Abstract:
In a developing device, a layer thickness regulating member, configured to regulate thickness of a layer of developer borne on a surface of a developer bearing member, includes: a first plate-shaped member having a pair of opposite ends in a perpendicular direction perpendicular to an axial direction of the developer bearing member, one end in the pair of opposite ends being in contact with the developer bearing member, the other end being supported by the casing; and a second plate-shaped member that is fixedly secured to the casing and that supports the first plate-shaped member. A seal member, which is in contact with an end portion of the developer bearing member in the axial direction of the developer bearing member, is in contact with an end portion of the first plate-shaped member in the axial direction of the developer bearing member. The second plate-shaped member holds the seal member.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority from Japanese Patent Application No. 2012-018201 filed Jan. 31, 2012. The entire content of this priority application is incorporated herein by reference. 
       TECHNICAL FIELD 
       [0002]    The present invention relates to a developing device that is for being mounted in an image forming apparatus, such as a color printer. 
       BACKGROUND 
       [0003]    There has been conventionally known an electrophotographic type printer to which a developing device is detachably attached. The developing device includes a casing, a developing roller supported by the casing and bearing toner thereon, and a layer thickness regulating member that regulates thickness of a layer of toner formed on a surface of the developing roller. 
         [0004]    There has been proposed, as such a developing device, a developing device having a configuration in which the layer thickness regulating member includes a thin plate spring having substantially a flat-plate shape, a chip which is made of a rubber member and provided at a free end portion of the thin plate spring, and a pair of seal members which are provided on a pair of longitudinal ends of the thin plate spring so as to be disposed adjacent to the chip in the longitudinal direction. 
         [0005]    In the developing device of this type, the chip constituting the layer thickness regulating member is brought into contact with the developing roller to regulate the layer thickness of toner carried on the surface of the developing roller. The seal members are each disposed between the longitudinal end portion of the thin plate spring and an axial end portion of the developing roller, and therefore prevent leakage of toner from between the longitudinal end portion of the thin plate spring and the axial end portion of the developing roller. 
         [0006]    In recent years, there is an increasing demand to reduce the number of parts constituting a developing device, in order to reduce a manufacturing cost of the developing device. So, such a layer thickness regulating member has been proposed, in which the free end portion of a thin plate spring is provided with no chip, and therefore is brought into direct contact with a developing roller to regulate the layer thickness of toner carried on the surface of the developing roller. This layer thickness regulating member will be referred to as “no-chip-mounted layer thickness regulating member”, hereinafter. 
       SUMMARY 
       [0007]    It is conceivable to provide the no-chip-mounted layer thickness regulating member with the conventional seal members described above such that the seal members are provided on the pair of longitudinal end portions of the thin plate spring. In this conceivable configuration, however, a gap may be generated, due to thickness of the seal members, between the free end portion of the thin plate spring and the developing roller. So, the layer thickness of toner carried on the surface of the developing roller cannot be regulated adequately, and further toner may leak from the gap between the free end portion of the thin plate spring and the developing roller. 
         [0008]    An object of the present invention is, therefore, to provide an improved developing device that is capable of reliably regulating the layer thickness of developer borne on the surface of a developer bearing member and that is capable of preventing leakage of developer from the casing of the developing device, while reducing the number of parts constituting the developing device. 
         [0009]    In order to attain the above and other objects, the invention provides a developing device including: a casing; a developer bearing member; a layer thickness regulating member; and a seal member. The casing is configured to accommodate developer therein. The developer bearing member is mounted in the casing so as to be rotatable about its axis and configured to bear developer thereon. The layer thickness regulating member is mounted in the casing and configured to regulate thickness of a layer of developer borne on a surface of the developer bearing member. The seal member is in contact with an end portion of the developer bearing member in an axial direction of the developer bearing member. The layer thickness regulating member includes: a first plate-shaped member having a pair of opposite ends in a perpendicular direction that is perpendicular to the axial direction of the developer bearing member, one end in the pair of opposite ends being in contact with the developer bearing member, the other end being supported by the casing; and a second plate-shaped member that is fixedly secured to the casing and that supports the first plate-shaped member. The seal member is in contact with an end portion of the first plate-shaped member in the axial direction of the developer bearing member. The second plate-shaped member holds the seal member. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The particular features and advantages of the invention as well as other objects will become apparent from the following description taken in connection with the accompanying drawings, in which: 
           [0011]      FIG. 1  is a side cross-sectional view of a printer according to a first embodiment of the present invention; 
           [0012]      FIG. 2  is a plan view of a developing cartridge according to the first embodiment; 
           [0013]      FIG. 3  is an exploded perspective view of the developing cartridge shown in  FIG. 2 ; 
           [0014]      FIG. 4  is a bottom view of a layer thickness regulating blade shown in  FIG. 2 ; 
           [0015]      FIG. 5A  is a cross-sectional view taken along a line VA-VA in  FIG. 2 ; 
           [0016]      FIG. 5B  is a cross-sectional view taken along a line VB-VB in  FIG. 2 ; 
           [0017]      FIGS. 6A and 6B  illustrate how a blade member and a side edge seal contact a developing roller, wherein  FIG. 6A  illustrates a state before the blade member and side edge seal contact the developing roller, and  FIG. 6B  illustrates a state where the blade member and side edge seal contact the developing roller; 
           [0018]      FIGS. 7A and 7B  illustrate how a blade member and a side edge seal in a developing cartridge according to a second embodiment contact a developing roller, wherein  FIG. 7A  illustrates a state before the blade member and side edge seal contact the developing roller, and  FIG. 7B  illustrates a state where the blade member and side edge seal contact the developing roller; and 
           [0019]      FIG. 8  is a side view of a holder of a layer thickness regulating blade in a developing cartridge according to a third embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    A developing device according to embodiments of the 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. 
