Patent Publication Number: US-9423728-B2

Title: Fixing device comprising reflecting member arranged between heat source and supporting member and image forming apparatus including the same

Description:
TECHNICAL FIELD 
     The present invention relates to a fixing device configured to fix a toner image onto a recording medium and an image forming apparatus including the fixing device. 
     BACKGROUND ART 
     Conventionally, an electrographic image forming apparatus, such as a copying machine, a printer, a facsimile or a multifunction peripheral includes a fixing device configured to fix a toner image onto a recording medium, such as a sheet. For the fixing device, a heat roller manner is widely used. The heat roller manner is a manner to form a fixing nip by using a pair of rollers. 
     On the other hand, a fixing manner is being shifted from the above-mentioned heat roller manner to a belt manner to reduce a heat capacity of the fixing device and to shorten a warm-up time. The belt manner is a manner to form a fixing nip by using a fixing belt. 
     For example, Patent Document 1 discloses a fixing device including a fixing belt, a pressuring member (see “pressuring roller 22” of Patent Document 1) configured to come into pressure contact with the fixing belt so as to form a fixing nip, a heat source (see “halogen heater 23” of Patent Document 1) arranged at an inside in a radial direction of the fixing belt, a pressing member (see “nip forming member 24” of Patent Document 1) configured to press the fixing belt to a side of the pressuring member and a supporting member (see “stay 25” of Patent Document 1) configured to support the pressing member. 
     With regard to the fixing device with such a configuration, if radiant heat from the heat source is directly radiated to the supporting member, the heat escapes to the supporting member. Accompanying to this, it becomes impossible to efficiently heat the fixing belt and there is a concern that temperature rise performance of the fixing belt is deteriorated. Thus, in Patent Document 1, a reflecting member is arranged between the heat source and the supporting member so as to prevent the radiant heat from the heat source from being directly radiated to the supporting member and to efficiently heat the fixing belt. 
     [Patent Document 1] Japanese Unexamined Patent Application, Publication No. 2013-145288 
     SUMMARY OF INVENTION 
     Technical Problem 
     In Patent Document 1, a major part of the heat source is covered by the reflecting member. Accordingly, a major part of the radiant heat from the heat source is radiated not to the fixing belt but to the reflecting member and a major part of the heat escapes to the reflecting member because the reflecting member itself has a heat capacity. Accompanying to this, it becomes impossible to efficiently heat the fixing belt and there is a concern that temperature rise performance of the fixing belt is deteriorated. 
     Taking the above-mentioned situation into consideration, an object of the present invention is to improve the temperature rise performance of the fixing belt. 
     Solution to Problem 
     A fixing device according to the present invention includes a fixing belt configured to be rotatable, a pressuring member configured to be rotatable and to come into pressure contact with the fixing belt so as to form a fixing nip, a heat source arranged at an inside in a radial direction of the fixing belt and configured to radiate a radiant heat, a reflecting member configured to reflect the radiant heat radiated from the heat source to an inner circumference face of the fixing belt, a pressing member configured to press the fixing belt to a side of the pressuring member and a supporting member configured to support the pressing member. The reflecting member is arranged between the heat source and the supporting member and configured to be curved or bent so as to project toward a side of the heat source. Straight lines connecting a center of the heat source with both end parts of the supporting member in a conveying direction of a recording medium pass through the reflecting member. 
     An image forming apparatus according to the present invention includes the above-mentioned fixing device. 
     Advantageous Effects of Invention 
     The present invention makes it possible to improve the temperature rise performance of the fixing belt. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic diagram schematically showing a printer according to an embodiment of the present invention. 
         FIG. 2  is a sectional view showing a fixing device according to the embodiment of the present invention. 
         FIG. 3  is a perspective view showing the fixing device according to the embodiment of the present invention. 
         FIG. 4  is an exploded perspective view showing an upper frame part and a fixing belt in the fixing device according to the embodiment of the present invention. 
         FIG. 5  is a sectional view showing the fixing belt and its periphery in the fixing device according to the embodiment of the present invention. 
         FIG. 6A  is a sectional view showing a case where an upper face of a reflecting member is covered with an insulating material in a fixing device according to another embodiment of the present invention. 
         FIG. 6B  is a sectional view showing a case where a lower face of a reflecting member is covered with an insulating material in a fixing device according to another embodiment of the present invention. 
         FIG. 6C  is a sectional view showing a case where an upper face of a supporting member is covered with an insulating material in a fixing device according to another embodiment of the present invention. 
         FIG. 7A  is a sectional view showing a case where a second reflecting part is directly connected to a first reflecting part in a reflecting member in a fixing device according to another embodiment of the present invention. 
         FIG. 7B  is a sectional view showing a case where a reflecting member is curved so as to project toward an upper side in a fixing device according to another embodiment of the present invention. 
