Patent Publication Number: US-11048200-B2

Title: Guide structure and image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2018-137962 filed Jul. 23, 2018. 
     BACKGROUND 
     (i) Technical Field 
     The present disclosure relates to a guide structure and an image forming apparatus. 
     (ii) Related Art 
     Japanese Unexamined Patent Application Publication No. 2006-003404 describes an image forming apparatus including a fixing unit and a negative-pressure transport belt. The fixing unit fixes a toner image formed on a paper sheet to the paper sheet by heating the toner image. The negative-pressure transport belt, which is disposed downstream of the fixing unit along a sheet transport path, transports the paper sheet further downstream while the toner image that has been heated and fixed by the fixing unit does not come into contact with a certain member. 
     SUMMARY 
     A guide member for guiding the recording medium from the fixing unit to a transport roller unit, which discharges the recording medium to the outside of the apparatus, is provided between the fixing unit and the transport roller unit. According to the related art, the guide member is made of a resin material, and guides the recording medium to the transport roller unit by coming into contact with the recording medium to which an image has been fixed by the fixing unit. 
     The recording medium is heated to a high temperature in the region where the image has been fixed thereto by the fixing unit. When the recording medium comes into contact with the transport roller unit while the temperature thereof is high, contact marks, or “roller marks”, are formed on the image on the recording medium due to contact with the transport roller unit. 
     Aspects of non-limiting embodiments of the present disclosure relate to a technology for making the occurrence of contact marks on an image formed on a recording medium due to contact with a transport roller unit less than that in the case where guide members that guide the recording medium from a fixing unit to the transport roller unit are made of materials having similar thermal conductivities over the entirety thereof. 
     Aspects of certain non-limiting embodiments of the present disclosure overcome the above disadvantages and/or other disadvantages not described above. However, aspects of the non-limiting embodiments are not required to overcome the disadvantages described above, and aspects of the non-limiting embodiments of the present disclosure may not overcome any of the disadvantages described above. 
     According to an aspect of the present disclosure, there is provided a guide structure including a first guide member that guides a recording medium from a fixing unit to a transport roller unit, the fixing unit fixing an image formed on the recording medium to the recording medium by heating the recording medium that is transported, the transport roller unit transporting the recording medium; and a second guide member that comes into contact with the recording medium to which the image has been fixed by the fixing unit and guides the recording medium to the transport roller unit, the second guide member being disposed downstream of the first guide member in a transporting direction in which the recording medium is transported and being made of a material having a thermal conductivity higher than a thermal conductivity of a material of the first guide member. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the present disclosure will be described in detail based on the following figures, wherein: 
         FIG. 1  is a side view of a guide structure according to a first exemplary embodiment of the present disclosure; 
         FIGS. 2A, 2B, and 2C  illustrate the manner in which the guide structure according to the first exemplary embodiment of the present disclosure guides a sheet member; 
         FIGS. 3A, 3B, and 3C  illustrate the manner in which the guide structure according to the first exemplary embodiment of the present disclosure guides a sheet member; 
         FIGS. 4A, 4B, and 4C  illustrate the manner in which the guide structure according to the first exemplary embodiment of the present disclosure guides a sheet member; 
         FIGS. 5A, 5B, and 5C  illustrate the manner in which the guide structure according to the first exemplary embodiment of the present disclosure guides a sheet member; 
         FIGS. 6A, 6B, and 6C  illustrate the manner in which the guide structure according to the first exemplary embodiment of the present disclosure guides a sheet member; 
         FIG. 7  is a perspective view of a first guide member included in the guide structure according to the first exemplary embodiment of the present disclosure; 
         FIG. 8  is a perspective view of a second guide member included in the guide structure according to the first exemplary embodiment of the present disclosure; 
         FIG. 9  illustrates an image forming unit included in an image forming apparatus according to the first exemplary embodiment of the present disclosure; 
         FIG. 10  illustrates the image forming apparatus according to the first exemplary embodiment of the present disclosure; 
         FIG. 11  is a perspective view of a first guide member included in a guide structure according to a second exemplary embodiment of the present disclosure; and 
         FIG. 12  is a perspective view of fans and a second guide member included in the guide structure according to the second exemplary embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     First Exemplary Embodiment 
     An example of a guide structure and an image forming apparatus according to a first exemplary embodiment of the present disclosure will be described with reference to  FIGS. 1 to 10 . In the drawings, arrow H indicates an apparatus up-down direction (vertical direction), arrow W an apparatus width direction (horizontal direction), and arrow D an apparatus depth direction (horizontal direction). 