       1. Printer 
       [0021]    As illustrated in  FIG. 1 , a printer  1  according to a first embodiment of the present invention is a color printer of a direct tandem type. 
         [0022]    The terms of directions, such as “upward”, “downward”, “upper”, “lower”, “above”, “below”, “beneath”, “right”, “left”, “front”, “rear” and the like, for the printer  1  will be used throughout the description assuming that the printer  1  is disposed in a horizontal orientation in which the printer  1  is intended to be used.  FIG. 1  shows the state that the printer  1  is disposed in the horizontal orientation. The directions for the printer  1  are therefore indicated in  FIG. 1 . 
         [0023]    The terms of directions, such as “upward”, “downward”, “upper”, “lower”, “above”, “below”, “beneath”, “right”, “left”, “front”, “rear” and the like, for a developing cartridge  23  (to be described later) will be used throughout the description assuming that the developing cartridge  23  is disposed outside the printer  1  and is disposed in a horizontal orientation in which the developing cartridge  23  is normally disposed when the developing cartridge  23  is outside the printer  1 .  FIG. 2  shows the state that the developing cartridge  23  is disposed in the horizontal orientation when the developing cartridge  23  is disposed outside the printer  1 . The directions for the developing cartridge  23  are indicated in  FIGS. 2-6B . 
         [0024]    That is, up-down and front-rear directions defined for the printer  1  and those defined for the developing cartridge  23  differ from each other. More specifically, the developing cartridge  23  is attached to the printer  1  such that front and rear sides of the developing cartridge  23  are disposed facing upper-front and lower-rear sides of the printer  1 , respectively. 
         [0025]    The printer  1  includes a main casing  2 . In the main casing  2 , a plurality of (four) photosensitive drums  3  are juxtaposed along the front-rear direction for the printer  1 . The plurality of (four) photosensitive drums  3  correspond to respective colors (black, yellow, magenta, and cyan) of a toner image (to be described later). 
         [0026]    A scorotron charger  4 , an LED unit  5 , and a developing roller  6  are disposed opposite to each photosensitive drum  3 . 
         [0027]    The photosensitive drum  3  is uniformly charged on a surface thereof by the scorotron charger  4  and thereafter exposed by the LED unit  5 . As a result, an electrostatic latent image is formed on the surface of the photosensitive drum  3  based on image data. The electrostatic latent image is developed by toner borne or carried on the developing roller  6 . So, a toner image is formed on the surface of the photosensitive drum  3 . 
         [0028]    Sheets P are accommodated in a sheet cassette  7  provided in the main casing  2 . The sheets P accommodated in the sheet cassette  7  are fed one sheet at a time to a conveying belt  8  by various rollers. 
         [0029]    The conveying belt  8  is disposed between the plurality of (four) photosensitive drums  3  and transfer rollers  9  facing the photosensitive drums  3 , respectively. The toner image on the surface of the photosensitive drum  3  is transferred by a transfer bias applied to the transfer roller  9 , onto a sheet P conveyed by the conveying belt  8 . With this operation, the toner images formed on the four photosensitive drums  3  are sequentially transferred onto the sheet P in an overlapping manner as one toner image. 
         [0030]    The sheet P onto which the toner image including four colors has been transferred is conveyed to a fixing portion  10 . The toner image thus transferred onto the sheet P is thermally fixed by the fixing portion  10 . Thereafter, the sheet P is discharged onto a discharge tray  11  by various rollers. 
       2. Process Cartridge 
       [0031]    The printer  1  includes a plurality of (four) process cartridges  21  which correspond to respective colors (black, yellow, magenta and cyan). 
         [0032]    The process cartridges  21  are detachably attached in the main casing  2  and are juxtaposed in the main casing  2  along the front-rear direction for the printer  1 . 
         [0033]    A top cover  12  is openably/closably mounted to an upper wall of the main casing  2 , and the process cartridges  21  can be attached to and detached from the main casing  2  in a state where the top cover  12  is opened. 
         [0034]    Each process cartridge  21  includes a drum cartridge  22  detachably attached to the main casing  2  and a developing cartridge  23  detachably attached to the drum cartridge  22 . 
         [0035]    (1) Drum Cartridge 
         [0036]    The drum cartridge  22  includes a drum frame  24 . The drum frame  24  includes a drum support portion  25  and a developing cartridge accommodating portion  26 . 
         [0037]    The drum support portion  25  is provided on the lower-rear side of the drum frame  24  so as to support the photosensitive drum  3 , the scorotron charger  4 , and a drum cleaning roller  15 . 
         [0038]    The photosensitive drum  3  is substantially in a cylindrical shape elongated in the left-right direction. The photosensitive drum  3  is rotatably supported at a lower end of the drum support portion  25  so as to be exposed from the lower surface of the drum support portion  25 . The scorotron charger  4  is disposed so as to be opposed to and spaced apart from the photosensitive drum  3  at the upper-rear side of the photosensitive drum  3 . The drum cleaning roller  15  is disposed so as to be opposed to and contact the photosensitive drum  3  at the rear side of the photosensitive drum  3 . 
         [0039]    The developing cartridge accommodating portion  26  is disposed at the upper-front side of the drum support portion  25  and is opened rearward and upward so as to allow the developing cartridge  23  to be detachably attached to the developing cartridge accommodating portion  26 . 
         [0040]    (2) Developing Cartridge 
         [0041]    As illustrated in  FIGS. 2 and 3 , the developing cartridge  23  includes a developing frame  30 . 
