Patent Publication Number: US-8995894-B2

Title: Image fusing apparatus using carbon nano-tube heater

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the priority benefit from Korean Patent Applications No. 2011-0091270 filed Sep. 8, 2011 and No. 2011-0137747 filed Dec. 19, 2011 in the Korean Intellectual Property Office, the disclosures of which are incorporated herein by reference in their entirety. 
     BACKGROUND 
     1. Field 
     Embodiments relate to an image fusing apparatus used in an electro photographic type image forming apparatus. More particularly, the present disclosure relates to an image fusing apparatus including a heater using carbon nano-tubes. 
     2. Description of the Related Art 
     As an image fusing apparatus fusing a developer image on a printing medium, a heating roller method that heats an entire surface of a heat roller has been widely used. However, nowadays, a belt fusing method having a low heat capacity is widely used in order to reduce time it takes and energy used to heat to a fusing temperature. 
       FIG. 1  illustrates an example of a belt type image fusing apparatus using the belt fusing method. Referring to  FIG. 1 , the belt type image fusing apparatus  200  includes a pressing roller  201 , a fusing belt  203  that receives a rotation force from the pressing roller  201  so as to rotate, a guiding member  205  that is disposed inside the fusing belt  203  to guide rotation of the fusing belt  203 , and a ceramic heater  207 , that is, a heating member that is disposed on the guiding member  205 , and heats a nip portion of the fusing belt  203 . 
     Since the belt type image fusing apparatus  200  is a local heating method that heats only the nip portion of the image fusing apparatus  200  and thus has a low heat capacity, a temperature rising (increasing) standby time can be reduced and a width of the nip portion can be increased. However, the fusing belt  203  is formed in a thin film shape in order to increase thermal conductivity and is rotated by friction with the pressing roller  201  in the nip portion. A slip may occur between a printing medium P and the fusing belt  203  when the fusing belt  203  rotates at a high speed due to the structure of the fusing belt  203  as described above. Accordingly, reliability problems of the fusing belt  203  may occur. In order to solve the friction problem, lubrication may be applied. However, external contamination problems may occur due to the lubrication. Further since the ceramic heater  207  of the heating member is formed in a substantially flat plate shape, the belt type image fusing apparatus  200  has an advantage that when a printing medium P passes through the nip portion, curl does not occur. However, since there is an area where radius of curvature of the fusing belt  203  rapidly changes, durability of the fusing belt  203  may be reduced due to cumulative fatigue caused by bending. 
     For solving the problems, a belt type image fusing apparatus using a fusing belt having a resistance heating layer is provided. However, when this belt type image fusing apparatus performs continuously printing, temperature of a paper non-contact area of the fusing belt with which a printing medium is not in contact is highly increased so that the fusing belt and parts around the fusing belt are damaged. 
     SUMMARY 
     Embodiments have been developed in order to overcome the above drawbacks and other problems associated with the conventional arrangement. An aspect of the present disclosure relates to an image fusing apparatus that has a fast temperature rising (increasing) speed, a large energy saving effect and excellent heating uniformity, and can prevent temperature of a paper non-contact area of a fusing belt from increasing. 
     According to an aspect of one or more embodiments, there is provided an image fusing apparatus, which may include a heating belt including a resistance heating layer, an insulating layer formed on an inner surface of the resistance heating layer, and a release layer formed on an outer surface of the resistance heating layer; a heating supporting roller disposed (positioned) inside the heating belt and rotating with the heating belt; a pressing roller disposed (positioned) parallel to the heating supporting roller and in contact with the outer surface of the heating belt to form a nip; and an electricity supplying member to supply electricity to the resistance heating layer of the heating belt, wherein a thickness of paper non-contact areas of opposite side end portions of the resistance heating layer of the heating belt is the same as or thicker than the thickness of a paper contact area of a middle portion of the resistance heating layer thereof. 
     A width of the paper contact area of the resistance heating layer may be the same as that of a maximum size printing medium that the resistance heating layer can fuse. 
     The thickness of the paper non-contact area of the resistance heating layer may be once to three times to the thickness of the paper contact area. 
     An outer diameter of the resistance heating layer may be constant throughout a whole length of the resistance heating layer. an outer diameter of the heating supporting roller may be constant throughout a whole length of the heating supporting roller, and the insulating layer disposed between the resistance heating layer and the heating supporting roller may have an outer diameter that complementarily changes depending on change of thickness of the resistance heating layer throughout a whole length of the insulating layer. 
     An outer diameter of the resistance heating layer may be constant throughout a whole length of the resistance heating layer. an outer diameter of the heating supporting roller may have steps corresponding to the thickness of the resistance heating layer, and the insulating layer may have the same thickness through a whole length of the insulating layer. 
     The resistance heating layer may include carbon nano-tubes. 
     The resistance heating layer may be formed so that the carbon nano-tubes on which metal as conductive filler is doped are dispersed in a silicon rubber or a polyamide of an elastic member. 
     The electricity supplying member may be disposed on opposite ends of the heating supporting roller to supply electricity to the resistance heating layer. 
     The electricity supplying member may be disposed along the opposite side end portions of the heating belt, and the electricity supplying member receives electricity from a brush that is disposed in a direction perpendicular to an axis direction of the heating supporting roller. 
     The electricity supplying member may be formed in a cap shape to wrap one end of the heating supporting roller, and the cap shape electricity supplying member may be supplied with electricity by a brush that is disposed in contact with the cap shape electricity supplying member in an axial direction of the heating supporting roller. 
     The image fusing apparatus may include an inner supporting cap supporting an inner surface of the cap shape electricity supplying member; and an outer fixing cap that supports an outer surface of the cap shape electricity supplying member and fixes the cap shape electricity supplying member with respect to the resistance heating layer of the heating supporting roller. 
     The heating supporting roller may include an elastic layer supporting the heating belt and formed in a cylindrical shape; and a center shaft disposed at a center of the elastic layer. 
     The pressing roller may be formed so that an elastic layer and a release layer are in sequence laminated on a pressing rotation shaft. 
     The heating supporting roller may include a hollow cylinder having a width corresponding to the heating belt; and a pair of supporting shafts disposed on opposite ends of the hollow cylinder, and the hollow cylinder and the pair of supporting shafts may be formed of a metal. 
     The image fusing apparatus may include an auxiliary pressing roller spaced apart at a predetermined interval from the pressing roller, the auxiliary pressing roller disposed to press the heating belt to the heating supporting roller. 
     The pressing roller may include at least two supporting rollers and a pressing belt rotated by the at least two supporting rollers. 
     According to an aspect of one or more embodiments, an image fusing apparatus may include a heating belt including a resistance heating layer, a release layer formed on an outer surface of the resistance heating layer and an electricity supplying member to supply electricity to the resistance heating layer; a heating roller disposed (positioned) inside the heating belt and including a non-conductive shaft in contact with the resistance heating layer; and a pressing roller disposed (positioned) parallel to the heating roller and in contact with an outer surface of the heating belt to form a nip, wherein a thickness of paper non-contact areas of opposite side end portions of the resistance heating layer of the heating belt is the same as or thicker than a thickness of a paper contact area of a middle portion of the resistance heating layer thereof. 
     A width of the paper contact area of the resistance heating layer may be the same as that of a maximum size printing medium that the resistance heating layer can fuse, and the thickness of the opposite side end portions of the resistance heating layer may be once to three times to the thickness of the middle portion. 
     According to an aspect of one or more embodiments, an image fusing apparatus may include a heating belt including a resistance heating layer, an insulating layer formed on an inner surface of the resistance heating layer, and a release layer formed on an outer surface of the resistance heating layer; a heating supporting roller disposed (positioned) inside the heating belt and rotating with the heating belt; a pressing roller disposed (positioned) parallel to the heating supporting roller and to be in contact with an outer surface of the heating belt to form a nip; and a pair of electricity supplying members to supply electricity to the resistance heating layer of the heating belt and disposed on opposite ends of the heating supporting roller along an outer circumference of the heating supporting roller, wherein the electricity supplying member and the resistance heating layer are electrically connected with each other through a plurality of contacting portions formed in a predetermined shape in a circumferential direction of the heating belt. 
     The electricity supplying member may include a body portion disposed at one end of the heating supporting roller; and a plurality of projecting portions formed to project at a predetermined interval from the body portion and disposed in contact with the resistance heating layer of the heating belt, and the plurality of projecting portions may form the plurality of contacting portions. 
