JPH08298201A - Ptc element and production thereof - Google Patents

Abstract

PURPOSE: To obtain a PTC element having extremely low resistivity at 20 deg.C but a high peak resistivity, i.e., the resistivity increases abruptly in a limited temperature range, along with a production method thereof. CONSTITUTION: The PTC element is produced by providing metal foil electrodes on the opposite sides of a conductive sheet composed of a matrix of crystalline polyolefin and a conductive filter. The PTC element has resistivity ρ20 of 1.8Ω.cm or less at 20 deg.C and a peak resistivity ρP of 2.0×10<6> Ω.cm. The difference [Ta ( deg.C)-Tb ( deg.C)] between the temperature Ta ( deg.C) where the resistivity is 10<6> times as high as that at 20 deg.C ρ20 and the temperature Tb ( deg.C) where the resistivity is 10 times as high as that at 20 deg.C ρ20 is 10 deg.C or less.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a PTC (Positive).
The present invention relates to a temperature coefficient (positive temperature coefficient) element and a manufacturing method thereof.

[0002]

2. Description of the Related Art Barium titanate-based PTC elements have been most well known conventionally. However, recently, a PTC element using a conductive sheet in which conductive particles are uniformly dispersed in a polymer substance has been developed because it is small and can reduce resistance. For example, JP-A-61-218117 and JP-A-62-167358.
Japanese Patent Publication, Japanese Patent Publication No. 64-3322, Japanese Patent Publication No. 4-28
No. 743 discloses a PTC composed of a crystalline polymer such as polyolefin and a conductive sheet made of conductive particles such as carbon black and conductive nickel particles and an electrode.
A device is disclosed.

[0003]

In any case, the PTC element disclosed in the above publication shows a low specific resistance at room temperature and a high specific resistance at the peak time. However, since the temperature range that changes from a low specific resistance value to a high specific resistance value is wide, the element shifts to a high resistance state with a relatively low current value when used as an overcurrent protection element. Therefore, it is difficult to apply to a circuit in which a large current flows, and there is a drawback that the application range is narrow.

Therefore, an object of the present invention is to provide a PTC element having a very low specific resistance at 20 ° C., a large specific resistance at the peak, and a sharp increase in the specific resistance in a narrow temperature range, and a manufacturing method thereof. To provide.

[0005]

Means for Solving the Problems As a result of intensive studies for solving the above problems, the present inventors have found that the temperature T _a (° C.) at which the specific resistance is 10 ⁶ times the specific resistance ρ ₂₀ at 20 ° C. Temperature T at which the resistivity becomes 10 times the resistivity ρ ₂₀ at 20 ° C
_b (° C.) the difference between _{[T a (℃) -T b (} ℃) ] is a very important factor as PTC element that can be a large current, the PTC element this value is 10 ° C. or less The inventors have found that the above objects can be achieved and have reached the present invention.

That is, the gist of the present invention is a PTC element in which electrodes of metal foil are provided on both surfaces of a conductive sheet composed of a crystalline polyolefin matrix and a conductive filler, and having a specific resistance ρ _{20 at} 20 ° C. 1.8 Ω · cm
And the peak specific resistance ρ _P is 2.0 × 10 ⁶ Ω
・ It is more than cm and the specific resistance is ρ _{20 at} 20 ℃.
The difference between the 10 becomes ⁶ times the temperature T _a (° C.) and temperature resistivity is the ratio 10 times the resistance [rho ₂₀ at 20 ℃ T _b (℃) _{[T a (℃) -T b (} ℃) ] Is 10 ° C. or less, and such a PTC element was obtained by mixing a crystalline polyolefin and a conductive filler and molding the mixture to form a conductive sheet. Thermocompression bonding the metal foil to both sides of the conductive sheet, after which,
It can be produced by repeating heating / cooling treatment in which the crystalline polyolefin is heated to a temperature of (melting point-5 ° C) or higher and then cooled to a temperature lower than (melting point-5 ° C).

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.
Specific resistance ρ ₂₀ at 20 ° C. of the PTC element of the present invention
Is 1.8 Ω · cm or less, preferably 1.7 Ω · cm or less, and more preferably 1.5 Ω · cm or less. The smaller ρ ₂₀ is, the more preferable, but the practical lower limit is 0.1 Ω · cm. When ρ ₂₀ is larger than 1.8 Ω · cm, it becomes difficult to manufacture a small PTC element having low resistance.

