JPH05234716A - Zinc oxide varistor - Google Patents

Abstract

PURPOSE:To provide a zinc oxide varistor used at a stabilized varistor voltage and designed for a low voltage service lower than specific voltage having high surge resistance. CONSTITUTION:This zinc oxide varistor is mainly composed of zinc oxide to which 0.1 to 2.0 mode % of bismuth oxide, 0.1 to 1.0 mole % of cobalt oxide, 0.1 to 1.5 mole % of manganese oxide, 0.01 to 0.5 mole % of antimony oxide, 0.0005 to 0.0100 mole % of aluminum oxide and 0.1 to 3.0 mole % of zinc titanate (Zn2TiO4) are added. Or ZnO is adopted as its main component to which 1 to 2.0 mole % of Bi2O3, 0.1 to 1.0 mole % of Co2O3, 0.1 to 1.5 mole % of MnO2, 0.01 to 0.5 mol % of Sb2O3, 0.0005 to 0.0100 mole % of Al2O3, 0.1 to 3.0 mol % of TiO2 and 0.005 to 0.2 mole % Cr(NO3) in terms of Cr2O3 are added, thereby forming a ZnO varistor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low voltage zinc oxide varistor having a stable varistor voltage and a high surge resistance.

[0002]

2. Description of the Related Art In recent years, there have been remarkable developments of various zinc oxide varistors. Among them, bismuth oxide (Bi
Zinc oxide type zinc oxide varistor containing ₂ O ₃ ) has been widely used as a varistor for protection against lightning surge and abnormal voltage because of its excellent voltage non-linearity and surge absorption. However, with the recent progress of semiconductor devices, the drive voltage of electronic devices has been reduced, and therefore, the varistor used for protecting the semiconductor device also corresponds to a lower drive voltage, that is, one with a low varistor voltage. Is being sought after.

In such a varistor containing zinc oxide (ZnO) as a main component, the varistor voltage depends on the number of zinc oxide particles in the sintered body, which are arranged in the thickness direction. It suffices to increase the particle size of zinc (ZnO). For this purpose, by containing titanium oxide (TiO ₂ ), this titanium oxide (TiO ₂ ) can contribute greatly to the grain growth of zinc oxide (ZnO). Known as a technology to meet such demands
There was a thing disclosed by 6-3646 gazette.

In the technique disclosed in the above publication, 0.1 to 5 mol% of bismuth oxide (Bi ₂ O ₃ ) and 0.1 to 5 mol of cobalt oxide (Co ₂ O ₃ ) are added to zinc oxide (ZnO). %,
0.1 to 5 mol% of manganese oxide (MnO ₂ ), 0.1 to 5 mol% of nickel oxide (NiO), and titanium oxide (T
0.1 to 5 mol% of iO ₂ ) and 0.01 to 0.25 wt% of bismuth borosilicate glass frit containing 5 to 30 wt% of silver oxide (Ag ₂ O) are added, mixed, ground and dried. Then, granulation and molding are performed, and the molded body is fired to obtain a varistor for low voltage.

[0005]

However, in the conventional zinc oxide varistor for low voltage, the particle size of the zinc oxide particles is 20 to 1 in order to obtain a varistor voltage of 100 V or less.
Since the grains are grown to 00 μm, abnormal grain growth occurs locally and the varistor voltage varies. Also,
Abnormal grain growth of zinc oxide particles causes current concentration of a surge current, and thus a desired surge withstand cannot be stably obtained. Therefore, chromium oxide (Cr ₂ O ₃₎ having an effect of suppressing grain growth is obtained. ) Is known to reduce variations in varistor voltage and to improve surge withstand capability. In such conventional zinc oxide varistors for low voltage, chromium oxide (Cr ₂ O ₃ ) is added as a powder in a trace amount, so it is difficult to disperse it uniformly, and uneven distribution of chromium (Cr) conversely hinders the uniform grain growth of zinc oxide particles. There was a problem that the surge resistance could not be improved at all.

