Polyamide resin foam particles and polyamide resin foam particle molded articles

Abstract

To provide polyamide-based resin foam particles that have superior moldability within the mold, and yield an excellent molded article under various molding pressures.SOLUTION: There are provided polyamide-based resin foam particles comprising a polyamide-based resin as a base material resin, the foam particles containing carbon nanotubes, wherein a closed-cell ratio of the foam particles is 70% or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to polyamide resin foam particles and polyamide resin foam particle molded articles. [Background technology]

[0002] Polyamide resins are known as plastics with high heat resistance, as well as excellent abrasion resistance and chemical resistance. Foamed molded products made from these polyamide resins can be made lighter while maintaining excellent properties such as heat resistance, abrasion resistance, and chemical resistance, and are therefore expected to have further applications in automotive parts, electrical products, and other fields. For example, Patent Document 1 discloses polyamide resin foam particles and a foam particle molded article obtained by in-mold molding of the foam particles. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] International Publication No. 2020 / 050301 [Overview of the project] [Problems that the invention aims to solve]

[0004] In the technology for obtaining a foamed particle molded article, such as in the aforementioned Patent Document 1, it is necessary to fill the mold with foamed particles and fuse the foamed particles together, and furthermore, there was a need for polyamide resin foamed particles with excellent moldability. Therefore, the problem that the present invention aims to solve is to provide polyamide resin foam particles that have excellent in-moldability and can produce good polyamide resin foam particle molded articles over a wide range of molding pressures. [Means for solving the problem]

[0005] In response to the aforementioned problems, the inventors have conducted extensive research and found that polyamide resin foam particles containing carbon nanotubes and having a specific range of closed-cell ratios can solve the aforementioned problems.

[0006] In other words, the present invention relates to polyamide resin foam particles using a polyamide resin as a base resin, wherein the foam particles contain carbon nanotubes and the closed-cell ratio of the foam particles is 70% or more, and to a molded polyamide resin foam particle molded article obtained by in-mold molding the polyamide resin foam particles. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide polyamide resin foam particles that exhibit excellent in-moldability and can produce good polyamide resin foam particle molded articles over a wide range of molding pressures. [Brief explanation of the drawing]

[0008] [Figure 1] This is an example of a DSC curve obtained by differential scanning calorimetry (DSC). [Modes for carrying out the invention]

[0009] [Polyamide resin foam particles] The polyamide resin foam particles of the present invention are polyamide resin foam particles using a polyamide resin as the base resin, wherein the foam particles contain carbon nanotubes and the closed-cell ratio of the foam particles is 70% or more.

[0010] (Polyamide resin) Examples of polyamide resins that serve as the base resin for the polyamide resin foam particles of the present invention include polyamides and polyamide copolymers, with polyamide copolymers being preferred. Examples of polyamides include poly(6-aminohexanoic acid) (polycaproamide, nylon 6), also known as poly(caprolactam), poly(laurolactam) (nylon 12), poly(hexamethylene adipamide) (nylon 66), poly(7-aminoheptanoic acid) (nylon 7), poly(8-aminooctanoic acid) (nylon 8), poly(9-aminononanoic acid) (nylon 9), poly(10-aminodecanoic acid) (nylon 10), poly(11-aminoundecanoic acid) (nylon 11), poly(hexamethylene sebacamide) (nylon 610), poly(decamethylene sebacamide) (nylon 1010), poly(hexamethylene azelamide) (nylon 69), poly(tetramethylene adipamide) (nylon 46), poly(tetramethylene sebacamide) (nylon 410), poly(pentamethylene adipamide) (nylon 56), and poly(pentamethylene sebacamide) (nylon 510), etc. A polyamide copolymer means a polymer having two or more repeating units and having an amide bond in at least a part of each repeating unit. Examples of polyamide copolymers include polycaproamide / polyhexamethylene adipamide copolymer (nylon 6 / 66), caprolactam / hexamethylenediaminoadipic acid / laurolactam (nylon 6 / 66 / 12), and caprolactam / laurolactam copolymer (nylon 6 / 12), etc. These polyamides and polyamide copolymers may be used alone or in combination of two or more. Among the above polyamide-based resins, it is preferable that the polyamide-based resin is one or a combination of two or more selected from nylon 6, nylon 66, nylon 6 / 66, and nylon 6 / 66 / 12, and more preferably one or two selected from nylon 6 / 66 and nylon 6 / 66 / 12. In addition, as the above polyamide-based resin, polyamides and polyamide copolymers incorporating plant-derived raw materials can also be used.

[0011] The polyamide copolymer may be a block copolymer in which a certain amount of the same repeating unit amide is followed by a certain amount of different types of amides, or a random copolymer in which different types of amides repeat randomly, but it is preferably a random copolymer. If the polyamide copolymer is a random copolymer, it becomes easier to mold at a relatively low molding pressure when molding the foamed particles in a mold.

[0012] The polyamide-based resin used in the present invention preferably has a flexural modulus of 1000 MPa or more, more preferably 1200 MPa or more, and even more preferably 1500 MPa or more. If the flexural modulus of the polyamide-based resin is within the above range, it is generally different from an amide-based elastomer having a flexural modulus of 600 MPa or less, and it is preferable because it is difficult to shrink even when exposed to room temperature after foaming, and high magnification foamed particles are easily obtained. The upper limit of the flexural modulus of the polyamide-based resin is generally about 3000 MPa.

[0013] The flexural modulus of the polyamide-based resin can be determined by measuring in accordance with JIS K7171:2016 after leaving a test piece standing for 24 hours at a temperature of 23 °C and a humidity of 50%.

[0014] The melting point (Tm0) of the polyamide-based resin used in the polyamide-based resin particles and constituting the obtained polyamide-based resin foamed particles is preferably 175 °C or higher, more preferably 180 °C or higher, and even more preferably 185 °C or higher from the viewpoint of obtaining polyamide-based resin foamed particles having excellent heat resistance. On the other hand, from the viewpoint of easy temperature control during foaming, the melting point (Tm0) of the polyamide-based resin is preferably 230 °C or lower, more preferably 220 °C or lower, and even more preferably 200 °C or lower. The melting point of the polyamide-based resin refers to the melting point of the polyamide-based resin when used alone. When the polyamide-based resin is composed of a mixture of two or more polyamide-based resins, or a mixture of a polyamide-based resin and another thermoplastic resin, the maximum endothermic peak of the mixture is taken as the melting point.

[0015] In this specification, the melting point (Tm0) of the resin is determined based on JIS K7121-1987, using the conditional heating and cooling methods (both heating and cooling rates in the conditional heating and cooling of the test specimens are 10°C / min) to obtain the peak temperature of the melting peak in the DSC curve obtained at a heating rate of 10°C / min. If the DSC curve has multiple melting peaks, the peak temperature of the melting peak with the largest area is adopted as the melting temperature. Test specimens of polyamide resins should be stored in a way that avoids hydrolysis by avoiding high temperature and high humidity conditions, such as by placing them in a desiccator and then storing them under vacuum.

[0016] The polyamide resin used in this invention has a density of 1.05 g / cm³. 3 Preferably, it is 1.1 g / cm³ or more. 3 The above is preferable. The density can be determined based on the method described in ISO 1183-3.

[0017] The polyamide resin used in this invention is preferably a end-bound polyamide resin in which the functional groups at the ends of the molecular chain are sealed. This makes it possible to more reliably suppress hydrolysis during the manufacturing process of foamed particles, and makes it easier to obtain foamed particles suitable for in-mold molding. Furthermore, the durability of the foamed particle molded body (hereinafter also simply referred to as "molded body") obtained by in-mold molding is improved. Examples of end-capping agents that can be used to seal the ends of the above molecular chains include carbodiimide compounds, oxazoline compounds, isocyanate compounds, epoxy compounds, and the like. Among these, carbodiimide compounds are preferred. Specifically, examples include aromatic monocarbodiimides such as bis(dipropylphenyl)carbodiimide (e.g., "Stabaxol 1-LF" from Rhein Chemie), aromatic polycarbodiimides (e.g., "Stabaxol P", "Stabaxol P100", "Stabaxol P400" from Rhein Chemie), and aliphatic polycarbodiimides such as poly(4,4'-dicyclohexylmethanecarbodiimide) (e.g., "Carbodilite LA-1" from Nisshinbo Chemical Co., Ltd.). These end-capping agents may be used alone or in combination of two or more. Furthermore, the amount of end-capsulating agent is preferably 0.1 to 5 parts by mass, and more preferably 0.5 to 3 parts by mass, per 100 parts by mass of polyamide resin. Thus, the polyamide resin used in the present invention is preferably a polyamide resin whose ends are sealed with one or more end-capping agents selected from carbodiimide compounds, epoxy compounds, and isocyanate compounds, and more preferably a polyamide resin whose ends are sealed with a carbodiimide compound.

[0018] (Carbon nanotubes) The polyamide resin foam particles of the present invention contain carbon nanotubes. The carbon nanotubes contained in the polyamide resin foam particles of the present invention are not particularly limited as long as they achieve the effects of the present invention, but the carbon nanotubes shown below are preferred.

[0019] The average diameter of the carbon nanotubes is preferably 5 to 25 nm, and more preferably 10 to 20 nm. The average length of the carbon nanotubes is preferably 0.2 to 50 μm, more preferably 0.5 to 50 μm, and even more preferably 2 to 40 μm. Furthermore, the aspect ratio of the carbon nanotube is preferably 20 to 1000, and more preferably 100 to 1000. The aspect ratio is determined by dividing the average length by the average diameter. The average diameter and average length of the carbon nanotubes can be measured, for example, by the following method. First, a surface image of the foamed particles is obtained using a scanning electron microscope. The diameters of the carbon nanotubes present in this surface image are measured at 50 randomly selected locations. The average value of the obtained diameters can then be used as the average diameter.

[0020] Similarly, 50 carbon nanotubes are randomly selected from surface images obtained using a scanning electron microscope, and the length of each carbon nanotube is measured by image analysis. If the carbon nanotubes are not straight but have a bent shape, the length along the shape of the carbon nanotube can be measured using a curvimeter or similar device. The average value of the lengths obtained in this way can be used as the average length.

[0021] As the carbon nanotube, a multi-walled carbon nanotube may be used. The carbon nanotube content in the polyamide resin foam particles of the present invention is preferably 0.1 parts by mass or more and 10 parts by mass or less per 100 parts by mass of the base resin. More preferably, the carbon nanotube content in the polyamide resin foam particles of the present invention is 0.3 parts by mass or more, even more preferably 0.6 parts by mass or more, even more preferably 0.8 parts by mass or more, and even more preferably 5 parts by mass or less, even more preferably 3 parts by mass or less, and even more preferably 2 parts by mass or less per 100 parts by mass of the base resin. By having the carbon nanotube content within the above range, a good polyamide resin foam particle molded article can be obtained over a wide range of molding pressures. When producing the polyamide resin foam particles of the present invention, it is preferable to use a masterbatch containing carbon nanotubes, and resins other than the polyamide resin contained in the masterbatch may be included in the base resin. As the above carbon nanotubes, commercially available ones can be used and can be purchased from, for example, Nanocyl.

[0022] In this invention, the polyamide resin foam particles exhibit excellent in-moldability, and the reason why good polyamide resin foam particle molded articles can be obtained over a wide range of molding pressures is not entirely clear, but the following is considered to be the reason. When molding polyamide resin foam particles in a mold, it is necessary to sufficiently melt the crystalline components of the polyamide resin by heating and pressurizing with steam. After in-mold molding, as the temperature and pressure decrease, crystallization of the resin progresses, causing shrinkage (deformation that reduces volume). At this time, the carbon nanotubes suppress the volume shrinkage, so the molding shrinkage rate is kept low, and it is thought that good polyamide resin foam particle molded articles can be obtained over a wide range of molding pressures.

[0023] (Coloring agent) The foamed particles of the present invention may contain a coloring agent to improve the appearance and design of the resulting molded article. When producing a black molded article, it is possible to obtain a colored molded article using only the carbon nanotubes, but a further coloring agent may be included to improve the degree of coloration or adjust the hue. Inorganic or organic pigments or dyes can be used as colorants. Colorants are used.

[0024] Examples of inorganic pigments include titanium dioxide, carbon black, titanium yellow, iron oxide, ultramarine, cobalt blue, calcined pigments, metallic pigments, mica, pearl pigments, zinc oxide, precipitated silica, and cadmium red. Examples of organic pigments include monoazo pigments, condensed azo pigments, anthraquinone pigments, isoindolinone pigments, perinone pigments, quinacridone pigments, perylene pigments, thioindigo pigments, dioxazine pigments, phthalocyanine pigments, nitroso pigments, and organic fluorescent pigments. Examples of dyes include anthraquinone dyes, perinone dyes, basic dyes, acid dyes, and mordant dyes. Among these colorants, it is preferable to use organic or inorganic pigments from the viewpoint of weather resistance. Inorganic pigments are preferred from the viewpoint of heat resistance and weather resistance.

[0025] The content of coloring pigment in the foamed particles is preferably 0.5 to 10% by mass, more preferably 0.8 to 5% by mass, and even more preferably 1 to 3% by mass. In particular, when carbon black is used as the coloring pigment, the carbon black content in the foamed particles is preferably 0.5 to 10% by mass, more preferably 0.8 to 5% by mass, and even more preferably 1 to 3% by mass. By having the coloring pigment content within the above range, the resulting foamed particle molded article can be given excellent design properties.

