JP2000173804A - Composit ptc material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable repeated use as a current-limiting element by dispersing conductive material composed of metal or alloy whose volume is rapidly reduced at the fusing point in electric insulating resin, setting the room temperature resistance to at most a specified value and setting resistance increasing rate to at least a specified value. SOLUTION: This composit PTC material in which conductive material composed of metal or alloy whose volume is rapidly reduced at the fusing point is dispersed in base material of electric insulating resin can be practically used as a current-limiting element whose room temperature resistance is at most 10 Ωcm, and resistance increasing rate is has at lest three-digit number. This base material may be composed of electric insulating resin and high thermal expansion insulating substance like cristobalite. Cristobalite has characteristic that rapid expansion is generated when crystal structure changes from a αtype to a β type. The cristobalite whose grain diameter is 0.1-100 μm is used in the state being dispersed in resin, and its vol.% is in a range of 40-85 vol.%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite PTC suitably used for a current limiting element for suppressing a fault current, and the like.
It is about materials.

[0002]

2. Description of the Related Art PTC (positive temperature coeff)
Since the material has a property that the electric resistance value rapidly increases at a specific temperature, the material is used as a current limiting element for suppressing a fault current in a breaker, for example. Conventionally, as a PTC material, barium titanate-based ceramics, whose electrical properties change at the Curie point, are best known. However, due to high room temperature resistivity, high power loss or high manufacturing cost. PTC properties of other substances have been searched.

As a result, a PTC characteristic similar to that of barium titanate-based ceramics has been found in a composite material using a crystalline resin as a base material and particles of a conductive substance dispersed in the base material. For example, when particles of a conductive substance such as carbon are mixed with a base material made of a crystalline resin such as high-density polyethylene, a conductive path is formed in the base material at a specific mixing ratio, so that the electric resistance is reduced. Decreases sharply, causing an insulator-conductor transition to form a conductive composite material.

[0004] Such a composite material expands rapidly when the crystalline resin changes amorphously at its melting point. That is, the thermal expansion of the base material at the melting point of the crystalline resin is extremely large as compared with the particles of the conductive substance. Therefore, while showing conductivity at room temperature, when the temperature rises to the melting point of the crystalline resin, the particles of the conductive material are separated from each other in the base material, the conductive paths are cut at once, and the electrical resistance rises sharply. That is, the PTC characteristics that can be exhibited.

[0005]

The above-mentioned resin-based PTC material is superior to barium titanate-based ceramics in that a low room temperature resistivity and a high resistance increase rate can be obtained. First, since the base material is a resin, heat resistance and withstand voltage (that is, dielectric breakdown strength) are low, so that operation as a current limiting element is maintained when a high-temperature state due to an accident current continues for a long time. Things impossible,
Secondly, there is a problem that there is a risk of combustion due to temperature rise due to combustibles, and thirdly, the resistance rise rate decreases when pressure is applied due to its low elastic modulus.

[0006] Further, firstly, there is a limitation in selection of a base material due to an operation mechanism utilizing a change in properties of the base material itself.
The operating temperature and the like of the element are limited by the properties of the base material. Second, when the base material is melted and the current limiting element is operated,
NTC (nega) due to rearrangement of conductive material particles in the base material
tive temperature coefficient of resistance) phenomenon,
Third, once the current-limiting element operates, even if the temperature decreases to room temperature, the resistance does not decrease to the initial room temperature resistivity, and it is difficult to repeatedly use the current-limiting element. , Etc.

As one of the methods for avoiding the above-mentioned problems, a method is conceivable in which an operating mechanism uses contraction of a conductive material instead of expansion of a base material. As a PTC material having such an operation mechanism, a composite material in which bismuth having a property of rapidly decreasing its volume at its melting point is dispersed as a conductive substance in a base material made of ceramics such as alumina and titania has been proposed. (Ceramics Association 10th Autumn Symposium Preliminary Book 2C1
0).

[0008] However, in the case of the composite material, although a material having a low room temperature resistivity or a material having a high resistance rise rate has been obtained, a practically usable level having both a low room temperature resistivity and a high resistance rise rate has been obtained. No PTC material has been obtained. Further, the base material is based on ceramics to the last, and there is no mention of the applicability of the resin-based PTC material.

