Polyamide resin foam particles and polyamide resin foam particle molded articles

Abstract

To provide polyamide-based resin foam particles which can provide a foam particle molding that exhibits good in-mold moldability and excellent flame retardancy, and to provide a polyamide-based resin foam particle molding which is excellent in moldability and flame retardancy.SOLUTION: Polyamide-based resin foam particles comprises: a polyamide-based resin; a specific flame retardant a; and a specific flame retardant b, wherein with respect to 100 pts. mass of a base material resin comprising a polyamide-based resin, the total of a blending amount of the flame retardant a and a blending amount of the flame retardant b is 10 pts. mass or more and 30 pts. mass or less, a 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 (where the total of the flame retardant a and the flame retardant b is 100 mass%), and the polyamide-based resin foam particles are so constituted that their average air bubble diameter A is 5 μm or more and 100 μm or less and, among air bubbles observed as cross sections formed by equally dividing the polyamide-based resin foam particles into two, five air bubbles selected in the descending order of an area per air bubble give an average air bubble diameter B of 250 μm or less. Further, the polyamide-based resin foam particle molding is obtained by in-mold molding the polyamide-based resin foam particles.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to polyamide resin foam particles containing a flame retardant and a polyamide resin foam particle molded article with excellent flame retardancy obtained by in-mold molding of the above polyamide resin foam particles. [Background technology]

[0002] Polyamide resins are known for their high heat resistance, abrasion resistance, and chemical resistance compared to other common resin materials. Foamed molded articles made from these polyamide resins can be made lighter while maintaining these excellent properties. Therefore, foamed molded articles made from polyamide resins are expected to be used in automotive parts and other applications. In particular, foamed particle molded articles made from polyamide resins are expected to be used in engine hoods and engine covers in vehicles as materials with excellent heat insulation and sound insulation properties.

[0003] In various applications, including the automotive parts mentioned above, polyamide resin foam particle molded articles are sometimes required to have excellent flame retardancy.

[0004] For example, Patent Document 1 describes that various flame retardants can be incorporated into polyamide resin foam particles. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] WO2016 / 001109 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] However, Patent Document 1 does not contain any specific studies regarding the use of flame retardants, nor does it disclose any specific polyamide resin foam particles containing flame retardants or molded articles of polyamide resin foam particles with improved flame retardancy.

[0007] The present invention has been made in view of the above problems, and provides polyamide-based resin foam particles capable of providing a foam particle molded body that exhibits good in-mold formability and excellent flame retardancy, and a polyamide-based resin foam particle molded body excellent in flame retardancy.

Means for Solving the Problems

[0008] The polyamide-based resin foam particles of the present invention are polyamide-based resin foam particles containing a flame retardant and a polyamide-based resin, wherein the flame retardant comprises a phosphorus-based flame retardant (flame retardant a) composed of a metal salt of phosphinic acid and / or diphosphinic acid, and one or more nitrogen / phosphorus-based flame retardants (flame retardant b) selected from the group consisting of a reaction product of melamine and polyphosphoric acid, a reaction product of a condensate of melamine and polyphosphoric acid, and mixtures thereof. The total amount of the compounding amount of the flame retardant a and the compounding amount of the flame retardant b is 10 parts by mass or more and 30 parts by mass or less with respect to 100 parts by mass of the base resin containing the polyamide-based resin, and the mass ratio of the compounding amount of the flame retardant a to the compounding amount of the flame retardant b is 90:10 to 30:70 (where the total of the flame retardant a and the flame retardant b is 100% by mass). The average cell diameter A of the polyamide-based resin foam particles is 5 μm or more and 100 μm or less, and among the cells observed in the cut surface formed by bisecting the polyamide-based resin foam particles, the average cell diameter B of the five cells selected in descending order of the area per cell is 250 μm or less.

[0009] The polyamide-based resin foam particle molded body of the present invention is characterized in that it is formed by in-mold molding of the polyamide-based resin foam particles of the present invention.

Effects of the Invention

[0010] The present invention can provide polyamide-based resin foam particles capable of providing a foam particle molded body that exhibits good in-mold formability and excellent flame retardancy, and a polyamide-based resin foam particle molded body excellent in flame retardancy.

Brief Description of the Drawings

[0011] [Figure 1] This is a DSC curve obtained in accordance with the method for measuring the transition heat of plastics described in JIS K7122:1987 in order to obtain the total heat of fusion and the heat of fusion at the high-temperature peak of the polyolefin resin foam particles which are one embodiment of the present invention.

Embodiments for Carrying Out the Invention

[0012] Hereinafter, the polyamide resin foam particles of the present invention (hereinafter, may be simply referred to as the foam particles of the present invention) and the polyamide resin foam particle molded body of the present invention (hereinafter, may be simply referred to as the foam particle molded body of the present invention) will be described.

[0013] The foam particles of the present invention are polyamide resin foam particles containing a flame retardant and a polyamide resin. The above flame retardant includes a flame retardant a and a flame retardant b. The flame retardant a is a phosphorus-based flame retardant composed of a metal salt of phosphinic acid and / or diphosphinic acid. The flame retardant b is one or more nitrogen / phosphorus-based flame retardants selected from the group consisting of a reaction product of melamine and polyphosphoric acid, a reaction product of a condensate of melamine and polyphosphoric acid, and a mixture thereof. In the foam particles of the present invention, the flame retardant a and the flame retardant b are blended within a predetermined range. Details regarding such a predetermined range will be described later. [[ID=!17]] The foam particles of the present invention containing the flame retardant a and the flame retardant b, with respect to the bubbles observed on the cut surface formed by bisecting the foam particles, an average bubble diameter A that reflects the average bubble diameter of the bubbles in the entire foam particles and an average bubble diameter B that is the average value of five bubbles selected in descending order of the area per bubble each show values within a predetermined range. Details of the average bubble diameter A and the average bubble diameter B will be described later.

[0014] The foamed particles of the present invention contain the above-mentioned predetermined flame retardant a and flame retardant b as flame retardants. According to the inventors' studies, it was found that in polyamide resin foamed particles, sufficient flame retardancy is difficult to obtain even when various flame retardants that are conventionally used as flame retardants for resins, such as halogenated flame retardants, are blended in appropriate amounts. Further studies revealed that the desired flame retardancy can only be achieved by using predetermined amounts of flame retardant a and flame retardant b in combination. However, a new problem arose: polyamide resin foamed particles in which flame retardants a and flame retardant b are blended to the extent necessary to achieve the desired flame retardancy have significantly deteriorated in-moldability. Therefore, by focusing on the bubble diameter of polyamide resin foam particles and adjusting two types of average bubble diameters, average bubble diameter A and average bubble diameter B, to a predetermined range, it became possible to maintain good moldability and provide foam particles that enable in-mold molding of polyamide resin foam particle molded articles exhibiting excellent flame retardancy.

[0015] The foamed particles of the present invention will be described in more detail below. In the following description, preferred numerical ranges of the present invention may be indicated as appropriate. In this case, preferred ranges, more preferred ranges, and particularly preferred ranges regarding the upper and lower limits of the numerical range can be determined from all combinations of the upper and lower limits. In the following description, "base material" refers to the component that constitutes the polyamide resin foam particles, including the base resin, flame retardant, and other optional additives. The base resin is a polymer contained in the polyamide resin foam particles, and specifically includes the polyamide resin and other polymers that are optionally blended. Furthermore, in the following explanation, "good in-moldability or moldability" for foamed particles means that a foamed particle molded body in which all three indicators described later—fusionability, surface properties, and recovery properties—are evaluated to a predetermined level or higher can be molded in a mold.

[0016] [Flame retardant] The foamed particles of the present invention are prepared such that 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 per 100 parts by mass of the base resin. From the viewpoint of exhibiting better flame retardancy while maintaining good moldability, the above 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. Furthermore, in the foamed particles of the present invention, the mass ratio of the amount of flame retardant a to the amount of flame retardant b is adjusted to be in the range of 90:10 to 30:70. The above mass ratio is the blending ratio of the two when the total amount of flame retardant a and flame retardant b is 100% by mass. If the amount of flame retardant a exceeds 90% by mass in the total 100% by mass, sufficient flame retardancy may not be exhibited. From the viewpoint of exhibiting better flame retardancy, the amount of flame retardant a in the total 100% by mass is preferably 85% by mass or less, more preferably 80% by mass or less, and even more preferably 75% by mass or less. On the other hand, if the amount of flame retardant b exceeds 70% by mass in the total 100% by mass, the moldability of the foamed particles may be impaired. From the viewpoint of exhibiting better moldability, the amount of flame retardant b in the total 100% by mass is preferably 60% by mass or less, more preferably 50% by mass or less, and even more preferably 45% by mass or less. From the above viewpoint, the mass ratio of the amount of flame retardant a to the amount of flame retardant b is preferably in the range of 80:20 to 40:60, more preferably in the range of 75:25 to 50:50, and even more preferably in the range of 70:30 to 55:45.

[0017] As described above, when only flame retardant a is used as a flame retardant, it is difficult to achieve good flame retardancy, and it is essential to use flame retardant b in combination in a predetermined proportion. On the other hand, as described above, flame retardant b tends to reduce the moldability of polyamide resin foam particles. Therefore, the amount of flame retardant b blended per 100 parts by mass of base resin is preferably adjusted to 2 parts by mass or more and 10 parts by mass or less, more preferably to 3 parts by mass or more and 9 parts by mass or less, and even more preferably to 4 parts by mass or more and 8 parts by mass or less.

[0018] (Flame retardant a) In the present invention, flame retardant a is a phosphorus-based flame retardant comprising a metal salt of phosphinic acid and / or diphosphinic acid. In other words, flame retardant a is one or more phosphorus-based flame retardants selected from the group consisting of a phosphorus-based flame retardant comprising a metal salt of phosphinic acid, a phosphorus-based flame retardant comprising a metal salt of diphosphinic acid, and a mixture of a phosphorus-based flame retardant comprising a metal salt of phosphinic acid and a phosphorus-based flame retardant comprising a metal salt of diphosphinic acid. The above phosphinate metal salt is represented by the following formula (I). The above diphosphinate metal salt is represented by the following formula (II).

