JPS6330768B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a novel method for manufacturing a voltage nonlinear resistor containing zinc oxide as a main component. Voltage nonlinear resistors as functional elements used in earth arresters, surge absorbers, etc. are made mainly of zinc oxide, and ceramics produced by firing at a high temperature of about 1200°C are becoming mainstream. The resistor is manufactured by adding a small amount of additives such as bismuth oxide and cobalt oxide to zinc oxide and using these as raw materials by ordinary ceramic methods. The manufacturing method usually includes
Includes a granulation process. There are various methods of granulation, but any method can improve the fluidity of the powder (granulated powder) and the ability to fill it into a mold, resulting in improved performance in the next process. Pressing work becomes easier, and the uniformity of the press-formed product obtained also improves. Among the various granulation methods, one method that is especially suitable for mass production is to uniformly disperse powder in water or the like, add a binder such as polyvinyl alcohol (PVA), etc., and make a slurry. This is a spray drying method. Mass production of large-diameter elements used as power surge arresters requires
This method is suitable, and a spray dryer is an excellent device to use. The reason is that the particles (granulated powder) made using a spray dryer are almost perfectly spherical.
This is because they generally have a small angle of repose and therefore have excellent fluidity and filling properties. In order to use a spray dryer, it is necessary to prepare a slurry, and the slurry is required to contain as much powder as possible and have a low viscosity. Slurry viscosity is determined by various conditions, but for example, when dispersing oxides such as zinc oxide in water, (1) the type, shape, and particle size of the oxide powder; (2) the size of the powder and The ratio of water to water, (3) wetting between powder and liquid (surface activity), and (4) temperature have a major influence. When silicon oxide is added to a voltage nonlinear resistor whose main component is zinc oxide, V ₁₀₀ 〓 _A (in the element
It is known that when a current of 100 μA is applied, the value of the voltage required to flow can be increased, and the nonlinearity index can be improved. The microstructure of the resistor has been investigated using scanning electron microscopy (SEM), It is known to form zinc silicate and inhibit the particle growth of zinc oxide. Although the energy withstand capacity per volume is small, silicon oxide is indispensable for resistors of devices used at high voltages. In this way, the electrical characteristics of the resistor can be improved by adding silicon oxide, but when a granulation method using a spray dryer is used for mass production, silicon oxide is added when preparing the slurry. The more added, the more viscous the slurry becomes, making it virtually impossible to atomize with a spray dryer. It depends on the type of silicon oxide used, but if a highly reactive amorphous one is used,
Since it is easy to self-agglomerate and does not soak well with water, it is difficult to form solid aggregates that are quite large (for example, 0.5
mm to several mm in diameter). In this case, it becomes difficult to homogenize the slurry, so
The stability of the electrical properties and yield of the element after firing deteriorates, and it often shows failure in various durability tests. Although it is possible to improve the electrical characteristics of a resistor element whose main component is zinc oxide by adding a large amount of silicon oxide as mentioned above, it is difficult to add silicon oxide in a very small amount in mass production. The current situation is that The present invention was developed in view of the current situation, and the amount of silicon oxide can be freely controlled, the viscosity does not increase even in the slurry preparation process, and it can be easily granulated with a spray dryer in a low viscosity state. The object of the present invention is to provide a method for manufacturing a voltage nonlinear resistor. That is, in the present invention, silicon oxide and transition metal compound are mixed in a ratio of 1:2 to 3:1.
