JPS6188501A - Manufacture of voltage non-linear resistance element - 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 the Invention] The present invention relates to a method for manufacturing a voltage nonlinear resistance element that is used for overvoltage protection and has zinc oxide as a main component.

[Prior art and its problems]

Ceramic electronic components such as voltage nonlinear resistance elements are usually manufactured through a series of processes of mixing raw materials, granulating, molding, and firing. Particularly when processing a large amount of raw materials, a method of spray drying is used during granulation. In this method, spherical particles are easily obtained by spraying a slurry of raw material powder mixed with an organic binder into a high-temperature air stream and instantaneously drying the slurry. However, in this granulation method using spray drying, the resulting granulated powder particles take various forms depending on the granulation conditions, and in particular, granulated powder particles with a hollow interior and a low bulk density are often obtained.

When a fired body is made using granulated powder with a low bulk density and a hollow interior, various problems occur during the process. For example, since the granulated powder is hollow, pressure transmission during molding is poor, which causes cracks and lamination in the molded product.

In this way, non-uniformity of pressure inside the compact occurs (a). Therefore, it is highly required that the density inside the element be uniform, such as in voltage nonlinear resistance elements whose main component is zinc oxide. In those cases, using granulated powder with a low bulk density poses a major problem, and therefore, granulated powder with a high bulk density is required as a membership fee. Granulated powder with a solid interior and high bulk density can be obtained by increasing the powder concentration of the slurry and performing spray drying. Increasing the concentration of the slurry can greatly increase the amount of raw material powder processed, and is therefore also effective in improving the efficiency of the manufacturing process.

However, when the present inventors manufactured a voltage nonlinear resistance element, even if they used granulated powder with a high concentration of sulfur and a large bulk density, it was difficult to obtain any advantage by using the same manufacturing conditions as before. The VlmA value of the fired body was extremely high, the leakage current was high, and the long wave tail surge resistance was insufficient, so that it was not satisfactory as a voltage nonlinear resistance element.

In order to investigate the cause of this, we closely observed these molded bodies and found that the granulated powder was not sufficiently compressed compared to the case of conventional elements, and there were many voids inside the molded bodies. It was also found that some remained. In other words, depending on the manufacturing conditions, granulated powder made from highly concentrated slurry can only have a lower υ firing density than conventional elements, and because sintering does not progress sufficiently, it may have a high V1 value or a large leakage current value. It shows.

In addition, as a result of investigating the particle size distribution of these elements with poor characteristic values, it was found that there was a region of particularly small particles in the periphery of the device, and that this small particle size region was formed over a fairly wide area even inside the device. I found out that there is. This is due to the fact that the more voids there are in the compact, the more easily the components that contribute to grain growth evaporate from the periphery during firing. This increases the current concentration in the area, reducing the long wave tail surge resistance.

Based on the above, in order to create a voltage nonlinear resistance element with excellent current-voltage characteristics and long-wave tail surge resistance using granulated powder with high bulk density, appropriate molding is necessary, especially in relation to the manufacturing process and element characteristics. It is desirable to establish conditions.

[Purpose of the invention]

The present invention has been made in view of the above points, and its purpose is to provide a method for manufacturing a voltage nonlinear resistance element with excellent current-voltage characteristics and long wave tail surge resistance using granulated powder with high bulk density. It's about doing.

[Key points of the invention]

In the present invention, when manufacturing a voltage nonlinear resistance element mainly composed of zinc oxide, the bulk density obtained by spray drying is 1.
Using granulated powder of 4gr15 or more, the molding pressure Cπ force is set to 0.3 to 0.4t0-, and the density of the fired body is set to 5.3.
5g- to 5.50g73, the current-voltage characteristics.

This provides an element with excellent long wave tail surge resistance.

[Embodiments of the invention]

The present invention will be explained below based on examples.

Powder containing zinc oxide as the main component and supplementary components was mixed in a ball mill with pure water and a binder to create a slurry, and this slurry was spray-dried using a co-current spray dryer to obtain granulated powder. .

