Patent Publication Number: US-11036169-B2

Title: Fixing device

Description:
BACKGROUND OF THE DISCLOSURE 
     Field of the Disclosure 
     The present disclosure relates to a fixing device used in an image forming apparatus, such as a copying machine or a laser beam printer (LBP), which employs an image formation process using, for example, an electrophotographic method, and an electrostatic recording method 
     Description of the Related Art 
     A film fixing method has been used for a fixing device included in an image forming apparatus that employs, for example, an electrophotographic method, and an electrostatic recording method. In a fixing device that employs the film fixing method, a fixing film and a pressing member are disposed in pressure contact with each other. Inside the fixing film, a heating member for heating the fixing film is disposed while the fixing film is driven in close contact with the pressing member at an inner surface of a portion opposed to the pressing member. 
     As the heating member, a ceramic heater having a structure in which a heating resistor element is formed on a substrate made of a ceramic material, such as alumina or aluminum nitride, is typically used. In a film heat fixing unit including the heating member, a phenomenon in which the temperature in a non-sheet-passing area of a heater through which paper does not pass becomes higher than the temperature in a sheet-passing area of the heater through which paper passes, i.e., a so-called non-sheet-passing-portion temperature rise, is likely to occur. Thus, the substrate of the heater can be broken by a thermal stress caused due to a temperature difference between the sheet-passing area and the non-sheet-passing area when the non-sheet-passing-portion temperature rise occurs. In this regard, there is a known structure in which a thermally conductive member is provided between a heater and a heater support member so as to facilitate heat transfer within the surface of the heater and obtain a substantially uniform temperature distribution in a longitudinal direction of the heater (Japanese Patent Application Laid-Open No. 11-84919). 
     On the other hand, the thermally conductive member can be deformed due to a difference between a thermal expansion amount (thermal expansion rate) of the heater and that of the thermally conductive member in a case the thermally conductive member between the heater and the heater support member are provided. Since the heater repeatedly performs heating and cooling (heat cycle), the heater and the heater support member repeatedly expand and contract. Accordingly, the heater and the heater support member exert forces on each other, so that a stress is applied to each of the heater and the heater support member. As a result, if a low-strength material, such as an aluminum plate, is used as the thermally conductive member, the thermally conductive member can be deformed due to the applied stress. If the thermally conductive member is deformed, adhesion properties between the thermally conductive member and the heater can deteriorate and the effect of temperature leveling caused by the thermally conductive member may be reduced. In order to prevent deformation of the thermally conductive member due to the heat cycle, there has been a technique for preventing deformation due to the heat cycle by arranging a plurality of members as thermally conductive members in the longitudinal direction (Japanese Patent Application Laid-Open No. 2016-95397). The use of thermally conductive members consisting of the plurality of members reduces the length of each of the thermally conductive members in the longitudinal direction. This reduction reduces an expansion amount of the thermally conductive members, and thereby alleviating the stress applied to the thermally conductive members due to the heat cycle and preventing deformation of the thermally conductive members. 
     However, in a case of using the plurality of members arranged as thermally conductive members in the longitudinal direction, the effect of leveling the temperature distribution in the longitudinal direction of the heater by the thermally conductive members cannot be obtained in a gap formed between the members of the thermally conductive members. Specifically, the thermally conductive members are not present at the gap, and thus the temperature of the heater rises locally, which may cause a defective image such as hot offset corresponding to the width of the gap (length in the longitudinal direction of the heater). Thus, a width of the gap may be desirably minimized. On the other hand, since the thermally conductive members thermally expand, the gap may desirably have a constant width to prevent deformation of the thermally conductive members due to the contact between adjacent thermally conductive members. 
     Thus, in order to minimize the width of the gap in consideration of thermal expansion, the thermally conductive member to engage with the heater support member can be located at a position as close to the gap as possible. This is because the thermal expansion amount of the thermally conductive member can be reduced by reducing the distance of the engagement portion from the gap. However, for example, in a case where a temperature detection element, a safety element, or the like is disposed in contact with the heater at a position close to the gap, there may be a case where a portion with a shape that allows the thermally conductive member to engage with the heater support member cannot be disposed near the gap. 
     SUMMARY OF THE DISCLOSURE 
     The present disclosure is directed to providing a fixing device capable of preventing the occurrence of a defective image by suppressing a local temperature rise in a heating member at a gap between adjacent thermally conductive members, while preventing deformation of the thermally conductive members due to a contact between the adjacent thermally conductive members in the fixing device including thermally conductive members composed of a plurality of members arranged in a longitudinal direction. 
     According to an aspect of the present disclosure, a fixing device includes a cylindrical film, a support member disposed on an inner peripheral surface of the film, a heating member supported by the support member and provided slidably with the film, and a pressing member that forms a pressure contact portion together with the heating member through the film, the pressure contact portion being configured to heat a recording medium while pressing the recording medium. A first thermally conductive member and a second thermally conductive member are provided between the heating member and the support member, each of the first thermally conductive member and the second thermally conductive member having thermal conductivity higher than thermal conductivity of the support member. The first thermally conductive member and the second thermally conductive member are configured to engage with each other. 
     Further features and aspects of the present disclosure will become apparent from the following description of example embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic sectional view illustrating a structure of an example fixing device. 
         FIG. 2  is a schematic front view illustrating the structure of the fixing device. 
         FIG. 3  illustrates an explanatory diagram of an example ceramic heater. 
         FIG. 4  illustrates an explanatory diagram of an example thermistor and a thermal fuse. 
         FIGS. 5A and 5B  are sectional views each illustrating an example method for holding a heater and a metal plate according to related art. 
         FIGS. 6A, 6B and 6C  are explanatory diagrams each illustrating an example layout of a heater holding member and metal plates. 
         FIGS. 7A and 7B  are enlarged views each illustrating a gap between the metal plates according to the related art. 
         FIGS. 8A and 8B  are enlarged views each illustrating the gap between the metal plates during thermal expansion according to the related art. 
         FIGS. 9A to 9D  are schematic diagrams each illustrating a method for holding a heater and metal plates according to a first example embodiment. 
         FIGS. 10A and 10B  are enlarged views each illustrating a gap between the metal plates according to the first example embodiment. 
         FIGS. 11A and 11B  are enlarged views each illustrating the gap between the metal plates during thermal expansion according to the first example embodiment. 
         FIGS. 12A to 12D  are schematic diagrams each illustrating a method for holding a heater and metal plates according to a second example embodiment. 
