Patent Publication Number: US-8532523-B2

Title: Toner cartridge having a toner flowing-out preventing member and image forming apparatus using the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to Japanese Patent Application No. 2009-213813, which was filed on Sep. 15, 2009, the content of which is incorporated herein by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a toner cartridge for use in an image forming apparatus such as a laser beam printer or a multi-functional peripheral, particularly to a toner cartridge for containing toner disposed so as to be exchangeable such as a toner hopper and a toner bottle, and an image forming apparatus using the same. 
     2. Description of the Related Art 
     Conventionally, an image forming apparatus using electrophotography such as a copying apparatus, a facsimile apparatus, a printer or a multi-functional peripheral having these functions, using a two-component developer is configured to perform a continuous operation of outputting an image by automatically supplying toner to a developing device by a toner supply apparatus using a toner cartridge or the like. Then, in toner shortage, a toner cartridge, a process cartridge, etc. can be easily replaced to supply toner. 
     Toner containers such as toner cartridges or process cartridges are, when stored in a warehouse or the like, sometimes stacked to face various directions without the stacking directions being controlled. For example, for toner cartridges of a type which discharges toner from one end side of a cartridge main body thereof, when stacked vertically so that a side of a toner discharge port face downward, toners inside the cartridges go down with their own weight as time elapses, therefore, toner density near the toner discharge port becomes high. As a result, toners may aggregate or become an agglomerate to clog the toner discharge port in a serious case. 
     In the case where the toner cartridge in the above-described state is newly mounted on the image forming apparatus, toner is hard to be discharged from the toner cartridge, and in the worst case, it is possible to be judged as being out of toner even though a large amount of the toner are left in the toner cartridge. Therefore, when newly mounting a toner cartridge, although such a countermeasure that the cartridge is shaken several times before mounting is performed, nevertheless such a problem occurs. Particularly, with a latest toner whose low temperature fixation property is improved for an energy saving measure, preservation stability is deteriorated, and therefore, in a state of being naturally left, there is a tendency that the toner aggregation easily occurs. 
     In a latest image forming apparatus, reducing the size thereof is required, and therefore, the sizes of a toner container and a developing device are reduced in association therewith, and thus a space of setting those is also made to be smaller. Accordingly, the condition where each of units is closely stuffed up causes a condition where the toner aggregation easily occurs. In mounting the toner cartridge has been stored in the warehouse on the image forming apparatus, even though the user or the like is requested to mount the toner cartridge after shaking it, the user or the like often forgets to do so, so that the toner may not be discharged as a result, and thus causing a trouble such as detection of shortage of toner concentration in a developer or stopping of an image forming apparatus itself. To counter with this problem, for example, Japanese Unexamined Patent Publication JP-A 2000-214667 discloses a developer supplying apparatus in which a part of a conveying spiral of a conveying auger provided in a toner cartridge is cut to reduce pressure of the toner. 
     However, even in the case of JP-A 2000-214667, there has been a problem that when fluidity of the toner is lost (to be put into a state of loose aggregation) as the toner cartridge has been left for a long time while a toner discharge port is faced downward, in a first toner supply operation after mounted in the image forming apparatus, that is, in rotation of the auger screw, toner near the toner discharge port is not discharged to the outside of the toner cartridge and as a result, toner which had nowhere to go is fixed as compressed by the pressure of the auger screw, and thus the rotation of the auger screw is locked. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide a toner cartridge capable of preventing agglomeration of toner at a toner discharge port and preventing such a defect that rotation of an auger screw is locked, and an image forming apparatus using the same. 
     The invention provides a toner cartridge comprising: 
     a container for containing toner, having an opening for discharging the contained toner; 
     a toner discharge section provided through a communicating part at a side part of the container where the opening is provided, having a discharge port for discharging toner; 
     an auger screw provided with a rotation shaft and a spiral blade and rotatably supported in the container, for conveying toner in the container from the opening to the toner discharge section; 
     a shutter for opening and closing the discharge port; and 
     a toner flowing-out preventing member provided in the communicating part, for opening and closing the opening, 
     the toner flowing-out preventing member being operated in conjunction with the shutter such that when the discharge port is in an opened state, the opening is in an opened state, and when the discharge port is in a closed state, the opening is in a closed state. 
     According to the invention, by action of the spiral blade accompanying a rotation of the rotation shaft of the auger screw provided in the container, toner contained in the container is conveyed to the toner discharge section. Then, by providing the toner flowing-out preventing member in the communicating part between the container and the toner discharge section, toner flowing into the toner discharge section having the toner discharge port is able to be controlled. As a result, in shipping the toner cartridges, locking phenomenon of the auger screw which occurs by the toner compressed by the pressure of the auger screw to be fixed is able to be prevented by preventing the toner from entering into the toner discharge section from the toner container. Further, an unexpected flowing out of the toner which is triggered by vibrations or the like when the auger screw is stopped is able to be prevented. Moreover, the toner flowing-out preventing member is configured to open and close the opening in conjunction with the opening operation of the shutter, and thus a special mechanism for releasing the toner flowing-out preventing member is not necessary to be provided, therefore, it is possible to design the toner cartridge to be compact. 