Further, since titanium oxide (TiO ₂ ) is not uniformly dispersed in the zinc oxide powder but is sintered in a segregated state, abnormal grain growth of zinc oxide particles occurs and variations in varistor voltage occur. However, there is also a problem that local current concentration occurs and a desired surge withstand cannot be stably obtained.

The present invention solves the above-mentioned conventional problems, and mainly relates to a low-voltage zinc oxide varistor for a low voltage of 100 V or less, which has a small variation in the varistor voltage and has a high surge resistance. It is intended to be provided.

[0008]

In order to solve the above problems, a zinc oxide varistor for low voltage according to the present invention contains zinc oxide (ZnO) as a main component, and bismuth oxide (Bi ₂ O) is added to this component. ₃ ) 0.1-2.0 mol%, cobalt oxide (Co ₂ O ₃ ) 0.1-1.0 mol%, manganese oxide (MnO ₂ ) 0.1-1.5 mol%, oxidation Antimony (Sb ₂ O ₃ ) is 0.01 to 0.50 mol%, aluminum oxide (Al ₂ O ₃ ) is 0.0005 to 0.0100 mol%, and zinc titanate (Zn ₂ TiO ₄ ) is 0.1. ~ 3.0
It has a composition in which mol% is added.

Alternatively, zinc oxide (ZnO) is the main component, and bismuth oxide (Bi ₂ O ₃ ) is added to this component in an amount of 0.
1 to 2.0 mol%, cobalt oxide (Co ₂ O ₃ ) 0.1
~ 1.0 mol%, manganese oxide (MnO ₂ ) 0.1 ~
1.5 mol%, 0.01% antimony oxide (Sb ₂ O ₃ )
.About.0.50 mol%, aluminum oxide (Al ₂ O ₃ ) 0.0005 to 0.0100 mol%, titanium oxide (Ti
0.1 to 3.0 mol% of O ₂ and chromium nitrate (Cr
(NO ₃ ) ₃ ) The aqueous solution was converted to chromium oxide (Cr ₂ O ₃ ) and added in an amount of 0.005 to 0.20 mol%.

[0010]

With this configuration, zinc titanate (Zn ₂ Ti
O ₄ ) is mixed with zinc oxide (ZnO) in advance and pulverized and sintered, so that zinc titanate (Zn ₂
TiO ₄ ) is uniformly dispersed, so that the zinc oxide particles during sintering can achieve uniform grain growth, can reduce variations in varistor voltage and variations in surge resistance, and have high surge resistance. A zinc oxide varistor can be obtained.

Further, chromium (Cr), which has the effect of suppressing abnormal grain growth of zinc oxide particles, is replaced by chromium nitrate (Cr (NO
₃ ) ₃ ) Chromium (Cr) can be uniformly dispersed when a small amount of liquid is added as an aqueous solution, which improves the uniformity of zinc oxide particles in the sintered body and causes abnormal grain growth. It is possible to prevent current concentration on the zinc oxide particles, so that it is possible to obtain a zinc oxide varistor having a low varistor voltage variation and a high surge resistance.

[0012]

(Embodiment 1) A first embodiment of the present invention will be described below.

First, zinc oxide (ZnO) and titanium oxide (TiO ₂ ) were weighed so as to have a ratio of 2 mol%: 1 mol%, wet-mixed and ground in a pot mill for 10 hours,
After dehydration, heat treatment was performed at a temperature of 900 ° C. or higher for 1 hour to obtain zinc titanate (Zn ₂ TiO ₄ ). After that, bismuth oxide (Bi ₂ O ₃ ) was added to zinc oxide (ZnO) as the main component.
0.05 to 5.0 mol%, cobalt oxide (Co ₂ O ₃ )
0.05-3.0 mol%, manganese oxide (MnO ₂ )
0.05-5.0 mol%, antimony oxide (Sb
₂ O ₃ ) 0.005 to 3.0 mol%, aluminum oxide (Al ₂ O ₃ ) 0.0001 to 0.2 mol%, and zinc titanate (Zn ₂ TiO ₄ ) 0.05 to 3. 5 mol% was added, wet-mixed in a pot mill, dehydrated, and then polyvinyl alcohol 5 wt% was added as a binder to granulate. The obtained granulated powder is compression-molded under a molding pressure of 1000 kg / cm ² to a size of 13 mm in diameter and 1.3 mm in thickness,
A sintered body was obtained by firing at 1200 ° C. for 2 hours. An electrode containing silver (Ag) as a main component was formed on both surfaces of this sintered body, a lead wire was soldered to the electrode, and the electrode was covered with an epoxy resin to form a zinc oxide varistor.

