JP7249630B2 - THERMALLY CONDUCTIVE BEADS, METHOD FOR MANUFACTURING SAME, RESIN COMPOSITION AND MOLDED PRODUCT - Google Patents

Description

TECHNICAL FIELD The present invention relates to thermally conductive beads, methods for producing the same, resin compositions, and molded articles.

Organic polymer materials such as resins have the characteristic of having a smaller specific gravity than inorganic materials such as metals and ceramics. Taking advantage of these characteristics, in various fields such as electronic equipment and transportation equipment, techniques have been proposed to replace inorganic materials with organic polymer materials for the purpose of weight reduction.

For example, in a heat generator such as a motor mounted in an electronic component mounted in a personal computer, a mobile terminal, an automobile, an LED lighting, etc., an electric vehicle, a hybrid vehicle, etc., it is possible to efficiently dissipate the heat generated from the heat generator. Desired. However, organic polymer-based materials have a problem of lower thermal conductivity than inorganic materials. Attempts have therefore been made to obtain a lightweight and highly thermally conductive composition by adding a highly thermally conductive filler to an organic polymer material.

In this type of composition, fine particles having so-called shape anisotropy, such as flaky or rod-like particles, are sometimes used as fillers. Fine particles having shape anisotropy can form heat paths in the composition by contacting each other in the composition, thereby improving the thermal conductivity of the composition.

For example, Patent Literature 1 describes a resin composition for thermally conductive sheets containing a thermosetting resin and a filler dispersed in the thermosetting resin. In the filler of Patent Document 1, (a) voids are formed in the central portion, and (b) communicating holes are formed starting from the voids and communicating with the outer surfaces of the secondary aggregated particles, (c) contains secondary aggregated particles in which the ratio of the average pore diameter of the communicating pores to the average pore diameter of the pores is 0.05 or more and 1.0 or less; In addition, the secondary agglomerated particles are composed of scale-like primary particles of hexagonal boron nitride.

JP 2016-94599 A

When the resin composition of Patent Document 1 is molded by a method such as injection molding or transfer molding, the secondary aggregated particles are subjected to shear force due to the flow of the composition during molding, and the secondary aggregated particles may collapse. The primary particles and their aggregates produced by the collapse of the secondary aggregate particles tend to be oriented so that the major diameter direction of the primary particles, that is, the direction in which the outer dimension is maximized, follows 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 article obtained by injection molding or the like. As a result of the above, the thermal conductivity of the molded article made of the resin composition of Patent Document 1 is no longer isotropic, and desired thermal conductivity properties may not be obtained.

The present invention has been made in view of this background. An object of the present invention is to provide a resin composition having beads and a molded article.

One reference embodiment of the present invention is a resin part made of a cured product of a curable polymer,
a filler that has higher thermal conductivity than the resin portion, has shape anisotropy, and is held by the resin portion;
Thermally conductive beads having a spherical shape,
The thermally conductive bead has an orientation layer on the surface of the thermally conductive bead, in which the filler is oriented such that the long axis extends along the surface.

One aspect of the present invention is a method for producing a thermally conductive bead according to the aspect described above,
A bead for producing an uncured bead having a spherical shape containing the filler and the uncured curable polymer, and having an orientation layer on the surface thereof in which the filler is oriented such that the long axis is along the surface. a manufacturing process;
curing the curable polymer in the uncured beads ;
The bead production step includes:
a granulation step of making a bead precursor consisting of a mixture of the filler and the curable polymer;
Filler alignment for orienting the filler existing on the surface of the bead precursor such that the long axis is along the surface of the bead precursor while shaping the bead precursor into a spherical shape using a rotation-revolution mixer. A method for producing thermally conductive beads, comprising the steps of:

An orientation layer is provided on the surface of the thermally conductive bead, in which the filler is oriented such that the long axis extends along the surface. By orienting the fillers on the surfaces of the thermally conductive beads in this manner, heat paths in which the fillers are connected to each other can be easily formed in the orientation layer. Therefore, the thermally conductive beads can efficiently transfer heat along the alignment layer. Furthermore, by bringing the thermally conductive beads into contact with each other, heat can be efficiently transferred to the adjacent thermally conductive beads via the orientation layer.

