JP2020164590A - Heat-conductive bead, method for producing the same, resin composition, and molded body - Google Patents

Abstract

To provide: a heat-conductive bead that can be used to make a molded body having an excellent heat-conduction property and an isotropic heat-conduction property; a method for producing the same; a resin composition including said heat-conductive bead; and a molded body.SOLUTION: A heat-conductive bead 1 includes a resin part 2 made of a cured product of a curable polymer, and a filler 3 having a higher heat-conductivity than the resin part 2, having a shape anisotropy, and held by the resin part 2. The heat-conductive bead 1 exhibits spherical shape. A surface 11 of the heat-conductive bead 1 is provided with an orientation layer 12 in which the filler 3 is oriented so that a major axis is along the surface 11.SELECTED DRAWING: Figure 1

Description

The present invention relates to thermally conductive beads, a method for producing the same, a resin composition, and a molded product.

Organic polymer materials such as resins have the property of having a lower specific gravity than inorganic substances such as metals and ceramics. Taking advantage of these characteristics, in various fields such as electronic devices and transportation devices, a technique for replacing a member made of an inorganic substance with an organic polymer-based material has been proposed for the purpose of weight reduction.

For example, in a heating element such as an electronic component mounted on a personal computer, a mobile terminal, an automobile, an LED lighting, or a motor mounted on an electric vehicle, a hybrid vehicle, etc., the heat generated from the heating element can be efficiently dissipated. It is desired. However, the organic polymer-based material has a problem that the thermal conductivity is lower than that of the inorganic material. Therefore, attempts have been widely made to obtain a lightweight and highly thermally conductive composition by adding a filler having high thermal conductivity to the organic polymer-based material.

In this kind of composition, fine particles having so-called shape anisotropy such as flakes and rods may be used as a filler. The fine particles having shape anisotropy can form a heat path in the composition by contacting each other in the composition, and can improve the thermal conductivity of the composition.

For example, Patent Document 1 describes a resin composition for a heat conductive sheet containing a thermosetting resin and a filler dispersed in the thermosetting resin. In the filler of Patent Document 1, (a) a void is formed in the central portion, and (b) a communication hole is formed starting from the void and communicating with the outer surface of the secondary agglomerated particles. (C) Secondary agglomerated particles in which the ratio of the average pore diameter of the communicating holes to the average pore diameter of the voids is 0.05 or more and 1.0 or less are included. Further, the secondary aggregated particles are composed of scaly hexagonal boron nitride primary particles.

Japanese Unexamined Patent Publication No. 2016-94599

When the resin composition of Patent Document 1 is molded by a method such as injection molding or transfer molding, the secondary agglomerated particles may receive a shearing force due to the flow of the composition during molding, and the secondary agglomerated particles may collapse. The primary particles and their agglomerates generated by the decay of the secondary agglomerated particles are likely to be oriented in the major axis direction of the primary particles, that is, the direction in which the outer dimensions are maximized, along the flow of the composition. Therefore, a heat path along the flow direction of the composition is more likely to be formed inside the molded product obtained by injection molding or the like. As a result, the heat conductivity of the molded product made of the resin composition of Patent Document 1 is not isotropic, and there is a possibility that the desired heat conduction characteristics cannot be obtained.

The present invention has been made in view of this background, and is a heat conductive bead capable of producing a molded product having excellent heat conductivity and isotropic heat conductivity, a method for producing the same, and the heat conductivity. It is intended to provide a resin composition and a molded product provided with beads.

One aspect of the present invention is a resin portion made of a cured product of a curable polymer and a resin portion.
It has a higher thermal conductivity than the resin portion, has shape anisotropy, and contains a filler held in the resin portion.
Spherical thermal conductive beads
The heat conductive beads have an orientation layer in which the filler is oriented so that the major axis is along the surface of the heat conductive beads.

Another aspect of the present invention is the method for producing the thermally conductive beads according to the above aspect.
Bead production for producing uncured beads containing the filler and the uncured curable polymer and having a spherical shape and having an orientation layer in which the filler is oriented so that the major axis is along the surface. Process and
A method for producing thermally conductive beads, which comprises a curing step of curing the curable polymer in the uncured beads.

On the surface of the thermally conductive beads, an orientation layer in which the filler is oriented so that the major axis is along the surface is provided. By orienting the filler on the surface of the heat conductive beads in this way, it is possible to easily form a heat path in which the fillers are connected to each other in the alignment layer. Therefore, the heat conductive beads can efficiently transfer heat along the alignment layer. Further, by bringing the heat conductive beads into contact with each other, heat can be efficiently transferred to the adjacent heat conductive beads via the alignment layer.

Further, the filler of the heat conductive beads is held in a resin portion made of a cured product of a curable polymer. Therefore, when an external force such as a shearing force is applied, the collapse of the heat conductive beads can be suppressed and the orientation state of the filler in the alignment layer can be maintained.

Further, since the heat conductive beads are spherical, when the resin composition containing the heat conductive beads is molded by a molding method involving the flow of the resin composition such as injection molding, heat conduction into the resin composition. The sex beads can be isotropically dispersed. Therefore, a heat path including an orientation layer is likely to be isotropically formed in the molded body containing the heat conductive beads.

As a result of the above, the heat conductive beads are excellent in heat conductivity, and a molded product having isotropic heat conductivity can be produced.

Further, according to the production method of the above-described embodiment, the thermally conductive beads provided with the oriented layer can be easily produced.

