Patent Publication Number: US-7587164-B2

Title: Cleaning device, image carrier unit and image-forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2006-297007 filed on Oct. 31, 2006. 
   BACKGROUND 
   Technical Field 
   The present invention relates to a cleaning device to be used in an image-forming apparatus using the electrophotographic system, and an image carrier unit and image-forming apparatus which use the device. 
   SUMMARY 
   According to an aspect of the invention, there is provide a cleaning device including a first cleaning member that includes a surface layer formed by a cloth made of conductive fibers, contacts an image carrier holding an image and cleans the image carrier with a predetermined voltage applied to the first cleaning member; a second cleaning member that contacts the image carrier and cleans the image carrier with a predetermined voltage applied to the second cleaning member; a first collection member that contacts the first and second cleaning members and collects adhering substances from the first and second cleaning member with a predetermined voltage applied to the first collection member; and a second collection member that contacts the second cleaning member and collects adhering substances form the second cleaning member with a predetermined voltage applied to the second collection member. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Exemplary embodiment(s) of the present invention will be described in detail based on the following figures, wherein: 
       FIG. 1  is a view showing the configuration of a color printer that is an example of an image-forming apparatus to which the invention is applied; 
       FIG. 2  is a view showing the configuration of an image-forming unit; 
       FIG. 3  is a view showing the configuration of a drum cleaner in the exemplary embodiment; 
       FIG. 4  is a sectional view of a first cleaning roll; 
       FIG. 5  is a diagram illustrating relationships among axial lengths of cleaning rolls, collection rolls, and scrapers; 
       FIG. 6  is a view of a configuration example in which the collection rolls are placed so that a first collection roll is not positioned in a toner drop path; 
       FIG. 7  is a view showing an example of bias voltages applied to the rolls of the drum cleaner; 
       FIG. 8  is a view shows results of measurements of an amount of toner which is held in a fiber layer of the first cleaning roll; 
       FIG. 9  is a view showing a chart used in an experiment; 
       FIG. 10  is a view for evaluating relationships between the held amount of toner held in the fiber layer of the first cleaning roll and the occurrence or non-occurrence of image deletion due to discharge products of the surface of the photosensitive drum, etc; 
       FIG. 11  is a view showing results of measurements in which the amount of toner held by the fiber layer is measured in the case where a bias voltage supplied to the first cleaning roll and that supplied to the first collection roll are changed; and 
       FIG. 12  is a view showing the configuration of another color printer, 
   

   wherein  1  denotes Color Printer (Image-forming Apparatus),  31  denotes Photosensitive Drum (Image Carrier),  33  denotes Developer (Developing Portion),  36  denotes Drum Cleaner (Cleaning Device, Toner Removing Portion),  365 A denotes First Cleaning Roll (First Cleaning Member),  365 B denotes Second Cleaning Roll (Second Cleaning Member),  365   a  denotes Fiber Layer (Surface Layer),  365   b  denotes Elastic Layer,  366 A denotes First Collection roll (First Collection member),  366 B denotes Second Collection roll (Second Collection member),  41  denotes Intermediate Transfer Belt (Transfer Member),  42  denotes Primary Transfer Roll (Transferring Portion),  60  denotes Controlling Portion (Controlling Unit),  65  denotes Power Source Portion,  651 A denotes First Cleaning Roll Bias Power Source,  651 B denotes Second Cleaning Roll Bias Power Source,  652 A denotes First Collection roll Bias Power Source, and  652 B denotes Second Collection roll Bias Power Source. 
   DETAILED DESCRIPTION 
   Hereinafter, an exemplary embodiment of the invention will be described in detail with reference to the accompanying drawings. 
     FIG. 1  is a view showing the configuration of a color printer  1  as an example of an image-forming apparatus to which the exemplary embodiment is applied.  FIG. 2  is a view showing the configuration of an image-forming unit. 
   The color printer  1  shown in  FIG. 1  is configured by: an image-forming process portion  20  which is configured as a so-called tandem type one, and which performs image formation correspondingly with image data of respective colors; an image-processing portion  22  which is connected to, for example, a personal computer (PC)  3  and an image-reading apparatus  4  such as a scanner, and which applies a predetermined image process on the image data received therefrom; a controlling portion  60  which controls various portions constituting the color printer  1 ; and a power source portion  65  which supplies a power to various portions of the color printer  1 . 
   The image-forming process portion  20  includes four image-forming units  30 Y,  30 M,  30 C,  30 K (hereinafter, generally referred to as “image-forming units  30 ”) which are arranged in a parallel manner at constant intervals. 
   As shown in  FIG. 2 , each of the image-forming units  30  includes: a photosensitive drum  31  serving as an image carrier on which an electrostatic latent image is formed while the image carrier rotates in the direction of the arrow A, and a toner image is then formed; a charger  32  which uniformly charges the surface of the photosensitive drum  31  to a predetermined potential, and which is configured by, for example, a scorotron; a developer  33  serving as a developing portion which toner-develops the electrostatic latent image formed on the photosensitive drum  31 , to form the image as a toner image; a pre-cleaning charger  34  which, after the toner image is transferred onto an intermediate transfer belt  41  by a primary transferring portion T 1 , causes a toner and the like remaining on the surface of the photosensitive drum  31  to have the same charge polarity (for example, a minus polarity); a destaticizing lamp  35  which removes surface charges from the photosensitive drum  31  after the transfer; a drum cleaner  36  which is an example of a cleaning device for cleaning a toner and the like remaining on the surface of the photosensitive drum  31  after the transfer; and a pre-charge lamp  37  which erases latent image hysteresis produced before charging. 
   The image-forming units  30 Y,  30 M,  30 C,  30 K are configured in a substantially same manner except the toner stored in the developer  33 . 
   The unit configuration of the image-forming process portion  20  is not restricted to the image-forming units  30 . Alternatively, an image carrier unit may be configured by integrating the photosensitive drum  31  with the drum cleaner  36 , and the portion may be configured so as to be replaceable in the unit of the image carrier unit. Such image carrier units may constitute the image-forming units  30 . 
