JPH0669004A - Manufacture of voltage dependent nonlinear resistor element - Google Patents

Abstract

PURPOSE:To avoid the mixture of any foreign matters in a mixing step while cutting down the mixing time by specifying the ball mill medium used for the mixing step to be a small diameter ball with high specific gravity. CONSTITUTION:Specific amounts of zinc oxide as a main component as well as bismuth oxide, cobalt oxide, manganese oxide, antimony oxide, etc., as additives of subcomponents are to be weighed and then wet-mixed up in a bowl mill. At this time, as for the ball mill medium, a small-diameter ball with specific gravity in diameter exceeding 1.5mm but not exceeding 5mm is used. Next, the zinc oxide and said additives mixed with one another for specific time are dried up to produce the mixture particles. Through these procedures, the mixing performance can be notably enhanced while cutting down the mixing time furthermore enabling the mixture of any foreign matters from the ball with the element compositions to be avoided as well as the detrioration in the varristor characteristics to be prevented.

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 resistance element containing zinc oxide as a main component.

[0002]

2. Description of the Related Art A voltage non-linear resistance element (hereinafter referred to as a varistor) containing zinc oxide as a main component is mounted on a wide variety of electronic component devices for surge voltage absorption and voltage stabilization for the purpose of protecting electronic circuits. . In the production of a varistor, it is necessary to add a small amount of an additive as a sub-component to zinc oxide which is the main component and to sufficiently mix this with dispersion and pulverization.

Usually, the mixing is performed using a ball mill or the like. A ceramic ball such as alumina or magnesia or a resin ball is used as a ball mill medium, and a predetermined amount of a main component and a subcomponent are charged together with a liquid such as water and mixed for a predetermined time, and the obtained mixture is granulated and molded. After that, it is manufactured by sintering.

If the components are not sufficiently mixed, the varistor obtained as a sintered body has drawbacks such as deterioration in electrical characteristics and unstable variations in characteristics. Therefore, conventionally, it was necessary to carry out the mixing process for a long time.

FIG. 2 shows the relationship between the mixing time and the specific surface area value of the mixture.

[0006]

However, when mixing is performed for a long time, there is a problem that the components of the ball mill medium are mixed into the component of the element, which causes the characteristics of the varistor to deteriorate. It is also apparent that long-time mixing increases the load on equipment related to mixing such as a ball mill and a ball mill medium, promotes deterioration of equipment conditions, and causes a decrease in productivity.

It is an object of the present invention to provide a method for manufacturing a voltage non-linear resistance element which does not mix foreign matter due to mixing and can shorten the mixing time.

[0008]

In order to achieve the above-mentioned object, a method of manufacturing a voltage non-linear resistance element according to the present invention comprises a mixing step, and a voltage non-linear resistance element for manufacturing an element using a mixed composition. In the method of manufacturing a linear resistance element, the mixing step is a step of adding zinc oxide as a main component, a necessary trace amount of an additive as a sub-component to this, and mixing in a ball mill. A high specific gravity small diameter ball of 1.5 mm or more and 5 mm or less is used.

The ball mill medium is a ball having a specific gravity of 5 or more.

[0010]

The size of the high specific gravity small diameter ceramic balls used for the ball mill medium is preferably 1.5 mm or more and 5 mm or less in diameter. Even if the high specific gravity small diameter ceramic balls within this range have a small diameter, a large mass is obtained for each individual ball, so that the mixing performance of the components does not deteriorate. Diameter is 1.5
If it is less than mm, the mass of each ball is insufficient, the mixing is not sufficiently performed, the mixed powder becomes non-uniform, and variations in characteristics increase. Further, if the diameter exceeds 5 mm, the contact points between the balls are reduced, and the mixing property of the components is reduced, so that it is impossible to shorten the mixing time, and foreign substances are mixed into the element components from the balls. It causes deterioration of varistor characteristics.

