Patent Publication Number: US-10317827-B2

Title: Fixing device for forming a nip portion with a heater for image forming

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     Aspects of the present disclosure generally relate to a fixing device for use in an image forming apparatus, such as a copying machine or a laser beam printer, of the electrophotographic type. 
     Description of the Related Art 
     The following configuration is known as a fixing device for use in an image forming apparatus of the electrophotographic type. That configuration includes a cylindrical film, a heater which contacts the film, and a pressure roller which forms a nip portion in conjunction with the heater via the film. A recording material bearing an unfixed toner image thereon is heated at the nip portion while being conveyed, so that the toner image is fixed to the recording material. 
     Furthermore, if the film of the fixing device is rotated at high speed in such a way as to be compatible with high-speed printing, supplying of heat from the heater to the film may become too late. Therefore, a configuration capable of also transferring heat from the heater to the film via a portion other than a surface of the heater contacting the film is known (Japanese Patent Application Laid-Open No. 2003-257592). For a specific example of such a configuration, a heat conducting member (metallic plate) is brought into contact with a surface of the heater opposite to the surface thereof contacting the film and the heat conducting member is then brought into contact with the film. This configuration enables performing fixing processing at higher speed. 
     However, a portion of the heat conducting member extending to an upstream side in the recording material conveyance direction and contacting the film is also in contact with a heater holder, so that heat from the heat conducting member is likely to undesirably dissipate to the heater holder. 
     SUMMARY OF THE INVENTION 
     Aspects of the present disclosure are generally directed to providing a fixing device capable of efficiently transferring heat generated by a heater to a film via a heat conducting member contacting the heater. 
     According to an aspect of the present disclosure, a fixing device that heats a toner image to fix the toner image to a recording material includes a rotatable cylindrical film, an elongated plate-like heater which has a first surface and a second surface opposite to the first surface and which contacts an inner surface of the film with the first surface, a heat conducting member which extends in a longitudinal direction of the heater and which includes a heater contact portion contacting the second surface of the heater, and a supporting member which supports the second surface of the heater via the heat conducting member, wherein the heat conducting member includes an extension portion which extends along a direction opposite to a rotation direction of the film from a portion extending in a direction along a thickness surface of the heater perpendicular to the first surface outside an end portion at one side of the heater in the rotation direction of the film and which contacts the inner surface of the film, wherein the supporting member includes a facing portion which faces the extension portion in a thickness direction of the heater, and wherein a void space is provided between the extension portion of the heat conducting member and the facing portion of the supporting member. 
     Further features of the present disclosure will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic sectional view of an image forming apparatus according to a first exemplary embodiment. 
         FIG. 2  is a perspective view of a fixing device according to the first exemplary embodiment. 
         FIG. 3  is a sectional view of the fixing device according to the first exemplary embodiment. 
         FIG. 4  is a sectional view of a fixing device according to a second exemplary embodiment. 
         FIG. 5  is a plan view of a heater holder and a heat conducting member according to the second exemplary embodiment. 
         FIG. 6  is a sectional view of a heater holder and a heat conducting member according to a third exemplary embodiment. 
         FIGS. 7A and 7B  are perspective views of the heater holder and the heat conducting member according to the third exemplary embodiment. 
         FIGS. 8A, 8B, and 8C  are diagrams as viewed from the direction of arrow A illustrated in  FIG. 6  in the third exemplary embodiment. 
         FIG. 9  is a sectional view of a heater, the heater holder, and the heat conducting member according to the third exemplary embodiment. 
         FIGS. 10A, 10B, and 10C  are diagrams as viewed from the direction of arrow A illustrated in  FIG. 6  in the third exemplary embodiment. 
         FIG. 11  is a sectional view of a fixing device according to a fourth exemplary embodiment. 
         FIG. 12  is a sectional view of a heater holder and a heat conducting member according to the fourth exemplary embodiment. 
         FIGS. 13A and 13B  are perspective views of the heater holder and the heat conducting member according to the fourth exemplary embodiment. 
         FIG. 14  is a sectional view of a fixing device according to a fifth exemplary embodiment. 
         FIG. 15  is a sectional view of a heater holder and a heat conducting member according to the fifth exemplary embodiment. 
         FIGS. 16A and 16B  are perspective views of the heater holder and the heat conducting member according to the fifth exemplary embodiment. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     A first exemplary embodiment of the present disclosure is described below with reference to the drawings. 
     First, a configuration of an image forming apparatus according to the present exemplary embodiment is described with reference to  FIG. 1 .  FIG. 1  is a schematic sectional view of a laser beam printer  50  serving as an image forming apparatus of the electrophotographic type according to the present exemplary embodiment. 
