Patent Publication Number: US-9405272-B2

Title: Image forming apparatus including a duct filter having corrugated surface shape

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an image forming apparatus. 
     2. Description of the Related Art 
     In an electrophotographic image forming apparatus, it is known that a plurality of kinds of chemical substances are discharged from an image forming apparatus during image forming. For example, as a representative of the discharged chemical substances, there is ozone generated when a photosensitive drum is charged, or toner dust generated during developing or fusing. In the related art, in order to not allow the generated chemical substances to be discharged outside the image forming apparatus, for example, a measure of providing a filter or the like is performed. 
     In a volatile chemical substance collection device of an electronic apparatus disclosed in Japanese Patent Unexamined Publication No. 2009-282455, a technology is disclosed in which an electric field is generated in an atmosphere from an electric field generating collection member in an exhaust duct provided above a fuser unit, and volatile organic compounds (VOC) included in the atmosphere are drawn to the surface of the electronic field generating collection member by the operation of the electric field so as to be collected. 
     In an image forming apparatus disclosed in Japanese Patent Unexamined Publication No. 2011-180235, a technology is disclosed as follows. That is, a duct which includes a take-in port for taking-in minute particles generated from a heat roller inside a fusing device is provided in the vicinity of the fusing device. An exhaust fan which generates a flow of air from the take-in port toward an outlet is provided in an expansion portion of the duct, and a first filter member is provided on the upstream side of the exhaust fan. The first filter member captures ultrafine particles (for example, siloxane) generated from a rubber layer configuring the fusing device. A shutter which closes a gap between the first filter member and the expansion portion is provided, and a control portion of the image forming apparatus switches a state where the shutter closes a first filter portion and a state where the shutter does not close the first filter portion according to a predetermined initial burst condition. 
     In an odor removing device of a multi-function image forming apparatus disclosed in Japanese Patent Unexamined Publication No. 2011-180283, a technology is disclosed as follows. That is, a plurality of air passage portions for introducing air inside a housing are formed on a housing bottom portion. Each air passage portion is a cylindrical body in which an inner diameter of the upper portion side inside the housing is smaller than an inner diameter of the housing bottom portion, and an ozone decomposition filter including an ozone decomposition catalyst is disposed on an inner diameter surface of the cylindrical body. A waste liquid absorbing material is disposed on the bottom portion inside the housing, a deodorizing absorbent is disposed on an upper cover inside the housing, and an exhaust port of the air passing through a portion between the waste liquid absorbing material and the deodorizing absorbent is provided on the side surface of the housing. 
     Japanese Patent Unexamined Publication No. 2002-8943 discloses a technology, in which a filter is pleat-molded into a cross-sectional wave shape, and thus, a surface area of a filter base material is increased and deodorization performance is improved. 
     SUMMARY OF THE INVENTION 
     According to an exemplary embodiment of the present invention, there is provided an image forming apparatus including: a fuser unit which includes a heat roller and a pressure roller which heats and pressurizes a sheet on which an unfused toner image is carried and fuses the unfused toner image on the sheet; a duct which is formed in a long shape in a direction along an axis of the heat roller, is disposed in the vicinity of the fuser unit along the axis of the heat roller, and is exhausted by an exhaust fan which is provided on one end side in a long-side direction; an exhaust port which is opened to a first side wall of the fuser unit side of the duct and causes the fuser unit and the duct to communicate with each other; and a planar filter which is attached to an inner wall surface of the duct, in which the filter includes a filter base material having an irregular surface shape in which ditches and convex portions are alternately disposed and a frame which is bonded to both ends orthogonal to an irregularity direction of the filter base material, and the convex portion of the filter base material protrudes from the frame, and the convex portion of the filter base material is bonded or stuck to the inner wall surface. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a longitudinal cross-sectional view of a multi-function printer of the present embodiment; 
         FIG. 2  is a perspective view when a first side wall of the multi-function printer shown in  FIG. 1  is viewed from a fuser unit container side; 
         FIG. 3  is a perspective view when  FIG. 2  is cut at an approximately center position in a long-side direction of a heat roller; 
         FIG. 4  is a perspective view when  FIG. 3  is viewed from the lower portion of a duct side; 
         FIG. 5  is a perspective view when an exhaust port of a first side wall is viewed from the upper portion in a state where a ceiling surface of the duct is not shown; 
         FIG. 6  is a perspective view of a filter in which ditches and convex portions extend so as to be orthogonal to each other in a long-side direction of the duct; 
         FIG. 7  is a perspective view of a filter in which ditches and convex portions extend in an inclination direction in the long-side direction of the duct; 
         FIG. 8  is a perspective view of a filter in which ditches and convex portions extend so as to be parallel with each other in the long-side direction of the duct; and 
         FIG. 9  is a perspective view of a thru-beam type filter. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, an embodiment (hereinafter, referred to as the “present embodiment”) of an image forming apparatus according to the present invention will be described with reference to the drawings. In the present embodiment below, as an example of the image forming apparatus according to the present invention, an electrophotographic multi-function printer will be described. However, the image forming apparatus according to the present invention is not limited to the multi-function printer, and for example, may be also applied to a copier or printer. 
