JP2015044908A - Conductive composition and heat insulating conductive member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat insulating conductive member which has excellent conductivity and mechanical characteristics and also heat insulating property, especially a small thermal conductivity in the penetration direction even if it has a flat plate shape, and to provide a method for producing the same.SOLUTION: A conductive composition contains: 100 pts.mass of resin beads A having a thermal conductivity of 0.5 W/m K or less and an average particle diameter of 50-500 μm; and a conductive material B in a specific ratio, which is selected from the group comprising particles whose average particle diameter is smaller than that of the resin beads A and is 1 nm to 200 μm and fibers whose average fiber diameter is smaller than the average particle diameter of the resin beads A and is 1 nm to 200 μm.

Description

  The present invention relates to a conductive composition and a heat insulating conductive member obtained using the conductive composition. More specifically, the present invention relates to a conductive composition including resin beads and a conductive material, and a heat insulating conductive member obtained by molding the conductive composition.

  Conventionally, metals and carbon materials have been used as materials used in applications requiring high conductivity. Among these, carbon materials are used in various fields where electrical conductivity is required due to the improvement in freedom of molding processability by compounding with polymer materials (Patent Document 1).

  By the way, metals and carbon materials are excellent in conductivity, and at the same time have high thermal conductivity. For this reason, the example which manufactured the member excellent in electroconductivity and low heat conductivity using these is not known so much.

  An example of a member that is required to have both excellent conductivity and low thermal conductivity is a fuel cell heat insulating plate. A fuel cell usually has a fuel cell stack in which a plurality of single cells are stacked. Among the stacked single cells, those located at the end of the fuel cell stack have large heat dissipation to the outside, so the temperature is not uniform among the cells in the stack, and the power generation performance may be reduced. Are known. For this reason, it is necessary to keep the temperature in the cell uniform by installing a member having heat insulation between the cell at the end and the member other than the fuel cell stack. This heat insulating member is also required to have high conductivity in order to transmit electricity generated by the cell to an external member. In addition, if there is an error in the dimensions, electrical conduction inside the fuel cell deteriorates, so high dimensional accuracy is required, and heat resistance that maintains the dimensional accuracy near the operating temperature is also required. In addition, in a heat insulating plate for a fuel cell that is used for an application such as an automobile where vibration is applied during operation, it is required that the mechanical characteristics are good.

  As a heat insulating plate for a fuel cell, a heat insulating plate made of a metal corrugated plate is known (Patent Document 2). Although this heat insulating plate is made of metal but has a corrugated shape, an air layer for heat insulation is formed between the cell and an external member, and heat insulation can be imparted.

JP 2007-169461 A JP 2004-152502 A

  Since the metal heat insulating plate has a complicated shape as described above, mass production is difficult, and heat insulating properties are not exhibited as expected.

  Therefore, the present invention has been made paying attention to the above-mentioned problems, and its purpose is not only excellent in conductivity and mechanical properties, but also in a flat plate shape, it has heat insulation properties, particularly heat conduction in the penetration direction. An object of the present invention is to provide a heat insulating conductive member having a low rate and a method for manufacturing the same.

The present invention relates to the following [1] to [7].
[1]
For 100 parts by mass of resin beads A having a thermal conductivity of 0.5 W / m · K or less and an average particle diameter of 50 to 500 μm,
Selected from the group consisting of particles having an average particle diameter smaller than the average particle diameter of the resin beads A and 1 nm to 200 μm and fibers having an average fiber diameter smaller than the average particle diameter of the resin beads A and 1 nm to 200 μm. A conductive composition containing 15.5 to 70 parts by mass of conductive material B.
[2]
The conductive composition according to [1] or [2], further including 0.1 to 30 parts by mass of a binder resin C with respect to 100 parts by mass in total of the resin beads A and the conductive material B.
[3]
The conductive composition according to [1] or [2], wherein the conductive material B is flaky particles.
[4]
The conductive composition according to [2], wherein the resin beads A are acrylic resin beads and the binder resin C is an epoxy resin.
[5]
A heat-insulating conductive member obtained by molding the conductive composition according to any one of [1] to [4].
[6]
The heat insulating conductive member according to [5], which is a member provided at a cell end of the fuel cell.
[7]
100 parts by mass of resin beads A having a thermal conductivity of 0.5 W / m · K or less and an average particle size of 50 to 500 μm;
Selected from the group consisting of particles having an average particle diameter smaller than the average particle diameter of the resin beads A and 1 nm to 200 μm and fibers having an average fiber diameter smaller than the average particle diameter of the resin beads A and 1 nm to 200 μm. A method for producing a heat-insulating conductive member, comprising dry blending 15.5 to 70 parts by mass of a conductive material B to be heated and then compression-molding.