         [0042]    The developing frame  30  is substantially in a box-shape elongated in the left-right direction, and includes a lower frame  31  and an upper frame  32  fitted to the lower frame  31  (see  FIG. 5A ). 
         [0043]    (2-1) Lower Frame 
         [0044]    As illustrated in  FIG. 3 , the lower frame  31  integrally includes: a pair of side walls  35  disposed opposite to and spaced apart from each other in the left-right direction; a bottom wall  36  connecting lower end portions of the side walls  35 ; and a front wall  37  (see  FIG. 5A ) connecting front end portions of the side walls  35  and bottom wall  36 . 
         [0045]    Each of the pair of side walls  35  is substantially in a flat-plate shape. The side walls  35  include a left side wall  35  disposed on the left and a right side wall  35  disposed on the right. A first fixing portion  40  is formed on an inner side surface of each side wall  35  in the left-right direction. That is, one first fixing portion  40  (left-side first fixing portion  40 ) is formed on a right side surface of the left side wall  35 , and another first fixing portion  40  (right-side first fixing portion  40 ) is formed on a left side surface of the right side wall  35 . 
         [0046]    Each first fixing portion  40  is substantially in a flat-plate shape that extends continuously from an upper end of the corresponding side wall  35  inward in the left-right direction. That is, the left-side first fixing portion  40  is substantially in a flat-plate shape that extends continuously from an upper end of the left side wall  35  rightward, and the right-side first fixing portion  40  is substantially in a flat-plate shape that extends continuously from an upper end of the right side wall  35  leftward. A first screw hole  41  and a positioning protrusion  42  are formed in each first fixing portion  40 . 
         [0047]    The first screw hole  41  is positioned at a center portion of the first fixing portion  40  in the front-rear direction, and penetrates the plate-shaped first fixing portion  40  in the up-down direction (vertical direction). 
         [0048]    The positioning protrusion  42  is positioned on the front side of the first screw hole  41 . The positioning protrusion  42  is substantially in a columnar shape protruding upward from the first fixing portion  40 . A tip end portion of the positioning protrusion  42  is formed into substantially a circular arc shape in cross section bulging upward. 
         [0049]    As illustrated in  FIG. 5A , the bottom wall  36  is formed such that a front side of the bottom wall  36  has substantially a W-shape in side cross section and a rear side of the bottom wall  36  has substantially a semi circular shape in side cross section opened upward. 
         [0050]    The bottom wall  36  is integrally formed with a partition wall  45 , a lower sponge holding portion  50 , a plurality of (two) second fixing portions  46  (see  FIG. 3 ), and a plurality of (two) bulkheads  47  (see  FIG. 3 ). 
         [0051]    The partition wall  45  is provided in a connecting portion between the front side and rear side portions of the bottom wall  36 . The partition wall  45  is formed into substantially a triangle shape in side cross section protruding upward from the bottom wall  36 . The partition wall  45  is elongated in the left-right direction (see  FIG. 3 ). 
         [0052]    The lower sponge holding portion  50  is formed into substantially a T-shape in side cross section protruding rearward from a rear end portion of the bottom wall  36 . 
         [0053]    The two second fixing portions  46  are disposed adjacent to the front side of the partition wall  45  and spaced apart from each other in the left-right direction, as illustrated in  FIG. 3 . Each of the second fixing portions  46  is formed into substantially a cylindrical shape extending upward from the bottom wall  36 . A second screw hole  49  is formed in an upper end surface of the second fixing portion  46 . 
         [0054]    The bulkheads  47  are each formed into substantially a flat-plate shape protruding upward from an upper surface of the bottom wall  36  at a position rearward of the partition wall  45 , as illustrated in  FIG. 5A . The bulkheads  47  are disposed spaced apart inward from the both side walls  35  in the left-right direction, as illustrated in  FIG. 3 . That is, among the two bulkheads  47 , one bulkhead  47  that is disposed on the left side (left side bulkhead  47 ) is disposed to the right of the left side wall  35  and is apart from the left side wall  35 , and another bulkhead  47  that is disposed on the right side (right side bulkhead  47 ) is disposed to the left of the right side wall  35  and is apart from the right side wall  35 . 
         [0055]    A part of the lower frame  31  between each bulkhead  47  and a corresponding side wall  35  is defined as a side seal accommodating portion  48 . That is, one side seal accommodating portion  48  (left side seal accommodating portion  48 ) is defined between the left side wall  35  and the left side bulkhead  47 , and another side seal accommodating portion  48  (right side seal accommodating portion  48 ) is defined between the right side wall  35  and the right side bulkhead  47 . As illustrated in  FIG. 5B , the side seal accommodating portion  48  is formed into substantially C-shape in side cross section opened in the upper-rear direction. 
         [0056]    As illustrated in  FIG. 5A , the front wall  37  is formed continuously from the front end portion of the bottom wall  36  so as to extend upward. 
         [0057]    An abutted portion  51  is formed at an upper end portion of the front wall  37 . The abutted portion  51  is formed into substantially a flat-plate shape extending frontward continuously from the upper end of the front wall  37 . 
         [0058]    (2-2) Upper Frame 
         [0059]    The upper frame  32  integrally includes a front-side upper wall  54  and a rear-side upper wall  55 . 
         [0060]    The front-side upper wall  54  includes a bulging portion  56  and an abutting portion  57 . 
         [0061]    As illustrated in  FIG. 3 , the bulging portion  56  is formed at a center portion of the front-side upper wall  54  so as to bulge upward. 
