JP2007250911A - Conductive composition, conductive composition sheet and organic positive temperature coefficient thermistor element using them as well as method for manufacturing organic positive temperature coefficient thermistor element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic positive temperature coefficient thermistor which exhibits a small resistance value at room temperature but exhibits a high increasing rate of resistance value in a high-resistance state, whose resistance value at room temperature does not increase, and by which no abnormal phenomenon such as ignition occurs even when its high-resistance state is repeated. <P>SOLUTION: Conductive powder and boron nitride powder are dispersed in an organic polymer to form a conductive composition. In this case, the boron nitride powder is contained in the conductive composition at the rate of 1-20% by volume with respect to the total volume. The formed conductive composition is processed into a sheet, and is provided with at least a pair of electrodes on both sides. It is irradiated with a predetermined amount of electron beam or γ beam to obtain the organic positive temperature coefficient thermistor. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a conductive composition, a conductive composition sheet, an organic positive temperature coefficient thermistor element using the same, and a method for manufacturing the organic positive temperature coefficient thermistor element.

  A conductive composition in which a conductive material such as carbon black or metal powder is dispersed in an organic polymer such as polyethylene or ethylene copolymer has a positive temperature coefficient that increases its resistance as the temperature rises. ) Is known to have properties. Such a composition is disclosed in Patent Documents 1 and 2, for example.

  An element having a PTC characteristic (positive characteristic thermistor element) rapidly becomes high resistance (trip state) when the temperature of the element reaches a certain threshold temperature. Such a high resistance state can be caused by excessive current flowing through the positive temperature coefficient thermistor element and when the element temperature reaches a certain threshold temperature, or when the environmental temperature of the device rises and the element temperature reaches the threshold temperature. The case where it reaches is considered.

  As described above, the positive temperature coefficient thermistor element rapidly becomes high resistance (trip state) when the temperature of the element reaches a certain threshold temperature. Thereby, the electric current which flows into an element can be interrupted | blocked. For this reason, the positive temperature coefficient thermistor element is used for the purpose of protecting an electric circuit from overcurrent.

  When the electric circuit is used for protection from overcurrent, the following characteristics are required for the positive temperature coefficient thermistor element. The resistance value at room temperature is small, the rate of increase in resistance value when the trip state is reached, the resistance value at room temperature does not increase even if the trip state is repeated, and firing is repeated even if the trip state is repeated. The abnormal phenomenon does not occur.

  However, in the case of a polymer-based positive temperature coefficient thermistor element, since the polymer is softened by heat in the trip state, the conductive substance is easy to move. For this reason, changes such as a decrease in the resistance value in the trip state are likely to occur due to re-aggregation of the conductive material. Furthermore, the resistance value at room temperature increases due to repeated tripping, and the polymer may ignite.

US Pat. No. 3,591,526 US Pat. No. 3,673,121

  The present invention has been made in view of such problems, and the resistance value at room temperature is small, while the increase rate of the resistance value when the trip state is reached is large, and the trip state is repeated. An object of the present invention is to provide an organic positive temperature coefficient thermistor element in which the resistance value at room temperature does not increase and an abnormal phenomenon such as ignition does not occur. It is another object of the present invention to provide a conductive composition and a conductive composition sheet used for manufacturing the thermistor element.

  The conductive composition according to the present invention is a conductive composition in which conductive powder and boron nitride powder are dispersed in an organic polymer, and the boron nitride powder is added to the total capacity of the conductive composition. 1 to 20% by volume.

  It is preferable that the conductive powder is contained in an amount of 20 to 65% by volume with respect to the total volume of the conductive composition.

  Metal powder and / or non-metal powder can be used as the conductive powder. Nickel, copper, platinum, cobalt and the like can be used for the metal powder, but nickel powder, nickel-based alloy powder, or nickel-based coated powder is preferably used from the viewpoint of price and weather resistance. The non-metallic powder is preferably at least one powder selected from the group consisting of carbon black powder, titanium nitride powder and zirconium nitride powder.

  As the organic polymer, at least one selected from the group consisting of polyethylene, ethylene copolymer, vinylidene fluoride, and polyamide can be used.

  The conductive composition sheet according to the present invention is formed using the conductive composition, and becomes stable when the sheet is irradiated with an electron beam or γ-ray. The irradiation amount of electron beam or γ ray is preferably 80 to 4000 kGy.

