Polyolefin resin foamed particles and foamed particle molded body

Abstract

Provided is a polyolefin resin foamed particle that can easily be in-molded into a polyolefin resin foamed particle molded body, the polyolefin resin foamed particle molded body exhibiting high flame retardancy while having excellent weldability and surface properties. A polyolefin resin foamed particle having a foamed layer, wherein the foamed layer contains a base resin, a phosphonate compound, and a NOR-type hindered amine compound, the base resin being composed of a polyolefin resin, the amount of the phosphonate compound in the foamed layer being 5 mass parts or more and 25 mass parts or less with respect to 100 mass parts of the base resin, the amount of the NOR-type hindered amine compound in the foamed layer being 0.3 mass parts or more and 5 mass parts or less with respect to 100 mass parts of the base resin, and the closed cell volume percentage of the foamed particle being 60% or more.

Description

Technical Field

[0001] This invention relates to flame-retardant polyolefin resin foamed granules and molded foamed granules. Background Technology

[0002] Polyolefin resin foam granules are widely used as materials for in-mold molding of polyolefin resin foam granule molded bodies. The polyolefin resin foamed granules are used in a variety of applications, such as packaging materials, vehicle components, and building materials. In particular, considering their excellent properties, such as lightweight, impact resistance, and energy absorption characteristics, polyolefin resin foamed granules are suitable as vehicle components, such as automotive bumpers and seat cores.

[0003] In the past, vehicle components were sometimes required to meet FMVSS 302 standards (Federal Motor Vehicle Safety Standard No. 302). However, in recent years, with the increasing popularity of electric vehicles, in addition to requiring low combustion speeds, higher flame retardancy, such as self-extinguishing properties, is sometimes also required.

[0004] For example, Patent Document 1 discloses polypropylene resin foamed granules containing polypropylene resin, organophosphorus compounds, and hindered amines within a specified range (hereinafter also referred to as Prior Art 1). Furthermore, Patent Document 2 discloses polyolefin resin pre-foamed granules containing specific organophosphorus compounds and specific hindered amines within a specified range (hereinafter also referred to as Prior Art 2). Both Patent Documents 1 and 2 describe how the proposed foamed granules can provide a foamed granule molded article with excellent flame retardancy. Existing technical documents Patent documents

[0005] Patent Document 1: WO2022 / 203035A1 Patent Document 2: WO2016 / 052739A1 Summary of the Invention (a) Technical problems to be solved

[0006] However, through the research of the inventors of this application, the following problems have been found in prior art 1 and 2. That is, although both existing technologies 1 and 2 can improve flame retardancy by including organophosphorus compounds and hindered amines within a specified range, it is known that when manufacturing foamed granule molded bodies by in-mold molding, problems such as insufficient fusion between foamed particles and insufficient surface properties of the manufactured foamed granule molded bodies may occur. In addition, in the following text, the fusion properties and surface properties of foamed granule molded bodies are sometimes collectively referred to as the "molding state".

[0007] The present invention addresses the aforementioned problems. Specifically, the present invention provides polyolefin resin foam particles that can be easily in-mold molded into a polyolefin resin foam particle molded body, and a polyolefin resin foam particle molded body with excellent molding condition. The olefin resin foam particles exhibit high flame retardancy and excellent molding condition. (II) Technical Solution

[0008] The polyolefin resin foamed particles of the present invention have a foamed layer, characterized in that the base resin of the foamed layer is composed of a polyolefin resin, and the foamed layer comprises a phosphonate ester compound and a NOR-type hindered amine compound. The amount of phosphonate compound in the foamed layer is 5 parts by mass and 25 parts by mass relative to 100 parts by mass of the base resin, the amount of NOR-type hindered amine compound in the foamed layer is 0.3 parts by mass and 5 parts by mass relative to 100 parts by mass of the base resin, and the closed-cell volume percentage of the foamed particles is 60% or more. Furthermore, the polyolefin resin foamed granule molded body of the present invention is characterized in that it is formed by in-mold molding of the polyolefin resin foamed granules of the present invention. (III) Beneficial Effects

[0009] This invention provides polyolefin resin foamed granules that can be manufactured into polyolefin resin foamed granule molded articles exhibiting high flame retardancy and excellent molding properties. Furthermore, the polyolefin resin foamed granule molded articles of this invention exhibit high flame retardancy and excellent weldability and surface properties. Detailed Implementation

[0010] The polyolefin resin foamed particles of the present invention will now be described. In the following description, the polyolefin resin foamed particles of the present invention will sometimes be referred to as foamed particles of the present invention or simply as foamed particles, and the polyolefin resin foamed particle molded body of the present invention will sometimes be referred to as a foamed particle molded body of the present invention or simply as a foamed particle molded body. Furthermore, in the following description, preferred numerical ranges of the present invention will sometimes be appropriately shown. In such cases, preferred, more preferred, and particularly preferred ranges of the upper and lower limits of the numerical range can be determined based on all combinations of the upper and lower limits. Furthermore, the high flame retardancy of this invention is not only characterized by a slow burning rate but also by self-extinguishing properties. In this invention, self-extinguishing property is evaluated using V-0, V-1, or V-2 standards in tests based on UL94 (Underwriters Laboratories 94). The foamed granule molded body exhibiting excellent flame retardancy in tests based on these specifications not only has a slow burning rate but also demonstrates excellent self-extinguishing properties. The foamed granule molded body exhibiting self-extinguishing properties also exhibits relatively good flame retardancy in tests based on other specifications. Therefore, the range of applications applicable to the foamed granule molded body constituting such a highly flame-retardant foamed granule molded body is broad.

[0011] The foamed granules of the present invention have a foamed layer, the base resin of which is composed of a polyolefin resin. The foamed layer comprises a phosphonate ester compound and a NOR-type hindered amine compound. Therefore, desired flame retardancy can be imparted to the foamed granules and the molded foamed granule articles formed by in-mold molding of the foamed granules. The amount of phosphonate compound in the foamed layer is 5 parts by mass and 25 parts by mass, relative to 100 parts by mass of the base resin. Furthermore, the amount of NOR-type hindered amine compound in the foamed layer is 0.3 parts by mass and 5 parts by mass, relative to 100 parts by mass of the base resin. The foamed particles of the present invention having the above-described configuration have a closed-cell volume percentage of 60% or more. Examples of methods for adjusting the closed-cell volume percentage to the preferred range are described below.

[0012] In order to provide a foamed particle that can be in-mold molded to exhibit high flame retardancy and improve the problem of moldability degradation, the inventors of this application conducted careful research. The inventors then discovered that the anticipated technical problem could be solved by using foamed particles containing phosphonate ester compounds and NOR-type hindered amine compounds within a specified range and having a closed-cell volume percentage of 60% or more, thus providing this invention. The causal relationship between the percentage of closed-cell volume and the aforementioned problem of declining molding condition is unclear, but the following is a hypothesis.

[0013] Firstly, generally speaking, there are two main methods for manufacturing foamed granules comprising polyolefin resins, phosphonate compounds, and NOR-type hindered amine compounds. One method involves melt-mixing the aforementioned raw materials, further supplying a foaming agent, and then extruding the mixture to form a foam. The foam is then cut to obtain foamed granules of a specified size. This method is sometimes referred to as manufacturing method 1 below. The other method involves extruding and cutting a molten mixture obtained by melt-mixing the aforementioned raw materials to manufacture resin granules of a specified size, and then foaming these resin granules to obtain foamed granules. This method is sometimes referred to as manufacturing method 2 below. Both manufacturing methods 1 and 2 include a step of melt-mixing the aforementioned raw materials within an extruder. It is speculated that in the above series of processes, compared with the case where phosphonate compounds and NOR-type hindered amine compounds are not used, the melt mixture obtained by melt mixing polyolefin resins, phosphonate compounds and NOR-type hindered amine compounds can produce changes in viscosity and an increase in hygroscopicity. More specifically, it is speculated that by melt-mixing polyolefin resins with phosphonate compounds, the hygroscopicity of the molten mixture containing the phosphonate compounds increases. Furthermore, it is speculated that by melt-mixing polyolefin resins with NOR-type hindered amine compounds, free radicals from the NOR-type hindered amine compounds are generated. Due to the action of these free radicals, the polyolefin resin deteriorates, causing a change in its viscosity. Moreover, it is speculated that the viscosity of the molten mixture containing the polyolefin resin that has undergone this viscosity change also changes. Therefore, it is speculated that by using a molten mixture that produces an unexpected increase in hygroscopicity and viscosity change, it is difficult to form bubbles and bubble films during foaming, resulting in a lower closed-cell volume percentage in the obtained foamed particles. Furthermore, it is speculated that this results in reduced weldability between the foamed particles during in-mold molding, and an incomplete molding state of the resulting foamed particle molded body.

[0014] The closed-cell volume percentage of the foamed particles of the present invention is 60% or more, preferably 65% ​​or more, more preferably 70% or more, further preferably 75% or more, and particularly preferably 80% or more. Because the closed-cell volume percentage of the foamed particles is relatively high, there is a tendency to easily in-mold mold the well-formed foamed particle molded body. In particular, the foamed particles of the present invention with a closed-cell volume percentage of 75% or more exhibit excellent weldability in foamed particle molded bodies formed using these foamed particles.

[0015] For the present invention, the percentage of closed-pore volume is determined by the following method. First, the volume of the stack is approximately 20cm. 3The foamed granule assembly was immersed in water, and its apparent volume Va was measured. Next, after thoroughly drying the foamed granule assembly from which the apparent volume Va was measured, the true volume Vx of the foamed granules was measured according to step C described in ASTM D2856-70. Furthermore, the true volume Vx of the foamed granules referred to here is the sum of the volume of the resin constituting the foamed granules and the total volume of the individual air bubbles within the foamed granules. In the determination of the true volume Vx, an air comparative hydrometer was used. An example of a commercially available air comparative hydrometer is the "930" manufactured by Toshiba Beckman Co., Ltd. Next, the closed-cell volume percentage was calculated using the following formula (1). Using different test samples, the closed-cell volume percentage was determined five times using the same steps as described above. The arithmetic mean of the values ​​obtained in each determination was calculated and used as the closed-cell volume percentage of the foamed particles. [Mathematical Expression 1] Closed-cell volume percentage (%) = (Vx - W / ρ) × 100 / (Va - W / ρ) ···(1) Vx: The true volume (cm³) of the foamed granule group determined by the above method. 3 ) Va: Apparent volume of the foamed particle assembly (cm³) measured from the rise in water level when the foamed particle assembly is submerged in a graduated cylinder. 3 ) W: Mass of the foamed granule group (g) ρ: Density of the resin constituting the foamed particles (g / cm³) 3 )

[0016] The foamed particles containing the flame retardant of the present invention are preferably spherical. As flame retardants, foamed particles containing phosphonate compounds and NOR-type hindered amine compounds tend to be flat. From the perspective of being able to mold well-formed foamed particle bodies in-mold, having good filling properties in the mold, and excellent storage stability, the average value of the ratio of the long diameter to the short diameter (long diameter / short diameter) of the foamed particles is preferably 1.0 or more and 2.5 or less, more preferably 1.0 or more and 2.1 or less, and even more preferably 1.0 or more and 2.0 or less. In particular, if the upper limit of the above ratio is 2.0 or less, foamed particles with particularly excellent weldability can be provided. It is further preferred that the average value of the above ratio (long diameter / short diameter) is 1.2 or more and 1.8 or less. Examples of methods for adjusting the (long diameter / short diameter) to the preferred range are described below. For the present invention, the closer the average value of the ratio (long diameter / short diameter) is to 1.0, the more spherical the appearance of the foamed particles; the larger the average value of the ratio, the more flat the appearance of the foamed particles. In addition, for the foamed particles of the present invention, spherical and flattened refer to the shape of the foamed particles as observed by the naked eye.