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

Furthermore, since the thermally conductive beads are spherical, when the resin composition containing the thermally conductive beads is molded by a molding method such as injection molding that involves the flow of the resin composition, heat conduction in the resin composition does not occur. The beads can be isotropically dispersed. Therefore, a heat path including the orientation layer is likely to be isotropically formed in the molding including the thermally conductive beads.

As a result of the above, the thermally conductive beads are excellent in thermal conductivity and can produce a molded article having isotropic thermal conductivity.

Moreover, according to the manufacturing method of the above aspect, the thermally conductive beads having the alignment layer can be easily manufactured.

1 is a cross-sectional view showing a main part of a thermally conductive bead in Example 1. FIG. FIG. 2 is an explanatory diagram showing a method of calculating the orientation angle of the filler. 3 is an example of an optical microscope image of the thermally conductive beads of Production Example 1. FIG. FIG. 4 is an explanatory view showing the essential parts of a rotation-revolution mixer used for producing thermally 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. FIG. 6 is a partial cross-sectional view showing a main part of a molded body containing thermally conductive beads in Example 2. FIG. FIG. 7 is a partial cross-sectional view showing a main part of the test body T3 in Example 2. FIG. FIG. 8 is a partial cross-sectional view showing the main part of the test body T4 in Example 2. FIG.

A. Thermally Conductive Bead The thermally conductive bead has 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 in the resin part has fluidity in an uncured state and has a property of becoming solid after curing. The curable polymer may be a thermosetting polymer that is cured by heating, a photocurable polymer that is cured by light irradiation, or a moisture-curable polymer that is cured by moisture. Specific examples of curable polymers that can be used include epoxy resins, phenol resins, melamine resins, urea resins, unsaturated polyester resins, alkyd resins, oxazine resins, bismaleimide resins and triazine resins. As the curable polymer, only one kind of these polymers may be used, or two or more kinds thereof may be used in combination.

-Filler The filler in the thermally conductive beads has shape anisotropy and thermal conductivity higher than that of the resin portion. Here, the filler "has shape anisotropy" means that the minor diameter _Sf [μm] of the filler, that is, the value of the smallest outer dimension among the outer dimensions of the filler measured in various directions It means that the major axis L _f [μm], that is, the value of the ratio L _f /S _f of the largest outer dimension value is 3 or more. Fillers having shape anisotropy include, for example, flake-like or scale-like shapes whose length or width is sufficiently wider than thickness, and rod-like or fiber-like shapes whose length is sufficiently long compared to 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 long relative to the minor axis, the fillers tend to get entangled with each other during the production process of the thermally conductive beads. It can be difficult to mold 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 making spherical thermally conductive beads more easily, the major axis L _f of the filler is preferably less than 1 mm.

The ratio D _b /L _f of the major diameter L _f [μm] of the filler to the diameter D _b [μm] of the thermally conductive beads is preferably 10 or more and 1000 or less, and 20 or more and 500 or less. It is more preferable to have In this case, the filler present near the surface can be more easily oriented in a desired direction in the process of producing the thermally conductive beads. Also, 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.

It is preferable that the filler be made of a material having a higher thermal conductivity than the resin portion. Examples of fillers include carbon-based materials such as graphite, carbon fibers, and carbon nanotubes; ceramic materials such as hexagonal boron nitride, aluminum oxide, aluminum nitride, silicon nitride, magnesium oxide, and silicon carbide; and copper, silver, and gold. , PBO (polyparaphenylenebenzoxazole) fibers, highly crystalline organic fibers such as cellulose nanofibers, and the like.

In addition, the filler may be composed of a thermally isotropic substance, that is, a substance that can conduct heat equally in any direction, or a thermally anisotropic substance, that is, It may be composed of a material having a property that heat is easily conducted in a specific direction. When the filler is composed of a substance having thermal anisotropy, it is preferable that the longitudinal direction of the filler coincides with the direction in which heat is easily conducted. In this case, heat transfer can be performed more efficiently within the alignment layer. As a result, the thermal conductivity of the molded article 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 filler content in the thermally conductive beads is too low, it may be difficult to form the thermally conductive beads into a spherical shape. Moreover, 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, if the content of the filler in the thermally conductive beads is excessively high, the resin portion becomes insufficient, so voids are likely to be formed between the fillers, resulting in a decrease in strength and thermal conductivity. There is a risk. By setting the content of the filler within the specific range, these problems can be easily avoided and the thermal conductivity of the thermally conductive beads can be sufficiently enhanced.

