Patent Publication Number: US-2006017775-A1

Title: Substrate structure for forming an alignment film thereon by ink-jet printing and liquid crystal panel formed by using the same

Description:
RELATED APPLICATIONS  
      The present application is based on, and claims priority from, Taiwan Application Serial Number 93121534, filed Jul. 19, 2004, the disclosure of which is hereby incorporated by reference herein in its entirety.  
     FIELD OF THE INVENTION  
      The present invention relates to a mechanism for forming an alignment film, and more particularly, to a substrate structure for forming an alignment film thereon by ink-jet printing and a liquid crystal panel formed by using the same.  
     BACKGROUND OF THE INVENTION  
      Alignment films are key components for the control of the display quality of a liquid crystal display (LCD) and are respectively deposed on an upper and a lower indium tin oxide (ITO) transparent electrode in a liquid crystal cell, to control the arrangement directions of liquid crystal elements and to provide pretilt angles required by various LCD structures. The alignment film is typically composed of polyimide (PI) which has properties of high heat resistance, high chemical solvent resistance, high radiation resistance and superior insulation.  
      A conventional method for forming an alignment film uses a screen printing technique, in which the ITO transparent electrode is coated with an alignment agent and then baked to remove all traces of solvent and water, so as to leave an alignment film. The alignment film is rubbed along a fixed direction by using nylon or artificial silk, so as to make the liquid crystals in the liquid crystal cell arrange along a fixed direction. However, in the screen printing technique, the effective utility rate of the alignment agent is low, and the method for exchanging the material species is complicated and time-consuming. Therefore, an ink-jet printing method has been developed to fabricate an alignment film.  
      In the ink-jet printing technique, an alignment agent is dispensed on an ITO electrode by using an ink-jet head and a nozzle, in which the dispensing procedure may be performed repeatedly for obtaining a planar alignment film, and is followed by a drying step and a rubbing step. The viscosity of the alignment agent used in the ink-jet printing technique is low, so it is difficult to control the spreading of the edge of the alignment film. As a result, the edge of the film is uneven, and the size of the film is difficult to control. When the alignment film passes the seal area, the seal intensity is lowered to degrade the seal quality. Moreover, the alignment agent dries inward from the edge and is gradually pushed outward from the center, so that the edge region is thicker than the central region of the alignment film. The non-uniform thickness of the alignment film easily causes a non-uniform alignment issue, which degrades the display quality.  
     SUMMARY OF THE INVENTION  
      Therefore, one objective of the present invention is to provide a substrate structure for forming an alignment film thereon by ink-jet printing, to control the area and the size of the ink-jet printed alignment film and to solve the problems of unevenness and inequality occurring at the edge of the alignment film.  
      According to the aforementioned objectives, an aspect of the present invention provides an alignment film substrate structure with a bump formed thereon, which can effectively control the scope and the size of the ink-jet printed area of the alignment film, so as to make the alignment film formed within the seal area.  
      According to a preferred embodiment of the present invention, at least one bump is deposited on a non-display area to prevent an alignment film from diffusing inappropriately, so as to prevent the alignment film from passing over a seal area to decrease the intensity of the seal. The ratio of a height of the bump to the gap between an upper substrate and a lower substrate is between about 1:2 and 1:50, which is preferably between about 1:1 and 1:3, and is more preferably about 1:2.  
      Another aspect of the present invention provides an alignment film substrate structure with a groove formed therein, which can effectively control the thickness of the edge of the alignment film, so as to prevent the edge of the alignment film from being thicker than the center of the alignment film, conforming with the thickness uniformity requirement.  
      According to another preferred embodiment of the present invention, the at least one groove is formed in a non-display area for receiving the superfluous alignment agent, which can decrease a thickness of the edge of the alignment film, so that the issue that the edge of the alignment film has a larger thickness can be avoided. A depth of the groove may be modified according to the process requirements and the ink-jet printing frequency.  
