Abstract:
A method of fabricating a liquid crystal display apparatus having a liquid crystal layer sandwiched between a first substrate and a second substrate comprises the steps of forming the liquid crystal layer by dripping a liquid crystal composition containing a photopolymerizable component upon the first substrate, and sandwiching the liquid crystal layer between the first and second substrates by mounting the second substrate upon the first substrate, wherein the dripping step of the liquid crystal composition is conducted in a state in which the liquid crystal composition is shielded from a radiation of a wavelength that causes polymerization in the photopolymerizable component.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention generally relates to display apparatuses and more particularly to a fabrication process of a liquid crystal display apparatus of vertical alignment mode and production apparatus therefor.  
         [0002]      FIGS. 1A and 1B  show the principle of a vertical alignment liquid crystal display apparatus  10  called also an MVA apparatus according to the inventor of the present invention, wherein  FIG. 1A  shows the liquid crystal display apparatus  10  in a non-activated state in which no drive voltage is applied thereto, while  FIG. 1B  shows the liquid crystal display apparatus  10  in a drive state in which a drive voltage is applied.  
         [0003]     Referring to  FIG. 1A , a liquid crystal layer is sandwiched between glass substrates  11 A and  11 B, and the glass substrates  11 A and  11 B constitute, together with the liquid crystal layer  12 , a liquid crystal panel.  
         [0004]     The glass substrates  11 A and  11 B are formed with respective alignment films not illustrated, wherein the alignment films cause alignment of liquid crystal molecules in the liquid crystal layer  12  in the direction generally perpendicular to the liquid crystal layer  12  in the non-activated state of  FIG. 1A .  
         [0005]     Thus, in the state of  FIG. 1A , the optical beam incident to the liquid crystal display apparatus undergoes no substantial rotation of polarization plane as it travels through the liquid crystal layer  12 , and thus, the optical beam incident to the liquid crystal layer  12  through a polarizer disposed underneath the liquid crystal panel is shutoff by an analyzer disposed above the liquid crystal panel with the construction in which the analyzer and the polarizer are disposed above and below the liquid crystal panel in a crossed Nicol state.  
         [0006]     In the driving state of  FIG. 1B , on the other hand, the liquid crystal molecules are tilted in the liquid crystal layer  12  as a result of the electric field applied to the liquid crystal layer  12 , and there is induced a rotation of polarization plane in the optical beam incident to the liquid crystal layer  12 . As a result, the optical beam passed through the polarizer and incident to the liquid crystal layer  12  can pass through the analyzer without being shutoff.  
         [0007]     Further, with the liquid crystal display apparatus  10  of  FIGS. 1A and 1B , there are formed. projecting patterns  13 A and  13 B respectively on the glass substrates  11 A and  11 B so as to extend parallel with each other, wherein the projecting patterns  13 A and  13 B are provided for restricting the direction in which the liquid crystal molecules are tilted at the time of transition from the non-activated state to the activated state of the liquid crystal display apparatus  10 , in the prospect of improving the response speed at the time of the transition.  
         [0008]     By forming such projecting patterns  13 A and  13 B, the response speed of the liquid crystal display apparatus  10  is improved, and at the same time, the viewing angle characteristics of the liquid crystal display apparatus are improved significantly as a result of formation of plural domains with respective, different tilting direction for the liquid crystal molecules in the liquid crystal layer  12 .  
       REFERENCES  
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                 PATENT REFERENCE 1 
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                 Publication 2002/0159018 
               
               
                   
                 PATENT REFERENCE 2 
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                 PATENT REFERENCE 3 
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                 PATENT REFERENCE 4 
                 United Sates Patent 6977794 
               
               
                   
                 PATENT REFERENCE 3 
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                 Publication 2005/0146664 
               
               
                   
                   
               
             
          
         
       
     
       SUMMARY OF THE INVENTION  
       [0010]      FIG. 2  shows a schematic construction of an active-matrix liquid crystal display apparatus  30  based on the construction of  FIGS. 1A and 1B .  