         [0062]    The abutting portion  57  has substantially a flat-plate shape and is formed on left, right, and front sides of the bulging portion  56  so as to surround the bulging portion  56 . The abutting portion  57  is formed so as to confront the abutted portion  51  and the front-side upper surfaces of the side walls  35  when the upper frame  32  and lower frame  31  are fitted to each other. 
         [0063]    The rear-side upper wall  55  is formed into substantially a flat-plate shape extending rearward continuously from a rear end portion of the front-side upper wall  54 . The rear-side upper wall  55  has a plurality of (two) upper frame through-holes  58 . The upper frame through-holes  58  are formed in a front portion of the rear-side upper wall  55 . The rear-side upper wall  55  further has a side upper seal accommodating portion  60  formed in a portion rearward of the upper frame through-holes  58 . 
         [0064]    The plurality of (two) upper frame through-holes  58 , each of which has substantially a circular shape as viewed from above, are formed in correspondence with the plurality of (two) second fixing portions  46 . A hole diameter of the upper frame through-hole  58  is larger than an outer diameter of the second fixing portion  46 . 
         [0065]    As illustrated in  FIG. 5A , the side upper seal accommodating portion  60  is formed by cutting an upper-rear edge of the rear-side upper wall  55  into substantially an L-shape in side cross section. The side upper seal accommodating portion  60  is elongated over the entire length of the rear side portion of the rear-side upper wall  55  in the left-right direction. 
         [0066]    As illustrated in  FIG. 5A , a side upper seal  59  is accommodated in the side upper seal accommodating portion  60 . 
         [0067]    The side upper seal  59  is formed of elastic foam such as an urethane sponge member and has substantially a U-shape, as viewed from above, opened rearward, as illustrated in  FIG. 3 . 
         [0068]    The side upper seal  59  includes an upper portion  61  and side portions  62 . 
         [0069]    The upper portion  61  is formed into substantially a rectangular shape, as viewed from above, elongated in the left-right direction and has lengths in the front-rear and left-right directions substantially equal to those of the side upper seal accommodating portion  60 . 
         [0070]    The side portions  62 , each of which is formed into substantially a rectangular shape as viewed from above, protrude rearward from a pair of left and right end portions of the upper portion  61 . 
         [0071]    Seal cut portions  63  each cut into substantially a rectangular shape as viewed from above are formed in connecting portions between the upper portion  61  and side portions  62 , respectively. 
         [0072]    The seal cut portion  63  is formed so as to expose the first screw hole  41  and the positioning protrusion  42  of the first fixing portion  40  from above when the upper frame  32  and the lower frame  31  are fitted to each other. 
         [0073]    A lower surface of the upper portion  61  is adhesively bonded to an upper surface of the side upper seal accommodating portion  60  to thereby fix the side upper seal  59  to the side upper seal accommodating portion  60 . 
         [0074]    (2-3) Developing Frame 
         [0075]    As illustrated in  FIG. 5A , the developing frame  30  is formed by fitting the upper frame  32  and the lower frame  31  to each other such that the abutting portion  57  of the upper frame  32  abuts against the abutted portion  51  and the front-side upper surfaces of the side walls  35  in the lower frame  31 . 
         [0076]    As illustrated in  FIG. 3 , in the developing frame  30 , the plurality of (two) second fixing portions  46  of the lower frame  31  are inserted through the corresponding upper frame through-holes  58 , respectively, and the second screw holes  49  are exposed through the upper frame through-holes  58  from the upper surface of the rear-side upper wall  55 . 
         [0077]    As illustrated in  FIG. 5A , in the developing frame  30 , a space on the front side relative to the partition wall  45  is defined as a toner chamber  38 , and a space on the rear side relative to the partition wall  45  is defined as a developing chamber  39 . 
         [0078]    Toner of one of the four colors (black, yellow, magenta and cyan) is accommodated in the toner chamber  38 . 
         [0079]    The developing chamber  39  has an opening portion  69  opened rearward. More specifically, the opening portion  69  is defined by rear end portions of the both side walls  35 , a rear end portion of the lower sponge holding portion  50 , and a rear end portion of the rear-side upper wall  55 . 
         [0080]    The developing chamber  39  includes the developing roller  6 , a lower sponge  70 , a pair of (two) side seals  71  (see  FIG. 3 ), a layer thickness regulating blade  76 , and a pair of (two) side edge seals  78 . 
         [0081]    The developing roller  6  is disposed at a rear end portion of the developing chamber  39  such that a rear side and an upper side of the developing roller  6  are exposed through the opening portion  69 . 
         [0082]    As illustrated in  FIG. 3 , the developing roller  6  includes a developing roller shaft  67  and a rubber roller  68 . 
         [0083]    The developing roller shaft  67  is formed into substantially a columnar shape elongated in the left-right direction. 
         [0084]    The rubber roller  68  is formed so as to cover the developing roller shaft  67 , exposing both left and right end portions of the developing roller shaft  67 . 
         [0085]    The both left and right end portions of the developing roller shaft  67  are rotatably supported by the both side walls  35 , respectively, and thereby the developing roller  6  is rotatably mounted to the developing frame  30 . 
         [0086]    At developing time, the developing roller  6  receives drive force from a drive source (not illustrated) such as a motor provided in the main casing  2 . Further, the developing roller  6  is applied, at the developing time, with a developing bias from a power supply (not illustrated). Upon reception of the drive force from the drive source (not illustrated), the developing roller  6  rotates in a rotation direction X denoted by an arrow (clockwise direction as viewed from the right side) about its axis Z, as illustrated in  FIG. 5A . As a result, toner supplied from the toner chamber  38  is borne or carried on a surface of the rubber roller  68 . 
