Patent Publication Number: US-2006012059-A1

Title: Method for manufacturing an optical sheet

Description:
BACKGROUND  
      1. Field of Invention  
      The present invention relates to an optical sheet for a flat display. More particularly, the present invention relates to a method for manufacturing an optical sheet.  
      2. Description of Related Art  
      Liquid crystal display (LCD) has many advantages over other conventional types of displays including high display quality, small volume, light weight, low driving voltage and low power consumption. Hence, LCDs are widely used in small portable televisions, mobile telephones, video recording units, notebook computers, desktop monitors, projector televisions and the like, and have gradually replaced the conventional cathode ray tube (CRT) as a mainstream display unit.  
      In a flat display, polarizers are main elements for the display panel thereof. In general, a polarizer is made of one or more than one optical sheets; the polarizer therefore has other functions, such as anti-peeping or optical compensation, in addition to the function of polarizing. In order to achieve the functions mentioned above, various additional processes are carried out on the surfaces of the optical sheets, like sputtering, exposure and development, and dry etching.  
      However, sizes of special structures formed on the surfaces of the optical sheets by the foregoing processes, such as trenches or other patterns, are in the micrometer scale. Therefore, complex and delicate semiconductor techniques are typically applied on these surfaces to form the special and subtle structures. The implication is that complicated and expensive manufacturing devices are used to manufacture these optical sheets with additional functions.  
      Therefore, the optical sheets manufactured by conventional techniques are expensive and require complex processes, and are difficult to mass produce.  
     SUMMARY  
      The optical sheets manufactured by the conventional techniques generally have some disadvantages, like complex manufacturing processes and high manufacturing cost. The complex manufacturing processes reduce the yields of the optical sheets, and the high manufacturing cost is adverse to product popularization.  
      It is therefore an objective of the present invention to provide a method for manufacturing an optical sheet, in which strip structures with various functions are directly formed by spreading resin with a suitable viscosity to simplify manufacturing processes and decrease manufacturing costs.  
      In accordance with the foregoing and other objectives of the present invention, a method for manufacturing an optical sheet is provided. A transparent substrate is provided, and a resin is spread on the transparent substrate to form a resin layer. The resin layer has a plurality of strip structures, and a viscosity of the resin is between 20 and 1000 cps. Next, the resin layer is cured such that a combination of the transparent substrate and the resin layer becomes an optical sheet.  
      According to preferred embodiments of the present invention, a solid content of resin to solvent in the resin is greater than 40%. The resin layer is cured by UV light. The two sides of the transparent substrate are exposed to UV light of more than 80 Watts to cure the resin layer. The transparent substrate is triacetate cellulose, polyethylene terephthalat, polycarbonate or acrylic. The resin is acrylic resin or epoxy resin.  
      When the resin is spread, a wire bar can be used to spread the resin on the transparent substrate, and the strip structures are oriented in a single direction. Sizes of the strip structures are controlled by a spreading speed and spacings of the wire bar. Alternatively, a gravure can be used to spread the resin on the transparent substrate, and the strip structures are oriented in at least two directions. Sizes of the strip structures are controlled by a spreading speed and pattern widths of the gravure.  
      According to several embodiments of the present invention, the optical sheet of the invention can be an optical compensation film, a privacy film or an optical sheet with another function. When the optical sheet is an optical compensation film, the optical compensation film has a retardation value to compensate for light leakage or view-angles of the display. When the optical sheet is a privacy film, the strip structures are oriented in a predetermined direction, and a predetermined thickness of the strip structures limits viewing angles of the privacy film to between 40 and 90 degrees. Moreover, during manufacturing of the privacy film, a dark dye can be mixed into the resin to enhance the anti-peeping effect.  
      The optical sheet of the present invention is entirely manufactured by the existent and simple processes for manufacturing polarizers. The present invention, of which the manufacturing processes are simple and the manufacturing cost is very low, does not require addition of any additional manufacturing devices for mass production.  
      It is to be understood that both the foregoing general description and the following detailed description are examples, and are intended to provide further explanation of the invention as claimed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings, where:  
       FIG. 1  illustrates a flow chart of one preferred embodiment of the present invention;  
       FIG. 2  illustrates a schematic view of an optical sheet of the preferred embodiment; and  
       FIG. 3  illustrates a schematic view of UV light exposure of one preferred embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts.  
      The present invention provides a method for manufacturing an optical sheet, as a substitution for the conventional techniques the need complex processes and are very expensive.  
       FIG. 1  illustrates a flow chart of one preferred embodiment of the present invention, and  FIG. 2  illustrates a schematic view of an optical sheet of the preferred embodiment. The following descriptions are made with reference to  FIG. 1  and  FIG. 2 .  
