JPS6019122B2 - Manufacturing method of voltage nonlinear resistor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a voltage nonlinear resistance element that is mainly made of zinc oxide and has a high resistance layer on the side surface of a crystal structure that itself has voltage nonlinearity. .

The purpose is to provide a device that is stable against humidity and impact current without impairing voltage nonlinearity, and to develop a manufacturing method that simplifies the coating process for moisture-proofing or creeping discharge prevention. It is about providing.

A voltage nonlinear resistance element is generally called a varistor, and is widely used for voltage stabilization, surge absorption, and the like.

The current (1)-voltage (V) characteristic is generally expressed approximately by the following equation. 1:〈Q〉Q However, C: Quantity equivalent to resistance value, Q: Voltage nonlinear index For convenience, the characteristics of the varistor are expressed by the terminal voltage at a constant current and the index Q.

As a typical example of such a varistor, a silicon carbide varistor that utilizes the voltage sensitivity of the contact resistance of silicon carbide SIC particles has been widely used.

Although these have the advantage of being inexpensive, they have a small voltage nonlinearity index Q of 3 to 7, so even when used for voltage stabilization, surge absorption, etc., the results are not very satisfactory. For this reason, it has been strongly desired to put into practical use a varistor with a large voltage nonlinearity index Q. In order to meet this demand, varistors whose main ingredient is zinc oxide have been developed in recent years.
It has been put into practical use.

This zinc oxide varistor is made by adding a small amount of bismuth oxide, lead oxide, barium oxide, etc. to zinc oxide, mixing it uniformly, molding it, and then freezing it in the air at a temperature in the range of 800 to 150,000 degrees Celsius. It is obtained by forming electrodes on a sintered body. The voltage nonlinearity is due to the grain boundary layer mainly composed of additives surrounding the sintered fine particles mainly composed of zinc oxide, and voltage nonlinearity index values of 50 or more were obtained. ing. This application is extremely wide ranging from low voltage and small current for electronic equipment to high voltage and large current for power transmission and distribution and power equipment. Zinc oxide varistor is
Although it has many advantages as mentioned above, there are still problems that must be solved due to its high performance.

One of these is that when used in humid conditions, the resistance value of the side surfaces of the varistor element decreases. i.e. 90%
If left in an atmosphere of moderate relative humidity, the resistance value will decrease and the voltage nonlinearity index Q will be significantly impaired. This tendency becomes particularly remarkable when current and voltage are applied in humid conditions. All such characteristic deterioration results in an increase in leakage current due to a decrease in the resistance value on the side surface of the varistor element. In order to prevent such deterioration of characteristics, attempts have been made to coat the side surfaces with epoxy resin or the like.

However, such moisture-proofing measures were not sufficiently effective because the adhesion between the sintered element body mainly composed of zinc oxide and the epoxy resin was not very good. Moreover, since the number of manufacturing steps is increased, there is a drawback that the manufacturing price becomes high. The present invention has been able to solve these drawbacks, and is capable of creating a voltage nonlinear resistance element with excellent temperature resistance by increasing the resistance of the side surface of a sintered element body mainly made of zinc oxide. We were able to obtain this product, and we were able to establish a method for its production.

Hereinafter, the manufacturing method and the voltage nonlinear resistance element obtained thereby will be described in detail based on Examples. First, add Bi20 to the total amount of Zn○ powder.
0.5 mol% of 3, 0.5 mol% of Co203, Mn0
0.5 mol% of 2, 1.0 mol% of SQ03, Cr20
3 was added at a ratio of 0.5 mol % and thoroughly mixed.

This was molded to a diameter of 4 mm and a thickness of 3 mm, and some of the samples were fired in air at 900 qC, and the remaining samples were fired for 2 hours in air at 1250 qC. Next, oxide powder having the composition shown in Table 1 was prepared and sprayed onto the side surface of each sintered body by plasma spraying to form a high resistance layer of oxide. Thereafter, the samples fired at 900 qC were fired again in air at 1250 oo for 2 hours. Next, both flat surfaces of each sintered body were polished, and aluminum sprayed electrodes were provided. In addition, for some samples baked only at 1250 oo, before forming a high-resistance layer by plasma spraying, both flat surfaces were polished and a sprayed aluminum electrode was provided, and then only the electrode part was covered with a mask. A high resistance layer of oxide was formed on the surface other than the electrode by plasma spraying. Figure 1 shows the cross-sectional structure of a sample with electrodes provided after plasma spraying and film formation, and Figure 2 shows the cross-sectional structure of a device with electrodes formed and a plasma sprayed film formed on all exposed parts other than the electrodes. This is what is shown.

