Abstract:
A touch panel that includes a polarizing plate, and used as an input device of a display unit of a personal computer, a word processor, an electronic notebook and the like is structured by one or more films that have a low heat contraction coefficient and a low water absorption coefficient, which remarkably suppress occurrence of concave deformations of the polarizing plate after exposure to a high temperature and soaking in water, avoiding short circuits.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention generally relates to a touch panel and an input device therewith, and specifically relates to a touch panel that employs a resistance film, and that is provided on a screen of a personal computer, a word processor, an electronic notebook, etc. for inputting. 
   2. Description of the Related Art 
   When using a personal computer and the like equipped with a touch panel, a problem is that readability, therefore, operability is reduced by reflection of fluorescent light indoors, and the sun light outdoors. The problem has been coped with by providing a λ/4 phase-difference film and a polarizing plate on the surface of a touch panel, such that reflection of an external light is suppressed in order to enhance the readability. Here, the polarizing plate is generally structured by an extended film of dye mixed polyvinyl alcohol, which has polarization properties, and is sandwiched by films of triacetyl cellulose (TAC). The heat expansion coefficient of triacetyl cellulose (TAC) films  17   b  and  17   c  is 5.4×10 −5  cm/cm/degree C., which is comparatively large. The heat expansion coefficient of the polarizing plate, due to its structure, is approximately equal to the heat expansion coefficient of the triacetyl cellulose (TAC) films. 
   A touch panel is exposed to the external environment, and is influenced by ambient temperature and humidity. Under a high ambient temperature, the polarizing plate provided for improvement in visibility expands greatly, causing a curvature, that is, the central part of the touch panel swells outward. If the touch panel swells, the force required for the pushing operation increases, giving a different feeling of operation and reducing operability. Therefore, resistance to ambient conditions, such as heat and humidity, is also important for a touch panel. 
     FIG. 1(A)  shows a conventional touch panel  10  indicated by Japanese Patent 2001-34418. The touch panel  10  is structured by a touch panel main part  15  that includes a glass substrate  11 , a film  12  layered on the glass substrate  11  attached by double-sided adhesive tape  13 , on which a λ/4 phase-difference film  16 , and a polarizing plate  17 , both for suppressing reflected lights are provided, and further a polyethylene terephthalate (PET) film  18  for resisting environmental conditions is provided. On the glass substrate  11 , a transparent resistance film  11   a  and dot-like spacers  11   b  are formed. Under the film  12 , a transparent resistance film  12   a  is formed. 
   The polarizing plate  17  is structured by a film (polarizing film)  17   a  that is made by extending a film of dye mixed polyvinyl alcohol (PVA) to provide a polarization property, sandwiched by films  17   b  and  17   c  that are made from triacetyl cellulose (TAC). Thickness of the films  17   b  and  17   c  is several times the thickness of the film  17   a . Thus, the heat expansion coefficient of the polarizing plate  17  becomes approximately that of the films  17   b  and  17   c  made from TAC, that is, 5.4×10 −5  cm/cm/degree C. 
   The heat expansion coefficient of the film  18  made from PET is 1.5×10 −5  cm/cm/degree C., and is about ¼ of the heat expansion coefficient of the films  17   b  and  17   c  made from TAC. The thickness of the film  18  made from PET is about the same as the thickness of the polarizing plate  17 . 
   The film  18  made from PET pasted on the surface of the polarizing plate  17  functions such that the above-mentioned swelling phenomenon is suppressed under a severe high temperature condition. 
   Inventors of the present invention closely examined the touch panel  10  that contains the film  18  made from PET pasted on the surface of the polarizing plate  17 , and through experiments, found the following matters relative to resistances to heat and humidity. 
   The touch panel was left under a high temperature and high humidity condition, then put back to the usual temperature and humidity condition. Then, the touch panel  10  was deformed into a concave shape as shown in  FIG. 1(B) . 
   If the surface of the touch panel  10  is deformed into a concave shape, there is a possibility that the film  12  will contact the glass substrate  11 , causing a short circuit of the touch panel  10 . If the resistance films  11   a  and  12   a  touch each other, making a short circuit, the touch panel  10  will not function properly. Therefore, concave deformation of the surface of a touch panel  10  is a more serious problem than the above-mentioned swelling phenomenon. 
   Further, when the surface of the touch panel  10  was deformed into a concave shape, exfoliation  19  occurred at a part of the adhesion portion of the film  12  to the glass substrate  11 . 
   The inventors of the present invention analyzed the concave deformation and determined a cause thereof as follows. 
   When the polarizing plate  17  was exposed to an environment of high temperature, and then returned to a normal temperature, the polarizing plate  17  had become a little shorter than the original length. 
   Here, the heat contraction rate is defined as {(L 0 −L 1 )/L 0 }×100, where L 0  is the original length, and L 1  is the length after the exposure to high temperature and returning back to a normal temperature. 