・Other components The thermally conductive beads may contain additives such as flame retardants, stabilizers, plasticizers, surfactants, and antistatic agents within the range that does not impair the effects described above. good.

- Shape of Thermally Conductive Bead The thermally conductive bead has a spherical shape. Here, the above-mentioned "spherical shape" is a concept including a perfect sphere, an elliptical sphere, and a shape obtained by imparting unevenness to the surface of these shapes. Whether or not the thermally conductive beads are spherical can be determined by the average value of the oblateness calculated by the following method.

In calculating the oblateness, first, thermally conductive beads are placed on a flat plate and an optical microscope image is obtained. Two points are set on the outline of the thermally conductive bead in this optical microscope image so that the distance between them is the longest, 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 _Lb of the thermally conductive bead. Next, based on the optical microscope image, the outer dimension in the direction perpendicular to the major axis _Lb is measured, and this value is defined as the minor axis _Sb of the thermally conductive bead.

The flatness of each thermally 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 method described above.
Oblateness = (L _b - S _b )/L _b (1)

The flattening of a plurality of thermally conductive beads can be calculated by the above method, and the arithmetic mean of the flattening can be used as the average flattening. In calculating the average flattening ratio, the more the number of beads used for measuring the flattening ratio, the more accurate the calculation. The number of thermally conductive beads used for calculating the average flattening value may be, for example, 100 or more.

The oblateness 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 thermally conductive bead is to a true sphere. The average flatness of the thermally conductive beads is 0.4 or less.

The average flattening ratio is preferably less than 0.2, more preferably 0.1 or less. In this case, since the thermally conductive beads have a shape that is closer to a true sphere, uneven placement of the thermally conductive beads in the compact can be suppressed. As a result, a molded article having isotropic thermal conductivity can be obtained more easily.

In addition, the size of unevenness on the surface of the thermally conductive bead can be evaluated based on the average value of surface unevenness calculated by the following method. First, a thermally conductive bead is placed on a flat plate and an optical microscope image is obtained. Then, the length of the contour of the thermally conductive bead in the optical microscope image is measured, and this value is defined as the peripheral length P [μm]. Also, 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 degree of surface unevenness is a value calculated by the following formula (2) based on the peripheral length P of the thermally conductive beads and the projected area S of the thermally conductive beads.
Surface unevenness=P ² /4πS (2)

The surface unevenness is calculated for a plurality of thermally conductive beads by the above method, and the arithmetic mean of the surface unevenness can be used as the average value of the surface unevenness. When calculating the average value of the degree of surface unevenness, the more the number of beads used for measuring the degree of surface unevenness, the more accurate the value can be calculated. The number of thermally conductive beads used for calculating the average value of surface unevenness may be, for example, 100 or more.

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

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

-Internal Structure of Thermally Conductive Bead The thermally conductive bead has, on its surface, an orientation layer in which the filler is oriented such that the long axis is along the surface of the thermally conductive bead. For example, when the filler is in the form of flakes, the filler present in the vicinity of the surface of the thermally conductive bead has a thickness direction along the radial direction of the thermally conductive bead and a plate surface of the thermally conductive bead. is oriented to face the Further, for example, when the filler is rod-shaped, the filler present near the surface of the thermally conductive bead extends in the circumferential direction of the thermally conductive bead.

From the viewpoint of sufficiently obtaining the effects of the orientation layer, the orientation layer preferably has a thickness of 5% or more of the diameter of the thermally conductive beads.

Thermally conductive beads can easily achieve isotropic thermal conductivity if the filler near the surface is oriented in the specific direction. Therefore, the arrangement of the filler present inside the alignment layer in the thermally conductive beads is not particularly limited. For example, the filler in the thermally conductive bead may be oriented in the specific direction over the entire radial direction of the thermally conductive bead. The thermally conductive bead may also have a two-layer structure comprising an orientation layer and a core layer inside the orientation layer and having randomly oriented fillers. Furthermore, the thermally conductive beads may be configured such that the orientation of the filler gradually changes from the surface toward the inside in the radial direction.

