Abstract:
Powder coating apparatus is equipped with a shutter for opening and closing the space between an object to be coated and a screen electrode. First, a powder is supplied onto the screen electrode from a hopper while the shutter is closed. Next, a brush is slidingly rubbed against the surface of a powder layer while the shutter is closed. The powder is thereby uniformed on the screen electrode without being transferred to the object. Subsequently, a high voltage is applied between the screen electrode and a transfer electrode to form a static electric field, and the shutter is opened. Then, the brush is slidingly rubbed against the powder layer again, and the powder on the screen electrode is coated on the object.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a national phase application based on the PCT International Patent Application No. PCT/JP2010/053039 filed on Feb. 26, 2010, the entire contents of which are incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to a powder coating apparatus and a powder coating method for applying powder to an object. More particularly, the present invention relates to a powder coating apparatus and a powder coating method for transferring powder onto an object by use of electrostatic force. 
       BACKGROUND ART 
       [0003]    Heretofore there is widely known an electrostatic coating technique of transferring powder onto an object by use of electrostatic force. In recent years, this electrostatic coating technique attracts attention in various fields as well as for coating of an object. For instance, this electrostatic coating technique is also under review for manufacture of electrodes for nonaqueous type secondary batteries. 
         [0004]    The powder coating method utilizing the electrostatic coating technique is disclosed in for example Patent Literature 1 in which powder is supplied to a sponge-like roller surface and then the roller is rotated while being pressed against a screen electrode, thereby supplying the powder onto an object through holes of the screen electrode. Further, Patent literature 2 discloses a method of supplying powder by dispersing the powder onto a screen electrode and vibrating the screen electrode up and down, thereby supplying the powder onto an object through holes of the screen electrode. 
       CITATION LIST 
     Patent Literature 
       [0005]    Patent Literature 1: JP 64(1989)-9955 B2 
         [0006]    Patent Literature 2: JP 61(1986)-116578 A 
       SUMMARY OF INVENTION 
       [0007]    However, the above conventional techniques have the following disadvantages. Specifically, the thickness of a film (a coating layer) formed on the object varies. For instance, in the case where the powder is applied from a roller as disclosed in Patent Literature 1, the uniformity of the thickness of the coating layer formed on the object is almost equal to the uniformity of the amount of powder to be pushed out of the screen electrode by the roller. This uniformity of the powder amount depends on the uniformity of the powder amount supplied from the hopper to fall down onto the roller. However, it is very difficult to supply a fixed amount of powder from the hopper. Further, a part of the powder supplied onto the roller is absorbed into the sponge-like roller and another part of the powder bounces back from a curved surface of the roller. It is therefore very difficult to control the powder amount to be pushed out of the roller. 
         [0008]    On the other hand, in the case where no roller is used as in Patent Literature 2, nonuniformity of thickness of the coating layer will not occur. However, in the case where the powder is dispersed from the hopper as in Patent Literature 2, the uniformity of the thickness of the coating layer is almost equal to the uniformity of the amount of powder dispersed onto the screen electrode. This uniformity of the powder amount depends on the uniformity of the amount of powder supplied from the hopper. It is therefore hard to form a coating layer with high accuracy. 
         [0009]    The present invention has been made to solve the above problems and has a purpose to provide a powder coating apparatus and a powder coating method capable of forming a coating film or layer with high thickness uniformity on an object. 
       SOLUTION TO PROBLEM 
       [0010]    To achieve the above purpose, one aspect of the invention provides a powder coating apparatus for applying powder to an object, the apparatus comprising: a screen electrode formed with a number of holes; supply means for supplying the powder onto the screen electrode; a transfer electrode placed to face an opposite surface of the screen electrode from a surface to be supplied with the powder from the supply means, the transfer electrode being configured to form an electrostatic field between the screen electrode and the transfer electrode when high voltage is applied to the transfer electrode; smoothing means located above the surface of the screen electrode to which the powder is supplied from the supply means, the smoothing means being movable in parallel to the screen electrode to smooth a powder layer formed on the screen electrode; and a shutter placed between the screen electrode and the transfer electrode to open and close between the object and the screen electrode placed between the electrodes, the apparatus being adapted to, while the shutter is in a closed state, supply the powder onto the screen electrode from the supply means and move the smoothing means in parallel to the screen electrode and on the powder layer formed on the screen electrode, and the apparatus being adapted to, while the shutter is in an open state, apply the powder supplied on the screen electrode to the object placed between the screen electrode and the transfer electrode. 
