JPH0969410A - Current limiting element and current limiting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a sudden increase in resistance value in a specific temperature region and also to prevent the lowering of the resistance value even when temperature exceeded the above-mentioned temperature by a method wherein an electrode is provided on the current limiting element, which is a blend of a conductive filler and a water crosslinking polyolefin and a current is applied thereto. SOLUTION: This current limiting element is formed as follows. Water crosslinking polyolefin, which generates no heat-fusion, is used as a matrix, a current limiting element 1 is formed by comprising the conductive filler such as carbon black, graphite, etc., low molecular weight polyolefin wax, with which the resistance variation by the change of temperature can be made larger, and an oxidation preventing agent. After molding and heat treatment, conductive coating materials 2 and 3 are applied, so that the current element is obtained. After the element has been dried up, conductive metal electrodes 4 and 5 are mounted. As a result, the element is not fluidized even when a specific temperature is exceeded, and a highly reliable current limiting device, in which resistance value does not decrease, can be obtained.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a current limiting element and a current limiting device. More specifically, the property that the temperature coefficient of resistance of the current limiting element sharply increases in the positive direction when reaching a specific temperature region (hereinafter referred to as PTC (Positive Temper).
referred to as the characteristic coefficient)
And relates to a current limiting element and a current limiting device for preventing overcurrent.

[0002]

2. Description of the Related Art Conventionally, a current limiting element formed by molding a crystalline polymer such as polyethylene as a matrix and kneading a conductive filler such as carbon black or graphite into a desired form has a PTC at a temperature near the melting point of the matrix. It is well known to exhibit properties. Typical P
The TC characteristic curve is shown by the curve a in FIG. Note that the vertical axis in FIG. 3 is the specific resistance (Ω · cm) expressed in ohm · cm, and the horizontal axis is the temperature (° C.) expressed in degrees Celsius. As shown by the curve a in FIG. 3, the resistance value of the current limiting element is gradually increased below the melting point of the matrix, but is rapidly increased when approaching the melting point of the matrix, for example, about 130 ° C.
Therefore, by utilizing this property, it is possible to form a current limiting element which has a high resistance due to overcurrent and cuts off the current.
However, when the resistance value of the current limiting element reaches a peak at about the melting point and the temperature further rises, the resistance may gradually decrease. Therefore, if the temperature of the current limiting element exceeds this peak temperature for some reason, the resistance value decreases, and the current tends to flow more and more, which may cause burnout.

As described above, a PTC characteristic of a current limiting element formed by kneading a crystalline polymer as a matrix and kneading a conductive filler such as carbon black or graphite into a desired shape is the melting of the crystalline polymer. This is because the volume expansion occurs, the intervals of the conductive fillers dispersed therein are widened, and the contact resistance rapidly increases.

As a method for producing a PTC element having a relatively low resistance in which carbon black is mixed in a polymer substance, a crystalline polymer and carbon black are used as disclosed in, for example, Japanese Patent Publication No. 5-66001. There is a method for producing an element having PTC characteristics in which the above components are mixed and molded into a predetermined shape by an extruder, and the crystalline polymers are crosslinked by irradiation with radiation to form a network structure to improve thermal deformability.

Further, as disclosed in, for example, Japanese Patent Application Laid-Open No. 56-8443, rubber-like substances, carbon black, graphite, organic peroxides, etc. are mixed and molded into a predetermined shape, and then heated. It is known to produce a resistor having PTC characteristics with improved thermal deformability by decomposing an organic peroxide to give a rubber-like substance a network structure.

Further, in Japanese Patent Laid-Open No. 58-32382,
By using a linear low-density polyethylene cross-linked by electron beam irradiation for the matrix, improvement has been made so that the peak value of the resistance value does not decrease as shown by curves b and c in FIG.

[0007]

When the resin is three-dimensionally crosslinked by electron beam irradiation or organic peroxide to suppress the fluidity, the resistance value does not decrease, but these conventional crosslinking methods are as follows. There is a problem.

