperature exhibiting ferromagnetism, the magnetic field lines generated by the IH heater 80 pass through the inside of the temperature-sensitive heat storage member 641 along the shape of the temperature-sensitive heat storage member 641. A path is formed (see FIG. 5A).
On the other hand, in the temperature range exceeding the permeability change start temperature, the magnetic field lines generated by the IH heater 80 are transmitted so as to cross the thickness direction of the temperature-sensitive heat storage member 641 and pass through the heat storage member 644. A magnetic path returning to the IH heater 80 is formed (see FIG. 5B).
The “permeability change start temperature” here is a temperature at which the permeability (for example, the permeability measured by JIS C2531) starts to decrease continuously, and is the Curie point at which the magnetism disappears. However, it has a different concept from the Curie point.

Specifically, the material used for the temperature-sensitive heat storage member 641 is, for example, an Fe—Ni alloy (permalloy) in which the magnetic permeability change start temperature is set to a fixing set temperature (for example, 140 ° C. to 200 ° C.) or more. A ternary thermosensitive magnetic alloy such as a binary thermosensitive magnetic alloy or Fe—Ni—Cr alloy is used. Such metal alloys such as permalloy and temperature-sensitive magnetic alloy are suitable for the temperature-sensitive heat storage member 641 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 heat storage member 641 is formed with a thickness larger 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 μm to 600 μm.

FIG. 8 shows an example of the appearance of the heating member 642.
The heating member 642 includes two electrodes 642a and 642c, a resistance member 642b that connects the two electrodes, and two insulating sheets 642d that sandwich the resistance member 642b from both sides.
Specifically, for example, the resistance member 642b can be made of stainless steel having a thickness of 30 μm. The two insulating sheets 642d have thermal conductivity and electrical insulation, for example, a PET (polyethylene terephthalate) sheet laminated with a thin layer such as PP (polypropylene) or PE (polyethylene), or PI (polyimide). A film or the like can be used, and each has a thickness of 50 μm.

The electrodes 642a and 642c are made of a metal such as Ag, Al, Cu, Ni, SUS, and Mo. Here, SUS is used as a base material and is bonded and fixed to the resistance member 642b using a silver paste. A current-carrying wiring (not shown) is connected to the electrodes 642a and 642c. When the current is passed between the pair of electrodes 642a and 642c, the resistance member 642b generates heat (Joule heat) and is sensed through the insulating sheet 642d. The heat storage member 641 is heated.

The elastic member 643 is disposed between the heating member 642 and the heat storage member 644 in close contact with one surface of the heating member 642 and one surface of the heat storage member 644, respectively.
The elastic member 643 is preferably a silicone rubber or a fluorine rubber from the viewpoint of obtaining excellent elasticity and heat resistance. In this embodiment, a silicone rubber having a hardness of 10 ° to 50 ° (JIS-A) is used. Used.
If the thickness of the elastic member 643 is too thin, the adhesion between one surface of the heating member 642 and one surface of the heat storage member 644 is not sufficient, and if it is too thick, the heat capacity becomes too large and the warm-up time becomes long. Therefore, the thickness of the elastic member 643 is preferably 100 μm to 1000 μm in consideration of the balance between adhesion and heat capacity.

The thermal conductivity of the elastic member 643 is set lower than the thermal conductivity of the temperature-sensitive heat storage member 641. Therefore, the elastic member 643 functions as a heat insulating layer, restricts the movement of Joule heat generated by the heating member 642 to the elastic member 643, and promotes the movement to the temperature-sensitive heat storage member 641. The thermal conductivity is a value indicating how easily heat is transmitted for a certain substance. In the present embodiment, specifically, the thermal conductivity of the elastic member 643 is 0.15 W / m · K to 0. .50 W / m · K, and the thermoelectric coefficient of the temperature-sensitive heat storage member 641 is 10 W / m · K to 30 W / m · K.
The thermal conductivity of the silicone rubber can be adjusted to a desired thermal conductivity value by a filler mixed into the silicone rubber during production.

