Abstract:
A developing apparatus for an image forming apparatus includes a frame having a developer container; a developing roller; a blade for regulating a developer layer thickness on the roller, the blade including a base end portion supported by the frame, and a free end portion contacted to the roller; and an elastic seal provided between the frame and the blade to prevent leakage of the developer from the developer container in an axial direction of the roller at an end portion, wherein in a state before the roller is mounted to the frame, a thickness of the seal, measured in a compression direction in which the seal is compressed by the blade, is larger in a free end portion side than in a base end portion side with respect to a direction crossing with the axial direction.

Description:
FIELD OF THE INVENTION AND RELATED ART 
     The present invention relates to a development apparatus (device) and a cartridge. 
     It has been a common practice to provide an image forming apparatus which uses an electrophotographic image formation process is provided with a development device for developing an electrostatic latent image formed on a photosensitive drum as an image bearing member. The development device is provided with a development frame in which toner as developer is stored, and a rotatable development roller as a developer bearing member. 
     There is positioned a development blade as a developer layer thickness regulating member, in the adjacencies of the development roller. This development blade regulates in thickness the layer of toner borne (coated) on the peripheral surface of the development roller to form a toner layer having a preset thickness. The development blade extends across the entire range of the development roller in terms of the direction (which hereafter may be referred to simply as “lengthwise direction”) of the rotational axis of the development roller. It is supported by a metallic support formed of a piece of steel plate or the like, in such a manner that one of its lengthwise edge portions is layered upon the metallic support. Hereafter, this integrated combination of the metallic blade support and development blade will be referred to as “development blade unit”. 
     The development device has a development end sealing member as a development blade bottom seal, as a developer sealing member for preventing toner from leaking from the development unit through the gaps between the development roller and development frame and the gaps between the development blade unit and development frame. 
     The development end seal is positioned in the adjacencies of both of the lengthwise ends of the development roller, between the development roller and development device frame, to prevent the toner from leaning out of the development frame at the lengthwise ends of the development roller. 
     The development blade bottom seal prevents the toner from leaking out of the development frame, by being airtightly adhered to the aforementioned end seal, on the rear side of the development blade unit, in such a manner that it fills the gap between the development frame and development blade unit. 
     As the development blade is placed in contact with the development roller, the blade is made to deform, by the reaction force resulting from the contact between the development blade and development roller, in such a manner that its center portion in terms of the lengthwise direction is likely to separated from the development roller. 
     On the other hand, the development blade is attached to the development frame in such a manner that the end seals and bottom seals are sandwiched between the lengthwise end portions of the development blade and development frame, being thereby compressed. Therefore, the contact pressure between each end seal and development roller, and the contact pressure between each bottom seal, are likely to be higher across the end portion than the center portion in terms of the range of contact in terms of the lengthwise direction. 
     If the area of contact is nonuniform in contact pressure in terms of the lengthwise direction, the development blade is likely to be nonuniform in its ability to electrically charge toner, which in turn is likely to cause an image forming apparatus to output an image which is nonuniform in density in terms of the lengthwise direction. 
     For example, there is disclosed in Japanese Laid-open Patent Application H07-160116, a method for making the lengthwise end portions of a development blade longer in the free length (distance from developer regulating edge of development blade to base edge of development blade) than the center portion of the development blade, by partially cutting away the lengthwise end portions of the metallic support plate for the development blade, in the direction perpendicular to the lengthwise direction. With the use of this method, it is possible to set the contact pressure between the development blade and development roller to be less across the lengthwise end portions of the development blade the than the center portion, to make the development blade uniform in its contact pressure upon the development roller in terms of the lengthwise direction. 
     SUMMARY OF THE INVENTION 
     The primary object of the present invention is to reduce the occurrence of nonuniformity in image density, by reducing the contact pressure of a development blade (regulating member), across its lengthwise end portions in terms of the direction parallel to the axial line of the development roller (developer bearing member, in order to minimize the problem that an image forming apparatus outputs an image which is nonuniform in density. 
     According to an aspect of the present invention, there is provided a developing apparatus for use with an image forming apparatus, comprising a frame; a developer accommodating portion formed by said frame; a developer carrying member, provided in said frame, for developing a latent image formed on the image bearing member with a developer; a regulating member for regulating a layer thickness of the developer carried on said developer carrying member, said regulating member including a base end portion supported by said frame, and a free end portion contacted to said developer carrying member; and a sealing member provided between said frame and said regulating member to prevent leakage of the developer from said developer accommodating portion in an axial direction of said developer carrying member at an end portion of said developer carrying member with respect to the axial direction, said sealing member having an elasticity, wherein in a state before said developer carrying member is mounted to said frame, a thickness of said sealing member, measured in a compression direction in which said sealing member is compressed by said regulating member, is larger in a free end portion side than in a base end portion side with respect to a direction crossing with the axial direction. 
     According to another aspect of the present invention, there is provided a cartridge detachably mountable to a main assembly of an image forming apparatus; the cartridge comprising a frame; a developer carrying member, provided in said frame, for developing a latent image formed on the image bearing member with a developer; a regulating member for regulating a layer thickness of the developer carried on said developer carrying member, said regulating member including a base end portion supported by said frame, and a free end portion contacted to said developer carrying member; and a sealing member provided between said frame and said regulating member to prevent leakage of the developer from said developer accommodating portion in an axial direction of said developer carrying member at an end portion of said developer carrying member with respect to the axial direction, said sealing member having an elasticity, wherein in a state before said developer carrying member is mounted to said frame, a thickness of said sealing member, measured in a compression direction in which said sealing member is compressed by said regulating member, is larger in a free end portion side than in a base end portion side with respect to a direction crossing with the axial direction. 
     Further, features of the present invention will become apparent from the following description of exemplary embodiments (with reference to the attached drawings). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic sectional view of the image forming apparatus in the first embodiment of the present invention, and shows the structure of the apparatus. 
         FIG. 2  is a schematic sectional view of the cartridge in the first embodiment, and shows the structure of the cartridge. 
         FIG. 3  is an external perspective view of the cartridge in the first embodiment. 
         FIG. 4  is a schematic sectional view of the image forming apparatus in the first embodiment when the cartridge tray of the apparatus is in its outermost position into which it can be pulled out of the main assembly of the apparatus. 
         FIG. 5  is a schematic sectional view of the image forming apparatus, which shows the operation for installing a cartridge into the cartridge tray, and the operation for removing a cartridge from the cartridge tray. 
         FIG. 6  is a drawing of the development device in the first embodiment. 
         FIG. 7  is an enlarged perspective view of the drive side of the development device, in the first embodiment. 
         FIG. 8  is an external perspective view of a development end sealing member. 
         FIG. 9  is an exploded perspective view of the development blade unit, which is for showing the steps through which the development blade is attached to the development blade supporting metallic plate. 
         FIG. 10  is a partially exploded front view of the development blade unit, which is for showing the steps through which the development blade unit is attached to the development frame. 
