Abstract:
A liquid crystal display includes a liquid crystal layer, a holding assembly for internally holding the liquid crystal layer, and a diffusion mollifying layer that reduces the diffusion of light entering into the assembly. The holding assembly includes a plate having a rugged surface resulting from a surface-roughening process. The rugged surface is covered by the diffusion mollifying layer to reduce the frequency of light diffusion.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a reflective-type or transflective-type liquid crystal display (LCD).  
           [0003]    2. Description of the Related Art  
           [0004]    As is known, liquid crystal displays (LCDs) are classified into three different types depending upon their illumination methods. They are reflective-type, transflective-type and transmissive-type. Of these, the reflective-type and the transflective-type are advantageous in saving power over the transmissive-type because in the former two types, ambient light (such as indoor illumination and sun light) can be utilized for image display, while in the latter type, such light cannot be used.  
           [0005]    Generally, a typical reflective-type LCD includes a LC panel and a polarizing plate disposed in front of the LC panel. Specifically, the LC panel may a transparent first substrate, a second substrate facing the first substrate, and a liquid crystal layer contained between the first and the second substrates. Further, the reflective-type LCD may include a reflective plate disposed in back of the second substrate (or reflective electrodes disposed in front of the second substrate). In this arrangement, the ambient light passes through the polarizing plate, the first substrate and the LC layer, and then is reflected forward by the reflective plate to the viewer for image display.  
           [0006]    In such a reflective-type LCD, the reflective rear plate is often subjected to surface roughening (by sand-blasting for example), thereby providing a rugged reflective surface. The ambient light, entering into the LCD, is reflected on this rugged surface and diffused. This light diffusion is caused to occur in expectation of making the viewing area bright and providing good viewability.  
           [0007]    However, the reflective surface of the conventional reflective plate is extremely rugged, so that the vibrating direction of the polarized light is unduly changed when the light is reflected on the reflective plate. Consequently, the polarized state of the light deteriorates, thereby resulting in drawbacks such a poor contrast of displayed images.  
         SUMMARY OF THE INVENTION  
         [0008]    The present invention has been proposed under the circumstances described above. It is, therefore, an object of the present invention to provide a liquid crystal display with an improved light diffuser which can diffuse light to an appropriate degree. Another object of the present invention is to provide a method of making such an advantageous light diffuser for use in an LCD.  
           [0009]    According to a first aspect of the present invention, there is provided a liquid crystal display that includes: a liquid crystal layer; a holding assembly including at least one plate for internally holding the liquid crystal layer; and a diffusion mollifying layer that reduces diffusion of light entering into the assembly. The above-mentioned plate includes a rugged surface resulting from surface roughening, and the rugged surface is covered by the diffusion mollifying layer.  
           [0010]    The surface roughening may be performed by a blasting process or etching process.  
           [0011]    Preferably, the diffusion mollifying layer may include a non-flat surface that is smoother than the rugged surface of the above-mentioned plate. The diffusion mollifying layer may be made of resin.  
           [0012]    Preferably, the holding assembly may include a transparent front panel, and the liquid crystal layer may be disposed between the front panel and the above-mentioned plate. In this case, the plate may be made of soda glass, while the diffusion mollifying layer may be made of silicon dioxide.  
           [0013]    Preferably, the LC display of the present invention may further include a polarizer disposed in front of the front panel.  
           [0014]    Preferably, the LC display of the present invention may further include a metal layer formed on the non-flat surface of the diffusion mollifying layer.  
           [0015]    Preferably, the metal layer may include a non-flat reflective surface.  
           [0016]    Preferably, the LC display of the present invention may further include a polarizer. The above-mention plate and the diffusion mollifying layer may be disposed between the polarizer and the liquid crystal layer.  
           [0017]    Preferably, the holding assembly may include a reflecting surface that causes light passing through the liquid crystal layer to be reflected toward the above-mentioned plate.  
