JPH10214705A - Organic positive temperature coefficient thermistor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an organic positive temperature coefficient thermistor which operates at a temperature having no danger to the human body and which has an acute rise in resistance at the time of starting operation, by kneading polyethylene oxide having a specified range of weight average molecular weight and conductive particles having spike-like protrusions. SOLUTION: An organic positive temperature coefficient thermistor is formed by using polyethylene oxide (PEO) having a weight-average molecular weight Mw not less than 2,000,000 as a crystalline polymer, and kneading conductive particles having spike-like protrusions with the polyethylene oxide. The weight- average molecular weight Mw of PEO is more preferably 3,000,000 to 6,000,000. It is preferred that the melting point of PEO is approximately 60 to 70 deg.C and that the density is approximately 1.15 to 1.22g/cm<3> . The conductive particles having spike-like protrusions are made of primary particles each of which has acute protrusions, and a plurality of (normally 10 to 500) conical spike-like protrusions having a height which is 1/3 to 1/50 of the grain diameter exist on each particle. The material of the particles is preferably nickel.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic positive temperature coefficient thermistor.
organic positive temperature coefficient thermistor having a characteristic of resistivity.

[0002]

2. Description of the Related Art Organic positive temperature coefficient thermistors exhibiting PTC characteristics by kneading and dispersing conductive particles such as carbon black and metal in a crystalline polymer (polymer) are known in the art. For example, it is disclosed in U.S. Pat. Nos. 3,243,753 and 3,351,882. This can be used as a self-control heater, a temperature detector, and an overcurrent protection element. The characteristics required for this are that the initial resistance value at room temperature (when not operating) is sufficiently low,
The change rate between the initial resistance value and the resistance during operation is large, and the characteristics are stable even after repeated operation.

In general, in a conventional organic positive temperature coefficient thermistor, it is known that the crystalline polymer is melted during operation, so that when cooled, the dispersed state of the conductive particles changes and the initial resistance increases. .

In conventional organic positive temperature coefficient thermistors, carbon black has been frequently used as conductive particles.
When the filling amount of carbon black is increased to lower the initial resistance value, there is a drawback that a sufficient resistance change rate cannot be obtained. In addition, there is an example in which general metal particles are used for the conductive particles, but it has been similarly difficult to achieve both a low initial resistance and a large resistance change rate.

As a method for solving the above-mentioned drawbacks, a method using conductive particles having spike-like projections is disclosed in Japanese Patent Application Laid-Open No. HEI 5 (1993) -5.
-47503. More specifically, using polyvinylidene fluoride as a crystalline polymer,
As the conductive particles having spike-like projections, those using spike-like Ni powder are disclosed. It is stated that this makes it possible to achieve both low initial resistance and large resistance change. However, this one has insufficient stability of characteristics due to repetitive operations. When using polyvinylidene fluoride, the operating temperature is about 160 ° C. However, considering the use as a protective element such as a secondary battery, an electric blanket, a toilet seat, a heater for a vehicle seat, and the like, at an operating temperature of 100 ° C. or more, there is a great danger to the human body. In consideration of safety for the human body, the operating temperature needs to be lower than 100 ° C., particularly about 60 to 70 ° C.

In US Pat. No. 5,378,407, a filament-shaped N having spike-shaped projections is also disclosed.
The use of i and a polyolefin, an olefin-based copolymer, or a fluoropolymer is disclosed. It has low initial resistance, large resistance change,
It is considered that the stability of the characteristics by the repetition operation is sufficient. However, in the high-density polyethylene and polyvinylidene fluoride polymer used in the examples, the operating temperatures are about 130 ° C. and about 160 ° C., respectively. In this specification, ethylene / ethyl acrylate copolymer,
Ethylene / vinyl acetate copolymers, ethylene / acrylic acid copolymers and the like can be used. However, there is no embodiment. These polymers have an operating temperature of 60
The temperature is 明 ら か に 70 ° C., as will become clear from the examples described later, but the characteristics become unstable due to repeated operation.

It is to be noted that the one disclosed in US Pat. No. 4,545,926 also discloses spherical, flake-like and rod-like Ni.
And a polyolefin, an olefin-based copolymer, a vinyl halide, and a vinylidene polymer. In the examples, ethylene / ethyl acrylate copolymer, ethylene / acrylic acid copolymer have an operating temperature of 60-70.
° C and other polymers have operating temperatures above 100 ° C. However, ethylene / ethyl acrylate copolymer and ethylene / acrylic acid copolymer are, as described above,
Characteristics become unstable due to repeated operation.

