Patent Publication Number: US-9836014-B2

Title: Waste toner storing container, and image forming apparatus including waste toner storing container

Description:
INCORPORATION BY REFERENCE 
     This application is based upon and claims the benefit of priority from the corresponding Japanese Patent Application No. 2015-167209 filed on Aug. 26, 2015, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     The present disclosure relates to a waste toner storing container for storing waste toner discharged from an image carrying member, and relates to an image forming apparatus that includes the waste toner storing container. 
     In general, in an electrophotographic image forming apparatus such as a copier, a printer, or a facsimile apparatus, an electrostatic latent image formed on a photoconductor drum (an image carrying member) is visualized by developer in a developing device, and the visualized image is transferred to a recording medium such as a print sheet. At this time, some toner may not be transferred to the recording medium and remain on the surface of the photoconductor drum. The remnant toner is removed from the surface of the photoconductor drum by a cleaning device, and is collected, as waste toner, in a waste toner storing container. 
     The cleaning device includes a storage portion for temporarily storing the waste toner. The storage portion is provided with a screw. The waste toner stored in the storage portion is conveyed in one direction by the screw and is discharged from a discharge portion of the storage portion to a waste toner storing portion connected to the storage portion. The waste toner discharged from the discharge portion flows into a waste toner storing container and is stored therein. 
     Meanwhile, a color image forming apparatus including a plurality of photoconductor drums includes a plurality of cleaning devices that are respectively provided in correspondence with the photoconductor drums. In addition, a color image forming apparatus includes an intermediate transfer belt (image carrying member) for carrying a color toner image formed from toner images transferred from the photoconductor drums. The color toner image is transferred from the intermediate transfer belt to a recording medium by a transfer device. At this time, some toner may not be transferred to the recording medium and remain on the surface of the intermediate transfer belt. As a result, the color image forming apparatus includes a cleaning device for removing the remnant toner from the intermediate transfer belt. In the color image forming apparatus, the waste toner storing container is elongated in a direction in which the plurality of cleaning devices are arranged, so as to store the waste toner discharged from the plurality of cleaning devices. In addition, a conventional waste toner storing container is provided with a conveyance screw that conveys the stored waste toner in the longitudinal direction of the waste toner storing container to make the bulk of the stored waste toner even. 
     SUMMARY 
     A waste toner storing container according to an aspect of the present disclosure includes a container main body, a first conveyance portion, and a second conveyance portion. The container main body includes a plurality of reception ports that receive waste toner discharged from a plurality of image carrying members provided in an image forming apparatus, and stores the waste toner carried in from the reception ports. The first conveyance portion is rotatably provided in the container main body and, by being rotated when an image forming operation is performed by the image forming apparatus, conveys the waste toner toward one side in a rotation axis line direction. The second conveyance portion is rotatably provided below and parallel to the first conveyance portion in the container main body and, by being rotated when the image forming operation is performed, conveys the waste toner toward another side that is opposite to the one side. The plurality of reception ports are arranged in alignment in the rotation axis line direction. The second conveyance portion does not have a conveyance force with regard to waste toner stored in a side-end storage portion in the container main body, the side-end storage portion corresponding to a side-end reception port among the plurality of reception ports that is located closest to the one side in the rotation axis line direction. 
     An image forming apparatus according to an aspect of the present disclosure includes the waste toner storing container, a plurality of image carrying members, and a plurality of waste toner removing portions. The plurality of image carrying members each carry a toner image. The plurality of waste toner removing portions remove waste toner from surfaces of the plurality of image carrying members and discharge the removed waste toner to the waste toner storing container. 
     This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description with reference where appropriate to the accompanying drawings. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. Furthermore, the claimed subject matter is not limited to implementations that solve any or all disadvantages noted in any part of this disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram showing a configuration of an image forming apparatus according to an embodiment of the present disclosure. 
         FIG. 2  is a diagram showing an internal configuration of the image forming apparatus of  FIG. 1 . 
         FIG. 3  is a diagram showing a configuration of an image forming portion included in the image forming apparatus of  FIG. 1 . 
         FIG. 4  is a diagram for explaining a toner flow path in which waste toner that has been removed from photoconductor drums and an intermediate transfer belt by cleaning devices flows before flowing into a waste toner storing container. 
         FIG. 5  is a diagram showing a configuration of the waste toner storing container according to an embodiment of the present disclosure. 
         FIG. 6  is a diagram showing an internal configuration of the waste toner storing container of  FIG. 5 . 
         FIG. 7  is a cross-sectional diagram taken along a cut plane VII-VII shown in  FIG. 5  and  FIG. 6 . 
         FIG. 8A - FIG. 8C  are diagrams showing states where the waste toner is stored in the waste toner storing container according to an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The following describes an embodiment of an image forming apparatus of the present disclosure with reference to the drawings. It should be noted that the following embodiment is an example of a specific embodiment of the present disclosure and should not limit the technical scope of the present disclosure. 
       FIG. 1  is an outer appearance perspective view showing a configuration of an image forming apparatus  1  according to an embodiment of the present disclosure. In the following, the present embodiment is explained by using an up-down direction D 1 , a front-rear direction D 2 , and a left-right direction D 3  that are defined in  FIG. 1  on the basis of a normal use state of the image forming apparatus  1 . 
