Abstract:
A plasma display panel for multi-screen system comprising a front and a back dielectric plates; transparent and addressing electrodes orthogonally located between the plates; display cells defined by the mutually orthogonal electrodes; barrier ribs for separating and defining display cells from each other; and a very narrow sealing seam for sealing edge parts of the two plates. The sealing seam has a width ranging from about 0.3 mm to about 1.5 mm. The sealing material is a glass powder having a special composition that enables a low melting point. A concave groove accommodates the sealing material. The present invention prevents the image from missing between the adjacent units in the display matrix and eliminates the dark matrix border lines.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to plasma display panels and more particularly to a structure of a plasma display panel for multi-screen screen system in which the sealing seams are substantially narrowed, thereby reducing width of noticeable connected portion on the screen. 
     2. Description of the Related Art 
     An exemplary prior art plasma display panel (PDP) is shown in  FIG. 1 . This plasma display panel comprises a front glass plate, a back glass plate, sealing seams  3 , barrier ribs  9 , phosphor layer  10 , and display cells  11 . The front glass plat consists of transparent glass sheet  1 , transparent electrodes  4 , dielectric layer  5 , and protective layer  6 . The back glass plate consists of a glass sheet  2 , addressing electrodes  7 , and dielectric layer  8 . 
     The front plate and back plate are bonded together with low melting point glass to form a discharge gas space therebetween. To make four line of sealing seam on the inside surface of the plates along matrix border line, it is necessary to first coat or print the sealing seams  3  with a special sealing material comprising of SiO 2 , PbO, and B 2 O 3 . Consequently, after coating, there is a heat treatment process within the range of temperature of 400° C.–500° C. The front glass plate and back glass plate are then sealed to form a semi-finished assembly of the PDP. Next, the residual gas is drawn from the space between the front glass plate and the back glass plate. Finally, the inert gas is filled into the space to finish the PDP assembly. 
     Some disadvantages exist in prior art PDPs as illustrated in  FIG. 1 . The width of the sealing seam displayed on the edge part of the panel is hard to control in coating process and varies depending on the flowability of the glass powder. Consequently, the width of the peripheral edge of light-absent region on the plate is typically within the range of 10 mm–15 mm. It is a big width of the sealing seam. Unfortunately, this means that the light-absent area between adjacent units is noticeable to viewers, and there is a “mosaic” like appearance present on the screen, further degrading the images provided thereby. 
     SUMMARY OF THE INVENTION 
     Accordingly, in consideration of the disadvantages of PDPs exist in the art, a primary object of the present invention is to provide a multi-screen PDP having improved, narrower sealing parts. 
     The PDP for multi-screen system of the present invention has a web-less appearance. Special sealing material and construction of the present invention prevent the images from missing between the adjacent units in the display matrix, thereby advantageously eliminating the dark matrix border lines. 
     To accomplish the object, the present invention provides a new and inventive PDP comprising a front glass substrate (plate) having transparent electrodes, dielectric layer and protective layer, and a back glass substrate (plate) having addressing electrodes, dielectric layer, and barrier ribs (spacer partition wall). The transparent electrodes and addressing electrodes are orthogonally located between said plates. The transparent electrodes are parallel to each other and are arranged in the display region at a predetermined pitch. 
     The addressing electrodes have a similar arrangement. The transparent electrodes and the addressing electrodes form a so-called matrix structure. A peripheral portion of the electrode extends outwardly beyond the partition wall, which is the outer end. Both kinds of electrodes are bended and contacted with the peripheral side wall of the plates, extending from the peripheral side wall and turn to the bottom surface of the back plate. The electrodes of both kinds may be the belt-like electrodes. 
     Electrodes and barrier ribs separate and define display cells from each other. The cells between adjacent barrier ribs (spacer partition wall) have phosphor layers deposited within it. The barrier ribs also separate the front plate and the back plate to form a discharge space therebetween. 
     The front plate and back plates are bonded or sealed together with lower melting point glass powder. The lower melting point glass powder is heated under the confining temperature. In the sealing procedure, to improve the air-tightness, a concave groove that accommodates the sealing material may be used. The concave groove is constituted on the edge of inside surfaces of the plates, along a sealing seam between the two plates. 
     The sealing seam may have such a section characterized as having a shape of semi-circle, rectangular, triangle, or trapezoid. The sealing seam may occupy the space given by the front plate or on the back plate, or the both. The groove may have a depth from about 0.05 mm to about 2.0 mm from the side-wall of the PDP. The mouth of the groove opens outwardly. The open mouth may have a width from about 0.05 mm to about 0.5 mm. 
     The size of the back plate may be smaller than the size of the front plate from about 0.3 mm to about 1.5 mm when the sealing seam is arranged on inside surface along the edge of the front plate. The sealing material is embedded in the concave groove along the joint seams between the two plates by coating or screen-printing. The special sealing compositions comprises PbO, SiO 2 , B 2 O 3 , Al 2 O 3 , ZnO, CaO. The PbO ranges from about 50 to about 80 (wt.)%. The SiO 2  ranges from about 2 to about 20 (wt.)%. The B 2 O 3  ranges from about 10 to about 30 (wt.)%. The Al 2 O 3  ranges from about 2 to about 18 (wt.)%. The ZnO ranges from about 3 to about 10 (wt.)%. The CaO ranges from about 2 to about 25 (wt.)%. 
