Abstract:
An apparatus for printing an alignment layer of a liquid crystal display device includes a dispenser dropping an alignment material, an anilox roll receiving the dropped alignment material, a doctor roll evenly spreading the dropped alignment material coated onto the anilox roll, and a printing roll receiving the alignment material from the anilox roll, and transferring the alignment material onto a substrate, wherein the printing roll has a plurality of masks each having a numerical aperture of about 5% to 25%.

Description:
This application is a Divisional of U.S. patent application Ser. No. 10/271,743 filed Oct. 17, 2002 now U.S. Pat. No. 6,999,148 and claims the benefit of the Korean Application No. P2001-66045 filed on Oct. 25, 2001, both of which are hereby incorporated by reference in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a liquid crystal display device, and more particularly, to a device and method for printing an alignment layer and a mask for printing an alignment layer. 
     2. Background of the Related Art 
     In general, different types of flat panel displays are commonly implemented in various display apparatus, including Liquid Crystal Display (LCD), Plasma Display Panel (PDP), Electro Luminescent Display (ELD), and Vacuum Fluorescent Display (VFD). Of these different types, the LCD devices have commonly replaced apparatus that used Cathode Ray Tubes (CRTs) because of their excellent picture quality, light weight, thin profile, and low power consumption. In addition to mobile apparatus that use LCDs, such as monitors of notebook computers, the LCDs are increasingly being implemented for televisions and for monitors of home computers. 
     In general, an LCD device includes a liquid crystal display panel for displaying a picture, and a driving part for providing a driving signal to the liquid crystal display panel. The liquid crystal display panel includes first and second substrates bonded together with a gap formed between the first and second substrates, and a liquid crystal material is injected into the gap between the first and second glass substrates. 
     On the first substrate (commonly referred to as a TFT array substrate), there are a plurality of gate lines arranged along one direction at fixed intervals, a plurality of data lines arranged along a second direction perpendicular to the gate lines at fixed intervals, a plurality of pixel electrodes disposed within pixel regions defined by an intersection of the gate and data lines that form a matrix, and a plurality of thin film transistors switchable in response to a signal transmitted by the gate lines for conducting a signal from the data line to the pixel electrodes. On the second substrate (commonly referred to as a color filter substrate), there is a black matrix layer for shielding light from portions other than the pixel regions, a red (R), green (G), and blue (B) color filter layer for displaying colors, and a common electrode for implementing a picture. 
     The first and second substrates are spaced apart by spacers, and bonded together by a sealant material. The sealant material includes a liquid crystal material injection hole, through which the liquid crystal material is injected. Physical characteristics of the liquid crystal material are dependent on molecular arrangement of the liquid crystal molecules, and may be altered by application of an external force, such as electric field. Accordingly, filling of the liquid crystal material between the first and the second substrates cannot provide uniform molecular arrangement required for proper operation of the LCD device. Thus, an alignment layer is formed upon a surface of each of the first and second substrates. 
     In general, main composition materials for forming the alignment layers commonly include inorganic or organic substances. Of these main composition materials, polyimide group materials are generally considered better as compared to other organic polymers with respect to printing, rubbing, alignment control performance, and chemical stability. Currently, the polyimide group materials are commonly employed as a material for forming alignment layers of various LCD devices. 
     During formation of the alignment layers, diamine and acid anhydride are made to react in a solvent to prepare formation of polyamic acid. The material used during printing is the polyamic acid, whereby the polyimide is obtained as the polyamic acid is dried and set by application of heating. The polyimide alignment layer may be formed by various processes including spinning, spraying, dipping, and printing. 
       FIG. 1  is a schematic view of a device for printing an alignment layer according to the related art. In  FIG. 1 , the device includes a raw material tank  103  having raw material  101 , a raw material supply tube  104 , a dispenser  100 , an anilox roll  120 , a doctor roll  110 , and a printing roll  130 . 
     A mask  210  is positioned on the printing roll  130 , and is formed of a printing rubber plate with a 30% numerical aperture. The numerical aperture is defined as a ratio of a portion of mask that does not have the raw material  101  to a portion of the mask that has the raw material  101 . Generally, a mask  210  with a numerical aperture below 30% is employed for an LCD device having a resolution class below a high resolution XGA (1024×768 class). 
