Polyamide composition and molded article

Abstract

The purpose of the present invention is to provide a polyamide composition capable of forming a molded article having excellent heat dissipation properties, strength, and moisture resistance. The purpose of the present invention is also to provide a molded article having excellent heat dissipation properties, strength, and moisture resistance. The polyamide composition contains a polyamide, a fibrous inorganic reinforcing material, and a sintered body containing magnesium oxide, the sintered body being covered with a silica film, and the content of the sintered body being 35 mass% or more. The molded article contains the polyamide composition.

Description

Technical Field

[0001] The present invention relates to a polyamide composition and a molded article. Background Art

[0002] It is known that in order to impart thermal conductivity to a polyamide composition, that is, in order to impart heat dissipation properties to the polyamide composition, an inorganic substance having a high thermal conductivity (hereinafter, sometimes referred to as "thermal conductive inorganic filler") is compounded.

[0003] Among thermal conductive inorganic fillers, magnesium oxide particles are particularly useful because they are inexpensive, have excellent thermal conductivity, and have low hardness. In addition, the low hardness has the advantage of suppressing wear of the screw of an extruder or a molding machine when manufacturing a polyamide composition or a molded article.

[0004] However, magnesium oxide particles (e.g., light-burned magnesium oxide) reduce the strength of the polyamide composition. This is because the dispersibility of magnesium oxide particles in polyamide and the adhesion to polyamide are poor, resulting in embrittlement of the polyamide composition. Magnesium oxide particles also reduce the moisture resistance of the polyamide composition. This is because magnesium oxide constituting the magnesium oxide particles reacts with moisture. The reduction in strength and moisture resistance becomes particularly significant when a large amount of magnesium oxide particles are compounded.

[0005] As a method for improving such disadvantages of magnesium oxide particles, for example, a method of covering magnesium oxide particles with a fatty acid metal salt (see Patent Document 1), a method of compounding a maleic anhydride-modified product of an ethylene-octene copolymer together with a thermal conductive inorganic filler (see Patent Document 2) have been proposed. In addition to these, a method of using a sintered body containing magnesium oxide, calcium oxide, and silicon oxide (see Patent Document 3), a method of surface-treating magnesium oxide particles with an oligomeric reactive siloxane (see Patent Document 4) have been proposed. [Prior Art Documents] [Patent Documents]

[0006] Patent Document 1: WO2018 / 180123 Patent Document 2: Japanese Patent No. 6296197 Patent Document 3: Japanese Patent No. 5993824 Patent Document 4: Japanese Patent No. 5602650 Summary of the Invention [Problems to be Solved by the Invention]

[0007] In recent years, with the requirements for weight reduction and the spread of electric vehicles (EVs), a polyamide composition having not only excellent heat dissipation properties but also excellent other physical properties (e.g., strength, moisture resistance) has been sought.

[0008] An object of the present invention is to provide a polyamide composition capable of forming a molded article having excellent heat dissipation, strength, and moisture resistance. Another object of the present invention is to provide a molded article having excellent heat dissipation, strength, and moisture resistance. [Means for Solving the Problem]

[0009] To solve this problem, the present invention has the structure of the following [1]. [1] A polyamide composition comprising: a polyamide, a fibrous inorganic reinforcing material, and a sintered body containing magnesium oxide, the sintered body is covered with a silica film, the content of the sintered body is 35% by mass or more. Here, the "sintered body containing magnesium oxide" is a granular sintered body formed by binding several magnesium oxide-containing particles.

[0010] According to [1], the strength (specifically, flexural strength) can be improved by the fibrous inorganic reinforcing material.

[0011] Moreover, by the sintered body containing magnesium oxide, the heat dissipation and strength can be improved as compared with the case of using unsintered magnesium oxide particles (specifically, lightly burned magnesium oxide). This will be explained. Magnesium oxide reacts with moisture to form magnesium hydroxide. As this reaction proceeds, the volume of magnesium oxide expands. When this reaction occurs in the polyamide composition, voids are generated at the interface between magnesium oxide and the resin (for example, polyamide). In contrast, according to [1], by using a sintered body containing magnesium oxide, this reaction can be suppressed, so that the generation of voids can be suppressed, and the size of the voids that can be generated can be reduced. It is considered that this is because during sintering in the production of the sintered body, parts (i.e., necks) or certain layers are formed between the magnesium oxide-containing particles in the particles. Therefore, the reduction in heat dissipation and strength caused by voids can be suppressed. Therefore, the heat dissipation and strength can be improved by the sintered body.

[0012] By using a sintered body containing magnesium oxide, the moisture resistance can be improved compared with the case of using unsintered magnesium oxide particles (specifically, lightly burned magnesium oxide). Specifically, the reduction of the tensile strength in a high-humidity environment can be suppressed. This will be described. Magnesium oxide reacts with moisture to form magnesium hydroxide. As this reaction proceeds, the volume of magnesium oxide expands. When this reaction occurs in the polyamide composition, the tensile strength of the polyamide composition decreases. In contrast, according to [1], by using a sintered body containing magnesium oxide, this reaction can be suppressed. It is considered that this is because during the sintering in the production of the sintered body, parts where the magnesium-oxide-containing particles are bonded to each other (i.e., necks) or certain layers are formed in the particles. Therefore, the reduction of the tensile strength caused by this reaction (i.e., the reaction between magnesium oxide and moisture) can be suppressed. Therefore, by using the sintered body, the reduction of the tensile strength in a high-humidity environment can be suppressed, that is, the moisture resistance can be improved.

[0013] Moreover, by covering the sintered body with a silica film, the sintered body has more excellent moisture resistance, and thus, the heat dissipation, strength, and moisture resistance of the polyamide composition can be further improved.

[0014] Furthermore, when the content of the sintered body is 35% by mass or more, the heat dissipation can be further improved.

[0015] The present invention preferably has the following structures [2] to [9].

