JPH0737485A - Oxide negative electrode and manufacture thereof - Google Patents

Abstract

PURPOSE:To improve the adhesion strength of a ternary carbonate coated layer without reducing the emission characteristic. CONSTITUTION:An oxide negative electrode is provided by forming an electron emission coated layer 3 of ternary alkaline earth metal carbonate primarily consisting of Ba, Sr, Ca on a metal core 1. The coated layer 3 has a metal oxide layer 2 between the core 1 and the carbonate layer 3, and the metal oxide concentration of the oxide layer indicates a maximum value on the surface of a core electrode, while its concentration grading is gradually lowered to the carbonate side.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a vacuum tube, a cathode ray tube (C
The present invention relates to an oxide cathode used in various electron tubes such as RT), electron microscopes, and fluorescent display tubes, and a manufacturing method thereof.

[0002]

2. Description of the Related Art Conventionally, as an oxide cathode filament, a very thin core wire made of a tungsten alloy or the like having a diameter of 10 to 30 μm is used, and as an electron emitting substance, an alkaline earth metal carbonate of barium carbonate, calcium carbonate or strontium carbonate A fine powder of ternary carbonate) coated with a film thickness of about 8 to 15 μm is used. When this oxide cathode is used in a fluorescent display tube, it is installed in a tube and then the inside of the fluorescent display tube is evacuated to a high vacuum.
Heat decomposition at a temperature of about ℃. As a result, the ternary carbonate is converted into an oxide (Ba, Sr, Ca) O, and then activated to produce free Ba to serve as an electron emission source.

As a method of coating a ternary carbonate on a core wire made of tungsten or the like, conventionally, a suspension of the ternary carbonate is placed in a container and the base metal core wire is immersed in the suspension to form a base metal surface. Dip coating with ternary carbonate, spraying with ternary carbonate mixed with alcohol and spraying on the base metal with a spray gun, and basing the base metal on a solution in which the ternary carbonate is suspended. An electrodeposition method applying the electrophoresis principle is adopted.

Among them, the coating method by electrodeposition is extremely dense in the coating layer to be formed, and the surface can be made smooth, so that the CR
It is used for cathodes such as T, TWT, magneto-electric tubes, and fluorescent display tubes that are subject to impact from ions, electrons, etc. and require high density, and cathodes such as rectifying tubes that resist sparks.

On the other hand, problems to be solved in the oxide cathode by such an electrodeposition method include improvement of emission characteristics and improvement of adhesion force for preventing peeling of the coating layer and achieving a long life. .

Regarding the former improvement of emission characteristics, for example, Japanese Patent Publication No. 28218/1990 and Japanese Patent Laid-Open No. 1-118 / 1989
24926, JP-A-63-271843,
JP-A-63-32836, JP-A-59-9162
Various manufacturing techniques have been proposed in Japanese Patent Publication No. 5, etc., and these have achieved tentative results.

However, the manufacturing technique of the oxide cathode disclosed in the above publication is limited to improving the emission characteristics, and the second problem to be solved is to improve the adhesive force of the ternary carbonate coating layer. Has not contributed to.

Further, in Japanese Patent Laid-Open No. 53-963, the problems of the conventional manufacturing method using acrylic resin or nitrocellulose as a binder are solved, the mechanical strength is large, and the peeling to the reel is effective. The manufacturing technique of the cathode which can be prevented is described.

However, even in the method disclosed in the publication, nitrocellulose is basically used as a binder, and it is not a fundamental solution.

That is, by adding a small amount of nitrocellulose to the electrodeposition solution, the electrodeposition rate and the green strength before thermal decomposition are improved, but if the amount is too large, not only the electrodeposition characteristics deteriorate, but also the carbon dioxide. When the salt is decomposed, nitrocellulose is also decomposed, which causes cracks to occur, resulting in a reduction in strength when used as a cathode ray tube.
Further, when this nitrocellulose is used as a fluorescent display tube, it does not contribute to the improvement of the adhesive force during use because it is fired at the same time when the ternary carbonate is oxidized as described above. There is also a problem that the gas component remaining in the pipe due to thermal decomposition damages the emission characteristics.

