Composite material and method for manufacturing the same

Abstract

To provide a manufacturing method which can obtain a composite material exhibiting high heat conductivity.SOLUTION: A method for manufacturing a composite material includes: an orientation step of applying a local or ununiform magnetic field to a mixture of flat or fibrous heat conductive particles to which a magnetic material is attached with a resin; and a solidification step of solidifying a mixture in a state where the heat conductive particles are oriented. The heat conductive particles have, for example, flat or fibrous base particles, and a magnetic film coating at least a part of the surface of the base particles. For example, the base particles are boron nitride particles (BN particles), and the magnetic film is an iron film. A composite material having high heat conductivity in a specific direction (for example, a-axis direction of oriented BN particles) while suppressing a blending amount of the base particles and reducing an applied magnetic field can be obtained.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] This invention relates to a method for manufacturing composite materials with excellent thermal conductivity. [Background technology]

[0002] High-density and high-performance electronic devices (such as semiconductor modules) require heat dissipation to maintain their functionality and lifespan. Heat dissipation from electronic devices is typically achieved through heat dissipation components (heat sinks, housings, etc.) made of metal or other materials. In this process, heat dissipation sheets (thermal conductive sheets, thermally conductive insulating sheets, etc.) are often interposed to absorb irregularities and undulations between the surfaces of the electronic device (heat source) and the heat dissipation component.

[0003] For example, heat dissipation sheets can be made of composite materials (including compositions) consisting of a filler with high thermal conductivity and a resin (including elastomers, rubber, etc.) with excellent flexibility (elasticity) and adhesion. Various proposals have been made regarding such composite materials, and for example, there are descriptions related to the following patent documents. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2004-51852 [Patent Document 2] Japanese Patent Publication No. 2012-169599 [Overview of the project] [Problems that the invention aims to solve]

[0005] Patent Document 1 describes a thermally conductive sheet formed by uniformly oriented a magnetically anisotropic thermally conductive filler (boron nitride) in the thickness direction within a liquid crystalline polymer (thermally liquid crystalline total aromatic polyester) (Examples 3 and 4 of Patent Document 1). However, a high magnetic field (15T) using a superconducting magnet is applied to orient the boron nitride, a nonmagnetic material that exhibits a demagnetic field, which is not practical.

[0006] Patent Document 2 describes a thermally conductive film obtained by coating a glass plate with a coating solution in which flaky boron nitride coated with γ-ferrite (Fe2O3) is dispersed in a polyamic acid solution (100 Pa·S), and then heating and drying the film while uniformly applying a magnetic field (2T) in the direction of the film thickness (Example 1 of Patent Document 2). Because the magnetic field is applied uniformly, a large amount of particulate γ-Fe2O3 is required, which may actually hinder the orientation of the boron nitride and the thermal conductivity of the thermally conductive film.

[0007] This invention has been made in view of these circumstances, and aims to provide a new manufacturing method and the like that can be obtained for a composite material with excellent thermal conductivity. [Means for solving the problem]

[0008] As a result of diligent research, the inventors succeeded in obtaining a composite material with excellent thermal conductivity by locally oriented thermal conductive particles, which are formed by attaching a magnetic material in a thin film. By further developing this result, the present invention described below was completed.

[0009] Method for manufacturing composite materials The present invention relates to a method for manufacturing a composite material, comprising: an orientation step of applying a localized or non-uniform magnetic field to a slurry obtained by mixing flat or fibrous heat-conducting particles on which a magnetic material is attached to the surface with a resin; and a solidification step of solidifying the slurry while the heat-conducting particles are oriented.

[0010] According to the manufacturing method of the present invention, a composite material (thermal conductive material) with excellent thermal conductivity can be obtained while suppressing the amount of thermal conductive particles and the applied magnetic field. The reason for this is currently thought to be as follows.

[0011] Flat or fibrous heat-conducting particles (in other words, high-aspect-ratio heat-conducting particles) can change their orientation along the magnetic direction when subjected to magnetic torque (rotational torque) in a magnetic field due to magnetic material attached to their surface. When a localized or non-uniform magnetic field is applied to a mixture (slurry) of such heat-conducting particles and resin, the heat-conducting particles become oriented longitudinally or planarly, and also become denser and more closely packed in areas where the magnetic field distribution is uneven (local areas). The resulting composite material can easily form heat conduction paths between adjacent heat-conducting particles, thus exhibiting high thermal conductivity.

