Patent Publication Number: US-7593666-B2

Title: Developing device with overlapping sealing members with reduced thicknesses

Description:
FIELD OF THE INVENTION 
   The present invention relates to a development device used for an image forming apparatus of an electrophotographic type, and particularly relates to a development device that prevents leakage of toner from a gap between members provided in the development device. 
   BACKGROUND OF THE INVENTION 
   In an image forming apparatus of an electrophotographic type, toner is stored in a development device constructing a process unit, transported from a supply roller to a development roller of the development device, and supplied to a photoreceptor drum through the development roller. A section that performs toner supply to the photoreceptor drum is arranged with an opening of the development device so as to supply toner toward outside from inside of the development device. Such a section or region that performs toner supply to a photoreceptor drum through a development roller is hereinafter referred to as a development region. 
   It is required to efficiently supply toner to a photoreceptor drum in a development region, while leakage of toner from other sections must be avoided because toner splash affects the exposure optical path and causes contamination of the inside of an image forming apparatus, including a charger. Therefore, sealing is applied to gaps of a development device, from which toner is preferably prevented from leaking. 
   In many cases, gaps formed between components of a development device have complicated shapes. Accordingly, in order to seal such sections, members for sealing (hereinafter, also referred to as sealing members) to fit a complicated shape are required. In such a situation, sealing members are forced to have a complicated shape. Forming such a sealing member into one body increases the difficulty of making the sealing member, and further, it becomes difficult to incorporate it to a portion of a gap, from which leakage of toner is to be avoided. Accordingly, it is practical to produce several divided sealing members, incorporate the sealing members in a combination at a desired section of a development device, and thus sealing is done. 
   As examples of concrete technologies for the purpose of prevention of toner leaking to outside of a process unit, Patent Document 1 (Japanese Patent Publication TOKKAI No. H11-316500) discloses a technology in which a protrusion is provided at a portion where a side seal and bottom seal of a development roller are superposed with each other, and Patent Document 2 (Japanese Patent Publication TOKKAI No. 2000-75656) discloses a technology which specifies the shape of an end portion of a lower seal in a region where a development roller and a side seal are superposed with each other. 
   However, the above development device, having a structure which is sealed such that several divided sealing members in a combination are incorporated at a desired section of the development device, may be insufficiently prevented from toner leakage at the jointing section of the combined sealing members. In other words, a structure in which end surfaces of the sealing members are brought into contact with each other tends to cause a gap between end surfaces of the sealing members that are brought into contact with each other, and accordingly toner leaks through the gap once it is generated. 
   Further, even in a case where a structure with superposed sealing members in a combination at the jointing section is employed so as to prevent generation of a gap between end surfaces of sealing members at the jointing section, a step may be generated at the boundary section of the superposed sealing members, and toner may leak through the step. As described above, for a structure for sealing by incorporating a combination of several divided sealing members at a desired section of a development device, sealing members can be easily produced and incorporated, but there is still a problem to be solved for prevention of toner leakage. 
   An object of the present invention is to provide a development device having a structure for sealing at a desired section of the development device by incorporating a combination of several divided sealing members so as to prevent leakage of toner from the jointing section of the sealing members. 
   SUMMARY OF THE INVENTION 
   To solve problems, as described above, in an aspect of the present invention, there is provided a development device, including: 
   a plurality of soft members, 
   wherein at least one of the plurality of soft members has an end portion having a shape section of which width is smaller toward a tip end of the end portion; 
   and wherein the end portion is placed on another one of the soft members. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an entire view of an image forming apparatus in which a development device in accordance with an embodiment of the present invention is incorporated; 
       FIG. 2  is a cross-sectional view showing the schematic structure of a development device as an example in the present embodiment of the invention; 
       FIG. 3  is a conceptual view of the development position of the development device in accordance with the present embodiment of the invention, viewed from the photoreceptor drum side; 
       FIGS. 4   a  and  4   b  are diagrams showing the details of a sealing member A; 
       FIGS. 5   a  and  5   b  are diagrams showing the details of a sealing member B; 
       FIGS. 6   a  and  6   b  are diagrams showing the details of a sealing member C; 
       FIGS. 7   a  to  7   c  are diagrams illustrating the shapes of the sealing members A and B at the A-B superposing section; and 
       FIGS. 8   a  to  8   c  are diagrams illustrating the shapes of the sealing members A and C at the A-C superposing section. 
   