The heat storage member 644 is disposed with the heating member 642 and the elastic member 643 between the inner peripheral surface of the temperature-sensitive heat storage member 641.
The heat storage member 644 stores heat generated by the fixing belt 61 and the temperature-sensitive heat storage member 641. Therefore, the heat storage member 644 is made of a nonmagnetic metal having a relatively small specific resistance value such as Ag, Cu, or Al.
When the temperature-sensitive heat storage member 641 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. Therefore, the heat storage member 644 is formed with a predetermined thickness (for example, 0.5 mm) sufficiently thicker than the skin depth δ (see the above formula (1)) so that the eddy current I flows easily. .

(3) Action and Effect of Fixing Device (3.1) Operation of Fixing Device Next, the operation of the fixing device 60 according to the present embodiment will be described.
First, in the fixing device 60, for example, a toner image forming operation in the image forming apparatus 1 is started, and the driving transmission member 67 is driven by the driving motor 90 in a state where the fixing belt 61 and the pressure roller 62 are separated (latch OFF). And the fixing belt 61 is rotationally driven in the direction of arrow A (see arrow A in FIG. 2).

The fixing belt 61 is driven to rotate, and an alternating current is supplied from the excitation circuit 88 to the excitation coil 82 constituting the IH heater 80. When an alternating current is supplied to the exciting coil 82, a magnetic flux (magnetic field) repeatedly generates and disappears around the exciting coil 82. When this magnetic flux (magnetic field) crosses the temperature-sensitive heat storage member 641, an eddy current is generated in the temperature-sensitive heat storage member 641 so as to generate a magnetic field that hinders the change in the magnetic field, and the skin resistance and temperature sensitivity of the temperature-sensitive heat storage member 641. Heat is generated in proportion to the square of the magnitude of the current flowing through the heat storage member 641.
Further, the resistance member 642b of the heating member 642 closely attached to one surface of the temperature-sensitive heat storage member 641 via the elastic member 643 is energized between the pair of electrodes 642a and 642c to generate heat, and is heated via the insulating sheet 642d. Is done.

Here, the fixing belt 61 has a conductive heat generating layer 612 made of a non-magnetic metal such as Cu (relative magnetic permeability is approximately 1). The fixing belt 61 penetrates the magnetic flux (magnetic field) and transmits the magnetic flux (magnetic field). The conductive heat generating layer 612 generates heat by the action.
The temperature-sensitive heat storage member 641 heats the fixing belt 61 while being rubbed against the inner peripheral surface of the fixing belt 61. As a result, the fixing belt 61 is heated to a set temperature (for example, 150 ° C.) in about 10 seconds, for example.

Next, in a state where the pressure roller 62 is pressed against the fixing belt 61, the paper P sent to the fixing device 60 is sent to the nip portion N between the fixing belt 61 and the pressure roller 62, and the conductive heat generating layer. The toner image is fixed on the surface of the paper P by being heated and pressed by the fixing belt 61 and the pressure roller 62 heated by the heat generation and temperature-sensitive heat storage member 641.
When the sheet P is fed from the nip N between the fixing belt 61 and the pressure roller 62, the sheet P is peeled off from the surface of the fixing belt 61.

(3.2) Operation of Fixing Device Next, the fixing operation of the fixing device 60 according to the present embodiment will be described with reference to the drawings.
The permeability change start temperature of the temperature-sensitive heat storage member 641 is set within a temperature range (for example, 200 ° C. to 240 ° C.) that is equal to or higher than the fixing set temperature and equal to or lower than the heat resistance temperature of the fixing belt 61.

