JPH1140402A - Organic ptc compound - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a low cost compound having low resistivity in an ambient temperature, an excellent PTC(positive temperature coefficient) characteristic without generating an internal arc phenomenon, and can be made to an overcurrent protection device. SOLUTION: An electrical conductive particle comprising a graphite particle 1 coated by a high melting point metal 2 is dispersed in an organic polymer. The high melting point metal is at least one type of metal selected from a metal having a melting point of 2700 degree C or more and comprises at least one type of W, WC, TaC, TiC, TiN, TiB2 , or ZrB2 . The coating rate of the high melting point metal 2 to the graphite particle 1 is 30 to 100%. The average diameter of the graphite particle 1 coating its surface by the high melting point metal 2 is 1 to 50 μm. The packing volume in the organic PTC compound by the graphite particle 1 coated on its surface by the high melting point metal 2 is 25 to 48 vol.%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric material, and more particularly, to a PTC (Positive Temperatu) having a property that electric resistance rapidly increases in a relatively narrow temperature range with a rise in temperature.
re Coefficient) material composition having properties, that is,
The present invention relates to a PTC composition, particularly an organic PTC composition.

[0002]

2. Description of the Related Art A PTC composition has the above-mentioned PTC characteristics, and is used for an overcurrent protection element for home / industrial wiring, a heater for stopping heat generation when the temperature rises to a certain temperature, a PTC thermistor,
PTC when circuit including thermal sensor, battery, etc. is short-circuited
It is used as a circuit protection element or the like that limits the current of a circuit by its characteristics and restores the circuit when the cause of the short circuit is removed. When this PTC composition is used as an overcurrent or overheat protection element or the like that exhibits the self-temperature control action as described above, for example, the composition is molded and at least two electrodes are electrically connected to the PTC composition to form a PTC composition. Used as an element.

[0003] Further, here, the overcurrent protection mechanism when a PTC element is used will be described in detail. Since the resistivity (ρL) of the PTC composition at room temperature is sufficiently low, current usually flows through the circuit. However, when a high current flows through the circuit due to a short circuit accident or the like, Joule heat is generated in the PTC element due to the high current, the temperature of the element increases, and the resistivity increases (exhibition of PTC characteristics). And the circuit is protected (this mechanism is called current limiting performance). In addition, the PTC element needs to have current limiting performance that can be used repeatedly even under a high voltage. The peak resistivity at a high temperature in the PTC curve is called ρH.

Various substances have been developed as PTC compositions, and one of them is BaTiO ₃ .
Addition of a trivalent or trivalent metal oxide is conventionally known. However, this involves NTC characteristics (Negative Temperature Coefficien
There is a problem that a current flows within 1 msec or less in order to exhibit t). For this reason, polyethylene (P
E), an organic polymer such as polypropylene or an ethylene-acrylic acid copolymer, and conductive particles such as carbon black (abbreviated as CB), carbon fiber, graphite or metal fine particles dispersed therein. . The PTC composition is generally produced by adding a necessary amount of conductive particles to one or more resins used as an organic polymer and kneading the resulting mixture.

As conductive particles of the organic PTC composition, C
When B, carbon fiber or graphite is used, the initial resistivity cannot be sufficiently reduced,
The PTC characteristics are also small, and the current limiting performance cannot be sufficiently improved. In addition, P containing conventional known metal particles
Although the TC composition can be expected to reduce the initial resistivity, when it is used under a large current and a high voltage, it causes an internal arc phenomenon (a minute arc is generated between the conductive particles) and causes a failure such as electric breakdown of the element. was there.

Further, Japanese Patent Publication No. 4-28743 discloses that
An organic PTC composition containing nickel particles as conductive particles is disclosed. The nickel particles as the first filler,
It is described that particles having lower conductivity than the first filler and particles made of carbon black or a non-conductive material are used as the second filler. However, the present inventors have further studied and studied the organic PTC composition using nickel particles in detail, and found that when nickel particles or molybdenum particles are used, the room temperature resistivity is lowered, but the overcurrent blocking performance is poor. Was.

[0007]

As conductive particles of the PTC composition, metal particles have a very low resistivity as compared with CB, but are not used in overcurrent protection devices. One of the major reasons is that the PTC composition containing the known metal particles as described above causes an internal arc phenomenon (a minute arc is generated between conductive particles) when used under a large current and a high voltage, This is because the composition causes electrical breakdown. When the internal arc phenomenon occurs, the metal particles in the PTC composition are melted and the metal particles are combined to form a local conductive circuit, and a large current is concentrated on a part of the element, leading to destruction of the element. It is. In addition, discharge is likely to occur in the micro-voids at the interface between the composition and the electrode, and the resin in the discharge part is degraded and decomposed, which causes rapid weakening and sometimes explosion, especially at a voltage of several tens of volts or more. It is.

