Patent Application
20110159772
The present invention relates to a method for manufacturing an AC-type surface discharge plasma display panel used for a plasma display device.
An AC-type surface discharge plasma display panel has become dominance in plasma display panels (hereinafter simply referred to as a panel). A panel contains a front plate and a back plate oppositely disposed with each other and a plurality of discharge cells therebetween. The front plate has a glass-made front substrate, display electrodes each of which is formed as a pair of a scan electrode and a sustain electrode, and over which, a dielectric layer and a protective layer are formed to cover the display electrodes. The protective layer not only generates initial electrons for stable discharge but also protects the dielectric layer from sputtering by ions generated by the discharge. The back plate has a glass-made back substrate, data electrodes, a dielectric layer for covering the data electrodes, barrier ribs, and phosphor layers. The front plate and the back plate are oppositely disposed and sealed with each other in a manner that the display electrodes and the data electrodes cross with each other via a discharge space formed inside. The discharge space is filled with discharge gas. Discharge cells are formed at positions where the display electrodes face the data electrodes. In the panel structured above, a gas discharge is generated selectively in each discharge cell, by which phosphors of red, green, and blue are excited. Color image display is thus attained (see patent literature 1).
In the panel, as described above, the protective layer not only generates initial electrons for stable discharge but also protects the dielectric layer from sputtering by ions generated by the discharge. That is, stabilizing the characteristics of the protective layer allows a panel to have excellent image display.
Patent literature 1: Unexamined Japanese Patent Publication No. 2003-131580
The present invention provides a method for manufacturing a panel having a front plate with the following components: a front substrate; display electrodes formed on the front substrate; a dielectric layer formed so as to cover the display electrodes; and a protective layer formed so as to cover the dielectric layer. In the method above, after the protective layer has been formed, the front plate is processed under moisture-free atmosphere only for the period where the front plate has a temperature of 400° C. or lower.
Hereinafter, a method for manufacturing a panel in accordance with an exemplary embodiment of the present invention will be described with reference to drawings.
Front plate 20 has glass-made front substrate 21, display electrodes 24 formed of scan electrodes 22 and sustain electrodes 23, dielectric layer 26, and protective layer 27. On front substrate 21, display electrodes 24, each of which is a pair of scan electrode 22 and sustain electrode 23, are formed in parallel with each other. Although
Dielectric layer 26 is formed so as to cover display electrodes 24, and protective layer is formed over dielectric layer 26. Protective layer 27 is a magnesium oxide (MgO)-based film made by sputtering or vapor deposition.
Back plate 30 has glass-made back substrate 31, data electrodes 32, dielectric layer 33, barrier ribs 34, and phosphor layers 35. On back substrate 31, a plurality of data electrodes 32 is formed in parallel with each other. Dielectric layer 33 is formed so as to cover data electrodes 32, and grid-like barrier ribs 34 having vertical ribs 34a and horizontal ribs 34b are formed on dielectric layer 33. In addition, phosphor layers 35 of red, green, and blue are formed on the surface of dielectric layer 33 and on the side surface of barrier ribs 34.
Front plate 20 and back plate 30 are oppositely disposed so that display electrodes 24 are located orthogonal to data electrodes 32. Discharge cells are formed at which display electrodes 24 face data electrodes 32. Front plate 20 and back plate 30 are sealed with low-melting-point glass at the peripheries outside the image display area in which the discharge cells are formed. The discharge space is filled with discharge gas.
As described above, panel 10 of the embodiment has front plate 20 provided with the following components: front substrate 21; display electrodes 24 formed on front substrate 21; dielectric layer 26 covering display electrodes 24; and protective layer 27 covering dielectric layer.
In manufacturing panel 10 with the structure above, protective layer 27 of front plate 20 is exposed to water (H2O) or carbon dioxide (CO2) in the following processes: a heating/baking process for degassing front plate 20 after protective layer 27 has been formed thereon by sputtering or vapor deposition, and a sealing process for sealing front plate 20 and back plate 30 with sealing material.
Magnesium oxide (MgO), which is the material of protective layer 27, easily reacts with water and carbon dioxide (CO2) and often undergoes a chemical change through the processes mentioned above, causing some problems below.
For example, through the reaction with water (H2O), magnesium oxide (MgO) can partially change into magnesium hydroxide (Mg(OH)2). If it occurs, resistance to sputtering of protective layer 27 can deteriorate, shortening the life of a panel as an image display device. As another case, through the reaction with carbon dioxide (CO2), magnesium oxide (MgO) can partially change into magnesium carbonate (MgCO3). This causes increase in discharge start voltage, which can invite serious reduction in luminance and shortened life as an image display device.
