JPH0555011A - Manufacture of voltage-dependent nonlinear resistor - Google Patents

Abstract

PURPOSE:To obtain a voltage-dependent nonlinear resistor whose characteristics are stable and not irregular by means of a granulation operation using a spray drier without temporarily baking silicon dioxide even when the amount of silicon dioxide added is large. CONSTITUTION:In the manufacturing method of a voltage-dependent nonlinear resistor, a zinc oxide raw material powder which contains zinc oxide as its main component and at least silicon dioxide as its additive is granulated, molded and baked. In the manufacturing method, a silicon dioxide powder is covered with a resistor-constituent-element simple substance or its oxide.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a voltage non-linear resistor containing zinc oxide as a main component, which is used for lightning arresters and the like.

[0002]

2. Description of the Related Art Conventionally, zinc oxide has been a main component, and silicon dioxide, antimony oxide, nickel oxide, chromium oxide,
It is widely known that a resistor containing a small amount of additives such as bismuth oxide and manganese oxide exhibits excellent voltage non-linearity, and it is used for a lightning arrester or the like by utilizing the property. In particular, since silicon dioxide is effective for improving the electric characteristics, 0.1 to 10 mol% of silicon dioxide has been added.

[0003]

However, when silicon dioxide is added as in the above-mentioned conventional example, when the mixture is mixed with zinc oxide and other additives and then granulated by a spray dryer or the like, the viscosity of the mixture slurry is changed. The fluctuations are large,
There was a problem that the characteristics were not stable. When 4 mol% or more of silicon dioxide is added, the viscosity of the mixture slurry becomes too high and granulation by a spray dryer or the like becomes difficult. Therefore, the additive is calcined to reduce the surface activity of the additive. After that, the zinc oxide powder is mixed, and granulation by a spray drier is possible, but there is a problem that cost and time are required.

The object of the present invention is to solve the above problems,
It is possible to reduce the fluctuation of viscosity of the mixture slurry and obtain a voltage non-linear resistor with stable characteristics, and granulate with a spray dryer without calcining the additive even if the amount of silicon dioxide added is large. The present invention is intended to provide a method of manufacturing a voltage non-linear resistor that can be used.

[0005]

In the method for producing a voltage non-linear resistor according to the present invention, a zinc oxide raw material powder containing zinc oxide as a main component and at least silicon dioxide as an additive is granulated, molded and fired. The method for producing a voltage non-linear resistor is characterized in that a silicon dioxide powder is coated with a resistor constituent element alone or an oxide thereof.

[0006]

In the above-mentioned constitution, since the silicon dioxide powder among the additives is coated with the elemental element of the resistor such as zinc, antimony, bismuth or the oxide thereof,
The surface activity of the silicon dioxide powder can be reduced, the fluctuation of the viscosity of the mixture slurry can be reduced, and as a result, a voltage nonlinear resistor having stable characteristics can be obtained. Also,
Even if the amount of silicon dioxide added is large, the viscosity of the mixture slurry can be lowered, so that it is possible to granulate with a spray dryer without calcination of the additive, and it is possible to obtain a voltage nonlinear resistor at low cost. it can.

This is for the following reason. That is, since silicon dioxide has a smaller heat of adsorption of water on the surface (heat of formation of surface hydroxyl groups) than zinc oxide or the like, it is more likely to adsorb water. Therefore, when the amount of silicon dioxide is large, the amount of adsorbed water (bound water) is large, the free water (unbound water) in the slurry is relatively reduced, and the viscosity becomes high. This is because it can be prevented by suppressing the adsorption of water. As the material to be coated, any resistor elemental element or its oxide can be used. However, since the amount of various additives added to zinc oxide is very small, the composition of zinc oxide as a coating material is small. It is preferable because it is easy to control.

[0008]

EXAMPLE To obtain a voltage non-linear resistor containing zinc oxide as a main component, first, a zinc oxide raw material prepared to a predetermined particle size and bismuth oxide, cobalt oxide, magan oxide, antimony oxide prepared to a predetermined particle size, A predetermined amount of an additive consisting of chromium oxide, silicon dioxide (preferably amorphous), nickel oxide, boron oxide and silver oxide 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. At this time, a predetermined amount of binder (for example, polyvinyl alcohol aqueous solution) or the like is added to these raw material powders. Also preferably, an aluminum nitrate aqueous solution is added.