FIG. 5A is a schematic diagram for explaining the operation of the temperature-sensitive heat storage member 641 when the temperature of the fixing belt 61 is not more than the magnetic permeability change start temperature.
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 heat storage member 641 adjacent to the fixing belt 61 is also equal to or lower than the magnetic permeability change start temperature corresponding to the temperature of the fixing belt 61. It becomes. Therefore, the magnetic field lines H of the alternating magnetic field generated by the IH heater 80 pass through the fixing belt 61 and then spread in the temperature-sensitive heat storage member 641 (in a direction orthogonal to the thickness direction of the temperature-sensitive heat storage member 641). Form a magnetic path that passes along.
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. The eddy current I generated in the conductive heat generating layer 612 generates Joule heat that is the product of the specific resistance value R of the conductive heat generating layer 612 and the square of the eddy current I.
Further, the amount of heat generated in the temperature-sensitive heat storage member 641 through which the magnetic lines of force H pass increases, and the temperature-sensitive heat storage member 641 functions as a heat storage member, and heat transfer from the temperature-sensitive heat storage member 641 to the fixing belt 61 occurs.
Further, the temperature-sensitive heat storage member 641 is heated by the heating member 642 that is in close contact with the elastic member 643.

On the other hand, FIG. 5B is a schematic diagram for explaining the action of the temperature-sensitive heat storage member 641 when the temperature of the fixing belt 61 exceeds the magnetic permeability change start temperature.
In the temperature range where the temperature of the fixing belt 61 exceeds the permeability change start temperature, the magnetic field lines H generated by the IH heater 80 are transmitted across the thickness direction of the temperature-sensitive heat storage member 641, and the heat storage member 644 A magnetic path that passes through the inside and returns to the IH heater 80 is formed. That is, the heat storage member 644 is made of a nonmagnetic metal having a relatively small specific resistance value such as Ag, Cu, or Al so that the eddy current I flows easily. In addition, since the thickness is set to a predetermined thickness (for example, 0.5 mm) sufficiently thicker than the skin depth δ (see the above formula (1)), the magnetic lines of force H penetrate the heat storage member 644. Instead, a magnetic path is formed that passes through the inside of the heat storage member 644 along the spreading direction (direction orthogonal to the thickness direction of the heat storage member 644).
Since the eddy current I flowing through the heat storage member 644 acts in a direction that cancels the magnetic lines of force H passing through the temperature-sensitive heat storage member 641, the magnetic flux density penetrating the fixing belt 61 becomes low. As a result, the temperature increase rate of the fixing belt 61 is reduced as compared with the case where the fixing belt 61 is in the state of the magnetic permeability change start temperature or lower.

(3.3) Temperature Distribution of Fixing Device Next, the temperature distribution generated in the fixing belt 61 by the configuration according to the present embodiment will be described. First, problems of the fixing device 60A of the comparative example will be described. The fixing device 60A of the comparative example is different from the fixing device 60 according to the present embodiment in that the heat transfer section 64A does not include the elastic member 643 between the heating member 642 and the heat storage member 644, and other configurations are common. To do.
Therefore, in the following description, common components in the respective fixing devices are denoted by the same reference numerals, and detailed description thereof is omitted.

"Fixing device of comparative example"
FIG. 9 is a schematic cross-sectional view of a comparative fixing device 60A. The heat transfer section 64A does not have the elastic member 643, and the temperature-sensitive heat storage member 641, the heating member 642, and the heat storage member 644 are arranged from the inner peripheral surface side of the fixing belt 61 toward the central axis O1 of the fixing belt 61. It is laminated in order.
Further, the heat transfer section 64A is arranged in contact with the inner peripheral surface of the fixing belt 61 without being pressed while the fixing belt 61 is maintained in a cylindrical shape without being in contact with the holder main body 65a by the spring member 65b of the holder 65. ing. Therefore, the temperature-sensitive heat storage member 641 and the heating member 642 are in contact with each other without being pressed. Similarly, the heating member 642 and the heat storage member 644 are also in non-pressing contact.

On the other hand, the temperature-sensitive heat storage member 641 and the heat storage member 644 are formed with a thickness larger 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, the temperature-sensitive heat storage member 641 is set to about 50 to 600 μm using an Fe—Ni alloy, and the heat storage member 644 is set to about 0.5 mm using Al.
The temperature-sensitive heat storage member 641 is formed in an arc shape (arc-shaped portion) that follows the inner peripheral surface of the fixing belt 61, and the heat storage member 644 is also formed in a similar arc shape (arc-shaped portion).

Therefore, the temperature-sensitive heat storage member 641 and the heat storage member 644 have a certain rigidity, and there is a difference in shape (variation) in the axial direction (Y direction) and the inner peripheral surface direction of the temperature-sensitive heat storage member 641 and the heat storage member 644. When it occurs, there is a non-contact location on the contact surface between the temperature-sensitive heat storage member 641 and the heating member 642, and heat transfer from the heating member 642 to the temperature-sensitive heat storage member 641 becomes uneven.
When the heat transfer from the heating member 642 to the temperature-sensitive heat storage member 641 becomes uneven, the temperature distribution of the temperature-sensitive heat storage member 641 in the axial direction (Y direction) and the inner circumferential surface becomes uneven, and the temperature-sensitive heat storage member 641 The temperature distribution in the axial direction (Y direction) and the inner peripheral surface direction of the fixing belt 61 that is in contact is non-uniform.
As a result, fixing failure and uneven gloss (fixed image gloss) may occur in the fixed image.

FIG. 6A shows the fixing device 60A of the comparative example after the start of energization of the surface temperature of the heating member 642 when a non-contact portion occurs on the contact surface between the temperature-sensitive heat storage member 641 and the heating member 642. It is the figure which showed transition.
If there is a non-contact location on the contact surface between the temperature-sensitive heat storage member 641 and the heating member 642 and there is no heat transfer from the heating member 642 to the temperature-sensitive heat storage member 641, a non-contact portion of the heating member 642 is required. As a result, the temperature rises, causing problems such as thermal deterioration and damage.

"Fixing device of this embodiment"
In the fixing device 60 according to this embodiment, the heat transfer unit 64 includes the temperature-sensitive heat storage member 641, the heating member 642, the elastic member 643, and the heat storage member 644 from the inner peripheral surface side of the fixing belt 61 to the center of the fixing belt 61. The layers are laminated in this order toward the axis O1. The heat transfer section 64 is disposed in contact with the inner peripheral surface of the fixing belt 61 without being pressed while the fixing belt 61 is maintained in a cylindrical shape without contact with the holder main body 65a by the spring member 65b of the holder 65. (See FIG. 2).

FIG. 7 is a schematic diagram showing the layer configuration of the heat transfer section 64. Each arrow in FIG. 7 schematically shows heat transfer from the heating member 642 to the temperature-sensitive heat storage member 641 and the elastic member 643.
In the heat transfer unit 64, the elastic member 643 is disposed between the heating member 642 and the heat storage member 644 in close contact with one surface of the heating member 642 and one surface of the heat storage member 644.
In this embodiment, the elastic member 643 is made of silicone rubber having a hardness of 10 ° to 50 ° (JIS-A) and a thickness of 100 μm to 1000 μm. Therefore, the elastic member 643 has elasticity and its thermal conductivity is temperature sensitive. It is set lower than the thermal conductivity of the heat storage member 641.
Therefore, a contact pressure acts from the elastic member 643 on the contact surface between the temperature-sensitive heat storage member 641 and the heating member 642 to improve the adhesion, and heat transfer from the heating member 642 to the temperature-sensitive heat storage member 641 occurs. Done uniformly.
Furthermore, the elastic member 643 has a thermal conductivity lower than the thermal conductivity of the temperature-sensitive heat storage member 641, and is specifically set to 0.15 W / m · K to 0.50 W / m · K. In addition, a heat insulating function is provided, heat transfer from the heating member 642 to the elastic member 643 is limited, and Joule heat generated by the heating member 642 can be efficiently transferred to the temperature-sensitive heat storage member 641.

