JPH1197208A - Ptc element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a PTC element, wherein it represents a very low specific resistance at 20 deg.C while being high at peak time, the specific resistance abruptly rises within a narrow temperature range, and withstand voltage is high. SOLUTION: In a PTC element, wherein a metal plate electrode is provided on either surface of a conductive sheet comprising crystalline polyorefine matrix and conductive filler, the conductive filler is granular glassy carbon of average particle size of 10 μm or less, and the PTC element has following characteristics: (1) a thickness including an electrode is 0.35 mm or less, (2) a specific resistance ρ20 at 20 deg.C is 1.8 Ω.cm or less, while that at peak time is 2.0×10<6> Ω.cm or above, (3) [Ta( deg.C)-Tb ( deg.C)] is 10 deg.C or less, where Ta ( deg.C) is such temperature at which specific resistance is 10<6> times of specific resistance ρ20 at 20 deg.C and Tb ( deg.C) is a temperature at which specific resistance is 10 times that of the specific resistance ρ20 at 20 deg.C, and (4) a withstand voltage is 50 V or higher.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a PTC (Positiv
e, Temperature, Coefficient, positive temperature coefficient).

[0002]

2. Description of the Related Art As a PTC element, a barium titanate-based element has hitherto been best known. However, recently, a PTC element using a conductive sheet in which conductive particles are uniformly dispersed in a polymer substance has been developed because of its small size and low resistance. For example, JP-A-61
JP-A-218117, JP-A-62-167358, JP-A-9-35906, JP-A-9-6941
No. 6, Japanese Patent Publication No. 64-3322, Japanese Patent Publication No. 4-2
No. 8743 discloses a PTC element composed of a polyolefin, a crystalline polymer such as polyvinylidene fluoride, and a conductive sheet and an electrode made of conductive particles such as carbon black and conductive nickel particles. In any case, the PTC element disclosed in the above publication is
It shows low specific resistance at room temperature and high specific resistance at the peak. However, since the temperature range from a low specific resistance value to a high specific resistance value is wide, when used as an overcurrent protection element, the element transitions to a high resistance state at a relatively low current value. Therefore, it is difficult to apply the present invention to a circuit through which a large current flows, and has a drawback that the range of use is narrow.

[0003]

SUMMARY OF THE INVENTION
As a TC element, the present inventors have disclosed in JP-A-8-298201.
In the publication, the specific resistance ρ _{20 at} 20 ° C. is 1.8Ω ·
cm or less, and the peak specific resistance ρ _P is 2.0 × 10
Is a ⁶ Omega · cm or more, the specific resistance becomes 10 ⁶ times the electrical resistivity [rho ₂₀ at 20 ° C. temperature T _a becomes 10 times the electrical resistivity [rho ₂₀ at (℃) and 20 ° C. temperature T _b (℃) Difference [ _Ta
(° C.) − T _b (° C.)] is 10 ° C. or less. Such a PTC element has a very low specific resistance at 20 ° C., a high specific resistance at the peak, and a sharp increase in the specific resistance in a narrow temperature range, so that it can be suitably used in a circuit in which a large current flows.

However, the PTC element disclosed in the above publication has a problem that it is difficult to apply the PTC element to a circuit that requires a high voltage when the PTC element is miniaturized.

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 a peak, and a sharp increase in specific resistance in a narrow temperature range, and having a withstand voltage. It is to provide a high PTC element.

[0006]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, the conductive filler is a granular glassy carbon having an average particle diameter of 10 μm or less and a specific resistance of 20 ° C. 10 ⁶ of the specific resistance ρ ₂₀ at
The difference between the doubled temperature T _a (° C.) and temperature resistivity is the ratio 10 times the resistance [rho ₂₀ at _{20 ℃ T b (℃) [} T
_a (° C.) − T _b (° C.)] is 10 ° C. or less, and it has been found that the above object can be achieved.

That is, the gist of the present invention is a PTC element in which electrodes of a metal plate are provided on both sides of a conductive sheet comprising a matrix of a crystalline polyolefin and a conductive filler, wherein the conductive filler has an average particle size. Is a granular glassy carbon of 10 μm or less, and the PTC element has (1) a thickness including an electrode of 0.35 mm or less, and (2) a specific resistance ρ _{20 at} 20 ° C. of 1.8 Ω · c.
m or less, and the peak specific resistance ρ _P is 2.0 × 10 ⁶
And the Omega · cm or more, (3) specific resistance temperature resistivity and resistivity [rho ₂₀ temperature T _a becomes 10 ⁶ times at 20 ° C. (° C.) is the ratio 10 times the resistance [rho ₂₀ at 20 ° C. T
_b (° C.) the difference between _{[T a (℃) -T b} (℃)] is not more 10 ° C. or less, a PTC element characterized in that it is (4) withstand voltage higher than 50V.

