Abstract:
A plasma display panel that prevents color mixture between adjacent cells is provided. The plasma display panel includes a plurality of discharge cells defined by a corresponding plurality of barrier ribs, and a phosphor layer formed on the bottom surface of the discharge cells and side surfaces of the barrier ribs. A ratio of the thickness of the phosphor layer formed on the side surface of the barrier ribs to the thickness of the phosphor layer formed on the bottom surface of the discharge is between approximately 0.8 and 1.3. A phosphor layer formed in this manner provides improved emission characteristics, and allows for a simplified, more cost effective manufacturing process.

Description:
This application claims the benefit of the Korean Patent Application No. P2002-24782 filed on Dec. 27, 2002, which is hereby incorporated by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a plasma display panel and a manufacturing method thereof, and more particularly to a plasma display panel and a manufacturing method thereof that is adaptive for preventing color mixture between adjacent cells. 
   2. Description of the Related Art 
   Generally, a plasma display panel (PDP) excites a phosphor material to emit light by using an ultraviolet ray of 147 nm generated when discharging an inactive mixture gas such as He+Xe, Ne+Xe or He+Ne+Xe, thereby displaying a picture including characters or graphics. Such a PDP is easy to be made into a thin-film and large-dimension type. Moreover, the PDP provides highly improved picture quality owing to a recent technical development. Especially, a three-electrode AC surface discharge PDP has an advantage in low voltage drive and long life span because wall charges are accumulated on a surface upon discharge and electrodes are protected from sputtering generated by the discharge. 
   Referring to  FIG. 1 , a discharge cell of a conventional three-electrode AC surface-discharge PDP includes a scan electrode Y and a sustain electrode Z provided on an upper substrate  10 , and an address electrode X provided on a lower substrate  18 . Each of the scan electrode Y and the sustain electrode Z includes a transparent electrode  12 Y and  12 Z, respectively, each having a metal bus electrode  13 Y and  13 Z, respectively, formed on one side edge of the corresponding transparent electrode. The metal bus electrode  13 Y,  13 Z has narrower line width than the transparent electrode  12 Y,  12 Z. 
   The transparent electrode  12 Y,  12 Z is formed of Indium Tin Oxide (ITO) on the upper substrate  10 . The metal bus electrode  13 Y,  13 Z is generally formed of metal such as Chrome Cr on the transparent electrode  12 Y,  12 Z and it acts to reduce voltage drop caused by the transparent electrode  12 Y,  12 Z, resistance of which is high. An upper dielectric layer  14  and a protective film  16  is deposited on the upper substrate  10  where the scan electrode Y and the sustain electrode Z are formed in parallel. The wall charges generated upon plasma discharge are accumulated in the upper dielectric layer  14 . The protective film  16  prevents the damage of the upper dielectric layer  14  caused by the sputtering generated upon plasma discharge and also increases emission efficiency of secondary electrons. The protective film  16  is generally made of Magnesium Oxide MgO. 
   A lower dielectric layer  22  and barrier ribs  24  are formed on the lower substrate  18  provided with the address electrode X and a phosphorous layer  26  is formed on the surface of the barrier ribs  24  and the lower dielectric layer  22 . The address electrode X is formed to cross the scan electrode Y and the sustain electrode Z. The barrier ribs  24  are formed in stripe or lattice shape to prevent the ultraviolet ray and the visible ray, which are generated by discharge, from leaking to the adjacent discharge cells. Inactive mixture gas is injected into a discharge space provided among the upper substrate  10 , the lower substrate  18  and the barrier ribs  24 . 
   The phosphorous layer  26  is made of a type of phosphor material excited by the ultraviolet ray emitted by vacuum ultraviolet ray VUV, and is divided into red phosphor, green phosphor and blue phosphor in accordance with the wavelength of the emitted light. Normally, the red phosphor is (YGd)BO3:Eu3+, the green phosphor is Zn2SiO4:Mn2+, and the blue phosphor is BaMgAl10017:Eu2+. Such red, green and blue phosphor is printed inside the PDP in screen printing method while it is in paste state. 