FIG. 6B is a diagram illustrating a transition of the surface temperature of the heating member 642 in the fixing device 60 according to the present embodiment after the start of energization.
A contact pressure acts from the elastic member 643 on the contact surface between the temperature-sensitive heat storage member 641 and the heating member 642 to improve adhesion, and heat transfer from the heating member 642 to the temperature-sensitive heat storage member 641 is performed uniformly. Is called. Therefore, the surface temperature of the heating member 642 is controlled within a preset temperature range without excessively increasing the temperature.

As described above, in the fixing device 60 according to the present embodiment, the adhesion between the temperature-sensitive heat storage member 641 and the heating member 642 is improved, and heat transfer from the heating member 642 to the temperature-sensitive heat storage member 641 is performed uniformly.
In addition, the elastic member 643 has a heat insulating function and can efficiently move the heat generated by the heating member 642 to the temperature-sensitive heat storage member 641.
Further, the adhesion between the temperature-sensitive heat storage member 641 and the heating member 642 is improved, the surface temperature of the heating member 642 does not rise excessively, and the heating member 642 is not thermally deteriorated or damaged. .

The embodiments of the present invention have been described with specific examples. However, the technical scope of the present invention is not limited to the above-described embodiments, and various modifications are made without departing from the spirit of the present invention. It is possible.

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus 10 ... Control apparatus 20 ... Paper feed apparatus 30 ... Photoconductor unit 40 ... Developing apparatus 50 ... Transfer apparatus 60, 60A ... Fixing apparatus 61 ... Fixing belt 611: base material layer 612 ... conductive heat generating layer 613 ... elastic layer 614 ... surface release layer 62 ... pressure roller 63 ... pressure pad 64, 64A ... Heat-transfer part 641 ... Temperature-sensitive heat storage member 642 ... Heating member 643 ... Elastic member 644 ... Heat storage member 65 ... Holder 67 ... Drive transmission member 70 ... Peeling auxiliary member 80- ..IH heater 81 ... support 82 ... excitation coil 84 ... magnetic core 90 ... drive motor 200 ... moving mechanism P ... paper N ... nip portion

Claims (6)

A fixing member having a conductive layer and fixing the toner to the recording medium by electromagnetically heating the conductive layer;
A pressure member that conveys the recording medium between the fixing member and the fixing member;
A magnetic field generating means disposed opposite to the fixing member to generate a magnetic field;
A temperature-sensitive heat storage member that is provided in contact with the inner peripheral surface of the fixing member while sliding, and generates heat by electromagnetic induction of the magnetic field to heat the fixing member;
A heating member provided in contact with the inside of the temperature-sensitive heat storage member and heating the temperature-sensitive heat storage member;
A heat storage member that is provided inside the heating member and stores heat;
An elastic member provided in contact with one surface of each of the heating member and the heat storage member;
With
A fixing device. The elastic member has a hardness defined by JIS type A of 50 degrees or less.
The fixing device according to claim 1. The elastic member has a thickness in the range of 100 μm to 1000 μm;
The fixing device according to claim 1. The elastic member has a lower thermal conductivity than the temperature-sensitive heat storage member,
The fixing device according to claim 1. The heating member heats the temperature-sensitive heat storage member by Joule heat generated by power supply;
The fixing device according to claim 1. A photoreceptor on which an electrostatic latent image is formed;
Charging means for charging the photoreceptor;
Latent image forming means for forming a latent image by exposing the photoreceptor charged by the charging means;
A developing device for developing the latent image formed by the latent image forming means;
Transfer means for transferring an image obtained by development of the developing device to a recording medium;
The fixing device according to any one of claims 1 to 5, wherein an image transferred to a recording medium by the transfer unit is fixed.
With
An image forming apparatus.

Images