[0026] (Other resins and additives) The polyamide resin foam particles of the present invention use a polyamide resin as the base resin. In this specification, "using a polyamide resin as the base resin" means that the polyamide resin foam particles are composed of a resin whose main component is a polyamide resin. The polyamide resin foam particles of the present invention may contain other resins other than the polyamide resin, as long as they do not impede the effects of the present invention. In this case, the content of the resin other than the polyamide resin in the polyamide resin foam particles is preferably 40 parts by mass or less, more preferably 30 parts by mass or less, even more preferably 20 parts by mass or less, even more preferably 10 parts by mass or less, and particularly preferably 5 parts by mass or less, per 100 parts by mass of the polyamide resin. Other resins include, for example, polyethylene resins, polypropylene resins, polystyrene resins, vinyl acetate resins, thermoplastic polyester resins, acrylic ester resins, methacrylic ester resins, modified polyphenylene ether resins, polycarbonate resins, polyacetal resins, polybutylene terephthalate resins, polysulfone resins, polyethersulfone resins, polyamide-imide resins, polyetherimide resins, and polyetheretherketone resins. Among these, polypropylene resins are preferred.

[0027] The foamed particles of the present invention may contain various additives such as commonly used antistatic agents, conductivity imparters, lubricants, ultraviolet absorbers, flame retardants, metal deactivators, crystal nucleating agents, and fillers, as needed. The amount of these additives added varies depending on the intended use of the molded article, but is preferably 25 parts by mass or less per 100 parts by mass of the base resin. More preferably 15 parts by mass or less, even more preferably 10 parts by mass or less, and even more preferably 5 parts by mass or less.

[0028] (Properties of polyamide resin foam particles) The closed-cell ratio of the polyamide resin foam particles of the present invention is 70% or more. Preferably, the closed-cell ratio of the polyamide resin foam particles of the present invention is 75% or more, more preferably 80% or more, even more preferably 85% or more, and even more preferably 90% or more. When the closed-cell ratio of the foam particles satisfies the above range, foam particles with a low apparent density are easily obtained. Furthermore, a molded article of foam particles molded in a mold using foam particles with a closed-cell ratio satisfying the above range is likely to yield a molded article with excellent fusion properties and recovery properties. The closed-cell ratio is the ratio of the volume of closed cells to the volume of all cells in the foam particles, and can be determined using an air-comparison hydrometer based on ASTM-D2856-70.

[0029] The apparent density of the foamed particles of the present invention is preferably 50 kg / m³. 3 More than 500kg / m 3 The following applies: The apparent density of the foamed particles of the present invention is more preferably 70 kg / m³. 3 More preferably 100 kg / m 3 That is all, and more preferably 300 kg / m 3 More preferably, 200 kg / m 3 The following applies: If the apparent density of the foam particles is within the above range, the in-moldability will be good, and a good foam particle molded product will be easier to obtain. The apparent density of the foam particles is measured by the following method. A graduated cylinder filled with water at 23°C was prepared and left for two days under the conditions of 50% relative humidity, 23°C, and 1 atm, yielding approximately 500 cm³ of water.3 Measure the mass W1 of the expanded particles. Next, immerse the expanded particles in the graduated cylinder using a wire mesh. Considering the volume of the wire mesh, measure the volume V1 [cm 3 of the expanded particles read from the rise in the water level, divide the mass W1 [g] of the expanded particles by V1 (W1 / V1), and convert the unit to [kg / m 3 to obtain the apparent density of the expanded particles.

[0030] The average bubble diameter of the expanded particles of the present invention is preferably 20 μm or more and 200 μm or less. The average bubble diameter of the expanded particles of the present invention is more preferably 30 μm or more, still more preferably 40 μm or more, and is more preferably 150 μm or less, still more preferably 100 μm or less. If the average bubble diameter of the expanded particles is within the above range, the in-mold formability is good, and the appearance of the molded body obtained using the expanded particles is good. Further, the outermost bubble diameter, which is the bubble diameter of the bubbles on the outermost surface side of the expanded particles, is preferably 30 to 150 μm, more preferably 50 to 130 μm. Also, the ratio of the outermost bubble diameter to the average bubble diameter is preferably 0.5 to 1.5, and preferably 0.7 to 1.3 from the viewpoint of formability. The average bubble diameter and the outermost bubble diameter of the polyamide resin expanded particles are measured by the method described later.

[0031] The polyamide resin expanded particles of the present invention preferably have a crystal structure in which, in the DSC curve obtained under the following condition 1, a melting peak (intrinsic peak) specific to the polyamide resin and a melting peak (high-temperature peak) having a peak temperature on the higher temperature side than the peak temperature of the intrinsic peak appear. (Condition 1) Based on the heat flux differential scanning calorimetry method of JIS K7121-1987, use the polyamide resin expanded particles as a test piece, heat and melt them from 30°C to a temperature 30°C higher than the end of the melting peak at a heating rate of 10°C / min, and measure the DSC curve.

[0032] Next, it will be described in more detail. The aforementioned DSC curve refers to the DSC curve obtained by heating the foamed particles using the measurement method described above (the DSC curve during the first heating). Furthermore, the melting peak (intrinsic peak) specific to the polyamide resin is the melting peak that appears due to the melting of the crystals normally present in the polyamide resin constituting the foamed particles. On the other hand, a melting peak (high-temperature peak) having a peak temperature higher than the intrinsic peak is a melting peak that appears higher than the intrinsic peak in the DSC curve during the first heating. When this high-temperature peak appears, it is presumed that secondary crystals are present in the resin. Note that when foamed particles are heated at a heating rate of 10°C / min from 30°C to a temperature 30°C higher than the end of the melting peak (first heating), then cooled at a cooling rate of 10°C / min from a temperature 30°C higher than the end of the melting peak to 23°C, and then heated again at a heating rate of 10°C / min from 23°C to a temperature 30°C higher than the end of the melting peak (second heating), the DSC curve obtained (DSC curve during the second heating) shows only the melting peak due to the melting of crystals normally present in the polyamide resin constituting the foamed particles. This intrinsic peak appears in both the DSC curve during the first heating and the DSC curve during the second heating, and the peak temperature may differ slightly between the first and second heating, but the difference is usually less than 5°C. This allows us to identify which peaks are eigenpeaks.

[0033] The heat of fusion of the high-temperature peak of the polyamide resin foam particles of the present invention is preferably 0.1 J / g or more and 20 J / g or less. By containing carbon nanotubes, the polyamide resin foam particles of the present invention can be molded in a wide range of molding pressures, even when the heat of fusion of the high-temperature peak is small or when the foam particles have a crystalline structure in which a high-temperature peak does not appear. If the heat of fusion of the high-temperature peak of the foam particles is within the above range, the moldability is further improved. The heat of fusion of the high-temperature peak of the polyamide resin foam particles of the present invention is more preferably 1 J / g or more, even more preferably 3 J / g or more, even more preferably 5 J / g or more, and more preferably 10 J / g or less, and even more preferably 7 J / g or less. The heat of fusion at the high-temperature peak can be determined using polyamide resin foam particles as a test specimen, based on the differential scanning calorimetry method of JIS K7121-1987. Specifically, it can be determined from the DSC curve (DSC curve for the first heating) obtained by heating the test specimen at a heating rate of 10°C / min from 30°C to a temperature 30°C higher than the end of the fusion peak. More specifically, it can be measured by the method described in the examples.

