JP2007103276A - Coating device, coating method, and manufacturing method of plasma display panel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coating device capable of stably discharging coating liquid for long time. <P>SOLUTION: On a process of forming a crystalline MgO layer of the PDP, a cooling device 511A, cooling the coating liquid 501 so that the temperature thereof becomes lower than boiling point of solvent by 30°C or more, is arranged on a coating liquid tank 511 storing coating liquid 501 prepared by dispersing MgO powder in the solvent by a sprat method. A layer of powdered-MgO crystal, to be turned into the crystalline MgO layer by baking, is formed by discharging the stored coating liquid 501 by a spray gun 514. The temperature of the flowing coating liquid 501 is kept lower than the boiling point of the solvent by 30°C until it is discharged. By the above, such a phenomenon that the MgO powder becomes easy to coagulate or separate in accordance with the increase of temperature can be prevented by a simple constitution, and an appropriate coating with stable discharging quantity can be performed. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention is a coating apparatus that discharges a coating liquid in which inorganic particles are dispersed in a solvent, a coating method, and a coating liquid containing magnesium oxide powder as a protective layer of a plasma display panel. The present invention relates to a method of manufacturing a plasma display panel formed by the method.

  The plasma display panel includes a front substrate and a rear substrate, which are a pair of flat glass substrates disposed to face each other through a discharge space, and a partition wall such as a cross-beam is provided on the inner surface of the rear substrate to form the discharge space. An image is displayed by dividing into a plurality of discharge cells and selectively emitting light in the plurality of discharge cells.

  On the inner surface side of the front substrate of such a plasma display panel, a plurality of display electrode pairs including a plurality of transparent electrodes opposed via a discharge gap and a bus electrode laminated on one end of these transparent electrodes, and these displays A plurality of black stripes provided between the electrode pairs, a dielectric layer covering the display electrode pairs and the black stripes, a protective layer covering the dielectric layers, and the like are provided.

  The protective layer prevents the dielectric layer from being sputtered by discharge and also serves as a secondary electron emission layer for generating discharge at a low voltage. Further, since light emission is observed from the front substrate side through the protective layer, transparency to visible light is also required. For this reason, magnesium oxide (hereinafter referred to as MgO) is widely used as a material for the protective layer due to characteristics such as a low sputtering rate, a high secondary electron emission coefficient, and transparency to visible light.

  Conventionally, as a method for forming such a protective layer with MgO, there is known a method in which a coating liquid in which MgO microcrystalline powder is dispersed in a solvent is sprayed onto a substrate by a spray method using a spray gun ( For example, see Patent Document 1).

  In the configuration described in Patent Document 1, MgO microcrystalline powder having a diameter of 1 to 2 μm is dispersed in ethyl alcohol as a dispersion solvent to form a suspension used for spraying. Then, the suspension and high-pressure air for atomization are supplied to the spray gun, and the suspension is spray-coated on the glass substrate. Then, the glass substrate is heated to 200 ° C. to sufficiently evaporate ethyl alcohol. A configuration for obtaining an MgO film in which crystals are stacked is employed.

  Conventionally, as shown in FIG. 1 and FIG. 2, a coating apparatus that performs application by such a spray method is known. Here, FIG. 1 is a schematic view showing a conventional coating apparatus. FIG. 2 is a schematic view showing a coating apparatus having a conventional three-way valve.

A coating apparatus 800 shown in FIG. 1 is an apparatus that sprays a glass substrate K with a coating liquid LQ in which a single crystal MgO powder is dispersed in a solvent. The coating apparatus 800 is connected to the coating liquid tank 810 for storing the coating liquid LQ, and is connected to the coating liquid tank 810 via a pipe 811 so as to suck the coating liquid LQ in the coating liquid tank 810. A liquid feed pump 820 and a spray gun 830 that is connected to the liquid feed pump 820 via a pipe 821 and sprays the coating liquid LQ onto the glass substrate K are provided.
In such a coating apparatus 800, only when spray coating is performed, the liquid feed pump 820 is driven to supply the coating liquid LQ to the spray gun 830.

  A coating apparatus 900 shown in FIG. 2 is an apparatus that sprays a glass substrate K with a coating liquid LQ in which a single crystal MgO powder is dispersed in a solvent, like the coating apparatus 800 shown in FIG. The coating apparatus 900 is connected to the coating liquid tank 910 for storing the coating liquid LQ and the coating liquid tank 910 via a pipe 911 and sucks the coating liquid LQ in the coating liquid tank 910. A liquid feed pump 920, a three-way valve 930 connected to the liquid feed pump 920 via a pipe 921, and a coating liquid LQ connected to the three-way valve 930 via a pipe 931 to the glass substrate K. And a spray gun 940 for spray application. The three-way valve 930 is connected to the coating liquid tank 910 via a pipe 932.

  In such a coating apparatus 900, the liquid feed pump 920 is always driven, and only when spray coating is performed, the three-way valve 930 is switched to the spray gun 940 side to supply the coating liquid LQ to the spray gun 940. To do. On the other hand, while the spray application is not performed, the coating liquid LQ is circulated in the order of the coating liquid tank 910, the pipe 911, the liquid feed pump 920, the pipe 921, the three-way valve 930, the pipe 932, and the coating liquid tank 910. In this way, the coating liquid LQ is constantly circulated regardless of whether or not spray coating is performed, so that the single crystal MgO powder can be prevented from settling in each part of the apparatus.

  Here, in the case where the flow rate of the coating liquid LQ is slow in each pipe of the coating apparatus 800, 900, or in the part where the coating liquid LQ stays, the inclined part of each pipe, the part where the flow rate difference occurs in the valve, etc. Therefore, single crystal MgO tends to settle and stick.

Specifically, the sedimentation rate of the particles dispersed in the solvent is given by the following formula (1).
As can be seen from the formula (1), since the single crystal MgO has a true specific gravity of about 3 and the solvent specific gravity is usually 1 or less, the sedimentation speed v of the MgO powder increases. Easily settles in solvent. In particular, since the settling velocity v is proportional to the square of the particle diameter, the larger the particle diameter d of the MgO powder, the easier it is to settle.

[Formula]
v∝d ² × (ρ _p −ρ _l ) × g / μ (1)
v: terminal sedimentation velocity d: particle size ρ _p : particle density ρ _l : solvent density g: acceleration of gravity μ: solvent viscosity

  In addition, since MgO powder has high cohesiveness, MgO powder aggregates and grows when settling occurs in the coating liquid tanks 810 and 910 and in each pipe. Thereby, the aggregate of MgO powder adheres to the flow path of the coating liquid LQ, causing sticking or blockage.

  As described above, when the MgO powder is fixed or blocked in the flow path of the coating liquid LQ, the flow of the coating liquid LQ is hindered, and the discharge amount from the spray guns 830 and 940 is reduced or unstable. Become. As a result, the amount of MgO adhering on the glass substrate K is not constant, and there is a risk of uneven coating.

  In a plasma display panel, if a predetermined amount of single crystal MgO is not deposited with a sufficient thickness as a protective layer, the discharge delay becomes large, which may cause problems such as poor selection. In addition, when variation in the amount of MgO applied locally occurs, there is a risk of causing characteristic defects such as luminance unevenness.

JP-A-7-296718

  And in the structure of the said patent document 1, since the suspension is comprised by disperse | distributing the fine crystal powder of MgO in ethyl alcohol, MgO will become easy to precipitate and aggregate as mentioned above. As a result, the MgO powder is likely to be fixed or clogged in the suspension flow path, and the discharge onto the substrate may become unstable and the amount of MgO dispersed may vary.

