Polyamide resin composition

Abstract

The present invention is a polyamide resin composition containing (A) 54-75 mass% of a polyamide resin, (B) 24-45 mass% of talc, and (C) 0.01-1 mass% of a silane-based coupling agent, wherein the melt mass flow rate (MFR) of said polyamide resin composition at a moisture content of 0.05 mass% or less is 15-75 g / 10 min (exclusive of 75), and the bending strength is 120 MPa or greater. Said polyamide resin composition has a high mechanical strength and a low molding shrinkage rate, and has excellent moldability, strength, and rigidity.

Description

[Technical Field]

[0001] The present invention relates to a polyamide resin composition filled with a particulate inorganic material, and more particularly, to a polyamide resin composition in which bulky particulate inorganic material is uniformly filled, thereby providing a molding material with significantly improved mechanical properties, heat resistance, dimensional stability, etc. The polyamide resin composition can be used in a wide range of applications, including but not limited to automobile interior parts such as consoles and cup holders. [Background technology]

[0002] Polyamides, such as nylon 6 and nylon 66, are widely used as engineering plastics in machine and electrical parts such as rollers, gears, and bearings because of their excellent mechanical and electrical properties, such as tensile strength and impact strength. However, polyamides generally have a low heat distortion temperature and undergo dimensional changes and a significant loss of rigidity when they absorb water, limiting their use in applications where they come into frequent contact with water or are exposed to high temperatures.

[0003] To overcome these drawbacks of polyamide, polyamide has been reinforced with glass fiber, granular inorganic materials, etc. However, although these glass fiber reinforced polyamides improve thermal properties such as tensile strength and heat distortion temperature, they also suffer from significant anisotropy in strength and the glass fibers and other particles emerge on the surface, impairing surface smoothness.

[0004] On the other hand, when a large amount of granular inorganic material is blended with polyamide, a low-cost compound can be obtained, meeting the needs of the resource-saving era. However, if the blended inorganic material only functions as a bulking agent, it will be completely worthless. To make the granular inorganic material function as a reinforcing material rather than just an extender, it is important to blend fine inorganic material and chemically bond it to the polyamide resin matrix. Such fine inorganic material is very bulky and has a large difference in bulk density from the polyamide resin matrix pellets. Therefore, when blending a large amount of inorganic material, it is difficult to achieve uniform mixing by simple dry blending. Furthermore, even if small amounts are artificially dry blended, in the case of a single-screw extruder, the screw engagement is significantly impaired, significantly reducing productivity.

[0005] Furthermore, in order to chemically bond the polyamide resin and the granular inorganic material, it is necessary to subject the granular inorganic material to a surface treatment in advance. Generally, the surface treatment of these granular inorganic fillers is very complicated in many cases, and this surface treatment process increases the price of inexpensive granular inorganic fillers, making it impossible to inexpensively produce compounds containing the granular inorganic fillers.

[0006] In view of the above circumstances, in order to inexpensively produce an inorganic-filled polyamide resin having excellent mechanical properties, thermal properties, and dimensional stability, a method has been proposed in which a silane coupling agent and water are attached to the surface of a polyamide resin, and a mixture of the polyamide resin and the inorganic filler is kneaded (Patent Document 1). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Special Publication No. 53-42352 Summary of the Invention [Problem to be solved by the invention]

[0008] However, Patent Document 1 uses a high-viscosity polyamide resin with a relative viscosity of more than 3, which has low fluidity and makes it difficult to manufacture molded products with high flow resistance, such as thin-walled or complex shapes.On the other hand, when a low-viscosity polyamide resin is used, the mechanical properties are extremely reduced and the molding shrinkage rate is large, narrowing the range of applications.

[0009] The present invention has been made to solve these problems, and an object of the present invention is to provide a talc-reinforced polyamide resin composition that has high flowability, high mechanical strength, low molding shrinkage, and excellent moldability, strength, and rigidity, even when the talc-reinforced polyamide resin composition uses a low-viscosity polyamide. [Means for solving the problem]

[0010] The present inventors have conducted extensive research to obtain mechanical strength and molding shrinkage equivalent to those of high-viscosity polyamide resins in talc-reinforced polyamide resin compositions, even when using low-viscosity polyamide resins. As a result, they have found that the mechanical properties and molding shrinkage are related not to the viscosity of the polyamide resin but to the particle size of the talc-dispersed phase in the composition.

