JPH0686322B2 - Zinc oxide raw material for voltage nonlinear resistors - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a zinc oxide raw material that can be suitably used for a voltage nonlinear resistor containing zinc oxide as a main component.

(Prior Art) Conventionally, zinc oxide (ZnO) was the main component and Bi ₂ O ₃ , Sb ₂ O ₃ , SiO
It is widely known that resistors containing a small amount of additives such as ₂ , Co ₂ O ₃ and MnO ₂ as an auxiliary component exhibit excellent voltage non-linearity. It is used.

It is known that in this voltage nonlinear resistor containing zinc oxide as a main component, it is preferable to reduce internal defects in the fired body in order to improve the discharge withstand amount. As described in JP-A-56-115503, foreign matter is removed by passing the slurry through a sieve before granulation.

(Problems to be Solved by the Invention) However, in the above-described conventional method of reducing internal defects, sufficient effects cannot be obtained yet because internal defects cannot be sufficiently reduced. There is a problem that the discharge withstand capability cannot be improved sufficiently. In particular, the occurrence of internal defects may increase depending on the properties of the zinc oxide raw material, which accounts for about 90 wt% of the device.

An object of the present invention is to solve the above-mentioned problems and to provide a zinc oxide raw material which can reduce internal defects and improve the uniformity of the element to obtain a voltage non-linear resistor having a good discharge withstand capability. It is a thing.

(Means for Solving the Problems) The zinc oxide raw material for a voltage nonlinear resistor of the present invention has an average particle size.
7 between the particle size of 0.1 to 2.0 μm and 1/2 to 2 times the average particle size
It is characterized by having a particle size distribution of 0 wt% or more, acicular crystals of 20 wt% or less, and an SiC content of 0.001 wt% or less as an impurity.

(Operation) In the above-mentioned structure, if a voltage nonlinear resistor is manufactured by using zinc oxide particles having a predetermined particle size and particle size distribution, a predetermined crystal morphology, a predetermined impurity, especially a reduced amount of SiC, internal defects will be generated. It can be sufficiently reduced and the uniformity of the element is improved,
It has been found that a voltage non-linear resistor having a good discharge withstand capability can be obtained.

Zinc oxide is generally produced by oxidizing zinc, but the crystal system is mainly a hexagonal system, and its form is a lump or a plate. However, depending on the manufacturing conditions, acicular crystals are also formed and mixed in the zinc oxide raw material.

In the present invention, the average particle size of zinc oxide is limited to 0.1 to 2.0 μm, more preferably 0.3 to 0.8 μm, and the particle size distribution is 1 / average of the average particle size.
2 to 2 times is limited to 70 wt% or more, more preferably 80 wt% or more, because the zinc oxide particles are uniformly grown in the firing process of the zinc oxide device, and the internal defects such as voids are reduced. . Further, limiting the needle-like crystals to 20 wt% or less, more preferably 10 wt% or less is advantageous for preventing abnormal particle growth of zinc oxide in the firing process, which causes deterioration of the characteristics of the voltage nonlinear resistor. Because there is. When this zinc oxide grows abnormally, the uniformity of the device is greatly deteriorated and the discharge withstand capability is also decreased.

On the other hand, the content of SiC as an impurity in zinc oxide was 0.001 wt%
The more preferable limit is 0.00001 wt% or less.
This is because internal defects such as voids in the element can be sufficiently reduced, and a good discharge withstand capability can be obtained. The reason for this is that if SiC is mixed in zinc oxide, it decomposes during the firing process and the SiC decomposition gas forms closed pores at about 1000 ° C or higher in that process, causing internal defects. To be done. In addition, bismuth oxide was added as an additive to the zinc oxide element.
Converted to Bi ₂ O ₃ 0.5 wt% or more (not less than 2 wt%),
Converting antimony oxide to Sb ₂ O ₃ 0.3 wt% or more (1.5 wt%
% Or more), and if praseodymium oxide is contained in 0.01 wt% or more in terms of Pr ₆ O ₁₁ (more than 0.05 wt%), the decomposition reaction of SiC is promoted and the sintering reaction of the element is also promoted. Therefore, the decomposed gas easily forms closed pores, which adversely affects the characteristics of the zinc oxide element. In addition, when the bismuth oxide as the additive is 2 wt% or more, the antimony oxide is 1.5 wt% or more, and the praseodymium oxide is 0.05 wt% or more, the above-described decomposition reaction of SiC is further promoted, so that the zinc oxide element is obtained. The properties are significantly adversely affected.
Therefore, it is extremely important to control the content of SiC in the zinc oxide raw material to a predetermined amount or less in order to manufacture a zinc oxide element having excellent and uniform characteristics.