         [0011]     Referring to  FIG. 2 , the liquid crystal display apparatus  30  includes a TFT glass substrate  31 A carrying thereon a large number of thin-film transistors (TFTs) together with transparent pixel electrodes cooperating with the respective, corresponding TFTs. Further, an opposing glass substrate  31 B is provided over the TFT substrate  31 A so as to carry thereon an opposing electrode, wherein a liquid crystal layer  31  is confined between the substrates  31 A and  31 B by a seal member  31 C.  
         [0012]     With the liquid crystal display apparatus  30  of  FIG. 2 , a TFT corresponding to a selected pixel electrode is activated, and the alignment of the liquid crystal molecules in the liquid crystal layer  31  is changed selectively in correspondence to the selected pixel electrode.  
         [0013]     Further, a polarizer  31   a  and an analyzer  31   b  are disposed at respective outer sides of the glass substrates  31 A and  31 B in a crossed Nicol state.  
         [0014]     Further, alignment films not illustrated are formed at respective inner sides of the glass substrates  31 A and  31 B in contact with the liquid crystal layer  31 , and the alignment direction of the liquid crystal molecules is restricted generally perpendicular to the plane of the liquid crystal layer  31  in the non-activated state of the liquid crystal display apparatus.  
         [0015]     For the liquid crystal layer  31 , it is possible to use a liquid crystal having a negative dielectric anisotropy marketed by Merck KGaA, while it is possible to use a vertical alignment film provided by JSR Corporation for the alignment film. In a typical example, the substrates  31 A and  31 B are assembled by using a suitable spacer such that the thickness of the liquid crystal layer becomes about 4 μm.  
         [0016]      FIG. 3A  shows the liquid crystal display apparatus  30  of  FIG. 2  in a cross-sectional view, while  FIG. 3B  shows a part of the TFT glass substrate  31 A in an enlarged scale.  
         [0017]     Referring to  FIG. 3A , there is formed a pixel electrode  34  in electrical connection to a TFT  31 T not illustrated in  FIG. 3A , and the pixel electrode  34  is covered by an orientation film  35 . Similarly, there is formed an opposing electrode  36  on the upper glass substrate  31 B uniformly, wherein the opposing electrode  36  is covered by another vertical alignment film  37 . Further, the liquid crystal layer  22  is sandwiched between the substrates  31 A and  31 B in a state contacting with the alignment films  35  and  37 .  
         [0018]     Referring now to  FIG. 3B , there are formed a large number of pad electrodes  33 A on the glass substrate  31 A for receiving scanning signals, and a large number of scanning electrodes  33  are formed so as to extend over the glass substrate  31 A from respective pad electrodes  33 A. Further, there are formed a large number of pad electrodes  32 A on the glass substrate  31 A for receiving image signals, and a large number of signal electrodes  32  are formed so as to extend over the glass substrate  31 A in a direction generally perpendicular to an extending direction of the scanning electrodes  33 . Further, TFTs  31 T are formed at the intersections of the scanning electrodes  33  and the signal electrodes  32 .  
         [0019]     On the substrate  31 A, there are formed transparent pixel electrodes  34  in correspondence to the TFTs  31 T, wherein each TFT  31 T is selected by a scanning signal on a corresponding scanning electrode  33  and drives a corresponding transparent electrode  34  of ITO, or the like, by the video signal supplied to a corresponding signal electrode  32 .  
         [0020]     In the non-activated state of the liquid crystal display apparatus  30 , there is no drive voltage applied to the transparent pixel electrode and the liquid crystal molecules are aligned generally perpendicularly to the plane of the liquid crystal layer  31 . Thereby, the liquid crystal display apparatus  30  provides a black representation as a result of the polarizing action of the polarizer  31   a  and the analyzer  31   b.    
         [0021]     On the other hand, when a drive voltage is applied to the transparent pixel electrode  34  in correspondence to the activated state thereof, the liquid crystal molecules are aligned generally horizontally, and the liquid crystal display apparatus  30  provides a white representation in the pixel thus activated.  
         [0022]     As shown in  FIG. 3A , there is formed a projecting pattern  36  on the upper electrode  36  on the glass substrate  31 B as a result of patterning of a resin such as a resist film. Thereby, the projecting pattern  36 A causes tilting in the liquid crystal molecules similarly to the projecting pattern  13 B of  FIGS. 1A and 1B . Further, there are formed cutout patterns in the transparent electrode  34  wherein the cut out patterns thus formed in the transparent electrode  34  induce tilting of the liquid crystal molecules similarly to the projecting patterns  13 A shown in  FIGS. 1A and 1B  by causing localized modulation of the electric field.  
         [0023]      FIG. 4  shows the construction of a single pixel electrode  34  formed on the substrate  31 A in detail.  
         [0024]     Referring to  FIG. 4 , there extend a signal electrode  32  and a scanning electrode  33  over the glass substrate  31 A in a crossing manner, and a TFT  31 T and a corresponding pixel electrode  34  are formed in correspondence to the intersection of the electrodes  32  and  33 . Further, it can be seen in  FIG. 4  that there is formed an auxiliary electrode  34 C (Cs) parallel to the scanning electrode  33 .  
         [0025]     In  FIG. 4 , the electrode  34  represented with mat pattern is divided into regions A-D, wherein each region is formed with minute cutout patterns  34 A represented by white such that the minute cutout patterns  34 A extend parallel with each other.  
         [0026]     It should be noted that such minute cutout patterns  34 A extending parallel with each other induce localized modulation of driving electric field applied to the liquid crystal layer  31  in the activated state of the liquid crystal display apparatus  30 , and as a result, the liquid crystal molecules in the liquid crystal layer  31  are tilted in the extending direction of the cutout patterns  34 A in the activated state of the liquid crystal display apparatus  30 .  
         [0027]     In the pixel electrode  34 , it will be noted that the direction of tilting of the liquid crystal molecules is restricted symmetrically with regard to the center of the pixel electrode in correspondence to the regions A-D disposed symmetrically about the center of the pixel electrode, and thus, the viewing angle characteristics of the liquid crystal display apparatus  30  is improved remarkably.  
         [0028]     With such an MVA liquid crystal display apparatus  30 , it is advantageous, for the purpose of improvement of response speed of the liquid crystal display device, that the liquid crystal molecules contacting with the orientation films  35  and  37  are aligned with a pre-tilt toward the direction in which the liquid crystal molecules are to be tilted in the activated state with regard to the direction exactly perpendicular to the substrates  31 A and  31 B in the non-activated state of the liquid crystal display apparatus  30 .  
         [0029]     In relation to this, there is a proposal of PSA (polymer-sustained alignment) technology shown in  FIGS. 5A-5C .  
         [0030]     Referring to  FIG. 5A , the liquid crystal layer  31  contains liquid crystal molecules  31 L and further a photocurable resin composition  31  in the form of monomers or oligomers.  
         [0031]     In the non-activated state of  FIG. 5A , the liquid crystal molecules  31 L are aligned in a direction substantially perpendicular to the substrates  31 A and  31 B as a result of the action of the orientation films  35  and  37 , while in the PSA technology, the liquid crystal molecules are tilted in a desired direction by applying a driving voltage between the electrodes  34  and  36  in the step of  FIG. 5B .  
         [0032]     In the PSA technology, a ultraviolet radiation is applied further to the liquid crystal layer  31  in the tilted state of the liquid crystal molecules and polymerization is induced in the photocurable resin compound. With this, there is formed a polymer network in the liquid crystal layer  31 .  
         [0033]     By forming a polymer network in the liquid crystal layer  31  as such, the liquid crystal molecules  31 L are tilted slightly in the desired direction to form a pre-tilt as a result of the action of the polymer network, even after application of the drive voltage is eliminated as shown in  FIG. 5C .  
         [0034]     Generally, a liquid crystal display apparatus is formed by: assembling a pair of mutually opposing glass substrates via a seal member; evacuating the gap between the substrates to a vacuum state; and injecting a liquid crystal into the gap.  
