Patent Publication Number: US-7595591-B2

Title: Plasma display panel

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
     This application claims the benefit of Korean Patent Application No. 10-2006-0009025, filed on Jan. 27, 2006, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present embodiments relate to a plasma display panel, and more particularly, to a plasma display panel in which color temperature is compensated by mixing a phosphor raw material having low luminous efficiency within barrier ribs. 
     2. Description of the Related Art 
     Conventionally, a plasma display panels is a flat display device that displays desired numbers, letters, or a graphic by exciting a phosphor material in a phosphor layer using ultraviolet rays generated by discharge of a discharge gas filled between two substrates on which a plurality of electrodes are formed. 
     A conventional three-electrode surface discharge type plasma display panel has the following structure. 
     The plasma display panel includes front and rear substrates. An X electrode and a Y electrode are alternately formed on an inner surface of the front substrate, and the X and Y electrodes are buried by a front dielectric layer. A protective layer is formed on a surface of the front dielectric layer. A plurality of address electrodes are formed on an inner surface of the rear substrate in a direction crossing the X and Y electrodes. The address electrodes are buried by a rear dielectric layer. A plurality of barrier ribs that define a plurality of discharge cells are disposed between the front and rear substrates. Phosphor layers of red, green, and blue colors are coated in the barrier ribs. 
     In a conventional plasma display panel having the above configuration, when an electrical signal is applied between the address electrodes and the Y electrode, discharge cells for generating light are selected, and when an electrical signal is alternately applied to the X and Y electrodes, visible light is emitted from the phosphor layers coated in the selected discharge cells, thereby displaying a stationary image of a moving image. 
     However, the conventional plasma display panel has a drawback of low color temperature since the blue color phosphor layer has relatively low luminous efficiency compared to the red and green color phosphor layers. 
     Therefore, various methods for increasing the luminous efficiency of the blue color phosphor layer have been studied. For example, some methods that have been used include forming the coating area of the blue color phosphor layer greater than the coating area of the red and green color phosphor layers, or increasing the brightness of the blue color phosphor layer by using a blue color filter separately provided. 
     However, the increase in the coating area of the blue color phosphor layer to be greater than the coating area of the red and green color phosphor layers causes non-uniformity of discharge cells. Also, the increase in the luminous efficiency of the blue color phosphor layer using an additional blue color filter complicates the structure of the plasma display panel. 
     SUMMARY OF THE INVENTION 
     The present embodiments provide a plasma display panel in which color temperature is compensated for by mixing a blue phosphor raw material having low luminous efficiency within the barrier ribs. 
     According to an aspect of the present embodiment, there is provided a plasma display panel comprising: a plurality of substrates disposed facing each other; a plurality of discharge electrodes disposed within the substrates and a predetermined discharge voltage is applied to the discharge electrodes; barrier ribs which are disposed between the substrates and define discharge cells; and a plurality of phosphor layers coated in the discharge cells to emit a plurality of colors for color images, wherein a raw material for forming at least one phosphor layer of the phosphor layers is mixed in the barrier ribs. 
     The raw material for forming the phosphor layer that has relatively low luminous efficiency may be mixed in the barrier ribs. 
     The phosphor layers may comprise red, green, and blue phosphor layers, and the raw material for forming a phosphor layer mixed with the barrier ribs may be a raw material for forming a blue color phosphor layer. 
     The raw material for forming a blue color phosphor layer may be mixed in the barrier ribs that define the blue color discharge cells. 
     The raw material for forming a blue color phosphor layer may be mixed in throughout the barrier ribs that the define discharge cells. 
     According to another aspect of the present embodiment, there is provided a plasma display panel comprising: a front substrate; a rear substrate facing the front substrate; a plurality of discharge electrodes disposed in he front and rear substrates and a predetermined discharge voltage is applied to the discharge electrodes; a dielectric layer that buries the discharge electrodes; a protective layer formed on the surface of the dielectric layer; barrier ribs disposed between the front and rear substrate to define discharge cells; and phosphor layers of red, green, and blue color coated in the discharge cells, wherein a raw material for forming at least one phosphor layer of the phosphor layers of red, green, and blue color is mixed in the barrier ribs. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features and advantages of the present embodiments will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
         FIG. 1  is a partial cutaway exploded perspective view illustrating a plasma display panel according to an embodiment; and 
         FIG. 2  is a cross-sectional view taken along a line I-I according to the present embodiment of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present embodiments will now be described more fully with reference to the accompanying drawings in which exemplary embodiments are shown. 
       FIG. 1  is a partial cutaway exploded perspective view illustrating a plasma display panel  100  according to an embodiment, and  FIG. 2  is a cross-sectional view taken along a line I-I of  FIG. 1 . 
