JPH03116903A - Manufacture of varistor - Google Patents

Abstract

PURPOSE:To make it possible to stably obtain larger surge resistivity by a method wherein MnO and Ci2O3 only of auxiliary raw material are uniformly dispersed into ZnO in advance separately from other auxiliary component. CONSTITUTION:A first mixed material, which is formed by weighing MnO and Co2O3 in the ratio of 97.8mol%, 0.5mol% and 0.5mol%, and by mixing and pulverizing them by a ball mill, and Mn and Co are solidified into ZnO. Into the obtained first mixed raw material, Bi2O3 and Sb2O3 of other auxiliary composition raw materials of 0.5 and 0.7mol% are added, they are wet mixed and pulverized by a ball mill, and the second mixed raw material is obtained. To be more precise, as Mn and Co are uniformly dispersed and solidified in ZnO in the stage of the first mixed raw material, the irregularity of surge resistivity can be reduced by deforming and calcinating the second mixed raw material which is obtained by mixing and pulverizing other auxiliary component. As a result, a varistor on which local current concentration is hardly generated can be obtained in a stable manner.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing a varistor containing ZnO as a main component, and in particular, to a method for uniformly dispersing Mn and Co oxides as subsidiary component raw materials. The present invention relates to a method for manufacturing a ZnO varistor that enables the following.

[Conventional technology]

A varistor is known as a voltage nonlinear resistor element whose resistance value changes nonlinearly depending on an applied voltage, and is widely used as a surge absorbing element, a voltage stabilizing element, and the like.

Varistors used for the above applications include disk-type varistors, laminated-type varistors, and the like.

A disc-type varistor has electrodes formed on both sides of a plate-shaped varistor element made of a material that exhibits voltage non-linearity, a lead wire connected to the electrode, and a part from which the lead wire is drawn out. The entire structure is covered with exterior resin except for. In addition, a multilayer varistor has a plurality of internal electrodes arranged inside a sintered body having varistor properties, which overlap with each other via varistor layers, and these internal electrodes are drawn out alternately on both opposing end faces of the sintered body. has been
The sintered body has a structure in which external electrodes electrically connected to the internal electrodes are formed on opposite end surfaces of the sintered body.

By the way, Z
Those mainly composed of nO are widely used. In addition, during manufacturing, ZnO is used to improve varistor characteristics.
A sintered body exhibiting varistor properties is obtained by adding an oxide such as Bi, co, Mn or sb as a subcomponent raw material, mixing and pulverizing the mixture, and firing a molded body of the obtained mixed raw material. was.

[Technical problem to be solved by the invention] However,
In the varistor using the sintered body manufactured by the above manufacturing method, it was not possible to obtain the desired surge resistance.

For example, in a varistor used for a 200μ power supply, 1
When a surge current of about 500A is applied for 8 x 20μ seconds, the rate of change of V+@A (indicates the voltage applied to both ends of the varistor when a current of 1mA flows through the varistor) is ±
It is required that it be within 10%. However, with varistors obtained by conventional manufacturing methods, it has been difficult to stably obtain surge resistance of 150 OA or more.

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

[Means for solving technical problems]

As a result of various studies on the above-mentioned problems, the inventors of the present application discovered that Z
The cause of variation in surge resistance in nO varistors is due to non-uniformity in the dispersion state of oxides such as Bi, Co, Mn, or sb, which are auxiliary component materials, relative to ZnO, which is the main component material, during the manufacturing process. Headings, especially Zn
We discovered that Mn and Co, which are solid-dissolved in O, are important subcomponent raw materials for improving nonlinearity and surge resistance, and that if they are not uniformly dissolved in ZnO, variations in surge resistance occur. The present invention has been accomplished.

That is, the present invention provides at least M as a subcomponent raw material.
A method for manufacturing a ZnO varistor containing nO and CozOz, which is characterized by comprising the following steps.

In the present invention, first, ZnO as a main component raw material is mixed with MnO, Co, and O as subcomponent raw materials, pulverized, and further heat-treated to form a first powder in which Mn and Co are dissolved as a solid solution in ZnO. A mixed raw material is obtained.

Next, MnO and Co2O3 are added to the first mixed raw material.
The subcomponent raw materials other than the above are mixed and pulverized to obtain a second mixed raw material.

Thereafter, the second mixed raw material is molded to obtain a molded body, and this molded body is fired to obtain a sintered body having varistor characteristics.

[Effect]

Among the various subcomponent raw materials, Mn and Co, which play an important role in improving voltage nonlinearity and surge resistance, are mixed with ZnO in advance and are pulverized and heat treated.
In the mixed raw material, Mn and Co are uniformly dissolved and dispersed in ZnO.

Therefore, since Mn and Co are uniformly dispersed, local current concentration is prevented, thereby reducing variations in surge resistance.

That is, the present invention uses MnO and Co, O, which are subcomponent raw materials that greatly affect surge resistance and voltage nonlinearity.
, is unique in that it is uniformly dispersed in advance in ZnO separately from the other one-component raw materials. Note that as other subcomponent raw materials, various conventionally used subcomponent raw materials such as oxides such as Bi and sb can be used.

