JP4261727B2 - Image heating device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to an electromagnetic (magnetic) induction heating method.imageHeating equipmentIn placeRelated.
[0002]
[Prior art]
  In an image forming apparatus such as a copying machine, a printer, or a fax machine, an image forming process means such as electrophotography, electrostatic recording, or magnetic recording is used to apply toner (developer) made of heat-meltable resin or the like. An unfixed toner image formed directly or indirectly on the surface of the recording materialHard2. Description of the Related Art Conventionally, a heat roller type fixing device has been widely used as a heating device (image heating device) for performing heat fixing processing as a received image.
[0003]
In recent years, from the viewpoint of quick start and energy saving, a film heating type fixing device (Japanese Patent Laid-Open Nos. 63-313182, 2-157878, 4-44075, 4-204980) is disclosed. However, an electromagnetic induction heating type fixing device that heats a metal film itself has been proposed as a more efficient device.
[0004]
Japanese Utility Model Laid-Open No. 51-109739 discloses an induction heating fixing apparatus in which an eddy current is induced in a metal layer of a fixing film (heating roller) by an alternating magnetic field and the metal layer generates heat by Joule heat. This is because the fixing film can directly generate heat by using the generation of eddy current, and by using input power more effectively than a heat roller type fixing device using a halogen lamp as a heat source, low power consumption is achieved. The warm-up time can be shortened.
[0005]
FIG. 16 shows a schematic configuration of an example of an electromagnetic induction heating type fixing device.
[0006]
Reference numeral 10 denotes a cylindrical fixing film as a heating rotator having an electromagnetic induction heating layer (conductive magnetic member).
[0007]
Reference numeral 16 denotes a saddle-shaped film guide having a substantially semicircular cross section, which is made of a heat-resistant synthetic resin or the like. The cylindrical fixing film 10 is loosely fitted outside the film guide 16.
[0008]
Reference numeral 15 denotes a magnetic field generating means disposed inside the film guide 16 and includes an exciting coil 18, an E-type magnetic core 17, and an exciting circuit (not shown).
[0009]
Reference numeral 30 denotes a pressure roller. The fixing film 10 is sandwiched between the pressure roller 30 and the film guide 16 and a predetermined pressure is applied from the pressure roller 30 to the film guide 16, so that the film guide 16 and the pressure roller 30 have a predetermined width. A fixing nip portion N is formed and mutually pressed.
[0010]
The magnetic core 17 of the magnetic field generating means 15 is disposed corresponding to the position where the fixing nip N is formed.
[0011]
The pressure roller 30 is rotationally driven by the driving means M in the counterclockwise direction indicated by an arrow a. By the rotational driving of the pressure roller 30, a frictional force is generated between the pressure roller 30 and the outer surface of the fixing film 10 in the fixing nip portion N, and the rotational force acts on the fixing film 10. Then, the fixing film 10 has a peripheral speed substantially corresponding to the peripheral speed of the pressure roller 30 while sliding in close contact with the lower surface of the film guide 16 in the fixing nip portion N, and in the clockwise direction of the arrow b. The outer periphery of the guide 16 is rotated (pressure roller driving method).
[0012]
The film guide 16 serves to pressurize the fixing nip N, support the exciting coil 18 and the magnetic core 17 as the magnetic field generating means 15, support the fixing film 10, and transport stability when the fixing film 10 rotates. To do. The film guide 16 is an insulating member that does not hinder the passage of magnetic flux, and a material that can withstand a high load is used.
[0013]
The exciting coil 18 generates an alternating magnetic flux by an alternating current supplied from an exciting circuit (not shown). Since the E-shaped magnetic core 17 is provided corresponding to the position of the fixing nip portion N, the alternating magnetic flux is intensively distributed in the fixing nip portion N, and the alternating magnetic flux is fixed in the fixing nip portion N at the fixing film. An eddy current is generated in 10 electromagnetic induction heating layers. This eddy current generates Joule heat in the heat generating layer due to the specific resistance of the heat generating layer.
[0014]
The temperature of the fixing nip portion N is controlled by supplying a current to the exciting coil 18 by a temperature control system (not shown) including the temperature sensor 26 so that the amount of magnetic flux is controlled and a predetermined temperature is maintained. Adjusted to.
[0015]
Thus, the pressure roller 30 is driven to rotate, and the cylindrical fixing film 10 rotates around the outer periphery of the film guide 16, and electromagnetic induction heat generation of the fixing film 10 is performed by supplying power to the exciting coil 18 from the exciting circuit. As a result, the fixing nip N is heated to a predetermined temperature. Then, in a state where the temperature is adjusted, the recording material P on which the unfixed toner image t is conveyed, which is conveyed from the image forming means (not shown), has an image surface facing upward, that is, facing the surface of the fixing film 10. It is introduced between the fixing film 10 in the fixing nip N and the pressure roller 30.
[0016]
  The image of the recording material P is in close contact with the outer surface of the fixing film 10 at the fixing nip N, and the fixing nip N is nipped and conveyed together with the fixing film 10. In the process in which the recording material P is nipped and conveyed together with the fixing film 10, the fixing film 10 is heated at the fixing nip portion N, and the unfixed toner image t on the recording material P is heated and fixed., SolidA landing image t ′ is formed.
[0017]
After passing through the fixing nip N, the recording material P is transported away from the outer peripheral surface of the fixing film 10.
[0018]
In the fixing device having the above-described configuration, the alternating magnetic flux distribution from the exciting coil 18 as the magnetic field generating means 15 is concentrated in the fixing nip portion N. If the alternating magnetic flux distribution generated by the exciting coil 18 spreads throughout the fixing film 10, the energy of the alternating magnetic flux is used to raise the temperature of the entire fixing film 10, so that the heat dissipation loss is large. For this reason, the ratio of the energy acting on the fixing to the input energy is low and the efficiency is poor. Therefore, in order to obtain the energy acting on the fixing process with high efficiency, in the fixing device shown in FIG. 16, the exciting coil 18 is brought close to the fixing film 10 having the electromagnetic induction heating layer, and the alternating magnetic flux distribution of the exciting coil 18 is fixed. By concentrating in the vicinity of the nip portion N, high efficiency is achieved.
[0019]
[Problems to be solved by the invention]
In an electromagnetic induction heating type fixing device disclosed in Japanese Patent Laid-Open No. 7-319312, a temperature detecting element such as a thermostat is provided as a heat-sensitive safety device at a heat-opposing portion of an electromagnetic induction heating member (heating member). A method of preventing thermal runaway of the apparatus by shutting off the power supply to the exciting coil when detecting a temperature rise above the temperature is used.
[0020]
When the electromagnetic induction heating member is a magnetic member, if the temperature of the electromagnetic induction heating member exceeds the Curie temperature of the electromagnetic induction heating member, the magnetic permeability of the magnetic member rapidly decreases. For this reason, magnetic flux leaks from the electromagnetic induction heat generating member, and this leakage magnetic flux is guided to the magnetic member around the heat generating member. And in the part facing the said magnetic member of a heat generating member, since a leakage magnetic flux concentrates, it generates high heat locally by generation | occurrence | production of an eddy current.
[0021]
  If local high heat generation occurs outside the area facing the heat-sensitive safety device of the electromagnetic induction heating member, the fixing device itself will be damaged before the heat-sensitive safety device is activated.etcCauseYouThere is a fear.
[0022]
  Therefore, the present inventionimageAbnormal temperature rise of the heating member even when the heating device causes a thermal runaway due to failure of the temperature control system and the temperature of the heating layer of the heating member exceeds the Curie temperature of the conductive magnetic member constituting the heating layer Surely detectimageShut off the power supply to the heating deviceimageHeating equipmentPlaceOfferDoFor the purpose.
[0023]
[Means for Solving the Problems]
  The present invention is characterized by the following configuration.imageIt is a heating device.
