Polyamide-based resin foamed particles and

Abstract

The present invention provides polyamide-based resin foamed particles and a polyamide-based resin foamed particle molded body, the polyamide-based resin foamed particles exhibit good in-mold moldability and can provide a foamed particle molded body exhibiting excellent flame retardancy, and the polyamide-based resin foamed particle molded body has excellent moldability and flame retardancy. The polyamide-based resin foamed particles contain a polyamide-based resin, a specific flame retardant a and a specific flame retardant b, and the total of the blending amount of the flame retardant a and the blending amount of the flame retardant b is 10-30 parts by mass per 100 parts by mass of a base resin containing the polyamide-based resin, and the total of the blending amount of the flame retardant a and the blending amount of the flame retardant b is 10-30 parts by mass per 100 parts by mass of the base resin containing the polyamide-based resin. The mass ratio of the blending amount of the flame retardant a to the blending amount of the flame retardant b is 90: 10 to 30: 70 (the total of the flame retardant a and the flame retardant b is 100% by mass), the average bubble diameter A of the polyamide-based resin foamed particles is 5 [mu] m to 100 [mu] m, and the average bubble diameter A of the polyamide-based resin foamed particles observed in a cross-section formed by halving the polyamide-based resin foamed particles is 5-100 [mu] m, and the average bubble diameter A of the polyamide-based resin foamed particles observed in a cross-section formed by halving the polyamide-based resin foamed particles is 5-100 [mu] m. The average bubble diameter (B) of five bubbles selected in the order from large to small per bubble area is 250 [mu] m or less. In addition, the polyamide-based resin foamed particle molded body is obtained by in-mold molding of the polyamide-based resin foamed particles.

Description

Technical Field

[0001] The present invention relates to polyamide resin foamed particles containing a flame retardant, and a polyamide resin foamed particle molded article having excellent flame retardancy, which is obtained by in-mold molding the polyamide resin foamed particles. Background Art

[0002] In common resin materials, polyamide resin is well known as the resin that heat resistance is high and wear resistance, chemical resistance etc. are also excellent. The foam molding that this polyamide resin is foamed to form can also seek further lightweighting while maintaining these excellent characteristics. Therefore, can expect to carry out and use polyamide resin foam molding for other purposes of automobile parts. Particularly, for the polyamide resin foam particle molded body that polyamide resin foam particle is carried out in-mold molding to form, as the component of thermal insulation material and sound insulation excellence, can expect to be used for the hood and the engine cover of vehicle.

[0003] In various applications including the above-mentioned automobile parts, the polyamide resin foamed particle molded article is sometimes required to have excellent flame retardancy.

[0004] For example, Patent Document 1 describes that polyamide resin foamed particles can contain various flame retardants.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: International Publication No. WO2016 / 001109 Summary of the Invention

[0008] (1) Technical issues to be resolved

[0009] However, Patent Document 1 does not specifically study polyamide-based resin foamed beads containing a flame retardant, nor does it specifically disclose a polyamide-based resin foamed particle molded article having improved flame retardancy.

[0010] The present invention is completed in view of the above-mentioned technical problems, and its purpose is to provide polyamide resin foamed particles and polyamide resin foamed particle molded bodies, wherein the polyamide resin foamed particles show good in-mold moldability and can provide foamed particle molded bodies showing excellent flame retardancy, and the polyamide resin foamed particle molded bodies have excellent flame retardancy.

[0011] (2) Technical solution

[0012] The polyamide resin foamed particles of the present invention are foamed particles containing a flame retardant, characterized in that the flame retardant comprises: one or more flame retardants (flame retardant a) selected from the group consisting of metal salts of phosphinic acid, metal salts of diphosphonic acid, and mixtures thereof; and one or more flame retardants (flame retardant b) selected from the group consisting of reaction products of melamine and polyphosphoric acid, reaction products of melamine condensates and polyphosphoric acid, and mixtures thereof, the base resin of the foamed particles comprises a polyamide resin, and the total amount of the flame retardant a and the flame retardant b blended relative to 100 parts by mass of the base resin is 10 parts by mass or more. The polyamide resin foamed particles are characterized in that the amount of the flame retardant a is less than 30 parts by mass, the mass ratio of the blending amount of the flame retardant a to the blending amount of the flame retardant b is 90:10 to 30:70 (the total of the flame retardant a and the flame retardant b is 100% by mass), the average bubble diameter A of the above-mentioned polyamide resin foamed particles is greater than or equal to 5 μm and less than or equal to 100 μm, and the average bubble diameter B of 5 bubbles observed in the cross-section formed by dividing the above-mentioned polyamide resin foamed particles into two equal parts is less than or equal to 250 μm.

[0013] Furthermore, the polyamide-based resin foamed bead molded article of the present invention is characterized in that it is formed by in-mold molding the polyamide-based resin foamed beads of the present invention.

[0014] (3) Beneficial effects

[0015] The present invention can provide polyamide resin foamed particles and polyamide resin foamed particle molded products. The polyamide resin foamed particles exhibit good in-mold moldability and can provide foamed particle molded products exhibiting excellent flame retardancy. The polyamide resin foamed particle molded products have excellent flame retardancy. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a DSC curve obtained according to the method for measuring transition heat of plastics described in JIS K7122:1987 for obtaining the total heat of fusion and the heat of fusion of the high temperature peak of the polyamide resin foamed particles according to one embodiment of the present invention. DETAILED DESCRIPTION

[0017] The polyamide resin foamed beads of the present invention (hereinafter, sometimes simply referred to as foamed beads) and the polyamide resin foamed bead molded article of the present invention (hereinafter, sometimes simply referred to as foamed bead molded article or molded article) are described below.

[0018] The foamed particles are polyamide resin foamed particles containing a flame retardant and a polyamide resin. The flame retardant includes flame retardant a and flame retardant b.

[0019] Flame retardant a is one or more phosphorus-based flame retardants selected from the group consisting of metal salts of phosphinic acid, metal salts of diphosphinic acid, and mixtures thereof. Flame retardant b is one or more nitrogen / phosphorus-based flame retardants selected from the group consisting of reaction products of melamine and polyphosphoric acid, reaction products of melamine condensates and polyphosphoric acid, and mixtures thereof. The foamed particles are blended with flame retardant a and flame retardant b within a specified range. Details of this specified range will be described later.

[0020] For the foamed beads containing flame retardants a and b, the bubbles observed in a cross section formed by bisecting the foamed beads exhibit values ​​within specified ranges, including an average bubble diameter A, which reflects the average bubble diameter of the bubbles in the foamed beads as a whole, and an average bubble diameter B, which is the average of five bubbles selected in descending order of area. Details of the average bubble diameter A and the average bubble diameter B will be described later.

[0021] The foamed particles contain the flame retardants a and b as specified above. Research by the inventors of this application has revealed that even when appropriate amounts of halogen-based flame retardants, or other conventional flame retardants, are added to polyamide resin foamed particles as flame retardants for the resin, sufficient flame retardancy is difficult to achieve. Furthermore, further research has revealed that the desired flame retardancy is demonstrated for the first time by simultaneously using the specified amounts of flame retardant a and flame retardant b. However, polyamide resin foamed particles that incorporate the required amounts of flame retardant a and flame retardant b have presented a new problem: in-mold moldability can sometimes be significantly deteriorated.

[0022] Therefore, focusing on the bubble diameter of the polyamide resin foamed particles, by adjusting the two average bubble diameters, the average bubble diameter A and the average bubble diameter B, it is possible to maintain good moldability and provide foamed particles that can be in-mold molded into polyamide resin foamed particle molded bodies exhibiting excellent flame retardancy.

[0023] The following describes the expanded beads of the present invention in further detail. In the following description, preferred numerical ranges of the present invention may be indicated as appropriate. In such cases, the preferred, more preferred, and particularly preferred ranges of the numerical ranges, including upper and lower limits, may be determined by any combination of the upper and lower limits.

[0024] In addition, in this specification, "A to B" which represents a numerical range has the same meaning as "A or more and B or less", and represents a numerical range including A and B as the endpoints of the numerical range.

[0025] In the following description, the term "base material" refers to a component comprising a base resin, a flame retardant, and any other additives, and constituting the polyamide resin foamed particles. Furthermore, the base resin is the polymer contained in the polyamide resin foamed particles, specifically comprising a polyamide resin and any other polymers blended therein.

[0026] In the following description, regarding expanded beads, "good in-mold moldability" means that an expanded bead molded article can be in-mold molded with the three indicators of weldability, surface properties, and recovery properties described below all exceeding specified evaluation levels.

[0027] [Flame retardant]

[0028] In the foamed beads, the total amount of flame retardant a and flame retardant b is 10 parts by mass or more and 30 parts by mass or less relative to 100 parts by mass of the base resin. From the perspective of maintaining good moldability while exhibiting superior flame retardancy, the total is preferably 12 parts by mass or more and 28 parts by mass or less, and more preferably 15 parts by mass or more and 25 parts by mass or less.

[0029] In the foamed beads, the mass ratio of flame retardant a to flame retardant b is in the range of 90:10 to 30:70. The mass ratio is the ratio of flame retardant a to flame retardant b when the total of the flame retardant a and flame retardant b is 100% by mass.

[0030] In the total 100 mass%, when the blending amount of flame retardant a exceeds 90 mass%, sufficient flame retardancy may not be exhibited. From the perspective of exerting better flame retardancy, the blending amount of flame retardant a in the total 100 mass% is preferably 85 mass% or less, more preferably 80 mass% or less, further preferably 75 mass% or less, and particularly preferably 70 mass% or less.

[0031] On the other hand, in the total 100 mass %, when the blending amount of flame retardant b is greater than 70 mass %, the moldability of the foamed beads may be damaged. From the perspective of showing better moldability, in the total 100 mass %, the blending amount of flame retardant b is preferably 60 mass % or less, more preferably 55 mass % or less, further preferably 50 mass % or more, and particularly preferably 45 mass % or less. From the above perspective, the mass ratio of the blending amount of flame retardant a to the blending amount of flame retardant b, in the total 100 mass %, is preferably in the range of 85:15 to 40:60, more preferably in the range of 80:20 to 45:55, further preferably in the range of 75:25 to 50:50, and particularly preferably in the range of 70:30 to 55:45.

[0032] As mentioned above, when only flame retardant a is added as a flame retardant, it is difficult to show good flame retardancy. The key point is to use flame retardant b at a specified ratio. On the other hand, as mentioned above, flame retardant b easily causes the moldability of polyamide resin foam particles to decrease. Therefore, relative to 100 parts by mass of the base resin, the amount of flame retardant b is preferably adjusted to more than 2 parts by mass and less than 10 parts by mass, more preferably adjusted to more than 3 parts by mass and less than 9 parts by mass, and further preferably adjusted to more than 4 parts by mass and less than 8 parts by mass.

[0033] (Flame retardant a)

[0034] The flame retardant a in the present invention is one or more phosphorus-based flame retardants selected from the group consisting of metal salts of phosphinic acid, metal salts of diphosphinic acid, and mixtures thereof. The metal phosphinic acid salt is represented by the following formula (I). The metal diphosphinic acid salt is represented by the following formula (II).

