WO2017159882A1

WO2017159882A1 - Cylindrical fixing member, fixing device and image forming apparatus

Info

Publication number: WO2017159882A1
Application number: PCT/JP2017/011558
Authority: WO
Inventors: Masatake Usui; Takaaki Tsuruya; Yasuo Yoda; Yasunari Kobaru; Akira Kato; Hiroki Eguchi; Michio Uchida; Tetsuya Sano; Atsuyoshi Abe; Aoji Isono; Minoru Hayasaki; Hiroshi Mano; Yuki Nishizawa; Akira Kuroda
Original assignee: Canon Kabushiki Kaisha
Priority date: 2016-03-15
Filing date: 2017-03-15
Publication date: 2017-09-21

Abstract

A cylindrical fixing member for use with a fixing device (B) includes a heat generating layer (la) and an electrode layer (lb) contacting the heat generating layer (la). The electrode layer (lb) is smaller in volume resistance value than the heat generating layer (la). The electrode layer (la) is formed in a helical shape so that a helical axis thereof extends in a direction along a generatrix direction of the fixing member. One end and the other end of the electrode layer (lb) are electrically open.

Description

DESCRIPTION

[TITLE OF THE INVENTION]

CYLINDRICAL FIXING MEMBER, FIXING DEVICE AND IMAGE FO'RMING APPARATUS

[TECHNICAL FIELD-]

[0001] The present invention relates to a

circumference (rotatable heating member) suitable as a cylindrical film of a fixing device of an

electromagnetic induction heating type, mounted in an image forming apparatus, such as an

electrophotographic copying machine or an

electrophotographic printer, and relates to the fixing device and the image forming apparatus which include the cylindrical fixing member.

[BACKGROUND ART]

[0002] In the electrophotographic copying machine or printer, a fixing device for fixing a toner image on a recording material by heating the recording material while feeding the recording material on which the toner image which has not been fixed is carried is mounted. As this fixing device, a fixing device of an electromagnetic induction heating type has been known. The fixing device of this type has advantages such that a temperature rise of the cylindrical film (rotatable heating member) for heating the recording material is quick and that also electric power

consumption is low.

[0003] In Japanese Laid-Open Patent Application

(JP-A) 2014-26267, a fixing device of an

electromagnetic induction heating type in which an exciting coil and a magnetic core are provided inside of a cylindrical rotatable heating member and an alternating magnetic field Is generated with respect to an axial direction of the rotatable heating member, and then the rotatable heating member is heated by a circumferential current generating around an

electroconductive layer of the rotatable heating member with respect to a circumferential direction has been disclosed. In JP-A 2014-26267, as a material of the electroconductive layer as a heat generating layer of the rotatable heating member, metal is employed.

The metal is low in volume resistivity, and therefore even at a voltage value of a commercial power source level, the circumferential current sufficiently flows, so that also temperature rise is quick.

[0004] On the other hand, when a resin film of

polyimide or the like can be employed as the rotatable heating member, it is desirable from viewpoints of a cost and flexibility. However, even when

electroconductivity is imparted to the resin film by adding an electroconductive agent such as carbon black, there was a limit that the volume resistivity of the resin film is lowered to about lxlO-^ Qm. For that reason, at the voltage of the commercial power source level, the circumferential current merely flows a little, and therefore a temperature rising speed is slow, so that there is a problem that it is difficult to employ the resin film as the rotatable heating member. [SUMMARY OF THE INVENTION]

[0005] A principal object of the present invention is to provide a cylindrical fixing member excellent in temperature rising speed, a fixing device including the cylindrical fixing member, and an image forming apparatus including the cylindrical fixing member.

[0006] According to as aspect of the present

invention, there is provided a cylindrical fixing member for use with a fixing device, comprising: a heat generating layer; and an electrode layer

contacting the heat generating layer, wherein the electrode layer is smaller in volume resistance value than the heat generating layer, wherein the electrode layer is formed in a helical shape so that a helical axis thereof extends in a direction along a generatrix direction of the fixing member, and wherein one end and the other end of the electrode layer are

electrically open. [0007] According to another aspect of the present invention, there is provided a fixing device

comprising: a cylindrical fixing member, wherein the cylindrical fixing member includes, a heat generating layer and an electrode layer contacting the heat generating layer, wherein the electrode layer is smaller in volume resistance value than the heat generating layer, wherein the electrode layer is formed in a helical shape so that a helical axis thereof extends in a direction along a generatrix direction of the fixing member, and wherein one end and the other end of the electrode layer are

electrically open; a coil provided at a hollow portion of the cylindrical fixing member, wherein the coil includes a helical-stepped portion having a helical axis extending in a direction along the generatrix direction of the cylindrical fixing member, and a magnetic field is formed for subjecting the heat generating layer to electromagnetic induction heating by causing an alternating current to flow through the coil; and a magnetic core provided inside the

helical-stepped portion of the coil and extending in the generatrix direction, wherein an image formed on a recording material is fixed on the recording material by heat from the cylindrical fixing member.

[0008] According to a further aspect of the present invention, there is provided an image forming apparatus comprising: an image forming portion for forming an image on a recording material; and a fixing portion for fixing the image on the recording material, wherein the fixing portion includes a cylindrical fixing member including a heat generating layer and an electrode layer contacting the heat generating layer, wherein the electrode layer is smaller in volume resistance value than the heat generating layer, wherein the electrode layer is formed in a helical shape so that a helical axis thereof extends in a direction along a generatrix direction of the fixing member, and wherein one end and the other end of the electrode layer are electrically open; a coil provided at a hollow portion of the cylindrical fixing member, wherein the coil includes a helical-stepped portion having a helical axis extending in a direction along the" generatrix direction of the cylindrical fixing member, and forms a magnetic field for subjecting the heat generating layer to electromagnetic induction heating by causing an alternating current to flow through the coil; and a magnetic core provided inside the helical-stepped portion of the coil and extending in the generatrix direction, wherein the image

recording material is fixed on the recording material by heat from the cylindrical fixing member.

[0009] Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings .

[BRIEF DESCRIPTION OF THE DRAWINGS]

[0010] Figure 1 is a sectional view of a fixing device according to Embodiment 1.

[0011] Figure 2 is a front view of the fixing device.

[0012] Figure 3 is a schematic view for illustrating electromagnetic induction heating of a heat generating layer.

[0013] In Figure 4, (a) and (b) are schematic views for illustrating a structure of a film.

[0014] In Figure 5, (a) and (b) are schematic views for illustrating a current and a magnetic field of the heat generating layer.

[0015] Figure 6 is a circuit diagram for illustrating a series resonant circuit and a relationship between an exciting coil and the heat generating layer.

[0016] Figure 7 is a schematic model view of a transformer including the exciting coil and the heat generating layer.

[0017] In Figure 8, (a) and (b) are schematic views showing a shape of the heat generating layer and a calculating method of a circumferential resistance.

[0018] Figure 9 is a schematic model view of a transformer including the exciting coil and an

electrode layer. [0019] Figure 10 is a schematic view for illustrating an induced electromotive force generated with respect to a generatrix direction of the heat generating layer.

[0020] In Figure 11, (a) and (b) are schematic views showing a shape of the heat generating layer and a calculating method of a resistance of the heat

generating layer with respect to the generatrix

direction.

[0021] In Figure 12, (a) and (b) are schematic views for illustrating a state in which an electrode layer of a film is cut in Embodiment 4.

[0022] In Figure 13, (a) to (c) are circuit views each showing an equivalent circuit including two

electrode layers of the film and a heat generating layer at a portion sandwiched between the two

electrode layers in Embodiment 4.

[0023] Figure 14 is a graph showing a result of repetitive calculation of a combined resistance Rcf of the film in Embodiment 4.

[0024] Figure 15 is a graph showing a relationship between a diameter between adjacent electrode layers and the combined resistance Rcf obtained by the

repetitive calculation in Embodiments 4-1 and 4-2.

[0025] Figure 16 is a graph showing a relationship between the diameter between adjacent electrode layers and the combined resistance Rcf of a film in

Comparison Example described in Embodiment 4. [0026] Figure 17 is a graph showing a relationship between the diameter between adjacent electrode layers and the combined resistance Rcf of a film in

Embodiment 5.

[0027] Figure 18 is a sectional view of an image forming apparatus.

[0028] In Figure 19, (a) and (b) are schematic. views for illustrating a structure of a film in Embodiment 6.

[0029] In Figure 20, (a) to (c) are schematic views for illustrating a structure of a film in Embodiment 7.

[0030] Figure 21 is a flowchart showing manufacturing steps of the film in Embodiment 7.

[0031] Figure 22 is a schematic view for illustrating a method of coating an electroconductive resin

material by dipping.

[0032] Figure 23 is a schematic view for illustrating a method of coating the electroconductive resin

material by spray coating.

[0033] Figure 24 is a schematic view for illustrating a method of coating the electroconductive resin

material by a dispenser.

[0034] Figure 25 is a flowchart showing manufacturing steps of the film in Embodiment 7.

[0035] Figure 26 is a schematic view showing a

positional relationship with respect to a longitudinal direction of a film in Embodiment 2.

[0036] Figure 27 is a schematic view showing a heat generating region with respect to the longitudinal direction of the film in Embodiment 2.

[0037] Figure 28 is a graph showing a temperature distribution of the film with respect to the

longitudinal direction in Embodiment 2.

[0038] Figure 29 is a schematic view for illustrating a structure of a coil and a. core of a fixing device in Embodiment 2.

[0039] In Figure 30-, (a) and (b) are schematic views for illustrating magnetic flux formed by the fixing device in Embodiment 2.

[0040] Figure 31 is a development of a fixing film including no electrode layer in Embodiment 3.

[0041] Figure 32 is a development of a fixing film including an electrode layer in Embodiment 3.

[0042] Figure 33 is a schematic model view showing an electric circuit of the fixing film including the electrode layer in Embodiment 3.

[0043] Figure 34 is a schematic view for illustrating a measuring method of a resistance of a heat

generating layer between adjacent electrode layers in Embodiment 3.

[0044] Figure 35 is a perspective view of the fixing film including the electrode layer in Embodiment 3.

[0045] Figure 36 is a sectional view, of the fixing film in Embodiment3, for illustrating a current path between the adjacent electrode layers. [DESCRIPTION OF EMBODIMENTS]

[0046] Embodiments of the present invention will be described specifically with reference to the drawings. Although the following embodiments are examples of preferred embodiments of the present invention, the present invention is not limited thereto, but various constitutions thereof can also be replaced with other known constitutions within the scope of the concept of the present invention.

[Embodiment 1]

1. Image forming apparatus 100

[0047] With reference to Figure 18, an image forming apparatus 100 according to the present invention will be described. Figure 18 is a sectional view showing a general structure of the image forming apparatus 100 (monochromatic printer in this embodiment) using electrophotographic technology.

[0048] In the image forming apparatus 100, an image forming portion A for forming a toner image (which has not been fixed) on a recording material P includes a photosensitive drum 101 as an image bearing member, a charging member 102, a laser scanner 103 and a

developing device 104. The image forming portion A further includes a cleaner 109 for cleaning the photosensitive drum 101, and a transfer member 108. An operation of the image forming portion A is well known and therefore will be omitted from detailed

description .

[0049] The recording material P, such as recording paper,, accommodated in a cassette 105 in a main assembly 100A of the image forming apparatus 100 is fed one by one by rotation of a roller 106. The recording material P is fed by rotation of a roller 107 to a transfer nip formed by the photosensitive drum 101 and a transfer member 108. The recording material P on which a toner image is transferred at the transfer nip is sent to the fixing portion

(hereinafter referred to as a fixing device) B via a feeding guide 110. An unfixed toner image T formed on the recording material P is heat-fixed on the

recording material. P by the fixing device B. The recording material P coming out of the fixing device B is discharged onto a tray 113 by rotation of a roller pair 111 and a roller pair 112.

1. Fixing device (first heating device) B

[0050] The fixing device B is a fixing device of an electromagnetic induction heating type. Figure 1 is a sectional view showing a general structure of the fixing device B in this embodiment. Figure 2 is a front view of the fixing device B as seen from an upstream side with respect to a. feeding direction X of the recording material P.

[0051] A pressing roller 8 as a pressing member includes a more metal 8a, an elastic layer 8b formed on an outer peripheral surface of the core metal 8a, and a parting layer 8c formed at on outer peripheral surface of the elastic layer 8b. As a material of the elastic layer 8b, a material having a good

heat-resistant property such as a silicone rubber, a fluorine-containing rubber or a fluorosilicone rubber may preferably be used. As the parting layer 8c, a material, having a good parting property and a good heat-resistant property, such as PFA, PTFE or FEP can be selected. With respect to a direction (hereinafter referred to as a Y-axis direction) perpendicular to the feeding direction (hereinafter referred to as an X-axis direction) of the recording material P, both end portions of the core metal 8a are rotatably supported by left and right side plates (not shown) of the fixing device B via bearings.

[0052] With respect to Z-axis direction perpendicular to both of the X-axis direction and the Y-axis

direction, a cylindrical film 1 as a cylindrical rotatable heating member (fixing member) is provided opposed to a pressing roller 8. On a film guide 6 inserted into a hollow portion of the film 1, a metal-made sty 5 for reinforcing the guide 6 is provided. The guide 6 is prepared using PPS

(polyphenylene sulfide) resin or the like having a heat-resistant property. [0053] With respect to the Y-axis direction, at both end portions of the stay 5, flanges 9a and 9b formed of a heat-resistant resin material are externally engaged. The flange 9a is fixed to a left-hand frame by a regulating member 10a, and the flange 9b is fixed to a right-hand frame by a regulating member 10b. Each of the flanges 9a and 9b holds an inner peripheral surface (inner surface) of an associated film end portion by a holding portion (not shown) thereof inserted into the hollow portion of the film 1.

Further, the respective flanges 9a and 9b receive the end portions of the film 1 by film-side regulating surfaces 9al and 9bl during rotation of the film 1 and regulate (limit) lateral movement of the film 1 along a generatrix direction of the film 1.

[0054] With respect to the Y-axis direction, between both end portions of the stay 5 and left and right side plate-side spring-receiving members 12a and 12b, pressing springs 11a and lib (Figure 2) are

compressedly provided, so that a pressing-down force is caused to act on the stay 5. In the fixing device in this embodiment, a pressing force of about

100N - 250N (about kgf - 25 kgf) in total pressure is applied to the stay 5. A plate-like slidable member 7 held on a flat surface of the guide 6 in the pressing roller 8 side is pressed on the film 1 toward an outer peripheral surface of the pressing roller 8 by the pressing force, so that the pressing roller 8 forms a nip N (Figure 1) with a predetermined width in

cooperation with the film 1.

[0055] The pressing roller 8 is rotated in an arrow direction (Figure 1) by drive of a motor M: as a driving means. The film 1 is rotated in an arrow direction by the rotation of the pressing roller 8 while sliding with a sliding surface 7a of the

slidable member 7 at an inner surface thereof in the pressing roller 8 side. During a rotational operation of. the film 1, in order to reduce a sliding frictional force between the inner surface of the film 1 and the sliding surface 7a, it is possible to interpose a lubricant such as heat-resistant grease between the film inner surface and the sliding surface. With respect to the Y-axis direction, at both end portions of the guide 6, the flanges 9a and 9b as regulating (limiting) members for regulating (limiting) the lateral movement of the film 1 by receiving the end portions of the film 1 during the rotation of the film 1 are externally engaged.

[0056] Figure 3 is a schematic view for illustrating electromagnetic induction heating of a heat generating layer la by a magnetic core 2 and an exciting coil 3.

[0057] The magnetic core 2 as a magnetic core material has a cylindrical shape of La in length with respect to the Y-axis direction, and is disposed by an unshown fixing means so as to penetrate through the hollow portion of the film 1. That is, the core 2 is inserted into the hollow portion of the film 1 and is disposed along the generatrix direction of the film 1.

[0058] The core 2 induces magnetic lines of force (magnetic fluxes) , by an alternating magnetic field generated by the exciting coil 23 as a magnetic field generating, means, into (the inside of) the film 1, and functions as a member for forming a path (magnetic path) of the magnetic lines of force.

[0059] The core 2 may preferably be formed of a material having small hysteresis loss and high

relative permeability. For example, ferromagnetic materials constituted by high-permeability oxides or alloy materials such as calcined ferrite, ferrite resin, amorphous alloy and permalloy are used. It is desirable that the core 2 has a large cross-sectional area to the extent possible within a range in which the core 2 is accommodatable in the film 1 which is a cylindrical member. The shape of the core 2 is not limited to the cylindrical shape, but it is also

possible to select a polygonal prism shape or the like.

[0060] The coil 3 is formed by winding an ordinary single lead wire helically around the core 2 at the hollow portion of the film 1 in a winding number

(number of turns) of about 10 to about 40. In this embodiment, the coil 3 is constituted by the winding in the winding number of 18. The coil 3 is wound inside the film 1 in the direction crossing a

rotational axis lo of the film 1. For this reason, when a high-frequency current is caused to flow into the coil 3 via a high-frequency converter 13 and energization contact portions 23a and 23b, the

alternating magnetic field, in which a polarity is periodically reversed, can be generated in a

rotational axis direction of the film 1. The coil 3 includes a helical-shaped portion where the coil 3 is helically wound so that a helical axis thereof extends in a direction along the generatrix direction of the film 1. The core 2 is provided inside the

helical-shaped portion of the coil 3.

[0061] A control circuit 14 controls the

high-frequency converter 13 on the basis of a^■ .

temperature detected by a temperature detecting element 4 provided at a center of a passing region (230 mm) of the film 1, with respect to the Y-axis direction, in which the recording material P passes. As a result, a surface temperature of the film 1 is maintained at a predetermined target temperature

(about 150°C - 200°C) by subjecting the film 1 to electromagnetic induction heating.

[0062] The recording material P carrying thereon the unfixed toner image T is heated at the nip N while being fed through the nip N, so that the toner image is fixed on the recording material.

3. Structure and manufacturing method of film

[ 0063 ] In Figure 4, (a) is a perspective view showing the heat generating layer la of the film 1 and an electrode layer lb formed on an outer peripheral surface of the heat generating layer la, and (b) is a schematic view for illustrating a layer structure of the film 1.

[0064 ] As shown in (b) of Figure 4, the film 1 is a cylindrical rotatable member having a composite structure including a cylindrical heat generating layer la, the electrode layer lb, an elastic layer lc and a parting layer Id. That is, the film 1 includes the electrode layer lb helically formed on an outer peripheral surface of the cylindrical heat generating layer la prepared with an electroconductive member. The electrode layer lb contacts the surface of the heat generating layer la. The elastic layer lc is laminated so as to cover the electrode layer lb formed on the surface of the heat generating layer la, and then the parting layer Id is laminated on an outer peripheral surface of the elastic layer lc.

[0065] A detailed structure and a manufacturing method of the film 1 will be described while making reference to (a) and (b) of Figure 4.

[0066] First, the heat generating layer la is formed of a heat-resistant resin material such as polyimide, polyamideimide, PEEK or PES in which electroconductive particles such as carbon black or metal powder are added and dispersed, and is molded in a cylindrical shape of 30 μιη - 100 μπι in thickness. In this

embodiment, the polyimide resin material is molded using a die in a cylindrical shape of 30 mm in inner diameter, 240 mm in longitudinal length and 50 ]l in thickness, so that the heat generating layer la was formed.

[0067] Next, the electrode layer lb is prepared by helically forming an electroconductive wire, on the surface of the heat generating layer la, formed of a material smaller in volume resistivity than the material of the heat generating layer la. Here, the electroconductive wire is formed of iron, copper, silver, aluminum, nickel, chromium, tungsten, SUS 304 containing these metals, an alloy such as nichrome, or an electroconductive resin material such as CFRP

(carbon fiber reinforced plastic) or carbon nanotube resin. The electrode layer lb has a helical shape such that a helical axis thereof extends in a direction along the generatrix direction of the film 1.

[0068] Here, a helical pitch interval of the

electrode layer lb most suitable for a heat generation principle described later will be described. The helical pitch interval of the electrode layer lb varies depending on a volume resistivity of the electroconductive member used as the material of the heat generating layer la. Further, when a diameter (layer thickness) of the electroconductive member of the electrode layer lb is excessively large, an unevenness shape thereof is not completely absorbed by the elastic layer lc to result in hardness

non-uniformity, and pressure non-uniformity due to the hardness non-uniformity appears as an image

non-uniformity in some cases. Therefore, the diameter (layer thickness) of the electroconductive member of the electrode layer lb may be 200 μπι or less and may desirably be small to the extent possible.

[0069] In this embodiment, a core was inserted into a hollow portion of the heat generating layer la so that the heat generating layer la was not deformed during formation of the electrode layer lb, and with respect to the Y-axis direction, a winding start end portion of the electroconductive wire formed of SUS 304 in a diameter of 50 μπι was bonded with a heat-resistant adhesive in Comparison Example side of the surface of the heat generating layer la. Then, the

electroconductive wire is equidistantly wound around the heat generating layer surface along the generatrix direction of the heat generating layer la by an axis rotation method, whereby the electrode layer lb having the helical shape was formed. Also a winding end .

portion of the electroconductive wire was bonded with the heat-resistant adhesive in the other end side of the surface of the heat generating layer la.

[0070] Then, the elastic layer lc was formed along the generatrix direction of the heat generating layer la so as to cover the electrode layer lb on the surface of the heat generating layer la in a state shown in (a) of Figure 4. The elastic layer lc is formed in an entire passing region (230 mm) shown in Figure 2. In this embodiment, the elastic layer lc was formed of silicone rubber of 20 degrees in hardness

(JIS-A, load: 9.8 N (1 kgf) by spray coating so as to have a thickness of 300 mm (350 ]lm at a portion free from the electrode layer lb) . The elastic layer lc has functions of suppressing the pressure-uniformity and the heat non-uniformity. An optimum thickness of the elastic layer lc varies depending on the diameter and a helical pitch of the electrode layer lb. Here, the thickness is a dimension with respect to the Z-axis direction .

[0071] Then, a 30 m-thick fluorine-containing resin tube was coated as the parting layer Id on the surface of the elastic layer lc along the generatrix direction of the heat generating layer la by a heat contraction method. The parting layer Id has a function of

preventing contamination of the surface of the film 1 with the toner or paper dust deposited thereon.

4. Heat generation principle of film 1 [0072 ] First, the case where the electrode layer lb does not exist, i.e., a heat generation principle in a conventional type will be- described.

[0073 ] In Figure 5, (a) is a schematic view showing a current and a magnetic field in cross-section of the heat generating layer la, and (b) is a schematic view showing the current and the magnetic field with respect to the generatrix direction of the heat generating layer la.

[0074 ] In (a) of Figure 5, from the center of the heat generating layer la, the core 2, the coil 3 and the heat generating layer la are concentrically disposed. With respect to the Y-axis direction, the magnetic lines of force indicated by arrows toward a depth direction on the drawing sheet are represented by "Bin" (x in o) , and the magnetic lines of force indicated by arrows toward a front direction on the drawing sheet are represented by "Bout" (· in o) .

[0075] At the instant when the current increases in the coil 3 with respect to an arrow I direction, the magnetic lines of force are formed in the magnetic path as indicated by the arrows (x in o) toward the depth direction on the drawing sheet. That is, the number of the magnetic lines of force "Bin" passing through the core, 2, inside the heat generating layer la, in the depth direction, and also the number of the magnetic lines of force "Bout" return toward the front direction outside the heat generating layer 21a is are the same. When the alternating magnetic field is formed in actuality, an indicated electromotive force is exerted over a full circumferential region of the heat generating layer la so as to cancel, the magnetic lines of force which are formed as described above, so that the current passes through the heat generating layer la so as to move in the circumferential

direction of the heat generating layer la as indicated by an arrow J (hereinafter, referred to as a

circumferential current J) .

[0076] The indicated electromotive force is exerted in the circumferential direction of the heat

generating layer la, and therefore the circumferential current J uniformly flows inside the heat generating layer 21a . The magnetic lines of force repeats generation and extinction and direction reversal by the high-frequency current and therefore the loop current J flows in synchronism with the high-frequency current while repeating the generation and extinction and the direction reversal. When the current flows into the heat generating layer la, due to an electric resistance of the heat generating layer la, Joule heat generates in the heat generating layer la.

[0077 ] The Joule heat generation is called "iron loss (core loss) " in general, and a heat generation amount Pe is represented by the following formula (1):

Pe: heat generation amount

t : film thickness

f : frequency

Bm: maximum magnetic flux density

resistivity

ke: constant of proportionality [0078] The magnetic lines of force generated . by the core 2 generates in parallel to the direction of the rotational axis of the film 1, and therefore the circumferential current J flows in the direction perpendicular to the rotational axis direction of the film 1.

[0079] The circumferential current J generated as described above depends on the magnetic flux in the film 1 and the resistance value of the heat generating layer la. Further, in a range in which the resistance value of the heat generating layer la does not change extremely, the circumferential current J is

independent of also the thickness of the material of the heat generating layer la. Further, even in the case where as the material of the heat generating layer la, an electroconductive resin material or the like other than the metal material is used, it is possible to cause the heat generating layer la to generate heat in principle. Therefore, in the type using the circumferential current J as in this

embodiment, compared with an electromagnetic induction heating type using eddy current, it is possible to enlarge a degree of design latitude in terms of the material, the thickness and the frequency of the heat generating layer la.