     A charging device  2 , an exposure device  3 , which irradiates a photosensitive drum  1  serving as an image bearing member with laser light L, a developing device  5 , a transfer roller  10 , and a photosensitive drum cleaner  16  are located on the circumferential surface of the photosensitive drum  1  in sequence along the rotation direction thereof (the direction of arrow R 1 ). First, with regard to the photosensitive drum  1 , the surface thereof is charged with minus polarity by the charging device  2 . Next, with regard to the charged photosensitive drum  1 , an electrostatic latent image is formed on the surface of the photosensitive drum  1  by the laser light L radiated from the exposure device  3  (the surface potential of an exposed portion increasing). Since toner for use in the present exemplary embodiment is charged with minus polarity, minus-charged toner adheres to only an electrostatic latent image portion on the photosensitive drum  1  by the developing device  5 , in which black toner is contained, so that a toner image is formed on the photosensitive drum  1 . When a recording material P is fed by a feed roller  4 , the recording material P is conveyed to a transfer nip portion N by a conveyance roller  6 . A transfer bias with plus polarity, which is a polarity reverse to the polarity of toner, is applied from a power supply (not illustrated) to the transfer roller  10 , so that the toner image on the photosensitive drum  1  is transferred to the recording material P at the transfer nip portion N. With regard to the photosensitive drum  1  after transfer is performed, untransferred toner remaining on the surface of the photosensitive drum  1  is removed by the photosensitive drum cleaner  16 , which includes an elastic member blade. The recording material P bearing the toner image thereon is conveyed to a fixing device  100 , in which heat fixing of the toner image on the surface of the recording material P is performed. 
     Next, the fixing device  100  according to the present exemplary embodiment is described with reference to  FIG. 2  and  FIG. 3 .  FIG. 2  and  FIG. 3  are a perspective view and a sectional view of the fixing device  100  according to the present exemplary embodiment, respectively. The fixing device  100  according to the present exemplary embodiment employs a film heating method, which can achieve shortening of a warming-up time and saving of energy. 
     The fixing device  100  includes a cylindrical fixing film  112 , a heater  113 , a pressure roller  110 , and a heat conducting member  140 . The heater  113  contacts the inner surface of the fixing film  112  to form a nip portion N in conjunction with the pressure roller  110 . The recording material P having a toner image formed thereon is heated while being conveyed at the nip portion N, so that the toner image is fixed to the recording material P. 
     Here, the conveyance direction of the recording material P at the nip portion N is defined as the X-axis direction, the longitudinal direction of the heater  113  is defined as the Y-axis direction, and the direction of pressure at the nip portion N is defined as the Z-axis direction. 
     The fixing film  112 , the heater  113 , and the heat conducting member  140  are unitized as a film unit  105 . The film unit  105  further includes a heater holder  130  serving as a supporting member, a reinforcement stay  120  serving as a reinforcement member, and flanges R 121  and L 122  serving as a regulating member. The heater holder  130  is a member used to support the heater  113 . The reinforcement stay  120  is a member used to reinforce the heater holder  130 . The flanges R 121  and L 122  are members used to regulate the movement of the fixing film  112  in the Y-axis direction (the longitudinal direction of the heater  113 ), and are located at positions opposite to both longitudinal end portions of the fixing film  112 . 
     The film unit  105  is mounted to a fixing frame  123 , at which both end portions of the pressure roller  110  are supported in such a way as to be rotatable. Sliding the film unit  105  along groove portions  124  of the fixing frame  123  is employed to mount the film unit  105  to the fixing frame  123 . The film unit  105  is pressed against the pressure roller  110  by pressure plates  125  and pressure springs  126 . With regard to a pressure configuration, the pressure force exerted by the pressure springs  126  is transmitted to the pressure plates  125 , the flanges R 121  and L 122 , the reinforcement stay  120 , the heater holder  130 , the heat conducting member  140 , and the heater  113  in sequence. Then, the heater  113  is pressed against the pressure roller  110  via the fixing film  112 , so that the nip portion N is formed. 
     Here, in  FIG. 3 , a surface of the heater  113  contacting the fixing film  112  is referred to as a “first surface  113   a ”, and a surface of the heater  113  opposite to the first surface  113   a  is referred to as a “second surface  113   b”.    
     The heat conducting member  140  is provided in such a way as to contact the second surface  113   b  of the heater  113  and to be sandwiched between the heater  113  and the heater holder  130 . The heater  113  is supported by the heater holder  130  via the heat conducting member  140 . 
     The heater holder  130  is provided with arc-like guide portions in such a way as to allow the fixing film  112  to smoothly rotate. This allows the fixing film  112  to smoothly rotate in the direction of arrow R 1  according to the rotation of the pressure roller  110  in the direction of arrow R 2 . The first surface  113   a  of the heater  113  is in sliding contact with the inner surface of the fixing film  112  and is used to heat the fixing film  112  from the inside thereof. The pressure roller  110  presses the heater  113  from the outside of the fixing film  112 . The nip portion N is a region in which the pressure roller  110  and the fixing film  112  are in contact with each other. When the recording material P having an unfixed toner image T formed thereon is conveyed to the nip portion N from the direction of arrow A 1  in  FIG. 3 , the toner image T is fixed to the recording material P. 