   The heat contraction rate of the polarizing plate  17  was 0.9%, after a 30-minute exposure to a 100 degrees C. ambient environment. 
   Further, when the polarizing plate  17  was put in a high humidity ambient environment, and returned to the usual environment afterwards, it was noticed that the polarizing plate  17  had become a little shorter than the original length. 
   Then, a moisture absorption contraction rate is defined as {(L 0 −L 2 )/L 0 }×100, where L 0  is the original length, and L 2  is the length after the exposure to the humidity. 
   The moisture absorption contraction rate of the polarizing plate  17  was 1.5% at an exposure to 60 degrees C. and 95% RH for 100 hours. The water absorption rate of the polarizing plate  17  was 2–4.5%, when it was soaked in 23-degree C. water for 24 hours. 
   As above, the polarizing plate  17  expands thermally when exposed to high temperature, and shrinks to shorter than the original length when it is returned to room temperature, resulting in a permanent deformation. The polarizing plate  17  thereby becomes shorter than the film of the touch panel immediately underneath. Further, when the polarizing plate  17  is exposed to high humidity, it expands due to moisture absorption. When it is returned to room temperature, the moisture is reduced and the polarizing plate  17  contracts to shorter than the original length, resulting in a permanent deformation. The polarizing plate  17  shrinks to shorter than the film of the touch panel immediately underneath. Analysis indicates that the central part of the touch panel deforming into a concave shape is a permanent deformation, with the polarizing plate  17  shrinking to a shorter length than the film of the touch panel. 
   From above, it is determined that the permanent deformation of the polarizing plate caused by heat and humidity is the real problem to solve. 
   SUMMARY OF THE INVENTION 
   It is a general object of the present invention to provide a touch panel and an input device that includes the touch panel that substantially obviate one or more of the problems caused by the limitations and disadvantages of the related art. 
   Features and advantages of the present invention will be set forth in the description that follows, and in part will become apparent from the description and the accompanying drawings, or may be learned by practice of the invention according to the teachings provided in the description. Objects as well as other features and advantages of the present invention will be realized and attained by the touch panel and the input device equipped therewith particularly pointed out in the specification in such full, clear, concise, and exact terms as to enable a person having ordinary skill in the art to practice the invention. 
   To achieve these and other advantages and in accordance with its purpose, as embodied and broadly described herein, the invention provides a touch panel that employs a film that has a small heat contraction rate and a small water absorption rate, and is made from one of polyethylene naphthalate, polynorbornen, polycycloolefin, polycarbonate, polyether sulphon, and polyarylate. Therein, a polarizing plate is covered by the film, and the polarization plate is configured by two sheets of the film sandwiching a polarizing film. The touch panel may include a fluororesin film that covers the polarizing plate. The touch panel of the present invention may include a λ/4 phase-difference film pasted to an upper surface of a glass substrate. The present invention also includes an input device that includes the touch panel. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1(A)  is a diagram showing a conventional touch panel; 
       FIG. 1(B)  is a diagram showing a conventional touch panel that experiences a concave deformation; 
       FIG. 2  is a diagram showing a touch panel of the first embodiment of the present invention; 
       FIG. 3  is a diagram showing relations of direction of the absorption axis of the polarizing plate, and a λ/4 phase-difference film that constitute the touch panel of  FIG. 2 ; 
       FIGS. 4(A) ,  4 (B),  4 (C),  4 (D), and  4 (E) are diagrams showing the first five variations of the first embodiment; 
       FIGS. 5(A) ,  5 (B) and  5 (C) are diagrams showing the second group of three variations of the first embodiment; 
       FIG. 6  is a diagram showing a third group containing one variation of the first embodiment; 
       FIGS. 7(A) ,  7 (B),  7 (C),  7 (D),  7 (E) and  7 (F) are diagrams showing the fourth group containing six variations of the first embodiment; 
       FIG. 8  is a diagram showing a touch panel of the second embodiment of the present invention; 
       FIGS. 9(A) ,  9 (B),  9 (C),  9 (D) and  9 (E) are diagrams showing five variations of the second embodiment; 
       FIG. 10  is a diagram showing a touch panel of the third embodiment of the present invention; 
       FIG. 11  is a diagram showing a touch panel of the fourth embodiment of the present invention; 
       FIG. 12  is a table showing a composition and an evaluation of the embodiments of the present invention; 
       FIG. 13  is a continuation of  FIG. 12 ; and 
       FIG. 14  is a table showing properties of films. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   In the following, embodiments of the present invention will be described with reference to the accompanying drawings. 
     FIG. 2  shows a touch panel  20  of the first embodiment of the present invention. The touch panel  20  is formed on the upper surface of a liquid crystal display  30 . The liquid crystal display  30  and the touch panel  20  are components of an input device  35 . 