[0016] [2] The polyamide composition according to [1], wherein the content of the fibrous inorganic reinforcing material is 10% by mass or more. According to [2], when the content of the fibrous inorganic reinforcing material is 10% by mass or more, the strength can be further improved.

[0017] [3] The polyamide composition according to [1] or [2], wherein the polyamide is a crystalline polyamide. According to [3], by using a crystalline polyamide, the mechanical properties can be improved.

[0018] [4] The polyamide composition according to [3], wherein the relative viscosity of the crystalline polyamide is 2.0 or more and 3.6 or less. Here, the relative viscosity is a value measured according to JIS K6920-2:2009, using 98% sulfuric acid, at 1 g / dL of the sample (i.e., polyamide) and 25 °C.

[0019] [5] The polyamide composition according to any one of [1] to [4], wherein the polyamide composition further contains an antioxidant. According to [5], by using an antioxidant, the oxidative degradation of the polyamide composition can be suppressed.

[0020] [6] The polyamide composition according to any one of [1] to [5], wherein the polyamide composition further contains a hindered phenol antioxidant.

[0021] [7] The polyamide composition according to any one of [1] to [6], wherein the polyamide composition further contains a mold release agent. According to [7], since the polyamide composition contains a mold release agent, when molding the polyamide composition with a mold, it is easy to take out the molded product from the mold.

[0022] [8] The polyamide composition according to [7], wherein the mold release agent is a higher fatty acid ester compound.

[0023] [9] The polyamide composition according to any one of [1] to [8], wherein the flexural strength is 120 MPa or more, the thermal conductivity is 0.60 W / m·K or more, when subjected to a high humidity treatment of standing for 168 hours in an environment of 80 °C and a relative humidity of 95% RH, the retention rate of the tensile strength is 40% or more, and the retention rate of the tensile strength is a value calculated by the following formula: Retention rate of tensile strength = (Tensile strength of the polyamide composition test piece after high humidity treatment / Tensile strength of the polyamide composition test piece without high humidity treatment) × 100

[0024]

[10] A molded product comprising the polyamide composition according to any one of [1] to [9].

[0025] The present invention also preferably has the following structures of

[11] to

[23] .

[0026]

[11] The polyamide composition according to any one of [1] to [9], wherein the polyamide contains polyamide 6.

[0027]

[12] The polyamide composition according to any one of [1] to [9] and

[11] , wherein the content of the polyamide is 25% by mass or more.

[0028]

[13] The polyamide composition according to any one of [1] to [9],

[11] and

[12] , wherein the content of the polyamide is 50% by mass or less.

[0029]

[14] The polyamide composition according to any one of [1] to [9] and

[11] to

[13] , wherein the fibrous inorganic reinforcing material contains at least one of glass fiber and carbon fiber.

[0030]

[15] The polyamide composition according to any one of [1] to [9] and

[11] to

[14] , wherein the fibrous inorganic reinforcing material is glass fiber.

[0031]

[16] The polyamide composition according to any one of [1] to [9] and

[11] to

[15] , wherein the fibrous inorganic reinforcing material is carbon fiber.

[0032]

[17] The polyamide composition according to any one of [1] to [9] and

[11] to

[16] , wherein, in the fibrous inorganic reinforcing material, the ratio of the average fiber length to the average fiber diameter is 100 or more and 1000 or less.

[0033]

[18] The polyamide composition according to any one of [1] to [9] and

[11] to

[17] , wherein the median particle size of the sintered body is 1 μm or more and 200 μm or less.

[0034]

[19] The polyamide composition according to any one of [1] to [9] and

[11] to

[18] , wherein the total content of the fibrous inorganic reinforcing material and the sintered body is 50% by mass or more.

[0035]

[20] The polyamide composition according to any one of [1] to [9] and

[11] to

[19] , wherein the total content of the fibrous inorganic reinforcing material and the sintered body is 70% by mass or less.

[0036]

[21] The polyamide composition according to any one of [1] to [9] and

[11] to

[20] , wherein the polyamide composition is in a granular form.

[0037]

[22] The polyamide composition according to any one of [1] to [9] and

[11] to

[21] , wherein the polyamide is polyamide 6.

[0038]

[23] A molded article, wherein the molded article contains the polyamide composition according to any one of

[11] to

[22] . [Effects of the Invention]

[0039] According to the present invention, a polyamide composition capable of molding a molded article excellent in heat dissipation, strength, and moisture resistance can be provided. According to the present invention, a molded article excellent in heat dissipation, strength, and moisture resistance can also be provided. Detailed Embodiments

[0040] Hereinafter, embodiments of the present invention will be described in detail.

[0041] <1. Polyamide composition> <1.1. Polyamide> The polyamide composition of this embodiment contains polyamide. Polyamide is a polymer having an amide bond (-NHCO-) in the main chain.

[0042] As the polyamide, crystalline polyamide is preferred for the reason that it can improve the mechanical properties of the polyamide composition. Examples of the crystalline polyamide include: polyamide 6 (PA6), polyamide 66 (PA66), polyamide 46 (PA46), polyamide 11 (PA11), polyamide 12 (PA12), polyamide 610 (PA610), polyamide 612 (PA612), polyhexamethylene adipamide (PAMXD6), hexamethylenediamine - terephthalic acid polymer (PA6T), hexamethylenediamine - terephthalic acid and adipic acid polymer (PA6T / 66), hexamethylenediamine - terephthalic acid and ε - caprolactam copolymer (PA6T / 6), trimethylhexamethylenediamine - terephthalic acid polymer (PATMD - T), m - xylylenediamine and adipic acid and isophthalic acid copolymer (PAMXD6 / MXDI), trimethylhexamethylenediamine and terephthalic acid and ε - caprolactam copolymer (PATMDT / 6), diaminodicyclohexylmethane and isophthalic acid and lauryllactam copolymer. It should be noted that they can be used alone or two or more of them can be used. Among them, polyamide 6 is preferred for its excellent formability, melt fluidity and mechanical properties.