     The image forming apparatus  1  shown in  FIG. 1  is a printer. The image forming apparatus  1  prints an input image on a print sheet by using toner. It is noted that the image forming apparatus  1  is not limited to a printer, but may be a facsimile, a copier, or a multifunction peripheral having functions of these. 
     The image forming apparatus  1  is a so-called tandem color printer. As shown in  FIG. 1 , the image forming apparatus  1  includes a housing  2  that includes a cover of an external frame and an internal frame. In addition, as shown in  FIG. 2 , the image forming apparatus  1  includes a plurality of image forming portions  3 , an intermediate transfer unit  4 , a secondary transfer device  5 , a fixing device  6 , an exposure device  7 , a sheet feed portion  8 , a sheet discharge portion  9 , a control portion  10 , a belt cleaning device  16  (an example of the waste toner removing portion of the present disclosure), and a waste toner storing container  50 . 
     The plurality of image forming portions  3  ( 3 A- 3 D) are arranged in alignment in the front-rear direction D 2 . The plurality of image forming portions  3  respectively form toner images of different colors. In  FIG. 2 , the image forming portion  3 A that is positioned in the most rear side forms a toner image by black toner. The image forming portion  3 B, the second from the rear, forms a toner image by yellow toner. The image forming portion  3 C, the third from the rear, forms a toner image by cyan toner. And the image forming portion  3 D that is positioned in the most front side forms a toner image by magenta toner. Each of the image forming portions  3  includes a photoconductor drum  11  (an example of the image carrying member of the present disclosure), a charging device  12 , a developing device  13 , a primary transfer device  14 , and a drum cleaning device  15  (an example of the waste toner removing portion of the present disclosure). As a result, the image forming apparatus  1  includes a plurality of photoconductor drums  11 , a plurality of developing devices  13 , and a plurality of drum cleaning devices  15 . 
     The intermediate transfer unit  4  includes an intermediate transfer belt  4 A (an example of the image carrying member and the transfer belt of the present disclosure), a driving roller  4 B, and a driven roller  4 C. The intermediate transfer belt  4 A carries a toner image that is formed from toner images of a plurality of (in the present embodiment, four) colors. Supported by the driving roller  4 B and the driven roller  4 C so as to be rotationally driven, the intermediate transfer belt  4 A can move (run) in the state where its surface is in contact with the surfaces of the photoconductor drums  11 . When the intermediate transfer belt  4 A is rotationally driven, its surface passes through between the photoconductor drums  11  and the primary transfer devices  14 . At that time, the toner images of respective colors are transferred in sequence from the photoconductor drums  11  to the surface of the intermediate transfer belt  4 A in such a way as to be overlaid with each other. 
     The secondary transfer device  5  transfers the toner image transferred on the intermediate transfer belt  4 A, to a print sheet that is conveyed from the sheet feed portion  8 . The print sheet with the toner image transferred thereon is conveyed to the fixing device  6 . The fixing device  6  includes a heating roller  6 A and a pressure roller  6 B. The fixing device  6  conveys the print sheet with the toner image transferred thereon while applying heat and pressure thereto. This allows the toner image to be fused and fixed to the print sheet. The print sheet with the toner image fixed thereto is further conveyed toward the downstream side, and then discharged onto the tray-like sheet discharge portion  9  disposed above the intermediate transfer unit  4 . 
     The belt cleaning device  16  is disposed in front of the intermediate transfer unit  4 . The belt cleaning device  16  includes a cleaning roller  24  as a cleaning member, a screw member  25 , and a toner box  26 . The cleaning roller  24  is disposed to face the driven roller  4 C, and its surface is in contact with the intermediate transfer belt  4 A. The cleaning roller  24  is rotatably supported in the toner box  26 . The cleaning roller  24  rotates when a rotation driving force is input to the rotation shaft of the cleaning roller  24 . The cleaning roller  24  has approximately the same length as the width of the intermediate transfer belt  4 A. The cleaning roller  24  removes toner that has remained on the surface of the intermediate transfer belt  4 A after the transfer of the toner image by the secondary transfer device  5 , by being rotated while contacting the intermediate transfer belt  4 A. The removed toner (hereinafter referred to as “waste toner”) is taken into the toner box  26  by the action of gravity or by the rotation of the cleaning roller  24 . The waste toner taken into the toner box  26  is conveyed by the screw member  25 . A discharge port  27  (see  FIG. 4 ) is formed on the bottom of the toner box  26  in a right end portion thereof. The screw member  25  has helical blades around a cylindrical shaft member. Upon receiving the action of the blades while the screw member  25  is rotated, the waste toner is conveyed in the toner box  26  toward the discharge port  27 . The waste toner is then discharged from the discharge port  27  to the outside. That is, the toner that has remained on the surface of the intermediate transfer belt  4 A is removed by the belt cleaning device  16  and is discharged, as the waste toner, from the intermediate transfer belt  4 A. 
       FIG. 3  is a cross-sectional view schematically showing the photoconductor drum  11 , the developing device  13 , and the drum cleaning device  15  of an image forming portion  3 . The plurality of image forming portions  3  have the same configuration except that they use toners of different colors. 
