Patent Publication Number: US-7215902-B2

Title: Developing cartridge, process cartridge, image forming device, and sliding sealing element

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a developing cartridge, a process cartridge, and an image forming device. 
   2. Description of Related Art 
   A process cartridge is detachably mounted in a conventional image forming device such as a laser printer. A developing cartridge is detachably mounted in the process cartridge. The developing cartridge has a housing in which toner is accommodated. The housing of the developing cartridge is formed with an opening. A developing roller is rotatably supported in the housing at the opening. 
   When the developing cartridge is mounted on the process cartridge, the developing roller is placed in confrontation with a photosensitive drum in the process cartridge. By rotating the developing roller while in confrontation with the photosensitive drum, an electrostatic latent image formed on the photosensitive drum is developed into a visual toner image. By transferring the toner image onto a sheet of paper, it is possible to form a desired image on the sheet of paper. 
   The developing cartridge further includes side seals for preventing toner carried on the developing roller from leaking outside from the housing of the developing cartridge. The side seals are disposed at both ends of the developing roller with respect to its axial direction so as to make sliding contact with a circumferential surface of the developing roller at the both ends. 
   U.S. Pat. No. 6,356,723 and U.S. patent application Publication No. 2003/118364 have proposed a configuration in which the side seal includes: a sponge seal that is formed of urethane sponge and that is affixed to the housing: and a sliding sealing element that is formed of felt or a woven fabric and that is affixed to the upper surface of the sponge seal. 
   SUMMARY OF THE INVENTION 
   It is preferable to recycle the developing cartridge in order to protect the environment and to reduce waste. 
   It is highly likely that the sliding sealing element that makes sliding contact against the developing roller will become damaged. Accordingly, it is preferable to replace the used sliding sealing element with a new one during a recycling stage. If the sliding sealing element is peeled off from the sponge seal, however, the surface of the sponge seal to which the sliding sealing element is affixed will possibly be damaged by the separation, making it necessary to replace the sponge seal as well. 
   It is troublesome to peel the sponge seal cleanly from the housing and then re-affix the sponge seal. This will make it difficult to increase the efficiency of the recycling. The replacement of the sponge seal leads to an increase in costs. 
   An objective of the present invention is to provide an improved developing cartridge, an improved process cartridge, and an improved image forming device, in which a sliding sealing element can be replaced with a new one while reducing damage to the sponge seal, enabling an improvement in the efficiency of recycling and also reducing costs. 
   In order to attain the above and other objects, the present invention provides a developing cartridge, including: a housing; a developing member; and a pair of sealing elements. The housing accommodates developer therein and is formed with an opening. The developing member holds the developer on a surface thereof. The developing member is movably supported in the housing to be exposed at the opening. The pair of sealing elements are provided on the housing at a pair of portions confronting both lengthwise ends of the developing member to prevent leakage of the developer out of the housing by being compressed by the developing member. Each sealing element includes: an elastic seal member; a sliding sealing element; and an adhesive member. The elastic seal member is supported in the housing at a portion confronting a corresponding lengthwise end of the developing member. The sliding sealing element has a first surface and a second surface opposite to the first surface. The first surface has an overlapping region that confronts a part of the elastic seal member and a non-overlapping region that confronts a part of the housing. At least a part of the second surface makes a sliding contact with the surface of the developing member. The adhesive member is provided on at least a part of the non-overlapping region in the first surface of the sliding sealing element thereby being located between the sliding sealing element and the housing. At least a part of the overlapping region in the first surface of the sliding sealing element directly confronts the elastic seal member with no adhesive member being positioned between the at least a part of the overlapping region of the sliding sealing element and the elastic seal member. 
   According to another aspect, the present invention provides a sliding sealing element, including: a rectangular-shaped flat sheet; and a first double-faced adhesive tape attached to at least a first location on a surface of the rectangular-shaped flat sheet. The first double-faced adhesive tape includes: a first base member made of elastic material and having a pair of opposite surfaces; a pair of first adhesive layers made of adhesive agent and provided on the pair of opposite surfaces of the first base member, one of the pair of first adhesive layers being attached to the rectangular-shaped flat sheet: and a first release paper attached to the other one of the pair of first adhesive layers, the first release paper being releasable from the other one of the pair of first adhesive layers. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and advantages of the invention will become more apparent from reading the following description of the preferred embodiments taken in connection with the accompanying drawings in which: 
       FIG. 1  is a side sectional view of a laser printer according to a preferred embodiment of the invention; 
       FIG. 2(   a ) is a side sectional view of a process cartridge in the laser printer shown in  FIG. 1 ; 
       FIG. 2(   b ) is a side sectional view of a developing cartridge in the process cartridge shown in  FIG. 2(   a ); 
       FIG. 3(   a ) is a perspective view of a sealing structure at the end of the developing cartridge shown in  FIG. 2(   b ), where a blade side seal is not yet affixed, a sponge seal of a side seal is affixed, and the supply roller is not yet mounted; 
       FIG. 3(   b ) is a perspective view of the sealing structure at the end of the developing cartridge, where a sliding sealing element is overlaid on the sponge seal and the supply roller is attached; 
       FIG. 4  is a front view of the end of the developing cartridge seen from a direction indicated by an arrow IV in  FIG. 3(   b ); 
       FIG. 5  is a side sectional view of the sealing structure, taken along a line V—V in  FIG. 4 ; 
       FIG. 6(   a ) is a cross-sectional view of the sealing structure and the supply roller in the developing cartridge, taken along a line VIa—VIa in  FIG. 2(   b ), where showing of the developing roller is omitted; 
       FIG. 6(   b ) illustrates an enlarged view of a portion VIb in  FIG. 5  encircled by a two-dot-and-one-chain line; 
       FIG. 6(   c ) is a cross-sectional view taken along a along a line VIc–Vic in  FIG. 4  and illustrates the thickness of a layer-thickness regulating blade and the total thickness of the sliding sealing element and a first double-faced adhesive tape before the developing roller is mounted in the developing cartridge; 
       FIG. 6(   d ) illustrates how the first double-faced adhesive tape in  FIG. 6(   c ) is compressed by the developing roller when the developing roller is mounted in the developing cartridge; 
       FIG. 6(   e ) illustrates a comparative example of a manner of attaching a sliding sealing element onto a plate spring; 
       FIG. 6(   f ) is a perspective view of the sliding sealing element before the sliding sealing element is attached on the developing cartridge; 
       FIG. 6(   g ) is a cross-sectional view of the sliding sealing element of  FIG. 6(   f ) taken along the line VIg—VIg in  FIG. 6(   f ); 
       FIG. 7  is a front view of the end of the developing cartridge seen from a direction indicated by an arrow IV in  FIG. 3(   b ) according to a first modification; 
       FIG. 8  is a side sectional view of the sealing structure, taken along a line VIII—VIII in  FIG. 7 ; 
       FIG. 9  is a cross-sectional view of the sealing structure and the supply roller, taken along a line VIa—VIa in  FIG. 2(   b ) according to the first modification, where showing of the developing roller is omitted; 
       FIG. 10  is a front view showing the end of the developing cartridge seen from a direction indicated by the arrow IV in  FIG. 3(   b ) according to a second modification; 
       FIG. 11  is a side sectional view of the sealing structure, taken along a line XI—XI in  FIG. 10 ; 
       FIG. 12  is a cross-sectional view of the sealing structure and the supply roller, taken along a line VIa—VIa in  FIG. 2(   b ) according to the second modification, where showing of the developing roller is omitted; 
       FIG. 13  is a front view showing the end of the developing cartridge seen from a direction indicated by an arrow IV in  FIG. 3(   b ) according to a third modification; 
       FIG. 14  is a side sectional view of the sealing structure, taken along a line XIV—XIV in  FIG. 13 ; and 
       FIG. 15  is a cross-sectional view of the sealing structure and the supply roller, taken along a line VIa—VIa in  FIG. 2(   b ) according to the third modification, where showing of the developing roller is omitted. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   A developing cartridge, a process cartridge, and an image forming device according to a preferred embodiment of the present invention will be described while referring to the accompanying drawings wherein like parts and components are designated by the same reference numerals to avoid duplicating description. 
     FIG. 1  is a cross-sectional side view of a laser printer  1  according to the preferred embodiment of the present invention. 
   In the following description, the expressions “front”, “rear”, “upper”, “lower”, “right”, and “left” are used to define the various parts when the laser printer  1  is disposed in an orientation in which it is intended to be used. 
   The laser printer  1  includes a main casing  2 . The laser printer  1  further includes: a feeder section  4  and an image forming section  5 . The feeder section  4  and the image forming section  5  are housed in the main casing  2 . The feeder section  4  supplies sheets  3  to the image forming section  5 . The image forming section  5  forms desired images on the supplied sheets  3 . 
