Polyolefin-based resin foamed particles and foamed particle molded article

Abstract

Provided are polyolefin-based resin foamed particles with which it is possible to easily mold a polyolefin-based resin foamed particle molded article exhibiting high flame retardancy as well as exceptional fusion properties and surface properties.　These polyolefin-based resin foamed particles comprise a foam layer. The foam layer contains a base material resin, a phosphonic-acid-ester-based compound, and a NOR-type hindered-amine-based compound. The base material resin is configured from a polyolefin-based resin. The blending amount of the phosphonic-acid-ester-based compound in the foam layer is 5-25 parts by mass per 100 parts by mass of the base material resin. The blending amount of the NOR-type hindered-amine-based compound in the foam layer is 0.3-5 parts by mass per 100 parts by mass of the base material resin. The closed cell ratio of the foamed particles is 60% or greater.

Description

Polyolefin resin expanded beads and expanded bead molded articles

[0001] The present invention relates to flame-retardant expanded polyolefin resin beads and expanded bead moldings.

[0002] Expanded polyolefin resin beads are widely used as a material for in-mold molding of expanded polyolefin resin beads. The expanded polyolefin resin beads are used for various purposes, such as packaging materials, vehicle components, and building materials. In particular, from the viewpoint of excellent properties such as light weight, impact resistance, and energy absorption properties, expanded polyolefin resin beads are suitable for vehicle components such as automobile bumpers and seat cores.

[0003] Conventionally, the above-mentioned vehicle components have sometimes been required to satisfy the FMVSS 302 standard (Federal Motor Vehicle Safety Standard No. 302). However, with the recent spread of electric vehicles, in addition to a slow burning rate, higher flame retardancy, exemplified by self-extinguishing properties, may be required.

[0004] For example, Patent Document 1 proposes expanded polypropylene resin beads (hereinafter also referred to as Prior Art 1) containing a polypropylene resin, an organic phosphorus compound, and a hindered amine in predetermined ranges. Patent Document 2 proposes pre-expanded polyolefin resin beads (hereinafter also referred to as Prior Art 2) containing a specific organic phosphorus compound and a specific hindered amine in predetermined ranges. Both Patent Documents 1 and 2 state that by using the proposed expanded beads, it is possible to provide an expanded bead molding having excellent flame retardancy.

[0005] WO2022 / 203035A1 WO2016 / 052739A1

[0006] However, studies by the present inventors have revealed that Prior Art 1 and 2 have the following problems. That is, although Prior Art 1 and 2 both show improved flame retardancy by including a predetermined range of an organophosphorus compound and a hindered amine, they have found that when an expanded bead molding is produced by in-mold molding, the fusion strength between the expanded beads may be insufficient and the surface properties of the produced expanded bead molding may be insufficient. Hereinafter, the fusion strength and surface properties of the expanded bead molding may be collectively referred to as the "molded state."

[0007] The present invention has been made in view of the above problems, and provides expanded polyolefin resin beads that exhibit high flame retardancy and can be easily molded into an expanded polyolefin resin bead molding that provides an excellent molded state, and an expanded polyolefin resin bead molding that provides an excellent molded state.

[0008] The expanded polyolefin resin beads of the present invention are characterized in that they are expanded polyolefin resin beads having an expanded layer, wherein the base resin of the expanded layer is made of a polyolefin resin, the expanded layer contains a phosphonate ester compound and a NOR hindered amine compound, the amount of the phosphonate ester compound in the expanded layer is 5 to 25 parts by mass per 100 parts by mass of the base resin, the amount of the NOR hindered amine compound in the foam layer is 0.3 to 5 parts by mass per 100 parts by mass of the resin, and the closed cell rate of the expanded beads is 60% or more. Alternatively, the expanded polyolefin resin bead molding of the present invention is characterized in that it is produced by molding the expanded polyolefin resin beads of the present invention in a mold.

[0009] The present invention provides expanded polyolefin resin beads that can be used to produce expanded polyolefin resin beads that exhibit high flame retardancy and excellent molding conditions. The expanded polyolefin resin beads of the present invention also exhibit high flame retardancy and excellent fusion properties and surface properties.

[0010] The expanded polyolefin resin beads of the present invention will be described below. In the following description, the expanded polyolefin resin beads of the present invention may be referred to as "expanded beads" or simply "expanded beads," and the expanded polyolefin resin bead molding of the present invention may be referred to as "expanded bead molding" or simply "expanded bead molding." In the following description, preferred numerical ranges of the present invention may be indicated as appropriate. In this case, preferred, more preferred, and particularly preferred ranges regarding the upper and lower limits of the numerical ranges can be determined from all combinations of the upper and lower limits. Furthermore, in the present invention, high flame retardancy means not only a slow burning rate but also self-extinguishing properties. In the present invention, self-extinguishing properties are evaluated according to the UL94 (Underwriters Laboratories 94) standard, with a rating of V-0, V-1, or V-2. Expanded bead moldings that exhibit excellent flame retardancy in tests based on this standard not only have a slow burning rate but also excel in self-extinguishing properties. Expanded bead moldings that exhibit self-extinguishing properties also exhibit relatively good flame retardancy when tested based on other standards. Therefore, the expanded beads constituting the expanded bead moldings exhibiting such high flame retardancy and the expanded bead moldings can be used in a wide range of applications.

[0011] The expanded beads of the present invention have a foam layer, and the base resin of the foam layer is composed of a polyolefin resin. The foam layer contains a phosphonate ester compound and a NOR hindered amine compound. This makes it possible to impart desired flame retardancy to the expanded beads and to the expanded bead molded article obtained by molding the expanded beads in a mold. The amount of the phosphonate ester compound in the foam layer is 5 to 25 parts by mass per 100 parts by mass of the base resin. The amount of the NOR hindered amine compound in the foam layer is 0.3 to 5 parts by mass per 100 parts by mass of the base resin. The expanded beads of the present invention having the above configuration have a closed cell ratio of 60% or more. Examples of methods for adjusting the closed cell ratio to this preferred range will be described later.

[0012] The present inventors conducted extensive research to provide expanded beads that can be molded in a mold, exhibiting high flame retardancy while improving the problem of deterioration in molding quality. The inventors discovered that the desired problem can be solved by using expanded beads that contain a phosphonate ester compound and a NOR-type hindered amine compound in specified ranges and have a closed cell content of 60% or more, leading to the provision of the present invention. The causal relationship between the closed cell content and the occurrence of the problem of deterioration in molding quality described above is unclear, but is speculated as follows.

[0013] First, there are generally two main methods for producing expanded beads containing a polyolefin resin, a phosphonate ester compound, and a NOR hindered amine compound. One method involves melt-mixing the above-mentioned raw materials, adding a blowing agent, and extruding the mixture to form a foam, which is then cut to obtain expanded beads of a predetermined size. This method may be referred to as Production Method 1 below. The other method involves melt-mixing the above-mentioned raw materials, extruding the resulting molten mixture, cutting it to produce resin beads of a predetermined size, and then expanding the resin beads to obtain expanded beads. This method may be referred to as Production Method 2 below. Both Production Methods 1 and 2 include a step in which the above-mentioned raw materials are melt-mixed in an extruder. In these series of steps, the molten mixture obtained by melt-mixing a polyolefin resin, a phosphonate ester compound, and a NOR hindered amine compound is thought to experience changes in viscosity and increased hygroscopicity compared to when the phosphonate ester compound and the NOR hindered amine compound are not used. More specifically, it is speculated that melt-mixing a polyolefin resin with a phosphonic acid ester compound increases the hygroscopicity of the molten mixture containing the phosphonic acid compound. Furthermore, melt-mixing a polyolefin resin with a NOR hindered amine compound generates free radicals derived from the NOR hindered amine compound, which accelerates the degradation of the polyolefin resin and changes the viscosity of the polyolefin resin. It is speculated that the viscosity of the molten mixture containing the polyolefin resin with a viscosity change changes accordingly. It is speculated that using a molten mixture with an unintended increase in hygroscopicity and a viscosity change makes it difficult to form bubbles and cell membranes during foaming, resulting in a low closed-cell content of the resulting expanded beads. It is speculated that this results in a decrease in the fusion strength of the expanded beads during in-mold molding, and an insufficient molding state of the resulting expanded bead molding.

[0014] The closed cell ratio of the expanded beads of the present invention is 60% or more, preferably 65% ​​or more, more preferably 70% or more, even more preferably 75% or more, and particularly preferably 80% or more. A high closed cell ratio of the expanded beads tends to facilitate in-mold molding of expanded bead moldings in a good state. In particular, the expanded beads of the present invention having a closed cell ratio of 75% or more exhibit excellent fusion properties in the expanded bead moldings molded in-mold using the expanded beads.

[0015] In the present invention, the closed cell ratio is measured by the following method. ３ The expanded beads are immersed in water to measure the apparent volume Va of the expanded beads. After measuring the apparent volume Va, the expanded beads are thoroughly dried, and the true volume Vx of the expanded beads is measured according to procedure C described in ASTM-D2856-70. The true volume Vx of the expanded beads is the sum of the volume of the resin constituting the expanded beads and the total volume of the closed cells in the expanded beads. An air-comparison hydrometer is used to measure this true volume Vx. An example of a commercially available air-comparison hydrometer is the "930" air-comparison hydrometer manufactured by Toshiba Beckman Co., Ltd. The closed cell ratio is then calculated according to the following formula (1). Using different measurement samples, the closed cell ratio is measured five times using the same procedure as above, and the arithmetic mean of the values ​​obtained in each measurement is calculated and used as the closed cell ratio of the expanded beads. [Equation 1] Closed cell ratio (%) = (Vx - W / ρ) × 100 / (Va - W / ρ) (1) Vx: true volume (cm) of the expanded particle group measured by the above method ３ ) Va: Apparent volume (cm) of the expanded particles measured from the rise in the water level when the expanded particles are submerged in water in a measuring cylinder ３ ) W: Mass of the expanded particle group (g) ρ: Density of the resin constituting the expanded particle (g / cm ３ )

[0016] Expanded beads containing the flame retardant of the present invention are preferably approximately spherical. Expanded beads containing a phosphonate ester compound and a NOR-type hindered amine compound as a flame retardant tend to be flat. From the viewpoints of enabling in-mold molding of expanded bead moldings with good molding conditions, good mold filling properties, and excellent storage stability, the average ratio of the major axis to the minor axis of the expanded beads (major axis / minor axis) is preferably 1.0 to 2.5, more preferably 1.0 to 2.1, and even more preferably 1.0 to 2.0. In particular, if the upper limit of the above ratio is 2.0 or less, expanded beads with particularly excellent fusibility can be provided. More preferably, the average ratio (major axis / minor axis) is 1.2 to 1.8. Examples of means for adjusting the (major axis / minor axis) within a preferred range will be described later. In the present invention, the closer the average value of the ratio (major axis / minor axis) is to 1.0, the more nearly spherical the expanded beads are in appearance, and the larger the average value of the ratio is, the more flattened the expanded beads are in appearance. Note that, in the expanded beads of the present invention, the terms "nearly spherical" and "flat" refer to the external shapes of the expanded beads observed with the naked eye.

[0017] The major and minor diameters of the expanded beads are measured using an image analysis particle size distribution analyzer. More specifically, the expanded beads are allowed to freely fall within the analyzer, and the expanded beads are then photographed at high speed with a camera to obtain multiple images of the expanded beads during free fall. From the multiple images of the expanded beads during free fall obtained by the high-speed photography, multiple images of the same expanded beads photographed from different angles are extracted. For the multiple images of the same expanded beads photographed from different angles, image analysis is used to measure the maximum and minimum lengths of the distance between two parallel lines sandwiching the expanded beads. The maximum length of the distance between the two parallel lines in the multiple images is determined as the major diameter, and the minimum length is determined as the minor diameter. The ratio of the major diameter to the minor diameter of a single expanded bead is then calculated. The ratio is then determined for each of the multiple expanded beads, and the arithmetic mean of each ratio is calculated, thereby allowing the average ratio of the major diameter to the minor diameter (major diameter / minor diameter) of the expanded beads to be calculated. An example of an image analysis type particle distribution measuring device is a dynamic image analysis type particle shape and particle size distribution measuring device and analysis software (product name: PARTAN 3D) manufactured by Microtrac Bell Corporation.

