Patent Application
20100176710
The present invention relates to a plasma display panel used for image display.
Recently, a plasma display panel (hereinafter referred to as “PDP”) has received attention as a color display device capable of having a large screen and being thin and light in weight.
An AC surface discharge type PDP typical as a PDP has many discharge cells between a front substrate and a rear substrate that are faced to each other. The front substrate has the following elements:
The front substrate and rear substrate are faced to each other so that the display, electrode pairs and the data electrodes three-dimensionally intersect, and are sealed. Discharge gas is filled into a discharge space in the sealed product. Discharge cells are formed in intersecting parts of the display electrode pairs and the data electrodes. In the PDP having this structure, ultraviolet rays are emitted by gas discharge in each discharge cell. The ultraviolet rays excite respective phosphors of red, green, and blue to emit light, and thus provide color display.
A subfield method is generally used as a method of driving the PDP. In this method, one field period is divided into a plurality of subfields, and the subfields at which light is emitted are combined, thereby performing gradation display. Each subfield has an initializing period, an address period, and a sustain period. In the initializing period, initializing discharge occurs in each discharge cell, and a wall charge required for a subsequent address discharge is formed. In the address period, address discharge is selectively caused in a discharge cell where display is to be performed, thereby forming a wall charge required for a subsequent sustain discharge. In the sustain period, a sustain pulse is alternately applied to the scan electrodes and the sustain electrodes, sustain discharge is caused in the discharge cell having undergone the address discharge, and a phosphor layer of the corresponding discharge cell is light-emitted, thereby displaying an image.
The PDP is manufactured by a front substrate preparing process, a rear substrate preparing process, a sealing process, an exhausting process, and a discharge gas supplying process. In the sealing process, the front substrate prepared in the front substrate preparing process is stuck to the rear substrate prepared in the rear substrate preparing process. In the exhausting process, gas is exhausted from the space inside the PDP. Since the front substrate is stuck to the rear substrate using frit in the sealing process, they are superimposed on each other and are fired at the temperature of a softening point of the frit or higher, for example, at about 440° C. to 500° C.
Impure gas such as water (H2O), carbon dioxide gas (CO, CO2), and hydrocarbon (CnHm) is exhausted from the frit or the like, and part of the impure gas is adsorbed into the PDP. The air inside the PDP and the impure gas are exhausted in the subsequent exhausting process. However, it is difficult to completely exhaust all gases including the impure gas adsorbed in the PDP, and some impure gas inevitably remains inside the PDP. Additionally, as the screen size and definition of the PDP have been recently increased, the remaining amount of the impure gas is apt to increase.
However, it is known that the material of the protective layer or phosphor reacts with the impure gas and its characteristic degrades. Especially, much water remaining inside the PDP adversely affects the discharge characteristic of the protective layer, reduces the breakdown voltage of the discharge cells, and causes a “bleeding” degradation of the image quality on the display screen, disadvantageously. When a still image is displayed for a long time, “burning into” is caused, namely the image becomes an afterimage, disadvantageously. The hydrocarbon reduces the surface of the phosphor, or degrades the light emission luminance of the phosphor, disadvantageously.
Therefore, it is one of important issues that the impure gas remaining inside the PDP, especially water and hydrocarbon, is reduced, the discharge characteristic is stabilized, and variation with time is suppressed. As a method of removing the impure gas, an attempt where water is removed by disposing an adsorbent such as crystalline aluminosilicate, γ activated alumina, or amorphous activated silica inside the PDP is disclosed in patent document 1, for example. An attempt where water is removed by disposing a magnesium oxide film in a region other than the image display region inside the PDP is disclosed in patent document 2. An attempt where hydrocarbon gas is removed by disposing an oxide or an adsorbent in a region other than the image display region inside the PDP is disclosed in patent document 3. Here, the adsorbent is produced by adding a platinum-group element as hydrocarbon decomposing catalyst to the oxide. The oxide is alumina (Al2O3), yttrium oxide (Y2O3), lanthanum oxide (La2O3), magnesium oxide (MgO), nickel oxide (NiO), manganese oxide (MnO), chrome oxide (CrO2), zirconium oxide (ZrO2), iron oxide (Fe2O3), barium titanate (BaTiO3), or titanium oxide (TiO2). Patent document 4 discloses an attempt where a metal getter such as zircon (Zr), titanium (Ti), vanadium (V), aluminum (Al), or iron (Fe) is disposed on the barrier rib in the PDP and an organic solvent is absorbed.
In spite of these attempts, it is difficult to sufficiently remove impure gas such as water, hydrocarbon, or organic solvent, and it is difficult to suppress the degradation of the protective layer and phosphor.
[Patent document 1] Japanese Patent Unexamined Publication No. 2003-303555
[Patent document 2] Japanese Patent Unexamined Publication No. H05-342991
[Patent document 3] International Publication No. 2005/088668 Brochure
[Patent document 4] Japanese Patent Unexamined Publication No. 2002-531918
The present invention addresses these problems, and provides a PDP that sufficiently removes impure gas such as water or hydrocarbon and suppresses the degradation of the protective layer and phosphor.