         [0087]    As illustrated in  FIG. 3 , the lower sponge  70  is formed into substantially a rectangular shape as viewed from side, and is elongated in the left-right direction (see  FIG. 5A ). As illustrated in  FIG. 5A , the lower sponge  70  is held on an upper surface of the lower sponge holding portion  50  so as to be opposed to and contact a lower portion of the developing roller  6 . 
         [0088]    As illustrated in  FIG. 5B , the side seals  71  are each formed into substantially a C-shape, as viewed from side, opened rearward. 
         [0089]    The side seal  71  includes a first base material  72  and a first raised fabric member  73 . 
         [0090]    The first base material  72  is formed of elastic foam such as an urethane sponge member and has substantially a C-shape, as viewed from side, opened rearward. 
         [0091]    The first raised fabric member  73  is formed of fabric such as a fiber material of cashmere and has substantially a C-shape, as viewed from side, opened rearward. 
         [0092]    The first raised fabric member  73  is adhesively bonded to a rear surface of the first base material  72  such that an upper end portion of the first raised fabric member  73  and an upper end portion of the first base material  72  are flush with each other. 
         [0093]    The side seals  71  described above are accommodated in the side seal accommodating portions  48 , respectively, so as to be brought into contact with a peripheral surface at both end portions of the rubber roller  68  in the left-right direction (see  FIG. 3 ). 
         [0094]    (2-4) Layer Thickness Regulating Blade 
         [0095]    As illustrated in  FIG. 5A , the layer thickness regulating blade  76  is provided for regulating the layer thickness of toner carried on the surface of the rubber roller  68  and is supported on an upper surface of the rear-side upper wall  55 . Further, as illustrated in  FIGS. 3 and 4 , the layer thickness regulating blade  76  includes a holder  79  and a blade member  77 . 
         [0096]    (2-4-1) Holder 
         [0097]    As illustrated in  FIG. 5A , the holder  79  is formed by bending a metal plate through a bending work and has substantially a crank-like shape as viewed from side. The holder  79  includes a seal holder  90  and a blade holder  91 . 
         [0098]    The blade holder  91  constitutes a front side portion of the holder  79  and is formed into substantially a rectangular flat-plate shape, as viewed from above, elongated in the left-right direction as illustrated in  FIG. 3 . As illustrated in  FIG. 4 , a lower surface of the blade holder  91  is formed as a blade holding surface  94 . 
         [0099]    As illustrated in  FIG. 3 , the blade holder  91  has first holder through-holes  95 , positioning through-holes  97 , and second holder through-holes  96  formed therein. The first holder through-holes  95 , positioning through-holes  97 , and second holder through-holes  96  penetrate the blade holder  91  in the up-down direction (vertical direction). 
         [0100]    The first holder through-holes  95 , each of which has substantially a circular shape as viewed from above, are positioned at both left and right end portions of the blade holder  91  in correspondence with the plurality of (two) first screw holes  41 , respectively. 
         [0101]    The positioning through-holes  97 , each of which has substantially a circular shape as viewed from above, are positioned on the front side of the first holder through-holes  95  and in correspondence with the plurality of (two) positioning protrusions  42 . That is, the first holder through-hole  95  and the positioning through-hole  97  are disposed in series in the front-rear direction at each of the both left and right end portions of the holder  79 . 
         [0102]    The second holder through-holes  96 , each of which has substantially a circular shape as viewed from above, are positioned at a center portion of the blade holder  91  in the left-right direction. The second holder through-holes  96  are spaced apart from each other in the left-right direction in correspondence with the plurality of (two) second screw holes  49 . 
         [0103]    The seal holder  90  is formed into substantially a flat-plate shape, as viewed from above, elongated in the left-right direction. As illustrated in  FIG. 4 , a lower surface of the seal holder  90  is formed as a seal holding surface  93 . 
         [0104]    As illustrated in  FIG. 5A , a rear end portion of an upper surface of the blade holder  91  and a front end portion of a lower surface (seal holding surface  93 ) of the seal holder  90  are connected to each other. 
         [0105]    As a result, a rear surface of the blade holder  91  and lower surface (seal holding surface  93 ) of the seal holder  90  constitute a step portion  92  at the rear end portion of the blade holder  91  and front end portion of the seal holder  90 . 
         [0106]    (2-4-2) Blade Member 
         [0107]    As illustrated in  FIGS. 3 ,  4 , and  5 A, the blade member  77  is formed of a thin metal plate having elasticity and has substantially a flat-plate shape elongated in the left-right direction. A front side portion of the blade member  77  is formed as a held portion  80  to be held by the blade holding surface  94 , and a rear side portion of the blade member  77  is formed as an elastic portion  82 . 
         [0108]    As illustrated in  FIG. 3 , the held portion  80  is formed into substantially a rectangular flat-plate shape, as viewed from above, elongated in the left-right direction. 
         [0109]    The elastic portion  82  is formed into substantially a rectangular flat-plate shape, as viewed from above, elongated in the left-right direction and is connected to the held portion  80  so as to be inclined upward toward the rear from a rear end portion of the held portion  80 , as illustrated in  FIG. 5A . 
         [0110]    A rear end portion of the elastic portion  82  is bent by bending work so as to curve upward. More specifically, the rear end portion of the elastic portion  82  is formed into a contact portion  84  that has substantially a circular arc shape as viewed from side. 
         [0111]    Further, as illustrated in  FIG. 3 , the blade member  77  has blade through-holes  81  and blade cut portions  85  formed therein. 
         [0112]    The blade through-holes  81 , each of which has substantially a circular shape as viewed from above, are positioned at both left and right end portions of the held portion  80  in correspondence with the plurality of (two) first screw holes  41 . The blade through-holes  81  penetrate the blade member  77  in the up-down direction (vertical direction). 
