Patent Publication Number: US-10775723-B2

Title: Fusing device with lubricant supplying unit and image forming apparatus having the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is a continuation application of PCT international patent application no. PCT/KR2017/006292, filed on Jun. 16, 2017, which is based on and claims priority under 35 U.S.C. § 119 to Korean Patent Application No. 10-2016-0117095, filed on Sep. 12, 2016, in the Korean Intellectual Property Office, the disclosure of which is incorporated by reference herein in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     Apparatuses consistent with the disclosure relate to a fusing device of which a lifespan may be increased by stably supplying a lubricant to a fusing belt, and an image forming apparatus including the same. 
     Description of the Related Art 
     Generally, an image forming apparatus that uses an electrophotographic manner supplies a toner to an electrostatic latent image formed on a photoreceptor to form a visible toner image on the photoreceptor, transfers the visible toner image to a recording medium, and then fuses the transferred toner image on the recording medium to print the image on the recording medium. 
     To fuse the transferred toner image on the recording medium in a process of printing the image on the recording medium as described above, the image forming apparatus includes a fusing device heating and pressing the recording medium to which the toner image is transferred. 
     The fusing device includes a pressing roller pressing the recording medium and a fusing belt heating the recording medium while rotating in a state of being circumscribed to the heating roller. A nip forming member forming a fusing nip is disposed at a contact portion between the pressing roller and the fusing belt on an inner surface of the fusing belt. 
     Such a fusing device has a structure in which the fusing belt rotates with respect to the nip forming member, and friction is thus generated at a contact portion between the fusing belt and the nip forming member. A speed difference between the fusing belt and the pressing roller may be generated due to the friction, and a torque of a predetermined magnitude or more may be applied to the pressing roller. 
     Therefore, a slip phenomenon in which a non-fused toner image slips on the recording medium may occur, and there is a risk that the fusing belt may be damaged due to abrasion of the nip forming member or the fusing belt caused by the friction. To prevent the slip phenomenon or the damage to the fusing belt, a lubricant is applied between the fusing belt and the nip forming member to reduce the friction between the fusing belt and the nip forming member. 
     It is preferable that the lubricant stays for a long period of time between the fusing belt and the nip forming member for the purpose of stable fusion. However, as the fusing belt rotates, the lubricant applied between the nip forming member and the fusing belt may be leaked out. In this case, a similar result may be ensued even though a large amount of lubricant is applied between the nip forming member and the fusing belt at a time. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
       The above and/or other aspects of the present disclosure will be more apparent by describing certain exemplary embodiments of the present disclosure with reference to the accompanying drawings, in which: 
         FIG. 1  is a cross-sectional view schematically illustrating a configuration of an image forming apparatus according to an embodiment of the disclosure; 
         FIG. 2  is a perspective view illustrating a fusing device according to an embodiment of the disclosure; 
         FIG. 3  is an exploded perspective view illustrating the fusing device according to the embodiment of the disclosure; 
         FIG. 4  is a side view illustrating the fusing device according to the embodiment of the disclosure; 
         FIG. 5  is a cross-sectional view illustrating the fusing device according to the embodiment of the disclosure; 
         FIG. 6  is an enlarged view of part A illustrated in  FIG. 5 ; 
         FIG. 7  is a view for describing a position of a lubricant supplying unit according to the embodiment of the disclosure; 
         FIGS. 8 to 11  are views for describing various modified examples of a fixing member according to the embodiment of the disclosure; 
         FIGS. 12A and 12B  are cross-sectional views illustrating a fusing device according to another embodiment of the disclosure; and 
         FIG. 13  is a graph for describing a temperature change depending on a printing condition. 
     
    
    
     DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS 
     Hereinafter, embodiments of the disclosure will be described in more details with reference to  FIGS. 1 through 13 . Embodiments to be described below will be described on the basis of embodiments most appropriate for understanding technical features of the disclosure, and these embodiments do not limit the technical features of the disclosure, but exemplify that the disclosure may be implemented like these embodiments. 
     Therefore, the disclosure may be variously modified without departing from the technical scope of the disclosure through embodiments to be described below, and these modifications will fall within the technical scope of the disclosure. In addition, to assist in the understanding of embodiments to be described below, related components among components performing the same operations in the respective embodiments will be denoted by the same or similar reference numerals throughout the accompanying drawings. 
       FIG. 1  is a cross-sectional view schematically illustrating a configuration of an image forming apparatus according to an embodiment of the disclosure. Referring to  FIG. 1 , the image forming apparatus includes a body  2 , a recording medium supplying unit  3 , a plurality of photoreceptors  4   a , a developing unit  4 , a transfer unit  7 , a fusing device  10 , a recording medium discharging unit  9 , and a light irradiating unit (not illustrated). 