In the case of the coating apparatus 800 shown in FIG. 1, since the flow of the coating liquid LQ does not flow when spray coating is not performed, the MgO powder tends to settle, and sticking / blocking easily occurs in the liquid path.
In the case of the coating apparatus 900 shown in FIG. 2, since the coating liquid LQ is constantly circulated, there is little occurrence of sticking / blocking in the circulating liquid path. Similarly, in order to disperse MgO, the coating apparatus 800 shown in FIG. 1 requires a large energy for applying a high shearing force to the coating liquid LQ, and the temperature of the coating liquid LQ due to friction between the MgO powder and the solvent. As a result, the MgO powder tends to settle and agglomerate. In both of the coating apparatuses 800 and 900, in the portion where the coating liquid LQ is likely to stay, the MgO powder is fixed, and it is likely to grow and become clogged. As a result, in the conventional coating apparatus 800 shown in Patent Document 1 and FIG. 1 and the coating apparatus 900 shown in FIG. May occur and ejection onto the substrate may become unstable.
As described above, when unevenness occurs in the coating amount of the coating liquid LQ, in the manufactured plasma display panel, the discharge delay / discharge probability varies depending on the cell. For this reason, there is a risk of non-uniform luminance and poor scanning.

  SUMMARY OF THE INVENTION In view of the above-described problems, an object of the present invention is to provide a coating apparatus, a coating method, and a plasma display panel manufacturing method capable of stably discharging a coating liquid for a long period of time. And

  The invention according to claim 1 is a coating liquid tank that stores a coating liquid in which inorganic particles are dispersed in a solvent, and a flow path that is connected to the coating liquid tank and distributes the coating liquid. The discharge means connected to this flow path for discharging the flowing coating liquid and the coating liquid flowing from the coating liquid tank to the discharge means are adjusted to a temperature lower by 30 ° C. or more than the boiling point of the solvent. And a liquid temperature adjusting means.

  The invention according to claim 6 is a coating method in which a coating liquid in which inorganic particles are dispersed in a solvent is supplied to a discharge means and discharged, wherein the coating liquid is discharged from the boiling point of the solvent by 30. The coating method is characterized in that the temperature is adjusted to a temperature lower than C.degree.

  According to a seventh aspect of the present invention, a pair of substrates opposed to each other through a discharge space, a plurality of electrode pairs formed on the inner surface of one of the pair of substrates, and the electrode pairs A plasma display panel manufacturing method for manufacturing a plasma display panel comprising a dielectric layer to be coated and a protective layer covering the dielectric layer, wherein the protective layer forming step for forming the protective layer comprises oxidizing Coating that forms a MgO powder layer that forms a protective layer by applying and dispensing a coating liquid in which magnesium (MgO) powder is dispersed in a solvent at a temperature lower than the boiling point of the solvent by 30 ° C. or more. It is a manufacturing method of the plasma display panel characterized by including a process.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
In this embodiment, the structure for manufacturing a plasma display panel in which the protective layer of the front substrate has a two-layer structure composed of a thin-film MgO layer and a crystalline MgO layer is illustrated. The protective layer is composed of a crystalline MgO layer. A single layer structure may be used.

[Configuration of plasma display panel]
Hereinafter, the structure of the plasma display panel to be manufactured will be described with reference to the drawings.
FIG. 3 is an exploded perspective view showing the internal structure of the plasma display panel according to the embodiment of the present invention. FIG. 4 is a front view schematically showing the plasma display panel. 5 is a cross-sectional view taken along line VV in FIG. 6 is a cross-sectional view taken along line VI-VI in FIG.

  In this embodiment, as shown in FIG. 3, reference numeral 1 denotes a plasma display panel (PDP). The PDP 1 is formed in, for example, a substantially planar rectangular shape, and displays an image using light emission by plasma discharge. It is a device to display. The PDP 1 includes a rear substrate 2 and a front substrate 3 which are a pair of substrates disposed to face each other via a discharge space H constituting an image display area.

The back substrate 2 and the front substrate 3 are sealed by providing seal frits (not shown) at their outer peripheral edges. The sealed interior of the space is in a reduced pressure state of, for example, about 6.7 × 10 ⁴ Pa (500 Torr), and the space is He—Xe (helium-xenon) or Ne—Xe (neon-xenon). The system is filled with inert gas.

  The back substrate 2 is formed in a planar rectangular shape with, for example, a sheet glass material. As shown in FIG. 3, a plurality of linear address electrodes 21, an address electrode protection layer 22 covering the address electrodes 21, and the address electrode protection layer 22 are integrated on the inner surface of the rear substrate 2. The barrier ribs 23 provided in this manner and the phosphor layers (24R, 24G, 24B) filled in the discharge cells 231 of the barrier ribs 23 are provided.

  Specifically, the address electrodes 21 are made of, for example, Al (aluminum) or the like, and are arranged at regular intervals substantially perpendicular to the longitudinal direction of the back substrate 2 as shown in FIGS. Yes. An address electrode lead portion (not shown) is formed at one end of each address electrode 21, and a voltage pulse from a column electrode driving portion (not shown) is applied to each address electrode 21 via the address electrode lead portion. ing.

  The address electrode protective layer 22 is formed of, for example, glass paste, and is provided over substantially the entire surface excluding the address electrode lead portion on the inner surface of the back substrate 2 as shown in FIGS. 3, 5, and 6. Yes. The address electrode protective layer 22 functions as a dielectric layer for preventing the wear of the address electrode 21 due to discharge and accumulating charges necessary for driving during panel driving. The above-described seal frit is provided on the outer peripheral edge portion of the address electrode protection layer 22.

  As shown in FIGS. 3 and 5, the partition wall 23 is formed in a substantially ladder shape with a glass paste having the same component as that of the address electrode protection layer 22, for example. On the address electrode protection layer 22, a plurality of linear gaps S (see FIG. 5) substantially orthogonal to the address electrodes 21 are provided in parallel with each other. The partition wall 23 divides the discharge space H into a plurality of sections, thereby forming a plurality of rectangular discharge cells 231. The partition wall 23 is set to have a predetermined height dimension from the base end portion to the top portion, and defines the gap dimension between the back substrate 2 and the front substrate 3.

  As shown in FIGS. 3, 5, and 6, the phosphor layers (24 R, 24 G, and 24 B) are composed of three primary colors of phosphor pastes of red (R), green (G), and blue (B). It is formed by sequentially filling the inside and firing it. These phosphor layers (24R, 24G, 24B) are excited by ultraviolet light generated in the respective discharge cells 231 and emit visible light of three primary colors of red (R), green (G), and blue (B). .

  The front substrate 3 constitutes the display surface of the PDP 1 and is formed, for example, in substantially the same shape with the same material as the rear substrate 2. On the inner surface of the front substrate, as shown in FIG. 3, a plurality of display electrode pairs 31 that are substantially orthogonal to the address electrodes 21 and arranged at regular intervals are provided between the display electrode pairs 31. A plurality of black stripes 32, a dielectric layer 33 covering the display electrode pairs 31 and the black stripes 32, a protective layer 34 covering the dielectric layer 33, and the like are provided.

  Specifically, as shown in FIGS. 4 and 5, the display electrode pair 31 includes a plurality of pairs of transparent electrodes 311a and 311b facing each other via a discharge gap G (see FIG. 4), and these transparent electrodes 311a and 311b. And a pair of linear bus electrodes 312a and 312b stacked on one end of each.

  As shown in FIG. 4, the transparent electrodes 311 a and 311 b are formed in a substantially T shape with a transparent conductive film such as ITO (Indium Tin Oxide), and are provided in pairs corresponding to predetermined discharge cells 231. Yes.

The bus electrodes 312a and 312b are provided to be stacked on the opposite ends of the pair of transparent electrodes 311a and 311b, respectively, with respect to the discharge gap G (see FIG. 4). A bus electrode lead portion (not shown) is formed at one end of each of the bus electrodes 312a and 312b, and a voltage pulse from a row electrode driving portion (not shown) is applied to each of the transparent electrodes 311a and 311b via the bus electrode lead portion. It has become so.
As shown in FIG. 5, such bus electrodes 312a and 312b include bus electrode black layers 313a and 313b made of a black inorganic pigment or the like provided on the transparent electrodes 311a and 311b, and the bus electrode black layers. It has a two-layer structure including main conductive layers 314a and 314b made of a metal material mainly composed of Ag (silver) or the like provided by being laminated on 313a and 313b.

