Thermally conductive resin composition and molded article made from the same

Abstract

The present invention is a polyester-elastomer-free thermally conductive resin composition containing (A) a thermoplastic resin and (B) flaky graphite, the thermally conductive resin composition having exceptional toughness and thermal conductivity, wherein: the (A) thermoplastic resin content is 45-60 parts by mass, and the B) flaky graphite content is 40-55 parts by mass (the total of (A) thermoplastic resin and (B) flaky graphite is 100 mass parts); the (B) flaky graphite contains flaky graphite (B1) in which the average particle size D50 is 150-400 μm, and flaky graphite (B2) in which the average particle size D50 is 10-40 μm, the mass ratio thereof being B1:B2=94:6-60:40; and the plane-direction thermal conductivity of a molded article obtained from the thermally conductive resin composition is 8 W / (m・K) or higher.

Description

[Technical Field]

[0001] The present invention relates to a thermally conductive resin composition having excellent toughness and thermal conductivity. [Background technology]

[0002] As electrical and electronic devices become smaller and more highly integrated, heat generation from mounted components and temperatures in operating environments become more pronounced, increasing the demand for improved heat dissipation from component parts. Currently, components made of metals and ceramics with high thermal conductivity are used for heat dissipation, particularly in automotive components and high-power LEDs. However, resin materials with high thermal conductivity and toughness are required to reduce weight, improve processability, and increase flexibility in shape.

[0003] As a method for imparting thermal conductivity to a resin, a method of adding a highly thermally conductive filler such as graphite has been disclosed.

[0004] Patent Document 1 discloses a resin composition with excellent thermal conductivity achieved by adding graphite particles having specific properties, particle size, and aspect ratio to the resin. However, the addition of a large amount of graphite reduces toughness, and the molded product is likely to have insufficient strength.

[0005] Furthermore, as a technique for improving thermal conductivity, the filling of resins with graphite and nano-sized carbon-based fillers has been investigated. For example, Patent Document 2 discloses a method for continuously obtaining sheets with high thermal conductivity by forming a resin composition in which flat graphite and nano-sized carbon nanofibers are dispersed in a thermoplastic elastomer into string-like strands using a twin-screw extrusion mixer and then pressing the strands with a roll. This method orients the graphite during roll pressing, and the nanofibers are dispersed between the layers, forming highly efficient heat conduction paths. This allows for the continuous production of processed products while achieving high thermal conductivity. However, because this method relies on roll pressing, there is a problem in that the degree of freedom in the shape of the resulting processed products is extremely limited.

[0006] In contrast, Patent Document 3 describes a thermally conductive resin composition that uses flake graphite and carbon nanofibers or carbon nanotubes, and adds a fluororesin to prevent the destruction of the nanomaterials due to shear during melt mixing, and maintains the dispersion of the nanomaterials between the layers of the oriented surface of the graphite even during melt kneading and injection molding, thereby achieving high thermal conductivity. However, this requires the use of very expensive carbon nanofibers, etc., making it difficult to use for general purposes.

[0007] On the other hand, in Patent Document 4, flake graphite, expandable graphite, and a polyester elastomer are added to a polyester resin to impart flexibility and improve toughness. However, new problems were discovered in that under special molding conditions that cause retention, the retention stability of the polyester elastomer is poor, resulting in a decrease in the toughness of the molded product under those molding conditions, and a deterioration in appearance due to difficulty in applying pressure during molding. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] WO2015 / 190324 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-36383 [Patent Document 3] Japanese Patent Application Laid-Open No. 2016-204570 [Patent Document 4] WO2018 / 181146 Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention has been made to solve the above problems, and an object of the present invention is to provide a thermally conductive resin composition which is excellent in toughness and thermal conductivity and does not contain polyester elastomer. [Means for solving the problem]

[0010] The present inventors have conducted extensive research to solve the above-mentioned problems. As a result, they have discovered that by mixing specific large-diameter flake graphite and specific small-diameter flake graphite in a specific ratio with a thermoplastic resin such as a thermoplastic polyester resin, the small-diameter graphite particles are present between the large-diameter graphite particles, forming good heat conduction paths and improving thermal conductivity, thereby reducing the amount of graphite required to achieve a target thermal conductivity and solving the problem of reduced toughness due to the amount of graphite, and have completed the present invention. More specifically, the present invention provides the following.

