Abstract:
A master mold for an offset process is disclosed which enables formation of electrodes with a complex pattern or a very-fine pattern. A pattern formation method using the master mold is also disclosed. The master mold includes a plate having a predetermined thickness, and an intaglio pattern formed in a surface of the plate. The intaglio pattern has a cross-section having a surface inclined in a transfer direction of a material to be transferred.

Description:
[0001]     This application claims the benefit of Korean Patent Application No. 10-2005-0082620, filed on Sep. 6, 2005, which is hereby incorporated by reference as if fully set forth herein.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to an offset process, and more particularly, to a master mold for an offset process enabling formation of electrodes with a complex pattern or a very-fine pattern and a pattern formation method using the master mold.  
         [0004]     2. Discussion of the Related Art  
         [0005]     Plasma display panels are well known as an emissive device which displays an image using a discharge phenomenon. Such a plasma display panel is being highlighted as a display for an image display device having a large screen because the plasma display panel has many advantages of simple manufacture, large screen size, and rapid response speed in that it is unnecessary to provide active elements for respective cells.  
         [0006]     Referring to  FIG. 1 , a structure of such plasma display panel (PDP) is illustrated. As shown in  FIG. 1 , the PDP has a structure in which an upper panel  10  and a lower panel  20  are overlapped with each other such that they face each other. For each cell, the upper panel  10  includes a pair of sustain electrodes arranged on an inner surface of a transparent substrate  11 . Typically, the sustain electrodes include a transparent electrode  12  and a bus electrode  13 .  
         [0007]     Such sustain electrodes are coated with a dielectric layer  14  for an AC driving operation. A protective film  15  is formed over the dielectric layer  14 .  
         [0008]     On the other hand, the lower panel  20  includes address electrodes  22  arranged on an inner surface of the lower panel  20  over a dielectric layer  21 . An insulating layer  23  is formed over the address electrodes  22 . Stripe-shaped barrier ribs  24  are formed on the insulating layer  23 , to define discharge cell spaces. Red, blue, and green phosphor layers  26  are coated on the barrier ribs  24  in grooves each formed between the adjacent barrier ribs  24 , to form sub-pixels, respectively.  
         [0009]     Discharge cells  25  are defined by the barrier ribs  24  for respective sub-pixels. Discharge gas is sealed in each discharge cell  25 . The above-mentioned three different sub-pixels constitute one pixel.  
         [0010]     Typically, the formation of the electrodes, in particular, the bus electrodes  13 , is achieved in accordance with a method using an electrode paste or a dry film method using a green sheet.  
         [0011]     In the method, which uses an electrode paste, a black matrix paste is coated over the overall portion of the upper substrate  11  included in the upper panel  10  in accordance with a printing process such that the black matrix paste covers the transparent electrodes  12  on the upper panel  10 . The resulting black matrix layer is then dried.  
         [0012]     Thereafter, the dried black matrix layer is subjected to a light exposure process using a black matrix mask. An electrode paste is then coated on the light-exposed black matrix layer, using a printing process, in the same manner as the formation of the black matrix layer, to form an electrode layer for the bus electrodes  13 . The resulting electrode layer is then dried.  
         [0013]     Subsequently, the dried electrode layer is subjected to a light exposure process using an electrode mask. The light-exposed electrode layer is then developed using a developing solution, so that the electrode layer is patterned. The patterned electrode layer is finally baked. Thus, the formation of the bus electrodes  13  is completed.  
         [0014]     In the method using pastes, as described above, however, it is necessary to use a printer and printing masks for the printing and drying processes. Furthermore, the drying process causes waste of time and requirement of a separate space.  
         [0015]     In addition, half or more of the electrode material coated in the printing process is removed in the developing process. For this reason, there is a drawback of large waste of the material, and thus, an increase in the manufacturing costs.  
         [0016]     In order to overcome the above-mentioned problems, an electrode formation method using an offset process has recently been used.  
         [0017]     When the offset process is applied to formation of electrodes, it is carried out as follows.  
         [0018]     First, an electrode ink  32  is applied to a master mold  30  having an intaglio pattern  31  such that the electrode ink  32  is filled in the intaglio pattern  31 . The electrode ink  32  patterned by the intaglio pattern  31  in the master mold  30  is then transferred to a blanket  40 .  
         [0019]     The blanket  40  includes a roller  41  made of a metal material, and a sheath made of a silicon material. The blanket  40  has a circumferential length identical to the length of the master mold  30 .  
         [0020]     Thereafter, the electrode ink  32  transferred to the blanket  40  is re-transferred to the substrate  11  of the upper panel in the PDP, and is then baked. Thus, the formation of the bus electrodes  13  is completed.  