The present invention has been made to solve the above-mentioned problems, and has a low room temperature resistivity, has excellent PTC characteristics without causing an internal arc phenomenon, and provides an overcurrent protection element. It is intended to obtain a low-cost organic PTC composition.

[0009]

The organic PTC composition according to the first aspect of the present invention is obtained by dispersing graphite particles whose surface is coated with a high melting point metal as conductive particles and dispersing the conductive particles in an organic polymer. Things.

The organic PT according to the second structure of the present invention
In the C composition, the high melting point metal in the first configuration is at least one selected from metals having a melting point of 2700 ° C. or higher.

The organic PT according to the third aspect of the present invention
The C composition has a high melting point metal in the second configuration,
It contains at least one of W, WC, TaC, TiC, TiN, TiB ₂ , and ZrB ₂ .

The organic PT according to the fourth aspect of the present invention
In each of the above structures, the C composition has a coverage of the high melting point metal on the graphite particles of 30 to 100%.

An organic PT according to a fifth aspect of the present invention.
In each of the above structures, the C composition has a graphite particle whose surface is coated with a high-melting-point metal, and has an average particle diameter of 1 to 50 μm.

An organic PT according to a sixth aspect of the present invention.
In each of the above structures, the C composition has a filling amount of the graphite particles whose surface is coated with the high melting point metal in the organic PTC composition of 25 to 48 vol%.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 FIG. The PTC composition according to the present invention is obtained by dispersing, as conductive particles, graphite particles whose surfaces are coated with a high melting point metal in an organic polymer. By combining an organic polymer with graphite having a surface coated with a high melting point metal in an optimal amount, a composition having good PTC characteristics was obtained.
The refractory metal-coated graphite dispersed in the organic polymer has excellent electric conductivity, heat conductivity, and melting resistance to a small arc as a PTC composition, and has excellent PTC composition.
It can provide characteristics. Further, by using at least one kind of metal having a melting point of 2700 ° C. or more as the high melting point metal, graphite particles coated with the high melting point metal under a large current and a high voltage do not melt. It has been clarified from experiments that the circuit is protected from overcurrent by increasing the resistance of the PTC element without forming a conductive circuit. The refractory metals are W, WC, TaC, TiC, Ti
It contains at least one of N, TiB ₂ and ZrB ₂ and has a melting point of 2700 ° C. or more, and is mainly made of low-cost graphite and its surface is coated with high-priced tungsten or other metal. Accordingly, the conductive particles can be kept low and relatively inexpensive conductive particles can be obtained.

Next, a method for producing graphite particles whose surface is coated with a high melting point metal will be described with reference to a case of WC coated graphite as an example. WC particles (Nihon Shinkin Co., Ltd.)
Product name: WC-10, 0.7 μm, true specific gravity
8) and graphite particles (manufactured by Showa Denko KK, trade name:
UFG-30, 10 μm, true specific gravity 2.25) is treated at 16,000 rpm for 3 minutes with a special pulverizer / stirrer (trade name: Hybridizer manufactured by Nara Machinery Co., Ltd.) to produce WC-coated graphite particles. In this case, the average particle size of the graphite particles is 10 μm, and the average particle size of the WC particles is, for example, 0.7 μm, which is smaller by one digit than that. Also,
100% coverage of WC particles on graphite particles
In order to achieve this, the composition is such that graphite is 1 and WC is 0.2 by volume ratio. FIG. 1A shows the appearance of a WC-coated graphite particle having a coverage of 100%, and FIG.
It was shown to. In the figure, 1 is graphite and 2 is WC. 1 (a) and 1 (b) show the case where the WC2 covers the surface of the graphite particles 1 in the form of particles, but as shown in FIG. 1 (c), the WC particles are stuck together. The boundaries may be ambiguous.

The coverage of graphite particles with a high melting point metal is, for example, 70% in WC coverage.
It can be controlled by controlling the blending ratio of the high melting point metal to graphite, such that the volume ratio of graphite is 1 and WC is 0.1. The relationship between the WC coverage of the WC-coated graphite particles and the resistivity at room temperature is, for example, as shown in FIG.
In the case of 1 vol%, the resistivity gradually increases up to a coverage of WC of 100 to 30%, but increases sharply at a coverage of 30% or less. Therefore, 100 to 30% is desirable. The relationship between the coverage and the room temperature resistivity slightly varies depending on the particle size of the graphite particles coated with the high melting point metal and the type of the high melting point metal, but almost the same results as in FIG. 2 are obtained.