[0011] [1] A thermally conductive resin composition containing (A) a thermoplastic resin and (B) flake graphite, but not containing a polyester elastomer, wherein the (A) thermoplastic resin is contained in an amount of 45 to 60 parts by mass, and the (B) flake graphite is contained in an amount of 40 to 55 parts by mass (the total of the (A) thermoplastic resin and the (B) flake graphite is 100 parts by mass), the (B) flake graphite contains flake graphite (B1) having an average particle size D50 of 150 to 400 μm and flake graphite (B2) having an average particle size D50 of 10 to 40 μm, the mass ratio of B1:B2 being 94:6 to 60:40, and a molded article obtained from the thermally conductive resin composition has a thermal conductivity in the plane direction of 8 W / (m·K) or more. [2] The thermally conductive resin composition according to [1], wherein the thermoplastic resin (A) is a polyester resin. [3] The thermally conductive resin composition according to [1], wherein the thermoplastic resin (A) is polyethylene terephthalate and / or polybutylene terephthalate. [4] A molded article made of the thermally conductive resin composition according to any one of [1] to [3]. [Effects of the Invention]

[0012] According to the present invention, a resin composition excellent in toughness and thermal conductivity can be obtained by mixing specific amounts of flake graphite (B1) and (B2) with specific properties and ratios into a thermoplastic resin (A). Furthermore, the excellent toughness results in excellent heat shock resistance, and the low graphite content in the resin composition also results in excellent fluidity of the resin composition. DETAILED DESCRIPTION OF THE INVENTION

[0013] The following describes in detail the embodiments of the present invention, but the present invention is not limited to the following embodiments and can be implemented with appropriate modifications within the scope of the object of the present invention. Note that redundant explanations may be omitted as appropriate, but this does not limit the gist of the invention.

[0014] Below, (A) thermoplastic resin, (B) flake graphite, other components, and a method for producing a thermally conductive resin composition will be described in that order. (B) Flake graphite includes flake graphite (B1) having an average particle size D50 of 150 to 400 μm and flake graphite (B2) having an average particle size D50 of 10 to 40 μm. Hereinafter, the former may be referred to as "flake graphite (B1)" and the latter as "flake graphite (B2)."

[0015] [(A) Thermoplastic resin] In the thermally conductive resin molded article of the present invention, the thermoplastic resin (A) used as the base component (matrix component) is not particularly limited, but representative examples include polyarylene resins, polyamide resins, polyolefin resins, polyester resins, etc. In particular, polyester resins with high dimensional stability are desirable from the viewpoint of heat shock resistance.

[0016] Among these, specific examples of polyarylene resins include polyphenylene sulfide (PPS), polyether ketone (PEK), polyether ether ketone (PEEK), and polyarylene oxide-based poly(2,6-dimethyl-1,4-phenylene) ether (PPE). Styrenic resins such as polystyrene and high-impact polystyrene can be added to polyarylene oxide. Among these, PPS is more preferred from the viewpoints of heat resistance, chemical resistance, and cost.

[0017] Polyamide resins are resins obtained using amino acids, lactams, or diamines and dicarboxylic acids as the main raw materials. Specific examples include polyamide 6, polyamide 66, polyamide 46, polyamide 11, polyamide 12, polyamide 610, polyamide 69, polyamide 6T, polyamide 9T, polyamide MXD6, polyamide 6 / 66 copolymer, polyamide 6 / 610 copolymer, polyamide 6 / 6T copolymer, polyamide 6 / 66 / 610 copolymer, polyamide 6 / 12 copolymer, polyamide 6T / 12 copolymer, polyamide 6T / 66 copolymer, polyamide 6 / 6I copolymer, polyamide 66 / 6I / 6 copolymer, polyamide 6T / 6I copolymer, polyamide 6T / 6I / 66 copolymer, polyamide 6 / 66 / 610 / 12 copolymer, and polyamide 6T / M-5T copolymer. Among these, polyamide 6, polyamide 66, polyamide 12 and copolymers having these as the main components are preferred, from the viewpoint of providing a good balance between chemical resistance, impact resistance and fluidity in the resulting resin molded product, and polyamide 6 and copolymers having polyamide 6 as the main component are more preferred.

