Patent Publication Number: US-8126355-B2

Title: Developing device with seal member that abuts toner carrier roller

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The disclosure of Japanese Patent Application No. 2008-012149 filed on Jan. 23, 2008 including specification, drawings and claims is incorporated herein by reference in its entirety. 
     BACKGROUND 
     1. Technical Field 
     This invention relates to a developing device, an image forming apparatus and an image forming method for conveying toner in a housing to outside the housing by causing a toner carrying roller to carry the toner and thereafter collecting the toner again into the housing. 
     2. Related Art 
     In a developing device and an image forming apparatus for conveying toner in a housing to outside the housing by causing a toner carrying roller to carry the toner and thereafter collecting the toner again into the housing, the leakage of the toner to the outside of the housing is prevented by bringing a seal member into contact with a surface of the toner carrying roller. For example, in a developing device disclosed in JP-A-H06-075469, the leakage of toner is prevented by bringing a seal member into contact with a surface of a development sleeve. 
     In the apparatus constructed as above, the seal member discharges the electric charges of the toner, thereby making the toner easily separable from the toner bearing roller. In return, the seal member itself is electrically charged and electric charges produce repulsive forces to the toner on the toner carrying roller, thereby scattering the toner and weakening an action of the seal member to discharge the toner. Therefore, the toner on the toner carrying roller may not be satisfactorily renewed and problems such as image fogging could occur. 
     Concerning this, it is disclosed in the above literature that a discharging member or the seal member having a discharging function is directly brought into contact with the development sleeve near an end of the development sleeve to set the neutralizing member or the seal member at the same potential as the development sleeve. 
     SUMMARY 
     Since the discharging member or the seal member in the above structure is made of a resin material, in which carbon powder is dispersed, and the electrical conductivity thereof is not very high, it is difficult to allow the electric charges of the seal member to sufficiently escape particularly in a middle part distant from the contact part. As a result, in the above structure, toner scattering and fogging are likely to occur near the middle part in a direction of a rotary shaft of the development sleeve. 
     An advantage of some aspects of the invention is to provide technology capable of preventing problems such as toner scattering and fogging resulting from the electrical charging of a seal member in a developing device, an image forming apparatus and an image forming method for conveying toner in a housing to outside the housing by causing the toner carrying roller to carry the toner and thereafter collecting the toner again into the housing. 
     According to a first aspect of the invention, there is provided a developing device, comprising: a housing that stores toner inside; a toner carrier roller that is shaped approximately like a cylinder, is mounted to the housing rotatably about a rotational axis, rotates while carrying the toner on a surface thereof to convey the toner to outside of the housing, and is provided, on the surface thereof, with a plurality of convex sections which are regularly arranged and a concave section which surrounds the convex sections, the convex sections including top surfaces that coincide with a part of a curved surface of single cylinder and have electrical conductivity; and a seal member that is arranged in abutting contact with the surface of the toner carrier roller moving from the outside the housing toward the inside the housing at a position downstream of the opposed position in a rotation direction of the toner carrier roller to prevent toner leakage from the housing, a contact surface of the seal member being made of a material located at a position to charge the toner with a polarity opposite to its charging polarity in triboelectric series. 
     Conventionally, as a toner carrier roller, a roller whose surface is roughened by a blast process or the like to carry a sufficient amount of toner by increasing the surface area has been generally used. An irregular convexo-concave pattern is formed on the surface of the roller finished with the blast process and, thus, even if a seal member is brought into contact with this surface, the seal member actually touches only projecting parts. Therefore, an action of allowing electric charges of the seal member to escape to the toner bearing roller could be hardly expected. 
     In contrast, in the invention constructed as above, the top surfaces of the respective convex sections on the toner carrying roller surface form parts of the same cylindrical surface. Accordingly, at each point of time during the rotation of the toner carrying roller, the top surfaces of the respective convex sections at positions facing a contact surface of the seal member come into contact with the seal member at substantially uniform contact pressures. By bringing a multitude of electrically conductive top surfaces of the convex sections with the seal member in this way, electric charges accumulated on the seal member are allowed to stably escape toward the toner bearing roller in the entire area of the seal member. As a result, problems such as toner scattering and fogging resulting from the electrical charging can be effectively prevented by suppressing the electrical charging of the seal member. 
     According to a second aspect of the invention, there is provided an image forming apparatus, comprising: a latent image carrier that carries an electrostatic latent image; a housing that stores toner inside; a toner carrier roller that is shaped approximately like a cylinder, is mounted to the housing rotatably about a rotational axis, rotates while carrying the toner on a surface thereof to convey the toner to an opposed position to the latent image carrier outside the housing, and is provided, on the surface thereof, with a plurality of convex sections which are regularly arranged and a concave section which surrounds the convex sections, the convex sections including top surfaces that coincide with a part of a curved surface of single cylinder and have electrical conductivity; and a seal member that is arranged in abutting contact with the surface of the toner carrier roller moving from the outside the housing toward the inside the housing at a position downstream of the opposed position in a rotation direction of the toner carrier roller to prevent toner leakage from the housing, a contact surface of the seal member being made of a material located at a position to charge the toner with a polarity opposite to its charging polarity in triboelectric series. 
     According to a third aspect of the invention, there is provided an image forming method, comprising: causing a toner carrier roller to carry toner stored in a housing, the toner carrier roller being shaped approximately like a cylinder and being provided, on a surface thereof, with a plurality of convex sections which are arranged regularly and a concave section which surrounds the convex sections, the convex sections including top surfaces that coincide with a part of a curved surface of single cylinder and have electrical conductivity; rotating the toner carrier roller to convey the toner to an opposed position facing a latent image carrier that carries an electrostatic latent image, thereby developing the electrostatic latent image with the toner; and bringing a seal member into abutting contact with the surface of the toner carrier roller at a position downstream of the opposed position in a rotation direction of the toner carrier roller, thereby collecting the toner into the housing, a contact surface of the seal member being made of a material located at a position to charge the toner with a polarity opposite to its charging polarity in triboelectric series. 
     According to these aspects of the invention, similar to the above developing device, the electrical charging of the seal member can be suppressed by allowing the electric charges accumulated on the seal member to stably escape toward the toner bearing roller and problems such as toner scattering and fogging resulting from the electrical charging can be effectively prevented. 
     The above and further objects and novel features of the invention will more fully appear from the following detailed description when the same is read in connection with the accompanying drawing. It is to be expressly understood, however, that the drawing is for purpose of illustration only and is not intended as a definition of the limits of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram showing an embodiment of an image forming apparatus according to the invention. 