     The electricity supplying member may include a body portion disposed at one end of the heating supporting roller; and an extension portion extended from the body portion to correspond to a paper non-contact area of the heating belt; wherein an electrode insulating layer is disposed between the extension portion and the resistance heating layer of the heating belt, a plurality of through holes having a predetermined shape is formed on the electrode insulating layer in a circumferential direction of the heating supporting roller, and the resistance heating layer and the electricity supplying member are electrically connected with each other through a material forming the resistance heating layer and filling up the plurality of through holes. 
     Each of the plurality of contacting portions may be formed in a band shape. 
     The plurality of contacting portions may be inclined with respect to a center shaft of the heating supporting roller. 
     According to an aspect of one or more embodiments, an image fusing apparatus may include a heating belt including a resistance heating layer, a release layer formed on an outer surface of the resistance heating layer, and a conductive layer; a heating supporting member disposed (positioned) inside the heating belt and supporting rotation of the heating belt; a pressing roller disposed (positioned) parallel to the heating supporting member and to be in contact with an outer surface of the heating belt to form a nip; and an electricity supplying member to supply electricity to the resistance heating layer of the heating belt, wherein the conductive layer is formed to be electrically connected with the resistance heating layer on a paper non-contact area of the heating belt, and electrical conductivity of the conductive layer is the same as or larger than electrical conductivity of the resistance heating layer. 
     The resistance heating layer may be formed so that carbon nano-tubes on which metal as conductive filler is doped are dispersed in a silicon rubber or a polyamide of an elastic member. 
     The electrical conductivity of the conductive layer may be once to 500 times larger than electrical conductivity of the resistance heating layer. 
     The conductive layer may be formed of a conductive resin or metal. 
     When the conductive layer is formed of a metal, the conductive layer may be formed of a metal film having a thickness of 1 nm˜999 μm. 
     The conductive layer may include at least one conductive layer formed on at least one between a top surface of the resistance heating layer and a bottom surface of the resistance heating layer. 
     The heating belt may include an insulating layer formed on a bottom surface of the resistance heating layer. 
     The heating belt may include an elastic layer formed between the resistance heating layer and the release layer. 
     The heating supporting member may include a heating supporting roller, and a nip forming member. 
     The nip forming member may include a pressure supporting member disposed inside the heating belt and supporting the nip forming member toward the pressing roller. 
     The conductive layer of the heating belt may be electrically connected with directly the electricity supplying member. 
     According to an aspect of one or more embodiments, an image fusing apparatus may include a heating belt including a resistance heating layer, and a release layer formed on an outer surface of the resistance heating layer; a heating supporting member disposed (positioned) inside the heating belt and supporting rotation of the heating belt; a pressing roller disposed (positioned) parallel to the heating supporting member and to be in contact with an outer surface of the heating belt to form a nip; and an electricity supplying member to supply electricity to the resistance heating layer of the heating belt, wherein electrical resistance of a paper non-contact area of the heating belt is smaller than electrical resistance of a paper contact area of the heating belt. 
     Thickness or electrical conductivity of the resistance heating layer of the paper non-contact area of the heating belt may be adjusted to control the electrical resistance. 
     According to an aspect of one or more embodiments, there is provided an image forming apparatus including an image fusing apparatus, the image fusing apparatus including a heating belt including a resistance heating layer, an insulating layer formed on an inner surface of the resistance heating layer, and a release layer formed on an outer surface of the resistance heating layer; a heating supporting roller positioned inside the heating belt and rotating with the heating belt; a pressing roller positioned parallel to the heating supporting roller and in contact with an outer surface of the heating belt to form a nip; and an electricity supplying member to supply electricity to the resistance heating layer of the heating belt, wherein a thickness of paper non-contact areas of opposite side end portions of the resistance heating layer of the heating belt is the same as or thicker than the thickness of a paper contact area of a middle portion of the resistance heating layer thereof. 
     According to an aspect of one or more embodiments, there is provided an image fusing apparatus including a heating belt including a resistance heating layer, an insulating layer formed on an inner surface of the resistance heating layer, and a release layer formed on an outer surface of the resistance heating layer; a heating supporting roller positioned inside the heating belt and rotating with the heating belt; and an electricity supplying member to supply electricity to the resistance heating layer of the heating belt, wherein a thickness of paper non-contact areas of the resistance heating layer of the heating belt is the same as or thicker than the thickness of a paper contact area of the resistance heating layer thereof. 
     According to an aspect of one or more embodiments, there is provided an image fusing apparatus including a heating belt including a resistance heating layer, an insulating layer formed on an inner surface of the resistance heating layer, and a release layer formed on an outer surface of the resistance heating layer; a heating supporting roller positioned inside the heating belt and rotating with the heating belt; and a pair of electricity supplying members to supply electricity to the resistance heating layer of the heating belt and positioned on opposite ends of the heating supporting roller along an outer circumference of the heating supporting roller, wherein the electricity supplying member and the resistance heating layer are electrically connected with each other through a plurality of contacting portions formed in a predetermined shape in a circumferential direction of the heating belt. 
     According to an aspect of one or more embodiments, there is provided an image fusing apparatus including a heating belt including a resistance heating layer, a release layer formed on an outer surface of the resistance heating layer, and a conductive layer; a heating supporting member positioned inside the heating belt and supporting rotation of the heating belt; and an electricity supplying member to supply electricity to the resistance heating layer of the heating belt, wherein the conductive layer is formed to be electrically connected with the resistance heating layer on a paper non-contact area of the heating belt, and electrical conductivity of the conductive layer is the same as or larger than electrical conductivity of the resistance heating layer. 
     According to an aspect of one or more embodiments, there is provided an image fusing apparatus, including a heating belt including a resistance heating layer, and a release layer formed on an outer surface of the resistance heating layer; a heating supporting member positioned inside the heating belt and supporting rotation of the heating belt; and an electricity supplying member to supply electricity to the resistance heating layer of the heating belt, wherein electrical resistance of a paper non-contact area of the heating belt is smaller than electrical resistance of a paper contact area of the heating belt. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects of embodiments will become apparent and more readily appreciated from the following description of embodiments, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  is a sectional view schematically illustrating a conventional belt type image fusing apparatus; 
         FIG. 2  is a perspective view illustrating an image fusing apparatus according to an embodiment; 
         FIG. 3  is a front view illustrating the image fusing apparatus of  FIG. 2 ; 
         FIG. 4  is a sectional view illustrating the image fusing apparatus taken along a line  4 - 4  in  FIG. 3 ; 
         FIG. 5  is a partially enlarged sectional view illustrating the portion of the image fusing apparatus of  FIG. 3  illustrated in rectangular A; 
         FIG. 6  is a graph illustrating temperature distributions in a paper contact area and a paper non-contact area according to change of thickness ratio of a resistance heating layer 
         FIG. 7  is a graph illustrating changes of temperature difference between a paper contact area and a paper non-contact area according to changes of thickness ratio of a resistance heating layer; 
         FIG. 8  is a graph illustrating simulation of heating status in a paper contact area and a paper non-contact area according to changes of thickness ratio of a resistance heating layer; 
         FIG. 9  is a partially enlarged sectional view illustrating a heating supporting roller having an outer diameter changed in order to change a thickness of a resistance heating layer; 
         FIG. 10  is a partially perspective view illustrating an example of a heating supporting roller that can lower temperature of a paper non-contact area of a heating belt by an electricity supplying member in an image fusing apparatus according to an embodiment; 
         FIG. 11  is a partially cutaway view illustrating the heating supporting roller of  FIG. 10 ; 
         FIGS. 12A-12C  are perspective views illustrating a manufacturing process of the heating supporting roller of  FIG. 10 ; 
         FIG. 13  is a view illustrating an example of the electricity supplying member of  FIG. 10 ; 
         FIG. 14  is a view illustrating an example of the electricity supplying member of  FIG. 10 ; 
         FIG. 15  is a partially perspective view illustrating an example of a heating supporting roller that can lower temperature of a paper non-contact area of a heating belt by an electricity supplying member in an image fusing apparatus according to an embodiment; 
         FIG. 16  is a partially cutaway view illustrating the heating supporting roller of  FIG. 15 ; 
         FIGS. 17A-17D  are perspective views illustrating a manufacturing process of the heating supporting roller of  FIG. 15 ; 
