JPH04163824A - Discharge display tube and cathode forming composition therefor - Google Patents

Abstract

PURPOSE:To reduce an operating voltage so as to enhance the light emitting efficiency and reduce the driving cost, and enhance color through avoidance of use of mercury by using conductive oxide expressed by a specific composition formula as a cathode forming material for a DC type discharge display tube. CONSTITUTION:Conductive oxide expressed by a formula XxYO3 (wherein X is one kind of elements of Ia group in the element periodic table; Y, one kind selected from a group consisting of Re, W, Mo and Nb; and (x), a value greater than 0 and less than 1) is used as a cathode forming material for a DC type discharge display tube. If the conductive oxide including an element of Ia group as a component element is used, an operating voltage can be reduced and sufficient conductivity can be obtained. Consequently, it is possible to enhance light emitting efficiency so as to aim at high luminance, and reduce power consumption. Additionally, color purity can be enhanced without any visible emission spectrum since gas occlusion cannot be generated even if Hg is not sealed in discharge gas.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a DC discharge display tube and a cathode forming composition thereof, and more particularly to a discharge display tube using a conductive oxide as a cathode forming material; The present invention also relates to a conductor composition for forming the cathode.

[Prior art and problems to be solved by the invention] Generally, discharge display tubes (plasma display panels)
When classifying PDPJ), the electrode is exposed to the discharge space,
There are two types of discharge display tubes: direct-type discharge display tubes, which are operated by applying a DC voltage, and AC-type discharge display tubes, whose electrode surfaces are covered with a dielectric material and which are operated by applying an AC voltage.

Among these, DC discharge display tubes have the drawbacks of low luminous efficiency and higher operating voltage (approximately 150 to 200 V) than other display elements such as fluorescent display tubes, liquid crystals, and light emitting diodes.

For this reason, various proposals have been made regarding cathode forming materials for DC discharge display tubes, but none have yet been found to be satisfactory, and further improvements are required.

The following conditions are required for the cathode forming material for the DC discharge display tube. In other words, ■Low work function and high secondary electron radiation efficiency; ■Resistance to ion bombardment and resistance to scattering; ■Conductivity; ■Low occlusion of discharge gas; ■Easy to manufacture. , ■The structure should not be complicated, etc.

Metals can be used as cathode forming materials that satisfy the following conditions, but metals are usually susceptible to ion bombardment, so it is necessary to prevent this by mixing mercury into the gas sealed inside the tube (discharge gas). Ta. However, in this way F
Even if metals such as E group metals or alloys thereof were used as cathode forming materials, there were no satisfactory materials for condition (2). Therefore, the operating voltage of the conventional DC discharge display tube using metal was high as described above.

Various methods have been tried in the past to solve this problem.

For example, there is a method of coating a conductive material such as a metal with a low work function material such as Mg02Bad, Cab, Sro, etc. However, this method has the following drawbacks and has not been put into practical use. In other words, when using the above insulator, the tunneling phenomenon is utilized, so the film thickness is 10
It must be thin and uniform, about 0A. Forming such a film is not easy, and it is also difficult to pass a large amount of current. Furthermore, if a large amount of current is passed in order to obtain sufficient brightness, there is a risk of damaging the film due to dielectric breakdown, and furthermore, since the film is thin, it cannot be said to have sufficient strength against ion bombardment.

Another method is to use a high melting point conductive compound such as a boride, nitride, or carbide of a rare earth element or alkaline earth metal and a low work function material.

However, since these have a high melting point, it is generally not easy to form a cathode, and furthermore, in many cases, an oxidizing atmosphere cannot be used during the formation. Furthermore, among these, a method of easily forming a cathode using borides with strong oxidation resistance, particularly La B b , Ce B 6, etc., has been proposed (Japanese Patent Laid-Open Nos. 80-221926 to 1983-221928). etc). However, it has been found that cathodes made of these non-oxide conductive materials have the following drawbacks. That is, Penning gas is generally used as a method to reduce the operating voltage of discharge display tubes, but the non-oxide cathode absorbs gas when the discharge continues, and the composition of the discharge gas changes, reducing the Penning effect. The operating voltage increases. Incidentally, if a single gas composition is used, such a drawback will not occur, but the operating voltage will be considerably higher than that of Penning gas. Further, gas occlusion can be prevented to some extent by simultaneously filling Hg, but the operating voltage increases.

