JP2020038291A - Image heating device - Google Patents

Abstract

To provide an image heating device of electromagnetic induction heating system which can achieve both prevention of the oxidation of metal of a heating layer and sufficient suppression of an excessive temperature rise when a crack, etc., occurs in a cylindrical heating rotor.SOLUTION: The image heating device comprises: a cylindrical rotor having a base layer, a heating layer and a protective layer in a radial direction, with the heating layer divided into multiple portions so as to be provided with a heating region and a non-heating region in a longitudinal direction in the order stated; a counter body facing the rotor; a nip part forming member for forming a nip part together with the counter body; and magnetic field generation means for forming an alternating magnetic field in a direction of revolving shaft of the rotor by sending an AC current and causing an induction current to occur in the circumferential direction of the rotor. The heating layer is composed of a first metal and the protective layer is composed of a second metal so as to cover the heating layer, electric resistance per unit length of a first region provided with the heating layer and the protective layer in the radial direction as the heating region is smaller than electric resistance per unit length of a second region provided not with the heating layer as the non-heating region but with the protective layer.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an electromagnetic induction heating type image heating apparatus used for a copying machine, a printer, or the like as an image forming apparatus such as an electrophotographic method.

  In recent years, as an image heating device, an electromagnetic induction heating type image heating device capable of directly generating heat from a heating layer of a heating rotator has been proposed (Patent Document 1). Patent Literature 1 describes that even when a crack or the like occurs in a cylindrical heating rotator, the heat generating layer is divided into a plurality of portions in the rotation axis direction so that excessive heating of the heating rotator can be suppressed. Have been. That is, in Patent Literature 1, the heat generation layer is formed so that the current flows in the rotation direction orthogonal to the rotation axis direction, and almost no current flows in the rotation axis direction (the current flowing around the end of the damaged portion decreases). Are electrically divided in the rotation axis direction.

JP-A-2015-118232

  Here, from the viewpoint of speeding up the temperature rise, it is desirable to reduce the heat capacity by reducing the thickness of the heating layer of the heating rotator, and when a metal having a low electric resistivity such as copper is employed, copper may come into contact with air. , The resistance of the heat generating layer may be increased or peeling may occur. Therefore, a method of plating with nickel so as to cover the heat generating layer with a non-permeable metal material and prevent oxidation can be considered.

  However, when the divided heat generating layer proposed in Patent Document 1 is used, copper which is the heat generating layer is covered with a metal (nickel alloy), so that the divided copper is short-circuited in the rotation axis direction, and the effect of the division is obtained. The problem may be that the color fades. Therefore, it is necessary to achieve both the prevention of oxidation of the metal in the heat generating layer and the sufficient suppression of excessive temperature rise when a crack or the like occurs in the cylindrical heating rotator.

  An object of the present invention is to provide an image heating apparatus of an electromagnetic induction heating type capable of achieving both the prevention of oxidation of metal in a heat generating layer and sufficient suppression of excessive temperature rise when a crack or the like occurs in a cylindrical heating rotator. Is to do.

  In order to achieve the above object, an image heating apparatus according to the present invention includes a base layer, a heat generating layer, and a protective layer in a radial direction, and the heat generating layer has a plurality of heat generating regions and a non-heat generating region in a longitudinal direction. Nip section formation for forming a divided cylindrical rotating body, an opposing body facing the rotating body, and a nip section for nipping and conveying the recording material carrying the toner image via the rotating body together with the opposing body A member, and a magnetic field generating means for forming an alternating magnetic field in a rotation axis direction of the rotating body by flowing an alternating current to generate an induced current in a circumferential direction of the rotating body; The protective layer is made of a metal, and the protective layer is made of a second metal different from the first metal so as to cover the heat generating layer. In a cross section including the rotation axis direction, the heat generating layer is formed in a radial direction as the heat generating region. And first region provided with the protective layer Unit electrical resistance per length, characterized in that the smaller than the electrical resistance per unit length of the second region having the protective layer without providing the heating layer in the radial direction as a non-heating area.

  According to the present invention, there is provided an image heating apparatus of an electromagnetic induction heating type capable of both preventing oxidation of a metal in a heat generating layer and sufficiently suppressing excessive temperature rise when a crack or the like occurs in a cylindrical heating rotator. can do.

