KR20020006109A - heater for CRT - Google Patents

Abstract

PURPOSE: A heater for cathode ray tube is provided to improve thermal conductivity of an insulating and lengthen a lifetime of the heater by adding an insulating material having prominent thermal conductivity to an insulating layer including an alumina material formed on a surface of a heater. CONSTITUTION: Alumina coated on a metal line of a heater for cathode ray tube is used as a main ingredient. An insulating layer(9) is formed by adding one or more material of SiC or BeO to the alumina. Thermal conductivity of the insulating layer(9) is improved by mixing the alumina with one or more material of SiC or BeO according to a predetermined ratio and forming the insulating layer(9) as the mixed material. The insulating layer(9) is coated on a metal line of the heater for cathode ray tube. One or more material of SiC or BeO is 20 to 40 weight percent and the alumina is 60 to 80 weight percent. A graphite layer(8) is formed on the insulating layer(9) in order to prevent diffused reflection.

Description

Cathode ray tube heater {heater for CRT}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heater for a cathode ray tube, and in particular, an insulating film composed mainly of alumina coated on a metal wire of a heater is mixed with a material having excellent thermal conductivity and insulation property, thereby improving thermal efficiency of the insulating film, thereby reducing the disconnection of a metal wire or a heat source of the heater. The present invention relates to a heater suitable for reducing power consumption applied to the heater while preventing cracks and the like.

Cathode ray tubes are the most widely used display devices for color television, oscilloscope and radar observations. Such a cathode ray tube focuses an electron beam emitted from an electron gun on a fluorescent surface of a screen to realize an image, and a cathode as an initial source of an electron beam plays a very important role.

Cathode is divided into an oxide cathode and an impregnated cathode according to the material of electron-spinning, the oxide cathode is the most widely used because of the easy manufacturing method and low-cost materials, but it is insufficient to operate under high current density. Therefore, an impregnated cathode is applied for driving under high current density. In order for the oxide cathode and the impregnated cathode to operate, a predetermined amount of heat must be applied to the cathode, and much more heat is applied to the impregnated cathode than the oxide.

In other words, while the operating temperature of the oxide cathode is approximately 800 ° C, the impregnated cathode reaches almost 1000 ° C.

Therefore, the cathode ray tube is equipped with a heater to heat the cathode, the design of the heater is determined by the type of the cathode. That is, since the operating temperature of the oxide cathode and the impregnated cathode is different, the amount of heat applied to the cathode from the heater is different, so the heater is designed in consideration of this.

The oxide cathode is sprayed with carbonates (BaCO ₃ , SrCO ₃ , CaCO ₃ ) on a base metal containing nickel (Ni) and then decomposed into oxides (BaO, SrO, CaO) by aging. Form.

On the other hand, the impregnated cathode is a high melting point metal powder, such as tungsten (W), which acts as a reducing agent, as shown in FIG. After making a porous pellet-shaped sintered compact, the cathode body 1 is formed by impregnating electron emitting materials such as BaO, CaO, and Al ₂ O _{3 in the} sintered body, and the cathode gas is placed inside a cathode cup 2 that is a heat-resistant metal. Inserted and laser-welded the side, the cylindrical negative electrode sleeve (3) is fixed to the outer surface of the negative electrode cup (2), this negative electrode sleeve is welded to the negative electrode holder (4).

In addition, a heater 5 for negative electrode heating is inserted into the inside of the cathode sleeve 3, and the upper surface of the cathode gas 1 is platinum group elements osmium (Os), ruthenium (Ru), and irinium (Ir). The coating layer 6 is formed by the sputtering method with a rare earth metal such as).

In the above structure, when a constant voltage is applied through the welded portion of the heater 5, heat of a required amount of heat within 4 to 6 seconds is generated in the heat generating portion of the heater and is conducted to the base metal 1 through the cathode cup 2. Ba / BaO produced by the reaction of the electron-spinning material impregnated with tungsten in the cathode gas diffuses to the upper portion of the cathode gas to form a monoatomic layer at the top, contributing to the electron radiation.

