JP2013130707A - Image heating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an image defect due to rise of temperature in a non-sheet-passing part when thin paper is used, in a heating device of an electromagnetic induction heating system, including magnetic shunt alloy having a predetermined Curie temperature.SOLUTION: The heating device of the electromagnetic induction heating system applies a magnetic field to a conductive member 1 (1a) by magnetic field generation means 3, to heat material P to be heated by heat evolution caused by an eddy current generated at the conductive member. The conductive member is composed of magnetic shunt alloy of which composition is adjusted so as to have a predetermined Curie temperature, and a maximum power value of a high-frequency electric current to be applied to a coil is made small, when thin paper whose fixing temperature is lower than plain paper is used.

Description

  The present invention relates to an image heating apparatus that heats an image on a recording material used in an image forming apparatus such as an electrophotographic or electrostatic recording type copying machine, printer, or facsimile. More specifically, the present invention relates to an image heating apparatus of a suitable electromagnetic induction heating type for heating and fixing an unfixed toner image formed on a recording material.

  An image forming apparatus such as an electrophotographic system includes an image heating apparatus that heats and fixes a toner image formed on a recording material onto the recording material. The image heating apparatus generally includes an image heating member that heats toner on a recording material, and a pressure member that forms a nip portion that presses the recording material and sandwiches and conveys the recording material. As a configuration for heating the image heating belt, for example, as disclosed in Patent Document 1, a configuration using an electromagnetic induction heating method with high heat generation efficiency (induction heating device) has been proposed. This induction heating device generates an eddy current in a metal conductor (conductive member, magnetic material, induction heating element) and generates Joule heat by the skin resistance of the metal conductor itself. According to this induction heating apparatus, since the heat generation efficiency is extremely improved, the warm-up time can be shortened.

  Even with such an induction heating device, when passing a recording material having a short length in the width direction of the image heating member, a portion that does not pass through a portion (sheet passing portion) through which the recording material passes The temperature of the (non-sheet passing portion) becomes high (hereinafter referred to as non-sheet passing portion temperature rise). For this reason, a difference occurs in the conveyance speed of the recording material due to the difference in thermal expansion of the rubber layer between the paper passing portion having the rubber layer and the non-paper passing portion. Due to this speed difference, the transportability of the recording material may decrease, and an image defect of the recording material may occur.

  As a configuration for reducing the temperature rise of the non-sheet passing portion, an induction heating device using a magnetic shunt alloy in which the Curie temperature of the image heating member is adjusted to a predetermined fixing temperature as disclosed in, for example, Patent Document 2 is proposed. Has been. By using a magnetic shunt alloy having a Curie temperature adjusted to a predetermined temperature, the image heating member can suppress heating to a predetermined temperature or higher. Therefore, it is possible to improve the non-sheet passing portion temperature rise.

JP 59-33787 JP 2000-39797 A

  In recent years, due to diversification of output images, there has been an increasing demand for image output to thin paper. Since these thin papers have a smaller heat capacity than normal papers, the heating operation is performed in the thin paper mode with the temperature controlled to be a set temperature lower than that of a normal recording material.

When a recording material that can heat an image with a small amount of heat such as thin paper is passed, if the image heating member as described above is used in an image heating apparatus that sets the image heating temperature to a low temperature, the following Such a problem arises.
In other words, if the maximum power value for temperature control is set in the same manner as for a normal recording material in a state where a low image heating temperature is set, if a recording material with a small width is passed, a non-sheet passing portion This temperature is close to the saturation temperature of the non-sheet passing portion, which is the same as the case of passing a normal recording material. In the thin paper mode, the set temperature is lower than normal, so that the temperature difference between the paper passing portion and the non-paper passing portion becomes too large. As a result, the stability of the conveyance of the recording material is lowered. For this reason, when passing such a recording material, it is desirable to minimize the temperature rise in the non-sheet passing portion.

