Polyamide resin foam particles

Abstract

To provide polyamide resin foamed particles capable of shortening the molding cycle during in-mold molding.SOLUTION: There are provided polyamide resin foamed particles having a mixed resin of a polyamide resin A and a polyamide resin B as a base resin, wherein the polyamide resin A is an aliphatic polyamide, the polyamide resin B is a xylylene group-containing polyamide resin and the mass ratio (polyamide resin A:polyamide resin B) between the polyamide resin A and the polyamide resin B is 97:3 to 60:40.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to polyamide resin foam particles. [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.

[0003] For example, Patent Document 1 discloses a polyamide resin foam molded article comprising a polyamide resin, wherein, when calculated based on the peak having the narrowest peak width in the X-ray diffraction profile, the crystallite size D is greater than or equal to a specific value and the degree of crystallinity X is within a specific range, and it is stated that a polyamide resin foam molded article with excellent heat resistance and sound insulation can be industrially provided. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] International Publication No. 2016 / 147582 [Overview of the project] [Problems that the invention aims to solve]

[0005] Due to their high softening temperature, polyamide resins tend to require higher molding pressure during in-mold foaming compared to polystyrene resins. This results in higher molding costs and longer molding cycles.

[0006] Patent Document 1 did not examine the molding cycle of polyamide resin foam molded articles, and there was room for improvement in shortening the molding cycle of polyamide resin foam molded articles.

[0007] The problem that this invention aims to solve is to provide polyamide resin foam particles that can shorten the molding cycle during in-mold molding. [Means for solving the problem]

[0008] The inventors have found that polyamide resin foam particles can solve the above-mentioned problems. In other words, the present invention is as follows: <1> Polyamide resin foam particles having a mixed resin of polyamide resin A and polyamide resin B as the base resin, wherein polyamide resin A is an aliphatic polyamide, polyamide resin B is a xylylene group-containing polyamide resin, and the mass ratio of polyamide resin A to polyamide resin B (polyamide resin A:polyamide resin B) is 97:3 to 60:40. <2> The melt flow rate of the aforementioned polyamide resin B at 275°C and a load of 0.325 kg is 5 g / 10 min or less. <1> Polyamide resin foam particles as described above. <3> The foamed particles contain carbon black, <1> or <2> Polyamide resin foam particles as described above. <4> The melting point (TmA) of the polyamide resin A is greater than 180°C and less than or equal to 250°C. <1> ~ <3> Polyamide resin foam particles as described in any one of the following. <5> The difference (TmB-TmA) between the melting point (TmA) of the polyamide resin A and the melting point (TmB) of the polyamide resin B is 30°C or more and 100°C or less. <1> ~ <4> Polyamide resin foam particles as described in any one of the following. <6> The apparent density of the foamed particles is 10 kg / m³ 3 More than 300kg / m 3 The following is: <1> ~ <5> Polyamide resin foam particles as described in any one of the following. <7> The closed-cell ratio of the foamed particles is 70% or more. <1> ~ <6> Polyamide resin foam particles as described in any one of the following. <8> A polyamide resin foam particle molded in a mold according to any one of <1> to <7>, and a polyamide resin foam particle molded body.

Advantages of the Invention

[0009] According to the present invention, a polyamide resin foam particle capable of shortening the molding cycle during in-mold molding can be provided.

Brief Description of the Drawings

[0010] [[ID=十四]] [Figure 1] It is a diagram illustrating the first DSC curve of polyamide resin foam particles.

Embodiments for Carrying Out the Invention

[0011] [Foam Particles] The polyamide resin foam particles of the present invention (hereinafter, also simply referred to as "polyamide resin foam particles" or "foam particles") are polyamide resin foam particles having a mixed resin of polyamide resin A and polyamide resin B as a base resin, wherein the polyamide resin A is an aliphatic polyamide, the polyamide resin B is a polyamide resin containing a xylylene group, and the mass ratio of the polyamide resin A to the polyamide resin B (polyamide resin A: polyamide resin B) is 97:3 to 60:40.

[0012] <Base Resin> (Polyamide Resin A) The polyamide resin A constituting the mixed resin serving as the base resin of the polyamide resin foam particles of the present invention is an aliphatic polyamide. Examples of the aliphatic polyamide include aliphatic homopolyamides, aliphatic polyamide copolymers, and mixtures thereof. The polyamide copolymer means a copolymer having two or more repeating units and having an amide bond in at least a part of each repeating unit. Examples of aliphatic homopolyamides include poly(6-aminohexanoic acid) (polycaproamide, nylon 6), also known as poly(caprolactam), poly(laurolactam) (nylon 12), poly(hexamethyleneadipamide) (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), and poly(11 Examples include -amino undecanoic acid) (nylon 11), poly(hexamethylene sebakamid) (nylon 610), poly(decamethylene sebakamid) (nylon 1010), poly(hexamethylene azeramide) (nylon 69), poly(tetramethylene adipamide) (nylon 46), poly(tetramethylene sebakamid) (nylon 410), poly(pentamethylene adipamide) (nylon 56), and poly(pentamethylene sebakamid) (nylon 510). Examples of aliphatic polyamide copolymers include polycaproamide / polyhexamethylene adipamide copolymer (nylon 6 / 66), caprolactam / hexamethylenediaminoadipic acid / lauryl lactam (nylon 6 / 66 / 12), and caprolactam / lauryl lactam copolymer (nylon 6 / 12). Polyamide resin A may be used alone, in combination of two or more types, or as a mixture of aliphatic homopolyamide and aliphatic polyamide copolymer. Among these, polyamide resin A is preferably one or more selected from the group consisting of nylon 6, nylon 66, nylon 6 / 66, and nylon 6 / 66 / 12, and more preferably one or more selected from the group consisting of nylon 6 / 66 and nylon 6 / 66 / 12.

[0013] The polyamide copolymer may be a block copolymer in which a certain amount of the same repeating amide unit is followed by a certain amount of a different type of amide, or a random copolymer in which different types of amides are repeated randomly, but a random copolymer is preferred. If the polyamide copolymer is a random copolymer, it becomes possible to mold the foamed particles at a relatively low molding pressure when molding them in a mold.

[0014] The polyamide resin A 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 the foamed particles, making it easier to obtain foamed particles that can withstand in-mold molding, and improving the durability of the polyamide resin foamed particle molded article (hereinafter also simply referred to as "foamed particle molded article" or "molded article"). 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, the end-capping agent is preferably a carbodiimide compound. Examples of carbodiimide compounds 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. The amount of end-capsulating agent blended is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and preferably 5% by mass or less, more preferably 3% by mass, in the base resin. Thus, the polyamide resin A is preferably a polyamide resin whose ends are sealed with one or more end-sealing agents selected from the group consisting of carbodiimide compounds, epoxy compounds, and isocyanate compounds, more preferably a polyamide resin whose ends are sealed with a carbodiimide compound, and even more preferably a polyamide resin whose ends are sealed with an aromatic polycarbodiimide.