[0018] The reason why expanded beads containing a phosphonate ester compound and a NOR-type hindered amine compound tend to have the flattened shape is unclear, but the following is speculated. When expanding resin beads by preparing them and expanding them, the resin beads can be produced as follows. Specifically, raw materials such as resin are generally supplied to an extruder and melt-mixed. The strand-like molten mixture is then extruded through a circular orifice. While being drawn in the extrusion direction, the strand-like molten mixture is then cut to a predetermined length transverse to the extrusion direction to produce pellet-like resin beads with a circular cut surface. Resin beads thus produced under a force applied in the extrusion direction are extruded from the high-temperature extruder and rapidly cooled, causing stress due to the force applied in the extrusion direction to remain inside the resin beads. Therefore, during expansion, these resin beads are more likely to expand in a direction transverse to the extrusion direction than in the extrusion direction. Therefore, when cutting the molten mixture extruded from the extruder, the internal stress of the resin beads and the length of the resin beads in the extrusion direction can be adjusted by adjusting the drawing speed and cutting width. By expanding the resin beads obtained by the above adjustments, approximately spherical expanded beads can be obtained. On the other hand, when resin particles are produced using a polyolefin resin together with a phosphonate ester compound and a NOR-type hindered amine compound, the strand-shaped molten mixture extruded from the extruder tends to shrink in a direction perpendicular to the extrusion direction. Pellets of resin particles cut in this shrunk state tend to become flat. Furthermore, when the flat resin particles are expanded, the expanded particles tend to become flat. As explained above, it is believed that flat expanded particles are generated due to the influence of unintended changes in viscosity and increased hygroscopicity of the molten mixture during the resin particle production process.

[0019] The foam layer of the present invention has a base resin composed of a polyolefin resin and contains a phosphonate ester compound and a NOR hindered amine compound. In other words, the foam layer of the present invention is composed of a base resin, and the base resin is a polyolefin resin. The foam layer may further contain any other resin as long as the objects and effects of the present invention are not impaired. Furthermore, the foam layer may contain any additive used in producing expanded beads, in addition to the resin, phosphonate ester compound, and NOR hindered amine compound.

[0020] (Polyolefin-based resin) Examples of the polyolefin-based resin constituting the base resin include polypropylene-based resin, polyethylene-based resin, etc. The foam layer may be composed of one type of polyolefin-based resin or two or more types of polyolefin-based resins.

[0021] The base resin refers to a resin and polymer constituting the foam layer that accounts for more than 50% by mass, preferably more than 70% by mass, more preferably more than 80% by mass, even more preferably more than 90% by mass, even more preferably more than 95% by mass, and particularly preferably 100% by mass. From the viewpoint of obtaining a foamed bead molding having higher compressive strength, the foam layer in the present invention preferably contains a polypropylene-based resin as the polyolefin-based resin base resin, and the polypropylene-based resin is preferably contained in an amount of 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, and particularly preferably 100% by mass, based on 100% by mass of the base resin of the foam layer. In other words, it is particularly preferred that the base resin of the foam layer is composed solely of a polypropylene-based resin.

[0022] Polypropylene-based resin: In this specification, the term "polypropylene-based resin" refers to a propylene homopolymer and / or a propylene-based copolymer containing 50% by mass or more of structural units derived from propylene. Examples of the propylene homopolymer include propylene-based resins such as isotactic polypropylene, syndiotactic polypropylene, and atactic polypropylene. These resins exemplified as propylene homopolymers may be used alone or in combination of two or more. The content of propylene-derived structural units in the propylene-based copolymer is preferably 80% by mass or more, more preferably 90% by mass or more. The content of propylene-derived structural units in the propylene-based copolymer is preferably 99% by mass or less, more preferably 98% by mass or less. Examples of such propylene-based copolymers include copolymers of propylene and ethylene and / or an α-olefin having 4 to 20 carbon atoms. Examples of the α-olefin include 1-butene, 1-pentene, 1-hexene, 1-octene, and 4-methyl-1-butene. Other examples of propylene-based copolymers include ethylene-propylene random copolymers, propylene-butene random copolymers, and ethylene-propylene-butene random copolymers. These propylene-based copolymers may be, for example, random copolymers or block copolymers, with random copolymers being preferred. Examples of the propylene-based copolymers include impact-resistant polypropylenes (block polypropylenes) composed of two or more phases including a continuous phase of propylene polymer and a rubber phase such as an ethylene-α-olefin copolymer present as a dispersed phase within the continuous phase. These resins exemplified as propylene-based copolymers may be used alone or in combination of two or more.

[0023] When the propylene-based random copolymer contains a component derived from ethylene (ethylene component) and / or a component derived from butene (butene component) as copolymerization components, from the viewpoint of further improving the in-mold moldability of the expanded beads under low molding pressure conditions, the total content of the ethylene component and the butene component in the propylene-based random copolymer is preferably 1% by mass or more, more preferably 1.5% by mass or more, and even more preferably 2% by mass or more. Furthermore, from the viewpoint of stably obtaining expanded bead molded articles having excellent mechanical properties such as compressive strength, the total content of the ethylene component and the butene component in the propylene-based random copolymer is preferably 15% by mass or less. That is, the total content of the ethylene component and the butene component in the propylene-based random copolymer is preferably 1% by mass or more and 15% by mass or less, more preferably 1.5% by mass or more and 15% by mass or less, and even more preferably 2% by mass or more and 15% by mass or less. The contents of the components derived from ethylene and α-olefin in the propylene-based random copolymer are determined by IR spectroscopy.

[0024] The polypropylene resin may be a linear polypropylene resin, a branched polypropylene resin, or a combination thereof. From the viewpoint of easily obtaining expanded beads with a small amount of blowing agent, the amount of the branched polypropylene resin contained in 100% by mass of the base resin of the foamed layer in the present invention is preferably 50% by mass or less, more preferably 30% by mass or less.

[0025] The inventors have confirmed that, when the base resin of the foamed layer contains a polypropylene resin, a phosphonate ester compound, and a NOR-type hindered amine compound, the viscosity of the molten mixture used to produce the foamed beads tends to decrease during production. From the viewpoint of suppressing this decrease in viscosity, the base resin of the foamed layer is preferably composed of a linear polypropylene resin (A) and a branched polypropylene resin (B) having a melt tension of 50 mN or more measured at 230°C and / or a polyethylene resin (C) having a melt flow rate of 3 g / 10 min or less measured at 190°C under a load of 2.16 kg. The melt flow rate may also be abbreviated as MFR. From the same viewpoint as above, it is particularly preferable that the base resin of the foamed layer be composed of a linear polypropylene resin (A) and a branched polypropylene resin (B) having a melt tension of 50 mN or more measured at 230°C. From the same viewpoint, the base resin of the foam layer is preferably composed of a linear polypropylene resin (A) and a polyethylene resin (C) having an MFR of 3 g / 10 min or less, measured at 190°C under a load of 2.16 kg. Furthermore, it is more preferable that the total content of the branched polypropylene resin (B) and the polyethylene resin (C) is 5% by mass or more and 30% by mass or less, where the total content of the linear polypropylene resin (A), the branched polypropylene resin (B), and the polyethylene resin (C) is 100% by mass. According to the preferred embodiment described above, the specific closed cell ratio of the foamed beads of the present invention can be easily achieved, and foamed beads capable of being molded in a mold with a better molding state can be provided. Furthermore, according to the preferred embodiment described above, viscosity change is suppressed, so that the average ratio of the major axis to the minor axis of the foamed beads (major axis / minor axis) can be easily adjusted within a predetermined range, and substantially spherical foamed beads can be easily obtained. In the present invention, the branched polypropylene resin refers to a polypropylene resin having a long-chain branched structure in its molecular structure, which promotes entanglement between molecular chains of the resin.The long-chain branched structure mentioned above is to be distinguished from a branched structure formed by copolymerizing propylene and an α-olefin. The copolymer is classified as a linear polypropylene. For example, a resin having a molecular chain consisting of 21 or more carbon skeletons is known as a branched polypropylene resin having a long-chain branched structure, but is not limited thereto. Examples of the branched polypropylene resin include branched homopolypropylenes manufactured by Borealis (trade names: Daploy WB130HMS, Daploy WB135HMS, Daploy WB140HMS) and branched homopolypropylene resins manufactured by SunAllomer (trade name: PF814). In the present invention, the linear polypropylene resin refers to a polypropylene resin other than the branched polypropylene resins mentioned above, and specific examples include linear propylene homopolymers and linear propylene random copolymers.

[0026] Polyethylene-based resin: In this specification, polyethylene-based resin refers to an ethylene homopolymer or an ethylene-based copolymer containing 50% by mass or more of structural units derived from ethylene. Specific examples include polyethylenes exemplified by high-density polyethylene (PE-HD), medium-density polyethylene (PE-MD), low-density polyethylene (PE-LD), linear low-density polyethylene (PE-LLD), and linear very low-density polyethylene; and ethylene-based copolymers exemplified by ethylene-vinyl acetate copolymer and ethylene-methyl methacrylate copolymer. The content of structural units derived from ethylene in the polyethylene-based copolymer is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and particularly preferably 98% by mass or more.

[0027] Other Resins: The foam layer of the present invention may contain a thermoplastic resin other than the polyolefin-based resin, as long as the object and effect of the present invention are not impaired. Examples of the thermoplastic resin include thermoplastic resins other than polyolefin-based resins, such as polystyrene-based resins, polyamide-based resins, polyester-based resins, polycarbonate-based resins, and modified polyphenylene ether-based resins. The thermoplastic resin may be one type or a combination of two or more types.

[0028] In the foam layer, the content of thermoplastic resins other than the polyolefin-based resin is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 0% by mass, relative to 100% by mass of the base resin. In other words, it is particularly preferable that the foam layer contains substantially only polyolefin-based resins as thermoplastic resins.

[0029] In addition to the thermoplastic resins described above, the foam layer of the present invention may contain a thermoplastic elastomer or other polymers exemplified as non-thermoplastic resins. Examples of thermoplastic elastomers include thermoplastic elastomers such as olefin-based thermoplastic elastomers (TPO) and urethane-based thermoplastic elastomers (TPU), while examples of non-thermoplastic resins include thermosetting resins and rubber. When the foam layer contains the other polymers, the content of the other polymers in the foam layer is preferably 20% by mass or less, more preferably 10% by mass or less, even more preferably 5% by mass or less, even more preferably 3% by mass or less, and particularly preferably 0% by mass. In other words, it is particularly preferable that the foam layer does not substantially contain any polymers other than the thermoplastic resin.

[0030] (Melting Point of Polyolefin Resin) When the polyolefin resin contains a polypropylene resin, the melting point of the polypropylene resin is preferably 130°C or higher, more preferably 135°C or higher, and even more preferably 140°C or higher, from the viewpoint of improving the mechanical properties of the resulting expanded bead molding. On the other hand, the melting point of the polypropylene resin is preferably 155°C or lower, more preferably 150°C or lower, and even more preferably 148°C or lower, from the viewpoint of improving the in-mold moldability of the expanded beads under conditions of low molding pressure. In other words, the melting point of the polypropylene resin is preferably 130°C or higher and 155°C or lower, more preferably 135°C or higher and 150°C or lower, and even more preferably 140°C or higher and 148°C or lower. When the polyolefin resin contains a polyethylene resin, the melting point of the polyethylene resin is preferably 110°C or higher, more preferably 112°C or higher, and even more preferably 115°C, from the viewpoint of improving the mechanical properties of the resulting expanded bead molding. On the other hand, from the viewpoint of improving the in-mold moldability of the expanded beads under conditions of low molding pressure, the melting point of the polyethylene resin is preferably 130° C. or lower, more preferably 128° C. or lower, and even more preferably 125° C. or lower. In other words, the melting point of the polyethylene resin is preferably 110° C. or higher and 130° C. or lower, more preferably 112° C. or higher and 128° C. or lower, and even more preferably 115° C. or higher and 125° C. or lower. The melting point of the polyolefin resin is measured in accordance with JIS K7121:2012 using the polyolefin resin or expanded polyolefin resin beads as a test piece. Specifically, the test piece was conditioned as described in "(2) Measuring the melting temperature after a certain heat treatment," in which the test piece was heated from 23°C to 200°C at a heating rate of 10°C / min under conditions of a nitrogen inflow rate of 30 mL / min, then held at that temperature for 10 minutes, cooled to 23°C at a cooling rate of 10°C / min, and then heated again to 200°C at a heating rate of 10°C / min to obtain a DSC curve (DSC curve at the second heating). Next, the apex temperature of the melting peak in the DSC curve at the second heating is determined, and this value is taken as the melting point of the polyolefin resin.When multiple melting peaks appear in the DSC curve after the second heating, the apex temperature of the melting peak having the highest melting peak height relative to the baseline is used as the melting point.