     Image Forming Apparatus  10   
     As illustrated in  FIG. 10 , an image forming apparatus  10  includes a storage unit  14 , a transport unit  16 , and an image forming section  20 , which are arranged in that order from the bottom toward the top in the up-down direction. The storage unit  14  stores sheet members P, which serve as recording media. The transport unit  16  transports the sheet members P stored in the storage unit  14 . The image forming section  20  forms images on the sheet members P transported from the storage unit  14  by the transport unit  16 . The image forming apparatus  10  also includes a controller  44  that controls each unit. 
     Storage Unit 
     The storage unit  14  includes a storage member  26  that may be pulled forward from an apparatus body  10   a  of the image forming apparatus  10  in the apparatus depth direction. The sheet members P are stacked on the storage member  26 . The storage unit  14  also includes a feed roller  30  that feeds the top sheet member P of the stack on the storage member  26  to a transport path  28 , which is included in the transport unit  16 . 
     Transport Unit 
     The transport unit  16  includes plural transport roller units  32  that transport the sheet member P along the transport path  28 , and a discharge roller unit  48  that discharges the sheet member P to the outside of the apparatus body  10   a  along the transport path  28  after a toner image is formed on the sheet member P. The discharge roller unit  48  is an example of a transport roller unit. 
     The transport unit  16  also includes a guide structure  60  that guides the sheet member P to which the toner image has been fixed by a fixing unit  34 , which will be described below, toward the discharge roller unit  48 . The discharge roller unit  48  and the guide structure  60  will be described in detail below. 
     Image Forming Section 
     The image forming section  20  includes four image forming units  18 Y,  18 M,  18 C, and  18 K, which are yellow (Y), magenta (M), cyan (C), and black (K) image forming units, respectively. In the following description, the characters Y, M, C, and K may be omitted when it is not necessary to distinguish between Y, M, C, and K. 
     As illustrated in  FIG. 9 , each image forming unit  18  includes an image carrier  36  that carries an image and a charging roller  38  that charges the peripheral surface of the image carrier  36 . Each image forming unit  18  also includes an exposure device  42  that irradiates the charged peripheral surface of the image carrier  36  with exposure light to form an electrostatic latent image and a developing device  40  that develops and visualizes the electrostatic latent image into a toner image. 
     As illustrated in  FIG. 10 , the image forming section  20  also includes an endless transfer belt  22  to which the toner images formed by the image forming units  18  of the respective colors are transferred and first transfer rollers  24  that transfer the toner images formed by the image forming units  18  onto the transfer belt  22 . The image forming section  20  also includes a second transfer roller  46  that transfers the toner images that have been transferred to the transfer belt  22  onto the sheet member P. The image forming section  20  also includes the fixing unit  34  that fixes the toner image on the sheet member P to the sheet member P by heating and pressing the toner image. The structure of the fixing unit  34  will be described in detail below. 
     Operation of Image Forming Apparatus 
     The image forming apparatus  10  forms an image in the following manner. 
     First, the charging rollers  38  of the respective colors, to which a voltage is applied, come into contact with the peripheral surfaces of the image carriers  36  of the respective colors and uniformly charge the peripheral surfaces of the image carriers  36  to a predetermined negative potential. Subsequently, the exposure devices  42  of the respective colors form electrostatic latent images by irradiating the charged peripheral surfaces of the image carriers  36  of the respective colors with exposure light based on data input from the outside. 
     Thus, the electrostatic latent images corresponding to the image data are formed on the peripheral surfaces of the mage carriers  36 . The developing devices  40  of the respective colors develop and visualize the electrostatic latent images into toner images. The first transfer rollers  24  transfer the toner images formed on the peripheral surfaces of the image carriers  36  of the respective colors onto the transfer belt  22 . 
     The feed roller  30  feeds the top sheet member P of the stack on the storage member  26  toward a transfer position T, at which the transfer belt  22  and the second transfer roller  46  are in contact with each other, along the transport path  28 . The second transfer roller  46  and the transfer belt  22  transport the sheet member P while nipping the sheet member P therebetween at the transfer position T, so that the toner image on the peripheral surface of the transfer belt  22  is transferred to the sheet member P. 
     The fixing unit  34  fixes the toner image that has been transferred to the sheet member P to the sheet member P. The sheet member P to which the toner image is fixed is discharged to the outside of the apparatus body  10   a  by the discharge roller unit  48 . 
     Relevant Structure 
     The discharge roller unit  48 , the fixing unit  34 , and the guide structure  60  according to the present exemplary embodiment will now be described. 
     Discharge Roller Unit  48   
     As illustrated in  FIG. 1 , the discharge roller unit  48  includes a first roller  52  and a second roller  54 . 
     The first roller  52  includes a shaft  52   a  that extends in the apparatus depth direction and plural roller portions  52   b  that are cylindrical and through which the shaft  52   a  extends. The roller portions  52   b  are arranged with similar gaps therebetween, and both end portions of the shaft  52   a  are supported by support members (not shown) so that the first roller  52  is rotatable. 