In the figure, 1 is a sintered body mainly composed of Zn○, 2 is a high resistance layer formed by plasma spraying, and 3 and 4 are electrodes. Table 1 shows the properties of the samples obtained.

In the table, V and V are the voltages per unit thickness when currents of 1 μA and 1 mA are applied, respectively. Q is the voltage nonlinear index, and the current is 0.1 mA, l
Using the voltage value between the electrodes when mA is applied, it is determined by the relational expression between current and voltage shown above. Also, the voltage change rate △V. The mountain ^ indicates the change in voltage V, 1^ in the humidity charging test^. Here, the test conditions are an ambient temperature of 70
qo, the relative humidity was 95%, the applied voltage was 500 V DC, and the voltage application time was 500 hours. For comparison, Table 1 also shows the characteristics of the Akatsuki concretion without any protective film formed thereon.

Table 1 However, * indicates a comparative example ** is a unit of mole ※ As is clear from comparing the results in Table 1, the voltage V, m
Although the effect of forming the high resistance layer on the ^/ side and Q is not so obvious, the voltage V, the mountain A/yanagi and its rate of change △V, shi^ depend on the presence or absence of the high resistance layer. It's obvious what you're doing.

If the voltages Vim'yanagi are almost the same, then the voltages V,
It can be said that those with higher rA/skin are better as baristas. This is because the leakage current decreases when the same voltage is applied. Furthermore, it can be said that the smaller the rate of change △V, the better the characteristics. The reason for the difference in characteristics in such a small current castle of one peak A is that
It is assumed that this is because it depends on the resistance value of the lateral layer of the Akatsuki concretion.
To confirm, we measured the resistance on the side, and found that it was significantly higher than the resistance inside the Akatsuki body. It is thought that by forming a high resistance layer in such a necessary part, the leakage current will be reduced, the voltage V and the peak will be increased, and deterioration will be less likely to occur even in a humidity test. Also, characteristically, 125
After firing at 0o0, a high-resistance layer is formed only on the side surface part.After firing at 900℃, a high-resistance layer is formed on this pre-fired mold body, and then re-fired at 1250oo. A structure in which an oxide film is provided on the surface of all exposed parts of the twill body other than the electrode-applied part is superior in terms of characteristics.

The stability against humidity of the voltage non-linear resistor obtained by the method of the invention is more markedly observed by the boiling test.

Table 2 shows the rate of change △V, 1^ of V, peak^ of the voltage non-linear resistor according to the present invention, along with comparative examples. The sample numbers in the table correspond to those in Table 1. The boiling test was conducted by boiling various samples in pure water for 200 hours.

Table 2. However, as is clear from Table 2 of Comparative Examples, the device obtained by the method of the present invention shows little deterioration in characteristics.

This is because a delicate protective film is formed on the sides of the body, which prevents moisture absorption. By the way, in order to form a high resistance layer on the side surface, SiQ, SQ03, Bi
A method is known in which 203 is made into a paste together with an organic binder, applied to the side surface of a temporary body, and then baked.

This also has some improvement effect. Representative results are shown in Tables 1 and 2 (Sample Shame.17). The method of the present invention yields better results than that method. The elements that are stable against humidity as explained above are
They are extremely useful when used outdoors, such as in earth arresters for power transmission and distribution lines, but devices with high-resistance layers on their sides prevent creeping flash when large shock currents are applied. It is also very effective. Table 3 shows the impact current resistance of the device according to the method of the present invention, together with that of the comparative example.

Here, the impact current used a waveform of 4×10 microseconds, and was applied twice each. In the table, a 0 mark indicates that creeping flash did not occur, and an x mark indicates that creeping flash occurred. Table 3 However, * indicates a comparative example.As is clear from the table above, those coated with epoxy resin and those without surface treatment are 20kA and 50kA, respectively.
kA, whereas the device according to the invention can withstand impact currents several times these.

This effect is obtained because the high resistance layers formed along the sides confine the impact current to the central portion of the composite body. Next, we will show the effect of the calcination temperature when calcination is performed once after molding, a high resistance layer is formed by plasma spraying, and calcination is performed again.

Table 4 shows sample no. This figure shows the difference in electrical properties when the calcination temperature was changed for No. 5. From Table 4, it can be seen that a pseudo dawn temperature of 700 to 115,000 is good in terms of characteristics.

