JPH02241003A - Manufacturing method of zinc oxide type varistor - Google Patents

Abstract

PURPOSE:To prevent the generation of defects in the inside of a sintered body, and increase the capability of surge energy absorption by a method wherein material powder containing zinc oxide as main component and metal powder of an amount larger than or equal to a specified value is mixed, ground and granulated to obtain granular powder, and the powder is subjected to compression, molding, and baking after the water content of the powder is adjusted at a specified value. CONSTITUTION:Material powder containing zinc oxide as main component and containg at least metal powder, metal carbide, or metal nitride of 0.3mol% or more is mixed, grinded, and granulated to obtain granular powder. The powder is subjected to compres sion, molding and baking after the water content is adjusted at 0.8-2.0wt.%. For exam ple, as to the above metal powder and the like, the following metal powder, carbide, or nitride are used; Si, Co, Zn, Mg, Al, Ti, Cr, Mn, Ni, Ce, Sn, Sb, Ge, Pr, etc. The molded body is calcinated at 800-1000 deg.C in the air: in order to form a high resistance layer 2, paste type side surface agent is spread on the side surface of the calcinated body, and baked at 1100-1200 deg.C in the air. After a glass stoved layer 3 is formed on the side surface of the sintered body 1 in the above manner, aluminum spraying electrodes are formed by polishing both of the end surfaces.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for manufacturing a zinc oxide varistor, and more particularly to a method for manufacturing a zinc oxide varistor that has few internal defects and has good surge absorption ability.

Conventional technology Zinc oxide varistors have excellent voltage non-linearity and current absorption ability, and are widely used in surge absorbers, voltage stabilizing elements, lightning arresters, etc.

The conventional manufacturing method for zinc oxide type varistors involves grinding metal oxides such as bismuth oxide, cobalt oxide, manganese oxide or antimony oxide, chromium oxide, nickel oxide, and aluminum oxide into a predetermined particle size using a ball mill, vibration mill, etc. After that, it is thoroughly mixed with the main raw material, zinc oxide, using a disper mill or the like to obtain a slurry. In this grinding/mixing process, in order to improve the moldability of the granulated powder, a binder such as polyvinyl alcohol is added to the raw material powder at a ratio of 1.0%.
Add approximately % by weight. Additionally, a dispersant such as a surfactant is also added to ensure that the additives are sufficiently dispersed in the zinc oxide. The raw material slurry obtained as described above is dried and granulated into particles of about 60 to 100 μm using a spray dryer or the like to obtain granulated powder. Next, this granulated powder is compressed and molded into a predetermined shape, and if necessary, SOO~1
After calcining at 0oO℃ and removing the binder, 10oO
The zinc oxide type varistor is produced by firing at a temperature of ~1300°C.

In recent years, with the aim of improving the voltage nonlinearity and surge absorption ability of zinc oxide type varistors, some additives have been added in place of the conventional oxide form, as disclosed in Japanese Patent Application Laid-open No. 61-242004.
Manufacturing methods have been devised in which additions are made in the form of metal powders, metal carbides or metal nitrides.

Problems to be Solved by the Invention However, in the above-mentioned conventional manufacturing method for zinc oxide type varistors, the metal powder, metal carbide, or metal nitride in the additives is rapidly oxidized during the firing process, resulting in defects inside the sintered body. This has led to problems such as cracks occurring in the central part of the element, and the ability to absorb surge energy being reduced.

The present invention is intended to solve such problems.Is there a problem with the occurrence of defects inside the sintered body? The purpose of this is to significantly improve the surge energy absorption ability by preventing this.

Means for Solving the Problem In order to solve this problem, the method for manufacturing a zinc oxide type varistor of the present invention includes zinc oxide as a main component, and at least 0.3 mol% or more of metal powder, metal carbide, or metal nitride. It is characterized in that the raw material powders contained are mixed, crushed and granulated to obtain granulated powder, and after adjusting the moisture content of the granulated powder to a moisture content of 08 to 2.0% by weight, it is compressed, molded and fired.

Effect: According to the method for producing a zinc oxide type varistor of the present invention, by controlling the water content of the granulated powder to 0.a to 2.0% by weight,
By increasing the bonding force between particles of granulated powder during the molding process and improving the uniformity of the molded body, defects inside the sintered body are reduced, making it possible to obtain a zinc oxide type varistor with high surge energy absorption capacity. can.

