JPH0510804B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field of the Invention] The present invention relates to a method for manufacturing a voltage nonlinear resistor with excellent electrical characteristics. [Technical Background of the Invention] A voltage nonlinear resistor (hereinafter referred to as an element) is generally called a varistor, and its excellent nonlinear voltage -
Taking advantage of its current characteristics, it is widely used in lightning arresters and surge absorbers for the purpose of voltage stabilization or surge absorption. A typical example is the recently developed zinc oxide varistor. The main component is zinc oxide, to which a small amount of oxides such as bismuth, antimony, cobalt, manganese, chromium, etc. are added, mixed, granulated, molded, and then fired at high temperature in air to form a sintered body. It is constructed by attaching electrodes. Its non-linear resistance properties are very good, and the sintered body consists of grain boundary layers formed by zinc oxide particles and additives surrounding them. It is believed that this is due to the interface between [Problems with Background Art] By the way, the following problems arise when using these zinc oxide-based varistors in power surge arresters. In recent years, in order to reduce the construction costs of power transmission and substation facilities, there has been a demand for ultra-high transmission voltages and lower insulation protection levels.
Efforts are continuing to (1) improve nonlinear characteristics and (2) extend life at high charge rates. Specific measures to address these issues include (a) changing the sintering temperature and sintering pattern, (b) changing the amount of additives added, (c) adding new additives, and (d) particularly improving the life characteristics. Therefore, methods such as adding glass containing boron oxide have been adopted. However, in the methods (a) to (d), when one of the nonlinear characteristics or the life characteristics is improved, the other tends to deteriorate, making it difficult to improve both characteristics at the same time. In order to simultaneously improve nonlinear characteristics and lifetime characteristics, recent research has attempted to add oxides such as B ₂ O ₃ , Ag ₂ O, and SiO ₂ to raw materials. When these oxides are added, devices with improved nonlinear characteristics and lifetime characteristics can be obtained in some cases, but there is a problem in that the lifetime characteristics tend to vary between manufacturing rods, that is, between devices. Such variations in lifespan have been a very serious problem for stable industrial production of lightning arrester elements. [Object of the Invention] The present invention was made in view of the above-mentioned needs, and it is an object of the present invention to provide a method for manufacturing a voltage nonlinear resistor that has stable life characteristics and good nonlinear characteristics. [Summary of the Invention] In order to achieve the above object, the present invention includes ZnO as a main component and at least Bi ₂ O ₃ and as subcomponents.
In a method for manufacturing a voltage nonlinear resistor comprising the steps of mixing raw materials obtained by adding Sb ₂ O ₃ , molding, and sintering, in the mixing step, at least boron, which has been adjusted in advance, is The present invention provides a method for manufacturing a voltage nonlinear resistor, which comprises mixing the raw materials with an aqueous solution in which a compound and a silver compound are dissolved. By manufacturing an element using this manufacturing method, trace amounts of boron and silver can be uniformly dispersed among other components, making it possible to obtain an element with small variations in life characteristics and good nonlinear characteristics. . [Embodiments of the Invention] Examples of the present invention will be described in detail below. The composition of the device according to the present invention is that the main component, ZnO, is 99.7%
~86.9%, subcomponent _{Bi2O3 0.1} ~3.0 mol%,
Contains 0.05 to _3.0 mol% of _Sb2O3 , 0.05 to 2.0 mol% of _Co2O3 , 0.05 to 2.0 mol% of MnO, 0.05 to 3.0 mol% of NiO, and 0.0005 _{to 0.1} mol% of _Al2O3 . A suitable composition is based on B and Ag in an amount of 0.002 to 0.1% by weight. In addition, other subcomponents may be added for the purpose of improving other properties. To manufacture a device with such a configuration, first, zinc oxide (ZnO) powder, bismuth oxide (Bi ₂ O ₃ ), cobalt oxide (Co ₂ O ₃ ), manganese oxide (MnO), and antimony oxide (Sb ₂ O ₃ ), nickel oxide (NiO)
The powders were weighed, water, a dispersant, a binder, and a lubricant were added to these raw powders, and the mixture was placed in a mixing device. On the other hand, add H ₃ BO ₃ (boric acid) as a boron compound to water and AgNO ₃ (silver nitrate) as a silver compound.
was dissolved to prepare an aqueous solution, this aqueous solution was added to the mixture in the mixing device, and Al ₂ O ₃ was further added and mixed for a predetermined time. The resulting mixture slurry is granulated using a spray dryer to give an average particle size of, for example, 120 microns, and the resulting granulated powder is press-molded to give particles with a diameter of 50 microns.
It was molded into a disk with a thickness of 30 mm. In order to remove the dispersant, binder and lubricant added from the obtained molded body in advance, it was fired in air at 500°C, and then plate fired at 1020°C. A previously prepared slurry for forming a high resistance layer was applied to the obtained calcined body using a spray gun, and the calcined body was fired at a temperature of 1200° C. in an air atmosphere. Both sides of the sintered element thus obtained were polished in parallel to a thickness of 20 mm, and then electrodes were formed by spraying aluminum to obtain an element. The characteristic measurement results of elements 1 to 13 of this example thus obtained are shown in Table 1 together with conventional examples A and B and comparative examples 14 and 15.