The heater 5 used for the cathode ray tube electron gun applies a necessary voltage on an aging schedule during the cathode ray tube manufacturing process, and the heat generating unit generates instantaneous heat at 1150 to 1200 ° C. in the cathode ray tube manufacturing process and about 100 ° C. during TV normal operation. As a result, the heater must maintain its shape even at high temperature and insulate even at high voltage when voltage is applied.

Therefore, as shown in FIG. 2, the insulating film 7 and the blackened film 8 as the heat insulating film are formed.

That is, the heater 5 winds the tungsten wire (B), which is a heating wire, on the molybdenum wire (A), which is a mandrel wire, forms an insulating film (7) using alumina solution on the surface thereof, and then increases the emissivity and prevents diffuse reflection upon heating. In order to form the blackening coating 8 layer, the blackening agent powder is formed. And sintered in a high temperature hydrogen atmosphere to obtain a heater having a strength that can withstand thermal, electrical and external shocks.

The main heat flow of the cathode from the heater is made through the vacuum between the insulating film, the blackening film and the blackening film and the cathode sleeve, the insulating film is a porous material formed of alumina powder and pores, but there is a slight difference depending on the porosity As heat transfer is performed by about 85% of heat conduction and about 15% of heat radiation, the film thickness is very thin in blackening film, and most of heat transfer is made by heat conduction. Heat is transferred between the blackening film and the cathode sleeve by heat radiation.

As described above, the heat transfer from the heater to the cathode is very complicated because the heat conduction and heat radiation through various media are mixed. Therefore, in order to increase the heat transfer efficiency from the heater to the cathode, it must be approached from various angles. However, in the past, attention has focused mainly on the improvement of the thermal radiation efficiency of the cathode sleeve from the blackening film of a heater (Japanese Patent Laid-Open No. 11-250799, etc.).

However, the heat loss due to the insulating film surrounding the metal wire of the heater as described above should not be overlooked. For example, alumina, which is a main component of the insulating film, has a very low thermal conductivity at high temperatures, thereby decreasing the heat transfer efficiency from the metal wire, which is the heat source of the heater, to the blackened film outside the insulating film. As a result, the radiant heat of the cathode sleeve is reduced from the blackening film, which in turn leads to an effect of inhibiting the thermal efficiency of the heater.

In particular, in the case of a heater used with an impregnated cathode that requires a high operating temperature, it is necessary to increase the temperature of the metal wire by supplying more power to the metal wire of the heater, thereby increasing the energy consumption of the heater, and disconnection of the metal wire due to the temperature rise of the metal wire. Or reliability problems such as breakdown of the insulating film.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and by mixing and forming a material having excellent insulation and thermal conductivity in an insulating film made of alumina formed on the surface of the heater, thereby improving the thermal conductivity of the heater insulating film to improve the heater metal wire. It is intended to have an insulating film that reduces the power supplied to the heater during operation of the cathode ray tube while reducing the temperature, prevents disconnection of metal wires by heat, and increases the life of the heater and suppresses reliability problems such as destruction of the insulating film due to high temperature. There is this.

Figure 1 is a conventional impregnated cathode structure diagram inserted heater

2 is an enlarged cross-sectional view of the heater for "A" in FIG.

3 is a detailed view of a heater cross section according to the present invention;

Figure 4 is a state diagram of the thermal conductivity change according to the temperature associated with the material of the present invention

Explanation of symbols for main parts of drawings

5 Heater 8 Black Film 9 Insulation Film

The present invention for achieving the above object is an insulating film composed mainly of alumina coated on the metal wire of the cathode ray tube heater, the insulating film formed by adding at least one of silicon carbide (SiC) or beryllium oxide (BeO) to the alumina It consists of a provided heater.

According to the present invention, at least one of silicon carbide (SiC) or beryllium oxide (BeO), which is added with alumina to improve thermal conductivity of the insulating film coated on the metal wire of the heater, has excellent thermal conductivity compared to alumina while having excellent insulation. By mixing one or more with alumina in a constant ratio, an insulating film having improved thermal conductivity is formed.