Zinc oxide is the main ingredient, which is characterized in that the aqueous slurry containing powder and zinc oxide is mixed at a molar ratio of The present invention relates to a method of manufacturing a voltage nonlinear resistor as a component. Examples of the transition metal compound used in the present invention include salts or oxides containing manganese, nickel, cobalt, iron, zirconium, or zinc, with oxides being particularly preferred. By mixing these transition metal compounds with silicon oxide at a molar ratio of 1:2 to 3:1 and firing at 1000 to 1300°C, a fired product thereof can be obtained. The firing time is appropriately determined depending on the type and amount of the transition metal compound used. For example, if silicon oxide and zinc oxide are mixed in a molar ratio of 1:2, 2
When calcining is performed for a period of time, zinc silicate can be obtained by reacting as shown in the following formula. SiO ₂ +2ZnO→Zn ₂ SiO _4These silicon oxide-transition metal compound fired products contain a small amount of activator such as manganese,
Zinc silicate, which is commercially available as a phosphor, may also be used. By using these baked products of silicic acid,
Perhaps because the slurry has excellent wettability with water, no extreme thickening phenomenon is observed in the slurry, making granulation using a spray dryer possible. As the molar ratio of silicon oxide to the transition metal compound increases, the drawbacks that appear when silicon oxide is added as is, as described above, appear, but if the molar ratio is up to about 3 times, these drawbacks are almost completely eliminated. I can't. In addition, if the amount is less than 1/2 mole, the transition metal compound must increase relatively in order to add a certain amount of SiO ₂ , and this relative increase in the amount increases the voltage of the device. This causes deterioration of nonlinearity, etc. These fired products generally do not exhibit extreme particle growth if they are obtained at a firing temperature of up to about 1200°C, and the grain size depends on the type of transition metal compound used, but is usually about 10 μm or less. be. but,
Materials calcined at temperatures higher than 1200°C have some grain growth, so they must be pulverized before slurry preparation. Such pulverization can be easily carried out using commonly used pulverizers such as ball mills and vibration mills. The particle size of this powder needs to be such that it can pass through a sieve of at least 400 mesh in order to ensure that the powder is uniformly distributed within the resistive element when it is manufactured. The slurry is prepared by a general method, and according to the present invention, even if silicon oxide (converted amount) is added to the solid content in an amount of 0.5% (weight %, the same shall apply hereinafter) or more, there is no significant increase in viscosity. It can be suitably used for granulation using a spray dryer. Next, the manufacturing method of the present invention will be explained in more detail with reference to Reference Examples, Examples, and Comparative Examples, but the present invention is not limited only to these Examples. Reference example 1 91 parts of zinc oxide (parts by weight, same below), 2.70 parts of bismuth oxide, 3.38 parts of antimony oxide, 0.88 parts of cobalt oxide, 0.43 parts of nickel oxide, manganese carbonate
A mixture consisting of 0.67 parts (hereinafter referred to as mixture A)
By adding silicon oxide at various proportions in the total solid content, six types of powder mixtures with different proportions of silicon oxide were prepared. After adding polyvinyl alcohol aqueous solution to these powder mixtures, they were mixed using a stirrer or a crusher, and then lightly pressed. This was granulated by mechanical forcing (for example, using a Power Mill (trade name)) through a sieve of several tens of meshes, and formed into a resistor according to a conventional method. V100μA (V/mm) of each resistor obtained
FIG. 1 shows a graph in which the nonlinear index 10 μα 100 μA (nonlinear index when the current value flowing through the device is 10 to 100 μA) is plotted against the addition ratio of silicon oxide. As can be seen from this reference example, as the content of silicon oxide increases, the electrical characteristics of the resistance element improve. Example 1 Zinc silicate (Zn ₂ SiO ₄ , average particle size: about 5 μ), which is commercially available as a phosphor, was added to mixture A in various proportions when converted to silicon oxide, and silicon oxide Six types of solids with different blending ratios were prepared. Separately, prepare a liquid component (hereinafter referred to as liquid component B) containing water, polyvinyl alcohol, and a cationic surfactant (trade name: cationic MA), and then mix the solid component and liquid component B at a weight ratio of 2:1. The mixture was mixed to obtain a slurry. A graph plotting the addition ratio (%) of silicon oxide in the total solid content and the viscosity of the obtained slurry is shown in FIG. 2 with a mark (ⓓ). These slurries were then granulated using a spray dryer and molded into resistors using a conventional method. V100μA (V/mm) of each resistor obtained
FIG. 3 shows a graph in which the non-linearity index 10 μAα100 μA is plotted against the addition ratio of silicon oxide. Comparative Example 1 An experiment was conducted in the same manner as in Example 1, except that silicon oxide (SiO ₂ ) was used instead of zinc silicate and the addition ratio (%) in the total solid content was varied, and a slurry was obtained. . A graph plotting the viscosity of each slurry against the addition ratio (%) of silicon oxide is shown in FIG. 2 with a mark (ⓓ). Example 2 Equimolar amounts of silicon oxide and manganese carbonate (MnCO ₃ ) were mixed and fired at 1000 to 1100°C to obtain manganese silicate (MnSiO ₃ ). This material was sufficiently ground using a vibrating mill to obtain a powder that could pass through a 400-mesh sieve. This manganese silicate powder was added to Mixture A at various blending ratios when converted to the weight of silicon oxide, to prepare six types of solid contents with different blending ratios of silicon oxide. Next, these solid components were mixed with liquid component B at a weight ratio of 2:1 to obtain six types of slurries. A graph in which the viscosity of each slurry is plotted against the amount of silicon oxide added (converted amount) is shown in FIG. 4 by (○) marks. These slurries were then granulated using a spray dryer, and then molded into resistors using a conventional method. A graph plotting V ₁₀₀ 〓 _A of each resistor obtained against the addition ratio of silicon oxide is shown in the fourth graph.
