Patent Publication Number: US-2013234065-A1

Title: Polymer dispersed liquid crystal composition for lowering driving voltage of polymer dispersed liquid crystal display device and manufacturing method thereof

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a polymer dispersed liquid crystal composition for lowering driving voltage of a polymer dispersed liquid crystal display device and a manufacturing method thereof, and more particularly, to a polymer dispersed liquid crystal composition including a polymer material partially replaced by non-conducting particles for lowering driving voltage of a polymer dispersed liquid crystal display device and a manufacturing method thereof. 
     2. Description of the Prior Art 
     A conventional operating principle of a polymer dispersed liquid crystal is through controlling the birefringence of liquid crystal molecules and the refraction ratio difference between a polymer material and the liquid crystal molecules to generate two different states such as a transmitting state and a scattering state. Please refer to  FIG. 1  and  FIG. 2 .  FIG. 1  and  FIG. 2  are schematic diagrams illustrating a conventional polymer dispersed liquid crystal.  FIG. 1  is a diagram illustrating the condition of the polymer dispersed liquid crystal when no voltage is applied to the polymer dispersed liquid crystal.  FIG. 2  illustrates the condition of the polymer dispersed liquid crystal when voltage is applied to the polymer dispersed liquid crystal. As shown in  FIG. 1  and  FIG. 2 , the conventional polymer dispersed liquid crystal  100  includes a polymer material  111  and a plurality of liquid crystal molecules  120 . The liquid crystal molecules  120  are dispersed in a plurality of liquid crystal encapsulators  112  formed by the polymer material  111 . The polymer material  111  has a refraction ratio n 1 , and each of the liquid crystal molecules  120  has a parallel axis refraction ratio n 2  and a vertical axis refraction ratio n 3 . Generally, the parallel axis refraction ratio n 2  of the liquid crystal molecules  120  is preferably equal to the refraction ratio n 1  of the polymer material  111 . Accordingly, a presenting refraction ratio of each of the liquid crystal molecules  120  may be similar to the refraction ratio n 1  of polymer material  111  when the liquid crystal molecules  120  are arranged in a direction by voltage applied (as shown in  FIG. 2 ), and it helps to present a better transparent condition. In other words, when voltage is applied to the polymer dispersed liquid crystal  100 , an incident light L 1  passing through the polymer dispersed liquid crystal  100  will not be affected by the polymer dispersed liquid crystal  100  and will become a transmitting light L 2  since the parallel axis refraction ratio n 2  of the liquid crystal molecules is similar to the refraction ratio n 1  of the polymer material  111 . Oppositely, when there is no voltage applied to the polymer dispersed liquid crystal  100  (as shown in  FIG. 1 ), the liquid crystal molecules  120  disposed in each liquid crystal encapsulator will be randomly arranged, so the incident light L 1  irradiating toward the polymer dispersed liquid crystal  100  will be scattered to different directions. 
     However, the most unfavorable point of PDLC is that the driving voltage is too high. For solving this problem, the conventional ways to lower the driving voltage include decreasing the liquid crystal cell gap, and adding conducting particles into the liquid crystal molecules. However, the method of decreasing the liquid crystal cell gap will cause deterioration in contrast ratio and the film thickness will be limited. The method of adding conducting particles might cause the polymer material to be conducting and the manufacturing and the cost of the transparent conductive substance may also be a problem. 
     SUMMARY OF THE INVENTION 
     It is one of the objectives of the present invention to provide a polymer dispersed liquid crystal composition for lowering driving voltage of a polymer dispersed liquid crystal display device and a manufacturing method thereof. By adding non-conducting particles into the polymer dispersed liquid crystal composition, the driving voltage can be lowered and the scattering effect can be enhanced. 
     To achieve the purposes described above, a preferred embodiment provides a polymer dispersed liquid crystal composition for lowering driving voltage of a polymer dispersed liquid crystal display device. The polymer dispersed liquid crystal composition comprises a polymer material, a plurality of liquid crystal molecules and a plurality of non-conducting particles. The liquid crystal molecules are dispersed in the polymer material, and the liquid crystal molecules are disposed in a plurality of liquid crystal encapsulators formed by the polymer material. The non-conducting particles are dispersed in the polymer material. 
     To achieve the purposes described above, a preferred embodiment provides a polymer dispersed liquid crystal composition. The polymer dispersed liquid crystal composition comprises a polymer material, a plurality of liquid crystal molecules and a plurality of non-conducting particles. The liquid crystal molecules are dispersed in the polymer material, and the liquid crystal molecules are disposed in a plurality of liquid crystal encapsulators formed by the polymer material. The non-conducting particles are dispersed in the polymer material for lowering driving voltage of a polymer dispersed liquid crystal composition. 