[0017] Furthermore, the major and minor diameters of the aforementioned foamed particles are measured using an image-analytical particle size distribution measuring device. More specifically, using the aforementioned measuring device, the foamed particles are allowed to fall freely within the device, and multiple images of the freely falling foamed particles are obtained by taking high-speed photographs using a camera. From the multiple images of the freely falling foamed particles obtained by the high-speed photography, multiple images of the same foamed particle taken from different shooting directions are extracted. Among the multiple images of the same foamed particle taken from different shooting directions, the lengths of the two parallel lines that clamp the foamed particle, where the distance between them is at its maximum and minimum, are determined by image analysis. After determining the length of the two parallel lines with the maximum distance between them as the major diameter and the length of the distance with the minimum distance as the minor diameter, the ratio of the major diameter to the minor diameter of a foamed particle is calculated. Then, the ratios of multiple foamed particles are calculated, and the arithmetic mean of each ratio is calculated, thereby allowing the calculation of the average value of the ratio of the major diameter to the minor diameter (major diameter / minor diameter) of the foamed particles. As an image-analytical particle distribution measuring device, an example is the dynamic image-analytical particle shape-size distribution measuring device and analysis software (product name: PARTAN 3D) manufactured by Microtrac BELCo., Ltd.

[0018] The reason why foamed particles containing phosphonate compounds and NOR-type hindered amine compounds tend to have the aforementioned flat shape is not yet clear, but it is speculated as follows. When foamed granules are obtained by manufacturing resin granules and then foaming them, the resin granules can be manufactured in the following manner: Typically, after feeding raw materials such as resin into an extruder and performing melt mixing, a bundle-shaped molten mixture is extruded from a circular orifice. While being drawn along the extrusion direction, it is cut to a predetermined length perpendicular to the extrusion direction, thereby producing spherical resin granules with a circular cross-section. Resin granules manufactured under such a force applied in the extrusion direction are quenched after being extruded from a high-temperature extruder, resulting in residual stress within the resin granules due to the force applied in the extrusion direction. Therefore, when foaming, these resin granules expand more easily in the direction perpendicular to the extrusion direction than in the extrusion direction itself. Therefore, when cutting the molten mixture extruded from the extruder, the internal stress of the resin granules and the length of the resin granules in the extrusion direction can be adjusted by adjusting the traction speed or the cutting width. By foaming the resin granules obtained through this adjustment, near-spherical foamed granules can be obtained. On the other hand, when polyolefin resins are used simultaneously with phosphonate compounds and NOR-type hindered amine compounds to manufacture resin granules, the filament-like molten mixture extruded from the extruder tends to shrink in a direction perpendicular to the extrusion direction. Pellet-shaped resin granules manufactured by cutting them in this shrunken state tend to be flattened. Furthermore, when these flattened resin granules are foamed, the foamed granules tend to be flattened as well. As explained above, it is speculated that flattened foamed granules may be produced during the resin granule manufacturing process due to unexpected changes in the viscosity and hygroscopicity of the molten mixture.

[0019] The base resin of the foamed layer of the present invention is composed of a polyolefin resin and includes phosphonate compounds and NOR-type hindered amine compounds. In other words, the foamed layer of the present invention is composed of a base resin, which is a polyolefin resin. Without hindering the purpose or effect of the present invention, the foamed layer may further optionally include other resins. Furthermore, in addition to the resin, phosphonate compounds, and NOR-type hindered amine compounds, the foamed layer may also include any additives used in the manufacture of the foamed particles.

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

[0021] The substrate resin refers to the resin that contains more than 50% by mass of the resin and polymer constituting the foam layer in 100% 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 perspective of obtaining a foamed granule molded body with higher compressive strength, the foamed layer of the present invention preferably comprises a base resin, which is a polypropylene-based resin as a polyolefin-based resin. In 100% by mass of the base resin of the foamed layer, it is preferable to include 70% by mass or more of a polypropylene-based resin, more preferably 80% by mass or more, further preferably 90% by mass or more, even more preferably 95% by mass or more, and particularly preferably 100% by mass. That is, the base resin of the foamed layer is particularly preferably composed only of a polypropylene-based resin.

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

[0023] When the propylene-based random copolymer contains components from ethylene (ethylene component) and / or from butene (butene component) as copolymerizing components, from the perspective of further improving the in-mold moldability of the foamed granules under low molding pressure conditions, the total content of ethylene and butene components 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 perspective of being able to stably obtain foamed granule molded articles with good mechanical properties such as compressive strength, the total content of ethylene and butene components in the propylene-based random copolymer is preferably 15% by mass or less. That is, the total content of ethylene and butene components 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. In addition, the content of components from ethylene and α-olefins in the propylene-based random copolymer can be determined by IR spectroscopy.

[0024] The polypropylene resin can be a linear polypropylene resin, a branched polypropylene resin, or a combination of the two. From the perspective of easily obtaining foamed particles with a smaller amount of foaming agent, the amount of branched polypropylene resin contained in 100% by mass of the base resin of the foamed layer of the present invention is preferably 50% by mass or less, more preferably 30% by mass or less.

[0025] However, according to the inventors' research, it has been confirmed that in foamed particles containing polypropylene resin, phosphonate compounds, and NOR-type hindered amine compounds in the base resin of the foamed layer, there is a tendency for the viscosity of the molten mixture to decrease when manufacturing resin particles for producing the foamed particles. From the perspective of suppressing this viscosity decrease, the base resin of the foamed layer is preferably composed of the following components: linear polypropylene resin (A); branched polypropylene resin (B) with a melt tension of 50 mN or more measured at 230°C; and / or polyethylene resin (C) with a melt flow rate of 3 g / 10 min or less measured at a temperature of 190°C and a load of 2.16 kg. In addition, melt flow rate is sometimes appropriately abbreviated as MFR. From the same perspective as above, the base resin of the foamed layer is particularly more preferably composed of linear polypropylene resin (A) and branched polypropylene resin (B) with a melt tension of 50 mN or more measured at 230°C. Furthermore, from the same perspective, the substrate resin of the foaming layer is more preferably composed of linear polypropylene resin (A) and polyethylene resin (C) with a melt flow rate of 3 g / 10 min or less as measured under conditions of 190°C and a load of 2.16 kg. Moreover, when the total content of the linear polypropylene resin (A), the branched polypropylene resin (B), and the polyethylene resin (C) is set to 100% by mass, the total content of the branched polypropylene resin (B) and the polyethylene resin (C) is more preferably 5% by mass or more and 30% by mass or less. According to the preferred embodiment described above, a foamed particle can be provided that can be in-mold molded to achieve the closed-cell volume percentage of the foamed particle specific to this invention and with a superior molding state. Furthermore, according to the preferred embodiment described above, since viscosity changes are suppressed, the average value of the ratio of the major diameter to the minor diameter (major diameter / minor diameter) of the foamed particle can be easily adjusted to a specified range, making it easy to obtain near-spherical foamed particles. Furthermore, in this invention, branched polypropylene resin refers to a component in the molecular structure of a polypropylene resin that has a long-chain branched structure, thereby promoting the entanglement between the resin's molecular chains. Additionally, the long-chain branched structure is distinct from the branched structure formed by copolymerizing propylene with α-olefins. The copolymer is classified as linear polypropylene. For example, as branched polypropylene resins with a long-chain branched structure, resins having molecular chains consisting of 21 or more carbon skeletons are known, but are not limited to this. Examples of such branched polypropylene resins include branched homopolymer polypropylene (product names: Daploy WB130HMS, Daploy WB135HMS, Daploy WB140HMS) manufactured by Borealis AG, and branched homopolymer polypropylene resin (product name: PF814) manufactured by SunAllomer Ltd. Furthermore, in this invention, linear polypropylene resin refers to polypropylene resin other than the branched polypropylene resin, specifically including linear propylene homopolymers, linear propylene random copolymers, etc.

[0026] Polyethylene resins: In this specification, polyethylene resin refers to an ethylene copolymer containing 50% by mass or more structural units derived from ethylene homopolymer and ethylene. Specifically, examples include polyethylene represented by high-density polyethylene (PE-HD), medium-density polyethylene (PE-MD), low-density polyethylene (PE-LD), linear low-density polyethylene (PE-LLD), and linear ultra-low-density polyethylene; and ethylene copolymers represented by ethylene-vinyl acetate copolymer and ethylene-methyl methacrylate copolymer. The content of the ethylene-derived structural units of the ethylene copolymer in the polyethylene resin 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: To the extent that it does not impede the purpose and effect of the present invention, the foamed layer of the present invention may comprise thermoplastic resins other than the polyolefin resins mentioned above. Examples of thermoplastic resins include polystyrene resins, polyamide resins, polyester resins, polycarbonate resins, and modified polyphenylene ether resins, and other thermoplastic resins besides polyolefin resins are also listed. The thermoplastic resin may be one type or a combination of two or more types.

[0028] In the base resin of the 100% by mass foam layer, the content of other thermoplastic resins besides the polyolefin resin is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 0% by mass. That is, the foam layer particularly preferably contains substantially only polyolefin resin as a thermoplastic resin.

[0029] In addition to the thermoplastic resins mentioned above, the foam layer of the present invention may also contain other polymers, such as thermoplastic elastomers and non-thermoplastic resins. Examples of thermoplastic elastomers include olefin-based thermoplastic elastomers (TPO) and urethane-based thermoplastic elastomers (TPU), while examples of non-thermoplastic resins include thermosetting resins or rubbers. 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. That is, the foam layer particularly preferably does not contain polymers other than thermoplastic resins.

[0030] (Melting point of polyolefin resins) When the polyolefin resin includes a polypropylene resin, from the perspective of improving the mechanical properties of the obtained foamed granule molded article, 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. On the other hand, from the perspective of improving the in-mold moldability of the foamed granules under low molding pressure conditions, 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. 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 includes a polyethylene resin, from the perspective of improving the mechanical properties of the obtained foamed granule molded article, 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. On the other hand, from the perspective of improving the in-mold moldability of the foamed granules under low molding pressure conditions, 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. Polyolefin resins or polyolefin resin foamed particles were used as test pieces, and the melting point of the polyolefin resins was determined according to JIS K7121:2012. Specifically, the test piece was prepared under the condition of "(2) determining the melting temperature after a certain heat treatment" with a nitrogen inflow rate of 30 mL / min. The test piece was heated from 23°C to 200°C at a heating rate of 10°C / min, then held at that temperature for 10 minutes, cooled to 23°C at a cooling rate of 10°C / min, and then heated to 200°C again at a heating rate of 10°C / min to obtain the DSC curve (DSC curve during the second heating). Then, the peak temperature of the melting peak in the DSC curve during the second heating was determined, and this value was taken as the melting point of the polyolefin resin. In addition, if multiple melting peaks appeared in the DSC curve during the second heating, the peak temperature of the melting peak with the highest melting peak height relative to the baseline was taken as the melting point.