  As shown in FIGS. 4 and 5, the black stripe 32 is formed in a straight line with the same material as the bus electrode black layers 313a and 313b. Visible light irradiated from the outside of the front substrate 3 is absorbed by the black stripe 32 and the bus electrode black layers 313a and 313b.

  As shown in FIGS. 5 and 6, the dielectric layer 33 is formed of, for example, glass paste or the like, and is provided to face the address electrode protection layer 22 of the back substrate 2. This dielectric layer 33 prevents wear of the display electrode pair 31 due to discharge during panel driving, and accumulates charges necessary for driving.

  As shown in FIGS. 3, 5, and 6, the protective layer 34 includes a thin film MgO layer 341 made of MgO (magnesium oxide) covering the entire inner peripheral surface of the dielectric layer 33, and the thin film MgO layer 341. It has a two-layer structure including a crystalline MgO layer 342 to be covered.

The thin film MgO layer 341 is formed by, for example, vapor deposition or sputtering. The crystalline MgO layer 342 is formed by a spray method using a coating apparatus 500 described later.
Such a protective layer 34 functions as a secondary electron emission layer for preventing the dielectric layer 33 from being sputtered by a discharge and generating a discharge at a low voltage.

[Configuration of coating equipment]
Hereinafter, the configuration of a coating apparatus for forming a crystalline MgO layer in the plasma display panel described above will be described with reference to the drawings.
FIG. 7 is a conceptual diagram showing a schematic configuration of the coating apparatus.

{Configuration of coating device}
In FIG. 7, reference numeral 500 denotes a coating apparatus. The coating apparatus 500 applies a coating liquid 501 having a predetermined composition, which will be described later in detail, to the above-described thin film MgO layer 341 by a spray method, and crystallization of PDP1 by firing. This is an apparatus for forming a single crystal MgO powder layer to be the MgO layer 342. And the coating apparatus 500 is provided with the coating part 510 which functions also as a coating apparatus, and the control apparatus 520. FIG.

  The coating unit 510 is configured to apply the coating liquid 501. The coating unit 510 includes a coating liquid tank 511, a distribution path 512, a switching valve 513, a discharge unit 514, and a return pipe 515.

The coating liquid tank 511 is a tank for storing a coating liquid 501 described later in detail. The coating liquid tank 511 includes, for example, a cooling device 511A as a liquid temperature adjusting means for cooling the coating liquid 501 stored by circulation of cooling water as a cooling liquid on the outer surface side, and the coating liquid 501 stored. A stirrer (not shown) is provided as a stirring means such as a disperser for stirring and dispersing the MgO powder.
The cooling device 511A is not limited to the configuration in which the cooling water is circulated as the cooling liquid, but includes a configuration in which cooling is performed by supplying power, such as a Peltier element, and a heat exchanger that circulates the refrigerant as the cooling liquid and performs heat exchange. Various cooling configurations such as a configuration can be applied. Further, the cooling device 511A is not limited to the configuration for cooling the outer surface side of the coating liquid tank 511, and a cooling pipe for circulating the cooling liquid is disposed in the coating liquid tank 511 to directly apply the coating liquid 501. It is good also as a structure to cool.
The coating liquid tank 511 is provided with a temperature sensor (not shown) that detects the temperature of the coating liquid 501 and outputs a detection signal to the control device 520.

Further, a preparation apparatus 600 that prepares the coating liquid 501 and supplies the prepared coating liquid 501 to the coating liquid tank 511 is connected to the coating liquid tank 511.
The preparation apparatus 600 includes a preparation tank 610, a disperser 620 having a stirring blade 621 and a drive unit 622 that disperses and mixes MgO powder and a solvent, and a coating liquid tank 511 containing the prepared coating liquid 501. And a transfer pipe 630 provided with a pump 631 to be introduced. The preparation tank 610 may have a cooling device 511 </ b> A similarly to the coating liquid tank 511.

The flow path 512 includes a flow pipe 512 </ b> A that has one end connected to the coating liquid tank 511 and the other end connected to the switching valve 513 and distributes the coating liquid 501 stored in the coating liquid tank 511 to the switching valve 513. ing.
The flow pipe 512A is provided with a liquid feed pump 512B. As the liquid feed pump, various pumps such as a metering pump such as a gear pump, a tube pump and a plunger pump, and a constant pressure pump such as an Invera pump can be used.

As the switching valve 513, for example, a three-way valve or the like is used. A flow pipe 512A, discharge means 514, and return pipe 515 are connected to the switching valve 513, and the application state in which the flow pipe 512A and the discharge means 514 are communicated to allow the coating liquid 501 to flow to the discharge means 514. Then, the circulation pipe 512A and the return pipe 515 are communicated with each other to switch to a circulating state in which the coating liquid 501 is passed through the return pipe 515 and returned to the coating liquid tank 511. As the switching valve 513, various configurations such as a configuration in which a flow path can be controlled by combining a bellows type three-way valve, a piston type three-way valve, and a two-way valve can be applied.
For switching the switching valve 513, any method such as manual switching by an operator's operation or automatic switching by a timer or the like can be applied.

The discharge means 514 includes a discharge pipe 514A having one end connected to the switching valve 513, and a spray gun 514B connected to the other end of the discharge pipe 514A. As the spray gun 514B, a so-called two-fluid air atomization system that atomizes and discharges the coating liquid 501, the cleaning liquid 502, and air into a two-liquid state is used. Not limited to this, various configurations such as a bell method and a one-fluid method in which atomization is performed only by the pressure of the coating liquid 501 can be applied.
And the discharge means 514 distribute | circulates the coating liquid 501 which flows out out of the switching valve 513 to the spray gun 514B via the discharge pipe 514A, and makes it discharge from the spray gun 514B.

  The return pipe 515 has one end connected to the switching valve 513 and the other end connected to the coating liquid tank 511, and circulates the coating liquid 501 flowing out from the switching valve 513 through the coating liquid tank 511.

The control device 520 controls the operation of the switching valve 513 and the liquid feed pump 512B. Further, the control device 520 may be able to drive and control the cooling device 511A and the stirring device of the coating liquid tank 511. Examples of the operation control by the control device 520 include operation control for appropriately supplying electric power to the liquid feed pump 512B and driving, switching operation of the switching valve 513, and the like.
In the present embodiment, the liquid feed pump 512B is exemplified as a structure that is always driven in the coating step of the coating liquid 501, but may be configured to be appropriately driven to feed the liquid. Further, as the switching operation, for example, a configuration in which the switching timing is controlled by a timer (not shown) provided in the control device 520 is exemplified. However, the switching timing is set by a program set by various timing means such as a clocking device based on a clock, for example. It may be controlled.

{Composition of coating solution}
And the coating liquid 501 apply | coated with the above-mentioned coating apparatus 500 becomes the following compositions.
The coating liquid 501 is an inorganic substance-containing slurry containing MgO powder that is an inorganic powder. The coating liquid 501 is prepared by dispersing MgO powder in a solvent. In addition, it is preferable to add a dispersing agent suitably.

(Configuration of MgO powder)
As the MgO powder, for example, a vapor phase magnesium oxide single crystal powder (hereinafter referred to as single crystal MgO powder) having an average particle diameter measured by the BET method of 500 mm or more (preferably 2000 mm or more) is used. The MgO powder is not limited to this.
By forming the crystalline MgO layer 342 using such single crystal MgO powder, the discharge characteristics of the PDP 1 are improved (decrease in discharge delay and increase in discharge probability). That is, in addition to CL emission having a peak at 300 to 400 nm from single crystal MgO particles having a large particle size contained in the crystalline MgO layer 342 by irradiation with an electron beam generated by discharge, a wavelength region of 200 to 300 nm (particularly, CL emission having a peak in the vicinity of 235 nm and within 230 to 250 nm) is excited. The single crystal MgO grains have an energy level corresponding to the peak wavelength, and can trap electrons for a long time (several milliseconds or more) by the energy level. By taking out these electrons by the electric field, initial electrons necessary for the start of discharge are obtained. As a result, the discharge delay is reduced and the discharge probability is improved.

