JPH05101911A - Nonlinear resistor - Google Patents

Abstract

PURPOSE:To offer a non-linear resistor being little affected by firing while being able to sharply improve a discharge-proof amount characteristic. CONSTITUTION:A high-resistant layer is provided on the surface of a sintered body 1 mainly composed of zinc oxide. The high-resistant layer consists of a first layer 3, which is a ceramic coating layer having inorganic macro molecular structure, and a second layer 4, which is an amorphous ceramic coating layer provided on this first layer 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-linear resistor used in a lightning arrester or the like, and more particularly to a non-linear resistor having an improved high resistance layer formed on the surface of an element containing zinc oxide as a main component.

[0002]

2. Description of the Related Art As is well known in the art, a lightning arrester is used to suppress an abnormal voltage generated in a power system and protect the power system. This lightning arrester is a non-linear resistor, that is, it exhibits insulating characteristics at a normal voltage and exhibits a low resistance value when an abnormal voltage is applied. Non-linear resistors are usually called varistor, and a representative one is zinc oxide as a main component.

Non-linear resistors made of metal oxides, which are generally used in lightning arresters and the like, contain zinc oxide (ZnO) as a main component, and bismuth (Bi), antimony (Sb), cobalt (Co), manganese (Mn), It is configured to include a subcomponent such as an oxide of nickel (Ni), chromium (Cr), or silicon (Si).

To manufacture the non-linear resistor, the above raw materials are thoroughly mixed with water and an organic binder, granulated by a spray dryer or the like, molded, and temporarily sintered,
In order to prevent creeping flash on the surface of this temporary sintered body, by applying a substance that becomes high resistance after firing, baking to form a high resistance layer, further polishing both end faces, and attaching electrodes Has been done.

As the manufacturing method, (1) silicon dioxide (SiO ₂ ), bismuth oxide (Bi ₂ O ₃ ), antimony oxide (Sb ₂ O ₃ ) are mixed with water and an organic binder, and the surface of the calcined body is mixed. 1000-1200 after applying to
A method of forming a high resistance layer by sintering at 0 ° C., and (2) applying a substance containing an inorganic polymer or an organometallic compound as a main component, as shown in, for example, JP-A-2-7401; Methods such as dehydration condensation, hydrolysis, polycondensation or thermal decomposition at 350 ° C. to form a high surface resistance layer are known.

[0006]

In recent years, electric power systems have become larger in capacity and higher in voltage in order to reduce power transmission costs, and accordingly, lightning arresters of about 500 kV have been put into practical use. In the near future, 1000 kV (UH
V) lightning arrester is also planned.

The non-linear resistors used in these arresters are required to handle extremely large surge energy, and means such as increasing the capacity of the non-linear resistors and increasing the number of parallel connections are used.

However, since the increase in the number of parallel-connected elements tends to cause imbalance in current sharing, the number of parallel-connected elements is limited, and inevitably the capacity of the non-linear resistor must be increased. I have to. However, since the thickness is limited by the limiting voltage of the lightning arrester, it is necessary to increase the element diameter. In this way, the shape of the non-linear resistor for 500 kV or the like has a diameter of 100 to 120 mm, and a wall thickness of 20 to 45 mm due to deformation and economy during sintering.

Such a non-linear resistor is difficult to sinter,
It often appears as variations in electrical characteristics. For example, in the non-linear resistor manufactured by the above method (1), in the case of industrial mass production, not only the deterioration of the non-linear resistance characteristic and the variation in the characteristic but also the variation in the discharge withstand characteristic and the like occur. However, there is a problem that it occurs, and various difficulties are encountered in stabilizing the device characteristics.

Further, the non-linear resistor manufactured by the method (2) often has excellent characteristics, and the discharge withstand characteristic is significantly improved, but since these high resistance layers are single layers,
In rare cases, the characteristics may be deteriorated by the presence of partial structural defects such as pores and pinholes.