[0011]

Therefore, an object to be solved in the present invention is to provide an oxide cathode excellent in adhesion strength of a ternary carbonate coating layer without lowering emission characteristics and a method for producing the same. It is in.

[0012]

In order to improve the adhesion strength of the ternary carbonate coating layer, the present inventor tried to add various metal oxides into the electrodeposition solution to complete the present invention. It has come.

That is, the oxide cathode of the present invention is an oxide cathode in which a coating layer for electron emission of a ternary alkaline earth metal carbonate containing Ca, Ba and Sr as the main components is formed on a metal core wire. In the above, the coating layer has a metal oxide layer between the core wire and the carbonate, the metal oxide concentration of the oxide layer shows the highest value on the surface of the core wire, and the concentration gradient becomes low on the carbonate side. It is characterized by having.

Here, the average particle size of the metal oxide is fine powder smaller than the average particle size of the carbonate, and the amount of the metal oxide in the coating layer is 0.5 to 20% by weight of the carbonate. In addition, the metal oxide is In ₂
O ₃ , ZnO, Al ₂ O ₃ , La ₂ O ₃ , ZrO ₂ , T
One or more of hO ₂ , SnO ₂ , MgO and Ta ₂ O ₅ can be used.

Further, according to the present invention, an electrodeposition solution comprising a ternary alkaline earth metal carbonate containing Ba, Sr and Ca as main components, a binder and a solvent is formed, and this solution is used for an oxide cathode. In the method for producing an oxide cathode by an electrodeposition method in which the surface of the core wire is coated with the carbonate by electrophoresis, a fine powder smaller than the average particle size of the carbonate salt is contained in the electrodeposition liquid. In ₂ O ₃ , ZnO, Al ₂ O ₃ , La
₂ O ₃ , ZrO ₂ , ThO ₂ , SnO ₂ , MgO and T
It is characterized in that 0.5 to 20% by weight of a carbonate is added to any metal oxide of a ₂ O ₅ or a mixture of two or more kinds of these metal oxides.

Here, pure tungsten can be preferably used as the core wire for the oxide cathode, but the core wire is not limited to this, and for example, a tungsten alloy such as thorium tungsten can be used.

The average particle size of the metal oxide needs to be smaller than the average particle size of the ternary carbonate. Particularly, about 1/10 of the average particle size of the ternary carbonate is the highest value on the surface of the core wire. The tendency is to have a concentration gradient that decreases toward the carbonate side, and the effect of improving the carbonate adhesion strength can be exhibited even with a small amount of addition.

Further, the addition amount of the metal oxide to be added is 0.
If it is less than 5%, a sufficient effect of improving the adhesive force cannot be exhibited, and as the addition amount increases, the emission characteristics deteriorate, and if it exceeds 20%, the emission characteristics remarkably decrease.

Among the above eight kinds of metal oxides, ZnO and In ₂ O ₃ exhibit excellent effects in terms of emission characteristics and adhesion.

Further, it is necessary that these metal oxides are uniformly dispersed together with the ternary carbonate in the electrodeposition liquid by ultrasonic dispersion or ball mill dispersion during electrodeposition.

[0021]

In FIG. 1, a tungsten wire having a diameter of 13 μm is used as the core wire 1, and 5% by weight of In ₂ O ₃ having an average particle diameter of 0.3 μm is added to ternary carbonate having an average particle diameter of about 3.0 μm.
Schematic diagram of the cross section of the oxide cathode when added, FIG.
₂ shows a concentration gradient of ₂ O ₃ (measures the characteristic X-ray intensity of In by EPMA), and a metal oxide 2 having a small particle size is attached to a portion closer to the surface of the core wire 1, and a ternary carbonate 3 is provided around this It has a structure in which an intermediate layer of the metal oxide 2 is formed between the core wire 1 and the ternary carbonate 3 attached.