Sectional view of a fixing device as an image heating device according to an embodiment Front view of the fixing device according to the embodiment Diagram for explaining electromagnetic induction heating of the heating layer Diagram for explaining the configuration of a film as a heating rotator Schematic diagram showing the current and magnetic field of the heating layer Explanatory drawing of the current flow when the heating layer of the film is broken Graph of resistance ratio per unit width between non-heating part and heating part and temperature at end of damaged part Sectional view of an image forming apparatus equipped with an image heating device according to an embodiment

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

<< 1st Embodiment >>
(Image forming device)
Referring to FIG. 8, an image forming apparatus equipped with an image heating device according to an embodiment of the present invention will be described. FIG. 8 is a cross-sectional view illustrating a schematic configuration of an electrophotographic monochrome printer as an example of the image forming apparatus 100.

  The image forming apparatus 100 includes a photosensitive drum 101 as an image carrier, a charging member 102, a laser scanner 103, and a developing device 104 for forming an unfixed toner image on the recording material P. Further, the image forming apparatus includes a cleaner 109 for cleaning the photosensitive drum 101 and a transfer member 108. Since the operation of forming an unfixed toner image is well known, a detailed description thereof will be omitted.

  The recording material P such as recording paper stored in a cassette 105 in the image forming apparatus 100 is fed one by one by rotation of a roller 106. The recording material P is conveyed to a transfer nip formed by the photosensitive drum 101 and the transfer member 108 by the rotation of the roller 107. The recording material P on which the toner image has been transferred at the transfer nip portion is sent to a fixing unit (hereinafter, a fixing device) B as an image heating unit via a conveyance guide 110. The unfixed toner image T formed on the recording material P is heated and fixed on the recording material by the fixing device B.

  The recording material P that has left the fixing device B is discharged to a tray 113 by rotation of rollers 111 and 112.

(Image heating device)
The fixing device B as an image heating device in the present embodiment is an electromagnetic induction heating type device. FIG. 1 is a cross-sectional view illustrating a schematic configuration of a fixing device B according to the present embodiment. FIG. 2 is a front view when the fixing device B is viewed from the upstream side in the transport direction X of the recording material P.

  Here, regarding the fixing member constituting the fixing device B, the longitudinal direction is a direction orthogonal to the recording material conveyance direction and the recording material thickness direction. That is, the longitudinal direction is the Y direction shown in FIG. In FIG. 1, a sliding member 7 as a nip portion forming member (backup member) is provided on an outer peripheral surface (surface) of a pressure roller 8 as an opposing member via a film 1 as a heating rotator (rotating member). Pressurized. As a result, the pressure roller 8 forms a nip portion N having a predetermined width through the film 1 together with the sliding member 7, and the nip portion N nips and conveys the recording material P carrying the toner image.

  The pressure roller 8 is provided on a cored bar 8a in the radial direction, an elastic layer 8b formed in a roller shape on the outer peripheral surface of the cored bar, and on the outer peripheral surface (outermost surface) of the elastic layer. A release layer 8c. Both ends in the longitudinal direction of the cored bar 8a are rotatably held by left and right side plates (not shown) of the fixing device B via bearings. The elastic layer 8b is preferably made of a material having good heat resistance, such as silicone rubber, fluorine rubber, or fluorosilicone rubber.

  As the release layer 8c, a material having good releasability and heat resistance can be selected. For example, PFA (tetrafluoroethylene / perfluoroalkyl vinyl ether resin), PTFE (polytetrafluoroethylene resin), and FEP (tetrafluoroethylene / hexafluoropropylene resin) can be selected. Alternatively, ETFE (tetrafluoroethylene / ethylene resin), ECTFE (chlorotrifluoroethylene / ethylene resin) or the like can be selected.

  In the Z-axis direction shown in FIG. 1, a film 1 as a cylindrical rotating body is arranged so as to face the pressure roller 8. On a film guide (hereinafter referred to as a guide) 6 inserted into a hollow portion of the film 1, a metal stay 5 for reinforcing the guide is arranged. The guide 6 is made of a heat-resistant PPS (polyphenylene sulfide) resin or the like.

  At both ends in the longitudinal direction (Y direction) of the stay 5, flanges 9a and 9b made of heat-resistant resin shown in FIG. The flange 9a is fixed to the left frame by a regulating member 10a. The flange 9b is fixed to the right frame by a regulating member 10b. Each of the flanges 9a and 9b holds an inner peripheral surface (inner surface) of a longitudinal end portion of the film 1 by a holding portion (not shown) inserted into a hollow portion of the film 1. Furthermore, when the film 1 rotates, the flanges 9a and 9b receive the ends of the film 1 on the regulating surfaces 9a1 and 9b1 on the film 1 side, and regulate the shift movement of the film 1 along the Y-axis direction.