     Further, in the invention, it is preferable that a cross section perpendicular to the rotation shaft of an internal space enclosed by the toner discharge section and the shutter is composed of a rectangular part on a side of the shutter and a semi-arc part on a side opposite to the shutter, which rectangular part and semi-arc part continue into each other, and 
     the toner flowing-out preventing member has a circular hole section whose shape is the same as the sectional shape of the rotation shaft of the auger screw, has an entire shape the same shape as the sectional shape of the internal space, and has a side end of the rectangular part fixed to the shutter, and when the opening is in the closed state, the rotation shaft of the auger screw is inserted to the circular hole section, and the toner flowing-out preventing member is held by the auger screw in a state of being perpendicular to an axial line of the rotation shaft. 
     According to the invention, since the sectional shape of the internal space which is enclosed by the toner discharge section and the shutter is formed to be the same as the sectional shape of the toner flowing-out preventing member, and in the closed state of the opening, the toner flowing-out preventing member is held in the state of being perpendicular to the axial line of the rotation shaft with respect to the auger screw, and thereby flowing-out of the toner in the toner container is able to be prevented effectively by the toner flowing-out preventing member. Further, since the toner flowing-out preventing member is held by the auger screw in the state where the rotation shaft is inserted to the circular hole section thereof, a load of departing from the auger screw in releasing the toner flowing-out preventing member in conjunction with the opening operation of the shutter will not be excessively high. 
     Further, in the invention, it is preferable that a notch section for the toner flowing-out preventing member having a width equal to or more than a thickness of the toner flowing-out preventing member is provided on the spiral blade of the auger screw, and when the opening is in the closed state, a part of the toner flowing-out preventing member is positioned in the notch section. 
     According to the invention, in the holding state of the toner flowing-out preventing member by the auger screw, a part of the toner flowing-out preventing member is positioned in the notch section, and therefore, in transporting the toner cartridges, even when the auger screw rotates, the spiral blade does not act on the toner flowing-out preventing member. Therefore, flowing-out of the toner from the container is able to be prevented without the toner flowing-out preventing member being deformed or fallen down so as to be held stably. 
     Further, in the invention, it is preferable that the toner flowing-out preventing member has a notch from the circular hole section to a peripheral part of a region corresponding to the semi-arc part of the internal space. 
     According to the invention, in opening the opening in conjunction with the opening operation of the discharge port of the shutter, the notch is widely opened receiving the action of the rotation shaft of the auger screw in the circular hole section, thereby the load of the toner flowing-out preventing member departing from the auger screw becomes small, and the release of the toner flowing-out preventing member is able to be achieved more smoothly. 
     The invention provides an image forming apparatus comprising: 
     a photoreceptor drum on which an electrostatic latent image is to be formed; 
     a developing device for developing a toner image by supplying toner to the electrostatic latent image formed on the surface of the photoreceptor drum; 
     the toner cartridge mentioned above, for supplying toner to the developing device; 
     a transfer device for transferring on a recording medium the toner image developed on the surface of the photoreceptor drum; and 
     a fixing device for fixing the transferred toner image on the recording medium. 
     According to the invention, image formation is achieved by a series of processing of electrophotography comprising forming an electrostatic latent image on the surface of the photoreceptor drum, forming a toner image by developing the electrostatic latent image by the developing device, transferring the toner image on the recording medium by the transfer device, and then fixing it thereon by the fixing device. In the process of the image formation, the auger screw in the toner cartridge is activated as needed so that supplying of toner from the toner cartridge to the developing device is achieved. In the process of the toner cartridge from a state of being kept to a state of being mounted in the image forming apparatus, inflow of the toner from the container to the toner discharge section is prevented, and therefore, a situation where toner near the toner discharge port is compressed to be fixed by the pressure of the auger screw during rotation of the auger screw after opening the shutter and after releasing the toner flowing-out preventing member at the time of mounting the toner cartridge in the image forming apparatus so that auger screw is locked, will not occur and supplying of toner to the developing device is able to be achieved without fail. Thereby the toner concentration is able to be controlled stably so as to obtain the stable image concentration over a long term. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other and further objects, features, and advantages of the invention will be more explicit from the following detailed description taken with reference to the drawings wherein: 
         FIG. 1  is a schematic view showing an entire configuration of an image forming apparatus according to a first embodiment of the invention; 
         FIG. 2  is a perspective view showing the configuration of a toner cartridge unit having toner cartridges which are mounted on the image forming apparatus; 
         FIGS. 3A to 3C  are sectional views showing the configuration of the toner cartridge; 
         FIGS. 4A and 4B  are external views of an auger screw and a toner flowing-out preventing member; 
         FIGS. 5A to 5C  are views showing releasing operation process of the toner flowing-out preventing member during attachment of the toner cartridge in the image forming apparatus; and 
         FIG. 6  is an external view of the auger screw according to a second embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Now referring to the drawings, preferred embodiments of the invention are described below. 
