Abstract:
A developing apparatus includes a roller-shaped developer carrying member, a frame for holding the developer carrying member, and a magnetic seal member for preventing leakage of a developer from an end of the developer carrying member in a longitudinal direction of the developer carrying member. The magnetic seal member includes an arcuate magnet portion to be disposed along a circumferential direction of the developer carrying member, and a non-arcuate portion which extends from an end, in the circumferential direction, of the magnet portion away from a peripheral surface of the developer carrying member and is different in material from the magnet portion.

Description:
FIELD OF THE INVENTION AND RELATED ART 
   The present invention relates to a developing apparatus for developing an electrostatic latent image formed on an electrophotographic photosensitive member and a magnetic seal member used in the developing apparatus. 
   In a conventional electrophotographic image forming apparatus which forms an image on a recording medium by employing an electrophotographic process, a process cartridge scheme wherein an electrophotographic photosensitive member and a plurality of process means acting on the photosensitive member are integrally supported to form a cartridge which is detachably mountable to a main body of the image forming apparatus, has been adopted. According to this process cartridge scheme, it is possible to perform maintenance o the apparatus by a user alone without relying on a service engineer, so that an operability can be greatly enhanced. For this reason, the process cartridge scheme has been employed widely in the image forming apparatus. 
   In a developing means (developing apparatus) incorporated in such a process cartridge, a seal member for preventing leakage of toner toward the outside of a developing area is disposed at both ends of a rotating developer carrying member (developing sleeve). 
   In the conventional image forming apparatus, an elastic member formed of, e.g., felt or foam rubber, has been widely utilized as the seal member for preventing the toner leakage. 
   However, in view of advantages such as a reduction of rotation torque of the developing sleeve, a stability of sealing ability and a recycling efficiency of the seal member, there has been proposed a method wherein at each of both ends of the developing sleeve, a seal member for preventing toner leakage by the action of magnetic force is disposed with a predetermined gap to the developing sleeve to prevent the toner leakage, as shown in, e.g., FIG.  8 . Referring to  FIG. 8 , such a magnetic seal member  71 ′ includes a magnet  73 ′ which is an injection-molded product comprising a nylon binder containing a magnetic powder of Nd—Fe—B, and a magnetic plate  74 ′ formed of an iron material. A gap g′ between a developing sleeve  5 ′ and the magnetic seal member  71 ′ is 0.1-0.7 mm (as shown in (d) of FIG.  11 ). At that time, a magnetic flux density at the surface of the developing sleeve  5 ′ given by magnetic force of the magnetic seal member  71 ′ is about 1000-2000 Gs. Further, with respect to a positional relationship between the magnet  73 ′ and the magnetic plate  74 ′, as shown in  FIG. 10 , the magnet  73 ′ is disposed on a side closer to an opening  26 ′ of a developing device frame  12 ′, and the magnetic plate  74 ′ is disposed on a side opposite from the side closer to the opening  26 ′. 
   By this positional relationship between the magnet  73 ′ and the magnetic plate  74 ′, magnetic lines of force are formed between the magnet  73 ′ and the magnetic plate  74 ′, as shown in  FIG. 3 , and enter the magnetic plate  74 ′ which has a high (magnetic) permeability. As a result, it is possible to prevent generation of magnetic lines of force extending out from a width of the magnetic seal member  71 ′. Further, the generated magnetic lines of force are concentrated at the magnetic plate  74 ′, so that a resultant magnetic flux density at the surface of the magnet  73 ′ is increased, thus creating a large magnetic force. As a result, a sealing performance of the magnetic sealing member  71 ′ is improved. 
   Next, a method of mounting and positioning the magnetic sealing member  71 ′ will be described. 
   As shown in  FIG. 9 , on an outer peripheral surface side (back side) of the magnet  73 ′ and the magnetic plate  74 ′, an elastic lining  77 ′ of an elastic material is disposed. The elastic lining  77 ′ has a width, in a longitudinal direction of the developing sleeve  5 ′, which is substantially equal to a total of widths of the magnet  73 ′ and the magnetic plate  74 ′. Further, the elastic lining  77 ′ is disposed so that its lower (bottom) end surface on an outer side in the longitudinal direction of developing sleeve  5 ′ (right-hand side on the figure) covers a lower end surface  71 ′ f  of the magnetic seal member and a lower end surface  77 ′ f  on an inner side (left-hand side on the figure) and the lower end surface  71 ′ f  of the magnetic seal member are substantially in one plane. On the other hand, an upper (top) end surface  77 ′ g  of the elastic lining  77 ′ is located at a position somewhat below an upper end surface  73 ′ g  of the magnet  73 ′. The elastic lining  77 ′ is applied to the backside of the magnet  73 ′ and the magnet plate  74 ′ with a double-faced (adhesive) tape. 