[0031] (Mel flow rate of polyolefin resins) When a polyolefin resin includes a polypropylene resin, from the perspective of improving the foaming properties of the resin particles during foaming and the secondary foaming properties of the foamed particles during in-mold molding, the melt flow rate (MFR) 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. On the other hand, from the perspective of improving the uniformity of bubbles in the foamed particles and improving the physical properties of the molded foamed particles, the melt flow rate (MFR) 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. 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 polypropylene resins was determined according to JIS K7210-1:2014, at a temperature of 230℃ and a load of 2.16 kg. When a polyethylene resin is included in a polyolefin resin, from the perspective of improving the foaming properties of the resin particles during foaming and the secondary foaming properties of the foamed particles during in-mold molding, the melt flow rate (MFR) of the polyethylene resin is preferably 0.5 g / 10 min or more, more preferably 0.8 g / 10 min or more. On the other hand, from the perspective of improving the uniformity of bubbles in the foamed particles and improving the physical properties of the molded foamed particles, the melt flow rate of the polyethylene resin is preferably 4 g / 10 min or less, more preferably 3 g / 10 min or less. In other words, the MFR of the polyethylene 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 was measured according to JIS K7210-1:2014 at a temperature of 190°C and a load of 2.16 kg.

[0032] (phosphonate compounds) The foaming layer of the present invention contains phosphonate compounds. Phosphonate compounds are compounds that contain phosphonate sites in their molecules, such as cyclic phosphonate compounds and alkyl phosphonate compounds.

[0033] Cyclic phosphonate compounds: Cyclic phosphonate compounds are compounds containing one or more cyclic phosphonate sites in their molecules, preferably at least one selected from the group consisting of compounds represented by general formula (1), general formula (2), general formula (3), and general formula (4), and more preferably pentaerythritol diphosphonate represented by general formula (1). Pentaerythritol diphosphonate of general formula (1) is a spirocyclic compound containing two cyclic phosphonate sites in its molecule. Cyclic phosphonate compounds can be used alone or in combination of two or more. [Chemical Formula 1] In the general formula, R 1 and R 2 These are alkyl groups with 1 to 10 carbon atoms, alkenyl groups with 2 to 10 carbon atoms, benzyl groups, phenethyl groups, phenyl groups, or naphthyl groups, respectively. 3 R is an alkyl group having 1 to 22 carbon atoms or an aryl group having 6 to 15 carbon atoms. 4 R 8 R 9 and R 12 They are alkyl groups with 1 to 4 carbon atoms, R 5 R 7 and R 11R represents either a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. 6 and R 10 They are alkyl groups with 1 to 22 carbon atoms, cycloalkyl groups with 9 to 22 carbon atoms, aryl groups with 9 to 22 carbon atoms, or aralkyl groups with 9 to 22 carbon atoms, respectively.

[0034] In general formula (1), R 1 With R 2 They can be the same or different, but the same is preferred. R 1 It 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. R 2 It 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. In summary, among the compounds represented by general formula (1), R is further preferred. 1 and R 2 All are compounds containing methyl groups.

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

[0036] In general formula (3), R 4 With R 8 They can be the same or different, but the same is preferred. R 4 It is an alkyl group having 1 to 4 carbon atoms, preferably a methyl group. R 8 It is an alkyl group having 1 to 4 carbon atoms, preferably a methyl group. In general formula (3), R 5 With R 7 They can be the same or different, but the same is preferred. R 5 It is an alkyl group having 1 to 4 hydrogen atoms or carbon atoms, preferably an ethyl group. R 7 It is an alkyl group having 1 to 4 hydrogen atoms or carbon atoms, preferably an ethyl group. R 6 It 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, preferably a straight-chain alkyl group having 1 to 12 carbon atoms.

[0037] In general formula (4), R 9 With R12 They can be the same or different, but the same is preferred. R 9 It is an alkyl group having 1 to 4 carbon atoms, preferably a methyl group. R 12 It is an alkyl group having 1 to 4 carbon atoms, preferably a methyl group. R 10 It 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, preferably a straight-chain alkyl group having 1 to 12 carbon atoms. R 11 It is an alkyl group having 1 to 4 hydrogen atoms or carbon atoms, preferably an ethyl group.

[0038] The melting point TmA of the cyclic phosphonate 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 cyclic phosphonate compounds was determined according to JIS K0064:1992.

[0039] Relative to 100 parts by weight of the base resin of the foamed layer, the amount of the phosphonate compound in the foamed layer of the polyolefin resin foamed particles of the present invention is 5 parts by weight or more and 25 parts by weight or less. If the amount of the phosphonate compound is too small, a foamed particle molded body with high flame retardancy cannot be obtained. On the other hand, if the amount is too large, a foamed particle molded body with excellent weldability cannot be obtained. From the perspective of obtaining a foamed granule molded body with higher flame retardancy, the amount of phosphonate compound in the foamed layer is preferably 6 parts by mass or more, more preferably 7 parts by mass or more, further preferably 8 parts by mass or more, and particularly preferably 9 parts by mass or more, relative to 100 parts by mass of the base resin of the foamed layer. From the perspective of obtaining a foamed granule molded body with better weldability, the amount of phosphonate compound in the foamed layer is preferably 22.5 parts by mass or less, more preferably 20 parts by mass or less, further preferably 19 parts by mass or less, and particularly preferably 16 parts by mass or less, relative to 100 parts by mass of the base resin of the foamed layer. In other words, relative to 100 parts by mass of the base resin of the foamed layer, the amount of phosphonate compound in the foamed 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. As described above, the phosphonate compounds mentioned in this paragraph are compounds that contain a phosphonate site in their molecules, such as cyclic phosphonate compounds and alkyl phosphonate compounds.

[0040] (NOR-type hindered amine compounds) The foaming layer of the present invention comprises NOR-type hindered amine compounds. NOR-type hindered amine compounds can improve the flame retardancy of molded articles by having a 2,2,6,6-tetramethyl-4-piperidineamine moiety with a hydrocarbon group bonded to the nitrogen atom via an oxygen atom, as shown in the following general formula (5). [Chemical Formula 2] In general formula (5), R 13 It indicates a hydrocarbon group.

[0041] In the general formula (5), R 13 In the case where a molecule of hindered amine compound contains two or more hindered amine groups represented by general formula (5), multiple R groups represent hydrocarbon groups. 13 They can be the same or different, but multiple Rs are preferred. 13 same. R 13 Preferably, it is selected from at least one of the groups consisting of alkyl and cycloalkyl groups, more preferably cycloalkyl. In R 13 In the case of an alkyl group, R 13 More preferably, it is an alkyl group having 1 to 20 carbon atoms, and even more preferably an undecylalkyl group. In R 13 In the case of cycloalkyl, R 13 More preferably, it is a cycloalkyl group having 4 to 10 carbon atoms, and even more preferably, it is a cyclohexyl group. NOR-type hindered amine compounds can be used alone or in combination of two or more.

[0042] From the perspective of suppressing exudation from self-foaming granular molded articles, the molecular weight of the NOR-type hindered amine compound is preferably 600 or more, more preferably 1500 or more. Furthermore, from the perspective of ensuring good dispersion of the NOR-type hindered amine compound in the resin, the molecular weight of the NOR-type hindered amine compound is preferably 3000 or less, more preferably 2500 or less. The number of 2,2,6,6-tetramethyl-4-piperidineamine groups having a hydrocarbon group bonded to the nitrogen atom represented by the general formula (5) via an oxygen bond in the NOR-type hindered amine compound is preferably 2 or more and 8 or less, more preferably 2 or more and 6 or less, and even more preferably 2 or 6.

[0043] Relative to 100 parts by weight of the base resin of the foamed layer, the amount of the NOR-type hindered amine compound in the foamed layer of the polyolefin resin foamed particles of the present invention is 0.3 parts by weight or more and less than 5 parts by weight. If the amount of the NOR-type hindered amine compound is too small, a foamed particle molded body with high flame retardancy cannot be obtained. On the other hand, if the amount is too large, a foamed particle molded body with excellent weldability cannot be obtained. From the perspective of obtaining a foamed granule molded body with higher flame retardancy, the amount of NOR-type hindered amine compound in the foamed 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, relative to 100 parts by mass of the base resin of the foamed layer. From the perspective of obtaining a foamed granule molded body with better weldability, the amount of NOR-type hindered amine compound in the foamed 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, even 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 foamed layer. In other words, relative to 100 parts by mass of the base resin of the foamed layer, the amount of NOR-type hindered amine compound in the foamed 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, even 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.

[0044] As described above, the base resin of the foam layer contains, within a specified range, phosphonate compounds and NOR-type hindered amine compounds, relative to 100 parts by weight. From the perspective of exhibiting higher flame retardancy, the ratio of the amount of the NOR-type hindered amine compound in the foamed layer to the amount of the phosphonate ester compound is preferably 0.04 or more, more preferably 0.05 or more. From the perspective of further improving the weldability of the foamed granule molded body, the ratio of the amount of the NOR-type hindered amine compound in the foamed layer to the amount of the phosphonate ester compound 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-type hindered amine compound in the foamed layer to the amount of the phosphonate ester compound 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] (Any additives) To the extent that it does not impede the purpose and effects of the present invention, the foamed particles of the present invention may appropriately contain any additives. For example, various conventionally known additives, such as conductive materials, antioxidants, flame retardant synergists, bubble regulators, lubricants, crystal nucleating agents, light stabilizers such as UV stabilizers, antistatic agents, and colorants, can be listed as such. These additives can be incorporated into the foamed particles, for example, by adding them during the manufacturing process of resin particles. Several arbitrary additives will be described below.

[0046] Conductive carbon materials: Conductive materials that can be used as any additive include conductive carbon materials. The foamed layer preferably contains a conductive carbon material. Examples of conductive carbon materials include conductive carbon black, single-walled carbon nanotubes, and multi-walled carbon nanotubes. When using conductive carbon black as the conductive carbon material, it is preferable that the DBP oil absorption of the conductive carbon black, as measured according to JIS K6217-4:2008, is 150 cm³. 3 / 100g~700cm 3 / 100g, more preferably 200cm 3 / 100g~500cm 3 / 100g. Relative to 100 parts by weight of the base resin of the foamed layer, the content of conductive carbon material in the foamed layer is preferably 1 part by weight or more and 10 parts by weight or less, more preferably 1.5 parts by weight or more and 8 parts by weight or less, and even more preferably 2 parts by weight or more and 6 parts by weight or less. In other words, from the perspective of conductivity, relative to 100 parts by weight of the base resin of the foamed layer, the content of conductive carbon material in the foamed layer is preferably 1 part by weight or more, more preferably 1.5 parts by weight or more, and even more preferably 2.0 parts by weight or more. On the other hand, from the perspective of formability, relative to 100 parts by weight of the base resin of the foamed layer, the content of conductive carbon material in the foamed layer is preferably 10 parts by weight or less, more preferably 8 parts by weight or less, and even more preferably 6 parts by weight or less. In this invention, it is presumed that the viscosity of the molten mixture changes due to the influence of phosphonate compounds and NOR-type hindered amine compounds. In contrast, by including the aforementioned conductive carbon material within a specified range, a network structure of conductive carbon material can be effectively formed in the polyolefin resin, suppressing the viscosity change of the molten mixture. Therefore, the closed-cell volume percentage of the foamed particles specific to this invention can be easily achieved, and foamed particles with good molding properties can be easily obtained through in-mold molding. Furthermore, by incorporating the aforementioned conductive carbon material, the viscosity change of the resin during molten mixing is suppressed, thus making it easy to adjust the average value of the ratio of the major axis to the minor axis (major axis / minor axis) of the foamed particles to a specified range, easily obtaining near-spherical foamed particles.