         [0011]    The above powder apparatus includes the shutter to open and close the space between the object and the screen electrode. While the shutter is closed, the powder is supplied onto the screen electrode. While the shutter is closed, furthermore, the smoothing means slides and rubs against the powder layer. Thereby, the powder layer on the screen electrode is made uniform over the screen electrode without moving to the object. Thereafter, high voltage is applied between the screen electrode and the transfer electrode to form an electrostatic field. Then, the shutter is opened and the powder on the screen electrode is allowed to move to the object through the electrostatic field. 
         [0012]    In the above powder coating apparatus, specifically, while the shutter is in a closed state once, the powder is supplied and the smoothing means is moved in parallel to and on the powder layer formed on the screen electrode, thereby uniformizing the powder layer. When the thickness of the powder layer becomes uniform, the shutter is opened, allowing the powder to be applied to the object. In other words, the powder is applied after the thickness of the powder layer becomes uniform. This can achieve high uniformity of thickness of the coating film formed on the object. 
         [0013]    The above powder coating apparatus may further comprise a protective wall placed on the surface of the screen electrode to which the powder is to be supplied from the supply means, the protective wall surrounding a region to which the powder is to be supplied from the supply means. 
         [0000]    Specifically, since the surface of the screen electrode on which the powder layer is to be formed is surrounded, the powder is prevented from scattering to the outside of the apparatus. 
         [0014]    Furthermore, the above scattering prevention wall may include at least a portion made of an insulating member, the portion being in contact with the screen electrode. 
         [0000]    Specifically, the portion contacting with the screen electrode is made of the insulating member and therefore leakage of electricity can be prevented. 
         [0015]    In the above powder coating apparatus, preferably, the shutter in the closed state is placed in contact with the screen electrode. Such shutter closes the holes of the screen electrode and can contribute to a reduction in the amount of powder that leaks from the screen electrode to the shutter while the smoothing means smoothes against the powder layer. 
         [0016]    In the above powder coating apparatus, the shutter in the closed state may be placed in noncontact with the screen electrode. 
         [0000]    Specifically, any mechanism for bringing the shutter into contact with the screen electrode is unnecessary. Thus, the apparatus can have a simpler configuration. 
         [0017]    In the above case, the shutter may include at least a portion made of an insulating member, the portion being in contact with the screen electrode. 
         [0000]    Specifically, the portion which will contact with the screen electrode is made of the insulating member, thereby enabling prevention of leakage of electricity. 
         [0018]    In the above powder coating apparatus, while the shutter is in the open state, the smoothing means may be moved in parallel to the screen electrode to apply the powder to the object. 
         [0000]    Specifically, it is conceivable to include an additional means for coating the smoothed powder to the object. The smoothing means utilized for smoothing is also used for powder coating. In other words, the smoothing means is used both for smoothing and coating. Thus, the apparatus can have a simpler configuration. 
         [0019]    Another aspect of the invention provides a powder coating method of applying powder to an object, the method comprising the steps of: placing the object between a screen electrode formed with a number of holes and a transfer electrode facing the screen electrode, the transfer electrode being configured to form an electrostatic field between the screen electrode and the transfer electrode; closing the shutter between the screen electrode and the object and supplying the powder onto the screen electrode while the shutter is in a closed state; placing smoothing means onto a powder layer formed on the screen electrode after start of supplying the powder while the shutter is in the closed state, and moving the smoothing means in parallel to the screen electrode to slide on and smooth the powder layer; applying high voltage between the screen electrode and the transfer electrode to form the electrostatic field; and applying the powder supplied on the screen electrode to the object through the electrostatic field while the shutter is in an open state. 
       ADVANTAGEOUS EFFECTS OF INVENTION 
       [0020]    According to the present invention, a powder coating apparatus and a powder coating method can be realized, capable of forming a coating film or layer with high thickness uniformity on an object. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0021]      FIG. 1  is a schematic configuration view of a powder coating apparatus (with a shutter closed and a cover opened) of an embodiment; 
           [0022]      FIG. 2  is a schematic configuration view of a screen electrode; 
           [0023]      FIG. 3  is a cross sectional view of the screen electrode taken along a line A-A in  FIG. 2 ; 
           [0024]      FIG. 4  is a schematic configuration view of the powder coating apparatus (with the shutter and the cover closed) of the embodiment; 
           [0025]      FIG. 5  is a flowchart showing a powder coating process to be performed by the powder coating apparatus of the embodiment; 
           [0026]      FIG. 6  is a schematic configuration view of the powder coating apparatus (with the shutter closed and a brush active) of the embodiment; 
           [0027]      FIG. 7  is a schematic configuration view of the powder coating apparatus (with the shutter opened and the brush active) of the embodiment. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0028]    A detailed description of a preferred embodiment of the present invention will now be given referring to the accompanying drawings. In the following embodiment, the present invention is applied to a powder coating apparatus for use in manufacturing an electrode plate for a lithium ion battery. 