[0019] [ka]

[0020] [ka]

[0021] In formulas (I) and (II) above, R1 and R2 may be the same or different. R1 and R2 are linear or branched alkyl and / or aryl atoms having 1 to 6 carbon atoms, respectively. In formula (II), R3 is linear or branched alkylene having 1 to 10 carbon atoms, arylene having 6 to 10 carbon atoms, alkylarylene having 6 to 10 carbon atoms, or arylalkylene having 6 to 10 carbon atoms. In formulas (I) and (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.

[0022] The flame retardant a may be one compound represented by formula (I) or formula (II), or it may contain two or more compounds, and it is preferable that the flame retardant a contains a phosphinate metal salt represented by formula (I). Specific examples of phosphinate metal salts include calcium dimethylphosphinate, aluminum dimethylphosphinate, zinc dimethylphosphinate, calcium ethylmethylphosphinate, aluminum ethylmethylphosphinate, zinc ethylmethylphosphinate, calcium diethylphosphinate, aluminum diethylphosphinate, and zinc diethylphosphinate. Among these, it is more preferable that the flame retardant a contains an aluminum salt of phosphinate, and it is particularly preferable that it contains aluminum diethylphosphinate.

[0023] (Flame retardant b) The flame retardant b in this invention is one or more nitrogen / phosphorus-based flame retardants selected from the group consisting of reaction products of melamine and polyphosphate, reaction products of melamine condensates and polyphosphate, and mixtures thereof. Here, melamine condensates include melamine, melem, melon, etc. For example, polyphosphate melamine, a reaction product of melamine and polyphosphate, is represented by the following formula (III). The reaction product of melamine condensates and polyphosphate is obtained by adding melam, melem, melon, etc., in place of melamine in the following formula (III).

[0024] [ka]

[0025] The flame retardant b may be one compound represented by formula (III) or two or more compounds, but it is preferable that the flame retardant b includes polyphosphate melamine represented by formula (III). In formula (III), n is the degree of condensation, which is generally 2 to 500, and preferably 3 to 50.

[0026] From the viewpoint of successfully solving the intended problems of the present invention, it is preferable that the foamed particles of the present invention contain aluminum salt of phosphinic acid as the main component of flame retardant a, and melamine polyphosphate as the main component of flame retardant b, and it is more preferable that flame retardant a contains only aluminum salt of phosphinic acid, and flame retardant b contains only melamine polyphosphate. Note that containing y as the main component of flame retardant x means that y accounts for 60% by mass or more in 100% by mass of flame retardant x. In the above combinations, it is particularly preferable that the phosphorus content is 15% by mass or more and 30% by mass or less in 100% by mass of melamine polyphosphate, and the nitrogen content is 10% by mass or more and 20% by mass or less. An example of a flame retardant containing flame retardant a and flame retardant b as described above is the commercially available "Exolit OP1312" manufactured by Clariant.

[0027] Other flame retardants: The foamed particles of the present invention may further contain, in addition to the flame retardants a and b described above, other flame retardants that do not fall under either flame retardant a or flame retardant b. Examples of other flame retardants include zinc borate. When zinc borate is blended together with flame retardants a and b, better flame retardancy is more easily achieved, and the average bubble diameter A and average bubble diameter B can be easily adjusted to a predetermined range. This is presumed to be because the synergistic effect of flame retardants a and b and zinc borate further improves flame retardancy, and zinc borate acts well as a bubble nucleus during foaming of the resin particles, making it easier to produce foamed particles with a desirable bubble diameter. When other flame retardants are further blended in addition to flame retardants a and b, it is preferable that the amount of other flame retardants is 1 to 10 parts by mass, and preferably 2 to 8 parts by mass, per 100 parts by mass of the total amount of flame retardants a and b.

[0028] [Polyamide resin] Examples of polyamide resins in the present invention include polyamides or polyamide copolymers, with polyamide copolymers being preferred. Examples of the above polyamides include poly(6-aminohexanoic acid) (polycaproamide, nylon 6), also known as poly(caprolactam), poly(laurolactam) (nylon 12), poly(hexamethyleneadipamide) (nylon 66), poly(7-aminoheptanoic acid) (nylon 7), poly(8-aminooctanoic acid) (nylon 8), poly(9-aminononanoic acid) (nylon 9), poly(10-aminodecanoic acid) (nylon 10), and poly(11-amino Examples of homopolymers include poly(ndecanoic acid) (nylon 11), poly(hexamethylene sebamid) (nylon 610), poly(decamethylene sebamid) (nylon 1010), poly(hexamethylene azeramide) (nylon 69), poly(tetramethylene adipamide) (nylon 46), poly(tetramethylene sebamid) (nylon 410), poly(pentamethylene adipamide) (nylon 56), and poly(pentamethylene sebamid) (nylon 510). A polyamide copolymer is defined as a material having two or more repeating units, with at least a portion of each repeating unit having an amide bond. Examples of the polyamide copolymers mentioned above include polycaproamide / polyhexamethylene adipamide copolymer (nylon 6 / 66), caprolactam / hexamethylenediaminoadipic acid / lauryl lactam (nylon 6 / 66 / 12), and caprolactam / lauryl lactam copolymer (nylon 6 / 12). The polyamide resin may be made by using one of these polyamides and polyamide copolymers alone, or by using two or more in combination. Among the above polyamide resins, it is preferable to use a polyamide resin made by combining one or more selected from nylon 6, nylon 66, nylon 12, and nylon 6 / 66, and more preferably one or more selected from nylon 6 / 66 / 12 and nylon 6 / 66.

[0029] The polyamide resin used in this invention preferably has a flexural modulus of 1000 MPa or more, more preferably 1200 MPa or more, and even more preferably 1500 MPa or more. A flexural modulus within the above range of the polyamide resin is preferable because, unlike amide elastomers with a flexural modulus of 600 MPa or less, it is less prone to shrinkage when exposed to room temperature after foaming, making it easier to obtain foamed particles with a high magnification. The upper limit of the flexural modulus of the polyamide resin is approximately 3000 MPa.

[0030] The flexural modulus of polyamide resin can be determined by leaving a test specimen undisturbed for 24 hours at a temperature of 23°C and a humidity of 50%, and then measuring it in accordance with JIS K7171:2016.

[0031] (Melting point of polyamide resins) From the viewpoint of improving the heat resistance of the foam particle molded article obtained by in-mold molding of the foam particles of the present invention, the melting point of the above polyamide resin is preferably 180°C or higher, more preferably 185°C or higher, and even more preferably 190°C or higher. On the other hand, from the viewpoint of reducing the load on the equipment due to the heating medium during in-mold molding, the above melting point is preferably 280°C or lower, more preferably 260°C or lower, and even more preferably 240°C or lower. Furthermore, the melting point of the polyamide resin mentioned above refers to the melting point of the polyamide resin when the resin constituting the foamed particles is a single type of polyamide resin. When the foamed particles are composed of a mixture of two or more types of polyamide resins, the melting point of the polyamide resin mentioned above refers to the melting point of the mixture obtained by pre-mixing each polyamide resin, mixed in a predetermined composition ratio, using an extruder or the like.

[0032] The melting point of polyamide resins can be determined according to JIS K7121-1987 by differential scanning calorimetry (DSC). The sample is heated from 23°C to a temperature 30°C higher than the end of the melting peak at a heating rate of 10°C / min (first heating), then maintained at that temperature for 10 minutes, cooled to 30°C at a cooling rate of 10°C / min, and then heated again to a temperature 30°C higher than the end of the melting peak at a heating rate of 10°C / min (second heating). The melting point of the DSC curve obtained is the temperature at the peak of the melting peak (melting peak temperature). If the DSC curve has multiple melting peaks, the melting peak temperature of the melting peak with the largest area is adopted as the melting point of the polyamide resin. For the above measurement, a sample of polyamide resin that has been conditioned by standing for 24 hours or more in an environment of 23°C and 50% relative humidity is used. Furthermore, a high-sensitivity differential scanning calorimeter such as the "EXSTAR DSC7020" (manufactured by SII Nanotechnology Co., Ltd.) can be used as the measuring device.

[0033] (Base resin) The base resin used to produce the foamed particles of the present invention may consist solely of the polyamide resin described above, or it may contain other polymers other than polyamide resins, to the extent that they do not hinder the purpose and effects of the present invention.

[0034] Other polymers mentioned above include polymers other than polyamide resins, such as thermoplastic resins and thermoplastic elastomers. Other thermoplastic resins include, for example, polyethylene resins, polypropylene resins, polystyrene resins, vinyl acetate resins, thermoplastic polyester resins, acrylic ester resins, methacrylic ester resins, and polyarylene sulfide resins. Examples of thermoplastic elastomers include styrene-based thermoplastic elastomers, olefin-based thermoplastic elastomers, and amide-based thermoplastic elastomers. The content of the above-mentioned other polymers is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, even more preferably 5 parts by mass or less, and particularly preferably 0, i.e., the base resin contains only polyamide resin as a polymer.

[0035] (base material) The base material constituting the foamed particles of the present invention comprises a base resin and flame retardants a and b, and may also contain other flame retardants and optional additives to the extent that they do not hinder the purpose and effects of the present invention. The resin particles formed by melting and kneading the base material and extruding it from an extruder into granules are used in the production of the foamed particles of the present invention.

[0036] As the above optional additives, various additives such as colorants including carbon-based colorants, flame retardant aids, end-sealing agents, antistatic agents, conductivity imparting agents, weathering agents, lubricants, antioxidants, ultraviolet absorbers, metal deactivators, and crystal nucleating agents can be appropriately blended as needed. The total amount of these optional additives varies depending on the intended use of the molded article, but is preferably 25 parts by mass or less per 100 parts by mass of the base resin, more preferably 15 parts by mass or less, even more preferably 10 parts by mass or less, and even more preferably 5 parts by mass or less.

[0037] Carbon-based colorants: For example, foamed particle molded articles provided for automotive parts and the like may be manufactured using foamed particles containing carbon-based colorants. However, polyamide resin foamed particles containing carbon-based colorants tend to have lower moldability and lower flame retardancy compared to polyamide resin foamed particles that do not contain carbon-based colorants. In contrast, the foamed particles of the present invention contain the aforementioned flame retardants a and b within predetermined ranges, and the average cell diameter A and average cell diameter B are adjusted to predetermined ranges. As a result, moldability is ensured and flame retardancy is sufficiently improved, making it possible to in-mold polyamide resin foamed particle molded articles exhibiting good flame retardancy even when containing carbon-based colorants.