[0047] Phenolic antioxidants: In this invention, it is preferred that the foaming layer contains a phenolic antioxidant. The phenolic antioxidant is an antioxidant having a phenolic structure with one or more hydroxyl groups bonded to an aromatic ring in the molecule, preferably having two or more phenolic structures in the molecule, and more preferably having three or more phenolic structures in the molecule. For example, in processes such as melt mixing of resins, at high temperatures (e.g., above 180°C), there is a tendency for the resin and additives to decompose in a short time. In contrast, by containing the phenolic antioxidant in the molten mixture comprising the resin constituting the foam layer, the decomposition of the resin and additives in a short time can be suppressed even at such high temperatures. Specific examples of the phenolic antioxidants mentioned above include 1,3,5-trimethyl-2,4,6-tris(3',5'-di-tert-butyl-4'-hydroxybenzyl)benzene, 2,6-di-tert-butyl-p-cresol, triethylene glycol bis[3-(3-tert-butyl-5-methyl-4-hydroxyphenyl)propionate], 2,2-methylene bis(4-methyl-6-tert-butylphenol), 1,6-hexanediol bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and pentaerythritol tetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]. These phenolic antioxidants can be used alone or in combination of two or more. Among these phenolic antioxidants, from the perspective of further improving flame retardancy, pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and / or 1,3,5-trimethyl-2,4,6-tris(3',5'-di-tert-butyl-4'-hydroxybenzyl)benzene are preferred, with 1,3,5-trimethyl-2,4,6-tris(3',5'-di-tert-butyl-4'-hydroxybenzyl)benzene being particularly preferred.

[0048] From the perspective of obtaining foamed granules with higher flame retardancy, the melting point TmB of the phenolic antioxidant is preferably 50°C or higher and 350°C or lower, more preferably 80°C or higher and 330°C or lower, even more preferably 100°C or higher and 320°C or lower, even more preferably 150°C or higher and 310°C or lower, and particularly preferably 200°C or higher and 300°C or lower. The melting point TmB of the phenolic antioxidant is determined according to JIS K0064:1992.

[0049] <Blending ratio of phenolic antioxidants to 100 parts by weight of base resin> From the perspective of providing a foamed granule molded body with higher flame retardancy, the amount of the phenolic antioxidant in the foamed 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 foamed layer. Furthermore, from the perspective of obtaining a foamed granule molded body with a better molding state, the amount of phenolic antioxidant in the foamed 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 foamed layer. In other words, relative to 100 parts by weight of the base resin of the foamed layer, the amount of phenolic antioxidant in the foamed layer is preferably 0.01 parts by weight or more and 0.5 parts by weight or less, more preferably 0.02 parts by weight or more and 0.3 parts by weight or less, even more preferably 0.04 parts by weight or more and 0.2 parts by weight or less, and particularly preferably 0.08 parts by weight or more and 0.15 parts by weight or less.

[0050] <The blending ratio of the phenolic antioxidant in the foam layer to the amount of NOR-type hindered amine compound> From the perspective of providing foamed particles that can be in-mold molded to exhibit higher flame retardancy while maintaining excellent formability, the ratio of the amount of the phenolic antioxidant to the amount of the NOR-type hindered amine compound is preferably 0.03 or more, more preferably 0.04 or more, further preferably 0.06 or more, and particularly preferably 0.08 or more. In other words, the ratio is the blending ratio of the phenolic antioxidant to the NOR-type hindered amine compound in the foamed layer. Furthermore, from the perspective of obtaining a foamed granule molded body with higher flame retardancy, the ratio of the blending amount is more preferably 0.9 or less, further 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 phenolic antioxidant to the amount of NOR-type 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 even more preferably 0.08 or more and 0.15 or less.

[0051] Based on the above insights, from the perspective of further fully solving the technical problems anticipated by the present invention, the foamed layer contains a phenolic antioxidant, and 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 relative to 100 parts by mass of the base resin of the foamed layer, and preferably 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 antioxidants: The foaming layer of the polyolefin resin foamed particles of the present invention preferably contains a sulfur-based antioxidant. As sulfur-based antioxidants, esters having thioether bonds in their molecules can be listed. Specific examples of esters having thioether bonds in their molecules include didodecyl-3,3'-thiodipropionate, ditridecyl-3,3'-thiodipropionate, ditetradecyl-3,3'-thiodipropionate, dioctadecyl 3,3'-thiodipropionate, pentaerythritol tetra(3-dodecyl thiopropionate), pentaerythritol tetra(3-tridecyl thiopropionate), pentaerythritol tetra(3-tetradecyl thiopropionate), and pentaerythritol tetra(3-octadecyl thiopropionate). These esters can be used alone or in combination of two or more.

[0053] <Amount of sulfur-based antioxidant relative to 100 parts by weight of base resin> From the perspective that the mechanical properties such as compressibility remain excellent even when the foamed granule molded body is placed in a high-temperature environment for a long time, the amount of sulfur-based antioxidant in the foamed layer of the foamed granules 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, relative to 100 parts by mass of the base resin of the foamed layer. Furthermore, from the perspective of obtaining a foamed granule molded body with high flame retardancy, the amount of the sulfur compound in the foamed 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, relative to 100 parts by mass of the base resin of the foamed layer. In other words, the amount of sulfur-based antioxidant incorporated relative to 100 parts by weight of the base resin of the foamed layer is preferably 0.01 parts by weight or more and 0.5 parts by weight or less, more preferably 0.04 parts by weight or more and 0.4 parts by weight or less, and even more preferably 0.06 parts by weight or more and 0.3 parts by weight or less.

[0054] <Ratio of sulfur-based antioxidants to NOR-type hindered amine compounds> From the perspective that the mechanical properties such as compressibility remain excellent even when the foamed granules are placed in a high-temperature environment for a long time, the ratio of the amount of the sulfur-based antioxidant to the amount of the NOR-type 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 perspective of obtaining a foamed granular molded body with high flame retardancy, the blending 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 blending ratio is expressed as a blending ratio of sulfur-based antioxidant / NOR-type hindered amine compound. In other words, in the foamed layer, the ratio of the amount of sulfur-based antioxidant to the amount of NOR-type 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] Based on the above insights, from the perspective of further fully solving the technical problems anticipated by the present invention, the foamed layer contains a sulfur-based antioxidant, and the amount of sulfur-based antioxidant in the foamed layer relative to 100 parts by weight of the base resin of the foamed layer is 0.01 parts by weight or more and 0.5 parts by weight or less, and the ratio of the amount of sulfur-based antioxidant to the amount of NOR-type hindered amine compound is preferably 0.03 or more and 0.9 or less.

[0056] Bubble control agent: Examples of bubble regulators include inorganic powders such as metal borates, talc, mica, calcium carbonate, borax, aluminum hydroxide, and silica; polyols such as glycerol, polyethylene glycol, and pentaerythritol; and aliphatic alcohols such as cetyl alcohol and stearyl alcohol. Preferably, metal borates such as zinc borate or magnesium borate are used as bubble regulators, and zinc borate is more preferred. The amount of bubble regulator included in the foaming layer is preferably 0.005 parts by mass or more and 0.5 parts by mass or less, more preferably 0.01 parts by mass or more and 0.2 parts by mass or less, and even more preferably 0.015 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 foaming layer. Furthermore, when zinc borate is used as the bubble regulator, its arithmetic mean particle size based on the number of particles is preferably 0.5 μm or more and 15 μm or less, more preferably 1 μm or more and 10 μm or less. The arithmetic mean particle size based on the number of particles of zinc borate is obtained by: based on the particle size distribution based on the volume standard determined by laser diffraction scattering, assuming the particle shape is spherical, converting it to the particle size distribution based on the number of particles to obtain the particle size distribution based on the number of particles, and then arithmetically averaging the particle size based on this particle size distribution. Additionally, the aforementioned particle size refers to the equivalent diameter of a sphere of equal volume.

[0057] UV absorber: Examples of ultraviolet absorbers include benzophenone compounds, benzotriazole compounds, triazine compounds, and benzoate compounds. Examples of benzophenone compounds include 2-hydroxy-4-octyloxybenzophenone. Examples of benzotriazole compounds include 2-(5-methyl-2-hydroxyphenyl)benzotriazole, 2-[2-hydroxy-3,5-bis(α,α-dimethylbenzylphenyl)]-2H-benzotriazole, 2-(3,5-di-tert-butyl-2-hydroxyphenyl)benzotriazole, 2-(3-tert-butyl-5-methyl-2-hydroxyphenyl)-5-chlorobenzotriazole, 2-(3,5-di-tert-butyl-2-hydroxyphenyl)-5-chlorobenzotriazole, 2-(3,5-di-tert-butyl-2-hydroxyphenyl)-5-chlorobenzotriazole, 2-(3,5-di-tert-pentyl-2-hydroxyphenyl)benzotriazole, and 2-(2'-hydroxy-5'-tert-octylphenyl)benzotriazole. Examples of triazine compounds 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 benzoic acid ester compounds include 2,4-di-tert-butylphenyl-3,5-di-tert-butyl-4-hydroxybenzoate and hexadecyl-3,5-di-tert-butyl-4-hydroxybenzoate. When the foamed layer contains an ultraviolet absorber, the amount of ultraviolet absorber in the foamed 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 foamed layer. In addition, the ultraviolet absorber is a compound that has the property of absorbing ultraviolet light, and it mainly absorbs light with a wavelength of 300μm to 400μm.

[0058] Light stabilizers: As light stabilizers, non-NOR type hindered amine compounds can be listed. Non-NOR type hindered amine compounds are compounds with a 2,2,6,6-tetramethyl-4-piperidineamine moiety in which only hydrogen or carbon atoms are directly bonded to the nitrogen atom. Relative to 100 parts by weight of the base resin of the foamed layer, the content of the light stabilizer in the foamed layer is preferably 0.01 parts by weight or more and 2 parts by weight or less, more preferably 0.05 parts by weight or more and 1.5 parts by weight or less, and even more preferably 0.1 parts by weight or more and 1 part by weight or less.

[0059] (Any characteristic of polyolefin resin foam particles) As described above, the foamed particles of the present invention contain phosphonate compounds and NOR-type hindered amine compounds in specific ranges and preferably further have the following characteristics. Any of the following characteristics (i.e., multilayer structure, bulk density, high temperature peak, average particle size, and average mass) will be described, and the foamed particles of the present invention preferably possess one or more of these characteristics.

[0060] Multi-layered foamed granules: The polyolefin resin foamed particles of the present invention can be single-layer foamed particles having only a granular foamed layer, or multi-layer foamed particles having a granular foamed layer as a core layer and a covering layer covering the foamed layer. The covering layer can cover the entire surface of the foamed layer or a portion of the surface of the foamed layer. In addition, the foamed layer can have through-holes. From the perspective of giving the foamed particles a coating layer so that the foamed particle molded body obtained by in-mold molding the foamed particles exhibits a higher degree of flame retardancy, or from the perspective of obtaining a foamed particle molded body with better surface properties and weldability, the foamed particles are preferably multi-layered.

