Patent Publication Number: US-2009232536-A1

Title: Image Forming Apparatus and Image Forming Method

Description:
BACKGROUND 
     1. Technical Field 
     The present invention relates to a technical field of an electrophotographic image forming apparatus, such as a copying machine, a facsimile apparatus, or a printer, and a technical field of an image forming method, which carry out an image formation by means of a liquid developer, using an intermediate transfer medium. 
     2. Related Art 
     To date, an electrophotographic image forming apparatus has been known which carries out an image formation by means of dry toner, using an intermediate transfer belt (for example, JP-A-2006-317986). In JP-A-2006-317986, the title of the invention is “a wet type image forming apparatus”, but no wet toner is used in this image forming apparatus. In the image forming apparatus described in JP-A-2006-317986, toner remaining on an intermediate transfer belt after a secondary transfer is removed by a bias cleaning method whereby a bias is applied to a cleaning roller. 
     Meanwhile, in an image forming apparatus which carries out an image formation by means of a liquid developer, using an intermediate transfer medium, it is difficult to remove solid toner contained in the liquid developer, which remains on an intermediate transfer belt after a secondary transfer, by means of the bias cleaning method described in JP-A-2006-317986. The reason is as follows. In the case of using a liquid developer, steps for an image formation, such as a developing step, a primary transfer step, an intermediate transfer belt squeeze step unique to the liquid developer, and a secondary transfer step, are sequentially carried out at an image formation time. As the steps are carried out in this way, an amount of carrier oil in the liquid developer decreases gradually. For this reason, as shown in Table 1, a ratio of solid toner in the liquid developer increases, and a ratio of solid toner from the liquid developer on the intermediate transfer belt after the secondary transfer becomes higher than a ratio of solid toner from the liquid developer on a photoreceptor after the primary transfer. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                 Solid amount 
                 Carrier amount 
               
               
                   
                 Solid ratio (%) 
                 (mg/cm 2 ) 
                 (mg/cm 2 ) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 Photoreceptor 
                 25.6 
                 0.11 
                 0.32 
               
               
                 Intermediate transfer belt 
                 40.7 
                 0.11 
                 0.16 
               
               
                 (monochrome) 
               
               
                 Intermediate transfer belt 
                 42.0 
                 0.29 
                 0.40 
               
               
                 (three colors) 
               
               
                   
               
               
                 Solid ratio (%) = {(solid amount)/(solid amount + liquid carrier amount)} · 100 
               
            
           
         
       