     The fixing film  112  is described here. The fixing film  112  is configured to be rotatable, and has a cylindrical shape with an outer diameter ϕ of 18 mm taken when no external force is applied thereto. The fixing film  112  has a multi-layer structure as viewed in the thickness direction thereof. The fixing film  112  includes a base layer and a release layer, which is formed on the outer side of the base layer. The material of the base layer to be used includes, in view of heat resistance and stiffness, metal, such as stainless steel or nickel, and heat resistant resin, such as polyimide. In the present exemplary embodiment, a polyimide resin is used as the material of the base layer of the fixing film  112 , and a carbon-based filler is added thereto to increase heat conductivity and strength. Since the thinner the thickness of the base layer, the more likely the base layer is to transmit heat of the heater  113  to the surface of the fixing film  112  but the lower the strength of the base layer becomes, it is desirable that the thickness of the base layer be about 15 μm to 100 μm, and, in the present exemplary embodiment, the thickness of the base layer is set to 50 μm. The desirable material of the release layer includes fluorine resin, such as perfluoroalkoxy alkane resin (PFA), polytetrafluoroethylene resin (PTFE), and tetrafluoroethylene-hexafluoropropylene (fluorinated ethylene propylene) resin (FEP). In the present exemplary embodiment, PFA, which excels in releasability and heat resistance among fluorine resins, is used. The release layer can be a layer covered with a tube or a layer coated with paint, and, in the present exemplary embodiment, the release layer is molded with a coat excellent in thin-wall molding. Since the thinner the thickness of the release layer, the more likely the release layer is to transmit heat of the heater  113  to the surface of the fixing film  112  but the lower the durability of the release layer becomes, it is desirable that the thickness of the release layer be about 5 μm to 30 μm, and, in the present exemplary embodiment, the thickness of the release layer is set to 10 μm. Furthermore, although not being used in the present exemplary embodiment, an elastic layer can be provided between the base layer and the release layer. In that case, for example, silicone rubber or fluorine-contained rubber is used as the material of the elastic layer. 
     The pressure roller  110  is described here. The outer diameter ϕ of the pressure roller  110  is 20 mm, and the pressure roller  110  is formed of a core metal with a diameter ϕ of 12 mm and an elastic layer with a thickness of 4 mm. Solid rubber or foamed rubber is used as the material of the elastic layer. Since foamed rubber has a low heat capacity and is low in heat conductivity and heat of the surface of the pressure roller  110  is unlikely to be absorbed into the inside thereof, foamed rubber has such an advantage that the surface temperature is likely to rise and the rise time can be shortened. In the present exemplary embodiment, foamed rubber formed by foaming silicone rubber is used. Since the smaller the outside diameter of the pressure roller  110 , the lower the heat capacity becomes but the narrower the width of the nip portion N becomes, an appropriate outer diameter of the pressure roller  110  is required, and, in the present exemplary embodiment, the outer diameter ϕ is set to 20 mm. Even with regard to the wall thickness of the elastic layer, since, if the elastic layer is too thin, heat dissipates to the core metal made of metal, an appropriate thickness of the release layer is required, and, in the present exemplary embodiment, the thickness of the release layer is set to 4 mm. On the elastic layer, a release layer, which is made from perfluoroalkoxy alkane resin (PFA), is formed as a release layer for toner. While the release layer can be a layer covered with a tube or a layer coated with paint as with the release layer of the fixing film  112 , in the present exemplary embodiment, a tube, which is excellent in durability, is used. The material of the release layer to be used includes, in addition to PFA, for example, fluorine contained resin, such as PTFE or FEP, and fluorine-contained rubber and silicone rubber, which are excellent in releasability. The lower the surface hardness of the pressure roller  110 , the wider the width of the nip portion N becomes. In the present exemplary embodiment, to verify a relationship between a variation of the width of the nip portion N and the heat conduction related to the heat conducting member  140 , which is described below, pressure rollers with three levels of Asker-C hardness (4.9 N load) of 48°, 50°, and 52° are used. The outer diameter ϕ of the pressure roller  110  in the present exemplary embodiment is 20 mm, and the pressure roller  110  is formed of a core metal with a diameter ϕ of 12 mm and an elastic layer with a thickness of 4 mm. Solid rubber or foamed rubber is used as the material of the elastic layer. Since foamed rubber has a low heat capacity and is low in heat conductivity and heat of the surface of the pressure roller  110  is unlikely to be absorbed into the inside thereof, foamed rubber has such an advantage that the surface temperature is likely to rise and the rise time can be shortened. In the present exemplary embodiment, foamed rubber formed by foaming silicone rubber is used. The pressure roller  110  is pressed against the heater  113  by a pressure unit (not illustrated). Even with regard to a pressure force, to verify a relationship between a variation of the width of the nip portion N and the heat conduction of the heat conducting member  140 , which is described below, three levels of the total pressure of 13 kgf, 14 kgf, and 15 kgf are used. The pressure roller  110  is configured to be rotated by a rotation unit (not illustrated) at a surface movement speed of 200 mm/sec in the direction of arrow R 2  in  FIG. 3 . 