         FIGS. 13A and 13B  are enlarged views each illustrating a gap between the metal plates according to the second example embodiment. 
         FIGS. 14A and 14B  are enlarged views each illustrating the gap between the metal plates during thermal expansion of a fixing device according to the second example embodiment. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     A first example embodiment according to the present disclosure will be described with reference to the accompanying drawings. First, an outline of a fixing device according to the present example embodiment will be described. Next, features of the present example embodiment will be described. In the following description, unless otherwise specified, a longitudinal direction of a fixing device  18  that is identical to an axial direction of a pressing roller  32  and a generatrix direction of a film  36  is simply referred to as a “longitudinal direction”. A transverse direction of the fixing device  18  that is identical to a conveyance direction of a recording medium is simply referred to as a “transverse direction”. 
     (Example Fixing Device) 
       FIG. 1  is a schematic sectional view illustrating the fixing device  18  according to the present example embodiment as viewed along the longitudinal direction of the fixing device  18 .  FIG. 2  is a schematic view illustrating the fixing device  18  as viewed from one end of the fixing device  18  in the transverse direction. 
     The fixing device  18  includes a film unit  31  including the cylindrical flexible film  36 , and the pressing roller  32  serving as a pressing member. The film  36  and the pressing roller  32  are disposed substantially in parallel with each other between right and left side plates  34  of a frame  33 . The fixing device  18  is configured to fix unfixed toner on a recording medium at a nip portion N, which is a contact portion between the film  36  and the pressing roller  32 . 
     The pressing roller  32  includes a cored bar  32   a , an elastic layer  32   b  formed on the outside of the cored bar  32   a , and a release layer  32   c  formed on the outside of the elastic layer  32   b . Materials used for the elastic layer  32   b  include silicone rubber, and fluororubber. Materials used for the release layer  32   c  include perfluoroalkoxy polymer (PFA), polytetrafluoroethylene (PTFE), and polyhexafluoropropylene (FEP). 
     The pressing roller  32  according to the present example embodiment has a structure in which the silicone rubber layer (elastic layer)  32   b  having a thickness of about 3.5 mm is formed by mold ejection on the cored bar  32   a . The cored bar  32   a  is made of stainless steel and has an outer diameter of 11 mm. On the outside of the silicone rubber layer  32   b , a PFA resin tube (release layer)  32   c  having a thickness of about 40 μm is formed. The outer diameter of the pressing roller  32  is 18 mm. The hardness of the pressing roller  32  is desirably in a range from 40° to 70° under a load of 9.8 N measured by an ASKER-C hardness meter in terms of, for example, securement, and endurance of the nip portion N. In the present example embodiment, the hardness of the pressing roller  32  is adjusted to 54°. The length of the elastic layer in the longitudinal direction of the pressing roller  32  is 226 mm. The pressing roller  32  is rotatably supported between the side plates  34  of the frame  33  by bearing members  35  at both ends of the cored bar  32   a  in the longitudinal direction. A drive gear G is fixed to one end of the pressing roller cored bar  32   a . A rotary force is transmitted to the drive gear G from a drive source (not illustrated), and the pressing roller  32  is rotationally driven. 
     The film unit  31  illustrated in  FIG. 1  includes the film  36 , a plate-shaped heater  37  that contacts the inner peripheral surface of the film  36 , a support member  38  that supports the heater  37 , and a metal plate  39  serving as a thermally conductive member having thermal conductivity higher than that of the support member  38 . The film unit  31  is fixed to the support member  38  through the metal plate  39  with a power feed connector  47  and a heater clip  48 . The power feed connector  47  is provided at one end of the heater  37  in the longitudinal direction, and the heater clip  48  is provided at the other end of the heater  37  in the longitudinal direction. The film unit  31  further includes a pressing stay  42  that reinforces the support member  38 , and flanges  43  that regulate a movement of the film  36  in the longitudinal direction. 
     The film  36  is a cylindrical flexible member including a base layer, an elastic layer formed on the outside of the base layer, and a release layer formed on the outside of the elastic layer. The film  36  according to the present example embodiment has an inner diameter of 18 mm and has a structure in which a polyimide base material having a thickness of 60 μm is used as the base layer. As the elastic layer, silicone rubber having a thickness of about 150 μm is used. As the release layer, a PFA resin tube having a thickness of 15 μm is used. 
     The heater  37  includes an insulating substrate  37   a , heating resistor elements  37   b , and an electrical contact portion  37   c  as illustrated in  FIG. 3 . The insulating substrate  37   a  is made of a ceramic material such as alumina or aluminum nitride. The heating resistor elements  37   b  are made of a material such as a silver-palladium alloy, and are formed by screen printing or the like on the substrate  37   a . The electrical contact portion  37   c  is made of a material such as silver, and is connected to the heating resistor elements  37   b . Power can be supplied to the heating resistor elements  37   b  through a connection of the power feed connector  47  and the electrical contact portion  37   c , which is provided at one end of the heater  37  in the longitudinal direction. 
     The heater  37  includes a glass coat  37   d  on the heating resistor elements  37   b  as a protective layer for protecting the heating resistor elements  37   b . The heater  37  is disposed along the generatrix direction of the film  36  in such a manner that one of the surfaces of the heater  37  is opposed to the pressing roller  32  through the film  36  and the other one surface, which is opposed to the one surface, is opposed to a support surface of the support member  38 . The heater  37  is provided slidably with the film  36 . 
     The substrate  37   a  of the heater  37  according to the present example embodiment has a rectangular parallelepiped shape with a longitudinal length of 270 mm, a transverse length of 5.8 mm, and a thickness of 1.0 mm. The substrate  37   a  is made of alumina. In the present example embodiment, the two heating resistor elements  37   b  are connected in series and configured to have a resistance value of 18Ω. Thus, the heating resistor elements  37   b  have such a pattern that the heating resistor elements  37   b  are connected with each other via an electrical contact portion  37   c  at one end portion in the longitudinal direction. The heating resistor element  37   b  located on an upstream side and the heating resistor element  37   b  located on a downstream side have the same shape with a longitudinal length of 222 mm and a transverse length of 0.9 mm. 
     As for transverse positions of the upstream and downstream heating resistor elements  37   b , both the heating resistor elements  37   b  are disposed at positions of 0.7 mm from edges of the substrate  37   a . The heating resistor elements  37   b  are printed at symmetrical positions with respect to a transverse center. The heater  37  is provided not only with the glass coat  37   d  but also with a heat-resistant grease applied onto the inner surface of the film  36 . This improves sliding properties of the inner peripheral surface of the film  36  with the heater  37 . 