       FIG. 1  is a longitudinal cross-sectional view of multi-function printer  11  of the present embodiment.  FIG. 2  is a perspective view when first side wall  57  of multi-function printer  11  shown in  FIG. 1  is viewed from fuser unit container  51  side.  FIG. 3  is a perspective view when  FIG. 2  is cut at an approximately center position in a long-side direction of heat roller  41 .  FIG. 4  is a perspective view when  FIG. 3  is viewed from the lower portion of duct  53  side.  FIG. 5  is a perspective view when exhaust port  63  of first side wall  57  is viewed from the upper portion in a state where ceiling surface  71  of the duct is not shown.  FIG. 6  is a perspective view of filter  65  in which ditches  77  and convex portions  79  extend so as to be orthogonal to each other in a long-side direction of duct  53 .  FIG. 7  is a perspective view of filter  65 A in which ditches  77 A and convex portions  79 A extend in an inclination direction in the long-side direction of duct  53 .  FIG. 8  is a perspective view of filter  65 B in which ditches  77 B and convex portions  79 B extend so as to be parallel with each other in the long-side direction of duct  53 .  FIG. 9  is a perspective view of thru-beam type filter  85 . 
     For example, multi-function printer  11  of the present embodiment includes functions such as scanning, copying, or printing, form (fuses) a monochromatic or multicolor image on a sheet (for example, a recording material or a recording sheet) based on print job data input from an external device (for example, a personal computer (PC) (not shown)), and discharges the sheet. 
     Multi-function printer  11  shown in  FIG. 1  is configured to include at least photosensitive drum  13 , charging unit  15 , developing roller  17 , transfer roller  19 , exposure device  21 , fuser unit  23 , sheet feeding cassette (not shown), sheet transport roller  25 , sheet discharging roller  27 , and sheet discharging tray  29  in main body casing  31 . 
     For example, one set of visible image forming units (process units)  33  is disposed at an approximately center inside main body casing  31  of multi-function printer  11  shown in  FIG. 1 . For ease of explanation, for example, it is described that one set of visible image forming units  33  is disposed to form a black image in multi-function printer  11  shown in  FIG. 1 . However, the visible image forming unit having the similar configuration for each different color (yellow, magenta, cyan) may be disposed. 
     Photosensitive drum  13  which has a role as an electrostatic latent image carrier according to print job data input into multi-function printer  11  is provided in visible image forming unit  33 , and charging unit  15 , developing roller  17 , transfer roller  19 , and cleaning unit  35  are disposed in the vicinity of photosensitive drum  13 . 
     Charging unit  15  uniformly charges a predetermined potential (for example, negative potential) on the surface of photosensitive drum  13 . For example, preferably, charging unit  15  is a charge roller type which can uniformly charge the surface of photosensitive drum  13  without generating ozone as much as possible during charging with respect to photosensitive drum  13 . However, charging unit  15  is not limited to the charge roller type, and for example, may use a contact type brush or a non-contact charger type. 
     Developing roller  17  develops electrostatic latent image formed on photosensitive drum  13  by exposure device  21  described below using toner supplied to developing roller  17 . Accordingly, a toner image corresponding to the print job data is obtained. In the present embodiment, for example, black toner is supplied to developing roller  17 . In multi-function printer  11 , toner of each color may be supplied to each developing roller of a visible image forming unit corresponding to each color of yellow, magenta, and cyan, and having the same configuration as the visible image forming unit  33 . 
     Transfer roller  19  is disposed to oppose photosensitive drum  13 , and transfers the toner image formed on the surface of photosensitive drum  13  to sheet  37  which is transported along sheet transport path  45 . Hereinafter, the toner image transferred to sheet  37  by transfer roller  19  is referred to as an “unfused toner image”. 
     Cleaning unit  35  removes and recovers the toner which remains on the surface of photosensitive drum  13  after the transfer processing is performed in transfer roller  19 . 
     Exposure device  21  includes a laser scanning unit (LSU)  39 . Laser scanning unit  39  is configured to include a laser light source, a polygon mirror which performs scanning with the laser light emitted from the laser light source, a lens which introduces the laser light which performs the scanning by the polygon mirror into photosensitive drum  13 , and a reflecting mirror. Laser scanning unit  39  exposes the surface of photosensitive drum  13  by the light from the polygon mirror according to the input print job data, and forms the electrostatic latent image according to the print job data on photosensitive drum  13 . 
