Patent Publication Number: US-6992443-B2

Title: Plasma display panel

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a plasma display panel (PDP), and in particular to a plasma display panel having a closed delta cell structure and an electromagnetic interference (EMI) device. 
     2. Description of the Related Art 
     In a PDP, high voltage through a low pressure gas produces a large magnetic field, thus generating light. The electromagnetic emissions from the magnetic field are governed by Class A and Class B limits of Federal Communications Commission (FCC) standards. Thus, the PDP must be designed in compliance with FCC EMI testing and verification. In the U.S., the FCC requires compliance with Class A for PDP operated in industrial settings and Class B—the stricter standard—in PDP for home use. Additionally, due to high manufacturing costs, most conventional PDPs are designed for industry use. 
     Due to rapid development of the PDP market in recent years, manufacturing costs have decreased, and particularly when residential space is limited, PDP has gradually become a popular display apparatus. However, PDP meeting FCC EMI Class A is inadequate for home use since the high EMI current of the PDP may interfere with other household appliances such as a home stereo system. Additionally, high EMI level is harmful to health. Thus, home-use PDP must also meet the Class B requirement. 
       FIG. 1  is a schematic diagram showing an internal structure of a conventional PDP  100 ′. The conventional PDP  100 ′ comprises a filter substrate  10 ′, a front panel  20 ′ and a rear panel  30 ′. The filter substrate  10 ′ is disposed on the exterior edge of the PDP  100 ′, above the front panel  20 ′. The rear panel  30 ′ is disposed at the bottom position of  FIG. 1 . The filter substrate  10 ′ and the front panel  20 ′ are connected by a frame (not shown here) with a gap  15 ′ therebetween. 
     The front panel  20 ′ includes a front glass  22 ′, a pair of transparent electrodes  24 ′, a bus electrode  26 ′, a dielectric layer  25 ′ and a protective layer  28 ′. The rear panel  30 ′ includes phosphor  33 ′, barrier ribs  31 ′, a second dielectric layer  34 ′, a pair of address electrodes  35 ′ and a second substrate  36 ′. The barrier rib  31 ′ is formed above the address electrodes  35 ′ of the rear panel  30 ′. Many barrier ribs  31 ′ constitute a discharge region or cell. The conventional PDP  100 ′ can be implemented with different cell structures, such as a strip-cell structure, a grid-cell structure, and the delta-cell structure. 
     The filter substrate  10 ′ not only protects the panel from damage, but also blocks infrared rays to improve optical performance and prevent electromagnetic interference. The filter substrate  10 ′ has two types of structure. As shown in  FIG. 2A , the first filter substrate  10   a ′ comprises an anti-reflection film  12 ′ (hereinafter called the “AR film”), an EMI mesh film  11   a ′, a glass substrate  23 ′, and a near-infrared radiation (NIR) film  14 ′. The EMI mesh film  11   a ′ is an etching or conductive mesh film. The EMI mesh film  11   a ′ and other films are disposed on both sides of the glass substrate  23 ′. Next, the filter substrate  10 ′ is disposed on the front panel  20 ′ with a gap  15 ′ between the filter substrate  10 ′ and the front panel  20 ′, as shown in  FIG. 1 . The AR film  12 ′ reduces light reflection from the outside and absorbs infrared ray for better optical performance. 
     The EMI mesh film  11   a ′ of the first filter substrate  10   a ′ is only applicable for the strip- or grid-cell structure type PDP. The delta cell structure, especially the closed type, is the most advanced cell structure. If the EMI mesh film  11   a ′ is disposed in a PDP with closed-type delta cell structure, the EMI mesh film  11   a ′ acts as an optical grating, producing an adverse effect of visible lines on the display, interfering with users. As a result, if the conventional filter substrate  10 ′ is disposed in the PDP with closed-type delta cell structure, the PDP cannot pass Class B standards, and its display quality further suffers. 
       FIG. 2  is a schematic diagram showing another filter device  10   b ′ with a glass substrate  24 ′ and a silver (Ag) or indium tin oxide (ITO) sputtered thin film disposed thereon. Conventional filter device  10   b ′ may comprise ITO film. However, a more recently developed filter device  10   b ′ has silver sputtered film disposed on the glass substrate  23 ′ for better EMI and NIR blocking ability. 
     Generally, neither the resistance of silver nor ITO is high enough for sufficient EMI shielding. For example, ITO film has a low resistance of 150Ω. If the film is thicker, despite improved blocking ability, light penetration ability is decreased. Also, the PDP may only meet FCC Class A requirement, not FCC Class B. Thus, since the conventional EMI mesh film insufficient for blocking electromagnetic waves, the PDP with such EMI film is inappropriate for domestic use. 