     Referring to  FIGS. 1 and 2 , the plasma display panel  100  includes a front substrate  101  and a rear substrate  102  disposed parallel to the front substrate  101 . The front substrate  101  and the rear substrate  102  seals a discharge space from the outside by frit glass (not shown) coated along edges of surfaces of the front and rear substrates  101  and  102  facing each other. 
     The front substrate  101  is a transparent substrate formed of soda lime glass. Alternately, the front substrate  101  can be a semi-transparent plate, a colored substrate, or a reflection plate. The rear substrate  102  can also be formed of substantially the same material as the front substrate  101 . 
     Barrier ribs  103  that define a plurality of discharge cells together with the front and rear substrates  101  and  102  are disposed between the front and rear substrates  101  and  102 . The barrier ribs  103  include first barrier ribs  104  disposed in an X direction of the plasma display panel  100  and second barrier ribs  105  disposed in a Y direction of the plasma display panel  100 . The barrier ribs  103  define the discharge cells in a lattice type. 
     Alternatively, the barrier ribs  103  can be arranged to various types such as, for example, a meander type, a delta type, a waffle type, or a honeycomb type. The discharge cells defined by the barrier ribs  103  can have various shapes of horizontal cross-section such as, for example, a polygon shape, a circle, or an oval shape in addition to the rectangular shape as in the current embodiment. 
     An X electrode  106  and a Y electrode  107  are disposed on an inner surface of the front substrate  101  along the X direction of the plasma display panel  100 . The X and Y electrodes  106  and  107  are alternately disposed along the Y direction of the plasma display panel  100 . 
     The X electrode  106  includes first transparent electrodes  108  formed on an inner surface of the front substrate  101  and a first bus electrode  109  that electrically connects the transparent electrodes  108 . The cross-section of the first transparent electrodes  108  is a rectangular shape, but the present embodiment is not limited thereto. 
     The Y electrode  107  has a shape substantially identical to the X electrode  106 , and includes second transparent electrodes  110  formed on an inner surface of the front substrate  101  and a second bus electrode  111  that electrically connects the second transparent electrodes  110 . The second transparent electrodes  110  are disposed in each of the discharge cells in a rectangular shape, but the shape of the second transparent electrodes  110  is not limited thereto. The second transparent electrode  110  is separated a predetermined distance from the first transparent electrode  108  in the discharge cell to form a discharge gap. 
     In order to increase the opening ratio of the front substrate  101 , the first and second transparent electrodes  108  and  110  are formed of a transparent conductive film, for example, indium tin oxide (ITO). The first and second bus electrodes  109  and  111  are formed in multiple layers using a metal having high conductivity, for example, an Ag paste or a Cr—Cu—Cr alloy to increase the electrical conductivity of the first and second transparent electrodes  108  and  110 . 
     A space between a pair of the X and Y electrodes  106  and  107  and adjacent pair of the X and Y electrodes  106  and  107  corresponds to a non-discharge region. A black stripe layer can further be formed on the non-discharge region to increase contrast of the plasma display panel  100 . 
     The X and Y electrodes  106  and  107  are contained within a front dielectric layer  112 . The front dielectric layer  112  is formed of a high dielectric material, for example, ZnO—B 2 O 3 —Bi 2 O 3 . The front dielectric layer  112  can be selectively printed on portions where the X and Y electrodes  106  and  107  are formed or can be printed on the entire surface of the front substrate  101 . 
     A protective layer  113  formed of, for example, MgO is deposited on a surface of the front dielectric layer  112  to prevent the damage of the front dielectric layer  112  and to increase the emission of secondary electrons. 
     A plurality of address electrodes  115  are disposed on an inner surface of the rear substrate  102 . The address electrodes  115  are disposed in a direction crossing the X and Y electrodes  106  and  107 . The address electrodes  115  are buried by a rear dielectric layer  114 . The rear dielectric layer  114  is formed of a high dielectric material, for example, PbO—B 2 O 3 —SiO 2 . 
     A discharge gas such as, for example, a Ne—Xe gas or a He—Xe gas is filled in the discharge cells defined by the coupling of the first substrate  101 , the second substrate  102 , and the barrier rib  103 . 
     A plurality of phosphor layers  116  that emit colored visible light when the phosphor layers  116  are excited by ultraviolet rays generated from the discharge gas are formed in the discharge cells. The phosphor layers  116  can be coated on any region of the discharge cells, and, in the current embodiment, the phosphor layers  116  are coated to a predetermined thickness on the inner surface of the rear substrate  102  and inner walls of the barrier ribs  103 . 
     The barrier ribs  103  of the discharge cells include a raw material for forming a phosphor layer that corresponds to a phosphor layer having relatively low luminous efficiency, which will now be described in detail. 
     The barrier ribs  103  are formed between the front and rear substrates  101  and  102 . The barrier ribs  103  are formed of a dielectric material that can induce charges during discharges, and preferably, the dielectric material is glass powder to which an organic vehicle and various fillers, such as, for example, ZrO 2 , TiO 2  or Al 2 O 3  are added. The first barrier ribs  104  are disposed between the adjacent second barrier ribs  105 , and are combined to one unit with the second barrier ribs  105  by extending away from the inner walls of the second barrier ribs  105 . 
     The phosphor layers  116  are formed in the discharge cells defined by the barrier ribs  103 , and in the current embodiment, the phosphor layers  116  include a red phosphor layer  116 R (see  FIG. 2 ), a green phosphor layer  116 G, and a blue phosphor layer  116 R, but not limited thereto. 
