Polyamide resin composition

Abstract

The present invention is a polyamide resin composition which contains 50-90% by mass of a crystalline polyamide resin (A) and 9-49% by mass of a talc (B), and which is configured such that: the average particle diameter of the secondary particles of the talc (B) in the polyamide resin composition is 30 μm or less; and in the cooling process of the measurement of the polyamide resin composition by means of a differential scanning calorimeter, the exothermic peak is observed on the high temperature side of the maximum exothermic peak of the crystallization temperature during cooling. According to the present invention, variations of the physical characteristics such as molding shrinkage, mechanical characteristics and heat distortion temperature of the polyamide resin composition are suppressed among different production machines or different production lots, and consequently, characteristics within the desired ranges are able to be stably achieved.

Description

Technical Field

[0001] The present invention relates to a polyamide resin composition, and more particularly to a polyamide resin composition containing a large amount of talc as a reinforcing material.

Background Art

[0002] As a method for improving drawbacks of polyamide resins such as dimensional change due to water absorption, reduction in rigidity, and low heat distortion temperature, it has long been widely known to blend fibers such as glass fiber and carbon fiber, and inorganic fillers such as talc and calcium carbonate as reinforcing materials.

[0003] When attempting to blend a large amount of granular inorganic filler such as talc, since the difference in bulk density between the polyamide resin and the granular inorganic filler is large, it is difficult to sufficiently mix them by simple dry blending using a single-screw extruder. For this reason, a polyamide resin composition having a desired talc content is produced by devising such as sprinkling talc after attaching a coupling agent and water to the polyamide resin, or by mixing talc in a side feed method using a twin-screw extruder (for example, Patent Document 1).

[0004] However, even when the talc content is the same, physical properties such as the molding shrinkage rate, mechanical properties, and heat distortion temperature of the polyamide resin composition may vary depending on the difference in the production machine or the production lot. In particular, in the case of molded parts, stable molding shrinkage rate, mechanical properties, heat distortion temperature, etc. are required due to the relationship with other parts to be assembled, and there is room for improvement at present.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] Therefore, the present invention aims to solve the above-mentioned problems, that is, to obtain a polyamide resin composition in which, given the same talc content, the physical properties such as molding shrinkage rate, mechanical properties, and heat distortion temperature of the polyamide resin composition vary little even with differences in manufacturing machines or manufacturing lots, and in which properties within a desired range can be stably obtained. [Means for solving the problem]

[0007] In order to solve the above problems, the inventors diligently researched the aggregation characteristics of talc powder itself, the dispersibility of talc in polyamide resin, and the morphology of polyamide resin compositions. As a result, they found that the dispersion and aggregation state of talc fluctuates depending on the manufacturing machine or manufacturing lot, and is not always consistent. They discovered that by adjusting the maximum outer diameter of the talc aggregates to a size below a specific value, the properties of the resin composition become stable, leading to the present invention.

[0008] In other words, the present invention is "[1] A polyamide resin composition containing 50 to 90% by mass of crystalline polyamide resin (A) and 9 to 49% by mass of talc (B), wherein the average particle size of the secondary particles of talc (B) in the polyamide resin composition is 30 μm or less, and the exothermic peak exists at a temperature higher than the maximum exothermic peak of the cooling crystallization temperature during the cooling process measured by differential scanning calorimeter of the polyamide resin composition." [2] The polyamide resin composition according to [1], further comprising a coupling agent (C) and a fatty acid metal salt (D). [3] The polyamide resin composition according to [1] or [2], wherein the crystalline polyamide resin (A) contains an aliphatic polyamide resin. [4] The polyamide resin composition according to any one of [1] to [3], wherein the crystalline polyamide resin (A) contains polymetaxylylene adipamide.

