Abstract:
A touch panel has an upper board having an upper conductive layer, a lower board having a lower conductive layer, a pair of upper electrodes along the periphery of the upper conductive layer and having an upper electrode lead, a pair of lower electrodes along the periphery of the lower conductive layer and having a lower electrode lead, and a slit formed at the upper and lower conductive layers. One of the upper electrodes is formed along a side of the upper conductive layer, and the other of the upper electrodes is formed in a substantially U shape surrounding a whole periphery excluding the upper electrode lead. One of the lower electrodes is formed in a direction orthogonal to the side of the upper conductive layer, and the other of the lower electrodes is formed in a substantially U shape surrounding a whole periphery excluding the lower electrode lead.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to touch panels to be used primarily for operating various electronic equipment. 
     2. Background Art 
     In recent years, advance in multifunctionality and diversification of various electronic equipment such as mobile phones, car navigation systems or the like has been seen. Along with this trend, there has been an increase in electronic equipment in which various functions can be switched by pushing with a finger or a pen an optically transparent touch panel provided on the front surface of a display device such as a liquid crystal display while visually identifying through the touch panel what is displayed on the display behind the touch panel. Accordingly, touch panels are being sought that have good visibility and which assure precise operation. 
     Referring to  FIGS. 4 through 6 , description will now be given of a conventional touch panel. For easy understanding of the construction, the drawings are partially enlarged. 
       FIG. 4  is a sectional drawing of a conventional touch panel.  FIG. 5  is a plan view of the upper board and the wiring board of  FIG. 4 .  FIG. 6  is a plan view of the lower board and the wiring board of  FIG. 4 . In  FIG. 4 , upper board  1  and lower board  2  are films or thin sheets and are optically transparent. On the rear face of upper board  1  is formed optically transparent upper conductive layer  3  made of indium tin oxide. On the top face of lower board  2  is formed optically transparent lower conductive layer  4  made of indium tin oxide. 
     As shown in  FIG. 5 , a pair of upper electrodes  5 ,  6  made of silver and the like is formed on the top and bottom edges of upper conductive layer  3 . Upper electrodes  5 ,  6  extend along the outer periphery of upper conductive layer  3 , and plural leads  5 A,  6 A are provided on upper conductive layer  3 . Also, as shown in  FIG. 6 , a pair of lower electrodes  7 ,  8  is provided at the left and right edges of lower conductive layer  4 . Lower electrodes  7 ,  8  extend along the outer periphery of lower conductive layer  4 , and plural leads  7 A,  7 B are provided at edges of lower conductive layer  4 . 
     Also, as shown in  FIG. 5 , dummy pattern  9 A and plural dummy patterns  9 B are formed on the lower edge of upper board  1 , and dummy pattern  9 C is provided at the right edge in order to keep parallelism between upper board  1  and lower board  2 . Slits  10 A,  10 B,  10 C are formed at the inner right of upper electrode  5  of upper board  1 , between upper electrodes  5 ,  6 , between leads  5 A,  5 B, between leads  5 A,  6 A, at inner left of dummy pattern  9 C, and between upper electrode  6  and dummy pattern  9 A, by removing upper conductive layer  3  by means of laser processing and the like. 
     Also, as shown in  FIG. 6 , dummy pattern  9 D is provided on the upper edge of lower board  2  and plural dummy patterns  9 E are provided on the bottom edge in order to keep parallelism between upper board  1  and lower board  2 . Slits  10 D,  10 E are formed at the inner top of lower electrodes  7 ,  8  of lower board  2 , between leads  7 A,  7 B, and at the inner bottom of dummy pattern  9 D, by removing lower conductive layer  4  by means of laser processing and the like. With these slits, short-circuiting between each electrode and the dummy patterns can be prevented thus maintaining insulation. 
     Also, plural dot spacers (not shown) are formed with an insulating resin at a predetermined interval on the top face of lower conductive layer  4 . Nearly-frame-shaped spacer  11  is provided on the outer periphery on the top face of lower board  2 , and outer peripheries of upper board  1  and lower board  2  are glued together with adhesive layer  12  coated on the top face of spacer  11 . Upper conductive layer  3  and lower conductive layer  4  are oppositely disposed with a predetermined gap in between. 