Since this metal oxide has a smaller particle size than the ternary carbonate, it is excellent in electrophoretic property and adheres to the surface of the core wire before the ternary carbonate in the electrodeposition liquid and is a fine particle. ,
The contact area between the particles and the core wire and particles increases, and as a result, the particles strongly adhere to the core wire. Further, it is speculated that the presence of these fine particles has the effect of smoothing the surface irregularities by filling the inter-particle voids of the ternary carbonate, and the adhesiveness of the ternary carbonate is excellent and the adhesion strength is improved. .

It is generally said that the presence of the intermediate layer formed on the core wire and the coating layer is not preferable for forming the resistance layer as a semiconductor. It does not mean that it develops, but it is sufficient that the intermediate layer is in a fully activated state even if it occurs. The intermediate layer of the oxide cathode according to the present invention can maintain this activated state.

Further, in the conventional oxide cathode having no intermediate layer of metal oxide, the coating layer of the ternary carbonate contracts and cracks occur during thermal decomposition at the time of mounting, which grows to form a cylindrical shape. Although it leads to peeling, in the product of the present invention, the intermediate layer of the metal oxide suppresses shrinkage in the film thickness direction during thermal decomposition, exerts a buffering effect, and the occurrence of cracks after thermal decomposition and Peeling resulting from this can be effectively prevented.

[0025]

Example: (Ba, Sr, Ca) CO having an average particle size of 3 μm
_Using the ternary carbonate of 3 and an acrylic resin (manufactured by DuPont: Elvasite 2045) as a binder, acetone (special reagent grade): 45% by weight, MIBK (special grade reagent): 24% by weight, IPA (special grade reagent) : 24 wt%, Elvacite 2045: 5 wt%, and ternary carbonate: 2 wt% are mixed by a well-known mixing method, and the average particle size is added to this liquid in order to confirm the effect due to the difference in the addition amount. 0.3~3.0μm was varied _{between, ZnO, Al 2 O 3,} La 2 O 3, ZrO
₂ , ThO ₂ , SnO ₂ , In ₂ O ₃ , Ta ₂ O ₅ , M
0.5% by weight, 2% by weight, 5% by weight, 10% by weight and 20% by weight of gO were added to prepare an electrodeposition solution. The particle sizes of the ternary carbonate and the metal oxide were measured using a laser diffraction particle size analyzer (Microtrac FRA).

A tungsten wire having a diameter of 13 μm was passed through the electrodeposition solution at a rate of 16 m / min to form a carbonate coating layer by electrodeposition. The electrodeposition conditions were a constant current power supply, current value was 60 ± 10 μA, and voltage value was 60-1.
It was set to 00V.

Further, as a comparative example, SiO having a similar particle size.
_A filamentary cathode was manufactured under the same conditions by using ₂ , TiO ₂ , and WO ₃ .

First, in order to confirm the carbonate adhesion growth strength after electrodeposition, it was wound on a spool every 500 m, and a total of 10 spools were passed while contacting a glass tube having an inner diameter of 1 mm, and the peeling condition was confirmed. .

FIG. 3 shows the positional relationship between the glass tube and the spool. In the figure, 10 indicates the spool and 11 indicates the glass tube. FIG. 4 shows the relationship between the amount of metal oxide added and the number of occurrences of peeling for 10 spools (the number of peeled portions having a length of 0.5 mm or more was counted).

As shown in FIG. 4, in the conventional product, the number of peeling occurrences was about 50, and it was found that the adhesive strength was weak. On the other hand, the metal oxide-added products of the Examples are irrespective of their types,
The effect starts to appear from the addition amount of 0.5% by weight, and the effect is more remarkable especially in the case where the average particle size is small. In addition,
No peeling was observed in the sample containing 1% by weight or more of 0.3 μm metal oxide.

Further, this filament cathode is mounted on the fluorescent display tube shown in FIGS. 5 and 6, and the inside of the tube is evacuated to a high vacuum to be thermally decomposed at a temperature of about 1000 ° C. to change the ternary carbonate into an oxide. Then, activation treatment was performed to obtain an oxide cathode to serve as an electron emission source.