         FIG. 11  is a partially exploded perspective view of the development device after the attachment of the development blade bottom seal to the development frame. 
         FIG. 12  is a schematic view of the development device after the attachment of the development blade unit to the development frame. 
         FIG. 13  is a schematic sectional view of the development device, which is for showing the flow of the resin which occurs during the formation of the development blade bottom seal. 
         FIG. 14  is a drawing for showing how the development blade bottom seal is formed. 
         FIG. 15  is a drawing for showing the structure of the development blade bottom seal in the first embodiment. 
         FIG. 16  is a drawing for showing the state of the center portion of the development blade bottom seal in the first embodiment. 
         FIG. 17  is a schematic sectional view of a part of the development device, which is for describing the attachment of the development blade unit and development roller. 
         FIG. 18  is a schematic drawing for showing the internal stress of the development blade, which occurs as the development blade is bent. 
         FIG. 19  is a schematic sectional a conventional development blade bottom seal. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, the embodiments of the present invention are described with reference to the appended drawings. However, the measurements, materials, and shapes of the structural components in the following embodiments of the present invention, and the positional relationship among the structural components, are to be modified according to the structure of the apparatus to which the present invention is applied, and various conditions under which the apparatuses are used. That is, they are not intended to limit the present invention in scope. 
     Embodiment 1 
     The electrophotographic image forming apparatus (which may be referred to simply as “image forming apparatus”, hereafter) in this embodiment is an electrophotographic full-color image forming apparatus in which four process cartridges (which may be referred to simply as “cartridge”) are removably installable. However, this embodiment is not intended to limit the present invention in terms of the number of cartridges which are removably installable in this image forming apparatus; the number of cartridges removably installable is to be suitably set as necessary. For example, in the case of an image forming apparatus for forming a monochromatic image, the number of cartridge to be installed in the apparatus has only to be one. Further, the image forming apparatus in this embodiment is a full-color laser print which is based on four primary colors and uses an electrophotographic process. However, this embodiment is not intended to limit the present invention. That is, the present invention is applicable to an image forming apparatus other than the one in this embodiment. For example, it is applicable to a copying machine, a facsimile machine, or an image forming apparatus capable of performing the functions of two or more of the preceding machines. 
     &lt;Image Forming Apparatus&gt; 
     First, referring to  FIGS. 1 and 2 , the overall structure of the image forming apparatus  1  in this embodiment is described.  FIG. 1  is a schematic sectional view of the image forming apparatus  1  in this embodiment. It shows the structure of the apparatus  1 .  FIG. 2  is a schematic sectional view of the cartridge in this embodiment. It shows the structure of the cartridge. The image forming apparatus  1  in this embodiment is of the cartridge type. That is, it forms a color image on a sheet S of recording medium with the use of cartridges which are removably installable in the apparatus main assembly  2 . 
     Incidentally, in the following description of this embodiment, regarding the direction of the image forming apparatus  1 , the side of the apparatus  1 , which is provided with a door  3  is referred to as the front side (front surface) of the apparatus. The opposite surface of the apparatus  1  from the front surface is referred to as the rear surface (back surface). Further, the right and left sides of the image forming apparatus  1  as seen from the front surface side, are referred to as drive side and non-drive sides, respectively. Regarding  FIG. 2 , a seal  36  for the bottom side of the development blade (which will be described later) is simplified in terms of its shape. The description of the detailed shape of the development blade bottom seal  36  is given later. 
     In this embodiment, the first-fourth cartridges P (PY, PM, PC and PK) which are removably installed in the apparatus main assembly  2  have four similar electrophotographic process systems, one for one, although they are different in the color of the toner they store. To each of the first-fourth cartridges P (PY, PM, PC and PK), bias voltage (charge bias, development bias, etc.) are supplied from the apparatus main assembly  2 . 
     The first cartridge PY stores yellow (Y) toner in its development frame  29 . It forms a toner image of the yellow color, on the peripheral surface of its photosensitive drum  4 . The second cartridge PM stores magenta (M) toner in its development frame  29 . It forms a toner image of the magenta color, on the peripheral surface of its photosensitive drum  4 . The third cartridge PC stores cyan (C) toner in its development frame  29 . It forms a toner image of the cyan color, on the peripheral surface of its photosensitive drum  4 . The fourth cartridge PK stores black (K) toner in its development frame  29 . It forms a toner image of the black color, on the peripheral surface of its photosensitive drum  4 . 
     Referring again to  FIG. 1 , there is provided a laser scanner unit LB as an exposing means, above the group of the first-fourth cartridges P (PY, PM, PC and PK). This laser scanner unit LB outputs a beam Z of laser light in response to the information of the image to be formed. The beam Z of laser light scans (exposes) the peripheral surface of the photosensitive drum  4 , through the exposure window  10  of the cartridge P. 
     Also referring to  FIG. 1 , there is provided an intermediary transfer belt unit  11  as a transferring means below the group of the first-fourth cartridges P (PY, PM, PC and PK). This intermediary transfer belt unit  11  has a driver roller  13 , a turn roller  14 , and a tension roller  15 . It has also a flexible transfer belt  12 , which is suspended by the preceding three rollers  13 ,  14  and  15 . The transfer belt  12  is suspended so that it can be circularly moved in the direction indicated by an arrow mark C in  FIG. 1 . 
     The photosensitive drum  4  in each of the first to fourth cartridges P (PY, PM, PC and PK) is in contact with the top surface of the transfer belt  12 , by its bottom surface. The area of contact between the photosensitive drum  4  and transfer belt  12  is the primary transfer station, in which the toner image formed on the photosensitive drum  4  is transferred (primary transfer) onto the transfer belt  12 . On the inward side of the transfer belt  12 , in terms of the loop which the transfer belt  12 , a primary transfer roller  16  is positioned so that it opposes the photosensitive drum  4 . Further, against the turn roller  14 , a secondary transfer roller  17  is kept pressed, with the presence of the transfer belt  12  between itself and the turn roller  14 . The area of contact between the transfer belt  12  and secondary transfer roller  17  is the secondary transfer station in which the toner image having been transferred (primary transfer) onto the transfer belt  12  is to be transferred (secondary transfer) onto a sheet S of recording medium. 
     There is provided a recording medium feeding/conveying unit  18  below the intermediary transfer belt unit  11 . This recording medium feeding/conveying unit  18  has a sheet feeder tray  19 , in which multiple sheets S of recording medium are stored in layers, and a sheet feeder roller  20 . Further, there are provided a fixation unit  21  and a discharger unit  22  in the top left portion (in  FIG. 1 ) of the internal space of the apparatus main assembly  2 . The top surface of the apparatus main assembly  2  serves as a delivery tray  23 . To the sheet S of recording medium, the toner image thereon is fixed by the fixing means with which the above described fixation unit  21  is provided. Then, the sheet S is discharged onto the above described delivery tray  23 . 
     &lt;Image Forming Operation&gt; 
     Next, referring to  FIG. 1 , the image forming operation of the image forming apparatus  1  in this embodiment is described. First, the photosensitive drums  4  in the first to fourth cartridges P (PY, PM, PC and PK) begin to be rotationally driven (in counterclockwise direction indicated by arrow mark D in  FIG. 2 ) at a preset speed. At the same time, the laser scanner unit LB begins to be driven. In synchronism with the driving of the laser scanner unit LB, the charge roller  5  in each cartridge P uniformly charges the peripheral surface of the photosensitive drum  4  to a preset polarity and a preset potential level. The laser scanner unit LB scans (exposes) the peripheral surface of each photosensitive drum  4  with the beam Z of laser light which it outputs while modulating the beam Z with the image signals which correspond to the primary colors. Consequently, an electrostatic latent image, which reflects the image formation signals which correspond one for one to the primary colors, is formed on the peripheral surface of each photosensitive drum  4 . Then, the formed electrostatic latent image is developed by the development roller  6  which is being rotationally driven (in clockwise direction in  FIG. 1 , indicated by arrow mark E in  FIG. 2 ) at a preset speed. 
     Through the electrophotographic image formation process such as the one described above, a toner image of the yellow color, which corresponds to the yellow component of the full-color image, is formed on the photosensitive drum  4  of the first cartridge PY. Then, this toner image is transferred (primary transfer) onto the transfer belt  12 . Similarly, on the photosensitive drum  4  of the second cartridge PM, a toner image of the magenta color which corresponds to the magenta component of the full-color image is formed. Then, this toner image is transferred (primary transfer) onto the intermediary transfer belt  12  in such a manner that it is layered on the toner image of the yellow color, which has been transferred onto the transfer belt  12 . Similarly, on the photosensitive drum  4  of the third cartridge PC, a toner image of the cyan color, which corresponds to the cyan component of the full-color image is formed. Then, this toner image is transferred (primary transfer) onto the transfer belt  12  in such a manner that it is layered upon the toner image of the yellow color and the toner image of the magenta color, which have already been transferred onto the transfer belt  12 . Similarly, on the photosensitive drum  4  of the fourth cartridge PK, a toner image of the black color, which corresponds to the black component of the full-color image, is formed. Then, this toner image is transferred (primary transfer) onto the transfer belt  12  in such a manner that it is layered on the toner image of the yellow color, toner image of the magenta color, and toner image of the cyan color. 
     Through the above described processes, an unfixed full-color toner image is effected on the transfer belt  12  by the yellow, magenta, cyan and black toner images. Meanwhile, the sheets S of recording medium are separated one by one from the rest, with a preset control timing, and conveyed. Then, each sheet S of recording medium is introduced into the secondary transfer station, which is the area of contact between the secondary transfer roller  17  and transfer belt  12 , with a preset control timing. Consequently, the layered four toner images, different in color, on the transfer belt  12  are transferred together onto the sheet S of recording medium, as if they are peeled away from the transfer belt  12 , while the sheet S is conveyed through the above described secondary transfer station. 
     Thereafter, the sheet S of recording medium, onto which the layered four toner images, different in color, have been transferred, is conveyed to the fixation unit  21 , in which it is subjected to pressure and heat, being thereby fixed to the sheet S. Then, the sheet S to which the toner images have just been fixed, is discharged onto the delivery tray  23  by a discharge unit. Through the above-described operational sequence, the image forming operation is ended. 
     &lt;Structure of Cartridge&gt; 
     Next, referring to  FIGS. 2 and 3 , the structure of the cartridge in this embodiment is described.  FIG. 3  is an external perspective view of the cartridge in this embodiment. As is evident from  FIG. 3 , the cartridges P (PY, PM, PC and PK) are roughly in the form of a rectangle parallelepiped, the lengthwise direction of which is parallel to the direction of the rotational axis a of the photosensitive drum  4  (which may be referred to simply as “lengthwise direction”, hereafter). Each cartridge P has a cleaning unit  8 , a development device  9 , a cover  24  on the drive side, a cover  25  on the non-drive side. The cleaning unit  8  and development device  9  are in connection to each other. 
     Referring to  FIG. 2 , the cleaning unit  8  is made up of the photosensitive drum  4 , charge roller  5 , and a cleaning unit container  26  which has a cleaning blade  7 . Next, referring to  FIG. 3 , the photosensitive drum  4  is rotatably supported by the drive side cover  24  and non-drive side cover  25 . It rotates (in direction indicated by arrow mark D in  FIG. 2 ) by obtaining the driving force of the motor (unshown) of the apparatus main assembly  2  through the drum drive coupling  4   a . The charge roller  5  is rotatably supported by the pair of charge roller bearings  27  of the cleaning device container  26 , by its lengthwise end portions. It is kept in contact with the peripheral surface of the photosensitive drum  4 , being thereby rotated by the rotation of the photosensitive drum  4 . It charges the peripheral surface of the photosensitive drum  4  by being supplied with charge bias. In order to ensure that the peripheral surface of the photosensitive drum  4  is uniformly charged, the lengthwise ends of the charge roller  5  are pressed upon the peripheral surface of the photosensitive drum  4 , by a pair of compression springs  28 , one for one. 
     The cleaning blade  7  is fixed to the cleaning device container  26 , and is placed in contact with the peripheral surface of the photosensitive drum  4  in such a manner that its cleaning edge made of elastic rubber is placed in contact with the peripheral surface of the photosensitive drum  4  in the counter direction relative to the rotational direction (direction indicated by arrow mark D in  FIG. 2 ). The cleaning blade  7  cleans the peripheral surface of the photosensitive drum  4  by scraping away the transfer residual toner remaining on the peripheral surface of the photosensitive drum  4 . In order to ensure that the transfer residual toner is completely scraped away, the cleaning edge of the cleaning blade  7  is kept pressed upon the peripheral surface of the photosensitive drum  4  with the application of a preset amount of pressure. 
     Further, the transfer residual toner scraped away from the peripheral surface of the photosensitive drum  4  by the cleaning blade  7  is stored as waste toner in the waste toner storage  26   a  of the cleaning device container  26 . Therefore, the cleaning device container  26  is provided with a waste toner recovery sheet  44  for preventing the waste toner from leaking out of the container  26  through the gap between the photosensitive drum  4  and container  26 , and the gap between the container  26  and cleaning blade  7 . The waste toner recovery sheet  44  is positioned so that it extends in the lengthwise direction of the photosensitive drum  4 . Further, the lengthwise end portions of the cleaning blade  7  are provided with a pair of cleaning blade end seals (unshown) one for one. 
     The cartridge in this embodiment is made up of the photosensitive drum  4 , and the processing means for processing the photosensitive drum  4 , more specifically, the development roller  6  as a developing means, cleaning blade  7  as a cleaning means, and waste toner storage  26   a , which are unitized as parts of the cartridge. However, this embodiment is not intended to limit the present invention in terms of the cartridge. For example, one or more among the photosensitive drum  4 , developing mans, charging means, and cleaning means, may be unitized as parts of the cartridge, so that they can be removably installable in the apparatus main assembly  2 . 
     &lt;Structural Arrangement for Allowing Cartridge to be Removably Installed&gt; 
     Next, referring to  FIGS. 4 and 5 , the operation for installing the cartridge P (PY, PM, PC or PK) into the apparatus main assembly  2 , or removing the cartridge P from the apparatus main assembly  2 , is described.  FIG. 4  is a schematic sectional view of the image forming apparatus  1  when the cartridge tray is in the outermost position into which the cartridge is pulled out, and in which the cartridges can be installed into, or removed from, the cartridge tray.  FIG. 5  is a schematic sectional view of the image forming apparatus  1 , which shows the operation for installing a cartridge into the cartridge tray, or removing a cartridge from the cartridge tray. The apparatus main assembly  2  is provided with the cartridge tray  43  in which the cartridges P are removably installable. Referring to  FIG. 4 , the apparatus main assembly  2  is structured so that the cartridge tray  43  is linearly movable (can be pushed into, or pulled out of, apparatus main assembly  2 ) in the directions G 1  and G 2 , which are practically parallel to the horizontal direction of the apparatus main assembly  2 . The cartridge tray  43  can be positioned in its cartridge tray home position which is in the apparatus main assembly  2 , and the outermost positioned into which the cartridge tray  43  can be pulled out of the apparatus main assembly  2 . 
     First, the operation for installing the cartridges P (PY, PM, PC and PK) into the apparatus main assembly  2  is described. To begin with, a user (operator) is to open the apparatus door  3 , and move the cartridge tray  43  in the direction indicated by the arrow mark G 1  in  FIG. 4 , so that the cartridge tray  46  will be in its outermost position. It is when the cartridge tray  43  is in the state shown in  FIG. 5  that the cartridge can be installed into the cartridge tray  43  in the direction indicated by an arrow mark H 1  in  FIG. 5 , and is held in the tray  43 . Then, the cartridge tray  43  in which the cartridges P are held is to be moved in the direction indicated by an arrow mark G 2  in  FIG. 4 , so that the cartridge tray  43  will be positioned in its home position in the apparatus main assembly  2 . Then, the user is to close the door  3  to end the installation of the cartridges P into the apparatus main assembly  2  as shown in  FIG. 1 . 
     Next, the operation for removing the cartridge P from the apparatus main assembly  2  is described. Referring to  FIG. 4 , the user is to move the cartridge tray  43  into the cartridge removal position, or the outermost position, in the same manner as the manner in which the cartridge tray  43  is moved to install the cartridge P into the apparatus main assembly  2 . It is when the cartridge tray  43  is in the state shown in  FIG. 5  that the cartridge P can be removed from the cartridge tray  43  in the direction indicated by an arrow mark H 2  in  FIG. 5  to complete the operation for removing the cartridge P from the apparatus main assembly  2 . That is, the cartridges P are removably installable in the apparatus main assembly  2  through the above described operation. 
