JP2000235901A - Ptc resistive element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a PTC resistive element which is stable with respect to repeated use, satisfactory in reproducibility and has positive temperature coefficient(PTC) characteristics. SOLUTION: In this PTC resistive element, thermosetting resin and conductive composition containing carbon interstitial metal-based conductive filler are used as the material. The conductive composition is molded in a sheet shape, and the mean grain diameter of the metal-based conductive filler is 0.5-50 μm. The aspect ratio of the conductive filler is desirably at least 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a PTC resistance element, and more particularly, to a PTC (Positive Temperature Coeffic).
The present invention relates to a PTC resistance element for protecting an electric circuit using a conductive composition having a characteristic of a positive temperature coefficient.

[0002]

2. Description of the Related Art As an electric circuit protection element used in electric equipment and electronic equipment including secondary batteries, an organic conductive composition in which a carbon-based conductive filler is dispersed in a crystalline polymer matrix is known. Have been.

[0003] In the organic conductive composition, while the temperature is lower than the crystal melting point of the crystalline polymer matrix, the carbon-based conductive filler is present only in the non-crystalline region of the crystalline polymer matrix. And exhibits a low resistivity due to a conductive mechanism in which electrons move through the conductive filler.

When the temperature rises and the crystalline polymer matrix begins to melt, the volume of the crystalline polymer matrix increases, so that the distance between the carbon-based conductive fillers in the crystalline polymer matrix decreases. As a result, the conductive path is broken and the resistance increases.

An electric circuit protection element using the above operation principle includes a conductive composition which has a low resistance at room temperature and increases the resistance as the temperature rises to limit the current, particularly a desired switching temperature (the resistance is rapidly increased). A PTC conductive composition whose resistance rapidly increases at a rising temperature) is used.

[0006]

However, a conventional PTC conductive composition using a crystalline polymer matrix is:
Since a thermoplastic resin is used, the heat resistance is limited and cannot be used repeatedly. Therefore, it is conceivable to use a thermosetting resin as a polymer matrix. However, the thermosetting resin has a complicated relationship between thermal expansion and volume shrinkage due to cross-linking during heat molding, which makes it difficult to suppress PTC characteristics. .

An object of the present invention is to provide a PTC resistance element for protecting an electric circuit, which is stable against repeated use and has PTC characteristics with good reproducibility.

[0008]

The PTC resistance element of the present invention is obtained by thermosetting a PTC conductive composition containing a thermosetting resin and a conductive filler having an average particle size of 0.5 to 50 μm. The ratio between the volume fraction of the conductive filler and the volume fraction of the thermosetting resin is from 35:64 to 65:35. Thereby, the resistivity at 20 ° C. of the PTC resistance element becomes 30 Ωcm or less, and the resistivity shows 10 ³ Ωcm or more at a switching temperature or higher.

When the PTC resistance element is manufactured, it is preferable that the PTC resistance element is heated to a desired switching temperature or more to be thermally cured.

In the present invention, the type of thermosetting resin and curing agent to be used is selected based on a desired switching temperature,
By using a thermoplastic filler according to the purpose of use, 7
It has been found that a conductive composition exhibiting stable PTC characteristics in a medium temperature range of 0 to 135 ° C. can be obtained.

The conductive filler exhibits stable conductivity when used together with a material having an irregular particle diameter by reducing a polymer component which is liable to change in volume. However, in the case of a PTC conductive composition, PTC switching is instantaneous. Preferably it occurs.

In the present invention, as the particle size of the conductive filler is larger, the distance between the particles formed by the polymer component serving as a resistance source is more varied during molding, and a short-circuit portion is more likely to occur. If it is large, it does not react sensitively to the thermal deformation of the polymer, and the switching effect becomes dull. If the particle is too small, the thermal deformation of the polymer is dispersed, the resistance change becomes small, and the PTC effect becomes small. Accordingly, it has been found that it is effective to use conductive fillers having a uniform particle size. It has also been found that the use of a conductive filler having an aspect ratio of 3 or more improves the conductivity and PTC characteristics.

That is, the present invention relates to a PTC resistance element, in which the material is a conductive composition containing a thermosetting resin and a carbon intrusion type metal-based conductive filler, and the conductive composition is formed into a sheet. It is a molded PTC resistance element.

Further, the present invention provides the above-mentioned conductive filler,
The PTC resistance element has an average particle size of 0.5 to 50 μm.

