JPH0547502A - Organic positive temperature coefficient thermistor - Google Patents

Abstract

PURPOSE:To provide an organic positive temp. coefficient thermistor showing steep rise of PTC characteristics and large variation in resistance value, and also having the small initial resistance value at room temperature. CONSTITUTION:An organic positive temp. coefficient thermistor is obtained by kneading carbon fibers into a crystalline polymer. The short carbon fibers of 100 to 1000mum in average length are used. According to this constitution, a large change of resistance value can be displayed, and an organic positive temp. coefficient thermistor, having a small initial resistances value at the normal temperature, can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic positive temperature coefficient thermistor, and more specifically, to a characteristic in which a resistance value rapidly increases in a specific temperature range during temperature rise, that is, PTC (Positive Tem
The present invention relates to an organic positive temperature coefficient thermistor having a perature coefficient.

[0002]

2. Description of the Related Art Heretofore, an organic positive temperature coefficient thermistor having a PTC characteristic in which fine metal powder, carbon black or the like is dispersed in a crystalline polymer such as polyethylene or polypropylene has been known in the art. For example, US Patent No.
No. 3591526 and No. 3673121.

By the way, the PTC characteristic of the crystalline polymer shows a rapid volume expansion when the crystalline polymer changes from crystalline to amorphous at its melting point, so that the particles of the conductive fine powder dispersed therein are separated from each other. This occurs because the spacing is widened and the contact resistance between the particles rapidly increases.

Such an organic positive temperature coefficient thermistor can be used as, for example, a temperature detector or a self-controlled heater, but the performance required for this organic positive temperature coefficient thermistor is such that the PTC characteristic has a sharp rise and a large resistance value. It is necessary to show a change and to have a small initial resistance value at room temperature.

[0005]

However, the conventional organic positive temperature coefficient thermistor is often filled with a particulate conductive material such as carbon black or metal fine powder, and in order to reduce the initial resistance value, It was necessary to increase the filling amount. In such a case, there has been a problem that the rate of change in resistance becomes small and it is difficult to apply it to a heater or the like.

Therefore, an object of the present invention is to provide an organic positive temperature coefficient thermistor having a sharp rise in PTC characteristics, a large resistance value change, and a small initial resistance value at room temperature.

[0007]

The organic positive temperature coefficient thermistor according to claim 1 is obtained by kneading a crystalline polymer with carbon fiber.

In the organic positive temperature coefficient thermistor according to a second aspect, the carbon fiber in the organic positive temperature coefficient thermistor according to the first aspect is a short fiber having an average length of 100 μm to 1000 μm.

[0009]

According to the organic positive temperature coefficient thermistor of claim 1, since the crystalline polymer is obtained by kneading carbon fibers, the PTC characteristics show a sharp rise and a large change in resistance value. The initial resistance value at

According to the organic positive temperature coefficient thermistor of the second aspect, the carbon fiber in the organic positive temperature coefficient thermistor of the first aspect has an average length of 100 μm to 1000 μm.
Since it is a short fiber, the initial resistance value at room temperature is small, and at the transition temperature, the resistance value sharply rises, the PTC characteristic rises sharply, and exhibits a large resistance value change.

[0011]

EXAMPLES Examples of the present invention will be described in detail below.

The organic positive temperature coefficient thermistor of this embodiment is obtained by kneading a crystalline polymer with carbon fibers.
The carbon fibers have an average length of 100 μm to 1000 μm.
m short fibers are used. If the average length is 100 μm or less, the resistance value cannot be lowered, and conversely, the average length is 1000 μm or less.
If it is more than μm, the rate of resistance change does not increase, which is not practical. Therefore, the above range is preferable.

The filling amount of carbon fiber with respect to the crystalline polymer is 15 to 40 wt%. When the filling amount of this carbon fiber is 15 wt% or less, the resistance value is too high and it becomes unpractical. If it is 40 wt% or more, the rate of change in resistance becomes small.

Further details will be described below.

Example 1 Polyvinylidene fluoride was used as the crystalline polymer, and carbon fiber having a length of 700 μm and a diameter of 10 μm (length / diameter ratio of 70) was used as the conductive material, and the polyvinylidene fluoride was used. Carbon fibers were added at a ratio of 30 parts by weight, kneaded with a Labo Plastomill, and press-formed into a sheet having a thickness of 0.7 mm. Furthermore, N is used as an electrode on both sides of this molded product.
The i foil was pressure-bonded and punched into a disk shape having a diameter of 10 mm to obtain a sample.

Next, the PTC characteristics of this sample were measured. In this measurement, the temperature of the sample was raised and lowered in a constant temperature bath, the resistance value at each predetermined temperature was measured, and the relationship between the temperature and the resistance value was obtained. The measurement result is shown in FIG.

From the measurement results shown in FIG. 1, the resistance value (R ₂₅ ) at room temperature is as low as 0.2 Ω, but the resistance rapidly increases at the transition temperature, and the maximum resistance value (R _max) )
Is 10 ⁶ Ω, and the rate of change in resistance (= log (R _max / R ₂₅ ))
) Is a high value of 6.0 or more.

Further, even at a temperature of 176 ° C. or higher, which is the maximum resistance value, the resistance value did not decrease, and the sample was not deformed by heat.

Example 2 Example 2 was repeated except that the content of carbon fiber was changed to 15 parts by weight. Although the resistance value at room temperature is as low as 1.2Ω, the resistance rapidly increases at the transition temperature, the maximum resistance value becomes 4 × 10 ⁷ Ω, and the resistance change rate is as high as 7.0 or higher. Became.

Example 3 Example 3 was repeated except that the crystalline polymer was high density polyethylene. Although the resistance value at room temperature is as low as 0.5Ω, the resistance rapidly increases at the transition temperature and the maximum resistance value becomes 4 × 10 ⁷ Ω, and the resistance change rate is 8.
It became a high value of 0 or more.

Comparative Example A comparative sample was prepared in the same manner as in Example 3 except that the conductive material was carbon black and the content was 40 parts by weight. The measurement results of this comparative sample are shown in FIG. As is clear from FIG. 2, the resistance value at room temperature was about 0.2Ω, the maximum resistance value was 4 × 10 ⁴ Ω, and the resistance change rate was about 5.0.

As described in detail above, the organic positive temperature coefficient thermistor of this embodiment has both a low resistance value and a steep PTC characteristic, and is suitable for application to a heater or the like.

The present invention is not limited to the above-described embodiments, but various modifications can be made within the scope of the gist thereof.

[0024]

According to the present invention described in detail above, it is possible to provide an organic positive temperature coefficient thermistor which has a sharp rise in PTC characteristics, exhibits a large resistance value change, and has a small initial resistance value at room temperature.

[Brief description of drawings]

FIG. 1 is a graph showing a specific resistance temperature characteristic of an organic positive temperature coefficient thermistor of this embodiment.

FIG. 2 is a graph showing a specific resistance temperature characteristic of an organic positive temperature coefficient thermistor of a comparative example.

Claims (2)

[Claims] 1. An organic positive temperature coefficient thermistor obtained by kneading a crystalline polymer with carbon fibers. 2. The carbon fibers have an average length of 100 μm.
The organic positive temperature coefficient thermistor according to claim 1, wherein the thermistor is a short fiber having a diameter of from 1000 to 1000 μm.