   DETAIL DESCRIPTION OF THE PREFERRED EMBODIMENT 
   In the present invention, soft members are used as sealing members of a development device. For sealing with a combination of these members, at least one of the soft members has an end portion which has a shape section having a width smaller toward the tip end, and this end portion is placed on another soft member to make sealing. Thus, it is possible to provide a development device, wherein toner leakage from jointing sections of the sealing members and jointing sections of other members of the development device is prevented, neither contamination in the apparatus nor image contamination occurs in image recording, and stable printing is realized. 
   The present invention relates to a development device employing a plurality of soft members, wherein a gap formed between the members is sealed. The inventor has considered a method which prevents generation of a step which may be generated when soft members are superposed. The inventor paid attention to the fact that when a soft member is pressed, as the pressed area of the member is smaller, the compressed amount of the member is larger and the volume of the member becomes smaller. Consequently, the inventor determined that a soft member and another soft member can be jointed, without causing a step therebetween, by making the contact area between the soft members in a region of superposing the soft members be small, and thus devised the present invention. 
   A soft member referred to in the present invention is one that is elastically deformed with a center at the position where a force is applied, and returns to the original shape when the force is released. Soft polyurethane foam (hereinafter, also referred to as soft urethane foam) is a representative with specific commodities of, for example, “Moltplane produced by INOAC Corporation” and “Superseal WG produced by NHK Spring CO., Ltd.”. Other soft members applicable to the present invention include urethane eslastomer and rubber sponge, which is available in the market. Specific commodities of urethane elastomer are, for example, “G mat produced by Trusco Nakayama Corporation) and “Geltape produced by GELTECH Co., Ltd.” 
   Characteristics of a soft member can be quantified by measuring hardness, rebound resilience, and the like. Herein, measurement of the hardness of a soft member is, for example, carried out, in accordance with D method of JIS K 6400 (obtaining hardness under a constant compression of 25%) using a compression testing machine for urethane foam. D method of JIS K 6400 defines the value of hardness by the force (unit; Newton) required to compress a urethane foam of a disk shape with a diameter of 200 mm, by 25% from the original thickness. The measurement method by D Method of JIS K 6400 is carried out in the following procedure.
         (1) To dispose a test piece on a testing table at the center.   (2) To press a pressing plate against the test piece, read the thickness of the test piece by a unit of 0.1 mm when a predetermined force specified by D Method of JIS K 6400 is applied, and define the thickness as the initial thickness of the test piece.   (3) To press the pressing plate at a speed of 100±20 mm/min to the thickness of 75±2.5% of the initial thickness of the test piece and then instantly release the pressing plate.   (4) To press the pressing plate at a speed of 100±20 mm/min to the thickness of 25±1% of the initial thickness of the test piece, and maintain a static state.   (4) To read the value of the force at the time when 20 seconds have elapsed since the start of the static state, and define this value as “hardness”.       

