Patent Publication Number: US-2020292961-A1

Title: Image forming apparatus

Description:
FIELD 
     Embodiments described herein relate generally to an image forming apparatus. 
     BACKGROUND 
     There has been an image forming apparatus such as a multi function peripheral (hereinafter referred to as “MFP”) or a printer. The image forming apparatus includes a developing device that stores a developer. The developing device includes a developing roller. If the air enters the developing device according to rotation of the developing roller, the pressure in the developing device increases. If the pressure in the developing device increases, the air including toner in the developing device sometimes blows out to the outside of the developing device. If the air including the toner blows out to the outside of the developing device, the toner scatters to the outside of the developing device. As a result, some components in the image forming unit such as a charging device are likely to be soiled. In an image forming apparatus including a plurality of image forming units, i.e., including a plurality of developing devices therein, the other components in each image forming unit may be soiled by toner scattering from the adjacent developing devices. 
     DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an exterior view of an image forming apparatus in an embodiment; 
       FIG. 2  is a schematic diagram of the image forming apparatus; 
       FIG. 3  is a sectional view of a developing device in the embodiment; 
       FIG. 4  is a IV arrow view of  FIG. 3 ; 
       FIG. 5  is a side view of a first image forming unit and a second image forming unit in the embodiment; 
       FIG. 6  is a side view of the first and the second image forming unit for explaining a flow of air around the developing device; 
       FIG. 7  is a side view of image forming units for explaining a flow of air around a developing device in a comparative example; 
       FIG. 8  is a sectional view of the developing device for explaining a flow of air therein in the embodiment; 
       FIG. 9  is a sectional view of the developing device for explaining toner scattering therein; 
       FIG. 10  is a sectional view of a circulation-type developing device for explaining a flow of air therein; 
       FIG. 11  is a side view of a first image forming unit and a second image forming unit in a first modification of the embodiment; 
       FIG. 12  is a side view of a developing device for explaining a flow of air around therein in the first modification; 
       FIG. 13  is a side view of a first image forming unit and a second image forming unit in a second modification of the embodiment; 
       FIG. 14  is a diagram including a XIV-XIV section of  FIG. 13 ; 
       FIG. 15  is a side view of a first image forming unit and a second image forming unit in a third modification of the embodiment; and 
       FIG. 16  is a side view of a first image forming unit and a second image forming unit in a fourth modification of the embodiment. 
    
    
     DETAILED DESCRIPTION 
     In general, according to one embodiment, an image forming apparatus includes first and second image forming units, each including a developing device, a non-developing device, and an image carrier between the developing device and the non-developing device. The non-developing device of the first image forming unit is adjacent to the developing device of the second image forming unit. The apparatus includes a belt above the developing device, the non-developing device, and the image carrier of the image forming units, that moves as the image carrier rotates. A first gap between an upper surface of the non-developing device of the first image forming unit and the belt is larger than a second gap between an upper surface of the developing device of the second image forming unit and the belt. A third gap between aside surface of the non-developing device of the first image forming unit and a side surface of the developing device of the second image forming unit is smaller than the second gap. 
     The image forming apparatus in the embodiment is explained below with reference to the drawings. In the figures, the same components are denoted by the same reference numerals and signs. 
       FIG. 1  is an exterior view of an image forming apparatus  1  in the embodiment. For example, the image forming apparatus  1  is a multi function peripheral (MFP). The image forming apparatus  1  reads an image formed on a sheet-like recording medium (hereinafter referred to as “sheet”) such as paper and generates digital data (an image file). The image forming apparatus  1  forms an image on the sheet using toner on the basis of the digital data. 
     The image forming apparatus  1  includes a display  110 , an image scanner  120 , an image forming unit  130 , and a sheet tray  140 . 
     The display  110  operates as an output interface and displays characters and images. The display  110  operates as an input interface as well and receives an instruction from a user. For example, the display  110  is a touch panel-type liquid crystal display. 
     For example, the image scanner  120  is a color scanner. As the color scanner, there are a contact image sensor (CIS) and a charge coupled device (CCD). The image scanner  120  reads an image formed on a sheet using a sensor and generates digital data. 
     The image forming unit  130  forms an image on a sheet using toner. The image forming unit  130  forms an image on the basis of image data read by the image scanner  120  or image data received from an external apparatus. For example, the image formed on the sheet is an output image called hard copy or printout. 
     The sheet tray  140  supplies, to the image forming unit  130 , a sheet used for image output. 
       FIG. 2  is a schematic diagram of the image forming apparatus  1  in the embodiment. The image forming apparatus  1  is an electrophotographic image forming apparatus. The image forming apparatus  1  is a quintuple tandem type image forming apparatus. 
     Examples of the toner include a decoloring toner, a non-decoloring toner (e.g., a regular toner), and a decorative toner. The decoloring toner is decolored by an external stimulus. “Decoloring” means that an image formed in a color (including not only a chromatic color but also an achromatic color such as white or black) different from a color of a foundation of paper is made invisible. For example, the external stimulus is temperature, light having a specific wavelength, or pressure. In the embodiment, the decoloring toner is decolored if the temperature of the decoloring toner reaches a specific decoloring temperature or more. The decoloring toner develops a color if the temperature of the decoloring toner reaches a specific restoration temperature or less after being decolored. 
     Any toner may be used as the decoloring toner if the toner has the characteristics explained above. For example, a coloring agent of the decoloring toner may be a leuco dye. A color developing agent, a decoloring agent, a discoloring temperature adjusting agent, and the like maybe combined with the decoloring toner as appropriate. 
     A fixing temperature of the decoloring toner is low compared with a fixing temperature of the non-decoloring toner. The fixing temperature of the decoloring toner means temperature of a heat roller during a decoloring toner mode explained below. A fixing temperature of the non-decoloring toner means temperature of the heat roller during a monochrome toner mode or during a color toner mode explained below. 
     The fixing temperature of the decoloring toner is low compared with temperature of decoloring processing of the decoloring toner. The temperature of the decoloring processing of the decoloring toner means temperature of the heat roller of a fixing device  32  during a decoloring mode. 
     The image forming apparatus  1  includes a scanner  2 , an image processor  3 , an exposure device  4 , an intermediate transfer body  10  (e.g., a belt), a cleaning blade  11 , image forming units  12  to  16 , primary transfer rollers  17 - 1  to  17 - 5 , a paper feeder  20 , a secondary transfer unit  30 , a fixing device  32 , a paper discharger  33 , and a controller (not illustrated in  FIG. 2 ). In the following explanation, the primary transfer rollers  17 - 1  to  17 - 5  are simply described as primary transfer rollers  17  if the primary transfer rollers  17 - 1  to  17 - 5  are not distinguished. 
     In the following explanation, since a sheet is conveyed from the paper feeder  20  to the paper discharger  33 , the paper feeder  20  side is set as an upstream side with respect to a sheet conveying direction Vs and the paper discharger  33  side is set as a downstream side with respect to the sheet conveying direction Vs. 
     As transfer in the image forming apparatus  1 , there are a first transfer process and a second transfer process. In the first transfer process, the primary transfer rollers  17  transfer images by toners on photoconductive drums of the image forming units onto the intermediate transfer body  10 . In the second transfer process, the secondary transfer unit  30  transfers images by toners of colors stacked on the intermediate transfer body  10  onto a sheet. 
     The scanner  2  reads an image formed on a sheet set as a scanning target. For example, the scanner  2  reads the image on the sheet and generates image data of the three primary colors of red (R), green (G), and blue (B). The scanner  2  outputs the generated image data to the image processor  3 . 
     The image processor  3  converts the image data into color signals of the colors. For example, the image processor  3  converts the image data into image data (e.g., color signals) of four colors of yellow (Y), magenta (M), cyan (C), and black (K). The image processor  3  controls the exposure device  4  on the basis of the color signals. 
     The exposure device  4  irradiates or exposes light on the photoconductive drums of the image forming units. The exposure device  4  includes an exposure light source such as a laser or an LED. 
     The intermediate transfer body  10  is an endless belt. The intermediate transfer body  10  is rotating in an arrow A direction in  FIG. 2 . Images of toners are formed on the surface of the intermediate transfer body  10 . The intermediate transfer body  10  is in contact with the respective photoconductive drums of a plurality of image forming units  12  to  16 . The intermediate transfer body  10  moves according to rotation of the photoconductive drums. 
     The cleaning blade  11  removes toner adhering to the intermediate transfer body  10 . For example, the cleaning blade  11  is a tabular member. For example, the cleaning blade  11  is made of resin such as urethane resin. 
     The image forming units  12  to  16  form images using toners of colors (e.g., five colors in  FIG. 2 ). The image forming units  12  to  16  are arranged along the intermediate transfer body  10 . 
     The primary transfer rollers  17  (i.e.,  17 - 1  to  17 - 5 ) are used when the images by the toners formed by the image forming units  12  to  16  are transferred onto the intermediate transfer body  10 . 