     FIGS. 2A to 2C  are views representing a prior art phosphor printing method. 
   Referring to  FIG. 2A , firstly a phosphor paste  30  is prepared by mixing the phosphor material R, G and B, resin and solvent together. Herein, the resin is high molecular Ethyl Cellulose, the solvent is a solution, which has a boiling point higher than 100° C., such as N-methyl Pyrrolidone, Ethyleneglycol, 2-Butoxy ethoxy ethanol, cellosolve and so on. 
   More specifically describing, the phosphor should be prepared to be in paste state in order to print the phosphor. That is, the phosphor material is mixed with the resin and the solvent in order that the phosphor can be inserted into the discharge space  39  located inside the PDP. Herein, the resin is high molecular Ethyl Cellulose, the molecular weight of which is high. If the high molecular resin is mixed with the phosphor material, the phosphor material can have a viscosity which is required for printing. 
   The phosphor paste  30  is spread on a mask  34  as in  FIG. 2A  in order to print the phosphor in the discharge space  39 . The mask  34  includes a printing area  36  and a shielding area  38  as in  FIG. 3 . The printing area  36  is formed in mesh to allow the phosphor paste  30  to pass through to the discharge space  39 . For this, the printing area  36  is located to overlap the discharge space  39 . The shielding area  38  is formed to overlap the barrier ribs  24  to prevent the phosphor paste  30  from being supplied to the barrier ribs  24 . 
   After the phosphor paste  30  is spread over the mask  34 , a squeeze  32  is moved in one direction and applies a designated pressure to the phosphor paste  30 , accordingly the phosphor paste  30  is passed through the printing area  36  of the mask  34  to the discharge space  39 . In fact, the phosphor paste  30  that passed by the printing area  36  is printed in the discharge are  39  inside the PDP as in  FIG. 2B . 
   However, such a prior art phosphor paste  30  is mixed with the high molecular resin, i.e., it has high viscosity, thus a lot of the phosphor paste  40  remain at the border area of the shielding area  38  and the printing area  36 . In this way, the remaining phosphor paste  40  flows into the upper part of the barrier ribs  24  and the adjacent discharge cells as in  FIG. 2C  when the mask  34  is eliminated. Herein, the remaining phosphor paste  40  that flew into the upper part of the barrier ribs  24  and the adjacent discharge cells causes color mixture when driving PDP, thereby deteriorating the display quality. 
   Therefore, in the end, the phosphor paste  40  remaining at the mask  34  is eliminated by use of a cleaning tape. However, even though the phosphor paste  40  remaining at the mask  34  is removed by use of a cleaning tape, plenty of the remaining phosphor paste  40  flows into the barrier ribs  24  and the adjacent discharge cell. In addition, because the phosphor paste  30  with high viscosity is used in prior art, a lot of phosphor paste  40  remains at the mask  34 , thus the cleaning tape must be used more frequently. However, if the cleaning tape is frequently used, there is a problem in that its process time and manufacturing cost increase. In addition, the phosphor paste  30  is manufactured in use of the high molecular resin. However, the phosphor including the high molecular resin has a disadvantage in a short life span according to the experiment. 
   SUMMARY OF THE INVENTION 
   Accordingly, it is an object of the present invention to provide a plasma display panel and a manufacturing method thereof that is adaptive for preventing color mixture between adjacent cells. 
   In order to achieve these and other objects of the invention, a plasma display panel according to an aspect of the present invention includes a plurality of discharge cells; barrier ribs to partition off the discharge cells; and a phosphor layer formed on the bottom surface of the discharge cells and the side surface of the barrier ribs, wherein if the thickness of the phosphor layer formed on the side surface of the barrier ribs is D 1  and the thickness of the phosphor layer formed on the bottom surface of the discharge cell is D 2 , the value of D 1 /D 2  ranges from 0.8 to 1.3. 
   The phosphor layer is formed by coating and firing phosphor paste with its viscosity-elasticity ratio in the range of 68-73. 
   The D 1  and the D 2  range from 15 μm to 25 μm. 
