JPH0782806B2 - Indirect heating cathode heater - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an indirectly heated cathode heater having a structure suitable for thermal shock resistance, and more particularly to an indirectly heated cathode heater useful for a color picture tube.

[Prior Art] A conventional method for manufacturing an indirectly heated cathode heater is disclosed in, for example, Japanese Patent Laid-Open No.
As described in JP-A-41694, the surface of a coiled coil in which a primary coil wound around a Mo core wire is further wound in a double helical shape, alumina (Al ₂ O ₃ ) is electrodeposited by an electrophoretic method,
It is to be fired.

Further, only the Mo core wire is acid-dissolved and removed, and many are finally used in a hollow state. A conventional cathode heater will be described with reference to the drawings. FIG. 3 is a partially sectional external view of a conventional type indirectly heated cathode heater, and FIG. 4 is a schematic vertical sectional view of the heater shown in FIG. In each figure, reference numeral 1 is a tungsten coil, 2 is an alumina film, 3 is a void, and (A) is a tip. The void 3 in FIG. 4 is generated by removing the Mo core wire.

[Problems to be solved by the invention]

A drawback of the cathode heater having the conventional structure is that cracks are likely to occur in the alumina film between the tungsten wires due to repeated heating in the cathode ray tube. If a crack is generated in this part, Ta or Ni discharged from the sleeve that covers the coil or Ni or
Ni ions attack the tungsten coil on the opposite side through the gap of the crack portion, and as a result, the crystal grains of tungsten are coarsened and then lead to embrittlement and fracture. This will be explained with reference to FIG. That is, FIG. 5 is a vertical cross-sectional view schematically showing a state in which the alumina film is cracked when the heater of FIG. 3 is incorporated in a cathode ray tube. Fifth
In the figure, reference numeral 4 is a Ta or Ni ion emission path, 5
Represents a crack, and 6 represents a Ta or Ni sleeve.

An object of the present invention is to provide an indirectly heated cathode heater having a structure excellent in thermal shock resistance.

[Means for solving problems]

Briefly describing the present invention, the present invention relates to an indirectly heated cathode heater, wherein in the indirectly heated cathode heater used for heat generation of a cathode structure that emits an electron beam, the tungsten coil has a porous alumina insulating film. The alumina forming the insulating film is a single crystal particle having an average particle diameter of 2 to 5 μm, and the purity of the alumina particle is 99.95% or more in terms of Al ₂ O ₃ , The alumina is characterized in that the alumina particle size does not change even after heating in a vacuum atmosphere for a long time.

According to the experiments conducted by the inventors of the present invention, a conventional type heater having a hollow state in which a so-called Mo core wire is pulled out has a high probability of causing a crack during use in a portion between tungsten wires, as described above. . The reason is that the alumina density of the film between the tungsten coils is low and the sintering strength is low as compared with the density of the alumina of the film electrodeposited on the surface of the tungsten coil.

Therefore, in the present invention, the indirectly heated cathode heater has the above-described structure. This will be specifically described with reference to FIGS. 1 and 2.

That is, FIG. 1 is an external view of the product of the present invention, which is (A) ′.
Is an improved part of the product of the present invention. FIG. 2 is a schematic vertical cross-sectional view of the tip portion of the product of the present invention, and reference numerals 1 and 2 have the same meanings as in FIG. As shown in FIG. 2, at the tip portion of the cathode heater of the present invention, the tungsten coil is coated with alumina, which is characteristic in that there is no hollow after melting the Mo core wire unlike the conventional product.

As a method for manufacturing such a cathode heater, a method of previously melting and removing the Mo core wire at the tip of the cathode heater and electrodepositing alumina over the entire circumferential direction of the tungsten coil is preferable.

Alumina constituting the insulating film is composed of single crystal particles having an average particle diameter of 2 to 5 μm, and the alumina particles have a purity of 99.95% or more, and the alumina particles are heated even in a vacuum atmosphere for a long time. It is preferable to use alumina which does not cause a change in particle size.

The indirectly heated cathode heater of the present invention is particularly suitable for a color picture tube.

〔Example〕

Hereinafter, the present invention will be described more specifically with reference to Examples and Test Examples, but the present invention is not limited to these Examples.

Example 1 A tungsten coil is wound around a Mo core wire and wound into the shape shown in FIG. Before electrodepositing this on alumina, the portion corresponding to (A) 'in FIG. 1 is dipped in an equal volume mixture of hydrochloric acid and nitric acid. As a result, the Mo core wire in the portion corresponding to (A) ′ is melted and only the tungsten coil remains. Thereafter, when the alumina electrodeposition operation is performed in the alumina suspension, alumina is electrodeposited on the entire tungsten coil as shown in FIG.