[0043] Polyamide 6 is preferably a polyamide mainly made of ε-caprolactam. The polyamide mainly made of ε-caprolactam can be obtained by polycondensation. Other monomers can be copolymerized in polyamide 6. As such monomers, for example, amino acids such as 11-aminoundecanoic acid, 12-aminododecanoic acid, p-aminomethylbenzoic acid, and lactams such as ω-laurolactam can be listed; aliphatic diamines such as tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, 2-methylpentamethylenediamine, undecamethylenediamine, dodecamethylenediamine, 2,2,4- / 2,4,4-trimethylhexamethylenediamine, 5-methylnonamethylenediamine; aromatic diamines such as m-xylylenediamine, p-xylylenediamine; alicyclic diamines such as 1,3-bis(aminomethyl)cyclohexane, 1,4-bis(aminomethyl)cyclohexane, 1-amino-3-aminomethyl-3,5,5-trimethylcyclohexane, bis(4-aminocyclohexyl)methane, bis(3-methyl-4-aminocyclohexyl)methane, 2,2-bis(4-aminocyclohexyl)propane, bis(aminopropyl)piperazine, aminoethylpiperazine; aliphatic dicarboxylic acids such as adipic acid, suberic acid, azelaic acid, sebacic acid, dodecanedioic acid; aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, 2-chloroterephthalic acid, 2-methylterephthalic acid, 5-methylisophthalic acid, sodium 5-sulfoisophthalate, hexahydroterephthalic acid, hexahydroisophthalic acid; alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, 1,3-cyclopentanedicarboxylic acid. Two or more of them can be copolymerized.

[0044] In the total 100 mol% of the monomer units constituting polyamide 6, the units derived from ε-caprolactam are preferably 60 mol% or more, more preferably 70 mol% or more, further preferably 80 mol% or more, and still further preferably 90 mol% or more. It can be 100 mol%.

[0045] The relative viscosity of the crystalline polyamide is preferably 1.5 or more, more preferably 1.8 or more, and further preferably 2.0 or more. When it is 1.5 or more, the strength can be further improved. The relative viscosity of the crystalline polyamide is preferably 4.5 or less, more preferably 4.0 or less, and further preferably 3.6 or less. When it is 4.5 or less, an excessive decrease in the fluidity during melting of the polyamide composition can be suppressed, and the dispersibility of the sintered body can be improved. The relative viscosity is a value measured at 1 g / dL of the sample (i.e., polyamide) and 25 °C using 98% sulfuric acid according to JIS K6920-2:2009.

[0046] In 100% by mass of the polyamide contained in the polyamide composition of the present embodiment, the content of the crystalline polyamide is preferably 80% by mass or more. The content of the crystalline polyamide can be 90% by mass or more, or can be 95% by mass or more, or can be 98% by mass or more, or can be 100% by mass.

[0047] The polyamide composition of the present embodiment may further contain an amorphous polyamide. When the polyamide composition contains an amorphous polyamide, it is easily transferred (i.e., die transfer) to the molded article when injection molding the polyamide composition. The amorphous polyamide can be a polyamide in which no melting peak of crystallization is observed in the thermogram in differential scanning calorimetry (DSC) measurement. As the amorphous polyamide, for example, polymers obtained by polycondensation of diamines such as 4,4'-diamino-3,3'-dimethyl dicyclohexylmethane (CA), 4,4'-diamino dicyclohexylmethane (PACM), meta-xylylenediamine (MXD), trimethylhexamethylenediamine (TMD), isophoronediamine (IA), 4,4'-diamino dicyclohexylpropane (PACP), hexamethylenediamine, dicarboxylic acids such as terephthalic acid, isophthalic acid, adipic acid, sebacic acid, dodecanedicarboxylic acid, and lactams such as caprolactam and lauryllactam as needed can be cited. It should be noted that they can be used alone or two or more of them can be used. Of course, other monomers are also copolymerized in the amorphous polyamide.

[0048] In particular, from the viewpoint of easily suppressing crystallization, the amorphous polyamide preferably contains an aromatic component. As the amorphous polyamide containing an aromatic component, polyamide 6T / 6I made from terephthalic acid, isophthalic acid and adipic acid, and polyamide 6T / 66 made from terephthalic acid, adipic acid and hexamethylenediamine are preferred. Among them, from the viewpoint of moldability, polyamide 6T / 6I is more preferred.

[0049] In the polyamide composition of the present embodiment, the content of the polyamide is preferably 25% by mass or more, more preferably 30% by mass or more, and further preferably 38% by mass or more. The content of the polyamide is preferably 50% by mass or less, more preferably 45% by mass or less, and further preferably 42% by mass or less.

[0050] <1.2. Fibrous inorganic reinforcing material> The polyamide composition of the present embodiment contains a fibrous inorganic reinforcing material. By the fibrous inorganic reinforcing material, the strength can be improved, specifically, the flexural strength can be improved. In addition, the rigidity, heat resistance, etc. can also be improved.

[0051] As the fibrous inorganic reinforcing material, for example, the following can be cited: glass fiber, carbon fiber, aramid fiber, alumina fiber, silicon carbide fiber, zirconia fiber. As the fibrous inorganic reinforcing material, whiskers such as aluminum borate and potassium titanate, acicular wollastonite, milled fiber, etc. can also be cited. Among them, glass fiber and carbon fiber are preferred. It should be noted that they can be used alone or two or more of them can be used.

[0052] As the glass fiber, for example, the following can be cited: chopped strand-shaped glass fiber. The fiber length of the glass fiber is preferably 1 mm to 20 mm. The cross-sectional shape of the glass fiber can be a circular cross-section or a non-circular cross-section. Here, the "cross-sectional shape" refers to the shape of the cross-section perpendicular to the length direction of the glass fiber. As the non-circular cross-section, a substantially elliptical cross-section, a substantially oblong cross-section, and a substantially cocoon-shaped cross-section can be cited. The flatness of the glass fiber with a non-circular cross-section is preferably 1.5 to 8. Here, the flatness means the ratio of the major axis to the minor axis (i.e., major axis / minor axis) when, on the basis of assuming a rectangle with the minimum area circumscribing the cross-section perpendicular to the length direction of the glass fiber, the length of the long side of the rectangle is set as the major axis and the length of the short side is set as the minor axis. The minor axis of the glass fiber is preferably 1 μm to 20 μm. The major axis of the glass fiber is preferably 2 μm to 100 μm.

[0053] For the fibrous inorganic reinforcing material, the ratio of the average fiber length to the average fiber diameter is preferably 100 or more, more preferably 200 or more. This ratio is preferably 1000 or less, more preferably 800 or less. This ratio can be 500 or less.

[0054] The fibrous inorganic reinforcing material is preferably treated with a coupling agent. Thereby, the affinity with polyamide can be improved, and the mechanical properties can be improved. In addition, the appearance characteristics can also be improved. As the coupling agent, for example, the following can be cited: organosilane compounds, organotitanium compounds, organoborane compounds, epoxy compounds. It should be noted that as the coupling agent, a coupling agent that easily reacts with a carboxylic acid group and / or a carboxylic anhydride group is preferred. If the coupling agent is exemplified from a slightly different perspective, for example, silane coupling agents, titanate coupling agents, and aluminum coupling agents can be cited. Among them, silane coupling agents such as amino silane coupling agents and epoxy silane coupling agents are preferred. It should be noted that although the treatment with the coupling agent is preferably carried out in advance, the coupling agent can also be added later.

[0055] In the polyamide composition of this embodiment, the content of the fibrous inorganic reinforcing material is preferably 5% by mass or more, more preferably 10% by mass or more, and still more preferably 15% by mass or more. When it is 5% by mass or more, the flexural strength (i.e., strength) can be further improved. On the other hand, the content of the fibrous inorganic reinforcing material is preferably 40% by mass or less, more preferably 30% by mass or less, and still more preferably 25% by mass or less. When it is 40% by mass or less, it is possible to avoid making it difficult to produce a molded article of the polyamide composition.

[0056] <1.3. Sintered body> The polyamide composition of this embodiment contains a sintered body containing magnesium oxide. Here, the "sintered body containing magnesium oxide" is a granular sintered body obtained by binding several magnesium oxide-containing particles. Since the sintered body contains magnesium oxide, it has a high thermal conductivity.

[0057] By using the sintered body containing magnesium oxide, the heat dissipation and strength can be improved compared with the case of using unsintered magnesium oxide particles (specifically, light-burned magnesium oxide). This will be explained. Magnesium oxide reacts with moisture to form magnesium hydroxide. As this reaction proceeds, the volume of magnesium oxide expands. When this reaction occurs in the polyamide composition, voids are generated at the interface between magnesium oxide and the resin (e.g., polyamide). In contrast, according to [1], by using a sintered body containing magnesium oxide, this reaction can be suppressed, so the generation of voids can be suppressed, and the size of the voids that can be generated can be reduced. It is considered that this is because during the sintering in the production of the sintered body, parts (i.e., necks) and certain layers where the magnesium oxide-containing particles are combined with each other are formed in the particles. Therefore, the reduction in heat dissipation and strength caused by voids can be suppressed. Therefore, the heat dissipation and strength can be improved by the sintered body.

[0058] By using the sintered body containing magnesium oxide, the moisture resistance can also be improved compared with the case of using unsintered magnesium oxide particles (specifically, light-burned magnesium oxide). Specifically, the reduction in tensile strength in a high-humidity environment can be suppressed. This will be explained. Magnesium oxide reacts with moisture to form magnesium hydroxide. As this reaction proceeds, the volume of magnesium oxide expands. When this reaction occurs in the polyamide composition, the tensile strength of the polyamide composition decreases. In contrast, according to [1], by using a sintered body containing magnesium oxide, this reaction can be suppressed. It is considered that this is because during the sintering in the production of the sintered body, parts (i.e., necks) and certain layers where the magnesium oxide-containing particles are combined with each other are formed in the particles. Therefore, the reduction in tensile strength caused by this reaction (i.e., the reaction between magnesium oxide and moisture) can be suppressed. Therefore, by using the sintered body, the reduction in tensile strength in a high-humidity environment can be suppressed, that is, the moisture resistance can be improved.

[0059] The sintered body can be manufactured, for example, by the following method: Mix purified magnesium hydroxide (Mg(OH)2), silicon dioxide (SiO2), and calcium oxide (CaO), and heat the mixture at a high temperature. Sintering can be promoted by silicon dioxide and calcium oxide. Heating can be carried out, for example, using a rotary kiln under the conditions of about 1800 °C for about 30 minutes. The sintered body obtained by heating can be sieved as needed and classified as needed. The sintered body can be surface-treated as needed.

[0060] The sintered body preferably contains silicon dioxide (SiO2), and more preferably contains silicon dioxide (SiO2) and calcium oxide (CaO). This is because by adjusting the molar ratio of calcium oxide to silicon dioxide (hereinafter sometimes referred to as the "Ca / Si ratio").), the strength and moisture resistance of the sintered body can be controlled (see Japanese Patent No. 5993824). Here, the number of moles of silicon dioxide refers to the number of moles (MSi) obtained by converting the silicon element contained in the sintered body into silicon oxide (SiO2). The number of moles of calcium oxide refers to the number of moles (MCa) obtained by converting the calcium element contained in the sintered body into calcium oxide (CaO). Therefore, the Ca / Si ratio is the value represented by MCa / MSi. It should be noted that the number of moles, molar ratio, mass%, etc. of each oxide contained in the sintered body can be measured by methods such as ICP method using a dielectric coupling plasma (ICP) emission analysis device and chelation titration method using a chelating agent such as EDTA.

