JPH04292829A - Indirectly-heated cathode - Google Patents

Abstract

PURPOSE:To obtain an indirectly-heated cathode having a short temperature drop zone (end cooling zone) generated at the end of the cathode due to heat absorption through a support body, and ensuring high heating efficiency. CONSTITUTION:A coil heater 5 comprising a heater wire 3 and an insulation layer 4 is wound around a core 2, while a coil cathode 8 comprising a fine metal wire 6 and an electron emission material layer 7 is wound around the core 2 adjacent to the coil heater 5. According to this construction, the heating value of the coil heater 5 is large, and the coil cathode 8 is heated by the coil heater 5 from two directions.

Description

[Detailed description of the invention]

0001

[Industrial Application Fields] In fluorescent display tubes, fluorescent light emitting tubes, light emitting units for large displays, light sources for optical printers, etc., electrons emitted from a linear cathode are made to collide with the phosphor layer of the anode to emit light. I'm getting an indication. The present invention relates to a linear cathode as an electron source used in this type of display element or light emitting element, and in particular, the present invention relates to a linear cathode as an electron source used in this type of display element or light emitting element. This relates to a heated cathode.

0002

[Prior Art] A conventional indirectly heated cathode 100 shown in FIG.
It has a linear heater section 103 in which an insulating layer 102 is coated around a heater wire 101, and a thin metal wire 105 coated with a thermionic emission substance 104 is wound around the linear heater section 103. It is configured. In the above configuration, by applying a cathode potential to the thin metal wire 105 and heating the thermionic emission material 104 with the heater wire 101, electron emission can be obtained.

0003

(1) When mounting the indirectly heated cathode 100, both ends of the heater wire 101 are welded to the support. Therefore, at both ends of the linear heater section 103, parts where the temperature decreases are created because heat is conducted to the support and escapes. Linear heater section 103
When the surface temperature of the thermionic emission material 104 heated by the above temperature drops to 500° C. or lower, electrons are no longer emitted from this portion. Such a portion of the indirectly heated cathode 100 is generally referred to as an end cool, and no anode segment can be provided below this portion. In order to improve the display density of a fluorescent display tube, it is necessary to shorten the end cool as much as possible, but the end cool of conventional indirectly heated cathodes is 7 mm.
For this reason, it did not fully meet these demands.

(2) Large display devices that apply the principle of fluorescent display tubes usually have a fairly large pixel pitch, but in recent years large indoor display devices have 8 pixels (22 mm pixel pitch) in one tube. 24 segments) or 32 segments with a pixel pitch of 10 mm.
Light-emitting cells with pixels (96 segments) are being used. As the pixel pitch within a light-emitting cell becomes smaller, the pixel pitch between adjacent light-emitting cells must be similarly reduced, which reduces the installation space for the filament cathode at the end of the light-emitting cell, and also reduces the space at the end of the cathode. Cool also needs to be small. However, the conventional indirectly heated cathode, which has an end cool of as much as 7 mm, has a problem in that it cannot be used in light emitting cells with a pixel pitch of 30 mm or less.

(3) In the conventional indirectly heated cathode 100, the thin metal wire 105 is connected only to the heater wire 101 through the insulating layer 102.
The electron-emitting material 104 was heated. That is, since the electron-emitting material 104 is heated only from the side of the linear heater section 103, the heat of the heater wire 101 is not efficiently transferred, resulting in poor thermal efficiency and a large amount of wasted current.

An object of the present invention is to provide an indirectly heated cathode with a short end cool and good thermal efficiency.

[0007]

[Means for Solving the Problems] The indirectly heated cathode of the present invention is
a wire-wound heater comprising a core wire having heat resistance, one or more heater wires wound on the core wire, and an insulating layer coated on the surface of the heater wire; The device includes a thin metal wire wound around a core wire and a wound cathode made of an electron-emitting material layer deposited on the surface of the thin metal wire.

