Patent Application
20100056010
The present invention relates to methods of manufacturing a plasma display panel (hereinafter referred to as PDP), which is a flat plate display device, used in a large size television, a public display, and the like, more specifically, to a method of manufacturing a PDP in which the periphery of a front plate and a rear plate of the PDP is sealed with frit glass.
Since the PDP realizes higher definition and larger screen, product commercialization towards a television receiver of 65 inches class and a large public display device is advancing, and products exceeding even 100 inches are also being commercialized. In particular, the PDP for television receiver is advancing towards application to full spec high vision in which the number of scan lines is greater than or equal to twice of that of the conventional NTSC method.
The PDP is configured by a front plate and a rear plate. The front plate is formed by a glass substrate made of sodium borosilicate glass manufactured through float method, a display electrode including transparent electrode and bus electrode in stripe form formed on one of the main surfaces, a dielectric layer serving as a capacitor that covers the display electrode, and a protective layer made of magnesium oxide (MgO) formed on the dielectric layer. The rear plate is configured by a glass substrate, address electrodes in stripe form formed on one of the main surfaces thereof, a base dielectric layer that covers the address electrode, a barrier rib formed on the base dielectric layer, and phosphor layers formed between each barrier ribs to emit light of red, green, and blue.
The front plate and the rear plate have the respective electrode forming surface side facing each other, and the periphery air tightly sealed by a sealing material. The exhaust of a discharge space partitioned by the barrier rib and enclosure of discharge gas (in the case of Ne-Xe, pressure of 53.2 kPa to 79.8 kPa) are performed through exhaust pipe, which exhaust pipe is locally heated and melted (chip off) to be air tightly sealed after enclosing the discharge gas.
The finished PDP realizes color image display by selectively applying picture signal voltage to the display electrode to cause discharge, and exciting each phosphor layer with ultraviolet light generated by such discharge to emit light of red, green, and blue.
Low melting point frit glass having lead oxide as the main component is generally used for the dielectric layer of the PDP and the sealing material. The frit glass includes amorphous frit glass that does not crystallize when heated and in which the amorphous property still remains, and crystallized frit glass that crystallizes when heated. Each material has merits and demerits, and thus is selected in view of matching with the manufacturing step in most cases. When the frit glass of either the crystallized type or the amorphous type serves as the sealing material, filler is first mixed and kneaded with organic solvent to prepare sealing material in paste form. The sealing material is arranged at the periphery of at least one of the substrates of the front plate and the rear plate using film thickness printing, ink jet, or an application device equipped with a dispenser. Next, tentative firing is performed at a predetermined temperature at which the frit glass will not completely soften, so that the front plate and the rear plate are assembled while facing each other, and sealing is carried out at a sealing temperature higher than the temperature of tentative firing.
Use of no-lead material referred to as “lead free” or “leadless” that does not contain lead component even for the PDP is desired in view of recent environmental problems. An example of phosphoric acid (phosphoric acid-tin oxide etc.) sealing material and bismuth oxide sealing material that does not contain lead component is disclosed as the sealing material (see e.g., patent document 1, patent document 2 and the like). However, water resistance tends to be inferior in the sealing material having as the main component low melting point glass of phosphoric acid-tin oxide proposed as the sealing material of no-lead compared to the lead oxide sealing material used conventionally, and air tightness of the PDP cannot be substantially maintained. To this end, the bismuth oxide sealing material is getting attention as the no-lead material.
In the above-described manufacturing step of the PDP, the phosphor layers are fired in a phosphor baking oven immediately after the phosphor layers are formed on the rear plate. Thereafter, the sealing material is arranged on the peripheral edge of at least one of the substrates of the front plate and the rear plate, the sealing material of the substrate arranged with the sealing material is tentatively fired, and then the temperature is raised to the sealing temperature higher than the tentative firing temperature to soften (melt) the sealing material for air tight sealing. The phosphor layers are thus fired over a plurality of times.
