Patent Publication Number: US-2012024475-A1

Title: Display bonding device and method

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority of Japanese Patent Application No. 2010-171272, filed on Jul. 30, 2010, the entire contents of which are incorporated herein by reference. 
     FIELD 
     The embodiments discussed herein relate to a display bonding device and a display bonding method. 
     BACKGROUND 
     Conventionally, a pressure sensitive adhesive double coated tape is used for bonding a display to an electronic device, such as a mobile phone. When attaching the adhesive tape to a display, which is an adherend (workpiece), a method configured to press the adhesive tape by a roller is used in order to apply a uniform load to the adhesive tape to achieve a secure contact between the adhesive tape and an attaching surface of the adherend and expel air bubbles that easily enter between the adhesive tape and the adherend. 
     On the other hand, a pressure head method can be used instead of the method using a roller in order to speed up the attaching operation in mass production of electronic devices, and further, in order to realize an operation to attach the adhesive tape to a display with a high degree of accuracy, or because it is difficult to attach an adhesive tape to an attaching surface of an adherend which has concaves and convexes. The pressure head method is a method for applying pressure by pressing a pressure head having a shape corresponding to the shape of the attaching surface of the adherend to the attaching surface between the adhesive tape and the adherend. 
     As illustrated in  FIG. 10 , when attaching a glass plate  102  to a housing  100  of a mobile phone or the like with a pressure sensitive adhesive double coated tape  104 , an attaching surface of the adhesive tape  104  is pressed to an attaching surface of the housing  100 , and the adhesive tape  104  is pressed by a pressure head, so that the adhesive tape is attached to the housing  100 . Protective paper is peeled from the surface of the adhesive tape  104  and the glass plate  102  is pressed and attached to the adhesive tape  104  attached to the housing  100  with the pressure head. 
     The pressure head method and the method for applying pressure with a roller are disclosed, for example, in Japanese Unexamined Patent Application Publication No. 06-48640 or Japanese Unexamined Patent Application Publication No. 2004-42270. 
     However, in a conventional attaching method using a pressure head, as illustrated in  FIGS. 11A to 11D , adhesive failure  106  and residual air bubbles  108  occur in the adhesive tape, so the bonding strength of the adhesive tape may be decreased. In particular, when attaching an adhesive tape to a display such as a large scale liquid crystal display panel, the adhesive failure  106  and the residual air bubbles  108  easily occur. In conventional methods, the rate of attaching failure due to the adhesive failure  106  or the residual air bubbles  108  is about 0.2%. 
     The adhesive failure  106  here means, for example, that the adhesive tape does not come in contact with the adherend as illustrated in  FIGS. 11A and 11B  and a certain range of area is formed where the adhesive tape is not sufficiently pressed to the adherend and the adhesive tape does not adhere to the adherend. The residual air bubbles  108  means, for example, a plurality of air bubbles that are enclosed between the adhesive tape and the adherend as illustrated in  FIGS. 11C and 11D . 
     On the other hand, in the method for applying pressure with a roller, if there are concaves and convexes on the attaching surface of the adherend, the adhesive failure  106  or the residual air bubbles  108  easily occur, so the method is effective only when the adhesive tape is attached to a flat and smooth surface. Further, the method using a roller takes a long operation time in mass production, and it is difficult for a small-sized display to be attached. 
     SUMMARY 
     According to an embodiment of the invention, a display bonding device includes a stage configured to place an adhesive tape and an adherend thereon, a pressure head configured to press the adhesive tape onto the adherend with a pressure surface having a tapered shape or a curved shape which is tilted with respect to the stage, and a movement mechanism configured to move the pressure head toward the adhesive tape through a pressure rod which is coupled to the pressure head. The pressure head is configured to rotate around the pressure rod. 
     The object and advantages of embodiments of the invention will be realized and achieved by means of the elements and combinations particularly pointed out in the claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory, and are not restrictive of the invention. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1A  is a front view showing a schematic configuration of a display bonding device of an embodiment; 
         FIG. 1B  is a side view of the display bonding device. 
         FIG. 2  is a schematic view of a pressure head used in an embodiment. 
         FIGS. 3A to 3C  are views for explaining variation of tilt angle of a pressure surface of the pressure head used in an embodiment. 
         FIGS. 4A and 4B  are views for explaining a first modified example of an embodiment. 
         FIGS. 5A and 5B  are views for specifically explaining an operation of the first modified example. 
         FIG. 6  is a view for explaining a second modified example of an embodiment. 
         FIGS. 7A and 7B  are views for explaining a third modified example of an embodiment. 
