Patent Publication Number: US-2009239003-A1

Title: Optical plate, backlight module and liquid crystal display using the same

Description:
This application claims the benefit of Taiwan Patent Application Serial No. 97109556, filed Mar. 18, 2008, the subject matter of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to an optical plate, a backlight module using the same and a liquid crystal display panel using the same, and especially relates to an optical plate having better light recycling. 
     2. Description of Related Art 
     Liquid crystal displays are commonly used for digital cameras, personal digital assistants, mobile phones and television etc. Besides its basic function of displaying, better backlight modules are becoming important therefore. 
     As mentioned, how to improve the power consumption and light recycling has become one of the most important topics. 
     Referring to  FIG. 1 ,  FIG. 1  shows a conventional liquid crystal display. Liquid crystal display  1  includes liquid crystal display panel  12 , polarizers  14 A and  14 B attached to the upper and lower surfaces of the liquid crystal display panel  12 , respectively, and backlight module  10  located beneath the liquid crystal display panel  12 . Liquid crystal display panel  12  includes upper and lower substrates, and liquid crystal layer sealed therebetween, which is known by persons having ordinary skill in the art. Further explanations are omitted. Backlight module  10  is taken a direct type backlight module for an example. Backlight module  10  includes a plurality of light sources  16 . The light sources  16  provide light to the liquid crystal display panel  12  for displaying desired images. Light includes S-polarized light  16 S and P-polarized light  16 P. Polarizer  14 A only permits S-polarized light  16 S to pass there through and absorbs/reflects P-polarized light  16 P, and therefore S-polarized light  16 S is provided to liquid crystal display panel  12 . Direction of polarized axis of polarizer  14 B is perpendicular to that of polarizer  14 A, so polarizer  14 B permits P-polarized light  16 P to pass there through and absorbs/reflects S-polarized light  16 S. 
     As mention above, because polarizer  14 A only permits S-polarized light  16 S to pass there through and absorbs/reflects P-polarized light  16 P, P-polarized light  16 P emitted by light source  16  will pass through polarizer  14 A and then transfer to P-polarized light  16 P′ by liquid crystal of the liquid crystal display panel  12 , wherein the P-polarized light  16 P′ can pass through polarizer  14 B, therefore liquid crystal display panel  12  can achieve display results. 
     However, S-polarized light  16 S provided by light source  16  is half of the total light from the light source  16 . In other words, P-polarized light  16 P which is half of the total light from the light source  16  is wasted and without use. As a result, for backlight module  10 , low light usage is a problem. How to improve light recycling of backlight module  10  is what engineers want to study. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is directed to an optical plate for providing better light recycling. 
     The present invention is also directed to an optical plate for providing specific polarized light. 
     An objective of the present invention is to increase efficiency of backlight module, decrease power consumption and lower cost by using the optical plate provided by the embodiments of the present invention. 
     In accordance with the above objective and other objectives, the present invention provides an optical plate. 
     In accordance with the above objectives and other objectives, the present invention provides a liquid crystal display panel. 
     In accordance with the above objective and other objectives, the present invention provides a liquid crystal display. 
     In an embodiment of the present invention, the optical plate comprises a substrate having a plurality of protrusions and a plurality of flat portions, wherein the protrusions and the flat portions are arranged alternately; at least one auxiliary structure disposed on the protrusions wherein the at least one auxiliary structure has a birefraction index; and an adjusting layer disposed on the substrate and the protrusions. 
     In an embodiment of the present invention, a backlight module comprises an optical plate comprising a substrate having a plurality of protrusions and a plurality of flat portions, wherein the protrusions and the flat portions are arranged alternately; at least one auxiliary structure disposed on the protrusions wherein the at least one auxiliary structure has a birefraction index; and an adjusting layer disposed on the substrate and the protrusions; and at least one light source disposed adjacent to the optical plate. 
     In an embodiment of the present invention, a liquid crystal comprises an optical plate, comprising a substrate having a plurality of protrusions and a plurality of flat portions, wherein the protrusions and the flat portions are arranged alternately; at least one auxiliary structure disposed on the protrusions wherein the at least one auxiliary structure has a birefraction index; and an adjusting layer disposed on the substrate and the protrusions; a liquid crystal display panel disposed over the optical plate; and at least one light source disposed adjacent to the optical plate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
         FIG. 1  is a conventional liquid crystal display. 
         FIG. 2  is a liquid crystal display according to the first embodiment of the present invention. 
         FIG. 3  is a liquid crystal display according to the second embodiment of the present invention. 