[0080] As the heat generation other than that of the film 1 in a system in which the induction heating is carried out, heat generation of a primary-side coil winding due to copper loss and heat generation of the core 2 due to iron loss also exist. The heat

generation of the primary-side coil winding and the heat generation of the core 2 do not contribute directly to the heat generation of the film 1, and therefore a material which does not readily generate the copper loss and the iron less so as to efficiently heat the film 1 while minimizing degrees of the heat generation of the primary-side winding and the heat generation of the core 2.

[0081] Figure 6 is a circuit diagram for illustrating a series resonant circuit and a relationship between the coil 3 and the heat generating layer la. In this circuit diagram, a circuit is divided into a

commercial power source 20, a rectifying circuit 21,. a high-frequency switching circuit 22, a resonant circuit 24, an ideal transformer 25 and the heat generating layer la.

[0082] A commercial AC voltage (e.g., AC 100 V or AC

200 V, 50/60 Hz) obtained from the commercial power source 20 is converted into an undulating voltage by the rectifying circuit 21, and is supplied to the high-frequency switching circuit 22.

[0083] Then, a voltage Va converted into the

undulating voltage is supplied to the resonant circuit 24 in the form of a high-frequency current (e.g., at 20.5 kHz - 100 kHz) by a switching element such as an insulated gate bipolar transistor (hereinafter simply referred to as "IGBT"). Drive (switching between an on-state and an off-state) of the IGBT is controlled by a driving circuit 23.

[0084] In the resonant circuit 24, a resonant capacitor CR and an exciting coil LR constitute the series resonant circuit. In the high-frequency converter 13, a relationship between an effective voltage Va supplied to the high-frequency switching circuit 22 and an effective voltage Vp^ supplied to the resonant circuit 24 can be represented by a formula (2) shown below according to description of publica w.

Va : effective voltage of commercial power source [0085] The publication 1 is "LLC resonant half-bridge converter design guideline, APPLICATION NOTE AN2450". The publication 2 is "Half-Bridge LLC Resonant

Converter Design Using FSFR-Series Fairchild Power Switch (FPS), APPLICATION NOTE AN4151".

[0086] Incidentally, the relationship between the effective voltage Vp^¾ and a maximum of the voltage of the commercial power source 20 is represented, by the following formula (3).

Vm: maximum of voltage of commercial power source 5. Calculating method of power by transformer model

[0087] Figure 7 is a schematic model view of a transformer including the coil 3 and the heat

generating layer la. A relationship between a voltage ^VFHA applied to the coil 3 and a heat quantity (= electric power) PSLV generating in the heat generating layer la can be estimated from a formula of a

transformer ratio of the transformer. The

high-frequency voltage is generated in a primary winding side (coil 3), with the result that an induced electromotive force VgLV is exerted on a secondary winding side (heat generating layer la) via a core F and then is consumed as heat by a resistor sLV' ^so that the heat quantity (= electric power) PSLV ^^S generated . [0088] In the case where the electrode layer lb having the helical shape does not exist, only the heat generating layer la constitutes the secondary-side coil. In this case, the winding number (number of turns) of the secondary-side coil can be regarded as 1 and therefore when the winding number of the

primary-side coil (coil 3) is defined as QQ IL' from the formula of the transformer ratio, a relationship of the following formula (4) is satisfied among Vj¾¾, ^vSLVa ^{and N}C0IL- i N^va)! „ ^yVF!IA . . . . . . . (₄ J

I ¹ V^y SM'a

QOI L" winding number of primary-side coil (coil 3) VFHA^: voltage applied to primary-side coil (coil 3) V^"SLVa" induced electromotive force of

secondary-side (heat generating layer la)

[ 0089] By modifying the formula (4), the following formula (5) is obtained. con.

[0090 ] When, heat quantity (= electric power)

generating in the heat generating layer la is defined as PsLVa ^{and a} circumferential resistance of the heat generating layer la is defined as RsLVa ' ky using the formula (5) , a relationship of the following formula (6) is obtained. V - ^* N· <·<o*n'-. / . ( ( )

[0091] The circumferential surface RsLVa °f ^tne heat generating layer la is an electric resistance when the current flows in the circumferential direction of the heat generating layer la.

[0092] In (a) of Figure 8, a shape of the heat generating layer la and a calculating method of the circumferential resistance RsLVa ^are shown. In the case where the heat generating layer la is LgLv (^m) i-ⁿ length with respect to the Y-axis direction, dgLy (m) in diameter, tgLv (m) in thickness and PSLV (Ωπι) in volume resistivity, the electric resistance when the cylinder is cut and developed as shown in (b) of

Figure 8 and then the current is caused to flow in an arrow R direction is represented by the following formula ( 7 ) .

[0093] A generated heat quantity in the case of the commercial power source of 100 V will be described. Respective numerical values are shown in Table 1.

Table 1

Item Symbol Numerical value Unit D*l d 0x10 m

_T*2 t 5x10 m

L*3 L 3x10 m

WN*4 ^NCOIL 16

*1 "D" is the diameter.

*2 "T" is the thickness.

*3 *L" is the length.

*4 "WN" is the winding number (number of turns)

[0094] In the above condition, in each of the case where as the material of the heat generating layer la, SUS 304 is employed and the case where as the material of the heat generating layer la, polyimide to which electroconductivity is imparted by adding carbon black is employed, the generated heat quantity will be

calculated. The volume resistivity of SUS 304 is about 7.0xl0-^ Qm. The generated heat quantity calculated from this volume resistivity value is shown in Table 2.

Table 2 em Symbol Numerical value Un

^RSLVa 8.2xl0^-3 Ω pSLVa 965.9 W *1: "CR" is the circumferential resistance.

*2: "GHQ" is the generated heat quantity.

[ 0095] The circumferential resistance is a value capable of providing a heat quantity enough to ensure a fixing property while satisfying a rating of the 100 V-commercial power source. In actuality, when heat generation was checked using the film formed of SUS 304 as the heat generating layer la, it was able to be confirmed that the heat was quickly generated at a sufficient speed.

[0096] On the other hand, the volume resistivity of carbon black is about l.OxlO^-5 and therefore the

volume resistivity of polyimide to which

electroconductivity is imparted by adding carbon black, is not lower than the volume resistivity of carbon black. In actuality, the volume resistivity of the polyimide to which electroconductivity is imparted by adding carbon black is about 5.0xl0-^ Qm. The

generated heat quantity calculated from this volume resistivity value of the electroconductxve polyimide is shown in Table 3.

Table 3

Item Symbol Numerical value Unit

CR* ¹ RsLVa 5.9xl0^_0 Ω GHQ*² P_SLVa

*1: "CR" is the circumferential resistance.

*2: "GHQ" is the generated heat quantity.

[0097] The circumferential resistance is excessively high and therefore the circumferential current little flows, and thus is a value failing to provide a heat quantity necessary for the fixing device B. In actuality, when heat generation was checked using the film formed of the electroconductive polyimide as the heat generating layer la, a result thereof was such that the heat generating layer la little generates heat .

[0098] Next, the heat generation principle in the case where the constitution of the film 1 in this embodiment is employed will be described, and then an estimated value of the generated heat quantity and an experimental result will be described.

[0099] A feature of the film 1 in this embodiment is in that the helically shaped electrode layer lb is formed on the heat generating layer la. As the heat generating layer la, the above-described

electroconductive polyimide of about 5.0xl0-^ Qm in volume resistivity was used. Further, the helically shaped electrode layer lb, the layer of SUS 304 having a diameter of 50 μπι and a volume resistivity of about 7.0x10 ' was used.

[0100] As described above, in the heat generating layer la, although the circumferential current J generates but an amount thereof is slight, and

therefore the heat generating layer la itself little generates the heat due to the circumferential current. However, the volume resistivity of the electrode- layer lb is low equivalently to the metal and the electrode layer lb has the helical shape, and therefore a sufficient induced electromotive force sLVb generates at both ends of the electrode layer lb. That is, in the case where the helically shaped electrode layer lb exists, also the electrode layer lb constitutes the secondary-side coil. Figure 9 is a schematic model view of a transformer including the coil 3 and the electrode layer lb. The winding number (number of turns) of the secondary-side coil is a helical winding number of the electrode layer lb, and from the formula of the transformer ratio, a relationship of the following formula ( 8 ) is satisfied among Vp^A' ^SLVb' ^NCOIL ^{and N}SLVb-

NrjoiL^: winding number of primary-side coil (coil 3)

VFHA^: voltage applied to primary-side coil (coil 3)

N SLV^: helical width number of electrode layer

VgLVa ^: induced electromotive force of secondary-side (heat generating layer la)

[0101] By modifying the formula (8) , the following formula (9) is obtained.

_V -— L*!/ . ... . . .. . . ( Q ) [0102] A potential difference formed is proportional to the helical winding number of the electrode layer lb. That is, with an increasing helical winding number, the potential difference formed by the electrode layer lb with respect to the generatrix direction of the heat generating layer la becomes larger.. Then, as shown in Figure 10, by the potential difference of the induced electromotive force ^Ly^ generated with respect to the generatrix direction of the heat

generating layer la, a current L flows through the electroconductive polyimide of the heat generating layer la in the generatrix direction of the heat generating layer, and is at a level such that the heat quantity generates.

[0103] In a conventional type, the diameter in which the current flows is the circumferential direction, but in the type in this embodiment, the current

flowing direction is the generatrix direction of the heat generating layer la as a feature of this

embodiment. Thus, even when the volume resistivity of the heat generating layer la is large, it becomes possible to increase the induced electromotive force ^vSLVb ky increasing the helical winding number of the electrode layer lb. That is, even a material high in volume resistivity to some extent can provide a sufficient generated heat quantity.

[0104] When, heat quantity (= electric power) generating in the heat generating layer la by the current flowing in the generatrix direction of the heat generating layer la is defined as PsLVb ^{anc a} resistance of the heat generating layer la with respect to the generatrix direction is defined as

^SLVb' ky using the formula (9), a relationship of the follo

[0105] As is understood from the formula (10), even when the surface RsLVb i^s high, by increasing HsLVb' the heat quantity can be increased.

[0106] In (a) of Figure 11, a shape of the heat generating layer la and a calculating method of the resistance sLVb with respect to the generatrix direction of the heat generating layer la are shown. The heat generating layer la is LgLy (^m) in length with respect to the generatrix direction of the heat generating layer la, dsL (^m) iⁿ diameter, tgLV (m) in thickness and PSLV (Ωπι) in volume resistivity. Then, the electric resistance when the cylinder is cut and developed as shown in (b) of Figure 11 and then the current is caused to flow in an arrow L direction (generatrix direction of the heat generating layer la) is represented by the following formula (11).

[0107] Here, a calculation example in the case where the volume resistivity of the heat generating layer la is about 5.0xl0^~4 Qm will be described.

Table 4

Item Symbol Numerical value Unit

HWN*1 R_SLVa 55

GHQ*² P_SLVa 980.7 W

*1: "HWN" is the helical winding number.

*2: "GHQ" is the generated heat quantity.

[0108] The helical winding number of the electrode layer lb is made 55, so that it is estimated that the heat quantity which is the same level as that in the case where the stainless steel is used as the material of the heat generating layer la in the conventional type can be obtained. In actually, as the material of the heat generating layer la, the electroconductive polyimide of about 5.0xl0^-4 Qua in volume resistivity was employed, and heat generation of the film 1 formed as the electrode layer lb by winding the wire of SUS 304 in the helical shape by 55 turns was checked. Then, it was confirmed that the entirety of the film 1 was able to be increased in temperature at a sufficient speed.

[0109] The calculation under the assumption that the commercial power source voltage is 100 V and the experimental results were described above. In the case where the commercial power source voltage is 200 V, for example, the voltage VF#I of the primary-side coil is 200/100 times, i.e., 2 times. In this case, by changing the helical winding number of the electrode layer lb to 55/2 = 27.5 turns, the substantially same generated heat quantity can be obtained without

changing the constitution of the primary-side coil between the commercial power source voltages of 100 V and 200 V. That is, only be exchanging (replacing) the film 1, without exchanging the parts such as the core 2, the same temperature control can be effected so as to meet both of the cases of the commercial power source voltages of 100 V and 200 V.

[Embodiment 2]

[0110] This embodiment is an embodiment in which a positional relationship between a maximum image

forming region and longitudinal end portions (one end portion and the other end portion) of an electrode layer and in which a desired region can be uniformly heated. In this embodiment, the same constitution as that of Embodiment 1 is employed except that a

longitudinal width of the electrode layer lb is

defined.

[0111] The longitudinal width of the electrode layer lb formed in the helical shape is set in the following manner. That is, the helically shaped electrode layer lb is formed so that when a point corresponding to a position on the electrode layer lb apparently wound from a helical shape starting point on the (adjacent) electrode layer lb so as to provide a shortest

distance-therebetween at a longitudinal end portion of the electrode layer lb is defined as a reference point, a width between reference points at both longitudinal end portions is at least (equal to or more than) a width of the maximum image forming region.

