JPS625613A - Manufacture of voltage non-linear resistor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is directed to the manufacture of a voltage non-linear resistor which is mainly made of zinc oxide and has a high resistance layer on the side surface of a sintered body which itself has voltage non-linearity. It is about the method.

BACKGROUND OF THE INVENTION Voltage nonlinear resistance elements are generally called varistors and are widely used for voltage stabilization and surge absorption.

The current (I)-voltage (2) characteristic is generally expressed approximately by the following equation. I=(V/C)" where C: quantity corresponding to the resistance value α: voltage non-linear index For convenience, the characteristics of the varistor are expressed by the terminal voltage at a constant current and the index α.

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 this has the advantage of being inexpensive, the voltage nonlinearity index α is as small as 3 to γ, so even if it is used for voltage stabilization, surge absorption, etc., the results are not very satisfactory. Therefore, it has been strongly desired to put into practical use a varistor with a large voltage nonlinearity index α.

In order to meet these demands, varistors containing zinc oxide as a main component have been developed and put into practical use in recent years. This zinc oxide varistor is made by adding a small amount of bismuth oxide, lead oxide, barylam oxide, etc. to zinc oxide, mixing it uniformly, molding it, and sintering it in air at a temperature within the range of SOO to 1 soot. It is obtained by forming electrodes on a sintered body.

In this case, the voltage nonlinearity is due to a grain boundary layer mainly composed of additives surrounding sintered fine particles mainly composed of zinc oxide, and a voltage nonlinearity index α value of 60 or more is obtained. It is being Its applications are extremely wide ranging from low voltage, small current for electronic equipment to high voltage, large current for power transmission and distribution and power equipment.

Although the zinc oxide varistor has many advantages as mentioned above, there are problems that must be solved because of its high performance. One of these is when an abnormally high voltage is applied to a zinc oxide varistor, creeping discharge may occur on the side surface of the varistor element, causing a significant decrease in resistance and an increase in leakage current.

In order to prevent such characteristic deterioration, attempts have been made to form an inorganic insulating layer on the side surfaces of the varistor element to protect the side surfaces (Japanese Patent Publication No. 53-21516).
Publication No.). In this method, the side surface Vc Bi of the varistor molded body
2O5+ 5IO2, 5b2O. A mixture paste is applied, and an inorganic insulating layer is formed on the side surface of the molded body at the same time as the molded body is fired. FIG. 2 shows its cross-sectional view. 4 is a sintered body whose main component is zinc oxide, 5 is Bi2O3, 5i02, 5
A high-resistance layer is formed by applying a b2O3 mixture paste and firing, and 6 is an electrode made of Al or the like formed on both end faces of the sintered body 40.

Problems to be Solved by the Invention However, such conventional methods have the following problems. That is, since a mixture paste is applied, the coating thickness tends to vary, which results in variations in the peak value of the current that can be applied to the varistor element until creeping discharge occurs (this is called the discharge withstand capacity). Furthermore, since the shrinkage rate during firing of the varistor body and the shrinkage rate of the mixture paste coating film are different, in order to obtain a uniform film thickness, the varistor molded body is pre-fired and shrunk in advance, and then The process was complicated, such as applying a mixture paste, which was a factor in high costs.

The present invention is intended to solve these problems, and aims to provide a varistor element that has a high discharge withstand capacity, has small variations in resistance, and is low in cost.

Means for Solving the Problem In order to solve this problem, the present invention provides bismuth oxide (Bi2O5) on the side surface of a sintered body whose main component is zinc oxide.
, silicon oxide (Si02), antimony oxide (Sb2O
A high-resistance layer is formed by spraying a mixture with at least one of s) by a plasma spraying method.

Function: With this method, a high-resistance layer is formed directly on the side surface of the sintered body, resulting in a uniform film thickness, improved discharge resistance, and less variation. Furthermore, the steps of pre-baking the molded body and drying the coating paste, which were necessary in the conventional method, are no longer necessary, resulting in fewer man-hours and lower costs.

Embodiment FIG. 1 is a cross-sectional view of a voltage nonlinear resistor (varistor) according to an embodiment of the present invention, in which 1 is a sintered body of a varistor whose main component is zinc oxide, and 2 is a varistor formed by plasma spraying. 3 is a metallicon electrode of A/.

First, 0 Bi2O3 was added to the ZnO powder based on the total amount.
, 5 mol%, Co2O3 0.5 mol/L/%,
0.6 mol% MnO2, 1.0 mol% 5b2o5, 0.5 mol% Cr2O5, 0.5 mol% 5i02.
5. -F-/I/% and Mu12o3 were added at a ratio of 0.005 molti and mixed thoroughly. This was molded into 40 pieces in diameter and 4 degrees thick, and fired in air at 1250°C for 6 hours.

Next, oxide powder shown in Table 1 below was prepared and sprayed onto the side surface of the sintered body by plasma spraying to form a high resistance layer of oxide. Next, both end surfaces of the sintered body are polished, and A
7! A metallicon electrode was formed.

Note that the plasma spraying method is a method in which an oxide is melted at a high temperature using an electric arc, and at the same time is blown away using a high-pressure inert gas to adhere to the object and form a film. The thermal spraying conditions in this example were 60~so KW, the thermal spraying distance was 10 holes, and rainbow gas was used as the inert gas.

Table 1 also shows the characteristics of the obtained samples.

In the table, the discharge withstand capacity is determined by applying an impact current with a waveform of 4×10 microseconds twice and increasing the current value step-up until creeping discharge occurs, and indicates the maximum current value that does not cause creeping discharge. For comparison, the case of the conventional oxide paste application method is also shown.

As is clear from Table 1, it can be seen that the method of the present invention improves the discharge withstand capacity of the varistor and at the same time reduces its dispersion.

(Left below) Note that the composition of the sintered body is of course not limited to the above, and the composition of the oxide forming the high resistance layer is not limited to the above examples. be.

Effects of the Invention As described above, according to the present invention, the side surface of the zinc oxide varistor sintered body K B 12O3 and 5io2.5k12O5
(By plasma spraying an oxide powder consisting of at least one of D, a high resistance layer is formed, the discharge withstand capacity is improved, there is little variation, the cost is low, and it is suitable for lightning arresters. As an element, its practical value is great.

[Brief explanation of drawings]

Figure 1 shows a voltage nonlinear resistor (
FIG. 2 is a cross-sectional view of a conventional example. 1... Zinc oxide sintered body, 2... High resistance layer formed by plasma spraying, 3... Electrode.

Claims (1)

[Claims] Bismuth oxide (Bi_2O_3) and silicon oxide (SiO_2) are added to the side surface of a sintered body whose main component is zinc oxide, which contains additive components such that the sintered body itself has voltage nonlinearity.
, spraying a mixture with at least one kind of antimony oxide (Sb_2O_3) by a plasma spraying method,
A method for manufacturing a voltage nonlinear resistor, comprising forming a high resistance layer.