Further, since the high specific gravity small diameter ceramic balls within the above range have a small diameter, the number of contact points between the balls is increased, and the mixing performance is remarkably improved, so that the mixing time can be shortened, so that the ball is included in the element component. Since no foreign matter is mixed in from the inside, deterioration of varistor characteristics can be prevented. In addition, the effect of reducing the load on the equipment related to mixing and improving the productivity can be obtained. Therefore, according to the method of the present invention, it is possible to provide a varistor which is generally inexpensive and has excellent characteristics.

[0012]

EXAMPLES Examples of the present invention will be described below. Predetermined amounts of zinc oxide, which is the main component, and bismuth oxide, cobalt oxide, manganese oxide, antimony oxide, and the like, which are added to the main component as additives of subcomponents, were weighed. As the ball mill medium, zirconia balls having a ball diameter of 5 mm and a specific gravity of 5 to 6 were used, and the volume of the balls was 10% of the ball mill internal volume.
Installed so as to be 40%, put a predetermined amount of water, the above-mentioned measured amount of zinc oxide and additives into a ball mill, and let the ball mill medium act on them to mix the zinc oxide with the additives for a predetermined time. did. This mixed slurry was dried to obtain a mixed powder.

Next, a predetermined amount of a binder is added to this mixed powder for granulation, and a molding die is used to obtain a diameter of 12.5 mm and a thickness of 20.
After pressure molding to mm, it was baked at 1000 ° C to 1300 ° C. The sintered body thus obtained was cut into a thickness of 2 mm, and a silver electrode having a diameter of 8 mm was baked on the opposed plane of the sintered body to obtain a varistor.

In the above process, when the specific surface area of the mixed powder was measured when the mixing time was variously changed, the results shown in FIG. 1 were obtained. From the results of FIG. 1, it can be seen that the larger the specific surface area value, the better the mixing performance.

[0015]

[Table 1]

Table 1 shows the specific surface area value of the mixed powder and the electrical characteristics of the varistor obtained in the present invention in comparison with the conventional example. V1mA is a voltage when a current of 1 mA is applied to the varistor. The limit voltage ratio is the voltage V1250A when the lightning surge current 1250A of 8/20 μS is applied.
And V1mA. The smaller the limiting voltage ratio, the better the electrical characteristics of the varistor. ΔV / V is 8 / 20μ
V1m before and after passing S lightning surge current of 3000A
This is the degree of change in A.

As is apparent from Table 1, the electrical characteristics of this embodiment are equal to or superior to those of the conventional example.

In this embodiment, an example in which zirconia balls are used as the ball mill medium has been shown, but the present invention is not limited to this, and balls having a specific gravity of 5 or more have the same effect. Needless to say.

[0019]

As described above, according to the present invention, when a composition containing zinc oxide as a main component and a trace amount of an additive as an accessory component is mixed in a ball mill, a high specific gravity small diameter ceramic ball is added to a ball mill medium. Since it was used, the mixing performance was remarkably improved, the mixing time could be shortened, moreover, there was no mixture of foreign matter from the ball in the element composition, the deterioration of varistor characteristics could be prevented, and the load on the equipment related to mixing was reduced. Therefore, it is possible to obtain the effect that productivity can be improved.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a mixing time and a specific surface area value according to an example of the present invention.

FIG. 2 is a diagram showing a relationship between a mixing time and a specific surface area value according to a conventional example.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takanori Aoki 2-15-12 Nakane, Meguro-ku, Tokyo Tama Denki Kogyo Co., Ltd.

Claims (2)

[Claims] 1. A method of manufacturing a voltage non-linear resistance element, which comprises a mixing step and uses the mixed composition to manufacture an element, wherein the mixing step comprises zinc oxide as a main component and a sub-component. Is a step of adding a necessary trace amount of additive as described above and mixing in a ball mill, wherein a high specific gravity small diameter ball having a diameter of 1.5 mm or more and 5 mm or less is used as a ball mill medium. Production method. 2. The method of manufacturing a voltage nonlinear resistance element according to claim 1, wherein the ball mill medium is a ball having a specific gravity of 5 or more.