JPH083976B2 - Heater for electron tube and impregnated cathode assembly including the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application] The present invention relates to a heater for an electron tube suitable for use in, for example, a cathode ray tube or an image pickup tube, and an impregnated-type cathode assembly including the heater.

(Prior Art) A heater for an indirectly heated cathode is generally composed of a metal wire wound in a coil shape made of tungsten or rhenium-tungsten on the surface of which alumina particles having a particle diameter of 1.5 μm are subjected to electrophoresis, spraying, etc. After being coated with, a dark layer composed of alumina particles and tungsten particles is further coated and baked.

(Problems to be Solved by the Invention) However, in the conventional heater formed as described above, deformation is likely to occur during firing, and cracks are likely to occur in the alumina layer. As shown in FIG. 10 (b), this is because the distance between the metal wire and the dark layer is short, and the alumina layer having irregularities has a weak strength and causes cracks. In particular, when it is used for an impregnated cathode, the heater temperature is several hundreds higher than in the prior art, so that there is a problem in that insulation failure between the heater and the cathode occurs due to deformation or cracks, and heater breakage occurs.

An object of the present invention is to provide a heater that is not easily deformed or cracked and has an excellent withstand voltage, and an impregnated-type cathode assembly including the heater.

[Structure of the Invention] (Means for Solving the Problems) The present invention relates to a metal wire wound in a double helix,
In an electron tube heater having an insulating alumina layer coated with this metal wire and a dark layer coated with this insulating alumina layer, mixed alumina particles of the insulating alumina layer are 9
The purity is 9.8% or more, the average particle size is in the range of 7 to 12 μm, and the particle size distribution is 15 μm or more in particle size and 6 μm in particle size.
The heater for an electron tube has the following particles in the range of 10 to 30% by weight, and the balance being particles in the range of more than 6 μm and less than 15 μm.

Further, the present invention is an impregnated-type cathode assembly comprising a cathode base, a cathode sleeve supporting the cathode base, and the heater of the present invention installed in the cathode sleeve.

(Operation) By using the heater according to the present invention, the withstand voltage between the heater and the cathode is significantly improved, and the withstand voltage defect due to the high operating temperature of the impregnated cathode can be prevented.

Embodiment An embodiment of the present invention will be described in detail below with reference to the drawings.

The heater 1 of the present invention is configured as shown in FIG.
A metal wire 2 serving as a core wire wound in a double helix, an insulating alumina layer 3 covered with the metal wire 2, and a dark layer 4 covered with the insulating alumina layer 3.

In this case, the insulating alumina layer 3 contains 99.8 alumina particles.
% Or more, the average particle size is 7 to 12 μm, and the particle size distribution of alumina particles is 15 μm or more.
10 to 30% by weight of particles each having a size of less than μm, and the balance of 6
It is more than μm and less than 15 μm. The thickness of such an insulating alumina layer 3 is set in the range of 70 to 150 μm. The packing density of the insulating alumina layer 3 is 50 to 70%.
Is set in the range. The alumina particles are made by crushing fused alumina.

The dark layer 4 is composed of mixed particles of tungsten and alumina.

Next, the reason why the above numerical values are set will be described.

The reason why the purity of the alumina particles used is required to be 99.8% or more is as shown in FIG. That is, as a result of investigating the relationship between the purity and the withstand voltage failure occurrence rate with respect to factors other than the purity in the same manner as the embodiment of the present invention, the withstand voltage failure occurrence rate was 0% at 99.8% or more.

The withstand voltage failure rate was obtained by measuring 50 heaters coated with each purity. The withstand voltage defect test was conducted at a heater temperature of 7V against a rated voltage of 6.3V, and the voltage between the heater and the cathode was increased by 100V per 100V for 1 minute, and insulation breakdown at 1000V or less was regarded as a defect. .

The relationship between the average particle size and the pressure resistance was experimentally determined. The condition is that the heater temperature is 7V against the rated 6.3V, and the voltage between the heater and the cathode is 100VDC for 1 minute.
It carried out by raising every 100V. The filling rate and coating thickness at this time were the same. The results are shown in FIG. From this result, it was found that the average particle size of 7 to 12 μm was excellent in withstand voltage. It was found that the insulation breakdown voltage deteriorates due to insufficient firing strength at 12 μm or more and deformation and cracks at 7 μm or less (in FIGS. 5 and 6, when the filling rate is 50 to 70%, the powder drop occurrence rate Is 0% and the crack occurrence rate is low).