[0009] By adopting the above configuration, the present invention has made it possible to solve the problem. [Effects of the Invention]

[0010] The polyamide resin composition of the present invention, despite containing a large amount of talc, exhibits little variation in physical properties such as molding shrinkage rate, mechanical properties, and heat distortion temperature, and stably displays properties within a desired range. [Brief explanation of the drawing]

[0011] [Figure 1] This figure shows the results of observing the cross-section of the test piece obtained in Example 1 using a scanning electron microscope. [Figure 2] This figure shows the results of observing the cross-section of the test piece obtained in Comparative Example 1 using a scanning electron microscope. [Figure 3] This figure shows the exothermic peaks in the cooling crystallization charts of the polyamide resin compositions obtained in Example 1 and Comparative Example 1, as measured by differential scanning calorimeter. [Modes for carrying out the invention]

[0012] The present invention will be described in detail below. The crystalline polyamide resin (A) in the present invention is a polyamide resin having an acid amide bond (-CONH-) in its molecule and having a crystalline melting point. The crystalline polyamide resin (A) preferably contains an aliphatic polyamide resin (A1). Specifically, examples include polycaproamide (polyamide 6), polyhexamethylene adipamide (polyamide 66), polytetramethylene adipamide (polyamide 46), polyhexamethylene sevacamide (polyamide 610), polylauryl lactam (polyamide 12), poly-11-aminoundecanoic acid (polyamide 11), etc., and other examples include copolymers of these and blends of these polymers, but are not limited to these. As the aliphatic polyamide resin (A1), polyamide 6 and polyamide 66 are preferred, and polyamide 6 is more preferred.

[0013] In the present invention, in addition to the above-mentioned aliphatic polyamide resin (A1), it is preferable from the viewpoint of moldability to use a polyamide resin (A2) that delays the crystallization of the aliphatic polyamide resin (A1) in the crystalline polyamide resin (A). The polyamide resin (A2) is not particularly limited as long as it can delay the crystallization of the aliphatic polyamide resin (A1), but for example, a polyamide with a higher crystallization temperature than the aliphatic polyamide resin (A1) or a polyamide that morphologically inhibits crystallization can be used. Specifically, examples include polyamide MXD6 (polymetaxylylene adipamide), hexamethylene terephthalate / hexamethylene isophthalate copolymer (6T / 6I), 4,4'-diamino-3,3'-dimethyl-dicyclohexylenemethane (CA) / isophthalic acid (I) / lauryl lactam (LL) copolymer (I / CA / LL), and terephthalic acid (T) / trimethyl-hexamethylenediamine (TMD) polymer (T / TMD). Polyamide MXD6 is preferred as the polyamide resin (A2) because it can improve the appearance of the molded article. Polyamide MXD6 is particularly preferred because it can improve not only the appearance of the molded article but also its mechanical properties.

[0014] The preferred ratio of aliphatic polyamide resin (A1) to polyamide resin (A2) is 70 to 99.5 parts by mass of aliphatic polyamide resin (A1) and 0.5 to 30 parts by mass of polyamide resin (A2), with 100 parts by mass of crystalline polyamide resin (A), and more preferably 80 to 95 parts by mass of aliphatic polyamide resin (A1) and 5 to 20 parts by mass of polyamide resin (A2).

[0015] The relative viscosity (96% sulfuric acid method) of the crystalline polyamide resin (A) is preferably in the range of 1.8 to 3.5, and more preferably in the range of 2.0 to 3.2. Below 1.8, toughness decreases, and above 3.5, fluidity tends to decrease. This preferred range of relative viscosity is the same for aliphatic polyamide resin (A1) and polyamide resin (A2). When using aliphatic polyamide resin (A1) and polyamide resin (A2) in combination, the weighted average calculated from the respective content ratios is used as the relative viscosity of the crystalline polyamide resin (A).

[0016] The amount of crystalline polyamide resin (A) blended (contained) in the polyamide resin composition is 50 to 90% by mass, preferably 55 to 80% by mass, more preferably 56 to 74% by mass, and even more preferably 60 to 68% by mass. Below 50% by mass, uniform dispersion of talc is difficult, and performance such as mechanical properties becomes unstable. Above 90% by mass, the effect of improving impact resistance is small.

[0017] In the present invention, the talc (B) has an average primary particle size of 1 to 15 μm, and more preferably 2 to 10 μm. If the average particle size exceeds the above range, it is difficult to satisfy the requirement that the average particle size of the secondary particles of talc (B) in the polyamide resin composition be 30 μm or less, resulting in a decrease in the flexural modulus and appearance of the molded product. On the other hand, if the average particle size is below the above range, dispersion problems are likely to occur. The average particle size can be measured by laser diffraction (e.g., LA920W manufactured by Horiba, Ltd.) or by liquid-layer sedimentation type optical transmission method (e.g., CP type manufactured by Shimadzu Corporation), and the particle size value at a cumulative amount of 50% by weight is read from the particle size cumulative distribution curve. In the present invention, the former method was used for measurement.

[0018] These talcs are obtained by further precisely classifying those obtained by mechanically pulverizing naturally produced ones. Also, it is possible to further classify those that have been roughly classified once. As a method of mechanical pulverization, it can be pulverized using a pulverizer such as a jaw crusher, a hammer crusher, a roll crusher, a screen mill, a jet mill, a colloid mill, a roller mill, a vibration mill, etc. These pulverized talcs are wet or dry classified once or repeatedly using devices such as a cyclone, a cyclone air separator, a microseparator, a cyclone air separator, a sharp cut separator, etc. in order to adjust to the average particle size shown in the present invention. When producing the talc used in the present invention, in order to obtain talc of a specific particle size fraction, it is preferable to perform a classification operation with a sharp cut separator after pulverizing to a specific particle size.

[0019] These talcs in the present invention are talcs that do not particularly require surface treatment, etc., but for the purpose of improving the adhesiveness or dispersibility with polyamide resin, various organic titanate-based coupling agents, organic silane-based coupling agents, unsaturated carboxylic acids, or modified polyolefins grafted with their anhydrides, fatty acids, fatty acid metal salts, fatty acid esters, etc. may be used for surface treatment. Also, granular talc granulated using a water-soluble polymer binder may be used.

[0020] The blending (content) amount of talc (B) is 9 to 49% by mass, preferably 19 to 44% by mass, more preferably 25 to 43% by mass, and still more preferably 31 to 39% by mass in the polyamide resin composition. If it is less than 9% by mass, the effect of improving mechanical properties is small, and if it exceeds 49% by mass, it is difficult to uniformly disperse in the polyamide resin, and the mechanical properties and the appearance of the molded product tend to become unstable.

[0021] The polyamide resin composition of the present invention preferably contains a coupling agent (C) and a fatty acid metal salt (D) in addition to the crystalline polyamide resin (A) and talc (B).

[0022] As the coupling agent (C), silane-based coupling agents, titanate-based coupling agents, etc., can be used. Examples of silane coupling agents include alkoxy group-containing silanes such as methyltrimethoxysilane, octadecyltrimethoxysilane, phenyltrimethoxysilane, and methacryloxypropyltrimethoxysilane; aminosilane coupling agents such as aminopropyltrimethoxysilane, aminopropyltriethoxysilane, ureidopropyltriethoxysilane, N-phenylaminopropyltrimethoxysilane, and N-2-(aminoethyl)aminopropyltrimethoxysilane; and glycidoxypropyltrimethoxysilane, glycidoxypropyl Examples include epoxysilane coupling agents such as riethoxysilane, glycidoxypropylmethyldiethoxysilane, glycidylbutyltrimethoxysilane, and (3,4-epoxycyclohexyl)ethyltrimethoxysilane; mercaptosilane coupling agents such as mercaptopropyltrimethoxysilane and mercaptopropyltriethoxysilane; and organosilazane compounds such as hexamethyldisilazane, hexaphenyldisilazane, trisilazane, cyclotrisilazane, and 1,1,3,3,5,5-hexamethylcyclotrisilazane.

[0023] Examples of titanate coupling agents include tetrakis(2-ethylhexyloxy)titanium, titanium-i-propoxyoctylene glycolate, di-i-propoxybis(acetylacetonate)titanium, propanedioxytitanium bis(ethylacetoacetate), tri-n-butoxytitanium monostearate, di-i-propoxytitanium distearate, butyl titanate dimer, titanium octylene glycolate, diisopropoxytitanium bis(triethanolamine), dihydroxytitanium bislactate, dihydroxybis(ammonium lactate)titanium, bis(dioctyl pyrophosphate)ethylene titanate, bis(dioctyl pyrophosphate)oxyacetate titanate, tri-n-butoxytitanium monostearate, and tetra-n-buty Examples include lutitanate, tetraisopropylbis(dioctylphosphite) titanate, tetraoctylbis(ditridecylphosphite) titanate, tetra(2,2-diallyloxymethyl-1-butyl)bis(ditridecyl)phosphite titanate, isopropyltrioctanoyl titanate, isopropyltricumylphenyl titanate, isopropyltriisostearoyl titanate, isopropylisostearoyldiacrylic titanate, isopropyldimethacrylateisostearoyl titanate, isopropyltri(dioctylphosphate) titanate, isopropyltridodecylbenzenesulfonyl titanate, isopropyltris(dioctylpyrophosphate) titanate, and isopropyltri(N-amidoethyl / aminoethyl) titanate.