         FIGS. 18 ,  19  and  20  are sectional views schematically illustrating image fusing apparatuses according to an embodiment; 
         FIG. 21  is a sectional perspective view illustrating a cap type electricity supplying member disposed on a heating supporting roller; 
         FIG. 22  is a partially enlarged perspective view illustrating the portion of the heating supporting roller of  FIG. 21  illustrated in circle D; 
         FIG. 23  is a front view illustrating an image fusing apparatus according to an embodiment; 
         FIG. 24  is a partially enlarged sectional view illustrating the portion of the image fusing apparatus of  FIG. 23  illustrated in rectangular C; 
         FIGS. 25A-25B  are graphs illustrating changes of temperature of a paper non-contact area according to changes of resistance of the paper non-contact area; 
         FIG. 26  is a partially sectional view illustrating a heating belt having a conductive layer formed between a resistance heating layer and a release layer thereof; 
         FIGS. 27A-27B  are a partially sectional view illustrating a heating belt having a different layer structure; 
         FIGS. 28A-28B  are a partially sectional view illustrating a heating belt having a conductive layer formed between a resistance heating layer and an elastic layer thereof; 
         FIG. 29  is a partially sectional view illustrating an image fusing apparatus having a nip forming member according to an embodiment; and 
         FIG. 30  is a sectional view schematically illustrating an image forming apparatus having an image fusing apparatus according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. Throughout the drawings, like reference numerals will be understood to refer to like parts, components and structures. 
     The matters defined herein, such as a detailed construction and elements thereof, are provided to assist in a comprehensive understanding of this description. Thus, it is apparent that embodiments may be carried out without those defined matters. Also, well-known functions or constructions are omitted to provide a clear and concise description of embodiments. Further, dimensions of various elements in the accompanying drawings may be arbitrarily increased or decreased for assisting in a comprehensive understanding. 
       FIG. 2  is a perspective view illustrating an image fusing apparatus according to an embodiment of the present disclosure, and  FIG. 3  is a front view illustrating the image fusing apparatus of  FIG. 2 .  FIG. 4  is a sectional view illustrating the image fusing apparatus taken along a line  4 - 4  in  FIG. 3 , and  FIG. 5  is a partially enlarged sectional view illustrating the portion of the image fusing apparatus of  FIG. 3  illustrated in rectangular A. 
     Referring to  FIGS. 2 to 5 , an image fusing apparatus  1  according to an embodiment may include a heating belt  10 , a heating supporting roller  20 , an electricity supplying member  30 , and a pressing roller  50 . 
     The heating belt  10  generates heat that can heat a printing medium P passing through the image fusing apparatus  1  and includes a resistance heating layer  12  that can uniformly generate heat from the entire surface thereof. The resistance heating layer  12  may be formed in a hollow cylindrical shape. An insulating layer  11  that blocks electricity from flowing into the heating supporting roller  20  inside the resistance heating layer  12  is formed on an inner surface of the resistance heating layer  12 . A release layer  13  that allows the printing medium P to be easily separated from the resistance heating layer  12  is formed on an outer surface of the resistance heating layer  12 . Accordingly, the heating belt  10  is formed in a laminated structure which the insulating layer  11 , the resistance heating layer  12 , and the release layer  13  are in sequence stacked. 
     An aspect of one or more embodiments is to prevent temperature of an area of the heating belt  10  with which the printing medium P is not in contact during printing, (that is, a paper non-contact area of the heating belt  10  from increasing higher than temperature of an area of the heating belt  10  with which the printing medium P is in contact, that is, a paper contact area of the heating belt  10 ). A paper non-contact area of the heating belt  10  may also be referred to as a non-contact area of the heating belt  10 . A paper contact area of the heating belt  10  may also be referred to as a contact area of the heating belt  10 . For this, the heating belt  10  is formed so that electrical resistance of the paper non-contact area is smaller than electrical resistance of the paper contact area. 
     In an embodiment illustrated in  FIGS. 3 ,  4  and  5 , in order to make the electrical resistance of the paper non-contact area of the heating belt  10  smaller than the electrical resistance of the paper contact area of the heating belt  10 , the resistance heating layer  12  of opposite side end portions L 2  and L 3  of the heating belt  10 , the paper non-contact area of the heating belt  10 , is formed to have a thickness thicker than that of a middle portion L 1  of the heating belt  10 , the paper contact area of the heating belt  10 . This is explained in detail hereinafter. 
     The resistance heating layer  12  may be formed to include carbon nano-tubes. For example, the resistance heating layer  12  may be formed to disperse carbon nano-tubes on which metal is doped as conductive filler into silicone rubber or polyamide which is elastomers. 
     The heating supporting roller  20  is disposed (positioned) inside the heating belt  10  and is a heating supporting member that supports the heating belt  10  to rotate. The heating supporting roller  20  can rotate with the heating belt  10 . Accordingly, slip is not generated between the heating supporting roller  20  and the heating belt  10 . The heating supporting roller  20  supports the heating belt  10  and may include an elastic layer  22  formed in a cylindrical shape and a center shaft  21  disposed in the center of the elastic layer  22 . The elastic layer  22  may be formed of an elastic material having elasticity such as rubber, sponge, etc. The center shaft  21  is a rigid rotation shaft that supports the heating supporting roller  20  to rotate. 
     The pressing roller  50  applies a predetermined pressure to a printing medium P passing through the image fusing apparatus  1 . The pressing roller  50  is disposed parallel to the heating supporting roller  20  and contacts with the outer surface of the heating belt  10  to form a nip N. The pressing roller  50  may include a rotation shaft  51  and an elastic layer  52  disposed coaxially on the rotation shaft  51 . Accordingly, since the printing medium P passing through the nip N between the pressing roller  50  and the heating belt  10  receives heat and pressure, an infused developer image is fused on the printing medium P. 
     A rotation driving source (not illustrated) is connected to at least one of the heating supporting roller  20  and the pressing roller  50 . Accordingly, when one roller  20  or  50  connected to the rotation driving source between the heating supporting roller  20  and the pressing roller  50  is rotated by the rotation driving source, the other roller  50  or  20  also receives the rotation force and then rotates. 
     The electricity supplying member  30  serves as an electrode to supply electricity to the resistance heating layer  12  of the heating belt  10 , and is disposed on circumferential surfaces of opposite side end portions of the heating belt  10 . Accordingly, some area of the top surface of the electricity supplying member  30  is overlapped with one side end portion of the resistance heating layer  12  of the heating belt  10  and the other area of the top surface thereof is exposed. Further, the bottom surface of the electricity supplying member  30 , that is, a surface that contacts with the heating supporting roller  20 , is covered by the insulating layer  11 . A brush  41  is disposed in contact with the other area of the electricity supplying member  30  that is not in contact with the resistance heating layer  12  of the heating belt  10 . The brush  41  is disposed perpendicular to the center shaft  21  of the heating supporting roller  20  and pressurized by the elastic member  42  such as a spring in order to maintain contact with the electricity supplying member  30  by a predetermined pressure. The brush  41  may be manufactured from carbon. The brush  41  and the elastic member  42  constitute a brush assembly  40 . The brush assembly  40  is connected to an electric power source (not illustrated) of an image forming apparatus, and then, supplies electricity to the electricity supplying member  30 . When electricity is applied to the brushes  41  of the opposite side ends of the heating supporting roller  20 , current flows due to voltage difference between the opposite side ends of the resistance heating layer  12  so as to heat the resistance heating layer  12 . The heating belt  10  may be controlled at a proper temperature by a temperature sensor (not illustrated) and a control portion (not illustrated). 
     In one or more embodiments, in order to prevent temperatures of the areas of the opposite side end portions of the heating belt  10  in non-contact with the printing medium P, that is, the paper non-contact area L 2  and L 3  from rapidly increasing so as to damage the reliability and stability of the image fusing apparatus  1 , the thickness of the heating belt  10 , specifically the thickness of the resistance heating layer  12  is formed to change along the lengthwise direction of the heating supporting roller  20 . In other words, the resistance heating layer  12  of the middle portion of the heating belt  10  that is in contact with the printing medium P and discharges heat, that is, the paper contact area L 1 , is formed to have a thickness thinner than that of the resistance heating layer  12  of the opposite side end portions of the heating belt  10  in non-contact with the printing medium P, that is, the paper non-contact areas L 2  and L 3 . 
     If the thickness t 1  of the paper non-contact areas L 2  and L 3  of the opposite side end portions is thicker than the thickness t 2  of the paper contact area L 1  of the middle portion, the electrical resistance of the resistance heating layer  12  of the heating belt  10  is decreased, and then, heating temperature of the heating belt  10  is lowered. Therefore, during printing heat is not accumulated in the opposite side end portions L 2  and L 3  of the heating belt  10 . 
     Here, the width of the paper contact area L 1  of the resistance heating layer  12  refers to the width W of the maximum size printing medium P that the resistance heating layer  12  can fuse. 