[0015] (Polyamide resin B) Polyamide resin B is a xylylene group-containing polyamide resin. The xylylene group-containing polyamide resin is a polymer obtained by polycondensation of a diamine containing xylylenediamine and a dicarboxylic acid, and has constituent units derived from xylylenediamine and constituent units derived from the dicarboxylic acid. The xylylene group-containing polyamide resin preferably contains 50 mol% or more of the constituent units derived from xylylenediamine among the constituent units derived from the diamine (diamine units), more preferably 70 mol% or more, even more preferably 80 mol% or more, even more preferably 90 mol% or more, and may contain 100 mol%. The xylylenediamine preferably contains at least one of metaxylylenediamine and paraxylylenediamine, and more preferably contains metaxylylenediamine. The diamine units constituting the xylylene group-containing polyamide resin preferably contain 50 mol% or more, more preferably 70 mol% or more, even more preferably 80 mol% or more, even more preferably 90 mol% or more, and may also contain 100 mol%.

[0016] The diamine units in the xylylene group-containing polyamide resin may consist solely of constituent units derived from xylylenediamine, but may also contain constituent units derived from diamines other than xylylenediamine. Examples of diamines other than xylylenediamine include aliphatic diamines having a linear or branched structure such as ethylenediamine, tetramethylenediamine, pentamethylenediamine, 2-methylpentanediamine, hexamethylenediamine, heptamethylenediamine, octamethylenediamine, nonamethylenediamine, decamethylenediamine, dodecamethylenediamine, 2,2,4-trimethyl-hexamethylenediamine, and 2,4,4-trimethyl-hexamethylenediamine; and 1,3-bis(aminomethyl)cycline diamine. Examples include alicyclic diamines such as oxahexane, 1,4-bis(aminomethyl)cyclohexane, 1,3-diaminocyclohexane, 1,4-diaminocyclohexane, bis(4-aminocyclohexyl)methane, 2,2-bis(4-aminocyclohexyl)propane, bis(aminomethyl)decalin, and bis(aminomethyl)tricyclodecane; and aromatic ring-containing diamines such as bis(4-aminophenyl) ether, paraphenylenediamine, metaphenylenediamine, and bis(aminomethyl)naphthalene.

[0017] In xylylene group-containing polyamide resins, compounds that can constitute a dicarboxylic acid unit include α,ω-linear aliphatic dicarboxylic acids having 4 to 20 carbon atoms, such as succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanediic acid, and dodecanediic acid; alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid; other aliphatic dicarboxylic acids such as dimer acids; and aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, orthophthalic acid, xylylenedicarboxylic acid, and naphthalenedicarboxylic acid. Among these, the compounds that can constitute a dicarboxylic acid unit are preferably α,ω-linear aliphatic dicarboxylic acids having 4 to 20 carbon atoms, more preferably one or more selected from the group consisting of adipic acid and sebacic acid, and even more preferably adipic acid. The xylylene group-containing polyamide resin preferably contains 50 mol% or more of adipic acid-derived structural units (dicarboxylic acid units) among the structural units derived from dicarboxylic acids, more preferably 70 mol% or more, even more preferably 80 mol% or more, even more preferably 90 mol% or more, and may also contain 100 mol%.

[0018] In other words, polyamide resin B preferably has a constituent unit derived from a diamine containing 50 mol% or more of constituent units derived from metaxylylenediamine and a constituent unit derived from a dicarboxylic acid containing 50 mol% or more of constituent units derived from adipic acid; more preferably has a constituent unit derived from a diamine containing 80 mol% or more of constituent units derived from metaxylylenediamine and a constituent unit derived from a dicarboxylic acid containing 80 mol% or more of constituent units derived from adipic acid; even more preferably has a constituent unit derived from a diamine containing 90 mol% or more of constituent units derived from metaxylylenediamine and a constituent unit derived from a dicarboxylic acid containing 90 mol% or more of constituent units derived from adipic acid; and may also have a constituent unit derived from a diamine containing 100 mol% of constituent units derived from metaxylylenediamine and a constituent unit derived from a dicarboxylic acid containing 100 mol% of constituent units derived from adipic acid. As for the remaining diamine units after removing metaxylylenediamine, constituent units derived from paraxylylenediamine are preferred. The remaining dicarboxylic acid units, excluding adipic acid, are preferably derived from α,ω-linear aliphatic dicarboxylic acids having 4 to 20 carbon atoms.

[0019] In addition to the diamines and dicarboxylic acids mentioned above, other components that do not impair the effects of the present invention, such as lactams like ε-caprolactam and laurolactam, aliphatic aminocarboxylic acids like aminocaproic acid and aminoundecanoic acid, and aromatic aminocarboxylic acids like p-aminomethylbenzoic acid, can also be used as copolymer components for the xylylene group-containing polyamide resin, to the extent that they do not impair the effects of the present invention.

[0020] ≪Meltflow Rate (MFR)≫ The melt flow rate (MFR) of polyamide resin B at 275°C and a load of 0.325 kg is preferably 10 g / 10 min or less, more preferably 8 g / 10 min or less, and even more preferably 5 g / 10 min or less, from the viewpoint of shortening the molding cycle, and the lower limit is not particularly limited, but is 0.1 g / 10 min or more. The melt flow rate of polyamide resin B is a value measured according to JIS K7210-2:2014 at a test temperature of 275°C and a nominal load of 0.325 kg. The sample used for measurement has a moisture content of 1000 ppm by mass or less.

[0021] (Mass ratio of polyamide resin A to polyamide resin B) The mass ratio of polyamide resin A to polyamide resin B in the base resin (polyamide resin A:polyamide resin B) is 97:3 to 60:40. From the viewpoint of shortening the molding cycle during in-mold molding, the mass ratio of polyamide resin B is preferably 5% by mass or more, more preferably 7% by mass or more, and even more preferably 10% by mass or more (provided that the total content of polyamide resin A and polyamide resin B in the base resin is 100% by mass). On the other hand, from the viewpoint of further suppressing shrinkage of the molded article, the mass ratio of polyamide resin A is preferably 70% by mass or more, more preferably 75% by mass or more, and even more preferably 80% by mass or more (provided that the total content of polyamide resin A and polyamide resin B in the base resin is 100% by mass).

[0022] (Melting point of polyamide resin A (TmA) and melting point of polyamide resin B (TmB)) The melting points (TmA) of polyamide resin A and (TmB) of polyamide resin B can be determined from the second DSC curve obtained under the following condition 1.

[0023] Condition 1 Based on the differential scanning calorimetry method of JIS K7121-1987, foamed particles are used as test specimens. The DSC curve measured when heating and melting the particles from 30°C to a temperature 30°C higher than the end of the melting peak at a heating rate of 10°C / min is defined as the first DSC curve. Then, after maintaining this temperature for 10 minutes, the particles are cooled to 30°C at a cooling rate of 10°C / min, and the DSC curve measured when heating and melting the particles again to a temperature 30°C higher than the end of the melting peak at a heating rate of 10°C / min is defined as the second DSC curve. The sample used for measurement has a water content of 1000 ppm by mass or less.

