JPH081778B2 - Indirect heating type cathode for cathode ray tube - Google Patents

Description

TECHNICAL FIELD The present invention relates to an indirectly heated cathode used in a cathode ray tube such as a picture tube for television, an observation tube for oscilloscope, or an image pickup tube.

2. Description of the Related Art Generally, an indirectly heated cathode for a cathode ray tube includes a heater for heating, a metal sleeve having one end closed therein, and an electron emitting emitter attached to the outer surface of the closed end wall of the sleeve. Further, a black or gray heat absorbing film is also provided on the inner surface of the sleeve, and this heat absorbing film helps the metal sleeve to efficiently absorb the radiant heat from the heater. On the other hand, the radiation heat loss from the outer surface of the metal sleeve is large, and it is about the same as the impregnated cathode.
In the case of a cathode operating at a temperature higher than 1,000 ° C, most of the heating value of the heater can be reached. Therefore, it is desirable that the outer surface of the sleeve is left with metal selection.

As a means for blackening only the inner surface of the metal sleeve, there is a cladding method as disclosed in JP-A-56-73834. This is a method of forming a sleeve by using a composite plate obtained by bonding a thin plate of nickel and a thin plate of nickel-chromium alloy as a material, and then performing heat treatment to blacken the nickel-chromium alloy thin plate inside. Also known is an Al-clad method in which an aluminum thin plate closely formed on the inner surface of the sleeve is heat-treated to be blackened.

Problems to be Solved by the Invention However, the production of the cathode by the clad method as described above causes a high cost. In the case of a cathode that operates at high temperature such as an impregnated cathode, the metal sleeve must be made of a refractory metal such as molybdenum (Mo) or tantalum (Ta), and the Al-clad is formed on the inner surface of the sleeve made of such a material. When the blackened layer is formed by the method, there is a risk that aluminum will evaporate from the hot cathode and adhere to the in-tube electrode or the like to cause dielectric breakdown. Furthermore, since the metal sleeve is made of a composite plate of different metals, there is a risk of warping due to the bimetal coefficient due to the difference in the thermal expansion coefficients of the composite plates, causing thermal deformation and peeling of the blackening layer after long-term use.

Therefore, it is an object of the present invention to provide a thermal cathode which is capable of easily forming a stable heat absorbing film on the inner surface of a refractory metal sleeve without using the clad method and which is highly efficient for a long period of time.

Means for Solving the Problems According to the present invention, a heater, a metal sleeve having one end closed therein, which includes the heater, an electron emitting emitter attached to an outer surface of a closed end wall of the sleeve, and an inner surface of the sleeve. And a heat absorbing film facing the heater, wherein the metal sleeve is formed of a material containing at least one of molybdenum (Mo), tantalum (Ta), and tungsten (W) as a main component, and The heat-absorbing film is formed of powder of a metal or its oxide containing at least one of molybdenum (Mo), tantalum (Ta) and tungsten (W) as a main component, Al ₂ O ₃ , zirconia (Zr).
O ₂ ), beryllia (BeO), spinel (MgAl ₂ O ₄ ) and zircon (ZrO ₂ · SiO ₂ ), which is a sintered film containing at least one inorganic binder.

The powder of the refractory metal or metal oxide as a material for the action heat absorbing film is dispersed in an organic solvent together with the powder of the inorganic binder such as alumina, and applied on the inner surface of the metal sleeve in the form of slurry. Since this coating film is sintered to obtain a heat-absorbing film, the above-mentioned inconvenience in the case of applying the clad method is eliminated, and an extremely stable high-quality heat-absorbing film can be obtained at a relatively low cost. Obtainable. In addition, since the heat-absorbing film has almost the same thermal expansion formation as the metal sleeve material, it does not peel off from the inner surface of the metal sleeve even during a long-term cold and high temperature thermal cycle, which prevents radiant heat from the heater. Can maintain a good heat absorption efficiency.

