Abstract:
A transparent touch panel (TTP) comprising a fixed substrate of transparent resin, an adhesion layer disposed on the fixed substrate, an antireflection layer disposed on the adhesion layer, a first transparent conductive layer disposed on the antireflection layer, a second transparent conductive layer opposed to and spaced apart from the first transparent conductive layer, and a flexible transparent film disposed on the upper surface of the second transparent conductive layer. In one embodiment, rather than having a separate adhesion layer and antireflection layer, the adhesion layer may also serve as the antireflection layer, the rest of the above components remaining the same. The use of transparent resin in the TTP of the present invention reduces weight and increases resistance to breaking. The antireflection layer decreases the light reflection at respective boundary surfaces, thus increasing light transmittance. The adhesion layer strengthens adhesion of the antireflection layer and the first transparent conductive layer onto the fixed substrate, thus providing for even and uniform electrical resistance in the transparent conductive layer. An electronic apparatus thus comprises at least a control circuit, an LCD device for display, and a TTP disposed on the display surface of the LCD device. The TTP may comprise the TTP described above and/or may comprise a polarizing plate on an operating surface of the transparent touch panel.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to-a transparent touch panel attached on the display surface of a display device such as an LCD (liquid crystal display), a CRT (cathode ray tube), a plasma display, or the like, as well as to an electronic apparatus using the transparent touch panel. The touch panel is used to input control signals into an electronic apparatus by a user pressing a certain specific region of the display surface corresponding to the signal with a pen or a finger.  
         BACKGROUND OF THE INVENTION  
         [0002]    A transparent touch panel (hereinafter referred to as a “TTP”) of the prior art is described below with reference to FIG. 7, which shows a sectional view of a conventional TTP. In FIG. 7, a first transparent conductive layer  2 , typically made mainly of indium tin oxide (hereinafter referred to as “ITO”), is formed, typically by a sputtering process, on the upper surface of a fixed substrate  1 , typically made of glass. Provided on the first ITO layer  2  is a very small dot spacer  3 , typically made of an insulating epoxy resin or the like, disposed at regular intervals. The ITO layer  2  is provided at the perimeter edge with an insulating pattern  4  of a certain specific width. Above the first ITO layer  2 , a movable substrate formed of a transparent film, etc. having a second transparent conductive layer  5 , typically ITO, on the bottom surface, is provided opposing first ITO layer  2 , with insulating pattern  4  interposed between the surfaces. The upper surface of movable substrate  6  is covered with a hard coating layer  7  for protecting movable substrate  6  from getting scratched by a pressing pen or finger. Normally, the surface of movable substrate  6  having said hard coating film  7  is used as the operating surface of a TTP. The first ITO layer  2  and the second ITO layer  5  are connected with an outside circuit (not shown) through a circuit pattern  8 A formed on a flexible circuit board  8 , via a connection section  9 , typically made of silver paste.  
           [0003]    Operation for inputting a control signal is conducted by pushing movable substrate  6  from above in a designated position such that first ITO layer  2  and second ITO layer  5  make contact. Regions not intended for contact between layers  2  and  5  are separated by the dot spacers  3  so that no control signal input can be made from such regions. The location of the designated position is identified by the electrical resistance ratio in the first ITO layer  2  and the second ITO layer  5 . In particular, the designated position is identified by an outside circuit that detects the voltage ratio when there is contact at the designated position. The resistance is measured by applying a certain specific voltage on first ITO layer  2  and second ITO layer  5  via electrodes  10 A and  10 B provided at both edges of the respective layers, as shown in FIG. 8.  
           [0004]    A conventional TTP configured above using a glass plate for the fixed substrate  1 , however, has various drawbacks. For example, because glass has a large specific gravity, it is relatively heavy, and furthermore, glass is easily breakable by an excessive load or a shock.  