Hereinafter, the present invention will be described in detail. When a PTC element is used in an electronic device, the thinner the element, the better. Therefore, the thickness including the electrodes of the PTC element in the present invention is 0.35 mm or less, preferably 0.34 mm or less.
mm or less, and more preferably 0.33 mm or less.

The specific resistance ρ ₂₀ at 20 ° C. of the PTC element according to the present invention is 1.8 Ω · cm or less, preferably 1.
It is 5 Ω · cm or less, more preferably 1.3 Ω · cm or less. ρ preferably as ₂₀ it is small, the practical lower limit 0.
It is 1 Ω · cm. If [rho ₂₀ is greater than 1.8Ω · cm, the production of low resistance of the PTC element becomes difficult in compact.

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 × 10 ⁶ Ω · cm or more.
10 ⁷ Ω · cm or more. The larger the value of ρ _P , the better, 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 the circuit in a circuit that requires a high voltage.

[0011] In the present invention, temperature resistivity and resistivity is 10 ⁶ times the electrical resistivity [rho ₂₀ at 20 ° C. temperature T _a (° C.) is the ratio 10 times the resistance [rho ₂₀ at 20 ° C. T
The difference from _b (° C.) [T _a (° C.) − T _b (° C.)] is 10 ° C. or less. This temperature difference is preferably 8 ° C. or less, more preferably 6 ° C. or less. The smaller the temperature difference, the better, but the practical lower limit is 1 ° C. _{[T a (℃) -T b} (℃)]
Is larger than 10 ° C., it is difficult to apply to a circuit in which a large current flows.

The PTC element in the present invention is one in which electrodes of a metal plate are provided on both sides of a conductive sheet comprising a matrix of a crystalline polyolefin and a conductive filler. Here, the crystalline polyolefin has a crystallinity of at least 10%, preferably at least 30%, more preferably at least 50%, as measured by differential scanning calorimetry (DSC). Such crystalline polyolefins include low-density polyethylene, medium-density polyethylene, high-density polyethylene, polypropylene, polyolefins such as copolymers of ethylene and propylene, and one or more crystalline polyolefins can be used. Preferably, high density polyethylene is more preferred.

The melt flow rate of the polyolefin used in the present invention is preferably from 0.01 to 15, and from 0.1 to 12
Is more preferable, and 0.5 to 8 is further preferable. If the melt flow rate is more than 15, [T _a (℃) -T
_b (° C.)] tends to be higher than 10 ° C., which makes it difficult to apply to a circuit through which a large current flows. When the melt flow rate is less than 0.01, the moldability of the conductive sheet tends to decrease.

In the present invention, the melt flow rate is
It is the weight (g) of polyolefin extruded within a certain time under specific test conditions.
It is measured by the method specified in 7210. In the present invention, in the case of polyethylene, JIS K
7210 test conditions (test temperature 190 ° C., test load 2.16 kgf [21.18N]), and in the case of polypropylene, JIS K 7210 test conditions (test temperature 2
The measurement is performed at 30 ° C. under a test load of 2.16 kgf [21.18 N].

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

The conductive filler used in the present invention is a glassy carbon obtained by carbonizing a thermosetting resin such as a furfuryl alcohol resin or a phenol resin in an inert atmosphere or in a vacuum. Granular glassy carbon obtained by baking the resin at a temperature of 1000 ° C. or more in an inert atmosphere or vacuum is preferable. The method for producing the spherical phenol resin is described in Japanese Patent Publication 5-72.
No. 924, and a commercial product is also available. The average particle size of the granular glassy carbon used in the present invention is 10 μm or less, preferably 8 μm or less,
5 μm or less is more preferable. When the average particle size is larger than 10 μm, the withstand voltage tends to decrease. In the present invention, the average particle size refers to an average particle size of 100 or more particles of 100 or more granular glassy carbons observed with a microscope having a scale of 200 in the visual field and a magnification of 200 times.

As the electrode, a metal plate of copper, aluminum, nickel, stainless steel, iron, iron alloy, copper alloy or the like can be used. Among them, electrolytic foil or rolled foil of copper, aluminum, nickel, stainless steel or the like, It is preferable that these metal foils are plated with a different kind of metal, and it is preferable to use a nickel foil or a nickel-plated foil whose resistance hardly increases due to oxidation at the time of heat and pressure molding. Further, a metal foil subjected to a surface roughening treatment can also be used. Note that gold, silver and the like can be used, but the cost increases.

The mixing ratio of the crystalline polyolefin and the conductive filler is preferably from 20:80 to 80:20 by weight, more preferably from 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, sufficient conductivity may not be easily obtained. In addition, the conductive sheet has a range that does not impair the effects of the present invention (10% by weight or less).
With alumina, aluminum hydroxide, calcium carbonate,
Inorganic fillers such as magnesium silicate, talc and glass beads, and antioxidants can also be added.

The PTC element of the present invention is obtained by forming a metal plate electrode on both surfaces of a conductive sheet comprising a predetermined amount of crystalline polyolefin and a conductive filler by heating and pressing.
It can be manufactured by repeatedly heating and cooling the crystalline polyolefin to a temperature lower than the melting point of -5 ° C, and then cooling to a temperature lower than the heating temperature. In the present invention, melting point is defined as differential scanning calorimetry (DS).
This is the temperature at which the peak of the curve formed by C) appears. When two or more crystalline polyolefins are used as the matrix, the melting point is taken from the minimum of the peak.

Next, the method of manufacturing the PTC element of the present invention will be described in more detail. First, the crystalline polyolefin and the conductive filler are premixed using a melt-kneading device such as a kneader, a roll mill, a Banbury mixer, a plast mill, an extruder (single-screw, multi-screw), or a dry-blending device such as a Henschel mixer. Next, a conductive sheet is prepared by molding the mixture using a melt molding method such as heat and pressure molding, extrusion molding, or injection molding. In addition, a conductive sheet can be produced in one step by melt molding without going through the premixing step, but it is preferable to perform premixing in order to obtain a more uniform conductive sheet. The molding temperature during melt molding (including melt kneading) is from the melting point of the crystalline polyolefin to the melting point + 150 ° C.
Is preferable, and the melting point + 10 ° C to the melting point + 100 ° C is more preferable. If the temperature is lower than the melting point, uniform mixing tends to be impossible, and if the temperature is higher than the melting point + 150 ° C., the crystalline polyolefin tends to deteriorate.

Next, an electrode is formed by sandwiching the both surfaces of the obtained conductive sheet between metal plates by heating and pressing. The heating temperature at this time is from the melting point of the crystalline polyolefin to
Melting point + 150 ° C. is preferable, and melting point + 10 ° C. to melting point + 10
0 ° C. is more preferred. When the temperature is lower than the melting point, the bonding strength between the metal plate and the conductive sheet is not sufficient, and the melting point +1
At a temperature higher than 50 ° C., the crystalline polyolefin tends to deteriorate. The molding pressure is 1 to 3000 Kg / cm ²
Is preferable, and ² to 2000 kg / cm ² is more preferable. The molding time is preferably 1 to 3600 seconds,
1800 seconds is more preferred. When the pressure is less than 1 kg / cm ² or the molding time is shorter than 1 second, the adhesive strength between the metal plate and the conductive sheet is not sufficient. Also,
If the pressure exceeds 3000 Kg / cm ² or if the molding time exceeds 3600 seconds, it is uneconomical.

Next, the conductive sheet having the electrodes formed on both sides is heated to a temperature lower than the melting point of the crystalline polyolefin minus 5 ° C., and then repeatedly heated and cooled to a temperature lower than the heating temperature. Apply. This heating / cooling treatment is performed to reduce the resistance value of the obtained PTC element. The heating / cooling treatment is usually performed by cutting the conductive sheet into a desired size. The heating temperature in the heating / cooling process is a temperature lower than the melting point -5 ° C,
0 ° C to melting point -6 ° C is preferred, and melting point -30 ° C to melting point -1
0 ° C. is more preferred. The heating time is preferably 1 second to 1 hour, more preferably 5 seconds to 30 minutes, and 10 seconds to 1 hour.
0 minutes is more preferred. When the heating temperature and the heating time are in the ranges other than the above, the resistance value does not tend to decrease sufficiently. The cooling temperature is lower than the above-mentioned heating temperature, preferably a heating temperature of −20 ° C. or less, and a heating temperature of −30 ° C.
C. or lower is more preferable. The cooling time is not particularly limited. The number of repetitions of the heating / cooling treatment is preferably 3 or more, more preferably 5 or more, and even more preferably 10 or more. When the number of repetitions is less than 3, the resistance value tends to not sufficiently decrease.