         [0113]    The blade cut portions  85  are formed at both left and right end portions of the blade member  77 . The blade cut portions  85  are formed by cutting both left and right end portions of the elastic portion  82  and portions of the held portion  80  on the rear sides of the blade through-holes  81  each in substantially a rectangular shape as viewed from above (see  FIG. 4 ). 
         [0114]    As illustrated in  FIG. 4 , the held portion  80  is adhesively bonded to the blade holding surface  94  such that the blade through-holes  81  and the first holder through-holes  95  (see  FIG. 3 ) communicate with each other in the up-down direction (vertical direction) and, thereby, the blade member  77  is held by the blade holder  91 . 
         [0115]    As a result, as illustrated in  FIG. 5A , in the layer thickness regulating blade  76 , the seal holder  90 , the blade holder  91 , and the blade member  77  are arranged such that the seal holding surface  93  is located on an opposite side of the blade member  77  with respect to the blade holding surface  94 . In other words, the blade member  77  is attached onto the blade holding surface  94  that confronts downwardly in the up-down direction (vertical direction), and the seal holding surface  93  is located at a higher level than the blade holding surface  94  in the up-down direction (vertical direction). 
         [0116]    (2-5) Side Edge Seal 
         [0117]    As illustrated in  FIGS. 3 and 4 , the side edge seals  78  are attached to the seal holding surface  93  of the seal holder  90  at a pair of left and right side positions that are adjacent to the left and right edges of the seal holder  90  in the left-right direction so that the elastic portion  82  of the blade member  77  is sandwiched between the side edge seals  78  in the left-right direction. Among the side edge seals  78 , one side edge seal  78  that is positioned near the right edge of the seal holder  90  will be referred to as “right side edge seal  78 ”, while the other side edge seal  78  that is positioned near the left edge of the seal holder  90  will be referred to as “left side edge seal  78 ” hereinafter. 
         [0118]    Each of the side edge seals  78  is formed into substantially a rectangular shape as viewed from above and includes a second base member  87  and a second raised fabric member  88 . 
         [0119]    The second base member  87  is formed of elastic foam such as an urethane sponge member and has substantially a rectangular shape as viewed from above. 
         [0120]    The second raised fabric member  88  is formed of fabric such as a fiber material of Teflon (registered trade mark) and has lengths in the front-rear and left-right directions substantially equal to those of the second base member  87 . The second raised fabric member  88  is adhesively bonded to a lower surface of the second base member  87 . 
         [0121]    As illustrated in  FIG. 6A , upper surfaces of the second base members  87  of the side edge seals  78  are adhesively bonded to the seal holding surface  93  and, thereby, the side edge seals  78  are held by the seal holder  90  such that both left and right end faces (left and right end surfaces) of the elastic portion  82  of the blade member  77  abut against left-right directional inner-side edge faces (left-right directional inner-side end surfaces) of the respective second raised fabric members  88 . More specifically, the right side edge face of the elastic portion  82  of the blade member  77  abuts against the left side edge face of the second raised fabric member  88  in the right side edge seal  78  (see  FIG. 6A ), and the left side edge face of the elastic portion  82  of the blade member  77  abuts against the right side edge face of the second raised fabric member  88  in the left side edge seal  78 . Further, a lower end portion of the second raised fabric member  88  protrudes further downward from the elastic portion  82  of the blade member  77 . 
         [0122]    (2-6) Assembly of Developing Frame and Layer Thickness Regulating Blade 
         [0123]    The layer thickness regulating blade  76  is assembled to the developing frame  30 , to which the side seals  71  and developing roller  6  have already been mounted in the manner described above. 
         [0124]    In order to assemble the layer thickness regulating blade  76  to the developing frame  30 , first, as illustrated in  FIG. 3 , the layer thickness regulating blade  76  is mounted, from above, on the rear-side upper wall  55  of the developing frame  30 . At this time, the positioning protrusions  42  of the first fixing portions  40  are inserted through the positioning through-holes  97  of the blade holder  91 . At the same time, the first screw holes  41  of the first fixing portions  40  are exposed through the blade through-holes  81  and the first holder through-holes  95 , and the second screw holes  49  of the second fixing portions  46  are exposed through the second holder through-holes  96 . 
         [0125]    Then, two screw members  99  are screwed into the first screw holes  41  through the first holder through-holes  95  and the blade through-holes  81 . Further, two screw members  99  are screwed into the second screw holes  49  through the second holder through-holes  96 . 
         [0126]    Thus, as illustrated in  FIG. 2 , the holder  79  is fixed to the developing frame  30 , whereby the assembly of the layer thickness regulating blade  76  to the developing frame  30  is completed. 
         [0127]    At this time, as illustrated in  FIG. 6B , the side edge seals  78  and the contact portion  84  of the layer thickness regulating blade  76  are brought into contact from above with the rubber roller  68  of the developing roller  6 . 
         [0128]    More specifically, the second raised fabric members  88  of the side edge seals  78  are brought into contact with the both left and right end portions of the peripheral surface of the rubber roller  68 , and a lower surface of the contact portion  84  is brought into contact with the left-right directional center portion of the peripheral surface of the rubber roller  68 . That is, lower surfaces of the second raised fabric members  88  and the lower surface of the contact portion  84  are flush with each other in the up-down direction. 
         [0129]    Before the layer thickness regulating blade  76  is assembled to the developing frame  30 , the lower end portions of the second raised fabric members  88  protrude further downward from the elastic member  82  of the blade member  77 . So, when the lower surfaces of the second raised fabric members  88  and the lower surface of the contact portion  84  are flush with each other in the up-down direction, the second base members  87  are elastically deformed by the protruding amount. 