[0024] In the second DSC curve, a melting peak (I) specific to polyamide resin A and a melting peak (III) specific to polyamide resin B appear at a higher temperature than melting peak (I). The temperature at the peak of melting peak (I) in the second DSC curve corresponds to the melting point (TmA) of polyamide resin A, which is the raw material for producing foamed particles, and the temperature at the peak of melting peak (III) in the second DSC curve corresponds to the melting point (TmB) of polyamide resin B, which is the raw material for producing foamed particles. Melting peaks (I) and (III) appear in both the first and second DSC curves. The temperatures at the peaks of melting peaks (I) and (III) may differ slightly between the first and second DSC curves, but the difference is usually less than 5°C.

[0025] (Difference (TmB-TmA)) The difference (TmB-TmA) between the melting point (TmA) of polyamide resin A and the melting point (TmB) of polyamide resin B in the base resin is preferably 20°C or higher, more preferably 30°C or higher, even more preferably 35°C or higher, and even more preferably 40°C or higher, and preferably 100°C or lower, more preferably 80°C or lower, even more preferably 60°C or lower, and even more preferably 55°C or lower, from the viewpoint of secondary foaming and fusion properties of foamed particles during in-mold molding. The difference (TmB-TmA) between the melting point (TmA) of polyamide resin A and the melting point (TmB) of polyamide resin B is determined from the difference between the melting point (TmA) of polyamide resin A and the melting point (TmB) of polyamide resin B in the second DSC curve using foamed particles as a test specimen.

[0026] ≪Melting Point (TmA)≫ The melting point (TmA) of polyamide resin A is preferably 150°C or higher, more preferably 160°C or higher, even more preferably 170°C or higher, and even more preferably exceeding 180°C, from the viewpoint of improving the heat resistance of the polyamide resin foam particle molded article formed by fusing the polyamide resin foam particles of the present invention with each other, and preferably 250°C or lower, more preferably 230°C or lower, even more preferably 210°C or lower, even more preferably 200°C or lower, and even more preferably 190°C or lower, from the viewpoint of improving the fusion properties of the foam particles and improving the lightness of the molded article.

[0027] ≪Melting point (TmB)≫ The melting point (TmB) of polyamide resin B is preferably 200°C or higher, more preferably 210°C or higher, even more preferably 220°C or higher, and even more preferably 230°C or higher, from the viewpoint of improving the heat resistance of the molded article, and preferably 270°C or lower, more preferably 260°C or lower, even more preferably 250°C or lower, and even more preferably 240°C or lower, from the viewpoint of improving the fusion properties of foamed particles.

[0028] In condition 1 described above, the first DSC curve using foamed particles as the test specimen may contain a melting peak (II) that is higher in temperature than the melting peak (I) specific to polyamide resin A, and is caused by secondary crystals of the polyamide resin formed by the thermal history from foaming the resin particles to obtaining the foamed particles. In this specification, melting peak (II) is referred to as the high-temperature peak. There may be two or more high-temperature peaks (melting peaks (II)). Furthermore, high-temperature peaks (melting peaks (II)) are not observed in the second DSC curve. The temperature at the peak of the high-temperature peak (melting peak (II)) appears higher in temperature than melting peak (I) in the first DSC curve using foamed particles as the test specimen. Furthermore, although it depends on the difference between the temperature at the peak of the melting peak specific to polyamide resin A and the temperature at the peak of the melting peak specific to polyamide resin B, it is preferable that the temperature at the peak of the high-temperature peak (melting peak (II)) lies between melting peak (I) and melting peak (III) in the first DSC curve. In other words, it is preferable that the first DSC curve obtained under condition 1 has melting peaks (I), melting peaks (II), and melting peaks (III) in the order from the low temperature side. The high-temperature peak appears at a higher temperature than the melting peak (I) specific to polyamide resin A. Therefore, it is considered that the crystals of the high-temperature peak are less likely to melt during in-mold molding than the melting peak (I) specific to polyamide resin A, and that the crystals are more likely to remain. In addition to containing polyamide resin B, if polyamide resin A has a high-temperature peak, it is considered that excessive secondary foaming is more easily suppressed, and the maximum surface pressure is also less likely to become excessively high. As a result, if polyamide resin A has a high-temperature peak, it is considered that the decrease in surface pressure during water cooling is faster, and the water cooling time is further shortened.

[0029] The difference between the temperature at the peak of the melting peak (I) and the temperature at the peak of the high-temperature peak is preferably 10°C or more, more preferably 12°C or more, and even more preferably 15°C or more. On the other hand, the difference between the temperature at the peak of the melting peak (I) and the temperature at the peak of the high-temperature peak is preferably 40°C or less, more preferably 30°C or less, and even more preferably 25°C or less. When comparing the temperature difference between the peaks of the melting peak (I) and the high-temperature peak, if two or more high-temperature peaks appear in the first DSC curve, the temperature at the peak of the lowest-temperature high-temperature peak is compared with the temperature at the peak of the melting peak (I).

[0030] In the first DSC curve, the heat of fusion of the melting peak (I) specific to polyamide resin A is preferably 25 J / g or more, more preferably 30 J / g or more. The heat of fusion of the melting peak (I) specific to polyamide resin A is preferably 60 J / g or less, more preferably 50 J / g or less. In the first DSC curve, the heat of fusion of the melting peak (III) specific to polyamide resin B is preferably 3 J / g or more, more preferably 4 J / g or more. The heat of fusion of the melting peak (III) specific to polyamide resin B is preferably 15 J / g or less, more preferably 10 J / g or less. In the first DSC curve, the heat of fusion of the high-temperature peak (melting peak (II)) is preferably 1 J / g or more, more preferably 2 J / g or more. The heat of fusion of the high-temperature peak (melting peak (II)) is preferably 13 J / g or less, more preferably 10 J / g or less. Here, the temperature and heat of fusion at the peak of each melting peak can be determined as follows.

[0031] Under condition 1, when the temperature is raised from 30°C to 30°C higher than the end of the melting peak using differential scanning calorimetry with a heat flux, at a heating rate of 10°C / min, the temperature at the peak of each melting peak can be determined from the melting peak obtained in the first DSC curve. The heat of fusion for each melting peak can be determined based on the DSC curve obtained under condition 2 below. A high-sensitivity differential scanning calorimeter "EXSTAR DSC7020" (manufactured by SII Nanotechnology Co., Ltd.) can be used as the measuring device.

[0032] Condition 2 Based on the differential scanning calorimetry method of thermal flux metric measurement in JIS K7122-1987, foamed particles were used as test specimens and 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 to obtain the first DSC curve.