[0061] In the case of multi-layered foamed particles, the mass ratio of the foamed layer to the coating layer is not particularly limited. The preferred mass ratio of the foamed layer to the coating layer is 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 high, the foamed particle molded body obtained by in-mold molding of the foamed particles with the coating layer exhibits higher flame retardancy, and it is easy to achieve the closed-cell volume percentage of the foamed particles specific to this invention, exhibiting superior surface properties and weldability. Furthermore, according to the preferred embodiment described above, it is easy to adjust the average value of the ratio of the major diameter to the minor diameter (major diameter / minor diameter) of the foamed particles to a specified range, making it easy to obtain near-spherical foamed particles.

[0062] The base resin of the coating layer can be a polyolefin resin, represented by polyethylene resin or polypropylene resin, or a resin and / or polymer other than polyolefin resin. For the base resin of the coating layer, please refer to the description of the resin used in the foamed layer described above. Furthermore, the base resin of the coating layer refers to the resin and polymer constituting the coating layer. The base resin of the coating layer can be the same as or different from the base resin of the foam layer. From the perspective of obtaining good weldability, the melting point or softening point of the base resin of the coating layer is preferably lower than that of the base resin of the foam layer. The coating layer may contain phosphonate compounds and NOR-type hindered amine compounds. From the perspective of obtaining a foamed granule molded body with good flame retardancy even with a reduced amount of flame retardant, the ratio I of the amount of phosphonate compound in the coating layer to the base resin of the coating layer of the foamed granules is preferably less than the ratio II of the amount of phosphonate compound in the foam layer to the base resin of the foam layer. That is, the ratio I is (the amount of phosphonate compound in the coating layer) / (the mass of the base resin of the coating layer), and the ratio II is (the amount of phosphonate compound in the foam layer) / (the mass of the base resin of the foam layer), and preferably the ratio I < the ratio II. Furthermore, it is more preferable that the coating layer does not contain phosphonate compound. From the perspective of obtaining a foamed granule molded body with good flame retardancy even with a reduced amount of flame retardant, the ratio III of the amount of NOR-type hindered amine compound in the coating layer to the base resin of the coating layer of the foamed granules is preferably less than the ratio IV of the amount of NOR-type hindered amine compound in the foam layer to the base resin of the foam layer. That is, the ratio III is (the amount of NOR-type hindered amine compound in the coating layer) / (the mass of the base resin of the coating layer), and the ratio IV is (the amount of NOR-type hindered amine compound in the foam layer) / (the mass of the base resin of the foam layer), and preferably the ratio III < the ratio IV. Furthermore, it is more preferable that the coating layer does not contain any NOR-type hindered amine compound. From the perspective of obtaining a foamed granule molded body with good flame retardancy even with a reduced amount of flame retardant, the preferred ratio in the foamed granules is: ratio I < ratio II, and ratio III < ratio IV.

[0063] The coating layer can be in a foamed or non-foamed state. From the perspective of improving the molding state of the foamed granules, the coating layer is preferably substantially non-foamed. Substantially non-foamed means: including the state in which the coating layer has not been foamed and does not contain air bubbles, and the state in which the air bubbles have disappeared after foaming, with almost no air bubble structure.

[0064] Bulk density of foamed granules: The bulk density of the foamed particles of the present invention is not particularly limited, but the bulk density is preferably 30 kg / m³. 3 The above, more preferably 50 kg / m 3 The above is further optimized to 70 kg / m 3 The above is further optimized to 80 kg / m 3 The above is particularly preferred, with 90 kg / m³ being the optimal value. 3 That's all. Furthermore, the bulk density of the foamed particles of the present invention is preferably 200 kg / m³. 3 The following is more preferably 180 kg / m 3 The following is a further preferred value: 150 kg / m 3 The following is particularly preferred: 130 kg / m 3 the following. In other words, the bulk density of the foamed particles of the present invention is preferably 30 kg / m³. 3 Above and 200kg / m 3 The following is more preferably 50 kg / m 3 Above and 180kg / m 3 The following is a further preferred value: 70 kg / m 3 Above and 150kg / m 3 The following is a further preferred value: 80 kg / m 3Above and 130kg / m 3 The following is particularly preferred: 90 kg / m 3 Above and 130kg / m 3 The following is a preferred method. By adjusting the bulk density of the foamed particles within the specified range, it is possible to obtain a foamed particle molded body that exhibits excellent flame retardancy, is lightweight, and also has excellent weldability.

[0065] The bulk density of foamed granules can be determined using the following method. First, the foamed granules to be tested are allowed to stand for at least 24 hours in an environment with an air temperature of 23℃, a relative humidity of 50%, and a humidity of 1 atm to allow for conditioning. Then, a mass W (g) of the conditioned foamed granules is filled into a graduated cylinder by natural stacking. The filling height of the foamed granules is stabilized by gently tapping the bottom of the graduated cylinder several times relative to a horizontal plane. The bulk volume V (L) of the foamed granules is read from the graduated cylinder scale. The mass W of the foamed granules is divided by the bulk volume V, and the units are converted to obtain the bulk density (kg / m³). 3 ).

[0066] High temperature peak: The polyolefin resin foamed particles of the present invention preferably have one or more melting peaks (high temperature peaks) on the high-temperature side of the resin-inherent melting peak (resin-inherent peak) in the DSC curve obtained by differential scanning calorimetry (DSC) measured according to JIS K7122-2012. These melting peaks can be obtained using the method described below. Specifically, using a differential scanning calorimeter (DSC), 1–3 mg of foamed particles are heated from 23 °C to 200 °C at a heating rate of 10 °C / min, and a DSC curve is obtained. The melting peak (high-temperature peak) can be confirmed from this DSC curve. Furthermore, the peak with the maximum heat of fusion is designated as the inherent melting peak of the olefin-based resin (resin-specific peak), and melting peaks appearing closer to the high-temperature side of the peak are designated as high-temperature peaks. In this case, the DSC curve refers to the DSC curve obtained by heating the foamed particles using the aforementioned measurement method. Sometimes, the DSC curve obtained by this heating is referred to as the DSC curve of the first heating. Furthermore, the resin-inherent melting peak (resin-inherent peak) refers to the endothermic peak generated by the inherent melting of the crystals of the polyolefin resin constituting the foamed particles. Additionally, the resin-inherent peak is considered to be an endothermic peak resulting from the endothermic melting of the crystals of the polyolefin resin constituting the foamed particles, which is typically present. On the other hand, the high-temperature melting peak (high-temperature peak) of the resin's inherent peak refers to an endothermic peak that appears closer to the high-temperature side than the inherent peak in the DSC curve of the first heating. The presence of this high-temperature peak suggests secondary crystallization in the resin. Furthermore, in the DSC curve obtained by heating the foamed particles from 23°C to 200°C at a heating rate of 10°C / min (first heating), cooling them from 200°C to 23°C at a cooling rate of 10°C / min, and then heating them again from 23°C to 200°C at a heating rate of 10°C / min (second heating), only the melting peak resulting from the inherent crystallization of the polyolefin resin constituting the foamed particles appears. Sometimes, the DSC curve obtained through the second heating is referred to as the second-heated DSC curve. This inherent peak appears in both the first-heated and second-heated DSC curves, and the temperature of the peak apex sometimes differs slightly between the first and second heating, but this difference is usually less than 5°C. This allows identification of which peak is the inherent peak of the resin. Furthermore, in the DSC curve obtained from the second heating process, where the temperature is increased from 23°C to 200°C at a heating rate of 10°C / min, then cooled from 200°C to 23°C at a cooling rate of 10°C / min, and then heated from 23°C to 200°C again at a heating rate of 10°C / min, the foamed particles are preferably foamed particles that exhibit only the inherent melting peak (inherent peak) in the polyolefin resin.

[0067] From the perspective of broadening the range of molding conditions that result in a good foamed particle molded body when in-mold molding of foamed particles, the melting heat of the high-temperature peak of the polyolefin resin foamed particles 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. In addition, the melting heat of the high-temperature peak can be measured by the aforementioned method, and more specifically, by the method described in the examples.

[0068] Average particle size of foamed granules: From the perspective of improving the filling performance in the molding die, the average particle size of the foamed particles is preferably 0.3 mm or more and 8 mm or less, more preferably 0.5 mm or more and 5 mm or less, and even more preferably 0.8 mm or more and 4.5 mm or less. The average particle size of the foamed particles is determined by the following method. First, based on the volumetric particle size distribution of the foamed particles, assuming the particle shape is spherical, the particle size distribution is converted to a number-based distribution, thus obtaining the number-based particle size distribution. Then, the particle size based on this number-based particle size distribution is arithmetically averaged, thereby obtaining the number-based arithmetic mean particle size. Furthermore, the particle size refers to the diameter of an imaginary sphere having the same volume as the particle. The volumetric particle size distribution of the foamed particles can be measured using a particle size distribution measuring device (e.g., the dynamic image analysis particle shape and particle size distribution measuring device and analysis software (product name: PARTAN 3D) manufactured by Microtrac BEL Co., Ltd.). The number of foamed particles used for measurement is, for example, only 2000 or more.

[0069] Average mass of foamed granules: From the same perspective, the average mass of the foamed particles 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 foamed particles can be determined by randomly selecting more than 100 foamed particles, measuring the mass [mg] of the foamed particle group, and dividing it by the number of foamed particles used for measurement.

[0070] (Manufacturing method of polyolefin resin foamed granules) The foamed particles of the present invention are polyolefin resin foamed particles, comprising polyolefin resin as the base resin, and including phosphonate ester compounds and NOR-type hindered amine compounds within a specified range. Typically, the aforementioned problems arise when polyolefin resins, phosphonates, and NOR-type hindered amine compounds are melt-blended. To prevent these problems, the key to the method for manufacturing foamed particles of the present invention lies in including the specific raw materials described above and adjusting the closed-cell volume percentage of the obtained foamed particles to a predetermined range. Any raw materials may be appropriately included. In view of the above, the method for manufacturing foamed particles of the present invention is not particularly limited. For example, the method for manufacturing foamed particles of the present invention can be modeled after manufacturing method 1 or manufacturing method 2 described above. An example of a preferred method for manufacturing foamed particles of the present invention is shown below.

[0071] A preferred method for manufacturing the foamed particles of the present invention comprises the following: a resin particle manufacturing step of producing resin particles comprising a phosphonate ester compound and a NOR-type hindered amine compound; a dispersion step of dispersing the resin particles in an aqueous dispersion medium comprising an inorganic dispersant within a pressure vessel; a foaming agent impregnation step of impregnating the resin particles with a foaming agent within a pressure vessel; and a foaming step of simultaneously releasing the resin particles containing the foaming agent and the aqueous dispersion medium from the pressure vessel to allow them to foam. These steps may be performed in this order, or one step may be repeated with part or all of the next step.

[0072] (Resin particle manufacturing process) First, a resin particle manufacturing process is performed. For the resin particles, a base resin, a phosphonate compound, a NOR-type hindered amine compound, other resins to be blended as needed, a polymer, and any additives are first supplied to an extruder, and then heated and mixed to obtain a molten mixture. This molten mixture is then extruded through a die orifice attached to the front end of the extruder, and resin particles are produced by any of the following cutting methods: wire harness pelletizing, hot-cut pelletizing, or underwater pelletizing. Furthermore, in the case of manufacturing multilayer resin particles, a manufacturing apparatus equipped with a core-forming extruder, a multilayer wire harness forming die attached downstream of the core-forming extruder, and a coating layer forming extruder can be used; specific examples can be seen in the description of Example 1 below.