The preferred mixing ratio in the present invention is 100% by weight, at least one of silicon carbide (SiC) or beryllium oxide (BeO) is 20 to 40% by weight, the remainder is composed of alumina. In addition, since the thermal radiation rate of silicon oxide, beryllium oxide, and magnesium oxide, which is a material applied in the present invention, is excellent, the amount of heat radiation through pores in the insulating film can be increased, thereby contributing to the thermal efficiency of the insulating film.

3 is a view illustrating a heater structure applied to the present invention, in which a metal coil of the same heater as that of FIG. 2 (that is, a tungsten wire (B) that is a heating wire is wound around a molybdenum wire (A) which is a mandrel wire) Metal Coil] After the insulating film 9 is formed on the surface using the composition of the present invention, a blackening film 8 is formed of a blackening agent powder in order to increase the emissivity and prevent diffuse reflection upon heating. And sintered in a high temperature hydrogen atmosphere to obtain a heater having a strength that can withstand thermal, electrical and external shocks.

Figure 4 shows the thermal conductivity according to the temperature of silicon carbide, beryllium oxide, alumina, as shown in each material, the thermal conductivity is lowered as the temperature increases, but compared to the alumina at the temperature of the impregnated cathode 1000 ℃ or more The thermal conductivity of silicon carbide and beryllium oxide applied to the present invention is excellent.

It is preferable that the alumina particles used in the present invention have an average particle diameter of about 4 μm, and those having a particle size of 3 μm or less occupy 30 to 45%. As the material for forming the black film 8, alumina having the above-described particle distribution and Tungsten powder having a particle diameter of 1 µm or less was used. The black film 8 is formed by mixing alumina and tungsten powder with a binder and then dipping to form a black film having a thickness of 5 to 10 μm.

The method of forming the insulating film using an electrophoretic coating (Electrophoretic Coating), the alumina and the additive material is mixed in a predetermined ratio in a powder state, and then mixed with an electrolyte such as magnesium nitrate and aluminum nitrate and ethanol to complete the insulating solution.

An insulating layer is formed by holding a rhenium-tungsten alloy wire coil, which is a heat source of a heater, as a negative electrode, immersing it in the insulating liquid together with a platinum positive electrode, and applying a voltage of 50 to 100V. At this time, the thickness of the insulating film is 75 to 90 µm.

Here, the productivity and the thermal conductivity of the heater are different depending on the particle diameters of silicon carbide and beryllium oxide added together with alumina when forming the insulating film.

That is, when the particle diameter of the additive material such as silicon carbide and beryllium oxide is smaller than the particle size of the alumina used, the particles of the additive material agglomerate with the alumina particles in the suspension insulated solution and a solid state reaction occurs to form an insulating film on the heater. Rather, it results in a drop in thermal conductivity, and the smaller the particle size, the lower the productivity. Therefore, the particle diameter of the additive material such as silicon carbide or beryllium oxide should be equal to or greater than that of alumina.

The following is described according to the embodiment.

In order to compare the thermal conductivity characteristics of the insulating film, an insulating film having a predetermined thickness is formed on the rhenium-tungsten metal wire, which is the heat source of the heater, and a blackening film is formed on the outside thereof, followed by drying and sintering to complete the heater. The temperature of the negative electrode was measured by mounting together with the impregnated negative electrode. In this case, the higher the temperature of the cathode, the better the thermal conductivity.

Example 1

Table 1 shows the cathode temperatures for each particle size of silicon carbide and beryllium oxide, and is data when the mixing ratio (weight ratio) of alumina and silicon carbide or beryllium oxide is 80:20. The cathode temperature is the value measured when a voltage of 6.3V is applied to the heater.

