Patent Publication Number: US-2006019814-A1

Title: Pb-free glass composition for barrier ribs of plasma display panel, and plasma display panel comprising the Pb-free glass barrier ribs prepared therefrom

Description:
CROSS REFERENCE TO RELATED APPLICATION  
      This application claims priority to and the benefit of Korean Patent Application No. 10-2004-0049412, filed on Jun. 29, 2004, which is hereby incorporated by reference for all purposes as if fully set forth herein.  
     FIELD OF THE INVENTION  
      The present invention relates to a Pb-free glass composition for barrier ribs of a plasma display panel (hereinafter referred to as “PDP”) and a plasma display panel comprising the Pb-free glass barrier ribs prepared therefrom. More particularly, it relates to an environmentally benign Pb-free glass composition for barrier ribs of a PDP in which the etching rate is fast and the barrier ribs can be prepared with high density and precision, and a plasma display panel comprising the Pb-free glass barrier ribs prepared therefrom.  
     BACKGROUND OF THE INVENTION  
      A PDP is a display device using a plasma phenomenon. A discharge takes place when an electric potential difference over a certain level is applied to two electrodes separated spatially in a non-vacuum gaseous state. Such a discharge is called a gas discharge phenomenon.  
      A plasma display device is a flat display device using the gas discharge phenomenon to produce a visual display. Recently, generally used PDPs have been driven by a reflective alternating circuit, wherein a phosphor layer is formed in the discharge cells divided by barrier ribs provided on a rear substrate.  
      The rear substrate and a front substrate (for convenience, called a first substrate and a second substrate, respectively) are aligned substantially in parallel to each other with a predetermined gap between them to provide an assembly such as is provided for a vacuum fluorescent display (VFD), a field emission display (FED), and other flat display devices. The discharge cell is in a vacuum state defined by the substrates and sealed by an adhesive coated around the border of the assembly.  
      Sand Blast (SB) and Wet Chemical Etching (WCE) methods are mainly employed for forming the barrier ribs on the first substrate of a PDP. In the SB method, a colored material is coated on a glass substrate to a predetermined thickness and dried to form a mask having SB-resistant properties in some pattern, then the region other than the barrier ribs is removed by sand blasting, and sintered to prepare the preferred barrier ribs. The WCE method is a method in which different kinds of colored materials are coated on the glass substrate, sintered at a temperature higher than 500° C., and then an acid resistant mask pattern is formed and the colored materials are selectively etched by an acid-based liquid mixture to form the barrier ribs.  
      Presently, a mixture paste of a glass powder including lead-oxide at more than 50% by weight and an organic material is mainly used as the material for forming the barrier ribs. However, since lead-oxide is known to be harmful to humans and the environment, the use of lead oxide has shortcomings in that process efficiency is reduced and fabricating cost is increased because additional environmental protection equipment is necessary for producing and using the glass.  
      Furthermore, the etching rate of the glass powder for barrier ribs including the conventionally used lead-oxide is very low. Therefore, a process preparing the barrier ribs of a single layer is superior to a process of preparing the barrier ribs of two or more layers in that it is less expensive and can be produced at improved efficiency. The slope and the shape of the barrier ribs may be controlled by forming, sintering, and etching the barrier rib layer. In addition, barrier rib material with a low etching rate has shortcoming in that it is harmful to the environment due to the need to use a highly concentrated acid-based mixture during the chemical process.  
     SUMMARY OF THE INVENTION  
      In one embodiment of the present invention, a Pb-free glass composition is provided for barrier ribs for a PDP which is environmentally friendly, has a fast etching rate, and can be used to prepare barrier ribs with high density and precision without using lead oxide.  
      In another embodiment of the present invention, a PDP including the Pb-free glass barrier ribs is provided which is fabricated from the above mentioned Pb-free glass composition.  
      In one embodiment of the present invention, a Pb-free glass composition is provided for barrier ribs of a PDP which includes 20 to 70 wt % of ZnO; 10 to 50 wt % of BaO; 10 to 40 wt % of B 2 O 3 ; 0 to 20 wt % of P 2 O 5 ; 0 to 20 wt % of SiO 2 ; 0 to 20 wt % of Bi 2 O 3 ; 0 to 30 wt % of V 2 O 5 ; 0 to 10 wt % of one or more oxides selected from the group consisting of Na 2 O, Li 2 O, and K 2 O; 0 to 10 wt % of CaO; 0 to 10 wt % of MgO; 0 to 30 wt % of SrO; 0 to 20 wt % of MoO 3 ; 0 to 10 wt % of Al 2 O 3 ; 0 to 10 wt % of one or more oxides selected from the group consisting of Sb 2 O 3 , CuO, Cr 2 O 3 , As 2 O 3 , CoO, and NiO; and 0 to 10 wt % of TiO 2 .  
      According to an embodiment of the present invention, a Pb-free glass composition for use in producing barrier ribs for a PDP is provided. The composition includes ZnO, BaO, and B 2 O 3 ; and one or more oxides selected from the group consisting of P 2 O 5 , SiO 2 , Bi 2 O 3 , V 2 O 5 , Na 2 O, Li 2 O, K 2 O, CaO, MgO, SrO, MoO 3 , Al 2 O 3 Sb 2 O 3 , CuO, Cr 2 O 3 , As 2 O 3 , CoO, NiO, and TiO 2 .  
