JPH08195302A - Positive temperature coefficient thermistor - Google Patents

Abstract

PURPOSE: To obtain an equivalent positive resistance-temperature coefficient at different resistance valves by constituting three layers, which comprise two layers of front and rear surface parts formed of the main material of a positive temperature coefficient thermistor, whose main component is barium titanate, and an intermediate layer formed of the secondary material, whose positive resistance-temperature coefficient is equal to that of the main material and a specific resistance is different. CONSTITUTION: The amount of main material for rear surface layer part 2b is inputted into a molding die and temporaily pressed. Then, the amount for an intermediate layer part 3 is inputted and temporarily pressed. Finally, the amount for an upper surface layer part 2a is mainly pressed and formed in a disk shape. For the composition ratio of the granulation powder of the intermediate layer part 3, the mixing ratio of two materials of TiO2 and CaTiO3 is made larger than the main material. Then, the temperature of the molded material is increased in a furnace. After the burning for one hour at the temperature of 1300 deg.C, the material is slowly cooled to the room temperature. Thereafter, alumi-metallikon thermal- spraying electrodes 1a and 1b are provided on both surfaces of the obtained sintered body, and the positive characteristic thermistor element is obtained. Thus, the positive temperature coefficient thermistor having the equivalent positive resistance-temperature coefficient at the different resistance value can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a temperature compensator,
The present invention relates to a PTC thermistor used as a color TV degaussing device, various switching elements for current control, or a constant temperature heating element.

[0002]

2. Description of the Related Art A cross-sectional view of a conventional positive temperature coefficient thermistor is shown in FIG.
Shown in It has a structure in which electrodes 1a and 1b are provided on both front and back surfaces of a PTC thermistor material 5 which is a disk-shaped pellet.

Conventionally, as a method of manufacturing such a positive temperature coefficient thermistor element, one kind of material is molded into a predetermined disk shape by dry or wet molding, and then a firing process is performed to attach an electrode thereafter. I was getting a thermistor element. As a manufacturing method for increasing or decreasing the resistance value of the positive temperature coefficient thermistor element, a method of controlling an oxygen atmosphere during firing, extending the firing keeping time, and gradually cooling during cooling is generally used.

[0004]

In the control method by firing as described above, the positive resistance temperature coefficient also increases as the resistance value increases. Positive temperature coefficient thermistors have the property that the resistance value increases rapidly at the Curie temperature.
This is due to the potential barrier formed at the crystal grain boundary portion. The higher the barrier, the greater the rate of resistance change and the more positive the temperature coefficient of resistance. The height of this barrier is proportional to the amount of adsorbed oxygen. That is, since the amount of adsorbed oxygen increases in the above-mentioned firing method, the positive resistance temperature coefficient also increases as the resistance value increases.

Therefore, when used as various switching elements for current control or the like, since the positive resistance temperature coefficient differs depending on the resistance value, the same current-time characteristic cannot be obtained with different resistance values, and the resistance values differ. However, there is a problem in that the characteristics required by the above cannot be satisfied.

In view of the above points, an object of the present invention is to provide a positive temperature coefficient thermistor having different resistance values and having the same positive temperature coefficient of resistance.

[0007]

In order to achieve this object, the present invention provides two layers of front and back surfaces made of the main material of a positive temperature coefficient thermistor containing barium titanate as a main component, the main material and the positive resistance temperature. It is composed of three layers including an intermediate layer made of sub-materials having the same coefficient and different specific resistances.

[0008]

With this configuration, since the resistivity of the intermediate layer is higher than that of the main material, the resistance value of the entire positive temperature coefficient thermistor element increases,
The resistance value can be adjusted by the ratio of the thicknesses of the intermediate layer and the front and back layers. Further, since the positive resistance temperature coefficients of the three layers are the same, the positive resistance temperature coefficients are the same even if the resistance values are different. As a result, the same current-time characteristic (heat generation characteristic) can be obtained even with different resistance values.

[0009]

