JPH0782922B2 - Method for manufacturing voltage non-linear resistor - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to a method for producing a voltage nonlinear resistor containing zinc oxide as a main component, and in particular, in order to obtain a homogeneous sintered body, a raw material powder is dispersed. The present invention relates to a method for manufacturing a voltage non-linear resistor having an improved mixing process.

[Technical Background of the Invention] A voltage non-linear resistor is generally called a varistor, and by utilizing its excellent non-linear voltage-current characteristics, it is used as a lightning arrester or surge absorber for the purpose of voltage stabilization or surge absorption. Widely used. A typical example of such a varistor is a zinc oxide varistor developed in recent years. This zinc oxide varistor is mainly composed of zinc oxide,
A small amount of oxides of bismuth, antimony, cobalt, manganese, chromium, etc. are added to this, mixed granulation and molding, followed by high temperature firing in air, and electrodes are attached to the sintered body. Yes, it has very good non-linear resistance characteristics. The sintered body consists of a zinc oxide particle and a grain boundary layer formed by additives surrounding it, and it is thought that the excellent nonlinear resistance characteristics are due to the interface between this grain boundary layer and the zinc oxide particle. . In addition to this, it has many advantages such as the voltage-current characteristics can be adjusted to some extent.

Conventionally, during the manufacturing process of such a voltage nonlinear resistor containing zinc oxide as a main component, in the mixing process of dispersing and mixing the raw material powder, a ball mill, a vibration mill, an emulsifier, etc. are used,
A dispersant was added for dispersion and mixing.

[Problems of the Background Art] However, the voltage nonlinear resistor manufactured by the above-described mixing process has the following drawbacks.

That is, when mixed using a ball mill, a vibration mill, an emulsifier, etc., there is a limit to uniformly disperse the raw materials,
Therefore, the manufactured voltage non-linear resistor has a small hole called a pinhole with a diameter of 0.5 mm or less, a few major axes, and a few minor axes.
A large defect of about 0.5 mm often occurred. These voids and defects not only become the largest cause of lowering the discharge withstand voltage of the voltage non-linear resistor, but also lower the long-term reliability, which is a serious problem.

On the other hand, as shown in JP-A-58-188102, the raw material powder was put into a pulverizer together with a large number of small-diameter pulverizing media,
A method of uniformly dispersing the particles has been proposed, which makes it possible to prevent the generation of voids and defects and improve the discharge withstand voltage characteristics, but on the other hand, the following problems occur.

That is, since a large number of crushed media are used, the raw materials are contaminated due to wear of the media, impurities are mixed into the nonlinear resistor composition, and various electrical characteristics are excluded. One of such drawbacks is deterioration of life characteristics.
That is, a minute leakage current flows when a voltage is applied to the element, but when impurities are mixed, the increase of the leakage current with time is accelerated. Therefore, if such a non-linear resistor mixed with impurities is applied to a lightning arrester or the like, the heat generated by leakage current exceeds the heat dissipated by the element and the element temperature rises, which reduces the resistance of the element itself and further heat generation. Due to the synergistic vicious circle of acceleration, the heat will eventually run out of control. There is also a problem that the non-linear characteristic in the low current region is deteriorated due to the inclusion of impurities.

[Object of the Invention] The present invention has been proposed in order to solve the above-mentioned drawbacks of the prior art. An object of the present invention is to improve discharge withstand capability characteristics by using a grinding medium, and Manufactures voltage non-linear resistors that have good life characteristics and excellent non-linear characteristics in the low current region by preventing contamination of raw materials due to abrasion of grinding media and preventing impurities from mixing into the non-linear resistance composition. It is an object of the present invention to provide a method for manufacturing such a voltage non-linear resistor.

[Summary of the Invention] A method for manufacturing a voltage non-linear resistor according to the present invention is a rotor composed of a rotor having a rotor shaft formed on a rotary shaft in a mixing step of dispersing and mixing raw material powders, and a rotor similar to this rotor. A container for accommodating the rotor, the inner space of which is formed by an inner wall surface and the rotor shaft is extended from the center of the lid, and is inserted into a gap formed between the inner wall surface of the container and the rotor. And a crushing medium that drives the rotor shaft and rotates the rotor in the container to crush and disperse the raw material supplied to the container.