  Therefore, the present invention forms a coil that generates magnetic flux, an image heating member that generates heat by the magnetic flux generated from the coil, and heats the recording material by heat, and a nip portion that presses the image heating member and sandwiches and conveys the recording material. A pressurizing member, an energization control unit for controlling energization of the coil so that the temperature of the image heating unit becomes a preset image heating temperature, a first heating mode for heating at a first set temperature, and a first Execution means capable of executing a plurality of heating modes including a second heating mode for heating at a second set temperature that is lower than the set temperature, and the Curie temperature of the image heating member is the first set temperature In an image heating apparatus having a higher temperature than the heat resistance temperature of the image heating apparatus, the maximum power applied to the coil during execution of the second heating mode is the execution of the first heating mode. In front And setting smaller than the maximum power applied to the coil.

  According to the present invention, in the configuration using the image heating member in which the Curie temperature is set, when the mode for widening the difference between the Curie temperature and the set temperature for image heating is executed, the temperature increase rate of the non-sheet passing portion is reduced. Can do.

1 is a schematic configuration diagram of an example of an image forming apparatus according to an embodiment of the present invention. The cross-sectional view of the heating apparatus of the electromagnetic induction heating system in the embodiment of the present invention Front model in an embodiment of the present invention Longitudinal front view in an embodiment of the present invention Diagram showing the heat generation principle of the fixing roller The figure which shows the temperature characteristic of the magnetic permeability of the magnetic body which has the predetermined Curie temperature of this invention

(1) Example of Image Forming Apparatus FIG. 1 is a schematic configuration model diagram of an example of an image forming apparatus provided with an electromagnetic induction heating type image heating and fixing apparatus according to the present invention.
First, an image forming unit that forms a toner image on a recording material will be described.
Reference numeral 41 denotes a rotating drum type photosensitive member (photosensitive drum) serving as an image carrier, which is driven to rotate at a predetermined peripheral speed in the direction of an arrow. In the rotation process, the primary charger 42 generates a predetermined negative dark potential Vd. It is charged uniformly. A laser beam scanner 43 outputs a laser beam L modulated in response to a digital image signal input from a host device such as an image reading device or a computer (not shown), and the uniformly charged surface of the photosensitive drum 41 Scanning exposure. By this laser beam scanning exposure, the exposed portion of the photosensitive drum 41 has a small potential absolute value and becomes a bright potential Vl, and an electrostatic latent image corresponding to the image signal is formed on the surface of the photosensitive drum 41. The electrostatic latent image is visualized as a toner image by the negatively charged toner adhering to the exposure light potential Vl portion of the photosensitive drum surface by the developing unit 44.

  On the other hand, the recording material P fed from a paper feed tray (not shown) is synchronized with the rotation of the photosensitive drum 41 to the pressure roller (transfer portion) between the transfer roller 45 and the photosensitive drum 41 as a transfer member to which a transfer bias is applied. It is conveyed at the appropriate timing. Then, the toner images t on the photosensitive drum 41 are sequentially transferred onto the surface of the recording material P. The recording material P on which the toner image t is formed is separated from the photosensitive drum 41, introduced into a fixing device F, which is an image heating device described later, and subjected to a fixing process for the toner image t by being heated under pressure. Discharged outside the machine. After the recording material P is separated, the surface of the photosensitive drum 41 is subjected to removal of transfer residues such as toner remaining on the surface of the photosensitive drum by the cleaning device 46 and then repeatedly used for image formation.

(2) Fixing device F
Next, the fixing device F as an image heating device will be described.
2 is an enlarged cross-sectional model view of the main part of the fixing device F, FIG. 3 is a front model view of the main part, and FIG. 4 is a longitudinal front model view thereof.
The fixing device F is a fixing roller type heating device using an electromagnetic induction heating method, and serves as an image heating member that forms a fixing nip portion N having a predetermined nip width (nip length) by being pressed against each other with a predetermined pressing force. It has a fixing roller and a pressure roller 2 as a pressure member.