[0033] The following provides a detailed explanation using Figure 1 (the first DSC curve) as an example. For example, in the first DSC curve shown in Figure 1, there are three melting peaks. The lowest temperature peak is the melting peak (I) specific to polyamide resin A, the second peak is the high temperature peak (melting peak (II)), and the highest temperature peak is the melting peak (III) specific to polyamide resin B. The temperature at the top of each melting peak is the temperature at the point where the heat absorption is greatest for that peak.

[0034] The heat of fusion at the peak of each melting peak corresponds to the area of ​​each melting peak in the DSC curve shown in Figure 1, and can be determined as follows: Draw a straight line connecting the point at 120°C on the DSC curve and the point indicating the melting end temperature of melting peak (II) on the DSC curve (baseline of the melting peak originating from polyamide resin A). Divide melting peak (I) and melting peak (II) with a straight line perpendicular to the temperature on the horizontal axis of the graph, from the point on the DSC curve corresponding to the valley between melting peak (I) and melting peak (II) to the baseline of the melting peak originating from polyamide resin A. The area 1 of the divided low-temperature side peak corresponds to the heat of fusion of melting peak (I) intrinsic to polyamide resin A, and the area 2 of the divided high-temperature side peak corresponds to the heat of fusion of the high-temperature peak (melting peak (II)) caused by the secondary crystals of the polyamide resin formed by the thermal history from foaming the resin particles to obtaining foamed particles.

[0035] A straight line is drawn connecting the point indicating the melting start temperature of the melting peak (III) on the DSC curve and the point indicating the melting end temperature of the melting peak (III) specific to polyamide resin B (baseline of the melting peak specific to polyamide resin B). The area 3 enclosed by the baseline of the melting peak originating from polyamide resin B and the DSC curve corresponds to the heat of fusion of the melting peak (III) specific to polyamide resin B.

[0036] The base resin may contain other thermoplastic resins in addition to polyamide resin A and polyamide resin B, to the extent that it does not hinder the objectives and effects of the present invention. Examples of other thermoplastic resins include polyethylene resins, polypropylene resins, polystyrene resins, vinyl acetate resins, thermoplastic polyester resins, acrylic acid ester resins, methacrylic acid ester resins, modified polyphenylene ether resins, polycarbonate resins, polyacetal resins, polybutylene terephthalate resins, polysulfone resins, polyethersulfone resins, polyamide-imide resins, polyetherimide resins, polyetheretherketone resins, and polyamide resins other than polyamide resin A and polyamide resin B. The content of other thermoplastic resins in the base resin is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less, from the viewpoint of obtaining foamed particles with excellent heat resistance, abrasion resistance, and chemical resistance. It is particularly preferable that the base resin consists only of polyamide resin A and polyamide resin B.

[0037] (Heat stabilizer) Depending on the intended use of the molded article, a heat stabilizer may be added to the foamed particles of the present invention. A heat stabilizer is a substance that has the effect of suppressing the deterioration of the resin due to heat when the foamed particles or the molded article of foamed particles are placed in a high-temperature environment. It is preferable to add a heat stabilizer to the foamed particles. When incorporating a heat stabilizer into foamed particles, examples of heat stabilizers include hindered amine compounds, hindered phenol compounds, phosphorus compounds, copper compounds, and halides. Specific examples of hindered amine compounds include Bis(2,2,6,6,-tetramethyl-4-piperidyl)sebacate (trade name: Tinuvin 770, manufactured by BASF Japan Ltd.). Specific examples of hindered phenol compounds include N,N'-hexane-1,6-diylbis(3-(3,5-di-tert-butyl-4-hydroxyphenylpropionamide)) (trade name: Iruganox 1098, manufactured by BASF Japan Ltd.). Specific examples of phosphorus compounds include Tris(2,4-di-tert-butylphenyl)phosphite (trade name: Irugafos 168, manufactured by BASF Japan Ltd.). Copper compounds, excluding the halides described later, include, for example, copper chloride, copper bromide, copper iodide, copper phosphate, copper stearate, as well as natural minerals such as hydrotalcite, stichtite, and pyrolite. Examples of halides include ammonium iodide, stearyltriethylammonium bromide, benzyltriethylammonium iodide; and alkali metal halides such as potassium chloride, sodium chloride, potassium bromide, potassium iodide, and sodium iodide. Among these, the heat stabilizer is preferably one or more selected from the group consisting of hindered amine compounds, hindered phenol compounds, phosphorus compounds, copper compounds, and halides, more preferably one or more selected from the group consisting of copper compounds and halides, even more preferably one or more selected from the group consisting of copper compounds and alkali metal halides, even more preferably one or more selected from the group consisting of copper iodide and potassium iodide, and even more preferably contains copper iodide and potassium iodide.

[0038] The amount of heat stabilizer blended is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, and preferably 5% by mass or less, and more preferably 3 parts by mass or less, in the foamed particles. If two or more types of heat stabilizers are included, it is preferable that their total amount be within the above range.

[0039] (Coloring agent) The foamed particles of the present invention preferably contain a coloring agent. Inorganic or organic pigments or dyes can be used as the coloring agent. The coloring agent is used to improve the appearance and design of the resulting molded article. 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, the coloring agent is preferably an organic pigment or an inorganic pigment from the viewpoint of weather resistance, more preferably an inorganic pigment from the viewpoint of heat resistance and weather resistance, and even more preferably carbon black from the viewpoint of easily shortening the molding cycle.

[0040] When the foamed particles contain a coloring agent, the amount of coloring agent added is preferably 0.5% by mass or more, more preferably 0.8% by mass or more, even more preferably 1% by mass or more, and preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less, from the viewpoint of giving the resulting foamed particle molded article excellent design properties.

[0041] Antistatic agents, conductivity-imparting agents, lubricants, ultraviolet absorbers, flame retardants, metal deactivators, crystal nucleating agents, fillers, and other various additives that are commonly used can be appropriately blended into the expanded particles as necessary. The addition amounts of these various additives vary depending on the intended use of the molded product, but are preferably 25 parts by mass or less, more preferably 15 parts by mass or less, still more preferably 10 parts by mass or less, and even more preferably 5 parts by mass or less, based on 100 parts by mass of the expanded particles.

[0042] <Apparent density> The apparent density of the expanded particles is preferably 10 kg / m 3 or more, more preferably 30 kg / m 3 or more, still more preferably 50 kg / m 3 or more, and even more preferably 70 kg / m 3 or more, from the viewpoint of suppressing shrinkage of the molded product and, as a result, obtaining a more excellent molded product, and is preferably 300 kg / m 3 or less, more preferably 250 kg / m 3 or less, still more preferably 200 kg / m 3 or less. The apparent density of the expanded particles is measured by the following method. Prepare a graduated cylinder filled with water at a temperature of 23°C, and measure the mass W1 of about 500 cm 3 of the expanded particles that have been left standing for 2 days under conditions of a relative humidity of 50%, a temperature of 23°C, and a pressure of 1 atm. 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.

[0043] <Average bubble diameter> The average bubble diameter of the foamed particles is preferably 30 μm or more, more preferably 50 μm or more, even more preferably 70 μm or more, even more preferably 90 μm or more, and preferably 250 μm or less, more preferably 200 μm or less, even more preferably 170 μm or less, and even more preferably 150 μm or less, from the viewpoint of easily obtaining a molded article with excellent surface properties. The average bubble diameter of foamed particles is measured by the following method. First, the foamed particle is divided into approximately two halves, passing through its center, and the cross-section is photographed using a scanning electron microscope. Next, in the obtained cross-sectional photograph, straight lines are drawn at equal intervals in eight directions from near the center of the foamed particle's cross-section, and the number of bubbles intersecting these lines is counted. The value obtained by dividing the total length of these lines by the number of counted bubbles is taken as the bubble diameter of the foamed particle. This operation is repeated for 10 or more foamed particles, and the arithmetic mean of the bubble diameters of each foamed particle is taken as the average bubble diameter of the foamed particle.

[0044] <Closed cell diameter> From the viewpoint of obtaining a molded article with excellent fusion properties and recovery, the percentage of closed cells in the foamed particles is preferably 70% or more, more preferably 80% or more, even more preferably 85% or more, and even more preferably 90% or more. The closed-cell ratio of foamed particles is the ratio of the volume of closed cells to the total volume of cells in the foamed particles, and can be determined using an air-comparison hydrometer based on ASTM-D2856-70.

[0045] [Method for producing foamed particles] The present invention provides a method for producing polyamide resin foam particles, which involves foaming resin particles using a mixed resin of polyamide resin A and polyamide resin B as a base resin.

[0046] <Resin particles using a mixed resin as a base resin and methods for producing the same> 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 mg and 15.0 mg. Within this range, the apparent density can be increased. From this viewpoint, the mass of the resin particle is more preferably 1.0 mg or more, even more preferably 1.5 mg or more, and more preferably 10.0 mg or less, even more preferably 7.0 mg or less, and even more preferably 5.0 mg or less.

[0047] The melting point (Tm) of the resin particles is preferably 180°C or higher, more preferably 183°C or higher, and even more preferably 185°C or higher, from the viewpoint of obtaining foamed particles with excellent heat resistance, and preferably 250°C or lower, more preferably 220°C or lower, and even more preferably 200°C or lower, from the viewpoint of easy temperature control during foaming. The melting point of the resin particles refers to the melting point of the mixture obtained by pre-mixing polyamide resin A and polyamide resin B in an extruder or the like. If the DSC curve has multiple melting peaks, the peak temperature of the melting peak with the largest area is adopted as the melting point.

[0048] A mixed resin of polyamide resin A and polyamide resin B can be obtained by melt-kneading polyamide resin A and polyamide resin B using a general-purpose extruder. Either a single-screw or twin-screw extruder can be used. The method for producing the resin particles is not particularly limited and can be obtained by known methods. For example, resin particles can be obtained by a strand-cut method in which polyamide resin A, polyamide resin B, and optionally additives such as colorants and foam regulators are put into an extruder, kneaded to form a molten mixture, the molten mixture is extruded in a strand shape through small holes in a die attached to the tip of the extruder, and after the extruded molten material is cooled and solidified it is cut with a pelletizer to a predetermined mass; a hot-cut method in which the molten mixture is cut immediately after being extruded into the gas phase; or an underwater-cut method (UWC method) in which the molten mixture is cut immediately after being extruded into water.

[0049] (Example of a method for manufacturing foamed particles) The foamed particles of the present invention can be produced, for example, by a manufacturing method that includes a "foaming step" in which a foaming agent is impregnated into resin particles using the mixed resin as a base resin, and the foamed resin particles using the mixed resin as a base resin that have been impregnated with the foaming agent are foamed by heating, pressure changes, volume changes, etc.

[0050] ≪Foaming agent addition process≫ The foaming agent addition step is a step of adding a foaming agent to a sealed container. Preferably, the foaming agent can be impregnated into the resin particles in this step to make foamy resin particles. The foaming agent can be impregnated into the resin particles in this step and in each of the steps described later (dispersion step, heating step, holding step) to obtain foamy resin particles. In addition, when impregnating with a foaming agent in this step, it is preferable to disperse the resin particles in an aqueous solvent in a pressurized sealed container such as an autoclave and impregnate the resin particles with the foaming agent. Furthermore, from the viewpoint of sufficiently impregnating the resin particles with the foaming agent in a short time, it is preferable to impregnate the resin particles with the foaming agent under pressure and / or heat.

[0051] (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 hydrofluoroolefins, 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.

[0052] Furthermore, in order to sufficiently impregnate the resin particles with the foaming agent in a short time, this process is preferably carried out under pressure. The maximum pressure during impregnation under pressure (hereinafter also referred to as impregnation pressure) is preferably such that, from the viewpoint of sufficiently impregnating the resin particles with the foaming agent in a short time, the pressure inside the sealed container becomes 1.5 MPa(G) or higher, more preferably 2.5 MPa(G) or higher, preferably 7 MPa(G) or lower, and more preferably 5 MPa(G) or lower when the foaming agent is added to the container containing the dispersion liquid. Note that "1.5 MPa(G)" means a gauge pressure of 1.5 MPa.

[0053] (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 "foaming agent addition 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.

[0054] The manufacturing method for producing foamed particles of the present invention preferably comprises the following steps. (1) A dispersion step in which resin particles, with a mixed resin as the base resin, are dispersed in water in a sealed container to obtain a dispersion liquid, (2) A heating step to raise the temperature of the dispersion, (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.

[0055] ≪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.

[0056] ≪Heating Process≫ The heating step is an optional step in the production of foamed particles. The heating step may be performed before, after, or during the foaming agent addition step. In this step, it is preferable to heat the dispersion to the foaming temperature or the holding temperature described later. It is believed that during the heating process described above, water in the aqueous solvent becomes more easily absorbed by the polyamide resin. The heating step includes heating a dispersion of resin particles in water from room temperature to the temperature of the holding step (hereinafter also referred to as the holding temperature).

[0057] The temperature after 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)).

[0058] The dispersion and heating steps 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 steps to obtain the dispersion and impregnate 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, from the viewpoint of allowing the resin particles to absorb enough water and become plasticized, the heating rate in the heating process is preferably 10°C / min or less, and more preferably 7°C / min or less. 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.

[0059] ≪Holding process≫ The holding step involves holding the dispersion at a temperature preferably 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 preferably 90°C lower than the melting point (Tm) of the resin particles (Tm-90°C), more preferably 80°C lower (Tm-80°C), even more preferably 70°C lower (Tm-70°C), and even more preferably 65°C lower (Tm-65°C), and preferably less than 50°C lower (Tm-50°C), more preferably 53°C lower (Tm-53°C), and even more preferably 55°C lower (Tm-55°C).