   The thickness of each soft member returns to a range of 40% to 100% of an original thickness, after a hardness of the soft member is measured by D Method of JIS K6400. 
   For measurement of a soft member, it is possible to use a testing device for soft foam, such as “automatic hardness testing machine AF-200 type (product of KOUBUNSHI KEIKI CO., Ltd.)”. 
   The hardness applicable to the present invention is preferably in the range of 10 to 400 N. Adopting a soft member in this range of hardness achieves both a sufficient sealingness and forming of a smooth superposition at the superposition section. 
   Further, it is possible to quantify the characteristics of a soft member applicable to the present invention, by measuring the rebound resilience. Herein, the rebound resilience is, for example, a measure indicating the energy that a soft member absorbs when it receives a shock load, and is measured with a Ryupke type rebound resilience testing machine in accordance with JIS K 6255 (Testing methods of rebound resilience for vulcanized rubber or thermoplastic), for example. Concrete Ryupke type rebound resilience testing machines are, for example, “No. 200 type testing machine produced by YASUDA-SEIKI-SEISAKUSHO Ltd.” and “VR-6500 series produced by UESHIMA SEISAKUSHO CO., Ltd.”. 
   An example of a full-color image forming apparatus that forms full-color images by the use of a development device in accordance with the present embodiment of the invention will be described, referring to  FIG. 1 . 
   Around a photoreceptor drum  10  rotationally driven in the full-color image forming apparatus, shown in  FIG. 1 , there are provided a charging brush  111  to uniformly charge the surface of a photoreceptor drum  10  to a predetermined electric potential, a cleaner  112  to wipe off toner remaining on the photoreceptor drum  10 , and the like. 
   Further, a laser scanning optical system  20  is provided that scan-exposes, with laser beams, the photoreceptor drum  10  charged by the charging brush  111 . The laser scanning optical system  20  is a known one and contains a laser diode, polygon mirror, and fθ optical device. Printing data is transmitted for yellow, Magenta, cyan, and black respectively, from a host computer to the control section of the laser scanning optical system  20 . The laser scanning optical system  20  outputs laser beams sequentially, based on the printing data for the respective colors, scan-exposes on the photoreceptor  10 , and thus sequentially forms static latent images on the photoreceptor drum  10  for the respective colors. 
   Further, a full-color development device  30  that performs development in full-color, supplying toners in respective colors to a photoreceptor drum  10  on which electrostatic latent images have been formed, is provided with development units  31 Y,  31 M,  31 C, and  31 Bk storing respective non-magnetic single component toners of yellow, magenta, cyan, and black, around a support shaft  33 . These development units  31 Y,  31 M,  31 C, and  31 Bk are rotated with the supporting shaft at the center, and guided to a position facing the photoreceptor drum  10 . 
   With regard to development units  31 Y,  31 M,  31 C, and  31 Bk of the full cooler development device  30 , toner restricting members are in press-contact with the circumferential surfaces of development agent carriers (development rollers)  32  that rotate and feed toner, as shown in  FIG. 1 . These toner restricting members restrict the amounts of toners fed by the development rollers  32  and charge the fed toners. Herein, the full color development device  30  may be provided with two toner restricting members for each development roller in order to properly restrict and charge toners fed by the development rollers. 
   Each time a respective electrostatic latent image is formed, as described above, on the photoreceptor drum  10  by the laser scanning optical system  20 , the full-color development device  30  is rotated around the support shaft  33 , as described above. Thus, each of development unit  31 Y,  31 M,  31 C, and  31 Bk storing the toners in the respective colors is sequentially guided to the position facing the photoreceptor drum  10 . A development roller  32  of each of development unit  31 Y,  31 M,  31 C, and  31 Bk is made contact with the photoreceptor drum  10 , and thus each charged toner in respective color is sequentially supplied onto the photoreceptor drum  10  on which each electrostatic latent image for the respective color has been formed, thus development being performed. 
   Still further, an intermediate transfer belt  40 , which is in an endless form and rotationally driven, is provided, as an intermediate transferor, at a position on the downstream side in the rotation direction of the photoreceptor drum  10  with respect to the full-color development device  30 . The intermediate transfer belt  40  is rotationally driven, synchronizing with the photoreceptor drum  10 . The intermediate transfer belt  40  is pressed by a rotatable primary transfer roller  41  to contact the photoreceptor drum  10 . Further, a secondary transfer roller  43  is rotatably provided at the position of a support roller  42  for supporting the intermediate transfer belt  40  so that a recording material S, such as a recording paper sheet, is pressed against the intermediate transfer belt  40  by the secondary transfer roller  43 . 
   Yet further, a cleaner  50  for wiping off toner remaining on the intermediate transfer belt  40  is provided attachably to and detachably from the intermediate transfer belt  40 , in a space between the full-color development device  30  and the intermediate transfer belt  40 . 
   Further, a sheet feeding unit  60  for guiding a recording material S, such as a plain paper sheet, to the intermediate transfer belt  40  is constructed with a sheet feeding tray  61  for storing recording material S, a sheet feed roller  62  for feeding the recording material S stored in the sheet feeding tray  61  one by one, and a timing roller  63  for conveying a recording material S having been fed, to the position between the intermediate transfer belt  40  and the secondary transfer roller  43 , in synchronization with an image formed on the intermediate transfer roller  40 . The recording material S having been conveyed to the position between the intermediate transfer belt  40  and the secondary transfer roller  43  is pressed against the intermediate transfer belt  40  by the secondary transfer belt  43  so that the toner image is transferred from the intermediate transfer belt  40  to the recording material S by pressing. 
   The recording material S to which the toner image has been transferred, as described above, is then guided to the fixing device  70  by a conveying unit  66  constructed with an air suction belt or the like. This fixing device  70  fixes the transferred toner image on the recording material S, and then the recording material S is ejected through a vertical conveying path  80  to the top surface of the apparatus main body  100 . 
   Now, operation of image forming in full-color by the use of this full-color image forming apparatus will be specifically described. 
   First, the photoreceptor drum  10  and the intermediate transfer belt  40  are rotationally driven at the same speed in the respective directions, and the photoreceptor  10  is charged by the charging brush  111  to the predetermined electric potential. 