[0018] Furthermore, specific examples of polyolefin-based resins include homopolymers or copolymers primarily composed of repeating units derived from α-olefins such as ethylene and propylene. Examples include propylene homopolymers, ethylene homopolymers, and block or random copolymers obtained by copolymerizing ethylene with other α-olefins (e.g., propylene, butene-1, etc.). These may be used alone or in combination to the extent that they contribute to the properties of the resin material. The polyolefin-based resin used in the present invention may be either linear or branched. When the polyolefin-based resin is a polypropylene-based resin, any polypropylene-based resin, such as isotactic, atactic, or syndiotactic, may be used. When the polyolefin-based resin is a polyethylene-based resin, examples of polyethylene include linear low-density polyethylene (LLDPE), low-density polyethylene (LDPE), high-density polyethylene (HDPE), ultra-low-density polyethylene (ULDPE), and ultra-high molecular weight polyethylene (UHMW-PE).

[0019] Specific examples of polyester resins include polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, polycyclohexanedimethylene terephthalate, polyhexylene terephthalate, polyethylene naphthalate, polypropylene naphthalate, polybutylene naphthalate, polyethylene isophthalate / terephthalate, polypropylene isophthalate / terephthalate, polybutylene isophthalate / terephthalate, polyethylene terephthalate / naphthalate, polypropylene terephthalate / naphthalate, polybutylene terephthalate / decanedicarboxylate, polyethylene terephthalate / cyclohexanedimethylene terephthalate, polyethylene terephthalate / succinate, and polypropylene terephthalate. Examples of suitable terephthalate / isophthalate copolymers include phthalate / succinate, polybutylene terephthalate / succinate, polyethylene terephthalate / adipate, polypropylene terephthalate / adipate, polybutylene terephthalate / adipate, polyethylene terephthalate / sebacate, polypropylene terephthalate / sebacate, polyethylene terephthalate / isophthalate / adipate, polypropylene terephthalate / isophthalate / adipate, polybutylene terephthalate / isophthalate / succinate, polybutylene terephthalate / isophthalate / adipate, polybutylene terephthalate / isophthalate / sebacate, bisphenol A / terephthalic acid, bisphenol A / isophthalic acid, and bisphenol A / terephthalic acid / isophthalic acid. Among these, polyethylene terephthalate (PET) and polybutylene terephthalate (PBT) are preferred from the viewpoint of heat resistance and heat shock resistance, and polyethylene terephthalate (PET) is particularly preferred.

[0020] The intrinsic viscosity (IV) of polyethylene terephthalate is not particularly limited, but is preferably 0.4 to 1.2 dL / g, and more preferably 0.5 to 1.1 dL / g. The intrinsic viscosity (IV) of polybutylene terephthalate is not particularly limited, but is preferably 0.6 to 1.0 dL / g, and more preferably 0.7 to 0.9 dL / g. The intrinsic viscosity (IV) was measured at 30°C using an Ubbelohde viscosity tube (unit: dL / g) after dissolving 0.1 g of resin in 25 ml of a mixed solvent of phenol / tetrachloroethane (mass ratio 6 / 4). Having an intrinsic viscosity within the above range results in good toughness.

