JPH0729707A - Manufacture of voltage-dependent nonlinear resistor - Google Patents

Abstract

PURPOSE:To enhance a voltage-dependent nonlinear resistor in resistance to an impulse discharge current and long-term reliability by a method wherein material metal oxide is uniformly dispersed into liquid and finely ground into primary particles when the material metal oxide consisting mainly of zinc oxide is mixed into liquid and ground into slurry. CONSTITUTION:A mixing process is separated into two sub-processes, a first sub-process wherein material metal oxide is uniformly dispersed into liquid by a mixer such as a ball mill where balls smaller than 8mm in diameter are used and a second sub-process wherein the metal oxide is finely ground into primary particles by another ball mill where balls smaller than 2mm in diameter are used. Or, the above two sub-processes are carried out at the same time. Slurry containing primary particles is sprayed and dried out into sintering material.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a voltage non-linear resistor made of a metal oxide containing zinc oxide as a main component.

[0002]

2. Description of the Related Art A voltage non-linear resistor is required to have a large voltage non-linear coefficient, a large shock discharge withstand capability, and high long-term reliability. This voltage nonlinear resistor is manufactured, for example, in the following process. First, zinc oxide is mixed with praseodymium oxide, cobalt oxide, bismuth oxide, antimony oxide, aluminum oxide, magnesium oxide, potassium carbonate, boron oxide, chromium oxide, calcium carbonate, and other trace amounts of additives such as polyvinyl alcohol. Such a binder and pure water are added and mixed in a ball mill containing roughly spherical balls of zirconium oxide (ZrO ₂ ) of 97.25% and the balance of yttrium oxide (Y ₂ O ₃ ) to form a slurry. Spray with a spray dryer granulator, dry with hot air and granulate to obtain a uniform fine powder material. A die is filled with this powder material and pressed at a pressure of 1 ton / cm ² to obtain a molded body. The compact is fired in air at 1300 ° C. for 2 hours to obtain a cylindrical sintered body having a diameter of 14 mm and a thickness of 1.0 mm.
Ag paste is printed and baked on both main surfaces of this sintered body to form an Ag electrode having a diameter of 11 mm. Then, the lead wire is fixed on the silver electrode by Ag-Pb-Sn eutectic solder, and then heated to 130 ° C. by a heater, and the lead wire is partially left in the epoxy resin. The heater is heated and the lead wire is partially immersed in the epoxy resin. This operation is performed three times in total to secure a resin thickness of about 2 mm, and then the resin is kept at 150 ° C for 2 hours for curing. As a result, a voltage non-linear resistor covered with the resin layer is obtained. In the ball used in the ball mill in the above process,
For example, those having a diameter of 2 to 8 mm are used as described in JP-B-1-31683.

Line 11 in FIG. 1 is the sun created as described above.
For pull, 8 / 20μsec shock release at intervals of 3000A to 1000A
The electric current is applied twice at intervals of 2 minutes, and the varistor voltage before and after that is applied.
Pressure V _1mAThe result of having calculated | required the change rate of is shown. From around 7000A
Varistor voltage V_1mAIs it clear that the change rate of
It A method for evaluating the long-term reliability performance of voltage nonlinear resistors.
As one method, pressure cooker test (PC
T) This PCT is steam at 121 ° C and 2 atm.
When a voltage non-linear resistor sample is specified in a pressure chamber containing
It is left for a while and evaluated by the change in characteristics before and after that.
It Line 21 of Fig. 2 shows the PCT of the conventional voltage non-linear resistor.
The results are shown. Varistor voltage V from around 160 H_1mAchange of
You can see that the rate exceeds 10%.

[0004]

The mixing process requires the following two functions. First, it must have a function of uniformly dispersing zinc oxide, other additives, pure water, and a binder. Zinc oxide and other additives are powders, and pure water is a liquid. It is necessary to uniformly disperse the powder in pure water, and sufficient uniform dispersion reduces the variation in characteristics and increases the impact discharge withstand capacity. Second, the primary particles of powdered zinc oxide and other additives (0.5 μm to several μm).
m) must be capable of finely crushing. By making the primary particles finer, the contact points of each particle increase,
The sintering reaction is promoted during firing, which contributes to an increase in firing density which affects reliability and the like. However, the voltage non-linear resistor manufactured by the above-mentioned conventional technique may not have satisfactory characteristics in the impact discharge current withstand capacity or PCT time.

An object of the present invention is to solve the above problems and to make a slurry in which a raw material is uniformly dispersed in a liquid and finely pulverize the slurry into primary particles to improve the withstand discharge current and long-term reliability. An object of the present invention is to provide a method of manufacturing a voltage non-linear resistor that can be improved.

