JPH0329162B2 - - Google Patents

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention relates to a conductive polymer composition having a property (hereinafter referred to as PTC property) that the positive temperature coefficient of resistance increases rapidly in a specific temperature range when the temperature is increased. The present invention relates to a resistance element consisting of.

[Technical Background of the Invention] Conventionally, resistance elements (hereinafter referred to as resistance elements) having PTC characteristics have been used.
Generally used as a PTC element (PTC element) is one in which metal foil electrodes are adhered to both sides of a flat element body made of barium titanate-based metal oxide.

However, such conventional PTC elements
The reality is that it has a high specific resistance and a large heat capacity, so it is only used for limited purposes.

In contrast, it consists of a conductive polymer composition in which conductive particles are uniformly dispersed in a crystalline polymer.
Since PTC elements have low specific resistance and small heat capacity, studies are currently underway to apply them to fields where barium titanate-based PTC elements cannot be used.

The PTC properties of such conductive polymer compositions are due to the rapid volume expansion exhibited by the base crystalline polymer as it changes from crystalline to amorphous at its melting point. It is expressed by widening the distance between conductive particles.

This PTC element has a low specific resistance and becomes a conductor below the temperature at which the conductive polymer composition rapidly increases its electrical resistance (hereinafter referred to as the switching temperature), but in an overcurrent state it becomes a conductor due to self-heating. The temperature rises rapidly and reaches the switching temperature, which limits the current and protects equipment from destruction due to overcurrent.When used as a heating element, it also prevents self-damage due to heating. be.

1 and 2 show metal foil electrodes 2, 2 on both sides of a disk-shaped element body 1 made of a conductive polymer.
and attach lead wires 3, to these metal foil electrodes 2, 2.
3 is shown as an example of a PTC element in which parts 3 are connected by solder 4.

The element body 1 is formed by forming a conductive composition in which a crystalline polymer such as polyethylene is blended with an adhesive polymer and conductive particles such as conductive carbon into a plate shape, and then metal foil electrodes are placed on both sides of the conductive composition. The conductive composition is cross-linked by irradiating the metal foil electrode with an electron beam, thereby imparting heat resistance to the entire element.

[Problems in the Background Art] In a PTC element using such a conventional conductive polymer composition, as shown in Fig. 3, the thermal expansion of the element body 1 is approximately 40 times that of the metal electrode at around 100°C. As a result, shear force acts on the adhesive interface between the two as a result of the heat cycle, which is one of the factors that promotes peeling of the metal foil electrode.

That is, when this resistance element has a cross section as shown in FIG. 4a, it exhibits a thermal expansion distribution in the current direction as shown in FIG.
As shown in Figure c, a strong shearing force acts on the interface between the two, which causes the electrode to peel off.

Furthermore, during cold working of nickel foil, as shown in Figure 5, the hardness of the nickel foil increases rapidly as the working rate increases, and flexibility is lost.
Residual stress generated during cold working is released by heating during use, causing distortion in the electrode, and this distortion also acts as stress on the electrode, becoming one of the factors that promotes electrode peeling.

[Object of the Invention] The present invention has been made to solve these conventional difficulties, and it alleviates the stress caused by the shear force acting on the adhesive interface between the electrode and the element body and the stress caused by the distortion of the electrode, thereby improving the adhesion between the two. The object of the present invention is to provide a resistance element with improved resistance.

[Summary of the Invention] That is, the resistance element of the present invention includes an element body made of a conductive polymer composition, and an electrode closely adhered to the surface of the element body, sandwiching the element body. The electrode is characterized by being made of nickel foil that has been annealed to have an elongation of 30% or more.

[Embodiment of the Invention] The details of the present invention will be described below with reference to an embodiment shown in the drawings.

FIG. 6 is a partially cutaway perspective view showing one embodiment of the resistance element of the present invention, and parts common to those in FIG. 1 are given the same reference numerals.

In FIG. 6, the resistance element of this example is composed of a conductive polymer having PTC characteristics, which is made by blending a crosslinkable crystalline polymer with conductive particles such as conductive carbon and an adhesive polymer as necessary. It consists of a disk-shaped element body 1, electrodes 2, 2 attached to both surfaces thereof, and lead wires 4, 4 electrically connected to the center thereof by solder 3.

Examples of crystalline polymers used in the conductive polymer composition of this example include polyolefins such as high-density, medium-density, and low-density polyethylene and polypropylene, and adhesive polymers added as necessary include , for example, ethylene
There are ethylene copolymers such as ethyl acrylate copolymer and ethylene/vinyl acetate copolymer.

In addition, in the resistance element of this example, nickel plates are rolled to a thickness of 20 mm as the electrodes 2, 2.
~40μm foil shape and annealed to elongate 30%
After the above, a plurality of circular punched holes 5, 5, 5,
Nickel foil with perforations is used.

FIG. 7 is a graph showing the annealing effect of this nickel foil. As is clear from Figure 7, approximately
Maximum flexibility of 30% at annealing temperatures above 600℃
The above elongation can be obtained.

In the resistance element of the present invention using nickel foil whose elongation has been increased to 30% or more by such annealing, the metal foils 2, 2 and the element body 1 are bonded due to its flexibility.
The shear force caused by the difference in thermal expansion between the two electrodes and the stress caused by the release of residual stress are alleviated, and electrode peeling can be prevented.

830 for nickel foil with a thickness of 20 to 40 μm
It can be annealed by heat treatment at ℃ for 3 to 6 minutes until the elongation becomes 30% or more.

In the present invention, the elongation of annealed nickel foil is
The reason why the elongation is set to be 30% or more is because if the elongation is less than 30%, the effect of alleviating the shear force due to the difference in linear expansion coefficient between the element body 1 and the electrode 2 when the temperature reaches high temperatures is insufficient. Also, the thickness of nickel foil is 20~
A range of 40 μm is preferable; if it is thicker than this, the heat capacity of the electrode will increase, reducing the quick response and cooling characteristics required for a resistive element, as well as reducing its flexibility. On the other hand, if it is thinner than this, it will shrink due to heat. This causes wrinkles to appear. Further, the thickness ratio between the element body and the nickel foil is preferably about 11/20.

Note that, as shown in the example, the adhesion can be further improved by forming a plurality of punched holes 5 in the electrodes 2, 2.

[Effects of the Invention] As explained above, in the resistance element of the present invention, nickel foil that has been annealed to have an elongation of 30% or more is used as the electrode, so the shearing force due to the difference in thermal expansion between the electrode and the element body is alleviated. In addition, residual stress during processing is alleviated, and electrode peeling can be prevented.

[Brief explanation of drawings]

Fig. 1 is a perspective view of the PTC element, Fig. 2 is a partial cross-sectional view thereof, Fig. 3 is a graph showing the thermal expansion of the element body and electrodes, and Fig. 4 is the thermal expansion distribution and thermal stress distribution in the current direction of the resistance element. FIG. 5 is a graph showing the relationship between processing rate and hardness of nickel foil, FIG. 6 is a partially cutaway perspective view showing an embodiment of the resistance element of the present invention, and FIG. 7 is a graph showing the relationship between the processing rate and hardness of nickel foil. It is a graph showing the relationship between annealing temperature, hardness, and elongation. 1...Element body, 2...Electrode, 3...Solder, 4
……Lead.

Claims (1)

[Claims] 1. An element body made of a conductive polymer composition;
A resistance element comprising electrodes sandwiching the element body and closely adhered to the surface thereof, wherein the electrodes are made of nickel foil whose elongation is 30% or more by annealing. 2. The resistance element according to claim 1, wherein the annealed nickel foil has a thickness of 20 to 40 μm.