[0038] From the viewpoint of providing a foamed particle molded article in which polyamide resin foamed particles contain a carbon-based colorant, exhibit a desired color such as black, and have good flame retardancy, it is preferable that the amount of carbon-based colorant blended in 100% by mass of foamed particles is 0.5% by mass or more and 5% by mass or less, and more preferably 1% by mass or more and 4% by mass or less.

[0039] In the present invention, a carbon-based colorant is a colorant containing carbon. Carbon-based colorants are usually black and can be components that exhibit black color when contained in foamed particles. Typical examples include carbon black and carbon nanotubes. Carbon black includes gas furnace black, oil furnace black, acetylene black, channel black, roller black, thermal black, and Ketjen black.

[0040] Flame retardant additive: An example of an additive that can be optionally added to the base material is a NOR-type hindered amine having a substructure represented by the following formula (IV). Examples of R in formula (IV) below include alkyl groups, cycloalkyl groups, aralkyl groups, aryl groups, etc. Any structure can be bonded to * in formula (IV) below. In the present invention, the NOR-type hindered amine mainly acts as a flame retardant aid, and by using it in combination with flame retardants a and b, good flame retardancy can be achieved even if the amounts of flame retardants a and b are reduced. Furthermore, the use of a NOR-type hindered amine having a substructure represented by the following formula (IV) makes it easier to suppress blocking during the production of foamed particles. Blocking refers to the phenomenon in which foamed particles adhere to each other immediately after being released from a sealed container during the single-stage foaming process described later. Examples of commercially available compounds having the substructure shown in formula (IV) include the flame retardant additives NOR116 and Tinuvin123 manufactured by BASF Japan Ltd., and FP-T80 manufactured by ADEKA Corporation. When a NOR-type hindered amine is blended into polyamide resin foam particles, the amount blended is preferably 0.5 parts by mass or more and 8 parts by mass or less, and more preferably 1 part by mass or more and 5 parts by mass or less, per 100 parts by mass of the total of flame retardant a and flame retardant b.

[0041] [ka]

[0042] [Average bubble diameter A and average bubble diameter B] The average bubble diameter A of the polyamide resin foam particles of the present invention is 5 μm or more and 100 μm or less. An average bubble diameter A within the above range means that the bubbles formed in the foam particles are relatively small. If the average bubble diameter A of the polyamide resin foam particles is too small, the in-moldability of the foam particles will deteriorate significantly, and it may not be possible to obtain a molded foam particle article. From this viewpoint, the average bubble diameter A is preferably 10 μm or more, and more preferably 15 μm or more. The upper limit of the average bubble diameter A of the polyamide resin foam particles is preferably 80 μm or less, and more preferably 50 μm or less.

[0043] (Method for measuring average bubble diameter A) In relation to the present invention, the average bubble diameter A is measured as follows. First, divide the foam particle into approximately two equal parts to expose the cut surface. Then, take a photograph so that the entire cut surface is visible. On the photograph, draw four line segments at equal angles (i.e., 45°) from the periphery of the foam particle, through the center of the foam particle, to the opposite periphery. Next, divide the sum of the lengths of the four line segments L by the total number of bubbles N tangent to each line segment (L / N) and define the average bubble diameter a of one foam particle as this value. Perform this operation for 20 or more foam particles and define the arithmetic mean as the average bubble diameter A of the foam particles.

[0044] Furthermore, the polyamide resin foam particles of the present invention have an average cell diameter B of 250 μm or less, as measured by the method described later. If the average cell diameter B is too large, the in-moldability of the foam particles will deteriorate significantly, and it may not be possible to obtain a foam particle molded article. From the viewpoint of providing foam particles that exhibit excellent moldability while showing sufficient flame retardancy, the average cell diameter B is preferably 180 μm or less, more preferably 170 μm or less, and even more preferably 160 μm or less.

[0045] (Method for measuring average bubble diameter B) In relation to the present invention, the average bubble diameter B is measured as follows. First, divide the foam particle into approximately two equal parts to expose the cut surface. Then, take a photograph so that the entire cut surface is visible. By performing image analysis on all bubbles observed in the cut surface, measure the area of ​​each bubble. Then, select the five bubbles in descending order of their area from the above-mentioned cut surface. Assume a virtual circle with the same area as each of the five selected bubbles, and calculate the diameter of this virtual circle. The value obtained by arithmetic mean of these calculated diameters is defined as the average bubble diameter b of one foam particle. Perform this operation for 20 or more foam particles, and the arithmetic mean is defined as the average bubble diameter B of the foam particles.

[0046] As described above, foamed particles containing flame retardants a and b tend to have a small average bubble diameter A, and in such foamed particles, if the average bubble diameter B is excessively large, the moldability may deteriorate significantly. This is because foamed particles containing flame retardants a and b tend to have weaker bubble film strength, and if excessively large bubbles are formed, the bubbles are prone to bursting during molding. On the other hand, since the foamed particles of the present invention have an average bubble diameter B adjusted to a predetermined level or less, it is possible to maintain moldability even in foamed particles containing flame retardants a and b and having a small average bubble diameter A.

[0047] The lower limit of the average bubble diameter B is not particularly limited, but it is preferably larger than the average bubble diameter A, and preferably 1.3 times or more than the average bubble diameter A, and more preferably 1.5 times or more. In other words, the ratio of the average bubble diameter B to the average bubble diameter A [B / A] is greater than 1, preferably 1.3 or more, and more preferably 1.5 or more. When the ratio of the average bubble diameter B to the average bubble diameter A is within the above range, it means that relatively large bubbles are formed in the foamed particles relative to the average bubble diameter A of the foamed particles. When flame retardant a and flame retardant b are used in combination in polyamide resin foamed particles, the bubbles formed in the foamed particles become smaller overall, and relatively larger bubbles are more easily formed. From the viewpoint of more reliably maintaining the moldability of the foamed particles, the ratio of the average bubble diameter B to the average bubble diameter A (average bubble diameter B / average bubble diameter A) is preferably 10 or less.

[0048] The foamed particles of the present invention preferably have a difference [BA] between the average bubble diameter A and the average bubble diameter B of 200 μm or less, more preferably 180 μm or less, and even more preferably 150 μm or less. As described above, the present invention uses flame retardant a and flame retardant b in combination within a predetermined range from the viewpoint of improving flame retardancy, so relatively large diameter bubbles tend to form within the foamed particles. In foamed particles in which large and small bubbles are mixed in this way, from the viewpoint of more reliably suppressing the loss of moldability due to the average bubble diameter B becoming too large relative to the average bubble diameter A, it is preferable that the upper limit of the difference [BA] is within the above range. The lower limit of the difference [BA] is not limited, but it is preferably 60 μm or more, and more preferably 80 μm or more.

[0049] From the viewpoint of maintaining better moldability while exhibiting excellent flame retardancy, it is particularly preferable that the average cell diameter B is 180 μm or less, and the difference between the average cell diameter A and the average cell diameter B [BA] is 60 μm or more and 200 μm or less.

[0050] (Method for adjusting the average bubble diameter) The method for adjusting the average bubble diameter A and average bubble diameter B in the foamed particles of the present invention to fall within the above-described range is not particularly limited, but examples include the means shown in configurations 1 to 6 in the method for producing polyamide resin foamed particles described later.

[0051] [Polyamide resin foam particles] Next, the physical properties of the foamed particles of the present invention will be described. In relation to the foamed particles of the present invention, single-stage foamed particles and double-stage foamed particles will be described as appropriate. Single-stage foamed particles refer to foamed particles obtained by the first foaming process. This first foaming process may be called single-stage foaming or the single-stage foaming process. Double-stage foamed particles refer to foamed particles obtained by a second foaming process using the single-stage foamed particles. This second foaming process may be called double-stage foaming or the double-stage foaming process. In the production of the foamed particles of the present invention, if only a single-stage foaming process is performed, single-stage foamed particles will be the final foamed particles of the present invention provided. If a double-stage foaming process is performed, double-stage foamed particles will be the final foamed particles of the present invention provided. The foamed particles of the present invention include multi-stage foamed particles produced by multi-stage foaming of three or more stages using double-stage foamed particles. In this specification, foamed particles subjected to in-mold molding may be referred to as the final foamed particles or the final foamed particles.

[0052] (Apparent density of foam particles) The apparent density of the foamed particles of the present invention is 150 kg / m³, from the viewpoint of the lightweight and flame retardancy of the foamed particle molded article provided. 3 Preferably, it is 100 kg / m 3 It is more preferable that the following is true: 80 kg / m 3 It is even more preferable that the following be the case. Also, from the viewpoint of the rigidity of the foamed particle molded article provided, the apparent density is 10 kg / m³. 3 Preferably, it should be 30 kg / m 3 It is more preferable that it be 50 kg / m 3 It is even more preferable that the above conditions are met. A preferred range for the apparent density of the foamed particles of the present invention is, for example, 10 kg / m³. 3 More than 80kg / m3 It is like this. The means for adjusting the apparent density within such a range is not particularly limited. For example, it is preferable to perform the two-stage foaming process described later.

[0053] The apparent density of the foamed particles is measured by the following method. First, the foamed particles to be measured are left in an environment with a temperature of 23°C, a relative humidity of 50%, and 1 atm for 24 hours or more. The group of foamed particles with a mass w (g) thus obtained is submerged in a graduated cylinder filled with alcohol (for example, ethanol) at 23°C using a wire mesh or the like, and the volume v (cm 3 ) of the group of foamed particles is obtained from the rise in the water level, and the mass w of the group of foamed particles is divided by the volume v of the group of foamed particles (w / v). By converting the value thus obtained to kg / m 3 , the apparent density (kg / m 3 ) of the foamed particles can be obtained.

[0054] The bulk density of the foamed particles is measured by the following method. First, the foamed particles to be measured are left in an environment with a temperature of 23°C, a relative humidity of 50%, and 1 atm for 24 hours or more. The group of foamed particles with a mass W (g) thus obtained is filled into a graduated cylinder, and the filling height of the group of foamed particles in the graduated cylinder is stabilized by gently tapping the floor surface a few times at the bottom of the graduated cylinder. The bulk volume V (L) of the group of foamed particles indicated by the scale of the graduated cylinder is read, and the mass W of the group of foamed particles is divided by the bulk volume V of the group of foamed particles (W / V). By converting the value thus obtained to kg / m 3 , the bulk density (kg / m 3 ) of the foamed particles can be obtained.