           [0005]    In order to evade such drawbacks, transparent resins have been tried for fixed substrate  1 . An ITO layer formed on a plastic substrate, however, also has drawbacks. One drawback is that the ITO layer poorly adheres to the plastic substrate. Another problem is that the light transmittance of a TTP with a plastic substrate is relatively less than the light transmittance of a TTP with a glass substrate. The poor adhesion of the ITO layer onto the plastic substrate may lead to a broken ITO layer after repetitive use of the TTP, or to the ITO layer peeling off from the substrate. Even if the ITO layer does not peel off, uniformity in resistance of the ITO layer may deteriorate after repetitive use of the TTP.  
           [0006]    For improving the transmittance, it has been a common practice to form a multi-layered film of inorganic compounds over the transparent plastic substrate, such as by sputtering or vacuum deposition. This increases the manufacturing cost of a TTP, however, and additionally requires expensive production facilities for manufacture of large area TTPs. Furthermore, the adhesion of the multi-layered inorganic film onto the plastic substrate is poor.  
           [0007]    The present invention addresses the drawbacks described above, and aims to offer a TTP that is lightweight and not easily breakable. The present invention also offers an electronic apparatus using such a TTP.  
         SUMMARY OF THE INVENTION  
         [0008]    A TTP of the present invention comprises:  
           [0009]    a fixed substrate comprising transparent plastic,  
           [0010]    an adhesion layer disposed on the fixed substrate,  
           [0011]    an antireflection layer disposed on the adhesion layer,  
           [0012]    a first transparent conductive layer, such as ITO, disposed on the antireflection layer,  
           [0013]    a second transparent conductive layer, such as ITO, provided opposed to the first transparent conductive layer and spaced therefrom, and  
           [0014]    a flexible transparent film provided on the upper surface of the second transparent conductive layer.  
           [0015]    Because the TTP of the present invention uses a plastic fixed substrate, it is lightweight and does not break easily. The antireflection layer provided between the fixed substrate and the first ITO layer reduces the reflection of light incident to respective boundary surfaces between the fixed substrate and the first ITO layer, thus improving light transmittance. Furthermore, the adhesion layer supports the tight adhesion of the antireflection layer and the first ITO layer onto the fixed substrate, providing uniform electrical resistance in the ITO layer. Thus the present invention provides a TTP that is superior in visibility, in durability against repetitive input operations, and that has superior positional accuracy. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    [0016]FIG. 1 is a sectional view of a TTP in a first exemplary embodiment of the present invention.  
         [0017]    [0017]FIG. 2 is a partially cutaway perspective view of the TTP of FIG. 1. FIG. 3 is a sectional view showing another TTP in the first exemplary embodiment.  
         [0018]    [0018]FIG. 4 is a sectional view showing a still other TTP in the first exemplary embodiment.  
         [0019]    [0019]FIG. 5 is a sectional view of a TTP in a second exemplary embodiment of the present invention.  
         [0020]    [0020]FIG. 6 is an exploded perspective view of an electronic apparatus in a third exemplary embodiment of the present invention.  
         [0021]    [0021]FIG. 7 is a sectional view of a conventional TTP of the prior art.  
         [0022]    [0022]FIG. 8 is a perspective view showing a portion of the conventional TTP of the prior art. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0023]    Exemplary embodiments of the present invention are described hereunder referring to the drawings. Each of the drawings has been shown magnified in the direction of thickness for an easier illustration of the structure.  