The peak specific resistance ρ _P of the PTC element of the present invention is 2.0 × 10 ⁶ Ω · cm or more, preferably 5.0 × 10 ⁶ Ω · cm or more, more preferably 1.0 ×.
It is 10 ⁷ Ω · cm or more. The larger ρ _P is, the more preferable, but the practical upper limit is 1 × 10 ¹⁰ Ω · cm. When ρ _P is less than 2.0 × 10 ⁶ Ω · cm, it is difficult to use it in a high voltage circuit.

In the present invention, the temperature T _a (° C.) at which the resistivity becomes 10 ⁶ times the resistivity ρ ₂₀ at 20 ° C. and the temperature T at which the resistivity becomes 10 times the resistivity ρ ₂₀ at 20 ° C.
_b the difference between (℃) [T _a (℃) -T _b (℃)] is 10 ° C. or less. This temperature difference is preferably 8 ° C. or lower, more preferably 6 ° C. or lower. The smaller this temperature difference is, the more preferable, but the practical lower limit is 1 ° C. [T _a (° C) -T _b (° C)]
Is higher than 10 ° C., it becomes difficult to apply to a circuit in which a large current flows.

The specific resistance of the PTC element in the present invention is P
It is calculated using the resistance value of the TC element and the following equation (1). ρ = R · A / t (1) ρ; specific resistance of PTC element (Ω · cm) R; resistance value of PTC element (Ω) A; electrode area of PTC element (cm ² ) t; between electrodes of PTC element Therefore, the average process length (thickness including electrodes) (cm) at which the current flows is, therefore, the specific resistance ρ _{20 at} 20 ° C is ₂₀ % of that of the PTC element.
It can be obtained from the resistance value at ° C using the formula (1). Also,
The PTC element is externally heated to increase the temperature from 20 ° C. at 1 ° C./min, and the specific resistance value with respect to temperature is obtained from the measured resistance value and the equation (1). From this result, ρ _P , T _a ,
T _b is easily obtained.

The PTC element in the present invention is one in which metal foils are provided on both sides of a conductive sheet composed of a crystalline polyolefin matrix and a conductive filler.
Here, the crystalline polyolefin is analyzed by differential scanning calorimetry (D
SC) at least 10%, preferably 3
It has a crystallinity of 0% or more, more preferably 50% or more, and as such crystalline polyolefin, low density polyethylene, medium density polyethylene, high density polyethylene,
Polyolefins such as polypropylene and copolymers of ethylene and propylene may be mentioned, and one or more crystalline polyolefins thereof may be used, with polyethylene being preferred and high density polyethylene being more preferred.

The melt flow rate of polyethylene used in the present invention is preferably 0.01 to 15, more preferably 0.1 to 12, and even more preferably 1 to 8. If the melt flow rate exceeds 15, [T _a (° C) -T
_b (° C.)] becomes larger than 10 ° C., and it becomes difficult to apply it to a circuit in which a large current flows. When the melt flow rate is less than 0.01, the moldability of the conductive sheet is likely to decrease.

In the present invention, the melt flow rate means
It is the weight (g) of a polyolefin extruded within a certain period of time under a specific test condition, and is specifically measured by the method specified in JIS K7210. In the case of polyethylene in the present invention,
JIS K 7210 test conditions (test temperature 190 ° C,
Test load 2.16 Kgf [21.18 N]), in the case of polypropylene, JIS K 7210 test conditions (test temperature 230 ° C., test load 2.16 Kgf [21.18]).
N]) was adopted and measured.

The shape of the crystalline polyolefin used for producing the conductive sheet is not particularly limited, such as a particle shape or a pellet shape.

As the conductive filler that constitutes the conductive sheet together with the crystalline polyolefin, a metal filler such as Ni or Cu, carbon black such as graphite or acetylene black, or a thermosetting resin such as furfuryl alcohol resin or phenol resin is used. A carbon-based conductive filler such as glassy carbon obtained by carbonizing in an inert atmosphere (including vacuum) can be used. Among these, the conductive filler made of glassy carbon is preferable. Above all, spherical phenol resin is used in an inert atmosphere at 100%.
Granular glassy carbon obtained by firing at a temperature of 0 ° C. or higher is preferable. The method for producing the spherical phenol resin is disclosed in JP-B-5-72924, and a commercial product can be obtained. The average particle size of the granular glassy carbon used in the present invention is preferably 1 to 50 μm, and 5 to 20 μm.
More preferred is m. When the average particle size is less than 1 μm, the specific resistance ρ _P at the peak tends to be small, while when it is more than 50 μm, sparks are easily generated between the particles. In the present invention, the average particle size means the average particle size of 100 particles or more of 100 or more granular glassy carbons observed under a microscope of 200 times magnification.

