Patent Publication Number: US-6708010-B2

Title: Developing apparatus having magnetic seal

Description:
FIELD OF THE INVENTION AND RELATED ART 
     The present invention relates to a developing apparatus for developing an electrostatic image, usable with an image forming apparatus such as a copying machine, a printer or the like of an electrophotographic type or an electrostatic recording type. 
     In developing means (developing apparatus) provided in the copying machine or printer, there is provided a sealing member for preventing leakage of the toner to outside of a developing zone at each end of a developer carrying member such as a rotatable developing roller of the developing apparatus. The sealing member for preventing the owner leakage is generally of felt, foam rubber or another elastic member. 
     The developing roller includes a magnet roller therein and is rotatably supported on a developing device frame through sleeve bearings. Therefore, the toner supplied from the developer container is deposited on the surface of the developing roller by the magnetic force of the magnet roller, and the thickness of a layer of the developer is regulated by a developing blade and is then fed to the developing zone where the developing roller is opposed to a latent image on the photosensitive drum by the rotation of the developing roller. 
     In addition, at a rear portion opposite from an opening side of the developing roller mounted to the developing device frame at each of the longitudinal ends of the developing roller outside the developing zone, an elastic sealing member is provided. The elastic sealing member is press-contacted to an outer surface of the developing roller to prevent leakage of the toner. 
     However, in the developing apparatus having such a structure, the elastic sealing member is press-contacted to one half of the outer surface of the developing roller, and therefore, the load of the developing roller against rotation thereof during the developing operation is large. By the contact to the developing roller, the elastic sealing member is deteriorated with results of insufficient sealing performance. Moreover, the toner, even if the amount thereof is small, enters between the developing roller and the elastic sealing member in some cases, with the result of increased torque or a large variation of the torque (non-uniform rotation). If this occurs, the image information is influenced. 
     In order to provide a solution to such problems, a proposal has been made to provide a magnetic sealing member (magnetic seal) with a predetermined gap at each end of the developing roller to prevent leakage of the toner. 
     The magnetic seal is made of a magnet, and is spaced from the outer surface of the developing roller with a predetermined gap (0.1-0.7 mm approx.) and wound around the developing roller. The magnetic sealing member is magnetized at the surface opposed to the developing roller to form a magnetic brush by the erected chains of toner particles along the magnetic lines of force. The magnetic brush fill the gap between the outer surface of the developing roller and the surface of the magnetic sealing member to prevent the toner from leaking out of the developing zone. 
     Since such a sealing method using the magnetic seal is based on the magnetic force the retain the toner in the gap between the magnetic sealing member and the surface of the developing roller, it is required to increase the magnetic flux density in the gap in order to enhance the sealing property. Particularly in the case that developing apparatus is of a cartridge type detachably mountable to the image forming apparatus, the toner leakage tends to occur due to vibration or shock upon the mounting and demounting operation thereof. Therefore, the magnetic force provided by the magnet for the magnetic seal has to be increased in such a case. 
     However, in the structure using the magnetic seal, a part of the toner in the gap between the magnetic seal and the surface of the developing roller comes out through the gap depositing on the surface of the developing roller by the rotation of the developing roller. By this, a toner layer is formed on the surface of the developing roller opposed to the photosensitive drum. 
     The toner is collected into an inlet portion of the gap by the further rotation of the developing roller, but if the magnetic flux density provided by the magnetic seal is high, the toner tends to stagnate at the inlet portion. With repetition of the developing operation, the amount of the stagnated toner gradually might increase even to such an extent that toner leaks to the outside of the developing apparatus. 
     In order to solve such a problem, U.S. Pat. Nos. 5,790,923 and 6,266,500 which have been assigned to the assignee of this application, proposes provision of a scraper for scraping the toner at the outlet of the gap between the magnetic seal and the surface of the developing roller to prevent the toner coming out through the gap between the magnetic seal and the surface of the developing roller from moving to the surface opposed to the photosensitive member. 
     However, in the case of apparatus in which the toner capacity is large in order to meet a large amount of prints, the amount of the toner scraped by the scraper with the result of gradually leaking out. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is a principal object of the present invention to provide a developing apparatus capable of suppressing leakage of the developer. 
     It is another object of the present invention to provide a developing apparatus in which the developer stagnated in a space at the outlet of the magnetic sealing portions is effectively prevented from leaking out of the space. 
     According to an aspect of the present invention, there is provided a developing apparatus comprising a container, having an opening, for containing magnetic developer; a developer carrying member, rotatably disposed in the opening, for carrying the magnetic developer; a magnetic sealing member disposed spaced from a peripheral surface of said developer carrying member; and a removing member, disposed contacted to said developer carrying member, for removing the developer from the surface of said developer carrying member, said removing member being disposed adjacent an end, in a peripheral direction of said developer carrying member, of said magnetic sealing member; and a second sealing member for limiting movement of the developer from a space between said magnetic sealing member and said removing member toward a longitudinal end of said developer carrying member. 
     According to another aspect of the present invention, there is provided a developing apparatus comprising a container, having an opening, for containing magnetic developer; a developer carrying member, rotatably disposed in the opening, for carrying the magnetic developer; a magnetic sealing member disposed spaced from a peripheral surface of said developer carrying member; and a removing member, disposed contacted to said developer carrying member, for removing the developer from the surface of said developer carrying member, said removing member being disposed adjacent an end, in a peripheral direction of said developer carrying member, of said magnetic sealing member, wherein a surface facing the removing member and without facing to the peripheral surface of said developer carrying member of said magnetic sealing member includes two or more magnetic poles. 
     These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a main sectional view of a process cartridge according to an embodiment of the present invention. 
     FIG. 2 is a main schematic sectional view of the main assembly of the apparatus according to an embodiment of the present invention. 
     FIG. 3 is a perspective view of a process cartridge according to an embodiment of the present invention. 
     FIG. 4 is a perspective view of a process cartridge according to an embodiment of the present invention. 
     FIG. 5 is an exploded perspective view of a process cartridge frame according to an embodiment of the present invention. 
     FIG. 6 is a front view of a developing apparatus. 
     FIG. 7 is a sectional view taken along a line A—A in FIG.  6 . 
     FIG. 8 is a sectional view taken along a line A—A in FIG.  6 . 
     FIG. 9 is a sectional view taken along a line A—A in FIG.  6 . 
     FIG. 10 is a perspective view of a developing apparatus in which parts are assembled. 
     FIG. 11 is a perspective view of the magnetic sealing member per se. 
     FIG. 12 is a perspective view of the development bearing frame and the developing device frame before they are assembled with each other. 
     FIG. 13 is a perspective view of a development bearing frame of another example. 
     FIG. 14 is a perspective view of the developing roller and magnetic seal. 
     FIG. 15 is a sectional view taken along a line E—E in FIG. 14 (a), and an enlarged view of A part (b). 
