JPH03161902A - Manufacture of varistor - Google Patents

Abstract

PURPOSE:To manufacture a varistor high in surge resistance by a method wherein ZnO heat-treated at specific temperature is crushed and after mixed with the secondary constituent material, crushed, molded and baked. CONSTITUTION:ZnO as the main constituent material is heat-treated at a temperature within a range of 800-1400 deg.C. Next, said material is crushed and then Bi2O3, Co2O3, Sb2O3 as the secondary constituent materials are added thereto to be wet-mixed for 10 hours and then crushed for producing a mixed material powder. Next, the mixed material powder, after calcination and with a binder added thereto is wet-mixed again using a ball mill to produce granulated powder. Then, the granulated powder after compression molding, is heat-treated to scatter the binder and then further baked to produce a varistor element. Through these procedures, the aggregation of ZnO powder can be effectively avoided so that the secondary constituent can be evenly scattered thus enhancing the surge resistance.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing a varistor using ZnO as a main raw material, and more specifically to a method for producing a varistor in which the process of obtaining rice powder as a raw material for ZnO is improved. Relating to a manufacturing method.

[Conventional technology]

A varistor is known as a resistor element whose resistance value changes non-linearly depending on the applied voltage, and is used as a surge absorption element to prevent overvoltage from being applied to electronic circuits. There is.

Varistors can be broadly classified into two types: disk-type varistors and laminated-type varistors.

In either type of material, materials containing ZnO as a main raw material are widely used as the material exhibiting voltage nonlinearity.

During production, Bi, Co., etc. are used as auxiliary raw materials for ZnO, which is the main raw rice. A metal oxide such as Mn or Sb is added at the same time. Thereafter, mixed raw material powder is obtained by mixing and pulverizing. A sintered body exhibiting voltage nonlinearity can be obtained by firing the molded body obtained by molding this mixed raw material powder. Furthermore, a varistor is manufactured by forming a predetermined electrode on the obtained sintered body.

In addition, the above-mentioned subcomponent raw materials, namely Bi, Co, Mn
Alternatively, subcomponent raw materials such as sb are added for the purpose of imparting voltage nonlinearity or improving stability.

[Technical problem that the invention seeks to solve]? The conventional manufacturing method described above has a problem in that it is difficult to obtain a varistor with sufficient surge resistance. Surge resistance is Vl-
It represents the magnitude of the current value when the rate of change of A (the voltage value applied to both ends of the varistor when a current of lmA flows through the varistor) is ±10% or less. 1 for disc type varistors
When a surge current of about 500 A and a duration of 8×20 μm seconds was applied, the rate of change in (1) did not stably fall below ±10%, making it difficult to stably obtain a surge withstand capacity of 1500 A or more.

Therefore, an object of the present invention is to provide a method for manufacturing a varistor that can stably obtain surge resistance of 1500 A or more.

[Means for solving technical problems]

The inventors of the present application have discovered that the above-mentioned variation in surge resistance in varistors is due to Bi. We thought that this may be caused by the non-uniformity of the dispersion state of oxides such as Co, Mn, or sb, and investigated the particle size 3 and agglomeration state of ZnO and subcomponent raw materials. As a result, ZnO I)
Although so is 1 μm or less, ZnO tends to aggregate, and some of the secondary particles are found to be 5 μm to 10 μm or more.

That is, it has been found that due to the agglomeration of Zn◯, it is difficult to uniformly disperse the by-product material 1'1, which causes variations in the surge resistance.

Based on the above-mentioned novel findings, the inventors of the present application thought that the surge resistance could be increased by preventing the aggregation of ZnO, and as a result of various studies on methods for preventing the aggregation of Zn○, the present invention was developed. I came to do this.

That is, the method for manufacturing a varistor of the present invention involves heat-treating Zn○, which is a main raw material, at a temperature in the range of 800°C to 1400°C, pulverizing it to obtain ZnO powder, and adding side effects to the Zn○ powder. It is characterized by comprising the steps of adding raw materials, mixing and pulverizing, shaping the obtained mixed raw material powder, and then burning the oval body.

The heat treatment of Zn○ was performed at 800°C-1400°C as described above.
This is done by maintaining Zn○ at a temperature in the range of 4°C. Although the time for this heat treatment is not particularly limited, it is preferable to hold the heat treatment for a time necessary to sufficiently increase the ζ potential described below. Usually, heat treatment is performed for about 2 hours.

The reason why it is necessary to perform heat treatment at a temperature of 800"C or more and 1400C or less is because if Zn○ is heat treated at a temperature outside the above range, a surge resistance of 1500A or more cannot be achieved.

The present invention is characterized by the above-mentioned heat treatment process for ZnO, and the ZnO obtained by crushing after the heat treatment
The powder is mixed with the subcomponent raw material and ground again to obtain a mixed raw material powder. Various materials conventionally used to obtain Zn○ varistors can be used as the secondary ingredient raw materials. For example, Bi, Pr, Sb, Mn or Co
Metal oxides such as the following are used as appropriate.

In addition, for shaping, burning, etc. after obtaining the mixed raw material powder, conventional methods used in conventional varistor manufacturing methods may be used.

[Effect]

5 The aggregation factor of Zn○ powder is thought to be the ζ potential of ZnO, and aggregation is most likely to occur when the ζ potential is ±0. That is, the closer the ζ potential of the ZnO particles is to ±0, the more likely the ZnO particles are to agglomerate without repelling each other. In fact, the ζ potential of the ZnO raw material powder obtained by the conventional method is about +4 mV. Therefore, at a ζ potential of this magnitude, the repulsive force between ZnO particles is small;
It is thought that aggregation is likely to occur.