[0112] Figure 26 is a schematic view showing a

positional relationship between the maximum image forming region and the electrode layer lb. Figure 26 schematically shows a state of the electrode layer lb when the fixing film 1 is cut and developed along rectilinear lines XI - X2 with respect to the

generatrix direction of the heat generating layer la.

[0113] As shown in Figure 26, at a longitudinal end portion (one end portion) a of the electrode layer lb, a reference point Pal as an electrode layer point corresponding to a point on the electrode layer lb apparently wound from the helical shape starting point PaO on the (adjacent) electrode layer lb so as to provide the shortest distance therebetween is set. The point Pal is the point moved perpendicular from the point PaO thereto (shortest distance). That is, the point. Pal is the closest point, to the point PaO, of points on adjacent portions of the electrode layer lb with respect to the generatrix direction of the heat generating layer la. Also at another longitudinal end portion (the other end portion) b, points PbO and Pbl are similarly set. The helical shaped electrode layer lb is constituted so that a width between the points Pal and Pbl set as described above is not less than the width of the maximum image forming region.

[0114] Incidentally, the maximum image forming region is a printing region of a maximum width toner image formable on the recording material at the image forming portion and refers to a region obtained by subtracting a margin from a maximum width of the recording material which is capable of passing through the fixing device. In this embodiment, the material image forming region is 208 mm obtained by subtracting 8 mm, which is the sum of the margin of 4 mm in

Comparison Example side and the margin of 4 mm in the other end side, from the maximum width of 216 mm of the recording material. [0115] As described in Embodiment 1, in the case where the electroconductive polyimide of about

5.0xl0^~4 Q_m i_s used as the material of the heat generating layer and the SUS 304 wire is used as the electrode layer, a desired amount of the heat quantity can be obtained by winding the electrode layer around the heat generating layer by 55 turns.. In the case where the electrode layer is wound helically around the heat generating layer by 55 turns and the width between Pal and Pbl is not less than the width (208 mm) of the maximum image forming region, a pitch of the helical shape (longitudinal interval) is about 4 mm. Further, in the case_, where the film of 30 mm in inner diameter is used, an inclination angle of the electrode layer is about 6° from a circumferential direction in a state in which the electrode layer is cut and developed along the longitudinal direction.

[0116] In Embodiment 1, for convenience, description was made such that the current roughly flows in the generatrix direction, but strictly, it would be considered that the current flows in a. direction

(PaO - Pal direction in Figure 26) in which adjacent portions of the electrode layer provide the shortest distance. In the case where the electrode layer is wound around the heat generating layer by 55 turns as described above, the current flows in a direction inclined from a generatrix by about 6° . [0117] Figure 27 is a schematic view showing a heat generation distribution with respect to the

longitudinal direction of the film.

[0118] The current flowing through the heat

generating layer of the film flows between adjacent portions of the electrode layer in a shortest distance, and therefore a portion, indicated as a hatched line portion S, where adjacent electrode layer portions are connected with each other in the shortest distance generates heat. Accordingly, a region inside the points Pal and Pbl is a region where the heat

generates uniformly with respect to the

circumferential direction. That is, in regions outside the points PaO and PbO, i.e., in end portion-side regions, the current does not flow and therefore heat does not generate. Further, in a region between the points PaO and Pal and a region between the points PbO and Pbl, there is a portion where the current does not flow and heat does not generate depending on a

circumferential place, so that heat generation

non-uniformity occurs with respect to the

circumferential direction. On the other hand, in the region inside the points Pal and Pbl, the current flows and heat generates at all of points with respect to the circumferential direction.

[0119] Figure 28 is a graph showing a longitudinal temperature distribution at portions indicated by broken lines (a) and (b) in Figure 27. As shown in Figure 28, temperature distribution curves (a) and (b) are different in temperature with respect to the longitudinal direction, and the curve (a) shifts toward a right-hand side relative to the curve (b) .

[0120], Thus, the film 1 is different in longitudinal temperature distribution depending on the

circumferential place. Here, the region inside the points Pal and Pbl is a region in which heat generates at any portion and the temperature is constant.

Accordingly, as in this embodiment, by employing a constitution in which the image forming region is provided between the points Pal and Pbl, a uniform temperature can be maintained to image end portions, so that improper fixing can be suppressed. In

actuality, when a fixed image was checked using the film in this embodiment, a good image can be obtained without causing the improper fixing.

[0121] In this embodiment, the embodiment in which the width between the reference points Pal and Pbl on the electrode layer lb is substantially the same as the width of the maximum image forming region was described, but a constitution in which the width between the reference points Pal and Pbl is broader than the width of the maximum image forming region may also be employed. For example, a constitution in which the width of the electrode layer lb between the points PaO and PbO is 230 mm and the width between the points Pal and Pbl is 222 mm which is larger than the image forming region width of 208 mm may also be employed. By employing such a constitution, tolerance during manufacturing and positional deviation during

rotational drive can be allowed.

[0122] In the constitution of this embodiment, the heat generation width is set by providing the

electrode layer on the heat generating layer of the film and is set by the electrode layer. For this reason, by suppressing heat generation of unnecessary portions at layer end portions, heat can be generated at a necessary portion, so that it becomes possible to suppress non-sheet-passing portion temperature rise or the like. For example, in the case where SUS 304 in the conventional type is used as the heat generating layer of the film, "heat generation width" = "film width" and therefore heat generation extends to the unnecessary portions at the longitudinal end portions. As a result, in the case where further speed-up of the apparatus is intended to be realized, suppression of the non-sheet-passing portion temperature rise is a problem. On the other hand, in this embodiment, a constitution of "heat generation width" < "film width" can be employed, and therefore heat generation at the non-sheet-passing portions which are the unnecessary portions can be suppressed and it becomes possible to suppress the non-sheet-passing portion temperature rise .

[Modified Embodiment]

[0123] Figure 29 is a schematic view showing a positional relationship among the film 1, the coil 3 and the core 2 is Modified Embodiment of Embodiment 2.

[0124] The coil 3 is helically wound around the core 2 so that a helical axis is parallel to the generatrix direction of the rotatable member. Both end portions of the core 2 and the helical-shaped portion of the coil 3 extends to outsides of both end portions of Pal and Pbl of the rotatable member with respect to the generatrix direction (In the figure, the end portions of the core 2 and the helical-shaped portion of the coil 3 extend to the outside of the film 1) . By employing such a constitution, magnetic flux can be efficiently induced into the electrode layer of the film.

[0125] In Figure 20, (a) is a schematic view showing generating magnetic flux 221. As is understood from the figure, the magnetic flux passing through a central portion of the core 2 passes in substantially parallel to the surface of the film 1. On the other hand, as regards the magnetic flux coming out from one end portion of the core 2, due to a difference in permeability between the core 2 and a core outside portion, a component extending perpendicularly to the surface of the film increases. Then, the magnetic flux 221 passes, through an outside space of the film 1 and flows into the other end portion of the core 2.

[0126] The generating magnetic flux also includes a component passing through a space between the film 1 and the coil 3 and flowing into the other end portion of the core 2. This component of the magnetic flux is opposite in direction from the magnetic flux passing through the inside of the core 2, and therefore the magnetic flux components are cancelled by each other inside the film 1, so that the magnetic flux passing through the inside of the core 2 decreases. That is, of the magnetic flux generated by the high-frequency current supplied from the power source to the coil, the magnetic flux component contributing to the heat generation of the film decreases. Thus, the magnetic flux component passing through the space between the film and the coil lowers heat generation efficiency. The heat generation efficiency refers to a proportion of a heat quantity generated by the film to electric power supplied to the power source, and can be defined by an amount of the magnetic flux contributing to the heat generation of the film as described above.

[0127] In this embodiment, by setting the lengths of the coil 3 and the core 2 so as to be longer than the length of the electrode layer (Pi - PI), the

perpendicular component of the magnetic flux 221 extends outside the film 1 (Pal - Pbl) . For that reason, in the region between Pla and Plb, the

magnetic flux component passing through the space between the film and the coil can be decreased, and therefore a decrease in magnetic flux component contributing to the heat generation in the region between Pla and Plb is suppressed, so that it is possible to suppress a lowering in heat generation efficiency.

[0128] In Figure 30, (b) is a schematic view showing the magnetic flux 221 when a cyclic core is used in place of a non-endless core in (a) of Figure 30. In the case of a constitution using the cyclic core as shown in the figure, the magnetic flux passing through the core forms a closed loop, and therefore the above-described magnetic flux component passing through the space between the film and the core can be further decreased, so that the lowering in heat generation efficiency can be further suppressed.

[Embodiment 3]

[0129] In this embodiment, a relationship between a resistance value and a heat quantity of the electrode layer lb and the heat generating layer la of the fixing film 1 is defined, so that a difference in temperature rising speed between the electrode layer lb and the heat generating layer la can be suppressed to a small value. In this embodiment, constitutions other than the fixing film 1 are the same as those in Embodiment 1, and therefore will be omitted from description.

[0130] In the conventional electromagnetic induction heating type disclosed in JP-A 2014-26267, the

resistance value of the fixing film heat generating layer la is set at a sufficiently low value, and therefore the circumferential current flows through the heat generating layer la in the circumferential direction and generates heat. On the other hand, the resistance value of the fixing film heat generating layer la described in Embodiment 1 is set at a high value, and therefore the circumferential current with respect to the circumferential direction does not flow little at a commercial power source level. However, the electrode layer lb contacting the heat generating layer la is provided, and the resistance value of the electrode layer lb^; is set at a sufficiently low value. Further, the electrode layer lb is formed in the helical shape along the generatrix direction of the heat generating layer la. In such a constitution, a current with respect to the fixing film axial

direction flows through the heat generating layer la and generates heat.

[0131] Here, the case where the volume resistivity of the heat generating layer la is substantially equal to that of the electrode layer lb, i.e., the case where the resistance of the heat generating layer la is sufficiently low also in the constitution including the helical-shaped electrode layer lb will be

considered. This case corresponds to the case where the resistance value of the heat generating layer la in the conventional type disclosed in JP-A 2014-26267 is low. In such a case, it would be considered that the circumferential current with respect to the

circumferential direction flows through also the

electrode layer lb via the heat generating layer la and generates heat. That is, when the resistance of the heat generating layer la is gradually decreased, it would be considered that the heat generation type finally approaches the conventional heat generation type.

[0132] Based on this consideration, when a

relationship of heat generation between the electrode layer resistance and the heat generating layer

resistance is studied, the following phenomena were observed.

Comparison Example 1

[0133] A cylindrical fixing film 1 including a heat generating layer la and an electrode layer lb

helically formed on the heat generating layer la was prepared, and a state of temperature rise was observed. As the heat generating layer la, a cylindrical

polyimide film of 30 mm in inner diameter, 220 mm in longitudinal length and 60 μπι in thickness was used. In order to cause the polyimide film to function as a layer which generates heat, there is a need to impart electroconductivity to the polyimide film. Therefore, a value of the polyimide film was adjusted to about 1.0xl0-2 Qm by dispersing an electroconductive filler into the polyimide recording material. For measurement of the volume resistivity, a resistivity meter

( "Loresta-GP" , manufactured by Mitsubishi Chemical Analytech Co., Ltd.) was used. The helical-shaped electrode layer lb was formed of nickel of about

7.0xl0^~ n volume resistivity through electroless plating. The electrode layer 2b was formed in the helical shape of 2.0 mm in electrode layer width and 20 μηα in thickness, and the width number (number of turns) was 55 (turns), i.e., the helical shape was 2 mm in interval.

[0134] The thus-prepared fixing film 1 in Comparison Example 1 was heated by the electromagnetic induction heating type described in Embodiment 1, and a

temperature rising state was observed through a thermo-viewer . In the case of Comparison Example 1, the temperature rise of the electrode layer lb was observed little, and the temperature rise of the heat generating layer la was observed.

Comparison Example 2

[0135] Comparison Example 2 is the case where the volume resistivity of the electroconductive polyimide film as the heat generating layer la is lowered. As the heat generating layer la, the electroconductive polyimide film of about l.OxlO-^ j__n volume resistivity was used. Other constitutions are the same as those in Comparison Example 1. In the case of Comparison

Example 2, in addition to the heat generating layer la, the temperature rise was observed also in the

electrode layer lb. However, the temperature rising speed was faster in the heat generating layer la than in the electrode layer lb.

Comparison Example 3

[0136] Comparison Example 3 is the case where the volume resistivity of the electroconductive polyimide film as the heat generating layer la is further

lowered. As the heat generating layer la, the

electroconductive polyimide film of about l.OxlO-^ i_n volume resistivity was used. Other constitutions are the same as those in Comparison Example 1. Also in the case of Comparison Example 3, in addition to the heat generating layer la, the temperature rise in the

electrode layer lb was observed. Further, a result that the temperature rising speed was faster in the electrode layer lb than in the heat generating layer la was obtained.