     The support member  38  is a member that has a U-shape in cross section as illustrated in  FIG. 1 . The support member  38  has rigidity, heat resistance, and thermal insulation properties. In the present example embodiment, the support member  38  is formed of liquid crystal polymer. The support member  38  has two functions: a function of supporting the film  36  externally fitted with the support member  38 , and a function of supporting one of the surfaces of the heater  37 . 
     The support member  38  is provided with through-holes  38   f  and  38   g  as illustrated in  FIG. 4 . A thermistor  44   a  serving as a temperature detection element is disposed to contact the metal plate  39  from the through-hole  38   f . A thermal switch  44   b  serving as a safety element is disposed to contact the metal plate  39  from the through-hole  38   g . In other words, a temperature sensor, such as a temperature detection element and a safety element, is provided on the metal plate  39  so that heat of the heater  37  can be sensed through the metal plate  39 . 
     The thermistor  44   a  is prepared by providing a thermistor element in a housing via ceramic paper or the like for stabilizing a contact state with the metal plate  39 , and then coating the thermistor element with an insulating material such as polyimide tape. The thermal switch  44   b  is a part for detecting abnormal heat generation in the heater  37  to interrupt electrical power supply to the heater  37  when the heater  37  causes an abnormal temperature rise. 
     The thermal switch  44   b  is provided with a bimetal portion prepared by firmly bonding two or more types of metal or alloy with different thermal expansion coefficients and then finishing the bonded material in a plate shape. Due to abnormal high temperature generated by the heater  37 , the metal portion having a large thermal expansion coefficient is bent toward the metal portion having a small thermal expansion coefficient. By using this displacement, the thermal switch  44   b  opens or closes an electrical contact, thereby interrupting a circuit for supplying electrical power to the heater  37 . 
     The pressing stay  42  is a member that has a U-shape in cross section, and is elongated in the generatrix direction of the film  36  as illustrated in  FIG. 1 . The pressing stay  42  has a function of enhancing the bending rigidity of the film unit  31 . The pressing stay  42  according to the present example embodiment is formed by bending a stainless steel plate with a thickness of 1.6 mm. 
     The right and left flanges  43  hold both ends of the pressing stay  42 . Ends  34   a  of the side plates  34 , which are opposed to each other on the upstream side and the downstream side in the conveyance direction, each enter vertical groove portions  43   a , which are provided on the upstream side and the downstream side in the conveyance direction. In other words, the vertical groove portions  43   a  of the flanges  43  that are provided on the upstream side and the downstream side in the conveyance direction engage with the two opposed ends  34   a  of the side plates  34 . Thus, the right and left flanges  43  are configured such that the right and left side plates  34  cause the film unit  31  to approach the pressing roller  32  or move away from the film unit  31 . In the present example embodiment, a liquid crystal polymer resin is used as a material for the flanges  43 . 
     A pressing spring  46  is disposed between a pressing arm  45  and a pressing portion  43   b  of each of the right and left flanges  43 . The pressing spring  46  urges the film  36  against the pressing roller  32  through the right and left flanges  43 , the pressing stay  42 , the support member  38 , and the heater  37  as illustrated in  FIG. 2 . In the present example embodiment, a press-contact force between the film  36  and the pressing roller  32  is 180 N as a total pressure. Thus, the heater  37  and the pressing roller  32  form the nip portion N (pressure contact portion) of about 6 mm against the elasticity of the pressing roller  32  through the film  36 . 
     During the operation of the fixing device  18 , a rotary force is transmitted from the drive source (not illustrated) to the drive gear G of the pressing roller  32 . Thus, the pressing roller  32  is rotationally driven at a predetermined speed in a clockwise direction as illustrated in  FIG. 1 . In the present example embodiment, the rotational speed of the pressing roller  32  is set such that the recording medium is conveyed at a conveyance speed of 100 mm/sec. The rotational force acts on the film  36  by a frictional force acting between the pressing roller  32  and the film  36  at the nip portion N along with rotational driving of the pressing roller  32 . As a result, the film  36  slides on one surface of the heater  37  while contacting the surface of the heater  37 , and is driven and rotated in a counterclockwise direction around the support member  38  along with the rotation of the pressing roller  32 . In this manner, the film  36  is rotated and electrical power is supplied to the heater  37 , and a recording medium P is introduced in a state where the temperature of the heater  37  detected by the thermistor  44   a  reaches a target temperature. A fixing entrance guide  30  has a function of guiding the recording medium P having an unfixed toner image t formed thereon toward the nip portion N. 
     The recording medium P bearing the unfixed toner image t is introduced to the nip portion N, and the surface of the recording medium P that bears the toner image comes into close contact with the film  36  at the nip portion N, and then the recording medium P and the film  36  are nipped and conveyed by the nip portion N. In the conveyance process, the unfixed toner image t on the recording medium P is heated and pressed on the recording medium P by heat supplied from the film  36  heated by the heater  37 . Thus, the unfixed toner image t is fused and fixed onto the recording medium P. 
     (Thermally Conductive Member) 
     Next, the metal plate  39  serving as a thermally conductive member of related art and a method for holding the metal plate  39  will be described.  FIGS. 5A and 5B  are sectional views each illustrating an end of each of the heater  37  and the support member  38 . The metal plate  39  is disposed between the support member  38  and the heater  37  as illustrated in  FIGS. 1 and 2 . One of the power feed connector  47  and the heater clip  48 , each of which serves as a holding member, is provided at one end of the heater  37  in the longitudinal direction, and the other one of the power feed connector  47  and the heater clip  48  is provided at the other end of the heater  37  in the longitudinal direction as illustrated in  FIGS. 5A and 5B . Thus, the heater  37  is supported by the support member  38  in such a manner that a central portion of the heater  37  in the longitudinal direction contacts the support member  38  via the metal plate  39 . Further, ends of the heater  37  in the longitudinal direction directly contacting the support member  38  are supported by the support member  38 . 
     The power feed connector  47  is formed of a housing portion  47   a , which is made of a recessed resin material, and a contact terminal  47   b . The power feed connector  47  nips and holds the heater  37  and the support member  38 . Further, the contact terminal  47   b  contacts the electrical contact portion  37   c  of the heater  37 , and thus the power feed connector  47  is electrically connected to the heater  37 . In the present example embodiment, the power feed connector  47  is used as a heater holding member. However, the power feed connector  47  may be divided into separate members, i.e., a member having the function of feeding power to the heater  37 , and a member serving as the heater holding member. The contact terminal  47   b  is connected to a wire  49 . The wire  49  is connected to an alternating current (AC) power supply and a triac which are not illustrated. 