The plasma display panel has a front substrate including a plurality of display electrode pairs, a dielectric layer, and a protective layer, and a rear substrate including a plurality of data electrodes, a barrier rib, and a phosphor layer. The front substrate and rear substrate are faced to each other so that the display electrode pairs and the data electrodes intersect, and a hydrogen-absorbing material containing palladium inside is disposed.
PDPs in accordance with exemplary embodiments of the present invention will be described hereinafter with reference to the accompanying drawings.
In the first exemplary embodiment, hydrogen-absorbing materials 38 for selectively absorbing and storing hydrogen are disposed on phosphor layer 35.
In
Front substrate 21 and rear substrate 31 are faced to each other so that display electrode pairs 24 cross data electrodes 32 with a micro discharge space sandwiched between them, and the outer peripheries of them are stuck and sealed by a sealing material (not shown) such as frit. The discharge space is filled with discharge gas containing xenon (Xe), for example. The discharge space is partitioned into a plurality of sections by barrier rib 34. Discharge cells are formed in the intersecting parts of display electrode pairs 24 and data electrodes 32. The discharge cells discharge and emit light to display an image. The structure of PDP 10 is not limited to the above-mentioned one. For example, dielectric layer 33 may be eliminated, and barrier rib 34 may have a stripe shape.
Next, the material of PDP 10 is described. Each scan electrode 22 is formed by stacking narrow bus electrode 22b containing metal such as silver (Ag) on wide transparent electrode 22a made of conductive metal oxide in order to improve the conductivity. The conductive metal oxide used for transparent electrode 22a is indium tin oxide (ITO), tin oxide (SnO2), or zinc oxide (ZnO). Each sustain electrode 23 is similarly formed by stacking narrow bus electrode 23b on wide transparent electrode 23a. Dielectric layer 25 is made of bismuth oxide based low-melting glass or zinc oxide based low-melting glass. Protective layer 26 is a thin film layer made of alkaline earth oxide mainly containing magnesium oxide. Each data electrode 32 is made of a material that contains metal such as silver and has high conductivity. Dielectric layer 33 may be made of a material similar to that of dielectric layer 25, but may be made of a material in which titanium oxide is mixed so as to serve also as a visible light reflecting layer. Barrier rib 34 is made of a low-melting glass material, for example. For phosphor layer 35, BaMgAl10O17: Eu can be used as blue phosphor, Zn2SiO4: Mn can be used as green phosphor, and (Y,Gd)BO3: Eu can be used as red phosphor. However, the present invention is not limited to these phosphors.
Hydrogen-absorbing materials 38 for absorbing and storing hydrogen can be platinum-group powder of one or more of platinum (Pt), palladium (Pd), ruthenium (Ru), rhodium (Rh), iridium (Ir), and osmium (Os). Among them, palladium is especially preferable. Hydrogen-absorbing materials 38 may be compound of one or more of platinum, palladium, ruthenium, rhodium, iridium, and osmium and one of titanium (Ti), manganese (Mn), zirconium (Zr), nickel (Ni), cobalt (Co), lanthanum (La), iron (Fe), and vanadium (V). In this case, also, an alloy containing palladium is preferable.
As a method of dispersing hydrogen-absorbing materials 38 on phosphor layer 35, a spray method can be used. As a method of dispersing hydrogen-absorbing materials 38 in phosphor layer 35, the platinum-group powder is previously mixed when phosphor layer 35 is formed. Preferably, the grain size of the platinum-group powder is 0.1 to 20 μm, and the mixing ratio to powder of the phosphor is 0.01% to 2%. The filling factor of the phosphor in phosphor layer 35 is low, namely 60% or lower, so that the effect of absorbing and storing hydrogen is kept even when the platinum-group powder is dispersed in phosphor layer 35.
The thickness of dielectric layer 25 of PDP 10 in the present embodiment is 40 μm, and the thickness of protective layer 26 is 0.8 μm, for example. The height of barrier rib 34 is 0.12 mm, and the thickness of phosphor layer 35 is 15 μm, for example. The discharge gas is mixed gas of neon (Ne) and xenon (Xe), for example, the gas pressure of the discharge gas is 6×104 Pa, and the content of xenon is 10 vol % or more, for example.
Next, the function of hydrogen-absorbing materials 38 is described. A metal getter or an oxide getter is conventionally used for removing water or hydrocarbon, but such impure gas has a large molecular diameter and hence does not sufficiently infiltrate into the getter, and the adsorbing amount of the impure gas is restricted.
Inventors pay attention to the fact that discharging the PDP causes impure gas to be exhausted from the protective layer, barrier rib, and phosphor layer, and the water molecules and hydrocarbon molecules in the impure gas are decomposed into hydrogen atoms, oxygen atoms, and carbon atoms. The inventors pay attention to the fact that the platinum-group elements have a property of absorbing and storing much hydrogen, and consider that the water or hydrocarbon can be removed by making the platinum-group elements absorb and store hydrogen atoms of small radius.