[0024] The amount of coupling agent (C) in the polyamide resin composition is preferably 0.01 to 1% by mass, more preferably 0.05 to 0.8% by mass, and even more preferably 0.1 to 0.5% by mass. Furthermore, relative to talc (B), it is preferably 0.1 to 4.0% by mass, more preferably 0.2 to 2.0% by mass.

[0025] The fatty acid metal salt (D) is added to suppress the aggregation of talc and to achieve good appearance and physical properties. Preferably, the fatty acid metal salt (D) is a metal salt of a fatty acid having 9 to 30 carbon atoms. Examples include calcium stearate, magnesium stearate, zinc stearate, calcium behenate, magnesium behenate, zinc behenate, zinc montanate, calcium montanate, magnesium montanate, calcium melisinate, magnesium melisinate, zinc melisinate, calcium serotinate, magnesium serotinate, zinc serotinate, calcium lignocerate, magnesium lignocerate, and zinc lignocerate. Among these metal salts, calcium, magnesium, or zinc salts of fatty acids having 15 to 28 carbon atoms are preferred, and calcium stearate, magnesium stearate, zinc stearate, calcium behenate, magnesium behenate, zinc behenate, zinc montanate, calcium montanate, and magnesium montanate are particularly preferred due to their performance and availability. These metal salts can be produced by a synthesis method (re-decomposition method) in which a carboxylic acid compound is reacted with a metal hydroxide, followed by washing, dehydration, and drying, or by a direct reaction method that does not use water.

[0026] The amount of fatty acid metal salt (D) blended (contained) in the polyamide resin composition is preferably 0.01 to 2% by mass, more preferably 0.05 to 1.5% by mass, and even more preferably 0.1 to 1% by mass.

[0027] In the polyamide resin composition of the present invention, a crystalline polyamide resin (A) and talc (B) (preferably talc with an average primary particle size of 15 μm or less) are melt-kneaded in a ratio of 50 to 90% by mass of polyamide resin (A) and 9 to 49% by mass of talc (B), and it is necessary that the average particle size of the secondary particles of talc (B) in the polyamide resin composition is 30 μm or less. The average secondary particle size is preferably 25 μm or less, more preferably 20 μm or less. If the average secondary particle size exceeds 30 μm, the mechanical properties and appearance of the molded product will be inferior. The lower limit is the average particle size of the primary particles (single particle dispersion) of talc (B), which is about 1 μm. Depending on the average particle size of the primary particles of talc (B) used, the average particle size of the secondary particles of talc (B) in the polyamide resin composition is more preferably 5 μm or more, and even more preferably 10 μm or more.

[0028] The method for measuring the average particle size of secondary particles involves observing molded products obtained by injection molding a polyamide resin composition using a scanning electron microscope (SEM) at 500x magnification. The maximum lengths of 500 secondary particles with a maximum length greater than the average particle size of the primary talc (B) particles are measured, and the average of the maximum lengths of the 100 largest secondary particles is calculated.