     The second roller  54  faces the first roller  52  with the transport path  28 , along which the sheet member P is transported, disposed therebetween. More specifically, the second roller  54  is disposed below the first roller  52  and faces the first roller  52  with the transport path  28 , along which the sheet member P is transported, disposed therebetween. Thus, a portion of the transport path  28  along which the sheet member P is transported by the first roller  52  and the second roller  54  extends in the apparatus width direction when viewed in the apparatus depth direction. 
     The second roller  54  includes a shaft  54   a  that extends in the apparatus depth direction and plural roller portions  54   b  that are cylindrical and through which the shaft  54   a  extends. The roller portions  54   b  are arranged with similar gaps therebetween, and are in contact with the roller portions  52   b . A rotational force is transmitted to the shaft  54   a  from a driving member (not shown), so that the second roller  54  is rotated in the direction of arrow F 1  and the first roller  52  is rotated by the second roller  54  in the direction of arrow F 2 . 
     According to the present exemplary embodiment, the transport speed at which the discharge roller unit  48  transports the sheet member P is lower than the transport speed at which the fixing unit  34  transports the sheet member P. The transport speed at which the discharge roller unit  48  transports the sheet member P is, for example, 99% of the transport speed at which the fixing unit  34  transports the sheet member P. 
     Fixing Unit  34   
     As illustrated in  FIG. 1 , when viewed in the apparatus depth direction, the fixing unit  34  is disposed on one side of the discharge roller unit  48  (same side as the second transfer roller  46  in  FIG. 10 ) in the apparatus width direction and below the discharge roller unit  48 . The distance from the fixing unit  34  to the discharge roller unit  48  along the transport path  28  in the transporting direction in which the sheet member P is transported is set such that the sheet member P that is being transported by the fixing unit  34  may also be transported by the discharge roller unit  48 . In other words, the sheet member P may simultaneously receive a transporting force applied by the fixing unit  34  and a transporting force applied by the discharge roller unit  48 . The fixing unit  34  includes a heating roller  58  that heats the sheet member P and a pressing roller  56  that presses the sheet member P against the heating roller  58 . 
     Pressing Roller  56   
     The pressing roller  56  is disposed on the same side of the transport path  28 , along which the sheet member P is transported, as the side on which the second transfer roller  46  is disposed (see  FIG. 10 ). The pressing roller  56  includes a shaft  56   a  that extends in the apparatus depth direction, a cylindrical rubber portion  56   b , and a coating (not shown) that covers the rubber portion  56   b.    
     The shaft  56   a  extends through the rubber portion  56   b , and both end portions of the shaft  56   a  project from the rubber portion  56   b . The end portions of the shaft  56   a  are supported by support members (not shown) so that the pressing roller  56  is rotatable, and the support members are urged by urging members so that the pressing roller  56  is urged against the heating roller  58 . Accordingly, the pressing roller  56  presses the sheet member P that is transported against the heating roller  58 . More specifically, the pressing roller  56  comes into contact with a non-image surface (surface on which no toner image is formed) of the sheet member P that is transported and presses the sheet member P against the heating roller  58 . 
     Heating Roller  58   
     As illustrated in  FIG. 1 , the heating roller  58  faces the pressing roller  56  with the transport path  28 , along which the sheet member P is transported, disposed therebetween. More specifically, the heating roller  58  is disposed on the other side of the pressing roller  56  (same side as the discharge roller unit  48 ) in the apparatus width direction and below the pressing roller  56 . Thus, the line tangent to a portion of the transport path  28  along which the sheet member P is transported by the heating roller  58  and the pressing roller  56  is inclined upward in the up-down direction and toward the discharge roller unit  48  when viewed in the apparatus depth direction. 
     The portion of the transport path  28  between the fixing unit  34  and the discharge roller unit  48  is curved such that the side thereof facing the pressing roller  56  is convex when viewed in the apparatus depth direction. 
     The heating roller  58  includes a cylindrical shaft  58   a  that extends in the apparatus depth direction, a coating (not shown) that covers the shaft  58   a , and a heating portion  58   b  disposed in the shaft  58   a . In this configuration, the surface temperature of the heating roller  58  is, for example, 190° C. 
     A rotational force is transmitted to the heating roller  58  from a driving member (not shown), so that the heating roller  58  is rotated in the direction of arrow E 1  and the pressing roller  56  is rotated by the heating roller  58  in the direction of arrow E 2 . 
     In the present exemplary embodiment, the transport speed at which the fixing unit  34  transports the sheet member P is, for example, 60 mm/s, and the transport speed at which the above-described discharge roller unit  48  transports the sheet member P is, for example, 59.4 mm/s. 