(Composition of solvent)
As the solvent for dispersing the MgO powder, the stronger the polarity, the more advantageous it is for the dispersion. Examples of the solution exhibiting strong dispersion include alcohols such as glycol and IPA (2-propanol). In the spray method, since it is necessary to volatilize quickly, alcohol having a low boiling point and easy to disperse is particularly preferable.
Dispersion is also possible in ester compounds such as ethyl acetate and isopropyl acetate, sulfur compounds such as dimethyl sulfoxide, and nitrogen compounds such as dimethylformamide. The non-polar solvent (hydrocarbon type) cannot disperse the MgO powder.
The MgO powder is dispersed in the solvent by hydrogen bonding or electrostatic attraction (depending on the polarity) of oxygen or magnesium of MgO and a hydrophilic group (hydroxyl group, carboxyl group, sulfone group, amine group, etc.).

(Configuration of dispersant)
The dispersant has a hydrophilic group and a hydrophobic group. That is, the dispersibility of the MgO powder can be improved by using a dispersant having a hydrophobic group and a hydrophilic group. This is because dispersibility can be improved by attracting the hydrophilic group and MgO and decreasing the apparent specific gravity due to the presence of a hydrophobic group having a large molecular weight.
And it is preferable that the density | concentration in the coating liquid 501 of a dispersing agent is 0.1 to 3 wt%. With such a dispersant concentration, the precipitation of MgO powder can be prevented, and the MgO powder can be suitably dispersed.
As the hydrophilic group, a hydroxyl group (—OH) exhibits particularly strong dispersibility. An aldehyde group, an amine group, a sulfone group, and the like can be dispersed, but a hydroxyl group is preferred from the viewpoint of dispersibility because it has a weak dispersant function. A substance having a carboxyl group (carboxylic acid) (such as acetic acid) is not preferable because it dissolves MgO.

In particular, the dispersant preferably contains hydroxyl groups in the same number or more as the solvent. The dispersant preferably has a molecular weight of 100 or more when the hydroxyl group is monovalent, a molecular weight of 62 or more when the hydroxyl group is divalent, and a molecular weight of 64 or more when the hydroxyl group is trivalent. . Examples of the dispersant having a high effect as a dispersant having a hydroxyl group include glycerin, ethylene glycol, acetylene glycol, and acetylene alcohol. In the case of a hydroxyl group, the greater the valence of the hydroxyl group, the better the dispersibility. Therefore, glycerin having a trivalent hydroxyl group has the highest dispersion performance.
When such glycerin, ethylene glycol, or acetylene glycol is used as a dispersant, the dispersant has the effect of coating the surface of a liquid flow path such as a pipe, thereby preventing adhesion of MgO powder in the liquid path. By reducing the pressure loss in the liquid path, stable discharge is possible.
Examples of the hydrophobic group include alkanes, alkenes, fatty acids, and the like. By using a dispersant that combines a hydroxyl group and a hydrophobic group, the dispersibility of the MgO powder is improved.

  Based on the above, examples of the dispersant include acetylene alcohol, 1-heptanol (heptyl alcohol), 1-octanol (octyl alcohol), 1-nonanol (nonyl alcohol), 1-decanol (decyl alcohol), 1-undecanol ( Any of undecyl alcohol), 1-dodecanol (dodecyl alcohol), 1,2-propanediol (propylene glycol), 1,2-ethanediol (ethylene glycol), acetylene glycol, and glycerin can be appropriately employed.

Further, as a dispersant having a hydrophilic group and a hydrophobic group, at least one of an anionic surfactant and an anionic polymer may be used.
That is, an anionic surfactant and an anionic polymer generate a negative charge and are adsorbed on MgO by the electrostatic attraction of MgO (Mg ²⁺ ). And while forming a colloid and reducing an apparent specific gravity, the distance between particle | grains leaves | separates by the Coulomb repulsion between anionic surfactant or anionic polymers. Thereby, aggregation / sedimentation of the MgO powder hardly occurs and the dispersibility of the MgO powder is improved.
In addition, by using a mixture of an anionic surfactant and an anionic polymer, the apparent specific gravity can be further reduced greatly, so that the dispersibility is further improved.
When an anionic polymer that generates a strong negative charge is used, the bond between MgO and the polymer becomes strong, and the polymer acts as a flocculant, so that MgO aggregates and promotes sedimentation, thereby dispersing. This is not preferable because there is a risk of not being present.
Examples of the anionic surfactant include carboxylic acid-based, sulfate-based, sulfonic acid-based, and acrylic acid-based anionic surfactants.

Examples of the carboxylic acid anionic surfactant include sodium alkyl ether carboxylate (RO (CH ₂ CH ₂ O) nCH ₂ COONa). R in the structural formula is an alkyl group. In particular, sodium lauryl ether carboxylate having 12 carbon atoms in the R moiety, sodium myristyl ether carboxylate having 14 carbon atoms in the R moiety, sodium valmityl ether carboxylate having 16 carbon atoms in the R moiety, carbon in the R moiety The number 18 sodium stearyl ether carboxylate is preferred.
Other examples of carboxylic acid anionic surfactants include acrylates, fatty acid salts, polyvalent carboxylates, rosinates, dimates, and polymerates. Acid salts) are preferred.

Examples of the sulfate-based anionic surfactant include sodium alkyl ether sulfate (RO (CH ₂ CH ₂ O) nSO ₃ Na). R in the structural formula is an alkyl group. In particular, sodium lauryl ether sulfate having 12 carbon atoms in the R portion, sodium myristyl ether sulfate having 14 carbon atoms in the R portion, sodium valmityl ether sulfate having 16 carbon atoms in the R portion, carbon number in the R portion Is a sodium stearyl ether sulfate of 18 is preferred.
In addition, sulfate anionic surfactants include alkyl sulfate, polyoxyalkylene alkyl sulfate, polyoxyalkylene alkyl phenyl ether sulfate, tristyrenated phenol sulfate, polyoxyalkylene distyrene. And phenol sulfate sulfate.

Examples of the sulfonic acid-based anionic surfactant include sodium alkyl sulfonate (R—SO ₃ Na). R in the structural formula is an alkyl group. In particular, sodium lauryl sulfonate having 12 carbon atoms in the R portion, sodium myristyl sulfonate having 14 carbon atoms in the R portion, sodium valmityl sulfonate having 16 carbon atoms in the R portion, and 18 carbon atoms in the R portion. Sodium steamyl sulfonate is preferred.
In addition, examples of the sulfonic acid-based anionic surfactant include alkylbenzene sulfonate, alkyl naphthalene sulfonate, naphthalene sulfonate, and diphenyl ether sulfonate.

Examples of the anionic polymer include carboxylic acid-based polyacrylamide / acrylate, and acrylamide / sodium acrylate (-(CH ₂ CHCONH ₂ ) m- (CH ₂ -CH-COONa) n-) is particularly preferable. . In the structural formula, m is acrylamide, and n is sodium acrylate.
[PDP manufacturing method]
Next, a manufacturing operation in the method for manufacturing the PDP 1 having the above-described configuration will be described.
FIG. 8 is a schematic view showing a process of forming a single crystal MgO powder layer by a spray method.

  When manufacturing the PDP 1, in the manufacturing line for the back substrate 2 of the PDP 1, the inner surface side of the glass substrate is sufficiently cleaned by an ultrasonic cleaning process or a water cleaning process using a neutral detergent. Thereafter, a metal thin film is formed on the entire inner surface of the glass substrate, and a pattern of the address electrode 21 is formed by photolithography. A glass paste is applied onto the address electrode 21, and the address paste protective layer 22 and the partition wall 23 are formed by molding and baking the glass paste. Then, phosphor pastes of the three primary colors of red (R), green (G), and blue (B) are applied to the inside of the discharge cell 231 by screen printing or the like, and this is fired to obtain phosphor layers (24R, 24G, 24B). Thereby, the back substrate 2 of the PDP 1 is completed.