           [0018]    Preferably, the diffusion mollifying layer may allow the passage of ambient light entering into the assembly and the passage of light reflected by the above-mentioned reflecting surface.  
           [0019]    Preferably, the diffusion mollifying layer may be held in contact with the polarizer.  
           [0020]    Preferably, the LC display of the present invention may further include a front glass panel disposed between the diffusion mollifying layer and the liquid crystal layer. The front glass panel may be held in contact with the diffusion mollifying layer.  
           [0021]    According to a second aspect of the present invention, there is provided a method of making a light diffusion assembly used for a liquid crystal display. The method includes the steps of: subjecting a base member to surface roughening for providing the base member with a rugged surface; and forming a coating layer on the rugged surface in a manner such that the coating layer is provided with a non-flat surface. The rugged surface of the base member may result from a blasting process or etching process. The coating layer may be formed by applying resin onto the rugged surface of the base member by a spin coat method.  
           [0022]    Other features and advantages of the present invention will become apparent from the detailed description given below with reference to the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]    [0023]FIG. 1 is a sectional view showing the basic structure of a liquid crystal display according to a first embodiment of the present invention;  
         [0024]    [0024]FIG. 2 is a perspective view showing first and second substrates used for the LCD of FIG. 1;  
         [0025]    FIGS.  3 A˜ 3 C illustrate how reflective electrodes are formed on the second substrate;  
         [0026]    [0026]FIG. 4 is a sectional view showing the basic structure of a liquid crystal display according to a second embodiment of the present invention;  
         [0027]    [0027]FIG. 5 is a sectional view showing the basic structure of a liquid crystal display according to a third embodiment of the present invention;  
         [0028]    [0028]FIG. 6 is a sectional view showing the basic structure of a liquid crystal display according to a fourth embodiment of the present invention;  
         [0029]    [0029]FIG. 7 illustrates how the ambient light passes through the light diffusion assembly of the LCD shown in FIG. 6; and  
         [0030]    [0030]FIG. 8 is a sectional view showing the basic structure of a liquid crystal display according to a fifth embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0031]    Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.  
         [0032]    [0032]FIG. 1 shows the basic structure of a liquid crystal display (LCD) according to a first embodiment of the present invention. As illustrated, the LCD A is of a reflective-type, including a first substrate  1 , a second substrate  2  (spaced from and parallel to the first substrate  1 ), liquid crystal  18  (contained between the first and the second substrates), a plurality of transparent electrodes  4 A and a plurality of reflective electrodes  4 B.  
         [0033]    The first and the second substrates  1 ,  2  may be made of glass or acrylic resin. The first substrate  1  is transparent, while the second substrate  2  may be transparent or not. A polarizing plate  19  is attached to the upper surface (front surface) of the first substrate  1 , thereby causing light waves vibrating only in a prescribed direction to pass through.  
         [0034]    The transparent electrodes  4 A may be made of indium tin oxide (ITO) and arranged on the lower side of the first substrate  1 . In the illustrated embodiment, three kinds of color filters  3 R(red),  3 G(green) and  3 B(blue) are provided between the electrodes  4 A and the substrate  1 . FIG. 1 depicts the electrodes  4 A as being directly formed on the color filters  3 R,  3 G and  3 B. Preferably, the lower surface of the respective filters  3 R,  3 G and  3 B may be formed with a transparent layer of silicon oxide upon which an transparent electrode  4 A is formed. The LCD A may operate by simple matrix driving method. As shown in FIG. 2, the parallel, strip-like electrodes  4 A are regularly distanced from each other.  
         [0035]    The reflective electrodes  4 B are disposed on the upper side of the second substrate  2  and have a strip-like configuration, as shown in FIG. 2, like the transparent electrodes  4 A. The reflective electrodes  4 B and the transparent electrodes  4 A are elongated perpendicularly to each other. Each intersection of the electrodes  4 A and  4 B corresponds to one dot to which required voltage is applied selectively. The combination of three dots (red, green and blue dots) provides one pixel for color display. The transparent electrodes  4 A and the reflective electrodes  4 B are coated by alignment layers  5 A and  5 B, respectively, for twisting the molecules of the liquid crystal, as required. The liquid crystal may be nematic one, though the present invention is not limited to this.  