[0008]

[Operation] The electron-emitting material layer of the wire-wound cathode is heated from both sides by the wire-wound heaters adjacent to each other on the core wire.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An indirectly heated cathode 1 according to a first embodiment shown in FIG. 1 has a core wire 2 made of ceramic fiber or glass fiber as a base. This core wire 2 has insulating properties and also has heat resistance capable of withstanding temperatures of about 1000°C.

A heater wire 3 made of tungsten is wound around the core wire 2. The diameter of the heater wire 3 is in the range of 5 to 50 μm, and the winding pitch around the core wire 2 is 200 μm or less, but in this example, the wire diameter is 15 μm and the winding pitch is 85 μm. An insulating layer 4 made of Al2O3 is deposited on the surface of the heater wire 3, forming a wire-wound heater 5. This insulating layer 4 is made by depositing Al2O3 fine powder on the surface of the heater wire 3 by electrodeposition, and then sintering and fixing it in a hydrogen furnace. Here, the thickness of the insulating layer 4 is 20 μm.

A thin metal wire 6 made of tungsten-rhenium is wound around the core wire 2 adjacent to the wire-wound heater 5 . This thin metal wire 6 has a wire diameter of 5~
The wire diameter is in the range of 50 μm, especially in this example, the wire diameter is 15 μm.
are used.

The surface of the thin metal wire 6 is coated with alkaline earth metal oxides that emit electrons well at low temperatures, such as (Ca,
An electron-emitting material layer 7 of Sr,Ba)CO3 is deposited to form a wire-wound cathode 8. To form this electron-emitting material layer 7, the electrodeposition method used to form the insulating layer 4 can be used. To explain the electrodeposition method here, first, add a small amount of binder to an organic solvent (Ca,
Sr,Ba)CO3 is added and suspended, and the core wire 2 around which the thin metal wire 6 is wound is immersed in this solution. Then, by connecting the thin metal wire 6 to the cathode, connecting the counter electrode disposed in the liquid to the anode, and applying a voltage, the carbonate will adhere to the thin metal wire 6 on the cathode side according to the principle of electrophoresis. Once the appropriate amount has adhered, remove it from the liquid.

As a method for attaching the carbonate to the thin metal wire 6, in addition to the electrodeposition method described above, an electrostatic spray method can also be used. This electrostatic spray method is a method in which a liquid in which an electron-emitting substance is suspended in an organic solvent is sprayed onto the thin metal wire 6.

In order to mount the indirectly heated cathode 1 constructed as described above in a fluorescent display tube, the core wire 2 is attached to the cathode support.
are fixed by caulking, the heater wire 3 is connected to the heater terminal, and the metal thin wire 6 is connected to the cathode terminal. Then, the display tube is brought into a vacuum state and the heater wire 3 is heated to decompose the electron emitting material layer 7 made of carbonate into an oxide.

To light up a fluorescent display tube having such an indirectly heated cathode 1, a heater voltage is applied to the heater terminal to heat the heater wire 3 of the wire-wound heater 5. The electron emitting material layer 7 of the wire-wound cathode 8 is sandwiched between the wire-wound heaters 5 on the core wire 2, and the wire-wound heater 5 is sandwiched between the wire-wound heaters 5 from both sides over a large area.
is in contact with. Therefore, heating of the electron emitting material layer 7 by the wire-wound heater 5 is efficient, and sufficient electron emission can be obtained with a small heater current.

Furthermore, since the wire-wound heater 5 is wound around the core wire 2, its total length is considerably longer than the total length of the indirectly heated cathode 1. This increases the resistance and the amount of heat generated is greater than that of conventional indirectly heated cathodes. Therefore, the end cool, which was a problem with conventional indirectly heated cathodes, was shortened to about 2 mm in the product of this example.