      The present invention also provides a Pb-free glass composition for barrier ribs of a PDP which includes 30 to 45 wt % of ZnO, 10 to 25 wt % of BaO, 20 to 35 wt % of B 2 O 3 , 5 to 20 wt % of P 2 O 5 , 0 to 2 wt % of Na 2 O, 0 to 2 wt % of Li 2 O, and 0 to 2 wt % of TiO 2 .  
      Furthermore, in an embodiment of the present invention, a plasma display panel is provided comprising: a) a first substrate and a second substrate aligned facing each other; b) address electrodes prepared on the first substrate with a dielectric layer covering the first substrate and the address electrodes, and discharge sustain electrodes formed on the second substrate with a dielectric layer covering the second substrate and the discharge sustain electrodes and a protecting layer covering the dielectric layer; c) barrier ribs which are positioned between the first substrate and the second substrate, prepared on the first substrate to divide a plurality of discharge cells, and which are Pb-free glass barrier ribs comprising ZnO, BaO, B 2 O 3 , and one or more oxides selected from the group consisting of P 2 O 5 , SiO 2 , Bi 2 O 3 , V 2 O 5 , Na 2 O, Li 2 O, K 2 O, CaO, MgO, SrO, MoO 3 , Al 2 O 3 Sb 2 O 3 , CuO, Cr 2 O 3 , As 2 O 3 , CoO, NiO, and TiO 2 ; and d) red, green, and blue phosphor layers which are prepared in the discharge cells divided by the barrier ribs. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
      The accompanying drawing, which is included to provide further understanding of the invention and is incorporated in and constitutes a part of this specification, illustrates an embodiment of the invention and together with the description serves to explain the principles of the invention.  
       FIG. 1  is an exploded perspective view showing an embodiment of a PDP according to the present invention. 
    
    
     DETAILED DESCRIPTION  
      Discharge cells on a first substrate are divided by a Pb-free glass composition of barrier ribs of a PDP in which ZnO, BaO and B 2 O 3  are main components, without lead oxide (PbO).  
      In one embodiment, the Pb-free glass composition includes ZnO, BaO, B 2 O 3 , and one or more oxides selected from the group consisting of P 2 O 5 , SiO 2 , Bi 2 O 3 , V 2 O 5 , Na 2 O, Li 2 O, K 2 O, CaO, MgO, SrO, MoO 3 , Al 2 O 3 , Sb 2 O 3 , CuO, Cr 2 O 3 , As 2 O 3 , CoO, NiO, and TiO 2 .  
      In another embodiment, the above-mentioned Pb-free glass composition includes ZnO, BaO, B 2 O 3 , P 2 O 5 , and one or more oxides selected from the group consisting of SiO 2 , Bi 2 O 3 , V 2 O 5 , Na 2 O, Li 2 O, K 2 O, CaO, MgO, SrO, MoO 3 , Al 2 O 3 , Sb 2 O 3 , CuO, Cr 2 O 3 , As 2 O 3 , CoO, NiO and TiO 2 .  
      The above-mentioned components affect, according to their contents, the glass transition temperature (Tg), softening temperature (Ts), thermal expansion coefficient (TEC), etching rate, dielectric constant, gelation degree, and hue of the Pb-free glass composition for barrier ribs of a PDP according to the present invention. The influences of the respective components on the properties of the Pb-free glass composition according to the present invention are described below.  
      ZnO is a glass modifier that lowers the Tg, dielectric constant, TEC, and gelation frequency, and improves the etching rate. If the content of ZnO is less than 20 wt % of the total amount of Pb-free glass composition, the etching rate is increased little. In the case of a ZnO content of more than 70 wt %, although the etching rate is increased, the composition cannot work as the barrier ribs due to its low dielectric constant. Therefore, the content of ZnO is preferably from 20 to 70 wt %, and more preferably from 30 to 45 wt %.  
      BaO is a dark colored glass modifier that lowers Tg of the Pb-free glass composition, and heightens the etching rate, dielectric constant, TEC, and gelation frequency. If the content of BaO is less than 10 wt % of the total amount of Pb-free glass composition, the etching rate is increased little. If the BaO content is more than 50 wt %, the shape stability of the PDP barrier ribs can be hindered due to an increase of TEC. Therefore, the content of BaO is preferably from 10 to 50 wt %, and more preferably from 10 to 25 wt %.  
      B 2 O 3  is a bright colored glass former that lowers the TEC of the Pb-free glass composition, and heightens Tg, the etching rate, and gelation frequency. If the content of B 2 O 3  is less than 10 wt % of the total amount of Pb-free glass composition, the etching rate is increased little. If the B 2 O 3  content is more than 40 wt %, Tg is increased excessively. Therefore, the content of B 2 O 3  is preferably from 10 to 40 wt %, and more preferably from 20 to 35 wt %.  