The average particle size of the graphite particles coated with the high melting point metal can be appropriately selected depending on the application and desired characteristics of the PTC composition. However, it is 1 to 50 μm because of the restrictions on the production of graphite particles and refractory metal particles which are desirably one digit smaller than the graphite particles.
Is desirable, and 5 to 10 μm is more desirable. With this particle size, an organic PTC composition having a low resistivity at room temperature can be obtained.

The mixing ratio of the organic polymer and the conductive particles can be appropriately selected according to the particle content of the target composition, the type of the polymer, the kneader such as a Banbury mixer, a pressure kneader, and a roll mill. When the filling amount of the conductive particles is small, the room temperature resistivity increases, and when the filling amount is large, the composition cannot be mixed and molded. Therefore, the filling amount of the conductive particles in the organic PTC composition is desirably 25 to 48 vol%, and more preferably 29 to 48 vol%. ~
45 vol% is more desirable. As an example, FIG. 3 shows the relationship between the filling amount of WC-coated graphite (coverage 80%, particle diameters 1 μm and 3 μm) and the room temperature resistivity of the PTC element. Note that the relationship between the filling amount and the resistivity slightly varies depending on the particle size of the high melting point metal-coated graphite particles and the type of the high melting point metal, and in particular, it becomes difficult to fill when the particle size of the high melting point metal coated graphite particles becomes small. Therefore, the upper limit value of the filling amount tends to be small, but a result substantially similar to that of FIG. 3 is obtained.

Examples of the organic polymer according to the present invention include polyethylene, polyethylene oxide, polybutadiene, polyethylene acrylate, ethylene-ethyl acrylate copolymer, ethylene-acrylic acid copolymer, polyester, polyamide, polyether, polycaprolactam, and fluorine. Ethylene-propylene copolymer, chlorinated polyethylene, chlorosulfonated ethylene, ethylene-vinyl acetate copolymer, polypropylene, polystyrene, styrene-acrylonitrile copolymer, polyvinyl chloride,
Polycarbonate, polyacetal, polyalkylene oxide, polyphenylene oxide, polysulfone, and fluororesin are used, and a blend polymer of these alone or a mixture of at least two or more selected from these is used. The type, composition ratio, and the like of the organic polymer may be appropriately selected according to desired performance, use, and the like.

In preparing the PTC composition, various additives may be mixed as necessary, in addition to the above-mentioned organic polymer and conductive particles. Examples of additives include flame retardants such as antimony compounds, phosphorus compounds, chlorine compounds, and bromine compounds, antioxidants, and stabilizers. The PTC composition is prepared by mixing and kneading an organic polymer, conductive particles, and other additives as required at a predetermined ratio. The organic polymer may be prepared by mixing and kneading conductive particles or both at the same time.

The organic PTC composition obtained according to the present invention can be used for various applications. When used as a PTC element, the PTC composition is formed into a plate shape, for example, and an electrode plate is pressed on the back surface of the plate or a metal foil electrode is pressed by heat to form a laminate, and the laminate is formed on the electrode surface. The PTC element can be manufactured by connecting the terminals by crimping, soldering, brazing, spot welding, screwing, or the like.

[0023]

EXAMPLES Hereinafter, specific Examples 1 to 3 of the present invention shown in the table will be described.
12 will be described together with Comparative Examples 1 to 3, but of course the present invention is not limited by these.

[0024]

[Table 1]

Embodiment 1 High density polyethylene (manufactured by Mitsubishi Chemical Corporation, trade name: HJ560) as an organic polymer
0 parts by weight, the same WC-coated graphite particles as described in the embodiment as conductive particles (100% WC coverage,
33 parts by weight of an average particle size of 3 μm) and 2 parts by weight of a phenolic antioxidant (manufactured by Nippon Ciba Geigy Co., Ltd., trade name: Irganox 1010) were manufactured by Labo Plast Mill (manufactured by Toyo Seiki Seisakusho, Ltd.) 200 ° C, 1
The mixture was kneaded for 5 minutes to obtain a PTC composition in which 31 vol% of conductive particles were dispersed and filled in the composition. This PTC composition was formed into a 40 × 60 × 1 mm thick plate by hot pressing. A polyethylene frame was formed by injection molding around 2 mm around the plate in order to provide insulation during interruption. Next, the obtained molded plate was sandwiched between electrodes, and PTC characteristics were measured and an overcurrent interruption experiment was performed. The PTC curve is shown in FIG. The room temperature resistivity (ρL) of the PTC composition was 0.015 Ω · cm, the peak resistivity (ρH) was 10 ⁵ Ω · cm, and ρH / ρL was 10 ⁷ .
When the room temperature resistance of this PTC element is 1.0 mΩ, 300
V, the current-limiting peak value (Ip) for an overcurrent of 50 kA was 8.5 kA. FIG. 5 shows the relationship between the resistance of the PTC element and the peak current limit value at the time of overcurrent interruption.