   Further, the developing device frame  12 ′ is provided with a mounting groove  72 ′ for mounting the magnetic seal member  71 ′, which groove extending from a flat surface  12   ′i  to an arcuate surface  12   ′j  as shown in FIG.  10 . The groove  72 ′ includes an arcuate groove  72 ′ a  extended along an arcuation of the arcuate surface  12   ′j , a linear groove  72 ′ b  formed substantially vertically along the flat surface  12   ′j , and a positioning groove  72 ′ d , formed in the longitudinal direction of the developing sleeve  5 ′, with which a bent engage (fitting) portion  73 ′ e  of the magnetic seal member  71 ′ is engaged. A vertical dimension  72 ′ x  of the positioning groove  72 ′ d  is slightly larger than a vertical dimension  73 ′ x  of the bent engage portion  73 ′ e  of the magnetic seal member  71 ′. By engaging the bent engage portion  73 ′ e  in the positioning groove  72 ′ d , it is possible to perform positioning of the magnetic seal member  71 ′ in a substantially vertical direction. A depth  72 ′ w  of the mounting groove  72 ′ for mounting the magnetic seal member  71 ′ is, as shown in (a) of  FIG. 11 , smaller than a thickness  71 ′ w  of the magnetic seal member  71 ′ at its upper portion plus the thickness of the elastic lining  77 ′ by a compression margin of the elastic lining  77 ′. Further, a lower end abutting portion  72 ′ f  to which the lower end surface  71 ′ f  of the magnetic seal member  71 ′ directly abuts is formed at an inner portion of the lower end surface of the arcuate groove  72 ′ a  in the longitudinal direction of the developing sleeve  5 ′. 
   As shown in (a) of  FIG. 11 , the magnetic seal member  71 ′ is engaged into the mounting groove  72 ′ (for mounting the magnetic seal member  71 ′) of the developing device frame  12 ′ as indicated by an arrow. Then, a semicircular arcuate portion  71   a ′ ( FIG. 8 ) of the magnetic seal member  71 ′ is fitted into the arcuate groove  72 ′ a , and a linear surface portion  71 ′ b  ( FIG. 8 ) of the magnetic seal member  71 ′ is fitted into the linear groove  72 ′ b , as shown in (b) of FIG.  11 . When the magnetic seal member  71 ′ is lightly pressed in a direction of an arrow B, a lower portion  77 ′ a  ( FIG. 9 ) of the elastic lining  77 ′ is compressed. At the same time, the lower end surface  71 ′ f  of the magnetic seal member  71 ′ presses the lower end abutting portion  72 ′ f , and an upper end surface  73 ′ g  ( FIG. 8 ) of the magnetic seal member  71 ′ (the magnet  73 ′) is flush with an upper end surface  72 ′ g  of the groove  72 ′. Accordingly, when the upper portion of the magnetic seal member  71 ′ is pushed toward the rear side in the direction crossing the arrow B, the magnetic seal member  71 ′ is engaged with the groove  72 ′. 
   Then, a developing blade  9 ′ d  is mounted to the developing device frame  12 ′. When a plate  9 ′ d   1  of the developing blade  9 ′ d  is closely contacted to the flat (bearing) surface  12   ′i  of the developing device frame  12 ′, an upper front side  73 ′ h  of the magnet  73 ′ is pressed by the plate  9 ′ d   1  of the developing blade  9 ′ as shown in (c) of  FIG. 11 , whereby the upper portion of the magnetic seal member  71 ′ is pressed into the groove  72 ′. This rotates the upper portion of the magnetic seal member  71 ′ about the lower end surface  71 ′ f , so that the elastic lining  77 ′ is compressed rearwardly. The reaction force thereof is received by the lower end abutting portion  72 ′ f  of the groove  72 ′ of the developing device frame  12 ′ to which the lower end surface  71 ′ f  of the magnetic seal member  71 ′ is contacted and by the plate  9 ′ d   1  to which the upper front side  73 ′ h  portion is contacted. Then, a developer roller unit G is mounted. This is shown in (d) of FIG.  11 . 