[0024]
  (1) Excitation coilAnd magneticIt is composed of sex membersEddy current flows due to the action of an alternating magnetic field generated by the power supply to the exciting coil and generates heat.Has a heating layerTubularA heating member;A pressure member that forms a nip portion that sandwiches the recording material together with the heating member, and an element for cutting off the power supply to the exciting coil when the heating member is abnormally heated.Of the heating memberThermal safety activated by abnormal temperature riseElement and,HaveA recording material that carries an image that is nipped and conveyed by the nip portion.Heat generation layerUsing the heat generated inElectromagnetic induction heating method of heatingimageIn the heating device,AboveThe temperature of the heat generation layer is the heat generationLayeredA leakage flux induction member comprising a magnetic member for inducing leakage flux from the heat generation layer that occurs when the Curie temperature is exceeded;Thermal safetyArranged at or near the element locationWhen the leakage magnetic flux is generated, a magnetic flux distribution is formed such that the leakage magnetic flux concentrates on the leakage magnetic flux guiding member, thereby increasing the temperature of the region of the heating member facing the thermal safety element to increase the thermal safety. Advance the operation of the elementCharacterized byimageHeating device.
[0025]
  (2) The distance from the leakage magnetic flux guiding member to the excitation coil is the shortest among the magnetic members disposed at positions facing the excitation coil across the heating member ( As described in 1)imageHeating device.
[0026]
  (3) The magnetic permeability of the leakage magnetic flux guiding member is the largest among the magnetic members disposed at positions facing the exciting coil across the heating member (1) or ( 2)imageHeating device.
[0027]
  (4)The image heating according to any one of claims 1 to 3, wherein the Curie temperature of the magnetic member constituting the leakage magnetic flux induction member is higher than the Curie temperature of the magnetic member of the heat generating layer of the heating member. apparatus.
[0028]
  (5)An exciting coil, a cylindrical heating member that is composed of a magnetic member and has a heat generating layer that generates heat due to an eddy current flowing by the action of an alternating magnetic field generated by power supply to the exciting coil, and a recording material together with the heating member A pressure member that forms a nip portion that sandwiches the heating element, and an element for shutting off the power supply to the exciting coil when the heating member is abnormally heated, and is activated by the abnormal heating of the heating member And an electromagnetic induction heating type image heating apparatus that heats a recording material carrying an image that is nipped and conveyed by the nip portion using heat generated in the heat generation layer,
  Leakage magnetic flux induction member composed of a magnetic member for inducing leakage magnetic flux from the heat generation layer, which is generated when the temperature of the heat generation layer exceeds the Curie temperature of the heat generation layer, or the position where the thermal safety element is disposed An image heating apparatus, wherein the heat-sensitive safety element is accelerated by utilizing heat of the leakage magnetic flux guiding member that is disposed in the vicinity and generates heat by the action of the leakage magnetic flux.
[0039]
  <Operation>
  If the temperature control system does not operate normally due to a device failure or the like and excessive power supply continues to the excitation coil of the magnetic field generating means, the temperature of the heating member rises. At this time, if the temperature of the heat generating layer of the heating member exceeds the Curie temperature of the magnetic member used in the heat generating layer, the magnetic permeability of the heat generating layer rapidly decreases and a magnetic path is formed in the heat generating layer. Magnetic flux leaks. Since most of this leakage magnetic flux is induced by the leakage magnetic flux guiding member, the magnetic flux in the heat generating layer of the heating member portion at the position opposite to the leakage magnetic flux guiding member is relatively higher than other portions, and the temperature of the heating member is increased. It becomes locally high in that part. Therefore, the heat-sensitive safety provided at the same position as or near the leakage magnetic induction member.WholeThe child can be operated quickly.
[0040]
  As a result, even if the device causes a thermal runaway due to a failure of the temperature control system, the temperature of the heating layer of the heating member becomes an abnormal temperature rise state exceeding the Curie temperature of the conductive magnetic member constituting the heating layer. It is possible to shut down the power supply to the device by reliably operating the temperature sensing element, which is a thermal safety deviceThe
[0041]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below.
[0042]
First Embodiment (FIGS. 1 to 13)
A first embodiment of the present invention will be described.
[0043]
(1) Example of image forming apparatus
FIG. 1 is a schematic configuration model diagram of an example of an image forming apparatus. The image forming apparatus of this example is a color laser printer using an electrophotographic process.
[0044]
Reference numeral 101 denotes a photosensitive drum (image bearing member) made of an organic photosensitive member or an amorphous silicon photosensitive member, and is rotationally driven in a counterclockwise direction indicated by an arrow A at a predetermined process speed (circumferential speed).
[0045]
The photosensitive drum 101 is charged to a uniform potential with a predetermined polarity by a charging device 102 such as a charging roller during the rotation process.
[0046]
Next, the charging processing surface is subjected to a scanning exposure process of target image information by a laser beam 103 output from a laser optical box (laser scanner) 110. The laser optical box 110 outputs a laser beam 103 modulated (on / off) corresponding to a time-series electric digital pixel signal of image information from an image signal generator such as an image reading device (not shown). An electrostatic latent image corresponding to the image information is formed on the charging surface of the photosensitive drum 101 by this scanning exposure. Reference numeral 109 denotes a mirror that deflects the output laser light from the laser optical box 110 to the exposure position of the photosensitive drum 101. The electrostatic latent image formed on the photosensitive drum 101 in this way is developed by the four color developer 104.
[0047]
In the case of full-color image formation, scanning exposure and latent image formation are performed on a first color separation component image of a target full-color image, for example, a yellow component image, and the latent image is yellow in the color developer 104 of four colors. The developing device 104Y is operated to develop a yellow toner image. The yellow toner image is transferred onto the surface of the intermediate transfer drum 105 at the primary transfer portion T1 which is a contact portion (or proximity portion) between the photosensitive drum 101 and the intermediate transfer drum 105. The surface of the photosensitive drum 101 after the transfer of the yellow toner image to the surface of the intermediate transfer drum 105 is cleaned by the cleaner 107 from which adhesion residue such as transfer residual toner is removed.
[0048]
The process cycle of charging, scanning exposure, development, primary transfer, and cleaning as described above includes a second color separation component image (for example, a magenta component image, the magenta developer 104M is activated) of a target full color image, and a third color. The intermediate transfer drum is sequentially executed for each color separation component image of the separation component image (for example, cyan component image, cyan developing device 104C is activated) and the fourth color separation component image (for example, black component image, black developing device 104BK is activated). A toner image of four colors, a yellow toner image, a magenta toner image, a cyan toner image, and a black toner image, is sequentially superimposed and transferred onto the surface 105 to form a color toner image corresponding to the target full-color image.
[0049]
The intermediate transfer drum 105 is provided with a middle resistance elastic layer and a high resistance surface layer on a metal drum. The intermediate transfer drum 105 is rotated in the clockwise direction indicated by an arrow B at substantially the same peripheral speed as the photosensitive drum 101 in contact with or close to the photosensitive drum 101. By applying a bias potential to the metal drum of the intermediate transfer drum 105, a potential difference is generated between the intermediate transfer drum 105 and the photosensitive drum 101. Due to this potential difference, the toner image on the photosensitive drum 101 side is transferred to the intermediate transfer drum. Transferred to the surface of 105.
[0050]
The color toner image formed on the surface of the intermediate transfer drum 105 as described above is not shown in the secondary transfer portion T2 in the secondary transfer portion T2 which is a contact nip portion between the intermediate transfer drum 105 and the transfer roller 106. Are transferred to the surface of the recording material P fed from the paper feeding unit at a predetermined timing. The transfer roller 106 supplies a charge having a polarity opposite to that of the toner from the back surface of the recording material P, thereby sequentially transferring the combined color toner images sequentially from the surface of the intermediate transfer drum 105 to the recording material P side.
[0051]
  The recording material P that has passed through the secondary transfer portion T2 is separated from the surface of the intermediate transfer drum 105 and introduced into a heating device (image heating device, fixing device) 100 to heat and fix an unfixed toner image.(Heat treatment)Is discharged to a discharge tray (not shown) outside the apparatus.