The present invention has been made in view of such a conventional technique, and aims at low room temperature resistivity and high resistance increase rate.
An object of the present invention is to provide a composite PTC material which has high heat resistance and withstand voltage and can be used repeatedly as a current limiting element.

[0010]

That is, according to the present invention, a composite PTC in which a conductive material made of a metal or an alloy whose volume rapidly decreases at its melting point is dispersed in a base material made of an electrically insulating resin. A composite PTC material is provided, wherein the composite PTC material has a room temperature resistivity of 10 Ωcm or less and a resistance increase rate of 3 digits or more.

Further, according to the present invention, a conductive material made of a metal or an alloy whose volume decreases sharply at its melting point is dispersed in a base material made of an electrically insulating resin and a high thermal expansion insulating material. A composite PTC material having a room temperature resistivity of 10 Ωcm or less and a resistance increase rate of 3 digits or more.
A TC material is provided. In the composite PTC material, it is preferable to use cristobalite as the high thermal expansion insulating material, and the high thermal expansion insulating material is 40 to 80% by volume based on the entire composite PTC material.
Is preferably included within the range.

Further, any of the above composite PTs
Also in the C material, it is preferable that the volume reduction rate at the melting point of the conductive substance is 1% or more, and specifically, it is preferable to use bismuth or an alloy containing bismuth as the conductive substance. Further, it is preferable that the conductive substance is contained in the range of 5 to 40% by volume based on the entire composite PTC material.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The composite PTC material of the present invention (hereinafter, simply referred to as “PTC material”) is made of a metal or an alloy whose volume rapidly decreases at the melting point of a base material made of an electrically insulating resin. A conductive material is dispersed therein, and furthermore, a room-temperature resistivity of 10 Ωcm or less and a resistance rise rate of 3 digits or more, which achieve a practical level as a current limiting element.

(Electrically Conductive Substance) The electrically conductive substance in the present invention may be any substance which has electrical conductivity and whose volume decreases sharply at its melting point. Is also good. According to such a conductive substance, a resin-based PTC material having an operation mechanism utilizing contraction of the conductive substance can be configured.

Therefore, the operating temperature of the PTC material is not limited by the type of the base material, and the operating temperature of the element can be designed to a desired value by adjusting the melting point of the conductive substance. There are advantages. In addition, since the operation mechanism does not use melting of the base material, NTC (negative tempe) due to rearrangement of conductive material particles in the melted base material is performed.
It is also possible to prevent a phenomenon (rature coefficient of resistance), that is, a decrease in resistance.

In order to constitute a material having PTC characteristics, it is preferable that the volume reduction rate at the melting point of the conductive substance is 1% or more. A specific example of the conductive substance having such characteristics is bismuth. Bismuth exhibits a volume reduction of about 2.9 to 3.4% at a melting point of 271.3 ° C., and thus can be suitably used in the present invention.

As the conductive substance, an alloy obtained by adding another metal to bismuth may be used. Since the bismuth alloy to which other metals are added can have a lower melting point than bismuth alone, it is possible to design the operating temperature of the element to a desired value by adjusting the addition rate of other metals. Become.

The metal to be added to bismuth is indium, lead, which is alloyed with bismuth and has a low melting point.
It is preferable to use tin, gallium, or the like. However, when these metals are excessively added, the element may not cause a change in resistance due to a decrease in the volume reduction rate of bismuth, so that the volume reduction rate of the conductive material as a whole is 1% or more. It is preferable to maintain.

The conductive material is dispersed in the base material in the form of particles, and the particle size is preferably in the range of 0.1 to 100 μm, and more preferably in the range of 1 to 5 μm. If the particle size is too small, it is not preferable in that the resistance rise rate of the PTC material decreases and the room temperature resistivity increases. If the particle size is too large, it becomes difficult to uniformly disperse the conductive substance in the base material. Therefore, it is not preferable in that it is difficult to form a uniform conductive path in the PTC material. Furthermore, when the particle size is increased while the content of the conductive material is the same, the number of particles of the conductive material decreases, and the number of contacts between the particles decreases. Cases can also occur.

The content of the conductive substance in the present invention varies depending on the particle diameter, particle dispersibility, etc. of the conductive substance, but is contained within the range of 5 to 40% by volume based on the entire composite PTC material. Is preferred. If the volume percentage of the conductive substance is less than 5%, there is a problem in that the resistivity of the material increases, and if it exceeds 40%, the rate of increase in resistance decreases, which is not preferable.