     Furthermore, filmy wiring board  13  is sandwiched between upper board  1  and lower board  2 . Upper edges of plural wiring patterns  14 ,  15  formed on the top and bottom faces of wiring board  13  are bonded and connected with leads  5 A,  6 A, leads  7 A,  8 A, respectively, with an anisotropic conductive adhesive (not shown) thereby completing a touch panel. Here, the anisotropic conductive adhesive is manufactured by dispersing conductive particles in a synthetic resin. 
     A touch panel constructed in this way is disposed on a front face of a display device such as a liquid crystal display and mounted on electronic equipment. And, plural wiring patterns  14 ,  15  of wiring board  13  are connected to electronic circuits (not shown) of the electronic equipment with a connector or by soldering. 
     In the above configuration, by pressing top face of upper board  1  with a finger or a pen in accordance with what is displayed on the display device behind the touch panel, upper board  1  is warped making upper conductive layer  3  of the pressed location come in contact with lower conductive layer  4 . Subsequently, a voltage is sequentially applied from the electronic circuit through plural wiring patterns  14 ,  15  of wiring board  13  to both edges of upper electrodes  5 ,  6  and lower electrodes  7 ,  8  and to both edges of lower conductive layer  4  which is in an orthogonal direction. The electronic circuit detects the pressed location based on the ratio of these voltages, and switching of various functions of the electronic equipment is enabled. 
     That is, under a condition in which plural menus are displayed on the display device behind the touch panel, when the top face of upper board  1  on top of a desired menu is pressed, the electronic circuit detects the pressed location through plural wiring patterns  14 ,  15  of wiring board  13 . In this way, selection of a desired menu from among plural menus can be made. 
     In such a touch panel, plural dummy patterns are formed in order to maintain parallelism between upper board  1  and lower board  2  in addition to upper electrodes  5 ,  6  and lower electrodes  7 ,  8 . In addition, in order to prevent short-circuiting between electrodes and dummy patterns and maintain insulation, gap  17 A is provided between upper right edge of upper electrode  5  of upper board  1  and upper edge of dummy pattern  9 C, and gap  17 B is provided between lower edge of dummy pattern  9 C and right edge of dummy pattern  9 A, for example. 
     Similarly, gap  17 C is provided between upper edge of lower electrode  7  of lower board  2  and left edge of dummy pattern  9 D, and gap  17 D is provided between right edge of dummy pattern  9 D and upper edge of lower electrode  8 . Nearly-frame-shaped spacer  11  and adhesive layer  12  are formed by printing and the like method on the top face of lower board  2 , and outer peripheries of upper board  1  and lower  2  are bonded together. During this process, at the edges of upper board  1  and lower board  2  where these gaps exist, plural openings are formed that communicate the gaps between upper conductive layer  3  and lower conductive layer  4  to the air. 
     As a result, when the top face of upper board  1  is pressed, air goes in and out through these gaps and openings. Sometimes, dusts or moisture attach to upper conductive layer  3  or to lower conductive layer  4  thus making electrical on-off action unstable. Furthermore, depending on the atmospheric pressure of the environment of the use of the touch panel, swelling or depression of upper board  1  may be caused, further causing interference fringes, the so-called Newton rings, due to reflection of external light and making displayed information on the display device behind the touch panel difficult to read. 
     Accordingly, in order to prevent these inconveniences and ensure reliable electrical on-off action and good visibility, the following is generally practiced at the expense of extra work. Namely, an adhesive is applied to these gaps and openings after bonding upper board  1  and lower board  2  together, and the air space between upper conductive layer  3  and lower conductive layer  4  is sealed. 
     As related art information of the invention of this application, Japanese Unexamined Patent Application Publication No. 2003-58319 is known. 
     As discussed above, conventional touch panels disadvantageously require sealing of plural gaps and openings with an adhesive in order to maintain insulation between electrodes and dummy patterns, costing time for fabrication and resulting in a higher cost. 
