JPH10294202A - Positive characteristic thermistor and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive temperature coefficient thermistor having a positive resistance temperature characteristic used as a heating element or a switching element, with little characteristic deterioration and high reliability even when used in a reducing atmosphere. It is an object of the present invention to provide an element having a neutral property. SOLUTION: A main component composed of barium titanate or a solid solution thereof, as a semiconducting element, at least one of oxides of rare earth elements such as Y, La, Sm or oxides of Nb, Sb, Bi and Si, Mn. M ₂ Ti ₃ O ₇ powder (where M is at least one selected from the elements of Li, Na and K) in the composition containing each oxide of
And a positive temperature coefficient thermistor with improved reduction resistance performance can be obtained.

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 more particularly to a highly reliable positive temperature coefficient characteristic which causes less characteristic deterioration when used in a reducing atmosphere. The present invention relates to a thermistor and a method for manufacturing the thermistor.

[0002]

2. Description of the Related Art Barium titanate is converted into a semiconductor by adding a trace amount of a rare earth element, and has a positive resistance-temperature characteristic (Positive Temperatur) at a temperature near its Curie point.
It has been widely known to show reCoefficient (PTC characteristic). Utilizing the PTC characteristics, it has been applied to various uses such as an overcurrent protection element, a temperature control element, a motor starting element, a degaussing element, and a heater element. On the other hand, as a method of manufacturing such a PTC thermistor, the following method is generally used. First, ceramic raw materials blended to have a predetermined composition are mixed using a wet ball mill, a disper mill, or the like, dehydrated and dried using a filter press, a drum dryer, or the like, and then the mixed powder is calcined. Next, the calcined powder is pulverized by a wet ball mill, a medium stirring mill, or the like, and a slurry obtained by adding a binder is granulated by a spray drier or the like, formed into a desired shape, and then subjected to main baking. An electrode is formed on the obtained sintered body to obtain a final product. In recent years, the environmental conditions in which such devices are used are severe, and in particular, applications in which reduction resistance performance is required have been diversified.

[0003]

It has long been pointed out that the characteristics of such a positive temperature coefficient thermistor depend on the crystal grain boundaries. However, when used in a reducing atmosphere or a neutral atmosphere, the resistance of the positive temperature coefficient thermistor becomes low. The characteristics are deteriorated such that the value is greatly reduced and the temperature coefficient of resistance is significantly reduced. In particular, under the operating conditions of equipment using a heater element, it is composed of organic components such as chemicals, fabric softeners, gasoline, machine oil, edible oil, and seasonings, and adheres to the element. There is a possibility that various characteristics may be degraded due to a reduction effect caused by the combustion of the components, so that it is necessary to prevent contact or adhesion with such organic components, and the use of the components has been limited. An object of the present invention is to provide a positive temperature coefficient thermistor excellent in reduction resistance performance, which can be adapted to the above uses.

[0004]

[MEANS FOR SOLVING THE PROBLEMS] PT in a reducing atmosphere
The mechanism of deterioration of the C characteristic is generally considered to be due to the fact that electrons generated by the generation of oxygen defects contribute to conduction.

[0005] Therefore, in order to improve the reduction resistance performance, it is necessary to prevent generation of oxygen vacancies (it is difficult to release oxygen).
Have a crystal structure. A dense microstructure in which a reducing substance or the like does not easily enter the inside of the element is formed. Introduce an element that acts as an acceptor to trap generated electrons. And so on.

[0006] The present invention is the result of intensive studies on composition aspects and manufacturing methods based on such material design.

Therefore, in order to achieve the above object, a positive temperature coefficient thermistor of the present invention comprises barium titanate or a solid solution thereof as a main component, and at least one of rare earth elements and oxides of Nb, Sb and Bi as subcomponents. And S
i and Mn oxide and M ₂ Ti ₃ O ₇ (where M is Li, N
and at least one element selected from the elements a and K), whereby the above object can be achieved.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The invention according to claim 1 of the present invention comprises barium titanate or a solid solution thereof as a main component, and a rare earth element or Nb, Sb, Bi as a subcomponent.
Characterized in that it contains at least one oxide of the following, an oxide of Si and Mn, and M ₂ Ti ₃ O ₇ (where M is at least one selected from the elements Li, Na and K). The acceptor concentration at the grain boundary is increased by the M ₂ Ti ₃ O ₇ powder, and electrons generated in a reduced state are trapped, so that a positive thermistor excellent in reduction resistance performance can be obtained. .

According to a second aspect of the present invention, there is provided M ₂ Ti ₃ O
₇ (where M is at least one element selected from the elements of Li, Na, and K) is 0.005 to 1 mol of the main component.
2 to 0.03 mol.
And a device excellent in reduction resistance performance can be obtained.

