JP2002008904A - Positive temperature characteristic themistor composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive temperature characteristic thermistor composition improved in PTC characteristics. SOLUTION: A positive temperature characteristic thermistor composition contains crystalline polymer and conductive filler, including particles whose surfaces are coated with carbon where the particles included in the filler are silicon dioxide.

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 (PTC thermistor) composition having a property that the volume resistivity increases as the temperature rises.

[0002]

2. Description of the Related Art Conventionally, a PTC thermistor has been known as an overcurrent protection element for preventing an overcurrent from flowing into an electronic device or the like. As the organic PTC thermistor, a composition in which a conductive filler such as carbon black or metal fine powder is mixed with a crystalline polymer is generally used. That is, such a composition has a characteristic that a conductive path is cut due to a rapid volume expansion near the melting point of the crystalline polymer and the volume resistivity increases, that is, a so-called PTC characteristic. Is used as a PTC thermistor.

[0003]

However, in such a composition, when a filler such as an extender or a reinforcing agent is used in addition to the conductive filler in the crystalline polymer, the conductivity is reduced. There is.

In view of such circumstances, an object of the present invention is to provide a positive temperature coefficient thermistor composition exhibiting excellent PTC characteristics at low cost.

[0005]

According to a first aspect of the present invention, there is provided a positive temperature coefficient thermistor comprising a crystalline polymer and a conductive filler having a particle surface coated with carbon. In the composition.

A second aspect of the present invention is the positive temperature coefficient thermistor composition according to the first aspect, wherein the particles constituting the conductive filler are made of an inorganic substance.

A third aspect of the present invention is the positive temperature coefficient thermistor composition according to the second aspect, wherein the inorganic substance is silicon dioxide.

[0008] Since the PTC thermistor composition of the present invention comprises a crystalline polymer and a conductive filler, the filler does not cause a decrease in conductivity and substantially has a P content.
TC characteristics can be improved.

Here, the particles constituting the conductive filler are preferably inorganic substances, particularly silicon dioxide, but are not limited thereto, and include, for example, oxides, carbonates, silicates and nitrides. Can be used.

[0010] Specifically, examples of the oxide include alumina, zinc oxide, titanium oxide, calcium oxide, magnesium oxide, iron oxide, tin oxide and antimony oxide. Examples of the carbonate include calcium carbonate, magnesium carbonate, zinc carbonate and barium carbonate. In addition, as silicate,
Examples include calcium silicate, talc, clay, mica or glass beads. Furthermore, examples of the nitride include aluminum nitride, boron nitride, and silicon nitride.

The shape of the particles constituting the conductive filler is not particularly limited. However, it is preferable that the particles have a substantially spherical shape because the number of contact points is small. Also, the particle size of the particles,
It is not particularly limited and may be appropriately determined. In addition, if the particle diameter is several nm to several μm, carbon coating can be performed.

The shape of the particles may be a shape having a plurality of projections, such as a tetrapod shape, in addition to a substantially spherical shape. As described above, since the properties of the positive temperature coefficient thermistor composition vary depending on the material, shape, particle size, and the like of the particles, the material, shape, and particle size of the particles are appropriately determined so that desired characteristics are obtained. Good.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on embodiments.

(Example 1) An approximately spherical silicon dioxide (SiO ₂ ) particle was coated with carbon with respect to 100 parts by weight of polyethylene as a crystalline polymer. Mitsui Mining Co., Ltd.)
00 parts by weight and kneading with an electric heating roll. afterwards,
Crosslinking treatment was performed with an organic peroxide. PTC obtained
After the composition was pressed into a flat plate having a thickness of 0.5 mm,
A test piece of Example 1 was manufactured by depositing gold on the surface of this flat plate.

The conductive filler used in this embodiment is
The carbon content was 9.4% by weight.

Comparative Example 1 A test piece was produced in the same manner as in Example 1 except that 160 parts by weight of carbon black was used as a conductive filler.

Comparative Example 2 A test piece was produced in the same manner as in Comparative Example 1 except that 40 parts by weight of a calcium carbonate-based extender was added as an extender.

(Comparative Example 3) A test piece was produced in the same manner as in Comparative Example 1, except that 80 parts by weight of a calcium carbonate-based extender was added as an extender.

(Test Example) The volume resistivity when the temperature of the test pieces of Example 1 and Comparative Examples 1 to 3 was raised from 30 ° C. to about 150 ° C. was measured, and the temperature resistance characteristics were examined. The results are shown in FIGS.

As shown in FIG. 1, the test piece of Example 1
It can be seen that the volume resistivity significantly increased from around 120 ° C. in each case. That is, it can be seen that the positive temperature coefficient thermistor composition comprising the crystalline polymer and the conductive filler having the particle surface carbon-coated exhibits good PTC characteristics despite the low carbon content.

On the other hand, as shown in FIG. 2, in the test piece of Comparative Example 1 in which carbon black was used in a large amount of 160 parts by weight, the increase in volume resistivity was about two orders of magnitude smaller than that in the example, and It was found that the test pieces of Comparative Examples 2 and 3 in which the agent was added in an amount of 40 parts by weight and 80 parts by weight, respectively, had further reduced volume resistivity and reduced PTC characteristics.

[0022]

As described above, the positive temperature coefficient thermistor composition of the present invention is a completely novel composition containing a crystalline polymer and a conductive filler whose surface is coated with carbon. Such a positive temperature coefficient thermistor composition has an effect that good PTC characteristics can always be obtained, and good PTC characteristics can be obtained even when the carbon content is substantially small.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the temperature of a test piece and the volume resistivity of each example.

FIG. 2 is a graph showing the relationship between the temperature and the volume resistivity of a test piece of each comparative example.

Claims (3)

[Claims] 1. A positive temperature coefficient thermistor composition comprising a crystalline polymer and a conductive filler whose surface is coated with carbon. 2. The positive temperature coefficient thermistor composition according to claim 1, wherein the particles constituting the conductive filler are made of an inorganic substance. 3. The positive temperature coefficient thermistor composition according to claim 2, wherein said inorganic substance is silicon dioxide.