JPH09330804A - Manufacture of positive characteristic thermistor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive characteristic thermistor which is low in its resistive value especially at room temperature and is large in its breakdown voltage. SOLUTION: At least one of rare earth elements and Nb, Bi, Sb oxides as semiconductor formation elements is added to and mixed with such a raw material powder as to generate barium titanate or its solid solution, the raw material powder is calcined in a temperature range of 1200-1300 deg.C in an air or reducing atmosphere to form a composition, oxides of Si, Mn and Ti are added to the calcined composition and mixed therewith, the mixture is properly burned at a temperature above 1300 deg.C, and raw material containing the semiconductor formation elements having particle diameters of 1.0μm or less and SiO2 having particle diameters of 3.0μm or less is used to form a positive characteristic thermistor.

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 having a low resistance value at room temperature and a high withstand voltage.

[0002]

2. Description of the Related Art First, a raw material containing barium titanate as a main component and a trace amount of a rare earth element added to form a semiconductor is mixed by using a wet ball mill or a disper mill, and dehydrated and dried by a filter press, a drum dryer or the like. Calcination of these mixed powders is performed. Next, the calcined powder was pulverized by a wet ball mill or a sand mill or the like, and a slurry was added to the binder, granulated by a spray drier or the like, formed into a desired shape, and then subjected to main baking. An electrode was formed on the sintered body to obtain a final product.

[0003]

The positive temperature coefficient thermistor is
It has been applied to various uses such as an overcurrent prevention element, a temperature control element, a motor starting element, a demagnetizing element, and a heater element. In particular, in order to reduce the size of the overcurrent preventing element or the degaussing element, it is required that the specific resistance at room temperature is low, the resistance temperature coefficient is high, and the withstand voltage is high. In order to obtain such a positive temperature coefficient thermistor, research has been conducted intensively from the aspect of composition and construction method, but the positive temperature coefficient thermistor manufactured by the above method has low withstand voltage and low withstand voltage if the specific resistance at room temperature is low. The one with a high voltage has a high resistivity at room temperature and is currently in practical use. The resistivity at room temperature is 5 Ωcm and the withstand voltage is 30.
The limit was about 40 V / mm.

Therefore, an object of the present invention is to provide a positive temperature coefficient thermistor having a small specific resistance and a high withstand voltage. More specifically, if the specific resistance is 5 Ωcm or less,
Another object is to provide an unprecedented excellent positive temperature coefficient thermistor having a withstand voltage of 40 V / mm or more.

[0005]

The mechanism of semiconductor conversion in a thermistor with a positive characteristic is caused when a rare earth element such as Y or La or a metal element such as Nb or Sb is dissolved in barium titanate as a main component. It has been explained by the so-called valence control that electrons contribute to conduction. However, there is an optimum range for the concentration of such a semiconducting element, and it tends to be difficult to be a semiconducting element even if the concentration is low or high. Therefore, the point of solving the problem of lowering the resistance of the positive temperature coefficient thermistor was how to dissolve the semiconductor-forming element in barium titanate. On the other hand, with respect to the improvement of the withstand voltage, it was important to increase the temperature coefficient of resistance in view of the electrical characteristics, and to make the crystal grain diameter uniform and fine in porcelain.

In order to achieve the above object, therefore, the method for producing a positive temperature coefficient thermistor according to the present invention uses a rare earth element or an oxide of Nb, Sb or Bi as a semiconducting element as a raw material for producing barium titanate or its solid solution. At least one of the above is added to and mixed with the raw material powder from 1200 to 1
Calcined in air at a temperature range of 300 ° C to obtain calcined powder,
Next, at least Si and Mn oxides are added to and mixed with the calcined powder, and then molded to obtain a molded body, and then this molded body is fired at 1300 ° C. or higher, thereby achieving the above object. be able to.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The invention according to claim 1 of the present invention is a raw material for producing barium titanate or a solid solution thereof, wherein a rare earth element or Nb, S is used as a semiconductor element.
The raw material powder obtained by adding and mixing at least one of the oxides of b and Bi is 1200 to 130, which is lower than the temperature of the main calcination.
Calcination is performed in the temperature range of 0 ° C. in the air to obtain a calcined powder, and then, at least oxides of Si and Mn are added to and mixed with the calcined powder to obtain a compact, and then the compact is obtained. Molded body 13
This is a method of manufacturing a positive temperature coefficient thermistor that is fired at a temperature of 00 ° C. or higher, which facilitates solid solution of the semiconducting element to the main component, thereby achieving low resistance. Further, by adding the oxides of Si and Mn, these oxides segregate near the grain boundaries, so that the PTC characteristics are improved, and a positive temperature coefficient thermistor having low resistance and high withstand voltage can be obtained.