     Each of the photoconductor drums  11  is a cylindrical rotator with a photosensitive layer formed on its surface. The photoconductor drum  11  is rotatably supported in the housing  2 , and rotates in a predetermined direction upon input of a rotation driving force. A toner image of a corresponding color is held on the surface of the photoconductor drum  11 . Specifically, when the exposure device  7  exposes the surface of the photoconductor drum  11  to light in the state where the surface of the photoconductor drum  11  has been charged to a predetermined potential by the charging device  12 , an electrostatic latent image is formed on the surface of the photoconductor drum  11 . The electrostatic latent image is developed by the developing device  13  that is described below. This allows a toner image to be held on the surface of the photoconductor drum  11 . The toner image on the photoconductor drum  11  is transferred onto the intermediate transfer belt  4 A by the primary transfer device  14 . 
     Each of the developing devices  13  visualizes, by developer, the electrostatic latent image formed on the surface of the photoconductor drum  11 . The developing device  13  includes a developer case  37  and a magnet roller  38 . The developer case  37  stores the developer that includes the toner. The magnet roller  38  is used for development and is rotatably supported in the developer case  37 . Stirring screw members  33  are provided in the developer case  37 . With the rotation of the stirring screw members  33 , the developer is stirred and the toner is charged to a predetermined potential. In addition, the charged toner is conveyed by the magnet roller  38  to a position that faces the photoconductor drum  11 , and at the position, the toner is caused to fly toward the electrostatic latent image on the surface of the photoconductor drum  11 . This allows the electrostatic latent image on the surface of the photoconductor drum  11  to be developed. The developer case  37  has a toner replenishing port  40 , and the toner is replenished to the developer case  37  via the toner replenishing port  40  from a toner container (not shown). 
     As shown in  FIG. 4 , the developer case  37  of the developing device  13  includes a partition wall  35 . The partition wall  35  is erected on a bottom of the developer case  37  to extend along the longitudinal direction of the developer case  37  (a direction that matches the left-right direction D 3 ). The inner space of the developer case  37  is partitioned into two spaces by the partition wall  35 . The two spaces communicate with each other via communication portions  31  and  32  that are provided at opposite ends thereof in the longitudinal direction. In addition, the two spaces are each provided with a stirring screw member  33  (see  FIG. 3 ) that conveys the developer while stirring it. With the rotation of the stirring screw members  33 , the developer in the developer case  37  is conveyed and circulated in the two spaces along a circulation path  30  (see the two-dotted line in  FIG. 4 ). 
     The drum cleaning device  15  is disposed in the rear side of the photoconductor drum  11 . The drum cleaning device  15  is disposed for each of the photoconductor drums  11 . The drum cleaning device  15  includes a cleaning blade  41  as a cleaning member, a cleaning roller  42 , a screw member  43 , and a toner box  44 . The cleaning blade  41  and the cleaning roller  42  have approximately the same length as the photoconductor drum  11 . The cleaning blade  41  is disposed such that its edge is in contact with or close to the surface of the photoconductor drum  11 . The cleaning roller  42  is rotatably supported in the toner box  44 . The cleaning roller  42  rotates when a rotation driving force is input to the rotation shaft of the cleaning roller  42 . When the photoconductor drum  11  is rotated, the cleaning blade  41  removes toner that has remained on the surface of the photoconductor drum  11  after the transfer of toner image by the primary transfer device  14 . The removed toner (hereinafter referred to as “waste toner”) is taken into the toner box  44  by the action of gravity or by the rotation of the cleaning roller  42 . The waste toner taken into the toner box  44  is conveyed by the screw member  43  in a discharge direction as indicated by the arrow  47  in  FIG. 4 . A discharge port  45  (see  FIG. 4 ) is formed in the right-end side wall of the toner box  44 . The screw member  43  has helical blades around a cylindrical shaft member. Upon receiving the action of the blades while the screw member  43  is rotated, the waste toner is conveyed in the toner box  44  toward the discharge port  45 . The waste toner is then discharged from the discharge port  45  to the outside. That is, the toner that has remained on the surface of the photoconductor drum  11  is removed by the drum cleaning device  15  and is discharged, as the waste toner, from the photoconductor drum  11 . 
     Each pair of the photoconductor drum  11  and the drum cleaning device  15  is unitized as a drum unit  17  (see  FIG. 4 ). The discharge ports  45  included in the drum cleaning devices  15  project respectively from housings (not shown) of the drum units  17  to outside and are connected to reception ports  65  ( 65 A- 65 D) of the waste toner storing container  50  that is described below. 
       FIG. 4  is a diagram for explaining a discharge flow path in which waste toner that has been removed from photoconductor drums  11  by the drum cleaning devices  15 , and waste toner that has been removed from the intermediate transfer belt  4 A by the belt cleaning device  16 , flow until they are discharged into the waste toner storing container  50 . 
     As shown in  FIG. 4 , the waste toner removed from the photoconductor drum  11  by the drum cleaning device  15  is conveyed in the toner box  44  (see  FIG. 3 ) by the screw member  43  in the discharge direction (see the arrow  47 ) which is oriented rightward in the left-right direction D 3  of the image forming apparatus  1 . The waste toner that has been conveyed and arrived at the right end of the toner box  44  passes through the discharge ports  45  and the reception ports  65  ( 65 A- 65 D) of the waste toner storing container  50 , and is discharged into a container main body  52  that is described below. 
     In addition, the waste toner removed from the intermediate transfer belt  4 A by the belt cleaning device  16  is conveyed in the toner box  26  by the screw member  25  in the discharge direction (see the arrow  48 ) which is oriented rightward in the left-right direction D 3  of the image forming apparatus  1 . The waste toner that has been conveyed and arrived at the right end of the toner box  26  passes through the discharge port  27  that is provided in the bottom of the toner box  26 , passes through a reception port  65  ( 65 E) of the waste toner storing container  50 , and is discharged into the container main body  52  that is described below. 
     The waste toner storing container  50  is provided in the housing  2 . As shown in  FIG. 2 , the waste toner storing container  50  is disposed below the intermediate transfer belt  4 A. In addition, as shown in  FIG. 4 , the waste toner storing container  50  is disposed more on the right side than the right ends of the drum cleaning devices  15  and the belt cleaning device  16 . 
     Meanwhile, a conventional waste toner storing container is provided with a conveyance screw that conveys the stored waste toner in the longitudinal direction of a storage portion of the waste toner storing container to make the bulk of the stored waste toner even. However, the configuration of the conventional waste toner storing container has a problem that, since the conveyance screw conveys the waste toner in one direction, the waste toner is difficult to accumulate in an upstream side of the storage portion in the conveyance direction. For example, in the case where the conveyance screw is rotated by a driving force that is applied when an image formation operation is performed in a color image forming apparatus, the conveyance screw is also rotated during a so-called idling driving that is performed in the image formation operation. In this case, since the conveyance screw is rotated although no waste toner flows in, the waste toner is stored in the state of being deviated to the downstream side in the conveyance direction. As a result, according to the conventional waste toner storing container, the storage space inside the waste toner storing container is not used efficiently. On the other hand, as described below, the waste toner storing container  50  of the present disclosure includes an upper conveyance screw  61  and a lower conveyance screw  62 , so that waste toner can be efficiently stored in the container, without a wasteful space in the container. 
     As shown in  FIG. 5  to  FIG. 7 , the waste toner storing container  50  includes the container main body  52 , an upper conveyance screw  61  (an example of the first conveyance portion and the third conveyance portion of the present disclosure), and a lower conveyance screw  62  (an example of the second conveyance portion of the present disclosure). Here,  FIG. 5  is a perspective view viewing the waste toner storing container  50  from the right side.  FIG. 6  is a side view viewing the waste toner storing container  50  from the right side.  FIG. 7  is a cross-sectional view of the waste toner storing container  50 . It is noted that in  FIG. 5 , a cover portion  52 B that constitutes a part of the container main body  52  is omitted for the sake of convenience in explanation. 
     The container main body  52  includes a main body case  52 A and the cover portion  52 B (see  FIG. 7 ). The container main body  52  is long in the front-rear direction D 2 . The main body case  52 A constitutes a left part of the container main body  52  (the image forming portions  3  side), and the cover portion  52 B constitutes a right part of the container main body  52 . 
     The waste toner discharged from the drum cleaning devices  15  and the belt cleaning device  16  is stored in the container main body  52 . Specifically, as shown in  FIG. 5 , five reception ports  65  ( 65 A- 65 E) are provided on the left-side surface of the main body case  52 A, and the waste toner flows in from the reception ports  65 . The reception ports  65  are arranged in alignment in the longitudinal direction of the container main body  52 . It is noted that the longitudinal direction of the container main body  52  matches the rotation axis line direction of the lower conveyance screw  62 . 
     As shown in  FIG. 5 , four reception ports  65  ( 65 A- 65 D) having the same shape are provided in the left-side surface of the main body case  52 A. The reception ports  65 A- 65 D are provided to allow the waste toner discharged from the corresponding drum cleaning devices  15  to flow in. The reception ports  65 A- 65 D are provided at equal intervals in the front-rear direction D 2 , and disposed at approximately the same height position. The reception port  65 A is positioned in the most rear side. The reception port  65 A is disposed at a position corresponding to the image forming portion  3 A that forms a black toner image, and is connected to the discharge port  45  of the drum cleaning device  15  of the image forming portion  3 A. That is, the black waste toner that has been removed from the photoconductor drum  11  and discharged by the drum cleaning device  15  of the image forming portion  3 A flows into the container main body  52  from the reception port  65 A. Similarly, the reception port  65 B is disposed at a position corresponding to the image forming portion  3 B that forms a yellow toner image. The reception port  65 C is disposed at a position corresponding to the image forming portion  3 C that forms a cyan toner image. The reception port  65 D is disposed at a position corresponding to the image forming portion  3 D that forms a magenta toner image. The reception ports  65 A- 65 D are respectively formed at the tips of cylindrical portions  66  that project leftward from the left-side surface of the main body case  52 A. The cylindrical portions  66  play a role of conveyance paths that guide the waste toner having entered the reception ports  65 A- 65 D to the inside of the container main body  52 . 