     When the thickness of the resistance heating layer  12  changes along the lengthwise direction of the heating supporting roller  20 , in terms of a manufacturing process, the resistance heating layer  12  may be formed so that an outer diameter D of the resistance heating layer  12  is constantly maintained across the full length thereof and an inner diameter Hd thereof changes. At this time, the thickness t 1  of the paper non-contact areas L 2  and L 3  of the resistance heating layer  12  may be formed once to three times of the thickness t 2  of the paper contact area L 1 . In order to change the inner diameter Hd of the resistance heating layer  12  formed on the heating supporting roller  20 , the thickness of the insulating layer  11  of the heating belt  10  may be changed or the outer diameter r of the heating supporting roller  20  may be changed. 
     As illustrated in  FIG. 5 , if the thickness of the resistance heating layer  12  in the paper non-contact area L 2  refers to t 1  and the thickness of the resistance heating layer  12  in the paper contact area L 1  refers to t 2 , thickness ratio a of the resistance heating layer  12  may be defined as a=t 1 /t 2 . 
     When a voltage is applied to the electricity supplying member  30  of the heating belt  10 , computer simulation results of joule heat generated in the paper contact area L 1  and the paper non-contact area L 2  of the resistance heating layer  12  are illustrated in  FIGS. 6 and 7 . 
     Referring to  FIG. 6 , it is found that increasing the thickness ratio a of the resistance heating layer  12  allows temperature of the paper non-contact areas L 2  and L 3  to be decreased. Further, referring to  FIG. 7 , it is found that increasing the thickness ratio a of the resistance heating layer  12  allows temperature difference between the paper non-contact areas L 2  and L 3  and the paper contact area L 1  to be increased. 
     When the image fusing apparatus  1  is initially heated and then maintained in a certain control temperature,  FIG. 8  illustrates a computer simulation result of affection of the passing printing medium P in the paper contact area L 1  and the paper non-contact areas L 2  and L 3  depending on the change of the thickness ratio a of the resistance heating layer  12 . 
     Referring to  FIG. 8 , if the thickness t 2  of the paper contact area L 1  is the same as the thickness t 1  of the paper non-contact areas L 2  and L 3  (namely, a=1), temperature of the paper non-contact areas L 2  and L 3  continues to be increased above a control temperature. If the thickness t 1  of the paper non-contact areas L 2  and L 3  is thicker than the thickness t 2  of the paper contact area L 1 , degree of temperature rise is decreased. If the thickness ratio a of the resistance heating layer  12  is larger than 1.4 (namely, a 1.4), the temperature of the paper non-contact areas L 2  and L 3  is maintained below the control temperature. 
     Referring to  FIG. 5 , it is found that the thickness t 1  of a portion of the resistance heating layer  12  corresponding to the paper non-contact areas L 2  and L 3  is thicker than the thickness t 2  of a portion of the resistance heating layer  12  corresponding to the paper contact area L 1 . 
     The resistance heating layer  12  having thickness that is changed in the lengthwise direction of the heating supporting roller  20  may be formed as described below. 
     The insulating layer  11  that has thickness changed along the lengthwise direction of the heating supporting roller  20  is formed on the outer surface of the heating supporting roller  20  that has the same outer diameters across full-length thereof. In other words, the insulating layer  11  that is disposed between the resistance heating layer  12  and the heating supporting roller  20  is formed to have a diameter Hd complementarily changed depending on the thickness change across the full-length of the resistance heating layer  12 . In other words, the thickness d 1  of a portion of the insulating layer  11  corresponding to the paper non-contact areas L 2  and L 3  is formed to be thinner than the thickness d 2  of a portion of the insulating layer  11  corresponding to the paper contact area L 1 . At this time, the thickness difference d 2 −d 1  of the insulating layer  11  is the same as the thickness difference t 1 −t 2  of the resistance heating layer  12 . The insulating layer  11  is formed so that d 2 −d 1 =t 1 −t 2 . After that, the resistance heating layer  12  is stacked on the insulating layer  11  and then is machined to have a desired size of an outer diameter D so as to obtain the heating belt  10  having the paper contact area L 1  the thickness t 2  of which is thinner than the thickness t 1  of the paper non-contact areas L 2  and L 3 . At this time, the heating belt  10  is formed so that the inner diameter of the resistance heating layer  12  and the outer diameter of the insulating layer  11  have the same size across the full-length of the heating supporting roller  20 . 
     In a method of an embodiment, the resistance heating layer  12  the thickness of which is changed in the lengthwise direction of the heating supporting roller  20  may be formed as described below. First, the outer diameter r of the heating supporting roller  20  is formed to have steps changed to correspond to the thickness change of the resistance heating layer  12 . As illustrated in  FIG. 9 , the heating supporting roller  20  is formed so that the radius r 1  of a portion of the heating supporting roller  20  corresponding to the paper non-contact areas L 2  and L 3  is smaller than the radius r 2  of a portion of the heating supporting roller  20  corresponding to the paper contact area L 1 . At this time, the radius difference r 2 −r 1  of the heating supporting roller  20  is the same as the thickness difference t 1 −t 2  of the resistance heating layer  12 . In other words, the heating supporting roller  20  is formed so that r 2 −r 1 =t 1 −t 2 . After that, the insulating layer  11  is formed to have a uniform thickness d on the outer surface of the heating supporting roller  20 . Then, the resistance heating layer  12  is laminated on the insulating layer  11  to have a predetermined height, and then, is machined to have a desired size of an outer diameter D so as to obtain the heating belt  10  having the thickness changed in the lengthwise direction thereof. In other words, the heating belt  10  having thickness t 2  of the resistance heating layer  12  of the paper contact area L 1  thinner than the thickness t 1  of the resistance heating layer  12  of the paper non-contact areas L 2  and L 3  may be obtained. 
     Hereinafter, in order to lower temperature of the paper non-contact areas L 2  and L 3  below temperature of the paper contact area L 1 , a method using a pattern shape of an area on which the electricity supplying member  30  and the resistance heating layer  12  are in contact with each other will be explained instead of the above-described method to change the thickness in the lengthwise direction of the resistance heating layer  12  of the heating belt  10 . 
     This method reduces the area of the contacting portion where the electricity supplying member  30  and the resistance heating layer  12  are in contact with each other so as to lower the temperature of the paper non-contact areas L 2  and L 3  below the temperature of the paper contact area L 1 . 
       FIGS. 10 ,  11  and  12 A- 12 C illustrate an example of the heating belt  10  to which the method for reducing the area of the contacting portion between an electricity supplying member  60  and the resistance heating layer  12  of the heating belt  10  is applied. 
       FIG. 10  is a partially perspective view illustrating an example of the heating supporting roller  20  on which the heating belt  10  that can lower temperature of the paper non-contact area L 2  thereof by using the electricity supplying member  60  is disposed in an image fusing apparatus  1  according to an embodiment, and  FIG. 11  is a partially cutaway view illustrating the heating belt  10  and the heating supporting roller  20  of  FIG. 10 .  FIGS. 12A-12C  are perspective views illustrating a process manufacturing the heating belt  10  of  FIG. 10 . 
     Referring to  FIGS. 10 ,  11 , and  12 A- 12 C, the electricity supplying member  60  and the resistance heating layer  12  are electrically connected with each other through a plurality of contacting portions formed in a predetermined shape in a circumferential direction of the heating belt  10 . In other words, the plurality of contacting portions may be formed in band shapes separated by a regular interval in the circumferential direction of the heating belt  10 . 
     The electricity supplying member  60  includes a body portion  61  disposed on an end of the heating supporting roller  20  and a plurality of projecting portions  63  that project from the body portion  61  by a regular interval. Each of the plurality of projecting portions  63  is formed to have a length corresponding to the width of the paper non-contact area L 2  and a predetermined width. The plurality of projecting portions  63 , as illustrated in  FIG. 13 , may be formed to project vertically from the body portion  61  Accordingly, if the electricity supplying member  60  is disposed on the heating supporting roller  20 , the plurality of projecting portions  63  are parallel to the center shaft  21  of the heating supporting roller  20 . However, in this case, portions of the heating belt  10  corresponding to spaces  64  among the plurality of projecting portions  63  may have too low temperatures. 
     For preventing this, the plurality of projecting portions  63  may be formed to be inclined to the center shaft  21  of the heating supporting roller  20 .  FIG. 14  illustrates an electricity supplying member  60 ′ having a plurality of projecting portions  63 ′ inclined at a predetermined angle θ with respect to the body portion  61 . If the electricity supplying member  60 ′ as illustrated in  FIG. 14  is disposed on the heating supporting roller  20 , there are no portions on which the electricity supplying member  60 ′ does not exist in the lengthwise direction of the heating supporting roller  20 . Therefore, the temperature of the paper non-contact area L 2  can be prevented from lowering too much. 