     Fuser unit  23  is configured to include heat roller  41  and pressure roller  43  which extend so as to be perpendicular to sheet  37 . Heat roller  41  is heated to a predetermined target temperature (for example, fuse temperature within a range from 180° C. to 200° C.) by a heater which is a heat source. Pressure roller  43  is biased toward heat roller  41  by a spring (not shown). Fuser unit  23  heats and pressurizes sheet  37  to which the toner image is transferred in pressure roller  43  and heat roller  41 , and thus, the unfused toner image is fused on sheet  37 . 
     Sheet transport path  45  is formed from a sheet feeding cassette (not shown) to sheet discharging tray  29  in main body casing  31 . Sheet transport path  45  is configured of a transport path which passes through fuser unit  23  from sheet transport roller  25  via a portion between photosensitive drum  13  and transfer roller  19 , and reaches sheet discharging roller  27  (refer to an arrow A in  FIG. 1 ). Sheet transport path  45  becomes sheet discharging path  47  immediately before sheet discharging roller  27 . For example, a switchback transport path (not shown) for feeding sheet  37  to the position of transfer roller  19  again when a duplex printing is performed is provided in sheet discharging path  47 . 
     A control portion (not shown) for integrally controlling all operations of multi-function printer  11  is provided in main body casing  31 . The control portion is configured using a processor (for example, Central Processing Unit (CPU), Micro Processing Unit (MPU), and Digital Signal Processor (DSP)). The control portion controls each operation in each portion of multi-function printer  11 , that is, photosensitive drum  13 , charging unit  15 , developing roller  17 , transfer roller  19 , exposure device  21 , fuser unit  23 , sheet transport roller  25 , and sheet discharging roller  27 . Control portion also controls the operation of exhaust fan  49  (refer to  FIG. 2 ) described below. 
     In multi-function printer  11  having the above-described configuration, an image forming process is performed as follows by control portion of multi-function printer  11 . 
     When the image forming is performed, first, sheets  37  are discharged from a sheet feeding cassette (not shown) to sheet transport path  45  one by one using sheet transport roller  25 . 
     After charging unit  15  uniformly charges the surface of photosensitive drum  13 , exposure device  21  exposes a charge region on the surface of photosensitive drum  13  by laser light according to the print job data input from the external device. Accordingly, the electronic latent image corresponding to the print job data is formed on the surface of photosensitive drum  13 . Continuously, developing roller  17  develops the electronic latent image formed on the surface of the photosensitive drum  13  using the toner supplied by developing roller  17 . Accordingly, the toner image corresponding to the print job data is obtained. 
     Transfer roller  19  transfers the toner image formed on the surface of photosensitive drum  13  to sheet  37  which is fed from the sheet feeding cassette (not shown) by sheet transport roller  25  and is transported. Accordingly, the unfused toner image corresponding to the print job data is transferred to sheet  37 . The unfused toner image transferred to sheet  37  is transported to fuser unit  23 . Fuser unit  23  sufficiently heats and pressurizes the unfused toner image in heat roller  41  and pressure roller  43  and fuses the unfused toner image on sheet  37 . Accordingly, the image corresponding to the print job data is formed on sheet  37 , and sheet  37  is discharged to sheet discharging tray  29  by sheet discharging roller  27 . 
     Here, in multi-function printer  11  of the present embodiment, fuser unit container  51  for accommodating fuser unit  23  is provided in the vicinity of fuser unit  23 . Fuser unit container  51  is formed as a cavity which has airtightness on a level in which the ultrafine particles (UFP) generated inside fuser unit container  51 , that is, in fuser unit  23  are not leaked to the outside of fuser unit container  51 . 
     More specifically, fuser unit container  51  is formed by connecting a plurality of metal plates and molding resin plates fixed to main body casing  31  to one another. Since fuser unit container  51  becomes a negative pressure by suction of exhaust fan  49  described below, existence of a small gap such as sheet transport path  45  communicating with the outside of the cavity is admitted. Outside air flows into fuser unit container  51  from the gap, and thus, fuser unit container  51  does not become a vacuum. An exclusive air feeding port may be provided in fuser unit container  51 . 
     Duct  53  is provided so as to be adjacent to fuser unit container  51 . Duct  53  is formed in a long shape in a direction along axis  59  (refer to  FIG. 2 ) of heat roller  41 , and is disposed in the vicinity of fuser unit  23  along axis  59  of heat roller  41 . More specifically, duct  53  is formed in a long shape in the direction along axis  59  (refer to  FIG. 2 ) of heat roller  41  with a portion of wall portion  55  in fuser unit container  51  as first side wall  57 . Exhaust fan  49  (refer to  FIG. 2 ) is provided on one end side in a long-side direction of duct  53 , and exhaust fan  49  exhausts exhaust emissions including air existing in air transport space  61  (refer to  FIG. 1 ) of duct  53  to the outside of main body casing  31 . 