Embodiment 2 FIG. High density polyethylene (manufactured by Mitsubishi Chemical Corporation, trade name: HJ560) as an organic polymer
0 parts by weight, 33 parts by weight of the same WC-coated graphite particles (80% coverage, average particle size 3 μm) as described in the embodiment as the conductive particles, and a phenolic antioxidant (Nippon Ciba Geigy Co., Ltd.) And 2 parts by weight of Irganox 1010) at 200 ° C. and 1 ° C. with a Labo Plastomill apparatus (trade name, manufactured by Toyo Seiki Seisaku-sho, Ltd.).
Kneaded for 5 minutes. This PTC composition is heated to 40 ×
A plate having a thickness of 60 × 1 mm was formed. A polyethylene frame was formed by injection molding around 2 mm around the plate in order to provide insulation during interruption. Next, an overcurrent interruption experiment was performed with the obtained molded plate interposed between electrodes. The room temperature resistivity (ρL) of this composition was 0.020 Ω · cm. When the room temperature resistance of this PTC element was 1.2 mΩ, the current-limiting peak value (Ip) for 300 V and 50 kA was 8.0 kA. FIG. 5 shows the relationship between the resistance of the PTC element and the peak current limit value at the time of overcurrent interruption.

Embodiment 3 FIG. High density polyethylene (manufactured by Mitsubishi Chemical Corporation, trade name: HJ560) as an organic polymer
0 parts by weight, 33 parts by weight of the same WC-coated graphite particles (WC coverage 50%, average particle diameter 3 μm) as described in the embodiment as conductive particles, and a phenolic antioxidant (Nippon Ciba Geigy Co., Ltd.) And 2 parts by weight of Irganox 1010) at 200 ° C. and 1 ° C. with a Labo Plastomill apparatus (trade name, manufactured by Toyo Seiki Seisaku-sho, Ltd.).
Kneaded for 5 minutes. This PTC composition is heated to 40 ×
A plate having a thickness of 60 × 1 mm was formed. A polyethylene frame was formed by injection molding around 2 mm around the plate in order to provide insulation during interruption. Next, an overcurrent interruption experiment was performed with the obtained molded plate interposed between electrodes. The room temperature resistivity (ρL) of this composition was 0.025 Ω · cm. When the room temperature resistance of this PTC element was 1.5 mΩ, the current-limiting peak value (Ip) for 300 V and 50 kA was 7.5 kA. FIG. 5 shows the relationship between the resistance of the PTC element and the peak current limit value at the time of overcurrent interruption.

Embodiment 4 FIG. High density polyethylene (manufactured by Mitsubishi Chemical Corporation, trade name: HJ560) as an organic polymer
0 parts by weight, 33 parts by weight of the same WC-coated graphite particles (WC coverage 30%, average particle size 3 μm) as described in the embodiment as the conductive particles, and a phenolic antioxidant (Nippon Ciba Geigy Co., Ltd.) And 2 parts by weight of Irganox 1010) at 200 ° C. and 1 ° C. with a Labo Plastomill apparatus (trade name, manufactured by Toyo Seiki Seisaku-sho, Ltd.).
Kneaded for 5 minutes. This PTC composition is heated to 40 ×
A plate having a thickness of 60 × 1 mm was formed. A polyethylene frame was formed by injection molding around 2 mm around the plate in order to provide insulation during interruption. Next, an overcurrent interruption experiment was performed with the obtained molded plate interposed between electrodes. The room temperature resistivity (ρL) of this composition was 0.050 Ω · cm. When the room temperature resistance of this PTC element was 2.0 mΩ, the current-limiting peak value (Ip) for 300 V and 50 kA was 7.0 kA. FIG. 5 shows the relationship between the resistance of the PTC element and the peak current limit value at the time of overcurrent interruption.