[0073] The average mass of a single 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 referred to here means the sum of the average masses of individual particles obtained by measuring the mass of 100 randomly selected resin particles. Furthermore, the shape of the resin particles is not particularly limited as long as it is within the range that achieves the intended purpose of this invention. In the wire bundle pelletizing method, a cylindrical shape as determined by the naked eye is preferred. When the resin particles are cylindrical, the particle size measured in the extrusion direction is preferably 0.1 mm to 3.0 mm, more preferably 0.3 mm to 1.5 mm. Furthermore, the ratio (particle size / diameter) of the length (particle size) of the resin particles in the extrusion direction to the maximum length (diameter) in the direction perpendicular to the extrusion direction is preferably 0.5 to 5.0, more preferably 1.0 to 3.0. When this ratio is within the above range, spherical foamed particles are easily formed, which is therefore preferred.

[0074] Furthermore, as described above, by employing one or more of the following methods, the following advantages in the manufacturing process can be obtained: the method of configuring resin particles as multi-layered resin particles having a core layer and a coating layer covering the core layer; the method of mixing linear polypropylene resin, which serves as the base resin of the foaming layer, with branched polypropylene resin and / or polyethylene resin with low flowability; or the method of incorporating conductive carbon material into the foaming layer. That is, when at least one of these methods is employed, by appropriately adjusting the extrusion speed, traction speed, and cutter speed of the molten mixture during wire harness pelletizing, the particle shape of the resin particles can be effectively adjusted, and spherical foamed particles can be easily manufactured using these resin particles.

[0075] (Distributed processes) Next, a dispersion process is carried out, in which the resin particles obtained by the above method are dispersed in an aqueous dispersion medium inside a pressure vessel. The aqueous dispersion medium is a dispersion medium with water as the 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 can be 100% by mass. Other than water, the dispersion medium in the aqueous dispersion medium can include any one or more of ethylene glycol, glycerol, methanol, ethanol, etc.

[0076] In the dispersion process, a dispersant is preferably added to the aqueous dispersion medium in a manner that prevents the resin particles, which have been heated in the container, from fusing together. The dispersant only needs to prevent the resin particles from fusing together in the container. Any type of dispersant, whether organic or inorganic, can be used, but inorganic dispersants are preferred, and for ease of operation, particulate inorganic dispersants are more preferred. Examples include natural or synthetic clay minerals such as kaolin, mica, and clay; alumina; titanium dioxide; basic magnesium carbonate; basic zinc carbonate; calcium carbonate; and iron oxide. One or more of these components can be used. Natural or synthetic clay minerals are preferred as the dispersant. Preferably, the amount of dispersant added per 100 parts by weight of the resin particles is 0.001 to 5 parts by weight.

[0077] Furthermore, when using a dispersant, it is preferable to use an anionic surfactant, such as sodium dodecylbenzenesulfonate, sodium alkyl sulfonate, or sodium oleate, as a dispersing aid together with the dispersant. It is preferable to add 0.001 to 1 part by weight of the dispersing aid per 100 parts by weight of the resin particles in an aqueous dispersion medium.

[0078] (Foaming agent impregnation process) A foaming agent impregnation step is performed after or overlapping with the dispersion step. As the foaming agent used in the foaming agent impregnation step to foam the resin particles, a physical foaming agent is preferred. Examples of physical foaming agents include inorganic and organic physical foaming agents. Examples of inorganic physical foaming agents include carbon dioxide, air, nitrogen, helium, and argon. Examples of organic physical foaming agents include aliphatic hydrocarbons such as propane, n-butane, isobutane, n-pentane, isopentane, hexane, cyclopentane, and cyclohexane; and halogenated hydrocarbons such as chlorofluoromethane, trifluoromethane, 1,1-difluoroethane, 1-chloro-1,1-difluoroethane, 1,1,1,2-tetrafluoroethane, chloromethane, chloroethane, and dichloromethane. Furthermore, these physical foaming agents can be used alone or in combination. In addition, it is possible to use both inorganic and organic physical foaming agents simultaneously. From the perspective of environmental impact and further improving the flame retardancy of foamed granule molded articles, the foaming agent is preferably an inorganic physical foaming agent, and more preferably carbon dioxide.

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

[0080] As a method for impregnating resin particles with a foaming agent, the following method is preferred: after dispersing the resin particles in an aqueous dispersion medium in a pressure vessel, the foaming agent is injected into the pressure vessel, and the pressure vessel is maintained at a specified temperature and pressure, thereby impregnating the resin particles with the foaming agent.

[0081] (Foaming process) The lower limit of the pressure inside the pressure vessel during foaming (internal pressure), and the pressure inside the pressure vessel before releasing the resin particles and aqueous dispersion medium together, is preferably 0.5 MPa(G) or higher, more preferably 0.8 MPa(G) or higher. Furthermore, the upper limit is preferably 4 MPa(G) or lower, more preferably 3 MPa(G) or lower. Within these ranges, there are no concerns about pressure vessel rupture or explosion, and the desired foamed particles can be safely manufactured. After adjusting to the above pressure, the resin particles containing the foaming agent, along with the aqueous dispersion medium, are released from the pressure vessel into an atmosphere with a pressure lower than the pressure inside the pressure vessel (e.g., atmospheric pressure) to cause foaming. Furthermore, before performing the foaming process, it is preferable to raise the temperature inside the pressure vessel to 100°C or higher and 200°C or lower, more preferably to 120°C or higher and 160°C or lower, and maintain this temperature for 5 to 30 minutes. This allows the crystallization state of the resin particles to be adjusted to exhibit the aforementioned high-temperature peak.

[0082] In addition, the polyolefin resin foamed particles obtained by the above method can be further foamed by using air or the like to increase the pressure (internal pressure) inside the bubbles of the foamed layer, and then by using steam or the like to heat it (two-stage foaming) to produce foamed particles with a higher foaming ratio (lower bulk density).

[0083] (Polyolefin resin foamed granules) By using the foamed particles of the present invention manufactured as described above for in-mold molding, a foamed particle molded body of the present invention can be obtained. For example, the foamed particle molded body can be manufactured in the following manner. First, the foamed particles of the present invention are filled into a molding die having a cavity corresponding to the desired shape of the foamed particle molded body, and the foamed particles filled into the molding die are heated. The foamed particles in the cavity soften due to heating, and their surfaces melt and fuse together during secondary foaming. As a result, the foamed particles become integrated with each other, and a foamed particle molded body corresponding to the shape of the cavity is obtained. As a method for heating the foamed particles, the following methods can be exemplified: a method of introducing a heating medium such as steam into the molding die and heating the foamed particles with the heating medium; a method of irradiating the foamed particles with electromagnetic waves such as microwaves and heating the foamed particles; and a method combining the above two methods. As a method for filling the molding die with foamed particles, known methods can be used. Examples of known methods include pressure filling, compression filling, and crack filling. The pressurized filling method involves using pressurized gas to pressurize the foamed particles, imposing a specified internal pressure, and then filling them into a mold. The compression filling method involves using pressurized gas to fill the foamed particles into a pressurized mold under compression, and then releasing the pressure inside the mold. The crack filling method involves pre-opening the mold to expand the molding space before filling the mold with foamed particles, and then closing the mold after filling to physically compress the foamed particles. These filling methods can be implemented individually or in combination.

[0084] In the in-mold molding process, to improve the secondary foaming properties of the heated foamed particles, internal pressure can be applied to the foamed particles before they are filled into the molding die, and the particles are filled into the molding die while the pressure inside the bubbles of the foamed particles is increased. The pressure inside the bubbles (internal pressure) can be measured, for example, by the method described in Japanese Patent Application Publication No. 2003-201361.

[0085] The density of the foamed granule molded body of the present invention is preferably 30 kg / m³. 3 The above, more preferably 50 kg / m 3 The above is further optimized to 70 kg / m 3 The above is further optimized to 80 kg / m 3The above is particularly preferred, with 90 kg / m³ being the optimal value. 3 That's all. Furthermore, 200 kg / m³ is preferred. 3 The following is more preferably 180 kg / m 3 The following is a further preferred value: 150 kg / m 3 The following is a further preferred value: 130 kg / m 3 The following. In other words, 30 kg / m² is more preferred. 3 Above and 200kg / m 3 The following is a further preferred value: 50 kg / m 3 Above and 180kg / m 3 The following is a further preferred value: 70 kg / m 3 Above and 150kg / m 3 The following is a further preferred value: 80 kg / m 3 Above and 130kg / m 3 The following is a further preferred value: 90 kg / m 3 Above and 130kg / m 3 The foamed granule molded body described below has excellent flame retardancy, is lightweight, and also has excellent weldability, making it a preferred choice.

[0086] The foamed particle molded body formed by in-mold molding of the foamed particles of the present invention exhibits high flame retardancy, as well as excellent weldability and surface properties, and is suitable for applications requiring high flame retardancy, such as protective materials for automotive batteries or electronic devices. Example

[0087] The present invention will be described in detail below through embodiments, but the present invention is not limited thereto. Tables 1-3 show the composition, blending amount, blending ratio, foaming conditions, and molding pressure of the foamed granules used to manufacture the foamed granules of each embodiment and comparative example, and also show the evaluation results of each embodiment and comparative example. Furthermore, the tables also show the ratio of the blending amount (parts by mass) of the phenolic antioxidant in the core layer to the blending amount (parts by mass) of the NOR-type hindered amine compound, the ratio of the blending amount (parts by mass) of the sulfur-based antioxidant in the core layer to the blending amount (parts by mass) of the NOR-type hindered amine compound, the total blending amount (mass%) of the phosphonate ester compound in 100% by mass of the resin granules, and the ratio of the blending amount (mass%) of the NOR-type hindered amine compound in the resin granules to the blending amount (mass%) of the phosphonate ester compound. In addition, the table of examples should be understood to mean that the amount of each component is the same as the amount of each raw material contained in the core layer, the coating layer, and the foamed particles.

[0088] The various raw materials used in the examples and comparative examples are described below. Furthermore, in the examples and comparative examples shown below, the resins incorporated into the core layer and the coating layer are all polyolefin resins; no other resins or polymers are used. In each example and comparative example, the polyolefin resin incorporated into the core layer and the coating layer is 100 parts by weight.

[0089] (resin) • Polypropylene resin (PP1) Ethylene-propylene random copolymer (linear propylene random copolymer), melting point 143℃, density 0.900 g / cm³ 3 The ethylene content was 2.1% by mass, and the MFR (load of 2.16 kg, 230 °C, JIS K7210-1:2014) was 6 g / 10 min. • Polypropylene resin (PP2) Ethylene-propylene random copolymer (linear propylene random copolymer), melting point 133℃, density 0.900 g / cm³ 3 The ethylene content was 3.5% by mass, and the MFR (load of 2.16 kg, 230 °C, JIS K7210-1:2014) was 6 g / 10 minutes. • Polypropylene resin (PP3) Branched polypropylene, melting point 159℃, density 0.905 g / cm³ 3 The MFR (load of 2.16 kg, 230℃, JISK7210-1:2014) is 1.7 g / 10 minutes. Polyethylene-based resin (PE1) Linear low-density polyethylene has a melting point of 120℃ and a density of 0.923 cm³ / cm³. 3 The MFR (load of 2.16 kg, 190℃, JIS K7210-1:2014) is 1.5 g / 10 minutes.

