JPH0370102A - Manufacture of voltage non-linear resistor - Google Patents

Abstract

PURPOSE:To eliminate warping of sintered member and facilitate silver electrode application by splashing slurry of zinc oxide containing added oxide and dropping zinc oxide crystal grains therein and mixing them and drying the mixture thus forming a mixed material. CONSTITUTION:Slurry 3 is poured on a rotating disk 2 provided at the top part of a dryer vessel 1. The slurry is splashed in fine grain state by centrifugal force produced by the rotation of the disk 2. A powder supplying port 4 opened toward the peripheral part of the disk 2 is separately provided at the top part of the dryer vessel 1 and zinc oxide crystal grains 5 are dropped from this supplying port 4. The splashed slurry 3 is dried by hot air 6 at 200-300 deg.C blown into the vessel from outside, and the zinc oxide crystal grains 5 collide against this slurry being dried and they are fixed together as they are dried. The raw material mixture 7 thus formed is dropped to the bottom part of the dryer vessel 1. The obtained raw material mixture 7 is taken out and filled into a die and is compressed to obtain a molded body. When this molded body is baked in the air, the sintered body is not bent so that a silver electrode can be applied uniformly by screen printing process.

Description

[Detailed description of the invention] [Industrial application field] The present invention uses a powder whose main component is zinc oxide.

The present invention relates to a method for manufacturing a voltage nonlinear resistor, particularly for a low voltage varistor, which is produced by firing.

[Conventional technology]

Silicon carbide varistors, zinc oxide varistors, and the like are known as varistors. Zinc oxide varistors are often used because they have excellent nonlinear voltage-current characteristics, limited voltage, and discharge withstand capacity. Zinc oxide varistors used in low voltage circuits such as 12V DC must have their operation start voltage reduced to about 20V, for example.

Conventionally, B was added to zinc oxide to make low-voltage varistors.
By leaching a zinc oxide fired body which has been fired with addition of a or Sr in boiling water, a crystal grain body consisting of one or a few large crystals of zinc oxide is obtained, and then this zinc oxide crystal grain body is The method used is to mix it with zinc oxide varistor powder, form it into a type, and then fire it. Varistor powder is formed by adding oxides such as praseodymium and cobalt to zinc oxide powder to produce voltage non-linearity to form a slurry, and granulating the slurry using a spray dryer. As the zinc oxide crystal grains, those having an average grain size of 50 mm or less are usually used.

This particle size is selected depending on the required starting voltage. Conventionally, varistor powder with an average particle size of 100 μm has been used.

[tllj that the invention tries to solve! However, as mentioned above, zinc oxide crystal grains of 50 tna or less and 1
When mixing, molding, and baking using varistor powder of about 1001r, the dense zinc oxide crystal grains fall into the mold first during molding, and are evenly mixed with the less dense varistor powder. The mold is not filled and the sintered body is bent.
There was a problem in that the silver electrode could not be uniformly applied to both main surfaces of the sintered body.

An object of the present invention is to solve the above-mentioned problems, and to create a voltage nonlinear resistor by uniformly mixing zinc oxide crystal grains and varistor powder so that the sintered body does not warp and silver electrodes can be easily coated. The purpose of this invention is to provide a method for manufacturing the same.

[Means to solve the problem]

In order to achieve the above object, the present invention provides voltage non-linearity in which a mixture of zinc oxide crystal grains and zinc oxide varistor powder containing an added oxide for producing voltage non-linearity is molded and fired. In a method for manufacturing a resistor, a slurry of zinc oxide containing an additive oxide is scattered, zinc oxide crystal grains are dropped into the scattered slurry and mixed, and the mixture is dried to produce a mixture. shall be taken as a thing.

[Effect]

When zinc oxide crystal grains fall into a slurry of zinc oxide containing an oxide added to produce voltage nonlinearity, the slurry and crystal grains collide and become fixed while drying. As a result, the varistor powder adhered to the zinc oxide crystal grains becomes one particle.

When molding a mixture made of such particles, the less dense varistor powder adheres to the denser zinc oxide crystal grains and falls, making it possible to uniformly fill both into the mold. .

〔Example〕

Barium carbonate is added to zinc oxide powder with Ba content of 0.07 atomic%.
Fill it into a mold with a diameter of 90 m, and
It was molded to a thickness of 5 pieces under a pressure of 2 t/-. 135 in the air
It was fired at a temperature of 0°C for 5 hours, and the fired body was crushed into 5fi square pieces and boiled in pure water for 10 hours. I changed the water several times during this time. When the obtained powder was dried, zinc oxide crystal grains having an average particle size of 40 μm were obtained. The obtained crystal grains were released from 1 to 3 single crystals, and Ba used for grain growth was almost completely removed. In addition, zinc oxide powder contains praseodymium oxide,
Additives such as cobalt oxide and chromium oxide, a predetermined amount of binder, and pure water were added and mixed in a ball mill to form a slurry.

FIG. 1 shows a rotating disk type spray dryer device. The above slurry 3 is poured into the rotating disk 2 installed at the top of the dryer tank 1.The slurry is dispersed into fine particles due to the centrifugal force caused by the rotation of the disk 2, but a separate disk 2 is placed at the top of the dryer tank 1. A powder supply port 4 that opens toward the periphery is provided, and the zinc oxide crystal grains 5 mentioned above are allowed to fall from this supply port 4.

The amount of crystal grains 5 supplied is 10% by weight based on the dry weight of the slurry 3. The scattered slurry 3 is dried by hot air 6 of 200 to 300° C. blown from outside the tank, but the zinc oxide crystal grains 5 collide with the slurry during drying and become fixed while drying.

The raw material mixture 7 shaped in this way is dried in the dryer tank 1.
Fall to the bottom of the. The air in the tank is exhausted from an exhaust port 8 attached to the bottom to facilitate this fall. The obtained raw material mixture 7 having an average particle diameter of 100 nm was taken out, filled into a mold, and squeezed at a pressure of 1 t/aJ to obtain a molded body having a thickness of la+ and a diameter of 20 m. This molded body was heated to 1300℃ for 2 hours.
Calcined in air for an hour. The sintered body at this time was not curved, and the silver electrode could be uniformly applied and baked by the screen printing method, so the electrode application area ratio was 100%.

As the spray dryer, in addition to the above-mentioned rotating disk type, a nozzle spraying type in which the slurry is ejected from a nozzle, or a combined rotating disk and nozzle spraying type can also be used.

〔Effect of the invention〕

According to the present invention, when a slurry containing an added oxide for producing voltage nonlinearity is dried using a spray dryer, zinc oxide crystal grains are dropped into the scattered slurry to form zinc oxide crystal grains. The body and the varistor powder adhere to each other to form a single particle, and this mixture is molded.
A voltage nonlinear resistor is manufactured by firing. As a result, the crystal grains and varistor powder are uniformly distributed during molding, and the unevenness of sintering shrinkage during firing is eliminated, resulting in a sintered body that does not warp and improves the electrode coating area ratio. We were able to manufacture a voltage nonlinear resistor with excellent discharge resistance.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a spray dryer device used in one embodiment of the present invention. 1: dryer tank, 2: rotating disk, 3: barista powder slurry, 4: powder supply port, 5: zinc oxide crystal grains, 6: hot hood, 7: raw material mixture. 3 Varistor powder slurry Figure 1

Claims (1)

[Claims] 1) In a method for manufacturing a voltage nonlinear resistor in which a mixture of zinc oxide crystal grains and zinc oxide varistor powder containing an additive oxide for producing voltage nonlinearity is molded and fired, the additive oxide Sprinkle a slurry of zinc oxide containing
A method for manufacturing a voltage nonlinear resistor, which comprises dropping zinc oxide crystal grains into a scattered slurry, mixing it, and drying the slurry to produce a mixture.