      P 2 O 5  is a bright colored glass former that lowers the dielectric constant of the Pb-free glass composition, lowers TEC and gelation frequency a little, and heightens Tg and the etching rate a little. If the content of P 2 O 5  is more than 20 wt % of the total amount of the Pb-free glass composition, the dielectric constant is excessively lowered. Therefore, the content of P 2 O 5  is preferably from 0 to 20 wt %, and more preferably from 5 to 20 wt %.  
      SiO 2  is a bright colored glass former that drastically lowers TEC and etching rate of the Pb-free glass composition, lowers gelation frequency, and heightens Tg. If the content of SiO 2  is more than 20 wt % of the total amount of the Pb-free glass composition, the etching rate is drastically lowered due to an excessive increase of Tg. Therefore, the content of SiO 2  is preferably from 0 to 20 wt %.  
      Bi 2 O 3  is a brown colored glass former or glass modifier that lowers Tg of the Pb-free glass composition, heightens TEC and the dielectric constant, heightens the etching rate a little, and has no influence on the gelation frequency. If the content of Bi 2 O 3  is more than 20 wt % of the total amount of the Pb-free glass composition, the shape stability of PDP barrier ribs can be hindered due to increase of TEC. Therefore, the content of Bi 2 O 3  is preferably from 0 to 20 wt %.  
      V 2 O 5  is a red colored glass former that lowers TEC and the etching rate of the Pb-free glass composition, heightens Tg, affects the hue of the composition by controlling of glass coordination number and surface tension, and has no influence on the gelation frequency. If the content of V 2 O 5  is more than 30 wt % of the total amount of the Pb-free glass composition, Tg is excessively increased and the composition is colored. Therefore, the content of V 2 O 5  is preferably from 0 to 30 wt %.  
      Na 2 O, Li 2 O, and K 2 O are yellow colored glass formers that lower Tg of the Pb-free glass composition to control sintering temperature, heighten the dielectric constant, and heighten TEC and the etching rate a little. If the content of the sum of the one or more oxides selected from Na 2 O, Li 2 O, and K 2 O, is more than 10 wt % of the total amount of the Pb-free glass composition, Tg may be drastically lowered and the shape stability of the PDP barrier ribs can be hindered due to the increase of TEC. Therefore, the content of such oxides is preferably from 0 to 10 wt %.  
      CuO, NiO, Cr 2 O 3 , As 2 O 3 , Sb 2 O 3 , or CoO is used as a glass additive to control coordination number, stability, and mobility of the Pb-free glass composition. The Pb-free glass composition for PDP barrier ribs according to the present invention may include one or more of these oxides, and it is preferable that the content of the oxide is from 0 to 10 wt % of the total amount of the Pb-free glass composition. If the content of the oxide is more than 10 wt %, excessive coloring and deterioration of glass stability occurs.  
      CaO is a bright colored glass modifier that heightens Tg of the Pb-free glass composition a little, lowers TEC a little, and lowers the etching rate and the gelation frequency. If the content of CaO is more than 10 wt % of the total amount of the Pb-free glass composition, the etching rate is lowered. Therefore, the content of CaO is preferably from 0 to 10 wt %.  
      MgO is a bright colored glass modifier that heightens Tg of the Pb-free glass composition a little, lowers TEC a little, and lowers the etching rate and the gelation frequency. In particular, it heightens the high temperature viscosity of the Pb-free glass composition. The content of MgO of the total amount of the Pb-free glass composition is preferably from 0 to 10 wt %.  
      SrO is a dark colored glass modifier that heightens Tg and etching rate of the Pb-free glass composition a little, lowers TEC a little, and heightens the dielectric constant and the gelation frequency. The content of SrO of the total amount of the Pb-free glass composition is preferably less than 30 wt %.  
      MoO 3  is a dark colored glass modifier that lowers Tg of the Pb-free glass composition, heightens the etching rate and the gelation frequency, and lowers TEC a little. The content of MoO 3  of the total amount of the Pb-free glass composition is preferably less than 20 wt %.  
      Al 2 O 3  is a white colored glass stabilizer that heightens Tg and the dielectric constant of the Pb-free glass composition, and lowers TEC, the etching rate, and the gelation frequency. If the content of Al 2 O 3  is more than 10 wt % of the total amount of the Pb-free glass composition, the etching rate is drastically lowered. Therefore, the content of Al 2 O 3  of the total amount of the Pb-free glass composition is preferably from 0 to 10 wt %.  
      TiO 2  is a white colored glass stabilizer that heightens Tg and the dielectric constant of the Pb-free glass composition, and lowers TEC, the etching rate, and the gelation frequency. If the content of TiO 2  is more than 10 wt % of the total amount of the Pb-free glass composition, the etching rate is lowered a little. Therefore, the content of TiO 2  of the total amount of the Pb-free glass composition is preferably from 0 to 10 wt %.  