With such a structure, the discharge amount characteristic can be improved and the amount of the crushing media can be made minute, so that the contamination of the raw material can be prevented and the contamination of the nonlinear resistor composition with impurities can be eliminated. There is.

Also, the crushing media is made into a nearly spherical shape of 0.5 mm to 3.0 mmφ,
It is more effective to use zirconium oxide (ZrO ₂ ), steatite, zirconium silicate (ZrSiO ₄ ), or silicon dioxide (SiO ₂ ) as the main component of the media, and use water or a solvent in the mixing process. is there.

[Embodiment of the Invention] An embodiment of the method of manufacturing the voltage nonlinear resistor according to the present invention as described above will be specifically described.

The mixer used in this embodiment will be described with reference to FIG. Reference numeral 1 is a container in which the rotor 2 is stored. The rotor 2 is composed of a rotating body having an axis O as a rotating shaft, and a rotor shaft 2a is formed on the rotating shaft. On the other hand, container 1
Is a container in which an inner space having a shape similar to that of the rotor 2 is formed by an inner wall surface 1a, the thickness of which is omitted, and an annular lid in which a hole 1b for extending the rotor shaft 2a is formed in a central portion. It has 1c. A rotor shaft 2a is extended from the hole 1b in the container 1 to accommodate the rotor 2, so that a gap d is formed around the rotor 2 by the rotor 2 and the inner wall surface 1a. A crushing medium 3 made of zirconium silicate having a diameter of 1.5 mm is inserted in the gap d. Further, the slurry supply port 4 and the slurry take-out port 5 are formed in the container 1 so as to communicate with the gap d. In the present embodiment, the mixing step is performed by using the mixer having such a configuration, and by driving the rotor shaft 2a, the rotor 2 is rotated in the container 1 at a peripheral speed of about 12 m / s, and the slurry is not supplied from the slurry supply port 4. This is performed by supplying all the raw materials of the linear resistor composition. All the raw materials of the non-linear resistor composition to be supplied are weighed together with pure water, a dispersant and a binder and premixed, and this slurry is passed through the gap filled with the medium 3 by rotating the rotor 2. . The slurry is supplied from a slurry supply port 4 provided on the bottom surface of the container 1 of the mixer using a hydraulic pump or the like. At this time, it is necessary to appropriately select the number of rotations of the rotor, the diameter of the medium, the filling amount of the medium, the amount of the slurry passing through the gap, the number of times, etc. according to the purpose of use of the voltage nonlinear resistor to be manufactured. It is suitable that the size of 4 to 5 times the size of the medium.

The raw material slurry thus pulverized and dispersed is taken out from the slurry outlet 5 provided at the upper part of the container 1 of the mixer, spray-dried and molded, then fired, and post-treated such as electrode attachment (metallikon). Then, the voltage nonlinear resistor element is completed.

As described above, according to the present invention, by rotating the rotor at a high speed, the dispersion effect is enhanced and the grinding medium is present in the gap, so that the same effect as that of the conventional agitator can be obtained with respect to the grinding. Is excellent. Moreover, in the present invention, since the grinding media is inserted into the minute gap, the amount of the grinding media can be drastically reduced to about 1/100 of that of the conventional one, and the contamination of the raw material due to the abrasion of the media can be extremely reduced. , Non-linear characteristics and life characteristics are improved.

The improvement of the characteristics according to the present invention will be described more specifically based on the experimental results shown in FIGS.

FIG. 2 and FIG. 3 show the results of examining the leakage current ratio and the current-voltage characteristics of each device by manufacturing the device of 4.5 mmφ × 20 mmt by the conventional process and the process of the above-mentioned embodiment of the present invention. In each drawing, a solid line A shows characteristics of an element manufactured by a conventional method in which a large number of grinding media are used and an agitator is rotated to mix and disperse,
The solid line B shows the characteristics of the element manufactured according to one embodiment of the present invention as described above.