As described above, according to the prior art, since a material having a high resistance after firing is applied to the calcined element body, the material is fired to form a high resistance layer. In many cases, the appropriate temperature for forming the high resistance layer does not match, and an element having stable electric characteristics has been desired.

The present invention has been made under such circumstances, and an object of the present invention is to provide a non-linear resistor which has little influence at the time of sintering and which can greatly improve discharge withstand voltage characteristics.

[0013]

Means and Actions for Solving the Problems The inventors have conducted various studies in order to obtain a non-linear resistor having excellent discharge withstand characteristics. As a result, the following things became clear.

That is, in the conventional non-linear resistor, the high resistance layer is obtained by applying a substance having a high resistance after firing to the calcined element body and then firing it. The temperature does not match the suitable temperature for forming the high resistance layer. Therefore, it was found that the firing temperature was conventionally adjusted to a temperature suitable for the element body, and as a result, a good high resistance layer was not formed and the discharge withstand voltage characteristic was deteriorated.

By the way, when aluminum orthophosphate or the like is subjected to a dehydration bond reaction at a temperature extremely lower than the firing temperature of general Al ₂ O ₃ , it has a —P—O—P— structure,
Phosphate molecular around the metal ions ^{O - -P-O-M-} O-P- molecular structure such as that with a coordinating, for example A
It is a high resistance material represented by 1H ₂ P ₃ O ₁₀ .nH ₂ O having excellent heat resistance and water resistance.

Therefore, a ceramic having such an inorganic polymer structure or a ceramic having an inorganic polymer structure containing aluminum and silicon as main components is
It is considered that an excellent high resistance layer can be formed by applying it to the surface of the sintered body and performing a dehydration coupling reaction.

On the other hand, metal alkoxide and the like undergo hydrolysis and polycondensation reaction at a low temperature of 200 ° C. or lower, and become an amorphous material having excellent heat resistance and water resistance.

Therefore, if a metal alkoxide or the like is applied as an upper layer of a high resistance layer made of ceramic having an inorganic polymer structure and subjected to hydrolysis and polycondensation reaction,
It is considered to form an amorphous ceramic coating film having excellent heat resistance and water resistance.

Further, the metal alkoxide has a good permeability because it is an alcohol solution, and it is considered that the metal alkoxide enters into defective portions such as pores and pinholes of the high resistance layer made of ceramic having an inorganic polymer structure to strengthen the hardening. Be done.

Therefore, if the above two types of layers are used, a good two-layer ceramic coating film with extremely few defects is formed, and if the thickness is controlled to an appropriate value, the discharge withstand voltage characteristic is good, and It is considered that the variation in withstand voltage characteristics is reduced.

Based on the above findings, the invention of claim 1 is
In a non-linear resistor in which a high resistance layer is provided on the surface of a sintered body containing zinc oxide as a main component, the high resistance layer includes a first layer which is a ceramic coating film having an inorganic polymer structure, and the first layer. And a second layer which is an amorphous ceramic coating film provided on the above layer.

In the invention of claim 1, aluminum orthophosphate is suitable as a material for the ceramic coating film having an inorganic polymer structure which is the first layer, and pyrophosphate containing another phosphate group is preferred. Aluminum, aluminum tripolyphosphate, aluminum tetrapolyphosphate, etc. can be applied.

Phosphoric acid has a general formula of Mn + 2PnO.
It is represented by _{3n + 1} . Here, M is metal, P is phosphorus, O
Is oxygen and n is a natural number. This M contains Mg, Ca,
Cu, Zr, Si, etc. can be applied.

Further, as a material of the ceramic coating film having an amorphous structure which becomes the second layer, isopropoxy silica which is a kind of metal alkoxide is suitable, and in addition, an alkyl group of isopropoxy silica is used. change,
It is also possible to employ a methyl group, an ethyl group, a butyl group, a pentyl group, or a hexyl group.