     The paper feeder  20  feeds a sheet. 
     The secondary transfer unit  30  includes a secondary transfer roller  30   a  and a secondary transfer counter roller  30   b.  The secondary transfer unit  30  transfers the images formed by the toners on the intermediate transfer body  10  onto the sheet. 
     In the secondary transfer unit  30 , the intermediate transfer body  10  and the secondary transfer roller  30   a  are in contact. In view of improving a paper jam, the intermediate transfer body  10  and the secondary transfer roller  30   a  may be separable. 
     The fixing device  32  fixes the images by the toners transferred onto the sheet on the sheet with heating and pressurization. The sheet on which an image is formed by the fixing device  32  is discharged to the outside of the apparatus from the paper discharger  33 . 
     The image forming units  12  to  16  are explained. The image forming units  12  to  15  respectively store toners of colors corresponding to four colors for color printing. The four colors for color printing are colors of yellow (Y), magenta (M), cyan (C), and black (K). The toners of the four colors for color printing are non-decoloring toners. The image forming unit  16  stores a decoloring toner. The image forming units  12  to  15  and the image forming unit  16  have the same configuration, although the toners stored therein are different. Therefore, the image forming unit  12  representing the image forming units  12  to  16  is explained. Explanation about the other image forming units  13  to  16  is omitted. 
     The image forming unit  12  includes a developing device  12   a,  a photoconductive drum  12   b,  a charging device  12   c,  and a cleaning unit  12   d.    
     The developing device  12   a  stores a developer. The developer includes toner. The developing device  12   a  deposits the toner on the photoconductive drum  12   b.  For example, the toner is used as a one-component developer or combined with a carrier and used as a two-component developer. For example, as the carrier, iron powder or polymer ferrite particles having a particle diameter of several ten micrometers are used. In the embodiment, a two-component developer including a nonmagnetic toner is used. 
     The photoconductive drum  12   b  is one specific example of an image carrier. The photoconductive drum  12   b  includes a photoconductive body (or a photoconductive region) on the outer circumference of the photoconductive drum  12   b.  For example, the photoconductive body is an organic photoconductor (OPC). 
     The charging device  12   c  uniformly charges the surface of the photoconductive drum  12   b.    
     The cleaning unit  12   d  includes a cleaning blade  12   d   1  and a cleaner case  12   d   2 . The cleaning blade  12   d   1  removes toner adhering to the photoconductive drum  12   b.  The cleaner case  12   d   2  covers the cleaning blade  12   d   1  from the opposite side of the photoconductive drum  12   b.    
     An overview of the operation of the image forming unit  12  is explained. 
     The photoconductive drum  12   b  is charged to predetermined potential by the charging device  12   c.  Subsequently, light is irradiated on the photoconductive drum  12   b  from the exposure device  4 . Consequently, the potential of a region where the light is irradiated in the photoconductive drum  12   b  changes. According to the change, an electrostatic latent image is formed on the surface of the photoconductive drum  12   b.  The electrostatic latent image on the surface of the photoconductive drum  12   b  is developed by the developer of the developing device  12   a.  That is, an image developed by the toner (hereinafter, “developed image”) is formed on the surface of the photoconductive drum  12   b.    
     The developed image formed on the surface of the photoconductive drum  12   b  is transferred onto the intermediate transfer body  10  by the primary transfer roller  17 - 1  opposed to the photoconductive drum  12   b  in a first transfer process. 
     The first transfer process in the image forming apparatus  1  is explained. First, the primary transfer roller  17 - 1  opposed to the photoconductive drum  12   b  transfers the developed image on the photoconductive drum  12   b  onto the intermediate transfer body  10 . Subsequently, the primary transfer roller  17 - 2  opposed to a photoconductive drum  13   b  transfers a developed image on the photoconductive drum  13   b  onto the intermediate transfer body  10 . Such processing is performed in photoconductive drums  14   b,    15   b,  and  16   b  as well. At this time, developed images on the photoconductive drums  12   b  to  16   b  are transferred onto the intermediate transfer body  10  so as to overlap one another. For that reason, the developed images by the toners of the colors are superimposed and transferred onto the intermediate transfer body  10  that is passed through the image forming unit  16 . 
     However, if image formation using only the non-decoloring toner is performed, the image forming units  12  to  15  operate. A developed image formed using only the non-decoloring toner is formed on the intermediate transfer body  10  by such operation. If image formation using only the decoloring toner is performed, the image forming unit  16  operates. A developed image formed using only the decoloring toner is formed on the intermediate transfer body  10  by such operation. 
     A second transfer process is explained. A voltage (a bias) is applied to the secondary transfer counter roller  30   b.  For that reason, an electric field is generated between the secondary transfer counter roller  30   b  and the secondary transfer roller  30   a.  The secondary transfer unit  30  transfers, with the electric field, the developed image formed on the intermediate transfer body  10  onto a sheet. 
     Types of image formation processing executed by the image forming apparatus  1  (see  FIG. 1 ) in the embodiment are explained. The image forming apparatus  1  executes printing in three modes described below. 
     Monochrome toner mode: An image is formed by a non-decoloring toner of a black single color. 
     Color toner mode: An image is formed by a non-decoloring monochrome toner and non-decoloring color toners. 
     Decoloring toner mode: An image is formed by only a decoloring toner. 
     The user can select one of the modes, by operating the display  110  of the image forming apparatus  1 . 
     In the monochrome toner mode, an image forming unit using a non-decoloring toner of black (K) operates, whereby an image is formed. The monochrome toner mode is a mode selected if the user desires to print a general monochrome image. For example, the monochrome toner mode is used, for example, if the user desires to store important documents and the like without recycling paper. 
     In the color toner mode, four image forming units using respective non-decoloring toners of yellow (Y), magenta (M), cyan (C), and black (K) operate, whereby an image is formed. The color toner mode is a mode selected if the user desires to print a color image. 
     In the decoloring toner mode, only an image forming unit using a decoloring toner operates, whereby an image is formed. The decoloring toner mode is a mode selected if paper on which an image is formed is recycled. 
     The fixing device  32  is controlled to a fixing mode and a decoloring mode. In the fixing mode, a toner image is fixed on a sheet. In the decoloring mode, the toner image is decolored on the sheet. In the decoloring mode, the temperature of a heat roller is set higher than the temperature during the fixing mode. That is, the controller (not illustrated in  FIG. 2 ) causes the fixing device  32  to operate at least at two or more target temperatures. Specifically, two target temperatures of the fixing device  32  are stored in a memory (not illustrated in  FIG. 2 ). The controller reads a target temperature from the memory according to a selected mode and causes the fixing device  32  to operate. The two target temperatures are a first temperature and a second temperature. The first temperature is temperature during the decoloring mode. The second temperature is temperature during the fixing mode. That is, the second temperature is temperature lower than the first temperature. As illustrated in  FIG. 1 , the display  110  includes a button  150  for switching the fixing device  32  from the decoloring mode to the fixing mode. 
     The developing device  12   a  is explained.  FIG. 3  is a sectional view of the developing device  12   a  in the embodiment. In  FIG. 3 , cross section hatching is omitted. 
     As illustrated in  FIG. 3 , the developing device  12   a  includes a housing  60 , a first mixer  61 , a second mixer  62 , a developing roller  63 , a shield section  64 , a gap forming member  71 , a blocking member  72 , and a guide section  74 . 
     The housing  60  stores a developer. The developer includes a carrier, which is a magnetic body, and toner functioning as a coloring material. The first mixer  61  and the second mixer  62  are disposed on the inside of the housing  60 . An opening section  60   h  for exposing a part of the developing roller  63  is formed on a side opposed to the photoconductive drum  12   b  (see  FIG. 2 ) in the housing  60 . In this embodiment, the housing  60  includes the developing device  12   a.  However, the housing  60  may include a frame of the image forming apparatus  1  other than the developing device  12   a.  The housing  60  and the gap forming member  71  may be integrally molded or may be separate members. 
       FIG. 4  is a IV arrow view of  FIG. 3 . In  FIG. 4 , illustration of the gap forming member  71 , the blocking member  72 , and the like is omitted. 
     As illustrated in  FIG. 4 , the first mixer  61  and the second mixer  62  are disposed in parallel to each other. The first mixer  61  functions as a developer agitating section that agitates the developer. The second mixer  62  functions as a developer supplying section that supplies the developer. 
     A first chamber  60   a,  in which the first mixer  61  is disposed, is formed in the housing  60 . A second chamber  60   b,  in which the second mixer  62  is disposed, is formed in the housing  60 . A partition wall  65  that partitions the first chamber  60   a  and the second chamber  60   b  is provided in the housing  60 . The first chamber  60   a  and the second chamber  60   b  are adjacent to each other across the partition wall  65 . Side openings  60   c  and  60   d  for circulating the developer between the first chamber  60   a  and the second chamber  60   b  are formed on both sides in a rotation axis direction Vg of the developing roller  63  in the housing  60 . In the following explanation, the rotation axis direction Vg of the developing roller  63  is referred to as “roller axis direction Vg” as well. 
     As illustrated in  FIG. 3 , the developing roller  63  is rotatable in the housing  60 . The developing roller  63  carries the developer with a magnetic force of a magnetic body. The developing roller  63  is opposed to the photoconductive drum  12   b  (see  FIG. 2 ) via the opening section  60   h.  The developing roller  63  is disposed on the second chamber  60   b  side. 
     The developing roller  63  includes a shaft section  63   a,  a plurality of magnetic pole sections N 1 , S 1 , N 2 , N 3 , and S 2 , and a sleeve  63   b.    
     The shaft section  63   a  extends in the roller axis direction Vg (see  FIG. 4 ). Both end portions of the shaft section  63   a  are fixed to the housing  60 . 
     The plurality of magnetic pole sections N 1 , S 1 , N 2 , N 3 , and S 2  are fixed to the shaft section  63   a.  The plurality of magnetic pole sections N 1 , S 1 , N 2 , N 3 , and S 2  are fixed in fixed positions at intervals in the circumferential direction of the shaft section  63   a.  For example, the plurality of magnetic pole sections N 1 , S 1 , N 2 , N 3 , and S 2  are magnets. 
     The plurality of magnetic pole sections N 1 , S 1 , N 2 , N 3 , and S 2  are a development pole N 1 , a first conveyance pole S 1 , a peeling pole N 2 , a grasping pole N 3 , and a second conveyance pole S 2 . The development pole N 1  is opposed to the photoconductive drum  12   b  across the sleeve  63   b  to bring the developer carried on the developing roller  63  close to the photoconductive drum  12   b  (see  FIG. 2 ). The plurality of magnetic pole sections N 1 , S 1 , N 2 , N 3 , and S 2  are disposed in the order of the first conveyance pole S 1 , the peeling pole N 2 , the grasping pole N 3 , and the second conveyance pole S 2  downstream in a rotating direction J 1  of the developing roller  63  on the basis of the development pole N 1 . In the following explanation, the rotating direction J 1  of the developing roller  63  is referred to as “roller rotating direction J 1 ” as well. The development pole N 1 , the peeling pole N 2 , and the grasping pole N 3  are N poles. The first conveyance pole S 1  and the second conveyance pole S 2  are S poles. 
     The first conveyance pole S 1  is an intra-housing most upstream magnetic pole section located on the most upstream side in the roller rotating direction J 1  on the inside of the housing  60 . The first conveyance pole S 1  is located on the downstream side in the roller rotating direction J 1  with respect to a position where the developing roller  63  is opposed to the photoconductive drum  12   b  (see  FIG. 2 ) and on the most upstream side in the roller rotating direction J 1  on the inside of the housing  60 . 
     The sleeve  63   b  is formed in a cylindrical shape that includes the shaft section  63   a  and the plurality of magnetic pole sections N 1 , S 1 , N 2 , N 3 , and S 2 . The sleeve  63   b  is rotatable by a not-illustrated driving source. The sleeve  63   b  rotates counterclockwise (i.e., an arrow J 1  direction). The photoconductive drum  12   b  (see  FIG. 2 ) rotates clockwise along the rotating direction J 1  of the sleeve  63   b  (i.e., the roller rotating direction J 1 ). 
     The developer moves on the developing roller  63  according to the rotation of the sleeve  63   b.  The developer stands like ears of rice by a magnetic force when the developer passes on the magnetic pole sections N 1 , S 1 , N 2 , N 3 , and S 2 . Since the developer stands like ears of rice, the toner is separated from the developer and toner cloud occurs. The toner cloud is a cause of toner scattering. 
     The developer adheres to the developing roller  63  with a magnetic force of the grasping section N 3 . The developer adhering to the developing roller  63  is conveyed to the development pole N 1  through the second conveyance pole S 2 . The development pole N 1  forms a development region. In the development region, the toner included in the developer moves from the developing roller  63  toward the photoconductive drum  12   b  (see  FIG. 2 ). A developed image is formed on the surface of the photoconductive drum  12   b  by the toner. After the developed image is formed on the surface of the photoconductive drum  12   b,  the developer is conveyed to the peeling pole N 2  through the first conveyance pole S 1 . The developer adhering to the developing roller  63  is peeled by repulsion of magnetic forces of the peeling pole N 2  and the grasping pole N 3 . 
     A doctor blade  66  of the opening section  60   h  in the housing  60  restricts a layer thickness of the developer carried by the developing roller  63 . 
     The shield section  64  blocks a flow of air from the developing device  12   a  to the photoconductive drum  12   b  (see  FIG. 2 ). The shield section  64  is provided between the doctor blade  66  and the photoconductive drum  12   b.  The shield section  64  extends from the housing  60  to close a gap between the doctor blade  66  and the developing roller  63 . 
     The gap forming member  71  forms a first gap G 1  between the gap forming member  71  and the developing roller  63 . The gap forming member  71  is opposed to the developing roller  63  via the first gap G 1 . The gap forming member  71  is located on the opposite side of the second mixer  62  across the developing roller  63 . The gap forming member  71  forms a second gap G 2  between the gap forming member  71  and the housing  60 . The gap forming member  71  is opposed to the housing  60  via the second gap G 2 . In the following explanation, a portion  73  of the housing  60  facing the gap forming member  71  via the second gap G 2  is referred to as “case body  73 ” as well. The gap forming member  71  extends in the roller axis direction Vg (see  FIG. 4 ). 
     The blocking member  72  is disposed in the first gap G 1 . The blocking member  72  is provided between the gap forming member  71  and the developing roller  63 . The blocking member  72  is provided on the downstream side in the roller rotating direction J 1  with respect to the development pole N 1 . The blocking member  72  is formed in a loop shape. The blocking member  72  is supported by the gap forming member  71 . The blocking member  72  extends in the roller axis direction Vg. The blocking member  72  is attached to a rib  82  via the gap forming member  71 . For example, a not-illustrated double-sided tape is provided in the gap forming member  71 . For example, the blocking member  72  is attached to the rib  82  by the double-sided tape of the gap forming member  71 . 
     A part of the blocking member  72  is disposed in contact with the developing roller  63 , whereby, according to the rotation of the developing roller  63 , the blocking member  72  functions as a wall and blocks an air current flowing into the developing device  12   a.  The first gap G 1  is a gap between the developing roller  63  and the gap forming member  71 . The blocking member  72  has a function of a valve that blocks a flow of wind including the toner flowing back in a direction opposite to the roller rotating direction J 1  to flow out from the inside to the outside of the housing  60  via the first gap G 1 . The blocking member  72  is in contact with a developer layer (not illustrated in  FIG. 3 ) on the developing roller  63  with a low pressure of a degree not preventing developer conveyance of the developing roller  63 . The blocking member  72  does not completely prevent a flow of an air current but restricts the flow of the air current. The blocking member  72  generates an air current circulating around the gap forming member  71  and contributes to a flow of air in the developing device  12   a  caused by the generated air current. The blocking member  72  bends to be convex toward the developing roller  63 . The blocking member  72  has flexibility. For example, the blocking member  72  is an elastic body such as urethane. 
     The blocking member  72  is disposed in a position opposed to the first conveyance pole S 1 , which is the intra-housing most upstream magnetic pole section, on the inside of the housing  60 . The blocking member  72  is disposed in a position overlapping the first conveyance pole S 1  in the normal direction of the developing roller  63 . In other words, the blocking member  72  is disposed on the first conveyance pole S 1  in the roller rotating direction J 1 . 
     An inclined surface  72   a  inclined toward a position where the blocking member  72  is in contact with the developer layer (not illustrated in  FIG. 3 ) is provided in a portion opposed to the developing roller  63  on the upstream side in the roller rotating direction J 1  in the blocking member  72 . For example, the inclined surface  72   a  forms an angle equal to or larger than 1 degree and equal to or smaller than 45 degrees with respect to the tangential line of the developing roller  63 . 
     A first opening E 1  and a second opening E 2  are provided between the case body  73  and the gap forming member  71 . 
     The first opening E 1  is formed on the downstream side in the roller rotating direction J 1  with respect to the gap forming member  71 . The first opening E 1  is located on the downstream side in the roller rotating direction J 1  in the second gap G 2 . 
     The second opening E 2  communicates with the first opening E 1  through the second gap G 2 . The second opening E 2  is formed on the upstream side in the roller rotating direction J 1  with respect to the gap forming member  71 . The second opening E 2  is located on the upstream side in the roller rotating direction J 1  in the second gap G 2 . 
     A third opening E 3  is formed on the downstream side in the roller rotating direction J 1  with respect to the blocking member  72 . The third opening E 3  communicates with the downstream side in the roller rotating direction J 1  in the first gap G 1 . The third opening E 3  is located near the peeling pole N 2 . 
