JPH0391201A - Voltage nonlinear resistor - Google Patents

Abstract

PURPOSE:To obtain a highly moisture-resistant and surge-current-resistant inexpensive voltage nonlinear resistor which can be made easily by coating the side faces of a voltage nonlinear resistor with composite glass layers composed of PbO.B2O3 glass and the specified ceramic powder added thereto for dispersion strengthening. CONSTITUTION:Powder of zinc oxide (ZnO) with added components such as praseodymia (Pr6O11), cobalt oxide (Co3O4), and potassium carbonate (K2CO3) mixed therein are granulated and baked and both end faces are polished to obtain a sintered body 1. ZrO2.SiO2 (zircon) powder is added to and sufficiently mixed in PbO.B2O3 glass and binder is added to and sufficiently mixed in composite glass powder thus made to obtain glass paste. The glass paste is applied to the side faces of the sintered body with a brush and hat-treated to form glass layers 3a. The upper and lower end faces of the sintered body are sand-blasted and spray electrodes 2 are made to obtain a voltage nonlinear resistor.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a voltage nonlinear resistor that is used in arresters and the like and has a glass layer coated on the side surface of a sintered body mainly composed of ZnO.

[Conventional technology]

The main component is zinc oxide (ZnO), which also contains rare earth elements,
Cobalt (Co), potassium (K), chromium (Cr)
Voltage nonlinear resistors obtained by adding and mixing oxides and the like in the form of oxides and the like using ordinary ceramic manufacturing methods are widely used in arresters, varistors, and the like.

FIG. 4 is a schematic cross-sectional view showing an example of the shape of a voltage nonlinear resistor. In Fig. 4, this voltage nonlinear resistor is
Electrodes 2 are provided on each of the upper and lower end surfaces of a resistor 1 having voltage nonlinearity that is formed into a disk or cylinder shape and then bottomed out at high temperature.A glass layer 3 is provided on the side surface of the resistor 1 to prevent moisture from entering. The insulator layer 4 is formed through the insulator layer 4. The insulator layer 4 protects the resistor 1 from secondary environmental contamination such as moisture and foreign matter adhesion, ensures reliability of characteristics, and protects the resistor 1 from external flash shorting such as air discharge when absorbing shock current. This is to prevent creepage flashover.

The composition of the glass layer 3 is, for example, PbO・B2O3・Si0g
The thermal expansion coefficient is 60 x that of the resistor 1 to prevent the glass layer 3 from cranking during glass baking.
A temperature close to 10-'/°C is used. Further, the insulator layer 4 is made of, for example, epoxy resin.

However, such a voltage non-linear resistor still has the following problems.

[Problem to be solved by the invention]

In the process of forming the glass layer 3 of the voltage nonlinear resistor having the structure shown in FIG.
When baking the glass of the system, there is a problem that this glass has a narrow baking temperature range, has poor moisture resistance at low temperatures, and large deterioration of voltage-current characteristics due to the baking process at high temperatures, making it difficult to manufacture voltage nonlinear resistors. Upper management is difficult. In addition, the glass layer 3 mentioned above has low strength, and when an impact current is applied, the temperature of the resistor l and the glass layer 3 rises, and a crank occurs in the glass layer 3 due to the slight difference in their thermal expansion coefficients, resulting in creepage flashover. It also has the disadvantage of being susceptible to shock current application. Moreover, the epoxy resin that forms the insulator layer 4 has poor adhesion with the resistor 1 and the glass layer 3, and also has a large difference in coefficient of thermal expansion with the resistor 1, which tends to cause cranking. Even if the insulating layer 4 is formed using the same, the moisture resistance and impact current resistance are not satisfactory. Furthermore, since two layers, the glass layer 3 and the insulator layer 4, are provided, there is another problem in that the cost increases due to the number of manufacturing steps.

The aim of the invention is to eliminate the above-mentioned drawbacks and provide moisture resistance.

The object of the present invention is to provide a voltage nonlinear resistor that has excellent shock current resistance, is simple to manufacture, and is inexpensive.

[Means to solve the problem]

In order to solve the above problems, the voltage nonlinear resistor of the present invention has its side surfaces made of PbO-o, o, Zr0t glass.
HSing (Zircon), 2Mg0 ・2AZz
Os' 5SiOz (cordierite), 31Vt
It is coated with a composite glass layer which is dispersion-strengthened by adding ceramic powder of at least one of O1.2SiO□ (mullite) and ZnlSiOt (zinc orthosilicate).

[Effect]

pbo/B2O3 glass and conventional pbo/B
2O3・Sin.

