JPH1126206A - Ptc composition, ptc element, and overcurrent protective element using the ptc element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a PTC composition which has a sufficiently low resistance value in a normal state (at a room temperature), does not catch fire when a current is made to flow to the composition, and can be set to an arbitrary operating temperature, a PTC element, and an overcurrent protective element using the PTC element. SOLUTION: A PTC composition is a composite composition, which is composed mainly of a polymer component and the powder of a metal carbide and has an electrical resistance indicating a positive temperature characteristic (PTC), and the mixing ratio of the powder of the metal carbide in the composition is adjusted to 10-60 vol.% of the total volume of the composite. It is preferable to select the metal carbide from among TiC, WC, W2 C, ZrC, VC, NbC, TaC, and Mo2 C. It is preferable, in addition, to prepare the polymer component by mixing a copolymer having a melting point of >=100 deg.C with polyethylene having a melting point of <100 deg.C at a mixing ratio of 0-80 %.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a PTC (Positive
More specifically, the present invention relates to a conductive composition having a positive temperature coefficient (hereinafter, referred to as a PTC composition). More specifically, an overcurrent protection element for preventing an overcurrent flowing when an abnormality occurs in a sheet heating element, a battery, or an electronic device. Used for PTC
It relates to a composition.

[0002]

2. Description of the Related Art Conventionally, as a material having a PTC characteristic, an inorganic conductive composition (ceramic PTC) such as BaTiO ₃ to which a trace amount of Y ₂ O ₃ is added or a carbon material having conductivity with a crystalline polymer such as polyethylene. An organic conductive composition (polymer PTC) obtained by kneading a powder such as black is known. The conventional PTC composition generates heat by so-called Joule heating (I ² R heating) with a resistance value R unique 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 resistance increases.

[0003]

However, ceramic-based PTC compositions have a steady state resistivity of ~ 100.
Since it is as high as about Ω · cm, a relatively large current of about several A cannot flow. This is because ceramic PT
This means that the C composition cannot be used as an overcurrent protection element for preventing an overcurrent flowing when an abnormality occurs in a battery or an electronic device.

On the other hand, since the resistance of a semiconductor material usually decreases with an increase in temperature, an overcurrent easily flows when an abnormality occurs. If an overcurrent flows through the circuit, the ambient temperature will rise further, causing ignition and, in the worst case, a fire. Therefore, the overcurrent protection element is required to have a low resistance at room temperature and a characteristic that the resistance increases as the temperature rises to limit the current.

[0005] Further, the ceramic PTC composition is difficult to process and mold into a desired shape and has a problem in impact resistance, so that it is not generally used as a sheet heating element. On the other hand, a polymer PTC composition in which a conductive powder is kneaded with a crystalline polymer has a low room temperature resistance, is easy to process and mold, and has excellent impact resistance. It is widely used for protection elements and sheet heating elements.

Here, the characteristic required for the overcurrent protection element is that it has a sufficiently small resistivity of about 2 Ω · cm or less at room temperature. Also, in the case of the sheet heating element, if the room temperature resistance is high, there is a danger of handling due to rapid heat generation.

In a polymer PTC composition using a conductive powder having a relatively small particle size, such as carbon black, which is the most common conductive powder, while the temperature is lower than the crystal melting point of the polymer matrix, the conductivity of the polymer is reduced. The conductive particles are present only in the amorphous regions of the polymer matrix and exhibit a lower resistivity for electrons traveling through a network of interconnected conductive particles. In this polymer PTC element, when the polymer matrix begins to melt due to a rise in temperature, the volume of the non-crystalline phase relatively increases while maintaining the viscosity of the polymer matrix, and is present only in the amorphous state due to the melting of the crystalline phase. Since the conductive particles thus diffused throughout the matrix, the network between the conductive particles is cut and the resistivity sharply increases (positive temperature characteristic). Thereafter, when the temperature of the PTC composition returns to normal temperature, the conductive particles exhibit a low resistivity because they re-concentrate in the amorphous region of the polymer matrix and the interparticle network is rearranged.

Incidentally, in order to lower the room temperature resistivity, it is necessary to increase the amount of conductive powder dispersed in the PTC composition. However, when the dispersion amount of the conductive powder having a relatively small particle size such as carbon black in the polymer PTC composition is increased in order to lower the room temperature resistivity, the partial conductivity in the polymer matrix amorphous region is increased. Agglomeration of the powder occurs and a partial conductive path is formed.
When a relatively large current flows there to generate a positive temperature characteristic, ignition of the polymer PTC composition occurs as follows. First, the temperature of the polymer PTC composition rises, then the average resistivity of the polymer PTC composition rises, and then the current concentrates on the partial conductive path (conductive powder aggregation part), or in the aggregation part, Dielectric breakdown occurs, causing partial abnormal heat generation and ignition.

