JPH03257902A - Manufacture of voltage nonlinear resistor - Google Patents

Abstract

PURPOSE:To obtain a voltage nonlinear resistor whose element uniformity and electric characteristics are improved, by pulverizing metal oxide to be equal to or smaller than specified grain size, and mixing the obtained impalpable powder with zinc oxide in a specified manner. CONSTITUTION:In a manufacturing method of a voltage nonlinear resistor wherein metal oxide like bismuth oxide is added to material whose main component is zinc oxide, and mixed and backed, the mixture of metal oxide is pulverized to be equal to or smaller than specified grain size. The obtained mixture after pulverization is mixed together with zinc oxide, binder, and dispersant at a temperature of 40 deg.C or lower for a specified time by an attritor using zirconia balls. Then granulation, molding, and baking are performed. Since the pulverized mixture, zinc oxide, binder, and dispersant are mixed at a temperature of 40 deg.C or lower for a specified time by the attritor using zirconia balls, the mixing and dispersing of zinc oxide and metal oxide are improved, the contamination from media is avoided, and the gelation of slurry is prevented. Thereby the uniformity of an element can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing a voltage nonlinear resistor containing zinc oxide as a main component.

(Conventional technology) Conventionally, zinc oxide (ZnO) is the main component, and Biz0
3. PrJ++, 5b2o2.5io2. CO2
Resistors containing small amounts of additives such as 0a and MnL as subcomponents are widely known to exhibit excellent voltage nonlinearity, and are used in lightning arresters and the like by taking advantage of this property.

To manufacture this voltage nonlinear resistor whose main component is zinc oxide, the various metal oxides mentioned above are added to the raw material whose main component is zinc oxide, and the mixture is mixed using a disper mill or an attritor. , granulation, molding, and firing.

(Problem to be solved by the invention) However, when mixing using the above-mentioned disper mill, the mixing may be insufficient due to the mechanism of the device, and as a result, the elements after firing are uneven and the electrical characteristics are deteriorated. There was a problem.

In addition, when using an attritor, additive raw materials and Zn
When mixing O raw materials, if the particle size of the additive raw materials is too large, mixing and dispersion will be insufficient, resulting in a problem that the fired device will be non-uniform and its electrical properties will deteriorate. Furthermore, when steatite balls are used as the grinding media, contamination of the element raw material increases, and if there is no temperature control, slurry or gelation occurs, and in either case there is a problem that the electrical characteristics of the element deteriorate.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for manufacturing a voltage nonlinear resistor that can solve the above-mentioned problems, achieve element uniformity, and obtain good electrical characteristics.

(Means for Solving the Problems) The method for manufacturing a voltage nonlinear resistor of the present invention involves adding a metal oxide such as bismuth oxide to a raw material whose main component is zinc oxide, mixing it, and firing it. In a method for manufacturing a non-linear resistor, a mixture of metal oxides is pulverized to a predetermined particle size or less, and the resulting pulverized mixture is mixed with zinc oxide, a binder,
After mixing with a dispersant in an attritor using zirconia balls at a temperature of 40°C or less for a predetermined time, granulation, molding,
It is characterized by being fired.

(Function) In the above configuration, the metal oxide is finely pulverized to a predetermined particle size or less, preferably an average particle size of 5 μm or less, more preferably 3 μm or less, and the difference in particle size from the particle size of the zinc oxide raw material, which accounts for the majority, is reduced. By reducing the size, the zinc oxide and metal oxide can be mixed and dispersed well, and as a result, the uniformity of the device can be improved and good electrical characteristics can be obtained. In particular, mixing using an attritor requires pretreatment to finely pulverize the metal oxide.

In addition, since the finely ground mixture, zinc oxide, binder, and dispersant are mixed in an attritor using zirconia balls at a temperature of 40°C or less for a predetermined period of time, the mixing and dispersion of zinc oxide and metal oxide is better. At the same time, contamination from the media is eliminated, gelation of the slurry can be prevented, the uniformity of the device is improved, and even better electrical characteristics can be obtained.