   The touch panel  20  includes a λ/4 phase-difference film  22  pasted on the back of a touch panel main part  21  in order to suppress light reflection, another λ/4 phase-difference film  23  and a polarizing plate  24  pasted on the upper surface of the main part  21  of the touch panel in order to suppress light reflection, and a polyethylene naphthalate (PEN) film  25  pasted on the surface of the polarizing plate  24  in order to enhance resistance to high temperature and humidity. 
   Absorption axes of the λ/4 phase-difference film  22 , the λ/4 phase-difference film  23 , and the polarizing plate  24  have relations as shown in  FIG. 3 . An absorption axis  24   a  of the polarizing plate  24  and an absorption axis  30   a  of the liquid crystal display  30  are the same at 45 degrees. An absorption axis  23   a  of the λ/4 phase-difference film  23  is in a +45 degree direction to the absorption axis  24   a  of the polarizing plate  24 . An absorption axis  22   a  of the λ/4 phase-difference film  22  is in a −45 direction to the absorption axis  24   a  of the polarizing plate  24 . 
   The touch panel main part  21  includes a polycarbonate film  27  whose thickness is 100 micrometers and pasted by double-sided tape  29  on the upper surface of a glass substrate  26  whose thickness is 1.1 mm, and functions as a resistance film. A transparent resistance film  26   a  and dot-like spacers  26   b  are formed on the upper surface of the glass substrate  26 . A transparent resistance film  27   a  is formed on the undersurface of the polycarbonate film  27 . 
   The thickness of each of the λ/4 phase-difference film  22  and the λ/4 phase-difference film  23  is 50 micrometers. 
   The polarizing plate  24  includes an extended film  24   a  that is made by extending a hydrophilic resin film of polyvinyl alcohol that is mixed with dye, and giving a polarization property, sandwiched by films  24   b  and  24   c  made from triacetyl cellulose (TAC). Sumitomo Chemical&#39;s dye-mixed polarizing plate SQ-1852AP, with a thickness of 180 micrometers, is used as the polarizing plate  24 . 
   As the polyethylene naphthalate (PEN) film  25 , Kaladex 1030 made by Teijin DuPont is used. Thickness of the PEN film  25  that is pasted by an acrylic adhesion agent is 100 micrometers. 
   An antireflection film  28  is formed on the upper surface of the PEN film  25 . 
   As shown in  FIG. 14 , the heat contraction rate of the PEN film  25  is 0.1% or less after it is exposed to 100 degrees C. for 30 minutes, and the water absorption rate is 0.4%, after it soaks in 23-degree C. water for 24 hours, which are considerably smaller than the heat contraction rate and the water absorption rate of the film  18  that is made from polyethylene terephthalate. 
   An evaluation result of the touch panel  20  that is configured as above is as follows (refer to  FIG. 12 ). 
   The total light reflection factor was 1.1%. Specifically, neither a fluorescent ceiling light nor an operator&#39;s face was reflected by the surface of the touch panel  20 ; there was little reflection of sunlight outdoors; images presented by the liquid crystal display  30  were clear; and visibility was excellent. 
   A result of the high temperature storage examination of the touch panel  20  is as follows. The examination was made after exposing the touch panel  20  to a temperature of 100 degrees for 240 hours, and then returning it to room temperature. No concave deformations and no convex deformations were found; no short circuits were generated; and no exfoliations of the film  27  from the glass substrate  26  were found. These are owing to the film  25  suppressing contraction of the polarizing plate  24  that tends to contract when the touch panel  20  is exposed to high temperature for a long period of time, and then, put back to the usual environment, due to the property that the heat contraction rate of the film  25  is 0.1% or less. 
   A result of a high humidity storing examination of the touch panel  20  is as follows. The examination was made after storing the touch panel  20  at 60 degrees C. and 95% RH for 100 hours, and returning it to room temperature after that. No concave deformations and no convex deformations were found; no short circuits were generated; and no exfoliations of the film  27  from the glass substrate  26  were found. Due to the low water absorption rate of the film  25 , the film  25  prevents contraction of the polarizing plate  24  by protecting the surface and by suppressing water absorption of the polarizing plate  24 , when the touch panel  20  is stored at high humidity for a long period of time and put back to the usual environment afterward. 
   Next, a first group of variations of the first embodiment are explained. 
     FIGS. 4(A) through 4(E)  show five variations belonging to the first group. 
     FIG. 4(A)  shows a touch panel  20 A of a first variation of the first group. On the polarizing plate  24 , a polynorbornen film  40  (ARTON made by Japan Synthetic Rubber and thickness being 125 micrometers) is provided, which replaces the PEN film  25 . 
   The heat contraction rate of the polynorbornen was 0.1% or less after exposing it to a temperature of 100 degrees C. for 30 minutes. When it soaked in 23-degree C. water for 24 hours, the water absorption rate was 0.4%. The rates are considerably smaller than the heat contraction rate and the water absorption rate (the moisture absorption contraction rate) of the polyethylene terephthalate film  18 . 