         [0029]    (Configuration of Powder Coating Apparatus) 
         [0030]    A powder coating apparatus  100  of this embodiment includes a screen electrode  1 , a hopper  2 , a transfer electrode  3 , a shutter  4 , a scattering prevention wall  6 , and a brush  8 , as shown in  FIG. 1 . An object  10  (an electrode plate for a lithium ion battery, in this embodiment) is placed between the screen electrode  1  and the transfer electrode  3 , more concretely, between the shutter  4  in a closed state and the transfer electrode  3 . Further, the screen electrode  1  and the transfer electrode  3  are electrically connected to a DC high-voltage power supply  31 . 
         [0031]    The screen electrode  1  includes a mesh  11  made of stainless steel and a frame  12  made of aluminum (aluminium) as shown in  FIG. 2 . In this embodiment, each of the mesh  11  and the frame  12  has an outer dimension of 200 mm×200 mm.  FIG. 3  is a cross-sectional view taken along a line A-A in  FIG. 2 . The mesh  11  is formed with about five-hundred holes  14  arranged at equal intervals. In this embodiment, each hole  14  has a maximum width of 25 μm. These holes  14 , which are through holes, allow the powder supplied onto one surface of the screen electrode  11  to pass through the screen electrode  11  to the other surface thereof. A part of the holes  14  is filled with insulating resin  15 . Specifically, the insulating resin  15  blocks the holes  14  located corresponding to a region other than a region of the object  10  desired to be coated with the powder, i.e., a coating region. Accordingly, the powder can be applied to a desired region. 
         [0032]    The hopper  2  is used to supply, onto the screen electrode  1 , powder  21  (an electrode material for a lithium ion battery in this embodiment) which will be applied to the object  10 . The hopper  2  is placed to be movable in three directions; an up-and-down, a right-and-left direction in  FIG. 1 , and a depth direction to the drawing sheet of  FIG. 1 , by a moving mechanism not shown, thereby supplying the powder  21  uniformly within the surface of the screen electrode  1 . 
         [0033]    The transfer electrode  3  is placed to face an opposite surface of the screen electrode  1  from a surface to which the powder  21  is supplied from the hopper  2 . Under application of transfer bias from the DC high-voltage power supply  31 , the transfer electrode  3  forms an electrostatic field between the screen electrode  1  and the electrode  3 . In this embodiment, a distance between the transfer electrode  3  and the screen electrode  1  is 1.5 mm. Further, the transfer electrode  3  is made of an aluminum sheet and is also used to support the object  10 . 
         [0034]    The shutter  4  is placed between the screen electrode  1  and the transfer electrode  3  and slidable in a direction (the right-and-left direction in  FIG. 1  or the depth direction to  FIG. 1 ) perpendicular to a direction in which the screen electrode  1  and the transfer electrode  3  face each other. In this embodiment, the shutter  4  is made of a stainless sheet with a thickness of 1.0 mm and entirely coated with fluorocarbon resin. While the shutter  4  is in a position between the electrodes  1  and  3 , i.e., in a closed state, the shutter  4  restrains movement of the powder  21  to the object  10 . While the shutter  4  is in a position not between the electrodes  1  and  3 , i.e., in an open state, the powder  21  is allowed to move to the object  10 . In the open state, the shutter  4  does not always have to be located completely outside the space between the electrodes  1  and  3 . The shutter  4  may be located in at least a position that does not face the coating region of the object  10 . 
         [0035]    The scattering prevention wall  6  is fixed on the surface of the screen electrode  1  to which the powder  21  will be supplied form the hopper  2 . This wall  6  is placed to surround a region of the screen electrode  1  to which the hopper  2  supplies the powder  21 . In this embodiment, the scattering prevention wall  6  has a height of 100 mm and fixed to the frame  12  of the screen electrode  1 . The scattering prevention wall  6  prevents scattering of the powder  21  to the outside of the apparatus. This wall  6  is made of polypropylene (PP) and thus does not cause leakage of electricity even when it touches other object. 
