JP2003077707A - Method for manufacturing non linear resistor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a nonlinear resistor capable of easily improving energy toleration and electrochemical characteristic with simple means. SOLUTION: In a method for manufacturing a nonlinear resistor comprising the steps of: wet blending a mixture including zinc oxide as a main component and at least bismuth compound as additive; granulating slurry obtained by the wet blending with spray drying; and forming in a prescribed shape and sintering the granulated powder, spraying boron oxide aqueous solution concentrations of 1.0 to 3.0% to the granulated powder to include 0.005 to 0.025 wt.% boron oxide to granulated powder weight and adjust water content of the granulated powder to 0.3 to 2.0 wt.%.

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 non-linear resistor, which is used in an overvoltage protection device such as a lightning arrester and whose main component is zinc oxide and whose resistance value changes according to an applied voltage. Regarding the method.

[0002]

2. Description of the Related Art A non-linear resistor generally called a varistor has a characteristic that its resistance value changes depending on an applied voltage, that is, it exhibits a high resistance value and an insulating characteristic when a normal voltage is applied. It has a non-linear voltage-current characteristic that exhibits a low resistance value when an abnormally high voltage is applied. Among the non-linear resistors having such characteristics, the non-linear resistor containing zinc oxide as a main component has an excellent non-linear voltage −
It has current characteristics.

A non-linear resistor containing zinc oxide as a main component is
By adding a small amount of bismuth, antimony, cobalt, manganese, or other oxides that cause non-linear voltage-current characteristics to zinc oxide, which is the main component, and wet-mixing the mixture, the slurry obtained by the wet-mixing is spray-dried. After granulating and molding the granulated powder into a columnar shape, the molded body is fired to produce a sintered body. Then, a side surface high resistance layer for preventing flashover is formed on the side surface of the sintered body by applying and baking a glass material for insulation treatment, and furthermore, electrodes are sprayed on the upper and lower end surfaces of the sintered body by aluminum spraying or the like. I am trying to form.

Since this kind of non-linear resistor has excellent non-linear voltage-current characteristics, it has been widely used in surge arresters and surge absorbers for the purpose of voltage stabilization or surge absorption. There is a demand for a non-linear resistor having a high energy resistance and a good electric charging characteristic.

In order to increase the energy resistance of the non-linear resistor, it is necessary to reduce the occurrence of pores (cavities) inside the sintered body and to limit the voltage ratio (both ends of the non-linear resistor when a minute current of 1 mA flows). Voltage V between both terminals V Voltage between both terminals of the same non-linear resistor when a large current of _{1 mA} and 5 kA flows
It is necessary to improve the non-linearity of the voltage in the large current region) with the ratio of _5kA . It can be said that the smaller the value of the limiting voltage ratio V _5kA / V _1mA , the better the nonlinear voltage-current characteristics.

Various improvements have been proposed in the past regarding the charging characteristics of the non-linear resistor. When boron oxide is added, the grain boundary layer inside the non-linear resistor is stabilized and the excellent charging characteristics are improved. It is a well-known fact that Here, the grain boundary layer surrounds the zinc oxide particles in the fine structure of the non-linear resistor, is made of an oxide added to the above-mentioned main component zinc oxide, and has a non-linear voltage-current characteristic. Contribute to.

[0007]

However, in the above-described conventional method for manufacturing a non-linear resistor, when boron oxide is added when the zinc oxide raw material and the additive are wet-mixed, the viscosity of the slurry becomes high. There is a problem that the productivity of the non-linear resistor is deteriorated.

Further, as a conventionally adopted method, there is a method in which bismuth borosilicate glass is added at the time of wet mixing. However, since silicon oxide is usually added at the same time, the growth of zinc oxide particles is hindered, which is desirable. In order to obtain the varistor voltage (voltage V _1mA between both terminals of the non-linear resistor when a minute current of 1 mA flows), the firing temperature of the molded body must be raised. When a non-linear resistor is manufactured by raising the firing temperature, not only the power consumption increases, but also the problem that the furnace material and the container are worn due to the scattering of bismuth oxide which is another additive. there were.