   The image-forming process portion  20  further includes: a laser exposing device  26  which exposes the photosensitive drum  31  disposed in each of the image-forming units  30 ; the intermediate transfer belt  41  serving as a transfer member onto which color toner images formed on the photosensitive drums  31  of the image-forming units  30  are multiple-transferred; primary transfer rolls  42  serving as a transferring portion which causes the color toner images formed by the image-forming units  30  to be sequentially transferred (primarily transferred) onto the intermediate transfer belt  41  in the primary transferring portions T 1 ; a secondary transfer roll  40  which causes the superimposed toner image transferred onto the intermediate transfer belt  41  to be collectively transferred (secondarily transferred) in a secondary transferring portion T 2  onto a recording sheet P; and a fixing device  80  which fixes the secondarily transferred toner image onto the recording sheet P. 
   The intermediate transfer belt  41  is stretched in a path circulating through the image-forming units  30 Y,  30 M,  30 C,  30 K by: a driving roll  45 ; a backup roll  46  which supports the intermediate transfer belt  41  in the secondary transferring portion T 2  from the back side; an idle roll  47  which supports the intermediate transfer belt  41 ; and the like, and. circularly moved in the direction of the arrow B in  FIG. 1  by rotation of the driving roll  45  caused by rotating unit (not shown). The intermediate transfer belt  41  includes a belt cleaner  50  which is disposed in contact therewith. 
   The color printer further includes a sheet tray  71  which stores recording sheets P serving as recording media, and a recording-sheet conveying mechanism which conveys the recording sheets P stored in the sheet tray  71 . 
   The recording-sheet conveying mechanism is configured by: a pickup roll  72  which takes out the recording sheet P from the sheet tray  71 ; a conveyor roll  73  which conveys the recording sheet P to the secondary transferring portion T 2 ; a register roll  74  which defines the position of the recording sheet P; a conveyor belt  75  which conveys the recording sheet from the secondary transferring portion T 2  to the fixing device  80 ; and the like. 
   In the color printer  1  of the exemplary embodiment, an image-forming operation is implemented in the image-forming process portion  20  under the control of the controlling portion  60 . Specifically, image data of respective color components supplied from the personal computer  3  or the image-reading apparatus  4  are subjected to a predetermined imaging process by the image-processing portion  22 , and then supplied to the laser exposing device  26 . The laser exposing device  26  scan-exposes the photosensitive drums  31  of the image-forming units  30 . In the image-forming unit  30 Y for yellow (Y), for example, the photosensitive drum  31  which is uniformly charged to the predetermined potential by the charger  32  is scan-exposed by a laser beam which is modulated by the laser exposing device  26  on the basis of image data of the yellow (Y) component, whereby an electrostatic latent image of the yellow (Y) component is formed on the photosensitive drum  31 . The formed electrostatic latent image is developed by the developer  33 , so that a toner image of yellow (Y) is formed on the photosensitive drum  31 . Also in the image-forming units  30 M,  30 C,  30 K, similarly, toner images of magenta (M), cyan (C), and black (K) are formed. In the exemplary embodiment, the toner is charged to the minus polarity by the developer  33 . 
   The color toner images formed in the respective image-forming units  30  are sequentially electrostatically transferred by the primary transfer rolls  42  onto the intermediate transfer belt  41  which is circularly moved in the direction of the arrow B in  FIG. 1 , whereby a toner image (superimposed toner image) in which the color toner images are superimposed is formed on the intermediate transfer belt  41 . In accordance with the movement of the intermediate transfer belt  41 , the superimposed toner image is conveyed to the secondary transferring portion T 2  in which the secondary transfer roll  40  and the backup roll  46  are disposed. On the other hand, the recording sheets P are taken out from the sheet tray  71  by the pickup roll  72 , and conveyed one by one to the position of the register roll  74  by the conveyor roll  73 . 
   When the superimposed toner image is conveyed to the secondary transferring portion T 2 , the recording sheet P is supplied from the register roll  74  to the secondary transferring portion T 2  in timing with the conveyance of the toner image to the secondary transferring portion T 2 . In the secondary transferring portion T 2 , the superimposed toner image is collectively transferred (secondarily transferred) onto the recording sheet P by the function of the transfer electric field formed between the secondary transfer roll  40  and the backup roll  46 . 
   Then, the recording sheet P onto which the superimposed toner image is transferred is separated from the intermediate transfer belt  41 , and conveyed to the fixing device  80  while being attracted and supported by the conveyor belt  75 . The unfixed toner image on the recording sheet P which is conveyed to the fixing device  80  is subjected to the fixing process by the fixing device  80  by means of heat and pressure to be fixed onto the recording sheet P. The recording sheet P on which the fixed image is formed is conveyed to a discharged sheet stack portion  91  which is disposed in a discharge portion of the image-forming apparatus. On the other hand, a toner (post-transfer residual toner) adheres to the intermediate transfer belt  41  after the secondary transfer is removed by the belt cleaner  50  butting against the intermediate transfer belt  41 , so that the unit is prepared for the next image-forming cycle. 
   On the other hand, in the surface of the photosensitive drum  31  after the transferring process is performed in the primary transferring portion T 1 , the charge polarities of the toner remaining on the surface of the photosensitive drum  31 , a toner which is retransferred from the intermediate transfer belt  41 , and the like are uniformly set to the minus polarity by the pre-cleaning charger  34 . The surface charges of the photosensitive drum  31  after the transfer are reduced to about 0 V by the destaticizing lamp  35 . The toner and the like remaining on the surface of the photosensitive drum  31  are removed by the drum cleaner  36 . The whole surface of the photosensitive drum  31  which is passed through the drum cleaner  36  is exposed by the pre-charge lamp  37 , whereby a process of erasing the latent image hysteresis produced in the previous image-forming cycle is performed before the charging process conducted by the charger  32 . 
   In the color printer  1 , the above-described image-forming cycle is performed for each image formation. 
   Next, the drum cleaner  36  which is a characteristic of the exemplary embodiment will be described. 
     FIG. 3  is a view showing the configuration of the drum cleaner  36  of the exemplary embodiment, and  FIG. 4  is a sectional view of a first cleaning roll  365 A of the cleaner. 
   Inside a housing  361 , the drum cleaner  36  includes two cleaning rolls (the first cleaning roll  365 A serving as a first cleaning member, and a second cleaning roll  365 B serving as a second cleaning member) which remove a toner adhering to the photosensitive drum  31 . The drum cleaner further includes: a first collection roll  336 A serving as a first collection member which collects a toner removed by the cleaning rolls  365 A,  365 B; and a first scraper  367 A which scrapes off a toner transferred to the surface of the first collection roll  366 A. The drum cleaner further includes: a second collection roll  366 B serving as a second collection member which collects a toner removed by the second cleaning roll  365 B; and a second scraper  367 B which scrapes off a toner transferred to the surface of the second collection roll  366 B. 