  The organic positive temperature coefficient thermistor element according to the present invention can be obtained by providing at least a pair of electrodes on both surfaces of a conductive composition sheet after irradiation with an electron beam or γ-ray. Alternatively, the organic positive temperature coefficient thermistor element according to the present invention may be obtained by providing at least a pair of electrodes on both surfaces of the conductive composition sheet before irradiation with an electron beam or γ-ray, and then irradiating with an electron beam or γ-ray. it can.

  A method for producing an organic positive temperature coefficient thermistor element according to the present invention includes a step of adding a metal powder and / or a non-metal powder and a boron nitride powder to an organic polymer and kneading to obtain a conductive composition; Processing the conductive composition to obtain a conductive composition sheet; irradiating the conductive composition sheet with an electron beam or γ-ray; attaching an electrode to the conductive composition sheet; It is characterized by having.

  Since the conductive composition according to the present invention contains 1 to 20% by volume of boron nitride powder with respect to the total capacity of the conductive composition, an organic positive temperature coefficient thermistor formed using the conductive composition The element has a low resistance value at room temperature. On the other hand, the rate of increase in resistance value when tripped is large, and the resistance value does not increase even when tripping is repeated, causing abnormalities such as ignition. It has excellent characteristics that do not cause any phenomenon.

  In order to manufacture an organic positive temperature coefficient thermistor element, it is necessary to manufacture a conductive composition in which a conductive powder such as carbon black or metal powder is dispersed in an organic polymer such as polyethylene or ethylene copolymer. The inventors have obtained a conductive composition by adding a specific amount of boron nitride powder to an organic polymer at the same time as adding conductive powder such as carbon black or metal powder for the purpose of improving electrical characteristics. An organic positive temperature coefficient thermistor device was fabricated using the conductive composition.

  When the fabricated organic positive temperature coefficient thermistor element was evaluated, the resistance value at room temperature was small. On the other hand, the increase rate of the resistance value in the trip state was sufficiently large as the positive temperature coefficient thermistor element, and the trip state The resistance value at room temperature did not increase even when the process was repeated, and abnormal phenomena such as ignition did not occur.

  The present inventor has come to make the present invention based on this finding. Hereinafter, the organic positive temperature coefficient thermistor element according to the present invention will be described in detail.

  First, a general description of the organic positive temperature coefficient thermistor element will be given. The organic positive temperature coefficient thermistor element has a structure in which a sheet made of a conductive composition in which a conductive powder is dispersed in an organic polymer is sandwiched between two metal electrode foils.

  PTC properties depend on the melting point of the organic polymer. That is, when the temperature of the organic polymer is raised, a large volume expansion occurs in the organic polymer near the melting point, the conductive path is cut, and the resistance value rises.

  As the organic polymer, polyethylene or ethylene copolymer is generally used. As the conductive powder, carbon black or metal powder is generally used. In the organic positive temperature coefficient thermistor element, generally, about 20 to 65% by volume of conductive powder is contained, and the rest is an organic polymer.

  Next, the organic positive temperature coefficient thermistor element according to the present invention will be described. In the organic positive temperature coefficient thermistor element according to the present invention, a conductive composition in which conductive powder and boron nitride powder are dispersed in an organic polymer is used. Boron nitride powder has a function of preventing a decrease in resistance value in a trip state and suppressing an increase in resistance value at room temperature due to repeated trips and occurrence of abnormal phenomena such as ignition.

  Boron nitride powder is contained in an amount of 1 to 20% by volume with respect to the total volume of the conductive composition. The boron nitride powder used preferably has an average particle size of 0.01 to 20 μm. When the average particle diameter of the boron nitride powder is less than 0.01 μm, the oxygen content increases and boron oxynitride is formed, and the above-described function is hardly obtained. On the other hand, when the average particle size of the boron nitride powder exceeds 20 μm, the particle size becomes larger than that of the conductive powder, and even if mixed, it is difficult to obtain the effect of addition.

  The average particle size referred to here is D50 (measured using a laser diffraction / scattering particle size distribution measuring device Microtrac (manufactured by Nikkiso Co., Ltd.)), and a cumulative curve was determined with the total volume of the powder group as 100%. The particle diameter at which the cumulative curve becomes 50%.

  The boron nitride powder may be added simultaneously with the addition of the conductive powder in the organic polymer, or the conductive composition is obtained by adding the boron nitride powder to a dispersion of the conductive powder in the organic polymer. It may be produced.

