Polyolefin-based resin foam particles

Abstract

To provide polyolefin-based resin foam particles which facilitate in-mold molding of a polyolefin-based resin foam particle molding that exhibits high flame retardancy and is excellent in fusion property and surface property.SOLUTION: Polyolefin-based resin foam particles have a foam layer, wherein the foam layer contains a base material resin, a phosphonate-based compound and an NOR type hindered amine-based compound, the base material resin is composed of a polyolefin-based resin, a blended amount of the phosphonate-based compound in the foam layer is 5 pts.mass or more and 25 pts.mass or less with respect to 100 pts.mass of the base material resin, a blended amount of the NOR type hindered amine-based compound in the foam layer is 0.3 pts.mass or more and 5 pts.mass or less with respect to 100 pts.mass of the base material resin, and an isolated cell ratio of the foam particles is 60% or more.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to flame-retardant polyolefin-based resin foam particles.

Background Art

[0002] Polyolefin-based resin foam particles are widely used as materials for molding polyolefin-based resin foam particle molded bodies in a mold. The polyolefin-based resin foam particle molded body is used in various applications such as, for example, packaging materials, vehicle members, and building materials. In particular, from the viewpoints of excellent light weight, impact resistance, energy absorption characteristics, etc., the polyolefin-based resin foam particle molded body is suitable as vehicle members such as automobile bumpers and seat core materials.

[0003] Conventionally, the above vehicle members are sometimes required to meet standards such as FMVSS302 (Federal Motor Vehicle Safety Standard No. 302). However, recently, with the spread of electric vehicles, etc., in addition to a slow burning rate, higher-level flame retardancy such as self-extinguishing properties may be required.

[0004] For example, Patent Document 1 proposes polypropylene-based resin foam particles (hereinafter also referred to as Prior Art 1) containing a polypropylene-based resin, an organic phosphorus compound, and a hindered amine within a predetermined range. Further, Patent Document 2 proposes polyolefin-based resin pre-foam particles (hereinafter also referred to as Prior Art 2) containing a specific organic phosphorus compound and a specific hindered amine within a predetermined range. Both Patent Documents 1 and 2 describe that by using the proposed foam particles, a foam particle molded body excellent in flame retardancy can be provided.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] However, as a result of the studies by the present inventors, it has become clear that the prior arts 1 and 2 have the following problems. That is, although the prior arts 1 and 2 both show improved flame retardancy by containing an organophosphorus compound and a hindered amine within a predetermined range, when producing a foamed particle molded body by in-mold molding, the fusing property between the foamed particles becomes insufficient, and there may occur a problem that the surface property of the produced foamed particle molded body becomes insufficient. Incidentally, hereinafter, the fusing property and the surface property in the foamed particle molded body may be collectively referred to as the "molding state".

[0007] The present invention has been made in view of the above problems. That is, the present invention provides polyolefin-based resin foamed particles that exhibit high flame retardancy and are easily moldable in a mold, and a polyolefin-based resin foamed particle molded body having excellent molding state. [Means for Solving the Problems]

[0008] The polyolefin-based resin foamed particles of the present invention are polyolefin-based resin foamed particles having a foamed layer, wherein the base resin of the foamed layer is composed of a polyolefin-based resin, the foamed layer contains a phosphonate-based compound and a NOR type hindered amine-based compound, the blending amount of the phosphonate-based compound in the foamed layer is 5 parts by mass or more and 25 parts by mass or less with respect to 100 parts by mass of the base resin, the blending amount of the NOR type hindered amine-based compound in the foamed layer is 0.3 parts by mass or more and 5 parts by mass or less with respect to 100 parts by mass of the resin, and the closed cell ratio of the foamed particles is 60% or more. Alternatively, the polyolefin-based resin foamed particle molded body of the invention is characterized by being constituted by in-mold molding of the polyolefin-based resin foamed particles of the present invention.

Advantages of the Invention

[0009] The present invention can provide polyolefin-based resin foam particles capable of producing a polyolefin-based resin foam particle molded body that exhibits high flame retardancy and excellent molding state. Further, the polyolefin-based resin foam particle molded body of the present invention exhibits high flame retardancy and is excellent in molding states such as fusion bonding properties and surface properties.

Modes for Carrying Out the Invention

[0010] The polyolefin-based resin foam particles of the present invention will be described below. In the following description, the polyolefin-based resin foam particles of the present invention may be referred to as the foam particles of the present invention or simply foam particles, and the molding of the polyolefin-based resin foam particles of the present invention may be referred to as the foam particle molded body of the present invention or simply the foam particle molded body. In addition, in the following description, the preferable numerical ranges of the present invention may be shown as appropriate. Moreover, the high flame retardancy in the present invention means not only a slow burning rate but also self-extinguishing properties. In the present invention, self-extinguishing properties are evaluated according to the criteria of V-0, V-1, or V-2 in a test based on UL94 (Underwriters Laboratories 94). A foam particle molded body that exhibits excellent flame retardancy in the test based on the above standard is excellent not only in having a slow burning rate but also in showing self-extinguishing properties. A foam particle molded body showing self-extinguishing properties also shows relatively good flame retardancy when tests based on other standards are conducted. Therefore, the foam particles constituting such a foam particle molded body showing such high flame retardancy and the foam particle molded body have a wide range of applicable uses.

[0011] The foam particles of the present invention are provided with a foam layer, and the base resin of the foam layer is composed of a polyolefin-based resin. The foam layer contains a phosphonate ester-based compound and a NOR type hindered amine-based compound. Thereby, it is possible to impart desired flame retardancy to the foam particles and a foam particle molded body formed by molding the foam particles in a mold. The compounding amount of the phosphonate compound in the foamed layer is 5 parts by mass or more and 25 parts by mass or less with respect to 100 parts by mass of the base resin. Further, the compounding amount of the NOR type hindered amine compound in the foamed layer is 0.3 parts by mass or more and 5 parts by mass or less with respect to 100 parts by mass of the base resin. The closed cell ratio of the foamed particles of the present invention having the above configuration is 60% or more. Examples of methods for adjusting the closed cell ratio to such a preferable range will be described later.

[0012] The present inventors have intensively studied to provide foamed particles that can be molded in a mold and have a foamed particle molded body with improved formability while exhibiting high flame retardancy. And the present inventors have found that foamed particles containing a phosphonate compound and a NOR type hindered amine compound within a predetermined range and having a closed cell ratio of 60% or more can solve the intended problems, leading to the provision of the present invention. The causal relationship between the closed cell ratio and the occurrence of the problem of deterioration of the formability described above is not clear, but it is presumed as follows.

[0013] First, generally, there are roughly two methods for producing foamed particles containing a polyolefin resin, a phosphonate compound, and a NOR type hindered amine compound. One is a method in which the above-mentioned raw materials are melt-mixed, a foaming agent is further supplied and then extruded to form a foam, and then the foam is cut to obtain foamed particles of a predetermined size. Such a method may be referred to as Production Method 1 in the following. The other is a method in which resin particles of a predetermined size are produced by extruding and cutting the melt mixture obtained by melt-mixing the above-mentioned raw materials, and the resin particles are foamed to obtain foamed particles. Such a method may be referred to as Production Method 2 in the following. In both of the two methods of Production Methods 1 and 2, the step of melt-mixing the above-mentioned raw materials is included in the extruder. In a series of steps like these, compared to the case where a phosphonate compound and a NOR type hindered amine compound are not used, a molten mixture obtained by melt-mixing a polyolefin resin, a phosphonate compound, and a NOR type hindered amine compound is likely to experience a change in viscosity and an increase in hygroscopicity. More specifically, it is presumed that when a polyolefin resin and a phosphonate compound are melt-mixed, the hygroscopicity of the molten mixture containing the phosphonate compound increases. Also, when a polyolefin resin and a NOR type hindered amine compound are melt-mixed, free radicals derived from the NOR type hindered amine compound are generated, and the action of these free radicals is thought to promote the deterioration of the polyolefin resin, resulting in a change in the viscosity of the polyolefin resin. Then, it is presumed that the viscosity of the molten mixture containing the polyolefin resin with a changed viscosity also changes. By using such a molten mixture in which an unintended increase in hygroscopicity and a change in viscosity occur, it is presumed that it becomes difficult to form bubbles and bubble films during foaming, and the closed cell ratio of the obtained foamed particles decreases. As a result, it is presumed that the fusion property between the foamed particles during in-mold forming decreases, and the formed state of the obtained foamed particle molded body becomes insufficient.

[0014] The closed cell ratio of the foamed particles of the present invention is 60% or more, preferably 65% or more, more preferably 70% or more, still more preferably 75% or more, and particularly preferably 80% or more. When the closed cell ratio of the foamed particles is high, there is a tendency that a foamed particle molded body with a good formed state can be easily formed in a mold. In particular, the foamed particles of the present invention with a closed cell ratio of 75% or more exhibit excellent fusion property in a foamed particle molded body formed in a mold using them.