      According to still another preferred embodiment of the present invention, at least one composition structure is deposed on a non-display area, in which the composition structure is composed of a bump and a groove. When an alignment agent is ink-jet printed, the bump is used to prevent the alignment agent from spreading over a sealing area of the substrate, and the groove is engaged in receiving the superfluous alignment agent. Therefore, the area of the alignment film is confined and the uniformity of the alignment film is greatly improved. Therefore, the scope and the size of the ink-jet printed area of the alignment film can be effectively controlled, and the thickness of the edge of the alignment film can be decreased to obtain an alignment film having an even edge and a uniform thickness.  
      According to the aforementioned description, with the application of the substrate structure for forming an alignment film thereon by an ink-jet printing of the present invention, the area covered by the ink-jet printed alignment film can be effectively controlled, and can avoid the issue that the edge of the alignment film has a larger thickness, thereby obtaining an alignment film of a precise size and a uniform thickness. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The foregoing aspects and many of the attendant advantages of this invention will become 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:  
       FIG. 1  is a lateral view showing an alignment film substrate structure with a bump formed thereon in accordance with a preferred embodiment of the present invention;  
       FIG. 2  is a lateral view showing an alignment film substrate structure with a groove formed thereon in accordance with another preferred embodiment of the present invention;  
       FIG. 3  is a lateral view showing an alignment film substrate structure in accordance with still another preferred embodiment of the present invention;  
       FIG. 4  is a lateral view showing a combination structure composed of an upper substrate having a bump formed thereon and a lower substrate having a bump formed thereon; and  
       FIG. 5  is a lateral view showing a combination structure composed of an upper substrate having a combination structure formed thereon and a lower substrate having a combination structure formed thereon. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
      The preferred embodiments of a substrate structure for forming an alignment film thereon by ink-jet printing in the present invention are stated with reference to the attached drawings.  
      After a substrate is bonded with an indium tin oxide conductive material layer, an alignment film is formed on a surface of the ITO conductive material layer by ink-jet printing.  FIG. 1  is a lateral view showing an alignment film substrate structure with a bump formed thereon in accordance with a preferred embodiment of the present invention. A substrate  100  is divided into a display area  120  and a non-display area, in which the non-display area is a seal area  140 . The ink-jet printing technique is to dispense an alignment agent on the substrate  100 , and to confine the alignment agent to the seal area  140 . In the present invention, a bump  160  is used as an adjusting unit and is deposed on the seal area  140  to prevent the alignment agent from spreading over the seal area  140  and reducing the seal integrity when the alignment agent is dispensed. Accordingly, with the installation of the bump  160 , the scope and the size of the ink-jet printed area of the alignment film can be exactly controlled, which can confine the alignment film within the seal area  140 .  
      The bump  160  may be located anywhere on the seal area  140 , and is preferably located between one-third and one-half of the seal area width. Referring to  FIG. 4 , when a display area of an upper substrate  402  and a display area of a lower substrate  408  are combined oppositely to form a liquid crystal panel, bumps  460  are used for aligning the upper substrate  402  and the lower substrate  408  and for precisely controlling the seal. A height of the bump  460  is between about one-fiftieth width of a gap  495 , which is between the upper substrate  402  and the lower substrate  408 , and about one width of the gap  495 ; and is preferably between about one width of the gap  495  and about one-third width of the gap  495 , and is more preferably about one-half width of the gap  495  (such as shown in  FIG. 4 ). Various materials may be selected to manufacture the bump  160  according to different processes. For example, when a thin-film transistor array process is performed, ITO, Cr, CrO, Cu, Al, Al 2 O 3 , SiN x , SiO 2  or any combination thereof is used to manufacture the bump  160 ; when a color filter (CF) process is performed, resin, Cr, CrO or any combination thereof is used to manufacture the bump  160 .  
      With the application of the alignment film substrate structure with the bump formed thereon of the present embodiment, the size of the alignment film can be effectively confined, so the present embodiment is particularly suitable to a multi-domain vertical alignment liquid crystal display, which does not need an alignment process.  