[0055] (Bulk magnification of foamed particles) In the present invention, the bulk magnification M of the foamed particles used for in-mold molding is preferably 15 times or more, preferably 20 times or more, and more preferably 25 times or more from the viewpoint of obtaining a molded body with excellent lightness. To obtain foamed particles with a large bulk ratio M as described above, it is preferable to carry out multi-stage foaming, such as the two-stage foaming described later. When carrying out two-stage foaming, it is preferable to adjust the ratio (M2 / M1) of the bulk ratio M2 of the foamed particles obtained by two-stage foaming (two-stage foamed particles) to the bulk ratio M1 of the foamed particles obtained by the first foaming step (single-stage foamed particles) so that it is between 1.2 and 3.0. A ratio (M2 / M1) of 1.2 or more makes it easier to obtain the desired bulk ratio M2, and a ratio (M2 / M1) of 3.0 or less suppresses the average bubble diameter B from becoming too large, making it easier to provide foamed particles with good moldability. From this viewpoint, it is more preferable that the above ratio (M2 / M1) is between 1.2 and 2.0.

[0056] The bulk ratio M1 of the single-stage foamed particles obtained by the single-stage foaming process is determined by the density of the base resin constituting the single-stage foamed particles (unit: kg / m³). 3 ) Bulk density of single-stage foamed particles (unit: kg / m³) 3 It can be obtained by dividing by ). The bulk ratio M1 of the single-stage foamed particles can be adjusted by, for example, the amount of foaming agent added in the single-stage foaming process, the temperature during foaming, and the pressure difference between the pressure inside the sealed container and the pressure of the environment from which the contents are released from the sealed container. The bulk density of the single-stage foamed particles can be obtained by using the single-stage foamed particles and performing the bulk density measurement method of foamed particles described above.

[0057] Furthermore, the bulk ratio M2 of the two-stage foamed particles obtained by performing two-stage foaming using single-stage foamed particles is determined by the density of the base resin constituting the two-stage foamed particles (unit: kg / m³). 3 ) the bulk density of the two-stage foamed particles (unit: kg / m³) 3 It can be obtained by dividing by ). The bulk ratio M2 of the two-stage foamed particle can be adjusted by, for example, the pressure difference between the pressure inside the bubbles of a single-stage foamed particle with internal pressure applied and the pressure of the heating environment, as well as the heating temperature and heating time. The bulk density of the two-stage foamed particle can be obtained by using the two-stage foamed particle and performing the bulk density measurement method of the foamed particle described above. Furthermore, the density of the base resin constituting the single-stage foamed particles and the density of the base resin constituting the double-stage foamed particles are the same as the density of the base resin constituting the resin particles used to produce them.

[0058] (Percentage of closed cells in foamed particles) From the viewpoint of providing foamed particles that exhibit excellent flame retardancy while maintaining good moldability, the closed-cell ratio of the foamed particles of the present invention is preferably 40% or more, more preferably 50% or more, and even more preferably 60% or more. There is no particular upper limit to the closed-cell ratio of the foamed particles, but it is generally around 99%.

[0059] The percentage of closed cells in foamed particles is measured as follows: First, the bulk volume is approximately 20 cm³. 3 The apparent volume Va of the foamed particle group is measured by immersing it in water. Next, after thoroughly drying the foamed particle group whose apparent volume Va has been measured, the true volume Vx is measured according to procedure C described in ASTM-D2856-70 (the sum of the volume of the resin constituting the foamed particle and the total volume of the closed-cell portion of the foamed particle). An air-comparison hydrometer is used to measure this true volume Vx. An example of such an air-comparison hydrometer is the "Beckman Model 1000 Air Comparison Pycnometer" manufactured by Tokyo Science Co., Ltd. Next, the closed-cell ratio is calculated using the following formula (1). Using different measurement samples, the closed-cell ratio is measured five times using the same procedure as described above, and the arithmetic mean of the values ​​obtained in each measurement is calculated and taken as the closed-cell ratio of the foamed particle. [Mathematics 1] Closed cell ratio (%)=(Vx-W / ρ)×100 / (Va-W / ρ) (1) Vx: True volume (cm³) of the foamed particle group measured by the above method 3 ) Va: The apparent volume (cm³) of the foaming particle group, measured from the rise in water level when the foaming particle group is submerged in water in a graduated cylinder. 3 ) W: Mass of foaming particles (g) ρ: Density of the resin constituting the foam particles (g / cm³) 3 )

[0060] (High temperature peak) In the foamed particles of the present invention, it is preferable that a crystalline structure exhibiting the high-temperature peak described below is formed. Foamed polyamide resin particles exhibiting a high-temperature peak effectively prevent blocking, where foamed particles produced in the first foaming step adhere to each other. Therefore, the first-stage foamed particles obtained in the first foaming step can be easily supplied to the second-stage foamed particles, allowing for a successful second-stage foaming process. Furthermore, the heat resistance and moldability of the foamed particles are more reliably ensured.

[0061] Here, the term "high temperature peak" refers to the melting peak (high temperature peak b) in the first DSC curve (see Figure 1) measured using differential scanning calorimetry based on JIS K7122-1987, where 1-3 mg of polyamide resin foam particles are 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. In this curve, the peak temperature appears higher than the melting peak (intrinsic peak a) specific to the polyamide resin. Figure 1 is an example of a DSC curve measured using differential scanning calorimetry for polyamide resin foam particles. Although Figure 1 shows one high temperature peak b, there may be two or more high temperature peaks b.

[0062] Intrinsic peak a is a peak that arises from the melting of the intrinsic crystals of the base resin constituting the foamed particles, and is considered to be a peak that appears due to the melting of the crystals normally present in the base resin constituting the foamed particles. On the other hand, high-temperature peak b, which has its peak temperature on the high-temperature side of intrinsic peak a, is presumed to appear when secondary crystals different from the crystals normally present in the base resin constituting the foamed particles are present.

[0063] The peak temperature of intrinsic peak a roughly coincides with the peak temperature of the melting peak that appears in the second DSC curve, which will be discussed later. On the other hand, the 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 of the first and second DSC curves with their peak positions. Here, the second DSC curve refers to the DSC curve measured when the polyamide resin foam particles, after the measurement of the first DSC curve, are kept at a temperature 30°C higher than the end of the melting peak after the measurement of the first DSC curve for 10 minutes, then cooled to 30°C at a cooling rate of 10°C / min, and then heated again to a temperature 30°C higher than the end of the melting peak at a heating rate of 10°C / min.

[0064] From the viewpoint of obtaining a foam particle molded article with an excellent balance of cushioning and rigidity, the total amount of heat of fusion of high-temperature peak b, whose peak temperature is higher than the peak temperature of intrinsic peak a, is preferably 3 J / g or more, more preferably 5 J / g or more, and even more preferably 7 J / g or more. Furthermore, from the viewpoint of widening the range of steam pressure at which molding is possible during in-mold molding of foam particles, the total amount of heat of fusion is preferably 30 J / g or less, more preferably 20 J / g or less, and even more preferably 15 J / g or less. Note that if two or more high-temperature peak b appear, the amount of heat of fusion of high-temperature peak b refers to the total amount of heat of all high-temperature peak b.

[0065] The heat of fusion for the high-temperature peak b is calculated as follows: In the DSC curve shown in Figure 1, a straight line is drawn connecting point I, which corresponds to 80°C on the DSC curve, and point II, which corresponds to the melting termination temperature of the foamed particles. Note that the melting termination temperature is the high-temperature endpoint of the high-temperature peak b, and is the intersection point of the high-temperature peak b and the baseline on the higher side of the DSC curve. Next, as shown in Figure 1, let IV be the intersection point of the line passing through the maximum point III, which lies between the intrinsic peak a and the high-temperature peak b, and the line connecting point I and point II. The area enclosed by the straight line connecting point I and point IV, the straight line connecting point III and point IV, and the DSC curve connecting point I and point III is defined as the area of ​​intrinsic peak a. The area enclosed by the straight line connecting point IV and point II, the straight line connecting point III and point IV, and the DSC curve connecting point III and point II (shaded area) is defined as the area of ​​high-temperature peak b. The total heat of fusion value of the foamed particles is calculated from the sum of the areas of intrinsic peak a and high-temperature peak b, as determined above, and the heat of fusion value of high-temperature peak b is calculated from the area of ​​high-temperature peak b. The means for obtaining the high-temperature peak b will be explained later in the section on the method for producing foamed particles.

[0066] [Method for producing polyamide resin foam particles] Next, a preferred embodiment of the method for producing foamed particles of the present invention (hereinafter also simply referred to as the present production method) will be described. This manufacturing method comprises a resin particle production step and a foaming step, and adjusts the average bubble diameter A and average bubble diameter B of the foamed particles to be within a predetermined range. According to this manufacturing method, it is possible to produce foamed particles that exhibit good moldability and excellent flame retardancy, making it possible to provide foamed particle molded articles.

[0067] (Resin particle manufacturing process) The resin particle manufacturing process involves preparing a molten mixture by melting and kneading a substrate containing a flame retardant and a polyamide resin, and then extruding the molten mixture from an extruder to produce polyamide resin particles. Generally, the molten mixture extruded from the extruder is cut into desired masses and shapes. For example, cylindrical resin particles can be obtained by extruding the molten mixture as strands with a circular cross-section, water-cooling them, and then cutting them with a pelletizer. The flame retardant used herein comprises a phosphorus-based flame retardant (flame retardant a) consisting of a metal salt of phosphinic acid and / or diphosphinic acid, and one or more nitrogen / phosphorus-based flame retardants (flame retardant b) selected from the group consisting of reaction products of melamine and polyphosphate, reaction products of melamine condensates and polyphosphate, and mixtures thereof. When compounding flame retardants a and b, the total amount of flame retardant a and flame retardant b should be between 10 and 30 parts by mass per 100 parts by mass of the base resin containing polyamide resin, and the mass ratio of flame retardant a to flame retardant b should be 90:10 to 30:70 (provided that the total of flame retardants a and b is 100% by mass).

[0068] (Foaming process) The foaming process is a step in which polyamide resin particles obtained in the resin particle manufacturing process are foamed to produce polyamide resin foam particles. This manufacturing method may produce foamed particles by performing only a single foaming step, or by performing a two-stage foaming step after the single-stage foaming step. Furthermore, a three-stage or more foaming step may be performed after the two-stage foaming step. In this embodiment, the method of producing foamed particles by performing a two-stage foaming step will be mainly explained as an example.