         FIG. 4  is a liquid crystal display according to the third embodiment of the present invention. 
         FIG. 5A  is a liquid crystal display according to the fourth embodiment of the present invention. 
         FIG. 5B  shows curves, of viewing angles vs. brightness of P-polarized light and S-polarized light provided by light source of the backlight module in  FIG. 5A , simulated by TracePro. 
         FIG. 5C  shows ratios, of comparison values of brightness of S-polarized light to P-polarized light, calculated from  FIG. 5A . 
         FIGS. 6A and 6B  are examples of substrates or auxiliary structures according to embodiments of the present invention. 
     
    
    
     DESCRIPTION OF THE 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. 
     First Embodiment 
       FIG. 2  is a liquid crystal display according to the first embodiment of the present invention. Liquid crystal display  2  comprises liquid crystal display panel  22 , polarizers  24 A and  24 B attached to the upper and lower surfaces of the liquid crystal display panel  22 , respectively, and backlight module  20  located beneath the liquid crystal display panel  22 . Components of liquid crystal display panel  22  and polarizers  24 A and  24 B are shown as description of related art and detail description about them is omitted for convenience. 
     Backlight module  20  comprises optical plate  200  and light sources  26 . Backlight module  20  of the present embodiment is taken direct type backlight module for an example. As shown, light sources  26  are located beneath the optical plate  200 . Light sources  26 , for example, are Cold cathode fluorescent lamps (CCFLs), External Electrode Fluorescent Lamps (EEFLs), mercury lamps, Halogen Lamps or light emitting diodes (LEDs). Reflector  28  may be selectively disposed beneath the light sources  26 , for reflect light provided from the light sources  26  for increasing light usage. Optical plate  200  comprises substrate  201 , auxiliary structures  202  and adjusting layer  203 . Substrate  201  may be a diffuser for diffusing. Substrate  201  has protrusions  2012  and flat portions  2011 . Protrusions  2012  and flat portions  2011  are arranged alternately. Auxiliary structures  202  are only formed on the protrusions  2012 . Auxiliary structures  202  have a birefraction index. Auxiliary structures  202  are comprised of, for example, cured liquid crystal, Calcite, Cat&#39;s Eye, crystal or Ruby etc. Auxiliary structures  202  have a horizontal refraction index (Nx) of about 1.3 to about 2 and a vertical refraction index (Ny) of about 1.3 to about 2, preferably, a horizontal refraction index (Nx) of about 1.8 and a vertical refraction index (Ny) of about 1.49. Auxiliary structures  202  have a thickness of 0.1 micrometer to about 10 micrometer, preferably 1 micrometer. Preferably, a method for forming auxiliary structures  202  comprises, for example, forming bar-type liquid crystal or plate-type liquid crystal having high birefraction index on top of the protrusions  2012  by dropping; flowing the liquid crystal by gravity to cover sides  2012 A of the protrusions  2012 ; and curing the liquid crystal by ultraviolet ray. Selectively, prior to the step of dropping the liquid crystal, form an alignment layer on the protrusions  2012  and then rubbing the alignment layer for having regular directions. Selectively, prior to the step of curing the liquid crystal, add monomer into the liquid crystal for enhancing curing efficiency of liquid crystal. Liquid crystal formed on the alignment layer has regular arrangements because of anchoring force, however, the way to make alignment layer have regular directions is not limited, which may be instead by emitting alignment layer using polarized ultraviolet ray (photo alignment) or sticking (SWV, for example). Cured liquid crystal becomes auxiliary structures  202 . Cross section of protrusions  2012  comprise an isosceles triangle having a vertex angle of about 30 degree to about 70 degree. The pitch of the protrusions  2012  is about 10 micrometer to about 500 micrometer. Substrate  201  has a refraction index of about 1.5, for example, equal to that of the adjusting layer  203 . The substrate and the adjusting layer are comprised of polymethylmethacrylate (PMMA), (Polyethylene Naphthalene &#39; PEN) or (Polyethylene terephthalate &#39; PET). 