Further, the present invention is a PTC resistance element in which the conductive filler has an aspect ratio of 3 or more.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS PTC according to an embodiment of the present invention
An example of the resistance element will be described below.

[0017]

(Example 1) 36 parts by weight of a bisphenol-based epoxy resin (trade name: Adallite) and 4 parts by weight of a curing agent for epoxy were mixed, and a needle-shaped conductive filler;
60 parts by weight of iC was added, and the mixture was uniformly dispersed with a three-roll mill to produce a conductive composition of the present invention.

Then, one side is roughened to a thickness of 25 μm.
Sandwiching the conductive composition between two rough surfaces of nickel foil of
Pressed to a thickness of 300 μm.
Heat cured for 5 minutes.

The PTC resistance element was produced by cutting out the conductive composition bonded to the nickel foil into a ring shape having an outer diameter of 10 mmφ and an inner diameter of 6 mmφ.

The resistance change of the PTC resistance element when the current was repeatedly interrupted was measured. The results are shown in Tables 1 and 2.

[0021]

[Table 1]

[0022]

[Table 2]

That is, even when the resistivity at room temperature is 10 Ωcm, a voltage of 30 V and a current of 5 A are applied, switching is performed in 3 seconds, and the current is repeatedly interrupted 10 times, the temperature is lowered when cooled down to room temperature naturally. It was confirmed that the resistance value was within twice the initial resistance.

(Example 2) 36 parts by weight of a bisphenol-based epoxy resin (trade name: Adallite) and 4 parts by weight of a curing agent for epoxy were mixed, and further, a conductive filler having an average particle size of 1.5 μm by classification; 60 parts by weight of TiC was added, and the mixture was uniformly dispersed with a three-roll mill to produce a conductive composition of the present invention.

Next, one side is roughened to a thickness of 25 μm.
Sandwiching the conductive composition between two rough surfaces of nickel foil of
Pressed to a thickness of 300 μm.
Heat cured for 5 minutes.

The PTC resistance element was prepared by cutting the conductive composition bonded to the nickel foil into a ring shape having an outer diameter of 10 mmφ and an inner diameter of 6 mmφ.

The resistance change of the PTC resistance element when the current was repeatedly interrupted was measured. The results are shown in Tables 3 and 4.

[0028]

[Table 3]

[0029]

[Table 4]

That is, when a resistivity at room temperature is 10 Ωcm, a voltage of 30 V and a current of 5 A are applied, switching is performed in 3 seconds. The resistance value was within 1.55 times the initial resistance, and the PTC characteristic was improved by about 30% as compared with the case where the classifying powder was not used, and it was confirmed that stable repetitive current interruption was possible.

Example 3 36 parts by weight of a bisphenol-based epoxy resin (trade name: Adallite) and 4 parts by weight of a curing agent for epoxy were mixed, and the major axis was 3 μm, and the minor axis was 1 μm. Conductive filler; TiC60
The conductive composition of the present invention was produced by adding a part by weight and uniformly dispersing the mixture using a three-roll mill.

Then, one side is roughened to a thickness of 25 μm.
Sandwiching the conductive composition between two rough surfaces of nickel foil of
After being pressurized and spread to a thickness of 300 μm, it was thermally cured at 150 ° C. for 15 minutes.

The PTC resistance element was prepared by cutting the conductive composition bonded to the nickel foil into a ring shape having an outer diameter of 10 mmφ and an inner diameter of 6 mmφ.

As a result of measuring the initial resistance value of this PTC resistance element, the resistivity at room temperature was 8 Ωcm, and the resistance value was 20% higher than that of a PTC resistance element manufactured using spherical particles (average particle size: 1.5 μm). It could be reduced to a degree.

[0035]

As described above, according to the present invention, it is possible to provide a PTC resistance element which is stable against repeated use and has good PTC characteristics with good reproducibility.

Claims (3)

[Claims] 1. A PTC resistor element comprising a conductive composition containing a thermosetting resin and a carbon interstitial metal-based conductive filler, wherein the conductive composition is formed into a sheet. A PTC resistance element characterized by the above-mentioned. 2. The PTC resistance element according to claim 1, wherein the conductive filler has an average particle size of 0.5 to 50 μm. 3. An aspect ratio of the conductive filler is 3
The P according to claim 1 or 2, wherein
TC resistance element.