     In order to flow the raw material  101  through the raw material supply tube  104 , nitrogen gas (N 2 ) is injected into the raw material tank  103 . When the nitrogen gas (N 2 ) is supplied to the raw material tank  103 , the raw material  101  is dropped from the dispenser onto the rotating doctor roll  110  and the anilox roll  120  via the raw material supply tube  104 . The raw material  101  supplied to the doctor roll  110  and the anilox roll  120  is kneaded between the doctor roll  110  and the anilox roll  120 , whereby the raw material  101  is evenly coated onto the surface of the anilox roll  120 . Then, the evenly coated raw material  101  on the anilox roll  120  is transferred onto the substrate  150  that is positioned on the printing table  160  by the printing roll  130 . Accordingly, the masks  210  positioned on the printing roll  130  each have a 30% numerical aperture such that the substrate includes portions having the raw material  101  and portions not having the raw material  101 . Finally, the raw material  101  positioned on the substrate  150  is cured, thereby forming the alignment layer. 
       FIGS. 2A–2C  are plan and perspective views of a mask for printing an alignment layer according to the related art. In  FIG. 2A , a matrix of masks  210  having a plurality of projections  220  are positioned on a substrate  200 , wherein each of the masks  210  is formed of printing rubber plate. 
     In  FIG. 2B , during transfer of the raw material  101  from the printing roll  130  onto the substrate  150  (in  FIG. 1 ), no raw material  101  is transferred from regions having the projections  220 . Accordingly, the raw material  101  cannot be transferred to the substrate  150  (in  FIG. 1 ) where the projections  220  contact the substrate  150 . If a mask  210  without the projections  220  is used, the raw material  101  cannot be uniformly coated onto the surface of the mask  210  uniformly, thereby forming blots of raw material onto the substrate  150  (in  FIG. 1 ). Thus, a plurality of openings  220  are formed in the surface of the mask  210  for uniform transfer of the raw material  101  onto the substrate  150  (in  FIG. 1 ). In addition, defective printing of the raw material  101  onto the substrate  150  is proportional to an area of the substrate  150  having no raw material  101  printed thereon. Moreover, LCD devices classified below the high resolution class that have large sized pixels also have a lower ratio of defect occurrence caused by infiltration of contaminants than LCD devices classified above the high resolution class even using the mask  210  having a 30% numerical aperture. 
     In  FIG. 2C , the raw material  101  is transferred onto the substrate  150  (in  FIG. 1 ) except where regions correspond to the projections  220  on the mask  210 . Accordingly, the 30% numerical aperture mask  210  is problematic when implemented for fabricating LCD devices classified in the high resolution class or higher having small unit pixels. Since the 30% numerical aperture mask  210  includes the projections  220 , contaminates, such as dirt, are transferred onto the printing roll and onto the substrate. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is directed to an apparatus, method, and mask for printing an alignment layer that substantially obviates one or more of the problems due to limitations and disadvantages of the related art. 
     An object of the present invention is to provide an apparatus, mask, and method for printing an alignment layer that is applicable to LCD devices in the high resolution XGA (1024×768) class. 
     Another object of the present invention is to provide an apparatus, mask, and method for printing an alignment layer that can reduce influence of contamination of the projections from a printing roll and onto a substrate. 
     Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
     To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, an apparatus printing an alignment layer of a liquid crystal display device includes a dispenser dropping an alignment material, an anilox roll receiving the dropped alignment material, a doctor roll evenly spreading the dropped alignment material coated onto the anilox roll, and a printing roll receiving the alignment material from the anilox roll, and transferring the alignment material onto a substrate, wherein the printing roll has a plurality of masks each having a numerical aperture of about 5% to 25%. 
     In another aspect, a method for printing an alignment layer of a liquid crystal display device includes preparing an alignment material, dropping the alignment material onto a doctor roll and an anilox roll by a dispenser, printing the alignment material onto a substrate by using a printing roll having at least one mask with a numerical aperture of about 5% to about 25%, and curing the alignment material printed on the substrate. 
     In another aspect, a mask for printing an alignment layer of a liquid crystal display device includes a plurality of protrusions, wherein a numerical aperture of the mask is about 5% to about 25%. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. In the drawings: 
         FIG. 1  is a schematic view of a device for printing an alignment layer according to the related art; 
         FIGS. 2A–2C  are plan and perspective views of a mask for printing an alignment layer according to the related art; 
         FIG. 3  is a schematic view of an exemplary device for printing an alignment layer according to the present invention; and 
         FIGS. 4A–4C  are plan and perspective views of an exemplary mask for printing an alignment layer according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. 
