JP3334332B2 - Cathode ray tube - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cathode ray tube such as a picture tube, a picture tube and a transmission tube.

[0002]

2. Description of the Related Art In general, a normal operating temperature of an indirectly heated cathode provided with an impregnated cathode base in a cathode ray tube is 1000-1.
100 ° C and 1200 ° C in the cathode activation process
May be exceeded. Further, it is practically required that the impregnated cathode guarantees a lifetime of tens of thousands of hours. Therefore, the material of the cathode support of the impregnated cathode should have a melting point of about three times, or at least 2.5 times, the operating temperature when long-term stability is expected.

As such a material, a thin metal wire or a ribbon-like flat plate made of tungsten, rhenium, tantalum, molybdenum, an alloy thereof, or the like has been conventionally used. In particular, tungsten containing rhenium has a lower thermal conductivity and a higher Young's modulus than tantalum and molybdenum, so that heat loss from the cathode can be prevented, heater power can be saved, and rigidity can be improved. (Japanese Unexamined Patent Publication (Kokai) No. 3-40331).

[0004]

However, in a cathode ray tube having an electron gun employing such an impregnated cathode, there is a problem that the cutoff voltage, which is a characteristic of extracting an electron beam, changes with time. there were. When the cutoff voltage changes, the electron beam drive characteristic of the electron gun changes and the beam current changes even if the electron emission performance of the cathode body does not change at all. In particular, the impregnated cathode cannot take advantage of the fact that the electron emission performance is almost constant and does not decrease until the end of its life.In recent receivers, the cut-off voltage adjustment mechanism has been simplified, and general users can freely adjust it. Considering that it is no longer possible, it is important to reduce the change over time of the cutoff voltage.

Conventionally, the cause of such a change of the cut-off voltage with time is that an electron-emitting substance such as barium evaporates from the cathode during operation and adheres and deposits on the cathode side around the electron beam passage hole of the control electrode G1 of the electron gun. This has been considered to cause a change in the distance between the electron beam passage hole and the electron emission surface of the impregnated cathode.

However, the inventor has found that the cause of the fluctuation of the cutoff voltage is that the cathode support contracts during operation. That is, the operating temperature of the impregnated type cathode is high, and therefore the temperature of the cathode support is also high. During the long-term operation of 1000 to 5000 hours, the rhenium-metal alloy wire is formed inside the rhenium-tungsten alloy thin wire of the cathode support material. A compound is formed. At this time, the volume contraction of the rhenium-tungsten alloy thin wire occurs because the average lattice constant when separated into tungsten and a rhenium intermetallic compound is smaller than the lattice constant of the rhenium-tungsten alloy in the initial stage of operation. Due to the time-dependent volume contraction of the cathode support, the distance between the electron beam passage hole of the control electrode G1 and the electron emission surface of the impregnated emitter is reduced, and the cutoff voltage fluctuates. When the cutoff voltage fluctuates, there arises a problem that the luminance fluctuates with time during operation.

An object of the present invention is to provide a cathode ray tube capable of suppressing such a change in cutoff voltage and suppressing a change in luminance over time during operation.

[0008]

In order to achieve the above object, a cathode ray tube of the present invention, the scan
Comprising an indirectly heated cathode which impregnated cathode and a cathode supporting element for a cathode Hol da supporting and fixing is formed by rhenium-tungsten alloy having a sleeve, the cathode Shijiko is of the sleeve
The cathode support has a rhenium content in tungsten of 20% by weight or less,
Alternatively, it has a configuration that is 80% by weight or more.

[0009]

[Function] With this configuration, rhenium in the initial stage of operation can be obtained.
Since the difference between the lattice constant of the tungsten alloy and the lattice constant when the rhenium intermetallic compound is formed after a lapse of 1000 to 5000 hours of operation is reduced, the temporal shrinkage ratio of the cathode support is reduced. The variation with time of the distance between the electron beam passage hole and the electron emission surface of the impregnated emitter is reduced, and the variation with time of the cutoff voltage can be reduced.

