JPS6161522B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention is capable of coating a side surface of one or more elements by simultaneously firing a plurality of elements housed in the same firing container with an appropriate application mode of the coating agent for forming an insulating film in the firing container. The present invention relates to a method of manufacturing a voltage nonlinear resistor element that forms a uniform and good insulation film. Conventionally, this kind of high-purity zinc oxide ZnO is the main component, and other materials include bismuth Bi, cobalt Co, manganese Mn,
The side insulation method for a voltage nonlinear resistor element (hereinafter referred to as an element) containing a small amount of oxide such as antimony Sb is to apply an epoxy-based organic substance to the side surface of the element after firing to form an insulating film, or to bake the element. First, various inorganic compounds are applied to the side of the device and then baked.
The actual situation is that an insulating coating that becomes a glass or crystalline insulator after firing is formed. However, the former method has the disadvantage that the adhesion between the applied epoxy-based organic substance and the element body is poor, and as a result, moisture is adsorbed to the element, resulting in significant deterioration of characteristics and weakening of short-wave tail resistance. Furthermore, since there is a difference in thermal expansion between the element body and the epoxy resin, there is a drawback that thermal shock can cause cracks in the epoxy resin coated on the side surfaces of the element, causing deterioration. On the other hand, in the latter method, it is necessary to match the shrinkage rates of the element body and the side insulating material during firing. For this purpose, the compression-molded element is first fired to shrink the element to some extent, and then an inorganic compound or a mixture thereof is applied to the side surface of the first fired element and then main fired to form an inorganic insulating side surface coating. in this case,
Since it is fired in two batches, the fuel (including electricity)
This method has the disadvantage that the manufacturing cost increases because the firing equipment is used twice. Furthermore, both methods have the disadvantage that considerable skill and equipment are required to make the side insulating coating uniform to the required thickness. Therefore, it has been possible to form an insulating film that has no pinholes, has dense and uniform crystal grains, and has good adhesion to the device body, and has little deterioration in device characteristics, such as current discharge withstand capacity, corona resistance, and resistance. A method for firing a voltage nonlinear resistor element with excellent arc properties has not been considered. In this firing method, antimony oxide is placed in a container used for firing, and a molded body whose main component is ZnO is placed in the same container, and an insulating film is formed on the side surface of the body at the same time as the body is fired. It is something. This method will be further explained below with reference to FIGS. 1a and 1b. As shown in the figure, a pedestal 6 made of a heat-resistant ceramic material such as alumina is placed on the bottom of an alumina firing container 1, and a compression-molded element 3 is placed on the pedestal 6 with a layer of powder 5 interposed therebetween. Make sure to put the .
In this case, the bedding powder 5 prevents the pedestal 6 and the element 3 from welding. Further, a coating agent 2 for forming an insulating film on the side surface of the element 3 is applied to the inner surface of the firing container 1, and a lid 4 having the same properties as the firing container 1 is provided on the upper part of the firing container 1. The material of the pedestal 6 is preferably alumina or a zinc oxide sintered plate. In particular, a zinc oxide sintered plate is the same as the main component of the element 3, so it is preferable since there is no risk of impairing the characteristics of the sintered element. ing. The bed powder 5 is made of alumina or ZnO element powder, or calcined and crushed powder of the ZnO element, and is more strongly required than the case of the pedestal 6 to be similar or the same as the components of the ZnO element. . Note that if the pedestal 6 is made of the same material as the element 3, the bedding powder 5 may be omitted. By the way, element 3 contains ZnO (91 mol%), Sb ₂ O ₃ ,
A mixture of Bi ₂ O ₃ , Co ₂ O ₃ , Cr ₂ O ₃ , MnO ₂ , SiO ₂ etc. in total (9 mol %) is added, thoroughly mixed, and then compression molded into a suitable shape, for example, a cylindrical shape. For example, it is molded into a cylindrical shape with a diameter of 40 mmφ and a thickness of about 30 mm. Moreover, coating agent 2 contains Sb ₂ O ₃ , Sb ₂ O ₄ ,
It is a compound mainly composed of antimony oxide containing at least one of Sb ₂ O ₅ , which is made into a slurry with water, and is applied to the inner surface of the firing container 1 and then dried. The coating agent 2 may contain any of Bi ₂ O ₃ and SiO ₂ . The molded element 3 is placed in the firing container 1 coated with the coating agent 2 in this manner, and the lid 4 is closed to perform firing. In this closed state
1000°C to 1400°C (from the point of view of the electrical characteristics of element 3)
When fired at a temperature range of 1100°C to 1300°C (preferably 1100°C to 1300°C), antimony oxide, which is the main component of coating agent 2, sublimates, creating an atmosphere of antimony oxide in container 1, and ZnO and Bi ₂ O on the surface of element 3. ₃ , etc., and a high resistance insulating film is formed on the surface of the element 3. To briefly explain the above solid-gas phase reaction, Sb ₂ O ₃ of antimony oxide turns into Sb ₂ O ₄ at about 570°C.