This is thought to be caused by the complete welding of the crystalline solids and the high-resistance layer of oxide formed by plasma spraying by re-firing. Therefore, the firing temperature after forming the high-resistance layer is preferably higher than the melting temperature of Bi203 in the additive, that is, higher than 80,000, and is also a temperature of 15°C at which the characteristics do not deteriorate due to evaporation of Bi203.
0000 or less is desirable. The reason why it is better to cover the surface of all parts of the sintered body with a high-resistance layer of oxide other than the electrode-applied part is that the influence of the atmosphere is better if there is no exposed part in the creeping part between the electrodes. It is thought that this is due to certain things.

The plasma spraying method is a method in which an oxide is melted at a high temperature (in an inert gas atmosphere) using an electric arc, and at the same time, it is blown away by a high pressure inert gas and attached to an object to form a film.

Argon gas or the like is usually used as the inert gas. The temperature of the plasma formed by melting can be raised from 1000q○ to a high temperature of 5000oo or more in some parts. The thickness of the film can be easily changed by changing the spraying time, and a film with a uniform thickness of several meters to several hundred meters can be easily formed. The present invention applies this unique plasma spraying technology to easily form a high-resistance layer on the side surface of a voltage nonlinear resistor, making it possible to easily create an element that is extremely stable against humidity and impact current. can be made.

In the examples, only elements with specific compositions have been described, but considering the principles and effects of the present invention, as long as the main component is Zn○ and the sintered silk body itself exhibits voltage nonlinearity, It is clear that it is effective for any composition.

As described in detail above, the present invention significantly improves the stability of the element against humidity and shock current by coating the side surfaces of the sintered Zn0 varistor with a high-resistance material, and it is possible to significantly improve the stability of the element against humidity and shock current. It is useful for application as a protection element.

[Brief explanation of the drawing]

1 and 2 show an example of the structure of a voltage nonlinear resistor according to the present invention. 1...Bran concretion mainly composed of Zn○, 2...
...High resistance layer, 3, 4... Electrode. Figure 1 Figure 2

Claims (1)

[Claims] 1. A high-resistance inorganic substance is coated on the side surface of a sintered body mainly composed of zinc oxide, which contains an additive component that causes the sintered body itself to have voltage nonlinearity, using a plasma spraying method. A method for manufacturing a voltage nonlinear resistor, which comprises thermal spraying to form a high resistance layer. 2 As high-resistance inorganic substances, MgO, Ml_2O_3,
In_2O_3, SiO_2, ZrO_2, Zn_7S
b_2O_1_2, Zn_2SiO_4, Zircon (Z
rO_2・SiO_2), cordierite (2MgO・2
Al_2O_3・5SiO_2), MgAl_2O_4
The method for manufacturing a voltage nonlinear resistor according to claim 1, characterized in that a mixture of two or more of these is used. 3. On the side surface of a shaped calcined body mainly composed of zinc oxide, which contains additive components such that the sintered body itself has voltage nonlinearity,
A method for manufacturing a voltage nonlinear resistor, which comprises spraying a high-resistance material using a plasma spraying method, and then firing the formed calcined body again to obtain a sintered body containing a high-resistance layer as a main component. . 4. A molded calcined body containing zinc oxide as a main component,
4. The method of manufacturing a voltage nonlinear resistor according to claim 3, wherein the voltage nonlinear resistor is obtained by calcining at a temperature within the range of 00 to 1150°C. 5 MgO, M as high-resistance inorganic substances
l_2O_3, In_2O_3, SiO_2, ZrO_
2, Zn_7Sb_2O_1_2, Zn_2SiO_4
, zircon (ZrO_2・SiO_2), cordierite (2MgO・2Al_2O_3・5SiO_2), Mg
4. The method for manufacturing a voltage nonlinear resistor according to claim 3, characterized in that Al_2O_4 or a mixture of two or more thereof is used. 6 After forming an electrode on a sintered body mainly composed of zinc oxide, which contains an additive component such that the sintered body itself has voltage nonlinearity, the surface of other parts of the sintered body other than the electrode part To,
A method for manufacturing a voltage nonlinear resistor, comprising spraying a high resistance inorganic material by a plasma spraying method to form a high resistance layer. 7 As high resistance inorganic substances, MgO, Ml_2O_3,
In_2O_3, SiO_2, ZrO_2, Zn_7S
b_2O_1_2, Zn_2SiO_4, Zircon (Z
rO_2・SiO_2), cordierite (2MgO・2
Al_2O_3・5SiO_2), MgAl_2O_4
7. The method of manufacturing a voltage nonlinear resistor according to claim 6, characterized in that a mixture of two or more of these is used.