JPH0541308A - Manufacturing method of potential non-linear resistor - Google Patents

Abstract

PURPOSE:To provide the title manufacturing method of potential nonlinear resistor wherein the no-contact region mainly in the interface of a metallic oxide sintered body mainly comprising zinc oxide and layer electrodes is reduced while enhancing the discharge breakdown strength and reliability of said resistor as well as the bond properties of said layer electrodes making the formation of the layer electrodes easy in high productivity. CONSTITUTION:A mixed particles mainly comprising zinc oxide and containing at least bismuth compound and silicon compound as additive components is molded and then this molded body is baked to make a metallic sintered body 1 further forming layer electrodes 2 on the polished surface 1a of this metallic oxide sintered body 1. At this time, the polished surface is coated with a noble metal paste so as to make the noble metal paste seize up on this polished surface 1a in the atmosphere containing 1-15 volume % of oxygen and comprising the residual % of inert gas (He, Ar, N2, CO2 etc.).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a voltage non-linear resistor mainly used in a gapless lightning arrester or the like.

[0002]

2. Description of the Related Art A small amount of zinc oxide is contained as a main component.
Metal oxide sintered body containing _{SiO 2, Sb 2 O 3,} Bi 2 O 3, Co 2 O 3, additive such as MnO _2, since the show excellent voltage non-linearity, use the lightning arrester, etc. Has been done.

That is, when an electrode is attached to the polished surface of the above metal oxide sintered body and used as a lightning arrester, even if an excessively large current flows instantaneously due to a lightning strike or the like, the metal oxide sintered body has an excessive voltage. Correspondingly, the resistance becomes low and it is grounded through this metal oxide sintered body. This prevents accidents due to lightning strikes.

In order to produce such a voltage non-linear resistor, it is necessary to attach a layered electrode to the polished surface of the metal oxide sintered body so that a voltage can be applied. The most common method as such is to form electrodes made of aluminum metallikon or the like by a metal spraying method on a pair of opposed polishing surfaces of a disk-shaped metal oxide sintered body. Then, the disc-shaped metal oxide sintered bodies are stacked and the layered electrodes are brought into contact with each other. This reduces the contact resistance between the resistors when stacking the voltage non-linear resistors, and
The current flowing inside each resistor is distributed uniformly.

[0005]

However, in the above-mentioned resistor, since the metal sprayed electrode having large particles is used, a portion where the electrode is not in contact with minute irregularities on the surface of the sintered body is generated. was there. As a result, when the surge arrester operates due to a large current surge such as lightning impulse current,
Since partial discharge occurs and the current does not flow evenly in the sintered body, the original characteristics of the voltage non-linear resistor cannot be fully exerted, and there is a drawback that breakdown occurs at a low surge current.

A method for uniformly forming fine particle metal electrodes on the surface of a sintered body by a vapor deposition method is also disclosed in Japanese Patent Laid-Open No. 61-17110.
As disclosed in Japanese Patent Laid-Open No. 2-5, the electrode on the surface of the sintered body is broken by a surge current and does not exhibit a stable effect unless the electrode has a certain thickness of 5 to 10 μm or more. It is economically difficult to achieve a thickness of 10 μm or more. That is, in order to form a noble metal film by, for example, a vapor deposition method, not only a large-scale apparatus that is inconvenient to handle is required, but also the film deposition rate is slow, the processing area is small, and the processing rate is slow.

There is also a method in which a silver paste is applied to the polished surface of the sintered body and baked to form an electrode.
However, silver in the silver paste is mainly present in the form of Ag ₂ O, and the following reactions occur during baking of the silver paste. Ag ₂ O → 2Ag + 1 / 2O _{2, that} is, oxygen is generated during baking of the silver paste, and thus pores are generated in the electrode after baking. Particularly important are pores generated at the interface between the layered electrode and the sintered body, and the layered electrode and the sintered body do not come into contact with each other in this pore portion. For this reason, not only the adhesion between the layered electrode and the sintered body is lowered, but also the discharge withstand capability is lowered due to partial discharge. Especially, the varistor voltage (V _1mA ) is 300V
In a voltage non-linear resistor for a gapless lightning arrestor having a value of / mm or more, this problem is serious, and there is a need to solve it.