The metal alkoxide is represented by the general formula M (PR) n. Here, M is a metal, O is oxygen, R is an alkyl group, and n is a natural number. And, as the metal M, T
i, Al, Zr, Cr, Mg, and the alkyl group may be a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, or the like.

Although an oxide raw material is suitable as an additive for the non-linear resistor, other components may be added as long as they can be converted into an oxide by firing to improve the non-linear characteristics.

By the way, the high resistance layer is 70 × 70 ⁻⁷ / ° C.
A ceramic coating film having a coefficient of thermal expansion of more than 1 is inferior in discharge withstand characteristic, and there is a possibility that the element body is broken or cracked. The cause is guessed as follows.

That is, when ceramics such as a non-linear resistor is sintered, residual stress may exist. Causes include non-uniform mixing in the mixing process, non-uniform temperature distribution in the firing process, and uneven atmosphere. It is considered that these influence each other and the element body contracts non-uniformly to cause residual stress.

However, when a material coated with high resistance layer materials having different thermal expansion coefficients is sintered, residual stress is generated only by itself. When a material having a thermal expansion coefficient smaller than that of the element body is applied and sintered, the element body cannot be fully shrunk and a tensile stress remains, and the high resistance layer is affected by the shrinkage force of the element body and excessively contracts. Compressive stress remains. The coefficient of thermal expansion of the non-linear resistor was measured and found to be 70 × 70 ⁻⁷ / ° C. Therefore, if a material of 70 × 70 ⁻⁷ / ° C. or less is applied, compressive stress remains in the high resistance layer, and if it is more than that, tensile stress remains.

Further, the compressive stress of the high resistance layer effectively acts on the breakage and cracks entering from the outer peripheral portion. It is considered that the breakage and cracks that occur in the outer peripheral portion due to the discharge withstand test are caused by thermal expansion of the element body by the applied energy.

Therefore, even if compressive stress is applied to the elemental body where compressive stress remains in the ceramic coating film on the outermost periphery of the elemental element, the energy is consumed until the compressive stress disappears. It will show a large value.

Therefore, the invention of claim 2 is a nonlinear resistor in which a high resistance layer is provided on the surface of a sintered body containing zinc oxide as a main component, wherein the high resistance layer is a ceramic coating having an inorganic polymer structure. The first layer, which is a film, and the second layer, which is an amorphous ceramic coating film provided on the first layer, are 70 × 70 ⁻⁷ / both layers.
It is characterized by having a coefficient of thermal expansion of ℃ or less.

According to the second aspect of the present invention, both the first layer which is the ceramic coating film and the second layer which is the amorphous ceramic coating film provided on the first layer are both formed. By using a non-linear resistor having a coefficient of thermal expansion of 70 × 70 ⁻⁷ / ° C. or less, it is possible to provide a highly reliable non-linear resistor having excellent discharge withstand characteristics.

In the second aspect of the present invention, aluminum pyrophosphate is suitable as the material of the ceramic coating film having the inorganic polymer structure which is the first layer, and other phosphoric acid is suitable if the thermal expansion coefficient is suitable. Salt can be applied.

Further, as a material of the ceramic coating film having an amorphous structure to be the second layer, methoxy silica which is one kind of metal alkoxide is suitable, and other metal alkoxide may be used as long as it has a thermal expansion coefficient. It is also possible to employ a ceramic material such as an alkali metal salt that forms an amorphous film.

Although the oxide raw material is suitable as the additive of the non-linear resistor, other components may be added as long as they can be converted into an oxide by firing to improve the non-linear characteristics.

[0037]

Embodiments of the present invention will be described below with reference to the drawings.

Example 1 This example relates to a non-linear resistor applied as a lightning arrester, and FIG. 1 shows a cross-sectional structure of the non-linear resistor according to this example.