From the comparison with the glass of the system, it appears that SiO□ in the glass composition is involved in the deterioration of voltage-current characteristics during baking, and Pb
With O.B2O3 glass, the temperature during baking can be set higher, so that the reaction between the resistor 1 and the glass layer 3a progresses, and good adhesion, moisture resistance, and impact current resistance are improved. That is, the glass has good fluidity during baking and penetrates into the uneven parts and pores on the surface of the resistor 1, thereby further strengthening the adhesion between the resistor 1 and the glass layer 3a. And PbO・B2
By adding and dispersing ceramic powder to O3-based glass, the strength of the glass can be increased and cracks caused by thermal shock can be prevented. The reason why ceramic powder can increase the strength of glass by dispersing it is because ceramic powder alleviates the mechanical stress caused by thermal shock, and depending on the amount of ceramic powder added, it can increase the strength of glass. It also has the role of adjusting the coefficient to almost match that of the resistor 1.

〔Example〕

The present invention will be explained below with reference to Examples.

FIG. 1 is a schematic cross-sectional view showing the structure of a voltage nonlinear resistor according to the present invention, and parts common to those in FIG. 2 are indicated by the same reference numerals. The difference between FIG. 1 and FIG. 2 is that the insulator layer 4 is not provided and the side surfaces of the resistor 1 are PbO/B2O3.
It has only a high-resistance insulating coating glass layer 3a in which ceramic powder is dispersed in the base glass.

In the present invention, the reason why the glass layer 3a was formed is based on the following reason.

As already mentioned, depending on the temperature conditions when baking the glass layer 3, there are problems such as poor moisture resistance, deterioration of voltage and current characteristics due to baking, and the weak strength of the glass layer 3, which is prone to cranking. As a result of various experimental studies conducted by the present inventors regarding the necessity of adding an insulating layer, we found that the composition of the glass forming the glass layer 3 includes PbO-B, 0. This is because we were able to reach the conclusion that by using glass that is mainly composed of glass and dispersion-strengthening it with ceramic powder, the deterioration of voltage-current characteristics due to baking temperature conditions can be minimized.

Hereinafter, a voltage nonlinear resistor according to the present invention will be manufactured! Describe the procedure.

First, praseodymium oxide (P) was added to zinc oxide (ZnO) powder.
Raw materials to which a predetermined amount of subcomponents such as cobalt oxide (raO++) + cobalt oxide (cosoaL potassium carbonate (KIC(h)) and chromium oxide (Cr*Os) are added are sufficiently wet-mixed in a ball mill.

After adding a binder such as polyvinyl alcohol to this raw material slurry, it is granulated using a spray dryer.

Next, the bottom was shaped to have a diameter of 38 mΦ and a thickness of 34 mm, and this cylindrical molded body was bottomed in the atmosphere at a temperature range of 1100 to 1300°C, and both end faces were polished to form a bottom with a diameter of 30 mΦ and a thickness of 2 mm.
A sintered body (resistance element 1) of 5n is used.

On the other hand, ZrO2 Stow (zircon) powder is added to the above-mentioned pbo BzOs glass powder, which is the main focus of the present invention.
60% by weight is added and thoroughly mixed, and a binder such as nitrocellulose or butyl calpitol is added to this composite glass powder and thoroughly kneaded to obtain a glass paste. This glass paste was applied with a brush to the side surface of the sintered body with a diameter of 30 mΦ and a thickness of 25 m in an amount of 30 mg/aa, and then heat treated in the air at a temperature of 700°C for 20 minutes to form the glass layer 3a. Form. The rate of temperature rise and fall at that time was 40°C/min, and the thickness of the glass layer 3a was 5°C/min.
It is 0jrm. Next, after sandblasting both the upper and lower end surfaces of the sintered body, a voltage nonlinear resistor similar to that shown in FIG. 1 can be obtained by providing a sprayed electrode of M with a diameter of 28 mΦ.

The moisture resistance of the voltage nonlinear resistor of the present invention obtained as described above was tested and the results obtained in comparison with a conventional voltage nonlinear resistor are shown in Table 1.

V III A I V 10 JIA in Table 1 Table 1
is the voltage between the electrodes when a current of 1 mA + 10 #A is passed, and ■.

/l is VIIIA per unit thickness. vl. #A
/V1mA is the ratio of ■1° to ■1□, and the closer the value is to 1, the better the voltage nonlinearity is. ΔV lsA.

Δv1°, A indicates the rate of change in V IIIA + V 10 after the test. The test conditions for leaving the mixture together was at a temperature of 60°C.