   Then, the charged photoreceptor drum  10  is exposed by the laser scanning optical system  20  for a yellow image, and thereby an electrostatic latent image is formed for a yellow image. Then, charged yellow toner is supplied to the photoreceptor drum  10  by the toner restricting member, as described above, from the development unit  31 Y storing yellow toner so as to develop the yellow image. The intermediate transfer belt  40  is pressed, with the primary transfer roller  41 , against the photoreceptor drum  10  on which a yellow toner image has been formed by, and thereby the yellow toner image formed on the photoreceptor drum  10  is primarily transferred to the intermediate transfer belt  40 . 
   After the yellow toner image is transferred to the intermediate transfer belt  40  in such a manner, the full-color development device  30  is rotated around the support shaft  33 , and the development unit  31 M storing magenta toner is guided to the position facing the photoreceptor drum  10 . Same as in the case of the yellow image, the charged photoreceptor drum  10  is exposed by the laser scanning optical system  20  for a magenta image to form an electrostatic latent image, and the electrostatic latent image is developed by the development unit  31 M storing the magenta toner. The developed magenta toner image is primarily transferred from the photoreceptor drum  10  to the intermediate transfer belt  40 . Further, exposure, development, and primary transfer are sequentially performed, likewise, for a cyan image and black image, and accordingly yellow, magenta, cyan, and black toner images are sequentially superimposed on the intermediate transfer belt  40 , thereby forming a toner image in full-color. 
   When the black toner image, which is the last, has been primarily transferred onto the intermediate transfer belt  40 , the recording material S is conveyed to the position between the secondary transfer roller  43  and the intermediate transfer belt  40  by the timing roller  63 , and the recording material S is pressed by the secondary roller  43  against the intermediate transfer belt  40 . Thus, the full-color toner image having been formed on the intermediate transfer belt  40  is secondarily transferred to the recording material S. 
   When the full-color tone image has been secondarily transferred onto the recording material S in such a manner, the recording material S is guided to the fixing device  70  by the conveying unit  66 , described above, and the transferred full-color toner image is fixed by the fixing device  70  onto the recording material S. Then, the recording material S is ejected through the vertical conveying path  80  onto the top surface of the apparatus main body  100 . 
   Now, the development device in accordance with the present invention will be described. 
   As described above, the image forming apparatus in the present embodiment of the invention is provided with four development units  31 Y,  31 M,  31 C and  31 Bk having the same structure. The four development units  31 Y,  31 M,  31 C and  31 Bk are respectively provided with development rollers  32 Y,  32 M,  32 C and  32 Bk, and store toners in respective different colors of yellow, magenta, cyan and black in containers formed in a combination of plural hard members. The respective development rollers  32 Y,  32 M,  32 C and  32 Bk are made contact with the photoreceptor drum  10  on which electrostatic latent images of the respective colors have been sequentially formed by the laser scanning optical system  20 , and toners in the respective colors are sequentially supplied to perform development. It is required to efficiently supply toner through the respective development rollers  32 Y,  32 M,  32 C and  32 Bk to the photoreceptor drum, from the section, namely development region, that supplies the toners in the respective colors stored in the development units  31 Y,  31 M,  31 C and  31 Bk. Herein, leaking of toner from a section other than the development section, without through the development rollers  32 Y,  32 M,  32 C and  32 Bk, must be prevented, because toner having leaked spatters to affect the exposure optical path and causes contamination of the inside of the image forming apparatus. Each of development units  31 Y,  31 M,  31 C and  31 Bk is formed in a combination of plural hard members, and the jointing section of the plural hard members is subjected to sealing, provided with soft members, so as to prevent leakage of toner. 
     FIG. 2  is a schematic diagram showing the cross-section of the development unit  31 Y as a usable example of the four development units  31 Y,  31 M.  31 C and  31 Bk of the full-color development device  30 .  FIG. 2  shows the state where the full-color development device  30  has rotated, and the development unit  31 Y is guided to the position facing the photoreceptor drum  10 . The structure of the development units will be described below, taking an example of the development unit  31 Y. However, as described above, since the development units  31 Y,  31 M,  31 C and  31 Bk have the same structure, description of the other development units  31 M,  31 C and  31 Bk will be omitted. In the following description, members and structures common to the development units  31 Y,  31 M,  31 C and  31 Bk will be represented by numeric symbols, wherein in order to represent members and structures of the development units  31 Y,  31 M,  31 C and  31 Bk, characters Y, M, C and Bk will be added following the numeric symbols representing the common members and structures. 
   In  FIG. 2 , the development roller  32 Y is located at the position facing the photoreceptor drum  10 . The container  34 Y of the development unit  31 Y is constructed with plural hard members. Yellow toner is stored in the container  34 Y, and supplied from an opening of the container  34 Y in the development region through the development roller  32 Y to the photoreceptor drum  10 . The sealing member A, represented by  35 Y, corresponds to a soft member referred to in the present invention, and prevents leakage of toner from the lower part, in the figure, of the development unit  31 Y. Further, the sealing member B, represented by  36 Y, corresponds to a soft member referred to in the present invention, and prevents leakage of toner from an end portion of the development roller  32 Y of the development unit  31 Y. Further, a sealing member C ( 37 Y), is arranged at the other end portion of the development roller  32 Y. Accordingly, the sealing member B ( 36 Y) and sealing member C ( 37 Y) prevent toner leakage from the vicinity of the development region of the development roller  32 Y. 
   The sealing members A, B and C will be described later in more details. 
   A lower part press member  38 Y formed of a hard material is a press member to fix the sealing members A, B and C to the development unit container  34 Y. The lower part press member  38 Y is screw fixed at a predetermined position of the development unit container  34 Y with plural screws, not shown, and sandwiches the sealing members A, B and C with the development unit container  34 Y to fix them. The AB superposition, shown in  FIG. 2 , is a section where the sealing members A and B are superimposedly sandwiched by the lower part press member  38 Y and the development unit container  34 Y. Likewise, on the front side in the perpendicular direction with respect to the page of  FIG. 2 , located is AC superposition, not shown in  FIG. 2 , where the sealing members A and C are superimposedly sandwiched by the lower part press member  38 Y and the development unit container  34 Y. 
