JPH0429205B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a voltage non-linear resistor whose main component is zinc oxide (ZnO), and in particular, a voltage non-linear resistor with good characteristics with less variation in various characteristics such as surge withstand capacity and energized life. It's about the body. (Conventional technology) Conventionally, zinc oxide is the main component, and Bi ₂ O ₃ , Sb ₂ O ₃ ,
It is widely known that resistors containing small amounts of additives such as SiO ₂ , Co ₂ O ₃ , MnO ₂ , etc. exhibit excellent voltage nonlinearity, and are used in lightning arresters etc. by taking advantage of this property. ing. In particular, when used as a lightning arrester, even if an excessive current flows due to a lightning strike, the current is grounded by a voltage nonlinear resistor that is normally an insulator and becomes a conductor when a voltage higher than the specified voltage is applied. Accidents caused by lightning can be prevented. (Problems to be Solved by the Invention) In the voltage non-linear resistor described above, when a surge current such as lightning is applied to the element, a so-called creeping discharge mainly occurs along the side of the element and the element is destroyed. Although it is necessary to provide a high-resistance layer on the circumferential side surface, there is a drawback that depending on the state of this high-resistance layer, the effect of preventing creeping discharge is small. That is,
There was a drawback that creeping discharge was likely to occur due to the boundary between the high resistance layer and the sintered element near the end face of the resistor. SUMMARY OF THE INVENTION An object of the present invention is to provide a voltage nonlinear resistor which eliminates the above-mentioned problems, prevents creeping discharge, and has stable electrical characteristics, particularly good surge resistance. (Means for Solving the Problems) The voltage nonlinear resistor of the present invention is a voltage nonlinear resistor comprising a high resistance layer provided on the side surface of a sintered body element mainly composed of zinc oxide. The thickness of the central portion of the resistance layer is within the range of 20 to 200 μm, and the thickness of both edge portions of the high resistance layer is 1.2 to 3.0 times thicker than the central portion. . (Function) In the above structure, by making both edges of the high-resistance layer thicker than the center, the thicker edges can be maintained while maintaining close contact between the high-resistance layer and the sintered element at both edges. By forming a current barrier with a high resistance layer at the edge, surge resistance can be improved and creeping discharge can be prevented when a lightning surge is applied. Further, after the main firing, it is necessary that the thickness of the edge portion of the high-resistance layer is 1.2 to 3.0 times the thickness of the central portion. The reason for this regulation is that if the edge thickness is less than 1.2 times, the desired effect cannot be obtained, and if the edge thickness exceeds 3.0 times, surges may occur. The resistance tends to decrease, and such coating is also difficult and the high-resistance layer is likely to peel off. More preferably, the thickness of the edge part is 1.5 of the thickness of the central part.
Make it ~2.0 times. Furthermore, the thickness of the central part of the high resistance layer is 20 to 200μ.
It must be within the range of m. The reason for this limitation is that the edges are thicker than the center, and if the center is thicker than 200 μm, the high-resistance layer in the center will easily peel off, and the edges will be thicker than the center. This is because it becomes difficult to apply the layer thickly and the desired effect cannot be obtained.On the other hand, if the thickness is less than 20 μm, the role of the high-resistance layer is significantly reduced. In addition, as a voltage nonlinear resistor in which both edges of a high resistance layer are thicker than the center part, there are structures a and b shown in FIG. structure a in which the edges face toward the center
is preferred. This is considered to be due to the fact that in structure a, the concentration of electric field at both ends of the element portion is relaxed compared to structure b. (Example) To obtain a voltage nonlinear resistor containing zinc oxide as the main component, first, a zinc oxide raw material adjusted to a predetermined particle size and Bi ₂ O ₃ , Co ₂ O ₃ , MnO ₂ adjusted to a predetermined particle size are used. ,
A predetermined amount of additives such as Sb ₂ O ₃ , Cr ₂ O ₃ , SiO ₂ , NiO, etc. are mixed. At this time, a predetermined amount of polyvinyl alcohol aqueous solution or the like is added to these raw material powders, mixed preferably in a disper mill, and then granulated, preferably in a spray dryer, to obtain a granulated product. After granulation, molding pressure 800-1000Kg/
Form into the desired shape under cm ² . The molded body is held at a temperature of 800 to 1000°C for 1 time at a heating and cooling rate of 50 to 70°C/hr.
The binder is scattered and removed by pre-firing for ~5 hours. Next, an insulating coating layer is formed on the side surface of the calcined body. _In the present invention _{, ethyl cellulose and}
An oxide paste containing butyl carbitol, n-butyl acetate, etc. is applied to the side surface of the calcined body to a thickness of 60 to 500 μm. In this case, according to the present invention, the oxide paste is again applied to both end edges of the calcined body to provide a thick coating. Preferably, after the main firing, the thickness of the edge portion of the high-resistance layer is equal to the thickness of the center portion of the high-resistance layer.
Make it 1.2 to 3.0 times. Furthermore, the range of the thickened edge portion is preferably within 1/8 of the thickness of the element from each end surface after polishing. Next, this is heated at a temperature increase/decrease rate of 30~60℃/hr, 1000~
Main firing is carried out at 1300°C, preferably 1100 to 1250°C, for 3 to 7 hours. A glass paste prepared by adding ethyl cellulose, butyl carbitol, 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 100 to 300 μm. 200℃/hr, 400～
It is preferable to form the glass layer by heat treatment at 600° C. for 0.5 to 2 hours. After that, both end faces of the obtained voltage nonlinear resistor are
Polishing is performed using water, preferably oil, with an abrasive equivalent to #400 to 2000 such as SiC, Al ₂ O ₃ or diamond. Next, after cleaning the polished surfaces, aluminum electrodes are provided on the entire surfaces of both polished end surfaces using, for example, aluminum metallicon or the like by thermal spraying to obtain a voltage nonlinear resistor. Note that the electrodes may be formed 0.5 to 1.5 mm inside the ends of both polished end surfaces. The above-mentioned method is one example, and any method may be used as long as a thick high-resistance layer is formed at the side edge of the resistor, which is a feature of the present invention. For example, the above-mentioned high-resistance layer can be obtained by applying an oxide paste that will become a high-resistance layer after chamfering the edges of the molded or calcined body after molding or calcination. You can also do it. The structure of the high-resistance layer is comprised of a spinel phase, a zinc silicate phase, and a bismuth phase, which are conventionally known structures. The results of actually measuring the lightning surge withstand capacity and switching surge withstand capacity of voltage nonlinear resistors within and outside the scope of the present invention are shown below. Example 1 In the oxide paste application step of the method described above, a voltage nonlinear resistor with a diameter of 47 mm and a thickness of 20 mm was obtained by applying thick coating over 2.0 mm from the upper and lower end surfaces of the calcined body. Sample No. 1 within the scope of the present invention
- 8 and samples Nos. 1 and 2 outside the scope of the present invention were prepared, and the lightning surge withstand capacity and switching surge withstand capacity of each were measured. The results are shown in Table 1. In addition,
Lightning surge resistance is 100KA, 120KA and 130KA
A device that was destroyed after repeatedly applying a current of 4/10 μs twice in a current waveform was marked as ×, and a device that was not destroyed was marked as ○. In addition, the opening/closing surge withstand capacity is 1000A,
1100A and 1200A current with 2ms current waveform
Elements that were destroyed after 20 repeated applications were marked as x, and those that were not destroyed were marked as ○.