In the organic peroxide cross-linking method, it is premised that the molding processing temperature is lower than the decomposition temperature of the organic peroxide. Therefore, the molding processing temperature range is narrowed, and the molding processing methods that can be adopted are limited. Also, the polyethylene that can be used is almost limited to low density polyethylene. Further, the crosslinking of the uncrosslinked molded product obtained under such severe conditions is carried out at the decomposition temperature of the organic peroxide, that is, at a temperature higher than the melting point of the polyethylene used while maintaining its shape, Extremely harsh methods are taken. Therefore, there is a problem that a special high-priced crosslinking device is required.

On the other hand, the electron beam irradiation method requires very high-priced irradiation equipment, and it is difficult to uniformly cross-link thick-walled molded products and irregularly shaped products due to radiation characteristics. In this case, there were problems such as generation of residual charge and generation of gas and foaming.

The present invention has been made to solve the above problems, and the resistance value rapidly increases in a specific temperature range, and the resistance value does not decrease even if the temperature is exceeded, and the reliability is high. The purpose is to obtain a current limiting device.

[0011]

The first aspect of the present invention is characterized by including a current limiting element formed by mixing a water-crosslinking polyolefin with a conductive filler, and an electrode for energizing the current limiting element. Regarding vessels.

The second aspect of the present invention is a current limiting device comprising a water-crosslinked polyolefin and a conductive filler, wherein the water-crosslinked polyolefin is water-crosslinked polyethylene, water-crosslinked polypropylene and water-crosslinked ethylene-vinyl acetate copolymer. The present invention relates to a current limiting element characterized by comprising at least one selected from the group consisting of:

A third invention of the present invention relates to the current limiting element of the second invention, wherein the conductive filler is at least one selected from the group consisting of carbon black, graphite, carbon fibers and metal powder. .

According to a fourth aspect of the present invention, the current limiting element of the second aspect is characterized in that the mixing ratio of the conductive filler to the entire composition for forming a current limiting element is in the range of 50% by weight to 60% by weight. Regarding

A fifth invention of the present invention relates to the current limiting device of the second invention, characterized in that the water-crosslinked polyolefin is blended with a low molecular weight polyolefin wax.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION In the current limiting device of the present invention, a conductive filler such as graphite or carbon black is added to a water-crosslinking type polyolefin, and if necessary, a low molecular weight polyolefin wax, an antioxidant and the like are added. After that, for example, the mixture is heated and kneaded with a mixing roll or the like, then molded into a predetermined shape by, for example, an injection molding method, and then allowed to act with water (for example, immersed in hot water or immersed in heated steam) to crosslink. You can get it by doing. Since the water-crosslinkable polyolefin in the present invention does not melt even if it exceeds a specific temperature, it does not exhibit fluidity and accordingly does not lower the resistance value.

FIG. 1 is a perspective view showing a current limiting device according to an embodiment of the present invention, in which 1 is a current limiting element, 2 and 3 are conductive paint coating films, and 4 and 5 are electrodes.

As one embodiment of the current limiting element of the present invention, a water-crosslinked polyolefin that does not melt by heating is used as a matrix,
A current limiting element 1 formed by adding a conductive filler, a low molecular weight polyolefin wax, and an antioxidant thereto will be described.

Examples of the water-crosslinking type polyolefin that does not melt by heating include water-crosslinking type low density polyethylene, water-crosslinking type high density polyethylene, water-crosslinking type polypropylene,
A water-crosslinking ethylene-vinyl acetate copolymer or the like is used.

The water-crosslinkable polyolefin used in the present invention preferably has a gel fraction of 60% or more after crosslinking.
If the gel fraction after cross-linking is less than the above range, the temperature coefficient of resistance of the current limiting element increases in the negative direction after the PTC characteristic is exhibited (hereinafter referred to as NTC (negative negative temperature).
referred to as the characteristic coefficient)
Tends to show. The gel fraction was calculated from the weight change before and after extraction of the crosslinked water-crosslinked polyolefin with xylene at 110 ° C. for 24 hours, followed by vacuum drying at 100 ° C. for 24 hours (JIS C 3005).

As the water-crosslinked polyolefin, for example, an organosilane-modified polyolefin is preferably used.

The organosilane-modified polyolefin is, for example, one obtained by introducing active silyl groups into polyolefins by a graft copolymerization method or a random copolymerization method. When the active silyl groups come into contact with water, as shown in the following schematic diagram. A cross-linking reaction occurs to form a network polymer.

[0023]

Embedded image

Here, R ¹ , R ² and R ³ are the same or different and each represents an alkyl group (for example, one having 1 to 2 carbon atoms) or the like.

These water-crosslinking type polyolefins have an easy processability such that they can be molded on a general-purpose molding machine under the same conditions as general-purpose polyolefins. Furthermore, the obtained molded product is placed in an atmosphere containing water. When left to stand, crosslinking easily proceeds at a temperature below the melting point.

The mixing ratio of the water-crosslinkable polyolefin to the entire composition for forming a current limiting element is preferably in the range of 40 to 50% by weight.

As the conductive filler, for example, carbon black, graphite, carbon fibers, metal particles, etc. are used, and the blending amount thereof is in the range of about 50 to 60% by weight based on the entire composition for molding a current limiting element. Is desirable. As carbon black, for example, # 3050 manufactured by Mitsubishi Chemical Co., Ltd., and as graphite,
For example, UFG-5 manufactured by Showa Denko KK and the like are preferably used.

In the present invention, it is preferable to use carbon black and graphite in combination as the conductive filler, whereby a resistance value lower than that of carbon black alone can be imparted to the element. The mixing ratio of carbon black and graphite is preferably in the range of 10: 3 to 2: 8 by weight.

In the present invention, it is preferable to use carbon black and metal powder in combination as the conductive filler, whereby a resistance value lower than that of carbon black alone can be imparted to the element. The mixing ratio of carbon black and metal powder is preferably in the range of 7: 3 to 2: 8 by weight. As the metal powder, nickel powder, silver powder, copper powder, aluminum powder, brass powder and the like can be used.

In the present invention, it is preferable to mix a low molecular weight polyolefin wax with the water-crosslinkable polyolefin. By adding a low molecular weight polyolefin wax, in addition to the effect of using a water-crosslinkable polyolefin, it is possible to increase the resistance change due to temperature change,
The resistance value of the molded current limiting element sharply increases near the melting point of the low molecular weight polyolefin wax.

As the low molecular weight polyolefin wax, one having a melting point in the range of 100 to 160 ° C. is preferably used. As a specific example, the melting point is 105 ° C.
Crystal Wax 220 (manufactured by Sazol), high wax with a melting point of 130 ° C (manufactured by Mitsui Petrochemical Industry Co., Ltd.)
Are used. The compounding amount is preferably in the range of, for example, about 10 to 50% by weight based on the entire composition for molding a current limiting element.

As the antioxidant, for example, phenols, sulfides and phosphites are used, and N, N'-di-β-naphthyl-p-phenylenediamine is particularly preferably used. Since the addition of the antioxidant suppresses the deterioration of the matrix due to oxidation, P
It also suppresses fluctuations in TC characteristics and contributes to improved reliability. The blending amount of the antioxidant is preferably, for example, about 0.05 to 0.5% by weight based on the entire composition for molding a current limiting element.

In addition to the above-mentioned components, a lubricant for improving the fluidity at the time of molding, a stabilizer, a flame retardant and the like can be appropriately added to the composition for molding a current limiting element in the present invention.

[0034]

EXAMPLES The present invention will be specifically described below with reference to examples.

Example 1 In this example, an organosilane-modified polyethylene, which is an organosilane-modified polyolefin, was used as the water-crosslinking polyolefin. Organosilane-modified high-density polyethylene (HM-600A, density 0.955,
MI = 10, gel fraction 60%, Mitsubishi Chemical Co., Ltd.) 10
0 parts by weight, carbon black (#
3050) 160 parts by weight, N, N'- as an antioxidant
After 0.1 part by weight of di-β-naphthyl-p-phenylenediamine and 10 parts by weight of Crystal Wax 220 (manufactured by Sazol Co.) as a low molecular weight polyolefin wax were kneaded with a mixing roll until uniform, they were pelletized by a pelletizer.

As a kneading device, a test mixing roll machine was used, and kneading was performed under the following conditions.

Roll size Diameter 150 mm x Length 300 mm Roll rotation speed Front roll: 20 times / min Rear roll: 25 times / min Heating method Oil heating Roll interval during kneading Approximately 0.5 mm Kneading work is performed by the following procedure .

The surface temperature of the roll is set to about 140 ° C. Add a specified amount of water-crosslinked polyolefin. Melts into a sticky sticky substance and wraps around a roll. Charge a specified amount of graphite powder. Turn around with a gold spatula for about 5 minutes. A specified amount of carbon black (CB) is added. Carry back with a gold spatula for about 15 minutes. Add a specified amount of low molecular weight polyolefin wax. Carry back with a gold spatula for about 10 minutes. Add the specified amount of antioxidant. Carry back with a gold spatula for about 10 minutes.

In the above procedure, the procedure for materials not used is omitted (the same applies hereinafter).

The kneaded product thus obtained was pelletized by applying a pelletizer.

Next, molding was carried out by the injection molding machine under the conditions shown in Table 1.

A current limiting element (50 × 50 m) as shown in FIG.
m, thickness 1 mm), and then hot water treatment (90 ° C × 120
Conductive paint 2, 3 (with a specific resistance of 10 ^-5 Ω.
(about cm) to form a current limiting element. After drying, the initial specific resistance measured by attaching the metal electrodes 4 and 5 as shown in FIG. 1 was 0.15 Ω · cm.

[Example 2] Carbon black per 100 parts by weight of water-crosslinked high-density polyethylene (HF-700N, density 0.958, MI = 0.8, gel fraction 65%, manufactured by Mitsubishi Chemical Corporation) (# 3050) was added in an amount of 120 parts by weight, and 0.1 part by weight of an antioxidant (N, N'-di-β-naphthyl-p-phenylenediamine) was added. Other conditions were the same as in Example 1 to obtain a current limiting element.

As shown in FIG. 1, the initial specific resistance measured by attaching the electrodes 4 and 5 to the current limiting device 1 obtained in Example 2 was 0.20 Ω · cm.

Example 3 110 parts by weight of carbon black (# 3050) was added to 100 parts by weight of water-crosslinked high-density polyethylene (HF-700N) to prepare an antioxidant (N, N'-di-β-naphthyl). 0.1 parts by weight of -p-phenylenediamine) and 10 parts by weight of low molecular weight polyethylene wax (crystal wax 220) were added.
Other conditions were the same as in Example 1.

As shown in FIG. 1, the initial specific resistance measured by attaching the electrodes 4 and 5 to the current limiting device 1 obtained in Example 3 was 0.25 Ω · cm.

[Comparative Example 1] 180 parts by weight of carbon black (# 3050) was added to 100 parts by weight of water-crosslinked high density polyethylene (HF-700N) to prepare an antioxidant (N, N'-di-β-naphthyl). -P-phenylenediamine) was added in an amount of 0.1 part by weight. Other conditions were the same as in Example 1.

With the ratio of the conductive filler in Comparative Example 1, the element was not obtained because the amount of the filler was too large to be kneaded.

Comparative Example 2 70 parts by weight of carbon black (# 3050) was added to 100 parts by weight of water-crosslinked high-density polyethylene (HF-700N) to prepare an antioxidant (N, N'-di-β-naphthyl). -P-phenylenediamine) was added in an amount of 0.1 part by weight. Other conditions were the same as in Example 1.

As shown in FIG. 1, the initial specific resistance measured by attaching the electrodes 4 and 5 to the current limiting element 1 obtained in Comparative Example 2 was 0.5 Ω · cm. With this specific resistance, for example, when current is applied at a rated current of 30 amps, the element itself generates a large amount of heat and is not practical.

[Comparative Example 3] High-density polyethylene (melting point 1
Carbon black (# 3
050) 120 parts by weight was added, and the mixture was heated and kneaded with a heating roll and molded into a predetermined element shape to obtain a current limiting element.

As shown in FIG. 1, the initial specific resistance measured by attaching the electrodes 4 and 5 to the current limiting element 1 obtained in Comparative Example 3 was 0.2 Ω · cm.

[Embodiment 4] This embodiment is an example in which carbon black and graphite are used in combination as the conductive filler.

Water cross-linked high density polyethylene (HF-700
N) 100 parts by weight of carbon black (# 350
0) 100 parts by weight and graphite (UFG-5) 30 parts by weight were added, and further 0.1 part by weight of an antioxidant (N, N'-di-β-naphthyl-p-phenylenediamine) was added. Other conditions were the same as in Example 1 to obtain a current limiting element. The initial resistivity of the obtained element is 0.15 Ω · cm.
Met.

[Embodiment 5] This embodiment is an example in which a low molecular weight polyolefin wax is used in combination so as to remarkably exhibit PTC characteristics.

Water cross-linked high density polyethylene (HF-700
N) 100 parts by weight of carbon black (# 305
0) 100 parts by weight and 30 parts by weight of graphite (UFG-5) were added, and further 10 parts by weight of low molecular weight polyolefin wax (crystal wax 220, melting point 105 ° C.), antioxidant (N, N′-di-β-naphthyl). 0.1 part by weight of (-p-phenylenediamine) was added. Other conditions were the same as in Example 1 to obtain a device. The obtained element had an initial specific resistance of 0.15 Ω · cm.

[Embodiment 6] This embodiment is an example in which nickel powder is used in combination with carbon black as a low resistance current limiting element.

Water cross-linked high density polyethylene (HF-700
N) 100 parts by weight of carbon black (# 305
0) 100 parts by weight and nickel powder (UFG-5) 50 parts by weight were added, and further 0.1 part by weight of an antioxidant (N, N'-di-β-naphthyl-p-phenylenediamine) was added. Other conditions were the same as in Example 1 to obtain a device. The obtained element had an initial specific resistance of 0.14 Ω · cm.

[Embodiment 7] This embodiment is an example in which a low molecular weight polyolefin wax is used together with graphite as a conductive filler in order to remarkably exhibit PTC characteristics.

Water cross-linked high density polyethylene (HF-700
N) 100 parts by weight of graphite (UFG-5)
170 parts by weight was added, and low molecular weight polyolefin wax (crystal wax 220, melting point 105 ° C) 1
0 parts by weight, antioxidant (N, N'-di-β-naphthyl-
0.1 part by weight of p-phenylenediamine) was added. Other conditions were the same as in Example 1 to obtain a device. The obtained element had an initial specific resistance of 0.14 Ω · cm.

[Embodiment 8] In this embodiment, a foam is used as the water-crosslinked polyolefin.

120 parts by weight of carbon black (# 3050) was added to 100 parts by weight of the foaming type water-crosslinked high-density polyethylene, and an antioxidant (N, N'-di-β-naphthyl-p-phenylenediamine) of 0. 1 part by weight is added, and the mixture is heated and kneaded with a hot roll to form a predetermined element shape, then treated with hot water at 80 ° C. for 8 hours to crosslink, and 240 ° C.
It was left in the oven for 1 hour to obtain a foamed element. The initial resistance value of the obtained device was 0.3 Ω · cm.

[Embodiment 9] In this embodiment, as the water-crosslinked polyolefin, an organosilane-modified low density polyethylene which is an organosilane-modified polyolefin was used. Organosilane modified low density polyethylene (CH-750T, density 0.9
24, MI = 2.5, gel fraction 70%, Mitsubishi Chemical Corporation
100 parts by weight, 160 parts by weight of carbon black (# 3050, manufactured by Mitsubishi Chemical Corporation) as a conductive filler,
0.1 part by weight of N, N'-di-β-naphthyl-p-phenylenediamine was added as an antioxidant, and 10 parts by weight of Crystal Wax 220 (manufactured by Sazol Co.) was added as a low molecular weight polyolefin wax. Other conditions were the same as in Example 1 to obtain a current limiting element. As shown in FIG.
The initial specific resistance measured by attaching the electrodes 4 and 5 to the obtained current limiting element 1 was 0.23 Ω · cm.

Example 10 In this example, an organosilane-modified ethylene-vinyl acetate copolymer, which is an organosilane-modified polyolefin, was used as the water-crosslinking polyolefin. Organosilane-modified ethylene-vinyl acetate copolymer (V
E-800N, density 0.938, MI = 0.3, gel fraction 80%, Mitsubishi Chemical Co., Ltd. 100 parts by weight, carbon black (# 3050, Mitsubishi Chemical Co., Ltd.) as a conductive filler 160 Parts by weight, N, N'-as an antioxidant
0.1 parts by weight of di-β-naphthyl-p-phenylenediamine and 10 parts by weight of Crystal Wax 220 (manufactured by Sazol Co.) as a low molecular weight polyolefin wax were added. Other conditions were the same as in Example 1 to obtain a current limiting element.
As shown in FIG. 1, the initial specific resistance measured by attaching the electrodes 4 and 5 to the current limiting element 1 obtained in Example 10 was 0.2.
It was 4 Ω · cm.

Example 11 In this example, an organosilane-modified polypropylene, which is an organosilane-modified polyolefin, was used as the water-crosslinking polyolefin. Organosilane-modified polypropylene (XPM-800HM, density 0.91
0, MI = 16, gel fraction 80%, manufactured by Mitsubishi Chemical Corporation)
100 parts by weight, 160 parts by weight of carbon black (# 3050, manufactured by Mitsubishi Chemical Corporation) as a conductive filler, 0.1 part by weight of N, N'-di-β-naphthyl-p-phenylenediamine as an antioxidant, As a low molecular weight polyolefin wax, 10 parts by weight of Crystal Wax 220 (manufactured by Sazol Co.) was added. Other conditions were the same as in Example 1 to obtain a current limiting element. As shown in FIG. 1, Example 11
The initial specific resistance measured by attaching the electrodes 4 and 5 to the obtained current limiting element 1 was 0.25 Ω · cm.

With respect to the current limiting devices obtained in Examples 1 and 2 and Comparative Example 3, the relationship between temperature and specific resistance was determined. The results are shown in FIG. Curves a, b and c in FIG. 3 correspond to the current limiting devices of Comparative Example 3, Example 2 and Example 1, respectively. Figure 3 shows that each current limiting element is placed in a constant temperature bath,
It is a PTC characteristic curve showing the resistance value of the current limiting element at each temperature, where the vertical axis is the specific resistance value (Ω · cm) expressed in ohm-centimeter, and the horizontal axis is the temperature (° C). As is clear from the graph of FIG. 3, the current limiting element of Comparative Example 3 (curve a in FIG. 3) exhibits remarkable NTC characteristics after the PTC characteristics are exhibited, but the current limiting element of Example 1 (curve c in FIG. 3). Also, in the current limiting element of Example 2 (curve b in FIG. 3), N
It can be seen that the TC characteristics are significantly suppressed. Further, in the current limiting element of Example 2 (curve b in FIG. 3), the resistance value rapidly increases in the vicinity of the melting point of the low molecular weight polyolefin wax (105 ° C. in this case), and even if the melting point is exceeded, the temperature coefficient of resistance is Maintained a positive value.

As described above, when the water-crosslinking type polyolefin that does not melt by heating is used, it does not flow even if it exceeds the specific temperature, and the resistance value does not decrease.

Although the electrodes are pressure-bonded in the above-mentioned embodiment, the present invention is not limited to this, and the surface of the current limiting element may be sprayed with a metal, or a silver-plated copper plate may be heat-sealed.