The number of steps can be reduced and the steps can be simplified if the firing process immediately after the phosphor layers are formed on the rear plate is omitted and the phosphor layers are fired in the process of tentative firing and the sealing process of the sealing material.
Although the softening point temperature barely changes with respect to the heating temperature in the sealing material made of the conventional lead frit glass, the softening point temperature changes with respect to the heating temperature in the no-lead sealing material having bismuth oxide frit glass as the main component. Therefore, defects arise in the subsequent sealing if the sealing material is tentatively fired at the usual phosphor layer firing temperature.
[Patent document 1] Unexamined Japanese Patent Publication No. 2004-182584
[Patent document 2] Unexamined Japanese Patent Publication No. 2003-095697
A manufacturing method of a PDP of the present invention is a method of manufacturing a plasma display panel including a sealing step of arranging a front plate formed with a display electrode, a dielectric layer, and a protective layer on a transparent substrate and a rear plate formed with an address electrode, a barrier rib, and a phosphor layer so as to face each other and sealing a periphery of the front plate and the rear plate with a sealing material, wherein the sealing step includes a sealing material application step of applying the sealing material to the rear plate, a tentative firing step of tentatively firing the applied sealing material, and a sealing and bonding step of arranging the front plate and the rear plate so as to face each other and sealing the plates by softening and melting the sealing material; and the sealing material is configured by a glass frit having bismuth oxide, with properties in that the softening point temperature changes with respect to the heating temperature and rate of change of the softening point temperature differs with respect to the heating temperature, as the main component, and the tentative firing temperature in the tentative firing step is set to a temperature lower by 10° C. through 60° C. from the temperature at which the rate of change changes.
According to such manufacturing method, air tight sealing between the front plate and the rear plate is reliably performed using the sealing material that does not contain lead component, and furthermore, firing of the phosphor layers can be performed with the tentative firing step of the sealing step, whereby the number of manufacturing steps is reduced and the PDP having high reliability is achieved taking environment into consideration.
The PDP according to the embodiment of the present invention is described in detail with reference to the drawings.
The basic configuration of the PDP is similar to the general alternating current discharge type PDP. As shown in
A pair of band shaped display electrode 4 including scan electrode 2 and sustain electrode 3 and light shielding layer 5 are arranged on front glass substrate 1 of front plate 22 in a plurality of columns parallel to each other. Dielectric layer 6 serving as a capacitor is formed on front glass substrate 1 so as to cover display electrode 4 and light shielding layer 5, and protective layer 7 containing magnesium oxide (MgO) is formed on the surface thereof.
A plurality of band shaped address electrodes 10 are arranged parallel to each other on rear glass substrate 8 of rear plate 23 in a direction orthogonal to scan electrode 2 and sustain electrode 3 of front plate 22, and covered with base dielectric layer 9. Barrier ribs 11 of a predetermined height for dividing discharge space 14 are formed on base dielectric layer 9 between address electrodes 10. Phosphor layers 12R, 12G, 12B that respectively emit light of red, blue, and green by ultraviolet light are sequentially applied and formed for every address electrode 10 in the groove between barrier ribs 11. A discharge cell is formed at a position where scan electrode 2 and sustain electrode 3, and address electrode 10 intersect, and the discharge cells having phosphor layers 12R, 12G, 12B of red, blue, and green lined in the direction of display electrodes 4 become the pixels for color display.
The method of manufacturing PDP 20 is described hereinafter. First, scan electrode 2 and sustain electrode 3, as well as light shielding layer 5 are formed on front glass substrate 1. Scan electrode 2 and sustain electrode 3 are respectively formed by transparent electrode 2a, 3a and metal bus electrode 2b, 3b. Transparent electrodes 2a, 3a and metal bus electrodes 2b, 3b are formed by patterning through photolithography method and the like. Transparent electrodes 2a, 3a are formed using thin film process etc., and metal bus electrodes 2b, 3b are solidified by firing paste containing silver material at a desired temperature. Light shielding layer 5 is formed through the method of screen printing paste containing black pigment or forming black pigment on the entire surface of the glass substrate and then performing patterning and firing through photolithography method.