[0029] The polyamide resin composition of the present invention requires that, during the cooling process of temperature measurement of the cooling crystallization temperature using a differential scanning calorimeter, the exothermic peak exists on the higher side of the maximum exothermic peak. Although the details of the exothermic peak in this cooling crystallization chart are unknown, it is thought to depend on the polyamide resin crystals (spherulites) formed on the finely dispersed talc. Talc has a nucleating effect, and on the talc surface in the polyamide resin composition, polyamide resin crystals begin to form at a temperature higher than the normal crystallization temperature. When the average particle size of the secondary particles consisting of component (B) is 30 μm or less, the total surface area of ​​the talc increases, making the nucleating effect of the talc more pronounced, which is thought to increase the degree of crystallization and lead to improved mechanical properties. At the same time, it is thought that this also has the effect of improving the adhesion between talc and polyamide resin, and synergistically improving the mechanical strength. Since these crystals are easily formed uniformly within the molded product, it is thought that the mechanical properties of the molded product are improved and stable properties are obtained.

[0030] In this invention, the cooling crystallization temperature (TC2) is measured using a differential scanning calorimeter (DSC). The temperature is raised to 300°C at a heating rate of 20°C / min under a nitrogen atmosphere, held at that temperature for 5 minutes, and then cooled to 100°C at a rate of 10°C / min. The peak temperature obtained during this measurement is the highest peak if multiple peaks appear.

[0031] The dispersed phase consisting of component (B), in which the average particle size of the secondary particles described above is 30 μm or less, tends to be generated more easily when the relative viscosity of the polyamide resin (A) is high, because the shear force during melt mixing increases. Specifically, this effect is greatly exhibited when the relative viscosity of the polyamide resin (A) is 3.0 or higher, which is a preferred embodiment.

[0032] On the other hand, even when the relative viscosity of the polyamide resin (A) is 3.0 or less, by adjusting the manufacturing conditions, it becomes possible to generate a dispersed phase consisting of component (B) with an average particle size of 30 μm or less for the secondary particles.

[0033] In addition to the above, the polyamide resin composition of the present invention may optionally contain, to the extent known, light or heat stabilizers, antioxidants, ultraviolet absorbers, light stabilizers, plasticizers, lubricants, crystal nucleating agents, mold release agents, antistatic agents, halogenated flame retardants and antimony trioxide combinations, various phosphoric acid-based flame retardants, melamine-based flame retardants, inorganic pigments, organic pigments, dyes, or other polymers.

[0034] Examples of stabilizers include organic antioxidants such as hindered phenol antioxidants, sulfur antioxidants, and phosphorus antioxidants, as well as heat stabilizers, light stabilizers such as hindered amine, benzophenone, and imidazole types, as well as ultraviolet absorbers, metal deactivators, and copper compounds. Examples of copper compounds 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, it is preferable to include alkali metal halide compounds as components other than copper compounds. 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 individually or in combination. The amount of stabilizer to add should be selected to the optimal amount, but it is possible to add up to 5 parts by mass per 100 parts by mass of polyamide resin (A).

[0035] As flame retardants, a combination of halogenated flame retardants and flame retardant additives is preferable. Preferred halogenated flame retardants include brominated polystyrene, brominated polyphenylene ether, brominated bisphenol-type epoxy polymer, brominated styrene maleic anhydride polymer, brominated epoxy resin, brominated phenoxy resin, decabromodiphenyl ether, decabromoviphenyl, brominated polycarbonate, perchlorocyclopentadecane, and brominated crosslinked aromatic polymers. Examples of flame retardant additives include antimony trioxide, antimony pentoxide, sodium antimonate, zinc stagnate, zinc borate, layered silicates such as montmorillonite, fluorinated polymers, and silicones. In particular, from the standpoint of thermal stability, a combination of dibrom polystyrene as the halogenated flame retardant and any of antimony trioxide, sodium antimonate, or zinc stagnate as the flame retardant additive is preferred. Examples of non-halogenated flame retardants include melamine cyanurate, red phosphorus, metal salts of phosphinic acid, and nitrogen-containing phosphate compounds. In particular, a combination of a phosphinate metal salt and a nitrogen-containing phosphate compound is preferred. The nitrogen-containing phosphate compound includes melamine or a reactive compound of melamine condensates such as melam or melon, and polyphosphate, or mixtures thereof. As for other flame retardants and flame retardant aids, when using these flame retardants, the addition of hydrotalcite compounds or alkali compounds is preferred to prevent metal corrosion of molds, etc. The amount of flame retardant to be added should be selected to the optimal amount, but it is possible to add up to 20 parts by mass per 100 parts by mass of polyamide resin (A).

