Abstract:
A screen for displaying an image received from a projector includes an anisotropic base diffusion layer having a fine pattern; a lens layer formed on a rear surface of the anisotropic base diffusion layer; a reflection layer deposited on a rear surface of the lens layer; and a surface protection layer coupled with a front surface of the anisotropic base diffusion layer. The screen for a projector enables a viewer to view an image from a single focus projector inside a bright room, brightness to be uniformly distributed throughout the screen, and a desirable viewing angle to be obtained.

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates to a screen for reflective projectors. 
     2. Background Art 
     A projector projects an image to a screen and a user views the image reflected by the screen. Here, since an angle of incidence and an angle of reflection are symmetrical, when a conventional projector emitting an image at a long distance is used, the image emitted by the projector may be reflected by a screen and transmitted to a user. 
     However, in the case of a monofocal projector emitting an image at a short distance, the image is incident upon a screen from a short distance from the screen and thus, an angle of incidence is greater than the angle of incidence of the conventional projector. If an angle of incidence is great, an angle of reflection is great and thus, most light is not reflected toward user&#39;s eyes but is reflected toward the ceiling and a user views a dark image, and, in the case of a 3D image, an angle of reflection of the 3D image deviates from the position of 3D glasses and it is impossible for a user to view the 3D image. 
     Particularly, if a conventional screen is used in a monofocal projector, lowering of contrast in a bright indoor space, non-uniformity of distribution of front surface brightness, and difficulty in securing a wide viewing angle are generated and, thus, common use of the screen is restricted. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a screen for projectors which may be watched in a bright indoor place and used in a 3D projector. 
     Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
     In one embodiment of the present invention, a screen for projectors for displaying an image received from a projector, including an anisotropic base diffusion layer provided with fine patterns formed thereon, a lens layer formed on the rear surface of the anisotropic base diffusion layer, a reflective layer deposited on the rear surface of the lens layer, and a surface protective layer coupled with the front surface of the anisotropic base diffusion layer. 
     The anisotropic base diffusion layer may have small change of a retardation value according to angles of incidence of the image received from the projector. 
     The anisotropic base diffusion layer may have a retardation value of 10 nm or less if the angle of incidence of the image received from the projector is 50°, or a retardation value difference of 5 nm or less if the angles of incidence of the image received from the projector are 0° and 50°. 
     The anisotropic base diffusion layer may be a polymethylmethacrylate (PMMA) film. 
     The polymethylmethacrylate (PMMA) film may be manufactured by solution casting. 
     The anisotropic base diffusion layer may include a plurality of unit layers having parallel fine patterns with a designated pitch, and the fine pattern formed on one unit layer may intersect the fine pattern formed on at least another unit layer. 
     The anisotropic base diffusion layer may include two unit layers. 
     The lens layer or the surface protective layer may include a black material. 
     The black material may be carbon black. 
     The surface protective layer may include an anisotropic base diffusion layer for the surface protective layer and a surface protective coating layer formed on the front surface of the anisotropic base diffusion layer for the surface protective layer. 
     The anisotropic base diffusion layer and the surface protective layer may be bonded using an adhesive and the adhesive may be a black primer. 
     The lens layer may be a Fresnel lens provided with a rear surface portion segmented into a plurality of surfaces. 
     The lens layer may be formed of a thermosetting resin or an ultraviolet-curable resin on the rear surface of the anisotropic base diffusion layer. 
     The reflective layer may include black pearls. 
     A screen for projectors in accordance with the present invention allows a user to watch a monofocal projector in a bright indoor place and secures uniform distribution of brightness throughout the screen and a viewing angle. 
     Further, since a diffusion sheet is omitted and, thus, a cross torque value decreases, the screen may be used as a screen for passive type 3D projectors. 
     Effects obtained by the present invention are not limited to the above-described effects, and other effects which are not described will be apparent to those skilled in the art based on the following description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view illustrating a screen for projectors in accordance with the present invention in use. 
         FIG. 2  is a longitudinal-sectional view of a screen for projectors in accordance with one embodiment of the present invention. 
         FIG. 3  is a longitudinal-sectional view of the screen for projectors in accordance with one embodiment of the present invention. 
         FIG. 4  is a conceptual view illustrating a measured angle to measure retardation of a screen for projectors. 
         FIG. 5  is an exploded perspective view of a layered structure of an anisotropic base diffusion layer of a screen for projectors in accordance with one embodiment of the present invention. 
         FIG. 6  is a longitudinal-sectional view of a conventional screen for projectors. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, a mobile terminal in accordance with the present invention will be described in detail with reference to the accompanying drawings. The suffixes “module” and “unit” in elements used in the description below are given or used together only in consideration of ease in preparation of the specification and do not have distinctive meanings or functions. 
       FIG. 1  is a view illustrating a screen  10  for projectors in accordance with the present invention in use, and a monofocal projector  20  projects an image at a short distance from the screen. Although this figure illustrates the monofocal projector  20  and the screen  10  separately, a display type in which the projector  20  is fixed to the lower end of the screen  10  may be implemented. 