[0015] Regarding the present invention, the closed cell ratio is measured by the following method. First, the bulk volume is about 20 cm 3The apparent volume Va of the foamed particle group is measured by immersing the foamed particle group in water. Next, after sufficiently drying the foamed particle group whose apparent volume Va has been measured, the true volume Vx of the foamed particles is measured in accordance with Procedure C 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 bubble volume of the independent bubble portions in the foamed particles. An air comparison type pycnometer is used to measure this true volume Vx. As an example of a commercially available air comparison type pycnometer, the air comparison type pycnometer "930" manufactured by Toshiba Beckman Co., Ltd. can be mentioned. Next, the closed cell ratio is calculated by the following formula (1). Using different measurement samples, the closed cell ratio is measured 5 times in the same procedure as described above, and the arithmetic mean value of the values obtained in each measurement is obtained and taken as the closed cell ratio of the foamed particles. [Equation 1] Closed cell ratio (%) = (Vx - W / ρ) × 100 / (Va - W / ρ) ··· (1) Vx: True volume of the foamed particle group measured by the above method (cm 3 ) Va: Apparent volume of the foamed particle group measured from the rise in the water level when the foamed particle group is submerged in water in a graduated cylinder (cm 3 ) W: Mass of the foamed particle group (g) ρ: Density of the resin constituting the foamed particles (g / cm 3 )

[0016] The foamed particles containing the flame retardant of the present invention are preferably substantially spherical. Foamed particles containing a phosphonate ester compound and a NOR type hindered amine compound as the flame retardant tend to be flat. From the viewpoint of being able to mold a foamed particle molded body with a good molding state in a mold, having good fillability into the mold, and excellent storage stability, the average of the ratio of the major axis to the minor axis (major axis / minor axis) 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 fusibility can be provided. Examples of means for adjusting the (major axis / minor axis) to a preferable range will be described later. Regarding the present invention, the closer the average value of the ratio (major axis / minor axis) is to 1.0, the more substantially spherical the appearance of the foamed particles is, and the larger the average value of the ratio is, the flatter the appearance of the foamed particles is. In addition, regarding the foamed particles of the present invention, substantially spherical and flat mean the outer shape of the foamed particles observed visually.

[0017] In addition, the major axis and minor axis of the foamed particles described above are measured using an image analysis type particle size distribution measuring device. More specifically, using the above measuring device, the foamed particles are allowed to fall freely in the device, and a plurality of images of the foamed particles during free fall are obtained by performing high-speed imaging of the freely falling foamed particles with a camera. From a plurality of images of the foamed particles during free fall obtained by the high-speed imaging, a plurality of images of the same foamed particle taken in different imaging directions are extracted. In a plurality of images of the same foamed particle taken in different imaging directions, the length of the maximum value and the minimum value of the distance between two parallel lines sandwiching the foamed particle are measured by image analysis. After determining the length of the maximum value of the distance between the two parallel lines and the length of the minimum diameter as the major axis and minor axis, respectively, for one foamed particle, the ratio of the major axis to the minor axis of the foamed particle is calculated. Then, the ratio for each of the plurality of foamed particles is obtained, and the arithmetic mean value of each ratio is calculated, whereby the average value of the ratio of the major axis to the minor axis (major axis / minor axis) of the foamed particles can be calculated. Examples of the image analysis type particle distribution measuring device include, for example, a dynamic image analysis type particle shape and particle size distribution measuring device and analysis software (trade name: PARTAN 3D) manufactured by Microtrac Bell Co., Ltd.

[0018] The reason why the foamed particles containing the phosphonate ester compound and the NOR type hindered amine compound tend to be flat is not clear, but it is presumed as follows. When obtaining foamed particles by producing and foaming resin particles, the resin particles can be produced as follows. That is, generally, after a raw material such as a resin is supplied to an extruder and melt-mixed, a strand-like molten mixture is extruded from a circular pore and cut to a predetermined length while being drawn in the extrusion direction and intersecting the extrusion direction, whereby pellet-shaped resin particles having a circular cut surface are produced. The resin particles produced in a state where a force is applied in the extrusion direction, after being extruded from the high-temperature extruder, are rapidly cooled, so that the stress against the force applied in the extrusion direction remains inside the resin particles. Therefore, such resin particles tend to expand in a direction intersecting the extrusion direction rather than in the extrusion direction during foaming. Therefore, when cutting the molten mixture extruded from the extruder, the stress inside the resin particles and the length of the resin particles on the extrusion direction side can be adjusted by adjusting the take-up speed and the cut width. By foaming the resin particles obtained by the above adjustment, substantially spherical foamed particles can be obtained. On the other hand, when producing resin particles using a phosphonate ester compound and a NOR type hindered amine compound together with a polyolefin resin, the strand-like molten mixture extruded from the extruder tends to contract in a direction perpendicular to the extrusion direction. The pellet-shaped resin particles produced by cutting in such a contracted state tend to be flat. Further, when the flat resin particles are foamed, the foamed particles tend to be flat. As described above, it is presumed that the flat foamed particles are generated by being affected by an unintended viscosity change and an increase in hygroscopicity of the molten mixture in the process of manufacturing the resin particles.

[0019] In the foamed layer of the present invention, the base resin is composed of a polyolefin resin and contains a phosphonate compound and a NOR type hindered amine compound. In other words, the foamed layer of the present invention is composed of a base resin, and the base resin is a polyolefin resin. The foamed layer may further optionally contain other resins as long as the objects and effects of the present invention are not inhibited. Further, the foamed layer may contain any additives used in the production of foamed particles in addition to the resin, the phosphonate compound, and the NOR type hindered amine compound.

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

[0021] The base resin is contained in an amount exceeding 50% by mass, preferably exceeding 70% by mass, more preferably exceeding 80% by mass, still more preferably exceeding 90% by mass, even more preferably exceeding 95% by mass, and particularly preferably 100% by mass based on 100% by mass of the resin and polymer constituting the foamed layer. From the viewpoint of obtaining a foamed particle molded body having higher compressive strength, the foamed layer in the present invention preferably contains a polypropylene resin as the polyolefin resin which is the base resin. In 100% by mass of the base resin of the foamed layer, the polypropylene resin is preferably contained in an amount of 70% by mass or more, more preferably 80% by mass or more, still more preferably 90% by mass or more, even more preferably 95% by mass or more, and particularly preferably 100% by mass. That is, it is particularly preferable that the base resin of the foamed layer is composed only of a polypropylene resin.

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

[0023] When the propylene-based random copolymer contains a component derived from ethylene (ethylene component) and / or a component derived from butene (butene component) as a copolymerization component, from the viewpoint of further enhancing the in-mold formability of the foam particles under low molding pressure conditions, the total content of the ethylene component and the butene component in the propylene-based random copolymer is preferably 1% by mass or more, more preferably 1.5% by mass or more, and still more preferably 2% by mass or more. Also, from the viewpoint of stably obtaining a foam particle molded body having good mechanical properties such as compressive strength, the total content of the ethylene component and the butene component in the propylene-based random copolymer is preferably 15% by mass or less. That is, the total content of the ethylene component and the butene component in the propylene-based random copolymer is preferably 1% by mass or more and 15% by mass or less, more preferably 1.5% by mass or more and 15% by mass or less, and still more preferably 2% by mass or more and 15% by mass or less. Incidentally, the content of the components derived from ethylene and α-olefin in the propylene-based random copolymer is determined by IR spectrum measurement.

[0024] The polypropylene-based resin may be a linear polypropylene-based resin, a branched polypropylene-based resin, or a combination thereof. From the viewpoint of easily obtaining foam particles with a small amount of foaming agent, in 100% by mass of the base resin of the foam layer in the present invention, the content of the branched polypropylene-based resin is preferably 50% by mass or less, and more preferably 30% by mass or less.

[0025] Incidentally, according to the study by the present inventors, in the expanded particles containing a polypropylene-based resin, a phosphonate compound, and a NOR type hindered amine compound in the base resin of the expanded layer, it was confirmed that the viscosity of the molten mixture tends to decrease during the production of the resin particles used for the production of the expanded particles. From the viewpoint of suppressing such a decrease in viscosity, the base resin of the expanded layer is preferably composed of a linear polypropylene-based resin (A), a branched polypropylene-based resin (B) having a melt tension of 50 mN or more measured under the condition of 230°C, and / or a polyethylene-based resin (C) having a melt flow rate of 3 g / 10 min or less measured under the conditions of a temperature of 190°C and a load of 2.16 kg. Incidentally, the melt flow rate may be abbreviated as MFR as appropriate. From the same viewpoint as described above, in particular, the base resin of the expanded layer is more preferably composed of a linear polypropylene-based resin (A) and a branched polypropylene-based resin (B) having a melt tension of 50 mN or more measured under the condition of 230°C. Also, from the same viewpoint, the base resin of the expanded layer is more preferably composed of a linear polypropylene-based resin (A) and a polyethylene-based resin (C) having an MFR of 3 g / 10 min or less measured under the conditions of a temperature of 190°C and a load of 2.16 kg. Furthermore, when the total content of the linear polypropylene-based resin (A), the branched polypropylene-based resin (B), and the polyethylene-based resin (C) is 100% by mass, the total content of the polypropylene-based resin (B) and the polyethylene-based resin (C) is more preferably 5% by mass or more and 30% by mass or less. According to the above-described preferred embodiment, it is possible to provide expanded particles capable of achieving a closed cell ratio of the expanded particles specified by the present invention and forming an expanded particle molded body having a better molding state in a mold. Also, according to the above-described preferred embodiment, since the viscosity change is suppressed, the average of the ratio of the major axis to the minor axis (major axis / minor axis) of the expanded particles is easily adjusted within a predetermined range, and substantially spherical expanded particles are easily obtained. In the present invention, the branched polypropylene-based resin refers to a resin having a long-chain branched structure in the molecular structure of the polypropylene-based resin, which promotes entanglement between the molecular chains of the resin. The long-chain branched structure in the above is distinguished from the branched structure formed by copolymerizing propylene and α-olefin. The copolymer is classified as linear polypropylene. For example, as the branched polypropylene-based resin having a long-chain branched structure, resins having a molecular chain composed of 21 or more carbon skeletons are known, but are not limited thereto. Examples of the branched polypropylene-based resin include branched homopolypropylene (trade names: Daploy WB130HMS, Daploy WB135HMS, Daploy WB140HMS) manufactured by Borealis, and branched homopolypropylene resin (trade name: PF814) manufactured by Sun Allomer. In the present invention, the linear polypropylene-based resin refers to a polypropylene-based resin other than the branched polypropylene-based resin, and specifically includes a linear propylene homopolymer, a linear propylene-based random copolymer, and the like.