[0012] Furthermore, when applying a localized or non-uniform magnetic field, the form of the magnetic material on the surface of the heat-conducting particles is irrelevant. For example, the magnetic material may be in the form of a (thin) film or granules.

[0013] 《Composite material》 The present invention can also be understood as a composite material (thermal conductive material). For example, the present invention may be a composite material in which flattened or fibrous thermal conductive particles are held in a resin, and the thermal conductive particles may be oriented and unevenly distributed. The composite material is not limited in form (shape, size, etc.) or application, but examples include thermal conductive films, thermal conductive sheets, substrates or cases that also serve as heat dissipation members, etc.

[0014] 《Heat-conducting particles》 The present invention can also be understood as thermal conductive particles (powder). For example, the present invention may be thermal conductive particles having flattened or fibrous base particles and a magnetic film covering at least a portion of the surface of the base particles.

[0015] Furthermore, when the magnetic material (magnetic body) formed on the surface of the heat-conducting particles is in the form of a film, the magnetic field applied during the manufacture of the composite material may be non-uniform (localized) or uniform. Moreover, heat-conducting particles having a magnetic film on their surface may be used as fillers in composite materials manufactured in a magnetic-free state without the application of a magnetic field.

[0016] "others" (1) As used in this specification, "flat or fibrous" means that one dimension (thickness, diameter, width) is significantly larger than the other dimension (length, etc.). Specifically, the (average) aspect ratio (longest dimension / shortest dimension) is, for example, 2 or more, 3 or more, and even 5 or more. The upper limit is not limited, but is, for example, 100 or less, 50 or less, and even 25 or less.

[0017] "Orientation" means a state in which the heat-conductive particles are oriented substantially in one direction. Specifically, it is a state in which the degree of orientation (details will be described later) obtained by XRD of the crystals of the base particles constituting the heat-conductive particles is, for example, 15% or more, 20% or more, and even 25% or more.

[0018] "Non-uniform distribution" means a state in which the heat-conductive particles are aggregated, accumulated, etc. in a part or a specific region of the composite material. Specifically, it is a state in which, for example, 50% by volume or more, and even 70% by volume or more of the heat-conductive particles are present in a region of 60% by volume or less, and even 40% by volume or less of the composite material.

[0019] (2) As used in this specification, "~ material" means "material" or "member". The member may be an intermediate product (raw material before processing) or a finished product. Together with the heat-conductive particles and the composite material, it is appropriately referred to as a heat-conductive material. The magnetic material may also be referred to as a magnetic body.

[0020] (3) As used in this specification, "x~y" includes the lower limit value x and the upper limit value y unless otherwise specified. Any numerical value included in the various numerical values or numerical ranges described in this specification can be used as a new lower limit value or upper limit value to newly establish a range such as "a~b". As used in this specification, "x~ynm" means xnm~ynm unless otherwise specified. The same applies to other unit systems (such as W / mK, etc.).

Brief Description of the Drawings

[0021] [Figure 1] SEM image and EDX image observing the vicinity of the surface of heat-conductive particles (an example). [Figure 2] Graph showing the relationship between the magnetization of heat-conductive particles and their anisotropic magnetic susceptibility. [Figure 3] This graph shows the relationship between the magnetization of thermally conductive particles having a magnetic film (Fe film) and the film thickness ratio. [Figure 4] This graph shows the relationship between the amount of xylene added and the viscosity of the slurry. [Figure 5] This is a schematic diagram illustrating the manufacturing process of composite materials. [Figure 6] These are SEM images of the surfaces of composite materials (sample 11, sample 32). [Figure 7] This is a scatter plot showing the relationship between the amount of BN particles and the thermal conductivity of the composite material. [Figure 8] These are schematic diagrams illustrating composite materials with different orientations of heat-conducting particles. [Modes for carrying out the invention]

[0022] The components of the present invention may be modified by adding one or more components arbitrarily selected from this specification. The contents described herein appropriately relate to thermal conductive materials (composite materials, thermal conductive particles, etc.) and their manufacturing methods. Even methodological components can be material components. Which embodiment is best depends on the subject, required performance, etc.

[0023] 《Heat-conducting particles》 The thermal conductive particles consist of a base particle and a magnetic material attached to at least a portion of its surface. The base particle and magnetic material are described in detail below.

[0024] (1) Base particle The base particles are preferably flattened or fibrous and have excellent thermal conductivity. Flattened (scaly, plate-like, etc.) or fibrous base particles can improve the thermal conductivity of the composite material (thermal conductive material) in a specific direction through the orientation, density, and aggregation of thermal conductive particles.

[0025] The shape anisotropy (flattening or fibrous) of the base particles (and similarly for heat-conducting particles) is indicated, for example, by the (average) aspect ratio (AR). The aspect ratio is the ratio (long dimension / short dimension) of the length in the longitudinal direction (long dimension) measured for each object to the length in the direction perpendicular to it (short dimension). The long dimension is the maximum length of the object (particle) (e.g., the maximum length of the line segment appearing in the observed image), and the short dimension is its minimum length (e.g., the minimum length of the line segment appearing in the observed image). The "average" is, for example, the arithmetic mean obtained for particles randomly sampled (e.g., 10 to 50 particles) or particles within the field of view of the observed image (e.g., 440 μm × 630 μm). Calculations based on the observed image are performed, for example, using image processing software (e.g., ImageJ) (the same applies below). The average aspect ratio (AR) obtained in this way can be, for example, 2 to 100, 3 to 50, or even 5 to 30.

[0026] The (average) aspect ratio may be calculated for the particles (individually) at the raw material stage (before mixing with resin raw materials) or for the particles in the composite material. For flattened particles (such as BN particles), the average aspect ratio may be calculated as average particle size / average thickness based on their average thickness and average particle size.

[0027] The average particle size may be calculated based on the observation image described above, or it may be determined as the 50% diameter (D50: median diameter) from the particle size distribution obtained by laser diffraction. When determined from the observation image, regardless of the particle shape, the particle size is defined as the maximum length in the longitudinal direction of the particle, and the thickness is defined as the minimum thickness in the transverse direction of the particle.

[0028] The average particle size is, for example, 0.1-10 μm, 0.5-7 μm, and 1-5 μm. The average thickness of flattened particles (such as BN particles) is, for example, 0.01-1 μm, 0.05-0.7 μm, and even 0.1-0.5 μm.

[0029] Incidentally, the particle size in the composite material may also be measured for particles obtained by dissolving and removing the resin from the composite material. Even if the particle size is determined in this way, there is no significant difference before and after composite formation. Furthermore, since magnetic materials (especially magnetic films) are usually thinly attached to the surface of the base particles, there is no significant difference in morphology (shape, size, aspect ratio, volume, etc.) between the base particles and the heat-conducting particles. For this reason, in this specification, the morphology of the heat-conducting particles is appropriately indicated by the morphology of the base particles.

[0030] The base particles can be of any type (material, manufacturing method, etc.) as long as they satisfy the above-described morphology. Base particles with excellent thermal conductivity include, for example, boron nitride (BN), silica (SiO2), alumina (Al2O3), and aluminum nitride (AlN). In particular, boron nitride particles ("BN particles") have a higher thermal conductivity than silica particles and alumina particles, and are more chemically stable than aluminum nitride particles. For this reason, composite materials containing thermally conductive particles made of BN particles are excellent not only in thermal conductivity but also in heat resistance, reliability, and electrical insulation.

[0031] Incidentally, boron nitride has a hexagonal atmospheric pressure phase (sometimes referred to as "h-BN") and a cubic high-pressure phase (sometimes referred to as "c-BN"). h-BN consists of flaky (high aspect ratio flattened) layers of hexagonal network structures similar to graphite, and exhibits thermal conductivity anisotropy, where the thermal conductivity differs greatly between the plane direction (a-axis direction) and the thickness direction (c-axis direction).

[0032] The thermal conductivity of the composite material is increased by orienting the plane direction of thermal conductive particles made of h-BN (simply referred to as "BN particles") toward the main direction of thermal conduction (for example, from the heat source side toward the cooling source side). The base particles may consist only of BN particles, or may include other types of particles (ceramic particles, metal particles, c-BN particles, etc.). The BN particles may be h-BN single layers, or laminates or aggregates (aggregates, secondary particles) of h-BN.

[0033] (2)Magnetic material Magnetic materials (magnetic substances) adhere to (including coating) the surface of base particles and contribute to the orientation of heat-conducting particles. Magnetic materials can take on various compositions and forms. Different materials with different compositions and forms may be mixed together in the magnetic material.

[0034] The magnetic material may be a soft magnetic material or a hard magnetic material. The magnetic material may consist of, for example, a ferromagnetic element (e.g., iron group elements: Fe, Co, Ni) in its elemental form (e.g., pure Fe), an alloy (e.g., FeNi alloy), or a compound (e.g., spinel-type ferrite such as NiFe2O4 (including Fe3O4)). It is also preferable that the magnetic material has high thermal conductivity.

[0035] The magnetic material is preferably a magnetic film that covers at least a portion of the surface of the base particles. Furthermore, if the magnetic film is in the form of a thin film, thermal conductive particles can be obtained in which the high properties of the base particles are almost maintained. The thickness of the magnetic thin film is, for example, 1 to 500 nm, 5 to 250 nm, or even 10 to 100 nm.

[0036] The film thickness ratio, which is the ratio of the thickness of the magnetic film to the particle size of the base particles, is, for example, 0.0001 to 0.3, 0.001 to 0.1, and even 0.005 to 0.01. The average particle size of the base particles can be the average particle size mentioned above. The thickness of the magnetic film is, for example, the average thickness calculated from the mass ratio of the magnetic material to the total number of heat-conducting particles, the true density of the magnetic material, and the surface area of ​​the base particles. The surface area of ​​the base particles can be, for example, the average surface area obtained from the average particle size and average thickness (average particle size / average aspect ratio) of the base particles. When such estimation is difficult, the specific surface area measured by gas adsorption or the like may be used.

[0037] Thermal conductive particles coated with a magnetic material (magnetic film) only need to have a magnetization of about 5-40 emu / g, or even 10-35 emu / g. This allows the thermal conductive particles to exert the magnetic moment necessary for changes in orientation and movement, even in low magnetic fields. If the magnetic material consists of an iron substrate (especially pure iron / saturation magnetization: 220 emu / g), the iron substrate may be present in an amount of 1-10% by mass, or even 3-7% by mass, relative to the total thermal conductive particles (the sum of the base particles and the magnetic material).

[0038] The thermal conductive particles may contain dissimilar materials (particles) in addition to the base particles and magnetic material described above. For example, carbon particles such as nanocarbon particles (CNTs, etc.), graphite particles (including carbon black), and diamond particles may be attached to (supported) the surface of the base particles or magnetic material.

[0039] 《Composite material》 The composite material is formed by holding heat-conducting particles with resin.

[0040] (1) Resin (matrix) The resin is typically a synthetic resin (or even a polymer) which is a high-molecular-weight compound, and may be either a thermoplastic or a thermosetting resin. Furthermore, the resin referred to herein may also be rubber, elastomer, etc., and may be a single type or a mixture of multiple types (mixed resins). Using a single type of resin simplifies compounding and manufacturing processes. Using multiple types of resins allows for adjustment of resin properties (thermal conductivity, wettability with thermal conductive particles, softening point, melting point, etc.).

[0041] Thermoplastic resins include, for example, polystyrene, acrylic resins such as polymethyl methacrylate (PMMA), polycarbonate, and polyphenylene sulfide. Thermosetting resins include, for example, polysiloxane, epoxy resin, phenolic resin, and silicone resin.

[0042] Elastomers include thermoplastic elastomers such as olefin-based (TPO), polystyrene-based (TPS), polyvinyl chloride-based (TPVC), polyurethane-based (TPU), polyester-based (TPC), and polyamide-based (TPAE). Rubber may be ethylene-propylene-diene rubber (EPDM), butyl rubber, or thermosetting elastomers (urethane rubber, silicone rubber, fluororubber, etc.). In this specification, unless otherwise specified, rubber and elastomers are simply referred to as "resins."

[0043] (2) Heat-conducting particles The thermal conductive particles are present in a volume percentage of, for example, 3-50%, 5-45%, or even 10-40% relative to the total volume of the thermal conductive particles and resin. The composite material of the present invention makes it possible to ensure high thermal conductivity while reducing the content (percentage) of thermal conductive particles. The volume percentage of thermal conductive particles can be calculated, for example, from the mass ratio (composition mass ratio) of resin to thermal conductive particles and the true density of each, even if it is not measured directly.

[0044] The thermal conductive particles are preferably oriented within the composite material. The degree of orientation can be, for example, 5-50%, 10-45%, or even 15-40%. The degree of orientation as used herein is determined from the profile (pattern) of the thermal conductive particles (substrate particles) obtained by X-ray diffraction (XRD) of the composite material. Specifically, the degree of orientation is determined as 100 × I1 / (I1 + I2) from the peak intensity in one direction (I1) and the peak intensity in the other direction (I2), which are the orientation directions. The two directions are usually orthogonal.