     If the monofocal projector  20  projects an image at a short distance, there is a large difference between angles of incidence at the upper and lower regions of the screen  10 , as shown in the figure. An image incident upon the screen  10  is reflected by the screen  10  and then enters user&#39;s eyes. When there is a large difference between angles of incidence at the upper and lower regions of the screen  10 , the reflection path of light is directed to the ceiling not the user&#39;s eyes and, thus, an amount of light reaching the user&#39;s eyes decreases. 
     Therefore, light may be reflected in the forward direction and, thus, the reflected light may move to the user&#39;s eyes, only if a reflective surface of the screen  10  for monofocal projectors faces down. The entirety of the screen  10  may be tilted in the forward direction so that light emitted by the projector  20  may be reflected by the reflective surface and thus reach the user&#39;s eyes located at the front. However, it is difficult to install the screen  10 , the reflective surface of which is tilted downwards and, thus, as exemplarily shown in  FIG. 2 , which is a longitudinal-sectional of a screen for projectors in accordance with one embodiment of the present invention, a Fresnel lens which is divided into a plurality of surfaces may be used. 
       FIG. 3  illustrates a reflection path if a lens layer  13  includes a Fresnel lens  13  and, here, an image emitted from the lower region may be reflected by the Fresnel lens  13  having a plurality of reflective surfaces tilted in the forward-downward direction and be incident upon viewer&#39;s eyes. 
     The Fresnel lens  13  serves to reduce the thickness of a curved lens and is characterized in that the surface of a curved lens is divided into planar surfaces. The cross-section of the Fresnel lens  13  has a saw-toothed shape, as exemplarily shown in  FIG. 2 . Although the Fresnel lens may be formed in a circular shape about a concentric circle, in this embodiment, a linear-type Fresnel lens  13  in which a plurality of surfaces facing in the downward direction is formed in parallel may be used. 
       FIG. 6  is a longitudinal-sectional view of a conventional screen  5  for projectors. With reference to  FIG. 6 , a layered structure including a rear coating layer  1 - 1 , a reflective surface  1 - 2 , a lens layer  1 - 3 , a base layer  1 - 4 , an adhesive layer  2 - 1 , an isotropic diffusion layer  3 , an adhesive layer  2 - 2 , a base layer  4 - 1 , a black layer  4 - 2  and a front coating layer  4 - 3  is provided. 
     In the conventional screen  5  for projectors, the lens layer  1 - 3  is formed on the base layer  1 - 4 , the reflective layer  1 - 2  is applied thereto, the rear coating layer  1 - 1  is formed as a first layer to protect the reflective layer, the isotropic diffusion layer  3  is attached to the base layer  1 - 4  located on the front surface of the first layer using the adhesive layer  2 - 1 , and surface protective layers  4 - 1 ,  4 - 2  and  4 - 3  including the black layer  4 - 2  to protect the front surface of the screen  5  for projectors and to produce a clear image is attached thereto using the adhesive layer  2 - 2 . 
     In such a conventional structure in which several layers are stacked, as the number of the stacked layers increases, an angle of refraction varies according to an angle of incidence and an image reflected by the screen is severely distorted. If a difference between an angle of incidence of light incident upon the upper portion of the screen from the projector  20  and an angle of incidence of light incident upon the lower portion of the screen from the projector  20  is great as in the present invention, distortion becomes more severe and, thus, the conventional complicated layered structure needs to be simplified. 
       FIG. 2  is a longitudinal-sectional view of a screen for projectors in accordance with one embodiment of the present invention. The screen of the present invention has a layered structure including a plurality of layers. The layered structure includes a rear coating layer  11 , a reflective layer  12 , a lens layer  13 , an anisotropic base diffusion layer  14 , an adhesive layer  15  and a surface protective layer  16 . Only one adhesive layer may be used by omitting the conventional isotropic diffusion layer  3 , and a simple layered structure may be obtained by eliminating the black layer  4 - 2  from the conventional surface protective layers  4 - 1 ,  4 - 2  and  4 - 3 . 
     Hereinafter, the configuration of the present invention will be described in more detail with reference to  FIG. 2 . 
     The lens layer  13  may be formed on the anisotropic base diffusion layer  14 . The lens layer  13  is formed of a resin, such as an ultraviolet-curable resin or a thermosetting resin, and thus, requires a base layer. However, since the anisotropic base diffusion layer  14  of the present invention, serving as a base when the lens layer  13  is formed, is located on the front surface of the lens layer  13 , as exemplarily shown in  FIG. 2 , the anisotropic base diffusion layer  14  influences a path of light which is incident upon and reflected by the screen  10 . 
     A degree of distortion of light incident upon of reflected by the lens layer  13  is determined by a retardation value of the anisotropic base diffusion layer  14  according to refraction of light. Retardation is a phenomenon in which the velocity of light in a specific medium varies and, thus, differs from the velocity of light in the air, and such a velocity difference varies according to an angle of incidence. As an angle of incidence increases, resistance to a medium increases and a retardation value increases. 
     In the case of a screen for projectors separated by a large distance from the screen and emitting light, an angle of incidence is almost uniform regardless of the position of the screen. Therefore, only a retardation value at an angle of incidence of 0° is measured and a material having a small retardation value at an angle of incidence of 0° is used. 
     However, in the screen  10  for monofocal projectors in accordance with the present invention, a difference between an angle of incidence at the upper portion of the screen  10  and an angle of incidence at the lower portion of the screen  10  is great, as exemplarily shown in  FIG. 1 . Therefore, referring to  FIG. 4 , by measuring a retardation value at an angle of incidence of 0° (a) and a retardation value at an angle of incidence of 50° (b) and comparing the measured retardation values, a clear image having a high quality may be obtained using a material having a small retardation value which is less changed even if the angle of incidence is changed. 
     [Table 1] states retardation values according to thicknesses of polycarbonate, which is a representative thermosetting resin, and angles of incident light. 
     
