JPH0831362B2 - Method of manufacturing voltage non-linear resistor - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a voltage nonlinear resistor containing zinc oxide as a main component.

(Prior Art) Voltage nonlinear resistors containing zinc oxide as a main component are widely used for lightning arresters and surge absorbers for the purpose of voltage stabilization or surge absorption because of their excellent nonlinear voltage-current characteristics. This voltage non-linear resistor is obtained by adding a small amount of an oxide such as bismuth, antimony, cobalt, or manganese that exhibits voltage non-linearity to zinc oxide as a main component, mixing, granulating, molding, and then firing. Can be manufactured by applying an inorganic substance to form a side surface high resistance layer, firing again, and attaching an electrode to the sintered body.

When manufacturing such a voltage non-linear resistor, conventionally, spread powder or the like was laid inside a hermetically sealed casing to actively protect the atmosphere inside the casing. Then, at the time of firing, it is necessary to add a predetermined amount of an additive component that becomes a liquid phase, particularly bismuth oxide, so that the zinc oxide particles that are the main component are uniformly wetted by the liquid phase.

(Problems to be Solved by the Invention) However, bismuth oxide does not form a solid solution in zinc oxide even after firing, and forms a grain boundary between zinc oxide particles. For this reason, when the amount of bismuth oxide added was large, the grain boundaries became thicker, which resulted in a decrease in the surge withstand voltage of the voltage non-linear resistor, an electric charge life and a dielectric constant characteristic, and an increase in flatness.

On the other hand, if the amount of bismuth oxide added is reduced, the surface of the zinc oxide particles will not be sufficiently wet during firing, and the sintering of the zinc oxide particles will be uneven.

The object of the present invention is to overcome the above-mentioned problems, discharge withstand capability,
It is an object of the present invention to provide a method for manufacturing a voltage nonlinear resistor that can improve the voltage-carrying life and the dielectric constant and can reduce the flatness.

(Means for Solving the Problems) The present invention provides a mixture containing zinc oxide as a main component and at least bismuth oxide as an additional component,
In the method for producing a voltage non-linear resistor by granulating, molding and firing, 10% or more of the added weight of bismuth oxide added to the mixture is removed by scattering during the firing, and the voltage non-voltage of the bismuth oxide after firing is removed. The content rate in the linear resistor is 6
The present invention relates to a method for manufacturing a voltage non-direct resistance resistor, which is characterized in that the content is not more than wt%.

(Operation) According to the method for manufacturing a voltage non-linear resistor according to the present invention,
Since the content of bismuth oxide after firing in the voltage non-linear resistor is set to 6% by weight or less (preferably 0.5 to 4% by weight), the bismuth oxide is excessively present in the grain boundary layer, so that The adverse effect on the characteristics can be suppressed, and the flatness rate, dielectric constant, and discharge withstand amount can be improved. If the content of bismuth oxide exceeds 6% by weight, the flatness increases and the dielectric constant and discharge withstand capability decrease.

In the present invention, it should be noted that 10% or more (preferably 15 to 25% by weight) of the added amount of bismuth oxide added to the mixture is scattered and removed during firing. Therefore, initially, bismuth oxide can be added in excess of the optimum addition amount by the amount removed by scattering during firing. That is, in the stage of the first mixture, excess bismuth oxide is added to improve the wettability of the zinc oxide particle surface during firing, and 10% of the added amount of bismuth oxide during firing is used.
By scattering and removing the above, the content ratio of zinc oxide in the sintered body can be finally reduced to 6% by weight or less.

At this time, 10% or more of the added amount of bismuth oxide was scattered and removed at the time of firing because when it was less than 10%, the discharge withstand amount and the dielectric constant were not so much improved.

Thus, in order to scatter and remove the bismuth oxide during firing, it is preferable to employ the following method, for example.

That is, conventionally, as described above, it was considered essential to hermetically seal the casing for firing to protect the atmosphere.

However, in order to realize the constitution of the present invention, contrary to this common sense, for example, a window is provided in the casing for firing to make it breathable, and the atmosphere is depressurized during the main firing to scatter bismuth oxide. At this time, more preferably 1000 to 1300 ℃
(Preferably 1100 ~ 1250 ℃) in a closed state first calcination, then once more than 900 ℃ (preferably 900
After reducing the temperature to 1050 ° C), the pressure is reduced and the temperature is maintained for a predetermined time to remove bismuth oxide by scattering.