  On the other hand, in the production line of the front substrate 3 of the PDP 1, the inner surface side of the glass substrate is sufficiently cleaned by ultrasonic cleaning processing, water washing processing using a neutral detergent, or the like. Thereafter, a transparent electrode material layer is formed on the entire inner surface of the glass substrate, and a plurality of transparent electrodes 311a and 311b are formed by a photolithography method or the like. A paste pattern of black inorganic pigment is laminated on the transparent electrode pair by screen printing or the like, and an Ag paste pattern is further laminated on the pattern. Then, these patterns are fired to form bus electrodes 312a and 312b having a two-layer structure including bus electrode black layers 313a and 313b and main conductive layers 314a and 314b. Thereafter, a paste pattern of black inorganic pigment is applied between the bus electrodes 312a and 312b by a screen printing method or the like, and this is fired to form a plurality of black stripes 32. Further, a dielectric layer 33 is formed by applying glass paste with a die coater or the like so as to cover the transparent electrodes 311a and 311b, the bus electrodes 312a and 312b, and the black stripes 32. Then, a thin film MgO layer 341 is formed on the dielectric layer 33 by vapor deposition or sputtering. Further, as shown in FIG. 8, a single crystal MgO powder layer is formed on the thin film MgO layer 341 by a spray method using the coating apparatus 500 shown in FIG. 7 (detailed below). By baking, a crystalline MgO layer 342 is formed. Thereby, the front substrate 3 of the PDP 1 is completed.

That is, as a coating process by the coating apparatus 500 shown in FIG. 7, the coating liquid 501 prepared in advance is stored in the coating liquid tank 511. In addition, a condition for applying the coating liquid 501 and a condition for cleaning are set in the control device 520.
Then, when the operator performs a setting input for performing the coating process on the control device 520 in which these various operating conditions are set, the control device 520 appropriately sets the switching state of the switching valve 513.
Specifically, first, the switching valve 513 is controlled to be switched so that the flow pipe 512A is connected to the return pipe 515, and the coating liquid 501 is circulated through the flow pipe 512A, the switch valve 513, and the return pipe 515. A circulation state that is a state. In this state, the controller 520 drives the liquid feed pump 512B under a predetermined driving condition, whereby the coating liquid 501 flows from the flow pipe 512A through the switching valve 513 to the return pipe 515, and the coating liquid tank It returns to 511 and it will be in the circulation state which circulates. By this circulation and the stirring device of the coating liquid tank 511, the coating liquid 501 maintains a substantially uniform composition without solid-liquid separation.

When the coating liquid 501 is applied, the control device 520 recognizes that the front substrate 3 on which the thin film MgO layer 341 has been formed is carried in a predetermined position based on a detection signal from the sensor. The switching state of the switching valve 513 is appropriately set to a state where the flow pipe 512A communicates with the spray gun 514B and discharges the coating liquid 501, that is, a coating state where the flow pipe 512A is connected to the discharge pipe 514A.
By this switching control, the flow pipe 512A is connected to the discharge pipe 514A, and the circulating coating liquid 501 flows from the flow pipe 512A through the switching valve 513 to the discharge pipe 514A, and from the spray gun 514B. It is applied onto the thin film MgO layer 341 in an atomized state that is liquefied with air. At the time of this application, it is preferable that the front substrate 3 is heated, the solvent is immediately dried, and the MgO powder is deposited on the thin film MgO layer 341.
When this application is completed, for example, when the control device 520 recognizes that a predetermined amount of the coating liquid 501 has been applied to the front surface of the thin-film MgO layer 341 over time, the control device 520 switches the switching valve 513 again. The circulation state described above is assumed.

[Operation of coating equipment]
{Experiment}
Next, an experiment for confirming the coating processing effect in the coating apparatus 500 in the present embodiment will be described with reference to the drawings.
FIG. 9 is a conceptual diagram showing a schematic configuration of an experimental apparatus for confirming the coating treatment effect in the present embodiment.
9 shows the configuration of the coating unit 510 in which the configurations of the cooling device 511A, the preparation device 600, and the control device 520 are omitted.

(Configuration of experimental equipment)
As the coating apparatus 500 of the present embodiment in the confirmation experiment, a cleaning unit 550 for cleaning the spray gun 514B in the coating unit 510 is provided.
That is, as shown in FIG. 9, a two-way valve 951 is provided in the discharge pipe 514A between the switching valve 513 and the spray gun 514B in the coating unit 510, and a washing liquid tank for storing the washing liquid 502 in the two-way valve 951. A cleaning tube 953 having one end connected to 952 is connected. The two-way valve 951 is in a coating state where the coating liquid 501 is discharged from the spray gun 514B, and the cleaning liquid 502 flows from the cleaning liquid tank 952 into the discharge pipe 514A via the cleaning pipe 953 and is discharged from the spray gun 514B. The cleaning state can be switched.
In the experimental apparatus, the coating liquid tank 511 having the configuration shown in FIG. 7 was provided with a stirring device having two stirring blades having a diameter of 50 mm and rotating the stirring blades at a rotation speed of 300 rpm.
As the liquid feed pump 512B, a gear pump is used, and the motor frequency connected to the gear pump is changed by changing the inverter frequency.
The flow pipe 512A from the coating liquid tank 511 to the switching valve 513 is 10 m, the return pipe 515 from the switching valve 513 to the coating liquid tank 511 is 10 m, and the discharge pipe 514A from the switching valve 513 to the spray gun 514B is 20 m. As described above, piping was performed using a PFA tube having an inner diameter of 2 mm and relatively low adhesion of MgO powder.
In addition, a heater was provided in the coating liquid tank 511 so that the temperature of the coating liquid 501 was within the target temperature ± 1 ° C. by feedback control.

(experimental method)
As an experimental method, an experiment was performed on the change state of the discharge of the coating liquid 501, the powder adhesion state on the switching valve 513, the application state applied to the glass substrate, and the measurement of the discharge delay.
In each experiment, magnesium oxide powder having an average particle diameter of 1 μm was used as the coating liquid 501, and methanol, ethanol, isopropanol (2-propanol: IPA), and ethylene glycol (1,2-ethanediol) were used. Each was prepared by dispersing with an ultrasonic disperser at a concentration of 5 wt%.
Further, as the cleaning liquid 502, a solvent having the same quality as that of the coating liquid 501 was used as a main component, that is, a solvent having the same composition.
And as application | coating conditions of the coating liquid 501, the liquid feed pump 512B was driven in the state which circulates and apply | coats with the flow volume of 15 ml / min. The flow rate of the cleaning liquid 502 was 50 ml / min.
Furthermore, the spray gun 514B set the air atomization pressure to 0.2 MPa when the coating liquid 501 was applied.

(1) Experiment of discharge change situation As a coating process, the coating state in which the coating liquid 501 is ejected is 1 minute, and the circulation state in which the coating liquid 501 is circulated is 1 minute in one cycle, and each is repeated 200 times. Moreover, as a washing | cleaning process, after implementing the application | coating process, it implemented for 10 second each time.
Then, the temperature of the coating liquid 501 is appropriately set in a range from 15 ° C. to 70 ° C., and the discharge amount at the time of discharging the coating liquid 501 using each solvent by the coating apparatus 500 is measured, respectively. Variation, ie, standard deviation, was calculated. The temperature of the cleaning liquid 502 was normal temperature. Note that the temperature of the coating liquid 501 discharged from the spray gun 514B was 30 ° C. or less even when the coating liquid 501 in the coating liquid tank 511 was cooled to 70 ° C. during cooling.
Moreover, after the experiment of the discharge change state, the coating apparatus 500 was disassembled and the internal state was observed. The decomposition observation site is a liquid feed pump 512B and a switching valve 513.
The result of the standard deviation, which is the variation in the discharge amount of the coating liquid 501, is shown in FIG.