[0031] (Melt flow rate of polyolefin resin) When the polyolefin resin contains a polypropylene resin, the melt flow rate of the polypropylene resin is preferably 1 g / 10 min or more, more preferably 3 g / 10 min or more, and even more preferably 5 g / 10 min or more, from the viewpoint of improving the expandability during expansion of the resin particles and the secondary expandability during molding of the expanded beads. On the other hand, the melt flow rate of the polypropylene resin is preferably 20 g / 10 min or less, more preferably 15 g / 10 min or less, and even more preferably 10 g / 10 min or less, from the viewpoint of improving the uniformity of the cells in the expanded beads and the physical properties of the expanded bead molding. In other words, the MFR of the polypropylene resin is preferably 1 g / 10 min or more and 20 g / 10 min or less, more preferably 3 g / 10 min or more and 15 g / 10 min or less, and even more preferably 5 g / 10 min or more and 10 g / 10 min or less. The MFR of the polypropylene-based resin is measured in accordance with JIS K7210-1:2014 under conditions of a temperature of 230°C and a load of 2.16 kg. When the polyolefin-based resin contains a polyethylene-based resin, the MFR of the polyethylene-based resin is preferably 0.5 g / 10 min or more, more preferably 0.8 g / 10 min or more, from the viewpoint of improving the expandability during expansion of the resin beads and the secondary expandability during in-mold molding of the expanded beads. On the other hand, the melt flow rate of the polyethylene-based resin is preferably 4 g / 10 min or less, more preferably 3 g / 10 min or less, from the viewpoint of improving the uniformity of the cells in the expanded beads and the physical properties of the expanded bead molding. In other words, the MFR of the polyethylene-based resin is preferably 0.5 g / 10 min or more and 4 g / 10 min or less, more preferably 0.8 g / 10 min or more and 3 g / 10 min or less. The MFR of the polyethylene resin is measured based on JIS K7210-1:2014 under conditions of a temperature of 190°C and a load of 2.16 kg.

[0032] (Phosphonate Ester Compound) The foam layer of the present invention contains a phosphonate ester compound. The phosphonate ester compound is a compound containing a phosphonate ester moiety in the molecule, and includes, for example, a cyclic phosphonate ester compound and an alkylphosphonate ester compound.

[0033] Cyclic phosphonate ester compound: The cyclic phosphonate ester compound is a compound containing one or more cyclic phosphonate ester moieties in the molecule, and is preferably at least one selected from the group consisting of compounds represented by the following general formula (1), compounds represented by the following general formula (2), compounds represented by the following general formula (3), and compounds represented by the following general formula (4), and is more preferably pentaerythritol diphosphonate represented by the following general formula (1). The pentaerythritol diphosphonate of general formula (1) is a spirocyclic compound containing two cyclic phosphonate ester moieties in the molecule. The cyclic phosphonate ester compound may be used alone or in combination of two or more. (In the general formula, R １ and R ２ are each an alkyl group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, a benzyl group, a phenylethyl group, a phenyl group, or a naphthyl group, and R ３ is an alkyl group having 1 to 22 carbon atoms or an aryl group having 6 to 15 carbon atoms, and R ４ , R ８ , R ９ and R １２ are each an alkyl group having 1 to 4 carbon atoms, and R ５ , R ７ and R １１ are each a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and R ６ and R １０ are each an alkyl group having 1 to 22 carbon atoms, a cycloalkyl group having 9 to 22 carbon atoms, an aryl group having 9 to 22 carbon atoms, or an aralkyl group having 9 to 22 carbon atoms.

[0034] In general formula (1), R １ and R ２ may be the same or different, and are preferably the same. １R is an alkyl group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, a benzyl group, a phenylethyl group, a phenyl group, or a naphthyl group, preferably an alkyl group having 1 or 2 carbon atoms, and more preferably a methyl group. ２ is an alkyl group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, a benzyl group, a phenylethyl group, a phenyl group, or a naphthyl group, preferably an alkyl group having 1 or 2 carbon atoms, and more preferably a methyl group. １ and R ２ are more preferably methyl groups.

[0035] In general formula (2), R ３ is an alkyl group having 1 to 22 carbon atoms or an aryl group having 6 to 15 carbon atoms, and is preferably a phenyl group.

[0036] In general formula (3), R ４ and R ８ may be the same or different, and are preferably the same. ４ is an alkyl group having 1 to 4 carbon atoms, preferably a methyl group. ８ is an alkyl group having 1 to 4 carbon atoms, preferably a methyl group. ５ and R ７ may be the same or different, and are preferably the same. ５ is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, preferably an ethyl group. ７ is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, preferably an ethyl group. ６ represents an alkyl group having 1 to 22 carbon atoms, a cycloalkyl group having 9 to 22 carbon atoms, an aryl group having 9 to 22 carbon atoms, or an aralkyl group having 9 to 22 carbon atoms, and is preferably a linear alkyl group having 1 to 12 carbon atoms.

[0037] In general formula (4), R ９ and R １２ may be the same or different, and are preferably the same. ９is an alkyl group having 1 to 4 carbon atoms, preferably a methyl group. １２ is an alkyl group having 1 to 4 carbon atoms, preferably a methyl group. １０ R is an alkyl group having 1 to 22 carbon atoms, a cycloalkyl group having 9 to 22 carbon atoms, an aryl group having 9 to 22 carbon atoms, or an aralkyl group having 9 to 22 carbon atoms, and is preferably a linear alkyl group having 1 to 12 carbon atoms. １１ is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, preferably an ethyl group.

[0038] The melting point TmA of the cyclic phosphonate ester compound is preferably 80° C. or higher and 350° C. or lower, more preferably 150° C. or higher and 330° C. or lower, and even more preferably 200° C. or higher and 300° C. or lower. The melting point TmA of the cyclic phosphonate ester compound is measured in accordance with JIS K0064:1992.

[0039] The amount of the phosphonate ester compound in the foam layer of the expanded polyolefin resin beads of the present invention is 5 to 25 parts by mass per 100 parts by mass of the base resin of the foam layer. If the amount of the phosphonate ester compound is too small, a foamed bead molding having high flame retardancy cannot be obtained. On the other hand, if the amount is too large, a foamed bead molding having excellent fusion properties cannot be obtained. From the viewpoint of obtaining a foamed bead molding having higher flame retardancy, the amount of the phosphonate ester compound in the foam layer is preferably 6 parts by mass or more, more preferably 7 parts by mass or more, even more preferably 8 parts by mass or more, and particularly preferably 9 parts by mass or more per 100 parts by mass of the base resin of the foam layer. From the viewpoint of obtaining a foamed bead molding having excellent fusion properties, the amount of the phosphonate ester compound in the foam layer is preferably 22.5 parts by mass or less, more preferably 20 parts by mass or less, even more preferably 19 parts by mass or less, and particularly preferably 16 parts by mass or less per 100 parts by mass of the base resin of the foam layer. In other words, the amount of the phosphonate ester compound in the foam layer is preferably 6 parts by mass or more and 22.5 parts by mass or less, more preferably 7 parts by mass or more and 20 parts by mass or less, even more preferably 8 parts by mass or more and 19 parts by mass or less, and particularly preferably 9 parts by mass or more and 16 parts by mass or less, relative to 100 parts by mass of the base resin of the foam layer. The phosphonate ester compound described in this paragraph is a compound containing a phosphonate ester moiety in the molecule, as described above, and includes, for example, cyclic phosphonate ester compounds and alkylphosphonate ester compounds.

[0040] (NOR-Type Hindered Amine Compound) The foam layer in the present invention contains a NOR-type hindered amine compound. The NOR-type hindered amine compound has, in its structure, a 2,2,6,6-tetramethyl-4-piperidinamine moiety having a hydrocarbon group bonded to a nitrogen atom via an oxygen atom, as shown in the following general formula (5), and thereby can improve the flame retardancy of the molded article. (In general formula (5), R １３ represents a hydrocarbon group.)

[0041] In the general formula (5), R represents a hydrocarbon group. When two or more hindered amine moieties represented by the general formula (5) are contained in one molecule of the hindered amine compound, the plurality of R １３ may be the same or different, but multiple R １３ are preferably the same. １３ is preferably at least one selected from the group consisting of an alkyl group and a cycloalkyl group, and more preferably a cycloalkyl group. １３ is an alkyl group, R １３ is more preferably an alkyl group having 1 to 20 carbon atoms, and even more preferably an undecyl group. １３ When R is a cycloalkyl group, １３ is more preferably a cycloalkyl group having 4 to 10 carbon atoms, and even more preferably a cyclohexyl group. The NOR type hindered amine compounds may be used alone or in combination of two or more.

[0042] From the viewpoint of suppressing bleed-out from the expanded bead molding, the molecular weight of the NOR hindered amine compound is preferably 600 or more, more preferably 1500 or more. Furthermore, from the viewpoint of improving dispersion of the NOR hindered amine compound in the resin, the molecular weight of the NOR hindered amine compound is preferably 3000 or less, more preferably 2500 or less. In the NOR hindered amine compound, the number of 2,2,6,6-tetramethyl-4-piperidinamine moieties having a hydrocarbon group bonded to nitrogen via an oxygen bond, represented by general formula (5), is preferably 2 or more and 8 or less, more preferably 2 or 6 or less, and even more preferably 2 or 6.

[0043] The amount of the NOR hindered amine compound in the foam layer of the expanded polyolefin resin beads of the present invention is 0.3 parts by mass or more and less than 5 parts by mass per 100 parts by mass of the base resin of the foam layer. If the amount of the NOR hindered amine compound is too small, an expanded bead molding having high flame retardancy cannot be obtained. On the other hand, if the amount is too large, an expanded bead molding having excellent fusion properties cannot be obtained. From the viewpoint of obtaining an expanded bead molding having higher flame retardancy, the amount of the NOR hindered amine compound in the foam layer is preferably 0.4 parts by mass or more, more preferably 0.5 parts by mass or more, and even more preferably 0.6 parts by mass or more per 100 parts by mass of the base resin of the foam layer. From the viewpoint of obtaining an expanded bead molding having better fusion-bonding properties, the amount of the NOR hindered amine compound in the foam layer is preferably 4 parts by mass or less, more preferably 3 parts by mass or less, even more preferably 2 parts by mass or less, still more preferably 1 part by mass or less, and particularly preferably 0.9 parts by mass or less, relative to 100 parts by mass of the base resin of the foam layer. In other words, the amount of the NOR hindered amine compound in the foam layer is preferably 0.4 parts by mass or more and 4 parts by mass or less, more preferably 0.5 parts by mass or more and 3 parts by mass or less, even more preferably 0.6 parts by mass or more and 2 parts by mass or less, still more preferably 0.6 parts by mass or more and 1 part by mass or less, and particularly preferably 0.6 parts by mass or more and 0.9 parts by mass or less, relative to 100 parts by mass of the base resin of the foam layer.

[0044] As described above, the phosphonate ester compound and the NOR hindered amine compound are contained in a predetermined range relative to 100 parts by mass of the base resin of the foam layer. From the viewpoint of achieving higher flame retardancy, the ratio of the amount of the NOR hindered amine compound to the amount of the phosphonate ester compound in the foam layer is preferably 0.04 or more, and more preferably 0.05 or more. From the viewpoint of further improving the fusion properties of the foamed bead molding, the ratio of the amount of the NOR hindered amine compound to the amount of the phosphonate ester compound in the foam layer is preferably 0.50 or less, more preferably 0.40 or less, and even more preferably 0.30 or less. That is, the ratio of the amount of the NOR hindered amine compound to the amount of the phosphonate ester compound in the foam layer is preferably 0.04 or more and 0.50 or less, more preferably 0.04 or more and 0.40 or less, and even more preferably 0.05 or more and 0.30 or less.

[0045] (Optional Additives) The expanded beads of the present invention described above may contain any additives as appropriate, as long as the additives do not impair the objects and effects of the present invention. For example, the optional additives may include various conventionally known additives such as conductive materials, antioxidants, flame retardant aids, cell regulators, lubricants, crystal nucleating agents, light stabilizers such as ultraviolet inhibitors, antistatic agents, and colorants. These additives can be incorporated into the expanded beads by adding them, for example, during the process of producing resin beads. Some optional additives are described below.