         [0035]     On the other hand, there is a new technology of assembling a liquid crystal panel in these days, in which a seal member is formed along a periphery of a glass substrate in the form of a frame and a liquid crystal is dripped into a region of the glass substrate defined by the seal member with a predetermined amount. Thereafter, an opposing glass substrate is. attached to the foregoing glass substrate via the frame member in a vacuum environment and assembling of the liquid crystal panel is completed.  
         [0036]     By using such a technology, it is possible to inject the liquid crystal quickly and uniformly, even in the case there are formed large projecting structures such as the alignment control structure  36 A shown in  FIG. 3A  on the opposing substrate  31 B with large number.  
         [0037]     In the liquid crystal display apparatus that uses the PSA technology, on the other hand, the liquid crystal used for the injection contains photocurable resin compounds (monomers or oligomers) as explained before, and because of this, there arises a problem, when such monomers or oligomers have caused reaction during the injection process of the liquid crystal, of precipitation of polymers in the liquid crystal before the photopolymerization process of  FIG. 5C . Such premature polymerization leads to formation of defects such as bright spots in the display of the liquid crystal display apparatus. Further, in the case there is caused partial polymerization in the monomers or oligomers during the dripping process of the liquid crystal, there tends to occur non-uniform polymer concentration in the liquid crystal layer  31 , while such non-uniform polymer concentration leads to irregularity of display.  
         [0038]     In a first aspect of the present invention, there is provided a method of fabricating a liquid crystal display apparatus having a liquid crystal layer sandwiched between a first substrate and a second substrate, comprising the steps of:  
         [0039]     forming said liquid crystal layer by dripping a liquid crystal composition containing a photopolymerizable component upon said first substrate; and  
         [0040]     sandwiching said liquid crystal layer between said first and second substrates by mounting said second substrate upon said first substrate,  
         [0041]     wherein said dripping step of said liquid crystal composition is conducted in a state in which said liquid crystal composition is shielded from a radiation of a wavelength that causes polymerization in said photopolymerizable component.  
         [0042]     According to the present invention, exposure of the liquid crystal composition containing a photocurable resin compound to light is prevented during the dripping process of the liquid crystal composition in the fabrication process of a liquid crystal display apparatus that achieves control of alignment of the liquid crystal molecules in the liquid crystal layer by using the PSA technology. Thereby, occurrence of defects such as bright spots or uneven display originating from unintended exposure is effectively suppressed.  
         [0043]     Other objects and further features of the present invention will become apparent from the following detailed description when read in conjunction with the attached drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0044]      FIGS. 1A and 1B  are diagrams explaining the principle of an MVA liquid crystal display apparatus;  
         [0045]      FIG. 2  is a diagram showing the construction of an MVA liquid crystal display apparatus according to a related art of the present invention;  
         [0046]      FIGS. 3A and 3B  are diagrams showing the construction of the MVA liquid crystal display apparatus of  FIG. 2 ;  
         [0047]      FIG. 4  is a diagram showing an example of a pixel electrode used with the liquid crystal display apparatus of  FIG. 2 ;  
         [0048]      FIGS. 5A-5C  are diagrams showing the fabrication process of a liquid crystal display apparatus according to a related art of the present invention;  
         [0049]      FIG. 6  is a flowchart showing the fabrication process of a liquid crystal display apparatus according to a first embodiment of the present invention;  
         [0050]      FIG. 7  is a diagram showing the dripping process of liquid crystal in the process of  FIG. 6 ;  
         [0051]      FIG. 8  is a diagram showing the panel assembling process in the process of  FIG. 6 ;  
         [0052]      FIG. 9  is a diagram showing a second embodiment of the present invention; and  
         [0053]      FIG. 10  is a diagram showing a third embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     First Embodiment  
       [0054]      FIG. 6  is a flowchart showing a part of the fabrication process of a liquid crystal display apparatus according to a first embodiment of the present invention.  