A metal foil is used as the electrode. As the metal foil, an electrolytic foil of copper, aluminum, nickel or the like, or
Although a rolled foil can be used, it is preferable to use a nickel foil whose resistance hardly increases due to oxidation during thermocompression bonding. Further, a metal foil that has been subjected to a surface roughening treatment can also be used. Although gold, silver, etc. can be used, the cost is high.

The mixing ratio of the crystalline polyolefin to the conductive filler is preferably 20:80 to 80:20 by weight, more preferably 30:70 to 70:30. If the crystalline polyolefin is less than 20% by weight, the strength of the conductive sheet tends to be weak, and if it exceeds 80% by weight, it may be difficult to obtain sufficient conductivity. In addition, the conductive sheet contains alumina, aluminum hydroxide, calcium carbonate in an amount of 10% by weight or less in a range that does not impair the effects of the present invention.
Inorganic fillers such as magnesium silicate, talc, and glass beads, and antioxidants may be added.

In the PTC element of the present invention, a predetermined amount of crystalline polyolefin and a conductive filler are mixed by a method such as dry blending or melt kneading, and then the mixture is molded to obtain a metal on both surfaces of the obtained conductive sheet. After thermocompressing the foil, it is heated to a temperature of (melting point-5 ° C) or higher of the crystalline polyolefin,
Then, it can be produced by repeatedly performing heating / cooling treatment for cooling to a temperature lower than (melting point −5 ° C.). In the present invention, the melting point is the differential scanning calorimetric analysis (DS
It is the temperature at which the peak of the curve formed by C) appears. When two or more types of crystalline polyolefins are used as the matrix, the melting point is taken from the minimum of peaks. As an example of the production method, the case where polyethylene and granular glassy carbon are mixed by melt-kneading, the mixture is heat-pressed to obtain a conductive sheet, and a metal foil is thermocompression-bonded and then heat-treated is shown. It should be noted that the same production can be performed when other crystalline polyolefin and a conductive filler are used.

When polyethylene and granular glassy carbon are mixed, a predetermined amount of polyethylene and granular glassy carbon is put into a melt kneader such as a plast mill, kneader, roll mill, Banbury mixer, twin-screw extruder or the like and mixed. The mixing temperature at this time is preferably (melting point) to (melting point + 150 ° C.) of polyethylene, and (melting point +1
0 ° C.) to (melting point + 100 ° C.) is more preferable. If the temperature is lower than the melting point, uniform mixing tends to be impossible,
Polyethylene tends to deteriorate at a temperature higher than (melting point + 150 ° C.). The mixing time is preferably 1 to 600 minutes, more preferably 3 to 180 minutes. If the mixing time is shorter than 1 minute, uniform mixing tends to be impossible.
If it is longer than 0 minutes, it is uneconomical.

The mixture obtained by melt-kneading as described above is then molded under heat and pressure. The heating temperature at this time is preferably (melting point) to (melting point + 100 ° C.) of polyethylene, and more preferably (melting point + 5 ° C.) to (melting point + 80 ° C.). At a temperature lower than (melting point), sufficient strength tends not to be obtained, and at a temperature higher than (melting point + 100 ° C.), the polyethylene melted by heat melting has sufficient conductivity to cover the surface of the granular glassy carbon. It tends to be difficult.

The molding pressure is preferably ² to 200 Kg / cm ² , and more preferably 5 to 100 Kg / cm ² . Molding time is preferably 10 to 3600 seconds, 20 to 800
Seconds are more preferred. If the pressure is less than ² Kg / cm ² or if the molding time is shorter than 10 seconds, it tends to be difficult to obtain sufficient strength. Also, the pressure is 200K
If it exceeds g / cm ² or if the molding time exceeds 3600 seconds, it is uneconomical.