[0046] Conductive carbon material: An example of a conductive material that is an optional additive is a conductive carbon material. The foam layer preferably contains a conductive carbon material. Examples of the conductive carbon material include conductive carbon black, single-walled carbon nanotubes, and multi-walled carbon nanotubes. When conductive carbon black is used as the conductive carbon material, the DBP oil absorption of the conductive carbon black measured in accordance with JIS K6217-4:2008 is 150 cm ３ / 100g~700cm ３ / 100g, and 200cm３ / 100g~500cm ３ / 100g is more preferable. The content of the conductive carbon material in the foam layer is preferably 1 part by mass or more and 10 parts by mass or less, more preferably 1.5 parts by mass or more and 8 parts by mass or less, and even more preferably 2 parts by mass or more and 6 parts by mass or less, per 100 parts by mass of the base resin of the foam layer. In other words, from the viewpoint of conductive properties, the content of the conductive carbon material in the foam layer is preferably 1 part by mass or more, more preferably 1.5 parts by mass or more, and even more preferably 2.0 parts by mass or more, per 100 parts by mass of the base resin of the foam layer. On the other hand, from the viewpoint of moldability, the content of the conductive carbon material in the foam layer is preferably 10 parts by mass or less, more preferably 8 parts by mass or less, and even more preferably 6 parts by mass or less, per 100 parts by mass of the base resin of the foam layer. In the present invention, it is presumed that the viscosity of the molten mixture changes due to the influence of the phosphonate ester compound and the NOR-type hindered amine compound. In contrast, by incorporating the conductive carbon material in a predetermined range, a network structure of the conductive carbon material can be efficiently formed in the polyolefin resin, and changes in the viscosity of the molten mixture can be suppressed. Therefore, it is easy to achieve the closed cell ratio of the expanded beads specified in the present invention, and it is easy to obtain expanded beads that can be molded into an expanded bead molding in a mold with good molding condition. Furthermore, according to the embodiment in which the conductive carbon material described above is blended, since the change in viscosity of the resin during melt mixing is suppressed, it is easy to adjust the average ratio of the major axis to the minor axis of the expanded beads (major axis / minor axis) within a predetermined range, and it is easy to obtain approximately spherical expanded beads.

[0047] Phenolic Antioxidant: In the present invention, a preferred embodiment is one in which the foam layer contains a phenolic antioxidant. The phenolic antioxidant is an antioxidant having one or more phenolic structures in the molecule, each of which has one or more hydroxyl groups bonded to an aromatic ring, preferably two or more phenolic structures in the molecule, and more preferably three or more phenolic structures in the molecule. For example, at high temperatures (e.g., 180°C or higher), such as in the process of melt-kneading a resin, decomposition of the resin and additives tends to occur in a relatively short period of time. In contrast, by including the phenolic antioxidant in the molten mixture containing the resin that constitutes the foam layer, decomposition of the resin and additives can be suppressed in a short period of time at such high temperatures. Specific examples of the phenolic antioxidant include 1,3,5-trimethyl-2,4,6-tris(3',5'-di-t-butyl-4'-hydroxybenzyl)benzene, 2,6-di-t-butyl-p-cresol, triethylene glycol bis[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)propionate], 2,2-methylenebis(4-methyl-6-t-butylphenol), 1,6-hexanediol-bis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], and pentaerythritol tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]. These may be used alone or in combination of two or more. Among these, from the viewpoint of further improving flame retardancy, pentaerythritol tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] and / or 1,3,5-trimethyl-2,4,6-tris(3',5'-di-t-butyl-4'-hydroxybenzyl)benzene is preferred, and 1,3,5-trimethyl-2,4,6-tris(3',5'-di-t-butyl-4'-hydroxybenzyl)benzene is particularly preferred.

[0048] From the viewpoint of obtaining a foamed bead molding having higher flame retardancy, the melting point TmB of the phenolic antioxidant is preferably from 50° C. to 350° C., more preferably from 80° C. to 330° C., even more preferably from 100° C. to 320° C., still more preferably from 150° C. to 310° C., and particularly preferably from 200° C. to 300° C. The melting point TmB of the phenolic antioxidant is measured in accordance with JIS K0064:1992.

[0049] <Ratio of Phenolic Antioxidant to 100 Parts by Mass of Base Resin> From the viewpoint of providing a foamed bead molding having higher flame retardancy, the amount of the phenolic antioxidant in the foam layer is preferably 0.01 parts by mass or more, more preferably 0.02 parts by mass or more, even more preferably 0.04 parts by mass or more, and even more preferably 0.08 parts by mass or more, relative to 100 parts by mass of the base resin of the foam layer. Furthermore, from the viewpoint of obtaining a foamed bead molding having a better molding state, the amount of the phenolic antioxidant in the foam layer is preferably 0.5 parts by mass or less, more preferably 0.3 parts by mass or less, even more preferably 0.2 parts by mass or less, and particularly preferably 0.15 parts by mass or less, relative to 100 parts by mass of the base resin of the foam layer. In other words, the amount of the phenolic antioxidant in the foamed layer is preferably 0.01 parts by mass or more and 0.5 parts by mass or less, more preferably 0.02 parts by mass or more and 0.3 parts by mass or less, even more preferably 0.04 parts by mass or more and 0.2 parts by mass or less, and particularly preferably 0.08 parts by mass or more and 0.15 parts by mass or less, relative to 100 parts by mass of the base resin of the foamed layer.

[0050] <Ratio of the phenolic antioxidant to the amount of the NOR hindered amine compound in the foam layer> From the viewpoint of providing expanded beads that can be molded in a mold to produce an expanded bead molding having a higher level of flame retardancy and an excellent molding state, the ratio of the amount of the phenolic antioxidant to the amount of the NOR hindered amine compound is preferably 0.03 or more, more preferably 0.04 or more, even more preferably 0.06 or more, and particularly preferably 0.08 or more. This ratio of the amounts is, in other words, the ratio of the phenolic antioxidant to the NOR hindered amine compound in the foam layer. Furthermore, from the viewpoint of producing an expanded bead molding having a higher level of flame retardancy, this ratio is more preferably 0.9 or less, even more preferably 0.5 or less, even more preferably 0.3 or less, and particularly preferably 0.15 or less. That is, the ratio of the amount of the phenolic antioxidant to the amount of the NOR hindered amine compound is preferably 0.03 or more and 0.9 or less, more preferably 0.04 or more and 0.5 or less, even more preferably 0.06 or more and 0.3 or less, and still more preferably 0.08 or more and 0.15 or less.

[0051] From the viewpoint of more fully solving the intended problem of the present invention based on the above-mentioned findings, it is preferred that the foam layer contains a phenolic antioxidant, the amount of the phenolic antioxidant in the foam layer is 0.01 parts by mass or more and 0.5 parts by mass or less per 100 parts by mass of the base resin of the foam layer, and the ratio of the amount of the phenolic antioxidant to the amount of the NOR-type hindered amine compound is 0.03 or more and 0.9 or less.

[0052] Sulfur-Based Antioxidant: The foamed layer of the expanded polyolefin resin beads of the present invention preferably contains a sulfur-based antioxidant. Examples of the sulfur-based antioxidant include esters having a sulfide bond in the molecule. Specific examples of esters having a sulfide bond in the molecule include didodecyl-3,3'-thiodipropionate, ditridecyl-3,3'-thiodipropionate, ditetradecyl-3,3'-thiodipropionate, dioctadecyl-3,3'-thiodipropionate, pentaerythritol tetrakis(3-dodecylthiopropionate), pentaerythritol tetrakis(3-tridecylthiopropionate), pentaerythritol tetrakis(3-tetradecylthiopropionate), and pentaerythritol tetrakis(3-octadecylthiopropionate). These may be used alone or in combination of two or more.

[0053] <Amount of Sulfur-Based Antioxidant Blended Per 100 Parts by Mass of Base Resin> From the viewpoint of providing an expanded bead molding with excellent mechanical properties such as compression properties even when placed in a high-temperature environment for a long period of time, the amount of the sulfur-based antioxidant blended in the foam layer of the expanded beads of the present invention is preferably 0.01 parts by mass or more, more preferably 0.04 parts by mass or more, and even more preferably 0.06 parts by mass or more, per 100 parts by mass of the base resin of the foam layer. Furthermore, from the viewpoint of providing an expanded bead molding with high flame retardancy, the amount of the sulfur-based compound blended in the foam layer is preferably 0.5 parts by mass or less, more preferably 0.4 parts by mass or less, and even more preferably 0.3 parts by mass or less, per 100 parts by mass of the base resin of the foam layer. In other words, the amount of the sulfur-based antioxidant blended per 100 parts by mass of the base resin of the foam layer is preferably 0.01 parts by mass or more and 0.5 parts by mass or less, more preferably 0.04 parts by mass or more and 0.4 parts by mass or less, and even more preferably 0.06 parts by mass or more and 0.3 parts by mass or less.

[0054] <Ratio of the amount of sulfur-based antioxidant to the amount of NOR hindered amine compound> From the viewpoint of achieving excellent mechanical properties such as compression properties even when the expanded bead molding is placed in a high-temperature environment for a long period of time, the ratio of the amount of sulfur-based antioxidant to the amount of NOR hindered amine compound is preferably 0.03 or more, more preferably 0.04 or more, even more preferably 0.06 or more, and particularly preferably 0.08 or more. Furthermore, from the viewpoint of obtaining an expanded bead molding having high flame retardancy, the ratio is preferably 0.9 or less, more preferably 0.5 or less, even more preferably 0.3 or less, and particularly preferably 0.15 or less. In other words, the ratio of the amounts is the ratio expressed as sulfur-based antioxidant / NOR hindered amine compound. In other words, in the foamed layer, the ratio of the amount of the sulfur-based antioxidant to the amount of the NOR hindered amine compound is preferably 0.03 or more and 0.9 or less, more preferably 0.04 or more and 0.5 or less, even more preferably 0.06 or more and 0.3 or less, and particularly preferably 0.08 or more and 0.15 or less.

[0055] From the viewpoint of more fully solving the intended problem of the present invention based on the above-mentioned findings, it is preferred that the foam layer contains a sulfur-based antioxidant, the amount of the sulfur-based antioxidant in the foam layer is 0.01 parts by mass or more and 0.5 parts by mass or less per 100 parts by mass of the base resin of the foam layer, and the ratio of the amount of the sulfur-based antioxidant to the amount of the NOR-type hindered amine compound is 0.03 or more and 0.9 or less.

[0056] Foam Regulator: Examples of the foam regulator include inorganic powders such as metal borate, talc, mica, calcium carbonate, borax, aluminum hydroxide, and silica, polyhydric alcohols such as glycerin, polyethylene glycol, and pentaerythritol, and aliphatic alcohols such as cetyl alcohol and stearyl alcohol. Metal borate salts such as zinc borate and magnesium borate are preferably used as the foam regulator, and zinc borate is more preferred. The amount of foam regulator contained in the foam layer is preferably 0.005 to 0.5 parts by mass, more preferably 0.01 to 0.2 parts by mass, and even more preferably 0.015 to 0.15 parts by mass, per 100 parts by mass of the base resin of the foam layer. Furthermore, when zinc borate is used as the foam regulator, its arithmetic mean particle diameter based on the number of particles is preferably 0.5 μm to 15 μm, and more preferably 1 μm to 10 μm. The number-based arithmetic mean particle diameter of zinc borate is determined by converting the volume-based particle size distribution measured by a laser diffraction scattering method into a number-based particle size distribution by assuming that the particles have a spherical shape, and then calculating the arithmetic mean of the particle diameters based on this number-based particle size distribution. Note that the particle diameter refers to the diameter of the particles equivalent to a sphere of equal volume.