     Hereinafter, description will be given for preferred embodiments of the invention with reference to the drawings.  FIG. 1  is a schematic view showing an entire configuration of an image forming apparatus  1  according to a first embodiment of the invention. The image forming apparatus  1  according to the embodiment includes, as shown in  FIG. 1 , photoreceptor drums  2 ,  3 ,  4  and  5  on which electrostatic latent images are to be formed, developing devices  6 ,  7 ,  8  and  9  which form toner images by supplying toners to the electrostatic latent images on the surfaces of the photoreceptor drums  2 ,  3 ,  4 , and  5 , toner cartridges  14 ,  15 ,  16  and  17  which supply toners to the developing devices  6 ,  7 ,  8  and  9  through toner supply pipes  10 ,  11 ,  12  and  13  as toner supply members, a secondary transfer roller  19  as a transfer device configured to transfer the toner images on the surfaces of the photoreceptor drums  2 ,  3 ,  4  and  5  to a paper sheet with an intermediate transfer belt  18  interposed therebetween, and a fixing device  20  configured to fix the toner images on the paper sheet, and forms an image with using toner by electrophotography. Then, it is preferable that the toner cartridges  14 ,  15 ,  16  and  17  for use in the image forming apparatus  1  are provided with unique configurations which will be described below. 
     The image forming apparatus  1  according to the embodiment forms as a visible image a multi-color image on a predetermined sheet (recording paper) as a recording medium based on image data included in an input command such as image data transmitted from outside through a communication network or the like. The image forming apparatus  1  includes, as shown in  FIG. 1 , an exposure unit  21 , photoreceptor drums  2 ,  3 ,  4  and  5  corresponding to image bearing members on which latent images are to be formed by the exposure unit  21 , developing devices  6 ,  7 ,  8  and  9 , charging rollers  22 ,  23 ,  24  and  25 , cleaning units  26 ,  27 ,  28  and  29 , the intermediate transfer belt  18 , primary transfer rollers  30 ,  31 ,  32  and  33 , the secondary transfer roller  19 , the fixing device  20 , paper conveyance paths P 1 , P 2 , P 3 , a paper feeding cassette  34 , a manual paper feeding tray  35 , a paper discharge tray  36 , a toner cartridge unit  37  and the like. 
     As the image data of a color image which the image forming apparatus  1  deals with, the image data corresponding to each color of four colors including black (K), cyan (C), magenta (M), and yellow (Y) is used to perform formation of visible images in image forming sections  38 ,  39 ,  40  and  41 . The image forming sections  38 ,  39 ,  40  and  41  correspond to color images using each of the colors. Accordingly, the charging rollers  22 ,  23 ,  24  and  25 , the photoreceptor drums  2 ,  3 ,  4  and  5  and developing devices  6 ,  7 ,  8  and  9  are provided by four pieces respectively so that four kinds of latent images and toner images corresponding to each color are formed, and the cleaning units  26 ,  27 ,  28  and  29  and the primary transfer rollers  30 ,  31 ,  32  and  33  are also provided by four pieces corresponding thereto respectively. Each of the image forming sections  38 ,  39 ,  40  and  41  is configured similarly, and for example, the image forming section  38  of the black is configured by the photoreceptor drum  2 , the developing device  6 , the charging roller  22 , the transfer roller  30  and the cleaning unit  26 , etc. 
     The image forming sections  38 ,  39 ,  40  and  41  are arrayed in a line in a moving direction (sub-scanning direction) of the intermediate transfer belt  18 . Note that, the image forming section  38  corresponds to black, the image forming section  39  corresponds to cyan, the image forming section  40  corresponds to magenta, and the image forming section  41  corresponds to yellow, and four image stations are configured by the above-described each section distinguished by each of these numeral references. 
     The exposure unit  21  which is the exposure device of the embodiment includes a semiconductor laser (not shown) as a laser light source, a polygonal mirror  210 , first reflection mirrors  211 ,  212 ,  213  and  214 , and second reflection mirrors  215 ,  216  and  217  etc., and with the image data of each color of black, cyan, magenta and yellow, each light beam of modulated laser beam or the like is irradiated to each of the photoreceptor drums  2 ,  3 ,  4 , and  5 . To each of the photoreceptor drums  2 ,  3 ,  4  and  5 , an electrostatic latent image by the image data of each color of black, cyan, magenta and yellow is formed. 
     In the embodiment, although the exposure unit  21  is one with a technique using a laser scanning unit (LSU) including a laser irradiation section and a reflection mirror, one with a technique in which light emitting elements are arranged in an array using EL or LED write head, for example, may be used. 