         FIG. 2  is a block diagram of an electric structure of the image forming apparatus which is shown in  FIG. 1 . 
         FIG. 3  is a diagram showing the appearance of the developer. 
         FIG. 4A  is a cross sectional view showing a structure of the developer. 
         FIG. 4B  is a graph showing the relationship between a waveform of a developing bias and a surface potential of the photosensitive member. 
         FIG. 5  is a group of diagrams showing a side view of the developing roller and a partially expanded view of the surface of the developing roller. 
         FIGS. 6A and 6B  are plan development views showing the structure of the surface of the developing roller in further detail. 
         FIGS. 7A and 7B  are diagrams showing contact states of the developing roller and the seal member. 
         FIGS. 8A and 8B  are diagrams showing grain structures of seal members. 
         FIG. 9  is a table showing constitutions and evaluation results of seal members. 
         FIGS. 10A and 10B  are diagrams showing a cross section structure of the developing roller surface when viewed in the axial direction. 
         FIG. 11  is a flow chart showing the operation of the image forming apparatus including the seal discharging operation. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       FIG. 1  is a diagram showing an embodiment of an image forming apparatus according to the invention.  FIG. 2  is a block diagram of an electric structure of the image forming apparatus which is shown in  FIG. 1 . This apparatus is an image forming apparatus which overlays toner (developing powder) in four colors of yellow (Y), cyan (C), magenta (M) and black (K) one atop the other and accordingly forms a full-color image, or forms a monochromatic image using only black toner (K). In the image forming apparatus, when an image signal is fed to a main controller  11  from an external apparatus such as a host computer, a CPU  101  provided in an engine controller  10  controls respective portions of an engine part EG in accordance with an instruction received from the main controller  11  to perform a predetermined image forming operation, and accordingly, an image which corresponds to the image signal is formed on a sheet S. 
     In the engine part EG, a photosensitive member  22  is disposed so that the photosensitive member  22  can freely rotate in an arrow direction D 1  shown in  FIG. 1 . Around the photosensitive member  22 , a charger unit  23 , a rotary developer unit  4  and a cleaner  25  are disposed in the rotation direction D 1 . A predetermined charging bias is applied upon the charger unit  23 , whereby an outer circumferential surface of the photosensitive member  22  is charged uniformly to a predetermined surface potential. The cleaner  25  removes toner which remains adhering to the surface of the photosensitive member  22  after primary transfer, and collects the toner into a waste toner tank which is disposed inside the cleaner  25 . The photosensitive member  22 , the charger unit  23  and the cleaner  25 , integrated as one, form a photosensitive member cartridge  2 . The photosensitive member cartridge  2  can be freely attached to and detached from an apparatus main body as one integrated unit. 
     An exposure unit  6  emits a light beam L toward the outer circumferential surface of the photosensitive member  22  charged by the charger unit  23 . This exposure unit  6  exposes the photosensitive member  22  by the light beam L in accordance with the image signal given from the external apparatus to form an electrostatic latent image corresponding to the image signal. 
     The developer unit  4  develops thus formed electrostatic latent image with toner. Specifically, the developer unit  4  includes a support frame  40  which is provided rotatable about a rotation shaft orthogonal to a plane of  FIG. 1  and a yellow developer  4 Y, a cyan developer  4 C, a magenta developer  4 M and a black developer  4 K which are freely attachable to and detachable from the support frame  40  as cartridges and house toner of the respective colors. An engine controller  10  controls the developer unit  4 . The developer unit  4  is driven into rotation based on a control instruction from the engine controller  10 . When the developers  4 Y,  4 C,  4 M and  4 K are selectively positioned at a predetermined developing position which is faced with the photosensitive member  22  over a predetermined gap, the developing roller  44  which is disposed in this developer and carries a toner of a selected color is positioned facing the photosensitive member  22 , and the developing roller  44  supplies the toner onto the surface of the photosensitive member  22  at the facing position. In this way, the electrostatic latent image on the photosensitive member  22  is visualized with the toner of the selected color. 
       FIG. 3  is a diagram showing the appearance of the developer.  FIG. 4A  is a cross sectional view showing a structure of the developer, and  FIG. 4B  is a graph showing the relationship between a waveform of a developing bias and a surface potential of the photosensitive member. The developers  4 Y,  4 C,  4 M and  4 K have identical structures. Therefore, the structure of the developer  4 K will now be described in further detail with reference to  FIGS. 3 and 4A . The other developers  4 Y,  4 C and  4 M have the same structures and functions, to be noted. 
     In the developer  4 K, a feed roller  43  and a developing roller  44  are rotatably attached with a shaft to a housing  41  which houses monocomponent toner T inside. When the developer  4 K is positioned at the developing position described above, the developing roller  44  is positioned at a facing position which is faced with the photosensitive member  22  over a developing gap DG, and these rollers  43  and  44  are engaged with a rotation driver (not shown) which is provided in the main body to rotate in a predetermined direction. The feed roller  43  is shaped like a cylinder and is made of an elastic material such as foamed urethane rubber and silicone rubber The developing roller  44  is shaped like a cylinder and is made of metal or alloy such as copper, aluminum and stainless steel. The two rollers  43  and  44  rotate while staying in contact with each other, and accordingly, the toner is rubbed against the surface of the developing roller  44  and a toner layer having a predetermined thickness is formed on the surface of the developing roller  44 . Although negatively-charged toner is used in this embodiment, positively-charged toner may be used instead. 
     The space inside the housing  41  is divided by a partition wall  41   a  into a first chamber  411  and a second chamber  412 . The feed roller  43  and the developing roller  44  are both provided in the second chamber  412 . With a rotation of these rollers, toner within the second chamber  412  flows and is fed to the surface of the developing roller  44  while getting agitated. Meanwhile toner stored inside the first chamber  411  would not be moved by the rotation since it is isolated from the feed roller  43  and the developing roller  44 . This toner is mixed with toner stored in the second chamber  412  and is agitated by the rotation of the developer unit  4  while holding the developer. 
     As described above, in this developer, the inside of the housing is separated into the two chambers, and the side walls of the housing  41  and the partition wall  41   a  surround the feed roller  43  and the developing roller  44 , and accordingly, the second chamber  412  of relatively small volume is provided. Therefore, even when a remaining toner amount is small, toner is supplied efficiently to near the developing roller  44 . Further, supply of toner from the first chamber  411  to the second chamber  412  and agitation of the whole toner are performed by the rotation of the developer unit  4 . Hence, an auger-less structure is realized that an agitator member (auger) for agitating toner is not provided inside the developer. 