     Guide Structure  60   
     As illustrated in  FIG. 1 , the guide structure  60  is disposed between the fixing unit  34  and the discharge roller unit  48  in the transporting direction of the sheet member P. The guide structure  60  guides the sheet member P on which the toner image has been fixed by the fixing unit  34  toward the discharge roller unit  48 . The guide structure  60  includes a first guide member  62 , a second guide member  72 , and a third guide member  82 . The first guide member  62  and the second guide member  72  are disposed on the same side of the transport path  28  as the side on which the pressing roller  56  is disposed. The third guide member  82  is disposed on the same side of the transport path  28  as the side on which the heating roller  58  is disposed. In other words, the first guide member  62  and the second guide member  72  face the non-image surface of the sheet member P that is transported, and the third guide member  82  faces an image surface (surface on which the toner image is formed) of the sheet member P that is transported. 
     The first guide member  62  is disposed adjacent to the fixing unit  34 , and the second guide member  72  is disposed adjacent to the discharge roller unit  48 . In other words, the first guide member  62  and the second guide member  72  are arranged in that order in the transporting direction of the sheet member P from the upstream side toward the downstream side. 
     First Guide Member  62   
     As illustrated in  FIG. 1 , the first guide member  62  is spaced from the fixing unit  34  in the transporting direction of the sheet member P. The first guide member  62  is made of acrylonitrile-butadiene-styrene resin (hereinafter referred to as “ABS resin”), which is an example of a resin material, and includes a flat plate-shaped plate portion  64  and plural ribs  66  that project from the plate portion  64  toward the transport path  28 . The ABS resin has a thermal conductivity of 0.25 W/mK. The plate portion  64  is an example of a plate member, and the ribs  66  are an example of a projecting portion. 
     When viewed in the apparatus depth direction, the plate portion  64  is inclined upward in the up-down direction and toward the discharge roller unit  48  along the transport path  28 . In addition, when viewed in the thickness direction of the plate portion  64 , the plate portion  64  has a rectangular shape that extends in the apparatus depth direction (width direction of the sheet member P) to cover the transported sheet member P in the apparatus depth direction (see  FIG. 7 ). 
     The plate portion  64  has a front surface  64   a  that faces the transport path  28  and a back surface  64   b  that is opposite to the front surface  64   a  and that faces away from the sheet member P that is transported. The ribs  66  are formed on the front surface  64   a  of the plate portion  64 . 
     The ribs  66  project from the front surface  64   a  of the plate portion  64  toward the sheet member P that is transported, and extend in the transporting direction of the sheet member P (see  FIG. 7 ). Each rib  66  has a rectangular shape that extends in the thickness direction of the plate portion  64  in cross section taken in a direction that crosses the longitudinal direction of the rib  66 . The ribs  66  are arranged in a direction (apparatus depth direction) that crosses the transporting direction of the sheet member P. The ribs  66  are provided to reduce the contact area between the first guide member  62  and the sheet member P that is transported, and at least include ribs  66  that come into contact with the end portions of the sheet member P that is transported and a rib  66  that supports a central portion of the sheet member P. The ribs  66  function as contact-area-reducing members for reducing the contact area between the first guide member  62  and the sheet member P that is transported. 
     In this configuration, the leading end of the sheet member P that is transported while being nipped between the pressing roller  56  and the heating roller  58  may be curved (curled) toward the first guide member  62 . In such a case, as illustrated in  FIGS. 2A, 2B, and 2C , the leading end of the sheet member P comes into contact with the ends of the ribs  66  of the first guide member  62 . The sheet member P moves downstream in the transporting direction while the leading end thereof is in contact with the ends of the ribs  66 . Thus, the first guide member  62  guides the sheet member P toward the discharge roller unit  48 . 
     Second Guide Member  72   
     As illustrated in  FIG. 1 , when viewed in the apparatus depth direction, the second guide member  72  is spaced from the first guide member  62  in a direction along the plate surface of the plate portion  64  of the first guide member  62 . Here, the expression “spaced in a direction along the plate surface” means that the second guide member  72  does not overlap the first guide member  62  in the plate thickness direction. The second guide member  72  is composed of a stainless steel plate, which is an example of a metal material, and includes a flat plate-shaped plate portion  74  and plural heat dissipation plates  76  that project from the plate portion  74  in a direction away from the transport path  28 . The stainless steel has a thermal conductivity of 18 W/mK, which is higher than that of the ABS resin. Accordingly, heat more easily transfers in the second guide member  72  than in the first guide member  62 . More specifically, the second guide member  72  more easily receives heat from the outside and dissipates heat to the outside than does the first guide member  62 . In other words, the material of the second guide member  72  has higher thermal emissivity and absorptivity than those of the material of the first guide member  62 . The heat dissipation plates  76  are an example of a heat dissipating unit. 
