Abstract:
A television screen is provided with one or more substrates made of a thin film. A number of materials may be used for the film substrate. Further, structures are formed on one or more resin bearing surfaces of the film substrates using a number of techniques, including using patterned rollers to press against the resin bearing film surfaces. The resin can be liquid resin that is cured to set the patterned structures. The thin film results in stronger yet lightweight televisions screens that are safe and easy to handle.

Description:
This application is a continuation-in-part claiming benefit under 35 U.S.C. § 120 of U.S. patent application Ser. No. 09/446,812, filed Dec. 23, 1999 now abandoned, which is a continuation of PCT/KR99/00043 filed Jan. 23, 1999 hereby incorporated by reference in its entirety. 

   BACKGROUND OF INVENTION 
   1. Field of the Invention 
   The present invention relates to a projection television receiver and, more particularly, to a viewing screen for a projection television receiver. 
   2. Description of the Related Art 
   The viewing screen of a projection television receiver (hereinafter “projection television screen”) is usually wider than the viewing screen of a conventional television receiver and thus weighs much more than the viewing screen of the conventional television receiver. A projection screen should be mechanically strong but not too heavy. Since a projection television screen is an exposed component of the television receiver, it is vulnerable to impact damage when the receiver is handled, used or moved. 
   A conventional projection television screen is made from an extruded polymethylmetacrylate(PMMA) sheet, which may be either a plain sheet or a sheet with shapes formed upon it to facilitate its various functions. PMMA sheets are heavy and have low mechanical strength and especially low impact strength. When a conventional projection screen is broken by an external impact, the pieces are very dangerous because they have many sharp edges. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to provide a projection television screen that it is safe, light, and mechanically strong. 
   Another object of the present invention is to provide a continuous-mode process for making a projection television screen that is safe, light, and mechanically strong. 
   In order to accomplish the above objects, the projection television screen of the present invention is made of a thin transparent film with high mechanical strength. Shapes may be formed on the surface of the film made of photo-curing resin in order to perform the necessary functions. After that, another type of film could be attached onto the shape formed on the substrate. The resultant structure according to the present invention is used as a projection television screen. 
   Yet another object of the present invention is to provide a manufacturing process for providing a screen which is described above. While in prior an a screen has been manufactured in a non-continuous way because only a planar shaped die is available in the prior art, with the manufacturing process of the present invention, a roll-shaped die can be easily fabricated using an electroforming method. Thus, continuous manufacture of a screen can be accomplished. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
     These and other advantages and features of the present invention can be better understood with reference to the following description which will be described in conjunction with the accompanying drawings in which: 
       FIG. 1  illustrates the use of a projection television screen. 
       FIG. 2  illustrates the structure of a projection television screen according to an embodiment of the present invention. 
       FIG. 3  illustrates the detailed structure of the projection television screen shown in FIG.  2 . 
       FIG. 4  illustrates a process of manufacturing a projection television screen according to an embodiment of the present invention. 
       FIG. 5  illustrates a conventional process of manufacturing a lenticular sheet. 
       FIG. 6  illustrates a conventional process of manufacturing a Fresnel sheet. 
       FIG. 7  illustrates a second conventional process of manufacturing a Fresnel sheet. 
       FIG. 8  illustrates a process of fabricating an electroforming roll suitable for manufacturing the Fresnel sheet and the lenticular sheet of the present invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   As shown in  FIGS. 2 and 3 , a projection television screen  1  of the present invention comprises a Fresnel sheet  4 ; a lenticular sheet  5  adjacent to and optically aligned with the Fresnel sheet  4 ; and a transparent protective sheet  6  adjacent to the surface of the lenticular sheet  5  furthest from the Fresnel sheet  4 . 
   The Fresnel sheet  4  comprises: a first transparent substrate  8 ; and a Fresnel lens  7  mounted on the surface of the first substrate  8  nearest the lenticular sheet  5 . The Fresnel sheet  4  collimates light from an image protector  3  and uniformly projects the collimated light onto the surface of the lenticular sheet  5  nearest the Fresnel sheet  4 . The Fresnel lens  7  is formed from a resin that is cured by exposure to ultraviolet light (hereinafter “ultra-violet resin”) after the shape of the lens has been impressed upon the fluid resin. 
   The lenticular sheet  5  comprises: a second transparent substrate  10 ; a plurality of lenticular lenses  9  mounted on both surfaces of the second substrate  10 ; and light absorbing parts  11  mounted on the surface of the second substrate  10  furthest from the Fresnel sheet  4 . The lenticular sheet  5  collects parallel red, green, and blue image beams from the Fresnel sheet  4  at a predetermined position of each of the pixels. The light absorbing parts  11  absorb stray ambient light and thus enhance the contrast of the images on the screen. 
   The ultra-violet resin used to make the Fresnel lens  7  may also be employed to make the lenticular lens  9 . The type of film used for the substrate  8  of the Fresnel sheet  4  may also be employed for the substrate  10  of the lenticular sheet  5 . A diffusion agent may be used, depending on the degree of light diffusion required, the ultra-violet resin used to make the Fresnel lens  7  or the lenticular lens  9 . An ultra-violet curing black ink with extinction and adhesion characteristics is employed for the light absorbing parts  11 . 