What is important in the present invention is that, among the above-mentioned additives, silicon dioxide powder, preferably amorphous silicon dioxide powder, is coated with a resistor constituent element simple substance or its oxide such as zinc oxide or bismuth oxide. .. Any method may be used for coating the resistive element-constituting element alone or the oxide thereof, as long as the coating can be completed. However, the target child particles (silicon dioxide powder in the present invention) (child particles 1 / Microparticles (such as zinc oxide particles with a particle size of about 10 or less) are placed in a mixer and sprinkled, and then mechanical thermal energy, which is mainly an impact force, is applied to the particles to perform immobilization or film formation processing in a short time. It is preferable to use the encapsulation method. In addition, a coating method, a mechanochemical reaction method, an interfacial precipitation method and the like can be preferably used. The average particle size of the silicon dioxide powder is preferably 6 μm or less.

Next, decompression and deaeration are preferably carried out at a vacuum degree of 200 mmHg or less, and the water content of the mixed slurry is preferably about 30 to 40 wt%. Then, the obtained mixed sludge is supplied to a spray dryer to have an average particle size of 50 to 150 μm, preferably 80 to 120 μm,
Moisture content 0.5-2.0 wt%, more preferably 0.7-1.5 wt
% Granulated powder. 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.

Then, the molded body is heated and lowered 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, a mixture paste for insulation coating having a predetermined amount of bismuth oxide, antimony oxide, zinc oxide, silicon oxide, etc., added with ethyl cellulose, butyl carbitol, n-butyl acetate as an organic binder, has a thickness of 30 to 300 μm. Apply to the side of the calcined body.

Next, this is heated at a heating rate of 20 to 100 ° C./hr and a maximum holding temperature of 1000 to 1300 ° C., preferably 1050 to 1250 ° C., 3 to
The main firing is performed under the condition of 7 hours. It is preferable that the temperature lowering rate during the main firing is 200 ° C./hr.

Then, a glass paste obtained by adding ethyl cellulose, butyl carbitol, n-butyl acetate or the like to the glass powder as an organic binder is applied to the high resistance layer on the side surface by 50 to 50%.
Apply it to a thickness of 300 μm and raise and lower the temperature in air at a rate of 50 to 200.
It is preferable to form the glass layer by heat treatment under the conditions of 400 ° C./hr and 400 to 800 ° C. holding time of 0.5 to 4 hours.

Thereafter, both end faces of the obtained voltage non-linear resistor are polished with a diamond grindstone or the like. Next, after cleaning the polished surface, electrodes are provided on the polished both end surfaces by, for example, aluminum or the like by, for example, thermal spraying to obtain a voltage nonlinear resistor.

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 According to the above-mentioned manufacturing method, as shown in Table 1 of the additives, the coating treatment was performed on the raw material powder of zinc oxide and the silicon dioxide powder within the scope of the present invention in which the silicon dioxide powder was coated with the single element of the resistor or its oxide. From the zinc oxide raw material powder outside the scope of the present invention and the same zinc oxide raw material powder outside the scope of the present invention that was calcined, a diameter of 50 mm,
Disc-shaped present invention samples No. 1 to 14 having a thickness of 20 mm and comparative sample
The voltage nonlinear resistors of Nos. 1 to 7 were prepared.

At that time, the viscosity of the mixed slurries obtained from the respective zinc oxide raw material powders was measured, and the limiting voltage (V _1mA ) per unit length and the limiting voltage at a current of 1 mA of the obtained voltage nonlinear resistor were measured. Variation range (RV
_1mA ) and switching surge discharge withstand capability were determined. The average particle size of the zinc oxide used was also measured. The results are shown in Table 1. In Table 1, the switching surge resistance was determined from the energy resistance (clear value) after converting the switching surge current having a current waveform of 2 ms for 20 times.

[0017]

[Table 1]

From the results shown in Table 1, among the additives, the present invention example in which silicon dioxide powder was coated with a resistor constituent element simple substance such as zinc oxide, metallic zinc, bismuth oxide, antimony oxide, nickel oxide or the like was obtained, It can be seen that the variation in the limiting voltage (V _1mA ) is small and the switching surge discharge withstand is high as compared with the comparative example in which the coating is not performed.

[0019]

As is clear from the above description, according to the present invention, the silicon dioxide powder among the additives is coated with the resistor constituent element simple substance or its oxide to reduce the limiting voltage (V _1mA ). It is possible to obtain a voltage non-linear resistor having a small variation and a good resistance to switching surge discharge. Further, according to the present invention, due to the action of the coating layer, the viscosity of the mixed slurry can be lowered even when a large amount of silicon dioxide is contained, and granulation by a spray dryer is possible without calcination. Therefore, the voltage nonlinear resistor can be mass-produced at low cost.

Claims (1)

[Claims] 1. A method for producing a voltage nonlinear resistor, which comprises granulating, shaping, and firing a zinc oxide raw material powder containing zinc oxide as a main component and at least silicon dioxide as an additive, wherein the silicon dioxide powder is used as a resistor. A method of manufacturing a voltage non-linear resistor, characterized by being coated with an elemental element or its oxide.