     The red color phosphor layer  116 R may be formed of (Y,Gd)BO 3 ;Eu +3 , the green color phosphor layer  116 G may be formed of Zn 2 SiO 4 :Mn 2+ , and the blue color phosphor layer  116 B may be formed of BaMgAl 10 O 17 :Eu 2+ . Alternately, the blue color phosphor layer  116 B can be formed of CaMgSi 2 O 8 :Eu 2+ . (The CaMgSi 2 O 8 :Eu 2+  is an organic compound of Ca, MgO 6 , and SiO 4 .) 
     In some examples, the plasma display panel  100  has a low color temperature due to the blue color phosphor layer  116 B coated on the blue color discharge cell B having relatively low luminous efficiency compared to the red color phosphor layer  116 R coated in the red color discharge cell R and the green color phosphor layer  116 G coated in the green color discharge cell G. 
     To prevent the low color temperature of the plasma display panel  100 , a raw material  103   b  for forming the blue color phosphor layer  116 B is mixed in a raw material  103   a  for forming the barrier ribs  103 . That is, the barrier ribs  103  are formed of a glass powder to which an organic vehicle and various fillers, such as, for example, ZrO 2 , TiO 2  or Al 2 O 3  are added. The raw material  103   b  for forming the blue color phosphor layer  116 B can be a mixture of CaMgSi 2 O 8 :Eu 2+  with at least one of BaMgAl 10 O 17 :Eu 2+ , CaMgSi 2 O 8 :Eu 2+ , and BaMgAl 10 O 17 :Eu 2+ . 
     The raw material  103   b  for forming the blue color phosphor layer  116 B can be mixed with the entire barrier ribs  103  that define red, green, and blue discharge cells, or can be selectively mixed with the barrier ribs  103  that surround the blue color discharge cell B. 
     A method of manufacturing the barrier ribs  103  of the plasma display panel  100  having the above structure according to the current embodiment will now be described. 
     A rear substrate  102  formed of glass is prepared. Stripe shaped address electrodes  115  are patterned on an upper surface of the rear substrate  102  using a material having conductivity. Next, the address electrodes  115  are buried by printing a rear dielectric layer  114 . 
     Next, a screen having substantially the same pattern as the barrier ribs  103  is tightly contacted on an upper surface of the rear dielectric layer  114 . A paste is manufactured by mixing a raw material for forming the barrier ribs, formed of glass powder to which an organic vehicle and various fillers, such as, for example, ZrO 2 , TiO 2  or Al 2 O 3  are added with a raw material  103   b  for forming a blue color phosphor layer, formed of one mixture, for example, BaMgAl 10 O 17 :Eu 2+ , CaMgSi 2 O 8 :Eu 2+ , or a mixture of CaMgSi 2 O 8 :Eu 2+  and BaMgAl 10 O 17 :Eu 2+ . The paste is printed on the screen and baked to complete the manufacture of the barrier ribs  103 . 
     An exemplary operation of the plasma display panel  100  having the above structure will now be described. 
     When a predetermined pulse voltage from an external power source is applied between address electrodes  114  and a Y electrode  107 , discharge cells that emit light are selected. Wall charges are accumulated on an inner surface of the selected discharge cells. 
     Next, when a positive (+) voltage is applied to an X electrode  106  and a relatively higher voltage that the voltage applied to the X electrode  106  is applied to a Y electrode  107 , wall charges migrate due to a voltage difference between the X and Y electrodes  106  and  107 . 
     Plasma is generated by the collision between the moving wall charges and discharge gas atoms in the discharge cells. The discharge begins at a gap where a relatively strong field is formed between the X and Y electrodes  106  and  107  and expands outwards. 
     When the voltage difference between the X and Y electrodes  106  and  107  is reduced lower than a discharge voltage due to the discharge, a further discharge is not generated, but space charges and wall charges are formed in the discharge cell. 
     When the polarity of the voltages applied to the X and Y electrodes  106  and  107  is reversed, discharge is re-generated with the aid of the wall charges. If the polarity of the X and Y electrodes  106  and  107  is reversed again, the initial discharge process is repeated. Discharge is stably generated by repeating this process. 
     Ultraviolet rays generated by the discharge excite a phosphor material included in the phosphor layers  116  coated in each of the discharge cells. Through this process, visible light is generated. The generated visible light displays stationary images or moving images by emission from the discharge cells. 
     Since the raw material  103   b  for forming a blue color phosphor layer  116 B is mixed in the barrier ribs  103 , energy enters into the barrier ribs  103  and the raw material  103   b  for forming a blue color phosphor layer  116 B generates blue light. Accordingly, blue light is generated in the red, green, and blue color discharge cells. The generation of blue light in the red, green, and blue color discharge cells can compensate for the emission of blue light from the blue color discharge cells B that have relatively low luminous efficiency, and can increase a color temperature of the entire plasma display panel  100 . The addition of the raw material  103   b  for forming a blue color phosphor layer  116 B to the barrier ribs  103  may be in a range that the color mixing of the red and green color discharge cells R and G does not occur due to the other color. Also, the raw material  103   b  for forming a blue color phosphor layer  116 B may be appropriately added to the barrier ribs  103  so as not to affect the light emission of the red color discharge cells R which have a relatively low brightness compared to the green color discharge cells G. The mixing ratio of the raw material  103   b  for forming a blue color phosphor layer  116 B with respect to the barrier ribs  103  may be from about 1 to about 20%, preferably, from about 5 to about 10%. 
     Experimental results of the luminous efficiency of blue color and the variation of color temperature are summarized in Table 1. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
             