   Hereinafter, in the case where it is not required to describe particularly separately the cleaning rolls, the first cleaning roll  365 A and the second cleaning roll  365 B are referred to simply as the cleaning rolls  365 A,  365 B. Furthermore, the first collection roll  366 A and the second collection roll  366 B are referred to as the collection rolls  366 A,  366 B, and the first scraper  367 A and the second scraper  367 B are referred to as the scrapers  367 A,  367 B. 
   The first cleaning roll  365 A and the second cleaning roll  365 B are disposed in contact with the photosensitive drum  31 . The second cleaning roll  365 B is positioned on the downstream side of the first cleaning roll  365 A in the moving direction of the peripheral surface due to the rotation of the photosensitive drum  31 . 
   The first collection roll  366 A is placed between the first cleaning roll  365 A and the second cleaning roll  365 B so as to be in contact with both the cleaning rolls. According to the configuration, the first collection roll  366 A can collect a toner from both the first cleaning roll  365 A and the second cleaning roll  365 B. 
   The second collection roll  366 B is placed in contact with only the second cleaning roll  365 B. According to the configuration, the second collection roll  366 B collects a toner from only the second cleaning roll  365 B. 
   To the first cleaning roll  365 A, a predetermined bias voltage is supplied from a first cleaning roll bias power source  651 A disposed in the power source portion  65 . 
   To the second cleaning roll  365 B, a predetermined bias voltage is supplied from a second cleaning roll bias power source  651 B disposed in the power source portion  65 . 
   To the first collection roll  366 A, a predetermined bias voltage is supplied from a first collection roll bias power source  652 A disposed in the power source portion  65 . 
   To the second collection roll  366 B, a predetermined bias voltage is supplied from a second collection roll bias power source  652 B disposed in the power source portion  65 . 
   The cleaning rolls  365 A,  365 B and the collection rolls  366 A,  366 B are rotated by the rotating mechanism which is not shown. 
   The housing  361  forms a toner storing portion  362  which stores a collected toner, and includes: downstream and upstream seals  363 ,  364  which close gaps between the hosing and the photosensitive drum  31 ; and a conveyor screw  368  which discharges the toner stored in the toner storing portion  362  to a collection box which is not shown, and which is placed outside the image-forming units  30 . 
   The power source portion  65  is controlled by the controlling portion  60  of the color printer  1  (see  FIG. 1 ). Namely, the bias voltages applied to the cleaning rolls  365 A,  365 B and the collection rolls  366 A,  366 B are controlled by the controlling portion  60 , and also the rotations of the cleaning rolls  365 A,  365 B and the collection rolls  366 A,  366 B are controlled by the controlling portion  60 . 
   Hereinafter, the portions of the drum cleaner  36  will be described in detail. 
   The first cleaning roll  365 A is a roll which is rotatably supported on the housing  361 , and which has a predetermined outer diameter. As shown in  FIG. 4 , the roll is configured by forming an elastic layer  365   b  having a predetermined thickness around a shaft  365   c  having a predetermined diameter, and a fiber layer  365   a  serving as a surface layer having a thickness of, for example, 900 μm so as to cover the surface of the elastic layer  365   b.    
   The shaft  365   c  is made of a metal such as iron or SUS. The elastic layer  365   b  is formed by, for example, sponge-like foamed polyurethane with which a conductive agent such as carbon black is mixed so as to be adjusted to have a predetermined resistance. In the exemplary embodiment, foamed polyurethane is used. Alternatively, a rubber material such as NBR, SBR, or EPDM may be adequately used. 
   The fiber layer  365   a  is configured by, for example, a cloth-like member into which conductive fibers are knitted, that into which conductive fibers are woven, or a nonwoven cloth which is configured by conductive fibers. As the conductive fibers, for example, divided fibers of conductive nylon yarns (manufactured by KB SEIREN, LTD.) in which carbon black is dispersed, and which have a thickness of 0.5 deniers (248 T/450 F) are used. When very thin conductive fibers are used in this way, the surface area of the fiber layer  365   a  is increased, so that a large amount of toner can be held, and the cleaning performance can be enhanced. In this case, from the viewpoints of the toner holding property and the cleaning performance, conductive fibers having a thickness of 2 deniers (a diameter of about 15 μm) or less, preferably 1 denier (a diameter of about 11 μm) or less are suitably used. 
   As a nonwoven cloth, for example, a dry nonwoven cloth, a sponge band, and a wet nonwoven cloth are known. In the exemplary embodiment, a dry nonwoven cloth can be used. Specifically, a dry nonwoven cloth is formed by a process in which fibers of a length of several cm are formed into a thin sheet-like shape by a card or an air-random machine and several such sheets are stacked as required. Bonding of fibers is realized by twining the fibers by using a water jet. 
   As described above, in the first cleaning roll  365 A, the fiber layer  365   a  made of soft conductive fibers is placed in the surface, and the elastic layer  365   b  is formed under the fiber layer  365   a , whereby the sliding contact force to the surface of the photosensitive drum  31  is reduced. 
   The first cleaning roll  365 A is placed so as to butt against the photosensitive drum  31  along the axial direction, and configured so that, in the butted portion, the roll is rotated in the opposite direction (a clockwise direction in  FIG. 3 ) from the photosensitive drum  31 . In this case, the rotation speed (peripheral speed) of the first cleaning roll  365 A is set to be about 0.9 times the peripheral speed of the photosensitive drum  31 . Namely, the first cleaning roll  365 A slidingly moves with respect to the peripheral surface of the photosensitive drum  31 . The rotation direction and speed can be set in accordance with the kinds of the photosensitive drum  31  and the toner, and the like. 
   The second cleaning roll  365 B is a roll which is rotatably supported on the housing  361 , and which has a predetermined outer diameter, or specifically a brush roll in which a soft conductive brush is disposed around a metal shaft having a predetermined diameter. The conductive brush is made of, for example, conductive nylon yarns in which carbon black is dispersed. As the conductive yarn, the same yarn as the conductive yarn constituting the surface of the first cleaning roll  365 A can be used. However, the thickness, density, and length of the brush are adequately determined in consideration of the hardness of the photosensitive drum  31 , the compatibility with the toner, and the like. 