  The content of boron nitride powder is preferably 1 to 20% by volume, and more preferably 5 to 15% by volume. If the amount of boron nitride powder added to the conductive composition is less than 1% by volume, the effect of adding boron nitride powder will not be sufficiently produced, and the resistance value in the trip state will decrease, or the trip may be repeated at room temperature due to repeated trips. There is a risk that the resistance value may increase or abnormal phenomena such as ignition may occur. On the other hand, if the amount of boron nitride powder added to the conductive composition is more than 20% by volume, the resistance value may become too large to exhibit PTC characteristics.

  In the conductive composition according to the present invention, not only a metal powder but also a nonmetal powder such as carbon black, titanium nitride, and zirconium nitride can be suitably used as the conductive powder. The total content of these conductive powders is preferably 20 to 65% by volume with respect to the total volume of the conductive composition comprising the polymer and the conductive powder. If it is less than 20% by volume, the conductivity becomes insufficient, and if it exceeds 65% by volume, PTC characteristics may not be exhibited. Moreover, it is preferable to use the conductive powder having an average particle diameter of 0.005 to 100 μm. When the average particle size of the conductive powder is less than 0.005 μm, mixing becomes difficult, and when it exceeds 100 μm, the resistance may be increased.

  As the metal powder, nickel, copper, platinum, cobalt, or the like can be used. From the viewpoint of price and weather resistance, nickel powder, nickel-based alloy powder, or nickel-based coated powder can be preferably used. Nickel powder, nickel-based alloy powder, and nickel-based coating powder that can be dispersed in the organic polymer are not particularly limited. For example, commercially available nickel powder for filler (having an average particle diameter of several μm to several tens of μm) Can be used. Moreover, nickel powder produced by reducing a nickel aqueous solution with a reducing agent such as hydrazine can also be used.

  Examples of the nickel-based alloy powder include alloy powders with cobalt, chromium, aluminum, titanium, zinc, copper, tin and the like. In addition, as for nickel-based coating powder, the surface of nickel powder is a non-conductive metal such as cobalt, chromium, aluminum, titanium, zinc, copper, tin or alloy with nickel, or carbon black, titanium nitride, zirconium nitride. Examples thereof include those coated with a metal substance.

  The mechanism by which boron nitride is added to improve electrical characteristics is not clear, but the excellent thermal conductivity, insulation, lubricity, environmental stability, etc. of boron nitride contribute. It is thought that.

  In the conductive composition according to the present invention, as the organic polymer, in addition to polyethylene and an ethylene copolymer, vinylidene fluoride, polyamide and the like can be used.

  Next, the conductive composition produced as described above is processed into a sheet using a heating press or the like. Electrodes, such as nickel foil, are pressure-bonded to both surfaces of the produced conductive composition sheet using a hot press.

  The conductive composition sheet having the electrode bonded thereto is irradiated with an electron beam or γ-ray. Irradiation with an electron beam or γ-ray stabilizes the PTC characteristics. The amount of electron beam or γ-ray to be irradiated is preferably 80 to 4000 kGy. If the amount of electron beam or γ-ray to be irradiated exceeds 4000 kGy, the cost will be high. Depending on the combination of materials and the properties of the required PTC thermistor, there is no need to irradiate an electron beam or γ-ray. Note that the electrode may be pressure-bonded after the conductive composition sheet is irradiated with an electron beam or γ-ray.

  The conductive composition sheet after the electrodes are pressure-bonded and irradiated with an electron beam or γ-ray is punched into a predetermined size using a punching machine. An organic positive temperature coefficient thermistor element can be obtained by soldering a metal foil to be a lead to the electrode.

(Examples 1-5, Comparative Examples 1-3)
An organic positive temperature coefficient thermistor element was fabricated using nickel powder as the conductive material. The nickel powder was prepared by reduction precipitation in two stages as follows.

  An aqueous sodium hydroxide solution (1125 mL) containing tartaric acid was heated to 85 ° C. with stirring, an aqueous solution of nickel chloride containing 19.5 g of nickel and 89.1 g of hydrazine as a reducing agent were added, and nickel powder was reduced and precipitated. Thereafter, a nickel chloride aqueous solution containing 19.5 g of nickel was further added to reduce and precipitate nickel, and then filtered and washed with water, followed by drying in vacuum at 80 ° C. to obtain nickel powder. The average particle diameter of the obtained nickel powder was 30 μm.