Tables 1 and 2 show the varistor voltage (V _1mA / mm) per unit thickness of the zinc oxide varistor thus obtained and its variation (σ _n ), the limiting voltage ratio,
The results of evaluation of surge withstand characteristics are shown. Here, the varistor voltage (V _1mA ) is the voltage applied to both ends of the varistor when a current of 1 mA flows through the varistor, and was measured with a DC constant current power supply. Limiting voltage ratio is 8 / 20μs, 10A
Was measured with an impulse current of ₁ and evaluated by the ratio of V _10A / V _1mA . The surge withstand characteristic is the varistor voltage change rate (ΔV _1mA ) when a 500A or 1500A surge current is applied.
It was evaluated by.

In Tables 1 and 2, the samples marked with * are comparative examples, and the samples marked with ** are conventional examples, that is, zinc titanate (Zn).
₂ indicates that the sample was obtained by adding titanium oxide (TiO ₂ ) instead of ₂ TiO ₄ .

[0016]

[Table 1]

[0017]

[Table 2]

The reasons for limiting the range of each additive will be described below based on the results of Example 1 above.

First, when the amount of zinc titanate (Zn ₂ TiO ₄ ) added was less than 0.1 mol%, the varistor voltage varied greatly and the surge withstand characteristic deteriorated. Also, 3.
If it exceeds 0 mol%, the varistor voltage exceeds 100 V, and the surge withstand characteristic deteriorates. Therefore, the amount of zinc titanate (Zn ₂ TiO ₄ ) added is set to 0.1 to 3.0 mol%.

Next, if the amount of bismuth oxide (Bi ₂ O ₃ ) added is less than 0.1 mol%, the surge withstand characteristic deteriorates.

On the other hand, if it exceeds 2.0 mol%, the varistor voltage varies greatly and the surge withstand characteristic deteriorates. Therefore, the addition amount of bismuth oxide (Bi ₂ O ₃ ) is set to 0.
It was set to 1 to 2.0 mol%.

Next, when the amount of cobalt oxide (Co ₂ O ₃ ) added was less than 0.1 mol%, the surge withstand characteristic deteriorated. Further, when it exceeds 1.0 mol%, the varistor voltage rises and the surge withstand characteristic deteriorates. Therefore, the amount of cobalt oxide (Co ₂ O ₃ ) added is set to 0.1 to 1.0 mol%.

Next, if the added amount of manganese oxide (MnO ₂ ) is less than 0.1 mol%, the surge resistance deteriorates and 1.
If it exceeds 5 mol%, the varistor voltage rises and
The surge withstand characteristic deteriorated. Therefore, manganese oxide (M
The amount of nO ₂ ) added was 0.1 to 1.5 mol%.

Next, when the amount of antimony oxide (Sb ₂ O ₃ ) added is less than 0.01 mol%, the surge withstand characteristic deteriorates, and when it exceeds 0.50 mol%, the varistor voltage increases. The variability has become quite large. Therefore, the addition amount of antimony oxide (Sb ₂ O ₃ ) is 0.01 to 0.50.
It was defined as mol%.

Next, when the amount of aluminum oxide (Al ₂ O ₃ ) added is less than 0.0005 mol%, the surge withstand characteristic deteriorates, and when it exceeds 0.010 mol%, the limiting voltage ratio becomes extremely high. It got worse. Therefore, aluminum oxide (Al
_The amount of ₂ O ₃ ) added was 0.0005 to 0.010 mol%.

