Abstract:
An image heating apparatus includes a heating rotatable member for heating a toner image on a recording material at a nip; an axial flow fan for cooling the heating rotatable member at a longitudinal end portion thereof; wherein an axis of the axial flow fan extends from its outlet disposed adjacent the longitudinal end portion inclinedly toward a longitudinally central portion of the heating rotatable member.

Description:
FIELD OF THE INVENTION AND RELATED ART 
   The present invention relates to an image heating apparatus employed by an electrophotographic or electrostatic image forming apparatus, such as a copying machine, a printer, a facsimile machine, etc., in order to heat the image on recording medium. 
   As the examples of an image heating apparatus, a fixing apparatus for fixing an unfixed image on recording medium, a glossiness increasing apparatus for heating the fixed image on recording medium in glossiness to increase the fixed image in glossiness, etc., may be listed. 
   When an electrophotographic image forming apparatus is used to form an image, a toner image, which is in the unfixed state, is formed on recording medium (recording paper) by an image forming means, and then, the unfixed toner image is fixed to the recording medium. 
   There have been proposed various fixing means. Among these fixing means, a fixing apparatus which fixes an unfixed toner image by the application of heat and pressure to the unfixed toner image is mostly commonly in use. A fixing apparatus of this type has a heat applying rotatable member (fixation roller, fixation belt, etc.), and a pressure applying rotatable member (pressure roller, pressure belt, etc.). The heat applying rotatable member is heated by a heating means. The pressure applying rotatable member is kept in contact with the heat applying member, forming thereby a fixation nip. As for the operation of a fixing apparatus, the two rollers are rotated together, and a sheet of recording medium, on which an unfixed toner image is borne, is introduced into the fixation nip between the two rotatable members, and is conveyed through the fixation nip, while remaining pinched by the two rotatable members. While the recording medium is conveyed through the fixation nip, the toner image on the recording medium is fixed to the recording medium by the heat from the heat applying rotatable member, and the nip pressure. 
   A fixing apparatus of the above described type is designed to accommodate various recording media, that is, recording mediums different in width (dimension in terms of the direction parallel to rotational axes of rotatable members). Thus, when a substantially number of small sheets of recording medium, that is, sheets of recording medium narrower than the widest sheet of recording medium conveyable through the fixing apparatus, are continuously conveyed through the fixing apparatus, the portions of the heat applying rotatable member, which are outside the path of the small sheet of recording medium, tend to increase in surface temperature, for the following reason. That is, when a small sheet of recording medium is conveyed through the fixing apparatus, the portions of the heat applying rotatable member, which are outside the path of the recording medium is not robbed of heat. Thus, as a substantial number of small sheets of recording medium are continuously conveyed through the fixing apparatus, heat tends to accumulate in the portions of the heat applying rotatable member, which are outside the path of the small sheet of recording medium. 
   The above described phenomenon is referred to as “peripheral temperature increase” or “out-of-sheet-path temperature increase” of a fixing apparatus. If this “peripheral temperature increase” exceeds a certain level, problems such as the “hot offset”, and/or thermal deterioration of the structural components of the fixing apparatus, is likely to occur. 
   One of the countermeasures for the above described problems is disclosed in Japanese Laid-open Patent Applications H04-51179, 2003-076209, for example. According to these applications, the fixing apparatuses are structured to air cool the out-of-sheet-path portions of the fixing apparatus, in order to prevent the peripheral temperature increase, that is, the phenomenon which occurs when a substantial number of small sheets of recording medium are conveyed through a fixing apparatus. 
   In the case of the prior technologies, however, the cooling fan(s) and ducts for guiding the cooling draft, are aimed virtually perpendicular to the rotational axis of the heat applying rotatable member. Therefore, it is possible that the following problem will occur, which will be described next with referent to  FIG. 11 . 
   Referring to  FIG. 11 , designated by a referential number  101  is a fixation roller. Designated by a referential number  102  is an elastic pressure applying roller, which is a pressure applying rotatable member (which hereafter will be referred to as pressure roller). The pressure roller  102  is kept pressed upon the fixation roller  101 , forming a fixation nip N. The fixation roller  101  is heated by a heat source disposed within the hollow of the fixation roller  101 , so that its surface temperature remains at a preset fixation temperature. The pair of rollers  101  and  102  are rotated together, and a sheet of recording medium, on which an unfixed toner image is borne, is introduced into, and conveyed through, the fixation nip N between the rotating two rollers  101  and  102 . As the recording medium is conveyed through the fixation nip N while remaining pinched by the two rollers, the unfixed toner image on the recording medium is fixed to the surface of the recording medium by the heat from the fixation roller  101  and the nip pressure. In the case of the fixing apparatus in this embodiment, recording medium is introduced into, and conveyed through, the fixing apparatus so that, in terms of the direction perpendicular to the recording medium conveyance direction, the center of the recording medium coincides with the centerline of the recording medium passage of the fixing apparatus. Designated by alphanumeric referential symbols  103 L and  103 R are the left and right cooling means which cool the out-of-sheet-path portions of the fixation roller  101 , by sending cooling draft to the out-of-sheet-path portions. The left and right cooling means  103 L and  103 R are provided with ducts  104 L and  104 R, and cooling fans  105 L and  105 R, respectively, which send cooling draft into these ducts  104 L and  104 R, respectively. The ducts  104 L and  104 R are provided with an air outlet a aimed toward the corresponding lengthwise end portion of the fixation roller  101 . The cooling means  103 L and  103 R are also provided with movable shutter  106 L and  106 R, respectively, which are in the form of a plate. The shutter  106  is used to control the width (in the direction parallel to rotational axis of fixation roller) of the air outlet a of the duct  104 . The cooling fans  105 L and  105 R, and the duct  104 L and  10 R, are aimed roughly perpendicular to the axial line O-O of the fixation roller  101 . 
   As for the recording medium width in terms of the direction perpendicular to the direction in which recording medium is conveyed through the fixing apparatus, widest and narrowest sheets of recording paper, which can be conveyed through the fixing apparatus will be referred to as a large recording paper and a small recording paper, respectively, hereafter. A sheet of recording paper, the width of which is between those of large and small recording papers, will be referred to as a medium recording paper. 