     
     However, as a charge amount of solid toner decreases when the ratio of solid toner increases, a charge amount of solid toner on the intermediate transfer belt becomes smaller than a charge amount of solid toner on the photoreceptor. Furthermore, by passing through a nip in each heretofore described step, the solid toner, after the secondary transfer, adheres to the intermediate transfer belt with an adhesion greater than an adhesion to the photoreceptor. 
     Therein, in order to remove the solid toner on the intermediate transfer belt after the secondary transfer by means of the heretofore described bias cleaning method described in JP-A-2006-317986, it is necessary to increase a bias applied to the cleaning roller. 
     However, on an excess bias simply being applied to the cleaning roller in the way heretofore described, the intermediate transfer belt being charged due to a charge injection, there is a problem in that it is impossible to effectively carry out an image formation after a cleaning of the intermediate transfer belt. 
     SUMMARY 
     An advantage of some aspects of the invention is to provide an image forming apparatus, and an image forming method, which, even using a liquid developer, can effectively carry out an image formation after a cleaning of an intermediate transfer medium while more effectively carrying out a removal of solid toner remaining on the intermediate transfer medium after a transfer. 
     In an image forming apparatus and image forming method according to some aspects of the invention, by bringing a latent image carrier cleaning roller into contact with a latent image carrier, and applying a latent image carrier cleaning bias to the latent image carrier cleaning roller, a liquid developer remaining on the latent image carrier after a transfer is removed. Also, by bringing a transfer medium cleaning roller into contact with a transfer medium at a second nip width, which is larger than a first nip width at which the latent image carrier cleaning roller is nipped on the latent image carrier, and applying a transfer medium cleaning bias to the transfer medium cleaning roller, a liquid developer remaining on the transfer medium from which an image has been transferred to a recording material is removed. 
     Consequently, even in the event that solid toner from the liquid developer adheres to the transfer medium with an adhesion greater than an adhesion to the latent image carrier, as in the heretofore known apparatus heretofore described, it is possible to efficiently remove solid toner adhering to the latent image carrier after the transfer, and solid toner adhering to the transfer medium after the transfer, by means of biases applied to the latent image carrier cleaning roller and the transfer medium cleaning roller, respectively. 
     In particular, by means of the fact that the second nip width of the transfer medium cleaning roller is larger than the first nip width of the latent image carrier cleaning roller, it is possible to set a solid toner nip transit time (a solid toner electrophoresis time) in the transfer medium, which has a high solid toner adhesion and is hard to clean, so as to be longer than a solid toner nip transit time in the latent image carrier. Consequently, it is possible to effectively remove solid toner on the transfer medium which is hard to remove. Also, by this means, as it is possible to make the bias applied to the transfer medium cleaning roller comparatively low, it is possible to suppress an effect on the transfer medium due to the bias. As a result, as it is possible to suppress charge on the transfer medium, it is possible to effectively carry out an image formation after a cleaning of the transfer medium. 
     Meanwhile, the transfer medium cleaning roller, when viewed in cross-section of a central portion of a second roller in an axial direction, is disposed on a second roller side of a contact point at which an imaginary tangent line common to the second roller and a third roller makes contact with the third roller. Consequently, it is possible to set a nip width between a transfer belt cleaning roller and a transfer belt so as to be larger. As a result, as well as it being possible to reduce a transfer belt cleaning bias per unit area, it is possible to increase a time for which the transfer belt cleaning roller makes contact with the transfer belt. By this means, even in the event that the transfer belt cleaning bias is set so as to be comparatively high, it is possible to effectively clean the transfer belt while suppressing an effect on the transfer belt due to the cleaning bias. 
     Furthermore, as the heretofore described nip widths are made different from each other by adjusting a supporting position, a contact pressure, or a hardness, of each of the latent image carrier cleaning roller and the transfer medium cleaning roller, it is possible to easily carry out a setting of each nip width. Then, by the nip widths being set in such a way that the latent image carrier and the transfer medium can be cleaned at the same bias, it is possible to supply each bias by means of one and the same power supply. Consequently, as well as it being possible to reduce a number of parts, it is possible to effectively realize a miniaturization of the apparatus. 
     Furthermore, a transfer medium cleaning blade is provided which, being brought into abutment with the transfer medium, removes the liquid developer remaining on the transfer medium cleaned by the transfer medium cleaning roller. In this case, after a cleaning of solid toner from the liquid developer by the transfer medium cleaning roller, most of the liquid developer remaining on the transfer medium is liquid carrier. Consequently, as the transfer medium cleaning blade only removes the liquid carrier, it is possible to reduce a pressure at which the transfer medium cleaning blade abuts against the transfer medium. Although the transfer medium is generally softer than the latent image carrier, by the pressure at which the transfer medium cleaning blade abuts against the transfer medium being reduced, it is possible to suppress damage to the transfer medium, and achieve an increase in life span of the transfer medium. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements. 
         FIG. 1  schematically and partially shows one example of an embodiment of an image forming apparatus according to an embodiment of the invention. 
         FIG. 2A  illustrates a nip width of a photoreceptor cleaning roller, using a fixed position method, while  FIG. 2B  illustrates a nip width of an intermediate transfer belt cleaning roller, using the fixed position method. 
         FIG. 3A  illustrates the nip width of the photoreceptor cleaning roller, using a fixed load method, while  FIG. 3B  illustrates the nip width of the intermediate transfer belt cleaning roller, using the fixed load method. 
         FIG. 4  schematically and partially shows another example of the embodiment of the image forming apparatus according to an embodiment of the invention. 
         FIGS. 5A to 5C  illustrate a nip width measuring method in a photoreceptor cleaning. 
         FIG. 6  shows a relationship between an applied bias and a non-cleaned amount (OD value) in an example 1. 
         FIG. 7  shows a relationship between an applied bias and a non-cleaned amount (OD value) in a comparison example 1. 
         FIG. 8  shows a relationship between an applied bias and a non-cleaned amount (OD value) in a comparison example 2. 
         FIG. 9  partially shows still another example of the embodiment of the invention. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Hereafter, a description will be given, using the drawings, of embodiments of the invention. 
       FIG. 1  schematically and partially shows one portion of one example of an embodiment of an image forming apparatus according to an embodiment of the invention. 
     As shown in  FIG. 1 , an image forming apparatus  1  of the example includes photoreceptors  2 Y,  2 M,  2 C and  2 K, disposed in tandem, which are yellow (Y), magenta (M), cyan (C), and black (K) latent image carriers. Herein r in each photoreceptor  2 Y,  2 M,  2 C and  2 K,  2 Y represents a yellow photoreceptor,  2 M a magenta photoreceptor,  2 C a cyan photoreceptor, and  2 K a black photoreceptor. Also, with respect to other members too, in the same way, Y, M, C and K for the individual colors are suffixed one to each of reference numbers of the members, representing a member of each color. 
     In the example shown in  FIG. 1 , each of the photoreceptors  2 Y,  2 M,  2 C and  2 K is configured of a photoreceptor drum. It is also possible to configure each photoreceptor  2 Y,  2 M,  2 C and  2 K as an endless belt. 
     Each of the photoreceptors  2 Y,  2 M,  2 C and  2 K is arranged in such a way as to rotate in an a direction shown by the arrow in  FIG. 1 , that is, in a clockwise direction in  FIG. 1 , when actuated. Charging devices  3 Y,  3 M,  3 C and  3 K are provided on peripheries of the photoreceptors  2 Y,  2 M,  2 C and  2 K, respectively. Exposure devices  4 Y,  4 M,  4 C and  4 K, developing devices  5 Y,  5 M,  5 C and  5 K (equivalent to a developing section according to the invention), photoreceptor squeeze devices  6 Y,  6 M,  6 C and  6 K, primary transfers  7 Y,  7 M,  7 C and  7 K (equivalent to a first transfer member according to the invention), neutralization devices  8 Y,  8 M,  8 C and  8 K, and photoreceptor cleaning devices  9 Y,  9 M,  9 C and  9 K are disposed, in order, in a rotation direction of the photoreceptors  2 Y,  2 M,  2 C and  2 K from the charging devices  3 Y,  3 M,  3 C and  3 K, respectively. 