It is difficult to control the volume percentage of the above-described conductive substance in a conventionally known PTC material in which bismuth is dispersed in a ceramic base material and then fired. This is because the boiling point of bismuth is 1560 ° C., which is low for a metal, so that bismuth is volatilized and the volume percentage fluctuates during firing. In such a case, it is necessary to increase the amount of bismuth added, assuming volatile components.

On the other hand, if the base material is a resin as in the present invention, firing such as ceramics is unnecessary and the molding temperature is low, so that the volatilization of bismuth is suppressed and the composition of the conductive substance is controlled. It is easy to construct a PTC material. In addition, there is also an advantage that the manufacturing cost can be reduced because a firing step is not required.

(Base Material) The resin in the conventional PTC material has a function as a base material (so-called matrix),
It was also necessary to have a function of cutting the conductive path due to the volume expansion. However, since the PTC material of the present invention is provided with an operation mechanism utilizing a change in the properties of a conductive substance, the resin only has to function as a matrix.

Therefore, as a base material in the present invention,
It is not particularly limited as long as it is an electrically insulating resin,
It is not necessary to use a crystalline resin. Furthermore,
Previously, when the current limiting element was used due to the heat resistance, withstand voltage, flammability, or structural strength of the resin, problems sometimes occurred. May be avoided.

For example, a phenol resin, a polyimide or the like having a high heat resistance, a vinyl chloride or polyphenylene oxide having a high withstand voltage, a phenol resin or a silicone resin having a flame-retardant base material having a high structural strength. By using polycarbonate, polyamide, or the like as the base material, it becomes possible to add various functions not available in the conventional resin-based PTC materials.

The shape and state of the electrically insulating resin are not particularly limited, and a liquid or pellet resin can be used. However, it is preferable that the material is liquid at the time of mixing the raw materials from the viewpoint that the conductive particles can be more uniformly dispersed, and it is preferable that the material does not melt and has high structural strength after the PTC material is used. Examples of such a resin include a phenolic resin which is in a liquid state at room temperature but is cured by heating.

The base material of the present invention does not need to be composed of only an electrically insulating resin, and may be composed of another electrically insulating substance. For example, the base material may be composed of an electrically insulating resin and a high thermal expansion insulating material. In the present invention, when a high thermal expansion insulating material is used, it has insulating properties and its volume rapidly increases (ie, expands) at a specific temperature.
And specifically, cristobalite (diaphragmite), which is a kind of polymorph of SiO ₂ mineral.

Cristobalite is an insulator and has an alpha-type (tetragonal) crystal structure at about 230 ° C.
Has a property of rapidly expanding as it changes from a to a beta type (cubic crystal form). Therefore, in combination with the contraction of the conductive substance, it is possible to form a material having more sensitive PTC characteristics.

Further, by adding cristobalite having a high melting point of 1730 ° C. and having excellent heat resistance, withstand voltage, and structural strength, and reducing the amount of the resin in the base material, the base material is a resin. Problems such as low heat resistance, low withstand voltage, risk of combustion due to temperature rise, and a decrease in resistance rise rate during pressurization can be suppressed.

Cristobalite has a particle size of 0.1 to 10
A material having a thickness of 0 μm can be suitably used, and is used in a state of being dispersed in a resin as a base material. In this case, it is preferable that the volume percentage of the high thermal expansion insulating material with respect to the entire composite PTC material is in the range of 40 to 85% by volume.

If the volume percentage is less than 40%, the contribution rate of cristobalite to the change in resistance decreases, and the change in resistance during operation of the element becomes unfavorable. On the other hand, if it exceeds 85%, the relative density of the PTC material decreases (that is, the porosity increases),
It is not preferable because the resistance of the material becomes high, the resistance change becomes unstable, or it becomes difficult to use the element repeatedly.

Cristobalite is obtained by calcining quartz powder at a high temperature, or calcining quartz in the presence of an alkali metal or alkaline earth metal to form cristobalite, and then pulverizing it with a wet pot mill. be able to.

(Production Method) The above-mentioned PTC material of the present invention can be produced, for example, by the following method. First,
Prepare the main raw material. As the resin serving as the base material, a commercially available liquid resin or pellet-like resin is appropriately used.
The conductive substance and the high thermal expansion insulating substance are pulverized by a pot mill, a jet mill or the like, and preferably classified to prepare a powder having an average particle size of about 0.1 to 100 μm.