[0011] That is, the present invention is as follows. [1] A polyamide resin composition comprising: (A) 54 to 75% by mass of a polyamide resin; (B) 24 to 45% by mass of talc; and (C) 0.01 to 1% by mass of a silane coupling agent, The polyamide resin composition is characterized in that the melt mass-flow rate (MFR) of the polyamide resin composition at a moisture content of 0.05 mass% or less is 15 g / 10 min or more and less than 75 g / 10 min, and the bending strength is 120 MPa or more. [2] The polyamide resin composition according to [1], wherein the (A) polyamide resin contains 70 to 99.5 parts by mass of (a1) polyamide 6 and 0.5 to 30 parts by mass of (a2) polyamide MXD6, relative to 100 parts by mass of the (A) polyamide resin. [3] The polyamide resin composition according to [1] or [2], wherein the talc (B) is contained in the polyamide resin composition as a dispersed phase having an average secondary particle size of less than 30 μm. [4] The polyamide resin composition according to any one of [1] to [3], wherein during the cooling process in DSC measurement of the polyamide resin composition, a maximum point or an exothermic peak exists on the higher temperature side than the maximum exothermic peak at the cooling crystallization temperature. [Effects of the Invention]

[0012] The polyamide resin composition of the present invention exhibits a dramatic improvement in mechanical strength and can ensure good moldability even when a low-viscosity polyamide resin is used. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention will be specifically described below. First, each component used in the present invention will be described. The (A) polyamide resin is a polymer having an amide bond (-NHCO-) ​​in the main chain. The (A) polyamide resin is preferably crystalline, and examples thereof include polyamide 6 (PA6), polyamide 66 (PA66), polyamide 46 (PA46), polyamide 11 (PA11), polyamide 12 (PA12), polyamide 610 (PA610), polyamide 612 (PA612), polymetaxylylene adipamide (PAMXD6), hexamethylenediamine-terephthalic acid polymer (PA6T), hexamethylenediamine-terephthalic acid / adipic acid copolymer (PA6T / 66), hexamethylenediamine One or more of the following crystalline polyamide resins can be used: a copolymer of hexamethylenediamine-terephthalic acid and ε-caprolactam (PA6T / 6), a copolymer of trimethylhexamethylenediamine-terephthalic acid (PATMDT), a copolymer of metaxylylenediamine-adipic acid / isophthalic acid (PAMXD6 / MXDI), a copolymer of trihexamethylenediamine-terephthalic acid and ε-caprolactam (PATMDT / 6), a copolymer of diaminodicyclohexylenemethane (CA), isophthalic acid, and lauryllactam. The polyamide resin (A) may be in any form, such as chips, pellets, flakes, or granules.

[0014] The relative viscosity (96% sulfuric acid method) of the (A) polyamide resin is not particularly limited, but is preferably 2.0 to 3.0, more preferably 2.0 to 2.8, and even more preferably 2.1 to 2.6. If the relative viscosity is less than 2.0, flash tends to occur during injection molding and impact resistance tends to decrease, while if it exceeds 3.0, fluidity tends to decrease. When multiple types of polyamide resins are used in combination as the (A) polyamide resin, it is desirable that all of the polyamide resins satisfy this relative viscosity range, but the relative viscosity of the (A) polyamide resin may also be a weighted average of the relative viscosities calculated from the content ratios of the polyamide resins used in combination.

[0015] The blending (content) amount of (A) polyamide resin in the polyamide resin composition is 54 to 75 mass %, preferably 56 to 74 mass %, more preferably 60 to 68 mass %. If it is less than 54 mass %, it is difficult to uniformly disperse (B) talc, and performance such as mechanical properties becomes unstable. If it exceeds 75 mass %, the effect of improving impact resistance is small.

[0016] Furthermore, when the (A) polyamide resin is primarily composed of (a1) polyamide 6, it is preferable from the viewpoint of moldability to use (a2) polyamide in combination, which delays the crystallization of (a1). The (a2) polyamide is not particularly limited as long as it can delay the crystallization of (a1) polyamide 6. For example, a polyamide with a higher crystallization temperature than (a1) polyamide 6 or a polyamide that morphologically inhibits crystallization can be used. Specifically, polyamide MXD6 (polymetaxylylene adipamide) can be used. The blending (content) amounts of (a1) polyamide 6 and (a2) polyamide MXD6 are preferably 70 to 99.5 parts by mass and 0.5 to 30 parts by mass, and more preferably 80 to 95 parts by mass and 5 to 20 parts by mass, based on 100 parts by mass of the (A) polyamide resin.

