JPH07211511A - Positive temperature coefficient thermistor and its production - Google Patents

Abstract

PURPOSE:To provide a positive temperature coefficient thermistor whose resistance temperature coefficient and resistance changing degree are large and voltage dependency is low, in the positive temp. coefficient thermistor used for a heat generating body and switching element that has a positive resistance temperature characteristic. CONSTITUTION:This thermistor essentially consists of barium titanate, lead titanate and calcium titanate, and at least one kind out of Y, La, Ce, Nb, Bi, Sb, W, and Th is added as an oxide to main composition for rendering it semiconducting, and further SiO2 and Mn are given as an axide, then Al2O3 is also given, thereby reducing the composition ratio of barium site to 0.970-0.997 of titanium site, in main composition consisting of barium titanate, lead titanate and calcium titanate.

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 Barium titanate becomes a semiconductor when a rare earth element such as Y, La, Ce or a transition element such as Nb, Ta is added in a trace amount, and has a positive resistance temperature characteristic (hereinafter referred to as PTC characteristic) at a temperature near its Curie point. It is widely known from the past. Utilizing the PTC characteristics, it has been applied to various applications such as an overcurrent protection element, a temperature control element, a motor starting element, and a heater.

In addition, the required electrical characteristics have been diversified according to the spread of such applications. In particular, heater elements are required to have a higher heat generation start temperature, which is usually called a switching temperature, and have a switching temperature of 200 to 300 ° C due to barium lead titanate-based material in which barium sites of barium titanate are partially replaced with lead. Is commonly used.

By the way, as a method for producing such a positive temperature coefficient thermistor, the blended raw materials are mixed using a ball mill, a disper mill or the like, granulated by a filter press, a drum dryer or the like, and molded into a desired shape. After that, the main firing is usually performed at a high temperature of 1300 to 1400 ° C,
An electrode is applied to the obtained sintered body to obtain a final product.

[0005]

In the heater element, it is usually required to raise the heat generation start temperature, which is usually called the switching temperature, and the barium site of barium titanate is partially replaced with lead, so that the Curie point of barium titanate ( 120 ° C)
A barium lead titanate-based material having a switching temperature of 200 to 300 ° C. is generally used. Although it is possible to move the switching temperature to a higher temperature side by substitution of lead, lead volatilization during firing is large and there is a problem in the sinterability of the ceramic, so that a dense and homogeneous ceramic cannot be obtained. As a result, there are large variations in characteristics, the electrical characteristics also have a small temperature coefficient of resistance after the switching temperature is exceeded, and large variations in resistance value due to voltage, and poor withstand voltage.

Further, since the change width of the resistance value is small, there is a risk that the element may be broken due to thermal runaway. The larger the temperature coefficient of resistance and the variation range of the resistance value, the more stable the target temperature will be, even if the resistance value of the element body fluctuates due to external factors such as voltage fluctuations. Obtainable.

It is an object of the present invention to provide a positive temperature coefficient thermistor having a large temperature coefficient of resistance and a large resistance change width and improved withstand voltage having a small voltage dependence, which are improved in these drawbacks.

[0008]

In order to solve this problem, in the present invention, the composition is barium titanate, lead titanate,
Y, La, Ce, Nb, Bi, Sb, W
At least one of the elements of Th is added and contained as an oxide, SiO ₂ and Mn are further contained in the form of an oxide, and Al ₂ O ₃ is further added and contained, and barium titanate, lead titanate, titanium A stable positive temperature coefficient thermistor element can be obtained by reducing the composition ratio of barium sites to 0.970 to 0.997 with respect to titanium sites among the main components composed of calcium acid.

Further, barium titanate is 40 to 95 mol%, lead titanate is 4 to 40 mol%, and calcium titanate is 1 to 20 mol% as main components. La, Ce, Nb, Bi, Sb, W,
At least one of the Th elements is used as an oxide, and
Addition of 1 to 0.4 mol% and addition of SiO ₂ of 1.0 to
5.0 mol%, 0.01 to 0.15 with Mn as oxide
% Of Al ₂ O ₃ and barium titanate, lead titanate, and calcium titanate. In the range of 0.970 to 0.997, it is effective to reduce the number of titanium sites.

In order to make the composition ratio of barium site smaller than that of titanium site, the composition ratio of barium site and titanium site is simply set to 0.
It may be shifted at the time of the first blending to 970 to 0.997: 1, or after calcining at a composition ratio of 1: 1 and adding 0.003 to 0.030 mol of titanium oxide to 1 mol of the main component. Is also effective.

[0011]

In the present invention, by adjusting the composition ratio of barium site to 0.970 to 0.997 with respect to titanium site, the compound of titanium and barium as the main components and titanium and the sintering additive which are in excess are added. Sintering is promoted by the formation of the compound with the silicon dioxide, and a dense and stable positive temperature coefficient thermistor can be obtained. As a result, even in the electrical characteristics, even if the resistance value of the element body fluctuates due to external factors such as the resistance temperature coefficient, the resistance value variation range is large, the voltage dependence is small, and the voltage variation, the temperature may fluctuate significantly. It is possible to obtain an excellent positive temperature coefficient thermistor, because the desired temperature can be stably obtained without the need.

[0012]

EXAMPLES Examples of the present invention will be described below.

Example 1 Barium carbonate (BaC)
O ₃ ), titanium oxide (TiO ₂ ), lead oxide (PbO), and calcium titanate (CaTiO ₃ ) as the main components, and Y, La, Ce, Nb, Bi,
(Ba _0.7 Pb _0.2 Ca _0.1 ) xTiyO ₃ + 0.002M is obtained by using an oxide of at least one element of Sb, W, and Th and each raw material of SiO ₂ , MnO _2, and Al ₂ O _3.
+ 0.002SiO ₂ + 0.01Al ₂ O ₃ +0.001
It is weighed so as to have a composition of Mn (M: oxide of a semiconducting agent). Note that x and y of this composition are adjusted so as to have the ratio of (Table 1).

