Patent Publication Number: US-11650528-B2

Title: Resistance heating component, method of manufacturing the same, fixing device, and image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2021-085902 filed on May 21, 2021. 
     BACKGROUND 
     (i) Technical Field 
     The present disclosure relates to a resistance heating component, a method of manufacturing the resistance heating component, a fixing device, and an image forming apparatus. 
     (ii) Related Art 
     For example, the fixing device described in Japanese Unexamined Patent Application Publication No. 2-134667 has been already known as a conventional fixing device. 
     Japanese Unexamined Patent Application Publication No. 2-134667 discloses a fixing device including: a heating element fixed and supported; a film that slides with the heating element; and a pressurizing device that pressure-bonds a recording material to the film, the heating element having a heat generating layer provided on a substrate, an electrode which carries current to the heat generating layer, and a thermally meltable part which is provided on the substrate, and melts at a predetermined temperature to prevent current carrying to the heat generating layer. 
     SUMMARY 
     Aspects of non-limiting embodiments of the present disclosure relate to a resistance heating component with a short start-up time without increasing a heat capacity, the resistance heating component allowing a fixing device to be easily built, the fixing device having a large fixing area and being capable of coping with high productivity. 
     Aspects of certain non-limiting embodiments of the present disclosure address the above advantages and/or other advantages not described above. However, aspects of the non-limiting embodiments are not required to address the advantages described above, and aspects of the non-limiting embodiments of the present disclosure may not address advantages described above. 
     According to an aspect of the present disclosure, there is provided a resistance heating component which is to come into contact with and heat a fixing belt made of a heat resistant material, and is to be provided at a position away from a fixing area between which and the fixing belt, a recording material is held and conveyed, the resistance heating component including: a metal base material having a low heat capacity; and a resistance heating layer laminated on a front surface or a rear surface of the base material with an insulating layer interposed between the base material and the resistance heating layer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the present disclosure will be described in detail based on the following figures, wherein: 
         FIG.  1 A  is an explanatory view illustrating an overview of an exemplary embodiment of an image forming apparatus which uses a fixing device including a resistance heating component to which the present disclosure is applied,  FIG.  1 B  is an explanatory view illustrating a configuration example of the resistance heating component illustrated in  FIG.  1 A , and  FIG.  1 C  is an explanatory view illustrating a method of manufacturing the resistance heating component; 
         FIG.  2    is an explanatory view illustrating the whole configuration of an image forming apparatus according to Exemplary Embodiment 1; 
         FIG.  3    is an explanatory view illustrating the fixing device used in Exemplary Embodiment 1; 
         FIG.  4 A  is an explanatory view illustrating a configuration example of the resistance heating component which is one component of the fixing device, and  FIG.  4 B  is an explanatory view illustrating a state in which a drive gear is removed on one end side of the resistance heating component; 
         FIG.  5    is an explanatory view illustrating a configuration example of power supply to a resistance heating layer of the resistance heating component used in Exemplary Embodiment 1; 
         FIG.  6 A  is an explanatory view illustrating a cast molding coating method used in a method of manufacturing the resistance heating component, and  FIG.  6 B  is a cross-sectional explanatory view of the resistance heating component; 
         FIG.  7 A  is an explanatory view schematically illustrating the operation principle of a fixing device according to the exemplary embodiment, and  FIG.  7 B  is an explanatory graph schematically illustrating a change state of the surface temperature distribution of the fixing belt from a position P 1  of the resistance heating component to a position P 2  of a fixing area of the fixing belt; and 
         FIG.  8 A  is an explanatory view illustrating a fixing device according to Modification 1,  FIG.  8 B  is an explanatory view illustrating a resistance heating component according to Modification 2, and  FIG.  8 C  is an explanatory view illustrating a resistance heating component according to Modification 3. 
     
    
    
     DETAILED DESCRIPTION 
     Overview of Exemplary Embodiment 
       FIG.  1 A  illustrates an overview of an exemplary embodiment of an image forming apparatus which uses a fixing device including a resistance heating component to which the present disclosure is applied. 
     In  FIG.  1 A , the image forming apparatus includes an image producing device  15  that produces an image on a recording material  16 , and a fixing device  10  that fixes an unfixed image produced by the image producing device  15 . 