  In FIG. 2, pressing springs 11a and 11b are contracted between both ends in the longitudinal direction of the stay 5 and the spring receiving members 12a and 12b on the left and right side plates, so that a pressing force is applied to the stay 5. Let me. In the fixing device B of this embodiment, a pressing force of a total pressure of about 100 N to 250 N (about 10 kgf to about 25 kgf) is applied to the stay 5. By the pressing force, the plate-shaped sliding member 7 held on the flat surface of the guide 6 on the pressure roller 8 side is pressed through the film 1 to the outer peripheral surface (surface) of the pressure roller. As a result, the sliding member 7 and the pressure roller form a nip portion N (FIG. 1) having a predetermined width via the film 1.

  The pressure roller 8 is rotated in a direction indicated by an arrow in FIG. 1 by driving a motor M as a driving unit. Then, the film 1 rotates following the rotation of the pressure roller 8 while the inner surface of the film slides on the sliding surface 7 a of the sliding member 7 on the pressure roller 8 side. During the rotation operation of the film 1, a lubricant such as heat-resistant grease is applied between the inner surface of the film 1 and the sliding surface 7a in order to reduce the sliding friction force between the inner surface of the film 1 and the sliding surface 7a. It can be interposed.

  At both ends in the longitudinal direction of the guide 6, flanges 9a and 9b (FIG. 2) as restricting members for receiving the end of the film 1 when the film 1 rotates and restricting the shift of the film 1 are fitted outside. I have.

  FIG. 3 is a diagram for explaining electromagnetic induction heating by a magnetic core (hereinafter, core) 2 as a magnetic core material and an exciting coil 3. The core 2 has a columnar shape with a length La in the longitudinal direction (Y-axis direction), and is arranged so as to penetrate through the hollow portion of the film 1 by fixing means (not shown). That is, the core 2 is inserted into the hollow portion of the film 1 and is arranged along the rotation axis 1o (Y-axis direction) of the film 1. The core 2 guides lines of magnetic force (magnetic flux) due to an alternating magnetic field (alternating magnetic field) generated by an exciting coil (hereinafter, a coil) 3 as a magnetic field generating means (magnetic field generating means) into the film 1, and passes the magnetic force lines. (Magnetic path).

  The core 2 is desirably formed of a material having a small hysteresis loss and a high relative magnetic permeability. For example, it is a ferromagnetic material composed of an oxide or alloy material having high magnetic permeability such as fired ferrite, ferrite resin, amorphous alloy (amorphous alloy), and permalloy. Preferably, the cross-sectional area should be as large as possible within a range that can be accommodated in the film 1 which is a cylindrical member. The shape is not limited to a cylindrical shape, and a prism shape or the like can be selected.

  The coil 3 is formed by spirally winding a normal single conductive wire around the core 2 in the hollow portion of the film 1 with about 10 to 40 turns. In the present embodiment, the coil 3 is configured with 18 turns. The coil 3 is wound inside the film 1 in a direction intersecting the rotation axis 1o of the film. Therefore, when a high-frequency current (alternating current) is applied to the coil 3 via the high-frequency converter 13 and the power supply contacts 3a and 3b, an alternating magnetic field (alternating magnetic field) whose polarity is periodically inverted is generated in the rotation axis direction of the film 1. It can be generated in a certain Y-axis direction.

  In FIG. 3, the control circuit 14 detects the temperature in the longitudinal direction (Y-axis direction) of the film 1 by the temperature detection element 4 disposed at the center of the passage area (230 mm) of the film 1 through which the recording material P passes. The high frequency converter 13 is controlled based on the temperature. Thereby, the film 1 is heated by electromagnetic induction to maintain the surface temperature of the film 1 at a predetermined target temperature.

  The recording material P carrying the unfixed toner image T is heated while being conveyed in the nip N, whereby the toner image is fixed on the recording material.

