JPH10289645A - Cathode heater and cathode ray tube using the same - Google Patents

Abstract

(57) [Problem] To provide a cathode heater having high heat dissipation characteristics and a dark layer having excellent insulation characteristics, low power consumption, long life, and high reliability. SOLUTION: An insulating film 2 and a dark layer 3 are applied to a metal wire 1 serving as a heater coil, and a heater H is provided in a sleeve 4 having an impregnated cathode member 5 at a tip portion. Those composed of hafnium oxide or silicon carbide. [Effect] Since a high thermal emissivity can be obtained in the dark layer 3,
The heater temperature can be reduced, and as a result, power consumption is reduced, the heater load is reduced, and a highly reliable and long-life cathode heater can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a heater used for an indirectly heated cathode of an electron tube, and more particularly to a heater suitable for heating a cathode of an electron gun of a cathode ray tube.

[0002]

2. Description of the Related Art A general cathode ray tube is a hot cathode type.
In particular, in a cathode ray tube or the like, an indirectly heated cathode is usually used, and therefore, a heater for heating the cathode is used. FIG. 1 shows a cathode called an impregnated cathode among cathodes used for an electron gun of a cathode ray tube. First, a metal wire 1 wound in a coil shape is used as a heater H. An insulating film 2 is provided, and a dark layer (radiation film) 3 is provided on the outside of the insulating film 2. This is inserted into a sleeve 4 made of a cylindrical metal member. I have.

In this impregnated cathode, an impregnated cathode member 5 is provided on the top of the sleeve 4.
By heating the sleeve 4 by the heater H, the impregnated cathode member 5 is maintained at a predetermined temperature, for example, close to 1000 ° C., so that a necessary electron emission function can be obtained.

Here, the metal wire 1 constituting the heater H
For example, a wire made of a heat-resistant conductive material such as tungsten (W) or rhenium-tungsten alloy (Re-W) is used. After forming the wire into a coil as shown in the drawing, the wire is heated in a hydrogen atmosphere. Then, after cleaning the surface, an insulating film 2 such as alumina is formed on the surface, and a dark layer 3 is further formed on the surface of the insulating film 2 to complete the heater H.

Here, the dark layer 3 increases the thermal emissivity by blackening the color of the surface of the insulating film 2 so that the heat radiated from the heater is efficiently transmitted to the sleeve 4 and the cathode member 5. For example, tungsten and alumina are conventionally used.

The insulating film 2 and the dark layer 3
Depends on the usage environment and productivity of the film to be formed,
It is usually formed by various methods such as vapor deposition, CVD (Chemical Vapor Deposition), spraying, dip coating, and electrodeposition (electrophoresis).

[0007]

In the above prior art, it cannot be said that sufficient consideration has been given to the improvement of the heat dissipation characteristics of the cathode heating heater by the dark layer. There was a problem with reliability. In electron tubes using a hot cathode such as a cathode ray tube, reduction of the power for heating the cathode is demanded. For this reason, a heater with high thermal efficiency capable of efficiently heating the cathode is required along with promotion of miniaturization of the heater itself. ing.

[0008] The main heat flow from the heater at the cathode flows through the insulating film and the dark layer by heat conduction, and then is transmitted to the sleeve by heat radiation in a vacuum, and from the sleeve by heat conduction, the cathode member. Is transmitted to Therefore, in order to increase the heating efficiency of the heater, it is necessary to efficiently transfer heat from the dark layer to the sleeve. As a result, it is important to increase the emissivity of the dark layer.

As described above, the material of the dark layer used for the heater in the prior art is generally tungsten and alumina. However, the use environment of the CRT heater is high vacuum and high temperature. In addition, low vapor pressure is required in order to avoid contamination inside the cathode ray tube. Here, the use of tungsten as the heater material and alumina as the insulating film material causes a problem in terms of reliability. Is selected because of lack of material and easy availability of materials.

In the prior art, tungsten particles are mixed with alumina for use. However, this is because tungsten particles alone have poor adhesion to the alumina of the insulating film, and the tungsten particles remain inside the insulating film during operation of the heater. This is because there is a possibility that they may be diffused and cause a decrease in insulating property. Therefore, by using the same mixture of alumina as the constituent material of the insulating film, the adhesion is improved.