     &lt;Structure of Development Device&gt; 
     Next, referring to  FIGS. 6 and 7 , the details of the development device  9  in this embodiment are described.  FIG. 6(   a ) is an exploded perspective view of the development device  9  in this embodiment, and  FIG. 6(   b ) is an enlarged perspective view of the drive side of the development device  9  in this embodiment.  FIG. 7(   a ) is an enlarged, exploded, and perspective view of the drive side of the development device  9  in this embodiment, and  FIG. 7(   b ) is an enlarged perspective view of the non-drive side of the development device  9  in this embodiment. 
     Referring to  FIGS. 3 and 6(   a ), the development device  9  is in the form of a rectangular parallelepiped, the lengthwise direction of which is parallel to the direction of the axial line (which may be referred to as “lengthwise direction” hereafter) of the development roller  6  as a developer bearing member. The development device  9  has a development frame  29 , a development blade  31  as a regulating member, a developer supply roller  33 , a pair of developer end seals  34 R and  34 L as second sealing members, a flexible sheet  35 , and a pair of supply roller shaft seals  37 R and  37 L, in addition to the development roller  6 . 
     The development frame  29  is made up of the first frame  29   a  to which the development roller end seals  34 R and  34 L are attached, and a second frame  29   b  to which the flexible sheet  35  is attached. The first and second frames  29   a  and  29   b  are welded to each other by ultrasonic welding or the like, whereby the toner storage chamber  29   c  as the developer storage for storing toner, and an opening  29   d  through which toner is released from the toner storage chamber  29   c , are created. 
     The development roller  6  is positioned so that in order for the development roller  6  to bear the toner discharged from the toner storage chamber  29   c , it extends from one end of the opening  29   d  to the other in terms of the lengthwise direction. Further, the developer supply roller  33  is positioned so that it hypothetically invades into the development roller  6  in the radius direction of the developer supply roller  33 . Next, referring to  FIG. 6(   a ), the development roller  6  and developer supply roller  33  are rotatably supported by the drive side bearings  38  and non-drive side bearings  39  attached to the lateral walls of the development frame  29 , one for one, by their ends in terms of the direction parallel to their axles. Referring also to  FIG. 6(   a ), the drive side end of the core  6   a  of the development roller  6  is fitted with a development roller gear  40 , and the drive side end of the core  33   a  of the developer supply roller  33  is fitted with a developer supply roller gear  41 . The development roller gear  40  and developer supply roller gear are in mesh with the development drive input gear  42 . The development drive input gear  42  is provided with a development drive coupling  42   a , with which the drive output coupling (unshown) with which the apparatus main assembly  2  is provided is in engagement to transmit the driving force of the motor (unshown) to the development drive coupling  42   a  to rotationally drive the development roller  6  and developer supply roller  33  at a preset speed. The developer supply roller  33  is rotatable in the direction indicated by an arrow mark F in  FIG. 2 . 
     The development blade  31  is a piece of thin and elastic metallic plate, which is roughly 0.1 mm in thickness. It is positioned so that its free edge in terms of its widthwise direction is placed in contact with the development roller  6  in the counter direction relative to the rotational direction (indicated by arrow mark E in  FIG. 2 ). Further, referring to  FIG. 2 , the development blade bottom seal  36  as the first seal is positioned so that it fills the gap between the development frame  29  and development blade unit  30 , across the entirety of the gap in terms of the lengthwise direction, to prevent toner leak. 
     Referring also to  FIG. 6(   a ), the development end seals  34 R and  34 L are positioned at the lengthwise ends of the opening of the development frame  29 , to prevent toner from leaking from the development device through the gap between the development blade  31  and development frame  29 , and the gap between the development roller  6  and development frame  29 . The detailed description of the structure of the development end seals  34 R and  34 L is given later with reference to  FIG. 8 . 
     The flexible sheet  35  shown in  FIGS. 6(   a ) and  6 ( b ) is made of plastic film made of polyethylene-terephthalate, polyphenylene sulfide, etc., for example. It is roughly 50 μm in thickness. The flexile sheet  35  is positioned so that it contacts the development roller  6 , on the opposite side of the opening  29   d  of the development frame  29  from the development blade  31 . It prevents toner from leaking through the gap between the development frame  29  and development roller  6 . 
     Next, referring to  FIG. 6(   b ), in order to plug the gap formed by the first frame  29   a , second frame  29   b , development end seal  34 R and flexible sheet  35 , an elastic seal  60  is fitted in the gap to prevent toner leak. Further, the gap formed by the first frame  29   a , second frame  29   b , development end seal  34 L and flexible sheet  35  is similarly filled with elastic seal  60  to prevent toner leak. The elastic seal  60  is formed of thermoplastic resin such as polystyrene. It is desired to be no less than 110-300 mPa·s in viscosity when it is in the melted state. 
     The developer supply roller shaft seals  37 R and  37 L shown in  FIG. 6(   a ) are attached to the portions of the core  33   a  of the developer supply roller  33 , which are exposed outward from the development frame  29 . They prevent toner from leaking through the gap between the wall of a hole  29   e  with which the development frame  29  is provided to allow the core  33   a  of the developer supply roller  33  to be put through the lateral wall of the development frame  29 , and the core  33   a.    
     The development device  9  is kept pressured by the compression springs (unshown) in such a manner that it is pivotally moved about the pivot (axial line b) shown in  FIG. 3  in the direction (indicated by arrow mark L in  FIG. 2 ) to place the development roller  6  in contact with the photosensitive drum  4 . During an image forming operation, the development roller  6  is kept in contact with the photosensitive drum  4 , whereas when no image is formed, the development roller  6  is kept separated from the photosensitive drum  4  by an unshown separating means, against the resiliency of the above described compression springs. That is, when an image is formed, the development roller  6  is placed in contact with the photosensitive drum  4 , whereas when no image is formed, the development roller  6  is kept separated from the photosensitive drum  4 ; the development roller  6  is repeatedly placed in contact with, or separated from, the photosensitive drum  4 . 
     When an image is formed, the developer supply roller  33  and development roller  6  are rotationally driven while rubbing against each other. Thus, the toner in the development frame  29  is borne on the development roller  6 . The development blade  31  regulates in thickness the toner layer formed on the peripheral surface of the development roller  6 , and also, gives toner triboelectric charge in the interface between itself and development roller  6 , by being kept pressed upon the development roller  6 . Thus, the charged toner on the development roller  6  adhere to the electrostatic latent image on the photosensitive drum  4 , developing thereby the latent image, in the area of contact between the development roller  6  and photosensitive drum  4 . 
     &lt;Structure of Development End Seal&gt; 
     Next, referring to  FIG. 8 , the structure of the development end seal  34  is described.  FIG. 8  is an external perspective view of the development end seal  34 . As shown in  FIG. 8 , the development end seal  34  is made up of a surface layer, an adhesive layer  51 , an intermediary layer  52 , and an adhesive layer  53 . The development end seal  34  is attached so that it remains compressed between the lengthwise end portions of the development roller  6  in terms of the direction parallel to the axial line of the development roller  6 , and the development frame  29 . More concretely, it is positioned between the development end seal seat  29   a   1  ( FIGS. 7 and 15 ) of the development frame  29  and the development roller  6 . It has a sealing function to prevent toner leaking through the gap between the development frame  29  and development roller  6 . 
     Referring to  FIG. 8 , in this embodiment, the surface layer  50  is made up of a substrative cloth  50   a  and multiple upright strands  50   b  of fiber implanted in the substrative cloth  50   a . However, this embodiment is not intended to limit the present invention in terms of the surface layer  50 . For example, the surface layer  50  may be made up of the substrative cloth and multiple short strands of fiber electrostatically implanted in the substrative cloth, or the substrative cloth alone. The surface layer  50  is attached to the surface of the intermediary layer  52  with the placement of the adhesive layer  51 , for example, a piece of two-sided adhesive tape, a layer of adhesive, or the like, between the surface layer  50  and intermediary layer  52 . As the material for the strands of fiber, synthetic fiber made of polyethylene, polypropylene, polyester, Nylon, acrylic resin, polyethylene-terephthalate, or the like, semi-synthetic fiber made of rayon or the like, natural fiber such as cotton, may be used. Further, the combination of the preceding materials, and the twined version of the preceding materials, may also be listed as the material for the strands. 