     In addition, the reception port  65 E (an example of the side-end reception port of the present disclosure) is provided in the most front side of the left-side surface of the main body case  52 A. The reception port  65 E is provided to allow the waste toner discharged from the belt cleaning device  16  to flow in the inside of the container main body  52 . In the most front side of the left-side surface of the main body case  52 A, a guide portion  67  projecting leftward from the left-side surface is provided. An upper surface  67 A of the guide portion  67  is horizontally flat, and the reception port  65 E is formed in an end portion of the upper surface  67 A at the tip of the projection. The reception port  65 E is an opening that is opened upward. The inside of the guide portion  67  is hollow and the reception port  65 E is communicated with the inside of the container main body  52 . The bottom surface of the guide portion  67  is an inclined surface  67 B that is inclined diagonally downward from the reception port  65 E toward the inside of the container main body  52 . The reception port  65 E is formed at a position that corresponds to the belt cleaning device  16 . Specifically, the reception port  65 E is formed at a position where it can be connected to the discharge port  27  of the toner box  26 . The discharge port  27  and the reception port  65 E may be directly connected to each other or indirectly connected via a conveyance guide member (not shown) or the like. Accordingly, the waste toner that is discharged from the discharge port  27  flows into the reception port  65 E. As a result, the waste toner that has been removed from the intermediate transfer belt  4 A and discharged by the belt cleaning device  16  enters the reception port  65 E, passes through the inside of the guide portion  67 , and flows into the container main body  52  by sliding down on the inclined surface  67 B. 
     Meanwhile, in the image forming apparatus  1 , the primary transfer device  14  and the secondary transfer device  5  transfer toner images at approximately the same transfer rate. As a result, when a comparison is made between the amount of residual toner on a single photoconductor drum  11  after the transfer and the amount of residual toner on the intermediate transfer belt  4 A after the transfer, it is found that the amount of residual toner on the intermediate transfer belt  4 A is larger than the amount of residual toner on a single photoconductor drum  11 . This is because toner images of the plurality of colors are overlaid on the intermediate transfer belt  4 A. For example, suppose that the same amount of toner is used for each color and that the transfer rate in each of the first transfer and the second transfer is 90%, then the amount of toner discharged from the intermediate transfer belt  4 A is 3.6 times the amount of toner discharged from a single photoconductor drum  11 . That is, among the five reception ports  65  ( 65 A- 65 E), a reception port having the highest inflow rate of waste toner is the reception port  65 E that is disposed in the most front side. In other words, among the plurality of photoconductor drums  11  and the intermediate transfer belt  4 A, an image carrying member having the largest discharge amount of waste toner is the intermediate transfer belt  4 A. In this way, there is a deviation in the inflow rate when the waste toner flows in from the five reception ports  65 , thus the bulk of the waste toner in the container main body  52  is uneven in the longitudinal direction of the container main body  52 . That is, the bulk of the waste toner having flowed in from the reception port  65 E is higher than the bulk of the waste toner that has flowed in from each of the other reception ports. In this case, the reception port  65 E is clogged with waste toner even if there is an empty space in the other portions of the container main body  52 , and inflow of the waste toner from the reception port  65 E to the container main body  52  is interrupted. Accordingly, in the present embodiment, to eliminate a malfunction caused by the deviation in the inflow amount, the upper conveyance screw  61  is provided in the container main body  52 , and further the lower conveyance screw  62  is provided below the upper conveyance screw  61 . 
     In addition, in the case where the lower conveyance screw  62  is rotated by a driving force that is applied when an image formation operation is performed in the image forming apparatus  1 , the lower conveyance screw  62  is also rotated during a so-called idling driving that is performed in the image formation operation. In this case, since the lower conveyance screw  62  is rotated although no waste toner flows in the container main body  52 , the waste toner is stored in the container main body  52  in the state of being deviated to the downstream side in the conveyance direction by the conveyance of the lower conveyance screw  62 , and the storage space inside the container main body  52  may not be used efficiently. In view of this, in the present embodiment, the lower conveyance screw  62  has a feature that is not included in the conventional techniques. It is noted that the idling driving is an operation performed in the image forming operation, and is performed before the execution of the image forming process (the exposure-scanning, the developing process and the like) so as to drive the intermediate transfer belt  4 A to remove the dust, and rotate the photoconductor drum  11  to charge the circumferential surface thereof uniformly. 
     The upper conveyance screw  61  and the lower conveyance screw  62  are rotatably provided in the container main body  52 . 
     The upper conveyance screw  61  is rotatably provided in the container main body  52  at about the middle thereof in the up-down direction D 1 . The upper conveyance screw  61  is rotatably supported by bearings  101  and  102  in the state of passing through side walls  54  and  55  provided at opposite ends in the longitudinal direction and being suspended between the side walls  54  and  55 . The upper conveyance screw  61  is rotationally driven by a driving motor (not shown) via a drive transmission mechanism  110  that is described below, the driving motor being used in the image forming operation in the image forming apparatus  1 . The driving motor is used to rotationally drive, for example, the intermediate transfer belt  4 A and the photoconductor drum  11 , and is used to rotationally drive the upper conveyance screw  61  and the lower conveyance screw  62 , as well. By being rotated, the upper conveyance screw  61  conveys the waste toner in the container main body  52  in the rotation axis line direction. 