     SUMMARY OF THE INVENTION 
     The touch panel of the present invention includes an optically transparent upper board having an upper conductive layer formed on its lower face, an optically transparent lower board having a lower conductive layer, which is formed on its upper face and faces to the upper conductive layer with a predetermined gap in between, a pair of upper electrodes extending along an outer periphery of the upper conductive layer and having an upper electrode lead, a pair of lower electrodes extending along an outer periphery of the lower conductive layer and having a lower electrode lead, a slit in a predetermined shape formed on the upper conductive layer and the lower conductive layer. One of the pair of upper electrodes is formed along a side of the upper conductive layer, and the other of the pair of upper electrodes is formed in substantially U shape surrounding whole periphery excluding the upper electrode lead. One of the pair of lower electrodes is formed in a direction orthogonal to the side of the upper conductive layer, and the other of the pair of lower electrodes is formed in substantially U shape surrounding whole periphery excluding the lower electrode lead. 
     Because the upper electrodes and the lower electrodes extend in a manner enclosing the entire periphery along the outer periphery of the upper conductive layer and the lower conductive layer, gaps and openings are not formed except at the portions where upper electrode leads and the lower electrode leads exist, both of which are connected with a wiring board. As a result, there is no need to seal gaps or openings, so that fabrication becomes simple. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sectional view of a touch panel in an embodiment of the present invention. 
         FIG. 2  is a plan view of an upper board and a wiring board in  FIG. 1 . 
         FIG. 3  is a plan view of a lower board and the wiring board in  FIG. 1 . 
         FIG. 4  is a sectional view of a conventional touch panel. 
         FIG. 5  is a plan view of the upper board and the wiring board in  FIG. 4 . 
         FIG. 6  is a plan view of the lower board and the wiring board in  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring to the drawings, description of an embodiment of the present invention will be given. This invention is not limited by the preferred embodiment. 
     In the following, description of the embodiment of the present invention will be given referring to  FIG. 1  through  FIG. 3 . 
     For easy understanding of the structure, each drawing is rendered with some of the partial dimensions enlarged. Also, elements similar to those in the BACKGROUND ART have the same reference numbers, and the descriptions of those elements are omitted. 
     Preferred Embodiment 
       FIG. 1  is a sectional view of a touch panel in a preferred embodiment of the present invention.  FIG. 2  is a plan view of the upper board and the wiring board in  FIG. 1 .  FIG. 3  is a plan view of the lower board and the wiring board in  FIG. 1 . 
     In  FIG. 1 , optically transparent upper board  1  is made of a film of polyethylene terephthalate (PET) or polycarbonate (PC) or a thin sheet of glass. Optically transparent lower board  2  is also made of a film of PET or PC or a thin sheet of glass. Optically transparent upper conductive layer  3  made of indium tin oxide or tin oxide is formed on the lower face of upper board  1  while similarly made lower conductive layer  4  is formed on the top face of lower board  2  by sputtering and the like method. 
     In  FIG. 2 , upper electrode  25  is formed with silver or carbon on the top edge of upper conductive layer  3 . Upper electrode  26 , which pairs with upper electrode  25 , is formed along a side of the lower edge of upper conductive layer  3 . Upper electrode leads  25 A,  26 A are provided on upper electrodes  25 ,  26 , respectively. Upper electrode  25  extends along the outer periphery of upper conductive layer  3  and is formed nearly in the shape of letter U enclosing the entire periphery of upper conductive layer  3  except upper electrode leads  25 A,  26 A. 
     Also, as shown in  FIG. 3 , a pair of lower electrodes  27 ,  28  is formed on the outer periphery of lower conductive layer  4  in the direction orthogonal to upper electrodes  25 ,  26 , respectively. At least lower electrode  27  is formed in a direction orthogonal to the side of upper conductive layer  3 . Lower electrode leads  27 A,  28 A are provided at the edges of lower electrodes  27 ,  28 , respectively. Lower electrode  27  is formed nearly in the shape of the letter L. Lower electrode  28  extends from the upper edge of lower conductive layer  4  to the left edge and further to the outer periphery at the left bottom edge thus enclosing the entire periphery of lower conductive layer  4 _nearly in the shape of the letter U excluding lower electrode leads  27 A,  28 A. 