  The fixing roller 1 has an outer diameter of 40 mm, a thickness of 0.5 mm, and a length of 340 mm. The core metal 1a of the fixing roller 1 is made of a magnetic shunt alloy in which a material such as iron, nickel, or chromium is blended so that the Curie temperature Tc is 220 ° C. in this embodiment. Further, the surface layer 1b is formed of a fluororesin such as PFA or PTFE in order to improve toner releasability with a thickness of 30 μm. In order to obtain a high-quality fixed image such as a color image, a heat-resistant elastic layer such as silicone rubber may be provided between the core metal 1a and the surface layer 1b.

  The fixing roller 1 is disposed such that both end portions thereof are rotatably supported via bearings 23 between front and back side plates (fixing unit frames) 21 and 22 of the fixing device, respectively. In addition, a coil assembly 3 as a magnetic flux generating means is inserted and arranged in the inner space portion in order to induce an induction current (eddy current) in the fixing roller 1 to generate Joule heat.

  The pressure roller 2 has an outer diameter of 38 mm and a length of 330 mm. And, a core metal 2a having an outer diameter of 28 mm and a wall thickness of 3 mm, a heat-resistant elastic layer 2b having a thickness of 5 mm formed on the peripheral surface of the core metal 2a, and PFA, PTFE, etc. formed on the peripheral surface of the heat-resistant elastic layer 2b And a surface layer 2c made of a fluororesin and having a thickness of 30 μm.

  The pressure rollers 2 are arranged in parallel below the fixing roller 1, and both end portions of the cored bar 2a are interposed between the front and back side plates 21 and 22 of the fixing device via bearings 26, respectively. It is held rotatably.

  Then, the fixing roller 1 and the pressure roller 2 are pressed against each other against the elasticity of the elastic layer 2b by a pressure mechanism (not shown), and a recording material as a material to be heated is interposed between the rollers 1 and 2. A fixing nip N having a width of about 5 mm, which is a width for heating and fixing the toner image by sandwiching and conveying P, is formed.

  Here, in the present invention, the longitudinal direction of the apparatus constituent member is a direction orthogonal to the conveyance direction of the recording material P on the plane including the fixing nip portion N (or the rotation axis direction of the fixing roller). Moreover, a center part and an edge part are the center part and edge part of the longitudinal direction.

  A coil assembly 3 as a magnetic field generating means inserted into the inner space of the fixing roller 1 is an assembly of a bobbin 4, a magnetic core 5 (1, 2), a coil 6, a stay 7 made of an insulating member, and the like. The core 5 is held by the bobbin 4, and the coil 6 is formed by winding an electric wire around the bobbin 4. The bobbin 4, core 5, and coil 6 unit is fixedly supported on the stay 7.

  The coil assembly 3 is inserted into the inner space of the fixing roller 1 so as to maintain a predetermined gap between the inner surface of the fixing roller 1 and the coil 6 at a predetermined angular posture. The portions 7a and 7a are fixedly supported non-rotatably by holding members 24 and 25 on the front side and the back side of the fixing device, respectively.

  The core 5 is a material having high magnetic permeability and low residual magnetic flux density, such as ferrite and permalloy, and serves to guide the magnetic flux generated by the coil 6 to the fixing roller 1. The core 5 in this embodiment has a T-shaped cross section, and is constituted by a combination of two plate-like cores 5 (1) and 5 (2) that constitute a T-shaped horizontal bar portion and a vertical bar portion. ing.

  As shown in FIG. 4, the coil 6 extends in parallel with the longitudinal direction of the fixing roller 1, winds around the core 5 in a horizontal long boat shape a plurality of times according to the shape of the bobbin 4, and is bent at both ends. It is a bundle of litz wires. Then, it is arranged so as to be curved along the inner periphery of the fixing roller 1. 6a and 6b are two lead wires (coil supply wires) of the coil 6, which are pulled out from the back side of the stay 7 and connected to a high frequency inverter (excitation circuit) 101 for supplying a high frequency current to the coil 6. It is.

  The thermistor 11 is a thermistor as a temperature detection member that detects the temperature of the fixing roller 1. This thermistor will be described later.