     The body  2  forms an appearance of the image forming apparatus  1 , and supports various components installed in the image forming apparatus  1 . A portion of the body  2  is provided to be openable or closable. A user may replace or repair various components through the opened portion or remove a recording medium jammed inside the body  2 . 
     The recording medium supplying unit  3  supplies recording media toward the transfer unit  7 . As an example, the recording medium supplying unit  3  includes a cassette in which recording media S are stored, a pick-up roller picking up the recording media stored in the cassette one by one, and transport rollers transporting the picked-up recording media to the transfer unit  7 . 
     The light irradiating unit irradiates light corresponding to image information to the photoreceptors  4   a  to form electrostatic latent images on surfaces of the photoreceptors  4   a . Although not illustrated in the drawings, the light irradiating unit may include a light source emitting a light beam, a deflecting device deflecting the emitted light beam through a polygon mirror rotating by a motor, and an F-theta lens converging the deflected light beam on the photoreceptors. 
     The developing unit  4  supplies toners, which are developers, to the electrostatic latent images formed on the photoreceptors  4   a  to form visible toner images. The developing unit  4  includes four developing machines with developers having different colors, for example, the developers having black (K), cyan (C), magenta (M), and yellow (Y) are accommodated, respectively. 
     Each of the developing machines has a charger, a developer storing portion, a developer transporting member, and a developing member. The respective chargers charge the surfaces of the photoreceptors  4   a  before the electrostatic latent images are formed on the photoreceptors  4   a . The developers stored in the developer storing portions are transported toward the developing members by the developer transporting members, and the developing members supply the developers to the electrostatic latent images formed on the photoreceptors  4   a  to form visible images. 
     An example in which four photoreceptors  4   a  are included in the respective developing machines has been illustrated, but the image forming apparatus  1  according to the embodiment of the disclosure may also be configured so that four developing machines form a visible image on one photoreceptor. 
     The transfer unit  7  receives the visible images formed on the photoreceptors  4   a  and transfers the visible images to the recording medium S. The transfer unit  7  includes a transfer belt, a driving roller, a support roller, tension rollers, and transfer rollers. 
     The transfer belt is rotatably supported by the driving roller and support roller. The driving roller rotates by receiving a driving force delivered from a driving source (not illustrated) mounted in the body. The support roller is disposed on an opposite side to the driving roller to support an inner surface of the transfer belt. 
     An outer circumferential surface of the transfer belt faces the respective photoreceptors  4   a . The transfer rollers are disposed to correspond to the respective photoreceptors  4   a , and support an inner peripheral surface of the transfer belt. 
     When the image forming apparatus  1  performs a color printing operation, the transfer rollers are pressed toward the respective photoreceptors  4   a . In this case, the respective visible images formed on the photoreceptors  4   a  are transferred to and overlapped with one another on the transfer belt by the transfer rollers, and an image of the transfer belt is transferred to the recording medium S supplied from the recording medium supplying unit  3  and then passing between the transfer rollers and the transfer belt. 
     The recording medium passing through the transfer unit  7  enters the fusing device  10 . The fusing device  10  is configured to apply heat and pressure to the recording medium to fix a non-fused toner image on the recording medium to the recording medium. 
     The recording medium passing through the fusing device  10  is guided to the recording medium discharging unit  9 , and the recording medium discharging unit  9  discharges the recording medium from the image forming apparatus  1 . The recording medium discharging unit  9  includes a discharging roller and a discharging back-up roller installed to face the discharging roller. Hereinafter, the fusing device  10  included in the image forming apparatus  1  according to the embodiment of the disclosure will be described in detail. 
       FIG. 2  is a perspective view illustrating a fusing device according to an embodiment of the disclosure, and  FIG. 3  is an exploded perspective view illustrating the fusing device according to the embodiment of the disclosure. In addition,  FIG. 4  is a side view illustrating the fusing device according to the embodiment of the disclosure, and  FIG. 5  is a cross-sectional view illustrating the fusing device according to the embodiment of the disclosure. In addition,  FIG. 6  is an enlarged view of part A illustrated in  FIG. 5 , and  FIG. 7  is a view for describing a position of a lubricant supplying position according to the embodiment of the disclosure. 
