JPH11126702A - Manufacture of positive temperature coefficient thermistor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent cracks by using material powder with lower calcining temperature than that of the center of a formed body to form the periphery of the formed body and firing the same even if a sheathing method or a firing condition is changed. SOLUTION: Predetermined materials such as barium carbonate and the like are mixed and divided into two, the two divided materials are put in calcining sheathes, calcined, for example at 1080 deg.C and 1060 deg.C, respectively, and then granulating powder is prepared by adding a binder. The granulating powder of the calcined material at a temperature of 1060 deg.C is filled into a mortar 3c, a frame 4 is positioned in the center of the mortar 3c and the granulating powder of the material calcined at 1080 deg.C is filled into the flame 4. The granulating powder of the material calcined at 1060 deg.C is further filled into the periphery circumferentially surrounding the frame 4. The granulating powder of the material calcined at 1060 deg.C is filled into the mortar 3c except for the frame to form a formed body. In the formed body, the periphery 2 of the material calcined at 1080 deg.C in the center 1 is covered with the material calcined at 1060 deg.C. Then, the formed body is calcined at, for example 1280 deg.C and a thermistor element is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a PTC thermistor element.

[0002]

2. Description of the Related Art A method for manufacturing a conventional positive temperature coefficient thermistor element (hereinafter referred to as a thermistor element) will be described below.

In a conventional thermistor element, barium carbonate and titanium oxide as main components, lead oxide, yttrium oxide, aluminum oxide, manganese oxide, silicon oxide, and the like as main components are weighed in predetermined amounts, mixed, dried, and dried. 1000
Perform calcination at a temperature of ° C. Next, crush the calcined material obtained,
Granulation is performed to produce a barium titanate material powder. Next, after being formed into a predetermined shape, it was baked at a temperature of about 1200 ° C. in the air to produce a thermistor element. At this time, it is common to use material powder having the same calcining temperature as the material powder used for molding.

[0004]

However, in the above-mentioned conventional manufacturing method, cracks are formed on the outer peripheral portion of the thermistor element after firing, depending on the firing sheath packing method for packing the green body when firing the green body or the firing conditions. Occurred. One of the causes is that the binder component added at the time of granulation during the firing process of the thermistor element molded body does not pass through the outer periphery of the molded body and cannot be completely removed. It becomes partially uneven and cracks occur. As a countermeasure, it is conceivable to set the calcining temperature of the mixed material lower in order to facilitate the scattering of the binder.In this case, the obtained thermistor element becomes porous and the finished thermistor element is reduced. When exposed to an atmosphere, there was a problem that electrical characteristics deteriorated.

[0005]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional problems. When molding a thermistor element, the outer peripheral portion of the molded body is molded using a material powder having a lower calcination temperature than the central portion. And baking the same to obtain a thermistor element which does not cause cracking even if the method of shrinking or changing the baking conditions is changed.

[0006]

DETAILED DESCRIPTION OF THE INVENTION The invention according to claim 1 of the present invention is directed to a positive temperature coefficient thermistor element containing barium titanate as a main component, in which the outer peripheral portion of the element is at a lower temperature than the material forming the central portion. A method of manufacturing a positive temperature coefficient thermistor element, characterized in that the calcined material is molded using the same composition material, and then calcined at a predetermined temperature. By forming
The binder component contained in the material can be evenly scattered from the outer periphery of the molded body during the firing process of the molded body, and the entire molded body is uniformly fired and shrunk, and the outer periphery generated due to uneven progress of firing shrinkage. Cracks in the part can be prevented.

Hereinafter, an embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG. (Embodiment 1) FIG. 1 shows a molded article formed by the production method of the present invention. Reference numeral 1 denotes a central portion using a material having a high calcining temperature, and reference numeral 2 denotes an outer peripheral portion using a material having a low calcining temperature.

First, barium carbonate, lead oxide, titanium oxide, yttrium oxide,
The specified amount of each of silicon oxide, aluminum oxide, and manganese oxide is weighed.

[0009]

Embedded image

[0010] Pure water was added thereto, and the mixture was mixed by a ball mill for 18 hours, followed by dehydration and drying. Next, the mixed material is divided into two parts, placed in a sinter for calcination and calcined at a temperature of 1080 ° C. and a temperature of 1060 ° C. for 2 hours each. Then, each calcined material is pulverized by a ball mill for 18 hours. Further, a binder was added, and the mixture was dried with a spray drier to produce granulated powder.