       FIG. 3  is a schematic view of an exemplary device for printing an alignment layer according to the present invention. In  FIG. 3 , the device may include a raw material tank  303  having a raw material  301  for forming the alignment layer stored therein, a raw material supply tube  304  for supplying the raw material  301  in the raw material tank  303 , a dispenser  300  for dropping the raw material  301  supplied by the raw material supply tube  304 , an anilox roll  320  for receiving the raw material  301  dropped from the dispenser  300  onto a surface thereof (shown as  302 ), a doctor roll  310  rotatably fitted and spaced apart from the anilox roll  320  for even spreading of the raw material  301  onto the anilox roll  320 , and a printing roll  330  for receiving the raw material  301  from the surface of the anilox roll  320 , and printing the raw material  301  onto the substrate  350  disposed on a printing table  360 . A mask  410  may be positioned on the printing roll  330 . 
     In order to flow the raw material  301  through the raw material supply tube  304 , nitrogen gas (N 2 ) may be injected into the raw material tank  303 . Accordingly, the nitrogen gas (N 2 ) may be of high purity and is supplied to the raw material tank  303  from a nitrogen gas supply part (not shown) through a gas supply tube  305 . When the nitrogen gas (N 2 ) is supplied to the raw material tank  303 , the raw material  301  is dropped from the dispenser onto the rotating doctor roll  310  and the anilox roll  320  via the raw material supply tube  304 . The raw material  301  supplied to the doctor roll  310 , and the anilox roll  320  is kneaded between the doctor roll  310  and the anilox roll  320 , whereby the raw material  301  is evenly coated onto the surface of the anilox roll  320 . A thickness of the raw material  301  transmitted onto the substrate  350  is dependent upon the gap between the doctor roll  310  and the anilox roll  320 . Then, the evenly coated raw material  301  on the anilox roll  320  is transferred onto the substrate  350  that is positioned on the printing table  360  by the printing roll  330 . Then, the raw material  301  positioned on the substrate  350  may be cured at a temperature ranging from about 60° C.–80° C. for about 90 seconds as a first period of time, and at a temperature ranging from about 80° C.–250° C. for about 780 seconds as a second period of time. Finally, the cured raw material  301  may be rubbed, or irradiated with light to form the alignment layer. 
       FIGS. 4A–4C  are plan and perspective views of an exemplary mask for printing an alignment layer according to the present invention. In  FIG. 4A , a matrix of masks  410  each having projections  420  about 0.75 mm from a surface of the mask  410  may be formed at fixed intervals on a substrate  400 . The mask  410  may be formed of a printing rubber plate or an APR rubber plate, and may have a size similar to a size of the substrate  400 . Alternatively, the mask  410  may have a size smaller than a size of the substrate  400 , thereby accommodating a plurality of masks  410 . Moreover, positioning of the plurality of masks  410  may include offset and staggered relative positions. 
     In  FIG. 4B , a total thickness of the mask  410  may be about 2.09 mm, and the projections  420  may project from a surface of the substrate  400  by about 0.75 mm. The mask  410  may have a numerical aperture of about 5% to about 25%. Accordingly, since the projections  420  may project as much as about 0.75 mm from the surface of the mask  410 , the projections  420  do not interfere with rotation of the printing roll  330 . In addition, the total thickness of the mask  410  and the height of the projections  420  may be varied without changing the numerical aperture. Moreover, the numerical aperture may be changed by varying the total thickness of the mask  410  and the height of the projections  420 . Alternatively, the projections  420  may include different cross sectional geometries. For example, each of the projections  420  may have a circular, oval, or square cross section. Alternatively, each of the projections  420  may have different cross sections. For example, projections  420  positioned along an outer perimeter of the mask  410  may have a first type of cross sectional geometry and projections  420  positioned within the outer perimeter of the mask  410  may have a second type of cross sectional geometry different from the first type. Accordingly, an amount of contact between the mask  420  and the substrate  350  may be varied based upon on the numerical aperture of the mask  420 . 
     In  FIG. 4C , when the raw material  301  is coated on an entire surface of the mask  410 , the raw material  301  is transferred onto the substrate  410  except at regions corresponding to the projections  420  on the mask  410 . Accordingly, since the mask  410  has the numerical aperture of about 5% to 25%, alignment layers of LCD devices of the high resolution class may be achieved. In addition, since the mask  410  has the numerical aperture of about 5% to about 25%, contact areas between the protrusions  420  of the mask  410  and the substrate  350  (in  FIG. 3 ) is reduced, thereby reducing contamination of the printing roll  330  (in  FIG. 3 ) and the substrate  350  (in  FIG. 3 ). 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the device and method for printing an alignment layer of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.