     The intermediary layer  52  is a cushion layer formed of elastic substance. As the material for the intermediary layer  52 , a foamed version of synthetic resin such as polyurethane may be used. In this embodiment, the abovementioned elastic seal  60  to be formed of thermoplastic resin, and development blade bottom seal  36  as the first sealing member, are formed so that they airtightly contact the intermediary layer  52  of the development end seal  34  as the second sealing member. More specifically, the thermoplastic resin, which is kept melted at a high level of temperature, is filled into the aforementioned gap. Thus, the melted thermoplastic resin penetrates into the cells of the intermediary layer  52  (made of foamed substance). Thus, the gap (space) formed by the development end seal  34 , elastic seal  60  formed of thermoplastic resin, and development blade bottom seal  36  is airtightly filled. 
     The adhesive layer  53  is formed of two-sided adhesive tape, pressure sensitive adhesive, or the like. The material for the adhesive layer  53  may be other material than the abovementioned ones, as long as it allows the adhesive layer  53  to be flexible and is adherent enough to ensure that the adhesive layer  53  remains adhered to the intermediary layer  52 . As for the shape of the development end seal  34 , it may be different from the one in this embodiment. For example, a part or parts of the development end seal  34  may be carved away to make the shape of the development end seal  34  conform to the shape of the development end seal seat  29   a   1  ( FIGS. 7 and 15 ), and the structure of the adjacencies of the seat  29   a   1 . 
     &lt;Structure of Development Blade Unit&gt; 
     Next, referring to  FIGS. 9 and 10 , the details of the structure of the development blade unit  30  are described.  FIG. 9  is an exploded perspective view of the development blade unit  30  and is for describing the process for attaching the development blade  31  to the metallic support.  FIG. 10  is an exploded front view of the development device  9 , and is for showing the process for attaching the development blade unit  30  to the development frame  29 . 
     Referring to  FIG. 9(   a ), the development blade unit  30  is made up of a metallic support plate  32  made of steel plate, and the development blade  31  made of thin plate of stainless steel or phosphor bronze, which is attached to the metallic support plate  32 . The development blade  31  is fixed to the portion of the metallic support plate  32 , which corresponds in position to the area of contact  32   b  shown in  FIG. 9(   a ). This fixation is done by welding, with the use of adhesive, or the like means. The development blade  31  shown in  FIGS. 9(   a ) and  9 ( b ) may be such a blade which is formed of thin plate of stainless steel or phosphor bronze. It is coated with polyamide elastomer (PAE) across its portion which is placed in contact with the development roller  6 . As for the shape of the development blade  31 , the blade  31  may be shaped so that its edge portion, by which it contacts the development roller  6 , is L-shaped in cross section. Further, the portion of the surface of the development blade  31 , which contacts the development roller  6 , may be coated with Nylon or rubber, or a sheet formed of Nylon or rubber may be adhered to the portion of the surface of the development blade  31 , which contacts the development roller  6 . 
     As for the material for the development blade  31 , instead of a thin plate of stainless steel, a plate of rubber or the like may be used. In such a case, a plate of rubber or the like is fixed to the metallic support plate  32 . Regarding the rubber as the material for the development blade  31 , urethane rubber, silicon rubber, butyl rubber, or the like can be used. Regarding the material for the metallic support plate  32 , in order to prevent the rusting or the like of the metallic support plate  32  from negatively affecting the development, stainless steel is used as the material for the metallic support plate  32 . Further, the material for the metallic support plate  32  may be steel plate plated with nickel, zinc, or the like. Referring to  FIG. 10 , the metallic support plate  32  is fixed to the development blade attachment seats  29   z L and  29   z R, with which the lengthwise end portions of the development frame  29  of the development device  9  are provided, with the use of small screws  74  or the like, respectively. 
     &lt;Development Blade Bottom Seal&gt; 
     Next, referring to  FIGS. 11 and 12 , the development blade bottom seal  36  is described.  FIG. 11  is a partially broken perspective view of the development device  9 , and shows how the development blade bottom seal  36  is attached to the development frame  29 .  FIG. 12  is a schematic front view of the development device  9  immediately after the development blade unit  30  was attached to the development frame  29 . Regarding  FIG. 12 , the contour of the development blade  31  is indicated by a two-dot chain line. 
     Referring to  FIG. 12 , the development blade bottom seal  36  is made up of a center portion  36   c , and end portions  36 L and  36 R which contact the development end seal  34 L and  34 R, respectively, on the opposite side of the development roller  6  from the area of contact between the development blade  31  and development roller  6 . The end portions  36 L and  36 R of the development blade bottom seal  36  are positioned so that they are layered upon the lengthwise end portions of the development blade  31 . Referring to  FIG. 11 , the development device  9  is structured so that the development end seal  34 L and the end portion  36 L of the development blade bottom seal  36  airtightly contact each other. 
     Referring to  FIG. 12 , with the development device  9  being structured as described above, the development blade bottom seal  36  fills the gap between the development blade  31  in such a manner that the center portion  36 C of the development blade bottom seal  36  fills the gap between the metallic support plate  32  and development frame  29 , and the end portions  36 L and  36 R fill the gaps formed by the development blade  31 , development frame  29 , and development end seal  34 L and  34 R, respectively, whereby the toner within the development frame  29  is prevented from leaking out of the development frame  29  through the development opening  29   d.    
     &lt;Molding of Development Blade Bottom Seal&gt; 
     Next, referring to  FIGS. 13 and 14 , the molding of the development blade bottom seal  36  is described.  FIG. 13  is a schematic front view of the development frame  29 , which is for showing the resin flow which occurs during the molding of the development blade bottom seal  36 .  FIG. 14  is a sectional view of the development frame  29  at a plane M 2 -M 2  in  FIG. 13 . It is for describing the molding of the development blade bottom seal  36  in this embodiment. More specifically,  FIG. 14(   a ) is a schematic sectional view of the resin injecting portion of the development frame  29  after the clamping of a seal mold  183 .  FIG. 14(   b ) is a schematic sectional view of the resin injecting portion of the development frame  29  when the development blade bottom seal  36  is being molded. 
     The development blade bottom seal  36  in this embodiment is molded of elastic thermoplastic resin, in such a manner that it becomes a virtually integral part of the development frame  29  as it is molded. It is molded by injecting the resin into the space created by the placement of a seal mold  183  in contact with the development frame  29 . 
     Next, referring to  FIGS. 13 and 14 , the structure for molding the development blade bottom seal  36  is described. Referring to  FIG. 13 , there is provided above the development opening  29   d  of the development frame  29  (upward direction in  FIG. 13 ), a seal forming portion  29   f  which extends in the lengthwise direction between the development end seal  34 L and development end seal  34 R. The seal forming portion  29   f  has a recess  29   f   1  into which the seal material is injected, and surfaces (areas) of contact  29   f   2  and  29   f   3  which the mold contact. There is also provided a cylindrical injection opening  29   g , which is positioned at a preset point in terms of the lengthwise direction, and is in connection to the recess  29   f   1  of the seal forming portion  29   f  as shown in  FIG. 13 . In this embodiment, only one injection opening  29   g  is provided, which is positioned at roughly the center of the seal formation portion  29   f  in terms of the lengthwise direction. However, the development frame  29  may be structured so that two injection openings  29   g  are provided at roughly the center portion in terms of the lengthwise direction. 
     Next, the steps to be followed to mold the development blade bottom seal  36  are sequentially described. Referring to  FIG. 14(   a ), the first step to be followed for molding the development blade bottom seal  36  is to place the seal mold  183  having a seal-shaped recess  36 C, in contact with the surfaces of contact  29   f   2  and  29   f   3  of the seal forming portion  29   f . Then, the injection nozzle  182   a  of an unshown resin injection apparatus is fitted in the resin injection opening  29   g , which is at roughly the center of the development frame  29  in terms of the lengthwise direction, from the direction indicated by an arrow mark YG-C in  FIGS. 13 and 14(   a ). Then, the thermoplastic elastomer as the material for the development blade bottom seal  36  is to be injected into the injection opening  29   g  of the development frame  29  from the injection nozzle  182   a  of the abovementioned resin injection device. 