     FIG. 16 is a perspective view of a toner scraping member per se. 
     FIG. 17 is a perspective view as seen from a back side of FIG.  16 . 
     FIG. 18 is a sectional view illustrating stagnation of the toner in a toner retention portion in the case of long term use. 
     FIG. 19 is an illustration of a Loner leakage prevention in another example and is a front view of the developing apparatus as seen in the direction perpendicular to the longitudinal direction of the developing roller with the developing roller and developing blade omitted. 
     FIG. 20 is an illustration of toner leakage prevention of another example, and is a sectional view of a developing roller taken along a direction perpendicular to longitudinal direction. 
     FIG. 21 is a sectional view illustrating an example in which a plurality of magnetic poles are provided at an end surface  50   c  of the magnetic sealing member. Referring to FIGS. 1-20, the description will be made as to Embodiments of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following descriptions, the longitudinal direction means the direction parallel to the surface of the recording material and perpendicular to the feeding direction of the recording material. The longitudinal direction of the process cartridge is an axial direction of the developing roller, and is the same as the longitudinal direction when the process cartridge dismounted to the main assembly of the image forming apparatus. 
     (Process Cartridge and Main Assembly of Apparatus) 
     FIG. 1 is a main sectional view of a process cartridge according to an embodiment of the present invention, and FIG. 2 is a main sectional view of an image forming apparatus according to an embodiment of the present invention. The process cartridge comprises an image bearing member and process means actable on said Image bearing member. The process means includes charging means for electrically charging the surface of the image bearing member, a developing apparatus for developing an image formed on the image bearing member into a toner image, and cleaning means for removing toner remaining on the surface of the image bearing member. 
     In the process cartridge  15  of this embodiment, around the image bearing member which is in the form of an electrophotographic photosensitive drum (photosensitive drum)  11 , as shown in FIG. 1, there are provided a charging roller  12  (the charging means); a developing device including a developing roller  18 , a developer regulating member  26  and a toner accommodation frame  16  accommodating the toner; and a cleaning blade  14  (the cleaning means). They are housed in a housing as a unit which is detachably mountable to the main assembly C of the image forming apparatus. 
     FIG. 2 shows a state in which the process cartridge  15  is placed in the main assembly C of the apparatus, and therefore, an image forming operation is capable. In order to remove the process cartridge  15 , an arm  2  capable of supporting a left-hand end portion of the process cartridge  15  is lifted by an unshown handle by which the process cartridge  15  is rotated about a pivot leg  5  of the process cartridge  15  on a guide rail  4  of the main assembly C of the apparatus until the guide portion  15   a  of the process cartridge  15  is a line with the guiding rail  24  of the main assembly C of the apparatus. Then, the process cartridge  15  is pulled with a grip  25  (FIG.  4 ). 
     The mounting of the process cartridge  15  to the main assembly C of the apparatus is performed in the reverse order from the order described for removing the process cartridge. 
     The process cartridge  15  is mounted to the main assembly C of the image forming apparatus shown in FIG.  2  and is used for image formation. A sheet S (recording material) is fed out of a sheet cassette  6  disposed at a lower portion of the apparatus by a feeding roller  7 . In synchronize with the sheet feeding, the light modulated in accordance with image information is projected from an exposure device  8  onto the photosensitive drum  11  which has been uniformly charged by the charging roller  12  so that electrostatic latent image is formed. On the other hand, the toner accommodated in the toner accommodation frame  16  is discharged to the developing roller  18  and is carried on the surface of the developing roller in a predetermined thickness regulated by a developer regulating member  26 . By applying a developing bias to the developing roller  18 , the latent image formed on the surface of the photosensitive drum  13  is developed. The toner image provided by the development is transferred onto a sheet S by bias voltage application to the transfer roller  9 . The sheet S is then fed to the fixing device  10 , where the transfer image is fixed. The sheet S is then discharged to the discharging portion  3  provided at an upper portion of the apparatus by the sheet discharging roller  1 . 
     (Frame of Process Cartridge) 
     Referring to FIGS.  1  and  3 - 5 , the structure of the process cartridge  15  will be described. FIG. 5 is a perspective view of a frame before the process cartridge is assembled. The process cartridge  15  mainly comprises three frames, namely, a cleaning frame  13  integrally supporting the photosensitive drum  11 , the charging roller  12 , and cleaning blade  14 ; a developing device frame  17  integrally supporting the developing roller  18  and the developer regulating member  26  (not shown in FIG. 5 but shown in FIG.  1 ); a toner accommodation frame  16  accommodating the toner T. In addition, it comprises side covers  19 ,  20  at opposite and portions in order to integrally support the three frames to constitute the process cartridge. 
     The cleaning frame  13  supports the cleaning blade  14  by small screws, and charging roller  12  is rotatably supported by bearing members (unshown) at the core metal portion at the end portions. The photosensitive drum  11  comprises, at the opposite end portions, respective flange portions  11   a,    11   b  which are rotatably supported on the cleaning frame  13  by bearing members  22 ,  23 . As shown in FIG. 3, the flange portion  11   a  has a so-called triangular coupling  11   c  for engagement with a driving coupling provided in the main assembly C of the apparatus at the end of the flange to receive a driving force from the driving device of the main assembly C of the apparatus in order to drive the photosensitive drum  11 . The toner accommodation frame  16  has a toner feeding member  27  therein and accommodates the toner T. 
     In the developing device frame  17 , there are provided a developing roller  18  containing therein a magnet roller  18   a,  a developer regulating member  26  and a magnetic seal (unshown). The developing roller  18  is rotatably supported by unshown bearings fixed to a projection  18  at one end and to the developing device frame  17  at the other end. The magnet roller  18   a  is supported by a projection  17 C (developing roller shaft reception) at one end and by the developing device frame  17  at the other end so as to maintain a gap relative to the developing roller  18 . The developing roller  18  is supplied with electric energy through all electrical contact provided in the developing roller  18 . In addition, the developing roller  18  is provided with a roller (unshown) to maintain a constant gap relative to the photosensitive drum  11 . 
     The developing device frame  17  is supported for rotation relative to the cleaning frame  13  in such a direction that center of the developing roller moves toward the center of the photosensitive drum about a hook hole  17   d  provided in the developing device frame  17  at the other side of the developing roller  18 . 
     At a side of the developing device frame  17  at one end of the developing roller  18 , a projection  17 C is fixed on the axis of the developing roller  18  so as to press the projection  17 C toward the center of the photosensitive drum. The projection  17 C is inserted into a groove  19 C provided in the side cover  19  (in this embodiment, a linear elongated hole extending substantially parallel toward the center of the photosensitive drum), so as to permit motion toward the photosensitive drum. In the groove  19 C, there is an elastic member (unshown) to press against the projection  17 C to urge that developing roller  18  to the photosensitive drum  11 . 