According to a third aspect of the present invention, barium titanate or a solid solution thereof is a main component, and at least one of rare earth elements or oxides of Nb, Sb, and Bi as subcomponents, and an oxide of Si and Mn. A first step of obtaining a calcined powder by calcining a mixed powder obtained by mixing the above powder with M ₂ Ti ₃ O ₇ powder (where M is selected from elements of Li, Na, and K) (At least one type) is added and mixed to form a molded body, and then a third step of firing the molded body to obtain a sintered body is a method for producing a positive temperature coefficient thermistor. In addition, since the acceptor concentration increases more effectively in the vicinity of the grain boundary, which is where PTC characteristics are exhibited, it is possible to obtain a PTC thermistor having more excellent reduction resistance performance.

According to a fourth aspect of the present invention, in the second step, M ₂ Ti ₃ O ₇ (where M is at least one selected from the elements of Li, Na and K), and 0 mol per 1 mol of the main component. The method for producing a positive temperature coefficient thermistor according to claim 3, wherein 0.005 to 0.03 mol is added, and an element excellent in reduction resistance performance can be obtained.

[0012] The invention according to claim 5, in a second step, M ₂ Ti ₃ O ₇ powder (where M is Li, Na, at least one selected from the elements K) an average particle diameter of D _A When the average particle diameter of the calcined powder and D _B, according to claim 3 or claim 4 particle size ratio D _a / D _B of D _a and D _B is set to be 1.0 to 2.0 The reaction of the positive characteristic thermistor of the above is suppressed, and the reaction with the intragranular component is suppressed, so that the effect of claim 3 or 4 at the grain boundary is more effectively achieved, thereby further improving the reduction resistance performance. A positive temperature coefficient thermistor can be obtained.

Hereinafter, the present invention will be described with reference to embodiments. (Embodiment 1) First, (Ba _0.90 Pb _0.10 ) TiO ₃
+ 0.02SiO ₂ + 0.001MnO ₂ + 0.002N
BaCO ₃ , PbO, Ti so that the composition becomes b ₂ O ₅
O ₂ , Nb ₂ O ₅ , SiO ₂ and MnO ₂ were weighed,
At the same time, Na ₂ Ti ₃ O ₇ powder (hereinafter abbreviated as NTO powder) is weighed with respect to 1 mol of the main component so as to become (Table 1), and all the raw materials are wet-mixed with a ball mill.

[0014]

[Table 1]

Next, after drying this mixture,
And calcine for 2 hours. Then, wet grinding is performed again with a ball mill and drying is performed. Next, a binder made of polyvinyl alcohol was added to the dried and pulverized powder, and the mixture was granulated to form a disc having a diameter of 20 mm and a thickness of 2.5 mm at a pressure of 800 kg per square centimeter. Next, this molded body is
It was fired in air at 300 ° C. for 2 hours to obtain a sintered body. Next, after a Ni plating was formed on the thus obtained sintered body, a silver paste was printed and baked to form an electrode. Next, at room temperature resistance R
₂₅ After measuring the temperature coefficient of resistance α and the width of change in resistance (Ψ), the resistance to reduction was further evaluated in nitrogen gas.
For 0 hour, a voltage of 100 V is applied and R ₂₅ , α, Ψ
Was measured.

The results are shown in (Table 1). still,
Sample No. 1 in Table 1 is a sample having the same composition as described above and prepared by the same process as above without the addition of NTO powder.

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 ; twice the resistance value of R ₂₅ and the temperature at that time R ₂ , T ₂ ; the resistance value of (T ₁ +30) ° C. and its temperature.

As is clear from Table 1, the devices of Sample Nos. 3 to 8 in which the amount of NTO powder added is within the range of the present invention are Sample Nos. 1, 2, 9 and 10 which are out of the range of the present invention.
No deterioration of the characteristics was observed as compared with the sample No. 2, and the decrease in the resistance change width 少 な く was small, and improvement in the reduction resistance performance was observed.

(Embodiment 2) First, (Ba_0.90Pb
_0.10) TiO_Three+ 0.02SiO_Two+ 0.001MnO_Two
+ Nb_TwoO_FiveBaCO so that the composition becomes_Three, PbO, T
iO_Two, Nb_TwoO_Five, SiO _Two, MnO_TwoWeigh each
And wet mixing with a ball mill. Then dry this mixture.
After drying, it is calcined at 1050 ° C. for 2 hours. To this calcined powder
NTO powder was added to sample Nos. 11-20 in Table 2
Weighed to 1 mol of the main component
And wet-mix.

[0020]

[Table 2]

After drying the mixture (Embodiment 1)
In the same manner as described above, granulation, molding, and firing are performed to form an electrode, and a PTC thermistor element is obtained. The evaluation of the electrical characteristics and reduction resistance of the obtained device is performed in the same manner as in (Embodiment 1). The evaluation results are shown in Sample Nos. 11 to 20 in (Table 2).

