Abstract:
A transparent display cover ( 100 ) and a method of forming such includes forming ( 204 ) a transparent polymer material ( 104 ) having a thickness between 0.2 and 38 micrometers on a glass material ( 102 ) and disposing ( 216 ) one of the materials ( 106 ) selected from the group consisting of an antireflective coating and a vacuum metallized coating on the transparent polymer material ( 104 ). The transparent polymer material ( 104 ) may comprise one of a polyimide, siloxane, polyurethane, polyester, polycarbonate, and polyethylene applied ( 204 ) by spin coat or meniscus with a thickness of less than 38 micrometers.

Description:
FIELD 
       [0001]    The present invention generally relates to coatings for lenses or display covers, and more particularly to a method for a coating a thin, supportive layer on a glass lens. 
       BACKGROUND 
       [0002]    In many portable electronic devices, such as mobile communication devices, displays present video and text information to a user. These optical displays, for example touch panel displays, typically comprise a transparent protective layer including a high gloss reflective surface of glass or a polymer. Glass typically offers a higher scratch resistance. While these transparent protective layers have excellent transparency and are relatively physically strong, they may suffer physical damage due to harsh treatment by the user. This is particularly true for the displays of products which receive significant handling, such as personal digital assistants (PDAs) and cell phones. 
         [0003]    In order to reduce distracting reflections from the surface of the transparent protective layer, conventional displays place either an antireflective coating or a decorative vacuum metallized coating over the surface by laminating a dry stack of adhesive polymer film, and a hard film such as titanium dioxide or silicon oxide onto the glass. Placement of these hard films directly onto the glass layer is known to decrease the impact or fracture strength of the glass due to the mismatch of the mechanical and structural properties of the glass and these coatings. 
         [0004]    Accordingly, it is desirable to provide a method for applying a relatively thin antireflective or vacuum metallized coating onto glass that improves the impact or fracture strength of the glass. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]    Embodiments of the present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and 
           [0006]      FIG. 1  is a partial cross section of the lens in accordance with an exemplary embodiment; 
           [0007]      FIG. 2  is a flow chart of the process for making the exemplary embodiment; 
           [0008]      FIG. 3  is a front view of a mobile communication device having a touch screen in accordance with an exemplary embodiment; and 
           [0009]      FIG. 4  is a partial cross-section of a conventional touch screen taken along line  4 - 4  of  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION 
       [0010]    The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any theory presented in the preceding background or the following detailed description. 
         [0011]    An optically clear polymer material disposed between a glass lens and an antireflective coating or a vacuum metallized optical coating improves the impact or fracture strength of the glass lens. The polymer material preferably is spin, spray, or meniscus coated so molecules of the polymer material attach to the glass lens, preferably at a thickness below 38 micrometers, and more preferably at a thickness below 25 micrometers. The application of the polymer material prior to deposition of the antireflective or vacuum metallized optical coating provides a soft coating and buffer-like quality, thereby allowing for the use of a thinner glass lens. 
         [0012]    Referring to  FIG. 1 , a partial cross section of an exemplary embodiment of a lens  100  includes a glass layer  102 , which may be referred to in the industry by any one of several names such as lens, substrate, and protective cover. The glass layer  102  is preferably rigid and may be formed of any suitable translucent material having suitable optical properties and by any suitable method. The glass layer  102  has a thickness preferably in the range of 0.5 to 0.85 millimeters, although it could be much thinner. It is preferred to clean the glass layer  102  using an industry standard cleaning process. One known process includes submerging the glass layer  102  into a 90° C. 4:1 Piranha (four part sulfuric acid to one part hydrogen peroxide) solution for five minutes followed by a SC-1 MegaSonic clean process (D.I. water, ammonium hydroxide, and hydrogen peroxide solution) for 30 minutes at 60° C. The glass layer  102  is then rinsed clean and dried prior to the next step in the process. 
         [0013]    In accordance with the exemplary embodiment, a thin layer  104  of a polymer material is formed on the glass layer  102 . The layer  104  is preferably spin, spray, or meniscus coated so molecules of the polymer material attach to the glass. The thin layer  104  is disposed on the “inside” of the layer  102 . In other words, the side  103  of the layer  102  faces the viewer of the lens  100 . These methods allow for the layer  104  to be thin when compared to previously known methods, by having a thickness preferably less than 38 micrometers, and more preferably less than 25 micrometers, for example when maintaining anti-splinter characteristics. The polymer layer  104  may be any polymer, but preferably is one of a polyimide, siloxane, polyurethane, polyester, polycarbonate, and polyethylene material. A polyurethane layer has shown good anti-splintering qualities. 
         [0014]    A coating  106 , for example a metal or an alloy such as indium tin oxide, titanium oxide, or a conductive polymer, of either an antireflective material to reduce reflection or a vacuum metallization for decoration is deposited on the polymer layer  104 . The coating  106  may have a thickness in the range of 0.05 to 0.25 micrometers, but preferably has a thickness of about 0.15 micrometers. The polymer layer  104  provides a buffer-like quality that maintains the fracture strength of the glass layer  102  when the coating  106  is applied. The combination of layers  102 ,  104 ,  106  has a light transmission value of 65-98% between the wavelengths of 400 to 700 nanometers to maintain the desired optical quality and an index of refraction that closely matches glass to reduce any optical aberrations or image distortion. 
         [0015]    The layers  102 ,  104 ,  106  have the right balance of tensile strength, Young&#39;s Modulus, modulus of elasticity, and coefficient of thermal expansion to maintain the integrity of the layers  102 ,  104 ,  106  through environmental conditions while reducing the negative effects of the layers  104 ,  106  on the fracture and impact strength of the glass layer  102 . Tensile strength of a material is the maximum amount of tensile stress that it can be subjected to before failure. Stress is a measure of the average amount of force exerted per unit area. It is a measure of the intensity of the total internal forces acting within a body across imaginary internal surfaces, as a reaction to external applied forces and body forces, and is measured in units of pascals (Pa), or Newtons per square meter. Young&#39;s modulus, synonymously with modulus of elasticity, is the ratio of tensile stress to the resulting strain, which reflects the resistance of a material to elongation. The higher the Young&#39;s modulus, the larger the force needed to deform the material. 
         [0016]    This process produces a favorable situation where a relatively soft (low Young&#39;s Modulus) layer is interposed between the harder glass and optical coating layers. This allows for easier relative movement of the hard layers thereby reducing the possibility that these layers might fracture. 
         [0017]    The method  200  of the exemplary embodiments is shown in  FIG. 2  and includes the steps of optionally diluting  202  an optically clear polymer material  104  with an appropriate solvent, ethyl lactate for example, and applying  204  the polymer material  104  to a clean glass layer  102  by spin, spray, or meniscus coating. Other coating processes that may be used include roller coating, screen printing, and dip coating, for example. The layers  102 ,  104  are then baked  206  at a temperature in the range of 80° to 120° C., but preferably at 100° C., for about 120 seconds. If the polymer layer  104  is photo-imageable  208 , it can be patterned, if deemed necessary, using industry standard photolithography methods, such as UV pattern expose  210 , post exposure bake  212 , and developing techniques  213 . The layers  102 ,  104  are then cured  214 , preferably below 250° C. in air or an industry standard nitrogen atmosphere process for two hours. Once cured, the layer  102  film properties consist of the right balance of tensile strength, Young&#39;s Modulus, modulus of elasticity, and coefficient of thermal expansion to maintain the integrity of the layers  102 ,  104 ,  106  through environmental conditions while reducing the negative effects of the layers  104 ,  106  on the fracture and impact strength of the glass layer  102 . Material property values of layer  102  can range from 6.0 to 176 MPa for tensile strength, 90 MPa to 7.8 GPa for Young&#39;s modulus, and 25 to 125% for elongation. The antireflective or vacuum metallized coating is then deposited  216 . 
         [0018]    Although the apparatus and method described herein may be used with an exposed display surface for any type of device, the exemplary embodiment as shown in  FIG. 3  comprises a mobile communication device  300  implementing a touchscreen. While the electronic device shown is a mobile communication device  300 , such as a flip-style cellular telephone, the touchscreen can also be implemented in cellular telephones with other housing styles, personal digital assistants, television remote controls, video cassette players, household appliances, automobile dashboards, billboards, point-of-sale displays, landline telephones, and other electronic devices. Non-electric apparatus in which the exemplary embodiment could be used include lens for eyewear, glass windows, clocks and the like. 
         [0019]    The mobile communication device  300  has a first housing  302  and a second housing  304  movably connected by a hinge  306 . The first housing  302  and the second housing  304  pivot between an open position and a closed position. An antenna  308  transmits and receives radio frequency (RF) signals for communicating with a complementary communication device such as a cellular base station. A display  310  positioned on the first housing  302  can be used for functions such as displaying names, telephone numbers, transmitted and received information, user interface commands, scrolled menus, and other information. A microphone  312  receives sound for transmission, and an audio speaker  314  transmits audio signals to a user. 
         [0020]    A keyless input device  350  is carried by the second housing  304 . The keyless input device  350  is implemented as a touchscreen with a display. A main image  351  represents a standard, twelve-key telephone keypad. Along the bottom of the keyless input device  350 , images  352 ,  353 ,  354 ,  356  represent an on/off button, a function button, a handwriting recognition mode button, and a telephone mode button. Along the top of the keyless input device  350 , images  357 ,  358 ,  359  represent a “clear” button, a phonebook mode button, and an “OK” button. Additional or different images, buttons or icons representing modes, and command buttons can be implemented using the keyless input device. Each image  351 ,  352 ,  353 ,  354 ,  356 ,  357 ,  358 ,  359  is a direct driven pixel, and this keyless input device uses a display with aligned optical shutter and backlight cells to selectively reveal one or more images and provide contrast for the revealed images in both low-light and bright-light conditions. 
         [0021]    Referring to  FIG. 4 , a cross section of a lens  400  is depicted that is usable for either the display  310  or the keyless input device  350  with the cross-section, for example, being a portion of a view taken along line  4 - 4  or  5 - 5  of  FIG. 3 . The lens  400  is a stack with a user-viewable and user-accessible face  401  and multiple layers below the face  401 , including layers  102 ,  104 ,  106 , and an imaging device  408 . The layer  102  provides an upper layer viewable to and touchable by a user and may provide some glare reduction. The layer  102  also provides scratch and abrasion protection to the layers  104 ,  106 ,  408  contained below. 
         [0022]    While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims.