JPH07107825B2 - Electron tube cathode - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cathode for an electron tube used in a cathode ray tube for a television.

[0002]

2. Description of the Related Art FIG. 3 is a sectional view of a cathode for an electron tube used in a conventional television cathode ray tube disclosed in, for example, Japanese Patent Publication No. Sho 64-5417. In FIG. 3, (1) is a substrate containing a small amount of reducing elements such as silicon (Si) and magnesium (Mg), the main component is nickel (Ni), (2) is a sleeve made of nichrome, ( 6) is an electron emission material layer deposited on the upper surface of the substrate (1). This electron emitting material layer
(6) contains alkaline earth metal oxide (61) containing barium (Ba) at least and strontium (Sr) and / or calcium (Ca) in addition to rare earth metal oxide such as scandium oxide. (62) is contained in an amount of 0.1 to 20% (weight%, the same shall apply hereinafter). Reference numeral (3) is a heater arranged in the substrate (1), and by heating the heater (3), thermoelectrons are emitted from the electron-emitting substance layer (6).

Next, a method for depositing and forming the electron-emitting material layer (6) on the substrate (1) for producing the cathode for an electron tube having such a structure will be described.

First, a ternary carbonate of barium, strontium, and calcium and a predetermined amount of scandium oxide are mixed with a binder and a solvent to prepare a suspension, and this suspension is sprayed onto a substrate (1). Applied to a thickness of about 80 μm by the heater (3) during the vacuum evacuation process of the cathode ray tube.
Heating by. At this time, the alkaline earth metal carbonate is changed to the alkaline earth metal oxide (61). After that, by performing activation, a part of the alkaline earth metal oxide (61) is reduced, and the electron-emitting substance layer (6) has a semiconducting property. An electron emissive material layer (6) made of a mixture of an earth metal oxide (61) and a rare earth metal oxide (62) is formed.

In this activation step, a part of the alkaline earth metal oxide (61) reacts as follows. That is, reducing elements such as silicon and magnesium contained in the substrate (1) are diffused to form an alkaline earth metal oxide.
It moves to the interface between (61) and the substrate (1) and reacts with the alkaline earth metal oxide (61). For example, alkaline earth metal oxides
Taking barium oxide (BaO) as an example of (61),
It reacts like (I) and (II).

2BaO + 1 / 2Si → Ba + 1 / 2Ba ₂ SiO ₄ (I) BaO + Mg → Ba + MgO (II) As a result of this reaction, the alkaline earth metal oxide deposited on the substrate (1) (61) Is partially reduced to an oxygen-deficient semiconductor, which facilitates electron emission. If the electron emitting material layer (6) does not contain the rare earth metal oxide (62), it can operate at a current density of 0.5 to 0.8 A / cm ² at an operating temperature of the cathode temperature of 700 to 800 ° C. When the oxide (62) is included, a current density operation of 1.32 to 2.64 A / cm ² is possible.

As described above, the operating current density is small when the rare earth metal oxide (62) is not contained. Generally, in the case of an oxide cathode, the electron emission capability is excessive Ba in the oxide.
This is because the supply of sufficient excess Ba required for high current density operation cannot be performed because it depends on the existing amount. That is,
Barium silicate (Ba ₂ SiO ₄ ) and magnesium oxide (MgO), which are by-products generated during the reaction and are called the intermediate layer, are the base materials.
(1) Nickel grain boundaries and substrate (1) and electron-emitting material layer
Since it is formed intensively at the interface with (6), the above formulas (I) and (I
The reaction of I) is controlled by the diffusion rate of magnesium and silicon in this intermediate layer, and the supply of excess Ba is insufficient. On the other hand, a rare earth metal oxide (62) is formed on the electron emitting material layer (6).
In the case of scandium oxide (Sc ₂ O ₃ ), the interface between the substrate (1) and the electron emitting material layer (6) during cathode operation is A part of the reducing agent that has diffused and scandium oxide react as shown in the following formula (III) to generate a small amount of metallic scandium (Sc), and a part of the metallic scandium of the substrate (1) It forms a solid solution in nickel, and some of it exists at the interface.

