JPH08213206A - Positive characteristic thermistor and manufacture thereof - Google Patents

Abstract

PURPOSE: To provide a positive characteristic thermistor which is low in resistance, large in resistance temperature coefficient, and excellent in withstand voltage characteristic. CONSTITUTION: 1mol of barium titanate or its solid solution as a main component, 0.001 to 0.004mol of rare earth element as auxiliary element which serves as agent to turn material semiconductive. 0.005 to 0.04mol of SiO2 as PTC sintering agent, and material composed of Xmol of TiO2 , Ymol of Al2 O3 , and Zmol of MnO2 as characteristic-enhancing agent (X, Y, and Z are so set as to satisfy a formula, Y=Y+Z, where 0.002<=X<=0.02, 0.001<=Y<=0.02, and 0.0003<=Z<=0.0015) are mixed together and kneaded, molded, and burned to form an electrode.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positive temperature coefficient thermistor whose resistance value rapidly increases at a specific temperature and a method for manufacturing the thermistor.

[0002]

2. Description of the Related Art PTC thermistors are elements for overcurrent protection,
It is used in various applications such as temperature control element, motor starting element and heater element.

Conventionally, barium titanate is used as a main component, and a trace amount of a rare earth element or a transition element is added to this as a subcomponent to form a semiconductor, and a Mn compound, SiO ₂ , Al ₂ O _{3 is} added.
Is added to improve the rate of change in resistance temperature after exceeding the Curie point or stabilize the characteristics to form a thermistor element, and an electrode is formed on this thermistor element to obtain a positive temperature coefficient thermistor. It was

[0004]

With the spread of applications of positive temperature coefficient thermistors, the required electrical characteristics have been diversified, and recently, the specific resistance at room temperature is small and stable, and the positive resistance temperature is large. Those having characteristics are desired.

However, the above-mentioned structure has a problem that the use thereof is restricted because the resistance temperature characteristic and the withstand voltage characteristic deteriorate as the specific resistance decreases.

Therefore, the present invention has excellent withstand voltage characteristics,
It is an object of the present invention to provide a positive temperature coefficient thermistor having a small specific resistance at room temperature and a large resistance temperature change rate.

[0007]

In order to achieve this object, the positive temperature coefficient thermistor of the present invention contains a barium titanate or a solid solution of barium titanate as a main component of 1 mol, and a secondary component of 0. 001-0.004mo
1, 0.002 to 0.04 m of SiO ₂ as a sintering aid
ol is added for calcination, and then Xmol of TiO ₂ as a PTC characteristic improving agent and Al ₂ are added to 1 mol of the main component.
When O ₃ is Ymol and MnO ₂ is Zmol, X = Y
+ Z (however 0.002 ≦ X ≦ 0.02, 0.001 ≦
Y ≦ 0.02, 0.0003 ≦ Z ≦ 0.0015), the above-mentioned respective elements are added, mixed and molded,
It is baked to form an electrode.

[0008]

In general, BaTiO ₃ serves as an acceptor when the Ba site of BaTiO ₃ has a +1 valence ion or the Ti site has a valence of less than +4 valence. Mn, Al, etc. are considered as typical acceptors, and have the function of increasing the hole concentration and decreasing the electron concentration. In addition, the segregation of TiO ₂ added as a property improving agent at the crystal grain boundaries increases the hole concentration particularly at the crystal grain boundaries. (Chemical formula 1)
This is shown in (Chemical Formula 2).

[0009]

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[0010]

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As a result, a PTC thermistor having improved PTC characteristics, excellent withstand voltage characteristics, a small specific resistance at room temperature, and a large resistance temperature change rate can be obtained.

Therefore, by adopting the configuration of the present invention,
It is possible to obtain a positive temperature coefficient thermistor having high reactivity in (Chemical formula 1) and (Chemical formula 2), excellent in withstand voltage characteristics, low in specific resistance at room temperature and high in resistance temperature change rate.

[0013]

Embodiments of the present invention will be described below.

Example 1 BaCO ₃ , TiO ₂ , Pb
O, CaTiO ₃ , and rare earth element oxides as a semiconducting agent, SiO ₂ , MnO _2, and Al ₂ O ₃ were used as raw materials and weighed to have the composition shown in (Table 1).
I got 22.

[0015]

[Table 1]

Then, by the following steps, a positive temperature coefficient thermistor was obtained for each sample number. First, the weighed raw materials were wet mixed in a ball mill, dried, and then calcined at 1100 ° C. for 2 hours. Next, the calcined powder was wet pulverized with a ball mill, dried, and then added with 5% by weight of polyvinyl alcohol as a binder to granulate, and press-molded at a pressure of 800 kg / cm ² . This compact was fired in air at about 1300 ° C. for 1 hour to obtain a disk-shaped sintered body having a diameter of 12 mm and a thickness of 3.0 mm. Further, after Ni-plating was applied to this sintered body, Ag paste was applied and a baking electrode was formed to obtain a positive temperature coefficient thermistor.

Then, the room temperature resistance value (R ₂₅ ), the temperature coefficient of resistance (α) and the withstand voltage of the thus obtained sample were measured. The room temperature resistance value (R ₂₅ ) is the resistance value at 25 ° C., the resistance temperature coefficient (α) is calculated by the equation (1), and the withstand voltage is the maximum applied voltage just before the sample is broken.