   As a result, the magnetic seal member  71 ′ is held by the mounting groove  72 ′ (for mounting the magnetic seal member  71 ′) provided in the developing device frame  12 ′ and the upper portion thereof is pressed by the plate  9 ′ d   1  of the developing blade  9 ′ d , thus being correctly positioned. 
   However, in such a mounting and positioning method as described above, the magnetic seal member  71 ′ is made of the magnet not only at its arcuate portion but also its linear portion, thus leading to an increase in cost. 
   SUMMARY OF THE INVENTION 
   In view of the above problem, the present invention has been accomplished. 
   An object of the present invention is to provide a developing apparatus and a magnetic seal member, which are inexpensive while retaining a good toner sealing performance. 
   Another object of the present invention is to provide a developing apparatus to which a magnetic sealing member is readily mounted. 
   Another object of the present invention is to provide such a magnetic sealing member. 
   According to the present invention, there is provided a developing apparatus, comprising: 
   a roller-shaped developer carrying member, 
   a frame for holding the developer carrying member, and 
   a magnetic seal member for preventing leakage of a developer from an end of the developer carrying member in a longitudinal direction of the developer carrying member, the magnetic seal member including an arcuate magnet portion to be disposed along a circumferential direction of the developer carrying member, and a non-arcuate portion which extends from an end, in the circumferential direction, of the magnet portion away from a peripheral surface of the developer carrying member and is different in material from the magnet portion. 
   According to the present invention, there is also provided a magnetic seal member adapted to a developing apparatus, comprising: 
   an arcuate magnet portion to be disposed along a circumferential direction of a developer carrying member, and a non-arcuate portion which extends from an end, in the circumferential direction, of the magnet portion away from a peripheral surface of the developer carrying member and is different in material from the magnet portion. 
   The present invention provides a developing apparatus, comprising: 
   a roller-shaped developer carrying member, 
   a frame for holding the developer carrying member, and 
   a magnetic seal member for preventing leakage of a developer from an end of the developer carrying member in a longitudinal direction of the developer carrying member, the magnetic seal member including an arcuate magnet portion to be disposed along a circumferential direction of the developer carrying member, and a non-arcuate portion which extends from an end, in the circumferential direction, of the magnet portion away from a peripheral surface of the developer carrying member; 
   wherein the non-arcuate portion is elastically deformable. 
   The present invention also provides a magnetic seal member adapted to a developing apparatus, comprising: 
   an arcuate magnet portion to be disposed along a circumferential direction of a developer carrying member, and a non-arcuate portion which extends from an end, in the circumferential direction, of the magnet portion away from a peripheral surface of the developer carrying member; 
   wherein the non-arcuate portion is elastically deformable. 
   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 perspective view of a magnetic seal member according to Embodiment 1 of the present invention. 
       FIG. 2  is a perspective view of the magnetic seal member according to Embodiment 1 to which an elastic lining is applied. 
       FIG. 3  is a sectional view illustrating a state of magnetic lines of force with respect to the magnetic seal member according to Embodiment 1. 
       FIG. 4  is a perspective view of a mounting portion of the magnetic seal member according to Embodiment 1. 
       FIG. 5  is a side view illustrating mounting of the magnetic seal member according to Embodiment 1 to a developing device frame. 
       FIG. 6  is a schematic cross-section of a process cartridge according to Embodiment 1 of the present invention. 
       FIG. 7  is a sectional view illustrating principal parts of an image forming apparatus used in Embodiment 1. 
       FIG. 8  is a perspective view of a conventional magnetic seal member. 
       FIG. 9  is a perspective view of the conventional magnetic seal member to which an elastic lining is applied. 
       FIG. 10  is a perspective view of a mounting portion of the conventional magnetic seal member. 
       FIG. 11  is a side view illustrating mounting of the conventional magnetic seal member to a developing device frame. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Hereinbelow, the embodiments of the present invention will be described in detail with reference to the drawings. 
   In the following description, however, a dimension, a material and a shape of respective constituent members, their relative arrangement, etc., may be appropriately modified and should be understood that the scope of the present invention is not restricted thereto unless otherwise specified. 