      Therefore, in one embodiment of the invention, it is preferable that the Pb-free glass composition according to the present invention includes from 20 to 70 wt % of ZnO; from 10 to 50 wt % of BaO; from 10 to 40 wt % of B 2 O 3 ; from 0 to 20 wt % of P 2 O 5 ; from 0 to 20 wt % of SiO 2 ; from 0 to 20 wt % of Bi 2 O 3 ; from 0 to 30 wt % of V 2 O 5 ; from 0 to 10 wt % of one or more oxides selected from the group consisting of Na 2 O, Li 2 O, and K 2 O; from 0 to 10 wt % of CaO; from 0 to 10 wt % of MgO; from 0 to 30 wt % of SrO; from 0 to 20 wt % of MoO 3 ; from 0 to 10 wt % of Al 2 O 3 ; from 0 to 10 wt % of one or more oxides selected from the group consisting of Sb 2 O 3 , CuO, Cr 2 O 3 , As 2 O 3 , CoO, and NiO; and from 0 to 10 wt % of TiO 2 .  
      Furthermore, in another embodiment of the invention, it is preferable that the Pb-free glass composition according to the present invention includes from 30 to 45 wt % of ZnO; from 10 to 25 wt % of BaO; from 20 to 35 wt % of B 2 O 3 ; from 5 to 20 wt % of P 2 O 5 ; from 0 to 20 wt % of SiO 2 ; from 0 to 20 wt % of Bi 2 O 3 ; from 0 to 30 wt % of V 2 O 5 ; from 0 to 10 wt % of one or more oxides selected from the group consisting of Na 2 O, Li 2 O, and K 2 O; from 0 to 10 wt % of CaO; from 0 to 10 wt % of MgO; from 0 to 30 wt % of SrO; from 0 to 20 wt % of MoO 3 ; from 0 to 10 wt % of one or more oxides selected from the group consisting of Sb 2 O 3 , CuO, Cr 2 O 3 , As 2 O 3 , CoO, and NiO; from 0 to 10 wt % of Al 2 O 3 ; and from 0 to 10 wt % of TiO 2 .  
      Moreover, in another embodiment of the invention, it is preferable that the Pb-free glass composition according to the present invention includes a) from 20 to 70 wt % of ZnO, from 10 to 50 wt % of BaO, and from 10 to 40 wt % of B 2 O 3 ; and b) one or more oxides selected from the group consisting of i) first one or more oxides selected from the group consisting of from 0 to 20 wt % of P 2 O 5 , from 0 to 20 wt % of SiO 2 , from 0 to 20 wt % of Bi 2 O 3 , and from 0 to 30 wt % of V 2 O 5 , ii) second one or more oxides selected from the group consisting of from 0 to 10 wt % of one or more oxides selected from the group consisting of Na 2 O, Li 2 O, and K 2 O, from 0 to 10 wt % of CaO, from 0 to 10 wt % of MgO, from 0 to 30 wt % of SrO, and from 0 to 20 wt % of MoO 3 , and iii) third one or more oxides selected from the group consisting of from 0 to 10 wt % of one or more oxides selected from the group consisting of Sb 2 O 3 , CuO, Cr 2 O 3 , As 2 O 3 , CoO, and NiO, from 0 to 10 wt % of Al 2 O 3 , and from 0 to 10 wt % of TiO 2 .  
      In still another embodiment of the invention, it is preferable that the Pb-free glass composition includes; a) from 20 to 70 wt % of ZnO, from 10 to 50 wt % of BaO, from 10 to 40 wt % of B 2 O 3 , and from 5 to 20 wt % of P 2 O 5 ; and b) one or more oxides selected from the group consisting of i) first one or more oxides selected from the group consisting of from 0 to 20 wt % of SiO 2 , from 0 to 20 wt % of Bi 2 O 3 , and from 0 to 30 Wt % of V 2 O 5 , ii) second one or more oxides selected from the group consisting of from 0 to 10 wt % of Na 2 O, from 0 to 10 wt % of Li 2 O, from 0 to 10 wt % of K 2 O, from 0 to 10 wt % of CaO, from 0 to 10 wt % of MgO, from 0 to 30 wt % of SrO, and from 0 to 20 wt % of MoO 3 , and iii) third one or more oxides selected from the group consisting of from 0 to 10 wt % of one or more oxides selected from the group consisting of Sb 2 O 3 , CuO, Cr 2 O 3 , As 2 O 3 , CoO, and NiO, from 0 to 10 wt % of Al 2 O 3 , and from 0 to 10 wt % of TiO 2 .  
      In still another embodiment of the present invention, it is preferable that the Pb-free glass composition includes from 30 to 45 wt % of ZnO, from 10 to 25 wt % of BaO, from 20 to 35 wt % of B 2 O 3 , from 5 to 20 wt % of P 2 O 5 , from 0 to 2 wt % of Na 2 O, from 0 to 2 wt % of Li 2 O, and from 0 to 2 wt % of TiO 2 . But, it is more preferable that the contents of Na 2 O, Li 2 O, and TiO 2  are not all zero.  