         [0036]    Further, the scattering prevention wall  6  includes a cover  61  on an upper opening as shown in  FIG. 4 . This cover  61  is used to close the opening. When the cover  61  is to be closed, the hopper  2  is moved outside of the region surrounded by the scattering prevention wall  6 . When the cover  61  is closed, a powder layer  22  on the screen electrode  1  is confined within the region surrounded by the scattering prevention wall  6 , thereby almost completely preventing the powder from scattering to the outside of the apparatus. Further, foreign matters are also prevented from entering in the region. It is to be noted that the cover  61  is not indispensable. 
         [0037]    The brush  8  is a flat planar brush, including a frame member  81  movable in three directions; i.e., an up-and-down direction, a right-and-left direction in  FIG. 1 , and the depth direction to  FIG. 1  and a urethane foam  82  bonded to a lower surface of the frame member  81 . The frame member  81  is made of an aluminum sheet of 195 mm×195 mm×5 mm. This frame member  81  is a member for supporting the urethane foam  82  and may be made of any material as long as it has a desired rigidity. The urethane foam  82  is a plastic sponge of 195 mm×195 mm×5 mm. The urethane foam  82  may be made of any member having an insulating property. The brush  8  is placed so that the urethane foam  82  faces the screen electrode  1 . 
         [0038]    (Configuration of Lithium Ion Battery) 
         [0039]    A brief explanation is given to the configuration of a lithium ion battery which is a nonaqueous secondary battery. A power generating element of the lithium ion battery includes a negative electrode consisting of a metal foil and a negative active material coated on both surfaces of the foil and a positive electrode consisting of a metal foil and a positive active material coated on both surfaces of the foil, the electrodes being placed to face each other with a separator interposed therebetween. For coating the active materials which are powder to the metal foils for electrodes, the powder coating apparatus  100  of this embodiment is used. 
         [0040]    In this embodiment, to be concretely, an aluminum foil with a thickness of 15 μm is used for the metal foil for a positive electrode plate and lithium cobalt oxide (LiCoO2) having a particle diameter of 2 μm to 15 μm and a mean particle diameter of 5 μm is used for the positive electrode active material. Further, a copper foil with a thickness of 15 μm is used for the metal foil for a negative electrode plate and graphite carbon having a particle diameter of 5 μm to 20 μm and a mean particle diameter of 8 μm is used for the negative electrode active material. A polytetrafluoroethylene (PTFE) powder of a concentration of 5 weight percent is used for a binder. It is to be noted that the above materials used for the positive electrode plate, the powder active material layer, the negative electrode plate, the negative active material layer, and the binder are mere examples and may be appropriately selected from commonly used materials for batteries. 
         [0041]    (Sequence of Powder Coating) 
         [0042]    The sequence of operation of the powder coating apparatus  100  is explained below referring to a flowchart in  FIG. 5 . It is assumed that, at the start, no voltage is applied between the screen electrode  1  and the transfer electrode  3  and the cover  61  is in a closed position. 
         [0043]    Firstly, the object  10  (an aluminum foil for the positive electrode plate or a copper foil for the negative electrode plate) is carried onto the transfer electrode  3  (S 00 ). Carrying of the object  10  in S 00  is not limited to the timing just after the start but may be conducted before the shutter  4  is opened in S 06  mentioned later. 
         [0044]    Secondly, the cover  61  is moved away from the scattering prevention wall  6  (S 01 ). Thereby, the region surrounded by the scattering prevention wall  6  is open, so that the hopper  2  and the brush  8  are moved into the relevant region. In the case where the cover  61  is in an open position from the beginning, this step is skipped. 
         [0045]    The shutter  4  is moved to between the screen electrode  1  and the object  10  and set in the closed state (S 02 ). In the closed state, the shutter  4  is in contact with the screen electrode  1 , closing the holes  14  of the screen electrode  1 . 
         [0046]    Successively, the hopper  2  is moved so that an outlet thereof comes into the region surrounded by the scattering prevention wall  6  and to a position at a height of 50 mm from the screen electrode  1 . While the hopper  2  is being moved horizontally (in the right-and-left or depth direction in  FIG. 1 ), the powder  21  (lithium cobalt oxide for the positive electrode plate or graphite carbon for the negative electrode plate) is supplied to the entire screen electrode  1  (S 03 ). In S 03 , the powder is supplied until the powder layer  22  is formed with a thickness of about 10 mm on the screen electrode  1 . 
