JPH09162016A - Zinc oxide varistor, manufacture thereof and crystalline glass composition for coating use which is used for that - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a zinc oxide varistor, which is superior in discharge breakdown current characteristics and moreover, inhibits the reduction in voltage nonlinearity at the time of a baking treatment to the minimum, by a method wherein side surface high-resistance layers consisting of a crystalline glass layer, which contains PbO containing at least a specified wt.% of ZrO2 as its main component, are respectively provided on the side surfaces of a sintered body containing zinc oxide as its main component. SOLUTION: Side surface high-resistance layers 3 consisting of a crystalline glass layer, which contains PbO containing at least 0.1 to 5.0wt.% of a zirconium oxide calculated in terms of the form of ZnO2 as its main component, are respectively formed on the side surfaces of a sintered body 1, which contains zinc oxide as its main component and has varistor characteristics in the sintered body itself. The layers 3 are constituted of a PbO-ZnO-B2 O3 -SiO2 -ZnO2 crystalline glass layer or a PbO-ZnO-B2 O3 -SiO2 -ZnO2 crystalline glass layer. The linear expansion coefficient of the crystalline glass layer is set to 65 to 90×10<-7> 1 deg.C.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a zinc oxide varistor mainly used in the field of electric power, a method for producing the same, and a crystallized glass composition for coating used therefor.

[0002]

BACKGROUND OF THE INVENTION ZnO as the main component, Bi ₂ O _3, Co
Zinc oxide varistor which contains a metal oxide of a kind such as O, Sb ₂ O ₃ , Cr ₂ O ₃ and MnO ₂ as a sub-component has a large surge resistance and an excellent voltage non-linearity. It is well known that the conventional silicon carbide varistor has been widely used as an element for the device instead of the conventional silicon carbide varistor.

Conventionally, as a method for producing a zinc oxide varistor, for example, Japanese Unexamined Patent Publication (Kokai) No. 62-101002 has been disclosed. The contents of the above-mentioned prior art are as follows.
First, ZnO as a main component is mixed with Bi ₂ O ₃ , Sb ₂ O ₃ , and Cr ₂
Metal oxides such as O ₃ , CoO, and MnO ₂ are added to each of 0.
The raw material powder added with 01 to 6.0 mol% was mixed and granulated, and the granulated powder was pressed and formed into a columnar shape, and then 1200 mm in an electric furnace.
Baking for 6 hours at ℃. Next, on the side surface of the obtained sintered body,
A glass paste consisting of 80% by weight of PbO-based glass frit containing 60% by weight of PbO, 20% by weight of feldspar and an organic binder was used in a screen printing machine for 5 to 5%.
After applying 00 mg / cm ² , baking treatment is performed. The both end faces of the element thus obtained are polished in a plane, an aluminum metallikon electrode is formed, and a zinc oxide varistor is obtained.

[0004]

However, since the zinc oxide varistor according to the above-mentioned conventional manufacturing method uses the screen printing method, the side glass layer is formed to have a uniform thickness and the variation in discharge withstand voltage characteristics is small. However, since it is a composite glass of PbO-based glass frit and feldspar, it has the drawbacks of low discharge withstand characteristic, voltage non-linearity at the time of glass baking treatment, and deterioration of voltage application life characteristic.

The present invention solves the above-mentioned conventional problems, and an object thereof is to provide a highly reliable zinc oxide varistor, a method for producing the same, and a crystallized glass composition for coating used therefor.

[0006]

To achieve this object, the present invention mainly comprises PbO containing 0.1 to 5.0% by weight of ZrO ₂ on the side surface of a sintered body containing ZnO as a main component. The side high resistance layer made of crystallized glass as a component is provided. In addition, a glass paste composed of crystallized glass containing PbO as a main component containing at least 0.1 to 5.0% by weight of ZrO ₂ and an organic binder is provided on the side surface of the sintered body in an amount of 10.0 to 150.0 mg / cm ^2. Apply
A side surface high resistance layer is formed by baking in a temperature range of 450 to 650 ° C.