         FIG. 8A  is a sectional view showing a case where a heater is arranged above a reflecting member with a U shape in a fixing device according to another embodiment of the present invention. 
         FIG. 8B  is a sectional view showing a case where two heaters are arranged above a reflecting member with a U shape in a fixing device according to another embodiment of the present invention. 
         FIG. 9A  is a sectional view showing a case where a plurality of heaters are arranged in a row in a left and right direction in a fixing device according to another embodiment of the present invention. 
         FIG. 9B  is a sectional view showing a case where a plurality of heaters are arranged in a row in an upper and lower direction in a fixing device according to another embodiment of the present invention. 
         FIG. 9C  is a sectional view showing a case where a plurality of heaters are arranged in a row in a left and right direction and an upper and lower direction in a fixing device according to another embodiment of the present invention. 
         FIG. 10A  is a sectional view showing a main part of a fixing device according to a related art. 
         FIG. 10B  is a sectional view showing a main part of a fixing device according to Example 1 of the present invention. 
         FIG. 10C  is a sectional view showing a main part of a fixing device according to Example 2 of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     First, with reference to  FIG. 1 , the entire structure of a printer  1  (an image forming apparatus) will be described. 
     The printer  1  includes a box-like formed printer main body  2 . In a lower part of the printer main body  2 , a sheet feeding cartridge  3  storing sheets (recording mediums) is installed and, in a top face of the printer main body  2 , an ejected sheet tray  4  is formed. To the top face of the printer main body  2 , an upper cover  5  is openably/closably attached at a lateral side of the ejected sheet tray  4  and, below the upper cover  5 , a toner container  6  is installed. 
     In an upper part of the printer main body  2 , an exposure device  7  composed of a laser scanning unit (LSU) is located below the ejected sheet tray  4 . Below the exposure device  7 , an image forming part  8  is arranged. In the image forming part  8 , a photosensitive drum  10  as an image carrier is rotatably arranged. Around the photosensitive drum  10 , a charger  11 , a development device  12 , a transfer roller  13  and a cleaning device  14  are located along a rotating direction (refer to an arrow X in  FIG. 1 ) of the photosensitive drum  10 . 
     Inside the printer main body  2 , a conveying path  15  for the sheet is arranged. At an upstream end in the conveying path  15 , a sheet feeding part  16  is positioned. At an intermediate stream part in the conveying path  15 , a transferring part  17  composed of the photosensitive drum  10  and transfer roller  13  is positioned. At a downstream part in the conveying path  15 , a fixing device  18  is positioned. At a downstream end in the conveying path  15 , a sheet ejecting part  19  is positioned. Below the conveying path  15 , an inversion path  20  for duplex printing is arranged. 
     Next, the operation of forming an image by the printer  1  having such a configuration will be described. 
     When the power is supplied to the printer  1 , various parameters are initialized and initial determination, such as temperature determination of the fixing device  18 , is carried out. Subsequently, in the printer  1 , when image data is inputted and a printing start is directed from a computer or the like connected with the printer  1 , image forming operation is carried out as follows. 
     First, the surface of the photosensitive drum  10  is electrically charged by the charger  11 . Then, exposure corresponding to the image data is carried out to the photosensitive drum  10  by a laser light (refer to a two-dot chain line P in  FIG. 1 ) from the exposure device  7 , thereby forming an electrostatic latent image on the surface of the photosensitive drum  10 . Subsequently, the development device  12  develops the electrostatic latent image to a toner image by a toner. 
     On the other hand, a sheet picked up from the sheet feeding cartridge  3  by the sheet feeding part  16  is conveyed to the transferring part  17  in a suitable timing for the above-mentioned image forming operation, and then, the toner image on the photosensitive drum  10  is transferred onto the sheet in the transferring part  17 . The sheet with the transferred toner image is conveyed to a downstream side in the conveying path  15  to be inserted to the fixing device  18 , and then, the toner image is fixed onto the sheet in the fixing device  18 . The sheet with the fixed toner image is ejected from the sheet ejecting part  19  to the ejected sheet tray  4 . The toner remained on the photosensitive drum  10  is collected by the cleaning device  14 . 
     Next, the fixing device  18  will be described in detail. Hereinafter, it will be described so that the front side of the fixing device  18  is positioned at the near side of  FIG. 2 , for convenience of explanation. An arrow Y of each figure indicates a conveying direction of the sheet (in the present embodiment, left and right direction). Arrow Fr of  FIGS. 3 and 4  indicates a front side of the fixing device  18 . An arrow I of  FIG. 4  indicates an inside in a front and rear direction and an arrow O of  FIG. 4  indicates an outside in the front and rear direction. 
     As shown in  FIG. 2  or the like, the fixing device  18  includes a box-like formed fixing frame  21 , a fixing belt  22  housed in an upper part of the fixing frame  21 , a pressuring roller  23  (a pressuring member) housed in a lower part of the fixing frame  21 , a heater  24  (a heat source) arranged at an inside of the fixing belt  22  in a radial direction, a reflecting member  25  arranged at the inside of the fixing belt  22  in the radial direction and at a lower side of the heater  24 , a supporting member  26  arranged at the inside of the fixing belt  22  in the radial direction and at a lower side of the reflecting member  25 , a pressing member  27  arranged at the inside of the fixing belt  22  in the radial direction and at a lower side of the supporting member  26 . 
