Abstract:
A color cholesteric liquid crystal display device and a manufacturing method for the same are proposed. A color cholesteric liquid crystal display device has a bistable single-layer or stacked structure. The display is made of cholesteric liquid crystal material via an inkjet process and ultraviolet exposure processes that induce a phase separation reaction. In addition, the display provided in the present invention enhances the reflective brightness. Furthermore, the techniques of the present invention can be applied to make flexible color cholesteric liquid crystal display devices.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention is related to a color cholesteric liquid crystal display device and a manufacturing method for the same, and more particularly, to a color cholesteric liquid crystal display device with a bistable single-layer (or stack) structure. The display is made of cholesteric liquid crystal material via an inkjet process and two ultraviolet exposure processes. In addition, the display provided in the present invention has enhanced reflective brightness and is flexible.  
         [0003]     2. Description of Related Art  
         [0004]     In recent years, flexible displays, electronic papers and electronic books have been developed vigorously. The display media include liquid crystal displays, electronphoretic displays, electrochromic displays and electrolytic displays. In the application of electronic papers, compared with displays made of other display materials, the display made of a cholesteric liquid crystal material has higher brightness and better contrast. In addition, the cholesteric liquid crystal display can be driven passively and produced easily.  
         [0005]     Conventionally, for manufacturing color cholesteric liquid crystal display devices, two methods are often used. The first one uses a cholesteric structure with three layers. By stacking three cholesteric liquid crystal layers capable of reflecting different colors and using various driving methods, the display can reflect various colors. Its drawback is that the alignment of the panel with the three-layer structure cannot be achieved easily and this kind of display can only be bent a little. The second one uses a cholesteric structure with a single layer only. It mixes a twist agent that can first be decomposed by light and a cholesteric liquid crystal material. Then, ultraviolet light with different intensities is used to destroy or reduce the twist agent located at a single area. Thus, a single-layer display capable of reflecting various colors can be provided. However, this device with the single-layer structure is unreliable. The environment affects it easily. Hence, this device needs to use an additional ultraviolet-proof layer for protection.  
         [0006]     In the prior art, such as U.S. Pat. No. 6,356,323, a “Color display using cholesteric liquid crystals” is disclosed. Reference is made to  FIG. 1 , which is a schematic diagram of a structure of a conventional color cholesteric liquid crystal display device. The structure includes an absorbing surface  10 , a clear flexible substrate  12 , a first patterned ITO layer  14 , a second patterned ITO layer  16 , a third patterned ITO layer  18 , a fourth patterned ITO layer  20 , a fifth patterned ITO layer  22 , a first light modulation layer  24 , a second light modulation layer  26  and a third light modulation layer  28 .  
         [0007]     Furthermore, U.S. Pat. No. 6,331,884, “method of making a liquid crystal display,” discloses a method that uses a liquid crystal material to make a liquid crystal device. Reference is made to  FIG. 2 , which is a schematic diagram for showing the manufacturing process of the conventional liquid crystal device. The liquid crystal device has multiple liquid crystal materials  30 , multiple precursors  32 , a first base  34 , a second base  36 , multiple conductive films  38 , multiple insulating films  40 , multiple bank structures  42  and an absorbing layer  44 .  
         [0008]     However, the above method for making the liquid crystal display disclosed in U.S. Pat. No. 6,331,884 has a drawback. In the above method, a resin material must first be smeared on multiple insulating films  40 . Then, multiple liquid crystal materials  30  are arranged by a printing process and a second base is placed thereafter. Lastly, an exposure process is provided to form multiple precursors  32 . In this way, the thickness and manufacturing process of the display device is difficult to control. A higher driving voltage is required, and image effects thereof are poor.  
       SUMMARY OF THE INVENTION  
       [0009]     An objective of the present invention is to provide a color cholesteric liquid crystal display device with a bistable single-layer (or stack) structure. The display is made of cholesteric liquid crystal material via an inkjet process and ultraviolet exposure processes. In addition, the display provided in the present invention has enhanced reflective brightness and is flexible.  