[0034] <Method for producing polyamide resin foamed particles> The polyamide resin foam particles of the present invention may be obtained by any method, but it is preferable to produce the polyamide resin foam particles by foaming resin particles containing carbon nanotubes using the polyamide resin as a base resin. A more preferable method for producing polyamide resin foam particles is to have the steps of kneading the polyamide resin and a masterbatch containing carbon nanotubes, granulating them to obtain resin particles, and foaming the resin particles. Examples of foaming methods for the foam particles of the present invention include extrusion foaming, gas impregnation pre-foaming, dispersion medium release foaming, or other foaming methods based on these methods and the principles of these methods. A more preferable method for producing polyamide resin foam particles is to have the steps of kneading the polyamide resin and a masterbatch containing carbon nanotubes, granulating them to obtain resin particles, and foaming the resin particles. A detailed explanation follows below.

[0035] (Resin particles using polyamide resin as a base resin and manufacturing method) The mass of a single resin particle is appropriately set according to the desired size of the foamed particle, apparent density, etc., but is preferably between 0.5 and 15.0 mg. Within this range, the apparent density can be increased. From this viewpoint, the lower limit of the mass of the resin particles is more preferably 1.0 mg, and even more preferably 1.5 mg. On the other hand, the upper limit is more preferably 10.0 mg, even more preferably 7.0 mg, and particularly preferably 5.0 mg.

[0036] The method for producing resin particles is not particularly limited and can be obtained by known methods. For example, resin particles can be obtained by kneading a polyamide resin and carbon nanotubes and granulating them, and it is preferable to obtain resin particles by kneading a polyamide resin and a masterbatch containing carbon nanotubes and granulating them. Specifically, a polyamide resin, carbon nanotubes or a carbon nanotube masterbatch, and optionally additives such as a foam regulator can be put into an extruder, kneaded to form a molten mixture, and the molten mixture can be cut to obtain resin particles of a predetermined mass. Methods for cutting a molten material to a predetermined mass include the strand-cut method, in which the molten mixture is extruded in a strand-like manner from a small hole in a die attached to the tip of an extruder and the extruded molten material is cut to a predetermined mass by a pelletizer; the hot-cut method, in which the molten mixture is cut immediately after being extruded into the gas phase; and the underwater-cut method (UWC method), in which the molten mixture is cut immediately after being extruded into water.

[0037] As described above, when manufacturing polyamide resin particles, it is preferable to first prepare a masterbatch in which carbon nanotubes are dispersed in a thermoplastic resin, and then put the polyamide resin, the masterbatch, and any additional additives as needed into an extruder. Using carbon nanotubes as the masterbatch makes it easier to uniformly disperse the carbon nanotubes in the polyamide resin particles.

[0038] The concentration of carbon nanotubes in the masterbatch is preferably 1 to 40% by mass, more preferably 5 to 30% by mass, and even more preferably 10 to 20% by mass. Furthermore, from the viewpoint of making it easier to disperse carbon nanotubes in the polyamide resin, the thermoplastic resin in the masterbatch is preferably one or more selected from polyamide resins and polyolefin resins, and more preferably one or more selected from polyamide resins and polypropylene resins.

[0039] (Example of a method for producing polyamide resin foam particles) The present invention provides a method for producing polyamide resin foam particles, which includes an "impregnation step" in which a foaming agent is impregnated into resin particles using the polyamide resin as a base resin, and a "foaming step" in which the resin particles using the polyamide resin as a base resin, which have been impregnated with the foaming agent, are foamed by heating, pressure changes, volume changes, etc.

[0040] (Foaming agent) In the method for producing foamed particles of the present invention, a physical blowing agent is preferably used as the blowing agent. Examples of physical blowing agents include organic physical blowing agents such as aliphatic hydrocarbons such as propane, butane, pentane, hexane, and heptane; alicyclic hydrocarbons such as cyclopentane and cyclohexane; halogenated hydrocarbons such as chlorofluoromethane, trifluoromethane, 1,1-difluoroethane, 1,1,1,2-tetrafluoroethane, methyl chloride, ethyl chloride, and methylene chloride; and dialkyl ethers such as dimethyl ether, diethyl ether, and methyl ethyl ether. Examples of inorganic physical blowing agents include carbon dioxide, nitrogen, helium, argon, and air. Among physical blowing agents, inorganic physical blowing agents are preferred from the viewpoint of having less impact on the environment, being non-flammable, and having excellent safety, with carbon dioxide or nitrogen being more preferred, and carbon dioxide being even more preferred.

[0041] (Example of manufacturing method) As for the method for producing the foamed particles of the present invention, there are no limitations as long as it has the "impregnation step" and the "foaming step" described above, but [1] a method in which resin particles are impregnated with a foaming agent, the resin particles impregnated with the foaming agent are removed without foaming, and then heated in a foaming device to obtain foamed particles, and [2] a method in which resin particles dispersed in a dispersion medium in a sealed device are impregnated with a foaming agent, the temperature is raised to near the softening temperature of the resin, and then the resin particles are released outside the device together with the dispersion medium under low pressure to obtain foamed particles, with method [2] being more preferred. A preferred manufacturing method, which is the method described in [2], is described below.

[0042] The manufacturing method for producing polyamide resin foam particles of the present invention preferably comprises the following steps. (1) A dispersion step in which resin particles, with a polyamide resin as the base resin, are dispersed in water in a sealed container to obtain a dispersion liquid, (2) An impregnation step of impregnating the resin particles in the dispersion with a physical foaming agent, (3) Holding step of holding the dispersion at a temperature of 90°C lower than the melting point (Tm) of the resin particles (Tm-90°C) or more but less than 50°C lower (Tm-50°C) for a holding time of 1 minute or more but 60 minutes or less. (4) A foaming process in which the temperature of the dispersion (Te) immediately before foaming is set to a temperature of 90°C lower (Tm-90°C) or more and 50°C lower (Tm-50°C) than the melting point (Tm) of the resin particles, and the resin particles containing the foaming agent are released from a sealed container together with water under a pressure lower than the pressure inside the sealed container to cause foaming. The manufacturing method for producing foamed particles of the present invention may include steps other than those described above, and other components may be added in the above steps. The impregnation step and the holding step may be performed simultaneously, or the holding step may be performed before the impregnation step.

[0043] [Dispersion process] The dispersion step is a step of dispersing the resin particles in water in a sealed container to obtain a dispersion liquid. The method for dispersing resin particles in water is not particularly limited, and known methods can be used. For example, a dispersion can be obtained by adding resin particles to water while stirring the water using a stirrer, and then stirring further. Furthermore, it is preferable to add dispersants such as inorganic substances like aluminum oxide, tricalcium phosphate, magnesium pyrophosphate, zinc oxide, kaolin, mica, talc, and smectite, and dispersing aids such as anionic surfactants like sodium dodecylbenzenesulfonate and sodium alkanesulfonate to the dispersion as needed. The mass ratio of resin particles to dispersant (resin particles / dispersant) is preferably 20 to 2000, and more preferably 30 to 1000. The mass ratio of dispersant to dispersing aid (dispersant / dispersing aid) is preferably 1 to 500, and more preferably 1 to 100.

[0044] [Impregnation process] The impregnation process involves impregnating resin particles in a dispersion with a foaming agent. Simultaneously, the resin particles can also be allowed to absorb water. While the method of impregnating the resin particles with the foaming agent is not particularly limited, it is preferable to disperse the resin particles in water within a pressurized, sealed container such as an autoclave and impregnate the resin particles with the foaming agent. Furthermore, from the viewpoint of ensuring sufficient impregnation of the resin particles with the foaming agent in a short time, it is preferable to impregnate the resin particles with the foaming agent using heat in addition to pressurization. The impregnation process, when pressurized, includes a step in which the pressure inside the sealed container rises from atmospheric pressure to the pressure at the time of impregnation (hereinafter also referred to as the impregnation pressure). Furthermore, the process of impregnating with a foaming agent includes a step of heating the dispersion, in which resin particles are dispersed in water, from room temperature to the impregnation temperature (hereinafter also referred to as the impregnation temperature).

[0045] The temperature during impregnation, which is carried out under heating, is preferably 50°C or higher, more preferably 80°C or higher, and preferably below the melting point (Tm(°C)) of the resin particles, more preferably below (Tm-20(°C)), from the viewpoint of sufficiently impregnating the resin particles with the foaming agent in a short time.

[0046] Furthermore, regarding the pressure during impregnation under pressure (hereinafter also referred to as impregnation pressure), from the viewpoint of sufficiently impregnating the resin particles with the foaming agent in a short time, it is preferable that the pressure inside the sealed container becomes 1.5 MPa(G) or higher, more preferably 2.5 MPa(G) or higher, and more preferably 7 MPa(G) or lower, and more preferably 5 MPa(G) or lower, by adding the foaming agent to the container containing the dispersion liquid. Note that "1.5MPa(G)" means a gauge pressure of 1.5 MPa.

[0047] The dispersion and impregnation processes also serve to allow the resin particles to absorb water. From the viewpoint of ensuring that the resin particles absorb sufficient water and become plasticized, the total time for the process of obtaining the dispersion and the process of impregnating with the foaming agent is preferably 20 minutes or more, and more preferably 30 minutes or more. On the other hand, from the viewpoint of the productivity of foamed particles, it is preferable that the above time be 60 minutes or less. Furthermore, the heating rate in the impregnation process is preferably 10°C / min or less, and more preferably 7°C / min or less, from the viewpoint of allowing the resin particles to absorb enough water and become plasticized. On the other hand, from the viewpoint of the productivity of foamed particles, the heating rate is preferably 1°C / min or more, and more preferably 2°C / min or more.

[0048] [Holding process] The holding process involves holding the dispersion at a temperature between 90°C (Tm-90°C) and 50°C (Tm-50°C) below the melting point (Tm) of the resin particles for a holding time of 1 minute to 60 minutes. The holding temperature of the dispersion during the holding process is, from the viewpoint of allowing the polyamide resin to absorb enough water and plasticize, and from the viewpoint of uniformly impregnating the polyamide resin with the foaming agent, at least 90°C lower than the melting point (Tm) of the resin particles (Tm-90°C), preferably at least 80°C lower (Tm-80°C), more preferably at least 70°C lower (Tm-70°C), even more preferably at least 65°C lower (Tm-65°C), and less than 50°C lower (Tm-50°C), preferably at least 55°C lower (Tm-55°C), more preferably at least 57°C lower (Tm-57°C), and even more preferably at least 59°C lower (Tm-59°C).

[0049] Normally, when manufacturing foamed particles using general-purpose resins such as polypropylene resins as the base resin, the particles are held near the melting point of the raw material resin. However, in the method for manufacturing polyamide resin foamed particles of the present invention, the particles are manufactured by holding them at a temperature of 90°C lower (Tm-90°C) or higher and 50°C lower (Tm-50°C) than the melting point (Tm) of the resin particles. This is thought to be because, since polyamide resins are hygroscopic, the resin particles are plasticized by the water used as the dispersion liquid, significantly lowering the melting point. As a result, it becomes possible to manufacture foamed particles with the desired apparent density and closed-cell ratio at a temperature significantly lower than the melting point of the resin particles.

[0050] The holding time in the holding step is 1 minute or more, preferably 5 minutes or more, more preferably 10 minutes or more, and even more preferably 13 minutes or more, from the viewpoint of uniformly impregnating the polyamide resin with the foaming agent and obtaining foamed particles with a high closed-cell ratio. Furthermore, from the viewpoint of productivity of foamed particles and from the viewpoint of preventing hydrolysis of the polyamide resin, the holding time in the holding step is 60 minutes or less, preferably 40 minutes or less, more preferably 30 minutes or less, even more preferably 20 minutes or less, and even more preferably 18 minutes or less. By holding for the above time, it is possible to obtain polyamide resin foamed particles with low apparent density and a high closed-cell ratio. The holding step can be set in multiple stages within the above temperature range, or the temperature can be slowly raised over a sufficient period of time within the temperature range. From the viewpoint of easy manufacturing, it is preferable to set it in one stage (constant holding temperature) within the above temperature range and hold for the above time.

[0051] The holding process is preferably carried out under pressure, from the viewpoint of uniformly impregnating the polyamide resin with the foaming agent, and it is preferable to maintain the same pressure as the impregnation pressure. The pressure inside the container containing the dispersion is preferably 1.5 MPa(G) or higher, and more preferably 2.5 MPa(G) or higher. Furthermore, the pressure inside the container containing the dispersion is preferably 7 MPa(G) or lower, and more preferably 5 MPa(G) or lower.

[0052] [Foaming process] The foaming process is the process of foaming resin particles that have been impregnated with a foaming agent. The foaming method for resin particles is not particularly limited, but a preferred foaming method involves releasing the resin particles impregnated with the foaming agent along with water into a pressure atmosphere lower than the pressure used in the holding step (usually atmospheric pressure) to cause foaming, following the holding step.

[0053] The temperature Te of the dispersion immediately before foaming (hereinafter also referred to as the foaming temperature) is, from the viewpoint of obtaining foamed particles with low apparent density and a high percentage of closed cells, at least 90°C lower than the melting point (Tm) of the resin particles (Tm-90°C), preferably at least 80°C lower (Tm-80°C), more preferably at least 70°C lower (Tm-70°C), and even more preferably at least 65°C lower (Tm-65°C), and less than 50°C lower than the melting point (Tm) of the resin particles (Tm) (Tm-50°C), preferably at least 55°C lower (Tm-55°C), more preferably at least 57°C lower (Tm-57°C), and even more preferably at least 59°C lower (Tm-59°C).

[0054] The pressure immediately before release in the foaming process (foaming pressure) is preferably 0.5 MPa(G) or higher, more preferably 1.5 MPa(G) or higher, even more preferably 2.5 MPa(G) or higher, and preferably 10 MPa(G) or lower, more preferably 7 MPa(G) or lower, and even more preferably 5 MPa(G) or lower.

