Abstract:
A method of manufacturing an optical film includes: providing a template; coating an aluminum film on one surface of the template; electrolyzing the aluminum film and generating a plurality of regular microstructures on the aluminum film; providing a substrate; transferring the microstructures of the template to the substrate to form a plurality of microstructures on the substrate; and modifying the surfaces of the microstructures of the substrate to obtain a layer containing hydrophobic functional groups on the surfaces of the microstructures of the substrate.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The present invention relates to an optical film and a method of manufacturing an optical film which has anti-reflective and self-cleaning properties. 
         [0003]    2. Description of the Related Art 
         [0004]    It is very important to reduce reflection of optoelectronic devices so as to improve the utilization efficiency of light. Multilayer anti-reflective films are used to achieve anti-reflective effect, but the cost of the multilayer anti-reflective film is high and the bond between the layers of the multilayer anti-reflective film is weak. Furthermore, the multiplayer anti-reflective film cannot be self-cleaning and may be dirty after a period of time. 
         [0005]    Therefore, what is needed is an optical film and a method of manufacturing an optical film having both anti-reflective and self-cleaning properties which can overcome the above mentioned shortcomings 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a schematic view of an optical film according to a first embodiment. 
           [0007]      FIGS. 2-9  are schematic views showing the successive stages of a method of manufacturing the optical film of  FIG. 1 , according to a second embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0008]    Referring to  FIG. 1 , an optical film  100 , according to a first embodiment, is shown. The optical film  100  includes a substrate  50  made of a transparent polymer material. The substrate  50  includes a number of cone-shaped micro-protrusions  51 . A layer  52  containing hydrophobic-functional-groups is formed on the surfaces of the cone-shaped micro-protrusions  51 . 
         [0009]    Referring to  FIGS. 2-9 , a method for manufacturing the optical film  100 , according to a second embodiment, is shown. The method includes steps as follows. 
         [0010]    In step 1, referring to  FIG. 2 , a template  10  is provided. The template  10  can be made from monocrystal or metal. In the embodiment, the template  10  is made from monocrystalline silicon. The template  10  includes a polished surface  101 . An aluminum film  11  is coated on the polished surface  101  of the template  10 . The aluminum film  11  may be coated by a vacuum deposition method, or a magnetron sputtering method, etc. 
         [0011]    In step 2, referring to  FIGS. 3 and 4 , a number of regular cone-shaped microstructures  21  are formed on a surface of the aluminum film  11 , the microstructures  21  are nano-scale protrusions. In one embodiment, the cone-shaped microstructure  21  is formed in the following manner. 
         [0012]    The template  10  with the aluminum film  11  is dipped in the electrolytic oxidation tank which contains an electrolyte solution and a voltage is applied on the electrolyte solution. The aluminum film  11  is anodized to form an alumina layer  12  with a number of micro pores  13 . The micro pores  13  are anodic aluminum oxide (AAO) holes. The electrolyte solution can be selected from the group consisting of a sulfuric acid solution, a phosphoric acid solution and an oxalic acid solution. In the embodiment, the electrolyte solution is an oxalic acid solution with a concentration of about 0.3 moles/liters, and the temperature of the electrolyte solution is about 17° C. The anodizing time is about 15 minutes and the voltage is about 40 volts. 
         [0013]    Then the template  10  with the micro pores  13  is dipped in a phosphoric acid solution with a concentration of about 5% by weight and the temperature of about 30° C. A voltage is then applied to the phosphoric acid solution to ream the micro pores  13 , and the reaming time is about 8 minutes. 
         [0014]    The template  10  is cleaned after reaming. The action of reaming and cleaning are repeated for 5 times. A number of regular cone-shaped microstructures  21  with the depth of about 150 nm is formed on the surface of aluminum film  11 . 
         [0015]    In step 3, referring to  FIGS. 5 and 6 , a self-assembled monolayer  22  is formed on the surfaces of the regular cone-shaped microstructures  21 . In one embodiment, the template  10  with the regular cone-shaped microstructures  21  is placed in a hot vacuum chamber. An inert gas is introduced into the vacuum chamber. The temperature of the vacuum chamber is adjusted to about 200° C. Then long carbon chain perfluorinated fatty acids  30  is introduced into the vacuum chamber. The volume ratio between the long carbon chain perfluorinated fatty acid  30  and the vacuum chamber is about 0.2%. The formula of the long carbon chain fluorinated fatty acid  30  is CF 3 (CF 2 ) n COOH wherein n=3, 6, 8, 10, or 16. The long carbon chain perfluorinated fatty acid  30  is gasified at a high temperature. The long carbon chain perfluorinated fatty acid  30  and the anodic aluminum oxide take place chemical grafting reaction under the condition of annealing in the vacuum chamber and a high hydrophobic self-assembled monolayer  22  is generated on the surfaces of the regular cone-shaped microstructures  21 . In the embodiment, the annealing time is about 3 hours. The purpose of generating the self-assembled monolayer  22  on the surfaces of the regular tapered microstructures  21  is to increase the mold release ability in a later hot embossing step. 
         [0016]    In step 4, the template  10  is washed after the chemical grafting reaction. In this step, the template  10  is cooled to room temperature, and then scoured successively by chloroform, acetone, ethanol and deionized water. The chloroform is used for removing the excess of long carbon chain perfluorinated fatty acid  30 . The acetone, ethanol and deionized water are used for reducing polarity and removing the organic solvent on a surface of the self-assembled monolayer  22 . 
         [0017]    In step 5, referring to  FIGS. 7 and 8 , a substrate  50  is provided. The cone-shaped microstructures  21  of the template  10  are transferred to the substrate  50 . The material of the substrate  50  is poly methyl methacrylate (PMMA). In one embodiment, the substrate  50  is placed facing with the cone-shaped microstructures  21 , and then the substrate  50  and the template  10  as a entirety are placed in a hot embossing machine  60 . The hot embossing machine  60  is heated to a glass transition temperature of the substrate  50 . The glass transition temperature of the substrate  50  is about 120° C. The shape of the cone-shaped microstructures  21  is printed on the substrate  50 . Accordingly, the substrate  50  with the cone-shaped micro-protrusions  51  is obtained. 
         [0018]    In step 6, referring to  FIG. 9 , a hydrophobic-functional-group layer  52  is formed on the surfaces of the cone-shaped micro-protrusions  51  and the optical film  100  is obtained. In one embodiment, the substrate  50  with the micro-protrusions  51  is placed in a plasma machine and a carbon tetrafluoride (CF 4 ) gas is gradually introduced into the plasma machine. Under the plasma condition, hydrogen atoms in the carbon chain of PMMA are replaced by the fluorine atoms of CF 4 . In this way, the layer  52  containing the hydrophobic-functional-groups is obtained. The surface energy of the PMMA is reduced by the chemical reaction. The contact angle between the surface of the optical film  100  and water is greater than 150 degrees according to Cassie-Baxter model. 
         [0019]    The optical film  100  manufactured by the above mentioned method has anti-reflective and self-cleaning properties. 
         [0020]    It is to be understood, however, that even though numerous characteristics and advantages of the present embodiments have been set forth in the foregoing description, together with details of the structures and functions of the embodiments, the disclosure is illustrative only, and changes may be made in detail, especially in the matters of shape, size, and arrangement of parts within the principles of the disclosure to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.