     A fourth opening E 4  is formed on the upstream side in the roller rotating direction J 1  with respect to the blocking member  72 . The fourth opening E 4  communicates with the upstream side in the roller rotating direction J 1  in the first gap G 1 . 
     A part of an air current passing through the blocking member  72  flows from the third opening E 3  to the first opening E 1 . The air current flowing to the first opening E 1  flows to the second opening E 2 , flows through the fourth opening E 4 , and passes through the blocking member  72  according to the rotation of the developing roller  63  again. That is, a circulating air current is formed around the gap forming member  71 . The gap forming member  71  has a function of adjusting an air current direction that determines a flow of the air current. 
     The case body  73  is provided on the opposite side of the developing roller  63  across the gap forming member  71 . The second gap G 2  is formed between the case body  73  and the gap forming member  71 . The second gap G 2  extends along the roller rotating direction J 1 . The second gap G 2  communicates with the first gap G 1  via the first opening E 1 and the third opening E 3  and via the second opening E 2  and the fourth opening E 4 . 
     An engaging section  93  extends to enter a recessed section  60 i of the housing  60  from the case body  73 . The case body  73  is detachably attached to the housing  60  by the engaging section  93 . A wall section  79  forming the recessed section  60 i is provided in the housing  60 . The wall section  79  forms a communication path with the first opening E 1  and the third opening E 3  between the wall section  79  and the gap forming member  71 . 
     The case body  73 , the gap forming member  71 , and the blocking member  72  configure a cover  70 . The cover  70  covers the developing roller  63  from the opposite side of the second mixer  62 . The cover  70  is detachably attached to the housing  60  by the engaging section  93 . 
     The guide section  74  guides the air current discharged from the second gap G 2  via the second opening E 2  to somewhere between the blocking member  72  and the developing roller  63 . That is, the guide section  74  guides the air discharged from the second gap G 2  via the second opening E 2  to the first gap G 1 . The guide section  74  includes a guide surface  74   a  opposed to the gap forming member  71  via the fourth opening E 4 . The guide surface  74   a  is the inner surface of the guide section  74  that is in contact with the air current guided by the guide section  74 . The guide section  74  extends from the end portion near the second opening E 2  in the housing  60  toward the developing roller  63 . The guide section  74  extends from the end portion on the opening section  60   h  side in the case body  73  toward the developing roller  63 . For example, the guide section  74  is integrally formed by the same member as the case body  73 . The distal end of the guide section  74  is separated from the developing roller  63 . A gap  74   h  is formed between the distal end of the guide section  74  and the developing roller  63 . 
     An arrangement of the plurality of image forming units is explained. 
     As illustrated in  FIG. 2 , the plurality of image forming units  12  to  16  are disposed side by side close to one another along the intermediate transfer body  10 . The plurality of image forming units  12  to  16  include a first image forming unit and a second image forming unit disposed side by side in order along a rotating direction A (i.e., a moving direction A 1  illustrated in  FIG. 5 ) of the intermediate transfer body  10 . In the image forming units  12  to  16 , the adjacent two image forming units have the same structure. Therefore, the image forming unit  12  representing the image forming units  12  to  16  is referred to as first image forming unit  12 . The image forming unit  13  representing the image forming units  12  to  16  is referred to as second image forming unit  13 . A disposition structure of the first image forming unit  12  and the second image forming unit  13  is explained. 
       FIG. 5  is a side view illustrating an example of the disposition structure of the first image forming unit  12  and the second image forming unit  13  in the embodiment. 
     As illustrated in  FIG. 5 , the respective photoconductive drums  12   b  and  13   b  of the first image forming unit  12  and the second image forming unit  13  are in contact with the intermediate transfer body  10  from below. The first image forming unit  12  is located on the upstream side of the second image forming unit  13  in the moving direction A 1  of the intermediate transfer body  10 . The first image forming unit  12  includes the cleaning unit  12   d  disposed on the opposite side of the developing device  12   a  across the photoconductive drum  12   b.  The first image forming unit  12  includes the charging device  12   c  disposed on the opposite side of the intermediate transfer body  10  across the photoconductive drum  12   b.    
     A developing device  13   a  of the second image forming unit  13  includes two wall sections  68  and  69  adjacent to each other. The two wall sections  68  and  69  configure a part of a housing of the developing device  13   a  of the second image forming unit  13 . The two wall sections  68  and  69  are adjacent to each other to form an L-shape in side view. The cleaning unit  12   d  of the first image forming unit  12  is surrounded by the two wall sections  68  and  69  adjacent to each other. The two wall sections  68  and  69  are a first wall section  68  and a second wall section  69 . 
     In the side view, the first wall section  68  extends in a direction orthogonal to the moving direction A 1  of the intermediate transfer body  10 . The first wall section  68  extends substantially in the vertical direction. The first wall section  68  is opposed to the cleaning unit  12   d  of the first image forming unit  12  in the horizontal direction. 
     In the side view, the second wall section  69  extends in a direction parallel to the moving direction A 1  of the intermediate transfer body  10 . The second wall section  69  extends substantially in the horizontal direction. The second wall section  69  is opposed to the cleaning unit  12   d  of the first image forming unit  12  in the vertical direction. 
     A cleaning device  101  includes the photoconductive drum  12   b,  the charging device  12   c,  and the cleaning unit  12   d.  The developing device  12   a  is separated from the cleaning device  101 . The developing device  12   a  is attached to an apparatus body (not illustrated in  FIG. 5 ) individually and independently from the cleaning device  101 . The developing device  12   a  and the cleaning device unit  101  are detachably attachable to the apparatus body. 
     A sub-unit  102  is configured by the photoconductive drum  12   b  and the cleaning unit  12   d.  The sub-unit  102  is separable from the charging device  12   c.  The charging device  12   c  is detachably attached to the photoconductive drum  12   b.  The sub-unit  102  and the charting device  12   c  are detachably attached to the apparatus body. 
     A disposition relation between the first image forming unit  12  and the second image forming unit  13  is explained. 
     In  FIG. 5 , the distance between the cleaning unit  12   d  of the first image forming unit  12  and the intermediate transfer body  10  is represented as H 1 , the distance between the developing device  13   a  of the second image forming unit  13  and the intermediate transfer body  10  is represented as H 2 , and the distance between the cleaning unit  12   d  of the first image forming unit  12  and the developing device  13   a  of the second image forming unit  13  is represented by H 3 . In the following explanation, the distance H 1  between the cleaning unit  12   d  of the first image forming unit  12  and the intermediate transfer body  10  is referred to as “first distance H 1 ” as well, the distance H 2  between the developing device  13   a  of the second image forming unit  13  and the intermediate transfer body  10  is referred to as “second distance H 2 ” as well, and the distance H 3  between the cleaning unit  12   d  of the first image forming unit  12  and the developing device  13   a  of the second image forming unit  13  is referred to as “third distance H 3 ” as well. 
     The first distance H 1  means an interval between the upper surface of the cleaning unit  12   d  of the first image forming unit  12  and the lower surface of the intermediate transfer body  10 . The upper surface of the cleaning unit  12   d  of the first image forming unit  12  means the upper surface of the cleaner case  12   d   2  of the image forming unit  12 . The upper surface of the cleaning unit  12   d  of the first image forming unit  12  is opposed to the lower surface of the intermediate transfer body  10 . The upper surface of the cleaning unit  12   d  of the first image forming unit  12  is substantially parallel to the lower surface of the intermediate transfer body  10 . 
     The second distance H 2  means an interval between the upper surface of the developing device  13   a  of the second image forming unit  13  and the lower surface of the intermediate transfer body  10 . The upper surface of the developing device  13   a  of the second image forming unit  13  means an upper surface of a case body of the housing in the developing device  13   a  of the second image forming unit  13 . The upper surface of the developing device  13   a  of the second image forming unit  13  is opposed to the lower surface of the intermediate transfer body  10 . The upper surface of the developing device  13   a  of the second image forming unit  13  is substantially parallel to the lower surface of the intermediate transfer body  10 . 
     The third distance H 3  means an interval between a side surface of the cleaning unit  12   d  of the first image forming unit  12  and a side surface of the developing device  13   a  of the second image forming unit  13 . The side surface of the cleaning unit  12   d  of the first image forming unit  12  means a side surface of the cleaner case  12   d   2  of the first image forming unit  12 . The side surface of the cleaning unit  12   d  of the first image forming unit  12  is opposed to the side surface of the developing device  13   a  of the second image forming unit  13 . The side surface of the cleaning unit  12   d  of the first image forming unit  12  is substantially parallel to the side surface of the developing device  13   a  of the second image forming unit  13 . The side surface of the developing device  13   a  of the second image forming unit  13  means the outer surface of the first wall section  68  in the developing device  13   a  of the second image forming unit  13 . 