     As mentioned above, PDP requires EMI mesh film to be disposed on a glass substrate  23 ′, and in a PDP with delta cell structure, use of the conventional EMI mesh film may only meet FCC Class A requirements. Hence, there is a need for a modified EMI mesh film for PDP, according to different cell structures, which can meet both FCC Class A and B requirements and improve display quality. 
     SUMMARY OF THE INVENTION 
     Thus, an object of the invention is to provide a PDP with a modified EMI film that can meet FCC Class B requirements even with delta cell structure. 
     Another object of the invention is to provide a PDP with effective EMI shielding without lowered display quality. 
     The present invention provides a PDP comprising a first panel, a second panel, and a filter device. The first panel has a first substrate, a plurality of first electrodes and a protective layer. The first electrode is disposed in the vicinity of the first substrate and the protective layer. The second panel has a second substrate, a plurality of barrier ribs, and a plurality of second electrodes. The barrier ribs and the second electrodes are formed on the second substrate. The barrier ribs create a plurality of cells. Center points of any three adjacent cells are connected in a delta configuration. The filter device includes a metallic mesh film, disposed on the first panel. The mesh film comprises wires intersecting each other. One wire and one side of the delta form an acute angle in a range of 0 to 15 or 45 to 60°. 
     A detailed description is given in the following embodiments with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
         FIG. 1  is a schematic diagram showing internal structure of a conventional PDP  100 ′; 
         FIG. 2A  is an exploded view of a conventional filter substrate; 
         FIG. 2B  is a side view of another conventional filter device; 
         FIG. 3  is a cross section of a plasma display panel according to the present invention; 
         FIG. 4  is a schematic view of another plasma display panel according to the present invention; 
         FIG. 5A  is a schematic view of a rectangular barrier rib structure viewed from Direction Y of  FIGS. 3 and 4 ; 
         FIG. 5B  is an enlarged view of  FIG. 5A  showing a dashed delta according to the present invention; 
         FIG. 6  is a local enlarged view of a metallic mesh film with respect to the dashed delta of  FIG. 5B ; 
         FIG. 7A  is a schematic view of a honeycombed barrier rib structure viewed from Direction Y of  FIGS. 3 and 4 ; 
         FIG. 7B  is an enlarged view of  FIG. 7A  showing a dashed delta according to the present invention; and 
         FIG. 8  is a local enlarged view of a metallic mesh film with respect to the dashed delta of  FIG. 7B . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Plasma display panels (PDP) are divided into DC and AC types. Recently, the most popular PDPs on the market are AC type. Thus, the present invention mainly focuses on discussion thereof. 
       FIGS. 3 and 4  are schematic views of plasma display panel  100  according to the present invention. The PDP  100  includes a plurality of cells, also referred to as discharge regions. For clear illustration, only one discharge region is shown in both figures. 
     As shown in  FIG. 3 , the PDP  100  includes a filter device  10 , a first panel  20 , and a second panel  30 . The filter device  10  is disposed on the top position of  FIG. 3 . The first panel  20  is disposed between the filter device  10  and the second panel  30 . The first panel  20  has a first substrate  22 , and the filter device  10  is disposed thereon. 
     The filter device  10  has a metallic mesh film  11 , an anti-reflection film  12 , and a near-infrared radiation film  14 . The metallic mesh film  11  comprises a plurality of wires intersecting each other. A detailed description of this intersection is discussed later. The anti-reflection film  12  and a near-infrared radiation film  14  are disposed on the metallic mesh film  11 . The anti-reflection film  12  and the near-infrared radiation film  14  are capable of blocking electromagnetic waves and near-infrared radiation, respectively. In this embodiment, the metallic mesh film  11  comprises copper wires. 
     The filter device  10  of the present invention can also be arranged as shown in  FIG. 4 , wherein the filter device  10   a  comprises another filter glass  23  and a metallic mesh film  11 . In this case, the metallic mesh film  11  is not directly disposed on the first panel  20 . The filter device  10   a  and the first panel  20  have a gap  15  therebetween. The filter device  10   a  also has an anti-reflection film  12  and a near-infrared radiation film  14 , respectively disposed on the metallic mesh film  11 . The anti-reflection film  12  is made of acrylic resin. 
     In the present invention, the metallic mesh film  11  is directly disposed on the first panel  20  or on an additional filter substrate  23 , with both arrangements providing full protection against EMI emissions. 
