JPS6320004B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an apparatus for forming a side insulating film of a nonlinear resistance element whose main component is ZnO. Conventionally, the side insulating film forming apparatus for this type of non-linear resistance element (hereinafter referred to as an element) whose main component is ZnO has been to apply an epoxy-based organic material to the side surface of the element for insulation after firing, or to insulate the side surface of the element after firing. Previously, various inorganic compounds were applied to the side surfaces of the device and then fired, and after firing, an insulating coating was formed that became a glassy or crystalline insulator for insulation. 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. Also,
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 it 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 the firing is performed in two steps, there is a drawback that the fuel (including electricity) cost and the firing device are used twice, which increases the manufacturing cost. Furthermore, both methods have the disadvantage that considerable technology and equipment are required to make the side insulating film uniform to the required thickness. However, in recent years, a technological method has been developed in which antimony oxide (Sb ₂ O ₃ ) is placed in the container used for firing, and the element is housed in the same container to form a side insulating coating on the element at the same time as the element is fired. . In this type of means, a pedestal is disposed within the container, and the element is placed on the pedestal via a bedding material. However, in such a structure, when an insulating film is formed on the element at the same time as the element is fired as described above, the following problems occur in the insulating film on the sides of the element due to the relationship between the pedestal and the element. In other words, the element whose temperature is being increased is
As shown in the figure, it contracts rapidly at 800°C to 1000°C. Also, _Sb2O3 in _the container is generally 920
Sublimation begins at around ℃ and turns into Sb ₂ O ₃ vapor, forming an insulating film on the surface of the element. When forming this film, if the diameter of the pedestal is smaller than the diameter of the element, a portion of the element protrudes from the pedestal, resulting in excessive reaction between the protruding portion and the Sb ₂ O ₃ vapor. For this reason,
As shown in FIG. 2, a bulge 3 is formed in the element circumferential portion (protruding portion) 1a of the insulating coating layer 2 of the element 1. Although not shown, this bulge may also occur in the upper part of the element 1 due to excessive reaction. The above element 1
The bulge 3 formed at the bottom of the element 1 and the bulge formed at the upper part of the element 1 may damage the element during handling.If the bulge 3 is large, pores 4 are formed inside the bulge 3, which prevents close contact with the element. This is a disadvantage of decreasing performance. This invention was made in view of the above circumstances, and it is possible to form an insulating coating that has dense and uniform crystal grains without pinholes, has good adhesion to the element body, and does not cause swelling. An object of the present invention is to provide a side insulation coating forming apparatus for a zinc oxide nonlinear resistor element. An embodiment of the present invention will be described below with reference to the drawings. In FIG. 3, a recessed pedestal 14 made of a heat-resistant ceramic material is placed on the bottom of an alumina sheath (firing container) 12. This pedestal 1
A compression-molded element 18 is placed on the inner bottom surface 15 of 4 with a layer of bedding powder 16 interposed therebetween. At this time, the inner diameter of the pedestal 14 is made larger than the diameter of the element 18 by several mm to several tens of mm or more as shown in the figure. In addition, the protruding body 17 at the end of the pedestal 14 is from several mm to several tens of mm from the inner bottom surface 15.
Form within mm. On the other hand, a disk body 19 made of a material that does not easily react with the element is placed on the upper surface of the element 18. The diameter of this disk body 19 is
Make it 2 mm or more larger than the diameter of 8. In addition, bed powder 16
This prevents welding of the base 14 and the element 18.
Further, a coating agent 20 is applied to the inner surface of the sheath 12 to form a side insulation coating on the element 18. The top of the sheath 12 is provided with a lid 22 that is homogeneous to the sheath 12. The material of the pedestal 14 is preferably alumina or a zinc oxide sintered plate. In particular, a zinc oxide sintered plate is preferable since it is of the same quality as the main component of the element and does not impair the characteristics of the sintered element. Bed powder 16 is made of alumina.
A powder made from a ZnO element or powder obtained by calcining and crushing a ZnO element is used. A component similar or the same as that of the ZnO element is required more strongly than in the case of the pedestal. Note that if the pedestal 14 is made of the same material as the element 18, the bedding powder 16 may be omitted. Further, the coating agent 20 for forming the side insulation coating may be applied to a part or the entire inner surface of the sheath 12 and the bottom surface of the lid 22. Next, a method for sintering the zinc oxide nonlinear resistance element of the present invention and forming an insulating coating on its side surfaces will be described. First, the element 18 is made of ZnO (91% by weight), Sb ₂ O ₃ ,
Total of Bi ₂ O ₃ , CO ₂ O ₃ , Cr ₂ O ₃ , MnO ₂ , SiO ₂ etc. (9
% by weight) is added, thoroughly mixed, and then compression molded into a suitable shape. For example, diameter 40mmφ, thickness approx.
Shape into a 30 mm cylinder to form a compact. Coating agent 20
In this method, an antimony oxide containing at least one of Sb ₂ O ₃ , Sb ₂ O ₄ , and Sb ₂ O ₅ as a starting material is applied as a slurry with water to the inner surface of the sheath 12 and dried. The element 18 in the form of a molded body is placed in the sheath 12 coated with the coating agent 20 in this manner, and the lid 22 is placed on the sheath 12 to create a substantially airtight state. When fired in this sealed state at a temperature range of 1000°C to 1400°C (1100°C to 1300°C is preferred from the viewpoint of the electrical characteristics of the device), the antimony oxide that is the coating agent 20 in the sheath 12 sublimates. The inside of the container becomes an atmosphere of antimony oxide, and ZnO on the surface of the element 18,
A high-resistance insulating film is formed on the surface of the element 18 through a solid-gas phase reaction with Bi ₂ O ₃ and the like. In the above solid-gas phase reaction, Sb ₂ O ₃ of antimony oxide changes to Sb ₂ O ₄ at about 570°C, and Sb ₂ O ₅ changes to 357
It becomes Sb ₂ O ₄ at temperatures above ℃. The formed Sb ₂ O ₄ is 920℃
It begins to sublimate from the vicinity and becomes extremely active at temperatures above 1000°C, creating an atmosphere of antimony oxide inside the sheath 12. On the other hand, element 18 shrinks by about 40% by volume in the temperature range of 800°C to 1000°C, and contains ZnO, Zn ₂ SiO ₄ , pyrochlore, Zn ₂ Bi ₃ Sb ₃ O ₄ , Zn _2.33 Sb _0.67 O ₄ ,
Crystal phases such as 14Bi ₂ O ₃ and Cr ₂ O ₃ are formed. On the surface of the element 18, antimony oxide generated in the container reacts with Zn ²⁺ diffused from inside the element 18, and Zn _2.33 Sb _0.67 O ₄ is formed on the element surface and sintered together with the element 18. In the insulating coating formed as described above, the inner diameter of the concave pedestal 14 is larger than the diameter of the element 18 and the protruding body 17 is particularly formed on the surface of the circumferential portion 18a of the lower part of the element 18 as shown in the figure. Because of this, the reaction between the element surface and the Sb ₂ O ₃ vapor occurs smoothly, and a uniform insulating film can be obtained without excessive reaction as in the conventional case. On the other hand, since the disk body 19 is also present on the upper part of the element 18, a uniform insulating film can be formed without causing excessive reactions as in the conventional case. Next, the following table shows an experiment of the discharge withstand capacity using a 4×10 μs current waveform of a resistor element formed in a conventional case and an embodiment of the present invention.