  A pre-fixing guide plate 12 guides the recording material P conveyed from the image forming mechanism side to the fixing device F to the entrance of the fixing nip N. Reference numeral 13 denotes a separation claw, which serves to prevent the recording material P introduced into the fixing nip portion N and coming out of the fixing nip portion N from being wrapped around the fixing roller 1 and separated from the fixing roller 1. Reference numeral 14 denotes a post-fixing guide plate that guides the recording material P that has exited the exit of the fixing nip N to be discharged.

  The bobbin 4, the stay 7, and the separation claw 13 are made of heat-resistant and electrically insulating engineering plastic.

  Reference numeral G1 denotes a fixing roller drive gear fixed to the back end side of the fixing roller 1. When the rotational force is transmitted from the drive source M1 to the drive gear G1 through the transmission system, the fixing roller 1 is rotationally driven in the clockwise direction indicated by the arrow A in FIG. 2 at a peripheral speed of 300 mm / sec in this embodiment. Is done. The pressure roller 2 is rotated in the counterclockwise direction B indicated by the arrow following the rotational driving of the fixing roller 1 by the frictional force with the fixing roller 1 at the fixing nip N.

  Reference numeral 15 denotes a fixing roller cleaner. This is because the web feeding shaft portion 15b holding the cleaning web 155a in roll form, the web winding shaft portion 15c, and the pressing roller 15d that presses the web portion between the shaft portions 15b and 15c against the outer surface of the fixing roller 1. Become. The toner offset to the surface of the fixing roller 1 is wiped by the web portion pressed against the fixing roller 1 by the pressing roller 15d, and the surface of the fixing roller is cleaned. The web portion pressed against the fixing roller 1 is gradually renewed by gradually feeding the web 15a from the feeding shaft portion 15b side to the winding shaft portion 15c side.

In the present embodiment, the sheet passing is performed based on the central reference. S is the central reference. In the image forming apparatus of the present embodiment, the maximum size of the recording material that can be passed (hereinafter referred to as large size paper) is, for example, A4 landscape (297 mm). The minimum size of the recording material that can be passed (hereinafter referred to as small size paper) is, for example, B5R (182 mm). P1 is the paper passing area width of the large size paper, and P2 is the paper passing area width of the small size paper.
The thermistor 11 serving as a central temperature detecting device is arranged on the surface of the fixing roller 1 so as to face the coil 6 across the fixing roller 1 in the central portion of the fixing roller corresponding to the substantially central portion of the sheet passing area width P2 of small size paper. It is arranged in pressure contact with. The fixing roller temperature detection signal of the main thermistor 11 is input to the control unit (CPU) 100.

  The control circuit unit 100 of the image forming apparatus starts the apparatus by turning on the main power switch of the apparatus and starts predetermined image forming sequence control. In the fixing device F, the rotation of the fixing roller 1 is started by the activation of the driving source M1. The pressure roller 2 also rotates following the rotation of the fixing roller 1. Further, the control circuit unit 100 activates the high frequency inverter 101 to flow a high frequency current (for example, 10 kHz to 100 kHz) through the coil 6. As a result, a high-frequency alternating magnetic flux is generated around the coil 6, and the fixing roller 1 generates heat by electromagnetic induction to increase the temperature toward a predetermined fixing temperature T. The temperature rise of the fixing roller 1 is detected by the thermistor 11, and the detected temperature information is input to the control circuit unit 100.

  The control circuit unit 100 controls the electric power supplied from the high frequency inverter 101 to the coil 6 so that the detected temperature of the fixing roller 1 input from the thermistor 11 is maintained at a predetermined fixing temperature (image heating temperature) T, and fixing. The roller 1 is heated and the temperature is adjusted at the fixing temperature T. The control circuit unit 100 has a function as energization control means for controlling energization to the coil.