     The heater clip  48  formed of a metal plate bent in a U-shape holds, as a holding member, the heater  37  owing to its spring properties in a state where an end of the heater  37  in the longitudinal direction contacts the support member  38 . The end of the heater  37  that is pressed by the heater clip  48  is configured to allow the movement of the heater  37  in the longitudinal direction. With this structure, expansion or contraction of the heater  37  is allowed during thermal expansion of the heater  37 , and thus an unnecessary stress from acting on the heater  37  is prevented. 
     A structure using two metal plates  40  and  41  according to the related art as the metal plate  39  will be described with reference to  FIGS. 6A to 6C . In the present example embodiment, an aluminum plate having a constant thickness of 0.3 mm (hereinafter referred to simply as an aluminum plate) is used as each of the metal plates  40  and  41 . A width M in the conveyance direction of each of contact portions of the aluminum plates  40  and  41  in contact with the heater  37  is 7 mm. A longitudinal length L 1  of the aluminum plate  40  is 102 mm, and a longitudinal length L 2  of the aluminum plate  41  is 115 mm. The aluminum plates  40  and  41  are placed on the support member  38  with a gap formed therebetween in the longitudinal direction. The aluminum plate  40  includes bent portions  40   a  and  40   b  at both ends in the longitudinal direction. The bent portions  40   a  and  40   b  are respectively inserted into mounting holes  38   a  and  38   b  of the support member  38 . Similarly, the aluminum plate  41  includes bent portions  41   a  and  41   b  at both ends in the longitudinal direction, and the bent portions  41   a  and  41   b  are respectively inserted into mounting holes  38   c  and  38   b  of the support member  38 . The bent portions  40   a  is inserted into the mounting hole  38   a , the bent portions  40   b  and  41   b  are inserted into the mounting hole  38   b , and the bent portion  41   a  is inserted into the mounting hole  38   c . Further, a downstream end in the conveyance direction of each of the bent portions  40   a ,  40   b ,  41   a , and  41   b  is brought into contact with an inner wall of the corresponding one of the mounting holes  38   a  to  38   c , thereby the aluminum plates  40  and  41  are positioned in the conveyance direction. On the other hand, the mounting holes  38   a  to  38   c  have a width greater than that of the bent portions  40   a ,  40   b ,  41   a , and  41   b  of the aluminum plates  40  and  41 , and thereby allowing stretching of the aluminum plates  40  and  41  in the longitudinal direction due to thermal expansion. 
     The aluminum plate  40  includes a bent portion  40   c  at an end in the conveyance direction, and the bent portion  40   c  is inserted into a mounting hole  38   d  of the support member  38 . Similarly, the aluminum plate  41  includes a bent portion  41   c  at an end in the conveyance direction, and the bent portion  41   c  is inserted into a mounting hole  38   e  of the support member  38 . The bent portions  40   c  and  41   c  are inserted into the mounting holes  38   d  and  38   e , respectively. Further, one end in the longitudinal direction of each of the bent portions  40   c  and  41   c  is brought into contact with an inner wall of the corresponding one of the mounting holes  38   d  and  38   e , and thereby the aluminum plates  40  and  41  are positioned in the longitudinal direction. On the other hand, in view of manufacturing tolerance, the mounting holes  38   d  and  38   e  have a width greater than that of the bent portions  40   c  and  41   c  of the aluminum plates  40  and  41 , and thereby allowing the movement in the conveyance direction. 
     Next, a gap located at a central portion in the longitudinal direction when the aluminum plates  40  and  41  according to the related art thermally expand will be described with reference to  FIGS. 7A and 7B  and  FIGS. 8A and 8B .  FIG. 7A  is a sectional view illustrating the central portion in the longitudinal direction before thermal expansion in a state where the aluminum plates  40  and  41  are provided on the support member  38  below the heater  37 .  FIG. 7B  illustrates the support member  38  as viewed from a mounting surface of the heater  37  in a state where the heater  37  is omitted. In other words,  FIG. 7A  is a sectional view of  FIG. 7B  in which the illustration of the heater  37  is omitted. The aluminum plates  40  and  41  include hooking portions  40   d  and  41   d , respectively. The hooking portions  40   d  and  41   d  engage with protrusions  38   i  and  38   j , respectively, which are provided on the support member  38  and protrude toward the inside of the mounting hole  38   b  in the longitudinal direction. The hooking portions  40   d  and  41   d  and the protrusions  38   i  and  38   j  overlap each other in the longitudinal direction by the amounts corresponding to a width A 1  and a width B 1 , respectively, as viewed from the mounting surface of the heater  37 . Thus, the hooking portions  40   d  and  41   d  regulate the movement of the aluminum plates  40  and  41  in a direction away from the support member  38  toward the mounting surface of the heater  37 . A gap with a width D 1  is provided between the aluminum plates  40  and  41 , so that the aluminum plates  40  and  41  are prevented from contacting each other and being deformed due to thermal expansion. A width C 1  corresponds to a portion where the heater  37  and the aluminum plates  40  and  41  are not in contact with each other in the longitudinal direction at the gap of the central portion. 
       FIG. 8A  is a sectional view illustrating the central portion in a state where the aluminum plates  40  and  41  provided on the support member  38  thermally expand, in a state where the heater  37  is omitted.  FIG. 8B  illustrates the central portion as viewed from the mounting surface of the heater  37 . When the aluminum plates  40  and  41  thermally expand, a width C 2  of a portion where the heater  37  and the aluminum plates  40  and  41  are not in contact with each other in the central portion is smaller than the width C 1  before thermal expansion. Similarly, a width D 2  of the gap at the central portion is smaller than the width D 1  of the gap before thermal expansion. This is because the aluminum plates  40  and  41 , which are positioned in the longitudinal direction with respect to the support member  38 , stretch toward the central portion from the bent portions  40   c  and  41   c  due to thermal expansion of portions having lengths L 3  and L 4 , respectively. The respective lengths L 3  and L 4  are the lengths between the bent portions  40   c  and  41   c  and the central portion. Even when thermal expansion occurs, the gap with the width D 2  prevents the aluminum plates  40  and  41  from contacting each other and being deformed. However, the width C 2  of the portion where the heater  37  and the aluminum plates  40  and  41  are not in contact with each other causes a local temperature rise at the central portion of the heater  37 , which may cause a defective image such as hot offset corresponding to the width C 1 . In this case, overlapping widths A 2  and B 2  of the hooking portions  40   d  and  41   d  of the aluminum plates  40  and  41  with the protrusions  38   i  and  38   j  of the support member  38  are smaller than the overlapping widths A 1  and B 1  before thermal expansion occurs. However, the aluminum plates  40  and  41  maintain the function of regulating the movement in a direction away from the support member  38  toward the mounting surface of the heater  37 . 