[0036] The polyamide resin composition of the present invention preferably contains 85% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, of the total of polyamide resin (A), talc (B), coupling agent (C), and fatty acid metal salt (D) (the coupling agent (C) and fatty acid metal salt (D) are optional components).

[0037] The manufacturing apparatus for producing the polyamide resin composition of the present invention is not particularly limited as long as it can melt-knead the polyamide resin and talc. It can be used with any single-screw extruder, twin-screw extruder, kneader, Banbury mixer, roll, etc., which are well known to those skilled in the art and capable of melt-kneading, but it is preferable to use a twin-screw extruder.

[0038] When using a twin-screw extruder, it is preferable to control the resin pressure in the extruder plasticizing section where the non-molten polymer phase and molten polymer phase coexist by appropriately selecting the extruder barrel temperature and screw configuration to improve the dispersibility of talc. In other words, in the polymer plasticizing region where talc agglomerates are likely to form, it is important to allow the non-molten polymer phase and molten polymer phase to coexist, and to increase the viscosity of the polymer as the matrix phase to prevent the formation of talc agglomerates due to shear stress and to control internal heat generation due to shear force, thereby improving dispersion. The resin pressure is preferably around 0.1 to 1 MPa.

[0039] The screws of a twin-screw extruder are used in appropriate combinations of full-flight screws, reverse full-flight screws, orthogonal kneading discs, progressive kneading discs, and reverse kneading discs. In the present invention, it is preferable to incorporate a progressive kneading disc as the screw configuration for the plasticizing region.

[0040] Furthermore, it is preferable that the ratio 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 operational problems, a smaller L / D is preferable from the viewpoint of fine dispersion of talc. Note that if it exceeds 100, the mechanical strength of the resin composition tends to decrease due to thermal degradation.

[0041] Furthermore, the melting temperature of the resin composition during melt mixing is preferably 180 to 330°C, and more preferably 200 to 300°C. If the melting temperature is below 180°C, melting will be insufficient, and a large amount of unmelted gel is likely to occur. Conversely, if it exceeds 330°C, the resin composition is prone to thermal degradation.

[0042] The screw rotation speed N during melting and mixing is preferably 100 to 1,500 rpm, and more preferably 150 to 1,000 rpm. If the screw rotation speed is less than 100 rpm, the talc tends not to disperse finely, and conversely, if it exceeds 1,500 rpm, the talc tends to aggregate and not disperse finely. The discharge rate Q is preferably 5 to 3,000 kg / hr, and more preferably 10 to 2,000 kg / hr. If the discharge rate is less than 5 kg / hr, the dispersibility of the talc tends to decrease, and even if it exceeds 2,000 kg / hr, the dispersibility tends to decrease due to the re-aggregation of the talc.

[0043] 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. Below 0.01, the mechanical strength of the resin composition tends to decrease due to thermal degradation. Also, above 1, the conveying force becomes insufficient, and talc is more likely to be ejected. It should be noted that a smaller Q / N tends to result in easier fine dispersion of talc. This is thought to be because, in addition to the screw, shearing between the raw material pellets also contributes to promoting fine dispersion.

[0044] Furthermore, while it is possible to introduce talc, which tends to impede well into the polyamide resin during extrusion, through the side port of the twin-screw extruder, this is not a limitation. Also, component (C) may be added simultaneously with other raw material components, or it may be added after being pre-applied to the talc. From the viewpoint of finely dispersing the talc, it is preferable to introduce it from the original feed to apply more shear.

[0045] Furthermore, in order to remove gaseous components associated with the talc during melt-kneading, it is preferable to perform vacuum degassing in the melt-kneading section after plasticization is complete. [Examples]

[0046] The present invention will now be specifically described using examples and comparative examples, but the present invention is not limited to these.

[0047] The characteristics and physical properties shown in the following examples and comparative examples were measured using the test methods described below. 1) Average particle size of talc secondary particles: Cross-sectional sections were prepared using a microtome from test pieces prepared according to 4) below, platinum sputtering was performed, and the sections were observed at 500x magnification using a scanning electron microscope (SEM). The maximum lengths of 500 secondary particles with a maximum length greater than the average particle size of the primary talc particles were measured, and the average of the maximum lengths of the 100 largest secondary particles was calculated to determine the average particle size of the secondary particles.