[0006]

In order to achieve the above-mentioned object, the present invention provides a method of mixing a metal oxide raw material containing zinc oxide as a main component with a liquid in a mixer and pulverizing it. In the method for producing the linear resistor, the hard spherical body used in the mixer has a diameter of 8 mm or more and a diameter of 2 mm or less. The step of mixing and pulverizing the metal oxide raw material with the liquid in the mixer is a dispersion step of mixing in a mixer using a hard spherical body having a diameter of 8 mm or more, and the subsequent mixing machine using a hard spherical body having a diameter of 2 mm or less. It may consist of a pulverizing step of mixing inside, or a step of putting a hard spherical body having a diameter of 8 mm or more and a hard spherical body having a diameter of 2 mm or less at the same time in a mixer. Then, the slurry obtained by the dispersion and pulverization process is sprayed, dried and granulated into a powder material,
It is effective to press and mold this powder material and then fire it. Further, it is effective that the hard spherical body used in the mixer is made of a ceramic containing zirconium oxide and yttrium oxide as components.

[0007]

According to the above-mentioned conventional manufacturing method, a ball sphere of the mixing process is performed by using a hard spherical body having a diameter of 0.5, 2.5, 6, 8, 10, 15, 20 mm to produce a voltage non-linear resistor. Make a sample,
The intermediate characteristics, impact discharge current withstand capability and PCT time in the intermediate process were measured. The total mixing time was 40 hours. Figure 3,
4 and 5 show the results. As shown in the ratio of powder that does not become a slurry in the mixing process in Fig. 3, the diameter is 8 mm.
When smaller spheres are used, the liquid and powder cannot be sufficiently dispersed, resulting in powder lumps that do not form a slurry. This is because the rotational force of the ball mill is transmitted to the spherical body having a small weight, but the spherical body having a small weight has no force to destroy and disperse the lump of the powder which does not become a slurry. The impulsive discharge current resistance is inferior because the dispersion is not sufficient. When a spherical body having a size larger than 2 mm is used, the firing density decreases as the average particle size of the primary particles of the powder increases, as shown in FIG. As a result,
The PCT time is reduced as shown in FIG. This is because the powder can be sufficiently dispersed in the liquid to form a slurry, but the contact area between the balls and zinc oxide and other additives is not sufficient, and the primary particles cannot be finely pulverized. is there. As can be seen from FIG. 3, the dispersion process using the hard spheres having a diameter of 8 mm or more enables sufficient dispersion of the liquid and the powder, and does not cause powder lumps that do not become a slurry. This is because the rotation force of the ball mill is transmitted to the spherical body having a large weight, and the balls having a large weight can break up the lumps of the powder that are not in the slurry state to form the slurry state and disperse it. In addition, the crushing process using spheres with a diameter of 2 mm or less increases the contact area of the spheres with zinc oxide and other additives, and as shown in FIG. 4, the primary particles can be finely crushed and fired. A dense sintered body can be obtained. As a result, as can be seen from FIG. 3, the shock discharge current withstand capability is increased, and as can be seen from FIG. 5, long-term reliability performance can be improved.

The same effect can be obtained by performing the dispersing step using the hard spheres having a diameter of 8 mm or more and the crushing step using the diameter of 2 mm or more separately or simultaneously using both the hard spheres. Is obtained.

[0009]

EXAMPLE As an example of the present invention, a voltage non-linear resistor was manufactured in the following steps. First, a small amount of additives such as praseodymium oxide, cobalt oxide, bismuth oxide, antimony oxide, aluminum oxide, magnesium oxide, potassium carbonate, boron oxide, chromium oxide and calcium carbonate, and a predetermined amount of polyvinyl alcohol and pure water are added to zinc oxide. In the first mixing step, zirconium oxide (ZrO ₂ )
Of 97.25% and the balance of yttrium oxide (Y ₂ O ₃ ) are dispersed in a ball mill containing roughly spherical balls with a diameter of 20 mm to form a slurry. Then, in the second mixing step, roughly spherical balls with a diameter of 1 mm are used. It was pulverized with a ball mill containing a mixture, and this slurry was sprayed with a spray dryer granulator, dried with hot air and granulated to obtain a powder material having uniform fine particles. A mold was filled with this powder material and pressed at a pressure of 1 ton / cm ² to obtain a molded body. The compact was fired in air at 1300 ° C. for 2 hours to obtain a cylindrical sintered body having a diameter of 14 mm and a thickness of 1.0 mm. Ag paste was printed and baked on both main surfaces of this sintered body to form an Ag electrode having a diameter of 11 mm. Then, the lead wire was fixed on the silver electrode with Ag-Pb-Sn eutectic solder, and then heated to 130 ° C. with a heater, and the lead wire was partially immersed in the epoxy resin. The heater heating and the operation of immersing the lead wire in epoxy resin while leaving a part of it are carried out three times in total to secure a resin thickness of about 2 mm, and then 150
It was kept at ℃ for 2 hours and cured. As a result, a voltage nonlinear resistor covered with the resin layer was obtained. The time required for both the first mixing step and the second mixing step was 20 hours for a 200 kg lot. ZrO ₂ used at this time,
The manufacturing process of the roughly spherical ball made of Y ₂ O ₃ is
It is made in the following way with the same manufacturing method as general ceramics. Prepare 97.25% ZrO ₂ powder and the balance Y ₂ O ₃ powder, and prepare a raw material powder by a neutralization coprecipitation method, an alkoxide method, or the like. Then, it is calcined at around 600 ° C., after which pure water and a binder such as polyvinyl alcohol are added, and the mixture is pulverized by a pulverizer such as a ball mill or an attritor. Then, it is dried with hot air using a spray dryer to obtain granulated powder. Then, a rubber mold is prepared and filled with granulated powder. Subsequently, a hydrostatic press (rubber press) was used to obtain a molded body,
After that, it is baked in the air at 1400-1500 ° C to complete.