   Herein, the sealing members A, B and C, corresponding to soft members referred to in the present invention, will be described further in details, referring to  FIGS. 3   a  to  3   d .  FIG. 3   a  is a fragmental conceptual view of the development unit  31 Y in the present embodiment, viewed from the side of the photoreceptor drum  10 . The development unit  31 Y in the present embodiment is provided with the sealing member A ( 35 Y), the sealing member B ( 36 Y), and the sealing member C ( 37 Y). The sealing member A ( 35 Y) prevents leakage of toner from the lower position, in the figure, of the development roller  32 Y. The sealing members B ( 36 Y) and C ( 37 Y) prevent leakage of toner from the left and right end portions, in the figure, of the development roller  32 Y. The back side, in the perpendicular direction with respect to the page sheet, of the sealing members B ( 36 Y) and C ( 37 Y) are respectively fixed to the development unit container  34 Y. The sealing member B ( 36 Y) and sealing member C ( 37 Y) are not fixed to the development unit container  34 Y at the AB superposition and the AC superposition. At the AB superposition and AC superposition, the end portions of the sealing member A ( 35 Y) are respectively inserted between the sealing member B ( 36 Y) and the development unit container  34 Y and between the sealing member C ( 37 Y) and the development unit container  34 Y to be superposed. The sealing member A ( 35 Y) is fitted to the development unit container  34 Y in a state where the left and right end portions of the sealing member A ( 35 Y) are respectively superposed with the sealing member B ( 36 Y) and the sealing member C ( 37 Y) and sandwiched by the lower part press member  38 Y and the development unit container  34 Y. Herein, the lower part press member  38 Y and the development unit container  34 Y hold the sealing members A, B and C being soft members, and are hard members referred to in the present invention. 
   In  FIG. 3   b , the development roller  32 Y is removed from  FIG. 3   a . Further, in  FIG. 3   c , the lower part press member  38 Y is removed from  FIG. 3   b . Still further, in  FIG. 3   d , the sealing members B ( 36 Y) and C ( 37 Y) are removed from  FIG. 3   c . As shown in  FIGS. 3   b ,  3   c , and  3   d , the sealing members B ( 36 Y) and C ( 37 Y) are fitted, with the respective end portions superposed with the sealing member A ( 35 Y). The AB superposition, shown in  FIG. 3   c , is the position where the sealing member A ( 35 Y) and sealing member B ( 36 Y) superpose with each other, and the AC superposition, shown in  FIG. 3   c , is the position where the sealing member A ( 35 Y) and sealing member C ( 37 Y) superpose with each other. The both end portions of the sealing member A ( 35 Y) are superposed respectively with the sealing member B ( 36 Y) at the AB superposition and with the sealing member C ( 37 Y) at the AC superposition, and thus incorporated to a predetermined position and fixed by the lower part press member  38 Y. Thus, the sealing members A ( 35 Y), B ( 36 Y), and C ( 37 Y) are sandwiched by the lower par press member  38 Y and the development unit container  34   y  at the AB superposition and AC superposition in a pressed state. 
   Now, the respective sealing members and the shapes of the respective sealing members at the superpositions will be described in details. 
     FIGS. 4   a  and  4   b  are diagrams showing the details of the sealing member  35 Y. The sealing member A ( 35 Y) is formed of a soft polyurethane foam of which hardness is 100 N by D method of JIS K 6400. As shown in  FIG. 4   a , the sealing member A ( 35 Y) is provided with A- 1  section and A- 2  section respectively at the left and right ends as end portions, shown in the figure, wherein the A- 1  and A- 2  sections have shape sections that the widths of the shape sections become smaller toward the tip end with a plurality of tapered segments. The A- 1  and A 2  sections have two shape sections, which are later called triangle shaped sections, with plural tapered segments. Herein, the number of the triangle shaped sections is not limited to two, and is preferably greater than one, namely, plural. Further, the angles of the vertexes of the plural triangle shapes at the end portions of the soft member are preferably in a range from 25 to 150 degrees. As shown in  FIG. 4   b , it is assumed that the angles of the vertexes of the plural triangle shapes that form plural tapered segments at the A- 1  section of the sealing member A ( 35 Y) are respectively θ A-1-1  and θ A-1-2 , and the angles of the vertexes of the plural triangle shapes that form plural tapered segments at the A- 2  section of the sealing member A ( 35 Y) are respectively θ A-2-1  and θ A-2-2 . With regard to the sealing member A ( 35 Y) in the present embodiment of the invention, the angles θ A-1-1  and θ A-1-2  of the vertexes of the triangle shapes of the A- 1  section are both 27 degrees, and the angles θ A-2-1  and θ A-2-2  of the vertexes of the triangle shapes of the A- 2  section are both 27 degrees. This structure corresponds to Inventive Example 1 in a confirmation test described later. 
     FIGS. 5   a  and  5   b  are diagrams showing the details of the sealing member B ( 36 Y). The sealing member B ( 36 Y) is formed of a soft polyurethane foam with a hardness of 100 N in accordance with D method of JIS K 6400.  FIG. 5   a  is an entire view of the sealing member B ( 36 Y), and  FIG. 5   b  is a fragmental enlarged view of it. As shown in  FIG. 5   a , the sealing member B ( 36 Y) has an end portion, namely B- 1  section, having shape sections, on the lower side in the figure, that form plural tapered segments and becoming thinner toward the tip end. The B- 1  section is provided with two triangle shaped sections that form plural tapered segments. Herein, the number of the triangle shaped sections at an end of the soft member is not limited to two, and is preferably greater than one, namely plural. Further, the angles of the vertexes of the plural triangle shapes at the end portion of the soft member are preferably in a range from 25 to 150 degrees. As shown in  FIG. 5   b , it is assumed that the angles of the vertexes of the plural triangle shapes that form plural tapered segments at the B- 1  section of the sealing member B ( 36 Y) are respectively θ B-1-1  and θ B-1-2 . With regard to the sealing member B ( 36 Y) in the present embodiment of the invention, the angles θ B-1-1  and θ B-1-2  of the vertexes of the triangle shapes of the B- 1  section are both 30 degrees. Herein, this structure corresponds to Inventive Example 1 in the later described confirmation test. 