Another method for lowering the room temperature resistivity is to replace the conductive powder dispersed in the polymer PTC composition with a powder having a low resistivity. For example, the resistivity of metal powder is about 1/1000 that of carbon black. However, when a metal powder is dispersed as a conductive powder in the PTC composition instead of carbon black, ignition occurs when a relatively large current flows through the PTC composition for the same reason as described above due to aggregation of the metal powder itself. Occurs. Further, the PTC composition in which the metal conductive powder is dispersed has a problem that the room temperature resistivity increases with each repetitive operation. This means that the polymer PTC composition in which the metal conductive powder is dispersed cannot withstand repeated use.

Further, the temperature at which the resistivity of the polymer PTC composition rapidly rises (operating temperature) is generally determined by the melting point of the polymer matrix. That is, polymer PT
Changing the operating temperature of the C composition requires changing the polymer matrix itself. This is because the polymer PTC
This means that it is virtually impossible to arbitrarily set the operating temperature of the composition.

Therefore, a technical problem of the present invention is that the resistance value in a steady state (room temperature) is sufficiently low, it does not ignite when a current flows, the resistance rise at each operation is small, and the operating temperature is arbitrarily set. It is an object of the present invention to provide a possible PTC composition and PTC device and an overcurrent protection device using the same.

[0012]

Means for Solving the Problems In order to solve the above problems, the present inventors have conducted various studies and found that it is effective to disperse a metal carbide powder as a conductive powder in a polymer component. This has led to the achievement of the present invention.

According to the present invention, the electric resistance mainly composed of the polymer component and the metal carbide powder has a positive temperature characteristic (PT
A PTC composition is obtained, which is a composite composition shown in (C), wherein the component ratio of the metal carbide powder is in the range of 10 to 60 vo1% of the entire composite composition.
Here, in the present invention, even when the metal carbide powder is dispersed, the same PTC characteristics as those obtained when carbon black is dispersed can be obtained, and when the metal carbide powder is dispersed,
Since the metal carbide powder does not concentrate in the amorphous region of the polymer matrix and the metal carbide powder itself does not agglomerate, even if the total amount of the conductive powder dispersed is increased to lower the room temperature resistivity, the partial dispersion may occur. No conductive path is formed, and no ignition occurs when current flows. Further, the polymer PTC composition in which the metal carbide powder is dispersed does not show a remarkable increase in the room temperature resistivity even when repeatedly operated.

According to the present invention, in the PTC composition, the metal carbide powder includes TiC, WC, W ₂
A PTC composition characterized by being at least one of C, ZrC, VC, NbC, TaC, and Mo ₂ C is obtained.

Further, according to the present invention, in any of the above PTC compositions, the polymer component comprises a polyethylene having a melting point of at least 100 ° C. and a copolymer having a melting point of at most less than 100 ° C. with respect to the polyethylene by volume. A PTC composition characterized by being a mixture of at least two of them so that the ratio is 0 to 80% is obtained. Here, in the present invention, as a polymer component of the high-molecular-weight PTC composition, when a polyethylene having a melting point of 100 ° C. or more and a copolymer having a melting point of less than 100 ° C. are compounded and metal carbide powder is dispersed, polyethylene Operating temperature from 20 to 130 depending on the compounding ratio of
It can be set arbitrarily in the range of about ° C.

[0016]

Embodiments of the present invention will be described below with reference to the drawings.

First, a specific method for manufacturing a polymer PTC device using the PTC composition according to the embodiment of the present invention will be described.

As a polymer component, a crystalline high-density polyethylene having a melting point of about 130 ° C. is mixed with an ethylene copolymer having a melting point of about 70 ° C.
The mixture was heated and kneaded on a roll mill so as to be 80 vol. The obtained polymer component was heated and kneaded with a metal carbide powder on a roll mill so as to be 10 to 60 vol% with respect to the polymer component to obtain a polymer composition. As the metal carbide powder, Ti particles each having a particle size of about 1 to 5 μm are used.
C, was used _{WC, W 2 C, ZrC,} VC, NbC, TaC, and Mo ₂ C.

After the obtained composition is powdered, the composition is heated and compression molded at a temperature of about 100 to 200 ° C. while being sandwiched between Ni foils to obtain a molded body having a thickness of 1 mm. 15 mm) A polymer PTC element was punched out into a ring shape having an inner diameter of 10.6 mm.

For comparison, a polymer PTC element using carbon black as a conductive powder was prepared in the same manner.

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 (after switching) to the resistivity at room temperature (R after switching / R at room temperature) is the overcurrent. It is determined to be 10 ⁴ or more, which sufficiently operates as a protection element and can be sufficiently used as a planar heating couple. Further, the room temperature resistivity / target value when the polymer PTC element is repeatedly switched does not exceed 2 Ω · cm even after switching 500 times.