  Then, nickel powder prepared as described above and polyethylene nitride as an organic polymer and boron nitride powder having an average particle diameter of 2 μm (manufactured by Electrochemical Co., Ltd., SP-2) are respectively shown in Table 1 (Examples 1 to 1). 5, it added so that it might become the ratio shown to Comparative Examples 1-3), it knead | mixed with the temperature of 180 degreeC with the resin kneader, and produced the electrically conductive composition. The produced conductive composition was processed into a sheet having a thickness of 0.5 mm using a heating press. And the nickel foil electrode was crimped | bonded to the both surfaces of this sheet | seat using the heating press machine at the temperature of 200 degreeC, and also the electron beam of 1000 kGy was irradiated. Thereafter, the sheet was punched into a size of 3 × 4 mm, and a metal foil serving as a lead was soldered to a nickel foil electrode to produce an organic positive temperature coefficient thermistor element.

  In order to evaluate the characteristics of the fabricated device, the resistance-temperature characteristics (hereinafter referred to as RT characteristics) are measured, the resistance increases due to repeated trips, and the presence or absence of ignition (hereinafter referred to as trip cycle characteristics and Measurement) was carried out.

  The RT characteristics were measured by forcibly raising the element temperature to cause a trip.

  Specifically, the device was placed in a dryer, and the temperature in the dryer was increased from room temperature to 160 ° C. at a temperature increase rate of 1.5 ° C./min and held for 30 minutes. Then, the temperature was decreased from 160 ° C. to 40 ° C. at a temperature decreasing rate of 1 ° C./min. This temperature cycle (room temperature → 160 ° C. → 40 ° C.) was defined as the first cycle.

  The temperature cycle of the second cycle was 40 ° C. → 160 ° C. → 40 ° C., and the temperature cycle of the third cycle was 40 ° C. → 160 ° C. → 40 ° C. Regarding the temperature increase rate, the temperature decrease rate, and the holding time at 160 ° C., the second and third cycles were the same as the first cycle.

  In such a temperature cycle, the temperature rise and the temperature fall were repeated three times, and during this time, the resistance value of the element was measured at intervals of 20 seconds, and the RT characteristic was measured.

As for the quality of the RT characteristic, the resistance value in the trip region is not recognized as good (good), and the resistance value in the trip region is recognized as low, but the resistance value is 1 × 10 ⁴ Ω. A case where the resistance value in the trip region was less than 1 × 10 ⁴ Ω was judged as × (defect).

  Trip cycle characteristics were measured by a trip cycle test. The trip cycle test is performed by using a constant current voltage device of 12V-18A, causing an overcurrent to flow through the element, repeatedly causing trips, measuring the resistance value at room temperature during this time, and observing the presence or absence of ignition. It was.

  Specifically, after applying a voltage for 6 seconds to cause a trip, the voltage is not applied for the next 54 seconds, and the process of zeroing the flowing current is defined as one cycle. This cycle is 1000 times and 3000 times. , 6000 times was repeated, the resistance value during this time was measured, and the presence or absence of ignition was observed.

  The trip cycle characteristic is good (good) when the cycle does not ignite even after repeating the cycle 6000 times, and the resistance value at room temperature is within 5 times the resistance value before the test, and the cycle is 6000. Although it does not ignite even if it is repeated a number of times, it is determined that the resistance value at room temperature has risen to 5 times or more of the resistance value before the test is conducted, and the one that has ignited before repeating the cycle 6000 times is judged as x (defect). .

  Table 1 shows the evaluation results of the RT characteristics and trip cycle characteristics of the fabricated devices. Moreover, about Example 2 and Comparative Example 1, the graph of the measurement result of RT characteristic is shown in FIG. 1 and FIG. 2, respectively, and the graph of the result of a trip cycle test is shown in FIG. In the evaluation test of the RT characteristic, since the upper limit of the measurable resistance value is 53.1 MΩ, the resistance value of the measurement value exceeding 53.1 MΩ is plotted in FIG. 1 as the resistance value of 53.1 MΩ. ing.

(Examples 6 to 8, Comparative Example 4)
A thermistor element was produced in the same manner as in Examples 1 to 3 and Comparative Example 1 except that the nickel powder used as the conductive material was a commercially available nickel powder (INCO210, manufactured by Inco Corporation). The same characteristic evaluation as in Comparative Example 1 was performed. The evaluation results are shown in Table 1.

(Examples 9 to 11)
Organic positive temperature coefficient thermistor elements were produced in the same manner as in Examples 1 to 3, except that nickel-based coated powder coated with a nickel-cobalt alloy was used as the metal powder used as the conductive material.