[0057] Ultraviolet absorbers: Examples of ultraviolet absorbers include benzophenone compounds, benzotriazole compounds, triazine compounds, and benzoate compounds. Examples of the benzophenone compounds include 2-hydroxy-4-octyloxybenzophenone. Examples of the benzotriazole compounds include 2-(5-methyl-2-hydroxyphenyl)benzotriazole, 2-[2-hydroxy-3,5-bis(α,α-dimethylbenzylphenyl)]-2H-benzotriazole, 2-(3,5-di-t-butyl-2-hydroxyphenyl)benzotriazole, 2-(3-t-butyl-5-methyl-2-hydroxyphenyl)-5-chlorobenzotriazole, 2-(3,5-di-t-butyl-2-hydroxyphenyl)-5-chlorobenzotriazole, 2-(3,5-di-t-amyl-2-hydroxyphenyl)benzotriazole, and 2-(2'-hydroxy-5'-t-octylphenyl)benzotriazole. Examples of the triazine-based compound include 2-[4,6-diphenyl-1,3,5-triazin-2-yl]-5-(hexyloxy)phenol and 2-[4,6-bis(2,4-dimethylphenyl)-1,3,5-triazin-2-yl]-5-(n-octyloxy)phenol. Examples of the benzoate-based compound include 2,4-di-t-butylphenyl-3,5-di-t-butyl-4-hydroxybenzoate and hexadecyl-3,5-di-t-butyl-4-hydroxybenzoate. When the foam layer contains an ultraviolet absorber, the amount of the ultraviolet absorber in the foam layer is preferably 0.01 to 2 parts by mass, more preferably 0.05 to 1.5 parts by mass, and even more preferably 0.1 to 1 part by mass, per 100 parts by mass of the base resin of the foam layer. The ultraviolet absorber is a compound that has the property of absorbing ultraviolet rays, and is a compound that can mainly absorb light with a wavelength of 300 μm to 400 μm.

[0058] Light stabilizer: Examples of the light stabilizer include non-NOR hindered amine compounds. Non-NOR hindered amine compounds are compounds having a 2,2,6,6-tetramethyl-4-piperidineamine moiety in which the only atoms directly bonded to the nitrogen atom are hydrogen or carbon. The content of the light stabilizer in the foam layer is preferably 0.01 parts by mass or more and 2 parts by mass or less, more preferably 0.05 parts by mass or more and 1.5 parts by mass or less, and even more preferably 0.1 parts by mass or more and 1 part by mass or less, relative to 100 parts by mass of the base resin of the foam layer.

[0059] (Optional Characteristics of Expanded Polyolefin Resin Beads) As described above, the expanded beads of the present invention contain a phosphonate ester compound and a NOR-type hindered amine compound in specific amounts within specific ranges, and preferably further have the following characteristics: The optional characteristics described below, namely, the multilayer structure, bulk density, high-temperature peak, average particle size, and average mass, will be explained, and it is preferred that the expanded beads of the present invention have one or more of these optional characteristics.

[0060] Expanded beads of multilayer structure: The expanded polyolefin resin beads of the present invention may be single-layer expanded beads having only a particulate foam layer, or may be expanded beads of multilayer structure having a particulate foam layer as a core layer and a coating layer covering the foam layer. The coating layer may cover the entire surface of the foam layer, or may cover only a portion of the surface of the foam layer. The foam layer may also have through holes. From the viewpoint that the expanded beads having a coating layer exhibit higher flame retardancy when molded in a mold, and from the viewpoint of obtaining an expanded bead molding with better surface properties and fusion properties, it is preferable that the expanded beads have a multilayer structure.

[0061] In the case of multilayered expanded beads, the mass ratio of the foam layer to the coating layer is not particularly limited, but is preferably 95:5 to 70:30, more preferably 92:8 to 72:28, even more preferably 91:9 to 75:25, even more preferably 90:10 to 78:22, and particularly preferably 88:12 to 80:20. When the mass ratio of the coating layer is relatively high, the expanded bead molding obtained by molding the expanded beads having the coating layer in a mold exhibits higher flame retardancy, is more likely to achieve the closed cell ratio of the expanded beads specified in the present invention, and exhibits better surface smoothness and fusion properties. Furthermore, according to the above-mentioned preferred embodiment, the average ratio of the major axis to the minor axis of the expanded beads (major axis / minor axis) can be easily adjusted within a predetermined range, making it easier to obtain substantially spherical expanded beads.

[0062] The base resin of the coating layer may be a polyolefin resin, such as a polyethylene resin or a polypropylene resin, or a resin and / or polymer other than a polyolefin resin. For the base resin of the coating layer, the explanation of the resin used in the foam layer described above may be referenced as appropriate. The base resin of the coating layer refers to the resin and polymer constituting the coating layer. The base resin of the coating layer and the base resin of the foam layer may be the same or different. From the viewpoint of obtaining good fusion properties, the melting point or softening point of the base resin of the coating layer is preferably lower than the melting point of the base resin of the foam layer. The coating layer may contain a phosphonate ester compound and a NOR-type hindered amine compound. From the viewpoint of obtaining an expanded bead molding having good flame retardancy while reducing the amount of flame retardant added, it is preferable that the ratio I of the amount of the phosphonate ester compound in the coating layer to the base resin of the coating layer of the expanded beads is smaller than the ratio II of the amount of the phosphonate ester compound in the foam layer to the base resin of the foam layer. That is, the ratio I is (amount of phosphonate ester compound in the coating layer) / (mass of the base resin of the coating layer), and the ratio II is (amount of phosphonate ester compound in the foam layer) / (mass of the base resin of the foam layer), with ratio I<ratio II being preferred. It is also more preferred that the coating layer does not contain a phosphonate ester compound. From the viewpoint of obtaining an expanded bead molding having good flame retardancy while reducing the amount of flame retardant added, it is preferred that the ratio III of the amount of NOR hindered amine compound in the coating layer relative to the base resin of the coating layer of the expanded beads is smaller than the ratio IV of the amount of NOR hindered amine compound in the foam layer relative to the base resin of the foam layer. That is, the ratio III is (amount of NOR hindered amine compound in the coating layer) / (mass of the base resin of the coating layer), and the ratio IV is (amount of NOR hindered amine compound in the foam layer) / (mass of the base resin of the foam layer), with ratio III<ratio IV being preferred. In addition, it is more preferable that the coating layer does not contain a NOR-type hindered amine compound. From the viewpoint of obtaining an expanded bead molding having good flame retardancy while reducing the amount of flame retardant added, it is preferable that the ratios in the expanded beads satisfy ratio I < ratio II and ratio III < ratio IV.

[0063] The coating layer may be in a foamed state or a non-foamed state. From the viewpoint of improving the molding state of the expanded bead molding, the coating layer is preferably in a substantially non-foamed state. The term "substantially non-foamed state" includes a state in which the coating layer is not foamed and does not contain bubbles, and a state in which the bubbles have disappeared after foaming, and means that there is almost no bubble structure.

[0064] Bulk density of expanded beads: The bulk density of the expanded beads of the present invention is not particularly limited, but the bulk density is preferably 30 kg / m ３ It is preferable that the saturation is 50 kg / m or more. ３ More preferably, it is 70 kg / m or more. ３ More preferably, it is 80 kg / m or more. ３ It is even more preferable that the value is 90 kg / m or more. ３ The bulk density of the expanded beads of the present invention is preferably 200 kg / m or more. ３ More preferably, it is 180 kg / m or less. ３ More preferably, it is 150 kg / m or less. ３ or less, and particularly preferably 130 kg / m ３ In other words, the bulk density of the expanded beads of the present invention is preferably 30 kg / m or less. ３ More than 200kg / m ３ More preferably, it is 50 kg / m or less. ３ More than 180kg / m ３ More preferably, it is 70 kg / m or less. ３ More than 150kg / m ３ and even more preferably 80 kg / m or less. ３ More than 130kg / m ３ and particularly preferably 90 kg / m ３ More than 130kg / m ３ The expanded beads having a bulk density in the above range are preferred because they can provide an expanded bead molding that is excellent in flame retardancy, lightweight, and fusible.

[0065] The bulk density of expanded beads is measured by the following method. First, the expanded beads to be measured are conditioned by standing for 24 hours or more in an environment of 23°C temperature, 50% relative humidity, and 1 atm. After conditioning, expanded beads with a mass W (g) are packed into a measuring cylinder so that they naturally accumulate, and the bottom of the measuring cylinder is lightly tapped several times against a horizontal surface to stabilize the packed height of the expanded beads in the measuring cylinder. The bulk volume V (L) of the expanded beads indicated on the measuring cylinder is read, and the mass W of the expanded beads is divided by the bulk volume V of the expanded beads (W / V), and the bulk density (kg / m) of the expanded beads is calculated by converting the unit. ３ ) can be obtained.

[0066] High-Temperature Peak: The expanded polyolefin resin beads of the present invention preferably have one or more melting peaks (high-temperature peaks) on the high-temperature side of the resin-specific melting peak (resin-specific peak) of the olefin resin in a differential scanning calorimetry (DSC) curve measured according to JIS K7122-2012. These melting peaks can be obtained by the following method. Specifically, a DSC curve is obtained by heating 1 to 3 mg of expanded beads from 23°C to 200°C at a heating rate of 10°C / min using a differential scanning calorimeter, and the melting peaks (high-temperature peaks) can be confirmed from the DSC curve. The peak with the largest heat of fusion is the melting peak (resin-specific peak) specific to the olefin resin, and the melting peak appearing higher in temperature is the high-temperature peak. The DSC curve in this case refers to a DSC curve obtained by heating the expanded beads using the above-mentioned measurement method. The DSC curve obtained by such heating is sometimes referred to as the DSC curve for the first heating. The resin-specific melting peak (resin-specific peak) refers to an endothermic peak due to the melting of crystals specific to the polyolefin resin constituting the expanded beads. The resin-specific peak is considered to be an endothermic peak that appears due to the endothermic heat caused by the melting of crystals typically found in the polyolefin resin constituting the expanded beads. Meanwhile, the melting peak (high-temperature peak) on the higher temperature side of the resin-specific peak is an endothermic peak that appears higher than the resin-specific peak in the DSC curve obtained in the first heating. The appearance of this high-temperature peak suggests the presence of secondary crystals in the resin. In addition, in a DSC curve obtained by heating expanded beads from 23°C to 200°C at a heating rate of 10°C / min (first heating), cooling from 200°C to 23°C at a cooling rate of 10°C / min, and then heating again from 23°C to 200°C at a heating rate of 10°C / min (second heating), only the melting peak due to the melting of crystals specific to the polyolefin resin constituting the expanded beads appears. The DSC curve obtained by the second heating may be referred to as the "DSC curve in the second heating." This resin-specific peak appears in both the DSC curve in the first heating and the DSC curve in the second heating, and the peak apex temperatures may differ slightly between the first and second heatings, but the difference is usually less than 5°C.This makes it possible to confirm which peak is the peak inherent to the resin. Preferably, the expanded beads are those in which only a melting peak (intrinsic peak) inherent to the polyolefin resin appears in a DSC curve obtained in a second heating cycle, which is obtained by heating the expanded beads from 23° C. to 200° C. at a heating rate of 10° C. / min, then cooling from 200° C. to 23° C. at a cooling rate of 10° C. / min, and then heating from 23° C. to 200° C. at a heating rate of 10° C. / min.

[0067] The heat of fusion of the high-temperature peak of the expanded polyolefin resin beads of the present invention is preferably 5 J / g or more and 40 J / g or less, more preferably 6 J / g or more and 30 J / g or less, and even more preferably 7 J / g or more and 25 J / g or less, because the range of molding conditions for obtaining a good expanded bead molding when the expanded beads are molded in a mold is wider. The heat of fusion of the high-temperature peak is measured by the method described above, but more specifically, it can be measured by the method described in the examples.

[0068] Average particle diameter of expanded beads: From the viewpoint of improving the fillability into a molding die, the average particle diameter of expanded beads is preferably 0.3 mm to 8 mm, more preferably 0.5 mm to 5 mm, and even more preferably 0.8 mm to 4.5 mm. The average particle diameter of expanded beads is a value determined by the following method. First, the volume-based particle size distribution of the expanded beads is converted to a number-based particle size distribution by assuming the shape of the particles as spherical, thereby obtaining the number-based particle size distribution. Then, the particle diameters based on this number-based particle size distribution are arithmetically averaged to obtain the number-based arithmetic mean particle diameter. Note that the particle diameter refers to the diameter of a hypothetical sphere having the same volume as the particles. The volume-based particle size distribution of expanded beads can be measured using a particle size distribution analyzer (e.g., a dynamic image analysis particle shape / particle size distribution analyzer and analysis software (product name: PARTAN 3D) manufactured by Microtrac Bell Corporation). The number of expanded beads used for measurement may be, for example, 2,000 or more.