     Furthermore, plural dummy patterns  29 A are provided at the lower edge of upper board  1  in  FIG. 2  at locations corresponding to lower electrode leads  27 A,  28 A of lower board  2 . Plural dummy patterns  29 B are provided on lower board  2  at the locations corresponding to upper electrode leads  25 A,  26 A of upper board  1  in  FIG. 3 . 
     Slits  30 A,  30 B are formed by removing upper conductive layer  3  by laser cutting process and the like. As shown in  FIG. 2 , slit  30 A is formed nearly in the shape of the letter L extending from inner left part of upper electrode  25 , passing between upper electrode  25  on the left bottom edge and left edge of upper electrode  26 , and between upper electrode leads  25 A,  26 A. Slit  30 B is formed nearly in the shape of an inverted letter L by extending from inner right of upper electrode  25  to between upper electrode  25  on the lower right edge and right edge of upper electrode  26 . Thus slits  30 A,  30 B are formed at upper conductive layer  3  in a predetermined shape. 
     Also, slits  30 C,  30 D are formed in the same manner by removing lower conductive layer  4 . As shown in  FIG. 3 , slit  30 C is formed nearly in the shape of the letter T by extending from inner lower edge of lower electrode  27  and lower electrode  28  to between lower electrode leads  27 A,  28 A. Slit  30 D is formed nearly in the shape of the letter U by extending from inner upper right edge of lower electrode  28  passing along the left and bottom edges of lower electrode  27 . With these slits  30 A,  30 B,  30 C,  30 D, short-circuiting between electrodes and dummy patterns can be prevented and insulation is maintained. Thus slits  30 C,  30 D are formed at lower conductive layer  4  in a predetermined shape. 
     Additionally, plural dot spacers (not shown) are formed with epoxy resin or silicone on the top face of lower conductive layer  4  at a predetermined spacing. Nearly-frame-shaped spacer  11  made of polyester resin or epoxy resin is provided on the outer periphery of the top face of lower board  2 . Outer peripheries of upper board  1  and lower board  2  are bonded together with adhesive layer  12  of acrylic resin or rubber coated on the top face of spacer  11 . Upper conductive layer  3  and lower conductive layer  4  face each other with a predetermined gap in between. 
     Also, filmy wiring board  13  is made of polyimide or PET. Wiring board  13  is sandwiched between upper board  1  and lower board  2 . The upper edges of plural wiring patterns  14 ,  15  made of copper foil, silver, carbon, etc., formed on the top and bottom faces of wiring board  13  are connected by bonding with anisotropic conductive adhesive (not shown) to upper electrode leads  25 A,  26 A and lower electrode leads  27 A,  28 A, thus completing a touch panel. The anisotropic conductive adhesive is made by dispersing plural conductive particles prepared by gold-plating nickel or resin in a synthetic resin such as epoxy, acrylic, or polyester. 
     Put simply, nearly-U-shaped upper electrode  25  is formed on the bottom face of upper board  1  in a manner enclosing the entire periphery except upper electrode leads  25 A,  26 A. In addition, nearly-U-shaped lower electrode  28  is formed on the top face of lower board  2  in a manner enclosing the entire periphery except lower electrode leads  27 A,  28 A. In the state in which the outer peripheries of upper board  1  and lower board  2  are bonded together with adhesive layer  12 , parallelism between upper board  1  and lower board  2  is maintained by upper electrode  25  and lower electrode  28  that extend over almost the entire circumference of the outer periphery. At the same time, no gaps or openings can be formed except at upper electrode leads  25 A,  26 A and lower electrode leads  27 A,  28 A. 
     Furthermore, at the locations on upper board  1  and lower board  2  where upper electrode leads  25 A,  26 A and lower electrode leads  27 A,  28 A are formed, wiring board  13  is sandwiched, bonded and connected with an anisotropic adhesive. As a result, in a completed touch panel, the entire outer peripheries of upper board  1  and lower board  2  are sealed, and the gap between upper conductive layer  3  and lower conductive layer  4  is sealed. 