     Referring to  FIGS. 2 to 7 , the fusing device  10  includes a fusing roller  20  and a nip forming member  80  which are disposed to face each other to form a fusing nip N through which the recording medium passes, a fusing belt  50  circumscribed to the fusing roller  20  to be driven and rotated by the fusing roller  20 , a heater  70  heating the fusing belt  50 , a lubricant supplying unit  94  supplying a lubricant  98  to an inner surface of the fusing belt  50 , and a fixing member  90  fixing an impregnating member  100  provided in the lubricant supplying unit  94  to the nip forming member  80 . 
     The fusing roller  20 , which is an example of a rotating roller that is rotatable, presses the recording medium passing through the fusing nip N. The fusing roller  20  rotates by receiving a driving force delivered through a driving source (not illustrated) mounted in the body  10  of the image forming apparatus  1 . In a process in which the recording medium passes through the fusing nip N between the fusing roller  20  and the fusing belt  50 , a toner image transferred to the recording medium S is fixed to the recording medium S by heat and pressure. 
     The fusing roller  20  includes a shaft  21  and an elastic layer  24 . The shaft  21  is disposed at a central portion of the fusing roller  20 , and functions as a rotating shaft. The shaft  21  may be formed of a metal material such as aluminum or steel. The elastic layer  24  is disposed to cover the surrounding of the shaft  21 , and forms the fusing nip N between the elastic layer  24  and the fusing belt  50  while being elastically deformed at the time of pressure-contact between the fusing roller  20  and the fusing belt  50 . The elastic layer  24  may be a heat-resistant elastomer layer. A heat-resistant elastomer may be, for example, a silicon elastomer, a fluoroelastomer, or the like. A release layer  22  preventing the recording medium S from being attached to the fusing roller  20  may be formed on a surface of the elastic layer  24 . The release layer  22  may be formed of one of, for example, perfluoroalkoxy (PFA), polytetrafluoroethylenes (PTFE), fluorinated ethylene propylene (FEP), or the like, a blend of two or more thereof, or a copolymer thereof. 
     The heater  70 , which is to provide the heat to the recording medium, may be installed on a bottom surface of the nip forming member  80 . As an example, the heater  70  may be provided at a position corresponding to a contact portion forming the nip, be disposed to be in contact with the fusing belt  50 , and heat the fusing belt  50 . 
     Meanwhile, the heater  70  may be spaced apart from the fusing belt  50 , and heat the fusing belt  50  by radiation heating. As an example of a heating source, a halogen lamp or an induction heating coil may be used. However, a position and a kind of heating source are not limited thereto. For example, the heating source may be disposed outside the fusing belt  50 . Meanwhile, the heating source may be a component separate from the fusing belt  50 , but may also be a heat generating layer included in the fusing belt  50 . 
     The fusing belt  50  is circumscribed to the fusing roller  20 , and is driven and rotated by the fusing roller  20 . The fusing belt  50  may have an endless shape. However, a structure of the fusing belt  50  is not necessarily limited thereto, and may be a film shape having an end portion and a structure in which a film is wound by a pair of rollers. 
     The fusing belt  50  is heated by the heating source. The heated fusing belt  50  is in contact with the recording medium passing through the fusing nip N to heat the recording medium, thereby fixing the toner image transferred to the recording medium to the recording medium. 
     The fusing belt  50  may include a base layer, an elastic layer, and a release layer although not illustrated in the drawings. The base layer may include at least one of a plastic material, such as a heat-resistant resin, or the like, or a metal material. The heat-resistant resin may be polyimide, polyimideamide, polyetherether ketone, or the like, and the metal material may include nickel (Ni), stainless steel, copper (Cu), and alloys thereof, or the like. The elastic layer may be a heat-resistant elastomer layer. A heat-resistant elastomer may be, for example, a silicon elastomer, a fluoroelastomer, or the like. 
     The release layer may be formed of one of, for example, perfluoroalkoxy (PFA), polytetrafluoroethylenes (PTFE), fluorinated ethylene propylene (FEP), or the like, a blend of two or more thereof, or a copolymer thereof. 
     A thickness of the fusing belt  50  may be about 30 μm to 200 μm. Therefore, rapid temperature rise performance of the fusing belt may be secured. 
     The nip forming member  80  is in contact with the inner surface of the fusing belt  50  to support the fusing belt  50  pressed by the fusing roller  20 . Therefore, the fusing nip N is formed between the fusing roller  20  and the fusing belt  50 . The nip forming member  80  is coupled to and fixed and supported by a pressing member  60 . The pressing member  60  may press the nip forming member  80 , and a pressing force may be applied toward the nip forming member  80  by a spring as an example. 