Further, at least Z for the lateral high-resistance layer.
including and rO ₂ 0.1 to 5.0 wt% PbO-ZnO-B ₂
Provided is a crystallized glass composition for coating an O ₃ —SiO ₂ —ZrO ₂ -based oxide ceramic.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION According to the invention of claim 1 of the present invention, compared with PbO-feldspar composite glass, PbO
The crystallized glass containing as a main component is excellent in discharge withstand characteristics because the addition of ZrO ₂ promotes crystallization, the addition of SiO ₂ improves the strength of the coating film, and the adhesion to the sintered body is good. Moreover, since the insulating property is high, it is possible to minimize the decrease in the voltage non-linearity during the baking process, and it is possible to obtain a highly reliable zinc oxide varistor which is excellent in the electric charge life characteristic.

[0009]

EXAMPLES Hereinafter, a zinc oxide varistor, a method for producing the same, and a coated crystallized glass composition of one example of the present invention will be described in detail based on examples.

First, for the total amount of ZnO powder, Bi
₂ O ₃ 0.5 mol%, Co ₂ O ₃ 0.5 mol%, MnO
₂ 0.5 mol%, Sb ₂ O ₃ 1.0 mol%, Cr ₂ O ₃
0.5 mol%, NiO 0.5 mol%, SiO ₂
0.5 mol% was added, thoroughly mixed with pure water, a binder, and a dispersant by, for example, a ball mill, pulverized, dried by a spray dryer and granulated to obtain a raw material powder. This raw material powder was compression molded into a size of 40 mm in diameter and 30 mm in thickness, and degreased at a temperature of 500 ° C. or higher. Then, it baked in the temperature range of 1100-1250 degreeC, and obtained the sintered compact.

On the other hand, the crystallized glass for coating is made of PbO, Z
A predetermined amount of nO, B ₂ O ₃ , SiO ₂ , and ZrO ₂ is weighed, mixed and crushed by, for example, a ball mill, and then 1 by a platinum crucible.
It was melted under the temperature condition of 000 to 1200 ° C. and rapidly cooled to be vitrified. This glass was roughly crushed and then finely crushed with a ball mill to obtain a glass frit. As a sample for comparison, PbO 70.0 wt%, ZnO 25.0
80.0% by weight of Garraf slit consisting of 5.0% by weight of B ₂ O ₃ and feldspar (feldspar is KAlSi ₃ O ₈ , NaA
A composite glass composed of 10.0 wt% of 1Si ₃ O ₈ and CaAl ₂ Si ₂ O _{8 as} a solid solution was prepared in the same process.

The composition, glass transition point Tg, linear expansion coefficient α and crystallinity of the glass frit produced as described above are shown in the following (Table 1).

In Table 1, the glass transition point Tg
The linear expansion coefficient α was measured by using a thermal analyzer. For crystallinity, observe the surface condition of glass with a metallographic microscope or electron microscope.
The mark indicates that no crystal was observed, and the mark indicates x.

[0014]

[Table 1]

When the amount of PbO added is larger than that shown in Table 1,
When the linear expansion coefficient α becomes high and the amount of ZnO added is large,
The glass transition point Tg becomes low, and crystallization becomes easy. Ma
B _TwoO_ThreeWhen the addition amount of is large, the glass transition point Tg is high.
When the addition amount exceeds 15.0% by weight, crystals
It is difficult to convert. Furthermore, SiO_TwoIncrease the amount of
Accordingly, the glass transition point Tg tends to increase and the linear expansion
The coefficient α tends to be low. And ZnO_TwoAddition of
Crystallization of the glass proceeded as the amount increased. Also,
PbO, B_TwoO_ThreeIn a system with few
It was easy.

Next, with 85% by weight of this glass frit,
15 wt% of an organic binder (a mixture of ethyl cellulose and butyl carbitol acetate) was sufficiently mixed with, for example, a three-roll mill to obtain a glass paste for coating. This coating glass paste was printed on the side surface of the sintered body using a screen of 125 to 250 mesh with a curved screen printer, for example. Here, the coating amount of the coating glass paste is 150 ° C. after coating the paste.
After drying for 30 minutes, the difference in weight of the sintered bodies was used. Also,
The coating amount was adjusted by adding an organic binder and n-butyl acetate to the coating glass paste. After that, 350-70
The coating glass paste was baked under the temperature condition of 0 ° C. to form a side surface high resistance layer on the sintered body. Next, both end surfaces of the sintered body were polished to form an aluminum metallikon electrode to obtain a zinc oxide varistor.

FIG. 1 is a sectional view of a zinc oxide varistor according to an embodiment of the present invention obtained as described above. In FIG. 1, 1 is a sintered body containing zinc oxide as a main component, 2 is electrodes formed on both end surfaces of the sintered body 1, and 3 is obtained by baking crystallized glass on the side surfaces of the sintered body 1. The side surface high resistance layer is formed.