         [0036]    The reflective electrodes  4 B, which may be made of aluminum, have a light-reflecting surface  40 . The second substrate  2  has an upper surface  20  which has been made rugged by abrasive blasting for example. The rugged surface  20  is covered by a coating layer (diffusion mollifying layer)  71 . The above-mentioned reflective electrodes  4 B are formed on this coating layer  71 .  
         [0037]    The rugged surface  20  of the second substrate  2  has a roughness of about 0.05 μm (center line average or CLA) The coating layer  71  is also rugged and has a thickness of about 0.1 μm. The roughness of the layer&#39;s surface  71  is about 0.02 μm (CLA). The coating layer  71  may be made of polyimide or acrylic resin. The reflective electrodes  4 B are made from a metal layer of a generally constant thickness that is formed on the surface  71   a  of the coating layer  71 . Thus, the surface  40  of each reflective electrode  4 B has generally the same roughness as the surface  71   a  of the coating layer  71 . In the illustrated embodiment, the exposed portions of the surface  71   a  of the coating layer  71  (i.e., the portions that are not covered by the reflective electrodes  4 B) are reflective as in the electrodes  4 B. Though the coating layer  71  can be transparent and still reflect light, it may preferably be non-transparent (white for example) for better light reflection.  
         [0038]    The reflective electrodes  4 B may be formed by a process shown in FIGS.  3 A˜ 3 C. First, the second substrate  2  is subjected to sand-blasting so that, as shown in FIG. 3A, the selected surface  20  becomes rugged. Then, as shown in FIG. 3B, a coating layer  71  is formed on the rugged surface  20  by e.g. a known spin-coating method using a resin material in a molten state. Then, a metal layer (e.g. aluminum layer) is formed, by vapor deposition or sputtering for example, on the solidified coating layer  71 . Finally, the obtained metal layer is subjected to etching to provide the desired reflective electrodes  4 B, as shown in FIG. 3C.  
         [0039]    According to the above process, the surface  71   a  of the coating layer  71  is made less rugged than that of the second substrate  2 , as seen from FIG. 3B, so that the surface  71   a  undulates smoothly. Also, the reflective electrodes  4 B, which are formed on this smooth undulating surface  71   a,  have a smooth undulating surface  40 .  
         [0040]    The image-displaying mechanism of the LCD A is basically the same as that of a conventional reflective-type LCD. Specifically, referring to FIG. 1, the ambient light passes through the polarizing plate  19 , the first substrate  1  and the liquid crystal  18 . Then, the light is reflected back by the reflective electrodes  4 B to the viewer. In the illustrated embodiment, as noted above, light reflection also occurs on the surface  71   a  of the coating layer  71 . This is advantageous to brightening the viewing area of the LCD and providing enhanced contrast.  
         [0041]    According to the above embodiment, the smooth undulating surfaces of the reflective electrodes  4 B and coating layer  71  reflect the penetrating ambient light. Advantageously, these smooth surfaces will scatter or diffuse light to a smaller degree than the raw sand-blasted surface  20  (see FIG. 3A). Thus, the polarization of the reflected light is so maintained as to provide good contrast. Further, since light-scattering is not totally prohibited in the LCD A, the viewing area of the display can be made bright enough to prevent an ambient object (such as a fluorescent lamp on the ceiling) from being mirrored on the display.  
         [0042]    FIGS.  4 ˜ 8  illustrate other embodiments of the present invention. Though these figures, elements that are identical or similar to those shown in FIG. 1 are indicated by the same reference signs.  
