Abstract:
A system and method for advantageously forming an alignment film are provided. An anilox roll is operably engaged with a printing roll to print an alignment film onto a substrate, in one example including a liquid crystal display panel. Multiple rotations of the printing roll are used to provide efficiency and flexibility in printing a variety of alignment film patterns onto a variety of substrates.

Description:
BACKGROUND  
       [0001]     (a) Field of the Invention  
         [0002]     The present invention relates to liquid crystal displays, and more particularly to a system and method for providing an alignment film.  
         [0003]     (b) Description of Related Art  
         [0004]     A liquid crystal display (LCD) is one of the most widely used flat panel displays. An LCD includes two panels having field generating electrodes and alignment films thereon. A liquid crystal layer is interposed between the panels. The alignment film determines initial orientations of the liquid crystal molecules, and the field generating electrodes generate an electric field to change the orientations of the liquid crystal molecules. An incident light passing through the liquid crystal layer experiences electromagnetic force depending on the orientations of the liquid crystal molecules to thereby change the polarization of the light due to the dielectric anisotropy of the liquid crystal. Appropriately arranged polarizers can then change the transmittance of the incident light depending on the polarization of the light, thereby displaying desired images.  
         [0005]     An active matrix LCD includes a plurality of pixel electrodes and a common electrode for generating electric fields, a plurality of switching elements such as thin film transistors (TFTs) for controlling data voltages applied to the pixel electrodes, a plurality of signal lines for transmitting data voltages and control signals for controlling the TFTs, a plurality of color filters for color display, and a seal for adhering the two panels and confining the liquid crystal. The above-described elements of an LCD are formed by several steps of deposition, photolithography, and etching, and the elements of each panel are then covered with an alignment film.  
         [0006]     Typically, the alignment film is formed by spin coating or printing. A printing device for the alignment film generally includes several metal rollers and a rubber plate, such as an anilox roll and a printing roll engaged with each other and the rubber plates attached on the printing roll. The size of the rolls and the rubber plates are established such that the alignment film is coated on the entire mother glass substrate by a single rotation of the printing roll.  
         [0007]     Disadvantageously, the size and the weight of the rolls and the rubber plates are required to be increased as the size of a mother glass substrate increases. Thus, it becomes difficult and costly to manufacture and/or modify the printing device. Accordingly, an efficient and easily modifiable system and method for providing an alignment film are desirable.  
       SUMMARY  
       [0008]     A system and method for advantageously forming an alignment film are provided. Multiple rotations of a printing roll are used to provide an alignment film on a substrate, allowing for efficiency and flexibility in providing a variety of alignment patterns onto a variety of substrates.  
         [0009]     In accordance with an embodiment of the present invention, a system for printing an alignment film is provided, comprising an anilox roll operably engaged with a dispenser for providing an alignment material on the anilox roll, and a printing roll operably engaged with the anilox roll to receive alignment material. The system further includes a table operably engaged with the printing roll, the table mounting a substrate onto which is transferred alignment material from the printing roll.  
         [0010]     In accordance with another embodiment of the present invention, another system for printing an alignment film is provided. An anilox roll and a printing roll are again included, and a table is operably engaged with the printing roll, the table mounting a substrate onto which is transferred alignment material from the printing roll via multiple rotations of the printing roll.  
         [0011]     In accordance with yet another embodiment of the present invention, a method of printing an alignment film is provided, comprising transferring alignment material from a dispenser to an anilox roll, transferring alignment material from the anilox roll to a printing roll including a printing pattern, and transferring alignment material from the printing roll to a substrate mounted on a table via multiple rotations of the printing roll.  
         [0012]     In accordance with yet another embodiment of the present invention, a method of printing an alignment film includes transferring alignment material from the printing roll to a substrate mounted on a table via multiple rotations of the printing roll to form an alignment film, and then patterning the alignment film.  