         [0021]     Where the electrode pattern to be formed on the substrate includes transversal electrode pattern portions extending in a direction perpendicular to the longitudinal direction of the pattern, to be transferred, corresponding to a transfer direction of the pattern, however, the offset process may incur problems in the procedure of transferring such transversal electrode pattern portions from the master mold to the blanket.  
         [0022]     That is, the electrode pattern may be transferred in the form of an incomplete structure having, for example, collapsed corners or an undesirable thickness. In particular, such problems should be overcome in association with the formation of electrodes on an upper panel having no transparent electrode because the upper panel must have a transversal electrode structure extending perpendicular to the electrode pattern.  
       SUMMARY OF THE INVENTION  
       [0023]     Accordingly, the present invention is directed to a master mold for an offset process and a pattern formation method using the same that substantially obviate one or more problems due to limitations and disadvantages of the related art.  
         [0024]     An object of the present invention is to provide a master mold for an offset process which includes a surface inclined from a vertical plane in a depth direction of the master mold, thereby being capable of achieving easy transfer of a pattern material from the master mold to a blanket without distortion of a pattern to be transferred, and enabling formation of electrodes with a complex pattern or a very-fine pattern, and to provide a pattern formation method using the master mold.  
         [0025]     Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.  
         [0026]     To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, a master mold for an offset process for transferring a material to be transferred, using a blanket, comprises: a plate having a predetermined thickness; and an intaglio pattern formed in a surface of the plate, wherein the intaglio pattern has a surface inclined in a transfer direction of the material.  
         [0027]     The intaglio pattern may comprise a first pattern extending in the transfer direction of the material, and a second pattern connected to the first pattern while extending perpendicular to the first pattern.  
         [0028]     The intaglio pattern may be adapted to form an electrode. In particular, the intaglio pattern may be adapted to form a bus electrode of a plasma display panel. In particular, the second pattern may be effectively applied to the case of a panel including bus electrodes alone, without including transparent electrodes.  
         [0029]     The second pattern may have an end surface inclined from a vertical plane at a leading end of the second pattern where the transfer of the material by the blanket is begun or at a trailing end of the second pattern where the transfer of the material by the blanket is ended. Alternatively, the second pattern may have end surfaces respectively inclined from a vertical plane at the leading end of the second pattern and the trailing end of the second pattern, in order to achieve more reliable and complete transfer of the material.  
         [0030]     The inclination of the intaglio pattern may be carried out in a direction that the second pattern is reduced in width as the second pattern extends in a depth direction. In accordance with this structure, it is possible to achieve more easy transfer of the material. Also, the structure finally formed on the panel in accordance with the transfer of the material can have a stable shape.  
         [0031]     In another aspect of the present invention, a master mold for an offset process comprises: a plate; and an intaglio pattern formed in the plate such that the intaglio pattern has an area reduced as the intaglio pattern extends inwardly.  
         [0032]     The intaglio pattern may comprise a first pattern extending in a transfer direction of a pattern ink filled in the intaglio pattern, and a second pattern connected to the first pattern while extending perpendicular to the first pattern.  
         [0033]     The second pattern may have an end surface inclined from a vertical plane at at least one of a leading end of the second pattern where the transfer of the pattern ink is begun and a trailing end of the second pattern where the transfer of the pattern ink is ended.  
         [0034]     In another aspect of the present invention, a pattern formation method for a display device using an offset process comprises: forming a pattern extending perpendicular to a direction that the offset process is advanced, using a master mold including an intaglio pattern having a cross-section with a surface inclined in the advance direction of the offset process.  
         [0035]     In another aspect of the present invention, a pattern formation method using the master mold comprises: applying a pattern ink to the master mold such that the pattern ink is filled in the intaglio pattern; transferring the pattern ink filled in the master mold in a patterned state to a blanket; and re-transferring the pattern ink from the blanket to a substrate.  
         [0036]     The pattern formation method may further comprise baking the pattern-transferred substrate after the retransferring step.  
         [0037]     It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0038]     The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principle of the invention. In the drawings:  
         [0039]      FIG. 1  is a perspective view illustrating a general plasma display panel;  
         [0040]      FIG. 2  is a schematic view illustrating a transfer procedure in a conventional offset process;  
         [0041]      FIG. 3  is a schematic view illustrating a retransfer procedure in the conventional offset process;  
         [0042]      FIG. 4  is a plan view illustrating a master mold for an offset process according to the present invention;  
         [0043]      FIG. 5  is a schematic view illustrating an example of a transfer procedure carried out using a master mold according to an embodiment of the present invention;  
         [0044]      FIG. 6  is a schematic view illustrating an example of a transfer procedure carried out using a master mold according to another embodiment of the present invention; and  
         [0045]      FIG. 7  is a plan view illustrating a master mold for an offset process according to another embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0046]     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.  