     FIG. 11(   a ) is a schematic vertical sectional view of the fixing apparatus through which a small recording paper is being conveyed. Designated by a referential letter Q is the range which corresponds to the path of a small recording paper, and designated by a referential R are the left and right out-of-sheet-path ranges, which occur as a small recording paper is conveyed through the fixing apparatus. The air outlets  a  of the left and right ducts  104 L and  104 R directly face the left and right lengthwise end portions of the fixation roller  101 , which correspond to the out-of-sheet-path range. Further, the air outlets  a  of the left and right ducts  104 L and  104 R are adjusted in width so that their width matches that of the left and right out-of-sheet-path portions of the fixation roller  101 . The left and right shutters  106 L and  106 R are in their positions in which they keep wide open the air outlets  a  of the left and right ducts  104 L and  104 R. Therefore, as a small recording paper is conveyed through the fixing apparatus, the left and right out-of-sheet-path portions R and R of the fixation roller  101  are cooled by the cooling draft blown out of the wide open air outlets  a  of the left and right ducts  104 L and  104 R, being thereby prevented from excessively increasing in temperature. Thus, even if a substantial number of small recording papers are continuously conveyed through the fixing apparatus, the out-of-sheet-path portions of the fixation roller  101  are prevented from increasing in temperature. 
     FIG. 11(   b ) is a schematic vertical sectional view of the fixing apparatus through which a medium recording paper is being conveyed. Designated by a referential letter Q is the range which corresponds to the path of a medium recording paper, and designated by a referential R are the left and right out-of-sheet-path ranges, which occur as a medium recording paper is conveyed through the fixing apparatus. When a medium recording paper is used as recording medium, the left and right shutters  106 L and  106 R are moved to their positions preset to match the width of the air outlets  a  of the left and right ducts  104 L and  104 R to the width of a medium recording paper. Therefore, as a medium recording paper is conveyed through the fixing apparatus, the left and right out-of-sheet-path portions R and R of the fixation roller  101  are cooled by the cooling draft blown out of the air outlets  a  of the left and right ducts  104 L and  104 R, which match in width the left and right out-of-sheet-path portions R and R. Therefore, the left and right out-of-sheet-path portions R and R of the fixation roller  101  are prevented from excessively increasing in temperature. Thus, even if a substantial number of medium recording papers are continuously conveyed through the fixing apparatus, the out-of-sheet-path portions of the fixation roller  101  are prevented from excessively increasing in temperature. 
     FIG. 11(   c ) is a schematic vertical sectional view of the fixing apparatus through which a large recording paper is being conveyed. In this case, there is no out-of-sheet-path range, and therefore, the problem that the out-of-sheet-path portions become excessive in temperature does not occur. Thus, the left and right shutters  106 L and  106 R are kept in their positions preset to keep the air outlets  a  of the left and right ducts  104 L and  104 R completely shut. Therefore, the fixation roller  101  is not subjected to the cooling draft. 
   However, a conventional setup, such as the above described one, for cooling the out-of-sheet-path portions of a fixation roller has the following problems. That is, as cooling draft is blown upon the out-of-sheet-path portions R of the fixation roller  101 , it partially diverts into the sheet path range Q as indicated by a flow line X in  FIG. 11(   a ). Thus, the portions of the fixation roller  101 , which correspond to the edge portions of the sheet path, are reduced in temperature. A problem similar to this problem is also likely to occur when the fixing apparatus is in the state shown in  FIG. 11(   b ). 
   In other words, the conventional setup for cooling the out-of-sheet-path portions of a fixation roller is problematic in that the portion of the fixation roller, which is in the sheet path range, is reduced in temperature by the diversion of the cooling draft, which sometimes results in the formation of an abnormal image, that is, an image which is abnormal in that it is inferior in fixation across its edge portions 
   SUMMARY OF THE INVENTION 
   Thus, the primary object of the present invention is to provide an image heating apparatus which does not suffer from the problem that an image is unsatisfactorily fixed because the cooling draft generated by a fan diverts into the sheet path range of the fixing apparatus. 
   According to an aspect of the present invention, there is provided an image heating apparatus comprising a heating rotatable member for heating a toner image on a recording material at a nip; an axial flow fan for cooling said heating rotatable member at a longitudinal end portion thereof; wherein an axis of said axial flow fan extends from its outlet disposed adjacent the longitudinal end portion inclinedly toward a longitudinally central portion of said heating rotatable member. 
   These and other objects, features, and advantages of the present invention will become more apparent upon consideration of the following description of the preferred embodiments of the present invention, taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic cross-sectional view of the fixing apparatus in the first preferred embodiment of the present invention. 
       FIG. 2  is a partially exploded schematic perspective view of the fixing mechanism portion and forced draft cooling mechanism portion of the fixing apparatus shown in  FIG. 1 . 
       FIG. 3  is a schematic partially cutaway front view of the fixing mechanism portion of the fixing apparatus. 
       FIG. 4  is a schematic vertical sectional view of the fixing mechanism portion of the fixing apparatus. 
       FIG. 5  is a schematic exploded perspective view of the forced draft cooling mechanism portion of the fixing apparatus. 
       FIG. 6  is a schematic vertical sectional view of the fixing apparatus, through which a substantial number of small sheets of recording medium are being continuously conveyed. 
       FIG. 7  is a schematic vertical sectional view of the fixing apparatus, through which a substantial number of medium sheets of recording medium are being continuously conveyed. 
       FIG. 8  is a schematic vertical sectional view of the fixing apparatus, through which a substantial number of large sheets of recording medium are being continuously conveyed. 
       FIG. 9  is a block diagram of the control system of the fixing apparatus. 
       FIG. 10  is a vertical cross-sectional view of the image forming apparatus in the preferred embodiment of the present invention. 
       FIG. 11  is a schematic drawing of a fixing apparatus in accordance with the prior art. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Hereinafter, the preferred embodiments of the present invention will be described with reference to the appended drawings. However, the preferred embodiments are not intended to limit the present invention in scope. 
   Embodiment 1 
   (1) Image Forming Portion 
     FIG. 10  is a schematic vertical sectional view of an electrophotographic full-color printer, which is an example of an image forming apparatus, the fixing apparatus of which is an image heating apparatus in accordance with the present invention. It shows the general structure of the image forming apparatus. First, the image forming portion of the apparatus will be briefly described. 
   This printer can output a full-color image on recording medium, in response to picture information inputted from an external host apparatus  200  connected to the control circuit portion  100  (controlling means: CPU) of the printer so that communication is possible between the printer and external host apparatus  200 . 
   The examples of the external host apparatus  200  are a computer, an image reader, and the like. The control circuit  100  exchanges signals with the external host apparatus  200 . Further, the control circuit  100  exchanges signals with various image forming devices, and controls the image formation sequence. 