[0017] (B) Talc is a layered mineral whose main component is hydrous magnesium silicate obtained by pulverizing talc through a milling process, and its manufacturing method is not particularly limited. Its true specific gravity is approximately 2.7, and its aspect ratio is usually 5 to 20. Furthermore, some of the magnesium atoms in this composition may be substituted with calcium atoms. Talc can be classified and defined by its weight-average particle size. While there are various methods for measuring the weight-average particle size, in recent years, the laser diffraction / scattering method using laser light has become widely used due to its high measurement accuracy.

[0018] The average primary particle size of (B) talc is not particularly limited, but is preferably 0.1 to 20 μm, more preferably 1 to 15 μm. If it is less than 0.1 μm, the reinforcing effect is difficult to exhibit, and for example, the effect of improving mechanical strength is small. On the other hand, if it exceeds 20 μm, the appearance of the molded product tends to deteriorate.

[0019] The apparent specific gravity of (B) talc is not particularly limited, but is preferably 0.05 to 1.5, more preferably 0.1 to 1.0, and even more preferably 0.2 to 0.8. If it is less than 0.05, it becomes difficult to incorporate into the resin and tends to fly up during handling, worsening the working environment. On the other hand, if it exceeds 1.5, the specific surface area tends to be small and the nucleating agent effect tends to be reduced. (B) Talc can be used alone or in combination of two or more types.

[0020] The blending (content) amount of (B) talc in the polyamide resin composition is 24 to 45% by mass, preferably 25 to 43% by mass, and more preferably 31 to 39% by mass. If it is less than 24% by mass, the effect of improving impact resistance is small, and if it exceeds 45% by mass, it is difficult to disperse it uniformly in the polyamide resin, and performance such as mechanical properties tends to become unstable.

[0021] The silane coupling agent (C) is a compound having the structural formula shown in formula (1) below. R a Six b ··· Equation (1) Here, X is OH or an atomic group that can be converted to OH upon reaction with water, specifically a halogen, a methoxy group, or an ethoxy group. R may be any organic group compatible with polyamide resin, but organic groups having an amino group or an epoxy group are particularly preferred. Note that a is an integer of 1 to 3, and b is an integer of 1 to 3, so that a + b = 4 is satisfied.

[0022] Specific examples of silane coupling agents include γ-aminopropyltriethoxysilane, n-β-aminoethyl-γ-aminopropyltrimethoxysilane, n-β-aminoethyl-γ-aminopropylmethyldimethoxysilane, γ-glycidoxypropyltrimethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, etc. Two or more types of silane coupling agents can also be used in combination.

[0023] The amount of the silane coupling agent (C) in the polyamide resin composition is 0.01 to 1 mass %, more preferably 0.05 to 0.8 mass %, and even more preferably 0.1 to 0.5 mass %, and is preferably 0.1 to 4.0 mass %, more preferably 0.2 to 2.0 mass %, relative to the amount of the talc (B).

[0024] In the present invention, a dispersed phase made of (B) talc is present in the polyamide resin composition, and the average secondary particle size thereof is preferably less than 30 μm. The average secondary particle size of the dispersed phase is more preferably less than 25 μm, and even more preferably less than 20 μm. The lower limit of the average secondary particle size of the dispersed phase is the primary particle size of (B) talc (average particle size of primary particles (single particle dispersion)), which is approximately 0.1 μm. Although it depends on the average particle size of the primary particles of (B) talc used, the average particle size of the secondary particles of (B) talc in the polyamide resin composition is more preferably 5 μm or more, and even more preferably 10 μm or more.

[0025] The average secondary particle size of the dispersed phase is a value obtained by measuring the particle sizes of 100 talc agglomerates present in the polyamide resin composition through scanning electron microscope (SEM) observation of a cross section of a molded article obtained by injection molding the polyamide resin composition, and calculating the average. Specifically, the maximum lengths of 500 secondary particles having a maximum length greater than the average primary particle size of talc were measured, and the maximum lengths of the top 100 secondary particles were averaged.

