JPH02125401A - Varistor - Google Patents

Abstract

PURPOSE:To reduce the shrinkage distortion of the outer surface of a material at the time of sintering and to obtain a varistor having excellent surge resistance by forming the outer surface of a varistor material of high formation density layer. CONSTITUTION:A disclike varistor material 3 is composed by incorporating, for example, zinc oxide as a main ingredient, employing ceramic powder suitably added with metal oxide to the zinc oxide to provide notches 1 of oblique outer peripheral edges at both front and rear faces, and forming the outer surfaces of the notches 1 in thicknesswise direction of high formation density layers 2, and electrodes 4 are formed, after sintering, on both front and rear faces of the material 3. As the material 3 forming means of the above structure, oblique protrusions 10, 11 formed from the inner faces on the outer peripheral edges of pressed faces 8, 9 of upper and lower punches 6, 7 for forming a molding press mold 5 are employed to press ceramic powder 12 by the faces 8, 9. The outer surfaces are formed of the layers 2 to largely reduce the remaining strain of the outer surface at the time of sintering and to prevent microcrack from occurring at the time of application of surge.

Description

[Detailed description of the invention] [Purpose of the invention] (Industrial application field) The present invention provides a varistor with an improved element structure.

(Prior art) Conventionally, film-formed varistors are made by forming ceramic powder, which is made mainly of curved lead oxide and mixed with several types of metal oxide parts, into a disk shape, and then sintering it. Electrodes are formed on both the front and back sides of the barristor body obtained by this process, a lead-out terminal is led out from the electrode, and the tip of the lead-out terminal is exposed and coated with resin or other material. .

The varistor body constituting the varistor generally uses a press die 31 as shown in FIG. 6, and an upper bunch 32. The ceramic powder 34 is sandwiched between the lower punch 33Iil, and the upper punch 32 and the lower punch 33m
The ceramic powder 34 is pressed and formed, and the pressing surfaces 35 of the upper bunch 32 and lower punch 33 are
．． Since numeral 36 is flat, the varistor body 37 formed as shown in FIG. 7 has a flat front and back surface, for example, a disk shape.

Therefore, the varistor body 35 formed in this way
Although the molding density is the same in all parts, the tensile stress due to shrinkage in the outer periphery during the heat shrinkage process during sintering is larger than in other parts, resulting in residual shrinkage strain in the outer periphery. ing.

Therefore, when a surge is applied during the process of commercializing the product and using it by incorporating it into various ms, there has been a problem in that microcracks (a phenomenon in which crystal grain boundaries separate) occur on the outer periphery.

Therefore, there is a risk that the subsequent application of a surge will cause a discharge phenomenon in the micro crank part, ionize the oxides that make up the varistor element, reduce the resistance value, cause short-circuit damage, and cause the varistor to lose its function. there were.

(Problems to be Solved by the Invention) As described above, in conventional varistors, shrinkage strain remains on the outer periphery during sintering of the varistor body, and as a result, when a surge is applied, the surge resistance deteriorates due to the generation of microcracks. As a ballista, this caused a fatal flaw.

The present invention has been made in view of the above-mentioned points, and it is an object of the present invention to provide a varistor with excellent surge resistance by reducing the shrinkage distortion of the outer periphery of the varistor body during sintering. be.

[Structure of the Invention] (Means for Solving the Problems) The varistor according to the present invention is characterized in that, as a varistor element structure, the outer periphery of the varistor element body is a high-density layer.

(Function) According to the varistor having the above configuration, since the molding density of the outer periphery of the varistor body is higher than that of other parts, shrinkage of this part can be reduced during sintering. It becomes possible to reduce residual shrinkage strain.

(Example) An embodiment of the present invention will be described below.

That is, for example, zinc oxide is the main component, and MGO is added to this.
,Nio,MnO,coo,cuo.

Cab, sro, AQo, 81203, 5b203
, TiO2, Crz03, Fe203
.

AfI203, S io2. SnO2, ZrO2
As shown in Fig. 1, using ceramic powder to which metal oxides such as Disc-shaped varistor body 3 with high mold density layer 2 on the outer periphery
After sintering, electrodes 4 are formed on both sides of the varistor body 3.

In addition, the outer periphery in the thickness direction of the cut-off portion 1 whose outer periphery edges on both the front and back sides of the above structure are sloped is highly molded! t11
! As shown in FIG. 2, the means for forming the varistor body 3 described in No. 2 is formed by forming the outer periphery of the press surfaces 8 and 9 of each of the upper and lower bunches 6 and 9 of the press mold 5 into a protrusion shape that is inclined from the inner surface. 10.11 is used to press the ceramic powder 12 with the press surfaces 8 and 9.

Therefore, the varistor body 3 having the above-mentioned structure has a lead-out terminal drawn out from the electrode 4 portion and is used as a single-plate structure, or a plurality of varistor bodies 3 are stacked as necessary.

According to the varistor having the varistor body 3 configuration as described above, since the outer periphery of the varistor cord 3 has a high molding density of 172, residual distortion in the outer periphery due to tensile stress due to thermal contraction during sintering can be greatly reduced. can be reduced.

Therefore, when a surge is applied during use, it is possible to prevent microcracks from occurring on the outer periphery.

Therefore, the surge resistance characteristics of the varistor can be significantly improved.

Next, a comparison of the surge resistance between the present invention (A) having the ballista cable structure shown in FIG. ff11 and the conventional example (B) having the ballista cable structure shown in FIG. 7 will be described.

That is, both the present invention (A) and the conventional example (B) mainly contain expanded lead oxide and have a diameter of 20 m.

The sample was a varistor body with a thickness of 1M, the electrode was a silver electrode, a lead wire was attached to the 'I5 pole, and an epoxy resin exterior was applied.
When a surge of 00A was applied 5 times each, the breakdown status of the ball valve was investigated with respect to the applied surge constant, and the results are as shown in the table below. Note that the number of samples was 10 each.

As is clear from the table above, in the conventional example (B), surge application ff
While Ltl 7000AT-3 pieces and 8000Ar811811 were all destroyed at 9000A, only 4 Ltl 0000A'T'' pieces of the present invention (A) were destroyed, demonstrating a significant improvement in surge resistance characteristics.

In addition, in the above embodiment, as the structure of the high molding density layer 2 on the outer peripheral part of the varistor body 3, an example in which the outer peripheral edges on both sides of the back side of the varistor cable body 3 are sloped is used as an example. However, by using a double-forming press mold 13 as shown in FIG.
After once pressing the relamic powder 18 in step 17, press surfaces 21° 22 of the outer punches 19 and 20 of the upper punch 14 and the lower punch 15 are pressed against the inner punch 16, as shown in FIG.
．． 17, each of the press surfaces 23 and 24 is pressed, and as shown in FIG. But it has the same effect. In the figure, 27 is an electrode.

Further, in the above embodiment, a disc-shaped varistor element body was exemplified and explained, but the same effect can be obtained even if the present invention is applied to a square plate-shaped varistor element body.

Further, in the above embodiments, a composition containing zinc oxide as the main component was exemplified, but it is of course applicable to compositions containing, for example, strontium titanate, barium titanate, silicon carbide, iron oxide, etc. as the main component.

[Effects of the Invention] According to the present invention, the shrinkage strain of the PU at the outer periphery of the varistor body
It is possible to obtain a varistor with high practical value that has less retention and can significantly improve surge resistance characteristics.

[Brief explanation of drawings]

1 and 2 relate to an embodiment of the present invention, in which FIG. 1 is a front view showing a varistor element, FIG. 2 is an explanatory view showing a means for forming the varistor element shown in FIG. 3 to 5 relate to other embodiments of the present invention, FIGS. 3 and 4 are explanatory diagrams showing the means for forming the varistor element, FIG. 5 is a front view showing the varistor element, and FIG. 7 and 7 relate to a conventional example, FIG. 6 is an explanatory view without showing the means for forming the varistor cable body, and FIG. 7 is a 1F side view showing the varistor body. 2... High mold density layer 3... Varistor cable patent application Hito Marcon Electronics Co., Ltd. Figure Figure

Claims (1)

[Claims] A varistor characterized by using a varistor body whose outer periphery is a high-density layer.