FIG. 1 is a cross-sectional view showing a main part of the heat conductive beads in the first embodiment. FIG. 2 is an explanatory diagram showing a method of calculating the orientation angle of the filler. FIG. 3 is an example of an optical microscope image of the heat conductive beads of Production Example 1. FIG. 4 is an explanatory diagram showing a main part of the rotation / revolution type mixer used for producing the heat conductive beads in Example 1. FIG. 5 is an electron microscope image of a cross section of the thermally conductive beads of Production Example 1. FIG. 6 is a partial cross-sectional view showing a main part of the molded product including the heat conductive beads in Example 2. FIG. 7 is a partial cross-sectional view showing a main part of the test body T3 in Example 2. FIG. 8 is a partial cross-sectional view showing a main part of the test body T4 in Example 2.

A. Thermally conductive beads The thermally conductive beads have a resin portion made of a cured product of a curable polymer and a filler held in the resin portion.

-Resin part The curable polymer used for the resin part has the property of being fluid in the uncured state and becoming a solid after curing. The curable polymer may be any of a thermosetting polymer that cures by heating, a photocurable polymer that cures by light irradiation, and a moisture-curable polymer that cures by moisture. As the curable polymer, specifically, epoxy resin, phenol resin, melamine resin, urea resin, unsaturated polyester resin, alkyd resin, oxazine resin, bismaleimide resin, triazine resin and the like can be used. Further, as the curable polymer, only one of these polymers may be used, or two or more of these polymers may be used in combination.

-Filler The filler in the thermally conductive beads has shape anisotropy and has a higher thermal conductivity than the resin portion. Here, the term "filler having shape anisotropy" means that the minor axis S _f [μm] of the filler, that is, the smallest outer dimension value among the outer dimensions of the filler measured in various directions. The major axis L _f [μm], that is, the value of the ratio L _f / S _f of the value of the largest outer dimension is 3 or more. Fillers with shape anisotropy include, for example, flakes and scaly shapes that are sufficiently long or wide compared to their thickness, and rods and fibers that are sufficiently long compared to their thickness. A shape called a shape is included.

The value of L _f / S _f is preferably 1000 or less. When the value of L _f / S _f is excessively large, that is, when the major axis of the filler is excessively longer than the minor axis, the fillers are likely to be entangled with each other in the process of producing the thermally conductive beads, and the above-mentioned non-existence It may be difficult to form the cured beads into a spherical shape. By setting the value of L _f / S _f to 1000 or less, such a problem can be avoided and spherical heat conductive beads can be easily produced.

From the viewpoint of more easily producing spherical heat conductive beads, the major axis L _{f of the} filler is preferably less than 1 mm.

The value of the ratio L _f / D _b between the major axis L _f [μm] of the filler and the diameter D _b [μm] of the heat conductive beads is preferably 10 or more and 1000 or less, and is 20 or more and 500 or less. More preferably. In this case, in the process of producing the thermally conductive beads, the filler existing near the surface can be more easily oriented in a desired direction. Further, in this case, the fillers in the alignment layer can be brought into contact with each other more easily, and more heat paths can be formed in the alignment layer. As a result, the thermal conductivity of the thermally conductive beads can be further improved.

The filler is preferably composed of a substance having a higher thermal conductivity than the resin portion. Examples of the filler include carbon-based materials such as graphite, carbon fiber and carbon nanotubes, ceramic materials such as hexagonal boron nitride, aluminum oxide, aluminum nitride, silicon nitride, magnesium oxide and silicon carbide, copper, silver and gold. One or more substances selected from metal materials such as, PBO (polyparaphenylene benzoxazole) fiber, highly crystalline organic fiber such as cellulose nanofiber, and the like can be adopted.

Further, the filler may be composed of a thermally isotropic substance, that is, a substance that can transfer heat to the same extent in any direction, or a substance that has thermal anisotropy, that is,. It may be composed of a substance having a property that heat is easily transferred in a specific direction. When the filler is composed of a substance having thermal anisotropy, it is preferable that the major axis direction of the filler and the direction in which heat is easily transferred coincide with each other. In this case, heat transfer can be performed more efficiently in the alignment layer. As a result, the thermal conductivity of the molded product containing the thermally conductive beads can be further improved.

The content of the filler in the thermally conductive beads is preferably 30% by volume or more and 95% by volume or less. If the content of the filler in the thermally conductive beads is excessively small, it may be difficult to form the thermally conductive beads into a spherical shape. Further, in this case, it becomes difficult to form a heat path through the filler in the alignment layer, which may lead to a decrease in thermal conductivity. On the other hand, when the content of the filler in the thermally conductive beads is excessively large, the resin portion is insufficient, so that voids are likely to be formed between the fillers, which causes a decrease in strength and thermal conductivity. There is a risk. By setting the content of the filler in the above-mentioned specific range, these problems can be easily avoided and the thermal conductivity of the thermally conductive beads can be sufficiently enhanced.

-Other components Even if the thermally conductive beads contain additives such as flame retardants, stabilizers, plasticizers, surfactants, and antistatic agents, as long as the above-mentioned effects are not impaired. Good.

-Shape of heat conductive beads The heat conductive beads have a spherical shape. Here, the above-mentioned "spherical shape" is a concept including a true sphere, an ellipsoidal sphere, and a shape having irregularities on the surface of these shapes. Whether or not the thermally conductive beads are spherical can be determined by the average value of the flatness calculated by the following method.

In calculating the flatness, first, the thermally conductive beads are placed on a flat plate and an optical microscope image is acquired. Two points are set on the contour of the heat conductive beads in this optical microscope image so that they are farthest from each other, and the length between the two points is measured. The length between these two points, that is, the value of the longest outer dimension measured based on the optical microscope image, is defined as the major axis L _b of the heat conductive beads. Next, based on the optical microscope image, the outer dimension in the direction orthogonal to the major axis L _b is measured, and this value is defined as the minor axis S _b of the heat conductive beads.