     In the present embodiment, the upper conveyance screw  61  includes a rear-side conveyance portion  61 A and a front-side conveyance portion  61 B. In the upper conveyance screw  61 , the rear-side conveyance portion  61 A and the front-side conveyance portion  61 B are disposed on the same axis. That is, the rear-side conveyance portion  61 A is positioned in rear of the front-side conveyance portion  61 B. The rear-side conveyance portion  61 A is an example of the first conveyance portion of the present disclosure, and by being rotated, conveys the waste toner frontward (corresponding to “toward one side” of the present disclosure) along the rotation axis line direction. In addition, the front-side conveyance portion  61 B is provided in the front side of the upper conveyance screw  61 . That is, the front-side conveyance portion  61 B is adjacent to the front portion of the rear-side conveyance portion  61 A in the rotation axis line direction. The front-side conveyance portion  61 B is an example of the third conveyance portion of the present disclosure, and by being rotated, conveys the waste toner rearward (corresponding to “toward another side that is opposite to the one side” of the present disclosure) along the rotation axis line direction. The conveyance of the waste toner is realized by the helical blades formed on the upper conveyance screw  61 . In the present embodiment, the blades of the rear-side conveyance portion  61 A and the blades of the front-side conveyance portion  61 B are formed at different angles. With this configuration, when the upper conveyance screw  61  is rotated, the rear-side conveyance portion  61 A and the front-side conveyance portion  61 B convey the waste toner in different directions (opposite directions). 
     It is noted that although the present embodiment describes the configuration where the upper conveyance screw  61  includes the rear-side conveyance portion  61 A and the front-side conveyance portion  61 B, the upper conveyance screw  61  may not include the front-side conveyance portion  61 B. That is, the upper conveyance screw  61  may be composed of only the rear-side conveyance portion  61 A. 
     The lower conveyance screw  62  is rotatably provided in the lower side of the container main body  52  in the up-down direction D 1 . Specifically, the lower conveyance screw  62  is provided below, and parallel to, the upper conveyance screw  61 . The lower conveyance screw  62  is rotatably supported by bearings  103  and  104  in the state of passing through the side walls  54  and  55  provided at the opposite ends in the longitudinal direction and being suspended between the side walls  54  and  55 . The lower conveyance screw  62  is rotationally driven by the driving motor (not shown) via the drive transmission mechanism  110  that is described below, the driving motor being used in the image forming operation in the image forming apparatus  1 . By being rotated, the lower conveyance screw  62  conveys the waste toner in the bottom side of the container main body  52  rearward along the rotation axis line direction. The lower conveyance screw  62  is rotated such that the waste toner that has flowed in from the reception port  65 E is conveyed rearward so as to be away from the reception port  65 E. 
     In the present embodiment, as shown in  FIG. 5 , a front-side part of the lower conveyance screw  62 , namely, a part of the lower conveyance screw  62  on the upstream side in the conveyance direction, does not have a blade. Specifically, no blade is provided in a shaft part  64 A of a rotation shaft  64  of the lower conveyance screw  62 , the shaft part  64 A corresponding to a region from the reception port  65 E to the adjacent reception port  65 D. As a result, the lower conveyance screw  62  does not have a conveyance force with regard to waste toner stored in the bottom of a side-end storage portion  53  in the container main body  52 , the side-end storage portion  53  corresponding to the reception port  65 E that is located on the most upstream side in the conveyance direction. Accordingly, even when the idling driving is performed and the lower conveyance screw  62  is rotated during the image forming operation in the image forming apparatus  1 , the waste toner stored in the bottom of the side-end storage portion  53  is not conveyed rearward. On the other hand, blades  62 A and blades  62 B having a conveyance force for conveying waste toner are provided on a part of the rotation shaft  64  that is more on the rear side than the side-end storage portion  53 . 
     Meanwhile, since the waste toner stored in the container main body  52  is under the influence of its own weight, waste toner in the upper layer is lower in toner density than waste toner in the lower layer. Accordingly, when it is supposed that the upper conveyance screw  61  and the lower conveyance screw  62  have the same conveyance force, the amount of actually conveyed waste toner is deviated therebetween. Specifically, the amount of waste toner conveyed by the lower conveyance screw  62  is larger than the amount of waste toner conveyed by the upper conveyance screw  61 . In view of this, in the present embodiment, the conveyance force of the upper conveyance screw  61  for conveying waste toner is set to be larger than the conveyance force of the lower conveyance screw  62 . Specifically, different conveyance forces are set to the upper conveyance screw  61  and the lower conveyance screw  62  by making the blades thereof different in size or inclination angle. Alternatively, the rotation speed may be made different between the upper conveyance screw  61  and the lower conveyance screw  62 . With such a configuration, a deviation in the amount of conveyed waste toner between the upper conveyance screw  61  and the lower conveyance screw  62  is reduced. It is noted that the conveyance force may be represented by an amount of waste toner moving per unit time (a conveyance amount). 
     The side wall  54  is provided with the drive transmission mechanism  110 . The drive transmission mechanism  110  includes a gear  111  and a gear  112 . The gear  111  is connected to an end portion of a rotation shaft  63  of the upper conveyance screw  61  that has passed through the side wall  54  to the outside, and is provided on the same axis as the upper conveyance screw  61 . The gear  112  is connected to an end portion of the rotation shaft  64  of the lower conveyance screw  62  that has passed through the side wall  54  to the outside, and is provided on the same axis as the lower conveyance screw  62 . The gear  111  and the gear  112  mesh with each other. The gear  111  is connected to the driving motor via an idle gear such that the drive can be transmitted. When a rotation driving force of the driving motor is transmitted to the drive transmission mechanism  110 , the gear  111  is rotated in a direction of the arrow  71 , and the upper conveyance screw  61  is rotated in the same direction. This allows the rear-side conveyance portion  61 A to convey the waste toner frontward and the front-side conveyance portion  61 B to convey the waste toner rearward. On the other hand, the gear  112  is rotated in a direction (indicated by the arrow  72 ) opposite to the rotation direction of the gear  111 , and the lower conveyance screw  62  is rotated in the same direction as the gear  112 . With this configuration, the lower conveyance screw  62  can convey the waste toner to the rear side. 