     Further, in the developer  4 K, a restriction blade  46  is disposed which restricts the thickness of the toner layer formed on the surface of the developing roller  44  into the predetermined thickness. The restriction blade  46  includes a plate-like member  461  made of elastic material such as stainless steel, phosphor bronze or the like and an elastic member  462  which is attached to a front edge of the plate-like member  461  and is made of a resin member such as silicone rubber and a urethane rubber. A rear edge of the plate-like member  461  is fixed to the housing  41 . The elastic member  462  attached to the front edge of the plate-like member  461  is positioned on the upstream side to the rear edge of the plate-like member  461  in a rotation direction D 4  of the developing roller  44  shown by an arrow in  FIG. 4 . The elastic member  462  elastically abuts on the surface of the developing roller  44  to form a restriction nip, thereby restricting the toner layer formed on the surface of the developing roller  44  finally into the predetermined thickness. 
     The toner layers thus formed on the surface of the developing roller  44  are transported, by means of the rotation of the developing roller  44 , one after another to the opposed positions against the photosensitive member  22  on the surface of which an electrostatic latent image is formed. The developing bias from a bias power source  140  controlled by the engine controller  10  is applied to the developing roller  44 . As shown in  FIG. 4B , a surface potential Vs of the photosensitive member  22  drops down approximately to a residual potential Vr at exposed segments exposed by the light beam L from the exposure unit  6  after getting uniformly charged by the charger unit  23 , but stays at an almost uniform potential Vo at non-exposed segments not exposed by the light beam L. Meanwhile, the developing bias Vb applied to the developing roller  44  is a rectangular-wave AC voltage on which a DC potential Vave is superimposed, and its peak-to-peak voltage will be hereinafter denoted at Vpp. With application of such a developing bias Vb, toner carried on the developing roller  44  is made jump across a developing gap DG and partially adheres to the respective sections in the surface of the photosensitive member  22  in accordance with the surface potential Vs of the photosensitive member  22 , whereby all electrostatic latent image on the photosensitive member  22  is visualized as a toner image in the color of the toner. 
     A rectangular-wave voltage having a peak-to-peak voltage Vpp of 1500V and a frequency of about 3 kHz, for example, may be used as the developing bias voltage Vb. Since an electric potential difference between the direct current component Vave of the developing bias voltage Vb and a residual potential Vr of the photosensitive member  22  constitutes a so-called development contrast which affects image density, the direct current component Vave may be set to a required value for obtaining a predetermined image density. 
     The housing  41  further includes a seal member  47  which is pressed against the surface of the developing roller  44  on the downstream side to the opposed position facing the photosensitive member  22  in the rotation direction of the developing roller  44 . The seal member  47  is a belt-like film made of a flexible fluororesin material such as PTFE (polytetrafluoroethylene) extending in a direction X parallel to a rotational axis of the developing roller  44 . One end of the seal member  47  in a direction perpendicular to the direction X is fixed to the housing  41 , and the other end of the seal member  47  abuts on the surface of the developing roller  44 . The other end of the seal member  47  is allowed to abut on the developing roller  44  as directed toward the downstream side in the rotation direction D 4  of the developing roller  44 , or directed in a so-called trail direction. The other end of the seal member  47  guides toner which remains on the surface of the developing roller  44  after moving past the opposed position facing the photosensitive member  22  to inside the housing  41  and prevents toner inside the housing from leaking to outside. The more detailed instruction about the seal member  47  is will be described later. 
       FIG. 5  is a group of diagrams showing a side view of the developing roller and a partially expanded view of the surface of the developing roller. The developing roller  44  is shaped like an approximately cylindrical roller. A shaft  440  is provided at the both ends of the roller in the longitudinal direction of the roller such that the shaft is coaxial with the roller. With the shaft  440  supported by the developer main body, the entire developing roller  44  is freely rotatable. A central area  44   a  in the surface of the developing roller  44 , as shown in the partially expanded view in  FIG. 5  (inside the dotted-line circle), is provided with a plurality of convex sections  441  which are regularly arranged and a concave section  442  which surrounds the convex sections  441 . 
     Each one of the convex sections  441  projects forward from the plane of  FIG. 5 , and a top surface of each convex section  441  forms a part of a single cylindrical surface which is coaxial with a rotational axis of the developing roller  44 . The concave section  442  is a continuous groove which surrounds the convex sections  441  like a net. The entire concave section  442  also forms a single cylindrical surface which is different from the cylindrical surface which is made by the convex sections and is coaxial with the rotational axis of the developing roller  44 . Moderate slants  443  connect the convex sections  441  to the concave section  442  which surrounds the convex sections  441 . That is, a normal line to the slants  443  contains a component which is outward in the radius direction of the developing roller  44  (upward in  FIG. 5 ), that is, which is in a direction away from the rotational axis of the developing roller  44 . The developing roller  44  having such a structure may be made by the manufacturing method described in JP-A-2007-140080 for instance. 
       FIGS. 6A and 6B  are plan development views showing the structure of the surface of the developing roller in further detail. Each one of the convex sections  441  in the surface of the developing roller  44  has a top section which is shaped like an approximately square projection rotated 45 degrees as shown in  FIG. 6A . A number of such convex sections  441  are arranged linearly at equal intervals in the width direction X which is parallel to the rotational axis of the developing roller  44 , thereby constituting convex section row. A plurality of convex section rows are provided also in a circumferential direction Y, which is orthogonal to the width direction X, at different positions on the circumferential surface of the developing roller  44 .  FIG. 6A  shows three convex section rows, which will be hereinafter referred to as “the first row”, “the second row” and “the third row” from the top in  FIG. 6A . 
     As shown in  FIG. 6A , the positions of the convex sections  441  along the width direction X are displaced half the arrangement pitch of the convex sections  441  from each other between the first and the second rows. This holds true as for the positions between the second and the third rows as well. That is, the convex section rows are arranged such that the convex sections  441  are in a staggered pattern in the surface of the developing roller  44 . Therefore, it can be said that rows of the convex sections which are arranged in an oblique direction which is at a degree of θ (=45 degree) with respect to the width direction X on the surface of the developing roller  44 . 