When scattering bismuth oxide, the internal pressure of the housing is 100-700
Torr is preferable, and 250 to 550 Torr is more preferable. If this is 100 Torr or less, the varistor characteristics deteriorate, and
When it exceeds 00 Torr, the scattering amount of bismuth oxide decreases. At this time, the temperature is kept at 900 ° C or higher for a certain period of time, for example, 1000 ° C.
When the temperature is held at 0 ° C, the temperature holding time is preferably 4 to 10 hours.

When bismuth oxide is bismuth trioxide, a particularly remarkable effect is obtained, which is preferable.

When the voltage non-linear low antibody produced by the present invention is applied to a lightning arrester with a gap, it is possible to increase the dielectric constant of this resistor (for example, 600 or more). This is very advantageous in terms of insulation emphasis.

That is, the lightning arrester with a gap is conceptually an arc horn of an insulator device having a lightning arresting function, and is composed of a current limiting element portion and a series gap. The current limiting element part is a series of zinc oxide elements having a voltage non-linear resistance characteristic and is housed in an insulator (insulator tube) or is made of an insulator (ethylene-
It is molded with propylene rubber). As a result, when the tower potential rises due to lightning strikes on the transmission line, the series gap is discharged, and the non-linear resistance characteristic of the current limiting element is used to shut off the follow-up current and shut off the substation. The aim is to prevent power outages due to the operation of vessels.

However, in such a lightning arrester with a gap, the current limiting element must be newly inserted and installed between the existing steel towers, so insulation coordination with the existing arc horn is a problem, and it is necessary to flash into the series gap during a lightning strike. It is necessary to prevent flashover in the arc horn. In this respect, since the voltage non-linear resistor manufactured according to the present invention has a high dielectric constant, it is possible to reduce the flashover voltage flashing in the series gap, so that it is easy to emphasize the insulation with the existing arc horn. Is.

(Example) In order 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.

Next, it is preferable to carry out degassing under reduced pressure, preferably at a vacuum degree of 200 mmHg or less, so that the water content of the mixed sludge is about 30 to 35 wt% and the viscosity of the mixed sludge is 100 ± 50 cp. Next, the mixed sludge obtained was fed to a spray dryer to give an average particle size of 50-
150μm, preferably 80-120μm, water content 0.5-2.0
Granules of wt%, more preferably 0.9-1.5 wt%, are granulated. 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 up / down at a temperature of 50 to 70 ° C / hr and at a temperature of 800.
Pre-baking is performed under the conditions of ~ 900 ° C and holding time of 1-5 hours. In addition, the temperature rising / falling rate of the molded body is 10 to 100 ° C. /
It is preferable to scatter and remove organic components such as a binder at a temperature of 400 to 600 ° C. for 1 hour and a holding time of 1 to 10 hours.

Next, a high resistance layer is formed on the side surface of the calcined body. In this example
A mixture paste for insulation coating with a predetermined amount of Bi ₂ O ₃ , Sb ₂ O ₃ , ZnO, SiO ₂ etc. added with ethyl cellulose, butyl carbitol, n-butyl acetate as an organic binder to a thickness of 60-300 μm Apply the side of the calcined body.

Then, increase and decrease the temperature by 20-100 ° C / hr, the maximum holding temperature
The main calcination is carried out under the conditions of 1000 to 1300 ° C, preferably 1050 to 1250 ° C. Then, in order to manufacture the voltage nonlinear resistor of the present invention, as described above, after the main firing is performed once at a high temperature,
The temperature is lowered to 900 to 1050 ° C, the inside of the housing is depressurized at this temperature, and the temperature is kept constant for a predetermined time to remove bismuth trioxide by scattering.

In addition, a glass paste obtained by adding ethyl cellulose, butyl carbitol, n-butyl acetate, etc. as an organic binder to glass powder is applied on the high resistance layer on the side surface to a thickness of 100 to 300 μm, and the temperature rising / falling rate is 50 in air. ~ 200 ℃ / hr, 400 ~ 9
It is preferable to form the glass layer by heat treatment under the conditions of 00 ° C. and a holding time of 0.5 to 4 hours.

After that, both end surfaces of the obtained voltage nonlinear resistor are
Polishing is performed with water, preferably oil, as a polishing liquid with an abrasive corresponding to # 400 to # 2000 such as ₂ O ₃ and diamond. Next, after cleaning the polished surface, electrodes are provided, for example, by spraying, on both polished end surfaces by, for example, aluminum or the like to obtain a voltage nonlinear resistor.

Hereinafter, the results of actually measuring various characteristics of the voltage nonlinear resistor within and outside the range of the present invention will be described.