Next, the weighed materials are wet mixed in a ball mill. The mixture is then dried and then calcined at 1100 ° C. for 2 hours. Then, the calcined powder is wet-milled with a ball mill. After drying the pulverized product, 5% of polyvinyl alcohol was added as a binder, the mixture was granulated, and press-molded at a pressure of 600 kg / cm ² . This molded body is about 1300 in air
Firing at 1 ° C. for 1 hour gave a disk-shaped positive temperature coefficient thermistor having a diameter of 12 mm and a thickness of 3.0 mm. Furthermore, Ni is added to this sintered body.
After plating, Ag paste was applied and baked to form an electrode.

Next, the electrical characteristics of the sample thus obtained are measured. From the resistance temperature characteristic curve, the room temperature resistance value (R ₂₅ ), the resistance temperature coefficient (α), and the resistance value change width (Ψ) (Ψ = Log ₁₀ (maximum resistance value / minimum resistance value)) were measured. The results are shown in (Table 1).

[0016]

[Table 1]

From these results, barium site (x)
And titanium site (y) ratio x / y is 0.970 to 0.9
It can be seen that in the range of 97, the resistance temperature coefficient (α) is large, the resistance value change width (Ψ) is large, and the PTC characteristic is excellent.

(Example 2) The same raw materials as in Example 1 were used, weighed so as to have the composition shown in (Table 2), and wet mixed in a ball mill. Next, a sample is prepared in the same manner as in Example 1 and its electrical characteristics are evaluated. The results are shown in (Table 3).

[0019]

[Table 2]

[0020]

[Table 3]

Sample Nos. 1 to 13 in Table 2 have compositions outside the scope of the present invention, and the other compositions are within the scope of the present invention. As is clear from (Table 3),
It can be seen that Sample Nos. 14 to 24 having compositions within the range of the present invention have a large temperature coefficient of resistance (α) and a variation range of resistance value (Ψ) and excellent PTC characteristics. In addition,
Sr may be added to the composition of the present invention to move the Curie point.

(Example 3) Using the same raw material as in Example 1, (Ba _0.7 Pb _0.2 Ca _0.1 ) xTiyO ₃ + 0.002Y
₂ O ₃ +0.002 SiO ₂ +0.01 Al ₂ O ₃ +0.0
Weigh so that the composition is 01 Mn. Then, a sample is prepared in the same manner as in Example 1. However, as shown in sample numbers 4 to 8 in (Table 4), x / y = 1.000 is set at the time of weighing, and TiO ₂ is added after calcination to prepare samples in the same manner.
Next, the electrical measurement is measured.

[0023]

[Table 4]

As is clear from these results, T after calcination
iO ₂ is 0.003 to 0.x for x / y = 1.000.
When added in an excess of 03 mol, the ratio x / y of barium site (x) and titanium site (y) after firing is 0.970 to.
Even in the range of 0.997, the resistance temperature coefficient (α) is large, and the resistance value change width (Ψ) is also large, as in the first embodiment.
It can be seen that the C characteristics are excellent.

[0025]

As described in detail above, the use of the present invention makes it possible to obtain a stable positive temperature coefficient thermistor having a large resistance temperature coefficient and a large variation range of the resistance value, which cannot be obtained in the past, and which has an excellent PTC characteristic. It can be manufactured, and its industrial utility value is great.

Claims (3)

[Claims] 1. Barium titanate, lead titanate, and calcium titanate as main components, and at least one of Y, La, Ce, Nb, Bi, Sb, W, and Th elements as a semiconducting agent for the main components. Barium among the main components of barium titanate, lead titanate, and calcium titanate, one of which is additionally contained as an oxide, SiO ₂ and Mn are contained as oxides, and Al ₂ O ₃ is further contained. Site composition ratio is 0.970 with respect to titanium site
A positive temperature coefficient thermistor with less than titanium sites in the range of up to 0.997. 2. Barium titanate in an amount of 40 to 95 mol%,
4-40 mol% lead titanate and 1 calcium titanate
.About.20 mol% as a main component, and as a semiconducting agent for the main component, at least one of Y, La, Ce, Nb, Bi, Sb, W, and Th as an oxide is used as an oxide.
0.4 mol% added and contained, and SiO ₂ 1.0 to 5.0
Mol%, 0.01 to 0.15 mol% of Mn as an oxide, and 0.1 to 2.0 mol% of Al ₂ O _3, and a main component composed of barium titanate, lead titanate, and calcium titanate. Among them, a positive temperature coefficient thermistor in which the composition ratio of barium site is less than that of titanium site in the range of 0.970 to 0.997 with respect to titanium site. 3. Barium titanate, lead titanate, and calcium titanate as main components, and at least one of Y, La, Ce, Nb, Bi, Sb, W, and Th elements as a semiconducting agent for the main components. Barium among the main components of barium titanate, lead titanate, and calcium titanate, one kind of which is added and contained as an oxide, SiO ₂ and Mn which are contained as oxides, and which further contains Al ₂ O _3. Site composition ratio is 0.970 with respect to titanium site
In the method for producing a positive temperature coefficient thermistor having a ratio of titanium sites less than 0.997 in the range of about 0.997, after calcining the main component with a composition ratio of barium site to titanium site of 1: 1,
0.003 to 0.0 based on 1 mol of titanium oxide as the main component
A method for producing a positive temperature coefficient thermistor in which 3 mol is added and final firing is performed.