   Further, on the upper surface of the polynorbornen film  40 , a hard coat  41  of an acrylic resin is formed in place of the antireflection film  28 . 
   An evaluation result of the touch panel  20 A is as follows. 
   The total light reflection factor was 3.2%. Further, the high temperature storing examination and the high humidity storing examination were performed under the same conditions as above. No concave deformations and no convex deformations were found; no short circuits were generated; and no exfoliations of the film  27  from the glass substrate  26  occurred. 
     FIG. 4(B)  shows a touch panel  20 B of the second variation. On the polarizing plate  24 , the polyethylene naphthalate (PEN) film  25  is replaced with a polycycloolefin film  42  (Zeonor 1600R, made by Nippon Zeon, and thickness being 100 micrometers). 
   The heat contraction rate of the polycycloolefin was 0.0% after exposing it to a temperature at 100 degrees C. for 30 minutes, and when it soaked in 23-degree C. water for 24 hours, the water absorption rate was 0.01%. The rates are considerably smaller than those of the polyethylene terephthalate film  18 . 
   Further, the hard coat  41  of an acrylic resin is formed on the upper surface of the polycycloolefin film  42 . 
   An evaluation result of the touch panel  20 B is as follows. 
   The total light reflection factor was 3.5%. Further, the high temperature storing examination and the high humidity storing examination were performed under the same conditions as above. No concave deformations and no convex deformations were found; no short circuits were generated; and no exfoliations of the film  27  from the glass substrate  26  occurred. 
     FIG. 4(C)  shows a touch panel  20 C of the third variation. On the polarizing plate  24 , the polyethylene naphthalate (PEN) film  25  is replaced with a polyethersulphone (PES) film  44  (VECTREX PES 5200G, made by ICI, and thickness being 175 micrometers). 
   When it soaked in 23-degree C. water for 24 hours, the water absorption rate of the polyethersulphone (PES) was 0.3–0.4%, and was considerably smaller than that of the film  18  made from polyethylene terephthalate. 
   Further, the hard coat  41  of an acrylic resin is formed on the upper surface of the film  44  made from polyethersulphone (PES). 
   An evaluation result of the touch panel  20 C is as follows. 
   The total light reflection factor was 4.3%. Further, the high temperature storing examination and the high humidity storing examination were performed under the same conditions as above. No concave deformations and no convex deformations were found; no short circuits were generated; and no exfoliations of the film  27  from the glass substrate  26  occurred. 
     FIG. 4(D)  shows a touch panel  20 D of the fourth variation. On the polarizing plate  24 , the film  25  made from polyethylene naphthalate (PEN) is replaced with a film  46  made from polycarbonate (PC) (made by Teijin Chemicals and thickness being 100 micrometers). 
   The heat contraction rate of polycarbonate was 0.04% or less after exposure to a temperature of 100 degrees C. for 30 minutes, and when it soaked in 23-degree C. water for 24 hours, the water absorption rate was 0.4%. The rates are considerably smaller than those of the film  18  made from polyethylene terephthalate. 
   Further, the hard coat  41  of an acrylic resin is formed on the upper surface of the film  46  made from polycarbonate (PC). 
   An evaluation result of the touch panel  20 D is as follows. 
   The total light reflection factor was 4.1%. Further, the high temperature storing examination and the high humidity storing examination were performed under the same conditions as above. No concave deformations and no convex deformations were found; no short circuits were generated; and no exfoliations of the film  27  from the glass substrate  26  occurred. 
     FIG. 4(E)  shows a touch panel  20 E of the fifth variation. On the polarizing plate  24 , the film  25  made from polyethylene naphthalate (PEN) is replaced with a film  48  (Emblate U-1, produced by Unitika) made from polyarylate (PAR). 
   When it soaked in 23-degree C. water for 24 hours, the water absorption rate of the polyarylate (PAR) was 0.15–0.26%, which is considerably smaller than that of the film  18  made from polyethylene terephthalate. 
   Further, the hard coat  41  of an acrylic resin is formed on the upper surface of the film  48  made from polyarylate (PAR). 
   An evaluation result of touch panel  20 E is as follows. 
   The total light reflection factor was 3.9%. Further, the high temperature storing examination and the high humidity storing examination were performed under the same conditions as above. No concave deformations and no convex deformations were found; no short circuits were generated; and no exfoliations of the film  27  from the glass substrate  26  occurred. 
     FIGS. 5(A) through 5(C)  show a second group of variations. 
   The variations of the second group additionally include a PEN film  25  made from polyethylene naphthalate on the upper surface of the polarizing plate  24 ; and the material of the film  27  of the touch panel main part  21  is changed. 
     FIG. 5(A)  shows a touch panel  20 F of the first variation of the second group. On the polarizing plate  24 , the film  25  made from polyethylene naphthalate (PEN) is formed, and the antireflection film  28  is formed on the upper surface of the film  25 . 
