JPH11283489A - Impregnated negative electrode structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-performance, long service life, impregnated negative electrode structure which can prevent degradation of an electron emission characteristic by decreasing emitter deterioration and emitter blow-off due to dew condensation. SOLUTION: A moisture resistant coating which will volatilizes by heating is formed on a negative electrode disk 14 in which emitter is impregnated and which is firmly fixed to a negative sleeve 16 and used for an impregnated negative electrode structure. For the moisture resistant coating, organic polymer films, especially a polyvinyl butyral film, are suitable. It is suitable that the thickness of the moisture resistant coating is 0.1 to 20 μm. By adopting this configuration, deterioration of the emitter due to water vapor and emitter blow- off due to dew condensation are eliminated, and therefore characteristics are improved to a large extent such as: that degradation of capability, of emitting electrons is suppressed; that emission of electrons is made to be uniform; that life is extended; etc.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-performance impregnated cathode structure used for a picture tube, an image pickup tube, a projection tube and the like.

[0002]

2. Description of the Related Art In recent years, a color picture tube having an increased number of scanning lines to increase the resolution and a cathode ray tube for a super high frequency display have been developed. In order to realize these, a cathode for an electron tube in which the electron emission density from the electron emission cathode is greatly increased is required.

[0003] Impregnated cathodes are suitable for applications in these fields because they can obtain a higher current density and have a longer life than oxide cathodes, and are particularly suitable for electron tubes such as cathode traveling wave tubes and klystrons. In some cases, an emitter-impregnated cathode has been used.

[0004] The impregnated cathode assembly is constructed by fixing a cup for holding a cathode disk having an emitter melt-impregnated in a high-temperature hydrogen atmosphere to one end of a cathode sleeve, and inserting a heater from the other end of the cathode sleeve. It is used by being supported and fixed by a plurality of (usually three) straps to a cylindrical holder coaxially disposed outside thereof.

[0005] However, in such a conventional impregnated cathode assembly, the emitter in a very active state is impregnated in the cathode disk, so that the cathode disk is impregnated during the assembly of the cathode assembly or during the assembly of the electron gun assembly. During the period up to the tube neck sealing, there is a problem that the emitter on the very surface may be deteriorated under the influence of moisture or the like.

It is considered that the deterioration of the emitter is mainly caused by the formation of hydroxide on the surface. However, the deterioration of the emitter causes the impregnated cathode to have a reduced electron emission ability.

[0007] In addition, if there is a temperature change in each step of assembling the impregnated cathode assembly, dew condensation occurs on the surface of the cathode disk. When such dew condensation occurs, the emitter swells and blows out to the surface, so that electrons are emitted to the surface. As the radiation effective area decreases, the work function partially increases, and the electron emission capability is significantly reduced.

Furthermore, if the emission of electrons from the cathode disk becomes non-uniform due to the blowing, a uniform electron beam cannot be obtained, which impairs the focus characteristics.

[0009] When the deterioration of the emitter is slight, it is difficult to cause initial characteristics failure, but the life is shortened.
Predicting market reliability becomes extremely difficult.

As described above, the impregnated type cathode has many problems which hinder mass production, such as difficulty in managing and handling during production and assembly as compared with the conventional oxide cathode, and shortening the storage period. Existed.

[0011]

As described above, the conventional impregnated type cathode assembly has a problem that water or the like is generated during the assembly of the cathode assembly and during the period from the assembly of the electron gun assembly to the sealing of the neck of the picture tube. When affected, the emitter on the surface of the cathode is deteriorated, which causes a problem that the electron emission capability is reduced, the electron emission is uneven, and the life is shortened.

SUMMARY OF THE INVENTION The present invention has been made in order to solve such a conventional problem, and an object of the present invention is to provide an impregnated cathode assembly which has solved the problems such as deterioration of the emitter due to the influence of moisture and the like and blowing of the emitter due to dew condensation. And

[0013]

According to the present invention, there is provided an impregnated-type cathode assembly comprising a cathode sleeve, a cathode disk impregnated with an emitter fixed to one end of a cathode sleeve, and a heater inserted from the other end. On the exposed surface of the cathode disk, a moisture-resistant film that volatilizes by heating is formed.

As the moisture-resistant coating, an organic coating,
In particular, an organic polymer soluble in a non-aqueous solvent such as ethyl alcohol or other alcohols, esters, ketones, or a mixed solvent thereof is suitable. Polyvinyl butyral is an organic polymer suitable for forming a moisture-resistant coating.

The thickness of the moisture-resistant organic coating is suitably in the range of 0.1 to 20 μm.

If the thickness of the moisture-resistant organic coating is less than 0.1 μm, the moisture-proof effect of the coating cannot be obtained. Outgassing is increased and combustion residues are left on the cathode surface.