The degree of orientation of the filler in the orientation layer can be evaluated based on the average value and standard deviation of orientation angles calculated by the following method. First, the thermally conductive bead is cut along a plane passing through its center of gravity to expose a cross section containing the center of gravity. This cross section is observed under a microscope to obtain a microscope image including the filler placed closest to the surface of the thermally conductive bead. Next, on the microscope image, a straight line passing through the center of gravity of the thermally conductive bead and the center of gravity of the filler arranged closest to the surface of the thermally conductive bead is drawn, and this straight line and the outline of the thermally conductive bead are matched. Determine the intersection of A tangent to the contour of the thermally conductive bead passing through this intersection is then determined. The orientation angle is defined as the angle between the tangent to the contour of the thermally conductive bead determined as described above and the straight line extending in the direction parallel to the major axis of the filler. In determining the orientation angle, the straight line extending in the direction parallel to the long axis of the filler is tilted in the counterclockwise direction with respect to the tangent line of the contour of the thermally conductive bead, and in the clockwise direction. There are cases where it is inclined to For the sake of convenience, it is assumed that the value of the orientation angle takes a positive value in the former case and takes a negative value in the latter case.

The orientation angles of a plurality of fillers can be calculated by the above method, and the arithmetic mean of these orientation angles can be used as the average orientation angle. Moreover, the standard deviation of the orientation angles can be calculated by statistically processing the orientation angles calculated for a plurality of fillers. In calculating the average value and standard deviation of the orientation angles, the more fillers used for the measurement of the orientation angles, the more accurate values can be calculated. The number of fillers used when 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 orientation angle of the filler is preferably −8° or more and +8° or less, more preferably −5° or more and +5° or less. Also, the standard deviation of the orientation angles is preferably 25° or less, more preferably 15° or less. In this case, a heat path along the surface of each thermally conductive bead can be more easily formed in the orientation layer of each thermally conductive bead. As a result, it is possible to further improve the thermal conductivity of the thermally conductive beads and the molded article provided therewith.

B. Method for producing thermally conductive beads The method for producing thermally conductive beads comprises:
A bead for producing an uncured bead having a spherical shape containing the filler and the uncured curable polymer, and having an orientation layer on the surface thereof in which the filler is oriented such that the long axis is along the surface. a manufacturing process;
and a curing step of curing the curable polymer in the uncured beads.

In the bead preparation step, any method may be employed 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 made of a mixture of the filler and the curable polymer;
A filler aligning step of forming the bead precursors into a spherical shape using a rotation-revolution mixer, and orienting the filler present on the surface of the bead precursors such that the long axis of the fillers is along the surface of the bead precursors. and can be employed.

In the granulation step, first, the filler and the uncured curable polymer are mixed using a kneader, a stirrer, or the like. The uncured curable polymer is liquid. In addition, the uncured curable polymer includes, for example, a base material that forms the skeleton of the polymer after curing, a curing agent that bonds and cures the base materials, and a curing accelerator that accelerates the curing reaction.

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

The viscosity of the curable polymer can also be adjusted 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 volatilization or other means after the completion of mixing with the filler until the uncured beads are cured.

The mixture of filler and curable polymer is then formed into granules to form bead precursors. As a method of molding the mixture into granules, for example, a pelletizer, a crusher, or the like can be used.

In the filler aligning step, the bead precursors are formed into a spherical shape using a rotation-revolution mixer, and the filler present on the surface of the bead precursors is oriented such that the long axis is along the surface of the bead precursors. Oriented to Here, the rotation-revolution type mixer is configured such that a vessel containing bead precursors is rotated around the revolution axis, and the vessel itself rotates around the rotation axis tilted with respect to the revolution axis. called a mixer. According to the rotation-revolution type mixer, it is possible to roll the bead precursors in the container by rotation while exerting a centrifugal force on the bead precursors in the container by revolution. As a result, molding of the bead precursor and formation of the alignment layer can be performed simultaneously to produce uncured beads.

In the curing step, the curable polymer in the uncured beads obtained in the bead making step is cured. As a method for curing the uncured beads, an appropriate method can be adopted according to the type of curable polymer. For example, if the curable polymer is a thermoset polymer, the uncured beads can be heated for a predetermined time and temperature.

C. Resin Composition A resin composition can be obtained by mixing the curable beads and a resin matrix made of a resin. The resin matrix may be composed of any resin. For example, the resin matrix may be thermosetting resins such as epoxy resins, phenolic resins, melamine resins, urea resins, unsaturated polyester resins, alkyd resins, oxazine resins, bismaleimide resins, triazine resins, polyamides, Thermoplastic resins such as polyester, polycarbonate, acrylic polymer, methacrylic polymer, polyimide, liquid crystal polymer, polyolefin, polystyrene, and polyphenylene ether may also be used. Moreover, 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.