The granulated powder of the calcined material at 1060 ° C. is filled into a mortar 3c having a length of 20 mm and a width of 15 mm by the internal method shown in FIG. Next, after lowering the lower punch 3a by 4 mm, a frame 4 having a length of 16 mm, a width of 11 mm, and a depth of 4 mm is placed at the center of the mill 3c, and the material calcined at 1080 ° C. inside the frame 4 is granulated. Fill the powder to a thickness of 4 mm and further surround the frame 4
A granulated powder of a material calcined at 1060 ° C. is filled in an outer peripheral portion having a width of mm. Next, after removing the frame 4, the lower punch 3a is
Then, the mill 3c is filled with 2 mm of granulated powder of the material calcined at 1060 ° C. Thereafter, the upper punch 3b and the lower punch 3a applied a pressure of 800 kg / cm ² from the upper and lower surfaces of the mill 3c to carry out molding, thereby producing a molded body having a shape of 20 mm in length, 15 mm in width and 4 mm in thickness. In the obtained molded body, the outer peripheral portion 2 of the material calcined at 1080 ° C. in the central portion 1 is covered with the material calcined at 1060 ° C. Separately, a compact was produced using only the powder calcined at 1060 ° C. and 1080 ° C. by a conventional molding method.

Thereafter, in order to prevent the lead oxide in the material components from evaporating during the firing process of the compacts, each compact is packed in a closed slag and baked at 1280 ° C. for 2 hours to produce a thermistor element. did.

After investigating the occurrence of cracks in the obtained thermistor element, electrodes having a length of 14 mm and a width of 9 mm were formed on both sides of the thermistor element, and the thermistor element was applied with a voltage of 100 V between the electrodes in a reducing atmosphere. A life test in which a time was applied was performed, and a change in resistance value at room temperature of the thermistor element before and after the life test was evaluated. The results are shown in (Table 1).

[0014]

[Table 1]

In Table 1, No. 1 and No. 2 are repetitive experimental products of the present invention.
Reference numeral 4 denotes a thermistor element using only a material calcined at 1060 ° C.

As shown in Table 1, the difference in the closed firing between the product of the present invention and the conventional product is clearly different, and the material using only the material calcined at 1080.degree. doing. On the other hand, No. 4 using only the material calcined at 1060 ° C. does not crack,
The room temperature resistance has been significantly degraded in a life test in a reducing atmosphere. On the other hand, in the product of the present invention, cracking and deterioration of the room temperature resistance value hardly occurred in a life test in a reducing atmosphere. This is because the product of the present invention is the central part 1 of the thermistor element.
Is composed of a material powder having a high calcining temperature, and the outer peripheral portion 2 is composed of a material powder having a low calcining temperature. It is considered that the sometimes added binder can be evenly scattered from the outer peripheral portion 2 of the thermistor element, whereby the shrinkage at the time of firing progresses uniformly and the generation of cracks can be suppressed. Further, when used in a reducing atmosphere, the central portion 1 of the thermistor element on which the electrodes are formed is made of a material having a high calcining temperature, so that the material has excellent sinterability and is dense, and does not lead to deterioration of electrical characteristics. I think that the.

From this, the outer peripheral portion 2 of the thermistor molded body
It can be seen that a thermistor element which does not cause cracking and can be used in a reducing atmosphere can be obtained by forming the material having a lower calcination temperature than that of the central portion 1.

(Embodiment 2) In Embodiment 1, a material which is calcined at 1080 ° C. in the central portion 1 of the thermistor element,
Although the material calcined at 1060 ° C. was used for the outer peripheral portion 2, in the present embodiment, a material having the same composition as that of (Embodiment 1) was further increased by 20 ° C. to 1100 ° C. and 1080 ° C., respectively. A molded body was produced in the same manner as in (Embodiment 1), and was processed under the same conditions as in (Embodiment 1), and the occurrence of cracks in the obtained thermistor element was investigated. The breakdown voltage characteristics were evaluated, and the results are shown in (Table 2).

[0019]

[Table 2]

In Table 2, No. 5 and No. 6 are the repetitive experimental products of the present invention, and No. 7 was at 1080 ° C.
Reference numeral 8 denotes a thermistor element using a material calcined at 1100 ° C.