[0061] The Ca / Si ratio is preferably 0.1 or more, more preferably 0.4 or more, and further preferably 0.8 or more. When it is 0.1 or more, the strength of the sintered body can be improved. On the other hand, the Ca / Si ratio is preferably less than 2.0, more preferably 1.5 or less, and further preferably 1.2 or less. When it is less than 2.0, the moisture resistance of the sintered body can be improved.

[0062] In the sintered body, in addition to magnesium oxide, silicon dioxide (SiO2), and calcium oxide (CaO), compounds obtained by their reaction may also be contained. The sintered body may contain, for example, B2O3, Al2O3, Fe2O3, Na2SO4, etc.

[0063] In 100% by mass of the sintered body, the content of magnesium oxide in the sintered body is preferably 85.0% by mass or more, more preferably 88.0% by mass or more, further preferably 90.0% by mass or more, further preferably 92.0% by mass or more, and further preferably 94.0% by mass or more. When it is 85.0% by mass or more, the thermal conductivity of the sintered body is excellent. On the other hand, in 100% by mass of the sintered body, the content of magnesium oxide is preferably 99.7% by mass or less. When it is 99.7% by mass or less, the sintered body contains other components in a certain amount, so the moisture resistance can be improved.

[0064] The particle size (specifically, the median particle size) of the sintered body is preferably 1 μm or more, more preferably 2 μm or more, still more preferably 5 μm or more, and still more preferably 10 μm or more. When it is 1 μm or more, the moisture resistance can be further improved. In addition, an excessive decrease in fluidity when melting and flowing the polyamide composition can be suppressed. The median particle size can be 30 μm or more, or can be 60 μm or more. On the other hand, the median particle size is preferably 200 μm or less, more preferably 150 μm or less, and still more preferably 100 μm or less. When it is 200 μm or less, the thermal conductivity can be further improved. The median particle size can be 80 μm or less. It should be noted that here, the median particle size is D50, specifically, the particle size at the cumulative 50% of the cumulative particle size distribution of the sintered body based on volume.

[0065] The sintered body is preferably covered with a silica film (i.e., an organosilicon compound layer). That is, preferably, the sintered body contains a silica film. By covering the sintered body with a silica film, the sintered body has more excellent moisture resistance, and thus the heat dissipation property, strength, and moisture resistance of the polyamide composition can be further improved.

[0066] In order to form a silica film, for example, oligomeric reactive siloxanes and silane coupling agents can be used. Among them, oligomeric reactive siloxanes are preferred.

[0067] The oligomeric reactive siloxane is preferably a polymer containing a silane coupling agent. Specifically, the oligomeric reactive siloxane is preferably a polymer containing an alkoxysilane having a reactive group. The oligomeric reactive siloxane contains a reactive group. Specifically, the silane coupling agent contained in the oligomeric reactive siloxane contains a reactive group. As the reactive group, for example, vinyl, amino, epoxy, methacryloxy, acryloxy, and mercapto can be cited. Among them, vinyl, amino, and epoxy are preferred, and vinyl and amino are more preferred.

[0068] The oligomeric reactive siloxane can be a copolymer of a silane coupling agent and an alkoxysilane having no reactive group. As the alkoxysilane having no reactive group, for example, alkyltrialkoxysilane, alkylmethyldialkoxysilane, phenyltrialkoxysilane, phenylmethyldialkoxysilane, and tetraalkoxysilane can be cited. Among them, alkyltrialkoxysilane is preferred. The number of carbon atoms of the alkyl group in the alkyltrialkoxysilane and alkylmethyldialkoxysilane is preferably 1 to 18. The alkyl group can be any of linear, branched, or cyclic. It should be noted that the oligomeric reactive siloxane can be a homopolymer of a silane coupling agent. Incidentally, as commercially available oligomeric reactive siloxanes, for example, Dynasylan 6490 and Dynasylan 1146 can be cited.

[0069] As a method of surface treatment with an oligomeric reactive siloxane, examples include: a method of adding an oligomeric reactive siloxane while stirring a sintered body before surface treatment and then heating it (see Japanese Patent No. 5602650). At this time, heating can be performed by frictional heat generated by high-speed stirring, or heating can be performed by supplying heat from the outside, or they can be combined for heating.

[0070] A sintered body covered with a silica film (i.e., a sintered body containing a silica film) can also be purchased. As a purchasable sintered body, “RF-50-AC” manufactured by Ube Materials Co., Ltd. can be cited.

[0071] In the polyamide composition of this embodiment, the content of the sintered body is 35% by mass or more. By being 35% by mass or more, the heat dissipation performance can be further improved. The content of the sintered body is preferably 37% by mass or more, more preferably 38% by mass or more, and further preferably 39% by mass or more. On the other hand, the content of the sintered body is preferably 55% by mass or less, more preferably 50% by mass or less, further preferably 47% by mass or less, and further preferably 45% by mass or less.

[0072] <1.4. Antioxidant> The polyamide composition of this embodiment preferably contains an antioxidant. By the antioxidant, the oxidative degradation of the polyamide composition can be inhibited.

[0073] As the antioxidant, a hindered phenol-based antioxidant is preferred. As the hindered phenol-based antioxidant, for example, N,N'-hexamethylene-bis-3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionamide, ethylene glycol bis(3,3-bis-(4'-hydroxy-3'-tert-butylphenyl) butyrate), 2,1'-thioethyl bis(3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate), 4,4'-butylidene-bis(3-methyl-6-tert-butylphenol), triethylene glycol-3-(3-tert-butyl-4-hydroxy-5-methylphenyl) propionate (“SONGNOX 2450”, molecular weight 633) can be cited. It should be noted that they can be used alone or two or more of them can be used.

[0074] In the polyamide composition of this embodiment, the content of the antioxidant is preferably 0.01% by mass or more, more preferably 0.1% by mass or more. When it is 0.01% by mass or more, the oxidative degradation of the polyamide composition over time can be prevented. On the other hand, the content of the antioxidant is preferably 1.0% by mass or less, more preferably 0.5% by mass or less.