The flatness of each thermal conductive bead is a value calculated by the following formula (1) based on the value of the major axis L _b and the minor axis S _b obtained by the above method.
Flattening = (L _b −S _b ) / L _b・ ・ ・ (1)

By the above method, the flatness of a plurality of thermally conductive beads can be calculated, and the arithmetic mean of these flatnesses can be used as the average value of the flatnesses. In calculating the average value of the flatness, the larger the number of beads used for measuring the flatness, the more accurate the value can be calculated. The number of thermally conductive beads used in calculating the average value of the flatness may be, for example, 100 or more.

The flatness takes a value of 0 or more and less than 1, and the closer the value is to 0, the closer the shape of the heat conductive beads is to a true sphere. The average value of the flatness of the thermally conductive beads is 0.4 or less.

The average value of the flatness is preferably less than 0.2, more preferably 0.1 or less. In this case, since the heat conductive beads have a shape closer to a true sphere, it is possible to suppress the bias of the arrangement of the heat conductive beads in the molded body. As a result, a molded product having isotropic thermal conductivity can be obtained more easily.

Further, the size of the unevenness on the surface of the heat conductive beads can be evaluated based on the average value of the surface unevenness calculated by the following method. First, the thermally conductive beads are placed on a flat plate to obtain an optical microscope image. Then, the length of the contour of the heat conductive beads in the optical microscope image is measured, and this value is defined as the peripheral length P [μm]. Further, the area of the thermally conductive beads in the optical microscope image is measured, and this value is defined as the projected area S [μm ² ].

The surface unevenness is a value calculated by the following formula (2) based on the peripheral length P of the heat conductive beads and the projected area S of the heat conductive beads.
Surface unevenness = P ² / 4πS ・ ・ ・ (2)

By the above method, the surface unevenness can be calculated for a plurality of thermally conductive beads, and the arithmetic mean of these surface irregularities can be used as the average value of the surface unevenness. In calculating the average value of the surface unevenness, the more beads used to measure the surface unevenness, the more accurate the value can be calculated. The number of thermally conductive beads used in calculating the average value of the surface unevenness may be, for example, 100 or more.

The surface unevenness takes a value of 1 or more, and the closer the value is to 1, the smaller the surface unevenness of the heat conductive beads. The average value of the surface unevenness is preferably less than 1.5, more preferably 1.2 or less. In this case, since the surface of the heat conductive beads becomes smoother, the heat conductive beads are likely to come into contact with each other in the molded body. As a result, the thermal conductivity of the molded product can be further improved.

The size of the heat conductive beads is not particularly limited, but can be appropriately set from, for example, a range of 10 μm or more and 3 mm or less in diameter. Specifically, the value of the diameter D _b of the heat conductive beads is the equivalent diameter of the sphere calculated by the following formula (3) based on the projected area S of the heat conductive beads, that is, true spheres having the same volume. Diameter is used.
D _b = (4S / π) ^1/2 ... (3)

-Internal structure of the heat conductive beads The heat conductive beads have an orientation layer on the surface of which the filler is oriented so that the major axis is along the surface of the heat conductive beads. For example, when the filler is in the form of flakes, the thickness of the filler existing near the surface of the thermally conductive beads is along the radial direction of the thermally conductive beads, and the plate surface thereof is the surface of the thermally conductive beads. It is oriented so that it faces. Further, for example, when the filler is rod-shaped, the filler existing near the surface of the thermally conductive beads extends in the circumferential direction of the thermally conductive beads.

From the viewpoint of sufficiently obtaining the above-mentioned effects of the oriented layer, the oriented layer preferably has a thickness of 5% or more of the diameter of the heat conductive beads.

The heat conductive beads can easily realize isotropic heat conductivity if the filler near the surface is oriented in the specific direction. Therefore, the arrangement of the filler existing inside the alignment layer in the heat conductive beads is not particularly limited. For example, the filler in the thermally conductive beads may be oriented in the particular direction over the entire radial direction of the thermally conductive beads. Further, the heat conductive beads may have a two-layer structure including an alignment layer and a core layer existing inside the alignment layer and having fillers arranged in a disorderly direction. Further, the heat conductive beads may be configured so that the orientation state of the filler gradually changes from the surface toward the inside in the radial direction.

The degree of orientation of the filler in the alignment layer can be evaluated based on the average value and standard deviation of the orientation angles calculated by the following method. First, the thermally conductive beads are cut along the surface passing through the center of gravity to expose the cross section including the center of gravity. This cross section is observed under a microscope to obtain a microscopic image containing the filler placed closest to the surface of the thermally conductive beads. Next, on the microscopic image, draw a straight line passing through the center of gravity of the heat conductive beads and the center of gravity of the filler arranged closest to the surface of the heat conductive beads, and draw a straight line and the contour of the heat conductive beads. Determine the intersection of. Then, the tangent line of the contour of the heat conductive bead passing through this intersection is determined. The angle formed by the tangent to the contour of the thermally conductive beads determined as described above and the straight line extending in the direction parallel to the major axis of the filler is defined as the orientation angle. In determining the orientation angle, the straight line extending in the direction parallel to the major axis of the filler is inclined in the counterclockwise direction with respect to the tangent to the contour of the heat conductive bead, and in the clockwise direction. It may be tilted. For convenience, the orientation angle value shall take a positive value in the former case and a negative value in the latter case.