Conducting a study on the aforementioned inconveniencies, the inventors have acquired the findings below. As described above, binding with water (H2O) or carbon dioxide (CO2) changes magnesium oxide (MgO) as the material of protective layer 27 into magnesium hydroxide (Mg(OH)2) or magnesium carbonate (MgCO3), respectively. Even if it has occurred, application of heat with temperature exceeding 400° C. can break the bonding. That is, the material of protective layer 27 gets back to the original form as magnesium oxide (MgO). In an atmosphere with temperature exceeding 400° C., even if water (H2O) and carbon dioxide (CO2) are found there, they cannot bond with magnesium oxide (MgO). However, the temperature decreases to 400° C. or less, magnesium oxide (MgO) bonds with water (H2O) or carbon dioxide (CO2) and changes into magnesium hydroxide (Mg(OH)2) or magnesium carbonate (MgCO3).
The study shows that, for protecting magnesium oxide (MgO) of completed protective layer 27 from change in quality, it should be processed in an H2O-free or CO2-free atmosphere only for a period with a temperature of 400° C. or lower. When there is a period with temperature exceeding 400° C. somewhere in the manufacturing process, the H2O-free or CO2-free atmosphere should be maintained only for a period with a temperature of 400° C. or lower in the cooling period that follows the high-temperature period.
In the manufacturing process of panel 10, the heat history on front plate 20 after protective layer 27 has been formed is determined by the processes below for the purpose of protecting magnesium oxide (MgO) from change in quality. Each of
After protective layer 27 has been formed, sealing material is applied to front plate 20 and undergoes a binder-removal process where resin component of the sealing material is baked, prior to a sealing process where front plate 20 and back plate 30 are sealed with the sealing material.
According to the pre-baking process shown in
In period 3, only for a period with a temperature of 400° C. or lower in the cooling period, front plate 20 is kept in the H2O-free atmosphere or CO2-free atmosphere.
Employing the heat history profile above allows impurity gases, such as water and carbon dioxide, to be removed from protective layer 27 in period 2, at the same time, the heat history profile prevents the impurity gases from sticking again to protective layer 27 in the cooling period in period 3. As a result, front plate 20 undergoes the pre-baking process without degradation of magnesium oxide (MgO) of protective layer 27.
According to the binder-removal process shown in
In period 3, only for a period with a temperature of 400° C. or lower in the cooling period, front plate 20 is kept in the H2O-free atmosphere or CO2-free atmosphere.
In period 2, employing the heat history profile above allows resin component of sealing material to be baked, but also allows impurity gases, such as water and carbon dioxide, to be removed from protective layer 27. Further, in period 3, employing the profile prevents the impurity gases from sticking again to protective layer 27. As a result, front plate 20 undergoes the binder-removal process without degradation of magnesium oxide (MgO) of protective layer 27.
According to the sealing process shown in
In period 3, only for a period with temperature of 400° C. or lower in the cooling period, front plate 20 is kept in the H2O-free atmosphere or CO2-free atmosphere.
Employing the heat history profile above, in period 2, not only allows the resin material to have a proper temperature for sealing front plate 20 and back plate 30 with each other, but also allows impurity gases, such as water and carbon dioxide, to be removed from protective layer 27. Further, in period 3, employing the profile prevents the impurity gases from sticking again to protective layer 27. As a result, front plate 20 undergoes the sealing process without degradation of magnesium oxide (MgO) of protective layer 27.
After the completion of the sealing process, protective layer 27 has an exposure in only discharge cells divided by barrier ribs 34 inside panel 10, that is, the chance that protective layer 27 is exposed in the atmosphere outside panel 10 is slim. The structure having undergone the sealing process significantly retards degradation of magnesium oxide (MgO) of protective layer 27, compared to that before the sealing process.
After the sealing process above, the inside of panel 10 is evacuated of the air in an evacuation/baking process and then filled with discharge gas to complete panel 10. The processes above allows panel 10 to have stabilized characteristics of protective layer 27, enhancing the quality of image display.
According to the embodiment of the present invention, employing all of the pre-baking process, the binder-removal process, and the sealing process described with reference to
To prevent degradation of magnesium oxide (MgO) of protective layer 27, as described above, the front plate on which protective layer 27 has been formed is processed in an H2O-free atmosphere or in a CO2-free atmosphere. Specifically, the H2O-free or CO2-free atmosphere is maintained for only a period with a temperature of 400° C. or lower in the cooling process where the front plate is cooled down to room temperature after having undergone a period with temperatures exceeding 400° C. at which carbon dioxide (CO2) and water (H2O) cannot bond with magnesium oxide (MgO).
In other words, atmosphere control does not need for the temperature-increasing period from room temperature and the high-temperature period exceeding 400° C. but need only for the period with a temperature of 400° C. or lower in the cooling period. Employing gas for atmosphere control in the temperature-increasing period or high-temperature period often brings difficulty in temperature control. The atmosphere control of the embodiment is effective in eliminating the problem above.