In order to confirm the adhesion strength of the oxide cathode thus obtained, SEM photograph observation after thermal decomposition was performed, and a peeling experiment of the oxide layer was performed when a product impact of 2000 G was applied. It was

FIG. 5 is a sectional view of the fluorescent display tube, and FIG. 6 is a perspective view showing the appearance of the fluorescent display tube shown in FIG. In the figure, 21 is a plate glass, 22 is a conductive layer, 23 is an anode electrode,
24 is an insulating layer, 25 is a phosphor, 26 is an exhaust pipe, 27 is a grid, 28 is a conductive paste, 29 is an oxide cathode (filament), 30 is a getter, 31 is a windshield,
32 is a spacer glass, 33 is a lead pin, and 34 is an anchor for disposing and supporting the filament.

The filament cathode 29 has an anchor 34.
Since it is stretched with tension applied, it has a structure that shakes when an impact is applied. In this experiment, excessive impact was applied to the fluorescent display tube, the filament cathode 29 and the grid 27 were brought into contact with each other, and the peeling state of the oxide layer was evaluated.

FIG. 7 shows, for each particle size, the relationship between the adhesion strength of the oxide layer and the addition amount of the metal oxide after a product impact of 2000 G is applied to the fluorescent display tube. Here, A group is Zn
O, In ₂ O ₃ and B group are Al ₂ O ₃ and La ₂
O ₃ , ZrO ₂ , ThO ₂ , SnO ₂ , Ta ₂ O ₅ , M
gO, and C group is SiO ₂ , TiO ₂ , WO
₃ represents the addition of ₃ respectively. As for the strength evaluation, the case where no peeling was observed was designated as strength 5, the case where partial peeling occurred was designated as strength 3, and the case where cylindrical peeling occurred was designated as strength 0. In addition, the intermediate values are set to 4 and 2, respectively.

As shown in FIG. 7, in the metal oxide-added product of this embodiment, the adhesion was improved from the addition amount of 0.5% by weight, and ZnO and In ₂ O ₃ were particularly remarkable. Further, it can be seen that the smaller the particle size, the more effective the effect can be.

Further, after carrying out this product impact test, the fluorescent display tube was disassembled and the filament cathode was observed by SEM. In the case of the present invention, as shown in FIG. 8, neither crack nor filamentous cylindrical peeling accompanying it was observed at all (as a representative example, a product containing 5% of In ₂ O ₃ added). As shown in FIG. 9, the conventional product has a cylindrical crack due to contraction during thermal decomposition.
Cylinder-shaped peeling as shown in 0 occurred.

Next, the fluorescent display tube mounted with an oxide cathode added with a metal oxide was driven to evaluate the emission capability of the oxide cathode.

FIG. 11 is a graph showing the relationship between the amount and type of metal oxide added and the amount of emission. The amount of emission is a relative value when the value when no metal oxide is added is 100. . Here, each group of A, B, and C shows the same thing as FIG. Note that 5% deterioration is an emission deterioration range that does not affect the luminance characteristics and is a level that can be cleared by minute control of the grid-filament distance, so 95% or more was set as the usable range.

As can be seen from the figure, in the A and B groups, when the addition amount is 20% by weight or less, the emission characteristics are not practically affected, and in particular, ZnO and In ₂ O _{3 in the} A group are included.
It was confirmed that the addition range of the above can be wide. Further, it was found that SiO ₂ , TiO ₂ , and WO ₃ are significantly deteriorated.

From the above, ternary alkaline earth metal carbonates can be added to In ₂ O ₃ , ZnO, Al ₂ O ₃ , La ₂ O ₃ ,
A filamentary cathode formed by adding 0.5 to 20% by weight of a metal oxide such as ZrO ₂ , ThO ₂ , SnO ₂ , Ta ₂ O ₅ , and MgO and forming an intermediate layer of this metal oxide is a ternary carbonate. The adhesion strength immediately after electrodeposition of Pd is improved, and the adhesion strength with the oxide layer after thermal decomposition is also excellent.
It was confirmed that and In ₂ O ₃ do not affect the emission characteristics.