   The feeder section  4  includes: a paper supply tray  6 , a paper pressing plate  7 , a sheet supply roller  8 , a separating pad  9 , paper dust removing rollers  10  and  11 , and registration rollers  12 . The paper supply tray  6  is detachably mounted in the bottom section of the main casing  2 . The paper pressing plate  7  is disposed inside the paper supply tray  6 . The sheet supply roller  8  and the separating pad  9  are disposed above one end of the paper supply tray  6 . The paper dust removing roller  10  and paper dust removing rollers  11  are disposed downstream of the sheet supply  15  roller  8  in the conveying direction of the paper  3 . The registration rollers  12  are disposed downstream of the paper dust removing roller  10  and the paper dust removing rollers  11  in the conveying direction of the paper  3 . 
   A stack of sheets  3  can be mounted on the sheet pressing plate  7 . The sheet pressing plate  7  is pivotably supported at its end furthest from the sheet supply roller  8  so that the end of the sheet pressing plate  7  that is the nearest to the sheet supply roller  8  can move vertically. Although not shown in the drawings, a spring for urging the sheet pressing plate  7  upward is provided to the rear surface of the sheet pressing plate  7 . Therefore, the sheet pressing plate  7  pivots downward in accordance with increase in the amount of sheets  3  stacked on the sheet pressing plate  7 . At this time, the sheet pressing plate  7  pivots around the end of the sheet pressing plate  7  farthest from the sheet supply roller  8 , downward against the, urging force of the spring. 
   The sheet supply roller  8  and the sheet supply pad  9  are disposed in confrontation with each other. A spring  13  is provided beneath the sheet supply pad  9  for pressing the sheet supply pad  9  toward the sheet supply roller  8 . Urging force of the spring under the sheet pressing plate  7  presses the uppermost sheet  3  on the sheet pressing plate  7  toward the sheet supply roller  8 . According to rotation of the sheet supply roller  8 , the uppermost sheet  3  is sandwiched between the sheet supply roller  8  and the separation pad  13 . Thereafter, one sheet  3  at a time is separated from the stack and supplied to the paper dust removing rollers  10 ,  11 . The paper dust removing rollers  10 ,  11  remove paper dust from the supplied sheet  3  and further convey the sheet  3  to the registration rollers  12 . The pair of registration rollers  12  performs a predetermined registration operation on the supplied sheet  3 , and transport the sheet  3  to a transport position (a location between a photosensitive drum  27  and a transfer roller  30  to be described later) in the image formation section  5 . 
   The feeder section  4  further includes a multipurpose sheet supply mechanism. The multipurpose sheet supply mechanism includes: a multipurpose tray  14 , a multipurpose sheet supply roller  15 , and a multipurpose sheet supply pad  25 . The multipurpose sheet supply roller  15  and the multipurpose sheet supply pad  25  are disposed in confrontation with each other and are for supplying sheets  3  that are stacked on the multipurpose tray  14 . A spring  25   a  provided beneath the multipurpose sheet supply pad  25  presses the multipurpose sheet supply pad  25  up toward the multipurpose sheet supply roller  15 . Rotation of the multipurpose sheet supply roller  15  moves sheets  3  one at a time from the stack on the multipurpose tray  14  to a position between the multipurpose sheet supply pad  25  and the multipurpose sheet supply roller  15  so that the sheets  3  on the multipurpose tray  14  can be supplied one at a time to the image formation section  5 . 
   The image forming section  5  includes: a scanner unit  16 , a process cartridge  17 , and a fixing section  18 . 
   The scanner  16  is provided at the upper section of the casing  2  and is provided with a laser emitting portion (not shown), a polygon mirror  19 , lenses  20  and  21 , and reflection mirrors  22 ,  23 ,  24 . The laser emitting portion emits a laser beam based on predetermined print data. As indicated by a chain line in  FIG. 1 , the laser beam passes through or is reflected by the polygon mirror  19 , the lens  20 , the reflection mirrors  22  and  23 , the lens  21 , and the reflection mirror  24  in this order so as to irradiate, in a high speed scanning operation, the surface of the photosensitive drum  27  in the process cartridge  17 . 
   The process cartridge  17  is disposed below the scanner unit  16 . The process cartridge  17  includes a drum cartridge  26 . The drum cartridge  26  can be attached to and detached from the main casing  2 . As shown in  FIG. 2(   a ), the drum cartridge  26  houses therein the photosensitive drum  27 , a scorotron charge unit  29 , and a transfer roller  30 . 
   A developing cartridge  28  is detachably mounted to the drum cartridge  26 . As shown in  FIG. 2(   b ), the developing is cartridge  28  includes a housing  51 . The developing cartridge  28  further includes a supply roller  33 , a developing roller  31 , and a layer thickness-regulating blade  32 , all of which are provided within the housing  51 . 
   The housing  51  has a housing frame  52 . The housing frame  52  has a pair of opposite side walls  53 . The housing frame  52  is formed entirely as a box shape, and is formed with an opening  40  at its front side. The opening  40  will face the photosensitive drum  27  when the developing cartridge  28  is attached to the drum cartridge  26  as shown in  FIG. 2(   a ). A developing chamber  34   a  is formed in the front side of the housing  51 . The developing chamber  34   a  is opened through the opening  40 . A toner box  34   b  is formed also in the housing  51 . The toner box  34   b  is located in the rear side of the developing chamber  34   a . A partitioning plate  37  is provided between the developing chamber  34   a  and the toner box  34   b . A toner supply port  37   a  is defined as an opening formed through a lower part of the partitioning plate  37 , to thereby allow communication between the developing chamber  34   a  and the toner box  34   b.    
   A pair of windows  38  are provided on the side walls  53  at a location that the windows  38  face each other through the toner box  34   b . The windows  38  are used for checking the amount of remaining toner in the toner box  34   b.    
   The toner box  34   b  contains positively charged nonmagnetic single-component toner as a developing agent. The toner used in this embodiment is a polymerized toner obtained through copolymerization of styrene-based monomers, such as styrene, and acryl-based monomers, such as acrylic acid, alkyl(C1–C4)acrylate, or alkyl(C1–C4)methacrylate, using a known polymerization method, such as suspension polymerization. The particle shape of such a polymerized toner is spherical, and thus the polymerized toner has excellent fluidity and is capable of forming high quality image. 
   A coloring agent, such as carbon black, and wax is added to the polymerized toner. An external additive, such as silica, is also added to the polymerized toner to improve fluidity. The particle size of the polymerized toner is approximately 6–10 μm. 
   The toner in the toner box  34   b  is stirred by an agitator  36  supported by a rotating shaft  35  provided at a central portion of the toner box  34   b , and is discharged through the toner supply port  37   a  toward the developing chamber  34   a . The window  38  is wiped clean by a cleaner  39  supported by the rotating shaft  35 . 
   The supply roller  33  and the developing roller  31  are mounted in the developing chamber  34   a . The supply roller  33  is disposed in the lower-front side of the toner supply port  37   a  and is rotatable in a counterclockwise direction. The supply roller  33  is formed by covering a metallic shaft  33   a  with a conductive sponge material  33   b.    
   The developing roller  31  is disposed in the upper-front side of the supply roller  33  and is rotatable also in a counterclockwise direction. The developing roller  31  confronts the supply roller  33 . The developing roller  31  is located as being exposed in the opening  40 . 
   As shown in  FIG. 2(   b ), the developing roller  31  is formed by covering a metallic roller shaft  31   a  with a roller portion  31   b  made of an electrically conductive elastic rubber material  31   b . More specifically, the roller portion  31   b  is made of an electrically conductive urethane or silicone rubber, containing fine carbon particles, and is coated with a urethane or silicone rubber containing fluorine. 
   A predetermined developing bias is applied to the developing roller  31  with respect to the photosensitive drum  27 . 
   The supply roller  33  and the developing roller  31  are disposed in contact with each other so that they are compressed against each other to an appropriate extent. 
   A metallic plate spring  59  is mounted in the developing chamber  34   a  as being exposed in the upper portion of the opening  40 . The plate spring  59  is located near to the developing roller  31 . The plate spring  59  is supported at its one base end to the housing frame  52  by a support member  58 . A layer thickness-regulating blade  32  is provided on a distal end of the plate spring  59  opposite to the base end, at which the plate spring  59  is attached to the housing frame  52 . The layer thickness-regulating blade  32  extends in an axial direction of the developing roller  31 . The layer thickness-regulating blade  32  is formed from an electrically insulating silicone rubber into a semicircular shape in section. 
   The layer thickness-regulating blade  32  is pressed against the developing roller  31  from the upper rear side of the developing roller  31  by the resilient force of the plate spring  59 , thereby regulating the thickness of a toner layer formed on the surface of the developing roller  31 . 