[0060] Normally, when manufacturing foamed particles using general-purpose resins such as polypropylene resins as the base resin, the material is held near the melting point of the raw material resin. However, in the method for manufacturing foamed particles of the present invention, the material is preferably manufactured by holding it at 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. This is because polyamide resins are hygroscopic, so the resin particles are plasticized by the water used as the dispersion, significantly lowering the melting point. As a result, it is 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.

[0061] The holding time in the holding step is preferably 1 minute or more, more preferably 5 minutes or more, even more preferably 10 minutes or more, and even more preferably 13 minutes or more, from the viewpoint of uniformly impregnating the mixed 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 preferably 60 minutes or less, more preferably 40 minutes or less, even 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.

[0062] The holding process is preferably carried out under pressure, from the viewpoint of uniformly impregnating the mixed 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.

[0063] ≪Foaming Process≫ The foaming process is a process of foaming resin particles impregnated with a foaming agent. The method of foaming the resin particles is not particularly limited, but a preferred foaming method is to release the resin particles impregnated with the foaming agent together with water under a pressure atmosphere lower than the pressure at which they were held (usually atmospheric pressure) following the holding process.

[0064] The temperature Te of the dispersion immediately before foaming (hereinafter also referred to as the foaming temperature) is preferably 90°C lower than the melting point (Tm) of the resin particles (Tm-90°C), more preferably 80°C lower (Tm-80°C), even more preferably 70°C lower (Tm-70°C), and even more preferably 65°C lower (Tm-65°C) or higher, from the viewpoint of obtaining foamed particles with low apparent density and a high percentage of closed cells. Furthermore, the foaming temperature is preferably less than 50°C lower than the melting point (Tm) of the resin particles (Tm-50°C), more preferably 53°C lower (Tm-53°C) or lower, and even more preferably 55°C lower (Tm-55°C) or lower.

[0065] 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, and even more preferably 2.5 MPa(G) or higher. Furthermore, the foaming pressure is preferably 10 MPa(G) or lower, more preferably 7 MPa(G) or lower, and even more preferably 5 MPa(G) or lower.

[0066] [Foam particle molded body] The polyamide resin foam particle molded article of the present invention is a foam particle molded article in which the foam particles are fused to each other. That is, the foam particle molded article of the present invention is a foam particle molded article (foam particle molded article) obtained by in-mold molding the foam particles of the present invention. The foamed particles of the present invention exhibit excellent fusion properties and recovery properties, and can suppress molding shrinkage after molding. As a result, the foamed particle molded article has suppressed molding shrinkage after molding and a good appearance. The foamed particle molded article obtained by in-mold molding of the foamed particles of the present invention can suppress molding shrinkage after molding, making it suitable for obtaining thick molded articles. The thickness of the foamed 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.

[0067] The foamed particles of the present invention can be used to form a foamed particle molded article with excellent in-mold moldability. Specifically, it is preferable because the water cooling time can be shortened, and as a result, the overall molding time can be shortened. 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 supplying steam from the moving side mold, and then supplying steam from the fixed side mold, and then heating up to the molding heating steam pressure (molding pressure = molding vapor pressure). After heating is complete, the pressure is released, and the molded body is water-cooled until the surface pressure due to the foaming force drops to 0.04 MPa (G), at which point 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 0.04 MPa (G). In this invention, the following reasons can be considered for shortening the water cooling time when foam particles are molded in a mold. During in-mold molding of foamed particles, heating and pressurizing with steam cause secondary foaming and fusion of the foamed particles with each other. At this time, the inclusion of a specific ratio of xylylene group-containing polyamide resin in the base resin suppresses excessive secondary foaming, thereby preventing the maximum surface pressure from becoming excessively high. As a result, it is believed that the decrease in surface pressure during water cooling will be faster, and the water cooling time can be shortened.

[0068] <Molded object density> From the viewpoint of obtaining a molded product with excellent lightness, resilience, and fusion properties, the density of the foamed particle molded product (molded product density) is preferably 10 kg / m³. 3 Above, a comfortable 30 kg / m 3 More preferably 50 kg / m 3 More preferably 60 kg / m 3 The above applies, and preferably 350 kg / m 3 More preferably 300 kg / m 3 More preferably 250 kg / m 3 More preferably, 200 kg / m 3 The following applies: The density of the molded body is measured by the following method: The foamed particle molded body is left for two days under conditions of 50% relative humidity, 23°C, and 1 atm. Next, a container filled with water at 23°C is prepared, and an arbitrary amount of foamed particle molded body (mass W [g]) is submerged in the water using a tool such as a wire mesh. Then, taking into account the volume of the tool such as the wire mesh, the volume of the foamed particle molded body V [L] is measured from the rise in water level. The mass W [g] of the foamed particle molded body in the container is divided by the volume V [L] (W / V), and the unit is expressed as [kg / m³]. 3 The density of the molded body can be determined by converting it to [ ]. [Examples]

[0069] The present invention will be described in detail below with reference to examples, but the present invention is not limited thereto.

[0070] The polyamide resins, resin particles, foam particles, and molded articles in the examples and comparative examples were measured and evaluated by the following methods.

[0071] [Measurement and Evaluation] <Resin particles> (Melting point) The melting point of polyamide resin particles was measured using differential scanning calorimetry (DSC) based on JIS K7121-1987. Under conditions of a nitrogen inflow of 30 mL / min, the particles were 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. The resin particles used as test specimens were stored in a desiccator under a nitrogen atmosphere to avoid hydrolysis under high temperature and high humidity conditions, and then stored for 24 hours under vacuum suction with a moisture content of 1000 ppm by mass or less before being used for melting point measurement. In cases where the DSC curve has multiple melting peaks, the peak temperature of the melting peak with the largest area was adopted as the melting point.

[0072] <Foaming particles> (Melting point and heat of fusion) 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 three melting peaks. The lowest temperature peak is the melting peak (I) specific to polyamide resin A, the second peak is the high temperature peak (melting peak (II)), and the highest temperature peak is the melting peak (III) specific to polyamide resin B. The temperature at the top of each melting peak is the temperature at the point with the greatest heat absorption for that peak. The heat of fusion at the top of each melting peak corresponds to the area of ​​each melting peak in the DSC curve shown in Figure 1, and was determined as follows. First, a straight line was drawn connecting the point at 120°C on the DSC curve and the point indicating the end temperature of melting peak (II) on the DSC curve (baseline of the melting peak originating from polyamide resin A). Melting peak (I) and melting peak (II) were divided by a straight line perpendicular to the temperature on the horizontal axis of the graph, from the point on the DSC curve corresponding to the valley between melting peak (I) and melting peak (II) to the baseline of the melting peak originating from polyamide resin A. The area 1 of the divided low-temperature peak corresponds to the heat of fusion of the melting peak (I) specific to polyamide resin A, and the area 2 of the divided high-temperature peak corresponds to the heat of fusion of the high-temperature peak (melting peak (II)) originating from polyamide resin A. Next, a straight line was drawn connecting the point indicating the melting start temperature of melting peak (III) on the DSC curve and the point indicating the melting end temperature of melting peak (III) specific to polyamide resin B (baseline of the melting peak specific to polyamide resin B). The area 3 of the region enclosed by the baseline of the melting peak originating from polyamide resin B and the DSC curve corresponds to the heat of fusion of the melting peak (III) specific to polyamide resin B.