[0026] Generally, the addition of talc to polyamide resin improves its mechanical properties, but when the average secondary particle size of the dispersed phase (B) made of talc is less than 30 μm, the mechanical properties, particularly mechanical strength such as flexural strength and tensile strength, and deflection temperature under load are dramatically improved. Furthermore, the molding shrinkage rate also tends to be reduced.

[0027] If the average secondary particle size of the dispersed phase consisting of (B) talc is less than 30 μm, when the cooling crystallization temperature (TC2) is measured using a differential scanning calorimeter (DSC), a maximum point or an exothermic peak (Peak 2) appears between the rising temperature of the crystallization curve and the temperature of the maximum exothermic peak (TC2, Peak 1).

[0028] In the present invention, the temperature-decreasing crystallization temperature (TC2) is measured using a differential scanning calorimeter (DSC) by increasing the temperature to 300°C at a rate of 20°C / min under a nitrogen stream, holding the temperature for 5 minutes, and then decreasing the temperature to 100°C at a rate of 10°C / min, and measuring the peak temperature (the highest peak when multiple peaks appear).

[0029] Talc has a nucleating effect, and polyamide resin crystals begin to form on the surface of the talc in the polyamide resin composition at temperatures higher than the normal crystallization temperature. (B) When the average secondary particle size of the dispersed phase consisting of talc is less than 30 μm, the total surface area of ​​the talc increases, making the nucleating effect of the talc more pronounced, increasing the degree of crystallization and improving mechanical properties. At the same time, it is thought that the effect of increasing the adhesion between the talc and the polyamide resin is also enhanced, resulting in a synergistic improvement in mechanical strength. Furthermore, if the average secondary particle size of talc is less than 30 μm, the solidification rate in the mold during injection molding will increase, which may result in poor mold transferability and poor appearance characteristics of the molded product. In this case, the appearance characteristics can be improved by adding a small amount of a substance that delays the crystallization of (a1) polyamide 6, such as (a2) polyamide MXD6.

[0030] The dispersed phase of (B) talc having an average secondary particle size of less than 30 μm tends to be generated more easily as the relative viscosity of (A) polyamide resin increases due to the increased shear force during melt-kneading. Therefore, it is generally considered preferable that the relative viscosity of (A) polyamide resin is higher than 3.0.

[0031] However, even when the relative viscosity of the polyamide resin (A) is 3.0 or less, it is possible to generate a dispersed phase of talc (B) having an average secondary particle size of less than 30 μm by adjusting the production conditions. This method enables the present invention to provide a highly fluid polyamide resin composition using a low-viscosity polyamide with high mechanical strength and low molding shrinkage.

[0032] The method for producing the polyamide resin composition of the present invention involves blending the above-mentioned components (A), (B), and (C), and, if necessary, other additives described below, in any desired blending order, and then melt-kneading the blend in a tumbler, Henschel mixer, etc. Any method known to those skilled in the art can be used for the melt-kneading, and a single-screw extruder, twin-screw extruder, kneader, Banbury mixer, roll mixer, etc. can be used, but it is particularly preferable to use a twin-screw extruder.

[0033] Furthermore, it is preferable that L / D, which is the ratio of the screw length L (mm) to the screw diameter D (mm), satisfies the relationship 10≦(L / D)≦100. If there are no other problems with operability, a smaller L / D is preferable from the viewpoint of fine dispersion of component (B). However, if the L / D exceeds 100, the mechanical strength of the resin composition tends to decrease due to thermal degradation.

[0034] The melting temperature of the resin composition during melt-kneading is preferably 180 to 330° C., and more preferably 200 to 300° C. If the melting temperature is less than 180° C., the resin composition will not melt sufficiently and will tend to produce a large number of unmelted gels. Conversely, if the melting temperature exceeds 330° C., the resin composition will be prone to thermal degradation.

[0035] The screw rotation speed N during melt-kneading is preferably 100 to 1,500 rpm, more preferably 150 to 1,000 rpm. If the screw rotation speed is less than 100 rpm, component (B) tends to be difficult to finely disperse. Conversely, if it exceeds 1,500 rpm, component (B) tends to aggregate and not be finely dispersed. Furthermore, the discharge rate Q is preferably 5 to 200 kg / hr, more preferably 10 to 100 kg / hr. If the discharge rate is less than 5 kg / hr, the dispersibility of component (B) tends to decrease. If it exceeds 100 kg / hr, the dispersibility tends to decrease due to re-aggregation of component (B).