     The nip forming member  80  is disposed to face the fusing roller  20  pressing an outer circumferential surface of the fusing belt  50 . Therefore, the nip forming member  80  presses the inner surface of the fusing belt  50 . 
     Because the nip forming member  80  is in a state in which it is fixed by the pressing member  60 , when the fusing belt  50  rotates, a frictional force acts on a region in which the fusing belt  50  and the nip forming member  80  are in contact with each other. The frictional force may increase a torque acting on the fusing roller  20  or cause slip of the recording medium and the fusing belt  50  on the fusing nip. To prevent such a phenomenon, the lubricant  98  may be supplied between the fusing belt  50  and the nip forming member  80  to prevent direct contact between the fusing belt  50  and the nip forming member  80 . 
     However, the lubricant  98  supplied between the fusing belt  50  and the nip forming member  80  tends to be easily leaked or disappear due to characteristics thereof. For example, the lubricant  98  may be leaked from a position between the fusing belt  50  and the nip forming member  80  at the time of rotation of the fusing belt  50  due to fluidity of the lubricant  98 . In addition, because a high temperature and a high pressure are applied between the fusing belt  50  and the nip forming member  80  by the heater  70  and the fusing roller  20 , the lubricant  98  supplied between the fusing belt  50  and the nip forming member  80  may be vaporized in such a high-temperature and high-pressure environment. 
     In the embodiment of the disclosure, for the fusing device  10 , the lubricant  98  may be supplied between the fusing belt  50  and the nip forming member  80  for a long period of time even though the lubricant  98  supplied between the fusing belt  50  and the nip forming member  80  is leaked or disappears. To this end, the fusing device  10  according to the embodiment of the disclosure may further include the lubricant supplying unit  94  having a predetermined structure and the predetermined lubricant  98  used in the lubricant supplying unit  94 . Hereinafter, the lubricant supplying unit  94  and the lubricant  98  according to the embodiment of the disclosure will be described in detail. 
     The lubricant supplying unit  94  is disposed in the fusing belt  50 , and serves to supply the lubricant  98  between the fusing belt  50  and the nip forming member  80 . As an example, the lubricant supplying unit  94  may supply the lubricant  98  to the inner surface of the fusing belt  50 . The lubricant supplied to the inner surface of the fusing belt  50  may move between the nip forming member  80  and the fusing belt  50  as the fusing belt  50  rotates. 
     The lubricant supplying unit  94  includes a lubricant accommodating portion  95  provided at one side of the nip forming member  80  for storing the lubricant  98  and the impregnating member  100  for impregnating the lubricant  98  from the lubricant accommodating portion and supplying the lubricant  98  to the inner surface of the fusing belt  50 . 
     The lubricant supplying unit  94  may be disposed at a rear of the nip forming member  80  in a rotation direction of the fusing belt  50 . In addition, the lubricant supplying unit  94  may be provided at an upper side of the rear of the nip forming member  80  and supply the lubricant  98  at an upstream of the nip forming member  80  to minimize exposure of the lubricant  98  to the heater  70  and stably supply the lubricant  98  between the nip forming member  80  and the fusing belt  50 . 
     However, a position of the lubricant supplying unit  94  is not limited to the upstream of the nip forming member  80 , and may be appropriately changed if necessary. 
     The lubricant accommodating portion  95  includes a cavity or a space in which the lubricant  98  may be stored. An opening through which the lubricant  98  stored in the lubricant accommodating portion  95  may be discharged is formed at least one side of the lubricant accommodating portion  95 . 
     A rear surface of the lubricant accommodating portion  95  may have an inclined shape. Such an inclined surface is installed to be inclined in a downward direction toward the opening. Here, the downward direction may be parallel with a direction of gravity. Therefore, the lubricant  98  accommodated in the lubricant accommodating portion  95  may be disposed through the opening along the rear surface by the gravity. 
     The lubricant accommodating portion  95  may be continuously formed in a lengthwise direction. A length of the lubricant accommodating portion  95  may correspond to a width of the recording medium. Here, the lengthwise direction may refer to a direction parallel with a width direction of the recording medium and perpendicular to the rotation direction of the fusing belt  50 . However, a structure of the lubricant accommodating portion  95  is not limited thereto. 
     Referring to  FIG. 7 , the number of lubricant accommodating portions  95   a ,  95   b ,  95   c , and  95   d  is plural, and the plurality of lubricant accommodating portions  95   a ,  95   b ,  95   c , and  95   d  may be spaced apart from each other by a predetermined interval in the lengthwise direction. In this case, the impregnating members  100  may have shapes corresponding to those of the lubricant accommodating portions  95   a ,  95   b ,  95   c , and  95   d  in the lengthwise direction. However, the shapes of the impregnating member  100  are not limited thereto. The impregnating members  100  may be continuously formed in the lengthwise direction to be longer than those of the lubricant accommodating portions  95   a ,  95   b ,  95   c , and  95   d.    