   Designated by a referential number  8  is a flexible intermediary transfer belt (which hereafter will be referred to as belt). The belt  8  is stretched between and around a belt backing roller  9  (which backs up belt  8  against secondary transfer roller) and a tension roller  10 . As the roller  9  is driven, the belt  8  is rotationally driven at a preset velocity in the counterclockwise direction indicated by an arrow mark. Designated by a referential number  11  is a secondary transfer roller, which is kept pressed against the abovementioned belt backing roller  9  with the presence of the belt  8  between the two rollers  9  and  11 . The interface between the belt  8  and secondary transfer roller  11  is the secondary transfer portion. 
   Designated by alphanumeric referential symbols  1 Y,  1 M,  1 C, and  1 Bk are four image forming portions, that is, first, second, third, and fourth image forming portions, respectively, which are on the underside of the belt  11 , being juxtaposed in parallel and series, with preset intervals, in the direction parallel to the direction in which the belt  11  is moved. Each image forming portion is an electrophotographic image forming portion which uses an exposing method based on laser. Each image forming portion has an image bearing member  2 , more specifically, an electrophotographic photosensitive member in the form of a drum (which hence will be referred to simply as drum, hereafter). The drum  2  is rotationally driven at a preset peripheral velocity in the clockwise direction indicated by an arrow symbol. Each image forming portion also has a primary charging device  3 , a developing apparatus  4 , a transferring means  5  in the form of a roller (transfer roller), and a drum cleaning apparatus  6 , which are in the adjacencies of the peripheral surface of the drum  2 . Each transfer roller  5  is inside the loop which the belt  8  forms, and is kept pressed against the corresponding drum  2 , with the portion of the belt  8 , which is moving through the bottom portion of the abovementioned belt loop, pinched between the transfer roller  5  and drum  2 . The interface between each drum  2  and the belt  8  is one of the primary transferring portions. Designated by a referential number  7  is a laser-based exposing apparatus of each image forming portion, which exposes the peripheral surface of the drum  2  of the image forming portion. The laser-based exposing apparatus is made up of a laser light emitting means, a polygon mirror, a deflection mirror, etc. The laser light emitting means emits a beam of laser light in response to sequential digital electrical picture element signals which reflect picture information given to the exposing apparatus. 
   The control circuit  100  causes each image forming portion to carry out an image forming operation, in response to picture signals (which are obtained by separating optical image of original into monochromatic images of primary colors) inputted from the external host apparatus  200 . That is, yellow, magenta, cyan, and black toner images are formed, with preset timing, on the peripheral surfaces of the rotating drums  2  in the first-fourth image forming portions  1 Y,  1 M,  1 C, and  1 Bk, respectively. Incidentally, the principle of the electrophotographic process for forming a toner image on the peripheral surface of the drum  2  is well-known, and therefore, will not be described here. 
   As the toner images are formed on the peripheral surfaces of the drums  2  in the image forming portions, they are sequentially transferred in layers onto the outward surface of the belt  8 , in the primary transferring portions. The belt  8  is circularly driven at a velocity which matches the peripheral velocity of each drum  2 , in such a direction that the belt  8  and the peripheral surface of each drum  2  move in the same direction in the primary transferring portion. As a result, an unfixed full-color toner image is synthetically effected by the four toner images layered on the surface of the belt  8 . 
   Meanwhile, the sheet feeder roller  14  of the sheet feeder cassette selected from among the sheet feeder cassettes  13 A,  13 B, and  13 C which are vertically stacked in the sheet feeder cassette chamber, and in which multiple large, medium, and small sheets of papers are stored in layers, respectively, is driven with a preset timing. As the sheet feeder roller  14  is driven, one of the sheets of recording medium P in the selected sheet feeder cassette is separated from the rest, and is conveyed to a pair of registration rollers  16  through a vertical sheet conveyance path  15 . When the image forming apparatus is in the manual feeding mode, a sheet feeder roller  18  is driven. As the sheet feeder roller  18  is driven, one of the sheets of recording medium P set in layers in a manual feeder tray  17  (multi-purpose tray) is separated from the rest, and is conveyed to the pair of registration roller  16  through the vertical sheet conveyance path  15 . 
   The registration rollers  16  are rotated to release and convey the recording medium P with such timing that the leading end of the recording medium P reaches the secondary transferring portion at the same time as the leading end of the abovementioned full-color toner image on the circularly moving belt  8  reaches the secondary transferring portion. Thus, as the recording medium P is conveyed through the secondary transferring portion, the four monochromatic toner images on the surface of the belt  8 , which make up the single full-color toner image, are transferred together onto the recording medium P on the belt  8 , in a manner of being peeled away from the surface of the belt  8 . After coming out of the secondary transferring portion, the recording medium P is separated from the belt  8 , and is guided into a fixing apparatus  20 , by which the abovementioned multiple monochromatic toner images on the recording medium P are fixed to the surface of the recording medium P; the four toner images are mixed, while being melted, and are permanently adhered to the surface of the recording medium P. After coming out of the fixing apparatus  20 , the recording medium P is sent out, as a full-color copy, from the main assembly of the image forming apparatus onto a delivery tray  23 , by a pair of sheet discharging rollers  22  through a sheet conveyance path  21 . 
   After the separation of the recording medium P from the belt  8  in the secondary transferring portion, the surface of the belt  8  is cleaned by a belt cleaning apparatus  12 , that is, the adherent residues, such as toner particles, remaining on the surface of the belt  8  after the secondary transfer, are removed by the belt cleaning apparatus  12 . Then, the cleaned portion of the surface of the belt  8  is used for the following round of image formation. 
   When the image forming apparatus is in the black-and-white print mode, only the fourth image forming portion  1 Bk, which is the portion for forming a black toner image, is operated under the control of the control circuit portion  100 . When the image forming apparatus is in the two-sided print mode, the recording medium P is conveyed in the direction to be discharged into the delivery tray  23  by the discharge rollers  22  until the trailing end of the recording medium P almost moves past the interface between the pair of discharge rollers  22 , after the printing of an image on the recording medium P. Then, immediately before the trailing end of the recording medium P moves past the sheet discharge rollers  22 , the rollers  22  are reversed in rotation. Thus, the recording medium P is introduced into a re-feeding path  24 . Then, it is conveyed through the re-feeding path  24  to be conveyed again to the registration rollers  16 , being thereby placed upside down. Thereafter, the recording medium P is conveyed through the secondary transfer portion and fixing apparatus  20  as it was when an image was printed on the first surface. Then, the recording medium P is sent out as a two-sided copy, onto the delivery tray  23 . 