     The heating belt  10  having the electricity supplying member  60  and  60 ′ as described above may be formed by a method as described below. First, as illustrated in  FIG. 12A , the insulating layer  11  configuring the heating belt  10  is formed on the top surface of the heating supporting roller  20  and the electricity supplying member  60  having a plurality of projecting portions  63  is disposed on a top surface of the insulating layer  11 . As illustrated in  FIG. 12B , the resistance heating layer  12  is formed on the insulating layer  11  and the electricity supplying member  60 . As a result, some portion of the resistance heating layer  12  is in contact with the plurality of projecting portions  63  and some portion of the body portion  61  of the electricity supplying member  60 , and the other portion of the resistance heating layer  12  is disposed on the insulating layer  11 . Accordingly, the plurality of projecting portions  63  of the electricity supplying member  60  forms contacting portions that allows the electricity supplying member  60  to be in contact with and to be electrically connected with the resistance heating layer  12 . After that, as illustrated in  FIG. 12C , a release layer  13  is formed on the resistance heating layer  12 . As a result, the heating belt  10  temperature of the paper non-contact area L 2  of which can be lowered by the shape of the contacting portion between the electricity supplying member  60  and the resistance heating layer  12  is formed. 
       FIGS. 15 ,  16  and  17 A- 17 D illustrate an example of the heating belt  10  which can reduce the area of the contacting portion between an electricity supplying member  70  and the resistance heating layer  12 . 
       FIG. 15  is a partially perspective view illustrating the heating supporting roller  20  on which an example of a heating belt  10  that can lower temperature of the paper non-contact area L 2  thereof by using an electricity supplying member  70  is disposed in an image fusing apparatus  1  according to an embodiment, and  FIG. 16  is a partially cutaway view illustrating the heating belt  10  and the heating supporting roller  20  of  FIG. 15 .  FIGS. 17A-17D  are perspective views illustrating a process manufacturing the heating belt  10  of  FIG. 15 . 
     Referring to  FIGS. 15 ,  16 , and  17 A- 17 D, the electricity supplying member  70  and the resistance heating layer  12  are electrically connected with each other through a plurality of contacting portions formed in a predetermined shape in a circumferential direction of the heating belt  10 . In other words, the plurality of contacting portions may be formed in band shapes separated at a regular interval in the circumferential direction of the heating belt  10 . 
     The electricity supplying member  70  includes a body portion  71  disposed on an end of the heating supporting roller  20  and an extending portion  73  that extends from the body portion  71  to correspond to the paper non-contact area of the heating belt  10 . An electrode insulating layer  75  to configure the contacting portions is formed on the top surface of the extending portion  73 . 
     In order words, the electrode insulating layer  75  is disposed between the extending portion  73  of the electricity supplying member  70  and the resistance heating layer  12 . A plurality of through holes  76  having a predetermined shape are formed on the electrode insulating layer  75  in the circumferential direction of the heating supporting roller  20 . Accordingly, the resistance heating layer  12  and the electricity supplying member  70  are electrically connected with each other by a material that forms the resistance heating layer  12  and fills up the plurality of through holes  76  of the electrode insulating layer  75 . At this time, the plurality of through holes  76  of the electrode insulating layer  75  may be formed a slot shape having a length corresponding to the width of the paper non-contact area L 2  and a predetermined width. As a result, each of the contacting portions where the electricity supplying member  70  is in contact with the resistance heating layer  12  forms substantially a band shape. 
     The heating belt  10  having the contacting portions as described above may be formed by a method as described below. First, the insulating layer  11  configuring the heating belt  10  is formed on the top surface of the heating supporting roller  20 , and as illustrated in  FIG. 17A , the electricity supplying member  70  having the extending portion  73  is disposed on the insulating layer  11 . Next, as illustrated in  FIG. 17B , the electrode insulating layer  75  having the plurality of through holes  76  is formed on the top surface of the extending portion  73  of the electricity supplying member  70 . After that, as illustrated in  FIG. 17C , the resistance heating layer  12  is formed on the top surfaces of the insulating layer  11  and the electrode insulating layer  75 . As a result, since the material configuring the resistance heating layer  12  is filled in the plurality of through holes  76  of the electrode insulating layer  75 , the resistance heating layer  12  and the electricity supplying member  70  form the plurality of contacting portions having a shape corresponding to a cross-section of each of the plurality of through holes  76 . Finally, as illustrated in  FIG. 17D , the release layer  13  is formed on the top surface of the resistance heating layer  12 . As a result, the heating belt  10  temperature of the paper non-contact area L 2  of which can be lowered by reducing the area of the contacting portion between the electricity supplying member  70  and the resistance heating layer  12  is formed. 
     In the above explanation, as the method for lowering temperature of the paper non-contact area L 2  of the image fusing apparatus  1 , in order to make the electrical resistance of the paper non-contact area L 2  smaller than that of the paper contact area L 1 , the method changing the thickness of the resistance heating layer  12  or the method changing the shape of the contacting portion between the electricity supplying member  60  and  70  and the resistance heating layer  12  is individually applied to the image fusing apparatus  1 . However, although not illustrated, in order to lower the temperature of the paper non-contact area L 2 , the above described two methods may be applied to manufacture the image fusing apparatus  1  at the same time. 
     Since the image fusing apparatus  1  according to an embodiment having the above-described structure uses the resistance heating belt  10  having a low thermal capacity, temperature rising time is short, energy saving effect is large, and excellent heating uniformity can be obtained. Further, the image fusing apparatus  1  according to an embodiment is formed to have a structure in that the heating belt  10  is rotated with the heating supporting roller  20  to avoid slip. Accordingly, since lubricant such as grease does not need to be used, contamination problems can be solved, and damage of the heating belt  10  by the friction force can be prevented. Specially, since the image fusing apparatus  1  according to an embodiment is configured so that heat is not accumulated in the paper non-contact areas L 2  and L 3  of the heating belt  10 , during continuous printing, overheating of the image fusing apparatus  1  can be avoided. 
     In the above explanation, the heating belt  10  is rotatably supported by the heating supporting roller  20  having the elastic layer  22 . However, one or more embodiments can be applied to image fusing apparatuses  2  and  3  of  FIGS. 18 and 19  having the heating belt  10  formed on a heating supporting roller  20 ′ and  20 ″ having no elastic layer  22 . 
       FIGS. 18 and 19  are sectional views schematically illustrating image fusing apparatuses  2  and  3  including a heating roller  20   a  and  20   b  having the heating belt  10  and  10 ′ formed on the heating supporting roller  20 ′ and  20 ″ having no elastic layer  22 . 
     In  FIG. 18 , the heating supporting roller  20 ′ is formed in a cylindrical shape having a hollow  20 ′- 1 . A pair of supporting shafts is formed on opposite ends of the hollow cylinder  20 ′ to allow the hollow cylinder  20 ′ to rotate. The hollow cylinder  20 ′ and the pair of supporting shafts are formed of a conductive rigid material, for example, a metal. Accordingly, the insulating layer  11  is formed on the surface of the hollow cylinder  20 ′, and the resistance heating layer  12  and the release layer  13  are in sequence laminated on the top surface of the insulating layer  11  so as to form the heating roller  20   a . At this time, since the heating supporting roller  20 ′ is a rigid member difficult to form a nip, the pressing roller  50 ′ needs to have an elastic layer  52 . In other words, the pressing roller  50 ′ has a structure in that an elastic layer  52  and a release layer  53  are laminated on a center shaft  51  having rigidity. If the nip formed by the structure is small, an auxiliary pressing roller  55  may additionally be disposed. 
     Although the heating supporting roller  20 ′ is formed of the rigid material, the temperature of the paper non-contact area can be prevented from increasing by adjusting the thickness of the lengthwise direction of the resistance heating layer  12  or reducing the area of the contacting portion with the electricity supplying member  60  and  70  as described above. The method for adjusting the thickness of the resistance heating layer  12  and the method for reducing the area of the contacting portion with the electricity supplying member  60  and  70  are described in detail above. Therefore, detailed descriptions thereof will be omitted. 
       FIG. 19  illustrates a heating supporting roller  20 ″ formed in a cylindrical shape having a hollow  20 ″- 1  similar to  FIG. 18 . The hollow cylinder  20 ″ is formed of a non-conductive rigid material. In other words, the heating supporting roller  20 ″ as illustrated in  FIG. 19  has not the elastic layer  22  formed on the center shaft  21  of the heating supporting roller  20  as illustrated in  FIGS. 2 ,  3  and  4 . A center shaft  20 ″ is formed as a non-conductive hollow cylinder. Although not illustrated, the center shaft  20 ″ may be formed as a non-conductive solid shaft having no hollow  20 ″- 1 . Therefore, the insulating layer  11  is not formed on the surface of the hollow cylinder  20 ″. The resistance heating layer  12  is directly formed on the surface of the hollow cylinder  20 ″ and the release layer  13  is formed on the resistance heating layer  12  so as to form the heating roller  20   b . At this time, since the heating supporting roller  20 ″ is a rigid member difficult to form a nip, the pressing roller  50 ′ needs to have an elastic layer  52 . In other words, the pressing roller  50 ′ has a structure in that an elastic layer  52  and a release layer  53  are laminated on a center shaft  51  having rigidity. If the nip formed by the pressing roller  50 ″ is small, an auxiliary pressing roller  55  may additionally be disposed to increase the nip area. 
     Although the heating supporting roller  20 ″ is formed of the rigid material, the temperature of the paper non-contact area can be prevented from increasing by adjusting the thickness of the lengthwise direction of the resistance heating layer  12  or reducing the area of the contacting portion with the electricity supplying member  60  and  70  as described above. The method for adjusting the thickness of the resistance heating layer  12  and the method for reducing the area of the contacting portion with the electricity supplying member  60  and  70  are described in detail above. Therefore, detailed descriptions thereof will be omitted. 
