JPH0555012A - Manufacture of voltage-dependent nonlinear resistor - Google Patents

Abstract

PURPOSE:To provide a method of manufacturing a voltage-dependent non-linear resistor wherein the discharge-resistant amount and the reliability of the voltage- dependent nonlinear resistor are enhanced, the close contact property of a layerlike electrode is enhanced, the layerlike electrode is formed easily and its productivity is high by a method wherein a noncontact region mainly at the interface between a metal oxide sintered body whose main component is zinc oxide and the layerlike electrode is reduced. CONSTITUTION:A mixed powder whose main component is zinc oxide and which contains at least a bismuth compound and a silicon compound as additive components is molded. Its molded body is baked; a metal oxide sintered body 1 is manufactured. Layerlike electrodes 2 are formed on polished faces 1a of the metal oxide sintered body 1. At this time, the polished faces 1a are coated with an organometallic compound paste; the paste is heat-treated; the organometallic compound is pyrolyzed. Thereby, the layerlike electrodes 2 are formed.

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-mentioned metal oxide sintered body and used as a lightning arrester, even if an excessively large current flows momentarily due to a lightning strike, the metal oxide sintered body has an excessive voltage. Correspondingly, it becomes a low resistance body and 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 Publication No. 2), 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 0.1 to 1.0 μm or more. It is economically difficult to achieve a thickness of ~ 1.0 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 300 V
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, by applying an organometallic compound paste on the polished surface, and heat-treating the paste to thermally decompose the organometallic compound. The present invention relates to a method of manufacturing a voltage non-linear resistor, characterized in that the layered electrode is formed.

Further, according to the present invention, a mixed powder containing zinc oxide as a main component and containing at least a bismuth compound and a silicon compound as an additive component is molded, and the molded body is fired to produce a metal oxide sintered body. When forming a layered electrode on the polished surface of the metal oxide sintered body, an organometallic compound paste and a noble metal paste are sequentially applied to the polished surface, and these pastes are heat-treated to thermally decompose the organometallic compound. The present invention relates to a method of manufacturing a voltage non-linear resistor, characterized in that the layered electrode is formed by baking a noble metal paste.

[0011]

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 polishing surface 1a
The organometallic compound paste is applied to the above, and the paste is heat-treated to thermally decompose the organometallic compound to form the layered electrode 2. According to such a method, as shown schematically in FIG. 2, bubbles and cavities are not generated in the layered electrode 2, and a dense layered electrode 2 can be obtained.

On the other hand, according to the prior art, if a normal precious metal paste is applied to the polished surface 1a and baked,
Oxygen gas generated by the decomposition of the noble metal oxide causes the formation of bubbles. That is, as schematically shown in FIG.
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 organometallic compound paste, the production facility is easy to handle, the production rate is high, and the cost is low unlike the vapor deposition method. it can.

Further, on the polishing surface 1a of the metal oxide sintered body 1,
It is also possible to apply the organometallic compound paste according to the present invention and then further apply the noble metal paste to form two applied layers. In this case, the organic metal compound is thermally decomposed by heat treatment to form the layered electrode 2 as shown in FIG. 4, and the noble metal paste is fired to form the layered electrode 12.

In this case, considerable bubbles or cavities still remain inside the layered electrode 12. However, since the layered electrode 2 is dense, the layered electrode 2 and the sintered body 1 are in close contact with each other. Therefore, the effects of the present invention described above can also be achieved.

As the metal element constituting the organometallic compound, gold, platinum, palladium, silver, copper, aluminum and the like are preferable, and gold, platinum, palladium and silver are particularly preferable. This is because when these noble metal elements are used, an oxide film is not formed on the surface of the layered electrode after thermal decomposition of the organometallic compound. When a base metal element is used, it is preferable to thermally decompose the organometallic compound in a non-oxidizing atmosphere. The polar group of the organometallic compound is preferably an alkyl mercaptide or a cyclic terpene mercaptide.

The layered electrode 2 preferably has a thickness of 0.1 to 1.0 μm. Here, in the case where the thickness of the layered electrode 2 is not sufficient by applying the organometallic compound paste only once, the organometallic compound paste can be applied twice or more times. A silver paste is particularly preferable as the noble metal paste applied on the organometallic compound paste.

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.

[0021]

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 degassing is preferably performed 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 a powder 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 / cooled at a rate of 20-100 ° 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, according to the present invention, a gold amyl mercaptide paste as an organometallic compound paste is screen-coated on the polished surface so that the coating thickness is 10 to 50 μm, and the paste is heat-treated to thermally decompose the organometallic compound. To form a layered electrode. Alternatively, the organometallic compound paste and the noble metal paste are sequentially applied to the polished surface, and the paste is heat-treated to thermally decompose the organometallic compound and the noble metal paste is baked to form a layered electrode.

The results of actually measuring various characteristics of voltage nonlinear resistors within and outside the range of the present invention will be described below. First, according to the method described above, a diameter of 40 mm,
A disk-shaped metal oxide sintered body having 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 : 7.0 mol%, NiO: 1.0 mol%, Al ³⁺ :
50ppm, balance ZnO. Then, the above composition is 100
When expressed as parts by weight, 0.02 parts by weight of Ag ₂ O and 0.02 parts by weight of
B ₂ O ₃ is further added.

As described above, the paste of the organometallic compound having each metal species shown in the following table was applied to the polished surface of the metal oxide sintered body and baked at 550 ° C. to form a layered electrode. 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. Further, as a control example, a silver paste was applied to the polished surface and baked at 550 ° C. to form a layered electrode. The voltage nonlinear resistor thus obtained was subjected to the same measurement as above.

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, etc., and its cross section was polished, followed by scanning electron microscopy (SEM).
The distribution of bubbles at the electrode-element interface was observed with. As a result, no bubbles were recognized as no bubbles, those without bubbles of 50 μm or more were considered as small bubbles, and those with bubbles exceeding 50 μm were considered as large bubbles. The results of these measurements are shown in Table 1.

[0029]

[Table 1]

From the above results, it can be seen that the present invention remarkably improves the switching surge resistance, the ΔV _{1 mA} change rate, and the electrode-element interface state. Furthermore, by using a noble metal as the metal species and gold or platinum, the characteristics of the voltage nonlinear resistor are further improved.

[0031]

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.

FIG. 4 shows the layered electrode 2, on the polished surface 1a of the metal oxide sintered body 1.
FIG. 12 is a schematic cross-sectional view showing a state in which 12 is provided.

[Explanation of symbols]

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

Claims (2)

[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 organometallic compound paste is applied to the polished surface, and the paste is heat-treated to thermally decompose the organometallic compound to form the layered electrode. A method of manufacturing a voltage non-linear resistor, comprising: 2. 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 an additive component, and firing the molded body. When forming a layered electrode on the polished surface of the sintered body, an organometallic compound paste and a noble metal paste are sequentially applied to the polished surface, and these pastes are heat-treated to thermally decompose the organometallic compound and form a noble metal paste. A method for producing a voltage non-linear resistor, comprising forming the layered electrode by baking.