[0036] Furthermore, the ratio Q / N, which is the ratio of the discharge rate Q (unit: kg / hr) to the screw rotation speed N (unit: rpm) during melt-kneading, is preferably 0.01≦(Q / N)≦1, and more preferably 0.05≦(Q / N)≦0.9. If it is less than 0.01, the mechanical strength of the resin composition tends to decrease due to thermal degradation. If it exceeds 1, the conveying force becomes insufficient, and component (B) tends to spray out. Note that a smaller Q / N tends to make component (B) more easily finely dispersed. This is thought to be because shear between the raw material pellets, in addition to the screw, promotes fine dispersion.

[0037] Furthermore, component (B), which tends to be poorly inserted into component (A) during extrusion processing, can be added through the side port of the twin-screw extruder, but this is not a particular limitation. Component (C) may be added simultaneously with the other raw materials, or it may be added to component (B) in advance. From the perspective of finely dispersing component (B), it is preferable to add it through the original feed so that more shear can be applied. Furthermore, to remove volatile components and decomposed low-molecular-weight components during processing and to enhance the reactivity of the reinforcement and polyamide resin, it is desirable to use a vacuum pump to suction between the side port and the die head at the tip of the extruder.

[0038] The polyamide resin composition of the present invention may contain various additives, such as stabilizers, impact modifiers, flame retardants, release agents, sliding properties improvers, colorants, plasticizers, and crystal nucleating agents.

[0039] Examples of stabilizers include organic antioxidants such as hindered phenol antioxidants, sulfur-based antioxidants, and phosphorus-based antioxidants, heat stabilizers, light stabilizers such as hindered amines, benzophenones, and imidazoles, UV absorbers, metal deactivators, and copper compounds. Examples of copper compounds that can be used include copper salts of organic carboxylic acids such as cuprous chloride, cuprous bromide, cuprous iodide, cupric chloride, cupric bromide, cupric iodide, cupric phosphate, cupric pyrophosphate, copper sulfide, copper nitrate, and copper acetate. Furthermore, as a component other than the copper compound, an alkali metal halide compound is preferably contained. Examples of alkali metal halide compounds include lithium chloride, lithium bromide, lithium iodide, sodium fluoride, sodium chloride, sodium bromide, sodium iodide, potassium fluoride, potassium chloride, potassium bromide, and potassium iodide. These additives may be used alone or in combination. The amount of stabilizer to be added can be selected optimally, but it is possible to add up to 5 parts by mass per 100 parts by mass of (A) polyamide resin.

[0040] As the flame retardant, a combination of a halogen-based flame retardant and a flame retardant aid is preferred. Preferred examples of the halogen-based flame retardant include brominated polystyrene, brominated polyphenylene ether, brominated bisphenol-type epoxy polymer, brominated styrene-maleic anhydride polymer, brominated epoxy resin, brominated phenoxy resin, decabromodiphenyl ether, decabromobiphenyl, brominated polycarbonate, perchlorocyclopentadecane, and brominated crosslinked aromatic polymer. Examples of the flame retardant aid include antimony trioxide, antimony pentoxide, sodium antimonate, zinc stannate, zinc borate, layered silicates such as montmorillonite, fluorine-based polymers, and silicones. Among these, from the viewpoint of thermal stability, a combination of dibromopolystyrene as the halogen-based flame retardant and antimony trioxide, sodium antimonate, or zinc stannate as the flame retardant aid is preferred. Furthermore, examples of non-halogen-based flame retardants include melamine cyanurate, red phosphorus, metal salts of phosphinic acid, and nitrogen-containing phosphate compounds. In particular, a combination of a metal phosphinate and a nitrogen-containing phosphoric acid compound is preferred. Examples of nitrogen-containing phosphoric acid compounds include reaction products of melamine, melamine condensates such as melam and melon, and polyphosphoric acid, or mixtures thereof. Other flame retardants and flame retardant assistants include hydrotalcite compounds and alkali compounds, which are preferably added to prevent metal corrosion of molds and the like when using these flame retardants. The amount of flame retardant added can be selected optimally, but up to 20 parts by mass can be added per 100 parts by mass of (A) polyamide resin.