[0052]
The fixing device 100 will be described in detail later.
[0053]
The intermediate transfer drum 105 after the color toner image has been transferred to the recording material P is removed by the cleaner 108 to remove residual residues such as transfer residual toner and paper dust. The cleaner 108 is normally held in a non-contact state with the intermediate transfer drum 105, and is in contact with the intermediate transfer drum 105 in the secondary transfer execution process of the color toner image from the intermediate transfer drum 105 to the recording material P. Retained.
[0054]
Also, the transfer roller 106 is normally held in a non-contact state with the intermediate transfer drum 105, and in the process of performing the secondary transfer of the color toner image from the intermediate transfer drum 105 to the recording material P, the transfer roller 106 is held on the intermediate transfer drum 105. The recording material P is held in contact.
[0055]
The image forming apparatus of this embodiment can also execute a mono-color image print mode such as a monochrome image. A double-sided image print mode can also be executed. When the double-sided image printing mode is used, the recording material P on which the first side of the image printed on the first side discharged from the fixing device 100 is reversed through a recirculation conveyance mechanism (not shown) and sent again to the secondary transfer unit T2. Then, the toner image is transferred to the second surface, and is again introduced into the fixing device 100, and the toner image is fixed to the second surface. In this way, double-sided image printing is performed.
[0056]
In the present invention, in the image forming apparatus of FIG. 15, the configuration excluding the fixing device 100 is used as the image forming means.
[0057]
  (2) Fixing device (heating device) 100
  Next, a fixing device as a heating device used in the above-described image forming apparatus(Heat fixing means for fixing the unfixed toner image to the recording material by heat and pressure)100 will be described. The fixing device 100 in this embodiment is an electromagnetic induction heating type device. 2 to 4 are diagrams showing the configuration of the main part of the fixing device 100 of this embodiment, FIG. 2 is a cross-sectional model diagram, FIG. 3 is a front model diagram, and FIG. 4 is (4)-( 4) A vertical cross-sectional model view taken along the line, and FIG. 5 is a perspective model view (fixing film 10 not shown) showing a cross section taken along the line (5)-(5) in FIG. In each figure, the same reference numerals are given to the same components and portions as those of the fixing device shown in FIG.
[0058]
The fixing device 100 of the present embodiment is an electromagnetic induction heating type device using a cylindrical fixing film 10 as in the fixing device of FIG.
[0059]
  In FIG. 2, a film guide 16 has a substantially cylindrical body formed as a whole by abutting the two left and right sectional semicircular arc shaped saddle-shaped members 16a and 16b with the openings facing each other. On the outer peripheral surface side of the film guide 16, a cylindrical fixing film(Cylindrical heating member)10 is loosely fitted.
[0060]
The magnetic field generating means 15 includes magnetic cores 17a, 17b, and 17c, an excitation coil 18, and an excitation circuit 27 (FIG. 5).
[0061]
The magnetic cores 17 a, 17 b, and 17 c are arranged in a T shape inside the right half 16 a of the film guide 16. The exciting coil 18 is held in a space surrounded by the magnetic cores 17a and 17c and the film guide 16a and a space surrounded by the magnetic cores 17a and 17b and the film guide 16a.
[0062]
The magnetic cores 17a, 17b, and 17c are high permeability members, and materials used for transformer cores such as ferrite and permalloy are preferable. Ferrite with less magnetic loss even at 100 kHz or more is more preferable.
[0063]
  As shown in FIG. 5, the excitation coil 18 has power supply portions 18a and 18b, and is connected to the excitation circuit 27 by these power supply portions 18a and 18b. The excitation circuit 27 generates a high frequency of 20 kHz to 500 kHz by a switching power supply. The exciting coil 18 generates an alternating magnetic flux by an alternating current (high-frequency current) supplied from an exciting circuit 27.(Alternating magnetic field)Is generated.
[0064]
  Pressure roller as pressure member(Pressure rotating body)30 is pressed against the sliding member 40 provided on the film guide 16 by a predetermined pressure. As a result, the fixing film 10 is sandwiched between the pressure roller 30 and the sliding member 40, and a fixing nip portion N having a predetermined width is formed at the pressure contact portion between the fixing film 10 and the pressure roller 30.
[0065]
The film guide 16 presses the fixing nip N, supports the exciting coil 18 and the magnetic cores 17a, 17b, and 17c as the magnetic field generating means 15, supports the fixing film 10, and transport stability when the fixing film 10 rotates. Plan. The film guide 16 is made of a material that has an insulating property that does not prevent the passage of magnetic flux and can withstand a high load. Examples of such materials include polyimide resins, polyamide resins, polyamideimide resins, polyether ketone resins, polyether sulfone resins, polyphenylene sulfide resins, and liquid crystal polymers.
[0066]
In the right half 16a of the film guide 16, as shown in FIG. 2, a sliding member 40 whose longitudinal direction is the vertical direction of the paper surface is located on the inner side of the fixing film 10 on the side facing the pressure roller 30 of the fixing nip N. It is arranged. That is, the sliding member 40 is disposed at a position facing the pressure roller 30 with the fixing film 10 in the fixing nip portion N. The sliding member 40 is a member that supports the fixing film 10 from the inner peripheral surface thereof against the pressure applied by the pressure roller 30 in the fixing nip portion N. The sliding member 40 is preferably a member having lubricity in order to reduce sliding resistance. Such members include fluororesin, glass, boron nitride, graphite and the like. The sliding member 40 is further preferably a member having high thermal conductivity in addition to lubricity. Such a sliding member 40 has an effect of making the temperature distribution in the longitudinal direction of the fixing nip portion N uniform. For example, when small-size paper is passed, the amount of heat in the non-sheet passing portion of the fixing film 10 is transferred to the sliding member 40 which is a good heat conducting member, and the heat conduction in the longitudinal direction in the member 40 causes non-passage. The amount of heat in the paper passing section is transferred to the small size paper passing section. Thereby, the effect of reducing the power consumption at the time of passing small-size paper is also obtained. Examples of the sliding member 40 include a composite material such as a metal such as mirror-polished aluminum and a metal in which a lubricant such as fluororesin particles, boron nitride particles, or graphite particles is dispersed. Further, a member having a two-layer structure in which a lubricious member is coated on a high thermal conductive member, for example, a glass coated on aluminum nitride may be used. In this example, a glass-coated member was used on an alumina substrate.
[0067]
When the sliding member 40 has conductivity, it is preferable to dispose the sliding member 40 outside the magnetic field so as not to be affected by the magnetic field generated from the exciting coil 18 and the magnetic cores 17a, 17b, and 17c. . Specifically, the sliding member 40 is disposed at a position separating the magnetic cores 17 b and 17 c from the excitation coil 18 and is disposed outside the magnetic path by the excitation coil 18.
[0068]
In order to further reduce the sliding frictional force between the sliding member 40 and the fixing film 10 in the fixing nip N, a lubricant such as heat resistant grease is provided between the sliding member 40 and the fixing film 10 in the fixing nip N. It can also be interposed. By applying the lubricant, the sliding resistance can be further reduced and the life of the apparatus can be extended.
[0069]
A laterally long pressurizing rigid stay 22 having a U-shaped cross-section is in contact with the inner surface plane portion of the film guide 16b. An insulating member 19 is provided between the pressurizing rigid stay 22 and the magnetic cores 17a, 17b, and 17c to insulate them.
[0070]
As a material of the insulating member 19, a material having excellent insulating properties and good heat resistance is preferable. For example, a phenol resin, a fluororesin, a polyimide resin, a polyamide resin, a polyamideimide resin, a polyether ketone resin, a polyether sulfone resin, a polyphenylene sulfide resin, a PFA resin, a PTFE resin, an FEP resin, an LCP resin, or the like may be selected.