     The first distance H 1  is larger than the second distance H 2  (H 1 &gt;H 2 ). That is, the upper surface of the cleaning unit  12   d  of the first image forming unit  12  is farther from the lower surface of the intermediate transfer body  10  than the upper surface of the developing device  13   a  of the second image forming unit  13 . 
     The third distance H 3  is smaller than the second distance H 2  (H 3 &lt;H 2 ). That is, the side surface of the cleaning unit  12   d  of the first image forming unit  12  is close to the side surface of the developing device  13   a  of the second image forming unit  13  at an interval smaller than the second distance H 2 . 
     The gap  74   h  of the developing device  13   a  of the second image forming unit  13  is explained. 
     The gap  74   h  of the developing device  13   a  of the second image forming unit  13  functions as an air discharge port for discharging the air on the inside of the developing device  13   a.  The gap  74   h  is located further on the downstream side in the roller rotating direction J 1  than a proximity section of the developing device  13   a  and the photoconductive drum  13   b.  The proximity section of the developing device  13   a  and the photoconductive drum  13   b  means a portion where the developing roller  63  of the developing device  13   a  and the photoconductive drum  13   b  are closest to each other. The gap  74   h  is located in a most upstream section of the housing of the developing device  13   a.  The most upstream section of the housing of the developing device  13   a  means a portion on the most upstream side in the roller rotating direction J 1  in a housing upper section of the developing device  13   a.    
     A flow of air around the developing device is explained. 
       FIG. 6  is a side view of the first and the second image forming unit for explaining a flow of air around the developing device in the embodiment. In  FIG. 6 , a flow of air around the developing device  13   a  located further on the downstream side in the moving direction A 1  of the intermediate transfer body  10  than the developing device  12   a  is explained. 
     As illustrated in  FIG. 6 , the air around the developing device  13   a  flows in an arrow B 1  direction in a space between the developing device  13   a  and the intermediate transfer body  10 . 
     Near the intermediate transfer body  10 , the air around the developing device  13   a  flows substantially in the same direction as the moving direction A 1  of the intermediate transfer body  10 . On the other hand, near the developing device  13   a,  the air around the developing device  13   a  flows in the opposite direction of the moving direction A 1  of the intermediate transfer body  10 . That is, the air around the developing device  13   a  circulates in the arrow B 1  direction in the space between the developing device  13   a  and the intermediate transfer body  10 . For that reason, even if the air including the toner leaks to the outside of the developing device  13   a,  the air including the toner circulates in the space between the developing device  13   a  and the intermediate transfer body  10 . The air including the toner scattering from the developing device  13   a  circulates in the space between the developing device  13   a  and the intermediate transfer body  10  so as to swirl. The toner scattering from the developing device  13   a  adheres to at least a part of the intermediate transfer body  10 , the developing device  13   a  (the housing), and the cleaner case  12   d   2 . The toner adhering to the intermediate transfer body  10  is removed by the cleaning blade  11  (see  FIG. 2 ). Even if the toner adheres to the developing device  13   a  or the cleaner case  12   d   2 , it is less likely that components such as the charging device  12   c  are soiled. 
     A flow of air around a developing device in a comparative example is explained. 
       FIG. 7  is a side view of image forming units for explaining the flow of air around the developing device in the comparative example. In  FIG. 7 , a flow of air around a developing device  13   a X located further on the downstream side in the moving direction A 1  of an intermediate transfer body  10 X than a developing device  12   a X is explained. 
     As illustrated in  FIG. 7 , the air around the developing device  13   a X flows in an arrow X 1  direction in a space between the developing device  13   a X and the intermediate transfer body  10 X. 
     In the comparative example, the upper surface of a cleaning unit  12   d X of a first image forming unit  12 X is closer to the lower surface of the intermediate transfer body  10 X than the upper surface of the developing device  13   a X of a second image forming unit  13 X. That is, the comparative example is equivalent to a case in which the first distance H 1  is smaller than the second distance H 2 . In this case, a part of the air flowing in the space between the developing device  13   a X and the intermediate transfer body  10 X flows toward a charging device  12   c X along a side surface of the cleaning unit  12   d X (see an arrow X 2 ). For that reason, the toner scattering from the developing device  13   a X is highly likely to adhere to the charging device  12   c X. 
     On the other hand, in the embodiment, as illustrated in  FIG. 5 , the upper surface of the cleaning unit  12   d  of the first image forming unit  12  is farther from the lower surface of the intermediate transfer body  10  than the upper surface of the developing device  13   a  of the second image forming unit  13 . That is, the first distance H 1  is larger than the second distance H 2  (H 1 &gt;H 2 ). In this case, the air flowing in the space between the developing device  13   a  and the intermediate transfer body  10  circulates in the space between the developing device  13   a  and the intermediate transfer body  10  so as to swirl (see  FIG. 6 ). For that reason, the toner scattering from the developing device  13   a  is less likely to adhere to the charging device  12   c.    
     A flow of air in the developing device  12   a  is explained. 
       FIG. 8  is a sectional view of the developing device  12   a  in the embodiment. 
     As illustrated in  FIG. 8 , the developing roller  63  rotates in the arrow J 1  direction, whereby the air flows into the housing  60  through the gap  74   h.  If the air flows into the housing  60 , a flow of wind in arrows Q 1  and Q 2  directions is generated in the first gap G 1 . If the air enters the housing  60 , since the pressure in the housing  60  increases, a flow of air in an arrow Q 3  direction from the inside to the outside of the housing  60  is generated in the third opening E 3 . 
     The air flowing in the arrow Q 3  direction flows toward the gap  74   h  while engulfing the toner separated from the developer in the housing  60 . Therefore, a flow of air in arrows Q 4  and Q 5  directions toward the fourth opening E 4  is generated in the second gap G 2 . If the air including the toner flows in the arrow Q 5  direction, since the air including the toner is guided toward the first gap G 1  by the guide surface  74   a,  most of the air including the toner flows into the first gap G 1 . 
     The air including the toner flowing into the first gap G 1  flows in the order of the arrow Q 1  direction, the arrow Q 2  direction, the arrow Q 3  direction, the arrow Q 4  direction, and the arrow Q 5  direction in the housing  60 . That is, a circulation path of the flow of the air including the toner is formed in the housing  60  by the first gap G 1 , the second gap G 2 , the first opening E 1 , the second opening E 2 , the third opening E 3 , and the fourth opening E 4 . 
     An example of toner scattering in the developing device is explained. 
       FIG. 9  is a sectional view of the developing device for explaining the toner scattering therein. In  FIG. 9 , cross sectional hatching is omitted. The developing device illustrated in  FIG. 9  does not include the gap forming member. In  FIG. 9 , reference numeral  160  denotes a housing,  161  denotes a first mixer,  162  denotes a second mixer,  163  denotes a developing roller,  164  denotes a shield section,  165  denotes a partition wall,  166  denotes a doctor blade,  170  denotes a cover member,  174  denotes a guide section, and  174   h  denotes a gap. 
     A developer (not illustrated in  FIG. 9 ) is carried on the developing roller  163 . As illustrated in  FIG. 9 , a flow of the developer drawn into the developing device is generated according to rotation of the developing roller  163 . The air enters the developing device from the gap  174   h  (an arrow Wa in  FIG. 9 ). If the air enters the developing device, the pressure in the developing device increases. If the pressure in the developing device increases, the air in the developing device including the toner leaks to the outside of the developing device, leading to toner scattering, indicated by an arrow Wb in  FIG. 9 . 
     A flow of air in a developing device of a circulation-type is explained. 
       FIG. 10  is a sectional view for explaining the flow of air in the circulation-type developing device. In  FIG. 10 , cross section hatching is omitted. In  FIG. 10 , reference numeral  271  denotes a gap forming member. For example, the gap forming member  271  is supported by a not-illustrated rib provided in the case body  73 . The blocking member  72  is attached to the gap forming member  271 . 
     The first gap G 1  is provided between the gap forming member  271  and the developing roller  63 . The gap forming member  271  forms the second gap G 2  between the gap forming member  271  and the case body  73  (the housing). An inlet opening Ea is provided in a position on the downstream side in the roller rotating direction J 1  with respect to the gap forming member  271 . An outlet opening Eb is provided in a position on the upstream side in the roller rotating direction J 1  with respect to the gap forming member  271 . The first gap G 1  and the second gap G 2  communicate via the inlet opening Ea and the outlet opening Eb. For example, the first gap G 1  and the second gap G 2  may be formed in parallel by superimposing the gap forming member  271  on the case body  73  in a portion close to the developing roller  63 . 