In this temperature control state, a recording material P as a heated material carrying an unfixed toner image t is introduced from the image forming unit side to the fixing nip portion N, and the fixing nip portion N is nipped and conveyed. As a result, the unfixed toner image t is heated and fixed on the surface of the recording material P by the heat of the fixing roller 1 and the pressure applied by the fixing nip N.
In the first embodiment, when the first basis weight (thickness) paper (for example, 80 g / m ² ) is heated and fixed, the fixing temperature T (first set temperature) in the plain paper mode as the first heating mode is used. ) Is set to 190 ° C. Also, when thin paper (for example, 60 g / m ² ) having the second basis weight (thickness) is heat-fixed, the fixing temperature T (second set temperature) in the thin paper mode as the second heating mode is set to 170 ° C. The The control circuit unit 100 has a function as an execution unit capable of executing a plurality of heating modes including a plain paper mode and a thin paper mode.

  Here, the principle of electromagnetic induction heat generation of the fixing roller metal core 1a, which is a conductive member, will be described with reference to FIG. An alternating current is applied to the coil 6 from the high-frequency inverter 101, whereby the magnetic flux indicated by the arrow H is repeatedly generated and extinguished around the coil 6. The magnetic flux H is guided along a magnetic path formed by the cores 5 (1, 2) and the cored bar 1a. In response to the change in the magnetic flux generated by the coil 6, an eddy current is generated in the core bar 1a so as to generate the magnetic flux in a direction that prevents the change in the magnetic flux. This eddy current is indicated by an arrow C.

  This eddy current C flows in a concentrated manner on the surface of the core bar 1a on the side of the coil 6 due to the skin effect, and generates heat with power proportional to the skin resistance Rs of the core bar 1a.

  Here, the skin depth δ () obtained from the frequency f (Hz) of the alternating current applied to the coil 6, the magnetic permeability μ (H / m) of the cored bar 1a, and the specific resistance ρ (Ω · m) of the cored bar 1a. m) and skin resistance Rs (Ω) are expressed by Equation 1 and Equation 2.

Further, the eddy current induced in the metallic core 1a I _{f (A)} is proportional to the amount of magnetic flux passing inside core metal 1a, the number of turns N (times) of the coil 6 is applied to the coil 6 Using the coil current I (A),

From the above, the electric power W (W) generated in the cored bar 1a is represented by Equation 4 because it is Joule heat generated by the eddy current _If and skin resistance induced in the cored bar 1a.

  From Equation 4, in order to increase the heat generation amount of the core metal 1a, the core metal 1a may be made of a material having high permeability and high resistance such as a ferromagnetic metal such as iron or nickel or an alloy thereof. It can be seen that the number of turns of the coil 6 may be increased.

  The high-frequency inverter 101 can optimally control the amount of heat generated by the cored bar 1a by controlling the coil current I applied to the coil 6 or the frequency f of the coil current.

Next, the Curie temperature Tc will be described. In general, a ferromagnetic material loses its spontaneous magnetization when heated to a Curie temperature Tc specific to the material. As a result, the magnetic permeability μ of the ferromagnetic material is substantially equal to the vacuum magnetic permeability μ ₀ and is constant. Therefore, when the temperature of the cored bar 1a, which is a conductive member of the fixing roller 1, exceeds the Curie temperature Tc, the heat generation amount W of the cored bar 1a decreases.

  However, in practice, the permeability μ does not change suddenly before and after the Curie temperature Tc, and the change starts from a permeability lowering temperature Tc ′ lower than the Curie temperature Tc, as shown in FIG. That is, the magnetic permeability lowering temperature is a temperature indicating the maximum value of the magnetic permeability. Note that the permeability lowering temperature Tc ′ of the cored bar 1a used in Example 1 is 200 ° C., and the Curie temperature Tc is 220 ° C.

  Here, when the thickness of the cored bar 1a is t (m), the temperature of the cored bar 1a increases, and when the skin depth δ of the cored bar 1a is equal to or greater than the thickness t of the cored bar 1a, the cored bar 1a The eddy current induced by flows in the entire cross-sectional direction of the cored bar 1a. In this case, the skin resistance Rs ′ (Ω) and the heat generation amount W ′ (W) are expressed by Expression 5 and Expression 6.

