Patent Publication Number: US-11650524-B2

Title: Fixing device and image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 16/924,727 filed Jul. 9, 2020, which is a continuation of U.S. application Ser. No. 16/172,442 filed Oct. 26, 2018, now U.S. Pat. No. 10,732,548. The entire contents of the applications identified above are incorporated herein by reference. 
    
    
     FIELD 
     Embodiments described herein relate generally to a fixing device and an image forming apparatus. 
     BACKGROUND 
     An image forming apparatus such as a multi function peripheral (MFP), a copying machine, or a printer includes a fixing device that fixes a toner image transferred on a recording medium such as recording paper. The fixing device includes a fixing rotating member such as a fixing belt that rotates in contact with the recording medium, a fixing pad that is disposed on an inner circumferential side of the fixing rotating member, and a pressurizing member such as a press roller that is disposed so as to face an outer circumferential surface of the fixing rotating member. The pressurizing member is pressed toward the fixing pad interposing a circumferential wall of the fixing rotating member therebetween. The pressurizing member and the fixing rotating member rotate in opposite directions, and a fixing nip is formed between the pressurizing member and the fixing rotating member. The recording medium such as recording paper is drawn by the fixing nip between the pressurizing member and the fixing rotating member, and fixing is performed as the recording medium passes through the fixing nip. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a side view of an image forming apparatus including a fixing device of at least one embodiment. 
         FIG.  2    is a partial section side view including a control block of the fixing device of at least one embodiment. 
         FIG.  3    is a cross-sectional view taken along line of  FIG.  2    of the fixing device of at least one embodiment. 
         FIG.  4    is a cross-sectional view similar to  FIG.  3    shown without showing a cross-section of a fixing belt. 
         FIG.  5    is an enlarged sectional view of a V portion in  FIG.  3   . 
         FIG.  6    is a partial section side view of a fixing device of another embodiment. 
         FIG.  7    is a view showing a relationship between a heating member and a printing region of a sheet of the fixing device of another embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In some fixing devices, since the fixing pad is pressed against an inner circumferential surface of the fixing rotating member, sliding resistance is generated between the fixing pad and the inner circumferential surface of the fixing rotating member during the fixing operation. As the sliding resistance increases, power loss of a drive unit such as the fixing rotating member increases, and problems such as abrasion of components, occurrence of wrinkles on a recording medium, deterioration in printing quality, and the like tend to occur. 
     As a countermeasure, a fixing device in which a lubricant is applied to the inner circumferential surface of the fixing rotating member is devised. However, the circumferential wall of the fixing rotating member is pushed in between the pressurizing member and the fixing pad with relatively large power during the fixing operation. Accordingly, it is possible that the lubricant applied to the inner circumferential surface of the fixing rotating member leaks to outside from an end portion of fixing rotating member in a longitudinal direction during the fixing operation. 
     Therefore, there is a demand for a fixing device that can suppress leaking of a lubricant applied to an inner circumferential surface of a rotating member and maintain a suppression effect of sliding resistance for a long period of time. 
     In general, according to one embodiment, there is provided a fixing device including a fixing rotating member, a heater, a fixing pad, a pressurizing member, a lubricant, and a surface layer. The fixing rotating member is rotatably configured to fix a toner image on a recording medium. The heater heats the fixing rotating member. The fixing pad is positioned on an inner circumferential side of the fixing rotating member, and presses the fixing rotating member from the inner circumferential side. The pressurizing member is disposed to face an outer circumferential surface of the fixing rotating member, and forms a nip for fixing between the pressurizing member and the fixing rotating member at a position facing the fixing pad. The lubricant is applied to an inner circumferential surface of the fixing rotating member. The surface layer is disposed in a vicinity of a longitudinal end portion of a pressurizing surface of the fixing pad in the inner circumferential surface of the fixing rotating member, and returns the lubricant to a longitudinal central side of the pressurizing surface. 