         [0055]     Hereinafter, the flowchart of  FIG. 6  will be explained for the example of  FIG. 2  showing the fabrication process of the liquid crystal display apparatus  30 , wherein those parts corresponding to the parts described previously are designated by the same reference numerals and the description thereof will be omitted.  
         [0056]     Referring to  FIG. 6 , the fabrication process of the liquid crystal display apparatus of the present embodiment comprises: a step  1  of dripping a liquid crystal composition upon the glass substrate  31 A; a step  2  of mounting and bonding the opposing glass substrate  31 B upon the glass substrate  31 A conducted in a vacuum environment to assemble a liquid crystal panel; and a step  3  of irradiating ultraviolet irradiation explained already with reference to  FIGS. 5A-5C .  
         [0057]      FIG. 7  shows the outline of the step  1  of dripping the liquid crystal composition upon the glass substrate  31 A.  
         [0058]     Referring to  FIG. 7 , the liquid crystal composition is dripped to a region of the glass substrate  31 A defined by the seal member  31 C from a dispenser  100 , wherein the present embodiment uses a liquid crystal composition having a negative dielectric anisotropy and added with an acrylic monomer for the photopolymerizable component with the proportion of 0.3 wt % in anticipation of use of the PSA technology. Here, it should be noted that the glass substrate  31 A is a TFT substrate formed with the TFTs  31 T as explained with reference to  FIGS. 3A and 3B . Thus, the glass substrate  31 A carries thereon the pixel electrodes  34  and the orientation film  35  already.  
         [0059]     The dispenser  100  includes, in a dispenser body  100 A of a metal, or the like, a dripping nozzle  101 , a syringe  101 A continuing to the dripping nozzle  101 , a plunger  101 B cooperating with the syringe  101 A, and the like, wherein the liquid crystal in a liquid crystal tank  102  is supplied to the syringe  101 A via a tube  103  and valves  103 A and  103 B. Here, the valve  103 A controls the communication between the tube  103  and the syringe  101 A while the valve  103 B controls the communication between the syringe  101 A and the nozzle  101 .  
         [0060]     The dispenser  101  is further provided with a screw rod  104 A driven by a motor  104 , wherein the screw rod  104 A is coupled mechanically to the plunger  101 B and drives the plunger  101 B in response to the rotation of the motor  104 . Further, the construction of  FIG. 7  includes a controller  105  for driving the motor  104 .  
         [0061]     Thus, the liquid crystal in the tank  102  is introduced into the syringe  101 A by pulling the plunger  101 B by the motor  104  while closing the valve  103 B and opening the valve  103 A, and the liquid crystal composition in the syringe is dripped to the region of the glass substrate  310 B surrounded by the seal member  31 C via the dripping nozzle  101  as the plunger  101 B is lowered in the state that the valve  103 A is closed and the valve  103 B is opened.  
         [0062]     Here, it should be noted that the liquid crystal tank  102  and the tube  103  are formed conventionally of a transparent plastic, while in the present embodiment in which the liquid crystal composition contains a photopolymerizable component, the apparatus of  FIG. 7  covers the liquid crystal tank  102  and the tube  103  continuously by an aluminum foil  107  so as to suppress photopolymerization inside the tank or tube.  
         [0063]     By using such a dripping apparatus, the problem that the photopolymerizable component added to the liquid crystal composition causes photopolymerization even partially when the liquid crystal composition is dripped upon the glass substrate  31 A in the step S 1  of  FIG. 1 , is effectively eliminated.  
         [0064]     Next, in the step  2  of  FIG. 6 , the opposing glass substrate  31 B is disposed upon the glass substrate  31 A and is jointed to the seal member  31 C on the glass substrate  31 A.  
         [0065]     With this, the liquid crystal panel is obtained such that the liquid crystal layer  31  is confined between the glass substrate  31 A and the glass substrate  31 B. It should be noted that the glass substrate  31 B is formed with the opposing electrode  36 , the alignment film  37  and further the alignment control structure  36 A. The jointing step of  FIG. 8  is conducted in a vacuum environment so as to avoid formation of bubbles in the liquid crystal layer  31 .  