     The heater  113  is described here. The heater  113  is configured with a heat generation resistor provided on a substrate made from ceramic, such as alumina or aluminum nitride. The heater  113  is a plate-like elongated member having a first surface  113   a , which contacts the inner surface of the fixing film  112 , a second surface  113   b , which is a surface opposite to the first surface  113   a , and a third surface (thickness surface)  113   c , which is perpendicular to the first surface  113   a . The heater  113  has a thin shape extending in the X-axis direction described above. The heater  113  to be used is formed by coating the surface of a substrate made from alumina of 6 mm in width in the recording material conveyance direction and 1 mm in thickness with a heat generation resistor made from silver-palladium (Ag/Pd) as much as 10 μm by screen printing and, then, covering the heat generation resistor with a glass of 50 μm in thickness as a heat generator protection layer. Moreover, electric power to be supplied to the heat generation resistor of the heater  113  is controlled according to a signal output from a temperature detection element (not illustrated), which detects the temperature of the heater  113  or the fixing film  112 . 
     The heat conducting member  140  is described here. The heat conducting member  140  includes a heater contact portion  140   a , which is a portion that contacts the second surface  113   b  of the heater  113 . The heat conducting member  140  further includes an upstream-side extension portion  140   e  which extends along a direction opposite to the rotation direction of the fixing film  112  from a portion extending in a direction along the thickness surface of the heater  113  outside an end portion at the upstream side of the heater  113  in the rotation direction of the fixing film  112  from the heater contact portion  140   a . The heat conducting member  140  further includes a downstream-side extension portion  140   d  which extends along the rotation direction of the fixing film  112  from a portion extending along the third surface  113   c  of the heater  113  outside an end portion at the downstream side of the heater  113  in the rotation direction of the fixing film  112  from the heater contact portion  140   a . The upstream-side extension portion  140   e  and the downstream-side extension portion  140   d  of the heat conducting member  140  are in contact with the inner surface of the fixing film  112  at the upstream side and the downstream side, respectively, of the heater  113  in the rotation direction of the fixing film  112 . 
     The heat conducting member  140  functions to transfer heat received from the heater  113  at the heater contact portion  140   a  to the fixing film  112  at the upstream-side extension portion  140   e  and the downstream-side extension portion  140   d . It is desirable that the heat conducting member  140  be a member having a heat conductivity of 100 W/m·K or more. In the present exemplary embodiment, an aluminum alloy with a heat conductivity of 140 W/m·K is used. It is desirable that the heat conductivity of the heat conducting member  140  be higher than that of the substrate made from ceramic, such as alumina or aluminum nitride, of the heater  113 . 
     The heater holder  130 , which is a feature of the present exemplary embodiment, is described here. The heater holder  130  is a supporting member which supports the second surface  113   b  of the heater  113 . The heater holder  130  is formed of, for example, a liquid crystalline polymer, which is a heat resistant resin. Portions of the heater holder  130  facing the upstream-side extension portion  140   e  and the downstream-side extension portion  140   d  of the heat conducting member  140  are respectively referred to as an “upstream-side facing portion  130   e ” and a “downstream-side facing portion  130   d”.    
     A characteristic configuration in the present exemplary embodiment is described here. A void space  200   e  of 0.3 mm is provided between the upstream-side extension portion  140   e  of the heat conducting member  140  and the upstream-side facing portion  130   e  of the heater holder  130 . Moreover, a void space  200   d  of 0.3 mm is provided between the downstream-side extension portion  140   d  of the heat conducting member  140  and the downstream-side facing portion  130   d  of the heater holder  130 . 
     These void spaces  200   d  and  200   e  enable preventing heat of the heat conducting member  140  from dissipating to the heater holder  130 . Accordingly, such an advantageous effect that the heat of the heater  113  is able to be efficiently transferred to the fixing film  112  via the heat conducting member  140  can be achieved. 
     Furthermore, in the present exemplary embodiment, the position of the heat conducting member  140  in the thickness direction of the heater  113  (in a direction from the second surface  113   b  toward the first surface  113   a ) is determined by the surface of the heat conducting member  140  opposite to the heater contact portion  140   a  contacting the surface of the heater holder  130  facing the opposite surface. 
     A second exemplary embodiment of the present disclosure is described with reference to  FIG. 4  and  FIG. 5 . The present exemplary embodiment differs from the first exemplary embodiment only in that the heater holder  130  has protruded portions  210  and  220 . The other configurations are similar to those of the first exemplary embodiment, and are, therefore, omitted from description. 