     The first panel  20  comprises a first substrate  22 , a pair of transparent electrodes  24 , a pair of auxiliary electrodes  26 , a first dielectric layer  25 , and a protective layer  28 . In  FIGS. 3 and 4 , viewer direction is indicated by an arrow Y. The glass substrate facing the viewer is first substrate  22 . The transparent electrodes  24  discharge and display. By controlling the discharge intensity of the transparent electrodes  24 , the intensity of the visible light generated by a UV-excitable phosphor  33  is controlled. Thus, light is emitted from the phosphor  33 , passing through the transparent electrode  24  and the first substrate  22 . The auxiliary electrodes  26  are disposed on the transparent electrodes  24  to increase conductivity thereof. The protective layer  28  is a magnesium oxide (MgO) layer disposed on the first dielectric layer  25 . The protective layer  28  is disposed on the electrodes  24 ,  26  to protect the first substrate  22  from damage, thereby preventing exhaustion of the electrodes  24 ,  26 . 
     The second panel  30  has phosphor  33 , barrier ribs  31 , a second dielectric layer  34 , address electrodes  35 , and a second substrate  36 . The second panel  30  is disposed below the first substrate  20 , namely, at the bottom position of  FIGS. 3 and 4 . The address electrode  35  receives the display data written thereonto. Since each address electrode  35  is linearly disposed, it must be arranged according to locations of the electrodes  24 ,  26  of the first panel  20  for correct writing thereto. The address electrode is also referred to as data electrode. Each intersection of an address electrode  35  and a pair of transparent electrodes  24  is a discharge region or cell  32 , formed by a plurality of barrier ribs  31  disposed above the address electrode  35  of the second panel  30 . The discharge cell may be rectangular or honeycombed. Thus, PDP uses UV light emitted by a gas arc in the discharge cell  32  to excite red (R), green (G) and blue (B) phosphorous materials  33 , finally generating visible light when the excited phosphorous materials  33  return to ground state. 
     In the present invention, the structure of the metallic mesh film  11  is the main factor in EMI blocking; thus, the following paragraph describes the angle required between the wires of the metallic mesh film  11  and the cell structure. By obtaining the optimum angle formed by the wires of the metallic mesh film  11  and the cell structure, the PDP according to the present invention can more thoroughly meet FCC Class B requirements. 
     As mentioned above, the discharge cells  32  can be arranged in a strip-cell structure, a grid-cell structure, or a delta-cell structure. Among these structures, the delta structure is the most recently developed. The PDP  100  according to the present invention has barrier ribs  31  forming the discharge cells  32  in a closed delta structure. As shown in  FIG. 5A , viewed from direction Y of  FIGS. 3 and 4 , the second panel  30  has a plurality of barrier ribs  31  forming rectangular discharge regions  32 .  FIG. 5B  is an enlarged view of  FIG. 5A  showing a dashed delta, formed by connecting center points of any three adjacent discharge regions  32 . Each center point is the vertex of the dashed delta with symbols of A, B, and C. The dashed delta has three sides X 1 , X 2 , and X 3 . 
       FIG. 6  is a local enlarged view of the metallic mesh film  11  with respect to the dashed delta of  FIG. 5B . The metallic mesh film  11  is formed by a plurality of wires  102   a ,  102   b . Each wire  102   a  and a side X 1  of the dashed delta form an angle θ. The preferred angle θ is found to be in a range from 0 to 15 or 45 to 60°. It has been experimentally found that an angle θ of 0 to 3 degrees provides optimized EMI shielding for PDP. 
     Each discharge cell  32  formed by the barrier ribs  31  can be honeycombed.  FIG. 7A  is a schematic view of honeycombed barrier rib  31  structure viewed from Direction Y of  FIGS. 3 and 4 .  FIG. 7B  is an enlarged view of  FIG. 7A  showing a dashed delta. As shown in  FIGS. 7A and 7B , center points A, B, C of any three adjacent honeycombed discharge cells  32  are connected to form a dashed delta having three sides X 1 , X 2 , and X 3 .  FIG. 8  is a local enlarged view of the metallic mesh film  11  with respect to the dashed delta of  FIG. 7B . One of the wires  102   a  of the metallic mesh film  11  and one side X 1  of the dashed delta form an angle θ. A preferred angle θ is found to be in a range from 0 to 15 or 45 to 60°. In several tests, it is shown that an angle θ of 0 to 3 degrees provide optimized EMI shielding for PDP. 
     Moreover, as mentioned, the metallic mesh film  11  is made of copper. The copper has resistance lower than that of silver or ITO, providing better EMI shielding. Thus, the PDP according to the present invention can pass FCC Class B standards. In addition, a PDP having a metallic mesh film with the designated angle θ of 0 to 15 or 45 to 60° can prevent visible lines. 
     While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.