On the other hand, Japanese Patent Application Laid-Open Nos. 62-65401, 62-122083 and 62-156159,
JP-A-2-72580, JP-A-2-172179,
In the publications 3-187201 and 4-14201,
A thermistor using carbon or a conductive metal and polyethylene oxide is disclosed. In this case, 60-70
° C operating temperature. However, since carbon or a conductive metal is used, it is impossible to achieve both a low initial resistance and a large resistance change as described above.

Further, these polyethylene oxides are
Each has a molecular weight of 100,000 or less. For this reason,
Even when Ni in the form of a filament having spike-like projections used in the above-mentioned US Pat. No. 5,378,407 is used in combination, the initial resistance is high, particularly the resistance rises slowly, and the rise degree is insufficient. It turned out to be.

As described above, an organic positive temperature coefficient thermistor exhibiting good characteristics and having stable characteristics at an operating temperature of less than 100 ° C. with little danger to the human body has not been obtained at present.

[0011]

SUMMARY OF THE INVENTION An object of the present invention is to operate at a temperature of 60 to 70.degree. C. which has no danger to the human body, to have a low initial resistance when not operating (room temperature), and to have a sharp rise in resistance during operation. An object of the present invention is to provide an organic positive temperature coefficient thermistor whose resistance change rate is large from non-operation to operation and whose characteristics are stable even after repeated operation.

[0012]

This and other objects are achieved by the present invention described below. (1) An organic positive temperature coefficient thermistor obtained by kneading polyethylene oxide having a weight average molecular weight of 2,000,000 or more and conductive particles having spike-shaped protrusions. (2) The organic positive temperature coefficient thermistor according to (1), wherein the conductive particles having the spike-like projections are connected in a chain. (3) The organic positive temperature coefficient thermistor according to (1), wherein the weight average molecular weight of said polyethylene oxide is 3,000,000 to 6,000,000. (4) The organic positive temperature coefficient thermistor according to the above (2), wherein the conductive particles having the chain-like spike-like projections have an average particle diameter of 0.1 μm or more. (5) The organic positive temperature coefficient thermistor according to (4), wherein said average particle diameter is 1.0 to 4.0 µm.

[0013]

According to the present invention, since polyethylene oxide is used, the operating temperature can be 60 to 70 ° C., and a protective element with reduced danger to the human body can be obtained. In the present invention, by using conductive particles having spike-shaped protrusions, a tunnel current easily flows due to the shape thereof, and a lower initial resistance can be obtained as compared with spherical conductive particles. Further, since the distance between the conductive particles is larger than that of the spherical particles, a large resistance value is obtained during operation.

Further, it has been found that by limiting the weight average molecular weight Mw of polyethylene oxide as a crystalline polymer to 2,000,000 or more, a change in characteristics during repeated operation is critically reduced. Although the reason for this is not clear at this stage, the wettability of the crystalline polymer to the conductive particles is improved, the dispersion is more uniform, and the change in the crystalline state of the crystalline polymer and the dispersion state of the mixture by heating and cooling. It is thought that is suppressed.

Incidentally, Japanese Patent Application Laid-Open No. 5-47503 discloses that
"An organic positive temperature coefficient thermistor comprising a crystalline polymer and conductive particles having spike-like projections kneaded with the crystalline polymer" is disclosed. However, the crystalline polymer used in that example is polyvinylidene fluoride. Although polyethylene oxide is exemplified as the crystalline polymer, there is no description that polyethylene oxide having a molecular weight within a predetermined range is used as in the present invention. Therefore, there is no description about the effect of the present invention of suppressing a change in characteristics due to the repetitive operation.

[0016]

Embodiments of the present invention will be described below in detail.

The organic positive temperature coefficient thermistor of the present invention uses polyethylene oxide (PEO) having a weight average molecular weight Mw of 2,000,000 or more as a crystalline polymer, and kneads conductive particles having spike-like projections. Things.

As a result, an operating temperature of about 60 to 70 ° C. becomes possible.

The polyethylene oxide used in the present invention has a weight average molecular weight Mw of 2,000,000 or more, and more preferably 3,000,000 to 6,000,000.
It is preferably 0. When Mw is less than 2,000,000, the viscosity at the time of melting is too low, and the dispersibility of the conductive particles is deteriorated, and it becomes difficult to lower the resistance at room temperature.

Polyethylene oxide having a Mw of 2,000,000 or more has a melting point of about 60 to 70 ° C. and a density of 1.15 to 1.22 g.
/ Cm3.

The conductive particles having spike-like projections used in the present invention are each formed of primary particles each having a sharp projection, and have a height of 1/3 to 1/50 of the particle size. Conical spike-like projections on one particle (usually 1
0 to 500). The material is preferably Ni or the like.

Such conductive particles may be a powder in which one particle is present individually, but the primary particles are 10 to 10 particles.
It is preferable that the chain is a chain of about 1,000. Some primary particles may be present in the chain.
As an example of the former, there is a spherical nickel powder having spike-shaped protrusions, and the trade name is INCO Type 123.
There is a commercially available nickel powder (manufactured by Inco Corporation) having an average particle size of about 3 to 7 μm, an apparent density of about 1.8 to 2.7 g / cm3, and a specific surface area of about 0.3 to 0.3 g / cm3.
It is about 4 to 0.44 m2 / g.

As an example of the latter, which is preferably used, there is a filamentous nickel powder having a trade name of IN.
CO Type 255, 270, 287 nickel powder and INCO Type 210 nickel powder (manufactured by INCO) are commercially available.
NCO Type 255, 277, 287 is preferred. The average particle size of the primary particles is preferably 0.1 μm or more, more preferably 0.5 or more and 4.0 μm.
Below. Among these, the average particle size of the primary particles is most preferably 1.0 or more and 4.0 μm or less.
Particles having an average particle size of 1 μm or more and less than 1.0 μm may be mixed at 50% by weight or less. The apparent density is 0.3 ~
About 1.0g / cm3, specific surface area is 0.4 ~ 2.5m2 /
g. FIG. 1 shows a scanning electron micrograph of such a chain filamentous nickel powder. The average particle size in this case was measured by the fish-sub-sieve method.

In the present invention, the ratio (weight) of the crystalline polyethylene oxide polymer to the conductive particles is preferably about 3 to 5 for the conductive particles / crystalline polymer. With such a ratio, the effect of the present invention is improved.
On the other hand, when the ratio is small, the conductive particles are too small, and the initial resistance during non-operation is not easily reduced sufficiently. If this ratio is too large and the number of conductive particles is too large, it is difficult to obtain a large resistance value during operation.

The kneading of the crystalline polymer and the conductive particles is carried out at a temperature higher than the melting point of the crystalline polymer (preferably at a temperature of +10 to 40 ° C.) by adding the conductive particles to the crystalline polymer. In the polyethylene oxide of the present invention, 80 to
This is performed at about 110 ° C. A specific kneading method may be a known method, for example, kneading for about 5 to 60 minutes using a mill or the like.

The thermistor is obtained by press-forming such a kneaded material into a sheet or the like having a predetermined thickness. After the molding, a crosslinking treatment may be performed if necessary.

Thereafter, electrodes of Ni, Cu, etc. are formed.
Also, press molding and electrode formation can be performed simultaneously.

The organic positive temperature coefficient thermistor of the present invention has a low initial resistance when not operating, and has a room temperature resistance of 0.0
The resistance rises steeply during operation, and the resistance change rate from non-operation to operation is as large as about 9 to 10 digits. In addition, deterioration of characteristics due to repeated operation is suppressed.

[0029]

EXAMPLES Examples of the present invention will now be described together with comparative examples to specifically describe the present invention.

Example 1 Mw 4,300,000-4,80 as a crystalline polymer
Polyethylene oxide I (mp 67 ° C.) of 0000 and chain-like filamentary nickel powder I (trade name ICO, manufactured by INCO) as conductive particles as shown in FIG.
NCO Type 255 nickel powder) was used.
The average particle size of the conductive particles is 2.2 to 2.8 μm, the apparent density is 0.5 to 0.65 g / cm 3, and the specific surface area is 0.6.
8 m2 / g.