Further, silicon oxide reacts with zinc oxide,
A high resistance portion called spinel is formed in the fine structure of the nonlinear resistor. The presence of such a high resistance portion impedes the characteristic of exhibiting a low resistance value when a high voltage is applied, reducing the effective area through which the current flows and increasing the limiting voltage ratio V _5kA / V _1mA. There was a problem.

Further, as a means for improving the energy resistance of the non-linear resistor, a method of adjusting the water content in the granulated powder and adjusting the density of the compact to an appropriate value to reduce the generation of pores in the sintered body. However, conventionally, the water content was adjusted by setting the conditions of a spray dryer for spray-drying the slurry in the step of producing the granulated powder. However, when this method is adopted, there is a problem in that the moisture content of the lots of granulated powder greatly varies in the process of manufacturing the granulated powder, and as a result, the variation in energy resistance of the nonlinear resistor also becomes large. It was

Although there is a method of adding chromium oxide as another oxide for the purpose of improving the electric charging characteristic of the non-linear resistor, the firing temperature should be raised to improve the electric charging characteristic by this chromium oxide. There must be. When this chromium oxide is used as an additive and sintered at a low temperature, a pyrochlore phase is formed in the fine structure of the non-linear resistor, and the temperature dependence of the minute current region of 1 mA or less increases. Charging characteristics deteriorate. In addition, since it reacts with harmful hexavalent chromium during sintering, it becomes a problem from the environmental aspect.

Therefore, the present invention has been proposed in view of the above problems, and an object of the present invention is to provide a non-linear resistor which can easily improve the energy withstand capability and the charging characteristic by a simple means. It is to provide a manufacturing method.

[0013]

Means for Solving the Problems As a technical means for achieving the above-mentioned object, the present invention wet mixes a mixture containing zinc oxide as a main component and at least a bismuth compound as an additional component, and carrying out this wet mixing. In the method for producing a non-linear resistor, the obtained slurry is granulated by spray drying, and the granulated powder is formed into a predetermined shape and fired, and an aqueous solution of boron oxide concentration of 1.0 to 3.0% is granulated. By spraying the powder, 0.005-0.025w based on the weight of the granulated powder
It is characterized by containing t% boron oxide. Further, in the above structure, the boron oxide concentration is 1.0 to 3.0.
It is possible to adjust the water content of the granulated powder to 0.3 to 2.0 wt% by spraying an aqueous solution of 100% on the granulated powder.

In the present invention, in the granulation step of granulating the slurry obtained by wet mixing, the boron oxide concentration is 1.
By spraying the 0 to 3.0% aqueous solution on the granulated powder, it is possible to avoid the increase in viscosity of the slurry that has been caused by adding boron oxide in the step of wet mixing the zinc oxide raw material and the additive. . Since it is possible to add only boron oxide without expressing the viscosity increase of the slurry in this way, as a result of introducing silicon oxide as in the case of adopting the method of adding bismuth borosilicate glass during wet mixing. It does not raise the firing temperature or generate high resistance spinel. As a result, the limiting voltage ratio can be reduced, and the energy withstand capability and the charging characteristic can be improved.

The amount of boron oxide added was regulated to 0.005 to 0.025 wt% with respect to the weight of the granulated powder by spraying an aqueous solution having a boron oxide concentration of 1.0 to 3.0% on the granulated powder. This is because when the amount of boron oxide added is less than 0.005 wt% and greater than 0.025 wt%, any one of the limiting voltage ratio, the energy withstand capability, and the charging characteristic deteriorates.