Sb ₂ O ₅ becomes Sb ₂ O ₄ at temperatures above 357°C. Been formed
Sb ₂ O ₄ begins to sublimate at around 920°C and becomes extremely active at temperatures above 1000°C, and the inside of the firing container 1 becomes an atmosphere of antimony oxide. On the other hand, element 3 is 800℃~1000℃
In addition to ZnO, which shrinks by about 40% by volume in the temperature range of °C,
Zn ₂ SiO ₄ , pyrochlore, Zn ₂ Bi ₃ Sb ₃ O ₄ , Zn ₂ .
Crystal phases such as ₃₃ Sb ₀ . ₆₇ O ₄ and 14 Bi ₂ O ₃ Cr ₂ O ₃ are formed. On the surface of the element 3, antimony oxide generated in the container 1 reacts with Zn ²⁺ diffused from inside the element 3, and the surface of the element 3 is covered with an insulating film.
Zn ₂ . ₃₃ Sb ₀ . ₆₇ O ₄ (spinel) is formed and sintered together with the element 3. Although the method for forming an insulating film by firing is as described above, this method is not without its problems.
This is because the coating agent 2 is opposite to the coating agent 2, and the coating agent 2
The insulating film is well formed on the side surface portion of the element 3 that is close to the side surface of the element 3, but the insulating film is not well formed on the other side surface portions. That is,
This means that the manner in which the insulating coating is formed on the side surface of the element 3 differs depending on the housing position of the element 3 in the firing container 1, and the thickness of the insulating coating on the side surface varies not only between elements 3 but also even for the same element. This suggests that this disadvantage becomes more pronounced as the number of elements accommodated increases. In addition, since the upper end surface of the element 3 is not masked in any way in FIGS. 1a and 1b, an insulating film will be formed also on the upper end, but this insulating film will be removed by polishing later. This is because electrodes need to be attached to the upper and lower end surfaces of the element 3 later. Of course, it is possible to prevent the formation of the insulating film by masking. Therefore, an object of the present invention is to provide a voltage nonlinear resistance that can form a uniform and good insulating film on the side surfaces of one or more elements as molded bodies or calcined bodies when they are fired in the same firing container. The present invention provides a method for manufacturing a body element. For this purpose, in the present invention, firing is performed with a coating agent being applied at least near the outer periphery of the upper part of the element or near the outer periphery of the lower part of the element without contacting the element. The present invention will be explained below with reference to FIGS. 2 to 4. First, to explain the first specific embodiment shown in FIGS. 2a and 2b, this is a firing container 1 (inner dimensions 300 mm (vertical) x 300 mm (horizontal) x 60 mm excluding the mounting surface of the pedestal 6).
(Height)) The firing was performed with the coating agent 2 uniformly applied to the bottom surface, and the other aspects were the same as in the conventional case. According to this, the coating agent 2 can be applied without contacting the vicinity of the bottom of any of the nine elements (40 mm (diameter) x 40 mm (thickness or height) molded body or calcined body) 3. Because of this, an insulating film is formed on the side surface of each element 3 even under substantially the same conditions, and an insulating film with a substantially uniform thickness is formed on the side surface of each element 3.
The results will be described later when the coating agent was applied so that Sb ₂ O ₃ was contained in amounts of 5 g, 10 g, and 15 g, respectively. Next, a second specific embodiment will be explained with reference to FIGS. 3a and 3b. In this embodiment, firing is performed with the coating agent 2 uniformly applied to the entire bottom surface of the lid 4 as shown in the figure. In the first embodiment, even though the insulating coating is formed on the side surface of each element 3 under substantially the same conditions, it cannot be denied that the conditions are somewhat uneven. Therefore, in this embodiment, the coating agent 2 is also applied to the bottom surface of the lid 4 in order to keep the interior space of the firing container 1 under more uniform conditions. It is not difficult to imagine that in this case, the insulating film could be formed more uniformly than in the first embodiment. In addition, the internal dimensions of the firing container 1 in this embodiment are 300 mm.
mm (length) x 300 mm (width) x 40 mm (height), the dimensions of the nine elements 3 are 40 mm (diameter) x 30 mm (thickness or height) molded body (or calcined body of this) Coating agent 2 was coated to contain 10 g of Sb ₂ O ₃ , and the results will be described later as well. Figures 4a and 4b show a third specific embodiment of the invention. In this embodiment (the internal dimensions of the firing container 1 and the dimensions of the element 3 are the same as those in the first specific embodiment), as shown in the figure, a pedestal (60 mm in diameter) is placed on the outer peripheral edge of the pedestal (diameter 60 mm) over a range of 10 mm from the outer peripheral edge. Apply coating agent 2 in a ring shape so that it contains about 1 g of Sb ₂ O ₃ , and
Coating agent 2 was similarly applied to the outer peripheral edge of the bottom surface of the alumina plate (diameter 60 mm) 7 placed on the top surface with bedding powder 5 interposed therebetween, so that about 1 g of Sb ₂ O ₃ was included. The results are shown in the table below.