Example 1 FIG. 1 shows an impregnated cathode according to the present invention.
The heating heater 2 inserted in the metal sleeve 1 which is closed at one end is a coil heater, and it is about 11
The temperature rises to 20 ° C. The metal sleeve 1 is obtained by pressing a molybdenum (Mo) plate and has one end closed, and has an outer diameter of 1.8 mm and a length of 2.5 mm. Further, a pellet-shaped impregnated electron emitting emitter 4 is provided in a metal cup 3 provided on the outer surface of the closed end wall of the metal sleeve 1, and the impregnated emitter 4 is provided with a bottom plate portion of the cup 3 interposed therebetween. It is welded to the metal sleeve 1.
The heat absorbing film 5 attached to the inner surface of the metal sleeve 1 and facing the heater 2 and having a thermal expansion coefficient substantially equal to that of the material of the metal sleeve 1 is a sintered film containing a high melting point metal powder having an average particle size of about 5 μm or less. It consists of the following:

In this embodiment, tungsten (W) powder having an average particle size of about 1 μm and a maximum particle size of 5 μm is used as the refractory metal powder, which is a sintered alumina (Al ₂ having an average particle size of about 5 to 10 μm). It is mixed with an inorganic binder powder consisting of O ₃ ). The mixing ratio of the W powder and the Al ₂ O ₃ powder can be set to 7: 5 by weight, and 1 Kg of this mixture is added to 1.8 methyl isobutyl ketone (MIKB) to form a slurry. When about 100 g of nitrified cotton in this slurry is mixed, not only the dispersion effect becomes good, but also the degree of bonding of the coating film after drying can be made good.

After stirring the slurry with a ball mill for about 100 hours, the slurry is transferred to a polyethylene pot and rolled for about 50 hours to stabilize the dispersion state. Then, about 0.005 cm ^{3 of the} prepared slurry is poured into the metal sleeve 1,
It is vacuum sucked after 3 seconds. As a result, a coating film of the slurry is uniformly formed on the inner surface of the metal sleeve 1, which is then naturally dried. The film thickness of the coating film after drying is about 5 μm to 20 μm, and this film thickness is mainly determined by the viscosity of the slurry and can be adjusted by increasing or decreasing the addition amount of MIKB or nitrification cotton. The dried coating film is baked in a reducing gas atmosphere at a temperature of about 1600 ° C. for about 10 minutes. In the figure, 6 is a heater connector, and 7 is a cathode supporting metal wire.

In the impregnated cathode manufactured in this manner, the heat absorbing film 5 is attached to the inner surface including the side surface of the metal sleeve 1 facing the large area of the heater 2. Therefore, the heat absorbing efficiency becomes very good. In addition, since the heat absorbing film 5 having substantially the same coefficient of thermal expansion as the material of the metal sleeve 1 is attached,
The heat-absorbing film 5 is not peeled off from the inner surface of the metal sleeve 1 even in a long-term cold / high-temperature heat cycle, which allows the heat-absorbing efficiency to be kept good even with respect to the radiant heat from the heater. Further, FIG. 2 shows the cathode temperature characteristic as shown by the curve a. That is, the heater power consumption required to obtain the cathode temperature at 1050 ° C is about 1.3W, which is about 0.2W compared to the same characteristics (curve c) of the same type of cathode without a heat absorbing film.
Will be reduced. Further, even when continuous heating was performed at 1200 ° C. for 10,000 hours in a high vacuum with a pressure of 1 × 10 ⁻⁶ mbar or less, no substance evaporated from the heat absorbing film was observed.

Second Embodiment Next, another embodiment of the present invention will be described. The electrode structure was an impregnated cathode similar to that shown in FIG. 1, but tantalum (Ta) was used as the material of the metal sleeve 1. Ta is Mo
Press molding is easier than As a high melting point metal powder, the average particle size is about 0.5 μm and the maximum particle size is about 2 μm.
m of tungsten (W) powder was used. Further, as the inorganic binding powder, high-purity alumina powder having an average particle size of about 1 μm to 2 μm and a sintering temperature of 1800 ° C. or higher, and alumina sol were used. Alumina sol is a feather-like fine particle, and is about 0.1
It has a particle size of μm × 0.02 μm and is dispersed in an acetic acid solution (CH ₃ COOH) having a pH of 4 to 6 at a solid content weight ratio of about 10%.