Furthermore, it has recently been announced that when zinc oxide containing alumina is used as a cathode, it has high spatter resistance even in discharge gas that does not contain Hg (Abstracts of the 1990 Television Society Annual Conference, pp. 79-80). ). However, although the above-mentioned conductive oxides do not have the problem of gas occlusion, a sufficient reduction in operating voltage has not been achieved.

Therefore, in the conventional DC discharge display tube, it is currently difficult to stably apply a sufficiently low operating voltage over a long period of time.

The present invention has been made in view of these problems in the prior art.The present invention has been made in view of these problems in the prior art. The present invention aims to provide a discharge display tube that can reduce and stabilize operating voltage, increase brightness, and improve color purity and is easy to manufacture by using a chemical substance. A further object of the present invention is to obtain a conductor composition useful for forming the cathode of the discharge display tube.

[Means for Solving the Problem] As a result of intensive studies to solve the problems of the above-mentioned conventional technology, the present inventors have developed a cathode forming material that has a tungsten bronze type crystal structure containing a group Ia element as a constituent element. The inventors have discovered that the above object can be achieved by using a conductive oxide, and have completed the present invention.

That is, the present invention provides a DC discharge display tube, in which the cathode forming material has a composition formula (1): 1 type, Y is at least one type selected from the group consisting of ReSWSMo and Nb, and X is a number larger than 0 and less than 1. It is a display tube.

Hereinafter, the DC type discharge display tube of the present invention will be explained in more detail.

In the DC discharge display tube of the present invention, a conductive oxide represented by the compositional formula (t): XxYO3 is used as the cathode forming material. The above oxide has a tungsten bronze crystal structure. In the above compositional formula (1), element X
are group Ia elements of the periodic table of elements, namely Li, Na,
In addition, it is necessary that the material be at least one selected from the group consisting of Rb, Cs, and Fr. This is because when a group Ia element is used as a constituent element, the operating voltage is significantly reduced. In the present invention, the larger the atomic number of the element X, the lower the operating voltage tends to be. In addition, element Y is Re5
Indicates at least one member selected from the group consisting of W, Mo, and Nb.

The tungsten bronze-type crystal structure oxide according to the present invention is an oxide having a perovskite-type crystal structure represented by the composition formula (2): Correspondingly, the numerical value X in the above compositional formula (1) is a number greater than 0 and less than 1. This numerical value X is selected depending on the element XSY, and is determined by taking into consideration operating voltage, ease of synthesis, stability, conductivity, and the like. In the present invention, the larger the numerical value X is, the lower the operating voltage tends to be.

Further, each constituent element of the conductive oxide can form a solid solution in a wide range, and each of the elements XSY in the composition formula (1) may be a solid solution consisting of a plurality of elements. Furthermore, even if the conductive oxide used as the cathode forming material in the present invention is of a single type,
It may be a mixture of multiple types.

The discharge display tube of the present invention is not particularly limited except that the conductive oxide described above is used as the cathode forming material, and other structures may be the same as those of conventionally known DC type discharge display tubes.

For example, an anode substrate having an anode on the lower surface (e.g. front glass), a cathode substrate having a cathode on the upper surface (e.g. rear glass), and a side substrate may be sealed to form a discharge cell between the two electrodes. For example, there may be mentioned a direct current discharge display tube having a partition wall and a discharge cell filled with a gas such as Penning gas.

The cathode of the discharge display tube of the present invention may contain the above-mentioned conductive oxide as a cathode-forming material, and may not contain other components such as adhesive components to the extent that the effects of the present invention are not adversely affected. You can. Further, the shape of the cathode according to the present invention is arbitrary, and may be appropriately selected such as a film shape or a tape shape.

Further, for example, when a plurality of discharge cells are connected by a common cathode, if the resistance value of the cathode is high, there will be a difference in discharge characteristics and aging characteristics at both ends, which is inconvenient. In such a case,
It is preferable to select a conductive oxide with low resistivity or to increase the thickness of the cathode.

