JP2000340402A - Ptc element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve adhesion with PTC compositions and to make a contact resistance with the PTC compositions low, by junctioning a metallic plate having through holes on the PTC composition surface made of conductive powder dispersed into polymer components and by making the plate an electrode. SOLUTION: Polymer kneaded material is obtained by kneading crystalline high density polyethylene with conductive powder on a heating roller. TiC, WC, W2C and ZrC is mixed as the conductive powder whose particle diameter is about 0.01 to 100 μm by 45 to 55 vol.% of PTC(positive temperature coefficient). Next, the obtained kneaded material is powdered, and after that, an electrode is formed by making a sheet by press molding and by junctioning a metallic plate having through holes of 0.01 to 1 mm and through hole area ratio to the metallic plate area being 1:9 to 9:1 by thermal pressing on both the surfaces of the kneaded material sheet. After that the PTC element is obtained by blanking.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a so-called PTC (Positive Temperature Characteristics) in which the resistance rises abruptly when a certain temperature (switching temperature) is reached.
More particularly, the present invention relates to a PTC element having reduced contact resistance with a metal plate serving as an electrode of the PTC element.

[0002]

2. Description of the Related Art A PTC element is made of a PTC composition obtained by kneading a conductive powder with a crystalline polymer, and shows a sharp increase in resistance at a specific temperature. The PTC composition generates heat by so-called Joule heating (I ² R heating) with a resistance value R inherent to the material and a current value I passed through the element. Therefore, when a relatively large current flows through the PTC composition, heat is generated and the resistivity increases.

A PTC element is used for a sheet heating element utilizing the above-described Joule heating, an overcurrent protection element utilizing an increase in resistivity, and the like. As such a PTC element, there is an element in which a metal plate surface made of stainless steel, nickel or the like is joined to a PTC composition surface, and this is used as an electrode.

In order to improve the adhesion between the PTC composition and the electrode, a metal plate whose surface in contact with the surface of the PTC composition is physically and chemically roughened is used as an electrode. .

[0005]

However, when the metal plate surface is joined to the PTC composition surface to form an electrode, good ohmic contact cannot be obtained, and the adhesion between the PTC composition and the electrode is poor. Practical problems remain, such as a large increase in resistance due to repeated operation.

Further, when a metal plate whose surface in contact with the surface of the PTC composition is physically and chemically roughened is joined to form an electrode, relatively good ohmic contact is obtained, and the PTC composition and the electrode Has good adhesion, but the problem remains that the contact resistance between the PTC composition and the metal plate is high.

Accordingly, it is an object of the present invention to provide a PTC element having an electrode having good adhesion to a PTC composition and having low contact resistance with the PTC composition.

[0008]

Means for Solving the Problems In order to solve this problem, the present inventors have made various studies, and as a result, have found that a polymer component and a conductive powder dispersed in the polymer component are used.
A metal plate having a through hole having a hole diameter of 0.01 to 1 mm and a hole area: metal plate area of 1: 9 to 9: 1 is joined to the surface of the TC composition, and this is used as an electrode. It has been found that the presence of the PTC composition in the through-hole results in good adhesion between the PTC composition and the PTC element having an electrode having low contact resistance with the PTC composition. The present invention has been accomplished.

According to the present invention, a metal plate having through holes is joined to the surface of a PTC composition comprising a polymer component and a conductive powder dispersed in the polymer component, and this is used as an electrode. A PTC element is obtained.

According to the present invention, in the PTC element, a PTC element characterized in that a metal plate joined to the PTC element has a through hole diameter of 0.01 to 1 mm.

Further, according to the present invention, in the PTC element, the ratio between the total area of the through-hole diameter of the metal plate joined to the PTC element and the area of the metal plate is as follows: through-hole area: metal plate area = 1. : 9 to 9: 1.

Further, according to the present invention, in the PTC element, the conductive powder dispersed in the PTC element is
A PTC element characterized by being at least one selected from the group consisting of iC, WC, W ₂ C and ZrC is obtained.

Further, according to the present invention, in the PTC element, the conductive powder dispersed in the PTC element includes:
A PTC element characterized by being dispersed at 45 to 55 vol% with respect to the PTC composition is obtained.

[0014]

Embodiments of the present invention will be described below.