     Hereinafter, an image forming apparatus of at least one embodiment will be described with reference to drawings. 
     First Embodiment 
       FIG.  1    is a side view showing an entire configuration of an image forming apparatus  10  of at least one embodiment. For example, the image forming apparatus  10  is a multi function peripheral. However, the image forming apparatus  10  is not limited to the above-described example, and may be a copying machine, a printer, or the like. 
     The image forming apparatus  10  includes a scanner unit  12 , a control panel  13 , a main unit  14 , and a system control unit  100  (a system controller). The main unit  14  includes a paper feed cassette unit  16 , a printer unit  18 , a fixing device  34 , and the like. The system control unit  100  controls the entire image forming apparatus  10 . For example, the system control unit  100  controls operations of the scanner unit (scanner)  12 , the control panel  13 , the paper feed cassette unit  16 , the printer unit (printer)  18 , the fixing device (fixer)  34 , and the like. 
     The scanner unit  12  reads an original image. The control panel  13  includes an input key  13   a  and a display unit  13   b . For example, the input key  13   a  receives an input from a user. For example, the display unit  13   b  is a touch panel type. The display unit  13   b  receives the input from a user, and displays to the user. 
     The paper feed cassette unit  16  includes a cassette body  16   a  and a pickup roller  16   b . The cassette body  16   a  stores a sheet P which is a recording medium. The pickup roller  16   b  takes out the sheet P from the cassette body  16   a . The sheet P taken out from the cassette body  16   a  is fed to a carrying path  33 . 
     The printer unit  18  forms an image on the sheet P. The printer unit  18  performs, for example, image formation of the original image read by the scanner unit  12 . The printer unit  18  includes an intermediate transfer belt  21 . The printer unit  18  supports the intermediate transfer belt  21  with a backup roller  40 , a driven roller  41 , and a tension roller  42 . The backup roller  40  includes a drive unit (not shown). The printer unit  18  rotates the intermediate transfer belt  21  in an arrow m direction. 
     The printer unit  18  includes four sets of image forming stations  22 Y,  22 M,  22 C, and  22 K. Each of the image forming stations  22 Y,  22 M,  22 C, and  22 K is used for image formation of each Y (yellow) image, M (magenta) image, C (cyan) image, and K (black) image. The image forming stations  22 Y,  22 M,  22 C, and  22 K are disposed in parallel along a rotation direction of the intermediate transfer belt  21  on a lower side of the intermediate transfer belt  21 . 
     The printer unit  18  includes cartridges  23 Y,  23 M,  23 C, and  23 K above the image forming stations  22 Y,  22 M,  22 C, and  22 K, respectively. Each of the cartridges  23 Y,  23 M,  23 C, and  23 K stores a toner for replenishment of Y (yellow), M (magenta), C (cyan), and K (black), respectively. 
     Hereinafter, among each of the image forming stations  22 Y,  22 M,  22 C, and  22 K, the image forming station  22 Y of Y (yellow) will be described as an example. Since the image forming stations  22 M,  22 C, and  22 K have the same configuration as the image forming station  22 Y, a detailed description will be omitted. 
     The image forming station  22 Y includes an electrifying charger  26 , an exposure scanning head  27 , a developing device  28 , and a photoconductive cleaner  29 . The electrifying charger  26 , the exposure scanning head  27 , the developing device  28 , and the photoconductive cleaner  29  are disposed around a photoconductive drum  24  that rotates in an arrow n direction. 
     The image forming station  22 Y includes a primary transfer roller  30 . The primary transfer roller  30  faces the photoconductive drum  24  via the intermediate transfer belt  21 . 
     The image forming station  22 Y electrifies the photoconductive drum  24  with the electrifying charger  26 , and exposes the photoconductive drum  24  by the exposure scanning head  27 . The image forming station  22 Y forms an electrostatic latent image on the photoconductive drum  24 . The developing device  28  develops the electrostatic latent image on the photoconductive drum  24  using two-component developer formed of toner and a carrier. 