Embodiment 5 FIG. High density polyethylene (manufactured by Mitsubishi Chemical Corporation, trade name: HJ560) as an organic polymer
0 parts by weight, the same WC-coated graphite particles as described in the embodiment as conductive particles (100% WC coverage,
33 parts by weight of an average particle size of 10 μm) and 2 parts by weight of a phenolic antioxidant (manufactured by Nippon Ciba-Geigy Co., Ltd., trade name: Irganox 1010) were manufactured by Labo Plastomill Co., Ltd. 200 ° C)
Kneaded for 15 minutes. The PTC composition is heated to 40
It was made into a plate of × 60 × 1 mm thickness. A polyethylene frame was formed by injection molding around 2 mm around the plate in order to provide insulation during interruption. Next, an overcurrent interruption experiment was performed with the obtained molded plate interposed between electrodes. Room temperature resistivity (ρL) of this composition
Was 0.015 Ω · cm. When the room temperature resistance of this PTC element was 1.0 mΩ, the current limiting peak value (Ip) at 300 V and 50 kA was 8.5 kA. FIG. 5 shows the relationship between the resistance of the PTC element and the peak current limit value at the time of overcurrent interruption.

Embodiment 6 FIG. High density polyethylene (manufactured by Mitsubishi Chemical Corporation, trade name: HJ560) as an organic polymer
0 parts by weight, 33 parts by weight of WC-coated graphite particles (WC coverage 80%, average particle diameter 10 μm) similar to those described in the embodiment as the conductive particles, and a phenolic antioxidant (Nippon Ciba Geigy Co., Ltd.) And 2 parts by weight of Irganox 1010) at 200 ° C. and 1 ° C. with a Labo Plastomill apparatus (trade name, manufactured by Toyo Seiki Seisaku-sho, Ltd.).
Kneaded for 5 minutes. This PTC composition is heated to 40 ×
A plate having a thickness of 60 × 1 mm was formed. A polyethylene frame was formed by injection molding around 2 mm around the plate in order to provide insulation during interruption. Next, an overcurrent interruption experiment was performed with the obtained molded plate interposed between electrodes. The room temperature resistivity (ρL) of this composition was 0.020 Ω · cm. When the room temperature resistance of this PTC element was 1.2 mΩ, the current-limiting peak value (Ip) for 300 V and 50 kA was 8.0 kA. FIG. 5 shows the relationship between the resistance of the PTC element and the peak current limit value at the time of overcurrent interruption.

Embodiment 7 FIG. High density polyethylene (manufactured by Mitsubishi Chemical Corporation, trade name: HJ560) as an organic polymer
0 parts by weight, W-coated graphite particles (W
33% by weight of a coating rate of 80% and an average particle size of 10 μm, and a phenolic antioxidant (Nippon Ciba Geigy Co., Ltd.)
(Trade name: Irganox 1010) was kneaded at 200 ° C. for 15 minutes using a Labo Plastomill apparatus (trade name, manufactured by Toyo Seiki Seisaku-sho, Ltd.). This PTC composition was formed into a 40 × 60 × 1 mm thick plate by hot pressing. A polyethylene frame was formed by injection molding around 2 mm around the plate in order to provide insulation during interruption. Next, an overcurrent interruption experiment was performed with the obtained molded plate interposed between electrodes. The room temperature resistivity (ρL) of this composition was 0.020 Ω · cm. When the room temperature resistance of this PTC element is 1.2 mΩ, 300
V, current limiting peak value (Ip) for 50 kA is 8.0 kA
showed that. FIG. 5 shows the relationship between the resistance of the PTC element and the peak current limit value at the time of overcurrent interruption.

Embodiment 8 FIG. High density polyethylene (manufactured by Mitsubishi Chemical Corporation, trade name: HJ560) as an organic polymer
0 parts by weight, 33 parts by weight of TaC-coated graphite particles (TaC coverage 80%, average particle diameter 3 μm) as conductive particles, and a phenolic antioxidant (trade name: Irganox 1010, manufactured by Nippon Ciba Geigy Co., Ltd.) 2 parts by weight of Labo Plastomill (Toyo Seiki Seisaku-sho, Ltd.)
(Trade name) at 200 ° C. for 15 minutes. This PTC
The composition was hot pressed into plates 40 × 60 × 1 mm thick.
A polyethylene frame was formed by injection molding around 2 mm around the plate in order to provide insulation during interruption. Next, an overcurrent interruption experiment was performed with the obtained molded plate interposed between electrodes. The room temperature resistivity (ρL) of this composition was 0.020 Ω · cm. When the room temperature resistance of this PTC element is 1.2 mΩ, 3
The current-limiting peak value (Ip) for 00 V and 50 kA is 8.0.
kA was indicated. FIG. 5 shows the relationship between the resistance of the PTC element and the peak current limit value at the time of overcurrent interruption.