[0075] <1.5. Release agent> The polyamide composition of the present embodiment preferably contains a mold release agent. By containing a mold release agent in the polyamide composition, when molding the polyamide composition using a mold, it is easy to remove the molded product from the mold.

[0076] Examples of the mold release agent include esters or metal salts of long-chain fatty acids. Amide compounds such as ethylenebis(p-phthalamide) and methylenebisstearamide can also be cited as the mold release agent. Waxes such as aliphatic hydrocarbon-based and polyethylene-based, and silicone-based silicone oils can also be cited as the mold release agent. Among them, fatty acid metal salt-based mold release agents and fatty acid ester-based mold release agents are preferred. That is, fatty acid metal salts and fatty acid ester-based compounds (i.e., fatty acid esters) are preferred. It should be noted that they can be used alone or two or more of them can be used.

[0077] Examples of the fatty acid metal salt include metal salts of fatty acids having 12 to 40 carbon atoms such as stearic acid, palmitic acid, behenic acid, erucic acid, oleic acid, lauric acid, and montanic acid. Among them, metal salts of aliphatic carboxylic acids having 22 to 30 carbon atoms are preferred. In particular, from the perspective of mold release properties, salts of alkali metals or alkaline earth metals such as behenic acid, lignoceric acid, and montanic acid are more preferred. Examples of the alkali metal or alkaline earth metal include lithium, sodium, magnesium, and calcium.

[0078] Examples of the fatty acid ester-based compound include higher fatty acid ester-based compounds. Examples of the higher fatty acid ester-based compounds include mixtures mainly composed of myricyl palmitate, stearyl stearate, behenyl behenate, behenyl stearate, glyceryl monopalmitate, glyceryl monostearate, glyceryl distearate, glyceryl tristearate, pentaerythritol monopalmitate, pentaerythritol monostearate, pentaerythritol distearate, pentaerythritol tristearate, and pentaerythritol tetrastearate.

[0079] In the polyamide composition of the present embodiment, the content of the mold release agent is preferably 0.01% by mass or more, more preferably 0.1% by mass or more. When it is 0.01% by mass or more, when injecting the polyamide composition into the mold, adhesion of the polyamide composition to the mold and wrinkles generated on the surface of the molded product during demolding can be prevented. On the other hand, the content of the mold release agent is preferably 1.0% by mass or less, more preferably 0.5% by mass or less.

[0080] <1.6. Other additives, etc.> The polyamide composition of the present embodiment may contain, for example, carbon black, copper oxide, alkali metal halides, light stabilizers, heat stabilizers, crystal nucleating agents, antistatic agents, pigments, dyes, coupling agents, light-burned magnesium oxide, etc. Of course, the polyamide composition of the present embodiment may contain resins other than polyamide.

[0081] In the polyamide composition of this embodiment, the total content of the fibrous inorganic reinforcing material and the sintered body is preferably 50% by mass or more, more preferably 55% by mass or more, and still more preferably 58% by mass or more. On the other hand, the total content of the fibrous inorganic reinforcing material and the sintered body is preferably 70% by mass or less, more preferably 65% by mass or less, and still more preferably 62% by mass or less.

[0082] <1.7. Physical properties> The higher the flexural strength of the polyamide composition of this embodiment, the better. The flexural strength is preferably 120 MPa or more, more preferably 150 MPa or more, still more preferably 160 MPa or more, and still more preferably 170 MPa or more. The flexural strength can be 230 MPa or less, or can be 220 MPa or less, or can be 215 MPa or less. It should be noted that the flexural strength of the polyamide composition is a value measured after making a test piece from the polyamide composition. Specifically, the flexural strength of the polyamide composition is a value measured by the method described in the examples.

[0083] The higher the thermal conductivity of the polyamide composition of this embodiment, the better. The thermal conductivity is preferably 0.60 W / m·K or more, more preferably 0.65 W / m·K or more, and still more preferably 0.70 W / m·K or more. The thermal conductivity of the polyamide composition can be 1.20 W / m·K or less, or can be 1.10 W / m·K or less, or can be 1.00 W / m·K or less. It should be noted that the thermal conductivity of the polyamide composition is a value measured after making a disk-shaped sample from the polyamide composition. Specifically, the thermal conductivity of the polyamide composition is a value measured by the method described in the examples.

[0084] The higher the retention rate of the tensile strength of the polyamide composition of this embodiment during high humidity treatment, the better. Specifically, the retention rate of the tensile strength when the test piece made of the polyamide composition, that is, the polyamide composition test piece, is left standing for 168 hours in an environment of 80 °C and a relative humidity of 95% RH (that is, during high humidity treatment) is preferably as high as possible. This is because the higher the retention rate of the tensile strength, the more the reduction in rigidity and embrittlement of the molded product using the polyamide composition when exposed to a high humidity environment can be suppressed. Here, the retention rate of the tensile strength is calculated by the following formula. Retention rate of tensile strength = (Tensile strength of the polyamide composition test piece after high humidity treatment / Tensile strength of the polyamide composition test piece before high humidity treatment) × 100 The retention rate of the tensile strength is preferably 40% or more, more preferably 42% or more, and still more preferably 45% or more. The retention rate of the tensile strength may be 60% or less, or may be 55% or less, or may be 52% or less, or may be 50% or less. It should be noted that the retention rate of the tensile strength is a value measured by the method described in the examples.

[0085] <1.8. Manufacturing method, uses> The polyamide composition of the present embodiment can be produced by kneading at least a polyamide, a fibrous inorganic reinforcing material, and a sintered body containing magnesium oxide using a kneading device. For kneading, an extruder (e.g., a single-screw extruder, a twin-screw extruder), a pressure kneader, etc. can be used. Among them, an extruder is preferred, and a twin-screw extruder is more preferred. As the kneading temperature, 220°C to 300°C can be cited. The kneading time can be, for example, about 2 minutes to 15 minutes.