Thereafter, the dielectric paste layer (dielectric material layer) is formed by applying dielectric paste on front glass substrate 1 through die coating method so as to cover scan electrode 2, sustain electrode 3, and light shielding layer 5. After applying the dielectric paste, the surface of the applied dielectric paste layer is leveled to become a flat surface by being left untouched for a predetermined time. The dielectric paste layer is then fired and solidified to form dielectric layer 6 covering scan electrode 2, sustain electrode 3, and light shielding layer 5. The dielectric paste is coating material containing dielectric material such as glass powder etc., binder and solvent. Protective layer 7 containing magnesium oxide (MgO) is formed on dielectric layer 6 through vacuum deposition method.
Display electrode 4 including scan electrode 2 and sustain electrode 3, light shielding layer 5, dielectric layer 6, and protective layer 7, which are predetermined components, are formed on front glass substrate 1 through the above steps, to complete front plate 22. Material containing lead is not used for each component of front plate 22 in the present embodiment of the present invention.
Rear plate 23 is formed in the following manner. First, material layer to become the component for address electrodes 10 is formed on rear glass substrate 8 through the method of screen printing paste containing silver material, method of forming a metal film on the entire surface and patterning through photolithography method etc., and then fired at a predetermined temperature to form address electrodes 10.
The base dielectric paste is applied on rear glass substrate 8 formed with address electrodes 10 through die coating method and the like so as to cover address electrodes 10 to form the base dielectric paste layer. Subsequently, the base dielectric paste layer is fired to form base dielectric layer 9. The base dielectric paste is coating material containing dielectric material such as glass powder, binder, and solvent.
The barrier ribs forming paste containing barrier rib material is applied on base dielectric layer 9 and then patterned to a predetermined shape to form a barrier rib material layer, and thereafter, fired to become barrier ribs 11. The method of patterning the barrier rib forming paste applied on base dielectric layer 9 includes photolithography method, sand blast method, and the like.
The phosphor paste containing phosphor material is applied on base dielectric layer 9 between adjacent barrier ribs 11 and the side surfaces of barrier ribs 11 on rear glass substrate 8 formed with barrier ribs 11 to form phosphor layers 12R, 12G, 12B. Rear plate 23 with predetermined components on rear glass substrate 8 is completed by firing phosphor layers 12R, 12G, 12B, but phosphor layers 12R, 12G, 12B are fired in a tentative firing step of sealing material 33 for sealing front plate 22 and rear plate 23 in the embodiment of the present invention. Materials containing lead are not used for each component of rear plate 23, similar to front plate 22.
A sealing step of air tightly sealing front plate 22 and rear plate 23 with respective electrode forming surface side facing each other at the periphery thereof with sealing material 33 is described below. In the embodiment of the present invention, the sealing step includes sealing material application step of applying and forming sealing material 33 at the peripheral edge of rear plate 23, tentative firing step of tentatively firing applied sealing material 33, and sealing and bonding step of arranging front plate 22 and rear plate 23 facing each other, and softening and melting sealing material 33 for sealing.
In the method of manufacturing the PDP according to the embodiment of the present invention, no-lead frit glass containing bismuth oxide (Bi2O3) is used as frit glass that does not contain low melting point lead component for sealing material 33. The paste sealing material in which frit glass, predetermined filler, resin and organic solvent are kneaded is used.
First, in the sealing material application step, sealing material 33 is arranged at a predetermined position on the peripheral edge of rear plate 23 using thick film printing, ink jet, or application device equipped with dispenser. Next, resin and organic solvent in the paste of sealing material 33 are removed in the tentative firing step, and the frit glass is slightly softened and tentatively fired at a predetermined temperature to fix the shape. Then, in the sealing and bonding step, front plate 22 and rear plate 23, which are arranged with respective electrode forming surface side facing each other, are entirely fired at a temperature higher than the tentative firing temperature in the tentative firing step, and the glass frit in sealing material 33 is softened so that front plate 22 and rear plate 23 are sealed and bonded. The firing process for phosphor layers 12R, 12G, 12B formed on rear plate 23 is simultaneously performed in the tentative firing step of sealing material 33 in the present invention, as previously described.