     If light provided by light source  26  pass through substrate  201  and reaches side surface of the auxiliary structures  202 , results of polarization division will happed. The light will transfer into S-polarized light  26 S, P-polarized light  26 P and P-polarized light  26 P 1 . S-polarized light  26 S will pass through upper surface of the adjusting layer  203  and reach polarizer  24 A. If P-polarized light  26 P is perpendicular to the upper surface of the adjusting layer  203 , it will directly pass through the adjusting layer  203  and reach polarizer  24 A. If P-polarized light  26 P 1  is not perpendicular to the upper surface of the adjusting layer  203 , because refraction index of the adjusting layer  203  is greater than that of the air, it will transfer partial polarized light which is reflected by and goes away from the upper surface of the adjusting layer  203 , and then pass into the substrate  201  again. Thereafter, it will become reflection light  26 R totally reflected by the lower surface of the substrate  201  and then the above steps repeat over and over again. Light reaching the sides of the auxiliary structures  202  will be reflected and generate results of polarized division. As a result, P-polarized light  26 P which is not directly provided to the polarizer  24 A will be recycled to produce more S-polarized light  26 S. As mentioned above, light usage will be increased efficiently, usage of enhancing light plate of backlight module  20  may be omitted, power consumption may be decreased and cost will be lowered. 
     Second Embodiment 
       FIG. 3  is a liquid crystal display according to the second embodiment of the present invention. Liquid crystal display  3  comprises liquid crystal display panel  32 , polarizers  34 A and  34 B attached to the upper and lower surfaces of the liquid crystal display panel  32 , respectively, and backlight module  30  located beneath the liquid crystal display panel  32 . Components of liquid crystal display panel  32  and polarizers  34 A and  34 B are shown as description of related art and detail description about them is omitted for convenience. 
     Backlight module  30  comprises optical plate  300  and light sources  36 . Backlight module  30  of the present embodiment is taken direct type backlight module for an example. As shown, light sources  36  are located beneath the optical plate  300 . Light sources  36 , for example, are Cold cathode fluorescent lamps (CCFLs), External Electrode Fluorescent Lamps (EEFLs), mercury lamps, Halogen Lamps or light emitting diodes (LEDs). Reflector  38  may be selectively disposed beneath the light sources  36 , for reflect light provided from the light sources  36  for increasing light usage. Optical plate  300  comprises substrate  301 , auxiliary structure  302  and adjusting layer  303 . Substrate  301  may be a diffuser for diffusing. Substrate  301  has protrusions  3012  and flat portions  3011 . Protrusions  3012  and flat portions  3011  are arranged alternately. Unlike the first embodiment, in the present embodiment, auxiliary structure  302  is entirely formed on the upper surface of the substrate  301 , in other words, auxiliary structure  302  is formed on all of the flat portions  3011  and protrusions  3012 . 
     Size, materials, shapes or methods for forming the auxiliary structure  302  are as same as that of the first embodiment. Principles of light usage increase and light paths can be referred to the first embodiment, and detail description is omitted for convenience. 
     Third Embodiment 
       FIG. 4  is a liquid crystal display according to the first embodiment of the present invention. Liquid crystal display  4  comprises liquid crystal display panel  42 , polarizers  44 A and  44 B attached to the upper and lower surfaces of the liquid crystal display panel  42 , respectively, and backlight module  40  located beneath the liquid crystal display panel  42 . Components of liquid crystal display panel  42  and polarizers  44 A and  44 B are shown as description of related art and detail description about them is omitted for convenience. 
     Backlight module  40  comprises optical plate  400  and light sources  46 . Backlight module  40  of the present embodiment is taken side type backlight module for an example. Substrate  401  can be a light guide plate for guiding light. Light sources  46  are located at one side of the substrate  401  as shown in  FIG. 4 . Light sources  46 , for example, are Cold cathode fluorescent lamps (CCFLs), External Electrode Fluorescent Lamps (EEFLs), mercury lamps, Halogen Lamps or light emitting diodes (LEDs). Reflector  48  may be selectively disposed beneath the optical plate  400 , for reflect light provided from the light sources  46  for increasing light usage. Substrate  401  has protrusions  4012  and flat portions  4011 . Protrusions  4012  and flat portions  4011  are arranged alternately. Unlike the first embodiment, in the present embodiment, light provided by the light source  46  enters side of the optical plate  400 . As shown in  FIG. 4 , light is reflected by the auxiliary structure  402  of the side of the protrusion  4012  to generate results of polarized division, and it transfers into S-polarized light  46 S and P-polarized light  46 P. S-polarized light  46 S goes away from the adjusting layer  403  and reach polarizer  44 A. If P-polarized light  46 P is not perpendicular to the upper surface of the adjusting layer  403 , because refraction index of the adjusting layer  403  is greater than that of the air, it will transfer partial polarized light which is reflected by and goes away from the upper surface of the adjusting layer  403 , and then pass into the substrate  401  again. Thereafter, it will become reflection light totally reflected by the lower surface of the substrate  401  and then the above steps repeat over and over again. Light reaching the sides of the auxiliary structures  402  will be reflected and generate results of polarized division. As a result, P-polarized light  26 P which is not directly provided to the polarizer  44 A will be recycled to produce more S-polarized light  46 S. As mentioned above, light usage will be increased efficiently, usage of enhancing light plate of backlight module  40  may be omitted, power consumption may be decreased and cost will be lowered. 