[Table] In addition, the following table shows an experimental example of the influence of the difference between the inner diameter of the pedestal 14 and the diameter of the element 18 on the discharge withstand capacity.

[Table] In the above examples, the evaporation temperature and speed of Sb ₂ O ₃ vary depending on the composition and formulation of the powder spread together with Sb ₂ O ₃ . Furthermore, the shrinkage of the element changes depending on the composition, formulation, molding pressure, calcination conditions, and firing conditions. From these considerations, the inner diameter of the pedestal 14 and the height of the protrusion 17 are selected to be appropriate sizes. Further, the protrusion 17 of the pedestal 14 may be formed as shown in FIG. 4. As described above, according to the present invention, the inner diameter of the concave pedestal on which the zinc oxide nonlinear resistance element is placed is larger than the diameter of the zinc oxide nonlinear resistance element, and a protrusion of a predetermined length is provided at the end of the pedestal, and Since the disk body is provided on the top of the element, the reaction between the element surface and the Sb ₂ O ₃ vapor occurs smoothly in the lower and upper circumferential parts of the element, and a uniform insulating coating is formed on the element. This has the advantage of being able to prevent the formation of bulges as in the conventional case.

[Brief explanation of the drawing]

Fig. 1 is a characteristic curve diagram showing the shrinkage rate with respect to temperature of the zinc oxide nonlinear resistance element, Fig. 2 is an explanatory diagram showing a state in which a bulge is formed in the insulating coating at the bottom of the element, and Fig. 3 is an illustration of the present invention. FIG. 4 is a partially sectional front view showing one embodiment of the present invention, and FIG. 4 is a front view showing a different example of the pedestal. 12... Sheath (container for firing), 14... Pedestal, 1
6...Bedding powder, 17...Protruding body, 18...Element, 1
8a... Circumference part, 19... Disc body, 20... Coating agent, 22... Lid.

Claims (1)

[Claims] 1. A pedestal placed in the firing container, a non-linear resistance element containing zinc oxide placed on the pedestal via a bed of powder, and antimony oxide placed at a predetermined location in the firing container. In the zinc oxide nonlinear resistor element manufacturing apparatus, the pedestal is formed in a concave shape, and the pedestal is formed in a concave shape, and the side insulating coating of the resistor element is formed by gas-solid phase reaction simultaneously with the firing of the resistor element. , the inner diameter of the pedestal is formed to be larger than the diameter of the non-linear resistance element, the protrusion at the end of the pedestal is made to protrude from the inner bottom surface of the pedestal by a predetermined length, and the upper part of the element is difficult to react with the element. 1. A side insulation coating forming apparatus for a zinc oxide non-linear resistor element, characterized in that a disk body having a diameter larger than the diameter of an element body formed of a member is placed thereon.