The inventors prepare a PDP where the powder of the platinum-group elements or the alloy powder of the platinum-group elements and transition metal is applied to the upside of the phosphor layer, the top of the barrier rib, and the upside of the protective layer. Here, this application is performed using a printing method, a spray method, a photo-lithography method, a dispenser method, or an ink jet method. The platinum-group elements are platinum, palladium, ruthenium, rhodium, iridium, or osmium. The transition metal is titanium, manganese, zirconium, nickel, cobalt, lanthanum, iron, and vanadium. The powder of the platinum-group elements is kneaded with an organic binder as required, and is used in a paste form. The platinum-group elements are applied to a part where discharge occurs during image display of the PDP or near the part.
An image is displayed using the prepared PDP, and existence of “bleeding” and “burning into” is visually recognized for about 1000 hours. As a result, reduction of the image quality degradation by the “bleeding” and “burning into” can be recognized. Especially, when the powder containing palladium is used, it can be recognized that the image quality degradation hardly occurs. When the powder containing palladium is used, it can be also recognized that the light emission luminance of the phosphor hardly reduces. That is considered to be because the water molecules and hydrocarbon molecules are decomposed into hydrogen atoms, oxygen atoms, and carbon atoms, the platinum-group elements, especially palladium, absorb and store much hydrogen, and hence the water molecules and hydrocarbon molecules are significantly reduced though oxygen and carbon remain.
As is clear from this experiment, when the platinum-group elements, especially palladium, are used as hydrogen-absorbing materials 38, hydrogen-absorbing materials 38 absorb and store the hydrogen generated by decomposition following the discharge and hence can significantly reduce the water molecules and hydrocarbon molecules. Additionally, the discharge characteristic is stabilized, the variation with time is suppressed, and the luminance reduction of the phosphor can be suppressed.
In the first exemplary embodiment, hydrogen-absorbing materials 38 are dispersed on or in phosphor layer 35. However, the present invention is not limited to this. The exemplary embodiment where hydrogen-absorbing materials 38 are disposed at the other part is described.
PDP 10 of the second exemplary embodiment of the present invention differs from the first exemplary embodiment in that hydrogen-absorbing materials 38 are disposed on the surface of barrier rib 34, especially on the top of barrier rib 34, in the second exemplary embodiment.
The grain size of the platinum-group powder used as hydrogen-absorbing materials 38 in the second exemplary embodiment must be set so that a large distance does not occur between barrier rib 34 and protective layer 26, and is preferably 0.1 to 5 μm. The thickness of the platinum-group powder layer is also preferably 5 μm or smaller, and the platinum-group powder may be simply interspersed on the top of barrier rib 34.
Hydrogen-absorbing materials 38 are disposed on the top of barrier rib 34 in the second exemplary embodiment, but hydrogen-absorbing materials 38 may be disposed on the surface of barrier rib 34 other than the top of barrier rib 34. When barrier rib 34 has a porous structure, a similar effect can be obtained even if hydrogen-absorbing materials 38 are contained in barrier rib 34.
PDP 10 of the third exemplary embodiment of the present invention differs from the first exemplary embodiment in that hydrogen-absorbing materials 38 are disposed on protective layer 26 of front substrate 21 in the third exemplary embodiment.
Similarly to the second exemplary embodiment, the grain size of the platinum-group powder used as hydrogen-absorbing materials 38 in the third exemplary embodiment must be set so that a large distance does not occur between barrier rib 34 and protective layer 26, and is preferably 0.1 to 5 μm. The coverage factor at which the platinum-group powder covers protective layer 26 is preferably set to 50% or lower so as to prevent the platinum-group powder from disturbing the transmission of visible light.
As discussed in the first through third exemplary embodiments, hydrogen-absorbing materials 38 such as palladium are disposed in the PDP. In the first through third exemplary embodiments, impure gas such as water molecules and hydrocarbon molecules having a large molecular diameter is not adsorbed as it is, but hydrogen-absorbing materials 38 such as palladium for absorbing and storing much hydrogen generated by decomposition following the discharge are disposed inside the PDP to significantly reduce the water and hydrocarbon. As a result, the discharge characteristic is stabilized, the variation with time is suppressed, and the luminance reduction of the phosphor can be suppressed.
The specific numerical values or the like used in the first through third embodiments are just one example, and are preferably set to optimal values in response to the specification of the PDP or the specification of the PDP material.
As is clear from the above-mentioned descriptions, the present invention can provide a PDP that sufficiently removes impure gas such as water or hydrocarbon and suppresses the degradation of the protective layer and the phosphor.
The present invention is useful as a PDP, because it can sufficiently remove impure gas such as water or hydrocarbon and can suppress the degradation of the protective layer and the phosphor.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007 286985 | Nov 2007 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2008/003170 | 11/5/2008 | WO | 00 | 3/9/2009 |