[0045] In the case of BN particles, the degree of orientation can be determined from the peak intensity I(100) in the direction along the (100) plane with high thermal conductivity (a-axis direction) and the peak intensity I(002) in the direction along the (002) plane with low thermal conductivity (c-axis direction), as follows. (Degree of Orientation) = I(100) / {I(100)+I(002)} × 100 (%)

[0046] 《Manufacturing method》 (1) Thermal conductive particles Thermal conductive particles, in which a magnetic material is attached (adhered or supported) to the surface of a base particle, can be obtained by various manufacturing methods. For example, thermal conductive particles can be obtained by physical vapor deposition (PVD), chemical vapor deposition (CVD), chemical reactions (precipitation, sedimentation, etc. of magnetic material), or by kneading magnetic powder (e.g., nano-iron powder, carbonyl iron powder, etc.) with base particle powder.

[0047] For thin magnetic films, they can be formed on the surface of base particles by methods such as vapor deposition, particularly PVD (Photovoltaic Veneer) such as sputtering. PVD allows for greater flexibility in adjusting the material composition and thickness of the magnetic material. Specifically, for example, by powder sputtering (barrel sputtering), which involves sputtering powder placed in a barrel, heat-conducting particles can be obtained in which a thin magnetic film is deposited on the surface of base particles.

[0048] The heat-conducting particles (powder) may be subjected to particle size adjustment (classification). Furthermore, the heat-conducting particles may be surface-treated to enhance their affinity with the resin (matrix). Surface treatment can improve the orientation, mobility, and dispersibility of the heat-conducting particles within the resin. Examples of surface treatments include hydrophobic treatment and (silane) coupling treatment. Coupling agents may be added or blended during the mixing of the heat-conducting particles and the resin.

[0049] (2) Composite material The composite material is obtained by solidifying a mixture of heat-conducting particles and resin (solidification step). The mixture may be a molten mixture obtained by heating (above the softening point and even above the melting point of the resin) and mixing it with heat-conducting particles, or it may be a slurry obtained by mixing the resin, heat-conducting particles and a solvent (including a dispersion medium). The type and amount of solvent are selected according to the viscosity of the resin and slurry. The slurry is adjusted to a viscosity of, for example, 0.005 to 8 Pa·s, 0.01 to 5 Pa·s, or 0.015 to 1 Pa·s.

[0050] The mixture is preferably in a state where the heat-conducting particles are oriented by applying a magnetic field before solidification (orientation step). The magnetic field may be applied uniformly to the entire mixture, or it may be applied locally or non-uniformly. The latter makes it easier to suppress the amount of heat-conducting particles and achieve high thermal conductivity in the composite material. The applied magnetic field may be, for example, 0.1 to 3 T, 0.3 to 1 T, or even 0.4 to 0.8 T.

[0051] In this specification, "local" refers to applying a magnetic field to a part or specific area of ​​the composite material. More specifically, it refers to applying a magnetic field to an area that represents, for example, 60% or less, 40% or less, or even 30% or less of the total area of ​​the composite material on the orientation side. "Non-uniform" refers to cases where the strength of the applied magnetic field differs depending on the position of the orientation surface of the composite material. For example, this refers to applying a magnetic field in a desired pattern (striped pattern, checkerboard pattern, etc.).

[0052] The solidification process is selected according to the state of the mixture and the form of the composite material. For molten mixtures, for example, they solidify into a composite material by cooling or curing. For slurries, for example, they solidify into a composite material by solvent evaporation, drying, curing, etc.

[0053] The mixture may be subjected to pressure or molding before it has completely solidified. For example, the mixture may be used for compression molding (mold molding, CIP, RIP, etc.), extrusion molding, injection molding, transfer molding, etc.

[0054] When using thermosetting resins, a heat curing treatment may be performed after or concurrently with the solidification process. The composite material may be in the shape of the final product or a shape close to it, or it may be a material or intermediate material that will be processed afterward.