     Also, the image forming apparatus  1  includes an endless intermediate transfer belt  10  which is an intermediate transfer medium. The intermediate transfer belt  10 , although not shown, is formed as a three-layer structure of a flexible substrate of, for example, resin or the like, an elastic layer of rubber formed on a surface of the substrate, and a superficial layer formed on a surface of the elastic layer. Needless to say, this is not limiting. Then, the intermediate transfer belt  10 , being stretched over a belt drive roller  11 , to which a drive force of an unshown motor is transmitted, and a pair of driven rollers  12  and  13 , is provided so as to be rotatable in a direction shown by an arrow β (a counterclockwise direction in  FIG. 1 ). In this case, the belt drive roller  11  and one driven roller  12  are adjacently disposed spaced a predetermined distance away from each other in a moving direction (an upward direction from below in  FIG. 1 ), shown by an arrow γ, of a recording material (not shown) such as paper conveyed thereto. Also, the belt drive roller  11  configures a first roller according to the invention, the driven roller  12  configures a second roller according to the invention, and furthermore, the driven roller  13  configures a third roller according to the invention. 
     Furthermore, the belt drive roller  11  and the other driven roller  13  are disposed spaced apart in a tandem disposition direction of the photoreceptors  2 Y,  2 M,  2 C and  2 K. In this example, as shown in  FIGS. 2A and 2B , a diameter d 2  of the driven roller  13  is set so as to be the same, or approximately the same, as a diameter d 1  of the photoreceptors  2 Y,  2 M,  2 C and  2 K (d 1 =d 2  or d 1 ≈d 2 ). 
     Furthermore, although not shown, the intermediate transfer belt  10  is arranged in such a way as to be provided with a predetermined tension by a tension roller, taking up a slack. In the same way, although not shown, the tension roller is arranged in such a way as to be cleaned by a tension roller cleaning device. 
     In the image forming apparatus  1 , the photoreceptors  2 Y,  2 M,  2 C and  2 K and the developing devices  5 Y,  5 M,  5 C and  5 K are disposed in the order of the colors Y, M, C and K from an upstream side (a left side in  FIG. 1 ) in a moving direction β of the intermediate transfer belt  10 , but it is possible to optionally set a disposition order of the colors Y, M, C and K. 
     Intermediate transfer belt squeeze devices  14 Y,  14 M,  14 C and  14 K are disposed respectively in vicinities of the primary transfers  7 Y,  7 M,  7 C and  7 K on downstream sides of the primary transfers  7 Y,  7 M,  7 C and  7 K in the rotation direction of the intermediate transfer belt  10 . Furthermore, a secondary transfer  15  (equivalent to a second transfer member according to the invention) is provided on a belt drive roller  11  side of the intermediate transfer belt  10 , and an intermediate transfer belt cleaning device  16  is provided on a driven roller  13  side of the intermediate transfer belt  10 . 
     Although not shown, the image forming apparatus  1  of this example, in the same way as a heretofore known general image forming apparatus which carries out a secondary transfer, includes a recording material storage device, which stores a recording material such as, for example, paper, and a registration roller pair, which conveys and feeds the recording material from the recording material storage device to the secondary transfer  15 , on an upstream side of the secondary transfer  15  in a recording material conveyance direction. Also, the image forming apparatus  1  includes a fixing device and a discharged paper tray, similarly on a downstream side of the secondary transfer  15  in the recording material conveyance direction. 
     Each of the charging devices  3 Y,  3 M,  3 C and  3 K is formed of a charging member such as, for example, a charging roller. A bias with the same polarity as a charge polarity of a liquid developer is applied to each charging device  3 Y,  3 M,  3 C and  3 K from an unshown power supply. Then, the charging devices  3 Y,  3 M,  3 C and  3 K are arranged in such a way as to charge the corresponding photoreceptors  2 Y,  2 M,  2 C and  2 K by means of the charging members. 
     Lights emitted from light emitting elements of the exposure devices  4 Y,  4 M,  4 C and  4 K are applied to the corresponding photoreceptors  2 Y,  2 M,  2 C and  2 K. By this means, a printing (a writing of an image) is carried out on each photoreceptor  2 Y,  2 M,  2 C and  2 K, and an electrostatic latent image of each color is formed on a surface of each corresponding photoreceptor  2 Y,  2 M,  2 C and  2 K. 
     The developing devices  5 Y,  5 M,  5 C and  5 K respectively include developer supply sections  17 Y,  17 M,  17 C and  17 K, developing rollers  18 Y,  18 M,  18 C and  18 K, developing roller cleaning blades  53 Y,  53 M,  53 C and  53 K, and developing roller cleaning blade recovered liquid reservoirs  54 Y,  54 M,  54 C and  54 K. 
     The developer supply sections  17 Y,  17 M,  17 C and  17 K respectively include anilox rollers  19 Y,  19 M,  19 C and  19 K, developer regulation blades  20 Y,  20 M,  20 C and  20 K, developer containers  21 Y,  21 M,  21 C and  21 K, and developer pumping rollers  22 Y,  22 M,  22 C and  22 K. 
     Each of the anilox rollers  19 Y,  19 M,  19 C and  19 K, being a cylindrical member, is a roller, on a surface of which a spiral groove (not shown) is formed finely and uniformly. Each of the anilox rollers  19 Y,  19 M,  19 C and  19 K is arranged in such a way as to rotate in a counterclockwise direction shown by the arrow in  FIG. 1 , in the same direction as that of each developing roller  18 Y,  18 M,  18 C and  18 K. It is also possible to arrange in such a way that each of the anilox rollers  19 Y,  19 M,  19 C and  19 K rotates in conjunction with each developing roller  18 Y,  18 M,  18 C and  18 K. That is, a rotation direction of the anilox rollers  19 Y,  19 M,  19 C and  19 K is not limited, but optional. 
     The developer regulation blades  20 Y,  20 M,  20 C and  20 K, being made of rubber such as, for example, urethane rubber, are brought into abutment with surfaces of the corresponding anilox rollers  19 Y,  19 M,  19 C and  19 K. Then, the developer regulation blades  20 Y,  20 M,  20 C and  20 K scrape off a liquid developer adhering to surfaces other than the grooves of the anilox rollers  19 Y,  19 M,  19 C and  19 K, respectively. Consequently, the anilox rollers  19 Y,  19 M,  19 C and  19 K supply the developing rollers  18 Y,  18 M,  18 C and  18 K with only a liquid developer adhering to interiors of their grooves. 
     The developer containers  21 Y,  21 M,  21 C and  21 K store liquid developers  23 Y,  23 M,  23 C and  23 K, respectively. Each of the liquid developers  23 Y,  23 M,  23 C and  23 K is one in which solid toner (toner particles: they are charged at an image formation time) is dispersed in a nonvolatile liquid carrier (referred to also as carrier oil. It is made from insulating oil such as, for example, silicone oil or mineral oil which prevents a charge of the toner from escaping). 
     The developer pumping rollers  22 Y,  22 M,  22 C and  22 K pump up the liquid developers  23 Y,  23 M,  23 C and  23 K in the developer containers  21 Y,  21 M,  21 C and  21 K, and supply them to the anilox rollers  19 Y,  19 M,  19 C and  19 K, respectively. Each of the developer pumping rollers  22 Y,  22 M,  22 C and  22 K is arranged in such a way as to rotate in a clockwise direction shown by the arrow in  FIG. 1 . 
     Each of the developing rollers  18 Y,  18 M,  18 C and  18 K has a cylindrical metallic shaft made of, for example, iron, and a conductive elastic layer such as, for example, a conductive urethane rubber or conductive resin layer is formed on an outer periphery thereof. The developing rollers  18 Y,  18 M,  18 C and  18 K are brought into contact with the photoreceptors  2 Y,  2 M,  2 C and  2 K, respectively, and arranged in such a way as to rotate in a counterclockwise direction shown by the arrow in  FIG. 1 . Then, the developing rollers  18 Y,  18 M,  18 C and  18 K convey the liquid developers of the colors corresponding to the corresponding photoreceptors  2 Y,  2 M,  2 C and  2 K, respectively. 
     The developing roller cleaning blades  53 Y,  53 M,  53 C and  53 K, being configured of, for example, rubber or the like which abuts against surfaces of the corresponding developing rollers  18 Y,  18 M,  18 C and  18 K, scrape off developer remaining on the developing rollers  18 Y,  18 M,  18 C and  18 K, respectively. Also, each developing roller cleaning blade recovered liquid reservoir  54 Y,  54 M,  54 C and  54 K accumulates the developer scraped off by each developing roller cleaning blade  53 Y,  53 M,  53 C and  53 K. 
     Although not shown, a compaction roller is disposed at predetermined intervals (in an order of μm) on an outer periphery of each of the developing rollers  18 Y,  18 M,  18 C and  18 K. The compaction rollers charge the corresponding developing rollers  18 Y,  18 M,  18 C and  18 K. By this means, the liquid developers  23 Y,  23 M,  23 C and  23 K on the developing rollers  18 Y,  18 M,  18 C and  18 K are pressed against the developing rollers  18 Y,  18 M,  18 C and  18 K. Developer remaining on each compaction roller is scraped off by each unshown compaction roller cleaner blade, and stored in each developer container  21 Y,  21 M,  21 C and  21 K. 
     Furthermore, although not shown, the image forming apparatus  1  of this example includes developer replenishing devices which replenish the developer containers  21 Y,  21 M,  21 C and  21 K with the liquid developers  23 Y,  23 M,  23 C and  23 K, respectively. 
     The photoreceptor squeeze devices  6 Y,  6 M,  6 C and  6 K respectively include squeeze rollers  24 Y,  24 M,  24 C and  24 K, squeeze roller cleaners  25 Y,  25 M,  25 C and  25 K, and squeeze roller cleaner recovered liquid reservoirs  26 Y,  26 M,  26 C and  26 K. 
     The squeeze rollers  24 Y,  24 M,  24 C and  24 K are rotated in a direction opposite to that of the photoreceptors  2 Y,  2 M,  2 C and  2 K (in the counterclockwise direction in  FIG. 1 ), removing carrier oil from the liquid developer on the photoreceptors  2 Y,  2 M,  2 C and  2 K, respectively. 
     Also, the squeeze roller cleaners  25 Y,  25 M,  25 C and  25 K scrape off carrier oil remaining on the corresponding squeeze rollers  24 Y,  24 M,  24 C and  24 K. Furthermore, the squeeze roller cleaner recovered liquid reservoirs  26 Y,  26 M,  26 C and  26 K accumulate the carrier oil scraped off by the corresponding squeeze roller cleaners  25 Y,  25 M,  25 C and  25 K. 