[0137] If the consideration that the heat generation type gradually approaches the conventional heat generation type with a decreasing resistance of the heat generating layer la is correct, the temperature rising speed of the electrode layer lb cannot be faster (higher) than that of the heat generating layer la. Therefore, a manner of flow of the current in the constitution including the helical-shaped electrode layer lb was further considered.

[0138] Figure 31 is a development of the fixing film 1 including no electrode layer lb. Magnetic lines of force generated by the core 2 provided inside the fixing film 1 extend in parallel to the rotation axis of the fixing film 1. An electromotive force generates in the circumferential direction so as to cancel the magnetic lines of force. In the case where there is no electrode layer lb and only the heat generating layer la exists, a resistance distribution uniform with respect to the circumferential direction is obtained. Further, in the case where the resistance value of the heat generating layer la is sufficiently low, the current flows in the circumferential direction in a large amount, and therefore a sufficient degree of heat generation can be obtained. In the development view, A, B, C, D and E represent the same point on the cut and developed fixing film 1. Flow of the

circumferential current means that a flow of the current starting from A in a lower side of Figure 31 reaches A in an upper side in Figure 31. In the case of a uniform resistor, the current flows in the circumferential direction, and therefore the current flows in a substantially perpendicular direction as indicated by a broken-line arrow in Figure 31. This is also true for B, C, D and E.

[0139] Figure 32 is a development of the fixing film 1 including the helical-shaped electrode layer. lb. In Figure 32, a hatched portion represents the electrode layer lb. The resistance value of the electrode layer lb is lower than the resistance value of the heat generating layer la, and therefore a non-uniform resistance distribution is obtained with respect to the circumferential direction. Similarly as in the case of Figure 31, the magnetic lines of force

generated by the core 2 extend in parallel to the rotation axis of the fixing film 1 and the

electromotive force generates in the circumferential direction so as to cancel the magnetic lines of force. However, in the case where the circumferential current flowing in a direction perpendicular to the rotation axis of the film is considered, the resistance of the heat generating layer la is high and therefore an amount of the current is very small, so that heat generation in the heat generating layer la and the electrode layer lb ought to occur little.

[0140] However, the current does not always flow in the same direction as the generated electromotive force. A current path ought to be path in which a resistance value is a minimum when the current path forms a loop. That is, it would be considered that the flow of the current starting from A in a lower side of Figure 32 forms, as the path in which the resistance value is the minimum, a path in which the current flows substantially in the axial direction, in the heat generating layer la and then flows substantially in the circumferential direction in the electrode layer lb as indicated by broken-line arrows in Figure 32. This is also true for B, C, D and E.

[0141] An amount of the current corresponding to one ^■ full circumference of the helical-shaped electrode layer lb can be regarded as the sum of current amounts from the path A to the path E. Further, the sum of the current amounts from the path A to the path E is equal to an amount of the current flowing in the heat generating layer la between adjacent electrode layer portions. That is, in the case where as regards one full circumference of the helical-shaped electrode layer lb, a circumferential resistance is Rb, a resistance of the heat generating layer la between adjacent electrode layer portions is Ra and an

electromotive force generating in the electrode layer lb through one full circumference is Vtl, an electric circuit thereof can be modeled as a series circuit of Ra and Rb as shown in Figure 33. [0142] A current value Itl generated by the

electromotive force Vtl is Vtl/ (Ra+Rb) , a partial electromotive force of the heat generating layer la is Vtl x Ra/ (Ra+Rb) , and a partial electromotive force of the electrode layer lb is Vtl x Rb/ (Ra+Rb) . Therefore, electric power consumption in the heat generating layer la is (Vtl/ (Ra+Rb) ) 2 χ Ra, and electric power consumption in the electrode layer lb is

(Vtl/ (Ra+Rb) ) ² x Rb . Accordingly, in the case of Rb < Ra, the electric power consumption in the heat

generating layer la becomes larger, so that the heat generation principally occurs in the heat generating layer la. This would be considered as being the cases of Comparison Examples 1 and 2. On the other hand, in the case of Rb > Ra, the electric power consumption in the electrode layer lb becomes larger, so that the heat generation principally occurs in the electrode layer lb. This would be considered as being the case of Comparison Example 3. Therefore, a resistance value between both ends of the electrode layer lb wound around the heat generating layer la by 55 turns and a resistance value between both ends of the heat

generating layer la with respect to the axial

direction were measured. For measurement of the resistance, a digital multi-meter ("Model 189", manufactured by Fuke Corp.) was used. The resistance value between the both ends of the electrode layer lb was measured by abu,tting measuring terminals of the digital multi-meter against the both ends of the electrode layer lb. The resistance value between the both ends of the heat generating layer la with respect to the axial direction was measured by applying a copper foil tape onto the heat generating layer la at both end portions and then by abutting the measuring terminals of the digital multi-meter against the copper foil tape at the both end portions of the heat generating layer la. Measurement results are shown in Table 5, in which in Comparison Examples 1 and 2, the heat generating layer resistance was larger, and in Comparison Example 3, the electrode layer resistance was larger.

Table 5

COMP. EX. ELRV*¹ (Ω) HGLRV*² (Ω)

390

39.5

4.1

*1: "ELRV" is the electrode layer resistance value.

*2: "HGLRV" is the heat generating layer

resistance value. [0143] From the above results, it turned out that in the case of the fixing film 1 including the

helical-shaped electrode layer lb, even when the volume resistivity of the electrode layer lb is lower than the volume resistivity of the heat generating layer la, the electrode layer lb generates heat and can be high in temperature rising speed.

[0144] In Comparison Example 2, the temperature rising speed of the heat generating layer la was higher, and in Comparison Example 3, the temperature rising speed of the electrode layer lb was higher. A difference in these two Comparison Examples is the volume resistivity of the heat generating layer la. Therefore, when the volume resistivity was adjusted so that the temperature rising speeds were substantially equal to each other, the temperature rising speeds were able to be made substantially the same value of about 3.2xl0^-4.

[0145] Next, a condition in which the temperature rising speeds of the electrode layer lb and the heat generating layer la are equal to each other will be considered. The temperature rising speed is determined by a heat generation amount and thermal capacity. In the case where the temperature rising speed is T, the heat generation amount is W and the thermal capacity is C, a relationship of T = W/C holds. The heat generation amount can be considered as being equal to generated electric power. That is, the heat generation amount in the heat generating layer la is

(Vtl/ (Ra+Rb) ) ² x Ra, and the heat generation amount in the electrode layer lb is (Vtl/ (Ra+Rb) ) ² x Rb. In the case where the thermal capacitance of the heat

generating layer la is Ca and the thermal capacitance of the electrode layer lb is Cb, a temperature rising speed Ta in the heat generating layer la is

(Vtl/ (Ra+Rb) ) ² χ (Ra/Ca) and a temperature rising speed Tb in the electrode layer lb is (Vtl/ (Ra+Rb) ) ² x (Pb/Cb) . Therefore, the condition for Ta = Tb is Ra/Ca = Rb/Cb. That is, it would be considered that under a condition that a value of (Ra/Ca) / (Rb/Cb) is 1, the two temperature rising speeds are equal to each other and uniform heat generation occurs.

[0146] The resistance value Rb through one full circumference of the helical-shaped electrode layer lb can be obtained by dividing the above-measured

resistance value between the both ends of the

electrode layer lb y the winding number. The

resistance value Rb of about 0.165 Ω can be obtained by dividing 9.1 Ω by 55.

[0147] Then, the resistance value Ra of a. heat generating portion of the heat generating layer la corresponding to one full circumference of the

helical-shaped electrode layer lb is obtained from measurement. The fixing film was cut in a width of 10 mm as shown in Figure 34, and the resistance value between the electrode layers lb and was converted into a value corresponding to one full circumference of the helical-shaped portion, so that the resistance value Ra was obtained. Here, the reason why the resistance value was measured after the fixing film was cut in a small width of 10 mm is that the resistance value was excessively small when the resistance value was

measured for the one full circumference of the

helical-shaped portion and therefore a measurement result was unstable. The width is not limited to 10 mm. When the resistance of the fixing film of 10 mm in width was measured, the resistance value was 1.5 Ω, and therefore the resistance value Pa corresponding to one full circumference of the helical-shaped portion ca be estimated as about 0.159 Ω.

[0148] In the case where specific heat is c and a weight is m, the thermal capacity can be represented by c x m. The weight can be obtained from mass density and a volume, and therefore when the shape, the mass density and the specific heat of the heat generating portion are known, the thermal capacity can be

estimated. When the mass density and the specific heat were measured, the electrode layer lb was about 440 J/(kg.K) in specific heat and about 8.9x10^"^ kg/mm^ in mass density. For measurement of the mass density, an automatic dry type density meter ("Accupyc 1330", manufactured by Shimadzu Corp.) was used. For

measurement of the specific heat, a differential scanning calorimeter ("DSC8000", manufactured by

Perkin Elmer Co., Ltd.) was used. Similarly, when the mass density and the specific heat of the heat

generating layer la were measured, the heat generating layer la was about 900 J/(kg.K) in specific heat and about 2.0xl0-6 kg/mm^ j__{n mass} density.

[0149] The shape of the electrode layer lb is 2.0 mm in electrode layer width and 20 ]lm in thickness. When thermal capacity Cb of the electrode layer lb for one full circumference of the helical-shaped portion was estimated from the volume obtained from (electrode layer width) x (thickness) x (length corresponding to ^' one full circumference of electrode layer) and the measured specific heat and mass density, a result of about 1.48xl0^~2 J/K was obtained.

[0150] Next, the thermal capacity of the heat

generating layer la will be estimated.

[0151] Figure 35 is a schematic perspective view of the fixing film 1 in cross section. In the heat generating layer la, assuming that the current flows in an entire region of a rectangular parallelopiped shape as indicated by a shade portion of the

perspective view, the volume resistivity is about

3.2xl0^~4 Qm, and therefore a resistance value

calculated from the shape ( (electrode layer width) x (thickness) x (length corresponding to one full circumference of electrode layer)) is about 0.107 Ω. However, a value obtained from a measurement result of an interelectrode layer resistance was about 0.159 Ω which was somewhat large value. This would be

considered because the current flowing through the inside of the heat generating layer la does not flow in an entire region of the heat generating layer la with respect to the thickness direction, but flows as indicated by broken-line arrows as shown in. Figure 36 in the case where the fixing film cross-section is considered. Therefore, as the volume in the case where the thermal capacity is estimated, not a volume calculated from (electrode layer width) x (thickness) x (length corresponding to one full circumference of electrode layer) , a volume such that it provides the resistance value measured between the electrode layers may only be required to be assumed. Therefore, a value obtained by multiplying a volume value obtained by (electrode layer width) x (heat generating layer thickness) x (length corresponding to one full

circumference of electrode layer) by (resistance value obtained from interelectrode layer resistance

measurement )/( resistance value estimated from volume resistivity) as a correction coefficient is used as the volume. That is, in this time, 0.107/0.159 is a correction value. When the thermal capacitance of the electrode layer lb corresponding to the one full circumference of the helical-shaped portion was estimated from the corrected volume and the measured specific heat and mass density, a value of about

1.37xl0^~2 J/K was obtained.

[0152] From the above estimated value, when

(Ra/Ca) / (Rb/Cb) is calculated, a value of 1.04 is obtained. That is, it was able to be confirmed that in a condition that the value of (Ra/Ca) / (Rb/Cb) is almost 1, the temperature rising speed was

substantially the same and that, the heat generated uniformly. Then, when the fixed image was checked using the fixing film in the condition in which the value of (Ra/Ca) / (Rb/Cb) was 1.04, it was able to obtain a good fixed image with no non-uniformity of the fixing property and no uneven glossiness.

[0153] If the good fixed image can be obtained, even when there is a temperature rising speed difference to some extent, fixing non-uniformity is allowed.

Therefore, in order to check that the fixing

non-uniformity is allowed to what degree, the volume resistivity of the electroconductive polyimide as the heat generating layer la was changed, and an image in the case where the value of (Ra/Ca) / (Rb/Cb) was

different was evaluated. A result is shown in Table 6.

Table 6 EPVR*¹ (Ra/Ca) / (Rb/Cb)

(xl0^~4 Qm)

1.1 0.360 X

1.2 0.388 Δ

1.5 0.485 οΔ

2.0 0.658 o

3.2 1.04 o

4.7 1.52 o

6.1 2.01 οΔ

7.8 2.56 Δ

8.2 2.70 X

*1: "EPVR" is the electroconductive polyimide volume resistivity.

*2: "FNE" is the fixing non-uniformity evaluation.