  Actually, the temperature of the cored bar 1a is a predetermined temperature under the condition that the relationship between the heat generation amount W ′ expressed by the equation 6 and the heat dissipation amount Q (W) from the cored bar 1a is W ′ ≦ Q. It becomes constant at the saturation temperature Ts.

  Here, the heat dissipation amount Q is the surface area and emissivity of the surface of the fixing roller 1, the temperature difference between the surface of the fixing roller 1 and the ambient atmosphere and the pressure roller 2, and the heat transfer rate to the ambient atmosphere and the pressure roller 2. Depends on.

  As described above, the Curie temperature Tc is adjusted so that the core metal 1a is higher than a predetermined temperature, specifically, the fixing temperature T, and lower than the allowable temperature for raising the non-sheet passing portion, which is the heat resistance temperature of the fixing device. By using a magnetic alloy, the temperature of the cored bar 1a becomes constant at a predetermined saturation temperature Ts. As a result, the temperature of the non-sheet passing portion is constant even when a small size recording material is passed.

  On the other hand, when the fixing temperature T is sufficiently lower than the magnetic permeability lowering temperature Tc ′ and the Curie temperature Tc as in the above-described thin paper mode, the temperature difference between the paper passing portion and the non-paper passing portion is rather large. It can happen. This is because the amount of heat generated in the non-sheet-passing portion is almost the same as that in the sheet-passing portion until it exceeds the permeability lowering temperature Tc ′, and the amount of heat generation starts to decrease after the permeability decreasing temperature Tc ′ is exceeded. Is the cause.

  Therefore, when the fixing temperature T is lower than the magnetic permeability lowering temperature Tc ′ and the Curie temperature Tc as in the thin paper mode, by reducing the heat generation amount W ′ of the non-sheet passing portion, The temperature difference in the non-sheet passing portion can be reduced.

  Specifically, from the above (Equation 6), in the thin paper mode, the maximum current value (upper limit value) of the high-frequency current applied to the coil is made smaller in the thin paper mode than in the normal mode. W ′ can be reduced.

In the configuration of this embodiment, when the maximum current value of the high-frequency current applied to the coils 6a and 6b is 30A in the plain paper mode (fixing temperature 190 ° C.) on an A4R paper having a basis weight of 80 g / m ² , The saturation temperature Ts of the non-sheet passing portion when continuously passing is 215 ° C. As a result, the temperature difference ΔT between the paper passing portion and the non-paper passing portion was 25 ° C., and image defects such as paper wrinkles and rubbing images did not occur on the recording material after fixing.

On the other hand, when the maximum current value of the high-frequency current applied to the coils 6a and 6b is 30A in the thin paper mode (fixing temperature 170 ° C.) on A4R paper having a basis weight of 60 g / m ² , it is continuous. The saturation temperature Ts of the non-sheet passing portion when the sheet is passed is 210 ° C. As a result, the temperature difference ΔT between the paper passing portion and the non-paper passing portion is 40 ° C., and there is a possibility that image defects such as a rubbing image may occur on the recording material after fixing.

  Therefore, in this embodiment, when the thin paper mode is selected, the maximum current value of the high frequency current applied to the coils 6a and 6b is the maximum current of the high frequency current applied to the coils 6a and 6b in the plain paper mode. It was set to 20 A, which is smaller than the value. As a result, the saturation temperature Ts of the non-sheet passing portion is 200 ° C., the temperature difference ΔT between the sheet passing portion and the non-sheet passing portion is 30 ° C., and image defects such as wrinkles and rubbing images occur on the recording material after fixing. I did not.

  As described above, in the thin paper mode in which the fixing temperature is lower than that in the plain paper mode, the maximum current amount of the high-frequency current applied to the coil is made smaller in the thin paper mode than in the plain paper mode. Can be reduced. For this reason, the temperature of the non-sheet passing portion can be made lower than the saturation temperature in the plain paper mode. For this reason, the temperature difference between the paper passing portion and the non-paper passing portion is reduced, and image defects such as wrinkles and rubbing images can be improved even in thin paper.