The H2O-free atmosphere in the description means the atmosphere with humidity of nearly 0%, such as a moisture-free air atmosphere with a dew point of −40° C. or lower and a moisture-free nitrogen atmosphere with a dew point of −40° C. or lower.
According to the embodiment, it is important that front plate 10 on which protective layer 27 has been formed is processed in an H2O-free atmosphere or in a CO2-free atmosphere only for a period with a temperature of 400° C. or lower in the cooling period. Preferably, front plate 10 should be heated as high as exceeding 400° C. after protective layer 27 has been formed thereon, and in the subsequent cooling period, front plate 10 should be cooled down to room temperature in an H2O-free atmosphere or in a CO2-free atmosphere only for the period with a temperature of 400° C. or lower.
The CO2-free atmosphere described above means, for example, a moisture-free nitrogen atmosphere or a nitrogen atmosphere having at least following conditions: a dew point of −40° C. or lower and CO2 concentration of 0.1% or lower; more preferably, 0.001% or lower.
According to the method for manufacturing a panel of the embodiment, front plate 20 has the following heat history after protective layer 27 has been formed thereon; front plate 20 is cooled down to room temperature in the H2O-free or CO2-free atmosphere for only the period with a temperature of 400° C. or lower in the cooling process. This contributes to easy temperature control of front plate 20 in the heating process. At the same time, it is effective in preventing magnesium oxide (MgO) from degradation. As a result, this not only allows protective layer 27 to have enhanced resistance to sputtering, but also suppresses increase in discharge start voltage and therefore suppresses decrease in luminance. Conventionally, for removing H2O or CO2 from MgO, i.e., for degassing, the inside of a panel has been evacuated with application of heat exceeding 400° C. in the sealing process before being filled with discharge gas. According to the method of the present invention, however, the aforementioned characteristics of the panel is obtained by application of heat with temperatures between 100-300° C.
In the first exemplary embodiment, the description is given on protective layer 27 made of magnesium oxide (MgO) film by sputtering or vapor deposition. However, it is not limited to; even in a case where protective layer 27 is formed by coating magnesium oxide (MgO) particles, the effect similar to that described in the first exemplary embodiment is obtained by employing the pre-baking process (
In protective layer 27 having the particle-layer structure described above, an amount of water (H2O) or carbon dioxide (CO2) stuck to magnesium oxide (MgO) increases because of its increased surface area, which increases tendency to degradation of magnesium oxide (MgO). However, in this case, too, processing the front plate after the protective layer has been formed thereon with the heat history described above effectively removes water (H2O) or carbon dioxide (CO2) from magnesium oxide (MgO) and prevents reattachment of them to MgO. As a result, in protective layer 27 with a MgO-based particle-layer structure, degradation of MgO is significantly suppressed. An MgO-based nanocrystalline particle with an average particle diameter of 10-100 nm is a specific example of magnesium oxide (MgO) particles.
Hereinafter, a method for forming protective layer 27 made of the aforementioned nanocrystalline-particle layer will be described in detail. First, single-crystal particles with an average particle diameter of 10-100 nm (i.e., nanocrystalline particles) are formed by a gaseous-phase generation method. Specifically, the nanocrystalline particles are generated in a manner that magnesium is vaporized in a high-energy environment, such as plasma and electronic beams, and the magnesium vapor is instantaneously cooled by a cooling gas including oxygen gas (for example, argon gas). Next, magnesium-oxide paste is generated by mixing the nanocrystalline particles into a vehicle formed of 60 wt % terpineol, 30 wt % butyl carbitol acetate, and 10 wt % acrylic resin so that the paste and the vehicle are equivalent in weight. The magnesium-oxide paste is coated on dielectric layer 26 by screen printing or other heretofore known techniques. After that, the paste is dried and then baked so as to be formed into protective layer 27 made of nanocrystalline-particle layers with a thickness of 0.5-5 μm.
When protective layer 27 has the aforementioned nanocrystalline-particle layer structure, the baking process—where coated and dried magnesium-oxide paste is baked—is added to the pre-baking process, the binder-removal process, and the sealing process described in the first exemplary embodiment. In the baking process, too, employing the heat history profile shown in
In period 5 above, only for the period with a temperature of 400° C. or lower in the cooling period, front plate 20 is kept in the H2O-free atmosphere or CO2-free atmosphere.
Employing the heat history profile above not only allows magnesium-oxide paste to be baked but also allows impurity gases to be removed from protective layer 27. At the same time, this prevents reattachment of the impurity gases, such as water and carbon dioxide, to protective layer 27 in the cooling period in period 5. As a result, front plate 20 undergoes the baking process without degradation of magnesium oxide (MgO) of protective layer 27.