     The photoreceptor drums  2 ,  3 ,  4  and  5  are arranged above the exposure unit  21 , are image bearing members each having a substantially cylinder shape, and are controlled to rotate in a predetermined direction (refer to an arrow attached to each of the photoreceptor drums  2 ,  3 ,  4  and  5 ) by a driving section and a control section which are not shown. The photoreceptor drums  2 ,  3 ,  4  and  5  are so configured that a photoconductive layer is formed on a conductive substrate. For example, a metal drum made of aluminum or the like is the substrate, and on the outer circumferential surface thereof, the photoconductive layer of amorphous silicon (a-Si), selenium (Se), or organic photo-semiconductor (OPC) etc., is formed as a thin film. Note that, the configuration of the photoreceptor drums  2 ,  3 ,  4  and  5  is not particularly limited to the above-described configuration. The charging rollers  22 ,  23 ,  24  and  25  are chargers of a contact type which charge the surfaces of the photoreceptor drums  2 ,  3 ,  4  and  5  uniformly to predetermined potential. In the embodiment, as shown in  FIG. 1 , although charging rollers  22 ,  23 ,  24  and  25  of a roller type and the contact type are used as the chargers, in replacement of such charging rollers  22 ,  23 ,  24  and  25 , chargers of a charger type or a brush type may be used. 
     The developing devices  6 ,  7 ,  8  and  9  supply toner to the surfaces of the photoreceptor drums  2 ,  3 ,  4  and  5  on which the electrostatic latent images are formed, to develop the electrostatic latent images to the toner images. Each of the developing devices  6 ,  7 ,  8  and  9  contains toner of each of the colors of black, cyan, magenta, and yellow, and visualize the electrostatic latent image corresponding to each of the colors formed on each of the surfaces of the photoreceptor drums  2 ,  3 ,  4  and  5  into the toner image of each of the colors of black, cyan, magenta and yellow. The cleaning units  26 ,  27 ,  28  and  29  remove and collect residual toners on the surfaces of the photoreceptor drums  2 ,  3 ,  4  and  5  with a lubricant or the like after development and image transfer. 
     The intermediate transfer belt  18  arranged above the respective photoreceptor drums  2 ,  3 ,  4  and  5  is supported around a driving roller  181  and a driven roller  182  with tension, and forms a loop-shaped moving path. The photoreceptor drum  5  (yellow), the photoreceptor drum  4  (magenta), the photoreceptor drum  3  (cyan) and the photoreceptor drum  2  (black) are arranged in this order to face the outer circumferential surface of the intermediate transfer belt  18  along with a moving direction  180  thereof. The primary transfer rollers  30 ,  31 ,  32  and  33  are arranged at positions facing the respective photoreceptor drums  2 ,  3 ,  4  and  5  with the intermediate transfer belt  18  interposed therebetween. The respective positions at which the intermediate transfer belt  18  faces the photoreceptor drums  2 ,  3 ,  4  and  5  are primary transfer positions. The intermediate transfer belt  18  is a film having a thickness of about 100 to 150 μm, and formed to be an endless-shape. A primary transfer bias having opposite polarity to charging polarity of the toner is applied by constant voltage control to the primary transfer rollers  30 ,  31 ,  32  and  33  in order to transfer the toner images borne on the surfaces of the photoreceptor drums  2 ,  3 ,  4  and  5  onto the intermediate transfer belt  18 . Thereby, the toner images of the respective colors formed on the photoreceptor drums  2 ,  3 ,  4  and  5  are transferred and overlaid onto the outer circumferential surface of the intermediate transfer belt  18  sequentially, and a full-color toner image is formed on the outer circumferential surface of the intermediate transfer belt  18 . 
     However, when image data for only a part of the colors of yellow, magenta, cyan and black is inputted, electrostatic latent images and toner images are formed at only a part of the photoreceptor drums corresponding to the color of the input image data among the four photoreceptor drums  2 ,  3 ,  4  and  5 . For example, during monochrome image formation, formation of an electrostatic latent image and formation of a toner image are performed only at the photoreceptor drum  2  corresponding to the color of black, and only a black toner image is transferred onto the outer circumferential surface of the intermediate transfer belt  18 . 
     Each of the primary transfer rollers  30 ,  31 ,  32  and  33  is configured by coating a surface of a shaft whose raw material is metal having a diameter of 8 to 10 mm (stainless steel, for example) with a conductive elastic material (such as EPDM, urethane foam, etc.), and applies high voltage uniformly to the intermediate transfer belt  18  by the conductive elastic material. In the embodiment, although the primary transfer rollers  30 ,  31 ,  32  and  33  are used as transfer electrodes, other than them, a brush or the like is also usable. The toner image transferred onto the outer circumferential surface of the intermediate transfer belt  18  at each primary transfer position is conveyed to a secondary transfer position, which is a position facing the secondary transfer roller  19 , by the rotation of the intermediate transfer belt  18  along the moving direction  180 . The secondary transfer roller  19  is in pressure-contact, at a predetermined nip pressure, with the outer circumferential surface of the intermediate transfer belt  18  whose inner circumferential surface is in contact with a circumferential surface of an intermediate transfer belt driving roller  181  during image formation. To obtain the nip pressure constantly, either of the secondary transfer roller  19  or the intermediate transfer belt driving roller  181  is formed by a hard material such as metal, and another one is formed by a soft material such as an elastic roller or the like (elastic rubber roller, foamable resin roller, etc.). 