Example 1 According to the method described above, a predetermined amount of Bi ₂ O ₃ , Co shown in Table 1 was used.
₂ O ₃ 1.0 mol%, MnO ₂ 0.5 mol%, Sb ₂ O ₃ 1.0 mol%, Cr ₂ O ₃
0.5 mol%, NiO 1.0 mol%, SiO ₂ 1.0 mol% and the balance
0.1 wt% of bismuth borosilicate glass was added to the raw material made of ZnO, and this mixture was molded, calcined, formed into a high resistance layer, baked, etc. The voltage non-linear resistors of the invention example and the comparative example were manufactured. However, in the main firing step, the temperature rise-temperature retention-as shown in the drawing
It was done according to the cooling schedule. That is, first, at normal pressure, 50 ° C / hr
The temperature was raised at a rate of 1, the temperature was maintained at 1200 ° C for 5 hours, and the temperature was lowered to 1000 ° C at a rate of 60 ° C / hr. Next, the inside of the housing (inside the kiln) was depressurized to the pressure shown in Table 1 and kept at a temperature of 1000 ° C. for a predetermined time shown in Table 1. Then, the pressure inside the kiln is returned to normal pressure, and 60
The temperature was lowered at a rate of ° C / hr. The scattering amount of bismuth trioxide was changed by changing the holding time at 1000 ℃ and the pressure in the kiln at this time.

The dielectric constant (ε), ΔV _1mA (%), and flatness V _40KA / V _1mA of each voltage nonlinear resistor thus obtained were measured. ΔV _1mA (%) is V after applying lightning surge (100 _KA )
The rate of change is _{1 mA} , and the flat rate V _40KA / V _1mA is the ratio of the limiting voltage between 40 _KA and 1 _mA . The results of these measurements are shown in Table 1.

As can be seen from the results in Table 1, according to the present invention, ΔV _1mA and flatness can be reduced, and at the same time, the dielectric constant can be increased. It is also clear that the amount of bismuth trioxide scattered can be controlled by changing the holding time at 1000 ° C and the pressure inside the kiln.

Example 2 In exactly the same manner as in Example 1, the voltage non-linear resistors of the present invention example and the comparative example shown in Table 2 were manufactured. However, in this example, the proportion of the scattered amount of bismuth trioxide was 10% or more, and the amount of bismuth trioxide in the sintered body after firing was variously changed. The same measurement as in Example 1 was performed for each of these voltage non-linear resistors. Table 2 shows the results.

As can be seen from the results shown in Table 2, it is important that the amount of bismuth trioxide remaining in the sintered body be 6.0% by weight or less.

Example 3 A voltage non-linear resistor was manufactured in the same manner as in Example 1.
However, in this example, the addition amount of bismuth trioxide was unified to 6.7% by weight, and the holding time when scattering bismuth trioxide at 1000 ° C. was 5 hours in all, and only the pressure inside the kiln at this time was set. As shown in Table 3, various changes were made to Bi ₂ O during firing.
_The voltage non-linear resistors shown in Table 3 were manufactured by changing the scattering amount of 3. Then, for each of these resistors, the same measurement as in Example 1 was performed, and the results are shown in Table 3.

(Effect of the Invention) According to the method of manufacturing the voltage nonlinear resistor of the present invention,
Since the content of bismuth oxide after firing in the voltage non-linear resistor is set to 6% by weight or less, the adverse effect of the grain boundary layer of bismuth oxide in the sintered body can be suppressed, and the flatness, the dielectric constant, and the discharge withstand capability can be reduced. Can be good.

Since 10% or more of the added amount of bismuth oxide added to the mixture is scattered and removed during firing, at the time of adding to the mixture, the amount of bismuth oxide that is scattered and removed during firing is less than the optimum amount. Can be added in excess only. That is, in the first stage, bismuth oxide is excessively added to improve the wettability of the zinc oxide particle surface during firing, and 10% or more of the added amount of bismuth oxide is scattered and removed during firing, so that finally The bismuth oxide grain boundary layer in the sintered body can be reduced and the content can be set to 6% by weight or less. Therefore, the insufficient wettability of the zinc oxide particles does not cause any trouble during firing, and the dielectric constant and discharge withstand capacity do not deteriorate.

[Brief description of drawings]

FIG. 1 is a graph showing a temperature schedule for scattering and removing bismuth trioxide in the main firing step.

Claims (1)

[Claims] 1. A mixture containing zinc oxide as a main component and at least bismuth oxide as an additional component,
In the method of producing a voltage non-linear resistor by granulating, molding and firing, 10% or more of the added weight of bismuth oxide added to the mixture is scattered and removed during the firing, and the voltage of the bismuth oxide after firing is removed. A method for producing a voltage non-linear resistor, characterized in that the content rate in the non-linear resistor is 6% by weight or less.