     The plate portion  74  extends in the apparatus width direction when viewed in the apparatus depth direction. When viewed in the thickness direction of the plate portion  74 , the plate portion  74  has a rectangular shape that extends in the apparatus depth direction (width direction of the sheet member P) to cover the transported sheet member P in the apparatus depth direction (see  FIG. 8 ). 
     The plate portion  74  includes a contact surface  74   a  that faces the transport path  28  and comes into contact with the sheet member P that is transported and a non-contact surface  74   b  that is opposite to the contact surface  74   a  and that does not come into contact with the sheet member P that is transported. The position of the contact surface  74   a  in the up-down direction is similar to the position of the contact portion between the first roller  52  and the second roller  54  of the discharge roller unit  48  in the up-down direction. The heat dissipation plates  76  are formed on the non-contact surface  74   b  (see  FIG. 8 ). 
     The heat dissipation plates  76  have plate surfaces that face in the transporting direction of the sheet member P. The heat dissipation plates  76  extend in the width direction of the sheet member P that is transported (apparatus depth direction). The heat dissipation plates  76  are arranged in the transporting direction of the sheet member P (see  FIG. 8 ). To dissipate heat from the second guide member  72  and to increase the flexural rigidity of the second guide member  72  when viewed in the transporting direction of the sheet member P, the heat dissipation plates  76  may extend in the width direction of the sheet member P within a limited range. More specifically, when the length of the plate portion  74  in the width direction of the sheet member P is 100, the length of the heat dissipation plates  76  may be greater than or equal to 70, and is preferably greater than or equal to 80. Thus, the heat dissipation plates  76  also function as reinforcing members for increasing the flexural rigidity of the second guide member  72 . 
     In this configuration, the leading end of the sheet member P guided toward the discharge roller unit  48  by the first guide member  62  comes into contact with the contact surface  74   a  of the plate portion  74  of the second guide member  72 , as illustrated in  FIGS. 3A, 3B, and 3C . The sheet member P moves downstream in the transporting direction of the sheet member P while the leading end thereof is in contact with the contact surface  74   a . Thus, the second guide member  72  guides the sheet member P toward the discharge roller unit  48 . 
     The second guide member  72  receives heat from the sheet member P, and the heat dissipation plates  76  dissipate heat from the second guide member  72 . 
     The sheet member P that is transported while being nipped between the pressing roller  56  and the heating roller  58  may have a leading end that is not curled. In such a case, according to the present exemplary embodiment, when viewed in the apparatus depth direction, the angle ( 01  in  FIG. 1 ) between the contact surface  74   a  of the second guide member  72  and the sheet member P in such a state that the leading end thereof is in contact with the contact surface  74   a  is less than or equal to 60 degrees. To enable the sheet member P to move along the contact surface  74   a , the angle θ 1  may be less than or equal to 55 degrees, and is preferably less than or equal to 50 degrees. 
     Third Guide Member  82   
     As illustrated in  FIG. 1 , when viewed in the apparatus depth direction, the third guide member  82  faces the first guide member  62  and the second guide member  72  with the transport path  28  disposed therebetween. The third guide member  82  is made of ABS resin, which is an example of a resin material, and is curved along the transport path  28  when viewed in the apparatus depth direction. The third guide member  82  has a curved surface  82   a  that faces the transport path  28 . 
     In this configuration, the leading end of the sheet member P that is transported while being nipped between the pressing roller  56  and the heating roller  58  may be curved (curled) toward the third guide member  82 . In such a case, as illustrated in  FIGS. 4A, 4B, and 4C , the leading end of the sheet member P comes into contact with the curved surface  82   a  of the third guide member  82 . Then, the sheet member P moves downstream in the transporting direction while the leading end thereof is in contact with the curved surface  82   a . Thus, the third guide member  82  guides the sheet member P toward the discharge roller unit  48 . 
     The leading end of the sheet member P guided toward the discharge roller unit  48  by the third guide member  82  comes into contact with the contact surface  74   a  of the plate portion  74  of the second guide member  72 , as illustrated in  FIGS. 5A, 5B, and 5C . The sheet member P moves downstream in the transporting direction of the sheet member P while the leading end thereof is in contact with the contact surface  74   a . Thus, the second guide member  72  guides the sheet member P toward the discharge roller unit  48 . 
     Operation of Relevant Structure 
     The operation of the relevant structure according to the present exemplary embodiment will now be described. 