     Here, any system, such as an ion flux recording system, including an electrophotographic system may be appropriately selected as the image producing device  15  as long as the system produces an unfixed image on the recording material  16 . 
     In addition, the fixing device  10  includes a fixing belt  11  made of a heat resistant material that moves in circulation; a fixing area formation device  12  that fixes an unfixed image of a recording material  16  at a fixing area m between which and the fixing belt  11 , the recording material  16  is held and conveyed; a resistance heating component  1  which comes into contact with and heats the fixing belt  11  at a position away from the fixing area m of the fixing belt  11 ; and a stretching member  13  that stretches the fixing belt  11  between the fixing area formation device  12  and the resistance heating component  1 . 
     The fixing belt  11  extensively includes a belt made of a heat resistant material such as polyimide (PI), polyetherimide (PEI). In addition, the fixing area formation device  12  may be configured to hold and convey the recording material  16  in the fixing area m of the fixing belt  11 , and is normally such that a receiving member  12   b  is provided on the rear surface side of the fixing belt  11 , a pressurizing member  12   a  is arranged on the surface side of the fixing belt  11 , and the fixing area m is ensured, in which the fixing belt  11  and the recording material  16  are held between the pressurizing member  12   a  and the receiving member  12   b.    
     Particularly, in this example, the resistance heating component  1  that heats the fixing belt  11  is provided at a position away from the fixing area m of the fixing belt  11 , thus the fixing area formation device  12  basically does not need to include a heating device. However, it is needless to say that a heating device may be provided supplementarily. 
     Thus, according to this example, as compared with when a heating area is provided in the fixing area of the fixing belt  11 , the fixing belt  11 , which has been sufficiently heated in the fixing area m, can be passed by separating the heating area and the fixing area m for the fixing belt  11  in function. 
     In the exemplary embodiment, as illustrated in  FIGS.  1 A and  1 B , the resistance heating component  1  is to be provided at a position away from the fixing area m of the fixing belt  11 , and includes a base material  2  made of metal having a low heat capacity, and a resistance heating layer  3  laminated on the front or rear surface of the base material  2  with an insulating layer  4  interposed between the base material  2  and the resistance heating layer  3 . 
     It is sufficient that the base material  2  be made of metal, and its form is not limited to a roll shape, but includes a flat plate shape. The resistance heating layer  3  may be on either the front or the rear surface of the base material  2 . However, in consideration of reducing start-up time and energy saving of the resistance heating layer  3 , a configuration in which the insulating layer  4  is interposed between the resistance heating layer  3  and the base material  2  is needed so that carried current to the resistance heating layer  3  does not leak to the base material  2  made of metal. 
     Next, a representative form or a desired form of the resistance heating component  1  according to the exemplary embodiment will be described. 
     First, as a desired form of the base material  2 , a metal roll  2   a  comprised of a cylindrical body made of metal may be used. 
     In this example, it is desirable that the metal roll  2   a  be configurated of high tensile strength steel which has a tensile strength of 490 MP or higher. The thickness of the metal roll  2   a  may be selected based on the stiffness and workability. 
     When the metal roll  2   a  is used, the resistance heating layer  3  may be laminated on the surface of the metal roll  2   a  with the insulating layer  4  interposed therebetween. 
     In addition, when the resistance heating layer  3  is formed on the surface of the base material  2 , regardless of the form of the base material  2 , it is desirable to form a protective layer  5  on the resistance heating layer  3  of the base material  2  using a material having low mold releasability (for example, polyimide and PEEK material) in order to increase wettability of a lubricant and tack power for drive against the fixing belt  11 . 
     Furthermore, the insulating layer  4  may be appropriately selected, however, in consideration of manufacturability, it is desirable to use the insulating layer  4  having an excellent surface property. 
     In particular, from the view point of maintaining the surface property of the resistance heating layer  3  in a good condition, it is desirable that the surface roughness of the insulating layer  4  be lower than the surface roughness of the base material  2 . 
     In addition, the method of manufacturing the resistance heating component  1  may be appropriately selected, however, for example, when the metal roll  2   a  is configurated of high tensile strength steel, the following manufacturing method is desirable. 