(Example) FIG. 1 is a view showing an example of a conventionally known apparatus for producing a zinc oxide raw material. In FIG. 1, 1 is metallic zinc as a raw material, 2 is a melting furnace having a melting tank made of SiC for melting metallic zinc 1, 3 is a retort furnace for carrying out an oxidation reaction, 4 is a cooling duct, 5 Is a collection tank, 6 is an exhaust fan, 7
Is a bag filter. In the apparatus having the above-mentioned configuration, when the metallic zinc 1 melted in the melting furnace 2 is put into the retort furnace 3 and heated to about 1100 to 1400 ° C from the outside, the zinc in the retort furnace 3 reaches the boiling point (about 900 ° C), It is ejected from the evaporation port and burned and oxidized in the oxidation chamber 3a in the retort furnace 3. The high temperature zinc oxide obtained by combustion and oxidation in the oxidation chamber 3a is sucked by the suction force of the exhaust fan 6, passes through the cooling duct 4 and is cooled, and then most of it is in the collection tank 5. In addition, a part of them can be obtained as zinc oxide in the bag filter 7.

In the apparatus shown in FIG. 1, in order to make the obtained zinc oxide raw material have a predetermined particle size and particle size distribution and a predetermined crystal form, the evaporation amount of metal zinc, the air amount by the exhaust fan, the temperature of the oxidation chamber and the high temperature It is necessary to control the cooling rate of zinc oxide.
In particular, cooling zinc oxide at high temperature is necessary to reduce needle crystals.
It is necessary to gradually cool to 400 ° C. In addition, in order to reduce the SiC content in the zinc oxide raw material, (1) the material of the melting furnace 2 should be changed from the current SiC material to another material such as Al ₂ O ₃ material. Is SiC with high thermal shock resistance
(Since SiC is mixed in the melting furnace 2 due to chemical erosion, mechanical impact, etc., and flows into the retort furnace 3), (2) SiC melting furnace 2 is used. When using, a weir 8 is provided on the surface of the molten metal in the melting furnace 2 so that the sludge 9 does not enter the retort furnace 3, (3)
Similarly, when using the SiC melting furnace 2, use the ZnO raw material obtained in the most downstream tank of the collection tank 5 that is usually configured by arranging several stages of tanks in series. Impurities such as SiC are mostly collected in the most upstream tank, and the least downstream tank is the most important).

In order to obtain a voltage nonlinear resistor whose main component is a zinc oxide raw material having a predetermined average particle size and particle size distribution, crystal morphology, and SiC content obtained by the above-mentioned method, first, a predetermined particle size of 0.1 to 2.0 μm is used. Zinc oxide raw material adjusted to and fine bismuth oxide and cobalt oxide adjusted to a predetermined particle size of 2 μm or less,
A predetermined amount of an additive made of manganese oxide, antimony oxide, chromium oxide, preferably amorphous silicon oxide, nickel oxide, boron oxide, silver oxide or the like is mixed. In this case, silver nitrate or boric acid may be used instead of silver oxide or boron oxide. Bismuth borosilicate glass containing silver is preferably used. Also, instead of the above additives, 2μ
You may use praseodymium oxide, cobalt oxide, bismuth oxide, manganese oxide, chromium oxide etc. which were adjusted to the predetermined particle size of m or less. Here, as the additive raw material, it is preferable to use fine powder of 2 μm or less, preferably 0.5 μm or less, so as to be sintered at a low temperature. At this time, a predetermined amount of a polyvinyl alcohol aqueous solution and a predetermined amount of an aluminum nitrate solution as an aluminum oxide source are added to these raw material powders to obtain a mixture.

Next, vacuum degassing is preferably performed at a vacuum degree of 200 mmHg or less to obtain a mixed sludge. The water content of the mixed slurry is 30-35wt%
The viscosity of the mixed slurry is preferably 100 ± 50 cp. Next, the obtained mixed sludge is supplied to a spray dryer to have an average particle size of 50 to 150 μm, preferably 80 to 120 μm.
And the water content is 0.5 to 2.0 wt%, more preferably 0.9 to 1.5 wt
Granulate% granulated powder. Next, the obtained granulated powder is molded into a predetermined shape under a molding pressure of 800 to 7000 kg / cm ^{2 in} a molding step. The molding may be carried out not only by ordinary compression molding but also by hydrostatic molding or the like.

Then, the molded body is heated at a temperature rising / falling rate of 100 ° C / hr or less to 800-1
Preliminary firing is performed under conditions of 000 ° C. and holding time of 1 to 5 hours.
In addition, the temperature of the molded body should be kept at 100 ° C / hr or less before calcination.
It is preferable to remove the binder and the like by scattering at 400 to 600 ° C. for a holding time of 1 to 10 hours.

Next, an insulating coating layer is formed on the side surface of the calcined body that has been calcined.
In the present _{invention, Bi 2 O 3, Sb 2} O 3, ZnO, ethyl cellulose as an organic binder to a predetermined amount of SiO ₂ or the like, butyl carbitol,
A mixture paste for insulation coating containing n-butyl acetate, etc.
Apply to the side of the calcined body to a thickness of 60-300 μm. next,
This is main-baked under the conditions of a temperature raising / lowering rate of 20 to 60 ° C./hr, 1000 to 1300 ° C., preferably 1050-1250 ° C. for 3 to 7 hours.
In addition, a glass paste obtained by adding ethyl cellulose, butyl carbitol, n-butyl acetate, etc. as an organic binder to glass powder is applied on the above-mentioned insulating coating layer to a thickness of 100 to 300 μm, and the temperature rising / falling rate is 50 to 50 ° C. in air. 200 ° C / hr, 400-800
It is preferable to form a glass layer by heat-treating at a temperature of 0.5 ° C. and a holding time of 0.5 to 2 hours.