Embodiment 9 FIG. High density polyethylene (manufactured by Mitsubishi Chemical Corporation, trade name: HJ560) as an organic polymer
0 parts by weight, 33 parts by weight of TiB ₂ -coated graphite particles (80% coverage of TiB ₂ , average particle size of 3 μm) as conductive particles, and a phenolic antioxidant (manufactured by Nippon Ciba Geigy Co., Ltd., trade name: Irganox 1010) ) Was kneaded at 200 ° C for 15 minutes with a Labo Plastomill apparatus (trade name, manufactured by Toyo Seiki Seisaku-sho, Ltd.). This P
The TC composition was pressed into a 40 × 60 × 1 mm thick plate by hot pressing. A polyethylene frame was formed by injection molding around 2 mm around the plate in order to provide insulation during interruption. Next, an overcurrent interruption experiment was performed with the obtained molded plate interposed between electrodes. The room temperature resistivity (ρL) of this composition was 0.020 Ω · cm. When the room temperature resistance of this PTC element is 1.2 mΩ,
The current limit peak value (Ip) for 300 V, 50 kA is 8.
It showed 0 kA. FIG. 5 shows the relationship between the resistance of the PTC element and the peak current limit value at the time of overcurrent interruption.

Embodiment 10 FIG. 30 parts by weight of high-density polyethylene (manufactured by Mitsubishi Chemical Corporation, trade name: HJ560) as an organic polymer, and 33 ZrB ₂ -coated graphite particles (ZrB ₂ coverage 80%, average particle size 3 μm) as conductive particles 33
Parts by weight, and 2 parts by weight of a phenolic antioxidant (trade name: Irganox 1010, manufactured by Ciba-Geigy Japan)
The parts by weight were kneaded at 200 ° C. for 15 minutes using a Labo Plastomill apparatus (trade name, manufactured by Toyo Seiki Seisaku-sho, Ltd.). This P
The TC composition was pressed into a 40 × 60 × 1 mm thick plate by hot pressing. A polyethylene frame was formed by injection molding around 2 mm around the plate in order to provide insulation during interruption. Next, an overcurrent interruption experiment was performed with the obtained molded plate interposed between electrodes. The room temperature resistivity (ρL) of this composition was 0.020 Ω · cm. When the room temperature resistance of this PTC element is 1.2 mΩ,
The current limit peak value (Ip) for 300 V, 50 kA is 8.
It showed 0 kA. FIG. 5 shows the relationship between the resistance of the PTC element and the peak current limit value at the time of overcurrent interruption.

Embodiment 11 FIG. 30 parts by weight of high-density polyethylene (manufactured by Mitsubishi Chemical Corporation, trade name: HJ560) as an organic polymer, 33 parts by weight of TiC-coated graphite particles (TiC coverage 80%, average particle diameter 3 μm) as conductive particles, and phenol 2 parts by weight of an antioxidant (manufactured by Nippon Ciba Geigy Co., Ltd., trade name: Irganox 1010) was added to Labo Plast Mill (manufactured by Toyo Seiki Seisaku-sho, Ltd.)
(Trade name) at 200 ° C. for 15 minutes. This PTC
The composition was hot pressed into plates 40 × 60 × 1 mm thick.
A polyethylene frame was formed by injection molding around 2 mm around the plate in order to provide insulation during interruption. Next, an overcurrent interruption experiment was performed with the obtained molded plate interposed between electrodes. The room temperature resistivity (ρL) of this composition was 0.020 Ω · cm. When the room temperature resistance of this PTC element is 1.2 mΩ, 3
The current-limiting peak value (Ip) for 00 V and 50 kA is 8.0.
kA was indicated. FIG. 5 shows the relationship between the resistance of the PTC element and the peak current limit value at the time of overcurrent interruption.