     Next, aluminum plates  59  and  60  each serving as the metal plate  39  according to the present example embodiment and a method for holding the aluminum plates  59  and  60  by a support member  58  serving as the support member  38  according to the present example embodiment will be described with reference to  FIGS. 9A to 9D .  FIG. 9A  is a sectional view taken along a plane extending in the longitudinal direction.  FIG. 9B  illustrates a state where the aluminum plates  59  and  60  are provided on the support member  58  in a state where the heater  37  is omitted as viewed from the heater  37 .  FIG. 9C  is a perspective view illustrating engagement portions of the aluminum plates  59  and  60 .  FIG. 9D  is a perspective view illustrating a state where the aluminum plates  59  and  60  engage with each other at a central portion in the longitudinal direction. In  FIG. 9A , the illustration of the thermistor  44   a  and the thermal switch  44   b  is omitted. 
     The aluminum plates  59  and  60  and engagement portions of the aluminum plates  59  and  60  provided on the support member  58  will be described with reference to  FIGS. 9A to 9D . In the present example embodiment, the aluminum plates  59  and  60  each having a constant thickness of 0.3 mm are used. The width M in the conveyance direction of each of contact portions of the aluminum plates  59  and  60  in contact with the heater  37  is 7 mm. A longitudinal length L 5  of the aluminum plate  59  is 101 mm, and a longitudinal length L 6  of the aluminum plate  60  is 114 mm. The aluminum plates  59  and  60  are placed on the support member  38  with a gap formed therebetween in the longitudinal direction. The aluminum plate  59  includes bent portions  59   a  and  59   b  at both ends in the longitudinal direction. The bent portions  59   a  and  59   b  are respectively inserted into mounting holes  58   a  and  58   b  of the support member  58 . The bent portion  59   b  is provided with a hole  59   b   1  at a central portion in the conveyance direction. The aluminum plate  60  includes bent portions  60   a  and  60   b  at both ends in the longitudinal direction. The bent portion  60   a  (entering portion) is inserted into a mounting hole  58   c  of the support member  58 . The bent portion  60   b  is inserted into the hole  59   b   1  provided on the bent portion  59   b  of the aluminum plate  59 . The bent portion  59   a ,  59   b , and  60   a  are inserted into the mounting holes  58   a ,  58   b , and  58   c , respectively. Further, a downstream end of each of the bent portion  59   a ,  59   b , and  60   a  in the conveyance direction is brought into contact with an inner wall of the mounting holes  58   a ,  58   b , and  58   c , respectively, so that the aluminum plates  59  and  60  are positioned in the conveyance direction. The bent portion  60   b  is inserted into the hole  59   b   1 . Further, a downstream end of the bent portion  60   b  in the conveyance direction is brought into contact with an inner wall of the hole  59   b   1 , so that the aluminum plate  60  is positioned in the conveyance direction with respect to the aluminum plate  59 . On the other hand, the mounting holes  58   a  to  58   c  have a width greater than that of the bent portions  59   a ,  59   b ,  60   a , and  60   b  of the aluminum plates  59  and  60 , and thereby allowing stretching of the aluminum plates  59  and  60  in the longitudinal direction due to thermal expansion. 
     The aluminum plate  59  includes a bent portion  59   c  at an end in the conveyance direction. The bent portion  59   c  is inserted into a mounting hole  58   d  of the support member  58 . Similarly, the aluminum plate  60  includes a bent portion  60   c  at an end in the conveyance direction. The bent portion  60   c  is inserted into a mounting hole  58   e  of the support member  58 . The bent portions  59   c  and  60   c  are inserted into the mounting holes  58   d  and  58   e , respectively. Further, a longitudinal end of each of the bent portions  59   c  and  60   c  is brought into contact with an inner wall of the corresponding one of the mounting holes  58   d  and  58   e , so that the aluminum plates  59  and  60  are positioned in the longitudinal direction. On the other hand, the mounting holes  58   d  and  58   e  have, in view of manufacturing tolerance, a width greater than that of the bent portions  59   c  and  60   c  of the aluminum plates  59  and  60 , and thereby allowing the movement in the conveyance direction. 
     Next, a gap located at a central portion in the longitudinal direction when the thermally conductive members (aluminum plates  59  and  60 ) according to the present example embodiment thermally expand will be described with reference to  FIGS. 10A and 10B  and  FIGS. 11A and 11B .  FIG. 10A  is a sectional view illustrating the central portion in the longitudinal direction before thermal expansion in a state where the aluminum plates  59  and  60  are provided on the support member  58  below the heater  37 .  FIG. 10B  illustrates the support member  58  as viewed from the mounting surface of the heater  37  in a state where the heater  37  is omitted. 
     The bent portion  60   c  of the aluminum plate  60  has a crank shape, and includes a portion extending in a direction in which the portion enters the mounting hole  58   b  of the support member  58 , and a hooking portion  60   d , which leads to the portion and extends toward the outside (toward the aluminum plate  59 ) in the longitudinal direction. The hooking portion  60   d  overlaps a hooking portion  58   f , which is provided on the support member  58  and protrudes toward the inside of the mounting hole  58   b  in the longitudinal direction, by the amount corresponding to a width E 1  in the longitudinal direction as viewed from the mounting surface of the heater  37 . With this structure, the hooking portion  60   d  regulates the movement of the aluminum plate  60  in a direction away from the support member  58  toward the mounting surface of the heater  37 . On the other hand, the bent portion  59   b  of the aluminum plate  59  includes a hooking portion  59   d  that extends in a direction away from the heater  37  and is located at a position closer to an end than the hole  59   b   1 . The hooking portion  59   d  overlaps the hooking portion  60   d  by the amount corresponding to a width F 1  in the longitudinal direction as viewed from the mounting surface of the heater  37 . The hooking portion  60   d  is configured to engage with the hooking portion  59   d , so that the movement of the aluminum plate  59  is regulated in a direction away from the aluminum plate  60  toward the mounting surface of the heater  37 . Further, a gap with a width H 1  is provided between the aluminum plates  59  and  60  in the longitudinal direction, and thus the aluminum plates  59  and  60  are prevented from contacting each other and being deformed due to thermal expansion. A width G 1  corresponds to a portion where the heater  37  and the aluminum plates  59  and  60  are not in contact with each other in the longitudinal direction at the gap of the central portion. 
       FIG. 11A  is a sectional view illustrating the central portion in the longitudinal direction in a state where the aluminum plates  59  and  60  provided on the support member  58  thermally expand, in a state where the heater  37  is omitted.  FIG. 11B  illustrates the central portion as viewed from the mounting surface of the heater  37 . 
     When the aluminum plates  59  and  60  thermally expand, the aluminum plates  59  and  60  stretch toward the central portion from the bent portions  59   c  and  60   c  due to thermal expansion of portions having lengths L 7  and L 8 , respectively, of the aluminum plates  59  and  60 . Accordingly, as in the related art, a width G 2  of a portion, which is located at the central portion in the longitudinal direction and at which the aluminum plates  59  and  60  and the heater  37  are not in contact with each other, becomes smaller than the width G 1  before thermal expansion. Similarly, a width H 2  of a gap between the aluminum plates  59  and  60 , which is located at the central portion in the longitudinal direction, is smaller than the width H 1  of the gap before thermal expansion occurs. However, as in the related art, even when thermal expansion occurs, the gap (width H 2 ) prevents the aluminum plates  59  and  60  from contacting each other and being deformed. 
     In the structure according to the present example embodiment, the width G 1  of the area where the heater  37  and the aluminum plates  59  and  60  are not in contact with each other can be set to be smaller than the width C 1  of the area where the heater  37  and the aluminum plates  40  and  41  are not in contact with each other according to the related art. The width C 1  according to the related art is required to be set to a width greater than or equal to the total width of a width increased due to thermal expansion of the aluminum plates  40  and  41 , a width of a bent portion of the bent portion  40   b  leading to the heater contact surface of the aluminum plate  40 , and a width of a bent portion of the bent portion  41   b  leading to the heater contact surface of the aluminum plate  41 . Each bent portion is a portion where the plate material is bent. In other words, the bent portion of the bent portion  40   b  corresponds to an area where the aluminum plate  40  is opposed to the heater  37  and is not in contact with the heater  37 , and the bent portion of the bent portion  41   b  corresponds to an area where the aluminum plate  41  is opposed to the heater  37  and is not in contact with the heater  37 . However, the width G 1  according to the present example embodiment is required to be set to a width greater than or equal to the total width of a width increased due to thermal expansion of the aluminum plates  59  and  60  and a width of a bent portion of the bent portion  60   b  leading to the heater contact surface of the aluminum plate  60 . That is, in the structure according to the present example embodiment, the width G 1  can be reliably reduced by the amount corresponding to a single bent portion as compared with the width C 1  according to the related art. Thus, in the structure according to the present example embodiment, the interval between the aluminum plates  59  and  60  can be reduced as compared with the related art. In addition, the effect of leveling the temperature in a wide area of the heater  37  by the aluminum plates  59  and  60  can be obtained, and the occurrence of a defective image can be prevented. 
     An overlapping width E 2  of the hooking portion  60   d  of the aluminum plate  60  with the protrusion (hooking portion  58   f ) of the support member  58  in the longitudinal direction is greater than the overlapping width E 1  before thermal expansion. Accordingly, the function of regulating the movement of the aluminum plate  60  in a direction away from the support member  58  toward the mounting surface of the heater  37  is maintained. An overlapping width F 2  of the hooking portion  59   d  of the aluminum plate  59  with the hooking portion  60   d  of the aluminum plate  60  in the longitudinal direction is smaller than the overlapping width F 1  before thermal expansion occurs. However, the function of regulating the movement of the aluminum plate  59  in a direction away from the aluminum plate  60  toward the mounting surface of the heater  37  is maintained. That is, as in the related art, even when thermal expansion occurs, the movement of the aluminum plates  59  and  60  in a direction away from the support member  58  toward the mounting surface of the heater  37  is regulated. 
     In the present example embodiment as described above, the gap for preventing the aluminum plates from contacting each other and being deformed is secured, and the function of regulating the movement of the aluminum plates  59  and  60  in a direction away from the support member  58  toward the mounting surface of the heater  37  is secured, even when thermal expansion occurs as in the related art. In addition, in the present example embodiment, the width G 1  of the portion where the heater  37  and the aluminum plates  59  and  60  are not in contact with each other can be reduced, and the function of leveling the temperature in a wider area of the heater  37  by the aluminum plates  59  and  60  can be obtained. Furthermore, a temperature rise can be suppressed, so that the occurrence of a defective image can be prevented. 
     In the structure according to the present example embodiment as described above, the thermally conductive members adjacent to each other are disposed on the support member so that the thermally conductive members can engage with each other, and one of the thermally conductive members regulates the movement of the other one of the thermally conductive members in a direction away from the support member. Consequently, it is possible to prevent the gap between the thermally conductive members from being increased, while preventing deformation of the thermally conductive members due to the contact between the adjacent thermally conductive members. It is also possible to suppress a local temperature rise in the heating member between the thermally conductive members to thereby prevent the occurrence of a defective image. 
     The structure of the aluminum plates  59  and  60  is not limited to the structure according to the example embodiment described above, and instead can be appropriately changed by, for example, changing a structure of the contact portions of the aluminum plates  59  and  60  with the heater  37 . For example, the bent portion  59   b  may be provided with the hole  59   b   1  formed in an area including a bent portion, and the bent portion  60   b  may have a structure in which a portion that enters the hole  59   b   1  in the longitudinal direction while being in contact with the heater  37 , a portion that extends in a direction away from the heater  37 , and the hooking portion  60   d  are sequentially formed. With this structure, the width G 1  of the portion where the heater  37  and the aluminum plates  59  and  60  are not in contact with each other can be reduced, and the effect of leveling the temperature in a wider area of the heater  37  by the aluminum plates  59  and  60  can be obtained. In addition, a temperature rise is suppressed, and thus the occurrence of a defective image can be prevented. 
     A second example embodiment according to the present disclosure will be described below. An outline of a fixing device according to the second example embodiment is the same as that of the first example embodiment, and thus the description thereof is omitted and only the features of the second example embodiment will be described. 