         [0043]    In the structure shown in FIG. 4, a reflective plate  8  is attached to the back side of the second substrate  2 . The reflective plate  8 , made of e.g. synthetic resin, has its upper side subjected to sand-blasting so that the surface  80  is rugged. On the surface  80  are formed a coating layer  71  and a metal layer  73  that covers the entire surface of the coating layer  71 . The upper surface of the metal layer  73  is a reflective surface. Like the surface  71   a  of the coating layer  71 , the upper surface of the metal layer  73  is a smoothly curved uneven surface. A plurality of transparent electrodes  4 B are formed on the second substrate  2 . The ambient light penetrating the LCD passes through the electrodes  4 B to strike upon the metal layer  73 . Alternatively, the electrodes  4 B may be made of a non-transparent reflective material. In this case, the ambient light is partly reflected by the electrodes  4 B and partly passes between the electrodes  4 B to reach the metal layer  73 .  
         [0044]    With the structure shown in FIG. 4, the ambient light penetrating the LCD is scattered by the metal layer  73 . This scattering of light provides the same advantageous effects as in the above-described first embodiment, where light is scattered by the reflective electrodes  4 B.  
         [0045]    In accordance with the structure shown in FIG. 5, a coating layer  71  is formed on an uneven surface  80  of a reflective plate  8 , but no metal layer is formed on the coating layer  71 . Instead, the coating layer  71  has a reflective surface  71   a  for scattering light. For good reflectivity, the coating layer  71  may be made of a white resin material.  
         [0046]    In accordance with the structure shown in FIG. 6, a light-permeable member  6  is provided between a first substrate  1  and a polarizing plate  19 . As best shown in FIG. 7, the lower surface  60  of the light-permeable member  6  is a sand-blasted, rugged surface. On this rugged surface  60  is formed a coating layer (diffusion mollifying layer)  61 . The surface  60  and the coating layer  61  are the same in surface roughness as the rugged surface  20  and the coating layer  71  of the previous embodiment. Further, the surface  60  and the coating layer  61  may be formed in the same manner as the rugged surface  20  and the coating layer  71 . The coating layer  61  has a smooth undulating surface  61   a.  The coating layer  61  allows the passage of light and has a refractive index which is generally equal to that of the first substrate  1 .  
         [0047]    With the above arrangement, the ambient light passes through the polarizing plate  19 , the light-permeating member  6  and the coating layer  61 . As seen from FIG. 6, the coating layer  61  has an undulating surface  61   a  from which the passing light is emitted. Due to the undulation of the surface  61   a,  the light is scattered as being emitted from the surface  61   a  toward the first substrate  1 . The advantageous effects of this scattering of light are the same as those enjoyable in the above-described embodiments.  
         [0048]    The coating layer  61  may be attached to the upper side of the light-permeating member  6 . In this case, the upper surface of the light-permeating member  6  is subjected to e.g. sand-blasting before the coating layer  61  is fixed to the member  6 . As a third option, both the upper and the lower sides of the light-permeating member  6  may be covered by a coating layer.  
         [0049]    In accordance with the structure shown in FIG. 8, the upper surface  10  of a first substrate  1  is subjected to sand-blasting, to provide a rugged surface. A transparent coating layer  61  is formed directly on the rugged surface  10 .  
         [0050]    According to the present invention, the first and/or the second substrates may be made of soda glass. In this case, the substrate is subjected to surface roughening by a sand-blasting method for example, and then the obtained rugged surface of the substrate may be coated with a silicon oxide layer formed by a dip coating method. Since soda glass is not an expensive material, the production cost of an LCD employing soda glass substrates is advantageously reduced. The silicon oxide coating contributes to preventing the precipitation of alkali from the soda glass.  
         [0051]    According to the present invention, the surface roughening may be performed by a blasting process, an etching process, etc. For instance, when the first or second substrate is made of soda glass, the substrate may be dipped into an etchant of hydrofluoric acid, to provide the required rugged surface.  
         [0052]    The present invention being thus described, it is obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the present invention, and all such modifications as would be obvious to those skilled in the art are intended to be included within the scope of the following claims.