[0055] 《Application》 Thermal conductive particles can be used not only in composite materials with a resin matrix, but also as fillers in various components (substrates, cases, heat dissipation components, etc.). The composite materials are suitable for use in thermal conductive films, thermal conductive sheets, and the like. Their thermal conductivity can range from 0.3 to 3 W / mK, or even 0.5 to 2 W / mK, depending on the orientation of the thermal conductive particles. [Examples]

[0056] A composite material was fabricated by oriented and filling a resin (matrix) with thermal conductive particles (fillers), which consist of a base particle (BN particle) made of h-BN coated with a magnetic film made of Fe. The structure of the thermal conductive particles and the properties of the composite material (thermal conductivity, etc.) were then evaluated. The present invention will be explained in detail with reference to such specific examples.

[0057] 《Heat-conducting particles》 (1) Production As the base particle source (raw material), commercially available h-BN powder (AP-10S, manufactured by MARUKA Corporation) was prepared. This powder has an average aspect ratio ("AR") of 5, an average particle size of 3 μm (D50), and a specific surface area of ​​10 m². 2 It was / g.

[0058] Using a barrel sputtering apparatus (manufactured by Nippon Pillar Industries Co., Ltd.), h-BN powder was coated using the barrel sputtering method with Ar as the process gas and pure Fe as the target.

[0059] This resulted in Fe being deposited on the surface of each particle of the h-BN powder (referred to as "BN particles"). The mass ratio of Fe to the total thermal conductive particles (h-BN powder + Fe) was approximately 5% by mass, and the total magnetization of the thermal conductive particles was 10 emu / g. The film thickness ratio was 0.001 (1 × 10⁻⁶). -3 ) was the case. The relationship between magnetization and film thickness ratio will be discussed later.

[0060] (2) Observation As an example, the surface area of ​​thermal conductive particles (magnetization: 10 emu / g) coated with Fe and consisting of BN particles (AR: 5) was observed using a scanning electron microscope (SEM / Hitachi High-Technologies Corporation SU-3500) and elemental analysis was performed using the attached energy-dispersive X-ray spectrometer (EDX). The SEM image (backscattered electron image) and elemental map (EDX image) are shown in Figure 1.

[0061] (3) Anisotropic susceptibility For reference, the relationship between the magnetization imparted to the heat-conducting particles by the magnetic material and the anisotropic susceptibility (Δχ) generated in the heat-conducting particles was determined by numerical analysis. The anisotropic susceptibility of the heat-conducting particles is the difference (Δχ = χa - χc) between the susceptibility χa along the (100) plane direction (a-axis direction) of the base BN particles and the susceptibility χc along the (002) plane direction (c-axis direction) of the BN particles. The susceptibility is determined as the slope of the magnetization curve of the heat-conducting particles obtained for each direction. In this case, the magnetization curve of the electrical steel sheet (5A1300, magnetic flux density: approximately 2.14T (applied magnetic field 40000 A / m)) was corrected by the mass ratio of Fe to the total heat-conducting particles, and further corrected by the demagnetizing field corresponding to the AR of the BN particles. The relationship between the magnetization and anisotropic susceptibility of the heat-conducting particles obtained in this way is shown in Figure 2. Although Figure 2 illustrates the case for AR:5, the trend of the graph remains approximately the same even as AR increases. However, even if the magnetization of the heat-conducting particles is the same, the anisotropic susceptibility increases as AR increases.

[0062] (4) Film thickness ratio Figure 3 shows the relationship between the magnetization of the thermal conductive particles and the film thickness ratio of the thermal conductive particles. The film thickness ratio is the ratio of the thickness of the magnetic film to the particle size of the base BN particles. The average particle sizes of the BN particles described above were used. The thickness of the magnetic film is calculated using the average particle size of the BN particles, the AR, the mass ratio of Fe, the substrate of the magnetic film, and the true density (7.87 g / cm³). 3 ) was calculated from.

[0063] 《Composite material》 (1) Preparation of slurry The slurry used to produce the composite material was prepared as follows. As a raw material, thermal conductive particles (magnetization: 10 emu / g) were used as a filler, in which Fe (equivalent to approximately 5% by mass) was coated onto the surface of BN particles (AR: 5, average particle size: 3 μm). Polysiloxane (MOMENTIVE YE5822) was used as the matrix resin. Xylene was used as a solvent (dispersion medium) for viscosity adjustment. The polysiloxane used in this example was formulated with a main agent:curing agent ratio of 4:1 (by mass) and fully cured in about 120 minutes at room temperature.