This granulated powder has a highly concentrated slurry, and while the bulk density of conventional granulated powder is 1.2/45, the bulk density of the granulated powder obtained in this example is 1.2/45. It was 43 gr/.5. Next, using this granulated powder, the molding pressure was set to 0.2 to 0.
．． A molded body of 6040 was made as a range of 5t01,
After further removing the organic binder, 3
Bake for an hour. The obtained fired body was polished on both sides and heated to 1L.
The electrodes were baked and the device characteristics were measured. The characteristic value is the chisel pressure VlOμA + VImA when a current of 10μA, 1mA, 10KA flows through the element.
/ " is an fc diagram showing the firing density dependence of mA. In Figure 1, curve (1) is VlmA l vlo/lA
+ Song win (2) is for VIOKA/VlmA. As is clear from Figure 1, when granulated powder with high bulk density is used, the firing density is 5.35 g'r/, 3 or more.
11nA/v10μA<1・5Iv10KA/v1mA
<1.8, and good current-voltage characteristics can be obtained.

On the other hand, the long wave tail surge resistance was determined by applying a 2 ms rectangular wave equivalent to 8 KJ to each element and measuring the rate of change in VlmA after the test.

Figure 2 is a graph showing the relationship between these results and the firing density of the element.
If '=1☆ or more, the ashing rate of V1 sweetfish will be less than yuo%,
It can be seen that when the firing density exceeds 50g7m', the rate of change in VImA again exceeds the factor of 10.

Therefore, from the results shown in FIGS. 1 and 2, it can be said that it is most preferable for the density of the fired body to be in the range of 5.35 to 5.50 g7S. In addition, the bulk density of the granulated powder is the same between the granulated powder of 1,""g/,n' used in this example and the conventional granulated powder of 1.2'1g"/S. When a fired body is made under 10π conditions and compared with the rate of change in VlmA after a 2ms long wave tail surge resistance test, for example, when the granulated powder used in this example shows -0.2ch. , that using conventional granulated powder is -8.5 cm, and the larger the bulk density of granulated powder is, the smaller the rate of change in VlmA is.
Excellent long wave tail surge resistance can be obtained.

As stated above, by using granulated powder with a high bulk density, the final fired product has a sealing capacity of 5.35 g or more.5.
By making it within the range of 50g7s or less,
In order to obtain a voltage nonlinear resistance element with excellent current-voltage characteristics and long-wave tail surge resistance, and to keep the density of the fired product within the above range, the molding pressure must be reduced to 0, as described above.
．． It is best to set the molding pressure to 2 to 5 t%, but if you consider avoiding cracks and lamination that are likely to occur during molding, the optimum molding pressure range is 0.3 to 4 t%.
The present invention is realized by setting n/.

〔Effect of the invention〕

As explained above, when manufacturing a voltage nonlinear resistance element, it is better to use granulated powder obtained by spray drying that has a high bulk density and has a high slurry concentration. When using powder, it is necessary to set suitable manufacturing conditions, especially the molding conditions in each manufacturing process, and to keep the density of the final fired product within a preferable range. According to the present invention, as described in the examples, the bulk density is 1.4.
Using granulated powder of g'/s or more, the molding pressure is 0.2f.
i ~"'""cyl, and the density of the obtained fired body is 5
．． By setting it to 35 to 5.50 g7s, a voltage nonlinear resistance element with excellent current-voltage characteristics and long wave tail surge resistance can be obtained.

[Brief explanation of drawings]

Figure 1 shows the device characteristics V+mA/VloltA and vFOK.
A diagram showing the dependence of A/V + V on firing density, and FIG. 2 is a diagram showing the relationship between the rate of change of VlmA and firing density. Firing density (1/crn3) Figure 1

Claims (1)

[Claims] 1) A bulk density of 1.4 g obtained by spray drying in a method of manufacturing a voltage non-linear resistance element mainly composed of zinc oxide through the steps of mixing, granulating, molding, and firing.
Using granulated powder of r/cm^3 or more, molding pressure is 0.3~
A method for manufacturing a voltage non-linear resistance element, which comprises forming a molded body with a density of 0.4 ton/cm^2, and then firing it to obtain a fired body having a density of 5.35 to 5.50 gr/cm^3.