       FIG. 2  is a lateral view showing an alignment film substrate structure with a groove formed thereon in accordance with another preferred embodiment of the present invention. A transparent conductive material layer has been formed on a substrate  200 , which is divided into a display area  220  and a non-display area, such as a seal area  240 . The seal area  240  further includes a groove  280  formed thereon for adjusting the alignment film. When an alignment agent is ink-jet printed over a surface of the display area  220  and a surface of the seal area  240 , the groove  280  is engaged in receiving the superfluous alignment agent. Accordingly, while the alignment agent pushes outward in drying, the superfluous alignment agent flows into the groove  280  to reduce a thickness of the alignment film edge, so that the issue of the edge of the alignment film being thicker can be solved to obtain an alignment film with an even edge and uniform thickness.  
      A depth of the groove  280  may be modified according to the process requirements and the ink-jet printing frequency; and the groove  280  may be deposed anywhere on the seal area  240 , and is preferably located between one-third and one-half of the width of the seal area  240 .  
      With the application of the present embodiment, an alignment film with uniform thickness can be obtained, so the alignment film substrate structure with the groove formed thereon of the present embodiment is particularly suitable to a twisted nematic (TN) liquid crystal display or a super twisted nematic (STN) liquid crystal display, which needs a stricter alignment process.  
      Still another preferred embodiment of the present invention is to combine the bump and the groove described above to form a combination structure as an adjusting unit. Referring to  FIG. 3 , a substrate  300  has been divided into a display area  320  and a non-display area, such as a seal area  340 , surrounding and adjacent to the display area  320 . A bump  360  and a groove  380  are formed on the seal area  340 , in which the groove  380  is deposed at an inner side of the bump  360 . When an alignment agent is ink-jet printed over a surface of the display area  320  and a surface of the seal area  340 , the groove  380  receives the superfluous alignment agent, and the bump  360  prevents the alignment agent from going beyond the seal area  340  to degrade the seal intensity. Therefore, the area scope and the size of the alignment film can be effectively controlled, and the edge of the alignment film can thereby be even and uniformly thick.  
      In the fabrication of a liquid crystal panel, bumps  360  may be used for aligning an upper substrate and a lower substrate. Referring to  FIGS. 3 and 5 , an upper substrate  502  and a lower substrate  508  both have an adjusting unit composed of a combination structure including a bump  560  and a groove  580 . The sum of the heights of the two bumps  560  is equal to a gap  595  between the upper substrate  502  and the lower substrate  508 . The ratio of the height of the bump  560  to the gap  595  between the upper substrate  502  and the lower substrate  508  is between about 1:1 and about 1:50, is preferably between about 1:1 and about 1:3, and is more preferably about 1:2. The bump  560  may be composed of various materials, such as ITO, resin, Cr, CrO, Al, Al 2 O 3 , Cu, SiNe, SiO 2  or any composition thereof. The combination structure may be deposed anywhere on the seal area  340  and is preferably located between one-third and one-half of the width of the seal area  340 . The present embodiment may be suitable for an MVA liquid crystal display, a TN liquid crystal display or an STN liquid crystal display.  
      Furthermore, a plurality of bumps, grooves or the combination structures thereof may be formed on a substrate to form a substrate structure for forming an alignment film thereon, which can more effectively control the size of the alignment film and the film edge uniformity. Accordingly, with the application of the substrate structure of the present invention, the scope of the ink-jet printed area of the alignment film and the film edge flatness can be controlled no matter what kind of alignment film is used or how many times the film is ink-jet printed. Therefore, the size of the alignment film and the thickness uniformity of the film can be effectively controlled.  
      According to the aforementioned description, with the application of the substrate structure for forming an alignment film thereon by ink-jet printing, the alignment agent can be prevented from spreading over a sealing area of the substrate or the superfluous alignment agent can be received, so as to form an alignment film within the seal area, to maintain the intensity of the seal, and to accurately control the size of the alignment film and reduce the thickness of the edge, to thereby obtain an alignment film with an even edge and a uniform thickness.  
      As is understood by a person skilled in the art, the foregoing preferred embodiments of the present invention are illustrated of the present invention rather than limiting of the present invention. It is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims, the scope of which should be accorded the broadest interpretation so as to encompass all such modifications and similar structure.