The indirectly heated cathode 10 of the second embodiment shown in FIG. 2 has a core wire 11 made of tantalum, which is a metal with higher resistance than tungsten. The wire diameter of the core wire 11 is 5~
It is within the range of 50 μm, and in this example, it is 30 μm. A wire-wound heater 14 is wound around the core wire 11 and is made up of a heater wire 12 made of tungsten and an insulating layer 13 made of Al2O3. The wire diameter of the heater wire 12 is 18 μm, which is slightly larger than that of the first embodiment.
It becomes. The winding pitch is the same as in the first embodiment. Further, a wire heater 17 made of a thin metal wire 16 coated with an electron emitting material layer 15 is wound at a position between the wire heaters 14 on the core wire 11 . This thin metal wire 16
The wire diameter is the same as in the first embodiment.

In the above configuration, when a heater voltage is applied to the heater wire 12 of the wire-wound heater 14 wound around the core wire 11, some current also flows through the core wire 11, but the current mainly flows through the heater wire 12, which has a relatively low resistance. Heater current flows and generates heat. This embodiment also provides the same functions and effects as the first embodiment.

An indirectly heated cathode 20 according to a third embodiment shown in FIG. 3 has a core wire 23 having a structure in which the surface of a metal wire 21 is coated with an insulating layer 22. This metal wire 21 contains 3% rhenium.
It contains tungsten. Its outer diameter is 5-50μm
However, in this example, the outer diameter is 15 μm. Further, the insulating layer 22 is made of Al2O3 which also has heat resistance.
Consists of. Its thickness is 1 to 30 μm, but in this example it is 20 μm.

A wire-wound heater 5 and a wire-wound cathode 8 are wound around the core wire 23, and the structure thereof is the same as that of the first embodiment described above.

According to this embodiment, the core wire 23 also acts as a heater and heats the winding cathode 8 together with the winding heater 5. That is, since the wire-wound cathode 8 is in contact with the heating means on three sides, the contact area is larger than in each of the embodiments described above. Therefore, it becomes an indirectly heated cathode with excellent thermal efficiency.

[0022]

Effects of the Invention In the indirectly heated cathode of the present invention, a wire-wound heater is wound around a core wire, and a wire-wound cathode is provided adjacent to the wire-wound heater. Therefore, the degree of heat concentration is higher when the heater wire is wound like this wire-wound heater than when the heater wire is stretched in a straight line. be able to. In addition, the electron-emitting material layer of the wire-wound cathode has a larger contact area with the heating means than before, improving thermal efficiency.
Good electron emission can be achieved with low input power.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a first embodiment.

FIG. 2 is a sectional view of a second embodiment.

FIG. 3 is a sectional view of a third embodiment.

FIG. 4 is a sectional view showing an example of a conventional indirectly heated cathode.

[Explanation of symbols] 1, 10, 20... indirectly heated cathode, 2, 11, 23... core wire,
3, 12... Heater wire, 4, 13... Insulating layer of wire-wound heater,
5, 14... Wire-wound heater, 6, 16... Fine metal wire, 7, 15
...Electron emitting material layer, 8, 17... Winding cathode, 21... Metal wire, 22... Insulating layer of core wire.

Claims (5)

[Claims] 1. A wire-wound heater comprising a heat-resistant core wire, one or more heater wires wound on the core wire, and an insulating layer coated on the surface of the heater wire, and the wire-wound heater An indirectly heated cathode comprising: a thin metal wire wound around the core wire adjacent to the wire; and a wound cathode comprising an electron-emitting material layer deposited on the surface of the thin metal wire. 2. The indirectly heated cathode according to claim 1, wherein the core wire has insulating properties. 3. The indirectly heated cathode according to claim 1, wherein the core wire has a structure in which an insulating layer is coated on the surface of a metal wire. 4. The indirectly heated cathode according to claim 1, wherein the core wire is formed of a metal wire having a higher resistance than the heater wire. 5. The indirectly heated cathode according to claim 1, wherein the electron-emitting material layer of the wire-wound cathode is in contact with a surface of the adjacent wire-wound heater.