[Table] From the above table, it can be seen that according to the present invention, a voltage nonlinear resistor element with good characteristics can be obtained. Incidentally, referring to the first specific embodiment,
When the coating agent was applied so as to contain 5 g of Sb ₂ O ₃ , the thickness of the insulating film was insufficient, and when the amount of Sb 2 O 3 was 10 g, an insulating film with a uniform thickness could not be obtained. However, when the content was 15g, the thickness and uniformity were sufficient, and good discharge durability was obtained. The present invention is as described above, but the amount of coating agent to be applied generally depends on its composition, target insulation coating thickness, firing container dimensions, number of elements, capacity, dimensions, and more. It should preferably be determined experimentally, giving due consideration to firing conditions and the like. As explained above, the present invention provides a coating agent for forming an insulating film at least near the lower outer periphery or near the upper outer periphery of each element when firing elements as one or more molded bodies housed in the same firing container. Since the firing is performed in the presence of , a uniform, dense, and sufficiently thick high-resistance insulating film can be formed on the side surfaces of each element. Therefore, according to the present invention, voltage nonlinear resistors with excellent electrical characteristics can be mass-produced.

[Brief explanation of the drawing]

FIGS. 1a and 1b are a plan view and a cross-sectional view taken along the line A-A for explaining a method for manufacturing (firing) a voltage nonlinear resistor according to the prior art; FIGS. 2a and 3b are Figures a, b and Figures 4 a and b all show specific embodiments of the present invention, each figure a is a plan view, and each figure b is a line B-B in the corresponding figure a. FIG. 3 shows cross-sectional views taken along lines C-C and D-D. 1... Baking container, 2... Coating agent, 3... Element (molded body), 4... Lid, 5... Bedding powder, 6... Pedestal,
7...Alumina plate.

Claims (1)

[Claims] 1. A manufacturing method for obtaining a voltage nonlinear resistor element by adding a small amount of oxides such as bismuth, cobalt, manganese, antimony, etc. to high-purity zinc oxide as the main component, mixing, granulating, compression molding, and firing.
When firing one or more molded bodies housed in the same firing container, at least the vicinity of the upper outer periphery or the lower outer periphery of each molded body is kept in contact with the molded bodies, and antimony oxide is the main component. 1. A method for manufacturing a voltage nonlinear resistor element, characterized in that firing is performed in a state in which a compound is applied and arranged.