         [0130]    Thus, the second raised fabric members  88  are brought into pressingly contact with the left and right end portions of the peripheral surface of the rubber roller  68  due to the elastic force of the second base members  87 . That is, the second raised fabric members  88  are pressed against the peripheral surface of the rubber roller  68 . 
         [0131]    As illustrated in  FIG. 5A , the upper portion  61  of the side upper seal  59  is disposed so as to be sandwiched between a lower surface of a front side portion of the blade member  77  and the upper surface of the side upper seal accommodating portion  60 . 
         [0132]    Further, as illustrated in  FIG. 5B , the side seals  71  are disposed so as to be sandwiched between the left and right side ends (see  FIG. 3 ) of the peripheral surface of the rubber roller  68  and the rear surfaces of the side seal accommodating portions  48 . An upper end portion of each side seal  71  is brought into contact with the lower surface of the front side portion of the second raised fabric member  88 . In the upper end portion of the side seal  71 , a downstream end portion in the rotation direction X is disposed so as to be sandwiched between the second raised fabric member  88  and the rubber roller  68 . 
         [0133]    Further, as illustrated in  FIG. 5A , the blade member  77  is disposed such that, at a contact portion between the rubber roller  68  and the contact portion  84 , the rotation direction X of the developing roller  6  and a direction Y (from front to rear direction) directed from a front end portion of the blade member  77  toward a rear end portion of the blade member  77  coincide with each other. 
       3. Functions and Effects 
       [0134]    (1) In the developing cartridge  23 , the side edge seals  78  and blade member  77  are held by the holder  79  in a state that the side edge seals  78  are brought into contact with the left and right end portions of the blade member  77 . 
         [0135]    This prevents generation of a gap, which may occur due to the thickness of the side edge seals  78 , between the contact portion  84  and the rubber roller  68 . 
         [0136]    As a result, the layer thickness of the toner carried on the surface of the developing roller  6  can be reliably regulated, and also, the toner can be prevented from leaking from the gap between the blade member  77  and the rubber roller  68 . 
         [0137]    Thus, according to the developing cartridge  23  of the present embodiment, the layer thickness of the toner carried on the surface of the rubber roller  68  can be regulated reliably while the number of parts constituting the layer thickness regulating blade  76  can be reduced, and leakage of toner from the developing frame  30  can be prevented. 
         [0138]    (2) The seal holding surface  93  is located on the opposite side of the blade member  77 , which is held by the blade holding surface  94 , with respect to the blade holding surface  94 . Thus, even with a simple configuration, a space for holding the side edge seals  78  can be ensured. 
         [0139]    This reliably prevents generation of a gap, which may occur due to the thickness of the side edge seals  78 , at a boundary between the contact portion  84  and the rubber roller  68 . 
         [0140]    (3) Further, the seal holder  90  and blade holder  91  constitute the step portion  92 , allowing the seal holding surface  93  to be located on the opposite side of the blade member  77  with respect to the blade holding surface  94  with a simple and reliable manner. 
         [0141]    (4) Further, the seal holder  90  and blade holder  91  are integrally formed by bending a metal plate, so that as compared to a case where the seal holder  90  and blade holder  91  are formed from separate members, the number of parts can be reduced. 
         [0142]    (5) Further, as illustrated in  FIG. 6A , the left and right edge faces of the blade member  77  abut against the left-right directional inner-side end surfaces of the second raised fabric members  88  of the side edge seals  78 . Accordingly, when the contact portion  84  is brought into contact with the rubber roller  68  as illustrated in  FIG. 6B , the second raised fabric members  88  of the side edge seals  78  can be reliably brought into contact with the left and right end portions of the rubber roller  68 . 
         [0143]    Thus, leakage of toner from between the second raised fabric members  88  and rubber roller  68  can be reliably prevented. 
         [0144]    Particularly, the second base members  87  are elastically deformed, and the second raised fabric members  88  are brought into pressingly contact with the both left and right end portions of the peripheral surface of the rubber roller  68  due to the elastic force of the second base member  87 , thereby allowing the second raised fabric members  88  and left and right end portions of the rubber roller  68  to be stably brought into contact with each other. 
         [0145]    (6) Further, as illustrated in  FIG. 5A , the blade member  77  is disposed such that, at the contact portion between the rubber roller  68  and contact portion  84 , the rotation direction X of the developing roller  6  and direction Y directed from the front end portion of the blade member  77  toward the rear end portion of the blade member  77  coincide with each other, thereby allowing reduction in size of the developing cartridge  23 . 
         [0146]    Because the blade member  77  is thus disposed in the developing cartridge  23 , toner peeled off by the blade member  77  is accumulated at a portion on the upstream side of the contact part between the rubber roller  68  and contact portion  84  in the rotation direction X of the developing roller  6 . However, in the developing cartridge  23  of the present embodiment, generation of a gap between the blade member  77  and developing roller  6  is prevented. So, toner is prevented from leaking from between the blade member  77  and developing roller  6 . Leakage of toner from the developing frame  30  can be prevented, while the size of the developing cartridge  23  is reduced. 
       4. Second Embodiment 
       [0147]    A second embodiment of the developing device according to the present invention will be described with reference to  FIGS. 7A and 7B . In the second embodiment, the same reference numerals are given to the same components as in the first embodiment and a description thereof will be omitted. 
         [0148]    In the above-described first embodiment, as illustrated in  FIG. 6A , the left-right directional edge faces of the elastic portion  82  abut against the left-right directional inner-side end surfaces of the side edge seals  78 . 