     Surfaces of the impregnating members  100  are disposed at openings of the lubricant accommodating portions  95   a ,  95   b ,  95   c , and  95   d  to prevent lubricants  98  stored in the lubricant accommodating portions  95   a ,  95   b ,  95   c , and  95   d  from being discharged through the openings in a short time. In addition, the impregnating members  100  may be formed of a porous material impregnating the lubricants  98  discharged from the openings. Separate grooves in which the impregnating members  100  may be seated may be formed in the vicinity of the openings of the lubricant accommodating portions  95   a ,  95   b ,  95   c , and  95   d.    
     Meanwhile, the number of lubricant accommodating portions  95   a ,  95   b ,  95   c , and  95   d  is single, and the single lubricant accommodating portion may be formed along a width direction of the fusing belt  50 . In this case, the lubricant  98  to be described below may have two or more kinds of different oil separations, and the numbers and positions of lubricant accommodating portions  95  and impregnating members  100  are not limited thereto as long as the lubricants  98  may be supplied between the fusing belt  50  and the nip forming member  80 . 
     Referring to  FIGS. 2 to 6 , one surface of the impregnating member  100  is disposed toward the opening of the lubricant accommodating portion  95 , and another surface of the impregnating member  100  is disposed to be in contact with the inner surface of the fusing belt  50 . The impregnating member  100  impregnates or immerses the lubricant  98  supplied through the opening, and is in contact with the inner surface of the fusing belt  50  to deliver the impregnated lubricant to the inner surface of the fusing belt  50 . 
     The impregnating member  100  may include felt or fabric. The felt is a product in which fibers are entangled by compression, and a nylon or polyamide fiber, a polyethylene terephthalate (PET) fiber, an aramid fiber, a polytetrafluoroethylene (PTFE) fiber, a preoxidized polyacrylonitrile (PAN) fibers, or a wool fiber may be used as an example of the fiber. 
     However, the definition of the felt and the material of the fiber are not limited thereto, and known felt and fiber may be used. The fabric is a product in which fibers are woven in a lattice structure, and a glass fiber or an aramid fiber may be used as an example of the fiber. However, the definition of the fabric and the material of the fiber are not limited thereto, and known fabric and fiber may be used. The impregnating member  100  may have a structure in which a plurality of layers are stacked, if necessary. A weight of the impregnating member  100  per unit area on the basis of a thickness of 1 mm may be 50 g/m 2  to 600 g/m 2 . 
     The impregnating member  100  may impregnate some of components of the lubricant  98  stored in the lubricant accommodating portion  95 . For example, in a case in which the lubricant  98  includes base oil and a thickener or a gelling agent to be described below, the impregnating member  100  may impregnate the base oil and may not impregnate the thickener or the gelling agent. 
     An outer surface of the impregnating member  100  in contact with the fusing belt  50  may have a curved or rounded shape. Therefore, a contact area between the impregnating member  100  and the fusing belt  50  may be maximized. 
     A contact portion of the nip forming member  80  in contact with the inner surface of the fusing belt  50  may include at least one of metal, felt, or fabric. An example of the metal may include nickel (Ni), stainless steel, copper (Cu), and alloys thereof. The felt is a product in which fibers are entangled by compression, and a nylon or polyamide fiber, a polyethylene terephthalate (PET) fiber, an aramid fiber, a polytetrafluoroethylene (PTFE) fiber, a preoxidized polyacrylonitrile (PAN) fibers, or a wool fiber may be used as an example of the fiber. However, the definition of the felt and the material of the fiber are not limited thereto, and known felt and fiber may be used. The fabric is a product in which fibers are woven in a lattice structure, and a glass fiber or an aramid fiber may be used as an example of the fiber. However, the definition of the fabric and the material of the fiber are not limited thereto, and known fabric and fiber may be used. 
     The lubricant  98  stored in the lubricant accommodating portion  95  may include two or more kinds of lubricants having different oil separations. Here, the oil separation refers to a phenomenon in which oil constituting grease is separated in a case in which the grease is stored for a long period of time or during use of the grease, and may also be called a synersis phenomenon. The synersis phenomenon may occur when maintenance of oil is unstable in a case in which a gel structure is not sufficient or oxidation of a capillary diameter is caused by fiber binding. 