[0090] (Phosphine ester compounds) Manufactured by THOR Group, product name "Aflammit PCO900", melting point 240°C, using the compound represented by the following formula (6) as a cyclic phosphonate compound. This compound is listed as a phosphonate in the table. [Chemical Formula 3]

[0091] (NOR-type hindered amine compounds) Manufactured by BASF, the product name is "Flamestab NOR116", with a molecular weight of 2261. The compound represented by the following formula (7) is used as a NOR-type hindered amine compound. This compound is listed as a NOR-type hindered amine in the table. [Chemical Formula 4]

[0092] (Phenolic antioxidants) Manufactured by BASF, the product name is "Irganox 1330", with a melting point of 245°C. The compound represented by the following formula (8) is used as a phenolic antioxidant. [Chemical Formula 5]

[0093] (Sulfur-based antioxidants) 3,3'-Dioctadecyl thiodipropionate: Manufactured by BASF, using the product name "Irganox PS802" as a sulfur-based antioxidant.

[0094] <Example 1> (Manufacturing of resin particles) A manufacturing apparatus is prepared, comprising an extruder for forming a core layer with an inner diameter of 50 mm, a multilayer wire harness forming die attached to the downstream side of the extruder for forming the core layer, and an extruder for forming a coating layer with an inner diameter of 30 mm. Furthermore, the manufacturing apparatus is configured such that the downstream side of the extruder for forming the coating layer is connected to the multilayer wire harness forming die, enabling the stacking of the molten mixture used to form each layer within the die, and simultaneously enabling co-extrusion. PP1 is used as the base resin for the core layer. As the core layer molding material constituting the core layer, in addition to the resin mentioned above, phosphonate ester compounds, NOR-type hindered amine compounds, phenolic antioxidants, sulfur-based antioxidants, and zinc borate as a bubble regulator are supplied to the extruder in the proportions shown in Table 1. These components are melt-blended to prepare a melt mixture. The core layer of the resin particles is the foamed layer of the foamed particles manufactured by the method described below. PP2 is used as the base resin for the coating layer. It is supplied to an extruder for coating layer formation and melt-mixed to prepare a melt mixture. The molten mixture for forming each layer, obtained by melt mixing as described above, is introduced into a mold for forming a multilayer wire harness, where it merges within the mold. Then, a multilayer wire harness with a double-layer structure (coating layer / core layer) having a core layer and a coating layer covering the side circumferential surface of the core layer is extruded through a 2mm circular orifice in a die head mounted on the downstream side of the mold. While pulling the extruded multilayer wire harness, it is water-cooled in a water bath and cut into resin particles of 2mm length using a granulator to obtain resin particles with an average individual mass of 1.0mg.

[0095] (Manufacturing of foamed granules) 2 kg of resin particles obtained by the above method and 75 L of water as an aqueous dispersion medium were supplied into a pressure vessel with a capacity of 100 L. 65 g of kaolin as an inorganic dispersant and 43 g (based on active ingredient) of surfactant (product name: NEOGEN, manufactured by DKS Co. Ltd., sodium dodecylbenzenesulfonate) were added to the pressure vessel. Next, carbon dioxide, used as a foaming agent, was injected into the pressure vessel, pressurizing it to 0.5 MPa (G) on a gauge. (G) is a gauge pressure, meaning it is based on atmospheric pressure. Then, while stirring inside the pressure vessel, the temperature was increased at a rate of 2°C / min to the foaming temperature shown in Table 1, 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 process was adjusted until a high-temperature peak appeared in the endothermic curve obtained by DSC measurement of the resulting foamed particles. Then, the resin particles and aqueous dispersion medium, which are the contents of the pressure vessel, are released at atmospheric pressure, causing the core layer to foam, resulting in multi-layered foamed particles with a foamed layer and a non-foamed coating layer covering the foamed layer. The foaming pressure inside the pressure vessel shortly before foaming is shown in Table 1. The obtained foamed granules were placed in an oven at 80℃ for at least 24 hours to ensure thorough drying. The moisture content of the dried foamed granules was then measured. The moisture content was determined by weighing 200 cm³ of the dried foamed granules after placing them at room temperature for 30 minutes. 3 The dried foamed granule group was then weighed. Next, the foamed granule group, after weight measurement, was further heated in an oven at 150°C for 1 hour, and the weight of the heated foamed granule group was measured. The weight of the foamed granule group before heating was subtracted from the weight after heating, and the difference in weight obtained in this manner was divided by the weight of the heated foamed granule group to calculate a percentage. In this embodiment, the measured moisture content was 0.8%.

[0096] (Manufacturing of foamed granule molded bodies) Dried, unpressurized foamed granules are compressed and filled into a molding die with a molding cavity capable of forming a flat body with a length of 400 mm × width of 300 mm × height of 30 mm. A metal mold is used as the molding die. Compression filling is a filling method in which foamed granules are filled into the molding die under pressure. Then, steam is supplied into the molding die to heat the foamed granules, thereby obtaining a flat foamed granule molded body. The heating using steam is carried out as follows: First, with the drain valves provided on both sides of the molding die open, steam is supplied to the molding die for preheating (venting process). Then, steam is supplied from one side of the molding die for heating, and further steam is supplied from the other side of the molding die for heating. Next, steam is supplied from both sides of the molding die for heating until the molding pressure in the molding die is reached as described in Table 1. After heating, the pressure is released and water cooling is performed until the pressure generated on the molding surface of the molding die is 0.04 MPa (G), and then the molding die is opened and the foamed granule molded body is removed. After curing the obtained molded body in an oven at 80°C for 12 hours, it was slowly cooled to room temperature. The foamed granule molded body was obtained.

[0097] <Examples 2-8> Except for the changes shown in Tables 1 and 2, the foamed granules and the foamed granule molded body are manufactured in the same manner as in Example 1.

[0098] <Examples 9, 10, Comparative Examples 1, 5, 6> An extruder with an inner diameter of 50 mm and a wire harness forming die attached to the outlet side was prepared. Polyolefin resin, phosphonate compound, NOR-type hindered amine compound, phenolic antioxidant, sulfur-based antioxidant, and bubble regulator were fed into the extruder in the blending amounts shown in Tables 2 and 3. These components were melt-blended to form a melt mixture. In Example 9, 80 parts by weight of PP1 and 20 parts by weight of PE1 were used as 100 parts by weight of polyolefin resin. Furthermore, in Example 10, 80 parts by weight of PP1 and 20 parts by weight of PP3 were used as 100 parts by weight of polyolefin resin. The molten mixture is extruded into a wire bundle shape using a wire bundle forming die, cooled with water, and cut using a granulator to obtain resin particles with an average individual mass of 1.0 mg. Using the resin particles obtained in the above manner, except for the contents shown in Tables 2 and 3, the foamed particles and the foamed particle molded body are manufactured in the same way as the manufacturing method of the foamed particles and the foamed particle molded body of Example 1.

[0099] <Comparative Examples 2-4> Except for the changes shown in Table 3, the foamed particles were manufactured using the same method as the foamed particles of Comparative Example 1. Next, except that the pressure inside the bubbles of the foamed particles obtained by the above method was increased to 0.1 MPa (G) and then compressed and filled, and molding was performed under the conditions shown in Table 3, the foamed particle molded body was manufactured in the same way as the manufacturing method of the foamed particle molded body of Example 1. <Example 11> In addition to using 3 parts by weight of oil furnace black (product name: Ketjen Black (registered trademark) EC300J (manufactured by Lion Specialty Chemicals Co., Ltd.) as conductive carbon material relative to 100 parts by weight of resin, the DBP absorption is 360 cm⁻¹. 3 / 100g, particle size: 40nm) except for the contents of Table 2, the foamed particles and the foamed particle molded body are manufactured in the same manner as in Example 9.

[0100] The resin particles, foamed particles, and foamed particle molded articles obtained by the above method are measured or evaluated as described below, and the results are shown in Tables 1 to 3.

[0101] <Average value of the ratio of the major axis to the minor axis of the resin particle cross-section> The resin particle is cut in a direction perpendicular to the extrusion direction during manufacturing, passing through its center to form a cross-section. Using a microscope, the major diameter and the minor diameter shown in a direction perpendicular to the major diameter and passing through the center are measured in this cross-section. This measurement is performed on 20 resin particles, and the ratio of the major diameter to the minor diameter of the cross-section for each particle is calculated and then arithmetically averaged to obtain the average value of the ratio of the major diameter to the minor diameter of the cross-section for each resin particle.

[0102] <Heat of fusion at the high temperature peak of foamed particles> The heat of fusion at the high-temperature peak of the foamed particles was determined using differential scanning calorimetry (DSC) based on JIS K7122-2012. Specifically, approximately 2 mg of foamed particles were taken and measured using a differential scanning calorimeter (DSC7020 manufactured by Hitachi High-TechScience Corporation) at a temperature increase of 10 °C / min from 23 °C to 200 °C, resulting in a DSC curve with two or more melting peaks. The inherent resin peak described below is designated as A, and the high-temperature peak appearing closer to the high-temperature side than peak A is designated as B. Connect point α on the DSC curve, corresponding to 80°C, with point β on the DSC curve, corresponding to the melt termination temperature T of the foamed particles, and draw a straight line (α-β). Here, the melt termination temperature T refers to the endpoint of the high-temperature side of high-temperature peak B, specifically the intersection of high-temperature peak B and the high-temperature side baseline. Next, draw a straight line parallel to the vertical axis of the graph from point γ on the DSC curve, located in the valley between the aforementioned resin intrinsic peak A and high-temperature peak B. The point where this line intersects the straight line (α-β) is designated as δ. The area of ​​high-temperature peak B is the area enclosed by the curve, the line segment (δ-β), and the line segment (γ-δ) of the high-temperature peak portion of the DSC curve; this area is taken as the melting heat of the high-temperature peak.

[0103] <Bulk density of foamed particles> As mentioned earlier, after the foamed granules have been cured, a mass W (g) of foamed granules is filled into a graduated cylinder by natural stacking. The cylinder is then tapped gently several times relative to a horizontal plane to stabilize the filling height. The accumulated volume V (L) of the foamed granules is read from the graduated cylinder scale. The mass W of the foamed granules is divided by the accumulated volume V (W / V), and the units are converted to [kg / m³]. 3 From this, the bulk density (kg / m³) of the foaming particles can be calculated. 3 ).