The non-linear resistor according to the present embodiment has a disk-shaped element body 1 which is a sintered body, electrodes 2 provided on each axial end face of the element body 1, and an outer peripheral surface of the element body 1. The formed first layer 3 which is a high resistance layer and the second layer provided on the first layer 3
And a layer 4 of. The non-linear resistor has a diameter of 100 mm and a wall thickness of 22 mm.

The element body 1 is composed of a sintered body containing zinc oxide as a main component and has voltage non-linearity.

The first layer 3 is composed of a ceramic coating film having an inorganic polymer structure.

Further, the second high resistance layer 4 is composed of an amorphous ceramic coating film.

The non-linear resistor having such a structure is manufactured by the following method.

First, a method of manufacturing the element body 1 will be described.

Zinc oxide (ZnO) is mixed with bismuth oxide (B
i ₂ O ₃ ), manganese oxide (MnO), silicon dioxide (SiO ₂ ), chromium oxide (Cr ₂ O ₃ ) 0.5 mol%, cobalt oxide (Co ₂ O ₃ ), antimony oxide (Sb), respectively. ₂ O ₃ ) and nickel oxide (NiO) are added in an amount of 1 mol%. These raw materials are put into a mixing device together with water and an organic binder such as a dispersion material and mixed.

Next, the above mixture is spray-granulated with a spray dryer so that the particle size becomes 100 μm, for example. Then, these granulated powders are put into a mold and pressed to obtain a diameter of 12
After being molded into a disk having a thickness of 5 mm and a thickness of 30 mm, it is fired at 500 ° C. in air to remove the added organic binders, and further fired at 1200 ° C. in air. Thereby, the element body 1 is obtained.

Next, the first and second layers 3, which are high resistance layers,
The manufacturing method of No. 4 will be described.

First, a ceramic coating material forming an inorganic polymer structure, for example, an aqueous solution of aluminum orthophosphate (Al (H ₂ PO ₄ ) ₃ ) is applied to the outer peripheral surface of the element body 1 by a spray gun or the like. After application, the element body 1 is dried and cured at a temperature of 350 ° C. for 1 to 2 hours, for example. As a result, the first layer 3 which is a high resistance layer is formed on the outer peripheral surface of the element body 1.

Next, a material for forming an amorphous ceramic coating film, for example, isopaxic silica (Si (OC ₃ H7) ₄ ) which is one kind of metal alkoxide, is applied to the outer periphery of the first layer 3 by a spray gun or the like as described above. Apply to the side. Then, it is dried and cured at 350 ° C., whereby the second layer 4 made of an amorphous film is formed on the outer peripheral side of the first layer 3.
To form.

Both end surfaces in the axial direction of the sintered body obtained by the above method are polished, and aluminum is sprayed on the both end surfaces to form the electrode 2. As a result, the non-linear resistor shown in FIG. 1 can be obtained.

FIG. 2 shows measured values of discharge withstand characteristics of the non-linear resistor according to this example manufactured by the above method in comparison with the conventional non-linear resistor. That is,
The vertical axis represents the frequency, and the horizontal axis represents the energy value that the device withstood, which is shown as a distribution chart. In this experiment, a rectangular wave current of 2.5 ms was applied 5 times to the completed non-linear resistor to measure the discharge withstand voltage.

Curve A in FIG. 2 shows the discharge withstand characteristic of the non-linear resistor of this embodiment, and curve B shows the discharge withstand characteristic of the non-linear resistor according to the conventional manufacturing method. As is clear from the figure, in the conventional non-linear resistor, the variation in discharge withstand characteristic is large and the withstand energy is small, whereas in the non-linear resistor according to the present example, the variation in discharge withstand characteristic is small, It can be seen that the same characteristics are good.

Therefore, according to the present embodiment having the ceramic coating film having the inorganic polymer structure as the first layer 3 and the amorphous ceramic coating film as the second layer 4, the conventional non-linear resistor is used. In comparison, the discharge withstand voltage characteristic can be improved.