     The groove  19 C has also a positioning function for regulating the moving direction of the developing roller  18 . 
     When the driving force is applied, unshown engageable gears provided on the photosensitive drum  11  and the developing roller  18 , respectively, are urged toward each other to assure the engagement of the gears, thus preventing the force for disengaging the gears from each other. The developing roller  18  is normally pressed toward the photosensitive drum  18  by the elastic member provided in the groove  19 C, too. 
     One of the side movers  19  has a size large enough to cover the main section of the process cartridge  15 , and is disposed at one longitudinal end, and fixes the cleaning frame  13  and the toner accommodation frame  16  to integrally support them. The hole portion  19   a  of the side cover  19  is positioned coaxially with the center of the photosensitive drum, in the cleaning frame  13 . The positioning of the side cover  19  using the bearing member  22  is advantageous since then the positioning is accurate. A positioning portion  19   b  of a dowel provided at a position as far as possible from the photosensitive drum  11  is engaged with the positioning portion  13   b  which is in the form of a hole provided in the side of the cleaning frame  13  to determine the position in the rotational direction. The side cover  19  and the cleaning frame  13  are fixed together by several screws. One end of the toner accommodation frame  16  is provided with positioning portions  16   a,    16   b  for the dowel, and positioning portions  19   c,    19   d  in the form of holes in the side cover  19  is engaged with the positioning portion, and the side cover  19  and the toner accommodation frame  16  are fixed together by several screws. The same applies to the side cover  20  at the other side. 
     As described hereinbefore, the bearing member  22  also functions to determine the position relative to the main assembly C of the image forming apparatus. In order to supply the toner from the toner accommodation frame  16  to the developer roller  18 , the toner accommodation frame  16  and the developing device frame  17  are provided with openings  17   a,    16   c,  respectively. There are connected by a sealing member  21  for connecting the openings  17   a,    16   c  of the developing device frame  17  and the toner accommodation frame  16 . The toner accommodation frame  16  is positioned by the side covers  19 ,  20 , and the developing device frame  17  is positioned by the cleaning frame  13 , and therefore, a deformation may occur due to dimension errors of the developing device frame  17  and the toner accommodation frame  16 . Taking this into account, the sealing member  21  is made of a flexible material. With such a structure, even if the amount of the toner accommodated inn the toner accommodation frame  16  is large, the load of the toner is imparted on the side covers  19 ,  20  not on the developing roller  18 . Therefore, the image formation is stable without imparting an unnecessary load to the photosensitive drum  11 . By the connection of frames at the sides, the main body of the container can be correctly positioned by one part (side cover). 
     (Description of Developing Apparatus) 
     Next, the developing apparatus will be described in more detail. FIG. 6 is a plan view of the one of the lengthwise ends of the development roller, and its adjacencies, as seen from the front side of the image forming apparatus. FIG. 7 is a sectional view of the development roller at a plane A—A in FIG.  6 . FIG. 8 is a sectional view of the development roller, at a plane B- 8  in FIG.  7 . FIG. 9 is a sectional view of the development roller, at a plane C—C in FIG.  6 . FIG. 10 is an exploded perspective view of one of the lengthwise ends of the development roller, and its adjacencies. FIG. 11 is a perspective view of a magnetic scaling member. FIG. 12 is a perspective view of a combination of a development roller bearing, and the lengthwise end of a developing means holding frame, before the former is attached to the latter. FIG. 13 is a perspective view of a combination of a development roller bearing and a development means holding frame, different from the one shown in FIG.  12 . FIG. 14 is a perspective view of only a development roller and a pair of magnetic sealing members in such a manner that they will be positioned in a process cartridge. FIG. 15 is a sectional view of the combination of the development roller and the pair of magnetic sealing members, at a plane E—E in FIG.  14 . FIGS. 16 and 17 are perspective views of a toner scraping member. FIG. 18 is a schematic sectional view of the development roller, toner scraping member, and their adjacencies, for showing the manner in which toner will have accumulated in a toner collecting space toward the end of the service life a process cartridge. FIGS. 19 and 20 are drawings for showing a toner leakage preventing method different from the preceding toner leakage preventing method. FIG. 19 being a plan view of one of the lengthwise ends or the developing apparatus (in which development roller and development blade are unshown), as seen from the direction perpendicular to the lengthwise direction of the development roller, and FIG. 20 being a sectional view of the development roller and its adjacencics, at a plane perpendicular to the lengthwise direction. 
     As described before, the development roller  18  and developer regulating member  26  (development blade), as image formation components, are attached within the developing means holding frame  17 . 
     Referring to FIG. 10, the developer regulating member  26  comprises a blade supporting portion  26   a  formed of a piece of 1-2 mm thick metallic plate, and a developer regulating blade  26   b  fixed to the supporting portion  26   a  with the use of hot melt, two-sided adhesive tape, or the like. It is positioned so that the developer regulating blade  26   b  is placed in tangent to the development roller  18  to regulate the amount by which toner is coated on the peripheral surface of the development roller  18 . The developer regulating blade  26   b  in this embodiment is formed of urethane rubber, but sometimes, silicone rubber is used as the material for the developer regulating blade  26   b.  The developing means holding frame  17  is provided with a flat surface  17   f,  as a blade anchoring portion, and a positioning joggle (unshown in FIG. 10; designated by referential code  17   t  in FIG.  6 ). The blade anchoring flat surface  17   f  is provided with a threaded hole  17   g.  The positioning joggle  17   t  is located slightly toward the center of the developing means holding frame  17  relative to the blade anchoring flat surface  17   f.  When attaching the development blade  26 , the positioning joggle  17   t  is fitted into the positioning hole  26   d  of the blade supporting portion  26   a.  Then, the blade supporting portion  26   a  is solidly secured to the flat surface  17   f  by screwing a small screw  57  into the threaded hole  17   g  after putting it through the screw hole  58   a  of a developer removing member  58 , as a toner scraping member, which will be described later, and also through the screw hole  26   c  of the blade supporting portion  26   a.  During this procedure, the joggle  17   t  is engaged in the elongated hole  58   b  of the developer removing member  58 . In other words, the developer regulating member  26  and developer removing member  58  are attached to the developing means holding frame  17  with the same screw, or the small screw  57 , fixing the position of the regulating edge of the developer regulating blade  26   b,  the amount of the pressure by which the developer regulating blade  26   b  is kept in contact with the development roller  18 , and the distance between the regulating edge of the urethane rubber blade  26   b  to the interface between the development blade  26  (blade  26   b ) and development roller  18 . As a result, development condition is established. Further, in order to increase the rigidity of the blade supporting portion  26   a  of the developer regulating member  26 , the blade supporting portion  26   a  is bent 90 deg. at a predetermined line parallel to the lengthwise direction to form a rigidity increasing portion  26   e.    