Orientation angles can be calculated for a plurality of fillers by the above method, and the arithmetic mean of these orientation angles can be used as the average value of the orientation angles. Further, the standard deviation of the orientation angles can be calculated by performing statistical processing on the orientation angles calculated for the plurality of fillers. In calculating the average value and standard deviation of the orientation angle, the more the number of fillers used for measuring the orientation angle, the more accurate the value can be calculated. The number of fillers used for calculating the average value and standard deviation of the orientation angles may be, for example, 100 or more.

The average value of the orientation angles is −10 ° or more and + 10 ° or less.

The average value of the orientation angles of the filler is preferably −8 ° or more and + 8 ° or less, and more preferably −5 ° or more and + 5 ° or less. The standard deviation of the orientation angle is preferably 25 ° or less, more preferably 15 ° or less. In this case, a heat path along the surface of the heat conductive beads can be more easily formed in the alignment layer of each heat conductive bead. As a result, the thermal conductivity of the heat conductive beads and the molded product provided with the beads can be further improved.

B. Method for manufacturing the heat conductive beads The method for manufacturing the heat conductive beads is
Bead production for producing uncured beads containing the filler and the uncured curable polymer and having a spherical shape and having an orientation layer in which the filler is oriented so that the major axis is along the surface. Process and
It has a curing step of curing the curable polymer in the uncured beads.

In the bead production step, any method may be adopted as long as an orientation layer can be formed on the surface of the uncured beads. For example, the bead production step includes a granulation step of producing a bead precursor composed of a mixture of the filler and the curable polymer.
A filler alignment step in which the bead precursor is formed into a spherical shape using a rotation / revolution type mixer, and the filler existing on the surface of the bead precursor is oriented so that the major axis is along the surface of the bead precursor. And, a method provided with can be adopted.

In the granulation step, first, the filler and the uncured curable polymer are mixed using a kneader or a stirrer. The uncured curable polymer is in liquid form. Further, the uncured curable polymer includes, for example, a main agent that serves as a skeleton of the cured polymer, a curing agent that binds and cures the main agents to each other, and a curing accelerator that promotes a curing reaction.

In mixing the filler and the uncured curable polymer, these components may be mixed in any order. For example, the curable polymer and the filler may be mixed after the main agent and the like are mixed in a predetermined ratio to prepare a curable polymer, or the main agent and the filler are mixed in advance and then the curing agent and the like are added. May be further mixed.

It is also possible to adjust the viscosity of the curable polymer by diluting the uncured curable polymer with an organic solvent before or during mixing with the filler. In this case, the organic solvent may be removed by means such as volatilization after the mixing with the filler is completed and before the uncured beads are cured.

The mixture of filler and curable polymer is then granulated to produce a bead precursor. As a method for forming the mixture into granules, for example, a pelletizer, a crusher, or the like can be used.

In the filler alignment step, the bead precursor is formed into a spherical shape using a rotation / revolution type mixer, and the long axis of the filler existing on the surface of the bead precursor is along the surface of the bead precursor. Orient to. Here, the rotation / revolution type mixer is configured so that the container containing the bead precursor is swiveled around the revolution axis and the container itself rotates about the rotation axis inclined with respect to the revolution axis. Refers to a mixer. According to the rotation / revolution type mixer, the bead precursor in the container can be rotated by the rotation while the centrifugal force is applied to the bead precursor in the container by the revolution. As a result, uncured beads can be produced by simultaneously forming the bead precursor and forming the alignment layer.

In the curing step, the curable polymer in the uncured beads obtained in the bead manufacturing step is cured. As a method for curing the uncured beads, an appropriate method depending on the type of the curable polymer can be adopted. For example, when the curable polymer is a thermosetting polymer, the uncured beads may be heated at a predetermined time and temperature.

C. Resin composition A resin composition can be obtained by mixing the curable beads with a resin matrix made of a resin. The resin matrix may be composed of any resin. For example, the resin matrix may be a thermosetting resin such as an epoxy resin, a phenol resin, a melamine resin, a urea resin, an unsaturated polyester resin, an alkyd resin, an oxazine resin, a bismaleimide resin, or a triazine resin, or a polyamide resin. It may be a thermoplastic resin such as polyester, polycarbonate, acrylic polymer, methacrylic polymer, polyimide, liquid crystal polymer, polyolefin, polystyrene, polyphenylene ether and the like. Further, as the resin matrix, one of a thermosetting resin and a thermoplastic resin may be used, or two or more of them may be used in combination.

Further, the resin matrix may contain additives such as a filler, a flame retardant, a stabilizer, a plasticizer, a surfactant, and an antistatic agent. The filler in the resin matrix may have shape anisotropy or may have an isotropic shape. Even when the filler in the resin matrix has shape anisotropy, it is possible to prevent the filler in the resin matrix from being oriented in a specific direction after molding by mixing with the thermally conductive beads. .. As a result, a molded product having isotropic heat conduction characteristics can be easily obtained.

The resin composition may contain one type of thermally conductive beads, or may contain a plurality of types of thermally conductive beads having different fillers and / or curable polymers. Further, the thermally conductive beads in the resin composition may have a single diameter or may have various diameters. From the viewpoint of further improving the filling property of the heat conductive beads in the molded body, it is preferable to use a plurality of types of heat conductive beads having different particle size distributions in combination as the heat conductive beads.