[0064] The heat-conducting particles, resin, and solvent were mixed (kneaded) in a rotation / revolution mixer (ARE-310, manufactured by Thinky Co., Ltd.). The rotation conditions were 2000 rpm for 30 minutes, followed by 2200 rpm for another 30 minutes. Various slurries shown in Table 1 were prepared in this way. The proportion of heat-conducting particles shown in Table 1 is the volume ratio to the total of the heat-conducting particles (approximately the same as the base particles) and the resin. The volume ratio was calculated from the specific gravity (density) of the base particles (BN particles) and the resin (polysiloxane). The slurry viscosity was adjusted by the amount of solvent (xylene) added. The slurry viscosity of each measured sample is also shown in Table 1. "―" in Table 1 means not measured (the same applies below).

[0065] The viscosity of the slurry was measured using a vibrating viscometer (VM-10A, manufactured by Sekonic Corporation). The amount of slurry used for measurement was approximately 5 to 20 ml. For reference, Figure 4 shows the relationship between the measured slurry viscosity and the amount of xylene added. The amount of xylene added is the mass ratio to the total slurry (heat-conducting particles + resin + xylene).

[0066] (2) Fabrication of composite materials Using the slurry described above, the composite material was manufactured as follows. As shown in Figure 5, a 0.3 mm thick mold made of rectangular annular fluororubber (FKM) was attached to the outer edge of a glass plate (25.4 mm × 76.2 mm × t1 mm / material: soda glass) with polyvinyl alcohol (PVA) adhesive. The slurry was poured into the mold and applied to the glass plate. This resulted in the surface (14 cm) 2 An uncured coating film with exposed ) was formed for each slurry.

[0067] The localized magnetic field is applied by placing a cylindrical rare-earth permanent magnet (neodymium magnet: diameter φ1.5cm, end area 1.8cm²) in the center of the lower surface of the glass plate, as shown in Figure 5. 2 The devices were placed in close proximity to each other. This allowed a 0.5T magnetic field to be applied locally.

[0068] A uniform magnetic field was applied by adding a glass plate of the same shape to the upper side of the aforementioned glass plate, and placing the uncured coating, sandwiched between the two glass plates, on the sample stage of an electromagnet device (Tamagawa Seisakusho Co., Ltd. TM-WVS8515C-126 model). This uniformly applied a magnetic field of 2T.

[0069] Regardless of whether a magnetic field was applied or not, all coatings were left in an atmospheric environment for 120 minutes to dry and harden. Samples consisting of these hardened coatings (composite materials) were obtained.

[0070] (3) Observation The composite materials of sample 11 and sample 32 were observed using a scanning electron microscope (SEM). The observed images (including magnified images) are shown in Figure 6.

[0071] (4) Thermal conductivity The thermal conductivity (λ) of the composite material was calculated using the formula λ = α·Cp·ρ, based on the thermal diffusivity (α) measured with a thermal diffusivity measuring device (NETZSCH LFA447 Nanoflash), specific heat (Cp), and density (ρ). The thermal diffusivity was measured in the thickness direction of the composite material (the assumed heat transfer direction) in air (25°C). In the case of a sample to which an orientation magnetic field was applied, the thickness direction is approximately the orientation direction of the heat-conducting particles. The thermal conductivity of each sample obtained in this way is shown in Table 1. Furthermore, based on Table 1, Figure 7 shows the relationship between the amount (volume %) of BN particles (≒heat-conducting particles) and the thermal conductivity of the composite material.

[0072] (5) Magnetization The magnetization of the composite material was measured using a vibrating sample magnetometer (VSM / VSM-3S-15 manufactured by Toei Kogyo Co., Ltd.). In this specification, the magnitude of magnetization refers to the maximum value of the magnetization read from the magnetization curve. For example, the magnetization of the composite material (sample 11) fabricated under no magnetic field conditions was 1.6 emu / g. On the other hand, the magnetization of the composite material (sample 32) fabricated under an oriented magnetic field conditions was 3.3 emu / g.

[0073] (6) Degree of orientation The orientation degree of the heat conduction particles (base particles) in the composite material was determined by X-ray diffraction (XRD). Specifically, it was as follows. From the XRD profile obtained using an X-ray diffractometer (Ultima VI manufactured by Rigaku Corporation), the diffraction intensity I(100) of the (100) plane corresponding to the a-axis direction of the BN particles and the diffraction intensity I(002) of the (002) plane corresponding to the c-axis direction of the BN particles were determined, and the orientation degree was calculated using the following formula. Orientation degree (%) = 100 × I(100) / {I(100) + I(002)}

[0074] Note that XRD was performed in the fluorescence X-ray reduction mode with an X-ray source: Cu-Kα, a measurement range: 25 to 60°, a tube voltage: 4 kV, and a tube current: 40 mA. The orientation degrees thus obtained for the composite materials of each sample are also shown in Table 1.