     Further, the developing means holding frame  17  is provided with a roughly U-shaped elastic sealing member  51  for preventing toner from leaking out. The elastic sealing member  51  is formed of MOLTPRENE, or the like, and is pasted to the elastic sealing member anchoring surfaces  17   h  and  17   j  (FIG.  10 ). The surface  17   h  is a part of the end surface of the rib which extends in the lengthwise direction along the top edge of the opening  17   a,  and the surface  17   j  extends downward (in FIG. 10) from the lengthwise end of the surface  17   h  in the direction perpendicular to the lengthwise direction. More specifically, the first straight portion  51   c  of the elastic sealing member  51  is pasted to the elastic sealing member anchoring surface  17   h  of the developing means holding frame  17 , and the second straight portion  51   a  (third sealing member) of the elastic sealing member  51  is pasted to the elastic sealing member anchoring surface  17   j.  The elastic sealing member  51  is sandwiched between the developing means holding frame  17  and developer regulating member  26 , being elastically compressed to prevent toner from leaking out. The elastic sealing member  51  is also provided with an ear-like portion  51   b,  which outwardly protrudes several millimeters in the lengthwise direction from the intersection of the first and second straight portions  51   a  and  51   c.  This ear-like portion  51   b  bears the role of positioning the magnetic sealing member  50 , which will be described later, in addition to the role of preventing toner leakage. 
     Referring to FIG. 10, the magnetic sealing member  50  is attached to the developing means holding frame  17 ; more specifically, it is fitted in a groove  17   k  (FIG.  7 ), which is located at the lengthwise end of the opening  17   a,  and extends perpendicular to the lengthwise direction from the bottom edge of the opening  17   k  to the top edge of the opening  17   k,  following the arcuate surface  171 , and further to the top end of the flat surface connected to the arcuate surface  171 . This magnetic sealing member  50  will be described later in detail. 
     Further, the developing means holding frame  17  is provided with a thin elastic sealing member (unshown), which is pasted to the elastic sealing member anchoring surface  17   m   1  of the mandible-like portion  17   m  of the developing means holding frame  17 , being placed in contact with the development roller  18 , tangential to the peripheral surface of the development roller  18 . The development roller  18  is a cylindrical member formed of a metallic substance such as aluminum, stainless steel, or the like. It is approximately 16-20 mm in diameter, and approximately 0.5-1 mm in thickness. Its peripheral surface has been coated with carbon, blasted, or subjected to the like to enhance the charging property of the developer. The development roller  18  in this embodiment was simply coated with carbon. 
     The development roller  18  is provided with a pair of sleeve flanges  18   s  (one of which is shown in FIG.  10 ), which are cylindrical members formed of a metallic substance such as aluminum, stainless steel, or the like, and are attached to the lengthwise ends of the development roller  18 , one for one; they are pressed into the lengthwise ends of the development roller  18 . The sleeve flange  18   s  is stepped, comprising a first cylindrical portion  18   b  and a second cylindrical portion  18   c,  the axial lines of which coincide with the axial line of the development roller  18 . The first cylindrical portion  18   b  is greater in diameter than the second cylindrical portion  18   c.  Around the first cylindrical portion  18   b,  a spacer ring  53 , which is a member for regulating the distance between the development roller  18  and photoconductive drum  11 , and is formed of a dielectric material such as polyacetal or the like, is fitted. The second cylindrical portion  18   c  is fitted in the development roller bearing  55  (shown in FIG. 12, which is an enlarged perspective view of bearing  55 , as seen from the direction opposite to the direction from which it is seen in FIG.  10 ), which is for rotationally supporting the development roller  18 , as well as positioning the development roller  18  relative to the developing means holding frame  17 . Further, the second cylindrical portion  18   c  is provided with a flatted portion  18   d,  which constitutes the end portion thereof. Around the second cylindrical portion  18   c  with this flatted portion  18   d,  a development roller gear  54  formed of synthetic resin is fitted, being prevented by the flatted portion  18   d  from rotating relative to the second cylindrical portion  18   c.  This development roller gear  54  is driven by a helical drum gear (unshown) attached to one of the lengthwise ends of the photoconductive drum  11 , rotating thereby the development roller  18 . Its teeth are twisted in such a direction that as it is rotated in mesh with the helical drum gear, thrust is generated in the direction to push the development roller  18  toward the center of the development roller  18  in terms of the lengthwise direction. Within the hollow of the development roller  18 , a magnetic roll (reference code  18   a  in FIG. 15) for adhering toner to the peripheral surface of the development roller  18  is disposed. The sleeve flange  18   s  attached to the other end of the development roller  18  is similar in structure to the above described one, and its description will not be given here. 
     The developer roller bearing  55  is formed of lubricous resinous material, and is in the form of a piece of flat plate with a thickness of approximately 2-5 mm. This flat member, or the development roller bearing  55 , has a cylindrical hole  55   a,  as the bearing portion, in its center portion, which is approximately 8-15 mm in diameter. In this bearing portion (hole)  55   a,  the second cylindrical portion  18   c  of the sleeve flange  18   s  is fitted, so that the development roller  18  can be rotationally driven. Further, the flat surface  55   g  of the development roller bearing  55  is provided with joggles  55   c  and  55   f,  and screw holes  55   b.  The joggles  55   c  and  55   f  are roughly parallel to the axial line of the bearing portion  55   a,  and contribute to the positioning of the bearing  55  relative to the developing means holding frame  17 . The joggle  55   c  is stepped, its end portion forming a first cylindrical portion  55   d  slightly smaller in diameter than the base portion of the joggle  55   c,  and a second cylindrical portion  55   c  slightly smaller in diameter than the first cylindrical portion  55   d.  The axial lines of the first and second cylindrical portions  55   d  and  55   e  coincide with the axial line of the joggle  55   c.  The first and second cylindrical portions  55   d  and  55   e  of the joggle  55   c  are used for positioning the magnetic scaling member, which will be described later. The screw hole  55   b  is for securing the development roller bearing  55  to the developing means holding frame  17  with the use of small screws. The joggle  55   c  and  55   f  of the development roller bearing  55  are fitted in the positioning hole  17   c  (FIG. 12) and elongated hole  17   o,  respectively, and the flat surface  55   g  of the development roller bearing  55  is placed in contact with the surface  17   p  of the developing means holding frame  17 . Then, the small screws  56  are put through the screw holes  55   b  of the development roller bearing  55  and screwed into the threaded holes  17   q  and  17   r  of the developing means holding frame  17 , solidly securing the development roller bearing  55  to the developing means holding frame  17 . This arrangement assures that as the developer regulating member  26  and development roller  18  are attached to the developing means holding frame  17 , they are accurately positioned relative to each other for continuously outputting satisfactory images. 
