Zinc oxide varistor and process for the production thereof

Details Zinc oxide varistor and process for the production thereof Zinc oxide varistor and process for the production thereof

1993-10-01

1997-01-14

Hoang, Tu

Electrical resistors

Resistance value responsive to a condition

Current and/or voltage

338 20, 29620, 252518, H01C 710

Patent

active

055944060

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention relates to a zinc oxide varistor used for protecting various kinds of electronic instruments from unusually high voltages, and a process for producing the same.


BACKGROUND TECHNIQUES

Recently, there has been rapidly developed a high level integration of control circuits in instruments for general use and industry.
When an extraordinarily high voltage (surge) is applied to electronic parts of semiconductors used in such control circuits, such parts may be destroyed. Accordingly, it becomes indispensable to take a countermeasure to meet the situation. As such a counterplan, varistors are generally employed. Among the rest, the zinc oxide varistor is widely available for the protection of various kinds of electronic instruments from unusually high voltages because the zinc oxide varistor has an excellent voltage nonlinearity and surge absorbing ability.
Hithertofore, there has been widely known a zinc oxide varistor provided with at least two electrodes on the surface of varistor element having zinc oxide as its main component. Further, materials for said electrodes, are disclosed in, for example, Patent Application Kokai SHO 62-290104 Official Gazette, etc., whose content is as follows:
Electrode material for a zinc oxide varistor was produced by the process wherein 5.0% by weight of a lead borosilicate glass powder composed of 50.0-85.0% by weight of PbO, 10.0-30.0% by weight of B.sub.2 O.sub.3 and 5.0-25.0% by weight of SiO.sub.2 was weighed out and then said powder together with Ag powder (65.0% by weight) were milled in a vehicle (30.0% by weight), in which ethyl cellulose was dissolved in butyl carbitol, to obtain a silver paste which is the electrode material.
And then said electrode material was applied onto a surface of a fired varistor element and heated to form an electrode.
Although the above zinc oxide varistor is excellent in voltage nonlinearity as mentioned above, further improvement in the voltage nonlinearity has been sought due to the desire of energy-saving and efficiency increase in the zinc oxide varistor.
Thus, responding to the above requirements, the present invention aims to provide a zinc oxide varistor further improved in voltage nonlinearity.


DISCLOSURE OF THE INVENTION

In order to accomplish such an objective, according to the present invention, the following lead borosilicate-type glass was diffused into a fired varistor element from its surface, said lead borosilicate-type glass containing at least one metal oxide selected from cobalt oxide, magnesium oxide, yttrium oxide, antimony oxide, manganese oxide, tellurium oxide, lanthanum oxide, cerium oxide, praseodymium oxide, neodymium oxide, samarium oxide, europium oxide, gadolinium oxide, terbium oxide, dysprosium oxide, holmium oxide, erbium oxide, thulium oxide, ytterbium oxide and lutetium oxide.
When the above constitution is adopted, it follows that there is interposed at particle boundaries between zinc oxide particles composing a varistor element, the chemical elements composing a lead borosilicate-type glass containing at least one metal oxide selected from cobalt oxide, magnesium oxide, yttrium oxide, antimony oxide, manganese oxide, tellurium oxide, lanthanum oxide, cerium oxide, praseodymium oxide, neodymium oxide, samarium oxide, europium oxide, gadolinium oxide, terbium oxide, dysprosium oxide, holmium oxide, erbium oxide, thulium oxide, ytterbium oxide and lutetium oxide.
As a result, resistance values of the particle boundaries between zinc oxide particles will become higher, and a leakage current running between electrodes until reaching a varistor voltage becomes much lower. In conclusion, zinc oxide varistor improved in voltage nonlinearity can be obtained.


BRIEF EXPLANATION OF THE DRAWINGS

FIG. 1 is a front view showing one of the working examples of the zinc oxide varistor of the present invention. FIG. 2 is a sectional view of FIG. 1, and FIG. 3 is a front view showing varistor element of the zinc oxide varistor shown in FIG. 1.


BEST MODES FOR CARRYING OUT TH

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patent: 4147670 (1979-04-01), Shohata et al.
patent: 4319215 (1982-03-01), Yamazaki et al.
patent: 4460623 (1984-07-01), Levinson
patent: 4506285 (1985-03-01), Einzinger
patent: 4959262 (1990-09-01), Charles et al.
patent: 5091212 (1992-02-01), Sakai et al.

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