       FIG. 20  is a sectional view schematically illustrating an image fusing apparatus  4  using a pressing belt assembly  300  instead of the pressing roller  50 ′ of the image fusing apparatus  2  as illustrated in  FIG. 18 . 
     In this case, a pressing belt  301  supported by a pair of supporting rollers  302  and  303  to move endlessly in a closed loop can form a sufficient nip with the heating roller  20   a  having rigidity. In an embodiment, also the temperature of the paper non-contact area can be prevented from increasing by adjusting the thickness of the lengthwise direction of the resistance heating layer  12  of the heating belt  10  or reducing the area of the contacting portion with the electricity supplying member  60  and  70  as described above. The method for adjusting the thickness of the resistance heating layer  12  and the method for reducing the area of the contacting portion with the electricity supplying member  60  and  70  are described in detail above. Therefore, detailed descriptions thereof will be omitted. 
     In the above description, electricity is supplied by the brush  41  disposed perpendicular to the axial direction of the heating supporting roller  20  to be in contact with the electricity supplying members disposed on the opposite side end portions of the outer circumferential surface of the heating supporting roller  20 ′. In an embodiment, electricity can be supplied by a brush disposed on the heating supporting roller  20  in the axial direction thereof. 
     Referring to  FIGS. 2 and 3 , the electricity supplying member  30  is disposed on the outer circumferential surface of the heating supporting roller  20  and the brush  41  is disposed perpendicular to the center shaft  21  of the heating supporting roller  20  so as to supply with electricity. However, as an embodiment, the brush may be disposed in the axial direction of the heating supporting roller  20  to supply with electricity. This structure will be described with reference to  FIGS. 21 and 22 . 
       FIG. 21  is a sectional perspective view illustrating a cap type electricity supplying member  90  disposed on the heating supporting roller  20 , and  FIG. 22  is a partially enlarged perspective view illustrating the portion of the heating supporting roller  20  of  FIG. 21  illustrated in circle D; 
     Referring to  FIG. 21 , the electricity supplying member  90  is formed in a cap shape wrapping one end of the heating supporting roller  20 . In other words, the cap type electricity supplying member  90  is formed in a cylindrical container that can be inserted into the one end of the cylindrical heating supporting roller  20 . Accordingly, the electricity supplying member  90  is disposed to be inserted in the one end of the heating supporting roller  20 . At this time, the heating supporting roller  20  may be formed to include a hollow cylinder portion  20 ′ and a pair of supporting shafts  21 ′ projecting from the opposite ends of the hollow cylinder  20 ′. 
     The cap type electricity supplying member  90  can be supplied with electricity by the brush  99  disposed to contact with the cap type electricity supplying member  90  in the axial direction of the heating supporting roller  20 . In other words, the brush  99  elastically supported by a spring in the axial direction of the heating supporting roller  20  is disposed to be in contact with a bottom surface  90  a of the cap type electricity supplying member  90 . Accordingly, even when the heating supporting roller  20  rotates, the electricity supplying member  90  can be supplied with electricity by the brush  99 . At this time, the brush  99  may be formed of a carbon. 
     In addition, the above-described cap type electricity supplying member  90  is fixed to the heating supporting roller  20  by an inner supporting cap  91  and an outer fixing cap  95 . The inner supporting cap  91  is fixed to the supporting shaft  21 ′ of the heating supporting roller  20  and supports an inner surface of the cap type electricity supplying member  90 . Accordingly, the inner supporting cap  91  includes a fixing groove  92  corresponding to the supporting shaft  21 ′ of the heating supporting roller  20 . The outer diameter of the inner supporting cap  91  is formed to be inserted inside and support the cap type electricity supplying member  90 . 
     The outer fixing cap  95  supports the outer surface of the cap type electricity supplying member  90  and fixes the cap type electricity supplying member  90  to the resistance heating layer  12  of the heating supporting roller  20 . Accordingly, the outer fixing cap  95  is formed in a hollow cylindrical shape, has an inner diameter of the dimension in which the cap type electricity supplying member  90  can be inserted, and has one end on which a stepping portion  96  is formed to fix the cap type electricity supplying member  90 . 
     The cap type electricity supplying member  90  is disposed on the heating supporting roller  20  as described below. First, one end of the supporting shaft  21 ′ of the heating supporting roller  20  is inserted into the fixing groove  92  of the inner supporting cap  91 . As a result, the inner supporting cap  91  is fixed to the heating supporting roller  20 . After that, the cap type electricity supplying member  90  is inserted into the inner supporting cap  91 . Next, the outer fixing cap  95  is inserted into the cap type electricity supplying member  90  so that the cap type electricity supplying member  90  is fixed to the one end of the heating supporting roller  20 . At this time, as illustrated in  FIG. 22 , a top portion  90   b  of the cap type electricity supplying member  90  is in contact with the resistance heating layer  12  formed on the heating supporting roller  20  and fixed by the outer fixing cap  95 . Accordingly, the electricity supplied with by the brush  99  in contact with the bottom surface  90   a  of the cap type electricity supplying member  90  is supplied to the resistance heating layer  12  through the cap type electricity supplying member  90 . 
     Although not illustrated, in the same way as described above, the cap type electricity supplying member  90  is fixed to the opposite end of the heating supporting roller  20  as illustrated in  FIG. 20  by the inner supporting cap  91  and the outer fixing cap  95 . Accordingly, if the outer fixing caps  95  disposed on the opposite ends of the heating supporting roller  20  are rotatably supported, the heating supporting roller  20  can rotate. 
     In order to make the electrical resistance of the paper non-contact areas L 2  and L 3  of the heating belt  10 ′ smaller than the electrical resistance of the paper contact area L 1 , a case in that the paper non-contact areas L 2  and L 3  is formed to have electrical conductivity higher than that of the paper contact area L 1  will be explained hereinafter. 
       FIG. 23  is a front view illustrating an image fusing apparatus  5  according to an embodiment.  FIG. 24  is a partially enlarged sectional view illustrating the portion of the image fusing apparatus  5  of  FIG. 23  illustrated in rectangular C. 
     Referring to  FIGS. 23 and 24 , the image fusing apparatus  5  according to an embodiment may include a heating belt  10 ′, the heating supporting roller  20 , the electricity supplying member  30 , and the pressing roller  50 . 
     The heating belt  10 ′ generates heat that can heat a printing medium P passing through the image fusing apparatus  5  and includes the resistance heating layer  12  that can uniformly generate heat from the entire surface thereof. The resistance heating layer  12  may be formed in a hollow cylindrical shape. The release layer  13  that allows the printing medium P to be easily separated from is formed on the outer surface of the resistance heating layer  12 . \If the surface of the heating supporting roller  20  to be inserted in the heating belt  10 ′ is not insulated; the insulating layer  11  that blocks electricity from flowing into the internal heating supporting roller  20  is formed on the inner surface of the resistance heating layer  12 . Accordingly, the heating belt  10 ′ is formed in a laminated structure that the insulating layer  11 , the resistance heating layer  12 , and the release layer  13  are in sequence laminated. If the surface of the heating supporting roller  20  is insulated, the heating belt  10 ′ may be formed in a two-layer structure that the resistance heating layer  12  and the release layer  13  are in sequence laminated. 
     An aspect of one or more embodiments is to prevent temperature of an area of the heating belt  10 ′ with which the printing medium P is not in contact during printing, (that is, a paper non-contact area L 2  and L 3  of the heating belt  10 ′) from rising (increasing) higher than temperature of an area of the heating belt  10 ′ with which the printing medium P is in contact, that is, a paper contact area L 1  of the heating belt  10 ′. For this, the heating belt  10 ′ is formed so that the electric resistance of the paper non-contact area L 2  and L 3  is smaller than the electric resistance of the paper contact area L 1 . 
     In an embodiment as illustrated in  FIGS. 23 and 24 , in order to make the electrical resistance of the paper non-contact area of the heating belt  10 ′ smaller than the electrical resistance of the paper contact area, the opposite side end portions L 2  and L 3  of the heating belt  10 ′, the paper non-contact area, are formed to have electrical conductivity higher than that of the middle portion L 1  of the heating belt  10 ′, the paper contact area. 
     For this, in this embodiment, a conductive layer  80  is formed to be electrically connected with the resistance heating layer  12  on a portion corresponding to the paper non-contact area L 2  of the heating belt  10 ′. The conductive layer  80  may be formed of a metal or a conductive resin having electrical conductivity higher than that of the resistance heating layer  12 . The conductive layer  80  may be disposed close to or directly contact with the electricity supplying member  30 . Further, since electricity can flow through the resistance heating layer  12 , the conductive layer  80  may be formed to be separated from the electricity supplying member  30  by the resistance heating layer  12 . 
     If the conductive layer  80  is formed on the insulating layer  11 , the resistance heating layer  12  is formed on the conductive layer  80 , and the resistance heating layer  12  is machined to have a constant outer diameter D, the heating belt  10 ′ has the structure as illustrated in  FIG. 24  in the paper non-contact area L 2 . 
     The electrical resistance R of the paper non-contact area L 2  is represented as follows. 
     