     Exhaust port  63  (refer to  FIG. 2 ) is opened to first side wall  57  of fuser unit  23  side of duct  53 , that is, first side wall  57  of wall portion  55  of fuser unit container  51 . Exhaust port  63  causes fuser unit  23  and duct  53  to communicate with each other. More specifically, exhaust port  63  causes fuser unit container  51  which is provided so as to cover fuser unit  23  and duct  53  to communicate with each other. In the present embodiment, as shown in  FIG. 2 , a plurality of (two in  FIG. 2 ) exhaust ports  63  are formed in the long-side direction of first side wall  57 . A gap between exhaust ports  63  and an opening area of each exhaust port are set after container exhaust gas  87  described below is adjusted so as to be exhausted without variation in the long-side direction of fuser unit container  51 . 
     Planar filter  65  is detachably attached to the inner wall surface of duct  53  so as to be parallel with inner wall surface. Since filter  65  is disposed so as to be parallel with the inner wall surface, it is possible to easily perform direct fixation with respect to the inner wall surface using a bonding agent, a double-sided adhesive tape, or the like. In duct  53 , since filter  65  is directly fixed to the inner wall surface, a decrease in air transport space  61  is suppressed to the minimum. The inner wall surface of duct  53  is used as a collective name of ceiling surface  71 , first side wall  57 , second side wall  73 , and bottom surface  75  of the duct. 
     As shown in  FIG. 6 , filter  65  includes filter main body  67  which is a filter base material formed in the shape of irregular surface  81 , and frame body  69  which is a frame. In filter main body  67 , ditches  77  and convex portions  79  are alternately disposed. Frame body  69  is bonded to both ends orthogonal to an irregularity direction of filter main body  67 . Ditches  77  and convex portions  79  of filter main body  67  protrude from frame body  69 . “Both ends orthogonal to the irregularity direction” are a pair of ends which is positioned on both sides toward a direction in which irregularities are arranged. Frame body  69  is fixed to both ends of filter main body  67 . 
     For example, in the configuration of filter  65  of the present embodiment, ditches  77  and convex portions  79  are formed of V grooves, and crest portions in which V grooves are vertically inverted. The lowest portion of the V groove becomes a valley bottom at which a pair of valley surfaces crosses each other. The highest portion of the crest portion is an apex at which a pair of inclined sides crosses each other. Since filter main body  67  is formed to be folded upwardly or downwardly, the valley bottom and the apex have opposite phases on the front and rear surfaces. That is, the valley bottom on the front surface becomes the apex on the rear surface. 
     Frame body  69  of filter  65  may be formed of band shaped non-woven fabrics. Since frame body  69  is formed of non-woven fabrics, in addition to filter main body  67 , lots of minute voids, that is, fiber clearances and holes are also formed in frame body  69 . Accordingly, compared to a case where frame body  69  is formed of materials such as metal or resin which are not non-woven fabrics, in filter  65 , it is possible to increase efficiency of the entire filter  65  of capturing ultrafine particles. 
     In duct  53 , a rectangular ceiling surface (ceiling surface  71  of the duct) of duct  53  in which the inner wall surface is along the long-side direction of duct  53  is formed. Filter  65  is attached so as to be parallel with ceiling surface  71  of the duct. Specifically, preferably, filter is installed in a rectangular shape which covers ceiling surface  71  of the duct. As a result, if filter  65  has an area which can cover almost the entire ceiling surface  71  of the duct, filter  65  may be a single filter or a plurality of divided filters. 
     Filter  65  may be installed to cover all or a portion of first side wall  57 , second side wall  73 , and bottom surface  75  in addition to ceiling surface  71  of the duct. However, when filter  65  is provided on first side wall  57 , filter is provided on a portion other than exhaust port  63  so that exhaust port  63  is not blocked. 
     Ceiling surface  71  of the duct is formed to be upwardly inclined so as to be heightened as ceiling surface  71  is away from exhaust port  63 . In first side wall  57  and second side wall  73  opposing first side wall which are positioned in a state where ceiling surface  71  of the duct is interposed therebetween, an included angle between first side wall  57  and ceiling surface  71  and an included angle between second side wall  73  and ceiling surface  71  become acute angles. 
     As shown in  FIG. 6 , the surface of filter  65  is configured so as to have irregular surface  81  in which ditches  77  and convex portions  79  parallel with each other to be extended so as to be orthogonal to the long-side direction of duct  53  are alternately disposed in the long-side direction (arrow B direction in  FIG. 6 ) of ceiling surface  71  of the duct. Since filter  65  has irregular surface  81 , the surface area is increased. 
     Ditch  77  and convex portion  79  configuring irregular surface  81  may be formed in various shapes. For example, although it is not shown, ditch  77  may be formed in a V ditch, and convex portion  79  may be formed in an inverted V-shaped crest. Although it is not shown, in ditch  77  and convex portion  79 , a valley bottom of the V groove and an apex of the inverted-V shaped crest are curved, and a so-called waveform of a sine wave shape may be configured. Although it is not shown, ditch  77  and convex portion  79  may be a recessed groove having a flat groove bottom and a protruding convex portion  79  having a flat apex. 