     The lubricant  98  includes the base oil and the thickener or the gelling agent. The base oil may include a heat-resistant fluororesin not to be deformed at a high temperature. An example of the heat-resistant fluororesin may include perfluoro polyether (PFPE). However, the material of the base oil is not limited thereto, and may include other materials. 
     For example, the base oil may include at least one of mineral oil, ester oil, polyglycol oil, polyphenyl ether oil, silicone oil, or perfluoroalkyl ether oil. A viscosity index of the base oil can be 50 to 800. The viscosity index, which is an index indicating a change level of a viscosity depending on a temperature, indicates a change level of a viscosity depending on a temperature obtained by defining a viscosity index of paraffinic standard oil having a high viscosity index, for example, Pennsylvania oil as 100, defining a viscosity index of naphthenic standard oil having a low viscosity index, for example, Gulf Coast oil as 0, and comparing a viscosity index of any oil with these viscosity indices. The viscosity index is a well-known term, and a description for a detailed method of calculating the viscosity index will be omitted. 
     The lubricant  98  stored in the lubricant accommodating portion  95  may include the base oil and the thickener or the gelling agent as described above. The lubricant  98  stored in the lubricant accommodating portion  95  is discharged to the impregnating member  100  through the opening. The impregnating member  100  impregnates base oil that is separated from the thickener or the gelling agent or may not impregnate base oil that is not separated from the thickener or the gelling agent in the base oil. 
     The impregnating member  100  may be the felt or the fabric. At least a portion of the lubricant  98  may be separated into the thickener or the gelling agent and the base oil in a high-temperature environment, for example, an environment of 150 to 230° C. The base oil separated from the thickener or the gelling agent is impregnated in the impregnating member  100 . Therefore, a weight ratio of the thickener or the gelling agent may become significantly smaller in the lubricant  98  impregnated in the impregnating member  100  than in the lubricant  98  stored in the lubricant accommodating portion  95 . 
     The lubricant  98  delivered to the inner surface of the fusing belt  50  moves between the fusing belt  50  and the nip forming member  80  by rotation of the fusing belt  50 . Because the lubricant  98  in which the weight ratio of the thickener or the gelling agent becomes small moves between the nip forming member  80  and the fusing belt  50 , even though the high pressure acts between the nip forming member  80  and the fusing belt  50 , a friction problem due to the thickener or the gelling agent may be prevented. 
     In a case in which the lubricant  98  supplied between the nip forming member  80  and the fusing belt  50  includes a predetermined ratio (for example, 30% of an entire weight of the lubricant  98 ) or more of thickener or gelling agent unlike the disclosure, the lubricant  98  may be separated into the base oil and the thickener or the gelling agent by the high pressure and high temperature acting between the nip forming member  80  and the fusing belt  50 , and only the base oil in a liquid state may be leaked out or vaporized. Therefore, only the thickener or the gelling agent remains between the nip forming member  80  and the fusing belt  50 , which may act as a cause of an increase in friction. 
     In the embodiment of the disclosure, the lubricant  98  supplied between the nip forming member  80  and the fusing belt  50  hardly includes the thickener or the gelling agent. Therefore, even though the high temperature and the high pressure are applied between the nip forming member  80  and the fusing belt  50 , a phenomenon in which only the thickener or the gelling agent remains between the nip forming member  80  and the fusing belt  50  may be prevented. 
     A predetermined ratio of thickener or gelling agent is included in the lubricant  98  stored in the lubricant accommodating portion  95 , such that an amount of the lubricant  98  discharged from the lubricant accommodating portion  95  may be controlled. 
     In a case in which the impregnating member  100  is a member impregnating only the base oil of the lubricant  98 , an amount of thickener or gelling agent impregnated in the impregnating member  100  may be changed depending on a ratio of the thickener or gelling agent included in the lubricant  98  stored in the lubricant accommodating portion  95 . 
       FIGS. 8 to 11  are views for describing various modified examples of a fixing member according to the embodiment of the disclosure. Referring to  FIG. 8 , the fusing device  10  according to the embodiment of the disclosure further includes the fixing member  90  to prevent the impregnating member  100  from being separated from the nip forming member  80  due to a continuous contact external force of the fusing belt  50 . The fixing member  90  may have a clip shape having an elastic force, and may include a separate fastener so that at least a portion of an outer side of the impregnating member  100  is mounted in the nip forming member  80 . 