[0055] [Polyamide resin foam particle molded product] The polyamide resin foam particle molded article of the present invention is a polyamide resin foam particle molded article obtained by in-mold molding the polyamide resin foam particles. In other words, the polyamide resin foam particle molded article of the present invention is a polyamide resin foam particle molded article obtained by in-mold molding the polyamide resin foam particles of the present invention. The polyamide resin foam particles of the present invention exhibit excellent in-moldability, and good polyamide resin foam particle molded articles can be obtained over a wide range of molding pressures. As a result, the resulting foam particle molded articles have good strength and appearance. The foam particle molded articles obtained by in-mold molding the foam particles of the present invention can suppress post-molding shrinkage, making it suitable for obtaining thick molded articles. The thickness of the foam particle molded article is preferably 30 mm or more, and more preferably 40 mm or more. While conventionally known methods can be used for in-mold molding, it is preferable to use heating with steam. The steam causes the polyamide resin in the foamed particles to absorb water and plasticize, making it possible to lower the molding pressure. Furthermore, by drying the resulting molded body to remove moisture, the polyamide resin returns to its original properties, resulting in a molded body with high heat resistance.

[0056] The foamed particles of the present invention exhibit excellent in-moldability. Specifically, they exhibit excellent secondary foaming during in-mold molding to obtain a molded product. Furthermore, the water cooling time can be shortened, and as a result, the overall molding time can be reduced. The water cooling time for a foam particle molded body is determined as follows. First, the obtained foam particles are filled into a mold, and in-mold molding is performed by steam heating to obtain a plate-shaped foam particle molded body. The heating method involves opening the drain valves on both sides of the mold and supplying steam for 5 seconds to perform preheating (exhaust process). Then, steam is supplied from the moving side of the mold, followed by steam from the stationary side of the mold, and the body is heated to the molding heating steam pressure (molding pressure = molding vapor pressure). After heating is complete, the pressure is released, and the body is water-cooled until the surface pressure due to the foaming force of the molded body drops to 0.02 MPa (gauge pressure). Then the mold is opened and the molded body is removed from the mold. The water cooling time for the foam particle molded body is defined as the water cooling time (seconds) required from the start of water cooling until the surface pressure reaches 0.02 MPa (gauge pressure).

[0057] The density of a polyamide resin foam particle molded article obtained using the polyamide resin foam particles of the present invention is preferably 10 kg / m³. 3 More than 250kg / m 3 The following applies: The density of the polyamide resin foam particle molded article obtained using the polyamide resin foam particles of the present invention is more preferably 20 kg / m³. 3 More preferably 40 kg / m 3 That is all, and more preferably 200 kg / m 3 More preferably, 100 kg / m 3 The following applies. The density of the polyamide resin foam particle molded product is measured by the following method. A polyamide resin foam particle molded body is left for 2 days under the conditions of 50% relative humidity, 23°C, and 1 atm, and its mass (W [g]) is measured. Next, the volume V [cm³] of the foam particle molded body is calculated based on its dimensions. 3 Measure the mass W [g] of the foamed particle molded body by the volume V (W / V), and convert the unit to [kg / m³]. 3 By converting to [ ], the density of the foamed particle molded body can be determined. [Examples]

[0058] The present invention will be described in detail below with reference to examples, but the present invention is not limited thereto.

[0059] The various physical properties of the raw materials, foamed particles, and molded foamed particle products in each example were measured by the following method.

[0060] [Measurement method] [Melting point of polyamide resins] The melting point of polyamide resins was measured using differential scanning calorimetry (DSC) based on JIS K7121-1987. Under conditions of a nitrogen inflow of 30 mL / min, the resin was heated and melted from 30°C to a temperature 30°C higher than the end of the melting peak at a heating rate of 10°C / min (first heating), then maintained at that temperature for 10 minutes, cooled to 30°C at a cooling rate of 10°C / min, and then heated again to a temperature 30°C higher than the end of the melting peak at a heating rate of 10°C / min. The melting point was determined as the peak temperature of the melting peak in the second DSC curve obtained. A high-sensitivity differential scanning calorimetry instrument, "EXSTAR DSC7020" (manufactured by SII Nanotechnology Co., Ltd.), was used as the measuring device. Furthermore, the resin particles and foamed particles used as test specimens were stored in a desiccator under a nitrogen atmosphere to prevent hydrolysis, avoiding high temperature and high humidity conditions. After that, they were vacuum-suctioned and stored for 24 hours with a moisture content of 1000 ppm by mass or less before being used for melting point measurement.

[0061] [Density of polyamide resins] The results were obtained based on the method described in ISO 1183-3.

[0062] [Flexural modulus of polyamide resin (MPa)] The flexural modulus of polyamide resin was determined by measurement in accordance with JIS K7171:2016. A resin test specimen with a thickness of 4 mm, a width of 10 mm, and a length of 80 mm was prepared. The test specimen was left standing for 72 hours at room temperature (23°C) and humidity (50%). The flexural modulus was then measured using an Autograph AGS-10kNG (Shimadzu Corporation) testing machine under the following conditions: a support distance of 64 mm, an indenter radius of R15.0 mm, a support base radius of R25.0 mm, a test speed of 2 mm / min, room temperature (23°C), and humidity (50%). The average value of the calculated values ​​(5 points) was adopted.

[0063] [Percentage of closed cells in foamed particles] The true volume Vx of the foamed particles (the sum of the volume of the resin constituting the foamed particles and the total volume of the closed-cell portions within the foamed particles) was measured according to procedure C described in ASTM-D2856-70. A Toshiba Beckmann 930 air-comparison hydrometer was used to measure this true volume Vx. Next, the closed-cell ratio was calculated using the following formula (1), and the arithmetic mean of the five measurement results was obtained. Closed cell ratio (%)=(Vx-W / ρ)×100 / (Va-W / ρ) (1) Vx: True volume of foam particles measured by the above method (cm³) 3 ) Va: Apparent volume of foam particles (cm³) 3 ) W: Mass (g) of the sample used for measuring foam particles ρ: Density of the resin constituting the foam particles (g / cm³) 3 )

[0064] [Apparent density of foamed particles] A graduated cylinder filled with water at 23°C was prepared and left for two days under the conditions of 50% relative humidity, 23°C, and 1 atm, yielding approximately 500 cm³ of water. 3 The mass W1 of the foam particles was measured. Next, the foam particles were submerged in the graduated cylinder using a wire mesh. The volume V1 of the foam particles was read from the rise in water level, taking into account the volume of the wire mesh. 3Measure the volume [kg / m³] and divide the mass W1 [g] of the foam particles by the volume V1 (W1 / V1), and convert the unit to [kg / m³]. 3 The apparent density of the foamed particles was determined by converting to [a specific value].