[0069] Single-stage foaming process: A single-stage foaming process is carried out using the resin particles formed in the resin particle manufacturing process. In the single-stage foaming process, the resin particles, along with an aqueous medium such as water, an inorganic dispersant, and a surfactant, are supplied to a pressure vessel, and a foam particle manufacturing process including a dispersion process, a foaming agent impregnation process, and a release process is carried out to produce foam particles. The above dispersion step is a step of dispersing resin particles in an aqueous medium containing an inorganic dispersant in a pressure vessel. Examples of the inorganic dispersant include inorganic substances such as aluminum oxide, tricalcium phosphate, magnesium pyrophosphate, zinc oxide, kaolin, mica, talc, and smectite. Dispersion aids such as anionic surfactants such as sodium dodecylbenzenesulfonate and sodium alkanesulfonate may also be added along with the dispersant. In particular, when a compound having the substructure shown in formula (IV) above (flame retardant aid) is used in combination with flame retardant a and flame retardant b, it is preferable to use the above-mentioned inorganic dispersant and dispersion aid in combination in the dispersion step. This effectively prevents adhesion (blocking) between foamed particles during the release step. The above-described foaming agent impregnation process is a process in which a foaming agent such as carbon dioxide is impregnated into resin particles in a pressure vessel. The above-described discharge process involves releasing resin particles containing a foaming agent together with an aqueous medium from a pressure vessel under a pressure lower than the internal pressure of the pressure vessel to cause foaming and obtain one-stage foamed particles.

[0070] The one-stage foaming process described above is sometimes referred to as the "direct foaming method." However, the method for producing foamed particles in the present invention is not limited to this method. Instead of the direct foaming method, which is a one-stage foaming process, a method such as the "impregnation foaming method," in which resin particles impregnated with a foaming agent are heated and foamed, can be employed, and the foamed particles obtained by this method can be subjected to the two-stage foaming process described later as appropriate.

[0071] When producing foamed particles having the high-temperature peak b mentioned in the above description, the following methods can be used, for example. In other words, adjustments to obtain the high-temperature peak b are made in the dispersion step and / or foaming agent impregnation step described above by adjusting the rate at which the temperature inside the pressure vessel rises, or by maintaining the temperature inside the pressure vessel at a predetermined temperature for a predetermined time. More specifically, for example, in the dispersion step and / or foaming agent impregnation step described above, a first-stage holding step is performed in which the temperature is maintained at a temperature of (melting point of the base resin - 20°C) or higher but below (melting end temperature of the base resin) for about 10 to 60 minutes. After that, the temperature is adjusted to between (melting point of the base resin - 15°C) and below (melting end temperature of the base resin). Then, if necessary, a second-stage holding step is performed in which the temperature is maintained at that temperature for another 10 to 60 minutes. Subsequently, by performing a release step, foamed particles having a high-temperature peak can be produced.

[0072] In this manufacturing method, the single-stage foaming process may include any additional steps as appropriate, in addition to the steps described above. If the two-stage foaming process is not performed, the single-stage foamed particles produced by the single-stage foaming process will be provided as the foamed particles of the present invention.

[0073] Two-stage foaming process: The two-stage foaming process involves supplying the first-stage foamed particles, manufactured as described above, to a pressure vessel, injecting a foaming agent into the vessel to increase the internal pressure within the bubbles of the first-stage foamed particles, and then heating to induce foaming. By performing the two-stage foaming process, foamed particles exhibiting the desired apparent density can be easily produced. As mentioned above, by adjusting the ratio (M2 / M1) of the bulk ratio M2 of the two-stage foamed particles obtained by two-stage foaming to the bulk ratio M1 of the first-stage foamed particles to be between 1.2 and 3.0, preferably between 1.2 and 2.0, it is easier to obtain two-stage foamed particles exhibiting the desired bulk ratio M2, and the value of the average bubble diameter B in the two-stage foamed particles does not become too large.

[0074] (Adjustment of average bubble diameter) In this manufacturing method, which includes the resin particle preparation step and foaming step described above, it is essential to adjust the average bubble diameter A of the polyamide resin foam particles to be between 5 μm and 100 μm, and to adjust the average bubble diameter B of the five bubbles selected in descending order of area from the bubbles observed on the cross-section formed by dividing the polyamide resin foam particles into two equal parts, so that the average bubble diameter B of the bubbles is 250 μm or less.

[0075] The method for adjusting the average bubble diameter A and average bubble diameter B to fall within the above-described range is not particularly limited, but it is preferable to implement at least one of the following configurations 1 to 6, as this makes it easier to adjust the average bubble diameter.

[0076] Configuration 1: Zinc borate is added to the base material constituting the foamed resin in an amount of 0.5 parts by mass to 10 parts by mass per 100 parts by mass of the base resin contained in the base material. By adding zinc borate to the base material within this range, it is easier to adjust the average bubble diameter A and average bubble diameter B of the foamed particles to a predetermined range, and it is easier to provide a foamed particle molded article that exhibits superior flame retardancy.

[0077] Configuration 2: In the resin particle manufacturing process, the temperature of the molten mixture extruded from the extruder is adjusted to between 250°C and 275°C. This makes it easier to adjust the average bubble diameter A and average bubble diameter B of the resulting foamed particles to the predetermined range described above. The reason for this is not clear, but it is thought that this is because the decomposition of some of the flame retardant a and some of the flame retardant b, which generates gas, is suppressed, and this gas acts as a nucleating agent or foaming agent for bubbles.

[0078] Configuration 3: A twin-screw extruder is used as the extruder in the resin particle manufacturing process. Compared to a single-screw extruder, a twin-screw extruder can thoroughly knead the substrate supplied to the extruder. By using the molten mixture that has been thoroughly kneaded at this stage, it is easier to adjust the average bubble diameter A and average bubble diameter B of the foamed particles obtained to the predetermined range described above. The reason for this is not clear, but it is thought to be because the components that exhibit the action of a nucleating agent are more easily dispersed uniformly within the resin particles during the foaming process.

[0079] Configuration 4: Foamed particles are produced using a direct foaming method as the foaming process. By keeping the amounts of dispersant and surfactant added in the dispersion process within a predetermined range, blocking is more reliably suppressed, and the average bubble diameter A and average bubble diameter B of the resulting foamed particles can be easily adjusted to a predetermined range. Specifically, it is preferable that the amount of inorganic dispersant added in the aqueous medium is 0.3 parts by weight or more and 2.0 parts by weight or less per 100 parts by weight of resin particles, and the amount of surfactant added in the aqueous medium is 0.2 parts by weight or more and 1.5 parts by weight or less per 100 parts by weight of resin particles. When the aforementioned flame retardant is included, blocking of foam particles tends to occur during the foaming process. However, by adding an inorganic dispersant within the range described above, it is possible to effectively prevent the occurrence of the above-mentioned blocking.

[0080] Configuration 5: A NOR-type hindered amine having a substructure represented by formula (IV) is added to the base material constituting the foamed resin in an amount of 0.5 parts by mass to 8 parts by mass per 100 parts by mass of the total amount of flame retardant a and flame retardant b. By adding the above NOR-type hindered amine to the base material within this range, blocking is more reliably suppressed, and the average bubble diameter A and average bubble diameter B of the resulting foamed particles can be easily adjusted to a predetermined range. The reason for this is not clear, but it is thought that the NOR-type hindered amine readily attracts inorganic dispersants in an aqueous medium due to electrical interactions.

[0081] Configuration 6: As shown in this embodiment, having a foaming process that includes a single-stage foaming process and a double-stage foaming process is preferable from the viewpoint of adjusting the average bubble diameter. The first foaming step involves dispersing polyamide resin particles in a sealed container supplied with a dispersion medium such as water, impregnating them with a foaming agent to prepare foamable polyamide resin particles, and then releasing the foamable polyamide resin particles together with the dispersion medium under a lower pressure than the sealed container by opening one end of the sealed container to cause foaming. In other words, the first foaming step includes the dispersion step, the foaming agent impregnation step, and the release step described above. The second-stage foaming process involves supplying the first-stage foamed particles obtained in the first-stage foaming process to a pressure vessel, applying internal pressure, and heating to cause foaming, thereby obtaining polyamide resin foamed particles exhibiting a bulk ratio M2 greater than the bulk ratio M1 of the first-stage foamed particles.

[0082] In configuration 6, it is preferable that the ratio (M2 / M1) of the bulk ratio M1 of the single-stage foamed particles obtained in the single-stage foaming process to the bulk ratio M2 of the polyamide resin foamed particles, which are the double-stage foamed particles obtained in the double-stage foaming process, be adjusted to be between 1.2 and 3.0, and more preferably between 1.2 and 2.0. In this case, the growth of bubbles in the double-stage foaming process is suppressed, and it is easier to adjust the average bubble diameter A and average bubble diameter B of the foamed particles to a predetermined range.

[0083] Furthermore, with respect to configuration 6, in the two-stage foaming process, it is preferable to apply internal pressure to the first-stage foamed particles by adjusting the pressure inside the pressure vessel (pressurized pressure) to a range of 0.3 MPa to 1 MPa and holding it for at least 24 hours.

[0084] Furthermore, regarding configuration 6, in the two-stage foaming process, it is preferable to heat the first-stage foamed particles, to which internal pressure has been applied, 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. In this way, by heating the first-stage foamed particles, to which internal pressure has been applied, with steam at a lower pressure in the two-stage foaming process, bubble growth is suppressed, and the average bubble diameter A and average bubble diameter B of the foamed particles can be easily adjusted to a predetermined range.

[0085] [Polyamide resin foam particle molded product] The foamed particle molded article of the present invention is manufactured by in-mold molding the polyamide resin foamed particles of the present invention described above. Such a foamed particle molded article of the present invention exhibits excellent flame retardancy, superior surface properties and recovery properties, and a high fusion rate, making it a good foamed particle molded article. Such a molded article can be suitably used in various applications such as automotive components and building materials. For evaluation of the surface properties and recovery properties of the foamed particle molded article, and for measurement of the fusion rate, please refer to the examples described later.