     A feature of the present exemplary embodiment is described with reference to  FIG. 4 . The upstream-side facing portion  130   e  and the downstream-side facing portion  130   d  of the heater holder  130  are respectively provided with the protruded portions  220  and  210 , which are configured to protrude toward the upstream-side extension portion  140   e  and the downstream-side extension portion  140   d  of the heat conducting member  140 . The protruded portions  220  and  210  are in contact with the upstream-side extension portion  140   e  and the downstream-side extension portion  140   d  of the heat conducting member  140 , respectively. In order for such a contact area to be as small as possible, each of the protruded portions  220  and  210  has a conical shape. The shape of each of the protruded portions  220  and  210  is not limited to this, but can be a columnar rib. Each of the protruded portions  220  and  210  includes three portions provided at a middle position in the longitudinal direction and two end portions in the longitudinal direction of the heater holder  130  (portions  210   a ,  210   b ,  210   c ,  220   a ,  220   b , and  220   c ), as illustrated in  FIG. 5 . 
     An advantageous effect of the protruded portions  220  and  210  is described. When the upstream-side extension portion  140   e  and the downstream-side extension portion  140   d  receive an external force from, for example, the fixing film  112 , those are prevented from deforming in a direction to move away from the inner surface of the fixing film  112 , so that the void spaces  200   d  and  200   e  can be stably ensured in an advantageous manner. The void spaces  200   d  and  200   e  function as a heat-insulating layer. 
     Furthermore, each of the protruded portions  220  and  210  can be configured with an elastic member. Moreover, in a state in which no external force is applied to the upstream-side extension portion  140   e  and the downstream-side extension portion  140   d  of the heat conducting member  140 , the protruded portions  220  and  210  and the upstream-side extension portion  140   e  and the downstream-side extension portion  140   d  can be configured to be in non-contact with each other. When the upstream-side extension portion  140   e  and the downstream-side extension portion  140   d  receive an external force from, for example, the fixing film  112  and deform by a predetermined amount, those contact the protruded portions  220  and  210  and are thus prevented from deforming any further. This is because a configuration in which the position of the heat conducting member  140  in the pressing direction is determined only by a contact between the surface of the heat conducting member  140  opposite to the heater contact portion  140   a  and the surface of the heater holder  130  facing the opposite surface is more likely to improve the positional accuracy. Furthermore, the pressing direction is a direction from the second surface  113   b  toward the first surface  113   a.    
     Moreover, in the present exemplary embodiment, the protruded portions  220  and  210  are provided at the heater holder  130 , but can be provided at the heat conducting member  140  to achieve a similar advantageous effect. 
     In a third exemplary embodiment of the present disclosure, members similar to those of the first exemplary embodiment are omitted from description, and different members are described. 
     A positioning configuration of the heat conducting member  140  relative to the heater holder  130  is described with reference to  FIG. 6  to  FIGS. 8A, 8B, and 8C . First, a positioning configuration concerning two components, i.e., the heat conducting member  140  and the heater holder  130 , in the X-axis direction (along the rotation direction of the fixing film  112 ) is described.  FIG. 6  is a sectional view taken perpendicular to the heater  113 , illustrating only the above-mentioned two components. The heat conducting member  140  is provided in such a manner that a part of the heat conducting member  140  is fitted between a wall surface  130   g  at the downstream side and a wall surface  130   h  at the upstream side in the recording material conveyance direction of a groove portion provided along the longitudinal direction of the heater holder  130 . Here, a portion located between the heater contact portion  140   a  and the downstream-side extension portion  140   d  of the heat conducting member  140  and extending along the third surface  113   c  of the heater  113  is referred to as a “bent portion  140   g ”. The position of the heat conducting member  140  relative to the heater holder  130  in the X-axis direction is determined by the wall surface  130   g  of the heater holder  130  and the bent portion  140   g  of the heat conducting member  140  contacting each other. Here, a portion located between the heater contact portion  140   a  and the upstream-side extension portion  140   e  of the heat conducting member  140  and extending along the −Z-axis direction (along the third surface  113   c  of the heater  113 ) is referred to as a “bent portion  140   h ”. A clearance L 1  is provided between the bent portion  140   h  of the heat conducting member  140  and the wall surface  130   h  of the heater holder  130 , so that a void space is formed. 
     Furthermore, a configuration in which the bent portion  140   h  of the heat conducting member  140  and the wall surface  130   h  of the heater holder  130  are in contact with each other and a gap is provided between the bent portion  140   g  and the wall surface  130   g  can be employed. Moreover, a configuration in which clearances are respectively provided between the bent portion  140   g  and the wall surface  130   g  and between the bent portion  140   h  and the wall surface  130   h  so that void spaces are formed can be employed. 
     Next, positioning of the heat conducting member  140  relative to the heater holder  130  with respect to the Z-axis direction (the thickness direction of the heater  113 ) is described. As mentioned above, the film unit  105  is pressed against the pressure roller  110  by the pressure plates  125  and the pressure springs  126 , which serve as a pressure unit. With this, positioning is performed in such a manner that a surface of the heater contact portion  140   a  of the heat conducting member  140  facing the heater holder  130  contacts a supporting surface  130   f  of the groove provided on the heater holder  130 . 