As is clear from the above results, the zinc oxide varistor having the composition shown in this embodiment has a varistor voltage value (V) per unit thickness as compared with the comparative example and the conventional example.
_It can be seen that _{1 mA} / mm) is small and the variation (σ _n ) is also quite small. Further, the varistor voltage change rate (ΔV _1mA ) after applying the surge current is also small, and its variation (σ _n ) is also significantly improved, which is excellent in terms of the stability of the varistor voltage and the surge withstand capability and the high surge withstand capability. The effect is obtained.

From the above results, the composition range of a zinc oxide varistor having a stable low varistor voltage and a high surge withstand capability is such that bismuth oxide (Bi ₂ O ₃ ) is less than that of zinc oxide (ZnO) as the main component. 1 to 2.0 mol%, cobalt oxide (Co ₂ O ₃ ) 0.1 to 1.0 mol%, manganese oxide (MnO ₂ ) 0.1 to 1.5 mol%, antimony oxide (Sb ₂ O) ₃ ) 0.01 to 0.50 mol%, aluminum oxide (Al ₂ O ₃ ) 0.0005 to 0.0100 mol%, zinc titanate (Zn ₂ TiO ₄ ) 0.1 to 3.0 mol%. It can be seen that the optimum range is%.

In the examples of the present invention, as additives other than zinc titanate (Zn ₂ TiO ₄ ), bismuth oxide (Bi ₂ O ₃ ), cobalt oxide (Co ₂ O ₃ ), manganese oxide (MnO ₂ ), Although antimony oxide (Sb ₂ O ₃ ) and aluminum oxide (Al ₂ O ₃ ) were used, as additives, yttrium oxide (Y ₂ O ₃ ), nickel oxide (NiO),
It goes without saying that the effect of the present invention does not change even if other metal oxides such as chromium oxide (Cr ₂ O ₃ ) and tin oxide (SnO ₂ ) are used.

(Second Embodiment) A second embodiment of the present invention will be described below.

First, bismuth oxide (Bi ₂ O ₃ ) is 0.05 to 5.0 mol% and cobalt oxide (Co ₂ O ₃ ) is 0.05 to 3 with respect to zinc oxide (ZnO) as a main component. 0.0 mol%, manganese oxide (MnO ₂ ) 0.05 to 5.0 mol%, antimony oxide (Sb ₂ O ₃ ) 0.005 to ₃ .
0 mol%, aluminum oxide (Al ₂ O ₃ ) 0.000
1-0.2 mol%, titanium oxide (TiO ₂ ) 0.05
.About.5.0 mol%, and an aqueous solution of chromium nitrate (Cr (NO ₃ ) ₃ ) converted into chromium oxide (Cr ₂ O ₃ ) in an amount of 0.001 to 0.
5 mol% was added, wet-mixed in a pot mill, water was dehydrated and dried, and then a binder was added to granulate. The granulated powder obtained was molded under a molding pressure of 1000 kg / cm ² and had a diameter of 13 m.
It was formed to have a thickness of m and a thickness of 1.3 mm, and was sintered at 1200 ° C. for 2 hours to obtain a sintered body. On both surfaces of this sintered body, electrodes having silver (Ag) as a main component are formed, and lead wires are soldered to the electrodes,
A zinc oxide varistor was prepared by coating with an epoxy resin.

Tables 3, 4 and 5 show the varistor voltage per unit thickness of the zinc oxide varistor thus obtained (V _1mA / mm) and its variation (σ _n ). The results of evaluating the limiting voltage ratio and surge withstand characteristics are shown.

[0032]

[Table 3]

[0033]

[Table 4]

[0034]

[Table 5]

Here, the varistor voltage (V _1mA ) is a voltage applied to both ends of the varistor when a current of 1 mA flows through the varistor, and was measured by a DC constant current power supply. The limiting voltage ratio was measured at an impulse current of 8/20 μs and 10 A, and evaluated by the ratio of V _10A / V _1mA . Surge tolerance is 500
The varistor voltage change rate (ΔV _1mA ) when a surge current of A and 1500 A was applied was evaluated. In addition, (Table 3),
In (Table 4) and (Table 5), samples marked with * are comparative examples, and samples marked with ** are chromium oxide (Cr ₂ O ₃ ) powders added in the conventional method. Indicates an example.

