JPH05144611A - Manufacture of zno varistor - Google Patents

Abstract

PURPOSE:To provide a method for manufacturing a Zn varistor having stable high surge resistance and excellent load life characteristics in the varistor to be used as for protecting against a lightning surge or an abnormal voltage. CONSTITUTION:MmO2 powder 14 of a ZnO varistor element 13 is laid in a bottom of a baking vessel 11. In this case, 0.1g/cm<3> or more of MnO2 powder is filled in an inner volume of the vessel, sealed and baked. Thus, the varistor having stable high surge resistance and excellent load life can be manufactured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a varistor containing ZnO as a main component, and more particularly to a method for producing a ZnO varistor characterized by performing firing in a closed oxygen atmosphere.

[0002]

2. Description of the Related Art Recently, various ZnO varistors have been remarkably developed, and among them, ZnO containing Bi ₂ O ₃ is contained.
The varistor is recognized for its excellent voltage non-linearity and surge absorption, and is widely used as a ZnO varistor for protection against lightning surge and abnormal voltage.

Conventionally, there is a technique disclosed in Japanese Examined Patent Publication No. 56-3646 as a technique to meet such a demand. The technique disclosed in the above publication discloses ZnO containing Bi ₂ O _{3 in an amount} of 0.1
5 mol%, Co ₂ O ₃ 0.1-5 mol%, MnO ₂ 0.1-5 mol%, NiO 0.1-5 mol%, TiO
Bismuth borosilicate glass frit containing 0.1 to 5 mol% of ₂ and 5 to 30 wt% of Ag ₂ O is 0.01 to 0.
A ZnO varistor having excellent surge resistance and load life characteristics was manufactured by adding 25% by weight, mixing and pulverizing, and firing the mixed raw material compact in air at 1250 ° C.

[0004]

However, in the ZnO varistor manufactured by the conventional manufacturing method as described above, the oxygen concentration near the surface of the element is reduced by firing the molded element in air, Since the internal oxygen concentration varies, the surge withstand capability and the load life characteristic also vary.

The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide a method of manufacturing a ZnO varistor having stable high surge withstand capability and excellent load life characteristics.

[0006]

In order to achieve the above object, a method of manufacturing a ZnO varistor according to the present invention is a method in which manganese oxide powder is spread on the bottom of a firing container and sealed to form a molded element, or a manganese oxide powder is fired. It is characterized in that it is spread between the stacked elements and sealed and fired.

[0007]

According to the above manufacturing method, the manganese oxide powder spread in the lower part of the container or between the elements is heated to 53% during firing.
It decomposes into Mn ₂ O ₃ at 5 ° C. and MnO at 1080 ° C. and releases oxygen. Therefore, the oxygen atmosphere around the element in the sealed container, the oxygen concentration near the surface of the element does not decrease,
A sintered body having a uniform oxygen concentration distribution can be obtained.

Therefore, it is possible to obtain a ZnO varistor having a stable and high surge resistance and an excellent load life characteristic.

[0009]

Embodiments of the method of manufacturing a ZnO varistor according to the present invention will be described below in detail with reference to the drawings.

First, with respect to ZnO which is the main component, Bi ₂ O ₃ is 1.0 mol%, Co ₂ O ₃ is 0.5 mol%, MnO ₂ is 0.5 mol%, and NiO is 1 as auxiliary components. 0.0 mol%,
1.0 mol% of TiO ₂ was added, wet mixed in a pot mill, dehydrated, and then polyvinyl alcohol 5 was used as a binder.
Granulation was carried out by adding weight%. 1000 for the obtained granulated powder
Under a molding pressure of kg / cm ² , diameter 13 mm, thickness 1.3 m
It was compression molded into a size of m and fired at 1250 ° C. for 2 hours by the method shown in FIG. 1 or FIG. 2 to obtain a sintered body.