     Then, the thermoplastic elastomer is flowed into the space  29   f  created by the recess  19   f   1  of the seal forming portion  29   f  of the development frame  29  and the seal mold  183  as shown in  FIG. 14(   b ). Then, the thermoplastic elastomer flows toward both lengthwise ends, in the directions indicated by arrow marks YG-L and YG-R, respectively, through the space created by the recess  29   f   1  of the seal molding portion  29   f  and the seal mod  183  as shown in  FIG. 13 . Eventually, the thermoplastic elastomer reaches the portions of the space, which correspond to the ends surface  34 L 4  and  34 R 4  of the farthest ends of the development end seals  34 L and  34 R, in terms of the direction perpendicular to the lengthwise direction, ending thereby the injection of the material for the development blade bottom seal  36 . 
     As the final step, the seal mold  183  is to be retracted to yield the development blade bottom seal  36  shaped as shown in  FIG. 11 . Incidentally, the method to be used for molding of the development blade bottom seal  36  does not need to be the above described one. For example, the development blade bottom seal  36  may be formed as an integral part of the development frame  29  with the use of two-color molding, insert molding, or the like. 
     &lt;Shape of Center Portion of Development Blade Bottom Seal&gt; 
     Next, referring to  FIGS. 15 and 16 , the shape of the center portion  36 C of the development blade bottom seal  36  in this embodiment is described.  FIG. 15  is a drawing for showing the structure of the development blade bottom seal  36  in this embodiment. More specifically,  FIG. 15(   a ) is a front view of the development frame  29 , and  FIG. 15(   b ) is a schematic sectional view of the development frame  29  at the plane M 1 -M 1  in  FIG. 15(   a ).  FIG. 15(   c ) is a plan view of the development blade bottom seal  36  as seen from the direction indicated by an arrow mark A in  FIG. 15(   b ).  FIG. 15(   d ) is a schematic sectional view of the development blade bottom seal  36  at a plane M 3 -M 3  in  FIG. 15(   c ).  FIG. 16  is a drawing for showing the state of the center portion of the development blade bottom seal  36  in this embodiment. More specifically,  FIG. 16(   a ) is an enlarged sectional view of the area Q in  FIG. 15 . 
     Referring to  FIGS. 15(   b ) and  16 ( a ), the center portion  36 C of the development blade bottom seal  36  is formed as an integral part of the development frame  29 , in the recess  29   f   1  of the seal forming portion  29   f  of the development frame  29 . Next, referring to  FIGS. 15(   c ) and  15 ( d ), the development blade bottom seal  36  is an integral combination of the center portion  36 C, and end portions  36 R and  36 L. It keeps sealed between the development frame  29  and development blade unit  30  to prevent toner from leaking out of the development frame  29 . 
     Next, referring to  FIG. 16(   a ), which is a sectional view of the center portion  36 C of the development blade bottom seal  36  at a plane perpendicular to the lengthwise direction, the center portion  36 C of the development blade bottom seal  36  is in the form of a lip which is tilted by an angle of θ relative to the back surface  32 C 1  of the metallic support plate  32  of the development blade unit  30 . 
     Next, referring to  FIG. 16(   b ), the development blade unit  30  is attached to the development frame  29  by being moved in the direction indicated by an arrow mark X. As the development blade unit  30  is moved, the center portion  36 C comes into contact with the back surface  32 C 1  of the metallic support plate  32 , and then, is bent in the direction indicated by the arrow mark X, while remaining pinched between the development frame  29  and development blade unit  30 . Since the center portion  36 C is tilted by the angle of θ relative to the back surface of the metallic support plate  32 , the reaction force generated in the lip portion of the center portion  36 C of the center portion  36 C, by the bending of the lip portion of the center portion  36 C of the development blade bottom seal  36  in the direction indicated by the arrow mark X is relatively small. 
     Here, regarding the amount of the bending of the center portion  36 C of the development blade bottom seal  36  in the X direction, is desired to be set to a value within a range of 0.3-1.8 mm, from the standpoint of keeping toner sealed, and the amount of the reaction force of the center portion  36 C, to which the development blade unit  30  is subjected. Further, from the standpoint of the moldability of the thermoplastic elastomer, and the accuracy in the measurement of the development frame  29 , the lip height L 1  and lip width B 1  of the center portion  36 C of the development blade bottom seal  36  are desired to be set to a value in a range of 2.0-4.0 mm, and a value in a range of 1.0-2.5 mm, respectively. Further, the width B 2  of the surfaces  29   f   2  and  29   f   3  of the development frame  29 , with which the mold is placed in contact, is desired to be in a range of 1.5-2.0 mm. The width B 3  of the recess  29   f   1  is desired to be in a range of 1.5-2.0 mm. Further, the depth L 2  of the recess  71   d   1  is desired to be in a range of 0.5-2.0 mm, and the angle of the lip portion is desired to be in a range of 30°-80°. 
     Because the lip portion of the center portion  36 C of the development blade bottom seal  36  is shaped as described above, it is possible to prevent the deformation of the metallic support plate  32 . Therefore, it is possible to prevent the increase in the contact pressure between the development blade  31  and development roller  6 . 
     &lt;Shape of End Portion of Development Blade Bottom Seal&gt; 
     Next, referring to  FIGS. 17 and 18 , the end portions  36 L and  36 R of the development blade bottom seal  36  in this embodiment are described.  FIG. 17  is a schematic sectional drawing of the development blade unit  30  and development roller  6  in this embodiment, which is for describing the process for attaching the development blade unit  30  and development roller  6  to the development frame  29 . More specifically,  FIG. 17(   a ) is a schematic sectional view of the combination of the development frame  29 , development blade bottom seal  36 , and development blade unit  30 , prior to the attachment of the development blade unit  30  in this embodiment.  FIG. 17(   b ) is a schematic sectional view of the combination of the development frame  29 , development blade bottom seal  36 , and development blade unit  30 , after the attachment of the development blade unit  30  in this embodiment.  FIG. 17(   c ) is a schematic sectional view of the combination of the development frame  29 , development blade bottom seal  36 , development blade unit  30 , development roller  6 , after the attachment of the development blade unit  30  and development roller  6  in this embodiment.  FIG. 18(   a ) is a schematic sectional view of the combination of the development frame  29  and development blade unit  30  of an example of conventional development device. It is for showing the internal stress of the development blade  31  when the development blade  31  is bent.  FIG. 18(   b ) is a schematic sectional view of the combination of the development frame  29  and development blade  31  in this embodiment. It shows the internal stress of the development blade  31  when the development blade  31  is bent. Referring to  FIGS. 18(   a ) and  18 ( b ), the area contoured by a broken line shows the state of the end portion of the development blade bottom seal  36  prior to the attachment of the development blade  31 . Since the end portions  36 R and  36 L are the same in structure, only the end portion  36 L is described here. 
     Referring to  FIG. 17(   a ), the development end seal  34 L is adhered to the development end seal adhesion surface  29   a   1  of the development frame  29 , as if it becomes an integral part of the development frame  29 . The end portion  36 L of the development blade bottom seal  36  is positioned in the gap created by the end surface  34 L 4  of the metallic support plate  32 , back surface  31 L 2  of the development blade  31 , end surface  34 L 4  of the development end seal  34 L, and the surface  29 L 3  of the development frame  29  as shown in  FIG. 17(   a ). Further, the development blade bottom seal  36  has the first surface  36 L 2  of airtight contact, which is airtightly placed in contact with the back surface  31 L 2  of the development blade  31 , and the second surface  36 L 3  of airtight contact, which is airtightly placed in contact with the surface  29 L 3  of the development frame  29 . Further, it has a surface  36 L 1 , which comes into contact with the end surface  32 L 1  of the metallic support plate  32  during the assembly, and a surface  36 L 4 , which comes into airtight contact with the end surface  34 L 4  of the development end seal  34 . Thus, the toner in the development frame  29  is kept sealed in the development frame  29  by the airtight contact between the above described surfaces of the development blade bottom seal  36  and back surface  31 L 2  of the development blade  31 , surface  29 L 3  of the development frame  29 , end surface  32 L 1  of the metallic support plate  32 , end surface  34 L 4  of the development end seal  34 , one for one. 
       FIG. 17(   a ) shows the state of the end portion  36 L of the development blade bottom seal  36  prior to the attachment of the development blade unit  30 . In  FIG. 17(   a ), a referential code K 1  stands for the distance between the first and second surfaces  36 L 2  and  36 L 3  of airtight contact of the end portion  36 L supported by the metallic support plate  32 , at the base portion (point  31 P 1  of support), and a referential code K 2  stands for the distance between the first and second surfaces  36 L 2  and  36 L 3  of airtight contact of the end portion  36 L, at the end portion ( 31 PZ side), which contacts the development roller  6 . In this embodiment, the relationship between K 1  and K 2  is as follows:
 