     The second cylindrical portion  18   c  of the sleeve flange of the development roller  18  is slidably supported by the wall of the cylindrical bearing hole  55   a  of the development roller bearing  55 . Therefore, a material superior in lubricity is required as the material for the development roller bearing  55 , and such a material is relatively costly (for example, PPS or PA), which is a problem. This problem can be easily solved by dividing the development roller bearing  55  into a bushing portion  101 , or the actual bearing portion, and a housing portion  100 , so that the amount of highly lubricious material, or the costly material, necessary for providing the cylindrical bearing hole  55   a  with lubricious surfaces, can be reduced by using the highly lubricious material only for the bush portion  101 , and using a relatively inexpensive material such as HIPS as the material for the housing  100 . 
     (Magnetic Sealing Member) 
     The magnetic sealing member  50  (shown enlarged in FIG. 11) is 3-4 mm wide in terms of the lengthwise direction of the development roller  18 . It comprises a magnet  50   a  and a magnetic plate  50   b.  The magnet  50   a  is formed of a mixture of magnetic powder (Nd—Fe—B powder) and nylon binder, by injection molding. The magnetic plate  50   b  is a piece of 1-1.5 mm thick steel. The magnet  50   a  and magnetic plate  50   b  are attached to each other during the injection molding (insert molding) so that the magnetic plate  50   b  becomes the corner portion of the magnetic sealing member  50  between the arcuate surface on the inward side, in terms of the radius direction of the arcuate portion of the magnetic sealing member  50 , and the straight end surface on the inward side, in terms of the lengthwise direction of the development roller  18 , and that the surfaces of the magnetic plate  50   b  and magnet  50   a  become flush with each other. However, even if the magnet  50   a  and magnetic plate  50   b  are put together using adhesive, two-sided adhesive tape, or simply held together by magnetism, certain effects, which will be described later, can be obtained. The gap provided between the development roller  18  and magnetic sealing member  50  is 0.1-0.7 mm. In this condition, the density of the magnetic flux from the magnetic sealing member  50  at the peripheral surface of the development roller  18  is 1,000-2,000 Gs. As for the positional relationship between the developing means holding frame  17  and magnetic sealing member  50 , the magnet  50   a  is on the opening  17   a  (area corresponding to the center portion of the development roller  18  covered with dots in FIG. 14) side of the developing means holding frame  17  in terms of the lengthwise direction, whereas the magnetic plate  50   b  is on outward side (lengthwise ends of the development roller  18  in FIG. 14) of the magnetic sealing member  50 . 
     With the positioning of the magnet  50   a  on the opening  17   a  side of the developing means holding frame  17 , and the magnetic plate  50   b  on the outward side of the magnetic sealing member  50 , in terms of the lengthwise direction of the development roller  18 , the magnetic flux  75  from the magnetic sealing member  50  is concentrated between the magnet  50   a  and magnetic plate  50   b  as shown in FIG.  15 ( b ), an enlarged view of the portion A in FIG.  15 ( a ), and enters the magnetic plate  50   b,  which is high in permeability. In other words, the magnetic flux is prevented from spreading outward beyond the outward end surface of the magnetic sealing members  50  in terms of the lengthwise direction. 
     Therefore, it does not occur that toner is moved outward beyond the magnetic plate  50   b,  in terms of the lengthwise direction, by the magnetic force present at the surface of the magnetic sealing member  50 . Therefore, It does not occur that toner is made to contact the spacer rings  53 , that is, the distance regulating member, by the rotation of the development roller  18 . Therefore, it is possible to reduce the distance between the spacer ring  53  and magnetic sealing member  50 , which in turn makes it possible to reduce the size of the process cartridge C as well as the size of the image forming apparatus main assembly C. 
     Further, in terms of the lengthwise direction of a process cartridge, the toner on the magnetic sealing member  50  does not travel outward beyond the magnetic plate  50   b,  which is on the outward side of the opening  17   a  of the developing means holding frame  17 ; it is assured that the outwardly traveling toner is caught and held in the range in which the surface magnetism of the magnetic sealing member is strong. Therefore, even if the process cartridge  15  is subjected to shocks when the process cartridge  15  is mounted into, or dismounted from, the image forming apparatus main assembly C, the cartridge  15  remains well sealed; toner does not leak. 
     Attaching the magnetic plate  50   b  to the side surface of the magnet  50   a  causes a certain portion of the magnetic flux, which would simply diffuse if it were not for the magnetic plate  50   b,  to enter the magnetic plate  50  as described above, increasing the density of the magnetic flux at the surface of the magnet  50   a:  in other words, it increases the amount of magnetic force at the surface of the magnet  50   a,  improving the sealing performance of the magnetic sealing member  50 , which in turn affords the usage of a weaker magnet, that is, an inexpensive magnet. In other words, the employment of a magnetic sealing member, such as the one in this embodiment, structured as described above, makes it possible to reduce cost. 
     (Developer Removing Member) 
     The aforementioned developer removing member  58  (shown enlarged in FIG. 16) as a toner scraping member comprises a main section  58   d  having a screw hole  58   a,  an elongated positioning hole  58   b,  a cylindrical positioning joggle  58   c,  and a blade  58   e  (FIG.  6 ). The main section  58   d  is roughly rectangular and approximately 3-5 mm in thickness. It has a few holes and recesses resulting from the removal of structurally unnecessary portions. It is disposed roughly in parallel to the developer regulating member  26  (FIG.  6 ). The blade  58   e  elastically contacts the development roller  18  in a manner to cover the entirety of the lengthwise end of the magnetic sealing member  50 . It is relatively thin, having a thickness of 0.1-0.4 mm, and is attached to the end surface  58   d   1  of the main section  58   d,  by one of the edges. 
     Referring to FIG. 7, in terms of the moving direction of the peripheral surface of the development roller  18 , the developer removing member  58  is disposed between the upstream end of the area A in which the latent image on the photoconductive drum  11  is developed, and the downstream end, that is, the exit end g 1   a,  of the gap g 1  between the magnetic seal  50  and the peripheral surface or the development roller  18 , and adjacent to the exit end g 1   a.  As described before, in terms of the lengthwise direction, the width of the blade  58   e  of the developer removing member  58  is approximately 1-3 mm wider than that of the magnetic sealing member  50 , as shown in FIG.  6 . The blade  58   e  of the developer removing member  58  is placed in contact with the development roller  18  so that it extends in the direction counter to the rotational direction of the development roller  18 , and is tapered (at edge  58   e   1 ) so that as the development roller  18  rotates, the toner on the peripheral surface of the development roller  18  is scraped away toward the center of the development roller  18  in terms of the lengthwise direction (FIG.  6 ). Therefore, within the range of the magnetic sealing member  50  in terms of the lengthwise direction, toner is not left agglomerated in a layer on the portion of the peripheral surface of the development roller  18  on the area A side with respect to the blade  58   e.  Therefore, toner does not accumulate at the entrance portion g 1   b  of the gap g 1  between the magnetic sealing member  50  and the peripheral surface of the development roller  18 , making It possible to employ a magnetic sealing member with a higher level of magnetic force in order to improve the sealing performance of the magnetic scaling member. Therefore, it is possible to provide a process cartridge which does not leak toner while it is used whether the cartridge is brand-new or has been in usage for a long time. 