     The fixing frame  21  is made of a plate metal. As shown in  FIG. 3  or the like, the fixing frame  21  is composed of an upper frame part  31  and a lower frame part  32  connected to each other. 
     The upper frame part  31  of the fixing frame  21  includes a pair of front and rear upper side end plates  33  and a top plate  34  connecting upper end parts of the upper side end plates  33 . 
     As shown in  FIG. 4  or the like, to an outer face of each upper side end plate  33  of the upper frame part  31 , a heater attachment plate  35  is fixed. To an inner face of each upper side end plate  33 , a belt attachment base  36  is fixed. An arc-like belt supporting part  37  is arranged at an end part inside in the front and rear direction of each belt attachment base  36 . Around outer circumference of the belt supporting part  37 , annular meandering restriction ring  38  is arranged. 
     To the top plate  34  of the upper frame part  31 , a pair of front and rear first thermistors  40  are fixed. As shown in  FIG. 3  or the like, each first thermistor  40  comes into contact with a center part and a rear part of an outer circumference face of the fixing belt  22 . 
     The lower frame part  32  of the fixing frame  21  includes a pair of front and rear lower side end plates  41  and a bottom plate  42  connecting lower parts of the lower side end plates  41 . 
     To an inside in the front and rear direction of each lower side end plate  41  of the lower frame part  32 , swing frames  43  are arranged. At a right end side of each swing frame  43 , a spindle  44  is arranged and each swing frame  43  is configured to swing around each spindle  44  as a fulcrum. At a rear side (outside in the front and rear direction) of the rear lower side end plate  41 , an input gear  45  is arranged coaxially with each spindle  44 . The input gear  45  is connected to a drive source  46  composed of a motor or the like. 
     As shown in  FIG. 2  or the like, to the lower frame part  32 , a second thermistor  47  is fixed. The second thermistor  47  comes into contact with an outer circumference face of the pressuring roller  23 . At the lower frame part  32 , an entry guide  48  and an ejecting guide  49  is arranged. 
     The fixing belt  22  is formed in a roughly cylindrical shape elongated in the front and rear direction. The fixing belt  22  has flexibility and is formed in an endless shape in a circumferential direction. The fixing belt  22  includes, for example, a base material layer, an elastic layer provided around the base material layer and a release layer covering the elastic layer. The base material layer of the fixing belt  22  is made of, for example, metal, such as steel special use stainless (SUS). Incidentally, the base material layer of the fixing belt  22  may be made of resin, such as polyimide (PI). The elastic layer of the fixing belt  22  is made of, for example, a silicone rubber. The release layer of the fixing belt  22  is made of, for example, perfluoro alkoxy alkane (PFA) tube. Each figure shows the respective layers (the base material layer, the elastic layer and the release layer) of the fixing belt  22  without especially distinguishing. 
     Into both front and rear end parts of the fixing belt  22 , the belt supporting part  37  (refer to  FIG. 4  or the like) arranged at each belt attachment base  36  of the upper frame part  31  is inserted. Thereby, the fixing belt  22  is rotatably supported by the upper frame part  31 . The fixing belt  22  is rotatable around a rotation axis A (refer to  FIG. 4  or the like) extending in the front and rear direction. That is, in the present embodiment, the front and rear direction is a rotation axis direction of the fixing belt  22 . Both front and rear end faces of the fixing belt  22  are arranged at an inside in the front and rear direction of the meandering restriction ring  38  arranged in each belt attachment base  36  of the upper frame part  31 . Thereby, meandering (movement to an outside in the front and rear direction) of the fixing belt  22  is restricted. 
     The pressuring roller  23  (refer to  FIG. 2  or the like) is formed in a roughly columnar shape elongated in the front and rear direction. The pressuring roller  23  is composed of, for example, a columnar core material  50 , an elastic layer  51  provided around the core material  50  and a release layer (not shown) covering the elastic layer  51 . The core material  50  of the pressuring roller  23  is made of, for example, metal, such as iron. The elastic layer  51  of the pressuring roller  23  is made of, for example, silicone rubber. The release layer (not shown) of the pressuring roller  23  is made of, for example, PFA tube. 
     The pressuring roller  23  is arranged at a lower side (an outside) of the fixing belt  22 . The pressuring roller  23  comes into pressure contact with the fixing belt  22  and, between the fixing belt  22  and the pressuring roller  23 , a fixing nip  52  is formed. Incidentally, the conveying direction of the sheet is, for example, a conveying direction when the sheet passes through the fixing nip  52 . The pressuring roller  23  is rotatably supported by a center part in a longitudinal direction (in the present embodiment, a center part in the left and right direction) of each swing frame  43  of the fixing frame  21 . Each swing frame  43  is configured to swing around each spindle  44  to move the pressuring roller  23  in the upper and lower direction so that the pressure of the fixing nip  52  is shifted. 
     As shown in  FIG. 3 , to a rear end part of the pressuring roller  23 , a drive gear  53  is fixed. The drive gear  53  is meshed with the input gear  45  and connected to the drive source  46  via the input gear  45 . 