  When the conductive composition of the present invention is used, a heat insulating conductive member having both excellent conductivity and low thermal conductivity can be easily obtained. The heat insulating conductive member obtained by using the conductive composition of the present invention can be suitably used for heat insulation of the cell stack end of the polymer electrolyte fuel cell.

Embodiments of the present invention will be described below.
[Conductive composition]
The conductive composition of the present invention includes at least resin beads A and a conductive material B, and further includes a binder resin C as necessary.

<Resin beads A>
The thermal conductivity of the resin beads A is 0.5 W / m · K or less, preferably 0.4 W / m · K or less, more preferably 0.3 W / m · K or less. If the thermal conductivity of the resin beads A is within this range, a heat insulating conductive member having a low thermal conductivity can be obtained even if the amount of the conductive material B added is increased. It is easy to obtain a heat-insulating conductive member that satisfies both rates. The thermal conductivity of the resin beads A is preferably as low as possible, but is usually 0.05 W / m · K or more.

The thermal conductivity of the resin beads A is obtained by measuring the thermal conductivity of a sufficiently filled 1 cm thick bead layer by a hot wire method. For example, a rapid thermal conductivity meter QTM-500 manufactured by Kyoto Electronics Industry Co., Ltd. can be used for measuring the thermal conductivity.
It is preferable that the resin beads A have a hollow structure or a porous structure because the beads contain an air layer and have low thermal conductivity.

  Moreover, it is preferable that the resin beads A have high heat resistance so that the strength can be maintained when the heat insulating conductive member is formed by heating press. As a measure of heat resistance, it is preferable that the glass transition temperature (Tg) is 110 ° C. or higher and the thermal decomposition temperature is 200 ° C. or higher. The glass transition temperature is determined as an extrapolated glass transition start temperature after adjusting the sample in a standard state according to JIS K7121. The thermal decomposition temperature is obtained as a starting temperature of the first mass reduction by thermogravimetry performed according to JIS K7120. The higher the glass transition temperature and the thermal decomposition temperature of the resin beads A, the better, but usually it is 300 ° C. or lower.

  Further, when the beads themselves are partially softened and fused, a heat insulating conductive member having excellent mechanical strength can be obtained without using a large amount of binder, and thus beads made of a thermoplastic resin are preferable.

  Specific examples of the material of the resin beads A include polymethyl methacrylate (hereinafter referred to as PMMA) and a crosslinked polystyrene resin, and PMMA is preferable. Crosslinking is preferable because the strength and heat resistance of the beads are improved.

  The average particle diameter of the resin beads A is 50 to 500 μm, preferably 100 to 400 μm, and more preferably 150 to 350 μm. The average particle size of the resin beads A is measured on a volume basis using a laser diffraction particle size distribution measuring device.

<Conductive material B>
The conductive composition of the present invention is 15.5 to 70 parts by weight, preferably 15.5 to 40 parts by weight, more preferably 15.5 to 25 parts by weight with respect to 100 parts by weight of the resin beads A. B is included.
Examples of the conductive material B include particles and fibers made of graphite or metal, and are preferably graphite because they are resistant to corrosion and lightweight.