      In yet another embodiment of the present invention, it is preferable that the Pb-free glass composition is a powder composition, and more preferable that the average diameter of the powder is from 0.1 to 10 μm. If the average diameter of the powder is less than 0.1 μm, the powders dispersed in the slurry state, in which deterioration thereof is small, become unstable. If the diameter is more than 10 μm, the shape and microstructure of the barrier ribs is not controllable. In addition, it is preferable that the glass softening temperature of the Pb-free glass composition ranges from 350 to 590° C. If the glass softening temperature is lower than 350° C., the shape of the barrier ribs is unstable. If higher than 590° C., the fabricating process becomes difficult due to deformation of the substrate glass.  
      In still another embodiment of the invention, it is preferable that TEC of the Pb-free glass composition is from 51×10 −7  to 91×10 −7 /° C. If TEC is out of the range, the substrate glass is deformed and the shape of the barrier ribs becomes non-uniform due to a difference of TECs. The dielectric constant of the Pb-free glass composition is from 6 to 12.  
      In another embodiment of the present invention, it is preferable that the Pb-free glass composition is fabricated by melting, dry air-cooling, dry grinding and crushing. A Pb-free glass composition fabricated according to the above methods has excellent densification and hue.  
      A binder and an organic solvent may be mixed with the Pb-free glass composition for PDP barrier ribs so that it is used as a paste for PDP barrier ribs, and if necessary, a filler or other additives may be mixed therein.  
      The Pb-free glass composition for PDP barrier ribs may be prepared by a conventional fabricating method of the glass powder, that is, by mixing, melting, rapid cooling, grinding, drying, filtering, and crushing. The fabricating method of the Pb-free glass composition for PDP barrier ribs includes; a) mixing ZnO, BaO, B 2 O 3 , and one or more of P 2 O 5 , SiO 2 , Bi 2 O 3 , V 2 O 5 , Na 2 O, Li 2 O, K 2 O, Sb 2 O 3 , CuO, Cr 2 O 3 , As 2 O 3 , CoO, NiO, CaO, MgO, SrO, MoO 3 , Al 2 O 3 , and TiO 2  in the aforementioned predetermined contents; b) melting the resulting mixture; and c) rapidly cooling the mixture, followed by grinding, filtering, and crushing.  
      The melting temperature in the b) step is preferably from 1000 to 1500° C., and more preferably from 1150 to 1350° C. The melting time is preferably from 10 to 60 minutes so that the respective components are uniformly mixed in the melted state. If the melting temperature is lower than 1000° C., the respective components are not uniformly mixed due to their high viscosity, and if higher than 1500° C., a change of ingredients occurs due to volatilization of some components.  
      The melted Pb-free glass composition is crushed after rapid cooling. The rapid cooling may be performed in a dry or wet state, and it is preferable to use water in the wet process. The crushing process after the rapid cooling may also be performed in a dry or wet state, and water or an organic solvent may be used in the wet crushing process. Preferred examples of the organic solvent including ethanol, methanol, ethyl acetate, toluene, and isopropyl alcohol. The aqueous or organic solvent may be used alone, or two or more may be mixed. For an organic solvent, the degree of gelation and hue after sintering of Pb-free glass powders is controllable.  
      It is preferable that dry rapid cooling and grinding processes are performed to improve the densification and hue of the Pb-free glass powders.  
      The ground Pb-free glass powders are filtered, dried, and crushed to prepare powders in which the average diameter is from 0.1 to 10 μm.  
      The PDP of the present invention comprises a) a first substrate and a second substrate positioned opposite each other; b) address electrodes prepared on the first substrate with a dielectric layer covering both the address electrodes and the first substrate, and discharge sustain electrodes prepared on the second substrate with a dielectric layer covering both the discharge sustain electrodes and the second substrate, the dielectric layer being covered by a protecting layer; c) barrier ribs which are positioned between the first substrate and the second substrate, prepared on the first substrate to divide a plurality of discharge cells; and d) phosphor layers of a red, a green, and a blue color prepared in discharge cells which are divided by the above barrier ribs.  
       FIG. 1  is an exploded perspective view showing an embodiment of a PDP according to the present invention, but it is understood that the PDP according to the present invention is not limited by the structure in the  FIG. 1 .  
      With reference to the drawing, in the conventional PDP, address electrodes  3  are prepared along a direction (Y direction of the drawing) on the first substrate  1 , and a dielectric layer  5  is prepared on the entire surface of the first substrate  1 , covering the address electrodes  3 . Barrier ribs  7  are prepared between the respective address electrodes  3  on the dielectric layer  5 , and if necessary, the barrier ribs  7  may be prepared either as open or closed types. Phosphor layers  9  of a red, a green, and a blue color are positioned between the respective barrier ribs.  
      Discharge sustain electrodes  13 , which consist of a pair of a transparent electrode  13   a  and a bus electrode  13   b , are formed going along a direction perpendicular to the address electrodes on one side of the second substrate  11  facing the first substrate  1 , and a transparent dielectric layer  15  and a protecting layer  17  are positioned on the entire surface of the second substrate, covering the discharge sustain electrodes  13 . The areas where the address electrodes  3  and discharge sustain electrodes  13  intersect form discharge cells, which are filled with a discharge gas.  