     Next, positioning of the heat conducting member  140  relative to the heater holder  130  with respect to the Y-axis direction (the longitudinal direction of the heater  113 ) is described with reference to  FIGS. 7A and 7B  and  FIGS. 8A, 8B, and 8C .  FIG. 7A  is a perspective view of the above-mentioned two components, and  FIG. 7B  is a perspective view illustrating the above-mentioned two components in a vertically separate manner for convenience sake.  FIG. 8A  is a diagram as viewed from the direction of arrow A in  FIG. 6 , and  FIGS. 8B and 8C  are enlarged views of respective portions near both longitudinal end portions in  FIG. 8A . 
     As illustrated in  FIGS. 7A and 7B , a bent portion  140   k  of the heat conducting member  140  is inserted into a hole portion  130   k  provided on the heater holder  130  in such a manner that the bent portion  140   k  engages with the hole portion  130   k , so that the position of the heat conducting member  140  relative to the heater holder  130  in the longitudinal direction is determined. In this instance, the bent portion  140   k  provided on the heat conducting member  140  is formed by bending and raising a part of the heater contact portion  140   a  in a direction to come close to the heater holder  130 . Moreover, as illustrated in  FIG. 8B , a clearance L 2  is provided between one longitudinal end portion of the heat conducting member  140  and one longitudinal end surface of the groove portion of the heater holder  130  facing each other. Furthermore, as illustrated in  FIG. 8C , a clearance L 3  is provided between the other longitudinal end portion of the heat conducting member  140  and the other longitudinal end surface of the groove portion of the heater holder  130  facing each other. 
     Here, the reason why the clearances L 2  and L 3  are provided is described. The heat conducting member  140 , which is formed of pure aluminum or an aluminum alloy, and the heater holder  130 , which is formed of high-temperature resin such as a liquid crystalline polymer, differ from each other in linear expansion coefficient. Accordingly, the amount of expansion in the longitudinal direction of the heat conducting member  140  is larger than that of the heater holder  130 . The above-mentioned clearances L 2  and L 3  are set in consideration of the amount of expansion of each component and the dimensional tolerance of each component. 
     Next, a positioning configuration of the heater  113  relative to the heater holder  130  is described with reference to  FIG. 9  and  FIGS. 10A, 10B, and 10C . 
     Positioning of the above-mentioned two components with respect to the Y-axis direction (the longitudinal direction of the heater  113 ) is described with reference to  FIG. 9 .  FIG. 9  is a sectional view illustrating the heat conducting member  140  as well as the above-mentioned two components. The heater  113  is mounted in such a manner that a contact surface  130   i  provided on the heater holder  130  contacts a surface  113   cd  at the downstream side in the rotation direction of the fixing film  112  of the third surfaces  113   c  of the heater  113 . In this instance, a clearance L 4  is provided between a surface  113   cu  at the upstream side in the rotation direction of the fixing film  112  of the third surfaces  113   c  of the heater  113  and a wall surface  130   h  of the heater holder  130  facing each other, so that a void space is formed. 
     In this instance, even with regard to a positional relationship between the heater  113  and the heat conducting member  140 , positioning of them relative to each other is performed via the heater holder  130 . In the present exemplary embodiment, a clearance L 5  is provided between the third surface  113   cu  of the heater  113  and the bent portion  140   h  provided between the heater contact portion  140   a  and the upstream-side extension portion  140   e . A clearance L 6  is provided between the third surface  113   cd  of the heater  113  and the bent portion  140   g  provided between the heater contact portion  140   a  and the downstream-side extension portion  140   d.    
     Next, positioning of the heater  113  relative to the heater holder  130  in the Z-axis direction (the thickness direction of the heater  113 ) is described. With regard to a region of the heater  113  overlapping the heat conducting member  140  in the longitudinal direction of the heater  113 , the pressure force causes the second surface  113   b  of the heater  113  to contact the heater contact portion  140   a  of the heat conducting member  140 . Moreover, a surface of the heater contact portion  140   a  of the heat conducting member  140  facing the heater holder  130  is caused to contact the supporting surface  130   f  of the heater holder  130  facing that surface, so that the position of the heater  113  is determined. 
     Next, the positioning configuration with respect to the Y-axis direction is described with reference to FIGS.  10 A,  10 B, and  10 C.  FIG. 10A  is a diagram as viewed from the direction of arrow A in  FIG. 9 , and  FIGS. 10B and 10C  are enlarged views of respective portions near both longitudinal end portions in  FIG. 10A . The heater  113  is pressed in a state in which one longitudinal end surface  113   m  of the heater  113  contacts an arc surface  130   m  provided on the groove portion of the heater holder  130 , so that the position in the longitudinal direction of the heater  113  is determined. In this instance, a clearance L 7  is provided between the other longitudinal end surface  113   n  of the heater  113  and a surface  130   n  provided on the groove portion of the heater holder  130  facing each other. 
     With these clearances L 5  to L 7  provided, even when the heater  113  generates heat, members different in linear expansion coefficient can be prevented from interfering with each other and becoming deformed. 