   (2) Fixing Apparatus  20   
   In the following description of the fixing apparatus  20 , the “lengthwise direction” of the fixing apparatus  20  and the components thereof is synonymous to the direction parallel to the direction perpendicular to the recording medium conveyance direction. The “front side” of the fixing apparatus  20  is synonymous to the lateral side of the fixing apparatus  20 , from which the recording medium P is introduced into the fixing apparatus  20 , and the “left” or “right” side of the apparatus is synonymous to the left or right side of the apparatus as seen from the front side of the apparatus. The “width” of a sheet of recording medium is synonymous to the measurement of the sheet in terms of the direction perpendicular to the recording medium conveyance direction. 
     FIG. 1  is an enlarged schematic cross-sectional view of the fixing apparatus  20  of the image forming apparatus shown in  FIG. 10 . The fixing apparatus  20  is roughly separable into a fixing mechanism portion  20 A, and a forced draft cooling mechanism portion  20 B. The fixing mechanism portion  20 A employs a heating belt. The cooling mechanism portion  20 B uses forced draft of air as cooling medium. 
   (2-1) Fixing Mechanism Portion  20 A 
   First, referring to  FIGS. 1-4 , and  9 , the general structure of the fixing mechanism portion  20 A will be described.  FIG. 2  is an exploded perspective view of the combination of the fixing mechanism portion  20 A and forced draft cooling mechanism portion  20 B.  FIG. 3  is a schematic front view of the combination of the fixation belt assembly and pressure application roller of the fixing mechanism portion  20 A.  FIG. 4  is a vertical sectional view of the combination of the fixation belt assembly and pressure applying roller (which hereafter will be referred to simply as pressure roller), shown in  FIG. 2 , at a plane which coincides with the axial line of the pressure roller.  FIG. 9  is a block diagram of the control system of the fixing apparatus  20 . 
   Basically, the fixing mechanism portion  20 A is identical to the fixing apparatus disclosed in Japanese Laid-open Patent Applications H04-44075-44083, H04-204980-204984, etc. It is a fixing apparatus of the on-demand type, and employs the heating belt (heating film). Further, this fixing apparatus employs a pressure applying rotational member to circularly drive the belt; it is of the tension-less type. 
   Designated by a referential number  31  is a fixation belt assembly, and designated by a referential number  32  is an elastic pressure roller, which is a pressure applying rotating member. The fixation belt assembly  31  and pressure roller  32  are kept pressed against each other to form a fixation nip N. 
   Designated by a referential number  33  is a fixation belt of the fixation belt assembly  31 , which is a circularly movable member for heat application. The fixation belt  33  is cylindrical; it is endless and in the form of a sleeve. It is flexible. Designated by a referential number  34  is a belt guiding member (which hereafter will be referred to simply as guiding member), which is heat resistant and rigid. The guiding member  34  is in the form of a trough, and is semicircular in cross section. Designated by a referential number  35  is a ceramic heater (which hereafter will be referred to simply as heater) as a heat source (heating member). The guiding member  34  is provided with a groove, which is in the outwardly facing surface of the guiding member  34  and extends in the lengthwise direction of the guiding member  34 . The heater  35  is fitted in this groove of the guiding member  34 , being thereby solidly attached to the guiding member  34 . The fixation belt  33  is loosely fitted around the guiding member  33  fitted with the heater  35 . Designated by a referential number  36  is a pressure application stay (which hereafter will be referred to simply as stay). The stay  36  is rigid, and is U-shaped in cross section. It is on the inward side of the guiding member  34 . Designated by a pair of alphanumeric referential symbols  36   a  are a pair of arm portions extending outward from the left and right lengthwise ends of the stay  36 , one for one. Designated by a pair of referential numbers  37  are a pair of end holders in which the arm portions  36   a  are fitted, one for one. Designated by an alphanumeric symbol  37   a  is a flange portion, which is an integral part of the end holder  37 . 
   Ordinarily, the fixation belt  33  is a laminar belt, and is made up of a base layer, an elastic layer, a release layer, etc. The base layer is formed of heat resistant resin or metal. The fixation belt  33  is thin and flexible. It is high in thermal conductivity, and is low in thermal capacity. 
   The ceramic heater  35  is a linear heating member. It is low in thermal capacity. It is attached to the guiding member  35  so that it extends in the direction perpendicular to the moving direction of the fixation belt  33  and recording medium P. Basically, it is made up of a substrate and a heat generation layer. The substrate is formed of ceramic, such as aluminum titanate, alumina, or the like. The heat generation layer is formed on the substrate, of silver-palladium, or the like, and generates heat as electric current is flowed through it. There are various ceramic heaters, which are well-known. Thus, the ceramic heater  35  will not be described in detail here. 
   The pressure roller  32  is made up of a metallic core  32   a , and an elastic layer  32   b  formed around the metallic core  32   a , of silicone rubber or the like, to reduce the roller  32  in overall hardness. For the improvement of the surface properties of the pressure roller  32 , the peripheral surface of the elastic layer  32   b  may be coated with a fluorinated resin layer  32   c  formed of PTFE, PFA, FEP, or the like. The pressure roller  32  is rotatably supported between the left and right lateral plates  38 L and  38 R of the apparatus frame  38 ; the left and right end portions of the metallic core  32   a  are supported by a pair of bearing members  39  with which the left and right lateral plates  38 L and  38 R are fitted. 
   The fixation belt assembly  31  is positioned in parallel to the above described pressure roller  32 , with the heater side of the fixation belt assembly  31  facing the pressure roller  32 . It is kept pressed against the pressure roller  32 ; the left and right holders  37  are kept pressed with a preset amount of force F generated by an unshown pressure application mechanism, in the direction perpendicular to the axial direction of the pressure roller  32 . Thus, the surface of the heater  35  is kept pressed against the pressure roller  32 , that is, the elasticity of the elastic layer  32   b  of the pressure roller  32 , with the presence of the fixation belt  33  between the heater  35  and pressure roller  32 , forming thereby the fixation nip N necessary for thermal fixation. The amount of force F is controlled so that the width of the fixation nip N, in terms of the recording medium conveyance direction, will have a preset value. The pressure application mechanism is provided with a pressure removal mechanism. Thus, when necessary, for example, when dealing with a paper jam or the like, the pressure can be removed to make it easier to remove the jammed recording medium P in the fixation nip N. 
   Designated by a referential number  40  is an entrance guide attached to the apparatus frame  38 , and designated by a referential number  41  is a pair of sheet discharge rollers, which are also attached to the apparatus frame  38 . The entrance guide  40  plays the role of guiding the recording medium P so that after the recording medium P is moved past the secondary transfer nip N and is guided into fixing apparatus  20  by the vertical guide  19 , it is precisely guided into the fixation nip N. 
   Designated by a referential letter G is a drive gear solidly attached to one end of the metallic core  32   a  of the pressure roller  32 . It is to this gear G that the rotational force of a fixation motor M 1  is transmitted through an unshown driving force transmission mechanism. As the driving force is transmitted to the drive gear G, the pressure roller  32  is rotationally driven in the clockwise direction indicated by an arrow mark in  FIG. 1 . As the pressure roller  32  is rotationally driven, rotational force is transmitted to the fixation belt  33  by the friction between the outward surface of the fixation belt  33  and the pressure roller  32 . As a result, the fixation belt  33  rotates in the counterclockwise direction indicated by an arrow mark, with its inward surface remaining in contact with, and sliding on, the heater  35 , on the outward side of the guiding member  34  (pressure roller is driven to circularly move fixation belt  33 ). The fixation belt  33  circularly moves at a peripheral velocity which is roughly equal to the peripheral velocity of the pressure roller  32 . The left and right flange portions  37   a  catch the belt  33  by the corresponding lateral edges of the fixation belt  33  as the fixation belt  33  deviates in the left or right direction; they control the lateral movement of the fixation belt  33 . The inward surface of the fixation belt  33  is coated with grease (lubricant) to ensure that the fixation belt  33  smoothly slides on the heater  35  and guiding member  34 . 
   After the recording medium P is guided into the fixation nip N, it is conveyed through the fixation nip N by the rotation of the pressure roller  32  and fixation belt  33  while remaining pinched by the pressure roller  32  and fixation belt  33 . In this embodiment, the recording medium P is conveyed through the fixation apparatus  20  so that the centerline of the recording medium P in the fixing apparatus  20  coincides with the centerline of the recording medium conveyance passage, in terms of the lengthwise direction of the fixing apparatus (central alignment). That is, as the recording medium P is guided into the fixing apparatus  20 , it is conveyed through the fixing apparatus  20  so that the centerline of the recording medium P coincides with the centerline of the recording medium passage, regardless of the size of the recording medium conveyable through the fixing apparatus  20 . Designated by a referential letter S is the referential centerline (theoretical line) of the recording medium passage of the fixing apparatus  20 , which coincides with the centerline of the recording medium P when the recording medium P is conveyed through the fixing apparatus  20 . 
   Designated by alphanumeric referential symbols TH 1  and TH 2  are main and subordinate thermistors as first and second temperature detecting means, respectively. In terms of the lengthwise direction of the heater  35 , the main thermistor TH 1  is placed in contact with the roughly the center of the rear surface of the heater  35  to detect the temperature of the portion of the heater which remains within the recording medium path regardless of recording medium size. The subordinate thermistor TH 2  is placed elastically in contact with the inward surface of the fixation belt  33  to detect the temperature of the portion of the fixation belt  33  which corresponds to the portion of the recording medium passage, which is outside the path of a recording medium narrower than the path of a widest recording medium conveyable through the fixing apparatus  20 . More concretely, the subordinate thermistor TH 2  is supported by the free end portion of an elastic thermistor supporting member  42 , which is in the form of a leaf spring. The supporting member  42  is fixed to the guiding member  34 . In other words, the subordinate thermistor TH 2  is kept elastically in contact with the inward surface of the fixation belt  33  by the elasticity of the elastic thermistor supporting member  42 . 
   As electric current is flowed by a heater driver circuit  92  ( FIG. 9 ), as an electric power supplying portion, through the heat generation layer of the heater  35 , which is on the heater substrate, the heat generation layer generates heat. As a result, the heater  35  quickly increases in temperature across the entirety of its effective heat generation range in terms of its lengthwise direction. The temperature of the heater  35  is detected by the main thermistor TH 1 , and the electrical information regarding this heater temperature is inputted into the control circuit portion  100  through an A/D converter  81 . In addition, the temperature of the fixation belt  33  is detected by the subordinate thermistor TH 2 , and the electrical information regarding this temperature of the fixation belt  33  is inputted into the control circuit portion  100  through an A/D converter  82 . The control circuit portion  100  sets up a proper procedure for adjusting the temperature of the fixation heater  35  based on the outputs of the main and subordinate thermistors TH 1  and TH 2 , in order to control the amount of electric power supplied to the fixation heater  35  from the heater driver circuit  92 . That is, the temperature of the fixation heater  35  is controlled so that the heater temperature detected by the main thermistor TH 1  remains at a preset fixation temperature level. 
   The control circuit portion  100  starts to rotationally drive the pressure roller  32  by controlling the fixation motor driver circuit  91  in response to a print start signal from the external host apparatus  200 , or a control signal other than the print start signal. The control circuit portion  100  also starts to generate heat in the heater  35  by controlling the heater driver circuit  92 . As soon as the fixation belt  33  stabilizes in circulatory speed, and the temperature of the heater  35  reaches the preset level, the recording medium P bearing an unfixed toner image t is guided into the fixation nip portion N along the entrance guide  40  from the direction of the image forming portion, with the toner image bearing surface of the recording medium P facing the fixing belt  33 . The recording medium P, and the portion of the fixation belt  33 , which corresponds to the recording medium P, move together through the fixation nip N, with the recording medium P kept pressed against the heater  35 , with the presence of the fixation belt  33  between the heater  35  and recording medium P. While the recording medium P is conveyed through the fixation nip N, the recording medium P is given heat by the fixation belt  33  heated by the heater  35 . As a result, the toner image t on the recording medium P is thermally fixed to the surface of the recording medium P. After the conveyance of the recording medium P through the fixation nip N, the recording medium P is separated from the surface of the fixation belt  33 , and is conveyed further to be discharged from the apparatus main assembly. 
   (2-2) Forced Draft Cooling Mechanism Portion  20 B 
   Next, referring primarily to  FIGS. 5-8 , the forced draft cooling mechanism portion  20 B will be described. The forced draft cooling mechanism portion  20 B is a cooling means which cools the fixing mechanism portion  20 A by sending air thereto. More specifically, as a recording medium, which is narrower than a widest recording medium, is continuously conveyed through the fixing apparatus  20 , the portions of the fixing mechanism portion  20 A, which are outside the path of the narrower recording medium, are likely to increase in temperature. It is this increase in temperature of the portions of the fixing mechanism portion  20 A, which hereafter will be referred to as out-of-sheet-path temperature increase, that the forced draft cooling mechanism  20 B prevents by sending air thereto.  FIG. 5  is an exploded perspective view of the forced draft cooling mechanism portion  20 B.  FIGS. 6-8  are schematic drawings of the forced draft cooling mechanism portion  20 B, showing the operation of the shutter plates. 
   The forced draft cooling mechanism portion  20 B is provided with a left duct  51 L and a left cooling fan  52 L. The left duct  51 L is structured so that its air outlet a faces the left end portion of the fixation belt  33  in terms of the lengthwise direction of the fixation belt  33 . The left cooling fan  52 L sends the cooling draft into the left duct  51 L. The forced draft cooling mechanism portion  20 B is also provided with a right duct  51 R and a right cooling fan  52 R. The right duct  51 R is structured so that its air outlet  a  faces the right end portion of the fixation belt  33  in terms of the lengthwise direction of the fixation belt  33 . The right cooling fan  52 R sends the cooling draft into the right duct  51 R. Further, the forced draft cooling mechanism  20 A is provided with a shutter mechanism  53 , as an air outlet opening width adjusting means, for adjusting the left and right ducts  51 L and  51 R in the width of the openings of their air outlets  a . 
   As the cooling fans  51 L and  51 R, a pair of axial flow fans are employed, which are lower in cost than a sirocco fan and a cross-flow fan. 
   The shutter mechanism  53  has a shutter frame  54 , left and right shutter plates  55 L and  55 R, a shutter motor M 2 , shutter plate position detecting means  55   a ,  55   b , PH, etc. The shutter frame  54  is provided with left and right holes b and b (windows). The left and right holes b and b of the shutter frame  54  correspond in shape and size to the air outlets  a  and  a  of the left and right ducts  51 L and  51 R, respectively. The left and right ducts  51 L and  51 R are fixed to a substrate (shutter frame)  54  so that the air outlets  a  and  a  of the left and right ducts  51 L and  51 R align with the left and right holes b and b of the substrate  54  (shutter frame). 
   The pair of shutters, that is, the left and right shutter plates  55 L and  55 L, are located on the opposite side of the substrate  54  (shutter frame) from the side to which the ducts  51 L and  51 R are fixed. The left shutter plate  55 L is movable to adjust the width of the left hole b of the substrate  54  (shutter frame), that is, the width of the opening of the air outlet  a  of the left duct  51 L, whereas the right shutter plate  55 R is movable to adjust the width of the right hole b of the substrate  54 , that is, the width of the opening of the air outlet  a  of the right duct  51 R. The left and right shutter plates  55 L and  55 R are connected to each other with an unshown rack-and-pinion mechanism. Thus, as the pinion is rotationally driven forward or in reverse by the shutter motor M 2  (pulse motor), the left and right shutter plates  55 L and  55 R connected to the rack are moved to increase or reduce the width of the openings of the air outlets  a  and  a  of the left and right ducts  51 L and  51 R, respectively, while keeping the two openings equal in width. 
   For clarity,  FIGS. 6-8  show only the left and right ducts  51 L and  51 R, left and right cooling fans  52 L and  52 R, and left and right shutter plates  55 L and  55 R, of the forced draft cooling mechanism portion  20 B. 
   The left and right ducts  51 L and  51 R are tilted so that their center lines align with the approximate rotational axis O-O of the fixation belt  33 , and also, so that the draft inlet sides of the left and right ducts  51 L and  51 R are on the inward side of the fixing mechanism portion  20 A, in terms of the lengthwise direction of the fixation roller, relative to the outlet sides of the left and right ducts  51 L and  51 R, respectively. Therefore, the left and right cooling fans  52 L and  52 R send cooling draft toward the corresponding lateral edges of the fixation belt. That is, the forced draft cooling mechanism portion  20 B is structured so that the rotational axes of the cooling fans  52 L and  52 R (axial flow fans) are tilted relative to the rotational axis O-O of the fixation belt  33 . In other words, the forced draft cooling mechanism portion  20 B is structured so that a plane (plane Q in  FIG. 6 ) perpendicular to the direction of the forced draft is tilted relative to the rotational axis O-O of the fixation belt  33 . 
   A referential letter Y designates the flow line of the cooling draft sent into the ducts  51 L and  51 R by the cooling fans  52 L and  52 R, respectively. Incidentally, of the three lines designated by the referential letter Y in  FIG. 6 , the central line Y corresponds to the rotational axis of the fooling fan  52 . Further, the ducts  51 L and  51 R are tilted in parallel to the direction of the cooling draft generated by the cooling fans  52 L and  52 R, that is, the flow lines Y of the cooling draft, so that the ducts  51 L and  51 R guide the cooling draft toward the edge portions of the recording medium passage. The forced draft cooling mechanism portion  20 B is structured so that the angle φ ( FIG. 6 ) between the direction of the rotational axes of the cooling fans  52 L and  52 R (and/or direction in which ducts  51 L and  51 R extend), and the direction perpendicular to the rotational axis of the fixation belt  33  O-O, falls in a range of 10°-80°. 
   Incidentally, the range 10°-80° was selected for this embodiment through experiments. If the angle φ is no more than 10°, a substantial amount of cooling draft is lost, and therefore, the out-of-sheet-path portions of the fixation belt assembly  31  cannot be sufficiently cooled. In the case of a forced draft cooling mechanism provided with shutter plates, the cooling draft roughly perpendicularly hit the inward surface of the shutter plate, and therefore, a substantial amount of cooling draft is lost by being blocked by the shutter plate. On the other hand, if the angle φ is no less than 80°, the cooling draft is ineffective as cooling medium, allowing the out-of-sheet-path portions of the fixing mechanism portion  20 A to excessively increase in temperature. 
   That is, in this embodiment, the cooling means is structured so that the flow lines Y of the cooling draft blown toward the fixation belt  33  from the cooling means  51  and  52  for cooling the out-of-sheet-path portions of the fixation belt  33 , which is a heat applying rotational member, by blowing cooling draft toward the out-of-sheet-path portions, are tilted relative to the direction perpendicular to the rotational axis O-O of the fixation belt  33 . 