      With reference thereto, if an address voltage (Va) is applied between an address electrode and any one of the discharge sustain electrodes to perform address discharge, and thereafter if a sustain voltage (Vs) is applied between a pair of discharge sustain electrodes, vacuum ultraviolet light generated during sustain discharge excites the related phosphor layers  9  so that a visible light is emitted through the transparent front substrate (second substrate)  11 .  
      It is preferable that the barrier ribs  7  included in the above PDP are Pb-free glass barrier ribs prepared from the Pb-free glass composition for PDP barrier ribs.  
      Furthermore, barrier ribs of the PDP, if necessary, may further include a filler. The content of the filler is preferably less than 70 parts by weight based on 100 parts by weight of the Pb-free glass composition included in the Pb-free glass barrier ribs, and more preferably from 10 to 50 parts by weight. If the content of the filler is more than 70 parts by weight, densification of the barrier ribs may deteriorate after sintering.  
      Preferable examples of the filler include at least one selected from the group consisting of CrO, MnO 2 , CuO, MgO, Al 2 O 3 , ZnO, TiO 2 , mullite (3Al 2 O 3 .2SiO 2 ), and cordierite (Mg 2 Al 4 Si 5 O 18 ). But fillers according to the present invention are not limited by the above examples.  
      The dielectric constant of the PDP Pb-free glass barrier ribs according to the present invention, which does not include the above fillers, is from 6 to 12, and that of the PDP Pb-free glass barrier ribs according to the present invention, which includes the above fillers, is from 6 to 13.  
      The glass softening temperature of the Pb-free glass barrier ribs included in the PDP according to the present invention is from 350 to 590° C., and its TEC is from 51×10 −7  to 91×10 −7 /° C.  
      The fabrication method of the PDP comprises; a) coating a Pb-free glass composition paste for PDP barrier ribs prepared by mixing i) a Pb-free glass composition for the barrier ribs, ii) a binder, and iii) organic solvents, followed by sintering to form a barrier rib layer; b) coating a photosensitive film resist on the entire surface of the first substrate, covering the barrier rib layer; c) positioning a photo-mask with a predetermined pattern on the entire surface of the photosensitive film resist, followed by exposing and developing to result in patterning the photosensitive film resist; d) removing the region except at the barrier ribs depending on the patterned shape, to form barrier ribs; and e) coating phosphor layers on the first substrate as a rear substrate, including the barrier ribs, followed by assembling, sealing, degassing, gas injection, and aging to fabricate a PDP.  
      Among the steps for fabrication of the PDP, since a conventional method of PDP preparation can be used in step e), a detailed illustration thereof is not given. The barrier rib formation steps of a) to d) are mainly illustrated hereinafter.  
      The Pb-free glass composition, a binder, and organic solvents are mixed to prepare a Pb-free glass composition paste for PDP barrier ribs in step a). At this time, the content of each component is controllable according to the general method. Meanwhile, it is preferable that the content of solids included in the Pb-free glass composition paste is from 65 to 85 wt %. If the content of solids is less than 65 wt %, the microstructure does not become fine after film-forming, and if more than 85 wt %, it is difficult to achieve stable dispersion properties.  
      A general binder used for barrier rib preparation may be used as the binder, and is preferably at least one kind of polymer resin selected from the group consisting of acryl-based resins, epoxy-based resins, and ethyl-cellulose-based resin.  
      A general solvent used for barrier rib preparation may be used as the organic solvent, and is preferably at least one kind of organic solvent selected from the group consisting of butyl cellosolve (BC), butyl carbitol acetate (BCA), terpineol (TP), and texanol.  
      Furthermore, as necessary, a filler may be additionally mixed into the Pb-free glass composition paste for the PDP barrier ribs of step a). In this case, the filler is preferably mixed at less than 70 parts by weight based on 100 parts by weight of the Pb-free glass composition, more preferably at 10 to 50 parts by weight.  
      A preferable example of the filler may be at least one selected from CrO, MnO 2 , CuO, MgO, Al 2 O 3 , ZnO, TiO 2 , mullite (3Al 2 O 3 .2SiO 2 ), and cordierite (Mg 2 Al 4 Si 5 O 18 ).  
      When the Pb-free glass composition paste for the barrier ribs is prepared, the Pb-free glass composition paste is coated and sintered on the first substrate, on which address electrodes and a dielectric layer are formed, to form a barrier rib layer. The barrier rib layer may be formed as a single layer including the Pb-free glass composition for PDP barrier ribs according to the present invention. As necessary, barrier rib layers having different ingredients may also be included to form at least two layers. A photoresist is coated on the entire surface of the barrier rib layer such as in step b) after formation of the barrier rib layer. A dry film photoresist or liquid photoresist may be used for coating of the photoresist in step b).  
      A photomask with a predetermined pattern is positioned on the entire surface of the photoresist such as in step c) after coating of the photoresist, and is exposed and developed for patterning of the photosensitive film. The patterned shape is not limited to a specific shape, as it may be prepared as a stripe, closed, or waffle type according to the finally-formed barrier rib shape.  
      A region other than the barrier ribs is removed by chemical etching or sand blast methods after the patterning, and remaining photoresist film is removed to form barrier ribs. Preferably the chemical etching method is used for formation of barrier ribs.  