[0026] Polyethylene-based resin: In this specification, the polyethylene-based resin refers to an ethylene homopolymer and an ethylene-based copolymer containing 50% by mass or more of structural units derived from ethylene. Specifically, polyethylene such as 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; ethylene-based copolymers such as ethylene-vinyl acetate copolymer and ethylene-methyl methacrylate copolymer are exemplified. In the ethylene-based copolymer, the content of the structural unit derived from ethylene in the polyethylene-based resin is preferably 80% by mass or more, more preferably 90% by mass or more, still more preferably 95% by mass or more, and preferably 98% or more.

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

[0028] In the thermoplastic resin in the foamed layer, the content of other thermoplastic resins other than the polyolefin resin is preferably 10% by mass or less, more preferably 5% by mass or less, and still more preferably 0% by mass. That is, it is particularly preferable that the foamed layer contains substantially only a polyolefin resin as the thermoplastic resin.

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

[0030] (Melting point of polyolefin resin) When the polyolefin resin contains a polypropylene resin, from the viewpoint of enhancing the mechanical properties of the resulting foamed particle molded article, the melting point of the polypropylene resin is preferably 130°C or higher, more preferably 135°C or higher, still more preferably 140°C or higher. On the other hand, from the viewpoint of enhancing the in-mold formability of the foamed particles under conditions of low molding pressure, the melting point of the polypropylene resin is preferably 155°C or lower, more preferably 150°C or lower, still more preferably 148°C or lower. That is, 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, still more preferably 140°C or higher and 148°C or lower. When the polyolefin resin contains a polyethylene resin, from the viewpoint of enhancing the mechanical properties of the resulting foamed particle molded article, the melting point of the polyethylene resin is preferably 110°C or higher, more preferably 112°C or higher, still more preferably 115°C. On the other hand, from the viewpoint of enhancing the in-mold formability of the foamed particles under conditions of low molding pressure, the melting point of the polyethylene resin is preferably 130°C or lower, more preferably 128°C or lower, still more preferably 125°C or lower. That is, 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, still more preferably 115°C or higher and 125°C or lower. The melting point of the polyolefin resin is measured based on JIS K7121:2012 using the polyolefin resin or polyolefin resin foamed particles as test specimens. Specifically, as the state adjustment of the test specimens, “(2) When measuring the melting temperature after performing a certain heat treatment” is adopted. The test specimens are heated from 23°C to 200°C at a heating rate of 10°C / min under the condition of a nitrogen inflow rate of 30 mL / min, then held at that temperature for 10 minutes, cooled to 23°C at a cooling rate of 10°C / min, and then heated again to 200°C at a heating rate of 10°C / min to obtain a DSC curve (DSC curve during the second heating). Next, the peak temperature of the melting peak in the DSC curve is determined, and this value is taken as the melting point of the polyolefin resin. In the case where multiple melting peaks appear in the DSC curve, the peak temperature of the melting peak with the highest melting peak height based on the baseline is adopted as the melting point.

[0031] (Melt Flow Rate of Polyolefin Resin) When the polyolefin resin contains a polypropylene resin, the melt flow rate of the polypropylene resin is preferably 1 g / 10 min or more, more preferably 3 g / 10 min or more, still more preferably 5 g / 10 min or more, from the viewpoint of enhancing the foamability during foaming of resin particles and from the viewpoint of enhancing the secondary foamability during in-mold molding of foam particles. From the viewpoint of enhancing the uniformity of the bubbles of the foam particles and from the viewpoint of enhancing the physical properties of the foam particle molded body, it is preferably 20 g / 10 min or less, more preferably 15 g / 10 min or less, still more preferably 10 g / 10 min or less. That is, 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, still more preferably 5 g / 10 min or more and 10 g / 10 min or less. The MFR of the polypropylene resin is measured under the conditions of a temperature of 230 °C and a load of 2.16 kg based on JIS K7210-1:2014. When the polyolefin resin contains a polyethylene resin, the MFR of the polyethylene resin is preferably 0.5 g / 10 min or more, more preferably 0.8 g / 10 min or more, from the viewpoint of enhancing the foamability during foaming of resin particles and from the viewpoint of enhancing the secondary foamability during in-mold molding of foam particles. From the viewpoint of enhancing the uniformity of the bubbles of the foam particles and from the viewpoint of enhancing the physical properties of the foam particle molded body, it is preferably 4 g / 10 min or less, more preferably 3 g / 10 min or less. That is, 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 is measured under the conditions of a temperature of 190 °C and a load of 2.16 kg based on JIS K7210-1:2014.

[0032] (Phosphonic Acid Ester Compound) The foam layer in the present invention contains a phosphonic acid ester compound. A phosphonic acid ester compound is a compound containing a phosphonic acid ester moiety in the molecule, and includes, for example, cyclic phosphonic acid ester compounds and alkyl phosphonic acid ester compounds.

[0033] Cyclic phosphonic acid ester compounds: A cyclic phosphonic acid ester compound is a compound containing one or more cyclic phosphonic acid ester moieties in the molecule, preferably at least one selected from the group consisting of a compound represented by the following general formula (1), a compound represented by the following general formula (2), a compound represented by the following general formula (3), and a compound represented by the following general formula (4), and more preferably pentaerythritol diphosphonate represented by the following general formula (1). The pentaerythritol diphosphonate of general formula (1) is a spirocyclic compound containing two cyclic phosphonic acid ester moieties in the molecule. The cyclic phosphonic acid ester compounds may be used alone or in combination of two or more.

Chemical formula

[0034] In general formula (1), R1 and R2 may be the same or different, and are preferably the same. R1 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. R2 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, more preferably a methyl group. From the above, among the compounds represented by the general formula (1), those in which both R1 and R2 are methyl groups are more preferable.

[0035] In the general formula (2), R3 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 the general formula (3), R4 and R8 may be the same or different, and it is preferable that they are the same. R4 is an alkyl group having 1 to 4 carbon atoms, preferably a methyl group. R8 is an alkyl group having 1 to 4 carbon atoms, preferably a methyl group. In the general formula (3), R5 and R7 may be the same or different, and it is preferable that they are the same. R5 is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, preferably an ethyl group. R7 is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, preferably an ethyl group. R6 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 linear alkyl group having 1 to 12 carbon atoms.

[0037] In the general formula (4), R9 and R12 may be the same or different, and it is preferable that they are the same. R9 is an alkyl group having 1 to 4 carbon atoms, preferably a methyl group. R12 is an alkyl group having 1 to 4 carbon atoms, preferably a methyl group. R10 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 linear alkyl group having 1 to 12 carbon atoms. R11 is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, preferably an ethyl group.

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

[0039] The compounding amount of the cyclic phosphonate compound in the foamed layer of the polyolefin resin foamed particles of the present invention is 5 parts by mass or more and less than 25 parts by mass with respect to 100 parts by mass of the base resin of the foamed layer. If the compounding amount of the cyclic phosphonate compound is too small, a foamed particle molded body having a high degree of flame retardancy cannot be obtained. On the other hand, if the compounding amount is too large, a foamed particle molded body excellent in fusibility cannot be obtained. From the viewpoint of obtaining a foamed particle molded body having a higher degree of flame retardancy, the compounding amount of the cyclic phosphonate compound in the foamed layer is preferably 6 parts by mass or more, more preferably 7 parts by mass or more, still more preferably 8 parts by mass or more, and particularly preferably 9 parts by mass or more with respect to 100 parts by mass of the base resin of the foamed layer. From the viewpoint of obtaining a foamed particle molded body having better fusibility, the compounding amount of the cyclic phosphonate compound in the foamed layer is preferably 22.5 parts by mass or less, more preferably 20 parts by mass or less, still more preferably 19 parts by mass or less, and particularly preferably 16 parts by mass or less with respect to 100 parts by mass of the base resin of the foamed layer. That is, the compounding amount of the cyclic 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, still 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 with respect to 100 parts by mass of the base resin of the foamed layer.

[0040] (NOR type hindered amine compound) The foamed layer in the present invention contains a NOR type hindered amine compound. The NOR type hindered amine compound has a 2,2,6,6-tetramethyl-4-piperidineamine moiety having a hydrocarbon group bonded to the nitrogen atom represented by the following general formula (5) via an oxygen atom in its structure, whereby the flame retardancy of the molded body can be improved. [Chemical formula] (In general formula (5), R13 represents a hydrocarbon group.)