EXAMPLES Hereinafter, the manufacturing method of the present invention and the zinc oxide type varistor obtained thereby will be explained in detail based on examples.

(Example 1) First, Bi20! was added to the ZnO(7) powder based on the total amount. l
O, 5 mol%, Co20s O,s -F: Le%
*Mn0zO, 5 moh%.

5b20X, % to 0%, 0r2050.5 mo/L [,
NiOO, 5 mol%, metal silicon (Si) or metal cobalt (Go) powder, 0.1-1 nil%, 0.3
mole%, 1.0-1 nil%, s, o mole q6.10
．． Ten types of raw materials containing 0 moh% were prepared. Pure water is added to this raw material, thoroughly mixed and pulverized in a ball mill, then polyvinyl alcohol and a dispersant are added at 1.0% by weight each based on the solid content, and thoroughly mixed in a disper mill to form a raw material slurry. Created. This raw material slurry was dried in a spray dryer at a temperature of 200 to 250°C to obtain granulated powder. A predetermined amount of pure water was added to this granulated powder, and the water content was adjusted using a V-shaped mixer. After adjusting the moisture content, the mixture was passed through a 32 mesh sieve to cut coarse powder.

The moisture content-adjusted granulated powder obtained in this way was heated to 40φ (1
11111) and 40 t-).

The compact was then calcined in air at a temperature of 800-1000'C. In order to form a high resistance layer on the side surface of this calcined body, a paste-like side surface agent consisting of B1203.5b2o5+5i02 and an organic binder was applied for 6 to 5 o1s.
It was coated y/d and fired in air at a temperature of 1100 to 1200°C. A glass paste consisting of crystallized glass and an organic binder was baked on the side surfaces of the sintered body thus obtained at a temperature of 400 to 400°C, and then both end faces were polished and sprayed aluminum electrodes were provided. .

FIG. 1 is a sectional view of the zinc oxide type varistor obtained as described above. In FIG. 1, 1 is a sintered body mainly composed of ZnO, 2 is a side high resistance layer, 3 is a glass baked layer,
4 is an electrode formed by spraying aluminum.

FIG. 2 is a diagram showing the relationship between the amount of metal silicon added and the rate of occurrence of internal defects in zinc oxide type varistors manufactured by the manufacturing method of the present invention and the reference example. The moisture content was measured using an infrared moisture meter. As an example of the present invention, a sample was prepared with the moisture content adjusted to 1.6% by weight, and as a reference example, a sample using spray granulated powder (water content 0.6% by weight) without moisture content adjustment was created. I checked the rate. Here, internal defects were measured by ultrasonic flaw detection, and those with a diameter of 1.5 mm or more were judged as defective.

Figure 2 shows that when the water content is not adjusted, the internal defect occurrence rate is approximately 1% when the amount of metal silicon added is about 0.1 mol%, but when the amount of silicon metal added is 0.3 mol% or more, the internal defect occurrence rate is about 1%. It can be seen that the defective defect rate has reached 10% or more. Therefore,
Internal defects are a problem that only occurs when metallic silicon is added in an amount of 0.3 mol % or more. On the other hand, in the raw material powder whose water content was adjusted to 1.6% by weight, the amount of metal silicon added was 10.6%.
It can be seen that even in the case of 0 mol %, the internal defect occurrence rate is very low at about 2%.

FIG. 3 is a diagram showing the relationship between the water content and internal defect occurrence rate of zinc oxide type varistors manufactured by the manufacturing method of the present invention and the reference example. Here, the raw material used was metal powder to which 360 mol% of silicon was added.

Figure 3 shows that when the moisture content is 0.5% by weight, the internal defect rate is extremely high at 26.6%, but when the moisture content of the granulated powder is 0.
．． By adjusting the content to 8% by weight or more, the internal defect occurrence rate can be suppressed to 6% or less.

In addition, if the water content exceeds 2.0% by weight, the granulated powder will tend to aggregate and coarse powder will increase, so the water content should be 0.8 to 2.
．． 0% by weight is desirable.

Next, the energy absorption capacity (energy withstand capacity) of the zinc oxide type varistor element obtained as described above was investigated.

