JPH07161282A - Impregnation type cathode structure - Google Patents

Abstract

PURPOSE:To attain stable action without generating any leak between a heater and a cathode over a long period by applying black color treatment by a silicon carbide film to an internal surface of a cathode sleeve in an impregnation type cathode structure. CONSTITUTION:In this impregnation type cathode structure, a silicon carbide film 231 is formed by a CVD method in an internal surface of a cylindrical cathode sleeve 23 consisting of molybdenum material. The silicon carbide film 231 may be formed by applying silicon carbide fine powder sintered. In the cathode structure thus applying black color treatment, a heater temperature is decreased by a 140 deg.Cbr to a 1190 deg.Cbr, for instance, as compared with that of applying no treatment. In this way, a leak current between a heater 22 and the cathode sleeve 23 is suppressed to 1muA or less over a long operation period.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art FIG. 4 is a diagram showing a three-pole structure of an ordinary electron gun for a color cathode ray tube. The electron gun for a color cathode ray tube has three cathodes 2, and a heater 22 for heating is inserted in each cathode 2. The cathode 2 is joined to the support plate 29 via a support cylinder 28 by welding or the like. The heater 22 for heating is previously welded to the heater tab 25, and the heater tab 25 is joined to the heater support 27 via the heater connector 26. In order to control thermoelectrons emitted from each cathode, a control electrode 3 and an accelerating electrode 4 are arranged in front of the cathode 2, and together with the support plate 29 and the heater support 27, a predetermined bead is provided by the insulating bead glass 5. It is integrally fixed to the space.

The cathode current is controlled by the potential difference applied to the electrodes 3 and 4, and the electrons emitted from the cathode are irradiated to the phosphor to which a high voltage is applied to emit red, green and blue colors, A predetermined display is obtained.

Next, the structure near the cathode will be described with reference to FIG. The cathode 2 is usually a cathode substrate 21 obtained by impregnating a tungsten porous body with an oxide such as barium, a heater 22 for heating the cathode substrate, a cathode sleeve 23 for housing the heater 22 for heating, and a cathode substrate. Holding cup 2
4 and. By using these members, the cathode base 21 and the cup 24 can be caulked, etc.
The cathode sleeve 23 and the cathode sleeve 23 are connected by welding or the like.

Next, the features of the impregnated cathode will be described. The impregnated cathode can operate at a high current density for a long period of time and can secure stable electron emission, as compared with a so-called oxide cathode containing barium oxide as a main component. However, the operating temperature of the cathode base 21 is as high as about 1000 ° C. br, and when the conventional cathode sleeve having an exposed metal surface is used without blackening the inner surface as shown in FIG. Even when the dark heater described later is used, the temperature is required to be 1300 ° C. br or higher, and the operation at such a high temperature also affects the reliability of the cathode assembly.

In the cathode assembly having such a structure,
Normally, in order to control the cathode current, 50
A fixed voltage of 0 to 800 V is applied to the control electrode 3 with a ground voltage of 0.
V is applied, and the cathode 2 changes its voltage in the range of 0 to 200 V according to the degree of the cathode current. Also, the heater 22
, A voltage of several V is applied between the terminals so that a cathode operating temperature of about 1000 ° C. br is applied, but one of the heater terminals is at the ground voltage. Therefore, in general,
The maximum potential difference between the cathode substrate 21 and the heater 22 is 20.
It becomes 0 V, and the value is 0 V with respect to the heater 22.
Is the more positive direction.

By the way, as described above, when a predetermined voltage is applied to each terminal for operation, a maximum voltage of 200 V is applied between the cathode and the heater, so that alumina (Al ₂ It has a structure in which a sintered body of O ₃ ) particles is inserted to maintain insulation. Specifically, as shown in the cross section in FIG.
A dark heater is provided around the heater core wire 221. An alumina layer 222 is formed by electrodeposition and sintering of alumina to a thickness of about 100 μm, and a dark layer 223 is formed by coating a mixture of alumina and tungsten to a thickness of several μm. ing. The reason for forming the dark layer is to improve the heat radiation efficiency of the heater and lower the temperature of the heater itself.

However, since the impregnated cathode has a high cathode operating temperature, even when the above-mentioned dark heater is used, the cathode sleeve 23 has a metal surface which is not black-treated as shown in FIG. When using an exposed heat-resistant metal material, the heater temperature is 1300 ° C br
Due to the high temperature, the leakage current between the heater and the cathode is 1 μA or less in the initial stage after manufacturing the cathode ray tube, but the insulation characteristics deteriorate during long-term operation, and in some cases, the value is 10 μA or more. As a result, the cathode voltage is unnecessarily lowered, which is an obstacle to the practical application of the impregnated cathode.

[0009]

As described above, in the cathode ray tube using the impregnated cathode, the heater temperature becomes high because the cathode operating temperature is high. As one of the means for solving the problem, a black layer is formed on the outer surface of the heater. A dark heater that has been formed to improve the heat radiation efficiency and improve the heating characteristics has been used. However, even when this dark heater is used, the heater temperature is still higher than 1300 ° C br,
In many cases, the leakage current between the heater and the cathode during long-term operation increased, and a voltage drop at the cathode prevented the proper electrical signal from being applied.