[0041] In the general formula (5), R13 represents a hydrocarbon group. When a hindered amine compound contains two or more hindered amine moieties represented by the general formula (5) in one molecule, the plurality of R13s may be the same or different, but it is preferable that the plurality of R13s are the same. R13 is preferably at least one selected from the group consisting of an alkyl group and a cycloalkyl group, more preferably a cycloalkyl group. When R13 is an alkyl group, R13 is more preferably an alkyl group having 1 to 20 carbon atoms, still more preferably an undecyl group. When R13 is a cycloalkyl group, R13 is more preferably a cycloalkyl group having 4 to 10 carbon atoms, still more preferably a cyclohexyl group. The NOR type hindered amine compound may be used alone or in combination of two or more.

[0042] From the viewpoint of suppressing bleed-out from the foamed particle molded body, the molecular weight of the NOR type hindered amine compound is preferably 600 or more, more preferably 1500 or more. Also, from the viewpoint of 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. In the NOR hindered amine compound, the number of 2,2,6,6-tetramethyl-4-piperidineamine moieties having a hydrocarbon group bonded to the nitrogen represented by the general formula (5) via an oxygen bond is preferably 2 or more and 8 or less, more preferably 2 or more and 6 or less, and still more preferably 2 or 6.

[0043] The compounding amount of the NOR hindered amine compound in the foamed layer of the polyolefin resin foamed particles of the present invention is 0.3 parts by mass or more and less than 5 parts by mass with respect to 100 parts by mass of the base resin of the foamed layer. If the compounding amount of the NOR hindered amine compound is too small, a foamed particle molded body having a high degree of flame retardancy cannot be obtained. On the other hand, if the compounding amount is too large, a foamed particle molded body having excellent fusion properties cannot be obtained. From the viewpoint of obtaining a foamed particle molded body having a higher degree of flame retardancy, the compounding amount of the NOR 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 still more preferably 0.6 parts by mass or more with respect to 100 parts by mass of the base resin of the foamed layer. From the viewpoint of obtaining a foamed particle molded body having more excellent fusion properties, the compounding amount of the NOR hindered amine compound in the foamed layer is preferably 4 parts by mass or less, more preferably 3 parts by mass or less, still 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 with respect to 100 parts by mass of the base resin of the foamed layer. That is, the compounding amount of the NOR 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, still 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 phosphonate ester compound and the NOR hindered amine compound are contained within a predetermined range with respect to 100 parts by mass of the base resin of the foamed layer. From the viewpoint of exhibiting higher flame retardancy, the ratio of the blending amount of the NOR type hindered amine compound to the blending amount of the phosphonate ester compound in the foamed layer is preferably 0.04 or more, and more preferably 0.05 or more. From the viewpoint of further enhancing the fusion property of the foamed particle molded body, the ratio of the blending amount of the NOR type hindered amine compound to the blending amount of the phosphonate ester compound in the foamed layer is preferably 0.50 or less, more preferably 0.40 or less, and even more preferably 0.30 or less. That is, the ratio of the blending amount of the NOR type hindered amine compound to the blending amount of the phosphonate ester compound in the foamed layer is preferably from 0.04 to 0.50, more preferably from 0.04 to 0.40, and even more preferably from 0.05 to 0.30.

[0045] (Optional additive) The foamed particles of the present invention described above may appropriately contain an arbitrary additive as long as the object and effect of the present invention are not inhibited. For example, examples of the arbitrary additive include various conventionally known additives such as a conductive material, an antioxidant, a flame retardant aid, a bubble regulator, a lubricant, a crystal nucleating agent, a light stabilizer such as an ultraviolet absorber, an antistatic agent, and a colorant. These additives can be incorporated into the foamed particles, for example, by adding them in the process of producing the resin particles. Some of the optional additives will be described below.

[0046] Conductive carbon material: Examples of the conductive material, which is an arbitrary additive, include a conductive carbon material. The foamed layer preferably contains a conductive carbon material. Examples of the conductive carbon material include conductive carbon black, single-walled carbon nanotubes, multi-walled carbon nanotubes, etc. When using conductive carbon black as the conductive carbon material, the DBP oil absorption amount of the conductive carbon black measured based on JIS K6217-4:2008 is 150 cm 3 / 100 g to 700 cm 3 / 100 g is preferable, and 200 cm 3 / 100 g to 500 cm3 It is more preferably 1 / 100 g. The content of the conductive carbon material in the foamed layer is preferably 1 part by mass or more and 10 parts by mass or less, more preferably 1.5 parts by mass or more and 8 parts by mass or less, and still more preferably 2 parts by mass or more and 6 parts by mass or less with respect to 100 parts by mass of the base resin of the foamed layer. In the present invention, it is presumed that the viscosity of the molten mixture changes due to the influence of the phosphonate compound and the NOR type hindered amine compound. On the other hand, by containing the conductive carbon material within a predetermined range, a network structure of the conductive carbon material can be efficiently formed in the polyolefin resin, and a change in the viscosity of the molten mixture can be suppressed. Therefore, it is easy to achieve the closed cell ratio of the foamed particles specified in the present invention, and it is easy to obtain foamed particle moldings with a good molding state that can be molded in a mold. Further, according to the embodiment in which the above-described conductive carbon material is blended, since the change in the viscosity of the resin during melt mixing is suppressed, the average of the ratio of the major axis to the minor axis (major axis / minor axis) of the foamed particles is easily adjusted within a predetermined range, and substantially spherical foamed particles are easily obtained.

[0047] Phenolic antioxidant: In the present invention, an embodiment in which the foamed layer contains a phenolic antioxidant is preferable. The phenolic antioxidant is an antioxidant having one or more phenolic structures in which one or more hydroxyl groups are bonded to an aromatic ring, preferably having two or more phenolic structures in the molecule, and more preferably having three or more phenolic structures in the molecule. At high temperatures (for example, 180°C or higher) such as in the step of melt-kneading the resin, the decomposition of the resin and the additive tends to occur in a relatively short time. On the other hand, by including the phenolic antioxidant in the resin kneaded product constituting the foamed layer, the decomposition of the resin and the additive in a short time can be suppressed at such high temperatures. Specific examples of the phenolic antioxidant include 1,3,5-trimethyl-2,4,6-tris(3’,5’-di-t-butyl-4’-hydroxybenzyl)benzene, 2,6-di-t-butyl-p-cresol, triethylene glycol bis[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)propionate], 2,2-methylenebis(4-methyl-6-t-butylphenol), 1,6-hexanediol-bis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], pentaerythritol tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], and the like. These may be used alone or in combination of two or more. Among these, from the viewpoint of further improving the flame retardancy, pentaerythritol tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] and 1,3,5-trimethyl-2,4,6-tris(3’,5’-di-t-butyl-4’-hydroxybenzyl)benzene are preferable, and 1,3,5-trimethyl-2,4,6-tris(3’,5’-di-t-butyl-4’-hydroxybenzyl)benzene is particularly preferable.

[0048] 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, still 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 from the viewpoint of obtaining a foamed particle molded body having a higher degree of flame retardancy. The melting point TmB of the phenolic antioxidant is measured based on JIS K0064:1992.

[0049] <Mixing ratio of phenolic antioxidant with respect to 100 parts by mass of base resin> From the perspective of providing a foamed particle molded body having higher flame retardancy, the compounding amount of the phenolic antioxidant in the foamed layer is preferably 0.01 part by mass or more, more preferably 0.02 part by mass or more, still more preferably 0.04 part by mass or more, and still more preferably 0.08 part by mass or more with respect to 100 parts by mass of the base resin of the foamed layer. Also, from the perspective of obtaining a foamed particle molded body having a better molding state, the compounding amount of the phenolic antioxidant in the foamed layer is preferably 0.5 part by mass or less, more preferably 0.3 part by mass or less, still more preferably 0.2 part by mass or less, and particularly preferably 0.15 part by mass or less with respect to 100 parts by mass of the base resin of the foamed layer. That is, the compounding amount of the phenolic antioxidant in the foamed layer is preferably 0.01 part by mass or more and 0.5 part by mass or less, more preferably 0.02 part by mass or more and 0.3 part by mass or less, still more preferably 0.04 part by mass or more and 0.2 part by mass or less, and particularly preferably 0.08 part by mass or more and 0.15 part by mass or less.

[0050] <Mixing ratio of the phenolic antioxidant to the amount of NOR type hindered amine compound in the foamed layer> From the perspective of providing foamed particles capable of being molded in a mold into a foamed particle molded body that exhibits higher flame retardancy and has an excellent molding state, the ratio of the compounding amount of the phenolic antioxidant to the compounding amount of the NOR type hindered amine compound is preferably 0.03 or more, more preferably 0.04 or more, still more preferably 0.06 or more, and particularly preferably 0.08 or more. Incidentally, the ratio of the compounding amounts is, in other words, the mixing ratio represented by phenolic antioxidant / NOR type hindered amine compound in the foamed layer. Also, from the perspective of obtaining a foamed particle molded body having higher flame retardancy, the ratio of the compounding amounts is more preferably 0.9 or less, still more preferably 0.5 or less, even more preferably 0.3 or less, and particularly preferably 0.15 or less. That is, the ratio of the blending amount of the phenolic antioxidant to the blending amount of the 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, still 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] From the viewpoint of more fully solving the intended problems of the present invention based on the findings described above, the foamed layer contains a phenolic antioxidant, and the blending amount of the phenolic antioxidant in the foamed layer is 0.01 part by mass or more and 0.5 part by mass or less with respect to 100 parts by mass of the base resin of the foamed layer, and the ratio of the blending amount of the phenolic antioxidant to the blending amount of the NOR type hindered amine compound is preferably 0.03 or more and 0.9 or less.