Further, when the resistance value of the cathode is high, it is also effective in the present invention to form a metal layer under the cathode. Since the discharge characteristics are mainly determined by the surface, any underlying metal can be selected, and since the metal has a sufficiently low resistance, the resistance of the conductive oxide placed thereon only needs to be considered in the thickness direction. Therefore, even a conductive oxide having a specific resistance of about 10'Ω·cm (800°K) can be used satisfactorily. Another advantage of this method is that when connecting the cathode to an external circuit, it is possible to use a metal layer and leave part of it exposed.
It is possible to form patterns all at once without problems in bonding properties, plating properties, etc.

Furthermore, in the discharge display tube of the present invention, since the cathode is resistant to ion bombardment, there is no need to include toxic Hg in the gas filled in the tube, and therefore it is preferable to use a gas filled that does not contain Hg.

Next, a preferred method for manufacturing the oxide cathode according to the present invention will be explained.

In a normal DC discharge display tube, the cathode is formed in a film shape and has a pattern shape that matches the display pattern, and will be described below in accordance with this pattern.

Since the above-mentioned conductive oxide according to the present invention is a so-called oxide ceramic, various conventional ceramic film forming methods such as spraying, printing, doctor blade, sputtering, and vapor deposition can be applied.

In addition, various conventional thick film and thin film techniques can be applied to patterning the film.

By the way, when a DC discharge display tube is generally formed into a flat type, its cathode is formed on a low-cost glass plate (substrate). Low-cost glass has low heat resistance, and the applicable temperature is about 600°C.

Therefore, even if the conductive oxide according to the present invention has a low melting point, it is difficult to fix the film only by temperature. In this case, sputtering and vapor deposition are generally applied, but
These devices are generally expensive and cannot be said to be suitable for mass production.

The same applies to the method of patterning the formed film by etching or the like. Furthermore, if the film thickness is increased to lower the resistance, the cost will become even higher.

The present inventors have discovered that the oxide cathode according to the present invention can be easily manufactured by printing technology used in ordinary thick film technology by using the cathode-forming composition of the present invention described in detail below. I learned that it is possible.

That is, the cathode forming composition of the present invention has the composition formula (1)
:X, yo, [In formula (1), X is at least one element selected from Group Ia elements of the periodic table of elements, Y is Re, W, Mo
, at least one member selected from the group consisting of Nb, and X is 0
It is characterized by dispersing in a liquid vehicle a powder of a conductive oxide having an average particle diameter of 0.1 to 30 μm, each represented by a numerical value larger than 1 and less than 1.

The conductive oxide powder can be produced in the same manner as general ceramic powder. For example, common methods include pulverizing raw materials after melting or solid-phase reaction, or reacting raw materials in a solution to precipitate a desired powder. It is necessary that the above powder has an average particle size of 0.1 to 30 .mu.m.

If it is smaller than 0.1 μm, it is difficult to increase the powder density in the cathode film to be deposited, leading to an increase in discharge voltage and shortening of electrode life.

On the other hand, if the amount is larger than 30 μl, not only is it difficult to perform fine buttering, but also sufficient bonding between the powders cannot be achieved.

The liquid vehicle used in the cathode-forming composition of the present invention is not particularly limited, and is generally a liquid vehicle in which a resin is dissolved in a solvent. Resins include ethyl cellulose, nitrocellulose, acrylic, etc., while solvents include various cellosolves,
Esters, pine oil, etc. are preferred. When preparing the composition for forming a cathode of the present invention by dispersing the above-mentioned powder in a liquid vehicle, the same technique as for general thick film printing paste can be applied.

Further, it is preferable to add a tackifying component to the cathode-forming composition of the present invention in order to keep the powder adhered to the substrate even after the above-mentioned solvent and resin are scattered in the heating step. Various viscous components are known in the art, and a common method is to add them in the form of powder. -Glass is exemplified as a numerical adhesive component, for example, 5in2
-820, -BaO system, SiO2B203-PbO system,
B20. Examples include -ZnO-based glass compositions, and glass compositions in which various additive components are added thereto. Furthermore, crystalline materials that melt at low temperatures, such as B201, can also be used as other viscous components. Of course, if the conductive oxide powder itself has caking properties, there is no need to separately add a caking component.