[0065] [Average bubble diameter and outermost bubble diameter of foamed particles] First, the foam particle was divided approximately in half, passing through its center, and the cross-section was photographed using a scanning electron microscope. Next, in the resulting cross-sectional photograph, straight lines were drawn at equal intervals in eight directions from near the center of the foam particle's cross-section, and the number of bubbles intersecting these lines was counted. The total length of these lines was divided by the number of counted bubbles to obtain the value, which was defined as the bubble diameter of the foam particle. This procedure was repeated for 10 foam particles, and the arithmetic mean of the bubble diameters for each foam particle was defined as the average bubble diameter of the foam particle. Furthermore, the outermost bubble diameter of the foamed particle was determined by calculating the maximum length of the bubble at the outermost surface when a perpendicular line is drawn from the surface of the foamed particle in the cross-sectional photograph obtained in the same manner. This measurement was performed at 10 or more bubbles, and the average value was taken as the outermost bubble diameter.

[0066] [Heat of fusion (ΔH2) of the high-temperature peak of foamed particles] Using foamed particles as test specimens, the temperature and heat of fusion at the peaks of each melting peak were determined from the melting peaks obtained in the first DSC curve, which was measured by heating at a rate of 10°C / min from 30°C to a temperature 30°C higher than the end of the melting peak. A high-sensitivity differential scanning calorimeter "EXSTAR DSC7020" (manufactured by SII Nanotechnology Co., Ltd.) was used as the measurement device. The following explanation uses Figure 1 (first DSC curve). In the first DSC curve shown in Figure 1, there are two melting peaks; the lower temperature peak is the melting peak (a) specific to polyamide resins, and the higher temperature peak is the high-temperature peak (melting peak (b)). The heat of fusion of the high-temperature peak of the foamed particles corresponds to the area of ​​the high-temperature peak b that appears at a higher temperature than the intrinsic peak a in the DSC curve shown in Figure 1, and was determined as follows. First, as shown in Figure 1, a straight line was drawn connecting point I at 150°C on the DSC curve and point II, which indicates the melting termination temperature on the DSC curve. Next, point IV was defined as the intersection of a straight line perpendicular to the temperature on the horizontal axis of the graph, passing through point III on the DSC curve, which is in the valley between the intrinsic peak a and the high-temperature peak b, and the straight line connecting point I and point II. The area enclosed by the straight line connecting point IV and point II, the straight line connecting point III and point IV, and the DSC curve connecting point III and point II (shaded area) was defined as the heat of fusion of the high-temperature peak (J / g).

[0067] [Moldable range of foamed particles] Using the method described later in "[Manufacturing of Polyamide Resin Foam Particle Molded Articles]", foam particle molded articles were formed by varying the molding pressure (molding steam pressure) in increments of 0.02 MPa between 0.10 and 0.24 MPa (G). The in-moldability of the obtained molded articles was evaluated for the following items: fusion properties, surface appearance (degree of voids), and recovery properties (recovery of expansion or contraction after in-mold molding). Articles that met the criteria shown below were considered acceptable, and the steam pressure at which all items were accepted was defined as the steam pressure at which molding was possible. Note that pressures marked with (G) are gauge pressures, i.e., pressure values ​​relative to atmospheric pressure. Furthermore, the difference between the upper and lower limits of the moldable steam pressure (upper limit - lower limit) was calculated and defined as the moldable range. A wider range from the lower limit to the upper limit of the moldable steam pressure, that is, a larger difference between the upper and lower limits of the moldable steam pressure, indicates a wider moldable range and is therefore preferable. (Fusibility) The foam particle molded body was bent and fractured, and the number of foam particles present on the fracture surface (C1) and the number of fractured foam particles (C2) were determined. The ratio of the number of fractured foam particles to the number of foam particles (C2 / C1 × 100) was calculated as the material fracture rate. The above measurement was performed five times using different test pieces, and the material fracture rate for each was determined. A material fracture rate of 80% or higher obtained by arithmetic mean was considered a pass, and a rate below 80% was considered a fail. (Surface appearance) A 100mm x 100mm square was drawn in the center of the foam particle molded body, and a line was drawn diagonally from one corner of the square. The number of voids (gaps) of 1mm x 1mm or larger along this line was counted. A product was deemed acceptable if the number of voids was less than 5 and the surface was smooth; otherwise, it was deemed unacceptable. (Recoverability) For a flat foam particle molded body measuring 250 mm in length, 200 mm in width, and 50 mm in thickness, obtained by in-mold molding, the thickness was measured near the four corners (10 mm inward from the corners towards the center) and at the center (the intersection of the line that bisects the molded body vertically and the line that bisects it horizontally). Next, the ratio (%) of the thickness at the center to the thickness at the thickest point near the four corners was calculated. A ratio of 95% or higher was considered a pass, and a ratio below 95% was considered a fail.

[0068] [Molded object density] The foamed particle molded body was left for 2 days under conditions of 50% relative humidity, 23°C, and 1 atm. Next, its mass was measured and defined as W [g]. Next, based on the dimensions of the foamed particle molded body, the volume V [cm³] of the foamed particle molded body is calculated. 3 ] was measured. The mass W [g] of the foamed particle molded body is divided by the volume V (W / V), and the unit is [kg / m³]. 3 The density of the foamed particle molded body was determined by converting it to [ ].

[0069] [Surface smoothness] (Evaluation of surface smoothness of foamed particle molded products) The surface smoothness of the foam particle molded body was evaluated according to the following criteria: The more the gaps between the foam particles on the surface of the molded body are filled, the better the surface quality. Specifically, a 100mm x 100mm square was drawn in the center of the foam particle molded body, and the number of indentations with a depth of 1mm or more in that area was measured. ◎: 2 or less 〇: 3~9 pieces ×: 10 or more

[0070] Examples 1-12 [Manufacturing of polyamide resin particles] Polyamide resin "6434B" (manufactured by Ube Industries, Ltd.) was supplied to the extruder, and carbon nanotube masterbatches (MB1-MB4) shown in Tables 2 and 3 were supplied in amounts corresponding to those in Tables 2 and 3, respectively. Talc "Talcan Powder PK-S" (manufactured by Hayashi Chemical Co., Ltd.) was supplied at 0.3% by mass as a foam regulator, and "Stabaxol P" (manufactured by Rhein Chemie) was supplied as a chelating agent at 1 part by mass per 100 parts by mass of polyamide resin. The mixture was then melt-kneaded. The melt-kneaded mixture was extruded as a single-layer strand with a circular cross-section through the pores of a die attached to the tip of the extruder. After the extruded strand was water-cooled, it was cut in a pelletizer to a mass of approximately 2.0 mg per strand, and dried to obtain polyamide resin particles. The polyamide resin "6434B" is a polyamide 6 / 66 / 12 copolymer (nylon 6 / 66 / 12), with a melting point (Tm0) of 186°C and a density of 1.12 g / cm³. 3 The flexural modulus is 1070 MPa, and the product name is UBE Nylon 6434B. Table 1 shows the details of the carbon nanotube masterbatches (MB1-4) shown in Tables 2 and 3.