     Dimensions of the respective sections are described with reference to  FIG. 6B . A length L 1  of a diagonal of the top surface of the convex section  441  is 50 μm in both in X and Y directions, and a length L 2  of a diagonal of the bottom part of the convex section  441  is 100 μm both in the X and Y directions. An interval L 3  between the bottom parts of two convex sections located at the same position in the X direction and adjacent to each other in the Y direction is 50 μm, and an interval between the bottom parts of the two convex sections located at the same position in the Y direction and adjacent to each other in the X direction is same. From these relationships, an interval L 4  of two convex sections located at the same position in one direction (X direction or Y direction) and adjacent to each other in the other direction is 100 μm. The dimensions of the respective sections are not limited to these numerical values and may be appropriately changed. 
     Out of the slants  443  connecting the convex sections  441  and the concave sections  442 , the slants  443   a  located before the convex sections  441  in the moving direction D 4  of the surface according to the rotation of the developing roller  44  and the slants  443   b  located behind the convex sections  411  have different inclinations. The reason for this is described in detail later. 
     Referring back to  FIG. 1 , the description of the image forming apparatus is continued. The toner image developed by the developer unit  4  as described above is primarily transferred onto an intermediate transfer belt  71  of a transfer unit  7  in a primary transfer region TR 1 . The transfer unit  7  includes the intermediate transfer belt  71  mounted on a plurality of rollers  72  to  75  and a driver (not shown) for driving the roller  73  into rotation to rotate the intermediate transfer belt  71  in a specified rotating direction D 2 . In the case of transferring a color image onto the sheet S, the toner images of the respective colors formed on the photosensitive member  22  are superimposed on the intermediate transfer belt  71  to form the color image, which is secondarily transferred onto the sheet S dispensed one by one from a cassette  8  and conveyed to a secondary transfer region TR 2  along a conveyance path F. 
     At this time, for the purpose of correctly transferring the image on the intermediate transfer belt  71  onto the sheet S at a predetermined position, the timing of feeding the sheet S into the secondary transfer region TR 2  is controlled. To be more specific, there is a gate roller  81  disposed in front of the secondary transfer region TR 2  on the transportation path F. The gate roller  81  starts to rotate in accordance with the timing of rotation of the intermediate transfer belt  71 , and accordingly, the sheet S is fed into the secondary transfer region TR 2  at a predetermined timing. 
     Further, the sheet S on which the color image is thus formed is transported to a discharge tray  89  which is disposed at a top surface of the apparatus main body via a pre-discharge roller  82  and a discharge roller  83  after the toner image is fixed to the sheet S by a fixing unit  9 . Meanwhile, when images are to be formed on the both surfaces of the sheet S, the discharge roller  83  starts rotating in the reverse direction upon arrival of the rear end of the sheet S, which carries the image on its one surface as described above, at a reversing position PR located behind the pre-discharge roller  82 , thereby transporting the sheet S in the arrow direction D 3  along a reverse transportation path FR. The sheet S is returned back to the transportation path F again before arriving at the gate roller  81 . At this time, the surface of the sheet S which abuts on the intermediate transfer belt  71  in the secondary transfer region TR 2  and is to receive a transferred image is opposite to the surface which already carries the image. In this fashion, it is possible to form images on the both surfaces of the sheet S. 
     Further, as shown in  FIG. 2 , the respective developers  4 Y,  4 C,  4 M and  4 K comprise memories  91 ,  92 ,  93  and  94  respectively which store data related to the production lot, the use history, the remaining toner amount and the like of the developers. In addition, wireless telecommunication devices  49 Y,  49 C,  49 M and  49 K are provided in the developers  4 Y,  4 C,  4 M and  4 K, respectively. When necessary, the telecommunication devices selectively perform non-contact data telecommunication with a wireless telecommunication device  109  which is provided in the apparatus main body, whereby data transmission between the CPU  101  and the memories  91  through  94  via the interface  105  is performed to manage various types of information regarding the developers such as management of consumables. Meanwhile, in this image forming apparatus, non-contact data transmission using electro-magnetic scheme such as wireless telecommunication is performed. However, the apparatus main body and each developer may be provided with connectors and the like, and the connectors may be engaged mechanically to perform data transmission between each other. 
     Further, as shown in  FIG. 2 , the apparatus includes a display  12  which is controlled by a CPU  111  of the main controller  11 . The display  12  is formed by a liquid crystal display for instance, and shows predetermined messages which are indicative of operation guidance for a user, a progress in the image forming operation, abnormality in the apparatus, the timing of exchanging any one of the units, and the like in accordance with the control command from the CPU  111 . 
     In  FIG. 2 , a reference numeral  113  represents an image memory provided in the main controller  11  in order to store the image supplied from the external apparatus, such as a host computer, via the interface  112 . A reference numeral  106  represents a ROM for storage of an operation program executed by the CPU  101  and control data used for controlling the engine EG. A reference numeral  107  represents a RAM for temporary storage of operation results given by the CPU  101  and other data. 
     Further, there is a cleaner  76  in the vicinity of the roller  75 . The cleaner  76  moves nearer to and away from the roller  75  driven by an electromagnetic clutch not shown. In a condition that the cleaner  76  is moved nearer to the roller  75 , a blade of the cleaner  76  abuts on the surface of the intermediate transfer belt  71  mounted on the roller  75  and scrapes off the toner remaining on and adhering to the outer circumferential surface of the intermediate transfer belt  71  after the secondary transfer. 
     Furthermore, a density sensor  60  is disposed in the vicinity of the roller  75 . The density sensor  60  confronts a surface of the intermediate transfer belt  71  and measures, as needed, the density of the toner image formed on the outer circumferential surface of the intermediate transfer belt  71 . Based on the measurement results, the apparatus adjusts the operating conditions of the individual parts thereof that affects the image quality such as the developing bias applied to each developer, the intensity of the exposure beam L, and tone-correction characteristics of the apparatus, for example. 
     The density sensor  60  is structured to output a signal corresponding to a contrasting density of a region of a predetermined area defined on the intermediate transfer belt  71  using a reflective optical sensor, for example. The CPU  101  is adapted to detect image densities of individual parts of the toner image on the intermediate transfer belt  71  by periodically sampling the output signals from the density sensor  60  while moving the intermediate transfer belt  71  in rotation. 
     Restriction of a toner layer on the developing roller  44  within the developer  4 K, . . . of the image forming apparatus having the structure above will now be described in detail. In a structure as that described above in which the surface of the developing roller  44  for carrying toner has concavity and convexity, it is possible for both the convex sections  441  and the concave section  442  of the developing roller  44  to carry toner. However, in this image forming apparatus, it is structured that the restriction blade  46  abuts on the developing roller  44  within the surface of the developing roller  44  directly to remove toner on the convex sections  441 . The reason is as described below. 