   More concretely, as described above, the cooling fan  52  is positioned so that the flow lines Y of the cooling draft sent into the duct  51  by the cooling fan  52  are tilted relative to the direction perpendicular to the rotational axis O-O of the fixation belt  33 ; the duct  51  is positioned so that the axial line of the duct  51  is tilted relative to the direction perpendicular to the rotational axis O-O of the fixation belt  33 ; the cooling fan  52  is positioned so that the flow lines Y of the cooling draft sent to the duct  51  by the cooling fan  52  are tilted relative to the direction perpendicular to the rotational axis O-O of the fixation belt  33 , in such a manner that the upstream ends of the flow lines Y in terms of the direction of the cooling draft, are positioned higher than the downstream ends of the flow lines Y; or the duct  51  is positioned so that the axial line of the duct  51  is tilted relative to the direction perpendicular to the rotational axis O-O of the fixation roller  33 , in such a manner that the upstream side of the axial line of the duct  51  in terms of the direction of the cooling draft is positioned higher than the downstream side of the axial line of the duct  51 . 
   Regarding the size of the sheet recording medium conveyable through the fixing apparatus  20 , hereafter, a sheet of recording medium which is the largest in width will be referred to as the large recording paper, and a sheet of recording medium which is the smallest in width will be referred to as the small recording paper. Further, a sheet of recording medium whose width is between the width of the small recording paper that the width of the large recording paper, will be referred to as the medium recording paper. 
     FIG. 6  is a schematic drawing of the fixing mechanism portion  20 A in the state in which a small recording paper is being conveyed through the fixing apparatus  20 . In  FIG. 6 , designated by a referential letter Q is the path of a small recording paper, and designated by a referential letter R are the left and right out-of-sheet-path portions of the recording medium passage of the fixing apparatus  20 , which are on the left and right sides of the path Q, or the path of a small recording paper. The air outlets a and a of the left and right ducts  51 L and  51 R correspond to the left and right out-of-sheet-path portions R and R. The width of the openings of the air outlets  a  and  a  of the left and right ducts  51 L and  51 R are the same as those of the left and right out-of-sheet-path portion R and R, respectively. Further, when the fixing mechanism portion  20 A is in the state shown in  FIG. 6 , the left and right shutter plates  55 L and  55 R are in the position in which they leave fully open the air outlets  a  of the left and right ducts  51 L and  51 R. Thus, the left and right end portions of the fixation belt  33 , which correspond to the left and right out-of-sheet-path portions R and R, that is, the portions of the recording medium passage, which occur when a small recording paper is conveyed through the fixing apparatus  20 , are cooled by the cooling draft blown onto them through the air outlets  a  and  a  of the left and right ducts  51 L and  51 R, which are fully open. Therefore, the problem that the portions of the fixation belt  33 , which correspond to the out-of-sheet-path portions of the sheet conveyance passage, which occur when a small recording paper is conveyed through the fixing apparatus, increase in temperature when a substantial number of small sheets of recording paper are continuously conveyed through the fixing apparatus, is prevented. 
     FIG. 7  is a schematic drawing of the fixing mechanism portion  20 A in the state in which a medium recording paper is being conveyed through the fixing apparatus  20 . In  FIG. 7 , designated by a referential letter Q is the path of a medium recording paper, and designated by a referential letter R are the left and right out-of-sheet-path portions of the recording medium passage of the fixing apparatus  20 , which are on the left and right sides of the path Q, or the path of a medium recording paper. When medium sheets of recording medium are used as recording medium, the left and right shutter plates  55 L and  55 R are moved to the positions which were set in accordance with the width of a medium recording paper to reduce the width of the air outlets  a  and  a  of the ducts  51 L and  51 R to the values equal to the widths of the left and right out-of-sheet-path portions R and R which occur as a medium recording paper is conveyed. Thus, the portions of the fixation belt  33 , which correspond to the left and right out-of-sheet-path portions R and R, that is, the portions of the recording medium passage, which occur when a medium recording paper is conveyed through the fixing apparatus  20 , are cooled by the cooling draft blown onto them through the air outlets a and a of the left and right ducts  51 L and  51 R, which have been adjusted in width. Therefore, the problem that the portions of the fixation belt  33 , which correspond to the out-of-sheet-path portions, which occur when a medium recording paper is conveyed through the fixing apparatus, increase in temperature when a substantial number of medium sheets of recording paper are continuously conveyed through the fixing apparatus, is prevented. 
     FIG. 8  is a schematic drawing of the fixing mechanism portion  20 A in the state in which a large recording paper is being conveyed through the fixing apparatus  20 . When the fixing mechanism portion  20 A is in the state shown in  FIG. 8 , the out-of-sheet-path portion does not occur, and therefore, the problem that the portions of the fixation belt  33 , which correspond to the out-of-sheet-path portions, increase in temperature does not occur. Therefore, the left and right shutter plates  55 L and  55 R are moved into the position in which they keep completely blocked the air outlets a and a of the left and right ducts  51 L and  51 R. Thus, the fixation belt  33  is not cooled by the cooling draft. Incidentally, in this case, that is, when sheets of large recording medium are conveyed through the fixing apparatus  20 , the fixing mechanism portion  20 A may be controlled so that the cooling fans  52 L and  52 R are kept stationary. If the cooling fans  52 L and  52 R are kept stationary, the control for moving the left and right shutter plates  55 L and  55 R into the position in which they keep completely blocked the air outlets  a  and  a  of the left and right ducts  51 L and  51 R does not need to be executed. 
   The left and right shutter plates  55 L and  55 R are controlled so that they move to the positions which correspond to the width of the recording medium used for image formation. Thus, the width of the air outlets  a  and  a  of the left and right ducts  51 L and  51 R is adjusted to the optimum width, that is, the width matching the width of the sheet of recording medium used for the ongoing image forming operation. Therefore, the fixation belt  8  is optimally cooled by the forced draft cooling mechanism portion  20 B; the fixation belt  8  is cooled by the forced draft cooling mechanism  20 A, with its air outlets matching in width the sheet of recording medium in use. More concretely, of the left and right shutter plates  55 L and  55 R, the right shutter plate  55 R is provided with a rib  55   a  ( FIGS. 1 and 5 ), which is formed by cutting and bending a small portion of the shutter frame  54 . The rib  55   a  is provided with multiple smaller ribs  55   b , the position of which is set according to the various recording medium widths. Further, the shutter frame  54  is provided with a photosensor PH for detecting the smaller ribs  55   b . The photosensor PH is solidly fixed to the shutter frame  54 . The information regarding the detection of the small ribs  55   b  by the photosensor PH is inputted into the control circuit portion  100  through an A/D converter  83 . The control circuit portion  100  rotates the shutter motor M 2  forward or in reverse, moving the left and right shutter plates  55 L and  55 R, so that one of the small ribs  55   b , which matches the information regarding the recording medium size, which is inputted from the external host apparatus  200  or the like, is detected by the photosensor PH. Then, as the small rib  55   b , which matches the information regarding the width of the recording medium in use, is detected, the driving of the shutter motor M 2  is stopped. As a result, the left and right shutter plates  55 L and  55 R are stopped at the positions, one for one, which correspond to the width of the recording medium in use. 