[0069] Average mass of expanded beads: From the same viewpoint, the average mass of the expanded beads is preferably 0.2 mg or more and 5 mg or less, more preferably 0.5 mg or more and 4 mg or less, and even more preferably 0.8 mg or more and 3 mg or less. The average mass of the expanded beads can be determined by randomly selecting 100 or more expanded beads, measuring the mass [mg] of the expanded beads, and dividing the mass by the number of expanded beads used in the measurement.

[0070] (Method for Producing Expanded Polyolefin Resin Beads) The expanded beads of the present invention are expanded polyolefin resin beads, containing a polyolefin resin as a base resin and a phosphonate ester compound and a NOR hindered amine compound in predetermined ranges. Generally, the above-mentioned problems arise when a polyolefin resin, a phosphonate ester, and a NOR hindered amine compound are melt-kneaded. To prevent such problems, it is essential that the method for producing expanded beads of the present invention contains the specific raw materials described above and adjusts the closed cell content of the resulting expanded beads to fall within a predetermined range. Any other raw materials may be included as appropriate. Taking the above into consideration, the method for producing expanded beads of the present invention is not particularly limited. For example, the method for producing expanded beads of the present invention can be similar to Production Method 1 or Production Method 2 described above. An example of a suitable method for producing expanded beads of the present invention is shown below.

[0071] A preferred method for producing expanded beads of the present invention includes a resin particle production step of preparing resin particles containing a phosphonate ester compound and a NOR-type hindered amine compound, a dispersion step of dispersing the resin particles in an aqueous dispersion medium containing an inorganic dispersant in a pressure vessel, a blowing agent impregnation step of impregnating the resin particles with a blowing agent in the pressure vessel, and an expansion step of releasing the resin particles containing the blowing agent together with the aqueous dispersion medium from the pressure vessel to expand them. These steps may be performed in this order, or one step may be performed partially or entirely overlapping with the next step.

[0072] (Resin particle manufacturing process) First, the resin particle manufacturing process is carried out. The resin particles are prepared by first supplying a base resin, a phosphonate ester compound, a NOR-type hindered amine compound, other resins (if necessary), a polymer, and any additives into an extruder, heating and kneading the mixture to obtain a molten mixture. The molten mixture is then extruded through the fine holes in a nozzle attached to the tip of the extruder, and pelletized by a cutting method such as a strand cutting method, a hot cutting method, or an underwater cutting method, to produce resin particles. When producing multilayered resin particles, it is preferable to use a manufacturing device equipped with a core layer forming extruder, a multilayer strand forming die attached downstream of the core layer forming extruder, and a coating layer forming extruder. Specific examples will be described in Example 1 below.

[0073] The average mass per resin particle is preferably adjusted to 0.2 mg to 5 mg, more preferably 0.5 mg to 4 mg, and even more preferably 0.8 mg to 3 mg. The average mass here refers to the arithmetic mean value per particle obtained by measuring the mass of 100 randomly selected resin particles. The external shape of the resin particles is not particularly limited as long as it achieves the intended object of the present invention; however, in the strand cut method, resin particles that are visually determined to be cylindrical are preferred. When the external shape of the resin particles is cylindrical, the particle diameter of the resin particles measured in the extrusion direction is preferably 0.1 mm to 3.0 mm, more preferably 0.3 mm to 1.5 mm. The ratio (particle diameter / diameter) of the length of the resin particle in the extrusion direction (particle diameter) to the maximum length of the resin particle in the direction perpendicular to the extrusion direction (diameter) is preferably 0.5 to 5.0, more preferably 1.0 to 3.0. A ratio within the above range is preferred because spherical expanded beads are easily obtained.

[0074] As described above, by adopting one or more of the following modes, the resin particles have a multilayer structure including a core layer and a coating layer covering the core layer, the mode in which a linear polypropylene resin is blended with a branched polypropylene resin and / or a polyethylene resin with low fluidity as the base resin of the foam layer, or the mode in which a conductive carbon material is incorporated into the foam layer, the following advantages can be obtained in the manufacturing process. That is, when at least one of these modes is adopted, the particle shape of the resin particles can be effectively adjusted by appropriately adjusting the extrusion speed, take-up speed, cutter speed, etc. of the molten mixture during strand cutting, and spherical expanded beads can be easily produced using the resin particles.

[0075] (Dispersion step) Next, a dispersion step is carried out in which the resin particles obtained as described above are dispersed in an aqueous dispersion medium in a pressure vessel. The aqueous dispersion medium is a dispersion medium containing water as a main component. The proportion of water in the aqueous dispersion medium is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and may be 100% by mass. Examples of dispersion media other than water in the aqueous dispersion medium include one or more of ethylene glycol, glycerin, methanol, ethanol, etc.

[0076] In the dispersion step, a dispersant is preferably added to the aqueous dispersion medium to prevent the resin particles from fusing together when heated in the container. Any dispersant can be used as long as it prevents the resin particles from fusing together in the container. While both organic and inorganic dispersants can be used as the dispersant, inorganic dispersants are preferred, and particulate inorganic dispersants are more preferred due to their ease of handling. Examples of dispersants include natural or synthetic clay minerals such as kaolin, mica, and clay, as well as aluminum oxide, titanium oxide, basic magnesium carbonate, basic zinc carbonate, calcium carbonate, and iron oxide. One of these may be used alone, or two or more may be used in combination. Of these, natural or synthetic clay minerals are preferably used as the dispersant. The amount of the dispersant added is preferably 0.001 to 5 parts by mass per 100 parts by mass of the resin particles.

[0077] When a dispersant is used, it is preferable to use an anionic surfactant, such as sodium dodecylbenzenesulfonate, sodium alkylsulfonate, or sodium oleate, in combination with the dispersant as a dispersing aid. It is preferable to add 0.001 to 1 part by mass of the dispersing aid to the aqueous dispersion medium per 100 parts by mass of the resin particles.

[0078] (Blowing Agent Impregnation Step) After the dispersion step or overlapping with the dispersion step, a blowing agent impregnation step is carried out. The blowing agent used in the blowing agent impregnation step to expand the resin particles is preferably a physical blowing agent. Examples of the physical blowing agent include inorganic and organic physical blowing agents. Examples of inorganic physical blowing agents include carbon dioxide, air, nitrogen, helium, and argon. Examples of organic physical blowing agents include aliphatic hydrocarbons such as propane, n-butane, i-butane, n-pentane, i-pentane, hexane, cyclopentane, and cyclohexane, and halogenated hydrocarbons such as chlorofluoromethane, trifluoromethane, 1,1-difluoroethane, 1-chloro-1,1-difluoroethane, 1,1,1,2-tetrafluoroethane, methyl chloride, ethyl chloride, and methylene chloride. These physical blowing agents may be used alone or in combination. In addition, inorganic and organic physical blowing agents may also be used in combination. From the viewpoint of reducing the burden on the environment and further increasing the flame retardancy of the expanded bead molding, the blowing agent is preferably an inorganic physical blowing agent, more preferably carbon dioxide.

[0079] The amount of the foaming agent added to 100 parts by mass of the resin particles is preferably 0.1 to 30 parts by mass, and more preferably 0.5 to 15 parts by mass.

[0080] A preferred method for impregnating the resin particles with the blowing agent is to disperse the resin particles in an aqueous dispersion medium in a pressure vessel, then pressurize the blowing agent into the pressure vessel, and maintain the pressure vessel at a predetermined temperature and pressure, thereby impregnating the resin particles with the blowing agent.

[0081] (Expansion Process) The lower limit of the pressure (internal pressure) inside the pressure vessel during expansion, i.e., the pressure inside the pressure vessel immediately before releasing the resin particles together with the aqueous dispersion medium, is preferably 0.5 MPa (G) or more, more preferably 0.8 MPa (G) or more. The upper limit is preferably 4 MPa (G) or less, more preferably 3 MPa (G) or less. Within the above range, the desired expanded particles can be safely produced without risk of damage or explosion of the pressure vessel. After adjusting the pressure to the above-mentioned level, the resin particles containing the blowing agent are released from the pressure vessel together with the aqueous dispersion medium into an atmosphere (e.g., atmospheric pressure) with a pressure lower than the pressure inside the pressure vessel to expand them. Prior to carrying out the expansion process, the temperature inside the pressure vessel is preferably raised to 100°C or higher and 200°C or lower, more preferably 120°C or higher and 160°C or lower, and maintained at that temperature for 5 to 30 minutes. This allows the crystalline state of the resin particles to be adjusted to a state exhibiting the high-temperature peak.

[0082] The expanded polyolefin resin beads obtained as described above can be pressurized with air or the like to increase the pressure (internal pressure) within the cells of the foamed layer, and then heated with steam or the like to further expand (second-stage expansion) to produce expanded beads with an even higher expansion ratio (lower bulk density).

[0083] (Polyolefin Resin Expanded Bead Molding) The expanded bead molding of the present invention can be obtained by in-mold molding using the expanded beads of the present invention produced as described above. For example, the expanded bead molding can be produced as follows. First, the expanded beads of the present invention are filled into a mold having a cavity corresponding to the shape of the desired expanded bead molding, and the expanded beads filled in the mold are heated. The expanded beads in the cavity soften upon heating, undergo secondary expansion, and their surfaces melt and fuse together. This results in the expanded beads being integrated together, resulting in an expanded bead molding corresponding to the shape of the cavity. Examples of methods for heating the expanded beads include a method in which a heating medium such as steam is introduced into the mold and the expanded beads are heated by the heating medium, a method in which the expanded beads are heated by irradiating the expanded beads with electromagnetic waves such as microwaves, or a combination of both. Known methods can be used to fill the mold with the expanded beads. Known methods include pressure filling, compression filling, and cracking filling. The pressure filling method is a method in which expanded beads are pressurized with pressurized gas to impart a predetermined internal pressure to the expanded beads and then filled into a mold. The compression filling method is a method in which expanded beads are compressed with pressurized gas and filled into a pressurized mold, and then the pressure inside the mold is released. The cracking filling method is a method in which the mold is opened in advance to expand the molding space before filling the expanded beads into the mold, and then the mold is closed after filling to mechanically compress the expanded beads. These filling methods may be carried out alone or in combination.

[0084] In the in-mold molding, in order to improve the secondary expansion property of the expanded beads when heated, internal pressure may be applied to the expanded beads before they are filled into the mold, and the expanded beads may be filled into the mold in a state in which the pressure inside the cells of the expanded beads is increased. The pressure inside the cells (internal pressure) can be measured, for example, by the method described in JP-A-2003-201361.

[0085] The density of the expanded bead molding of the present invention is preferably 30 kg / m ３ More preferably, it is 50 kg / m or more. ３ More preferably, it is 70 kg / m or more. ３More preferably, it is 80 kg / m or more. ３ More preferably, it is 90 kg / m or more. ３ More preferably, it is 200 kg / m ３ More preferably, it is 180 kg / m or less. ３ More preferably, it is 150 kg / m or less. ３ and even more preferably 130 kg / m or less. ３ In other words, it is more preferably 30 kg / m or less. ３ More than 200kg / m ３ More preferably, it is 50 kg / m or less. ３ More than 180kg / m ３ and even more preferably 70 kg / m or less. ３ More than 150kg / m ３ and even more preferably 80 kg / m or less. ３ More than 130kg / m ３ and even more preferably 90 kg / m or less. ３ More than 130kg / m ３ The foamed bead molding is preferable because it has excellent flame retardancy, is lightweight, and has excellent fusion properties.

[0086] The expanded bead moldings obtained by molding the expanded beads of the present invention in a mold not only exhibit high flame retardancy but also have excellent fusion properties and surface properties, making them suitable for use in applications requiring high flame retardancy, such as protective materials for batteries and electronic components mounted in vehicles.

[0087] The present invention will be described in detail below with reference to examples, but is not limited thereto. Tables 1 to 3 show the composition, blending amount, blending ratio, expansion conditions, and molding pressure of the resin beads used to produce the expanded beads of each example and comparative example, as well as the evaluation results of each example and comparative example. The tables also show the ratio of the blending amount (parts by mass) of the phenolic antioxidant to the blending amount (parts by mass) of the NOR hindered amine compound in the core layer, the ratio of the blending amount (parts by mass) of the sulfur-based antioxidant to the blending amount (parts by mass) of the NOR hindered amine compound in the core layer, the total blending amount (% by mass) of phosphonate ester compounds per 100% by mass of resin particles, and the ratio of the blending amount (% by mass) of the NOR hindered amine compounds to the blending amount (% by mass) of the phosphonate ester compounds in the resin particles. It should be noted that, with respect to the example tables, the blending amount of each component is understood to be the same as the content of each raw material contained in the core layer, coating layer, and expanded beads.