   Embodiment 1 
     FIG. 7  shows a general structure of an image forming apparatus according to this embodiment. 
   Referring to  FIG. 7 , this image forming apparatus  51  (a laser beam printer in this embodiment) is an apparatus in which a latent image is formed on an electrophotographic photosensitive member  1  in the form of a drum (hereinafter referred to as a “photosensitive drum”) by irradiating the photosensitive drum  1  with a laser beam based on image data by an optical system  52 , and the latent image is developed with a toner (not shown) to form a toner image on the photosensitive drum  1 . 
   Meanwhile, a sheet material S is placed in a sheet feeding cassette  55  and is conveyed to a main assembly of the apparatus  51  by picking up the sheet material S sheet by sheet by means of a sheet feeding mechanism including a pickup roller  56 , a feed roller  57  and a retard roller  58 . The sheet material S fed by the feeding mechanism is conveyed from a pair of conveyer rollers  59  to a pair of resister rollers  60  to align the sheet material S in order, and is conveyed to a transfer portion. At the transfer portion, the toner image formed on the above-mentioned photosensitive drum  1  is transferred onto the sheet material S by a transfer roller  61  as a transfer means. The sheet material S is then conveyed to a fixing means by guiding it on a guiding plate  62 . The fixing means includes a pressure roller  63  and a fixing roller  64  containing a heater, and applies heat and pressure to the sheet material S which passes through the fixing means, so that the toner image having been transferred onto the sheet material S is fixed to the sheet material S. The sheet material S is conveyed farther by a pair of discharging rollers  65  to be discharged into a discharge portion  66  through a reversing path. Incidentally, the image forming apparatus  51  is capable of manually feeding the sheet material by manual feed tray and rollers (not shown). 
   Next, a process cartridge  67  detachably mountable to the image forming apparatus  51  described above will be explained with reference to  FIG. 6 , which illustrates a general structure of the process cartridge  67  used in this embodiment. 
   The process cartridge  67  includes a photosensitive drum  1  and at least one process means. Examples of the process means may include a charging means  2  for charging the surface of the photosensitive drum  1 , a developing means (developing apparatus)  4  for forming a toner image on the photosensitive drum  1 , and cleaning means  11  for removing a toner remaining on the photosensitive drum  1 . 
   As shown in  FIG. 6 , the process cartridge according to this embodiment includes, around the photosensitive drum  1 , the charging member  2 , the developer device frame  12 , the developing means including the developing sleeve  5  as an image bearing member and a developing blade  9   d , and the cleaning means  11 . These process means is covered with a housing which is formed by a frame to be integrally supported to provide a cartridge, which is detachably mounted to a main assembly of the image forming apparatus (not shown). 
   Hereinbelow, the developing means  4  according to this embodiment will be described. 
   The developing sleeve  5  include a magnetic roller  6  therein is rotatably mounted to the developing device frame  12  through a sleeve bearing (not shown). A toner supplied from the developing device frame  12  is attached to the surface of the developing sleeve  5  by a magnetic force of the magnetic roller  6  and is regulated to have a uniform thickness by the developing blade  9   d  which comprises a rubber blade and a D blade plate as a supporting plate for supporting the rubber blade. Thereafter, the toner is conveyed to a position opposite from a latent image on the photosensitive drum  1  by rotation of the developing sleeve  5  and is attached to the latent image to effect development. 
   Further, the developing means  4  is provided with a magnetic seal member  71  at both end portions of the developing sleeve  5  in a longitudinal direction of the developing sleeve  5  as shown in (d) of FIG.  5 . The magnetic seal member  71  is disposed with a gap g with respect to the peripheral surface of the developing sleeve  5  and is mounted to the developing device frame  12 . The magnetic seal member  71  is prepared by bonding a magnetic plate (magnetic member)  74  to a magnet  73  at an outer side surface thereof in a width direction of the magnet  73 . 
   Next, the magnetic seal member  71  used in this embodiment will be described in detail. 