   The rotation of the supply roller  33  supplies the developing roller  31  with toner that has been discharged through the toner supply port  37   a . At this time, the toner is triboelectrically charged to a positive charge between the supply roller  33  and the developing roller  31 . Then, as the developing roller  31  rotates, the toner supplied onto the developing roller  31  moves between the developing roller  31  and the layer-thickness regulating blade  32 . This reduces thickness of the toner on the surface of the developing roller  31  down to a thin layer of uniform thickness. 
   As shown in  FIG. 2(   a ), the photosensitive drum  27  is disposed in front of and in confrontation with the developing roller  31 . The photosensitive drum  27  is supported rotatably in a clockwise direction. The photosensitive drum  27  includes a drum-shaped member and a surface layer. The drum-shaped member is electrically grounded. The surface layer is formed from a photosensitive layer that is made from polycarbonate and that has a positively charging nature. 
   The scorotoron charge unit  29  is disposed above the photosensitive drum  27  and is spaced away from the photosensitive drum  27  by a predetermined distance so as to avoid direct contact with the photosensitive drum  27 . The scorotron charge unit  29  is a positive-charge scorotron type charge-unit for generating a corona discharge from a charge wire made from, for example, tungsten. The scorotoron charge unit  29  forms a blanket of positive-polarity charge on the surface of the photosensitive drum  27 . 
   As shown in  FIG. 1 , as the photosensitive drum  27  rotates, the scorotoron charge unit  29  first forms a blanket of positive charge on the surface of the photosensitive drum  27 , and then the surface of the photosensitive drum  27  is exposed to high speed scan of the laser beam from the scanner unit  16 . The electric potential of the positively is charged surface of the photosensitive drum  27  drops at positions exposed to the laser beam. As a result, an electrostatic latent image is formed on the photosensitive drum  27  based on print data. 
   Next, an inverse developing process is performed. That is, as the developing roller  31  rotates, the positively-charged toner borne on the surface of the developing roller  31  is brought into contact with the photosensitive drum  27 . Because of the developing bias voltage applied to the developing roller  27 , the toner on the developing roller  31  is supplied to lower-potential areas of the electrostatic latent image on the photosensitive drum  27 . As a result, the toner is selectively borne on the photosensitive drum  27  so that the electrostatic latent image is developed into a visible toner image. 
   The transfer roller  30  is rotatably supported at a position below and in confrontation with the photosensitive drum  27 . The transfer roller  30  is rotatably supported in the drum cartridge  26 . The transfer roller  30  is supported rotatably in a counterclockwise direction. The transfer roller  30  includes a metal roller shaft and a roller portion covering the roller shaft and made of conductive elastic rubber. 
   At times of toner image transfer, the transfer roller  30  is applied with a predetermined transfer bias. The visible toner image borne on the surface of the photosensitive drum  27  is transferred onto a sheet  3  as the sheet  3  from the registration rollers  12  passes between the photosensitive drum  27  and the transfer roller  30 . 
   The fixing section  18  is disposed in front of the process cartridge  17  and downstream of the same in the conveying direction of the paper  3 . The fixing section  18  includes a heating roller  41 , a pressure roller  42  applying pressure to the heating roller  41 , and transport rollers  43 . The transport rollers  43  are disposed downstream of the heating roller  41  and the pressure roller  42 . The pressure roller  42  is disposed below the heating roller  41  in confrontation with the heating roller  41 , and is compressed against the heating roller  41 . 
   The heating roller  41  is made of metal and encloses a halogen lamp (heater) therein. In the fixing section  18 , the heat generated by the halogen lamp thermally fixes the toner, which has been transferred to the sheet  3  by the process cartridge  17 , onto the sheet  3  while the sheet  3  passes through between the heating roller  41  and the pressure roller  42 . Thereafter, the sheet  3  is transferred to a sheet discharging path  44  by the transport rollers  43 . The sheet  3  transported to the sheet discharging path  44  is conveyed to discharge rollers  45 , which in turn discharge the sheet  3  onto a discharge tray  46 . 
   The laser printer  1  is further provided with an inverting transport section  47  for inverting sheets  3  that have been printed on once and for returning the sheets  3  to the image forming section  5  so that images can be formed on both sides of the sheets  3 . The inverting transport section  47  includes the sheet-discharge rollers  45 , an inversion transport path  48 , a flapper  49 , and a plurality of inversion transport rollers  50 . 
   The sheet-discharge rollers  45  are a pair of rollers that can be rotated selectively forward or in reverse. The sheet-discharge rollers  45  are rotated forward to discharge sheet  3  onto the sheet-discharge tray  46  and rotated in reverse when sheets  3  are to be inverted. 
   The inversion transport rollers  50  are disposed below the image forming section  5 . The inversion transport path  48  extends vertically between the sheet-discharge rollers  45  and the inversion transport rollers  50 . The upstream end of the inversion transport path  48 , is located near the sheet-discharge rollers  45  and the downstream end is located near the inversion transport rollers  50  so that sheets  3  can be transported downward from the sheet-discharge rollers  45  to the inversion transport rollers  50 . 
   The flapper  49  is swingably disposed at the junction between the sheet-discharge path  44  and the inversion transport path  48 . By activating or deactivating a solenoid (not shown), the flapper  49  can be selectively swung between the orientation shown in broken line and the orientation shown by solid line in  FIG. 1 . The orientation shown in solid line in  FIG. 1  is for transporting sheets  3  that have one side printed to the sheet-discharge rollers  45 . The orientation shown in broken line in  FIG. 1  is for transporting sheets from the sheet-discharge rollers  45  into the inversion transport path  48 , rather than back into the sheet-discharge path  44 . 
   The inversion transport rollers  50  are aligned horizontally at positions below the image forming section  5  and above the sheet supply tray  6 . One pair of inversion transport rollers  50  that is farthest upstream is disposed near the rear end of the inversion transport path  48 . Another pair of inversion transport rollers  50  that is located farthest downstream is disposed below the registration rollers  12 . 
   The inverting transport unit  47  operates in the following manner when a sheet  3  is to be formed with images on both sides. A sheet  3  that has been formed an one side with an image is transported by the transport rollers  43  from the sheet-discharge path  44  to the sheet-discharge rollers  45 . The sheet-discharge rollers  45  rotate forward with the sheet  3  pinched therebetween until almost all of the sheet  3  is transported out from the laser printer  1  and over the sheet-discharge tray  46 . The forward rotation of the sheet-discharge rollers  45  is stopped once the rear-side end of the sheet  3  is located between the sheet-discharge rollers  45 . Then, the sheet-discharge rollers  45  are driven to rotate in reverse while at the same time the flapper  49  is switched to, change transport direction of the sheet  3  toward the inversion transport path  48 . As a result, the sheet  3  is transported into the inversion transport path  48  with its leading and trailing ends being reversed from the original state. The flapper  49  reverts to its initial position once transport of the sheet  3  to the inversion transport path  48  is completed. That is, the flapper  49  switches back to the position for transporting sheets from the transport rollers  43  to the sheet-discharge rollers  45 . Next, the inverted sheet  3  is transported through the inversion transport path  48  to the inversion transport rollers  50  and then from the inversion transport rollers  50  to the registration rollers  12 . The registration rollers  12  align the front edge of the sheet  3 . Afterward, the sheet  3  is transported toward the transfer position in the image formation section  5 . At this time, the upper and lower surfaces of the sheet  3  are reversed from the first time that an image has been formed on the sheet  3  so that an image can be formed on the other side as well. In this way, images are formed on both sides of the sheet  3 . 
   The laser printer  1  uses the developing roller  31  to collect residual toner that remains on the surface of the photosensitive drum  27  after toner is transferred onto the sheet  3  via the transfer roller  30 . In other words, the laser printer  1  uses a “cleanerless development method” to collect the residual toner. By using the cleanerless development method to collect residual toner, there is no need to provide a separate member, such as a blade, for removing the residual toner or an accumulation tank for the waste toner. Therefore, the configuration of the laser printer can be simplified. 
   As shown in  FIG. 2(   b ),  FIG. 3(   a ) and  FIG. 3(   b ), the housing frame  52  is open at the opening  40 . Each of the opposite side walls  53  of the housing frame  52  is provided with a cutout  54  for mounting the developing roller  31  in the housing frame  52 . The cutout  54  is formed in substantially a U-shape so as to receive the roller shaft  31   a  of the developing roller  31 . In this way, the developing roller  31  is rotatably mounted in the housing  51  with the axial ends of the roller shaft  31  being rotatably supported in the cutouts  54  on the opposite side walls  53 . 
   A supply roller mounting portion  68  is provided in the rear side of the cutout  54  in each of the opposite side walls  53 . 
   As shown in  FIG. 3(   a ),  FIG. 5 , and  FIG. 6(   a ), the housing frame  52  has a supply roller support plate  70  on the inner side of each of the opposite side walls  53  in the widthwise direction of the housing  51 . The supply roller support wall  70  on each side includes: an inner side plate  73 , an upper plate  71 , and a lower plate  72 , all of which are combined together into a substantially U-shape that is open at the front side thereof. The inner side plate  73  is located inside the housing  51  at a specified distance away from the corresponding side wall  53 . The upper plate  71  and the lower plate  72  connect the inner side plate  73  to the corresponding side wall  53 . The inner side plate  73  is formed with a notch  74 . The side wall  53  is formed with a through-hole  69 . The notch  74  on the inner side plate  73  confronts the through-hole  69  on the side wall  53  through the space surrounded by the inner side plate  73 , the upper plate  71 , the lower plate  72 , and the side plate  53 . On each of the opposite sides of the housing frame  52 , a corresponding end of the shaft  33   a  in the supply roller  33  rotatably passes through the notch  74  in the inner side plate  73  and the through-hole  69  in the side wall  53 . In this way, the supply roller  33  is rotatably supported by the supply roller support plates  70  and the side walls  53  on the opposite sides of the housing frame  52 . 
   As shown in  FIG. 6(   a ), when the supply roller  33  is thus mounted in the housing  51 , each end surface of the sponge material  33   b  in the supply roller  33 , with respect to the axial direction of the supply roller  31 , makes contact with a sponge seal  65  in a side seal  64  to be described later. With this contact, the supply roller  33  is positioned in its axial direction. 
   A roller shaft seal member  80 , made of a sponge, is fitted around the shaft  33   a  at a location between the inner side plate  73  and the side wall  53  at each of the opposite sides of the housing frame  52 , so as to prevent toner leakage through the notches  74  and the through-holes  69 . 
   As shown in  FIG. 3(   a ) and  FIG. 5 , the housing frame  52  has an intermediate attachment portion  75  and a lower attachment, portion  76 , and a blade side seal support portion  79 , at each of the opposite sides of the housing frame  52 . The intermediate attachment portion  75 , lower attachment portion  76 , and blade side seal support portion  79  are provided on the inner side of each of the opposite side walls  53  in the widthwise direction of the housing  51 . The intermediate attachment portion  75 , lower attachment portion  76 , and blade side seal support portion  79  are located adjacent to the cutout  54 . 
   The intermediate attachment portion  75  extends upwardly from the front side of the upper plate  71 , and is finally connected with the blade side seal support portion  79 . The housing frame  52  is curved at the intermediate attachment portion  75  following the circumferential surface of the developing roller  31  when the developing roller  31  is mounted in the housing  51 . The housing frame  52  has a right-angled corner  79   a  in the middle of the blade side seal support portion  79 . 
   The lower attachment portion  76  extends forwardly and downwardly from the front side of the lower plate  72 . The housing frame  52  is curved also at the lower attachment portion  76  following the circumferential surface of the developing roller  31  when the developing roller  31  is mounted in the housing  51 . The lower attachment portion  76  is then folded back and then further extends rearwardly to some extent. 
   In other words, the lower attachment portion  76  includes: an upperside lower attachment portion  76   a  and an underside lower attachment portion  76   b . The upperside lower attachment portion  76   a  extends forwardly and downwardly from the front side of the lower plate  72 . The housing frame  52  is curved at the upperside lower attachment portion  76   a  following the circumferential surface of the developing roller  31  when the developing roller  31  is mounted in the housing  51 . The upperside lower attachment portion  76   a  finally ends at, its lower front edge. The underside lower attachment portion  76   b  extends rearwardly from the front end of the upperside lower attachment portion  76   a.    
   As will be described later, the upperside lower attachment portion  76   a  is divided into two regions: an upper region  76   a   1 , onto which a part of the sponge seal  65  is attached via a double-faced adhesive tape (not shown); and a lower region  76   a   2 , onto which no part of the sponge seal  65  is attached. A lower end attachment portion  77  is defined as a region covering; the lower region  76   a   2  in the upperside lower attachment portion  76   a ; and the underside lower attachment portion  76   b.    
   As shown in  FIG. 4 , the plate spring  59  is provided in the housing  51  to extend over the entire width of the housing frame  52  at the upper side of the opening  40 . The support member  58  is provided in the housing  51  to extend also over the entire width of the housing frame  52  at the upper side of the opening  40 . As shown in.  FIG. 5 , the support member  58  includes a back support member  60  and a front support member  61 . 
   The plate spring  59  is formed in a substantially long, thin rectangular shape and is located above the developing roller  31  in the opening  40 . The plate spring  59  extends along the axial direction of the developing roller  31 . The lower edge of the plate spring  59  faces an upper rear portion of the developing roller  31 . A pair of upper attachment portions  78  are defined on the front surface of the plate spring  59  at both end portions of the plate spring  59  with respect to the axial direction of the developing roller  31 . Each upper attachment portion  78  is located at the lower edge of the plate spring  59 . 
   The layer-thickness regulating blade  32  is provided on the lower edge of the plate spring  59 . The layer-thickness regulating blade  32  is provided on the plate spring  59  to extend along the axial direction of the developing roller  31  over the entire length of the plate spring  59  except for the upper attachment portions  78 . Accordingly, the layer-thickness regulating blade  32  extends over a region defined between the pair of upper attachment portions  78  along the axial direction of the developing roller  31 . 
   The back support member  60  is formed in a substantially long, thin rectangular shape plate and extends along the axial direction of the developing roller  31 . The front support member  61  is formed also in a substantially long, thin rectangular shape plate, extends along the axial direction of the developing roller  31 , and has an L-shape in cross section. The support member  58  is secured to the housing frame  52  at a location above the opening  40  using screws  62 , with the upper portion of the plate spring  59  being sandwiched between the back support member  60  and the front support member  61 . Accordingly, the back support member  60  confronts the upper portion of the rear surface of the plate spring  59 , while the front support member  61  confronts the upper portion of the front surface of the plate spring  59 . 
   As shown in  FIG. 2(   b ), a lower film  67 , made of a polyethylene terephthalate (PET) sheet or an urethane rubber film, is affixed with a double-faced adhesive tape (not shown) entirely to an upper surface of a lower front edge of the housing frame  52 . The lower film  67  prevents toner from leaking from the lower part of the housing frame  52 . 
   Sealing structures are disposed at both ends of the inside of the housing frame  52  with respect to the axial direction of the developing roller  31 . When the developing roller  31  is mounted in position in the developing cartridge  28 , the sealing structures prevent toner carried on the developing roller  31  from leaking from each end of the developing roller  31 . 
   Next will be described, with reference to  FIG. 3(   a ) through  FIG. 6(   g ), the sealing structure at each end of the inside of the developing cartridge  28  with respect to the axial direction of the developing roller  31 .  FIG. 3(   a ) through  FIG. 5  and  FIG. 6(   b ) through  FIG. 6(   e ) show structural elements only at one end of the inside of the developing cartridge  26 , and the following descriptions are made based on one end of the inside of the developing cartridge  28 . The structural elements at the one end are identical to those at the other end. 
   As shown in  FIG. 3(   a ),  FIG. 3(   b ), and  FIG. 5 , the sealing structure, including the side seal  64 , a lower side seal  57 , an upper side seal  55 , and a blade side seal  56 , are provided adjacent to a position of the side wall  53  where the cutout  54  is formed. All of the side seal  64 , lower side seal  57 , upper side seal  55 , and blade side seal  56  reliably prevent toner from leaking from each end of the developing roller  31  when the developing roller  31  is mounted in position in the developing cartridge  28 . 
   The upper side seal  55  is made of a sponge material (e.g. urethane) formed in a substantially rectangular shape having a fixed thickness. The upper side seal  55  is disposed at an upper portion of each widthwise end of the housing frame  52  facing the rear surface of the back support member  60 , and is affixed to the housing frame  52  with double-faced adhesive tape (not shown). 
   The blade side seal  56  is made of a sponge material (e.g. urethane) formed in a substantially rectangular shape having a fixed thickness. The blade side seal  56  is provided at a location between the rear surface of the plate spring  59  and the blade side seal support portion  79  on the housing frame  52  and below the upper side seal  55 , and is affixed to the rear surface of the plate spring  59 . Thus, the blade side seal  56  is provided on the rear surface of the plate spring  59 . 
   As shown in  FIG. 3(   a ) and  3 ( b ), the side seal  64  is provided adjacent to a portion of the side wall  53 , where the cutout  54  is formed, so as to make sliding contact with the circumferential surface of the developing roller  31  when the ends of the developing roller  31  are rotatably supported by the cutout  54 . 
   The lower side seal  57  made of a sponge material. (e.g. urethane) is formed in a substantially rectangular shape having a fixed thickness, is disposed adjacent to an inner side of the side seal  64 , and is affixed to a lower part of the housing frame  52  with double-faced adhesive tape (not shown). Provision of the lower side seal  57  can prevent the toner from leaking from a boundary between the side seal  64  and the lower film  67 . 