The relative humidity is 90%, the standing time is 2000 hours, and the PC
The test conditions for T (pressure test) are a temperature of 120° C., 2 atmospheres, and 50 hours. Table 1 shows pbo
・B! Zr0z・Si added to 03 series glass powder
Although the test results of samples with an amount of O□ powder of 20% by weight are listed, there was no significant difference in the test results of samples prepared with an amount of Zr0z・SiO□ powder of 0 to 60% by weight. . The conventional example is PbO as shown in Figure 4.
- A comparison is made with an insulator layer 4 made of epoxy resin formed through a BgOs 5ift glass layer 3.

As is clear from Table 1, the voltage nonlinear resistor according to the present invention has a PCT value of ΔVIIIA+ΔV when left in a mixed state.

, A is small and has excellent moisture resistance.

Next, Table 2 shows the results of evaluating the impact current withstand capacity using the current waveform 4/104 when the amount of ceramic powder contained in the PbO.B2O3 glass was changed, in comparison with the conventional glass. The ceramic used in the examples in Table 2 is Zr.
O!・SiO□ powder. The ○ marks in Table 2 are those that passed the test without causing creepage flashover, and the X
The mark indicates that creepage flashover occurred.

From Table 2, the voltage nonlinear resistor according to this example is ZrJ
- It can be seen that when the amount of SiO□ powder added is in the range of 5 to 40% by weight, it has excellent impact current resistance. Zr(
If the amount of h・Si0g powder added is less than 5% by weight,
The fact that the apparent coefficient of thermal expansion of this composite glass is larger than that of the voltage nonlinear resistor is one of the reasons why the impact current withstand capacity is reduced.

According to the measurement results of the stress intensity coefficient (Klc) of composite glass, when the amount of Zr0g・5ift powder added is less than 5% by weight, it becomes smaller than the critical value of Kle of 0.5MN/m"", and the crankshaft due to thermal shock This tends to occur, and the shock current withstand capacity decreases.

Table 2 Coefficient of thermal expansion of voltage nonlinear resistor 60 x 10-' /
℃, the apparent coefficient of thermal expansion of composite glass is 50
The range of x10-7 to 70 x10-'/'C is important for preventing the occurrence of cracks due to thermal shock when impact current is applied and maintaining a large impact current withstand capacity.

For example, PbO・B2O3 glass has a composition ratio of Pb.
The thermal expansion coefficient is approximately 120 Xl0-7/'C when the PbO-
By adding ceramic powder with a low coefficient of thermal expansion to BZO3 glass, the apparent coefficient of thermal expansion can be increased to 50
The temperature is adjusted to 10-7 to 70 x 10-7/'C to prevent cranking due to thermal shock.

On the other hand, when the amount of ZrO2/SiO□ powder added is more than 40% by weight, the apparent coefficient of thermal expansion is 50 x 10-
7/ If it becomes smaller than "C", the impact current withstand capacity will decrease.Also, the fact that the thickness of the glass layer becomes substantially thinner will also cause a decrease in the impact current withstand capacity, so the zro1sio! It is important to make sure that

Table 3 shows the results of evaluating the impact current withstand capacity of the voltage nonlinear resistor of the present invention having a diameter of 48 fi and a thickness of 22 m in comparison with a conventional example.

The ceramic powder added to the PbO-BtOz glass in the examples shown in Table 3 is ZrO□.SiO□, and the amount thereof is 30% by weight. The indications of ○ and × in Table 3 are the same as those in Table 2, and as is clear from Table 3, the voltage nonlinear resistor of the present invention has an excellent impact current withstand capacity.

Next, Figure 2 shows PbO/BzO3-based glass powder Zr (h
・The composite glass layer 3a of the present invention formed by adding 20% by weight of Stow powder and the conventional pbo ・B!
0. - It is a graph showing the change in the voltage nonlinear resistor Vl, A before and after baking in relation to the baking temperature when the SiO□-based glass layer 3 is baked and coated on the side surface of the resistor 1. In FIG. 2, the curve A of the composite glass layer 3a according to the present invention shows little change in Vl and A even at 850°C, while the curve B of the conventional PbO・B2O3・5
Since the VImA of the iOz-based glass layer 3 rapidly decreases when the temperature exceeds 680°C, the composite glass layer 3a has a temperature of 650°C.
It can be seen that the moisture resistance and impact current resistance are excellent in the range of ~850°C. FIG. 3 is a partially enlarged schematic cross-sectional view showing the state when this composite glass layer 3a is baked on the resistor 1 at a temperature range of 650 to 850°C, where 5 is the ceramic powder and 6 is the resistor. Pb0- penetrated into the pores of body 1
In the BzOs glass, 7 is a sintered particle. When the glass 6 flows well into the irregularities on the surface of the resistor 1 and penetrates into the pores of the resistor 1 for a distance of 0- or more, the resistor 1 and the glass layer 3
The adhesion with a becomes very strong. In order to make the penetration distance of the glass 6 into the pores of the resistor weight 10 or more, the temperature at the time of baking needs to be 650° C. or more. Baking temperature is 65
If the temperature is lower than 0° C., the adhesion between the resistor 1 and the glass layer 3a will deteriorate, and the moisture resistance and impact current resistance will decrease.