Indicated by (●) mark in the figure. Examples 3 to 6 Cobalt oxide (CoO) in place of manganese oxide,
Firing was performed using nickel oxide (NiO), ferrous oxide (Fe ₂ O ₃ ), and zirconium oxide (ZrO ₂ ) under the conditions shown in Table 1 to obtain a fired product. Slurries containing these pulverized baked products all had low viscosity and could be subjected to a granulation process using a spray dryer. After granulation, the electrical properties of the resistor obtained by molding according to a conventional method are shown in Table 1.

[Table] Comparative Examples 2 to 6 After thoroughly mixing the transition metal compounds shown in Table 2 and silicon oxide at a molar ratio of 4:1,
The mixture was calcined at ℃ and then ground to a powder that could pass through a 400-mesh sieve. The resulting powder was mixed with mixture A. At this time, the amount of silicon oxide in the total solid content was set to about 2%, which gave a good nonlinear index (see FIGS. 1 and 3). Next, the obtained solid content and liquid content B were mixed at a weight ratio of 2:1 to obtain a slurry, but the slurry did not thicken. The resulting slurry was granulated using a spray dryer, and then five types of resistors were obtained using a conventional method. Table 2 shows the V ₁₀₀ 〓 _A or nonlinear index of the obtained resistor.

[Table] From the results shown in Table 2, the value of V ₁₀₀ 〓 _A of the resistor of Comparative Example 2 is the value of V 100 〓 A of the resistor of Example 2 using the same manganese carbonate (the value of V ₁₀₀ 〓 _A of the resistor of Example 2 using the same manganese carbonate) (See figure 4)
It was smaller than. In addition, in Comparative Examples 3 to 6, the amount of silicon oxide in the total solid content was 2% (the first (see Fig. 3 and Fig. 3), but the values of the nonlinear index of Comparative Examples 3 to 6 differ slightly depending on the type of transition metal compound, but they are all better than the values of corresponding Examples 3 to 6. It was also small. As described above, according to the present invention, by using silicon oxide calcined with various transition metal compounds, problems such as increased viscosity that occur when untreated silicon oxide is added are solved. Therefore, the amount of silicon oxide can be controlled, and voltage nonlinear resistors with improved electrical characteristics can be mass-produced.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the change in electrical characteristics of the resistance element obtained in Reference Example 1 as a function of the silicon oxide compounding ratio, and FIG. A graph showing the change in viscosity; FIG. 3 is a graph showing the change in electrical properties with respect to the silicon oxide blending ratio of the resistor element obtained in Example 1; FIG. 4 is a graph showing the viscosity of the slurry obtained in Example 2. and FIG. 6 is a graph plotting the electrical characteristics of the resistance element against the silicon oxide blending ratio.

Claims (1)

[Claims] 1. Silicon oxide and transition metal compound in a ratio of 1:2 to 3:
Zinc oxide is produced by mixing an aqueous slurry containing zinc oxide and a powder obtained by mixing the powder at a molar ratio of 1:1 and then firing at 1,000 to 1,300°C, which is then granulated with a spray dryer and then molded. A method of manufacturing a voltage nonlinear resistor as the main component. 2 The transition metal compound is manganese, nickel,
The manufacturing method according to claim 1, which is a salt or oxide containing cobalt, iron, zirconium, or zinc.