     Incidentally, even though the blade  58   e  of the developer removing member  58  is in contact with the development roller  18 , the contact area is very small. Therefore, the contact does not result in a significant amount of increase in the torque necessary to rotate the development roller  18 . In other words, the provision of the above described developer removing member  58  does not significantly reduce the amount of decrease in the torque necessary to rotate the development roller  18 , realized by the employment of the magnetic sealing member  50 . 
     The developer removing member  58  is formed, with the use of injection molding, of synthetic resins, in particular, polyacetal, polycarbonate, polyphenylene oxide, or the like, which are superior in lubricity and are relatively small in the amount of permanent set resulting from fatigue. 
     As described before, the developer removing member  58  is solidly secured, along with the developer regulating member  26 , to the developing means holding frame  17 , with the use of the small screw  57 . The position of the developer removing member  58  relative to the developing means holding frame  17  becomes fixed as the cylindrical positioning joggle  58   c,  which is coaxial with the screw hole  58   a  of the developer removing member  58 , is fitted into the screw hole  26   c  of the metallic supporting portion  26   c  of the developer regulating member  26  (FIG.  7 ). Further, the attitude of the developer removing member  58  relative to the developing means holding frame  17  becomes fixed as the positioning joggle  17   t  of the developing means holding frame  17  for positioning the developer regulating member  26  is fitted into the elongated positioning hole  58   b  of the developer removing member  58 , which is elongated in the direction roughly parallel to the developer regulating member  26  in a manner to be aligned with the cylindrical positioning joggle  58   a  of the developer removing member  58  (FIG.  6 ). Since the developer removing member  58  can be positioned and solidly secured with the use of the above described means for positioning and solidly securing the development blade  26  as described above, it is possible to achieve reduction in the size of the developer removing member  58 , which leads to better special efficiency as well as cost reduction. 
     (Structure for Positioning Magnetic Sealing Member) 
     The position of the magnetic sealing member relative to the development roller is fixed by the above described developing means holding frame, elastic sealing member, and development roller bearing, More specifically, it is fixed by positioning the positioning hole  50   d  of the magnetic sealing member, and keeping the magnetic sealing member pressured so that the magnetic sealing member rotates about the axial line of the positioning hole  50   d,  as shown in FIG.  7 . This positioning of the magnetic sealing member will be described next in more detail with reference to FIGS. 6,  7 ,  8 , and  9 . 
     Referring to FIG. 7, in terms of the cross sectional view perpendicular to the lengthwise direction of the development roller, both the magnet  50   a  and magnetic plate  50   b  have semicircular portions  50   e  (semicircular portion of magnetic sealing member), which hold the gap g 1  from the development roller  18 , and straight end portions  50   c  (which faces the developer removing member  58 ), which extend upward toward the developing means holding frame  17  from the top ends of the semicircular portions  50   e  at an angle relative to the line connecting its base portion and the center of the curvature of the semicircular portions  50   e.  As for the cross section in terms of a given plane parallel to the radius direction of the semicircular portions  50   e,  the magnet  50   a  is roughly square, and the combination of the magnet  50   a  and magnetic plate  50   b  is square. The magnet  50   a  has a semicircular positioning lobe  50   h,  which protrudes from the peripheral surface  50   f  of the magnet  50   a.  The semicircular positioning lobe  50   h  is provided with a positioning hole  50   d,  the axial line of which coincides with the axial line of the semicircular positioning lobe  50   h.  Referring to FIG. 11, the top end of the magnetic plate  50   b  is embedded in the straight portion  50   c  of the magnet  50   a.  On the outward side in terms of the lengthwise direction of the development roller, the magnetic plate  50   b  is flush with the magnet  50   a.    
     Referring to FIGS. 7 and 10, the developing means holding frame  17  is provided with a magnetic sealing member attachment groove  17   k  ( 17   k   1 ,  17   k   2 , and  17   k   3 ), which extends from the flat surface  7   f  to the bottom end of the arcuate portion (surface)  171  (e 1 ). This groove  17   k  comprises an arcuate section  17   k   1  which follows the curvature of the arcuate surface  171  (FIG.  10 ), a straight vertical section  17   k   2  which follows the flat surface  17   f,  and a nondefinitively curved portion  17   k   3  in which the positioning lobe  50   h  (having positioning hole  50   d  coaxial with positional hole) of the magnetic sealing member  50  perfectly fits; the sections  17   k   1 ,  17   k   2 , and  17   k   3  are continuous. The section  17   k   3  of the groove  17   k  is deeper than the section  17   k   1  of the groove  17   k,  cutting deeper into the developing means holding frame  17  from the bottom of the section  17   k   1 . The width H (FIG. 8) of the groove  17   k  is made equal to that of the magnetic sealing member  50 . Thus, as the magnetic scaling member  50  is fitted into the groove  17   k,  the position of the magnetic sealing member  50  relative to the development roller  18  in terms of the lengthwise direction of the development roller  18  becomes fixed. The depth of each section of the magnetic sealing member attachment groove  17   k  is made to be such that after the fitting of the magnetic sealing member  50  into the groove  17   k,  there will be a 0.1-0.7 mm gap between the bottom wall of each section of the groove  17   k  and the corresponding portion of the magnetic sealing member  50 . In other words, a predetermined gap g 2  (FIG. 7) is kept between the peripheral surface  50   f  of the magnetic sealing member  50  and the bottom surface of the groove  17   k  of the developing means holding frame  17 . In order to prevent toner from leaking through this gap g 2 , the magnetic sealing member is magnetized so that its magnetic pole faces the peripheral surface of the development roller  18 , and that toner is prevented from leaking by magnetic force. Incidentally, in order to enhance the effect of the magnetic force, the magnetic plate  50   b  may be configured so that it reaches the peripheral surface of the magnetic sealing member  50  to prevent, as on the development roller side, the magnetic force from spreading. 