As is clear from Table 2, by adding the NTO powder after the calcination step as in Sample Nos. 13 to 18 within the scope of the present invention, a device having more excellent reduction resistance can be obtained. However, even if the NTO powder is added after calcination, if the added amount is out of the range of the present invention as in Sample Nos. 12, 19 and 20, the characteristics are deteriorated and no improvement in reduction resistance is observed. Sample No. 11 is the same sample as Sample No. 1 and is a comparative example.

(Embodiment 3) First, (Ba _0.90 Pb
_0.10 ) TiO ₃ + 0.02SiO ₂ + 0.001MnO ₂
BaCO ₃ , so as to have a composition of +0.002 Nb ₂ O ₅ .
PbO, TiO ₂ , Nb ₂ O ₅ , SiO ₂ and MnO ₂ are respectively weighed and wet-mixed in a ball mill. Next, after drying this mixture, it is calcined at 1050 ° C. for 2 hours. In this calcined powder, NTO powder was added in an amount of 0.02 to 1 mol of the main component.
Add 0 mol and mix. When the average particle diameter D _A of NTO powder this time, the average particle diameter of the calcined powder and D _B, D _A
And adjusting the addition mixed as the particle size ratio D _A / D _B of D _B (Table 3).

[0024]

[Table 3]

In the subsequent sample preparation process, as in (Embodiment 1), an electrode was formed by granulation, molding and firing to obtain a PTC thermistor. The electrical characteristics and reduction resistance of the device thus obtained were measured and evaluated in the same manner as in (Embodiment 1). The evaluation results are shown in (Table 3).

The sample (Table 3) D _A / D _B As is clear from within the scope of the present invention which is a 1.0 to 2.0 No. 2
Samples Nos. 3 to 28 are Sample No. 2 which is outside the scope of the present invention.
It can be seen that the reduction resistance performance is improved as compared with the samples 1, 22, 29 and 30.

In the present invention, the amount of semiconducting elements is 0.001 to 0.004 mol per 1 mol of the main component, and S
iO ₂ amount 0.01~0.05mol, the MnO ₂ amount of 0.
It is preferable to add in the range of 0001 to 0.0015 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.

On the other hand, in the above (embodiment), M ₂ Ti ₃
Although the embodiment in which only M is Na in the O ₇ powder has been described, a positive temperature coefficient thermistor having similarly improved reduction resistance can be obtained by using K and Li.

(Embodiment 1) to (Embodiment 3)
As described above, by using the positive temperature coefficient thermistor of the present invention and the method of manufacturing the same, a positive temperature coefficient thermistor having excellent reduction resistance performance can be obtained.

[0030]

As is apparent from the above description, the present invention relates to a method in which a main component consisting of barium titanate or a solid solution thereof includes a rare earth element oxide such as Y, La, Sm or Nb, Sb as a semiconducting element. , Bi and at least one oxide of Si and Mn
₂ Ti ₃ O ₇ powder (where, M is Li, Na, at least one selected from the elements of K) is characterized in that is included 0.005~0.03mol with respect to the main component 1 mol, As a result, it is possible to obtain a positive temperature coefficient thermistor with little characteristic deterioration even when used in a reducing atmosphere, and its industrial use value is great.

Claims (5)

[Claims] A barium titanate or a solid solution thereof as a main component, and a rare earth element or Nb, S as a subcomponent.
b and Bi oxides, at least one of Si and Mn
And M ₂ Ti ₃ O ₇ (where M is at least one selected from the elements of Li, Na and K). 2. M ₂ Ti ₃ O ₇ (where M is Li, Na, K
At least one element selected from the group consisting of
2. The positive temperature coefficient thermistor according to claim 1, wherein the content is 0.005 to 0.03 mol based on ol. 3. Barium titanate or a solid solution thereof as a main component, and a rare earth element or Nb, S as a subcomponent.
b and Bi oxides, at least one of Si and Mn
A first step of obtaining a calcined powder by calcining a mixed powder obtained by mixing the oxide of the present invention with an oxide of M ₂ Ti ₃ O ₇ (where M is an element of Li, Na, K) A second step of adding and mixing to form a molded body,
And a third step of firing the formed body to obtain a sintered body. 4. In the second step, M ₂ Ti ₃ O ₇ (where M is at least one element selected from the elements of Li, Na and K), and 0.005 to 0.03 with respect to 1 mol of the main component.
The method for producing a positive temperature coefficient thermistor according to claim 3, wherein mol is added. 5. In the second step, the average particle diameter of M ₂ Ti ₃ O ₇ powder (where M is at least one selected from the elements of Li, Na, and K) is D _A , and the average particle of calcined powder is When the diameter is D _B, 1.0 to particle diameter ratio D _a / D _B of D _a and D _B
The method of manufacturing a positive temperature coefficient thermistor according to claim 3 or 4, wherein the temperature is 2.0.