         FIGS. 8A and 8B  are views for explaining a fourth modified example of an embodiment. 
         FIG. 9  is a view for explaining a specific example of the fourth modified example. 
         FIG. 10  is a view for explaining an example of attaching a glass plate to a housing of an electronic device. 
         FIGS. 11A to 11D  are views for explaining a problem occurring in a conventional bonding method. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, a display bonding device and a display bonding method according to embodiments of the present invention will be described. 
       FIG. 1A  is a front view showing a schematic configuration of a display bonding device  10  of an embodiment of the present invention.  FIG. 1B  is a side view of the display bonding device  10 , according to an embodiment. 
     When bonding a display glass plate to, for example, a resin housing  12  of a mobile phone, which is an adherend, the display bonding device  10  performs an attaching operation using a pressure sensitive adhesive double coated tape (herein after referred to as “adhesive tape”)  14 . 
     The display bonding device  10  may have a device main body  16  and a drive unit  18 . 
     The device main body  16  may have a stage  19 , a pressure head movement mechanism  20 , and a pressure head  22 . 
     In one embodiment, the pressure head movement mechanism  20  is provided with a pressure gauge  24 , a pressure rod  26 , and a pressure rod connection unit  28 . The pressure head  22  can be provided with a pressure head connection unit  30 . 
     According to an embodiment, the stage  19  is attached to a base  32 , and has a mounting surface on which the housing  12  with an adhesive tape  14  thereon is mounted. 
     The pressure head movement mechanism  20  is attached to the base  32 . The pressure head movement mechanism  20  moves the pressure rod  26  toward the housing  12  and the adhesive tape  14  through a drive shaft extended from the drive unit  18 . The pressure head  22  may be connected to the bottom end of the pressure rod  26 , so the pressure head  22  may be pressed from above the adhesive tape  14  by lowering the pressure rod  26 . 
     The pressure gauge  24 , in one example, is a sensor configured to measure pressure information of the pressure head  22 . For example, the pressure gauge  24  is provided with a load cell and measures the pressure information. The measurement result is transferred to the drive unit  18  and used for feedback control of pressure of the pressure head  22 . A strain gauge may be used to measure the strain of the pressure rod  22  instead of the load cell. Or, the pressure rod  22  may be provided with a pressure spring instead of the load cell, and a reduction of the length of the pressure spring may be measured. 
     The drive unit  18  is a driving source configured to move the pressure rod  26  and includes, for example, a drive motor. 
       FIG. 2  is a view for specifically explaining the pressure head  22  and the periphery thereof. 
     The pressure head  22  is a member configured to press the housing  12  and the adhesive tape  14  with a pressure surface which is a tapered surface tilted in one direction with respect to the mounting surface of the stage  19 . The pressure head  22  is a metal member formed, for example, of SUS, SPCC (JIS G3141), or the like. The pressure rod  26  goes down to or up from the housing  12  and the adhesive tape  14 . The movements of going down and up may be fixed to one direction. 
     In one embodiment, a spherically concave portion facing the pressure rod  26  can be provided to the pressure rod connection unit  28  where the pressure rod  26  connects with the pressure head  22 . 
     On the other hand, in an embodiment, a spherical convex portion swingably connected with the concave portion of the pressure rod connection unit  28  can be provided to the pressure head connection portion  30  where the pressure head  22  connects with the pressure rod  26 . Thereby, the pressure head  22  may rotate around the pressure rod  26 . In other words, the pressure head  22  and the pressure rod  26  can be connected to each other via a ball joint. 
     The pressure surface of the pressure head  22  is a tapered surface tilted in one direction and the pressure head  22  may rotate around the pressure rod  26 . Therefore, as illustrated in  FIG. 3A to 3C , the tilt angle of the pressure surface decreases when the pressure head  22  goes down and starts to be in contact with the adhesive tape  14  and the tilt angle becomes 0 (becomes horizontal) with respect to the mounting surface of the stage  19  when the pressure surface comes in complete surface contact with the adhesive tape  14 . 
     In this way, the pressure surface of the pressure head  22  starts to be in contact with the adhesive tape  14  from the left end in  FIGS. 3A to 3C , so air bubbles between the adhesive tape  14  and the housing  12  are pressed in the X direction in  FIGS. 3A to 3C , and finally, in a state shown in  FIG. 3C , the air bubbles are pressed out from the right end of the pressure surface of the pressure head  22 . 