     To achieve the purposes described above, a preferred embodiment provides a manufacturing method of a polymer dispersed liquid crystal composition for lowering driving voltage of a polymer dispersed liquid crystal display device. The method comprises the following steps. First, a compound material and a plurality of liquid crystal molecules are provided. The compound material comprises a polymerization reactive material and a plurality of non-conducting particles. The compound material and the liquid crystal molecules are then mixed. A polymerization treatment is then performed to polymerize the polymerization reactive material for forming a polymer material, and make the liquid crystal molecules and the non-conducting particles being dispersed in the polymer material. The liquid crystal molecules are disposed in a plurality of liquid crystal encapsulators formed by the polymer material. 
     These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram illustrating a condition of a conventional polymer dispersed liquid crystal when no voltage is applied to the conventional polymer dispersed liquid crystal. 
         FIG. 2  is a schematic diagram illustrating a condition of the conventional polymer dispersed liquid crystal when voltage is applied to the conventional polymer dispersed liquid crystal. 
         FIG. 3  is a schematic diagram illustrating a polymer dispersed liquid crystal composition according to a preferred embodiment of the present invention. 
         FIG. 4  is a schematic diagram illustrating a condition of a display device when no voltage is applied to the display device according to a preferred embodiment of the present invention. 
         FIG. 5  is a schematic diagram illustrating a condition of the display device when voltage is applied to the display device according to the preferred embodiment of the present invention. 
         FIG. 6  is a flowchart describing a manufacturing method of a polymer dispersed liquid crystal composition according to a preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Please refer to  FIG. 3 .  FIG. 3  is a schematic diagram illustrating a polymer dispersed liquid crystal composition for lowering driving voltage of a polymer dispersed liquid crystal display device according to a preferred embodiment of the present invention. Please note that the figures are only for illustration and the figures may not be to scale. The scale may be further modified according to different design considerations. As shown in  FIG. 3 , a polymer dispersed liquid crystal composition  200  is provided in this embodiment. The polymer dispersed liquid crystal composition  200  comprises a polymer material  211 , a plurality of liquid crystal molecules  220 , and a plurality of non-conducting particles  230 . The liquid crystal molecules  220  are dispersed in the polymer material  211 , and the liquid crystal molecules  220  are disposed in a plurality of liquid crystal encapsulators  212  formed by the polymer material  211 . The non-conducting particles are dispersed in the polymer material for lowering driving voltage of the polymer dispersed liquid crystal composition  200 . 
     In this embodiment, the non-conducting particles  230  can comprise organic polymer particles or inorganic particles. The material of above mentioned organic polymer particles can comprise polymethyl methacrylate (PMMA), silicone, acrylic glue, foamed polystyrene, or other suitable organic polymer materials. The material of above mentioned inorganic particles can comprise silicon oxide, titanium oxide, zirconium oxide, zinc oxide or other suitable inorganic materials. It is worth noting that the non-conducting particles  230  in this embodiment are preferably polymethyl methacrylate particles, but not limited thereto. A diameter D of each of the non-conducting particles  230  is substantially between 0.3 micrometers and 10 micrometers, and the preferred value is between 1 micrometer and 3 micrometers for a better effect. In addition, the liquid crystal molecules  220  can comprise positive liquid crystal molecules or other suitable liquid crystal molecules. The polymer material  211  can comprise ultraviolet light curing resin (UV glue), thermoplastic resin or other suitable polymer materials. In other words, any material, which may be used to separate phases of the liquid crystal molecules and the polymer material and form the liquid crystal encapsulators, is suitable for this invention. This part belongs to ordinary skill and will not be redundantly described here. It is worth noting that the liquid crystal molecules  220  have a parallel axis refraction ratio n 5  and a vertical axis refraction ratio n 6 . The parallel axis refraction ratio n 5  of the liquid crystal molecules  220  is substantially equal to the refraction ratio n 4  of the polymer material  211 . When voltage is applied to the polymer dispersed liquid crystal composition  200 , the liquid crystal molecules  220  may be arranged in a direction and a presenting refraction ratio of each of the liquid crystal molecules  220  may be similar to the refraction ratio of the polymer material  211 , and it helps to present a better transparent condition. Furthermore, the refraction ratio n 4  of the polymer material  211  is preferably substantially equal to a refraction ratio n 7  of each of the non-conducting particles  230  to prevent the preformed transparent condition from being influenced by the non-conducting particles  230 . In this invention, numbers of interface which incident light passes through in the polymer dispersed liquid crystal composition  200  may be increased by partially replacing the constituent percentage of the polymer material  211  in the polymer dispersed liquid crystal composition  200  with the non-conducting particles  230 . The scattering effect of the polymer dispersed liquid crystal composition  200  when no voltage is applied to the polymer dispersed liquid crystal composition  200  may be accordingly enhanced, and it helps to lower the driving voltage of the polymer dispersed liquid crystal composition  200 . 