[Table] From the results in Table 1, the thickness of the central part of the present invention is 20
Samples Nos. 1 to 8, which are voltage nonlinear resistors with a high resistance layer of ~200 μm and 1.2 to 3.0 times thicker at the ends than at the center, have higher surge resistance than Comparative Examples Nos. 1 and 2. was found to be improving. Example 2 Before the oxide paste application step and pre-firing in the method described above, 2.0 mm from the upper and lower edges of the fired body
Samples Nos. 1 to 8 of voltage nonlinear resistors with a diameter of 47 mm and a thickness of 20 mm within the scope of the present invention obtained by performing notch processing over the area, and comparative examples obtained by conventional methods.
Nos. 1 and 2 were prepared, and the same measurements as in Example 1 were performed. The results are shown in Table 2.

[Table] From the results in Table 2, it was found that even when a high resistance layer was provided by this method, the surge resistance was improved in the same manner as in Example 1. For reference, see Figure 2a,
FIG. 3b shows cross-sectional shapes of voltage nonlinear resistors of the present invention and comparative examples. (Effects of the Invention) As is clear from the detailed explanation above, according to the voltage nonlinear resistor of the present invention, the thickness of the central portion of the high resistance layer is 20 to 200 μm, and
By making both edges 1.2 to 3.0 times thicker than the center, creeping discharge can be prevented, resulting in stable electrical characteristics, especially good lightning surge characteristics, switching surge characteristics, and energized life characteristics. can be obtained.

[Brief explanation of drawings]

FIGS. 1a and 1b are partially enlarged side views of the voltage nonlinear resistor of the present invention, and FIGS. 2a and 2b are cross-sectional views showing the cross-sectional structures of the voltage nonlinear resistors of the present invention and comparative examples. It is a diagram. 1... High resistance layer, 2... Sintered body element.

Claims (1)

[Claims] 1. In a voltage non-linear resistor comprising a high resistance layer provided on the side surface of a sintered body element mainly composed of zinc oxide, the thickness of the central part of the high resistance layer is 20 to 200 μm.
A voltage nonlinear resistor characterized in that the thickness of both end portions of the high resistance layer is 1.2 to 3.0 times thicker than the center portion.