     As illustrated in  FIG. 10 , if the air enters the developing device from the gap  74   h  according to the rotation of the developing roller  63 , the pressure in the developing device increases. If the pressure in the developing device increases, the air in the developing device passes through the second gap G 2  from the inlet opening Ea and is discharged from the outlet opening Eb (an arrow Va in  FIG. 10 ). The air discharged from the outlet opening Eb is drawn into the developing device by the action of the first conveyance pole S 1  (arrows Vb, Vc, and Vd in  FIG. 10 ). The first conveyance pole S 1  is an intra-housing most upstream magnetic pole section located on the most upstream side in the roller rotating direction J 1  in the housing. The first conveyance pole S 1  has a role of drawing the air discharged from the inside to the outside of the developing device into the developing device. A layer of the developer standing like ears of rice with the magnetic force of the first conveyance pole S 1  captures the air and draws the air into the developing device. 
     In the developing device using the technique explained above, toner scattering occurs near the gap located further on the downstream side in the roller rotating direction than the proximity section of the developing device and the photoconductive drum and in the most upstream section of the housing of the developing device. As illustrated in  FIG. 6 , the air including the toner scattering from the gap  74   h  circulates in the space between the developing device  13   a  and the intermediate transfer body  10  so as to swirl. Therefore, the configuration of this embodiment is particularly useful. 
     According to the embodiment, the image forming apparatus  1  includes the plurality of image forming units  12  to  16  and the intermediate transfer body  10 . The image forming units  12  to  16  include developing devices  12   a  to  16   a  and the photoconductive drums  12   b  to  16   b.  The intermediate transfer body  10  is in contact with the respective photoconductive drums  12   b  to  16   b  of the plurality of image forming units  12  to  16 . The intermediate transfer body  10  moves according to the rotation of the photoconductive drums  12   b  to  16   b.  The plurality of image forming units  12  to  16  include the first image forming unit  12  and the second image forming unit  13  disposed side by side in order along the moving direction A 1  of the intermediate transfer body  10 . The first image forming unit  12  includes the cleaning unit  12   d  disposed on the opposite side of the developing device  12   a  across the photoconductive drum  12   b.  The distance H 1  between the cleaning unit  12   d  of the first image forming unit  12  and the intermediate transfer body  10  is larger than the distance H 2  between the developing device  13   a  of the second image forming unit  13  and the intermediate transfer body  10 . The distance H 3  between the cleaning unit  12   d  of the first image forming unit  12  and the developing device  13   a  of the second image forming unit  13  is smaller than the distance H 2  between the developing device  13   a  of the second image forming unit  13  and the intermediate transfer body  10 . The configuration explained above achieves the following effect. 
     If the first distance H 1  is smaller than the second distance H 2 , a part of the air flowing in the space between the developing device  13   a X and the intermediate transfer body  10 X easily flows toward components such as the charging device  12   c X along the side surface of the cleaning unit  12   d X (see  FIG. 7 ). If the third distance H 3  is larger than the second distance H 2 , the air flowing in the space between the developing device  13   a  and the intermediate transfer body  10  easily flows toward the side surface of the cleaning unit  12   d.  The air flowing to the side surface of the cleaning unit  12   d  easily flows toward the components such as the charging device  12   c  along the side surface of the cleaning unit  12   d.  For that reason, the toner scattering from the developing device  13   a  is highly likely to adhere to the components such as the charging device  12   c.  According to the embodiment, since the first distance H 1  is larger than the second distance H 2 , the air flowing in the space between the developing device  13   a  and the intermediate transfer body  10  circulates in the space between the developing device  13   a  and the intermediate transfer body  10  so as to swirl. In addition, since the third distance H 3  is smaller than the second distance H 2 , the air flowing in the space between the developing device  13   a  and the intermediate transfer body  10  less easily flows toward the side surface of the cleaning unit  12   d.  For that reason, it is possible to reduce the likelihood that the toner scattering from the developing device  13   a  adheres to the components such as the charging device  12   c.  Therefore, it is possible to prevent occurrence of deficiencies such as an image defect. 
     The developing device  13   a  includes the gap  74   h  for discharging the air on the inside of the developing device  13   a.  The gap  74   h  is located further downstream in the roller rotating direction J 1  than the proximity section of the developing device  13   a  and the photoconductive drum  13   b  and in the most upstream section of the housing of the developing device  13   a.  The configuration explained above achieves the following effect. Toner scattering occurs near the gap  74   h  located further downstream in the roller rotating direction J 1  than the proximity section of the developing device  13   a  and the photoconductive drum  13   b  and in the most upstream section of the housing of the developing device  13   a.  The air including the toner scattering from the gap  74   h  circulates in the space between the developing device  13   a  and the intermediate transfer body  10  so as to swirl. Therefore, the configuration explained above is particularly useful in reducing the likelihood that the scattering toner adheres to the components such as the charging device  12   c  and preventing occurrence of deficiencies such as an image defect. 
     The cleaning unit  12   d  of the first image forming unit  12  is surrounded by the two wall sections  68  and  69  adjacent to each other in the developing device  13   a  of the second image forming unit  13 . The configuration explained above achieves the following effect. The air flowing in the space between the developing device  13   a  and the intermediate transfer body  10  less easily flows along the outer surface of the cleaning unit  12   d.  For that reason, it is possible to reduce, as much as possible, the likelihood that the toner scattering from the developing device  13   a  adheres to the components such as the charging device  12   c.  Therefore, it is possible to prevent occurrence of deficiencies such as an image defect as much as possible. 
     The image forming apparatus  1  includes the five image forming units  12  to  16  disposed side by side in order along the moving direction A 1  of the intermediate transfer body  10 . The configuration explained above achieves the following effect. Since the first distance H 1  is larger than the second distance H 2  and the third distance H 3  is smaller than the second distance H 2  in the image forming units  12  to  16 , it is possible to reduce the likelihood that scattering toner adheres to the components. Therefore, in the image forming apparatus of the quintuple tandem type, it is possible to prevent occurrence of deficiencies such as an image defect. 
     The cleaning device  101  includes the photoconductive drum  12   b,  the charging device  12   c,  and the cleaning unit  12   d.  The developing device  12   a  is separated from the cleaning device  101 . The configuration explained above achieves the following effect. It is possible to selectively detach the developing device  12   a  or the cleaning device  101  from the apparatus body. 
     The sub-unit  102  is configured by the photoconductive drum  12   b  and the cleaning unit  12   d.  The sub-unit  102  is separable from the charging device  12   c.  The configuration explained above achieves the following effect. It is possible to selectively detach the sub-unit  102  or the charging device  12   c  from the apparatus body. 
     The developing device  12   a  further includes the gap forming member  71 . The gap forming member  71  forms the first gap G 1  between the gap forming member  71  and the developing roller  63 . The gap forming member  71  forms the second gap G 2  between the gap forming member  71  and the housing  60 . The gap forming member  71  is provided in the housing  60 . The gap forming member  71  is provided on the downstream side in the roller rotating direction J 1  with respect to the development pole N 1 . The first opening E 1  and the second opening E 2  are provided between the housing  60  and the gap forming member  71 . The first opening E 1  is formed on the downstream side in the roller rotating direction J 1  with respect to the gap forming member  71 . The second opening E 2  communicates with the first opening E 1  through the second gap G 2 . The second opening E 2  is formed on the upstream side in the roller rotating direction J 1  with respect to the gap forming member  71 . The configuration explained above achieves the following effect. Since a circulation path of a flow of air including the toner is formed in the housing  60  by the first gap G 1 , the second gap G 2 , the first opening E 1 , and the second opening E 2 , it is possible to prevent the air including the toner from blowing out to the outside of the developing device. Therefore, it is possible to prevent scattering of the toner to the outside of the developing device. 
     The developing device  12   a  further includes the blocking member  72 . The blocking member  72  is disposed in the first gap G 1 . The blocking member  72  is provided on the downstream side in the roller rotating direction J 1  with respect to the development pole N 1 . The blocking member  72  is disposed in the position opposed to the first conveyance pole S 1 , which is the intra-housing most upstream magnetic pole section, on the inside of the housing  60 . The configuration explained above achieves the following effect. Toner cloud that occurs in the first conveyance pole S 1  can be confined in the developing device  12   a.  Therefore, it is possible to prevent scattering of the toner to the outside of the developing device  12   a.    
     Incidentally, there is a configuration in which a filter, a fan, and the like for collecting a scattering toner in order to reduce scattering of toner to the outside of a developing device are provided. However, the number of times of clogging of the filter that captures the toner is likely to increase before a product life is exhausted. If the filter is provided, it is necessary to provide a fan and a duct as well. The apparatus is likely to increase in size. According to the embodiment, since it is unnecessary to provide the filter, maintainability is improved. The embodiment is suitable in avoiding an increase in the size of the apparatus. 
     The developing device  12   a  includes the guide section  74  that directs the air current discharged from the second gap G 2  via the second opening E 2  to somewhere between the blocking member  72  and the developing roller  63 . The configuration explained above achieves the following effect. Since the air including the toner is guided to the first gap G 1  by the guide section  74 , it is possible to prevent the air including the toner from blowing out to the outside of the developing device  12   a.  Therefore, it is possible to prevent scattering of the toner to the outside of the developing device  12   a.    