[0071]
Further, flange members 23a and 23b (FIGS. 3 and 4) are fitted on the left and right ends of the assembly of the film guides 16a and 16b, respectively, so that the left and right positions are fixed and rotatably mounted. The flange members 23 a and 23 b receive the end portion of the fixing film 10 when the fixing film 10 rotates, and restrict the shift of the fixing film 10 along the longitudinal direction of the film guide 16.
[0072]
The pressure roller 30 as a pressure member is composed of a core metal 30a and a heat-resistant elastic material layer 30b made of silicone rubber, fluororubber, fluororesin or the like, which is formed and coated concentrically around the core metal in a roller shape. It is configured. The pressure roller 30 is disposed by rotatably supporting both ends of the core metal 30a between chassis side plates (not shown) of the fixing device.
[0073]
3 and 4, the pressure springs 25a and 25b are respectively compressed between the both ends of the pressure rigid stay 22 and the spring receiving members 29a and 29b on the apparatus chassis (not shown) side. A pressing force is applied to the pressure rigid stay 22. As a result, the lower surface of the sliding member 40 provided on the film guide 16a and the upper surface of the pressure roller 30 are pressed against each other with the fixing film 10 interposed therebetween, so that a fixing nip portion N having a predetermined width is formed.
[0074]
The pressure roller 30 is rotationally driven by the driving means M in the counterclockwise direction indicated by the arrow a in the figure. By the rotational driving of the pressure roller 30, a frictional force between the pressure roller 30 and the outer surface of the fixing film 10 is generated, and the rotational force acts on the fixing film 10. Then, the fixing film 10 has a peripheral speed substantially corresponding to the peripheral speed of the pressure roller 30 while sliding with its inner peripheral surface in close contact with the lower surface of the sliding member 40 in the fixing nip portion N. The outer periphery of the film guide 16 is rotated in the clockwise direction indicated by b. That is, the fixing film 10 is rotated in conjunction with the pressure roller 30 by the surface frictional force with the pressure roller 30.
[0075]
As shown in FIG. 5, a plurality of convex rib portions 16e are formed on the peripheral surface of the right half 16a of the film guide 16 at predetermined intervals in the longitudinal direction. Thereby, the contact sliding resistance between the peripheral surface of the film guide 16a and the inner surface of the fixing film 10 is reduced, and the rotational load of the fixing film 10 is reduced. Such a convex rib part can be similarly formed on the left half 16b of the film guide 16.
[0076]
FIG. 6 schematically shows how the alternating magnetic flux generated by the magnetic field generating means 15 is generated. C represents a part of the generated alternating magnetic flux. The alternating magnetic flux C guided to the magnetic cores 17a, 17b, and 17c is vortexed to the electromagnetic induction heating layer 10a of the fixing film 10 between the magnetic cores 17a and 17b and between the magnetic cores 17a and 17c. Generate current. This eddy current generates Joule heat (eddy current loss) in the heat generating layer 10a due to the specific resistance of the heat generating layer 10a. The calorific value Q here is determined by the density of the magnetic flux C passing through the heat generating layer 10a, and shows a distribution as shown in the graph of FIG. In the graph shown in FIG. 6, the vertical axis indicates the circumferential position in the fixing film 10 represented by an angle θ with the center of the magnetic core 17 a being 0, and the horizontal axis is the amount of heat generated in the heat generating layer 10 a of the fixing film 10. Q is indicated. Here, the heat generation region H is defined as a region where the maximum heat generation amount is Q and the heat generation amount is Q / e or more (e is the base of the natural logarithm). This is a region where the amount of heat generated for the fixing process can be obtained.
[0077]
The temperature of the fixing nip N is controlled such that a predetermined temperature is maintained by controlling the current supply to the exciting coil 18 by a temperature control system including the temperature sensor 26 (FIG. 2). The temperature sensor 26 is a temperature sensor such as a thermistor that detects the temperature of the fixing film 10. In this embodiment, the temperature of the fixing nip N is controlled based on the temperature information of the fixing film 10 measured by the temperature sensor 26.
[0078]
  As described above, when the fixing film 10 rotates and the exciting coil 18 is fed by the exciting circuit 27, the electromagnetic induction heat of the fixing film 10 is generated as described above, and the fixing nip portion N rises to a predetermined temperature. Then, the recording material P (corresponding to the heated material) on which the unfixed toner image t, which has been conveyed from the image forming unit in a state controlled to a predetermined temperature, is formed, is fixed to the fixing film 10 in the fixing nip N. And the pressure roller 30 so that the image surface faces upward, that is, faces the surface of the fixing film 10. The recording material P is nipped and conveyed together with the fixing film 10 with the image surface closely contacting the outer surface of the fixing film 10 at the fixing nip portion N. In the process in which the recording material P is nipped and conveyed through the fixing nip N, the fixing film 10 is heated by the electromagnetic induction heat and the unfixed toner image t on the recording material P is heated and fixed. When the recording material P passes through the fixing nip portion N, it is separated from the outer surface of the fixing film 10 and discharged and conveyed. The fixed toner image t on the recording material P is cooled after passing through the fixing nip N.HardAn image t ′ is obtained.
[0079]
In this embodiment, since the toner in which the toner t contains a low softening material is used, the fixing device 100 is not provided with an oil application mechanism for preventing offset (oil application to the fixing film 10), but contains a low softening material. An oil application mechanism may be provided in the case where non-performed toner is used. In addition, when a toner containing a low softening substance is used, oil application or cooling separation may be performed.
[0080]
  In this embodiment, as shown in FIG. 1, a temperature for cutting off the power supply to the exciting coil 18 at the position facing the heat generation area H (see FIG. 6) of the fixing film 10 when the fixing device 100 is thermally runaway. Thermal safety device that is a sensing element (temperature sensing means)(Thermal safety element)The thermoswitch 50 and the leakage magnetic flux guide member 60 are disposed. These will be described in detail later.
[0081]
If the width of the fixing nip portion N of the fixing device 100 of the full-color image forming apparatus is 7.0 mm or more, it is preferable because sufficient fixability of a full-color image with a large amount of applied toner can be secured. If the width of the fixing nip portion N is smaller than the above range, a sufficient amount of heat cannot be given to the unfixed toner image t and the recording material P for fixing.
[0082]
The surface pressure of the fixing nip N is 7.85 × 10.^Four Pa (0.8 kgf / cm² The above is preferable because when an OHP film is used as the recording material P, the light transmittance of a full-color image can be sufficiently ensured. If the surface pressure of the fixing nip N is smaller than the above range, the surface of the layer of the fixed toner image t ′ cannot be sufficiently smoothed, so that irregular reflection light increases and the image portion on the OHP film is transmitted. This is not preferable because the amount of light decreases.
[0083]
From the above viewpoint, in the fixing device 100 of the present embodiment, the pressure roller 30 and the fixing film 10 are pressed with 205.94 N (21 kgf), the width of the fixing nip N is about 8.0 mm, and the fixing nip N The surface pressure is 11.77 Pa (1.2 kgf / cm² (The length in the longitudinal direction of the fixing nip portion N is 220 mm).
[0084]
Hereinafter, each member used in the above-described fixing device (heating device) 100 will be described.
[0085]
A) Excitation coil 18
The exciting coil 18 constituting the magnetic field generating means 15 uses a bundle (bundled wire) of a plurality of thin copper wires each coated with an insulation coating as a conducting wire (electric wire) constituting a coil (wire ring). This is wound a plurality of times to form an exciting coil. In this example, the exciting coil 18 is formed by winding 10 turns.
[0086]
As the covering member for performing the insulating coating, it is preferable to use a coating having heat resistance in consideration of heat conduction due to heat generation of the fixing film 10. For example, a coating such as amideimide or polyimide may be used. The excitation coil 18 may improve the density by applying pressure from the outside.
[0087]
The shape of the exciting coil 18 is formed along the curved surface of the fixing film 10 as shown in FIGS. The distance between the heat generating layer 10a of the fixing film 10 and the exciting coil 18 was set to be about 2 mm.