[0075] 《Evaluation》 (1) Heat conduction particles As is clear from FIG. 1, it was found that Fe was uniformly distributed on the surface of the BN particles (base particles), and a magnetic film was formed.

[0076] As is clear from FIG. 2, it was found that a sufficient anisotropic magnetic susceptibility (Δχ) occurred in the heat conduction particles such that the magnetization of the heat conduction particles was 5 to 40 emu / g, and further 10 to 30 emu / g. At this time, the film thickness ratio was 10 -4 ~×10 -1 Furthermore, it can also be seen from FIG. 3 that it was about 10 -3 ~×10 -2 degree.

[0077] (2) Composite material As is clear from Table 1 and FIG. 7, it was found that when the amount of BN particles was the same, the thermal conductivity of the composite material was improved when using the thermal conductivity of the BN particles coated with a magnetic film as a filler. Furthermore, the thermal conductivity was higher when the heat conduction particles were magnetically oriented, and even higher when locally magnetically oriented. Also, when locally magnetically oriented, even if the applied magnetic field was small, the orientation degree of the heat conduction particles could be sufficiently increased.

[0078] Furthermore, as is evident from samples C1 and C2, it was confirmed that with fillers consisting only of BN particles (without a magnetic film), the degree of orientation and thermal conductivity do not improve even when a high magnetic field is applied.

[0079] 《Consideration》 The mechanism by which the thermal conductivity of a composite material changes depending on the presence or absence of magnetic field orientation of the heat-conducting particles is thought to be as shown in Figure 8. That is, in the absence of a magnetic field (no orientation), the orientation of the flattened or fibrous heat-conducting particles is disordered, and the thermal conductivity of the composite material is isotropic, so the overall thermal conductivity does not improve (Figure 8 left). With a uniform magnetic field (uniform orientation), the heat-conducting particles become oriented in one direction, and the thermal conductivity of the composite material becomes anisotropic and higher in a specific direction (Figure 8 center). Furthermore, with a local magnetic field (local orientation), the heat-conducting particles not only become oriented in one direction, but also aggregate (accumulate, concentrate) in that local area, making it easier to form heat conduction paths between the heat-conducting particles. As a result, by applying a local magnetic field, a composite material with even higher thermal conductivity in a specific direction can be obtained (Figure 8 right). Thus, it is thought that the composite material of the present invention exhibits high thermal conductivity.

[0080] [Table 1]

Claims

1. An orientation step is performed by applying a localized or non-uniform magnetic field to a mixture of thermal conductive particles, which are formed by depositing Fe onto flattened BN particles, and a resin. A solidification step in which the mixture is solidified with the heat-conducting particles oriented, A method for manufacturing composite materials that include [the specified features].

2. The method for manufacturing a composite material according to Claim 1, wherein the magnetization of the heat-conducting particles is 5 to 40 emu / g.

3. The method for producing a composite material according to claim 1 or 2, wherein the BN particles have an average particle size (D50) of 0.1 to 10 μm.

4. The method for manufacturing a composite material according to claim 1 or 2, wherein the magnetic field is 0.4 to 1 T.

5. A method for producing a composite material according to claim 1 or 2, wherein the heat conductive particles are present in an amount of 3 to 50% by volume relative to the total amount of the heat conductive particles and the resin.

6. The method for producing a composite material according to claim 1 or 2, wherein the mixture is a slurry.

7. Heat-conducting particles, which consist of flattened BN particles coated with Fe, are held in place by a resin. The heat-conducting particles are oriented and unevenly distributed in the composite material.

8. The composite material according to claim 7, wherein the magnetization of the heat-conducting particles is 5 to 40 emu / g.

9. The composite material according to claim 7 or 8, wherein the BN particles have an average particle size (D50) of 0.1 to 10 μm.

10. The composite material according to claim 7 or 8, wherein the heat conductive particles are present in an amount of 3 to 50% by volume relative to the total amount of the heat conductive particles and the resin.

11. The composite material according to claim 7 or 8, which is a thermally conductive insulating sheet.

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