Patent Publication Number: US-2011070453-A1

Title: Laminate of transparent conductive film

Description:
TECHNICAL FIELD OF THE INVENTION 
     The present invention generally relates to a laminate of a transparent conductive film, and more particularly to a transparent conductive film applied to a resistive touch panel or a capacitive touch panel to improve the color of displaying and reduce reflectivity of light when light transmits through the transparent conductive film. 
     DESCRIPTION OF THE PRIOR ART 
     An early conventional transparent conductive film is formed by depositing a layer of indium tin oxide (ITO) on a glass substrate, which is referred to as conductive glass. However, glass shows poor properties of flexibility and workability and is also poor in respect of impact resistance and being light weight. Thus, the transparent conductive film is now being gradually replaced by plastics, such as polyethylene terephthalate (PET). 
     The transparent conductive film is often used in resistive and capacitive touch panels and thus, in practical applications, transparency, deflectability, and scrape resistance are also properties of concerns. Severity of surroundings, including high humidity and high temperature, where the touch panel is used may also be factors to be handled. 
     The structure of the transparent conductive film that is currently available in the market includes a transparent substrate made of transparent plastics and a laminate composed of multiple layers is deposited on a surface of the substrate. 
       FIG. 1  of the attached drawings shows a known transparent conductive film, which is broadly designated at  1  and comprises a substrate  11  that is made of a transparent plastic material. The substrate  11  has a surface on which a laminate  12  that is composed of multiple layers is formed. The laminate  12  comprises a conductive layer  121 , a rigid coating layer  122 , and an adhesive layer  123 . The conductive layer  121  functions to conduct electrical current therethrough and is generally made of indium tin oxide (ITO) by means of vacuum deposition, sputtering, ion plating, spray pyrolysis, chemical plating, and electroplating, or any combination of these processes, among which vacuum deposition and sputtering are preferred processes. The rigid coating layer  122 , which provides protection against scraping, staining, and occurrence of Newton&#39;s rings, is preferably made of hardened resin material. The rigid coating layer  122  also offers the function of anti-glare. The substrate  11  and the rigid coating layer  122  are coupled to each other through the adhesive layer  123 . 
     Generally speaking, the electrical resistance of the currently available resistive and capacitive touch panels is around 100 Ω/μm to 600 Ω/μm. The conductive layer  121  of the transparent conductive film  1  usually has a thickness ranging from 15 nm to 75 nm. Under these conditions, as shown in  FIG. 2 , which provides color distribution in CIE Lab color system, when the thickness of the conductive layer  121  exceeds 10 nm, the b* value of the color coordinates gets greater than 1, meaning the color of the light transmitting through the transparent conductive film  1  gets significant change. As illustrated in  FIG. 2 , it can be found that the commonly used thickness of the conductive layer  121 , which ranges from 15 nm to 75 nm, may result in a b* value between 1 to 4, making the conductive layer  121  biased to yellow color. As shown in  FIG. 3 , the currently available substrate  11  that is provided with a rigid coating layer  122  has a b* value of the color coordinates between around 0.2 to 0.9. Thus, a completed product of the transparent conductive film  1  would show a b* value greater than 2. In other words, after passing through the transparent conductive film  1 , light would show biasing toward yellow color. 
     The manufacturers of resistive and capacitive touch panels set a requirement that the b* value be smaller than 3 to the suppliers of transparent conductive films. However, for high-end products, even smaller color deviation is required for the displays of these products and may sometimes need the displaying of the display devices to be blue biased, meaning the b* value of the color coordinates be −10≦b*≦2.5. This is now becoming a trend in this industry for making better products. 
     Further, as shown in  FIG. 4 , concerning the refractivity of the laminate  12  of the transparent conductive film  1 , the ITO-based conductive layer  121  shows the highest refractive index and a greater difference of refractive index is present between junction surfaces  1211 ,  1212  of the conductive layer  121  that serve to provide electrical contact. Since the surfaces  1211 ,  1212  of the conductive layer  121  are provided for electrical contact, additional processing or treatment for eliminating light reflection is not allowed to directly carry out thereon, so that there always exists significant light reflection. This cannot be properly handled heretofore and is a major challenge to the industry. 
     SUMMARY OF THE INVENTION 
     The present invention provides a laminate for a transparent conductive film. The transparent conductive film comprises a substrate made of plastics. A laminate formed of multiple layers including a conductive layer, a rigid coating layer, an adhesive layer, and an underside coating layer is set on a surface of the substrate. The conductive layer of the laminate is generally made of indium tin oxide (ITO) having a thickness from 15 nm to 75 nm. The rigid coating layer provides protection against scraping, staining, and occurrence of Newton&#39;s rings and is made of hardened resins. The rigid coating layer also offers a function of anti-glare. The substrate and the rigid coating layer are coupled together through the adhesive layer. 
     The underside coating layer of the transparent conductive film in accordance with the present invention is generally made of a material of silicon oxy-nitride (SiOxNy). Properly adjusting the fractions of nitrogen and silicon contained in the material of silicon oxy-nitrogen can make the transparent conductive film showing excellent transparency in the visible light zone and having a b* value of color coordinates between −10≦b*≦2.5 and also reducing light reflection, so as to make it showing a white color or blue biased color. 
