JPH011201A - organic positive temperature coefficient thermistor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Al Industrial Field of Application) The present invention relates to an organic positive temperature coefficient thermistor in which a metal foil is thermocompression bonded as an electrode to the surface of an organic positive temperature coefficient thermistor element body.

(bl Conventional technology) Conventionally, an organic positive temperature coefficient thermistor element is formed by kneading conductive particles such as carbon black into a polyolefin resin such as polyethylene, and electrodes made of metal foil are thermocompression bonded to the surface of the organic positive temperature coefficient thermistor element. It constitutes a positive temperature coefficient thermistor.It is also known that when bonding metal foil under heat and pressure, the bonding strength of the metal foil to the thermistor element can be increased by roughening the surface that contacts the thermistor element ( (Japanese Patent Application Laid-open No. 196901/1983).

(C1 Problem to be solved by the invention) The voltage-current characteristics of the thermistor have a low resistance state between a and a' and a low resistance state between b and b' as shown in FIG.
A high resistance state exists between. When an organic positive temperature coefficient thermistor having such characteristics is used as a circuit protection element, there is a stable point between a and a' during normal operation of the circuit.
During abnormal operation, the stable point moves between bb'.

By the way, when a conventionally roughened Cu foil, for example, is used as an electrode, when a normal operation test with a stable point between a and a' is performed, the resistance value increases significantly after 100 hours. began. This is considered to be because a resistive substance such as a metal oxide was formed between Cu7I5 and the thermistor element body. This increase in resistance value causes malfunction and is extremely dangerous. Also, b-b
Even during abnormal operation with a stable point in between, the resistance value changed greatly and stability deteriorated.

This change in resistance value can be prevented by using Ni as the material of the metal foil, but it has been found that in the case of Ni foil, the bonding strength changes greatly depending on the surface roughness. When testing was carried out by changing the surface roughness of the Ni foil, the surface roughness was 1.
It was found that when the thickness is less than 0 μm, it easily peels off from the thermistor body, and when it is 2.0 μm or more, peeling occurs between the rough surface of the Ni'; . Therefore, under normal operating conditions, the element is in a low-temperature, low-resistance state, so there is no change in resistance due to differences in the surface roughness of the metal foil, but in abnormal operating conditions, the element is in a high-temperature molten state, so the metal foil Due to the difference in coefficient of thermal expansion between the metal foil and the thermistor element, peeling easily occurs between the metal foil and the thermistor element, which promotes an increase in resistance value.

As described above, it has been found that the reliability of a positive temperature coefficient thermistor component is greatly influenced by the material of the metal foil used as an electrode and the degree of its surface roughness. An object of the present invention is to provide a highly reliable organic positive temperature coefficient thermistor that improves the bonding strength between a metal foil used as an electrode and a thermistor body, and stabilizes changes in resistance due to aging effects. .

Means for Solving the FD1 Problem The organic positive temperature coefficient thermistor of the present invention is an organic positive temperature coefficient thermistor in which a metal foil is thermocompression bonded to the surface of an organic positive temperature coefficient thermistor element body, and this metal foil is used as an electrode. is characterized in that the surface in contact with the organic positive temperature coefficient thermistor body is made of Ni7I5 having a surface roughness of 1.0 to 2.0 μm.

(e) Function In the organic positive temperature coefficient thermistor of this invention, Ni%
Using Q as an electrode, its surface roughness was determined as 1. 0-2.
Because we used 0 μm Ni foil, when we thermocompression bonded this Ni foil to the organic PTC thermistor element, we were able to obtain high bonding strength, and even after long-term use, there was no metal oxide etc. between the Ni foil and the thermistor element. No resistive material is formed, and the change in resistance value is small.

(f) Examples Examples of the present invention will be described along with test results using several samples.

First, the relationship between the electrode strength, that is, the bonding strength between the thermistor body and the metal foil was tested by changing the surface roughness of the metal foil used as the electrode, and the results shown in FIG. 1 were obtained. The test piece was a 1 mm thick organic positive temperature coefficient thermistor body with Ni foil coated on both sides at 190°C and 120kg/cm2 for 10 minutes.
After heat-compression bonding for minutes, cut into 1010 x 50 square pieces.
A 90° peel test was conducted with a width of mm. Further, the Ni foil used had its surface roughened by applying electricity in an electrolytic solution.

As shown in FIG. 1, when the surface roughness Ra is less than 1.0 μm, the degree of surface roughening is not sufficient and the bonding strength is low.

Moreover, if Ra=2.0 μm or more, the roughened particles will peel off from the foil, and the bonding strength will be extremely reduced.

Next, we will show the results of conducting a current conduction test with electrodes formed on the positive temperature coefficient thermistor body. The electrode conditions of the sample used were the third
As shown in the figure, each element was pressed to a thickness of 1 mm, cut into 1Q mm square pieces, and the lead points were soldered to the electrodes. Figure 4 shows the results of a DC 2A continuous current test on each of these samples.
The results of the Von-off cycle energization test are shown in FIG. (The numbers in both figures correspond to NO in Figure 3.) As shown in Figure 4, for Nos. 1 to 4, that is, those using Ni foil as an electrode, the resistance value shows a negative change and is stable. ing. However, in the case of the one using Cu foil, the resistance value started to increase after 100 hours and entered the abnormal operation region after 300 hours.

This increases the resistance value as shown in Figure 2.
This is because the peak of the I characteristic becomes low, which causes malfunction.

In addition, as shown in Figure 5, in the on-off cycle test, No. 3.4, that is, the surface roughness of the Ni foil was 1.0 μm.
The following types and those with a diameter of 2.0 μm or more have a large change in resistance value. This is because the peeling of the foil was promoted by the on-off cycle of heat generation and cooling. Also,
In No. 5.6, that is, the one using Cu foil, peeling of the foil did not occur, but since a resistive substance such as a metal oxide was generated between the electrode and the thermistor body, the resistance value still increased.

In sample No. 1.2, which is an example of this invention, the metal foil did not separate in any test, and no resistance substance was generated between the electrode and the thermistor body, and the resistance value change was stable. are doing. Moreover, the direction of change is negative, so when used as a circuit protection element,
Safety is ensured (g) Effect of the invention As described above, according to the present invention, the bonding strength of the electrode to the organic positive temperature coefficient thermistor element is high, and the resistive material such as metal oxide is used between the electrode and the element. Because substances are difficult to form,
No peeling of electrodes due to on-off cycles, expansion or contraction due to cold or heat, and no increase in resistance due to long-term use.
A highly reliable organic positive temperature coefficient thermistor can be obtained.

[Brief explanation of drawings]

Figure 1 shows the relationship between the bonding strength and the surface roughness of the electrode, Figure 2 shows the voltage-current characteristics of an organic positive temperature coefficient thermistor, Figure 3 shows the conditions for various electrodes, and Figure 4 and FIG. 5 shows test results using the various electrodes shown in FIG.

Claims (1)

[Claims] (1) In an organic positive temperature coefficient thermistor in which a metal foil is thermocompressed onto the surface of an organic positive temperature coefficient thermistor body and this metal foil is used as an electrode, the surface of the metal foil in contact with the organic positive temperature coefficient thermistor body is 1.0. An organic positive temperature coefficient thermistor characterized by being made of Ni foil having a surface roughness of ~2.0 μm.