     Next, the positioning of the magnetic sealing member  50  will be described in detail. Referring to FIG. 8, as the first cylindrical portion  55   d,  or the middle portion, of the step joggle, that is, the shaft for positioning/supporting the magnetic sealing member  50 , protruding from the aforementioned development roller bearing, is fitted into the positioning hole  50   d  of the magnetic sealing member  50 , the magnetic sealing member  50  is rotationally supported by the developer bearing  55 . Further, the second cylindrical portion  55   e,  or the end portion, of the step joggle is fitted into the positioning hole  17   s,  which is in the inward lateral wall of the magnetic sealing member attachment groove  17   k,  with respect to the cartridge, in terms of the lengthwise direction, and the axial line or which coincides with that of the positioning hole  17   c  of tie developing means holding frame  17 . As a result, the magnetic sealing member  50  is supported by the step joggle, or the magnetic sealing member  50  positioning/supporting shaft, which is secured to the developing means holding frame  17  by both lengthwise ends. By being secured to the developing means holding frame  17  by both lengthwise ends, the step joggle, or the magnetic sealing member  50  positioning/supporting shaft, is enabled to reliably support the magnetic sealing member  50  in spite of its relatively small diameter, contributing to the special efficiency. The positioning/supporting shaft Is likely to tilt due to its formation, whereas it is relatively easy to form the developing means holding frame  17  so that the axial lines of the positioning holes  17   c  and  17   s  of the developing means holding frame  17  coincide Thus, the above described structural arrangement assures that the magnetic sealing member  50  is kept precisely positioned in spite of the relatively small diameter of the magnetic sealing member positioning/supporting shaft. 
     Next, as for the positioning of the magnetic sealing member  50  relative to the developing means holding frame  17  in terms of its pivotal direction, it is fixed by placing the magnetic sealing member  50  in contact with the end surface  17   k   4 , on the bottom side, of the arcuate section  17   k   1  of the magnetic sealing member attachment groove  17   k  of the developing means holding frame  17 , that is, the end surface  17   k   4  which vertically extends to the bottom of the groove  17   k  from the elastic seal (unshown) anchoring surface  17   m   1  of the mandible-like portion  17   m  described before. The pressure F for assuring that the magnetic sealing member  50  is kept in contact with the bottom end surface  17   k   4  is mainly generated by the resiliency of the ear-like portion  51   b  of the elastic sealing member  51  kept compressed between the developer regulating member  26  and blade supporting portion  26   a.  With the presence of this pressure, it is ensured that the magnetic sealing member  50  is kept pressured in the direction to pivot clockwise about the axial line of the positioning hole  50   d,  so that the development roller and magnetic sealing member are precisely positioned relative to each other. Further, only the development roller bearing is involved in the positioning of the magnetic sealing member and development roller relative each other, minimizing the variation in the size of the gap g 1 , which manifests as one of the cumulative effects of the errors in component measurements, and therefore, affording the magnetic sealing member  50  a greater margin for error in terms of the toner leakage prevention performance. In the past, it was customary to measure the gap g 1  during the cartridge assembly. However, the above described structural arrangement drastically reduced the amount of the variation in the size of the gap g 1 , making it unnecessary to examine the gap g 1 . The usage of a part of the elastic sealing member  51  as the source for generating the pressure F makes it possible to eliminate the need for a component dedicated for generating the pressure F, reducing therefore the cost, while assuring that the magnetic sealing member  50  is precisely positioned. Further, the employment of a dielectric substance as the material for the elastic sealing member  51  enables the elastic sealing member  51  to play the rule of preventing electrical leakage, for example, when high voltage is applied to the metallic supporting portion of the development roller. 
     Next, referring to FIG. 10, the attachment of the magnetic sealing member will be described up to the point where the position of the magnetic sealing member becomes fixed. 
     First, the arcuate portion  50   e  and straight end portion  50   c  of the magnetic sealing member  50  are fitted into the arcuate section  17   k   1  and straight section  17   k   2 , respectively, of the magnetic sealing member attachment groove  17   k  of the developing means holding frame  17  by moving the magnetic sealing member  50  in the direction indicated by an arrow mark D in FIG. 10; the magnetic sealing member  50  is pushed into the groove  17   k  until the inward surface of the arcuate portion  50   e,  in terms of its curvature, becomes roughly flush with the arcuate surface  171  (e 1 ). Next, the first and second straight portions  51   c  and  51   a  (third sealing member) of the elastic sealing member  51  are pasted to the elastic seal anchoring surface  17   h,  that is, the end surface of the lengthwise rib, and the elastic seal anchoring surface  17   j,  respectively, of the developing means holding frame  17 . Also the ear-like portion  51   b  of the elastic sealing member  51  is pasted to the straight end portion  50   c  of the magnetic sealing member  50 . At this stage, the elastic sealing member anchoring surface  17   h  of the developing means holding frame  17 , and the surface of the straight portion  50   c  of the magnetic sealing member  50 , are not flush with each other. Therefore, in order to make it easier to paste the elastic sealing member  51  to both the surface  17   h  and the surface of the straight end portion  50   c,  the straight end portion of the magnetic sealing member  50  is provided with an inclined surface  50   g  (FIGS.  9  and  11 ). Incidentally, if necessary for the sake of material usage efficiency, the ear-like portion  51   b  and second straight portion  51   a  of the elastic sealing member  51  may be made discrete from the first straight portion  51   b.  Here, all that is required of the elastic sealing member  51  is to seal between the developing means holding frame  17  and developer regulating member  26 . Therefore, it is not mandatory that the sealing member  51  is formed of an elastic substance. However, the second straight portion  51   a  of the sealing member  51 , which is to be sandwiched between the straight end portion  50   c  of the magnetic sealing member  50  and the blade supporting portion  26   a  of the developer regulating member  26 , must be enabled to apply pressure to the magnetic sealing member  50 . Therefore, it must be formed of an elastic substance, whether it is formed as an integral part of the elastic sealing member  51  or a discrete part. As for the attachment of the developer regulating member  26 , first, the developer regulating member  26  is placed in contact with the developing means holding frame  17  so that aforementioned joggle  17   t  fits into the positioning hole  26   d  of the blade supporting portion  26   a.  Next, the developer removing member  58  is placed in contact with the developer regulating member  26  so that the positioning joggle  58   c  of the developer removing member  58  fits into the screw hole  26   c  of the blade supporting portion  26   a.  Then, the small screw  57  is put through the screw hole  58   a,  or the center hole, of the positioning joggle  58   c,  and is screwed into the threaded screw hole  17   g,  solidly anchoring the blade supporting portion  26   a  to the flat surface  17   f.  As the small screw  57  is screwed into the threaded hole  17   g  of the developing means holding frame  17  in order to solidly attach the developer regulating member  26  to the developing means holding frame  17 , the blade supporting portion  26   a  of the developer regulating member  26  causes the elastic sealing member  51  to be sandwiched and compressed by the developing means holding frame  17  and the arcuate portion  50   e  of the magnetic sealing member  50 . At this stage, in terms of the lengthwise direction of the cartridge, the end portion of the blade supporting portion  26   a  faces the straight end portion  50   c  of the magnetic sealing member  50 , with the presence of a space E between the two end portions. This space E is connected to the space between the blade portion  58   e  of the developer removing member  58  and the straight end portion  50   c  of the magnetic sealing member  50 . Next, the development roller unit is temporarily positioned so that the arcuate portion  50   e  of the magnetic sealing member  50  and development roller  18  become coaxial. At this stage, the development roller  18  is prevented from coming into direct contact with the magnetic sealing member  50 , by the resiliency of the elastic developer regulating portion  26   b  (elastic blade), being therefore prevented from being damaged by the magnetic sealing member  50  across its peripheral surface. 