         [0149]    On the other hand, in the second embodiment, as illustrated in  FIG. 7A , left-right directional inner side portions of the side edge seals  78  are disposed so as to be sandwiched between the seal holding surface  93  of the holder  79  and the left-right directional end portions of the upper surface of the elastic portion  82  of the blade member  77  in the up-down direction (vertical direction). That is, the left side portion of the right side edge seal  78  is sandwiched between the seal holding surface  93  and the right side end portion of the elastic portion  82  (see  FIG. 7A ) in the up-down direction (vertical direction), and the right side portion of the left side edge seal  78  is sandwiched between the seal holding surface  93  and the left side end portion of the elastic portion  82  in the up-down direction (vertical direction). 
         [0150]    Also in the second embodiment having the above-described configuration, the same functions and effects as those of the first embodiment can be obtained. 
         [0151]    Further, because the left-right directional inner side portions of the side edge seals  78  are sandwiched between the seal holding surface  93  and the left and right end portions of the elastic portion  82  of the blade member  77 , the left-right directional inner side portions of the second base members  87  are elastically deformed to cause the left-right directional outer side portions of the second raised fabric members  88  to protrude (bulge) further downward from the elastic portion  82  before the layer thickness regulating blade  76  is assembled to the developing frame  30  as shown in  FIG. 7A . 
         [0152]    When the layer thickness regulating blade  76  is assembled to the developing frame  30 , as illustrated in  FIG. 7B , the side edge seals  78  and contact portion  84  of the layer thickness regulating blade  76  are brought into contact from above with the rubber roller  68  of the developing roller  6 . 
         [0153]    More specifically, the lower surfaces of the left-right directional outer side portions of the second raised fabric members  88  of the side edge seals  78  are brought into contact with the both left-right directional end portions of the peripheral surface of the rubber roller  68 , and the lower surface of the contact portion  84  is brought into contact with the left-right directional center portion of the peripheral surface of the rubber roller  68 . That is, the lower surfaces of the left-right directional outer side portions of the second raised fabric members  88  and the lower surface of the contact portion  84  are flush with each other in the up-down direction. 
         [0154]    Before the layer thickness regulating blade  76  is assembled to the developing frame  30 , the lower end portions of the left-right directional outer side portions of the second raised fabric members  88  protrude further downward from the elastic portion  82  of the blade member  77 . So, when the lower surfaces of the left-right directional outer side portions of the second raised fabric members  88  and the lower surface of the contact portion  84  are flush with each other in the up-down direction, the left-right directional outer side portions of the second base members  87  are elastically deformed by the protruding amount. 
         [0155]    Thus, the left-right directional outer side portions of the second raised fabric members  88  are brought into pressingly contact with the left-right directional end portions of the peripheral surface of the rubber roller  68  due to the elastic force of the second base members  87 . 
         [0156]    As a result, leakage of toner from between the second raised fabric members  88  and the left-right directional end portions (left and right end portions) of the rubber roller  68  can be reliably prevented. 
       5. Third Embodiment 
       [0157]    A third embodiment of the developing device of the present invention will be described with reference to  FIG. 8 . 
         [0158]    In the first embodiment, as illustrated in  FIG. 5A , the holder  79  is formed by bending a metal plate and integrally includes the seal holder  90  and the blade holder  91 . 
         [0159]    On the other hand, in the third embodiment, as illustrated in  FIG. 8 , a holder  101  is employed in place of the holder  79 . The holder  101  includes, as separate members, a seal holder  102  and a blade holder  103 . 
         [0160]    The seal holder  102  is formed of metal material, for example, and has substantially a flat-plate shape extending in the front-rear direction. A lower surface of the seal holder  102  is formed as a seal holding surface  105 . 
         [0161]    The blade holder  103  is formed of plastic (resin) material, for example, and has substantially a flat-plate shape extending in the front-rear direction. A front-rear directional length of the blade holder  103  is shorter than that of the seal holder  102 . A lower surface of the blade holder  103  is formed as a blade holding surface  106 . 
         [0162]    The blade holder  103  is fixed to the seal holding surface  105  of the seal holder  102  by being adhesively bonded to the seal holding surface  105  such that a front end portion of the blade holder  103  and a front end portion of the seal holder  102  are flush with each other in the up-down direction (vertical direction). 
         [0163]    As a result, a rear side portion of the seal holding surface  105  is exposed from the blade holder  103 . Further, the seal holding surface  105  exposed from the blade holder  103  and a rear surface of the blade holder  103  constitute a step portion  104  at a rear end portion of the blade holder  103  and a front end portion of the exposed part in the seal holder  102 . 
         [0164]    Also in the third embodiment having the above-described configuration, the same functions and effects as those of the first embodiment can be obtained. 
         [0165]    Simply by fixing the blade holder  103  to the seal holding surface  105 , the step portion  104  is formed by the thickness of the blade holder  103 . So, in order to form the step portion  104 , it is unnecessary to perform any additional processing for forming the step portion  104 . This enhances production efficiency of the holder  101 . 
         [0166]    Further, the seal holder  102  is formed of metal material, for example, and the blade holder  103  is formed of plastic (resin) material, for example. So, material cost can be reduced while stiffness of the holder  101  is maintained. 
         [0167]    Although the seal holder  102  is formed of metal material and the blade holder  103  is formed of plastic (resin) material in the third embodiment, the present invention is not limited to this configuration. For example, the seal holder  102  may be formed of plastic (resin) material, and the blade holder  103  may be formed of metal material. 
         [0168]    The above-described configurations in the first through third embodiments can be combined in various ways. 
         [0169]    While the invention has been described in detail with reference to the embodiments 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.