     In filter  65 , ditches  77  and convex portions  79  of irregular surface  81  may be arranged in a different pattern. 
     As shown in  FIG. 7 , the surface of filter  65 A may be irregular surface  81 A in which ditches  77 A and convex portions  79 A extending in a direction inclined in the long-side direction of duct  53  are alternately disposed in the long-side direction of ceiling surface  71  of the duct. A pair of frame body  69 A is parallel with each other on both ends in the extension directions of ditches  77 A and convex portions  79 A extending in the inclination direction, and is bonded to each other while filter main body  67 A is interposed therebetween. 
     As shown in  FIG. 8 , the surface of filter  65 B may be irregular surface  81 B in which ditches  77 B and convex portions  79 B extending in parallel in the long-side direction of duct  53  are alternately disposed in the short-side direction of ceiling surface  71  of the duct. A pair of frame body  69 B is parallel with each other on both ends in the extension directions of ditches  77 B and convex portions  79 B extending in parallel with each other, and is bonded to each other while filter main body  67 B is interposed therebetween. 
     In the present embodiment, thru-beam type filter  85  shown in  FIGS. 5 and 9  is attached so as to cover exhaust opening surface  83  (refer to  FIG. 2 ) of exhaust fan  49 . As shown in  FIG. 9 , the surface of thru-beam type filter  85  is also formed to have irregular surface  81  in which ditches  77  and convex portions  79  parallel with each other are alternately disposed. Since thru-beam type filter  85  has irregular surface  81 , the surface area is increased. Thru-beam type filter  85  passes container exhaust gas  87  (see below) which flows into via exhaust port  63 . Similar to filter  65 , thru-beam type filter  85  is also detachably attached to exhaust opening surface  83 . 
     Next, an operation of multi-function printer  11  having the above-described configuration will be described. 
     In multi-function printer  11 , the unfused toner image corresponding to the print job data input from the external device is transferred to sheet  37  and is transported to fuser unit  23 . In fuser unit  23 , sheet  37  is held by heat roller  41  and pressure roller  43 . The unfused toner image carried to sheet  37  becomes an image fused on sheet  37  and is fused by heating of heat roller  41  and pressurizing of pressure roller  43 . 
     At this time, in fuser unit  23 , it is known that a very small quantity of toner configuring the unfused toner image is separated from the unfused toner image along water vapor according to vaporization of water included in sheet  37 . In general, the toner is configured of pigment, wax, and an external additive. A primary effect of the external additive is to improve response efficiency between the external additive and static electricity, and for example, is used to attach minute particles such as silica on the toner surface. In recent years, there is a report that it is considered that the external additive particularly separated along with water vapor is one of factors increasing ultrafine particles (UFP) in multi-function printer  11 . 
     In the present embodiment, the external additive separated from the toner surface along with the water vapor generated during the fusing of sheet  37  is carried to the upper portion of fuser unit container  51  along with air which is moved by natural convection and a suction force by exhaust fan  49 . First side wall  57  which is a portion of wall portion  55  is positioned on the upper portion of fuser unit container  51 . First side wall  57  becomes a partition between duct  53  provided to be adjacent to fuser unit container  51  and first side wall. Duct  53  is formed in a long shape in the direction along axis  59  of heat roller  41 . That is, duct  53  is disposed to be adjacent in parallel with fuser unit  23  across the partition, and thus, compactification of multi-function printer  11  is realized. Exhaust port  63  is formed on first side wall  57  which is the partition, and exhaust port  63  causes the inside of fuser unit container  51 , that is, an exposure space of fuser unit  23 , and the inside (air transport space  61 ) of duct  53  to communicate with each other. 
     In duct  53 , the air of air transport space  61  flows toward one end side in the long-side direction by exhaust fan  49  which is provided on one end side in the long-side direction. Accordingly, the air inside fuser unit container  51  is sucked into and flows into air transport space  61  of duct  53  which reaches a negative pressure via exhaust port  63 . The external additive (ultrafine particles: UFP) separated from the toner surface along with the water vapor generated during the fusing of sheet  37  is mostly included in suction air (hereinafter, referred to as “container exhaust gas”) along with other volatile organic compounds (VOC) and dust, and flows into air transport space  61  of duct  53 . 
     When container exhaust gas  87  shown in  FIGS. 2 and 3  is transferred to one end side in the long-side direction of duct  53 , the container exhaust gas comes into contact with the surface of planar filter  65  which is attached in parallel with the inner wall surface of duct  53 . Filter  65  and container exhaust gas  87  come into contact with each other, and thus, it is confirmed that the ultrafine particles (UFP) included in container exhaust gas  87  are captured by filter  65 . Specifically, it is possible to confirm the capturing of ultrafine particles by measuring the amount of emission of the ultrafine particles at the outlet side of exhaust fan  49  when filter  65  is provided in duct  53  and when filter  65  is not provided in duct  53 . It is considered that the reason why the ultrafine particles are captured by filter  65  disposed in parallel with container exhaust gas  87  is because container exhaust gas  87  becomes turbulent in the vicinity of the surface of filter  65  and as a result, a vortex is generated, and thus, the ultrafine particles are caught on the surface of filter  65  and therefore, are captured. 