1 and 2 show the internal structure of a container during firing showing an embodiment of the present invention. In FIG. 1, 11 is a baking container, and 12 is a lid provided on the upper part of the baking container 11, which is made of a material such as MgO or Al ₂ O ₃ . 13 is a molded ZnO varistor element, and 14 is M
It is nO ₂ powder and is spread over the bottom of the baking container 11. Further, in FIG. 2, reference numeral 21 denotes a firing container, 22
Is a lid of the firing container 21, 23 is a molded ZnO varistor element, and 24 is MnO ₂ powder. The above is the same as the configuration of FIG. The difference from the configuration of FIG. 1 is that the MnO ₂ powder 25 is not spread on the bottom of the container but is spread between the ZnO varistor elements 23. When fired at 1250 ° C. in the above state, MnO ₂ powders 14,2
4 is thermally decomposed to release oxygen, so that the firing containers 11 and 21 become an oxygen atmosphere, and the ZnO varistor element 1
The decrease in oxygen concentration inside 3,23 is prevented.

ZnO varistor is prepared by forming electrodes having silver (Ag) as a main component on both surfaces of the fired body obtained as described above, soldering lead wires to the electrodes and coating with an epoxy resin. did. Table 1 shows the varistor voltage (V) per unit thickness of the ZnO varistor thus obtained.
_1mA / mm), surge withstand test, and load life characteristic test results. Here, the surge tolerance is 8 for a varistor.
/ 20μsec current (surge current) 1000A, 200
The change rate (ΔV _1mA ) of the varistor voltage when 0 A and 3000 A are applied is shown.

The load life characteristic means that the varistor has 12
90% of the varistor voltage in a 5 ° C constant temperature DC voltage
Change rate of varistor voltage (ΔV
_1mA ) Further, Example 1a described in (Table 1) is the evaluation result of the sample fired in the configuration shown in FIG.
Example 1b is the evaluation result of the sample fired with the configuration shown in FIG. In addition, as a conventional example, the evaluation results of a sample in which MnO ₂ powder is fired without being spread over the bottom of the container and between the elements are shown.

[0014]

[Table 1]

As is clear from the above (Table 1), the ZnO varistor obtained by the manufacturing method according to this embodiment has a smaller varistor voltage change rate (ΔV _1mA ) after the surge current is applied, as compared with the conventional example. It can be seen that the load life characteristics are also excellent. As described above, according to the present embodiment, the MnO ₂ powder is spread at the bottom of the firing container or between the elements, so that the MnO ₂ powder is thermally decomposed to release oxygen during firing to release oxygen in the container. ZnO, which has excellent surge withstand characteristics and excellent load life
You can get a barista.

The composition of the sintered body is B in this embodiment.
Although oxides of i, Co, Mn, Ni and Ti were used, P
The effect remains the same even if other oxides such as r, Ca, and Ba are used. Further, in this example, the case where manganese oxide to be put into the firing container is MnO ₂ is described, but in principle, manganese oxide having an oxidation number of Mn ₃ O ₄ or more and capable of releasing oxygen is theoretically used. It is clear that it has a similar effect.

[0017]

INDUSTRIAL APPLICABILITY As described above, according to the present invention, the manganese oxide powder is spread on the bottom of the baking container or between the varistor elements and baked, whereby ZnO excellent in stable high surge resistance and load life is provided. A varistor can be manufactured.

[Brief description of drawings]

FIG. 1 is an internal structure diagram of a container during firing in a first embodiment of the present invention.

FIG. 2 is an internal structure diagram of the container during firing in the first embodiment of the present invention.

[Explanation of symbols]

11 Baking container 12 Baking container lid 13 Varistor element 14 MnO ₂ powder 21 Baking container 22 Baking container lid 23 Varistor element 24 MnO ₂ powder

Claims (1)

[Claims] 1. ZnO as a main component and Bi as a secondary component₂
O₃, Co₂O₃, MnO ₂Add and mix metal oxides such as
Dry, granulate, and mold to obtain a molded body, and with this molded body
0.1 g / cm with respect to the internal volume of the baking container³More oxidation man
It is characterized by putting gun powder in a baking container and baking it in a closed manner.
A method for manufacturing a ZnO varistor.