[0154] An allowable level was evaluated by "x", "Δ", 'ΌΔ" and "o" . "x" is a level at which the fixing non-uniformity (non-uniformity of the fixing property) is confirmed and is recognized as an image defect, and is an unacceptable level. "Δ" is a level at. which although the fixing non-uniformity is not confirmed, the uneven glossiness is recognized in the case where a solid image principally including a photographic image is outputted during a glossy paper mode in which gloss is enhanced by increasing a set fixing temperature or the like. When the image is outputted on plain paper in an ordinary process condition for the plain paper, somewhat uneven glossiness is

recognized, there is no problem for outputting an image principally including a character image. 'ΌΔ" is a level at which the fixing non-uniformity is not recognized and the uneven glossiness is unable to be recognized when the image is outputted on the plain paper in the ordinary process condition for the plain paper. At this level, although slight uneven

glossiness can be confirmed, there is no problem, "o" is a level at which the fixing non-uniformity is not confirmed and even in the glossy paper mode, the uneven glossiness is unable to be recognized. From the above result, in the case where the image is outputted by a monochromatic machine (image forming apparatus) as in this embodiment, it was confirmed that the fixing non-uniformity was at the allowable

(acceptable) level when the value of (Ra/Ca) / (Rb/Cb) was in a range from 0.39 to 2.5. Further, in the case where uniformity in gloss is required, it was able to be confirmed that when the value is in a range from 0.49 to 2.0, a further good result is obtained.

[Embodiment 4]

[0155] Another embodiment of the fixing device B will be described. The fixing device B in this embodiment is different in constitution of the film 1 from the fixing device B in Embodiment 1.

[0156] In the case where having a cylindrical shape is employed as the electrode layer lb of the film 1, when a diameter of the electrode layer of the metal wire is gradually decreased, there is a problem that the heat does not readily generate. The heat does not readily generate due to an increase in sum of the resistance of the heat generating layer and a contact resistance by increasing the contact resistance between the electrode layer and the heat generating layer since as described in Embodiment 1, the heat is generated by causing the current to flow through the heat generating layer based on a potential difference formed by the electrode layer lb with respect to the generatrix direction of the heat generating layer la.

[0157] In this embodiment, the heat generating layer la was formed in a cylindrical shape of 24 mm in inner diameter, 240 mm in length with respect to the

generatrix direction of the heat generating layer, and 50 μπι in thickness by subjecting a polyimide resin material to die molding. As form 1, the case where a tungsten wire of 50 μπι in diameter was employed as the electrode layer lb will be described. Further, as form 2, the case where a gold-plated tungsten wire of 60 μπι in diameter was employed as the electrode layer lb will be described. Further, as Comparison Example, the case where a SUS 304 wire of 20 μπι in diameter was employed as the electrode layer lb will be described.

[0158] Next, a verifying method of estimating a film resistance of the heat generating layer la and a contact resistance between the electrode layer lb and the heat generating layer la will be described.

[0159] The film resistance and the contact resistance are estimated by measuring the resistance of the electrode layer lb corresponding to one turn of the helical-shaped portion and the resistance between adjacent electrode layer portions with respect to the generatrix direction of the heat generating layer la. Here, the film resistance is Rf, the resistance of the electrode layer lb corresponding to one turn of the helical-shaped portion is Rw, and the contact

resistance between the electrode layer lb and the heat generating layer la is Rc. Further, a combined

resistance of the resistance Rw of the electrode layer lb corresponding to one turn of the helical-shaped portion, the contact resistance Rc between the

electrode layer lb and the heat generating layer la, ^■ and the film resistance Rf is Rwcf. A combined

resistance of the contact resistance Rc between the electrode layer lb and the heat generating layer la, and the film resistance Rf is Rcf.

[0160] A measuring method will be described.

[0161] In Figure 12, (a) is a schematic view showing a state in which the electrode layer lb is cut when the resistances are measured, and (b) is an enlarged schematic view of the electrode layer lb, after being developed, when the resistances are measured.

[0162] As the measuring method, first, as shown in (a) of Figure 12, the electrode layer lb is cut along a rectilinear line II - 12 extending in the generatrix direction of the heat generating layer la. Thus, the resistances can be measured every one turn of the electrode layer lb. As regards the combined resistance Rwcf, the resistance between cut two electrode layer portions lb and lb is obtained by measuring a

resistance between measuring points CI and C2 shown in (b) of Figure 12. Further, separately, the resistance Rw of the cut electrode layer lb corresponding to one turn of the helical-shaped portion is obtained.

[0163] Next, a calculating method of the value of the combined resistance Rcf will be described.

[0164] In Figure 13, (a) is a schematic view of a developed electrode layer lb, and (b) is an equivalent circuit of two electrode layer portions lb and a heat generating layer portion la sandwiched between the two electrode layer portions lb.

[0165] As shown in (a) of Figure 13, the electrode layer lb is divided into n portions consisting of R_2 Rl5_r ··· Rnln2 · The respective divided resistances are values obtained by dividing the resistance Rw of the electrode layer lb corresponding to one turn of the helical-shaped portion by n. The heat generating layer la is divided into n+1 portions consisting of R₂3, Ri4, R56 , Rn2n3' ^Rnln4■ The respective divided resistances are values obtained by multiplying the combined resistance Rwcf by n+1. By performing repetitive calculation in which n of the equivalent circuit is gradually increased, the combined

resistance Rcf can be calculated.

[0166] First, in (b) of Figure 13, the equivalent circuit of the electrode layer and the heat generating layer when n is 1, i.e., when the case where the electrode layer lb is subjected to one division and the heat generating layer la is divided into two portions is taken into consideration is shown. R^2 and R34 represent the resistances of the electrode layer lb. R23 and R34 represent the resistances of the heat generating layer la. A combined portion of the contact resistance Rc between the electrode layer lb and the heat generating layer la, and the film resistance Rf at this time is R_cf. This combined resistance R^cf is a combined resistance 123 of R]_ 2 r ^23 ^ano^ ^34 connected in series and parallely-connected R14 . The combined resistance R123 is represented by the following formula (12).

— !— =— + ( 1 2 )

^!2 ' ^12 ⁺ ^.21 ⁺ ^34 )

[0167] R]_ 2 and R34 are the resistance R_w. R23 and R_4 are the combined resistance R]_cf x 2. The combined resistance R_234 is the combined resistance Rwcf, and therefore by substituting the measured Rwcf and Rw for the corresponding resistances in the formula (12) , the combined resistance R]_ cf is calculated.

[0168] In (c) of Figure 13, an equivalent circuit of the electrode layer and the heat generating layer when n is 2, i.e., when the case where the electrode layer lb is divided into two portions and the heat

generating layer la is divided into three portions is taken into consideration is shown. R]_2/ ^R34_> ^R15 ^and R46 represent resistances of the electrode layer lb. R23, R]_4 and R5g represent resistances of the heat generating layer la. A combined resistance of the contact resistance between the electrode layer lb and the heat generating layer la, and the film resistance Rf at this time is R2 cf. A combined resistance of R 2' R23 and R34 connected in series and the

parallely-connected R]_4 is R_234- Further, a combined resistance R]_52346 i-^{s a} combined resistance of 15, R-1234 and R45 connected in series and

parallely-connected R55. The combined resistance

R152346 i-^s represented by the following formula (13) . 152346 ( 15+ 1234 + ₄<i ) #56

[0169] Rl2' ^R34' ^R15 ^anc R46 ^{are tne} resistance R_w/2, and R23f ^R14 ^anc^ ^R56 ^are the combined resistance R_cf x 3. The combined resistance R]_52346 ^^s the combined resistance Rwcf, and therefore. by substituting the measured Rwcf and Rw for the corresponding resistances in the formula (13), the combined resistance R2 cf is calculated.

[0170] By making the calculation as described above, it is possible to calculate the resistances in the case where the electrode layer lb is divided into n portions and the heat generating layer la is divided into n+1 portions.

[0171] In the Form 1 of this embodiment, when the resistance between the measuring points CI and C2 was measured in the case where a distance adjacent

electrode layer portions lb with respect to the generatrix direction of the heat generating layer la is 2 mm, Rw = 2 Ω and Rwcf = 4 Ω were obtained.

Incidentally, the measurement of the resistances was carried out using a digital multi-meter ("Model 189, manufactured by Fluke Corp.) was used.

[0172] Figure 14 shows a result of repetitive

calculation until n = 50 for the combined resistance Rcf .

[0173] As shown in Figure 14, in this embodiment, in the repetitive calculation of about n = 30, the combined resistance Rcf converges to a value of 2.8 Ω. The distance between the electrode layer portions is changed, and then a similar resistance measurement is carried out for a plurality of electrode layer

portions lb. In this embodiment, when the resistance was measured between the measuring points CI and C3 in the case where the distance between the electrode layer portions was 4 mm, Rwcf = 4.4 Ω was obtained.

In the repetitive calculation of n = 30, Rcf was 3.2 Ω.

[0174] Figure 15 shows a relationship between the distance between the electrode layer portions and the combined resistance Rcf calculated in the repetitive calculation in the Form 1 of this embodiment ("EMB.

4-1") and the Form 2 of this embodiment ("EMB. 4-2") .

[0175] As shown in Figure 15, the distance between electrode layer portions (the distance between

adjacent electrode layer points is 1) is taken as x-axis, and the combined resistance Rcf calculated in the repetitive calculation is taken as y-axis. Then, the film resistance Rf between the electrode layer portions is slope, and the contact resistance between the electrode layer lb and the heat generating layer la is 0.5 time of y-intercept, and therefore, it is possible to estimate Rf and Rc .

[0176] The film resistance Rf between the adjacent electrode layer portions calculated by the above

method was 0.4 Ω, and the contact resistance Rc

between the electrode layer lb and the heat generating layer la was 1.2 Ω. Further, when a film resistance between outermost electrode layer portions with respect to the generatrix direction of the heat generating layer la is an outermost electrode layer film resistance, this resistance was 46 Ω from the calculated film resistance between the adjacent electrode layer portions. The film resistance Rf between the adjacent electrode layer portions was a value lower than the contact resistance Rc between the electrode layer lb and the heat generating layer la. The outermost electrode layer film resistance was a value higher than the contact resistance Rc between the electrode layer lb and the heat generating layer la. The outermost electrode layer film resistance is a resistance value (Ω) of the heat generating layer la between one end and the other end of the electrode layer lb with respect to the generatrix direction of the heat generating layer la.

[0177] Further, in the Form 2 of this embodiment, when the resistance was measured in the case where a distance adjacent electrode layer portions lb is 2 mm, Rw = 1.5 Ω and Rwcf = 1.6 Ω were obtained, and

therefore, when the value of Rcf was obtained in the repetitive calculation of about n = 30, the value of Rcf was 0.9 Ω. The distance between the electrode layer portions is changed, and when the resistance was measured in the case where the distance between the electrode layer portions was 4 mm, Rwcf = 2.1 Ω was obtained. When the value of Rcf was measured in the repetitive calculation of about n = 30, Rcf was 1.3 Ω.

[0178] As shown in Figure 15, when the distance between electrode layer portions is taken as x-axis, and the combined resistance Rcf calculated in the repetitive calculation is taken as y-axis, the film resistance Rf between the electrode layer portions is slope, and the contact resistance between the

electrode layer lb and the heat generating layer la is 0.5 time of y-intercept. As a result, the calculated film resistance Rf between the adjacent electrode layer portions in this embodiment was 0.4 Ω, the outermost electrode layer film resistance was 46 Ω, and the contact resistance Rc between the electrode layer lb and the heat generating layer la was 0.25 Ω. The film resistance Rf between the adjacent electrode layer portions and the outermost electrode layer film resistance were values higher than the contact

resistance Rc between the electrode layer lb and the heat generating layer la.

[0179] Also in Comparison Example, a similar

measurement was carried out. In Comparison Example, when the resistance was measured in the case where a distance adjacent electrode layer portions lb is 2 mm, Rw = 200 Ω and Rwcf = 500 Ω were obtained, and

therefore, when the value of Rcf was obtained in the repetitive calculation of about n = 30, the value of Rcf was 378 Ω. The distance between the electrode layer portions is changed, and when the resistance was measured in the case where. the distance between the electrode layer portions was 4 mm, Rwcf = 501 Ω was obtained. When the value of Rcf was measured in the repetitive calculation of about n = 30, Rcf was 379 Ω.

[0180] Figure 16 shows a relationship between the distance between the electrode layer portions and the combined resistance Rcf calculated in the repetitive calculation for the film in Comparison Example.

[0181] As shown in Figure 16, when the distance between electrode layer portions is taken as x-axis, and the combined resistance Rcf calculated in the repetitive calculation is taken as y-axis, the film resistance Rf between the electrode layer portions is slope, and the contact resistance between the

electrode layer lb and the heat generating layer la is 0.5 time of y-intercept. As a result, the calculated film resistance Rf between the adjacent electrode layer portions in Comparison Example was 1 Ω, and the contact resistance Rc between the electrode layer lb and the heat generating layer la was 189 Ω. The film resistance Rf between the adjacent electrode layer portions was a value lower than the contact resistance Rc between the electrode layer lb and the heat

generating layer la.

[0182] When heat generation verification was

performed using the power source of the commercial power source level described in Embodiment 1, the heat was generated in the Form 1 of this embodiment and the Form 2 of this embodiment. Further, the heat

generation level in the Form 2 of this embodiment in which the contact resistance Rc between the electrode layer lb and the heat generating layer la was low was higher than that in the Form 1 of this embodiment. In this embodiment, the contact resistance Rc between the electrode layer lb and the heat generating layer la was high, and therefore, the heat was not generated.

[0183] In the case of the film constitution in this embodiment, the film resistance Rf between the

adjacent electrode layer portions may desirably be 1.0x10^"! to 1.0x10-3 Ω. The contact resistance Rc between the electrode layer lb and the heat generating layer la may preferably be low and may desirably be closer to 0 Ω.

[0184] In order to cause the heat generating layer la to generate heat, the film resistance Rf may

preferably be higher than the contact resistance Rc between the electrode layer lb and the heat generating layer la. It is desirable that the film resistance Rf between the adjacent electrode layer portions with respect to the generatrix direction of the heat generating layer la is higher than the contact

resistance Rc between the electrode layer lb and the heat generating layer la. That is, the contact resistance Rc between the electrode layer lb and the heat generating layer la is lower than the film

resistance Rf between the adjacent electrode layer portions with respect to the generatrix direction of the heat generating layer la. The contact resistance Rc between the electrode layer lb and the heat

generating layer la is made lower than the resistance of the heat generating layer la, whereby it becomes possible to ensure the heat generation of the heat generating layer la.

[Embodiment 5]

[0185] Another embodiment of the fixing device B will be described. The fixing device B in this embodiment is different in constitution of the film 1 from the fixing device B in Embodiment 1.

[0186] The fixing device B in this embodiment has a feature that the electrode layer lb of the film 1 was changed from the electroconductive wire to an

electroconductiv-e paste. Compared with the cylindrical electroconductive wire, by using the electroconductive paste, a contact area between the heat generating layer la and the electrode layer lb can be increased, so that the contact resistance between the heat

generating layer la and the electrode layer lb can be lowered.

[0187] The electrode layer lb can be prepared by applying an electroconductive paste, containing silver, carbon fiber, carbon nanotube or the like as a filler, onto the heat generating layer la. In this embodiment, as the electroconductive paste, a silver paste of 5.0xl0- Qm in volume resistivity is applied by screen printing. The silver paste is prepared by dispersing silver fine particles into a polyimide resin material in a solvent, and is dried after being applied onto the heat generating layer la. The electroconductive paste was formed in a helical shape of 200

in width and 10 ]lm in thickness.

[0188] In this embodiment, the resistance measurement similar to that in Embodiment 2 was carried out. The resistances in the case where a distance between the adjacent electrode layer portions lb was 2 mm were measured. Then, the resistance Rw of the electrode layer lb corresponding to one turn of the

helical-shaped portion was 2.6 Ω, and the combined resistance Rwcf of the resistance Rw of the electrode layer lb corresponding to one turn of the

helical-shaped portion, the contact resistance Rc between the electrode layer lb and the heat generating layer la, and the film resistance Rf was 1.7 Ω. Then, when the value of the combined resistance Rcf of the contact resistance Rc between the electrode layer lb and the heat generating layer la, and the film

resistance Rf was obtained in the repetitive

calculation of about n = 30, the value of the combined resistance Rcf was 0.6 Ω.

[0189] The distance between the electrode layer portions was changed, and when the resistance was measured in the case where the distance between the electrode layer portions was 4 mm, the combined resistance Rwcf = 2.3 Ω was obtained. When the value of the combined resistance Rcf was measured in the repetitive calculation of about n = 30, Rcf was 1.0 Ω.

[0190] Figure 17 shows a relationship between the distance between the electrode layer portions and the combined resistance Rcf calculated in the repetitive calculation for the film 1 in this embodiment.

[0191] As shown in Figure 17, when the distance between electrode layer portions is taken as x-axis, and the combined resistance Rcf calculated in the repetitive calculation is taken as y-axis, the film resistance Rf between the electrode layer portions is slope, and the contact resistance between the heat generating layer la and the electrode layer lb is 0.5 time of y-intercept. As a result, the calculated film resistance Rf between the adjacent electrode layer portions in this embodiment was 0.4 Ω, and the contact resistance Rc between the heat generating layer la and the electrode layer lb was 0.1 Ω. When the heat generation verification was performed using the power source of the commercial power source level described in Embodiment 1, the heat generation was obtained. [0192] As described above, by changing the electrode layer lb from the electroconductive wire to the electroconductive paste, it becomes possible to increase the contact area between the heat generating layer la and the electrode layer lb, so that the contact resistance Rc between the heat generating layer la and the electrode layer lb can be lowered.

[0193] In this embodiment, the electrode layer lb prepared by the screen printing of the

electroconductive paste was described, but another method capable of increasing the contact area between the heat generating layer la and the electrode layer lb may also be used. As a method of lowering the contact resistance between the heat generating layer la and the electrode layer lb, a portion, of the heat generating layer la, where the electrode layer lb is formed, is subjected to platable pretreatment, and then the electrode layer lb may also be formed by metal plating through electroless plating.

[0194], Particularly, a positional relationship between a screen and the film is controlled by forming the electrode layer through the screen printing or the like, so that a pitch interval and longitudinal positional accuracy can be ensured. For this reason, also during mass production, it becomes possible to form the electrode layer with a stable pitch interval. [Embodiment 6] [0195] Another embodiment of the fixing device B will be described. The fixing device B in this embodiment is different in constitution of the film 1 from the fixing device B in Embodiment 3.

[0196] In this embodiment, an elastic layer of the film is used as the heat generating layer, so that the temperature of the film surface can be quickly

increased, and therefore a time from a start of rising (actuation) of the fixing device until the image forming apparatus is in a printable state is made further quick.

[0197] A structure of the film in this embodiment will be described.

[0198] In Figure 19, (a) is a perspective view showing a base layer 30a of a film 30 and an electrode layer 30b formed on an outer peripheral surface of the base layer 30a, and (b) is a schematic view for illustrating a layer structure of the film 30.

[0199] As shown in (b) of Figure 19, the film 30 is a cylindrical rotatable member having a composite structure including a cylindrical base layer 30a, the electrode layer 30b, an elastic layer 30c also

functioning as a heat generating layer and a parting layer 30d. That is, the film 30 includes the electrode layer 30b helically formed on an outer peripheral surface of the cylindrical base layer 30a. The

electrode layer 30b contacts the surface of the base layer 30a. The elastic layer 30c also functioning as the heat generating layer is laminated so as to cover the electrode layer 30b formed on the surface of the base layer 30a, and then the parting layer 30d is laminated on an outer peripheral surface of the

elastic layer 30c also functioning as the heat

generating layer.

[0200] A detailed structure of the film 30 will be described below.

[0201] First, the base layer 30a is formed of a heat-resistant resin material such as polyimide, polyamideimide, PEEK or PES, and is molded in a

cylindrical shape of 30 μιτι - 100 μπι in thickness. In this embodiment, the polyimide resin material is

molded using a die in a cylindrical shape of 25 mm in inner diameter, 240 mm in longitudinal length and 50 μπι in thickness, so that the base layer 30a was formed. Incidentally, in this embodiment, electroconductive particles such as carbon black or metal powder are not added and dispersed in the polyimide resin material of the base layer 30a.

[0202] Next, the electrode layer 30b can be prepared by applying an electroconductive paste

(electroconductive member) , containing silver, carbon fiber, carbon nanotube or the like as a filler, onto the base layer 30a. In this embodiment, as the

electroconductive paste, a silver paste of 5.0xl0^-7 Qm in volume resistivity is applied by screen printing. The silver paste is prepared by dispersing silver fine particles into a polyimide resin material in a solvent, and is dried after being applied onto the heat

generating layer la. The electroconductive paste was formed in a helical shape of 200 ]im in width and 10 μπι in thickness.

[0203] Then, the elastic layer 30c also functioning as the heat generating layer was formed along the generatrix direction of the base layer 30a so as to cover the electrode layer 30b on the surface of the base layer 30a in a state shown in (a) of Figure 19. The elastic layer 30c also functioning as the heat generating layer is a heat-resistant rubber such as a silicone rubber or a fluorine-containing rubber in which an electroconductive material such as carbon black, carbon fibers or metal powder is added and dispersed. By adding and dispersing the

electroconductive material into the heat-resistant rubber, electroconductivity is imparted to the elastic layer 30c, so that the elastic layer 30c functions as the heat generating layer.

[0204] In this embodiment, as the elastic layer 30c also functioning as the heat generating layer, the silicone rubber adjusted to 3.0xl0^~3 Q_m j__n volume resistivity by adding and dispersing therein carbon black as electroconductive particles which are the electroconductive material ( electroconductive member) was formed in a layer of 300 μπι in thickness. In the constitution in this embodiment, the silicone rubber covers the electrode, and therefore a contact area between the silicone rubber and the electrode is large, so that the contact resistance can be suppressed to a low value.

[0205] Then, on the surface of the elastic layer 30c also functioning as the heat generating layer, a 30 μιη-thick fluorine-containing resin tube was coated as the parting layer 30d along the generatrix direction of the base layer 30a by a thermal contraction method. This parting layer .30d has a function of preventing the surface of the film 30 from being contaminated with the toner and the paper powder which are

deposited on the film surface.

[0206] The heat generating layer la in Embodiment 3 was formed as -the polyimide resin layer of about

5.0xl0^~3 Qrn j__n volume resistivity and 50 μπι in

thickness. On the other hand, in this embodiment, as the elastic layer 30c also functioning as the heat generating layer, the layer is formed so as to have the volume resistivity of about 3.0xl0^_3 Qm and the thickness of 300

Embodiment 3 and this embodiment are substantially the same in resistance RsLVb

obtained from the formula (11) with respect to the generatrix direction of the heat generating layer, so that also in this embodiment, it is possible to obtain the heat generation performance substantially equal to that in Embodiment 3.

[0207] In this embodiment, the case where the base layer has not electroconductivity and does not

generate the heat was described. However, the

electroconductivity may also be imparted to the base layer by adding and dispersing the electroconductive material such as the carbon black, the carbon fibers or metal powder into the polyimide resin material of the base layer. That is, both of the polyimide resin material of the base layer and the silicone rubber of the heat generating layer may also be caused to generate the heat.

[0208] As described above, in this embodiment, the elastic layer in a side closer to the surface layer is used as the heat generating layer, so that the film surface temperature can be increased more quickly and electric power necessary from a start of rising of the fixing device until the image forming apparatus is in a printable state can be suppressed to a low value. [Embodiment 7]

[0209] Another embodiment of the fixing device B will be described. The fixing device B in this embodiment is different in constitution of the film 1 from the fixing device B in Embodiment 1.

[0210] In the method of winding the metal wire at the resin film surface, contact between the metal wire and the resin film becomes unstable, so that heat

generation non-uniformity occurs in some cases. The nip is formed by the rotatable heating member and the pressing roller which are configured to sandwich the recording material, and fixing is carried out while feeding the recording material to the nip, and

therefore, even in the fixing device which is

susceptible to repetitive bending (flexion) due to deformation of the rotatable heating member, the heat is stably generated through a durability test.

[0211] A structure of the film in this embodiment will be described.

[0212] In Figure 20, (a) is a perspective view showing a heat generating layer 40a and an electrode layer 40b of a film 40, (b) is a schematic view for illustrating a layer■ structure of the film 40, and (c) is a schematic view showing a part of a cross section of the film 40 with respect to a longitudinal

direction.

[0213] The film 40 in this embodiment is a composite film including a cylindrical rotatable member

consisting of the heat generating layer 40a and a parting layer 40c formed on the surface of the heat generating layer 40a, and in the heat generating layer 40a, the electrode layer 40b is formed in a helical shape and is incorporated. By incorporating the electrode layer 40b in the heat generating layer 40a, a contact area between the heat generating layer 40a and the electrode layer 40b is increased, so that the contact resistance can be lowered.

[0214] A detailed structure of the film 40 will be described .

[0215] The heat generating layer 40a of the film 40 in this embodiment is prepared by dispersing carbon black and carbon fibers in the polyimide resin

material, so that the volume resistivity thereof is about 5.0xl0^~4 Qm. The film 40 is a cylindrical film having a size of 30 mm in inner diameter, 240 mm in longitudinal length and 80 μπτ. in thickness.

[0216] As another example of the heat generating layer 40a, a layer of a heat-resistant resin material such as polyimide, polyamideimide, PEEK or PES in which electroconductive particles such as carbon black or metal powder are added and dispersed can be used.

[0217] The electrode layer 40b was prepared using a SUS304 wire of 50 μιη in diameter and about 7.0xl0^-7 Qm and is formed in a helical shape in the heat

generating layer 40a by a manufacturing method

described later. Further, both end portions of the electrode are not short-circuited to an adjacent electrode, so that a closed loop is not formed.