         [0047]    The hopper  2  is then moved out of the region surrounded by the scattering prevention wall  6 . The brush  8  is moved into the region surrounded by the scattering prevention wall  6  so that the urethane foam  82  comes into contact with the powder layer  22 . And, as shown in  FIG. 6 , the brush  8  is moved horizontally (in the right and left of depth direction in  FIG. 6 ) (S 04 ), that is, the brush  8  is moved in parallel to the screen electrode  1 . During this movement of the brush  8 , the urethane foam  82  slides and rubs against the powder layer  22 , thereby smoothing the surface of the powder layer  22 . This smoothing of the brush  8  is continued for one minute to uniformize the thickness of the powder layer  22 . It is to be noted that, during smoothing of the brush  8 , the upper surface side (the powder layer  22  side) of the screen electrode  1  is covered by the scattering prevention wall  6 . This prevents scattering of the powder to the outside of the apparatus. On the other hand, the lower surface side (the object  10  side) of the screen electrode  1  is in contact with the shutter  4  and hence the powder does not leak from the screen electrode  1 . 
         [0048]    Specifically, in the case where the two-dimensional center of the screen electrode  1  is defined as (X, Y)=(0, 0), the brush  8  is moved so that the center of the brush  8  comes to a position defined as (+2 mm, +2 mm). Furthermore, the brush  8  is moved to a height at which a distance between the screen electrode  1  and the frame member  81  is 15 mm, that is, to a height at which the urethane foam  82  contacts with the powder layer  22 . At that height, the brush  8  is moved around at a speed of 4 sec/cycle so that the center of the brush  8  goes round to the positions defined as (+2 mm, −2 mm), (−2 mm, −2 mm), (−2 mm, +2 mm), and (+2 mm, +2 mm) in this order. This circulating movement is continuously performed for one minute. 
         [0049]    After the thickness of the powder layer  22  is made uniform, high voltage is applied between the screen electrode  1  and the transfer electrode  3  from the DC high-voltage power supply  31  (S 05 ). In this embodiment, a DC voltage of 3 kV is supplied. Accordingly, an electrostatic field is formed between the screen electrode  1  and the transfer electrode  3  while the object  10  and the shutter  4  are interposed therebetween. 
         [0050]    While a strong electric field is being formed between the screen electrode  1  and the transfer electrode  3 , the shutter  4  is moved out from between the screen electrode  1  and the object  10  and placed in the open state (S 06 ). 
         [0051]    After the shutter  4  is open, the brush  8  is driven again to move slightly downward from the position in S 04 , thereby increasing the pressure on the powder layer  22 , as shown in  FIG. 7 , and move around with the urethane foam  82  being pressed against the powder layer  22  (S 07 ). This causes the powder  21  on the screen electrode  1  to pass through the holes  14  and fall onto the region in which the electrostatic field is formed. The powder  21  is then charged in passing through the holes  14 . The powder  21  is applied onto the object  10  by the electrostatic force. At that time, the thickness of the powder layer  22  on the screen electrode  1  is uniform and therefore the powder  21  is applied uniformly over the object  10 . 
         [0052]    To be more concrete, the brush  8  is moved downward to a position at a distance of 10 mm between the screen electrode  1  and the frame member  81 . Thereby, the urethane foam  82  of the brush  8  is pressed against the powder layer  22 . At that height, the brush  8  is driven to move in a similar way to the above. If the pressure of the brush  8  placed at the height in S 04  to the powder layer  22  is also sufficient in S 07 , the brush  8  does not need to be moved down. 
         [0053]    After completion of supply of the powder  21 , the sliding and rubbing of the brush  8  is stopped and the application of voltage is stopped (S 08 ). Thereafter, the cover  61  is moved to the closed position on the scattering prevention wall  6  (S 09 ), the object  10  is taken out of the powder coating apparatus  100 , and the powder is fixed by a fixing device not shown. Consequently, the powder coating is completed. 
         [0054]    In this embodiment, while the shutter  4  is in the closed state, the shutter  4  is held in contact with the screen electrode  1 . The shutter  4  may be placed to face the screen electrode  1  in non-contact relation. This configuration does not need a mechanism for bringing the shutter  4  into contact with the screen electrode  1  (e.g., a mechanism for moving the shutter  4  up and down) and thus can achieve a simpler apparatus. On the other hand, in the case where the shutter  4  is placed in contact with the screen electrode  1 , it is possible to reduce the amount of powder that falls onto the shutter  4  during smoothing of the powder layer  22  (S 04 ). This can reduce waste of powder. 