   The protective sheet  6  protects the Fresnel and lenticular sheets against damage from the outside. The material of the protective sheet  6  may be the same as that of the substrate  8  of the Fresnel sheet or the substrate  10  of the lenticular sheet  5 . If desired, various coatings such as an anti-reflection coating and a scratch-resistant coating may be applied to the protective sheet  6 . The protective sheet may also be colored. 
   The viscosity of the resin curable by ultra-violet light used to make the Fresnel lens  7  and the lenticular lens  9  ranges from 100 to 3000 cps at 25° C. The resin transmits more than 75% of the light incident on it. Preferably, the viscosity of the ultra-violet resin lies within the range 500 to 1500 cps at 25° C., and the transmissivity of the resin is more than 85%. Although the resin could be sufficiently spread on the surface of a shaping roller  12 , when the viscosity is less than 100 cps, process control would not be easy and a significant amount of low-boiling point material would be lost. If the resin&#39;s viscosity were more than 3000 cps, spray coating process would be difficult and air bubbles could well be formed because the shaping roller  12  would not be sufficiently wet by the resin. 
   Materials which may be used for the ultra-violet resin of the Fresnel lens  7  and the lenticular lens  9  include: urethane acrylate resin, epoxy acrylate resin, ester acrylate resin, ether acrylate resin, and mixtures thereof. 
   The transparent substrate  8  of the Fresnel sheet  4 , the transparent substrate  10  of the lenticular sheet  5 , and the protective sheet  6  preferably have thickness of 10-250 μm, light transmissivity of 75% of more and a tensile strength of at least 600 kg/cm 2 , and more preferably thickness of 50-150 μm, light transmissivity of 85% or more and a tensile strength of at least 1000 kg/cm 2 . If the thickness were less than 10 μm or the tensile strength less than 600 kg/cm 2 , the screen  1  could be easily be damaged and the film torn during the preparation of the screen. If the thickness were more than 250 μm, the total thickness and weight of the screen  1  would be too great arid the advantages of employing a film in the present invention would be lost. If the transmissivity were less than 75%, the transmissivity of the screen  1  would be too low. 
   Materials which may be used for the transparent film of the substrate  8  of the Fresnel sheet  4 , the substrate  10  of the lenticular sheet  5  and the protective sheet  6  include: polyester, polyestersulfon, polyamide 6, polyamide 66, polycarbonate, polyestersulfon, polyester ketone, polyesterimide, polyacrylate, and mixtures thereof. 
     FIG. 4  illustrates an apparatus for making shapes on one surface or both surfaces of the substrate of the Fresnel sheet  4  and the lenticular sheet  5  according to the present invention, the apparatus comprising a shaping roller  12 ; a device  13  for applying liquid resin to the substrate; an ultra-violet irradiating device  14 ; and a roller  15  for supplying the substrate film. The shaping roller  12  is easily replaceable in order to impress one surface or both surfaces of the substrate with various shapes. 
     FIG. 5  illustrates a conventional apparatus used for manufacturing a lenticular sheet  5 . In  FIG. 5 , a film extruded by an extruder  17  is shaped by a shaping roller  12  and thereafter cooled by a cooling roller  18  and drawn by a drawing roller  19 . Such an apparatus cannot be used for manufacturing a thin-film lenticular sheet  5 . 
     FIG. 6  illustrates a conventional process of manufacturing a Fresnel sheet  4 . In the process shown in  FIG. 6 , a liquid ultraviolet resin  21  is poured into a flat mold  20  to shape a Fresnel lens. The flat mold  20  is then covered with a panel  22  which forms the substrate of the Fresnel lens. The resin  21  is passed through a roller  23  and is exposed to an ultra-violet irradiating device  14 . The conventional method of  FIG. 6  is not applicable to mass production and the process can be operated only in a batch mode. A thin-film substrate could not easily be used in the method illustrated by FIG.  6 . 
     FIG. 7  illustrates a conventional process of manufacturing a Fresnel lens using a press. In the process shown in  FIG. 7 , a Fresnel substrate  25  is inserted between the flat mold  20  and a planer upper die  24 . The Fresnel substrate  25  is then heated, pressed, rolled and released. However, this press process has the disadvantages of long manufacturing time, and short duration of the die, and consequent low productivity. 
     FIG. 8  illustrates a process of manufacturing a shaping roller for forming a Fresnel sheet  4  and a lenticular sheet  5  according to an embodiment of the present invention. According to the present invention, the Fresnel sheet  4  and the lenticular sheet  5  can be manufactured in continuous mode due to the use of a roll shaped die rather than the planar die of the prior art. 
   The electroforming method illustrated in  FIG. 8  may be used for manufacturing a shaping roller. In  FIG. 8 , a silicone rubber die mold  26  is patterned using a planar die  20 . The patterned silicone rubber die mold  26  is made into a tube-type die by a reinforcing steel tube  27 . After a metal electroforming die  28 , made, for example, of nickel chromium has been fabricated at the inner side of the tube-type silicone rubber die mold  26  by means of an electroforming method, the reinforcing steel tube  27  is removed, which leaves only the electroformed metal die  28 . Finally, the shaping roller is completed by inserting and fixing a cylindrical steel tube roller with a shaft into the electroformed metal die  28 . 
   The invention described above will be more fully understood with reference to the following Example and Comparative Example. 
   EXAMPLE 
   Urethane acrylate resin is used as the ultra-violet resin of the Fresnel lens  7  and the lenticular lens  9 . Polyester film is used for the substrate  8  of the Fresnel sheet  4 , the substrate  10  of the lenticular sheet and the protective sheet  6 . The properties of urethane acrylate resin and polyester film used in the present example are summarized in tables 1 and 2, respectively. 
   The process conditions are as follows: 
   surface temperature: 35±5° C.; and 
   manufacturing speed: 4 to 7 m/min. 
   COMPARATIVE EXAMPLE 
   A comparative product is manufactured as a prior art product. Polymethylmetacrylate is used for the substrate  8  of the Fresnel sheet  4  and the lenticular sheet  5 . Urethane acrylate is used for the Fresnel lens  7 . 
   