(Film composition)
FIG. 4 shows a schematic cross-sectional view of the film 1 of the present embodiment. FIG. 4A is a cross-sectional view in the short direction orthogonal to the longitudinal direction of the film 1. The film 1 has a cylindrical shape with a diameter of 10 to 100 mm. The layer structure of the film 1 includes a base layer 1a, a protective layer 1b in contact with the surface of the base layer 1a, a heat generating layer 1c sandwiched between the protective layers 1b, and an elastic layer 1d covering the protective layer 1b in the radial direction from the inner surface side of the film 1. The elastic layer 1d is laminated, and the release layer 1e is laminated on the outer peripheral surface of the elastic layer 1d. In the present embodiment, the outer diameter of the film 1 is set to 30 mm.

  In the present embodiment, as will be described in detail later, the heat generating layer 1c is made of copper having a low electric volume resistivity as the first metal, and the protective layer 1b provided so as to cover the heat generating layer 1c is formed of the first metal. The second metal different from the metal is composed of an alloy containing nickel.

  As the material of the base layer 1a, a substance having a high volume resistivity and excellent heat resistance is suitable. For example, there are heat-resistant resins represented by PI (polyimide), PAI (polyamideimide) and the like, and fiber-reinforced resins represented by CFRP (carbon fiber-reinforced resin) and GFRP (glass fiber-reinforced resin).

  When a heat-resistant resin is used, the thickness of the base layer 1a is preferably 20 to 200 μm, which is a thickness at which the strength of the film 1, the slidability due to the nip portion N of the film 1, and the rotational stability of the film 1 are easily obtained. Are suitable. In the present embodiment, the base layer 1a is formed of PI (polyimide) resin, and has a thickness of 60 μm.

  The protective layer 1b is provided to prevent the heating layer 1c from being oxidized, and prevents the heating layer 1c from being exposed to the outside air. The protective layer 1b is formed on the outer surface of the base layer 1a so as to cover the heat generating layer 1c (FIG. 4C). The protective layer 1b is preferably made of a metal material having no air permeability. In this embodiment, a nickel-phosphorus alloy is used.

As a specific process, in the present embodiment, a nickel phosphorus alloy having an electric volume resistivity of 2 × 10 ⁻⁶ Ωm and a thickness of 1 μm is formed as a protective layer 1b on the base layer 1a by electroless plating. Then, the heat generating layer 1 c is divided into a plurality of portions so as to sequentially include a heat generating region and a non-heat generating region in the longitudinal direction of the film 1.

In this regard, by masking, a heating layer 1c having a width (length) of 9.8 mm in the longitudinal direction and a cylindrical heating layer 1c having a longitudinal direction of 230 mm divided into 23 pieces are formed as a repetitive pattern having a gap of 0.2 mm. Was formed (FIG. 4B). Then, copper having an electric volume resistivity of 2 × 10 ⁻⁸ Ωm was formed to a thickness of 1 μm by electroplating so that the heat generating layer 1 c was formed to be extremely thin in order to increase the temperature rising rate.

After the heat generating layer 1c is formed, a nickel phosphorus alloy having an electric volume resistivity of 2 × 10 ⁻⁶ Ωm is formed to a thickness of 1 μm by electroless plating as a protective layer 1b (that is, in this embodiment, the protective layer 1b is formed). 1b is provided on the outside and inside of the heat generating layer 1c in the radial direction). By performing the above steps, the copper layer serving as the heat generating layer 1c is covered with the nickel phosphorus layer serving as the protective layer 1b to prevent oxidation of copper.

  FIG. 4B schematically shows a divided heat generating layer 1c in a part of the longitudinal section of the film 1. In FIG. 4B, the heat generating layer 1c is divided in the longitudinal direction, but the protective layer 1b is not divided in the longitudinal direction and is connected (FIG. 4C). The heat-generating portion (heat-generating region) Rh shown in FIG. 4B is a portion having the heat-generating layer 1c covered with the protective layer 1b, and does not include a portion dividing the heat-generating layer 1c. A cross section in the lateral direction of the film 1 cut along h1-h1 shown in FIG. 4B corresponds to FIG. 4A.

  FIG. 4C is an enlarged view of a gap portion of the divided heat generating layer 1c in FIG. 4B, and includes a non-heat generating portion (non-heat generating region) Rp not including the heat generating layer 1c. Become. A cross section in the short direction of the film 1 cut along p1-p1 shown in FIG. 4B corresponds to FIG. 4D. The non-heat-generating portion Rp is referred to as non-heat-generating. However, a small amount of current may flow and generate heat. However, heat is generated to such an extent that it does not function as a heat source for fixing.

  The elastic layer 1d was formed so as to cover the protective layer 1b. In the present embodiment, the elastic layer 1d is formed of a silicone rubber having a hardness of 20 degrees (JIS-A, 9.8 N (1 kgf) load) with a thickness of 300 μm by a spray coating method.

  The release layer 1e is provided in order to prevent toner from adhering to the surface of the film 1 and prevent image defects. The release layer 1e is formed on the outer surface of the elastic layer 1d. For the release layer 1e, a material having excellent non-adhesiveness is suitable, and for example, PTFE, PFA, FEP, ETFE, ECTFE and the like are suitable. In the present embodiment, PFA having a thickness of 15 μm is used as the release layer 1e.

(Principle of heat generation of film 1)
FIG. 5A is a schematic cross-sectional view showing the current (induction current) and the magnetic field of the heat generating layer 1c in the lateral direction (recording material conveyance direction). FIG. 5B shows the current and the magnetic field of the heat generating layer 1c. FIG. 3 is a schematic view in the longitudinal direction shown. FIG. 5A shows a configuration in which the core 2, the coil 3, and the heat generating layer 1c are arranged concentrically from the center of the heat generating layer 1c. In the drawing, in the Y-axis direction, an arrow magnetic force line heading in the depth direction of the paper is simulated by Bin (x in a circle), and an arrow magnetic force line heading in the front direction of the paper is simulated by Bout (a black circle in a circle). are doing.

  In FIG. 5A, at the moment when the current is increasing in the direction of arrow I in the coil 3, magnetic lines of force are formed in the magnetic path as indicated by the arrow (marked by x in the drawing) directed in the direction of the depth of the paper. Is done. That is, the same number of magnetic lines of force Bin that go in the depth direction of the paper inside the core 2 inside the heat generating layer 1c and the magnetic lines of force Bout that return outside of the heat generating layer 1c toward the front of the paper are formed. When an alternating magnetic field is actually formed, an induced electromotive force is applied to the entire circumferential direction of the heat generating layer 1c so as to cancel the magnetic field lines thus formed, and a circulating current J circling the heat generating layer 1c as indicated by an arrow J. Flows.

  Since the induced electromotive force is applied in the circumferential direction of the heat generating layer 1c, the circulating current J flows uniformly in each of the divided heat generating layers 1c. Since the lines of magnetic force repeat generation and disappearance and direction reversal by the high-frequency current, the circulating current J repeatedly flows through generation and disappearance and direction reversal in synchronization with the high-frequency current. When a current flows through the heating layer 1c, Joule heat is generated due to the electric resistance of the heating layer 1c.

  The heat value Pe of the Joule heat is expressed by the following equation (1).

Pe: Heat value t: Thickness Bm: Maximum magnetic flux density ρ: Resistivity ke: Proportional constant (Comparison with comparative example regarding excessive temperature rise due to breakage of film 1)
Hereinafter, an examination will be made of an excessive temperature increase due to breakage of the film 1 in the present embodiment. First, a comparative example with respect to the present embodiment is determined as follows, and a comparison with the comparative example is performed.

1) Comparative Example On a base layer 1a formed of the same PI (polyimide) resin as in the present embodiment, nickel having an electric volume resistivity of 9 × 10 ⁻⁸ Ωm was formed by electro-nickel plating as a protective layer 1b different from the present embodiment. Was formed to a thickness of 5 μm.

Next, the heat generating layer 1c was formed by electroplating copper having an electric volume resistivity of 2 × 10 ⁻⁸ Ωm to a thickness of 1 μm, as in the present embodiment. Then, similarly to the present embodiment, as a repetition pattern of a heating layer 1c having a width (length) of 9.8 mm in the longitudinal direction and a gap of 0.2 mm, a cylinder divided into 23 pieces having a longitudinal direction of 230 mm is formed in the same manner as in the present embodiment. A heating layer 1c having a shape was formed (FIG. 4B).

Then, after the heat generating layer 1c was formed, nickel having an electric volume resistivity of 9 × 10 ⁻⁸ Ωm was formed to a thickness of 5 μm as the protective layer 1b different from the present embodiment by electroplating as described above.