[0048] 2) Bending strength: Measured in accordance with JIS K 7171:2016. 3) Flexural modulus: Measured in accordance with JIS K 7171:2016.

[0049] 4) 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 (or the melting point of the highest polyamide resin if multiple types of polyamide resins were used) + 20°C, and the mold temperature was set to 90°C. 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. This evaluation was performed in some examples to confirm the effect of the blended raw materials. ◎: There is no lifting of the reinforcing material throughout the molded product. ○: There is slight lifting of the reinforcing material near the gate and at the end. ×: There is a large amount of lifting of the reinforcing material throughout the molded product.

[0050] 5) Molding shrinkage rate: A test specimen of a flat plate (film gate) with mold dimensions of 100 mm × 100 mm × 3 mm (thickness) was molded in the same manner as in 4), and after being left to stand for 24 hours at 23°C and 50% relative humidity, the dimensions of the test specimen in the flow direction and perpendicular direction were measured with a caliper to an accuracy of 0.1 mm. The molding shrinkage rates in the flow direction and perpendicular direction were calculated from the mold reference dimensions at the mold temperature during molding, which had been measured in advance using the same method.

[0051] 6) Cooling Crystallization Curve Exothermic Peak: A DSC measuring device (Seiko Instruments, EXSTAR6000) was used. The temperature was raised 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 defined as TC2, and the presence or absence of an exothermic peak (second peak) in the temperature range from the rise of the cooling crystallization curve to TC2 was evaluated. ○ indicated the presence of an exothermic peak, and × indicated its absence. The DSC measurement sample was cut from near the center of the 100mm × 100mm × 2mm flat plate used in evaluation 4).

[0052] 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 by dissolving 0.25 g of polyamide resin in 25 ml of 96% sulfuric acid, placing 10 ml of this solution in an Ostwald viscosity tube, and setting it at 20°C. (A11) Polyamide 6: Toyobo's "Gramide T-840" (RV2.2, melting point 223℃) (A12) Polyamide 6: Ube Industries "1013B" (RV2.5, melting point 224℃) (A13) Polyamide 6: Toyobo "T-820" (RV3.1, melting point 225℃) (A2) Polyamide MXD6: Toyobo's "Nylon T-600" (RV2.1, melting point 240℃) (B1) Talc: KST-W manufactured by Katsumitsuyama Mining Co., Ltd. (average particle size 7 μm, apparent specific gravity 0.4) (B2) Talc: Hayashi Chemical Co., Ltd. "Talcan Powder PK" (average particle size 10 μm, apparent specific gravity 0.8) (B3) Talc: Fukuoka Talc Industry Co., Ltd. "FU-51" (average particle size 13 μm, apparent specific gravity 0.3) (B4) Wollastonite: Kinsei Matec "FPW-350" (average particle size 20 μm, apparent specific gravity 0.6) (C) Silane coupling agent: Shin-Etsu Chemical Co., Ltd. "KBE-903" (3-aminopropyltriethoxysilane) (D1) Fatty acid metal salt: "NP-1500" (magnesium stearate) manufactured by Tannan Chemical Co., Ltd. (D2) Fatty acid metal salt: "CS-8CP" (calcium montanate) manufactured by Nitto Chemical Industries, Ltd. (E) Stabilizer: Potassium iodide manufactured by Mitsui Chemicals

[0053] Example 1 The raw materials were pre-mixed to achieve the composition shown in Table 1 and supplied to the main feed port of a twin-screw extruder with an L / D ratio of 34 (Toshiba Machine Co., Ltd. TEM48BS: referred to as machine base A) for melt-kneading. After being taken up in strand form from the die, the mixture was cooled and solidified in a water bath, and then cut with a pelletizer to obtain polyamide resin composition pellets. The barrel temperature of the extruder was set to 260°C, and the screw rotation speed and discharge volume were set to the manufacturing conditions shown in Table 1. The obtained pellets were dried in a hot air dryer until the moisture content was 0.05% or less, and then various properties were evaluated. The evaluation results are shown in Table 1. The average particle size of talc secondary particles observed with a scanning electron microscope is shown in Figure 1, and the cooling crystallization chart obtained with a differential scanning calorimeter is shown in Figure 3.