     The heater  24  (refer to  FIG. 5  or the like) is composed of, for example, a halogen heater. A lower end part (an end part of the fixing nip  52  side) of the heater  24  is arranged at an upper side (a further side from the fixing nip  52 ) than upper end parts (end parts far from fixing nip  52  side) of the pressing member  27 , the supporting member  26  and the reflecting member  25 . Both front and rear end parts of the heater  24  are attached to the heater attachment plate  35  (refer to  FIG. 4 ) of the upper frame part  31  of the fixing frame  21 . The heater  24  is configured to generate heat by energizing so as to radiate a radiant heat. 
     The reflecting member  25  (refer to  FIG. 5  or the like) is formed in a shape elongated in the front and rear direction. The reflecting member  25  is made of a metal, such as an aluminum alloy for brightening. The reflecting member  25  is arranged between the heater  24  and the supporting member  26 . A top face of the reflecting member  25  (a face at a side of the heater  24 ) is a reflecting face (mirror face) which reflects a radiant heat radiated from the heater  24 , to an inner circumference face of the fixing belt  22 . The reflecting member  25  is arranged to cover an upper side of the supporting member  26  (the side of the heater  24 ). 
     The reflecting member  25  includes a first reflecting part  61 , a second reflecting part  62  which is provided at a left side (a downstream side in the sheet conveying direction) of the first reflecting part  61  and a third reflecting part  63  which connects the first reflecting part  61  with the second reflecting part  62 . 
     The first reflecting part  61  inclines to a lower side (a side of the supporting member  26 ) toward a right side (an upstream side in the sheet conveying direction). The second reflecting part  62  inclines to a lower side (the side of the supporting member  26 ) toward a left side (the downstream side in the sheet conveying direction). The third reflecting part  63  is arranged along the left and right direction (the sheet conveying direction). The third reflecting part  63  faces the heater  24  at an interval. 
     The reflecting member  25  is bent so as to project toward an upper side (a side of the heater  24 ). In other words, the reflecting member  25  is bent so as to dent toward a lower side (a side of the supporting member  26 ). Hence, at a lower side (a side of the supporting member  26 ) of the reflecting member  25 , a concave part  66  is formed so as to be covered by the first reflecting part  61 , the second reflecting part  62  and the third reflecting part  63 . 
     The supporting member  26  is formed in a shape elongated in the front and rear direction. The supporting member  26  includes an upstream side stay  71  and a downstream side stay  72 . The upstream side stay  71  and the downstream side stay  72  are made of sheet metals, such as SECC (galvanized steel sheet), for example. An upper part of the supporting member  26  is inserted into the concave part  66  formed at the lower side of the reflecting member  25 . 
     The upstream side stay  71  includes an upstream side base plate  73  which extends in upper and lower direction, an upstream side support plate  74  which is bent from a lower end part of the upstream side base plate  73  to the right side (the upstream side in the sheet conveying direction) and an upstream side guide plate  75  which is bent from a right end part of the upstream side support plate  74  to an upper right side. 
     The downstream side stay  72  is arranged at a left side (the downstream side in the sheet conveying direction) of the upstream side stay  71 . The downstream side stay  72  includes a downstream side base plate  80  which extends in the upper and lower direction, a downstream side support plate  81  which is bent from a lower end part of the downstream side base plate  80  to the left side (the downstream side in the sheet conveying direction) and a downstream side guide plate  82  which is bent from a left end part of the downstream side support plate  81  to an upper left side. The downstream side base plate  80  is fixed to the upstream side base plate  73  by a screw  84 . 
     As shown in  FIG. 5 , straight lines L connecting a center Z of the heater  24  with left and right end parts (in the present embodiment, a distal end part of the upstream side guide plate  75  and a distal end part of the downstream side guide plate  82 ) of the supporting member  26  pass through the first reflecting part  61  and the second reflecting part  62  of the reflecting member  25 , respectively. Accordingly, seen from the heater  24 , the supporting member  26  is covered by the reflecting member  25 . 
     The pressing member  27  is formed in a plate-like shape elongated in the front and rear direction. The pressing member  27  is made of a heat resistant resin such as LCP (Liquid Crystal Polymer). 
     A top face of the pressing member  27  comes into contact with a bottom face of the supporting member  26  (more specifically, the bottom face of the upstream side support plate  74  of the upstream side stay  71  and the bottom face of the downstream side support plate  81  of the downstream side stay  82 ). Thus, the pressing member  27  is supported by the supporting member  26 , and a warp (deformation caused by a fixing load) of the pressing member  27  is suppressed. 
     The bottom face of the pressing member  27  inclines to a lower side (a side of the pressuring roller  23 ) from the right side (the upstream side in the sheet conveying direction) toward the left side (the downstream side in the sheet conveying direction). The bottom face of the pressing member  27  presses the fixing belt  22  to the lower side (the side of the pressing roller  23 ). 
     Between the bottom face of the pressing member  27  and the inner circumference face of the fixing belt  22 , a sheet member  90  is interposed. The sheet member  90  is made of a fluorine-based resin, such as PTFE, and has a lower friction coefficient than that of the pressing member  27 . In addition, between the bottom face of the pressing member  27  and the inner circumference face of the fixing belt  22 , a lubricant (grease) may be applied. 