However, if the baking temperature exceeds 850° C., fine ranks and bubbles will be generated in the glass, and the moisture resistance and impact current resistance will also decrease, and the VlmA will also decrease significantly. Therefore, the optimum baking temperature can be determined to be in the range of 650 to 850°C. When using conventional PbO-B2O2/SiO□ glass, the optimum baking temperature range considering moisture resistance and impact current resistance was very narrow, 660 to 680°C. Temperature is 650-85
The wide temperature range of 0°C is extremely advantageous in manufacturing.

Furthermore, zrO7 added to PbO-Btus glass.
The relationship between the baking temperature and VISA was investigated with respect to the amount of 5iOt powder varied in the range of 0 to 60% by weight.
Even when the amount of O□・5iOt powder was changed, no significant difference was observed in ■1□.

In the above embodiments, the thickness of the glass layer 3a was set to 50 -, but if it is thinner than 20 -, residual air bubbles, non-uniform thickness, and even parts where the glass layer 3a is hardly formed may occur, resulting in poor moisture resistance and impact resistance. If the thickness of the glass layer 3a exceeds 400 μm, the current withstand capacity is reduced, and if the thickness of the glass layer 3a exceeds 400 μm, cranking is likely to occur due to the application of an impact current, resulting in a decrease in the impact current capacity. Therefore, moisture resistant.

The optimum coating thickness of the glass layer 3a with good impact current resistance needs to be set in the range of 20 to 400 -.

As described above, the glass layer 3a formed in the voltage nonlinear resistor of the present invention
We have explained the case where Zr01・Sing is used as a ceramic powder that is added to PbO-BiOi glass to disperse and strengthen it.
11zOs ・5SiO□), Mullite (3MiO
s25iOz), zinc orthosilicate (Zn2SiO*
) by adding one or more of the following.
It is possible to obtain a voltage nonlinear resistor having excellent moisture resistance and impact current withstand capacity similar to those obtained by using rO□.SiO2 powder.

These ceramic powders have useful properties such as not reacting with the PbO-agos glass during baking, having a coefficient of thermal expansion smaller than that of the resistor 1, being resistant to thermal shock, and having high resistance. The present invention forms a high-resistance insulating glass layer that is dispersed and strengthened using these ceramic powders, and does not require an insulating layer separate from the glass layer as in the past, simplifying the manufacturing process. Because it can be done, it is also effective in contributing to cost reduction.

In FIG. 1, even if the glass layer 3a according to the present invention is provided on both the upper and lower end surfaces of the resistor 1 except for the electrodes 2, there is no difference in moisture resistance and impact current resistance from when the glass layer 3a is formed only on the side surfaces.

〔Effect of the invention〕

The glass layer provided on at least the side surface of the voltage nonlinear resistor is conventionally made of PbO・BzO1SiO□-based glass with an insulating layer attached to it. In contrast, in the present invention, as described in the examples, Pb
Since O-BZOs glass is formed as a composite glass layer dispersed and strengthened with ceramic powder such as Zr0=HSiO□, only one composite glass layer needs to be formed without the need for another insulating layer. There is very little deterioration in voltage and current characteristics over a wide temperature range during glass baking, and the adhesion to the resistor is good, providing excellent moisture resistance and shock current resistance, and the manufacturing process is simple. This is effective in many ways, including lower prices.

[Brief Description of the Drawings] Fig. 1 is a schematic cross-sectional view showing the structure of the voltage nonlinear resistor of the present invention, and Fig. 2 is a schematic cross-sectional view showing the structure of the voltage nonlinear resistor of the present invention. A diagram comparing vlo changes of linear resistors in relation to baking temperature, Figure 3 is a partially enlarged schematic cross-sectional view of a composite glass layer, and Figure 4 is a diagram of a conventional voltage non-linear resistor. FIG. 3 is a schematic cross-sectional view showing the configuration. 1: Resistor, 2: Electrode, 3 + 3a Niglass layer, 4
: insulator layer, 5: ceramic powder, 6: glass layer penetrated into pores, 7: sintered particles.

Claims (1)

[Claims] 1) A voltage characterized in that at least the side surfaces of a sintered body containing ZnO as a main component and having voltage non-linearity are covered with a composite glass layer consisting of PbO・B_2O_3 glass and ceramic powder dispersed within this glass. Non-linear resistor.