Then, the obtained conductive sheet and the metal foil are thermocompression bonded. As the thermocompression bonding conditions, the heating temperature is preferably (melting point) to (melting point + 100 ° C.) of polyethylene,
(Melting point + 5 ° C) to (melting point + 80 ° C) is more preferable. When the temperature is lower than the melting point, the adhesive strength between the metal foil and the conductive sheet is not sufficient, and when the temperature is higher than (melting point + 100 ° C.), the melted polyethylene covers the surface of the glassy carbon, so that the resistance value of the element is low. To rise. The pressure is 2
200 Kg / cm ² is preferable, 5 to 100 Kg / cm
² is more preferable. The pressure bonding time is preferably 10 to 3600 seconds, more preferably 20 to 800 seconds. Pressure is 2
When it is less than Kg / cm ² or when the pressure bonding time is shorter than 10 seconds, the adhesive strength between the metal foil and the conductive sheet is insufficient. In addition, it is uneconomical when the pressure exceeds 200 Kg / cm ² or when the pressure bonding time exceeds 3600 seconds.

After the metal foil is thermocompression-bonded to the conductive sheet as described above, it is preferable to further perform heat treatment in order to obtain better adhesion and stable PTC characteristics. The heat treatment temperature at this time is from (melting point) to (melting point + 10) of polyethylene.
0 ° C.) is preferable, (melting point) to (melting point + 60 ° C.) is more preferable, and (melting point) to (melting point + 40 ° C.) is further preferable. The heat treatment time is preferably 0.1 to 20 hours, more preferably 0.2 to 10 hours. If the heat treatment temperature and the heat treatment time are outside the above ranges, the PTC characteristics tend to be unstable. The sheet thus heat-treated is cut into a desired size, and then heated to a temperature not lower than the melting point of the polyolefin (−5 ° C.) in order to reduce the resistance value.
Then, heating / cooling treatment for cooling to a temperature lower than (melting point −5 ° C.) is repeatedly performed. The heating temperature is preferably (melting point-2 ° C) to (melting point + 50 ° C), more preferably melting point to (melting point + 20 ° C). The heating time is preferably 1 second to 1 hour, more preferably 5 seconds to 30 minutes, and 10 seconds to 10 minutes.
Minutes are more preferred. If the heating time is outside the above range, the resistance value tends not to be sufficiently reduced. The cooling temperature is preferably (melting point −20 ° C.) or lower, and (melting point −4)
0 ° C.) or less is more preferable. The cooling time is not particularly limited. The number of repetitions of the heating / cooling process is 3
It is preferably not less than 5 times, more preferably not less than 5 times, still more preferably not less than 10 times. When the number of repetitions is less than 3, the resistance value tends not to be sufficiently reduced. The PTC element of the present invention is manufactured as described above. And P
The size and thickness of the TC element differ depending on the circuit of the device used or the load voltage or load current, but generally the electrode area is 0.05 cm ^{2 to} 10 cm ² , and the thickness is 0.1 m.
It is used in the range of m to 5 mm. Further, the shape is also used in various shapes such as a disk shape, a square shape, and a donut shape. INDUSTRIAL APPLICABILITY The PTC element of the present invention can be used for semiconductor memory, CPU, etc.
It can be suitably used as an overcurrent protection element for protecting (central processing element) and the like from overcurrent.

[0024]

EXAMPLES Next, the present invention will be described more specifically with reference to examples. Example 1 45% by weight of a high-density polyethylene powder having a melt flow rate of 2.5 (melting point: 135 ° C., manufactured by Dow), a spherical phenol resin was fired at 1900 ° C., and a granular glassy carbon (GCP-30H) having an average particle size of 15 μm. 55% by weight was placed in a plastomill (R-60 type, manufactured by Toyo Seiki Seisakusho Co., Ltd.) and melt-kneaded at a kneading temperature of 150 ° C. for 10 minutes. This kneaded product was hot-pressed at a molding temperature of 140 ° C. and a molding pressure of 10 Kg / cm ² for 5 minutes and then cooled under pressure to obtain a conductive sheet having a thickness of 0.45 mm.
The conductive sheet obtained in this manner was replaced with a nickel foil (E
Ni-T, thickness 25 μm, manufactured by Fukuda Metal Foil & Powder Co., Ltd.), and hot-pressed at 140 ° C. and 10 Kg / cm ² for 3 minutes, and then cooled under pressure. Further, a heat treatment was performed at 150 ° C. for 1 hour to obtain a 0.5 mm-thick sheet in which a metal foil was thermocompression-bonded to both surfaces of the conductive sheet. After punching a disk with a diameter of 15 mm from this metal foil thermocompression-bonding conductive sheet,
The heating / cooling process of heating at a temperature of 135 ° C. for 20 seconds and then at a temperature of 20 ° C. for 5 minutes is performed 20 times.
A TC element was produced.