     In filter  65 , as the base material, vegetable fibers, mineral fibers, synthetic fibers, woven fabrics, non-woven fabrics, felts, webs, resin foamed bodies, porous films, or the like may be used. Even when any base material is used, lots of minute voids, that is, fiber clearances and holes are formed on the surface of filter  65 . 
     In a portion in which container exhaust gas  87  flowing to air transport space  61  of duct  53  is far away from filter  65 , the container exhaust gas uniformly flows and thus, a velocity gradient (velocity change) is not generated. Meanwhile, since sliding is not generated on the surface of filter  65 , flow velocities are continuously changed by influence of a friction force in the vicinity of filter  65 , and a region in which uniform flow is generated is formed. That is, a thin layer (boundary layer) having a great velocity gradient is covered on the surface of filter  65 . It is considered that the ultrafine particles, in which transport energy is decreased by the boundary layer and the above-described vortex generated by the turbulence, are caught on minute voids on the filter surface and are captured. The boundary layer is changed by ultrafine particles (UFP) which are captured and deposited. It is considered that there are optimal values with respect to a relationship between the ultrafine particles (UFP) and the sizes of the minute voids, and the flow velocity of container exhaust gas  87 . 
     In this way, in the present embodiment, since duct  53  is disposed in the vicinity of fuser unit  23  along axis  59  of heat roller  41 , a wasteful space is not generated in multi-function printer  11 . As a result, the configuration itself of multi-function printer  11  becomes simple and compact. 
     More specifically, in the present embodiment, duct  53  is also used as a portion of wall portion  55  of fuser unit container  51 , and thus, it is possible to easily manufacture multi-function printer  11 . Since duct  53  is disposed to be adjacent to fuser unit container  51  along (in parallel with) heat roller  41  only across the partition, wasteful space is not generated in multi-function printer  11 . As a result, the configuration itself of multi-function printer  11  becomes simple and compact. It is also possible to easily replace filter  65 , and thus, it is possible to improve maintenance of multi-function printer  11 . 
     Since filter  65  is configured in a long shape along the long-side direction of duct  53 , a contact time between container exhaust gas  87  and the filter is lengthened, probability of the ultrafine particles (UFP) being captured is increased, and it is possible to decrease the amounts of the ultrafine particles (UFP) exhausted to the outside of multi-function printer  11 . Filter  65  does not cross air transport space  61  of duct  53 , and is installed in parallel with the transport direction of container exhaust gas  87  in air transport space  61 . Accordingly, unlike the thru-beam type filter in the related art, filter  65  can prevent an increase of resistance when air is transported, and in other words, filter  65  can prevent an increase of output of the exhaust fan. 
     In multi-function printer  11 , filter  65  is installed on ceiling surface  71  of the duct, and thus, it is possible to allow container exhaust gas  87  including the water vapor generated during the fusing of sheet  37  and ultrafine particles (UFP) having buoyancy generated by ascending current to effectively come into contact with filter  65 . Particularly, since container exhaust gas  87  immediately after exhaust fan  49  is stopped is moved at a low flow velocity in the vicinity of ceiling surface  71  of the duct and thereafter, the container exhaust gas stagnates, it is possible to effectively capture the ultrafine particles (UFP). 
     In multi-function printer  11 , ceiling surface  71  of the duct is formed to be upwardly inclined so as to be heightened as ceiling surface  71  is away from exhaust port  63 , and the included angle between second side wall  73  and ceiling surface  71  of the duct becomes an acute angle. Accordingly, air transport space  61  interposed between second side wall  73  and filter  65  becomes a corner space which is gradually narrowed toward the upper portion. In the corner space, by friction forces of second side wall  73  and filter  65 , the flow velocity during the exhaust is gradually decreased toward the inner side which is the side remote from exhaust fan  49 . It is assumed that container exhaust gas  87  including the ultrafine particles (UFP) which moves upwardly along with the water vapor ascends toward the corner space. Accordingly, it is possible to deposit the ultrafine particles (UFP) on filter  65  from the inner side of the corner space. As a result, it is possible to effectively use the surface of filter  65  from the inner side of the corner space. 
     In multi-function printer  11 , filter  65  having irregular surface  81  in which ditches  77  and convex portions  79  are alternately disposed is installed in the transport direction of container exhaust gas  87 . Transported container exhaust gas  87  repeatedly collides with ditches  77  and convex portions  79 , and thus, a vortex is generated. Accordingly, in filter  65 , it is possible to improve probability of the ultrafine particles (UFP) being captured by minute voids of filter  65  itself. 