     Size, materials, shapes or methods for forming the auxiliary structure  402  are as same as that of the first embodiment. Principles of light usage increase and light paths can be referred to the first embodiment, and detail description is omitted for convenience. 
     Fourth Embodiment 
       FIG. 5A  is a liquid crystal display according to the first embodiment of the present invention. Liquid crystal display  5  comprises liquid crystal display panel  52 , polarizers  54 A and  54 B attached to the upper and lower surfaces of the liquid crystal display panel  52 , respectively, and backlight module  50  located beneath the liquid crystal display panel  52 . Components of liquid crystal display panel  52  and polarizers  54 A and  54 B are shown as description of related art and detail description about them is omitted for convenience. 
     Most components and assembly of backlight module  50  is as shown in the third embodiment. Unlike the third embodiments, in the present embodiment, auxiliary structure  502  is entirely formed on the upper surface of the substrate  501 . In other words, auxiliary structure  502  is on all of the protrusions  5012  and flat portions  5011 . 
       FIG. 5B  shows curves, of viewing angles vs. brightness of P-polarized light and S-polarized light provided by light source of the backlight module  50  in  FIG. 5A , simulated by TracePro. In the present simulation, protrusion  5012  is an isosceles triangle having a vertex angle of about 60 degree. Pitch of the protrusions  5012  is about 50 micrometer. Auxiliary structure  502  has a horizontal refraction index of about 1.8 and a vertical refraction index of about 1.49. As shown in  FIG. 5B , backlight module  50  provides more S-polarized light than P-polarized light. For 0 degree viewing angle, which means directly in front of the backlight module  50 , measure the comparison values of brightness of P-polarized light and S-polarized light. S-polarized light has a comparison values of brightness of about 0.33, and that of the P-polarized light is about 4.7×10 4 . However, for 27 degree viewing angle, S-polarized light has a comparison values of brightness of about 0.05, and that of the P-polarized light is about 1×10−3. As a result, for small viewing angles, comparison values of brightness of S-polarized light are significantly greater than that of the P-polarized light. Therefore, light usage is successively improved. 
       FIG. 5C  shows ratios, of comparison values of brightness of S-polarized light to P-polarized light, calculated from  FIG. 5A . As shown in  FIG. 5C , for 0 degree viewing angle, ratio of comparison values of brightness of S-polarized light to P-polarized light is up to 700. However, while using conventional DBEF film, ratio of comparison values of brightness of S-polarized light to P-polarized light is about 6. Therefore, the embodiments of the present invention can sufficiently achieve light polarized division and improve light usage successively. 
       FIGS. 6A and 6B  are examples of substrates or auxiliary structures according to embodiments of the present invention. 
     As shown in  FIG. 6A , there are protrusions  6012  and flat portions  6011  formed on the upper surface of the substrate  601 . Protrusions  6012  and flat portions  6011  are arranged alternately, however, which may be arranged uniformly or randomly. Particularly, although previous embodiments show protrusions having unique size, shape and material for example, size, shape and material of protrusions  6012  and  6013  can be selected and changed into different according designer&#39;s demands. As shown in  FIG. 6A , protrusions  6012  are larger than protrusions  6013 . Protrusions  6012 ,  6013  are arranged alternately. Auxiliary structure  602  can be only formed on the protrusions  6012 ,  6013 , or entirely formed on the upper surface of the substrate  601  which means auxiliary structure  602  is formed on all of the flat portions  6011 , protrusions  6012  and  6013 . Another example of the substrate  601 , in  FIG. 6B , substrate  601  includes first base  601 A and second base  601 B. Second base  601 B is formed on the first base  601 A. Flat portions  6011  and protrusions  6012  are formed on the surface of the second base  601 B. Materials, thickness and/or optical properties of the first base  601 A and second base  601 B can be the same or different. Materials of the first base  601 A and second base  601 B can be comprised of polymethylmethacrylate (PMMA), (Polyethylene Naphthalene &#39; PEN) or (Polyethylene terephthalate &#39; PET). For sure, variable types of the protrusions can refer to previous examples. Methods for forming auxiliary structures  602  and relationship between the substrate  601  can refer to previous embodiments of the present invention. Detail description is omitted for convenience. 
     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.