[0088]
When the distances between the magnetic cores 17a, 17b, and 17c and the exciting coil 18 and the heat generating layer 10a of the fixing film 10 are as close as possible, the magnetic flux absorption efficiency is increased. If this distance is 5 mm or less, it is preferable because the fixing film can absorb the magnetic flux with high efficiency. When this distance is larger than the above range, the magnetic flux absorption efficiency is remarkably lowered, which is not preferable. Further, if the distance between the heat generating layer 10a of the fixing film 10 and the exciting coil 18 is within 5 mm, this distance does not need to be constant.
[0089]
In FIG. 5, the power supply portions 18 a and 18 b drawn from the exciting coil 18 are provided with an insulating coating on the outside of the bundled wire.
[0090]
B) Fixing film (heating member having a heat generating layer) 10
FIG. 7 is a layer configuration model diagram of the fixing film 10 that generates electromagnetic induction heat as a heating member in the present embodiment.
[0091]
The fixing film 10 of this embodiment is composed of a heat generation layer (electromagnetic induction heat generation layer) 10a made of a metal film or the like as a base layer, an elastic layer 10b laminated on the outer surface, and a release layer 10c laminated on the outer surface. It has a composite structure. For adhesion between the heat generation layer 10a and the elastic layer 10b and adhesion between the elastic layer 10b and the release layer 10c, a primer layer (not shown) may be provided between the layers. In the fixing film 10 having a substantially cylindrical shape, the heat generating layer 10a is on the inner side in contact with the sliding member 40, and the release layer 10c is on the outer side in contact with the pressure roller 30 or the recording material (heated material).
[0092]
As described above, when the alternating magnetic flux acts on the heat generating layer 10a, an eddy current is generated in the heat generating layer 10a and the heat generating layer 10a generates heat. Since the heat is transmitted to the elastic layer 10b and the release layer 10c, the entire fixing film is heated, and the recording material P as the heating material to be passed through the fixing nip portion N is heated to thereby form the toner image. Heat fixing is performed.
[0093]
a. Heat generation layer 10a
As the heat generating layer 10a, magnetic and nonmagnetic metals can be used, but magnetic metals are preferably used. As such a magnetic metal, a ferromagnetic metal such as nickel, iron, ferromagnetic stainless steel, nickel-cobalt alloy or permalloy is preferably used. In addition, in order to prevent metal fatigue due to repeated bending stress received when the fixing film 10 rotates, a member in which manganese is added to nickel may be used.
[0094]
The thickness of the heat generating layer 10a is preferably greater than the skin depth σ [m] represented by the following formula and 200 μm or less. If the thickness of the heat generating layer 10a is within this range, the heat generating layer 10a can efficiently absorb electromagnetic waves, and therefore heat can be generated efficiently.
[0095]
σ = 503 × (ρ / fμ)^1/2
Here, f is the frequency [Hz] of the excitation circuit, μ is the magnetic permeability, and ρ is the specific resistance [Ωm] of the heat generating layer 10a.
[0096]
This skin depth indicates the depth of absorption of electromagnetic waves used for electromagnetic induction, and the intensity of electromagnetic waves is 1 / e or less deeper than this. Conversely, most of the energy is absorbed up to this depth. FIG. 8 shows the relationship between the heat generation layer depth and the electromagnetic wave intensity.
[0097]
The thickness of the heat generating layer 10a is more preferably 1 to 100 μm. When the thickness of the heat generating layer 10a is thinner than the above range, the efficiency is deteriorated because most of the electromagnetic energy cannot be absorbed. Further, when the heat generating layer 10a is thicker than the above range, the rigidity of the heat generating layer 10a becomes too high, and the flexibility becomes poor, so that it is not practical to use as a rotating body.
[0098]
b. Elastic layer 10b
The elastic layer 10b is preferably made of a material having good heat resistance and thermal conductivity, such as silicone rubber, fluorine rubber, and fluorosilicone rubber.
[0099]
The thickness of the elastic layer 10b is preferably 10 to 500 μm in order to guarantee the fixed image quality. When a color image is printed, a solid image is formed over a large area on the recording material P, particularly in a photographic image. In this case, if the heating surface (release layer 10c) cannot follow the unevenness of the recording material P or the unevenness of the toner layer t, uneven heating occurs, and uneven gloss occurs in the image where the heat transfer amount is large and small. . That is, the glossiness is high in the portion where the heat transfer amount is large, and the glossiness is low in the portion where the heat transfer amount is small.
[0100]
When the thickness of the elastic layer 10b is smaller than the above range, the release layer 10c cannot follow the unevenness of the recording material P or the toner layer t, and image gloss unevenness occurs. On the other hand, if the elastic layer 10b is too larger than the above range, the thermal resistance of the elastic layer becomes too large, making it difficult to realize a quick start. The thickness of the elastic layer b is more preferably 50 to 500 μm.
[0101]
If the hardness of the elastic layer 10b is too high, the unevenness of the recording material P or the toner layer t cannot be followed and image gloss unevenness occurs. Therefore, the hardness of the elastic layer 10b is preferably 60 ° (JIS-A; JIS-K (using A type measuring device)) or less, more preferably 45 ° or less.
[0102]
The thermal conductivity λ of the elastic layer 10b is 2.52 × 10^-1~ 8.4 × 10^-1W / m · ° C (6 × 10^-Four~ 2x10^-3cal / cm · sec · deg. ) Is preferable. When the thermal conductivity λ is smaller than the above range, the thermal resistance is too large, and the temperature rise in the surface layer (release layer 10c) of the fixing film 10 is slow. When the thermal conductivity λ is larger than the above range, the hardness of the elastic layer b becomes too high or compression set tends to occur. More preferably 3.35 × 10^-1~ 6.28x10^-1W / m · ° C (8 × 10^-Four~ 1.5 × 10^-3cal / cm · sec · deg. ) Is good.
[0103]
c. Release layer 10c
The release layer 10c is preferably made of a material having good release properties and heat resistance such as fluororesin, silicone resin, fluorosilicone rubber, fluororubber, silicone rubber, PFA, PTFE, FEP.
[0104]
The thickness of the release layer 10c is preferably 1 to 100 μm. When the thickness of the release layer 10c is smaller than the above range, uneven coating of the coating film occurs, and there arises a problem that a part having poor release properties is formed or durability is insufficient. Moreover, when a mold release layer is larger than the said range, heat conduction will deteriorate. In particular, when a resin material is used for the release layer 10c, the hardness of the release layer 10c becomes too high and the effect of the elastic layer 10b is lost.
[0105]
C) Temperature detection element 50 (thermal safety device)
As described above, in the present embodiment, the temperature detection element (temperature detection means) for cutting off the power supply to the excitation coil 18 at the time of the thermal runaway of the fixing device 100 is located at a position facing the heat generation area H of the fixing film 10. A thermoswitch 50 is provided as a heat-sensitive safety device.
[0106]
FIG. 9 shows a schematic cross-sectional view of the thermo switch 50. Reference numerals 51a and 51b denote first and second fixed contacts, and reference numeral 52 denotes a movable contact in which the two fixed contacts 51a and 51b are always electrically connected to each other (contact closing).
[0107]
The movable contact 52 is disposed so as to be movable around the connection portion g with the first fixed contact 51a, and is pushed upward as indicated by a two-dot chain line in the figure by the movement of the moving pin 53. By separating from the second fixed contact 51b (contact open), the electric circuit (power feeding circuit for the exciting coil) connected to the first and second fixed contacts 51a and 51b can be opened.
[0108]
The moving pin 53 is disposed in contact with the movable contact 52 and the heat sensitive part 54. The heat-sensitive part 54 is configured by a member such as a bimetal whose shape changes as the temperature rises. When the heat sensitive part 54 reaches a predetermined temperature or more, it is deformed into a convex shape in the figure. This predetermined temperature is the operating temperature at which the contact is opened. Along with the deformation of the heat sensitive part 54, the moving pin 53 moves upward, pushes up the movable contact 52, and opens the contact.
[0109]
A case 55 encloses the members 51a, 51b, 52, 53 and 54 described above.
