JPH0262507B2 - - Google Patents

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to the production of a zinc oxide-based voltage nonlinear resistor (hereinafter referred to as a varistor) containing magnesium oxide, which has excellent surge resistance. Regarding the method.

(Prior art) Zinc oxide varistors are recognized for their stability in terms of excellent nonlinearity, surge resistance, and constant voltage performance, and are widely used as protective varistors or constant voltage varistors against lightning surges and constant voltage. .

However, it is well known that magnesium oxide is added to this type of zinc oxide varistor for the purpose of improving the moisture resistance life.

Generally, the manufacturing method for this type of zinc oxide-based varistor includes ZnO powder as the main component, at least MgO as an additive, and further, for example, BiO ₃ .
Powders such as CoO, MnO, NiO, CrO, Al ₂ O ₃ and PbO are added as appropriate, and this is dispersed in H ₂ O and mixed.
After pulverization, the sintered body is granulated using a spray dryer, molded into a predetermined shape, and fired at high temperatures in the air. Electrode paste is printed and baked on the sintered body, or electrode metal is plated, metallized, or sintered. The process consists of forming an electrode by means such as vapor deposition, and attaching a lead terminal to the electrode.

However, in the above manufacturing method, MgO is used as an additive when mixing the raw material powder.
As MgO reacts with H ₂ O and changes to Mg(OH) ₂ , the viscosity of the slurry increases, which requires a large amount of water. Therefore, it is difficult to obtain a highly concentrated slurry and the bulk density when granulated is small, and when such raw material powder is used, the pressure stroke during molding becomes longer, which increases the friction of the mold and the raw material. The friction caused by the movement of the molded body is large, and the air removal is not sufficient, resulting in a large residual strain in the molded body, which reduces the surge resistance.

(Problems to be Solved by the Invention) As described above, for the purpose of improving the moisture resistance life, when mixing zinc oxide as the main component and at least magnesium oxide as an additive, MgO becomes H ₂ O.
As a result, the bulk density at the time of granulation is small and the surge _resistance is reduced due to large residual strain in the compact, making it difficult to obtain the desired surge resistance characteristics.

The present invention solves the above-mentioned drawbacks, and the mixing and
By eliminating the reaction between MgO and H ₂ O during the pulverization process, we prevent the increase in slurry viscosity, increase the bulk density after granulation, and reduce the residual strain of the compact.
The object of the present invention is to provide a method for manufacturing a varistor that does not reduce surge resistance.

[Structure of the Invention] (Means for Solving the Problems) The method for producing a varistor of the present invention is a method for producing a zinc oxide-based varistor containing magnesium oxide. This method is characterized by mixing and pulverizing other metal oxides.

(Function) According to the method for manufacturing a varistor having the above configuration, magnesium oxide reacts with zinc oxide to replace some Zn atoms in the zinc oxide crystal with Mg atoms, or Mg oxide is present in the zinc oxide crystal lattice. It becomes a zinc oxide magnesium solid solution into which atoms have entered,
Since the reaction between MgO and H ₂ O can be ignored,
It is possible to prevent an increase in slurry viscosity, to efficiently generate highly concentrated slurry, and to obtain a uniform molded product.

(Example) The present invention will be described in detail below. First, ZnO and MgO
In a mixed solution of ZnO and MgO mixed with powder and H ₂ O.
Add HCl to the resulting ZnCl ₂ + MgCl ₂ solution.
(NH ₄ ) ₂ CO ₃ is added to produce a suspension of ZnMgCO ₃ and 2NH ₄ Cl, and a zinc magnesium oxide solid solution is obtained by a so-called carbonate coprecipitation method in which a suspension of ZnMgCO 3 and 2NH 4 Cl is decarboxylated by heat treatment after washing and drying. Next, additives such as Bi ₂ O ₃ , CoO,
Metal oxides such as MnO, NiO, CrO, Al ₂ O ₃ and PbO are appropriately added, dispersed in H ₂ O together with an organic binder and a dispersant, mixed and pulverized wet, and then manufactured using a spray dryer, for example. A compact is obtained in the form of a granulated disk or square plate. Next, the molded body is fired in air at a high temperature of 1100 to 1400°C to obtain a sintered body. Next, electrodes are formed on the sintered body by known means, and lead terminals are attached to the electrodes.

According to the method for manufacturing a zinc oxide-based varistor containing magnesium oxide configured as described above,
Since magnesium oxide is used in the form of a zinc oxide magnesium solid solution in zinc oxide as the main component, magnesium oxide does not react with H ₂ O and change to magnesium hydroxide, which is a factor in increasing the viscosity of the slurry. This makes it possible to increase the slurry concentration, ensure a high bulk density when granulated, eliminate the need for a long pressurizing stroke during molding, and reduce the residual strain of the molded product, which significantly reduces the decrease in surge resistance. It has the advantage of being able to In addition, it is possible to easily obtain a zinc oxide-based varistor containing magnesium oxide, which has good grinding and mixing efficiency by preventing viscosity increase, reduces energy consumption during drying, and maintains the moisture-resistant life characteristics that are the basis for adding magnesium oxide. can.

Next, the advantages of the present invention will be described based on experimental results.

First, Figure 1 shows the relationship between concentration (raw material g/H ₂ Oc.c.) and viscosity, and Figure 2 shows the relationship between concentration (raw material g/H ₂ Oc.c.) and bulk density. It shows,
Furthermore, Fig. 3 shows the rate of change in the surge withstand capacity with respect to the number of surge applications in the varistor. C is a reference example in which MgO is not added.

The surge application conditions are waveform 8/20μsec, current
250A, impulse 30 seconds.

However, as is clear from Fig. 1, conventional example B
The viscosity of the product increases rapidly at a concentration of 0.7 (d/cc), whereas the viscosity of the product according to the present invention A increases.
At 10 ^-2 P level, the rapid increase did not occur until it exceeded 1.5 (g/cc), resulting in almost the same results as Reference Example C. Therefore, as is clear from Figure 2, the bulk density of Conventional Example B was 1.0g. /cm ³ , whereas the present invention A
The result was that the weight could be increased to 1.2 g/cm ³ or more. Therefore, as is clear from FIG. 3, the present invention A was significantly superior to the conventional example B in terms of surge resistance characteristics.

In the above embodiments, the carbonate coprecipitation method was used as the means for producing the zinc oxide solid solution, but the same effect can be obtained even if the method is applied to a method in which the solid solution is obtained by a heating method.

[Effects of the Invention] According to the present invention, slurry viscosity can be prevented by using a zinc oxide magnesium solid solution consisting of zinc oxide and magnesium oxide as a manufacturing method for a zinc oxide-based varistor containing magnesium oxide, and a high concentration It is possible to obtain a method for manufacturing a zinc oxide-based varistor that enables slurry generation, ensures moisture resistance due to the addition of magnesium oxide, and prevents deterioration of surge resistance characteristics.

[Brief explanation of the drawing]

FIG. 1 is a concentration-viscosity curve diagram, FIG. 2 is a concentration-bulk density curve diagram, and FIG. 3 is a surge application number-rate of change characteristic curve diagram.

Claims (1)

[Claims] 1. A method for manufacturing a voltage nonlinear resistor containing zinc oxide as a main component and at least magnesium oxide as an additive, characterized in that zinc oxide and magnesium oxide are used in the form of a zinc oxide solid solution. manufacturing method.