     The foregoing objectives and summary provide only a brief introduction to the present invention. To fully appreciate these and other objects of the present invention as well as the invention itself, all of which will become apparent to those skilled in the art, the following detailed description of the invention and the claims should be read in conjunction with the accompanying drawings. Throughout the specification and drawings identical reference numerals refer to identical or similar parts. 
     Many other advantages and features of the present invention will become manifest to those versed in the art upon making reference to the detailed description and the accompanying sheets of drawings in which a preferred structural embodiment incorporating the principles of the present invention is shown by way of illustrative example. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view showing a conventional transparent conductive film. 
         FIG. 2  shows CIE Lab color system diagram for thickness/color coordinates of a conductive layer. 
         FIG. 3  shows tables of b* values for substrates carrying a rigid coating layer that are currently available in the market. 
         FIG. 4  is a schematic view illustrating refractivity of each layer of a laminate of a conventional transparent conductive film. 
         FIG. 5  is a schematic view showing a transparent conductive film in accordance with the present invention. 
         FIG. 6  is a schematic view showing another transparent conductive film in accordance with the present invention. 
         FIG. 7  is a plot of a color-matching function of RGB color system of visible light. 
         FIG. 8  is a UV-visible transmission spectrum of silicon oxy-nitride. 
         FIG. 9  is a plot showing the relationship between component ratio of silicon oxy-nitride and refractivity. 
         FIG. 10  is a plot showing the relationship between an underside coating layer of the present invention and interface refractivity. 
         FIG. 11  is a table of data that establish the plot of  FIG. 10 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following descriptions are exemplary embodiments only, and are not intended to limit the scope, applicability or configuration of the invention in any way. Rather, the following description provides a convenient illustration for implementing exemplary embodiments of the invention. Various changes to the described embodiments may be made in the function and arrangement of the elements described without departing from the scope of the invention as set forth in the appended claims. 
     The present invention provides a transparent conductive film for a touch panel, as shown in  FIG. 5 . The transparent conductive film  2  comprises a substrate  21  made of a transparent material and having surfaces on which laminates  22  composed of multiple layers are formed. The material that makes the substrate  21  is not limited to any specific material and preferably comprises plastics including polyethylene terephthalate (PET), having a thickness between 2 μm to 300 μm, preferably between 10 μm to 188 μm. The multiple layers of the laminates  22  preferably include a conductive layer  221 , a rigid coating layer  222 , and an adhesive layer  223 . The conductive layer  221  functions to conduct electrical current therethrough and is composed of ITO as a major constituent material. The conductive layer  221  has a thickness ranging from 15 nm to 75 nm. The adhesive layer  223  is interposed between the substrate  21  and the rigid coating layer  222  to bridge and couple between the substrate  21  and the rigid coating layer  222 . The adhesive layer  223  is generally composed of a transparent adhesive substance and is preferably composed of materials of hardened resin, including melamine resin, urethane resin, alkyd resin, acrylic resin, and silicone resin. An underside coating layer  224  is arranged between the conductive layer  221  of the laminate  22  and the substrate  21  and the underside coating layer  224  is generally made of a material of silicon oxy-nitride (SiOxNy). As shown in  FIG. 6 , to enhance the mechanical performance of the transparent conductive film  2 , an additional laminate  22  composed of a rigid coating layer  222  and a adhesive layer  223  can be further set between the underside coating layer  224  and the substrate  21 . 
     Referring to  FIG. 7 , the visible light has a wavelength ranging between 380 nm to 760 nm and blue light wavelength is around 435.8 nm. Also referring to  FIG. 8 , the underside coating layer  224 , which is made of the material of silicon oxy-nitride, can be made to show high transmittance for blue light of 435.8 nm wavelength by adjusting the fractions of nitrogen and silicon contained in the material of silicon oxy-nitride, making b*≦0, which shows a blue-biased color. This helps to set the b* value of color coordinates of the whole transparent conductive film  2  in the range: −10≦b*≦2.5, lessening color deviation or making the color slightly biased toward blue. 
     Referring to  FIG. 9 , the ratio of the fractions of nitrogen and oxygen contained in silicon oxy-nitride shows a significant influence on light refraction. When adjustment is made to the ratio between nitrogen and oxygen contained in silicon oxy-nitride, the refraction of light is also adjusted. In other words, by properly adjusting the fractions of the constituent elements of the material of silicon oxy-nitride that makes the underside coating layer  224 , the refractivity/reflectivity of the transparent conductive film  2  with respect to light can be changed. The relationship between reflectivity and refractivity of the underside coating layer  224  that is obtained through conduction of experiments is shown in  FIGS. 10 and 11 , and it can be seen that adjusting the refractivity to 1.7 would make the reflectivity 0.62%. Preferred fractions of nitrogen and oxygen of the material of silicon oxy-nitride (SiOxNy) satisfy the formula: 2X(oxygen)+3Y(nitrogen)=4, wherein the value of X for oxygen is set as follows: 0≦X≦2 and the value of Y for nitrogen is set as follows: 0≦Y≦4/3. 
     While certain novel features of this invention have been shown and described and are pointed out in the annexed claim, it is not intended to be limited to the details above, since it will be understood that various omissions, modifications, substitutions and changes in the forms and details of the device illustrated and in its operation can be made by those skilled in the art without departing in any way from the spirit of the present invention.