     Specifically, the method of manufacturing the resistance heating component  1  which comes into contact with and heats a fixing belt  11  made of a heat resistant material, and is provided at a position away from a fixing area m between which and the fixing belt  11 , a recording material  16  is held and conveyed, the resistance heating component  1  including: a metal roll  2   a  formed of a cylindrical body as a metal base material  2  having a low heat capacity; and a resistance heating layer  3  laminated on an outer surface or an inner surface of the metal roll  2   a  with an insulating layer  4  interposed between the metal roll  2   a  and the resistance heating layer  1 . The method includes layer formation steps in which laminated layers are successively formed on an outer circumference or an inner circumference of the metal roll  2   a , the laminated layers including the insulating layer  4  and the resistance heating layer  3 , and in at least an insulating layer formation step of the layer formation steps, a cast molding coating method is used in which as illustrated in  FIG.  1 C , the metal roll  2   a  is positioned, and a mold  7  for partitioning a hollow section  7   b  between the metal roll  2   a  and the outer circumference or the inner circumference of the metal roll  2   a  is used, the hollow section  7   b  corresponding to a thickness of a layer to be formed, and the layer to be formed is coated by casting a coating material M for the layer to be formed into the hollow section  7   b  through an inlet  7   a  which communicates with the hollow section  7   b , and calcining the coating material M. 
     In this manufacturing method, the metal roll  2   a  is high tensile strength steel, and polyimide can be used as the coating material M for the insulating layer  4 . 
     In addition, according to this manufacturing method, the cylindricity of the outer surface of the insulating layer  4  depends on the surface accuracy of the inner surface of the hollow section  7   b  of the mold  7 , thus the cylindricity of the outer circumferential surface of the insulating layer  4  can be made closer to the cylindricity of a cylinder than the cylindricity of the metal roll  2   a.    
     In addition, in the method of manufacturing the resistance heating component  1  of this type, when the resistance heating layer  3  is formed using the cast molding coating method also in a resistance heating layer formation step of the layer formulation steps, the surface of the resistance heating layer  3  can also be formed smoothly like the surface property of the insulating layer  4 . 
     Next, a representative form or a desired form of the fixing device according to the exemplary embodiment will be described. 
     First, as a representative form of the resistance heating component  1 , the resistance heating component  1  may be disposed in contact with the rear surface of the fixing belt  11 . 
     In addition, from the view point of reducing the sliding resistance against the fixing belt  11 , it is desirable that the resistance heating component  1  function as a stretching member which stretches the fixing belt  11 . Furthermore, it is more desirable that the resistance heating component  1  function as a stretching member which stretches the fixing belt  11  and function as a driving member which drives the fixing belt  11 . 
     In addition, in an embodiment in which the rear surface of the fixing belt  11  is heated by the resistance heating component  1 , it takes time for the heat of the rear surface to conduct to the surface of the fixing belt  11 , thus it is desirable that the relationship of L 1 &gt;L 2  be satisfied, where L 1  (not illustrated in  FIG.  1   ) is the distance from a contact center position of the resistance heating component  1  with the fixing belt  11  to a central position of the fixing area m in a circulation movement direction of the fixing belt  11 , and L 2  (not illustrated in  FIG.  1   ) is the distance from the central position of the fixing area m to the contact center position in the circulation movement direction of the fixing belt  11 . 
     In addition, an auxiliary heating element may be provided, which reduces heat loss when the fixing belt  11  heated by the resistance heating component  1  passes through the fixing area m. 
     Hereinafter, the present disclosure will be described in more detail based on the exemplary embodiment illustrated in the accompanying drawings. 
     Exemplary Embodiment 1 
     —Whole Configuration of Image Forming Apparatus— 
       FIG.  2    is an explanatory view illustrating the whole configuration of an image forming apparatus according to Exemplary Embodiment 1. 