     Further, regarding the tilt angle of the pressure surface of the pressure head  22 , since the pressure head  22  may rotate around the pressure rod  26 , even if there are minute concaves and convexes of the housing  12  along the X direction or there are minute concaves and convexes along a direction perpendicular to the X direction (a direction perpendicular to the page surface of  FIGS. 3A to 3C ), the pressure surface may be rotated following the concaves and convexes. Therefore, a partial contact (see  FIGS. 11A and 11B ), which occurs in conventional techniques, is unlikely to occur. The rate of occurrence of attaching failure due to a partial contact  106  or residual air bubbles  108  is, for example, about 0.02%. 
     As illustrated in  FIGS. 2 and 3A  to  3 C, the left end portion of the pressure head  22  which first comes in contact with the adhesive tape  14  is rounded to a semicircular shape. One reason for this is to prevent the portion of the pressure head  22  which first comes in contact with the adhesive tape  14  from damaging the adhesive tape  14 . 
     Although, in this embodiment, a spherical concave portion is provided to the pressure rod connection unit  28  and a spherical convex portion is provided to the pressure head connection unit  30 , a spherical convex portion may be provided to the pressure rod connection unit  28  and a spherical concave portion may be provided to the pressure head connection unit  30 . 
     Although, in this embodiment, the pressure head connection unit  30  is connected to the pressure rod connection unit  28  by a combination of convex and concave portions so that the pressure head  22  may rotate around the pressure rod  26 , the connection form between the pressure rod connection unit  28  and the pressure head connection unit  30  is not limited to the connection formed by the combination of convex and concave portions. 
     It is preferable, according to one embodiment, that an anti-slip resin sheet having a thickness of 10 mm or less is provided on the pressure head  22 . The resin sheet may prevent the surface of the pressure head  22  from slipping on the adhesive tape  14 , so it is possible to more effectively suppress occurrence of partial contact and reduce residual air bubbles. It is preferable that the resin sheet is, for example, a natural rubber sheet, a urethane rubber sheet, or a silicone rubber sheet. 
     First Modified Example 
       FIGS. 4A and 4B  are views for explaining a first modified example of the pressure head  22  of the above-described embodiment. 
     The pressure head  22  of the first modified example may be different from the pressure head  22  illustrated in  FIG. 2 , and includes a pair of balancers  22   a  that may move on the pressure head  22 . Grooves extending in the X direction are provided on a surface opposite to the pressure surface of the pressure head  22 , and the balancers  22   a  may slide on the grooves. The display bonding device  10  used in the first modified example is similar to that of the above-described embodiment except for the pressure head  22 . 
     According to one embodiment, a pair of balancers  22   a  is provided in the Y direction. By providing the balancers  22   a,  it is possible to adjust the tilt angle of the pressure surface of the pressure head  22  with respect to the mounting surface of the stage  19  to a predetermined value. The tilt angle of the pressure surface is adjusted according to usage conditions such as the thickness of the adhesive tape  14  to be used and the hardness of the housing  12 . The reason for adjusting the tilt angle according to usage conditions is because the tilt angles at which the partial contact  106  or residual air bubbles  108  are unlikely to occur are different depending, for example, on the thickness of the adhesive tape  14  to be used, the hardness of the housing  12 , and the like. 
     As illustrated in  FIG. 5A , by placing the balancer  22   a  at the left end, it is possible to increase the tilt angle, for example, to about 10 to 15 degrees. By moving the balancer  22   a  to the center, it is possible to decrease the tilt angle, for example, to about 5 degrees. 
     Although, in the first modified example, a pair of balancers  22   a  are provided in the Y direction, the number of balancers  22   a  may be one or three or more. Although the balancer  22   a  slides on a groove, the moving method and the placing method of the balancer  22   a  are not particularly limited. 
     Second Modified Example 
       FIG. 6  is a view for explaining a second modified example of the pressure head  22  of the above-described embodiment. The display bonding device  10  used in the second modified example may be the same as that of the above-described embodiment except for the pressure head  22 . 
     Although the pressure head  22  of the embodiment has a tapered surface as a tilted pressure surface which is formed by a flat plate tilted in one direction, as illustrated in  FIG. 6 , the pressure head  22  of the second modified example has a curved surface  22   b  where the pressure surface is tilted in one direction. Further, the pressure head  22  may rotate around the pressure rod  26  and further with respect to the pressure rod  26 . Therefore, when the pressure head  22  moves down so as to be in contact with the adhesive tape  14 , the pressed position on the adhesive tape  14  moves in the X direction as the pressure head  22  moves down. Therefore, as illustrated in  FIGS. 3A to 3C , the air bubbles are pressed out in the X direction. Further, since the pressure head  22  may rotate around the pressure rod  26 , even if there are minute concaves and convexes of the housing  12  along the X direction or there are minute concaves and convexes along a direction perpendicular to the X direction, the pressure surface may be rotated following the concaves and convexes. Therefore, a partial contact (see  FIGS. 11A and 11B ) which occurs in conventional techniques is unlikely to occur. 