   The magnetic seal member  71  has a shape as shown in FIG.  1 . Referring to  FIG. 1 , the magnetic seal member  71  includes a magnet (arcuate portion)  73  which is an injection-molded product having a width of 3.4 mm and comprising a nylon binder which contains a magnetic powder of Nd—Fe—B, and a 0.6 mm-thick magnetic plate  74  formed of an SUS (stainless steel) material. As described hereinafter, the magnetic seal member  71  includes the magnetic plate disposed at the side surface of the magnet  73  and a magnetic plate which is extended linearly from the upper (top) end portion and is integral with the magnetic plate on the side of the magnet  73 . These magnetic plates are formed by bending a single magnetic plate. The thus bending-treated magnetic plate and the magnet are integrally molded in one piece to constitute the magnetic seal member. The gap g between a developing sleeve  5  and the magnetic seal member  71  is 0.1-0.7 mm (as shown in (d) of FIG.  5 ). At that time, a magnetic flux density at the surface of the developing sleeve  5  given by magnetic force of the magnetic seal member  71  is about 1000-2000 Gs. Further, with respect to a positional relationship between the magnet  73  and the magnetic plate  74  disposed at its side surface, the magnet  73  is disposed on a side closer to an opening  26  of a developing device frame  12 , and the magnetic plate  74  is disposed on a side opposite from the side closer to the opening  26  (i.e., an outer side surface of the magnet in a longitudinal direction of the developing sleeve) at a portion extending from an arcuate portion  71   a  of the magnetic seal member  71  to a linear portion  71   b  above the arcuate portion  71   a . Further, at a portion  74   c  (extending away from the peripheral surface of the developing sleeve) located above and other than the portions to be opposite to the developing sleeve  5 , there is no magnet  73 , and as shown in  FIG. 1 , the magnetic seal member  71  is formed only of the magnetic plate  74  at the portion  74   c . The portion  74   c  (other than the portions to be opposite to the developer sleeve  5 ) has a function of positioning the above-mentioned magnetic seal member  71  relative to the above-mentioned developing device frame  12 . The portion  74   c  includes a bent engage portion  74   c   1  for performing the positioning of the magnetic seal member  71  in a substantially vertical direction in  FIG. 5  relative to the frame  12  (at its upper and lower end surfaces), and an abutting surface  74   c   2  for performing the positioning in a substantially horizontal direction in  FIG. 5  by abutment with the D blade plate  9   d   1  (for supporting the developing blade). 
   The bent engage portion  74   c   1  is located in a position where it does not abut to the supporting plate  9   d   1  of the developing plate  9   d . More specifically, the bent engage portion  74   c   1  is located in a depressed position relative to the abutting surface  74   c   1 . By doing so, a positional relationship of the abutting surface  74   c   2  with other portions becomes clear, so that a surface accuracy of the abutting surface is readily ensured. In this regard, if the bent engage portion  74   c   1  and the abutting surface  74   c   2  are at the same level in the horizontal direction, it is necessary to design an angle between a flat surface  12 : of the frame  12  for positioning the supporting plate  9   d   1  of the developing blade  9   d  and an upper end surface  72   g  (which determines a position of the magnetic seal member in a substantially vertical direction by abutment thereof with the upper end surface of the bent engage portion  74   c   1 ) of an engage (mounting) groove  72  (of the frame  12 ) for engaging the magnetic seal member therein, to be a right angle. As a result, the magnetic seal member  71  is not readily engaged into the frame  12 . However, as in this embodiment, the bent engage portion  74   c   1  is designed to be in a depressed position relative to the abutting surface  74   c   2 , whereby it is possible to locate the upper end surface  72   g  of the groove  72  away from the mounting flat surface  12   i  of the developing blade  9   d . As a result, it is possible to form an oblique surface at a corner as shown in (a) of  FIG. 5 , thus facilitating engagement of the magnetic seal member  71  with the frame  12 . 
   Further, the portions of the magnetic seal member  71  to be opposite to the developing sleeve  5  are disposed so that the magnet is on the (inner) side closer to the opening  26  of the developing device frame  12  and the magnetic plate  74  is on the (outer) side opposite from the side closer to the opening  26 . Accordingly, magnetic lines  24  of force are formed between the magnet  73  and the magnetic plate  74 , as shown in  FIG. 3 , and enter the magnetic plate  74  which has a high (magnetic) permeability. As a result, it is possible to prevent generation of magnetic lines of force extending out from a width of the magnetic seal member  71 . Further, the generated magnetic lines of force are concentrated at the magnetic plate  74 , so that a resultant magnetic flux density at the surface of the magnet  73  is increased, thus creating a large magnetic force. As a result, a sealing performance of the magnetic sealing member  71  is improved. 