[0035] [Chemical Formula 1]

[0036]

[0037] [Chemical Formula 2]

[0038]

[0039] In the above formula (I) and formula (II), R 1 and R 2 Optional same or different. 1 and R 2 Each is a linear or branched alkyl group and / or aryl group having 1 to 6 carbon atoms. 3 It is a linear or branched alkylene group having 1 to 10 carbon atoms, an arylene group having 6 to 10 carbon atoms, an alkylarylene group having 6 to 10 carbon atoms, or an arylalkylene group having 6 to 10 carbon atoms. In formula (I) and formula (II), M is a calcium ion, a magnesium ion, an aluminum ion, and / or a zinc ion. m is 2 or 3, n is 1 or 3, and x is 1 or 2.

[0040] Flame retardant a can be a compound represented by formula (I) or formula (II), or can include two or more compounds. As flame retardant a, it is preferred to include a metal phosphinate represented by formula (I). As a metal salt of phosphinic acid, specifically, calcium dimethylphosphinate, aluminum dimethylphosphinate, zinc dimethylphosphinate, calcium ethylmethylphosphinate, aluminum ethylmethylphosphinate, zinc ethylmethylphosphinate, calcium diethylphosphinate, aluminum diethylphosphinate, zinc diethylphosphinate, etc. can be exemplified. Among them, as flame retardant a, it is more preferred to include an aluminum salt of phosphinic acid, and particularly preferably to include aluminum diethylphosphinate.

[0041] (flame retardant b)

[0042] The flame retardant b in the present invention is one or more nitrogen / phosphorus-based flame retardants selected from the group consisting of reaction products of melamine and polyphosphoric acid, reaction products of melamine condensates and polyphosphoric acid, and mixtures thereof. Examples of melamine condensates include melam, melem, and melon.

[0043] For example, melamine polyphosphate, which is a reaction product of melamine and polyphosphoric acid, is represented by the following formula (III). The reaction product of the condensate of melamine and polyphosphoric acid has melam, melem, or melon added thereto in place of melamine in the following formula (III).

[0044] [Chemical Formula 3]

[0045]

[0046] The flame retardant b may be a single compound represented by formula (III) or two or more compounds. Preferably, the flame retardant b comprises polyphosphate melamine represented by formula (III). In formula (III), n is the degree of condensation, which is approximately 2 to 500, preferably 3 to 50.

[0047] From the perspective of more easily obtaining foamed particles that exhibit excellent moldability and can mold a molded body with excellent flame retardancy, for the above-mentioned foamed particles, it is preferred that flame retardant a comprises an aluminum salt of phosphinic acid as the main component and flame retardant b comprises polyphosphate melamine as the main component, and more preferably flame retardant a comprises only an aluminum salt of phosphinic acid and flame retardant b comprises only polyphosphate melamine. In addition, flame retardant x comprising y as the main component means that in 100% by mass of flame retardant x, y is 60% by mass or more. In the 100% by mass of polyphosphate melamine in the above-mentioned combination, it is particularly preferred that the phosphorus content is 15% by mass or more and 30% by mass or less and the nitrogen content is 10% by mass or more and 20% by mass or less. As the flame retardant containing flame retardant a and flame retardant b, for example, the commercially available product "Exolit OP1312" manufactured by Clariant can be exemplified.

[0048] Other flame retardants:

[0049] In addition to the above-mentioned flame retardant a and flame retardant b, the above-mentioned foamed particles can further contain other flame retardants that are not any one of flame retardant a and flame retardant b. As other flame retardants, for example, zinc borate can be exemplified. By blending zinc borate with flame retardant a and flame retardant b, it is easy to show better flame retardancy, and it is easy to adjust average bubble diameter A and average bubble diameter B to a specified range. It is speculated that this is because the synergistic effect of flame retardant a and flame retardant b with zinc borate further improves flame retardancy, and zinc borate plays a good role as bubble nucleus when resin particles are foamed, thereby making it easy to manufacture foamed particles of desired bubble diameter. In addition to flame retardant a and flame retardant b, when further blending other flame retardants, relative to the blending amount of flame retardant a and flame retardant b totaling 100 mass parts, the blending amount of other flame retardants is preferably more than 1 mass part and less than 10 mass parts, more preferably more than 2 mass parts and less than 8 mass parts.

[0050] [Polyamide resin]

[0051] Examples of the polyamide-based resin contained in the base resin of the foamed beads include polyamide and polyamide copolymers, and polyamide copolymers are preferred.

[0052] Examples of the polyamide include homopolymers of poly(6-aminocaproic acid) (polycaprolactam, nylon 6), 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 nonamide) (nylon 69), poly(tetramethylene adipamide) (nylon 46), poly(tetramethylene sebacamide) (nylon 410), poly(pentamethylene adipamide) (nylon 56), and poly(pentamethylene sebacamide) (nylon 510).

[0053] The polyamide copolymer is a compound having two or more types of repeating units, wherein at least a part of each repeating unit has an amide bond.

[0054] Examples of the polyamide copolymer include polycaprolactam / polyhexamethylene adipamide copolymer (nylon 6 / 66), caprolactam / hexamethylenediaminoadipamide / laurolactam (nylon 6 / 66 / 12), and caprolactam / laurolactam copolymer (nylon 6 / 12).

[0055] As the polyamide resin, one of these polyamides and polyamide copolymers may be used alone, or two or more thereof may be used in combination. Among the above polyamide resins, a polyamide resin obtained by combining one or more selected from nylon 6, nylon 66, nylon 12, and nylon 6 / 66 is preferred, and one or more selected from nylon 6 / 66 / 12 and nylon 6 / 66 is more preferred.

[0056] The flexural modulus of above-mentioned polyamide-based resin is preferably more than 1000MPa, more preferably more than 1200MPa, further preferably more than 1500MPa.Be about different from the amide-based elastomer below 600MPa with the flexural modulus of above-mentioned polyamide-based resin, if the flexural modulus of above-mentioned polyamide-based resin is in above-mentioned scope, then after foaming, even if being exposed to normal temperature, also be difficult for shrinkage, be easy to obtain the expanded particles of high power, so preferred.In addition, the upper limit of the flexural modulus of above-mentioned polyamide-based resin is about about 3000MPa.From above-mentioned angle, the flexural modulus of above-mentioned polyamide-based resin is preferably more than 1000MPa and below 3000MPa, also preferably more than 1200MPa and below 2800MPa, further preferably more than 1500MPa and below 2500MPa.

[0057] The flexural modulus of the polyamide resin can be determined by allowing a test piece to stand at a temperature of 23° C. and a humidity of 50% for 24 hours, and then measuring the result in accordance with JIS K7171:2016.

[0058] (Melting point of polyamide resin)

[0059] From the perspective of improving the heat resistance of the expanded bead molded article formed by in-mold molding of the expanded beads, the polyamide resin preferably has a melting point of 180°C or higher, more preferably 185°C or higher, and even more preferably 190°C or higher. On the other hand, from the perspective of reducing the load on the apparatus caused by the heating medium during in-mold molding, the melting point is preferably 280°C or lower, more preferably 260°C or lower, and even more preferably 240°C or lower. From these perspectives, the preferred range of the melting point of the polyamide resin is preferably 180°C or higher and 280°C or lower, more preferably 185°C or higher and 260°C or lower, and even more preferably 190°C or higher and 240°C or lower.

[0060] The melting point of the polyamide resin refers to the melting point of a single polyamide resin when the foamed beads are composed of a single polyamide resin. When the foamed beads are composed of a mixture of two or more polyamide resins, the melting point of the polyamide resin refers to the melting point of the mixture prepared by kneading the polyamide resins in a predetermined composition ratio in advance using an extruder or the like.

[0061] The melting point of a polyamide resin can be determined according to JIS K7121:1987 using heat-flow differential scanning calorimetry as the temperature at the top of the melting peak (melting peak temperature) of a DSC curve. The DSC curve is obtained by heating a sample from 23°C at a heating rate of 10°C / min to a temperature 30°C higher than the end of the melting peak (first heating), then holding the sample at that temperature for 10 minutes, cooling the sample to 30°C at a cooling rate of 10°C / min, and heating the sample again at a heating rate of 10°C / min to a temperature 30°C higher than the end of the melting peak (second heating). If the DSC curve has multiple melting peaks, the melting peak temperature of the melting peak with the largest area is used as the melting point of the polyamide resin. For this measurement, a sample of the polyamide resin is used that has been conditioned by standing for 24 hours or more in an environment at 23°C and a relative humidity of 50%. As a measuring apparatus, for example, a high-sensitivity differential scanning calorimeter “EXSTAR DSC7020” (manufactured by SII Nono Technology Inc.) can be used.

[0062] (Base resin)

[0063] The base resin used for producing the foamed beads of the present invention may consist solely of the above-mentioned polyamide resin, or may contain other polymers in addition to the polyamide resin within a range not impairing the objects and effects of the present invention.

[0064] Examples of the other polymers include other thermoplastic resins other than polyamide resins, and polymers such as thermoplastic elastomers.

[0065] Examples of other thermoplastic resins include polyethylene resins, polypropylene resins, polystyrene resins, vinyl acetate resins, thermoplastic polyester resins, acrylate resins, methacrylate resins, and polyarylene sulfide resins.

[0066] Examples of the thermoplastic elastomer include styrene-based thermoplastic elastomers, olefin-based thermoplastic elastomers, and amide-based thermoplastic elastomers.

[0067] The content of the above-mentioned other polymers is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, further preferably 5 parts by mass or less, particularly preferably 3 parts by mass or less, and most preferably 0, that is, the base resin contains only the polyamide resin as a polymer.

[0068] (Base material)

[0069] The substrate constituting the foamed beads of the present invention comprises a substrate resin, flame retardant a, and flame retardant b, and may further comprise other flame retardants or arbitrary additives within the scope not impairing the purpose and effect of the present invention. The resin particles formed by melt-kneading the substrate and extruding it through an extruder to form particles can be used to manufacture the foamed beads of the present invention.

[0070] As the optional additives, various additives such as carbon-based colorants, flame retardants, terminal capping agents, antistatic agents, conductivity-imparting agents, weathering agents, lubricants, antioxidants, ultraviolet absorbers, metal deactivators, and crystal nucleating agents may be appropriately incorporated as needed. The total amount of these optional additives added varies depending on the intended use of the molded article, but is preferably 25 parts by mass or less, 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, relative to 100 parts by mass of the base resin.

[0071] Carbon colorants:

[0072] For example, expanded particle molded articles for automotive parts and the like are sometimes manufactured using expanded particles containing carbon-based colorants. However, compared to polyamide resin expanded particles without carbon-based colorants, those containing carbon-based colorants tend to have reduced moldability and, at the same time, reduced flame retardancy in the resulting molded articles. In contrast, the expanded particles of the present invention contain the aforementioned flame retardant a and flame retardant b within specified ranges, and the average cell diameters A and B are adjusted within specified ranges, thereby ensuring moldability and substantially improving flame retardancy. Therefore, even when containing carbon-based colorants, the expanded particles can be molded into polyamide resin expanded particle molded articles exhibiting excellent flame retardancy.

[0073] From the perspective of providing a foamed bead molded article exhibiting a desired color tone such as black and good flame retardancy by containing a carbon-based colorant in the polyamide resin foamed beads, the amount of the carbon-based colorant blended in 100% by mass of the foamed beads is preferably from 0.5% by mass to 5% by mass, and more preferably from 1% by mass to 4% by mass.

[0074] In this specification, a carbon-based colorant refers to a colorant containing carbon. Carbon-based colorants are typically black and can be rendered black by inclusion in foamed particles. Representative examples include carbon black and carbon nanotubes. Carbon black includes gas furnace black, oil furnace black, acetylene black, channel black, drum black, thermal black, and Ketjen black.