   Next will be described the side seal  64  with a greater detail. 
   The side seal  64  is provided at a region covering the upper attachment portion  76  on the plate spring  59  ( FIG. 4 ) and the intermediate attachment portion  75  and the lower attachment portion  76  of the housing frame  52  ( FIG. 5 ). 
   The side seal  64  includes: a sponge seal  65  ( FIG. 3(   a )) which is elastically compressed against the developing roller  31  when the developing roller  31  is mounted in the housing  51 ; and a sliding sealing element  66  ( FIG. 3(   b )) which is overlaid partly on the sponge seal  65  and performs a sliding contact against the circumferential surface of the developing roller  31 . 
   The sponge seal  65 , providing an urging force, is made of an elastic foamed material, i.e., a sponge material, such as urethane. More specifically, the sponge seal  65  is made of a high density, microcellular urethane foam (trade name: PORON, manufactured by Rogers Inoac Corporation), which has a comparatively great rigidity and resists permanent deformation among various sponge materials. The hardness of the microcellular urethane foam is 0.001 to 0.05 MPa (Mega-Pascal) under 25% compressive load, and preferably 0.005 to 0.025 MPa. The sponge seal  65  is formed in a substantially rectangular shape having a certain thickness to generate a fixed pressing force when compressed by the developing roller  31  mounted in position. 
   The sponge seal  65  includes a base portion  81 , an inner projecting portion  82 , and a pair of outer projecting portions  68 , which are formed integrally as shown in  FIG. 3(   a ). The base portion  81  is formed in a substantially rectangular shape, and a front surface thereof, which faces the opening  40 , is used as a surface onto which the sliding sealing element  66  is overlaid. The inner projecting portion  82  is formed in a rectangular shape projecting from a center of the base portion  61 , with respect to a rotational direction of the developing roller  31 , toward the center of the developing roller  31  along its axial direction. The outer projecting portions  83  are formed in rectangular shapes projecting from both ends of the base portion  81 , with respect to the rotational direction of the developing roller  31 , toward the end of the developing roller  31  along its axial direction. 
   The sponge seal  65  is disposed in such a manner that the outer projecting portions  83  make contact with the sidewall  53  of the housing frame  52 , thereby positioning the sponge seal  65  with respect to the width of the housing frame  52 . An upper end of the sponge seal  65  is pressed against a lower end of the blade side seal  56  as shown in  FIG. 5 . The sponge seal  65  is located side by side with the lower side seal  57  in the widthwise direction of the housing frame  52 , and is in intimate contact with thee lower side seal  57 . The lower end of the inner projecting portion  82  is pressed against the upper end of the lower side seal  57 . In this way, the sponge seal  65  is positioned also with respect to the rotational direction of the developing roller  31 , that is, with respect to a direction orthogonal to the widthwise direction of the housing frame  52 . 
   The sponge seal  65  is affixed to the housing frame  52  by double-faced adhesive tape (not shown), extending to cover both of the intermediate attachment portion  75  and the upper region  76   a   1  in the lower attachment portion  76 , spanning the supply roller support portion  68 . Affixing the sponge seal  65  in this manner ensures that the upper edge portion of the sponge seal  65  in the lengthwise direction thereof is located next to the upper attachment portion  78  on the plate spring  59  and that the lower edge portion of the sponge seal  65  in the lengthwise direction thereof is located next to the lower region  76   a   2  in the lower attachment portion  76  on the housing frame  52 . 
   By making the upper end of the sponge seal  65  be pressed against the blade side seal  56 , the sponge materials make contact with each other to reliably prevent toner leakage in the boundary between the sponge seal  65  and the blade side seal  56 . By making the lower end of the sponge seal  65  and the lower side seal  57  slightly overlap each other in the widthwise direction thereof, the sponge materials make contact with each other, thereby preventing toner leakage in the boundary between the sponge seal  65  and the lower side seal  57 . 
   As shown in  FIG. 3(   b ), the sliding sealing-element  66  is formed into a substantially rectangular-shaped elongated flat sheet, and is made of a fluorine-based felt, such as a polytetrafluoroethylene felt. The sliding sealing element  66  is mounted on the housing  61  as being oriented with its widthwise direction extending along the axial direction of the developing roller  31 . The width of the sliding sealing element  66  is uniform over the entire length of the sealing element  66 . 
   As shown in  FIG. 3(   b ) and  FIG. 4 , the sliding sealing element  66  is overlaid on a part of the sponge seal  65 . More specifically, as shown in  FIG. 5 , the sliding sealing element  66  extends in the rotational direction of the developing roller  31  to extend along: the entire upper attachment portion  78  on the plate spring  59 ; the entire length of the base portion  81  of the sponge seal  65  in the lengthwise direction thereof; and the entire length of the lower end attachment portion  77  on the housing frame  52 . It is noted that the lower end attachment portion  77  includes: the lower portion  76   a   2  in the upperside lower attachment portion  76   a ; and the underside lower attachment portion  76   b . Accordingly, the sliding sealing element  66  extends downwardly along: the upper attachment portion  78 ; the entire length of the base portion  81  of the sponge seal  65 ; and the entire length of the lower region  76   a   2  in the upperside lower attachment portion  76 ; and is finally folded back to further extend rearwardly along the underside lower attachment portion  76   b . In this way, the sliding sealing element  66  extends not only on the sponge seal  65  but also to extend further upwardly from the upper edge of the sponge seal  65  onto the plate spring  59  and further downwardly from the lower edge of the sponge seal  65  onto the housing, frame  52 . 
   As shown in  FIG. 5 , the developing roller  31 , indicated by the broken line, makes sliding contact with the sliding sealing element  66  at its areas over: a lower portion in the upper attachment portion  78 ; the sponge seal  65 ; and the upper region  76   a   1  in the upperside lower attachment portion  76   a . The developing roller  31  makes no sliding contact with the sliding sealing element  66  at its areas over: an upper portion in the upper attachment portion  78 ; and the lower end attachment portion  77  (lower region  76   a   2  in the upperside lower attachment portion  76   a  and the underside lower attachment portion  76   b ). In this way, the sliding sealing element  66  is provided to cover not only the region, with which the developing roller  31  makes sliding contact, but also the region, with which the developing roller  31  makes no sliding contact. 
   It is noted that an overlapping region Y is defined as an area of the rear surface of the sliding sealing element  66  that confronts the sponge seal  65 . A first non-overlapping region X- 1  is defined as another area of the rear surface of the sliding sealing element  66  that confronts the upper attachment portion  78  on the plate spring  59 . A second non-overlapping region X- 2  is defined as still another area of the rear surface of the sliding sealing element  66  that confronts the lower end attachment portion  77  (lower region  76   a   1  in the upperside lower attachment portion  76   a  and the underside lower attachment portion  76   b ) on the housing frame  52 . 
   The first non-overlapping region X- 1  is located on one longitudinal end of the sliding sealing element  66 , and the second non-overlapping region X- 2  is located on the other longitudinal end of the sliding sealing element  66 . The overlapping region Y is defined as an intermediate area defined between the non-overlapping regions X- 1  and X- 2 . The sliding sealing element  66  is overlapped with the sponge seal  65  at the overlapping region Y, while the sliding sealing element  66  is not overlapped with the sponge seal  65  at the non-overlapping regions X- 1  and X- 2 . 
   The upper attachment portion  78  has a rectangular shape whose width is equal to the width of the sliding sealing element  66 . The first non-overlapping region X- 1  also has a rectangular shape whose width is equal to the width of the sliding sealing element  66 . The lower end attachment portion  77  has a rectangular shape whose width is equal to the width of the sliding sealing element  66 . The second non-overlapping region X- 2  also has a rectangular shape whose width is equal to the width of the sliding sealing element  66 . 
   The sliding sealing element  66  is attached to the housing  51  by a first double-faced adhesive tape  84 - 1  and a second double-faced adhesive tape  84 - 2 . The first and second double-faced adhesive tapes  84 - 1  and  84 - 2  are provided on the rear surface of the sliding sealing element  66  to affix the sliding sealing element  66  to the housing  51 . 
   More specifically, the first double-faced adhesive tape  84 - 1  is provided on the first non-overlapping region X- 1  of the rear surface of the sliding sealing element  66 , and the second double-faced adhesive tape  84 - 2  is provided on the second non-overlapping region X- 2  of the rear surface of the sliding sealing element  66 . 
   The first double-faced adhesive tape  84 - 1  is provided entirely over the first non-overlapping region X- 1  of the sliding sealing element  66 . Accordingly, the first double-faced adhesive tape  84 - 1  also has a rectangular shape whose width is equal to the width of the sliding sealing element  66  and is uniform in the rotating direction of the developing roller  31 . 