     FIGS. 6   a  and  6   b  are diagrams showing the details of the sealing member C ( 37 Y). The sealing member C ( 37 Y) is formed of a soft polyurethane foam with a hardness of 100 N in accordance with D method of JIS K 6400.  FIG. 6   a  is an entire view of the sealing member C ( 37 Y), and  FIG. 6   b  is a fragmental enlarged view of it. As shown in  FIG. 6   a , the sealing member C ( 37 Y) has an end portion, namely C- 1  section, having shape sections, on the lower side in the figure, that form plural tapered segments and becoming thinner toward the tip end. The C- 1  section is provided with two triangle shaped sections that form plural tapered segments. Herein, the number of the triangle shaped sections at an end of the soft member is not limited to two, and is preferably greater than one, namely plural. Further, the angles of the vertexes of the plural triangle shapes at the end portion of the soft member are preferably in a range from 25 to 150 degrees. As shown in  FIG. 6   b , it is assumed that the angles of the vertexes of the plural triangle shapes that form plural tapered segments at the C- 1  section of the sealing member C ( 37 Y) are respectively θ C-1-1  and θ C-1-2 . With regard to the sealing member C ( 37 Y) in the present embodiment of the invention, the angles θ C-1-1  and θ C-1-2  of the vertexes of the triangle shapes of the C- 1  section are both 30 degrees. Herein, this structure corresponds to Inventive Example 1 in the later described confirmation test. 
     FIGS. 7   a  to  7   c  are diagrams showing shapes of the sealing member A ( 35 Y) and sealing member B ( 36 Y) at the AB superposition, which is one of the superpositions.  FIG. 7   a  is a top view of showing a state where the sealing member A ( 35 Y) and sealing member B ( 36 Y) are superposed with each other. As shown in  FIG. 7   a , the end portion A- 1  of the sealing member A ( 35 Y) and the end portion B- 1  of the sealing member B ( 36 Y) are superposed with each other at the AB superposition.  FIG. 7   b  is a cross-sectional view of the sealing member B ( 36 Y) with respect to a cross-section X-X passing through the vertex of one of the triangles at the tip end of the end portion B- 1 . As shown in  FIG. 7   b , the sealing member A ( 35 Y) and sealing member B ( 36 Y) are pressed at the AB superposition by the lower part press member  38 Y to be compressed such that the vertexes of the triangles at the end portion B- 1  of the sealing member B ( 36 Y) is at substantially the same height as the surface of the sealing member A ( 35 Y), causing no step at the superposition.  FIG. 7   c  is a cross-sectional view of the sealing member A ( 35 Y) with respect to a cross-section Y-Y passing through the vertex of one of the triangles at the tip end of the end portion A- 1 . As shown in  FIG. 7   c , the sealing member A ( 35 Y) and sealing member B ( 36 Y) are pressed at the AB superposition by the lower part press member  38 Y to be compressed such that the vertexes of the triangles at the end portion A- 1  of the sealing member A ( 35 Y) are at substantially the same height as the surface of the sealing member B ( 36 Y), causing no step at the superposition. 
     FIGS. 8   a  to  8   c  are diagrams showing shapes of the sealing member A ( 35 Y) and sealing member C ( 37 Y) at the AC superposition, which is one of the superpositions.  FIG. 8   a  is a top view of showing a state where the sealing member A ( 35 Y) and sealing member C ( 37 Y) are superposed with each other. As shown in  FIG. 8   a , the end portion A- 1  of the sealing member A ( 35 Y) and the end portion C- 1  of the sealing member C ( 37 Y) are superposed with each other at the AC superposition.  FIG. 8   b  is a cross-sectional view of the sealing member C ( 37 Y) with respect to a cross-section X-X passing through the vertex of one of the triangles at the tip end of the end portion C- 1 . As shown in  FIG. 8   b , the sealing member A ( 35 Y) and sealing member C ( 37 Y) are pressed at the AC superposition by the lower part press member  38 Y to be compressed such that the vertexes of the triangles at the end portion C- 1  of the sealing member C ( 37 Y) is at substantially the same height as the surface of the sealing member A ( 35 Y), causing no step at the superposition.  FIG. 8   c  is a cross-sectional view of the sealing member A ( 35 Y) with respect to a cross-section Y-Y passing through the vertex of one of the triangles at the tip end of the end portion A- 2 . As shown in  FIG. 8   c , the sealing member A ( 35 Y) and sealing member C ( 37 Y) are pressed at the AC superposition by the lower part press member  38 Y to be compressed such that the vertexes of the triangles at the end portion A- 2  of the sealing member A ( 35 Y) is at substantially the same height as the surface of the sealing member C ( 37 Y), causing no step at the superposition. 
   As described above, in order to seal a development unit constructing the development device in accordance with the present embodiment, a combination of several sealing members formed of a soft urethane foam is incorporated at a desired section of the development unit in such a manner that the widths of the shapes of the sealing members in a region of superposition with each other are smaller toward the respective tip ends, thereby making the contact areas between each other small. Thus, when the sealing members are pressed by a press member at the superpositions, the compression amounts of the sealing members, at positions where the areas of the sealing members are small, become large, causing no step at the superpositions. Accordingly, generation of steps at the superpositions, which could cause leakage of toner, is prevented. 
   INVENTIVE EXAMPLES 
   The present embodiment of the invention will be described in details below specifically with examples, however, the invention is not limited thereto. 
   1. Content of Experiment 
   Development units incorporated with various sealing members, described later in the description of Test 1 and Test 2, were produced, and the produced development units were mounted for evaluation on a color laser printer (Magicolor 2300DL produced by Konica Minolta Business Technologies Inc.), which is in the market. The evaluation was made on continuous printing of 3000 sheets for each development unit under environment of ordinary temperature and humidity (20° C. and 10% RH). 
   Printing was performed, using only toner in block color and an image with a picture element rate of 10% (an original image with equal quarters of a character image with a picture element rate of 7% (characters of 4, 6, and 8 points), a photograph of a person&#39;s profile, a solid white image, and a solid black image), and a monochrome image was formed on bond paper sheets in A4 size (CF paper produced by Konica Minolta Business Technologies Inc.). 
   2. Evaluation Items 
   (Contamination in Apparatus) 
   The state of scattering of toner from the development units after continuous printing of 3000 sheets by the respective development units was visually evaluated, and further staining of hands was evaluated when the task of removing the development units was carried out.
     A: Contamination in the apparatus was not observed, and the hands were not stained at all by removing the development units.   B: Adherence of toner to the upper lids adjacent to the development rollers was observed. However, the hands were not stained by removing the development units.   C: Adherence of toner to certain parts of the upper lids of the development units in the apparatus was observed. However, scattering of toner in the apparatus was not observed. Further, the hands were not stained by removing the development units.   D: Scattering of toner in the apparatus was recognized. Further, the hands were stained by removing the development units, to an extent that requires washing of the hands.   