[0021] In a preferred embodiment, the thermally conductive resin composition of the present invention does not contain a polyester elastomer, which significantly accelerates thermal degradation using a hot runner or the like, thereby reducing the toughness of molded articles obtained by molding and further worsening their appearance. Furthermore, in a preferred embodiment, the thermally conductive resin composition of the present invention uses only a polyester-based resin that does not contain a polyester elastomer as the thermoplastic resin (A), and does not contain any other resin components.

[0022] The content of the (A) thermoplastic resin is 45 to 60 parts by mass, preferably 47 to 58 parts by mass, and more preferably 48 to 57 parts by mass, when the total of the (A) thermoplastic resin and the (B) flake graphite in the thermally conductive resin composition is 100 parts by mass. In the thermally conductive resin composition of the present invention, the amount (addition ratio) of the raw material components added directly becomes the content (content ratio) in the thermally conductive resin composition.

[0023] [(B) Flake graphite] In the present invention, the flake graphite (B) preferably blended in the thermally conductive resin composition is not particularly limited, and various graphites can be used, including both natural and artificially produced flake graphite. These flake graphites may be dried, fired, pulverized, and / or classified. The pulverization process is not particularly limited, and can be carried out using conventionally known devices such as a rod mill, ball mill, or jet mill. Expandable graphite can achieve higher thermal conductivity than other graphites, but is brittle and prone to reduced toughness. Expandable graphite also has a low bulk density, making it prone to poor penetration during production. Therefore, flake graphite is more preferable from the standpoint of ease of handling.

[0024] In particular, the inventors have carefully studied the type of flake graphite, its average particle size, and its addition ratio, and have found that there is a combination that allows maximum thermal conductivity to be obtained with a smaller amount added, leading to the present invention. When the ratio of flake graphite (B1) to flake graphite (B2) is within a specific range and the average particle sizes of each are within specific ranges, a thermally conductive resin composition can be obtained that has an excellent balance of various properties such as thermal conductivity, toughness, and heat shock resistance.

[0025] The flake graphite (B1) has an average particle diameter D50 of 150 to 400 μm. The average particle diameter D50 of the flake graphite (B1) is preferably 180 to 370 μm, more preferably 250 to 350 μm. If the average particle diameter D50 is less than 150 μm, the thermal conductivity of the resin composition decreases, or a larger amount must be added. While the larger the particle diameter, the higher the thermal conductivity tends to be, if it exceeds 400 μm, the strength and fluidity of the resin composition decrease, or dispersion in the resin is poor, which may actually result in a decrease in thermal conductivity. The average particle diameter D50 is determined by measuring the volume distribution using a laser scattering particle size analyzer, and the particle diameter at 50% of the measured volume distribution is taken as the average particle diameter D50.

[0026] The flake graphite (B2) has an average particle diameter D50 of 10 to 40 μm. The average particle diameter D50 of the flake graphite (B2) is preferably 15 to 35 μm, more preferably 18 to 32 μm. By setting the average particle diameter D50 of the flake graphite (B2) within the above range, it is possible to achieve a targeted high thermal conductivity in combination with the flake graphite (B1). The method for measuring the average particle diameter D50 is as described above.

[0027] The maximum thermal conductivity of the (B) flake graphite can be obtained by using flake graphite (B1) and flake graphite (B2) in combination. The mass ratio (B1:B2) of the flake graphite (B1) to the flake graphite (B2) is 94:6 to 60:40, preferably 94:6 to 70:30, and more preferably 92:8 to 75:25. When the content of the flake graphite (B2) is more than 40 mass% of the total, the thermal conductivity of the resin composition, Endurance This is not preferred because the heat shock resistance is significantly reduced.

[0028] The content of the (B) flake graphite in the present invention is 40 to 55 parts by mass, preferably 42 to 53 parts by mass, and more preferably 43 to 52 parts by mass, when the total of the (A) thermoplastic resin and (B) flake graphite in the thermally conductive resin composition is 100 parts by mass. Even if flake graphite having the above-mentioned specific average particle size D50 is used in a specific ratio, if the amount of (B) flake graphite added itself is small, the thermal conductivity will be low. Conversely, if it exceeds 55 parts by mass, the handleability during production will be significantly poor and the fluidity, toughness, etc. of the resin composition will also be significantly reduced, which is not preferred.