[0218] As another example of the electrode layer 40b, a metal wire which is smaller in volume resistivity than the heat generating layer 40a and which is formed of iron, copper, silver, aluminum, nickel, chromium, tungsten or an alloy such as SUS 304 or nichrome can be used. Or, an electroconductive wire formed of an electroconductive resin material such as CFRP (carbon fiber-reinforced plastic) or carbon nanotube resin can be used. Further, the electrode layer 40b is not required to be the wire, but it is possible to use a sandwich structure in which an electroconductive paste in which silver, carbon fibers, carbon nanotube or the like is contained as a filler is formed on the heat generating layer surface, and thereon, a heat

generating layer is further formed.

[0219] Thus, by burying the electrode in the heat generating layer, the contact resistance between the electrode and the electroconductive resin material can be lowered, and at the same time, the electrode is prevented from floating from the electroconductive resin material even when the electrode is subjected to repetitive bending (flexion) by rotation of the film, so that stable heat generation can be realized.

[0220] Next, a film manufacturing method will be described.

[0221] The cylindrical film in which the electrode layer 40b is incorporated in the heat generating layer 40a can be manufactured by the following method.

[0222] Figure 21 is a flowchart of steps for illustrating a flow of film manufacturing steps.

[0223] First, a polyimide varnish is applied onto a cylindrical support having a surface which has been washed ( 50 ) .

[0224] The polyimide varnish is prepared by adding and dispersing an electroconductive agent, such as carbon black or carbon fibers, in a solution of a polyimide precursor in an organic solvent in advance. At this time, as regards an amount of the

electroconductive agent added in the polyimide varnish, when the electroconductive agent was added in an

amount of 10 wt. % or more in an entirety of a solid content of the polyimide varnish, the volume

resistivity is smaller than l.OxlO-^ Qm, _So that the heat can be sufficiently generated without increasing a voltage applied to the exciting coil to a so large value .

[0225] Then, the support on which the polyimide varnish is applied is placed in a heating oven and then is dried and heated (51) .

[0226] By this drying and heating process, not only the solvent of the polyimide varnish is volatilized but also imidization occurs, so that cross-linking of the resin is accelerated and a coating film is formed. A condition of the drying and heating process varies depending on the kind of the polyimide varnish used and the thickness of the coating film formed, but the coating film is first heated in a range of

100 - 150 °C . for several tens of minutes and then is stepwisely increased to 200 - 400 °C in several hours, so that a degree of expansion of the film is small and thus a dimension is stabilized.

[0227] Thereafter, the cylindrical support is once cooled as a whole and then is taken out from the heating oven.

[0228]^' At one end portion of a side surface of the thus-formed coating film, an end portion of the metal wire formed of SUS 304 and 50 μπι in diameter was bonded with a heat-resistant adhesive. Thereafter, by a shaft rotating method, the metal wire is wound around the coating film with regular intervals, so that the helical-shaped electrode layer 40b is

prepared (52) . Also in an end point side where the winding of the metal wire is ended, the other end portion of the metal wire is bonded and fixed.

[0229] Then, onto the wire-wound support, the polyimide varnish is applied again (53).

[0230] Thereafter, the support is placed in the heating oven and is subjected to the drying and heating process, so that the coating with the

electroconductive resin material can be carried out so as to cover the metal wire (54) .

[0231] Finally, after the cylindrical support is cooled, the support is taken out from the heating oven and is cut at the end portions so that the film has a desired length, and then the film is drawn out from the support (55) .

[0232 ] Here, a resin coating method will be described.

[ 0233] Figure 22 shows, as the resin coating method, a method of dipping an object-to-be-coated in a

solution of an organic solvent to form the coating film (herein referred to as a dipping (method) ) .

[0234 ] In a solution tank 57, a prepared polyimide varnish 58 is stored, and an object-to-be-coated 59 is dipped in the polyimide varnish 58 and then is pulled up at a predetermined speed, so that a coating film having a desired thickness is formed on the surface of the object-to-be-coated 59.

[ 0235] This method is suitable for the case where in the above-described coating steps (50) and (53), the object-to-be-coated 59 is coated with the same

material, and there is no need to effect masking of the object-to-be-coated, and therefore, a resin layer can be easily formed.

[0236] In the above-described coating steps (50) and (53), the same material is not necessarily be required to be used. For example, another solution tank is prepared, and in the coating step (53) after the

winding of the wire, the dipping of the

object-to-be-coated in a solution of an organic

solvent in which a viscosity of the polyimide varnish is large is performed, so that a degree of unevenness of the wire portion at the film surface can be reduced. Further, in the coating step (50) for forming an inner surface of the film, a polyimide varnish in which an addition amount of the electroconductive agent is suppressed is prepared, and only in the coating step (53) for forming the front (outer) surface of the film, the volume resistivity may also be decreased. As. a result, a sliding property of the inner surface of the electroconductive resin film can be improved.

[0237] Further, as another resin coating method, as shown in Figure 23, it is possible to select a method of blowing a resin material by a spray gun 60 while rotating the object-to-be-coated 59 (herein referred to as spray coating (method) ) . Or, as shown in Figure 24, it is possible to select a method of helically coating a polyimide varnish from above a rotating object-to-be-coated 59 by using a dispenser 61 capable of quantitatively discharging the polyimide varnish (herein referred to as a dispenser method) .

[0238] As another film manufacturing method, as shown in a flowchart of a film manufacturing process of

Figure 25, a method of first winding the metal wire around the cylindrical support.

[0239] Specifically, on the cylindrical support, a helically shaped electrode lb is prepared by

equidistantly winding the metal wire around the support by the shaft rotating method (70) .

[0240] Then, on the cylindrical support, the

polyimide varnish ( electroconductive member) is coated

(71) .

[0241] Subsequently, the resultant support is placed in the heating oven and is subjected to the drying and heating process (72).

[0242] The cylindrical support is taken out from the heating oven, and a prepared film (outer layer) is once drawn out from the support (73) .

[0243] Next, an inner surface of the film is coated with the polyimide varnish (electroconductive member)

(74) .

[0244] Thereafter, the coated film is placed in the heating oven again and is subjected to the drying and heating process, so that coating of the

electroconductive resin material is carried out so as to cover the metal wire (75) .

[0245] Finally, after the cylindrical support is cooled, the support is taken out from the heating oven, and end portions thereof are cut so that the film has a desired length, and thereafter the film is drawn out from the support (76) .

[0246] Here, as the method of coating the film inner surface with the polyimide varnish, the

above-described spray coating or the dispenser method can be selected. [ 0247 ] In the above, the manufacturing method until the heat generating layer 40a of the film 40 in which the electrode layer 40b is incorporated in the heat generating layer 40a was described.

[0248 ] Subsequently, on the surface of the heat generating layer 40a, a fluorine-containing resin material such as PTFE, PFA or FEP is coated, dried and baked, so that the film 40 to which a parting property from the toner and the paper powder is imparted is prepared. Here, PTFE is polytetrafluoroethylene, PFA is polytetrafluoroethylene-perfluoroalkylvinyl ether copolymer, and FEP is

polytetrafluoroethylene-hexafluoropropylene copolymer .

[0249] Further, in this embodiment, as the film the film having a two-layer structure in which the parting layer is coated on the heat generating layer was described, but a film in which a primer layer and the elastic layer are coated on the heat generating layer and the parting layer is coated on the elastic layer can also be used as the film. By forming the elastic layer between the film and the parting layer,

followability to paper having a large degree of unevenness is improved, so that a clearer fixed image can be obtained.

[0250 ] Further, in this embodiment, as the heat generating layer, the layer of the electroconductive resin material was described, but this layer is also applicable to the heat generating layer also

functioning as the heat generating layer as described in Embodiment 4.

[0251] As described above, in this embodiment, the electrode layer is helically incorporated in the heat generating layer, so that the contact between the heat generating layer and the electrode layer is stably maintained, and thus it is possible to stably generate the heat through continuous image formation

(durability test) .

[Other embodiments]

[0252] The image heating apparatus according to the present invention is not limited to use as the fixing devices as in the above-descried embodiments. The image heating apparatus can also be used as an image heating apparatus for heating an image in order to modify glossiness of an image (fixed image) once fixed on the recording material or an image (partly fixed image) temporarily fixed on the recording material.

[INDUSTRIAL APPLICABILITY]

[0253] According to the present invention, it is possible to provide a cylindrical fixing member excellent in temperature rising speed, a fixing device including the cylindrical fixing member, and an image forming apparatus including the cylindrical fixing member .

Claims

1. A cylindrical fixing member for use with a fixing device, comprising:

a heat generating layer; and

an electrode layer contacting said heat generating layer,

wherein said electrode layer is smaller in volume resistance value than said heat generating layer,

wherein said electrode layer is formed in a helical shape so that a helical axis thereof extends in a direction along a generatrix direction of said fixing member, and

wherein one end and the other end of said electrode layer are electrically open.

2. A cylindrical fixing member according to Claim 1, wherein a contact resistance between said electrode layer and said heat generating layer is lower than a resistance value of said heat generating layer between said one end and said the other end of said electrode layer with respect to the generatrix direction.

3. A cylindrical fixing member according to Claim

1, wherein a contact resistance between said electrode layer and said heat generating layer is smaller than a resistance of said heat generating layer between adjacent parts of said electrode layer with respect to the generatrix direction.

4. A cylindrical fixing member according to Claim

1, wherein said heat generating layer is a resin layer in which an electroconductive material is. dispersed, and said electrode layer is a layer formed of metal.

5. A cylindrical fixing member according to Claim

1, wherein said electrode layer is formed inside said heat generating layer.

6. A cylindrical fixing member according to Claim 1, wherein said electrode layer is formed on an outer peripheral surface of said heat generating layer.

7. A cylindrical fixing member according to Claim 6, further comprising an elastic layer formed outside said electrode layer.

8. A fixing device comprising:

a cylindrical fixing member, wherein said cylindrical fixing member includes, a heat generating layer and an electrode layer contacting said heat generating layer, wherein said electrode layer is smaller in volume resistance value than said heat generating layer, wherein said electrode layer is formed in a helical shape so that a helical axis thereof extends in a direction along a generatrix direction of said fixing member, and wherein one end and the other end of said electrode layer are

electrically open;

a coil provided at a hollow portion of said cylindrical fixing member, wherein said coil includes a helical-stepped portion having a helical axis extending in a direction along the generatrix

direction of said cylindrical fixing member, and a magnetic field is formed for subjecting said heat generating layer to electromagnetic induction heating by causing an alternating current to flow through said coil; and

a magnetic core provided inside the

helical-stepped portion of said coil and extending in the generatrix direction,

wherein an image formed on a recording material is fixed on the recording material by heat from said cylindrical fixing member.

9. A fixing device according to Claim 8, wherein a contact resistance between said electrode layer and said heat generating layer is lower than a resistance value of said heat generating layer between said one end and said the other end of said electrode layer with respect to the generatrix direction.

10. A fixing device according to Claim 8, wherein a contact resistance between said electrode layer and said heat generating layer is smaller than a

resistance of said heat generating layer between adjacent parts of said electrode layer with respect to the generatrix direction.

11. A fixing device according to Claim 8, wherein said heat generating layer is a resin layer in which an electroconductive material is dispersed, and said electrode layer is a layer formed of metal.

12. A fixing device according to Claim 8, wherein said electrode layer is formed inside said heat generating layer.

13. A fixing device according to Claim 8, wherein said electrode layer is formed on an outer. eripheral surface of said heat generating layer.

14. A fixing device according to Claim 13, further comprising an elastic layer formed outside said electrode layer.

15. An image forming apparatus comprising: an image forming portion for forming an image on a recording material; and

a fixing portion for fixing the image on the recording material, wherein said fixing portion includes a cylindrical fixing member including a heat generating layer and an electrode layer contacting said heat generating layer, wherein said electrode layer is smaller in volume resistance value than said heat generating layer, wherein said electrode layer is formed in a helical shape so that a helical axis thereof extends in a direction along a generatrix direction of said fixing member, and wherein one end and the other end of said electrode layer are

electrically open;

direction of said cylindrical fixing member, and forms a magnetic field for subjecting said heat generating layer to electromagnetic induction heating by causing an alternating current to flow through said coil; and a magnetic core provided inside the

helical-stepped portion of said coil and extending in the generatrix direction,

wherein the image recording material is fixed on the recording material by heat from said cylindrical fixing member.

16. An image forming apparatus according to Claim 15, wherein said electrode layer is formed so that with respect to the generatrix direction, a region between a part, of adjacent parts of said electrode layer, closest to said one end of said electrode layer and a part, of the adjacent parts of said electrode layer, closest to said the other end of said electrode layer is broader than or equal to a maximum image forming region where the image is formed on the recording material by said image forming portion.