   The second cleaning roll  365 B is placed so as to be in contact with the photosensitive drum  31  along the axial direction, and configured so that, in the contacted portion, the roll is rotated in the same direction (a counterclockwise direction in  FIG. 3 ) as the photosensitive drum  31 . 
   The rotation direction and speed can be set in accordance with the kinds of the photosensitive drum  31  and the toner, and the like. 
   The second cleaning roll  365 B is not restricted to such a brush roll, and may be a roll in which the surface layer is formed as a fiber layer in the same manner as the first cleaning roll  365 A. The first roll has a function of removing discharge products. Therefore, the cleaning parameters (for example, the contact pressure) of the second roll can be set to be lower than those of a conventional cleaning roll, and are advantageous in the viewpoints of a scratch, filming, and abrasion of the photosensitive member. However, they are adequately determined in accordance with the hardness of the photosensitive member, the kind of the toner, and the like. 
   The collection rolls  366 A,  366 B are rolls which are rotatably supported on the housing  361 , and which have a predetermined outer diameter. The rolls are formed by a phenol resin in which carbon black is dispersed to adjust the resistance. Alternatively, a metal such as an aluminum alloy or a stainless steel alloy may be used. In order to allow the scrapers  367 A,  367 B to smoothly slidingly move, a member in which a film of, for example, a fluorine resin such as Teflon (registered trademark) is formed may be used. However, the configuration is not restricted to the above-described ones, and may be suitably selected in accordance with the system. 
   As described above, the first collection roll  366 A is placed so as to butt against both the first cleaning roll  365 A and the second cleaning roll  365 B along the axial direction, and configured so as to rotate in the same direction as the first cleaning roll  365 A so that their moving directions are opposite to each other in the butted portion with respect to the first cleaning roll  365 A. The second collection roll  366 B is placed so as to butt against the second cleaning roll  365 B along the axial direction, and configured so as to rotate in the same direction as the second cleaning roll  365 B so that their moving directions are opposite to each other in the butted portion. The rotation direction and speed can be set in accordance with the efficiency of collecting a toner from the cleaning rolls  365 A,  365 B, and the like. 
   The scrapers  367 A,  367 B are plate-like members which are made of iron, a stainless steel alloy, or the like, and butted against the collection rolls  366 A,  366 B so as to be opposed thereto in the rotation direction, along the axial direction of the collection rolls  366 A,  366 B. The toner transferred to the collection rolls  366 A,  366 B is scraped off, and then stored in the toner storing portion  362 . 
   The toner which is stored in the toner storing portion  362  in this way is discharged by the conveyor screw  368  into the collection box (not shown) which is placed outside the image-forming units  30 . 
   The axial lengths of the cleaning rolls  365 A,  365 B, the collection rolls  366 A,  366 B, and the scrapers  367 A,  367 B are set to have the following relationships.  FIG. 5  is a diagram illustrating the length relationships. 
   Namely, the cleaning rolls  365 A,  365 B are set to be laterally longer by a predetermined margin than the charge width of the photosensitive drum  31 . The collection rolls  366 A,  366 B are set to be laterally longer by a predetermined margin than the lengths of the cleaning rolls  365 A,  365 B. The scrapers  367 A,  367 B are set to be laterally longer by a predetermined margin than the lengths of the collection rolls  366 A,  366 B. 
   The collection rolls  366 A,  366 B and the scrapers  367 A,  367 B are configured so as to have the following positional relationships. 
   As shown in  FIG. 3 , one (the first collection roll  366 A) of the collection rolls  366 A,  366 B is not positioned under (in the toner drop path of) the position where the scraper  367 B removes a toner and the like from the other collection roll (the second collection roll  366 B) situated on the upper side. In the configuration of  FIG. 3 , the first collection roll  366 A and the second collection roll  366 B are placed so as to vertically overlap with each other, but the diameter of the second collection roll  366 B is set to be larger, whereby the first collection roll  366 A is not positioned in the toner drop path. 
     FIG. 6  is a view of a configuration example in which the collection rolls  366 A,  366 B are placed so that the first collection roll  366 A is not positioned in the toner drop path. 
   In the placement configuration of  FIG. 6 , the collection rolls  366 A,  366 B having a substantially same diameter are used, and, in positional relationships including also the cleaning rolls  365 A,  365 B, the first collection roll  366 A is set so as not to be positioned under (in the toner drop path or) the position where the scraper  367 B scrapes off a toner from the second collection roll  366 B situated on the upper side. 
   Next, the function and the like of the thus configured drum cleaner  36  will be described. The reference numerals of the components in the description are identical with those of above-described  FIGS. 1 to 4 . 
   The drum cleaner  36  in which the predetermined bias voltages are applied to the rolls by the power source portion  65  (power sources) under the control of the controlling portion  60  functions as described below to clean the photosensitive surface of the photosensitive drum  31 . 
   Here, in the surface of the photosensitive drum  31  to be cleaned by the drum cleaner  36 , toners charged to both the polarities or the minus and plus polarities exist. 
   Namely, most of toners which remain on the surface of the photosensitive drum  31  maintain the minus polarity which is charged by the developer  33 , and are uniformly set to the minus polarity by the charging function of the pre-cleaning charger  34 . By contrast, toners which, when a toner image on the photosensitive drum  31  is electrostatically transferred in the primary transferring portion T 1  onto the intermediate transfer belt  41 , are charged to the plus polarity by the transfer voltage applied from the primary transfer roll  42 , and which remain on the surface of the photosensitive drum  31  while maintaining the plus polarity in spite of the charging function of the pre-cleaning charger  34  exist in no small amount (for example, about 10 to 20%). 
   In this configuration, the first cleaning roll  365 A and the second cleaning roll  365 B remove toners charged to both the polarities from the photosensitive drum  31 . The first cleaning roll  365 A holds a predetermined amount of toner, and removes filming, discharge products, and the like from the surface of the photosensitive drum  31 . 
   During the cleaning operation, the following bias voltages are applied to the first cleaning roll  365 A, the second cleaning roll  365 B, the first collection roll  366 A, and the second collection roll  366 B, respectively. In the bias voltages, different DC voltages respectively for the rolls  365 A,  365 B,  366 A,  366 B are superimposed on an AC voltage of the same voltage and phase. According to the configuration, the AC voltages are shifted by the corresponding DC voltage. 