Furthermore, the resin matrix may contain additives such as fillers, flame retardants, stabilizers, plasticizers, surfactants and antistatic agents. The filler in the resin matrix may have shape anisotropy or may have an isotropic shape. Even if the filler in the resin matrix has shape anisotropy, the filler in the resin matrix after molding can be prevented from being oriented in a specific direction by mixing it with the thermally conductive beads. . As a result, it is possible to easily obtain a molded article having isotropic heat conduction properties.

The resin composition may contain one type of thermally conductive beads, or may contain a plurality of types of thermally conductive beads with different fillers and/or curable polymers. Also, 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 thermally conductive beads in the compact, it is preferable to use a plurality of types of thermally conductive beads having different particle size distributions together as the thermally conductive beads.

The content of the thermally conductive beads in the resin composition can be appropriately set within a range of, for example, 10% by volume or more and 95% by volume or more. If the content of the thermally conductive beads is too low, it becomes difficult to form heat paths in the resin composition. As a result, there is a possibility that the thermal conductivity of the molded body will be lowered. Also, if the content of the thermally conductive beads is excessively high, the resin matrix may become insufficient, making it difficult to mold the resin composition into a desired shape. These problems can be easily avoided by setting the content of the thermally conductive beads within the specific range.

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 thermally conductive beads are more likely to come into contact with each other, so that heat paths are more likely to be formed in the compact. Therefore, in this case, the thermal conductivity of the molded body can be made higher.

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 can be selected from known molding methods such as compression molding, vacuum compression molding, transfer molding, injection molding, extrusion molding, and cast molding, and the type of resin matrix and desired molding. It can be appropriately selected according to the shape of the body and the like.

As described above, a heat path including an orientation layer of thermally conductive beads is formed inside the molded body formed by molding the resin composition. Therefore, the molded body has isotropic thermal conductivity, that is, the property that heat is transmitted to the same degree in any direction. More specifically, the molded body has a thermal conductivity λ _A [W/m·K] in the direction in which the thermal conductivity is maximized and a thermal conductivity λ _B [W /m·K], the value of thermal conductivity anisotropy λ _A /λ _B 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 body can be further improved. Molded bodies having such thermal conductivity are suitable for applications such as heat dissipating members, for example.

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

The thermally conductive bead 1 of this example has a spherical shape containing a filler 3 and an uncured curable polymer. and a curing step of curing the curable polymer in the uncured beads. The bead preparation step includes a granulation step of preparing bead precursors 100 composed of a mixture of filler 3 and a curable polymer, and a rotation-revolution mixer 4 shown in FIG. and a filler alignment step of orienting the fillers 3 present on the surfaces of the bead precursors 100 so that their long axes are aligned with the surfaces of the bead precursors 100 during molding.

Specifically, in this example, 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 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 . A bisphenol A type epoxy resin was used as the curable polymer. Specifically, the curable polymer includes a main agent having a bisphenol A skeleton ("jER (registered trademark) 827" manufactured by Mitsubishi Chemical Corporation) and 4-methylcyclohexane-1,2-dicarboxylic 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.

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 main agent to prepare an uncured curable polymer. Next, 15 parts by mass of filler 3 was added to 5 parts by mass of this curable polymer and mixed to obtain a clay-like mixture. After that, the obtained mixture was shaped into granules using a pelletizer to produce bead precursors 100 .

In the filler alignment step, after the bead precursor 100 described above was placed in the container 41 of the rotation-revolution mixer 4 ("ARE-310" manufactured by Thinky Co., Ltd.) shown in FIG. , and 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. Further, the rotation axis 42 of the container 41 is arranged so as to be inclined at 45° with respect to the revolution axis 43 . The container 41 is configured to revolve around the revolution axis 43 and rotate about the rotation axis 42 (that is, the central axis of the container 41).

The bead precursors 100 in the container 41 are subjected to centrifugal force due to the revolution of the container 41 and roll by rotation. As a result, the bead precursor 100 is formed into a spherical shape while the filler 3 existing on the surface of the bead precursor 100 is oriented in the specific direction, thereby obtaining the above-described uncured beads.