The main raw material thus prepared is weighed so as to have a predetermined ratio, and is distributed by a mixing mill, a kneader, or the like so that the distribution of the conductive material and the high thermal expansion insulating material in the base material is uniform. Mix. A conductive material or the like may be dispersed and mixed while being crushed via a base material, so as to make the distribution state uniform.

After uniformly mixing the base material, the conductive substance, and the high thermal expansion insulating substance, a PTC material formed into a desired shape by, for example, hot press molding using a heating press machine can be obtained.

[0036]

EXAMPLES Hereinafter, the present invention will be described with reference to specific examples, but the present invention is not limited to these examples.

Example 1 A commercially available liquid phenol resin (260 g) and a metal bismuth powder (740 g) having an average particle size of about 10 μm were mixed and dispersed by a kneader and then hot-pressed by a hot press to obtain a molded product. Obtained. The volume percentages of the phenolic resin and the metal bismuth were 73% and 27%, respectively. The obtained molded body is 5 × 5 ×
It was processed into a 30 mm column, and the room temperature resistivity and the temperature dependency of the resistivity were measured by a DC four-terminal method. Table 1 shows the composition ratio of the molded body, and Table 2 and FIG. 1 show the evaluation results.

[0038]

[Table 1]

[0039]

[Table 2]

Example 2 A quartz powder was pulverized by a wet ball mill in the presence of 1 mol% of sodium hydrogencarbonate of the quartz powder and classified to prepare cristobalite having an average particle diameter of 10 μm.

60 g of a commercially available liquid phenolic resin, 640 g of metal bismuth powder having an average particle diameter of about 10 μm, and 300 g of cristobalite having an average particle diameter of 10 μm are mixed and dispersed by a kneader, and then hot-pressed by a heating press to form a molded article. I got The volume percentages of the phenolic resin, bismuth metal, and cristobalite were 20%, 27%, and 53%, respectively. Hereinafter, the molded body was evaluated in the same manner as in Example 1. Table 1 shows the composition ratio of the molded body, and Table 2 and FIG. 2 show the evaluation results.

Example 3 139 g of commercially available liquid phenol resin, metal bismuth powder 6 having an average particle size of about 10 μm
81 g, and an average particle size of 10 μm prepared in the same manner as in Example 2.
180 g of cristobalite m were mixed and dispersed by a kneader, and then hot-pressed by a heating press machine to obtain a molded body. The phenol resin, bismuth metal, and cristobalite have a volume percentage of 43% and 27%, respectively.
% And 30%. Hereinafter, the molded body was evaluated in the same manner as in Example 1. Table 1 shows the composition ratio of the molded body, and Table 2 and FIG. 3 show the evaluation results.

Comparative Example 1 755 g of a commercially available liquid phenol resin and 245 g of a metal bismuth powder having an average particle diameter of about 10 μm were mixed and dispersed by a kneader, and then subjected to hot press molding by a heating press to form a molded body. Obtained. The volume percentages of the phenolic resin and the metal bismuth were 96% and 4%, respectively. Hereinafter, the molded body was evaluated in the same manner as in Example 1. Table 1 shows the composition ratio of the compact, and Table 2 and FIG. 4 show the evaluation results.

Comparative Example 2 114 g of a commercially available liquid phenol resin and 886 g of a metal bismuth powder having an average particle size of about 10 μm were mixed and dispersed by a kneader, and then hot-pressed by a heating press to obtain a molded article. Obtained. The volume percentages of the phenol resin and the metal bismuth were 50% and 50%, respectively. Hereinafter, the molded body was evaluated in the same manner as in Example 1. Table 1 shows the composition ratio of the compact, and Table 2 and FIG. 5 show the evaluation results.

Comparative Example 3 15 g of a commercially available liquid phenolic resin, metal bismuth powder 61 having an average particle size of about 10 μm
6 g, and an average particle size of 10 μm prepared in the same manner as in Example 2.
Was mixed and dispersed with a kneader, and then hot-pressed with a heating press to obtain a molded product. The volume percentages of phenolic resin, metallic bismuth and cristobalite are 5% and 27%, respectively.
%, 68%. Hereinafter, the molded body was evaluated in the same manner as in Example 1. Table 1 shows the composition ratio of the molded body, and Table 2 and FIG. 6 show the evaluation results.