   Namely, the voltage of the second cleaning roll  365 B is set so as to be changed to the plus polarity and the minus polarity in order that it can electrostatically attract and hold both the minus-charged toner and the plus-charged toner. 
   The voltage of the first cleaning roll  365 A is set to be higher by a predetermined value with respect to that of the second cleaning roll  365 B. The voltage of the first collection roll  366 A is set to be higher by a predetermined value than that of the first cleaning roll  365 A. 
   The voltage of the second collection roll  366 B is set to be lower by a predetermined value with respect to that of the second cleaning roll  365 B. The voltage difference is set to be large (the discharge inception voltage or less) as far as possible in the range where no discharge is produced. However, there is a case where a phenomenon that charges are injected from a cleaning roll to a toner prominently occurs depending on the kinds of the toner and an external additive, the environment, and the like. Therefore, the voltages are adequately determined in consideration of also the phenomenon. 
     FIG. 7  is a view showing an example of the bias voltages. In this example, the surface potential of the photosensitive drum  31  is set to 0 V. 
   A peak-to-peak AC voltage of 400 V and a DC voltage of +200 V are applied to the first cleaning roll  365 A. Therefore, the first cleaning roll  365 A always maintains the potential of 0 V or higher and the plus polarity. 
   Only a peak-to-peak AC voltage of 400 V (i.e., a DC voltage of +0 V) is applied to the second cleaning roll  365 B. Therefore, the second cleaning roll  365 B alternatingly repeats plus and minus potentials. 
   A peak-to-peak AC voltage of 400 V and a DC voltage of +175 V are applied to the first collection roll  366 A which collects a toner from the first cleaning roll  365 A and the second cleaning roll  365 B. In the first collection roll  366 A, therefore, a potential difference of −25 V is always produced with respect to the first cleaning roll  365 A, and a potential difference of +175 V is always produced with respect to the second cleaning roll  365 B. 
   A peak-to-peak AC voltage of 400 V and a DC voltage of −300 V are applied to the second collection roll  366 B which collects a toner from the second cleaning roll  365 B. In the second collection roll  366 B, therefore, a potential difference of −300 V is always produced with respect to the second cleaning roll  365 B. 
   The frequency of the applied AC voltage is 3.2 kHz. However, the frequency is not restricted to this. The frequency can be adequately selected in consideration of the cleaning performance, the cost of the power source, etc. 
   The drum cleaner  36  in which the potential differences among the rolls are set as described above operates in the following manner. 
   Since the first cleaning roll  365 A is always 0 V or higher although the AC voltage is applied to the roll, the first cleaning roll electrostatically attracts a minus-charged toner on the photosensitive drum  31  (removes the toner from the surface of the photosensitive drum  31 ), and holds the toner in the fiber layer  365   a.    
   At this timing, in the first collection roll  366 A which collects a toner from the first cleaning roll  365 A, the potential difference of −25 V is always set with respect to the first cleaning roll  365 A. This potential difference causes the first cleaning roll  365 A to always hold a predetermined amount of toner, and the first collection roll  366 A collects the excess amount of toner. The function relating to the holding of the predetermined amount of toner will be described later in detail. 
   The toner which is collected from the first cleaning roll  365 A by the first collection roll  366 A is scraped off from the surface of the first collection roll  366 A by the first scraper  367 A. 
   By contrast, the second cleaning roll  365 B attracts and holds both a plus-charged toner which is not removed by the first cleaning roll  365 A, and a minus-charged toner which is not removed by the first cleaning roll  365 A. Namely, the peak-to-peak voltage of AC 400 V and DC +0 V is applied to the second cleaning roll  365 B, and therefore the roll altematingly repeats plus and minus potentials. When the roll has the minus potential, the roll attracts and holds the plus-charged toner, and, when the roll has the plus potential, the roll attracts and holds the minus-charged toner. 
   The peak-to-peak voltage of AC 400 V and DC −300 V is applied to the second collection roll  366 B. Therefore, the roll always has a minus potential, and a potential difference of −300 V is always produced with respect to the second cleaning roll  365 B. Therefore, the second collection roll  366 B collects a substantially whole amount of the plus-charged toner held by the second cleaning roll  365 B. The toner collected by the second collection roll  366 B is scraped off from the surface of the second collection roll  366 B by the second scraper  367 B. 
   The minus-charged toner held by the second cleaning roll  365 B is collected by the first collection roll  366 A. Namely, the first collection roll  366 A always has a potential difference of +175 V with respect to the second cleaning roll  365 B, and, because of this potential difference, can collect the minus-charged toner held by the second cleaning roll  365 B. 
   Namely, the first collection roll  366 A which is disposed in contact with not only the first cleaning roll  365 A but also the second cleaning roll  365 B collects the minus-charged toner which is not collected by the second collection roll  366 B, from the second cleaning roll  365 B. Therefore, the whole amount of the toner is collected from the second cleaning roll  365 B, and the phenomenon that a toner is accumulated on the second cleaning roll  365 B to cause a cleaning failure does not occur. 
   As described above, the second cleaning roll  365 B can collect both the plus- and minus-charged toners from the photosensitive drum  31 . Even when the toner held by the first cleaning roll  365 A is suddenly discharged toward the photosensitive drum  31  and plus- and minus-charged toners mixedly exist in the discharged toner, therefore, all of the toners can be removed. In the case where a configuration in which the second cleaning roll  365 B removes only the plus-charged toner is employed, the minus-charged toner cannot be removed, and the toner remains to cause a point-like image defect in a formed image. According to the configuration, this phenomenon does not occur. 
   Next, the operations of holding a predetermined mount of toner by the first cleaning roll  365 A, collecting the toner from the first cleaning roll  365 A by the first collection roll  366 A, and removing discharge products and the like from the photosensitive drum  31  by the first cleaning roll  365 A will be described in detail. 
   As described above, the first cleaning roll  365 A electrostatically attracts the minus-charged toner on the photosensitive drum  31 , and holds the toner into the fiber layer  365   a . On the other hand, in the first collection roll  366 A, the potential difference of −25 V is always set with respect to the first cleaning roll  365 A. 
   When the amount of the toner which is held in the fiber layer  365   a  by the first cleaning roll  365 A is small, therefore, the state where the potential of the first collection roll  366 A is lower than that of the outermost surface layer of the first cleaning roll  365 A is maintained. Consequently, the toner held in the fiber layer  365   a  of the first cleaning roll  365 A is not collected by the first collection roll  366 A, and remains to be held in the fiber layer  365   a.    