  First, a sodium hydroxide aqueous solution (1125 mL) containing tartaric acid was heated to 85 ° C. while stirring, 19.5 g nickel chloride aqueous solution containing nickel and hydrazine 89.1 g as a reducing agent were added, and nickel powder was reduced and precipitated. After that, a mixed aqueous solution of nickel chloride and cobalt chloride containing 17.6 g of nickel and 2.0 g of cobalt was further added to further reduce and precipitate nickel and cobalt on the surface of the nickel powder. Obtained. Then, it filtered and washed with water, and it was made to dry in a vacuum at 80 degreeC, and obtained the nickel powder of the electrically conductive material. Table 1 shows the evaluation results of the RT characteristics and trip cycle characteristics of the fabricated devices.

  As can be seen from the test results shown in Table 1, Examples 1 to 11 in which the content of the boron nitride powder is within the scope of the present invention were good in both RT characteristics and trip cycle characteristics.

  In contrast, Comparative Examples 1, 2, and 4 in which the content of the boron nitride powder was less than 1% by volume, which is the lower limit of the range of the present invention, were not good in both RT characteristics and trip cycle characteristics. . In Comparative Example 3 in which the content of boron nitride powder exceeds 20% by volume, which is the upper limit of the range of the present invention, the resistance value was too large and PTC characteristics were not exhibited.

  FIG. 1 is a graph showing the measurement results of the RT characteristic of Example 2, and it can be seen that the resistance value in the trip region does not decrease even when the temperature increase and decrease are repeated three cycles. On the other hand, FIG. 2 is a graph showing the measurement results of the RT characteristic of Comparative Example 1, but the resistance in the trip region in the temperature rising process and the temperature decreasing process in the first cycle and the temperature rising process in the second cycle. Although no decrease in value has been observed, the resistance value in the trip region decreases in the temperature decrease process in the second cycle and the temperature increase process and temperature decrease process in the third cycle.

  FIG. 3 is a graph showing the results of the trip cycle test of Example 2 and Comparative Example 1. In Comparative Example 1, the rate of increase in resistance value at room temperature with an increase in the number of cycles is greater than that of Example 2. ing. In Example 2, even if the test was performed up to 6000 cycles, none of the 6 samples ignited. In Comparative Example 1, 1 out of 6 samples ignited by 1000 cycles. 3 out of 6 samples ignited by the number of cycles of 3000, and 6 out of 6 samples ignited by the number of cycles of 6000.

6 is a graph showing the measurement results of RT characteristics of Example 2. FIG. 10 is a graph showing the measurement results of the RT characteristic of Comparative Example 1. FIG. It is a graph which shows the result of the trip cycle test of Example 2 and Comparative Example 1.

Claims (10)

  A conductive composition in which conductive powder and boron nitride powder are dispersed in an organic polymer, the boron nitride powder being contained in an amount of 1 to 20% by volume based on the total volume of the conductive composition A conductive composition characterized by the above.   2. The conductive composition according to claim 1, wherein the conductive powder is contained in an amount of 20 to 65% by volume with respect to the total capacity of the conductive composition.   The conductive composition according to claim 1, wherein the conductive powder is a metal powder and / or a nonmetal powder.   The conductive composition according to claim 3, wherein the metal powder is nickel powder, nickel-based alloy powder, or nickel-based coating powder.   5. The conductive composition according to claim 3, wherein the non-metallic powder comprises at least one powder selected from the group consisting of carbon black powder, titanium nitride powder, and zirconium nitride powder.   The conductive composition according to claim 1, wherein the organic polymer is at least one selected from the group consisting of polyethylene, an ethylene copolymer, vinylidene fluoride, and polyamide.   The electroconductive composition sheet formed using the electroconductive composition in any one of Claims 1-6.   The conductive composition sheet according to claim 7, which has a history of electron beam irradiation or γ-ray irradiation.   The organic positive temperature coefficient thermistor element which provided at least a pair of electrode on both surfaces of the electrically conductive composition sheet | seat of Claim 8.   A step of adding a metal powder and / or non-metal powder and boron nitride powder to an organic polymer and kneading to obtain a conductive composition; and processing the conductive composition to form a conductive composition sheet A method for producing an organic positive temperature coefficient thermistor element comprising: a step of irradiating the conductive composition sheet with an electron beam or γ-ray; and a step of attaching an electrode to the conductive composition sheet. .