[0041] Examples of release agents include long-chain fatty acids or their esters or metal salts, amide compounds, polyethylene wax, silicone, and polyethylene oxide. Long-chain fatty acids, particularly those with 12 or more carbon atoms, are preferred, such as stearic acid, 12-hydroxystearic acid, behenic acid, and montanic acid. The carboxylic acid may be partially or entirely esterified with monoglycol or polyglycol, or may form a metal salt. Examples of amide compounds include ethylene bisterephthalamide and methylene bisstearylamide. These release agents may be used alone or in combination. The amount of release agent added can be selected as appropriate, but up to 5 parts by mass can be added per 100 parts by mass of (A) polyamide resin.

[0042] The polyamide resin composition of the present invention preferably contains (A) polyamide resin, (B) talc, and (C) silane coupling agent in a total amount of 85 mass % or more, more preferably 90 mass % or more, and even more preferably 95 mass % or more.

[0043] The polyamide resin composition of the present invention has a melt mass-flow rate (MFR) of 15 g / 10 min or more and less than 75 g / 10 min at a moisture content of 0.05% (0.05 mass%) or less, as measured at 255°C under a load of 2160 g in accordance with JIS K 7210-1:2014.

[0044] If the melt mass-flow rate is less than 15 g / 10 min, the fluidity is low, and good molded-product appearance cannot be obtained when molding thin-walled or complex-shaped parts with high flow resistance. Furthermore, if the molding temperature is set high and the MFR value is increased, retention stability decreases, which may cause gas to cause deterioration in the molded appearance and a decrease in mechanical strength. On the other hand, if the melt mass-flow rate is 75 g / 10 min or higher, flash is more likely to occur during injection molding, and if the injection pressure or holding pressure is lowered to suppress flash, mold transferability may decrease, resulting in poor molded-product appearance and the likelihood of sink marks.

[0045] To obtain a polyamide resin composition, the use of commonly used polyamide resins with a relative viscosity of over 3.0 can result in a melt mass-flow rate that falls short of the above range (less than 15 g / 10 min). Therefore, it is recommended to use a crystalline polyamide resin with a low viscosity (relative viscosity of 2.0 to 3.0) or to add a molecular chain scission agent for the polyamide resin during compound processing. Examples of molecular chain scission agents (also known as viscosity reducers) for the polyamide resin include aliphatic dicarboxylic acids and aromatic dicarboxylic acids. Specific examples include, but are not limited to, oxalic acid, malonic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, phthalic acid, and terephthalic acid. When a molecular chain scission agent is added (or contained), the amount added is approximately 0.1 to 3 parts by mass per 100 parts by mass of the polyamide resin composition of the present invention, and the melt mass-flow rate of the composition of the present invention will be 15 g / 10 min or higher. However, the effectiveness of the chain scission agent varies depending on the compound processing conditions, and naturally the higher the processing temperature and the longer the polymer residence time during compounding, the better the effect. Typically, the compound processing temperature is in the range of 230 to 290°C, and the polymer residence time during compounding is within 15 to 60 seconds.

[0046] The polyamide resin composition of the present invention has a flexural strength of 120 MPa or more. The upper limit of the flexural strength is not particularly limited, but is about 150 MPa. The flexural strength is measured in accordance with JIS K 7171:2016 using a 4 mm thick multipurpose test piece. Details of the flexural strength measurement method are as described in the Examples. [Example]

[0047] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples in any way.

[0048] The characteristics and physical properties shown in the following examples and comparative examples were measured by the following test methods.

[0049] 1) Melt mass-flow rate (MFR): Resin composition pellets were dried using a hot air dryer to a moisture content of 0.05% or less, and measured at 255°C under a load of 2160 g in accordance with JIS K 7210-1:2014.

[0050] 2) Average secondary particle size of dispersed phase: Cross-sectional slices were prepared using a microtome from the test piece prepared in 5) below, and platinum sputtered. These were then observed at 500x magnification using a scanning electron microscope (SEM). The maximum lengths of 500 secondary particles that had a maximum length greater than the average primary particle size of talc were measured, and the average value of the maximum lengths of the 100 largest secondary particles was calculated to obtain the average secondary particle size.

[0051] 3) Flexural strength: A 4 mm thick multipurpose test specimen was molded in accordance with JIS K 7171:2016. Using the obtained multipurpose test specimen, measurements were carried out in accordance with JIS K 7171:2016 at a temperature of 23°C, humidity of 50% RH, at a test speed of 2 mm / min, and a support distance of 64 mm. Measurements were carried out on five samples each, and the average value was calculated. 4) Flexural modulus: As in 3), it was measured in accordance with JIS K 7171:2016.

[0052] 5) Appearance evaluation of molded products: Using a Toshiba Machine EC-100 injection molding machine, the cylinder temperature was set to the melting point of the polyamide resin (if multiple polyamide resins were used in combination, the melting point of the highest polyamide resin) + 20°C, and the mold temperature was set to 90°C, and test pieces measuring 100 mm in length, 100 mm in width, and 2 mm in thickness were produced by injection molding. The appearance of these test pieces was evaluated visually. ◎: No floating of reinforcement material throughout the molded product. ○: There is slight lifting of reinforcement near the gate and at the end. ×: A large amount of reinforcement material is lifted throughout the molded product.

[0053] 6) Mold shrinkage: A flat (film gate) test piece with mold dimensions of 100 mm x 100 mm x 3 mm (thickness) was molded in the same manner as in 5), and after leaving it at 23°C and 50% relative humidity for 24 hours, the dimensions of the test piece in the machine direction and transverse direction were measured with a vernier caliper to an accuracy of 0.1 mm. The mold shrinkage in the machine direction and transverse direction was calculated from the reference mold dimensions at the mold temperature during molding, which had been measured in advance using the same method.

[0054] 7) Temperature-reducing crystallization curve, maximum point / exothermic peak: A DSC measurement device (Seiko Instruments Inc., EXSTAR6000) was used. The sample was heated to 300°C at a heating rate of 20°C / min under a nitrogen stream, held at that temperature for 5 minutes, and then cooled to 100°C at a rate of 10°C / min. The peak top of the maximum exothermic peak during cooling was designated TC2, and the presence or absence of a maximum point or exothermic peak (second peak) in the temperature range from the rise of the temperature-reducing crystallization curve to TC2 was evaluated. The presence of a maximum point / exothermic peak was marked with an ◯, and the absence was marked with an ×. The DSC measurement sample was cut from near the center of the 100 mm x 100 mm x 3 mm flat plate described in 6).

[0055] The raw materials used in the examples and comparative examples of the present invention are as follows. The relative viscosity (RV) of the polyamide resin was measured at 20°C by dissolving 0.25 g of the polyamide resin in 25 ml of 96% sulfuric acid and placing 10 ml of this solution in an Ostwald viscosity tube. (A11) Polyamide 6: Toyobo's "Glamide T-860" (RV 1.9, melting point 222°C) (A12) Polyamide 6: Toyobo's "Glamide T-840" (RV 2.2, melting point 223°C) (A13) Polyamide 6: Ube Industries "1013B" (RV2.5, melting point 224°C) (A14) Polyamide 6: MEIDA "M2800" (RV2.9, melting point 225°C) (A15) Polyamide 6: Toyobo "T-820" (RV3.1, melting point 225°C) (A2) Polyamide MXD6: Toyobo "Nylon T-600" (RV2.1, melting point 240°C) (B1) Talc: "KST-W" manufactured by Shokoyama Mining Co., Ltd. (average particle size 7 μm, apparent specific gravity 0.4) (B2) Talc: "Talc Powder PK" manufactured by Hayashi Kasei (average particle size 10 μm, apparent specific gravity 0.8) (B3) Talc: "FU-51" manufactured by Fukuoka Talc Industries (average particle size 13 μm, apparent specific gravity 0.3) (B4) Talc: Hayashi Kasei "KHP-400B" (average particle size 19 μm, apparent specific gravity 1.0) (B5) Wollastonite: Kinseimatec "FPW-350" (average particle size 20 μm, apparent specific gravity 0.6) (C) Silane coupling agent: Shin-Etsu Chemical Co., Ltd.'s "KBE-903" (3-aminopropyltriethoxysilane) (D) Stabilizer: Potassium iodide manufactured by Mitsui Chemicals (E) Release agent: "NP-1500" (magnesium stearate) manufactured by Tannan Chemical

[0056] Examples 1 to 9, Comparative Examples 1 to 4 The raw materials were premixed to obtain the composition shown in Table 1 and fed into the main feed port of a twin-screw extruder (TEM26-SS, manufactured by Toshiba Machine Co., Ltd.) with an L / D of 45, where they were melt-kneaded. After being drawn out of the die in the form of strands, they were passed through a water bath to cool and solidify, and then cut into pellets using a pelletizer to obtain polyamide resin composition pellets. The extruder barrel temperature was set to 260°C, the screw rotation speed was 650 rpm, and the output rate was 45 kg / hour. The resulting pellets were dried in a hot air dryer until the moisture content was 0.05% or less, after which various properties were evaluated. The evaluation results are shown in Table 1.

