Abstract:
A plasma display panel including a gas adsorption member is disclosed. An effort of gas adsorption is obtained sufficiently, and the presence of the gas adsorption member avoids problems at an exhausting operation in exhaust-baking step. The plasma display panel includes a pair of plates opposed to each other with an enclosed discharge space in between. The pair of plates refer to a front plate and a back plate, and at least one of the plates has a communication hole, around which the gas adsorption member having a hole is disposed.

Description:
This application is a continuation of U.S. patent application Ser. No. 10/524,885 filed Feb. 16, 2005, now U.S. Pat. No. 7,504,773, which is a National Phase of PCT International Application PCT/JP2004/006885 filed on May 14, 2004, all of which are incorporated by reference. 

   TECHNICAL FIELD 
   The present invention relates to a plasma display panel known as a video display device featuring of large and thin in size and light in weight. 
   BACKGROUND ART 
   A plasma display panel (hereinafter referred to simply as “PDP”) has drawn attention recently as a display panel excellent in visibility. The PDP can be grouped into AC-driven PDP and DC-driven PDP from the viewpoint of a driving method, or surface-discharge PDP and opposed-discharge PDP from the viewpoint of a discharge method. However, the present growing trend of higher resolution, larger screen and simpler fabrication makes the AC-driven and surface discharge PDP go mainstream. 
   The AC-driven and surface-discharge PDP comprises the following elements: 
   a front plate including plural display electrodes formed of scan electrodes and sustain electrodes; and 
   a back plate including plural data electrodes. 
   The front plate confronts the back plate with barrier ribs in between such that the display electrodes intersect with the data electrodes at right angles and a discharge space is formed therein. Discharge cells (a unit of emitting area) are formed at respective intersections of display electrodes and the data electrodes, and each one of the discharge cells includes a phosphor layer. 
   Application of a voltage between the display electrodes and the data electrodes generates discharge, and the phosphor layer is irradiated with ultraviolet rays resulting from the discharge, thereby producing visible light, which results in displaying a video. 
   In the steps of manufacturing the foregoing PDP, there is an exhaust-baking step for exhausting impurity gas outside a PDP. To be more specific, while a PDP is heated, the PDP is exhausted of air via an exhausting hole which is disposed on the back plate and communicates with the inside of the PDP. After this step, the discharge cells are filled with discharge gas. This procedure is disclosed at, e.g. pages 79-80, and pages 102-105 of “Everything about PDP” written by Messrs. Hiraki Uchiike and Shigeo Mikoshiba, and published from Industry Investigation Inc. on May 1, 1997. 
   A degasser (getter), i.e. gas adsorption member, is disposed in the vicinity of the exhausting hole for exhausting the PDP of air to a higher degree of vacuum in a shorter time, and the exhaust-baking step with the degasser results in more effective exhaust. In such a case, the degasser is placed in a space formed between the back plate and a pedestal of an exhausting pipe surrounding the exhausting hole. When the exhaust-backing step is carried out in the foregoing structure, the exhausting hole can be closed or clog with the degasser depending on a location of the degasser. As a result, the exhaust sometimes does not work functionally. 
   In case of such a trouble, the manufacturing operation of PDP must be temporarily halted, which causes an operation loss or reduces the yield because PDPs having insufficient degassing effect are produced. 
   The present invention addresses the problems discussed above, and aims to provide PDPs equipped with a degasser producing sufficient gas adsorption effort and free from problems at the exhaust-baking step. 
   DISCLOSURE OF THE INVENTION 
   The PDP of the present invention comprises the following elements in order to achieve the foregoing objectives: 
   a pair of plates opposed to each other to form a discharge space in between, at least one of which plates includes a communication hole that communicates with the inside of the PDP; and 
   a gas adsorption member having holes and being placed around the communication hole. 
   Since the gas adsorption member has holes, the PDP can be exhausted smooth regardless of a location of the gas adsorption member. As a result, quality PDPs are obtainable. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a plan view illustrating a schematic structure of a PDP in accordance with an exemplary embodiment of the present invention. 
       FIG. 2  shows a sectional perspective view illustrating a part of schematic structure of a display area of the PDP shown in  FIG. 1 . 