[0071] [Table 1]

[0072] The carbon nanotubes shown in Table 1 are all commercially available. In Table 1, the masterbatch resin types are as follows: "6434B" refers to the polyamide resin "6434B," and "FX4ET" refers to a polypropylene resin (propylene-1-butene-ethylene copolymer) with a melting point of 131°C and a density of 900 g / cm³. 3 It has a flexural modulus of 650 MPa and is manufactured by Nippon Polypropylene Co., Ltd. as "FX4ET". Furthermore, the end-capping agent is "Stabaxol P" (manufactured by Rhein Chemie), and the amount of end-capping agent is the amount of end-capping agent (mass %) relative to the resin used in the masterbatch.

[0073] [Manufacturing of polyamide resin foam particles] 500 g of the obtained polyamide resin particles and 3.5 liters of water as a dispersion medium were placed in a 5-liter autoclave equipped with a stirrer. Furthermore, 0.3 parts by mass of kaolin as a dispersant and 0.004 parts by mass of alkylbenzene sulfonate as a surfactant were added per 100 parts by mass of polyamide resin particles. While stirring the contents of the autoclave, the temperature was raised from room temperature (23°C) to the impregnation temperature (131°C), and carbon dioxide was injected into the autoclave as a foaming agent until the pressure inside the autoclave reached the impregnation pressure (4.0 MPa (G)). At this time, the heating time from room temperature (23°C) to the impregnation temperature (131°C) was 40 minutes. Next, it was maintained at 131°C and 4.0 MPa (G) for 15 minutes. Subsequently, polyamide resin particles impregnated with a foaming agent were released together with a dispersion medium under atmospheric pressure (0.1 MPa). The foaming temperature (temperature of the dispersion immediately before foaming) was 131°C. The resulting polyamide resin foam particles were cured in a 60°C oven for 24 hours, and then slowly cooled to obtain polyamide resin foam particles. The obtained polyamide resin foam particles were evaluated as described above. The results are shown in Tables 2 and 3.

[0074] [Manufacturing of polyamide resin foam particle molded products] Next, a molded polyamide resin foam particle body was prepared using polyamide resin foam particles. After clamping the mold, the obtained polyamide resin foam particles were filled into a flat mold measuring 200 mm in length, 65 mm in width, and 40 mm in thickness, and in-mold molding was performed by steam heating to obtain a plate-shaped polyamide resin foam particle molded body. The heating method involved preheating (exhaust process) by supplying steam for 5 seconds with the drain valves of both molds open, then supplying steam from the movable mold with the drain valve on the fixed side open, and then supplying steam from the fixed mold with the drain valve on the movable side open, after which the exhaust valve was closed and the mold was heated to a molding heating steam pressure of 0.12 MPa (G; gauge pressure). After heating was complete, the pressure was released, and the molded body was cooled with water until the surface pressure, which is the pressing force on the mold surface due to the foaming force of the molded body, decreased to 0.02 MPa (G). Then the mold was opened and the molded body was removed from the mold. After that, it was left to stand in an 80°C oven for 24 hours and removed to obtain a polyamide resin foam particle molded body. The obtained polyamide resin foam particle molded articles were evaluated as described above. The results are shown in Tables 2 and 3.

[0075] Comparative Examples 1-3 In Example 1, [Production of Polyamide Resin Particles], polyamide resin particles, polyamide resin foam particles, and polyamide resin foam particle molded articles were obtained in the same manner as in Example 1, except that a carbon black masterbatch shown in Table 4 was used in the amount shown in Table 4 instead of the carbon nanotube masterbatch. The obtained polyamide resin foam particles and polyamide resin foam particle molded articles were evaluated as described above. The results are shown in Table 4.

[0076] Comparative Example 4 In Example 1, polyamide resin particles, polyamide resin foam particles, and polyamide resin foam particle molded articles were obtained in the same manner as in Example 1, except that a carbon nanotube masterbatch was not used in the [production of polyamide resin particles]. The obtained polyamide resin foam particles and polyamide resin foam particle molded articles were evaluated as described above. The results are shown in Table 4.

[0077] Comparative Example 5 In Example 1, [Production of Polyamide Resin Particles], polyamide resin particles and polyamide resin foamed particles were obtained in the same manner as in Example 1, except that the high-temperature peak heat value of the foamed particles was set to 0 J / g. The obtained polyamide resin foamed particles had a closed-cell ratio of 58% and an apparent density of 178 kg / m³. 3 The foamed particles had an average bubble diameter of 150 μm and an outermost bubble diameter of 180 μm. These foamed particles had poor moldability, and even when molded, it was difficult to form a molded shape.

[0078] [Table 2]

[0079] [Table 3]

[0080] [Table 4]

[0081] The results shown in Tables 2 and 3 indicate that the polyamide resin foam particles obtained in the examples have a wide molding range and can be molded at a wide range of molding pressures. Thus, the polyamide resin foam particles of the present invention exhibit excellent in-moldability and enable the production of good polyamide resin foam particle molded articles at a wide range of molding pressures.

[0082] Based on the above description in this specification, the present invention may employ the following configurations [1] to [6]. [1] Polyamide resin foam particles having a polyamide resin as the base resin, wherein the foam particles contain carbon nanotubes and the closed-cell ratio of the foam particles is 70% or more. [2] Polyamide resin foam particles according to [1] above, wherein the average diameter of the carbon nanotubes is 5 to 25 nm and the average length of the carbon nanotubes is 0.2 to 50 μm. [3] Polyamide resin foam particles according to [1] or [2] above, wherein the aspect ratio of the carbon nanotubes is 20 to 1000. [4] Polyamide resin foam particles according to any one of [1] to [3] above, wherein the carbon nanotube content is 0.1 parts by mass or more and 3 parts by mass or less per 100 parts by mass of the base resin. [5] The apparent density of the foamed particles is 50 to 500 kg / m³ 3 Polyamide resin foam particles as described in any of the above [1] to [4]. [6] A molded polyamide resin foam particle body obtained by in-mold molding polyamide resin foam particles as described in any of [1] to [5] above.

Claims

1. Polyamide resin foam particles, which use a polyamide resin as the base resin, The foamed particles contain carbon nanotubes, Polyamide resin foamed particles having a closed-cell ratio of 70% or more.

2. The polyamide resin foam particles according to claim 1, wherein the average diameter of the carbon nanotubes is 5 to 25 nm and the average length of the carbon nanotubes is 0.2 to 50 μm.

3. The polyamide resin foam particles according to claim 1 or 2, wherein the aspect ratio of the carbon nanotubes is 20 to 1000.

4. The polyamide resin foam particles according to claim 1 or 2, wherein the carbon nanotube content is 0.1 parts by mass or more and 3 parts by mass or less per 100 parts by mass of the base resin.

5. The apparent density of the foamed particles is 50 to 500 kg / m³. 3 Polyamide resin foam particles according to claim 1 or 2.

6. A molded polyamide resin foam particle body obtained by in-mold molding the polyamide resin foam particles described in claim 1 or 2.

Images