When the resistance value (R ₂₀ ) of this PTC element at 20 ° C. was examined, it was 0.039Ω. If ρ ₂₀ is calculated from this resistance value according to equation (1), 1.38Ω ・
It was cm. This PTC element was externally heated and heated from 20 ° C. at a rate of 1 ° C./minute, and the measured resistance value was converted using the formula (1) to obtain the value of the specific resistance with respect to the temperature. As a result from the temperature indicating the ρ _P (Tρ _P) is the 130 ° C., [rho _P is ^{2.4 × 10 7 Ω · cm,} T a (℃) 129
℃, T _b (℃) was found to be 124 ℃, [ _Ta
(° C) -T _b (° C)] was 5 ° C. Table 1 shows these physical property values.

Example 2 40% by weight of high-density polyethylene powder having a melt flow rate of 6.0 (Flowsen M, melting point 127 ° C., manufactured by Sumitomo Seika Chemicals, Ltd.), spherical phenol resin was fired at 1900 ° C. with an average particle size of 15 μm. Certain granular glassy carbon (GCP-
30H, manufactured by Unitika Ltd. 60% by weight on a table kneader (P
BV-01 type, manufactured by Irie Shosha Co., Ltd., and kneading temperature 1
The mixture was melt-kneaded at 80 ° C. for 20 minutes. The kneaded product was hot-pressed at a molding temperature of 140 ° C. and a molding pressure of 10 kg / cm ² for 5 minutes, and then cooled under pressure to obtain a conductive sheet having a thickness of 0.45 mm. The conductive sheet thus obtained was sandwiched between nickel foils (ENi-T, thickness 25 μm, manufactured by Fukuda Metal Foil & Powder Co., Ltd.), hot pressed at 140 ° C. and 10 Kg / cm ² for 3 minutes, and then applied. Cooled under pressure. Further, heat treatment was performed at 150 ° C. for 1 hour to obtain a sheet having a thickness of 0.49 mm, in which metal foils were thermocompression bonded to both surfaces of the conductive sheet. 15mm diameter from this metal foil thermo-compression conductive sheet
After punching out the disc, heat it to 127 ° C for 20 seconds and then hold it at 20 ° C for 5 minutes.
The PTC element was manufactured by performing the cooling treatment 20 times. This PT
When the resistance value of the C element at 20 ° C. was examined, it was 0.04.
It was 6Ω. When ρ ₂₀ was calculated from this resistance value according to the equation (1), it was 1.66 Ω · cm. And Example 1
Table 1 shows the results of examining the physical properties in the same manner as in.

Example 3 Pelletized high-density polyethylene having a melt flow rate of 2.4 (Sholex 5020, melting point 130 ° C., Showa Denko KK) 45% by weight, spherical phenol resin 1900
55% by weight of granular glassy carbon (GCP-30H, manufactured by Unitika Ltd.) having an average particle size of 15 μm, which was calcined at 0 ° C., was put into a table kneader (PBV-01 type, manufactured by Irie Shosha Co., Ltd.), and kneading temperature was 40 ° C. at 40 ° C. Melt kneading for a minute. This kneaded product has a molding temperature of 160 ° C. and a molding pressure of 10 kg / cm.
After hot pressing at ² for 5 minutes, it was cooled under pressure to obtain a conductive sheet having a thickness of 0.46 mm. The conductive sheet thus obtained was applied to a nickel foil (ENi-T, thickness 2
5 μm, Fukuda Metal Foil & Powder Co., Ltd.), 160 ° C, 1
After hot pressing at 0 Kg / cm ² for 3 minutes, it was cooled under pressure. In addition, heat treatment at 150 ℃ for 1 hour,
Thickness 0.49 with metal foil thermocompression bonded to both sides of conductive sheet
A sheet of mm was obtained. After punching a disk with a diameter of 15 mm from this metal foil thermocompression-bonded conductive sheet, it is heated at 130 ° C. for 20 seconds, and then kept at 20 ° C. for 5 minutes to perform heating / cooling treatment 20 times to obtain a PTC element. It was made. When the resistance value of this PTC element at 20 ° C. was examined, it was 0.043Ω. When ρ ₂₀ was calculated from this resistance value according to the equation (1), it was 1.55 Ω · cm. Then, the results of examining the physical property values in the same manner as in Example 1 are shown in Table 1.