         [0024]    First Embodiment  
         [0025]    [0025]FIG. 1 shows a cross sectional view of a TTP in a first exemplary embodiment of the present invention. FIG. 2 is a perspective view of a TTP shown partially cut away. In FIG. 1, a first adhesion layer  12  is provided on the upper surface of substrate  11 , such as a polycarbonate substrate about 1.0 mm thick. The first adhesion layer  12  is a highly adhesive layer, such as an epoxy modified acrylic resin, for example formed by printing an epoxy acrylate ink and curing it. First adhesion layer  12  has adhesive properties on both the upper and lower surfaces of the adhesive layer so that the adhesion layer adheres well to substrate  11  and other layers adhere well to it. All adhesion layers discussed herein have similar dual-sided adhesive properties. Provided on first adhesion layer  12  is a first antireflection layer  13 . First antireflection layer  13  is preferably a five-layered structure, for example, a laminated structure of silica (referred to as “SiO 2 ”) having a refractive index of about 1.41 and titania (referred to as “TiO 2 ”) having a refractive index of about 2.00, provided by repetitive sputtering. On the first antireflection layer  13 , a first transparent conductive layer  14 , such as ITO, is formed by sputtering. On ITO layer  14 , very small dot spacers  15 , such as of an insulating epoxy resin, are provided at regular intervals, and an insulating pattern  16  having a certain specific thickness is provided at the outer perimeter.  
         [0026]    A second transparent conductive layer  18 , such as ITO, is formed, such as by sputtering, on a bottom surface of a flexible transparent film  17 , such as a biaxially oriented polyethylene terephthalate film about 0.175 mm thick. The second ITO layer  18  is disposed opposing the first ITO layer  14  with a certain space between the two ITO surfaces and with the insulating pattern  16  interposed between the two ITO surfaces.  
         [0027]    A hard coat layer  19  of an acrylic resin, for example having a pencil hardness of 3H, is covers the upper surface of film  17  for protecting the film from damage by the pushing pen or finger. The TTP is connected to a certain outside circuit (not shown), well-known in the art, by a flexible wiring board  20 . A wiring pattern  20 A on the flexible wiring board is connected to the end sections of first ITO layer  14  and second ITO layer  18  via a connector  21 , such as silver paste.  
         [0028]    The transparent touch panel configured above operates in the same manner as conventional touch panels.  
         [0029]    The TTP as configured above has a light transmittance of about 82%, and linearity in the position detection of about ±1.4%. The TTP demonstrated a change in linearity of less than about 0.1% after a durability test comprising writing one hundred thousand Japanese phonetic letters with a polyacetal pen having a tip radius of about 0.8 mm at a load of about 250 g. Even after about 500 hours on a shelf in a humid environment of about 60° C. at about 95% relative humidity, adhestion of first antireflection layer  13  and first ITO layer  14  to fixed substrate  11  was unaffected, and none of the characteristics, such as light transmittance, linearity in position detection, and durability against repetitive input operations, exhibited a change.  
         [0030]    A TTP having dimensions of about 100 mm×about 100 mm, supported at the perimeter, was pressed at the center of the panel with a polyacetal pen having a tip radius of about 0.8 mm at a load of about 30 kg. Fixed substrate  11  did not break. A TTP in the present embodiment weighs about half that of the glass-substrate counterpart.  
         [0031]    The above described TTP in the present embodiment, where the first ITO layer  14  has been formed on a fixed substrate  11  of a transparent resin, with the first adhesion layer  12  and the first antireflection  13  interposed, exhibits superior mechanical strength and high transmittance. First antireflection layer  13  reduces reflection of the light incident to respective boundary surfaces between fixed substrate  11  and first ITO layer  14 , providing increased light transmittance. Because of the tight adhesion of first antireflection layer  13  and first ITO layer  14  to fixed substrate  11 , the uniform electrical resistance of first ITO layer  14  is well maintained.  
         [0032]    Thus, a TTP may be obtained in accordance with the present invention that is lightweight, that does not break easily, that provides improved visibility of a display disposed underneath the TTP, that has superior linearity in the detection of the pressed position, and that has excellent durability against repetitive input operations.  
         [0033]    Furthermore, as shown in the sectional view FIG. 3, a second adhesion layer  22 , such as of an epoxy modified acrylic resin may be formed on the bottom surface of fixed substrate  11 , such as by printing an epoxy acrylate ink and curing it. Next, a second antireflection layer  23 , such as the five-layered structure of SiO 2  and TiO 2  formed by repetitive sputtering described above, may be provided on second adhesion layer  22 . These layers increase the overall transmittance of the TTP to about 85%, bringing about even greater further improvements in visibility.  