     To fix a toner image to a sheet in the fixing device  18  to which the above configuration is applied, the drive source  46  is driven. When the drive source  46  is driven in this way, a rotation of the drive source  46  is transmitted to the pressuring roller  23  via the input gear  45  and the drive gear  53 , and the pressuring roller  23  rotates as indicated by arrow B in  FIG. 2 . When the pressuring roller  23  rotates in this way, as indicated by arrow C in  FIG. 2 , the fixing belt  22  which comes into pressure contact with the pressuring roller  23  is driven and rotated in a direction opposite to that of the pressuring roller  23 . When the fixing belt  22  rotates in this way, the fixing belt  22  slides against the pressing member  27  and the sheet member  90 . 
     Further, to fix a toner image to a sheet, the heater  24  is activated (turned on). When the heater  24  is activated in this way, the heater  24  radiates a radiant heat. As indicated by arrow D in  FIG. 2 , a part of the radiant heat of the heater  24  is directly radiated on the inner circumference face of the fixing belt  22 , and is absorbed. Further, as indicated by arrow E in  FIG. 2 , another part of the radiant heat of the heater  24  is reflected to the inner circumference face of the fixing belt  22  by the upper face of the reflecting member  25  and is absorbed by the inner circumference face of the fixing belt  22 . According to the above function, the heater  24  heats the fixing belt  22 . When a sheet passes through the fixing nip  52  in this state, a toner image is heated and then melts, and then the toner image is fixed to the sheet. 
     By the way, to improve temperature rise performance of the fixing belt  22 , it is preferable to reduce heat capacities of the supporting member  26  and the pressing member  27  arranged at an inside of the fixing belt  22  in a radial direction. However, when volumes of the supporting member  26  and the pressing member  27  are reduced to reduce the heat capacities of the supporting member  26  and the pressing member  27 , strengths of the supporting member  26  and the pressing member  27  become insufficient. As a result, there is a problem that the supporting member  26  and the pressing member  27  deflect. Hence, in the present embodiment, as shown in  FIG. 5  or the like, a plurality of bent parts are provided to the supporting member  26  to secure the strengths of the supporting member  26  and the pressing member  27 . 
     Further, when the supporting member  26  is directly radiated by a radiant heat from the heater  24 , the heat escapes to the supporting member  26  and therefore it is difficult to efficiently heat the fixing belt  22 . However, in the present embodiment, straight lines L connecting a center Z of the heater  24  with both left and right end parts of the supporting member  26  pass through the first reflecting part  61  and the second reflecting part  62  of the reflecting member  25 . Consequently, it is possible to prevent the radiant heat from the heater  24  from being directly radiated to the supporting member  26 . According to this, it is possible to reduce a heat escaping to the supporting member  26  and improve the temperature rise performance of the fixing belt  22 . 
     Further, in the present embodiment, as described above, the reflecting member  25  is bent so as to project to the upper side (the side of the heater  24 ), so that it is possible to reduce a region of the heater  24  covered with the reflecting member  25 . According to this, it is possible to reduce the amount of the radiant heat radiated to the reflecting member  25 , and increase the amount of the radiant heat directly radiated to the inner circumference face of the fixing belt  22 . Consequently, it is possible to further improve the temperature rise performance of the fixing belt  22 . 
     As described above, in the present embodiment, while securing the strengths of the supporting member  26  and the pressing member  27 , it is possible to enhance the temperature rise performance of the fixing belt  22 . 
     Further, the reflecting member  25  includes the third reflecting part  63  which connects the first reflecting part  61  with the second reflecting part  62 . Hence, it is possible to separate a distance between the heater  24  and the reflecting member  25  and suppress a rise in the temperature of the reflecting member  25 . 
     Further, a lower end part (an end part of the fixing nip  52  side) of the heater  24  is arranged at an upper side (a further side from the fixing nip  52 ) than upper end parts (end parts far from fixing nip  52  side) of the pressing member  27 , the supporting member  26  and the reflecting member  25 . Hence, it is possible to directly radiate the radiant heat from the heater  24  to a wide range of the inner circumference face of the fixing belt  22  as much as possible. 
     Further, in the present embodiment, the heater  24  heats the fixing belt  22 , so that, compared to a case where the heater  24  heats a fixing roller, it is possible to reduce a heat capacity of a member heated by the heater  24 . According to this, it is possible to reduce a warm-up time of the fixing device  18 . 
     By the way, when a thin thickness of the reflecting member  25  is set, even if a radiant heat from the heater  24  is prevented from being directly radiated to the supporting member  26 , there is a concern that the heat escapes to the supporting member  26  due to transmission of the heat to the supporting member  26  and the temperature rise performance of the fixing belt  22  lowers. Hence, as shown in  FIGS. 6A to 6C , it is preferable to use an insulating material In to prevent the heat from being transmitted to the supporting member  26 . The insulating material In is made of a ceramic heat-resistant paint or a foamed or glass wool insulator, for example. 