   A touch panel main part  21 F includes a film  50  of polynorbornen (ARTON, made by Japan Synthetic Rubber, and thickness being 175 micrometers) in place of the film  27  of polycarbonate, attached on the upper surface of the glass substrate  26  by a double-sided tape. 
   An evaluation result of the touch panel  20 F is as follows. 
   The total light reflection factor was 1.3%. Further, the high temperature storing examination and the high humidity storing examination were performed under the same conditions as above. No concave deformations and no convex deformations were found; no short circuits were generated; and no exfoliations of the film  50  from the glass substrate  26  occurred. 
     FIG. 5(B)  shows a touch panel  20 G of the second variation of the second group. On the polarizing plate  24 , the film  25  made from polyethylene naphthalate (PEN) is formed, and the antireflection film  28  is formed on the upper surface of the film  25 . 
   A touch panel main part  21 G includes a film  51  of polycycloolefin (Zeonor 1600R, made by Nippon Zeon, and thickness being 125 micrometers) attached on the upper surface of a glass substrate  26  in place of the film  27  of polycarbonate, by double-sided tape. 
   An evaluation result of the touch panel  20 G is as follows. 
   The total light reflection factor was 1.2%. Further, the high temperature storing examination and the high humidity storing examination were performed under the same conditions as above. No concave deformations and no convex deformations were found; no short circuits were generated; and no exfoliations of the film  51  from the glass substrate  26  occurred. 
     FIG. 5(C)  shows a touch panel  20 H of the third variation of the second group. On the polarizing plate  24 , the film  25  made from polyethylene naphthalate (PEN) is formed, and the antireflection film  28  is formed on the upper surface of the film  25 . 
   A touch panel main part  21 H includes a polyethersulphone (PES) film  52  (VECTREX PES 5200G, made by ICI, and thickness being 175 micrometers) in place of the polycarbonate film  27 , pasted on the upper surface of a glass substrate  26  by double-sided tape. 
   An evaluation result of touch panel  20 H is as follows. 
   The total light reflection factor was 1.7%. Further, the high temperature storing examination and the high humidity storing examination were performed under the same conditions as above. No concave deformations and no convex deformations were found; no short circuits were generated; and no exfoliations of the film  52  from the glass substrate  26  occurred. 
     FIG. 6  shows a variation belonging to a third group. 
     FIG. 6  shows a touch panel  20 I. On the polarizing plate  24 , the film  25  made from polyethylene naphthalate (PEN) is formed, and the antireflection film  28  is formed on the upper surface of this film  25 . 
   An antireflection film  60  is formed under the lower surface of the λ/4 phase-difference film  22  that is pasted to the undersurface of the touch panel main part  21 . The antireflection film  60  includes a silicon dioxide (SiO 2 ) film  60   a , an ITO film  60   b , and another silicon dioxide film  60   c.    
   An antireflection film  61  is formed on the upper surface of the liquid crystal display  30 . The antireflection film  61  includes a silicon dioxide (SiO 2 ) film  61   a , an ITO film  61   b , and another silicon dioxide film  61   c.    
   An evaluation result of the touch panel  20 I is as follows. 
   The total light reflection factor was 0.1%. Compared with the touch panel  20  of  FIG. 2 , images presented by the liquid crystal display  30  were clearer. Further, the high temperature storing examination and the high humidity storing examination were performed under the same conditions as above. No concave deformations and no convex deformations were found; no short circuits were generated; and no exfoliations of the film  27  from the glass substrate  26  occurred. 
     FIGS. 7(A)  through (F) show variations belonging to a fourth group. 
   The fourth group of the variations is characterized by not providing the λ/4 phase-difference films  23  and  22  that are shown in  FIG. 2 . Reduction of cost is the aim. 
     FIG. 7(A)  shows a touch panel  20 J of the first variation of the fourth group. 
   On the polarizing plate  24 , the film  25  made from polyethylene naphthalate (PEN) is pasted, and the antireflection film  28  and a hard coat  41  of an acrylic resin are formed on the upper surface of the film  25 . 
   The λ/4 phase-difference films  23  and  22  shown in  FIG. 2  are not formed in this variation. 
   An evaluation result of the touch panel  20 J is as follows. 
   The total light reflection factor was 9.5%. Further, the high temperature storing examination and the high humidity storing examination were performed under the same conditions as above. No concave deformations and no convex deformations were found; no short circuits were generated; and no exfoliations of the film  27  from the glass substrate  26  occurred. 
     FIG. 7(B)  shows a touch panel  20 K of the second variation of the fourth group. 
   On the polarizing plate  24 , a film  40  made from polynorbornen is pasted, and the antireflection film  28  and the hard coat  41  are formed on the upper surface of the film  40 . 
   The λ/4 phase-difference films  23  and  22  shown in  FIG. 2  are not formed. 
   An evaluation result of the touch panel  20 K is as follows. 
