JPH04160719A - Discharge display tube and component for forming cathode thereof - Google Patents

Abstract

PURPOSE:To reduce the operating voltage, and improve light emitting efficiency, and improve the luminance by including the specified conductive oxide in the oxide having the K2NiF4 type crystal structure. CONSTITUTION:The conductive oxide, which is obtained by solid solution of the oxide showed with a formula X2O in the oxide having the K2NiF4 type crystal structure, is included in the material for forming a cathode of a direct current type discharge display tube. The element X in the formula shows at least one kind of elements to be selected among the Ia group element group of a periodic table of elements. The conductive material, of which gas occlusion is a little and a coefficient of work is low and secondary electron emitting efficiency is high and strong against the ion shock, is thereby obtained, and a discharge display tube, of which operating voltage is reduced and stabilized and of which luminance is improved and of which color purity is improved and of which manufacture is easy, is realized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a DC discharge display tube and a composition for forming a cathode 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.

[Issues to be solved by the prior art and the invention 1fil
Generally, discharge display tube (plasma display panel:
rPDPJ) can be classified into DC type discharge display tubes whose electrodes are exposed to the discharge space and operated by applying DC voltage, and AC type discharge display tubes whose electrode surfaces are covered with a dielectric material and operated by applying AC voltage. It is broadly divided into display tubes.

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 MgO1Bad or CaO1SrO. 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 100 mm.
It should be fairly thin and uniform. 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 LaBb, CeB6, etc., has been proposed (Japanese Unexamined Patent Application Publication No. 1983-1999).
-221926 to 60-221928, 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 Problems] As a result of intensive studies to solve the problems of the above-mentioned conventional technology, the present inventors found that 2N i F was used as a cathode forming material.
The inventors have discovered that the above object can be achieved by using a conductive oxide formed by dissolving an oxide of an RA group element in an oxide having a type 4 crystal structure, and have completed the present invention.

That is, the present invention provides a DC discharge display tube in which the cathode-forming material is an oxide having a K2NiF4 type crystal structure with the composition formula (1): At least one selected from group Ia elements]
This is a discharge display tube characterized by including a conductive oxide formed by dissolving an oxide represented by:

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, 2N i F, an oxide having a type crystal structure, is used as the cathode forming material. The above oxide is represented by the composition formula (2): Y2ZO4, where element Y is various rare earth elements, and element Z is C.
o, Ni5Cu, etc. are exemplified. Further, the above-mentioned oxides include those having a chemotactic composition, such as those having oxygen vacancies, and such oxides can also be used in the present invention.

Further, each constituent element of the oxide can form a solid solution over a wide range, and each of the elements Y and Z may be a solid solution consisting of a plurality of elements. Note that the above-mentioned oxide does not necessarily have to be conductive, and even if it is insulating, it can become conductive by dissolving the oxide represented by the composition formula (1) described below. good.

The above oxides having a 2NiF4 type crystal structure include:
It is preferable that a sufficient amount of the oxide represented by the compositional formula (1) described below can be solid-dissolved and the operating voltage can be lowered.

In the present invention, it is necessary to form a solid solution of the specific oxide represented by the compositional formula (1): X2O in the oxide having the 2NiF4 type crystal structure. This is because the operating voltage is significantly reduced by incorporating the oxide represented by the compositional formula (1) into solid solution. Element X in the above compositional formula (1) is a group Ia element of the periodic table of elements, namely Lt, Na5K, Rb,
At least one member selected from the group consisting of C8% Fr.

The solid solution amount of the oxide represented by the compositional formula (1) is the above K 2
It is selected as appropriate depending on the type of oxide having the N iFa type crystal structure, and is determined by taking into consideration ease of solid solution, stability, conductivity, operating voltage, etc. In general, the cations of the conductive oxide according to the present invention contain latoi+% of Group Ia elements.
If more than 100% of the oxides are present, the effect of reducing the operating voltage tends to be sufficiently exhibited.

The conductive oxide used as the cathode forming material in the present invention may be a single type of oxide or 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 material for sealing between the two substrates 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.

Furthermore, for example, when a plurality of discharge cells are connected by a hollow 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·c+g (300°K) can be used satisfactorily. Another advantage of this method is that when connecting the cathode to an external circuit, if you use a metal layer and leave a part of it exposed, you can create a pattern that does not have problems with normal solderability, bonding, plating, etc. This means that it can be formed all at once.

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 described.

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.

Furthermore, 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 by using the cathode-forming composition of the present invention, which will be described in detail below, the oxide cathode of the present invention can be manufactured into a package by printing technology used in ordinary thick film technology. I discovered that it is possible to

That is, the cathode forming composition of the present invention includes K2NiF,
An oxide represented by the composition formula (D: It is characterized by dispersing a conductive oxide powder having an average particle size of 0.1 to 30 μm in a liquid vehicle.