[0088] The various raw materials used in the examples and comparative examples are as follows. In the examples and comparative examples shown below, the resins blended into the core layer and the covering layer were all polyolefin-based resins, and no other resins or polymers were used. In each example and comparative example, the amount of polyolefin-based resin blended into the core layer and the covering layer was 100 parts by mass.

[0089] (Resin) Polypropylene resin (PP1) Ethylene-propylene random copolymer (linear propylene random copolymer), melting point 143°C, density 0.900 g / cm ３ , ethylene content 2.1 mass%, MFR (load 2.16 kg, 230 ° C, JIS K7210-1: 2014) 6 g / 10 min. Polypropylene resin (PP2) Ethylene-propylene random copolymer (linear propylene random copolymer), melting point 133 ° C, density 0.900 g / cm ３ , ethylene content 3.5 mass%, MFR (load 2.16 kg, 230 ° C, JIS K7210-1: 2014) 6 g / 10 min. Polypropylene resin (PP3) Branched polypropylene, melting point 159 ° C, density 0.905 g / cm ３, MFR (load 2.16 kg, 230 ° C, JIS K7210-1: 2014) 1.7 g / 10 min. Polyethylene resin (PE1) Linear low-density polyethylene, melting point 120 ° C, density 0.923 cm / cm ３ , MFR (load 2.16 kg, 190°C, JIS K7210-1:2014) 1.5 g / 10 min.

[0090] (Phosphonate ester compound) A compound represented by the following formula (6), manufactured by Thor under the trade name "Aflammit PCO900" and having a melting point of 240°C, was used as the cyclic phosphonate ester compound. In the tables, this compound is referred to as a phosphonate ester.

[0091] (NOR-type hindered amine compound) A compound represented by the following formula (7), manufactured by BASF and having a trade name of "Flamestab NOR116" and a molecular weight of 2261, was used as the NOR-type hindered amine compound. In the tables, this compound is referred to as NOR-type hindered amine.

[0092] (Phenol-Based Antioxidant) A compound manufactured by BASF under the trade name "Irganox 1330", having a melting point of 245°C and represented by the following formula (8), was used as the phenol-based antioxidant.

[0093] (Sulfur-Based Antioxidant) Dioctadecyl-3,3'-thiodipropionate: trade name "Irganox PS 802" manufactured by BASF was used as the sulfur-based antioxidant.

[0094] Example 1 (Preparation of Resin Particles) A ​​manufacturing apparatus was prepared, including a core layer extruder with an inner diameter of 50 mm, a multilayer strand die attached downstream of the core layer extruder, and a coating layer extruder with an inner diameter of 30 mm. The manufacturing apparatus was configured so that the downstream side of the coating layer extruder was connected to the multilayer strand die, allowing for lamination of the molten mixture for forming each layer within the die and co-extrusion. PP1 was used as the base resin for the core layer. As the core layer molding material constituting the core layer, in addition to the resins described above, a phosphonate ester compound, a NOR-type hindered amine compound, a phenolic antioxidant, a sulfur-based antioxidant, and zinc borate as a bubble nucleating agent were fed into the extruder in the amounts shown in Table 1, and these were melt-kneaded to prepare a molten mixture. The core layer of the resin particles is the layer that will become the foamed layer of the expanded beads produced as described below. PP2 was used as the base resin for the coating layer, and the mixture was fed to a coating extruder and melt-kneaded to prepare a molten mixture. The molten mixtures for forming each layer obtained by melt-kneading as described above were introduced into a multilayer strand die and merged within the die. A multilayer strand with a two-layer structure (coating layer / core layer) having a core layer and a coating layer covering the lateral surface of the core layer was extruded through a 2 mm circular hole in a nozzle attached downstream of the die. The extruded multilayer strand was collected and cooled in a water bath, and then cut into resin particles with a length of 2 mm using a pelletizer, yielding resin particles with an average mass of 1.0 mg per particle.

[0095] (Preparation of Expanded Beads) 2 kg of the resin particles obtained as described above was placed in a 100 L pressure vessel along with 75 L of water as an aqueous dispersion medium. 65 g of kaolin as an inorganic dispersant and 43 g (active ingredient) of a surfactant (trade name: NEOGEN, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., sodium dodecylbenzenesulfonate) were added to the pressure vessel. Carbon dioxide was then injected into the pressure vessel as a blowing agent, and the pressure was increased to a gauge pressure of 0.5 MPa (G). Note that the pressure indicated with (G) is a gauge pressure, i.e., a pressure value based on atmospheric pressure. The pressure vessel was then heated to the foaming temperature shown in Table 1 at a heating rate of 2°C / min while stirring, and carbon dioxide was further injected until the foaming pressure shown in Table 1 was reached. The pressure vessel was then maintained at the same temperature and pressure for 15 minutes. This adjustment allowed the endothermic curve of the resulting expanded beads to exhibit a high-temperature peak when measured by DSC. Thereafter, the resin particles and aqueous dispersion medium contained in the pressure vessel were released under atmospheric pressure to expand the core layer, thereby obtaining expanded beads having a multilayer structure comprising a foamed layer and a non-foamed coating layer covering the foamed layer. The expansion pressure in the pressure vessel immediately before expansion was the value shown in Table 1. The expanded beads obtained were left in an oven at 80°C for 24 hours or more to thoroughly dry the expanded beads. At this time, the moisture content of the expanded beads after drying was measured. The moisture content was measured by leaving the dried expanded beads at room temperature for 30 minutes and then subjecting them to a 200 cm ３ The expanded beads after drying to about 100°C were weighed and the weight of the expanded beads was measured. Next, the expanded beads weighed as above were further heated in an oven at 150°C for 1 hour, and the weight of the expanded beads after heating was measured. The weight of the expanded beads after heating was subtracted from the weight of the expanded beads before heating, and the weight difference obtained above was divided by the weight of the expanded beads after heating, and then converted into a percentage. In this example, the value obtained by measuring the moisture content was 0.8%.

[0096] (Production of Expanded Bead Molded Articles) The dried, unpressurized expanded beads were compressed and filled into a mold having a molding cavity capable of molding a flat-plate-shaped molded article measuring 400 mm long, 300 mm wide, and 30 mm high. A metal mold was used as the mold. Compression filling is a filling method in which the expanded beads are filled into the mold while under pressure. Steam was then supplied into the mold to heat the expanded beads, resulting in a flat-plate-shaped expanded bead molded article. Heating with steam was performed as follows: First, steam was supplied into the mold with the drain valves on both sides open to perform preheating (exhaust step). Steam was then supplied from one side of the mold to heat it, and then steam was supplied from the other side to heat it again. Next, steam was supplied from both sides of the mold to heat it until the molding pressure inside the mold reached the pressure listed in Table 1. After heating, the pressure was released and the mold was cooled with water until the pressure on the molding surface of the mold reached 0.04 MPa (G), after which the mold was opened and the expanded bead molding was removed. The obtained molding was cured in an oven at 80°C for 12 hours and then slowly cooled to room temperature to obtain an expanded bead molding.

[0097] Examples 2 to 8 Expanded beads and expanded bead moldings were produced in the same manner as in Example 1, except for the changes shown in Tables 1 and 2.

[0098] Examples 9 and 10, Comparative Examples 1, 5, and 6 An extruder with an inner diameter of 50 mm and a strand-forming die attached to the outlet side was prepared. A polyolefin resin, a phosphonic acid ester compound, a NOR-type hindered amine compound, a phenolic antioxidant, a sulfur-based antioxidant, and a bubble nucleating agent were fed into the extruder in the amounts shown in Tables 2 and 3, and melt-kneaded to form a molten mixture. In Example 9, 80 parts by mass of PP1 and 20 parts by mass of PE1 were used per 100 parts by mass of polyolefin resin. In Example 10, 80 parts by mass of PP1 and 20 parts by mass of PP3 were used per 100 parts by mass of polyolefin resin. The resulting molten mixture was extruded through the strand-forming die into strands, cooled with water, and cut using a pelletizer to obtain resin particles with an average mass of 1.0 mg per particle. Using the resin particles obtained as described above, expanded beads and expanded bead molded articles were produced in the same manner as in Example 1, except for the changes shown in Tables 2 and 3.

[0099] <Comparative Examples 2 to 4> Expanded beads were produced in the same manner as in the expanded bead production method of Comparative Example 1, except for the changes shown in Table 3. Next, expanded bead moldings were produced in the same manner as in the expanded bead production method of Example 1, except for the fact that the pressure inside the cells of the expanded beads obtained as described above was increased to 0.1 MPa (G) and then compression-filled, and molding was carried out under the conditions shown in Table 3. <Example 11> Oil furnace black (product name: Ketjenblack (registered trademark) EC300J (manufactured by Lion Corporation)) was used as a conductive carbon material relative to 100 parts by mass of resin, DBP absorption: 360 cm ３ Expanded beads and expanded bead moldings were produced in the same manner as in Example 9, except that 3 parts by mass of PEG-100 (particle size: 40 nm) was used and the contents were changed as shown in Table 2.

[0100] The resin beads, expanded beads, and expanded bead molded articles obtained as described above were measured or evaluated as follows, and the results are shown in Tables 1 to 3.

[0101] <Average Value of Cross-Section Major Axis / Cross-Section Minor Axis of Resin Particles> The resin particles were cut in a direction perpendicular to the extrusion direction during production, passing through the center of the resin particles to form a cross section, and the major axis and the minor axis passing through the center and indicated in a direction perpendicular to the major axis on the cross section were measured using a microscope. This measurement was performed on 20 resin particles, and the cross-section major axis / cut-section minor axis were determined for each resin particle, and the arithmetic average was taken to determine the average cross-section major axis / cut-section minor axis of the resin particles.

[0102] <Heat of Fusion of High-Temperature Peak of Expanded Beads> The heat of fusion of the high-temperature peak of the expanded beads was measured by heat flux differential scanning calorimetry based on JIS K7122-2012. Specifically, approximately 2 mg of expanded beads was sampled and heated from 23°C to 200°C at a rate of 10°C / min using a differential scanning calorimeter (DSC7020, manufactured by Hitachi High-Tech Science Corporation), resulting in a DSC curve with two or more melting peaks. In the following description, the resin-specific peak is designated A, and the high-temperature peak appearing higher than A is designated B. A straight line (α-β) was drawn connecting point α corresponding to 80°C on the DSC curve and point β on the DSC curve corresponding to the melting end temperature T of the expanded beads. The melting end temperature T is the high-temperature end point of high-temperature peak B, and refers to the intersection of high-temperature peak B with the high-temperature baseline. Next, a line parallel to the vertical axis of the graph was drawn from point γ on the DSC curve, which corresponds to the valley between the resin-specific peak A and the high-temperature peak B, and the point where this line intersected with the line (α-β) was designated as δ. The area of ​​high-temperature peak B was the area enclosed by the curve of the high-temperature peak B portion of the DSC curve, the line segment (δ-β), and the line segment (γ-δ), and this was designated as the high-temperature peak heat of fusion.

[0103] <Bulk Density of Expanded Beads> After curing the expanded beads as described above, a mass W (g) of expanded beads was filled into a measuring cylinder so that they would naturally pile up, and the bottom of the measuring cylinder was lightly tapped against a horizontal surface several times to stabilize the filling height of the expanded beads in the measuring cylinder. The bulk volume V (L) of the expanded beads indicated on the measuring cylinder was read, and the mass W of the expanded beads was divided by the bulk volume V of the expanded beads (W / V), and the unit was expressed as [kg / m ３ The bulk density of the expanded beads was calculated by converting the value into the value of the particle diameter.