     First, the distance between the restriction blade  46  and the convex sections  441  needs be controlled precisely in order to form a uniform toner layer on the convex sections  441 . However, for carrying of toner only by the concave section  442 , the restriction blade  46  may abut on the convex sections  441  and remove all toner on the convex sections  441 , which can be realized relatively easily. Further, since the volume of the space defined between the restriction blade  46  and the concave section  442  determines the amount of transported toner, it is possible to stabilize a transported toner amount. 
     This provides another advantage with respect to superiority of a transported toner layer. That is, carrying of toner by the convex sections  441  tends to degrade toner because of friction contact of the toner with the restriction blade  46 . More specifically, there are problems such as reduction of the fluidity and the charging performance of toner, clumping together due to toner particles pressed to each other, and filming due to fixedly adherence of toner to the developing roller  44 . In contrast, carrying of toner by the concave section  442  which is less influenced by the pressure from the restriction blade  46  is less likely to give rise to such problems. Further, the manner of friction contact on the restriction blade  46  is greatly different between toner carried by the convex sections  441  and toner carried by the concave section  442 . Hence, their charge levels are predicted to largely vary from each other. However, carrying of toner by the concave section  442  alone makes it possible to suppress such variations. 
     The recent years in particular have seen a growing demand for size reduction of toner particles and a lower fixing temperature to enhance the resolution of an image and reduce the amount of consumed toner and electric power consumption. The structure described above meets the demand. Small-particle toner generally has a high saturation charge level but gets charged slowly at the beginning, and hence, toner carried by the convex sections  441  tends to have a significantly higher charge level (get excessively charged) than toner carried by the concave sections  442 . A charge level difference thus created shows itself as a development history in an image. Further, with respect to toner having a low melting point, fixing of toner to each other and fixing of the toner to the developing roller  44  and the like could easily occur by the friction contact of toner with each other or with the developing roller  44 . However, such a problem is less likely to occur where the structure described above is used in which only the concave section  442  carries toner. 
     Next, the problem of the electrical charging of the seal member  47  as a subject matter of the invention is studied. The seal member  47  receives electric charges from the toner by touching the charged toner remaining on and adhering to the surface of the developing roller  44 . In this way, the toner is discharged and becomes more easily separable from the surface of the developing roller  44  to be collected into the housing  41 . The collected toner has the electrification charges reset and is mixed with the toner stored in the housing  41 . 
     In order to increase the action of discharging the toner, the seal member  47  preferably has a function of charging the toner with a polarity opposite to the charging polarity of the toner. Accordingly, at least a surface area of the seal member  47  which possibly comes into contact with the developing roller  44  is preferably made of a material located at a position to charge the toner with the polarity opposite to the charging polarity in triboelectric series. For example, widely used acrylic or styrene-acrylic toner is negatively chargeable toner, and fluororesin such as PTFE (polytetrafluoroethylene), vinyl chloride or PE (polyethylene) located at a more negative side (lower side) than the material of the toner in triboelectric series can be cited as a material for changing the charged potential of the toner toward a positive side. 
     On the other hand, the seal member  47  is charged with the same polarity with the charging polarity of the toner by the received electric charges. Particularly, any one of the materials cited above for itself has high electrical insulation and thus is easily charged by the accumulation of the electric charges received from the toner. If the seal member  47  is charged with the same polarity as the toner, it produces a repulsive force to the approaching charged toner. Since an ability to receive further electric charges decreases, the function of discharging the charged toner decreases. Further, the negatively charged seal member  47  adsorbs positively charged or electrically neutral toner particles, external additive particles and the like, which may be fixed to the seal member  47  and the surface of the developing roller  44  to cause filming. Any of these becomes a cause of toner scattering from the developing roller  44  in the vicinity of the seal member  47 , fogging and image defects such as image streaks. 
     In order to solve this problem, the image forming apparatus of this embodiment employs the following constructions: 
     (1) The surface of the developing roller  44  is provided with a multitude of convex sections  441  forming parts of the same cylindrical surface. 
     (2) The developing roller  44  is made of a metal to provide the top surfaces of the respective convex sections  441  with electrical conductivity and to electrically connect the respective convex sections with each other. 
     (3) The seal member  47  is made of a material in which carbon particles are dispersed in a resin base material having an action of discharging the toner to provide electrical conductivity. 
     (4) A PTFE resin having a particle diameter of 20 to 30 μm is used as the resin base material. 
     Next, reasons for employing the above constructions are separately described with reference to  FIGS. 7A to 10B . First of all, the above constructions (1) and (2) are described. 
       FIGS. 7A and 7B  are diagrams showing contact states of the developing roller and the seal member As described above (see  FIGS. 5 and 6A ), a multitude of convex sections  441  are provided on the surface of the developing roller  44  in this embodiment. The respective top surfaces of the convex sections  441  form the same cylindrical surface. Thus, as shown in  FIG. 7A , a contact surface  471  of the seal member  47  in contact with the developing roller  44  and the top surfaces of the respective convex sections  441  on the surface of the developing roller  44  are in surface contact and contact pressures are substantially uniform at positions where the contact surface  471  of the seal member  47  and a plurality of convex sections  441  face each other. As a result, at the respective positions, the seal member  47  and the convex sections  441  can be reliably held in contact. Although parts of the contact surface  471  of the seal member  47  facing the concave sections  442  look not to be in contact with the surface of the developing roller  44 , the convex sections belonging to other rows actually come into contact with these parts by a movement of the developing roller  44  in the Y direction of  FIG. 7A . 
     Since the developing roller  44  is metallic, the top surfaces of the respective convex sections  441  have electrical conductivity and the respective convex sections  441  are electrically connected to each other. Thus, electric charges accumulated in the respective parts of the seal member  47  can be reliably transferred toward the developing roller  44  by the contact with the convex sections  441 . Further, since the developing roller  44  is connected with the bias power source  140 , the electric charges from the seal member  47  are allowed to escape to the outside via the bias power source  140 . 
     A conventional structure obtained by finishing a developing roller surface by a sandblast process is shown as a comparative example in  FIG. 7B . As shown in  FIG. 7B , a multitude of round recesses are present in a surface of a developing roller  1044  finished with the blast process, and the depths of the recesses and the heights of projecting parts are not uniform and vary. Thus, if a seal member  1047  is brought into contact with this surface, areas of the developing roller surface actually in contact with the seal member  1047  are only parts largely projecting as compared with the surrounding and a state of this contact is substantially point contact. It can be hardly expected to smoothly transfer electric charges from the seal member  1047  to the developing roller  1044  via such unreliable contact parts. 