According to the embodiment of the present invention, employing all of the pre-baking process, the binder-removal process, the sealing process, and the baking process described above is most effective in enhancing the stability of characteristics of protective layer 27. That is, all the processes should preferably be employed for manufacturing panel 10 with excellent image display. However, it is also effective that making a choice—for example, employing only the sealing process as the final process—depending on circumstances.
Compared to the protective layer made of a magnesium-oxide thin film by sputtering or vapor deposition, employing the structure of the aforementioned nanocrystalline-particle layer contributes to cost-reduced protective layer 27. Besides, as an additional effect, an improvement in panel strength against impact is expected.
The method of the embodiment offers protective layer 27 formed of nanocrystalline-particle layer that enhances panel strength against impact, with degradation of magnesium oxide (MgO) suppressed. That is, the method of the embodiment minimizes the likelihood that magnesium oxide (MgO) is partially changed to magnesium hydroxide (Mg(OH)2) in a reaction with water (H2O) or that magnesium oxide (MgO) is partially changed to magnesium carbonate (MgCO3) in a reaction with carbon dioxide (CO2). No degradation in MgO enhances the resistance to sputtering of protective layer 27, providing the panel with long life as an image display device. Besides, the panel with the protective layer having the structure above has no increase in discharge start voltage and therefore no decrease in luminance.
The aforementioned structure of the embodiment imposes no specific limitation on each structure of the scan electrode and the sustain electrode; each of the electrodes may be formed of the structure where a bus electrode shaped into narrow-width stripes is disposed on a transparent electrode shaped into wide-width stripes, or may be formed differently.
According to the structure—where display electrode 24 is formed of bus electrodes 221, 222, 231, and 232—shown in
In the structure above, protective layer 27 has not a point contact with vertical ribs 34a but an area contact with ribs 34a as a result of deformed protective layer 27 pushed by vertical ribs 34a. By virtue of the area contact, a stress applied to vertical ribs 34a disperses, decreasing the risk of damage to vertical ribs 34a.
If the protective layer has high rigidity, it will make a point contact with the vertical ribs, exerting a large stress on the contact position, by which the vertical ribs can be damaged. If it occurs around a discharge gap, broken pieces of the vertical ribs can scatter inside the discharge cell. Besides, it can invite peel-off of the phosphor layers. These damages cause serious degradation in discharge characteristics of the discharge cell, resulting in abnormal discharge operations.
According to the embodiment, however, protective layer 27 is made of MgO-based nanocrystalline-particle layers having a thickness nearly the same as the difference in level caused by irregularities of the surface of dielectric layer 26. By virtue of the structure, on the position at which protective layer 27 makes contact with vertical ribs 34a, the surface of protective layer 27 has irregularities as a result of being pushed by vertical ribs 34a. This allows protective layer 27 and vertical ribs 34a to have an area contact, thereby protecting vertical ribs 34a from application of large stress, and therefore from damage.
As described above, employing nanocrystalline-partcle layers for protective layer 27 offers the following additional effects. Protective layer 27 with a flexible structure has an area contact—not a point contact—with vertical ribs 34a. That is, no increase in stress on vertical ribs 34, protecting it from damages.
Protective layer 27 may be formed of base protective layer 27a and particle layer 27b. Base protective layer 27a is made of MgO-based crystal particles with an average particle diameter of 10-100 nm. Particle layer 27b is an aggregated structure of a plurality of MgO single-crystal particles with particle diameter of 0.3-2 μm.
Particle layer 27b is formed in a manner that aggregated particles 29 of a plurality of MgO single-crystal particles 28 are stuck to base protective layer 27a (that is made of single-crystal particles 28 with an average particle diameter of 10-100 nm) so as to have uniform distribution over the entire surface.
Single-crystal particles 28 and aggregated particles 29 made of the aggregated single-crystal particles that satisfy the above conditions can be produced in the following manner. When a magnesium oxide (MgO) precursor, such as magnesium carbonate (MgCO3) and magnesium hydrate (Mg(OH)2), is baked to provide particles, the particle diameter can be controlled approximately in a range of 0.3 to 2 μm by setting a relatively high temperature of at least 1000° C. Further, baking the magnesium oxide (MgO) precursor provides aggregated particles 29 in which single-crystal particles 28 are aggregated or necked with each other.
Processing such structured protective layer with the heat history described in the present invention protects magnesium oxide (MgO) from degradation, allowing a panel to maintain high performance in electron emission and charge retention.
Specific values seen throughout the description and the drawings of the embodiment are cited merely by way of example and without limitation. They should be optimally determined according to characteristics and specifications of a panel.
The present invention is thus useful for providing a high-definition plasma display device with a large screen.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2008-288433 | Nov 2008 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2009/005968 | 11/10/2009 | WO | 00 | 4/26/2010 |