(2) Experiment of powder adhesion situation in switching valve As an experiment of the adhesion situation of MgO powder in this switching valve 513, the dry weight of the switching valve 513 decomposed in the above-mentioned (1) discharge change situation experiment was measured, The amount of adhering impurities, that is, MgO powder was measured. The switching valve 513 was dried in a hot air circulating furnace set at 50 ° C. for 1 hour, and then the weight was measured. Then, the dry weight of the switching valve 513 was measured in advance before the application experiment, and the weight difference with the dry weight after the measurement was calculated as the adhesion amount of the MgO powder.
The result is shown in FIG.

(3) Experiment of application state As an experiment of this application state, after carrying out the application process 200 times, the coating liquid 501 was applied on a substantially square soda glass having a side of 1000 mm, and the transmittance was comparatively evaluated. . The transmittance was measured at 20 locations in the in-plane region of soda glass.
The coating liquid 501 was made of two types using methanol and ethylene glycol as the solvent. And the glass substrate which apply | coated the coating liquid 501 which used ethylene glycol for the solvent was dried for 10 minutes with the warm air circulation furnace set to 80 degreeC for the drying of a solvent. In addition, when the transmittance | permeability of air was 100%, it set to the state from which the transmittance | permeability of the glass substrate after application | coating will be 70%, and apply | coated the coating liquid 501. FIG.
The measurement results of this transmittance are shown in FIGS. 12 is a graph showing the transmittance when methanol is used as the solvent, and FIG. 13 is a graph showing the transmittance when ethylene glycol is used as the solvent.

(4) Experiment of discharge delay As an experiment of this discharge delay, the temperature of the coating liquid 501 prepared by using methanol and ethylene glycol as a solvent as the coating liquid 501 is 23 ° C., which is room temperature, and 40 ° C. The temperature was set to 60 ° C., and (1) the coating liquid 501 was applied for 200 cycles in the same manner as in the discharge change state experiment, and then the coating liquid 501 was applied to manufacture PDP1. That is, each of the substrates formed by applying the coating liquid 501 on the dielectric layer 33 of the substrate used for manufacturing the PDP 1 to form a single crystal MgO powder layer and firing to form the crystalline MgO layer 342 is used. PDP1 was manufactured. In addition, as MgO powder used for the coating liquid 501, single crystal MgO powder with sufficiently high photoluminescence intensity and high discharge probability characteristics was used.
And the discharge delay in manufactured PDP1 was measured in 20 places in a panel surface. The discharge delay is the time from when a voltage for generating discharge is applied until when the discharge actually occurs, and is normalized by an average value in a PDP in which the crystalline MgO layer 342 is not provided.
FIG. 14 and FIG. 15 show the result of variation at each measurement location in this discharge delay measurement. 14 is a graph showing the measurement results of the discharge delay when methanol is used as the solvent, and FIG. 15 is a graph showing the measurement results of the discharge delay when ethylene glycol is used as the solvent.

(Experimental result)
(1) Experiment of discharge change state From the result shown in FIG. 10, the standard deviation of the discharge amount from the spray gun 514B increases exponentially as the temperature of the coating liquid 501 in the coating liquid tank 511 increases. It was recognized that In particular, when the solvent was methanol, the standard deviation of the discharge amount increased rapidly from a temperature of about 30 ° C. In the case where the solvent was ethanol or IPA, the standard deviation of the discharge amount increased rapidly from about 50 ° C. When the solvent was ethylene glycol, the standard deviation of the discharge amount was hardly increased up to a temperature of 70 ° C., and the discharge amount was stable.
That is, the boiling points of methanol, ethanol, IPA, and ethylene glycol are 65 ° C., 78 ° C., 82 ° C., and 198 ° C., respectively, and the discharge amount becomes unstable when the temperature is higher by 30 ° C. than the boiling point of the coating liquid 501. Thus, the standard deviation of the discharge amount is considered to have increased.
In the decomposition observation after 200 discharges, as the temperature setting of the coating liquid 501 in the application experiment of the coating liquid 501 increases, the MgO powder adheres more in the liquid feed pump 512B and the switching valve 513. It was recognized that

(2) Experiment of powder adhesion situation on switching valve From the results shown in FIG. 11, when methanol is used as the solvent, the amount of MgO powder deposited on the switching valve 513 starts to increase from around 30 ° C. Almost saturated. In addition, when ethanol and IPA were used as the solvent, the same tendency was observed as when methanol was used as the solvent. However, it was recognized that the temperature at which the amount of adhesion started increasing in the order of methanol, ethanol and IPA. It was. In addition, when ethylene glycol was used as the solvent, even when the coating liquid 501 was heated to 70 ° C., the adhesion amount did not increase rapidly and was stable.
In addition, even when the temperature was lower than 30 ° C., the amount of adhesion was recognized as slightly over 0.2 g. However, after the spray gun 514B was applied and washed, the switching valve 513 was removed from the coating unit 510 and dried. Therefore, it is considered to be MgO powder contained in the coating liquid 501 remaining in the switching valve 513.

(3) Application State Experiment From the results shown in FIG. 12, in the case of using methanol as the solvent, when the temperature of the coating liquid 501 is 40 ° C. or higher, the transmittance range is widened, and the temperature of the coating liquid 501 is high. It was observed that the transmittance range became larger as the time went on. And (1) Comparing with the result shown in FIG. 10 in the experiment of the discharge force change situation, it can be seen that the variation in the discharge amount increases corresponding to the rise in temperature.
Further, from the results shown in FIG. 13, when ethylene glycol is used as the solvent, even if the temperature of the coating liquid 501 is increased, the deviation of the variation in transmittance is stable, corresponding to the result shown in FIG. I found out.
(4) Experiment of discharge delay From the results shown in FIG. 14, in the case of using methanol as the solvent, when the temperature of the coating liquid 501 is 40 ° C. or higher, the variation in the discharge delay increases as the temperature increases. It was recognized that This is because an uneven single crystal MgO powder layer is formed without uniform application of MgO powder, and there is little or no MgO powder in this single crystal MgO powder layer. In addition, it is considered that it was not able to sufficiently contribute to the discharge delay.
From the results shown in FIG. 15, when ethylene glycol was used as the solvent, the variation range of the discharge delay hardly changed even when the temperature of the coating liquid 501 was increased from room temperature to 60 ° C. That is, it is considered that a stable coating was obtained and the MgO powder was uniformly applied.

As described above, since a solvent having a hydroxyl group with good dispersibility is used as the coating liquid 501, the dispersion of the MgO powder is considered to be due to hydrogen bonding between oxygen and hydroxyl groups of MgO. The MgO and the solvent adhering to the periphery form one large lump, so that the apparent specific gravity is lowered and dispersed.
Further, since the dispersed MgO powder has a particle size of several thousand nm to several μm, Brownian motion that is vibration of colloid occurs.
When the temperature is high, the absolute value of the zeta potential of the MgO particles becomes high due to active Brownian motion. Then, when it comes close to a conductive substance such as metal, electrostatic adhesion occurs.
Further, when the surface is activated by the active Brownian motion of MgO particles, aggregation tends to occur. The zeta potential is generated by the charged particles adhering to the periphery of the MgO particles. However, since this zeta potential has the opposite polarity to the MgO particles, an active surface of MgO appears and it is easy to attract the colloid by electrostatic attraction.
From these, as the temperature of the coating liquid 501 becomes close to the boiling point of the solvent or even higher, the MgO powder in the liquid feed pump 512B or the switching valve 513 in the flow path of the coating liquid 501 is particularly good. It is considered that the adhesion of the ink increases and the discharge amount tends to vary.

{Function and effect}
As described above, in the above embodiment, when the coating liquid 501 in which the MgO powder is dispersed in the solvent is discharged from the spray gun 514B, the coating liquid tank 511 for storing the coating liquid 501 to the spray gun 514B. The temperature of the coating liquid 501 that circulates is adjusted to a temperature that is at least 30 ° C. lower than the boiling point of the solvent.
For this reason, the state which MgO powder disperse | distributes appropriately in a solvent is obtained, and aggregation and fixation do not arise in the flow path of the coating liquid 501, and the coating liquid 501 can be discharged stably. Therefore, since MgO powder can be applied substantially uniformly, PDP 1 having stable characteristics can be obtained.