     As described above, since the upper conveyance screw  61  and the lower conveyance screw  62  are disposed separated from each other in the vertical direction in the waste toner storing container  50 , in the bottom side of the container main body  52 , the waste toner that has flowed in from the reception ports  65 A- 65 D is conveyed rearward by the lower conveyance screw  62 . In addition, since no blade is provided in the shaft part  64 A of the lower conveyance screw  62  that corresponds to the side-end storage portion  53 , when waste toner flows in from the reception port  65 E, waster toner stored in the bottom of the side-end storage portion  53  is not conveyed rearward, but is stored in the side-end storage portion  53  until the waste toner reaches a height position of the upper conveyance screw  61  as indicated by the dotted line in  FIG. 8A . Subsequently, when the waste toner reaches the height position of the upper conveyance screw  61 , the waste toner in the rear side in the upper layer of the container main body  52  is conveyed frontward by the rear-side conveyance portion  61 A of the upper conveyance screw  61 , and the waste toner in the front side is conveyed rearward by the front-side conveyance portion  61 B (see  FIG. 8B ). Furthermore, when inflow of waste toner continues and the storage amount of waste toner gradually increases, the bulk of the waste toner is made even by the conveyances of both the upper conveyance screw  61  and the lower conveyance screw  62 , as indicated by the dotted line in  FIG. 8C . That is, the bulk of the waste toner is made to have an equal height. As a result of this, the container main body  52  does not have any wasteful space inside, and the waste toner can be efficiently stored in the space in the container main body  52 . 
     In particular, with the configuration where the lower conveyance screw  62  always conveys the waste toner rearward in the bottom part of the container main body  52 , even when a large amount of waste toner flows in from the reception port  65 E, the waste toner is conveyed such that the bulk of waste toner is equal over the whole container main body  52 . In addition, with the above-described configuration, the wasteful space that is formed in the side-end storage portion  53  when the waste toner on the bottom of the side-end storage portion  53  is excessively conveyed by the idling driving, is eliminated, thereby the waste toner can be efficiently stored. 
     Meanwhile, when the waste toner storing container  50  has become full of waste toner, the waste toner storing container  50  needs to be replaced. As a result, in the present embodiment, a detection mechanism  80  is provided which detects that the inside of the container main body  52  is full of waste toner. As shown in  FIG. 6 , the detection mechanism  80  includes a partition wall portion  81  and a detection portion  87 . 
     The partition wall portion  81  forms an inner space  82  that is separated from the waste toner storage space in the container main body  52 , and is provided in the container main body  52 . Specifically, the partition wall portion  81  is formed in a rectangular shape extending upward from the bottom of the container main body  52 . As shown in  FIG. 7 , the upper end of the partition wall portion  81  is opened, forming an opening portion  83 . At the right end of the opening portion  83 , a cut  84  is formed. The cut  84  is an inlet from which waste toner flows into the inner space  82  when the waste toner stored in the container main body  52  exceeds a predetermined storage amount. In the present embodiment, the upper end position of the partition wall portion  81  is set to a position that corresponds to a limit height of waste toner stored in the container main body  52 . More specifically, the cut  84  is formed in the partition wall portion  81  at a position that matches the limit height of waste toner stored in the container main body  52 . The limit height of waste toner stored in the container main body  52  is a height position of a bulk of waste toner when the container main body  52  is evaluated as full. The limit height of waste toner is determined from a factor such as the storage volume of the container main body  52  or the height position of the reception ports  65 . 
     As shown in  FIG. 7 , the partition wall portion  81  is disposed on the left side of the container main body  52 , and is disposed more on the left side than the upper conveyance screw  61  and the lower conveyance screw  62 . Specifically, the partition wall portion  81  is disposed adjacent to a left side wall  56  constituting the left-side surface of the container main body  52  that extends in the longitudinal direction. The partition wall portion  81  forms the inner space  82  between itself and the left side wall  56  of the container main body  52 . 
     The detection portion  87  is provided in the partition wall portion  81 . The detection portion  87  detects that the container main body  52  is full when an amount of waster toner that allows the container main body  52  to be evaluated as full is stored in the storage space of the container main body  52 . The detection portion  87  is, for example, composed of a light-emitting element  88  and a light-receiving element  89 . In the partition wall portion  81 , the light-emitting element  88  and the light-receiving element  89  are respectively provided on side walls that face each other across the inner space  82 . When the container main body  52  becomes full of waste toner and the waste toner enters the inner space  82  from the cut  84 , the waste toner having entered the inner space  82  blocks the light path between the light-emitting element  88  and the light-receiving element  89 . The light-receiving element  89  is connected to the control portion  10 , and the control portion  10  determines whether or not the waste toner has entered the inner space  82  based on a level change of a signal from the light-receiving element  89 . 
     Since the detection mechanism  80  is provided in the waste toner storing container  50  as described above, it is possible, as shown in  FIG. 8C , to detect correctly that the container main body  52  is full of waste toner, without making any wasteful space in the container main body  52 . 