         [0055]    The concrete values presented in this embodiment, i.e., the amount of movement, circulating speed, smoothing time, voltage, the amount of supply of powder, a porous configuration of the screen electrode  1 , and others are mere examples and not limited to the above mentioned. In other words, those values and configurations are appropriately selected according to the coating amount and the kind of the powder  21 . 
         [0056]    The powder coating apparatus  100  in this embodiment explained in detail above includes the shutter  4  to open and close the space between the object  10  and the screen electrode  1 . While the shutter  4  is in the closed state, the powder  21  is supplied onto the screen electrode  1 . Further, the brush  8  is caused to slide on and rub against the powder layer  2  while the shutter  4  is in the closed state. Therefore, the powder  21  is smoothed on the screen electrode  1  without moving to the object  10 . A high voltage is then applied between the screen electrode  1  and the transfer electrode  3 , thus forming an electrostatic field. After that, the shutter  4  is brought to the open state and the brush  8  is driven again to slide on and rub against the powder layer  22 , thereby causing the powder on the screen electrode  1  to be applied over the object  10 . In the powder coating apparatus  100 , specifically, the powder is supplied while the shutter  4  is in the closed state once, the powder layer  22  on the screen electrode  1  is smoothed by sliding and rubbing, and then the shutter  4  is opened after the thickness of the powder layer  22  is made uniform, thus the powder  21  is applied to the object  10 . That is, after the thickness of the powder layer  22  is made uniform, the powder  21  is applied to the object  10 . Therefore, the thickness of a coating layer formed on the object  10  is expected to provide high uniformity. 
         [0057]    Especially, an electrode (an object) of the nonaqueous type secondary battery as typified by the lithium ion battery is demanded for the thickness uniformity of the coating layer with an accuracy of 10 μm or less per 1 square centimeter. It can be expected that the powder coating apparatus  100  of this embodiment can meet such high accuracy demand. 
         [0058]    The above embodiment merely shows examples without any limitations to the present invention. The present invention may be embodied in other specific forms without departing from the essential characteristics thereof. For instance, in the above embodiment, the present invention is applied to the process of manufacturing electrodes for lithium ion batteries. As an alternative, the present invention may be applied to a technique of manufacturing nonaqueous type secondary batteries other than the lithium ion battery. Further, the present invention may also be applied to, not only the manufacturing technique for the nonaqueous type secondary batteries, but alto a coating technique and a film-forming or deposition technique. The object may include products in general, electronic components, printed boards, and glass boards. 
         [0059]    The above embodiment uses the rectangular urethane foam  82  as the smoothing means which slides and rubs against the powder layer  22 . Instead thereof, a non-foam material may be used. The shape of the smoothing means may be roller-like and made of a frame member in which brush bristles are implanted. 
         [0060]    In the above embodiment, to prevent a short circuit, the urethane foam  82 , the shutter  4 , and the scattering prevention wall  6  are all made of insulating materials. As an alternative, only parts of them may be made of the insulating materials. Specifically, all the components do not necessarily need to be made of the insulating members as long as a contact portion or a joining portion with the screen electrode  1  is made of the insulating members. 
         [0061]    In the above embodiment, the brush  8  functions to smooth in S 04  and also coat in S 07 . These functions may be carried out by separate mechanisms. To be concrete, the coating means may be configured to push out powder by a vibrating mechanism, a squeegee, and others. However, the brush  8  usable for both smoothing and coating can make the apparatus structure simpler. 
         [0062]    In the above embodiment, the brush  8  is operated while the cover  61  is in the open position. However, the brush  8  may be configured to be movable even while the cover  61  is in the closed position. In this case, the brush  8  is operated to perform smoothing of the powder layer  22  and coating of the powder  21  while the cover  61  is in the closed position. In this case, the powder layer  22  is completely enclosed and thus the powder  21  can be more prevented from scattering to the outside of the apparatus. 
       REFERENCE SIGNS LIST 
       [0063]      1  Screen electrode 
         [0064]      14  Hole 
         [0065]      2  Hopper (Supply means) 
         [0066]      21  Powder 
         [0067]      22  Powder layer 
         [0068]      3  Transfer electrode 
         [0069]      31  DC high-voltage power supply 
         [0070]      4  Shutter 
         [0071]      6  Scattering prevention wall 
         [0072]      8  Brush (Smoothing means) 
         [0073]      81  Frame member 
         [0074]      82  Urethane foam 
         [0075]      10  Object 
         [0076]      100  Powder coating apparatus