[0042]

According to the present invention, the following effects can be obtained.

(1) The adhesion strength of the oxide cathode is increased without degrading the emission characteristics, and stable use is possible for a long period of time.

(2) Since the adhesion strength of the oxide cathode is increased without deteriorating the emission characteristics, the size between the grid and the filament can be reduced, and a high-brightness product can be obtained with less electric power. It can be suitably used for in-vehicle use which is susceptible to strong shock and vibration.

(3) An intermediate layer of metal oxide is formed by a simple method of adding a finely powdered metal oxide smaller than ternary carbonate to a conventional electrodeposition liquid, and the coating layer is not peeled off. An oxide cathode having strong adhesion can be obtained.

(4) Since the added metal oxide does not gasify even during the thermal decomposition of the ternary carbonate, the effect on the emission characteristics is extremely small.

[Brief description of drawings]

FIG. 1 is a schematic view of an oxide cathode obtained by the method of the present invention.

FIG. 2 is a graph showing changes in the concentration of In ₂ O ₃ from the surface of the core wire (intensity X-ray intensity of In).

FIG. 3 is a diagram showing a positional relationship between a glass tube and a spool.

FIG. 4 is a diagram showing the relationship between the amount of metal oxide added and the number of occurrences of peeling for 10 spools for each particle size.

FIG. 5 is a cross-sectional view of a fluorescent display tube.

6 is an external view of the fluorescent display tube shown in FIG.

FIG. 7 is a diagram showing, for each particle size, the relationship between the adhesion strength of the oxide layer and the amount of metal oxide added after a product impact of 2000 G is applied to the fluorescent display tube.

FIG. 8 is an SEM photograph showing a particle structure of the filamentary cathode of this example after an impact test.

FIG. 9 is an SEM photograph showing a particle structure of a conventional filament cathode after thermal decomposition.

FIG. 10 is an SEM photograph showing a particle structure of a conventional filamentary cathode after an impact test.

FIG. 11 is a graph showing the relationship between the amount of metal oxide added and the amount of emission.

[Explanation of symbols]

 1 core wire 2 metal oxide 3 ternary carbonate

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Taro Yoneda 2160 Yatsunami, Sannami, Yasu Town, Asakura-gun, Fukuoka Prefecture Kyushu Noritake Co., Ltd.

Claims (4)

[Claims] 1. An oxide cathode in which a coating layer for electron emission of a ternary alkaline earth metal carbonate mainly containing Ba, Sr, and Ca is formed on a metal core wire, wherein the coating layer is the core wire. An oxide having a metal oxide layer between the carbonates, the metal oxide concentration of the oxide layer exhibits the highest value on the surface of the core wire, and has a concentration gradient that decreases toward the carbonate side. cathode. 2. An average particle size of the metal oxide is a fine powder smaller than the average particle size of the carbonate, and the amount of the metal oxide in the coating layer is 0.5 to 20% by weight of the carbonate. The oxide cathode according to claim 1, wherein 3. The metal oxide is In ₂ O ₃ , ZnO,
Al ₂ O ₃ , La ₂ O ₃ , ZrO ₂ , ThO ₂ , SnO
The oxide cathode according to claim 1 or 2, which is one or more of ₂ , ₂ , MgO and Ta ₂ O ₅ . 4. An electrodeposition solution comprising a ternary alkaline earth metal carbonate containing Ba, Sr and Ca as main components, a binder and a solvent is formed, and a core wire for an oxide cathode is passed through the solution. In the method for producing an oxide cathode by an electrodeposition method in which the surface of the core wire is coated with the carbonate by electrophoresis, In ₂ which is a fine powder smaller than the average particle size of the carbonate in the electrodeposition solution O ₃ , ZnO, Al ₂ O ₃ , La ₂ O
₃ , ZrO ₂ , ThO ₂ , SnO ₂ , MgO and Ta ₂
0.5 to 20% by weight of a metal oxide of O ₅ or a mixture of two or more of these metal oxides with respect to the carbonate.
A method for producing an oxide cathode, characterized by being added.