       FIG. 3  shows a sectional view illustrating a schematic structure around a communication hole of the PDP shown in  FIG. 1 . 
       FIG. 4  shows a sectional view illustrating a schematic structure of a PDP undergoing an exhaust-baking step in accordance with an exemplary embodiment of the present invention. 
       FIG. 5  shows a sectional view illustrating a schematic structure of the PDP sealed. 
       FIG. 6  shows a block diagram illustrating a schematic structure of a plasma video display device employing the PDP shown in  FIG. 1 . 
       FIG. 7A  shows a perspective view illustrating a shape of a gas adsorption member. 
       FIG. 7B  shows a perspective view illustrating another shape of a gas adsorption member. 
       FIG. 8  shows a sectional view illustrating another schematic structure of a PDP undergoing an exhaust-baking step in accordance with an exemplary embodiment of the present invention. 
   

   DESCRIPTION OF PREFERRED EMBODIMENT 
   An exemplary embodiment about a PDP of the present invention is demonstrated hereinafter with reference to the accompanying drawings. A structure of the PDP in accordance with the exemplary embodiment is described with reference to  FIG. 1  and  FIG. 2 .  FIG. 1  shows a plan view illustrating a schematic structure of the PDP in accordance with an exemplary embodiment of the present invention, and  FIG. 2  shows a sectional perspective view illustrating a part of schematic structure of a display area of the same PDP. 
   PDP  1  includes front plate  2  and back plate  3  opposed to each other with barrier ribs  4  in between. Front plate  2  comprises the following elements: 
   transparent and insulating glass substrate  5 ; 
   display electrodes  8  placed on a principal plane of glass substrate  5  and formed of scan electrodes  6  and sustain electrodes  7 ; 
   dielectric layer  9  covering display electrodes  8 ; and 
   protective layer  10  made of, e.g. MgO, and covering dielectric layer  9 . 
   Scan electrode  6  and sustain electrodes  7  are formed by laminating bus electrodes  6   b  and  7   b  on transparent electrodes  6   a  and  7   a  respectively. 
   Back plate  3  comprises the following elements: 
   insulating glass substrate  11 ; 
   data electrodes  12  formed on a principal plane of glass substrate  11 ; 
   dielectric layer  13  covering data electrodes  12 ; 
   barrier ribs  14  formed on dielectric layer  13  at places corresponding to the places between data electrodes  12 ; and 
   phosphor layers  14 R,  14 G and  14 B in red, green and blue respectively and formed between barrier ribs  4 . 
   The foregoing front plate  2  and back plate  3  are opposed to each other such that display electrodes intersect with data electrodes  12  at right angles and discharge space  16  is formed between the two plates with barrier ribs  4  therein. Those two plates are bonded and sealed with sealing member  18  at their periphery, i.e. outer area of video display area  17 . 
   Discharge space  16  is filled with at least one of such rare gasses as helium, neon, argon, and xenon as discharge gas at a pressure of approx. 66500 Pa (500 Torr). The intersections of data electrodes  12  and display electrodes  8 , which includes scan electrodes  6  and sustain electrodes  7 , work as discharge cells  12  each of which is counted as a unit of light emission. 
   To be more specific, in each one of discharge cells  12  to be lit, cyclic applications of a voltage between display electrode  8  and data electrode  12  as well as between scan electrode  6  and sustain electrode  7  of display electrode  8  produces discharge. Ultraviolet rays resulting from the discharge energizes phosphor layers  14 R,  14 G and  14 B, thereby producing visible light. Then a combination of lights and non-lights of respective discharge cells  12  allows displaying a video. 
   On the other hand, as shown in  FIG. 1 , glass substrate  11  of back plate  3  has communication hole  15  for exhausting discharge space  16  of air and filling discharge space  16  with the discharge gas.  FIG. 3  shows a sectional view illustrating a schematic diagram around communication hole  15 . As shown in  FIG. 3 , exhausting pipe  19  including pedestal  19   a  is bonded to substrate  11  with binding member  19   b  at the circumference of an exhausting hole, namely, communication hole  15 . In a space formed between pedestal  19   a  and substrate  11 , a degasser, i.e. gas adsorption member  20 , is prepared. Gas adsorption member  20  is not rigidly placed but left movable within the space. 