     In  FIG.  2   , an image forming apparatus  20  is an intermediate transfer type image forming apparatus referred to as so-called tandem type, and has multiple image forming units  22  ( 22   a  to  22   d ) in which toner images of color components (four colors: yellow (Y), magenta (M), cyan (C), and black (K) in this example) are formed by an electrophotographic system. A belt-shaped intermediate transfer body  23  is disposed at a position corresponding to each of the image forming units  22 , and a first transfer unit  24  (for example, a first transfer roll) is disposed on the back surface of the intermediate transfer body  23  corresponding to the image forming units  22 . In addition, in part of the intermediate transfer body  23 , a second transfer unit (for example, a second transfer roll)  25  is disposed, in which a toner image of each color component, first transferred from a corresponding image forming unit  22  to the intermediate transfer body  23  by the first transfer unit  24 , is second transferred on a recording material S such as paper, a fixing device  60  is disposed on the downstream side of a conveyance direction of the recording material S on which the toner image of each color component has been transferred, and an unfixed toner image on the recording material S is fixed. 
     Each image forming unit  22  has a drum-shaped photoconductor  30  that rotates in a predetermined direction, and around the photoconductor  30 , includes: a charger  31  that charges the photoconductor  30 ; an exposure device  32 , such as a laser scanner, which writes an electrostatic latent image on the photoconductor  30  charged by the charger  31 ; a developing device  33  that develops the electrostatic latent image written on the photoconductor  30  by the exposure device  32  with corresponding color toner; and a cleaning device  34  that cleans residual material on the photoconductor  30  after a toner image developed by the developing device  33  is first transferred onto the intermediate transfer body  23  by the first transfer unit  24 . 
     The intermediate transfer body  23  is suspended on multiple stretching rolls  41  to  45 , and is designed to rotate in circulation in a predetermined direction using, for example, the stretching roll  41  as a drive roll. The stretching roll  44  also serves as an opposed roll to a second transfer roll as the second transfer unit  25 , and is designed to generate a second transfer electric field necessary for second transfer between the second transfer roll and the opposed roll. In addition, an intermediate transfer cleaning device  46  is disposed on the surface of the intermediate transfer body  23 , corresponding to the stretching roll  45 . 
     In addition, a recording material supply device  50  is provided below the intermediate transfer body  23 , and the recording material S supplied from the recording material supply device  50  is to be conveyed along a conveyance path  51  leading to the fixing device  60  through the second transfer unit  25 . Note that the conveyance path  51  is provided with an appropriate number of conveyance rolls  52 , a conveyance belt  53  for conveying the recording material S from the second transfer unit  25  to the fixing device  60 , and in addition, guide plates  54 ,  55  for guiding the recording material S to a second transfer position of the second transfer unit  25 , a fixing position of the fixing device  60 , respectively, and discharge rolls  56  to discharge the recording material S to a recording material discharge unit which is not illustrated. 
     —Fixing Device— 
     Next, the fixing device  60  used in the exemplary embodiment will be described with reference to  FIG.  3   . 
     In  FIG.  3   , the fixing device  60  includes: a fixing belt  61  made of a heat resistant material which moves in circulation; a fixing area formation unit  62  that fixes unfixed image of the recording material S at the fixing area m between which and the fixing belt  61 , the recording material S is held and conveyed; a stretching roll  63  that movably stretches the fixing belt  61  in circulation at a position away from the fixing area m of the fixing belt  61  to the upstream side of the movement direction of the fixing belt  61 ; a resistance heating roll  64  serving as a resistance heating component that movably stretches the fixing belt  61  in circulation, and comes into contact with and heats the fixing belt  61  at a position away from the fixing area m of the fixing belt  61  to the downstream side of the movement direction of the fixing belt  61 ; and a wick  65  that comes into contact with and applies lubricant to a section of the rear surface of the fixing belt  61 , located between the stretching roll  63  and the resistance heating roll  64 . 
     First, the components of the fixing device  60  other than the resistance heating roll  64  will be described, then the resistance heating roll  64  will be described in detail. 
     &lt;Fixing Belt&gt; 
     In this example, the fixing belt  61  uses the base material of a resin material having heat resistance, for example, polyimide (PI) resin, and is formed by laminating an elastic layer such as silicon rubber as well as a mold release layer made of a fluorine-based resin on the surface of the base material, thus the thermal conductivity in a thickness direction and a surface direction is low in general. 