   Next, a method of mounting and positioning the magnetic sealing member  71  will be described. 
   As shown in  FIG. 2 , on an outer peripheral surface side (back side) of the magnet  73  and the magnetic plate  74 , an elastic lining  77  of an elastic material is disposed. The elastic lining  77  has a width, in a longitudinal direction of the developing sleeve  5 , which is substantially equal to a total of widths of the magnet  73  and the magnetic plate  74 . Further, as shown in  FIG. 1 , the elastic lining  77  is disposed so that its lower (bottom) end surface on an outer side in the longitudinal direction of developing sleeve  5  (right-hand side on the figure) covers a lower end surface  71   f  of the magnetic seal member and a lower end surface  77   f  on an inner side (left-hand side on the figure) and the lower end surface  71   f  of the magnetic seal member are substantially in one plane. On the other hand, referring again to  FIG. 2 , an upper (top) end surface  77   g  of the elastic lining  77  is located at a position somewhat below an upper end surface  73   g  of the magnetic plate  74 . The elastic lining  77  is applied to the backside of the magnet  73  and the magnet plate  74  with a double-faced (adhesive) tape. 
   Further, the developing device frame  12  is provided with a mounting groove  72  for mounting the magnetic seal member  71 , which groove extending from a flat surface  12   i  to an arcuate surface  12   j  as shown in FIG.  4 . The mounting groove  72  has a shape shown in  FIG. 5 , and the shape corresponds to the cross section of the magnetic seal member  71 , so that the elastic lining  77  exhibits the same compression amount over its entire area (with respect to the arcuate portion  71   a  and the linear portion  71   b  of the magnetic seal member  71  and the positioning portion  74   c  of the magnetic plate  74 . Further, as shown in  FIG. 4 , at an entrance of the mounting groove  72  (positioning groove  72   d ) as an entering portion for the positioning portion  74   c , a relatively large C surface (oblique surface) is provided so as to permit easy entrance of the upper end surface (a first positioning portion for positioning the magnetic seal member relative to the frame in a substantially vertical direction) of the positioning portion  74   c  of the magnetic seal member  71  into the upper end surface  72   g  of the groove  72 . 
   As shown in (a) of  FIG. 5 , the magnetic seal member  71  is engaged into the mounting groove  72  (for mounting the magnetic seal member  71 ) of the developing device frame  12  as indicated by an arrow. Then, an arcuate portion  71   a  of the magnetic seal member  71  is fitted into an arcuate groove  72   a , and a linear surface portion  71   b  of the magnetic seal member  71  is fitted into a linear groove  72   b , as shown in (b) of FIG.  5 . At this time, a boundary portion  71   n  ( FIG. 1 ) between the linear portion  71   b  and the positioning portion  74   c  of the magnetic plate  74  is an oblique surface, thus resulting in smooth mounting in the mounting groove  72  at the time of assembly. When the magnetic seal member  71  is lightly pressed in a direction of an arrow A, a lower portion  77   a  ( FIG. 2 ) of the elastic lining  77  is compressed. At the same time, the lower end surface  71   f  of the magnetic seal member  71  presses the lower end abutting portion  72   f , and the bent engage portion  74   c   1  of the positioning portion  74   c  of the magnetic seal member  71  is flush with the groove  72   d . Accordingly, when the abutting surface  74   c   2  (a second positioning portion for positioning the magnetic seal member relative to the frame in the insertion direction) of the magnetic seal member  71  is pushed toward the rear side in the direction (right-hand direction, i.e., insertion direction) crossing the arrow A, the magnetic seal member  71  is engaged with the groove  72  as shown in (c) of FIG.  5 . 
   At the time of the pressing, a heavier load than that at the time of actual operation is applied to the magnetic seal member  71 . In order to pass the bent engage portion  74   c   1  of the positioning portion  74   c  of the magnetic seal member  71  to the entrance to the groove  72   d , the lower portion  77   a  of the elastic lining  77  has to be compressed when compared with the time of actual operation. 