Table 2 shows a list of the compounding ratios of the materials used in Examples 1 to 11 and Comparative Examples 1 to 3.
No. 11 and Comparative Examples 1 to 3 show a list of initial specific resistance and expression of NTC characteristics after PTC characteristics shown in Table 3 and used in Examples 1 to 11 and Comparative Examples 1 to 3. Table 4 shows a list of material properties and the like.

[0070]

[Table 1]

[0071]

[Table 2]

[0072]

[Table 3]

[0073]

[Table 4]

[0074]

The invention according to claim 1 is provided with a current limiting element formed by blending a water-crosslinking polyolefin with a conductive filler, and an electrode for energizing the current limiting element. Therefore, even if a specific temperature is exceeded. No decrease in resistance occurs without showing flow.

According to a second aspect of the present invention, there is provided a current limiting device comprising a water-crosslinking polyolefin and a conductive filler, wherein the water-crosslinking polyolefin is water-crosslinking polyethylene.
Since it consists of at least one selected from the group consisting of water-crosslinked polypropylene and water-crosslinked ethylene-vinyl acetate copolymer, the resistance value rapidly increases in a specific temperature range, and the resistance value decreases even if the temperature is exceeded. It is possible to obtain a current limiting element having improved reliability.

In the invention according to claim 3, since the conductive filler comprises at least one selected from the group consisting of carbon black, graphite, carbon fiber and metal powder, the resistance value rapidly increases in a specific temperature range. Even if the temperature rises and the temperature is exceeded, the resistance value does not decrease, and a current limiting element with improved reliability can be obtained.

In the invention according to claim 4, the compounding ratio of the conductive filler to the entire composition for forming a current limiting element is 5
Since the range of 0 wt% to 60 wt% is set, the resistance value rapidly increases in a specific temperature range, and the resistance value does not decrease even when the temperature exceeds the temperature range, and a current limiting element having improved reliability can be obtained. You can

In the invention of claim 5, since the low molecular weight polyolefin wax is blended with the water-crosslinked polyolefin, the resistance value rapidly increases in a specific temperature range, and the resistance value does not decrease even if the temperature is exceeded. Therefore, it is possible to obtain a current limiting element with improved reliability.

[Brief description of drawings]

FIG. 1 is a perspective view of a current limiting device according to an embodiment of the present invention.

FIG. 2 is a perspective view showing a current limiting element according to an embodiment of the present invention.

FIG. 3 is a PTC showing a relationship between temperature and specific resistance of a current limiting element.
It is a characteristic diagram.

[Explanation of symbols]

 1 Current limiting element, 4 electrodes, 5 electrodes.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masahiro Ishikawa 2-3-3 Marunouchi, Chiyoda-ku, Tokyo Sanryo Electric Co., Ltd. (72) Inventor Osamu Hasegawa 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Sanryo Electric Co., Ltd. (72) Inventor Shirou Murata 2-3-3 Marunouchi, Chiyoda-ku, Tokyo Sanryo Electric Co., Ltd. (72) Tatsuya Hayashi 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Sanryo Electric Machinery Co., Ltd. (72) Inventor Sadajiro Mori 2-3-3 Marunouchi, Chiyoda-ku, Tokyo Sanryo Electric Co., Ltd.

Claims (5)

[Claims] 1. A current limiting device comprising a current limiting element formed by mixing a water-crosslinking polyolefin with a conductive filler, and an electrode for energizing the current limiting element. 2. A current limiting element comprising a water-crosslinking polyolefin and a conductive filler, wherein the water-crosslinking polyolefin is selected from the group consisting of water-crosslinking polyethylene, water-crosslinking polypropylene and water-crosslinking ethylene-vinyl acetate copolymer. A current limiting element comprising at least one selected. 3. The current limiting element according to claim 2, wherein the conductive filler is at least one selected from the group consisting of carbon black, graphite, carbon fiber and metal powder. 4. The compounding ratio of the conductive filler to the entire composition for forming a current limiting element is 50% by weight to 60% by weight.
3. The current limiting element according to claim 2, wherein the current limiting element is in the range. 5. The current limiting element according to claim 2, wherein the water-crosslinked polyolefin is blended with a low molecular weight polyolefin wax.