  FIG. 6 is an explanatory diagram of a current flow when the heat generating layer 1c of the film 1 is damaged. FIGS. 6A and 6B show an example of the flow of current when the heating layer 1c of the present embodiment is damaged at different lengths. FIGS. 6C and 6D show examples of the current flow when the heat generating layer 1c of the comparative example is damaged at different lengths. In FIGS. 6A to 6D, whether a large amount of current flows to the end portion C of the damaged portion is determined by the magnitude relation of the resistance per unit width between the heat generating portion Rh and the non-heat generating portion Rp, that is, the non-heat generating portion R It is determined by the ratio of the resistance per unit width of the heat generating portion Rp.

2) Resistance Measurement Method A resistance measurement method for verifying the resistance ratio in the present embodiment will be described below. The resistance was measured using a low resistivity meter (Loresta-GP manufactured by Mitsubishi Chemical Analytech Co., Ltd.). For the measurement, a test piece was prepared by cutting open the film 1 and removing the elastic layer 1d and the release layer 1e at the portions in contact with the electrodes. Using the prepared test piece, the resistance was measured by the four probe method. A probe in which four needle-shaped electrodes are linearly arranged at an interval of 1.5 mm is pressed against a metal surface, a constant current flows between two outer probes, and a potential difference generated between the two inner probes is measured. The resistance was determined.

And resistor R _rh when not cross the non-heat generating portion Rp, the resistance measurement of the resistance R _{rh + p} when straddling the non-heating portions Rp was performed. The resistance R _rh when not straddling the non-heating part Rp is the resistance of the heating part Rh, and the resistance R _{rh + p} when straddling the non-heating part Rp is the combined resistance of the heating part Rh and the non-heating part Rp.

Resistance r _h per unit width of the heat generating portion Rh (unit length in the longitudinal direction), the resistance R _rh measurement and electrode spacing w _{h (present} embodiment in which does not cross the non-heat generating portion Rp, electrode spacing w _h Is obtained from 1.5 mm), and is represented by equation (2).

Resistance r _p per unit width of the non-heat generating portion Rp is the resistance R _{rh + p} measurement and electrode spacing w _h and when straddling the non-heat generating portion Rp, a non-heating portion width w _{p (the} present embodiment, the non-heating portion width w _p is obtained from 0.2 mm) and is expressed by the following equation (3).

A resistor _{r p} per unit width of the non-heat generating portion Rp, the ratio _r p / _{r h} of the resistance _{r h} per unit width of the heat generating portion Rh is expressed by Equation (4).

In this embodiment, the ratio r _{p /} r _h of the resistance per unit width of the non-heat generating portion Rp and the heating unit Rh is 100, per unit width of the non-heat generating portion Rp resistor is a high structure. On the other hand, in the comparative example, the ratio r _{p /} r _h of the resistance per unit width of the non-heat generating portion Rp and the heating unit Rh is 0.9, per unit width of the non-heat generating portion Rp resistance is lower structure I have. For this reason, in the comparative example, the non-heat-generating portion Rp is referred to as the non-heat-generating portion Rp in order to correspond to the film 1 of the present embodiment.

  In (a), (b), (c), and (d) of FIG. 6, “Za1”, “Zb1”, “Zc1”, “Zd1”, and “Za2” and “Zc2” are areas without damage. is there. In a region where there is no damage, an induced electromotive force is generated in the heat generating layer 1c by a magnetic flux penetrating the magnetic core 2 and in a direction parallel to the Y-axis direction which is the rotation axis 1o of the film 1, and as shown by the arrow, the induced electromotive force A circulating current J flows in the direction. Actually, since an AC voltage is applied, the current flows in the direction opposite to the arrow.

  As in the present embodiment of FIG. 6A and the comparative example of FIG. 6C, when the damaged area is within the longitudinal width of the heat generating layer 1c, the damaged area does not straddle the non-heat generating portion Rp. In the example, there is no difference in the current flowing around the areas "Za3" and "Zc3" where the end portion C of the damaged portion is located. However, if the damage width becomes larger than the longitudinal width of the heat generating layer 1c and the heat generating layer 1c straddles the non-heat generating portion Rp, a difference appears between the present embodiment and the comparative example.

That is, in this embodiment shown in FIG. 6 (b), the resistance r _p per unit width of the non-heat generating portion Rp is larger than the resistance r _h per unit width of the heat generating portion Rh, circumferential direction on the protective layer The current flowing through is not bypassed. Therefore, no current flows in the area of “Zb3” where the entire width is damaged. In addition, in the area of “Zb2” where the end portion C of the damaged portion is present, a current flowing around only the area of “Zb2” is generated. Therefore, the total amount of the sneak current is small, and the excessive temperature rise can be suppressed to an allowable level.