As shown in Table 2, as the material for the central portion 1 and the outer peripheral portion 2 of the product of the present invention, a material powder having a calcination temperature of 20 ° C. higher than that of (Embodiment 1) was used.
The No. 5 and No. 6 thermistor elements have less cracking and high withstand voltage characteristics. On the other hand, the thermistor element No. 8 manufactured using only the powder having the calcining temperature of 1100 ° C. has excellent sinterability and high withstand voltage, but generates many cracks during firing. On the other hand, the thermistor element No. 7 using only the calcining temperature material of 1080 ° C. has many occurrences of cracks and is inferior to the withstand voltage characteristic of No. 8. For this reason, by forming the outer peripheral portion 2 of the thermistor molded body from a material having a lower calcination temperature than the central portion 1, the withstand voltage characteristics are not reduced,
It can be seen that a thermistor element free from cracking can be obtained.

(Embodiment 3) In (Embodiment 1) and (Embodiment 2), the difference in the calcining temperature between the material of the central portion 1 and the material of the outer peripheral portion 2 is set to 20 ° C. The temperature difference was set to 40 ° C., the thermistor element was molded and fired under the same conditions as in (Embodiment 1), and the resulting thermistor element was evaluated for the occurrence of cracks and the life test in a reducing atmosphere. The results are shown in (Table 3).

[0023]

[Table 3]

In Table 3, No. 9 and No. 10 are repeated experimental products of the embodiment of the present invention.

As shown in Table 3, no cracking occurred in this embodiment, and no deterioration in the resistance value was observed in a reducing atmosphere.

For this reason, in the first embodiment, the difference in the calcining temperature between the material in the central portion 1 and the material in the outer peripheral portion 2 was set to 20 ° C., but the difference in the calcining temperature was 40 ° C. or more. It turns out to be desirable.

(Embodiment 4) In (Embodiment 1), a thermistor element whose outer peripheral portion 2 has a thickness of 2 mm is manufactured.
An electrode having a length of 14 mm and a width of 9 mm was formed, and an electrode portion formed on the surface of the thermistor element had the same shape as the central portion 1 using a material having a high calcining temperature.

In the present embodiment, 1060
The calcined material at 1 ° C. and the calcined material at 1100 ° C. for the central part 1 were used to form a sintered body having a thickness of 2 mm at the outer peripheral part 2 manufactured under the same conditions as in (Embodiment 1). ), The thermistor elements No. 11 to No. 13 in which the electrodes shown in FIG. 1 are formed, a material calcined at 1060 ° C. on the outer peripheral part 2, and 1100 ° C. on the central part 1
The width of the outer peripheral portion 2 was changed as shown in Table 3 by using the material calcined in the above, and the sintered body fired under the same conditions as in the first embodiment was applied to a 14 mm long, 9 mm wide electrode. No14 that formed
No. 16 to No. 16 were evaluated for the occurrence of cracks and withstand voltage characteristics, and the results are shown in (Table 4).

[0029]

[Table 4]

As shown in (Table 4), No. 1 electrode was formed up to the surface of the outer peripheral portion 2 using a material having a low calcining temperature.
In Nos. 3 and 16, the withstand voltage characteristics deteriorate. Nos. 14 and 15 in which the thickness of the outer peripheral portion 2 is smaller than 2 mm have cracks,
No. 16 of mm did not occur.

From these results, it is found that the electrode formed on the surface of the thermistor element is equal to or smaller than the area of the upper and lower surfaces of the central part 1 of the thermistor element, which leads to the improvement of the withstand voltage characteristic. It is understood that the occurrence of cracks can be suppressed by requiring the width of the portion 2 to be at least 2 mm or more.

[0032]

As described above, according to the present invention, in a positive temperature coefficient thermistor element containing barium titanate as a main component, the outer peripheral portion of the element is molded using the same composition material calcined at a lower temperature than the central portion. By firing at a predetermined temperature, cracks do not occur during firing, strong in reduction resistant atmosphere,
In addition, it is possible to provide a thermistor element having excellent withstand voltage characteristics.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a molded body according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view illustrating the molding method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Center part 2 Outer part 3a Lower punch 3b Upper punch 3c Dust 4 Frame

Claims (1)

[Claims] In a positive temperature coefficient thermistor element containing barium titanate as a main component, after molding an outer peripheral portion of the element using a material of the same composition which is calcined at a lower temperature than a material forming a central portion, the molding is performed at a predetermined temperature. A method of manufacturing a positive temperature coefficient thermistor element, characterized by performing firing.