     After the toner image is transferred to the image surface of the sheet member P, the sheet member P is transported to the fixing unit  34 , as illustrated in  FIGS. 2A and 4A . Then, the heating roller  58  and the pressing roller  56  of the fixing unit  34  rotate and nip the leading end of the sheet member P. The pressing roller  56  presses the sheet member P against the heating roller  58 , and the heating roller  58  heats the sheet member P. Thus, the heating roller  58  heats the sheet member P pressed thereagainst by the pressing roller  56  to, for example, about 100° C., so that the toner image is fixed to the sheet member P. 
     The leading end of the sheet member P that is transported while being nipped between the pressing roller  56  and the heating roller  58  may be curved (curled) toward the first guide member  62 . In such a case, as illustrated in  FIGS. 2B, and 2C , the leading end of the sheet member P comes into contact with the ends of the ribs  66  of the first guide member  62 . The sheet member P moves downstream in the transporting direction while the leading end thereof is in contact with the ends of the ribs  66 . Thus, the first guide member  62  guides the sheet member P toward the discharge roller unit  48 . 
     The leading end of the sheet member P that is transported while being nipped between the pressing roller  56  and the heating roller  58  may instead be curved (curled) toward the third guide member  82 . In such a case, as illustrated in  FIGS. 4B and 4C , the leading end of the sheet member P comes into contact with the curved surface  82   a  of the third guide member  82 . Then, the sheet member P moves downstream in the transporting direction while the leading end thereof is in contact with the curved surface  82   a . Thus, the third guide member  82  guides the sheet member P toward the discharge roller unit  48 . 
     The sheet member P that has been guided toward the discharge roller unit  48  by the first guide member  62  or the third guide member  82 , or that has been guided toward the discharge roller unit  48  without coming into contact with the first guide member  62  or the third guide member  82 , moves further downstream. 
     As illustrated in  FIGS. 3A and 5A , the leading end of the sheet member P comes into contact with the contact surface  74   a  of the plate portion  74  of the second guide member  72 . Then, the sheet member P moves further downstream in the transporting direction of the sheet member P while the leading end thereof is in contact with the contact surface  74   a . Thus, the second guide member  72  guides the sheet member P toward the discharge roller unit  48 . As illustrated in  FIGS. 3B, 3C, 5B, and 5C , the sheet member P is guided by the second guide member  72  while the non-image surface thereof on which no toner image is formed is in contact with the second guide member  72 . Then, the leading end of the sheet member P is nipped between the first roller  52  and the second roller  54  of the discharge roller unit  48 , and the discharge roller unit  48  starts to transport the sheet member P. More specifically, the discharge roller unit  48  starts to transport the sheet member P while sheet member P is transported by the fixing unit  34 . 
     As described above, the transport speed at which the discharge roller unit  48  transports the sheet member P is lower than the transport speed at which the fixing unit  34  transports the sheet member P. Therefore, as illustrated in  FIGS. 6A, 6B, and 6C , the sheet member P is transported while a portion thereof between the fixing unit  34  and the discharge roller unit  48  is bent toward the second guide member  72 . 
     Since the sheet member P is bent toward the second guide member  72 , the contact area between the sheet member P and the second guide member  72  is greater than that in the case where the transport speed at which the discharge roller unit  48  transports the sheet member P is similar to the transport speed at which the fixing unit  34  transports the sheet member P. 
     The second guide member  72  receives heat of the sheet member P from a portion of the sheet member P that is in contact with the second guide member  72 , and the heat dissipation plates  76  of the second guide member  72  dissipate heat from the second guide member  72 . The discharge roller unit  48  discharges the sheet member P to the outside of the apparatus body  10   a  by transporting the sheet member P while the sheet member P is continuously in contact with the second guide member  72 . 
     SUMMARY 
     As described above, the guide structure  60  is configured such that the thermal conductivity of the material of the second guide member  72  adjacent to the discharge roller unit  48  is higher than that of the material of the first guide member  62  adjacent to the fixing unit  34 . In other words, the thermal conductivity of the material of the first guide member  62  adjacent to the fixing unit  34  is lower than that of the material of the second guide member  72  adjacent to the discharge roller unit  48 . 
     Therefore, the amount of heat generated by the fixing unit  34  and transferred to the second guide member  72  through the first guide member  62  is less than that in the case where the thermal conductivity of the material of the first guide member  62  adjacent to the fixing unit  34  is similar to that of the material of the second guide member  72 . Also, the amount of heat which the second guide member  72  receives from the sheet member P is greater than that in the case where the thermal conductivity of the material of the second guide member  72  adjacent to the discharge roller unit  48  is similar to that of the material of the first guide member  62 . 
     Thus, according to the guide structure  60 , the temperature of the sheet member P transported toward the discharge roller unit  48  is lower than that in the case where the thermal conductivity of the material of the first guide member  62  is similar to that of the material of the second guide member  72 . When the temperature of the sheet member P is reduced, the toner image formed on the sheet member P are solidified, so that contact marks (so-called “roller marks”) due to contact with the discharge roller unit  48  are not easily formed on the toner image on the sheet member P. 