If necessary, after forming a metal plate electrode on the conductive sheet, prior to the heating / cooling treatment,
Strengthening the adhesion between the conductive sheet and the electrode,
In order to obtain more stable PTC characteristics, heat treatment is preferably performed. The heat treatment temperature at this time is preferably from the melting point of the crystalline polyolefin to the melting point + 100 ° C., more preferably from the melting point to the melting point + 60 ° C., even more preferably from the melting point to the melting point + 40 ° C. The heat treatment time is preferably from 0.1 to 20 hours, more preferably from 0.2 to 10 hours.

Although the size of the PTC element differs depending on the circuit of the equipment used or overvoltage or overcurrent,
It is generally employed in a range of electrode area 0.05cm ² ~10cm ^2. In addition, various shapes such as a cylindrical shape, a square shape, and a donut shape are used. INDUSTRIAL APPLICABILITY The PTC element of the present invention is used for overcurrent protection for protecting a semiconductor memory, a CPU (central processing element) and the like from overcurrent in a small electronic device or the like powered by a battery such as a notebook personal computer, a mobile phone, and a small printer. It can be suitably used as an element.

[0025]

Next, the present invention will be described more specifically with reference to examples. The characteristics in the present invention were evaluated by the following methods.

(1) Specific Resistance The specific resistance was calculated from the resistance value of the PTC element using the following equation.

Ρ = R (A / t) ρ; specific resistance of PTC element (Ω · cm) R; resistance value of PTC element (Ω) A: electrode area of PTC element (cm ² ) t; electrode of PTC element Average stroke length where current flows between (thickness including electrodes) (cm)

Therefore, the specific resistance ρ ₂₀ at 20 ° C. can be obtained from the resistance value of the PTC element at 20 ° C. using the above equation. Further, the PTC element is externally heated to 20 ° C to 1 ° C.
After heating, the temperature was held at each temperature for about 3 minutes, and then the resistance was measured. From this resistance and the above equation, the value of the specific resistance with respect to the temperature was obtained. Ρ _P , T _a , and T _b can be easily obtained from these results. In the above resistance measurement, the resistance value up to 20,000Ω was measured using a milliohm high tester (HIOKI3220, manufactured by Hioki Electric Co., Ltd.). For the resistance value exceeding 20,000Ω, a digital ultra-high resistance / microammeter ( R8340, manufactured by Advantest Corporation).

(2) Withstand Voltage After a predetermined voltage is applied to any 50 PTC elements, the voltage value at which the percentage of elements that can maintain a high resistance state for 5 minutes without destruction becomes 100% is set to 100%. Withstand voltage. Variable DC constant potential / constant current power supply (PAD110-2)
Using a pen recorder (LR4210, manufactured by Yokogawa Electric Corporation), the change in current after application of a predetermined voltage was measured using a 0 L, Kikusui Electronics Corporation, and the state of high resistance was confirmed. In addition,
When the device sparked, the device was destructed.

Example 1 4.2 kg of high-density polyethylene powder having a melt flow rate of 0.95 (Chemilletz 1010, melting point: 132 ° C., manufactured by Maruzen Polymer Co., Ltd.), and a spherical phenol resin fired at 2000 ° C., having an average particle size of 3 μm. 5.8 kg of granular glassy carbon (GCP-10H, manufactured by Unitika) was dry-blended using a Henschel mixer. The mixture is formed into chips using a twin-screw extruder (forming temperature: 200 ° C.), and then a 0.35 mm-thick conductive film is formed from the chips using a twin-screw extruder (forming temperature: 200 ° C.) connected to a T-die. A functional sheet was produced. The conductive sheet thus obtained is sandwiched between nickel foils (ENi-T, thickness 25 μm, manufactured by Fukuda Metal Foil & Powder Co., Ltd.), and
After hot-pressing at 10 Kg / cm ² for 5 minutes, the mixture was cooled under pressure.