To the voltage non-linear resistor sample prepared as described above, an impact discharge current of 8/20 μsec was applied twice at intervals of 3000 A to 1000 A twice at intervals of 2 minutes, and the change rate of the varistor voltage V _{1 mA} before and after that was applied. I asked. The result is shown by line 12 in FIG. It can be seen that the embodiment is significantly improved compared to the conventional example of line 11. Next, PCT was performed. The result is shown by the line 22 in FIG. It can be seen that the embodiment is significantly improved in reliability as compared with the conventional example of line 21.

In another embodiment, the same metal oxide raw material as that used in the above embodiment, to which pure water is added, is used to prepare two types of balls of about 20 mm and 1 mm, which are composed of 97.25% ZrO ₂ and the balance Y ₂ O ₃ . It was dispersed and crushed with a ball mill to obtain a slurry. Using this slurry, a voltage non-linear resistor covered with a resin layer was manufactured through the same steps as those in the above-mentioned examples. The balls used in the mixer were also made in the same manner as in the above-mentioned examples. The rate of change in varistor voltage at the time of impact discharge current application and PCT obtained for this voltage non-linear resistor was similar to the lines 11 and 12 in FIGS. 1 and 2.

As yet another embodiment, ZrO ₂ 97.25
%, And the balance Y ₂ O _{3 having} diameters of 20 mm, 8 mm, 2 respectively
The same result was obtained by dispersing and pulverizing with a ball mill containing mm and 0.5 mm roughly spherical balls. In the above embodiments, the ball mill is used in the mixing and crushing steps, but a mixing and crushing machine such as a vibration mill or an attritor may be used. In addition, the material of the ball as the grinding medium is Zr
Alumina, silicon carbide, and silicon nitride may be used in addition to the O ₂ · Y ₂ O ₃ ceramics.

[0013]

According to the present invention, the mixing step of making the raw material metal oxide of the voltage non-linear resistor into the slurry to which the granulation step is applied, the dispersion step using the hard spheres of large diameter, and the small diameter step. By performing the pulverization step separately or simultaneously with the hard spheres, the powder can be sufficiently dispersed in the liquid in the dispersion step, and fine primary particles can be obtained in the pulverization step. It is possible to obtain a high sintered body. As a result, it was possible to obtain a voltage nonlinear resistor having a large shock discharge current resistance and improved long-term reliability.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the impact discharge current and the varistor voltage change rate of a voltage nonlinear resistor according to an embodiment of the present invention and a conventional voltage nonlinear resistor.

FIG. 2 is a graph showing the relationship between the PCT time and the varistor voltage change rate of a voltage nonlinear resistor according to an embodiment of the present invention and a conventional voltage nonlinear resistor.

FIG. 3 is a relational diagram of the diameter of balls used in a mixer, the ratio of powder that does not become a slurry, and the impact discharge current withstand capacity.

FIG. 4 is a diagram showing the relationship between the diameter of balls used in a mixer, the average particle diameter of primary particles, and the firing density.

FIG. 5 is a diagram showing the relationship between the diameter of balls used in a mixer and the PCT time.

[Explanation of symbols]

 11, 21 Conventional sample 12, 22 Example sample

Claims (5)

[Claims] 1. A method for producing a voltage non-linear resistor comprising a step of mixing a metal oxide raw material containing zinc oxide as a main component with a liquid in a mixer and pulverizing the hard spherical body used in the mixer. A method of manufacturing a voltage non-linear resistor having a diameter of 8 mm or more and a diameter of 2 mm or less. 2. A step of mixing and crushing a metal oxide raw material with a liquid in a mixer, a dispersing step of mixing in a mixer using hard spheres having a diameter of 8 mm or more, and a subsequent diameter 2
The method for producing a voltage non-linear resistor according to claim 1, comprising a pulverization step of mixing in a mixer using a hard spherical body having a size of mm or less. 3. The step of mixing and pulverizing a metal oxide raw material with a liquid in a mixer is a step in which a hard spherical body having a diameter of 8 mm or more and a hard spherical body having a diameter of 2 mm or less are simultaneously put in the mixer. The method of manufacturing a voltage nonlinear resistor according to claim 1. 4. The voltage according to claim 1, wherein the slurry obtained by the dispersion and pulverization process is sprayed, dried and granulated into a powder material, and the powder material is pressed and molded and then fired. Manufacturing method of non-linear resistor. 5. The method for producing a voltage non-linear resistor according to claim 1, wherein the hard spherical body used in the mixer is made of a ceramic containing zirconium oxide and yttrium oxide as components.