         [0034]    In an alternative embodiment, a hard coat layer  19 , such as an acrylic resin having a pencil hardness of 3H, and a third antireflection layer  24 , such as formed from a single layer about 0.10 μm thick of SiO 2  having a refractive index of about 1.41, may be provided, in that order, on the upper surface of film  17 , as shown in the sectional view FIG. 4. A fourth antireflection layer  25 , such as a single layer about 0.10 μm thick of SiO 2  having a refractive index of about 1.41, and a second ITO layer  18  may be provided on the bottom surface of film  17 . Such a configuration improves the transmittance of the TTP to about 90%. Thus a significantly superior visibility may be attained despite the reduced process steps of layer formation.  
         [0035]    Fixed substrate  11  may be a polycarbonate sheet as described above, or an acrylic resin sheet, a poly methyl methacrylate sheet, a polyolefin resin sheet, a polystyrene resin sheet, or the like may also be used. The fixed substrate  11  typically has a thickness of between about 0.5 mm to about 10 mm, preferably between about 0.7 mm to about 3 mm.  
         [0036]    A polycarbonate fixed substrate as described above, typically has a bending modulus of about 24,000 kg/cm 2 . Rigidity of the fixed substrate  11  may be increased further by the use of a resin having a higher bending modulus, such as but not limited to, “Arton” polyolefin resin by JSR, typically having a bending modulus of about 30,000 kg/cm 2  or “APO” polyolefin resin by Mitsui Chemical, typically having a bending modulus of about 32,000 kg/cm 2 . The increased rigidity reduces bending of the TTP caused by the pressure of a pen or a finger, as a result, lowers the mechanical load transmitted to the display device disposed underneath the TTP. This is advantageous in reducing deformation of a display during operation and for assuring a clear and easy-to-see display.  
         [0037]    A biaxially oriented polyethylene terephthalate film is generally used for film  17 . Other films, such as but not limited to, biaxially oriented polyethylene naphthalate film, polycarbonate film, polyether sulphone film, polyarylate film, polyolefin film, and the like may also be used. The thickness of film  17  is typically between about 0.05 mm to about 0.4 mm, and preferably between about 0.1 mm to about 0.2 mm.  
         [0038]    Preferred materials for first and the second adhesion layers  12  and  22  include, besides epoxy modified acrylic resin as described above, acrylic modified resin such as urethane acrylate, polyester acrylate, silicone acrylate, and the like; urethane modified resin containing tolylene diisocyanate, hexamethylene diisocyanate, and the like as the main component; and an epoxy modified resin containing bis-phenol A, bis-phenol F, and the like as the main component. The first and second adhesion layers  12  and  22  may be applied by, for example, printing or coating, and then curing.  
         [0039]    An adhesion layer of SiO 2  having a refractive index of about 1.41 and a thickness of about a 0.05 μm to about 0.15 μm may also function as an antireflection layer. In this case, it is not necessary to provide an independent antireflection layer, and the manufacturing cost of a TTP may be reduced. A SiO 2  layer having a thickness less than about 0.05 μm or more than about 0.15 μm, may also be used as an adhesion layer, but typically does not provide the desired antireflection effect, and so typically still requires an independent antireflection layer. Adhesion layers comprising SiO 2  typically comprise silica formed at atmospheric pressure.  
         [0040]    Alternative embodiments for the first through fourth antireflection layers  13 ,  23 ,  24 ,  25 , respectively, in place of the earlier-described five-layered structure of SiO 2  and TiO 2  or the single layer of SiO 2 , include but are not limited to a three-layered structure or a seven-layered structure formed by repetition of SiO 2  and TiO 2  layers, a three—to seven—layered structure formed by repetition of SiO 2  and ITO layers, and a layer about 0.1±0.05 μm thick of acrylic modified resin having a refractive index of about 1.45, such as but not limited to polymethyl methacrylate. These antireflection layers may be formed by physical processes, such as but not limited to sputtering, CVD (chemical vapor deposition), and the like, or by chemical processes, such as but not limited to printing of ink, dipping and pull-up from a solution, and the like.  