The water content of the granulated powder is 0.3 to 2.0 w.
By adjusting to t%, the water content does not vary greatly from lot to lot of the granulated powder in the conventional process of manufacturing the granulated powder as a result, and as a result, the compact density is set to an appropriate value and baked. The generation of pores during tying can be reduced and the energy tolerance can be stabilized.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION As a preferred embodiment of the present invention, a method for producing a non-linear resistor containing zinc oxide as a main component will be described in detail.

Zinc oxide (Z
nO) raw material and bismuth oxide (Bi ₂O₃), Cobalt oxide
To (Co₂O₃), Manganese oxide (MnO₂), Anne
Chimon (Sb₂O₃), Nickel oxide (NiO), oxide
Luminium (Al₂O₃) Is added to the
Binder and dispersant such as aqueous solution of livinyl alcohol
Put it in a ball mill etc. and mix it wet to form a slurry.
To manufacture.

Then, the slurry obtained by the above-mentioned wet mixing is supplied to a spray dryer such as a spray dryer to produce granulated powder. By spraying and mixing an aqueous solution of boron oxide concentration of 1.0 to 3.0% to the granulated powder, 0.005 to 0.025 wt% of boron oxide is contained with respect to the weight of the granulated powder and the granulated powder is obtained. Water content of 0.3-2.0
Granulated powder adjusted to wt% is used.

Here, the reason why the water content is 0.3 to 2.0 wt% is that the pressure is uniformly transmitted when the granulated powder is molded, and the density of the molded body is set to an appropriate value. By setting the density of the molded body to an appropriate value, it is possible to reduce the generation of pores in the sintered body and improve the energy resistance. Further, the concentration of the boron oxide aqueous solution is 1.0 to 3.0.
When the content is less than 1.0%, the productivity is poor because the amount of the boron oxide aqueous solution added by spraying is large.
On the other hand, if it is more than 0%, it is difficult to uniformly mix the granulated powder due to the small amount of the boron oxide aqueous solution, and the characteristics of the non-linear resistor greatly vary.

The granulated powder obtained as described above is formed into a desired shape in the forming step, for example, a columnar shape, and the formed body is fired in air at 1000 ° C. to obtain the sintered body 1 shown in FIG. To get The side surface of the sintered body 1 is coated with an insulating material such as a glass material and baked to form the side surface high resistance layer 2 for preventing flashover, and thereafter, the upper and lower end surfaces of the sintered body 1 are covered with, for example, aluminum. Finally, the non-linear resistor 4 is manufactured by forming the electrode 3 by thermal spraying.

[0022]

[Examples] Zinc oxide (ZnO) raw material as a main component, bismuth oxide (Bi ₂ O ₃ ), cobalt oxide (Co ₂ O ₃ ),
Manganese oxide (MnO ₂ ), antimony oxide (Sb
₂ O ₃ ), nickel oxide (NiO), and aluminum oxide (Al ₂ O ₃ ) are mixed at the following compounding ratios. The compounding ratio is such that each additive is Bi ₂ O ₃ : 0.2.
_{5~1.50mol%, Sb 2 O 3:} 0.25~1.50
_{mol%, MnO 2: 0.05~0.50mol%} , C
_{o 2 O 3: 0.25~1.50mol%,} NiO: 0.0
5 to 0.50 mol%, Al ₂ O ₃ : 0.001 to 0.0
It is 1 mol% and the balance is ZnO. At this time, a predetermined amount of binder, dispersant and the like are added to zinc oxide and additives, and wet mixed in a ball mill for 20 hours to produce a slurry.

Then, the slurry is granulated by a spray dryer to produce granulated powder having an average particle size of 30 to 130 μm. This granulated powder had a boron oxide concentration of 1.0 to 3.
By spraying an aqueous solution adjusted between 0%, boron oxide is included in the addition amount of Table 1 with respect to the weight of the granulated powder, and the water content of the granulated powder becomes 0.3 to 2.0 wt%. Then, the mixture is mixed for 40 minutes with a V blender mixer.