       
         
           
             
               
                 
                   
                     
                       1 
                       R 
                     
                     = 
                     
                       
                         
                           1 
                           Rc 
                         
                         + 
                         
                           1 
                           Rn 
                         
                       
                       = 
                       
                         b 
                         Rc 
                       
                     
                   
                   ⁢ 
                   
                     
 
                   
                   ⁢ 
                   
                     
                       1 
                       Rn 
                     
                     = 
                     
                       
                         b 
                         - 
                         1 
                       
                       Rc 
                     
                   
                   ⁢ 
                   
                     
 
                   
                   ⁢ 
                   
                     Rc 
                     = 
                     
                       
                         ( 
                         
                           b 
                           - 
                           1 
                         
                         ) 
                       
                       ⁢ 
                       Rn 
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
     where, Rc is the electrical resistance of the resistance heating layer  12 , Rn is the electrical resistance of the conductive layer  80 , and b is a resistance reduction ratio (or electrical conductivity ratio) to the resistance heating layer  12  when the paper non-contact area L 2  is formed of only the conductive layer  80 . 
     Formula 1 is arranged with respect to the electrical conductivity as follows, 
     
       
         
           
             
               
                 
                   
                     
                       ρ 
                       n 
                     
                     = 
                     
                       
                         1 
                         
                           b 
                           - 
                           1 
                         
                       
                       ⁢ 
                       
                         
                           t 
                           n 
                         
                         
                           t 
                           c 
                         
                       
                       ⁢ 
                       
                         ρ 
                         c 
                       
                     
                   
                   ⁢ 
                   
                     
 
                   
                   ⁢ 
                   
                     
                       σ 
                       n 
                     
                     = 
                     
                       
                         ( 
                         
                           b 
                           - 
                           1 
                         
                         ) 
                       
                       ⁢ 
                       
                         
                           t 
                           c 
                         
                         
                           t 
                           n 
                         
                       
                       ⁢ 
                       
                         ϖ 
                         c 
                       
                     
                   
                   ⁢ 
                   
                     
 
                   
                   ⁢ 
                   
                     λ 
                     = 
                     
                       
                         ( 
                         
                           b 
                           - 
                           1 
                         
                         ) 
                       
                       ⁢ 
                       
                         
                           t 
                           c 
                         
                         
                           t 
                           n 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
     Where ρ n  is resistivity of the conductive layer  80 , ρ c  is resistivity of the resistance heating layer  12 , σ n  is electrical conductivity of the conductive layer  80 , σ c  is electrical conductivity of the resistance heating layer  12 , and λ is an electrical conductivity ratio of the conductive layer  80  and the resistance heating layer  12  (λ=σ n /σ c ). 
     Accordingly, material and thickness of the conductive layer  80  with respect to the resistance reduction ratio b may be determined from Formula 2 and  FIG. 24 . The conductive layer  80  may be formed of a metal film having thickness of 1 nm˜999 μm. Also, the conductive layer  80  may be formed to have the electrical conductivity 1˜500 times greater than that of the resistance heating layer  12 . 
     For example, when the electrical conductivity σ c  of the resistance heating layer  12  is 330.7 S/m, and the conductive layer  80  is made of Ni (σ n =1.56E7 S/m), the thickness t n  of the conductive layer  80  with respect to the resistance reduction ratio b is shown in Table 1. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 b 
                 t n,  μm 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 2 
                 0.00506 
               
               
                   
                 5 
                 0.02023 
               
               
                   
                 10 
                 0.04552 
               
               
                   
                 50 
                 0.24760 
               
               
                   
                 100 
                 0.49973 
               
               
                   
                 200 
                 1.00240 
               
               
                   
                   
               
            
           
         
       
     
     In an embodiment, if the conductive layer  80  is formed of a conductive resin, and the ratio of the conductive layer thickness and the entire thickness is 0.163, the electrical conductivity ratio of the resistance heating layer  12  and the conductive resin is shown in Table 2 below. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 b 
                 λ 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 1.5 
                 2.914 
               
               
                   
                 2 
                 5.829 
               
               
                   
                 5 
                 23.314 
               
               
                   
                 10 
                 52.457 
               
               
                   
                 50 
                 285.6 
               
               
                   
                 100 
                 577.029 
               
               
                   
                 200 
                 1159.996 
               
               
                   
                   
               
            
           
         
       