     FIG. 4  shows a sectional view illustrating a schematic structure of an exhaust-baking step of manufacturing PDP  1 . As shown in  FIG. 4 , exhausting pipe  19  is coupled to exhausting device  41  so that PDP  1  is exhausted of air into vacuum state.  FIG. 5  shows a schematic structure illustrating PDP  1  sealed. As shown in  FIG. 5 , after exhaust-baking is completed, PDP  1  is filled with the discharge gas via exhausting pipe  19 , then pipe  19  is sealed. 
     FIG. 6  shows a block diagram illustrating a schematic structure of a plasma video display device employing the foregoing PDP  1 . Plasma video display device  40  includes PDP  1  and PDP driver  46  coupled together. PDP driver  46  comprises controller  42 , sustain driver circuit  43 , scan driver circuit  44 , and data driver circuit  45 . In the case of driving plasma video displaying device  40 , sustain driver circuit  43 , scan driver circuit  44 , and data driver circuit  45  are hooked up to PDP  1 . Then a voltage is applied between scan electrode  6  and data electrode  12  at discharge cell  21 , which is to be lit following the control of controller  42 , for an address discharge to take place. After the address discharge, a voltage is applied between scan electrode  6  and sustain electrode  7 , so that a sustain discharge takes place. This sustain discharge generates ultraviolet rays in this discharge cell  21 , and phosphor layers  14 R,  14 G, and  14 B (cf  FIG. 2 ) are energized by the ultraviolet rays to emit light. Combination of lighting cells  21  and non-lighting cells  21  allows displaying a video. 
   In the manufacturing steps of PDP  1  discussed above, a pair of plates, namely, front plate  2  and back plate  3  opposed to each other, are bonded and sealed together. Then the sealed plates undergo the exhaust-baking step for exhausting PDP  1  of impurity gas. In this step, while being heated, PDP  1  is exhausted through communication hole  15  working as the exhausting hole. Then discharge gas is introduced, so that discharge cell  21  is filled with the discharge gas. As shown in  FIG. 4 , the exhaust-baking step exhausts PDP  1  of air to a vacuum condition with exhausting device  41  via communication hole  15  and exhausting pipe  19 , and heats PDP  1 . This step takes a rather long time among other steps of manufacturing PDP  1 . 
   In this exemplary embodiment, a degasser, i.e. gas adsorption member  20 , is disposed around communication hole  15  working as the exhausting hole. Gas adsorption member  20  is activated by the heat of the exhaust-baking step, and adsorbs the impurity gas in PDP  1 . This structure allows achieving a desirable degree of vacuum of PDP  1  in a shorter time than the case where only exhausting device  41  exhausts PDP  1  of air. As a result, the exhausting time can be shortened and a lead-time of the manufacturing steps can be shortened. 
   On the other hand, as shown in  FIG. 3 , exhausting pipe  19  is bonded to substrate  11  with binding member  19   b  such that its pedestal  19   a  surrounds communication hole  15 , i.e. the exhausting hole. The degasser, namely, gas adsorption member  20 , is placed in the space formed by pedestal  19   a  and substrate  11 . When the exhaust-baking takes place in the status shown in  FIG. 4 , gas adsorption member  20  smaller in size than the inner diameter of exhausting pipe  19  can clog pipe  19  or be sucked into exhausting device  41 . In order to overcome those problems, the outer diameter of member  20  is set larger than the inner diameter of exhausting pipe  19 , and hole  20   a  is disposed to member  20  as shown in  FIG. 7 . The foregoing structure allows pedestal  19   a  to regulate a location of gas absorption member  20  as shown in  FIGS. 3 and 4 , so that a possibility of pipe  19  clogging with member  20  is substantially reduced. Exhausting is carried out through hole  20   a  prepared in member  20 , so that problems about the exhausting can be reduced. 