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                 Retardation value  
                 Retardation value 
               
               
                   
                 Thickness 
                 (nm) at angle of  
                 (nm) at angle of  
               
               
                 Film kind 
                 (μm) 
                 incidence of 0°  
                 incidence of 50° 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Polycarbonate 
                 80 
                 4 
                 38 
               
               
                   
                 150 
                 5 
                 50 
               
               
                   
               
             
          
         
       
     
     In the case of polycarbonate, when light is incident upon a polycarbonate layer having a thickness of 80 μm at an angle of 0°, a retardation value of 4 nm is obtained and, when light is incident upon the polycarbonate layer having a thickness of 80 μm at an angle of 50°, a retardation value of 38 nm is obtained, thus causing a great retardation value difference. Such a difference increases as the thickness of the polycarbonate layer increases. 
     When light is incident upon a polycarbonate layer having a thickness of 150 μm at an angle of 0°, a retardation value of 5 nm is obtained and, when light is incident upon the polycarbonate layer having a thickness of 150 μm at an angle of 50°, a retardation value of 50 nm is obtained, thus causing a greater retardation value difference. Polycarbonate may be used as a base layer of a screen for projectors emitting light at a long distance but is not proper as a base layer of the screen  10  for monofocal projectors having a great difference of angles of incidence. 
     Therefore, in the present invention, the anisotropic base diffusion layer  14  is formed using a material having a small retardation value difference according to angles of incident light. For example, polymethylmethacrylate (PMMA) may be used as a material having a small retardation value difference according to angles of incident light. 
     When PMMA is manufactured into a film type, as stress is minimized, a retardation value may decrease. When an anisotropic base diffusion layer is formed using a manufacturing method without applying stress, such as solution casting in which a film is formed by applying a solution, a retardation value may further decrease. 
     Table 2 states retardation values according to thicknesses of PMMA and angles of incident light. 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                   
                   