The slurry is prepared by mixing 200 g of W powder and 20 parts of sintered alumina powder.
A mixture with 0 g is put into 1000 g of alumina sol liquid, stirred with a ball mill for about 100 hours, then transferred to a polyethylene pot and rolled for about 50 hours. The prepared slurry is fed into the metal sleeve in the same manner as in Example 1 to form a coating film. Since the viscosity of the slurry is higher than that in Example 1, it is possible to apply the slurry by incorporating it into a vinyl acetate sponge in the same manner as brush application. The film thickness of the coating film after natural drying is 2 μm ~
20 μm is suitable, and firing is performed in vacuum (pressure 1 × 10 ⁻⁵ mbar or less). This firing is accomplished by placing the coated metal sleeve in a molybdenum board and heating it with high frequency from outside the vacuum chamber. Heat at about 1600 ° C for 5 minutes. As a result, the feathery alumina in the alumina sol is sintered to become α-alumina, and the W powder and the sintered alumina powder are fixed. In particular, the binding force between α-alumina and sintered alumina is strong, and the adhesive strength of the heat-absorbing film to the metal sleeve becomes extremely large.

The temperature characteristics of the impregnated-type cathode manufactured in this manner were as shown by the curve b in FIG.

Although Ta is used as the material of the metal sleeve 1 in this embodiment, molybdenum (Mo) or tungsten (W) is used.
It is possible to use a high-melting point metal such as the above or a heat-resistant alloy (melting point of 1600 ° C. or higher) containing at least one of these metals.
Further, as for the high melting point metal powder, it is possible to use the high melting point metal as described above, a heat resistant alloy or a powder of a metal oxide thereof, but in any case, the melting point is 1600 ° C. or higher,
It is desirable that the average particle diameter is about 5 μm or less. Furthermore, as the inorganic binder powder, instead of sintered alumina, zirconia (ZrO ₂ ), beryllia (BeO), spinel (MgAl ₂ O ₄ ) or zircon (ZrO ₂ · SiO ₂ ) having a sintering temperature of 1200 It is possible to use an oxide ceramic having a mean particle size of 20 μm or less at ˜2000 ° C. or a mixture thereof. In particular, these oxide ceramics firmly bond the metal powder by blending with the alumina sol. Further, if necessary, impurities can be added to adjust the sintering temperature in the range of 1200 to 2000 ° C. For example, when using sintered alumina, MgO + TiO ₂ or CuO + TiO ₂ should be added in an amount of 3 to
By adding 4% by weight, the sintering temperature can be lowered to about 1300 ° C.

EFFECTS OF THE INVENTION Since the present invention is configured as described above, the heat absorbing film can be formed relatively easily, and the heat absorbing efficiency is extremely good. Further, it has a high mechanical strength such that it is stable in a vacuum at a high temperature, does not generate an evaporated substance, and does not peel off in a cold / high temperature heat cycle. In particular, since the inter-particle bonding force of the heat-absorbing film is moderately moderate, there is an advantage that the heat-absorbing film flexibly expands or contracts in response to a sudden temperature change and does not peel off or deform the metal sleeve.

[Brief description of drawings]

FIG. 1 is a partially cutaway perspective view of an indirectly heated cathode according to the present invention, and FIG. 2 is a characteristic diagram for comparing heating temperature characteristics of the cathode and a conventional cathode. 1 ... Metal sleeve, 2 ... Heater, 5 ... Heat absorbing film.

Claims (1)

[Claims] 1. A heater for heating, a metal sleeve having one end closed therein, an electron emitting emitter attached to the outer surface of the closed end wall of the sleeve, and a heat attached to the inner surface of the sleeve and facing the heater. And a metal film, wherein the metal sleeve is molybdenum (Mo), tantalum (Ta)
And tungsten (W) as a main component, and the heat-absorbing film contains at least one of molybdenum (Mo), tantalum (Ta) and tungsten (W) as a main component. Powder of metal or its oxide and Al ₂ O ₃ , zirconia (ZrO ₂ ),
An indirectly heated cathode for a cathode ray tube, comprising a sintered film containing at least one inorganic binder of beryllia (BeO), spinel (MgAl ₂ O ₄ ) and zircon (ZrO ₂ .SiO ₂ ).