     When a paper sheet fed from a paper feeding cassette  34  or a manual paper feeding tray  35  passes through between the secondary transfer roller  19  and the intermediate transfer belt  18 , high voltage with opposite polarity (+) to the charging polarity of the toner (−) is applied to the secondary transfer roller  19 . As described above, the electrostatic latent images formed on the surfaces of respective photoreceptor drums  2 ,  3 ,  4  and  5  are visualized by the toner corresponding to each of the colors to form respective toner images, and such toner images are layered on the intermediate transfer belt  18 . Thereafter, the layered toner images are moved to a contact position of the conveyed paper sheet with the intermediate transfer belt  18  by the rotation movement of the intermediate transfer belt  18 , and by the secondary transfer roller  19  arranged in this position, the toner images are transferred from the outer circumferential surface of the intermediate transfer belt  18  onto the paper sheet. 
     Toners adhered to the intermediate transfer belt  18  by the contact of the intermediate transfer belt  18  with the photoreceptor drums  2 ,  3 ,  4  and  5 , and toners remaining on the intermediate transfer belt  18  without being transferred in transferring the toner image from the intermediate transfer belt  18  to the paper sheet become a source of causing color mixture of the toner at the next step, therefore removal and collection thereof are performed by an intermediate transfer belt cleaning unit  42 . The intermediate transfer belt cleaning unit  42  is provided with, for example, a cleaning blade as a cleaning member that is in contact with the intermediate transfer belt  18 . A part of the intermediate transfer belt  18  where the cleaning blade is in contact therewith is supported by an intermediate transfer belt driven roller  182  from a backside thereof. 
     The paper sheet to which a toner image is transferred as a visible image is guided by the fixing device  20  comprised of a heating roller  20   a  and a pressure roller  20   b , passes through between the heating roller  20   a  and the pressure roller  20   b , and subjected to the processing of heating and pressurizing. Thereby, the toner image to be the visible image is fixed firmly on the surface of the paper sheet. The paper sheet on which the toner image has been fixed is discharged by paper discharge rollers  43  onto the paper discharge tray  36 . On the heating roller  20   a , a temperature sensor (such as thermistor, for example)  20   c  is provided, and based on surface temperature detection information of the heating roller  20   a  by the temperature sensor, heat generation control in a heat generating section of the heating roller  20   a  is performed by a control section (not shown). 
     The image forming apparatus  1  is provided with a paper conveyance path P 1  of a substantially vertical direction so that the paper sheet contained in the paper feeding cassette  34  is fed, through between the secondary transfer roller  19  and the intermediate transfer belt  18  and through the fixing device  20 , to the paper discharge tray  36 . Arranged in the paper conveyance path P 1  are a pick-up roller  44  for feeding the paper in the paper feeding cassette  34  into the paper conveyance path P 1  sheet by sheet, conveying rollers  45  for conveying the fed paper sheet upward, registration rollers  46  for guiding the conveyed paper sheet between the secondary transfer roller  19  and the intermediate transfer belt  18  at a predetermined timing, and the paper discharge rollers  43  for discharging the paper sheet to the paper discharge tray  36 . In addition, inside the image forming apparatus  1 , a paper conveyance path P 2  on which a pick-up roller  47  and conveyance rollers  48 ,  49  and  50  are arranged is formed between the manual paper feeding tray  35  and the registration rollers  46 . Further, a paper conveyance path P 3  is formed from the paper discharge rollers  43  to an upstream side of the registration rollers  46  in the paper conveyance path P 1 . 
     The paper discharge rollers  43  are rotatable in both forward and reverse directions, and are driven in the forward direction to discharge a paper sheet to the paper discharge tray  36  during single-sided image formation in which an image is formed on one side of the paper sheet, and during second side image formation of double-sided image formation in which an image is formed on both sides of the paper sheet. On the other hand, during first side image formation of the double-sided image formation, the paper discharge rollers  43  are driven in the forward direction until a tail end of the paper sheet passes through the fixing device  20 , and are then driven in the reverse direction to guide the paper sheet in the paper conveyance path P 3  in a state where the tail end of the paper sheet is held. In the paper conveyance path P 3 , a reverse conveyance rollers  51  and  52  are arranged and with these reverse conveyance rollers  51  and  52 , the paper sheet on which an image has been formed only on one side during double-sided image formation is guided from the paper conveyance path P 3  to the paper conveyance path P 1  in a state where the paper is turned over and upside down. 
     The paper sheet that has been fed from the paper feeding cassette  34  or the manual paper feeding tray  35  and has been conveyed through the paper conveyance path P 3  is guided by the registration rollers  46  between the secondary transfer roller  19  and the intermediate transfer belt  18  in synchronization with the rotation of the intermediate transfer belt  18 . Thus, the rotation of the registration rollers  46  is stopped when the operation of the photoreceptor drums  2 ,  3 ,  4  and  5  or the intermediate transfer belt  18  is started, and the movement of the paper sheet that has been fed or conveyed prior to rotation of the intermediate transfer belt  18  is stopped in the paper conveyance path P 1  in a state where a leading end thereof abuts against the registration rollers  46 . Then, rotation of the registration rollers  46  is started at timing when the leading end of the paper sheet faces a leading end of a toner image formed on the intermediate transfer belt  18  at a position where the secondary transfer roller  19  is in pressure-contact with the intermediate transfer belt  18 . 
