JP2736164B2 - Manufacturing method of impregnated cathode - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to a method for producing an impregnated cathode.

(Prior Art) In general, as a cathode for an electron tube such as a cathode ray tube, a hole portion of a porous tungsten thin plate is conventionally impregnated with an electron-emitting substance, and one surface (back surface) of the porous tungsten thin plate is ruthenium. Forming a molybdenum molten layer,
There is an impregnated cathode designed to prevent evaporation of the electron-emitting substance.

Various methods have already been known as a method for producing this type of impregnated cathode. One such method is disclosed in Japanese Patent Application Laid-Open No. 58-446.
No. 43 discloses the following method.

First, a tungsten powder is compression-molded and then sintered in a reducing atmosphere to form a large-diameter porous tungsten rod. Next, copper is impregnated into the holes of the porous tungsten rod. Then, this copper-impregnated porous tungsten rod is sliced into a thin plate having a thickness of about 0.5 mm and a diameter of about 30 mm by lathing or wire electric discharge machining.
Next, the copper in the thin plate is dissolved with nitric acid or heat-treated in a reducing atmosphere to remove the copper from the thin plate.

Thereafter, a suspension composed of a mixed powder of ruthenium and molybdenum and an organic binder was dropped on one surface of the porous tungsten thin plate and dried, and further dried in a reducing atmosphere for about 20 hours.
Heating to 00 ° C. melts ruthenium and molybdenum on one surface of the porous tungsten thin plate to form a ruthenium-molybdenum mixed molten layer for preventing evaporation of the electron-emitting substance. Thereafter, in a reducing atmosphere, the holes of the porous tungsten thin plate are impregnated with an electron-emitting substance composed of BaO, CaO, and Al ₂ O ₃ . Then, the porous tungsten thin plate impregnated with the electron-emitting substance is cut into a predetermined shape by electric discharge machining or laser machining to form a cathode.

(Problems to be Solved by the Invention) However, according to the conventional manufacturing method as described above, it is difficult to form a ruthenium / molybdenum mixed molten layer to a uniform thickness on one surface of a porous tungsten thin plate.
Therefore, when the cathode cut into a predetermined shape and size is subsequently joined to the support, the entire surface of the mixed molten layer of ruthenium / molybdenum may not come into close contact with the joining surface of the support and may be peeled off. As a result, there is a problem that heat conduction from the support to the cathode becomes unstable and stable electron emission cannot be obtained.

An object of the present invention is to solve the above problems and to provide a method for producing an impregnated cathode capable of obtaining an impregnated cathode of stable quality in mass production.

[Constitution of the Invention] (Means for Solving the Problems) According to the present invention, a printing paste containing ruthenium and molybdenum as main components is applied to one surface of a porous tungsten thin plate by screen printing, and then dried. Forming a ruthenium-molybdenum coating layer on one surface of the porous tungsten thin plate; and, after this step, melting the ruthenium-molybdenum coating layer to form a ruthenium-molybdenum molten layer; and Next, impregnating the hole portion of the porous tungsten thin plate on which the ruthenium-molybdenum molten layer is formed with an electron-emitting substance,
Forming a cathode having a predetermined shape by cutting out the porous tungsten thin plate impregnated with the electron-emitting substance after this step.

(Function) According to the present invention, a printing paste containing ruthenium and molybdenum as main components is applied by screen printing to one surface of a porous tungsten thin plate, whereby a layer in which ruthenium / molybdenum is uniformly mixed is formed. Can be formed.

As a result, a stable quality impregnated cathode can be easily manufactured.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 (a) shows a method for manufacturing an impregnated cathode according to the present invention.
First, as shown in FIG. 1A, a ruthenium (Ru) powder having an average particle size of 4 to 5 μm and a molybdenum (Mo) powder having an average particle size of 3 to 5 μm are formed as shown in FIG. Mix so that the weight ratio becomes 2: 3.

Next, ethyl cellulose as an organic binder, α-terpineol as a solvent, and a vehicle as an auxiliary agent are added to the mixed powder, and the mixture is sufficiently kneaded using a three-roll mill to print a liquid having a viscosity of about 400 Pa · s (Pascal second). A paste 1 is prepared.

The properties required for the organic binder are that it is easily thermally decomposed, and that it is soluble in a solvent and has a viscosity suitable for printing (fluidity).
Are easily obtained, and ethyl cellulose satisfies these characteristics. The characteristics required as a solvent are that it is easily soluble in a binder and has low volatility at room temperature. Further, the vehicle is for improving the dispersibility of the mixed powder.

Next, as shown in FIG. 3B, the paste 1 is uniformly applied to one surface of the porous tungsten thin plate 3 by screen printing, and then dried to form a uniform coating layer 2a of about 40 μm.
To form

The screen printing conditions at this time are the screen gap
1.0mm, squeegee Hs hardness 60 °, angle 45 °, printing speed 40mm /
s, printing pressure 3 kg / cm ² . The screen used was 100 mesh stainless steel and the emulsion thickness was 20 μm.

