JP2000021605A - Ptc composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a PTC composition (element) in which resistivity in a stationary state (room temperature) is sufficiently low, temperature does not increase abnormally when a current is made to flow, increase in resistivity at each operation is low, and operating temperature can be set arbitrarily. SOLUTION: By using powder of metal boride as conductive material to polymer based PTC composition, a stable PTC composition which shows sufficiently low resistivity at a normal temperature can be obtained. Especially, by compounding and using polyethylene whose melting point is at least 100 deg.C and copolymer whose melting point is at most 100 deg.C as polymer, PTC composite where resistivity in a stationary state is sufficiently low, temperature does not increase abnormally when a current is made to flow, increase in resistivity at each operation is low and an operation temperature can be arbitrarily set can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a PTC (Positive
Temperature Coefficent, which is abbreviated as "positive temperature coefficient", relates to a composition of an electric resistor having an electric resistance having a positive temperature coefficient. In particular, a polymer material (polymer) and a conductive substance are used as main components. And an organic conductive composition having an electric resistance having a positive temperature coefficient (hereinafter, referred to as a polymer PTC composition).

[0002]

2. Description of the Related Art A PTC composition is generally used as an electronic component as an overcurrent protection element for preventing an overcurrent flowing when an abnormality occurs in a battery or an electronic device, a heating element, or the like.

Conventionally, BaTiO containing a small amount of ceramic Y ₂ O ₃ has been proposed as having PTC characteristics.
Organic conductive compositions obtained by kneading an inorganic conductive composition such as ₃ or a crystalline polymer such as a high molecular weight polyethylene with a conductive powder such as carbon black fine particles are known. .

When a current flows through a resistor element (hereinafter, referred to as a PTC element) composed of a PTC composition, a so-called Joule heat which depends on a resistance value R of the element and a current value I flowing through the element is obtained. (I ² R) is generated, and the PTC element is heated by this heat and the temperature rises. As the temperature rise of the element itself, the electric resistance increases because the temperature coefficient of the electric resistance (resistivity) of the element is positive.

Therefore, when a relatively large current flows through the PTC element, heat is suddenly generated, the resistance value (resistivity) rises abruptly, and there is a function of suppressing the current. Utilizing this property, the PTC composition is used for a safe heating element capable of maintaining a constant temperature, an overcurrent protection element for preventing overcurrent, and the like. A characteristic required of the PTC element such as the overcurrent protection element is that it has a sufficiently small resistivity of about 2 Ω · cm or less at room temperature.

[0006]

However, the PTC element is required to have a characteristic of allowing a large current to flow with a low resistance at room temperature and increasing the resistance with the rise in temperature to limit the current. Therefore, when used in an overcurrent protection element, a relatively large current of about several amperes (A) must be applied to a ceramic PTC composition or the like since the resistivity at room temperature is as high as about 100 Ω · cm. Therefore, there is a problem that it cannot be used as an overcurrent protection element for preventing an overcurrent flowing when an abnormality occurs in a battery or an electronic device.

[0007] Forming into a desired shape requires complicated steps and is difficult, and also has a problem in impact resistance, so that it is difficult to use it as a heating element.

On the other hand, crystalline polymers (polymers)
Polymer-based PTC compositions are widely used for overcurrent protection elements and sheet heating elements because of their ability to set low room temperature resistance, easy molding and excellent impact resistance. ing.

For example, in a semiconductor device, since the resistance decreases as the temperature rises, in a circuit using the semiconductor device, when an abnormality occurs in the periphery and the temperature rises, an overcurrent easily flows. Further, when an overcurrent flows through the circuit, the temperature around the element may be further increased and the element may be damaged. Therefore, in such a circuit, the circuit is prevented from being damaged by an overcurrent protection element. Accordingly, there is a need for a PTC composition that has a low resistivity at room temperature, and whose resistance value sharply increases as the temperature rises, and that can suppress an increasing current.

Generally, conventional polymer-based PTC compositions include:
Uses conductive particles of relatively small particle size, such as carbon black powder.During the temperature lower than the crystal melting point of the polymer matrix, the conductive particles exist only in the amorphous region of the polymer matrix, Electrons traveling through a network of interconnected interconnected particles exhibit lower resistivity. When the polymer matrix begins to melt as the temperature increases, the volume of the non-crystalline phase relatively increases while maintaining the viscosity of the polymer matrix, and further progresses, the conductive particles existing only in the amorphous region, Spread throughout the matrix. Therefore, the network between the conductive particles is cut, and the resistivity sharply increases. That is, the resistivity has a positive temperature characteristic. afterwards,
When the temperature of the PTC composition returns to room temperature, the conductive particles again exhibit a low resistivity because they are concentrated in the amorphous regions of the polymer matrix and the interparticle network is rearranged.

In order to lower the resistivity at room temperature in this polymer-based PTC composition, it is necessary to increase the amount of conductive powder dispersed in the PTC composition. However, in order to lower the room temperature resistivity, a polymer-based PTC
Increasing the amount of small conductive particles dispersed in the composition causes partial agglomeration of the conductive powder in the amorphous regions of the polymer matrix, forming partial conductive paths with low resistivity Is done. When a relatively large current flows there,
The temperature of the polymer PTC composition increases, the average resistivity of the polymer PTC composition increases, current concentrates on the partial conductive path where the conductive particles are condensed, or dielectric breakdown occurs at the aggregated portion,
It is conceivable that the PTC element made of the polymer-based PTC composition may be burned out in the step of raising the temperature from partial abnormal heating to abnormal temperature.

As another method for lowering the resistivity at room temperature, it is conceivable 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 1/1 of that of carbon black.
It is about 000. However, when a metal powder is dispersed as a conductive powder in the PTC composition, the metal powder itself usually agglomerates. For the same reason as described above, when a relatively large current flows through the PTC composition, an abnormal rise occurs. Temperature develops. Further, the PTC composition in which the metal conductive powder is dispersed has a tendency 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 has a problem that it cannot withstand repeated use.

Further, the temperature at which the resistivity of the polymer PTC composition rapidly rises (operating temperature in the case of an overcurrent protection element) is:
Generally, it is determined by the melting point of the polymer matrix. That is, to change the operating temperature of the polymer PTC composition, the polymer matrix itself must be changed.
This means that it is virtually impossible to arbitrarily set the operating temperature of the polymer PTC composition.

Accordingly, an object of the present invention is to provide a semiconductor device having a sufficiently low resistivity in a steady state (room temperature), no abnormal temperature rise when a current is applied, a small increase in resistivity at each operation, and an optional operating temperature. It is an object of the present invention to provide a PTC composition which can be set to:

[0015]

In order to solve the above problems, the present inventors have conducted various studies and found that a metal boride powder was used as a conductive material powder of a polymer-based PTC composition. Has been found to be effective.

When a metal boride powder is used, the same PT is used as when a conventional carbon black powder or the like is used.
C characteristics are obtained. Further, when the metal boride powder is dispersed, the metal boride powder does not concentrate in the amorphous region of the polymer matrix, and the metal boride powder itself does not aggregate. Even if the amount of dispersion of the conductive powder added to reduce the resistivity is increased, a partial conductive path is not formed, and abnormal temperature rise when a large current flows does not occur. Further, in the polymer PTC composition in which the metal boride powder is dispersed, no remarkable increase in the room temperature resistivity is observed even when the composition is repeatedly operated.

Further, as the polymer of the high molecular weight PTC composition, polyethylene having a melting point of 100 ° C. or more,
When a copolymer with a copolymer having a temperature of less than 00 ° C. is mixed and a metal boride powder is dispersed therein, an operating temperature of about 20 ° C. to about 13 ° C. depends on the composite ratio of the polyethylene and the copolymer.
It can be set freely within the range of about 0 ° C.

That is, the present invention comprises, as main components,
In a PTC (electrical resistance has a positive temperature coefficient) composition comprising a polymer and a powder of a conductive substance, a metal boride is used as the conductive substance, and the content of the metal boride is 10 vol% of the entire composition. The PTC composition has a range of 60 vol% or less.

Further, the present invention provides the above PTC composition, wherein the metal boride is TiB ₂ , WB, Cr.
_{B, ZrB 2, NbB 2,} TaB 2, MoB , or,, L
PTC containing at least one of aB ₆
A composition.

Further, the present invention provides the PTC composition as described above or any one of the above, wherein
Polyethylene having a melting point of 100 ° C or higher, and a melting point of 100 ° C
A PTC composition in which the copolymer content is less than 80 vol% (not including 0) based on the polyethylene content.

