JPH01289211A - Manufacture of varistor - Google Patents

Abstract

PURPOSE:To obtain a zinc oxide varistor whose varistor voltage is low and whose voltage nonlinearity is high by adding a grain growth accelerator composed of MgO to a ZnO granulated powder having varistor characteristics. CONSTITUTION:Bi2O3, CoO, MnO2, Sb2O3, NiO, Cr2O3 and TiO2 in individually prescribed amounts are added to a ZnO powder; a binder and water are added to this mixture and are mixed, a slurry is produced, this slurry is dried by using a spray drier, this dried slurry is granulated and a basic material is obtained. Then, a binder and water are added to an MgO powder and are mixed, this mixture is dried by using the spray drier, this dried mixture is granulated, and a granulated powder is obtained as a grain growth accelerator. During this process, a drying condition is changed properly, and a grain growth accelerator whose average grain diameter is 10-50mum is obtained. This grain growth accelerator in a proper amount is added to the basic material, a raw material powder for a low-voltage varistor is produced, and this raw material powder is pressurized, molded and, after that, sintered. By this setup, a ZnO crystal is dispersed and arranged inside a sintered substrate, and an excellent voltage nonlinearity index can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for manufacturing a low voltage varistor for protecting semiconductor electronic components from surge currents.

Conventional technology Conventionally, the main component was ZnO, Bi2O3, Cod, 5
b205 *Zinc oxide type varistors containing several types of metal oxides including Cr2O5 as subcomponents have been widely used as surge absorption elements due to their excellent voltage nonlinearity. This zinc oxide type varistor can be applied to various voltage circuits by adjusting the rising voltage (varistor voltage: Vl, m) per 1ff of sintered body.

The v1mm/ff of zinc oxide type varistors currently in practical use is approximately 10 to 300V. In addition, the varistor voltage of a zinc oxide type varistor depends on the number of ZnO particles in series in the sintered body, and if the thickness of the sintered body is constant, in order to increase the varistor voltage, the growth of the ZnO particles must be inhibited. On the contrary, in order to lower it, it is necessary to promote it. For example, ZnOI
Bi 203 r Cool sb 2o 5 +S
In zinc oxide type varistors appropriately prepared from iO2, NiO* Or 2o 5 + MnO2,
The particle size is about 10 to 30 μm, and the V11!1 voltage is 80 to 300 V. On the other hand, TiO2 is added to these components.
The zinc oxide type varistor with added ZnO has a lower voltage, and the ZnO particle size is 60 to 100μ! a+V+ma/- is 20-6
It becomes ov.

In recent years, the use of microcomputers in the control circuits of home appliances and industrial equipment has progressed, and as a result, drive circuit voltages have decreased, and most of them are below 10V. However, semiconductor electronic components such as transistors and ICs are extremely susceptible to surge currents.
Countermeasures have become essential. Against this background, there is a strong demand in the market for zinc oxide type varistors for low voltage circuits with a varistor voltage of about 10V. For this purpose, it is necessary to set the ZnO particle diameter to 200 to 3004 m.

As a method for manufacturing the zinc oxide type varistor for the above-mentioned low voltage circuit, for example, the method described in Japanese Patent Publication No. 56-39526 is known. This is ZnO99-5% le%
+ After mixing 5 mol % of BaC050, it is sintered and hydrolyzed to obtain ZnO crystals of 30 to 200 μm. Furthermore, ZnO, Sb 20. , Coo.

After mixing MnO2, NiO, Or203, etc., it is sintered to obtain a spinel phase component. This spinel phase component and Zn
Appropriately classify the O crystals and add 1 to 60% by weight of the spinel phase component and 1 to 4% of the ZnO crystals to separately prepared ZnO powder.
Add oM amount, mix, mold, sinter, v1mm/fl
A low voltage varistor with a voltage of about 1 ov is created.

Problems to be Solved by the Invention However, according to the conventional method as described above, Zn
Hydrolysis and classification are required after firing to obtain O crystal grains, and a similar process is also required to create the spinel phase component, resulting in a very large number of man-hours and a high loss of time and energy. It had drawbacks. Furthermore, when mixing ZnO crystal grains, spinel phase components, and ZnO powder, it is difficult to mix them uniformly due to the difference in their specific gravity, and the uneven distribution of ZnO crystal grains also has the disadvantage that the varistor voltage is large and has large variations. was.

The present invention solves these problems and aims to provide a method for manufacturing a low voltage varistor for protecting semiconductor electronic components from surge currents.

Means for Solving the Problems In the present invention, in order to solve the above conventional problems, granulated powder of zinc oxide type varistor is used as a base material, and granulated powder made of MgO prepared separately in a spray dryer is granulated into this. Added as a growth promoter, mixed and molded.

It is characterized by being sintered.