Test Example 1 FIG. 6 shows the results of the heat cycle life test of the conventional indirectly heated cathode heater and the present invention in the elapsed time (Kh, horizontal axis).
And the heater current value If (vertical axis). In FIG. 6, (7) is the average value of the product of the present invention, and (8) is the average value of the conventional product.

As is clear from FIG. 6, in the case of the conventional product, the current value gradually decreases immediately after the start of the life test, and the decrease becomes more remarkable after about 6 Kh. On the other hand, the product of the present invention does not show a marked decrease in the heater current value even after 6 Kh, and withstands a life test of 10 Kh or more.

Test Example 2 FIG. 7 shows a graph comparing the crush strengths (Kgf / mm ² ) of the tips (A) and (A) ′ of the cathode heaters of the conventional product and the product of the present invention. This is because the heater requires the most strength at the tip.

As is apparent from FIG. 7, the strength of the heater of the double-layer alumina film electrodeposition having different bulk densities is relatively large among the conventional products, but the product of the present invention has a strength of about 40% larger than that. It became clear.

Example 2 and Test Example 3 For the conventional alumina film for insulation of the cathode heater, it was common to use crushed alumina particles. On the other hand, in this embodiment, the crushed alumina particles are replaced by a hydrothermal synthetic method, and the average particle size of the alumina particles used in the conventional method is 2 μm or more and 5 μm or less (high-purity alumina). Dressed The problem is to prevent alumina grain growth and flaking after long use. Each test result of the example 2 is
The results are shown by black circles in FIG. 7 and in FIG. 8, and the test results of crushed particles are shown in FIG.

That is, FIG. 8 is a graph showing the alumina particle size distribution before and after the heat cycle test of 10 Kh in the high-purity alumina insulating film as a relationship between the particle size (μm, horizontal axis) and the fraction (%, vertical axis), FIG. 9 is a similar alumina particle size distribution graph for crushed alumina.

As shown in FIG. 7, the strength of the product of the present invention, which is high-purity alumina, is slightly smaller than that of crushed particles,
This is because it is difficult for high-purity alumina particles to sinter at the same temperature, and the difference at this level is not a problem.

As shown in Fig. 9, the crushed alumina particles are 20-30 after 10Kh.
It has a peak at a particle size of μm. On the other hand, as shown in FIG. 8, the high-purity alumina grain electrodeposition film does not show a large change in the particle size distribution even after 10 Kh, suggesting that the alumina film properties before and after the life test have little change and are suitable as an insulating film. There is.

〔The invention's effect〕

As described above, according to the present invention, the strength is increased by eliminating the voids inside the tungsten coil at the tip of the heater and coating the alumina film on the inside as well, and the sleeve component (Ta or Ni) of the tungsten coil, etc. Since it is possible to prevent the embrittlement due to the attack due to the ions of, it is effective in extending the life.

In addition to the above-mentioned invention, if high-purity alumina particles are electrodeposited, the growth of alumina particles can be suppressed, which is effective for extending the life of the heater.

[Brief description of drawings]

1 is an external view of the product of the present invention, FIG. 2 is a schematic vertical cross-sectional view of the tip of the product of the present invention, FIG. 3 is a partial cross-sectional view of a conventional product, and FIG. 4 is a view of the heater of FIG. Fig. 5 is a schematic vertical sectional view, Fig. 5 is a vertical sectional view schematically showing a state in which the alumina film is cracked when the heater of Fig. 3 is incorporated in a cathode ray tube, and Fig. 6 is a conventional product and the present invention product. 7 is a graph showing the result of the heat cycle life test, FIG. 7 is a graph showing the result of the crushing strength test of the tip of the conventional product and the product of the present invention, and FIG. 8 is the alumina particle size before and after the life test in the high-purity alumina insulating film. A graph showing the distribution, FIG. 9 is an alumina particle size distribution graph similar to FIG. 8 in the crushed alumina insulating film. 1 ... Tungsten coil, 2 ... Alumina film, 3 ...
Void, 4 ... Ta or Ni ion emission path, 5 ... crack, 6 ... Ta or Ni sleeve

Claims (1)

[Claims] 1. In an indirectly heated cathode heater used for heat generation of a cathode structure that emits an electron beam, a tungsten coil is covered with a porous alumina insulating film, and the alumina constituting the insulating film is made of an average material. Single crystal particles having a particle diameter of 2 to 5 μm, and the purity of the alumina particles is 99.95% or more in terms of Al ₂ O ₃ , and the alumina particle diameter does not change even after heating in a vacuum atmosphere for a long time. An indirectly heated cathode heater characterized by being alumina.