     The granularity of the glass powder with lower melting point ranges from 1μ to 10μ, and preferably about 5μ. 
     A method of manufacturing a plasma display panel according to the present invention comprises the following steps: First, preparing the front and back plates on the inside surface of the front plate, the back plate, or the both. A groove or part of the groove which is hollowed inwardly from the surface of peripheral side wall along the seam between the front and back plates may be worked on the side wall of the PDP. The front glass substrate is located at a display side of said panel. Second, set the transparent electrodes and addressing electrodes and their connection electrodes on the plates. Third, construct barrier ribs, dielectric layer, protective layer, and then depositing phosphor layer within the cell located on the back glass substrate. Fourth, seal the semi-finished assembly then draw off the residual gas from the space between front glass plate and back glass plate. After that, the inert gas is filled into the space to finish the work, forming an airtight PDP. 
     The sealing process has three steps, the first step is the construction of the sealing seam with lower melting point glass powder utilized as a filler of the groove through multi-overlapping to form a melting layer which has a width ranging from about 0.3 mm to about 1.5 mm and a thickness ranging from about 0.05 mm to about 0.2 mm. The multi-overlapping process may be carried out by utilizing screen-printing technology. Each print results in forming of a thickness ranging from about 0.01 mm to about 0.03 mm, preferably about 0.02 mm. 
     The second step of the sealing process is to clamp the front and back plates together with special tools holding them even up and tightly joined. The third step involves a heating process under a confining temperature of about 400° C. to about 480° C. The coating process may be optionally used in forming the melting layer. 
     Still further objects and advantages of the present invention will become apparent to one of ordinary skill in the art upon reading and understanding the detailed description of the preferred embodiments and the drawings illustrating the preferred embodiments disclosed hereinafter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an exemplary prior art PDP. 
         FIG. 2  is a diagrammatic perspective view of the PDP of the first embodiment of the present invention. 
         FIG. 3  is a diagrammatic sectional view of  FIG. 2 . 
         FIG. 4  diagrammatically shows the second embodiment of the present invention. 
         FIG. 5  diagrammatically shows the third embodiment of the present invention. 
         FIG. 6  diagrammatically shows the fourth embodiment of the present invention. 
         FIG. 7  diagrammatically shows the fifth embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention offers a solution to the above-mentioned problems and disadvantages exist in prior art PDPs. Accordingly, it is an object of the present invention to provide an image display device having a large screen composed of a plurality of display panels capable of displaying a natural image on a large screen without noticeable connected portion of the display panels. 
     Referring to  FIGS. 2 and 3 , there is shown a first embodiment of the plasma display panel in accordance with the present invention. This embodiment discloses a plasma display panel (PDP) with a very narrow sealing seam  3  which surrounds the peripheral edges at the joint seam and provides an airtight bonding between a front plate  1  and a back substrate  2  of the PDP for multi-screen system. The front glass substrate (or plate)  1  and the back glass substrate (or plate)  2  are separated from each other, forming a discharge space therebetween. 
     The discharge space is partitioned by a partition wall  9  into a number of pixels (display cells)  11 . The partition wall (barrier ribs)  9  is in the form of a grid located between the front and the back glass substrates  1  and  2 . Each of the pixels  11  is defined by the front glass substrate  1 , the back glass substrate  2 , the partition wall  9 , and electrodes  4  and  7  as discussed below. The pixels  11  are separated from one another by the partition wall  9 , i.e., the barrier ribs separate and define display cells from each other. 
     The electrodes  4  and  7  are located between the plates  1  and  2  and are mutually orthogonal. The transparent electrode  4  is formed directly on the front plate  1 . The addressing electrodes  7  are arranged on the back substrate  2 . The front plate  1  also has a dielectric layer  5  and a protective layer  6 . Thus, there are addressing electrodes  7  and dielectric layer  8 , barrier ribs  9  being arranged on the back substrate  2 . 
     In this embodiment, the transparent electrodes  4  are scanning electrodes and the addressing electrodes  7  are signal electrodes. These electrodes form display cells  11  which are separated by barrier ribs  9 . Phosphor  10  is located on back substrate  2  within each of the display cells (or pixels)  11 . A sealing seam  3  for sealing the edge of the two plates  1  and  2  is embedded in a concave groove  12  along the joint seams between the two plates  1  and  2 . The concave groove  12  has a section characterized as having a shape of trapezoid with its mouth opened outwardly. As illustrated in  FIGS. 4–7 , the section can have other shapes such as semi-circle, rectangular, triangle, and so on. 