     In this case, a support groove (not illustrated) in which the fixing member  90  is provided in the nip forming member  80  so that an upper end of the fixing member  90  is stably supported by the nip forming member  80 , such that the fixing member  90  may press the impregnating member  100  in a state in which one end portion of the fixing member  90  is stably supported in the support groove. 
     Referring to  FIG. 9 , a fixing member  90   a  may have a lancing structure so that the impregnating member  100  is mounted on the nip forming member  80 . Here, the lancing structure is a structure in which lancing holes  95   a  are formed in the fixing member  90   a , and coupling brackets  96   a  are fitted into the lancing holes  95   a , such that the impregnating member  100  may be mounted on the nip forming member  80 . 
     As illustrated in  FIGS. 10 and 11 , it is possible to separate the impregnating member  100  from the nip forming member  80  using separate stop rings (cs-rings)  96   b  or fasteners  96   c.    
     As illustrated in  FIG. 10 , a fixing member  90   b  includes protrusions  95   b  formed on one side of the nip forming member  80  and the stop rings  96   b  pushed toward and fitted onto the protrusions  95   b  to fix the protrusions  95   b . The stop ring  96   b  may be a mechanical element forcibly pushed toward and fitted onto a counterpart without having a shaft to fix the counterpart. Meanwhile, the protrusion  95   b  may be formed integrally with the nip forming member  80  or may be formed separately from the nip forming member and be adhered to the nip forming member  80 . 
     In addition, as illustrated in  FIG. 11 , a fixing member  90   c  includes separate fasteners  96   c , and the fasteners  96   c  is fastened to screw holes (not illustrated) formed on one side of the nip forming member  80 . The impregnating member  100  is fixed to the nip forming member  80  by coupling the fasteners  96   c  (for example, bolts) into the screw holes in a state in which the impregnating member  100  is interposed. 
       FIG. 12A  is a cross-sectional view illustrating a fusing device according to another embodiment of the disclosure, and  FIG. 12B  is a cross-sectional view for describing an operation state of the fusing device according to another embodiment of the disclosure. Hereinafter, contents different from those of the fusing device according to the embodiment of the disclosure described with reference to  FIGS. 2 to 8  will be mainly described, and contents for which a description is omitted may be replaced by the abovementioned contents. 
     Referring to  FIGS. 12A and 12B , a fusing device  10  may include a fusing roller  20  and a nip forming member  80  that are disposed to face each other to form a fusing nip N through which a recording medium S passes, a fusing belt  50  circumscribed to the fusing roller  20  to be driven and rotated by the fusing roller  20 , a heater  70  heating the fusing belt  50 , lubricant supplying units  95  and  100  supplying a lubricant  98  to an inner surface of the fusing belt  50 , and a fixing member  90  fixing an impregnating member  100 ,  110  provided in the lubricant supplying units  95  and  100  to the nip forming member  80 . 
     The impregnating member  100 ,  110  includes a first impregnating member  100  disposed at a rear of the nip forming member  80  on the basis of a rotation direction of the fusing belt  50  and a second impregnating member  110  disposed at a front of the nip forming member  80  on the basis of the rotation direction of the fusing belt  50 . 
     In a case in which the fusing roller rotates in a forward direction as illustrated in  FIG. 12A , the lubricant  98  supplied to the inner surface of the fusing belt  50  may be impregnated in the second impregnating member  110  positioned at the front of the nip forming member  80 . Then, in a case in which the fusing roller  20  rotates in a reverse direction during a period in which printing is not performed as illustrated in  FIG. 12B , the lubricant  98  contained in the second impregnating member  110  may be supplied again to the inner surface of the fusing belt  50 . 
     Here, each of the first impregnating member  100  and the second impregnating member  110  may be formed of a porous material including felt and fabric. 
     Meanwhile, it has been described hereinabove that the impregnating members  100  and  110  are disposed at the rear and the front of the nip forming member  80 , respectively, but a plurality of lubricant supplying units  95  and  100  may also be provided at the rear and the front of the nip forming member  80 , respectively. 
       FIG. 13  is a graph for describing a temperature change depending on a printing condition. The graph of  FIG. 13  illustrates a result of an experiment performed so that the lubricant  98  may correspond to several temperature environments depending on a printing condition of a user. In Case 1, as a result of repeatedly performing for 120 minutes a process of printing images on three recording media and leaving the image forming apparatus as it is for five minutes, a temperature of the lubricant  98  was about 100° C. In Case 2, as a result of repeatedly performing for 240 minutes a process of printing images on three recording media and leaving the image forming apparatus as it is for thirty minutes, a temperature of the lubricant  98  was about 60° C. In addition, in Case 3, as a result of repeatedly performing for thirty minutes a process of printing images on three recording media and leaving the image forming apparatus as it is for ten seconds, a temperature of the lubricant  98  was about 155° C., and in Case 4, as a result of continuously printing images for thirty minutes, a temperature of the lubricant  98  was about 170° C. In addition, in Case 5, as a result of repeatedly performing for 120 minutes a process of printing images on three recording media and leaving the image forming apparatus as it is for fifteen minutes, a temperature of the lubricant  98  was about 72° C. 