     Lastly, the pair of development roller bearings  55  are attached to the corresponding lateral walls of the developing means holding frame  17  in the direction parallel to the lengthwise direction (drawing shows only one lengthwise end of the developing means holding frame  17 ; other end is virtually identical). More specifically, as described before with reference to FIG. 8, each development roller bearing  55  is solidly secured to the developing means holding frame  17  through the following steps: the joggle  55   c  of the development roller bearing  55  is fitted in the positioning hole  17   c;  the joggle  55   f  is fitted in the elongated hole  17   o  (vertically elongated in parallel to the plane of FIG.  8 ); the surface  55   g  of the development roller bearing  55  is placed in contact with the flat surface  17   p  of the developing means holding frame; and the small screws  56  (FIG. 10) are put through the screw holes  55   b  of the development roller bearing  55 , and screwed into the threaded holes  17   q  and  17   r  in the flat surface  17   p  shown in FIG.  12 . As a result, the magnetic sealing member  50  is precisely positioned, being enabled to pivot about the first cylindrical portion  55   d  of the step joggle, and the magnetic sealing member  50  is pivoted about the first cylindrical portion  55   d,  by the force generated by the resiliency of the elastic sealing member  51  sandwiched and compressed by the magnetic sealing member  50  and developer regulating member  26 , so that the bottom end surface of the magnetic sealing member  50  comes into contact with the bottom end surface  17   k   4  of the groove  17   k  of the developing means holding frame  17 , and is kept in contact therewith. 
     As is evident from the above description. this embodiment assures that the magnetic sealing member can be precisely positioned relative to the development roller using a simple assembly method. 
     (Measure Against Toner Leakage of Large Capacity Cartridge) 
     When the process cartridge is in use, the blade portion  58   e  of the developer removing member  58  is in contact with the peripheral surface of the development roller  18 , extending in the direction counter to the moving direction of the peripheral surface of the development roller  18 , as described before, and as the development roller  18  rotates, the toner on the peripheral surface of the development roller  18  is scraped away toward the center of the development roller  18  in terms of the lengthwise direction, by the edge  58   e   1  inclined relative to the axial line of the development roller  18 . Here, “inclined” means that when the edge  58   e   1  is in contact with the peripheral surface of the development roller  18 , the position of a given point of the contact line between the edge  58   e   1  and the peripheral surface of the development roller  18  does not align with another point of the contact line in the direction parallel to the axial line of the development roller  18 ; more specifically, assuming that a straight line is theoretically drawn on the peripheral surface of the development roller  18  in parallel to the axial line of the development roller  18 , as the development roller  18  is rotated, the inward side of the edge  58   e   1  comes into contact with the theoretical line slightly later than the outward side of the edge  58   e   1 . However, when there is a large amount of toner on the peripheral surface of the development roller  18 , a certain amount of toner fails to be scraped away toward the center, and such toner accumulates on the surface of the blade portion  58   e,  which faces the straight end portion  50   c  of the magnetic sealing member  50 . In the case of a process cartridge in accordance with the prior arts, the service life of which is relatively short, the amount of such toner which accumulates on the above described surface of the blade portion  58   e  throughout the service life of the cartridge is very small, creating no problem. However, in the case of a long-life process cartridge, the amount of such toner which accumulates on the surface of the blade portion  58   e,  which faces the straight end portion  50   c  of the magnetic scaling member  50 , throughout the service life of the cartridge is relatively large. Therefore, there is a possibility that as the cumulative usage time increases, too much toner will accumulate on the blade portion  58   e,  and overflow outward of the developer removing member  58 , into the internal space of the image forming apparatus. 
     Thus, in this embodiment, the space E is provided, as a toner storage space, between the straight end portion  50   c  of the magnetic sealing member  50  and the blade supporting portion  26   a  of the developer regulating member  26  (between the magnetic sealing member  50  and developer removing member  58 ) as shown in FIG.  7 . In addition, even the straight end portion  50   c  of the magnetic sealing member  50  is magnetized. Therefore, the portion of the toner scraped away by the developer removing member  58 , which otherwise might have leaked into the apparatus interior, collects in the space E; in other words, it does not leak into the apparatus interior. Further, the ear-like portion  51   b  of the aforementioned elastic sealing member  51 , that is, the member for positioning and pressuring the magnetic sealing member  50 , is positioned between the top end of the straight end portion of the magnetic sealing member  50  and the blade supporting portion  26   a,  blocking the top side of the space E, and therefore, preventing the toner from leaking from the top end of the space E. Even if the ear-like portion  51   b  is absent, the toner in the space E is retained therein by the magnetization of the straight end portion  50   c  or the magnetic sealing member  50 , as long as the amount of the toner in the space E remains below a certain level. In particular, magnetizing the straight end portion  50   c  in a manner to provide the surface of the portion  50   c  with a plurality of magnetic poles makes it possible to form a magnetic flux G on the surface of the portion  50   c  as shown in FIG. 21 so that a larger amount of toner can be held in the space E; it is an effective means for preventing toner leakage. 
     As described, according to this embodiment, the level of protection against toner leakage can be raised without the need for additional components. 
     In order to raise the level of protection against toner leakage even higher, the structure shown in FIGS. 19 and 20 may be adopted. That is, a sealing member  59  (second sealing member) is to be pasted to the sealing member anchoring portion  17   u  of the developing means holding frame, which is virtually flush with the straight end portion  50   c  of the magnetic sealing member  50 , so that the sealing member  59  contacts the straight end portion  50   c  (on the outward side, with respect to the space E, in terms of the lengthwise direction of the development roller). This sealing member  59  is a virtually cubic elastic member, the material for which is desired to be an inexpensive material such as foamed urethane or the like. By being pasted to the above described location, it overlaps 1-3 mm with the developer removing member  58  in the lengthwise direction of the development roller  18 , and is compressed by the blade portion  58   e  of the developer removing member  58  as shown in FIG.  20 . Thus, even when the space E is filled up with toner, the toner does not leak outward of the developer removing member  58  (does not leak from space E). At each end of the magnetic sealing member  50  in terms of the lengthwise direction of the cartridge, one side of the space E is blocked by the sealing member  59  (second sealing member), and the other side (side opposite to second sealing member) is blocked by the second straight portion  51   a  (third sealing member) of the elastic sealing member  51 . 
     As evident from the above description, the addition of the single inexpensive component described above further raises the level of protection against toner leakage. 
     In the above description of this embodiment of the present invention, the present invention was described with reference to a developing apparatus mounted in a process cartridge. However, the present invention is also applicable to a cartridge comprising only a developing means. 
     While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth, and this application is intended to cover such modifications or changes as may come within the purposes of the improvements or the scope of the following claims.