JPS6124776B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing 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 scratching 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.

The present invention has been made in view of the above-mentioned conventional drawbacks, and an object of the present invention is to provide a method for manufacturing an indirectly heated cathode ray tube heater that can prevent cracking of the insulating layer due to the difference in thermal expansion between the core wire and the insulating layer. .

Examples of the present invention will be described below.

An alumina suspension made of alumina powder and a metal that is difficult to form an alloy with the core wire, such as a metal or metal oxide powder such as molybdenum powder or molybdenum oxide powder, is sprayed around the core wire or fixed by electrophoresis.
Next, as in the past, firing is performed in a hydrogen atmosphere at approximately 1,600°C to sinter the alumina powder and form an insulating layer around the core wire. In this process, for example, molybdenum oxide powder is reduced to molybdenum powder. Thereafter, the molybdenum powder in the insulating layer is selectively dissolved in the heater using a mixed solution mainly composed of nitric acid and sulfuric acid.

As shown in Figure 3, the insulating layer of the heater manufactured in this way has pores 3 of dissolved molybdenum powder, so the insulating layer has more flexibility than conventional heaters. are doing. Therefore, the strain caused by the difference in coefficient of thermal expansion between the core wire and the insulating layer is alleviated by the presence of the pores, and cracks in the insulating layer are suppressed. Also, even if electrophoresis is used, there is no need to use coarse alumina particles as in the conventional method.
The insulating layer can be made sparse without significantly deteriorating the mechanical strength of the insulating layer.

In the above example, molybdenum was used as a material to be dissolved in alumina powder, but it is easily dissolved in certain chemicals, and it is also possible to use an alloy in the core wire when sintering the insulating layer. The material is not particularly limited as long as it is a material that is difficult to make. 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.

Further, the size and amount of the powder to be mixed can be freely selected depending on the porosity of the insulating layer after the powder is melted. For example, a few micrometers of molybdenum powder is about the weight of alumina.
When 1/2 was mixed, no alumina cracks occurred during heater operation.

As is clear from the above explanation, according to the present invention, the heater forms holes in the insulating layer, and the contact between the core wire and the insulating layer is reduced by the amount of the holes, so that the heat between the core wire and the insulating layer is reduced. The strain caused by the difference in expansion is alleviated, and alumina cracks and core wire breaks are eliminated.

[Brief explanation of the drawing]

FIG. 1 is an external view of a heater, FIG. 2 is a cross-sectional view of a foot portion of a conventional heater, and FIG. 3 is a cross-sectional view showing an example of a heater manufactured by a method according to an embodiment of the present invention. 1... Core wire, 2... Insulating layer, 3... Hole.

Claims (1)

[Claims] 1. In manufacturing an indirectly heated cathode ray tube heater in which a core wire is coated with an insulating layer, powder of a metal or metal oxide that is difficult to form an alloy with the core wire is added to the alumina powder around the core wire. A heater for an indirectly heated cathode ray tube, comprising the steps of: applying a suspended alumina suspension; sintering after application to form a coating layer; and selectively dissolving and removing powder in the coating layer. manufacturing method. 2. The method for manufacturing an indirectly heated cathode ray tube heater according to claim 1, wherein the powder is made of molybdenum or molybdenum oxide.