Conventional The present invention (average particle size: ㎛) 2.0 4.0 6.0 8.0 SiC added (℃ b) 980 983 980 1005 981 When BeO is added (℃ b) 980 981 985 997 979

* Conventional products do not contain silicon carbide or beryllium oxide

It can be seen from Table 1 that the size of silicon carbide or beryllium oxide particles is the best thermal conductivity when the average particle size of alumina is about 1.5 times, and the case of silicon carbide or beryllium oxide particles is smaller than the particles of alumina There is no difference in the temperature of the conventional one. On the other hand, when the size of silicon carbide or beryllium oxide particles is too large, the porosity of the insulating film is so large that not only the thermal conductivity is lowered but also the insulation is poor.

Example 2

The thermal conductivity of the silicon carbide, beryllium oxide particles, and alumina particles in the insulating solution was tested.

Although the particle size and the mixing ratio of the particles influence simultaneously, in this experiment, only the mixing ratio with the alumina was considered while keeping the average particle and particle distribution constant. The average particle diameter of alumina was 4.0 µm, and the average particle diameter of silicon carbide or beryllium oxide material was 6.0 µm.

As a result, the adhesion of the insulating film was inferior as the ratio of the alumina particles decreased. Therefore, up to a certain ratio, alumina particles should be included.

Table 2 shows the cathode temperatures according to the mixing ratio of silicon carbide, beryllium oxide particles and alumina particles. The cathode temperature is for the electron gun to which the impregnated cathode is applied. It was measured to indirectly compare the thermal conductivity. The higher the cathode temperature, the better the thermal conductivity.

Conventional Invention (mixed ratio) 20% 30% 40% 50% SiC added (℃ b) 980 1005 1011 1013 1014 When BeO is added (℃ b) 980 997 1002 1006 1008 Insulation state Good Good Good Good Bad

* Conventional products do not contain silicon carbide or beryllium oxide

* Mixing ratio is the weight ratio of additive when mixing alumina and additive

As can be seen from the above (Table 2), when the silicon carbide and beryllium oxide were 20 to 40% by weight, respectively, excellent thermal conductivity and adhesion were obtained.

When the mixing ratio is 50:50, the temperature of the cathode is higher, but the adhesion of the insulating film is not good, it can be seen that the mixing ratio is not suitable.

Example 3

Table 3 compares the power applied to the conventional heater and the heater through the present invention when the temperature of the impregnated cathode is 980 ° C. at a heater applied voltage of 6.3V.

In the experiment, silicon carbide having an average particle diameter of 6 μm was used and mixed with alumina particles at 80:20 wt%. The coil of the metal wire, which is the heat source of the heater, is designed to have a cathode temperature of 980 ° C. As shown in Table 3, it can be seen that the power consumption of the heater obtained through the present invention is lower than that of the conventional heater.

Conventional heater Heater of the present invention Heater current (mA) 370 335 Power Consumption 2.33 2.11

As described above, the present invention is prepared by mixing silicon carbide or beryllium oxide in an insulating film mainly composed of alumina coated on the surface of the metal wire of the heater, thereby improving the thermal conductivity of the insulating film and lowering the temperature of the heater metal wire while operating the cathode ray tube. In addition to reducing the power supplied to the heater, it is possible to prevent the disconnection of the metal wire due to heat, thereby improving the life of the heater and obtaining an insulating film in which reliability problems such as destruction of the insulating film due to high temperature are suppressed.

Claims (4)

An insulating film mainly composed of alumina coated on a metal wire of a cathode ray tube heater, the cathode ray tube heater comprising an insulating film formed by adding at least one of silicon carbide (SiC) or beryllium oxide (BeO) to the alumina. The method of claim 1, The insulating film is 100% by weight, at least one of silicon carbide (SiC) or beryllium oxide (BeO) is 20 to 40% by weight, the remainder is made of alumina, the heater for a cathode ray tube. The method of claim 1, A cathode ray tube heater, characterized in that the particle diameter of silicon carbide (SiC) or beryllium oxide (BeO) is equal to or larger than the particle size of alumina. The method of claim 3, wherein Cathode ray tube heater, characterized in that the particle size of silicon carbide (SiC) or beryllium oxide (BeO) is 1.5 times the size of the alumina particle size.