     Note that, during full-color image formation in which image formation is performed by all of the image forming sections  38 ,  39 ,  40  and  41 , the primary transfer rollers  30 ,  31 ,  32  and  33  cause the intermediate transfer belt  18  to be in pressure-contact with all of the photoreceptor drums  2 ,  3 ,  4  and  5 . On the other hand, during monochrome image formation in which image formation is performed only by the image forming section  38 , only the primary transfer roller  30  causes the intermediate transfer belt  18  to be in pressure-contact with the photoreceptor drum  2 . 
     Next, description will be given in detail for the configuration of the characteristic toner cartridges  14 ,  15 ,  16  and  17  according to the embodiment with reference to the drawings.  FIG. 2  is a perspective view showing the configuration of a toner cartridge unit  37  in which four pieces of the toner cartridges  14 ,  15 ,  16  and  17  are unitized in block. As the toner cartridges  14 ,  15 ,  16  and  17 , as shown in  FIG. 2 , four pieces of the toner cartridges  14 ,  15 ,  16  and  17  are mounted side by side on the toner cartridge unit  37 . When any of lock levers  37   a ,  37   b ,  37   c  and  37   d  provided on the toner cartridge unit  37  corresponding to respective toner cartridges  14 ,  15 ,  16  and  17  is raised up, any of toner containers  140 ,  150 ,  160  and  170  as toner containers is moved toward an arrow F direction so as to be held in a state of being pressed to a stopper plate  37   e . In this manner, the toner cartridge unit  37  on which four pieces of the toner cartridges  14 ,  15 ,  16  and  17  are mounted side by side is set on the intermediate transfer belt  18 . In the set state, it is configured that respective toner containers  140 ,  150 ,  160  and  170  and the toner supply pipes  10 ,  11 ,  12  and  13  are connected so that corresponding toners are able to be supplied to the developing devices  6 ,  7 ,  8  and  9  through toner supply pipes  10 ,  11 ,  12  and  13 . Note that,  FIG. 2  shows a state prior to attachment of a toner cartridge for cyan  15 . Operation of a shutter during attachment of the toner cartridges  14 ,  15 ,  16  and  17  will be described below in detail in  FIGS. 5A to 5C . 
     Next, description will be given in detail for the configuration of the toner cartridges  14 ,  15 ,  16  and  17  taking an example of the toner cartridge for black  14  with reference to  FIGS. 3A to 3C ,  FIGS. 4A and 4B  and  FIGS. 5A to 5C . Since other toner cartridges  15 ,  16  and  17  are configured similarly, description thereof will be omitted.  FIGS. 3A to 3C  are sectional views showing the configuration of the toner cartridge  14 .  FIG. 3A  shows a side sectional view prior to attachment of the toner cartridge  14  to the image forming apparatus  1 , and  FIG. 3B  shows a sectional view taken along a sectional line IIIb-IIIb of  FIG. 3A , and  FIG. 3C  shows a sectional view taken along a sectional line IIIc-IIIc of the same.  FIGS. 4A and 4B  show external views of an auger screw  142  and a toner flowing-out preventing member  143 .  FIG. 4A  shows the external view of the auger screw  142  and  FIG. 4B  shows the external view of the toner flowing-out preventing member  143 .  FIGS. 5A to 5C  are drawings showing releasing operation process of the toner flowing-out preventing member  143  during attachment of the toner cartridge  14  in the image forming apparatus  1 . 
     As shown in  FIGS. 3A to 3C , the toner cartridge  14  includes the toner container  140  which contains a black toner, a toner discharge section  141 , the auger screw  142  and the toner flowing-out preventing member  143 . The toner discharge section  141  is provided on one side part of the toner container  140  and has a toner discharge port  141   a . The auger screw  142  includes a rotation shaft  142   a  and a spiral blade  142   b  and is provided in the toner container  140  and conveys a black toner in the toner container  140  to the toner discharge section  141 . The toner flowing-out preventing member  143  is provided in a communicating part between the toner container  140  and the toner discharge section  141  and prevents flowing out of the toner. The toner discharge port  141   a  is provided with a shutter  144 . Furthermore, in a toner containing space  145  of the toner container  140 , a stirring paddle  146  which is parallel to the auger screw  142  is rotatably supported. 
     The toner container  140  includes the toner discharge section  141  which is cylindrical at one end thereof (a tip end side along the arrow F direction), and is a toner container of a substantially square column containing a black toner. The toner container  140  rotatably supports the auger screw  142  and the stirring paddle  146  in the toner containing space  145 . A sectional shape of the internal space  141   b  which is enclosed by the toner discharge section  141  and a shutter  144  is a continuous shape of a rectangular part on the side of the shutter  144  and a semi-arc part on a side opposite to the shutter. 