  The average particle diameter of the particulate conductive material B and the average fiber diameter of the fibrous conductive material B are smaller than the average particle diameter of the resin beads A and are 1 nm to 200 μm, preferably 1 μm to 100 μm, more preferably 10 μm to 100 μm. When the conductive material B is a fiber, the ratio of the average fiber length to the average fiber diameter is preferably 5 or more, and more preferably 10 or more. The ratio of the average fiber length to the average fiber diameter is usually 10,000 or less. The average particle diameter of the conductive material B is obtained on a volume basis using a laser diffraction particle size distribution meter. The average fiber diameter and average fiber length can be determined by observing 100 to 1000 fibers with a transmission electron microscope and arithmetically averaging them.

The conductive material B is preferably flaky particles or fibers because the conductive material B easily enters a gap between the particles of the resin beads A and easily forms a conductive path over the entire heat insulating conductive member. Examples of the flaky conductive material B include flaky graphite.
In addition, when the conductive material B is graphite, it is preferable that the boron-doped graphite is provided with particularly excellent conductivity to the heat insulating conductive member.

<Binder resin>
The conductive composition is preferably 0.1 to 30 parts by mass, more preferably 0.3 to 15 parts by mass, and still more preferably 0.5 to 100 parts by mass with respect to a total of 100 parts by mass of the resin beads A and the conductive material B. 5 parts by weight of binder resin C is included.
The binder resin C may be either a thermoplastic resin or a thermosetting resin, but is preferably a thermosetting resin.
The binder resin C preferably binds the resin beads A and the conductive material B and has a strong adhesive force in order to impart compressive strength to the heat insulating conductive member.

  It is preferable that the binder resin C is uniformly dispersed with the resin beads A and the conductive material B because the effect can be obtained with a small amount of addition. Therefore, the binder resin C is preferably a low-viscosity liquid resin. Specifically, in accordance with JIS Z8803, the rotor no. The viscosity measured at 25 ° C. using 4 is preferably 0.5 to 20 Pa · s, more preferably 1 to 15 Pa · s.

  When the heat insulating conductive member is used for heat insulation of the cell end of the polymer electrolyte fuel cell, the binder resin C has a glass transition temperature of a cured product of 110 ° C. or more of the upper limit temperature of the polymer electrolyte fuel cell. It is desirable that The higher the glass transition temperature of the cured product, the better, but it is usually 300 ° C. or lower. The measurement method of the glass transition temperature is the same as the measurement of the glass transition temperature of the resin beads A described above.

The binder resin C is preferably compatible with the resin beads A described above. Examples of the combination of the compatible resin beads A and the binder resin C or a precursor thereof include a combination of an acrylic resin such as PMMA and an epoxy resin.
Specific examples of the binder resin C include, for example, an epoxy resin and a phenol resin, and an epoxy resin is preferable.

<Other ingredients>
The conductive composition of the present invention may contain, in addition to the above components A to C, a heat insulating composition, a known additive contained in the conductive composition, and the like.

<Method for producing conductive composition>
In the conductive composition, for example, the above-described components are uniformly mixed using a generally used mixer or kneader. Examples of the mixer or kneader include a roll, an extruder, a kneader, a Banbury mixer, a Henschel mixer, and a planetary mixer. At the time of mixing, if a material in which the resin beads A and the conductive material B are previously dry-blended and uniformly dispersed is used, the conductive material B enters the gap between the resin beads A, and the conductive material B is spread over the entire heat insulating conductive member. Since it becomes easy to form a uniform network, the member excellent in electroconductivity and heat insulation is obtained, and it is preferable. In the kneading step, in order to uniformly disperse the binder resin C, a method is used in which the kneading step is performed a plurality of times, preferably three times or more, the material is taken out and charged again into the kneader. From the viewpoint of productivity of the conductive composition, the kneading step is usually 4 times or less.

[Insulated conductive member]
The heat-insulating conductive member of the present invention is obtained by molding the above-described conductive composition. The composition is the same as the composition of the conductive composition described above except that when the binder resin C is a thermosetting resin, it becomes a cured product after molding. Moreover, there is no restriction | limiting in particular in the shape of a heat insulation conductive member, However, From a viewpoint of making manufacture of a heat insulation conductive member easy, it is preferable that it is flat form.