[0110]
  The thermo switch 50 is located at a position facing the exciting coil 18 with the fixing film 10 interposed therebetween.InProvide. In this embodiment, the fixing film 10 is disposed in a non-contact manner on the outer surface. More preferably, as shown in FIG. 6, the fixing film 10 may be disposed so as to face the heat generating area H. The distance between the thermo switch 50 and the fixing film 10 was about 2 mm. Thereby, the fixing film 10 is not damaged by the contact of the thermo switch 50, and the deterioration of the fixed image due to durable use can be prevented.
[0111]
However, the thermo switch 50 may be disposed by contacting the heat-sensitive portion 54 directly to the fixing film 10 or indirectly with a lubricating layer or the like interposed therebetween.
[0112]
FIG. 10 is a circuit diagram of a thermal runaway prevention circuit used in this embodiment. The thermo switch 50 is incorporated in this thermal runaway prevention circuit. A thermo switch 50 as a temperature detecting element is connected in series with a 24V DC power source and a relay switch 70. When the thermo switch 50 is turned off, the power supply to the relay switch 70 is cut off, and the relay switch 70 is operated to cut off the power supply to the excitation circuit 27, thereby cutting off the power supply to the excitation coil 18 (ab). The structure to be taken is taken. In this embodiment, the operating temperature for opening the contact of the thermo switch 50 is set to 220 ° C.
[0113]
According to this embodiment, when the fixing device 100 is out of control due to a failure of the temperature control system or the like, the fixing device 100 stops with the recording material P sandwiched in the fixing nip portion N, and power is supplied to the excitation coil 18. Even if the fixing film 10 continues to generate heat, it does not generate heat at the fixing nip N where the recording material P is sandwiched, unlike the structure where heat is generated at the fixing nip N as shown in FIG. The recording material P is not directly heated. In addition, since the thermo switch 50 is disposed in the heat generation area H where the heat generation amount is large, when the thermo switch 50 senses a temperature of 220 ° C. or higher and the thermo switch is turned off, it is excited by the relay switch 70. The power supply to the coil 18 is cut off.
[0114]
According to this embodiment, since the ignition temperature of the paper as the recording material P is about 400 ° C., the heat generation of the fixing film 10 can be stopped without the paper igniting.
[0115]
As the temperature detecting element 50, a thermal fuse may be used in addition to the thermoswitch. In this embodiment, a non-contact type thermo switch is used. However, a contact type thermo switch may be used in contact with the fixing film 10.
[0116]
D) Leakage magnetic flux induction member 60
In this embodiment, as shown in FIGS. 2 and 6, a leakage flux guiding member 60 is disposed at or near the position where the thermo switch 50 is disposed.
[0117]
The leakage flux induction member 60 is for inducing leakage flux generated when the temperature of the heat generation layer 10a of the fixing film 10 exceeds the Curie temperature of the members constituting the heat generation layer 10a.
[0118]
The Curie temperature is a temperature at which a magnetic material such as a ferromagnetic material undergoes a magnetic transition to paramagnetism. The magnetic permeability of the ferromagnetic material gradually decreases as the temperature increases, but when the temperature reaches the Curie temperature, it rapidly decreases and becomes paramagnetic.
[0119]
The leakage magnetic flux guiding member 60 may be a plate-like member, or as shown in FIG. 11, a through hole 60a is provided at a position corresponding to the heat sensitive portion 54 of the thermoswitch 50 of the leakage magnetic flux guiding member 60 so It is also effective to have a shape that does not block the radiant heat to the heat sensitive part 54 of the switch 50. That is, since the radiant heat from the fixing film 10 is not blocked by adopting such a shape, when the heat capacity of the leakage flux guiding member 60 is large or when the thermal conductivity is small, that is, in the leakage flux guiding member 60. This is effective when a member with poor thermal response is used.
[0120]
Since this leakage flux induction member 60 induces the magnetic flux C, it is necessary to use a magnetic member such as a ferromagnetic material. Examples of such a magnetic member include iron, ferrite, nickel, permalloy and the like.
[0121]
  Further, the leakage flux guiding member 60 may be a conductive magnetic member. In this case, the leakage flux guiding member 60 can heat the leakage flux guiding member 60 itself due to the eddy current caused by the leakage flux, and the ambient temperature around the thermoswitch 50 can be further increased. Therefore, the ambient temperature around the heat sensitive part 54 of the thermo switch 50 can be increased. Examples of such members include magnetic metals such as iron, nickel, cobalt, permalloy, and magnetic stainless steel.(Ferromagnetic metal)Is mentioned. In this embodiment, iron is used for the leakage flux guiding member 60.
[0122]
The magnetic member constituting the leakage flux guiding member 60 may have a Curie temperature higher than the Curie temperature of the member constituting the heat generating layer 10a. In this case, since the magnetism of the leakage flux guiding member 60 can be ensured up to a temperature range higher than that of the heat generating layer 10a, the leakage flux can be reliably induced. For example, when nickel (Curie temperature 358 ° C.) is used for the heat generating layer 10 a, iron (Curie temperature 770 ° C.) may be used for the leakage flux induction member 60.
[0123]
In the fixing device 100, when a magnetic member other than the leakage flux guiding member 60 is disposed in a region facing the exciting coil 18 with the fixing film 10 interposed therebetween, the shortest distance from the leakage flux guiding member 60 to the exciting coil 18. However, it is necessary to make it the shortest among the magnetic members arranged at positions facing the exciting coil 18. As a result, the leakage magnetic flux generated when the heat generation layer 10 a exceeds the Curie temperature is induced toward the leakage magnetic flux guiding member 60.
[0124]
Further, the shape of the sheet metal member made of a magnetic member (for example, iron) constituting the fixing device 100 is set such that the distance between the sheet metal member and the exciting coil 18 is shortest than other portions only at the position where the thermo switch 50 is disposed. A shaped member can also be used as the leakage flux guiding member 60.
[0125]
E) Safe operation
Next, an outline of the safe operation of the apparatus at the time of thermal runaway of the fixing apparatus 100 due to failure of the temperature control system will be described.
[0126]
When the temperature control system does not operate normally due to a device failure or the like, and the excessive power supply to the exciting coil 18 continues, the temperature of the fixing film 10 rises above the control temperature. In particular, when the fixing film 10 is in the rotation stopped state, the position of the fixing film 10 where the eddy current is generated (the heat generation area H in FIG. 6) does not change, so the temperature is instantaneously increased.
[0127]
FIG. 12 shows the state of the magnetic path when the heat generating layer 10a of the fixing film 10 is heated to a temperature equal to or higher than the Curie temperature of the magnetic member constituting the layer. When the temperature of the heat generating layer 10a exceeds the Curie temperature (for example, 358 ° C. when the heat generating layer 10a is nickel), the magnetic permeability of the heat generating layer 10a rapidly decreases, forming a magnetic path in the heat generating layer 10a. Magnetic flux C leaks from the heat generating layer 10a. The magnetic flux leaking from the heat generating layer 10a makes the air part of the magnetic path.
[0128]
In the state where the heat generating layer 10a is heated to the Curie temperature or higher, it is possible to verify the difference in the temperature of the fixing film 10 due to the presence or absence of the leakage flux guiding member 60 by considering the magnetic circuit described below. .
[0129]
Considering the magnetic resistance in the magnetic path shown in FIG. 12, this is defined as the magnetic resistance per unit length in the longitudinal direction. It is considered that each magnetic resistance at each position in the longitudinal direction is distributed in the longitudinal direction from end to end of the exciting coil with respect to the exciting coil that generates magnetomotive force. Therefore, the magnetic circuit of the fixing device 100 of the present embodiment can be replaced with an equivalent circuit model in which the magnetic resistance at each position in the longitudinal direction is connected in parallel. This is shown in FIG.