     The curved surface  22   b  may also be curved in a cross section in a direction perpendicular to the page surface of the example of  FIG. 6 . In this case, if there are minute concaves and convexes of the housing  12  in a direction perpendicular to the X direction, the pressure surface may more uniformly press the adhesive tape  14  following the concaves and convexes. 
     The left edge  22   c  of the pressure surface in  FIG. 6  is chamfered with a curvature. One reason for this is to prevent the edge portion of the pressure head  22  from damaging the adhesive tape  14  when the edge portion first comes in contact with the adhesive tape  14 . 
     Third Modified Example 
       FIGS. 7A and 7B  are views for explaining a modified example of the pressure head  22  and the pressure rod  26  of the above-described embodiment. The display bonding device  10  used in the third modified example may be the same as that of the above-described embodiment except for the portions described below of the pressure head and the pressure rod in the third modified example. 
     The pressure rod connection unit  28  of the pressure rod  26  and the pressure head connection unit  30  of the pressure head  22  of the third modified example may be different from the pressure head  22  and the pressure rod  26  illustrated in  FIG. 2 , and a conical convex portion and a conical concave portion are formed. 
     Specifically, in one example, a conical convex portion facing the pressure head  22  is provided to the pressure rod connection unit  28  where the pressure rod  26  connects with the pressure head  22 . On the other hand, according to one embodiment, a conical concave portion which is swingably connected with the convex portion of the pressure rod  26  when the pressure head  22  presses the adhesive tape  14  can be provided to the pressure head connection portion  30  where the pressure head  22  connects with the pressure rod  26 . Thereby, the pressure head  22  may rotate around the pressure rod  26 . Although, in the example illustrated in  FIG. 7 , the pressure head  22  is the pressure head of the second modified example illustrated in  FIG. 6 , the pressure head  22  may be one of the pressure heads  22  shown in  FIGS. 2 ,  4 A to  4 C, and  5 A and  5 B. 
     In the third modified example, a connection holding body  31  is provided which is extended from the pressure head  22  and covers the pressure rod connection unit  28  and the pressure head connection unit  30 . The pressure rod  26  enters the internal space of the connection holding body  31  through an opening which is formed in the connection holding body  31  and has a diameter smaller than the maximum diameter of the conical shape of the pressure rod connection unit  28 . The diameter of the pressure rod  26  is smaller than the diameter of the opening of the connection holding body  31 . As a result, the pressure rod  26  passes through the opening of the connection holding body  31  so that play remains, and the pressure rod connection unit  28  cannot be pulled out from the connection holding body  31 . When the pressure rod  26  moves down and starts to press the pressure head  22 , the pressure rod  26  comes in contact with the conical concave portion of the pressure head  22  and applies pressure to the pressure head  22 . 
     At this time, the opening angle of the conical concave portion of the pressure head connection unit  30  may be larger than the opening angle of the conical convex portion of the pressure rod connection unit  28 , so the pressure head  22  may easily move in a certain range. 
     Therefore, the third modified example exerts the same effect as that of the above-described embodiment, the first modified example, and the second modified example by performing the same operation. 
     Although, in the third modified example, a conical convex portion is provided to the pressure rod connection unit  28  and a conical concave portion is provided to the pressure head connection unit  30 , a conical concave portion may be provided to the pressure rod connection unit  28  and a conical convex portion may be provided to the pressure head connection unit  30 . A circular truncated conical shape may be used instead of the conical shape. In these cases, the opening angle of the conical convex portion or the circular truncated conical convex portion of the pressure rod connection unit  28  is larger than the opening angle of the conical concave portion or the circular truncated conical concave portion of the pressure head connection unit  30 . 
     Fourth Modified Example 
       FIGS. 8A and 8B  are views for explaining a schematic configuration of a pressure head  22  of a fourth modified example. In the fourth modified example, a plurality of pressure heads  22  can be provided to the display bonding device  10 . 
     Regarding the pressure head  22  illustrated in  FIG. 8A , the pressure rod connection unit  28  has a spherical concave portion and the pressure head connection unit  30  has a spherical convex portion as illustrated in  FIG. 2 . Regarding the pressure head  22  illustrated in  FIG. 8B , the pressure rod connection unit  28  has a conical convex portion and the pressure head connection unit  30  has a conical concave portion as illustrated in  FIGS. 7A  and  7 B. Therefore, each pressure head  22  may rotate around the pressure rod  26 . Although the fourth modified example illustrated in  FIG. 8B  also has the connection holding body  31  as illustrated in  FIGS. 7A and 7B , the connection holding body  31  is not illustrated in  FIG. 8B . 