The content of the thermally conductive beads in the resin composition can be appropriately set from, for example, in the range of 10% by volume or more and 95% by volume or more. When the content of the heat conductive beads is excessively low, it becomes difficult for a heat path to be formed in the resin composition. As a result, the thermal conductivity of the molded product may decrease. Further, when the content of the heat conductive beads is excessively large, the resin matrix may be insufficient, and it may be difficult to mold the resin composition into a desired shape. By setting the content of the thermally conductive beads within the above-mentioned specific range, these problems can be easily avoided.

The content of the thermally conductive beads in the resin composition is preferably 30% by volume or more and 95% by volume or less. In this case, the heat conductive beads are more likely to come into contact with each other, so that a heat path is more easily formed in the molded body. Therefore, in this case, the thermal conductivity of the molded product can be increased.

D. Molded article By molding the resin composition, a molded article having isotropic thermal conductivity can be obtained. The molding method of the resin composition is not particularly limited, and from known molding methods such as compression molding, vacuum compression molding, transfer molding, injection molding, extrusion molding, and cast molding, the type of resin matrix and desired molding can be used. It can be appropriately selected according to the shape of the body and the like.

As described above, a heat path including the alignment layer of the heat conductive beads is formed inside the molded body obtained by molding the resin composition. Therefore, the molded product has isotropic thermal conductivity, that is, a property that heat is transferred to the same extent in any direction. More specifically, the molded body has a thermal conductivity λ _A [W / m · K] in the direction of maximum thermal conductivity and a thermal conductivity λ _B [W] in the direction of minimum thermal conductivity. It has the characteristic that the value of thermal conductivity anisotropy λ _A / λ _B , which is the ratio with [/ m · K], is 1.5 or less.

The thermal conductivity λ _B is preferably 7 W / m · K or more. In this case, the thermal conductivity of the entire molded product can be further improved. A molded product having such thermal conductivity is suitable for applications such as a heat radiating member.

(Example 1)
Examples of the thermally conductive beads and the method for producing the same will be described with reference to FIGS. 1 to 5. As shown in FIG. 1, the heat conductive beads 1 of this example have a resin portion 2 made of a cured product of a curable polymer and a thermal conductivity higher than that of the resin portion 2 and have shape anisotropy. The filler 3 held by the resin portion 2 is included. As shown in FIG. 3, the heat conductive beads 1 have a spherical shape. Further, as shown in FIG. 1, the surface 11 of the heat conductive beads 1 is provided with an orientation layer 12 in which the filler 3 is oriented so that the major axis is along the surface 11.

The heat conductive beads 1 of this example contain the filler 3 and the uncured curable polymer and have a spherical shape, and the surface thereof is provided with an alignment layer 12 in which the filler 3 is oriented so that the major axis is along the surface. It is produced by a production method including a bead production step of producing the uncured beads and a curing step of curing the curable polymer in the uncured beads. Further, in the bead manufacturing step, the bead precursor 100 is made spherical by using the granulation step of preparing the bead precursor 100 made of a mixture of the filler 3 and the curable polymer and the rotation / revolution type mixer 4 shown in FIG. It has a filler alignment step of aligning the filler 3 existing on the surface of the bead precursor 100 while molding so that the major axis is aligned with the surface of the bead precursor 100.

In this example, specifically, two types of thermally conductive beads 1 were produced as follows.

-Manufacturing example 1
In Production Example 1, flaky graphite (“UP-20” manufactured by Nippon Graphite Trading Co., Ltd.) having an average major axis of 3.37 μm and an average minor axis of 0.28 μm was used as the filler 3. Moreover, bisphenol A type epoxy resin was used as a curable polymer. Specifically, the curable polymer includes a main agent having a bisphenol A skeleton (“jER® 827” manufactured by Mitsubishi Chemical Industry Co., Ltd.) and 4-methylcyclohexane-1,2-dicarboxylic acid anhydride as a curing agent. (Manufactured by Tokyo Chemical Industry Co., Ltd.) and 2-ethyl-4-methylimidazole (manufactured by Tokyo Chemical Industry Co., Ltd.) as a curing accelerator are contained.

In the granulation step, first, 108 parts by mass of a curing agent and 1 part by mass of a curing accelerator were mixed with 100 parts by mass of the above-mentioned main agent to prepare an uncured curable polymer. Next, 15 parts by mass of the filler 3 was added to 5 parts by mass of the curable polymer and mixed to obtain a clay-like mixture. Then, the mixture obtained using a pelletizer was molded into granules to prepare a bead precursor 100.

In the filler alignment step, after the above-mentioned bead precursor 100 is placed in the container 41 of the rotation / revolution type mixer 4 (“ARE-310” manufactured by Shinky Co., Ltd.) shown in FIG. 4, the revolution speed of the container 41 is 2000 rpm. , The rotation speed was set to 800 rpm and stirring was performed for 2 minutes.

The container 41 of the rotation / revolution type mixer 4 used in this example has a cylindrical shape as shown in FIG. 4, and is arranged so that the central axis and the rotation axis 42 coincide with each other. Further, the rotation shaft 42 of the container 41 is arranged so as to be inclined by 45 ° with respect to the revolution shaft 43. The container 41 is configured to rotate around the revolution shaft 43 while rotating around the rotation shaft 42 (that is, the central axis of the container 41).

The bead precursor 100 in the container 41 rotates by rotation while receiving centrifugal force due to the revolution of the container 41. As a result, the uncured beads described above can be obtained by orienting the filler 3 existing on the surface of the bead precursor 100 in the specific direction while forming the bead precursor 100 into a spherical shape.