   The value of the D 1 /D 2  is about 1. 
   The phosphor layer is formed by coating and firing phosphor paste which includes a mixed resin by mixing a low molecular resin with a high molecular resin. 
   A manufacturing method of a plasma display panel according to another aspect of present invention includes the steps of: providing a mixed resin by mixing a high molecular resin with a low molecular resin; providing a phosphor paste by mixing a phosphor material a solvent into the mixed resin; and forming a phosphor layer by coating and firing the phosphor paste. 
   The mixed resin includes a low molecular resin of 20%˜50% and a high molecular resin of 50%˜80%. 
   In the method, the ratio of viscosity and elasticity of the phosphor paste in the range of 68-78. 
   In the method, the composition of the phosphor paste is a mixed resin of 8˜15 wt %, a phosphor material of 40˜50 wt % and a solvent of 40˜50 wt %. 
   In the method, the phosphor layer formed on the side surface of barrier ribs and the bottom surface of a discharge cell, and if the thickness of the phosphor layer formed on the side surface of the barrier ribs is D 1  and the thickness of the phosphor layer formed on the bottom surface of the discharge cell is D 2 , the value of D 1 /D 2  ranges from 0.8 to 1.3. 
   In the method, the D 1  and the D 2  range from 15 μm to 25 μm. 
   In the method, the value of the D 1 /D 2  is about 1. 
   In the method, Cellulose family derivative is selected as the high molecular resin and the low molecular resin. 
   In the method, any one of Ethyl Cellulose, Ethylhydroxyethyl Cellulose, Hydroxyalkylmethyl Cellulose and Dihydroxypropyl Cellulose is selected as the high molecular resin and the low molecular resin. 
   In the method, a high molecular Ethyl Cellulose resin with a molecular weight value in the range of 100,000-120,000 as the high molecular resin. 
   In the method, a low molecular Ethyl Cellulose resin with a molecular weight value in the range of 50,000-60,000 as the low molecular resin. 
   In the method, any one of Acrylamide, Diacetone Acrylamide and Vinyl Pyrrolidinone is selected as the high molecular resin and the low molecular resin. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other objects of the invention will be apparent from the following detailed description of the embodiments of the present invention with reference to the accompanying drawings, in which: 
       FIG. 1  is a perspective view representing a discharge cell structure of a prior art three-electrode AC surface discharge plasma display panel; 
       FIGS. 2A to 2C  are views representing a prior art phosphor printing method; 
       FIG. 3  is a view representing a mask shown in  FIGS. 2A to 2C  in detail; 
       FIG. 4  is a view representing a manufacturing method of a plasma display panel according to an embodiment of the present invention; 
       FIG. 5  is a graph representing the viscosity-elasticity ratio of a phosphor paste made in the method of  FIG. 4 ; 
       FIG. 6A to 6C  are a view representing the thickness of the phosphor formed at a discharge cell in response to the viscosity-elasticity ratio of the phosphor paste; and 
       FIG. 7  is a view representing the remaining amount of the phosphor paste at a mask, wherein the phosphor paste is made in the manufacturing method of  FIG. 4 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. 
   With reference to  FIGS. 4 to 7 , embodiments of the present invention will be explained as follows. 
     FIG. 4  is a view representing a manufacturing method of a plasma display panel according to an embodiment of the present invention. 
   Referring to  FIG. 4 , in a manufacturing method of phosphor paste according to an embodiment of the present invention, firstly, a low and high molecular resin is mixed to make a compound resin. (S 50 ) The high molecular resin has a long chain, thus it has high viscosity and low elasticity, i.e., its recovering power is low in correspondence to stress. On the contrary, the low molecular resin has a short chain, thus it has low viscosity and high elasticity, i.e., its recovering power is high in correspondence to stress. In this way, if the high molecular resin with high viscosity and low elasticity is mixed with the low molecular resin with low viscosity and high elasticity, the phosphor paste with desired elasticity and viscosity may be generated. 