     The concave portion of the pressure head  22  may have a conical concave shape having an opening angle larger than that of the convex portion of the pressure rod  26 . The shapes of the concave portion and the convex portion may be a circular truncated conical shape instead of a conical shape. 
     In the fourth modified example, each pressure head  22  may be provided with balancers that may move on the pressure head  22  as illustrated in  FIGS. 4A and 4B , and the tilt angle of the pressure surface of the pressure head  22  may be adjusted by the position of the balancers. 
     A resin sheet may be provided on the pressure surface of each pressure head  22 . 
     In the fourth modified example, the display bonding device  10  may also have the drive unit  18 , the stage  19 , a plurality of pressure heads  22 , and the pressure head movement mechanism  20 . 
     The drive unit  18  can be a driving source configured to move the pressure rod  26  of the pressure head movement mechanism  20  and includes, for example, a drive motor. 
     The housing  12  on which the adhesive tape  14  is placed may be mounted on the mounting surface of the stage  19 . 
     In an embodiment, the pressure head movement mechanism  20  moves the pressure heads  22  downward to the housing  12  and the adhesive tape  14  through the pressure rods  26  connected to each pressure head  22  so that the pressure heads  22  presses the housing  12  and the adhesive tape  14 . 
     The plurality of pressure heads  22  presses the adhesive tape  14  and the housing  12  with the tapered surface that is tilted in one direction with respect to the mounting surface of the stage  19  on which the adhesive tape  14  and the housing  12  are mounted or the curved surface that is tilted in at least one direction as the pressure surface. 
     The plurality of pressure heads  22  may be arranged in a row so that a position at which the adhesive tape  14  and the housing  12  are pressed moves sequentially in one direction. 
     The operation in which the plurality of pressure heads  22  attach the adhesive tape  14  to the housing  12  is performed in the flow described below. 
     First, a first pressure head  22   a  presses a first area of the adhesive tape  14 . Next, a second pressure head  22   b  presses a second area that partially overlaps the first area. In this way, an area is pressed so that a part of the pressed area overlaps the next area to be pressed. Therefore, air bubbles between the housing  12  and the adhesive tape  14  are gradually pushed and moved in one direction. Finally, the air bubbles between the housing  12  and the adhesive tape  14  are pushed out to the outside. Further, since the direction of the move of the pressed area corresponds to the tilt direction of the pressure surface of the pressure head, it is possible to efficiently push out the air bubbles between the housing  12  and the adhesive tape  14  in one direction. 
     Furthermore, it is repeated that an area which partially overlaps the area pressed previously by one of the pressure heads  22  is pressed by another pressure head. Thereby, even if the adhesive surface is long in one direction, it is possible to reduce residual air bubbles and perform the attaching operation in an extremely short time. 
     Such an operation of the pressure heads  22  may be performed by a pressure head movement mechanism  24 . For example, as illustrated in  FIG. 9 , the pressure head movement mechanism  24  may realize the operation of the pressure heads  22  by a dynamic mechanism using a pressure head rail  40  provided with a plurality of pressure heads  22 . 
     On the pressure head rail  40 , a plurality of pressure heads  22  move in a direction of arrows at a constant speed by a drive motor not illustrated in  FIG. 9 . An upper pressure rod  26   a  and a drive section of the upper pressure rod  26   a  may move in a left-right direction in the example of  FIG. 9  at a constant speed. When one of the pressure heads  22  comes to a position of the upper pressure rod  26   a  that is connected to the drive unit  18 , the upper pressure rod  26   a  moves down and presses the lower pressure rod  26   b.  Thereby, the pressure head  22  presses the adhesive tape  14  to the housing  12 . 
     In this way, in the fourth modified example, it is possible to press the adhesive tape  14  at a predetermined pressure position with the plurality of pressure heads  22  on the pressure head rail  40  provided with the plurality of pressure heads  22 . 
     All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventors to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention. Moreover, the term “or” is intended to mean an inclusive “or” rather than an exclusive “or.” That is, unless specified otherwise, or clear from the context, the phrase “X employs A or B” is intended to mean any of the natural inclusive permutations. That is, the phrase “X employs A or B” is satisfied by any of the following instances: X employs A; X employs B; or X employs both A and B. In addition, the articles “a” and “an” as used in this application and the appended claims should generally be construed to mean “one or more” unless specified otherwise or clear from the context to be directed to a singular form.