   Similarly, the second double-faced adhesive tape  84 - 2  is provided entirely over the second non-overlapping region X- 2  of the sliding sealing element  66 . Accordingly, the second double-faced adhesive tape  84 - 2  also has a rectangular shape whose width is equal to the width of the sliding sealing element  66  and is uniform in the rotating direction of the developing roller  31 . 
   In this way, the first double-faced adhesive tape  84 - 1  is located next to the layer-thickness regulating blade  32  in the widthwise direction of the housing  51 , and extends upwardly from the upper edge of the sponge seal  65 . The second double-faced adhesive tape  84 - 2  extends downwardly from the lower edge of the sponge seal  65  and is folded back along the underside surface of the housing frame  52 . 
   As shown in  FIG. 6(   b ), the second double-faced adhesive tape  84 - 2  includes: a second base member  84 - 2   a ; and a pair of second adhesive layers  84 - 2   b  and  84 - 2   c . The second base member  84 - 2   a  can be made of any material, such as elastic material, non-woven fabric, and PET (polyethylene terephthalate), that has a desired amount of rigidity. The second base member  84 - 2   a  has a pair of opposite surfaces. The pair of second adhesive layers  84 - 2   b  and  84 - 2   c  are made of adhesive agent and provided on the pair of opposite surfaces of the second base member  84 - 2   a , respectively. The second adhesive layer  84 - 2   c  is attached to the sliding sealing element  66 . The second adhesive layer  84 - 2   b  is attached onto the lower end attachment portion  77  of the housing frame  52 . 
   The thickness of the second double-faced tape  84 - 2  is not particularly limited, but needs to have an amount sufficiently large to fixedly secure the sliding sealing element  66  onto the housing frame  52 . More specifically, the thickness of the second base member  84 - 2   a  has an amount sufficiently large to fixedly secure the sliding sealing element  66  onto the housing frame  52 . 
   The thickness of the first double-faced tape  84 - 1  has an amount that allows a total thickness of the first double-faced adhesive tape  84 - 1  and the sliding sealing element  66  to be greater than or equal to the thickness of the layer-thickness regulating blade  32 , as shown in  FIG. 6(   c ), when the developing roller  31  is not mounted in the housing  51 . In this example, the thickness of the layer-thickness regulating blade  32  is 1.5 mm, the thickness of the sliding sealing element  66  is 0.8 mm, and the thickness of the first double-faced adhesive tape  84 - 1  is 0.8 mm. It is noted that the first double-faced adhesive tape  84 - 1  can have a thickness in the range of about 0.8 mm to 3 mm. 
   As shown in  FIG. 6(   c ), the layer-thickness regulating blade  32 , is located on the front surface, of the plate spring  59  that will confront the developing roller  31  when the developing roller  31  is installed in the housing  51 . The sliding sealing element  66  is provided via the first double-faced tape  84 - 1  on the front surface of the plate spring  59  at the upper attachment portion  78 , that is, at a location next to the layer-thickness regulating blade  32 . When the developing roller  31  is not installed in the housing  51 , the distance or height of the front surface of the sliding sealing element  66  from the front surface of the plate spring  59  is greater than the distance or height of the top surface of the layer-thickness regulating blade  32  from the surface of the plate spring  59 . 
   As shown in  FIG. 6(   c ), the first double-faced tape  84 - 1  includes: a first base member  84 - 1   a ; and a pair of first adhesive layers  84 - 1   b  and  84 - 1   c . The first base member  84 - 1   a  is made of elastic material, such as elastic foamed material. Representative examples of the first base member  84 - 1   a  include a sponge sheet and a urethane sheet. The first base member  84 - 1   a  has a pair of opposite surfaces. The pair of first adhesive layers  84 - 1   b  and  84 - 1   c  are made of adhesive agent and provided on the pair of opposite surfaces of the first base member  84 - 1   a , respectively. The first adhesive layer  84 - 1   c  is attached to the sliding sealing element  66 . The first adhesive layer  84 - 1   b  is attached to the plate spring  59 . The thickness of the first base member  84 - 1   a  is adjusted to allow the total thickness of the first double-faced adhesive tape  84 - 1  and the sliding sealing element  66  to be greater than or equal to the thickness of the layer-thickness regulating blade  32 . In this example, the thickness of the first base member  84 - 1   a  is greater than the thickness of the second base member  84 - 2   a.    
   When the developing roller  31  is installed in the housing  51 , as shown in  FIG. 6(   d ), the first base member  84 - 1   a  is compressed by the developing roller  31  to be elastically deformed due to its elasticity, as a result of which the front surface of the sliding sealing element  66  is brought into the same level with the front surface of the layer-thickness regulating blade  32 . This enables the sliding sealing element  66  to block any leakage of toner through the boundary between the layer-thickness regulating blade  32  and the sliding sealing element  66 . 
   It is now assumed that the first base member  84 - 1   a  were made of non-elastic material and had a thickness relatively small with respect to the layer-thickness regulating blade  32  as shown in  FIG. 6(   e ). In such a case, another elastic sheet  184 , such as a sponge sheet, and another double-faced adhesive sheet  185  have to be additionally provided between the first double-faced adhesive sheet  84 - 1  and the plate spring  59 , in order to adjust the distance between the front surface of the sliding sealing element  66  and the front surface of the plate spring  59  to be greater than or equal to the distance between the front surface of the layer-thickness regulating blade  32  and the front surface of the plate spring  59 . The laminate structure thus provided between the sliding sealing element  66  and the plate spring  59  will become complicated. It will become necessary to perform an additional troublesome work to attach the elastic sheet  184  onto the plate spring  59  via the double-faced adhesive sheet  185 , before attaching the sliding sealing element  66  on the elastic sheet  184  via the, first double-faced adhesive tape  84 - 1 . 
   Contrarily, according to the present embodiment, the first double-faced adhesive tape  84 - 1  has the first base member  84 - 1   a  made of elastic material. By simply adjusting the thickness of the first base member  84 - 1   a  dependently on the layer-thickness regulating blade  32 , it becomes unnecessary to provide any separate elastic member or any additional double-faced adhesive tape between the first double-faced adhesive tape  84 - 1  and the plate spring  59 . The configuration of the laminate structure between the sliding sealing element  66  and the plate spring  59  becomes simple. 
   It is noted that the second base member  84 - 2   a  in the second double-faced adhesive tape  84 - 2  may be made of elastic material, such as an elastic foamed material, similarly to the first base member  84 - 1   a  in the first double-faced adhesive tape  84 - 1 . In this case, the thickness of the second base member  84 - 2   a  may have the same thickness as that of the first base member  84 - 1   a  in the first double-faced adhesive tape  84 - 1 . In other words, the thickness of the second base member  84 - 2   a  may have such a value that allows the total thickness of the double-faced adhesive tape  84 - 2  and the sliding sealing element  66  to be greater than or equal to the thickness of the layer-thickness regulating blade  32  when the developing roller  31  is not installed in the housing  51 . 
   Next will be described with reference to  FIG. 6(   f ) and  FIG. 6(   g ) how to attach the sliding sealing element  66  onto the housing  51  during a manufacturing step of the developing cartridge  28 . 
   First, the sliding sealing element  66  is prepared in a state shown in  FIG. 6(   f ), in which the first and second double-faced adhesive tapes  84 - 1  and  84 - 2  are attached to two lengthwise ends of the sliding sealing element  66 . In this example, the first double-faced adhesive tape  84 - 1  has a thickness greater than the second double-faced adhesive tape  84 - 2 . At this time, the first double-faced adhesive tape  84 - 1  originally includes not only the first base member  84 - 1   a  and the first adhesive layers  84 - 1   b  and  84 - 1   c  but also a first release paper  84 - 1   d . The first release paper  84 - 1   d  is attached to the first adhesive layer  84 - 1   b . The first release paper  84 - 1   d  is releasable from the first adhesive layer  84 - 1   b . The second double-faced adhesive tape  84 - 2  originally includes not only the second base member  84 - 2   a  and the second adhesive layers  84 - 2   b  and  84 - 2   c  but also the second release paper  84 - 2   d . The second release paper  84 - 2   d  is attached to the second adhesive layer  84 - 2   b . The second release paper  84 - 2   d  is releasable from the second adhesive layer  64 - 2   b.    
   After attaching the side seal  65  on the housing frame  52  via double-faced adhesive tape (not shown) as shown in  FIG. 3(   a ), in order to mount the sliding sealing element  66  as partly overlying the side seal  65  as shown in  FIG. 3(   b ), the first and second release papers  84 - 1   d  and  84 - 2   d  are peeled off from the first and second adhesive layers  84 - 1   b  and  84 - 2   b , respectively. Then, the exposed first adhesive layer  84 - 1   b  is bonded to the upper attachment portion  78  on the plate spring  59 , and the exposed second adhesive layer  84 - 2   b  is bonded to the lower end attachment portion  77  on the housing frame  52 . 