   The total light reflection factor was 6.5%. Further, the high temperature storing examination and the high humidity storing examination were performed under the same conditions as above. No concave deformations and no convex deformations were found; no short circuits were generated; and no exfoliations of the film  27  from the glass substrate  26  occurred. 
     FIG. 7(C)  shows a touch panel  20 L of the third variation of the fourth group. 
   On the polarizing plate  24 , a film  42  made from the polycycloolefin is pasted, and the antireflection film  28  and the hard coat  41  are formed on the upper surface of the film  42 . 
   The λ/4 phase-difference films  23  and  22  shown in  FIG. 2  are not formed. 
   An evaluation result of the touch panel  20 L is as follows. 
   The total light reflection factor was 6.3%. Further, the high temperature storing examination and the high humidity storing examination were performed under the same conditions as above. No concave deformations and no convex deformations were found; no short circuits were generated; and no exfoliations of the film  27  from the glass substrate  26  occurred. 
     FIG. 7(D)  shows a touch panel  20 M of the fourth variation of the fourth group. 
   On the polarizing plate  24 , a film  44  made from polyethersulphone (PES) is pasted, and the antireflection film  28  and the hard coat  41  are formed on the upper surface of the film  44 . 
   The λ/4 phase-difference films  23  and  22  shown in  FIG. 2  are not formed. 
   An evaluation result of the touch panel  20 M is as follows. 
   The total light reflection factor was 7.3%. Further, the high temperature storing examination and the high humidity storing examination were performed under the same conditions as above. No concave deformations and no convex deformations were found; no short circuits were generated; and no exfoliations of the film  27  from the glass substrate  26  occurred. 
     FIG. 7(E)  shows a touch panel  20 N of the fifth variation of the fourth group. 
   On the polarizing plate  24 , a film  46  made from polycarbonate (PC) is pasted, and the antireflection film  28  and the hard coat  41  are formed on the upper surface of the film  46 . 
   The λ/4 phase-difference films  23  and  22  of the upper and lower sides in  FIG. 2  are not formed. 
   An evaluation result of the touch panel  20 N is as follows. 
   The total light reflection factor was 6.8%. Further, the high temperature storing examination and the high humidity storing examination were performed under the same conditions as above. No concave deformations and no convex deformations were found; no short circuits were generated; and no exfoliations of the film  27  from the glass substrate  26  occurred. 
     FIG. 7(F)  shows a touch panel  200  of the sixth variation of the fourth group. 
   On the polarizing plate  24 , a film  48  made from the polyarylate (PAR) is pasted, and the antireflection film  28  and the hard coat  41  are formed on the upper surface of the film  48 . 
   The λ/4 phase-difference films  23  and  22  shown in  FIG. 2  are not formed. 
   An evaluation result of the touch panel  200  is as follows. 
   The total light reflection factor was 7.1%. Further, the high temperature storing examination and the high humidity storing examination were performed under the same conditions as above. No concave deformations and no convex deformations were found; no short circuits were generated; and no exfoliations of the film  27  from the glass substrate  26  occurred. 
   From above examinations and evaluations of the variations of the first embodiment, it is determined that the aimed objectives, that is, there should be no concave deformations and no short circuits, are achieved by employing a material having a heat contraction rate smaller than 0.3% after exposure to 100 degrees C. for 30 minutes, and a water absorption rate smaller than 0.5% after being soaked in 23-degree C. water for 24 hours, as the material for the film of the upper surface of the polarizing plate  24 . 
   A touch panel  100  of a second embodiment of the present invention is shown in  FIG. 8 . The touch panel  100  is formed on the upper surface of a liquid crystal display  30 . The touch panel  100  and the liquid crystal display  30  are components of an input device  110 . 
   The touch panel  100  is configured with a polarizing plate that has an enhanced resistance to heat and humidity. In  FIG. 8 , components that are the same as shown in  FIG. 2  are referenced by the same reference numbers. 
   The touch panel  100  includes the touch panel main part  21 , under the lower surface of which the λ/4 phase-difference film  22  is pasted in order to suppress the reflected light, and on the upper surface of the touch panel main part  21 , the λ/4 phase-difference film  23  and a polarizing plate  101  are pasted in order to suppress the reflected light. 
   The polarizing plate  101  includes the extended film (polarizing film)  24   a  of polyvinyl alcoholic film with dye mixed and extended, and films  101   b  and  101   c  of polycycloolefin (Zeonor 1600R, made by Nippon Zeon, and thickness being 100 micrometers) in place of the films  24   b  and  24   c  of triacetyl cellulose (TAC). The film  24   a  is laminated with and sandwiched by the films  101   b  and  101   c  by a dry-laminating method. 