   When the amount of the toner held in the fiber layer  365   a  is increased to exceed a predetermined amount, however, the minus-charged toner causes the potential of the surface of the first cleaning roll  365 A to be lowered. As a result, a state where the potential of the first collection roll  366 A is higher than that of the outermost surface layer of the first cleaning roll  365 A is formed. When this state is attained, there occurs a phenomenon that the toner held in the fiber layer  365   a  of the first cleaning roll  365 A begins to be transferred to the first collection roll  366 A and is collected by the first collection roll  366 A. 
   When a predetermined amount of toner is transferred from the first cleaning roll  365 A to the first collection roll  366 A, the state where the potential of the first collection roll  366 A is lower than that of the outermost surface layer of the first cleaning roll  365 A is again formed, and the toner transfer to the first collection roll  366 A is stopped. 
   When the bias voltage to be applied to the first collection roll  366 A is set to be lower than that to be applied to the first cleaning roll  365 A in this way, the state where the predetermined amount of toner is always held in the fiber layer  365   a  of the first cleaning roll  365 A can be maintained. Namely, the held amount of toner in the fiber layer  365   a  can be adequately adjusted by adjusting the voltage difference between the bias voltage to be applied to the first collection roll  366 A and that to be applied to the first cleaning roll  365 A. 
   The toner held in the peripheral surface (the fiber layer  365   a ) by the first cleaning roll  365 A has a function of removing filming, discharge products, and the like formed on the surface of the photosensitive drum  31 . 
   Filming causes the following phenomenon. The components of the surface (photosensitive member) of the photosensitive drum  31  which are shaved off by the mechanical sliding contact force of the cleaning member (the first cleaning rolls  365 A,  365 B in the exemplary embodiment) are again fixed to the surface of the photosensitive drum  31 , thereby producing spot-like or raindrop-like attached regions in the surface of the photosensitive drum  31 . As a result, an image defect such as a spot-like or raindrop-like void is produced in a formed image. 
   Discharge products are produced by a discharge caused when, in the image-forming cycle, the photosensitive drum  31  is charged by the charger  32 . In a machine in which the process speed is high, such as a high-speed machine or a color copying machine, discharge products are produced in a large amount. When such discharge products adhere to the surface of the photosensitive drum  31 , the resistance is lowered particularly under a high-temperature and high pressure environment (for example, temperature: 28° C., humidity: 85%). This causes charges in the surface of the photosensitive drum  31  to leak, whereby the contrast of the latent image potential is lowered and a void portion is produced in an image. 
   When the sliding contact force is enhanced, discharge products can be removed also by a usual elastic or brush roll, or the like. In this case, however, the photosensitive member is shaved and the above-mentioned filming is caused. Furthermore, the life period of the photosensitive drum  31  is shortened. 
   In the drum cleaner  36  in the exemplary embodiment, the fiber layer  365   a  of the first cleaning roll  365 A holds a toner, and the fiber layer  365   a  in a state where the toner is held is in sliding contact with the surface of the photosensitive drum  31 . Therefore, the toner held by the fiber layer  365   a  removes discharge products and the like adhering to the surface of the photosensitive drum  31 . This is based on the finding obtained from experiments conducted by the inventors. The mechanism of the removal is not thoroughly known. However, it is presumed that the binder resin component constituting the toner, such as polyethylene or polystyrene adsorbs discharge products and the like. 
   Next, the relationship between the potential difference between the first cleaning roll  365 A and the first collection roll  366 A, and the amount of toner held in the fiber layer  365   a  of the first cleaning roll  365 A will be described. 
     FIG. 8  shows results of measurements of an amount (a weight per unit area: g/m 2 ) of a toner which is held in the fiber layer  365   a  of the first cleaning roll  365 A while setting the bias voltage to the first cleaning roll  365 A to DC +300 V, and that to the first collection roll  366 A to DC +275 V (the potential difference is −25 V).  FIG. 9  shows a chart used in the experiment. 
   In the experiment of  FIG. 8 , 1,000 strip charts in which a strip-like solid image portion of a predetermined width is formed in the traveling direction of the recording sheet P shown in  FIG. 9  are continuously subjected to a printing operation (1 KPV), and then 2,000 complete-white (solid) charts are continuously subjected to a printing operation (2 KPV). 
   When such a strip chart is subjected to a printing operation, in the region of the photosensitive drum  31  corresponding to the solid image portion of the strip chart, a toner of 0.5 g/m 2  is attached as a post-transfer residual toner. In the case of a white chart, a toner of 0.01 to 0.02 g/m 2  is attached as a post-transfer residual toner. 
   As a result, as shown in  FIG. 8 , when 1,000 strip charts are continuously subjected to a printing operation, a toner of 0.5 g/m 2  is supplied to a region of the fiber layer  365   a  corresponding to the solid image portion. Therefore, the held amount of toner is saturated to about 90 g/m 2  at the timing of about 500 printing operations. The state is maintained until 1,000 printing operations. At the timing of 1,000 printing operations, the strip charts are switched to the white charts, and a toner of 0.01 to 0.02 g/m 2  is supplied. Therefore, the toner held in the region of the fiber layer  365   a  corresponding to the solid image portion is gradually collected by the first collection roll  366 A, and then the amount is saturated to about 40 g/m 2 . 
   In a region of the fiber layer  365   a  corresponding to the portion other than the solid image portion, a toner of 0.01 to 0.02 g/m 2  is supplied in both the printing operations on the strip charts and the white charts. Therefore, the held amount of toner is saturated to about 40 g/m 2  at the timing of about 500 printing operations. The state is maintained until 3,000 printing operations. 
   As apparent from the result of  FIG. 8 , when the bias voltage to the first cleaning roll  365 A is set to +300 V and that to the first collection roll  366 A is set to +275 V, the held amount of toner in the region of the fiber layer  365   a  to which a toner of 0.5 g/m 2  for the solid image portion is supplied is maintained to about 90 g/m 2 , and that in the region of the fiber layer  365   a  to which a toner of 0.01 to 0.02 g/m 2  for the white region is supplied is maintained to about 40 g/m 2 . In this voltage setting, therefore, the held amount of toner in the fiber layer  365   a  is maintained between the lower limit of 40 g/m 2  and the upper limit of 90 g/m 2 . 