     Please refer to  FIG. 4  and  FIG. 5 , and also refer  FIG. 3 .  FIG. 4  and  FIG. 5  are schematic diagrams illustrating a display device according to a preferred embodiment of the present invention. As shown in  FIGS. 3-5 , this embodiment provides a display device  300 . The display device  300  comprises an upper electrode  322 , a lower electrode  321 , an upper substrate  312 , a lower substrate  311 , and a polymer dispersed liquid crystal composition  200 . The lower electrode  321  is disposed oppositely to the upper electrode  322 . The lower electrode  321  and the upper electrode  322  are respectively disposed on the lower substrate  311  and the upper substrate  312 . The polymer dispersed liquid crystal composition  200  is disposed between the upper electrode  322  and the lower electrode  321 . The composition and the material characteristic of the polymer dispersed liquid crystal composition  200  in this embodiment are detailed above and will not be redundantly described. It is worth noting that when voltage is applied to the polymer dispersed liquid crystal composition  200  through the upper electrode  322  and the lower electrode  321  (as shown in  FIG. 5 ), the liquid crystal molecules  220  disposed in each liquid crystal encapsulator  212  are substantially arranged in a vertical direction, and an incident light L 3  irradiating toward the display device  300  can pass through the polymer dispersed liquid crystal composition  200  to become a transmitting light L 4 . Oppositely, when there is no voltage applied to the polymer dispersed liquid crystal composition  200  (as shown in  FIG. 4 ), the liquid crystal molecules  220  disposed in each of the liquid crystal encapsulators  212  will be randomly arranged, so the incident light L 3  irradiating toward the display device  300  will be scattered to different directions. In other words, a transparent display effect and a scattering display effect in the display device  300  can be achieved by controlling the state of the liquid crystal molecules  220  in the polymer dispersed liquid crystal composition  200 . Moreover, in other preferred embodiments, a color filter can be disposed in the display device  300  or a dyeing material can be added into the polymer dispersed liquid crystal composition  200  to achieve color display effect, but not limited thereto. 
     Please refer to  FIG. 6 , and also refer to  FIG. 3 .  FIG. 6  is a flowchart describing a manufacturing method of a polymer dispersed liquid crystal composition according to a preferred embodiment of the present invention. As shown in  FIG. 3  and  FIG. 6 , a manufacturing method of a polymer dispersed liquid crystal composition  200  is provided in this embodiment. The manufacturing method comprises the following steps. First, in step S 110 , a compound material  240  and a plurality of liquid crystal molecules  220  are provided. The compound material  240  comprises a polymerization reactive material  210  and a plurality of non-conducting particles  230 . Next, in step S 120 , the compound material  240  and the liquid crystal molecules  220  are mixed. Then, in step S 130 , a polymerization treatment is performed to polymerize the polymerization reactive material  210  for forming a polymer material  211 , and make the liquid crystal molecules  220  and the non-conducting particles  230  being dispersed in the polymer material  211 . The liquid crystal molecules  220  are disposed in a plurality of liquid crystal encapsulators  212  formed by the polymer material  211 . The composition and the material characteristic of the polymer dispersed liquid crystal composition  200  in this embodiment are detailed above and will not be redundantly described. It is worth noting that the polymerization treatment in this embodiment preferably comprises polymerization induced phase separation (PIPS), temperature induced phase separation (TIPS), solvent induced phase separation (SIPS), or other suitable methods. In addition, the polymerization reactive material  210  in this embodiment may preferably comprise a monomer material (not shown) and a photo initiator (not shown). The above mentioned monomer material may preferably comprise an UV glue monomer or other suitable monomer material for polymerization. The above mentioned photo initiator is used to initiate a polymerization reaction of the monomer material. It is worth noting that the polymerization reactive material  210  is replaced by the non-conducting particles  230  in this invention, and a percentage of the polymerization reactive material  210  in the polymer dispersed liquid crystal composition  200  and a percentage of the photo initiator in the polymer dispersed liquid crystal composition  200  may be accordingly reduced. The negative effect such as a flicker problem which may be caused by residual ions of the photo initiator can be accordingly improved. 
     