         [0041]    Instead of the first transparent conductive layer  14  and the second transparent conductive layer  18  being ITO, transparent electrode materials such as but not limited to tin oxide (SnO 2 ), zinc oxide (ZnO), a thin film of gold, and a thin film of silver, may also be used.  
         [0042]    Second Embodiment  
         [0043]    [0043]FIG. 5 is a sectional view of a transparent touch panel in a second exemplary embodiment of the present invention where a polarizing plate  31  is provided, in addition to the structure of the first embodiment, on the upper surface of the flexible film  30 .  
         [0044]    In FIG. 5 a fixed substrate  32 , such as a polycarbonate sheet having low birefringence manufactured by a casting process for providing optical isotropy, has a first adhesion layer  33  on an upper surface thereof and a second adhesion layers  34  on a bottom surface thereof. Adhesion layers  33  and  34  are typically formed of a SiO 2  layer, typically about 0.10 μm thick, that functions also as an antireflection layer. The SiO 2  layer may be typically formed by dipping fixed substrate  32  in a solution containing silicone tetra-ethoxide as the main component, and then pulling up and drying the substrate at about 100° C. for about 30 min. A first transparent conductive layer  14 , such as ITO, is disposed on the upper surface of the first adhesion layer  33 , such as by a sputtering process.  
         [0045]    On the bottom surface of film  30 , which is typically a non-oriented, optically isotropic polycarbonate film, a fourth antireflection layer  35 , such as SiO 2  layer about 0.10 μm thick having a refractive index of about 1.41, is provided, on which is disposed a second transparent conductive layer  18 , such as ITO, formed, for example, by a sputtering process.  
         [0046]    A polarizing plate  31  is provided on the upper surface of film  30 , and a hard coat layer  19 , such as an acrylic resin having a pencil hardness of 3H, is formed covering the upper surface of polarizing plate  31 . Hard coat layer  19  is for protects polarizing plate  31  from getting scratched by a pushing pen or finger during input operations. In addition, a third antireflection layer  24 , such as a single layer about 0.10 μm thick of SiO 2  having a refractive index of about 1.41, is provided on hard coat layer  19 . This third antireflection layer reduces the light reflection at the boundary surface between polarizing plate  31  and the air.  
         [0047]    The above-configured TTP operates in the same was as in the first embodiment, and therefore a detailed description is omitted here. Light transmittance of the TTP of this embodiment decreases to less than half of that in the first embodiment because of the effect of polarizing plate  31 . At the same time, the light reflection can also be decreased to less than half. Because the polarizing plate is placed on the upper surface of the flexible film of the TTP, the normal process of attaching a polarizing plate on the display surface of the LCD device (not shown) disposed underneath the TTP, is unnecessary. By placing the polarizing plate on the upper surface of the flexible film of the TTP or on the operating surface, the amount of light reflected within the TTP can be reduced to less than half as compared to the first embodiment. Because the polarizing plate in the TTP eliminates the need for the polarizing plate normally attached to the LCD device, the amount of light incident to the LCD device is unchanged and the overall cost for manufacturing the TTP apparatus including an LCD device is reduced. In particular, in the conventional manufacture of an LCD device, a polarizing plate is attached individually to the LCD panel, whereas in the present embodiment, the process for laminating the polarizing plate  31  and the film  30  can be conducted continuously, which enables the manufacturing cost to be lowered.  
         [0048]    The advantage described above is even more remarkable when a TTP is used in combination with a reflective type LCD device. When a reflective type LCD device is combined with a TTP of this embodiment, the process for laminating a polarizing plate to the LCD panel can be completely eliminated in the production of the LCD devices.  