4 times (by weight) the amount of filamentary chain Ni powder based on polyethylene oxide was added and kneaded in a mill at 80 ° C. for 15 minutes.

Both sides of this kneaded material are Ni foil (30 μm thick)
, A Ni foil was pressure-bonded to the kneaded material, and the kneaded material was molded to obtain a pressed product having a total thickness of 1 mm. This was punched out into a disk having a diameter of 10 mm to obtain a thermistor sample having a cross-sectional view as shown in FIG. As shown in FIG. 2, the sample has a kneaded molded sheet 12 of a crystalline polymer and conductive particles sandwiched between electrodes 11 formed of Ni foil.

This sample was heated and cooled in a thermostat,
The resistance was measured at a predetermined temperature to obtain a temperature-resistance curve.
The result is shown in FIG.

From FIG. 3, the initial room temperature resistance at room temperature (25 ° C.) is 0.006 Ω, and when the sample is heated to a transition temperature (65 ° C.) or higher, a sharp rise in resistance is observed, and the maximum resistance value is observed. Is 6 × 10 7 Ω, indicating that the resistance change rate is 10.0 digits. In addition, an index indicating the sharpness of the rise of the resistance near the transition temperature (degree of rise of the resistance) was determined as follows.

(Rise rise of resistance) As shown in FIG. 4, first, tangent lines of the curves before and after the transition are drawn on the graph of the temperature-resistance curve, and the transition temperature is determined from the intersection.
Note that the transition temperatures are all determined in this way. Next, the resistance value at the transition temperature is determined, the rate of change (digit) A between this value and the resistance value at room temperature is determined, and the ratio A / B (% ). A / B
The smaller the is, the sharper the rise is.

Next, from room temperature to 120 ° C. at a rate of 2 ° C./min.
After a cycle test in which the temperature was raised to 120 ° C. and the temperature was lowered from 120 ° C. to room temperature at a rate of 2 ° C./min, and then repeated 10 times, a temperature-resistance curve was obtained in the same manner as above, The resistance value, the rate of change in resistance, and the degree of rise of the resistance were determined. Temperature after 10 cycles of heating and cooling-
FIG. 5 shows the resistance curve. There was almost no change from the initial one before the cycle test (FIG. 3).

The results are summarized in Table 1. In addition, there was almost no change in the degree of rise of the resistance after the cycle test. Table 2 summarizes characteristic values for determining the degree of rise of the resistance.

Example 2 In Example 1, the conductive particles were replaced with chain-like filamentous nickel powder II (trade name INCOT, manufactured by Inco Corporation).
ype 287 nickel powder, average particle size 2.6-3.
A sample was obtained in the same manner as in Example 1 except for changing the apparent density to 0.75 to 0.95 g / cm3 and the specific surface area to 0.58 m2 / g), and a temperature-resistance curve was obtained. The result is shown in FIG.

FIG. 6 shows that a sharp increase in resistance was observed at a transition temperature (65 ° C.) or higher. Further, the same characteristic values as in Example 1 including the transition temperature were obtained. Under the same conditions as in Practical Example 1, characteristic values were obtained after 10 heating and cooling cycles. The temperature-resistance curve after heating and cooling was almost unchanged from the initial one before the cycle test (FIG. 6).

The results are summarized in Table 1.

Example 3 In Example 1, the crystalline polymer was changed to Mw 3,300,0
00 to 3,800,000 polyethylene oxide II
(Mp 67 ° C.), and a sample was obtained in the same manner as in Example 1 except that the kneading temperature was 80 ° C., and a temperature-resistance curve was obtained. The result is shown in FIG.

Comparative Example 1 In Example 1, polyvinylidene fluoride (mp 175 ° C., Mw 300,000) was used as the crystalline polymer.
A sample was obtained in the same manner as in Example 1 except that the kneading temperature was 195 ° C., and a temperature-resistance curve was obtained. The result is shown in FIG.

As can be seen from FIG. 8, the transition temperature (159)
℃), a sharp increase in resistance was observed. Further, characteristic values were obtained in the same manner as in Example 1. Further, characteristic values after heating and cooling in 10 cycle tests were determined in the same manner as in Example 1 except that heating was performed up to 200 ° C. In addition,
The temperature-resistance curve after the heating and cooling was earlier than that of the samples of Examples 1 and 2 before the cycle test (FIG. 8).
The change from was big.