     As described above, in this embodiment, the multitude of convex sections  441  having electrical conductivity and forming parts of the same cylindrical surface are provided on the surface of the developing roller  44  and are brought into contact with the seal member  47 . In this way, electric charges accumulated on the seal member  47  are allowed to stably and reliably escape to the developing roller  44 , thereby preventing the electrical charging of the seal member  47 . Since a conduction path for the discharged electric charges is short, the electric charges can be efficiently discharged even by a short-lasting contact. The potential of the seal member  47  is the same as that of the developing roller  44 . By doing so, a useless transfer of electric charges between the developing roller  44  and the seal member  47  can be eliminated. The seal member  47  may be connected with the bias power source  140  to apply the same development bias potential as the one applied to the developing roller  44 . However, since the seal member  47  has electrical conductivity and is electrically connected with the surface of the developing roller  44  in this embodiment, potential may not be actively given. 
     Next, the above constructions (3) and (4) are described. As described above, the seal member  47  is preferably made of the material having the action of discharging the toner. Since the negatively chargeable toner is used in this embodiment, PTFE is used as a material having an action of positively charging this toner. Further, in order to allow the accumulated electric charges to smoothly escape, carbon particles are dispersed in a PTFE base material in the used material. The PTFE base material used is such that a particle diameter of crystals constituting the base material is about 20 to 30 μm. The reason for this is as follows. 
       FIGS. 8A and 8B  are diagrams showing grain structures of seal members. A resin material such as PTFE is microscopically an aggregate of many crystals. Additive particles such as carbon particles dispersed in the resin base material are not uniformly distributed in the entire base material but mostly penetrate into grain boundaries. Specifically, the electric charges accumulated on the seal member  47  transfer toward the developing roller  44  not inside the crystals, but via electrically conductive particles such as carbon particles distributed along the grain boundaries. In other words, conduction paths in the case of allowing the electric charges to escape from the seal member  47  are formed along the grain boundaries. From this perspective, a case where crystal grains are small as shown in  FIG. 8A  (representative particle diameter: d 1 ) and a case where crystal grains are large as shown in  FIG. 8B  (representative particle diameter: d 2 &gt;d 1 ) are compared and studied. In  FIGS. 8A and 8B , dotted line indicates the grain boundaries of the resin base material. 
     In this embodiment, the maximum length of the top surface of the convex section  441  is about 50 μm. This corresponds to the length L 1  of the diagonal of the rhombic shape of the top surface of the convex section  441 , for example, shown in  FIG. 6B . As shown in  FIG. 8A , a plurality of grains making up the seal member  47  come into contact with the top surfaces of the convex sections  441  if the particle diameter d 1  of the resin base material forming the seal member  47  is sufficiently smaller than the length L 1 . Thus, the grain boundaries of these crystals appear at the contact parts with the convex sections  441 . As a result, the conduction paths by way of the electrically conductive particles distributed in the grain boundaries and the top surfaces of the convex sections  441  are formed, and the electric charges accumulated on the seal member  47  are efficiently discharged toward the developing roller  44 . 
     On the other hand, if the particle diameter d 2  of the resin base material forming the seal member  47  is larger than the maximum length L 1  of the top surfaces of the convex sections  441  as shown in  FIG. 8B , there are cases where the contact part with the convex section  441  is taken up by a single crystal grain to weaken the action of discharging the electric charges via the crystal grains. 
     Accordingly, the resin base material having an average particle diameter (20 to 30 μm) smaller than the maximum length L 1  (50 μm) of the top surfaces of the convex sections  441  is used in this embodiment. By doing so, the electric charges accumulated on the seal member  47  can be efficiently discharged via the grain boundaries. 
       FIG. 9  is a table showing constitutions and evaluation results of seal members. The inventors of this application prepared a plurality of samples of the seal member from different materials and various evaluations were conducted by mounting these in the apparatus. PTFE and PE resins as representative materials for positively charging (or reducing the charged amount of) the negatively charged toner were used as the resin base material to prepare a plurality of samples of the seal member having different particle diameters. As evaluation items, a degree of fogging on a formed image, a toner scatter amount from the surface of the developing roller  44  and a degree of streaky defect (image streak) produced in the image were used. The lower these degrees and amount were, the higher the evaluations were. 
     As a result, as shown in  FIG. 9 , the best result was obtained in the respective evaluation items of fogging, toner scattering and image streaks when the PTFE base material, in which carbon particles were dispersed and whose average particle diameter was 25 μm was used. In other words, the levels of fogging, toner scattering and image streaks were all lowest. Further, the second best result was obtained when the PTFE base material, in which carbon particles were dispersed and whose average particle diameter was 50 μm was used. On the other hand, no good result was obtained when the particle diameter was 100 μm even if the PTFE base material, in which the same carbon particles were dispersed, was used. As described above, the average particle diameter of the base material is preferably equal to or smaller than the maximum length of the convex sections  441  in the X direction. 
     If the base material is a PE resin, the result was rather poor when the particle diameter was 80 μm and poor when the particle diameter was 150 μm. In the case of PE resins, those generally distributed in the market are only those having relatively large particle diameters. If the maximum length of the convex sections  441  is about 50 μm as in this embodiment, fluororesins such as PTFE having smaller particle diameters can be said to be most suitable as the base material of the seal member. Accordingly, in this embodiment, a material, in which carbon particles are dispersed in a PTFE resin base material having an average particle diameter of 20 to 30 μm was used as the material of the seal member  47 . 
     The fluororesin having such fine grains may be ground by being abraded against the convex sections  441  on the surface of the developing roller  44  and adhere to the surfaces of the convex sections  441 . However, since the resin adhering to the top surfaces of the convex sections  441  in this way has an effect of suppressing new toner adhesion, it also has an effect of preventing filming on the developing roller  44 . 
     In this embodiment, the developing roller  44  has the following surface structure to make the action of discharging the seal member  47  more effective. 
       FIGS. 10A and 10B  are diagrams showing a cross section structure of the developing roller surface when viewed in the axial direction. As shown in  FIG. 10A , out of the slants  443  connecting the convex sections  441  and the concave sections  442 , the inclination of the slants  443   a  located before the convex sections  441  in the moving direction D 4  according to the rotation of the developing roller  44  is set larger than that of the slants  443   b  located behind the convex sections  441  in the same direction in this embodiment. In other words, a relationship of α&gt;β holds between angles α, β shown in  FIG. 10A . 