     The primary transfers  7 Y,  7 M,  7 C and  7 K include primary transfer backup rollers  27 Y,  27 M,  27 C and  27 K which bring the intermediate transfer belt  10  into contact with the photoreceptors  2 Y,  2 M,  2 C and  2 K, respectively. A voltage with a polarity opposite to a charge polarity of the toner particles is applied to the backup rollers  27 Y,  27 M,  27 C and  27 K, and toner images (liquid developer images) of the colors on the photoreceptors  2 Y,  2 M,  2 C and  2 K are primarily transferred to the intermediate transfer belt  10 . 
     Also, the neutralization devices BY,  8 M,  8 C and  8 K remove charges remaining in the photoreceptors  2 Y,  2 M,  2 C and  2 K respectively, after the primary transfer. 
     The photoreceptor cleaning devices  9 Y,  9 M,  9 C and  9 K respectively include photoreceptor cleaning rollers  28 Y,  28 M,  28 C and  28 K, photoreceptor cleaning roller cleaners  29 Y,  29 M,  29 C and  29 K, photoreceptor cleaning roller cleaner recovered liquid reservoirs  30 Y,  30 M,  30 C and  30 K, photoreceptor cleaning blades  48 Y,  48 M,  48 C and  48 K, and photoreceptor cleaning blade recovered liquid reservoirs  49 Y,  49 M,  49 C and  49 K. 
     Each photoreceptor cleaning roller  28 Y,  28 M,  28 C and  28 K is formed of a conductive elastomer such as conductive rubber. As shown in  FIG. 2A , the photoreceptor cleaning rollers  28 Y,  28 M,  28 C and  28 K are pressed into contact with the photoreceptors  2 Y,  2 M,  2 C and  2 K, respectively, at a predetermined nip width w 1 . Then, each photoreceptor cleaning roller  28 Y,  28 M,  28 C and  28 K is rotated in a direction opposite to that of each photoreceptor  2 Y,  2 M,  2 C and  2 K (the counterclockwise direction in  FIG. 1 ), and removes a remaining liquid developer on each photoreceptor  2 Y,  2 M,  2 C and  2 K after a transfer. Also, the photoreceptor cleaning roller cleaners  29 Y,  29 M,  29 C and  29 K scrape off a liquid developer remaining on the corresponding photoreceptor cleaning rollers  28 Y,  28 M,  28 C and  28 K. Furthermore, the photoreceptor cleaning roller cleaner recovered liquid reservoirs  30 Y,  30 M,  30 C and  30 K accumulate the liquid developer scraped off by the corresponding photoreceptor cleaning roller cleaners  29 Y,  29 M,  29 C and  29 K. Furthermore, the photoreceptor cleaning blades  48 Y,  48 M,  48 C and  48 K remove carrier oil remaining on the photoreceptors  2 Y,  2 M,  2 C and  2 K after a cleaning by the photoreceptor cleaning rollers  28 Y,  28 M,  28 C and  28 K. Furthermore, the photoreceptor cleaning blade recovered liquid reservoirs  49 Y,  49 M,  49 C and  49 K collect and accumulate the carrier oil which the photoreceptor cleaning blades  48 Y,  48 M,  48 C and  48 K have scraped off the photoreceptors  2 Y,  2 M,  2 C and  2 K, respectively. 
     The intermediate transfer belt squeeze devices  14 Y,  14 M,  14 C and  14 K respectively include intermediate transfer belt squeeze rollers  31 Y,  31 M,  31 C and  31 K, intermediate transfer belt squeeze roller cleaners  32 Y,  32 M,  32 C and  32 K, and intermediate transfer belt squeeze roller cleaner recovered liquid reservoirs  33 Y,  33 M,  33 C and  33 K. 
     The intermediate transfer belt squeeze rollers  31 Y,  31 M,  31 C and  31 K collect carrier oil of the corresponding colors on the intermediate transfer belt  10 . Also, the intermediate transfer belt squeeze roller cleaners  32 Y,  32 M,  32 C and  32 K scrape off the carrier oil collected on the intermediate transfer belt squeeze rollers  31 Y,  31 M,  31 C and  31 K, respectively. Furthermore, the intermediate transfer belt squeeze roller cleaner recovered liquid reservoirs  33 Y,  33 M,  33 C and  33 K accumulate the carrier oil scraped off by the intermediate transfer belt squeeze roller cleaners  32 Y,  32 M,  32 C and  32 K, respectively. 
     The secondary transfer  15  includes a pair of secondary transfer rollers which are disposed spaced a predetermined distance away from each other in the recording material moving direction. A secondary transfer roller, of the pair of secondary transfer rollers, disposed on an upstream side in the recording material moving direction is an upstream side secondary transfer roller  34 . The upstream side secondary transfer roller  34  can be pressed into contact with the belt drive roller  11  through the intermediate transfer belt  10 . Also, a secondary transfer roller, of the pair of secondary transfer rollers, disposed on a downstream side in the recording material moving direction is a downstream side secondary transfer roller  35 . The downstream side secondary transfer roller  35  can be pressed into contact with the driven roller  12  through the intermediate transfer belt  10 . That is, the upstream and downstream side secondary transfer rollers  34  and  35  are arranged in such a way as to bring the recording material into contact with the intermediate transfer belt  10  stretched over the belt drive roller  11  and the driven roller  12 , respectively, and secondarily transfer a color toner image (a liquid developer image) on the intermediate transfer belt  10 , into which the toner images of the colors are combined, to the unshown recording material. In this case, the belt drive roller  11  and the driven roller  12  function as backup rollers of the secondary transfer rollers  34  and  35  respectively, at a secondary transfer time. 
     Consequently, the recording material conveyed to the secondary transfer  15  is brought into close contact with the intermediate transfer belt  10  (a long nip condition) in a predetermined moving area of the recording material from a position of being pressed into contact (a nip starting position) with the upstream side secondary transfer roller  34  and the belt drive roller  11  to a position of being released (a nip finishing position) from the downstream side secondary transfer roller  35  and the driven roller  12 . By this means, as a full-color toner image on the intermediate transfer belt  10  is secondarily transferred to the recording material over a predetermined time in the long nip condition, a good secondary transfer is carried out. In this way, the secondary transfer  15  of this example carries out the secondary transfer by means of a long nip transfer system. Consequently, in the invention, the long nip transfer system is defined as a system wherein, by pressing the intermediate transfer belt  10  stretched between a plurality of rollers spaced a predetermined distance apart (that is, in this example, the belt drive roller  11  and the driven roller  12 ) against the plurality of rollers by means of one or more of transfer rollers (that is, in this example, the upstream side secondary transfer roller  34  and the downstream side secondary transfer roller  35 ), a transfer is carried out using a transfer nip of a predetermined length formed between the plurality of rollers. 
     Also, the secondary transfer  15  includes secondary transfer roller cleaners  36  and  37 , and secondary transfer roller cleaner recovered liquid reservoirs  38  and  39  on the pair of secondary transfer rollers  34  and  35 , respectively. The secondary transfer roller cleaners  36  and  37  scrape off and remove developer remaining on surfaces of the secondary transfer rollers  34  and  35  respectively, after the secondary transfer. Also, the secondary transfer roller cleaner recovered liquid reservoirs  38  and  39  accumulate the developer scraped off from the secondary transfer rollers  34  and  35  by the secondary transfer roller cleaners  36  and  37 , respectively. 
     The intermediate transfer belt cleaning device  16  includes an intermediate transfer belt cleaning roller  40 , a roller cleaning blade  41 , a roller cleaning blade recovered liquid reservoir  42 , an intermediate transfer belt cleaning blade  43 , and an intermediate transfer belt cleaning blade recovered liquid reservoir  44 . 
     The intermediate transfer belt cleaning roller  40  is formed of a conductive elastomer such as conductive rubber. In this example, as shown in  FIGS. 2A and 2B , a diameter d 4  of the intermediate transfer belt cleaning roller  40  is set so as to be the same, or approximately the same, as a diameter d 3  of each photoreceptor cleaning roller  28 Y,  28 M,  28 C and  28 K (d 3 =d 4  or d 3 ≈d 4 ). Also, a hardness of the intermediate transfer belt cleaning roller  40  is set so as to be the same, or approximately the same, as a hardness of the intermediate transfer belt  10 . 
     Furthermore, the intermediate transfer belt cleaning roller  40  is pressed into contact with the intermediate transfer belt  10  at a predetermined nip width w 2 . In this case, the nip width w 2  of the intermediate transfer belt cleaning roller  40  is set so as to be larger than the nip width w 1  of each photoreceptor cleaning roller  28 Y,  28 M,  28 C and  28 K (w 1 &lt;w 2 ). In this case, in this example, a relationship in magnitude between the nip widths w 1  and w 2  is set by making a position L 1 , in which each photoreceptor cleaning roller  28 Y,  28 M,  28 C and  28 K supports each photoreceptor  2 Y,  2 M,  2 C and  2 K, different from a position L 2  in which the intermediate transfer belt cleaning roller  40  supports the driven roller  13 . In this case, as the roller supporting positions L 1  and L 2  are fixed positions, the nip widths w 1  and w 2  of this example are determined by a roller fixed position method. In  FIGS. 2A and 2B , by a thickness t of the intermediate transfer belt  10  being involved, L 2  is slightly much larger than L 1 , but the two nip widths w 1  and w 2  are set so as to be w 1 &lt;w 2 . 