     
       FIGS. 25A-25B  are graphs illustrating changes of temperature of the paper non-contact area L 2  according to changes of resistance of the paper non-contact area L 2 .  FIG. 25A  illustrates a graph illustrating changes of temperature of the paper non-contact area L 2  depending on time change and change of the resistance reduction ratio b.  FIG. 25B  is a graph illustrating temperatures reached after 600 seconds according to change of the resistance reduction ratio b.  FIGS. 25A and 25B  illustrate the results interpreting temperature changes depending on the resistance reduction of the paper non-contact area L 2  when the image fusing apparatus  5  is early heated and maintains a control temperature to 180° C. in the paper contact area L 1  of the heating belt  10 ′. 
     Referring to  FIGS. 25A-25B , it is found that when the resistance of the paper non-contact area L 2  is less than ⅓ times of the resistance of the resistance heating layer  12 , the temperature of the paper non-contact area L 2  is lower than the control temperature. In other words, the result means that if the thickness of the conductive layer  80  is the same as that of the resistance heating layer  12 , in order to make the temperature of the paper non-contact area L 2  lower than the control temperature, the electrical conductivity of the conductive layer  80  needs to be greater than three times of the electrical conductivity of the resistance heating layer  12 . Accordingly, in one or more embodiments, if the thickness and electrical conductivity of the conductive layer  80  is properly adjusted, the temperature of the paper non-contact area L 2  may be lower than the control temperature. 
     In the above description, the conductive layer  80  is disposed between the insulating layer  11  and the resistance heating layer  12 . However, position of the conductive layer  80  is not limited to that position. As long as it can lower the electrical resistance of the paper non-contact area L 2 , the conductive layer  80  may be formed in various positions. 
       FIG. 26  illustrates when the conductive layer  80  is formed between the resistance heating layer  12  and the release layer  13 . 
     Further, if the heating belt  10 ″ and  10 ″ includes an elastic layer  22  as illustrated in  FIGS. 27A-27B , the conductive layer  80  may be formed below the resistance heating layer  12 , that is, between the resistance heating layer  12  and the elastic layer  22  as illustrated in  FIGS. 28A-28B . Although not illustrated, even if the heating belt  10 ″ and  10 ″ includes an elastic layer  22  as illustrated in of  FIGS. 27A-28B , the conductive layer  80  may be disposed close to or in directly contact with the electricity supplying member  30  above on the resistance heating layer  12 . 
     If the conductive layer  80  is formed in the paper non-contact area L 2 , current flux is congested with depending on the electrical conductivity of the conductive layer  80  so that the electrical resistance of the paper non-contact area L 2  is reduced. As a result, temperature lowering effect is generated. Also, if the conductive layer  80  is formed in the paper non-contact area L 2 , there is no need to change the thickness of the paper non-contact area L 2 . Therefore, it is easy to manufacture the heating belt. 
     The heating supporting roller  20 , the electricity supplying member  30 , and the pressing roller  50  of the image fusing apparatus  5  according to the present embodiment are the same as the heating supporting roller  20 , the electricity supplying member  30 , and the pressing roller  50  of the image fusing apparatus  1  according to the an embodiment as described above. Therefore, detailed descriptions thereof will be omitted. 
       FIG. 29  illustrates an image fusing apparatus  6  supporting the heating belt  10 ′ by a heating supporting member configured of a pressure supporting member  400  and a nip forming member  401  instead of the heating supporting roller  20  unlike embodiments as described above. The pressure supporting member  400  is fixed inside the heating belt  10 ′ and supports and pressures the nip forming member  401  toward the pressing roller  50 . The nip forming member  401  supports the heating belt  10 ′ and then allows the heating belt  10 ′ to form a nip having a predetermined width with the pressing roller  50 . In this embodiment, when the pressing roller  50  rotates, the pressure supporting member  400  and the nip forming member  401  are not rotated but only the heating belt  10 ′ is rotated by the pressing roller  50 . 
     In this embodiment, also the heating belt  10 ′ includes the conductive layer  80  in order to lower the electrical resistance of the paper non-contact area L 2 . 
     Even if as illustrated in  FIGS. 18 ,  19  and  20 , the heating supporting roller  20  has a hollow cylindrical shape with no elastic layer  14 , the heating belt  10 ′ having the conductive layer  80  in the paper non-contact area L 2  can be used. 
     In  FIG. 18 , the hollow cylinder  20 ′ is formed of a conductive rigid material. Accordingly, the insulating layer  11  is formed on the surface of the hollow cylinder  20 ′, and the resistance heating layer  12  and the release layer  13  are in sequence laminated on the insulating layer  11  so as to form the heating roller  20   a . At this time, since the heating supporting roller  20 ′ is a rigid member, it is difficult to form a nip. Accordingly, the pressing roller  50 ′ may be formed to have an elastic layer  52  or an auxiliary pressing roller  55  may additionally be disposed to increase the area of the nip. 
       FIG. 19  illustrates the hollow cylinder  20 ″ formed of a non-conductive rigid material. Accordingly, the insulating layer  11  is not formed on the surface of the hollow cylinder  20 ″. The resistance heating layer  12  is formed directly on the surface of the hollow cylinder  20 ″ and the release layer  13  is formed on the resistance heating layer  12  so as to form the heating roller  20   b . At this time, since the heating supporting roller  20 ″ is a rigid member, it is difficult to form a nip. Accordingly, the pressing roller  50 ′ may be formed to have an elastic layer  52  or an auxiliary pressing roller  55  may additionally be disposed to increase the area of the nip. 
       FIG. 20  is a sectional view schematically illustrating the image fusing apparatus  4  using the pressing belt assembly  300  instead of the pressing roller  50 ′ of the image fusing apparatus  2  as illustrated in  FIG. 18  in order to form a sufficient nip. In this case, the pressing belt  301  supported to move endlessly in a closed loop by the pair of supporting rollers  302  and  303  can form a sufficient nip with the rigid heating roller  20   a.    
     Even when the heating supporting roller  20 ′ is formed of a rigid material, the temperature of the paper non-contact area L 2  can be prevented from increasing by forming the conductive layer  80  in the resistance heating layer  12  of the paper non-contact area L 2  so as to lower the electrical resistance as describe above. 
     Hereinafter, an image forming apparatus having the image fusing apparatus according to an embodiment will be explained.  FIG. 30  is a sectional view schematically illustrating an image forming apparatus having the image fusing apparatus according to an embodiment. 
     The image forming apparatus  100  according to an embodiment prints by an electro photographic image forming method and may include laser printers, copiers, facsimile machines, multifunctional products, or the like. 
     Referring to  FIG. 30 , the image forming apparatus  100  according to an embodiment may include a case  101 , a paper feeding apparatus  110 , a developing apparatus  130 , the image fusing apparatus  1 , and a paper discharging apparatus  150 . 
     The case  101  forms the outer appearance of the image forming apparatus  100  and supports the paper feeding apparatus  110 , the developing apparatus  130 , the image fusing apparatus  1 , and the paper discharging apparatus  150 . 
     The paper feeding apparatus  110  stores several printing media P, picks up the printing medium P one by one, and supplies the picked up printing medium P to the developing apparatus  130 . The printing medium P supplied from the paper feeding apparatus  110  is conveyed to the developing apparatus  130  by the plurality of conveying rollers  111 . 
     The developing apparatus  130  forms a predetermined image on the printing medium P supplied from the paper feeding apparatus  110 . The developing apparatus  130  may include a photosensitive medium  131  on which a predetermined electrostatic latent image is formed by an exposure apparatus  120 , a developing roller  132  that supplies the photosensitive medium  131  with developer to develop the electrostatic latent image into a developer image, and a transfer roller  140  that transfers the developer image formed on the photosensitive medium  131  onto the printing medium P. After the printing medium P passes through a transfer nip between the photosensitive medium  131  and the transfer roller  140 , the developer image is transferred onto the printing medium P. 
     The image fusing apparatus  1  fuses the transferred developer image onto the printing medium P and includes the heating belt  10 , the heating supporting roller  20 , and the pressing roller  50 . When the printing medium P enters the nip between the heating belt  10  and the pressing roller  50  of the image fusing apparatus  1 , the developer image is fused on the printing medium P by predetermined heat and pressure. At this time, the image fusing apparatus  1  according to an exemplary embodiment of the present disclosure is not overheated even continuous printing since temperature of the paper non-contact area L 2  of the heating belt  10  is low. 
     After fusing is completed, the printing medium P is discharged outside the image forming apparatus  100  through the conveying rollers  111  and the paper discharging apparatus  150 . 
     As described above, since the image forming apparatus according to an exemplary embodiment of the present disclosure is structured so that during printing temperature of the paper non-contact area does not rise significantly, even continuous printing the image forming apparatus is not damaged by heat. 
     Although a few embodiments have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the disclosure, the scope of which is defined in the claims and their equivalents.