   (Image Contamination) 
   Upon performing continuous printing of 3000 sheets by the respective development units, respective three continuous printed sheets centering on the 500 th , 1000 th , 2000 th , and 3000th were observed by a loupe with a scale and visually, and presence or non-presence of a black spot caused by dropping of toner from the development units was evaluated.
     A: Generation of a black spot was not recognized on three prints.   B: A black spot was recognized on one of three prints. However, the black spot was smaller than 0.4 mm, and it was concluded that there is no problem with the image.   C: A black spot was recognized on plural printed sheets. However, the black holes were smaller than 0.4 mm, and it was concluded that there is no problem with the image.   D: A black spot not smaller than 0.4 mm was recognized on plural printed sheets.
 
3. Test 1
   

   Development units incorporated with sealing members formed with the following angles of the respective vertexes of the above described triangle shapes were used for Inventive examples 1 to 3 and Comparative Examples 1 and 2. Herein, a soft polyurethane foam with a hardness of 100 N in accordance with D method of JIS K 6400-2 was employed for the respective sealing members. 
   Inventive Example 1 
   
       
       sealing member A θ A-1-1 , θ A-1-2 , θ A-2-1 , and θ A-2-2 =27° 
       sealing member B θ B-1-1  and θ B-1-2 =30° 
       sealing member C θ C-1-1  and θ C-1-2 =30° 
     
  
   Inventive Example 2 
   
       
       sealing member A θ A-1-1 , θ A-1-2 , θ A-2-1 , and θ A-2-2 =25° 
       sealing member B θ B-1-1  and θ B-1-2 =25° 
       sealing member C θ C-1-1  and θ C-1-2 =25° 
     
  
   Inventive Example 3 
   
       
       sealing member A θ A-1-1 , θ A-1-2 , θ A-2-1 , and θ A-2-2 =150° 
       sealing member B θ B-1-1  and θ B-1-2 =150° 
       sealing member C θ C-1-1  and θ C-1-2 =150° 
     
  
   Comparative Example 1 
   
       
       sealing member A θ A-1-1 , θ A-1-2 , θ A-2-1 , and θ A-2-2 =180° (no bend) 
       sealing member B θ B-1-1  and θ B-1-2 =180° (no bend) 
       sealing member C θ C-1-1  and θ C-1-2 =180° (no bend) 
     
  
   Occurrence/No Occurrence determination result of toner leakage in Inventive Examples 1 to 3 and Comparative Example 1 are shown in Table 1. 
   
     
       
         
             
             
             
           
             
                 
               TABLE 1 
             
           
          
             
                 
                 
             
             
                 
                 
               Toner Leakage 
             
             
                 
               Seal member C 
               Determination 
             
          
         
         
             
             
             
             
             
             
             
          
             
                 
                 
               Seal member B 
               Angle of 
                 
               Image Contamination 
                 
             
          
         
         
             
             
             
             
             
             
             
             
          
             
                 
               Seal member A 
               Angle of 
                 
               vertex 
                 
               (Number of 
                 
             
          
         
         
             
             
             
             
             
             
             
             
             
          
             
                 
               Angle of vertex (°) 
                 
               vertex (°) 
                 
               (°) 
                 
               Continuous prints) 
                 
             
          
         
         
             
             
             
             
             
             
             
             
             
             
             
             
             
             
             
             
             
          
             
                 
               θ A-1-1   
               θ A-1-2   
               θ A-2-1   
               θ A-2-2   
               *1 
               θ B-1-1   
               θ B-1-2   
               *1 
               θ C-1-1   
               θ C-1-2   
               *1 
               500 
               1000 
               2000 
               3000 
               *2 
             
             
                 
                 
             
          
         
         
             
             
             
             
             
             
             
             
             
             
             
             
             
             
             
             
             
          
             
               Inv. 1 
                27 
                27 
                27 
                27 
               100 
                30 
                30 
               100 
                30 
                30 
               100 
               A 
               A 
               A 
               A 
               A 
             
             
               Inv. 2 
                25 
                25 
                25 
                25 
                 
                25 
                25 
                 
                25 
                25 
                 
               A 
               A 
               A 
               A 
               A 
             
             
               Inv. 3 
               150 
               150 
               150 
               150 
                 