                 Retardation value 
                 Retardation value 
               
               
                   
                   
                 Thickness 
                 (nm) at angle of  
                 (nm) at angle of  
               
               
                   
                 Film kind 
                 (μm) 
                 incidence of 0° 
                 incidence of 50° 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 PMMA 
                 40 
                 4.3 
                 4.7 
               
               
                   
                   
                 400 
                 2 
                 38 
               
               
                   
                   
               
             
          
         
       
     
     With reference to Table 2, when a PMMA layer has a thickness of 40 μm, there is no retardation value difference even if light is incident upon the polycarbonate layer at angles of 0° and 50°. However, when the thickness of the PMMA layer increases, there is a retardation value difference according to angles of incidences. 
     The anisotropic base diffusion layer  14  in accordance with the present invention uses a material, the retardation value of which is small according to angles of incident light, but, if an angle of incidence increases as the thickness of the anisotropic base diffusion layer  14  increases, the retardation value increases and, thus, the thickness of the screen  10  needs to be reduced. 
     As exemplarily shown in  FIG. 6 , conventionally, the isotropic diffusion layer  3  is attached to the front surface of the lens layer  1 - 3 . The isotropic diffusion layer  3  serves to secure a viewing angle, and securing of the viewing angle means that a user may view an image emitted from the screen  10  even if the user watches the screen  10  from an oblique angle. 
     Therefore, efficiency of the screen is good as a viewing angle thereof increases but, when the isotropic diffusion layer  3  is stacked on the front surface of the lens layer  1 - 3 , as in the conventional screen  5  shown in  FIG. 6 , so as to increase the viewing angle, a retardation value increases and, thus, the screen  5  may be difficult to use as a screen for 3D projectors. 
     Particularly, in the case of a 3D projector  20 , an image incident upon a left eye of a user and an image incident upon a right eye of the user should not be mixed. However, the isotropic diffusion layer  3  used in the conventional screen  5  scatters light and an image for a left eye may be incident upon a right eye (hereinafter, this will be referred to as ‘crosstalk’). 
     In the present invention, in order to minimize crosstalk, the isotropic diffusion layer  3  is omitted and fine patterns to secure a viewing angle may be formed on the anisotropic base diffusion layer  14 . The fine patterns secure a viewing angle by scattering light but prevent crosstalk by scattering light only in a specific direction. That is, the fine patterns do not scatter incident light in all directions but scatters incident light only in a direction to secure a viewing angle, thus being capable of minimizing crosstalk and securing the viewing angle. 
       FIG. 5  is an exploded perspective view of a layered structure of the anisotropic base diffusion layer  14  and the anisotropic base diffusion layer  14  includes a plurality of stacked unit layers  14   a  and  14   b . Fine patterns  14   a ′ and  14   b ′ separated from each other by designated intervals and disposed in parallel are formed on the respective unit layers  14   a  and  14   b . These fine patterns  14   a ′ and  14   b ′ scatter light only in a specific direction, thus being capable of minimizing crosstalk and securing a viewing angle. 
     The directions of the fine patterns  14   a ′ and  14   b ′ formed on the respective unit layers  14   a  and  14   b  are different, one of the fine patterns  14   a ′ and  14   b  is a horizontal fine pattern and the other of the fine patterns  14   a ′ and  14   b  is a vertical fine pattern, and the patterns intersect when the horizontal unit layer  14   a  and the vertical unit layer  14   b  are stacked. Here, the horizontal fine pattern  14   a ′ is not always arranged in the horizontal direction and the vertical fine pattern  14   b ′ is not always arranged in the vertical direction. That is, these fine patterns may be tilted in oblique directions. 