[0073] (Apparent density) The apparent density of the foam particles was measured by the following method: A graduated cylinder filled with water at 23°C was prepared and left for 2 days under conditions of 50% relative humidity, 23°C, and 1 atm, yielding approximately 500 cm³. 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. 3 Measure 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].

[0074] (Average bubble diameter) The average bubble diameter of the foamed particles was measured by the following method. First, the foamed particle was divided approximately in half so as to pass through its center, and the cross-section was photographed using a scanning electron microscope. Next, in the obtained cross-sectional photograph, straight lines were drawn at equal intervals in eight directions from near the center of the foamed particle's cross-section, and the number of bubbles intersecting these lines was counted. The value obtained by dividing the total length of these lines by the number of counted bubbles was defined as the bubble diameter of the foamed particle. This procedure was repeated for 30 foamed particles, and the arithmetic mean of the bubble diameters of each foamed particle was defined as the average bubble diameter of the foamed particle.

[0075] (Percentage of closed cells) The independent cell diameter of the foamed particles was measured by the following method. The true volume Vx of the foamed particles (the sum of the volume of the resin constituting the foamed particle and the total volume of the independent cells within the foamed particle) was measured according to procedure C described in ASTM-D2856-70. A Toshiba Beckmann air-comparison hydrometer "930" was used to measure this true volume Vx. Next, the independent 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 )

[0076] <Molded body> (Molded object density) The density of the molded articles was measured by the following method. Using the foamed particles obtained in each example and comparative example, foamed particle molded articles were prepared using the method described in <Preparation of Mixed Resin Foamed Particle Molded Articles> below. The foamed particle molded articles were left for 2 days under conditions of relative humidity of 50%, temperature of 23°C, and 1 atm. Next, a container filled with water at 23°C was prepared, and an arbitrary amount of foamed particle molded article (mass W [g]) was submerged in the water in the container using a tool such as a wire mesh. Then, taking into account the volume of the tool such as the wire mesh, the volume of the foamed particle molded article V [L], which was read from the rise in water level, was measured. The mass W [g] of the foamed particle molded article in the container was divided by the volume V [L] (W / V), and the unit was expressed as [kg / m³]. 3 The density of the molded body was determined by converting it to [ ].

[0077] (Shrinkage rate) Using the foamed particles obtained in each example and comparative example, foamed particle molded articles were prepared using the method described in <Preparation of Mixed Resin Foamed Particle Molded Articles> below. After standing for 24 hours in an environment of 23°C and 50% relative humidity, the dimensions of the foamed particle molded articles were measured, with the length, width, and thickness being a', b', and c' respectively. The molding shrinkage rate (%) of the molded article was defined by the following formula, where the length, width, and thickness of the mold (internal dimensions) are a, b, and c, respectively. A smaller molding shrinkage rate indicates a more suppressed molding shrinkage rate, which is preferable. Molding shrinkage rate (%) = [(a-a') / a + (b-b') / b + (c-c') / c] × 100 / 3

[0078] (Water cooling time) Using the foamed particles obtained in each example and comparative example, a foamed particle molded body was prepared using the method described in <Preparation of Mixed Resin Foamed Particle Molded Body> below, and the time required from the start of water cooling until the surface pressure decreased to 0.04 MPa (G) was defined as the water cooling time (seconds).

[0079] (Molding cycle) Using the foamed particles obtained in each example and comparative example, a foamed particle molded body was prepared using the method described in <Preparation of Mixed Resin Foamed Particle Molded Body> below. The time taken from when the open mold was started to close until the surface pressure due to the foaming force of the molded body decreased to 0.04 MPa (G) and demolding was measured. A shorter molding cycle time is preferable as it indicates a shorter molding cycle.

[0080] (Fusion rate) The fusion rate of the foam particle molded body was measured by the following method. On one side of the surface of the foam particle molded body obtained in each example and comparative example, a cut approximately 10 mm deep was made in the thickness direction at a position that divided the vertical length of the test piece in half using a utility knife, and the molded body was bent and fractured from the cut. The ratio (m / n × 100 [%]) of the number of material-fractured foam particles m present at the fracture surface to the total number of foam particles n present at the fracture surface was calculated. If the molded body could not be fractured even when bent, the fusion rate was set to 100%. The above measurement was performed five times using different test pieces, the material fracture rate for each was determined, and the arithmetic mean of these was taken as the fusion rate.

[0081] (Recoverability) The resilience of the foam particle molded body was measured using the following method. The thickness of the edges (10 mm inward from the edge) and the center (the part that divides the foam particle molded body into two equal parts in both the vertical and horizontal directions) corresponding to the dimensions of the flat plate-shaped mold used in in-mold molding was measured. Next, the thickness ratio of the foam particle molded body (thickness of the center of the molded body / thickness of the edges of the molded body × 100 (%)) was calculated and evaluated as follows. Note that the thickness measurements were performed on foam particle molded bodies produced using the method described in <Preparation of Mixed Resin Foam Particle Molded Body> below. A: The thickness ratio is 95% or more. B: The thickness ratio is less than 95% or more than 90%. C: The thickness ratio is less than 90%.

[0082] (crystallite size) The crystallite size of the foamed particle molded body was measured by the following method. The foamed particle molded body was used as a test specimen, and X-ray diffraction (XRD) measurements were performed using the reflection method with the X-ray scattering instrument "Smart Lab SE" (manufactured by Rigaku Corporation). A one-dimensional semiconductor detector D / teX Ultra250 was used as the detector. The sample used was a foamed particle molded body sliced ​​to a sample thickness of approximately 1.0 mm. In addition, lanthanum hexaboride, a standard material, was measured to determine b. The obtained one-dimensional X-ray diffraction profile was separated into crystalline diffraction peaks and amorphous diffraction peaks using software (product name: Igor Pro Version 6.3.2.3, manufactured by Wavemetrics), assuming a Gaussian function as the peak shape. The peak separation was performed by automatic fitting. The full width at half maximum β (rad) of the peak with the narrowest peak width obtained by peak separation was calculated, and the crystallite size D of the foamed particle molded body was calculated using this full width at half maximum β according to the following equation (2). In equation (2), λ is the wavelength of the X-ray, and θ is the Bragg angle at the peak position (half of the diffraction angle 2θ).