   The heat contraction rate of triacetyl cellulose (TAC) is 0.8% after an exposure to a temperature of 100 degrees C. for 30 minutes, and the water absorption rate is 2–4.5% after soaking in water of 23 degrees C. for 24 hours. On the other hand, the heat contraction rate of the polycycloolefin is 0.0% after an exposure to a temperature of 100 degrees C. for 30 minutes, and the water absorption rate is 0.01% after soaking in water of 23 degrees C. for 24 hours, both rates being considerably smaller than those of the triacetyl cellulose (TAC). 
   Further, the antireflection film  102  is formed on the upper surface of the polarizing plate  101 , and the hard coat  103  of an acrylic resin is further formed on it. 
   An evaluation result of the touch panel  100  is as follows. 
   The total light reflection factor was 2.8%. Further, the high temperature storing examination and the high humidity storing examination were performed under the same conditions as above. No concave deformations and no convex deformations were found; no short circuits were generated; and no exfoliations of the film  27  from the glass substrate  26  occurred. This is due to the properties of the films  101   b  and  101   c , that is, the heat contraction rate is 0.0%, and the water absorption rate (the moisture absorption contraction rate) is small. The properties enhance the resistance to heat and humidity of the polarizing plate  101 . 
   Next, variations of the second embodiment of the present invention are explained. 
     FIG. 9(A)  shows a touch panel  100 A of a first variation of the second embodiment. 
   A polarizing plate  101 A includes films  104   b  and  104   c  made from polynorbornen in place of films  101   b  and  101   c  made from polycycloolefin. The films  104   b  and  104   c  sandwich the extended film  24   a  of polyvinyl alcohol with dye mixed by the dry-laminating method. 
     FIG. 9(B)  shows a touch panel  100 B of a second variation of the second embodiment. 
   A polarizing plate  101 B includes films  105   b  and  105   c  made from polycycloolefin in place of the films  101   b  and  101   c  made from polycycloolefin. The films  105   b  and  105   c  sandwich the extended film  24   a  of polyvinyl alcohol with dye mixed by the dry-laminating method. 
     FIG. 9(C)  shows a touch panel  100 C of a third variation of the second embodiment. 
   A polarizing plate  101 C includes films  106   b  and  106   c  made from polyethersulphone in place of the films  101   b  and  101   c  made from polycycloolefin. The films  106   b  and  106   c  sandwich the extended film  24   a  of polyvinyl alcohol with dye mixed by the dry-laminating method. 
     FIG. 9(D)  shows a touch panel  100 D of a fourth variation of the second embodiment. 
   A polarizing plate  101 D includes films  107   b  and  107   c  made from polycarbonate in place of the films  101   b  and  101   c  made from polycycloolefin. The films  107   b  and  107   c  sandwich the extended film  24   a  of polyvinyl alcohol with dye mixed by the dry-laminating method. 
     FIG. 9(E)  shows a touch panel  100 E of a fifth variation of the second embodiment. 
   A polarizing plate  101 E includes films  108   b  and  108   c  made from polyarylate in place of the films  101   b  and  101   c  made from polycycloolefin. The films  108   b  and  108   c  sandwich the extended film  24   a  of polyvinyl alcohol with dye mixed by the dry-laminating method. 
   An evaluation result of the touch panels  100 A through  100 E of the above variations is as follows. Under the same conditions as above, the high temperature storing examination and the high humidity storing examination were performed. No concave deformations and no convex deformations were found; no short circuits were generated; and no exfoliations of the film  27  from the glass substrate  26  occurred. 
   From the above examinations and evaluations of the second embodiments and variations thereof, it is determined that the objectives that no concave deformations occur and no short circuits are generated, are achieved by using a material having a heat contraction rate smaller than 0.3% after exposure to a temperature of 100 degrees C. for 30 minutes, and a water absorption rate smaller than 0.5% after being soaked in 23-degree C. water for 24 hours, as the material of the films that sandwich the extended film  24   a  of polyvinyl alcohol. 
   It is highly desirable that the material of the films that sandwich the extended film  24   a  of polyvinyl alcohol has the heat contraction rate smaller than 0.04% after exposure to a temperature of 100 degrees C. for 30 minutes, and the water absorption rate smaller than 0.4% when soaked in 23-degree C. water for 24 hours. 
   A touch panel  150  of a third embodiment of the present invention is shown in  FIG. 10 . The touch panel  150  is formed on the upper surface of the liquid crystal display  30 . The touch panel  150  and the liquid crystal display  30  are components of an input device  160 . 
   The touch panel  150  includes a film of fluororesin  151  on the upper surface of the polarizing plate  24 , which is provided aiming at improvement in resistance to heat and humidity. In  FIG. 10 , components that are the same as in  FIG. 2  are referenced by the same reference numbers. 
   The third embodiment provides a fluororesin film  151  that has a thickness of about 50 micrometers. The fluororesin is formed by applying a fluorine surface treatment agent to the upper surface of the polarizing plate  24 , a fluororesin coating, and then, dry-hardening. 
   An evaluation result of the touch panel  150  is as follows. 