     The primary transfer roller  30  primarily transfers the toner image formed on the photoconductive drum  24  to the intermediate transfer belt  21 . The image forming stations  22 Y,  22 M,  22 C, and  22 K form a color toner image on the intermediate transfer belt  21  by the primary transfer roller  30 . The color toner image is formed by overlapping the toner images of Y (yellow), M (magenta), C (cyan), and K (black) in sequence. The photoconductive cleaner  29  removes the toner left on the photoconductive drum  24  after the primary transfer. 
     The printer unit  18  includes a secondary transfer roller  32 . The secondary transfer roller  32  faces the backup roller  40  via the intermediate transfer belt  21 . The secondary transfer roller  32  collectively secondarily transfers the color toner image on the intermediate transfer belt  21  on the sheet P. The sheet P is fed by the paper feed cassette unit  16  or a manually feeding tray  17  along the carrying path  33 . 
     The printer unit  18  includes a belt cleaner  43  facing the driven roller  41  via the intermediate transfer belt  21 . The belt cleaner  43  removes the toner left on the intermediate transfer belt  21  after the secondary transfer. 
     The carrying path  33  is provided with a resist roller  33   a , the fixing device  34 , and a paper discharge roller  36 . On a downstream side of the fixing device  34  of the carrying path  33 , a branch portion  37  and a reverse carrying portion  38  are provided. The branch portion  37  sends the sheet P subjected to fixing to a paper discharging portion  20  or the reverse carrying portion  38 . In a case of double-sided printing, the reverse carrying portion  38  inverts and carries the sheet P sent from the branch portion  37  in a direction of the resist roller  33   a . The image forming apparatus  10  forms a toner image on the sheet P with the printer unit  18 , and discharges the sheet P to the paper discharging portion  20 . 
     The image forming apparatus  10  is not limited to a tandem development type, and the number of the developing devices  28  is not limited. Furthermore, the image forming apparatus  10  may directly transfer the toner image from the photoconductive drum  24  on the sheet P. 
     Hereinafter, the fixing device  34  will be described in detail. 
       FIG.  2    is a partial section side view including a control block of the fixing device  34  of at least one embodiment. 
     As shown in  FIG.  2   , the fixing device  34  includes a fixing belt  50 , a press roller  51 , and an electromagnetic induction heating coil unit  52  (hereinafter, referred to as IH coil unit  52 ). The fixing belt  50  makes up the fixing rotating member. The press roller  51  makes up the pressurizing member (pressurizer). The IH coil unit  52  makes up the heater that heats the fixing belt  50  (fixing rotating member). As a heater that heats the fixing belt  50  (fixing rotating member), it is possible to use a halogen heater or the like instead of the IH coil unit  52 . On an inner circumferential side of the fixing belt  50 , a nip pad  53  (fixing pad), an auxiliary heat generation plate  69 , a shield  76 , and a stay  77  for holding them is disposed. On the inner circumferential side of the fixing belt  50 , a center thermistor  61 , an edge thermistor  62 , and a bimetal type thermostat  63  are disposed close to an inner circumferential surface of the fixing belt  50 . 
     The fixing belt  50  is driven by the press roller  51 , or rotates in an arrow u direction independently from the press roller  51 . 
     The fixing belt  50  is formed by laminating a heat generation layer (heat generation portion), a cushion layer, a release layer, and the like on a base layer in order. The base layer is formed of, for example, a polyimide (PI) resin. The heat generation layer is formed of non-magnetic metal such as copper (Cu). The cushion layer is formed of, for example, a solid rubber such as a silicone rubber. The release layer is formed of, for example, a fluororesin such as a tetrafluoroethylene-perfluoroalkylvinylether copolymer resin (PFA). 
     An eddy-current is generated by the magnetic flux generated by the IH coil unit  52  in the heat generation layer inside the fixing belt  50 . The heat generation layer generates Joule heat according to the eddy-current generated at the time and a resistance value of the heat generation layer, and heats the entire fixing belt  50 . 