1 / 2Sc ₂ O ₃ + 3 / 2Mg → Sc + 3 / 2MgO (III) This metallic scandium is formed on the substrate (1) or at the grain boundary of nickel of the substrate (1) by the following intermediate layer. Since it has a decomposition action as in formula (IV), it is considered that the supply of excess Ba is improved and a higher current density operation becomes possible than when the rare earth metal oxide (62) is not included.

1 / 2Ba ₂ SiO ₄ + 4 / 3Sc → Ba + 1 / 2Si + 2 / 3Sc ₂ O ₃ (IV)

[0010]

In the cathode for an electron tube thus constructed, the rare earth metal oxide contributes to the supply of excess Ba, but the supply rate of excess Ba depends on the reducing agent present in the nickel of the substrate. Controlled by the diffusion rate of 2A / cm
^In high current density operation of ² or more, there is a problem that the lifetime characteristic is significantly deteriorated due to the evaporation loss of Ba due to the generation of local Joule heat in the electron passage region in the electron emitting material.

The present invention has been made to solve the above problems, and an object thereof is to obtain a good life characteristic even in a high current density operation of 2 A / cm ² or more.

[0012]

According to the present invention, an alkaline earth metal oxide containing a main component of nickel and a metal mixed layer formed on a substrate containing at least one reducing agent, on which at least barium is contained. A cathode for an electron tube having an electron emitting material layer containing a substance deposited thereon, wherein the metal mixed layer has a reducing property less than or equal to at least one reducing agent in the substrate and a reducing property more than nickel. Containing a powder of a large metal (hereinafter referred to as a specific reducing metal), an alkaline earth metal oxide containing at least barium, and a rare earth metal oxide, and the content rate of the rare earth metal oxide is 0.0
It relates to a cathode for an electron tube, which is a layer of 1 to 25%.

[0013]

In the present invention, in addition to the reducing agent in the substrate, the specific reducing metal in the metal mixed layer contributes to the supply of Ba and also contributes to the production of the rare earth metal having the decomposing effect on the intermediate layer. In addition, the specific reducing metal in the mixed metal layer improves conductivity, so the evaporation loss of Ba also decreases with the decrease of Joule heat, especially the life characteristics in high current density operation of 2 A / cm ² or more. Is significantly improved.

[0014]

EXAMPLES In the present invention, a base metal containing nickel as a main component and containing at least one kind, usually 2 to 4 kinds of reducing agents is used.

Examples of the reducing agent include silicon,
Examples include magnesium, zirconium, and tungsten.

The proportion of reducing agent in the substrate is preferably 0.01 to 3%.

On the substrate, a metal having a reducing property equal to or less than that of at least one reducing agent in the substrate and having a reducing property greater than that of nickel (a specific reducing metal).
A metal mixed layer containing powder, an alkaline earth metal oxide containing at least barium, and a rare earth metal oxide, the content of the rare earth metal oxide being 0.01 to 25%, is provided.

The specific reducing metal in the metal mixed layer contributes to the supply of Ba, the production of rare earth metal and the improvement of conductivity as described above. It is necessary that the reducibility of the particular reducing metal be less than or equal to at least one of the reducing agents in the substrate and greater than nickel that the reducibility of the particular reducing metal be less than nickel. And the effect of supplying excess Ba is small, and when it is larger than all reducing agents in the substrate, the main supply reaction of excess Ba occurs at the interface between the specific reducing metal and the alkaline earth metal oxide in the metal mixed layer. ,
This is because the excessive Ba supply effect of the reducing agent in the substrate becomes small, and the contribution of the rare earth metal oxide to the characteristics of the intermediate layer decomposition effect becomes small.