     Then, the intermediate transfer belt cleaning roller  40  is rotated in a direction opposite to that of the intermediate transfer belt  10  (a clockwise direction in  FIG. 2B ), scraping off developer (mainly, solid toner) remaining on the surface of the intermediate transfer belt  10  after the secondary transfer. In this case, the driven roller  13  also functions as a backup roller at an intermediate transfer belt cleaning time. Also, the roller cleaning blade recovered liquid reservoir  42  collects and accumulates the developer scraped off the intermediate transfer belt  10  by the intermediate transfer belt cleaning roller  40 . Furthermore, the intermediate transfer belt cleaning blade  43  removes carrier oil remaining on the intermediate transfer belt  10  after a cleaning by the intermediate transfer belt cleaning roller  40 . Furthermore, the intermediate transfer belt cleaning blade recovered liquid reservoir  44  collects and accumulates the carrier oil scraped off the intermediate transfer belt  10  by the intermediate transfer belt cleaning blade  43 . 
     Also, photoreceptor cleaning biases for cleaning the photoreceptors  2 Y,  2 M,  2 C and  2 K are applied to the photoreceptor cleaning rollers  28 Y,  28 M,  28 C and  28 K, respectively. Also, an intermediate transfer belt cleaning bias for cleaning the intermediate transfer belt  10  is applied to the intermediate transfer belt cleaning roller  40 . That is, the photoreceptor cleaning rollers  28 Y,  28 M,  28 C and  28 K, and the intermediate transfer belt cleaning roller  40  are all configured as roller bias cleaners. Then, the photoreceptor cleaning biases and the intermediate transfer belt cleaning bias are biases capable of removing solid toner from the liquid developer from the photoreceptors  2 Y,  2 M,  2 C and  2 K, and the intermediate transfer belt  10 , respectively, after a transfer. In this case, in the image forming apparatus  1  of this example, as shown in  FIG. 1 , the photoreceptor cleaning biases and intermediate transfer belt cleaning bias are all applied at the same voltage from one and the same power supply  45 . 
     According to the image forming apparatus  1  of this example configured in this way, in the same way as with the heretofore known one heretofore described, solid toner adheres to the intermediate transfer belt  10  with an adhesion greater than an adhesion to the photoreceptors  2 Y,  2 M,  2 C and  2 K, but it is possible to efficiently remove solid toner adhering to each photoreceptor  2 Y,  2 M,  2 C and  2 K after the primary transfer, and solid toner adhering to the intermediate transfer belt  10  after the secondary transfer, using the biases applied to each photoreceptor cleaning roller  28 Y,  28 M,  28 C and  28 K, and the intermediate transfer belt cleaning roller  40 . 
     In particular, the nip width w 2  of the intermediate transfer belt cleaning roller  40  is set so as to be larger than the nip width w 1  of each photoreceptor cleaning roller  28 Y,  28 M,  28 C and  28 K. By this means, it is possible to set a solid toner nip transit time (a solid toner electrophoresis time) for the intermediate transfer belt  10 , which has a high solid toner adhesion and is hard to clean, so as to be longer than a solid toner nip transit time for each photoreceptor  2 Y,  2 M,  2 C and  2 K. Consequently, it is possible to more effectively remove solid toner on the intermediate transfer belt  10  which is hard to remove. Also, as it is possible, by this means, to make the bias applied to the intermediate transfer belt cleaning roller  40  comparatively low, it is possible to suppress an effect on the intermediate transfer belt  10  due to the bias. As a result, as a charging of the intermediate transfer belt  10  is suppressed, it is possible to effectively carry out an image formation after a cleaning of the intermediate transfer belt  10 . 
     Furthermore, as the heretofore described nip widths w 1  and w 2  are made different from each other by adjusting the photoreceptor cleaning roller  28 Y,  28 M,  28 C and  28 K and intermediate transfer belt cleaning roller  40  supporting positions, it is possible to easily carry out a setting of the nip widths w 1  and w 2 . Then, by setting the nip widths w 1  and w 2  in such a way that the photoreceptors  2 Y,  2 M,  2 C and  2 K, and the intermediate transfer belt  10  can be cleaned at the same bias, it is possible to supply each bias using one and the same power supply  45 . Consequently, as well as it being possible to reduce a number of parts, it is possible to effectively realize a miniaturization of the apparatus. 
     Furthermore, the intermediate transfer belt cleaning blade  43  is provided which, being brought into abutment with the intermediate transfer belt  10 , removes a liquid developer remaining on the intermediate transfer belt  10  after a cleaning by the intermediate transfer belt cleaning roller  40 . In this case, most of the liquid developer remaining on the intermediate transfer belt  10  is liquid carrier after a cleaning of the solid toner from the liquid developer by the intermediate transfer belt cleaning roller  40 . Consequently, as the intermediate transfer belt cleaning blade  43  simply removes the liquid carrier, it is possible to reduce a pressure at which the intermediate transfer belt cleaning blade  43  abuts against the intermediate transfer belt  10 . Although the intermediate transfer belt  10  is generally softer than each photoreceptor, damage to the intermediate transfer belt  10  being suppressed by the pressure at which the intermediate transfer belt cleaning blade  43  abuts against the intermediate transfer belt  10  being reduced, it is possible to achieve an increase in life span of the intermediate transfer belt  10 . 
       FIGS. 3A and 3B  are partial diagrammatic views which are similar to  FIGS. 2A and 2B , respectively, schematically showing another example of the embodiment of the image forming apparatus according to the invention. 
     In an image forming apparatus  1  of this example, as shown in  FIG. 3A , photoreceptor cleaning roller biasing units  46 Y,  46 M,  46 C and  46 K are provided which, being formed of, for example, springs or the like, bias the photoreceptor cleaning rollers  28 Y,  28 M,  28 C and  28 K toward the corresponding photoreceptors  2 Y,  2 M,  2 C and  2 K, respectively. Consequently, the nip width w 1  between each photoreceptor cleaning roller  28 Y,  28 M,  28 C and  28 K, and each photoreceptor  2 Y,  2 M,  2 C and  2 K, is set depending on a bias force of each photoreceptor cleaning roller biasing unit  46 Y,  46 M,  46 C and  46 K. 
     Also, as shown in  FIG. 3B , an intermediate transfer belt cleaning roller biasing unit  47  is provided which, being formed of, for example, a spring or the like, biases the intermediate transfer belt cleaning roller  40  toward the intermediate transfer belt  10 . Consequently, a nip width w 2  (&gt;w 1 ) between the intermediate transfer belt cleaning roller  40  and the intermediate transfer belt  10  is set depending on a bias force of the intermediate transfer belt cleaning roller biasing unit  47 . In this case, as the bias force of each roller is a fixed load, the nip widths w 1  and w 2  in this example are determined by a roller fixed load method. 
     In this example, as each photoreceptor cleaning roller biasing unit  46 Y,  46 M,  46 C and  46 K, and the intermediate transfer belt cleaning roller biasing unit  47  are provided, a number of parts is increased in comparison with the heretofore described example. Other configurations and working effects of the image forming apparatus  1  of this example are the same as those of the heretofore described example. 
     As a method of setting the heretofore described two nip widths w 1  and w 2  so as to be w 1 &lt;w 2 , in the same way as in each heretofore described example, a diameter d 3  of each photoreceptor cleaning roller  28 Y,  28 M,  28 C and  28 K is set so as to be the same, or approximately the same, as a diameter d 4  of the intermediate transfer belt cleaning roller  40 . Furthermore, a hardness of the intermediate transfer belt cleaning roller  40  is set so as to be lower than a hardness of diameter d 4  each of photoreceptor cleaning roller  28 Y,  28 M,  28 C and  28 K. By this means too, it is possible to set the two nip widths w 2  and w 1  so as to be w 1 &lt;w 2 . Consequently, it is possible to obtain the same working effect as that of the heretofore described first example by applying the diameter d 3  of each photoreceptor cleaning roller  28 Y,  28 M,  28 C and  28 K, and the diameter d 4  of the intermediate transfer belt cleaning roller  40 , to the image forming apparatus  1  of the heretofore described example shown in  FIG. 1 . 
       FIG. 4  is a diagrammatic view which is similar to  FIG. 1 , schematically showing one portion of another example of the embodiment of the image forming apparatus according to the invention. 
     As shown in  FIG. 4 , with an image forming apparatus  1  of this example, the intermediate transfer belt  10  stretched between the belt drive roller  11  and the driven roller  12  is pressed against the belt drive roller  11  and the driven roller  12  by one secondary transfer roller  50 . That is, the secondary transfer roller  50 , being disposed between the belt drive roller  11  and the driven roller  12 , presses the intermediate transfer belt  10  in such a way as to push it into a space between the belt drive roller  11  and the driven roller  12  inside a tangent line common to the belt drive roller  11  and the driven roller  12 . By this means, a long nip transfer system is configured. 
     Also, the transfer roller  50  is also provided with the secondary transfer roller cleaner  51  and the secondary transfer roller cleaner recovered liquid reservoir  52 , in the same way as heretofore described. 
     Other configurations and working effects of the image forming apparatus  1  of this example are the same as those of the examples shown one in each of  FIGS. 1 to 3 . 
     Next, a description will be given of specific examples of the invention. 
     One specific example of each of a photoreceptor and an intermediate transfer belt, which is an intermediate transfer medium, in the image forming apparatus of the embodiment according to the invention is shown in Table 2. 
     