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. The above-mentioned powder needs to have an average particle size of 0.1 to 30 μ-.

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

On the other hand, if it is larger than 30μ, fine patterning is difficult and sufficient bonding between the powder particles cannot be obtained.

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 main 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 so that the powder can be adhered to the substrate even after the above-mentioned solvent and resin are scattered during the heating step. Various types of adhesive components are known in the field, and a common method is to add them in the form of powder.Glass is exemplified as a general adhesive component, for example, SiO□
-B, 0. -BaO system, 5i02 BzOi-pbo
system, B2O. Examples include -ZnO-based glass compositions, and glass compositions in which various additive components are added thereto. In addition, crystalline materials that melt at low temperatures, such as B2O3, 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 is set to a good value by appropriate simple experiments based on various characteristics, but the content of the above-mentioned adhesive component is determined based on 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, the resistance becomes high and the reaction between the cathode forming material and the adhesive component increases, which tends to deteriorate the discharge characteristics, which is not preferable.

Further, the viscosity of the cathode-forming composition of the present invention is preferably 10,000 to 400,000 centiboise. 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, adhesive components, etc., and for example, when soda lime glass is used as the substrate, the upper limit is 800°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 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 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
SA u.

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, it is possible to sufficiently sinter a material such as LaB6 whose melting point exceeds 2000°C. 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 sputtering will become excessive, which is undesirable. Therefore,
It is desirable to lower the voltage sequentially over time. Alternatively, it is also an effective method to cause discharge using a constant current power source. These series of operations are similar to those performed during aging treatment for ordinary metal cathodes,
It's 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] Generally, oxides of group Ia, group Ila, and group ma elements are known to have a low work function, but no single oxide of these elements exhibits sufficient electrical conductivity. However, K.
Many of the composite oxides according to the present invention, in which a group Ia element oxide is dissolved in an oxide having a 2NiF4 type crystal structure, have sufficient electrical 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, oxides are densely packed with large oxygen ions, so the gaps are small, making it difficult for gas occlusion to occur, or there may be some phenomenon, such as the formation of a molten layer on the very surface, which causes gas occlusion to the same extent. 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 IO and Comparative Examples 1 to 8 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 per 100 parts by volume of the obtained cathode forming material powder
2 6 parts by volume of B2O3-PbO-based low-melting glass powder (manufactured by Noritake Company Limited, Product No. NP-7903) were mixed, and the mixture was further kneaded with a liquid vehicle in which ethyl cellulose was dissolved in butyl calpitol acetate to reduce the viscosity. A paste-like cathode-forming composition having a density of 10,000 to 20,000 centipoise was prepared.

Subsequently, each of the above-mentioned cathode forming compositions was printed on a base metal formed on a glass plate so that the film thickness after firing was about 10μ- 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.

Table 1 shows the main specifications of the created DC discharge display tube.

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 mm Each of the DC discharge display tubes created in this way was aged under conditions of 150 to 300 V and 12 to 24 hrs to ensure sufficient stability. After that, 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, too regarding each of the above discharge display tubes.

When the brightness was measured after time 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 140V was required to continue the discharge for 1000 hours.

A conductive oxide in which oxide (b) is dissolved in a solid solution of (numerical value) SO1%.

*2: 140 to continue discharging for 1000 hours
■It was necessary.

*3: 0.5 wt% solid solution of ^1□03.

As is clear from the results shown in Table 2, Examples 1 to 1 in which the cathode forming material according to the present invention was used in a DC discharge display tube using Penning gas and without enclosing 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 a conventional Ni cathode and fills Hg in the discharge gas.
It was possible to reduce the operating voltage much more than in Comparative Example 4 using a ZnO cathode containing 5vt% solid solution, and other discharge characteristics were also good.

In addition, the discharge display tubes of Examples 1 to 10 are Comparative Examples 5 to 8 in which the oxide having a 2NiF type crystal structure according to the present invention is used as a cathode forming material without forming a solid solution of an oxide of a group 18 element. It was possible to lower the operating voltage, and other discharge characteristics were also good.

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
The composition formula (
1):X_2O [In formula (1), X is I of the periodic table of elements
1. A discharge display tube comprising a conductive oxide formed by dissolving an oxide represented by at least one selected from Group A elements. 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. An oxide having a K_2NiF_4 type crystal structure has a compositional formula (1):
A conductive oxide containing at least one element selected from group Ia elements] is dispersed in a liquid vehicle, and a conductive oxide powder having an average particle size of 0.1 to 30 μm is dispersed in a liquid vehicle. A composition for forming a cathode of a discharge display tube, characterized in that: 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.