     In multi-function printer  11 , the plurality of exhaust ports  63  are provided, and the gap and the area of each exhaust port  63  are appropriately set. Accordingly, compared to a case where one exhaust port  63  is provided, it is possible to suppress variation in an inflow amount of container exhaust gas  87  flowing in air transport space  61  of duct  53  in the long-side direction of duct  53 . 
     In multi-function printer  11 , container exhaust gas  87  passes through air transport space  61  of duct  53 , and thus, container exhaust gas  87  including the exhaust emissions from fuser unit  23  is exhausted from exhaust opening surface  83  of exhaust fan  49  in a state where the ultrafine particles (UFP) are decreased. At this time, container exhaust gas  87  including the exhaust emissions from fuser unit  23  passes through thru-beam type filter  85 , and thus, the remaining ultrafine particles are captured again. Thru-beam type filter  85  is provided over the entire cross-section of duct  53 , and thus, it is possible to capture ultrafine particle secondarily. Filter  65  inside duct  53  and thru-beam type filter  85  may be installed so that filter performance is appropriately adjusted. For example, a replacement period of filter  65  inside duct  53  may be set to be lengthened, and a replacement period of thru-beam type filter  85  may be set to be shortened. 
     Here, in the configuration of the related art in which filter  65  is not provided in duct  53 , the decrease of the ultrafine particles (UFP) is dependent on only thru-beam type filter  85 . In this case, when thru-beam type filter  85  is thickened to improve capture performance of ultrafine particles (UFP), exhaust fan  49  having greater power is required, and thus, noise is also increased. 
     In contrast, in multi-function printer  11  of the present embodiment including filter  65  in duct  53 , thru-beam type filter  85  may have an auxiliary performance. Accordingly, in multi-function printer  11  of the present embodiment, air resistance is not increased even when thru-beam type filter  85  is attached, and it is possible to suppress an increase in the output of exhaust fan  49 . 
     In filter  65 , filter main body  67  is formed in the irregular shape in which ditches  77  and convex portions  79  are alternately disposed. Frame body  69  is bonded to both ends orthogonal to an irregularity direction of filter main body  67 . “Both ends orthogonal to the irregularity direction” are a pair of ends which is positioned on both sides toward a direction in which irregularities are arranged. Since frame body  69  is fixed to both ends of filter main body  67 , extension and contraction, for example, of the filter  65  are regulated like an accordion, in the irregularity direction. That is, in filter  65 , pitch of the irregularities (ditch  77  (convex portion  79 ) and ditch  77  (convex portion  79 )) is not easily changed, and optimal pitch is always maintained. Accordingly, shape stability is increased, and handling becomes easy. 
     In filter  65 , convex portions  79  protrude from frame body  69 , and the entire region of convex portions  79  can be fixed so as to be bonded to the surface to be fixed. Accordingly, a sufficient bonding area is obtained. When the surface of filter  65  is attached so as to be parallel with respect to the flow of air including removal materials, the front and rear convex portions  79  protrude from frame body  69  into the flow of the air. Accordingly, the flow of the air is not blocked by frame body  69 , the air directly abuts the surfaces of convex portions  79  also in the vicinity of frame body  69 , and easily comes into contact with the surfaces of convex portions  79 . Therefore, efficiency of capturing the ultrafine particles is increased. 
     In filter  65 , since the front and rear convex portions  79  protrude from frame body  69 , even when convex portions  79  are bonded so as to be fixed to the inner wall surface, ditches  77  opposing the inner wall surface are opened to air transport space  61  of duct  53 . That is, it is possible to allow the front and the rear of filter main body  67  to communicate with air transport space  61 . Therefore, according to filter  65  in which ditches  77  and convex portions  79  protrude from frame body  69 , a closed space is not generated between the filter and the inner wall surface, and thus, it is possible to increase the efficiency of capturing the ultrafine particles. 
     In filter  65 , ditches  77  and convex portions  79  extend so as to be orthogonal to the long-side direction of duct  53 . That is, ditches  77  and convex portions  79  are alternately disposed in the long-side direction of duct  53 . Container exhaust gas  87  flowing into air transport space  61  of duct  53  from exhaust port  63  of first side wall  57  flows toward the direction approaching ceiling surface  71  of the duct by ascending current including water vapor. Particularly, the flow in the direction approaching ceiling surface  71  of the duct is remarkably generated immediately after exhaust fan  49  is stopped. Container exhaust gas  87  approaching ceiling surface  71  of the duct abuts the surface of filter  65  attached to ceiling surface  71  of the duct. At this time, ditches  77  and convex portions  79  extend so as to be orthogonal to first side wall  57  on the surface of filter  65 . Accordingly, in filter  65 , container exhaust gas  87  flowing in the long-side direction of duct  53  after flowing from exhaust port  63  easily abuts convex portions  79 . Container exhaust gas  87  collides with convex portions  79 , and thus, turbulence is easily generated, and numerous vortexes are generated in the vicinity of filter  65 . As a result, in filter  65 , probability of capturing the ultrafine particles at minute voids of filter  65  itself is improved. 