[0054] Example 2, Comparative Example 1 Except for supplying a portion of the talc from the side feed and using the manufacturing conditions shown in Table 1, pellets were prepared and evaluated in the same manner as in Example 1. Figure 2 shows the results of observing the average particle size of the secondary talc particles in Comparative Example 1 using a scanning electron microscope, and Figure 3 shows the cooling crystallization chart obtained using a differential scanning calorimeter.

[0055] Examples 3, 5-8, 10, Comparative Example 4 The raw materials were pre-mixed to achieve the composition shown in Table 1 and supplied to the main feed port of a twin-screw extruder with an L / D ratio of 45 (Toshiba Machine Co., Ltd. TEM26-SS: referred to as machine base B) for melt-kneading. After being taken out of the die in strand form, the mixture was cooled and solidified in a water bath, and then cut with a pelletizer to obtain polyamide resin composition pellets. The barrel temperature of the extruder was set to 260°C, and the screw rotation speed and discharge volume were set to the manufacturing conditions shown in Table 1. The obtained pellets were dried in a hot air dryer until the moisture content was 0.05% or less, and then various properties were evaluated. The evaluation results are shown in Table 1.

[0056] Comparative Example 2 Except for supplying the entire amount of talc from the side feed, pellets were prepared and evaluated in the same manner as in Example 3.

[0057] Examples 4, 11, Comparative Example 3 Pellets were prepared and evaluated in the same manner as in Example 3, except that the composition was as shown in Table 1, a portion of the talc was supplied from the side feed, and the manufacturing conditions in Table 1 were followed.

[0058] Example 9 Pellets were prepared and evaluated in the same manner as in Example 1, using the composition shown in Table 1.

[0059] [Table 1]

[0060] Table 1 shows that by including polyamide resin and talc in predetermined amounts and keeping the average particle size of the talc secondary particles within a predetermined range, a second peak appears in the crystallization fall curve, resulting in a polyamide resin composition with excellent bending properties and low molding shrinkage. Furthermore, since similar results have been obtained with different machines, it can be said that even with differences in manufacturing machines or manufacturing lots, the physical properties such as molding shrinkage, mechanical properties, and heat distortion temperature of the polyamide resin composition do not vary significantly, and the desired properties can be obtained stably. [Industrial applicability]

[0061] Molded articles made from the polyamide composition of the present invention exhibit remarkably excellent mechanical properties, heat resistance, and dimensional stability. Furthermore, they show little variation in physical properties such as molding shrinkage rate, mechanical properties, and heat distortion temperature, making them suitable for a wide range of applications, and particularly ideal for automotive interior parts such as consoles and cup holders.

Claims

1. A polyamide resin composition containing 50 to 90% by mass of crystalline polyamide resin (A) and 9 to 49% by mass of talc (B), wherein the average particle size of the secondary particles of talc (B) in the polyamide resin composition is 5 μm or more and 30 μm or less, and in the cooling process measured by differential scanning calorimeter of the polyamide resin composition, the exothermic peak exists at a temperature higher than the maximum exothermic peak of the cooling crystallization temperature. A polyamide resin composition characterized in that the crystalline polyamide resin (A) contains an aliphatic polyamide resin, and when the content of the crystalline polyamide resin (A) is 100 parts by mass, the content of the aliphatic polyamide resin is 70 parts by mass or more.

2. The content of the crystalline polyamide resin (A) is 55 to 90% by mass, The talc (B) content is 9 to 44% by mass, The polyamide resin composition may further contain a coupling agent (C) and a fatty acid metal salt (D). The total content of the polyamide resin (A), the talc (B), the coupling agent (C), and the fatty acid metal salt (D) (where the coupling agent (C) and the fatty acid metal salt (D) are optional components) is 95% by mass or more. The polyamide resin composition according to claim 1.

3. The polyamide resin composition according to claim 1, further comprising a coupling agent (C) and a fatty acid metal salt (D).

4. The polyamide resin composition according to any one of claims 1 to 3, wherein the crystalline polyamide resin (A) contains polymetaxylylene adipamide.

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