[0029] The thermally conductive resin composition of the present invention may contain, together with the thermoplastic resin (A) and the flake graphite (B), at least one selected from the group consisting of (B) a thermally conductive filler other than flake graphite and a filler other than the thermally conductive filler, to the extent that the effects of the composition are not impaired. The shape of the (B) thermally conductive filler other than flake graphite and the filler is not particularly limited, and examples thereof include various shapes such as flakes, fibers, flakes, plates, spheres, particles, fine particles, nanoparticles, aggregated particles, tubes, nanotubes, wires, rods, amorphous shapes, rugby ball shapes, hexahedrons, composite particles formed by combining large particles and fine particles, and liquids. Specific examples of thermally conductive fillers other than (B) flake graphite include metal fillers such as aluminum and nickel; low-melting-point alloys with a liquidus temperature of 300°C or higher and a solidus temperature of 150°C to 250°C; metal oxides such as aluminum oxide, magnesium oxide, silicon oxide, beryllium oxide, copper oxide, and cuprous oxide; metal nitrides such as aluminum nitride and silicon nitride; metal carbides such as silicon carbide; metal carbonates such as magnesium carbonate; insulating carbon materials such as diamond; metal hydroxides such as aluminum hydroxide and magnesium hydroxide; alumina, boron nitride, glass fiber, carbon fiber, potassium titanate whiskers, silicon nitride fiber, carbon nanotubes, talc, and wollastonite. One or more of these may be used. The amount of addition is not particularly limited, but increasing the amount can improve thermal conductivity. The thermally conductive fillers other than (B) flake graphite may be natural or synthetic. In the case of natural products, there are no particular restrictions on their origin and they can be selected appropriately.

[0030] In addition to the thermally conductive filler described above, a wide variety of known fillers can be used in the resin composition of the present invention depending on the intended purpose. Examples of fillers other than thermally conductive fillers include inorganic fibers such as diatomaceous earth powder, basic magnesium silicate, calcined clay, finely powdered silica, quartz powder, crystalline silica, kaolin, antimony trioxide, finely powdered mica, molybdenum disulfide, rock wool, ceramic fiber, and asbestos, as well as glass fillers such as glass fiber, glass powder, glass cloth, and fused silica. The use of these fillers can improve desirable properties for the application of the resin composition, such as thermal conductivity, mechanical strength, and abrasion resistance. Furthermore, organic fillers such as paper, pulp, wood, synthetic fibers such as polyamide fiber, aramid fiber, and boron fiber, and resin powders such as polyolefin powder can be used in combination as needed.

[0031] The thermally conductive filler and fillers other than the thermally conductive filler used in the present invention may be surface-treated with various surface treatment agents such as silane treatment agents, stearic acid, and acrylic monomers to improve the adhesion at the interface between the resin and the filler or to facilitate workability. The surface treatment agent is not particularly limited, and conventionally known agents such as silane coupling agents and titanate coupling agents can be used. Among these, epoxy group-containing silane coupling agents such as epoxy silane, amino group-containing silane coupling agents such as amino silane, and polyoxyethylene silane are preferred because they do not significantly deteriorate the physical properties of the resin. The surface treatment method for the filler is not particularly limited, and conventional treatment methods can be used.

[0032] In the present invention, when the total of the (B) flake graphite, the thermally conductive filler other than the (B) flake graphite, and the filler other than the thermally conductive filler is taken as 100% by mass, the (B) flake graphite preferably accounts for 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, and may even be 100% by mass. [Other ingredients]

[0033] The thermally conductive resin composition of the present invention may further contain various additives such as antioxidants, heat stabilizers, ultraviolet absorbers, antistatic agents, dyes, pigments, lubricants, plasticizers, mold release agents, crystallization accelerators, crystal nucleating agents, and epoxy compounds depending on the purpose.