As described above, the material properties required for the dark layer must have a high melting point, a high emissivity, a low vapor pressure, and a stability at a high vacuum and a high temperature. Also,
The dark layer is desirably insulating. Therefore, in addition to the above-mentioned conventional techniques, for example, in Japanese Patent Application Laid-Open No. 2-51821, zirconium (Zr), hafnium (Hf), titanium
JP-A-58-176845 discloses a dark layer using tungsten, molybdenum (Mo) and alumina, and discloses a dark layer to which one or more kinds of (Ti) and niobium (Nb) are added. However, in each case, the function of the dark layer is enhanced by adding high melting point metal particles.

Therefore, from the viewpoint of energy saving and reliability, the dark layer of the heater has excellent insulation properties,
Materials with even higher emissivity are desirable, but metals such as tungsten are electrically conductive and the emissivity of alumina is only about 0.47, so in the prior art,
Problems remain in terms of energy saving and reliability.

An object of the present invention is to provide a cathode heater having a high heat dissipation property and a dark layer having excellent insulation properties, low power consumption, a long life and a high reliability.
Another object of the present invention is to provide a cathode ray tube having low power consumption, long life and high reliability.

[0014]

The above objects can be attained by using hafnium oxide and silicon carbide as the material of the dark layer of the cathode heater. This is due to the finding that hafnium oxide and silicon carbide exist as high heat radiation materials satisfying the physical properties required for the dark layer.

For this reason, using a sample simulating a heater,
The thermal emissivity of each sample was measured. In this case, the sample was such that a 1-mm-thick tungsten plate was provided with an insulating film having a thickness of 100 to 150 μm, and a dark layer was formed to a thickness of 10 μm on the surface thereof. Table 1 shows the film configuration of the sample at this time.

[0016]

[Table 1]

Next, this sample was fired at 1600 ° C. in hydrogen. Two pairs of thermocouples were attached to the center of the sample at 10 mm intervals, and the sample was heated by energizing the tungsten plate in vacuum.
The temperature is measured with a thermocouple, and the emissivity ε
Was determined by the following equation (1). ^{ε = VI / σA (T 4} -T 0 4) ...... ...... (1) However, V: voltage between the thermocouple (V) I: electric current (A) A: surface area between the thermocouple (m ²⁾ T: thermocouple temperature (K) σ: Stefan-Boltzmann constant 5.67 ^-8 (W / m ² K ⁴ ) T ₀ : temperature in vacuum vessel (K)

The measurement results are as shown in FIG. 2. At the heater operating temperature of 1250 ° C., the emissivity ε of Sample 2 when the dark layer is hafnium oxide and Sample 3 when the dark layer is silicon carbide are 0.80, respectively. 0.85, and the emissivity of Sample 1 in the case of a mixture of tungsten and alumina in the prior art is 0.4.
6 was much higher.

Therefore, when these materials, that is, hafnium oxide and silicon carbide are used for the dark layer, the heat of the heater is efficiently transmitted to the cathode and the sleeve, and the temperature of the heater when the temperature of the cathode is equalized is reduced. As a result, it is understood that energy saving can be achieved by reducing power consumption, and improvement in reliability and long life of heater wires and insulating films can be achieved by reducing operating temperature.

The hafnium oxide and the silicon carbide may be used alone to form a dark layer. In order to enhance the adhesion to the insulating film, the constituent material of the insulating film, for example, alumina May be formed as a mixture with the above. However, when a mixture is used, the material is mixed with a material having a low thermal emissivity, so that the effect of increasing the thermal efficiency of the heater is reduced as compared with the case of using hafnium oxide alone or the case of using silicon carbide alone.

On the other hand, at this time, by reducing the particle diameter of the powder constituting the dark layer, the effective surface area can be increased, and the heat radiation efficiency of the heater can be further increased.
Next, although not shown, the electrical resistance at a temperature of 1250 ° C. is 7 × 10 ³ Ω · cm for hafnium oxide and 4 × 10 ³ Ω · cm for silicon carbide. Also has an insulating property, which indicates that it is suitable as a high radiation material formed on an insulating film.

In particular, when the insulating film is made of alumina and the heater wire is made of tungsten, hafnium oxide is excellent in that it hardly reacts with both and is stable. Furthermore,
The dark layer of hafnium oxide or silicon carbide can be formed by any method such as thermal spraying, vapor deposition, CVD, spraying, dip coating, and electrodeposition, and is advantageous in that it is not limited to a film forming method.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION

<Example 1> Hereinafter, a cathode heating heater according to the present invention,
The cathode ray tube using the same will be described in detail. In this embodiment, the case where the present invention is applied to the impregnated cathode shown in FIG. 1 will be described as an example.