[0086] For example, the polyamide composition of the present embodiment can be produced by the following method: melt-kneading at least a polyamide, a fibrous inorganic reinforcing material, and a sintered body containing magnesium oxide using a twin-screw extruder, then extruding strands, cooling the strands as needed, and cutting the strands as needed.

[0087] The shape of the polyamide composition of the present embodiment can be appropriately set. The polyamide composition of the present embodiment can be, for example, granular, or can be in the form of strands, or can be powdery, or can be formed into any shape. Among them, granular is preferred.

[0088] The polyamide composition of the present embodiment can be used as a raw material for various molded articles. Among them, it can be preferably used as a raw material for electrical / electronic components, motor vehicle components (e.g., electric vehicle components), industrial components, etc. that require high thermal conductivity. As such components, for example, lamp sockets, electrical components, radiators, components for semiconductor packages, components for cooling fans, connectors, switches, housing casings, components used in the periphery of battery casings, and components used inside battery casings can be cited. In particular, it can be preferably used for manufacturing peripheral components (e.g., components used in the periphery of battery casings, components used inside battery casings) of electrical and electronic components (e.g., batteries) that generate high Joule heat.

[0089] <2. Molded articles> The molded article of the present embodiment can be obtained by molding the above-described polyamide composition of the present embodiment. That is, the molded article of the present embodiment can be obtained from the above-described polyamide composition of the present embodiment. As the molding method, for example, injection molding, extrusion molding, blow molding, etc. can be cited. Among them, injection molding is preferred. [Examples]

[0090] Hereinafter, examples and comparative examples are listed to more specifically illustrate the present invention. Hereinafter, unless otherwise specified, "parts" means "parts by mass" and "%" means "% by mass".

[0091] <1. Raw materials> The following raw materials are used. <1.1. Polyamide> A1 ···· "M2000" manufactured by MEIDA Co., Ltd. (polyamide 6, relative viscosity 2.0, melting point 225 °C) A2 ···· "ZISAMIDE TP4208" manufactured by Jisheng Co., Ltd. (polyamide 6, relative viscosity 2.5, melting point 225 °C) A3 ···· "ZISAMIDE TP6603" manufactured by Jisheng Co., Ltd. (polyamide 6, relative viscosity 3.6, melting point 225 °C)

[0092] <1.2. Fibrous inorganic reinforcing material> B1 ···· "ECS301HP-3-H" (glass fiber) manufactured by Chongqing International Composite Materials Co., Ltd. (CPIC Co., Ltd.) B2 ···· "CFUW-MC" (carbon fiber) manufactured by Nippon Polymer Industry Co., Ltd.

[0093] <1.3. Thermally conductive inorganic filler> C1 ···· "RF-50-AC" manufactured by Ube Materials Co., Ltd. (surface-treated magnesium oxide sintered body with a particle size of 50 μm. The sintered body contains magnesium oxide, calcium oxide, and silicon oxide.) C2 ···· Surface-treated magnesium oxide sintered body with a particle size of 100 μm (described in detail later.) C3 ···· Surface-treated magnesium oxide sintered body with a particle size of 10 μm (described in detail later.) C4 ···· "STARMAG P" manufactured by Kojima Chemical Co., Ltd. (lightly burned magnesium oxide with a particle size of 10 μm. Without surface treatment) C5 ···· Magnesium oxide sintered body with a particle size of 70 μm (described in detail later.) C6 ···· Surface-treated lightly burned magnesium oxide with a particle size of 50 μm (described in detail later.)

[0094] Thermally conductive inorganic filler C2 A thermally conductive inorganic filler obtained by subjecting a magnesium oxide sintered body with a particle size of 100 μm (the sintered body contains magnesium oxide, calcium oxide, and silicon oxide.) manufactured according to Japanese Patent No. 5993824 to the same surface treatment as the thermally conductive inorganic filler C1 (i.e., "RF-50-AC").

[0095] Thermally conductive inorganic filler C3 A thermally conductive inorganic filler obtained by subjecting a magnesium oxide sintered body having a particle size of 10 μm produced according to Japanese Patent No. 5993824 (the sintered body contains magnesium oxide, calcium oxide, and silicon oxide) to the same surface treatment as that of the thermally conductive inorganic filler C1 (i.e., "RF-50-AC").

[0096] Thermally conductive inorganic filler C5 A magnesium oxide sintered body having a particle size of 70 μm produced according to Japanese Patent No. 5993824 (the sintered body contains magnesium oxide, calcium oxide, and silicon oxide).

[0097] Thermally conductive inorganic filler C6 Lightly burned magnesium oxide having a particle size of 50 μm that has been subjected to the same surface treatment as that of the thermally conductive inorganic filler C1 (i.e., "RF-50-AC").

[0098] <1.4. Antioxidant> D ···· "SONGNOX 2450" (hindered phenol antioxidant) manufactured by BASF Corporation

[0099] <1.5. Release agent> E1 ···· "Licolub WE-40" (aliphatic ester) manufactured by Clariant Japan Co., Ltd. E2 ···· "N.P. 1500-S" (magnesium stearate) manufactured by Tannan Chemical Industry Co., Ltd.

[0100] <2. Production of particles> Weigh each raw material according to the compounding ratios described in Tables 1 and 2, mix them in a tumbler, and then put them into a twin-screw extruder to obtain particles. The set temperature of the twin-screw extruder is 250°C to 300°C, and the kneading time is 5 minutes to 10 minutes.

[0101] <3. Evaluation method> <3.1. Relative viscosity of polyamide (98% sulfuric acid solution method)> Using an Ubbelohde viscometer, according to JIS K6920-2:2009, measure the relative viscosity using 98% sulfuric acid at 1 g / dL of polyamide and 25°C.

[0102] <3.2. Melting point of polyamide> Using a differential scanning calorimeter ("EXSTAR 6000" manufactured by Seiko Instruments Inc.), measure at a heating rate of 20°C / minute and determine the endothermic peak temperature.