First Embodiment First, as a polymer component, a crystalline high-density polyethylene having a softening point of 128 ° C. and conductive powder are kneaded on a heating roll at a temperature of about 140 to 200 ° C. to obtain a polymer kneaded product. I got As the conductive powder,
TiC, WC, W ₂ C having a particle size of 0.01 to 100 μm,
Each was mixed at 50 vol% using ZrC.

Next, after the obtained kneaded material is powdered,
The sheet was formed by press molding at a temperature of about 40 to 200 ° C. A metal plate having a through hole area of 0.1 mm and a metal plate area of 1: 1 was formed on both sides of the obtained kneaded material sheet.
The electrodes were formed by bonding by hot pressing at a temperature of about 40 to 200 ° C. Then, it was punched to a size of 1 cm ² to obtain a PTC element. At the same time, a PTC element (Example 1 of the present invention) using a metal plate having a through-hole area of 1 mm and a metal plate area of 1: 1 as an electrode was obtained by the same method.

For comparison, the steps up to sheet formation of the kneaded material were performed in the same manner as in the first embodiment. Thereafter, a metal plate was bonded to both surfaces of the kneaded material sheet by hot pressing at a temperature of about 140 to 200 ° C. to form electrodes. Then, it was stamped out to a size of 1 cm ² to obtain a PTC element (Comparative Example 1).

Further, for comparison, the kneaded material was formed into a sheet in the same manner as in the first embodiment. Thereafter, a metal plate having one surface in contact with the kneaded material sheet roughened with an electrolyte was bonded to both surfaces of the kneaded material sheet by hot pressing at a temperature of about 140 to 200 ° C. to form an electrode. Then, it was punched to a size of 1 cm ² to obtain a PTC element (Comparative Example 2).

(Second Embodiment) The process up to sheet formation of the kneaded material was performed in the same manner as in the first embodiment. Then, on both surfaces of the kneaded material sheet, a 0.1 mm through hole was formed by hot pressing a metal plate having a ratio of the through hole area to the metal plate area of 100: 0 to 5:95 in a range of about 140 to 200 ° C.
Each was joined to form an electrode. Then, it was punched to a size of 1 cm ² to obtain a PTC element (Example 2 of the present invention).

For comparison, the process up to sheeting the kneaded material was performed in the same manner as in the first embodiment. After that, a metal plate having a through-hole area of 2 mm and a metal plate area of 1: 1 on both surfaces of the kneaded material sheet at 140 to 20 was formed.
The electrodes were formed by bonding by hot pressing at a temperature of about 0 ° C. After that, it is punched to 1cm ²
C element (Comparative Example 3) was obtained.

(Third Embodiment) As in the first embodiment, a crystalline high-density polyethylene having a softening point of 128 ° C. and a conductive powder as a polymer component are heated at a temperature of about 140 to 200 ° C. The above mixture was kneaded to obtain a kneaded polymer.
As the conductive powder, a particle size of 0.01 to 100 μm, T
Using iC, WC, W ₂ C, and ZrC, 40 to 6
0 vol% each was mixed. Next, after the obtained kneaded material was powdered, it was press-molded at a temperature of about 140 to 200 ° C to form a sheet. 0.1% on both sides of the obtained kneaded material sheet
An electrode was formed by bonding a metal plate having a through-hole of 1 mm with a through-hole area: metal plate area of 1: 1 by hot pressing at a temperature of about 140 to 200 ° C. Then, it was punched to a size of 1 cm ² to obtain a PTC element.

A lead wire was connected to the surface of the PTC element electrode obtained as described above by soldering. Further, the periphery was covered with an epoxy resin to prepare a sample for measuring electrode bonding strength. Table 1 below shows the results of measuring the bonding strength between the electrode and the element by pulling the lead wire of the sample for measuring the electrode mating strength.

As apparent from Table 1 below, the bonding strength of the PTC element electrode according to the present invention is larger than that of Comparative Example 1 in which the metal plate is not roughened, and Comparative Example 2 in which the metal plate is roughened. Is equivalent to Also, it is larger than Comparative Example 3 in which a metal plate having a 2 mm through hole is used as an electrode. It can be seen that Comparative Example 3 has a higher bonding strength than Comparative Example 1 having no through hole. In addition, those having a through hole smaller than 0.01 mm have poor workability, and are also excluded from the scope of the present invention.

[0024]

[Table 1]

Here, the target characteristics of the polymer PTC element are as follows:
As described above, the room temperature resistance is 2 Ω · cm or less, and the ratio of the resistivity after the rapid rise in the resistivity (after switching) to the resistivity at room temperature (R after switching / R at room temperature) is:
The number is set to 10 ⁴ or more, which sufficiently operates as an overcurrent protection element and can be sufficiently used as a sheet heating element.