In the curing step, the uncured beads were heated to cure the curable polymer. In the curing step of this example, specifically, the uncured beads are heated with a temperature history of holding at a temperature of 80 ° C. for 1 hour, then holding at a temperature of 120 ° C. for 1 hour, and then holding at a temperature of 150 ° C. for 3 hours. did. As described above, the thermally conductive beads 1 in which the flake graphite filler 3 was dispersed in the resin portion 2 made of the cured product of the bisphenol A type epoxy resin were produced. The mass ratio and volume ratio of the filler 3 and the resin portion 2 in the heat conductive beads 1 of Production Example 1 are as shown in Table 1.

-Manufacturing example 2
In this example, hexagonal boron nitride (GP grade manufactured by Denka Co., Ltd.) having an average major axis of 3.44 μm and an average minor axis of 0.33 μm was used as the filler 3 instead of flaky graphite. Performed a granulation step, a filler alignment step, and a curing step under the same conditions as in Production Example 1. As a result, the thermally conductive beads 1 in which the filler 3 of hexagonal boron nitride was dispersed in the resin portion 2 made of the cured product of the bisphenol A type epoxy resin were produced. The mass ratio and volume ratio of the filler 3 and the resin portion 2 in the heat conductive beads 1 of Production Example 2 are as shown in Table 1. In Table 1, hexagonal boron nitride is referred to as "h-BN".

Next, the shapes of the heat conductive beads 1 of Production Examples 1 and 2 and the orientation state of the filler 3 were evaluated by the following methods.

-Shape of the heat conductive beads 1 The heat conductive beads 1 were observed with an optical microscope to obtain an optical microscope image. Using image analysis software (“WinROOF2015” manufactured by Mitani Shoji Co., Ltd.), the major axis L _b [μm], minor axis S _b [μm], and peripheral length P of the thermally conductive beads 1 in the optical microscope image shown in FIG. [Μm] and the projected area S [μm ² ] were calculated. Then, for each of the thermally conductive beads 1, the values of the flatness, the surface unevenness, and the diameter D _b were calculated based on the following equations (1) to (3).
Flattening = (L _b −S _b ) / L _b・ ・ ・ (1)
Surface unevenness = P ² / 4πS ・ ・ ・ (2)
D _b = (4S / π) ^1/2 ... (3)

After measuring the values of flatness, surface unevenness and diameter D _b of 100 or more thermally conductive beads 1, statistical processing was performed to calculate the average value and standard deviation. Table 1 shows the flatness, surface unevenness, average value and standard deviation of the diameter D _b of the thermally conductive beads 1.

-Orientation state of filler 3 After cutting the thermally conductive beads 1, the cross section was polished to expose the cross section passing through the center of gravity. This cross section was observed with a scanning electron microscope, and the electron microscope image shown in FIG. 5 was obtained. Although not shown in the figure, when the vicinity of the surface 11 of the heat conductive bead 1 was observed at a higher magnification, the filler 3 existing in the vicinity of the surface 11 was found to have the heat conductive bead 1 in the thickness direction of the filler 3. The major axis of the filler 3 was oriented along the radial direction of the heat conductive beads 1 along the surface 11 of the heat conductive beads 1. Further, in the thermally conductive beads 1 of Production Example 1 and Production Example 2, the filler 3 existing at least within a depth of 50 μm from the surface 11 was oriented in the specific direction. That is, the thickness of the alignment layer 12 in the heat conductive beads 1 of Production Example 1 and Production Example 2 was 50 μm or more.

Next, using image analysis software (“WinROOF2015” manufactured by Mitani Shoji Co., Ltd.), the orientation angle θ of the filler 3 arranged closest to the surface 11 of the heat conductive beads 1 by the following method (see FIG. 2). Was calculated. First, on the electron microscope image, a straight line L1 passing through the center of gravity W _b of the heat conductive beads 1 and the center of gravity W _f of the packing material 3 arranged at the position closest to the surface 11 of the heat conductive beads 1 is drawn. The intersection 13 between the straight line L1 and the surface 11 of the heat conductive beads 1 was determined. Then, the tangent line L2 of the contour of the heat conductive bead 1 passing through the intersection 13 was determined. The angle formed by the tangent line L2 determined as described above and the straight line L3 extending in the direction parallel to the major axis of the filler 3 was defined as the orientation angle θ. For convenience, the description of the filler 3 is partially omitted in FIG.

After measuring the value of the orientation angle θ for 100 or more fillers 3, statistical processing was performed to calculate the average value and standard deviation of the orientation angle θ. Table 1 shows the average value and standard deviation of the orientation angle θ in the thermally conductive beads 1 of Production Example 1 and Production Example 2.

As shown in Table 1, the thermally conductive beads 1 of Production Example 1 and Production Example 2 have an orientation layer 12 on the surface 11 of which the filler 3 is oriented in the specific direction. By orienting the filler 3 on the surface 11 of the heat conductive beads 1 in this way, it is possible to easily form a heat path in which the fillers 3 are connected to each other in the alignment layer 12. Therefore, the heat conductive beads 1 can efficiently transfer heat along the alignment layer 12. Further, by bringing the heat conductive beads 1 into contact with each other, heat can be efficiently transferred to the adjacent heat conductive beads 1 via the alignment layer 12.

Further, the filler 3 of the heat conductive beads 1 is held by the resin portion 2 made of a cured product of the curable polymer. Therefore, when an external force such as a shearing force is applied, the disintegration of the heat conductive beads 1 can be suppressed and the orientation state of the filler 3 in the alignment layer 12 can be maintained.

Further, since the heat conductive beads 1 are spherical, when the resin composition containing the heat conductive beads 1 is molded by a molding method involving the flow of the resin composition such as injection molding, heat is contained in the resin composition. The conductive beads 1 can be isotropically dispersed. Therefore, a heat path including the alignment layer 12 is likely to be isotropically formed in the molded body containing the heat conductive beads 1.