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

[0053] <Blending amount of sulfur-based antioxidant with respect to 100 parts by mass of base resin> From the viewpoint that the foamed particle molded body has excellent mechanical properties such as compression physical properties even when placed in a high-temperature environment for a long period of time, the compounding amount of the sulfur-based antioxidant in the foamed layer of the foamed particles of the present invention is preferably 0.01 part by mass or more, more preferably 0.04 part by mass or more, and still more preferably 0.06 part by mass or more with respect to 100 parts by mass of the base resin of the foamed layer. Also, from the viewpoint of obtaining a foamed particle molded body having high flame retardancy, the compounding amount of the sulfur-based compound in the foamed layer is preferably 0.5 part by mass or less, more preferably 0.4 part by mass or less, and still more preferably 0.3 part by mass or less with respect to 100 parts by mass of the base resin of the foamed layer. That is, the compounding amount of the sulfur-based antioxidant with respect to 100 parts by mass of the base resin of the foamed layer is preferably 0.01 part by mass or more and 0.5 part by mass or less, more preferably 0.04 part by mass or more and 0.4 part by mass or less, and still more preferably 0.06 part by mass or more and 0.3 part by mass or less.

[0054] <Ratio of the compounding amount of the sulfur-based antioxidant to the compounding amount of the NOR-type hindered amine compound> From the viewpoint that the foamed particle molded body has excellent mechanical properties such as compression physical properties even when placed in a high-temperature environment for a long period of time, the ratio of the compounding amount of the sulfur-based antioxidant to the compounding amount of the NOR-type hindered amine compound is preferably 0.03 or more, more preferably 0.04 or more, still more preferably 0.06 or more, and particularly preferably 0.08. Also, from the viewpoint of obtaining a foamed particle molded body having high flame retardancy, the blending ratio is preferably 0.9 or less, more preferably 0.5 or less, still more preferably 0.3 or less, and particularly preferably 0.15 or less. Incidentally, the ratio of the compounding amounts is, in other words, a compounding ratio represented by sulfur-based antioxidant / NOR-type hindered amine compound. That is, in the foamed layer, the ratio of the compounding amount of the sulfur-based antioxidant to the compounding amount of the 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, still more preferably 0.06 or more and 0.3 or less, and particularly preferably 0.08 or more and 0.15 or less.

[0055] From the viewpoint of more fully solving the intended problems of the present invention based on the above findings, the foamed layer contains a sulfur-based antioxidant, the compounding amount of the sulfur-based antioxidant in the foamed layer is 0.01 part by mass or more and 0.5 part by mass or less with respect to 100 parts by mass of the base resin of the foamed layer, and the ratio of the compounding amount of the sulfur-based antioxidant to the compounding amount of the NOR type hindered amine compound is preferably 0.03 or more and 0.9 or less.

[0056] Cell bubble regulator: Examples of the cell bubble regulator include inorganic powders such as metal borate, talc, mica, calcium carbonate, borax, aluminum hydroxide, and silica, polyhydric alcohols such as glycerin, polyethylene glycol, and pentaerythritol, or aliphatic alcohols such as cetyl alcohol and stearyl alcohol. As the cell bubble regulator, it is preferable to use metal borates such as zinc borate and magnesium borate, and more preferably to use zinc borate. The compounding amount of the cell bubble regulator contained in the foamed layer is preferably 0.005 part by mass or more and 0.5 part by mass or less, more preferably 0.01 part by mass or more and 0.2 part by mass or less, and still more preferably 0.015 part by mass or more and 0.15 part by mass or less with respect to 100 parts by mass of the base resin of the foamed layer. Further, when zinc borate is used as the cell bubble regulator, the arithmetic average particle diameter based on the number standard is preferably 0.5 μm or more and 15 μm or less, and more preferably 1 μm or more and 10 μm or less. The arithmetic average particle diameter based on the number standard of zinc borate is obtained by converting the volume-based particle size distribution measured by the laser diffraction scattering method into the particle size distribution based on the number standard assuming the particle shape as a sphere, and then arithmetically averaging the particle diameters based on this particle size distribution based on the number standard. Incidentally, the above particle diameter means the equivalent diameter of a sphere with the same volume as the particle.

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

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

[0059] (Optional characteristics of polyolefin resin foamed particles) As described above, the foamed particles of the present invention contain a phosphonate compound and a NOR type hindered amine compound in specific ranges of amounts, but preferably further have the following characteristics. Any of the characteristics described below, namely, the multilayer structure, bulk density, high temperature peak, average particle diameter, and average mass, will be described. The foamed particles of the present invention preferably have one or more of these optional characteristics.

[0060] Foamed particles having a multilayer structure: The polypropylene-based foamed particles of the present invention may be single-layer foamed particles having only a particulate foamed layer, or may be foamed particles having a multilayer structure including a particulate foamed layer serving as a core layer and a coating layer covering the foamed layer. The coating layer may cover the entire surface of the foamed layer or may cover a part of the surface of the foamed layer. Further, the foamed layer may have through holes. From the viewpoint that the foamed particle molded body obtained by molding the foamed particles having a coating layer shows higher flame retardancy and from the viewpoint of obtaining a foamed particle molded body having better surface properties and fusion properties, the foamed particles preferably have a multilayer structure.

[0061] In the case of foamed particles having a multilayer structure, the mass ratio of the foamed layer to the coating layer is not particularly limited, but the mass ratio of the foamed layer to the coating layer is preferably 95:5 to 70:30, more preferably 92:8 to 72:28, still more preferably 91:9 to 75:25, even more preferably 90:10 to 78:22, and particularly preferably 88:12 to 80:20. When the mass ratio of the coating layer is relatively high, the foamed particle molded body obtained by molding the foamed particles having the coating layer in a mold exhibits a higher degree of flame retardancy, easily achieves the closed cell ratio of the foamed particles specified in the present invention, and exhibits better surface properties and fusibility. Further, according to the above-described preferred embodiment, the average of the ratio of the major axis to the minor axis (major axis / minor axis) of the foamed particles is easily adjusted within a predetermined range, and substantially spherical foamed particles are easily obtained.

[0062] The base resin of the coating layer may be a polyolefin resin such as a polyethylene resin or a polypropylene resin, or may be a resin or polymer other than the polyolefin resin. For the base resin of the coating layer, the description of the resin used for the above-described foamed layer is appropriately referred to. Incidentally, the base resin of the coating layer refers to the resin and polymer constituting the coating layer. The base resin of the coating layer and the base resin of the foamed layer may be the same or different. From the viewpoint of obtaining good fusibility, the melting point or softening point of the base resin of the coating layer is preferably lower than the melting point of the base resin of the foamed layer. The coating layer may contain a phosphonate compound and a NOR type hindered amine compound. From the perspective of obtaining a foamed particle molded body with good flame retardancy while reducing the addition amount of the flame retardant, the ratio I of the blending amount of the phosphonate ester compound in the coating layer to the base resin of the coating layer of the foamed particles is preferably smaller than the ratio II of the blending amount of the phosphonate ester compound in the foamed layer to the base resin of the foamed layer. That is, the ratio I is (the blending amount of the phosphonate ester compound in the coating layer) / (the mass of the base resin of the coating layer), the ratio II is (the blending amount of the phosphonate ester compound in the foamed layer) / (the mass of the base resin of the foamed layer), and it is preferable that ratio I < ratio II. Further, it is more preferable that the coating layer does not contain a phosphonate ester compound. From the perspective of obtaining a foamed particle molded body with good flame retardancy while reducing the addition amount of the flame retardant, the ratio III of the blending amount of the NOR type hindered amine compound in the coating layer to the base resin of the coating layer of the foamed particles is preferably smaller than the ratio IV of the blending amount of the NOR type hindered amine compound in the foamed layer to the base resin of the foamed layer. That is, the ratio III is (the blending amount of the NOR type hindered amine compound in the coating layer) / (the mass of the base resin of the coating layer), the ratio IV is (the blending amount of the NOR type hindered amine compound in the foamed layer) / (the mass of the base resin of the foamed layer), and it is preferable that ratio III < ratio IV. Further, it is more preferable that the coating layer does not contain a NOR type hindered amine compound. From the perspective of obtaining a foamed particle molded body with good flame retardancy while reducing the addition amount of the flame retardant, it is preferable that in the foamed particles, the ratio is ratio I < ratio II and ratio III < ratio IV.

[0063] The coating layer may be in a foamed state or a non-foamed state. From the perspective of improving the molding state of the foamed particle molded body, the coating layer is preferably in a substantially non-foamed state. Substantially non-foamed state means a state where the coating layer does not foam and does not contain bubbles, and a state where the bubbles disappear after foaming, meaning that there is almost no bubble structure.

[0064] Bulk density of the foamed particles: The bulk density of the foamed particles of the present invention is not particularly limited, but the bulk density is 30 kg / m 3It is preferably the above, 50 kg / m 3 More preferably, it is the above, 70 kg / m 3 Even more preferably, it is the above, 80 kg / m 3 Even more preferably, it is the above, 90 kg / m 3 It is particularly preferably the above. Further, the bulk density of the foamed particles of the present invention is preferably 200 kg / m 3 or less, more preferably 180 kg / m 3 or less, even more preferably 150 kg / m 3 or less, particularly preferably 130 kg / m 3 . That is, the bulk density of the foamed particles of the present invention is preferably 30 kg / m 3 or more and 200 kg / m 3 or less, more preferably 50 kg / m 3 or more and 180 kg / m 3 or less, even more preferably 70 kg / m 3 or more and 150 kg / m 3 or less, even more preferably 80 kg / m 3 or more and 130 kg / m 3 , and particularly preferably 90 kg / m 3 or more and 130 kg / m 3 . Since the bulk density of the foamed particles is within the above range, a foamed particle molded body excellent in flame retardancy, lightweight, and also excellent in fusion bonding property can be obtained, which is preferable.