FIG. 1 is a diagram showing the measurement results of the temperature and the resistivity of the polymer PTC element. The measurement was carried out by a 4-short-needle method in an oil bath, and a digital multimeter was used for resistivity measurement. As can be seen from FIG. 1, the PTC element in which the metal carbide powder is dispersed in the high-density polyethylene shown by the curves 2 to 5 has a resistivity at room temperature of <2Ω · cm, which is lower than the target.
In addition, the behavior of the temperature-resistance curve is almost the same as that of the element in which only the carbon black shown in the curve 1 is dispersed, and the ratio of the resistivity is (R after switching / R at room temperature)> 10 ⁸ , greatly exceeding the target. In addition, when the polymer component is a composite of high-density polyethylene and an ethylene-based copolymer, it can be seen that the device operating temperature decreases as the composition ratio of the ethylene-based copolymer increases. This indicates that the operating temperature of the polymer PTC element can be arbitrarily set according to the application by the composite ratio of polyethylene and copolymer.

FIG. 2 is a graph showing a change in resistivity after device operation when a current of 10 A (50 V) is repeatedly applied to the polymer PTC device obtained as described above. As can be seen from FIG. 2, in the element in which only carbon black indicated by curve 11 is dispersed by 20 vol. 1%, the change in resistivity after repeated energization is small, but the initial room temperature resistance is higher than the target value. On the other hand, the element in which only carbon black shown by curve 12 was dispersed by 30 vol.
Ω · cm or less, but ignited at the first energization. On the other hand, the element in which the metal carbide powder shown by the curve 13 is dispersed has a room temperature resistivity of less than the target value of <2 Ω · cm, and maintains the target value of room temperature resistance of <2 Ω · cm even after repeated energization. .

Table 1 shows the characteristics of the polymer PTC element when switching (10 A (50 V) current) when the dispersion amount of the metal carbide powder in the PTC composition and the copolymer composite ratio to polyethylene were changed. Indicated.

[0025]

[Table 1]

As is clear from Table 1, when the dispersion amount of the conductive powder is less than 10 vol%, the room temperature resistivity does not reach the target, and is excluded from the scope of the present invention. When the dispersion amount of the conductive powder exceeds 60 vo 1%, the resistance at room temperature is remarkably reduced, and the element operation phenomenon upon energization is not observed. Therefore, it is excluded from the scope of the present invention. Further, when the copolymer composite ratio exceeds 80 vo1%, the room temperature resistivity does not reach the target, and thus is excluded from the scope of the present invention. That is, the range of the present invention is that the dispersion amount of the conductive powder is 10 vol% or more and 60 vol% or less.
vol% and the copolymer composite ratio is 80 v
o 1% or less.

Table 2 below shows each metal carbide and polymer PTC.
The relationship between the properties of the compositions is shown.

[0028]

[Table 2]

As is clear from Table 2, TiC, W
C, W ₂ C, ZrC, VC, NbC, TaC, and Mo
_Using any of the metal carbide powders of ₂ C, a high molecular weight PTC composition that achieves the above-mentioned target can be obtained.

[0030]

As described above, according to the present invention, according to the present invention, a PTC composition in which ignition is prevented when a current is applied by using a metal carbide powder in a polymer PTC composition, and a PTC element using the same. And can be provided.

According to the present invention, in addition to dispersing the metal carbide powder as the conductive powder, the polymer component further comprises a polyethylene having a melting point of 100 ° C. or more and a copolymer having a melting point of less than 100 ° C. By doing so, a PTC composition using a PTC composition that has a sufficiently low resistance value in a steady state, does not ignite when a current flows, has a small increase in resistance at each operation, and can arbitrarily set an operation temperature. And an element can be provided.

Further, according to the present invention, it is possible to provide an overcurrent protection element using a PTC element having the aforementioned advantages.

[Brief description of the drawings]

FIG. 1 is a diagram showing characteristics of a PTC element using a PTC composition according to an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between the number of operations and the resistivity of the PTC element of FIG.

[Explanation of symbols]

1 Temperature and resistivity characteristic curve of PTC element in which carbon black is dispersed 2-5 Temperature and resistivity characteristic curve of PTC element in which metal carbide powder is dispersed 11 PTC in which carbon black is dispersed after repeated application of 50 V, 10 A Curve indicating resistivity characteristic of element 12 Curve indicating resistivity characteristic of PTC element in which carbon black is dispersed 13 Curve indicating resistivity characteristic of PTC element in which metal carbide powder is dispersed

Claims (5)

[Claims] 1. A composite composition comprising a polymer component and a metal carbide powder as main components and exhibiting a positive temperature characteristic (PTC) in electrical resistance, wherein the metal carbide powder has a component ratio of the entire composite composition. A PTC composition characterized by being in the range of 10-60 vol1%. 2. The PTC composition according to claim 1, wherein
The metal carbide powder is TiC, WC, W ₂ C, Zr
A PTC composition, which is at least one of C, VC, NbC, TaC, and Mo ₂ C. 3. The PTC composition according to claim 1, wherein the polymer component has a melting point of at least 100 ° C.
Of polyethylene and a copolymer having a melting point of at most less than 100 ° C. with a volume ratio of 0-8
A PTC composition characterized by being a mixture of at least two kinds so as to be 0%. 4. A PTC element using the PTC composition according to any one of claims 1 to 3. 5. An overcurrent protection element using the PTC element according to claim 4.