In the curing step, the uncured beads were heated to cure the curable polymer. Specifically, in the curing step of this example, 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. bottom. As described above, the thermally conductive beads 1 were produced in which the flaky graphite filler 3 was dispersed in the resin portion 2 made of the cured bisphenol A type epoxy resin. The mass ratio and volume ratio of the filler 3 and the resin portion 2 in the thermally conductive beads 1 of Production Example 1 are as shown in Table 1.

・Manufacturing example 2
In this example, instead of flaky graphite, 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. performed the granulation step, the filler alignment step and the curing step under the same conditions as in Production Example 1. As a result, a thermally conductive bead 1 was produced in which the filler 3 of hexagonal boron nitride was dispersed in the resin portion 2 made of the cured bisphenol A type epoxy resin. Table 1 shows the mass ratio and volume ratio of the filler 3 and the resin portion 2 in the thermally conductive beads 1 of Production Example 2. In Table 1, hexagonal boron nitride is indicated as "h-BN".

Next, the shape of the thermally conductive beads 1 and the orientation state of the fillers 3 of Production Examples 1 and 2 were evaluated by the following methods.

- Shape of Thermally Conductive Bead 1 An optical microscope image was obtained by observing the thermally conductive bead 1 with an optical microscope. Using image analysis software (“WinROOF2015” manufactured by Mitani Shoji Co., Ltd.), the major axis L _b [μm], the minor axis S _b [μm], and the perimeter P of the thermally conductive beads 1 in the optical microscope image shown in FIG. [μm] and projected area S [μm ² ] were calculated. Then, for each thermally conductive bead 1, the values of flatness, surface unevenness and diameter _Db were calculated based on the following formulas (1) to (3).
Oblateness = (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 for 100 or more thermally conductive beads 1, statistical processing was performed to calculate the average value and standard deviation. Table 1 shows the average values and standard deviations of the flatness, surface unevenness, and 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 thermally conductive bead 1 was observed at a higher magnification, it was found that the filler 3 existing in the vicinity of the surface 11 was located in the direction of the thickness of the thermally conductive bead 1. , and the long axis of the filler 3 was oriented along the surface 11 of the thermally conductive bead 1 . In addition, in the thermally conductive beads 1 of Production Examples 1 and 2, the filler 3 present at least within a range of up to 50 μm in depth from the surface 11 was oriented in the specific direction. That is, the thickness of the orientation layer 12 in the thermally conductive beads 1 of Production Examples 1 and 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 thermally conductive bead 1 by the following method (see FIG. 2) was calculated. First, on an electron microscope image, draw a straight line L1 passing through the center of gravity W _b of the thermally conductive bead 1 and the center of gravity W _f of the filler 3 located closest to the surface 11 of the thermally conductive bead 1, An intersection point 13 between this straight line L1 and the surface 11 of the thermally conductive bead 1 was determined. Then, a tangent line L2 of the contour of the thermally conductive bead 1 passing through this intersection point 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 long axis of the filler 3 was defined as the orientation angle θ. For the sake of convenience, part of the description of the filler 3 is 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 Examples 1 and 2.

As shown in Table 1, the thermally conductive beads 1 of Production Examples 1 and 2 have, on their surface 11, an orientation layer 12 in which the filler 3 is oriented in the specific direction. By orienting the filler 3 on the surface 11 of the thermally conductive bead 1 in this manner, a heat path in which the fillers 3 are connected to each other can be easily formed in the orientation layer 12 . Therefore, the thermally conductive beads 1 can efficiently transmit heat along the alignment layer 12 . Furthermore, by bringing the thermally conductive beads 1 into contact with each other, heat can be efficiently transmitted to the adjacent thermally conductive beads 1 via the orientation layer 12 .

Also, the filler 3 of the thermally conductive beads 1 is held in the resin portion 2 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 thermally conductive beads 1 can be suppressed, and the orientation state of the filler 3 in the orientation layer 12 can be maintained.

Furthermore, since the thermally conductive beads 1 are spherical, when the resin composition containing the thermally conductive beads 1 is molded by a molding method such as injection molding that involves the flow of the resin composition, heat is generated in the resin composition. Conductive beads 1 can be isotropically dispersed. Therefore, a heat path including the orientation layer 12 is likely to be isotropically formed in the molding including the thermally conductive beads 1 .

As a result, according to the thermally conductive beads 1 of Production Examples 1 and 2, it is possible to isotropically form a heat path including the orientation layer 12 in the molded body and improve thermal conductivity. .