Next, the following Table 2 shows the appearance of a zinc oxide varistor prepared by using the coating glass of Table 1.

[0019]

[Outside 1]

The discharge withstanding characteristic and the charging life characteristic are shown. Here, the coating amount of the coating glass paste is 50 mg.
The viscosity of the paste was controlled to be / cm ² .
The baking treatment condition is 550 ° C. for 1 hour. Here, the number of samples is n = 5 for each lot. Also

[0021]

[Outside 2]

Was measured using a DC constant current power supply. The discharge withstanding characteristic is that a shock current of 4/10 μS is applied twice in the same direction at 5-minute intervals, stepping up from 40 kA, and visually observing whether or not there is an abnormality in the external appearance. It was investigated using. Here, ○ in the table indicates that no abnormalities were observed in the sample after the predetermined current was applied twice, Δ indicates 1-2 pieces, and × indicates 3-5.
It indicates that an abnormality was found in the individual. Furthermore, the life characteristics of charging are performed under conditions of an ambient temperature of 130 ° C. and a charging rate of 95% (AC, peak value), and a leakage current of 5 mA (peak value).
The time to reach was measured. Also,

[0023]

[Outside 3]

The applied voltage life is indicated by an average value of 5 pieces.
Number of samples above,

[0025]

[Outside 4]

Unless otherwise specified, the measuring method, the test method of discharge withstanding capability, and the evaluating method of the electric discharge life characteristic are as follows.
The same applies to each of the following embodiments.

[0027]

[Table 2]

From (Table 1) and (Table 2), coating crystals were obtained.
The coefficient of linear expansion of synthetic glass is 65 × 10 ^-7Less than / ° C
In the case of (G1, G5, G18 glass), the glass is easy to peel off
Becomes 90 × 10^-7/ C is exceeded (G4, G8
It can be seen that cracks are likely to occur in the strip). this
The sample with cracks and glass peeling from the side surface has high resistance
It is considered that the discharge withstand characteristics are low due to the poor insulation of the layers.
You.

Further, the addition of ZnO has no great influence on the electrical characteristics and reliability of the zinc oxide varistor, and is useful for lowering the glass transition point among the physical properties of glass. Further, the prior art example in which _{PbO-ZnO-B 2 O 3} , in the case of using the composite glass feldspar, voltage application life characteristic is it can be seen that a lower discharge withstand current rating characteristic is a practical level.

Next, the amount of ZrO ₂ added will be considered. First, in the composition system in which the added amount of ZrO ₂ is 0.1% by weight or more, the voltage non-linearity is improved regardless of which composition system, and accordingly, the life span characteristic is also improved. This is because by adding ZrO _{2 in an amount} of 0.1 wt% or more,
It is considered that this is because ZrO ₂ is slightly diffused on the side surface of the sintered body during the glass baking treatment, and the resistance of the ZnO particles is increased. On the other hand, when the added amount of ZrO ₂ is more than 5.0% by weight, the discharge withstand characteristic is low. This is considered to be because the fluidity of the glass during the baking process is poor, and the glass tends to be porous. Accordingly, in the _{PbO-ZnO-B 2 O 3} -SiO 2 -ZrO 2 based crystallized glass for the side surface high-resistivity layer of zinc oxide varistors, at least ZrO ₂ 0.1-5.
It is a necessary condition that the composition system contains 0% by weight.

From the above results, the composition of the crystallized glass for coating is 55.0 to 75.0% by weight of PbO and 1% of ZnO.
0.0-30.0 wt%, B ₂ O ₃ 5.0-10.0 wt%, SiO ₂ 0-15.0 wt%, ZrO ₂ 0.1
It can be seen that the range of up to 5.0% by weight is optimal. Further, for the side surface high resistance layer of the zinc oxide varistor, it is necessary that the coefficient of linear expansion be in the range of 65 to 90 × 10 ^-7 / ° C.

Next, the application amount of the glass paste was examined using the G16 glass of the present invention (Table 1). The results are shown in (Table 3) below. At this time, the application amount of the glass paste was 1.0 to 300.0 mg / cm ² , and was controlled by the viscosity of the paste and the number of times of application. At this time,
If the coating amount is less than 10.0 mg / cm ² , the strength of the coating film is low, and if the coating amount is more than 150.0 mg / cm ² , flow or pinholes occur in the glass. Since it is easy, the discharge withstand characteristic is poor. Therefore, it is understood that the optimum amount of glass paste applied is in the range of 10.0 to 150.0 mg / cm ² .