   The size of gas adsorption member  20  refers to the maximum dimension of member  20 , e.g. distance D of a diagonal line shown in  FIG. 7B . The number of holes  20   a  and their shapes can be determined according to an actual structure, and a larger cross section area of hole  20   a  than the inner cross section area of pipe  19  can suppress a resistance against the exhausting. To be more specific, providing gas adsorption member with plural holes  20   a  as shown in  FIG. 7A  can increase the total area of holes  20   a  to a greater one than the inner cross section area of pipe  19 , thereby suppressing the resistance against exhausting. In other words, in the case of preparing plural holes  20   a  as shown in  FIG. 7A , the total cross section areas of holes  20   a  becomes larger than the inner cross section area of exhausting pipe  19 , so that the resistance against the exhausting can be reduced. 
   In the case of carrying out the exhaust-baking with exhausting pipe  19  being held upward as shown in  FIG. 8 , gas adsorption member  20  greater in size than the inner diameter of the exhausting hole, i.e. communication hole  15 , may clog communication hole  15  depending on a location of gas adsorption member  20 . If communication hole  15  clogs with member  20 , external exhausting device  41  slows down the exhausting, so that a given exhausting condition becomes difficult to hold. This problem can be also overcome by using adsorption member  20  having the structure shown in  FIG. 7 . To be more specific, gas adsorption member  20  is provided with hole  20   a , and member  20  greater in size than communication hole  15  prevents itself from dropping into hole  15 , and reduces the resistance against the exhausting. In the case of preparing plural holes  20   a  as shown in  FIG. 7A , the total cross section areas of holes  20   a  becomes larger than the inner cross section area of exhausting pipe  19 , so that the resistance against the exhausting can be reduced. 
   The foregoing structure of PDP  1  can be manufactured by the following method. PDP  1  having the construction shown in  FIG. 4  undergoes the exhaust-baking. Sealing member  18  and biding member  19   b  employ glass frit of which melting point is 390° C. Glass substrate  11  is provided with communication hole  15  communicating with the inside of PDP  1  and working as the exhausting hole. Exhausting pipe  19  employs a glass tube having a thermal expansion coefficient similar to that of glass substrate  11 , and includes pedestal  19   a . Gas adsorption member  20  employs Zr-based material, or it can be made of Ti-based material. Member  20  shapes like a ring having an outer diameter smaller than the inner diameter of pedestal  19   a  but greater than the inner diameter of exhausting pipe  19 . The inner diameter of the ring-shape, i.e. forming a hole, has an outer diameter greater than the inner diameter of communication hole  15  and that of exhausting pipe  19 . 
   Then an end of exhausting pipe  19  is coupled to external exhausting device  41 , and entire PDP 1  is heated in a heating oven. Retaining PDP  1  at 450° C. for 20 minutes softens sealing member  18  and binding member  19   b , then PDP  1  is cooled down to 350° C. for solidifying, so that PDP  1  is sealed again. After that, while PDP  1  is retained at 350° C. for two hours, exhausting device  41  starts exhausting PDP  1  of air into vacuum status, so that the exhaust-baking is carried out. Then PDP  1  is cooled down to an ambient temperature, and is filled with discharge gas formed of Ne (95%) and Xe (5%) at 67 kPa, thereby completing PDP 1 . 
   The steps discussed above prove that gas adsorption member  20  does not clog exhausting pipe  19  nor block communication hole  15 . On top of that, PDP  1  can be exhausted in a shorter time, i.e. PDP  1  is exhausted in less than half of the time that is needed for the manufacturing steps having no gas adsorption member  20  to exhaust PDP  1  of air. PDP  1  thus manufactured has display characteristics equivalent to that manufactured without member  20 . 
   In the manufacturing steps discussed above, gas adsorption member  20  placed in pedestal  19   a  is eventually activated by the heating, which softens binding member  19   b  for exhausting pipe  19  to be fixed to glass substrate  11 . Therefore, in order to maintain the degassing effort of member  20  more effectively, it is preferable to put member  20  in an impurity gas atmosphere or vacuum atmosphere during the heating. This preparation allows achieving the PDP of higher performance. 
   In the exemplary embodiment discussed above, a PDP is taken as an example; however, the embodiment is applicable to any other display panels as long as their manufacturing steps employ a gas adsorption member in sealing and exhausting. 
   INDUSTRIAL APPLICABILITY 
   The present invention provides reliable PDPs excellent in video-display quality, and the PDPs are useful as a display device of a wall-hanging TV or a large-size monitoring device.