         [0013]     The scope of the invention is defined by the claims, which are incorporated into this section by reference. A more complete understanding of embodiments of the present invention will be afforded to those skilled in the art, as well as a realization of additional advantages thereof, by a consideration of the following detailed description of one or more embodiments. Reference will be made to the appended sheets of drawings that will first be described briefly.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     The present invention will become more apparent by describing embodiments thereof in detail with reference to the accompanying drawings in which:  
         [0015]      FIGS. 1 and 2  are lateral sectional views of apparatuses for forming an alignment film according to embodiments of the present invention;  
         [0016]      FIG. 3  schematically illustrates the printing of an alignment film by a printing roll of the apparatuses shown in  FIGS. 1 and 2 ;  
         [0017]      FIGS. 4 and 5  are expanded sectional views of the printing roll of the apparatuses shown in  FIGS. 1 and 2 , respectively;  
         [0018]      FIG. 6  is a sectional view of a rubber plate for a printing roll according to an embodiment of the present invention;  
         [0019]      FIG. 7  illustrates the formation of a printing pattern on the rubber plate shown in  FIG. 6  using a laser beam process in accordance with an embodiment of the present invention;  
         [0020]      FIG. 8  illustrates the formation of a printing pattern on the rubber plate shown in  FIG. 6  using a press process in accordance with an embodiment of the present invention;  
         [0021]      FIG. 9  is a schematic perspective view of a printing roll and a rubber plate including a printing pattern;  
         [0022]      FIGS. 10 and 11  are lateral sectional views of apparatuses for printing an alignment film according to other embodiments of the present invention; and  
         [0023]      FIG. 12  schematically illustrates the printing of an alignment film by a printing roll of the apparatuses shown in  FIGS. 10 and 11 . 
     
    
       [0024]     Embodiments of the present invention and their advantages are best understood by referring to the detailed description that follows. It should be appreciated that like reference numerals are used to identify like elements illustrated in one or more of the figures. It is also noted that the figures are not necessarily drawn to scale.  
       DETAILED DESCRIPTION  
       [0025]     Apparatuses and methods for providing an alignment film according to embodiments of the present invention will now be described more fully with reference to the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.  
         [0026]     Referring now to  FIGS. 1 through 5 , apparatuses for printing an alignment film according to embodiments of the present invention are described in greater detail.  FIGS. 1 and 2  are lateral sectional views of apparatuses for forming an alignment film according to embodiments of the present invention,  FIG. 3  schematically illustrates the printing of an alignment film by a printing roll of the apparatuses shown in  FIGS. 1 and 2 , and  FIGS. 4 and 5  are expanded sectional views of the printing roll of the apparatuses shown in  FIGS. 1 and 2 , respectively.  
         [0027]     Referring now to  FIGS. 1 and 2 , each of the respective apparatuses for printing an alignment film according to embodiments of the present invention includes three rollers engaged with one another, a dispenser  40 , a bucket  50 , and a printing table  60 .  
         [0028]     The three rollers include an anilox roll  10 , a doctor roll  20  engaged with the anilox roll  10 , and a printing roll  30  engaged with the anilox roll  10 .  
         [0029]     Dispenser  40  is disposed adjacent to anilox roll  10  and dispenses alignment material on a circumferential or contact surface of anilox roll  10 . The alignment material includes but is not limited to organic material, such as a polyimide-based material, and inorganic material.  
         [0030]     Doctor roll  20  moves forward and backward along its axis with its circumferential surface contacting the circumferential surface of anilox roll  10  to uniformly distribute the alignment material on the circumferential surface of anilox roll  10 . Doctor roll further doctors off excess alignment material from anilox roll  10  to provide better control over ink transfer.  
         [0031]     Bucket  50  is disposed under anilox roll  10  and receives and gathers the alignment material dropped from anilox roll  10  during the distribution of the alignment material by doctor roll  20 .  
         [0032]     Anilox roll  10  meters the alignment material to a uniform thickness onto printing roll  30 . The surface of anilox roll  10  may be engraved with tiny uniform cells that carry and deposit a uniform amount of alignment material onto printing roll  30 . Anilox roll  10  may vary in the size and configuration of the cells to carry different amounts of alignment material depending on printing requirements.  
         [0033]     Printing roll  30  carries a predetermined prominent printing pattern  35  on its circumferential surface, and the printing pattern  35  is integrated into printing roll  30  as shown in  FIGS. 1 and 4  or formed on a rubber plate  70  that is attached to the circumferential surface of printing roll  30  as shown in  FIGS. 2 and 5 . Rubber plate  70  may be attached to printing roll  30  by an adhesive, tape, or other known technique.  