 K 1 &lt;K 2.
 
     Referring also to  FIG. 17(   a ), the development blade unit  30  is attached to the development frame  29  by being moved in the direction indicated by an arrow mark YG 1 . Next, referring to  FIG. 17(   b ), as the development blade unit  30  is moved as described above, the end portion  36 L of the development blade bottom seal  36 , and development end seal  34 L, are compressed by the development blade  31  in the direction (direction of compression) in the direction indicated by an arrow mark YG 2 . Further, referring to  FIG. 17(   c ), as the development roller  6  is attached to the development frame  29 , the development roller  6  comes into contact with the development blade  31 , causing thereby the development blade  31  to bend in the direction indicated by the arrow mark YG 2 . Consequently, the distances K 1  and K 2  become distances K 1 ′ and K 2 ′. 
     Here, referring to  FIG. 18(   b ), a referential code  36 P 1  stands for the position of the base end side of the development blade bottom seal  36 , relative to the surface  36 L 2 , after the attachment of the development roller  6  and development blade  31 . Referential codes  36 P 2 ,  36 P 3 , . . .  36 Pn stand for the positions of the points of the development blade bottom seal  36 , which are apart from the base end of the seal  36  by multiples of a preset unit of distance, respectively. Further, a referential code  6   n  stands for the amount by which the development blade bottom seal  36 L is compressed by the deformation of the development blade  31  at a position  36 Pn. Further, a referential code βn stands for the distance between the first and second surfaces  36 L 2  and  36 L 3  of airtight contact  36 L 2  prior to the attachment of the development roller  6  and development blade  31  (starting point β1=K 1 ). 
     The amount Nn of the reaction force to which the development blade  31  is subjected by the development blade bottom seal  36 L at the position  36 Pn on the first surface  36 L 2  of airtight contact during the attachment of the development blade  31  and development roller  6  can be expressed by the following equation (Equation 1) in which E stands for Young&#39;s modulus.
 