Next, the granulated powder to which the aqueous solution of boron oxide was added was molded into a cylindrical shape at a molding pressure of 300 kg / cm ² , the molded body was degreased at 500 ° C., and then sintered at 1000 ° C. A cylindrical sintered body 1 having a diameter of 32 mm and a height of 29 mm was obtained. After that, the side surface high resistance layer 2 is formed by applying a glass material to the side surface of the sintered body 1 and baking the same, and the electrodes 3 are formed on the upper and lower end surfaces of the electrode 3 by spraying aluminum. ~ 5 non-linear resistors were obtained.

For comparison with these Examples 1-5, Table 1
The non-linear resistors of Comparative Examples 6 to 8 having a boron oxide concentration outside the range of the present invention as shown in FIG. In Comparative Examples 6 to 8, the steps other than the step of spraying the aqueous solution having the adjusted boron oxide concentration are the same as those in Examples 1 to 5. Further, a non-linear resistor of Conventional Example 9 in which the bismuth borosilicate glass shown in Table 1 was added at the time of compounding was manufactured. Also in this Conventional Example 9, the other steps after the molding step are the same as those in Examples 1 to 5.

Table 1 shows the results of measuring the voltage _application characteristics, the limiting voltage ratio (V _5kA / V _1mA ) and the energy withstand capability of the obtained non-linear resistor. Charging characteristics are 85%,
A test in which a voltage was applied at an ambient temperature of 115 ° C. for 1000 hours was performed. When the watt loss after 1000 hours had decreased from the watt loss immediately after the start of the test, ○ was evaluated, and when increased, was evaluated as x. The energy withstand capability was represented by ◯ when the current value shown in Table 1 was repeatedly applied 20 minutes at an interval of 2 minutes with a rectangular current waveform having a wavelength of 2 ms, and when the current value was not broken, and when it was broken, it was shown as x.

[0027]

[Table 1]

From the results shown in Table 1, Examples 1 to 5 in which the amount of boron oxide to be spray-added to the granulated powder falls within the range of the present invention, compared to Comparative Examples 6 to 8 and Conventional Example 9, It can be seen that good results were obtained for all of the limiting voltage ratio and the energy tolerance.

FIG. 2 shows that the non-linear resistor has a temperature of 115.
℃, the rate of charge 85% (the same voltage peak value as the voltage required to flow 1mA AC at 25 ℃), the watt loss when continuous AC power is applied, divided by the watt loss immediately after the start of the test Show. The charging characteristics of Examples 1 to 5 are more stable than those of Conventional Example 9.

[0030]

According to the present invention, the boron oxide concentration is 1.0.
By spraying a ~ 3.0% aqueous solution on the granulated powder to contain 0.005-0.025 wt% of boron oxide with respect to the weight of the granulated powder, the limiting voltage ratio can be reduced and the energy can be reduced. A high-quality non-linear resistor can be provided by improving and stabilizing the withstand voltage and the charging characteristic.

[Brief description of drawings]

FIG. 1 is a sectional view showing a structure of a non-linear resistor according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram showing a time change of a value obtained by dividing a watt loss when a non-linear resistor is continuously charged with alternating current by a watt loss immediately after the start of the test.

[Explanation of symbols] 4 Non-linear resistor

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Claims (2)

[Claims] 1. A wet mixture of a mixture containing zinc oxide as a main component and at least a bismuth compound as an additive component,
In the method for producing a non-linear resistor, the slurry obtained by this wet mixing is granulated by spray drying, and the granulated powder is formed into a predetermined shape and fired.
A method for producing a non-linear resistor, characterized in that 0.005 to 0.025 wt% of boron oxide is contained in the weight of the granulated powder by spraying an aqueous solution of 3.0% to 3.0% on the granulated powder. 2. The water content of the granulated powder is 0.3 to 0.3% by spraying a 1.0 to 3.0% aqueous solution of boron oxide on the granulated powder.
The non-linear resistor manufacturing method according to claim 1, wherein the content is adjusted to 2.0 wt%.