The results are summarized in Tables 1 and 2.

Comparative Example 2 The procedure of Example 1 was repeated except that carbon black (average particle size: 40 nm, specific surface area: 58 m 2 / g) was used as the conductive particles, and polyethylene oxide and carbon black were used in the same amount (weight). To obtain a sample, and a temperature-resistance curve was obtained. The result is shown in FIG. In the same manner as in Example 1, the initial (before the cycle test) and the characteristic values after heating and cooling were determined. However, the cycle test of heating and cooling is 3
Times. The results are shown in Tables 1 and 2.

Comparative Example 3 In Example 1, spherical nickel powder (INCO Type 110 nickel powder, trade name, manufactured by Inco; average particle diameter: 0.8 to 1.5 μm, apparent density: 0.9) was used as the conductive particles.
To 1.5 g / cm3 and a specific surface area of 0.9 to 2 m2 / g), and a temperature-resistance curve was obtained in the same manner. The result is shown in FIG. In the same manner as in Example 1, the initial (before the cycle test) and the characteristic values after heating and cooling were determined. The results are shown in Tables 1 and 2.

Comparative Example 4 In Example 1, the crystalline polymer Mw was 600,000
A sample was obtained in the same manner except that 1,100,000 polyethylene oxide was used, and a temperature-resistance curve was obtained.
The result is shown in FIG. In the same manner as in Example 1, the initial (before the cycle test) and the characteristic values after heating and cooling were determined. The results are shown in Tables 1 and 2.

Comparative Example 5 A sample was obtained in the same manner as in Example 1 except that an ethylene / vinyl acetate copolymer of a crystalline polymer (vinyl acetate content: 8 wt%, Novatec EVALV241 manufactured by Nippon Polychem) was used. The characteristic values were obtained in the same manner. This sample had a transition temperature of 61 ° C., a room temperature resistance of 0.29Ω, and a resistance rise A / B of Example 1 described above.
It was larger than ~ 3. Further, the same cycle test as in Example 1 was performed.
250Ω, and a remarkable increase in room temperature resistance was observed.

Comparative Example 6 A sample was obtained in the same manner as in Example 1 except that an ethylene / methacrylic acid copolymer of a crystalline polymer (methacrylic acid content: 15 wt%, Nucrel N1525 manufactured by DuPont-Mitsui Polychemicals) was used. The characteristic values were determined in the same manner as in Example 1. This sample has a transition temperature of 65
° C, room temperature resistance value 0.008Ω, resistance rise degree A /
B was larger than Examples 1 to 3 above. When a cycle test similar to that of Example 1 was performed, the room temperature resistance value was 0.04Ω after two heating and cooling operations, and a remarkable increase in room temperature resistance was recognized.

Comparative Example 7 In Example 1, an ethylene / ethyl acrylate copolymer of a crystalline polymer (ethyl acrylate content 6.
6% by weight, manufactured by Union Carbide), and a sample was obtained in the same manner as in Example 1 to determine characteristic values. Further, characteristic values after heating and cooling in the same cycle test as in Example 1 after 10 times were obtained. In Comparative Example 7, as in Comparative Examples 5 and 6, a remarkable increase in room temperature resistance was observed after heating and cooling.

[0051]

[Table 1]

[0052]

[Table 2]

From the results of Tables 1 and 2 and FIGS. 3 and 5 to 11, the samples of Examples 1 to 3 of the present invention have an operating temperature of 6 ° C.
At 0 to 70 ° C, the room temperature resistance is sufficiently low, a sharp rise in resistance is observed by heating above the transition temperature, the maximum resistance value is large, the resistance change rate is large, and there is almost no deterioration in characteristics after heating and cooling. I understand. In particular, since the transition temperature is low and the room temperature resistance is sufficiently low, it is particularly effective as an element for preventing heating of a secondary battery.

On the other hand, in the sample of Comparative Example 1 using vinylidene fluoride as the crystalline polymer, the resistance at room temperature after heating and cooling was particularly increased, and the degree of rise of resistance was also poor. In the sample of Comparative Example 2 using carbon black, the initial room temperature resistance was large, the resistance change rate was small, the room temperature resistance after heating and cooling was remarkably increased, and the resistance rise was also poor. Also spherical N
The sample of Comparative Example 3 using i had a small resistance change rate,
The resistance rise is also poor. In the sample of Comparative Example 4 using polyethylene oxide having a Mw of less than 2,000,000, the viscosity at the time of melting was too low, so that the dispersibility of the conductive particles was deteriorated. As a result, the room temperature resistance was high.