   During a recycling stage of the developing cartridge  28 , the used-up sliding sealing element  66  is separated from the sponge seal  65 . Then, a new sliding sealing element  66 , on which the first and second double-faced adhesive tapes  84 - 1  and  64 - 2  are already attached as shown in  FIG. 6(   f ), is mounted as partly overlaying the sponge seal  65  in the same manner as in the manufacturing step. 
   As described above, according to the present embodiment, the double-faced adhesive tapes  84 - 1  and  84 - 2  are provided on both lengthwise edges of the sliding sealing element  66  at its non-overlapping regions X- 1  and X- 2  where the sliding sealing element  66  does not confront the sponge seal  65 . The sliding sealing element  66  is attached to the housing  51  at the upper attachment portion  78  and the lower end attachment portion  77 . Accordingly, the sliding sealing element  66  can be fixed reliably to the housing  51 , improving the sealing capability. 
   No double-faced adhesive tape is provided in the overlapping region X where the sliding sealing element  66  confronts the sponge seal  65 . During the recycling of the developing cartridge  28 , the used-up sliding sealing element  66  can be separated cleanly from the sponge seal  65 . Since the used sliding sealing element  66  can thus be separated from the sponge seal  65  without damaging the sponge seal  65 , it is unnecessary to replace the sponge seal  65  with a new one. The efficiency with which the developing cartridge  28  is recycled can be improved and thus the cost thereof can be reduced. Running costs of the developing cartridge  28 , of the process cartridge  17 , and of the laser printer  1  can be reduced. The amount of waste can be reduced. 
   Since each sliding sealing element  66  is affixed by the double-faced adhesive tapes  64 - 1  and  84 - 2  at the two lengthwise end portions thereof along the rotating direction of the developing roller  31 , the end portions of the sliding sealing element  66  can be fixed reliably onto the housing  51 . The sealing capability can be improved while ensuring simple removal of the sliding sealing element  66  from the sponge seal  65 . 
   The sliding sealing element  66  is attached to the housing  51  at the upper portion of the upper attachment portion  78  and the lower end attachment portion  77 , at both of which the sliding sealing element  66  does not make sliding contact with the developer roller  31 . In this way, the sliding sealing element  66  is attached to the housing  51  at its portions that will be deteriorated little with time. The sealing capability can be further improved by affixing the sliding sealing element  66  at these portions. 
   The upper attachment portion  78  is defined as a location on the plate spring  59  adjacent to an edge of the layer-thickness regulating blade  32  in the axial direction of the developing roller  31 . Toner is most likely to leak at the upper attachment portion  78 . According to the present embodiment, the sliding sealing element  66  is securely attached to the plate spring  59  at the upper attachment portion  78  via the first double-faced adhesive tape  84 - 1 . Accordingly, it is possible to reliably prevent the leakage of toner from the portion at which toner is most likely to leak, enabling an improvement in the sealing capability. 
   The first double-faced adhesive tape  84 - 1  has a sufficiently large thickness that the total thickness of the first double-faced adhesive tape  84 - 1  and the sliding sealing element  66  is greater than or equal to the thickness of the layer-thickness regulating blade  32 . The first base member  84 - 1   a  in the first double-faced adhesive tape  84 - 1  is made of elastic material. When the developing roller  31  is mounted in position in the developing cartridge  28 , the first base member  84 - 1   a  is properly compressed, and the sliding sealing element  66  is intimately and slidingly contact with the developing roller  31 , thereby properly blocking any leakage of toner from the layer-thickness regulating blade  32 . It is possible to prevent toner leakage even more reliably. 
   &lt;First Modification&gt; 
   In the above-described embodiment, the first and second double-faced adhesive tapes  84 - 1  and  84 - 2  are provided on the rear side of the sliding sealing element  66  only at the non-overlapping portions X- 1  and X- 2 , that is, only at both of the longitudinal end portions of the sliding sealing element  66 . However, according to a first modification of the embodiment, as shown in  FIG. 7 ,  FIG. 8 , and  FIG. 9 , in addition to the first and second double-faced adhesive tapes  84 - 1  and  84 - 2 , a third double-faced adhesive tape  84 - 3  is additionally provided on the rear surface of the sliding sealing element  66 . The third double-faced adhesive tape  84 - 3  is located at an intermediate portion within the overlapping region Y, that is, at a longitudinal central portion of the sliding sealing element  66 , with predetermined spacings in the longitudinal direction from the first and second double-faced adhesive tapes  84 - 1  and  84 - 2 , respectively. 
   By attaching the lengthwise middle portion of the sliding sealing element  66  onto the sponge seal  65  and by attaching both the lengthwise ends of the sliding sealing element  66  onto the upper attachment portion  78  and the lower end attachment portion  77  of the housing  51 , it is possible to securely attach the sliding sealing element  66  to the housing  51 , thereby further improving sealing capability. It is possible to prevent the sliding sealing element  66 , from being mistakenly separated from the sponge seal  65 . 
   The third double-faced adhesive tape  84 - 3  is formed in a substantially rectangular shape, and is provided to cover the entire width of the sliding sealing element  66 . The width of the third double-faced adhesive tape  84 - 3  is the same as the width of the sliding sealing element  66 , and is unchanged along the lengthwise direction of the sliding sealing element  66 . 
   The surface area of a portion in the rear surface of of the sliding sealing element  66 , onto which the third double-faced adhesive tape  84 - 3  is attached, is less than a half of the entire surface area of the overlapping portion Y where the sliding sealing element  66  confronts the sponge seal  65 . 
   The surface area of the sliding sealing element  66 , onto which the third double-faced adhesive tape  84  is attached, is sufficiently small that during the recycling step, the third double-faced adhesive tape  84 - 3  can be peeled off the sponge seal  65  while reducing damage onto the sponge seal  65 . During the recycling step, it is possible to maintain small the possibility that the sponge seal  65  will be damaged when the third double-faced adhesive tape  84 - 3  is peeled off the sponge seal  65 . It is therefore possible to maintain small the possibility that the sponge seal  65  will have to be replaced with a new one. 
   The double-faced adhesive tape  84 - 3  may have the same configuration as the first double-faced adhesive tape  84 - 1 . That is, the double-faced adhesive tape  84 - 3  may have an elastic base member, which is made of elastic foamed material, for example, between a pair of adhesive layers. In this case, the thickness of the elastic base member in the double-faced adhesive tape  84 - 3  may have such a value that allows the total thickness of the double-faced adhesive tape  84 - 3  and the sliding sealing element  66  to be greater than or equal to the thickness of the layer-thickness regulating blade  32  when the developing roller  31  is not installed in the housing  51 . 
   Similarly to the embodiment as described above with reference to  FIGS. 6(   f ) and  6 ( g ), for the manufacturing and recycling stages, the sliding sealing element  66  may be prepared in a state in which the first, second, and third double-faced adhesive tapes  84 - 1 ,  84 - 2 , and  84 - 3  are attached on the sliding sealing element  66  at its corresponding locations. At this time, similarly to the first and second double-faced adhesive tapes  84 - 1  and  84 - 2 , the third double-faced adhesive tape  84 - 3  originally includes not only its base member and its pair of adhesive layers but also its release paper that is releasably attached to one of the adhesive layers. By releasing the release paper from the third double-faced adhesive tape  84 - 3 , the third double-faced adhesive tapes  84 - 3  can be attached to the sponge seal  65 . 
   &lt;Second Modification&gt; 
   According to a second modification of the present embodiment, as shown in  FIG. 10 ,  FIG. 11 , and  FIG. 12 , a single double-faced adhesive tape  84 - 3  is provided to extend continuously over the entire length of the sliding sealing element  66  at one widthwise edge of the sliding sealing element  66 , that is, at an inner-side widthwise edge of the sliding sealing element  66  that is more adjacent to the layer thickness regulating blade  32  than the other, outer-side widthwise edge. In this case, the double-faced adhesive tape  84 - 4  is provided continuously over all of the non-overlapping regions X- 1  and X- 2  and the overlapping region Y in its lengthwise direction. Accordingly, it is possible to prevent the sliding sealing element  66  from being easily peeled off the housing  51 . 
   The double-faced adhesive tape  84 - 4  is formed in a substantially rectangular shape, and is provided to extend over the entire length of the sliding sealing element  66 . The width of the double-faced adhesive tape  84 - 4  is unchanged along the lengthwise direction of the sliding sealing element  66 . It is possible to easily form the double-faced adhesive tape  84 - 4 . It is possible to easily attach the double-faced adhesive tape  84 - 4  onto the sliding sealing element  66 . It is possible to easily attach the sliding sealing element  66  via the double-faced adhesive tape  84 - 4  onto the housing  51 . 