            
               
                   
                   
               
               
                   
                 Comparative Example 
                 Example 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                   
                   
                   
                   
                 Color 
                   
                   
                   
                 Color 
               
               
                   
                 X 
                 Y 
                 Brightness 
                 temperature 
                 X 
                 Y 
                 Brightness 
                 temperature 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 Full white 
                 0.276 
                 0.287 
                 195.5 
                 10685 
                 0.275 
                 0.272 
                 196.7 
                 12108 
               
               
                 Full blue 
                 0.148 
                 0.047 
                 37.48 
                 — 
                 0.153 
                 0.056 
                 49.2 
                 — 
               
               
                 Blue 
                   
                   
                 100% 
                   
                   
                   
                 110.4% 
               
               
                 color 
               
               
                 efficiency 
               
               
                   
               
            
           
         
       
     
     For the comparative example, conventional barrier ribs are used, and for the current embodiment, barrier ribs into which a raw material for forming a blue color phosphor layer is mixed. 
     Referring to Table 1, in the case of the comparative example, X axis and Y axis of a color coordinate respectively are 0.276 and 0.287, brightness is 195.5, and color temperature is 10685 K, and in the case of the current embodiment, X axis and Y axis of a color coordinate respectively are 0.275 and 0.272, brightness is 196.7, and color temperature is 12108 K. That is, this exemplary embodiment has a color temperature improvement of approximately 1400 K compared to the comparative example. Also, the blue color efficiencies (brightness/Y) of the comparative example and the exemplary embodiment respective are 797.4 and 878.5. Assuming that the blue color efficiency of the comparative example is 100, that of the exemplary embodiment is 110.4, that is, the exemplary embodiment has the blue color efficiency improvement of 10.4%. 
     As described above, a plasma display panel according to the present embodiments can increase luminous efficiency of discharge cells that have low luminous efficiency and can increase color temperature at full white by manufacturing barrier ribs mixing with a raw material for forming a phosphor layer that has relatively low luminous efficiency. 
     While the present embodiments have been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present embodiments as defined by the following claims.