      A conventional etching method which uses acids such as hydrochloric acid, nitric acid, sulfuric acid, and hydrofluoric acid is employed for the chemical etching, and preferably the etching is done by an acidic aqueous solution including at least one acid selected from the above-mentioned acids at a concentration of from 0 to 10 wt %.  
      According to the chemical etching method, the etching rate of the Pb-free glass barrier ribs layer in the present invention is from 5 to 30 μm/min, preferably from 10 to 20 μm/min.  
      A phosphor layer is coated on the first substrate on which barrier ribs are formed by the above steps and the panel is assembled and sealed, followed by degassing, gas injection, and aging to prepare a PDP.  
      Preferable examples of the present invention are illustrated thereinafter, but the present invention is not limited by these examples.  
     EXAMPLE 1  
     Preparation of Pb-Free Glass Composition for PDP Barrier Ribs  
      20 wt % of BaO, 30 wt % of ZnO, 30 wt % of B 2 O 3 , 15 wt % of P 2 O 5 , and 5 wt % of K 2 O were mixed together by a ball mill, and the mixture was melted at 1200° C. in a blast furnace. The melted mixture was cooled rapidly using a twin roll, ground crudely by a disc mill, and then ground finely by a dry grinder. The dried mixture was crushed to prepare a Pb-free glass composition for PDP barrier ribs.  
     EXAMPLE 2  
     Preparation of a Pb-Free Glass Composition for PDP Barrier Ribs  
      A Pb-free glass composition for PDP barrier ribs was prepared by the same procedure as in Example 1, except that 30 wt % of BaO, 20 wt % of ZnO, 30 wt % of B 2 O 3 , 15 wt % of P 2 O 5 , and 5 wt % of K 2 O were mixed together.  
     EXAMPLE 3  
     Preparation of a Pb-Free Glass Composition for PDP Barrier Ribs  
      A Pb-free glass composition for PDP barrier ribs was prepared by the same procedure as in Example 1, except that 50 wt % of BaO, 20 wt % of ZnO, 10 wt % of B 2 O 3 , 5 wt % of P 2 O 5 , 10 wt % of SiO 2 , and 5 wt % of Na 2 O were mixed together.  
     EXAMPLE 4  
     Preparation of a Pb-Free Glass Composition for PDP Barrier Ribs  
      A Pb-free glass composition for PDP barrier ribs was prepared by the same procedure as in Example 1, except that 10 wt % of BaO, 20 wt % of ZnO, 35 wt % of B 2 O 3 , 20 wt % of P 2 O 5 , 5 wt % of SiO 2 , 5 wt % of Li 2 O, and 5 wt % of CaO were mixed together.  
     EXAMPLE 5  
     Preparation of a Pb-Free Glass Composition for PDP Barrier Ribs  
      A Pb-free glass composition for PDP barrier ribs was prepared by the same procedure as in Example 1, except that 25 wt % of BaO, 20 wt % of ZnO, 40 wt % of B 2 O 3 , 5 wt % of P 2 O 5 , 5 wt % of V 2 O 5 , and 5 wt % of MgO 5 wt % were mixed together.  
     EXAMPLE 6  
     Preparation of a Pb-Free Glass Composition for PDP Barrier Ribs  
      A Pb-free glass composition for PDP barrier ribs was prepared by the same procedure as in Example 1, except that 10 wt % of BaO, 70 wt % of ZnO, 10 wt % of B 2 O 3 , 5 wt % of K 2 O, and 5 wt % of SrO were mixed together.  
     EXAMPLE 7  
     Preparation of a Pb-Free Glass Composition for PDP Barrier Ribs  
      A Pb-free glass composition for PDP barrier ribs was prepared by the same procedure as in Example 1, except that 10 wt % of BaO, 45 wt % of ZnO, 10 wt % of B 2 O 3 , 5 wt % of Bi 2 O 3 , 20 wt % of SiO 2 , 5 wt % of Li 2 O, and 5 wt % of TiO 2  were mixed together.  
     EXAMPLE 8  
     Preparation of a Pb-Free Glass Composition for PDP Barrier Ribs  
      A Pb-free glass composition for PDP barrier ribs was prepared by the same procedure as in Example 1, except that 15 wt % of BaO, 30 wt % of ZnO, 10 wt % of B 2 O 3 , 20 wt % of Bi 2 O 3 , 15 wt % of P 2 O 5 , 5 wt % of K 2 O, and 5 wt % of MoO 3  were mixed together.  
     EXAMPLE 9  
     Preparation of a Pb-Free Glass Composition for PDP Barrier Ribs  
      A Pb-free glass composition for PDP barrier ribs was prepared by the same procedure as in Example 1, except that 15 wt % of BaO, 35 wt % of ZnO, 30 wt % of B 2 O 3 , 10 wt % of P 2 O 5 , 5 wt % of Na 2 O, and 5 wt % of Al 2 O 3  were mixed.  