         [0049]    Furthermore, by providing film  30  with a polarizing function, the process for attaching polarizing plate  31  to film  30  may also be eliminated. Film  30  may be provided with a polarizing function by, for example, adding an organic dye in the plastic material to be mixed together, and drawing the dye within the film into a monoaxial orientation in the process of film formation.  
         [0050]    As described in the foregoing, the present embodiment provides a TTP that is superior in the linearity of position detection at input operation, that has high durability against repetitive input operations, mechanical shocks and unexpected excessive loads, and that is lightweight with remarkable visibility and a significantly reduced amount of light reflection. The present invention provides such TTPs at a low cost.  
         [0051]    For fixed substrate  32 , besides the polycarbonate sheet used in the earlier example, any transparent plastic sheet that is optically almost-isotropic and having small birefringence is suitable, such as but not limited to a polyarylate sheet, a polyolefin sheet, and the like manufactured by a casting method.  
         [0052]    For film  30 , besides the polycarbonate film described above, any a transparent film that is optically almost-isotropic and that has small birefringence is suitable, such as but not limited to a polyarylate film, a polyether sulphone film, a polyolefin film, and the like.  
         [0053]    Third Embodiment  
         [0054]    [0054]FIG. 6 is an exploded perspective view of a handheld computer in accordance with a third exemplary embodiment of the present invention. In FIG. 6, a TTP  41  attached on the bottom surface of an upper case  42  is provided on an LCD device  43 . A control circuit  44  formed of electronic components such as central processing unit, memory device, etc. and a battery  45  for supplying power to the control circuit  44  are supported by the upper case  42  and a bottom case  46 . The TTP  41  and the LCD device  43  are coupled with the control circuit  44  by respective flexible wiring boards  47 ,  48  provided therefrom.  
         [0055]    A handheld computer in the present embodiment is put into operation by a pressing on a TTP  41  with a pen or a finger at a designated position representing an operational function, such as for example, power ON/OFF, selection of various software available, performing functions of a selected software, and the like, where icons or text corresponding to such operational functions are displayed on the LCD device  43 . The LCD device is configured to present various displays corresponding to the operational functions related to operation of the handheld computer as provided by the control circuit containing the central processing unit, the memory device, and the like.  
         [0056]    A handheld computer in the present embodiment using a TTP of this invention, among other items, has a sufficient physical strength to withstand the shock of a drop or an excessive load given unexpectedly on the computer while a user is carrying it. The handheld computer is lightweight. Visibility through the transparent touch panel is remarkably improved, and is particularly well suited for such complicated and large capacity information displays as letters, pictures, drawings, photos, and the like. Also, the linearity in the input position detection is superior, and the durability against repetitive input operations is high. Thus a handy and easy-to-use handheld computer can be obtained in accordance with the present embodiment of the present invention.  
         [0057]    The present invention uses a transparent plastic sheet for the fixed substrate. The fixed substrate has an adhesion-facilitating layer interposed between the substrate and each of the antireflection and ITO layers. The adhesion-facilitating layer not only improves the adhesion of the antireflection layer and the first ITO layer to the fixed substrate, but it also improves the evenness of the electrical resistance in the first ITO layer. Furthermore, the light transmittance of the TTP is also increased. By providing a polarizing plate on the upper surface of the flexible film on which the second ITO layer is disposed, light reflection is significantly reduced, and the electronic apparatus can be manufactured at a lower cost. Thus the present invention provides a low-cost, lightweight, portable electronic apparatus having high physical strength to resist shock or excessive loads, having outstanding visibility of the display device incorporated in the body, having superior linearity in position detection on the display screen, and having high durability physical strength against repetitive input operations conducted through the display screen.  
         [0058]    Although illustrated and described herein with reference to certain specific embodiments, the present invention is nevertheless not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims and without departing from the spirit of the invention.