[0130]
Among the magnetic resistances shown in FIG. 13, the magnetic resistance at the position where the leakage flux guiding member 60 is disposed is R_M The magnetic resistance R at the position where the leakage magnetic flux guiding part 60 is not disposed_N And The magnetic resistance is inversely proportional to the size of the magnetic permeability in the magnetic path. When the temperature of the heat generation layer 10a is equal to or higher than the Curie point, the magnetic flux C leaks from the heat generation layer 10a, and the leakage magnetic flux induction member 60 formed of a magnetic member is used as a part of the magnetic path. Magnetoresistance R at position_M Is R_M <R_N It becomes a relationship.
[0131]
The magnetomotive force F is determined by the product of the number of turns N of the exciting coil 18 and the current I flowing therethrough, and the magnetomotive force F acts on each of the magnetoresistors at each position in the longitudinal direction connected in parallel. That is, the magnetic resistance R_M And R_N Works with the same magnitude of magnetomotive force F. The magnetic flux at the position where the leakage flux guiding member 60 is arranged is φ_M The magnetic flux at the position where the leakage flux guiding member 60 is not disposed is φ_N Then, since the magnetomotive force F is equal regardless of the position in the longitudinal direction,
φ_M = F / R_M     φ_N = F / R_N
It becomes. Magnetoresistance is R_M <R_N Therefore, the magnetic flux is φ_M > Φ_N Thus, it can be seen that the magnetic flux at the position where the leakage flux guiding member 60 is disposed is larger than the position where the leakage flux guiding member 60 is not disposed. The total magnetic flux generated from the exciting coil 18 is φ_M + Φ_N + Φ_N + Φ_N In consideration of the fact that the magnetic flux distribution is concentrated in the longitudinal direction.
[0132]
As described above, when the heat generating layer 10a is equal to or higher than the Curie temperature, the magnetic flux generated from the exciting coil 18 is concentrated on the portion having a small magnetic resistance where the leakage flux guiding member 60 is disposed. The calorific value of 10 increases locally.
[0133]
In the vicinity of the portion of the fixing film 10 facing the leakage magnetic flux guiding member 60, the amount of heat generation is locally relatively larger than that of the other portions, so that the temperature of the fixing film 10 is locally increased. Therefore, the thermoswitch 50 provided at the same position as or near the leakage flux guiding member 60 can be operated more quickly.
[0134]
  As described above, in the fixing device of this embodiment, the device causes a thermal runaway due to a failure of the temperature control system, and the temperature of the heat generating layer 10a of the fixing film 10 serving as a heating member is the Curie temperature of the magnetic member of the heat generating layer 10a. It is possible to reliably operate the thermal safety device 50 even in a state exceedingThe
[0135]
<Second embodiment>
Next, a second embodiment will be described.
[0136]
The image forming apparatus of this embodiment is the same as the image forming apparatus described in the first embodiment except for the fixing device 100. Further, the configuration of the fixing device 100 of the present embodiment is the same as that of the fixing device 100 of the first embodiment except for the leakage magnetic flux guiding member 60.
[0137]
In the present embodiment, the leakage flux guiding member 60 is constituted by a magnetic member having the maximum permeability among magnetic members disposed at positions facing the exciting coil 18 with the fixing film 10 interposed therebetween. And
[0138]
For example, iron around the fixing film (permeability: 10² Order), a permalloy (permeability: 10) is applied to the leakage flux guiding member 60.^Three Order).
[0139]
With the configuration of this embodiment, even if another magnetic member is provided in the vicinity of the heat generation area H of the fixing film 10, the leakage magnetic flux generated when the heat generation layer 10 a exceeds the Curie point is transferred to the vicinity of the leakage magnetic flux guiding member 60. The guidance can be performed more reliably than in the first embodiment. Therefore, since the temperature of the fixing film 10 at the position where the leakage flux guiding member 60 is disposed can be relatively higher than other positions, the fixing film 10 is provided at the same position as or near the leakage flux guiding member 60. It is possible to operate the existing thermo switch 50 more quickly and reliably.
[0140]
  As described above, also in the fixing device of the present embodiment, as in the first embodiment, the device causes a thermal runaway due to the failure of the temperature control system, and the temperature of the heat generating layer 10a of the fixing film 10 becomes the heat generating layer 10a. Even when the Curie temperature of the magnetic member is exceeded, the thermal safety device 50 can be reliably operated.The
[0141]
<Third embodiment> (FIG. 14)
Next, a third embodiment will be described.
[0142]
The image forming apparatus of this embodiment is the same as the image forming apparatus described in the first embodiment except for the fixing device 100. The configuration of the fixing device 100 of the present embodiment is the same as that of the fixing device 100 of the first embodiment, except for the positions where the thermoswitch 50 and the leakage flux guiding member 60 are disposed.
[0143]
FIG. 14 is a front model view of the fixing device 100 in this embodiment. The fixing device 100 according to the present embodiment is characterized in that a thermo switch 50 and a leakage magnetic flux guiding member 60 as temperature detecting elements are arranged in a non-sheet passing area of the fixing film 10.
[0144]
In the configuration of the present embodiment, the portion where the thermo switch 50 is disposed is the non-sheet passing area of the fixing film 10, so that even if the surface of the fixing film 10 is damaged due to contact with the thermo switch 50, the quality of the fixed image may be degraded. There is no. For this reason, the thermo switch 50 can be disposed in contact with the fixing film 10.
[0145]
Further, even when a material to be heated such as paper or an OHP film is wound around the fixing film 10, the thermo switch 50 disposed in the non-sheet passing area can reliably detect the surface temperature of the fixing film 10. Therefore, the reliability of the operation of the thermo switch 50 can be improved.
[0146]
Further, since the high heat generation area of the fixing film 10 due to the leakage magnetic flux guiding member 60 when the heat generation layer 10a exceeds the Curie point is in the non-sheet passing area of the fixing film 10, the heated material wound around the fixing film 10 Since P is not locally concentrated and heated, ignition from the material to be heated P can be prevented.
[0147]
  As described above, also in the fixing device of the present embodiment, as in the first embodiment, the device causes a thermal runaway due to the failure of the temperature control system, and the temperature of the heat generating layer 10a of the fixing film 10 becomes the heat generating layer 10a. Even when the Curie temperature of the magnetic member is exceeded, the thermal safety device 50 can be reliably operated.The
[0148]
<Fourth Embodiment> (FIG. 15)
Next, a fourth embodiment will be described.
[0149]
The image forming apparatus of this embodiment is the same as the image forming apparatus described in the first embodiment except for the fixing device 100. The configuration of the fixing device 100 is the same as that of the fixing device 100 described in the first embodiment except for the thermo switch 50 and the leakage flux guiding member 60.
[0150]
FIG. 15 is a cross-sectional model diagram showing the positional relationship between the thermo switch 50 and the leakage flux guiding member 60 of the fixing device 100 in this embodiment. The fixing device 100 according to the present embodiment is characterized in that the heat sensitive part 54 of the thermo switch 50 and the leakage magnetic flux guiding member 60 are brought into contact with each other. In this embodiment, the leakage magnetic flux guiding member 60 is further incorporated in the thermo switch 50.
[0151]
As in the first embodiment, the thermo switch 50 that is a temperature detecting element is disposed at a position 2 mm away from the surface of the fixing film 10. Since the thermo switch 50 is incorporated in the thermal runaway prevention circuit (FIG. 10) as in the first embodiment, the power supply to the exciting coil 18 can be cut off when a predetermined temperature is detected.
[0152]
The leakage magnetic flux guiding member 60 is preferably a magnetic member having conductivity. In this case, an eddy current can be generated in the leakage magnetic flux guiding member 60 itself by the leakage magnetic flux to generate Joule heat, so that the temperature of the thermosensitive part 54 of the thermo switch 50 can be raised more quickly.
[0153]
The leakage magnetic flux induction member 60 is preferably a member having high thermal conductivity. In this case, since the radiant heat received from the fixing film 10 by the leakage magnetic flux guiding member 60 can be quickly transmitted to the heat sensitive part 54 of the thermo switch 50, similarly, the temperature of the heat sensitive part 54 can be raised quickly.