[0065] The bulk density of the foamed particles is measured by the following method. First, the foamed particles to be measured are left standing for 24 hours or more in an environment of an air temperature of 23°C, a relative humidity of 50%, and 1 atm for condition adjustment. A group of foamed particles with a mass W (g) after condition adjustment is filled into a graduated cylinder so as to naturally accumulate, and the bottom surface of the graduated cylinder is gently tapped several times with respect to the horizontal plane to stabilize the filling height of the group of foamed particles in the graduated cylinder. The bulk volume V (L) of the group of foamed particles indicated by the scale of the graduated cylinder is read, and the mass W of the group of foamed particles is divided by the bulk volume V of the group of foamed particles (W / V), and the bulk density (kg / m 3 ) of the foamed particles can be obtained.

[0066] High-temperature peak: The polyolefin-based resin foam particles of the present invention preferably have one or more melting peaks (high-temperature peaks) on the high-temperature side of the melting peak (resin-specific peak) specific to the resin of the olefin-based resin in a DSC curve obtained by differential scanning calorimetry (DSC) measured based on JIS K7122-2012. These melting peaks can be obtained by the following method. Specifically, a DSC curve can be obtained by heating 1 to 3 mg of the foam particles from 23°C to 200°C at a heating rate of 10°C / min using a differential scanning calorimeter, and the melting peak (high-temperature peak) can be confirmed from the DSC curve. The peak having the maximum heat of fusion is defined as the melting peak (resin-specific peak) specific to the olefin-based resin, and the melting peak appearing on the higher temperature side than that is defined as the high-temperature peak. The DSC curve in this case means a DSC curve (DSC curve in the first heating) obtained by heating the foam particles by the above measurement method. The endothermic peak specific to the resin (resin-specific peak) means an endothermic peak due to the melting of the crystals specific to the polyolefin-based resin constituting the foam particles. The resin-specific peak is considered to be an endothermic peak that appears due to the endotherm caused by the melting of the crystals that the polyolefin-based resin constituting the foam particles usually has. On the one hand, the endothermic peak (high-temperature peak) on the high-temperature side of the resin-specific peak is an endothermic peak that appears on the high-temperature side of the resin-specific peak in the first DSC curve. When this high-temperature peak appears, it is presumed that secondary crystals exist in the resin. Incidentally, after 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), in the DSC curve obtained at this time (DSC curve in the second heating), only the endothermic peak due to the melting of the crystals inherent to the polyolefin-based resin constituting the foamed particles appears. This resin-specific peak appears in both the DSC curve in the first heating and the DSC curve in the second heating. Although the temperature at the peak apex may slightly differ between the first and the second time, usually, the difference is less than 5°C. Thus, it is possible to confirm which peak is the resin-specific peak. Incidentally, the foamed particles preferably have only the melting peak (specific peak) inherent to the polyolefin-based resin appearing in the DSC curve in the second heating obtained when the foamed particles are heated 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 at a heating rate of 10°C / min.

[0067] The heat of fusion of the high-temperature peak of the polyolefin-based 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, still more preferably 7 J / g or more and 25 J / g or less, because the range of molding conditions for obtaining a good foamed particle molded body becomes wider when the foamed particles are molded in a mold. Incidentally, the heat of fusion of the high-temperature peak is measured by the above method, and more specifically, it can be measured by the method described in the examples.

[0068] Average particle diameter of the foamed particles: From the viewpoint of enhancing the fillability into the molding die, the average particle diameter 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 still more preferably 0.8 mm or more and 4.5 mm or less. The average particle diameter of the foamed particles is a value obtained by the following method. First, based on the volume-based particle size distribution of the foamed particles, assuming the particle shape as a sphere, the volume-based particle size distribution is converted into a number-based particle size distribution to obtain a number-based particle size distribution. Then, the number-based arithmetic mean particle diameter can be obtained by arithmetically averaging the particle diameters based on this number-based particle size distribution. Note that the particle diameter means the diameter of a virtual sphere having the same volume as the particle. The particle size distribution of the foamed particles on a volume basis can be measured using a particle size distribution measuring device (for example, a dynamic image analysis type particle shape and particle size distribution measuring device and analysis software (trade name: PARTAN 3D) manufactured by Microtrac Bell Corporation). The number of foamed particles used for the measurement may be, for example, 2000 or more.

[0069] Average mass of the foamed particles: From the same viewpoint, 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 still more preferably 0.8 mg or more and 3 mg or less. The average mass of the foamed particles can be obtained by randomly selecting 100 or more foamed particles, measuring the mass [mg] of the foamed particle group, and dividing by the number of foamed particles used for the measurement.

[0070] (Method for producing polyolefin-based resin foamed particles) The foamed particles of the present invention are polyolefin-based resin foamed particles, which contain a polyolefin-based resin as a base resin and contain a phosphonic acid ester-based compound and a NOR type hindered amine-based compound within a predetermined range. Generally, when a polyolefin resin, a phosphonate ester, and a NOR type hindered amine compound are melt-kneaded, the above-described problems occur. In order to prevent the occurrence of such problems, it is important that the method for producing foamed particles of the present invention includes the above-described specific raw materials and that the closed cell ratio of the obtained foamed particles is adjusted to be within a predetermined range. Any raw materials may be appropriately included. Based on the above matters, the method for producing foamed particles of the present invention is not particularly limited. For example, as the method for producing foamed particles of the present invention, it is possible to follow the above-described production method 1 or production method 2. Hereinafter, an example of a preferred production method of the foamed particles of the present invention will be shown.

[0071] A preferred method for producing foamed particles of the present invention includes a resin particle production step of producing resin particles containing a phosphonate ester compound and a NOR type hindered amine compound, a dispersion step of dispersing the resin particles in an aqueous dispersion medium containing an inorganic dispersant in a pressure vessel, a foaming agent impregnation step of impregnating the resin particles with a foaming agent in the pressure vessel, and a foaming step of discharging the resin particles containing the foaming agent from the pressure vessel together with the aqueous dispersion medium to cause foaming. These steps may be carried out in this order, or a part or all of one step and the next step may be carried out repeatedly.

[0072] (Resin particle production step) First, the resin particle production step is carried out. First, a base resin, a phosphonate ester compound, a NOR type hindered amine compound, other resins, polymers, and optional additives that are blended as necessary are supplied into an extruder, heated, and kneaded to obtain a molten mixture. Then, the molten mixture is extruded from the pores of a die attached to the tip of the extruder and pelletized by a strand cut method, a hot cut method, a water cut method, etc., thereby producing resin particles. When producing multilayer resin particles, it is preferable to use a production apparatus including a core layer forming extruder, a multilayer strand forming die attached downstream of the core layer forming extruder, and a coating layer forming extruder. A specific example will be confirmed in the description of Example 1 described later.

[0073] The average mass per resin particle is preferably adjusted to be 0.2 mg to 5 mg, more preferably 0.5 mg to 4 mg, and still more preferably 0.8 mg to 3 mg. The average mass referred to here means the arithmetic mean value per particle obtained by measuring the masses of 100 randomly selected resin particles. In addition, the outer shape of the resin particles is not particularly limited as long as the intended object of the present invention can be achieved. In the strand cut method, those that are visually judged to be columnar are preferable. When the outer shape of the resin particles is columnar, the particle diameter of the resin particles measured in the extrusion direction is preferably 0.1 mm to 3.0 mm, more preferably 0.3 mm to 1.5 mm. Further, the ratio (particle diameter / diameter) of the length (particle diameter) of the resin particles in the extrusion direction to the maximum length (diameter) in the direction perpendicular to the extrusion direction of the resin particles is preferably 0.5 to 5.0, more preferably 1.0 to 3.0. When the ratio is within the above-mentioned range, spherical foamed particles are easily obtained, which is preferable.

[0074] As described above, by adopting the mode of using multi-layer resin particles having a core layer and a coating layer covering the core layer, the mode of blending a linear polypropylene-based resin, a branched polypropylene-based resin and / or a low-fluidity polyethylene-based resin as the base resin of the foaming layer, or the mode of blending a conductive carbon material into the foaming layer, the following merits in the manufacturing process can be obtained. That is, when at least one of these modes is adopted, the particle shape of the resin particles can be effectively adjusted by appropriately adjusting the extrusion speed, take-up speed, cutter speed, etc. of the molten mixture at the time of strand cutting, and spherical foamed particles can be easily manufactured using the resin particles.

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

[0076] In the dispersion step, it is preferable to add a dispersant to the aqueous dispersion medium so that the resin particles heated in the container do not fuse with each other. Any dispersant can be used as long as it can prevent the resin particles from fusing in the container. As the dispersant, either an organic dispersant or an inorganic dispersant can be used, but it is preferable to use an inorganic dispersant, and a fine inorganic dispersant is more preferable because of its ease of handling. For example, natural or synthetic clay minerals such as kaolin, mica, and clay, aluminum oxide, titanium oxide, basic magnesium carbonate, basic zinc carbonate, calcium carbonate, iron oxide, etc. may be mentioned. One of these may be used, or two or more thereof may be used in combination. Among them, it is preferable to use a natural or synthetic clay mineral as the dispersant. The addition amount of the dispersant is preferably 0.001 parts by mass to 5 parts by mass per 100 parts by mass of the resin particles.

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

[0078] (Foaming agent impregnation step) After the dispersion step, or overlapping with the dispersion step, a foaming agent impregnation step is carried out. As the foaming agent for foaming the resin particles used in the foaming agent impregnation step, a physical foaming agent is preferred. Examples of the physical foaming agent include inorganic physical foaming agents and organic physical foaming agents. Examples of the inorganic physical foaming agent include carbon dioxide, air, nitrogen, helium, argon, etc. Examples of the organic physical foaming agent include aliphatic hydrocarbons such as propane, n-butane, i-butane, n-pentane, i-pentane, hexane, cyclopentane, cyclohexane, and halogenated hydrocarbons such as chlorofluoromethane, trifluoromethane, 1,1-difluoroethane, 1-chloro-1,1-difluoroethane, 1,1,1,2-tetrafluoroethane, methyl chloride, ethyl chloride, methylene chloride, etc. In addition, these physical foaming agents may be used alone or in combination of two or more as the foaming agent. Further, an inorganic physical foaming agent and an organic physical foaming agent can be used in combination. From the viewpoint of further reducing the environmental load and improving the flame retardancy of the foamed particle molded body, the foaming agent is preferably an inorganic physical foaming agent, more preferably carbon dioxide.

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

[0080] As a method for impregnating the resin particles with the foaming agent, after dispersing the resin particles in an aqueous dispersion medium in a pressure vessel, the foaming agent is press-fitted into the pressure vessel, and the inside of the pressure vessel is maintained at a predetermined temperature and pressure, so that A method of impregnating the resin particles with the foaming agent is preferably used.

[0081] (Foaming step) The lower limit of the pressure inside the pressure vessel (internal pressure) during foaming, that is, the pressure inside the pressure vessel immediately before discharging the resin particles together with the aqueous dispersion medium, is preferably 0.5 MPa(G) or more, more preferably 0.8 MPa(G) or more. Also, the upper limit is preferably 4 MPa(G) or less, more preferably 3 MPa(G) or less. Within the above range, there is no risk of damage or explosion of the pressure vessel, and the desired foamed particles can be safely produced. After adjusting to the above-mentioned pressure, the resin particles containing the foaming agent are discharged from the pressure vessel together with the aqueous dispersion medium into an atmosphere at a pressure lower than the pressure inside the pressure vessel (for example, under atmospheric pressure) and foamed. Incidentally, before carrying out the foaming step, the temperature inside the pressure vessel is preferably raised to 100°C to 200°C, more preferably 120°C to 160°C, and held at that temperature for about 5 to 30 minutes. Thereby, the crystalline state of the resin particles can be adjusted to a state showing the high-temperature peak.

[0082] Incidentally, the polyolefin-based resin foamed particles obtained as described above can be further foamed (two-stage foaming) by pressurizing with air or the like to increase the pressure (internal pressure) inside the bubbles of the foamed layer and then heating with steam or the like to obtain foamed particles with an even higher foaming ratio (lower bulk density).

[0083] (Polyolefin-based resin foamed particle molded body) By performing in-mold forming using the expanded particles of the present invention manufactured as described above, an expanded particle molded body of the present invention can be obtained. For example, the expanded particle molded body is manufactured as follows. First, the expanded particles of the present invention are filled into a mold having a cavity corresponding to the shape of the desired expanded particle molded body, and the expanded particles filled in the mold are heated. The expanded particles in the cavity soften by heating, secondary foam, and the surfaces melt and fuse with each other. As a result, the expanded particles are integrated with each other, and an expanded particle molded body corresponding to the shape of the cavity is obtained. Examples of the method of heating the expanded particles include a method of introducing a heating medium such as steam into the mold and heating the expanded particles with the heating medium, a method of irradiating the expanded particles with electromagnetic waves such as microwaves to heat the expanded particles, and a method combining both. As a method of filling the expanded particles into the mold, a known method can be adopted. Examples of known methods include a pressure filling method, a compression filling method, and a cracking filling method. The pressure filling method is a method of subjecting the expanded particles to a pressure treatment with a pressurized gas, applying a predetermined internal pressure to the expanded particles, and then filling them into the mold. The compression filling method is a method of filling the expanded particles into a pressurized mold in a compressed state with a pressurized gas and then releasing the pressure in the mold. The cracking filling method is a method of mechanically compressing the expanded particles by opening the mold in advance to expand the molding space before filling the expanded particles into the mold and closing the mold after filling. These filling methods may be carried out individually or in combination.

[0084] In the in-mold forming, for the purpose of improving the secondary foamability during heating of the expanded particles, an internal pressure may be applied to the expanded particles before filling them into the mold, and the expanded particles may be filled into the mold in a state where the pressure inside the bubbles of the expanded particles is increased. The pressure (internal pressure) inside the bubbles can be measured, for example, by the method described in JP-A-2003-201361.

[0085] The density of the expanded particle molded body of the present invention is preferably 30 kg / m 3 or more, more preferably 50 kg / m 3 or more, and still more preferably 70 kg / m 3or more, more preferably 80 kg / m 3 or more, particularly preferably 90 kg / m 3 or more. Also, preferably 200 kg / m 3 or less, more preferably 180 kg / m 3 or less, still more preferably 150 kg / m 3 or less, even more preferably 130 kg / m 3 or less. That is, more preferably 30 kg / m 3 or more and 200 kg / m 3 or less, still more preferably 50 kg / m 3 or more and 180 kg / m 3 or less, even more preferably 70 kg / m 3 or more and 150 kg / m 3 or less, even more preferably 80 kg / m 3 or more and 130 kg / m 3 or less, even more preferably 90 kg / m 3 or more and 130 kg / m 3 or less. The above-mentioned foamed particle molded body is excellent in flame retardancy, lightweight, and also excellent in fusion bonding property, and thus is preferable.

[0086] The foamed particle molded body formed by molding the foamed particles of the present invention in a mold exhibits high flame retardancy and is excellent in fusion bonding property and surface property, and thus is also suitably used for applications that require high flame retardancy such as protective materials for in-vehicle batteries and electronic components.

Examples

[0087] Hereinafter, the present invention will be described in detail by way of examples, but the present invention is not limited thereto. Table 1 to Table 3 show the composition, compounding amount, compounding ratio, foaming conditions of the resin particles for producing the foamed particles of each example and each comparative example, and the molding pressure of the foamed particle molded body, and also show the evaluation results etc. of each example and each comparative example. Also shown in the table are the ratio of the compounding amount (parts by mass) of the phenolic antioxidant to the compounding amount (parts by mass) of the NOR type hindered amine compound in the core layer, the ratio of the compounding amount (parts by mass) of the sulfur-based antioxidant to the compounding amount (parts by mass) of the NOR type hindered amine compound in the core layer, the total compounding amount (mass %) of the phosphonate ester compound in 100 mass % of the resin particles, and the ratio of the compounding amount (mass %) of the NOR type hindered amine compound to the compounding amount (mass %) of the phosphonate ester compound in the resin particles. Note that regarding the example table, it is understood that the compounding amount of each composition is the same as the content 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 as follows. Note that in the examples and comparative examples shown below, the resins compounded in the core layer and the coating layer are all polyolefin resins, and no other resins and other polymers were used. The polyolefin resin compounded in the core layer and the coating layer in each example and each comparative example is 100 parts by mass.

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

[0090] (Phosphonic acid ester compound) Manufactured by Thor, trade name "Aflammit PCO900", melting point 240 °C, the compound represented by the following formula (6) was used as a cyclic phosphonic acid ester compound. In the table, such a compound was described as a phosphonic acid ester. [Chemical formula]

[0091] (NOR type hindered amine compound) Manufactured by BASF, trade name "Flamestab NOR116", molecular weight 2261, the compound represented by the following formula (7) was used as a NOR type hindered amine compound. In the table, such a compound was described as a NOR type hindered amine. [Chemical formula]

[0092] (Phenolic antioxidant) Manufactured by BASF, trade name "Irganox 1330", melting point 245 °C, the compound represented by the following formula (8) was used as a phenolic antioxidant. [Chemical formula]

[0093] (Sulfur-based antioxidant) Dioctadecyl 3,3'-thiodipropionate: Manufactured by BASF, trade name "Irganox PS 802" was used as an antioxidant.

[0094] <Example 1> (Production of resin particles) A manufacturing apparatus equipped with an extruder for forming a core layer with an inner diameter of 50 mm, a die for forming a multi-layer strand 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 was prepared. The manufacturing apparatus was configured such that the downstream side of the extruder for forming the coating layer was connected to the die for forming the multi-layer strand, and it was possible to laminate the molten mixtures for forming each layer in the die and perform co-extrusion. PP1 was used as the base resin for the core layer. As the core layer forming material constituting the core layer, in addition to the above-mentioned resin, zinc borate as a nucleating agent, a phosphonate ester-based compound, a NOR type hindered amine-based compound, a phenolic antioxidant, and a sulfur-based antioxidant were supplied to the extruder so as to have the blending amounts shown in Table 1, and these were melt-kneaded to prepare a molten mixture. The core layer in the resin particles is the layer that becomes the foamed layer of the foamed particles manufactured as described later. PP2 was used as the base resin for the coating layer, supplied to the extruder for forming the coating layer, melt-kneaded, and a molten mixture was prepared. The molten mixtures for forming each layer obtained by melt-kneading as described above were introduced into the die for forming the multi-layer strand and merged in the die, and a multi-layer strand having a two-layer structure (coating layer / core layer) with a core layer and a coating layer covering the side circumferential surface of the core layer was extruded from a 2 mm circular pore of a die attached to the downstream side of the die. While pulling out the extruded strand, it was water-cooled in a water tank and cut by a pelletizer so that the length of the resin particles became 2 mm, and resin particles with an average mass of 1.0 mg per piece were obtained.