An object of the present invention is to reduce the non-contact area mainly at the interface between the metal oxide sintered body containing zinc oxide as a main component and the layered electrode to reduce the discharge withstand voltage of the voltage non-linear resistor.
It is an object of the present invention to provide a manufacturing method that improves reliability and adhesion of a layered electrode, facilitates formation of the layered electrode, and has high productivity.

[0009]

According to the present invention, a mixed powder containing zinc oxide as a main component and at least a bismuth compound and a silicon compound as an additive component is molded, and the molded product is fired to obtain a metal oxide sintered product. To form a layered electrode on the polished surface of the metal oxide sintered body, a precious metal paste is applied to the polished surface, containing 1 to 15% by volume of oxygen, and the balance from an inert gas. Characterized by baking the precious metal paste on the polishing surface in an atmosphere
The present invention relates to a method of manufacturing a voltage nonlinear resistor.

[0010]

The features of the manufacturing method of the present invention will be described with reference to the schematic view of FIG. First, the mixed powder is molded, and the molded body is fired to produce the metal oxide sintered body 1. A preferred embodiment of this step will be described later. Then, the layered electrode 2 is formed on the polished surface 1a of the metal oxide sintered body 1.

At this stage, in the present invention, the noble metal paste is applied to the polishing surface 1a, and the noble metal paste is baked onto the polishing surface 1a to form the layered electrode 2. Then, the baking of the noble metal paste is performed in an atmosphere containing 1 to 15% by volume of oxygen and the balance being inert gas. As a result, oxygen contained in the noble metal paste diffuses from the paste layer into the atmosphere as it is baked.

As a result, as schematically shown in FIG. 2, bubbles hardly remain in the layered electrode 2 after baking. On the other hand, according to the conventional technique, if a normal noble metal paste is applied to the polishing surface 1a and baked, all oxygen gas generated by the decomposition of the noble metal oxide causes bubble generation. That is, as shown schematically in FIG. 3, a large number of amorphous bubbles 12a are formed in the layered electrode 12.

Thus, according to the manufacturing method of the present invention,
Since it is possible to suppress the formation of bubbles or cavities inside the layered electrode 2, there are few non-contact portions at the interface between the layered electrode 2 and the metal oxide sintered body 1, and the two are in close contact with each other. Therefore, it is possible to prevent local discharge and potential concentration at the interface between the two, so that the discharge withstand capability of the resistor is improved and the reliability is also increased. And the layered electrode 2 and the metal oxide sintered body 1
The adhesion with is also improved. Such an effect is particularly remarkable in a voltage non-linear resistor for a gapless lightning arrester having a varistor voltage (V _1mA ) of 300 V / mm or more.

Moreover, since the layered electrode is formed by applying and baking the noble metal paste, the production facility is easy to handle, the production rate is high, and the cost can be kept low unlike the vapor deposition method and the like.

Silver paste is particularly preferable as the noble metal paste. The amount of oxygen contained in the atmosphere when baking the noble metal paste is 1 to 15% by volume. If it is less than 1% by volume, the metal oxide sintered body is affected, and the nonlinearity of the resistor and V _1mA are reduced. Also, 15
When it exceeds the volume%, the effect of the present invention is poor.

The baking of the noble metal paste is
Can be performed at 500-850 ° C, but usually 500-550
Often done at ° C. If this temperature exceeds 550 ° C, the high-resistance layer (glass layer) on the side surface of the resistor may melt. When this baking is performed, even if the oxygen content in the atmosphere is reduced at a low temperature of less than 400 ° C., the above effect of the present invention is poor and the discharge withstand capability is not so improved. Therefore, at least in the temperature range of 400 ℃ or higher,
The oxygen content in the atmosphere should be within the range of the present invention.

As the inert gas, nitrogen, argon, helium and carbon dioxide are preferable. If a reducing gas such as hydrogen or carbon monoxide is used instead of these inert gases, the discharge withstand capability and V _1mA are reduced.