     The IH coil unit  52  includes coils  56  that generate a magnetic flux by application of a high frequency current and a core  57  that concentrates the magnetic flux generated by the coils  56  in a direction of the fixing belt  50 . During the fixing belt  50  rotates in the arrow u direction in  FIG.  2   , the IH coil unit  52  generates an induced current to the heat generation layer inside the fixing belt  50  facing the IH coil unit  52 . The coil  56  generates a magnetic flux by application of a high frequency current from an inverter drive circuit  68 . The inverter drive circuit  68  includes, for example, an insulated gate bipolar transistor (IGBT) element  68   a.    
     The auxiliary heat generation plate  69  is disposed slidably abutted or close to the inner circumferential surface of the fixing belt  50 . The auxiliary heat generation plate  69  is formed of a magnetic shunt alloy in which the magnetic characteristics change by a temperature. When a temperature of the auxiliary heat generation plate  69  is the Curie temperature or higher, magnetic permeability is reduced. Accordingly, magnetic flux density passing through the fixing belt  50  decreases, and the amount of heat generated by the fixing belt  50  is limited. As a result, for example, it is possible to suppress excessive temperature rise in a non-paper passing region in the fixing belt  50 . Moreover, in a low temperature region where the temperature does not reach the Curie temperature, the auxiliary heat generation plate  69  is electromagnetically induced by an action of a magnetic field of the IH coil unit  52  to generate heat, and helps the heating of the fixing belt  50 . 
     The auxiliary heat generation plate  69  is formed in an arc shape along the inner circumferential surface of the fixing belt  50  as seen from an outer side of the fixing belt  50  in the longitudinal direction. The auxiliary heat generation plate  69  is disposed to face the core  57  with a circumferential wall of the fixing belt  50  interposed therebetween. Moreover, a length of the auxiliary heat generation plate  69  in a longitudinal direction is set longer than a maximum width of the sheet P to be used. The auxiliary heat generation plate  69  has, for example, the same longitudinal length as the nip pad  53 . A width direction of the sheet P (recording medium) means a direction along the longitudinal direction of the fixing belt  50  when the sheet P is pressed against an outer surface of the fixing belt  50  by a nip  54 . 
     The shield  76  is formed in an arc shape along the inner circumferential surface of the fixing belt  50  as seen from the outer side of the fixing belt  50  in the longitudinal direction. The shield  76  is disposed spaced apart on an inner side of the auxiliary heat generation plate  69  in the radial direction. The shield  76  is made of, for example, a non-magnetic member such as aluminium (Al), copper (Cu), or the like. The shield  76  shields the magnetic flux generated from the IH coil unit  52 , and prevents the magnetic flux from affecting the stay  77  on the inner circumferential surface of the fixing belt  50 , the nip pad  53 , and the like. 
     The nip pad  53  presses the inner circumferential surface of the circumferential wall of the fixing belt  50  toward the press roller  51  side to form the nip  54  for fixing between the fixing belt  50  and the press roller  51 . The nip pad  53  is formed of, for example, a heat resistant polyphenylene sulfide resin (PPS), a liquid crystal polymer (LCP), a phenol resin (PF), or the like. At a portion (pressurizing surface) that comes into contact with the inner circumferential surface of the fixing belt  50  in the nip pad  53 , a sheet  53   a  (low friction member) having good sliding property and good abrasion resistance is attached. At the portion (pressurizing surface) that comes into contact with the inner circumferential surface of the fixing belt  50  in the nip pad  53 , a release layer formed of a fluororesin or the like may be provided. Accordingly, it is possible to reduce friction resistance between the fixing belt  50  and the nip pad  53 . 