Using the average particle size of 7 to 12 μm, the filling rate is 50 to 70
As shown in FIG. 7, in order to set the
It is necessary to contain 10 to 30% by weight of particles each having a size of 15 μm or more (Fig. 7 shows that the average particle size should be kept at 9.0 μm.
(Experimental data showing the filling rate when particles of not more than μm and particles of not less than 15 μm were added in the same weight%).

Regarding the thickness of the coating, Fig. 8 shows the relationship between the coating thickness and the withstand voltage. As is clear from FIG. 8, the breakdown voltage sharply deteriorates below 70 μm. And, it is clear that the breakdown voltage values are almost proportional when the thickness is 70 μm or more. However, the coating thickness is limited by the size of the cathode diameter, and the thicker the coating thickness, the slower the cathode temperature rise speed. For example, the relationship between the image output time (the time when the heater is turned on and the emission that is sufficient to output an image, where the faster the temperature rises, the shorter the image output time) and the coating thickness is 5.7.
Seconds, 150 μm is 7.0 seconds, and 200 μm is 10.0 seconds.

Considering this, the coating thickness is 70-150μ
The range of m is appropriate.

Regarding the packing density, the packing density can be changed by adjusting the particle size. The relationship between the packing density, the crack occurrence rate (deformation rate), the dielectric breakdown voltage, and the coating powder falling occurrence rate are shown in FIGS. 5, 9, and 6, respectively. From this result, it is clear that the cracking rate and the coating peeling rate are low at the filling rate of 50 to 70%, and as a result, the dielectric breakdown voltage is high.

Further, it was revealed that the occurrence of deformation during firing almost coincides with the crack occurrence rate.

In addition to crushing fused alumina, the alumina particles are manufactured by a Bayer method, a thermal decomposition method of ammonium alum (reacting aluminum hydroxide with sulfuric acid to form aluminum sulfate, and then reacting with ammonium sulfate to react with ammonium alum. However, considering the shrinkage of particles during firing, it is preferable to use a powder made of pulverized fused alumina that has no particle shrinkage, which does not cause cracking or deformation, and has excellent pressure resistance. The result is obtained.

Next, a method for manufacturing the insulating alumina layer 3 as described above will be described.

Average particle size 9.0μm, 2.3μ% over 30μm, 30 ~ 15μ
Pulverized particles of fused alumina having a particle size distribution in which m is 15.3% by weight, 15 to 6 μm is 57.4% by weight, and 6 μm or less is 25.0% by weight and has a purity of 99.85% or more.

The particle size distribution of the alumina particles is adjusted so as to have a density of 55% when coated by the spraying method. The alumina particles were mixed at a solvent weight ratio of 1% (= alumina: solvent) in which 2% by weight of nitrocellulose was added to acetate, and the mixture was sprayed to give a thickness of 100 μ.
m coated.

The spray nozzles are attached at various angles so that the spray adheres to a uniform thickness (without uneven thickness).

After this, a mixture of tungsten having an average particle size of 1 μm, alumina powder having an average particle size of 2 μm and a binder in a weight ratio of 1: 4: 5 is applied to the dark layer 4 with a single thickness by a spraying method.
20 μm coating.

The dark layer 4 is effective in efficiently supplying the heat of the heater 1 to the cathode.

In this way, the alumina-coated heater was dried and then sintered in hydrogen at about 1700 ° C.

 However, the sintering time was twice as long as that in the conventional example.

In the heater 1 of the present invention as described above, the main element that constitutes impurities in the alumina particles of the insulating alumina layer is Na, which naturally moves in the alumina particles as Na ₊ ions. However, the dielectric strength is improved.

Further, by using the alumina particles as described above for the items of average particle size, particle size distribution, and appearance of particles, it is possible to obtain a product having sufficient strength during firing and little deformation during firing. That is, by using a fused alumina crushed product having a large average particle size, it is possible to suppress shrinkage during firing, and as a result,
The deformation of the heater can be prevented.

Furthermore, by using a distribution particle having a wide particle size distribution, that is, a packing rate of 50 to 70%, a sufficient strength of the insulating alumina layer at the time of firing can be obtained.