Example 4 42% by weight of low-density polyethylene powder having a melt flow rate of 1.5 (Flowsen UF-1.5, melting point 107 ° C., Sumitomo Seika Chemicals Ltd.), spherical phenol resin baked at 1900 ° C. average 58% by weight of granular glassy carbon (GCP-30H, manufactured by Unitika Ltd.) having a particle diameter of 15 μm was put into a plastomill (R-60 type, manufactured by Toyo Seiki Seisakusho), and melt-kneaded at a kneading temperature of 150 ° C. for 20 minutes. This kneaded product was hot-pressed at a molding temperature of 120 ° C. and a molding pressure of 10 Kg / cm ² for 5 minutes and then cooled under pressure to a thickness of 0.
A 45 mm conductive sheet was obtained. The conductive sheet thus obtained was applied to a nickel foil (ENi-T, thickness 25 μm).
m, manufactured by Fukuda Metal Foil & Powder Co., Ltd.), 120 ° C, 10K
After hot pressing at g / cm ² for 3 minutes, it was cooled under pressure. Furthermore, heat treatment was performed at 120 ° C for 1 hour, and a metal foil was thermocompression-bonded to both surfaces of the conductive sheet, and the thickness was 0.48 mm.
Got a sheet of. After punching a disc with a diameter of 15 mm from this metal foil thermocompression-bonded conductive sheet, the temperature was increased to 107 ° C.
A heating / cooling treatment of heating for 0 seconds and then holding at a temperature of 20 ° C. for 5 minutes was performed 20 times to manufacture a PTC element. When the resistance value of this PTC element at 20 ° C. was examined, it was 0.042 Ω. When ρ ₂₀ was calculated from this resistance value according to the equation (1), it was 1.55 Ω · cm. Then, the results of examining the physical property values in the same manner as in Example 1 are shown in Table 1.

Example 5 Polypropylene powder having a melt flow rate of 6.4 (P
N640, melting point 161 ° C, manufactured by Tokuyama) 45% by weight,
Average particle size of spherical spherical resin fired at 1900 ℃ 1
Granular glassy carbon (GCP-30
H, manufactured by Unitika Ltd.) 55% by weight on a table kneader (PBV
-01 type, manufactured by Irie Shosha Co., Ltd., and kneading temperature 220
Melt kneading was carried out at 0 ° C for 20 minutes. This kneaded product is molded at a molding temperature of
After hot pressing at 0 ° C. and a molding pressure of 10 kg / cm ² for 5 minutes, it was cooled under pressure to obtain a conductive sheet having a thickness of 0.44 mm. The conductive sheet thus obtained was sandwiched between nickel foils (ENi-T, thickness 25 μm, manufactured by Fukuda Metal Foil & Powder Co., Ltd.), and heat-pressed at 180 ° C. and 10 Kg / cm ² for 3 minutes, and then applied. Cooled under pressure. In addition, 18
Heat treatment was performed at 0 ° C. for 1 hour to obtain a 0.48 mm-thick sheet in which metal foils were thermocompression-bonded to both surfaces of the conductive sheet. After punching a disk with a diameter of 15 mm from this metal foil thermocompression-bonded conductive sheet, the PTC element is heated and cooled 20 times by heating it to a temperature of 161 ° C. for 20 seconds and then holding it at a temperature of 20 ° C. for 5 minutes to obtain a PTC element. It was made. When the resistance value of this PTC element at 20 ° C. was examined, it was 0.044Ω. When ρ ₂₀ was calculated from this resistance value according to the equation (1), it was 1.62 Ω · cm. Then, the results of examining the physical property values in the same manner as in Example 1 are shown in Table 1.