[0018]

[Equation 1]

The results are shown in (Table 2).

[0020]

[Table 2]

For sample Nos. 1 to 6 in Table 1, T
For io ₂ , Al ₂ O ₃ , MnO ₂ , rare earth elements, and SiO ₂ having compositions outside the scope of the present invention, and sample Nos. 7 and 8, TiO ₂ used as a PTC property improver was added to Xmo.
l, Al ₂ O ₃ is Ymol, and MnO ₂ is Zmol, the formula: X = Y + Z is not satisfied,
Within the scope of the invention for the sample numbers 9 to 22 the formula: X =
The composition satisfies the relationship of Y + Z. As is clear from (Table 2), Sample Nos. 9 to 22 of the present invention are excellent in the temperature coefficient of resistance (α) and withstand voltage characteristics, even though the room temperature resistance value is low.

(Example 2) The same raw materials as in Example 1 were used and weighed so that the composition shown in Chemical formula 3 was obtained.

[0023]

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Next, a sample was prepared in the same process as in Example 1, except that TiO ₂ and Al added as characteristic improvers were added.
₂ O ₃ and MnO ₂ were added after calcination to prepare samples. Next, the electrical characteristics were measured.

The results are shown in (Table 3) together with the values of x, y and z in (Formula 3).

[0026]

[Table 3]

As is clear from these results, it is understood that the characteristics are improved by adding TiO ₂ , Al ₂ O ₃ and MnO ₂ which are added as property improving agents after calcination.

Example 3 The same raw materials as in Example 1 were used and weighed so that the composition shown in Chemical formula 3 was obtained.
A sample was prepared in the same manner as in.

At that time, the relationship between the grain size of the TiO ₂ powder added as the PTC property improver and the grain size of the Al ₂ O ₃ powder is shown in Table 4.

[0030]

[Table 4]

As can be seen from Table 4, by using a raw material in which the particle size of the TiO ₂ powder is smaller than that of the Al ₂ O ₃ powder, the room temperature resistance value is low and the temperature coefficient of resistance (α) It can be seen that a thermistor having excellent withstand voltage characteristics can be obtained.

Here, the grain size of Ti is 0.5 μm <Ti <
2.0 μm, Al grain size is 1.5 μm <Al <3.0 μ
It is preferable to use m.

[0033]

As described above in detail, according to the present invention, it is possible to obtain a positive temperature coefficient thermistor having a low resistance, a high temperature coefficient of resistance, and an excellent withstand voltage, which cannot be obtained conventionally. And its industrial utility value is great.

Claims (4)

[Claims] 1. A thermistor element and an electrode provided on the surface of the thermistor element, wherein the thermistor element comprises:
Main component 1mo consisting of barium titanate or its solid solution
With respect to 1, 0.001 to 0.004 mol of a rare earth element as a semiconducting element, and Si as a sintering aid, as auxiliary components.
The O ₂ wherein 0.005～0.04Mol, further PTC
TiO ₂ as Xmol and Al ₂ O ₃ as Ym as characteristic improvers
ol and MnO ₂ are Zmol, X = Y + Z (provided that 0.002 ≦ X ≦ 0.02, 0.001 ≦ Y ≦ 0.
02, 0.0003 ≤ Z ≤ 0.0015), so that the positive temperature coefficient thermistor formed by containing each of the above elements. 2. To 1 mol of the main component made of barium titanate or a solid solution thereof, 0.001 to 0.004 mol of a rare earth element as a semiconducting element and 0.005 to SiO _{2 of a} sintering aid are added as auxiliary components. 0.04 mol, PT
X mol of TiO ₂ and Y of Al ₂ O ₃ were used as C characteristic improvers.
X = Y + Z, where mol and MnO ₂ are Z mol.
(However, 0.002 ≦ X ≦ 0.02, 0.001 ≦ Y ≦
0.02, 0.0003 ≦ Z ≦ 0.0015), a method for producing a positive temperature coefficient thermistor in which the above elements are added, mixed and molded, and then fired to form an electrode. 3. To 1 mol of the main component made of barium titanate or its solid solution, 0.001 to 0.004 mol of a rare earth element as a semiconducting element and 0.005 to SiO ₂ as a sintering aid are added as subcomponents. After adding 0.04 mol and calcining, Xmol of TiO ₂ and Ymo of Al ₂ O ₃ were used as PTC characteristic improving agents for 1 mol of the main component.
l and MnO ₂ are Zmol, X = Y + Z (where 0.002 ≦ X ≦ 0.02, 0.001 ≦ Y ≦ 0.0
2. The method for manufacturing a positive temperature coefficient thermistor according to claim ₂ , wherein TiO ₂ , Al ₂ O ₃ and MnO ₂ are added so that the following condition is satisfied: 0.0003 ≦ Z ≦ 0.0015). 4. TiO added as a PTC property improver
_The method for manufacturing a positive temperature coefficient thermistor according to claim ₂ , wherein ₂ has a particle size smaller than that of Al ₂ O ₃ .