     The blocking member  72  is disposed in the position opposed to the first conveyance pole S 1 , which is the intra-housing most upstream magnetic pole section, on the inside of the housing  60 . The configuration explained above achieves the following effect. Toner cloud that occurs in the first conveyance pole S 1  can be confined in the developing device  12   a.  The blocking member  72  is suitable in preventing scattering of the toner to the outside of the developing device  12   a.    
     A first modification of the embodiment is explained. 
       FIG. 11  is a side view of a first image forming unit  312  and a second image forming unit  313  in a first modification of the aforementioned embodiment. 
     As illustrated in  FIG. 11 , the image forming apparatus may further include a restricting member  300  located between the cleaning unit  12   d  of the first image forming unit  312  and the developing device  13   a  of the second image forming unit  313  when viewed from the intermediate transfer body  10 . 
     The restricting member  300  extends from the developing device  13   a  of the second image forming unit  313  toward the photoconductive drum  12   b  of the first image forming unit  312 . The restricting member  300  restricts a flow of air from the space between the developing device  13   a  of the second image forming unit  313  and the intermediate transfer body  10  toward the charging device  12   c.  The restricting member  300  is a plate member extending from an upper part of the case body of the housing in the developing device  13   a  of the second image forming unit  313 . The restricting member  300  is integrally formed by the same member as the case body of the housing in the developing device  13   a  of the second image forming unit  313 . The restricting member  300  is substantially parallel to the lower surface of the intermediate transfer body  10 . The restricting member  300  includes an overlapping section  301  where the cleaning unit  12   d  of the first image forming unit  312  and the developing device  13   a  of the second image forming unit  313  overlap when viewed from the intermediate transfer body  10 . 
     A disposition relation between the first image forming unit  312  and the second image forming unit  313  is explained. 
     In  FIG. 11 , the distance between the overlapping section  301  and the intermediate transfer body  10  is indicated by H 4 . In the following explanation, the distance H 4  between the overlapping section  301  and the intermediate transfer body  10  is referred to as “fourth distance H 4 ” as well. The fourth distance H 4  means an interval between the upper surface of the overlapping section  301  and the lower surface of the intermediate transfer body  10 . The upper surface of the overlapping section  301  linearly extends to the upper surface of the case body of the housing in the developing device  13   a  of the second image forming unit  313 . The upper surface of the overlapping section  301  is opposed to the lower surface of the intermediate transfer body  10 . The fourth distance H 4  is substantially the same as the second distance H 2  (see  FIG. 5 ). 
     The first distance H 1  is larger than the fourth distance H 4  (i.e., H 1 &gt;H 4 ). That is, the upper surface of the cleaning unit  12   d  of the first image forming unit  312  is farther from the lower surface of the intermediate transfer body  10  than the upper surface of the overlapping section  301  of the second image forming unit  313 . 
     A flow of air around the developing device is explained. 
       FIG. 12  is a side view of the developing device for explaining a flow of air around therein in the first modification of the aforementioned embodiment. In  FIG. 12 , a flow of air around the developing device  13   a  located further on the downstream side in the moving direction A 1  of the intermediate transfer body  10  than the developing device  12   a  is explained. 
     As illustrated in  FIG. 12 , the air around the developing device  13   a  flows in an arrow C 1  direction in a space between the developing device  13   a  and the restricting member  300  and the intermediate transfer body  10 . 
     Near the intermediate transfer body  10 , the air around the developing device  13   a  flows substantially in the same direction as the moving direction A 1  of the intermediate transfer body  10 . On the other hand, near the developing device  13   a,  the air around the developing device  13   a  flows in the opposite direction of the moving direction A 1  of the intermediate transfer body  10 . That is, the air around the developing device  13   a  circulates in the arrow Cl direction in the space between the developing device  13   a  and the restricting member  300  and the intermediate transfer body  10 . Therefore, even if the air including the toner leaks to the outside of the developing device  13   a,  the air including the toner circulates in the space between the developing device  13   a  and the restricting member  300  and the intermediate transfer body  10 . The air including the toner scattering from the developing device  13   a  circulates in the space between the developing device  13   a  and the restricting member  300  and the intermediate transfer body  10  so as to swirl. The toner scattering from the developing device  13   a  adheres to at least a part of the intermediate transfer body  10 , the developing device  13   a  (the housing), the restricting member  300 , and the cleaner case  12   d   2 . The toner adhering to the intermediate transfer body  10  is removed by the cleaning blade  11  (see  FIG. 2 ). Even if the toner adheres to the developing device  13   a,  the restricting member  300 , or the cleaner case  12   d   2 , the components such as the charging device  12   c  are less likely to be soiled. 
     According to the first modification, the image forming apparatus further includes the restricting member  300  located between the cleaning unit  12   d  of the first image forming unit  312  and the developing device  13   a  of the second image forming unit  313  when viewed from the intermediate transfer body  10 . The configuration explained above achieves the following effect. The air flowing in the space between the developing device  13   a  and the restricting member  300  and the intermediate transfer body  10  circulates in the space between the developing device  13   a  and the restricting member  300  and the intermediate transfer body  10  so as to swirl. For that reason, it is possible to reduce, as much as possible, the likelihood that the toner scattering from the developing device  13   a  adheres to the components such as the charging device  12   c.  Therefore, it is possible to prevent occurrence of deficiencies such as an image defect as much as possible. 
     The restricting member  300  includes the overlapping section  301  where the cleaning unit  12   d  of the first image forming unit  312  and the developing device  13   a  of the second image forming unit  313  overlap when viewed from the intermediate transfer body  10 . The configuration explained above achieves the following effect. A flow of air from the space between the developing device  13   a  and the intermediate transfer body  10  toward the charging device  12   c  can be sufficiently blocked by the overlapping section  301 . Therefore, it is possible to further reduce the likelihood that the toner scattering from the developing device  13   a  adheres to the components such as the charging device  12   c.  Therefore, it is possible to further prevent occurrence of deficiencies such as an image defect. 
     The restricting member  300  extends from the developing device  13   a  of the second image forming unit  313  toward the photoconductive drum  12   b  of the first image forming unit  312 . The configuration explained above achieves the following effect. It is easy to form a circulation path of the air in the space between the developing device  13   a  and the restricting member  300  and the intermediate transfer body  10 . Therefore, the restricting member  300  is suitable in reducing the likelihood that the scattering toner adheres to the components such as the charging device  12   c  and preventing occurrence of deficiencies such as an image defect. 
     The restricting member  300  is substantially parallel to the lower surface of the intermediate transfer body  10 . The configuration explained above achieves the following effect. Compared with a case where the restricting member  300  is nonparallel to the intermediate transfer body  10  (i.e., an extended line of the restricting member  300  crosses the intermediate transfer body  10 ), it is easy to form a circulation path of the air in the space between the developing device  13   a  and the restricting member  300  and the intermediate transfer body  10 . Therefore, the restricting member  300  is suitable in reducing the likelihood that the scattering toner adheres to the components such as the charging device  12   c  and preventing occurrence of deficiencies such as an image defect. 
     A second modification of the aforementioned embodiment is explained. 
       FIG. 13  is a side view of a first image forming unit  412  and a second image forming unit  413  in a second modification of the embodiment.  FIG. 14  is a diagram including a XIV-XIV section of  FIG. 13 . 
     As illustrated in  FIG. 13 , an extending end of a restricting member  400  extending from the developing device  13   a  of the second image forming unit  413  may be in contact with the cleaning unit  12   d  of the first image forming unit  412 . 
     The extending end of the restricting member  400  is detachably connected to the cleaning unit  12   d  of the first image forming unit  412 . An engaging member  402  that detachably engages the extending end of the restricting member  400  and the cleaning unit  12   d  is provided between the restricting member  400  and the cleaning unit  12   d.  The engaging member  402  engages with an overlapping section  401  of the restricting member  400 . 
     As illustrated in  FIG. 14 , the engaging member  402  includes a hook member  403  and an axially supporting section  404 . The hook member  403  is connected to the axially supporting section  404  turnably around the axially supporting section  404 . An engaging recessed section  401   a,  in which the distal end portion of the hook member  403  is engaged, is provided in the overlapping section  401 . The hook member  403  is movable between an engaging position U 1  where the hook member  403  engages with the overlapping section  401  and a disengaging position U 2  where the hook member  403  is disengaged from the overlapping section  401 . The axially supporting section  404  extends substantially in parallel to an extending direction of the overlapping section  401  (in the paper-surface depth direction). The axially supporting section  404  is supported by the cleaner case  12   d   2  of the cleaning unit  12   d.    