      As illustrated in  FIG. 2 , a transparent substrate  202  is provided (step  102 ). A material of the transparent substrate  202  is triacetate cellulose, polyethylene terephthalat, polycarbonate or acrylic. A resin is spread on the transparent substrate  202  to form a resin layer  204  (step  104 ). The resin layer has a plurality of strip structures  206 , such as triangular strip structures or semicircular strip structures. Shapes, sizes and positions of the strip structures  206  can be determined by a spreading tool, like spacings of a wire bar or patterns of a gravure.  
      In the preferred embodiment, the resin is acrylic resin or epoxy resin, and a viscosity of the resin is between 20 and 1000 cps. The suitable viscosity can help the strip structures  206  maintain the shapes and positions thereof formed by spreading, before they are subsequently cured. Moreover, a solid content of resin to solvent in the resin is greater than 40%. When the solid content of resin to solvent in the resin is greater, the sizes of the strip structures  206  can be prevented from shrinking because the solvent thereof is removed during baking.  
      During spreading the resin, the wire bar can be used to spread the resin when the strip structures  206  are oriented in a single direction. At this time, the positions of the strip structures  206  are determined by the wire bar, and a spreading speed and spacings of the wire bar can be used to control sizes of the strip structures  206 . When the strip structures  206  are oriented in at least two directions, the gravure can be used to spread the resin. At this time, the positions and shapes of the strip structures  206  are determined by the patterns of the gravure, and a spreading speed and pattern widths of the gravure can also be used to control the sizes of the strip structures  206 . Similarly, other conventional spreading techniques suitable for the present invention also can be used in the present invention, and all of them fall into the scope and fit the spirit of the present invention.  
      After spreading the resin, the resin layer  204  can optionally be baked to remove the solvent or other volatile components therein (step  106 ). Next, the resin layer  204  is cured, for example, by exposure to UV light of which the power is greater than 80 Watts, such that a combination of the transparent substrate  202  and the resin layer  204  becomes an optical sheet  200  (step  108 ).  
       FIG. 3  illustrates a schematic view of UV light exposure of one preferred embodiment of the present invention. As illustrated in  FIG. 3 , because the resin layer  202  having the strip structures  206  is thicker, UV light shines on the resin layer  202  from two sides of the transparent substrate  202  for mitigating curing incompletion or non-uniformity caused by the thickness. Of course, if the power of UV light is great enough or the transparency of the resin layer  204  for UV light is good, shining UV light from one single direction is sufficient to cure the resin layer  204  in the present invention.  
      According to another embodiment of the present invention, the resin layer  204  can be cured by an electron-beam. The energy of electron-beam is higher such that the resin layer  204  can be cured by it faster, and therefore the foregoing curing incompletion or non-uniformity can be substantially improved and the processing time is also reduced to raise yields of products. Moreover, the material cured by high energy generally has high resistance, and therefore enhances its abilities to resist chemistry and friction. In addition, under considerations of processing and specification, the resin layer  204  can be cured by UV light and an electron-beam with proper parameters to obtain optimum curing results.  
      The detailed conditions of the transparent substrate  202  and the strip structures  206  of the optical sheets  200  with various functions may be different because of their functions. The manufacturers can adjust the foregoing processes and parameters according to design and processing needs to get the suitable and optimum optical sheets  200 . In other words, in the processes for manufacturing the optical sheet  200 , the viscosity and solid content of the resin, the sizes and shapes of the strip structures  206 , the baking conditions and other processing parameters can be adjusted to obtain the optical sheet  200  suitable for the needs. Moreover, optical sheets with similar functions may be obtained by different processing parameters. Therefore, the present invention simplifies the manufacturing of optical sheets, and also substantially enhances the adjusting ability of manufacturing processes.  
      According to several embodiments of the present invention, the optical sheets  200  manufactured by the method of the present invention can be optical compensation films, privacy films or optical sheets with other functions. When the optical sheet  200  is an optical compensation film, the optical compensation film has a retardation value to compensate for light leakage or view-angles of the display. When the optical sheet  200  is a privacy film, the strip structures  206  are oriented in a predetermined direction, and a predetermined thickness of the strip structures  206  limits a range of viewing angles of the privacy film to between 40 and 90 degrees. Moreover, during manufacturing of the privacy film, a dark dye can be mixed into the resin (step  112 ) to enhance the effect of anti-peeping, as illustrated in  FIG. 1 .  
      Furthermore, the optical sheet  200  can be configured adjacent to the backlight source of the flat display to serve as a diffuser or a condenser, according to the shapes of the strip structures  206  and their positions relative to the backlight source. The strip structures  206  have features of anti-sticking, anti-slipping and high mechanical strength, and therefore can be configured on any place inside the flat display to achieve the functions of anti-sticking, anti-slipping and supporting.  
      The optical sheet of the present invention is entirely manufactured by existent and simple processes for manufacturing polarizers. The present invention, of which the manufacturing processes are simple and the manufacturing cost is very low, does not require addition of any additional manufacturing devices for mass production.  
      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 and their equivalents.