     This is for preventing toner T 2  adhering to the concave sections  442  or the slants  443   a ,  443   b  from climbing up the slants  443   a  to come onto the convex sections  441  while smoothly conveying toner T 1  adhering to the top surfaces of the convex sections  441  to the concave sections  442  along the slants  443   b  by the contact with the seal member  47  or by a repulsive force thereof. If the toner adheres to the top surfaces of the convex sections  441 , this toner is squeezed between the seal member  47  and the convex sections  441  to be abraded, whereby this toner is fixed to one surface or the external additive is caused to be separated, thereby deteriorating the property. In this embodiment, the occurrence of such problems is prevented by making the transfer of the toner T 2  adhering to the concave sections  442  or the slopes  443  to the convex sections  441  difficult while making the transfer of the toner T 1  adhering to the convex sections  441  to the concave sections  442  smoother. 
     Further, as shown in  FIG. 10B , an elevation difference H between the convex sections  441  and the concave sections  442  is set equal to or larger than a volume average particle diameter Dave of the toner. If toner T 0  having a particle diameter larger than the elevation difference H between the convex sections  441  and the concave sections  442  is carried in the concave sections  442 , the top thereof projects from the top surfaces of the convex sections  441 . In this case, the toner T 0  lifts the seal member  47  up to cancel the electrical connection with the convex sections  441 . If such a situation occurs with a high probability, the seal member  47  and the developing roller  44  are held in direct contact for a shorter time, whereby electric charges accumulated on the seal member  47  cannot efficiently escape. If the elevation difference H between the convex sections  441  and the concave sections  442  is set equal to or larger than the volume average particle diameter Dave of the toner, an occurrence probability of such a situation can be made quite small. For example, in an apparatus using toner having a volume average particle diameter of 5 μm, the elevation height H may be set to about 6 μm. 
     Next, an operation of more reliably preventing the electrical charging of the seal member  47  is described. As described above, it is preferable to carry no toner on the convex sections  441  in this embodiment. To this end, the restriction blade  46  acts to carry the toner only in the concave sections  442  on the developing roller surface. This is preferable in preventing the toner adhesion to the seal member  47  and the electrical charging of the seal member  47 . In other words, by bringing the convex sections  441  into contact with the seal member  47  without toner adhesion, the electrical connection between the seal member  47  and the developing roller  44  is ensured so that electric charges accumulated on the seal member  47  are allowed to reliably escape to the developing roller  44 . However, the adhesion of the toner jumped from the developing roller  44  to the convex sections  441  is actually thought to be unavoidable if an image forming operation is performed and a development bias is applied to the developing roller  44 . 
     Accordingly, in addition to the discharging action during the image forming operation, a seal discharging operation of actively discharging the seal member  47  by rotating the developing roller  44  to bring it into contact with the seal member  47  with no toner carried on the convex sections  441  may be performed at a specified timing. The operation of the image forming apparatus including the seal discharging operation may be set, for example, as follows. 
       FIG. 11  is a flow chart showing the operation of the image forming apparatus including the seal discharging operation. The apparatus waits on standby until an image formation command is given from the outside (Step S 101 ). Upon receiving the image formation command, an image forming operation is performed to form an image corresponding to the command (Step S 102 ). Then, a cumulative image number as a cumulative number of images formed using this developer is calculated (Step S 103 ). 
     Whether or not the cumulative image number has exceeded a specified threshold value is judged (Step S 104 ). Here, threshold values can be set, for example, in 100s, 500s or 1000s. Unless the cumulative image number has reached the threshold value, this flow returns to Step S 101  to wait for a new image formation command. On the other hand, if the cumulative image number has exceeded the threshold value, the seal discharging operation is performed (Step S 105 ). 
     For example, the following operation may be performed as the seal discharging operation. Specifically, the developing roller  44  is rotated for a specified time without applying any development bias thereto, more preferably while being grounded. By doing so, the surface of the developing roller  44  having toner adhesion to the convex sections  441  restricted by the restriction blade  46  directly reaches the contact position with the seal member  47 . As a result, the convex sections  441  carrying no toner directly come into contact with the seal member  47 , whereby electric charges accumulated on the seal member  47  are discharged. After the seal member  47  is discharged in this way, this flow returns to Step S 101  to wait for the input of a new image formation command. 
     By doing so, the occurrence of toner adhesion to the seal member  47  and the developing roller  44 , fogging, toner scattering and the like can be more reliably prevented by more reliably removing electric charges accumulated on the seal member  47 . Whether or not the toner is carried in the concave sections  442  in the seal discharging operation is optional. Even if the toner is carried in the concave sections  442 , it can be prevented that a part of the jumped toner moves onto the convex sections  441  by stopping the application of the development bias to the developing roller  44  as described above, whereby the convex sections  441  can be brought into contact with the seal member  47  with no toner carried on the convex sections  441 . 
     As described above, in this embodiment, a multitude of convex sections  441  whose top surfaces form parts of the same cylindrical surface are provided on the surface of the developing roller  44  and the seal member  47  made of the material having electrical conductivity by dispersing carbon particles in the PTFE resin base material having the action of discharging the toner is brought into contact with the surface of the developing roller  44 . According to such a construction, electrification charges of the seal member  47  produced by the contact with the charged toner are allowed to more reliably escape toward the developing roller  44  by the surface contact with the convex sections  441 , wherefore the occurrence of problems such as toner scattering, fogging and filming resulting from the electrical charging of the seal member  47  can be prevented. 
     Using the material whose grain size is smaller than the maximum length of the convex sections  441  as the resin base material of the seal member  47 , electric charges accumulated on the seal member  47  are allowed to more efficiently escape to the developing roller  44  by making the transfer of electric charges via the grain boundaries smoother. 
     The invention is not limited to the above embodiment, and various changes other than the above can be made without departing from the gist thereof. For example, though already mentioned above, the execution of the “seal discharging operation” in the above embodiment is optional and not essential. This is because it is difficult to think the electrical connection between the convex sections  441  and the seal member  47  is completely hindered with such a small amount of the toner adhering to the convex sections  441  in a normal image forming operation and the action of discharging the seal member  47  is not drastically reduced. 