The present invention has been made to solve the above-mentioned problems, and in order to further lower the heater temperature during operation, not only a dark heater whose surface is blackened but also a cathode sleeve inner surface is used. An object of the present invention is to provide an impregnated-type cathode that is subjected to black treatment and further lowers the heater temperature without changing the cathode temperature to enable stable operation without generating leakage current between the heater and the cathode for a long period of time.

[0011]

SUMMARY OF THE INVENTION An impregnated cathode assembly according to the present invention is a tubular cathode in which a cathode base for thermionic emission is provided at the closed top of the end and a heating heater is inserted therein. A silicon carbide thin film is formed on the inner surface of the sleeve. Further, a silicon carbide thin film is formed by CVD (Chemical).
It is formed by the Vapor Deposition method. Further, the silicon carbide thin film is formed by applying fine powder of silicon carbide and sintering it.

[0012]

A heat-resistant metal such as molybdenum or tantalum, which is usually used as a cathode sleeve material, has a thermal emissivity of about 0.3 to 0.4 on the metal surface. When fine powder is applied, it is about 0.6. By the way, as in the present invention, the thermal emissivity can be reduced to 0.
It is possible to improve it to about 8.

By improving the thermal emissivity, the cathode sleeve can efficiently absorb the heat transfer from the heater, and the heater temperature can be lowered when the amount of heat input to the heater is constant. The heater temperature reduction range in the present invention using the silicon carbide thin film is 10
It is about 0-150 ℃ br, and it is 1 with the conventional dark heater.
Change the heater temperature from 300 ° C br or higher to 1200 ° C br
You can: The heater temperature is 1200 when fine powder of tungsten and alumina is applied.
˜1250 ° C. br.

In this way, the heater temperature is set to 1200 ° C. br
In the following cases, dielectric breakdown does not occur even when a predetermined voltage is applied between the cathode and the heater, stable insulation characteristics are exhibited over a long period of time, and the leakage current can be maintained at 1 μA or less.

[0015]

【Example】

Example 1. FIG. 1 shows a cathode assembly of an impregnated cathode according to the present invention, in which a silicon carbide thin film 231 is formed by CVD on the inner surface of a cylindrical cathode sleeve 23 made of a molybdenum material.
(Chemical Vapor Deposition
n) method.

In FIG. 2, the cathode assembly shown in FIG. 1 is incorporated in an electron gun as shown in FIG.
The heater applied voltage is set to be 0 ° C.br, and the dark heater temperature at that time is measured. The results are shown in FIGS. 10A and 10B, and 10 cathode structures that are black-treated with a silicon carbide thin film and 10 untreated cathode structures. Are comparing. In addition, in order to determine the effect, the comparative product has the same configuration except for the presence or absence of black treatment. As is clear from this result, the heater temperature of the black-treated one was 140 ° C. br lower than that of the untreated one, which was 1190 ° C. br.

Example 2. Instead of the silicon carbide thin film formed by the CVD method according to the first embodiment shown in FIG. 1, black treatment may be performed using a silicon carbide thin film formed by coating and sintering fine powder of silicon carbide. FIG. 3 shows the heater temperature in this example, and the heater temperature can be lowered by 130 ° C. br and can be set to 1200 ° C. br as compared with the heater not subjected to the black treatment (see FIG. 2). .

Fine powder of silicon carbide having an average particle size of 3 μm is used, and a fine powder of silicon carbide dispersed in a solvent in which butyl acetate and nitrification cotton are mixed is applied to the inside of the cathode sleeve, and 160
A silicon carbide thin film was formed by sintering at 0 ° C. for 10 minutes.

[0019]

As described above, according to the present invention, the inner surface of the cathode sleeve of the impregnated cathode assembly is subjected to black treatment with a silicon carbide thin film so that the heater temperature is 100 to 150.
The temperature of the heater can be lowered to 1200 ° C. br or lower by combining with a dark heater. As a result, the leakage current between the heater and the cathode was suppressed to 1 μA over a long period of operation, and a highly reliable impregnated cathode was obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a cathode assembly according to first and second embodiments of the present invention.

FIG. 2 is a diagram showing a heater temperature characteristic of the first embodiment.

FIG. 3 is a diagram showing a heater temperature characteristic of the second embodiment.

FIG. 4 is a cross-sectional view showing a structure of a triode portion of an electron gun for a general color cathode ray tube.

FIG. 5 is an enlarged sectional view showing the vicinity of the cathode of FIG.

FIG. 6 is a cross-sectional view showing a conventional cathode assembly.

FIG. 7 is a cross-sectional view of a general dark heater.

[Explanation of symbols]

 2 cathode 21 cathode base 22 heating heater 221 heater core wire 222 alumina layer 223 dark layer 23 cathode sleeve 231 silicon carbide thin film

Claims (3)

[Claims] 1. A cylindrical cathode sleeve in which a cathode substrate for emitting thermoelectrons is provided at the closed top of the end, and a heater for heating is inserted therein, and a silicon carbide thin film formed on the inner surface of the cathode sleeve. An impregnated-type cathode assembly comprising: 2. A silicon carbide thin film is formed by CVD (Chemic).
2. The impregnated-type cathode assembly according to claim 1, wherein the impregnated-type cathode assembly is formed by an Al Vapor Deposition method. 3. The impregnated-type cathode assembly according to claim 1, wherein the silicon carbide thin film is formed by applying silicon carbide fine powder and sintering it.