In contrast, if 6 of (d) is a comparative example, the resistance r _p per unit width of the non-heat generating portion Rp is equally as low as the resistance r _h per unit width of the heat generating portion Rh, non-heat generating portion The current flowing in the circumferential direction bypasses Rp as a part of the conduction path. As a result, the currents in the damaged areas “Zd2” and “Zd3” flow around the damaged portion end C so that a large amount of current flows in the damaged portion end C, and the temperature becomes excessively high as compared with other regions.

  Table 1 shows that, in order to confirm the effect of the present embodiment, the heat fixing operation was actually performed for each of the case where the film 1 of the present embodiment (Example 1) and the comparative example 1 were attached to the fixing device B. The result of the temperature measurement at the time of this is shown. The temperature measurement result is obtained by measuring the temperature of the end portion C of the damaged portion of the heat generating layer 1c with a radiation thermometer. Specifically, an experiment was conducted in which the film 1 was heated and heated from room temperature (23 ° C.) to a target temperature of 160 ° C. under the conditions of a maximum input power of 900 W and a rotation speed of 300 mm / sec. ) Was measured for the temperature at the end portion C of the damaged portion when shaking.

  As shown in Table 1, there is no difference in the temperature of the damaged portion between the present embodiment (Example 1) and the comparative example up to a damage width of 8 mm, which is within 9.8 mm in the longitudinal width of the heat generating layer 1c. However, when the damage width is larger than the longitudinal width of the heat generating layer 1c, in the comparative example, the temperature of the end portion C of the damaged portion increases, and when the damage width reaches 18 mm, the temperature reaches 270 ° C. In other words, when the width of the damage of the film increases, the amount of current flowing toward the damaged end increases, the amount of heat generated at the damaged end C increases, and the temperature rises to 270 ° C.

  On the other hand, in the present embodiment (Example 1), the temperature of 220 ° C. when the damage width is 8 mm is the highest temperature. When the damage width is larger than the longitudinal width of the heat generating layer 1c, current does not flow to the portion where the entire longitudinal width of the heat generating layer 1c is damaged, so that less current flows as compared with the comparative example, and it can be seen that excessive temperature rise can be suppressed. .

  In the above experiment, when the excessive temperature rise was 270 ° C. or higher as in the comparative example, image defects became remarkable, and the durability of the film was significantly reduced due to thermal deterioration. As in the present embodiment (Example 1), when the excessive temperature was 220 ° C. or less, the image defect was slight, and the durability of the film due to thermal deterioration was at a level without any problem.

Further, a difference can be observed between the present embodiment (Example 1) and the comparative example in the temperature distribution of the film 1 immediately after the power is turned on. Thermography (TVS-8500 manufactured by NEC Avio) was used for the surface temperature distribution measurement. When power is applied from a room temperature (23 ° C.) state, in the film 1 of the present embodiment, the temperature of the non-heat generating portion Rp of the film 1 of the present embodiment rises first, and the temperature of the non-heat generating portion Rp increases later due to heat conduction from the heat generating portion. . This is, in the present embodiment, the ratio r _{p /} r _h of the resistor is large, is because the heat generating unit Rh is generating heat.

On the other hand, in the comparative example, the temperature of both the heat generating portion Rh and the non-heat generating portion Rp rises. In Comparative Example, the ratio r _{p /} r _h of the resistor is small, is to heat generation or non-heat generating portion Rp.

Here, the temperature of the damaged portion end C when varying the ratio r _{p /} r _h of the resistance per unit width of the non-heat generating portion Rp and the heating unit Rh, shown in FIG. The temperature of the end portion C of the damaged portion shown in FIG. 7 is a result estimated by calculation based on the temperature measurement results shown in Table 1. In a region where the ratio of resistance per unit width r _p / r _h between the non-heat generating portion Rp and the heat generating portion Rh is 10 or more (10 times or more), the temperature of the damaged portion end portion C hardly changes. The larger value of the ratio r _{p /} r _h of the resistor, since the current is a current which flows around through the non-heat generating portion Rp disappears, there is no upper limit to the ratio r _{p /} r _h of the resistor.