【table】

[Table] Here, the nonlinear characteristics are expressed as V _1KA /V _1nA and were determined using the following formula. V _1KA /V _1nA = V (voltage when 1KA current is applied) / V (voltage when 1mA current is applied) Furthermore, the life characteristics (ΔV _1nA /V _1nA ) are determined at a temperature of 120℃,
Assume that electricity is applied for 200 hours at a charging rate of 85% and calculated using the following formula. ΔV _1nA /V _1nA =V _1nA (after 200 hours) - V _1nA (initial) / V _1nA (initial) x 100 In Table 1, the glass frit of Conventional Example A uses glass containing boron oxide. Conventional Example B is an example in which boron, silver, and silicon are added in the form of water-insoluble oxides, such as B ₂ O ₃ , Ag ₂ O, and SiO ₂ . Examples 1 to 13 are based on the amounts of subcomponents added to ZnO and H ₃ BO ₃ in the aqueous solution mixed with the raw materials.
The amount of AgNO ₃ was changed respectively. In Comparative Examples 14 and 15, only either H ₃ BO ₃ or AgNO ₃ was added. As shown in Table 1, conventional example A in which the glass component is added with glass frit has a life characteristic (ΔV _1nA /
V _1nA ) is relatively good, but indirect characteristics (V _1KA /V _1nA ) are poor, and B ₂ O ₃ +Ag ₂ O + SiO ₂
In conventional example B, in which oxide was added in the form of an oxide,
Although the nonlinear characteristics (V _1KA /V _1nA ) are good, the life characteristics (ΔV _1nA /V _1nA ) are not necessarily satisfactory. On the other hand, it can be seen that in Examples 1 to 13 of the present invention, nonlinear resistors with excellent nonlinearity characteristics and life characteristics were obtained. On the other hand, as in Comparative Examples 14 and 15
When either H ₃ BO ₃ or AgNO ₃ is applied, the life characteristics deteriorate slightly. Figure 1 shows Sample 10 of Conventional Example B, in which a boron compound and a silver compound were added together with silica in the raw material form of B ₂ O ₃ +Ag ₂ O + SiO ₂ , and Conventional Example 1, in which they were added in the raw material form of H ₃ BO ₃ +AgNO ₃ . The results of testing the variation in life characteristics for each are shown below. As mentioned above, the sample conditions were a temperature of 120°C,
Electricity will be charged for 200 hours at a charging rate of 85%. As shown in FIG. 1, it can be seen that Example 1 exhibits good life characteristics with little variation among samples and all samples being stable. On the other hand, in conventional example B, 2 out of 10 samples (No.
3 and 7) exhibited life characteristics comparable to those of this example, but the remaining eight had a large rate of change in ΔV _1nA /V _1nA and also had large variations. i.e. B ₂ O ₃
It was found that when it is added in the form of an oxide raw material, such as +Ag ₂ O + SiO ₂ , the defective rate increases, making it undesirable for use in manufacturing sites where stable production is desired. Next, the effect will be explained. Although the direct cause of the stable life characteristics of the device according to the embodiment of the present invention is not clear, the following can be roughly considered. Past research has shown that in the composition systems of elements whose main component is ZnO, the life characteristics are often improved by adding components that form a glass phase. However, as shown in Conventional Examples A and B, there are various problems such as deterioration of non-linear characteristics and deterioration of life characteristics or large variations depending on the form of raw materials added, so it is impossible to satisfy both non-linear characteristics and life characteristics. The reality is that this has not been achieved. This is thought to be largely due to the fact that the total amount of components that form the glass phase, which has an effect on life characteristics, is extremely small, at most 0.1 wt%. That is, since the glass phase forming component added is in an extremely small amount, it is difficult to uniformly disperse it in the raw materials in the mixing step. Therefore, an element in which the glass phase-forming components are dispersed relatively uniformly has good life characteristics, but an element in which the glass phase forming components are dispersed unevenly has poor life characteristics, resulting in variations in the life characteristics within the element. The present invention focuses on this problem of dispersibility, and eliminates the addition of B ₂ O ₃ and Ag ₂ O, which are glass phase forming components, in the form of oxides with poor dispersion, and instead uses water-soluble H ₃ BO. ₃ and AgNO ₃ are used. By mixing an aqueous solution containing H ₃ BO ₃ and AgNO ₃ with the raw material, boron and silver are almost uniformly dispersed in the raw material. Note that the raw materials added in the form of H ₃ BO ₃ and AgNO ₃ are separated and oxidized during the calcination process, and become B ₂ O ₃ ,
It is thought to be in the form of Ag ₂ O. [Effects of the Invention] As explained above, according to the present invention, a nonlinear resistor having excellent nonlinear characteristics and life characteristics can be obtained by making an aqueous solution of a boron compound and a silver compound and mixing them with raw materials.

[Brief explanation of drawings]

The figure is a diagram showing the distribution of lifetime characteristics for each element according to an embodiment of the present invention.

Claims (1)

[Claims] 1 ZnO, which is the main component, contains at least
In a method for manufacturing a voltage nonlinear resistor comprising the steps of mixing raw materials obtained by adding Bi ₂ O ₃ and Sb ₂ O ₃ , molding, and sintering, in the mixing step, adjustment is performed in advance. A method for manufacturing a voltage nonlinear resistor, comprising mixing the prepared aqueous solution in which at least a boron compound and a silver compound are dissolved with the raw materials.