   On the other hand, the resin used in the step S 50  can be set variously. For example, the used resin might be any one of cellulose family derivatives such as Ethyl Cellulose, Ethylhydroxyethyl Cellulose, Hydroxyalkylmethyl Cellulose and Dihydroxypropyl Cellulose. Furthermore, the resin can be Acrylamide, Diacetone Arylamide or Vinyl Pyrrolidinone. 
   The embodiment of the present invention will be described assuming that Ethyl Cellulose is used as the resin for the sake of convenience of explanation. Instep S 50 , the low molecular Ethyl Cellulose resin (molecular weight 50,000 to 60,000) is mixed with the high molecular Ethyl Cellulose resin (molecular weight 100,000 to 120,000) to make a mixed resin. Herein, the mixing rate of the low molecular resin and the high molecular resin is set to be 20% to 50% of the low molecular resin and 80% to 50% of the high molecular resin. 
   If the mixed resin of 20% to 50% of the low molecular resin and 80% to 50% of the high molecular resin is made in the step S 50 , the viscosity and elasticity ratio of the phosphor paste to be made in the step S 52  can be positioned in the range of 68-73 as in  FIG. 5 . That is, the mixed resin made in the step S 50  is utilized to make the phosphor paste with its viscosity-elasticity ratio in the range of 68-73 in the step S 52 . Herein, if the viscosity-elasticity ratio is sustained in the range of 68-73, the phosphor paste is shown to have high printability in its experience. 
   These will be described more specifically by referring to  FIGS. 6A to 6C . If the phosphor  60  is made in use of the phosphor paste with its viscosity-elasticity ratio in the range of 60-65 as in  FIG. 6A , the phosphor  60  is formed in barrier ribs  64  to have high thickness. In other words, the phosphor paste with its viscosity-elasticity ratio in the range of 60-65 almost does not flow, accordingly the phosphor  60  formed in the barrier ribs  64  becomes thicker than the phosphor  60  formed in the lower part of the discharge space  62 , i.e., on the lower part of dielectric). In fact, if the phosphor  60  is made by use of the phosphor paste with the viscosity-elasticity ratio in the range of 60-65, the thickness of the phosphor  60  formed in the barrier ribs  64  is about 25 μm, and the thickness of the phosphor  60  formed at the lower part of the discharge space  62  is about 10 μm to 12 μm. That is, if the phosphor  60  is formed by use of the phosphor paste with its viscosity-elasticity ratio in the range of 60-65, the thickness value (side/lower part) of the phosphor  60  ranges from 2.1 to 2.5. In other words, if the phosphor  60  is formed by use of the phosphor paste with its viscosity-elasticity ratio in the range of 60-65, barrier ribs cannot be formed evenly within the discharge space  62  so that it is not possible to generate a light with evenness and high brightness in general within the discharge space  62 , i.e., discharge cell. 
   On the other hand, if the phosphor  66  is made in use of the phosphor paste with its viscosity-elasticity ratio in the range of 75-80 as in  FIG. 6B , the phosphor  66  is formed in the lower part of the discharge space  68  to have high thickness. In other words, the phosphor paste with its viscosity-elasticity ratio in the range of 75-80 has high liquidity, thus the phosphor  66  formed in the lower part of the discharge space  68  becomes thicker than the phosphor  66  formed in the barrier ribs  70 . In fact, if the phosphor  66  is made by use of the phosphor paste with the viscosity-elasticity ratio in the range of 75-80, the thickness of the phosphor  66  formed in the barrier ribs  70  is about 15 μm, and the thickness of the phosphor  66  formed at the lower part of the discharge space  68  is about 25 μm. That is, if the phosphor  66  is formed by use of the phosphor paste with its viscosity-elasticity ratio in the range of 75-80, the thickness value (side/lower part) of the phosphor  66  is set to 0.6. In other words, if the phosphor  66  is formed by use of the phosphor paste with its viscosity-elasticity ratio in the range of 75-80, barrier ribs cannot be formed evenly within the discharge space  68  so that it is not possible to generate a light with evenness and high brightness in general within the discharge space  68 , i.e., discharge cell. 