The ratio of various components constituting the composition for forming a cathode of the present invention can be set to a good value by appropriate simple experiments based on various characteristics, or the content of the above-mentioned adhesive component can be adjusted to 100 parts by volume of the above-mentioned powder. 0 to 67 parts by volume is preferable. The lower limit of the amount of caking component is determined by the caking force between the powder and the substrate, and the upper limit is determined within a range where deterioration of electrical properties is sufficiently small. usually,
If it exceeds 67 capacitance parts, it is not preferable because the resistance increases and the reaction between the cathode forming material and the adhesive component increases, which tends to deteriorate the discharge characteristics.

Further, the viscosity of the cathode-forming composition of the present invention is preferably 10,000 to 400,000 centipoise. This is because if the viscosity is outside this range, it tends to be difficult to form a pattern with appropriate precision and an appropriate film thickness.

In addition, it goes without saying that other than the above-mentioned examples, known techniques in the field can be widely used.

In a preferred method for producing an oxide cathode according to the present invention, a cathode pattern is formed on a substrate using the above-mentioned conductive oxide powder, more preferably using the composition for forming a cathode of the present invention. Subsequently, this is dried and fired to form a conductive oxide film fixed by the adhesive component or the conductive oxide powder itself. The firing temperature is selected depending on the substrate, the adhesive component, etc., and for example, when soda lime glass is used as the substrate, the upper limit is 600°C. At temperatures higher than this, the glass substrate deforms significantly.

Note that, at such a firing temperature, most of the conductive oxide powder according to the present invention is generally not sufficiently sintered. Therefore, the conductive oxide, which is a highly rigid ceramic powder, is connected only by the contact between each powder, and even if the specific resistance of the powder is small, the resistance of the patterned film becomes very large. Uniform discharge of a large number of cells tends to become difficult.

Therefore, as described above, it is preferable to form a metal film pattern on the base and then form the cathode pattern on this metal pattern. Furthermore, when forming a cathode pattern on this metal pattern, it is effective to cover the entire metal film on the discharge surface with a cathode forming material. This eliminates the need to consider metal sputtering; for example, Ag
5Au.

Any metal such as AI, Cu, Ni, etc. can be used without adding Hg to the fill gas. For forming the metal pattern, ordinary thick film, thin film technology, etc. can be applied. By configuring as described above, it becomes possible to uniformly cause discharge in a large number of cells.

By the way, the electric discharge current cannot flow sufficiently and stably only by the contact of the conductive oxide powder described above. but,
In the oxide cathode manufactured according to the present invention,
It has been found that the film of the cathode-forming material is sufficiently sintered by the discharge energy, that is, Joule heating by ion bombardment and discharge flow. Therefore, in the manufacturing method according to the present invention, it is preferable to sinter the cathode forming material by electric discharge.

For example, even materials such as LaB6, which have a melting point exceeding 2000° C., can be sufficiently sintered. At this time, a method of adding a sintering aid that has a lower melting point than the cathode forming material or reacts with the cathode forming material to produce a low melting point substance can also be used. It is also effective to add a small amount of metal to the cathode to supplement current flow, and this is within the scope of the present invention.

In order to sinter the cathode forming material by discharge in this manner, a voltage higher than the normal operating voltage is generally required at the beginning of the discharge. Although such a state ends in a short time, if a constant voltage is applied as it is, an excessive current will flow and the amount of splintering and ivy will become excessive, which is undesirable. Therefore, it is desirable to gradually lower the voltage over time. Alternatively, it is also an effective method to cause discharge using a constant current power supply. These series of operations are similar to those performed in aging treatment for ordinary metal cathodes, and are not particularly complicated.

In addition, although the above-mentioned manufacturing method is a preferable manufacturing method of the oxide cathode based on this invention, it is not specifically limited to this method.

[Function] It is generally known that oxides of Group Ia, Group IIa, and Ha group elements have low work functions, but none of the single oxides of these elements exhibits sufficient electrical conductivity. However, I
Many of the conductive oxides according to the present invention having a tungsten bronze crystal structure containing group a elements as constituent elements have sufficient conductivity. Moreover, they are thought to have a structure similar to that of the above-mentioned single oxide on part or all of their surface. This is thought to be the reason why the conductive oxide according to the present invention has a low work function and high secondary electron emission efficiency.

Regarding gas storage, it can be considered as follows.