         [0010]     For reaching the objective above, the present invention provides a method for manufacturing a color cholesteric liquid crystal display device. Multiple bank structures are made on a first electrode layer of a lower base. A first solution is printed among the bank structures to form multiple first cholesteric liquid crystal layers, in which the first solution is a mixture of first cholesteric liquid crystal materials and first monomers. Multiple cover layers are formed on the first cholesteric liquid crystal layers. A second solution is printed onto the bank structures to form multiple second cholesteric liquid crystal layers, in which the second solution is a mixture of second cholesteric liquid crystal materials and second monomers. Multiple upper covers are formed on the second cholesteric liquid crystal layers. The upper covers are coated with multiple conductive materials.  
         [0011]     The present invention provides a color cholesteric liquid crystal display device having a stacked structure. It includes an lower base having a first electrode layer; multiple bank structures distributed over the lower base; multiple first cholesteric liquid crystal materials provided among the bank structures; multiple cover layers coated on the first cholesteric liquid crystal materials; multiple second cholesteric liquid crystal materials provided on the cover layers; and multiple upper electrodes distributed on the cover layers.  
         [0012]     Numerous additional features, benefits and details of the present invention are described in the detailed description, which follows. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     The foregoing aspects and many of the attendant advantages of this invention will be more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:  
         [0014]      FIG. 1  is a schematic diagram of a structure of a conventional three-layer color cholesteric liquid crystal display device;  
         [0015]      FIG. 2  is a schematic diagram for showing the manufacturing process of a conventional liquid crystal device;  
         [0016]     FIGS.  3 A-E show a schematic diagram of a color cholesteric liquid crystal display device having a stacked structure in accordance with the first embodiment of the present invention; and  
         [0017]     FIGS.  4 A-E show a schematic diagram of a color cholesteric liquid crystal display device having a stacked structure and a dual-base structure in accordance with a preferred embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0018]     The prior art, such as U.S. Pat. No. 6,356,323, uses a conventional liquid crystal infusing method. The present invention uses an inkjet printing method to print the cholesteric liquid crystal materials with three colors on the defined display areas, and uses a phase separation processes to provide a color cholesteric liquid crystal display device with a single-layer structure or a stacked structure.  
         [0019]     Reference is made to FIGS.  3 A-E, which show schematic diagrams of a color cholesteric liquid crystal display device with a stacked structure manufactured via an inkjet printing process in accordance with the first embodiment of the present invention. In  FIG. 3A , multiple bank structures  60  are provided on a first electrode layer  54  of a lower base  52 . The foresaid lower base  52  can be a glass base or a plastic base. The first electrode layer can be made of an inorganic conductive material or an organic conductive material and includes an active or passive driving circuit. The bank structures  60  are provided via a lithography process, a die-casting process, a screening printing process and/or an inkjet printing process. The bank structures  60  can be made of a macromolecule material having a black pigment or dye.  
         [0020]     In  FIG. 3B , a first solution is printed among the bank structures  60  to form a solution layer  56 . The above first solution is a mixture of multiple first cholesteric liquid crystal materials and monomers. The first solution is printed via a nozzle  50 , i.e. via an inkjet printing process. The first cholesteric liquid crystal materials are cholesteric liquid crystals and/or nematic liquid crystals mixed with a twist agent. The first cholesteric liquid crystal materials can reflect multiple different colors. The first cholesteric liquid crystal materials can also reflect light with red, green and blue colors. The cholesteric liquid crystal materials further include a pigment or dye capable of reflecting visible light having a wavelength of 400-800 nm. The above first solution, the mixture of the first cholesteric liquid crystal materials and monomers, includes liquid crystals with different twisted features. Moreover, in the manufacturing process, an alignment layer is further coated on a first electrode layer of a lower base. The alignment layer is made of polyvinyl alcohol, polyimide, aramid, nylon, silica, micro-grooves or lecithin. When the step of printing the above first solution among the bank structures is completed, a single-layer color cholesteric liquid crystal display device is provided. It is thinner and has a simpler manufacturing process. Furthermore, the arrangement of the pixels of the single-layer cholesteric liquid crystal display device can have various combinative types of left-twisted and right-twisted features for increased reflectance.  