According to a fifth aspect of the present invention, a raw material powder obtained by adding and mixing at least one of rare earth elements or oxides of Nb, Sb and Bi as a semiconducting element to a raw material for producing barium titanate or a solid solution thereof. To 1200
Calcination is performed in a reducing atmosphere in the temperature range of 1300 ° C. to obtain a calcined powder, and then the calcined powder is mixed with at least oxides of Si and Mn and then molded to obtain a molded body. This is a method of manufacturing a positive temperature coefficient thermistor in which a molded body is fired at 1300 ° C. or higher. By calcination in a reducing atmosphere, conduction electrons are generated due to oxygen defects, and a positive temperature coefficient thermistor having a lower resistance can be obtained.

The inventions described in claims 2 and 6 are the method for manufacturing the positive temperature coefficient thermistor according to claim 1 in which Ti oxide is further added to the calcined powder, and the acceptor concentration is increased by the reaction of Mn and Ti. The temperature coefficient of resistance is increased, and a positive temperature coefficient thermistor having a higher withstand voltage can be obtained.

The invention described in claims 3 and 7 is a method of manufacturing a positive temperature coefficient thermistor using an average particle diameter of a semiconducting element of 1.0 μm or less. By being promoted, the resistance can be further reduced.

The invention described in claims 4 and 8 is a method for producing a positive temperature coefficient thermistor using an Si oxide having an average particle diameter of 3.0 μm or less, wherein the crystal particle diameter after the main firing is uniform and fine. It is possible to obtain a positive temperature coefficient thermistor having high withstand voltage and low resistance.

Embodiments of the present invention will be described below. (Embodiment 1) First, (Ba _0.90 Ca _0.10 ) TiO ₃
BaCO ₃ , C so that the composition becomes + 0.002Y ₂ O _3.
Each of aCO ₃ , TiO ₂ , and Y ₂ O ₃ is weighed and wet mixed with a ball mill. Then after drying the mixture,
Calcination is performed in air at the temperatures shown in Sample Nos. 2 to 8 of Table 1 (hereinafter referred to as calcination temperature).

[0013]

[Table 1]

Furthermore, the main component (Ba _0.90 Ca
_0.10 ). TiO _{3 (} 1 mol), SiO ₂ (0.02 mol) and MnO ₂ (0.0005 mol) were added and mixed, and then wet pulverized with a ball mill and dried. Next, a binder made of polyvinyl alcohol was added to the dried and pulverized powder, and the mixture was granulated at a pressure of 800 kg / cm 2 to form a disc having a diameter of 20 mm and a thickness of 2.5 mm. Next, these compacts were baked for 2 hours at the temperatures shown in Table 1 to obtain sintered compacts. After applying Ni plating to this sintered body,
A silver paste was applied by printing and baked to form an electrode. still,
Regarding the sample of Sample No. 1 in (Table 1), as a comparison with the conventional method, (Ba _0.90 Ca _0.10 ) TiO ₃ + 0.002Y ₂ O
_The same raw materials as described above are wet-mixed in a ball mill so as to have a composition of ₃ + 0.02SiO ₂ +0.0005 MnO ₂ , then dried and calcined at 1200 ° C. Subsequent sample preparation steps were performed by the same method as this embodiment. Next, various electrical characteristics of the sample thus manufactured are measured. From the resistance temperature characteristic, the room temperature resistance value R ₂₅ , the resistance temperature coefficient α, and the withstand voltage V _BD are evaluated. The evaluation results are shown in (Table 1).

Here, the temperature coefficient of resistance was determined according to the following equation. [Ln (R ₂ / R ₁ ) / (T ₂ −T ₁ )] × 100 (% /
C) where R ₁ , T ₁ ; a resistance value twice as high as R ₂₅ and the temperature at that time R ₂ , T ₂ ; the resistance value at (T ₁ +30) ° C. and the temperature at that time.

As is clear from (Table 1), sample numbers 4 to 6 whose calcination temperature and main calcination temperature are within the range of the present invention.
The positive temperature coefficient thermistor of (1) has a low resistance and a high withstand voltage, but the positive temperature coefficient thermistors of Sample Nos. 1 to 3 and 7, 8 outside the scope of the present invention have no effect.

(Embodiment 2) Raw materials having the same composition as in (Embodiment 1) are weighed, wet mixed in a ball mill and dried. Next, calcination is performed at the temperatures of sample numbers 9 to 16 shown in (Table 2).

[0018]

[Table 2]

However, the firing atmosphere at this time is 10% hydrogen.
Shall be performed in the green gas of. In the subsequent sample preparation process, similarly to the above-described (Embodiment 1), pulverization, granulation, and molding were performed, and main firing was performed for 2 hours at the temperature shown in (Table 2), and an electrode was added to the obtained sintered body. Formed. As a comparative example of the conventional method, a sample was prepared by the same method as in (Embodiment 1).