In a conductive non-oxide cathode, the discharge gas is occluded and the effect of Penning gas cannot be utilized. This phenomenon is that when discharge is continued using Penning gas, the operating voltage increases over time and eventually reaches the operating voltage of the single gas. More directly, it is revealed that the intensity of the emission spectrum due to the storage gas becomes weaker as the discharge time increases.

In this case, gas occlusion can be prevented by simultaneously sealing in Hg, but the operating voltage will increase. Furthermore, the visible emission spectrum of Hg also causes a decrease in color purity. However, in the conductive oxide cathode according to the present invention, even if Hg is not enclosed, gas occlusion does not occur, or even if it occurs, it occurs very little. The reason for this is not clear, but it can be considered as follows. In other words, the oxide is packed with large oxygen ions so that the gaps are small, which makes it difficult for gas storage to occur, or there is some phenomenon, such as the formation of a molten layer on the very surface, and even if gas storage occurs, it will be at the same level. There is a possibility that there is a protective effect in which more gas is released. It is also thought that it has a low affinity with commonly used rare gases.

In any case, the conductive oxide cathode according to the present invention can effectively use Penning gas without encapsulating Hg.

Next, ion bombardment will be explained.

Generally, the cathode of a DC discharge display tube is sputtered by ion bombardment. The substances scattered by sputtering contaminate the phosphor, reduce the light transmittance of the glass, and reduce the insulation between the electrodes. A simple way to reduce this spatter is to use high melting point materials to construct a dense cathode, and the application of conductive non-oxides has been successful in this regard. On the other hand, in the case of a metal such as Ni, a sputtering buffer layer is formed by encapsulating Hg to prevent sputtering.

Some of the conductive oxides according to the present invention have a melting point not so high or so low compared to that of Ni, but have sufficient spatter resistance. For example, a decrease in brightness and a decrease in insulation between electrodes after 5,000 hours of discharge are such that they do not cause problems. One of the causes of this is a decrease in ion energy due to a decrease in operating voltage. Also, although it is not clear,
It is also thought that there is a buffering effect due to melting of the very surface of the cathode.

Therefore, the oxide cathode according to the present invention can operate uniformly and stably during discharge of a large number of cells, and has a much lower operating voltage than conventional cathode forming materials. Furthermore, since the oxide cathode according to the present invention has little gas storage, Penning gas can also be used.

Furthermore, since it is resistant to ion bombardment, there is no need to encapsulate Hg, which is toxic. Therefore, it is not only safe and inexpensive, but also has good color purity in color discharge display tubes because it does not have the visible emission spectrum of Hg.

[Examples] Hereinafter, the present invention will be explained in more detail based on Examples and Comparative Examples.

Examples 1 to 1O and Comparative Examples 1 to 9 In Comparative Example 1, a commercially available Ni paste (manufactured by DuPont, product No. 9535) was used, and in the other cases, cathode forming compositions obtained by the following methods were used. . That is, the second
The cathode forming materials listed in the table were first ground to a particle size of 5 .mu.m or less, and sized to have an average particle size of 1 to 3 .mu.m. next,
5i0 for 10 volume parts of the obtained cathode forming material powder
2 B203-PbO-based low melting point glass powder (manufactured by Noritake Company Limited, product No. NP-7903)
A paste-like cathode-forming composition having a viscosity of 10,000 to 200,000 centipoise was prepared by mixing 6 parts by volume of ethyl cellulose with a liquid vehicle in which butyl carpitol acetate was dissolved.

Subsequently, each of the cathode forming compositions described above was printed on a base metal formed on a glass plate so that the film thickness after firing was approximately 10 μl to form a cathode pattern. After drying the cathode pattern, 580°C was applied in air or nitrogen.
A cathode was obtained by firing at ℃.

At that time, patterning was performed so that the discharge portion of the base metal pattern was covered with the cathode forming material. As the base metal of the cathode pattern, Ni paste was used only in Comparative Example 1, and commercially available Ag paste (manufactured by DuPont, product No. 771) was used in the other cases.
3) was formed by printing on the substrate.

A glass plate on which the cathode created in this way was formed,
A DC discharge display tube was created by combining it with a glass plate on which a separately prepared anode was formed.

The main specifications of the created DC discharge display tube are shown in Table 1.