[0075] Flame retardant additives:

[0076] As additives that can be added arbitrarily to the substrate, for example, NOR-type hindered amines having a partial structure represented by the following formula (IV) can be cited. In addition, as R in the following formula (IV), alkyl, cycloalkyl, aralkyl, aryl, etc. can be cited. In addition, any structure is bonded to * in the following formula (IV). When the foamed particles contain NOR-type hindered amines, the NOR-type hindered amines mainly act as flame retardant adjuvants. By using NOR-type hindered amines together with flame retardant a and flame retardant b, even if the blending amount of flame retardant a and flame retardant b is reduced within the above-specified range, good flame retardancy can be more reliably demonstrated. In addition, by using NOR-type hindered amines having a partial structure represented by the following formula (IV) at the same time, it is easy to suppress agglomeration during the manufacture of foamed particles. In addition, agglomeration refers to the phenomenon that the foamed particles just released from the closed container stick to each other in the first-stage foaming process described later. Examples of commercially available compounds having a partial structure represented by formula (IV) include flame retardant additives NOR116 and Tinuvin123 manufactured by BASF Japan Ltd., and FP-T80 manufactured by ADEKA CORPORATION, which are reaction products of N,N'-ethane-1,2-diylbis(1,3-propylenediamine), cyclohexane, 4-butylamino-2,2,6,6-tetramethylpiperidine peroxide, and 2,4,6-trichloro-1,3,5-triazine; a reaction product of sebacic acid, bis(2,2,6,6-tetramethyl-1-(octyloxy)-4-piperidinyl) ester, 1,1-dimethylethyl hydroperoxide, and octane; and bis(1-undecanyloxy-2,2,6,6-tetramethylpiperidin-4-yl) carbonate. When a NOR hindered amine is blended into the polyamide resin foamed particles, the blending amount is preferably 0.5 to 8 parts by mass, more preferably 1 to 5 parts by mass, per 100 parts by mass of the total of flame retardant a and flame retardant b.

[0077] [Chemical Formula 4]

[0078]

[0079] [Average bubble diameter A and average bubble diameter B]

[0080] The average bubble diameter A of the polyamide resin foamed particles is greater than or equal to 5 μm and less than or equal to 100 μm. If the average bubble diameter A is within the above range, it means that the bubbles formed in the foamed particles are relatively small. If the average bubble diameter A of the polyamide resin foamed particles is too small, the in-mold formability of the foamed particles may be significantly deteriorated, thereby failing to obtain a foamed particle molded body. From this perspective, the average bubble diameter A is preferably greater than or equal to 10 μm, more preferably greater than or equal to 15 μm. The upper limit of the average bubble diameter A of the polyamide resin foamed particles is preferably less than or equal to 80 μm, more preferably less than or equal to 50 μm.

[0081] From the above viewpoints, the average cell diameter A of the polyamide resin foamed particles is preferably 10 μm or more and 80 μm or less, and more preferably 15 μm or more and 50 μm or less.

[0082] (Method for measuring average bubble diameter A)

[0083] The average cell diameter A is measured as follows.

[0084] First, roughly divide the foamed beads into two equal parts to expose the cut surface. And, take a photo of the cut foamed beads in a way that covers the entire cut surface. On the photographed photo, draw four straight lines at equal angles (i.e., 45°) from the periphery of the foamed beads through the center of the foamed beads to the relative periphery. Then, the value (L / N) obtained by dividing the total length L of the four line segments by the total number N of bubbles in contact with each line segment is used as the average bubble diameter a of one foamed bead. Perform this operation on more than 20 foamed beads, and the arithmetic mean is used as the average bubble diameter A of the foamed beads.

[0085] Furthermore, the polyamide resin foamed particles have an average cell diameter B of 250 μm or less, as measured by the method described below. Excessively large average cell diameter B may significantly deteriorate the in-mold moldability of the foamed particles, making it impossible to obtain a foamed particle molded article. To provide foamed particles exhibiting sufficient flame retardancy and superior moldability, the average cell diameter B is preferably 200 μm or less, more preferably 180 μm or less, even more preferably 170 μm or less, and particularly preferably 160 μm or less.

[0086] (Method for measuring average cell diameter B)

[0087] The average cell diameter B is measured as follows.

[0088] First, the foamed particles are roughly divided into two equal parts to expose the cut surface. In addition, a photo of the foamed particles after cutting is taken in a manner that covers the entire cut surface. All bubbles observed on the cut surface are subjected to image analysis to determine the area of ​​each bubble. Then, 5 bubbles are selected on the cut surface in descending order of the area of ​​each bubble. For each of the 5 selected bubbles, the diameter of a virtual circle having the same area as the area of ​​the bubbles is calculated. The values ​​of the 5 diameters thus obtained are arithmetic averaged, and the value thus obtained is used as the average bubble diameter b of one foamed particle. This operation is performed on more than 20 foamed particles, and the arithmetic average is used as the average bubble diameter B of the foamed particles.

[0089] As mentioned above, the average cell diameter A of polyamide resin foamed particles containing flame retardants a and b tends to decrease. However, if the average cell diameter B is too large, moldability may be significantly deteriorated in such foamed particles. This is believed to be because the strength of the bubble membrane of foamed particles containing flame retardants a and b tends to weaken, and if excessively large bubbles are formed, the bubbles are prone to rupture during molding. On the other hand, the average cell diameter B of the foamed particles of the present invention is adjusted to below a specified value, so even foamed particles containing flame retardants a and b and having a small average cell diameter A can maintain moldability.

[0090] The lower limit of average bubble diameter B is not particularly limited, but is greater than average bubble diameter A, preferably more than 1.3 times of average bubble diameter A, more preferably more than 1.5 times. In other words, the ratio [B / A] of average bubble diameter B to average bubble diameter A is greater than 1, preferably more than 1.3, more preferably more than 1.5. The ratio of average bubble diameter B to average bubble diameter A is within the above range, indicating that relatively large bubbles are formed in the foamed particles relative to the average bubble diameter A of the foamed particles. By simultaneously using and including flame retardant a and flame retardant b in polyamide resin foamed particles, the bubbles formed in the foamed particles become smaller as a whole and are easily formed into relatively large bubbles. From the perspective of more effectively maintaining the moldability of the foamed particles, the ratio of average bubble diameter B to average bubble diameter A (average bubble diameter B / average bubble diameter A) is preferably less than 10, more preferably less than 8.

[0091] From the above viewpoints, the ratio [B / A] is preferably 1.3 or more and 10 or less, and more preferably 1.5 or more and 8 or less.

[0092] The difference [BA] between the average cell diameter A and the average cell diameter B of the expanded beads is preferably 200 μm or less, more preferably 180 μm or less, and even more preferably 150 μm or less.

[0093] As described above, the present invention utilizes both flame retardants A and B within a specified range to improve flame retardancy, thereby facilitating the formation of relatively large-diameter bubbles within the expanded beads. Therefore, in expanded beads containing a mixture of large and small bubbles, the upper limit of the difference [BA] is preferably within the above range to more reliably prevent the average cell diameter B from becoming excessively large relative to the average cell diameter A, which could impair moldability. The lower limit of the difference [BA] is not specifically defined, but is preferably 60 μm or greater, and more preferably 80 μm or greater.

[0094] From the above viewpoints, the difference [BA] is preferably 60 μm or more and 200 μm or less, more preferably 60 μm or more and 180 μm or less, and even more preferably 80 μm or more and 150 μm or less.

[0095] From the perspective of achieving excellent flame retardancy while maintaining better moldability, it is particularly preferred that the average bubble diameter B is 250 μm or less and the difference between the average bubble diameter A and the average bubble diameter B [BA] is 60 μm or more and 200 μm or less, more preferably the average bubble diameter B is 180 μm or less and the difference between the average bubble diameter A and the average bubble diameter B [BA] is 60 μm or more and 180 μm or less, and further preferably the average bubble diameter B is 160 μm or less and the difference between the average bubble diameter A and the average bubble diameter B [BA] is 80 μm or more and 150 μm or less.

[0096] (Method for adjusting the average bubble diameter)

[0097] In the above-mentioned foamed beads, the method for adjusting the average cell diameter A and the average cell diameter B to be within the above-mentioned range is not particularly limited, but examples thereof include means such as Configurations 1 to 6 shown in the method for producing polyamide resin foamed beads described later.

[0098] [Polyamide resin foam particles]

[0099] Next, the physical properties of the above-mentioned foamed particles will be described. In addition, regarding the above-mentioned foamed particles, the first-stage foamed particles and the second-stage foamed particles will be described as appropriate. The first-stage foamed particles refer to the foamed particles obtained by the initial foaming process. Sometimes this initial foaming process is referred to as the first-stage foaming or the first-stage foaming process. In addition, the second-stage foamed particles refer to the foamed particles obtained by the second foaming process using the above-mentioned first-stage foamed particles. Sometimes this second foaming process is referred to as the second-stage foaming or the second-stage foaming process. In the manufacture of the above-mentioned foamed particles, when only the first-stage foaming process is carried out, the first-stage foamed particles are the foamed particles finally provided, and when the second-stage foaming process is carried out, the second-stage foamed particles are the foamed particles finally provided. The above-mentioned foamed particles include multi-stage foamed particles manufactured by the third-stage foaming and more-stage multi-stage foaming carried out using the second-stage foamed particles. In this specification, the foamed particles provided for in-mold molding are sometimes referred to as the foamed particles finally provided or the final foamed particles.

[0100] (Apparent density of foamed particles)

[0101] From the perspective of lightness and flame retardancy of the foamed bead molded article provided, the apparent density of the foamed beads is preferably 150 kg / m3 Below, more preferably 100 kg / m 3 Below, more preferably 80kg / m 3 In addition, from the perspective of the rigidity of the foamed particle molded body provided, the above apparent density is preferably 10 kg / m 3 More than 30 kg / m 3 More than 50 kg / m 3 above.

[0102] The preferred range of the apparent density of the foamed particles is, for example, 10 kg / m 3 Above and 150kg / m 3 Below 30kg / m 3 Above and 100kg / m 3 Below 50kg / m 3 Above and 80kg / m 3 The means for adjusting the apparent density to this range is not particularly limited, but for example, it is preferable to carry out the second-stage foaming step described later.

[0103] The apparent density of the foamed beads can be measured by the following method. First, place the foamed beads to be measured in an environment with an air temperature of 23°C, a relative humidity of 50%, and 1 atm for at least 24 hours. Using a metal mesh or the like, sink the foamed beads having a mass w (g) thus obtained into a graduated cylinder filled with 23°C alcohol. The volume v (cm) of the foamed beads is determined from the rise in the water level. 3 ), the mass w of the foamed particle group is divided by the volume v of the foamed particle group (w / v). As the above-mentioned alcohol, ethanol can be cited as an example. The value thus obtained is converted into kg / m 3 , from which the apparent density of the foamed particles (kg / m 3 ).

[0104] The bulk density of the foamed particles is determined by the following method. First, the foamed particles to be measured are placed in an environment with an air temperature of 23°C, a relative humidity of 50% and 1 atm for more than 24 hours. The foamed particle group of mass W (g) thus obtained is filled in a measuring cylinder, and the bottom of the measuring cylinder is tapped on the ground several times to stabilize the filling height of the foamed particle group in the measuring cylinder. Read the bulk volume V (L) of the foamed particle group indicated by the scale of the measuring cylinder, and divide the mass W of the foamed particle group by the bulk volume V (W / V) of the foamed particle group. Convert the value thus obtained into kg / m 3 , from which the bulk density of the foamed particles (kg / m 3 ).

[0105] (Stacking ratio of foamed particles)

[0106] From the viewpoint of obtaining a molded article having excellent lightness, the bulk ratio M of the expanded beads used for in-mold molding is preferably 15 times or more, more preferably 20 times or more, and even more preferably 25 times or more.

[0107] In order to obtain foamed particles with a large stacking ratio M, for example, it is preferred to implement multi-stage foaming such as the second stage foaming described later. When implementing the second stage foaming, it is preferred to adjust the stacking ratio M2 of the foamed particles (second stage foamed particles) obtained by the second stage foaming relative to the stacking ratio M1 of the foamed particles (first stage foamed particles) obtained by the initial foaming process to be greater than 1.2 and less than 3.0. By having a ratio (M2 / M1) of greater than 1.2, it is easy to obtain the desired stacking ratio M2, and by having a ratio (M2 / M1) of less than 3.0, it is possible to suppress the value of the average bubble diameter B from becoming too large, and it is easy to provide foamed particles with good moldability. From this perspective, the above ratio (M2 / M1) is more preferably greater than 1.2 and less than 2.0.

[0108] The bulk ratio M1 of the first-stage expanded particles obtained in the first-stage expansion step can be determined by the density (unit: kg / m 3 ) divided by the bulk density of the first-stage expanded particles (unit: kg / m³). The bulk ratio M1 of the first-stage expanded particles can be adjusted by, for example, the amount of foaming agent added during the first-stage foaming process, the temperature during foaming, the pressure difference between the pressure within the sealed container and the pressure of the environment in which the contents are released from the sealed container, and the like. Alternatively, the bulk density of the first-stage expanded particles can be determined using the first-stage expanded particles and applying the method for measuring the bulk density of the expanded particles described above.

[0109] Furthermore, the bulk ratio M2 of the second-stage expanded beads obtained by performing the second-stage expansion using the first-stage expanded beads can be adjusted to the density (unit: kg / m 3 ) divided by the bulk density of the second stage foamed particles (unit: kg / m 3 ). The bulk ratio M2 of the second-stage expanded particles can be adjusted, for example, by the pressure difference between the pressure within the bubbles of the first-stage expanded particles, which are given an internal pressure, and the pressure of the heating environment, or by the heating temperature, heating time, and the like. Alternatively, the bulk density of the second-stage expanded particles can be determined by using the second-stage expanded particles and applying the method for measuring the bulk density of the expanded particles described above.

[0110] The density of the base resin constituting the first-stage expanded beads and the density of the base resin constituting the second-stage expanded beads are the same as the density of the base resin constituting the resin particles used to produce them.

[0111] (Independent cell ratio of foaming particles)

[0112] From the perspective of providing expanded beads that exhibit excellent flame retardancy while maintaining good moldability, the expanded beads of the present invention preferably have a closed cell fraction of 40% or greater, more preferably 50% or greater, and even more preferably 60% or greater. The upper limit of the closed cell fraction of the expanded beads is not particularly limited, but is approximately 99%.

[0113] The closed cell ratio of the foamed particles is determined as follows. First, a bulk volume of approximately 20 cm 3 The foamed particle group is immersed in water, thereby measuring the apparent volume Va of the foamed particle group. Then, after the foamed particle group whose apparent volume Va has been measured is fully dried, the volume of the foamed particle group (the sum of the volume of the resin constituting the foamed particles and the total volume of the bubbles in the independent bubble part of the foamed particles) is measured according to step C described in ASTM-D2856-70 (true volume Vx). An air comparative pycnometer is used in the measurement of the true volume Vx. As the above-mentioned air comparative pycnometer, for example, the air comparative pycnometer "Beckman Model 1000 Air Comparison Pycnometer" manufactured by Tokyo-Science.Co, Ltd. can be cited. Then, the independent bubble rate is calculated by the following formula (1). Using different measurement samples, the independent bubble rate is measured 5 times using the same steps as above, and the arithmetic mean of the values ​​obtained in each measurement is calculated and used as the independent bubble rate of the foamed particles.

[0114] [Mathematical formula 1]

[0115] Closed cell ratio (%) = (Vx-W / ρ) × 100 / (Va-W / ρ) (1)

[0116] Vx: The true volume of the foamed particles measured by the above method (cm 3 )

[0117] Va: Apparent volume of the expanded particles measured by the rise in water level when the expanded particles are submerged in water in a graduated cylinder (cm3)

[0118] W: Mass of the foamed particle group (g)

[0119] ρ: Density of the resin constituting the foamed particles (g / cm 3 )

[0120] (High temperature peak)

[0121] The foamed beads of the present invention preferably have a crystal structure exhibiting the high-temperature peak described below. Polyamide resin foamed beads exhibiting the high-temperature peak appropriately prevent the foamed beads produced in the first-stage foaming process from clumping together. Therefore, the first-stage foamed beads obtained in the first-stage foaming process can be easily supplied to the second-stage foamed beads, enabling the second-stage foaming process to be effectively implemented. Furthermore, the heat resistance and moldability of the foamed beads can be more reliably ensured.

[0122] The high temperature peak is the first DSC curve measured by heat flow differential scanning calorimetry according to JIS K7122:1987, where 1 to 3 mg of polyamide resin foamed particles are used as a test piece and heated at a heating rate of 10°C / min from 23°C to a temperature 30°C higher than the end of the melting peak (see Figure 1 ), a melting peak (high temperature peak b) having a top temperature appears on the higher temperature side than the melting peak (intrinsic peak a) inherent to the polyamide resin. Figure 1 This is an example of a DSC curve of polyamide resin foamed particles measured by heat flow differential scanning calorimetry. Figure 1 , one high-temperature peak b is shown, but there may be two or more high-temperature peaks b.

[0123] Intrinsic peak a is a peak generated by the melting of inherent crystals of the base resin constituting the foamed beads, and is considered to be a peak typically exhibited by the base resin constituting the foamed beads due to the melting of crystals. Meanwhile, high-temperature peak b, which has a peak temperature on the high-temperature side of intrinsic peak a, is presumably a peak that appears when secondary crystals different from the crystals typically present in the base resin constituting the foamed beads are present.

[0124] The apex temperature of intrinsic peak a roughly coincides with the apex temperature of the melting peak that appears in the second DSC curve described later. On the other hand, high-temperature peak b does not appear in the second DSC curve. Therefore, intrinsic peak a and high-temperature peak b can be distinguished by comparing the shapes and peak positions of the first and second DSC curves.

[0125] The second DSC curve refers to a DSC curve obtained by holding the polyamide resin foamed particles after the first DSC curve measurement at a temperature 30°C higher than the end of the melting peak after the first DSC curve measurement for 10 minutes, cooling them to 30°C at a cooling rate of 10°C / min, and heating them again at a heating rate of 10°C / min to a temperature 30°C higher than the end of the melting peak.

[0126] From the perspective of obtaining a foamed bead molded article having excellent balance between cushioning and rigidity, the total heat of fusion of the high-temperature peak b having a vertex temperature closer to the high-temperature side than the vertex temperature of the intrinsic peak a is preferably more than 3J / g, more preferably more than 5J / g, and further preferably more than 7J / g. In addition, from the perspective of the widening of the pressure range of the formable steam during foamed bead in-mold molding, the total heat of fusion of the above-mentioned high-temperature peaks is preferably less than 30J / g, more preferably less than 20J / g, and further preferably less than 15J / g. In addition, when there are more than two above-mentioned high-temperature peaks b, the heat of fusion of the high-temperature peaks b represents the total heat of all high-temperature peaks b.

[0127] From this perspective, the total heat of fusion of the high temperature peak b of the expanded beads is preferably 3 J / g to 30 J / g, more preferably 5 J / g to 20 J / g, and even more preferably 7 J / g to 15 J / g.

[0128] The heat of fusion of the high temperature peak b is obtained as follows. Figure 1 In the DSC curve shown, a straight line is drawn connecting point I corresponding to 80°C and point II corresponding to the melting end temperature of the expanded beads. The melting end temperature is the high-temperature endpoint of high-temperature peak b, which is the intersection of high-temperature peak b and the baseline located on the higher-temperature side of the DSC curve.

[0129] Then, if Figure 1 As shown, the intersection point IV is the straight line passing through the maximum point III between the intrinsic peak a and the high temperature peak b and parallel to the vertical axis of the graph and the straight line connecting the point I and the point II.

[0130] The area enclosed by the straight line connecting points I and IV, the straight line connecting points III and IV, and the DSC curve connecting points I and III is defined as the area of ​​intrinsic peak a. Furthermore, the area enclosed by the straight line connecting points IV and II, the straight line connecting points III and IV, and the DSC curve connecting points III and II (the shaded portion) is defined as the area of ​​high-temperature peak b. The total heat of fusion of the foamed particles is calculated from the sum of the areas of intrinsic peak a and high-temperature peak b, and the heat of fusion of high-temperature peak b is calculated from the area of ​​high-temperature peak b.

[0131] In addition, the means for obtaining the high temperature peak b will be described in the method for producing the expanded beads described later.

[0132] [Method for producing polyamide resin foamed particles]

[0133] Next, a preferred embodiment of the method for producing the expanded beads (hereinafter also simply referred to as the present production method) will be described.

[0134] This production method includes a resin particle production step and a foaming step, and adjusts the average cell diameter A and average cell diameter B of the produced foamed particles so as to fall within a predetermined range. This production method can produce foamed particles that exhibit good moldability and can provide a foamed particle molded article exhibiting excellent flame retardancy.

[0135] (Resin pellet production process)

[0136] The resin pellet production process involves melt-kneading a base material containing a flame retardant and a polyamide resin to produce a melt-kneaded product, and then extruding the melt-kneaded product from an extruder to produce polyamide resin pellets. Typically, the melt-kneaded product extruded from the extruder is cut into the desired mass and shape. For example, the melt-kneaded product can be extruded into a strand with a circular cross-section, water-cooled, and then cut using a pelletizer to produce cylindrical resin pellets.

[0137] The flame retardants used herein include: one or more phosphorus-based flame retardants (flame retardant a) selected from the group consisting of metal salts of phosphinic acid, metal salts of diphosphinic acid, and mixtures thereof; and one or more nitrogen / phosphorus-based flame retardants (flame retardant b) selected from the group consisting of reaction products of melamine and polyphosphoric acid, reaction products of melamine condensates and polyphosphoric acid, and mixtures thereof.

[0138] When flame retardant a and flame retardant b are blended, the total amount of flame retardant a and flame retardant b is adjusted to be greater than or equal to 10 parts by mass and less than or equal to 30 parts by mass relative to 100 parts by mass of the base resin containing the polyamide resin, and the mass ratio of the amount of flame retardant a to the amount of flame retardant b is 90:10 to 30:70 (the total amount of flame retardant a and flame retardant b is 100% by mass).

[0139] (Foaming process)

[0140] The foaming step is a step of foaming the polyamide-based resin particles obtained in the resin particle production step to produce foamed polyamide-based resin particles.

[0141] This manufacturing method can produce foamed particles by performing only the first-stage foaming step as the foaming step, or by performing a second-stage foaming step after the first-stage foaming step. Furthermore, a third-stage foaming step or more foaming steps can be performed after the second-stage foaming step. In this embodiment, the method of producing foamed particles by performing the second-stage foaming step is primarily described as an example.

[0142] The first stage of foaming process:

[0143] The resin particles formed in the resin particle production step are subjected to a first-stage foaming step. The first-stage foaming step involves supplying the resin particles, an aqueous medium such as water, an inorganic dispersant, and a surfactant to a pressure vessel, and performing a foaming particle production process comprising a dispersion step, a foaming agent impregnation step, and a release step to produce the foamed particles.

[0144] The above-mentioned dispersion process is a process of dispersing the resin particles in an aqueous medium containing an inorganic dispersant in a pressure vessel. Examples of the above-mentioned inorganic dispersant include inorganic substances such as aluminum oxide, calcium phosphate, magnesium pyrophosphate, zinc oxide, kaolin, mica, talc, and montmorillonite. In addition, a dispersant such as an anionic surfactant such as sodium dodecylbenzenesulfonate and sodium alkanesulfonate may be added together with the dispersant. In particular, when a compound (flame retardant aid) having a local structure represented by the above-mentioned formula (IV) is used together with flame retardant a and flame retardant b, it is preferred to use the above-mentioned inorganic dispersant or dispersant aid simultaneously in the dispersion process. This can effectively prevent the foamed particles from adhering to each other (caking) during the release process.

[0145] The blowing agent impregnation step is a step of impregnating the resin particles with a blowing agent such as carbon dioxide in a pressure vessel.

[0146] The releasing step is a step of releasing resin particles containing a foaming agent together with an aqueous medium from a pressure vessel to a pressure lower than the internal pressure of the pressure vessel to foam them, thereby obtaining first-stage expanded particles.

[0147] The first-stage foaming step is sometimes referred to as a "direct foaming method." However, the method for producing the foamed beads of the present invention is not limited to this method. For example, an "impregnation foaming method" in which resin particles impregnated with a foaming agent are heated to foam may be employed in place of the direct foaming method as the first-stage foaming step. The foamed beads obtained in this manner can then be suitably supplied to the second-stage foaming step described below.

[0148] When producing expanded beads having the high temperature peak b mentioned in the above description, for example, the following method can be used.

[0149] That is, the adjustment for obtaining the high temperature peak b can be implemented by adjusting the temperature increase rate of the temperature in the pressure vessel in the above-mentioned dispersion process and / or foaming agent impregnation process, or maintaining the temperature in the pressure vessel at a specified temperature for a specified time. More specifically, for example, in the above-mentioned dispersion process and / or foaming agent impregnation process, a first-stage holding process is performed at a temperature of (the melting point of the base resin - 20°C) or higher and lower than (the melting end temperature of the base resin) for about 10 minutes to 60 minutes. Then, the temperature is adjusted to (the melting point of the base resin - 15°C) or higher and lower than (the melting end temperature of the base resin). And, if necessary, a second-stage holding process is performed at this temperature for a further 10 minutes to 60 minutes. Next, a release process is performed, thereby producing foamed particles having a high temperature peak.

[0150] In addition to the above steps, any additional steps may be added to the first-stage foaming step in the present production method. In addition, when the second-stage foaming step is not performed, the first-stage foamed particles produced by the first-stage foaming process are provided as the foamed particles.

[0151] The second stage of foaming process:

[0152] The second-stage foaming step involves supplying the first-stage foamed particles produced as described above to a pressure-resistant container, injecting a foaming agent into the container to increase the internal pressure within the bubbles of the first-stage foamed particles, and then heating the container to cause foaming. The second-stage foaming step facilitates the production of foamed particles exhibiting a desired apparent density.

[0153] In addition, as described above, by adjusting the ratio (M2 / M1) of the stacking ratio M2 of the second-stage foamed particles obtained by the second-stage foaming to the stacking ratio M1 of the first-stage foamed particles to be greater than 1.2 and less than 3.0, preferably greater than 1.2 and less than 2.0, it is easy to obtain second-stage foamed particles showing the desired stacking ratio M2, and the value of the average bubble diameter B in the second-stage foamed particles can be prevented from becoming too large.

[0154] (Adjustment of average bubble diameter)

[0155] In the present manufacturing method having the above-mentioned resin particle production process and foaming process, the key points are to adjust so that the average bubble diameter A of the polyamide resin foamed particles is greater than 5 μm and less than 100 μm, and the average bubble diameter B of 5 bubbles observed on the cross-section formed by dividing the polyamide resin foamed particles into two equal parts is selected in order from large to small in terms of the area of ​​each bubble, so that it is less than 250 μm.

[0156] The method for adjusting the average cell diameter A and the average cell diameter B to fall within the above ranges is not particularly limited, but implementation of at least one of the following configurations 1 to 6 is preferred because it facilitates adjustment of the average cell diameter.

[0157] Composition 1:

[0158] Zinc borate is added to the substrate constituting the foamed beads in an amount of 0.5 parts by mass or more and 10 parts by mass or less relative to 100 parts by mass of the substrate resin contained in the substrate. By adding zinc borate to the substrate within this range, the average cell diameter A and the average cell diameter B of the foamed beads can be easily adjusted to within a specified range, and a foamed bead molded article exhibiting more excellent flame retardancy can be easily provided.

[0159] Composition 2:

[0160] In the resin pellet production step, the temperature of the melt-kneaded product extruded from the extruder is adjusted to 250°C or higher and 275°C or lower. This facilitates adjustment of the average cell diameter A and average cell diameter B of the resulting expanded particles within the specified ranges. While the reason for this is unclear, it is believed that the decomposition of part of the flame retardant a or part of the flame retardant b generates gas, which tends to suppress the gas from acting as a nucleating agent or foaming agent for the bubbles.

[0161] Composition 3:

[0162] A twin-screw extruder is used as the extruder in the resin pellet production process. Compared to a single-screw extruder, a twin-screw extruder can fully knead the substrate supplied to the extruder. By using a melt-kneaded product that has been fully kneaded at this stage, it is easy to adjust the average cell diameter A and average cell diameter B of the resulting foamed particles to within the above-specified ranges. Although the reason for this is unclear, it is believed that the component that acts as a nucleating agent during the foaming process is easily evenly dispersed in the resin particles.

[0163] Composition 4:

[0164] The foaming process utilizes a direct foaming method to produce the foamed particles. By ensuring that the amounts of the dispersant and surfactant added during the dispersion process are within specified ranges, agglomeration can be more effectively suppressed, making it easier to adjust the average cell diameter A and average cell diameter B of the resulting foamed particles to within specified ranges. Specifically, the amount of the inorganic dispersant added to the aqueous medium is preferably 0.3 parts by mass to 2.0 parts by mass per 100 parts by mass of the resin particles, and the amount of the surfactant added to the aqueous medium is preferably 0.2 parts by mass to 1.5 parts by mass per 100 parts by mass of the resin particles.

[0165] When the flame retardant is included, there is a tendency for the foamed particles to clump together during the foaming process. However, by adding the inorganic dispersant within the above range, the occurrence of such clumps can be effectively prevented.

[0166] A NOR-type hindered amine having a partial structure represented by formula (IV) is added to the base material constituting the foaming resin in an amount ranging from 0.5 parts by mass to 8 parts by mass relative to 100 parts by mass of the total of flame retardant a and flame retardant b. Adding the NOR-type hindered amine to the base material within this range more effectively suppresses agglomeration, making it easier to adjust the average cell diameter A and average cell diameter B of the resulting foamed particles to within the specified range. While the reason for this is unclear, it is believed that the NOR-type hindered amine facilitates moderate attraction of the inorganic dispersant in the aqueous medium through electrical interaction.

[0167] Composition 6:

[0168] As shown in this embodiment, from the perspective of adjusting the average cell diameter, it is preferable that the foaming step includes a first-stage foaming step and a second-stage foaming step.

[0169] The first-stage foaming step involves dispersing polyamide resin particles in a sealed container containing a dispersion medium such as water and impregnating the particles with a foaming agent to produce expandable polyamide resin particles. Subsequently, one end of the sealed container is opened to release the expandable polyamide resin particles and the dispersion medium to a pressure lower than the pressure within the sealed container, thereby foaming the particles. Specifically, the first-stage foaming step includes the dispersion step, the foaming agent impregnation step, and the release step.

[0170] In addition, the second-stage foaming process is a process in which the first-stage foamed particles obtained by the first-stage foaming process are supplied to a pressure-resistant container, and internal pressure is applied to heat them to cause them to foam, thereby obtaining polyamide resin foamed particles having a stacking ratio M2 greater than the stacking ratio M1 of the first-stage foamed particles.

[0171] In Configuration 6, the ratio (M2 / M1) of the bulk ratio M1 of the first-stage expanded particles obtained in the first-stage expansion step to the bulk ratio M2 of the polyamide resin expanded particles as the second-stage expanded particles obtained in the second-stage expansion step is preferably adjusted to be 1.2 or more and 3.0 or less, and more preferably adjusted to be 1.2 or more and 2.0 or less. In this case, the expansion of bubbles in the second-stage expansion step can be suppressed, making it easier to adjust the average cell diameter A and average cell diameter B of the expanded particles to within the specified range.

[0172] Furthermore, regarding Configuration 6, in the second-stage foaming step, it is preferred that the pressure (pressurization pressure) in the pressure-resistant container be adjusted to a range of 0.3 MPa to 1 MPa and then maintained for at least 24 hours to impart internal pressure to the first-stage foamed particles.

[0173] Furthermore, regarding Configuration 6, in the second-stage foaming step, the first-stage foamed particles, which have been given an internal pressure, are preferably heated with steam at a pressure of 0.01 MPa to 0.08 MPa, and more preferably with steam at a pressure of 0.01 MPa to 0.04 MPa. Thus, by heating the first-stage foamed particles, which have been given an internal pressure, with steam at a lower pressure in the second-stage foaming step, bubble expansion can be suppressed, making it easier to adjust the average cell diameter A and average cell diameter B of the foamed particles to within a predetermined range.

[0174] [Polyamide resin foamed particle molded article]

[0175] The foamed particle molded article of the present invention is produced by in-mold molding the polyamide resin foamed particles. This foamed particle molded article exhibits excellent flame retardancy, surface properties, resilience, and a high fusion rate. This molded article is suitable for various applications, including automotive components and building materials. For evaluation of the surface properties and resilience of the foamed particle molded article, as well as determination of the fusion rate, refer to the description in the Examples described below.

[0176] (Combustion test)

[0177] The flame retardancy of the expanded bead molded article was evaluated based on a horizontal burning test (UL94 horizontal burning test) in accordance with UL94 standards. The specific test method of the UL94 horizontal burning test is as follows.

[0178] Five test specimens with a skin surface measuring 150 ± 1 mm in length, 50 ± 1 mm in width, and 13 mm in thickness were cut from the expanded bead molded article. Marking lines were drawn on the test specimens at 25 mm, 60 mm, and 125 mm from one longitudinal end. After conditioning the test specimens at 23°C and 50% relative humidity for 24 hours, they were placed on a metal mesh with the markings facing upwards, and cotton was placed underneath. A winged burner was then adjusted to produce a blue flame of 38 mm ± 2 mm. The flame was ignited at one end of the test specimen. After one minute, the burner was moved at least 100 mm away from the test specimen, and the time and distance until the flame disappeared from the test specimen were measured.

[0179] To evaluate flame retardancy based on the UL94 horizontal combustion test, the flame retardancy rating of each of the five test pieces was determined as follows, based on the time and distance until the flame disappeared from the test piece. The rating for which four or more of the five test pieces met the requirements was determined as the flame retardancy of the expanded bead molded article.

[0180] HF-1: Meets all of the following conditions: The flame disappears within 2 seconds at a distance of 4 / 5 of the longitudinal dimension of the test piece from the end of the ignited flame; the flame disappears within 10 seconds at a distance of 1 / 5 of the longitudinal dimension of the test piece from the end of the ignited flame; the test piece remains open for 30 seconds or less; the cotton does not burn; and the combustion distance is 60 mm or less.

[0181] HF-2: The same conditions as HF-1 were met except that the cotton was burned.

[0182] HBF: Meets either of the following conditions: the burning rate between the line 25 mm from the end of the ignition flame and the line 125 mm from the end of the ignition flame is within 40 mm / min, or combustion stops between the line 25 mm from the end of the ignition flame and the line 125 mm from the end of the ignition flame.

[0183] (Molding body density)

[0184] From the perspective of achieving an excellent balance between lightness and physical properties such as rigidity and ensuring flame retardancy, the molded article density of the expanded beads is preferably 15 kg / m 3 Above and 100kg / m 3 Below, more preferably 20kg / m 3 Above and 70kg / m 3 the following.

[0185] The density of the expanded bead molded article is calculated by dividing the mass of the expanded bead molded article by the volume calculated based on the outer diameter. If the volume is difficult to calculate from the outer dimensions, the volume of the expanded bead molded article can be determined by three-dimensional measurement.

[0186] [Method for producing polyamide resin foamed particles molded article]

[0187] The above-mentioned foamed particle molded body is manufactured by in-mold molding using the above-mentioned foamed particles. The above-mentioned in-mold molding widely includes the well-known in-mold molding method using foamed particles. For example, the foamed particle molded body of the present invention is manufactured as described below. First, the above-mentioned foamed particles are filled in a molding mold having a cavity corresponding to the shape of the desired foamed particle molded body, and a heating medium such as steam is used to apply a prescribed molding pressure to the foamed particles filled in the molding mold and heat them. The above-mentioned molding pressure can be adjusted within a range of, for example, 0.12 MPa (G) or more and 0.30 MPa (G) or less. In addition, in this specification, (G) represents a gauge pressure, that is, a pressure value based on atmospheric pressure. Thus, the foamed particles in the cavity are heated to further foam them, and the foamed particles are fused with each other. After heating with steam or the like is completed, the pressure is released, and cooling of the mold and the molded article within the mold is rapidly initiated. Cooling is completed after confirming that the pressure (surface pressure) generated on the inner surface of the mold has reached 0.02 MPa (G), and the expanded bead molded article is removed from the mold. The cooling method herein is not specifically limited, but examples thereof include water cooling. Through this series of molding steps, an expanded bead molded article having a shape corresponding to the cavity is obtained.

[0188] Example

[0189] Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto.

[0190] Tables 1 to 3 show the composition (type) of the base material used for producing the foamed beads in each Example and each Comparative Example, and the blending amount of each component is shown as follows.

[0191] In Tables 1 to 3, the amount of flame retardant blended is the blending ratio (parts by mass) relative to 100 parts by mass of the base resin. The total amount of flame retardant blended and the blending amount of each component used as a flame retardant are also shown. In addition, the total amount of flame retardant a blended and flame retardant b blended (parts by mass) and the mass ratio (mass %) of flame retardant a and flame retardant b in the total amount of flame retardant a blended and flame retardant b blended (100 mass %) are also shown.

[0192] In Tables 1 to 3, the amount of the flame retardant auxiliary agent blended is a blending ratio (parts by mass) relative to 100 parts by mass of the base resin.

[0193] In Tables 1 to 3, the amount of the colorant blended is expressed as the blending ratio of the colorant in 100% by mass of the base material.

[0194] [Example 1]

[0195] <Production of Foamed Resin Pellets>

[0196] [Production of polyamide resin pellets]

[0197] A polyamide resin (type; 5033B, manufactured by UBE Corporation) as a base resin, a colorant (carbon black), flame retardants (flame retardant a, flame retardant b, zinc borate), and a flame retardant auxiliary were supplied to a twin-screw extruder in the amounts shown in Table 1 and melt-kneaded to produce a melt-kneaded product. Furthermore, talc as a bubble nucleating agent was supplied to the resin pellets obtained as described below at a concentration of 8000 ppm. The melt-kneaded product, adjusted to an extrusion temperature of 274°C, was extruded from the fine orifice of a die head mounted at the front end of the extruder into a single-layer strand with a circular cross-section. The extruded strands were water-cooled, cut into pieces with a mass of approximately 2 mg each using a pelletizer, and dried to produce polyamide resin pellets.

[0198] The polyamide resin (5033B) is a polyamide 6 / 66 copolymer (nylon 6 / 66), polyamide 6 / polyamide 66 = 85 / 15, with a melting point of 197°C and a density of 1.14 g / cm 3 , flexural modulus is 1300 MPa, melt flow rate (MFR) measured at 230°C and a load of 2.16 kg is 3.5 g / 10 min, product name: UBE NYLON 5033B.

[0199] Furthermore, model OP1312 is a flame retardant "Exolit OP1312" manufactured by Clariant, and contains an aluminum salt of phosphinic acid as flame retardant a and melamine polyphosphate as flame retardant b at a mass ratio of 2:1. Model OP1312 also contains 5% by mass of zinc borate.

[0200] <Manufacturing of Expanded Beads>

[0201] The first stage of foaming process:

[0202] Using the polyamide resin particles obtained as described above, a first-stage foaming step was carried out as follows.

[0203] First, 1000 g of polyamide resin particles and 3 liters of a dispersion medium (water) were placed in a 5-liter sealed container equipped with a stirrer. Then, 6 g of kaolin as a dispersant and 0.6 g of sodium alkylbenzene sulfonate as a surfactant were added to the dispersion medium relative to 100 parts by mass of the polyamide resin particles. The temperature of the dispersion medium was raised from room temperature (23°C) while stirring the contents of the sealed container. After the dispersion medium reached the impregnation temperature (135.2°C), carbon dioxide as a blowing agent was pressurized into the sealed container until the equilibrium vapor pressure within the sealed container reached 4 MPa. The temperature of the dispersion medium was raised from room temperature (23°C) to the impregnation temperature (135.2°C) over a period of 30 minutes. To demonstrate crystallinity with a high-temperature peak, the dispersion medium was maintained at a temperature of 135.2°C and an equilibrium vapor pressure of 4 MPa for 15 minutes, yielding resin particles impregnated with the blowing agent (expandable resin particles).

[0204] The expandable resin particles were then released together with the dispersion medium to atmospheric pressure (0.1 MPa) to expand. The resulting expandable particles were aged in an oven at 60°C for 24 hours and then slowly cooled to obtain first-stage expandable particles having a bulk ratio of 17.3.

[0205] The second stage of foaming process:

[0206] The first-stage foamed particles after aging are filled in a pressurized closed container. Then, the pressure in the closed container is increased from normal pressure to the pressurized pressure (0.6 MPa) shown in Table 1 for the time shown in Table 1 (1 day), thereby pressurizing the foamed particles. The foamed particles are kept in a pressurized state for 24 hours under this pressure so that air is impregnated into the bubbles of the foamed particles. Then, the foamed particles are taken out from the closed container. Then, the foamed particles are supplied to the second-stage foaming device, and steam (steam pressure 0.05 MPa) is supplied into the device to foam the foamed particles, thereby obtaining second-stage foamed particles with a stacking ratio of 26.6 times. Example 1 uses the second-stage foamed particles obtained by the second-stage foaming as the final foamed particles.

[0207] <Manufacturing of Foamed Bead Molded Articles>

[0208] [Production of Polyamide Resin Foamed Bead Molded Article]

[0209] First, the foamed particles are added to a pressure-resistant container, and the pressure in the pressure-resistant container is increased to the set pressure (0.08 MPa) shown in Table 1 over 12 hours. The pressurized state is maintained at this pressure for 24 hours to impart internal pressure to the foamed particles. Then, the foamed particles are filled into the cavity of the metal mold. As a molding mold, a metal mold with a flat-plate-shaped cavity of 200 mm in length, 65 mm in width, and 40 mm in thickness is used. The above-mentioned metal mold is set from a completely closed state to a state of opening 4 mm, and is adjusted in such a way that the opening amount is 10% relative to the thickness of the cavity of the metal mold of 40 mm. After the filling is completed, the metal mold is completely closed.

[0210] Steam was then supplied to the molding cavity, and in-mold molding was performed by heating to obtain a plate-shaped expanded bead molded article. The heating method was as follows: with the exhaust valves of both molds open, steam was supplied for 5 seconds to perform preheating (exhaust step), and then steam was supplied from the movable mold, followed by steam from the fixed mold, and then heating was performed to the molding pressure shown in Table 1 (0.16 MPa(G)).

[0211] After heating, the pressure was released and the mold was water-cooled until the surface pressure, caused by the foaming force of the molded product, dropped to 0.02 MPa(G). The mold was then opened and the molded product was removed. The molded product was aged in an 80°C oven for 12 hours and then gradually cooled to room temperature. This resulted in a foamed bead molded product.

[0212] [Examples 2 to 7 and Comparative Examples 1 to 7]

[0213] Except for changing the contents shown in Tables 1 to 3, expanded beads and expanded bead molded articles were produced in the same manner as in Example 1. These were designated as Examples 2 to 7 and Comparative Examples 1 to 7.

[0214] In Example 7, OP1230 used together with OP1312 was a flame retardant "Exolit OP1230" manufactured by Clariant, which is an aluminum salt of phosphinic acid. In Examples 2 and 4, NOR116 manufactured by BASF Japan Ltd. was used as a flame retardant auxiliary.

[0215] In addition, the model MC6000 used in Comparative Example 4 is a flame retardant manufactured by Nissan Chemical Corporation containing melamine cyanurate as a main component, the model SR-T20000 used in Comparative Example 5 is a flame retardant manufactured by Sakamoto Yakuhin Kogyo Co., Ltd. containing brominated epoxy as a main component, the model Hiromaster MA-80 used in Comparative Example 6 is a flame retardant manufactured by Suzuhiro Chemical Co., Ltd. containing brominated polystyrene as a main component, and the model PHOSMEL used in Comparative Example 7 is a flame retardant manufactured by Nissan Chemical Corporation containing melamine polyphosphate.

[0216] [Measurement of Physical Properties of Foamed Beads]

[0217] The physical properties of the first-stage expanded beads and / or the final expanded beads obtained as described above were measured as follows. Note that in Example 3 and Comparative Examples 3 to 7, no second-stage expansion was performed; therefore, the first-stage expanded beads were used as the final expanded beads. The measurement results are shown in Tables 1 to 3.

[0218] (Stacking ratio of foamed particles)

[0219] The density of the base resin constituting the first stage foamed particles (1140 kg / m 3 ) divided by the bulk density of the first stage foamed particles (unit: kg / m 3 ), and determine the stacking ratio M1 of the first-stage expanded particles obtained in the first-stage foaming step.

[0220] The density of the base resin constituting the second stage foam is 1140 kg / m 3 ) divided by the bulk density of the second-stage expanded particles described later (unit: kg / m 3 ), and determine the bulk ratio M2 of the second-stage expanded particles obtained by performing the second-stage expansion using the first-stage expanded particles.

[0221] Furthermore, the ratio (M2 / M1) of the stacking ratio M2 obtained as described above to the stacking ratio M1 is calculated.