         [0047]     Referring to  FIG. 3 , a master mold  100  according to the present invention is illustrated. The master mold  100  includes a plate  100 , and at least one intaglio pattern  120  formed in the plate  110 . In the illustrated case, three intaglio patterns  120  are shown. For the simplicity of description, the following description will be given only in conjunction with one intaglio pattern  120 .  
         [0048]     The intaglio pattern  120  may have a single pattern structure, or may have a multi-pattern structure as shown in  FIG. 4 . In the case of  FIG. 4 , the intaglio pattern  120  includes a first pattern  121  and a second pattern  122 .  
         [0049]     A pattern ink  300  ( FIG. 5  or  6 ) as a material for pattern formation may be injected into the intaglio pattern  120  such that the pattern ink  300  is filled in the intaglio pattern  120 . For the pattern ink  300 , various kinds of pattern inks may be used in accordance with the material of the pattern to be formed.  
         [0050]     That is, an electrode ink for formation of electrodes on a panel, a black ink for formation of a black matrix on a panel, or other various inks for other purposes may be used.  
         [0051]     A blanket  200  is used to transfer the pattern ink  300  filled in the intaglio pattern  120 .  
         [0052]     For the transfer of the pattern ink  300 , the blanket  200  is moved on and along the master mold  100 , to which the pattern ink  300  has been applied. In accordance with the movement of the blanket  200 , the pattern ink  300  filled in the intaglio pattern  120  is transferred to the blanket  200  while maintaining the patterned shape thereof.  
         [0053]     The intaglio pattern  120  may have a surface inclined from a vertical plane at at least one of a leading end  122   a  thereof where the transfer of the pattern ink  200  is begun, and a trailing end  122   b  thereof where the transfer of the pattern ink  200  is ended.  
         [0054]     By virtue of the inclined surface, the transfer of the pattern ink  300  can be easily achieved. In particular, such an inclined surface can provide an advantage when it is applied to pattern portions extending perpendicular to the movement direction of the blanket  200 , for example, the second pattern  122 .  
         [0055]     The transferred pattern ink  300  is then retransferred to an object to be formed with a corresponding pattern, such as a substrate, using the blanket  200  carrying the transferred pattern ink  300 . Thus, a desired pattern formation is completed.  
         [0056]     Hereinafter, the master mold  100  will be described in more detail, with reference to FIGS.  4  to  6 , in conjunction with the case in which the master mold  100  is used to form an electrode pattern.  
         [0057]     As shown in  FIG. 4 , the intaglio pattern  120 , which is adapted for formation of electrodes, includes a first pattern  121  and a second pattern  122 .  
         [0058]     The first pattern  121  extends in a direction that the blanket  200  ( FIG. 5  or  6 ) moves to transfer the pattern ink  300  filled in the intaglio pattern  120 .  
         [0059]     That is, the electrode pattern portion formed by the first pattern  121  forms a main portion of an electrode to be formed.  
         [0060]     The second pattern  122  is a pattern portion of the intaglio pattern  120  connected to the first pattern  121  while extending perpendicular to the first pattern  121 .  
         [0061]     As shown in  FIG. 4 , the second pattern  122  extends perpendicularly from the first pattern  121  which is a main pattern portion of the intaglio pattern  120  on the master mold  100 . This second pattern  122  may provide an advantage in forming bus electrodes alone, without formation of transparent electrodes.  
         [0062]      FIGS. 5 and 6  illustrate a procedure for transferring the pattern ink  300  filled in the master mold  100  to the blanket  200 . Referring to  FIG. 5  or  6 , the second pattern  122  of the intaglio pattern  120  on the master mold  100  has a cross-section having an end surface or end surfaces inclined from a vertical plane.  
         [0063]      FIGS. 5 and 6  are cross-sectional views taken along the line A-A of  FIG. 4 . Referring to  FIG. 5  or  6 , the second pattern  122  is intaglioed to have a cross-section having a width gradually reduced in a depth direction, and thus, having an end surface or end surfaces inclined from a vertical plane.  
         [0064]     The second pattern  122  of the master mold  100  may have a symmetrical cross-section or an asymmetrical cross-section, as shown in  FIG. 5  or  6 .  
         [0065]     That is, the second pattern  122  may be inclined only at one end surface thereof, as shown in  FIG. 5 , or may be inclined at both the opposite end surfaces thereof, as shown in  FIG. 6 .  
