JPS5986111A - Method of producing powder coated wire - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of coating a metal wire with a metal oxide or metal powder, such as alumina (A7203),
In particular, the present invention relates to a method for manufacturing a powder-coated wire in which powder is coated by an electrodeposition method using electrophoresis.

Powder-coated wires, which are metal wires coated with powder, have been used in various fields. For example, heaters for electron tubes are made of high melting point metal wire such as tungsten, which is formed into a desired shape, and then is made of insulating material to prevent short circuits between the heater coils or between the heater and the cathode sleeve into which the heater is inserted. The high melting point metal wire is coated with alumina or the like. Recently, in order to form a special-shaped direct heating type impregnating layer, a high melting point metal wire is formed into the desired shape, and then a high melting point metal powder is coated around the wire to form a porous body, which is then impregnated with an electron radioactive substance. It is also used as a directly heated cathode.

There are various methods for coating these powders, one of which is the electrodeposition method.

That is, the method for manufacturing a heater using this type of electrodeposition method is as follows.

For example, an electrodeposition solution in which alumina powder is suspended in a solution of a small amount of electrolyte such as aluminum nitrate or magnesium nitrate dissolved in an organic solvent such as methanol mixed with water is used. A voltage is applied so that the high melting point metal wire serves as a cathode, and alumina powder of the required thickness is deposited by electrophoresis.Then, the alumina powder is sintered by heat treatment in a hydrogen furnace, etc. There is.

The conventional composition of this type of electrodeposition solution is 1, for example,
No. 2444 (Table 1) 2% Kosho 55-24650 (Table 2
) or as shown in Japanese Patent Publication No. 56-1740 (Table 3), methanol (C
Hydrolic alcohols such as HaOH) or ethanol (C2H50H) have been used.

Table-1 Table-2 Table-3 The reason why methanol, air, and H-I-tal are used instead of organic solvents is to appropriately increase the electrical resistance of the electrolyte solution. The purpose is to effectively smooth out electrophoresis so that the alumina powder does not suddenly adhere and the surface becomes uneven, and the solvent evaporates easily after electrodeposition and the heater wire is removed from the electrodeposition solution. It is thought that this was intended for effect.

However, on the other hand, the fact that the organic solvent evaporates easily means that the organic solvent evaporates during the electrodeposition operation, causing a change in the composition of the electrodeposition solution. In particular, methanol and ethanol have low viscosity, and if the powder is large or dense, it tends to settle.

The mixing ratio at which the electrodeposition solution must be constantly stirred in the starter increases, and the specific gravity of the solution increases. The relationship between the deposition thickness under the same conditions and the specific gravity of the electrodeposition solution is approximately proportional as shown in Figure 1, so if electrodeposition is continued under the same conditions using an electrodeposition solution with increasing specific gravity, the thickness will be 1. The disadvantage is that the amount of alumina powder deposited on the feed increases and the electrodeposited surface becomes hollow. For example v Al 20330011+ H2
0210CC, C2H50H230CC, Y (NO3)
When electrodeposition is continued continuously with an electrodeposition solution having a composition of 371 (1
The electrodeposition time per piece is about 9 seconds), and after 5 hours, the specific gravity of the electrodeposition solution changes from 135 to 1.65, and when electrodeposited under the same conditions (applied voltage for 9 hours), the electrodeposition thickness changes from 35 μm. 55
Changes up to μ. This change makes electronic parts that require extremely precise dimensions, such as heaters for electron tubes, unsuitable for practical use.
It is very difficult to control the deposition thickness.

Furthermore, as mentioned above, since the viscosity of -hydric alcohol is relatively low, the powder tends to settle, and between electrodepositions, the powder is stirred with a starter to ensure uniformity (stirring during electrodeposition causes (I stopped the electrodeposition process because thin curling occurs in the deposited liquid and does not have any negative effects.) However, as soon as stirring in the starter is stopped, sedimentation begins and the composition differs between the upper and lower parts of the electrodeposition liquid, resulting in uniform electrodeposition. However, metal powders such as tungsten powder and molybdenum powder have a large specific gravity and are more likely to settle, making them difficult to electrodeposit. Furthermore, these alcohols are highly flammable and can cause fires due to sparks generated at electrical contacts, so they have the disadvantage of requiring constant attention during the work.

The present invention was developed in view of these drawbacks, and it is possible to produce a powder-coated wire with a constant powder coating thickness and a constant coated surface even when a large number of pieces are continuously electrodeposited and the electrodeposition time is long. The purpose is to provide a manufacturing method for. Specifically, conventional m
By using a polyhydric alcohol such as glycerin instead of alcohol, the evaporation of organic solvents during electrodeposition is prevented, and the solvent that adheres when powdered on the metal wire is removed during the next sintering process. The object of the present invention is to provide a manufacturing method for obtaining a powder-coated metal wire of stable quality by complete evaporation. This will be explained in detail below using a specific example.

As an embodiment of the present invention, a method for manufacturing a heater in which a high melting point metal wire, which has been widely used in the past, is coated with alumina powder will be described. First, the composition of an electrodeposition solution for electrodepositing alumina powder is prepared as shown in Table 4.