     FIG. 10  is a view for evaluating the relationships between, in the drum cleaner  36  of the exemplary embodiment in which a predetermined amount of toner is always held, the held amount (g/m 2 ) of toner held in the fiber layer  365   a  of the first cleaning roll  365 A and the occurrence or non-occurrence of image deletion due to discharge products of the surface of the photosensitive drum  31 , those between the held amount and the occurrence or non-occurrence of filming due to scratches or the like of the surface of the photosensitive drum  31 , and those between the held amount and the toner cleaning performance. 
   The evaluation of  FIG. 10  is performed by evaluating a first image obtained after 10,000 printing operations and subsequent non-operation during the day and night (about 24 hours). Discharge products adhering to the surface of the photosensitive drum  31  gradually adsorb moisture to lower the resistance of the photosensitive layer. As the resistance is lower, a void due to image deletion occurs more easily. Therefore, a print image obtained after non-operation during the day and night is evaluated. The occurrence or non-occurrence of filming is determined by observing the surface of the photosensitive drum  31  under a microscope. The cleaning performance is evaluated by observing the surface of the photosensitive drum  31  after the drum passes through the drum cleaner  36 . 
   From the result, it is noted that image deletion occurs in the range where the held amount of toner is 20 g/m 2  or less, and dose not occur in the range where the held amount of toner is 30 g/m 2  or more. Therefore, it is found that, when the fiber layer  365   a  holds a toner of 30 g/m 2  or more, discharge products adhering to the surface of the photosensitive drum  31  can be removed from the photosensitive drum  31  to a degree where occurrence of image deletion is suppressed. 
   In this case, as a result of observation of the surface of the photosensitive drum  31  under a microscope, it is confirmed that filming does not occur in any range of the held amount of toner. It seems that this is based on that the sliding contact force of the first cleaning roll  365 A against the surface of the photosensitive drum  31  is set to be low, and that the toner removes a filming material. 
   By contrast, in the range where the held amount of toner exceeds 150 g/m 2 , the toner collection ability of the fiber layer  365   a  is lowered, and hence the cleaning performance is not sufficiently exerted. 
   From the evaluation results of  FIG. 10 , in order to remove discharge products to suppress occurrences of image deletion and filming, and ensure the cleaning performance with respect to a toner, it is preferable that the amount of toner held by the fiber layer  365   a  is 30 to 150 g/m 2  or about 30 to about 150 g/m 2 . 
   From other experiments, however, a result that, when the photosensitive drum  31  is rotated for a predetermined time period (for example, 5 minutes) in a state where a toner is always held by the fiber layer  365   a , occurrence of image deletion can be suppressed even in the case where the held amount of toner is 20 g/m 2  is obtained. When assuming that such an operation is performed in a cycle before or after image formation, therefore, it is also possible that the amount of toner to be held by the fiber layer  365   a  is set to 20 to 150 g/m 2  or about 20 to about 150 g/m 2 . 
   Next, voltage relationships to be set between the first cleaning roll  365 A and the first collection roll  366 A in order to set the amount of toner held by the fiber layer  365   a  to 20 to 150 g/m 2  will be described. 
     FIG. 11  is a view showing results of measurements in which the amount of toner held by the fiber layer  365   a  is measured in the case where the bias voltage supplied to the first cleaning roll  365 A is fixed to +300 V and that supplied to the first collection roll  366 A is changed. 
   From the results shown in  FIG. 11 , in order to set the held amount of toner to 20 g/m 2  or more also in a white potion, the upper limit of the bias voltage supplied to the first collection roll  366 A is +325 V. 
   In order to set the held amount of toner to 150 g/m 2  or less also in a solid image potion, the lower limit of the bias voltage supplied to the first collection roll  366 A is +150 V. When the bias voltage supplied to the first collection roll  366 A is +300 V, therefore, it is preferable that the bias voltage supplied to the first collection roll  366 A is +150 to +325 V. 
   From the above, in order to set the amount of toner held by the fiber layer  365   a  to 20 to 150 g/m 2 , the difference between the voltage of the first cleaning roll  365 A and that of the first collection roll  366 A (=voltage of first cleaning roll  365 A−voltage of first collection roll  366 A) is required to be set to −25 to 150 V. Including also the case where a positive toner is used and a minus bias voltage is applied to the first cleaning roll  365 A and the first collection roll  366 A, usually, it is required to set the difference between the absolute value of the voltage of the first cleaning roll  365 A and that of the first collection roll  366 A (=|voltage of first cleaning roll  365 A|−|voltage of first collection roll  366 A|) to −25 to 150 V. 
   In the color printer  1  of the exemplary embodiment, as shown in  FIG. 10  described above, even in the case of a white chart, about 500 printing operations cause the amount of toner held by the fiber layer  365   a  to be about 40 g/m 2 . Also in initial installation of the color printer  1 , when a normal method of use is conducted, therefore, there occur fewer problems about removal of discharge products. Assuming a method of use in which sufficient removal of discharge products must be performed also in initial installation (for example, between 0 to 500 printing operations) of the color printer  1 , however, also setting of a toner supply mode is effective. According to the toner supply mode, in initial installation of the color printer  1 , in each of the image-forming units  30 , a strip-like solid image of a width of 3 cm is formed in, for example, the whole area in the width direction of the photosensitive drum  31 , the operation of the primary transfer roll  42  is turned off to disable the transferring process in the primary transferring portion T 1 , and all of the toner is supplied to the first cleaning roll  365 A. According to the configuration, even in the initial printing operation, it is possible to set the amount of toner held by the fiber layer  365   a  to about 40 g/m 2 . In the above, the operation of the primary transfer roll  42  is turned off, and a large amount of the developing agent is supplied to the first cleaning roll  365 A. However, the countermeasure may be suitably set in accordance with the system. For example, the operation of the primary transfer roll  42  is not completely turned off, and the transfer electric field is weakened, thereby increasing the amount of post-transfer residual toner in accordance with the transfer efficiency, or the like. 
   The toner supply mode is not restricted to the initial installation of the color printer  1 . For example, the mode may be performed for each time when a predetermined number of printing operations such as 500 printing operations are performed. According to the configuration, even when an image in which the image density is uneven is continuously printed, the held amount of toner can be uniformalized over the whole range in the axial direction of the first cleaning roll  365 A. 
   The timing of implementing the toner supply mode may be before or after the image-forming cycle, or between the image-forming cycles. 
   In this case, the toner supply mode is set by the controlling portion  60 , and the controlling portion  60  functions as a toner supply mode setting portion. 
   In the thus configured color printer  1  of the exemplary embodiment, a toner can be satisfactorily removed from the photosensitive drum  31 . Furthermore, a predetermined amount of toner is held by the fiber layer  365   a  of the first cleaning roll  365 A, so that adhering discharge products can be removed without causing abrasion or scratches in the photosensitive drum  31 . Therefore, image deletion and voids due to discharge products can be suppressed. Moreover, abrasion of the photosensitive member of the photosensitive drum  31  can be suppressed. Therefore, it is possible to prevent filming from occurring. Even when filming occurs, the filming can be removed, and an image defect can be prevented from being produced. 
   The color printer  1  having this configuration is subjected to a sheet passing test of 30,000 sheets. Voids due to discharge products, voids due to filming, and cleaning failure are not caused until the last passing. Also a point-like image defect is not caused. As a result, the effectiveness of the configuration is confirmed. 
   The first cleaning roll  365 A used in the test is a conductive nylon cloth roll in which the fiber layer  365   a  is formed by winding a sheet of about 90 μm configured by knitting conductive nylon of 0.5 d (deniers) on a sponge roll having a shaft diameter of φ6 mm, and the outer diameter is φ12 mm. 
   The second cleaning roll  365 B is the above-described conductive nylon brush. 
   In the sheet passing test, various parameters of image formation are as follows.
         Photosensitive drum (photosensitive drum  31 )       

   OPC, φ84 mm
         Charger (charger  32 )       

   Scorotron −945 μA, grid voltage: 620 V
         Exposing device (laser exposing device  26 )       

   Laser: 780 nm
         Intermediate transfer member (intermediate transfer belt  41 )       

   Polyimide
         Process speed       

   420 mm/s
         Latent image potential       

   Background portion: −600 V 
   Image portion: −300 V
         Developer (developer  33 )       

   Developing system: two-component developing system 
   Diameter of developing roll sleeve: φ16 mm 
   Rotation speed of sleeve: 800 mm/s 
   Gap between photosensitive member and developing roll: 0.3 mm
         Development bias       

   DC component: −500 V 
   AC component: 1.5 kVP-P (6 kHz)
         Transfer conditions       

   Primary transfer roll: +40 μA 
   Secondary transfer roll: +1600 V 
   As described above, in the color printer  1  of the exemplary embodiment, the drum cleaner  36  can remove toners charged to both the polarities from the surface of the photosensitive drum  31 , and a toner is held by the first cleaning roll  365 A including the fiber layer  365   a  made of conductive fibers in the surface, whereby discharge products and the like can be effectively cleaned away from the surface of the photosensitive drum  31 . Therefore, stable and excellent image formation can be performed for a long term. 
   The invention is not restricted to the exemplary embodiment, and may be adequately modified. 
   In the exemplary embodiment, for example, the first cleaning roll  365 A in which the fiber layer  365   a  made of conductive fibers is provided in the surface layer to hold a toner is placed on the upstream side in the rotation direction of the photosensitive drum  31 , and the second cleaning roll  365 B which collects a toner is placed on the downstream side. Alternatively, the cleaning rolls  365 A,  365 B may be placed while inverting the upstream and downstream relationship therebetween. 
   The cleaning device of the invention is not restricted to a cleaning device for cleaning a photosensitive drum. For example, the invention may be used in a cleaning device (the belt cleaner  50  of  FIG. 1  in the exemplary embodiment) for cleaning an intermediate transfer belt, etc. 
   The color printer may have a configuration shown as a color printer  1 ′ in  FIG. 12 . The reference numerals in the figure are used in common with the color printer  1  shown in  FIG. 1 . 
   The color printer  1 ′ has a configuration in which the image-forming units  30  ( 30 Y,  30 M,  30 C,  30 K) are placed under the intermediate transfer belt  41 , and the laser exposing device  26  is placed under the image-forming units. The intermediate transfer belt  41  circulates in a clockwise direction in the figure, and is configured so that a toner image held by the intermediate transfer belt  41  is transferred to the recording sheet P in the secondary transferring portion T 2  which is on the left side of the circulating path in the figure. According to the configuration, the moving distance of the intermediate transfer belt  41  carrying a toner image, between the primary transferring portion T 1  in which a toner image is transferred from the image-forming units  30  to the intermediate transfer belt  41 , and the secondary transferring portion T 2  in which a toner image is transferred from the intermediate transfer belt  41  to the recording sheet P can be set to be short. 
   It is a matter of course that the configuration of the invention may be applied to a monochrome image-forming apparatus. 
   The configuration and effects of the exemplary embodiment of the invention are as follows. 
   (1) The cleaning rolls  365 A,  365 B are set to be longer than the charge width of the photosensitive drum  31 , the collection rolls  366 A,  366 B are set to be longer than the cleaning rolls  365 A,  365 B, and the scrapers  367 A,  367 B are set to be longer than the collection rolls  366 A,  366 B. Therefore, the photosensitive drum can be surely cleaned, and the removed toner and the like can be surely discharged. 
   (2) In the collection rolls  366 A,  366 B, the first collection roll  366 A is set so as not to be positioned under the position where the scraper  367 B removes a toner and the like from the second collection roll  366 B situated on the upper side. Therefore, a phenomenon that the toner and the like removed by the scraper  367 B from the second collection roll  366 B fall on the first collection roll  366 A situated on the lower side to cause a problem does not occur. 
   (3) In the first cleaning roll  365 A, the fiber layer  365   a  made of soft conductive fibers is placed in the surface, and the elastic layer  365  is formed under the fiber layer  365   a . Therefore, the roll can be in contact also with the first collection roll  366 A with high contactness and at a low pressure. Consequently, scratches are hardly formed also in the surfaces of the collection rolls  366 A,  366 B, and a toner collection failure due to such scratches can be prevented from occurring. 
   (4) In the first cleaning roll  365 A, a sliding contact force at which discharge products can be removed by the effect of a toner can be set. Therefore, there is a low possibility that shaved components of the photosensitive drum  31  are fixed to the surface of the photosensitive drum  31  to cause filming. Moreover, not only discharge products, but also shaved components of the photosensitive drum  31 , and the like are adsorbed and removed by a toner. Therefore, the possibility that filming is caused is low.