     According to the second modification, the extending end of the restricting member  400  is in contact with the cleaning unit  12   d  of the first image forming unit  412 . The configuration explained above achieves the following effect. The air flowing in a space between the developing device  13   a,  the restricting member  400 , and the cleaning unit  12   d  and the intermediate transfer body  10  circulates in the space between the developing device  13   a,  the restricting member  400 , and the cleaning unit  12   d  and the intermediate transfer body  10  so as to swirl. Therefore, it is possible to reduce, as much as possible, the likelihood that the toner scattering from the developing device  13   a  adheres to the functional components such as the charging device  12   c.  Therefore, it is possible to prevent occurrence of deficiencies such as an image defect as much as possible. 
     The image forming apparatus  1  further includes the engaging member  402  that detachably engages the extending end of the restricting member  400  and the cleaning unit  12   d  of the first image forming unit  412 . The configuration explained above achieves the following effect. It is possible to selectively detach the first image forming unit  412  or the second image forming unit  413  from the apparatus body by disengaging the extending end of the restricting member  400  and the cleaning unit  12   d  of the first image forming unit  412 . 
     A third modification of the aforementioned embodiment is explained. 
       FIG. 15  is a side view of a first image forming unit  512  and a second image forming unit  513  in the third modification of the embodiment. 
     As illustrated in  FIG. 15 , the first distance H 1  may be larger than a fifth distance H 5  in portion where the cleaning unit  12   d  of the first image forming unit  512  and the developing device  13   a  of the second image forming unit  513  are close to each other. The fifth distance H 5  means an interval between the upper end of the developing device  13   a  of the second image forming unit  513  and the lower surface of the intermediate transfer body  10  in a portion where the cleaning unit  12   d  of the first image forming unit  512  and the developing device  13   a  of the second image forming unit  513  are closest to each other. The upper end of the developing device  13   a  of the second image forming unit  513  means one end of a taper section  501  of the case body of the housing in the developing device  13   a  of the second image forming unit  513 . 
     In the side view, the taper section  501  includes a taper surface  501   a  inclined with respect to the horizontal plane. In the side view, the taper surface  501   a  linearly extends obliquely such that a first end (e.g., an end close to the cleaning unit  12   d ) of the taper surface  501   a  is located below and a second end (e.g., an end on the opposite side of the first end) of the taper surface  501   a  is located above. 
     A fourth modification of the aforementioned embodiment is explained. 
       FIG. 16  is a side view of a first image forming unit  612  and a second image forming unit  613  in the fourth modification of the embodiment. 
     As illustrated in  FIG. 16 , the first distance H 1  may be larger than a sixth distance H 6  in a portion where the cleaning unit  12   d  of the first image forming unit  612  and the developing device  13   a  of the second image forming unit  613  are close to each other. The sixth distance H 6  means an interval between the upper end of the developing device  13   a  of the second image forming unit  613  and the lower surface of the intermediate transfer body  10  in a portion where the cleaning unit  12   d  of the first image forming unit  612  and the developing device  13   a  of the second image forming unit  613  are closest to each other. The upper end of the developing device  13   a  of the second image forming unit  613  means the distal end of a projecting section  601  of the case body of the housing in the developing device  13   a  of the second image forming unit  613 . 
     In the side view, the projecting section  601  includes an inclined surface  601   a  inclined with respect to the horizontal plane. In the side view, the inclined surface  601   a  linearly extends obliquely such that a first end (e.g., an end close to the cleaning unit  12   d ) of the inclined surface  601   a  is located above and a second end (e.g., an end on the opposite side of the first end) of the inclined surface  601   a  is located below. 
     Other modifications of the aforementioned embodiment are explained. 
     The distance H 3  between the cleaning unit  12   d  of the first image forming unit  12  and the developing device  13   a  of the second image forming unit  13  is not limited to be smaller than the distance H 2  between the developing device  13   a  of the second image forming unit  13  and the intermediate transfer body  10 . For example, the third distance H 3  may be equal to or larger than the second distance H 2 . 
     The restricting member  300  is not limited to include the overlapping section  301  where the cleaning unit  12   d  of the first image forming unit  312  and the developing device  13   a  of the second image forming unit  313  overlap when viewed from the intermediate transfer body  10 . For example, the restricting member  300  may not include the overlapping section  301 . For example, the restricting member  300  maybe disposed only between the cleaning unit  12   d  of the first image forming unit  312  and the developing device  13   a  of the second image forming unit  313 . 
     The cleaning unit  12   d  of the first image forming unit  12  is not limited to be surrounded by the two wall sections  68  and  69  adjacent to each other in the developing device  13   a  of the second image forming unit  13 . For example, the cleaning unit  12   d  of the first image forming unit  12  may not be surrounded by the two wall sections  68  and  69 . For example, the developing device  13   a  of the second image forming unit  13  may not include the two wall sections  68  and  69  adjacent to each other. 
     The developing device  12   a  is not limited to be separated from the cleaning device  101 . For example, the developing device  12   a  may be integral with the cleaning device  101 . 
     The sub-unit  102  is not limited to be separable from the charging device  12   c.  For example, the sub-unit  102  may be inseparable from the charging device  12   c.    
     The restricting member  300  is not limited to extend from the developing device  13   a  of the second image forming unit  313  toward the photoconductive drum  12   b  of the first image forming unit  312 . For example, the restricting member  300  may extend from the cleaning unit  12   d  of the first image forming unit  312  toward the developing device  13   a  of the second image forming unit  313 . 
     The restricting member  300  is not limited to be parallel to the intermediate transfer body  10 . For example, the restricting member  300  may be nonparallel to the intermediate transfer body  10 . 
     The non-developing device is not limited to be the cleaning unit  12   d.  For example, the non-developing device may be the photoconductive drum  12   b.  For example, the non-developing device may be a structure disposed on the opposite side of the developing device  12   a  across the photoconductive drum  12   b.    
     The belt is not limited to be the intermediate transfer body  10 . For example, the image forming apparatus  1  may not include the secondary transfer unit  30  that transfers the developed image formed on the intermediate transfer body  10  onto the sheet. For example, the belt maybe a belt that holds the sheet. For example, the developed image may be directly transferred to the sheet held by the belt. 
     According to the at least one embodiment explained above, the image forming apparatus  1  includes the plurality of image forming units  12  to  16  and the intermediate transfer body  10 . The image forming units  12  to  16  include the developing devices  12   a  to  16   a  and the photoconductive drums  12   b  to  16   b.  The intermediate transfer body  10  is in contact with the respective photoconductive drums  12   b  to  16   b  of the plurality of image forming units  12  to  16 . The intermediate transfer body  10  moves according to the rotation of the photoconductive drums  12   b  to  16   b.  The plurality of image forming units  12  to  16  include the first image forming unit  12  and the second image forming unit  13  disposed side by side in order along the moving direction A 1  of the intermediate transfer body  10 . The first image forming unit  12  includes the cleaning unit  12   d  disposed on the opposite side of the developing device  12   a  across the photoconductive drum  12   b.  The distance H 1  between the cleaning unit  12   d  of the first image forming unit  12  and the intermediate transfer body  10  is larger than the distance H 2  between the developing device  13   a  of the second image forming unit  13  and the intermediate transfer body  10 . The distance H 3  between the cleaning unit  12   d  of the first image forming unit  12  and the developing device  13   a  of the second image forming unit  13  is smaller than the distance H 2  between the developing device  13   a  of the second image forming unit  13  and the intermediate transfer body  10 . The configuration explained above achieves the following effect. 
     If the first distance H 1  is smaller than the second distance H 2 , apart of the air flowing in the space between the developing device  13   a  and the intermediate transfer body  10  easily flows toward the functional components such as the charging device  12   c  along the side surface of the cleaning unit  12   d  (see  FIG. 7 ). If the third distance H 3  is larger than the second distance H 2 , the air flowing in the space between the developing device  13   a  and the intermediate transfer body  10  easily flows toward the side surface of the cleaning unit  12   d.  The air flowing to the side surface of the cleaning unit  12   d  easily flows toward the functional components such as the charging device  12   c  along the side surface of the cleaning unit  12   d.  Therefore, the toner scattering from the developing device  13   a  is highly likely to adhere to the functional components such as the charging device  12   c.  According to the embodiment, since the first distance H 1  is larger than the second distance H 2 , the air flowing in the space between the developing device  13   a  and the intermediate transfer body  10  circulates in the space between the developing device  13   a  and the intermediate transfer body  10  so as to swirl. In addition, since the third distance H 3  is smaller than the second distance H 2 , the air flowing in the space between the developing device  13   a  and the intermediate transfer body  10  less easily flows toward the side surface of the cleaning unit  12   d.  Therefore, it is possible to reduce the likelihood that the toner scattering from the developing device  13   a  adheres to the components such as the charging device  12   c.  Therefore, it is possible to prevent occurrence of deficiencies such as an image defect. 
     While certain embodiments have been described, these embodiments have been presented by way of example only and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms: furthermore various omissions, substitutions and changes in the form of the embodiments described herein maybe made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the invention.