[0083]

number

[0084] [Preparation of mixed resin particles, mixed resin foam particles, and molded articles of mixed resin foam particles] Table 1 shows the polyamide resins and other materials used to produce the mixed resin particles and mixed resin foam particles.

[0085] [Table 1]

[0086] Examples 1, 2, 4-9, Comparative Examples 2, 4-7 <Preparation of mixed resin particles> Polyamide resins A and B, as listed in Tables 2-4, were supplied to an extruder in the blending ratios listed in Tables 2-4. Talc "Talcan Powder PK-S" (manufactured by Hayashi Chemical Co., Ltd.) was supplied in the amounts listed in Tables 2-4 as a foam regulator, 1.0% by mass of aromatic polycarbodiimide "Stabaxol P" (manufactured by Rhein Chemie) was supplied as a chelating agent, 0.05% by mass of copper iodide and 0.2% by mass of potassium iodide were supplied as heat stabilizers, and carbon black was supplied as a coloring agent in the amounts shown in Tables 2-4. The mixture was then melt-kneaded to obtain a molten mixture. The molten mixture was extruded as a 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 so that the average mass per strand was 2 mg, and dried to obtain pelletized mixed resin particles. The melting points of the resin particles are shown in Tables 2-4.

[0087] <Preparation of mixed resin foam particles> 500 g of the obtained mixed 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 the mixed resin particles. While stirring the contents of the autoclave, the temperature was raised from room temperature (23°C) to the holding temperature (melting point of the resin particles - 55°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 holding temperature (melting point of the resin particles - 55°C) was 40 minutes. Next, the mixture was held at the holding temperature (melting point of the resin particles - 55°C) and 4.0 MPa (G) for 15 minutes. Subsequently, the mixed resin particles impregnated with the foaming agent were released together with the dispersion medium under atmospheric pressure (0.1 MPa). The foaming temperature (temperature of the dispersion immediately before foaming) was -55°C, the melting point of the resin particles. The obtained mixed resin foam particles were cured in a 60°C oven for 24 hours, and then slowly cooled to obtain mixed resin foam particles. The measurements described above were performed on the obtained mixed resin foam particles. The results are shown in Tables 2 to 4.

[0088] <Water content, internal pressure applied> Using the above-mentioned mixed resin foam particles, the mixed resin foam particles and water were placed in a plastic bag, the opening of the bag was closed, and the bag was shaken well to thoroughly mix and allow the particles to absorb water. Then, 180g of the water-soaked mixed resin foam particles were placed in a 3-liter pressure-resistant container set to a pressurized temperature of 40°C. At the same time as the mixed resin foam particles were placed in the pressure-resistant container and sealed, air was injected as a physical foaming agent to apply internal pressure. The internal pressure was applied to a pressure of 0.12 MPa (G) inside the pressure-resistant container for 16 hours.

[0089] <Preparation of molded mixed resin foam particles> A foamed particle molded body was prepared using the above-mentioned mixed resin foamed particles. The mold was narrowed from an open state, and the obtained mixed resin foamed particles were filled into a flat mold measuring 200 mm in length, 65 mm in width, and 40 mm in thickness, with the mold slightly open so that the cracking was 4 mm larger (i.e., 10% cracking). After filling was complete, the mold was completely closed to compress the foamed particles and clamp the mold. Subsequently, in-mold molding by steam heating was performed to obtain a plate-shaped foamed 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, with the drain valve on the fixed side open, steam was supplied from the movable side mold, and then with the drain valve on the movable side open, steam was supplied from the fixed side mold. Finally, the exhaust valves were closed, and the mold was heated to a molding heating steam pressure of 0.12 MPa (G) (molding pressure = molding vapor pressure). After heating, the pressure was released, and the mold was water-cooled until the surface pressure due to the foaming force of the molded body decreased to 0.04 MPa (G). The mold was then 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 mixed resin foam particle molded body. The obtained mixed resin foam particle molded body was subjected to the aforementioned measurements and evaluations. The results are shown in Tables 2 to 4. Note that the foam particle molded bodies of Comparative Examples 4 to 6 did not have good secondary foaming properties and poor fusion properties, so the water-cooling time and molding cycle were not evaluated.

[0090] Example 3 Polyamide resin particles, polyamide resin foamed particles, and polyamide resin foamed particle molded articles were obtained in the same manner as in Example 1, except that the holding temperature and foaming temperature were set to (melting point of resin particles - 61) °C. The obtained polyamide resin foamed particles and polyamide resin foamed particle molded articles were subjected to the aforementioned measurements and evaluations. The results are shown in Table 2.

[0091] Comparative Examples 1 and 3 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 polyamide resin B was not used and only polyamide resin A as described in Table 3 was supplied. The obtained polyamide resin foam particles and polyamide resin foam particle molded articles were subjected to the aforementioned measurements and evaluations. The results are shown in Table 3.

[0092] [Table 2]

[0093] [Table 3]

[0094] [Table 4]

[0095] Tables 2-4 show that the foamed particles obtained in the examples shorten the molding cycle during in-mold molding, suppress shrinkage after molding, and produce a foamed particle molded article with good fusion properties. [Industrial applicability]

[0096] The polyamide resin foam particles according to the present invention shorten the molding cycle during in-mold molding, suppress shrinkage after molding, and produce a foam particle molded article with good fusion properties, thus offering potential for further applications in automotive parts, electrical products, and the like.

Claims

1. Polyamide resin foam particles having a mixed resin of polyamide resin A and polyamide resin B as the base resin, The polyamide resin A is an aliphatic polyamide copolymer. The polyamide resin B is a xylylene group-containing polyamide resin, The melt flow rate of the aforementioned polyamide resin B at 275°C and a load of 0.325 kg is 10 g / 10 min or less. Polyamide resin foam particles having a mass ratio (polyamide resin A:polyamide resin B) of 97:3 to 60:

40.

2. The polyamide resin foam particles according to claim 1, wherein the melt flow rate of the polyamide resin B at 275°C and a load of 0.325 kg is 5 g / 10 min or less.

3. The polyamide resin foamed particles according to claim 1, wherein the foamed particles contain carbon black.

4. The polyamide resin foam particles according to claim 1, wherein the melting point (TmA) of the polyamide resin A is greater than 180°C and less than or equal to 250°C.

5. The polyamide resin foam particle according to claim 1, wherein the difference (TmB - TmA) between the melting point (TmA) of the polyamide resin A and the melting point (TmB) of the polyamide resin B is 30°C or more and 100°C or less.

6. The apparent density of the foamed particles is 10 kg / m³ ３ More than 300kg / m ３ The polyamide resin foam particles according to claim 1, which are as follows:

7. The polyamide resin foamed particle according to claim 1, wherein the closed-cell ratio of the foamed particle is 70% or more.

8. A molded polyamide resin foam particle body obtained by in-mold molding polyamide resin foam particles according to any one of claims 1 to 7.

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