[0034] In the thermally conductive resin composition of the present invention, the combined weight of (A) the thermoplastic resin and (B) the flake graphite preferably accounts for 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more.

[0035] The thermally conductive resin composition of the present invention is produced by melt-kneading a thermoplastic resin (A), flake graphite (B), and other components. Generally, graphite tends to be crushed during melt-kneading and molding. Therefore, the larger the volume average particle size of the graphite before melt-kneading, the larger the volume average particle size of the flake graphite maintained after melt-kneading and molding, resulting in improved thermal conductivity and molding processability. During melt-kneading, flake graphite (B) is typically added and kneaded together with the resin from a hopper. However, in order to minimize crushing and maintain good thermal conductivity as described above, it is preferable to add flake graphite (B1) in particular by side feeding in the latter half of the melt-kneading process.

[0036] In the present invention, "thermal conductivity in the in-plane direction" refers to the thermal conductivity in the direction in which the molten resin flows when producing a molded article. The thermal conductivity of the thermally conductive resin composition of the present invention in the in-plane direction is 8 W / (m·K) or more, preferably 8.2 W / (m·K) or more. There is no particular upper limit, and the higher the better, but depending on the materials used, it is thought to be 11 W / (m·K) or less, more preferably 10 W / (m·K) or less.

[0037] The thermally conductive resin composition of the present invention has excellent toughness. Molded articles obtained by injection molding the thermally conductive resin composition of the present invention using the method described in the examples satisfy both a flexural strength of 60 MPa or more and a flexural deflection of 0.7% or more. Since the composition satisfies these physical properties, it can be determined that the composition has excellent toughness. [Example]

[0038] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0039] <Examples 1 to 7 and Comparative Examples 1 to 10> In Examples 1 to 7 and Comparative Examples 1 to 10, the following materials were used as components of the thermally conductive resin compositions.

[0040] [A: Thermoplastic resin] A-1: Polyethylene terephthalate (manufactured by Toyobo Co., Ltd., IV = 0.63 dl / g) A-2: Polyethylene terephthalate (manufactured by Toyobo Co., Ltd., IV = 1.10 dl / g) A-3: Polybutylene terephthalate (manufactured by Toyobo Co., Ltd., IV = 0.83 dl / g)

[0041] [B: flake graphite] B1-1: Flake graphite manufactured by Nippon Graphite Industries Co., Ltd. (average particle size D50: 200 μm) B1-2: Flake graphite manufactured by Nippon Graphite Industries Co., Ltd. (average particle size D50: 300 μm) B1-3: Flake graphite manufactured by Nippon Graphite Industries Co., Ltd. (average particle size D50: 600 μm) B2-1: Flake graphite manufactured by Nippon Graphite Industries Co., Ltd. (average particle size D50: 20 μm) B2-2: Flake graphite BF-30AK (average particle size D50: 30 μm) manufactured by Chuetsu Graphite Industries Co., Ltd. The flake graphite used had a fixed carbon concentration of 96%. The average particle diameter D50 was determined by placing a graphite sample in a 20% by mass aqueous solution of sodium hexametaphosphate in a 100 ml beaker, dispersing it for 30 minutes using an ultrasonic disperser, placing it in the chamber of a laser scattering particle size analyzer (MICROTRAC HRA (Nikkiso Co., Ltd.) 9320-X100), measuring the volume distribution over a measurement time of 120 seconds, and determining the particle diameter at 50% of the measured volume distribution as the average particle diameter D50.

[0042] [Polyester elastomer] C-1: Polyester elastomer (Pelprene P-70B, manufactured by Toyobo Co., Ltd.)

[0043] [Other additives] Antioxidant: IRGANOX1010 manufactured by BASF Release agent: LICOWAX-OP manufactured by Clariant Crystallization accelerator: KRM4004 manufactured by Sanyo Chemical Industries, Ltd.