     As shown in  FIG. 6A , the upper face of the reflecting member  25  (a face at the side of the heater  24 , i.e., a reflecting face) may be covered with the insulating material In. By applying such a configuration, it is possible to prevent the heat from being transmitted to the supporting member  26 , and prevent a color of the upper face (reflecting face) of the reflecting member  25  from changing. 
     Further, as shown in  FIG. 6B , the lower face of the reflecting member  25  (a face at the side of the supporting member  26 ) may be covered with the insulating material In. By applying such a configuration, it is possible to prevent a heat from being transmitted to the supporting member  26  without causing the insulating material In to inhibit the function of the upper face (reflecting face) of the reflecting member  25 . 
     Further, as shown in  FIG. 6C , the upper face of the supporting member  26  (a face at the side of the reflecting member  25 ) may be covered with the insulating material In. By applying such a configuration, it is possible to prevent a heat from being transmitted to the supporting member  26  without complicating a structure of the reflecting member  25 . 
     In the present embodiment, a case where the first reflecting part  61  and the second reflecting part  62  of the reflecting member  25  is connected with each other by the third reflecting part  63  is explained. On the other hand, in another embodiment, as shown in  FIG. 7A , a left end part (a downstream side end part in the sheet conveying direction) of the first reflecting part  61  of the reflecting member  25  may be directly connected with a right end part (an upstream side end part in the sheet conveying direction) of the second reflecting part  62  without arranging the third reflecting part  63  between them. By applying such a configuration, the reflecting member  25  is formed with a roughly V shape, thereby reducing the vending time of the reflecting member  25  and facilitate a form of the reflecting member  25 . 
     In the present embodiment, a case where the reflecting member  25  is bent so as to project toward an upper side (a side of the heater  24 ) is explained. On the other hand, in another embodiment, as shown in  FIG. 7B , the reflecting member  25  may be curved so as to project toward the upper side (the side of the heater  24 ). 
     In the present embodiment, a case where the reflecting member  25  includes a first reflecting part  61 , a second reflecting part  62  and the third reflecting part  63  is explained. On the other hand, in other embodiments, as shown in  FIGS. 8A and 8B , the reflecting member  25  may include a first plate part  101  arranged along an upper and lower direction (a direction crossing (orthogonal) to the sheet conveying direction) and arranged at a right side (a more upstream side in the sheet conveying direction) than the supporting member  26 , a second plate part  102  arranged along the upper and lower direction (a direction crossing (orthogonal) to the sheet conveying direction) and arranged at a left side (a more downstream side in the sheet conveying direction) than the supporting member  26  and a third plate part  103  configured to connect upper end parts (end parts far from fixing nip  52  side) of the first plate part  101  and the second plate part  102 . By applying such a configuration, the reflecting member  25  is formed with a U shape, thereby making a large space at a lower side (the supporting member  26  side) of the reflecting member  25 . Accompanying to this, it is possible to enhance flexibility of a layout of the supporting member  26 . 
     In the present embodiment, a case where a heater  24  is arranged at the inside in the radial direction of the fixing belt  22  is explained. On the other hand, in other embodiments, as shown in  FIGS. 9A to 9C , a plurality of heaters  24  are arranged at the inside in the radial direction of the fixing belt  22  and straight lines L connecting a center Z of each of a plurality of the heaters  24  with the left and right end parts of the supporting member  26  may pass through the reflecting member  25 . By applying such a configuration, it is possible to improve the heat rise performance of the fixing belt  22  with preventing radiant heats from a plurality of the heaters  24  from being directly radiated to the supporting member  26 . 
     In a case where a plurality of the heaters  24  are arranged as described above, as shown in  FIG. 9A , a plurality of the heaters  24  may be arranged in a row in the left and right direction (the sheet conveying direction). By applying such a configuration, it is possible to shorten the width in the upper and lower direction (the direction crossing to the sheet conveying direction) to be needed to arrange a plurality of the heaters  24 . 
     Further, as shown in  FIG. 9B , a plurality of the heaters  24  may be arranged in a row in the upper and lower direction (the direction crossing to the sheet conveying direction). By applying such a configuration, it is possible to shorten the width in the left and right direction (the sheet conveying direction) to be needed to arrange a plurality of the heaters  24 . 
     Furthermore, as shown in  FIG. 9C , a plurality of the heaters  24  may be arranged in a row in the left and right direction (the sheet conveying direction) and the upper and lower direction (a direction crossing to the sheet conveying direction). 
     In the present embodiment, a case where the halogen heater is used as a heater  24  is explained. On the other hand, in another embodiment, a ceramic heater or the like may be used as the heater  24 . 
     In the present embodiment, a case where the configuration of the present invention is applied to the printer  1  is explained. On the other hand, in another embodiment, the configuration of the invention may be applied to another image forming apparatus, such as a copying machine, a facsimile or a multifunction peripheral. 
     &lt;Demonstration Experiment&gt; 
     An experiment was conducted to demonstrate effects of the fixing devices  18  according to examples of the present invention. Experiment conditions are as follows. 
     Diameter of fixing belt  22 : 30 mm
     Material and thickness of fixing belt  22     