[0010]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view of an impregnated cathode structure used in the cathode ray tube of the present invention. As shown in FIG. 1, a cup 2 made of metal, such as molybdenum, containing an impregnated emitter 1 in the form of a pellet, a sleeve 3 made of metal, such as molybdenum, welded to its bottom plate, and a heater housed in the sleeve 3 4 together with an impregnated cathode 5. Cathode support 6 radially extending from impregnated cathode 5
Is welded to a cathode support 8 made of metal, for example, Kovar, of the cathode holder 7. The cathode holder 7 has a ceramic insulating ring 9 for insulatingly supporting a cylindrical cathode support 8, has a metal cylinder 10, and impregnates the cup-shaped control electrode G 1 with the metal cylinder 10. The electron emission surface 11 of the mold emitter is fixed so as to face the electron beam passage hole of the control electrode G1.

The cathode support 6 is made of a rhenium-tungsten alloy thin wire. These thin wires have a diameter of 0.05 mm and a length of about 1.6 mm, and fix the cathode to the cathode support 8 with four wires. In addition, before the thin wire is subjected to the cathode assembly, in order to improve the processability, a linear elongation of 10% or more is obtained in accordance with the content of rhenium.
A heat treatment at 1500 to 2000 ° C. is performed. Here, the rhenium content of the rhenium-tungsten alloy thin wire of the cathode support 6 is 20% by weight or less, preferably 3 to 15%.
% By weight or 80% by weight or more, preferably 85 to 97%
% By weight.

The rhenium content was 3, 15, 2 respectively.
A rhenium-tungsten alloy thin wire was manufactured by powder metallurgy at 0, 30, 50, 70, 80, 85 and 97% by weight.
A heat treatment at 00 ° C. was performed for about 5 seconds. Others with a rhenium content were subjected to a heat treatment at about 1700 ° C. for about 3 seconds. As a result, a linear elongation of about 11% was obtained for all the fine wires, and the cathode assembly was facilitated.

An impregnated cathode as shown in FIG. 1 was manufactured by the usual cathode manufacturing process using the thin wire thus manufactured. Then, the impregnated cathode was assembled into a 17-inch color display tube through a normal electron gun mounting process, and a practical operation life test was performed. At this time, the diameter of the electron beam passage hole of the control electrode G1 of the electron gun is 0.35 m.
m, the distance between the electron beam passage hole and the electron emission surface of the impregnated emitter is about 0.07 mm. The operating temperature of the cathode was set to 980 to 1000 ° C. for all the tested cathodes by adjusting the power of the heater while observing with an optical pyrometer. The cathode operating current is on average about 300 μA.
The second grid voltage is set so that the cathode spot cut-off voltage becomes 120 V at the beginning of life. At each evaluation time of the life test, the cathode spot cut-off voltage at the initially set second grid voltage is measured, and the spot cut-off voltage is measured. The voltage variation with time was determined.

FIG. 2 shows the time-dependent fluctuation rate of the cut-off voltage after 5000 hours of life. After 5000 hours, the change with time of the cutoff voltage was saturated and did not change. In practical operation, there is no problem if the change over time of the cutoff voltage is about 4% or less. Therefore, as is apparent from FIG. 2, good characteristics are obtained when the rhenium content is 20% by weight or less or 80% by weight or more. Is obtained.

[0016]

As described above, according to the present invention,
It is possible to reduce the variation over time of the cut-off voltage, and therefore obtain a good characteristic in which a reduction in the cathode current during operation, that is, almost no reduction in screen brightness is observed, and realize the same without changing the conventional manufacturing process. It is possible to provide a cathode ray tube capable of performing the following.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an impregnated cathode structure used for a cathode ray tube of the present invention.

FIG. 2 is a graph showing a change over time of a cutoff voltage with respect to a rhenium content of a rhenium-tungsten alloy thin wire.

[Explanation of symbols]

 5 Impregnated cathode 6 Cathode support 7 Cathode holder

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-7-37486 (JP, A) JP-A-2-121235 (JP, A) JP-B-62-62015 (JP, B1) (58) Field (Int.Cl. ⁷ , DB name) H01J 1/20 H01J 1/28 H01J 29/04

Claims (1)

(57) [Claims] An impregnated cathode having a sleeve and a cathode holder.
Comprising an indirectly heated cathode for cathode support element is formed by rhenium-tungsten alloy supporting and fixing the dust, the cathode Shijiko
Extends radially from the upper end of the sleeve.
A cathode ray tube , wherein the rhenium content in tungsten of the cathode support is 20% by weight or less, or 80% by weight or more.