     With the above-described configuration, an advantageous effect can be achieved in which, for example, the deformation of the heat conducting member  140  caused by thermal expansion or contraction of each member is prevented or reduced and the position of the heat conducting member  140  relative to the heater holder  130  becomes stable. 
     Next, a fourth exemplary embodiment of the present disclosure is described. Members similar to those in the third exemplary embodiment are assigned the respective same reference characters, and are omitted from description. 
     First, a fixing device  100  according to the present exemplary embodiment is described with reference to  FIG. 11 .  FIG. 11  is a sectional view taken perpendicular to the longitudinal direction of the heater  113  of the fixing device  100 . A heat conducting member  240  in the present exemplary embodiment receives heat at a heater contact portion  240   a , which contacts the second surface  113   b  of the heater  113  generating heat, and transfers the heat to the inner surface of the fixing film  112  via an upstream-side extension portion  240   e , as with the third exemplary embodiment. In the present exemplary embodiment, the downstream-side extension portion  140   d , which is included in the heat conducting member  140  in the third exemplary embodiment, is not provided. 
     Next, a positioning configuration of the heat conducting member  240  relative to the heater holder  130  is described with reference to  FIG. 12  to  FIGS. 13A and 13B . 
     First, positioning concerning two components, i.e., the heat conducting member  240  and the heater holder  130 , in the X-axis direction (the rotation direction of the fixing film  112 ) is described with reference to  FIG. 12 .  FIG. 12  is a sectional view illustrating only the above-mentioned two components. 
     The heat conducting member  240  is provided in such a manner that a part of the heat conducting member  240  is fitted between a wall surface  130   g  at the downstream side and a wall surface  130   h  at the upstream side in the recording material conveyance direction of a groove portion provided along the longitudinal direction of the heater holder  130 . Here, a downstream-side end surface  240   d  of the heat conducting member  240  contacts the wall surface  130   g  of the heater holder  130 , so that the position of the heat conducting member  240  relative to the heater holder  130  in the X-axis direction is determined. Here, a portion located between the heater contact portion  240   a  and the upstream-side extension portion  240   e  of the heat conducting member  240  and extending along the −Z-axis direction (along the third surface  113   c  of the heater  113 ) is referred to as a “bent portion  240   h ”. A clearance L 1  is provided between the bent portion  240   h  of the heat conducting member  240  and the wall surface  130   h  of the heater holder  130 , so that a void space is formed. 
     Furthermore, a configuration in which the wall surface  130   h  and the bent portion  240   h  are in contact with each other to determine the position in the X-axis direction of the heat conducting member  240  and a clearance L 1  is provided between the downstream-side end surface  240   d  of the heat conducting member  240  and the wall surface  130   g  of the heater holder  130  can be employed. Moreover, a configuration in which clearances are respectively provided between the wall surface  130   h  of the heater holder  130  and the bent portion  240   h  of the heat conducting member  240  and between the downstream-side end surface  240   d  and the wall surface  130   g  of the heater holder  130  can be employed. 
     Positioning concerning the Z-axis direction (the thickness direction of the heater  113 ) is similar to that in the third exemplary embodiment, and is, therefore, omitted from description. 
     Next, a positioning configuration concerning the Y-axis direction (the longitudinal direction of the heater  113 ) is described with reference to  FIGS. 13A and 13B .  FIG. 13A  is a perspective view illustrating only two components, i.e., the heater holder  130  and the heat conducting member  240 , and  FIG. 13B  is a perspective view illustrating the above-mentioned two components in a separate manner for convenience sake. 
     As illustrated in  FIGS. 13A and 13B , a bent portion  240   k  of the heat conducting member  240  is inserted into a hole portion  130   k  provided on the heater holder  130  in such a manner that the bent portion  240   k  engages with the hole portion  130   k , so that the position of the heat conducting member  240  relative to the heater holder  130  is determined. In this instance, the bent portion  240   k  provided on the heat conducting member  240  is formed by bending and raising a part of the downstream-side end surface  240   d  of the heat conducting member  240  in a direction to come close to the heater holder  130 . Moreover, the bent portion  240   k  is provided near the middle portion of the heat conducting member  240  with respect to the Y-axis direction. Furthermore, as illustrated in  FIG. 13A , a clearance L 8  is provided between one longitudinal end surface of the heat conducting member  240  and one longitudinal end surface of the groove portion of the heater holder  130  facing each other. A clearance L 9  is provided between the other longitudinal end surface of the heat conducting member  240  and the other longitudinal end surface of the groove portion of the heater holder  130  facing each other. With these clearances L 8  and L 9  provided, even when the heater  113  generates heat, members different in linear expansion coefficient can be prevented from interfering with each other and becoming deformed. 
     With the above-described configuration, an advantageous effect can be achieved in which, for example, the deformation of the heat conducting member  240  caused by thermal expansion or contraction of each member is prevented or reduced and the position of the heat conducting member  240  becomes stable. 