The reasons for limiting the range of each additive will be described below based on the results of Example 2 above.

First, when the amount of bismuth oxide (Bi ₂ O ₃ ) added was less than 0.1 mol%, the surge withstand characteristic deteriorated. On the other hand, when it exceeds 2.0 mol%, the varistor voltage varies greatly and the surge withstand characteristic deteriorates. Therefore, the addition amount of bismuth oxide (Bi ₂ O ₃ ) is 0.1 to 2.
It was 0 mol%.

Next, when the amount of cobalt oxide (Co ₂ O ₃ ) added was less than 0.1 mol%, the surge withstand characteristic deteriorated. Further, when it exceeds 1.0 mol%, the varistor voltage rises and the surge withstand characteristic deteriorates. Therefore, the amount of cobalt oxide (Co ₂ O ₃ ) added is set to 0.1 to 1.0 mol%.

Next, if the added amount of manganese oxide (MnO ₂ ) is less than 0.1 mol%, the surge withstand capability deteriorates and 1.
If it exceeds 5 mol%, the varistor voltage rises and
The surge withstand characteristic deteriorated. Therefore, manganese oxide (M
The amount of nO ₂ ) added was 0.1 to 1.5 mol%.

Next, when the amount of antimony oxide (Sb ₂ O ₃ ) added is less than 0.01 mol%, the surge withstand characteristic deteriorates, and when it exceeds 0.50 mol%, the varistor voltage increases. The variability has increased considerably. Therefore, the addition amount of antimony oxide (Sb ₂ O ₃ ) is 0.01 to 0.5.
It was defined as mol%.

Next, when the amount of aluminum oxide (Al ₂ O ₃ ) added is less than 0.0005 mol%, the surge withstand characteristic deteriorates, and when it exceeds 0.010 mol%, the limiting voltage ratio becomes extremely high. It got worse. Therefore, aluminum oxide (Al
_The amount of ₂ O ₃ ) added was 0.0005 to 0.010 mol%.

Next, when the added amount of titanium oxide (TiO ₂ ) is less than 0.10 mol%, the varistor voltage becomes considerably high, and when it exceeds 3.0 mol%, the varistor voltage variation becomes large and the surge is increased. Withstand capacity has deteriorated. Therefore, the addition amount of titanium oxide (TiO ₂ ) is set to 0.10 to 3.0 mol%.

Next, when the added amount of chromium nitrate (Cr (NO ₃ ) ₃ ) is less than 0.005 mol% in terms of chromium oxide (Cr ₂ O ₃ ), the varistor voltage variation becomes large,
The surge withstand capability deteriorated, and when it exceeded 0.20 mol%, the varistor voltage increased and the limiting voltage ratio deteriorated.
Thus, it was 0.005 to 0.20 mol% in terms of chromium nitrate (Cr (NO _{3) 3)} addition amount of chromium oxide (Cr ₂ O _3). Here, comparing the case of adding with a chromium nitrate (Cr (NO ₃ ) ₃ ) aqueous solution and the case of adding with a chromium oxide (Cr ₂ O ₃ ) powder, it is found that the chromium nitrate ( Cr (N
When added as an O ₃ ) ₃ ) aqueous solution, it is much better, indicating that chromium (Cr) is completely uniformly dispersed. In addition, when compared with the case of adding with chromium oxide (Cr ₂ O ₃ ) powder, when added with an aqueous solution of chromium nitrate (Cr (NO ₃ ) ₃ ), even if the addition amount is extremely small, the excellent addition effect is obtained. Can be obtained.