[0086] (Combustion test) The flame retardancy of foamed particle molded articles is evaluated based on a horizontal combustion test (UL94 horizontal combustion test) in accordance with the UL94 standard. The specific test method for the UL94 horizontal combustion test is as follows: Five test specimens with a skin surface measuring 150±1mm in length, 50±1mm in width, and 13mm in thickness are cut from the foam particle molded body. Marks are drawn on the 150±1mm in length and 50mm±1mm in width surface of each test specimen at positions 25mm, 60mm, and 125mm from one end in the vertical direction. After conditioning the test specimens by leaving them undisturbed for 24 hours at 23°C and 50% relative humidity, the test specimens are placed on a wire mesh with the markings facing upwards, and cotton is placed beneath them. Then, a wingtip burner is adjusted to produce a blue flame of 38mm±2mm, and the flame is applied to the edge of the test specimen. After one minute, the burner is moved more than 100mm away from the test specimen, and the time and distance until the flame disappears from the test specimen are measured.

[0087] The flame retardancy evaluation based on the UL94 horizontal combustion test determines the flame retardancy class for each of the five test specimens based on the time and distance until the flame is extinguished. Then, the class in which four or more of the five test specimens meet the conditions is determined as the flame retardancy of the foam particle molded product. HF-1: All conditions are met, including: the extinction time at a position where the distance from the end that was exposed to the flame is 4 / 5 of the vertical dimension of the test specimen is 2 seconds or less; the extinction time at a position where the distance from the end that was exposed to the flame is 1 / 5 of the vertical dimension of the test specimen is 10 seconds or less; the burning glow time of the test specimen is 30 seconds or less; the cotton is not burning; and the burning distance is 60 mm or less. HF-2: Except for the cotton burning, it meets the same conditions as HF-1. HBF: The burning rate from the 25mm mark to the 125mm mark, at a distance from the end where the flame was applied, is 40mm / min or less, or the burning stops between the 25mm mark and the 125mm mark.

[0088] (Molded body density) The molded density of the foamed particle molded article of the present invention is 15 kg / m³, from the viewpoint of achieving an excellent balance between lightness and mechanical properties such as rigidity, and from the viewpoint of reliably exhibiting flame retardancy. 3 More than 100kg / m 3 Preferably, it is 20 kg / m 3 More than 70kg / m 3The following is more preferable:

[0089] The density of a foam particle molded body is calculated by dividing the mass of the foam particle molded body by the volume calculated based on its outer dimensions. If it is difficult to calculate the volume from the outer dimensions, the volume of the foam particle molded body can be determined by three-dimensional measurement.

[0090] [Method for manufacturing polyamide resin foam particle molded articles] The foamed particle molded article of the present invention is manufactured by in-mold molding using the foamed particles of the present invention as described above. The above in-mold molding broadly includes known in-mold molding methods using foamed particles. For example, the foamed particle molded article of the present invention is manufactured as follows. First, the foamed particles of the present invention are filled into a mold having a cavity corresponding to the shape of the desired foamed particle molded article, and the foamed particles filled in the mold are heated by applying a predetermined molding pressure using a heating medium such as steam. The above molding pressure can be adjusted, for example, in the range of 0.12 MPa (G) or more and 0.30 MPa (G) or less. In this specification, (G) indicates gauge pressure, that is, the pressure value based on atmospheric pressure. By heating the foamed particles in the cavity in this way, they are further foamed and fused together. Next, after heating with steam or the like is completed, the pressure is released, and cooling of the mold and the molded article inside the mold is started immediately. When it is confirmed that the pressure (surface pressure) generated on the inner surface of the mold has become 0.02 MPa (G), cooling is stopped, and the foamed particle molded article is removed from the mold. The cooling method used here is not particularly limited, but examples include water cooling. Through this series of molding steps, a foamed particle molded body corresponding to the shape of the cavity is obtained. [Examples]

[0091] The present invention will be described in detail below with reference to examples, but the present invention is not limited thereto. Tables 1 to 3 show the composition (grade) of the base material used to produce the foamed particles for each example and comparative example, along with the proportions of each composition as follows. Tables 1 to 3 show the amount of flame retardant blended as a blending ratio (parts by mass) per 100 parts by mass of the base resin, and indicate the total amount of flame retardant blended and the blending amount of each composition used as flame retardant. In addition, the total amount of flame retardant a and flame retardant b (parts by mass), and the mass ratio (mass%) of flame retardant a and flame retardant b within 100% by mass of the total amount of flame retardant a and flame retardant b are also shown. In Tables 1 to 3, the amount of flame retardant additive is expressed as the proportion (parts by mass) relative to 100 parts by mass of the base resin. Tables 1 to 3 show the amount of colorant blended, representing the percentage of colorant blended in 100% by mass of the base material.

[0092] [Example 1] <Preparation of foamed resin particles> [Manufacturing of polyamide resin particles] A twin-screw extruder was supplied with the base resin, polyamide resin (grade 5033B, manufactured by Ube Industries, Ltd.), a colorant (carbon black), flame retardants (flame retardant a, flame retardant b, zinc borate), and a flame retardant additive in the proportions shown in Table 1. The mixture was melt-kneaded to obtain a molten compound. In addition, talc was supplied as a bubble nucleating agent so that it was present in the resulting resin particles at a concentration of 8000 ppm, as described below. The molten compound, adjusted to an extrusion temperature of 274°C, was extruded through the pores of a die attached to the tip of the extruder as a single-layer strand with a circular cross-section. After water-cooling the extruded strand, it was cut in a pelletizer to a mass of approximately 2 mg per strand, and dried to obtain polyamide resin particles. Furthermore, the polyamide resin (5033B) is a polyamide 6 / 66 copolymer (nylon 6 / 66), with a polyamide 6 / polyamide 66 ratio of 85 / 15, a melting point of 197°C, and a density of 1.14 g / cm³. 3 The product name is UBE Nylon 5033B, and it has a flexural modulus of 1300 MPa, a melt mass flow rate (MFR) of 3.5 g / 10 min measured at 230°C and a load of 2.16 kg. Furthermore, Grade OP1312 is the flame retardant "Exolit OP1312" manufactured by Clariant, and contains flame retardant a) an aluminum salt of phosphinic acid and flame retardant b) melamine polyphosphate in a mass ratio of 2:1. It also contains 5% by mass of zinc borate.

[0093] <Manufacturing of foamed particles> Single-stage foaming process: Using the polyamide resin particles obtained as described above, a single foaming process was carried out as follows. First, 1000 g of polyamide resin particles and 3 liters of dispersion (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 alkylbenzenesulfonate as a surfactant were added to the dispersion for every 100 parts by mass of polyamide resin particles. The contents of the sealed container were heated from room temperature (23°C) while stirring until the impregnation temperature (135.2°C) was reached. After that, carbon dioxide was injected into the sealed container as a blowing agent until the equilibrium vapor pressure inside the container reached 4 MPa. The heating time from room temperature (23°C) to the impregnation temperature (135.2°C) was 30 minutes. Next, the mixture was held at 135.2°C and 4 MPa for 15 minutes to obtain resin particles impregnated with the blowing agent (foaming resin particles) that exhibited crystalline properties with a high-temperature peak. Subsequently, the foamable resin particles were released together with the dispersion liquid under atmospheric pressure (0.1 MPa) to foam. The resulting foamed particles were cured in a 60°C oven for 24 hours, and then slowly cooled to obtain single-stage foamed particles with a bulk ratio of 17.3 times.

[0094] Two-stage foaming process: The first-stage foamed particles, after curing, were filled into a pressurized sealed container. The pressure inside the sealed container was then increased from atmospheric pressure to the pressurized pressure (0.6 MPa) shown in Table 1 over the time (1 day) shown in Table 1, thereby pressurizing the foamed particles. The foamed particles were maintained under this pressurized pressure for 24 hours to allow air to permeate the bubbles within the foamed particles. After that, the foamed particles were removed from the sealed container. These foamed particles were then supplied to a two-stage foaming device, and steam (steam pressure 0.05 MPa) was supplied into the device to foam the particles, obtaining two-stage foamed particles with a bulk ratio of 26.6 times. In Example 1, the two-stage foamed particles obtained by two-stage foaming were used as the final foamed particles.

[0095] <Manufacturing of foamed particle molded products> [Manufacturing of polyamide resin foam particle molded products] First, the foam particles were placed in a pressure vessel, and the pressure inside the vessel was increased over 12 hours until it reached the set pressure (0.08 MPa) shown in Table 1. This pressure was then maintained for 24 hours to apply internal pressure to the foam particles. After that, the foam particles were filled into the cavity of the mold. A flat plate mold measuring 200 mm in length, 65 mm in width, and 40 mm in thickness was used as the molding mold. The mold was opened 4 mm from its completely closed state, and the amount of cracking was adjusted to 10% of the 40 mm thickness of the mold cavity. After filling was complete, the mold was completely closed. Subsequently, steam was supplied into the molding cavity to perform in-mold molding by heating, thereby obtaining a plate-shaped foam particle molded body. The heating method involved preheating (exhaust process) by supplying steam for 5 seconds with the drain valves of both molds open, then supplying steam from the moving mold, followed by supplying steam from the fixed mold, and finally heating to the molding pressure (0.16 MPa(G)) shown in Table 1. After heating was complete, the pressure was released, and the molded body was water-cooled until the surface pressure due to the foaming force decreased to 0.02 MPa (G). Then the mold was opened and the molded body was removed from the mold. The obtained molded body was cured in an 80°C oven for 12 hours, and then slowly cooled to room temperature. In this way, a foamed particle molded body was obtained.

[0096] [Examples 2-7 and Comparative Examples 1-7] Except for the changes shown in Tables 1 to 3, foamed particles and molded foamed particle articles were manufactured in the same manner as in Example 1, and these were designated as Examples 2 to 7 and Comparative Examples 1 to 7. Furthermore, OP1230, which was used in Example 7 together with OP1312, is the flame retardant "Exolit OP1230" manufactured by Clariant, Inc., and is an aluminum salt of phosphinic acid. In addition, Examples 2 and 4 used the flame retardant NOR116 manufactured by BASF Japan Ltd. as a flame retardant additive. Furthermore, Grade MC6000 used in Comparative Example 4 is a flame retardant manufactured by Nissan Chemical Corporation containing melamine cyanurate as its main component, Grade SR-T20000 used in Comparative Example 5 is a flame retardant manufactured by Sakamoto Pharmaceutical Co., Ltd. containing brominated epoxy as its main component, Grade Hiromaster MA-80 used in Comparative Example 6 is a flame retardant manufactured by Suzuhiro Chemical Co., Ltd. containing brominated polystyrene as its main component, and Grade PHOSMEL used in Comparative Example 7 is a flame retardant manufactured by Nissan Chemical Corporation containing polyphosphate melamine.