Embodiment 12 FIG. 30 parts by weight of high-density polyethylene (manufactured by Mitsubishi Chemical Corporation, trade name: HJ560) as an organic polymer, 33 parts by weight of TiN-coated graphite particles (TiN coverage: 80%, average particle size: 3 μm) as conductive particles, and phenol 2 parts by weight of an antioxidant (manufactured by Nippon Ciba Geigy Co., Ltd., trade name: Irganox 1010) was added to Labo Plast Mill (manufactured by Toyo Seiki Seisaku-sho, Ltd.)
(Trade name) at 200 ° C. for 15 minutes. This PTC
The composition was hot pressed into plates 40 × 60 × 1 mm thick.
A polyethylene frame was formed by injection molding around 2 mm around the plate in order to provide insulation during interruption. Next, an overcurrent interruption experiment was performed with the obtained molded plate interposed between electrodes. The room temperature resistivity (ρL) of this composition was 0.020 Ω · cm. When the room temperature resistance of this PTC element is 1.2 mΩ, 3
The current-limiting peak value (Ip) for 00 V and 50 kA is 8.0.
kA was indicated. FIG. 5 shows the relationship between the resistance of the PTC element and the peak current limit value at the time of overcurrent interruption.

Comparative Example 1 High density polyethylene (manufactured by Mitsubishi Chemical Corporation, trade name: HJ560) as an organic polymer
0 parts by weight, 33 parts by weight of WC-coated graphite particles (WC coverage 20%, average particle diameter 3 μm) similar to those described in the embodiment as the conductive particles, and a phenolic antioxidant (Nippon Ciba Geigy Co., Ltd.) And 2 parts by weight of Irganox 1010) at 200.degree.
Kneaded for 5 minutes. This PTC composition is heated to 40 ×
A plate having a thickness of 60 × 1 mm was formed. A polyethylene frame was formed by injection molding to provide insulation at the time of interruption in 2 mm around the plate. Next, an overcurrent interruption experiment was performed with the obtained molded plate interposed between electrodes. The room temperature resistivity (ρL) of this composition was 1.000 Ω · cm. The room temperature resistance of this PTC element was 5.0 mΩ, which was higher than practical. In this case, the current-limiting peak value (Ip) at 300 V and 50 kA was 5.5 kA. FIG. 5 shows the relationship between the resistance of the PTC element and the peak current limit value at the time of overcurrent interruption.

Comparative Example 2 As the conductive particles, graphite particles coated with low melting point nickel instead of graphite particles whose surfaces are coated with high melting point metal as in each of the above examples (Ni coverage 85%, Ni melting point 1452 ° C., average particle size 116 μm, Nikko Fine Products Co., Ltd.)
33 parts by weight, 30 parts by weight of a high-density polyethylene (manufactured by Mitsubishi Chemical Corporation, trade name: HJ560) as an organic polymer, and a phenolic antioxidant (manufactured by Nippon Ciba-Geigy, trade name: Irganox 1010) ) With 2 parts by weight of Labo Plast Mill (manufactured by Toyo Seiki Seisaku-sho, Ltd.)
(Trade name) at 200 ° C. for 15 minutes. This PTC
The composition was hot pressed into plates 40 × 60 × 1 mm thick.
A polyethylene frame was formed by injection molding around 2 mm around the plate in order to provide insulation during interruption. Next, an overcurrent interruption experiment was performed with the obtained molded plate interposed between electrodes. The room temperature resistivity (ρL) of this composition was 0.020 Ω · cm. When the room temperature resistance of this PTC element is 1 mΩ, 300
V failed to block 50 kA. The reason why blocking was not possible is as follows. The PTC composition filled with low melting point metal-coated graphite causes an internal arc phenomenon (a minute arc is generated between conductive particles) when used under a large current and a high voltage, and the PTC composition causes electric breakdown. Conceivable. It is considered that when the internal arc phenomenon occurs, the nickel particles in the PTC composition are melted by the heat, and then the nickel particles are bonded to each other, a large current flows in the bonded portion, and the composition is considered to be electrically damaged.

Comparative Example 3 Copper particles (melting point 1083 ° C.,
124 parts by weight of specific gravity 8.96, average particle diameter 30 μm, manufactured by Fukuda Metal Foil Industry Co., Ltd., and high-density polyethylene as an organic polymer (manufactured by Mitsubishi Chemical Corporation, trade name: HJ560)
And 31 parts by weight of a phenolic antioxidant (manufactured by Nippon Ciba Geigy Co., Ltd., trade name: Irganox 101)
2) was kneaded at 200 ° C. for 15 minutes using a Labo Plastomill apparatus (trade name, manufactured by Toyo Seiki Seisaku-sho, Ltd.). This PTC composition is 40 × 60 × 1 mm in a hot press.
It was a thick plate. A polyethylene frame was formed by injection molding around 2 mm around the plate in order to provide insulation during interruption.
Next, an overcurrent interruption experiment was performed with the obtained molded plate interposed between electrodes. The room temperature resistivity (ρL) of this composition is 0.020Ω.
Cm. When the room temperature resistance of this PTC element was 1 mΩ, it could not be cut off at 300 V and 50 kA.