   Particularly, in the case of the conventional magnetic seal member  71 ′, the magnetic seal member  71 ′ does not enter the groove  72   d  if it is further pressed downwardly from the state of (b) of FIG.  11 . However, in the case of the conventional magnetic seal member, a load is liable to be applied to the magnet portion of the magnetic seal member to damage the magnetic seal member. 
   On the other hand, in this embodiment, the bent engage portion  74   c   1  is thin and is liable to enter the groove  72   d  due to the C surface provided to the entrance of the groove  72   d . In addition, the positioning portion  74   c  of the magnetic seal member  71  is a thin plate of SUS (stainless steel), thus being capable of being somewhat elastically deformed to be expected to improve an assembling performance. Further, the load applied to the magnetic portion  73  of the magnetic seal member  71  is reduced when compared with the conventional magnetic seal member  71 ′. Incidentally, the degree of the elastic deformation of the positioning portion  74   c  of the magnetic seal member  71  is minute and the load applied to the magnetic seal member  71  becomes smaller after the mounting, so that an amount of the deformation of the positioning portion  74   c  after the mounting is negligible. 
   Then, a developing blade  9   d  is mounted to the developing device frame  12 . When a plate  9   d   1  of the developing blade  9   d  is closely contacted to the flat (bearing) surface  12   i  of the developing device frame  12 , the abutting surface  74   c   2  of the positioning portion  74   c  is pressed by the plate  9   d   1  of the developing blade  9  as shown in (c) of  FIG. 5 , whereby the bent engage portion  74   c   1  of the positioning portion  74   c  of the magnetic seal member  71  is pressed into the groove  72   d . This rotates the upper portion of the magnetic seal member  71  about the lower end surface  71   f , so that the elastic lining  77  is compressed rearwardly. The reaction force thereof is received by the lower end abutting portion  72   f  of the groove  72  of the developing device frame  12  to which the lower end surface  71   f  of the magnetic seal member  71  is contacted and by the plate  9   d   1  to which abutting surface  74   c   2  of the magnetic plate  74  is contacted. Then, a developer roller unit G is mounted. This is shown in (d) of FIG.  5 . 
   As a result, the magnetic seal member  71  is held by the mounting groove  72  (for mounting the magnetic seal member  71 ) provided in the developing device frame  12  and the abutting surface  74   c   2  of the magnetic plate  74  is pressed by the plate  9   d   1  of the developing blade  9   d , thus being correctly positioned. 
   As described above, in this embodiment, the magnetic seal member  71  is formed of the magnetic plate  74 , not the magnet  73  at the portion other than the portion (the arcuate portion) to be opposite to the peripheral surface of the developing sleeve  5 , so that the amount of use of expensive magnet can be decreased to cut down on costs. 
   Further, in this embodiment, a part of (the magnetic plate of) the magnetic seal member, i.e., the portion other than the portion opposite to the developing sleeve  5 , is designed to be elastically deformable, thus improving the assembling performance. In addition, a probability of breakage of the magnetic seal member by the load applied at the time of the assembling is smaller than the case of the conventional magnetic seal member. 
   Incidentally, in this embodiment, the magnetic plate  74  located or the outer side of the magnet  73  is integral with the magnetic plate of the positioning portion since a single magnetic plate is subjected to bending to provide such magnetic plate portions. However, the magnetic plate  74  may be one which is not integral with the magnetic plate of the positioning portion. 
   [Other Embodiments] 
   In the above embodiment, as the process cartridge detachably mountable to the main assembly of the image forming apparatus, the process cartridge including the photosensitive drum and process means, acting on the photosensitive drum, which includes the charging means, the developing means and the cleaning means, integrally supported together with the photosensitive drum, is described but it is possible to employ a process cartridge including, in addition to the photosensitive drum and the developing means, either one of the charging means and the cleaning means. 
   Further, in the above embodiment, the process cartridge including the photosensitive drum, detachably mountable to the image forming apparatus main assembly but it is possible to independently mounting the respective constitutional components (means) to the image forming apparatus or such constitutional components may be those independently detachably mountable to the image forming apparatus. 
   Further, the image forming apparatus is the printer in the above embodiment but is also applicable to other image forming apparatus such as a copying machine, a facsimile apparatus and multiple function processing machine including functions of the copying machine and the facsimile apparatus. 
   Furthermore, the present invention is not limited to the above described embodiments, and variations and modifications may be made within the scope of the present invention.