     In the lubricant  98  according to the embodiment of the disclosure, a weight ratio of the thickener or the gelling agent may exceed 0% of an entire weight of the lubricant  98  and be equal to or less than 20% of the entire weight of the lubricant  98 , in consideration of these experiment results. Here, weights of the lubricant  98  and the thickener or the gelling agent may be measured before the lubricant  98  is discharged to the impregnating member  100 , and the entire weight of the lubricant  98  may be a value obtained by adding up weights of the base oil and the thickener or the gelling agent. 
     In a case in which the weight ratio of the thickener or the gelling agent is 0% of the entire weight of the lubricant  98 , that is, in a case in which the lubricant  98  does not include the thickener or the gelling agent, the lubricant  98  stored in the lubricant accommodating portion  95  is supplied to the impregnating member  100  within a short time by the high-temperature and high-pressure environment. Because it is not limited by the thickener or the gelling agent that the lubricant  98  that does not include the thickener or the gelling agent is supplied to the impregnating member  100 , the lubricant  98  is in a state in which the entirety thereof may be supplied to the impregnating member  100 . Therefore, the lubricant  98  stored in the lubricant accommodating portion  95  may be discharged within a short time. 
     However, in a case in which the weight ratio of the thickener or the gelling agent exceeds 0% of the entire weight of the lubricant  98 , the supply of a portion of the lubricant  98  to the impregnating member  100  is limited by the thickener or the gelling agent. In a predetermined temperature condition, for example, a condition of 150 to 230° C., a portion of the base oil is separated from the thickener or the gelling agent, but the other portion of the base oil is not separated from the thickener or the gelling agent. Therefore, only the base oil separated from the thickener or the gelling agent is supplied to the impregnating member  100 , and the base oil that is not separated from the thickener or the gelling agent is not supplied to the impregnating member  100 . Therefore, the lubricant  98  stored in the lubricant accommodating portion  95  is not supplied to the impregnating member  100  within the short time, and is slowly supplied to the impregnating member  100 . 
     However, in a case in which the weight ratio of the thickener or the gelling agent exceeds 20% of the entire weight of the lubricant  98 , the base oil and the thickener or the gelling agent are hardly separated from each other. Therefore, the lubricant  98  supplied to the impregnating member  100  is significantly reduced. In this case, it becomes difficult for the impregnating member  100  to perform a function of supplying the lubricant  98  to the inner surface of the fusing belt  50 . 
     Meanwhile, a state of the lubricant  98  including the base oil and the thickener or the gelling agent may be changed depending on a temperature condition. For example, in a case in which a temperature of the lubricant  98  satisfies a predetermined temperature, the base oil and the thickener or the gelling agent may be separated from each other. The predetermined temperature may be about 150 to 230° C., which is an internal temperature of the lubricant accommodating portion  95  during a period in which the fusion is performed. In a case in which the temperature of the lubricant  98  does not satisfy the predetermined temperature, for example, in a case in which the temperature of the lubricant  98  is less than about 150° C., the base oil and the thickener or the gelling agent are not separated from each other, such that the lubricant  98  may be maintained in a semi-solid state. Therefore, it is possible to prevent the lubricant  98  in the lubricant accommodating portion  95  from being discharged to the impregnating member  100  during the period in which the fusion is not performed. 
     In addition, according to the embodiment of the disclosure, it is possible to prevent the lubricant  98  from being leaked to the outside in a short time in the high-temperature and high-pressure environment. Further, it is possible to prevent meandering of and damage to the fusing belt  50  to significantly improve lifespans of the fusing device  10  and the image forming apparatus  1 . 
     Although the diverse embodiments of the disclosure have been individually described hereinabove, the respective embodiments are not necessarily implemented singly, and may also be implemented so that configurations and operations thereof are combined with those of one or more other embodiments. 
     In addition, specific embodiments have been illustrated and described hereinabove. However, the disclosure is not limited to only the abovementioned embodiments, but may be variously modified by those skilled in the art to which the disclosure pertains without departing from the scope and spirit of the disclosure stated in the claims.