(Example 2)
In this example, an example of a molded body 5 containing thermally conductive beads 1 will be described with reference to FIG. Note that, of the reference numerals used in the examples after this example, the same reference numerals as those used in the previous examples denote the same components and the like as those in the previous examples unless otherwise specified.

As shown in FIG. 6 , the molded body 5 of this example includes a resin matrix 51 and thermally conductive beads 1 dispersed in the resin matrix 51 . Specifically, in this example, two types of molded bodies 5 (specimens T1 and T2) were produced as follows.

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

In preparing the test sample 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 a main agent to prepare an uncured curable polymer. Next, 15 parts by mass of filler 512 was added to 5 parts by mass of this curable polymer and mixed to obtain an uncured resin matrix.

Next, 50 parts by volume of the thermally 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 molding was performed. In press molding, after heating under pressure of 37 MPa and temperature of 80° C. for 1 hour, the temperature was raised to 120° C. while maintaining the pressure, and the temperature of 120° C. was maintained for 1 hour. After that, the molded body 5 removed from the mold was heated at a temperature of 150° C. for 3 hours to sufficiently harden the resin matrix 51 . As a result, a disk-shaped compact 5 having a thickness of 1.2 mm and a diameter of 40 mm was obtained. This molded body 5 was designated as test body T1.

・ Specimen T2
As the filler 512 in the resin matrix 51, instead of flaky graphite, 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. A compact 5 was produced under the same conditions as those for the test sample T1, except that the thermally conductive beads 1 of Production Example 2 were used as the thermally conductive beads 1 instead of the thermally conductive beads 1 of Production Example 1. This molded body 5 was used as a test body T2.

In this example, molded bodies (specimens T3 to T6) produced without using the thermally conductive beads 1 were prepared for comparison with the specimens T1 and T2. A specific method for producing the specimens T3 to T6 is as follows.

・ Specimen T3
The granulation step and the filler alignment step were carried out in the same manner as for the thermally conductive beads 1 of Production Example 1 to produce 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 those for the specimen T1. As a result, a disk-shaped compact having a thickness of 1.2 mm and a diameter of 40 mm was obtained. This compact was designated as test sample T3.

・ Specimen T4
The uncured resin matrix used for the specimen T1 was placed in a cylindrical mold with an inner diameter of φ40 mm, and compression molding was performed under the same conditions as for the specimen T1. As a result, a disk-shaped compact having a thickness of 1.2 mm and a diameter of 40 mm was obtained. This compact was designated as test sample T4.

・ Specimen T5
Except for using the uncured beads of Production Example 2 in place of the uncured beads of Production Example 1, compression molding was performed under the same conditions as those for test sample T3. As a result, a disk-shaped compact having a thickness of 1.2 mm and a diameter of 40 mm was obtained. This compact was designated as test sample T5.

・ Specimen T6
Compression molding was performed under the same conditions as for test sample T4, except that the uncured resin matrix used in test sample T2 was used in place of the uncured resin matrix used in test sample T1. As a result, a disk-shaped compact having a thickness of 1.2 mm and a diameter of 40 mm was obtained. This compact was designated as test sample T6.

The thermal conductivity of the specimens T1 to T6 obtained above was evaluated by the following method.

・Method for measuring thermal conductivity and thermal conductivity anisotropy Using a thermophysical property measuring device ("Thermo Wave Analyzer TA35" manufactured by Bethel Co., Ltd.), the thickness direction and in-plane direction of the specimen (that is, the thickness direction ) ^{was measured} . Also, the constant pressure specific heat Cp [J·K ⁻¹ ·kg ⁻¹ ] of the specimen was measured using a differential scanning calorimeter (“DSC7000” manufactured by Hitachi High-Tech Science Co., Ltd.). Furthermore, the density ρ [kg·m ^-3 ] of the specimen 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 above into the following formula (4), the thermal conductivity value α [W m ^-1・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 specimens T1 to T6. In the manufacturing method of this example, one of the thickness direction of the specimen and the direction perpendicular to the thickness direction is the direction in which the thermal conductivity is maximized, and the other is the direction in which the thermal conductivity is minimized. estimated to be
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 maximized and the heat 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 specimens T1 and T2 have isotropic thermal conductivity.