(Evaluation Result) In Example 1, a low room temperature resistivity and a high resistance rise rate were obtained, and a practicable current limiting device could be constructed. Further, the conventional PTC material using crystalline polyethylene as a base material had low heat resistance, and there was a risk of combustion due to a rise in temperature.
Thus, such a problem was eliminated because a phenol resin having high heat resistance and flame retardancy was used as the base material. Further, since the temperature of the hot press is 180 ° C., unlike the conventional PTC material using a ceramic as a base material, bismuth is volatilized and the amount of addition cannot be controlled.

Also in Example 2, a low room temperature resistivity and a high resistance rise rate were obtained, and a practicable current limiting element could be constructed. In Example 2, by adding cristobalite, a steeper change in resistance than in Example 1 could be obtained. Also in Example 3, although the rate of increase in resistance was slightly lower due to the lower addition rate of cristobalite than that in Example 2, a material having a low room temperature resistivity and a high rate of resistance increase was obtained, and was practicable. A current limiting element could be constructed.

On the other hand, when the volume percentage of the conductive material is lower than the range of the present invention as in Comparative Example 1, no conductive path is formed, and thus the room temperature resistivity is high. When the percentage was higher than the range of the present invention, the resistance did not increase because the conductive path could not be cut even when the temperature was increased.

As shown in Comparative Example 3, when the volume percentage of the high thermal expansion insulating material exceeds the range of the present invention, the relative density of the PTC material decreases (that is, the porosity increases). As a result, the resistance of the PTC material increased, and once the element was operated, even if the temperature was lowered, the resistivity did not decrease to the initial room temperature resistivity, and the element could not be used repeatedly.

[0050]

As described above, according to the composite PTC material of the present invention, the room temperature resistivity is low, and
Provided is a composite PTC material which has a high resistance rise rate, a high heat resistance and a high withstand voltage, and which can be used repeatedly as a current limiting element.

[Brief description of the drawings]

FIG. 1 is a graph showing the temperature dependence of electric resistance of a PTC material of Example 1.

FIG. 2 is a graph showing the temperature dependence of the electric resistance of the PTC material of Example 2.

FIG. 3 is a graph showing the temperature dependence of electric resistance of the PTC material of Example 3.

FIG. 4 is a graph showing the temperature dependence of electric resistance of the PTC material of Comparative Example 1.

FIG. 5 is a graph showing the temperature dependence of electric resistance of the PTC material of Comparative Example 2.

FIG. 6 is a graph showing the temperature dependence of electric resistance of the PTC material of Comparative Example 3.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Shun Igami 2-56 Sudacho, Mizuho-ku, Nagoya, Aichi Prefecture Inside Nihon Insulators Co., Ltd. No. 56 F insulator in Japan Insulator Co., Ltd. (reference) 5E034 AA07 AB01 AC10 AC17 DA10 5G502 AA05 BB01 BE03

Claims (7)

[Claims] A composite PTC comprising a base material made of an electrically insulating resin and a conductive material made of a metal or an alloy whose volume rapidly decreases at the melting point thereof dispersed therein.
A composite PTC, wherein the composite material has a room temperature resistivity of 10 Ωcm or less and a resistance increase rate of 3 digits or more.
material. 2. A composite PTC in which a base material made of an electrically insulating resin and a high thermal expansion insulating material is dispersed with a conductive material made of a metal or an alloy whose volume decreases rapidly at its melting point.
A composite PTC, wherein the composite material has a room temperature resistivity of 10 Ωcm or less and a resistance increase rate of 3 digits or more.
material. 3. The composite PTC according to claim 2, wherein cristobalite is used as the high thermal expansion insulating material.
material. 4. The composite PTC material according to claim 2, wherein the high thermal expansion insulating material is contained in the range of 40 to 80% by volume based on the entire composite PTC material. 5. The composite PTC material according to claim 1, wherein a volume reduction rate of the conductive substance at a melting point is 1% or more. 6. The composite PTC material according to claim 1, wherein bismuth or an alloy containing bismuth is used as the conductive substance. 7. The composite PTC material according to claim 1, wherein the conductive substance is contained in the range of 5 to 40% by volume based on the entire composite PTC material.