(Operation) In the impregnated cathode assembly of the present invention, the cathode disc impregnated with the emitter is shielded from the outside air by the moisture-resistant coating, so that the cathode disc is deteriorated by water vapor or the cathode assembly is not assembled. During the period from the assembly of the electron gun assembly to the sealing of the neck of the picture tube, the emitter is prevented from blowing out by the dew condensation water.

The moisture-resistant organic film is such that an electron gun structure using an impregnated cathode structure is incorporated into a picture tube, and is burned and volatilized by the cathode heating when exhausting the neck sealing, thereby adversely affecting the electron emission ability. There is no.

[0019]

Embodiments of the present invention will be described below in more detail with reference to the drawings.

(Embodiment) FIG. 1 is a sectional view showing an electron gun structure of a color picture tube using an impregnated cathode of the present invention.

In FIG. 1, reference numeral 11 denotes a glass bead for electrode support, which holds a first control grid 12 and a support arm 13 for supporting an electron gun assembly.

An emitter-impregnated cathode disk 14, which is an electron-emitting portion, is held by a cathode disk holding cap 15, and is press-fitted and fixed to the tip of a cathode sleeve 16.

The cathode sleeve 16 has three straps 17
And is fixed to the cathode holding cylinder 18 held by the support arm 13. A heat reflection cylinder 19 is concentrically arranged on the outer periphery of the upper part of the cathode sleeve 16 and a support ring 20 is provided.
To the cathode holding cylinder 18.

A double coil type heater 21 for heating is inserted in the cathode sleeve 16. Reference numeral 22 denotes a heater terminal.

In this embodiment, as shown in an enlarged manner in FIG. 2, a moisture-resistant film 24 made of polyvinyl butyral is formed on the exposed surface of the upper surface of the cathode disk 14.

The moisture resistant coating 24 is formed by applying a 10% concentration solution of polyvinyl butyral in ethyl alcohol to the cathode disk 14 by a spray method and drying the coating. To 7 μm.

As shown in FIG. 3, the impregnated emitter-type cathode disk 14 is made of a porous tungsten 14a having a porosity of about 20% and a substrate of BaO: CaO: Al ₂ O _3.
It is impregnated with an emitter (electron emitting material) made of such as.

Incidentally, an iridium-tungsten alloy layer may be formed on the surface of the impregnated emitter type cathode disk 14 in some cases.

The cap 15 for holding the cathode disk is made of tantalum, and the insulation between the heater 21 and the cathode sleeve 16 is generated when the emitter material from the impregnated cathode disk 14, for example, the evaporated barium is scattered toward the heater 21. This is for preventing deterioration.

The heater 21 is made of a 3% rhenium-tungsten alloy, and its surface is coated with alumina for insulation. Furthermore, the surface of the alumina is
In order to improve the heat radiation characteristic, a dark layer made of a mixture of tungsten and alumina is coated.

The cathode disk holding cap 15, the cathode sleeve 16, and the three straps 17 are all made of tantalum, niobium, or molybdenum, or an alloy mainly containing at least one of them. On the inner surface of the cathode sleeve 16, a thin black coating 2 is formed to efficiently absorb the heat generated by the heater 21 into the cathode sleeve 16.
3 are formed. The cathode sleeve 16 is formed, for example, in a pipe shape having a diameter of 1.3 mm, a length of 4.5 mm, and a thickness of 20 μm, and the thickness of the black coating 23 is about 5 μm.

Next, the cathode structure on which the moisture-resistant coating 24 was formed was incorporated into an electron gun, and the electron gun assembly was assembled into a picture tube, after which required evacuation and activation were performed, and various tests were performed.

(Comparison of Electron Emission Ability) The electron emission ability of the impregnated cathode assembly of the example was equivalent to that of the case where the moisture-resistant coating was not formed, and the polyvinyl butyral coating was formed on the cathode disk. No adverse effect on electron emission was confirmed.

(Residue of Moisture-Resistant Coating) The impregnated cathode assembly of the example was disassembled to examine the residuals of the moisture-resistant coating by observation with an electron microscope. No residue was observed, and it was confirmed that the combustion was completely eliminated by heating the cathode during exhaust.

(Forced Condensation Test) The cathode assembly of the embodiment was incorporated into an electron gun assembly, left in a low-temperature room at 3 ° C. for 10 minutes, taken out of the room at room temperature, and formed dew on the surface of each part of the impregnated cathode assembly. After that, the electron gun assembly was sealed in a picture tube, evacuated, activated, and evaluated for electron emission capability and cathode image.

Table 1 shows the results.