First, a 3% Re-W wire having a diameter of 30 μm was wound around a molybdenum metal core wire having a diameter of 110 μm to form a heater coil (corresponding to metal wire 1 in FIG. 1). Next, aluminum nitrate and magnesium nitrate as electrolyte components were dissolved in an aqueous ethanol solution, and 20 vol% of alumina powder having an average particle diameter of 4 μm having a purity of 99.9% or more was blended as an inorganic substance to obtain a dispersion for an insulating film. . Similarly, aluminum nitrate and magnesium nitrate as electrolyte components are dissolved in an aqueous ethanol solution, and hafnium oxide powder having a purity of at least 99% and an average particle diameter of 0.6 μm is blended as a dark material in a volume of 15 vol% to form a dark layer dispersion. And

Next, using a film forming apparatus by electrodeposition shown in FIG. 3, 30 heater coils were suspended and held to form a negative electrode 6, and an aluminum plate was connected to a power source 8 as a positive electrode 7.
First, the insulating film dispersion 10 was placed in the electrodeposition container 9, and this was used as an electrolytic solution at a voltage of 80 V for 3 seconds from the power source 8 to the negative electrode 6 and the positive electrode 7 to form the insulating film 2. Thereafter, the electrolytic solution in the electrodeposition container 9 was replaced with a dispersion liquid for the dark layer.
Was formed.

Next, it was fired in a hydrogen atmosphere at 1600 ° C. for 5 minutes. At this time, the film thickness of the entire insulating film 2 including the dark layer 3 after firing was 110 μm. After completion of the firing, the molybdenum metal core wire was dissolved and removed with a mixed solution of nitric acid and sulfuric acid, washed with water, and dried to produce a heater of Example 1.

On the other hand, after the insulating film 2 was formed in the same process as in Example 1, the electrolyte components aluminum nitrate and magnesium nitrate were dissolved in an aqueous ethanol solution, and as a dark material, the average particle diameter was 1 μm having a purity of 99% or more. Tungsten powder of 4 vol% and an average particle size of 4μ with a purity of 99.9% or more
A dark layer was formed by blending 20 vol% of alumina powder of m with a dispersion liquid for a dark layer, and applying a current at a power supply voltage of 30 V for 3 seconds. Comparative Example 1 was made under the same other conditions.

Then, the heaters of Example 1 and Comparative Example 1 were subjected to an energization test, and the cathode temperatures of both heaters were set to 970 ° C.
Adjusted to b (brightness temperature). At this time, the temperature of the heater was controlled by adjusting the voltage. Since the voltage and the heater temperature at this time were confirmed to have the relationship shown in FIG. 4 in advance, it was estimated that the heater temperature was 1200 ° C. b in Example 1 and 1240 ° C. b in Comparative Example 1. Therefore, according to the first embodiment, in order to obtain the same cathode temperature of 970 ° C., the heater temperature had to be as low as 40 ° C., and as a result, power consumption was reduced and energy saving was achieved.

Next, according to the intermittent energization test in which the heater is energized for 5 minutes and then stopped for 3 minutes, the relationship between the heater temperature and the heater disconnection failure rate at the time of 60,000 times of heater intermittent operation is as shown in FIG. Has been confirmed to be. Therefore, this embodiment 1
As a result, it can be seen that as a result of a decrease in the heater temperature, the rate of defective heater breakage can be greatly reduced, and a long-life, highly reliable heater can be easily obtained.

<Embodiment 2> The dark layer of the embodiment 1 is formed by dip coating to form an embodiment 2. At this time, as a dark layer dispersion, a solution in which nitrocellulose was dissolved in methyl isobutyl ketone was added to a dark material having an average particle diameter of 0.6.
15 vol. of hafnium oxide powder with a purity of 99% or more in μm
% Was used.

In Comparative Example 2, the dark layer of Comparative Example 1 was formed by dip coating. At this time, as a dark layer dispersion liquid, nitrocellulose was dissolved in methyl isobutyl ketone, and a tungsten powder having an average particle diameter of 1 μm and a purity of 99% or more, which is a dark material, was added in an amount of 2 v.
% alumina and 14 vol% of alumina powder having an average particle diameter of 4 μm and a purity of 99% or more were used.

The heater temperature when these Example 2 and Comparative Example 2 were subjected to an energization test was as follows. When the cathode temperature of both was adjusted to 970 ° C. b (luminance temperature).
Is 1190 ° Cb, and Comparative Example 2 is 1240 ° Cb,
Therefore, according to Example 2, the heater temperature could be lowered by 40 ° C. or more.

As is clear from comparison of the result with the result in Example 1, in Example 1, the dark layer was formed by electrodeposition, and in Example 2, the dark layer was formed by the dip coating method. Regardless, as a result of the energization test, the two heater temperature reductions are equivalent to each other, and thus it is understood that the effect of the present invention does not depend on the film forming method.