As described above, the manufacturing method of the present invention is particularly useful for a voltage non-linear resistor having a varistor voltage (V _1mA ) of 300 V / mm or more. In this sense, the content of silica in the metal oxide sintered body is preferably 4.0 mol% or more, and if it is less than this, it is difficult to obtain a high varistor voltage. On the other hand, when the silica content exceeds 10.0 mol%, the electrical characteristics of the resistor deteriorate.

[0019]

EXAMPLE To obtain a voltage nonlinear resistor containing zinc oxide as a main component, first, a zinc oxide raw material adjusted to a predetermined particle size and bismuth oxide, cobalt oxide, manganese oxide, antimony oxide adjusted to a predetermined particle size, A predetermined amount of an additive made of chromium oxide, preferably amorphous silicon oxide, nickel oxide, boron oxide, silver oxide or the like is mixed. In this case, silver nitrate or boric acid may be used instead of silver oxide or boron oxide. Bismuth borosilicate glass containing silver is preferably used. Alternatively, the additive may be calcined at 800 to 1000 ° C. and then pulverized to adjust the particle size to a predetermined value, and the zinc oxide raw material may be mixed. At this time, a predetermined amount of polyvinyl alcohol aqueous solution or the like is added to these raw material powders. Also preferably an aluminum nitrate solution is added.

Next, vacuum deaeration is performed preferably at a vacuum degree of 200 mmHg or less, and the water content of the mixed slurry is adjusted to about 30 to 35 wt%.
The viscosity of the mixed sludge is preferably 100 ± 50 cp. Next, the obtained mixed sludge is supplied to a spray dryer to produce particles having an average particle size of 50 to 150 μm, preferably 80 to 120 μm, and a water content of 0.5 to 2.0 wt%, more preferably 0.9 to 1.5 wt%. Granulate granules. Next, the obtained granulated powder is molded into a predetermined shape under a molding pressure of 800 to 1000 Kg / cm ^{2 in} a molding step.

Next, the molded body is heated / cooled at a temperature of 10 to 100 ° C.
/ Hr at a temperature of 400 to 700 ° C to scatter and remove organic components to obtain a degreased body. Next, the degreased body is heated to 800 ~ at a heating rate of 50 ~ 70 ° C / hr.
Baking is performed at 1000 ° C. for a holding time of 1 to 5 hours to obtain a calcined body.
Next, a high resistance layer is formed on the side surface of the calcined body. In this example B
₃₀ to 300 μm of a mixture paste for insulation coating in which a predetermined amount of i ₂ O ₃ , Sb ₂ O ₃ , ZnO, SiO _{2 and the} like is added with ethyl cellulose, butyl carbitol, n-butyl acetate as an organic binder.
To the side of the calcined body.

Next, this is heated up / down at a temperature of 20 to 100 ° C./h.
r, maximum holding temperature 1000 ~ 1300 ℃, preferably 1050 ~ 1250
The main calcination is performed under the condition of 3 ° C. for 3 to 7 hours. Then, a glass paste prepared by adding ethyl cellulose, butyl carbitol, n-butyl acetate as an organic binder to glass powder is applied on the high resistance layer on the side surface to a thickness of 50 to 300 μm,
It is preferable to form the glass layer by heat treatment in the air at a temperature rising / falling rate of 50 to 200 ° C / hr, 400 to 800 ° C, and a holding time of 0.5 to 4 hours.

After that, both end faces of the obtained voltage non-linear resistor are polished with a diamond grindstone or the like. Then, after cleaning the polishing surface, according to the present invention, the precious metal paste is applied to the polishing surface, then, in an atmosphere containing 1 to 15% by volume of oxygen, the balance consisting of an inert gas, the noble metal paste Bake onto the polished surface.

The results of actually measuring various characteristics of voltage nonlinear resistors within and outside the range of the present invention will be described below. Example 1 A silver paste was used as a noble metal paste, and the effect was confirmed by variously changing the oxygen concentration when the silver paste was baked.