Next, this is heated in a reducing atmosphere at about 2000 ° C. for 5 seconds, so that a uniform ruthenium film having a thickness of about 20 μm is formed on one surface of the porous tungsten thin plate 3 as shown in FIG. Forming a molybdenum molten layer 2;

Next, as shown in FIG.
On the other surface of the porous tungsten thin plate 3 on which the molybdenum molten layer 2 is formed, an electron-emitting substance 4 made of BaO, CaO, and Al ₂ O ₃ is loaded, and this is placed in a reducing atmosphere. Of the remaining electron-emitting substance 4 by alcohol washing or the like.
Is removed.

Next, as shown in FIG. 5E, a disk having a diameter of, for example, 1.45 mm is cut out from the porous tungsten thin plate 3 impregnated with the electron-emitting substance 4 by electric discharge machining or laser machining. As shown in f), the pores of the porous tungsten thin plate 3 are impregnated with the electron-emitting substance 4, the surface of which is used as an electron-emitting surface, and the opposite surface, that is, the back surface, is made of uniform ruthenium. The impregnated cathode 5 on which the molybdenum molten layer 2 is formed is obtained.

By the way, when the impregnated cathode 5 is manufactured by the manufacturing method of the present invention, a uniform ruthenium-molybdenum molten layer 2 can be formed, so that the bondability of the impregnated cathode to a support (described later) is improved. In addition, heat conduction from the support to the cathode is stabilized, and stable electron emission can be obtained.

As described above, according to the manufacturing method of the present invention, an impregnated cathode having excellent mass productivity and stable quality can be obtained.

Next, a method of assembling a cathode assembly using the impregnated cathode of the present invention will be described.

That is, as shown in FIG. 2, the impregnated cathode 5 manufactured by the above method is inserted inside the cup-shaped support 6 made of tantalum so that the uniform ruthenium-molybdenum molten layer 2 is inside, By resistance welding or laser welding
The impregnated cathode 5 is joined to the bottom of the support 6.

Next, the cup-shaped support body 6 to which the impregnated cathode 5 is joined is fitted to the top of one end of a cathode sleeve 7 made of tantalum, and the side surfaces thereof are joined by welding.

Further, one end of a ribbon 8 made of three tantalums is joined to the side surface of the other end of the cathode sleeve 7 by welding, and the other end of the ribbon 8 is connected to a cathode support tube 9 made of an Fe-Ni-Co alloy.
The required impregnated cathode is completed by welding to the overhanging portion 10 that protrudes inside the one end portion.

According to the present invention, ruthenium powder and molybdenum powder are formed on one surface of a porous tungsten thin plate with an organic binder such as ethyl cellulose, a solvent such as α-terpineol, and an auxiliary agent such as a surfactant. Since the printing paste is uniformly applied by screen printing and then melted, a uniform ruthenium / molybdenum molten layer can be formed.

As a result, the bondability of the impregnated cathode to the support is improved, and peeling from the support does not occur.

Further, heat conduction from the support to the cathode becomes stable, and stable electron emission can be obtained.

[Brief description of the drawings]

1 (a) to 1 (f) are process explanatory views showing a method for manufacturing an impregnated cathode according to one embodiment of the present invention, and FIG. 2 is a partial cutaway of a cathode assembly using the impregnated cathode according to the present invention. FIG. 2 ... ruthenium / molybdenum molten layer, 3 ... porous tungsten thin plate, 4 ... electron emitting material, 5 ... impregnated cathode, 6 ... support.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-100233 (JP, A) JP-A-1-187801 (JP, A) JP-A-63-34830 (JP, A) 55942 (JP, B2) JP 60-47314 (JP, B2) JP 1-46976 (JP, B2)

Claims (4)

(57) [Claims] 1. A printing paste containing ruthenium and molybdenum as a main component is applied to one surface of a porous tungsten thin plate by screen printing, and then dried and ruthenium / molybdenum is applied to one surface of the porous tungsten thin plate. A step of forming a coating layer; a step of fusing the ruthenium / molybdenum coating layer to form a ruthenium / molybdenum molten layer after the step; and a step of forming the ruthenium / molybdenum molten layer after this step. A step of impregnating the holes of the porous tungsten thin plate with an electron-emitting substance, and, after this step, forming a cathode of a predetermined shape by cutting out the porous tungsten thin sheet impregnated with the electron-emitting substance, A method for producing an impregnated cathode, comprising: 2. The method for producing an impregnated cathode according to claim 1, wherein the printing paste contains at least a mixed powder of ruthenium and molybdenum, an organic binder and a solvent. 3. The method for producing an impregnated cathode according to claim 2, wherein the organic binder is ethyl cellulose. 4. The method for producing an impregnated cathode according to claim 2, wherein the solvent is α-terpineol.