     A degree of diffusion may be controlled by adjusting the pitch and width of the fine patterns  14   a ′ and  14   b ′. The width of the fine patterns  14   a ′ and  14   b ′ may be formed within the range of 200 nm to 1,000 nm, and the pitch of the fine patterns  14   a ′ and  14   b ′ may be formed within the range of about 5 μm to about 50 μm. The width and pitch of the fine patterns  14   a ′ and  14   b ′ may be different according to thicknesses and physical characteristics, such as a retardation value, of other members. 
     Patterning may be carried out by forming the fine patterns  14   a ′ and  14   b ′ by engraving or embossing figures corresponding to the fine patterns  14   a ′ and  14   b ′ on a mold when the unit layers  14   a  and  14   b  are formed, engraving the fine patterns  14   a ′ and  14   b ′ using a laser, or inserting louver structures into the unit layers  14   a  and  14   b.    
     Although this figure illustrates two unit layers  14   a  and  14   b , a horizontal layer and a vertical layer are stacked so as to form a set and, thus, the unit layers  14   a  and  14   b  may be prepared in an even number, such as four or six. However, as the number of the unit layers  14   a  and  14   b  increases, the thickness of the anisotropic base diffusion layer  14  increases and a retardation value increases, as described above. Therefore, in order to minimize a retardation value, two unit layers  14   a  and  14   b  may be stacked to form the anisotropic base diffusion layer  14 . 
     The lens layer  13  formed on the anisotropic base diffusion layer  14  may include a black material, such as carbon black. Since contrast increases and a clear picture may be produced if the background of an image is black, the independent black layer  4 - 2  is conventionally stacked, as exemplarily shown in  FIG. 6 . However, this increases the number of layers of the layered structure and causes increase of a retardation value and, thus, the conventional black layer  4 - 2  is omitted and a black material is included in the lens layer  13 , when the lens layer  13  is manufactured, so as to function as the conventional black layer  4 - 2 . 
     The lens layer  13  includes a plurality of surfaces segmented from the rear surface thereof, and a reflective layer to reflect light is formed on the rear surface of the lens layer  13 . The reflective layer may employ a mirror film and contain black pearls to increase contrast together with reflection performance. The rear coating layer  11  may be formed on the rear surface of the reflective layer so as to prevent damage to the reflective layer. 
     The surface protective layer  16  is stacked on the front surface of the anisotropic base diffusion layer  14  so as to prevent damage to the patterns formed on the anisotropic base diffusion layer  14 . The surface protective layer  16  may be formed through a coating method or a film stacking method. However, since the surface protective layer  16  formed as thin as possible may reduce a retardation value, the film stacking method rather than the coating method may form a thinner surface protective layer  16 . 
     Since the surface protective layer  16  needs to have a small difference between retardation values according to angles of incidence, the surface protective layer  16  may be formed of a material for the anisotropic base diffusion layer  14 , such as PMMA. For example, the surface protective layer  16  may include a base layer for the surface protective layer  16  formed of the same material as the material for the anisotropic base diffusion layer  14  and a surface protective coating layer applied to the base layer. 
     The adhesive layer  15  may be used to stack the surface protective layer  16  on the anisotropic base diffusion layer  14 . If the lens layer  13  does not include a black material, the adhesive layer  15  may be blackened using a member which has a thin thickness, less change of a retardation value according to angles of incidence and a small retardation value, such as a black primer layer. 
     As described above, a screen for projectors in accordance with the present invention may allow a viewer to watch a monofocal projector in a bright indoor space, uniformize distribution of brightness in the screen, and secure a viewing angle. 
     Further, since an isotropic diffusion sheet is omitted and a small crosstalk value is obtained, the screen for projectors in accordance with the present invention may be used as a screen for passive type 3D projectors. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. 
     Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.