     &lt;Fixing Area Formation Unit&gt; 
     In this example, in the fixing area formation unit  62 , a plate-like pressure pad  70  (made of SUS, liquid crystal polymer, for example) is held in a pad holder  71 , the pressure pad  70  serving as a plate-like receiving member and being disposed in contact with the rear surface of the fixing belt  61 , and a pressurizing roll  72  as a pressurizing member is pressurized and disposed on the surface of the fixing belt  61  opposed to the pressure pad  70 . 
     In this example, the pressurizing roll  72  is a metal roll with an elastic material such as polyurethane rubber laminated therearound, pressurizes the fixing belt  61  toward the pressure pad  70  to ensure a predetermined fixing area m, and holds and conveys the recording material S in the fixing area m along with movement of the fixing belt  61 .
 
&lt;Stretch Roll&gt;
 
     Since the stretch roll  63  is set on the downstream side of the movement direction of the fixing belt  61  with respect to the resistance heating roll  64 , the thermal energy of the fixing belt  61  heated by the resistance heating roll  64  may be lost at a contact point with the stretch roll  63 . Thus, in order to reduce heat loss from the stretch roll  63 , it is desirable that a protective layer for heat rejection (not illustrated) effective for heat rejection be provided on the surface of the stretch roll  63 . 
     &lt;Wick&gt; 
     In this example, a wick  65  allows a wick material  80  containing a lubricant to fix to a wick holder  81 , and the leading end of the wick material  80  to be arranged in contact with the rear surface of the fixing belt  61 . 
     —Resistance Heating Roll— 
     In this example, as illustrated in  FIGS.  5  and  6 B , the resistance heating roll  64  includes: a metal roll  90  comprised of a metal cylindrical tube as the base material; an insulating layer  91  laminated over substantially the entire area of the circumferential surface of the metal roll  90  with a predetermined thickness; a resistance heating layer  92  laminated over a region of the surface of the insulating layer  91 , the region excluding part in the vicinity of both ends of the circumferential surface of the metal roll  90 ; and a protective layer  93  made of polyimide and/or PEEK material laminated on the resistance heating layer  92 . 
     &lt;Metal Roll&gt; 
     In this example, the metal roll  90  is comprised of a cylindrical tube configurated of high tensile strength steel, for example, and a wall thickness t is 0.2 to 1.0 mm. When the thickness is less than 0.2 mm, the stiffness is likely to be insufficient, and when the thickness exceeds 1.0 mm, the effect of start-up performance is reduced. 
     &lt;Insulating Layer&gt; 
     In this example, the insulating layer  91  may be appropriately selected, however, it is desirable that the insulating layer  91  be formed using one of polyimide (PI), polyamide imide (PAI), diallyl phthalate (PDAP) and polyetheretherketone (PEEK), for example. In particular, when polyimide (PI) is used, it is possible to form the insulating layer  91  with high accuracy using the cast molding coating method described below. 
     &lt;Resistance Heating Layer&gt; 
     In this example, the resistance heating layer  92  is obtained by laminating a resistance heating material (for example, silver palladium, gold palladium, carbon metal filler mixture) on a region of the surface of the insulating layer  91  laminated on the surface of the metal roll  90  with a substantially uniform thickness, the region excluding part in the vicinity of both ends of the surface of the insulating layer  91 . Note that the resistance heating layer  92  may be formed by a patterned design on the surface of the insulating layer  91 . 
     &lt;Protective Layer&gt; 
     In this example, the protective layer  93  made of polyimide and/or PEEK material is formed on substantially the entire area of the resistance heating layer  92 , and when the rear surface of the fixing belt  61  is stretched by the resistance heating roll  64 , the resistance heating layer  92  does not come into contact with the rear surface of the fixing belt  61  directly, and the protective layer  93  comes into contact with the rear surface of the fixing belt  61 . The protective layer  93  has a low mold releasability, and is effective to increase wettability of a lubricant and tack power for drive. 
     &lt;Drive Roll Function of Resistance Heating Roll&gt; 
     In this example, the resistance heating roll  64  also functions as a drive roll which drives the fixing belt  61 . 