   The total light reflection factor was 1.5%. Further, the high temperature storing examination and the high humidity storing examination were performed under the same conditions as above. No concave deformations and no convex deformations were found; no short circuits were generated; and no exfoliations of the film  27  from the glass substrate  26  occurred. 
   A touch panel  170  of a fourth embodiment of the present invention is shown in  FIG. 11 . The touch panel  170  is formed on the upper surface of the liquid crystal display  30 . The touch panel  170  and the liquid crystal display  30  are components of an input device  180 . 
   The touch panel  170  includes a λ/4 phase-difference film  172  pasted on the upper surface of the touch panel main part  171 , and a PEN film  25  in order to enhance resistances to heat and humidity on the upper surface. 
   A touch panel main part  171  of the touch panel  170  includes the glass substrate  26  on which a transparent resistance film  26   a  and a dot-like spacer  26   b  are formed, and a λ/4 phase-difference film  172  that has a transparent resistance film  173  formed under the surface thereof formed by sputtering. As the λ/4 phase-difference film  172 , Sumitomo Chemical&#39;s Sumikalite SEF-400138 is employed, the thickness of which is 100 micrometers. The film  172  is pasted on the upper surface of the glass substrate  26  by the double-sided tape  29 . This λ/4 phase-difference film  172  elastically bends and restores as pushed by a fingertip and the like, such that the transparent resistance film  173  touches and separates from, according to the fingertip operation, the transparent resistance film  26   a . In this manner, a touch operation is detected, and a touch position is determined. That is, the λ/4 phase-difference film  172  plays the same role, in regard to touch operation, as the film  27  that constitutes the touch panel main part  21  shown in  FIG. 2 . 
   The polarizing plate  24  is pasted on the upper surface of the touch panel main part  171  by an acrylic adhesion agent. 
   Further, the film  25  made from polyethylene naphthalate (PEN) whose thickness is 100 micrometers is pasted on the upper surface of the polarizing plate  24  by an acrylic adhesion agent. The antireflection film  28  is formed on the upper surface of the film  25 . 
   The λ/4 phase-difference film  22  is pasted under the lower surface of the glass substrate  26  of the touch panel main part  171 . 
   An evaluation result of the touch panel  170  is as follows. 
   The total light reflection factor was 1.3%. Further, the high temperature storing examination and the high humidity storing examination were performed under the same conditions as above. No concave deformations and no convex deformations were found; no short circuits were generated; and no exfoliations of the λ/4 phase-difference film  172  from the glass substrate  26  occurred. 
   Further, since the touch panel  170  is configured such that the λ/4 phase-difference film arranged on the upper side serves as the film of the upper surface of the touch panel main part, the film  27  in  FIG. 2  is dispensed with. That is, the touch panel  170  has one fewer component parts than the touch panel  20  shown in  FIG. 2 . Therefore, the touch panel  170  can be produced at a lower manufacturing cost than the touch panel  20  shown in  FIG. 2 . 
   In addition, in order to make the λ/4 phase-difference film function as the film of the upper surface of the touch panel main part, the transparent resistance film  173  is directly formed under the lower surface of the λ/4 phase-difference film  172 . 
   In addition, the film  25  made from polyethylene naphthalate may be replaced with a film made from one of polynorbornen, polycycloolefin, polycarbonate, polyethersulphone, and polyarylate. 
   Further, it is also possible to consider a suitable combination of the first embodiment, the second embodiment, the third embodiment, and the fourth embodiment, and variations thereof. In this manner, the resistance to heat and humidity of a touch panel can be further enhanced. 
   Further, the touch panel of each of the embodiments and the variations thereof can be applied to an upper surface of other types of displays, such as plasma displays and CRT displays, besides liquid crystal displays. 
   The input devices  35 ,  110 ,  160  and  180  are configured, among other things, with any one of the touch panels as specifically described in their respective sections of the above description, such that the high readability and the high resistance to heat and humidity of the touch panels of the present invention may be enjoyed. 
   According to the present invention, as described above, no concave deformations occur by employing a film whose heat contraction rate and water absorption rate are small, as the film that is pasted on the upper surface of the polarizing plate, and as the films that sandwich the polarizing film of the polarizing plate, avoiding occurrence of short circuits, and resulting in a high resistance to ambient conditions, such as heat and humidity. In addition, by employing the polarizing plate, reflection of an external light is suppressed, resulting in a high readability. 
   Using a fluororesin film also achieves the objectives. 
   The present invention also provides a touch panel that is configured by one fewer component parts than conventional products. 
   The input device of the present invention employs the touch panel of the present invention, providing the enhanced resistance to heat and humidity. 
   Further, the present invention is not limited to these embodiments, but various modifications and variations may be made without departing from the scope of the present invention. 
   The present application is based on Japanese priority application No. 2001-241187 filed on Aug. 8, 2001 with the Japanese Patent Office, the entire contents of which are hereby incorporated by reference.