     The press roller  51  includes, for example, a heat resistant silicone sponge or a silicone rubber around a core bar, and a release layer formed of fluororesin or the like on the surface. The press roller  51  pressurizes, for example, the nip pad  53  with a pressurization mechanism  51   a . The press roller  51  rotates in an arrow q direction in  FIG.  2    by driving force of a motor  51   b . The motor  51   b  is driven by a motor drive circuit  51   c  that is controlled by a main body control circuit  101 . 
     The center thermistor  61  and the edge thermistor  62  measures a temperature of the fixing belt  50 , and outputs a detection signal to the main body control circuit  101 . The center thermistor  61  is disposed at a substantially central portion in the longitudinal direction (width direction) of the fixing belt  50 . The edge thermistor  62  is disposed in an end portion region on both sides in the longitudinal direction (width direction) of the fixing belt  50 . 
     The main body control circuit  101  receives the detection signal from the center thermistor  61  and the edge thermistor  62 , and controls the high frequency output current of the inverter drive circuit  68  through an IH control circuit  78 . The temperature of the fixing belt  50  is maintained within various control temperature ranges according to the output of the inverter drive circuit  68 . 
     The thermostat  63  functions as a safety device for the fixing device  34 . The thermostat  63  operates when the temperature of the fixing belt  50  rises to a predetermined shutoff threshold or higher, and shuts off energization with respect to the IH coil unit  52 . At this time, the image forming apparatus  10  stops driving to prevent abnormal heat generation of the fixing device  34 . 
       FIG.  3    is a cross-sectional view taken along line of  FIG.  2    of the fixing device  34 .  FIG.  4    is a cross-sectional view similar to  FIG.  3    shown without sectioning the fixing belt  50 . 
     As shown in  FIGS.  3  and  4   , a wheel  50   a  for keeping the cross-sectional shape of the fixing belt  50  substantially circular is attached on both end portions of the fixing belt  50  in the longitudinal direction. A longitudinal length L 1  of the fixing belt  50  is set longer than longitudinal lengths L 2  and L 3  of the nip pad  53  (sheet  53   a ) and the press roller  51 . The longitudinal length L 2  of the nip pad  53  is set longer than the longitudinal length L 3  of the press roller  51 . That is, a longitudinal length of a pressing portion of the press roller  51  with respect to an outer circumferential surface of the fixing belt  50  is set shorter than the longitudinal length of a pressing portion of the nip pad  53  with respect to the inner circumferential surface of the fixing belt  50 . An outer region A 1  in a longitudinal end portion of the fixing belt  50  is not directly pressed from either the nip pad  53  or the press roller  51  than the nip pad  53 . 
       FIG.  5    is an enlarged sectional view of a V portion in  FIG.  3   . 
     A lubricant  66  is applied to a region (region excluding vicinity of end portion in longitudinal direction) that comes into contact with the nip pad  53  (sheet  53   a ) and the auxiliary heat generation plate  69  in the inner circumferential surface of the fixing belt  50 . As the lubricant  66 , for example, silicone oil and the like can be used. As the silicone oil, for example, it is desirable to use a dimethyl silicone oil having kinetic viscosity at 25° C. 1,000 mm 2 /s or less. The viscosity of the silicone oil is measured, for example, using an Ubbelohde viscometer according to ASTM D 445-46T. The lubricant  66  reduces the friction resistance of the nip pad  53  (sheet  53   a ) and the auxiliary heat generation plate  69  that comes into contact with the inner circumferential surface of the fixing belt  50 . 
     Moreover, the outer region A 1  of the longitudinal direction and a region straddling a part inside from the outer region A 1  in the inner circumferential surface of the fixing belt  50 , is coated with a surface layer  67  formed of an oil repellent member such as polytetrafluoroethylene (PTFE) or perfluoroalkoxyalkane (PFA). The surface layer  67  formed of an oil repellent member functions to repel the lubricant  66  when the lubricant  66  such as silicone oil flows in. The outer region A 1  of the longitudinal direction and the region straddling a part inside from the outer region A 1  in the inner circumferential surface of the fixing belt  50  are disposed in a vicinity of a longitudinal end portion of the pressurizing surface of the nip pad  53  (fixing pad). The surface layer  67  functions to push the lubricant  66  trying to flow out from a longitudinal central region in a direction of the outer region A 1  back to the longitudinal central region in the inner circumferential surface of the fixing belt  50 . 