     Specifically, as illustrated in  FIGS.  4 A,  4 B  and  FIG.  5   , a portion, which is in the vicinity of both ends of the resistance heating roll  64  and in which the insulating layer  91  is exposed, is rotatably held by bearings  101 ,  102 . Then, a key groove  103  is formed at each of multiple positions (two positions in this example) on one end side of the metal roll  90 , a drive gear  104  is fitted into the outer side of the bearing  101  of a portion which is in the vicinity of one end of the metal roll  90  and in which the insulating layer  91  is exposed, an anti-rotation projection  105  formed at an inner circumferential portion of the drive gear  104  is caught in the key groove  103  of the metal roll  90 , retained by a clip  106 , and the drive gear  104  is fixed to the one end of the resistance heating roll  64 . The drive gear  104  is engaged with an input gear  111  to which a driving force from a drive motor  110  is transmitted, the drive motor  110  is controlled according to a control signal from a control device  120 , and the resistance heating roll  64  is driven as a drive roll with rotation of the input gear  111 . 
     &lt;Power Supply Structure of Resistance Heating Roll&gt; 
     In this example, for example, as illustrated in  FIG.  5   , the power supply structure of the resistance heating roll  64  is implemented as follows: the protective layer  93  in the vicinity of both ends of the resistance heating layer  92  is removed, a ring-shaped electrode  121  is formed at the portion removed, a power supply contact point  122  in contact with the electrode  121  is provided, and a heating start switch  123  is turned on by a control signal from the control device  120 , thus electric power from a power supply electric source  124  is supplied from the power supply contact point  122  to the resistance heating layer  92  through the electrode  121  to heat the resistance heating layer  92 . 
     Note that the power supply structure of the resistance heating roll  64  is not limited to this, and may be appropriately selected, for example, power is supplied from both shaft ends of the metal roll  90 . 
     &lt;Method of Manufacturing Resistance Heating Roll&gt; 
     Next, a method of manufacturing the resistance heating roll  64  according to the exemplary embodiment will be described. 
     In this example, the metal roll  90  is high tensile strength steel, and the insulating layer  91  is polyimide (PI), thus the cast molding coating method is used in the insulating layer formation step. 
     More specifically, in this example, the method of manufacturing the resistance heating roll  64  includes layer formation steps in which the insulating layer  91 , the resistance heating layer  92  and the protective layer  93  are successively formed on the outer circumference of the metal roll  90 . In at least the insulating layer formation step of the layer formation steps, as illustrated in  FIG.  6 A , a cast molding coating method is used in which the metal roll  90  is positioned by both end position determiners  131 , 132 , a mold  130  is used which partitions a hollow section  133  between the metal roll  90  and the outer circumference of the metal roll  90 , the hollow section  133  corresponding to the thickness of the insulating layer  91  to be formed, and the insulating layer  91  to be formed is coated by casting a coating material M for the insulating layer  91  to be formed into the hollow section  133 , and calcining the coating material M. 
     In this example, since the metal roll  90  is high tensile strength steel, due to the effect of processing accuracy, the cylindricity of the metal roll  90  is not closer to the cylindricity of a cylinder. However, using the cast molding coating method, when the outer circumferential surface of the mold  130  is produced accurately, the circularity of the insulating layer  91  after molding is closer to the circularity of a circle than the circularity of the metal roll  90 . Thus, when the resistance heating layer  92  is formed on the insulating layer  91 , it is advantageous in that the thickness of the resistance heating layer  92  is likely to be maintained more uniformly, as compared with when the resistance heating layer  92  is directly formed on the surface of the metal roll  90 . 
     In addition, regarding the surface roughness, it is advantageous in that the surface of the insulating layer  91  is likely to be smoother than the surface of the metal roll  90 . 
     Note that in  FIG.  6 A , laminated regions on the outer circumference of the metal roll  90  vary with the insulating layer  91 , the resistance heating layer  92 , the protective layer  93 , and a symbol  135  indicates a sealing member which regulates the region where the coating material M is spread in the hollow section  133  in the mold  130  to form each of the layers. In this example, a case has been described in which the insulating layer formation step is performed. When the insulating layer  91  is formed on substantially the entire area of the outer circumference of the metal roll  90 , the sealing member  135  is unnecessary. 