     To summarize, the occurrence of contact marks on the toner image formed on the sheet member P due to contact with the discharge roller unit  48  is less than that in the case where guide members that guide the sheet member P from the fixing unit  34  to the discharge roller unit  48  are made of materials having similar thermal conductivities over the entirety thereof. 
     In addition, the guide structure  60  is configured such that the first guide member  62  is made of a resin material and the second guide member  72  is made of a metal material. Therefore, the amount of heat generated by the fixing unit  34  and transferred to the second guide member  72  through the first guide member  62  is less than that in the case where the first guide member  62  and the second guide member  72  are both made of a metal material. Also, the amount of heat which the second guide member  72  receives from the sheet member P is greater than that in the case where the first guide member  62  and the second guide member  72  are both made of a resin material. 
     To summarize, the temperature of the sheet member P is lower than that in the case where the first guide member  62  and the second guide member  72  are both made of a metal material or that in the case where the first guide member  62  and the second guide member  72  are both made of a resin material. Accordingly, the occurrence of contact marks on the toner image formed on the sheet member P due to contact with the discharge roller unit  48  is reduced. 
     In addition, the guide structure  60  is configured such that the heat dissipation plates  76  dissipate heat from the second guide member  72 . Therefore, the temperature of the sheet member P that is in contact with the second guide member  72  is lower than that in the case where the heat of the second guide member  72  is accumulated in the second guide member  72  (in the case where the second guide member  72  includes only the plate portion). Accordingly, the occurrence of contact marks on the toner image formed on the sheet member P due to contact with the discharge roller unit  48  is reduced. 
     In addition, the guide structure  60  is configured such that the plate surfaces of the heat dissipation plates  76  face in the transporting direction of the sheet member P and that the heat dissipation plates  76  extend in the width direction of the sheet member P that is transported (apparatus depth direction). Therefore, the amount by which the plate portion  74  of the second guide member  72  is bent when viewed in the transporting direction of the sheet member P is less than that in the case where the plate surfaces of the heat dissipation plates face in the width direction of the sheet member P. 
     In addition, the guide structure  60  is configured such that the first guide member  62  and the second guide member  72  are spaced from each other. Therefore, the amount of heat transferred to the second guide member  72  through the first guide member  62  is less than that in the case where the first guide member  62  and the second guide member  72  are in contact with each other. Accordingly, the occurrence of contact marks on the toner image formed on the sheet member P due to contact with the discharge roller unit  48  is reduced. 
     In addition, the guide structure  60  is configured such that the first guide member  62  and the second guide member  72  are spaced from each other in a direction along the plate surface of the plate portion  64  of the first guide member  62  when viewed in the apparatus depth direction. Therefore, the amount of heat transferred to the second guide member  72  through the first guide member  62  is less than that in the case where the first guide member and the second guide member overlap in the thickness direction of the plate portion of the first guide member. Accordingly, the occurrence of contact marks on the toner image formed on the sheet member P due to contact with the discharge roller unit  48  is reduced. 
     In addition, the guide structure  60  is configured such that the ribs  66  are formed on the front surface  64   a  of the plate portion  64  of the first guide member  62 . Therefore, the contact area between the sheet member P and the first guide member  62  is less than that in the case where the first guide member includes only the plate portion. Thus, the amount of heat which the sheet member P receives from the first guide member  62  is reduced. Accordingly, an increase in the temperature of the sheet member P is suppressed, so that the occurrence of contact marks on the toner image formed on the sheet member P due to contact with the discharge roller unit  48  is reduced. 
     In addition, the guide structure  60  is configured such that the ribs  66  extend in the transporting direction of the sheet member P. Therefore, unlike the case in which the ribs extend in the width direction of the sheet member P that is transported, the movement of the sheet member P is not hindered. 
     According to the image forming apparatus  10 , the occurrence of contact marks on the toner image formed on the sheet member P due to contact with the discharge roller unit  48  is less than that in the case where the materials of all of the guide members have similar thermal conductivities. Accordingly, reduction in quality of the output image is suppressed. 
     In addition, according to the image forming apparatus  10 , the transport speed at which the discharge roller unit  48  transports the sheet member P is lower than the transport speed at which the fixing unit  34  transports the sheet member P. Accordingly, the sheet member P is transported while being bent toward the second guide member  72 , so that the contact area between the sheet member P and the second guide member  72  is increased. As a result, the temperature of the sheet member P is reduced. Accordingly, the occurrence of contact marks on the toner image formed on the sheet member P due to contact with the discharge roller unit  48  is reduced, and reduction in quality of the output image is suppressed. 