 Nn=E (δ n/βn )  (1)
 
     The sum F of the reaction force to which the development blade  31  is subjected by the development blade bottom seal  36 L can be expressed in the form of the following equation (Equation 2): 
     
       
         
           
             
               
                 
                   F 
                   = 
                   
                     
                       ∑ 
                       
                         k 
                         = 
                         1 
                       
                       n 
                     
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     
                       ( 
                       
                         N 
                         k 
                       
                       ) 
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
     Here, referring to  FIGS. 18(   a ) and  19 , the structure of the conventional development blade bottom seal is described.  FIG. 19  is a schematic sectional view of the conventional development blade bottom seal. Referring to  FIGS. 18(   a ) and  19 ( a ), in the case of the conventional development blade bottom seal, the distance between the first and second surfaces  136 L 2  and  136 L 3  at the point  36 P 1  is the same as that at the point  36 Pn (K 1 =J 1 ). Further, the amount of compression after the attachment of the development roller  6  is such that the closer to the base side, the smaller the amount; the farther from the base side, the greater the amount. Therefore, according to Equation 1 given above, βn remains unchanged (βn=K 1 =J 1 ), whereas the closer to the fourth surface  136 L 4  of airtight contact, the greater the amount of βn. That is, the closer to the fourth surface  136 L 4  of airtight contact, the greater, the amount of reaction force N′n. 
     In comparison, referring to  FIG. 18(   b ), in the case of the structure of the development blade bottom seal  36  in this embodiment, the relationship between the distance K 1 , that is, the distance between the first and second surfaces L 2  and L 3  of airtight contact at the point  36 P 1 , and distance K 2 , that is, the distance between the first and second surfaces L 2  and L 3  of airtight contact at the point  36 Pn is: K 1 &lt;K 2 . Further, as for the amount of compression after the attachment of the development roller  6 , it is such that it is smallest at the third surface  36 L 1  of airtight contact, and the closer to the fourth surface  34 L 4  of airtight contact, the greater it is. However, K 1 &lt;K 2 . Therefore, δn increases. Thus, according to Equation 1, the reaction force Nn is smaller than the reaction force N 1 ′n in the case of the conventional structure. 
     Therefore, according to the Equation 2, the development device  9  in this embodiment is smaller in the sum of the reaction force to which the development blade  31  is subjected, than the conventional development device. That is, according to this embodiment, it is possible to reduce the reaction force to which the development blade  31  is subjected as the end portion  36 L of the development blade bottom seal  36  is compressed. Further, in comparison to the conventional development device, the development device  9  in this embodiment is structured so that the contact pressure between the development blade  31  and development roller  6  across the lengthwise end portions of the development blade  31  and development roller  6  is not unnecessarily high. Therefore, the development device  9  in this embodiment is smaller than the conventional development device, in the difference between the amount of contact pressure between the development blade  31  and development roller  6  at the lengthwise ends of the development blade  31 , and that at the center portion of the development blade  6 . Thus, the development device  9  in this embodiment is uniform in its ability to give electrical charge to toner, across the entire range in terms of the lengthwise direction. Therefore, it is possible to obtain a satisfactory image, more specifically, an image, the center portion and end portions of which in terms of the lengthwise direction of the development device  9 , are not significantly different in density. 
     Further, referring to  FIG. 17(   c ), the development device  9  in this embodiment is structured so that the development blade bottom seal  36  is positioned on the downstream side of the development end seal  34  in terms of the rotational direction of the development roller  6 . Therefore, as the development roller  6  is rotated, such force that works in the direction to cause the development end seal  34  to be pressed upon the development blade bottom seal  36  is generated. That is, the portion of the development blade bottom seal  36 , which contacts the development end seal  34 , is increased in the amount of its compression. Therefore, it is likely that the reaction force which is generated in the development blade bottom seal  36 , and to which the regulating edge portion of the development blade  31  is subjected is likely to increase. In this embodiment, however, the portion of the development blade bottom seal  36 , which contacts the development end seal  34 , is made thicker. Therefore, it is possible to reduce the amount by which the reaction force, to which the development blade  31  is subjected, is generated by the rotation of the development roller  6 . 
     &lt;Material for Development Blade Bottom Seal&gt; 
     As for the material for the development blade bottom seal  3 , it is desired that elastomer which belongs to styrene group is used as the material for the development blade bottom seal  36 . Generally speaking, it is likely that the styrene resin is used as the material for the development frame. Thus, in a case where elastomer based on styrene is used as the material for the seals, both the development frame and seals are formed of the material based on styrene. Thus, as the seals are molded directly onto the development frame, they are excellent in terms of airtight adhesion to the development frame  29 . Further, using styrene resin as the material for both the development frame and seals is advantageous in that it makes it unnecessary to separate the seals from the development frame when pulverizing the development frame and seals to recycle the development device  9 , because both the development frame and seals are formed of the same material. 
     The structure of the development device  9  in this embodiment of the present invention was described assuming that elastomer was used as the material for the elastic components. However, the development device  9  may be structured so that a foamed substance is used as material for the elastic components, and the elastic components formed of the foamed substance are adhered to the development frame. As the material for the foamed substance, polyurethane based on ester, or ether, may be used. Using a foamed substance as the material for the elastic components makes it unnecessary to prepare molds and a molding machine, offering therefore a merit that it can reduce the initial investment for production facilities. Further, it is not mandatory that the development device  9  is structured so that the development end seal  34 L and  34 R directly contact the end portions  36 L and  36 R of the development blade bottom seal  36 , respectively. That is, the development device  9  may be structured so that elastic seals are placed between the development end seal  34 L and  34 R and the end portions  36 L and  36 R of the development blade bottom seal  36 , respectively. Further, the metallic support plate  32  may be eliminated; the development device  9  may be structured so that the blade  31  is directly attached to the development frame  29 . 
     Further, referring to  FIG. 18(   b ), in this embodiment, the development device  9  is structured so that the relationship between the distances K 1  and K 2  is linear. However, this embodiment is not intended to limit the present invention in terms of the relationship between the distances K 1  and K 2 . That is, all that is necessary it that K 1 &lt;K 2 . For example, the development device  9  may be structured so that the distance increases in steps. The effects of such an structural arrangement are the same as the structural arrangement for the development device  9  in this embodiment. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims priority from Japanese Patent Application No. 194998/2012 filed Sep. 5, 2012, which is hereby incorporated by reference.