The sample of Comparative Example 5 using an ethylene / vinyl acetate copolymer, the sample of Comparative Example 6 using an ethylene / methacrylic acid copolymer, and the sample of Comparative Example 7 using an ethylene / ethyl acrylate copolymer were heated and cooled. The characteristics deteriorate later.

Example 4 A load test was repeated in which a direct current of 10 A and 2 V was applied to the sample of Example 1, which was operated by Joule heat, held for 10 seconds, and after applying the current for 30 seconds, the current was passed again. went. A temperature-resistance curve was measured every predetermined number of loads.

As a result, the initial room temperature resistance before the load test was 0.006 Ω, the maximum resistance was 6 × 10 7 Ω, and the resistance change rate was 10.0 digits. 0.008Ω, maximum resistance value is 2.5 × 107
The change in Ω and resistance was 9.5 digits, and the change in characteristics after the load test was slight. The initial rise of the resistance before the load test was 5.2% as in the case of Example 1, and a sharp rise was shown even after the load test.

Comparative Example 8 A sample using the polyvinylidene fluoride of Comparative Example 1 was subjected to a load test in the same manner as in Example 4.

As a result, the initial room temperature resistance before the load test was 0.05 Ω, the maximum resistance was 5 × 10 6 Ω, and the resistance change rate was 8.0 digits. The resistance was 8 Ω, the maximum resistance was 2.5 × 10 8 Ω, and the resistance change rate was 7.5 digits. A remarkable increase in room temperature resistance after the load test was observed. The initial rise of the resistance before the load test was 40.1% as in Comparative Example 1.
There was no significant change after the load test,
The sharpness of the rise was poor.

[0060]

According to the present invention, the device operates at a temperature of 60 to 70.degree. C., which poses little danger to the human body, has a low initial room temperature resistance, has a large resistance change rate, and has a resistance rise at a temperature higher than the transition temperature. It is steep and stable characteristics can be obtained even by repeated operations.

[Brief description of the drawings]

FIG. 1 is a drawing substitute photograph showing a particle structure, and is a scanning electron microscope photograph of a filamentary nickel powder.

FIG. 2 is a cross-sectional view of a sample of an organic positive temperature coefficient thermistor.

FIG. 3 is a temperature-resistance curve of the sample of Example 1.

FIG. 4 is an explanatory diagram showing a transition temperature and a method of calculating a resistance value at the transition temperature in obtaining a degree of rise of resistance from a temperature-resistance curve.

FIG. 5 is a temperature-resistance curve of the sample of Example 1 after heating and cooling 10 times in a cycle test.

FIG. 6 is a temperature-resistance curve of a sample of Example 2.

FIG. 7 is a temperature-resistance curve of a sample of Example 3.

FIG. 8 is a temperature-resistance curve of a sample of Comparative Example 1.

FIG. 9 is a temperature-resistance curve of a sample of Comparative Example 2.

FIG. 10 is a temperature-resistance curve of a sample of Comparative Example 3.

FIG. 11 is a temperature-resistance curve of a sample of Comparative Example 4.

[Explanation of symbols]

 11 Electrode 12 Kneaded molded sheet of crystalline polymer and conductive particles

Claims (5)

[Claims] 1. An organic positive temperature coefficient thermistor obtained by kneading polyethylene oxide having a weight average molecular weight of 2,000,000 or more and conductive particles having spike-shaped projections. 2. The organic positive temperature coefficient thermistor according to claim 1, wherein said conductive particles having spike-like projections are continuous in a chain. 3. The organic positive temperature coefficient thermistor according to claim 1, wherein said polyethylene oxide has a weight average molecular weight of 3,000,000 to 6,000,000. 4. The organic positive temperature coefficient thermistor according to claim 2, wherein said conductive particles having chain-like spike-shaped projections have an average particle size of 0.1 μm or more. 5. The organic positive temperature coefficient thermistor according to claim 4, wherein said average particle diameter is 1.0 to 4.0 μm.