〔Effect of the invention〕

According to the present invention, Mn and Co are added at the stage of the first mixed raw material.
is uniformly dispersed and dissolved in ZnO, so by molding and firing the second mixed raw material obtained by mixing and pulverizing other subcomponents, there is little variation in surge resistance and local Therefore, it is possible to stably obtain a varistor in which current concentration is unlikely to occur.

In addition, since local current concentration can be prevented, the surge resistance and voltage nonlinearity of the varistor can also be improved.
For example, a surge withstand capacity of 1500 A or more can be stably obtained.

[Explanation of Examples]

Examples of the method for manufacturing a varistor of the present invention will be described below.

First, ZnO, which is the main component raw material, and MnO, Co, and O, which are subcomponent raw materials, are weighed so that the ratio is 97.8 mol%20.5 mol%20.5 mol%, and they are placed in a ball mill. The mixture was wetted and pulverized for 10 hours to obtain a mixed pulverized product. This mixed pulverized product was heat treated at a temperature of 700°C or higher for 2 hours, and
A first mixed material in which n and Co were dissolved in ZnO was obtained.

Bi, which is another subcomponent raw material, is added to the obtained first mixed raw material.
t'Os and 5bzOs were added at 0.5 mol% and 0.7%, respectively, and wet mixed for 10 hours using a ball mill and ground, thereby obtaining a second mixed raw material.

The obtained second mixed raw material was dehydrated and then calcined at a temperature of 760°C.

2% by weight of vinyl acetate and 1 polyvinyl alcohol were added as a binder to the calcined second mixed raw material.

5% by weight was added and wet-mixed again using a ball mill for 10 hours to obtain a granulated powder.

Next, the obtained granulated powder was heated to a diameter of 8 m+a and a thickness of 1°2.
Compression molded with a press to a size of N, molding density a, 8
A disc-shaped molded body of g/cIII was obtained.

The obtained molded body was heat-treated at a temperature of T'OO''C for 1 hour to scatter the binder, and then heated at 1100°C to 1
It was fired at a temperature of 400°C for 2 hours to obtain a sintered body, that is, a varistor element.

A paste made of Ag was applied to both surfaces of the obtained varistor element and baked at a temperature of 650° C. for 10 minutes to form electrodes.

Leads were connected to each of the obtained picture electrodes by soldering. Furthermore, the entire part except the part where the leads were pulled out was coated with epoxy resin to obtain a disk-shaped varistor (Sample No. 1 to be described later).

For the obtained varistor of sample number 1, the varistor voltage per unit thickness (V1mA/sJ and voltage nonlinearity coefficient (α) and 8× of 1000, 1500, and 2000A)
A surge current of 20 μsec was applied, and the rate of change (%) of the varistor characteristics was measured after 1 hour. The results are shown in Tables 1 and 2 below.

Note that the voltage nonlinearity coefficient α is 1/log(V+-A/
V. , +*A).

In addition, as a comparative example, a disk-shaped varistor (sample number 2 ~11) were prepared. Furthermore, using a conventional varistor manufacturing method, that is, a varistor element manufactured by simultaneously adding all the subcomponent raw materials to the main component raw material ZnO, a disk-type varistor (sample number 1
2) was prepared.

The disk-type varistors of the comparative example and conventional example were also measured in the same manner as the disk-type varistor of the example, and the results are also shown in Tables 1 and 2. In addition, the first
* in the table and Table 2 indicates that it is a comparative example and a conventional example.

(Hereinafter, margin) Table 2 (Hereinafter, margin) Table 2 As is clear from Tables 1 and 2, the disc type varistor of the example (sample number 1) is different from the comparative example (sample number 2).
~11) and the conventional example (sample number 12) disc type varistor, the initial value of the varistor voltage is smaller,
It can be seen that the voltage nonlinearity coefficient also increases.

Also, looking at the rate of change in varistor voltage after applying a surge current, the disc type varistor of the example has a smaller rate of change in varistor voltage after applying a surge current, within ±10% of the initial value. I understand.

In particular, even after applying a surge current of 2000 A, the rate of change in the varistor voltage was -6.5%, indicating that the surge resistance of the disk type varistor was also improved.

In addition, although the above-mentioned example shows the method applied to the manufacturing method of a disk-shaped varistor, the manufacturing method of the present invention is not limited to the method of manufacturing a varistor of this structure. For example, the present invention can be applied to a method of manufacturing a disc-shaped varistor having any planar shape such as a square plate shape.

In addition, it can be applied not only to the manufacture of disc-type varistors, but also to the production of multilayer varistors in which internal electrodes and varistor layers are alternately laminated, and it goes without saying that the same effects as in the case of disc-type varistors can be obtained. do not have.

Claims (1)

[Claims] At least MnO and Co_2O_3 as subcomponents.
A method for manufacturing a ZnO varistor comprising: ZnO as a main component raw material, MnO and Co as subcomponent raw materials.
Mixed with _2O_3, crushed and heat treated, Mn in ZnO
and a step of obtaining a first mixed raw material in which Co is dissolved as a solid solution; A step of mixing subcomponent raw materials other than MnO and Co_2O_3 with the first mixed raw material and pulverizing the mixture to obtain a second mixed raw material, A method for manufacturing a varistor, comprising: forming the second mixed raw material to obtain a molded body; and firing the molded body.