     The size of the back plate may be smaller than the size of the front plate from about 0.3 mm to about 1.5 mm when the groove  12  is constructed on the front plate. A special lower melting point glass powder is utilized for sealing the front plate  1  and the back plate  2  together to form a PDP. Preferably, the sealing materials of the present invention adopt special compositions comprising PbO, SiO 2 , B 2 O 3 , Al 2 O 3 , ZnO, CaO. More specifically, the composition would have the following formulas: (A) PbO 80(wt.)%, SiO 2  about 2(wt.)%; B 2 O 3  about 11(wt.)%, Al 2 O 3  about 2(wt.)%, ZnO 3(wt.)%, CaO about 2(wt.)%; (B) PbO 65(wt.)% SiO 2  about 10(wt.)%, B 2 O 3  about 14(wt.)%, Al 2 O 3  about 3(wt.)%, ZnO 5 (wt.)%, CaO about 3(wt.)%; (C) PbO 50(wt.)%, SiO 2  about 20(wt.)%; B 2 O 3  about 18(wt.)%, Al 2 O 3 about 3(wt.)%, ZnO about 5(wt.)%, CaO about 4(wt.)%. 
     The groove  12  for accommodation of the sealing material may have such a section with a trapezoid shape. In some embodiments, the section has a depth from about 0.05 to about 2.0 mm. The groove  12  has a mouth that opens outwardly with its width ranging from about 0.05 mm to about 0.5 mm. The groove  12  may occupy a space on both of the inside surfaces of the front and back plates  1  and  2 . 
       FIG. 4  illustrates the second embodiment, which has a similar structure to the PDP of the first embodiment. The composition of the sealing material is different and the groove  12  for accommodating the sealing material may have its section in a half-trapezoid shape. In this case, the composition of the sealing material comprises the following formulas: (A) PbO about 80(wt.)%, SiO 2  about 2(wt.)%; B 2 O 3  about 11(wt.)%, Al 2 O 3  about 2(wt.)%, ZnO about 3 (wt.)%, CaO about 2 (wt.)%; (B) PbO about 65 (wt.)%, SiO 2  about 10(wt.)%, B 2 O 3  about 14(wt.)%, Al 2 O 3  about 3 (wt.)%, ZnO about 5(wt.)%, CaO about 3(wt.)%; (C) PbO about 50(wt.)%, SiO 2  about 20(wt.)%; B 2 O 3  about 18(wt.)%, Al 2 O 3  about 3(wt.)%, ZnO about 5(wt.)%, CaO about 4(wt.)%. The groove  12  occupies the space of the back plate  2  at its peripheral parts. 
       FIG. 5  shows the third embodiment, which has a structure similar to the PDP of the first embodiment. Here, the composition of the sealing material is different and the groove  12  for accommodating the sealing material may have its section in a semi-circle shape. In this case, the composition of the sealing material  3  has the following formulas: (A) PbO about 80(wt.)%, SiO 2  about 2(wt.)%; B 2 O 3  about 11(wt.)%, Al 2 O 3  about 2(wt.)%, ZnO about 3(wt.)%, CaO about 2(wt.)%; (B) PbO about 65 (wt.)% SiO 2  about 10(wt.)%, B 2 O 3  about 14(wt.)%, Al 2 O 3  about 3(wt.)%, ZnO about 5 (wt.)%, CaO about 3(wt.)%; (C) PbO about 50(wt.)%, SiO 2  about 20(wt.)%; B 2 O 3  about 18(wt.)%, Al 2 O 3  about 3(wt.)%, ZnO about 5(wt.)%, CaO about 4(wt.)%. The groove  12  occupies the space of both the front plate  1  and the back plate  2 . 
       FIG. 6  diagrammatically shows the fourth embodiment, which has a structure similar to the PDP of the first embodiment. Again, the composition of the sealing material as well as the construction of groove  12  for accommodating the sealing material are different. The composition of the sealing material may utilize the formulas presented in any aforementioned embodiments. The shape of the section of the groove  12  is rectangular. It occupies a space on both the inside surface of the front plate  1  and the back plate  2 . 
     Shown in  FIG. 7  is the fifth embodiment, which has a structure similar to the PDP of the first embodiment. Comparing with the first embodiment, the difference is at the composition of the sealing material  3  and the groove  12  for accommodating the sealing material  3 . The composition of the sealing material may utilize the formulas presented in any aforementioned embodiments. The shape of the section of the groove  12  for accommodating the sealing material is triangle. It occupies a space on both the inside surface of the front plate  1  and the back plate  2 . The size of the back plate  2  may be smaller than the size of the front plate  1  from about 0.3 mm to about 1.5 mm. 
     The invention has thus been shown and described with reference to the specific embodiments. However, the above mentioned embodiments has been disclosed only for illustrating usefulness of the plasma display panel in accordance with the present invention. Therefore, it should be noted that the present invention is in no way limited by the details of the illustrated structures. As one of ordinary skill in the art will appreciate, various changes, substitutions, and alterations could be made or otherwise implemented without departing from the principles of the present invention. Accordingly, the scope of the present invention should be determined by the appended claims and their legal equivalents.