[0104] <Closed cell ratio of expanded particles> Bulk volume: approx. 20 cm ３ The expanded beads were immersed in water to measure the apparent volume Va of the expanded beads. The expanded beads whose apparent volume Va had been measured were then thoroughly dried, and the true volume Vx of the expanded beads was measured according to procedure C described in ASTM-D2856-70. The true volume Vx of the expanded beads referred to here is the sum of the volume of the resin constituting the expanded beads and the total volume of the closed cells in the expanded beads. This true volume Vx was measured using an air-comparison hydrometer (Toshiba Beckman Corporation; air-comparison hydrometer "930"). The closed cell ratio was then calculated according to the following formula (1). Using different measurement samples, the closed cell ratio was measured five times using the same procedure as above, and the arithmetic mean value of the values ​​obtained in each measurement was calculated and used as the closed cell ratio of the expanded beads. [Equation 2] Closed cell ratio (%) = (Vx - W / ρ) × 100 / (Va - W / ρ) (1) Vx: true volume (cm) of the expanded particle group measured by the above method ３ ) Va: Apparent volume (cm) of the expanded particles measured from the rise in the water level when the expanded particles are submerged in water in a measuring cylinder ３ ) W: Mass of the expanded particle group (g) ρ: Density of the resin constituting the expanded particle (g / cm ３ )

[0105] <Average value of the long diameter / short diameter of expanded beads> Measurement and analysis were performed using a dynamic image analysis particle shape and particle size distribution analyzer and analysis software (product name: PARTAN 3D, software version: 7.1.3.80) manufactured by Microtrap Bell Co., Ltd. Approximately 2,000 expanded beads obtained above were fed into the device as samples, and three-dimensional image analysis was performed. The long diameter and short diameter of each expanded bead were measured, and the ratio of the long diameter to the short diameter of the expanded bead was calculated. The long diameter of each expanded bead is the maximum diameter at which the distance between two parallel lines sandwiching a single particle is greatest, as determined by image analysis. The short diameter of each expanded bead is the minimum diameter at which the distance between two parallel lines sandwiching a single particle is smallest. The value obtained by arithmetically averaging the ratios for each expanded bead fed was used as the average value of the long diameter / short diameter of expanded beads. In the measurement method using this measuring device, the major axis of the expanded beads corresponds to the Feret Length, and the minor axis of the expanded beads corresponds to the Feret Thickness.

[0106] <Density of Expanded Bead Molded Article> The density (kg / m) of the expanded bead molded article was determined by dividing the mass of the expanded bead molded article obtained by the volume calculated based on the dimensions. ３ ) was calculated.

[0107] <Evaluation of fusion property of expanded bead molding> The expanded bead molding was bent and broken, and the number of expanded beads present on the fracture surface (C1) and the number of broken expanded beads (C2) were counted. The ratio of the number of broken expanded beads to the number of expanded beads present on the fracture surface [(C2 / C1) x 100] was calculated as the material failure rate. The above measurement was carried out five times using different test pieces, and the material failure rates were determined for each test piece, and the arithmetic mean value was calculated. The arithmetic mean value was evaluated according to the following evaluation criteria. The higher the material failure rate, the better the fusion property. A: Material failure rate is 70% or more B: Material failure rate is 50% or more but less than 70% C: Material failure rate is less than 50%

[0108] <Evaluation of Surface Properties of Expanded Bead Molded Article> To evaluate the surface appearance, a test piece was cut out from the center of the expanded bead molded article in an area of ​​100 mm x 100 mm, a line was drawn diagonally from the corner of the test piece, and a 1 mm ２The number of voids (gaps) of a size of 10 or more was counted and evaluated as follows: Good: The number of voids was less than 10. Bad: The number of voids was 10 or more.

[0109] <Evaluation of Flame Retardancy of Expanded Bead Moldings> UL94V Test (Judgment): The flame retardancy of expanded bead moldings was evaluated based on the results of a vertical flame test (20 mm vertical flame test) conducted in accordance with the UL94 standard. The specific test method is as follows. (Preparation of Measurement Samples) Five test specimens measuring 125 mm in length, 13 mm in width, and 13 mm in thickness were cut from near the center of an expanded bead molding, so that all surfaces of the test specimen were cut out. (Test Method) The upper part of the test specimen was fixed with a clamp to keep the vertical direction of the test specimen, and absorbent cotton was placed below the test specimen. After using a burner to flame the lower end of the test specimen for 10 seconds, the burning time from when the burner was moved away from the test specimen until the burning of the test specimen stopped (first burning time) was measured. After again, the burning time from when the burner was moved away from the test specimen until the burning of the test specimen stopped after 10 seconds of flame contact (second burning time) and the red-hot time (second red-hot time) were measured. The above test was performed on five test pieces, respectively, to evaluate the flame retardancy of the expanded bead moldings. The burning time here refers to the time during which a burning state in which a flame is visible from the test piece continues. The burning refers to the state in which the surface of the test piece and the gases near the surface of the test piece combust, causing the flame to be visible from the test piece. The red-hot time refers to the time during which the test piece remains red-hot after the burning state in which the flame is visible has ended. The red-hot refers to the state in which only the surface of the test piece burns, causing the red-hot state of the surface of the test piece to be visible without any visible flame. (Evaluation Criteria) The above test was performed five times on five test pieces of each molding, and evaluation was performed according to the UL94 standards V-0, V-1, and V-2. Tests that did not satisfy the UL94 standards V-0, V-1, or V-2 were evaluated as failing. The flame retardancy was evaluated in the order of V-0, V-1, and V-2, indicating higher flame retardancy. If a test piece satisfied both the V-0 and V-1 evaluation criteria, it was rated as V-0, and if it satisfied only the V-1 criteria, it was rated as V-1.V-0: The first and second burning times of each test were 10 seconds or less, and the sum of the first and second burning times of each test, i.e., the total burning time for all 10 tests, was less than 50 seconds, and the sum of the second burning time and second glow-up time of each test was 30 seconds or less, and there was no test in which the burning of the test specimen reached the fixing clamp, and there was no test in which the absorbent cotton placed below the test specimen was burned by drops dropped from the burning test specimen. V-1: The first and second burning times of each test were 30 seconds or less, and the sum of the first and second burning times of each test, i.e., the total burning time for all 10 tests, was less than 250 seconds, and the sum of the second burning time and second glow-up time of each test was 60 seconds or less, and there was no test in which the burning of the test specimen reached the fixing clamp, and there was no test in which the absorbent cotton placed below the test specimen was burned by drops dropped from the burning test specimen. V-2: The first and second burning times of each test were 30 seconds or less, and the total of the first and second burning times of each test, i.e., the total burning time for all 10 tests, was less than 250 seconds, and the total of the second burning time and second glow time of each test was 60 seconds or less, and there was no test in which the burning of the test specimen reached the fixing clamp, and there was a test in which the absorbent cotton placed below the test specimen was burned by dripping material that fell during the burning of the test specimen.

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[0113] The present invention as described above encompasses the following technical concepts: (1) Expanded polyolefin resin beads having a foamed layer, wherein the base resin of the foamed layer is made of a polyolefin resin, and the foamed layer contains a phosphonate ester compound and a NOR hindered amine compound, the amount of the phosphonate ester compound in the foamed layer is 5 to 25 parts by mass per 100 parts by mass of the base resin, and the amount of the NOR hindered amine compound in the foamed layer is 0.3 to 5 parts by mass per 100 parts by mass of the base resin, and the expanded beads have a closed cell rate of 60% or more. (2) Expanded polyolefin resin beads as described in (1) above, wherein the average ratio of the major axis to the minor axis (major axis / minor axis) of the expanded beads is 1.0 to 2.0. (3) The expanded polyolefin resin beads according to (1) or (2), wherein the expanded beads have a coating layer that coats the foam layer, and the mass ratio of the foam layer to the coating layer is 95:5 to 70:30. (4) The expanded polyolefin resin beads according to any one of (1) to (3), wherein the ratio of the amount of the NOR-type hindered amine compound to the amount of the phosphonate ester compound in the foam layer is 0.04 or more and 0.4 or less. (5) The expanded polyolefin resin particles according to any one of (1) to (4), wherein the base resin of the foamed layer is composed of a linear polypropylene resin (A), a branched polypropylene resin (B) having a melt tension of 50 mN or more as measured at 230°C, and / or a polyethylene resin (C) having an MFR of 3 g / 10 min or less as measured at 190°C under a load of 2.16 kg, and the total content of the branched polypropylene resin (B) and the polyethylene resin (C) is 5% by mass or more and 30% by mass or less relative to 100% by mass of the total content of the linear polypropylene resin (A), the branched polypropylene resin (B), and the polyethylene resin (C). (6) The expanded polyolefin resin particles according to any one of (1) to (5), wherein the foamed layer contains a conductive carbon material, and the amount of the conductive carbon material in the foamed layer is 1 part by mass or more and 10 parts by mass or less relative to 100 parts by mass of the base resin.(7) The expanded polyolefin resin particles according to any one of (1) to (6), wherein the foamed layer contains a phenolic antioxidant in an amount of 0.01 to 0.5 parts by mass relative to 100 parts by mass of the base resin of the foamed layer, and the ratio of the amount of the phenolic antioxidant to the amount of the NOR hindered amine compound is 0.03 to 0.9. (8) The expanded polyolefin resin particles according to any one of (1) to (7), wherein the foamed layer contains a sulfur-based antioxidant in an amount of 0.01 to 0.5 parts by mass relative to 100 parts by mass of the base resin of the foamed layer, and the ratio of the amount of the sulfur-based antioxidant to the amount of the NOR hindered amine compound is 0.03 to 0.9. (9) A foamed bead molding obtained by molding the foamed polyolefin resin beads according to any one of (1) to (8) above in a mold.

Claims

1. A polyolefin-based resin expanded particle having a foamed layer, wherein the base resin of the foamed layer is made of a polyolefin-based resin, the foamed layer contains a phosphonate ester compound and a NOR-type hindered amine compound, the amount of the phosphonate ester compound in the foamed layer is 5 parts by mass or more and 25 parts by mass or less per 100 parts by mass of the base resin, the amount of the NOR-type hindered amine compound in the foamed layer is 0.3 parts by mass or more and 5 parts by mass or less per 100 parts by mass of the base resin, and the closed cell rate of the expanded particles is 60% or more.

2. The expanded polyolefin resin beads according to claim 1, wherein the average ratio of the major axis to the minor axis (major axis / minor axis) of the expanded beads is 1.0 or more and 2.0 or less.

3. A polyolefin resin expanded bead according to claim 1 or 2, wherein the expanded bead has a coating layer that covers the foamed layer, and the mass ratio of the foamed layer to the coating layer is 95:5 to 70:

30.

4. A polyolefin resin expanded particle according to any one of claims 1 to 3, wherein in the foamed layer, the ratio of the amount of the NOR type hindered amine compound to the amount of the phosphonate ester compound is 0.04 or more and 0.4 or less.

5. A polyolefin-based resin expanded particle according to any one of claims 1 to 4, wherein the base resin of the foamed layer is composed of a linear polypropylene-based resin (A), a branched polypropylene-based resin (B) having a melt tension of 50 mN or more measured under conditions of 230°C, and / or a polyethylene-based resin (C) having an MFR of 3 g / 10 min or less measured under conditions of a temperature of 190°C and a load of 2.16 kg, and the total content of the branched polypropylene-based resin (B) and the polyethylene-based resin (C) is 5% by mass or more and 30% by mass or less relative to the total content of the linear polypropylene-based resin (A), the branched polypropylene-based resin (B), and the polyethylene-based resin (C) being 100% by mass.

6. A polyolefin resin foamed particle described in any one of claims 1 to 5, wherein the foamed layer contains a conductive carbon material, and the amount of the conductive carbon material in the foamed layer is 1 part by mass or more and 10 parts by mass or less per 100 parts by mass of the base resin.

7. The polyolefin resin expanded particles according to any one of claims 1 to 6, wherein the foamed layer contains a phenolic antioxidant, the amount of the phenolic antioxidant in the foamed layer is 0.01 parts by mass or more and 0.5 parts by mass or less per 100 parts by mass of the base resin of the foamed layer, and the ratio of the amount of the phenolic antioxidant to the amount of the NOR-type hindered amine compound in the foamed layer is 0.03 or more and 0.9 or less.

8. The polyolefin resin expanded particles according to any one of claims 1 to 7, wherein the foamed layer contains a sulfur-based antioxidant, the amount of the sulfur-based antioxidant in the foamed layer is 0.01 parts by mass or more and 0.5 parts by mass or less per 100 parts by mass of the base resin of the foamed layer, and the ratio of the amount of the sulfur-based antioxidant to the amount of the NOR-type hindered amine compound in the foamed layer is 0.03 or more and 0.9 or less.

9. A foamed bead molding obtained by molding the foamed polyolefin resin beads according to any one of claims 1 to 8 in a mold.

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