         [0066]     Further, with the step  3  of  FIG. 6 , a drive voltage is applied between the opposing electrode  36  and the pixel electrodes  34  and irradiation of ultraviolet radiation is conducted to the liquid crystal layer  31  in this state similarly to the step of  FIG. 5B . With this, it becomes possible to induce a desired pre-tilt in the liquid crystal molecules.  
         [0067]     According to such a procedure, it becomes possible to obtain a liquid crystal display apparatus capable of providing high-quality display free from optical defects such as bright spots.  
         [0068]     In the dispenser of FIG. e 7 , it is also possible to use a shading tape for covering the liquid crystal tank  102  and the tube  103 .  
       Second Embodiment  
       [0069]      FIG. 9  shows the construction of a dispenser  200  according to a second embodiment of the present invention, wherein those parts corresponding to the parts are designated by the same reference numerals and the description thereof will be omitted.  
         [0070]     Referring to  FIG. 9 , the liquid crystal tank  102  is accommodated into a holder  2  of a metal such as aluminum, and the tube  103  is covered by a shading cover  109  such as aluminum foil or tape. With this, exposure of the liquid crystal composition in the liquid crystal tank  102  or in the tube to the light is avoided before the liquid crystal composition is dripped upon the glass substrate  31 A.  
         [0071]     Further, with the embodiment of  FIG. 9 , there is formed a window  108 A in the aluminum holder  108 , wherein the window  108 A is closed by an acrylic resin plate that cuts out the ultraviolet radiation component of the wavelength of 400 nm or less.  
         [0072]     According to such a construction, it becomes possible to read the amount of the liquid crystal remaining in the liquid crystal tank  102 , by observing the liquid level. Thereby, it becomes possible to increase the productivity of a production line.  
       Third Embodiment  
       [0073]      FIG. 10  shows the construction of a dispenser  300  according to a third embodiment of the present invention, wherein those parts corresponding to the parts described previously are designated by the same reference numerals and the description thereof will be omitted.  
         [0074]     Referring to  FIG. 10 , the present embodiment uses a semi-transparent glass bottle of brown color for the liquid crystal tank  102 . Such a brown glass bottle cuts the ultraviolet component of the wavelength of 400 nm or less, and thus, there occurs no exposure in the liquid crystal composition held therein.  
         [0075]     Further, the tube  103  is covered by the shading cover  109  such as aluminum foil or tape, and thus, there occurs-no exposure in the liquid crystal composition in the liquid crystal tank  102  or in the tube  103  in advance to the dripping upon the glass substrate  31 A.  
         [0076]     The construction of  FIG. 10  allows visual observation of the liquid crystal composition remaining in the tank  102  and is thus advantageous for improving the productivity when used in the production line of liquid crystal display apparatus.  
         [0077]     While the present invention has been explained heretofore for the example of fabricating a liquid crystal display apparatus that uses the alignment control structure  36 A of liquid crystal shown in  FIG. 3A  and the multi-domain pixel electrode  34  shown in  FIG. 4 , the present invention can be used extensively to the production of liquid crystal display apparatuss that uses the PSA technology explained with reference to  FIGS. 5A-5C .  
         [0078]     In the present invention, it should be noted that the dripping of the liquid crystal composition by using the device  100  may be conducted also upon the glass substrate  31 B, in place of the glass substrate  31 A.  
         [0079]     Further, the proportion of the photopolymerizable component in the liquid crystal composition is not limited to 0.3 wt %, but may be changed from 0.01 wt % to 1.0 wt %.  
         [0080]     Further, the photopolymerizable component is not limited to the acrylic monomer, but compounds such as epoxy acrylic monomer or liquid crystal monomer may also be used.  
         [0081]     Further, the present invention is not limited to the embodiments described heretofore, but various variations and modifications may be made without departing from the scope of the invention.  
         [0082]     The present invention is based on Japanese patent application 2005-157584 filed on May 30, 2005, the entire contents of which are incorporated herein as reference.