[Electron emission capability]

[Table 1] As shown in Table 1, the electron gun using the cathode structure of the peritoneal membrane according to the present invention has much more G1 pulse emission and cathode efficiency than the electron gun using the conventional cathode structure (Comparative Example 1). It was confirmed that the moisture-resistant coating almost completely prevented the deterioration of the emitter due to dew condensation.

[Cathode Image (Uniformity of Electron Emission Ability on Cathode Disk Surface)] The cathode image is the area of the non-light-emitting portion (black portion) of the phosphor viewed from an image projected on an area on the image. Was evaluated as a percentage of the total.

Table 2 shows the comparison results.

[0040]

[Table 2] If the surface of the cathode disk has a non-uniform electron emission capability on the surface, the number of non-light-emitting portions will increase. Can be.

As is clear from Table 2, the electron gun using the cathode structure of the embodiment has almost no non-light-emitting portion as compared with the electron gun using the conventional emitter impregnated type cathode structure, and the electron gun uses the cathode disk surface. It can be seen that electrons are emitted almost uniformly.

(Disassembly investigation) The test sample was taken out of the picture tube and the surface of the cathode disk was observed with an electron microscope.

As a result, a large number of emitters were blown out on the surface of the conventional cathode disk in which the coating of the moisture-resistant film was not formed. No ballooning was observed.

From these observation results, it can be seen that many non-light-emitting portions in the conventional electron gun using the cathode structure are because the effective area of the cathode contributing to electron emission due to the emission of the emitter due to forced dew condensation is reduced, and the work function is reduced. It is considered that this is due to the increase in.

(Life Characteristics) The heater voltage of the cathode-ray tube incorporating the cathode structure of the embodiment (Example) and the cathode-ray tube incorporating the conventional cathode structure (Comparative Example 1) as the sample of the forced dew condensation test was rated at the heater voltage. 110% and the cathodic current is 2.5
The life test was performed under the following conditions with A / square cm. Also,
For reference, a life test was also performed under the same conditions for a picture tube (Comparative Example 2) incorporating a conventional cathode structure that does not cause forced condensation.

FIG. 4 shows the test results.

As is clear from the figure, the picture tube of the example hardly deteriorated, but the picture tube incorporating the cathode structure of the comparative example 1 in which the dew condensation was carried out was gradually started immediately after the start of the test. Decreased to about 60% or less of the initial ratio in about 4000 hours.

Further, even in the picture tube incorporating the conventional cathode structure of Comparative Example 2 in which forced dew condensation is not performed, deterioration does not occur as much as the picture tube incorporating the cathode structure of Comparative Example 2, but the test time becomes longer. As a result, the electron emission capability was significantly reduced.

From the above results, it has been clarified that the picture tube incorporating the cathode structure according to the present invention has excellent life characteristics.

In the above embodiment, an example was described in which the surface of the cathode disk 14 was provided with a moisture-resistant coating after assembling the cathode assembly. However, after the emitter was melted and impregnated, the cathode disk 14 was provided with a moisture-resistant coating. The same effect can be obtained even if the cathode structure is assembled after that.

[0051]

According to the present invention, deterioration of the emitter due to water vapor and emission of the emitter due to dew condensation are eliminated, so that a decrease in electron emission capability is suppressed, electron emission becomes uniform, and a life is prolonged. It is greatly improved.

[Brief description of the drawings]

FIG. 1 is an enlarged sectional view showing an electron gun structure using an impregnated cathode structure according to an embodiment of the present invention.

FIG. 2 is an enlarged sectional view of a coating portion of a cathode disk according to the embodiment of the present invention.

FIG. 3 is a sectional view showing a further enlarged main part of FIG. 2;

FIG. 4 is a graph showing the effect of the embodiment of the present invention.

[Explanation of symbols]

11: a glass bead for electrode support; 12: a first control grid; and 13: a support arm for supporting an electron gun assembly.
14 ... Emitter impregnated cathode disk, 15 ... Cathode holding cap, 16 ... Cathode sleeve, 17 ... Strap, 18 ... Cathode holding cylinder, 19 ... Heat reflection cylinder, 20 ... Support ring, 21: Double coil type heater, 22: Heater terminal, 24: Moisture resistant coating.

Claims (4)

[Claims] A cathode disk impregnated with an emitter is fixed to one end of a cathode sleeve, and a heater is inserted from the other end. In the impregnated cathode assembly, the exposed surface of the cathode disk is volatilized by heating. An impregnated cathode assembly having a moisture-resistant coating formed thereon. 2. The impregnated cathode assembly according to claim 1, wherein the moisture-resistant coating is an organic coating. 3. The impregnated cathode assembly according to claim 2, wherein the organic coating is made of an organic polymer soluble in a non-aqueous solvent. 4. The impregnated cathode assembly according to claim 1, wherein the thickness of the moisture-resistant organic coating is 0.1 to 20 μm.