[0104] <Percentage of closed-cell volume in foamed particles> By accumulating a volume of approximately 20cm 3 The foamed particle assembly was immersed in water, and its apparent volume Va was measured. Then, after thoroughly drying the foamed particle assembly with the measured apparent volume Va, the true volume Vx of the foamed particles was measured, based on step C as described in ASTM D2856-70. Here, the true volume Vx of the foamed particles refers to the sum of the volume of the resin constituting the foamed particles and the total volume of the individual air bubbles within the foamed particles. The true volume Vx was measured using an air comparative hydrometer (manufactured by Toshiba Beckman Co., Ltd., air comparative hydrometer "930"). Next, the closed-cell volume percentage was calculated using the following formula (1). Using different test samples, the closed-cell volume percentage was measured five times using the same procedure as described above. The arithmetic mean of the values ​​obtained from each measurement was calculated and used as the closed-cell volume percentage of the foamed particles. [Mathematical Expression 2] Closed-cell volume percentage (%) = (Vx - W / ρ) × 100 / (Va - W / ρ) ···(1) Vx: The true volume (cm³) of the foamed granule group determined by the above method. 3 ) Va: Apparent volume of the foamed particle assembly (cm³) measured from the rise in water level when the foamed particle assembly is submerged in a graduated cylinder. 3 ) W: Mass of the foamed granule group (g) ρ: Density of the resin constituting the foamed particles (g / cm³) 3 )

[0105] <Average of the major diameter of the foamed particle / Average of the minor diameter of the foamed particle> The measurement and analysis were performed using a dynamic image analysis particle shape and size distribution measuring device and analysis software (product name: PARTAN 3D, software version: 7.1.3.80) manufactured by Microtrac BEL Co., Ltd. Approximately 2000 of the foamed particles obtained above were fed into the device as samples for stereoscopic image analysis. The major and minor diameters of individual foamed particles were measured, and the ratio of the major diameter to the minor diameter of the foamed particle was calculated. The major diameter of an individual foamed particle is defined as the maximum value of the diameter with the largest distance between the two parallel lines holding the individual particle, as determined by image analysis. The minor diameter of an individual foamed particle is defined as the minimum value of the diameter with the smallest distance between the two parallel lines holding the individual particle, as determined by image analysis. The arithmetic mean of the ratios for each supplied foamed particle was taken as the average value of the major diameter / minor diameter of the foamed particle. In the measurement method using this measuring device, the major diameter of the foamed particle corresponds to the Feret Length, and the minor diameter of the foamed particle corresponds to the Feret Thickness.

[0106] <Density of foamed granules> The density (kg / m³) of the foamed granule molded body is calculated by dividing the mass of the obtained foamed granule molded body by the volume calculated based on its dimensions. 3 ).

[0107] <Evaluation of the weldability of foamed granule molded bodies> The foamed granule molded body is bent to break, and the number of foamed granules present on the fracture surface (C1) and the number of broken foamed granules (C2) are counted. The ratio of the number of broken foamed granules to the number of foamed granules present on the fracture surface [(C2 / C1)×100] is calculated as the material failure rate. Five measurements were performed using different test pieces. The material failure rate was calculated for each measurement, and the arithmetic mean was determined. This arithmetic mean was then evaluated according to the following evaluation criteria. A higher material failure rate indicates better weldability. A: The material failure rate is over 70%. B: The material failure rate is above 50% but less than 70%. C: Material failure rate is less than 50%.

[0108] <Surface property evaluation of foamed granule molded bodies> As an evaluation of the surface appearance, a 100mm × 100mm area was cut from the center of the foamed granule molded body as a test piece. A line was drawn along the diagonal from the corner of the test piece, and the number of voids (gap) along the diagonal was counted. 2 The quantity of items larger than or equal to the specified size shall be evaluated as follows. Good: Fewer than 10 gaps Bad: More than 10 voids

[0109] <Flame retardancy evaluation of foamed granule molded bodies> UL94V test (judgment): The flame retardancy of foamed granular molded bodies is evaluated based on the results of a vertical burning test (20mm vertical burning test) according to UL94 standard. The specific test method is described below. (Preparation of the test sample) Five test pieces were cut from the vicinity of the center of the foamed granule molded body, with dimensions of 125 mm longitudinally, 13 mm transversely, and 13 mm thick, so that all surfaces of the test pieces were cut. (Experimental Methods) The upper part of the test piece was fixed using a clamp to keep it vertical in the longitudinal direction, and degreased cotton was placed underneath it. A blowtorch was applied to the lower end of the test piece for 10 seconds, then the blowtorch was moved away from the test piece, and the burning time (first burning time) was measured. The same process was repeated, applying the blowtorch for another 10 seconds and then moving the blowtorch away again to measure the burning time (second burning time) and the red-hot time (second red-hot time). This test was performed on each of the five test pieces to evaluate the flame retardancy of the foamed granular molded body. The burning time here refers to the duration during which the flame is visible to the naked eye on the test piece. "Burning" refers to the state where the flame is visible to the naked eye due to the combustion of gases on and near the surface of the test piece. Furthermore, the red-hot time refers to the duration during which the test piece remains red-hot after the flame is no longer visible to the naked eye. "Red-hot" refers to the state where only the surface of the test piece burns, and although the flame is not visible, the red-hot state of the test piece surface is visible to the naked eye. (Evaluation Criteria) Five test pieces of each molded body were subjected to the aforementioned tests five times, and evaluated according to the UL94 standard V-0, V-1, and V-2 criteria. Furthermore, if any part did not meet the UL94 standard V-0, V-1, or V-2 criteria, it was deemed unqualified. Additionally, for flame retardancy evaluation, the order V-0, V-1, and V-2 represents the degree of flame retardancy. If a test piece met both the V-0 and V-1 evaluation criteria, it was judged as having a V-0 rating; if it only met the V-1 criterion, it was judged as having a V-1 rating. V-0: The first and second combustion times for each test batch were both less than 10 seconds, and The sum of the first and second combustion times of each test batch, i.e., the sum of the 10 combustion times, is less than 50 seconds, and The sum of the second combustion time and the second red-hot time for each test batch was less than 30 seconds, and There were no test batches where the test piece burned to the fixing fixture, and There were no test batches where the degreased cotton placed at the bottom of the test piece dripped and caused combustion due to the burning of the test piece. V-1: The first and second combustion times for each test batch were each less than 30 seconds, and The sum of the first and second combustion times of each test batch, i.e., the sum of the 10 combustion times, is less than 250 seconds, and The total second combustion time and second red-hot time for each test batch were each less than 60 seconds, and There were no test batches where the test piece burned to the fixing fixture, and There were no test batches where the degreased cotton placed at the bottom of the test piece dripped and caused combustion due to the burning of the test piece. V-2: The first and second combustion times for each test batch were each less than 30 seconds, and The sum of the first and second combustion times of each test batch, i.e., the sum of the 10 combustion times, is less than 250 seconds, and The total second combustion time and second red-hot time for each test batch were each less than 60 seconds, and There were no test batches where the test piece burned to the fixing fixture, and There were test batches where the degreased cotton placed at the bottom of the test piece dripped and caused combustion due to the burning of the test piece.

[0110] [Table 1]

[0111] [Table 2]

[0112] [Table 3]

[0113] The present invention described above includes the following technical concept. (1) A polyolefin resin foamed granule, comprising a foamed layer, wherein, The substrate resin of the foamed layer is composed of a polyolefin resin, and the foamed layer contains phosphonate compounds and NOR-type hindered amine compounds. Relative to 100 parts by weight of the base resin, the amount of phosphonate compound in the foamed layer is 5 parts by weight or more and 25 parts by weight or less; and relative to 100 parts by weight of the base resin, the amount of NOR-type hindered amine compound in the foamed layer is 0.3 parts by weight or more and 5 parts by weight or less. The closed-cell volume percentage of the foamed particles is 60% or more. (2) The polyolefin resin foamed particles according to (1) above, wherein the average value of the ratio of the major diameter to the minor diameter (major diameter / minor diameter) of the foamed particles is 1.0 or more and 2.0 or less. (3) The polyolefin resin foamed particles according to (1) or (2) above, wherein the foamed particles have 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) Polyolefin resin foamed particles according to any one of (1) to (3) above, wherein, in the foamed layer, the ratio of the amount of NOR-type hindered amine compound to the amount of phosphonate compound is 0.04 or more and 0.4 or less. (5) Polyolefin resin foamed particles according to any one of (1) to (4) above, wherein the substrate resin of the foamed layer is composed of linear polypropylene resin (A), branched polypropylene resin (B) with a melt tension of 50 mN or more as measured at 230°C, and / or polyethylene resin (C) with an MFR of 3 g / 10 min or less as measured at 190°C and under a load of 2.16 kg. The total content of the linear polypropylene resin (A), the branched polypropylene resin (B), and the polyethylene resin (C) is 100% by mass, 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. (6) The polyolefin resin foamed particles according to any one of (1) to (5) above, wherein the foamed layer comprises a conductive carbon material, and the amount of conductive carbon material in the foamed layer is more than 1 part by mass and less than 10 parts by mass relative to 100 parts by mass of the base resin. (7) Polyolefin resin foamed particles according to any one of (1) to (6) above, wherein, In the foamed layer, the foamed layer contains a phenolic antioxidant, and the amount of the phenolic antioxidant in the foamed layer is 0.01 parts by weight or more and 0.5 parts by weight or less relative to 100 parts by weight of the base resin of the foamed layer. 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. (8) Polyolefin resin foamed particles according to any one of (1) to (7) above, wherein, The foamed layer contains a sulfur-based antioxidant, and the amount of the sulfur-based antioxidant in the foamed layer is more than 0.01 parts by weight and less than 0.5 parts by weight relative to 100 parts by weight of the base resin of the foamed layer. In the foamed layer, 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. (9) A foamed granule molded body, wherein it is formed by in-mold molding of polyolefin resin foamed granules as described in any one of (1) to (8) above.

Claims

1. A polyolefin resin foamed granule, comprising a foamed layer, wherein, The substrate resin of the foamed layer is composed of a polyolefin resin, and the foamed layer contains phosphonate compounds and NOR-type hindered amine compounds. Relative to 100 parts by weight of the base resin, the amount of phosphonate compound in the foamed layer is 5 parts by weight or more and 25 parts by weight or less; and relative to 100 parts by weight of the base resin, the amount of NOR-type hindered amine compound in the foamed layer is 0.3 parts by weight or more and 5 parts by weight or less. The closed-cell volume percentage of the foamed particles is 60% or more.

2. The polyolefin resin foamed granules according to claim 1, wherein, The average ratio of the major diameter to the minor diameter (major diameter / minor diameter) of the foamed particles is greater than 1.0 and less than 2.

0.

3. The polyolefin resin foamed granules according to claim 1 or 2, wherein, The foamed particles have 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. The polyolefin resin foamed granules 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 compound is 0.04 or more and 0.4 or less.

5. The polyolefin resin foamed granules according to any one of claims 1 to 4, wherein, The base resin of the foamed layer is composed of linear polypropylene resin (A), branched polypropylene resin (B) with a melt tension of 50 mN or more as measured at 230°C, and / or polyethylene resin (C) with an MFR of 3 g / 10 min or less as measured at 190°C and under a load of 2.16 kg. The total content of the linear polypropylene resin (A), the branched polypropylene resin (B), and the polyethylene resin (C) is 100% by mass, 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.

6. The polyolefin resin foamed granules according to any one of claims 1 to 5, wherein, The foamed layer contains conductive carbon material, and the amount of conductive carbon material in the foamed layer is more than 1 part by mass and less than 10 parts by mass relative to 100 parts by mass of the base resin.

7. The polyolefin resin foamed granules according to any one of claims 1 to 6, wherein, The foamed layer contains a phenolic antioxidant, and the amount of the phenolic antioxidant in the foamed layer is more than 0.01 parts by weight and less than 0.5 parts by weight relative to 100 parts by weight of the base resin of the foamed layer. In the foamed layer, 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.

8. The polyolefin resin foamed granules according to any one of claims 1 to 7, wherein, The foamed layer contains a sulfur-based antioxidant, and the amount of the sulfur-based antioxidant in the foamed layer is more than 0.01 parts by weight and less than 0.5 parts by weight relative to 100 parts by weight of the base resin of the foamed layer. In the foamed layer, 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.

9. A foamed granule molded body, which is formed by in-mold molding of polyolefin resin foamed granules according to any one of claims 1 to 8.

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