Patent Publication Number: US-2011068249-A1

Title: Mold and Method for Manufacturing the Same

Description:
RELATED APPLICATIONS 
     The present application is a divisional of U.S. application Ser. No. 12/577,307, filed on Oct. 12, 2009, which was based on, and claims priority from, Taiwan Application Ser. No. 97144197, filed Nov. 14, 2008, which is herein incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present disclosure relates to a mold, more particularly, to a mold for manufacturing optical elements. 
     2. Description of Related Art 
     Recently, liquid crystal displays are developed by electro-optical engineers due to market demands of the digital age. Liquid crystal displays have many advantages, such as high definition, small volume, lightweight, low voltage drive, low consumption of power, a broad range of applications, etc. Therefore, liquid crystal displays are already broadly used in consumer electronic devices or computer products, such as portable televisions, cellular phones, camcorders, laptop computers, desktop displays, projection televisions, etc., thereby becoming the main stream for displays. 
     “Backlight module” is one of the critical parts of a liquid crystal display. Generally, a backlight module is needed to make the screen and the information become visible to the user because liquid crystals cannot self-illuminate. Furthermore, some optical elements, e.g. a light guide plate, light diffusion films, and/or brightness enhancement films, may be built in the backlight module to enhance the brightness or the uniformity of the illumination. 
     Commercial optical films with a single type of optical features are manufactured by molding. However, optical films with a single type of optical features can no longer satisfy the market demands. Accordingly, a new mold is needed to solve this problem. 
     SUMMARY OF THE INVENTION 
     According to one embodiment of the present invention, a method for manufacturing a mold includes the following steps. A substrate is provided, wherein the substrate has a supporting layer disposed thereon. A thermoplastic polymer layer is formed on the supporting layer. Both the thermoplastic polymer layer and the supporting layer are machined to form a plurality of micro-structures on the substrate. The machined thermoplastic polymer layer on the top of the micro-structures is reflowed. 
     According to another embodiment of the present invention, a mold includes a substrate and a plurality of micro-structures. The micro-structures are disposed on the substrate. Each of the micro-structures includes a supporting layer and a convex top portion. The supporting layer is disposed on the substrate, wherein the material of the supporting layer is amorphous metal. The convex top portion is disposed on the supporting layer, wherein the material of the convex top portion is a thermoplastic polymer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1-6  are cross-sectional views depicting a method for manufacturing a mold according to one embodiment of the present invention; 
         FIG. 7  is a three-dimensional view of the mold of  FIG. 4 ; 
         FIG. 8  is a three-dimensional view of a mold according to another embodiment of the present invention; and 
         FIG. 9  is a cross-sectional view of a mold according to yet another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following detailed description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the disclosed embodiments. It will be apparent, however, that one or more embodiments may be practiced without these specific details. In other instances, well-known structures and devices are schematically shown in order to simplify the drawings. 
       FIGS. 1-6  are cross-sectional views depicting a method for manufacturing a mold according to one embodiment of the present invention. The following steps are not recited in the sequence in which the steps are performed. That is, unless the sequence of the steps is expressly indicated, the sequence of the steps is interchangeable, and all or part of the steps may be simultaneously, partially simultaneously, or sequentially performed. 
     Reference is made to  FIG. 1 . A substrate  110  is provided, wherein the substrate  110  has a supporting layer  120  disposed thereon. In the present embodiment, the material of the supporting layer  120  is amorphous metal, e.g. an alloy of nickel and phosphorus containing about 9-13% of phosphorus by weight. It is appreciated that the alloy of nickel and phosphorus is only one of the examples, and the supporting layer  120  may be made of other amorphous metals. 
     The terms “about” as used herein may be applied to modify any quantitative representation which could permissibly vary without resulting in a change in the basic function to which it is related. For example, the alloy of nickel and phosphorus as disclosed herein containing about 9-13% of phosphorus by weight may permissibly contain less than 9% of phosphorus by weight or greater than 13% of phosphorus by weight within the scope of the invention if its amorphous structure is not materially altered. 
     Reference is made to  FIG. 2 . A thermoplastic polymer layer  130  is formed on the supporting layer  120 . The material of the thermoplastic polymer layer  130  is a positive photoresist or polymethylmethacrylate (PMMA), and the thickness of the thermoplastic polymer layer  130  is about 0.1-500 μm. It is appreciated that the above-mentioned thermoplastic polymer layer  130  is only one of the examples, and the thermoplastic polymer layer  130  may be made of other material or have other thickness. 