     The auger screw  142  includes a rotation shaft  142   a , a spiral blade  142   b , and a driving gear  142   c , and the rotation thereof conveys the black toner inside the toner container  140  toward the toner discharge port  141   a . The stirring paddle  146  is a stirring member that has four pieces of stirring blades around the rotation shaft and functions to disintegrate the black toner in the toner container  140  by the rotation. The toner discharge port  141   a  is a rectangular opening provided on a bottom part of the toner discharge section  141  of the toner container  140 , and discharges the black toner carried by the auger screw  142  to the outside of the toner cartridge  14 . The shutter  144  is a shutter member formed in a rectangular plate shape slidably provided to a position of closing the toner discharge port  141   a , and it is configured that when attached to the image forming apparatus  1 , receiving action of an upper end of the toner supply pipe  10 , slidingly moves in the arrow R direction against resilience of a spring of which illustration is omitted, so as to open the toner discharge port  141   a . By opening thereof, the black toner contained in the toner container  140  is supplied to the developing device  6  through the toner supply pipe  10 . 
     The toner flowing-out preventing member  143  is comprised of a plate-like member having flexibility, whose entire shape is formed to be almost the same shape as the sectional shape of the internal space  141   b . The toner flowing-out preventing member  143  includes a circular hole section  143   a  which has the same shape as the vertical section of the rotation shaft  142   a  of the auger screw  142 , and is arranged in the communicating part that divides the toner container into the toner discharge section  141  and the toner containing space  145 . As to the toner flowing-out preventing member  143 , one end (lower end) thereof is fixed to a tip end and side end along the arrow R direction of the shutter  144  by an adhesive so as to stand vertically through inside the toner discharge port  141   a , and inserts a rotation shaft  142   a  of the auger screw  142  into the circular hole section  143   a  so as to be held by the auger screw  142  in a state of being perpendicular to the axial line of the rotation shaft  142   a . Then, in this state, an outer peripheral part of the toner flowing-out preventing member  143  is in a state of closely attached to an inner wall of the toner discharge section  141 . Therefore, the toner flowing-out preventing member  143  acts as a seal member so that the black toner on the toner containing space  145  side does not flow out to the toner discharge section  141  side in the toner cartridge  14  prior to attaching to the image forming apparatus  1 . 
     The toner cartridge  14  is arranged above the developing device  6  as shown in  FIG. 1  so as to supply a black toner to the developing device  6  by being connected to the toner supply pipe  10 , however, prior to attaching the toner cartridge  14  to the apparatus main body, the black toner in the toner container  140  is shielded by the toner flowing-out preventing member  143  so as not to flow out to the toner discharge section  141 . The toner flowing-out preventing member  143  is so configured that since the lower end thereof is fixed to the end of the shutter  144 , the toner flowing-out preventing member  143  is drawn out to the outside of the toner container  140  in conjunction with the sliding operation of the shutter  144  in opening the toner discharge port  141   a . Then, as shown in  FIG. 3C  and  FIG. 4B , the toner flowing-out preventing member  143  further has a cutting slit section  143   b  from the circular hole section  143   a  to the peripheral part (forming a semi-arc) of a region corresponding to the semi-arc part of the internal space  141   b . Thereby, when the shutter  144  is slid so that the toner flowing-out preventing member  143  is drawn out to the outside of the toner container  140 , the slit section  143   b  is widely opened so that the toner flowing-out preventing member  143  comes off the rotation shaft  142   a , and the load of the toner flowing-out preventing member  143  departing from the auger screw  142  becomes small, and thus release of the toner flowing-out preventing member  143  is achieved further smoothly. 
     Further, in the embodiment, as shown in  FIG. 4A , at a position where the spiral blade  142   b  of the auger screw  142  intersects with the toner flowing-out preventing member  143 , a notch section  142   d  for the toner flowing-out preventing member having a width equal to or more than the thickness (slightly larger in width) of the toner flowing-out preventing member  143  is provided. The notch section  142   d  is formed such that in the holding state of the toner flowing-out preventing member  143  by the auger screw  142 , a part of the toner flowing-out preventing member  143  is positioned inside the notch section  142   d . Thereby, sealability between the auger screw  142  and the toner flowing-out preventing member  143  is able to be enhanced so that even though the auger screw  142  rotates in transporting the toner cartridge  14 , the spiral blade  142   b  does not act on the toner flowing-out preventing member  143 , and the toner flowing-out preventing member  143  is stably held without being deformed or fallen down, therefore, action to prevent flowing out of the black toner in the toner containing space  145  is maintained. 