     In addition, according to the image forming apparatus  10 , the portion of the transport path  28  between the fixing unit  34  and the discharge roller unit  48  is curved such that the side thereof facing the pressing roller  56  is convex when viewed in the apparatus depth direction. The second guide member  72  is disposed on the convex side. Accordingly, the sheet member P that is transported more easily comes into contact with the second guide member  72  than in the case where the second guide member is disposed on the concave side. 
     Second Exemplary Embodiment 
     An example of a guide structure and an image forming apparatus according to a second exemplary embodiment of the present disclosure will now be described with reference to  FIGS. 11 and 12 . Differences between the first and second exemplary embodiments will be basically described. 
     Structure 
     Referring to  FIG. 11 , a guide structure  160  according to the second exemplary embodiment includes a first guide member  162 . The first guide member  162  is made of ABS resin, and includes a flat plate-shaped plate portion  64  and plural projections  166  that project toward the transport path  28  (see  FIG. 1 ) from a front surface  64   a  of the plate portion  64 . 
     The projections  166  are hemispherical, and plural projections  166  are provided in the transporting direction of the sheet member P and in the width direction of the sheet member P. In the present exemplary embodiment, the projections  166  are arranged in the transporting direction of the sheet member P and in the width direction of the sheet member P. 
     Referring to  FIG. 12 , the guide structure  160  also includes a second guide member  172 . The second guide member  172  is formed of a stainless steel plate, and includes a flat plate-shaped plate portion  74 . The guide structure  160  also includes plural fans  180  that are arranged in the apparatus depth direction above the second guide member  172 . The fans  180  blow air toward a non-contact surface  74   b  of the plate portion  74 . The fans  180  are an example of a blowing member. 
     SUMMARY 
     As described above, the projections  166  are formed on the front surface  64   a  of the plate portion  64  of the first guide member  162 . Therefore, the amount by which the first guide member is bent is less than that in the case where the contact area between the sheet member P and the first guide member is reduced by forming plural recesses in the front surface. 
     In addition, the guide structure  160  includes the fans  180  that blow air toward the non-contact surface  74   b  of the plate portion  74  of the second guide member  172 . Therefore, unlike the case in which the surface area of the second guide member is increased to dissipate heat from the second guide member, heat is actively dissipated from the second guide member. 
     Although specific exemplary embodiments of the present disclosure are described in detail above, the present disclosure is not limited to the above-described exemplary embodiments. It is obvious to those skilled in the art that various other exemplary embodiments are possible within the scope of the present disclosure. For example, although not described in the above exemplary embodiments, the length of the second guide member  72 ,  172  may be longer than that of the first guide member  62 ,  162  when viewed in the width direction of the sheet member P that is transported. In this case, the contact area between the sheet member P and the second guide member  72 ,  172  is greater than that in the case where the length of the second guide member is shorter than that of the first guide member. Therefore, the temperature of the sheet member P is effectively reduced. Accordingly, the occurrence of contact marks on the toner image formed on the sheet member P due to contact with the discharge roller unit  48  is reduced. In this case, the above-described length is the length of a portion that directly faces the transport path  28 . When one of the guide members overlaps the other, the length of the overlapping portion that does not directly face the transport path  28  is not included. 
     In addition, in the above-described exemplary embodiments, the discharge roller unit  48  is the roller unit disposed downstream of the fixing unit  34  in the transporting direction of the sheet member P. However, the roller unit may instead be any other roller unit that transports the sheet member P. 
     In the above-described exemplary embodiments, the second guide member  72 ,  172  comes into contact with the non-image surface of the sheet member P on which no toner image is formed. However, the second guide member may instead come into contact with the image surface of the sheet member P on which the toner image is formed. In this case, however, the effect of suppressing a reduction in quality of the toner image by bringing the second guide member  72 ,  172  into contact with the non-image surface of the sheet member P cannot be obtained. 
     In addition, in the above-described exemplary embodiments, the first guide member  62 ,  162  is made of a resin material and the second guide member  72 ,  172  is made of a metal material so that the thermal conductivity of the material of the first guide member  62 ,  162  differs from that of the material of the second guide member  72 ,  172 . However, the first guide member and the second guide member may be made of different resin materials so that the thermal conductivities thereof differ from each other. In this case, however, the effect obtained when the second guide member  72 ,  172  is made of a metal material cannot be obtained. 
     Although not described in the above exemplary embodiments, heat may be dissipated from the second guide member by using both the heat dissipation plates and the fans. 
     The foregoing description of the exemplary embodiments of the present disclosure has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiments were chosen and described in order to best explain the principles of the disclosure and its practical applications, thereby enabling others skilled in the art to understand the disclosure for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the disclosure be defined by the following claims and their equivalents.