[0044] The components shown in Tables 1 and 2 were dry-blended in the content ratios (parts by mass) shown in Tables 1 and 2, and melt-kneaded using a twin-screw extruder (TEX-30, manufactured by The Japan Steel Works, Ltd.) under conditions of a cylinder temperature of 270°C, a discharge rate of 10 kg / hr, and a screw rotation speed of 150 rpm to produce pellets of a thermally conductive resin composition. Test pieces were prepared using the resulting pellets, and the thermal conductivity (in-plane direction) and toughness of the thermally conductive resin composition were measured, and the appearance was confirmed. The measurement results for the thermally conductive resin compositions of Examples 1 to 7 are shown in Table 1. The thermal conductivity (in-plane direction), toughness measurement results, and appearance confirmation results of the thermally conductive resin compositions of Comparative Examples 1 to 10 are also shown in Table 2. The physical properties of the thermally conductive resin compositions were measured according to the following methods.

[0045] <Thermal conductivity> Using a Toshiba Machine injection molding machine, a cylinder temperature was set at 280°C, and a mold temperature was set at 140°C, to produce a 100mm x 100mm x 1mm (thickness) flat plate. The center of the plate was then cut into a 25mm x 25mm square. The thermal diffusion coefficient and specific heat capacity in the planar direction (resin flow direction) were measured using the laser flash method with an Alpac-Riko TC-7000H. The thermal conductivity was calculated using these values ​​and the specific gravity measured separately on the same molded product.

[0046] <Toughness (bending strength, bending deflection rate)> Measurements were made in accordance with ISO-178. The test specimens were measured at a cylinder temperature of 280°C and a mold temperature of 140°C. of The material was injection molded under the following conditions: A material was determined to have excellent toughness if it had a bending strength of 60 MPa or more and a bending deflection rate of 0.7% or more.

[0047] <Appearance> Using an injection molding machine manufactured by Toshiba Machine Co., Ltd., the cylinder temperature was set to 280°C and the mold temperature to 140°C, and after a retention time of 10 minutes, a flat plate measuring 100 mm x 100 mm x 1 mm (thickness) was injection molded, and its appearance was visually observed. ○: The surface is glossy and there is no appearance defect, which is good. ×: The entire molded product lacks gloss and has poor appearance.

[0048] [Table 1]

[0049] [Table 2]

[0050] As is clear from Tables 1 and 2, the thermally conductive resin compositions of Examples 1 to 7 of the present invention have a good balance between thermal conductivity and toughness by mixing graphite of a specific particle size with a thermoplastic resin in a ratio within a specific range, whereas the thermal conductivity, toughness, or appearance of Comparative Examples 1 to 10 are low. [Industrial Applicability]

[0051] According to the present invention, a resin composition having excellent toughness and thermal conductivity can be obtained, and therefore the resin composition can be suitably used in applications where heat generation is an issue. In addition, by replacing metals and the like, the resin composition can be made lighter, the freedom of shape can be improved, and molded articles can be easily obtained, which will greatly contribute to the industrial world.

Claims

1. A thermally conductive resin composition containing (A) a thermoplastic resin and (B) flake graphite, but not containing a polyester elastomer, wherein the content of the (A) thermoplastic resin is 45 to 60 parts by mass, and the content of the (B) flake graphite is 40 to 55 parts by mass (the total of the (A) thermoplastic resin and the (B) flake graphite is 100 parts by mass), the (B) flake graphite contains flake graphite (B1) having an average particle diameter D50 of 250 to 400 μm and flake graphite (B2) having an average particle diameter D50 of 10 to 40 μm, the mass ratio of B1:B2 being 94:6 to 60:40, and a molded article obtained from the thermally conductive resin composition has a thermal conductivity in the plane direction of 8 W / (m K) or more.

2. The thermally conductive resin composition according to claim 1 , wherein the thermoplastic resin (A) is a polyester resin.

3. 2. The thermally conductive resin composition according to claim 1, wherein the thermoplastic resin (A) is polyethylene terephthalate and / or polybutylene terephthalate.

4. A molded article made from the thermally conductive resin composition according to any one of claims 1 to 3.

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