Further, a heat treatment was performed at 140 ° C. for 1 hour to obtain a 0.33 mm thick sheet in which metal foil electrodes were formed on both sides of the conductive sheet. From this sheet the diameter 15
After punching out a mm-sized disk, this disk was heated at 110 ° C. for 3 minutes, and then cooled at 50 ° C. for 10 minutes, and heated and cooled 50 times to produce a PTC element. When the resistance (R ₂₀ ) of this PTC element at 20 ° C. was examined, it was 22.4 mΩ. 1.20Omu · cm at calculating the [rho ₂₀ from the resistance value. The PTC element was externally heated and the temperature was raised from 20 ° C. every 1 ° C., and the specific resistance value with respect to the temperature was determined from the measured resistance value. From the result ρ
_The temperature (Tρ _P ) indicating _P is 131 ° C., and ρ _P is 2.
5 × a 10 ⁸ Ω · cm, T _a is 129 ° C., T _b is 1
Found to be _{23 ℃, [T a -T b} ] it became 6 ° C.. Subsequently, when the withstand voltage was measured, all the measured 50 samples maintained a high resistance state for 5 minutes when 68 V was applied.
When 69 V was applied, 8 out of 50 pieces broke within 5 minutes. Therefore, the withstand voltage was 68V. The physical properties are shown in the table.

Example 2 A crystalline polyolefin having a melt flow rate of 0.1 was used.
95 high-density polyethylene powder (Chemilets 1010,
Melting point 132 ° C, 4.7 kg of Maruzen Polymer Co., Ltd., spherical glass phenol resin as a conductive filler fired at 2000 ° C, granular glassy carbon (G
A PTC element was prepared in the same manner as in Example 1, except that 5.3 kg of CP-10H (manufactured by Unitika) was used.
Physical properties were measured. The results are shown in the table.

Example 3 The crystalline polyolefin has a melt flow rate of 6.
0 high-density polyethylene powder (Flosen M, melting point 12
4.7 Kg (7 ° C, manufactured by Sumitomo Seika Co., Ltd.), a granular glassy carbon (GCP-10) having an average particle size of 8 μm obtained by calcining a spherical phenol resin as a conductive filler at 2000 ° C.
H, manufactured by Unitika Ltd.) except that 5.3 kg was used.
A PTC element was produced in the same manner as in Example 1, and the physical properties were measured. The results are shown in the table.

Comparative Example The crystalline polyolefin had a melt flow rate of 6.
0 high-density polyethylene powder (Flosen M, melting point 12
4.7 kg of 7 ° C., manufactured by Sumitomo Seika Co., Ltd., a granular glassy carbon (GCP-30) having an average particle size of 15 μm obtained by calcining a spherical phenol resin as a conductive filler at 2000 ° C.
H, manufactured by Unitika Ltd.) except that 5.3 kg was used.
A PTC element was produced in the same manner as in Example 1, and the physical properties were measured. The results are shown in the table.

[0035]

[Table 1]

As is clear from Table 1, the PTC element of the present invention has a very low specific resistance at 20 ° C., a large peak specific resistance, a sharp increase in specific resistance in a narrow temperature range, and a high withstand voltage. Is high.

[0037]

The PTC element of the present invention has an extremely low specific resistance at 20 ° C., a high specific resistance at the peak, a sharp increase in the specific resistance in a narrow temperature range, and a high withstand voltage. . Therefore, it can be suitably used for a circuit in which a large current flows and a circuit in which a high voltage is applied.

Claims (1)

[Claims] 1. A PTC element comprising a conductive sheet comprising a crystalline polyolefin matrix and a conductive filler, wherein a metal plate electrode is provided on both sides of the conductive sheet, wherein the conductive filler has an average particle size of 10 μm or less. Carbon, the PTC element has (1) a thickness including an electrode of 0.35 mm or less, (2) a specific resistance ρ _{20 at} 20 ° C. of 1.8 Ω · cm or less, and a peak specific resistance ρ _P is 2.0 × 10 ⁶ Ω · cm or more; (3)
Resistivity 1 resistivity and temperature of 10 ⁶ times the electrical resistivity [rho ₂₀ at 20 ℃ T _a (℃) is the resistivity [rho ₂₀ at 20 ° C.
Difference to become 0 times the temperature _{T b (℃) [T a} (℃) -T
_b (° C.)] is 10 ° C. or less, and (4) the withstand voltage is 50
A PTC element, which is not less than V.