     In the meantime, by coating an adhesive of acrylic resin or silicone resin to the location where upper board  1 , lower board  2  and wiring board  13  are sandwiched, wiring board  13  can be more firmly secured. At the same time, the gap between upper conductive layer  3  and lower conductive layer  4  can be further securely sealed. 
     A touch panel constructed in this way is disposed on a front face of a display device such as a liquid crystal display and mounted on electronic equipment. Plural wiring patterns  14 ,  15  of wiring board  13  are electrically connected with electronic circuits (not shown) of the electronic equipment with a connector or by soldering. 
     In the above configuration, by pressing the top face of upper board  1  with a finger or a pen, upper board  1  is warped making upper conductive layer  3  of the pressed location come in contact with lower conductive layer  4 . 
     A voltage is sequentially applied from the electronic circuit to upper electrodes  25 ,  26  and lower electrodes  27 ,  28  via plural wiring patterns  14 ,  15  of wiring board  13 , and to both edges of upper conductive layer  3 , and to both edges of lower conductive layer  4  which is orthogonal to upper conductive layer  3 . Depending on the ratio of these voltages, the electronic circuit detects the pressed location and various functions of the equipment are switched. 
     That is, when the top face of upper board  1  on top of a desired menu is pressed under a state in which plural menus are displayed on the display device behind the touch panel, the electronic circuit detects the pressed location through plural wiring patterns  14 ,  15  of wiring board  13 . In this way, a desired menu can be selected from among plural menus. 
     The touch panel configured as described above extends to the outer periphery on the lower face of upper board  1  and upper face of lower board  2 , and is constructed in a manner such that the outer periphery is sealed leaving no gaps or openings by means of nearly-U-shaped upper electrodes  25  and lower electrodes  28  formed covering the entire periphery. As a result, no air enters the gap between upper conductive layer  3  and lower conductive layer  4  during pressing operation, and attachment of dust or moisture on upper conductive layer  3  or lower conductive layer  4  is prevented thus enabling stable electrical on-off action. 
     Also, as the gap between upper conductive layer  3  and lower conductive layer  4  is sealed, even when atmospheric pressure of the environment changes to some extent, there will be no swelling or denting of upper board  1  due to coming or going of air. Furthermore, the touch panel is configured in a manner such that an interference pattern, the so-called Newton&#39;s rings, due to reflection of external light can be prevented and good visibility of the display device behind the touch panel is obtained. 
     In addition, as the gap between upper conductive layer  3  and lower conductive layer  4  is sealed during fabrication of the touch panel, coating of an adhesive on gaps and openings is not required making fabrication easy. As a result, it becomes possible to manufacture touch panels at a low cost. 
     According to the preferred embodiment of the present invention as described above, upper electrode  25  extending from an edge of upper conductive layer  3  on the lower face of upper board  1 , and lower electrode  28  extending from an edge in a direction orthogonal to upper conductive layer  3  of lower conductive layer  4  on the top face of lower board  2  are extended along the outer peripheries of upper conductive layer  3  and lower conductive layer  4 , and are formed nearly in the shape of the letter U in a manner enclosing the entire periphery excluding upper electrode leads  25 A,  26 A, and lower electrode leads  27 A,  28 A. As a result, the parallelism between upper board  1  and lower board  2  can be maintained. As no gaps and openings are formed, the gap between upper conductive layer  3  and lower conductive layer  4  can be sealed by a simple structure. A touch panel is thus obtained which provides reliable electrical on-off action and good visibility. 
     In the above, description is made of a structure in which upper electrode  25  extending from the top edge of upper conductive layer  3  and lower electrode  28  extending from the right edge of lower conductive layer  4  are extended along the outer peripheries of upper conductive layer  3  and lower conductive layer  4  in a manner enclosing the entire periphery roughly in the shape of the letter U. In addition, in the case of lower board  2 , for example, lower electrode  27  extending from the left edge of lower conductive layer  4  may be extended along the outer periphery of lower conductive layer  4  nearly in the shape of the letter U in a manner enclosing the entire periphery. 
     The touch panel in accordance with the present invention has the advantage of providing reliable electrical on-off action and good visibility with a simple structure, and is useful for operation of a variety of electronic equipment.