[0103] <3.3. Flexural strength> Using an injection molding machine with a barrel temperature of 260 °C and a mold temperature of 80 °C, form a test piece into the shape specified in A1 of JIS K7139:2009. For this test piece, conduct a flexural test in accordance with ISO178:2010 to measure the flexural strength (i.e., the maximum flexural stress that the test piece can withstand in the flexural test). The flexural test is carried out by Method A with a span of 64 mm, a test speed of 2 mm / min, and no change in strain rate during the test.

[0104] <3.4. Thermal conductivity> Using an injection molding machine with a barrel temperature of 260 °C and a mold temperature of 90 °C, form a flat molded product with a thickness of 2 mm, a length of 100 mm, and a width of 100 mm. Cut the central part of the flat molded product into a disc shape with a width of about 10 mm. Measure the thermal diffusivity, density, and specific heat of the disc-shaped sample. The thermal diffusivity is measured by the laser flash method in accordance with ASTM E1461. The density is measured by the water displacement method in accordance with ISO 1183:1987. The specific heat is measured by the method in accordance with JIS K7123:1987. Then, calculate the thermal conductivity using the following formula. λ = ρ·Cp·α λ: Thermal conductivity (W / m·K) ρ: Density (kg / m 3 ) Cp: Specific heat (J / kg·K) α: Thermal diffusivity (m 2 / s)

[0105] <3.5. Retention rate of tensile strength> Using an injection molding machine with a barrel temperature of 260 °C and a mold temperature of 80 °C, form a test piece into the shape specified in A1 of JIS K 7139:2009. Leave this test piece standing in an environment of 80 °C and a relative humidity of 95% RH for 168 hours. That is, conduct high humidity treatment on this test piece. Then, conduct a tensile test in accordance with ISO527-1:2012 to obtain the tensile strength (i.e., the initial maximum stress observed in the tensile test). The tensile test is carried out at room temperature, a test speed of 5 mm / min, and a gauge length of 115 mm. Also conduct a tensile test on the test piece that has not undergone high humidity treatment to obtain the tensile strength. Then, calculate the retention rate of the tensile strength using the following formula. Retention rate of tensile strength = (Tensile strength of the test piece after high humidity treatment / Tensile strength of the test piece without high humidity treatment) × 100 It should be noted that in all examples and comparative examples, the test pieces after high humidity treatment and the test pieces without high humidity treatment did not break before yielding.

[0106] <4. Results> The table containing the results is shown below. [Table 1] [Table 2]

[0107] In the case of using the thermally conductive inorganic filler C3 (i.e., a surface-treated magnesia sintered body with a particle size of 10 μm), the retention rate of tensile strength, flexural strength, and thermal conductivity are excellent compared to the case of using the thermally conductive inorganic filler C4 (i.e., an un-surface-treated light-burned magnesia with a particle size of 10 μm) (see Examples 6 and Comparative Example 1).

[0108] In the case of using the thermally conductive inorganic filler C1 (i.e., a surface-treated magnesia sintered body with a particle size of 50 μm), the retention rate of tensile strength, flexural strength, and thermal conductivity are excellent compared to the case of using the thermally conductive inorganic filler C6 (i.e., a surface-treated light-burned magnesia with a particle size of 50 μm) (see Example 1 and Comparative Example 6).

[0109] In the case of using the thermally conductive inorganic fillers C1, C2, and C3, the retention rate of tensile strength, flexural strength, and thermal conductivity are excellent compared to the case of using the thermally conductive inorganic filler C5 (i.e., an un-surface-treated magnesia sintered body with a particle size of 70 μm) (see Examples 1, 5, and 6 and Comparative Example 5).

[0110] For the thermally conductive inorganic fillers C1, C2, and C3, the smaller the particle size, the more excellent the flexural strength and thermal conductivity (see Examples 1, 5, and 6). On the other hand, the smaller the particle size, the lower the retention rate of tensile strength (see Examples 1, 5, and 6).

[0111] The more fibrous inorganic reinforcing material, the more excellent the flexural strength (see Examples 1, 10, and 12).

[0112] The higher the relative viscosity of the polyamide, the more excellent the flexural strength, but the lower the thermal conductivity (see Examples 1, 2, and 3). [Industrial Applicability]

[0113] The present invention can provide a polyamide composition and a molded article, and thus can be utilized industrially.

Claims

1. A polyamide composition comprising: a polyamide, a fibrous inorganic reinforcing material, and a sintered body containing magnesium oxide, wherein the sintered body is covered with a silica film, the content of the sintered body is 35% by mass or more.

2. The polyamide composition according to claim 1, wherein, The content of the fibrous inorganic reinforcing material is 10% by mass or more.

3. The polyamide composition according to claim 1, wherein, The polyamide is a crystalline polyamide.

4. The polyamide composition according to claim 3, wherein, The relative viscosity of the crystalline polyamide is 2.0 or more and 3.6 or less.

5. The polyamide composition according to claim 1, wherein The polyamide composition further comprises an antioxidant.

6. The polyamide composition according to claim 1, wherein, The polyamide composition further comprises a hindered phenol-based antioxidant.

7. The polyamide composition according to claim 1, wherein, The polyamide composition further comprises a mold release agent.

8. The polyamide composition according to claim 7, wherein, The mold release agent is a higher fatty acid ester-based compound.

9. The polyamide composition according to claim 1, wherein the flexural strength is 120 MPa or more, the thermal conductivity is 0.60 W / m·K or more, when subjected to a high humidity treatment of standing for 168 hours in an environment of 80°C and a relative humidity of 95% RH, the retention rate of the tensile strength is 40% or more, and the retention rate of the tensile strength is a value calculated by the following formula: Retention rate of tensile strength = (Tensile strength of the polyamide composition test piece after high humidity treatment / Tensile strength of the polyamide composition test piece before high humidity treatment) × 100.

10. A molded article comprising the polyamide composition according to any one of claims 1 to 9.

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