First, FIG. 2 shows the time variation of the resistance leakage current when a voltage is applied so that an alternating current of 1 mA is applied to the device at an ambient temperature of 120 ° C. Here, Irof is the initial value of the leakage current, and Ir is the leakage current after a certain period of time. It can be said that the smaller the leakage current ratio is, the more the increase in leakage current is suppressed and the better the life characteristic is. First, as shown by the solid line A,
In the device manufactured by the conventional method, the leakage current is remarkably increased and the life characteristics are poor. In contrast,
As shown by the solid line B, the element manufactured according to the present invention shows almost no increase in leakage current. Therefore, it is clear that the device manufactured according to the present invention does not cause thermal runaway due to leakage current and has excellent life characteristics.

Further, FIG. 3 shows current-voltage characteristics in a low current region by DC measurement, so-called non-linear characteristics,
The closer to 1.0, the better. In the figure, as indicated by the solid line A, the voltage ratio of the element manufactured by the conventional method is
As the current value decreases, it decreases steeply,
At 10 μA, it fell to almost 0.5. On the other hand, as shown by the solid line B, the voltage ratio of the device manufactured by the method of the present invention has a much gentler slope and maintains a considerably high value even at 10 μA. Therefore, it is apparent that the non-linear characteristic in the low current region of the device manufactured by the method of the present invention is significantly improved as compared with the conventional one.

As described above, according to the method of the present invention, it is possible to obtain a voltage nonlinear resistor having excellent life characteristics and nonlinear characteristics in a low current region and having extremely stable characteristics. Therefore, when the device manufactured according to the present invention is used for a power surge arrester or the like, very excellent reliability is guaranteed.

The present invention is not limited to the above embodiment,
For example, zirconium oxide, steatite, and silicon dioxide were each used as a grinding medium to manufacture an element, and the same experiment was carried out. As a result, the same characteristics were obtained. Further, the effect of the method of the present invention is not affected by the non-linear resistance composition or the calcination of the mixed raw material. Further, the shape of the mixer used in the present invention can be appropriately selected, and a sufficient effect can be obtained even when water or a solvent is not used in the mixing step.

[Effects of the Invention] As described above, according to the method for manufacturing a voltage non-linear resistor of the present invention, the crushing medium is inserted into a narrow gap, and the slurry of the raw material is passed through the crushing medium, whereby the discharge withstand characteristic is improved. It is possible to provide a highly reliable voltage non-linear resistor having improved life characteristics and excellent non-linear characteristics in a low current region.

[Brief description of drawings]

FIG. 1 is a schematic view showing a mixer used in an embodiment of the present invention, and FIG. 2 is a graph relatively showing life characteristics of each element manufactured by the conventional method and the method of the present invention. FIG. 3 is a graph relatively showing the non-linear characteristics of the respective devices manufactured by the conventional method and the method of the present invention. 1 ... Container, 1a ... Inner wall surface, 1b ... Hole, 1c ... Lid, 2 ... Rotor, 2a ... Rotor shaft, 3 ... Grinding media, 4 ... Slurry supply port, 5 ... Slurry outlet, O ... Shaft, d ... Gap .

Claims (3)

[Claims] 1. A step of mixing raw materials containing zinc oxide as a main component,
A method of manufacturing a voltage non-linear resistor comprising a molding step, a high temperature firing step in air, an electrode attachment step to a sintered body, etc., wherein the mixing step comprises a rotor having a rotor shaft formed on the rotating shaft. Between the rotor, a container for accommodating the rotor by forming an inner space having a shape similar to the rotor by an inner wall surface and extending the rotor shaft from a central portion of the lid, and between the inner wall surface of the container and the rotor. A mixer for crushing and dispersing the raw material supplied to the container by driving the rotor shaft and rotating the rotor in the container. A method of manufacturing a voltage non-linear resistor, characterized by being used. 2. The crushing medium is made into a substantially spherical shape having a diameter of 0.5 mm to 3.0 mm, and its main component is zirconium oxide (Zr
O ₂ ), steatite, zirconium silicate (ZrSiO ₄ ),
The method for producing a voltage non-linear resistor according to claim 1, wherein the method is silicon dioxide (SiO ₂ ). 3. The method for producing a voltage non-linear resistor according to claim 1 or 2, wherein the mixing step is performed using water or a solvent.