     As shown in  FIG.  4   , the surface layer  67  coated on the inner circumferential surface of the fixing belt  50  has an annular base portion  67   a  having a substantially constant width along a circumferential surface of the fixing belt  50  and a plurality of projection portions  67   b  having a substantially triangular shape provided in succession to the inner region of the base portion  67   a . Each projection portion  67   b  may be formed in a substantially right triangular shape, although the projection portion  67   b  is not limited to such a shape. Each projection portion  67   b  has a base extending along a longitudinal direction of the fixing belt  50  and an inclined side inclined with respect to the base. A recessed portion surrounded by two adjacent projection portions  67   b  and the base portion  67   a  forms a trapping portion  71  that traps the lubricant trying to flow out to the end portion side from the longitudinal central region of the inner circumferential surface of the fixing belt  50 . The inclined side of each projection portion  67   b  forms an inclined portion  72  that returns the lubricant  66  flowing into the trapping portion  71  back to the longitudinal central side of the inner circumferential surface of the fixing belt  50  with rotational movement of the fixing belt  50 . The inclined portion  72  is inclined so as to push back the lubricant  66  in a forward direction in a rotation direction to the longitudinal central side of the fixing belt  50  at the time of rotational movement of the fixing belt  50 . 
     The fixing device  34  performs fixing with respect to the sheet P on which a toner image is attached when the fixing belt  50  is heated to a predetermined temperature by application of high frequency current with respect to the IH coil unit  52 . When the sheet P is carried to the fixing device  34 , the sheet P is drawn by the nip  54  between the fixing belt  50  and the press roller  51 , the sheet P is heated while the sheet is passing through the nip  54  and pressed by the press roller  51  and the nip pad  53 . Accordingly, a toner imaged is fixed on the sheet P. 
     In the fixing device  34 , while fixing is performed with respect to the sheet P as described above, the nip pad  53  comes into sliding contact with the inner circumferential surface of the fixing belt  50  via the low friction sheet  53   a  in a pressurized state. At this time, the auxiliary heat generation plate  69  also comes into sliding contact with the inner circumferential surface of the fixing belt  50 . In the fixing device  34  of at least one embodiment, since the lubricant  66  is applied to the inner circumferential surface of the fixing belt  50 , it is possible to suppress the sliding resistance between the inner circumferential surface of the fixing belt  50  with the nip pad  53  (sheet  53   a ) and the auxiliary heat generation plate  69  to a low level. Therefore, it is possible to suppress an increase in power loss of the fixing belt  50  and the drive unit of the press roller  51 , and it is possible to suppress the abrasion of components such as the fixing belt  50 , occurrence of wrinkles on the sheet P, deterioration in printing quality, and the like. 
     Since the nip pad  53  is pressed against the inner circumferential surface of the fixing belt  50  with great power during the fixing operation in the fixing device  34 , the lubricant  66  applied to the inner circumferential surface of the fixing belt  50  tries to flow out to the longitudinal outer side of the fixing belt  50  gradually. However, in the fixing device  34  of at least one embodiment, the surface layer  67  formed of an oil repellent member is applied to the end portion of the longitudinal direction (vicinity of longitudinal end portion of the pressurizing surface of nip pad  53 ) in the inner circumferential surface of the fixing belt  50 . Therefore, the lubricant  66  trying to flow out to the end portion side from the longitudinal central region of the fixing belt  50  is repelled by the surface layer  67  formed of an oil repellent member and returns to the central side of the fixing belt  50 . 