However, the firing atmosphere during calcination is 10% hydrogen.
I went in the green gas. Next, various electrical characteristics of the sample thus manufactured were evaluated in the same manner as in the first embodiment. The results are shown in (Table 2).

As is clear from (Table 2), the positive temperature coefficient thermistors of sample numbers 12 to 14 within the scope of the present invention have low resistance and high withstand voltage, but sample numbers 9 to 11 and 15, No effect is observed in 16 PTC thermistors which are outside the scope of the present invention.

(Embodiment 3) First, a calcined powder is produced under the same composition and process conditions as in (Embodiment 1).
Next, SiO ₂ was added to this calcined powder in an amount of 0.
02 mol and 0.0005 mol of MnO ₂ and 0.01 mol of TiO ₂ are added and mixed, and then wet-milled again by a ball mill and dried. Regarding the subsequent sample preparation process, under the same conditions as in (Embodiment 1), granulation and molding were performed and main firing was performed for 2 hours at the temperature shown in (Table 3), and the obtained sintered body was subjected to electrode formation. Was formed.

[0023]

[Table 3]

[0024] With respect to the sample of the sample No. 17 (Table 3), as compared to the conventional method (Ba _{0. 90} Ca _0.10) TiO
₃ + 0.002Y ₂ O ₃ + 0.02SiO ₂ +0.0005
The same raw material as in (Embodiment 1) is wet mixed in a ball mill so as to have a composition of MnO ₂ + 0.01TiO ₂ , dried, and calcined at 1200 ° C. in air. Subsequent sample preparation steps were performed in the same manner as in the above embodiment. Next, various electrical characteristics of the sample thus manufactured are measured, and the room temperature resistance value R ₂₅ , the temperature coefficient of resistance α, and the withstand voltage V _BD are evaluated from the resistance temperature characteristics. The evaluation results are shown in (Table 3).

As is clear from (Table 3), sample Nos. 20 to 20 whose calcination temperature and main calcination temperature are within the range of the present invention.
22 PTC thermistor has low resistance and high withstand voltage,
The effect is not observed in the positive temperature coefficient thermistors of the sample numbers 17 to 19 and 23 and 24 outside the scope of the present invention.

(Embodiment 4) Raw materials having the same composition as in (Embodiment 3) are weighed, wet mixed in a ball mill and dried. Next, calcination is performed at the temperatures of sample numbers 25 to 32 shown in (Table 4).

[0027]

[Table 4]

However, the firing atmosphere at this time is 10% hydrogen.
Shall be performed in the green gas of. In the subsequent sample preparation process, similarly to the above-mentioned (Embodiment 3), pulverization, granulation and molding were carried out, and main firing was carried out for 2 hours at the temperature shown in (Table 4), and electrodes were added to the obtained sintered body. Formed. As a comparative example of the conventional method, a sample was prepared by the same method as in (Embodiment 3).

However, the firing atmosphere during calcination is 10% hydrogen.
I went in the green gas. Next, various electrical characteristics of the sample thus manufactured were evaluated in the same manner as in the first embodiment. The results are shown in (Table 4).

As is clear from (Table 4), the positive temperature coefficient thermistors of sample numbers 28 to 30 within the scope of the present invention have low resistance and high withstand voltage, but sample numbers 25 to 27.
The effect is not observed in the positive temperature coefficient thermistors, which are outside the scope of the present invention of Nos. 31 and 32.

(Embodiment 5) First, (Ba _0.90 Ca)
BaCO ₃ , CaCO ₃ , TiO ₂ , and Y ₂ O ₃ are weighed so as to have a composition of _0.10 ) TiO ₃ + 0.002Y ₂ O ₃ and wet-mixed with a ball mill. At this time, the particle size of the Y ₂ O ₃ raw material shown in (Table 5) is used.

[0032]

[Table 5]

Next, this mixture is dried and then calcined at the calcination temperature shown in (Table 5). However, the calcination atmosphere is performed in air for sample numbers 33 to 37 and 39 to 43, and in green gas containing 10% hydrogen for sample numbers 38 and 44. The calcined powder contained 0.02 mol of SiO ₂ and MnO ₂ with respect to 1 mol of the main component.
0.0005 mol is added and mixed. At this time, sample number 3
For samples 9 to 44, 0.01 mol of TiO ₂ is further added and mixed. Further S added at this time
The particle size of iO ₂ shown in (Table 5) is used. In the subsequent sample preparation process, pulverization, granulation, molding, firing, and electrode attachment are performed under the same conditions as in (Embodiment 1). Various electrical characteristics of the sample manufactured as described above were measured, and from the resistance temperature characteristics thereof, R ₂₅ ,
Evaluate α, V _BD . The evaluation results are shown in (Table 5).