<Method of manufacturing a heat insulating conductive member>
It does not specifically limit as a method to shape | mold a heat insulation electrically-conductive member, It can shape | mold by the well-known method used for shaping | molding of an electroconductive composition. Specifically, a method such as compression molding is used. For example, a thermoplastic resin bead is used as the resin bead A, a thermosetting resin is used as the binder resin C, and molding and thermosetting are performed while heating with a compression molding machine. Next, the molded product is cooled while being compressed, and the temperature is set to 10 to 60 ° C. so that the resin beads A are solidified in a fused state to obtain a heat insulating conductive member. it can. It is preferable to perform the heating temperature condition below the thermal decomposition temperature of the resin beads A.

<Conductivity>
The heat insulating conductive member preferably has a volume specific resistance of 500 mΩ · cm or less, and more preferably 300 mΩ · cm or less. The volume resistivity is preferably as small as possible, but is usually 50 mΩ · cm or more. The volume resistivity can be measured by a four-probe method according to JIS K7194.

The heat insulating conductive member preferably has a resistivity in the penetration direction (representing a volume resistivity in the penetration direction) of 5.5 Ω · cm or less, and more preferably 4.0 Ω · cm or less. The resistivity in the penetration direction is preferably as small as possible, but is usually 0.5 mΩ · cm or more. The resistivity in the penetration direction is determined by sandwiching the test piece between the gold-plated electrodes (100 mm x 50 mm x 0.3 mm) on the copper plate, applying a 0.5 MPa load, and passing a constant current of 1 A in the penetration direction. The resistance is measured by measuring the voltage (measured value: Ra). From this, the resistivity in the penetration direction is calculated by the following equation.
Resistivity in penetration direction = Ra × (area of test piece) / (thickness of test piece)
It is preferable that the shape of the test piece is 20 mm × 20 mm × 4 mm, and the one prepared from the same conductive composition cut out from the heat insulating conductive member or used for manufacturing the heat insulating conductive member under the same molding conditions. Use. When the test piece of the said shape cannot be prepared for reasons, such as the shape of a heat insulation electrically-conductive member, it can be set as the plate shape which adjusted the magnitude | size suitably.

[Thermal conductivity]
The heat insulating conductive member preferably has a thermal conductivity in the thickness direction (through direction) of 1.0 W / m · K or less, and more preferably 0.5 W / m · K or less. When the thermal conductivity is greater than 1.0 W / m · K, for example, when used as a heat insulating member at the end of the fuel cell stack, a temperature gradient in the stack is formed, which is not preferable. The thermal conductivity is preferably measured on a test piece of 50 mm × 50 mm × 4 mm in accordance with US standard ASTM E1530. When a test piece having this shape cannot be prepared due to the shape of the heat insulating conductive member, the size may be changed as appropriate.

[Mechanical properties]
In addition, when the compressive properties are measured in accordance with JIS K7181, the heat insulating conductive member preferably has a compressive deformation under a compressive load of 3 MPa of 2% or less of the thickness of the test piece, preferably 1% or less. More preferably. The smaller the compressive deformation, the better, but usually 0.1% or more under the above test conditions. It is preferable that the test piece is obtained by cutting the heat insulating conductive member into 50 mm × 50 mm × 4 mm. However, if the test piece cannot be produced according to the shape of the heat insulating conductive member, the size of the test piece may be changed as appropriate. Alternatively, the same conductive composition used for the production of the heat insulating conductive member may be used which is molded under the same molding conditions.

EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to an Example at all.
(Example 1)
[Production of boron-doped graphite]
As scale-like natural graphite, 0.6 kg of boron carbide (B ₄ C) was added to Brazil-made scale-like natural graphite Micrograf 99860HP, and mixed with a Henschel mixer (registered trademark) at 800 rpm for 5 minutes. This was sealed in a graphite crucible with a lid having an inner diameter of 40 cm and a volume of 40 liters, placed in a graphitization furnace using a graphite heater, and graphitized at a temperature of 2,900 ° C. in an argon gas atmosphere. After standing to cool, the powder was taken out to obtain 14 kg of powder. The obtained graphite fine powder had an average particle size of 20.5 μm and a boron content of 1.3% by mass.