Table 4 In other words, this composition uses 300% glycerin, a trihydric alcohol, instead of 300% C2H50H230CC.
Use CC, H2O210CC is the same as glycerin <
Increased to 300CC and other Al2O3゜Y(NO
3) 3 is the same amount as before. The specific gravity of the electrodeposition liquid in this case is about 1.45, which is slightly higher than the specific gravity of 1.35 when prepared using conventional C2H50H. A high melting point metal wire used as a heater is immersed in this electrodeposition solution and a voltage of 10V is applied for 7 seconds to form a metal wire cathode.
2O3 powder is deposited around the metal wire. After applying a voltage for 7 seconds, electrodeposition can be continued by replacing the metal wire one after another, but the metal wire coated with Al2O3 powder is taken out from the electrodeposition solution and sintered at 1700°C in a hydrogen furnace. In this case, nzo- and glycerin, which are the solvents of the electrodeposition solution, are difficult to volatilize, so even after the metal wire is removed from the electrodeposition solution, H2O and glycerin remain attached to it, but the boiling point of H2O is 100℃, and the boiling point of glycerin is 1700℃ during sintering due to 290℃
It will completely evaporate and will have no effect after sintering.

The electrodeposition solution used in this example uses nonvolatile glycerin, so even if electrodeposition is continued for a long time, the solvent will not evaporate and the composition ratio can always be kept constant. . In other words, the alumina powder adheres to the metal wire and is reduced.
Since the solvent is also removed from the electrodeposition solution while remaining attached to the metal wire, it is reduced at approximately the same rate. (Conventionally, the reduction rate of the solvent was greater than the reduction rate of alumina because there was a reduction in the solvent by adhesion and a reduction by evaporation.)9 Therefore, the specific gravity of the electrodeposition solution of the present invention is 1.45 is maintained as it is, and as a result, the coating thickness of the alumina powder is also constant. FIG. 1 shows the results of measuring changes in the alumina deposition thickness when the electrodeposition solution of this example was used and the heaters were replaced one after another for 5 hours continuously. In the figure, the horizontal axis shows the elapsed time since the start of electrodeposition of the first heater, and the vertical axis shows the same conditions (applied voltage).

The thickness of the alumina powder deposited under a constant application time is taken, and A in the figure shows the one of this embodiment, and B shows the total injection when a conventional electrodeposition solution is used. As can be seen from the figure, it is possible to maintain a constant coating thickness (L: (U) over a very long period of time.

In the above example, only the minimum necessary components of the electrodeposition solution were listed in Example 3, but in order to prevent pinholes and cracks, urea and vinegar were used. l! The gist of the present invention does not fall within the scope of the present invention, even if all components are added, and even if other components are added for other purposes, metal oxide powders or metal powders other than alumina are not included. Furthermore, the same effect can be obtained by using other than glycerin, for example, ethylene glycol dihydric alcohol.

According to the present invention, for example, the viscosity of glycerin is 14 at 20°C.
95 cP Previously, for example, the viscosity of ethanol was 1 at 20°C.
．． Since the viscosity is much higher than 2 cP, the powder is difficult to settle. This improves the non-uniformity of the composition of the electrodeposited liquid depending on the location, as in the past, and enables electrodeposition without settling even when the powder is large or metal powder with a high density, such as Toughgesten powder or molybdenum powder, is used. .

Furthermore, according to the present invention, since polyhydric alcohol is used as the organic solvent, it is non-flammable and there is no risk of fire caused by sparks from electrical contacts, and the applied voltage can be selected within the range of Chem. It has the advantage that it is possible to do this, and there is no need to use unnecessary nerves during the 9-day work.

As explained above, 1.According to the present invention, when the powder is completely coated on the metal wire, since the electrodeposition solution containing polyhydric alcohol as the main component of the organic bath agent is used, the electrodeposition solution once prepared is The composition remains constant over a long period of time, and the powder coating thickness and coating surface are also constant. - Quality is stable, and there is no need to change small V-+- lines during one operation or to be careful of fire outbreaks. There is no need to do this, and it has the effect of contributing to cost reduction. Further, according to the present invention, it is easily possible to obtain a directly heated impregnated cathode by sintering a high melting point metal powder around a high melting point metal wire, which has a large ripple effect.

[Brief explanation of drawings]

Figure 1r shows the relationship between the deposition thickness and the specific gravity when electrodeposited under the same conditions using a conventional electrodeposition solution with varying specific gravity. Figure 2 shows the relationship between the deposition thickness and the elapsed time when the electrodeposition was performed under the same conditions. The changes shown are A according to the present invention and B according to the conventional method.

Claims (1)

[Claims] A method for producing a powder-coated wire in which a metal wire is coated with powder, the powder being suspended in a mixture of an organic solvent containing polyhydric alcohol as a main component and water, and using an electrodeposition solution containing at least an electrolyte. A method for manufacturing a powder-coated wire, comprising electrodepositing the powder on the metal wire and then sintering the powder.