However, the temperature of the ratio r _{p /} r _h of resistance is below 10 damaged portion end C starts to rise. This is because, as described above, a current flows around the non-heat-generating portion Rp. From the viewpoint of thermal deterioration, the temperature of the film used regularly is generally set to about 230 ° C. or less. Deflection of the fixing temperature control, considering the variation, the ratio r _{p /} r _h resistors, since it is desirable for use in areas where the temperature of the damaged portion end C is unchanged, the ratio r _{p /} r _h resistors It is more desirable to be 10 or more.

In this embodiment, the ratio r _{p /} r _h of the resistance per unit width of the non-heat generating portion Rp and the heating unit Rh is set to 100, if 10 or more, a current hardly flows in the non-heat generating portions Rp, It becomes easy to suppress the excessive temperature rise to an allowable level.

Incidentally, if the ratio r _{p /} r _h of the resistor is greater than 1, it may be used if damaged width (longitudinal width) is small.

  In the above-described embodiment, since the heat generating layer 1c of the film 1 has a configuration in which copper having a low electric resistivity is adopted, the heat generating layer 1c as a metal layer can be made thinner. Therefore, the heat capacity of the film 1 can be reduced, the temperature rising speed is faster, the quick start property is excellent, and the configuration is advantageous for shortening the print waiting time. Then, even when a crack or the like occurs in the film 1, it is possible to suppress excessive temperature rise and to suppress oxidation of copper which is the heat generating layer 1c.

  In the present embodiment, copper is used for the heat generating layer 1c. However, the same effect can be obtained when a metal that is easily oxidized such as a copper alloy, silver, or silver palladium is used for the heat generating layer 1c. The protective layer 1b may be made of a material other than a nickel alloy, such as nickel or hard chrome plating, as long as a desired resistance can be obtained by adjusting the thickness.

  In the present embodiment, the elastic layer 1c is provided, but if the fixing is satisfactory, the elastic layer 1d may not be provided, and the release layer 1e may be directly formed on the surface of the protective layer 1c.

  Although the above-described embodiment is an example of the best embodiment of the present invention, the present invention is not limited to this, and various configurations are replaced with other known configurations within the scope of the concept of the present invention. It is possible.

1. Film, 1a .. Base layer, 1b .. Protective layer, 1c .. Heating layer, 3 ... Exciting coil, 6 ... Film guide, 8 ... Pressure roller

Claims (9)

A cylindrical rotating body including a base layer, a heating layer, and a protection layer in a radial direction, and the heating layer divided into a plurality of portions so as to sequentially include a heating region and a non-heating region in a longitudinal direction,
An opposing body facing the rotating body,
A nip portion forming member that forms a nip portion that sandwiches and conveys a recording material carrying a toner image via the rotating body,
Magnetic field generating means for forming an alternating magnetic field in the rotation axis direction of the rotating body by flowing an alternating current to generate an induced current in the circumferential direction of the rotating body,
Has,
The heating layer is made of a first metal, and the protective layer is made of a second metal different from the first metal so as to cover the heating layer.
In a cross section including the rotation axis direction, the electric resistance per unit length of the first region including the heat generating layer and the protective layer in the radial direction as the heat generating region is the heat generation in the radial direction as the non-heat generating region. An image heating apparatus, wherein the second region provided with the protective layer without a layer has a smaller electrical resistance per unit length than the second region.   2. The image heating apparatus according to claim 1, wherein the electric resistance per unit length of the second region is at least 10 times the electric resistance per unit length of the first region. 3.   The magnetic field generating means includes an exciting coil inserted into a hollow portion of the rotating body, and has a magnetic core for inducing magnetic field lines of the alternating magnetic field inside the rotating body inside the exciting coil. The image heating device according to claim 1 or 2, wherein   The image heating apparatus according to claim 1, wherein the protective layer is provided outside the heat generating layer in a radial direction.   The image heating apparatus according to claim 4, wherein the protective layer is provided outside and inside the heat generating layer in a radial direction.   The image heating apparatus according to claim 1, wherein the first metal is made of copper.   The image heating apparatus according to claim 1, wherein the second metal is made of an alloy containing nickel.   The image heating apparatus according to claim 1, wherein the rotating body has a release layer on an outermost surface in a radial direction. The image heating apparatus according to claim 8, wherein the rotating body has an elastic layer between the protective layer and the release layer in a radial direction.

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