       
         
           
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
             
            
               
                 Photoreceptor 
                 Photosensitive layer 
                 Amorphous silicon 
               
            
           
           
               
               
               
               
            
               
                   
                 Cleaning 
                 Material 
                 Conductive urethane rubber + 
               
               
                   
                 roller 
                   
                 superficial layer fluorine resin coat 
               
               
                   
                   
                 Resistance 
                 Log7Ω 
               
               
                   
                   
                 Roller diameter 
                 φ20 
               
               
                   
                   
                 Nip width 
                 2 mm 
               
               
                   
                   
                   
                 (In case of fixed position method) 
               
               
                   
                   
                   
                 Biting amount 0.1 mm 
               
               
                   
                   
                   
                 (In case of fixed load method) 
               
               
                   
                   
                   
                 Bias load 1 kgf 
               
               
                   
                   
                 Rubber hardness 
                 JIS-A55° 
               
               
                   
                   
                 Applied voltage 
                 −300 to −1000 V 
               
               
                 Intermediate 
                 Belt 
                   
                 Substrate: polyimide, thickness 100 μm 
               
               
                 transfer medium 
                   
                   
                 Elastic layer: conductive urethane 
               
               
                   
                   
                   
                 rubber, thickness 200 μm, hardness 
               
               
                   
                   
                   
                 JIS-A30° 
               
               
                   
                   
                   
                 Superficial layer: fluorine resin coat, 
               
               
                   
                   
                   
                 thickness 10 μm 
               
               
                   
                 Cleaning 
                 Material 
                 Conductive urethane rubber + 
               
               
                   
                 roller 
                   
                 superficial layer fluorine resin coat 
               
               
                   
                   
                 Resistance 
                 Log7Ω 
               
               
                   
                   
                 Roller diameter 
                 φ20 
               
               
                   
                   
                 Nip width 
                 5 mm 
               
               
                   
                   
                   
                 (In case of fixed position method) 
               
               
                   
                   
                   
                 Biting amount 0.3 mm 
               
               
                   
                   
                   
                 (In case of fixed load method) 
               
               
                   
                   
                   
                 Bias load 4 kgf 
               
               
                   
                   
                 Rubber hardness 
                 JIS-A30° 
               
               
                   
                   
                 Applied voltage 
                 −300 to −1000 V 
               
               
                   
               
            
           
         
       
     
     As shown in Table 2, a photoreceptor, using amorphous silicon as a photosensitive layer, in the same way as heretofore known, is set so as to have an outer diameter of φ 40 mm. Also, a photoreceptor cleaning roller, using conductive urethane rubber as a material, is formed by providing a superficial layer fluorine resin coat on a surface of the conductive urethane rubber. At this time, as well as a resistance being set at Log 7Ω, a roller diameter d 3  is set at φ20 mm. Also, a nip width w 1  between the photoreceptor and the photoreceptor cleaning roller is set at 2 mm. In order to obtain the nip width w 1 , a biting amount is set at 0.1 mm in the fixed position method. Also, a bias load is set at 1 kgf in the fixed load method. Furthermore, a hardness of the photoreceptor cleaning roller (a hardness of the conductive urethane rubber) is set at JIS-A55°. Furthermore, a bias applied to the photoreceptor cleaning roller is set at −300 to −1000V. 
     Also, the intermediate transfer belt  10  is formed as a three-layer structure of a substrate, an elastic layer on a surface of the substrate, and a superficial layer on a surface of the elastic layer. Polyimide of 100 μm thickness is used as the substrate. Also, comparatively soft conductive urethane rubber of 200 μm thickness and JIS-A30° hardness is used as the elastic layer. Furthermore, a fluorine resin coat of 10 μm thickness is used as the superficial layer. Furthermore, the intermediate transfer belt cleaning roller, as a material of which conductive urethane rubber is used, is formed by providing a superficial layer fluorine resin coat on a surface of the conductive urethane rubber. At this time, as well as a resistance being set at Log 7Ω, a roller diameter d 4  is set at φ20 mm. Meanwhile, a diameter of the driven roller  13  is set at φ 40 mm. Then, a nip width w 2  between the intermediate transfer belt  10  and the intermediate transfer belt cleaning roller is set at 5 mm. In order to obtain the nip width w 2 , a biting amount is set at 0.3 mm in the fixed position method. Also, a bias load is set at 4 kgf in the fixed load method. Furthermore, a hardness of the intermediate transfer belt cleaning roller (a hardness of the conductive urethane rubber) is set at JIS-A30°. Furthermore, a bias applied to the intermediate transfer belt cleaning roller is set at −300 to −1000V. 
     Next, a description will be given of an example 1, and comparison examples 1 and 2, in which an experiment has been made on a cleaning property in the image forming apparatus  1  of the embodiment of the invention. A color printer LP9000C made by Seiko Epson Corporation is used in the experiment. In this case, a portion of the color printer LP9000C differing from the image forming apparatus  1  shown in  FIG. 1  has been modified. 
     Firstly, conditions of a photoreceptor cleaning and an intermediate transfer belt cleaning, which have been used in the experiment, are shown in Table 3 for the example 1, and in Table 4 and Table 5 for the comparison examples 1 and 2. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                 Photoreceptor 
                 Intermediate transfer belt 
               
               
                   
                 cleaning 
                 cleaning 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 Member to be cleaned 
                 Amorphous silicon 
                 Substrate: polyimide 100 μm 
               
