JPS624809B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an indirectly heated cathode ray tube heater.

Generally, a cathode that emits thermoelectrons is used as an electron beam source in a cathode ray tube, and a heater in which a core wire 1 is coated with an insulating layer 2 as shown in FIG. 1 is inserted inside the cathode. The core wire 1 is made of a conductor such as tungsten which has a high melting point and is difficult to evaporate. Further, as the insulating layer 2, alumina is used to maintain insulation between the heater and the cathode.

As shown in Figure 2, in conventional heaters, alumina powder is fixed around the core wire 1 by spraying, electrophoresis, or dipping, and then sintered at a high temperature of about 1600°C for about 5 minutes to form an insulating layer. 2 is formed. In addition, in this alumina fixing process, tungsten powder or tungsten oxide powder may be suspended in the alumina suspension, and the insulating layer may be colored black to improve the thermal radiation efficiency of the heater.

However, in order to maintain the withstand voltage between the heater and the cathode, it is better to apply the insulating layer 2 thickly, and to prevent it from being scratched due to contact with the cathode, it is better to apply it densely and firmly. However, in reality, during operational heating, the core wire 1 and the insulating layer 2 have different coefficients of thermal expansion, so they are mutually subjected to strain forces, and cracks occur in the insulating layer 2. This crack generated in the insulating layer 2 breaks down the insulation between the heater and the cathode, causing damage to the heater and significantly deteriorating the image of the cathode ray tube.

As a method for preventing such cracks in the insulating layer 2, it is effective to fix coarse alumina powder to the core wire 1 by electrophoresis, but this method does not provide sufficient mechanical strength to the insulating layer 2. Because there is no such thing, it is not generally practiced. Conventionally, core wire 1 and insulation layer 2
In order to alleviate the distortion caused by the difference in thermal expansion between the core wire and the core wire, alumina powder is loosely fixed around the core wire by spraying. However, fixing the alumina powder by this spraying method causes large irregularities and uneven coating on the insulating layer 2, making it difficult to fix an insulating layer with a stable thickness.

Furthermore, Japanese Patent Publication No. 36-1222 proposes applying nickel plating or nickel cladding to the core wire, applying and sintering an insulating layer, and then dissolving and removing the nickel to create a gap between the core wire and the insulating layer. There is. However, the nickel disclosed in this example has the drawback of forming an alloy with tungsten during sintering of the insulating layer, which deteriorates the strength of tungsten. When the clad material is removed, the inner surface of the electrical insulating layer has almost the same shape as the surface of the core wire. Therefore, if the core wire is slightly displaced and partially contacts the electrical insulating layer, the contact area is large and the cathode It could not be said that this was sufficient to prevent leakage current between the Furthermore, the difference in heat conduction between the contact portion and the non-contact portion causes heater temperature fluctuations, which poses a problem in terms of uniformity.

The present invention has been made in view of the above-mentioned conventional drawbacks, and it prevents cracking of the insulating layer due to the difference in thermal expansion between the core wire and the insulating layer, prevents deterioration in the strength of the core wire, and reduces leakage current between the heater and the cathode. It is an object of the present invention to provide a small but excellent indirect heating type cathode ray tube heater.

The present invention will be described in detail below based on embodiments shown in the drawings.

First, FIG. 3 is a sectional view of a main part of a heater according to an embodiment of the present invention, and the same parts as in FIGS. 1 and 2 are given the same symbols. In FIG. 3, numeral 3 indicates the unevenness of the insulating layer 2 facing the core wire 1, and 4 indicates the gap between the unevenness 3 and the core wire 1.

Further, FIG. 4 is a diagram for explaining an example of a method of manufacturing the heater shown in FIG. 3, and the same parts as in each of the figures described above are given the same symbols. In FIG. 4, a metal wire 5 made of molybdenum, which is difficult to form an alloy with the core wire 1, is uniformly and densely wound over the entire length of a core wire 1 made of a metal material used as a heater core wire material such as tungsten. After applying alumina to this, it is sintered to form an insulating layer 2.
After that, when the metal wire 5 is dissolved and removed with a mixed solution of nitric acid and sulfuric acid, the core wire 1 is removed as shown in FIG.
A gap 4 is formed between the insulating layer 2 and the insulating layer 2, and unevenness 3 is formed on the inner surface of the insulating layer 2.

Furthermore, since molybdenum wire is linear, there is little contact area with the core wire even if it is tightly wound around the core wire, and molybdenum rarely forms an alloy when sintering tungsten and alumina, which deteriorates the strength of the tungsten core wire. Never.

In addition, a core wire 1 and a metal wire 5 made of a molybdenum wire
Since the contact area of the metal wire 5 is small, the metal wire 5 can be selectively and accurately melted and removed.

If the inner surface of the insulating layer 2 is made uneven 3 in this way, even if the core wire 1 is slightly displaced and comes into contact with the insulating layer 2, the inner surface of the insulating layer 2 is uneven 3 and the contact area is small, so that the contact area between the heater and the cathode is small. Leakage current is low and high insulation can be maintained. Furthermore, since the contact area is small, the heat of the core wire 1 is less likely to be partially transmitted to the insulating layer 2, resulting in a uniform temperature distribution and a uniform product with little variation as a mass-produced product. Furthermore, if a gap 4 is provided between the core wire 1 and the tungsten 2, the core wire 1
Since the thermal expansion of the insulating layer 2 is absorbed by the gap 4, the core wire 1 and the insulating layer 2 are not subjected to strain caused by thermal expansion, and alumina cracks and breakage of the core wire are prevented. Therefore, the density, degree of sintering, etc. of alumina need only be set by paying attention to the pressure resistance between the heater and the cathode, scraping, and other characteristics.

In the above example, molybdenum was used as the material for the metal wire wound around the core wire, but molybdenum is easily dissolved in certain chemicals and
Moreover, the material is not particularly limited as long as it is a material that is difficult to form an alloy with the core wire when sintering the insulating layer. For example, copper is used instead of molybdenum. Further, the solvent for dissolving the core wire is not particularly limited as long as it does not dissolve the core wire.

As is clear from the above description, the heater according to the present invention has unevenness formed on the inner surface of the insulating layer, so the contact area between the heater and the cathode is small, so leakage current is small, and the temperature distribution of the heater is uniform. In addition, since a gap is formed between the core wire and the insulating layer, the strain caused by the difference in thermal expansion between the core wire and the insulating layer is alleviated, and alumina cracks and disconnection of the core wire are eliminated.

[Brief explanation of the drawing]

Fig. 1 is an external view of the heater, Fig. 2 is a sectional view of the foot of a conventional heater, Fig. 3 is a sectional view of essential parts showing an embodiment of the heater of the present invention, and Fig. 4 is the same as Fig. FIG. 3 is a sectional view of a main part for manufacturing a heater. 1...Core wire, 2...Insulating layer, 3...Irregularities, 4...Gap,
5...Metal wire.

Claims (1)

[Claims] 1. In an indirectly heated cathode ray tube heater comprising a core wire made of a high melting point metal material and an insulating layer that covers a part of the core wire with a predetermined gap, the insulating layer has many irregularities on the surface facing the core wire. 1. An indirectly heated cathode ray tube heater, characterized in that it has: