JPH0969413A - PTC element - Google Patents

Abstract

(57) Abstract: An object of the present invention is to obtain a PTC element capable of carrying a large load current. SOLUTION: A PTC polymer layer 1 having PTC characteristics
And a pair of electrode layers 2 pressed against both surfaces of the PTC polymer layer, wherein a metal film 3 is formed on the surface of the PTC polymer layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a PTC (positive temperatu) used for limiting a short circuit current or an overcurrent.
(hereinafter referred to simply as PTC) element. More specifically, it relates to a PTC element in which a PTC polymer layer and an electrode layer are in pressure contact with each other.

[0002]

2. Description of the Related Art FIG. 3 is a sectional view showing a conventional PTC element disclosed in Japanese Patent Application Laid-Open No. 4-266001. In FIG. 3, 1 is a PTC polymer layer having PTC characteristics, 2 is a pair of electrode layers, and the PTC polymer layer 1 and the electrode layer 2 are pressed against each other by a spring (not shown). PT
Since the surface of the C polymer layer 1 and the surface of the electrode layer 2 have minute irregularities, they are not in contact with each other over the entire surface. This is shown in FIG. 4, which is an enlarged view of part A in FIG. As shown in FIG. 4, the PTC polymer layer 1 and the electrode layer 2 are partially in contact with each other. The electric resistivity of the PTC polymer layer 1 is low up to the temperature T ₁ , as shown in FIG. 5, increases sharply above the temperature T ₁ , and gradually increases above the temperature T ₂ . In one example of a PTC polymer layer, T ₁ is 120
C. and T ₂ are 130 ° C., and the resistivity at temperature T ₂ is about 1000 times the resistivity at temperature T ₁ .

Next, the operation of the PTC element will be described. The load current flows in the PTC polymer layer 1 as shown by the arrow in FIG. When a load current flows, the temperature of the PTC polymer layer 1 rises due to Joule heat, but the temperature of the PTC polymer layer 1 is lower than T ₁ because the applied current is small. When short circuit current or over current flows, polymer layer 1 of PTC
The temperature rise of PTC polymer layer 1 becomes large and the temperature of PTC polymer layer 1 becomes higher than T ₂ , so that the resistivity of PTC polymer layer 1 becomes high. Therefore, short-circuit current or overcurrent is suppressed. The suppressed current is cut off by a switch (not shown). When the electric current is cut off, Joule heat is not generated in the PTC element and the heat in the PTC element is dissipated to the outside, so that the temperature of the PTC polymer layer 1 is lowered and the load current can be re-energized.

[0004]

The conventional PTC element operates as described above, but the PTC polymer layer 1 and the electrode layer 2 are used.
Since the contact resistance between and is high, when a large load current is applied, a large amount of heat is generated in the area where the current flow lines in Fig. 4 become dense and exceeds T ₁ in Fig. 5, so a large load current is applied. There is a problem that you cannot do it. An object of the present invention is to obtain a PTC element that can carry a large load current.

[0005]

A PTC element according to the present invention comprises a PTC polymer layer having PTC characteristics and the PT polymer layer.
A PTC element comprising a pair of electrode layers pressed against both surfaces of a C polymer layer, wherein a metal film is previously formed on the surface of the PTC polymer layer.

In the PTC element according to the present invention, the metal film is formed by vapor deposition or plating.

In the PTC element according to the present invention, the metal film is formed by thermal spraying.

In the PTC element according to the present invention, the metal material of the metal film is selected from the group consisting of gold, silver and copper.

In the PTC element according to the present invention, the metal material of the metal film is selected from the group consisting of indium, tin and lead.

The PTC element according to the present invention has the electrode layer plated with silver.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

[Embodiment 1] FIG. 1 is a sectional view showing an embodiment of the PTC element of the present invention, and FIG. 2 is an enlarged view of a portion A in FIG. In FIG. 1, 1 is P having PTC characteristics
Reference numeral 2 denotes a TC polymer layer, 2 denotes a pair of plate-shaped electrode layers, and 3 denotes a metal film formed on the surface of the PTC polymer layer 1. The PTC polymer layer has a thickness of, for example, about 0.5 to 2 mm and its electrical resistivity is, for example, 0.2.
Ω · cm, the metal film 3 is made of metal atoms or metal particles such as silver and copper, and is, for example, 0.05 to 2
It has a thickness of about μm, and its electrical resistivity is, for example, about 2 μΩ · cm. The electrode layer 2 has, for example, 0.
It is formed to have a thickness of about 3 to 2 mm. The PTC polymer layer 1 and the electrode layer 2 are pressed against each other via a metal film 3 by a spring (not shown). Although there are small irregularities on the surface of the PTC polymer layer 1 and the surface of the electrode layer 2, since the metal film 3 is provided on the surface of the PTC polymer layer 1 in the present embodiment, the metal film 3 having a low resistance has a current Flows in. The flow of the current is indicated by an arrow in the drawing of FIG.

Next, the operation of the PTC element of this embodiment will be described with reference to FIG. When a load current flows, the temperature of the PTC polymer layer 1 rises due to Joule heat, but the temperature of the PTC polymer layer 1 is lower than T ₁ because the applied current is small. When a short circuit current or an overcurrent flows, the temperature rise of the PTC polymer layer 1 becomes large and the temperature of the PTC polymer plate 1 becomes higher than T ₂ , so that the resistivity of the PTC polymer layer 1 becomes high. Therefore, short-circuit current or overcurrent is suppressed. The suppressed current is cut off by a switch (not shown). When the current is cut off, Joule heat is not generated in the PTC element and the heat inside the PTC element is dissipated to the outside, so that the temperature of the PTC polymer layer 1 is lowered, and the load current can be re-energized in the initial state. Becomes

In the present invention, on the surface of the PTC polymer layer 1,
Since the metal film 3 having an electric resistivity lower than that of the PTC polymer layer is formed, it is lower than the electric resistivity of the PTC polymer layer as indicated by an arrow in FIG. A current flows through the metal film 3 having an electrical resistivity. Therefore, the contact resistance between the electrode layer 2 and the PTC polymer layer 1 can be reduced. In addition, in this embodiment, as a material having PTC characteristics, PT
C polymer is used. PTC polymer is PT
Compared to C porcelain, it has a large elastic coefficient and low hardness. As a result, when pressed by a spring (not shown), the PTC polymer layer is easily deformed according to the unevenness of the electrode layer and the contact area between the electrode layer 2 and the metal film 3 increases, so that the electrode layer 2 and the PT
The contact resistance between the C polymer layers 1 can be further reduced. Therefore, a large load current can be continuously supplied.

[Embodiment 2] Next, Embodiment 2 will be described with reference to FIG. The metal film 3 of Example 2 is formed on the surface of the PTC polymer layer 1 by plating such as vapor deposition or electroless plating.
The metal film 3 preferably has a large thickness, for example, 0.1 μm. The method of vapor deposition or plating can be carried out in the same manner as the method usually used. In Example 2, since the metal film 3 was formed on the surface of the PTC polymer layer 1 by vapor deposition or plating, the metal film 3 was formed so as to cover the minute recesses of the PTC polymer layer 1. The contact resistance between the PTC polymer layers 1 could be significantly reduced. Therefore, a large load current can be continuously supplied.

[Example 3] In Example 3, the metal film 3 of Example 1 is formed on the surface of the PTC polymer layer 1 by thermal spraying. In the third embodiment, the metal film 3 is PT by thermal spraying.
Since the metal film 3 can be easily formed thick by being formed on the surface of the C polymer layer 1, the contact resistance between the electrode layer 2 and the PTC polymer layer 1 can be significantly reduced. Therefore, a large load current can be continuously supplied. The metal film 3 may be re-formed by thermal spraying after being formed by vapor deposition or plating. By this treatment, the contact resistance between the electrode layer 2 and the PTC polymer layer 1 can be more significantly reduced. Therefore, an even larger load current can be continuously applied.

[Embodiment 4] In Embodiment 4, the material of the metal film 3 of Embodiment 1 is gold, silver or copper having a low electric resistivity. In the fourth embodiment, the material of the metal film 3 is gold, silver or copper having a low electric resistivity, so that the contact resistance between the electrode 2 and the PTC polymer layer 1 can be further remarkably reduced. Therefore, an even larger load current can be continuously applied. If the material of the metal film 3 is chemically stable gold or silver, the contact resistance between the electrode layer 2 and the PTC polymer layer 1 is kept low even if a load current is applied for a long period of time. It is possible to obtain a highly reliable PTC element.

[Fifth Embodiment] In the fifth embodiment, the material of the metal film 3 of the first embodiment is indium, lead or tin.
In the fifth embodiment, the material of the metal film 3 is indium, lead or tin having low hardness, so that the metal film 3 is easily deformed when pressed by a spring material (not shown). As a result, the contact area between the electrode layer 2 and the metal film 3 is increased, so that the contact resistance between the electrode layer 2 and the PTC polymer layer 1 can be further significantly reduced. Therefore, an even larger load current can be continuously applied.

[Sixth Embodiment] In a sixth embodiment, the electrode layer of the first embodiment is preliminarily attached with a metal serving as a nucleus and silver-plated by electroless plating. Copper or brass is usually used as the material of the electrode layer. In Example 6, since the electrode layer was plated with silver having an electric resistivity lower than that of the electrode material, the contact resistance between the electrode layer 2 and the PTC polymer layer 1 can be further reduced significantly. . Therefore, an even larger load current can be continuously applied.

The PTC polymer used in the present invention is obtained by dispersing conductive particles in a crystalline polymer. As the crystalline polymer, as described above, when the crystal melts at its melting point, a rapid volume expansion occurs,
There is no particular limitation as long as it has the action of widening the distance between the conductive particles dispersed in the crystalline polymer. The crystallinity is preferably 20% or more, more preferably 40% or more. As a specific example, for example, Japanese Patent Publication No.
No. 22, JP-B 4-28744, JP-B 5-
Examples of the crystalline polymer are disclosed in Japanese Patent No. 66001, and among them, for example, polyethylene such as high-density polyethylene, medium-density polyethylene, and low-density polyethylene, polypropylene, poly-butene-1, polymethylpentine ( TPX), polyolefins such as ethylene propylene rubber; fluorocarbon polymers such as polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene, polychlorotrifluoroethylene;
One or a mixture of two or more kinds of other crystalline polymers such as polyamide, polyacetal, syndioctatic-polystyrene and saturated polyester is preferable. Among these, polyethylene is more preferable among the polyolefins from the viewpoint that a high rate of increase in resistance can be obtained due to its high crystallinity. As the conductive particles, for example, carbon black, graphite, metal fibers, carbon fibers having a particle diameter of about 0.02 to 200 μm,
40-80% by weight of metal particles in the crystalline polymer
It is preferable to mix the above density in order to keep the room temperature resistivity at about 0.5 Ω · cm or less. Further, in view of the balance between practical use and cost, carbon black having a particle size of about 0.03 to 0.2 μm is added to the crystalline polymer in an amount of 50 to 70.
Most preferably, it is mixed in by weight.

The metal used in the metal film of the present invention is not particularly limited as long as it can be easily plated or vapor-deposited. For example, silver, gold, copper, etc. can be used because of its low electric resistivity. Can be given.

The electrode layer of the present invention is preferably copper, brass, silver or the like from the viewpoint of high conductivity.