[0097] [Measurement of the physical properties of foamed particles] The physical properties of the single-stage foamed particles and / or final foamed particles obtained as described above were measured as follows. Note that in Example 3 and Comparative Examples 3-7, since two-stage foaming was not performed, the single-stage foamed particles were used as the final foamed particles. The measurement results are shown in Tables 1-3.

[0098] (Bulk ratio of foamed particles) The bulk ratio M1 of the single-stage foamed particles obtained by the single-stage foaming process is determined by the density (1140 kg / m³) of the base resin constituting the single-stage foamed particles. 3 ) refers to the bulk density of the single-stage foamed particles (unit: kg / m³) as described later. 3 This was obtained by dividing by ). The bulk ratio M2 of the two-stage foamed particles obtained by performing two-stage foaming using one-stage foamed particles is calculated using the density (1140 kg / m³) of the base resin constituting the two-stage foam. 3 ) refers to the bulk density of the two-stage foamed particles described later (unit: kg / m³). 3 This was obtained by dividing by ). Furthermore, the ratio of the bulk factor M2 to the bulk factor M1 obtained above (M2 / M1) was calculated.

[0099] (Bulk density of foamed particles) First, single-stage or double-stage foamed particles were left for at least 24 hours in an environment of 23°C, 50% relative humidity, and 1 atm. The resulting foamed particle group with mass W (g) was then filled into a graduated cylinder, and the filling height of the foamed particle group in the cylinder was stabilized by lightly tapping the floor several times with the bottom of the graduated cylinder. The bulk volume V (L) of the foamed particle group indicated by the scale on the graduated cylinder was read, and the mass W of the foamed particle group was divided by the bulk volume V (W / V). The value obtained from this was calculated in kg / m 3 By converting the units, the bulk density of the foamed particles (kg / m³) can be calculated. 3 ) was obtained.

[0100] (Apparent density of foam particles) The apparent density of the foam particles was measured by the following method. First, the foam particles to be measured were left in an environment of 23°C, 50% relative humidity, and 1 atm for more than 24 hours. The resulting group of foam particles with mass w (g) was then submerged in a graduated cylinder containing ethanol at 23°C using a wire mesh or similar, and the volume v (cm³) of the foam particle group was calculated from the rise in the water level. 3 ) is calculated, and the mass w of the foamed particle group is divided by the volume v of the foamed particle group (w / v). The value obtained from this is kg / m 3 By converting the units, the apparent density of the foamed particles (kg / m³) can be calculated. 3 ) was obtained.

[0101] (Average bubble diameter of foamed particles A) First, the foam particles were roughly divided in half to expose the cut surfaces. Then, a photograph was taken so that the entire cut surface was visible. On the photograph, four line segments were drawn at equal angles (i.e., 45°) from the periphery of the foam particle, through the center of the foam particle, to the opposite periphery. Next, the average bubble diameter a of one foam particle was defined as the value obtained by dividing the sum of the lengths of the four line segments L by the total number of bubbles N tangent to each line segment (L / N). This operation was performed for 50 foam particles, and the arithmetic mean was defined as the average bubble diameter A of the foam particles.

[0102] (Average bubble diameter of foamed particles B) The foam particles were roughly divided in half to expose the cut surfaces. A photograph was then taken so that the entire cut surface was visible. The area of ​​each bubble observed on the cut surface was measured by image analysis. From the above cut surface, five bubbles were selected in descending order of their area. A virtual circle with the same area as each of the five selected bubbles was assumed, and the diameter of this virtual circle was calculated. The average bubble diameter b of one foam particle was obtained by arithmetic mean of these calculated diameters. This operation was performed for 50 foam particles, and the arithmetic mean was taken as the average bubble diameter B of the foam particles. Furthermore, as described above, the difference (BA) between the average bubble diameter B value and the average bubble diameter A value was calculated.

[0103] (High-temperature peak heat of fusion for single-stage foamed particles) The high-temperature peak fusion heat of single-stage foamed particles was determined from the DSC curve obtained by heating 1 to 3 mg of single-stage foamed particles as test specimens at a heating rate of 10 °C / min from 23 °C to a temperature 30 °C higher than the melting peak end temperature of the test specimen, based on the method for measuring the transition heat of plastics described in JIS K7122:1987. Specifically, as explained above using Figure 1, a straight line was drawn connecting point I, which corresponds to 80 °C on the DSC curve, and point II, which corresponds to the melting end temperature of the foamed particles. The melting end temperature is the high-temperature endpoint of high-temperature peak b, and is the intersection of high-temperature peak b and the baseline on the high-temperature side of high-temperature peak b on the DSC curve. Next, as shown in Figure 1, point IV was defined as the intersection of a line parallel to the vertical axis of the graph, passing through the maximum point III located between intrinsic peak a and high-temperature peak b, and the line connecting point I and point II. The area enclosed by the straight line connecting point I and point IV, the straight line connecting point III and point IV, and the DSC curve connecting point I and point III was defined as the area of ​​intrinsic peak a. The area enclosed by the straight line connecting point IV and point II, the straight line connecting point III and point IV, and the DSC curve connecting point III and point II (shaded area) was defined as the area of ​​high-temperature peak b. The value of the high-temperature peak heat of fusion (J / g) of the single-stage foamed particle was calculated from the area of ​​high-temperature peak b obtained as described above. Note that the value of the high-temperature peak heat of fusion of the double-stage foamed particle usually coincides with the value of the high-temperature peak heat of fusion of the single-stage foamed particle used in the production of the double-stage foamed particle.

[0104] (Percentage of closed cells in foamed particles) Using single-stage or double-stage foamed particles, the bulk volume is approximately 20 cm³. 3 The apparent volume Va of the foamed particle group was measured by immersing it in water. Next, after thoroughly drying the foamed particle group whose apparent volume Va had been measured, the true volume Vx was measured according to procedure C described in ASTM-D2856-70 (the sum of the volume of the resin constituting the foamed particle and the total volume of the closed-cell portion of the foamed particle). A Beckman Model 1000 Air Comparison Pycnometer manufactured by Tokyo Science Co., Ltd. was used to measure this true volume Vx. Next, the closed-cell ratio was calculated using the following formula (1). Using different measurement samples, the closed-cell ratio was measured five times using the same procedure as described above, and the arithmetic mean of the values ​​obtained from each measurement was calculated and taken as the closed-cell ratio of the foamed particles. [Math 2] Closed cell ratio (%)=(Vx-W / ρ)×100 / (Va-W / ρ) (1) Vx: True volume (cm³) of the foamed particle group measured by the above method 3 ) Va: The apparent volume (cm³) of the foaming particle group, measured from the rise in water level when the foaming particle group is submerged in water in a graduated cylinder. 3 ) W: Mass of foaming particles (g) ρ: Density of the resin constituting the foam particles (g / cm³)3 )

[0105] [Measurement of physical properties of foamed particle molded products] The physical properties of the foam particle molded bodies manufactured as described above were measured or evaluated as follows. The results are shown in Tables 1 to 3. Regarding the evaluation, a rating of △ or ○ was considered to indicate that the product is suitable for practical use.

[0106] (Density of molded foam particle molded body) The mass of the foamed particle molded body was calculated by dividing it by the volume calculated based on the outer diameter.

[0107] (Surface properties evaluation of foamed particle molded products) The surface properties of the foam particle molded body were visually observed and evaluated as follows. ○...The gaps between the foam particles on the surface of the molded body are completely filled. △···Some areas were found to be unfilled in the gaps between foam particles on the surface of the molded body. ×...Several areas on the surface of the molded product show that the gaps between the foam particles are not filled.

[0108] (Fusion rate of foamed particle molded body) A test specimen (100 mm long x 100 mm wide x thickness: thickness of the foam particle molded body) was cut from the center of the foam particle molded body. An incision of approximately 5 mm in the thickness direction was made in each test specimen with a utility knife, and then the test specimen was fractured along the incision. Next, the number of foam particles present on the fracture surface of the foam particle molded body (n) and the number of foam particles that were fractured (b) were measured. The number of foam particles that were fractured (b) relative to the total number of foam particles (n) was expressed as a percentage to determine the fusion rate (%), and was evaluated as follows. ○...The fusion rate is 80% or higher. ×...The fusion rate is less than 80%.

[0109] (Recovery properties of foamed particle molded products) After in-mold molding, the foam particle molded body was removed from the mold and allowed to cure for 24 hours in an environment with a temperature of 23°C and a relative humidity of 50%. The thickness of the cured foam particle molded body was measured at four points 10 mm away from the center of the skin surface, in a plan view from the thickness direction. The largest of these thicknesses was taken as the corner thickness of the foam particle molded body. Separately, the thickness of the foam particle molded body was measured at the center in both the vertical and horizontal directions in a plan view from the thickness direction, and this value was taken as the central thickness of the foam particle molded body. The ratio (%) of the central thickness to the corner thickness of the foam particle molded body was then calculated and evaluated as follows. The ratio (%) is 90% or higher. △···Ratio (%) is between 85% and 90%. The ratio (%) is less than 85%.

[0110] (Flame retardancy of foamed particle molded material) The flame retardancy of the foamed particle molded material was evaluated as follows based on a horizontal combustion test (UL94 horizontal combustion test) in accordance with the UL94 standard. First, five test specimens with a skin surface measuring 150±1mm in length, 50±1mm in width, and 13mm in thickness were cut from the foam particle molded body. On the 150±1mm in length and 50mm±1mm in width surface of each test specimen, markings were drawn at positions 25mm, 60mm, and 125mm from one end in the vertical direction. After conditioning the test specimens by leaving them undisturbed for 24 hours at 23°C and 50% relative humidity, the test specimens were placed on a wire mesh with the markings facing upwards, and cotton was placed beneath them. Then, a wingtip burner was adjusted to produce a blue flame of 38mm±2mm, and the flame was applied to the edge of the test specimen. After one minute, the burner was moved more than 100mm away from the test specimen, and the time and distance until the flame disappeared from the test specimen were measured. Based on the time and distance measured as described above, the flame retardancy class was determined for each of the five test specimens, classifying them as HF-1, HF-2, or HBF. For details on HF-1, HF-2, and HBF, please refer to the description of the foamed particles mentioned above. Then, the class in which four or more of the five test specimens met the criteria was determined as the flame retardancy of the foam particle molded article, and this is shown in Tables 1 to 3. In addition, in Tables 1 to 3, for each example and each comparative example, the number of test specimens that met the HF-1 standard out of five is shown in parentheses next to the determined class.