Specific examples of the specific reducing metal include:
Depending on the composition of the reducing agent in the substrate, for example, W, Mo, T
Examples include a, Cr, Si, and Mg, and at least one metal may be selected.

The particle size of the specific reducing metal depends on the particle size of the alkaline earth metal oxide used, but is 10 μm or less,
Furthermore, 2-7 micrometers is preferable. If the particle size exceeds 10 μm, the total surface area of the specific reducing metal will increase even if the added concentration is the same.
This is because when it is 10 μm or less, it becomes smaller, a sufficient effect of improving the conductivity cannot be obtained, and the reduction reaction is less likely to occur.

The ratio of the specific reducing metal in the metal mixed layer is
It is preferably 10 to 50%, more preferably 20 to 40%. If the ratio is less than 10%, the above-described sufficient effect cannot be obtained, and if it exceeds 50%, the electron emission characteristics tend to be reduced.

Examples of the alkaline earth metal oxides include oxides of strontium and calcium in addition to barium, and those having a particle size of 3 to 10 μm are preferable.

The proportion of the alkaline earth metal oxide in the metal mixed layer is preferably 50 to 90%, more preferably 60 to 70%. If the ratio is less than 50%, sufficient electron emission characteristics cannot be obtained, and if it exceeds 90%, the concentration of specific reducing metal and rare earth metal oxides decreases and the improvement effect of life characteristics in high current density operation appears. It gets harder.

Examples of the rare earth metal oxides include scandium oxide and yttrium oxide.

The ratio of the rare earth metal oxide in the metal mixed layer is
It is 0.01 to 25%, preferably 0.1 to 10%. The ratio is 0.0
If it is less than 1%, the effect of decomposition of the intermediate layer represented by the reaction formula (IV) is small, and if it exceeds 25%, sufficient initial electron emission characteristics cannot be obtained.

The thickness of the metal mixed layer is preferably 10 to 40 μm, more preferably 20 to 30 μm. Thickness 10
This is because if the thickness is less than μm, the improvement in the conductivity of the electron emitting material layer tends to be insufficient, and if it exceeds 40 μm, it is difficult to obtain sufficient electron emitting properties in the initial and life characteristics.

An electron emitting material layer containing an alkaline earth metal oxide containing at least barium is deposited on the metal mixed layer in order to impart sufficient electron emitting ability to the cathode. In the case where only the metal mixed layer is formed by providing the electron emitting material layer on the metal mixed layer as described above, only the metal mixed layer has a specific reducing metal and rare earth metal oxide contained therein, and the alkaline earth metal oxide is oxidized. This is because the occupation ratio on the upper surface of the metal-mixed layer of the product becomes small and sufficient electron emission cannot be obtained.

Examples of the alkaline earth metal oxide include oxides of strontium, calcium and the like in addition to barium.

The thickness of the electron emitting material layer is preferably about 50 to 100 μm.

Next, an example of a method for producing the electron tube cathode of the present invention will be described.

First, after welding the base metal to the sleeve,
Heat treatment such as cleaning and hydrogen treatment is performed to remove surface dirt and oxide layer.

Then, a specific reducing metal powder, an alkaline earth metal carbonate powder and a rare earth metal oxide powder are mixed with a binder such as nitrocellulose together with an organic solvent such as butyl acetate to prepare a suspension. The metal mixed layer is provided by applying it on the substrate by a method such as a spray method. The ratio of the binder and the organic solvent used is not particularly limited.

Next, a suspension prepared by mixing powder of carbonate of an alkaline earth metal with nitrocellulose, butyl acetate or the like is applied onto the metal mixed layer by a spray method or the like to form a suspension. The cathode for an electron tube of the invention is manufactured.

The above-described cathode for an electron tube of the present invention can be applied to a cathode ray tube for a television tube or an image pickup tube, and can operate at a high current density, so that a high brightness of a projection type or a large-sized television can be realized. .