EXAMPLES Examples of the present invention will be described below. In this embodiment, a switching element used for current control or the like is used as an example. First, to prepare the main material, commercially available BaCO ₃ and Ti are adjusted so that the Curie temperature is 120 ° C.
O ₂ , PbO, SrCO ₃ , Y ₂ O ₃ , Al ₂ O ₃ , Mn (N
O ₃ ) ₂ and CaTiO ₃ are weighed, 280 g of the raw material is put in a 4 inch pot, 350 cc of pure water and YTZ ball 6 having a diameter of 5 mm
00g was added and wet-mixed for 20 hours, and dried at 150 ° C. Then, this mixture is crushed and calcined at 1100 ° C. for 2 hours, then calcined powder is put in a 4 inch pot, 300 cc of pure water and 600 g of YTZ balls having a diameter of 5 mm are added, and wet pulverized for 20 hours, and then 150 ° C. Dried in. Next, 10% by weight of a 5% polyvinyl alcohol aqueous solution was added to the obtained pulverized powder,
After granulating for 5 minutes with a Reiki machine, 20 mesh was passed to obtain granulated powder. This granulated powder is used for two layers on both the front and back sides. After that, the composition ratio was TiO ₂ and CaTiO ₃
A granulated powder for the intermediate layer was obtained in the same manner by using the sub-materials in which the mixing ratio of the two was increased. Then, the powder is weighed in the proportions shown in (Table 1), and the amount of 2b is put into a molding die having a diameter of 10 mm and temporarily pressed, then the amount of 3 parts is put and temporarily pressed, and finally the 2a part. Was put into a disk shape and subjected to main pressing at a pressure of 1000 kg / cm ² . Next, the molded product was heated in a firing furnace at a rate of 300 ° C./hr, fired at a temperature of 1300 ° C. for 1 hour, and then gradually cooled to room temperature at a temperature lowering rate of 250 ° C./hr. Then, aluminum metallikon sprayed electrodes were provided on both surfaces of the obtained sintered body to obtain a positive temperature coefficient thermistor element. A cross section of this thermistor is shown in FIG. Diameter is about 8
mm, and the total thickness of 2a, 3 and 2b is about 3 mm. The finished specific resistance of the auxiliary material is about twice that of the main material.

[0010]

[Table 1]

For comparison, as a conventional method, a sample having a firing keeping time and a cooling rate as shown in Table 2 was prepared. In the examples, the firing conditions are the same as those of the conventional example 1 because the resistance value is increased by changing the compounding ratio of the intermediate layer instead of changing the firing conditions.

[0012]

[Table 2]

The resistance value and the positive resistance temperature coefficient of the PTC thermistor element according to this embodiment and the resistance value and the positive resistance temperature coefficient of the conventional PTC thermistor element are shown in comparison with each other (Table 3).

[0014]

[Table 3]

In Table 3, when the resistance value is different in the conventional example, the temperature coefficient of resistance value is also different, but in the first, second and third embodiments, the same positive value is obtained even if the resistance value is different. The temperature coefficient of resistance of was obtained. In the conventional method, the positive temperature coefficient of resistance increases as the resistance value increases.

The method of measuring the resistance temperature characteristic of the positive temperature coefficient thermistor performed here will be described. First, room temperature to 300 ° C
Measure and plot the change in resistance value of the PTC thermistor with respect to temperature changes up to. Next, the temperature at which the resistance value is twice the room temperature resistance value is the Curie temperature, and the resistance value at the Curie temperature and the resistance value at the Curie temperature + 30 ° C are calculated, and the resistance change rate is calculated by (Equation 1) The temperature coefficient was used.

[0017]

[Equation 1]

[0018]

As described above, according to the present invention, in the positive temperature coefficient thermistor containing barium titanate as a main component, the two layers made of the main material have the same positive temperature coefficient of resistance as the main material and high specific resistance. By forming the intermediate layer into three layers, a positive temperature coefficient thermistor having the same positive temperature coefficient of resistance can be obtained even with different resistance values, and as a result, the same current-time characteristics can be obtained with different resistance values. It is possible.

Further, the effect of sandwiching the layer having a high resistance value between the two layers having a low resistance value is that the layer having a high resistance value and the layer having a low resistance value are combined into a total of two layers so that the resistance value is high. Electric power is applied only to the layers and heat generation and heat dissipation become uneven,
This is because only one of the front side and the back side has a large thermal expansion and warps and cracks. Therefore, also in the present invention, it is preferable that the two layers on the front and back sides to be sandwiched have substantially the same thickness, since warpage due to heat generation is eliminated.

[Brief description of drawings]

FIG. 1 is a sectional view of a positive temperature coefficient thermistor of the present invention.

FIG. 2 is a cross-sectional view of a conventional positive temperature coefficient thermistor.

[Explanation of symbols]

 1a Front surface electrode 1b Back surface electrode 2a Main material front surface layer 2b Main material back surface layer 3 Intermediate layer

Claims (2)

[Claims] 1. A front and back surface two layer composed of a main material of barium titanate having a positive characteristic as a main component, and an intermediate layer composed of a sub material having a positive temperature coefficient of resistance equal to that of the main material and a different specific resistance. Positive temperature coefficient thermistor with and. 2. The positive temperature coefficient thermistor according to claim 1, wherein the two layers of the front and back surfaces have the same layer thickness.