Thus, in this embodiment, when the plain paper mode is selected, the maximum current amount is set to 30A. When the thin paper mode is selected, the maximum current amount is set to 20 A, which is smaller than the maximum current amount in the plain paper mode. Thus, in this embodiment, the upper limit value of the maximum current amount during execution of the mode is set. On the other hand, instead of the method of setting the maximum current amount, the configuration for setting the maximum power value is also equivalent. That is, from the relationship of W = I ² × R, the resistance component R is the resistance component of the fixing roller and the coil, and since the fluctuation of the resistance component is small, the maximum power value is substantially defined as the maximum current value. The relationship is equal to the quantity specification.

  Note that each configuration and set value of the fixing device F shown in the above-described embodiment is an example, and may be changed as appropriate depending on the type of paper used, toner, process speed, and the like.

  In this embodiment, a plain paper mode and a thin paper mode having a fixing temperature lower than that of the plain paper mode are provided. However, the setting of the fixing temperature is not limited to this. For example, in addition to the plain paper mode and the thin paper mode, a thick paper mode or the like may be set as a third mode having a fixing temperature higher than that of the plain paper mode.

  In this embodiment, the normal paper mode and the thin paper mode whose fixing temperature is lower than that of the normal paper mode are exemplified as modes having different fixing temperatures. However, the present invention is not limited to this as long as the mode is applied to modes having different fixing temperatures. Absent. For example, in a heating apparatus that heat-fixes a full-color image, the present invention can be similarly applied to a full-color mode and a single-color mode having a fixing temperature lower than that of the full-color mode.

[Others]
1) The form of the heating member is not limited to the roller body, but may be another rotating body such as an endless belt body. In addition, the heating member can be configured as a member of a single conductive member that is an induction heating element, or a composite layer member having two or more layers including other material layers such as a heat resistant resin and ceramics, including a layer of the conductive member. It can also be configured as.

  2) The induction heating of the conductive member by the magnetic flux generating means is not limited to the internal heating method of the embodiment, and an external heating type apparatus configuration in which the magnetic flux generating means is disposed outside the conductive member may be employed.

  3) The temperature detection means 11 is not limited to the thermistor, and may be a temperature detection element, and may be a contact type or a non-contact type.

1 Fixing roller (conductive member)
2 Pressure roller 3 Coil assembly (magnetic field generating means)
5 Magnetic core material (magnetic core)
6 Excitation coil 11 Thermistor (temperature detection means)
27a, 27b Cooling fan (cooling means)
41 photoconductor (photosensitive drum)
42 Primary Charger 43 Laser Beam Scanner 44 Developer 45 Transfer Roller 46 Cleaning Device F Fixing Device P Recording Sheet (Heating Material)
t Toner image

Claims (2)

A coil that generates magnetic flux, an image heating member that generates heat by the magnetic flux generated from the coil and heats the recording material by heat, and a pressure member that presses the image heating member and forms a nip portion that sandwiches and conveys the recording material; Energization control means for controlling energization to the coil so that the temperature of the image heating means becomes a preset image heating temperature, a first heating mode for heating at a first set temperature, and a temperature lower than the first set temperature An execution means capable of executing a plurality of heating modes including a second heating mode for heating at a second preset temperature, wherein the Curie temperature of the image heating member is higher than the first preset temperature. In the image heating apparatus that is lower than the heat resistance temperature of the image heating apparatus,
The image heating apparatus, wherein the maximum power applied to the coil during execution of the second heating mode is set smaller than the maximum power applied to the coil during execution of the first heating mode.   The maximum current value of the high frequency current applied to the coil during execution of the second heating mode is set to be smaller than the maximum current value of the high frequency current applied to the coil during the execution of the second heating mode. The image heating apparatus according to claim 1.

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