[0033]

[Table 3]

Next, the conditions for baking the glass paste were examined using the G16 glass of the present invention (Table 1). The results are shown in (Table 4) below. At this time, the viscosity was controlled so that the coating amount of the glass paste was 50.0 mg / cm ² . Further, the baking treatment of the glass paste was performed in the air in the temperature range of 350 to 700 ° C. for a holding time of 1 hour. As a result, when the baking treatment is performed at a temperature lower than 450 ° C, the glass paste is not sufficiently melted, so the discharge withstand characteristic is low, and when the baking treatment is performed at a temperature higher than 650 ° C, the voltage ratio is remarkably reduced and The life characteristics deteriorate. Therefore, the baking condition for glass paste is 4
It can be seen that the temperature range of 50 to 650 ° C is optimum.

[0035]

[Table 4]

In this example, PbO-ZnO-B _{2
O 3 -ZrO 2, PbO-ZnO} -B 2 O 3 -SiO 2 -Z
Although the crystallized glass for coating of the rO ₂ 4- and 5-component system has been described, even if a trace amount additive that promotes the crystallization of the glass, such as Al ₂ O ₃ or SnO ₂ , is added as the sixth component. The effect of the present invention does not change. In addition, as a substance that lowers the glass transition point, ZnO is used in the above embodiment.
Was used, but this can of course be replaced by other substances. Further, in the present embodiment, as a typical example of the oxide ceramic, the PbO—ZnO—B ₂ O ₃ —SiO ₂ —ZrO ₂ system coating crystallized glass of the present invention is used for the zinc oxide varistor. It can be applied to any oxide ceramic such as a strontium-based varistor, a barium titanate-based capacitor, a positive characteristic thermistor, and a metal oxide-based negative characteristic thermistor.

[0037]

According to the present invention as described above, according to the present invention, ₂ PbO-ZnO-B comprises at least ZrO ₂ 0.1 to 5.0 wt% on the side surface of the sintered body containing zinc oxide as the main component O ₃ -S
By baking the crystallized glass for coating the oxide ceramic of io ₂ -ZrO _{2 at} a temperature condition of 450 to 650 ° C., a zinc oxide varistor having excellent discharge withstand characteristics and electric charge life characteristics can be obtained. .

[Brief description of the drawings]

FIG. 1 is a sectional view of a zinc oxide varistor according to an embodiment of the present invention.

[Explanation of symbols]

 1 Sintered body 2 Electrode 3 Side high resistance layer

Claims (6)

[Claims] 1. At least 0.1 to 5.0% by weight of zirconium oxide in the form of ZrO ₂ is contained on the side surface of the sintered body containing zinc oxide as a main component and the sintered body itself having varistor characteristics. A zinc oxide varistor having a side surface high resistance layer made of crystallized glass containing PbO as a main component. 2. The lateral high resistance layer is PbO—ZnO—B ₂ O ₃
The zinc oxide varistor according to claim 1, which is made of -ZrO ₂ -based crystallized glass. 3. The lateral high resistance layer is PbO—ZnO—B ₂ O ₃
-SiO ₂ -ZrO ₂ based zinc oxide varistor according to claim 1, wherein comprising a crystallized glass. 4. Zinc oxide is contained as a main component, and at least 0.1 to 5.0% by weight of zirconium oxide in the form of ZrO ₂ is contained on the side surface of the sintered body which itself has varistor characteristics. Crystallized glass containing PbO as a main component and a glass paste containing an organic substance in an amount of 10.0 to 150.0 mg / cm
^{(2) A} method for producing a zinc oxide varistor, which comprises applying and baking in a temperature range of 450 to 650 ° C. 5. The coefficient of linear expansion of crystallized glass is 65 to 90.
The method for producing a zinc oxide varistor according to claim 4, wherein the temperature is × 10 ^-7 / ° C. 6. PbO 55.0 to 75.0% by weight, Z
nO 10.0-30.0% by weight, B ₂ O ₃ 5.0-1
5.0% by weight, SiO _{2 0 to} 15.0% by weight, ZrO ₂
A crystallized glass composition for coating, comprising 0.1 to 5.0% by weight.