         [0034]     Printing roll  30  shown in  FIGS. 1 and 4  and rubber plate  70  shown in  FIGS. 2 and 5  may be made of synthetic rubber in one embodiment. An example of synthetic rubber used for printing roll  30  or rubber plate  70  is ethylene propylene diene monomer (EPDM) or terpolymer, that contains ethylene, propylene, and non-conjugated diene. EPDM can be vulcanized by several chemical or physical processes, including by treatment with sulfur, peroxide, phenol resin, and/or radiation. The vulcanization by sulfur can be enabled by diene. EPDM is highly durable and remarkably resistant to ozone, weather, heat, and solvent, for example. In addition, EPDM has a smaller specific gravity than other synthetic rubbers and enables high degree filling of tamping or oils due to a high wetting property. Accordingly, EPDM is a very cost effective synthetic rubber.  
         [0035]     The alignment material coated on anilox roll  10  is transferred to the raised surfaces or prominences of the printing pattern  35  by contacting the printing pattern  35  of printing roll  30  with the surface of anilox roll  10 .  
         [0036]     Printing table  60  mounts a substrate  1  and moves in a direction  3  perpendicular to the axis of printing roll  30 . During the movement of printing table  60 , printing roll  30  rotates around its axle  31  to transfer the alignment material from the surface of the printing pattern  35  to substrate  1  such that the alignment material is coated on substrate  1 . As a result, substrate  1  is covered with an alignment film having a pattern determined by the printing pattern  35  of printing roll  30 . Printing table  60  thus applies proper pressure to printing roll  30 , thereby enabling transfer of the printing pattern  35  onto substrate  1 .  
         [0037]     The alignment film printed on substrate  1  is cured at a predetermined temperature and rubbed with a rubbing roll (not shown). The rubbing orients or defines a pretilt of the liquid crystal molecules on the surface of the printed alignment film in one direction.  
         [0038]     In accordance with the present invention, the circumference of printing roll  30 , in one embodiment including rubber plate  70  and in another embodiment excluding rubber plate  70 , is smaller than the length L1 of substrate  1  such that more than one rotation of printing roll  30  completes the printing of the alignment material on substrate  1 . The circumference of printing roll  30  (including or excluding rubber plate  70 ) may be substantially equal to the length L1 of substrate  1  divided by an integer, i.e., the length L1 of substrate  1  may be equal to multiples of the circumference of printing roll  30 . The printing roll thus has a circumference which is substantially equal to a length of the substrate divided by a whole number. In this case, the alignment film pattern printed on substrate  1  includes a pattern unit repeatedly arranged in the moving direction of printing table  60 .  
         [0039]      FIG. 3  shows that a rectangular pattern unit  2  of the printed alignment film pattern is arranged three times along the moving direction of printing table  60  and arranged twice along the axis direction of printing roll  30 . The pattern unit  2  has a length L and a width W and adjacent pattern units  2  in the moving direction of printing table  60  are spaced apart by a distance d1, while adjacent pattern units  2  in the axis direction of printing roll  30  are spaced apart by a distance d2. Printing roll  30  rotates three times to form such an alignment film pattern. However, it should be understood that printing roll  30  may rotate a different number of times depending on the substrate length and alignment film pattern desired.  
         [0040]     In order to form such an alignment film pattern, the predetermined printing pattern  35  formed on printing roll  30  includes two identical prominences  35   a  and  35   b  arranged in the axis direction of printing roll  30 . Referring to  FIGS. 3-5 , each prominence  35   a  or  35   b  has a circumferential length equal to L and a width equal to W. The prominences  35   a  and  35   b  are spaced apart from each other along an axial direction by a distance equal to d2, and a circumferential distance between opposite edges of each prominence  35   a  or  35   b , which are concentric to axle  31  of printing roll  30 , is about equal to d1.  
         [0041]     Substrate  1  used for the LCD includes a plurality of device partitions that will be separated along lines after forming the alignment film. Each device partition serves as a panel for an LCD and includes a display area  1   a  ( FIG. 3 ) on which liquid crystal will be disposed. Each pattern unit  2  is disposed on a display area  1   a  of a device partition and a sealant (not shown) will be dispensed around the display area  1   a . The display area  1   a  may be provided with a plurality of pixel electrodes (not shown), a plurality of TFTs (not shown), a plurality of color filters (not shown), and a plurality of signal lines (not shown).  