       
         
           
               
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                 Polymer- 
                   
                   
                   
               
               
                   
                 Liquid 
                 ization 
                 Non- 
                 Replace- 
               
               
                   
                 crystal 
                 reactive 
                 conducting 
                 ment 
                 Driving 
               
               
                   
                 molecule 
                 material 
                 particles 
                 ratio 
                 voltage 
               
               
                   
                 (wt %) 
                 (wt %) 
                 (wt %) 
                 (%) 
                 (V) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 First 
                 70 
                 30 
                 0 
                 0 
                 can not 
               
               
                 compared 
                   
                   
                   
                   
                 drive 
               
               
                 example 
               
               
                 First 
                 70 
                 20 
                 10 
                 33 
                 20 
               
               
                 embodiment 
               
               
                 Second 
                 70 
                 15 
                 15 
                 50 
                 12 
               
               
                 embodiment 
               
               
                 Third 
                 70 
                 10 
                 20 
                 67 
                  6 
               
               
                 embodiment 
               
               
                 Second 
                 70 
                 0 
                 30 
                 100 
                 can not 
               
               
                 compared 
                   
                   
                   
                   
                 drive 
               
               
                 example 
               
               
                   
               
            
           
         
       
     
     In order to further explain the improvement of the driving voltage of the polymer dispersed liquid crystal composition according to the percentage of the non-conducting particles in the polymer dispersed liquid crystal composition, please refer to Table 1. The driving voltages of the polymer dispersed liquid crystal composition according to the variation of the percentage of the polymerization reactive material (an UV glue monomer in this embodiment) in the polymer dispersed liquid crystal composition and the percentage of the non-conducting particles (a PMMA in this embodiment) in the polymer dispersed liquid crystal composition are listed in Table 1. As shown in Table 1, the percentages of the polymerization reactive material and the non-conducting particles are variant while the percentages of the liquid crystal molecules are kept in a fixed value (70 wt %) in the first compared example, the second compared example, the first embodiment, the second embodiment and the third embodiment. There are only the polymerization reactive material which occupies 30% in the first compared example and only the non-conducting particles which occupy 30% in the second compared example respectively. Therefore, the polymer dispersed liquid crystal compositions in the first compared example and the second compared example can not be driven even the applied voltage is up to 30 volts. However, as the percentages of the non-conducting particles gradually increase from the first embodiment to the third embodiment, i.e., as the replacement ratios of polymer material replaced by the non-conducting particles increase, the driving voltage of the polymer dispersed liquid crystal composition may become lowered gradually. In fact, not only the percentages of the non-conducting particles shown in Table 1 can have this effect, but the driving voltage of the polymer dispersed liquid crystal composition may be lowered as long as the polymer material is partially replaced by the non-conducting particles. In this embodiment, the percentage of the non-conducting particles in the polymer dispersed liquid crystal composition is substantially between 1% and 30%, and the percentage is preferably between 10% and 20%. The replacement ratio of the polymerization reactive material replaced by the non-conducting particles is preferably between 33% and 67%. In other words, the percentage of the non-conducting particles in the compound material is between 33% and 67%, but not limited thereto. In addition, the percentage of the polymer material in the polymer dispersed liquid crystal composition is substantially between 10% and 30%, and the percentage of the liquid crystal molecules in the polymer dispersed liquid crystal composition is substantially between 70% and 90%, but not limited thereto. It is worth noting that the percentages in Table 1 can be adjusted regarding what kinds of liquid crystal molecules, what kinds of the polymerization reactive material and what kinds of the polymerization methods (such as above mentioned PIPS, TIPS, or SIPS) adopted. For example, in general polymerization induced phase separation, the percentage of the liquid crystal molecules is often between 60% and 90%, and the percentage of the polymerization reactive material (such as UV glue) is between 10% and 40%. Under this condition, the driving voltage may also be lowered by replacing the polymerization reactive material with the non-conducting particles, and the trend is that the driving voltage may become lowered more obviously with a higher replacement ratio of the polymerization reactive material replaced by the non-conducting particles. So, this invention is not limited by the data in Table 1, and it is only used to explain the effect of lowering the driving voltage. Furthermore, a diameter of each of the non-conducting particles is substantially between 0.3 micrometers and 10 micrometers, and the diameter of each of the non-conducting particles is preferably between 1 micrometer and 3 micrometers for a better effect. The refraction ratio of the polymer material is preferably substantially equal to the refraction ratio of each of the non-conducting particles so as to prevent the preformed transparent condition from being influenced by the non-conducting particles. 
     To summarize the above descriptions, the polymer dispersed liquid crystal composition in this invention is formed by partially replacing the compound material in the polymer dispersed liquid crystal composition with the non-conducting particles. The driving voltage of polymer dispersed liquid crystal composition may be lowered as the percentage of the polymer material in the polymer dispersed liquid crystal composition decreases. Additionally, the numbers of the interface which the incident light path passes through in the polymer dispersed liquid crystal composition may be increased to improve the scattering effect when no voltage is applied to the polymer dispersed liquid crystal composition. The objectives of lowering the driving voltage and improving the scattering effect can be achieved simultaneously by the polymer dispersed liquid crystal composition of this invention. 
     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.