As is clear from the above results, the zinc oxide varistor having the composition shown in this embodiment has a varistor voltage value (V) per unit thickness as compared with the comparative example and the conventional example.
_It can be seen that _{1 mA} / mm) is low and the variation (σ _n ) is also quite small. Further, the varistor voltage change rate (ΔV _1mA ) after applying the surge current is also small, and its variation (σ _n ) is also significantly improved, which is excellent in terms of the stability of the varistor voltage and the surge withstand capability and the high surge withstand capability. The effect is obtained. Also, by adding chromium (Cr) with chromium nitrate (Cr (NO ₃ ) ₃ ), the amount of varistor voltage variation and surge withstand capability can be significantly reduced compared to the addition with chromium oxide (Cr ₂ O ₃ ) powder. It is possible to obtain the same or higher addition effect in.

From the above results, the composition range of the zinc oxide varistor having a low varistor voltage variation and a high surge withstand capability is 0.1% of bismuth oxide (Bi ₂ O ₃ ) with respect to zinc oxide (ZnO) which is the main component. 2.0 mol%, cobalt oxide (Co ₂ O ₃₎ 0.1~1.0 mol%, manganese oxide (MnO ₂₎ 0.1 to 1.5 mol%, antimony oxide (Sb ₂ O ₃₎ 0 0.01 to 0.50 mol%, aluminum oxide (Al ₂ O ₃ ) 0.0005 to 0.0100 mol%,
Titanium oxide (TiO ₂ ) 0.1 to 3.0 mol% and chromium nitrate (Cr (NO ₃ ) ₃ ) are added to chromium oxide (Cr ₂ O ₃ ).
It is found that the optimum range is 0.005 to 0.20 mol% in terms of.

In the examples of the present invention, bismuth oxide (Bi ₂ O ₃ ) and cobalt oxide (Co) were used as additives.
₂ O ₃ ), manganese oxide (MnO ₂ ), antimony oxide (Sb ₂ O ₃ ), and aluminum oxide (Al ₂ O ₃ ) were used, but yttrium oxide (Y ₂ O ₃ ) and nickel oxide ( It goes without saying that the effect of the present invention does not change even if other metal oxides such as NiO) and tin oxide (SnO ₂ ) are used. Needless to say, the effect of the present invention does not change even if a salt of chromium (Cr) that becomes an aqueous solution at room temperature is used in addition to chromium nitrate (Cr (NO ₃ ) ₃ ).

[0047]

As described above, the zinc oxide varistor for low voltage according to the present invention is a zinc titanate (Zn titanate) prepared in advance.
₂ TiO ₄ ) or by adding chromium (Cr) as an aqueous solution of chromium nitrate (Cr (NO ₃ ) ₃ ), it is possible to achieve uniform grain growth of zinc oxide particles, and to achieve 100 V or less. It is possible to obtain a stable low varistor voltage and to have a high surge resistance.

Claims (2)

[Claims] 1. Zinc oxide (ZnO) as a main component, and bismuth oxide (Bi ₂ O ₃ ) 0.1 to 2.
0 mol%, cobalt oxide (Co ₂ O ₃ ) 0.1 to 1.0
Mol%, manganese oxide (MnO ₂ ) 0.1 to 1.5 mol%, antimony oxide (Sb ₂ O ₃ ) 0.01 to 0.5
0 mol%, aluminum oxide (Al ₂ O ₃ ) 0.000
5 to 0.0100 mol%, zinc titanate (Zn ₂ Ti
A zinc oxide varistor containing 0.1 to 3.0 mol% of O ₄ ). 2. Zinc oxide (ZnO) is a main component, and bismuth oxide (Bi ₂ O ₃ ) is added to this component in an amount of 0.1 to 2.0.
0.1% by mol of cobalt oxide (Co ₂ O ₃ ), 0.1 to 1.5% by mol of manganese oxide (MnO ₂ ), and 0.1% by mol of antimony oxide (Sb ₂ O ₃ ). 01 to 0.50
Mol%, aluminum oxide (Al ₂ O ₃ ) 0.0005
～0.0100 mol%, titanium oxide (TiO ₂₎ 0.
1 to 3.0 mole%, and chromium nitrate (Cr (NO _{3) 3)}
Is converted to chromium oxide (Cr ₂ O ₃ ) and 0.005 to 0.
Zinc oxide varistor containing 20 mol% added.