Here, the energy tolerance was evaluated by applying a rectangular wave current of 21118 in the same direction 20 times at 2 minute intervals, and by stepping up the current value to evaluate the limit performance. The results are shown in Table 1 below.

Table 1> From Table 1 above, when the water content is 0.5% by weight and the amount of metallic silicon or metallic cobalt is 0.3 mol% or more,
The internal defect rate is high and the energy withstand capacity is low, whereas the sample with a water content of 1.6% by weight has a low internal defect rate and an energy capacity of 26% regardless of the type of metal added.
It can be seen that the number of people is extremely high, ranging from 0 to 360 people.

(Example 2) Next, as a second example, 0.5 mol% of Bi203 and s mol% of CO2O3O were added to the ZnO powder based on the total amount.

MnO20.5 mol%, 5b20s1.0 mol%, 0r
2050.6 mol%, NiOO, 5 mol%, silicon carbide (SiO) or silicon nitride (Sin) powder, 0.1 mol%.

0.3 mol%, 1.0 mol% 13.0 mol%, 10.
Ten types of raw materials containing 0 mol% were prepared. This raw material f
: A zinc oxide type varistor was prepared by processing in exactly the same manner as in Example 1, and the internal defect rate and surge resistance test were conducted. The results are shown in Table 2 below. O water is a reference example and is outside the scope of the present invention.

Number one table> * is a reference example and is outside the scope of the present invention.

From Table 2, the amount of silicon carbide and silicon nitride added is 0.3 mol%.
As mentioned above, when the water content is 0.5% by weight (reference example), the internal defect occurrence rate is high and the energy tolerance is low, whereas the internal defect occurrence rate of the sample adjusted to a water content of t-1.5% by weight. is 2.0% or less, and it can be seen that the energy withstand capacity is also improved to 260 μm or more.

In this example, Si and Co were used as the metal powders, and S10. Although 5i5N4 was used as the metal nitride, additives that improve various properties of the zinc oxide type varistor, such as Zn, Mg, Mu/, Ti, Or, and Mn are also included.

Even if metal powders such as Ni, Ge, Sn, Sb, Co, and Pr, carbides, and nitrides are used, the effects of the present invention are not affected.

Effects of the Invention As described above, according to the present invention, the water content 'f of the granulated zinc oxide varistor powder containing 0.3 mol % or more of metal powder, metal carbide, or metal nitride in total is 0.8-2. By adjusting it to 0% by weight, the bonding force between the granulated powder during molding increases, and by suppressing the occurrence of defects inside the sintered body, it is possible to manufacture a zinc oxide type varistor with high surge resistance. .

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of a zinc oxide type varistor obtained by the manufacturing method of the present invention, and Figures 2 and 3 are internal defect incidence rates of zinc oxide type varistors obtained by the manufacturing method of the present invention and reference example. FIG. 1... Sintered body, 2... Side high resistance layer,
3...Glass baking layer, 4...Electrode. Name of agent: Patent attorney Shigetaka Awano and 1 other person m1
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Claims (3)

[Claims] (1) Main component is zinc oxide, with at least 0 metal powder
．． Mixing, crushing, and granulating raw material powders containing 3 mol% or more to obtain granulated powder, adjusting the moisture content of the granulated powder to 0.8 to 2.0% by weight, and then compressing, molding, and baking. A method for manufacturing a zinc oxide type varistor characterized by: (2) Mixing, crushing, and granulating raw material powder containing zinc oxide as the main component and at least 0.3 mol% or more of metal carbide;
Obtain granulated powder, and reduce the moisture content of the granulated powder to 0.8 to 2.0% by weight.
A method for manufacturing a zinc oxide type varistor, which comprises adjusting the zinc oxide type varistor to the desired temperature, and then compressing, molding, and firing the zinc oxide type varistor. (3) Mixing, crushing, and granulating raw material powder containing zinc oxide as the main component and at least 0.3 mol% or more of metal nitride,
Obtain granulated powder, and reduce the moisture content of the granulated powder to 0.8 to 2.0% by weight.
A method for manufacturing a zinc oxide type varistor, which comprises adjusting the zinc oxide type varistor to the desired temperature, and then compressing, molding, and firing the zinc oxide type varistor.