         [0066]     Referring to  FIG. 5 , the second pattern  122  has an inclined leading end  122   a  where the transfer of the pattern ink  300  filled in the second pattern  122  to the blanket  200  is begun, and a vertical trailing end  122   b  where the transfer of the filled pattern ink  300  is ended.  
         [0067]     Conversely, the leading end  122   a  of the second pattern  122  may extend vertically, and the trailing end  122   b  of the second pattern  122  may extend inclinedly.  
         [0068]     Alternatively, both the leading and trailing ends  122   a  and  122   b  of the second pattern  122  may be formed to extend inclinedly.  
         [0069]     The inclination direction of the second pattern  122  corresponds to a direction that the second pattern  122  is reduced in width as it extends in a depth direction thereof.  
         [0070]     The structures of  FIGS. 5 and 6  are desirable in that they enable more reliable and smooth transfer of the pattern ink  300  from the second pattern  122  of the master mold  100  to the blanket  200 .  
         [0071]     That is, in accordance with the structures of  FIGS. 5 and 6 , it is possible to easily achieve the transfer of the pattern ink  300  filled in the second pattern  122  to the blanket  200  by virtue of the inclined portion of the second pattern  122 , namely, the leading end  122   a  or trailing end  122   b  of the second pattern  122 .  
         [0072]     If necessary, the first pattern  121  may be formed to have portions inclined in a direction that the transfer of the pattern ink filled in the first pattern  121  is advanced. In this case, it is possible to achieve an improvement in the printing quality obtained when the offset process is used.  
         [0073]     Thereafter, the pattern ink  300  transferred to the blanket  200  in the above-described manner is transferred to an object to be formed with an electrode pattern, for example, a substrate.  
         [0074]     That is, the pattern ink  300  transferred from the second pattern  122  to the blanket  200 , as shown in  FIGS. 5 and 6 , is re-transferred to a substrate ( FIG. 3 ).  
         [0075]     Thus, an electrode is formed on the substrate by the re-transferred pattern ink  300 . In this case, the formed electrode has a trapezoidal structure having a width gradually reduced as the structure extends upwardly, because the intaglio pattern  120  has an inclined structure. That is, the formed electrode has a stable structure inverted from the structure of the second pattern  122 .  
         [0076]     Since the pattern having a trapezoidal structure as described above is more stable, it is possible to prevent the pattern from being peeled off or damaged in subsequent processes.  
         [0077]     Meanwhile, the intaglio pattern  120  of the master mold  100  may have a structure as shown in  FIG. 7 .  
         [0078]     The intaglio pattern  120  shown in  FIG. 7  is similar to those of the above-described embodiments in that the intaglio pattern  120  includes a first pattern  121  adapted to form a main portion of an electrode to be formed, and a second pattern  122  connected to the first pattern  121 .  
         [0079]     In accordance with this embodiment, the second pattern  122  has a portion  123  inclined when viewing from the upper side of the master mold  100 , as shown in  FIG. 7 .  
         [0080]     The inclined portion  123  functions to enable easy transfer of the pattern ink  300  in the transfer procedure carried out using the blanket  200 .  
         [0081]     In addition to the inclined portion  123 , the intaglio pattern  120  may have an end surface inclined from a vertical plane in the advance direction of the blanket  200  at the leading end  122   a  or trailing end  122   b  of the intaglio pattern  120 .  
         [0082]     In other words, the intaglio pattern  120  may have only the inclined portion  123  formed at the second pattern  122 . Alternatively, the intaglio pattern  120  includes an end surface inclined from a vertical plane at the leading end  122   a  or trailing end  122   b , in addition to the inclined portion  123 . In this case, the second pattern  122  is more advantageous in the transfer procedure carried out by the blanket  200 .  
         [0083]     Thus, in accordance with the present invention, it is possible to form an electrode having a structure causing no adverse affect on the characteristics of the panel while being more stable.  
         [0084]     The pattern formed in accordance with the above-described procedure is subsequently baked to be hardened. In particular, where the pattern is adapted to form electrodes of a plasma display panel, the hardening of the pattern may be carried out through a procedure for baking the overall portion of the upper substrate or lower substrate of the plasma display panel.  
         [0085]     Although the master mold  100  has been described as being applied to formation of electrodes of a plasma display panel using an offset process, it may be applied to other procedures using an offset process.  
         [0086]     That is, the present invention can be applied to patterning of various layers to be formed on a panel, or to form various structures to be formed on a panel.  
         [0087]     It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the inventions. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.