     In particular, in the fixing device  34  of at least one embodiment, the surface layer  67  provided on the inner circumferential surface of the fixing belt  50  has the trapping portion  71  and the inclined portion  72 , and it is possible to mechanically return the lubricant  66  to the longitudinal central side of the fixing belt  50  according to the rotational movement of the fixing belt  50 . Accordingly, in the fixing device  34  of at least one embodiment, it is possible to efficiently return the lubricant  66  to the central region of the fixing belt  50  with oil repellency of the surface layer  67  and a return mechanism of the trapping portion  71  and the inclined portion  72 . Therefore, in a case where the fixing device  34  of at least one embodiment is employed, it is possible to suppress the leakage of the lubricant  66  applied to the inner circumferential surface of the fixing belt  50 , and maintain a suppression effect of sliding resistance of the inner circumferential surface of the fixing belt  50  for a long period of time. 
     The surface layer  67  provided on the inner circumferential surface of the fixing belt  50  can be made of a member other than an oil repellent member. In a case where the surface layer  67  is formed of an oil repellent member as in the fixing device  34  of at least one embodiment, it is possible to efficiently return the lubricant  66  to the longitudinal central region of the fixing belt  50 . 
     In a case where the surface layer  67  is formed by coating an oil repellent member on the inner circumferential surface of the fixing belt  50  as in the fixing device  34  of at least one embodiment, the surface layer  67  becomes thin and occupied space on the inner circumferential side of the fixing belt  50  becomes small. 
     In the fixing device  34  of at least one embodiment, since the low friction sheet  53   a  is attached on the pressurizing surface of the nip pad  53 , it is possible to further reduce the sliding resistance between the fixing belt  50  and the nip pad  53  during the fixing operation. 
     In the fixing device  34  of at least one embodiment, the surface layer  67  is provided in a non-pressurized region not directly pressurized by the press roller  51  in the fixing belt  50 . Therefore, the surface layer  67  is pressed against the nip pad  53  by the press roller  51  with great power, and it is possible to suppress the surface layer  67  from peeling off from the inner circumferential surface of the fixing belt  50 . 
     Second Embodiment 
       FIG.  6    is a partial section side view of a fixing device  134  of another embodiment.  FIG.  7    is a view showing a relationship between a heating member  80  and a printing region of the sheet P which is a recording medium in the fixing device  134  of another embodiment. 
     The fixing device  134  of at least one embodiment is applied to the image forming apparatus  10  shown in  FIG.  1   , for example, similarly to the above-described embodiment. 
     The fixing device  134  includes an endless belt  81 , the press roller  51 , and the heating member  80 . The endless belt  81  makes up a rotating member rotating in an arrow u direction in  FIG.  6    in contact with the sheet P. The endless belt  81  is driven by a belt carrying roller  82 , and tension is applied by a tension roller  83 . The endless belt  81  is formed to be elongated in the width of the sheet P (direction orthogonal to carrying direction). 
     The press roller  51  is disposed to face an outer circumferential surface of the endless belt  81 , and makes up the pressurizing member that forms a nip  154  for fixing between the press roller  51  and the endless belt  81 . The press roller  51  is driven by a motor (not shown), and rotates in an arrow q direction in  FIG.  6   . The heating member  80  is disposed on an inner circumferential side of the endless belt  81 . The press roller  51  is disposed at a position facing the heating member  80  interposing the endless belt  81  therebetween. 
     The heating member  80  pressurizes the sheet P which is a recording medium from the inner circumferential side of the endless belt  81  interposing the endless belt  81  therebetween in the pressed state. The heating member  80  pressurizes the sheet P to be fixed while the sheet P passes through the nip  154  for fixing between the endless belt  81  and the press roller  51  in the pressed state. The heating member  80  is formed in a long plate shape along the longitudinal direction of the endless belt  81 . 