     EXAMPLE 10  
     Preparation of a Pb-Free Glass Composition for PDP Barrier Ribs  
      A Pb-free glass composition for PDP barrier ribs was prepared by the same procedure as in Example 1, except that 10 wt % of BaO, 20 wt % of ZnO, 10 wt % of B 2 O 3 , 10 wt % of P 2 O 5 , 5 wt % of K 2 O, 30 wt % of V 2 O 5 , 5 wt % of CaO, 5 wt % of Al 2 O 3 , and 5 wt % of TiO 2  were mixed together.  
     EXAMPLE 11  
     Preparation of a Pb-Free Glass Composition for PDP Barrier Ribs  
      A Pb-free glass composition for PDP barrier ribs was prepared by the same procedure as in Example 1, except that 20 wt % of BaO, 35 wt % of ZnO, 25 wt % of B 2 O 3 , 15 wt % of P 2 O 5 , 2 wt % of Na 2 O, 2 wt % of Li 2 O, and 1 wt % of TiO 2  were mixed together.  
     EXAMPLE 12  
     Preparation of a PDP  
      70 parts by weight of the Pb-free glass composition prepared according to Example 1, 3 parts by weight of ethyl-cellulose, 3 parts by weight of butyl carbitol acetate and fillers consisting of 3 parts by weight of TiO 2 , 5 parts by weight of Al 2 O 3 , and 10 parts by weight of ZnO were mixed by a 3 roll mill and bubbles were removed to produce a paste of a Pb-free glass composition. The paste of the Pb-free glass composition was coated to a thickness of 300 to 400 μm on the first substrate, on which address electrodes and a dielectric layer were formed, and dried.  
      The dried mixture was sintered at 560° C. to form a barrier rib layer, and thereafter a dried film resist was coated, exposed, and developed to form a pattern.  
      The barrier rib layer on which the pattern of the dried film resist was formed was etched by using a 5 wt % hydrochloric acid solution, and cleaned to form barrier ribs. It was observed that the etching rate measured during the etching process was 10 to 20 μm/min.  
      100 parts by weight of a mixed solvent, in which the weight ratio of butyl carbitol acetate and terpineol was 3:7, were mixed with 6 parts by weight of a binder, ethyl-cellulose, to prepare a binder solution, and 40 parts by weight of a red phosphor (Y,Gd)BO 3 :Eu, a green phosphor ZnSiO 4 :Mn, and a blue phosphor BaMgAl 10 O 17 :Eu were respectively mixed with 60 parts by weight of the binder solution. Then the red, green, and blue phosphors were coated in discharge cells of the first substrate divided by the barrier ribs, dried, and sintered to form a phosphor layer.  
      After the second substrate was prepared by forming discharge sustain electrodes, a dielectric layer, and a protecting layer thereon, a panel including the first substrate and the second substrate was assembled, sealed, and then the PDP was produced by degassing, discharge gas injection, and aging.  
     COMPARATIVE EXAMPLE 1  
     Pb-Free Glass Composition for Barrier Ribs of a PDP  
      A marketed mother glass material (powder ceramic: DGC-562S) including lead-oxide (PbO) was used.  
     COMPARATIVE EXAMPLE 2  
     Preparation of a PDP  
      A PDP was produced by the same procedure as in Example 12, except that the barrier ribs were formed on the first substrate by using the marketed mother glass material according to Comparative Example 1.  
      The Tg of the mother glass was 490˜500° C., its TEC was 75˜85×10 −7 /° C., and its average diameter was 2˜3 μm. It was etched by using a 5 wt % hydrochloric acid solution, revealing an etching rate of less than 1 μm/min.  
      The Tg, TEC, and average diameter of the Pb-free glass composition prepared according to Example 1 and the marketed mother glass material of Comparative Example 1 are shown in Table 1.  
      The Tg and TEC were measured by a Dilatometer (DIL402C, Netzsch, Germany), and average diameters of the powders were measured by a size-analyzer (Mastersizer 2000, Malvern, UK).  
                                   TABLE 1                                           Average               Tg   TEC   Diameter   Etching Rate           (° C.)   (/° C.)   (μm)   (μm/min)                                                        Example 1   505   88 × 10 −7     2   15       Comparative   490˜500   75˜85 × 10 −7     2˜3   &lt;1       Example 1                  
 
      The Pb-free glass composition for PDP barrier ribs prepared according to Example 1 of the present invention is environmentally friendly since lead-oxide is not included, and as shown in Table 1, and it has similar thermal properties and a much better etching rate.  
      Furthermore, the Pb-free glass composition for PDP barrier ribs prepared according to Examples 2 to 10 also reveal similar properties to the Pb-free glass composition for PDP barrier ribs prepared according to Example 1.  
      The Pb-free glass composition for PDP barrier ribs of the present invention is environmentally friendly since lead-oxide is not included, and the consumed electric power can be decreased since its permittivity is lower than that of a conventional Pb-based glass composition. In addition, a wet chemical etching method can be employed to form patterns of barrier ribs due to the excellent etching rate, and there is an advantage of being able to use a low concentration etching solution during chemical etching. Moreover, the PDP including PB-free glass barrier ribs produced according to the present invention makes, with only a single layer, possible formation of barrier ribs pattern with high density and precision.  
      While the present invention has been described in detail with reference to the preferred 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.