[0057] Example 10 The raw materials were premixed to obtain the composition shown in Table 1 and fed into the main feed port of a twin-screw extruder (TEM26-SS, manufactured by Toshiba Machine Co., Ltd.) with an L / D of 45, where they were melt-kneaded. After being drawn out of the die in the form of a strand, the strand was passed through a water bath to cool and solidify, and then cut into pellets using a pelletizer to obtain polyamide resin composition pellets. The extruder barrel temperature was set to 255°C, the screw rotation speed was 850 rpm, and the output rate was 30 kg / hour. The resulting pellets were dried in a hot air dryer until the moisture content was 0.05% or less, after which various properties were evaluated. The evaluation results are shown in Table 1.

[0058] Example 11 The raw materials other than talc and 1 / 3 of the talc were mixed in advance to obtain the composition shown in Table 1, and the mixture was fed into the main feed port of a twin-screw extruder (TEM26-SS manufactured by Toshiba Machine Co., Ltd.) with an L / D of 45, and the remaining 2 / 3 of the talc was fed from the side feed. Pellets were prepared in the same manner as in Example 1, and then evaluated.

[0059] Comparative Example 5 The raw materials other than talc and 1 / 3 of the talc were premixed to obtain the composition shown in Table 1. The mixture was fed into the main feed port of a 45L / D twin-screw extruder (TEM26-SS, manufactured by Toshiba Machine Co., Ltd.), with the remaining 2 / 3 of the talc fed through a side feed, and melt-kneaded. After being drawn off from the die in the form of strands, the mixture was passed through a water bath to cool and solidify, and then cut into pellets using a pelletizer to obtain polyamide resin composition pellets. The extruder barrel temperature was set to 260°C, the screw rotation speed was 90 rpm, and the output rate was 25 kg / hour. The resulting pellets were dried in a hot air dryer until the moisture content was 0.05% or less, after which various properties were evaluated. The evaluation results are shown in Table 1.

[0060] [Table 1]

[0061] From the results of Examples 1 to 8 and Comparative Examples 1 to 5 in Table 1, it is clear that when the polyamide resin, talc, and silane coupling agent are contained in the prescribed amounts and the MFR and flexural strength are within the prescribed ranges, a polyamide resin composition with high flowability and high strength, excellent in both flexural modulus and mold shrinkage, can be obtained. Furthermore, from Examples 9 to 11, it is clear that by further containing polyamide MXD6, a polyamide resin composition with excellent molded product appearance can also be obtained. [Industrial Applicability]

[0062] Molded articles made from the polyamide composition of the present invention have remarkably excellent mechanical properties, heat resistance, dimensional stability, etc., and are applicable to a wide range of uses, and are particularly suitable for automobile interior parts such as consoles and cup holders.

Claims

1. A polyamide resin composition comprising: (A) 54 to 75% by mass of a polyamide resin; (B) 24 to 45% by mass of talc; and (C) 0.01 to 1% by mass of a silane coupling agent, the polyamide resin composition contains the talc (B) as a dispersed phase having an average secondary particle size of less than 30 μm, The polyamide resin composition is characterized in that the melt mass-flow rate (MFR) of the polyamide resin composition at a moisture content of 0.05 mass% or less is 15 g / 10 min or more and less than 75 g / 10 min, and the flexural strength is 120 MPa or more.

2. The polyamide resin composition according to claim 1, wherein the polyamide resin (A) contains 70 to 99.5 parts by mass of (a1) polyamide 6 and 0.5 to 30 parts by mass of (a2) polyamide MXD6, based on 100 parts by mass of the polyamide resin (A).

3. 3. The polyamide resin composition according to claim 1, wherein a maximum point or an exothermic peak exists at a higher temperature than the maximum exothermic peak at the temperature-decreasing crystallization temperature during the cooling process in DSC measurement of the polyamide resin composition.

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