[0222] (Bulk density of foamed particles)

[0223] First, place the first-stage foamed particles or the second-stage foamed particles in an environment with an air temperature of 23°C, a relative humidity of 50% and 1 atm for more than 24 hours. Fill the foamed particle group with a mass W (g) obtained in this way into a measuring cylinder, and tap the ground with the bottom of the measuring cylinder several times to stabilize the filling height of the foamed particle group in the measuring cylinder. Read the bulk volume V (L) of the foamed particle group indicated by the scale of the measuring cylinder, and divide the mass W of the foamed particle group by the bulk volume V (W / V) of the foamed particle group. Convert the value thus obtained into kg / m 3 , thus obtaining the bulk density of the foamed particles (kg / m 3 ).

[0224] (Apparent density of foamed particles)

[0225] The apparent density of the foamed particles is determined by the following method. First, the foamed particles to be measured are placed in an environment with an air temperature of 23°C, a relative humidity of 50%, and 1 atm for more than 24 hours. The foamed particle group having a mass w (g) thus obtained is sunk into a graduated cylinder filled with 23°C ethanol using a metal mesh or the like, and the volume v (cm) of the foamed particle group is calculated based on the rise in the water level. 3 ), the mass w of the foamed particle group is divided by the volume v of the foamed particle group (w / v). The value thus obtained is converted to kg / m 3 , thus obtaining the apparent density of the foamed particles (kg / m 3 ).

[0226] (Average bubble diameter A of foamed particles)

[0227] First, roughly divide the foamed beads into two equal parts to expose the cut surface. Then, take a photo of the cut foamed beads in a manner that completely covers the cut surface. On the photographed photo, draw four line segments at equal angles (i.e., 45°) from the periphery of the foamed beads through the center of the foamed beads to the opposite periphery. Next, divide the total length L of the four line segments by the total number N of bubbles in contact with each line segment to obtain the value (L / N) as the average bubble diameter a of one foamed bead. Perform this operation on 50 foamed beads, and the arithmetic mean is the average bubble diameter A of the foamed beads.

[0228] (Average bubble diameter B of foamed particles)

[0229] Divide the foamed particles roughly into two equal parts to expose the cut surface. Then, take a photo of the foamed particles after cutting in a manner that covers the entire cut surface. Perform image analysis on all bubbles observed on the cut surface to determine the area of ​​each bubble. In addition, on the above-mentioned cut surface, select 5 bubbles in order from large to small in terms of the area of ​​each bubble. Calculate the diameter of a virtual circle with the same area as the 5 selected bubbles. Perform arithmetic average on the values ​​of the 5 diameters thus obtained, and use the value thus obtained as the average bubble diameter b of 1 foamed particle. Perform this operation on 50 foamed particles, and use the arithmetic average as the average bubble diameter B of the foamed particles.

[0230] Furthermore, the difference (BA) between the average cell diameter B obtained above and the average cell diameter A and the ratio (B / A) of the average cell diameter B to the average cell diameter A were calculated.

[0231] (High-temperature peak melting heat of foamed particles in the first stage)

[0232] According to the method for determining the transition heat of plastics described in JIS K7122:1987, 3 mg of the first-stage expanded particles were used as a test piece and heated at a heating rate of 10°C / min from 23°C to a temperature 30°C higher than the end of the melting peak of the test piece to obtain a DSC curve. The high-temperature peak melting heat of the first-stage expanded particles was determined from the DSC curve. Specifically, the high-temperature peak melting heat of the first-stage expanded particles was determined using Figure 1 As described above, in the DSC curve obtained using the expanded beads, a straight line is drawn connecting point I corresponding to 80°C on the DSC curve and point II corresponding to the melting end temperature of the expanded beads. The melting end temperature is the high-temperature endpoint of high-temperature peak b, which is the intersection of high-temperature peak b on the DSC curve and the baseline located on the higher-temperature side of high-temperature peak b.

[0233] Next, refer to Figure 1 As shown, the intersection point IV is the straight line passing through the maximum point III between the intrinsic peak a and the high temperature peak b and parallel to the vertical axis of the graph and the straight line connecting the point I and the point II.

[0234] And, the area of ​​the part surrounded by the straight line of connection point I and point IV, the straight line of connection point III and point IV, and the DSC curve of connection point I and point III is used as the area of ​​inherent peak a. In addition, the area of ​​the part (oblique line portion) surrounded by the straight line of connection point IV and point II, the straight line of connection point III and point IV, and the DSC curve of connection point III and point II is used as the area of ​​high temperature peak b. The value of the high temperature peak fusion heat (J / g) of the first stage foaming particles is calculated by the area of ​​high temperature peak b obtained as described above. In addition, the value of the fusion heat of the high temperature peak of the second stage foaming particles is generally consistent with the value of the fusion heat of the high temperature peak of the first stage foaming particles used in the manufacture of the second stage foaming particles. In the present embodiment, since the value of the fusion heat of the high temperature peak of the second stage foaming particles is consistent with the value of the fusion heat of the high temperature peak of the first stage foaming particles used in the manufacture of the second stage foaming particles in all examples, only the fusion heat of the high temperature peak of the first stage foaming particles is recorded in the table.

[0235] (Independent cell ratio of foaming particles)

[0236] Use the first-stage foaming particles or the second-stage foaming particles to build a volume of about 20cm 3 The expanded bead group was immersed in water to measure the apparent volume Va of the expanded bead group. The expanded bead group, after which the apparent volume Va was measured, was then thoroughly dried. The volume of the expanded beads (the sum of the volume of the resin constituting the expanded beads and the total volume of the closed cells within the expanded beads) (true volume Vx) was then measured according to procedure C of ASTM-D2856-70. This true volume Vx was measured using a Beckman Model 1000 Air Comparison Pycnometer manufactured by Tokyo-Science Co., Ltd.

[0237] Next, the closed cell ratio was calculated using the following formula (1): The closed cell ratio was measured five times using different measurement samples in the same procedure as above, and the arithmetic mean of the values ​​obtained in each measurement was calculated as the closed cell ratio of the expanded beads.

[0238] [Mathematical formula 2]

[0239] Closed cell ratio (%) = (Vx-W / ρ) × 100 / (Va-W / ρ) (1)

[0240] Vx: True volume of the foamed particle group measured in the above method (cm 3 )

[0241] Va: Apparent volume of the foamed particles measured by the rise in water level when the foamed particles are immersed in water in a graduated cylinder (cm3 )

[0242] W: Mass of the foamed particle group (g)

[0243] ρ: Density of the resin constituting the foamed particles (g / cm 3 )

[0244] [Measurement of Physical Properties of Expanded Bead Molded Articles]

[0245] The physical properties of the foamed bead molded article produced as described above were measured or evaluated as follows. The results are shown in Tables 1 to 3. The evaluations were considered practical if they were △ or 0.

[0246] (Molding density of foamed particle molded article)

[0247] It is calculated by dividing the mass of the expanded bead molded article by the volume calculated based on the outer diameter.

[0248] (Evaluation of Surface Properties of Foamed Bead Molded Articles)

[0249] The surface properties of the expanded bead molded article were visually observed and evaluated in the following manner.

[0250] ○ (Excellent)····The voids in the foamed beads on the surface of the molded article are completely filled.

[0251] △ (Fair)···Some areas on the surface of the molded article where the voids of the foamed beads were not filled were found.

[0252] × (poor)····Unfilled voids between foamed particles can be seen everywhere on the surface of the molded article.

[0253] (Fusion rate of foamed particle molded body)

[0254] A test piece (100 mm long x 100 mm wide x thickness = thickness of the foamed bead molded article) was cut from the center of the foamed bead molded article. A slit of approximately 5 mm was made in the thickness direction of each test piece with a utility knife, and the test piece was then cut at the slit. Next, the number of all foamed beads present on the fractured surface of the foamed bead molded article (n) and the number of foamed beads with material failure (b) were measured. The ratio of the number of foamed beads with material failure (b) to the number of foamed beads (n) was expressed as a percentage and evaluated as the fusion rate (%) as follows.

[0255] ○ (Excellent)···The fusion rate is 80% or more.

[0256] × (poor)···The fusion rate is less than 80%.

[0257] (Resilience of Foamed Bead Molded Articles)

[0258] After the in-mold molding, the expanded particle molded body was taken out from the molding mold and allowed to stand for 24 hours in an environment with an air temperature of 23° C. and a relative humidity of 50% for aging.

[0259] The thickness of the foamed particle molded body is measured at a position 10 mm away from the four corners toward the center of the surface surface in the top view when observing the matured foamed particle molded body from the thickness direction. And the largest value among these thicknesses is taken as the thickness of the corner of the foamed particle molded body. In addition, the thickness of the foamed particle molded body is measured at a position that is central in both the longitudinal and transverse directions in the top view when observing the same foamed particle molded body from the thickness direction, and this value is taken as the thickness of the central part of the foamed particle molded body. And the ratio (%) of the thickness of the central part of the foamed particle molded body to the thickness of the corner is calculated and evaluated in the following manner.

[0260] ○ (excellent)····ratio (%) is 90% or more.

[0261] Δ(normal)···The ratio (%) is 85% or more and less than 90%.

[0262] ×(inferior)····Ratio (%) is less than 85%.

[0263] (Flame Retardancy of Foamed Bead Molded Article)

[0264] The flame retardancy of the expanded bead molded article was evaluated in the following manner based on a horizontal burning test (UL94 horizontal burning test) in accordance with the UL94 standard.

[0265] First, cut five test pieces with a skin surface, measuring 150±1 mm in length, 50±1 mm in width, and 13 mm in thickness, from the expanded bead molded article. Mark lines on the 150±1 mm in length, 50±1 mm in width, at positions 25 mm, 60 mm, and 125 mm from one longitudinal end of the test piece. After conditioning the test piece at 23°C and 50% relative humidity for 24 hours, place the test piece on a metal mesh with the marked lines facing upwards, and place cotton underneath. Then, ignite a winged burner with a blue flame of 38 mm ± 2 mm at one end of the test piece. After one minute, move the burner at least 100 mm away from the test piece, and measure the time and distance until the flame disappears from the test piece.

[0266] Based on the time and distance measured as described above, the flame retardancy levels of the five test pieces were determined, classified as HF-1, HF-2, and HBF. For details on HF-1, HF-2, and HBF, refer to the description of the foamed beads above.

[0267] The flame retardancy of the expanded bead molded article was determined based on the number of test pieces satisfying the conditions for four or more of the five test pieces, and is shown in Tables 1 to 3. Furthermore, in Tables 1 to 3, the number of test pieces satisfying the HF-1 standard for each Example and Comparative Example is shown in parentheses in the row corresponding to the evaluation level.

[0268] (Dripping Evaluation of Foamed Bead Molded Articles)

[0269] In the UL94 level test, the presence or absence of resin dripping from the test piece was observed and evaluated in the following manner.

[0270] ○···No cotton ignition caused by dripping

[0271] ×···There are cases of cotton ignition caused by dripping

[0272] [Table 1]

[0273]

[0274] [Table 2]

[0275]

[0276] [Table 3]

[0277]

[0278] The present invention described above includes the following technical ideas.

[0279] (1) A polyamide resin foamed particle comprising a flame retardant and a polyamide resin, wherein:

[0280] The flame retardant comprises: one or more flame retardants selected from the group consisting of metal salts of phosphinic acid, metal salts of diphosphinic acid, and mixtures thereof (flame retardant a); and one or more flame retardants selected from the group consisting of reaction products of melamine and polyphosphoric acid, reaction products of melamine condensates and polyphosphoric acid, and mixtures thereof (flame retardant b).