In a preferred example of the present invention, high-density polyethylene is blended with 55% by weight of carbon black having a particle size of about 0.09 μm to form a PT having a thickness of about 1 mm.
C polymer and silver on both surfaces of the PTC polymer.
An example of the electrode is a metal film formed by vapor deposition or electroless plating of about 1 μm and having an electrode with a thickness of 1 mm. It has been confirmed by experiments that an excellent current limiting characteristic can be obtained in the PTC element configured as described above.

In the present invention, 55% by weight of carbon black having a particle size of about 0.09 μm is added to high density polyethylene.
A PTC polymer having a thickness of about 1 mm is blended to form a metal film by spraying silver on both surfaces of the PTC polymer by, for example, about 3 μm, and an electrode layer having a thickness of 1 mm is provided outside the metal film. To be PT configured in this way
It has been experimentally confirmed that the C element has excellent current limiting characteristics.

[0025]

According to the invention of claim 1, since the contact resistance between the PTC polymer layer and the electrode layer is reduced by forming the metal film on the surface of the PTC polymer layer,
The load current and the energizing current can be increased.

According to the invention of claim 2, since the contact resistance between the PTC polymer layer and the electrode layer is reduced by forming the metal film by vapor deposition or plating, the load current and the energizing current can be increased. You can

According to the third aspect of the present invention, since the metal film is formed by thermal spraying, the contact resistance between the PTC polymer layer and the electrode layer is reduced, so that the load current and the energizing current can be increased. .

According to the fourth aspect of the present invention, the metal material of the metal film is selected from the group of gold, silver or copper, so that the contact resistance between the PTC polymer layer and the electrode layer is reduced. Therefore, the load current can be increased.

According to the invention of claim 5, the metal material of the metal film is selected from the group of indium, tin or lead, whereby the contact resistance between the PTC polymer layer and the electrode layer is reduced. Therefore, the load current and the energizing current can be increased.

According to the sixth aspect of the invention, since the electrodes are plated with silver, the contact resistance between the PTC polymer layer 1 and the electrode layer 2 is reduced, so that the load current and the energizing current can be increased.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a PTC element that is an embodiment of the present invention.

2 is a partially enlarged cross-sectional view of the PTC element of FIG.

FIG. 3 is a sectional view showing an example of a conventional PTC element.

4 is a partially enlarged cross-sectional view of the PTC element of FIG.

FIG. 5 is an explanatory diagram of temperature-electrical resistivity of the PTC polymer layer.

[Explanation of symbols]

 1 PTC polymer layer, 2 electrode layer, 3 metal film.

 ─────────────────────────────────────────────────── ─── Continued front page (72) Inventor Itsuo Nishiyama 2-3-3 Marunouchi, Chiyoda-ku, Tokyo Sanryo Electric Co., Ltd. (72) Kenichi Nishina 2-3-2 Marunouchi, Chiyoda-ku, Tokyo 3 Ryoden Co., Ltd. (72) Inventor Masahiro Ishikawa 2-3-3, Marunouchi, Chiyoda-ku, Tokyo Sanryo Electric Co., Ltd. (72) Osamu Hasegawa 2-3-2, Marunouchi, Chiyoda-ku, Tokyo Sanryo Electric Machinery Co., Ltd. (72) Inventor Shirou Murata 2-3-3 Marunouchi, Chiyoda-ku, Tokyo Sanryo Electric Co., Ltd.

Claims (6)

[Claims] 1. A PTC element comprising a PTC polymer layer having PTC characteristics, and a pair of electrode layers pressed against both surfaces of the PTC polymer layer.
PTC with metal film formed on the surface of TC polymer layer
element. 2. The PTC element according to claim 1, wherein the metal film is formed by vapor deposition or plating. 3. The PTC element according to claim 1, wherein the metal film is formed by thermal spraying. 4. The PTC element according to claim 1, 2 or 3, wherein the metal material of the metal film is selected from the group consisting of gold, silver and copper. 5. The PTC element according to claim 1, 2 or 3, wherein the metal material of the metal film is selected from the group consisting of indium, tin and lead. 6. The PTC element according to claim 1, wherein the electrode layer is silver-plated.