   In comparison to these, if the phosphor  72  is made in use of the phosphor paste with its viscosity-elasticity ratio in the range of 68-73 as in  FIG. 6C , the phosphor  72  is formed within the discharge space  74  to have even height. In fact, if the phosphor  72  is made by use of the phosphor paste with the viscosity-elasticity ratio in the range of 68-73, the thickness of the phosphor  72  formed in the barrier ribs  70  is about 20 μm, and the thickness of the phosphor  72  formed at the lower part of the discharge space  74  is about 15 μm to 25 μm. That is, if the phosphor  72  is formed by use of the phosphor paste with its viscosity-elasticity ratio in the range of 68-73, the thickness value (side/lower part) of the phosphor  72  ranges from 0.8 to 1.3. Herein, the thickness ration of the phosphor  72  is preferably set to about 1 so that the phosphor  72  is distributed evenly inside the cell. 
   In other words, if the phosphor  72  is formed by use of the phosphor paste with its viscosity-elasticity ratio in the range of 68-73, barrier ribs can be formed evenly within the discharge space  74  so that it is possible to generate a light with evenness and high brightness in general within the discharge space  74 , i.e., discharge cell. 
   On the other hand, after the mixed resin is made in the step S 50 , the phosphor material R, G and B, the mixed resin and the solvent are mixed together to make the phosphor. (S 52 ) Herein, the ratio of the phosphor material, the mixed resin and the solvent is set to be 40˜50 wt %, 8˜15 wt % and 40˜50 wt % respectively. 
   Normally, the red phosphor is (YGd)BO3:Eu3+, the green phosphor is Zn2SiO4:Mn2+, and the blue phosphor is BaMgAl10017:Eu2+. In addition, the solvent is a solution, which has a boiling point higher than 100° C., such as N-methyl Pyrrolidone, Ethyleneglycol, 2-Butoxy ethoxy ethanol, cellosolve and so on. 
   After the phosphor paste being made in the step S 52 , the phosphor paste  48  is formed on the discharge space  49  of the PDP as shown in  FIG. 7 . (S 54 ) At this moment, the phosphor paste  48  of the present invention has higher elasticity than prior art, thus less phosphor paste  47  remains at the border part of the printing area  44  and the shielding area  46 . In this way, if less amount of phosphor paste  47  remains at the mask  42 , the phosphor paste  47  remaining upon removal of the mask  42  is not stuck to the barrier ribs  41  and the adjacent cells, thereby preventing the color mixture of the PDP. In addition, since less amount of the phosphor paste  47  remains at the mask  42 , the number of usage of cleaning tape can be reduced, and accordingly the process time and manufacturing cost decrease. After the phosphor paste  48  being printed in the step S 54 , the phosphor paste  48  is fired to form the phosphor layer  72  in the discharge space  49 . (S 56 ) 
   As described above, according to the manufacturing method of the plasma display panel of the present invention, the high molecular resin is mixed with the low molecular resin to make the phosphor paste with its viscosity-elasticity ratio in the range of 68-73. In this way, the phosphor paste with the viscosity-elasticity ratio in the range of 68-73 is shown to have high printability in the experiment, thus the amount of the phosphor paste remaining at the mask can be minimized, and accordingly the color mixture of the plasma display panel can be prevented. In addition, it is possible to reduce the number of usage of cleaning tape that is used for reducing the phosphor paste remaining at the mask, and accordingly the manufacturing cost and the process time can be reduced. Also, if the phosphor is formed by use of the phosphor paste with its viscosity-elasticity ratio in the range of 68-73, it is possible to fabricate the phosphor with even thickness in the discharge cell, i.e., the discharge space. In this way, if the phosphor with even thickness is formed in the discharge cell, light is evenly generated in the entire discharge cell. 
   Although the present invention has been explained by the embodiments shown in the drawings described above, it should be understood to the ordinary skilled person in the art that the invention is not limited to the embodiments, but rather that various changes or modifications thereof are possible without departing from the spirit of the invention. Accordingly, the scope of the invention shall be determined only by the appended claims and their equivalents.