Example 3 The dark material in the dark layer dispersion of Example 2 was silicon carbide (particle diameter 2 μm, purity 99%), and a heater was prepared in the same process as in Example 1. It was set to 3. Then, an energization test was performed together with Comparative Example 1, and both cathode temperatures were set to 970 ° C. b (luminance temperature).
, The temperature of the heater is set to 1 in the third embodiment.
The temperature was 195 ° C.b, and the temperature in Comparative Example 1 was 1240 ° C. Therefore, according to Example 3, it was found that the heater temperature could be reduced by as much as 45 ° C.

Example 4 The material for the dispersion for the dark layer of Example 2 was changed to silicon carbide (particle size 2 μm, purity 99%) 7 vol.
% And alumina (particle size 4 μm, purity 99% or more) 8 vo
A heater was prepared in the same manner as in Example 1 except that the temperature was changed to l%. An energization test was performed together with Comparative Example 1, and both cathode temperatures were set to 970 ° C. b (luminance temperature).
, The temperature of the heater is 122 in the fourth embodiment.
The temperature was 0 ° C.b and the temperature in Comparative Example 1 was 1240 ° C. Therefore, according to Example 4, it was found that the heater temperature could be lowered by 20 ° C.

<Embodiment 5> FIG. 6 shows Embodiment 5 of the present invention.
FIG. 4 is a cross-sectional view showing an example in which the present invention is applied to a cathode ray tube. In FIG. 6, the glass bulb 13 has a thin cylindrical neck portion and a bulging cone portion. An electron gun 11 is provided inside the neck portion, and a phosphor (electron gun irradiation) is provided at the bottom of the cone portion. A fluorescent screen 12 coated with a substance that emits fluorescent light is provided and sealed in a high vacuum state.

The electron gun 11 comprises a cathode 14 having a heater H according to any of the above-described embodiments 1 to 4, a Wehnelt electrode 15, and a cylindrical electrode 16 for accelerating and converging electrons. A socket pin 20 for electric wire connection is provided on one side.

Further, a conductive film 19 (an aluminum film covering the fluorescent screen 12) is provided on the inner surfaces of the neck portion and the cone portion of the glass bulb 13, and an anode button 18 serving as a terminal is provided on the outer side. . Further, a deflection yoke 17 is attached to the neck of the glass bulb 13.

Therefore, according to the cathode ray tube of the fifth embodiment, since the heater H according to any one of the first to fourth embodiments is used, the heater temperature can be lowered, and as a result,
Energy saving and improvement in reliability can be sufficiently obtained.

[0040]

According to the present invention, by using hafnium oxide or silicon carbide for the dark layer, the heat of the heater can be efficiently transmitted to the cathode or the sleeve. As a result, the temperature of the heater can be lowered, and as a result, energy saving by reducing the power consumption, and the improvement of the reliability and the long life of the heater wire or the insulating film by the reduction of the operating temperature can be reliably obtained.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an example of a heater to which the present invention is applied.

FIG. 2 is a characteristic diagram for explaining temperature dependency of emissivity.

FIG. 3 is an explanatory view showing an example of a film forming apparatus by electrodeposition.

FIG. 4 is a characteristic diagram showing a relationship between a heater voltage and a heater temperature.

FIG. 5 is a characteristic diagram showing a relationship between a heater temperature and a heater disconnection defect rate.

FIG. 6 is a sectional view showing an example of a cathode ray tube to which the present invention is applied.

[Explanation of symbols]

 H Heater 1 Metal wire 2 Insulating film 3 Dark layer 4 Sleeve 5 Impregnated cathode member 6 Negative electrode 7 Positive electrode 8 Power supply 9 Electrodeposition container 10 Dispersion liquid 11 Electron gun 12 Phosphor screen 13 Glass bulb 14 Cathode 15 Wehnelt electrode 16 Cylindrical electrode 17 Deflection Yoke 18 Anode button 19 Conductive film 20 Socket pin

Claims (2)

[Claims] 1. A cathode heater having an insulating film and a dark layer on a surface of a metal wire for current generation and heating, wherein the dark layer is formed of a layer containing at least one of hafnium oxide and silicon carbide. Characteristic heater for cathode heating. 2. A cathode heater comprising an insulating film and a dark layer on the surface of a metal wire for current generation and heating, wherein the dark layer is formed of a layer containing at least one of hafnium oxide and silicon carbide. A cathode ray tube provided on a cathode.