     Aluminum plates  79  and  80  each serving as the metal plate  39  according to the present example embodiment and a method for holding the aluminum plates  79  and  80  by a support member  78  serving as the support member  58  according to the present example embodiment will be described with reference to  FIGS. 12A to 12D .  FIG. 12A  is a sectional view illustrating the aluminum plates  79  and  80  in the longitudinal direction.  FIG. 12B  illustrates a state where the aluminum plates  79  and  80  are provided on the support member  78  as viewed from the heater  37  in a state where the heater  37  is omitted.  FIG. 12C  is a perspective view illustrating engagement portions of the aluminum plates  79  and  80 .  FIG. 12D  is a perspective view illustrating a state where the aluminum plates  79  and  80  engage with each other at a central portion in the longitudinal direction. In  FIG. 12A , the illustration of the thermistor  44   a  and the thermal switch  44   b  is omitted. 
     The aluminum plates  79  and  80  and engagement portions of the aluminum plates  79  and  80  provided on the support member  78  will be described with reference to  FIGS. 12A to 12D . In the present example embodiment, the aluminum plates  79  and  80  each having a constant thickness of 0.3 mm are used. The width M in the conveyance direction of each of the contact portions of the aluminum plates  79  and  80  in contact with the heater  37  is 7 mm. A longitudinal length L 9  of the aluminum plate  79  is 101 mm, and a longitudinal length L 10  of the aluminum plate  80  is 114 mm. The aluminum plates  79  and  80  are placed with a gap formed therebetween at a central portion. 
     The aluminum plate  79  includes bent portions  79   a  and  79   b  at both ends in the longitudinal direction. The bent portions  79   a  and  79   b  are respectively inserted into mounting holes  78   a  and  78   b  of the support member  78 . In the present example embodiment, the aluminum plate  79  has a structure in which a cutaway portion is provided at an upstream portion in the conveyance direction and the bent portion  79   b  extending from a downstream portion in the conveyance direction is provided, at one end opposed to the aluminum plate  80  in the longitudinal direction. The bent portions  79   a  and  79   b  are inserted into the mounting holes  78   a  and  78   b , respectively. Further, a downstream end of each of the bent portions  79   a  and  79   b  in the conveyance direction is brought into contact with an inner wall of the mounting holes  78   a  and  78   b , respectively, so that the aluminum plate  79  is positioned in the conveyance direction. On the other hand, the mounting holes  78   a  and  78   b  have a width greater than that of the bent portions  79   a  and  79   b  of the aluminum plate  79 , and thereby allowing stretching of the aluminum plate  79  in the longitudinal direction due to thermal expansion. 
     The aluminum plate  80  includes bent portions  80   a  and  80   b  at both ends in the longitudinal direction. The bent portions  80   a  and  80   b  are respectively inserted into mounting holes  78   b  and  78   c  of the support member  78 . In the present example embodiment, the aluminum plate  80  has a structure in which a cutaway portion is provided at a downstream portion in the conveyance direction and the bent portion  80   b  extending from an upstream portion in the conveyance direction is provided, at one end opposed to the aluminum plate  79  in the longitudinal direction. The bent portion  80   a  is inserted into the mounting hole  78   c  and a downstream end of the bent portion  80   a  in the conveyance direction is brought into contact with an inner wall of the mounting hole  78   c , so that the aluminum plate  79  is positioned in the conveyance direction. The bent portion  80   b  is inserted into the mounting hole  78   b  and a downstream end of the bent portion  80   b  in the conveyance direction is brought into contact with an upstream end of the bent portion  79   b  in the conveyance direction, so that the aluminum plate  80  is positioned in the conveyance direction with respect to the aluminum plate  79 . On the other hand, the mounting holes  78   b  and  78   c  have a width greater than that of the bent portions  79   a ,  79   b ,  80   a , and  80   b  of the aluminum plates  79  and  80 , and thereby allowing stretching of the aluminum plates  79  and  80  in the longitudinal direction due to thermal expansion. 
     The aluminum plate  79  includes a bent portion  79   c  at an end in the conveyance direction. The bent portion  79   c  is inserted into a mounting hole  78   d  of the support member  78 . Similarly, the aluminum plate  80  includes a bent portion  80   c  at an end in the conveyance direction, and the bent portion  80   c  is inserted into a mounting hole  78   e  of the support member  78 . The bent portions  79   c  and  80   c  are inserted into the mounting holes  78   d  and  78   e , respectively. Further, a longitudinal end of each of the bent portions  79   c  and  80   c  is brought into contact with an inner wall of the corresponding one of the mounting holes  78   d  and  78   e , so that the aluminum plates  79  and  80  are positioned in the longitudinal direction. On the other hand, in view of manufacturing tolerance, the mounting holes  78   d  and  78   e  have a width greater than that of the bent portions  79   c  and  80   c  of the aluminum plates  79  and  80 , and thereby allowing the movement in the conveyance direction. 
     Next, a gap located at a central portion in the longitudinal direction when the aluminum plates  79  and  80  according to the present example embodiment thermally expand will be described with reference to  FIGS. 13A and 13B  and  FIGS. 14A and 14B .  FIG. 13A  is a sectional view illustrating the central portion in the longitudinal direction before thermal expansion in a state where the aluminum plates  79  and  80  are provided on the support member  78  below the heater  37 .  FIG. 13B  illustrates the support member  78  as viewed from the mounting surface of the heater  37  in a state where the heater  37  is omitted. 
     The bent portion  80   b  of the aluminum plate  80  has a crank shape, and includes a portion extending in a direction in which the portion enters the mounting hole  78   b  of the support member  78 , and a hooking portion  80   d  that leads to the portion and extends toward the outside (toward the aluminum plate  79 ) in the longitudinal direction. The hooking portion  80   d  engages with a hooking portion  78   f , which is provided on the support member  78  and protrudes toward the inside of the mounting hole  78   b  in the longitudinal direction, and overlaps with the hooking portion  78   f  by the amount corresponding to a width I 1  in the longitudinal direction as viewed from the mounting surface of the heater  37 . With this structure, the hooking portion  78   f  regulates the movement of the aluminum plate  80  in a direction away from the support member  78  toward the mounting surface of the heater  37 . On the other hand, the bent portion  79   b  of the aluminum plate  79  includes a hooking portion  79   d  extending to the upstream side in the conveyance direction from a portion farther from the hooking portion  80   d  in a direction away from the heater  37 . The hooking portion  79   d  is configured to overlap the hooking portion  80   d  as viewed from the mounting surface of the heater  37  by the amount corresponding to a width J 1  in the longitudinal direction. Thus, the hooking portion  80   d  is configured to engage with the hooking portion  79   d , so that the movement of the aluminum plate  79  is regulated in a direction away from the aluminum plate  80  toward the mounting surface of the heater  37 . A gap with a width N 1  is provided between the aluminum plates  79  and  80  in the longitudinal direction, so that the aluminum plates  79  and  80  are prevented from contacting each other and being deformed due to thermal expansion. A width K 1  corresponds to a portion where the heater  37  and the aluminum plates  79  and  80  are not in contact with each other in the longitudinal direction, at the gap of the central portion. 