[0021]

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a polymer-based PTC composition comprising a polymer and a conductive substance powder as main constituents and a metal boride as a conductive substance. The content is 10 vol% or more and 60 vol of the whole composition.
% Of the PTC composition. Further, TiB2, WB, CrB, ZrB may be used as the metal boride.
2, a PTC composition containing at least one of NbB2, TaB2, MoB, and LaB6. Further, as the polymer, a polyethylene having a melting point of 100 ° C. or more and a copolymer having a melting point of less than 100 ° C. are used, wherein the content of the copolymer is 80 to the content of the polyethylene.
P used in combination within the range of vol% or less (excluding 0)
It is a TC composition.

As described above, the present invention provides a polymer-based PTC
By using a metal boride powder as a conductive material in the composition, a sufficiently low resistivity at room temperature can be obtained, and a stable PTC composition can be obtained. In particular, as a polymer, polyethylene having a melting point of 100 ° C. or more is used. And a copolymer having a melting point of less than 100 ° C. are used in combination, so that the resistance value in a steady state is sufficiently low, the temperature does not rise abnormally when a current is applied, and the resistivity rise at each operation is small. As a result, a PTC composition whose operating temperature can be arbitrarily set can be obtained.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below by way of embodiments with reference to the drawings.

FIG. 1 is a graph showing P and P of Examples of the present invention and Comparative Examples.
FIG. 2 shows a temperature-dependent characteristic of the resistivity of the TC composition, and FIG.
FIG. 10 is a diagram showing the number-of-operations-dependent characteristics of resistivity when repeatedly operating at 50 V and 10 A according to another embodiment of the present invention and a comparative example.

First, as a polymer, the melting point is about 130 ° C.
The crystalline high-density polyethylene is weighed with an ethylene copolymer having a melting point of about 70 ° C. in a volume ratio of 0 to 80 vol% with respect to the total amount of polyethylene, and the mixture is heated and kneaded with a roll mill to obtain a composite polymer. It was created. The resulting composite polymer was heated and kneaded with a metal boride powder in a roll mill so as to have a content of 10 to 65 vol% with respect to the polymer to obtain a polymer-based PTC composition. As the metal boride powder, T particles each having a particle size of about 1 to 5 μm are used.
iB ₂ , WB, CrB, ZrB ₂ , NbB ₂ , TaB ₂ , M
oB, using the LaB _6.

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

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

Here, the target characteristics of the polymer PTC composition of the example are as follows: the resistivity at room temperature is 2 Ω · cm or less, as described above, and the resistivity after a sharp rise in the resistivity (after switching). The ratio of the resistivity to the resistivity at room temperature (R after switching / R at room temperature) is 10 ⁴ which sufficiently operates as an overcurrent protection element and can be sufficiently used as a sheet heating element.
That is all. The target value of the room temperature resistivity when the polymer PTC composition is repeatedly switched is 5
It was determined that the value did not exceed 2 Ω · cm even after switching 100 times.

FIG. 1 shows the measurement results of the temperature and the resistivity of the PTC devices comprising the polymer PTC compositions of the examples and the comparative examples. The measurement used the four-terminal method in the oil bath. FIG.
As can be seen from FIG. 1, the PTC element (2 in FIG. 1) in which the metal boride powder is dispersed in the high-density polyethylene of the example is:
The resistivity at room temperature is 2Ω · cm or less, meeting the target. Further, the behavior of the resistivity-temperature curve is almost equivalent to that of the PTC element of Comparative Example (1 in FIG. 1) in which only carbon black is dispersed in polyethylene, and the ratio of the resistivity is (R after switching / R at room temperature R). )> 10 ⁸ , greatly exceeding the target.

The PT of the embodiment in which the polymer is a composite polymer of high-density polyethylene and an ethylene copolymer is used.
In the case of the C element (3, 4, and 5 in FIG. 1), it can be seen that the operating temperature of the PTC element decreases as the composition ratio of the ethylene copolymer increases. This indicates that the operating temperature of the PTC element made of the polymer-based PTC composition can be freely set depending on the composite ratio of the polyethylene and the copolymer.

Next, FIG. 2 shows a change in resistivity after operation when a current of 10 A (50 V) was repeatedly applied to the PTC elements of the example and the comparative example obtained as described above. As can be seen from FIG.
The PTC element of Comparative Example (6 in FIG. 2) in which
Although the change in resistivity after repeated energization is small, the resistivity at room temperature is higher than the target value.