As a result of the above, according to the heat conductive beads 1 of Production Example 1 and Production Example 2, a heat path including the alignment layer 12 can be formed isotropically in the molded body, and the heat conductivity can be improved. ..

(Example 2)
In this example, an example of the molded product 5 including the heat conductive beads 1 will be described with reference to FIG. Of the codes used in the examples after this example, the same codes as those used in the above-mentioned examples indicate the same components and the like as the components and the like in the above-mentioned examples unless otherwise specified.

As shown in FIG. 6, the molded product 5 of this example contains a resin matrix 51 and the heat conductive beads 1 dispersed in the resin matrix 51. In this example, specifically, two types of molded bodies 5 (test bodies T1 and T2) were produced as follows.

・ Specimen T1
The resin matrix 51 of the test body T1 contains a cured product 511 of a bisphenol A type epoxy resin and a filler 512 dispersed in the cured product. Specifically, the cured product 511 in the resin matrix 51 of the test body T1 is a main agent having a bisphenol A skeleton (“jER® 827” manufactured by Mitsubishi Chemical Corporation, 4-methylcyclohexane-1, as a curing agent, A bisphenol A type epoxy resin obtained by curing a mixture of 2-dicarboxylic acid anhydride (manufactured by Tokyo Kasei Kogyo Co., Ltd.) and 2-ethyl-4-methylimidazole (manufactured by Tokyo Kasei Kogyo Co., Ltd.) as a curing accelerator. Further, the filler 512 in the test piece T1 is specifically flaky graphite (“UP-20” manufactured by Nippon Graphite Trading Co., Ltd.).

In preparing the test body T1, first, 108 parts by mass of a curing agent and 1 part by mass of a curing accelerator were mixed with 100 parts by mass of the main agent to prepare an uncured curable polymer. Next, 15 parts by mass of the filler 512 was added to 5 parts by mass of the curable polymer and mixed to obtain an uncured resin matrix.

Next, 50 parts by volume of the heat conductive beads 1 of Production Example 1 were mixed with 50 parts by volume of the uncured resin matrix to prepare a resin composition. This resin composition was placed in a cylindrical mold having an inner diameter of φ40 mm and compression molded. In press molding, heating was performed while pressurizing under the conditions of a pressure of 37 MPa and a temperature of 80 ° C. for 1 hour, then the temperature was raised to 120 ° C. while maintaining the pressure, and the temperature of 120 ° C. was maintained for 1 hour. Then, the molded product 5 taken out from the mold was heated at a temperature of 150 ° C. for 3 hours to sufficiently cure the resin matrix 51. From the above, a molded body 5 having a disk shape with a thickness of 1.2 mm and a diameter of 40 mm was obtained. This molded body 5 was designated as a test body T1.

・ Specimen T2
As the filler 512 in the resin matrix 51, hexagonal boron nitride (GP grade manufactured by Denka Co., Ltd.) having an average major axis of 3.44 μm and an average minor axis of 0.33 μm is used instead of flaky graphite. The molded product 5 was produced under the same conditions as the test body T1 except that the heat conductive beads 1 of Production Example 2 were used instead of the heat conductive beads 1 of Production Example 1 as the heat conductive beads 1. This molded body 5 was designated as a test body T2.

In this example, for comparison with the test body T1 and the test body T2, molded bodies (test bodies T3 to T6) prepared without using the heat conductive beads 1 were prepared. The specific manufacturing method of the test bodies T3 to T6 is as follows.

・ Specimen T3
The granulation step and the filler alignment step were carried out in the same manner as in the heat conductive beads 1 of Production Example 1 to prepare uncured beads. The uncured beads were placed in a cylindrical mold having an inner diameter of φ40 mm, and compression molding was performed under the same conditions as the test piece T1. From the above, a molded body having a disk shape having a thickness of 1.2 mm and a diameter of 40 mm was obtained. This molded product was designated as a test body T3.

・ Specimen T4
The uncured resin matrix used in the test body T1 was placed in a cylindrical mold having an inner diameter of φ40 mm, and compression molding was performed under the same conditions as the test body T1. From the above, a molded body having a disk shape having a thickness of 1.2 mm and a diameter of 40 mm was obtained. This molded product was designated as a test body T4.

・ Specimen T5
Compression molding was performed under the same conditions as the test piece T3 except that the uncured beads of Production Example 2 were used instead of the uncured beads of Production Example 1. From the above, a molded body having a disk shape having a thickness of 1.2 mm and a diameter of 40 mm was obtained. This molded product was designated as a test body T5.

・ Specimen T6
Compression molding was performed under the same conditions as the test body T4 except that the uncured resin matrix used in the test body T2 was used instead of the uncured resin matrix used in the test body T1. From the above, a molded body having a disk shape having a thickness of 1.2 mm and a diameter of 40 mm was obtained. This molded product was designated as a test body T6.

The thermal conductivity of the test bodies T1 to T6 obtained as described above was evaluated by the following method.

-Measuring method of thermal conductivity and thermal conductivity anisotropy Using a thermal property measuring device ("Thermowave Analyzer TA35" manufactured by Bethel Co., Ltd.), the thickness direction and in-plane direction (that is, the thickness direction) of the test piece The thermal diffusivity λ [m ² · s ^-1 ] was measured in the direction perpendicular to. In addition, the constant pressure specific heat Cp [J ・ K ^-1・ kg ^-1 ] of the test piece was measured using a differential scanning calorimeter (“DSC7000” manufactured by Hitachi High-Tech Science Corporation). Furthermore, the density ρ [kg · m ^-3 ] of the test ^piece was measured by the Archimedes method. All of these measurements were performed in an environment of 25 ± 2 ° C.