[0040]

As described above, the organic PTC composition according to the first aspect of the present invention is obtained by dispersing the conductive particles in an organic polymer by using the graphite particles whose surfaces are coated with a high melting point metal as the conductive particles. Therefore, the high melting point metal-coated graphite has good electric conductivity, heat conductivity, and melting resistance to a minute arc as a PTC composition, and has excellent PT.
C characteristics are obtained.

The organic PT according to the second structure of the present invention
The C composition is such that the high melting point metal in the first configuration is at least one kind selected from metals having a melting point of 2700 ° C. or higher, so that graphite particles coated with the high melting point metal under a large current and a high voltage are used. Since the element does not melt, a conductive circuit is not locally formed in the element, and the circuit is protected from overcurrent by increasing the resistance of the PTC element.

Further, the organic PT according to the third configuration of the present invention
The C composition has a high melting point metal in the second configuration,
W, WC, TaC, TiC, TiN, TiB ₂ , and ZrB ₂ .
Since the surface is coated with high-priced tungsten or other metal mainly using low-priced graphite, it is possible to keep the electric resistance low and obtain relatively inexpensive conductive particles.

The organic PT according to the fourth structure of the present invention
In each of the above configurations, the C composition has a low melting point resistivity at room temperature since the coverage of the graphite particles with the high melting point metal is 30 to 100%.

The organic PT according to the fifth aspect of the present invention
In the C composition, the average particle size of the graphite particles whose surface is coated with the high melting point metal is 1 to 50 μm in each of the above-described configurations, so that a composition having low room temperature resistivity can be obtained.

The organic PT according to the sixth aspect of the present invention
In the C composition, the filling amount of the graphite particles whose surfaces are coated with the high melting point metal in the organic PTC composition is 25 to 48 vol% in each of the above-described configurations, so that a composition having a low room temperature resistivity can be obtained.

[Brief description of the drawings]

FIG. 1 shows WC-coated graphite particles according to an embodiment of the present invention, wherein (a) is a plan view and (b) and (c) are cross-sectional views.

FIG. 2 is a characteristic diagram showing the relationship between the WC coverage of WC-coated graphite particles and the room-temperature resistivity of the PTC composition.

FIG. 3 WC coated graphite particles (80% coverage)
FIG. 3 is a characteristic diagram showing a relationship between a filling amount of the PCT and a room temperature resistivity of the PCT composition.

FIG. 4 shows WC-coated graphite particles (80% coverage,
FIG. 4 is a characteristic diagram showing PTC characteristics when the filling amount is 31 vol%).

FIG. 5 is a characteristic diagram showing a relationship between the resistance of the PTC element and the current-crest peak value according to the first to twelfth examples.

[Explanation of symbols]

 1 graphite, 2 WC.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Manabu Sogabe 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Mitsui Electric Co., Ltd. (72) Inventor Shiro Murata 2-3-2 Marunouchi, Chiyoda-ku, Tokyo 3 Rishi Electric Co., Ltd. (72) Inventor Masahiro Ishikawa 2-3-2 Marunouchi, Chiyoda-ku, Tokyo, Japan Mitsui Electric Co., Ltd. (72) Inventor Tomoe Takahashi 2-3-2, Marunouchi, Chiyoda-ku, Tokyo, Mitsuishi Inside Electric Co., Ltd. (72) Inventor Teijiro Mori 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Mitsui Electric Co., Ltd. (72) Inventor Tatsuya Hayashi 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Mitsubishi Electric Co., Ltd. In company

Claims (6)

[Claims] 1. An organic PTC composition comprising, as conductive particles, graphite particles whose surfaces are coated with a high melting point metal, and the conductive particles dispersed in an organic polymer. 2. The organic PTC composition according to claim 1, wherein the high melting point metal is at least one selected from metals having a melting point of 2700 ° C. or higher. 3. The high melting point metal is W, WC, TaC, Ti.
C, TiN, TiB _2, and ZrB organic PTC composition according to claim 2 further comprising at least one type of the _two. 4. The organic PTC composition according to claim 1, wherein the coverage of the graphite particles with the high melting point metal is 30 to 100%. 5. The organic PTC composition according to claim 1, wherein the average particle size of the graphite particles whose surfaces are coated with a high melting point metal is 1 to 50 μm. 6. An organic PTC composition having a graphite particle whose surface is coated with a high melting point metal in an amount of 25 to 48 vol.
% Of the organic PTC according to any one of claims 1 to 5.
Composition.