Therefore, in the present invention, the ζ potential of ZnO is increased by performing the heat treatment as described above. That is, the present invention is characterized in that aggregation is prevented by increasing the ζ potential of ZnO by heat-treating ZnO at a temperature of 800°C or more and 1400°C or less, and increasing the electrostatic repulsion that acts between ZnO particles. has.

Preferably, heat treatment at a temperature of 1,000 to 1,200° C. can further reduce the ζ potential, thereby making it possible to obtain a varistor with even higher surge resistance.

6 [Effects of the Invention] According to the present invention, since the present invention includes the step of heat treating ZnO at a temperature in the range of 800°C to 1400°C, agglomeration of ZnO powder can be effectively prevented. Therefore, Zn
Since it becomes possible to uniformly disperse the subcomponent raw material in the O powder, a varistor with increased surge resistance can be obtained. In addition, it becomes possible to stably obtain a varistor that exhibits a surge resistance exceeding 1500A.

Furthermore, as will be clear from the embodiments described below, not only the surge resistance but also the voltage nonlinear coefficient can be increased by 5 or more compared to a comparable conventional example. Therefore, it is possible to obtain a varistor with better voltage control characteristics than conventional ones.

[Explanation of Examples]

First, ZnO was heat treated at various temperatures ranging from 800°C to 1400°C. The heat treatment was carried out by maintaining ZnO, which is the main component raw material, in the set heat treatment temperature atmosphere for several hours. Next, ZnO powder was obtained by crushing the heat-treated ZnO.

To the obtained ZnO powder (97.8 mol%), B iz Ox (0.5 mol%), Mn
○(0.5 mol%), Co,! 0, (0.5 mol%)
and Sbz 03 (0.7 mol %) were added, wet-mixed for 10 hours using a Pall mill, and then pulverized to obtain a mixed raw material powder.

The obtained mixed raw material powder is dehydrated, and then ao o'c
It was calcined for 2 hours. Furthermore, 2% by weight of vinyl acetate and 1.5% by weight of polyvinyl alcohol were added as a binder to the calcined mixed raw material powder, and the mixture was wet-mixed again in a bowl for 10 hours to obtain a granulated powder.

Next, the obtained granulated powder was sized to a diameter of 8 mm and a thickness of 1.2 m.
Compression molded with a press to a size of m, molding density 3.8
A molded article of g/c+1 was obtained.

The obtained molded body was heat-treated at a temperature of 700°C for 1 hour to scatter the binder, and then heated at +100°C to l
It was baked at 400°C for 2 hours to obtain a Pallister element.

A conductive base 1 consisting mainly of Ag was applied to both main surfaces of the obtained varistor element, and baked at 650'C for 10 minutes to form electrodes. With both shaped electrodes,
After attaching the lead wires by soldering,
The entire varistor element was coated with epoxy resin to obtain a disk-shaped varistor sample.

For the obtained sample, the varistor voltage per unit thickness (
VIIIA/+1111), voltage nonlinear coefficient (α)
and the rate of change in varistor voltage was measured. The results are shown in Table 1. Note that the voltage nonlinear coefficient is α-1/1og (V
imA/VQ. l, IA). Also,
The rate of change of Harisk voltage is 1000, 1500 and 20
Each surge current of 00 A for 8×20 μsec was applied, the varistor voltage was measured one hour later, and the rate of change in the varistor voltage before the surge current was applied is shown.

In addition, as a comparative example, a disk-shaped varistor sample (
Sample No. 11) was also measured in the same manner as in Example 9, and the results are also shown in Table 1.

Furthermore, samples whose heat treatment temperatures were outside the range of the present invention (sample numbers 1, 2.10) were also manufactured and measured in the same manner as in the examples, and the results are also shown in Table 1.

Note that the "*" mark in Table 1 indicates a comparative example and a sample outside the scope of the present invention.

As is clear from Table 1, the heat treatment temperature of ZnO was 80°C.
It can be seen that in the samples of the present invention (sample numbers 3 to 9) whose temperature was in the range of 0°C to 1400°C, the rate of change in varistor voltage with respect to a surge current of 1500A was significantly improved to less than ±10%.

Further, it can be seen that the voltage nonlinearity coefficient α is also larger by 5 or more compared to the sample of the comparative example (sample number 11).

Furthermore, in the samples of the present invention (sample numbers 3 to 10), in particular, the ZnO heat treatment temperature was set to 1000°C or higher and 1200°C or higher.
It can be seen that in the samples (sample numbers 5 to 7) kept at a temperature of 0.degree. Therefore, it is preferable to heat-treat ZnO at a temperature of 1000°C or more and 1200°C or less.

In addition, in the above embodiment, a method for manufacturing a disc-shaped varistor using a disc-shaped sintered body was explained, but the present invention can also be applied to a method for manufacturing a varistor of other shapes, such as a square plate-type varistor. It should be pointed out that this embodiment can also be applied to a multilayer varistor, and the same effects as in this embodiment can be obtained.

(Hereafter, margin) No. 1 table

Claims (1)

[Claims] After heat-treating ZnO, which is the main component raw material, at a temperature in the range of 800°C to 1400°C, it is pulverized to obtain ZnO powder,
A method for producing a varistor, comprising the steps of mixing the ZnO powder with a subcomponent raw material, pulverizing the ZnO powder, molding the obtained mixed raw material powder, and then firing a molded body.