     Also, in this example, the cast molding coating method has been described using the insulating layer formation step as an example. However, when the cast molding coating method is used for the resistance heating layer formation step or the protective layer formation step, a mold may be prepared in advance according to a selection of a position of the outer circumferential surface and a position of the inner circumferential surface of the hollow section  133 , or a setting position of the sealing member  135 , and the thicknesses of the resistance heating layer  92  and the protective layer  93  which are to be formed. 
     &lt;Layout of Resistance Heating Roll&gt; 
     In this example, the layout of the resistance heating roll  64  is as illustrated in  FIG.  3   . 
     First, as illustrated in  FIG.  3   , a metal roll  90  having a large outer diameter is used as the resistance heating roll  64 , thus the region HT where the fixing belt  61  is stretched is widely secured, and accordingly, a large amount of heat conduction from the resistance heating roll  64  to the fixing belt  61  is secured. 
     Let L 1  be the distance from a contact center position P 1  of the resistance heating roll  64  with the fixing belt  61  to a central position P 2  of the fixing area m in a circulation movement direction of the fixing belt  61 , and L 2  be the distance from the central position P 2  of the fixing area m to the contact center position P 1  in the circulation movement direction of the fixing belt  61 . In this example, selection is made so that L 1 &gt;L 2  is satisfied. 
     The reason for this selection is as follows. 
     That is, as illustrated in  FIG.  7 A , the rear surface side of the fixing belt  61  is heated by the resistance heating roll  64  with an amount of heat Q, however, the thermal conductivity of the fixing belt  61  is low, thus the temperature T of the surface side of the fixing belt  61  does not immediately increase. Thus, in this example, as illustrated in  FIG.  7 B , the time taken for heat to conduct to the surface side is increased by increasing the distance L 2  along the fixing belt  61  until the fixing belt  61  heated by the resistance heating roll  64  reaches the fixing area m, the heat being consumed for heating the rear surface of the fixing belt  61 , thus the surface temperature of the fixing belt  61  at P 1  has sufficiently increased at a stage when P 2  is reached, the fixing belt  61  which has reached the fixing area m assumes a state in which the surface side is sufficiently heated, and heating energy in the fixing area m provided by the fixing belt  61  is sufficiently secured. 
     —Modification of Resistance Heating Component— 
     Modification 1 
       FIG.  8 A  illustrates a fixing device  60  according to Modification 1. 
     In  FIG.  8 A , the basic configuration of the fixing device  60  is almost the same as that of Exemplary Embodiment 1, however, unlike Exemplary Embodiment 1, an auxiliary heating source  140  such as a halogen lamp is separately added into the pad holder  71  on the rear surface of the fixing area m. 
     When the recording material S is held and conveyed at the fixing area m, heat loss from the recording material S and each component of the fixing area formation unit  62  is inevitable, thus in this example, the auxiliary heating source  140  does not actively heat the fixing belt  61  located at the fixing area m, but rather avoids increase in the heat loss from the fixing belt  61  at the fixing area m by compensating the heat loss. 
     Modification 2 
       FIG.  8 B  illustrates a resistance heating roll according to Modification 2. 
     In  FIG.  8 B , the resistance heating roll  64  includes the insulating layer  91 , the resistance heating layer  92  and the protective layer  93  on the outer surface of the metal roll  90 , and in addition, a resistance heating layer  96  is formed on the inner surface of the metal roll  90  with an insulating layer  95  interposed between the heating layer  96  and the metal roll  90 . 
     Thus, it is advantageous in that the heat generation efficiency achieved by the resistance heating roll  64  is higher than the heat generation efficiency of Exemplary Embodiment 1. 
     Modification 3 
     In  FIG.  8 C , as the resistance heating component  150  in fixing belt  61 , a flat plate-shaped base material  151  rather than the metal roll  90  is prepared, an insulating layer  152 , a resistance heating layer  153  and a protective layer  154  made of polyimide and/or PEEK material are laminated on the surface of the base material  151 , and the resistance heating component  150  is brought into contact with the rear surface of the fixing belt  61 . 
     The foregoing description of the exemplary embodiments of the present disclosure has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiments were chosen and described in order to best explain the principles of the disclosure and its practical applications, thereby enabling others skilled in the art to understand the disclosure for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the disclosure be defined by the following claims and their equivalents.