As an example is shown in FIG. 6, it is presumed that the arrangement of the fillers 3 of the thermally conductive beads 1 is maintained inside the test bodies T1 and T2 even after molding. It is considered that the thermal paths including the alignment layers 12 are formed isotropically by the alignment layers 12 of the thermally conductive beads 1 coming into contact with each other.

On the other hand, the values of the thermal conductivity anisotropy λ _A /λ _B of the specimens T3 and T5 were larger than those of the specimens T1 and T2. Inside the specimens T3 and T5, as an example is shown in FIG. 7, the arrangement of the filler 3 derived from the uncured beads changes from a spherical shape to an ellipsoidal shape due to compression of the uncured beads during molding. presumed to have It is said that the change in the arrangement of the filler 3 to an ellipsoidal shape cuts off the heat path formed by the contact between the ends of the filler 3 in the longitudinal 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 specimens T4 and T6 were even larger than those of the specimens T3 and T5. Inside the test bodies T4 and T6, as an example is shown in FIG. 8, as the resin matrix 51 flows during molding, the long axis of the filler 512 and the thickness direction of the molded body become perpendicular to each other. It is presumed that the filler 512 was oriented at . It is considered that the value of thermal conductivity anisotropy is increased due to the orientation of the filler 512 in this manner.

Specific aspects of the thermally conductive beads 1, the resin composition, and the molded article 5 according to the present invention are not limited to the aspects described in Examples 1 and 2, which impairs the gist of the present invention. The configuration can be changed as appropriate within a range that is not necessary.

For example, in Example 2, an example of the resin composition and the molded article 5 using the resin matrix 51 having the same composition as the thermally conductive beads 1 was shown, but the composition of the resin matrix 51 is different from that of the thermally conductive beads. It can be different from 1.

REFERENCE SIGNS LIST 1 thermally conductive bead 11 surface 12 orientation layer 2 resin portion 3 filler

Claims (9)

a resin portion made of a cured product of a curable polymer;
a filler that has higher thermal conductivity than the resin portion, has shape anisotropy, and is held by the resin portion;
It has a spherical shape,
A method for producing thermally conductive beads, wherein the surface has an orientation layer in which the filler is oriented such that the long axis is along the surface,
An uncured bead having a spherical shape containing the filler and the uncured curable polymer and having the oriented layer on the surface thereof in which the filler is oriented such that the long axis is along the surface is produced. a bead making process;
curing the curable polymer in the uncured beads ;
The bead production step includes:
a granulation step of making a bead precursor consisting of a mixture of the filler and the curable polymer;
Filler alignment for orienting the filler existing on the surface of the bead precursor such that the long axis is along the surface of the bead precursor while shaping the bead precursor into a spherical shape using a rotation-revolution mixer. A method for producing thermally conductive beads, comprising the steps of : 2. The heat conduction according to claim 1 , wherein the ratio D _b /L _f of the major axis L f [μm] of the filler to the diameter D _b [μm] of _the thermally conductive beads is 10 or more and 1000 or less. Method for manufacturing sex beads. a resin portion made of a cured product of a curable polymer;
a filler that has higher thermal conductivity than the resin portion, has shape anisotropy, and is held by the resin portion;
Thermally conductive beads having a spherical shape,
The surface of the thermally conductive bead has an orientation layer in which the filler is oriented such that the long axis is along the surface,
Thermally conductive beads, wherein the ratio D _b /L _f of the major axis L _f [μm] of the filler to the diameter D _b [μm] of the thermally conductive beads is 10 or more and 1000 or less. 4. The thermally conductive bead according to claim 3 , wherein the orientation layer has a thickness of 5% or more of the diameter of the thermally conductive bead. 5. The thermally conductive bead according to claim 3 , wherein the content of said filler in said thermally conductive bead is 30% by volume or more and 95% by volume or less. a resin matrix made of resin;
and the thermally conductive beads according to any one of claims 3 to 5 dispersed in the resin matrix. 7. The resin composition according to claim 6, wherein the content of said thermally conductive beads is 30% by volume or more and 95% by volume or less. A molded article of the resin composition according to claim 6 or 7 ,
Thermal conductivity is the ratio of thermal conductivity λ _A [W/m・K] in the direction of maximum thermal conductivity to thermal conductivity λ _B [W/m・K] in the direction of minimum thermal conductivity A molded article having a value of conductivity anisotropy λ _A /λ _B of 1.5 or less. 9. The molded article according to claim 8 , wherein said thermal conductivity λ _B is 7 W/m·K or more.

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