Here, the time for mixing is preferably 1 to 10 hours,
More preferably, it is 2 to 5 hours. As a binder, polyvinyl alcohol, hydroxypropyl cellulose,
Polyethylene glycol, carboxymethyl cellulose, ethyl cellulose, etc. are used. As a dispersant,
Tetradecylamine acetate, polycarboxylic acid type polymer aqueous solution, etc. are used. Further, as the zirconia balls as the media, zirconia stabilized with magnesium oxide (MgO) or calcium oxide (Cab), etc. can also be used, but it is preferable to use zirconia stabilized with yttrium oxide (Y2O2). Also, these M
Zirconia balls manufactured by mixing zirconia powders stabilized with gO, Cab, and Y20a are advantageous in terms of cost and properties such as strength, and are therefore preferable. Further, the mixing temperature is 40° C. or lower, preferably 35° C. or lower to prevent slurry gelation.

(Example) To obtain a voltage nonlinear resistor whose main component is zinc oxide,
First, a zinc oxide raw material adjusted to a predetermined particle size of 0.1 to 3 μm, and a fine powder of bismuth oxide, cobalt oxide, manganese oxide, and antimony oxide adjusted to a particle size of less than a predetermined particle size, preferably less than 5 μm, and more preferably less than 3 μm. A predetermined amount of an additive consisting of chromium oxide, preferably amorphous silicon oxide, nickel oxide, boron oxide, silver oxide, etc., is mixed with a binder and a dispersant in an attritor. In addition,
In this case, silver nitrate or boric acid may be used instead of silver oxide or boron oxide. Preferably, bismuth borosilicate glass containing silver is used.

For mixing in the attritor, zirconia balls made of the material mentioned above are used as the media, and an agitator arm (stirring rod) is used.
It is also preferable to use the above-mentioned stabilized zirconia material, and to use an organic resin (preferably nylon resin) for the lining of the tank, since contamination will be extremely reduced. Furthermore, by controlling the slurry temperature so as not to exceed 40°C, gelation of the slurry can be prevented, and the zinc oxide and metal oxide can be well dispersed and mixed, which is preferable in terms of uniform mixing and mixing efficiency.

Next, deaeration is performed under reduced pressure, preferably at a vacuum level of 200 mmHg or less, to obtain a mixed slurry. Here, the water content of the mixed slurry is 3
0 to 35 wt%, and the viscosity of the mixed slurry is 10
It is preferable to set it to 0±50 cp. Next, the obtained mixed slurry was fed to a spray dryer to have an average particle size of 50 to 150 μm.
, preferably 80 to 120 μm, and a moisture content of 0.5 to 2
．． 0 wt%, more preferably 0.9-1.5 wt%
The granulated powder is granulated. Next, the obtained granulated powder is molded into a predetermined shape under a molding pressure of 800 to 7000 kg/a [12] in a molding step. Molding may be carried out not only by ordinary compression molding but also by isostatic pressing.

Then, the molded body is pre-fired under conditions of a heating/cooling rate of 100° C./hr or less, a temperature of 800° C. to 1000° C., and a holding time of 1 to 5 hours. In addition, before calcining, the molded body is heated at a temperature increase/decrease rate of 1.
400-600″C1 holding time 1- at 00℃/hr or less
It is preferable to scatter and remove the binder etc. in 10 hours.

Next, an insulating coating layer is formed on the side surface of the calcined body.

In the present invention, Bi2O3,5b20z, ZnO,S
An insulating coating mixture paste prepared by adding organic binders such as ethyl cellulose, butyl calpitol, n-butyl acetate, etc. to a predetermined amount of iO2, etc. is applied to the side surface of the calcined body to a thickness of 60 to 300 μm. Next, this temperature increase/decrease rate is 20-6
0°C/hr, 1000~1300″C preferably 10
Main firing is performed at 50 to 1250°C for 13 to 7 hours.