     Reference is made to  FIG. 3 . Both the thermoplastic polymer layer  130  and the supporting layer  120  are machined to form a plurality of micro-structures  140  on the substrate  110 . Specifically, the manufacturers may use a cutting tool to mechanically cut both the thermoplastic polymer layer  130  and the supporting layer  120  to form a plurality of grooves  145  therein. The grooves  145  can define the micro-structures  140 , while an exposure process and a development process are not needed in this step. 
     Reference is made to  FIG. 4 . The machined thermoplastic polymer layer  130  on the top of the micro-structures  140  is reflowed, and then a surface of the reflowed thermoplastic polymer layer  135  is formed into a smooth shape due to surface tension, such as a convex shape or a spherical segment. Another machining is not needed in this step. Specifically, the reflowing step includes the following steps. First, the machined thermoplastic polymer layer  130  on the top of the micro-structures  140  is melted by heating. Then, the melted thermoplastic polymer layer  130  on the top of the micro-structures  140  is solidified by cooling. 
     The machined thermoplastic polymer layer  130  on the top of the micro-structures  140  is melted by heating the machined thermoplastic polymer layer  130  to a desired temperature according to the material of the machined thermoplastic polymer layer  130 . Basically, the desired temperature is higher than the melting point of the machined thermoplastic polymer layer  130 . For example, the machined thermoplastic polymer layer  130  is heated to a temperature of about 150° C. to melt it when the material of the machined thermoplastic polymer layer  130  is a positive photoresist. 
     According to another embodiment of the present invention, a mold manufactured by the above method is provided.  FIG. 7  is a three-dimensional view of the mold of  FIG. 4 . The mold includes a substrate  110  and a plurality of micro-structures  140 . The micro-structures  140  are disposed on the substrate  110 . Each of the micro-structures  140  includes a supporting layer  120  and a convex top portion  135 . The supporting layer  120  is disposed on the substrate  110 , wherein the material of the supporting layer  120  is amorphous metal. The convex top portion  135  is disposed on the supporting layer  120 , wherein the material of the convex top portion  135  is a thermoplastic polymer. 
     The mold of  FIG. 4  and/or  FIG. 7  is used to electroform a metal die, such as a nickel die, a copper die, a chromium die, or a titanium die. Specifically, the die  150  is formed on the substrate  110  after the machined thermoplastic polymer layer  130  is reflowed, as shown in  FIG. 5 . This step is performed by electroforming. For example, if the manufacturers want to electroform a nickel die, a seeding layer (not shown) having a thickness of about 100-5000 Å is formed on the substrate  110  first, and then the nickel die is electroformed onto the substrate  110  through a nickel aminosulfonate bath. The thickness of the nickel die is about 0.05-10 mm. 
     Reference is made to  FIG. 6 . The die  150  and the substrate  110  is separated, and then the die  150  is used in injection molding, hot pressing, or ultraviolet curing to manufacture optical elements. As shown in  FIG. 6 , the die  150  has a plurality of prism features  152  formed by the machining step and a plurality of convex features  154  formed by the reflowing step. Accordingly, optical elements manufactured by the die  150  have a light concentrating capability of the prism features  152  and a light diffusing capability of the convex features  154 . Furthermore, the convex features  154  can prevent the optical elements from scraping other elements. 
     It is appreciated that  FIGS. 1-7  only depict some embodiments of the present invention, and some specific details may be adapted to satisfy different requirements. For example, although  FIG. 7  depicts each micro-structure  140  as a prism, i.e. a solid object with matching ends and several sides which are the same width all the way up, it is appreciated that each micro-structure  140  may be a pyramid as well (as shown in  FIG. 8 ). 
     Similarly, although  FIG. 4  depicts each groove  145  as a V-cut, the section of each groove  145  may be a spherical segment as well (as shown in  FIG. 9 ) if the manufacturers make some changes to the machining step. In other words, although  FIG. 4  depicts that a side surface of the supporting layer  120  includes a plane surface, a side surface of the supporting layer  120  may include a curved surface as well (as shown in  FIG. 9 ). Basically, a curvature of the side surface of the supporting layer  120  is different from a curvature of a surface of the convex top portion  135 . 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims.