JPH0745401A - Manufacture of positive temperature coefficient thermistor - Google Patents

Abstract

PURPOSE:To improve anti-reduction performance and to enable reliable use by carrying out oxidation treatment by baking a molded item at a temperature not exceeding a melting point of sintering assistant under a high oxygen concentration before baking the molded item regularly. CONSTITUTION:A molded item 1 is formed by adding sintering assistant to a barium titanate-based semiconductor porcelain material. The molded item 1 is baked at about 1000 to 1240 deg.C not exceeding a melting point of the sintering assistant under high oxygen concentration and oxidation treatment is performed for it. In the process, the molded item 1 is fully and uniformly oxidized as far as an inside thereof in a relatively porous state wherein denseness of a sintering body is not proceeded. Then, regular baking is carried out at a temperature exceeding a melting point of a sintering agent in usual atmosphere or under high oxygen concentration. Furthermore, an electrode 2 is provided to a surface of the molded item 1. Thereby, a thermistor of less characteristic deterioration can be acquired even under reducing atmosphere or in a state wherein oxygen does not exist.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a positive temperature coefficient thermistor used in, for example, a warm air heater or a packaged air conditioner.

[0002]

2. Description of the Related Art A barium titanate type positive temperature coefficient thermistor in which a part of barium of barium titanate is replaced with lead is prepared by first mixing the materials, mixing them, and then dehydrating and drying the mixed powders. Bake. And this calcinated powder is crushed,
After the binder was added and granulated and molded, the main firing was performed. An electrode was formed on the surface of the obtained sintered body. Further, firing is generally performed in the air, but for those required to have a low resistance, there is a case where the reoxidation treatment is performed after the heat treatment once in the reducing atmosphere.

[0003]

In the above positive temperature coefficient thermistor, when organic components such as machine oil, food oil, and seasonings adhere to the thermistor element, in a heat-generating state, the organic components such as mechanical oil, food oil, and seasoning are kept in a reducing atmosphere due to the combustion of these organic components. Will be placed. When a positive temperature coefficient thermistor is used in a reducing atmosphere or in the absence of oxygen, the resistance value is greatly reduced, and the temperature coefficient of resistance is significantly reduced. For this reason, there is a risk that it may lead to a serious accident, and thus there is a problem that its intended use is limited.

The present invention solves such problems, and an object of the present invention is to provide a method of manufacturing a positive temperature coefficient thermistor which is excellent in reduction resistance and can be used with confidence.

[0005]

In order to achieve this object, according to the present invention, before the main calcination of the molded body, it is carried out under a high oxygen concentration by calcination at a temperature below the melting point of the sintering aid. It is characterized by performing.

[0006]

According to this structure, the densification of the sintered body has not evolved, in other words, it oxidizes sufficiently and uniformly to the inside of the molded body in a relatively porous state in the process in which liquid phase sintering is not yet involved. . Then, by the main firing, liquid phase sintering proceeds while the inside of the molded body is sufficiently oxidized, and becomes dense.

As a result, it is possible to obtain a characteristic thermistor capable of preventing the deterioration of the characteristic such as a large decrease in resistance value without reducing even the inside of the thermistor element even if the thermistor is placed in a reducing atmosphere. .

[0008]

EXAMPLES An example of the present invention will be described below.

FIG. 1 is a perspective view of a positive temperature coefficient thermistor in this embodiment. First, (Ba _0.68 Pb _0.22 Ca _0.10 )
TiO ₃ + 0.002Y ₂ O ₃ +0.0003 MnO ₂ +
BaCO ₃ , Pb so that the composition is 0.02SiO _2.
O, CaCO ₃ , TiO ₂ , Y ₂ O ₃ , MnO ₂ and SiO ₂ are weighed and wet mixed in a ball mill. Next, this mixture is dried and then calcined at 1050 ° C. for 2 hours.
After that, it is wet-milled again with a ball mill and dried. Next, a binder made of polyvinyl alcohol was added to the dry pulverized powder and granulated, and
It was molded into a disk shape having a diameter of 20 mm and a thickness of 2.5 mm at a pressure of 0 kg.

Next, the molded body 1 was subjected to pretreatment under the conditions shown in (Table 1) and (Table 2), followed by main firing. After Ni plating was formed on the upper and lower surfaces of this molded body, a silver paste was applied by printing and baked to form the electrode 2, and the electrodes on the side surfaces were removed to prepare a sample.

[0011]

[Table 1]

[0012]

[Table 2]

After measuring the resistance value and temperature characteristic of the above sample, a voltage of 100 V was applied in nitrogen gas for 100 hours, the sample was taken out, and the resistance value and temperature characteristic were measured again. The results are shown in (Table 3) and (Table 4).

[0014]

[Table 3]

[0015]

[Table 4]

Here, the resistance value change width in (Table 3) and (Table 4) is a common logarithmic value of a value obtained by dividing the maximum resistance value by the minimum resistance value, and is represented by the following formula.

Resistance value change width = Log (maximum resistance value / minimum resistance value) As is clear from the above (Table 3) and (Table 4), in the material numbers 2, 4, 6, 11 and 16, the element itself was sintered. Not an insulator. This is because if the main calcination is performed at 1240 ° C. or lower, which is the melting point of the sintering aid SiO _2, the sintering does not proceed and the semiconductor is not formed. Therefore, the firing temperature must be 1240 ° C. or higher of the melting point of the sintering aid.

Further, the pretreatment temperature is lower than 1000 ° C. or 1240 as compared with Sample Nos. 1, 21 and 21.
When the temperature exceeds ℃, the resistance value after energization in nitrogen gas and the change width of the resistance value are remarkably reduced.
0 ° C is preferred.

On the other hand, for the sample numbers 2, 3, 10, 13, 16 and 17 which were pretreated in the air, the resistance value and the resistance value after energization in nitrogen gas were calculated from (Table 3) and (Table 4). It can be seen that the change width of is significantly reduced. On the other hand, sample numbers 5, 7 to 9, 12, 14, which were pretreated in high concentration oxygen or in air and then in high concentration oxygen,
The characteristics of 15 and 18 to 20 are almost unchanged.

Further, as the atmosphere for the main calcination, even if the sample Nos. 8, 9, 12, 15, 18, and 19 were used in normal air, the characteristics were not deteriorated.

From the above, the compact is pretreated once at a temperature below the melting point of the sintering aid, preferably at 1000 to 1240 ° C. under a high oxygen concentration, and then at a temperature above the melting point of the sintering aid. By performing the firing in a normal atmosphere or under a high oxygen concentration, it is possible to obtain a positive temperature coefficient thermistor with less characteristic deterioration such as a large decrease in resistance value even when used in an oxygen-free state or a reducing atmosphere.

[0022]

As described above, the positive temperature coefficient thermistor according to the manufacturing method of the present invention is heated and oxidized at a temperature below the melting point of the sintering aid under a high oxygen concentration before the main firing of the molded body.

As a result, since the inside of the molded body is sufficiently oxidized, it is possible to obtain a thermistor with little characteristic deterioration even in a reducing atmosphere or in the absence of oxygen.

[Brief description of drawings]

FIG. 1 is a perspective view of a positive temperature coefficient thermistor according to an embodiment of the present invention.

[Explanation of symbols]

 1 molded body 2 electrode

Claims (2)

[Claims] 1. A compact is made by adding a sintering aid to a semiconductor porcelain material containing barium titanate as a main component, and the compact is then heated to a temperature not higher than the melting point of the sintering aid under a high oxygen concentration. A method for producing a positive temperature coefficient thermistor in which an electrode is heat-oxidized at 1, the main body is subsequently fired at a temperature equal to or higher than the melting point of the sintering aid, and then an electrode is provided on the surface of the main body. 2. A compact is made by adding a sintering aid to a semiconductor ceramic material containing barium titanate as a main component, and then the compact is fired in air at a temperature not higher than the melting point of the sintering aid. Then, the compact is subjected to a heat oxidization treatment at a temperature equal to or lower than the melting point of the sintering aid under high concentration oxygen, and then the compact is subjected to main firing at a temperature equal to or higher than the melting point of the sintering aid, Then, a method for manufacturing a positive temperature coefficient thermistor in which an electrode is provided on the surface of this molded body.