   Next, the operation of the left and right cooling fans  52 L and  52 R of the fixing apparatus  20  in this preferred embodiment will be described. As a substantial number of small or medium recording papers, that is, recording papers smaller than a large recording paper, are continuously conveyed for fixation through the fixing apparatus during an image forming operation, the portions of the fixation belt  33 , which correspond to the out-of-sheet-path portions R and R ( FIGS. 6 and 7 ), increases in temperature. The subordinate thermistor TH 2 , as the second temperature detecting means, detects the temperature of the portion of the inward surface of the fixation belt  33 , which corresponds to one of the out-of-sheet-path portions. The control circuit portion  100  (controller) checks whether or not the temperature detected by the subordinate thermistor TH 2  has reached a preset level. As soon as it determines that the temperature has reached the preset level, it controls the shutter motor driver circuit  93  to move the shutter plates  55 L and  55 R to the positions which correspond to the width of the recording medium in use, by the shutter motor M 2 . In addition, the control circuit portion  100  (controller) controls the cooling fan driver circuit  94  ( FIG. 9 ) to start the left and right cooling fans  52 L and  52 R. As a result, the portions of the fixation belt  33 , which correspond to the out-of-sheet-path portions R and R are prevented from excessively increasing in temperature. Then, as the temperature detected by the subordinate thermistor TH 2  falls to a preset level because of the cooling of the out-of-sheet-path portions by the cooling draft generated by the cooling fans, the control circuit portion  100  stops the cooling fans  52 L and  52 R. 
   The forced draft cooling mechanism portion  20 B is controlled so that the level of the temperature detected by the subordinate thermistor TH 2 , at which the cooling fans  52 L and  52 R are turned on, and the level of the temperature detected by the subordinate thermistor TH 2 , at which the cooling fans  52 L and  52 R are turned off, are changed according to the condition under which the cooling fans operate. 
   The temperature range in which the cooling fans  52 L and  52 R are turned on or off in this embodiment is as follows: For example, in an image forming operation in which 100 sheets of recording paper of a size B4 (medium recording papers) are continuously conveyed through the fixing apparatus  20 , the operation is controlled in the following manner. That is, while the first-30th sheets of recording paper are conveyed, the cooling fans  52 L and  52 R are started as the temperature detected by the subordinate thermistor TH 2  reaches 200° C., whereas they are stopped as the temperature detected by the subordinate thermistor TH 2  falls to 190° C. While the 31st-60th sheets of recording paper are conveyed, the cooling fans  52 L and  52 R are started as the temperature detected by the subordinate thermistor TH 2  reaches 205° C., whereas they are stopped as the temperature detected by the subordinate thermistor TH 2  falls to 195° C. For the 61st sheet of recording medium and thereafter, the temperature level at which the cooling fans are started, and the temperature level at which they are stopped, are raised by 5° C. for every 30th sheet of recording paper. 
   The cooling fans  52 L and  52 R, and ducts  51 L and  51 R, are tilted so that the cooling draft is sent from the center line side of the recording medium passage of the fixing apparatus toward the lateral edge portions of the recording medium passage. Therefore, not only is the forced draft cooling mechanism portion  20 B in this embodiment is smaller in the spaces which the cooling fans  52 L and  52 R, and ducts  51 L and  51 R, occupy, but also, it is wider in the range of each of the out-of-sheet-path portions, which it can cool. In addition, it is structured so that the axial lines of the ducts  51 L and  51 R are parallel to the flow lines Y of the cooling drafts generated by the cooling fans  52 L and  52 R, respectively. Therefore, it is very small in the amount of the cooling draft loss. 
   Further, the forced draft cooling mechanism portion  20 B is structured so that the flow lines Y of the cooling draft are tilted in such a manner that the upstream side of the flow lines Y, in terms of the draft flow direction, is higher than the downstream side of the flow lines Y. Therefore, as the cooling draft hits the fixation belt  33 , it flows toward the corresponding lateral edge of the fixation belt  33 , and therefore, does not divert into the lateral edge portion of the recording medium path range Q. Therefore, the image forming apparatus in this embodiment does not yield a defective image, the defects of which are attributable to the unwanted decrease in the temperature of the portions of the fixing mechanism portions  20 A, which are within the recording medium path range Q. Further, the cooling draft hits the inward surface of the shutter plate at an angle. Therefore, even when the shutter plates  55 L and  55 R are positioned as shown in  FIG. 7 , the cooling draft flows along the inward surfaces of the shutter plates  55 L and  55 R as indicated by a flow line Ya. Therefore, the forced draft cooling mechanism portion  20 B is significantly smaller in the amount of the cooling draft loss than a forced draft cooling mechanism portion in accordance with the prior art. 
   Further, the cooling draft is guided toward the lateral edge portions of the fixing mechanism portions. Therefore, the bearing portions, that is, the flange portions  37   a , which are farther from the recording medium path range Q than the out-of-sheet-path range R, are efficiently cooled. Therefore, a substance which is relatively low in heat resistance temperature, being therefore lower in cost, can be used as the material for the flange portions  37   a.    
   1) The application of the present invention is not limited to a fixing mechanism, such as the fixing mechanism portion  20 A, in which an unfixed image is fixed by a heated fixation belt, and the fixation belt is driven by driving a rotational pressure applying member. That is, the present invention is also effectively applicable to various types of a fixing mechanism portion other than the above described ones, for example, a fixing mechanism portion of the heat roller type, a fixing mechanism portion employing a heating method based on electromagnetic induction, etc. 
   2) The present invention is also applicable to an image heating mechanism portion structured so that the positional relationship between recording medium and the image heating mechanism portion, in terms of the direction perpendicular to the recording medium conveyance direction, is controlled by placing one of the lateral edges of the recording medium in contact with the referential member with which the image heating mechanism portion is provided, just as effectively as it is to the image heating mechanism portion described above. 
   3) Not only is an image heating apparatus in accordance with the present invention usable as a fixing apparatus such as those described above, but also, as a glossiness increasing apparatus, or the like, for heating a fixed image on recording medium in order to increase the image in glossiness. 
   While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth, and this application is intended to cover such modifications or changes as may come within the purposes of the improvements or the scope of the following claims. 
   This application claims priority from Japanese Patent Application No. 232080/2006 filed Aug. 29, 2006, which is hereby incorporated by reference.