     In filter  65 A, ditches  77 A and convex portions  79 A extend in the inclined direction in the long-side direction of duct  53 . As for the “inclination in the long-side direction of duct  53 ”, two inclination directions are considered. One inclination direction is an inclination direction (separation inclination direction) in which the inclination end of one end side (exhaust fan  49  side) in the long-side direction of the duct of ditch  77 A and convex portion  79 A positioned on ceiling surface  71  of the duct is away from first side wall  57 . On the other hand, the other inclination direction is an inclination direction (approach inclination direction) in which the inclination end of exhaust fan  49  side of ditch  77 A and convex portion  79 A positioned on ceiling surface  71  of the duct approaches first side wall  57 . 
     Initially, container exhaust gas  87  flowing toward exhaust fan  49  in air transport space  61  of duct  53  flows into duct  53  in a direction orthogonal to the long-side direction of duct  53  from exhaust port  63  of first side wall  57 . That is, the flow direction of container exhaust gas  87  is gradually curved from exhaust port  63 , and is changed into a perpendicular direction. Strictly speaking, the flow direction becomes three-dimensional complicated flow lines which interfere with one another. 
     When ditches  77 A and convex portions  79 A are in the “separation inclination direction”, container exhaust gas  87  immediately after the container exhaust gas flows from exhaust port  63  easily flows to the downstream side without inversely flowing along the extension directions of ditches  77 A and convex portions  79 A. Accordingly, ditches  77 A and convex portions  79 A in the separation inclination direction easily come into contact with container exhaust gas  87  over the entire length in the extension direction. As a result, in the separation inclination direction, the time when ditches  77 A and convex portions  79 A come into contact with container exhaust gas  87  is lengthened. 
     Meanwhile, when ditches  77 A and convex portions  79 A are in the “approach inclination direction”, container exhaust gas  87  immediately after the container exhaust gas flows from exhaust port  63  easily abuts the convex portions in a direction approximately orthogonal to the extension direction of convex portion  79 A. That is, container exhaust gas  87  collides with convex portions  79 A, turbulence is easily generated, and numerous vortexes are generated in the vicinity of filter  65 . As a result, in ditches  77 A and convex portions  79 A in the approach inclination direction, probability of the ultrafine particles being captured by the minute voids of filter  65  itself is improved. 
     Which of the approach inclination direction and the separation inclination direction can capture more ultrafine particles can be confirmed by measuring the amounts of emission of the ultrafine particles in the outlet side of exhaust fan  49 . As a result of the confirmation, it is understood that compared to the separation inclination direction, ditches  77 A and convex portions  79 A in the approach inclination direction increase efficiency of capturing the ultrafine particles. 
     In filter  65 B, ditches  77 B and convex portions  79 B extend so as to be parallel to the long-side direction of duct  53 . Container exhaust gas  87  flowing into air transport space  61  of duct  53  from exhaust port  63  of first side wall  57  flows toward the direction approaching ceiling surface  71  of the duct by ascending current including water vapor. Particularly, the flow in the direction approaching ceiling surface  71  of the duct is remarkably generated immediately after exhaust fan  49  is stopped. Container exhaust gas  87  approaching ceiling surface  71  of the duct abuts the surface of filter  65 B attached to ceiling surface  71  of the duct. At this time, ditches  77 B and convex portions  79 B extend so as to be parallel to first side wall  57  on the surface of filter  65 B. Accordingly, in filter  65 B, container exhaust gas  87  immediately after flowing from exhaust port  63  easily abuts convex portions  79 B with a wider surface area. Container exhaust gas  87  collides with convex portions  79 B, and thus, turbulence is easily generated, and numerous vortexes are generated in the vicinity of filter  65 B. As a result, in filter  65 B, probability of capturing the ultrafine particles at minute voids of filter  65 B itself is improved. 
     When ditches  77 B and convex portion  79 B extend so as to be parallel in the longitudinal direction of duct  53 , container exhaust gas  87  flowing toward one end side in the long-side direction of duct  53  flows along ditches  77 B and convex portions  79 B. Accordingly, it is possible to suppress an increase of resistance during the air is transported. As a result, it is possible to suppress an increase in output of exhaust fan  49  or noise (sound generated when the air passes through duct  53 ). 
     As described above, various embodiments are described with reference to the drawings. However, it goes without saying that the present invention is not limited to the examples. It is clear to a person skilled in the art that various modifications and corrections may be applied within a scope described in claims, and various modifications and corrections are included in the technical range of the present invention. 
     According to the embodiments of the present invention, the present invention is useful as the image forming apparatus which decreases the amount of emission of the ultrafine particles and suppresses the increase in the output of the exhaust fan by the simple structure.