The filler has heat resistance property, and is used to adjust coefficient of thermal expansion of sealing material 33 and to control flowing state of the frit glass. In regards to the material thereof, in particular, cordierite, forsterite, β-eucryptite, zircon, mullite, barium titanate, aluminum titanate, titanium oxide, molybdenum oxide, tin oxide, aluminum oxide, silica glass etc. are preferably used alone or in combination. The sealing material may be laminated and formed in a sheet form without using thick film printing or application device in the sealing material application step of applying and forming sealing material 33.
In the sealing and bonding step of the sealing step, exhaust tube 31 arranged in exhaust narrow hole 30 provided at a predetermined position at the corner of rear plate 23 is fixed by softening and melting frit tablet 32 arranged at the periphery thereof, as shown in
After sealing and bonding front plate 22 and rear plate 23 and fixing exhaust tube 31, discharge space 14 partitioned by barrier rib 11 is vacuum exhausted by means of exhaust tube 31. Thereafter, discharge gas containing neon, xenon, and the like is enclosed from exhaust tube 31 at a predetermined pressure (e.g., pressure of 53.2 kPa to 79.8 kPa for Ne-Xe mixed gas). Exhaust tube 31 is then locally heated and melted (chip off) at an appropriate position to be closed so as to be air tightly sealed, thereby completing PDP 20.
PDP 20 completed with the above manufacturing method realizes color image display by selectively applying the picture signal voltage to display electrode 4 to cause discharge, and exciting each phosphor layer 12R, 12G, 12B by ultraviolet light generated by such discharge to emit light of red, green, and blue.
The sealing step of the manufacturing method of the PDP according to the embodiment of the present invention is described in detail below.
In the embodiment of the present invention, no-lead borosilicate frit glass containing at least bismuth oxide (Bi2O3) is used for sealing material 33. The composition of the no-lead frit glass containing bismuth oxide (Bi2O3) used herein is 70% by weight through 85% by weight of bismuth oxide (Bi2O3), 8% by weight through 10% by weight of zinc oxide (ZnO), 4% by weight through 6% by weight of boric acid (B2O3), 6% by weight through 8% by weight of aluminum oxide (Al2O3), and 1% by weight through 3% by weight of silicon oxide (SiO2) and magnesium oxide (MgO). In particular, the softening point temperature of the glass becomes difficult to lower when the amount of bismuth oxide (Bi2O3) is too small thus causing sealing defect, and reaction with silver (Ag) in display electrode 4 and address electrode 10 occurs, and in contrast, when too large thus easily foaming. Thus, the amount is preferably set in the range of 65% by weight through 80% by weight.
As shown in
As shown in
As shown in
In order to soften and melt the glass frit in which crystallization has advanced and the softening point temperature has risen so as to be sealed and bonded, the sealing temperature must be a higher temperature. However, increase in sealing temperature may adversely affect re-melting of the constituting materials such as glass and alignment of electrodes, barrier ribs, and the like. In particular, since the number of electrodes increases in the high-definition PDP for full spec high vision television in which the number of scan lines is twice or more of the conventional one, the affect thereof appears significantly if the tentative firing temperature of the sealing material is raised.
Furthermore, when attempting to re-melt the partially crystallized frit glass, in particular, when the screen size of the PDP 20 is large, in-plane evenness becomes difficult to ensure in the heating process and consequently, softened and melted state of the frit becomes uneven in the plane. For instance, at the sealing temperature or a temperature slightly higher than the conventional tentative firing temperature, softening cannot be sufficiently performed, and the gap between front plate 22 and rear plate 23 becomes larger than a predetermined gap, thereby degrading display performance etc. In the state where the frit glass is crystallized, adhesive bonding of front glass substrate 1 or rear glass substrate 8 and sealing material 33 becomes inadequate, and reliable air tightness cannot be ensured.
Therefore, in the present invention, the glass frit having bismuth oxide (Bi2O3) as the main component and in which the rate of change in the change of the softening point temperature changes according to the heating temperature is used for the sealing material, and the tentative firing temperature in the tentative firing step of the sealing step is set to a temperature lower by 10° C. through 60° C. from the temperature at which the rate of change changes.
That is, tentative firing is performed in the tentative firing temperature in the range of 480° C. through 430° C., which are temperatures lower by 10° C. through 60° C. from 490° C. or the heating temperature at which the rate of change changes as shown in
In FIG. 3, the heating temperature of 300° C. through 490° C. is shown with one approximate line so as to be rate of change A, but rate of change of the softening point temperature with respect to the heating temperature or the change thereof varies if lower than 430° C. Thus, softening and melting of the frit glass in the subsequent sealing process sometimes becomes uneven. The lower limit of the tentative firing temperature is thus set to 430° C. in the embodiment of the present invention.
When the sealing material using the conventional frit glass containing lead of the is used, a so-called simultaneous firing in which the tentative firing step in the sealing step and the firing step of the phosphor layer applied and formed on the rear plate are the same becomes possible since the softening point temperature does not change and is constant with respect to the heating temperature, as shown in
The glass frit containing bismuth oxide (Bi2O3) as the main component is used in the present invention, and the tentative firing temperature in the tentative firing step of the sealing step is set to lower than or equal to 490° C., specifically, between 430° C. and 480° C., as described above. The firing of the phosphor layers is aimed to completely remove the resin component and the organic solvent component contained in the applied phosphor layer. To this end, firing is performed in the temperature range of between 430° C. and 480°0 C. to adequately and reliably remove the resin component and the organic solvent component. The resin component and the organic solvent component contained in the applied phosphor layers become difficult to be completely removed at the temperature of lower than 430° C. Thus, the tentative firing temperature is set to the temperature between 430° C. and 480° C. to ensure the reliability of firing and the reliability of sealing and bonding for the reasons described above.
In the method of manufacturing the PDP according to the embodiment of the present invention, the tentative firing temperature in the tentative firing step of the sealing material is raised and set high to the temperature at which the phosphor layers can be fired. The phosphor layer firing step of phosphor layers 12R, 12G, 12B applied and formed on rear plate 23 and tentative firing step can be performed as the same heat process, that is, in simultaneous firing. As a result, the number of manufacturing steps is reduced, and PDP of high reliability is achieved taking environment into consideration.
Moreover, since the number of electrodes increases in high-definition PDP of full spec high vision television in which the number of scan lines is twice or more of the conventional one, properties and quality of the PDP are inevitably affected as the sealing temperature in the sealing step rises. However, according to the embodiment of the present invention, the sealing temperature can be set to the temperature range that does not affect the material of glass substrate etc., and alignment of the electrodes and barrier ribs even when the no-lead frit glass containing bismuth oxide (Bi2O3) is used.
In the above embodiment, exhaust tube 31 or frit tablet 32 may have a material composition that does not contain lead, similar to sealing material 33, and thus PDP is achieved that takes environment into consideration.
In a precise sense, the no-lead frit glass containing bismuth oxide (Bi2O3) used in the manufacturing method of the PDP according to the embodiment of the present invention described above is not completely leadless, and although lower than or equal to 500 PPM in analysis, a very small amount of lead is still detected. However, lead is assumed as not contained if lower than or equal to 10000 PPM in the regulation of EC-RoHS directive related to environment in Europe, and expressions such as “not contain lead” or “no-lead” are used in the embodiment of the present invention.
As described above, the PDP of the present invention realizes PDP having improved sealing reliability and excelling in display quality taking environment into consideration, and is effective in large screen display devices.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-051746 | Feb 2006 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2007/053736 | 2/28/2007 | WO | 00 | 7/25/2007 |