By substituting the values of the thermal diffusivity λ, the constant pressure specific heat Cp, and the density ρ obtained as described above into the following equation (4), the value of the thermal conductivity in the direction in which the thermal diffusivity was measured α [Wm ^-1].・ The value of K ^-1 ] can be calculated. Table 2 shows the thermal conductivity in the thickness direction and the thermal conductivity in the in-plane direction of the test pieces T1 to T6. In the manufacturing method of this example, one of the thickness direction of the test piece or the direction perpendicular to the thickness direction is the direction in which the thermal conductivity is the maximum, and the other is the direction in which the thermal conductivity is the minimum. It is estimated that
α = λ × Cp × ρ ・ ・ ・ (4)

As shown in Table 2, the thermal conductivity λ _A [W / m · K] in the direction in which the thermal conductivity is maximum and the heat in the direction in which the thermal conductivity is minimum in the test body T1 and the test body T2. The value of the thermal conductivity anisotropy λ _A / λ _B , which is the ratio to the conductivity λ _B [W / m · K], is 1.5 or less. From these results, it can be understood that the test body T1 and the test body T2 have isotropic thermal conductivity.

As shown in FIG. 6 as an example, it is presumed that the arrangement of the filler 3 of the heat conductive beads 1 is maintained inside the test body T1 and the test body T2 even after molding. Then, it is considered that the heat path including the alignment layer 12 is formed isotropically by the contact between the alignment layers 12 of the heat conductive beads 1.

On the other hand, the values of the thermal conductivity anisotropy λ _A / λ _B of the test body T3 and the test body T5 were larger than those of the test body T1 and the test body T2. Inside the test body T3 and the test body T5, as shown in FIG. 7, the arrangement of the filler 3 derived from the uncured beads changes from a spherical shape to an elliptical spherical shape due to the compression of the uncured beads during molding. It is estimated that it was done. Then, the arrangement of the filler 3 changed to an elliptical sphere, which cut off the heat path formed by the contact between the ends of the filler 3 in the major axis direction, resulting in a decrease in thermal conductivity in the thickness direction. Conceivable.

The values of the thermal conductivity anisotropy λ _A / λ _B of the test body T4 and the test body T6 were even larger than those of the test body T3 and the test body T5. Inside the test body T4 and the test body T6, as shown in FIG. 8, the major axis of the filler 512 and the thickness direction of the molded body are perpendicular to each other as the resin matrix 51 flows during molding. It is presumed that the filler 512 was oriented. It is considered that the value of the thermal conductivity anisotropy increased due to the orientation of the filler 512 in this way.

The specific embodiments of the heat conductive beads 1, the resin composition, and the molded product 5 according to the present invention are not limited to the embodiments described in Examples 1 and 2, and impair the gist of the present invention. The configuration can be changed as appropriate within the range.

For example, in Example 2, the resin composition and the molded product 5 using the resin matrix 51 having the same composition as the heat conductive beads 1 are shown, but the composition of the resin matrix 51 is the heat conductive beads. It may be different from 1.

1 Thermally conductive beads 11 Surface 12 Orientation layer 2 Resin part 3 Filler

Claims (10)

A resin part made of a cured product of a curable polymer and
It has a higher thermal conductivity than the resin portion, has shape anisotropy, and contains a filler held in the resin portion.
Spherical thermal conductive beads
A thermally conductive bead having an orientation layer in which the filler is oriented so that a major axis is along the surface of the thermally conductive bead. The heat conductive bead according to claim 1, wherein the thickness of the alignment layer is 5% or more of the diameter of the heat conductive bead. The value of the ratio L _f / D _b between the major axis L _f [μm] of the filler and the diameter D _b [μm] of the heat conductive beads is 10 or more and 1000 or less, according to claim 1 or 2. Thermally conductive beads. The heat conductive bead according to any one of claims 1 to 3, wherein the content of the filler in the heat conductive bead is 30% by volume or more and 95% by volume or less. The method for producing thermally conductive beads according to any one of claims 1 to 4.
Bead production for producing uncured beads containing the filler and the uncured curable polymer and having a spherical shape and having an orientation layer in which the filler is oriented so that the major axis is along the surface. Process and
A method for producing thermally conductive beads, which comprises a curing step of curing the curable polymer in the uncured beads. The bead manufacturing step is
A granulation step of producing a bead precursor composed of a mixture of the filler and the curable polymer.
While forming the bead precursor into a spherical shape using a rotation / revolution type mixer, the filler existing on the surface of the bead precursor is aligned so that the major axis is aligned with the surface of the bead precursor. The method for producing a thermally conductive bead according to claim 5, which comprises a step. A resin matrix made of resin and
A resin composition comprising the thermally conductive beads according to any one of claims 1 to 4 dispersed in the resin matrix. The resin composition according to claim 7, wherein the content of the thermally conductive beads is 30% by volume or more and 95% by volume or less. A molded product of the resin composition according to claim 7 or 8.
Thermal heat, which is the ratio of the thermal conductivity λ _A [W / m · K] in the direction of maximum thermal conductivity to the thermal conductivity λ _B [W / m · K] in the direction of minimum thermal conductivity. _A molded body having a conductivity anisotropy λ _A / λ _B value of 1.5 or less. The molded product according to claim 9, wherein the thermal conductivity λ _B is 7 W / m · K or more.