The reason why a non-linear resistor having excellent discharge withstand characteristics can be obtained by this example is considered as follows.

That is, in the prior art, a substance having a high resistance after firing is applied to a calcined element body and then fired to form a high resistance layer. Therefore, an appropriate firing temperature of the element body and formation of the high resistance layer can be achieved. The suitability temperature does not match, and as a result, the firing temperature suitable for the element body is adjusted, and a good high resistance layer cannot be formed, and the discharge withstand characteristic is deteriorated.

However, in the case of aluminum orthophosphate applied to the surface of the sintered body as in this example, dehydration was carried out at a temperature extremely lower than the firing temperature of a general fired coating film of Al ₂ O _3. the binding reaction and -P-O-P- structure, the phosphate molecular around the metal ions O ^- with a coordinated and -P-O-M-O- P- molecular structure such as, for example, Al
A high resistance cured coating having excellent heat resistance and water resistance, which is represented by H ₂ P ₃ O ₁₀ .nH ₂ O, is formed. Furthermore, the metal alkoxide as the upper layer also undergoes hydrolysis and polycondensation reaction at a low temperature of 300 ° C. or lower, resulting in amorphous heat resistance,
A ceramic coating film having excellent water resistance is formed.

Si (OC ₃ H ₇ ) ₄ + H ₂ O → Si (OH) ₄ + 4C ₃ H ₇ OH Si (OH) ₄ → SiO ₂ + 2H ₂ O ↑ These metal alkoxides form an amorphous second layer. It not only forms, but also has good permeability due to the alcoholic solution.
It enters into the defective parts such as pores and pinholes of the layer, and also functions to strengthen the hardening, so that it has very few defective parts.
It is considered that since the ceramic coating film of the layer is formed and the film thickness is controlled to an appropriate value, the discharge withstand voltage characteristic is good and the dispersion of the withstand voltage characteristic is small.

According to the above-mentioned embodiments, the ceramic coating film having the inorganic polymer structure is formed as the first layer 3 on the surface of the element body 1, and the amorphous coating is formed as the second layer 4 on the ceramic coating film. It was possible to provide a highly reliable non-linear resistor having excellent discharge withstand characteristics by forming a ceramic coating film having

In this example, aluminum orthophosphate was used as the material for the ceramic coating film having an inorganic polymer structure. However, aluminum pyrophosphate, aluminum tripolyphosphate, or tetrapolyphosphate may be used by changing the phosphate group. It was recognized that it showed various characteristics.

Phosphoric acid has a general formula of Mn + 2PnO.
It is represented by _{3n + 1} . Here, M is metal, P is phosphorus, O
Is oxygen and n is a natural number. As M, Mg, C
It was confirmed that the same effect as that of the above-mentioned embodiment can be obtained even if a, Cu, Zr, Si or the like is applied. That is, it is possible to use general phosphate as a material.

Further, as a material of the ceramic coating film having an amorphous structure to be the second layer, isopropoxy silica, which is a kind of metal alkoxide, is preferable, but the alkyl group of isopropoxy silica is also used. Change
It was confirmed that the same effect as that of the above-mentioned example can be obtained even if a methyl group, an ethyl group, a butyl group, a pentyl group, or a hexyl group is adopted.

The metal alkoxide is represented by the general formula M (PR) n. Here, M is a metal, O is oxygen, R is an alkyl group, and n is a natural number. And, as the metal M, T
Even if i, Al, Zr, Cr, and Mg are used and the alkyl group is a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, or the like, the same effect as that of the above-described embodiment can be obtained. Admitted.

The oxide raw material is suitable as the additive of the non-linear resistor, but the additive is not limited to this and may be any substance that can be converted into an oxide by firing. Further, additives other than those shown in the above examples may be added. For example, other components may be added for the purpose of improving the non-linear characteristic.

Although the non-linear resistor has a diameter of 100 mm and a wall thickness of 22 mm in the above embodiment, it is confirmed that the same effect as described above can be obtained even if the capacitance is smaller or larger than this. did it.

Embodiment 2 This embodiment is also related to a non-linear resistor applied as a lightning arrester, and FIG. 3 shows a cross sectional structure of the non-linear resistor according to this embodiment.

The non-linear resistor according to the present embodiment has a disk-shaped element body 11 which is a sintered body, electrodes 12 provided on each axial end surface of the element body 11, and an outer peripheral surface of the element body 11. It is configured to have the formed first layer 13 that is a high resistance layer and the second layer 14 provided on the first layer. The non-linear resistor has a diameter of 100 mm and a wall thickness of 22 mm.

The element body 11 is composed of a sintered body containing zinc oxide as a main component and has voltage non-linearity.

The first layer 13 is composed of a ceramic coating film having an inorganic polymer structure.

Further, the second high resistance layer 14 is composed of an amorphous ceramic coating film.

Then, the first layer 13 and the first layer 1
The second layer 14, which is an amorphous ceramic coating film, provided on the surface 3 is a non-linear resistor having a coefficient of thermal expansion of 70 × 70 ⁻⁷ / ° C. or less.

The non-linear resistor having such a structure is manufactured by the following method.

First, a method of manufacturing the element body 11 will be described.

Zinc oxide (ZnO) is mixed with bismuth oxide (B
i ₂ O ₃ ), manganese oxide (MnO), silicon dioxide (SiO ₂ ), chromium oxide (Cr ₂ O ₃ ) 0.5 mol%, cobalt oxide (Co ₂ O ₃ ), antimony oxide (Sb), respectively. ₂ O ₃ ) and nickel oxide (NiO) are added in an amount of 1 mol%. These raw materials are put into a mixing device together with water and an organic binder such as a dispersion material and mixed.

Next, the above mixture is spray-granulated with a spray dryer so that the particle size becomes 100 μm, for example. Then, these granulated powders are put into a mold and pressed to obtain a diameter of 12
After being molded into a disk having a thickness of 5 mm and a thickness of 30 mm, it is fired at 500 ° C. in air to remove the added organic binders, and further fired at 1200 ° C. in air. Thereby, the element body 11 is obtained.

Next, the first and second layers 1 which are high resistance layers
A method for manufacturing 3, 14 will be described.

First, a ceramic coating material forming an inorganic polymer structure, for example, an aqueous solution of aluminum pyrophosphate (Al ₁₂ H ₂ P ₂ O ₇ ) is applied to the outer peripheral surface of the element body 11 described above by a spray gun or the like. After the application, the element body 11 is dried and cured at a temperature of 350 ° C. for 1 to 2 hours, for example. As a result, on the outer peripheral surface of the element body 11,
The first layer 13 which is a high resistance layer is formed.

Next, a material for forming an amorphous ceramic coating film, for example, methoxy silica (Si (OCH ₃ ) ₄ ) which is one kind of metal alkoxide, is applied to the outer periphery of the first layer 13 by a spray gun or the like as described above. Apply to the side. Then, it is dried and cured at 350 ° C., thereby forming the second layer 14 made of an amorphous film on the outer peripheral side of the first layer 13.

The both ends in the axial direction of the sintered body obtained by the above method are polished, and aluminum is sprayed on the both ends to form the electrode 2. As a result, the non-linear resistor shown in FIG. 1 can be obtained.

The coefficient of thermal expansion of the ceramic coating material forming the inorganic polymer structure used here is 60 × 10.
Was ^{-7 /} ° C., the thermal expansion coefficient of the ceramic coating material to form an amorphous structure was 50 × 10 -7 ^/ ℃.

FIG. 4 shows the measured values of the discharge withstand characteristic of the non-linear resistor according to the present example manufactured by the above method, in comparison with the conventional non-linear resistor. That is,
The vertical axis represents the frequency, and the horizontal axis represents the energy value that the device withstood, which is shown as a distribution chart. In this experiment, a rectangular wave current of 2.5 ms was applied 5 times to the completed non-linear resistor to measure the discharge withstand voltage.

Curve C in FIG. 4 shows the discharge withstand characteristic of the non-linear resistor of this embodiment, and curve D shows the discharge withstand characteristic of the non-linear resistor manufactured by the conventional manufacturing method. As is clear from the figure, in the conventional non-linear resistor, the variation in discharge withstand characteristic is large and the withstand energy is small, whereas in the non-linear resistor according to the present example, the variation in discharge withstand characteristic is small, It can be seen that the same characteristics are good.

Therefore, as the first layer 13, a ceramic coating film having an inorganic polymer structure, the second layer 1
According to this embodiment having an amorphous ceramic coating film as No. 4, the discharge withstand characteristic can be improved as compared with the conventional non-linear resistor.

The reason why a non-linear resistor having excellent discharge withstand characteristics can be obtained by this example is considered as follows.

That is, in the prior art, since a material having a high resistance after firing is applied to a calcined element body, the material is fired to form a high resistance layer. Therefore, an appropriate firing temperature of the element body and formation of the high resistance layer are required. The suitability temperature does not match, and as a result, the firing temperature suitable for the element body is adjusted, and a good high resistance layer cannot be formed, and the discharge withstand characteristic is deteriorated.

However, as in the present embodiment, the sintered body 11
In the case of aluminum pyrophosphate applied to the surface of
A cured coating having a polymer structure is formed by a dehydration bonding reaction at a temperature extremely lower than the firing temperature of a fired coating film of general Al ₂ O ₃ . Furthermore, the metal alkoxide as an upper layer thereof also undergoes hydrolysis and polycondensation reaction at a low temperature of 300 ° C. or lower to form an amorphous ceramic coating film excellent in heat resistance and water resistance.

These metal alkoxides are amorphous second
Not only does it form a layer, but it also has good penetrability due to the alcohol solution, and it also works to harden and strengthen by entering into defective parts such as pores and pinholes in the first layer, so it is a good two-layer structure with very few defective parts. It is considered that since the ceramic coating film of No. 2 is formed and the film thickness is controlled to an appropriate value, the discharge withstand voltage characteristic is good and the variation of the withstand voltage characteristic is small.

In addition, in the present embodiment, the second
A ceramic coating film having a coefficient of thermal expansion of 70 × 70 ⁻⁷ / ° C. or less was used for the layer 14 of 70.degree.
A ceramic coating film having a coefficient of thermal expansion of more than ⁻⁷ / ° C. is inferior in discharge withstanding characteristic, and the element body may be broken or cracked. The cause is guessed as follows.

That is, when ceramics such as a non-linear resistor is sintered, residual stress may exist. Causes include non-uniform mixing in the mixing process, non-uniform temperature distribution in the firing process, and uneven atmosphere. It is considered that these influence each other and the element body contracts non-uniformly to cause residual stress.

However, when the materials coated with the high resistance layer materials having different thermal expansion coefficients are sintered, residual stress is generated only by the sintering. When a material having a thermal expansion coefficient smaller than that of the element body is applied and sintered, the element body cannot be fully shrunk and a tensile stress remains, and the high resistance layer is affected by the shrinkage force of the element body and excessively contracts. Compressive stress remains. By the way, the coefficient of thermal expansion of the non-linear resistor was measured and found to be 70 × 70 ⁻⁷ / ° C. Therefore, if a material of 70 × 70 ⁻⁷ / ° C. or less is applied, compressive stress remains in the high resistance layer, and if it is more than that, tensile stress remains.

The compressive stress of the high resistance layer effectively acts on the fracture and cracks entering from the outer peripheral portion. It is considered that the breakage and cracks that occur in the outer peripheral portion due to the discharge withstand test are caused by thermal expansion of the element body by the applied energy.