Effect By adopting the above method, 80 to 3
00 μm ZnO crystal grains are dispersed and arranged, and a low voltage varistor with an excellent voltage nonlinearity index can be easily obtained.

Example Hereinafter, details of the present invention will be explained based on examples.

First, Bi2O5+ Coo, MnO was added to ZnO powder.
2,5b2o,.

NiO, Cr2O5, and TiO2 were each 1. OO%/
l,%.

0.50%/I/%, 1.00 mol%, 0.05 mol.

0.6 molti, 0.10 molti, and 1.00 molti are added, and a binder and water are added and mixed to obtain a slurry.

This slurry is dried with a spray dryer and granulated to obtain a base material. Next, as a grain growth promoter,
A binder and water are added to and mixed with MgO powder pulverized to micrometers, dried with a spray dryer, and granulated to obtain granulated powder. At this time, the drying conditions of the spray dryer were changed appropriately and mesh cut was performed to obtain an average particle size of 6 μm! 11110μ!
1.25μ weight.

Five types of grain growth promoters of 50 μm and 75 μm weight were obtained. An appropriate amount of this grain growth promoter was mixed with a base material to obtain raw material powder for a low voltage varistor. After pressure molding this raw material powder, 1250
'C for 1 to 6 hours, and the varistor voltage, voltage nonlinearity index, etc. were investigated.

Figures 1 to 6 show average particle diameters of 6μml and 1゜μl on the base material.
l Grain growth promoter (MgO) mesh-cut to 25 μm + 60 pm and 76 pta to QO3-1
FIG. 2 is a characteristic diagram showing the relationship between the varistor voltage (V+mm/gg) per unit thickness and the voltage non-linearity index (α) of a sample added in a concentration range of 0.00%.

As a comparative study example, FIG. 6 shows the characteristics of a sample in which the base material and the grain growth promoter were not separated, and 0.03 to 10.00 mol of MgO was added to the starting material.

From FIG. 1, in the sample using a grain growth promoter with an average grain size of 6 μm, the amount added was 0.1 to 3.0 mol.

It can be seen that v1mm/H has decreased and ZnO grain growth has occurred. However, at the same time, α also decreases rapidly, making it unsuitable for use as a low voltage varistor. On the other hand, as shown in Figures 2 to 4, in the samples using a grain growth promoter with an average particle size of 10 to 60 μm, when the amount added was 0.03 to 3.00 molt, the target 'l'jm mm/ho decreases to about 10V, α becomes 30
It shows a good value of ~60. Moreover, when the amount added exceeds 3.0 molti, V1mm/i increases and α also decreases. Figure 5 shows that when a grain growth promoter with an average grain size of 75 μm is used, v',, mu/ff decreases, but α is 2o.
It can be seen that it decreases before and after. From Figure 6, when using the conventional method in which the base material and grain growth promoter are not added separately, M
It can be seen that when the amount of gO added is 0.3 to 1.0 molt, α decreases to about 10V, but α also decreases to about 20. From the above results, the average particle size of the grain growth promoter is 1o~60
μm, when the amount added is 0.1 to 3.0 mol, v1 mm/I
A low voltage varistor with an IM of about 10v1α3o~50 can be manufactured.

Effects of the Invention As described above, according to the present invention, a zinc oxide varistor with low varistor voltage and high voltage non-linearity can be produced by adding a grain growth promoter made of MgO to granulated powder having varistor properties. It can be manufactured extremely easily.

In addition, in this example, ZnO, Bi2O3, CoC is used as the base material.
L, MnO2, Cr2O5, NiO, 5b205
+ TiO2 was used, but other metal oxides that improve the characteristics as a varistor, e.g. t Ham 120y, 5i
n2. Even if PbO, 5n02, Mug20°Pr60H, etc. are used, the effects of the present invention will not change.

[Brief explanation of the drawing]

1 to 5 are characteristic diagrams of the present invention example and the reference example, with average particle diameters of 6 μm and 10 μm, respectively. Grain growth promoter addition amount and V 1 when using grain growth promoters of 26 μm, 60 μm, and 75 μm! l A /1M
FIG. 6 is a characteristic diagram showing the relationship between α and α, and FIG. 6 is a characteristic diagram of a varistor manufactured by a conventional manufacturing method. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 (topm) → hVo concentration (mol γ・) Figure 3 Figure 4 → N90 Hamataka (mol''/,)

Claims (2)

[Claims] (1) The sintered body itself uses granulated powder mainly composed of zinc oxide, which has varistor properties, as a base material, and uses MgO granulated to a size of 10 to 50 μm using a spray dryer as a grain growth promoter,
A method for manufacturing a varistor, which comprises molding and sintering raw material powder obtained by mixing the grain growth promoter with the base material. (2) The method for manufacturing a varistor according to claim 1, wherein the raw material powder contains 0.1 to 3.0 mol% of MgO.