     In the present embodiment, the partition wall portion  81  is disposed in the container main body  52  at a position closer to the center of the container main body  52  than to an end thereof in the longitudinal direction of the container main body  52  (a direction that matches the rotation axis line direction of the upper conveyance screw  61 ). Specifically, as shown in  FIG. 6 , the partition wall portion  81  is disposed between the reception port  65 D and the reception port  65 C, at a position closer to the reception port  65 D. This position is away from the front end by approximately one third of the length of the container main body  52  in the longitudinal direction. As described above, a larger amount of waste toner flows in from the reception port  65 E than from each of the other reception ports  65 A- 65 D. That is, there is a deviation in the inflow rate among the reception ports  65 . As a result, the partition wall portion  81  is disposed at such a position that divides the container main body  52  into two parts in the front-rear direction D 2  such that an approximately equal amount of waste toner flows into each of the two parts from the reception ports  65 . That is, a total of inflow amounts of waste toner from the reception ports  65 A- 65 C positioned in the rear side of the partition wall portion  81  is approximately the same as a total of inflow amounts of waste toner from the reception ports  65 D and  65 E positioned in the front side of the partition wall portion  81 . 
     When the partition wall portion  81  is disposed at such a position, the rear-side conveyance portion  61 A of the upper conveyance screw  61  conveys the waste toner that has flowed in from the reception ports  65 A- 65 C, frontward toward the partition wall portion  81 . In addition, the front-side conveyance portion  61 B of the upper conveyance screw  61  conveys the waste toner that has flowed in from the reception ports  65 D and  65 E, rearward toward the partition wall portion  81 . With this configuration, the waste toner is stored in a flat state in the container main body  52 . In addition, it can be detected in an early stage that the container main body  52  is full of waste toner. In addition, when the waste toner stored in the side-end storage portion  53  reaches the height position of the upper conveyance screw  61 , the waste toner is conveyed by the front-side conveyance portion  61 B toward the rear side in which a smaller amount of waste toner is stored. 
     Furthermore, with the configuration including the partition wall portion  81 , it is desired that the waste toner conveying force of the lower conveyance screw  62  is varied depending on the position in the rotation axis line direction. In the present embodiment, no blade is provided in the shaft part  64 A that corresponds to the side-end storage portion  53 , and there is no waste toner conveying force in the side-end storage portion  53 . On the other hand, the blades  62 A are provided in the vicinity of the partition wall portion  81  and more on the rear side than the side-end storage portion  53 , and blades  62 B are provided more on the rear side than the partition wall portion  81 . In addition, the conveyance force of the blades  62 A is larger than the conveyance force of the blades  62 B. Specifically, the blades  62 A are larger in size than the blades  62 B, and the angle of the blades  62 A with respect to the rotation shaft  64  is larger than the angle of the blades  62 B. With this configuration, even when waste toner is excessively conveyed to the vicinity of the partition wall portion  81 , the waste toner is smoothly conveyed in a direction to be away from the partition wall portion  81  (rearward). It is noted that, to make the conveyance force of the blades  62 A larger than that of the blades  62 B, the arrangement interval of the blades  62 A may be made shorter than the arrangement interval of the blades  62 B. In addition, the blades  62 A may be made larger than the blades  62 B in either size or angle. It is noted that in the present embodiment, no blade is provided in a shaft part  64 B which is the most rear-side part of the rotation shaft  64 , namely, in the shaft part  64 B that corresponds to the reception port  65 A. As a result, even when a large amount of waste toner is conveyed rearward in the bottom of the container main body  52  by the blades  62 A and the blades  62 B, an excessive deviation of the waste toner to a storage portion on the rear side in the container main body  52  is prevented. 
     In the above-described embodiment, an image forming apparatus  1  including a plurality of photoconductor drums  11  and the intermediate transfer belt  4 A is described as one example. However, the present disclosure is not limited to this. For example, the present disclosure is applicable to an image forming apparatus that includes a plurality of photoconductor drums  11 , but not the intermediate transfer belt  4 A, wherein toner images are directly transferred from the plurality of photoconductor drums  11  onto a print sheet. In that case, since, in general, black toner is used by the largest amount among the plurality of colors of toner, the largest amount of waste toner flows in from the reception port  65 A that is positioned in the most rear side, among the four reception ports  65  ( 65 A- 65 D). In other words, among the plurality of photoconductor drums  11 , the image carrying member that discharges the largest amount of waste toner is a photoconductor drum  11  that corresponds to the image forming portion  3 A. With respect to the configuration, the upper conveyance screw  61  conveys the waste toner in the container main body  52  frontward, and the lower conveyance screw  62  conveys the waste toner rearward. That is, the upper conveyance screw  61  conveys the waste toner frontward so that the waste toner is away from the reception port  65 A. 
     Furthermore, in the above-described embodiment, an image forming apparatus  1  including a plurality of image carrying members such as the plurality of photoconductor drums  11  and the intermediate transfer belt  4 A, is described as one example. However, the present disclosure is not limited to a specific combination of a plurality of image carrying members. That is, the present disclosure is applicable to, for example, an image forming apparatus that includes one photoconductor drum  11  and one intermediate transfer belt  4 A, or an image forming apparatus that includes at least two photoconductor drums  11 . 
     It is to be understood that the embodiments herein are illustrative and not restrictive, since the scope of the disclosure is defined by the appended claims rather than by the description preceding them, and all changes that fall within metes and bounds of the claims, or equivalence of such metes and bounds thereof are therefore intended to be embraced by the claims.