         [0021]     In  FIG. 3C , multiple bank structures  68  are formed in the solution layer (also called cholesteric liquid crystal layer). These bank structures are formed via ultraviolet exposure, which induces phase separation. In this step of the present invention, the device is directed exposed under ultraviolet light  64 .  
         [0022]     In  FIG. 3D , a second solution that includes multiple second cholesteric liquid crystal materials and monomers is printed onto the cover layers to form a solution layer. The second solution is printed via a nozzle  50 , i.e. via an inkjet printing process. The second cholesteric liquid crystal materials are cholesteric liquid crystals and/or nematic liquid crystals mixed with a twist agent. The second cholesteric liquid crystal materials can reflect multiple different colors. The second cholesteric liquid crystal materials can also reflect light with red, green and blue colors. The second cholesteric liquid crystal materials further include a pigment or dye capable of reflecting visible light having a wavelength of 400-800 nm. The above second solution, the mixture of the second cholesteric liquid crystal materials and monomers, includes liquid crystals with different twisted features. An ultraviolet exposure process is performed to induce the phase separation reaction to form multiple upper covers  62 . In this step of the present invention, the device is directed exposed under ultraviolet light  64 . The upper covers  62  form a macromolecule protective layer.  
         [0023]     In  FIG. 3E , multiple conductive materials  66  are coated on the upper covers  62 . The conductive materials are black, light absorbing materials. The coating step is performed via a screening printing process, an inkjet printing process, a spin-coating process, a dipping process, a blade process and/or a printing process. When the coating step is completed, a color cholesteric liquid crystal display device with a stacked structure is also accomplished.  
         [0024]     In the above first embodiment, when external light enters, the light matching the twisted feature is reflected while the light not matching the twisted feature passes. Hence, the reflectance is only 50%. Based on this structure, multiple bank structures are made in the present invention. Next, after a cholesteric liquid crystal material (left-twisted type) is printed to form the first cholesteric liquid crystal layer thereon, an ultraviolet exposure process is performed to form a cover layer. The cover layer is used to prevent the cholesteric liquid crystal material in the lower layer from being mixed with that in the upper layer. After the cover layer is formed, another cholesteric liquid crystal material (right-twisted type) is printed to form the second cholesteric liquid crystal layer thereon. Then, another ultraviolet exposure process is performed to form the upper covers that form a protective layer. The above two ultraviolet exposure processes can be different. Furthermore, the arrangement of cholesteric liquid crystal materials can have various combinative types of twisted features. For example, the three continuous portions have left-twisted feature and the next three continuous portions have right-twisted feature for increased reflectance.  
         [0025]     Reference is made to FIGS.  4 A-E, which show schematic diagrams of a color cholesteric liquid crystal display device having a stacked structure and a dual-base structure manufactured via an inkjet printing process in accordance with the present invention. The manufacturing steps shown in FIGS.  4 A-D are the same as those shown in FIGS.  3 A-D of the first embodiment. In  FIG. 4E , an upper base  72  having a second electrode layer  70  is provided on the upper covers. Thus, a color cholesteric liquid crystal display device having a stacked structure and two bases is formed.  
         [0026]     The manufacturing of the present invention uses an inkjet printing process. The inkjet printing process can be used to define the display areas. Using the inkjet printing process can infuse the liquid crystal materials into display areas to provide the full-color effect. The twist agent can be left-twisted or right-twisted. If a right-twisted agent is added, light with wavelength matching the right-twisted feature is reflected. Moreover, the ingredient proportion of the twist agent affects the spectral band of the reflected light. The advantage of the inkjet printing process is that the positioning is easily controlled, whereby the materials to be infused can be infused into the display areas correctly. Furthermore, the present invention uses the bank structures to separate different areas and the ultraviolet exposure process to simplify the manufacturing steps and prevent color mixing.  
         [0027]     Although the present invention has been described with reference to the preferred embodiment thereof, it will be understood that the invention is not limited to the details thereof. Various substitutions and modifications have been suggested in the foregoing description, and other will occur to those of ordinary skill in the art. Therefore, all such substitutions and modifications are embraced within the scope of the invention as defined in the appended claims.