       FIG. 14A  is a sectional view illustrating the central portion in the longitudinal direction in a state where the aluminum plates  79  and  80  provided on the support member  78  thermally expand, in a state where the heater  37  is omitted.  FIG. 14B  illustrates the central portion as viewed from the mounting surface of the heater  37 . 
     When the aluminum plates  79  and  80  thermally expand, the aluminum plates  79  and  80  stretch toward the central portion from the bent portions  79   c  and  80   c  due to thermal expansion of portions having lengths L 11  and L 12 , respectively, of the aluminum plates  79  and  80 . Accordingly, as in the related art, a width K 2  of a portion that is located at the central portion in the longitudinal direction and at which the heater  37  and the aluminum plates  79  and  80  are not in contact with each other is smaller than the width K 1  before thermal expansion occurs. Similarly, a width N 2  of a gap between the aluminum plates  79  and  80  that is located at the central portion in the longitudinal direction is smaller than the width N 1  of the gap before thermal expansion occurs. However, as in the related art, the gap N 2  prevents the aluminum plates  79  and  80  from contacting each other and being deformed even when thermal expansion occurs. On the other hand, in the structure according to the present example embodiment, the width K 1  of the area where the heater  37  and the aluminum plates  79  and  80  are not in contact with each other can be reduced as compared with the width C 1  of the area where the heater  37  and the aluminum plates  40  and  41  are not in contact with each other according to the related art. The width C 1  according to the related art is required to be set to a width greater than or equal to the total width of a width increased due to thermal expansion of the aluminum plates  40  and  41 , a width of a bent portion of the bent portion  40   b  leading to the heater contact surface of the aluminum plate  40 , and a width of a bent portion of the bent portion  41   b  leading to the heater contact surface of the aluminum plate  41 . Each bent portion is a portion where the plate material is bent. In other words, the bent portion of the bent portion  40   b  corresponds to an area where the aluminum plate  40  is opposed to the heater  37  and is not in contact with the heater  37 , and the bent portion of the bent portion  41   b  corresponds to an area where the aluminum plate  41  is opposed to the heater  37  and is not in contact with the heater  37 . However, the width K 1  according to the present example embodiment may be greater than or equal to the total width of a width increased due to thermal expansion of the aluminum plates  79  and  80 , and a width of a bent portion of the bent portion  79   b  leading to the heater contact surface of the aluminum plate  79  or a width of a bent portion of the bent portion  80   b  leading to the heater contact surface of the aluminum plate  80 . That is, in the structure according to the present example embodiment, the width K 1  can be reliably reduced by the amount corresponding to a single bent portion as compared with the width C according to the related art. Consequently, in the structure according to the present example embodiment, the interval between the aluminum plates  79  and  80  can be reduced as compared with the related art, and the effect of leveling the temperature in a wider area of the heater  37  by using the aluminum plates  79  and  80  can be obtained. In addition, a temperature rise is suppressed, and thus the occurrence of a defective image can be prevented. 
     An overlapping width  12  of the support member  78  of the hooking portion  80   d  of the aluminum plate  80  with the protrusion (hooking portion  78   f ) of the support member  78  in the longitudinal direction is greater than the overlapping width I 1  before thermal expansion occurs. Accordingly, the function of regulating the movement of the aluminum plate  80  in a direction away from the support member  78  toward the mounting surface of the heater  37  is maintained. Further, an overlapping width J 2  of the hooking portion  79   d  of the aluminum plate  79  with the hooking portion  80   d  of the aluminum plate  80  in the longitudinal direction is smaller than the overlapping width J 1  before thermal expansion occurs. However, the function of regulating the movement of the aluminum plate  79  in a direction away from the aluminum plate  80  toward the mounting surface of the heater  37  is maintained. That is, as in the related art, the movement of the aluminum plates  79  and  80  in a direction away from the support member  78  toward the mounting surface of the heater  37  is regulated even when thermal expansion occurs. 
     As described above in the present example embodiment, even when thermal expansion occurs, the gap for preventing the aluminum plates from contacting each other and being deformed is secured and the function of regulating the movement of the aluminum plates  79  and  80  in a direction away from the support member  78  toward the mounting surface of the heater  37  is secured, as in the related art. In addition, in the present example embodiment, it is possible to reduce the width K 1  of the portion where the heater  37  and the aluminum plates  79  and  80  are not in contact with each other, and it is also possible to obtain the effect of leveling the temperature in a wide area of the heater  37  by using the aluminum plates  79  and  80 , and thus the occurrence of a defective image can be prevented. 
     As described above, in the structure according to the example embodiments, the thermally conductive members adjacent to each other are disposed on the support member so that the thermally conductive members can engage with each other, and one of the thermally conductive members regulates the movement of the other one of the thermally conductive members in a direction away from the support member. Consequently, it is possible to prevent the gap between the thermally conductive members from being increased, while preventing deformation of the thermally conductive members due to the contact between the adjacent thermally conductive members. Therefore, it is possible to suppress a local temperature rise in the heating member between the thermally conductive members and prevent the occurrence of a defective image. 
     The structure of the aluminum plates  79  and  80  is not limited to the structure according to the example embodiments described above, but instead can be appropriately changed by, for example, changing the contact portions of the aluminum plates  59  and  60  with the heater  37 . For example, the aluminum plates  79  and  80  may have a structure in which a cutaway portion extending in the longitudinal direction is provided, and a contact surface of the bent portion  79   b  that contacts the heater  37  and a contact surface of the bent portion  80   b  that contacts the heater  37  may be arranged side by side in the conveyance direction. With this structure, the width N 1  of the portion where the heater  37  and the aluminum plates  79  and  80  are not in contact with each other can be reduced to “0”. Accordingly, the effect of leveling the temperature in a wider area of the heater  37  by the aluminum plates  79  and  80  can be obtained, and a temperature rise is suppressed. Thus, the occurrence of a defective image is prevented. 
     While the present disclosure has been described with reference to example embodiments, it is to be understood that the disclosure is not limited to the disclosed example 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. 2019-093232, filed May 16, 2019, which is hereby incorporated by reference herein in its entirety.