         [0042]     As describe above, printing roll  30  and rubber plate  70  according to these embodiments are made of light synthetic rubber and have a small size such that the cost for manufacturing printing roll  30  and rubber plate  70  is reduced. In particular, the device shown in  FIG. 1  requires no rubber plate such that it further reduces the manufacturing cost. Furthermore, the devices can be employed to a large substrate by rotating printing roll  30  multiple times.  
         [0043]     Now, a rubber plate including a printing pattern shown in  FIGS. 2 and 5  will be described in detail with reference to  FIGS. 6-9 .  FIG. 6  is a sectional view of a rubber plate for a printing roll according to an embodiment of the present invention,  FIG. 7  illustrates the formation of a printing pattern on the rubber plate shown in  FIG. 6  using a laser beam process,  FIG. 8  illustrates the formation of a printing pattern on the rubber plate shown in  FIG. 6  using a press process, and  FIG. 9  is a schematic perspective view of a printing roll and a rubber plate including a printing pattern.  
         [0044]     Referring to  FIG. 6 , a rubber plate  70 , in one example made of EPDM, is prepared. Rubber plate  70  can be mechanically processed in various ways. In one example, rubber plate  70  is processed in a similar manner as a photosensitive resin plate (not shown) that can be processed by photolithography. Rubber plate  70  is mechanically processed by a laser beam process shown in  FIG. 7 , a press process shown in  FIG. 8 , or a sputtering process (not shown) to form depressions  70   b  and prominences  70   a . Prominences  70   a  will receive the alignment material from anilox roll  10  for printing the alignment material pattern onto the substrate.  FIG. 7  schematically shows that a laser beam  101  from a laser beam generating device  100  may be illuminated onto portions of rubber plate  70  to form depressions  70   b .  FIG. 8  schematically shows that a press  200  may apply pressure to portions of the rubber plate  70  to form depressions  70   b.    
         [0045]     Advantageously, the above-described mechanical processes do not require a separate pattern film that is typically needed for photolithography. Accordingly, the mechanical processing can be advantageously applied to a large rubber plate including several prominences and depressions with less cost and greater efficiency.  
         [0046]     Now, apparatuses for printing an alignment film on a substrate according to other embodiments of the present invention are described in detail with reference to  FIGS. 10 through 12 .  FIGS. 10 and 11  are lateral sectional views of apparatuses for printing an alignment film according to other embodiments of the present invention.  FIG. 12  schematically illustrates the printing of an alignment film by a printing roll of the apparatuses shown in  FIGS. 10 and 11 .  
         [0047]     Referring to  FIGS. 10 and 11 , apparatuses for printing an alignment film according to these embodiments have similar configurations as those shown in  FIGS. 1 and 2 , respectively. Thus, each of the apparatuses also includes an anilox roll  10 , a doctor roll  20 , a printing roll  80 , a dispenser  40 , a bucket  50 , and a printing table  60  mounting a substrate  1 . A rubber plate  90  may also be attached to the circumferential surface of printing roll  80  in one embodiment.  
         [0048]     Different from  FIGS. 1 and 2 , printing roll  80  and rubber plate  90  do not have a predetermined pattern, as shown in  FIGS. 10 and 11 , respectively. Accordingly, the printing roll  80  coats an alignment film  4  having no pattern on substrate  1  as shown in  FIG. 12 .  
         [0049]     A desired pattern of printed alignment film  4  is then obtained by photolithography in one embodiment. In further detail, a photoresist film is coated on alignment film  4  and an exposure mask (not shown) having the alignment film pattern is aligned with substrate  1 . The photoresist film is exposed to light through the exposure mask and developed to form a photoresist pattern. Alignment film  4  is then dry etched using the photoresist pattern as an etch mask to form a desired pattern. When alignment film  4  is made of photosensitive material, there is no need to coat the photoresist film and the desired pattern of the alignment film  4  is obtained only by photolithography without the dry etching.  
         [0050]     Alternatively, a desired pattern of alignment film  4  may be formed by illuminating a laser beam.  
         [0051]     Advantageously, since printing roll  80  has no pattern, the diameter of printing roll  80  can be made as small as possible independent from the length of substrate  1 . In addition, the alignment between printing roll  80  and substrate  1  may not be significant, and the cleaning of printing roll  80  is very simple.  
         [0052]     While the present invention has been described in detail with reference to the above-described embodiments, those skilled in the art will appreciate that various modifications and substitutions can be made thereto without departing from the spirit and scope of the present invention as set forth in the appended claims that follow.