[0281] The base resin of the foamed particles comprises a polyamide resin,

[0282] The total amount of the flame retardant a and the flame retardant b is 10 parts by mass or more and 30 parts by mass or less relative to 100 parts by mass of the base resin comprising the polyamide resin, and the mass ratio of the flame retardant a to the flame retardant b is 90:10 to 30:70 (the total amount of the flame retardant a and the flame retardant b is 100% by mass).

[0283] The average bubble diameter A of the polyamide resin foamed particles is greater than or equal to 5 μm and less than or equal to 100 μm, and among the bubbles observed on the cross-section formed by dividing the polyamide resin foamed particles into two equal parts, the average bubble diameter B of 5 bubbles selected in descending order of the area of ​​each bubble is less than or equal to 250 μm.

[0284] (2) The polyamide resin foamed particles according to (1) above, wherein the average cell diameter B is 160 μm or less.

[0285] (3) The polyamide resin foamed beads according to (1) or (2) above, wherein the difference [BA] between the average cell diameter A and the average cell diameter B is 60 μm or more and 200 μm or less.

[0286] (4) The polyamide resin foamed beads according to any one of (1) to (3) above, wherein the flame retardant a is aluminum phosphinate, and the flame retardant b is melamine polyphosphate.

[0287] (5) The polyamide resin foamed particles according to any one of (1) to (4) above, wherein the flame retardant a is aluminum phosphinate.

[0288] The flame retardant b is melamine polyphosphate,

[0289] In 100% by mass of the melamine polyphosphate, the phosphorus content is 15% by mass or more and 30% by mass or less, and the nitrogen content is 10% by mass or more and 20% by mass or less.

[0290] (6) The polyamide resin foamed beads according to any one of (1) to (5) above, wherein the amount of the flame retardant b is 2 parts by mass or more and 10 parts by mass or less relative to 100 parts by mass of the base resin containing the polyamide resin.

[0291] (7) The polyamide resin foamed particles according to any one of (1) to (6) above, wherein the polyamide resin foamed particles contain a carbon-based colorant, and the amount of the carbon-based colorant blended in 100% by mass of the polyamide resin foamed particles is 0.5% by mass or more and 5% by mass or less.

[0292] (8) The polyamide resin foamed particles according to any one of (1) to (7) above, further comprising a NOR-type hindered amine having a partial structure represented by the following formula (IV), wherein the amount of the NOR-type hindered amine blended is greater than or equal to 0.5 parts by mass and less than or equal to 8 parts by mass relative to 100 parts by mass of the total of the flame retardant a and the flame retardant b.

[0293] (In formula (IV), R is any one of an alkyl group, a cycloalkyl group, an aralkyl group, and an aryl group, and * is a bond to any structure)

[0294] [Chemical Formula 5]

[0295]

[0296] (9) The polyamide resin foamed particles according to any one of (1) to (8) above, wherein the apparent density of the polyamide resin foamed particles is 10 kg / m 3 Above and 80kg / m 3 the following.

[0297] (10) The polyamide resin foamed particles according to any one of (1) to (9) above, further comprising zinc borate, wherein the amount of the zinc borate blended is 0.5 parts by mass or more and 10 parts by mass or less relative to 100 parts by mass of the base resin.

[0298] (11) A polyamide resin foamed bead molded article obtained by in-mold molding the polyamide resin foamed beads according to any one of (1) to (10) above.

[0299] (12) A method for producing polyamide resin foam particles, comprising:

[0300] a resin pellet production step of melt-kneading a base material containing a flame retardant and a polyamide resin to produce a melt-kneaded product, and extruding the melt-kneaded product from an extruder to produce polyamide resin pellets; and

[0301] a foaming step of foaming the polyamide resin particles to produce polyamide resin foamed particles;

[0302] The flame retardant comprises one or more flame retardants selected from the group consisting of metal salts of phosphinic acid, metal salts of diphosphinic acid, and mixtures thereof (flame retardant a), and one or more flame retardants selected from the group consisting of reaction products of melamine and polyphosphoric acid, reaction products of melamine condensates and polyphosphoric acid, and mixtures thereof (flame retardant b).

[0303] Relative to 100 parts by mass of the base resin containing the polyamide resin, the total amount of the flame retardant a and the flame retardant b is greater than 10 parts by mass and less than 30 parts by mass, and the mass ratio of the flame retardant a to the flame retardant b is 90:10 to 30:70 (the total amount of the flame retardant a and the flame retardant b is 100% by mass).

[0304] (13) A method for producing polyamide resin foamed particles, comprising: performing at least one of the following configurations 1 to 6 in the production method described in (12).

[0305] Configuration 1: Zinc borate is added to the base material in an amount ranging from 0.5 parts by mass to 10 parts by mass based on 100 parts by mass of the base resin.

[0306] Configuration 2: In the resin pellet production step, the temperature of the melt-kneaded product extruded from the extruder is adjusted to 250° C. or higher and 275° C. or lower.

[0307] Configuration 3: The extruder in the resin pellet production process is a twin-screw extruder.

[0308] Configuration 4: The foaming step includes at least a first-stage foaming step, wherein the polyamide resin particles, an inorganic dispersant, and a surfactant are dispersed in a sealed container supplied with a dispersion medium, and the particles are impregnated with a foaming agent to produce foamable polyamide resin particles. Subsequently, one end of the sealed container is opened, thereby releasing the foamable polyamide resin particles together with the dispersion medium to a pressure lower than the pressure in the sealed container, thereby foaming the particles.

[0309] The amount of the inorganic dispersant added to the aqueous medium is 0.3 parts by mass or more and 2.0 parts by mass or less relative to 100 parts by mass of the polyamide resin particles, and the amount of the surfactant added to the aqueous medium is 0.2 parts by mass or more and 1.5 parts by mass or less relative to 100 parts by mass of the polyamide resin particles.

[0310] Configuration 5: A NOR hindered amine having a partial structure represented by formula (IV) is added to the substrate in an amount of 0.5 parts by mass or more and 8 parts by mass or less relative to 100 parts by mass of the total of flame retardant a and flame retardant b.

[0311] (In formula (IV), R is any one of an alkyl group, a cycloalkyl group, an aralkyl group, and an aryl group, and * is a bond to any structure)

[0312] [Chemical Formula 6]

[0313]

[0314] Configuration 6: The foaming step comprises:

[0315] In a first-stage foaming step, the polyamide resin particles are dispersed in a sealed container supplied with a dispersion medium and simultaneously impregnated with a foaming agent to produce foamable polyamide resin particles. Subsequently, one end of the sealed container is opened to release the foamable polyamide resin particles together with the dispersion medium to a pressure lower than the pressure in the sealed container, thereby foaming the particles; and

[0316] In the second-stage foaming step, the first-stage foamed particles obtained in the first-stage foaming step are supplied to a pressure-resistant container, internal pressure is applied, and heating is performed to foam them, thereby obtaining polyamide resin foamed particles having a bulk ratio M2 greater than the bulk ratio M1 of the first-stage foamed particles.

[0317] (14) A method for producing polyamide resin foamed particles according to the above (13), wherein, in the configuration 6, the ratio (M2 / M1) of the bulking ratio M1 of the first-stage foamed particles obtained in the first-stage foaming process to the bulking ratio M2 of the polyamide resin foamed particles obtained in the second-stage foaming process is greater than 1.2 and less than 2.0.

[0318] (15) A method for producing polyamide resin foamed particles according to (13) or (14) above, wherein, in the second-stage foaming process of the structure 6, after the internal pressure (pressurization pressure) inside the first-stage foamed particles is adjusted to a range of greater than 0.3 MPa and less than 1.0 MPa, the above-mentioned pressure is maintained for at least 24 hours, thereby imparting internal pressure to the first-stage foamed particles.

[0319] (16) A method for producing polyamide resin foamed particles according to any one of (13) to (15) above, wherein the first-stage foamed particles to which an internal pressure is applied are heated using steam having a pressure of 0.01 MPa or more and 0.08 MPa or less in the second-stage foaming step of the structure 6.

[0320] (17) A method for producing polyamide resin foamed particles according to any one of (12) to (16) above, wherein the average bubble diameter A of the polyamide resin foamed particles is greater than or equal to 5 μm and less than or equal to 100 μm, and the average bubble diameter B of five bubbles selected in descending order of area of ​​each bubble among the bubbles observed at a cross section formed by dividing the polyamide resin foamed particles into two equal parts is less than or equal to 250 μm.

Claims

1. A polyamide resin foamed particle, which is a foamed particle containing a flame retardant, wherein The flame retardant comprises: One or more flame retardants selected from the group consisting of metal salts of phosphinic acid, metal salts of diphosphinic acid, and mixtures thereof (flame retardant a); and one or more flame retardants (flame retardant b) selected from the group consisting of reaction products of melamine and polyphosphoric acid, reaction products of melamine condensates and polyphosphoric acid, and mixtures thereof, The base resin of the foamed particles comprises a polyamide resin, The total amount of the flame retardant a and the flame retardant b is 10 parts by mass or more and 30 parts by mass or less relative to 100 parts by mass of the base resin, and the mass ratio of the flame retardant a to the flame retardant b is 90:10 to 30:70, wherein the total amount of the flame retardant a and the flame retardant b is 100 parts by mass. The average bubble diameter A of the polyamide resin foamed particles is greater than or equal to 5 μm and less than or equal to 100 μm, and among the bubbles observed on the cross-section formed by dividing the polyamide resin foamed particles into two equal parts, the average bubble diameter B of 5 bubbles selected in descending order of the area of ​​each bubble is less than or equal to 250 μm.

2. The polyamide resin foamed particles according to claim 1, wherein The difference [BA] between the average cell diameter A and the average cell diameter B is 60 μm or more and 200 μm or less.

3. The polyamide resin foamed particles according to claim 1 or 2, wherein The average bubble diameter B is 160 μm or less.

4. The polyamide resin foamed particles according to any one of claims 1 to 3, wherein The flame retardant a is an aluminum salt of phosphinic acid, The flame retardant b is melamine polyphosphate.

5. The polyamide resin foamed particles according to any one of claims 1 to 4, wherein The blending amount of the flame retardant b is 2 parts by mass or more and 10 parts by mass or less relative to 100 parts by mass of the base resin.

6. The polyamide resin foamed particles according to any one of claims 1 to 5, wherein The polyamide resin foam particles contain a carbon-based colorant, The amount of the carbon-based colorant blended in 100% by mass of the polyamide-based resin foamed particles is 0.5% by mass or more and 5% by mass or less.

7. The polyamide resin foamed particles according to any one of claims 1 to 6, wherein The polyamide resin foamed particles further contain a NOR hindered amine having a partial structure represented by the following formula (IV): The amount of the NOR hindered amine is 0.5 parts by mass or more and 8 parts by mass or less relative to 100 parts by mass of the total of the flame retardant a and the flame retardant b. [Chemical Formula 1] In formula (IV), R is any one of an alkyl group, a cycloalkyl group, an aralkyl group, and an aryl group, and * is bonded to any structure.

8. The polyamide resin foamed particles according to any one of claims 1 to 7, wherein The apparent density of the polyamide resin foamed particles is 10 kg / m 3 Above and 80kg / m 3 the following. 9 . A polyamide resin foamed particle molded article formed by in-mold molding the polyamide resin foamed particles according to claim 1 .

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