               
                   
                 φ78 
                 Elastic layer: conductive 
               
               
                   
                   
                 urethane rubber 200 μm, 
               
               
                   
                   
                 JIS-A30° 
               
               
                   
                   
                 Superficial layer: fluorine 
               
               
                   
                   
                 resin coat 10 μm 
               
            
           
           
               
               
               
               
            
               
                 Bias 
                 (V) 
                 −300 
                 Experimental range: −600 
               
               
                   
                   
                 (Settable range: −200 
                 to −1400 
               
               
                   
                   
                 to −400) 
                 (Good range: −800 to −1200) 
               
            
           
           
               
               
               
               
               
            
               
                 Roller 
                 Diameter 
                 (mm) 
                 φ20 
                 φ25 
               
               
                   
                 Wall thickness 
                 (mm) 
                 t2.5 
                 t5 
               
               
                   
                 Rubber hardness 
                 (JIS-A) 
                 30° 
                 30° 
               
               
                   
                 Resistance 
                 (Ω) 
                 Log7 
                 Log7 
               
            
           
           
               
               
               
            
               
                 Contact method 
                 Fixed position method 
                 Fixed load method 
               
               
                   
                 Bite 0.1 mm 
                 10 kgf 
               
            
           
           
               
               
               
               
            
               
                 Nip width 
                 (mm) 
                 2 
                 4 
               
               
                 Length in axial direction 
                 (mm) 
                 368 
                 352 
               
               
                   
               
            
           
         
       
     
     In the example 1 shown in Table 3, with respect to the photoreceptor cleaning, a photoreceptor which is a member to be cleaned, using amorphous silicon as a photosensitive layer, is set so as to have a diameter of φ 78 mm, Also, for a photoreceptor cleaning roller, a diameter is set at φ 20 mm, a rubber wall thickness t of a superficial layer at 2.5 mm, a rubber hardness at 30° on JIS-A scale, and an electrical resistance at Log 7Ω. A bias applied between the photoreceptor and the photoreceptor cleaning roller is set at −300V (in the present experimental apparatus, a bias settable range is from −200 to −400V). A method of bringing the photoreceptor cleaning roller into contact with the photoreceptor is the fixed position method, and a biting amount is set at 0.1 mm. A nip width w_at this time is 2 mm. A length of a nip portion in an axial direction is 368 mm. 
     A description will be given of a nip width measuring method in the photoreceptor cleaning. 
     Firstly, as shown in  FIG. 5A , an arc shaped molding rubber body of a predetermined width, which is formed of a material into which base paste and catalyst pastes are kneaded, is provided standing on the photoreceptor used in the experiment in a circumferential direction of the photoreceptor. This kneaded material is a GC Corporation&#39;s Exafine (trade name) injection type (hydrophilic vinyl silicon). Next, as shown in  FIG. 5B , the photoreceptor cleaning roller is pressed in such a way that a direction of axis thereof becomes a direction of axis of the photoreceptor, until an amount by which the photoreceptor cleaning roller bites into the photoreceptor reaches 0.1 mm. Then, after leaving in this condition for three to six minutes, the photoreceptor cleaning roller is removed, as shown in  FIG. 5C , and a width of a portion of an impression in the molding rubber body which corresponds to an outer peripheral surface of the photoreceptor is measured with a caliper. The width measured with the caliper is the nip width. 
     Also, with respect to the intermediate transfer belt cleaning, a substrate of an intermediate transfer belt which is a member to be cleaned is polyimide of 100 μm thickness, an elastic layer thereon is conductive urethane rubber of 200 μm thickness and 30° JIS-A hardness, and furthermore, a superficial layer thereon is a fluorine resin coat of 10 μm thickness. Also, a diameter of an intermediate transfer belt cleaning roller is set at φ 25 mm, a rubber wall thickness t of superficial layer at 5 mm, a rubber hardness at 30° on the JIS-A scale, and an electrical resistance at Log 7Ω. A belt cleaning bias setting range (experimental range) applied between the intermediate transfer belt and the intermediate transfer belt cleaning roller is from −600V to −1400V, and a good range (an OD value of 0.1 or less) in which it is possible to obtain a good cleaning is from −800V to −1200V. A method of bringing the intermediate transfer belt cleaning roller into contact with the intermediate transfer belt is the fixed load method, and a load of the roller is set at 10 kgf. A nip width w 2  at this time is 4 mm (w 1 &lt;w 2 ). A length of a nip portion in an axial direction is 352 mm. 
     A description will be given of a nip width measuring method in the intermediate transfer belt cleaning. 
     This nip width is measured by the heretofore described measuring method shown in  FIGS. 5A to 5C . In this case, in the same way as heretofore described, a molding rubber body is provided standing on an intermediate transfer belt which, as well as being a member to be cleaned, is wound around the driven roller  13 . The intermediate transfer belt cleaning roller is pressed against the molding rubber body at a load of 10 kgf until the intermediate transfer belt cleaning roller comes into contact with the intermediate transfer belt. The nip width is measured with a caliper, in the same way as heretofore described. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 4 
               
               
                   
                   
               
               
                   
                 Photoreceptor 
                 Intermediate transfer belt 
               
               
                   
                 cleaning 
                 cleaning 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 Member to be cleaned 
                 Amorphous silicon φ78 
                 Substrate: polyimide 
               
               
                   
                   
                 100 μm 
               
               
                   
                   
                 Elastic layer: conductive 
               
               
                   
                   
                 urethane rubber 200 μm, 
               
               
                   
                   
                 JIS-A30° 
               
               
                   
                   
                 Superficial layer: fluorine 
               
               
                   
                   
                 resin coat 10 μm 
               
            
           
           
               
               
               
               
            
               
                 Bias 
                 (V) 
                 −300 
                 Experimental range: −600 
               
               
                   
                   
                 (Settable range: −200 
                 to −1400 
               
               
                   
                   
                 to −400) 
                 No good area 
               
            
           
           
               
               
               
               
               
            
               
                 Roller 
                 Diameter 
                 (mm) 
                 φ20 
                 φ20 
               
               
                   
                 Wall thickness 
                 (mm) 
                 t2.5 
                 t2.5 
               
               
                   
                 Rubber hardness 
                 (JIS-A) 
                 30° 
                 30° 
               
               
                   
                 Resistance 
                 (Ω) 
                 Log7 
                 Log7 
               
            
           
           
               
               
               
            
               
                 Contact method 
                 Fixed position method 
                 Fixed position method 
               
               
                   
                 Bite 0.1 mm 
                 Bite 0.1 mm 
               
            
           
           
               
               
               
               
            
               
                 Nip width 
                 (mm) 
                 W1 = 2 
                 W2 = 1.5 
               
               
                 Length in axial direction 
                 (mm) 
                 368 
                 352 
               
               
                   
               
            
           
         
       
     
     In the comparison example 1 shown in Table 4, a photoreceptor cleaning is the same as in the heretofore described example 1. Also, with respect to an intermediate transfer belt cleaning, an intermediate transfer belt, which is a member to be cleaned, is the same as in the heretofore described example 1. Also, for an intermediate transfer belt cleaning roller, a diameter is set at +20 mm, a rubber wall thickness t of a superficial layer at 2.5 mm, a rubber hardness at 300 on the JIS-A scale, and an electrical resistance at Log 7ω. A belt cleaning bias setting range (experimental range) applied between the intermediate transfer belt and the intermediate transfer belt cleaning roller is from −600V to −1400V, and there exists no good range (OD value of 0.1 or less) in which it is possible to obtain a good cleaning. No bias is applied between the intermediate transfer belt and the intermediate transfer belt cleaning roller. A method of bringing the intermediate transfer belt cleaning roller into contact with the intermediate transfer belt is the fixed position method, and a biting amount of the roller is set at 0.1 mm. A nip width w 2  is 1.5 mm (w 1 &gt;w 2 ). A length of a nip portion in an axial direction is 352 mm. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 5 
               
               
                   
                   
               
               
                   
                 Photoreceptor 
                 Intermediate transfer belt 
               
               
                   
                 cleaning 
                 cleaning 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 Member to be cleaned 
                 Amorphous silicon 
                 Substrate: polyimide 100 μm 
               
               
                   
                 φ78 
                 Elastic layer: conductive 
               
               
                   
                   
                 urethane rubber 200 μm, 
               
               
                   
                   
                 JIS-A30° 
               
               
                   
                   
                 Superficial layer: fluorine resin 
               
               
                   
                   
                 coat 10 μm 
               
            
           
           
               
               
               
               
            
               
                 Bias 
                 (V) 
                 −300 
                 Experimental range: −600 
               
               
                   
                   
                 (Settable range: −200 
                 to −1400 
               
               
                   
                   
                 to −400) 
                 (Good range: −800 to −1200) 
               
            
           
           
               
               
               
               
               
            
               
                 Roller 
                 Diameter 
                 (mm) 
                 φ25 
                 φ25 
               
               
                   
                 Wall thickness 
                 (mm) 
                 t5 
                 t5 
               
               
                   
                 Rubber hardness 
                 (JIS-A) 
                 30° 
                 30° 
               
               
                   
                 Resistance 
                 (Ω) 
                 Log7 
                 Log7 
               
            
           
           
               
               
               
            
               
                 Contact method 
                 Fixed load method 
                 Fixed load method 
               
               
                   
                 10 kgf 
                 10 kgf 
               
            
           
           
               
               
               
               
            
               
                 Nip width 
                 (mm) 
                 W1 = 4.5 
                 W2 = 4 
               
               
                 Length in axial direction 
                 (mm) 
                 368 
                 352 
               
               
                   
               
            
           
         
       
     
     In the comparison example 2 shown in  FIGS. 5A to 5C , with respect to the photoreceptor cleaning, for a photoreceptor cleaning roller, a diameter is set at +25 mm, and a rubber wall thickness t of a superficial layer at 5 mm. A method of bringing the photoreceptor cleaning roller into contact with a photoreceptor is the fixed load method, and a load of the roller is set at 10 kgf. Other points regarding the photoreceptor cleaning are the same as in the heretofore described example 1. A nip width w 1  at this time is 4.5 mm. A length of a nip portion in an axial direction is 368 mm. Also, with respect to the intermediate transfer belt cleaning, this is the same as in the heretofore described example 1. 
     Non-cleaned amounts (OD values) in the example 1 and the comparison examples 1 and 2 are shown in  FIGS. 6 to 8 , respectively. 
     As shown in  FIG. 6 , in the example 1, in both the photoreceptor cleaning and the intermediate transfer belt cleaning, an OD value is comparatively low, and a cleaning is good. Meanwhile, as shown in  FIG. 7 , in the comparison example 1, the OD value in the photoreceptor cleaning is comparatively low, and it is possible to obtain a good cleaning property, while the OD value in the intermediate transfer belt cleaning is comparatively high, and it is not possible to obtain a good cleaning property. Also, as shown in  FIG. 8 , in the comparison example 2, in the same way as in the example 1, in both the photoreceptor cleaning and the intermediate transfer belt cleaning, it is possible to obtain a good cleaning property. However, in the comparison example 2, as a time of nipping between the photoreceptor and the photoreceptor cleaning roller is long, an electrical charge is injected into the photoreceptor. For this reason, it adversely affects a next image formation. 
     From the above experimental results, it has been confirmed that it is possible to obtain a desired advantage by means of the image forming apparatus of the embodiment of the invention. 
       FIG. 9  partially shows still another example of the embodiment of the invention. 
     In an image forming apparatus  1  of this example, as shown in  FIG. 9 , the intermediate transfer belt cleaning roller  40  is disposed on a driven roller  12  side of a contact point δ at which an imaginary tangent line (shown by the two-dot chain line) common to the secondary transfer  15  side driven roller  12  and the intermediate transfer belt cleaning device  16  side driven roller  13  makes contact with the driven roller  13 . 
     That is, the intermediate transfer belt cleaning roller  40  is pressed into contact on the driven roller  12  side of the contact point δ of the intermediate transfer belt  10  when viewed in cross-section of a central portion of the driven roller  12  in an axial direction. By the intermediate transfer belt cleaning roller  40  being pressed into contact with the intermediate transfer belt  10  in this way, the intermediate transfer belt  10  assumes a position, shown by the solid line, inside the common tangent line shown by the two-dot chain line. Consequently, the intermediate transfer belt  10  is wound partially around the intermediate transfer belt cleaning roller  40 . By this means, the intermediate transfer belt  10  has a nip width w 2  between the intermediate transfer belt cleaning roller  40  and the intermediate transfer belt  10  set so as to be larger than in the heretofore described examples. Also, an amount by which the intermediate transfer belt  10  is wound around the driven roller  13  is set so as to be larger than in the heretofore described examples. The driven roller  13 , in the same way as in the heretofore described examples, functions as a backup roller of the intermediate transfer belt cleaning roller  40 . 
     Other configurations of the image forming apparatus  1  of this example are the same as those of the heretofore described examples. 
     According to the image forming apparatus  1  of this example, the nip width w 2  between the intermediate transfer belt cleaning roller  40  and the intermediate transfer belt  10  is set so as to be larger than in the heretofore described examples. Consequently, as well as it being possible to reduce an intermediate transfer belt  10  cleaning bias per unit area, it is possible to increase a time for which the intermediate transfer belt cleaning roller  40  makes contact with the intermediate transfer belt  10 . By this means, even in the event that the intermediate transfer belt  10  cleaning bias is set so as to be comparatively high, it is possible to effectively clean the intermediate transfer belt  10  while suppressing an effect on the intermediate transfer belt  10  due to the cleaning bias. 
     Meanwhile, in the photoreceptor cleaning, as the nip width w 1  between each photoreceptor  2 Y,  2 M,  2 C and  2 K, and each photoreceptor cleaning roller  28 Y,  28 M,  28 C and  28 K is comparatively small, as well as each photoreceptor  2 Y,  2 M,  2 C and  2 K cleaning bias per unit area increasing, a time for which each photoreceptor cleaning roller  28 Y,  28 M,  28 C and  28 K makes contact with each photoreceptor  2 Y,  2 M,  2 C and  2 K decreases. At this time, by setting each photoreceptor  2 Y,  2 M,  2 C and  2 K cleaning bias so as to be lower than the intermediate transfer belt  10  cleaning bias, even in the event that each photoreceptor  2 Y,  2 M,  2 C and  2 K cleaning bias per unit area is high, it is possible to effectively clean each photoreceptor  2 Y,  2 M,  2 C and  2 K while suppressing an effect on each photoreceptor  2 Y,  2 M,  2 C and  2 K due to the cleaning bias. 
     The intermediate transfer medium can also be formed of a cylindrical drum, apart from the endless intermediate transfer belt. The invention is capable of various other modifications within the scope of the matters described in the claims. 
     The entire disclosure of Japanese Patent Application Nos: 2008-64087, filed Mar. 13, 2008 and 2008-239657, filed Sep. 18, 2008 are expressly incorporated by reference herein.