A glass paste prepared by adding ethyl cellulose, butyl calpitol, n-butyl acetate, etc. as an organic binder to glass powder is applied to a thickness of 100 to 300 μm on the above-mentioned insulating coating layer, and the temperature is raised and cooled in air at a rate of 50 to 300 μm. 200℃/h
r It is preferable to form the glass layer by heat treatment at 400 to 800°C for a holding time of 0.5 to 5 hours.

After that, both end faces of the obtained voltage nonlinear resistor were bonded to SiC,
Polishing is performed with a polishing agent equivalent to #400 to #2000 such as Al2O3 or diamond using water, preferably oil, as the polishing liquid. Next, after cleaning the polished surfaces, electrodes made of aluminum or the like are provided on both polished end surfaces by, for example, thermal spraying to obtain a voltage nonlinear resistor.

In the above embodiments, a bismuth oxide varistor was described, but the same method can be applied to a praseodymium oxide varistor in which bismuth oxide is replaced with praseodymium oxide.

An actual example will be explained below.

EXAMPLE According to the method described above, Bi2O3, CO3O4, Mn
O2゜5b203. Cr2O5,Nio, SiO□
A metal oxide additive consisting of 0.1 to 2.0 mol% of each and 0.01 to 0.3 wt% of bismuth borosilicate glass containing silver is pulverized by a ball mill or ground as shown in Table 1. A mixture was obtained. The values in parentheses in Table 1 indicate the average particle size of the additive. Next, the obtained mixture and the zinc oxide raw material are mixed by the mixing method shown in Table 1 at the temperature shown in Table 1 using the cobblestones shown in Table 1, and then granulated, molded, and fired. , diameter 47 mm, thickness 22.5 mm
The present invention tests Nα1-7 and the comparative example tests Nα1-7 shown in Table 1 with a shape of varistor voltage (vIA) of 280 V/mm
A voltage nonlinear resistor of No. 5 was obtained. The mixing time using the attritor was 3 hours, and the binder was polyvinyl alcohol,
Tetradecylamine acetate was used as a dispersant.

The defect occurrence rate, voltage nonlinearity index α, limiting voltage ratio, and switching surge withstand breakdown rate of the fired bodies were measured for the obtained resistors of the inventive example and the comparative example, respectively. The results are shown in Table 1. Here, the defect occurrence rate of the fired body was determined as the percentage of resistors in which defects with a diameter of 0.5 mm or more were present by an ultrasonic flaw detection test. The voltage nonlinearity index α is α= (1#og
(Vl, A/V100μA)). The limiting voltage ratio is the varistor voltage ■4°.

It was calculated from the ratio of VIA and VIA. The opening/closing surge resistance breakdown rate is 8
00A, 100OA current with 2ms current value form 20
It was calculated as the percentage of those that were destroyed after repeated application.

From the results in Table 1, it can be seen that the present invention tests Nα1 to Nα7, in which the predetermined additive pulverization and predetermined mixing were carried out, are the comparative example tests Nα1 to Nα7.
It was found that it had better electrical characteristics compared to cLl~5. Moreover, among the examples of the present invention, Y2O is used as a cobblestone.
Those using balls made of tri-stabilized zirconia are
It was found that better electrical characteristics could be obtained than the others.

(Effects of the Invention) As is clear from the above explanation, according to the method for manufacturing a voltage nonlinear resistor of the present invention, a metal oxide is finely pulverized to a predetermined particle size or less, and the obtained finely pulverized powder is By mixing it with zinc oxide in the method described above, the uniformity of the element is improved, and as a result, a voltage nonlinear resistor with improved electrical characteristics can be obtained.

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Claims (1)

[Claims] 1. In a method for manufacturing a voltage nonlinear resistor obtained by adding, mixing, and firing a metal oxide such as bismuth oxide to a raw material whose main component is zinc oxide, the mixture of metal oxides is pulverized to a predetermined particle size or less. The resulting finely pulverized mixture is mixed with zinc oxide, a binder, and a dispersant in an attritor using zirconia balls at a temperature of 40°C or less for a predetermined time, and then granulated, molded, and fired. A method of manufacturing a voltage nonlinear resistor.