After that, both end surfaces of the obtained voltage non-linear resistor are covered with SiC, Al ₂ O.
_3. Polishing is carried out with water, preferably oil, as a polishing liquid with a polishing agent corresponding to # 400 to 2000 such as diamond. next,
After cleaning the polished surface, an electrode made of, for example, aluminum is provided by thermal spraying on both polished surfaces to obtain a voltage non-linear resistor.

Hereinafter, the results of actually measuring various characteristics of the voltage linear resistor within and outside the range of the present invention will be described.

According to the method described above _{Example, Co 3 O 4, MnO 2} , Cr 2 O 3, NiO, and SiO ₂ each 0.1 to 2.0 _{mol%, Al (NO 3) 3} · 9H 2 O 0.005 mol%, borosilicate containing silver Bismuth acid glass 0.1wt%, Bi ₂
From a raw material consisting of ZnO having 4.5 wt% of O ₃ , 4.5 wt% of Sb ₂ O ₃ , and the average particle size, particle size distribution, needle crystal ratio and SiC content shown in Table 1, diameter 47 mm, thickness is molded into the shape of 20 mm, after sintering the varistor voltage (V ₁ m _a) first 200V / mm
The voltage non-linear resistors of the present invention tests No. 1 to 9 and the comparative example tests No. 1 to 5 shown in the table were prepared.

With respect to the prepared resistors of the present invention example and the comparative example, the defect rate of the fired body (%), the switching surge discharge withstand breakdown rate (%), the lightning surge discharge withstand breakdown rate (%) and the varistor voltage variation were measured. did. The results are shown in Table 1. Here, the fired body defect occurrence rate is 0.
It was calculated as the ratio of resistors having a defect of 5 mm or more.
Switching surge discharge withstand voltage destruction rate is 1200ms, 1300A current for 2ms
The current waveform was calculated as the ratio of those that were destroyed after being repeatedly applied 20 times. Lightning surge discharge withstand destruction rate is 120KA, 14
The current of 0 KA was repeatedly applied twice with a current waveform of 4/10 μs, and then it was determined as the ratio of the breakdown. As shown in FIG. 2 (a), the variation in varistor voltage was measured by cutting and polishing the central portion of the element 11 to prepare a sample with a thickness of a = 2 mm, and then measuring point 12 shown in FIG. 2 (b). In all of the above, as shown in Fig. 2 (c), the electrode 13 is applied to the bottom surface and the surface is
Measured varistor voltage (V ₁ m _{A /} mm) in the probe 14 of 1 mm, was evaluated Searching for the variation.

The SiC content is obtained by dissolving the raw material with acid, alkali, etc.,
After filtration and washing, the insoluble residue was determined by a method of quantifying by fluorescent X-ray and X-ray diffraction. The proportion of needle-like crystals was determined by observation with a scanning electron microscope (SEM).

From the results of Table 1, the present invention test Nos. 1 to 9 using the zinc oxide raw material having a predetermined average particle diameter and particle size distribution, a predetermined needle crystal ratio, and a SiC content reduced to a predetermined value or less are all In that respect, it is understood that various characteristics are better than those of Comparative Example Test Nos. 1 to 5, which do not satisfy the requirements of the present invention.

Although the bismuth oxide-based varistor is described in the above embodiment, the same applies to the praseodymium-based varistor in which bismuth oxide is replaced with praseodymium oxide. Although the method for producing zinc oxide is described as the method of oxidizing metallic zinc, the same applies to the zinc oxide raw material obtained by the method of thermal decomposition of basic zinc carbonate.

(Effect of the invention) As is clear from the above description, according to the zinc oxide raw material of the present invention having a predetermined average particle diameter and a predetermined particle size distribution and satisfying a predetermined needle crystal and a predetermined SiC content, By manufacturing a voltage nonlinear resistor using, it is possible to reduce internal defects, improve element uniformity, and obtain a voltage nonlinear resistor having good electrical characteristics.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of an apparatus for producing a zinc oxide raw material according to the present invention, and FIGS. 2 (a) to 2 (c) are diagrams for explaining a method of measuring variations in varistor voltage. 1 ... Metallic zinc, 2 ... Melting furnace 3 ... Retort furnace, 3a ... Oxidizing chamber 4 ... Cooling duct, 5 ... Collection tank 6 ... Blower, 7 ... Bag filter

Claims (1)

[Claims] 1. A particle size having an average particle size of 0.1 to 2.0 μm and a particle size distribution of 70 wt% or more between 1/2 to 2 times the average particle size, 20% by weight or less of needle crystals, and impurities. Si as
A zinc oxide raw material for a voltage non-linear resistor, which has a C content of 0.001 wt% or less.