The coating liquid tank 511 for storing the coating liquid 501 is provided with a configuration in which the coating liquid 501 is adjusted to a temperature lower by 30 ° C. or more than the boiling point of the solvent, that is, a cooling device 511A for cooling the coating liquid 501.
Further, as confirmed in the above-described (1) experiment on the discharge change situation, even when the coating liquid 501 is heated to 70 ° C. and circulated, the temperature discharged from the spray gun 514B is 30 ° C. or less. For this reason, by cooling the coating liquid 501 in the coating liquid tank 511 on the most upstream side in the flow path of the coating liquid 501 to a temperature that is 30 ° C. lower than the boiling point of the solvent, The temperature of the circulating coating liquid 501 is maintained at a temperature 30 ° C. lower than the boiling point of the solvent, and stable discharge can be obtained with a simple configuration as compared with the case where a configuration for cooling the entire flow path is provided. It is done.
The coating liquid tank 511 is provided with a stirring means to prevent the MgO powder from settling. Since the cooling device 511A is provided in such a configuration, by providing a configuration in which cooling is performed with the coating liquid tank 511, which may cause a large shearing force to act and maintain the dispersion state, thereby increasing the temperature. The temperature of the coating liquid 501 can be adjusted with a simple and efficient configuration.

Further, a cooling device 511A is provided in the coating solution tank 511 to which the preparation device 600 for preparing the coating solution 501 is connected. For this reason, even when the coating liquid 501 having a high temperature is supplied to the coating liquid tank 511 due to the action of a large shearing force when the coating liquid 501 is prepared in the preparation apparatus 600, it is cooled by the cooling device 511A before being discharged. Thus, a sufficiently stable coating can be obtained.
Furthermore, providing the cooling device 511 </ b> A in the preparation device 600 is particularly effective because the coating solution 501 is cooled before being supplied to the coating solution tank 511.

And since the coating liquid 501 is cooled by circulating cooling water as the cooling device 511A, the cost for cooling can be suppressed with a simple configuration, and an efficient coating can be obtained.
That is, since it may be set at a temperature 30 ° C. or more lower than the boiling point of the solvent, for example, tap water, ground water, sea water, etc. may be simply circulated, and the temperature of the coating liquid 501 is 30 ° C. or more than the boiling point of the solvent. Since it is sufficient to set it to a low temperature, it is sufficient to cool it to about room temperature, and the cooling water heat-exchanged with the coating liquid 501 does not increase in temperature so much that it may adversely affect the environment even if it is discharged as it is. And can be cooled easily.
Further, for example, the temperature is adjusted to a temperature at which the coating liquid 501 can be stably discharged simply by circulating tap water or groundwater, so that it is not necessary to set it with the control device 520 or the like, and the configuration can be simplified. .
In addition, it is good also as a structure which provides a temperature sensor etc. and distribute | circulates a cooling fluid when temperature rises. With this configuration, it is only necessary to distribute the coolant only when necessary, so that the operating cost can be further reduced and efficient application can be obtained.

The coating apparatus 500 is configured to apply an inorganic substance-containing slurry coating liquid 501 in which MgO powder, which is an inorganic powder, is dispersed in a solvent.
For this reason, even the coating liquid 501 of an inorganic substance-containing slurry that easily settles and separates and easily clogs in the flow path can be prevented from agglomeration and fixation by setting the temperature at 30 ° C. or more lower than the boiling point of the solvent. Even without providing a configuration for cleaning the route through which the 501 flows, stable ejection can be obtained, and the configuration can be more easily simplified.
Then, as in the experimental apparatus shown in FIG. 9, by providing the cleaning unit 550, the MgO powder in the coating liquid 501 remaining in the discharge pipe 514A and the spray gun 514B in a circulating state is separated and aggregated. Inconveniences that cause sticking can be prevented, and stable ejection can be obtained for a longer period of time.
Further, as the cleaning liquid 502 used for cleaning, a solvent having the same quality as the coating liquid 501 is used as a main component. In particular, the same solvent is used as the cleaning liquid 502.
For this reason, the coating liquid 501 can be easily washed away, and the required amount of the cleaning liquid 502 can be reduced and the cleaning time can be easily reduced. Furthermore, even if the cleaning liquid 502 is mixed with the coating liquid 501 and recovered as a waste liquid, the waste liquid can be easily treated. Moreover, even if it mixes in the coating liquid 501 accidentally, it does not produce an influence on the coating process, and the process control of the cleaning process can be made easier.
Further, the flow rate of the cleaning liquid 502 is made larger than the state in which the coating liquid 501 is applied.
For this reason, even in the configuration where the timer is controlled in terms of ease of control and simplification of the configuration, the cleaning can be performed reliably, and the MgO powder that tends to remain due to the unevenness of the switching valve 513 can be sufficiently washed away. Can be prevented for a long time, a stable coating can be obtained for a long time, the frequency of washing can be reduced, and the coating efficiency can be easily improved.

[Modification of Embodiment]
Note that the present invention is not limited to the above-described embodiment, and includes the following modifications as long as the object of the present invention can be achieved.

  That is, the structure for forming the single-crystal MgO powder layer by the spray method for forming the crystalline MgO layer 342 in the PDP 1 has been described as an example. However, the present invention is not limited to this. It can be applied to a coating apparatus that applies For example, the present invention is not limited to a slurry containing MgO powder, but can be applied to a configuration in which various coating liquids such as a liquid material containing an organic pigment, a slurry containing an inorganic pigment, a surface treatment agent and an antibacterial agent are applied.

And as a structure of PDP1 to manufacture, not only the structure mentioned above but various structures are applicable.
For example, the display electrode pair 31 is formed on the front substrate 3 and covered with the dielectric layer 33, and the phosphor layers (24R, 24G, 24B) and the address electrodes 21 are formed on the back substrate 2 side. However, the present invention is not limited to this. That is, the plasma display panel manufacturing method of the present invention includes a reflective AC PDP in which a display electrode pair and an address electrode are formed on the front substrate side and covered with a dielectric layer, and a phosphor layer is formed on the rear substrate, A transmission type AC PDP in which a phosphor layer is formed on the substrate side, a display electrode pair and an address electrode are formed on the back substrate side and covered with a dielectric layer, a discharge cell at the intersection of the display electrode pair and the address electrode in the discharge space The present invention can be applied to various types of PDPs such as a three-electrode AC PDP in which discharge cells are formed and a two-electrode AC PDP in which discharge cells are formed at intersections between display electrodes and address electrodes in the discharge space. Furthermore, the present invention can be applied not only to the plasma display panel but also to a configuration in which various materials in the manufacture of various display devices such as a liquid crystal panel and an organic EL panel are applied.
Furthermore, in the above-described embodiment, the partition wall 23 is formed in a ladder shape. However, the present invention is not limited to this, and a partition wall or a stripe-shaped partition wall may be used.
In the above embodiment, the thin film MgO layer 341 covers the entire surface of the thin film MgO layer 341. However, the present invention is not limited to this. For example, the portions facing the transparent electrodes 311a and 311b or conversely the transparent electrodes 311a and 311b. Alternatively, it may be formed by patterning a part such as a part other than the part opposite to the part.

And although the structure which provided the control apparatus 520 and controlled the distribution | circulation state of the coating liquid 501 automatically was demonstrated, for example, an operator may perform switching operation. Furthermore, the configuration is not limited to the configuration in which the control device 520 performs the single control, but a configuration may be adopted in which a timer or the like is provided in the switching valve 513 so that the switching operation is performed independently. In other words, the control device 520 may not be provided.
Moreover, as the coating apparatus 500, you may provide the structure which wash | cleans the inside of the path | route through which the coating liquid 501 distribute | circulates, such as providing the washing | cleaning part 550 like the experimental apparatus shown in FIG.
Furthermore, although it demonstrated as a structure which cools the coating liquid 501, as mentioned above, for example, when the coating liquid 501 does not rise from room temperature etc., it is not restricted to actively cooling, but the temperature rose to some extent. If the temperature is 30 ° C. or more lower than the boiling point of the solvent, such as cooling, the cooling may be omitted.

Moreover, although the structure which connected the preparation apparatus 600 to the coating liquid tank 511 was illustrated, it is good also as a structure which flows into the coating liquid tank 511 manually, for example, without using the pump 631 for example.
Furthermore, as a stirring apparatus, as shown in FIG. 16, it is good also as a structure which circulates the coating liquid 501 with the coating liquid tank 511 and the disperser 700. As shown in FIG. That is, the transfer pipe 630 having the pump 631 is connected to the coating liquid tank 511, and the pump 631 is driven to suck up the coating liquid 501 in the coating liquid tank 511 and distribute the transfer pipe 630. The state again flows into the coating liquid tank 511 and circulates. The transfer pipe 630 is provided with a disperser 700 that disperses the MgO powder of the coating liquid 501 that generates, for example, ultrasonic waves and circulates. Even with such a configuration, the coating liquid 501 can be stably stored with a uniform composition without causing sedimentation of the MgO powder. In the configuration in which the liquid is circulated and dispersed in this way, the temperature of the coating liquid 501 is likely to increase gradually due to the dispersion energy. Therefore, the cooling device 511A is also provided for the configuration as shown in FIG. Such a stable discharge is preferable.

  The present invention is not limited to the above-described embodiment and modifications of the embodiment, and various applications are possible without departing from the object of the present invention.

[Effects of Embodiment]
In the above embodiment, when the coating liquid 501 in which the MgO powder is dispersed in the solvent is discharged from the spray gun 514B, the coating liquid circulates from the coating liquid tank 511 storing the coating liquid 501 to the spray gun 514B. The temperature of the liquid 501 is adjusted to a temperature lower by 30 ° C. or more than the boiling point of the solvent.
For this reason, the state which MgO powder disperse | distributes appropriately in a solvent is obtained, and aggregation and fixation do not arise in the flow path of the coating liquid 501, and the coating liquid 501 can be discharged stably. Therefore, since MgO powder can be applied substantially uniformly, PDP 1 having stable characteristics can be obtained.

In addition, a pair of front substrate 3 and rear substrate 2 disposed to face each other via the discharge space H, and a plurality of display electrode pairs formed on the inner surface of one of the pair of front substrate 3 and rear substrate 2. In the process of forming the protective layer 34 in the manufacturing process of manufacturing the PDP 1 including the dielectric layer 33 covering the display electrode pair 31 and the protective layer 34 covering the dielectric layer 33, A single crystal that forms a crystalline MgO layer 342 constituting the protective layer 34 by applying a coating liquid 501 in which MgO powder is dispersed in a solvent at a temperature lower than the boiling point of the solvent by 30 ° C. An MgO powder layer is formed.
For this reason, a state in which the MgO powder is properly dispersed in the solvent is obtained, and aggregation and fixation do not occur in the flow path of the coating liquid 501, and the coating liquid 501 can be discharged stably. Since powder can be applied, a stable PDP1 can be obtained.

It is a schematic diagram which shows the conventional coating apparatus. It is a schematic diagram which shows the coating device provided with the conventional three-way valve. It is the disassembled perspective view which showed the internal structure of the plasma display panel which concerns on one embodiment of this invention. It is the front view which showed typically the plasma display panel in the said embodiment. It is sectional drawing in the VV line of FIG. It is sectional drawing in the VI-VI line of FIG. It is a conceptual diagram which shows schematic structure of the coating apparatus in the said embodiment. It is the schematic diagram which showed the formation process of the single crystal MgO powder layer by the spray method in the said embodiment. It is a conceptual diagram which shows schematic structure of the apparatus for experiment for confirming the coating process effect. It is a graph which shows the experimental result of the discharge change condition in the coating process effect confirmation experiment in the said embodiment. It is a graph which shows the experimental result of the adhesion condition of the MgO powder in the switching valve in the coating process effect confirmation experiment in the said embodiment. It is a graph which shows the experimental result of the application | coating state at the time of using methanol in the coating process effect confirmation experiment in the said embodiment as a solvent. It is a graph which shows the experimental result of the application | coating state at the time of using ethylene glycol for the solvent in the coating process effect confirmation experiment in the said embodiment. It is a graph which shows the experimental result of the discharge delay at the time of using methanol in the coating process effect confirmation experiment in the said embodiment as a solvent. It is a graph which shows the experimental result of the discharge delay at the time of using ethylene glycol for the solvent in the coating process effect confirmation experiment in the said embodiment. It is a conceptual diagram which shows schematic structure of the coating part of the coating apparatus in other embodiment of this invention.

Explanation of symbols

1. Plasma display panel (PDP)
2 ... Back substrate 3 ... Front substrate 31 ... Display electrode pair 33 ... Dielectric layer 34 ... Protective layer 500 ... Coating device 501 ... Coating solution 511 ... Coating solution tank 511A ... Temperature adjustment Cooling device as means 512 …… Distribution path 514 …… Discharging means 600 …… Preparation device

Claims (7)

A coating liquid tank for storing a coating liquid in which inorganic particles are dispersed in a solvent;
A distribution channel connected to the coating liquid tank and distributing the coating liquid;
Discharging means connected to the distribution path for discharging the circulating coating liquid;
A liquid temperature adjusting means for adjusting the coating liquid flowing from the coating liquid tank to the discharge means to a temperature lower by 30 ° C. or more than the boiling point of the solvent;
A coating apparatus characterized by comprising: The coating apparatus according to claim 1,
The coating liquid tank includes a stirring means for stirring the coating liquid,
The said liquid temperature adjustment means adjusts the temperature of the said coating liquid stored in the said coating liquid tank. The coating apparatus characterized by the above-mentioned. The coating apparatus according to claim 1,
The coating liquid tank is connected so that a preparation device for preparing the coating liquid by mixing the inorganic powder and the solvent can supply the prepared coating liquid,
The said liquid temperature adjustment means adjusts the temperature of the said coating liquid stored in the said coating liquid tank. The coating apparatus characterized by the above-mentioned. A coating apparatus according to any one of claims 1 to 3,
The said liquid temperature adjustment means cools the said coating liquid by circulation of a cooling liquid, and adjusts temperature. The coating apparatus characterized by the above-mentioned. A coating apparatus according to any one of claims 1 to 4,
In the coating liquid, the inorganic powder is magnesium oxide (MgO),
The discharge means includes a pair of substrates opposed to each other via a discharge space, a plurality of electrode pairs formed on the inner surface of one of the pair of substrates, and a dielectric covering the electrode pairs. The coating liquid is applied onto the dielectric layer in a plasma display panel having a layer and a protective layer covering the dielectric layer, thereby forming an MgO powder layer on which the protective layer is formed A coating device characterized by A coating method in which an inorganic powder is supplied and discharged to a discharge means with a coating liquid dispersed in a solvent,
The coating method is characterized in that the coating liquid is adjusted to a temperature 30 ° C. or more lower than the boiling point of the solvent and supplied to the discharge means. A pair of substrates opposed to each other through the discharge space, a plurality of electrode pairs formed on the inner surface of one of the pair of substrates, a dielectric layer covering the electrode pairs, and the dielectric A plasma display panel manufacturing method for manufacturing a plasma display panel comprising a protective layer covering a body layer,
In the protective layer forming step of forming the protective layer, the coating liquid in which magnesium oxide (MgO) powder is dispersed in a solvent is adjusted to a temperature lower than the boiling point of the solvent by 30 ° C. or more, and is applied by discharging. The manufacturing method of the plasma display panel characterized by including the application | coating process which forms the MgO powder layer which forms a protective layer.

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