The target value of the room temperature resistivity when the polymer PTC element is repeatedly switched does not exceed 2 Ω · cm even after switching 500 times.

Table 2 below shows the relationship between the respective conductive powders and the properties of the PTC element obtained in the first embodiment. Regardless of which conductive powder is used, the polymer PT
It was found that a C composition was obtained.

[0028]

[Table 2]

Table 3 below shows the relationship between the through hole area ratio, the metal plate area ratio, and the room temperature resistivity of the device obtained in the third embodiment. Those without a through-hole are excluded from the scope of the present invention because they do not reach the target characteristics.

[0030]

[Table 3]

Table 4 below shows the characteristics when the polymer PTC element was switched (10 A (50 V) applied) with respect to the dispersion amount of each metal powder in the PTC composition according to the third embodiment. Dispersion amount of conductive powder is 4
If it is 0 vol% or less, the room temperature resistivity does not reach the target, and is excluded from the scope of the present invention. On the other hand, when the dispersion amount of the conductive powder exceeds 60 vol%, the resistance at room temperature is remarkably reduced, and the element operation phenomenon upon energization is not observed.

[0032]

[Table 4]

Next, FIG. 1 shows a change in resistivity after device operation when a current of 10 A (50 V) was repeatedly applied to the PTC device obtained by the method according to the first embodiment.

Here, the element of Comparative Example 1 has an initial room temperature resistance of 2 Ω · cm or less, but is not shown in FIG. 1 because it was fired by the first energization.

Further, Comparative Example 2 shown by a curve 12 in FIG.
The element has little change in resistivity after repeated energization,
The initial room temperature resistance is higher than the target value.

Further, in the device of Comparative Example 3 shown by the curve 13 in FIG. 1, although the initial room temperature resistivity has reached the target value, the room temperature resistivity has been increased by repeated energization. This is because the contact resistance between the metal plate and the PTC composition increases because the PTC composition separates from the metal plate due to repeated energization.

For this reason, those having a through-hole area larger than 1 mm are excluded from the scope of the present invention. On the other hand, the element in which each conductive powder of Example 1 of the present invention shown by the curve 11 in FIG. 1 is dispersed has a room temperature resistivity <2 Ω · cm, which is lower than the target value, and is less than 2 Ω · cm and room temperature resistance within the target value.

In the embodiment of the present invention described above, a PTC composition comprising a polymer component and a conductive powder dispersed in the polymer component has a pore size of 0.01 mm.
Not less than 1 mm, hole area: metal plate area = 1: 9-
By joining a metal plate having a 9: 1 through-hole and using this as an electrode, a PTC element having an electrode with low contact resistance with the PTC composition can be obtained.

[0039]

As described above, according to the present invention,
By bonding a metal plate having a through hole to the surface of a PTC composition comprising a polymer component and a conductive powder dispersed in the polymer component and using this as an electrode, good adhesion between the PTC composition and the PTC composition is obtained. And a PTC element having an electrode with low contact resistance with the PTC composition is obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the number of times of repeated energization by an element and the room temperature resistivity.

[Explanation of symbols]

 11 Curve (Inventive Example 1) 12 Curve (Comparative Example 1) 13 Curve (Comparative Example 2)

Claims (5)

[Claims] 1. A PTC element characterized in that a metal plate having through holes is joined to the surface of a PTC composition comprising a polymer component and a conductive powder dispersed in the polymer component, and this is used as an electrode. 2. The PTC element according to claim 1, wherein a diameter of the through hole of the metal plate joined to the PTC element is 0.0.
A PTC element having a size of 1 to 1 mm. 3. The PTC element according to claim 1, wherein the ratio of the total area of the through-hole diameter of the metal plate joined to the PTC element to the area of the metal plate is as follows: through-hole area: metal plate area = 1: 9. PTC element, wherein the ratio is up to 9: 1. 4. The PTC element according to claim 1, wherein the conductive powder dispersed in the PTC element comprises TiC, W
A PTC element, which is at least one selected from the group consisting of C, W ₂ C, and ZrC. 5. The PTC element according to claim 1, wherein the conductive powder dispersed in the PTC element is dispersed at 45 to 55 vol% with respect to the PTC composition.