Comparative Example 1 42% by weight of high-density polyethylene powder having a melt flow rate = 23 (Chemilets 1210, melting point 131 ° C., manufactured by Maruzen Polymer Co., Ltd.), spherical phenolic resin was fired at 1900 ° C., and a granular glassy having an average particle size of 15 μm. 58% by weight of carbon (GCP-30H, manufactured by Unitika Ltd.) was put into a table kneader (PBV-01 type, manufactured by Irie Shosha Co., Ltd.),
Melt kneading was performed at a kneading temperature of 150 ° C. for 20 minutes. The kneaded product was hot-pressed at a molding temperature of 140 ° C. and a molding pressure of 10 Kg / cm ² for 5 minutes and then cooled under pressure to a thickness of 0.45.
A mm conductive sheet was obtained. The conductive sheet obtained in this manner was applied to a nickel foil (ENi-T, thickness 25 μm,
Fukuda Metal Foil & Powder Industry Co., Ltd.), 140 ℃, 10Kg /
After hot pressing at 3 cm ² for 3 minutes, it was cooled under pressure. Further, heat treatment was performed at 150 ° C. for 1 hour to obtain a sheet having a thickness of 0.49 mm, in which metal foils were thermocompression bonded to both surfaces of the conductive sheet. A disk having a diameter of 15 mm was punched out from this metal foil thermocompression-bonding conductive sheet to produce a PTC element. When the resistance value of this PTC element at 20 ° C. was examined, it was found to be 0.
It was 48Ω. When ρ ₂₀ was calculated from this resistance value according to the equation (1), it was 17.3 Ω · cm. Then, the results of examining the physical property values in the same manner as in Example 1 are shown in Table 1.

[0031]

[Table 1]

As can be seen from the table, the PTC element of the present invention exhibits an extremely low specific resistance value at 20 ° C., a large specific resistance value at the peak, and the resistance rapidly increases in a narrow temperature range. I understand.

[0033]

The PTC element of the present invention has a very low specific resistance at 20 ° C., a large specific resistance at the peak, and a rapid increase in the resistance in a narrow temperature range. Therefore, it can be applied to a circuit in which a large current flows. , The scope of application becomes wider. Therefore,
It can be suitably used for an electric device through which a large current flows. Further, such a PTC element can be easily manufactured by the manufacturing method of the present invention.

Front page continued (72) Inventor Yoshiaki Iwaya 23 Uji Kozakura, Uji City, Kyoto Prefecture Unitika Ltd. Central Research Laboratories (72) Inventor Yoshiaki Echigo 23 Uji Kozakura, Uji City Kyoto Prefecture Unitika Institute Central Research Laboratories

Claims (8)

[Claims] 1. A PTC element in which electrodes of a metal foil are provided on both surfaces of a conductive sheet composed of a crystalline polyolefin matrix and a conductive filler, and having a specific resistance ρ _{20 at} 20 ° C. of 1.8 Ω · cm or less. The temperature T _a at which the specific resistance ρ _P at the peak is 2.0 × 10 ⁶ Ω · cm or more and the specific resistance is 10 ⁶ times the specific resistance ρ ₂₀ at 20 ° C.
(° C) and the temperature T _b (° C.) at which the specific resistance is 10 times the specific resistance ρ ₂₀ at 20 ° C. [T _a (° C.) − T _b (° C.)]
Is 10 ° C. or less, a PTC element. 2. The PTC element according to claim 1, wherein the crystalline polyolefin is polyethylene. 3. The conductive filler has an average particle size of 1 to 50 μm.
The PTC element according to claim 1, wherein the PTC element is the granular glassy carbon. 4. The specific resistance ρ ₂₀ is 1 at a specific resistance of 20 ° C.
0 difference between ⁶ times becomes the temperature T _a (° C.) and temperature resistivity is the ratio 10 times the resistance [rho ₂₀ at 20 ℃ T _b (℃) [T _a
(℃) -T _b (℃)] is PTC element according to claim 1, characterized in that the 8 ° C. to 1 ° C.. 5. A crystalline polyolefin and a conductive filler are mixed and the mixture is molded to form a conductive sheet,
A metal foil is thermocompression-bonded to both sides of the obtained conductive sheet, followed by heating to a temperature of (melting point-5 ° C) or higher of the crystalline polyolefin, and then cooling to a temperature lower than (melting point-5 ° C). A method for manufacturing a PTC element, which is characterized by repeatedly performing cooling treatment. 6. The method for producing a PTC element according to claim 5, wherein the crystalline polyolefin is polyethylene. 7. The method for producing a PTC element according to claim 6, wherein the polyethylene has a melt flow rate of 0.01 to 15. 8. The conductive filler has an average particle size of 1 to 50 μm.
6. The method for manufacturing a PTC element according to claim 5, wherein the granular glassy carbon is used.