As is clear from Table 5, if the particle size of the semiconducting element added when the raw materials are mixed is 1.0 μm or less, a positive temperature coefficient thermistor having low resistance and high withstand voltage can be obtained. Furthermore, SiO ₂ added at the time of mixing after calcination
By using a raw material having a particle size of 3.0 μm or less,
It is possible to obtain a positive temperature coefficient thermistor having a low resistance and an improved withstand voltage. In addition, the amount of the semiconducting element in the present invention is the main component 1 which forms barium titanate or its solid solution.
0.001 to 0.004 mol, the SiO ₂ amount is 0.01 to 0.05 mol, and the MnO ₂ amount is 0.0001.
~ 0.0015 mol, TiO ₂ amount is 0.005-0.0
It is preferably added in the range of 3 mol. This is because if the temperature is outside these ranges, the resistance value at room temperature greatly increases, or the temperature coefficient of resistance decreases, and the withstand voltage cannot be improved.

In the present invention, as a raw material for producing barium titanate or a solid solution thereof, BaCO ₃ ,
Carbonate such as CaCO ₃ , SrCO ₃ or BaO, CaO, P
Examples thereof include oxides such as bO, and nitrates, hydrochlorides, hydroxides and the like that produce oxides by firing.

On the other hand, the temperature of the main calcination is 1300 ° C. or higher, preferably 13 as shown in the embodiment.
It is in the range of 00 to 1350 ° C. This is because, if the temperature is out of this range, the resistance value becomes high.

Above (first embodiment) to (fifth embodiment)
As described above, by using the method for manufacturing a positive temperature coefficient thermistor of the present invention, a positive temperature coefficient thermistor having a specific resistance of 5 Ωcm or less and a withstand voltage of 50 V / mm or more, which has a low resistance and a high withstand voltage, which has never been obtained, is obtained. be able to.

[0038]

As is apparent from the above description, the present invention uses a rare earth element or Nb, B as a semiconducting element as a raw material for producing barium titanate or its solid solution.
The raw material powder obtained by adding and mixing at least one of the oxides of i and Sb is 1200 to 130, which is at the temperature of the main firing or lower.
Oxides of Si, Mn, and Ti are added to and mixed with the composition that has been calcined in the air or in the temperature range of 0 ° C, and then main-calcined at a temperature of 1300 ° C or higher to further form a semiconductor. A positive temperature coefficient thermistor is constructed by preparing a sample using a raw material having an element particle size of 1.0 μm or less and SiO ₂ particle size of 3.0 μm or less. as a result,
A positive temperature coefficient thermistor with unprecedented low resistance and high withstand voltage can be obtained, and it has great industrial value because it can be expected to be miniaturized and applied to high power circuits.

Claims (8)

[Claims] 1. A raw material powder obtained by adding and mixing at least one of rare earth elements or oxides of Nb, Sb, Bi as a semiconducting element to a raw material for producing barium titanate or a solid solution thereof at 1200 to 1300 ° C. Calcination is performed in the temperature range in the air to obtain a calcined powder, then at least oxides of Si and Mn are added to and mixed with the calcined powder to obtain a compact, and then the compact is obtained. A method for manufacturing a positive temperature coefficient thermistor which is fired at 1300 ° C. or higher. 2. The method for producing a positive temperature coefficient thermistor according to claim 1, wherein a Ti oxide is further added to the calcined powder. 3. The semiconducting element has an average particle size of 1.0 μm.
The method for manufacturing a positive temperature coefficient thermistor according to claim 1, wherein a material having a thickness of m or less is used. 4. The Si oxide has an average particle diameter of 3.0 μm.
The method for manufacturing a positive temperature coefficient thermistor according to claim 1, wherein the following is used. 5. A raw material powder prepared by adding at least one of rare earth elements or oxides of Nb, Sb, Bi as a semiconducting element to a raw material for producing barium titanate or a solid solution thereof at a temperature of 1200 to 1300 ° C. Calcination is performed in a reducing atmosphere in a range to obtain a calcined powder, and then, at least oxides of Si and Mn are added and mixed with the calcined powder to be molded to obtain a molded body. A method for manufacturing a positive temperature coefficient thermistor which is fired at a temperature of ℃ or above. 6. The method for manufacturing a positive temperature coefficient thermistor according to claim 5, wherein a Ti oxide is further added to the calcined powder. 7. The semiconducting element has an average particle size of 1.0 μm.
The method for manufacturing a positive temperature coefficient thermistor according to claim 5, wherein a material having a thickness of m or less is used. 8. The Si oxide has an average particle diameter of 3.0 μm.
The method for manufacturing a positive temperature coefficient thermistor according to claim 5, wherein the following is used.