     In the endless belt  81 , for example, a silicone rubber layer having a thickness of 200 μm is formed on an outer side of a polyimide which is a heat resistant resin having a thickness of 70 μm or a SUS base material having a thickness of 50 μm, and an outermost circumference is covered with a surface protective layer such as PFA. In the press roller  51 , for example, a silicone sponge layer having a thickness of 5 mm is formed on an iron bar surface of ϕ10 mm, and an outermost circumference is covered with a surface protective layer such as PFA. 
     In the heating member  80 , a grace layer and a heat resistant layer are laminated on a ceramic substrate. The heating member  80  releases extra heat to opposite side of the pressurizing surface (surface abutting on inner circumferential surface of endless belt  81 ), and aluminum heat sink is bonded to prevent warpage of the substrate. The heat resistant layer is formed of a known material such as TaSiO 2 , for example, and is divided into a predetermined length and pieces in a main scanning direction (longitudinal direction of endless belt  81 ). 
     On the ceramic substrate of the heating member  80 , a plurality of heat generation members  84  having a predetermined width are disposed side by side in the main scanning direction. On both end portions of each heat generation member  84 , an electrode  85  is formed. Each heat generation member  84  is independently energized by a corresponding drive IC  86 . The drive IC  86  which is a switch unit of the heat generation members  84  can be made up by, for example, a switching element, an ETF, a triac, a switching IC, or the like. 
     Each heat generation member  84  of the heating member  80  (each drive IC  86 ) is energized and controlled by a main body control circuit (not shown). The main body control circuit selectively energizes, for example, only the heat generation member  84  corresponding to the position where a printing region W (image forming area) of the sheet P to be fixed passes. As a result, the heating member  80  intensively heats only the printing region W on the sheet P interposing the endless belt therebetween. In the main body control circuit, information on the printing region W of the sheet P is input before the sheet P is transported to the fixing device  134 . 
     In at least one embodiment, a lubricant such as a silicone oil is applied to the inner circumferential surface of the endless belt  81  which comes into sliding contact with the heating member  80 . A surface layer similar to the above-described embodiment is coated on an outer region in the longitudinal direction and a region straddling a part inside from the outer region in the inner circumferential surface of the endless belt  81 . The surface layer is formed of an oil repellent member such as polytetrafluoroethylene (PTFE) or perfluoroalkoxyalkane (PFA). The surface layer is disposed in the vicinity of the longitudinal end portion of a pressurizing surface of the heating member  80  in the inner circumferential surface of the endless belt  81 . It is desirable that the surface layer of at least one embodiment also has a trapping portion and an inclined portion similar to the above-described embodiment. The trapping portion traps the lubricant trying to flow out to an outer region from a longitudinal central region of the endless belt  81 . The inclined portion pushes the lubricant flowing into the trapping portion back to the longitudinal central side of the endless belt  81  by movement of the endless belt  81  in the rotating direction. 
     In the fixing device  134 , the heating member  80  is pressed against the inner circumferential surface of the endless belt  81  with great power during the fixing operation. Therefore, the lubricant applied to the inner circumferential surface of the endless belt  81  tries to flow out to the longitudinal outer side of the endless belt  81  gradually. In the fixing device  134  of at least one embodiment, a surface layer formed of an oil repellent member is applied to the longitudinal end portion region (vicinity of longitudinal end portion of pressurizing surface of heating member  80 ) in the inner circumferential surface of the endless belt  81 . Accordingly, it is possible to return the lubricant flow out (i.e., the outflow) to the end portion side from the longitudinal central region of the endless belt  81  to the longitudinal central side of the endless belt  81  by the surface layer. Therefore, in the fixing device  134  of at least one embodiment, it is possible to obtain lubricating effect of the lubricant on the inner circumferential surface of the endless belt  81  for a long period of time. 
     According to at least one embodiment described above, it is possible to suppress the leakage of the lubricant applied to the inner circumferential surface of the rotating member, and maintain a suppression effect of sliding resistance for a long period of time. 
     While certain embodiments have been described these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms. Furthermore various omissions, substitutions and changes in the form of embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the invention.