     
       
             
           
             
             
             
           
         
             
               TABLE 1 
             
           
           
             
                 
             
             
               Properties of Urethane Acrylate Resin used in Fresnel 
             
             
               lens and lenticular lens 
             
           
        
         
             
               Item 
               Properties 
               Remarks 
             
             
                 
             
             
               Composition 
               Urethaneacrylate 
               Sunkyung-UCB Co., 
             
             
                 
                 
               Ltd. 
             
             
               Viscosity (cps) 
               950 ± 50 
               25° C. 
             
             
               Transmission rate of 
               91 ± 1 
             
             
               total amount of 
             
             
               light (%) 
             
             
               Index of Reflection 
               1.52 ± 0.02 
             
             
               Specific Gravity 
               1.1 
             
             
                 
             
           
        
       
     
   
   
     
       
             
           
             
             
             
           
         
             
               TABLE 2 
             
           
           
             
                 
             
             
               Properties of Polyester Film [used in Protective Sheet] 
             
           
        
         
             
               Item 
               Properties 
               Remarks 
             
             
                 
             
             
               Composition 
               Polyester 
               SKC Co., Ltd. 
             
             
               Thickness (μm) 
               200 
               protective sheet 
             
             
                 
               100 
               Fresnel sheet 
             
             
                 
               50 
               lenticular sheet 
             
             
               Index of Reflection 
               1.64 ± 0.01 
             
             
               Transmission rate of 
               91 
             
             
               Total amount of 
             
             
               Light (%) 
             
             
               Specific Gravity 
               1.4 
             
             
               Tensile Strength 
               2,500 ± 50   
             
             
               (Kg/cm 2 ) 
             
             
                 
             
           
        
       
     
   
   
     
       
             
           
             
             
             
             
           
             
             
             
             
             
           
             
             
             
             
           
             
             
             
             
             
           
             
             
             
             
           
             
             
           
         
             
               TABLE 3 
             
           
           
             
                 
             
             
               Properties of the Screens. 
             
           
        
         
             
                 
               Example 
               Comparative 
                 
             
             
               Item 
               1 
               Example 1 
             
             
                 
             
           
        
         
             
               Weight 
               Protective sheet (6) 
               160 
               1260 
                 
             
             
               (gr) 
               Fresnel sheet (4) 
               140 
               504 
             
             
                 
               lenticular sheet (5) 
               191 
               1250 
             
             
                 
               total 
               491 
               3014 
             
           
        
         
             
               Thickness of Screen (mm) 
               0.85 
               5.00 
                 
             
           
        
         
             
               Tensile  
               Protective sheet (6) 
               2500/2500 
               550/550 
               *Polyester 
             
             
               Strength 
               Fresnel sheet (4) 
               2200/2200 
               480/480 
               film 
             
             
               (Kg/cm 2 ) 
               lenticular sheet (5) 
               2100/2050 
               500/120 
               0° direction 
             
             
                 
                 
                 
                 
               (90° 
             
             
                 
                 
                 
                 
               direction) 
             
           
        
         
             
               Transmission rate of total 
               89 
               85 
                 
             
             
               amount of light (%) 
             
           
        
         
             
               Particulars 
               Screen (1) diagonal length: 43 inch 
             
             
                 
               Aspect ratio = 4:3 
             
             
                 
             
           
        
       
     
   
   As can be seen from Table 3, the projection tv screen  1  according to an embodiment of the present invention weights of 84% less and has tensile strength 4.5 times greater than conventional television screen.