     Base Layer: SUS, thickness 30 μm 
     Elastic layer: silicon rubber, thickness 270 μm 
     Release layer: PFA tube, thickness 30 μm
     Rotation speed of fixing belt  22 : 180 mm/s   Diameter of pressuring roller  23 : 25 mm   Material and thickness of pressing roller  23 : silicon rubber, thickness 3.5 mm   Heater  24 : halogen heater of 800 W   Distance between center Z of each heater  24  and reflecting member  25 : 10 mm   Material and thickness of reflecting member  25 : aluminum alloy for brightening (mirror face), thickness 0.5 mm   Material of supporting member  26 : SECC (galvanized steel sheet)   Width of fixing nip  52 : 8 mm   

       FIGS. 10A to 10C  are sectional views showing main parts of fixing devices  18  used for this experiment.  FIG. 10A  is a sectional view showing a main part of a fixing device according to a related art.  FIG. 10B  is a sectional view showing a main part of a fixing device  18  according to Example 1 of the present invention.  FIG. 10C  is a sectional view showing a main part of a fixing device  18  according to Example 2 of the present invention. 
     When an angle formed by straight lines N connecting the center Z of the heater  24  with the both left and right end parts (both end parts in the sheet conveying direction) of the reflecting member  25  is Angle a, and an angle formed by the straight lines L connecting the center Z of the heater  24  with the both left and right end parts (both end parts in the sheet conveying direction) of the supporting member  26  is Angle b, a relationship between Angle a and Angle b according to Related Art 1 and Example 1 and 2 are as shown in following table 1. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
             
            
               
                   
                   
               
               
                   
                 Angle Condition 
                 Temperature 
               
            
           
           
               
               
               
               
            
               
                   
                 Angle a[°] 
                 Angle b[°] 
                 Rise Time[s] 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 Related Art1 
                 40 
                 60 
                 13.7 
               
               
                   
                 Example 1 
                 70 
                 50 
                 9.8 
               
               
                   
                 Example2 
                 80 
                 50 
                 9.5 
               
               
                   
                   
               
            
           
         
       
     
     As is clear from above table 1, according to Related Art 1, angle a&lt;angle b is true, and the straight lines L connecting the center Z of the heater  24  with the both left and right end parts of the supporting member  26  do not pass through the reflecting member  25  (see  FIG. 10A ). By contrast with this, according to Example 1 and 2, angle a&gt;angle b is true, and the straight lines L connecting the center Z of the heater  24  with the both left and right end parts of the supporting member  26  pass through the reflecting member  25  (see  FIGS. 10B and 10C ). 
     Under the above-described experiment condition, the heater  24  was activated (turned on) in a state where the fixing belt  22  was rotated, a time (referred to as a “temperature rise time” in the following description) for the temperature of the fixing belt  22  to reach a predetermined temperature (160° C.) from a normal temperature (23° C.) was measured. A measured result is shown in above-described table 1. 
     As is clear from above-described table 1, the temperature rise times according to Examples 1 and 2 of the present invention are shorter by about seconds than the temperature rise time according to Related Art 1. This is because, while, in Related Art 1, a part of a radiant heat from the heater  24  was directly radiated to the supporting member  26  and escaped to the supporting member  26 , in Examples 1 and 2, a radiant heat from the heater  24  was not directly radiated to the supporting member  26  and therefore the heat did not escape to the supporting member  26 . As described above, according to Example 1 and 2, it was possible to improve temperature rise performance of the fixing belt  22  compared to Related Art 1. 
     In addition, when the upper face of the reflecting member  25  was covered with the insulating material In (see  FIG. 6A ) and when the lower face of the reflecting member  25  was covered with the insulating material In (see  FIG. 6B ), it was possible to further reduce the temperature rise time by 1 second compared to values in above-described table 1. Further, when the upper face of the supporting member  26  was covered with the insulating material In (see  FIG. 6C ), it was possible to further reduce the temperature rise time by 0.6 second compared to the values in above-described table 1. 
     Further, by bending or curving the reflecting member  25  so as to project toward the upper side (the side of the heater  24 ), it was possible to reduce the temperature rise time by 0.5 second to 1.0 second compared to a case where the reflecting member  25  was bent so as to project toward the lower side (the side of the supporting member  26 ).