First table anode material: ITO (indium-tin oxide) Discharge gas:
N e -A r (1,0%> 300 Torr
(Comparative Examples 1 and 2 were filled with Hg) Distance between electrodes: 0.13 cm Each of the DC discharge display tubes thus produced was aged under conditions of 150 to 30 V and 12 to 24 hrs to ensure sufficient aging. After stabilization, the discharge sustaining voltage was measured. The results are shown in Table 2. Note that the discharge sustaining voltage here is defined as the voltage immediately before the discharge of a cell that has caused a discharge stops due to a drop in voltage.

Furthermore, when the brightness of each of the above discharge display tubes was measured after 1000 hours of discharge, the deterioration from the initial brightness at the same current value was within 10% in all cases except Comparative Example 3, and the spatter resistance was good. . In Comparative Example 3, the brightness deteriorated significantly, and 140 µ was required to continue the discharge for 1000 hours.

*2: 0.5vt% solid solution of ^120s.

As is clear from the results shown in Table 2, Examples 1 to 10 in which the cathode forming material according to the present invention was used in a DC discharge display tube using Penning gas and not containing Hg.
Comparative Example 1 uses a conventional Ni cathode and fills Hg in the discharge gas, Comparative Example 2 uses a LaB6 cathode and fills Hg in the discharge gas, and Comparative Example 2 uses Ag20i at 0.5V.
It was possible to reduce the operating voltage much more than in Comparative Example 4 using a ZnO cathode containing t% solid solution, and other discharge characteristics were also good.

In addition, the discharge display tubes of Examples 1 to 1O had the composition formula (1)
, yo, but in which X is not a Group Ia element, the operating voltage can be lowered than in Comparative Examples 5 to 9, in which conductive oxides are used as cathode forming materials, and other discharge characteristics are also good. there were.

As described above, the discharge display tubes of Examples 1 to 10 have low discharge sustaining voltages, which indicates that the conductive oxide according to the present invention has a low work function and high secondary electron emission efficiency. Ta.

In addition, the DC discharge display tube of Comparative Example 3, in which a LaB6 cathode was used without Hg being enclosed in the discharge gas, had a low initial discharge sustaining voltage, but was inferior in gas occlusion property.

[Effects of the Invention] As explained above, the discharge display tube of the present invention provides the following effects.

(2) The operating voltage can be lowered than that of conventional devices, and the low operating voltage can be stably applied over a long period of time. As a result, the cost of the drive circuit can be reduced, and the luminous efficiency can be improved, resulting in higher brightness and further reduction in power consumption.

(2) There is no need to enclose Hg in the discharge gas, which is favorable in terms of environmental hygiene and reduces costs.

Furthermore, since there is no Hg visible emission spectrum in the color discharge display tube, color purity is improved.

(2) The discharge display tube of the present invention can be easily produced using conventionally known techniques such as thick film technology, and new cost increases and new equipment investments are not particularly required.

Further, by using the composition for forming a cathode of the present invention, it becomes possible to manufacture the above-mentioned oxide cathode easily and at low cost. Therefore, the cathode-forming composition of the present invention is suitably employed in manufacturing the discharge display tube of the present invention.

Claims (1)

[Claims] 1. A DC discharge display tube, the cathode forming material of which is
Composition formula (1): X_xYO_3 [In formula (1),
Y is at least one member selected from the group consisting of Re, W, Mo, and Nb, and x is a numerical value greater than 0 and less than 1.] discharge display tube. 2. The discharge display tube according to claim 1, wherein a metal layer is formed under a film-like cathode made of the conductive oxide as a cathode forming material. 3. The discharge display tube according to claim 1 or 2, wherein the gas sealed inside the discharge display tube does not contain Hg. 4. Composition formula (1): X_xYO_3 [In formula (1),
species, Y is at least one member selected from the group consisting of Re, W, Mo, and Nb, and x is a numerical value greater than 0 and less than 1, respectively] with an average particle diameter of 0. 1
A composition for forming a cathode of a discharge display tube, comprising a powder of ~30 μm dispersed in a liquid vehicle. 5. The powder and 0 to 67 parts per 100 parts by volume of the powder.
5. The cathode-forming composition according to claim 4, wherein a volume portion of the viscous component is dispersed in a liquid vehicle.