JP2000286103A - Electrode of high-temperature ptc ceramics and method of producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain stable characteristics, even at higher temperature use than a specified temperature for a long period of time by using aluminum or an aluminum alloy as an electrode material to form the electrode by heating, while performing thermal spraying to a sintered surface. SOLUTION: An electrode is formed by thermally spraying aluminum or an aluminum alloy to a PTC ceramics 1 having 300 deg.C or higher Curie point, and sufficient anchor effect is easily obtained, when surface roughness of the PTC ceramics formed with the electrode is 1 μm or more. Since Pb is vaporized from the surface in sintering at 300 deg.C or higher Curie point, which is increased in quantity within the material as rising temperature, the electrode can be formed easily on the surface by thermal spraying. Also, since electrode layers 2a and 2b are adhered to the PTC ceramics 1 by adhesion properties due to anchor effect, the adhesion properties is not changed even under a high temperature environment of use, the sintered surface has stable properties.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a PTC ceramic electrode used at a high temperature of 300 DEG C. or more, and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, a PTC ceramic electrode is formed by adding a glass component to Ag, printing it in a paste form, drying it, and then baking it, so-called baking, to form an electrode. Further, there is a method in which a metal such as Ni is heat-treated by plating, and then an unnecessary portion of the electrode is ground. Further, Japanese Patent Application Laid-Open Nos. 59-111290 and 4-133403 disclose methods of spraying.

[0003]

However, according to the conventional method, the following problems occur when used in an environment of 300 ° C. or higher. In the method of baking, there is a problem that the glass contained in the electrode layer moves due to the high use environment temperature of the PTC ceramics, and the electrode becomes unstable. On the other hand, in the method of grinding unnecessary electrodes after heat-treating metals such as Ni by plating, the operating environment temperature is high, the metal on the surface has poor heat resistance, oxidation of the surface progresses, and the apparent resistance value Rises and eventually becomes an insulator. Further, in the electrode forming method by thermal spraying, there is a large temperature difference between the high temperature environment and the room temperature environment when the temperature is raised, so that stress is generated between the base body and the electrode, which may not endure use for a long term. by the way,
In PTC ceramics having a high temperature, that is, a high Curie point, Pb contained in a large amount of the material evaporates at the time of firing, and many closed pores as well as open pores are formed. Further, at the time of sintering, these are sealed by the evaporated Pb compound and serve to protect and stabilize the characteristics of the sintered body. Therefore, when the sintered body is processed after firing, the characteristics may be deteriorated.

[0004]

In order to achieve this object, the present invention forms an electrode by thermal spraying on a surface after sintering, and heats the PTC ceramic while forming the electrode.
By doing so, the purpose can be achieved.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention according to claim 1 is formed by spraying aluminum or an aluminum alloy on PTC ceramics having a Curie point of 300 ° C. or higher by thermal spraying. The electrodes are joined by the adhesion of the electrode layers due to the effect, and the adhesion does not change even in a high-temperature use environment. The surface condition of the surface after sintering is such that an electrode is easily formed by thermal spraying and is stable in characteristics. In addition, PTC ceramics and aluminum exhibit ohmic characteristics and exhibit a resistance value close to that of PTC ceramics. According to the second aspect of the present invention, when the surface roughness of the PTC ceramic on which the electrodes are formed is 1 μm or more, a sufficient anchor effect can be easily obtained. Also
When the Curie point of PTC ceramics is 300 ° C or higher, the higher the temperature, the more Pb contained in the material evaporates from the surface during firing,
The surface state becomes a state in which an electrode is easily formed by thermal spraying. According to the present invention, the PTC ceramic is heated to within ± 50 ° C. of the Curie point at the time of forming the electrode by thermal spraying, so that even when the PTC ceramic is used near the Curie point, the resistance due to the peeling due to thermal stress and the change in the contact state. The value does not increase, the adhesion is stable, and the change in the resistance value is small. Examples Hereinafter, examples of the present invention will be described with reference to the drawings.
FIG. 1 is a structural sectional view of a PTC ceramic according to the first embodiment of the present invention. In FIG. 1, 1 is a PTC ceramic, and 2a and 2b are electrodes. Example 1 First, a plate-like PTC ceramic having a Curie point of 350 ° C., which is an oxide semiconductor, was formed by molding a raw material containing barium lead titanate as a main component and a trace amount of a rare earth element or the like as an auxiliary component. I got An electrode mainly composed of aluminum was formed by plasma spraying on the sintered surface (surface roughness: 1 to 1.5 μm) of the entire lower surface of the PTC ceramic 1.
The obtained PTC ceramics was subjected to an intermittent test of 20 min ON-40 min OFF, and the resistance change was measured. After 5000 hours, the resistance change rate was 15%. If the rate of change in resistance is greater than 20%, the characteristics are sharply reduced and there is a problem in durability. However, since the PTC ceramics of the present invention is smaller than this, it was found that they can be used even at high temperatures.

Comparative Example 1 A PTC ceramics surface prepared in the same manner as in Example 1 was polished to a mirror surface (with a surface roughness of 0.01 μm or less).
The same test was performed. After 5000 hours, the resistance change rate is
25%. In addition, PTC ceramic surface roughness is 1μ
Similar results were obtained for those smaller than m. Since the rate of change in resistance is larger than 20%, there is a problem in durability, and it is understood that the surface roughness of the PTC ceramic needs to be 1 μm or more as in the present invention. Example 2 When forming an electrode mainly composed of aluminum on the entire upper and lower surfaces of the PTC ceramic element 1 prepared in the same manner as in Example 1 by plasma spraying, the same test as in Example 1 was performed while heating to 350 ° C. went. After 5000 hours, the resistance change rate is 2
%Met. In addition, when forming electrodes by plasma spraying,
Similar results were obtained even when heating was performed within ± 50 ° C of the Curie point (350 ° C) of TC ceramics. Since the PTC ceramic element of the present invention is heated to within ± 50 ° C. of the Curie point of the PTC ceramic at the time of forming the electrode, it can be seen that the resistance change rate is small even when used at a high temperature and has durability. The thermal spraying method includes flame spraying, arc thermal spraying, plasma thermal spraying and the like, and plasma thermal spraying is suitable for the present method because of its operability and functionality. Further, when the surface roughness of the sintered body is small, a method of performing thermal spraying after roughening the surface by heat treatment may be considered.

[0007]

According to the present invention, it is possible to obtain PTC ceramics having stable characteristics even when used at a high temperature of 300 ° C. or more for a long time.

[Brief description of the drawings]

FIG. 1 is a structural sectional view of a PTC thermistor of the present invention.

[Explanation of symbols]

 1 PTC ceramics 2a, 2b electrode

Claims (3)

[Claims] 1. An electrode of high-temperature PTC ceramics having a Curie point of 300 ° C. or higher, wherein the electrode material is made of aluminum or an aluminum alloy and formed by spraying on a sintered surface. 2. The high-temperature PTC ceramic electrode according to claim 1, wherein the surface roughness of the PTC ceramic on which the electrode is formed is 1 μm or more. 3. A PTC ceramic having a Curie point of 300 ° C. or higher, wherein the electrode material is made of aluminum or an aluminum alloy, and the PTC is formed by thermal spraying of an electrode of a high-temperature PTC ceramic formed on a sintered surface by thermal spraying.
A method for manufacturing a high-temperature PTC ceramic electrode, comprising heating the ceramic to within ± 50 ° C of the Curie point.