The PTC element (7 in FIG. 2) of the comparative example in which only carbon black was dispersed at 30 vol% had an initial room temperature resistance of 2 Ω · cm or less, but the temperature rose to the ignition point by the first energization. did. On the other hand, in the PTC element of the embodiment (8 in FIG. 2) in which the metal boride powder is dispersed by 50 vol%, the room temperature resistivity can be cleared to the target value of 2 Ω · cm or less, and even after repeated energization. The resistance was kept at 2 Ω · cm or less and within the target value of the room temperature resistance.

Next, Table 1 shows that a PTC element composed of a polymer-based PTC composition in the case where the dispersion amount of the metal boride powder in the PTC composition and the copolymer composite ratio with respect to polyethylene was changed, was switched [10A (50 V). ) Energization].

[0034]

As can be seen 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. Further, when the dispersion amount of the conductive powder exceeds 60 vol%, the resistivity at room temperature is remarkably reduced, and the phenomenon of the switching operation of the PTC element at the time of energization is not observed, so that it is excluded from the scope of the present invention. If the composite ratio of the copolymer exceeds 80 vol%, the resistivity at room temperature does not reach the target, and is excluded from the scope of the present invention. It is clear that the object of the present invention has been achieved even with polyethylene alone (composite ratio 0 vol%).

Table 2 shows the characteristics of the polymer PTC composition when each metal boride was used alone as the conductive substance.

[0037]

As can be seen from Table 2, it can be seen that a polymer PTC composition which achieved the target was obtained using any of the metal boride powders. In the above description, the case where each metal boride is contained alone is shown. However, the same effect can be obtained even if these are combined and contained. The selection of the compounding ratio depends on the compatibility with the polymer,
It is selected from the correlation between characteristics and cost.

[0039]

As described above, according to the present invention, as a polymer, a polyethylene having a melting point of 100 ° C. or more and a copolymer having a melting point of less than 100 ° C. are combined, and a metal boride powder is used as a conductive powder. By dispersing, a polymer PTC whose resistance value in a steady state is sufficiently low, does not cause abnormal temperature rise when a current is applied, has a small resistance rise at each operation, and can arbitrarily set an operation temperature A composition is obtained.

[Brief description of the drawings]

FIG. 1 is a graph showing the temperature dependence of the resistivity of PTC compositions of Examples of the present invention and Comparative Examples.

FIG. 2 shows 50 V and 10 A of an example of the present invention and a comparative example.
FIG. 6 is a graph showing the number-of-operations-dependent characteristics of the resistivity when the operation is repeatedly performed.

[Explanation of symbols]

1 PT containing carbon black only in polyethylene
Temperature dependence characteristic curve of resistivity of element C 2 PTC containing metal boride powder only in polyethylene
Temperature-dependent characteristic curve of resistivity of element 3 Temperature-dependent characteristic curve of resistivity of PTC element containing metal boride powder in (polyethylene 80 + copolymer 20) 4 PTC element containing metal boride powder in (polyethylene 60 + copolymer 40) Temperature-dependent characteristic curve of resistivity 5 Temperature-dependent characteristic curve of resistivity of PTC element containing metal boride powder in (polyethylene 40 + copolymer 60) 6 Characteristic curve of operation number dependence of resistivity of PTC element containing 20 vol% carbon black 7 30 vol % Operation characteristic curve of the resistivity of the PTC element containing 50% by volume of carbon black.

Claims (3)

[Claims] 1. A PTC (electrical resistance has a positive temperature coefficient) composition comprising a polymer and a powder of a conductive material as main constituents, wherein a metal boride is used as the conductive material. Content of 10 v of the entire composition
The PTC composition is in a range of not less than ol% and not more than 60 vol%. 2. The PTC composition according to claim 1, wherein
TiB ₂ , WB, CrB, Zr as the metal boride
_{B 2, NbB 2, TaB 2} , MoB , or of LaB _6, PTC composition characterized by containing at least any one. 3. The PTC composition according to claim 1, wherein the polymer has a melting point of 1%.
It is characterized in that a polyethylene having a temperature of at least 00 ° C. and a copolymer having a melting point of less than 100 ° C. are used in combination, and the content of the copolymer is in the range of 80 vol% or less (not including 0) with respect to the content of the polyethylene. PTC composition.