Therefore, even if compressive stress remains in the ceramic coating film on the outermost peripheral portion of the element body, even if the withstand energy is applied to the element body, the energy is consumed until the compressive stress disappears, and the discharge withstand characteristic is apparently large. Will indicate the value.

FIG. 5 shows the relationship between the coefficient of thermal expansion of the ceramic coating film and the discharge withstand voltage characteristic.
It can be seen that the characteristics deteriorate when the temperature exceeds ^-7 / ° C.

According to the above embodiments, the ceramic coating film having the inorganic polymer structure is formed as the first layer 13 on the surface of the element body 11, and the second layer 1 is further formed thereon.
By forming a ceramic coating film having an amorphous structure as No. 4 and having both layers having a thermal expansion coefficient of 70 × 70 ⁻⁷ / ° C. or less, excellent discharge withstand characteristics and high reliability are obtained. A non-linear resistor can be provided.

In this example, aluminum pyrophosphate was used as the material of the ceramic coating film having the inorganic polymer structure which becomes the first layer 13.
Other phosphates can be applied as long as they have the same coefficient of thermal expansion.

Although methoxysilica, which is a kind of metal alkoxide, is applied as the material of the ceramic coating film having the amorphous structure which becomes the second layer 14, other metal alkoxide may be used as long as the thermal expansion coefficient is suitable. It is also possible to employ a ceramic material such as an alkali metal salt that forms an amorphous film.

An oxide raw material is suitable as the additive for the non-linear resistor, but other components may be added as long as they can be converted into an oxide by firing to improve the non-linear characteristics.

In the above embodiment, the non-linear resistor has a diameter of 100 mm and a wall thickness of 22 mm, but it is confirmed that the same effect can be obtained even if the capacitance is smaller or larger than this. did it.

[0098]

As described above, according to the first aspect of the invention, the ceramic coating film having the inorganic polymer structure is formed as the first layer on the surface of the sintered body, and the second layer is further formed on the ceramic coating film. By forming a ceramic coating film having an amorphous structure as the layer 4, it is possible to obtain a highly reliable non-linear resistor having excellent discharge withstand voltage characteristics.

According to the invention of claim 2, a ceramic coating film having an inorganic polymer structure is formed as a first layer on the surface of the sintered body, and an amorphous film is formed as a second layer on the ceramic coating film. By forming a ceramic coating film having a structure and having both layers having a thermal expansion coefficient of 70 × 70 ⁻⁷ / ° C. or less, a highly reliable non-linear resistor having excellent discharge withstand characteristics can be obtained. Obtainable.

[Brief description of drawings]

FIG. 1 is a sectional view showing a linear resistor according to a first embodiment of the present invention.

FIG. 2 is a graph showing discharge withstand voltage characteristics of the nonlinear resistor according to the example.

FIG. 3 is a sectional view showing a linear resistor according to a second embodiment of the present invention.

FIG. 4 is a graph showing discharge withstand voltage characteristics of the non-linear resistor according to the example.

FIG. 5 is a graph showing discharge withstand voltage characteristics of the nonlinear resistor according to the example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Element body (sintered body) 3 1st layer 4 2nd layer 11 Element body (sintered body) 12 1st layer 13 2nd layer

Claims (2)

[Claims] 1. A non-linear resistor having a high resistance layer provided on the surface of a sintered body containing zinc oxide as a main component, wherein the high resistance layer is a ceramic coating film having an inorganic polymer structure. And a second layer, which is an amorphous ceramic coating film provided on the first layer, and a non-linear resistor. 2. A non-linear resistor having a high resistance layer provided on the surface of a sintered body containing zinc oxide as a main component, wherein the high resistance layer is a ceramic coating film having an inorganic polymer structure. And a second layer, which is an amorphous ceramic coating film provided on the first layer,
A non-linear resistor characterized in that both layers have a coefficient of thermal expansion of 70 × 70 ⁻⁷ / ° C. or less.