     Next, a fifth exemplary embodiment of the present disclosure is described. Members similar to those in the third exemplary embodiment are omitted from description. First, a fixing device  100  according to the present exemplary embodiment is described with reference to  FIG. 14 .  FIG. 14  is a schematic sectional view taken perpendicular to the longitudinal direction of the heater  113  of the fixing device  100 . A heat conducting member  340  in the present exemplary embodiment receives heat of the heater  113  at a heater contact portion  340   a , which contacts the second surface  113   b  of the heater  113 , and transfers the heat to the inner surface of the fixing film  112  via a downstream-side extension portion  340   d , as with the third exemplary embodiment. In the heat conducting member  340 , the upstream-side extension portion  140   e , which is included in the heat conducting member  140  in the third exemplary embodiment, is not provided. 
     Next, a positioning configuration of the heat conducting member  340  relative to the heater holder  130  concerning the X-axis direction is described with reference to  FIG. 15  to  FIGS. 16A and 16B . 
     First, positioning of the heat conducting member  340  concerning two components, i.e., the heat conducting member  340  and the heater holder  130 , in the X-axis direction is described.  FIG. 15  is a sectional view illustrating only the above-mentioned two components. 
     The heat conducting member  340  is provided in such a manner that a part of the heat conducting member  340  is fitted between a wall surface  130   g  at the downstream side and a wall surface  130   h  at the upstream side in the recording material conveyance direction of a groove portion provided along the longitudinal direction of the heater holder  130 . Here, a portion located between the heater contact portion  340   a  and the downstream-side extension portion  340   d  of the heat conducting member  340  and extending along the −Z-axis direction (along the third surface  113   c  of the heater  113 ) is referred to as a “bent portion  340   g ”. The bent portion  340   g  of the heat conducting member  340  contacts the wall surface  130   g  of the heater holder  130 , so that the position of the heat conducting member  340  relative to the heater holder  130  in the X-axis direction is determined. Then, a clearance L 1  is provided between the upstream-side end portion  340   e  of the heat conducting member  340  and the wall surface  130   h  of the heater holder  130 , so that a void space is formed. 
     Furthermore, a configuration in which the wall surface  130   h  and the upstream-side end portion  340   e  are in contact with each other to determine the position in the X-axis direction of the heat conducting member  340  and a clearance L 1  is provided between the bent portion  340   g  of the heat conducting member  340  and the wall surface  130   g  of the heater holder  130  can be employed. Moreover, a configuration in which clearances are respectively provided between the wall surface  130   h  of the heater holder  130  and the upstream-side end portion  340   e  of the heat conducting member  340  and between the bent portion  340   g  and the wall surface  130   g  of the heater holder  130  can be employed. 
     Positioning concerning the Z-axis direction (the thickness direction of the heater  113 ) is similar to that in the third exemplary embodiment, and is, therefore, omitted from description. 
     Next, a positioning configuration concerning the Y-axis direction (the longitudinal direction of the heater  113 ) is described with reference to  FIGS. 16A and 16B . FIG.  16 A is a perspective view illustrating only two components, i.e., the heater holder  130  and the heat conducting member  340 , and  FIG. 16B  is a perspective view illustrating the above-mentioned two components in a separate manner for convenience sake. 
     As illustrated in  FIGS. 16A and 16B , a bent portion  340   k  of the heat conducting member  340  is inserted into a hole portion  130   k  provided on the heater holder  130  in such a manner that the bent portion  340   k  engages with the hole portion  130   k , so that the position of the heat conducting member  340  relative to the heater holder  130  is determined. In this instance, the bent portion  340   k  provided on the heat conducting member  340  is formed by bending and raising a part of the upstream-side end portion  340   e  of the heat conducting member  340  in a direction to come close to the heater holder  130 . Moreover, the bent portion  340   k  is provided near the middle portion of the heat conducting member  340  with respect to the Y-axis direction. Furthermore, as illustrated in  FIG. 16A , a clearance L 10  is provided between one longitudinal end surface of the heat conducting member  340  and one longitudinal end surface of the groove portion of the heater holder  130  facing each other. A clearance L 11  is provided between the other longitudinal end surface of the heat conducting member  340  and the other longitudinal end surface of the groove portion of the heater holder  130  facing each other. With these clearances L 10  and L 11  provided, even when the heater  113  generates heat, members different in linear expansion coefficient can be prevented from interfering with each other and becoming deformed. 
     With the above-described configuration, an advantageous effect can be achieved in which, for example, the deformation of the heat conducting member  340  caused by thermal expansion or contraction of each member is prevented or reduced and the position of the heat conducting member  340  becomes stable. 
     Furthermore, the heat conducting member in each of the first to fifth exemplary embodiments is provided to extend over a sheet passing region and a sheet non-passing region for a small-sized recording material of the heater in the longitudinal direction of the heater. This configuration is employed to prevent or reduce a temperature rise of the sheet non-passing region which would be caused when fixing processing is continuously performed on the small-sized recording material. 
     While the present disclosure has been described with reference to exemplary embodiments, it is to be understood that the disclosure is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2017-128000 filed Jun. 29, 2017, which is hereby incorporated by reference herein in its entirety.