[0154]
The leakage magnetic flux guiding member 60 may be brought into direct contact with the heat-sensitive part 54 of the thermo switch 50 or may be brought into contact indirectly through another member.
[0155]
With the configuration of this embodiment, the temperature of the thermosensitive part 54 of the thermo switch 50 is increased more quickly due to Joule heat generation due to eddy current of the leakage flux induction member 60 and temperature rise due to radiant heat from the fixing film 10 of the leakage flux induction member 60. Can be warmed. Therefore, even if the thermo switch 50 is arranged in non-contact with the fixing film 10, it is possible to reduce a delay in response of the detected temperature of the thermo switch 50 from the temperature of the fixing film 10.
[0156]
  As described above, also in the fixing device of the present embodiment, as in the first embodiment, the device causes a thermal runaway due to the failure of the temperature control system, and the temperature of the heat generating layer 10a of the fixing film 10 becomes the heat generating layer 10a. Even when the Curie temperature of the magnetic member is exceeded, the thermal safety device 50 can be reliably operated.The
[0157]
  <Other Examples>
  1) The fixing device 100 in each of the first to fourth embodiments described above is driven manually by suspending and stretching an endless belt-like fixing film (rotating body) 10 as a heating member between a plurality of members. Rotating structureFinallyYou can also
[0158]
2) The fixing film 10 may have a configuration in which the elastic layer 10b is omitted in the case of heating and fixing such as a monochrome or one-pass multi-color image. Further, the release layer 10c may be omitted. It can also be made into the layer structure which added the other desired functional layer.
[0159]
3) The pressure member 30 is not limited to a roller, and may be a pressure member of another form such as a rotating belt type. Further, in order to supply thermal energy to the recording material P also from the pressing member side, a heat generating means such as electromagnetic induction heating is provided also on the pressing member side so as to heat and control the temperature to a predetermined temperature. You can also.
[0160]
When the pressure member 30 is a rotating body, it can be configured as a device that is rotationally driven as in the embodiment, or can be configured as a device that is driven and rotated by frictional contact with a heating member or the like. it can.
[0161]
  4) The heating device of the present invention is not limited to the image heating and fixing device of the embodiment, but an image heating device that heats a recording material carrying an image to improve surface properties such as gloss, and image heating that is supposed to be worn. Can be widely used as a device.
[0162]
【The invention's effect】
    As described above in detail, according to the present invention, an electromagnetic (magnetic) induction heating type image heating apparatus.In order to accelerate the operation of the thermal safety element using the leakage magnetic flux, for example, the power supply to the exciting coil cannot be normally performed and the rotation of the cylindrical heating member is stopped. Even in the case where the heating rate of the heating member is very fast, there is an effect that the power supply to the exciting coil can be cut off at an early stage after the leakage magnetic flux is generated.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment.
FIG. 2 is a schematic cross-sectional view of the main part of the fixing device.
[Fig. 3] Front view of the main part
4 is a longitudinal cross-sectional model view taken along line (4)-(4) in FIG. 2;
5 is a schematic perspective view taken along line (5)-(5) in FIG. 2 (a fixing film is not shown).
FIG. 6 is a diagram showing the relationship between magnetic field generation means and calorific value Q
FIG. 7 is a layer configuration model diagram of a fixing film.
FIG. 8 is a graph showing the relationship between the heat generation layer depth and the electromagnetic wave intensity.
FIG. 9 is a schematic longitudinal sectional view of the thermo switch of the first embodiment.
[Figure 10] Thermal runaway prevention circuit diagram
FIG. 11 is a perspective view showing a shape example of a leakage flux guiding member 60
FIG. 12 is a diagram showing a magnetic path when the heat generation layer of the fixing film exceeds the Curie temperature.
FIG. 13 is a diagram showing an equivalent circuit model of a magnetic circuit in the fixing device.
FIG. 14 is a front model view of a fixing device according to a third embodiment.
FIG. 15 is a vertical cross-sectional model view of a thermo switch of a fourth embodiment.
FIG. 16 is a schematic cross-sectional view of a main part of a conventional fixing device.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Fixing film, 10a ... Heat generating layer, 10b ... Elastic layer, 10c ... Release layer, 15 ... Magnetic field generating means, 16 (a * b) ... Film guide, 17 (ab * c) ... Magnetic core, 18 ... Excitation coil, 22 ... Pressure rigid stay, 23 (ab) ... Flange member, 25 (ab) ... Pressure spring, 26 ... Temperature sensor, 27 ... Excitation circuit, 30 ... Pressure roller, 40 DESCRIPTION OF SYMBOLS ... Sliding member, 50 ... Thermo switch (temperature detection element, heat-sensitive safety device) 54 ... Heat-sensitive part, 60 ... Leakage magnetic flux induction member, 70 ... Relay switch, 100 ... Fixing device (heating device), 101 ... Photosensitive drum, DESCRIPTION OF SYMBOLS 102 ... Charging device 103 ... Laser light 104 ... Developer 105 ... Intermediate transfer drum 106 ... Transfer roller 107 ... 108 Cleaner C ... Alternating magnetic flux H ... Heat generating position M ... Drive means N ... Fixing Nip part, P The recording material, t ... unfixed toner image, t '... fixed toner image, T1 ... primary transfer portion, T2 ... secondary transfer portion

Claims (5)

An excitation coil, a cylindrical heating member having a heat generating layer which eddy currents generate heat flows by the action of the alternating magnetic field generated by the power supply to the exciting coil is composed of a magnetic member, a recording with said heating member A pressure member that forms a nip portion that sandwiches the material, and an element for shutting off power supply to the exciting coil when the heating member is abnormally heated. includes a device, and the image heating apparatus of an electromagnetic induction heating type of the recording material carrying an image to be nipped and conveyed by the nip portion is heated by utilizing the heat generated by the heat generating layer,
Arrangement position or a said thermal safety device leakage flux guide elements consists of a magnetic member to induce leakage flux from the heat generating layer that occurs when the temperature of the heat generating layer exceeds the Curie temperature of the heating layer When the leakage magnetic flux is generated, a magnetic flux distribution is formed in which the leakage magnetic flux concentrates on the leakage magnetic flux guiding member, thereby raising the temperature of the region of the heating member facing the thermal safety element. An image heating apparatus characterized in that the operation of the heat-sensitive safety element is accelerated . The distance from the said leakage magnetic flux induction member to the said excitation coil is the shortest among the magnetic members arrange | positioned in the position facing the said excitation coil on both sides of the said heating member. The image heating apparatus described. The magnetic permeability of the leakage flux induction member is the largest among the magnetic members disposed at positions facing the excitation coil with the heating member interposed therebetween. Image heating device. The image heating according to any one of claims 1 to 3 , wherein the Curie temperature of the magnetic member constituting the leakage magnetic flux induction member is higher than the Curie temperature of the magnetic member of the heat generating layer of the heating member. apparatus. An exciting coil, a cylindrical heating member that is composed of a magnetic member and has a heat generating layer that generates heat due to an eddy current flowing by the action of an alternating magnetic field generated by power supply to the exciting coil, and a recording material together with the heating member A pressure member that forms a nip portion that sandwiches the heating element, and an element for shutting off the power supply to the exciting coil when the heating member is abnormally heated, and is activated by the abnormal heating of the heating member And an electromagnetic induction heating type image heating apparatus that heats a recording material carrying an image that is nipped and conveyed by the nip portion using heat generated in the heat generation layer,
Leakage magnetic flux induction member composed of a magnetic member for inducing leakage magnetic flux from the heat generation layer, which is generated when the temperature of the heat generation layer exceeds the Curie temperature of the heat generation layer, or the position where the thermal safety element is disposed An image heating apparatus, wherein the heat-sensitive safety element is accelerated by utilizing heat of the leakage magnetic flux guiding member that is disposed in the vicinity and generates heat by the action of the leakage magnetic flux.

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