       FIGS. 5A to 5C  show a state where, in attaching the toner cartridge  14  to the image forming apparatus  1 , the shutter  144  slidingly moves and the toner flowing-out preventing member  143  departs from the auger screw  142  so as to be drawn out to the outside of the toner container  140 .  FIG. 5A  shows a state immediately before attaching the toner cartridge  14  to the image forming apparatus  1 , that is, a state where the shutter  144  is closed,  FIG. 5B  is a state in the middle of attaching the toner cartridge  14  to the image forming apparatus  1 , that is, a state where the shutter  144  is half-opened, and  FIG. 5C  shows a state immediately after attaching the toner cartridge  14  to the image forming apparatus  1 , that is, a state where the toner flowing-out preventing member  143  departs from the auger screw  142  to be drawn out to the outside of the toner container  140  so that the black toner is able to be discharged to the toner supply pipe  10 . 
     The shutter  144  is maintained at a position of closing the toner discharge port  141   a  by the elastic force of a shot-shown spring, and when the toner cartridge  14  is attached to the image forming apparatus  1  along an arrow F direction, as shown in  FIG. 5A , the shutter  144  is arranged to be in contact with the toner supply pipe  10  provided in the insertion route thereof. Then, when the toner cartridge  14  is pressed to proceed toward a predetermined position of the image forming apparatus  1  along the arrow F direction, as shown in  FIG. 5B , the shutter  144 , receiving action of an upper end of the toner supply pipe  10 , slides to be pressed back against the resilience of the spring along the arrow R direction so as to open the toner discharge port  141   a . At this time, as to the toner flowing-out preventing member  143 , since the lower end thereof is fixed to the shutter  144 , drawing out thereof is performed so as to be drawn in between the outer surface of the toner container  140  and the shutter  144  in conjunction with the sliding operation of the shutter  144 . Along with this, the slit section  143   b  of the toner flowing-out member  143  widely opens so that the circular hole section  143   a  comes off the rotation shaft  142   a  of the auger screw  142 , and thereby the toner flowing-out preventing member  143  is released from the state of being held and restrained by the auger screw  142  to depart therefrom. 
     When attachment of the toner cartridge  14  to a predetermined position in the image forming apparatus  1  is completed, as shown in  FIG. 5C , the shutter  144  opens the toner discharge port  141   a  completely and at the same time, the toner flowing-out preventing member  143  departs from the auger screw  142  completely to intervene between the toner container  140  and the shutter  144  in a state of being pressed into. Thereby, as well as the toner discharge port  141   a  is connected with the toner supply pipe  10 , the toner containing space  145  communicates with the toner supply pipe  10 . Further, the driving gear  142   c  is connected to a power train or a driving source (not shown) in the image forming apparatus  1 . Then, when rotation driving around the axial line of the auger screw  142  is started by obtaining the driving force from the power train or the driving source, the black toner in the toner containing space  145  is discharged to the toner supply pipe  10  smoothly through the toner discharge section  141  and the toner discharge port  141   a  without the auger screw  142  locked by the fixed toners. Thereby, the black toner is supplied to the developing device  6  as needed to carry out image forming operation in the image forming section  38  without a hitch. When the black toner in the toner cartridge  14  has run out, the toner cartridge  14  is drawn out along the arrow R direction and replaced with a new toner cartridge  14 . In drawing out the toner cartridge  14 , the shutter  144  is released from the restraint by the toner supply pipe  10  to slidingly move to an original position by the resilience of the spring so that the toner discharge port  141   a  is closed. Accordingly, in the work of drawing out and taking out the toner cartridge  14  which has been emptied, there will be no spilling out of the black toner remaining in the toner cartridge  14  from the toner discharge port  141   a  to the inside of the image forming apparatus  1 . 
       FIG. 6  is an external view of the auger screw  142  showing a second embodiment of the invention. The auger screw  142  of the embodiment includes a stirring plate  142   e  which is fixed to the rotation shaft  142   a  at a position facing the toner discharge port  141   a  in the toner discharge section  141 , adding to the rotation shaft  142   a , the spiral blade  142   b , and the driving gear  142   c  which are the same as those described above. The stirring plate  142   e  is a rectangular plate-like member extended radially from the rotation shaft  142   a  to be fixed, and functions to disintegrate and scrape down the toner near the toner discharge port  141   a  by rotating along with the rotation of the rotation shaft  142   a . Furthermore, the auger screw  142  has a notch section  142   f  for the toner flowing-out preventing member whose thickness is equal to or more than the thickness of the toner flowing-out preventing member  143  at a position intersecting with the toner flowing-out preventing member  143  (illustration thereof is omitted), that is between the spiral blade  142   b  and the stirring plate  142   e . Thereby, as same as the notch section  142   d  for the toner flowing-out preventing member shown in  FIG. 4A , as well as sealability between the auger screw  142  and the toner flowing-out preventing member  143  is able to be enhanced, stable holding of the toner flowing-out preventing member  143  is also achieved. 
     Note that, although the image forming apparatus  1  of the embodiment is a full-color image forming apparatus, it may be an image forming apparatus exclusively used for monochrome. Moreover, the full-color image forming system is not limited to the tandem type as illustrated, and may be performed by another type. Further, as the developing device, an example of using the two-component developer is shown, however, a developing device of a developing system with a non-magnetic one component developer etc., may be usable. 
     The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description and all changes which come within the meaning and the range of equivalency of the claims are therefore intended to be embraced therein.