   The width of the double-faced adhesive tape  84 - 4  has such a sufficiently small value that allows the surface area of a portion in the overlapping region Y of the sliding sealing element  66 , to which a part of the double-faced adhesive tape  84 - 4  is attached, to be less than a half of the entire surface area of the overlapping portion y where the sliding sealing element  66  confronts the sponge seal  65 . The double-faced adhesive tape  84 - 4  can be peeled off the sponge seal  65  while reducing damage onto the sponge seal  65 . 
   The sliding sealing element  66  is attached to the housing  51  at its inner side edge that is located adjacent to the layer-thickness regulating blade  32 . It is possible to prevent leakage of toner at the location between the inner side widthwise edge of the sliding sealing element  66  and the layer-thickness regulating blade  32 , where toner leakage occurs most likely. 
   The double-faced adhesive tape  84 - 4  has the same configuration as the first double-faced adhesive tape  84 - 1  in the embodiment. That is, the double-faced adhesive tape  84 - 4  has an elastic base member, which is made of elastic foamed material, for example, between a pair of adhesive layers. The thickness of the elastic base member in the double-faced adhesive tape  84 - 4  has such a value that allows the total thickness of the double-faced adhesive tape  84 - 4  and the sliding sealing element  66  to be greater than or equal to the thickness of the layer-thickness regulating blade  32  when the developing roller  31  is not installed in the housing  51 . 
   Similarly to the embodiment as described above with reference to  FIGS. 6(   f ) and  6 ( g ), for the manufacturing and recycling stages, the sliding sealing element  66  may be prepared in a state in which the double-faced adhesive tape  84 - 4  is attached on the sliding sealing element  66  at its one widthwise edge. At this time, similarly to the first and second double-faced adhesive tapes  84 - 1  and  84 - 2  in the embodiment, the double-faced adhesive tape  84 - 4  originally includes not only its base member and its pair of adhesive layers but also its release paper that is releasably attached to one of the adhesive layers. By releasing the release paper from the double-faced adhesive tape  84 - 4 , the double-faced adhesive tape  84 - 4  can be attached to the upper attachment portion  78  on the plate spring  59 , the sponge seal  65 , and the lower end attachment portion  77  on the housing frame  52 . 
   &lt;Third Modification&gt; 
   According to a third modification of the present embodiment, as shown in  FIG. 13 ,  FIG. 14 , and  FIG. 15 , not only the double-faced adhesive tape  84 - 4  is provided to extend continuously over the entire length of the sliding sealing element  66  at the inner-side widthwise edge of the sliding sealing element  66 , but also another double-faced adhesive tape  84 - 5  is provided to extend continuously over the entire length of the sliding sealing element  66  at the outer-side widthwise edge of the sliding sealing element  66 . By attaching the sliding sealing element  66  at its both widthwise edges to the housing  51 , the sliding sealing element  66  can attain further improved sealing capability. 
   Similarly to the double-faced adhesive tape  84 - 4 , the double-faced adhesive tape  84 - 5  is formed in a substantially rectangular shape, and is provided to extend over the entire length of the sliding sealing element  66 . Similarly to the double-faced adhesive tape  84 - 4 , the width of the double-faced adhesive tape  84 - 4  is unchanged along the lengthwise direction of the sliding sealing element  66 . It is possible to easily form the double-faced adhesive tape  84 - 5 . It is possible to easily attach the double-faced adhesive tape  84 - 5  onto the sliding sealing element  66 . It is possible to easily attach the sliding sealing element  66  via the double-faced adhesive tapes  84 - 4  and  84 - 5  onto the housing  51 . 
   The widths of the double-faced adhesive tapes  84 - 4  and  84 - 5  have such sufficiently small values that allow the total surface area of the portions in the overlapping region Y of the sliding sealing element  66 , onto which parts of the double-faced adhesive tapes  84 - 4  and  84 - 5  are attached, to be less than a half of the entire surface area of the overlapping portion Y where the sliding sealing element  66  confronts the sponge seal  65 . The double-faced adhesive tapes  84 - 4  and  84 - 5  can be separated from the sponge seal  65  while reducing damage onto the sponge seal  65 . 
   The sliding sealing element  66  is attached to the housing  51  at its inner side widthwise edge that is located adjacent to the layer-thickness regulating blade  32 . It is possible to prevent leakage of toner at the location between the inner side widthwise edge of the sliding sealing element  66  and the layer-thickness regulating blade  32 , where toner leakage occurs most likely. 
   Similarly to the double-faced adhesive tape  84 - 4 , the double-faced adhesive tape  84 - 5  has the same configuration as the first double-faced adhesive tape  84 - 1  in the embodiment. That is, the double-faced adhesive tape  84 - 5  has an elastic base member, which is made of elastic foamed material, for example, between a pair of adhesive layers. The thickness of the elastic base member in the double-faced adhesive tape  84 - 5  has such a value that allows the total thickness of the double-faced adhesive tape  84 - 5  and the sliding sealing element  66  to be greater than or equal to the thickness of the layer-thickness regulating blade  32  when the developing roller  31  is not installed in the housing  51 . 
   Similarly to the embodiment as described above with reference to  FIGS. 6(   f ) and  6 ( g ), for the manufacturing and recycling stages, the sliding sealing element  66  may be prepared in a state in which the double-faced adhesive tapes  84 - 4  and  84 - 5  are attached on the sliding sealing element  66  at its both widthwise edges. At this time, similarly to the first and second double-faced adhesive tapes  84 - 1  and  84 - 2  in the embodiment, each of the double-faced adhesive tapes  84 - 4  and  84 - 5  originally includes not only its base member and its pair of adhesive layers but also its release paper that is releasably attached to one of the adhesive layers. By releasing the release papers from the double-faced adhesive tapes  84 - 4  and  84 - 5 , the double-faced adhesive tapes  84 - 4  and  84 - 5  can be attached to the upper attachment portion  78  on the plate spring  59 , the sponge seal  65 , and the lower end attachment portion  77  on the housing frame  52 . 
   While the invention has been described in detail with reference to the specific embodiment thereof, it would be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention. 
   For example, in the above-described embodiment, the sliding sealing element  66  is formed from a fluoride-based felt. However, the sliding sealing element  66  can be formed from other materials, such as woven cloth, knit, hair implant, or non-woven material. 
   In addition, in the above-described embodiment, the upper attachment portion  78  is defined on the plate spring member  59 . However, the upper attachment portion  78  may not be defined on the plate spring member  59 , but may be defined on the housing  51  at a location above the location where the sponge seal  66  is attached. 
   For example, the upper attachment portion  78  may be defined on the housing frame  52  at a location above the sponge seal  66 . The first non-overlapping region X- 1  is defined on a portion of the rear surface of the sliding sealing element  66  that confronts the upper attachment portion  78 . Or, the upper attachment portion  78  may be defined on a portion, of any member in the housing  51  other than the housing frame  52  and the sponge seal  66 , that is located above the upper edge of the sponge seal  66 . The first non-overlapping region X- 1  is defined on a portion of the rear surface of the sliding sealing element  66  that confronts the upper attachment portion  78 . 
   In the above-described embodiment, the lower end attachment-portion  77  is defined on the housing frame  52 . However, the lower end attachment portion  77  may be defined on a portion, of any member in the housing  51  other than the housing frame  52  and the sponge seal  66 , that is located below the lower edge of the sponge seal  66 . The non-overlapping portion X- 2  is defined on the rear surface of the sliding sealing element  66  as its portion that confronts the lower end attachment portion  77 . 
   In the second modification, the double-faced adhesive tape  84 - 4  is provided at the inner side widthwise edge of the sliding sealing element  66 . However, the double-faced adhesive tape  84 - 4  may be provided at any regions on the rear surface of the sliding sealing element  66  if the double-faced adhesive tape  84 - 4  covers at least a part of the first non-overlapping region X- 1  of the sliding sealing element  66  that confronts the upper attachment portion  78  on the plate spring  59 . Also in-this case, the double-faced adhesive tape  84 - 4  has the same configuration as the first double-faced adhesive tape  84 - 1  in the embodiment, and therefore has an elastic base member, which is made of elastic foamed material, for example, between a pair of adhesive layers. The thickness of the elastic base member in the double-faced adhesive tape  84 - 4  has such a value that allows the total thickness of the double-faced adhesive tape  84 - 4  and the sliding sealing element  66  to be greater than or equal to the thickness of the layer-thickness regulating blade  32  when the developing roller  31  is not installed in the developing cartridge  28 . Accordingly, when the developing roller  31  is installed in the developing cartridge  28 , the double-faced adhesive tape  84 - 4  is compressed against the circumferential surface of the developing roller  31  and is deformed elastically. It is possible to prevent any leakage of toner between the circumferential surface of the developing roller  31  and the double-faced adhesive tape  84 - 4 .