               150 
               150 
                 
               150 
               150 
                 
               A 
               A 
               B 
               B 
               B 
             
             
               Com. 
               180** 
               180** 
               180** 
               180** 
                 
               180** 
               180** 
                 
               180** 
               180** 
                 
               C 
               D 
               D 
               D 
               D 
             
             
               1 
             
             
                 
             
             
               Inv.: Inventive Example, 
             
             
               Comp.: Comparative Example 
             
             
               *1: Hardness (N), 
             
             
               **(No bend) 
             
             
               *2: Contamination in Apparatus 
             
          
         
       
     
   
   As shown in Table 1, in Inventive Examples 1 to 3 in accordance with the invention, occurrence of image contamination nor contamination in the apparatus was not observed, and it was confirmed that the present invention is effective. On the other hand, in Comparative Example 1, image contamination occurred at the time of printing 1000th sheet, and contamination in the apparatus was also recognized. 
   4. Test 2 
   Same as the sealing members used in Inventive Example 1, the vortex angles of triangle shapes of seal embers were set to 27° for a sealing member A and 30° for sealing members B and C. Development units were prepared, using the sealing members with the following values of hardness of the seals measured by JIS K 6400 D Method (for Inventive Examples 1, and 4 to 8).
     Inventive Example 1: 100 N   Inventive Example 4: 10 N   Inventive Example 5: 50 N   Inventive Example 6: 200 N   Inventive Example 7: 400 N   Inventive Example 8: 460 N   

   Sealing members of hard rubber (material: neoplane, JIS-A hardness 90) were used fore Comparative Example 2. Evaluation results of Inventive Examples 1, and 4 to 8, and Comparative Example 2 are shown in Table 2. 
   
     
       
         
             
             
             
           
             
                 
               TABLE 2 
             
           
          
             
                 
                 
             
             
                 
                 
               Toner Leakage 
             
             
                 
               Seal member C 
               Determination 
             
          
         
         
             
             
             
             
             
             
             
          
             
                 
                 
               Seal member B 
               Angle of 
                 
               Image Contamination 
                 
             
          
         
         
             
             
             
             
             
             
             
             
          
             
                 
               Seal member A 
               Angle of 
                 
               vertex 
                 
               (Number of 
                 
             
          
         
         
             
             
             
             
             
             
             
             
             
          
             
                 
               Angle of vertex (°) 
                 
               vertex (°) 
                 
               (°) 
                 
               Continuous prints) 
                 
             
          
         
         
             
             
             
             
             
             
             
             
             
             
             
             
             
             
             
             
             
          
             
                 
               θ A-1-1   
               θ A-1-2   
               θ A-2-1   
               θ A-2-2   
               *1 
               θ B-1-1   
               θ B-1-2   
               *1 
               θ C-1-1   
               θ C-1-2   
               *1 
               500 
               1000 
               2000 
               3000 
               *2 
             
             
                 
                 
             
          
         
         
             
             
             
             
             
             
             
             
             
             
             
             
             
             
             
             
             
          
             
               Inv. 1 
               27 
               27 
               27 
               27 
               100 
               30 
               30 
               100 
               30 
               30 
               100 
               A 
               A 
               A 
               A 
               A 
             
             
               Inv. 4 
                 
                 
                 
                 
               10 
                 
                 
               10 
                 
                 
               10 
               A 
               B 
               B 
               C 
               C 
             
             
               Inv. 5 
                 
                 
                 
                 
               50 
                 
                 
               50 
                 
                 
               50 
               A 
               B 
               B 
               B 
               B 
             
             
               Inv. 6 
                 
                 
                 
                 
               200 
                 
                 
               200 
                 
                 
               200 
               A 
               A 
               A 
               A 
               A 
             
             
               Inv. 7 
                 
                 
                 
                 
               400 
                 
                 
               400 
                 
                 
               400 
               A 
               A 
               B 
               B 
               B 
             
             
               Inv. 8 
                 
                 
                 
                 
               460 
                 
                 
               460 
                 
                 
               460 
               B 
               C 
               C 
               C 
               C 
             
             
               Comp. 2 
                 
                 
                 
                 
               — 
                 
                 
               — 
                 
                 
               — 
               C 
               D 
               D 
               D 
               D 
             
             
                 
             
             
               Inv. Inventive Example, 
             
             
               Comp. Comparative Example 
             
             
               *1: Hardness (N), 
             
             
               *2: Contamination in Apparatus 
             
          
         
       
     
   
   In Inventive Examples 1, and 4 to 8 in accordance with the invention, occurrence of image contamination nor contamination in the apparatus was not observed, and it was confirmed that the present invention is effective. On the other hand, in Comparative Example 2, image contamination occurred at the time of printing 1000 sheets, and contamination in the apparatus was also recognized. 
   As has been mentioned above in accordance with the invention, there is provided a development device sealed with a structure incorporated with a combination of several divided sealing members being soft members at a desired section, constructed with hard members, of the development unit, wherein the widths of the shape sections of the sealing members being soft members are thinner toward the respective tip ends, and the sealing members are disposed such that an end portion of one sealing member is superposed with another sealing member, thus making it possible to prevent leakage of toner from the jointing sections of the sealing members.