[Polymethyl methacrylate fine particles]
Multi-hollow crosslinked polymethyl methacrylate (PMMA) particles (hollowness 27%, average particle size 200 μm) manufactured by Sekisui Plastics Co., Ltd. were prepared. The thermal conductivity of the PMMA particles was 0.13 W / m · K.

[Epoxy resin]
As a binder resin precursor, an epoxy resin 2210 manufactured by Three Bond Co., Ltd. was prepared.

[mixture]
The aforementioned boron-containing graphite fine powder 9.5 g and multi-hollow PMMA particles 60 g were weighed.
Weighed graphite and PMMA particles were put into a bag, and the bag was sufficiently shaken to perform dry blending. When graphite and PMMA particles were uniformly dispersed, 0.8 g of the aforementioned epoxy resin 2210 was weighed into the graphite-PMMA particle mixture. Each weighed material was put into a lab plast mill (manufactured by Toyo Seiki Co., Ltd., Model 50C150) and kneaded at 15 rpm at room temperature for 4 minutes to obtain a conductive composition. Table 1 shows the amounts of boron-containing graphite fine powder, PMMA particles, and epoxy resin used in the examples.

[Molding]
40 g of the conductive composition obtained in the above mixing step is put into a flat plate mold (dimensions 100 mm × 100 mm × 4 mm thickness), and 135 ° C. and pressure 50 t with a 50 t hydraulic forming press (manufactured by Watanabe Machine Seisakusho). After heat-pressing for 15 minutes, the heat-insulating conductive member was obtained by cooling to 45 ° C. while applying a pressure of 50 t.

[Measurement of conductivity, thermal conductivity and compression characteristics]
About the obtained heat insulation electrically-conductive member, the resistivity, thermal conductivity, and compression characteristic of the penetration direction were measured by the above-mentioned method. These measurement results are shown in Table 1.

(Example 2)
In Example 1, a heat insulating conductive member was produced in the same manner as in Example 1 except that the amount of the epoxy resin used was changed as shown in Table 1.
Then, using the obtained heat insulating conductive member, the conductivity, thermal conductivity, and compression characteristics were measured in the same manner as in Example 1. The measurement results are shown in Table 1.

(Comparative Example 1)
A heat-insulating conductive member was produced in the same manner as in Example 1 except that the weight (content) of graphite was 8.9 g as shown in Table 1 in the “mixing” step of Example 1.
Then, about the obtained heat insulation electrically-conductive member, it carried out similarly to Example 1, and measured about electroconductivity, thermal conductivity, and the compression characteristic. The measurement results are shown in Table 1.

Claims (7)

For 100 parts by mass of resin beads A having a thermal conductivity of 0.5 W / m · K or less and an average particle diameter of 50 to 500 μm,
Selected from the group consisting of particles having an average particle diameter smaller than the average particle diameter of the resin beads A and 1 nm to 200 μm and fibers having an average fiber diameter smaller than the average particle diameter of the resin beads A and 1 nm to 200 μm. A conductive composition containing 15.5 to 70 parts by mass of conductive material B.   3. The conductive composition according to claim 1, further comprising 0.1 to 30 parts by mass of a binder resin C with respect to a total of 100 parts by mass of the resin beads A and the conductive material B. 4.   The conductive composition according to claim 1 or 2, wherein the conductive material B is flaky particles.   The conductive composition according to claim 2, wherein the resin beads A are acrylic resin beads and the binder resin C is an epoxy resin.   The heat insulation electrically-conductive member obtained by shape | molding the electrically conductive composition of any one of Claims 1-4.   The heat insulation electrically-conductive member of Claim 5 which is a member provided in the cell edge part of a fuel cell. 100 parts by mass of resin beads A having a thermal conductivity of 0.5 W / m · K or less and an average particle size of 50 to 500 μm;
Selected from the group consisting of particles having an average particle diameter smaller than the average particle diameter of the resin beads A and 1 nm to 200 μm and fibers having an average fiber diameter smaller than the average particle diameter of the resin beads A and 1 nm to 200 μm. A method for producing a heat-insulating conductive member, comprising dry blending 15.5 to 70 parts by mass of a conductive material B to be heated and then compression-molding.