JP2520699B2 - Method of manufacturing voltage-dependent nonlinear resistor - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing a voltage-dependent nonlinear resistor.

(Prior Art) Conventionally, as a method of manufacturing this kind of non-linear resistor, a raw material containing strontium titanate (SrTiO ₃ ) as a main component is wet-mixed, and a binder is added to this to obtain a molded product having a desired shape. And then heat the formed body in a reducing gas atmosphere such as a mixed gas of nitrogen gas and hydrogen gas at a temperature of 1300 to 1450 ° C., and then heat the sintered body in air at a temperature of 800 to 1200 ° C. And diffusing oxygen into the sintered body, or in the above method, instead of immediately subjecting the sintered body obtained by firing to heat treatment, apply Na-based glass to the surface of the sintered body. Then, the temperature of the sintered body in the air is 800 to 1200 ° C.
There is known a method of subjecting the sintered body to heat treatment to diffuse Na-based glass into the sintered body.

The voltage-dependent nonlinear resistor so-called varistor thus obtained has a large capacitance, and is therefore widely used as a component for protecting electronic devices and the like from surges such as lightning, inductive pulses, noises, and the like.

(Problems to be solved by the invention) In any of the above-mentioned manufacturing methods, impurity components are repelled to the periphery due to the growth of crystal grains during firing, and a silicic acid-based material is contained in the surface portion of the sintered body as compared with the inside. There is a lot of glass.

As a result, in the case of the former of the above manufacturing methods, the oxygen diffusion rate at the time of heat treatment is different between the surface portion having a large amount of silica glass when heat-treating the sintered body and the interior having a small amount of glass, so There is a problem that resistance variation in the ceramic body of the voltage-dependent nonlinear resistor occurs, and reliability of electrical characteristics deteriorates.

Further, in the latter case, Na-based glass is applied to the surface of the sintered body thereafter, and Na is not uniformly diffused between the surface portion having a large amount of silica glass during heat treatment and the inside having a small amount of glass quality. However, there is a problem that the obtained voltage-dependent non-linear resistor causes a variation in resistance within the ceramic body, resulting in deterioration in reliability of electrical characteristics.

An object of the present invention is to provide a method capable of solving the above-mentioned problems and manufacturing a voltage-dependent nonlinear resistor without causing deterioration in reliability of electric characteristics.

(Means for Solving the Problems) A first invention of the present invention relates to a method for producing an oxygen diffusion type voltage-dependent nonlinear resistor, which comprises forming a raw material powder containing strontium titanate as a main component into a desired shape. Formed into a body, the formed body is fired in a reducing gas atmosphere to form a sintered body, the surface of the sintered body is polished, and the polished sintered body is heated in an oxidizing atmosphere at a temperature of 950 to 1200. It is characterized in that it is subjected to a heat treatment at ℃.

The second invention relates to a method for manufacturing a Na-diffusion type voltage-dependent nonlinear resistor, which comprises forming a raw material powder containing strontium titanate as a main component into a molded body having a desired shape and reducing the molded body. A sintered body is prepared by firing in a gas atmosphere, the surface of the sintered body is ground, and the surface of the ground sintered body is polished.
Na-based glass is coated and the temperature is 950-1200 ℃ in oxidizing atmosphere.
It is characterized by performing the heat treatment of.

As the additive to be added to the strontium titanate as the main component in the present invention, WO ₃ , Nb ₂ O ₅ , La ₂ O ₃ , CeO ₂ , Nd ₂ O ₃ , Y ₂ O
_{At least one of 3} , Sm ₂ O ₃ , Dy ₂ O ₃ , Ag ₂ O, CuO and MnO ₂ and at least one of SiO ₂ and Al ₂ O ₃ are used, and 100 parts by mol of strontium titanate is used. In general, the addition amount to each is 0.01 to 5.0 parts by mole and 0.03 to 1.5 parts by mole, respectively.

Polyvinyl alcohol or the like is used as the binder, and the addition amount is generally about 1 to 10 parts by weight with respect to 100 parts by weight of strontium titanate.

Examples of the Na-based glass include NaCo ₃ , Na compounds such as NaF, ethyl cellulose, an organic solvent such as nitrocellulose added, and kneaded, and the addition amount when the organic solvent is used is Na compound. Generally, it is about 10 to 200 parts by weight with respect to 100 parts by weight.

Incidentally, in order to prevent the generation of bubbles in the Na-based glass and the lack of Na-based glass due to the bubbles, an organic solvent is added, and an antifoaming agent such as isopropyl alcohol is added during kneading. It may be added, and in that case, the addition amount is generally about 0.1 to 5 parts by weight with respect to 100 parts by weight of the Na compound.

As a gas for firing the molded body in a reducing gas atmosphere, for example, a mixed gas of nitrogen gas and hydrogen gas is used,
The ratio of nitrogen gas to hydrogen gas in the mixed gas is 95 to 99% by volume: 5 to 1% by volume, and the temperature is about 1300 ° C to 1450 ° C.

The surface of the sintered body is polished on the upper and lower surfaces of the sintered body in consideration of the uniform diffusion of oxygen or Na.

Air is used as the atmosphere for heat treatment of the sintered body in an oxidizing atmosphere, and the heat treatment temperature is 950 ° C to 120 ° C.
Keep it at about 0 ° C.

(Function) A layer containing much silicic acid glass on the surface of the sintered body is removed by polishing. Then, by subjecting the polished sintered body to a heat treatment at a temperature of 950 to 1200 ° C. in an oxidizing atmosphere, oxygen is uniformly diffused in the sintered body. Also, after coating the surface of the polished sintered body with Na-based glass, the sintered body is subjected to heat treatment at a temperature of 950 to 1200 ° C. in an oxidizing atmosphere, so that Na is uniformly dispersed in the sintered body. It

(Example) Next, a specific example of the present invention will be described together with a comparative example.

Example 1 Nb ₂ O ₅ was added to 100 mol parts of strontium titanate SrTiO ₃ powder.
Was added 0.02 mol parts, SiO ₂ 1.0 mol parts, Al ₂ O ₃ 0.1 mol parts respectively, respectively, after adding water and mixing for 15 hours in a ball mill,
After dehydration and drying, 15 parts by weight of polyvinyl alcohol was added as a binder, mixed and granulated to prepare a raw material powder.

Furthermore, this raw material powder is 1500 kg / c in a dry press using a die.
Molding was performed under a pressure of m ² to form a molded body having a diameter of 11 mm and a thickness of 1.5 mm.

Subsequently, the compact was fired at a temperature of 1400 ° C. for 3 hours in a mixed gas atmosphere containing 95% by volume of nitrogen gas and 5% by volume of hydrogen gas to obtain a sintered body made of semiconductor ceramics having a diameter of 9.0 mm and a thickness of 1.2 mm. It was created.

Then, using a lapping machine as shown in the first figure, the upper and lower surfaces of the sintered body (1) are polished by 0.2 mm each to have a diameter of 9.0.
A polished sintered body (2) having a thickness of 0.8 mm was obtained. In the drawing, (3) indicates a polished portion.

Then, the polished sintered body (2) was heated in air at a temperature of 1100 ° C for 3
Heat treatment was performed for a period of time to prepare 100 voltage-dependent nonlinear resistors in one lot.

Next, as shown in FIG. 2, silver electrodes (5) were baked on the upper and lower surfaces of each voltage-dependent nonlinear resistor (4) prepared by the above method at a temperature of 800 ° C., and this was designated as sample 1.

When the varistor voltage change rate and the capacitance change rate were examined as the electrical characteristics of 100 samples of one lot prepared by the above method, the results shown in the table were obtained.

The electrical characteristics are measured according to the high temperature load life test method,
DC40V was continuously applied for 1000 hours at a temperature of 85 ° C., and left at room temperature and normal humidity for 12 hours.

The rate of change (%) of the varistor voltage (V _1m "V") was calculated by the following formula.

The rate of change (%) in electrostatic capacity (C "pF") was calculated by the following equation.

Comparative Example 1 A sample was prepared in the same manner as in Example 1 except that the upper and lower surfaces of the sintered body obtained by firing were immediately subjected to heat treatment without being subjected to polishing treatment, and this was designated as sample 2.

When the electrical characteristics of Sample 2 were examined by the same method as that of Sample 1, the results shown in the table were obtained.

Example 2 1.0 part by weight of a paste of Na-based glass prepared by the following method was applied to each of the upper and lower surfaces of the polished sintered body (2) and dried in an oxidizing atmosphere at a temperature of 250 ° C. for 0.5 hour, followed by Na. A sample was prepared in the same manner as in Example 1 except that the sintered body coated with the system glass was heat-treated in air at a temperature of 1100 ° C. for 3 hours, and this was designated as sample 3.

When the electrical characteristics of Sample 3 were examined by the same method as that of Sample 1, the results shown in the table were obtained. The Na-based glass paste was prepared as follows.

 First, a mixture having the following composition was prepared.

NaCo ₃ 100 parts by weight Ethyl cellulose 20 parts by weight Butyl carbitol 80 parts by weight Isopropyl alcohol 1 part by weight Next, this prepared mixture was kneaded at a temperature of 20 ° C. for 15 hours to prepare a paste.

Comparative Example 2 Example 1 was repeated except that the same Na-based glass paste as in Example 2 was immediately applied to the upper and lower surfaces of the sintered body obtained by firing without polishing, and then heat treatment was performed. A sample was prepared by the same method as above, and this was designated as sample 4.

When the electrical characteristics of Sample 4 were examined by the same method as that of Sample 1, the results shown in the table were obtained.

As is clear from the table, the method of Example 1 of the present invention in which the surface of the sintered body is polished and then heat-treated, and the present invention in which the surface of the sintered body is polished and then Na-based glass is coated and heat-treated The rate of change of the varistor voltage and the electrostatic capacitance of the voltage-dependent nonlinear resistor obtained by the method of Example 2 was extremely small.

On the other hand, the method of Comparative Example 1 in which the heat treatment is performed immediately without polishing the surface of the sintered body, and the heat treatment is performed by immediately coating the surface of the sintered body with the Na-based glass without polishing the surface of the sintered body. The change rate of the varistor voltage and the capacitance of the voltage-dependent nonlinear resistor obtained by the method of Comparative Example 2 to be applied was large.

(Effect of the Invention) As described above, according to the manufacturing method of the first invention, since the surface of the fired sintered body is polished, the layer having a large amount of vitreous silicate glass on the surface portion of the sintered body is removed. The sintered body, which can be removed and is polished, has a temperature of 95 in an oxidizing atmosphere.
Since the heat treatment is performed at 0 to 1200 ° C, oxygen can be diffused uniformly in the sintered body, so that the voltage-dependent nonlinear resistor can be easily manufactured because the resistance variation in the ceramic body is extremely small. In addition, according to the manufacturing method of the second invention, since the surface of the fired sintered body is polished, the surface portion of the sintered body is made of the silicate glass material. Since many layers can be removed, and the surface of the polished sintered body is coated with Na-based glass, the sintered body is subjected to heat treatment at a temperature of 950 to 1200 ° C. in an oxidizing atmosphere. Since Na can be uniformly diffused in the sintered body, there is an effect that a voltage-dependent nonlinear resistor having very little resistance variation in the ceramic body can be easily manufactured.

[Brief description of drawings]

FIG. 1 is an explanatory view of a step of polishing the surface of a sintered body in the manufacturing method of the present invention, FIG. 2 shows a voltage-dependent nonlinear resistor having silver electrodes formed on both upper and lower surfaces, and (A) is a plan view thereof. ,
(B) is a side view thereof. (1) …… Sintered body (2) …… Grinded sintered body (4) …… Voltage-dependent nonlinear resistor

Claims (2)

(57) [Claims] 1. A raw material powder containing strontium titanate as a main component is formed into a compact having a desired shape, and the compact is fired in a reducing gas atmosphere to prepare a sintered body. The surface is polished, and the polished sintered body is heated at a temperature of 950 in an oxidizing atmosphere.
A method for manufacturing a voltage-dependent nonlinear resistor, characterized by performing a heat treatment at ~ 1200 ° C. 2. A raw material powder containing strontium titanate as a main component is formed into a compact having a desired shape, and the compact is fired in a reducing gas atmosphere to prepare a sintered body. A method for producing a voltage-dependent nonlinear resistor, which comprises polishing the surface, coating the surface of the polished sintered body with Na-based glass, and subjecting the sintered body to a heat treatment at a temperature of 950 to 1200 ° C. in an oxidizing atmosphere.