In the finished product, as shown in FIG. 10 (a), the metal wire and the dark layer are separated from each other, and there is no unevenness as compared with the conventional example shown in FIG. 10 (b).

Further, in this embodiment, the alumina particles were applied by the spraying method, but not limited to this, the electrodeposition method may be used.

Now, finally, an example of the impregnated type cathode assembly provided with the above-described electron tube heater 1 will be described. The impregnated type cathode assembly of the present invention is configured as shown in FIG. Is a cathode substrate, which is obtained, for example, by sintering tungsten powder having a particle size of about 3 μm so as to have a specific gravity of about 16 and impregnating the porous tungsten substrate with an electron emitting substance made of BaO, CaO, Al ₂ O _3. And is provided inside the cup-shaped fixing member 6. The fixing member 6 is joined to one end of a cathode sleeve 7 made of a high melting point metal by a brazing material. In the cathode sleeve 7, a heater 1 for heating the cathode substrate 5 to a desired operating temperature.
Is provided. Of course, the heater 1 is the heater according to the present invention described above.

A cylindrical holder 8 is coaxially arranged at a predetermined interval outside the cathode sleeve 7, and the cathode sleeve 7 is supported by the holder 8 via a plurality of, for example, three strip-shaped straps 9. There is. In this case, one end of the strap 9 is attached to the lower end of the cathode sleeve 7, and the other end is attached to the upper end of the holder 8.

[Advantages of the Invention] According to the present invention, the heater is set to the above-mentioned numerical value, and in the electron tube using the impregnated type cathode assembly provided with this heater, the withstand voltage characteristic between the heater and the cathode is 1.5 times that of the conventional one. It was possible to improve by about 2 times, and it was possible to prevent the breakdown voltage defect due to the high operating temperature of the impregnated cathode structure.

10 (a) and 10 (b) are 35 × micrographs showing the cross section of each heater of the present invention and the conventional example. In the conventional example, the distance between the metal wire and the dark layer is close. However, the alumina layer having irregularities has low strength and causes cracks. As a result, the breakdown voltage characteristic is poor.

However, in the present invention, the distance between the metal wire and the dark layer is large, and the uniform insulating alumina layer and the dark layer having no unevenness are formed as compared with the conventional example, so that the withstand voltage characteristic is excellent.

[Brief description of drawings]

FIG. 1 is a front view showing a heater for an electron tube according to an embodiment of the present invention, and FIG. 2 is a partially cutaway view of an impregnated cathode assembly having a heater for an electron tube according to another embodiment of the present invention. 3 is a perspective view, FIG. 3 is a characteristic diagram showing the relationship between the purity of alumina particles used in the insulating alumina layer of the heater of the present invention and the withstand voltage defect occurrence rate, and FIG. 4 is the same as the relationship between the average particle size and the breakdown voltage. 5 is a characteristic diagram showing the relationship between the alumina filling rate and the crack occurrence rate, and FIG. 6 is a characteristic diagram showing the relationship between the alumina filling rate and the powder drop occurrence rate of the coating. The same figure is a characteristic diagram showing the relationship between alumina particles and alumina filling rate, FIG. 8 is a characteristic diagram showing the relationship between coating thickness and dielectric breakdown voltage, and FIG. 9 is similarly showing alumina filling rate and dielectric breakdown voltage. 10 is a characteristic diagram showing the relationship between (A), (b) is a microscopic photograph showing the particle structure of the cross section of the heater each electron tube of the present invention and conventional example, respectively. 1 ... Heater, 2 ... Metal wire, 3 ... Insulating alumina layer,
4 ... Dark layer, 5 ... Cathode base, 7 ... Cathode sleeve.

Claims (2)

[Claims] 1. A heater for an electron tube comprising a metal wire wound in a double helix, an insulating alumina layer covered with the metal wire, and a dark layer covered with the insulating alumina layer. The mixed alumina particles of are those having a purity of 99.8% or more and an average particle size of 7 to 12 μm, and a particle size distribution of particles having a particle size of 15 μm or more and particles having a particle size of 6 μm or less in the range of 10 to 30% by weight, respectively. And the rest is 6 μm
A heater for an electron tube, characterized in that the particles are in the range of over 15 μm. 2. An impregnated cathode assembly comprising a cathode assembly, a cathode sleeve supporting the cathode assembly, and the heater for an electron tube according to claim 1, which is installed in the cathode sleeve.