First, according to the method described above, a disc-shaped metal oxide sintered body having a diameter of 40 mm and a thickness of 20 mm was produced. This composition is: Bi ₂ O ₃ : 1.0 mol%, Sb ₂ O ₃ : 1.0 mol%, Cr ₂ O
₃ : 0.5 mol%, MnO ₂ : 0.5 mol%, Co ₃ O ₄ : 0.6 mol%, SiO ₂ : 1.0 mol%, NiO: 1.0 mol%, Al ³⁺ : 50
ppm, balance ZnO. When the above composition is 100 parts by weight, 0.02 parts by weight of Ag ₂ O and 0.02 parts by weight of B ₂
O ₃ and is further added.

Then, the silver paste was applied onto the polished surface of the metal oxide sintered body as described above and baked at 550 ° C. to form a layered electrode. During this baking step, the atmosphere around the sintered body coated with the silver paste was a mixture of oxygen gas and nitrogen gas. Then, the proportion of oxygen gas in this mixed atmosphere was variously changed as shown in the following table. With respect to each voltage nonlinear resistor thus obtained, the limiting voltage V _1mA / mm and its standard deviation σ _n-1 (n = 50), switching surge resistance, ΔV _1mA change rate, and electrode-element interface state were measured.

The switching surge resistance is 500 A
The number of surges before the destruction by adding the switching surge of was shown. Regarding the ΔV _1mA change rate, the change rate (%) of the varistor voltage (V _1mA ) after applying a current of 100 KA with a current waveform of 4/10 μs was obtained. Regarding the electrode-element interface state, the evaluation sample was cut with a diamond cutter or the like, and its cross section was polished, followed by scanning electron microscopy (SE
As a result of observing the bubble distribution state of the electrode-element interface in M),
No bubbles were identified as no bubbles, those without bubbles of 50 μm or more were designated as small bubbles, and those with bubbles exceeding 50 μm were designated as large bubbles. The results of these measurements are shown in Table 1.

[0028]

[Table 1]

As can be seen from Table 1, the oxygen concentration is 1.0 to 1
With 5.0% by volume, switching surge resistance, ΔV
_{The 1 mA} change rate and the electrode-element interface state are both improved. If the oxygen concentration is 2.0 to 10.0% by volume, the effect will be even greater.

Example 2 A metal oxide sintered body was prepared in the same manner as in Example 1, a silver paste was applied to the polished surface of the sintered body, and baked at 550 ° C. At this time, the atmosphere was a mixed gas of gas X and oxygen gas shown in the table below. The oxygen concentration in the atmosphere was 5%, which had the best characteristics in Example 1.
And Various characteristics of each of the voltage non-linear resistors thus obtained were measured in the same manner as in Example 1, and the results are shown in Table 2.

[0031]

[Table 2]

As can be seen from the above results, good characteristics can be obtained by mixing oxygen gas with an inert gas (N ₂ , Ar, CO ₂ , He). On the other hand, when oxygen gas is mixed with a reducing gas such as N ₂ and CO, the electrode-element interface state is improved, but the element body is adversely affected, and the voltage nonlinear resistor ΔV _1mA , Switching surge resistance and ΔV _1mA change rate deteriorated.

[0033]

As described above, according to the present invention, bubbles can be reduced particularly at the interface between the layered electrode and the metal oxide sintered body, and both can be brought into close contact with each other. As a result, the discharge resistance of the voltage nonlinear resistor, the reliability, and the adhesion of the layered electrode could be improved.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing a state where a layered electrode 2 is provided on a polished surface 1a of a metal oxide sintered body 1.

FIG. 2 is a schematic cross-sectional view for explaining the fine structure of the layered electrode 2.

FIG. 3 is a schematic cross-sectional view for explaining a fine structure of a layered electrode 12 according to a conventional manufacturing method.

[Explanation of symbols]

 1 Metal oxide sintered body 1a Polished surface 2,12 Layered electrode 2a, 12a Bubble

Claims (1)

[Claims] 1. A metal oxide sintered body is produced by molding a mixed powder containing zinc oxide as a main component and at least a bismuth compound and a silicon compound as additive components, and firing the molded body. When forming the layered electrode on the polished surface of the sintered body, the precious metal paste is applied to the polished surface, containing 1 to 15% by volume of oxygen, the remainder of the precious metal paste in an atmosphere of an inert gas. A method of manufacturing a voltage non-linear resistor, comprising baking onto the polished surface.