     Although carbon particles are used as electrically conductive particles to be added to the PTFE resin as the base material of the seal member  47  in the above embodiment, it is also possible to use, for example, metal particulates as the electrically conductive particles. Further, any material other than the above PTFE resin can be used as the base material of the seal member  47  provided that it has a function of discharging toner and small grain sizes. 
     In the above embodiment, the invention is applied to the image forming apparatus employing a so-called rotary development method in which a plurality of developers are mounted in the rotating rotary developer unit. An application subject of the invention is not limited to this and the invention is also applicable, for example, to an image forming apparatus employing a so-called tandem development method in which a plurality of developers are arranged in a rotation direction of a transfer medium or to a monochromatic image forming apparatus including only one developer. 
     As described above, in the above embodiment, the developers  4 Y,  4 M,  4 C and  4 K respectively function as a “developing device” of the invention. In the above embodiment, the photosensitive member  22 , the developing roller  44  and the seal member  47  respectively function as a “latent image carrier”, a “toner carrier roller” and a “seal member” of the invention. Further, the housing  41  and the restriction blade  46  respectively function as a “housing” and a “restricting member” of the invention. Further, the carbon particles dispersed in the PTFE resin forming the seal member  47  function as “electrically conductive particles” of the invention. 
     In the developing device and the image forming apparatus according to the invention, the contact surface of the seal member preferably has electrical conductivity to more effectively prevent the electrical charging of the seal member. Even if the contact surface of the seal member has electrical conductivity, the electrical charging is unavoidable unless a discharge path is provided. However, in this structure, electric charges accumulated on the seal member are allowed to reliably escape to the toner carrier roller by the contact of the seal member having electrical conductivity with the top surfaces of the convex sections of the toner carrier roller. 
     For example, the contact surface of the seal member can be made of a material obtained by dispersing electrically conductive particles in a resin base material which is located at a position to charge the toner with a polarity opposite to its charging polarity in triboelectric series. By making the contact surface of the resin base material, toner leakage can be effectively prevented and the abrasion of the toner discharging roller can be suppressed. Further, by using the material for charging the toner with the polarity opposite to its charging polarity, the charged toner can be efficiently discharged. By dispersing the electrically conductive particles in the resin base material, it is possible to provide the contact surface with electrical conductivity and to efficiently discharge electric charges received from the toner to the toner carrier roller. 
     In this case, the grain size of the resin base material is more preferably equal to or smaller than the length of the respective convex sections in a direction parallel to the rotational axis of the toner carrier roller. Although electric charges accumulated on the seal member are discharged to the toner carrier roller via the electrical conductive particles, the electrically conductive particles dispersed in the resin base material are eccentrically located in large quantity in grain boundaries of the base material. In other words, electric charges accumulated on the seal member are mainly transferred along the grain boundaries and finally discharged to the toner carrier roller. Accordingly, in order to allow the accumulated electric charges to efficiently escape, the contact surface of the seal member held in contact with the top surfaces of the convex sections of the toner carrier roller preferably includes at least one grain boundary. To this end, the grain size of the resin base material is preferably equal to or smaller than the length of the respective convex sections. 
     Further, a fluororesin such as PTFE (polytetrafluoroethylene) can be, for example, suitably used as the resin base material. Such a fluororesin material can be suitably used for a seal member since the toner is difficult to adhere to the surface due to good slipperiness of the surface. In the case of using generally used negatively chargeable toner such as acrylic toner or styrene-acrylic toner, a good action of discharging the toner can be obtained since the fluororesin has a property of positively charging these. The fluororesin generally has high electrical insulation and is easily charged, but electric charges are allowed to effectively escape to the toner carrier roller to prevent the electrical charging by dispersing the electrically conductive particles. 
     An elevation difference between the convex sections and the concave section is preferably equal to or larger than a volume average particle diameter of the toner. If the elevation difference between the both sections is small, toner may lift the seal member up to make the contact with the convex sections unstable when the toner having particle diameters larger than this elevation difference are carried in the concave section. If the elevation difference between the convex sections and the concave section is set equal to or larger than the volume average particle diameter of the toner, most of toner particles have particle diameters equal to or smaller than the elevation difference between the convex sections and the concave section, wherefore such a problem is unlikely to occur. 
     On the toner carrier roller surface, the inclination of slants connecting the convex sections and the concave section may be larger at a front side than at a rear side in a moving direction of the surface according to the rotation of the toner carrier roller. According to such a construction, even if the toner adheres to the top surfaces of the convex sections, the toner is easily scraped off by the contact with the seal member, whereas it is difficult for the toner carried in the concave section to be carried onto the top surfaces of the convex sections by the seal member. In other words, by employing such a construction, the toner carried on the convex sections can be reduced, thereby preventing the toner from being pressed between the top surfaces of the convex sections and the seal member to adhere to either surface or a hindrance to the electrical connection between the top surfaces of the convex sections and the seal member. 
     A restricting member may be provided which restricts toner adhesion to the top surfaces of the convex sections by coming into contact with the toner carrier roller surface at a position upstream of a contact position of the toner carrier roller and the seal member in the rotation direction of the toner carrier roller. As described above, the contact surface of the seal member needs to directly come into contact with the electrically conductive top surfaces of the convex sections of the toner carrier roller in order to allow electric charges accumulated on the seal member to effectively escape. By providing the restricting member to restrict the toner adhesion to the top surfaces of the convex sections, the convex sections can be brought into contact with the seal member while being exposed. Further, by causing only the concave section to carry the toner, a toner conveyance amount can be controlled. 
     In the toner carrier roller, the top surfaces of the respective convex sections are more preferably electrically connected to each other. By doing so, it becomes possible to deprive the seal member of more electric charges by dispersing the electric charges the convex sections received from the seal member, wherefore the electrical charging of the seal member can be more effectively prevented. In order to realize such a construction, the convex sections and the concave section may be formed, for example, by forming a multitude of grooves in a metal tube surface. 
     In the image forming apparatus according to the invention, it is preferable to provide an operation mode in which the seal member abuts on the toner carrier roller while the toner carrier being rotated without the toner being carried at least on the convex sections of the toner carrier roller surface. By bringing the convex sections carrying no toner and the seal member into contact, electric charges accumulated on the seal member are allowed to more reliably escape to the toner carrier roller. 
     Although the invention has been described with reference to specific embodiments, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiment, as well as other embodiments of the present invention, will become apparent to persons skilled in the art upon reference to the description of the invention. It is therefore contemplated that the appended claims will cover any such modifications or embodiments as fall within the true scope of the invention.