Next, one embodiment of the present invention will be described more specifically with reference to FIG. In FIG. 1, (1) is a substrate,
(2) sleeve, (3) heater, (4) metal mixed layer, (5)
Is an electron emitting material layer. By heating the heater (3), thermoelectrons are emitted from the electron emitting material layer (5). Example 1 and Comparative Example 1 First, a main component of nickel, a trace amount of magnesium (0.05%),
The base (1) made of silicon (0.05%) was welded to the sleeve (2) and then heat-treated in a reducing atmosphere. Next, tungsten powder with a particle size of 5 μm, scandium oxide powder with a particle size of 10 μm, and ternary carbonate powder with a particle size of 5 μm (barium, strontium, calcium carbonate) were added at 30%, 5%, and 65%, respectively. Weighed in proportion
A suspension was prepared by mixing 100 g, 10 g of nitrocellulose as a binder and 200 ml of butyl acetate as an organic solvent. The obtained suspension is sprayed onto a substrate
It was applied onto (1) to form a metal mixed layer (4) having a thickness of 25 μm.

Then, barium, strontium, and calcium carbonate, a binder, nitrocellulose, and an organic solvent, butyl acetate, were mixed to prepare a suspension. The obtained suspension was applied by a spray method to form an electron-emitting substance layer (5) having a thickness of 60 μm, and a cathode as shown in FIG. 1 was produced.

The cathode for the electron tube thus obtained was attached to a CRT for an ordinary television device and completed by an ordinary exhaust process.
A life test was carried out by operating the CRT under the condition of a current density of 2 A / cm ² . The results are shown in Figure 2.

As a comparative example, instead of the metal mixed layer (4) and the electron emitting material layer (5) in the cathode for an electron tube,
A conventional cathode for an electron tube having an electron emitting material layer formed of an alkaline earth metal oxide containing 7% scandium oxide was similarly evaluated.

From FIG. 2, it can be seen that the deterioration of the emission current of the cathode for an electron tube of the present invention is significantly less than that of the conventional one.

The reason why the life characteristic of the cathode for an electron tube of the present invention is good is presumed as follows.

That is, excess Ba is supplied at the interface between the substrate (1) and the metal mixed layer (4) based on the reactions shown in the formulas (I) and (II). In addition to that, W in the metal mixed layer also has the formula
(V): It reacts as 2BaO + 1 / 3W → Ba + 1 / 3Ba ₃ W0 ₆ (V) and contributes to the formation of excess Ba. Furthermore, since W and Sc ₂ O ₃ coexist in the metal mixed layer (4), it also contributes to the production of Sc having an intermediate layer decomposition effect. Further, the W powder as the conductive material suppresses the local generation of Joule heat in the high current density operating region, which causes the generated excess Ba to disappear, and contributes to the improvement of the concentration of excess Ba.

[0042]

As described above, the cathode for an electron tube of the present invention enables a high current density operation of 2 A / cm ² or more, which has been difficult with the conventional oxide cathode.

[Brief description of drawings]

FIG. 1 is a partially enlarged sectional view of a cathode for an electron tube of the present invention.

FIG. 2 is a graph showing changes with time of emission current.

FIG. 3 is a partially enlarged sectional view of a conventional cathode for an electron tube.

[Explanation of symbols]

 1 substrate 4 metal mixed layer 5 electron emitting material

Claims (1)

[Claims] 1. The main component is nickel, and at least 1.
A cathode for an electron tube, wherein a metal mixed layer is formed on a substrate containing one kind of reducing agent, and an electron emitting material layer containing an alkaline earth metal oxide containing at least barium is formed on the metal mixed layer, the metal being A metal powder whose mixed layer is less than or equal to at least one reducing agent in the substrate and more reducible than nickel, an alkaline earth metal oxide containing at least barium, and a rare earth metal oxide. And a rare earth metal oxide content of 0.01 to 25% by weight in a layer for an electron tube.