[0111] (Drip evaluation of foam particle molded products) In the UL94 horizontal test described above, the presence or absence of resin dripping from the test specimen was observed and evaluated as follows. ○...No cotton ignition due to dripping material. ×...Cotton ignited by dripping material.

[0112] [Table 1]

[0113] [Table 2]

[0114] [Table 3]

[0115] The present invention described above encompasses the following technical concepts. (1) Polyamide resin foam particles containing a flame retardant and a polyamide resin, The aforementioned flame retardant, A phosphorus-based flame retardant (flame retardant a) consisting of a metal salt of phosphinic acid and / or diphosphinic acid, It comprises one or more nitrogen / phosphorus-based flame retardants (flame retardant b) selected from the group consisting of reaction products of melamine and polyphosphate, reaction products of melamine condensates and polyphosphate, and mixtures thereof, The base resin of the foamed particles includes a polyamide resin. With respect to 100 parts by mass of the base resin containing the polyamide resin, 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, and the mass ratio of the amount of flame retardant a to the amount of flame retardant b is 90:10 to 30:70 (where the total amount of flame retardant a and flame retardant b is 100% by mass). Polyamide resin foam particles wherein the average bubble diameter A of the polyamide resin foam particles is 5 μm or more and 100 μm or less, and the average bubble diameter B of the five bubbles selected in order of largest area from the bubbles observed in the cross-section formed by dividing the polyamide resin foam particles in half is 250 μm or less. (2) Polyamide resin foam particles as described in (1) above, wherein the average bubble diameter B is 160 μm or less. (3) Polyamide resin foam particles as described in (1) or (2) above, wherein the difference [BA] between the average bubble diameter A and the average bubble diameter B is 60 μm or more and 200 μm or less. (4) The flame retardant a is aluminum phosphinate, The flame retardant b is melamine polyphosphate, Polyamide resin foam particles according to any one of (1) to (3) above, wherein the phosphorus content is 15% by mass or more and 30% by mass or less in 100% by mass of the melamine polyphosphate, and the nitrogen content is 10% by mass or more and 20% by mass or less. (5) Polyamide resin foam particles according to any one of (1) to (4) above, wherein the amount of flame retardant b blended is 2 parts by mass or more and 10 parts by mass or less per 100 parts by mass of the base resin containing the polyamide resin. (6) The polyamide resin foam particles according to any one of (1) to (5) above, wherein the polyamide resin foam particles contain a carbon-based colorant, and the amount of the carbon-based colorant is 0.5% by mass or more and 5% by mass or less in 100% by mass of the polyamide resin foam particles. (7) Polyamide resin foam particles according to any one of (1) to (6) above, further comprising a NOR-type hindered amine having a substructure represented by the following formula (IV), wherein the amount of the NOR-type hindered amine is 0.5 parts by mass or more and 8 parts by mass or less per 100 parts by mass of the total of the flame retardant a and the flame retardant b. (However, in formula (IV), R is one of an alkyl group, cycloalkyl group, aralkyl group, or aryl group, and * is any structure to which it is attached.) [ka] (8) The apparent density of the polyamide resin foam particles is 10 kg / m³ 3 More than 80kg / m 3 The following are polyamide resin foam particles as described in any one of the above items (1) to (7). (9) A molded polyamide resin foam particle body obtained by in-mold molding polyamide resin foam particles as described in any one of items (1) to (8) above. (10) Polyamide resin foam particles according to any one of (1) to (8) above, further comprising zinc borate, wherein the amount of zinc borate is 0.5 parts by mass or more and 10 parts by mass or less per 100 parts by mass of the base resin. (11) A resin particle manufacturing step comprising preparing a molten kneaded product by melting and kneading a substrate containing a flame retardant and a polyamide resin, and extruding the molten kneaded product from an extruder to produce polyamide resin particles, The process includes a foaming step to produce foamed polyamide resin particles by foaming the aforementioned polyamide resin particles, The aforementioned flame retardant, A phosphorus-based flame retardant (flame retardant a) consisting of a metal salt of phosphinic acid and / or diphosphinic acid, It comprises one or more nitrogen / phosphorus-based flame retardants (flame retardant b) selected from the group consisting of reaction products of melamine and polyphosphate, reaction products of melamine condensates and polyphosphate, and mixtures thereof, With respect to 100 parts by mass of the base resin containing the polyamide resin, 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, and the mass ratio of flame retardant a to flame retardant b is 90:10 to 30:70 (where the total of flame retardant a and flame retardant b is 100% by mass). A method for producing polyamide resin foam particles, wherein the average bubble diameter A of the polyamide resin foam particles is 5 μm or more and 100 μm or less, and the average bubble diameter B of five bubbles selected in descending order of area from the bubbles observed in the cross-section formed by dividing the polyamide resin foam particles into two equal parts is 250 μm or less. (12) A method for producing polyamide resin foamed particles as described in (11) above, wherein at least one of the following configurations 1 to 6 is carried out in the above manufacturing method, Configuration 1 involves adding zinc borate to the base material in an amount of 0.5 parts by mass to 10 parts by mass per 100 parts by mass of the base resin. Configuration 2 adjusts the temperature of the molten mixture extruded from the extruder to 250°C or higher and 275°C or lower in the resin particle manufacturing process. Configuration 3 is that the extruder in the resin particle manufacturing process is a twin-screw extruder. Configuration 4 is the foaming process, The process includes at least one foaming step, in which the polyamide resin particles, an inorganic dispersant, and a surfactant are dispersed in a sealed container supplied with a dispersion medium such as water, and a foaming agent is impregnated to prepare foamable polyamide resin particles, and then the foamable polyamide resin particles are released together with the dispersion medium under a lower pressure than the sealed container by opening one end of the sealed container to cause foaming. The amount of inorganic dispersant added to the dispersion medium is 0.3 parts by weight or more and 2.0 parts by weight or less per 100 parts by weight of the polyamide resin particles, and the amount of surfactant added to the dispersion medium is 0.2 parts by weight or more and 1.5 parts by weight or less per 100 parts by weight of the resin particles. Configuration 5 involves adding a NOR-type hindered amine having a substructure represented by formula (IV) to the substrate in an amount of 0.5 parts by mass or more and 8 parts by mass or less per 100 parts by mass of the total of flame retardant a and flame retardant b (in formula (IV), R is one of an alkyl group, cycloalkyl group, aralkyl group, and aryl group, and * is a structure to which any structure is attached). [ka] Configuration 6 is the foaming process, A one-stage foaming process is performed by dispersing the polyamide resin particles in a sealed container supplied with a dispersion medium such as water and impregnating them with a foaming agent to prepare foamable polyamide resin particles, and then releasing the foamable polyamide resin particles together with the dispersion medium under a lower pressure than the sealed container by opening one end of the sealed container, thereby causing foaming. The process includes a second foaming step in which the first-stage foamed particles obtained in the first-stage foaming step are supplied to a pressure vessel, and internal pressure is applied and the vessel is heated to cause foaming, thereby obtaining polyamide resin foamed particles exhibiting a bulk ratio M2 greater than the bulk ratio M1 of the first-stage foamed particles. (13) The method for producing polyamide resin foam particles according to (12) above, wherein in the configuration 6, the ratio (M2 / M1) of the bulk ratio M1 of the single-stage foamed particles obtained in the single-stage foaming step to the bulk ratio M2 of the polyamide resin foamed particles obtained in the double-stage foaming step is 1.2 or more and 2.0 or less. (14) A method for producing polyamide resin foamed particles according to (12) or (13) above, wherein in the two-stage foaming step of the configuration 6, the internal pressure (pressurized pressure) inside the first-stage foamed particles is adjusted to a range of 0.3 MPa to 1.0 MPa, and the pressure is maintained for at least 24 hours to impart internal pressure to the first-stage foamed particles. (15) A method for producing polyamide resin foamed particles according to any one of (12) to (14) above, wherein the first-stage foamed particles to which internal pressure has been applied in the two-stage foaming step of the configuration 6 are heated with steam at 0.01 MPa or more and 0.08 MPa or less.

Claims

1. Foamed particles containing a flame retardant, The aforementioned flame retardant, A phosphorus-based flame retardant (flame retardant a) consisting of a metal salt of phosphinic acid and / or diphosphinic acid, The present invention comprises one or more nitrogen / phosphorus-based flame retardants (flame retardant b) selected from the group consisting of reaction products of melamine and polyphosphate, reaction products of melamine condensates and polyphosphate, and mixtures thereof. The base resin of the foamed particles includes a polyamide resin. With respect to 100 parts by mass of the base resin, 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, and the mass ratio of the amount of flame retardant a to the amount of flame retardant b is 90:10 to 30:70 (where the total amount of flame retardant a and flame retardant b is 100% by mass). Polyamide resin foam particles wherein the average bubble diameter A of the polyamide resin foam particles is 5 μm or more and 100 μm or less, and the average bubble diameter B of five bubbles selected in order of the largest area per bubble from the bubbles observed in the cross-section formed by dividing the polyamide resin foam particles into two equal parts is 250 μm or less.

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

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

4. The flame retardant a is an aluminum salt of phosphinic acid, The flame retardant b is polyphosphate melamine. Polyamide resin foam particles according to claim 1 or 2.

5. The polyamide resin foam particles according to claim 1 or 2, wherein the amount of the flame retardant b blended with 100 parts by mass of the base resin is 2 parts by mass or more and 10 parts by mass or less.

6. The polyamide resin foam particles according to claim 1 or 2, wherein the polyamide resin foam particles contain a carbon-based colorant, and the amount of the carbon-based colorant is 0.5% by mass or more and 5% by mass or less in 100% by mass of the polyamide resin foam particles.

7. Polyamide resin foam particles according to claim 1 or 2, further comprising a NOR-type hindered amine having a substructure represented by the following formula (IV), wherein the amount of the NOR-type hindered amine is 0.5 parts by mass or more and 8 parts by mass or less with respect to 100 parts by mass of the total of the flame retardant a and the flame retardant b (in formula (IV), R is any alkyl group, cycloalkyl group, aralkyl group, and aryl group, and * is any structure to which it is attached). 【Chemistry 1】

8. The apparent density of the polyamide resin foam particles is 10 kg / m³ ３ More than 80kg / m ３ The polyamide resin foam particles according to claim 1 or 2, which are as follows:

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

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