[0095] (Production of foamed particles) 2 kg of the resin particles obtained as described above were supplied into a pressure vessel with an internal volume of 100 L together with 75 L of water, which is an aqueous dispersion medium. 65 g of kaolin as an inorganic dispersant and 43 g (as the active ingredient) of a surfactant (trade name: Neogen, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., sodium dodecylbenzenesulfonate) were added into the pressure vessel, respectively. Next, carbon dioxide was injected into the pressure vessel as a foaming agent, and the pressure was increased until the gauge pressure reached 0.5 MPa (G). Note that the pressure with (G) attached is the gauge pressure, that is, the value of the pressure based on the atmospheric pressure. Then, while stirring the inside of 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. Then, it was held at the same temperature and the same pressure for 15 minutes. In this way, the endothermic curve measured by DSC of the obtained foamed particles was adjusted so that a high-temperature peak appeared. Thereafter, the resin particles and the aqueous dispersion medium, which are the contents of the pressure vessel, were discharged under atmospheric pressure to foam the core layer, and foamed particles having a multilayer structure including a foamed layer and a non-foamed coating layer covering the foamed layer were obtained. The foaming pressure inside the pressure vessel immediately before foaming was the value shown in Table 1. The obtained foamed particles were left in an oven at 80 °C for 24 hours or more to sufficiently dry the foamed particles. At that time, the moisture content of the foamed particles after drying was measured. The measurement of the moisture content was carried out by weighing out about 200 cm 3 of the foamed particle group after drying, and measuring the weight of the foamed particle group. Next, the foamed particle group whose weight was measured as described above was further heated in an oven at 150 °C for 1 hour, and then the weight of the foamed particle group after heating was measured. The weight of the foamed particle group after heating was subtracted from the weight of the foamed particle group before heating, and the obtained difference in weight was divided by the weight of the foamed particle group after heating and then converted into a percentage. In this example, the value obtained by measuring the moisture content was 0.8%.

[0096] (Manufacture of Foamed Particle Moldings) The foam particles that had been dried and had no internal pressure applied were filled into a mold having a molding cavity capable of molding a flat plate-shaped molded body with dimensions of 400 mm in length × 300 mm in width × 30 mm in height by compression filling. A metal mold was used as the said mold. Compression filling is a filling method in which the foam particles are filled into the mold while pressure is applied to them. Thereafter, steam was supplied into the mold to heat the foam particles, thereby obtaining a flat plate-shaped foam particle molded body. Heating with steam was carried out as follows. First, with the drain valves provided on both sides of the mold open, steam was supplied to the mold to perform preheating (exhaust process). Thereafter, steam was supplied and heated from one side of the mold, and further steam was supplied and heated from the other side of the mold. Subsequently, steam was supplied and heated from both sides of the mold until the molding pressure described in Table 1 was reached inside the mold. After the heating was completed, the pressure was released, and after water cooling until the pressure generated on the molding surface of the mold became 0.04 MPa (G), the mold was opened and the foam particle molded body was taken out. After curing the obtained molded body in an oven at 80°C for 12 hours, it was gradually cooled to room temperature to obtain a foam particle molded body.

[0097] <Examples 2 to 8> Foam particles and a foam particle molded body were produced in the same manner as in Example 1, except that the content shown in Tables 1 to 3 was changed.

[0098] <Examples 9, 10, Comparative Examples 1, 5, 6> An extruder with an inner diameter of 50 mm, having a die for strand formation attached to the outlet side, was prepared. A polyolefin resin, a phosphonic acid ester compound, a NOR type hindered amine compound, a phenolic antioxidant, a sulfur-based antioxidant, and a cell nucleating agent were supplied to the extruder so as to have the compounding amounts shown in the table, and these were melt-kneaded to form a molten mixture. Incidentally, in Example 9, PP1; 80 parts by mass and PE2; 20 parts by mass were used as 100 parts by mass of the polyolefin resin. Also, in Example 10, PP1; 80 parts by mass and PP3; 20 parts by mass were used as 100 parts by mass of the polyolefin resin. The obtained molten mixture was extruded into strands from a die for strand formation, water-cooled, and cut by a pelletizer to obtain resin particles with an average mass of 1.0 mg per piece. Using the resin particles obtained as described above, except that the contents shown in Tables 2 and 3 were changed, foamed particles and foamed particle molded articles were produced in the same manner as the production method of the foamed particles and foamed particle molded articles of Example 1.

[0099] <Comparative Examples 2 to 4> Except that the contents shown in Table 3 were changed, foamed particles were produced in the same manner as the production method of the foamed particles of Comparative Example 1. Next, except that the pressure inside the bubbles of the foamed particles obtained as described above was increased to 0.1 MPa (G) and then compression-molded, and molded under the conditions shown in Table 3, a foamed particle molded article was produced in the same manner as the production method of the foamed particle molded article of Example 1. <Example 11> With respect to 100 parts by mass of the resin, 3 parts by mass of oil furnace black (product name; Ketjenblack (registered trademark) EC300J (manufactured by Lion Corporation), DBP absorption; 360 cm 3 / 100 g, particle size; 40 nm) was used, and except that the contents of Table 2 were changed, foamed particles and foamed particle molded articles were produced in the same manner as in Example 9.

[0100] Regarding the resin particles, foamed particles, and foamed particle molded articles obtained as described above, the following measurements or evaluations were performed, and the results are shown in Tables 1 to 3.

[0101] <Average value of major axis / minor axis of cross-section of resin particles> The resin particles were cut from a direction perpendicular to the extrusion direction during the production of the resin particles so as to pass through the center of the resin particles to form a cut surface. On the cut surface, the major axis and the minor axis shown in the direction perpendicular to the major axis passing through the center were actually measured using a microscope. This measurement was performed on 20 resin particles, and the major axis / minor axis of the cut surface was determined for each resin particle and arithmetically averaged to obtain the average value of the major axis / minor axis of the cut surface of the resin particles.

[0102] <Heat of fusion at the high-temperature peak of the foamed particles> Based on the heat flux differential scanning calorimetry according to JIS K7122-2012, the heat of fusion at the high-temperature peak of the foamed particles was measured. Specifically, about 2 mg of the foamed particles were collected, and the temperature was raised from 23 °C to 200 °C at a rate of 10 °C / min using a differential scanning calorimeter (DSC7020 manufactured by Hitachi High-Technologies Corporation) to obtain a DSC curve having two or more melting peaks. In the following description, the resin-specific peak is designated as A, and the high-temperature peak appearing on the higher-temperature side thereof is designated as B. A straight line (α-β) was drawn connecting the point α corresponding to 80 °C on the DSC curve and the point β on the DSC curve corresponding to the melting end temperature T of the foamed particles. The melting end temperature T is the end point on the higher-temperature side in the high-temperature peak B and refers to the intersection of the high-temperature peak B and the higher-temperature baseline. Next, a straight line parallel to the vertical axis of the graph was drawn from the point γ on the DSC curve corresponding to the trough between the resin-specific peak A and the high-temperature peak B, and the intersection of this straight line and the straight line (α-β) was designated as δ. The area of the high-temperature peak B is the area surrounded by the curve of the high-temperature peak B portion of the DSC curve, the line segment (δ-β), and the line segment (γ-δ), and this was defined as the heat of fusion at the high-temperature peak.

[0103] <Bulk density of the foamed particles> After curing the foamed particles as described above, a group of foamed particles with a mass of W (g) was filled into a graduated cylinder so as to naturally settle, and the bottom surface of the graduated cylinder was gently tapped several times with respect to the horizontal plane to stabilize the filling height of the group of foamed particles in the graduated cylinder. The bulk volume V (L) of the group of foamed particles indicated by the scale of the graduated cylinder was read, and the mass W of the group of foamed particles was divided by the bulk volume V of the group of foamed particles (W / V), and the unit was converted to [kg / m 3 to determine the bulk density of the foamed particles.

[0104] <Closed-cell ratio of the foamed particles> Bulk volume of about 20 cm 3The apparent volume Va of the foamed particle group was measured by immersing the foamed particle group in water. Next, after the foamed particle group with the measured apparent volume Va was sufficiently dried, the true volume Vx of the foamed particles was measured according to Procedure C 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 bubbles in the independent bubble portion within the foamed particles. For the measurement of this true volume Vx, an air comparison type specific gravity meter (manufactured by Toshiba Beckman Co., Ltd.; air comparison type specific gravity meter "930") was used. Next, the closed cell ratio was calculated by the following formula (1). Using different measurement samples, the closed cell ratio was measured 5 times in the same procedure as described above, and the arithmetic mean value of the values obtained in each measurement was determined and taken as the closed cell ratio of the foamed particles. [Equation 2] Closed cell ratio (%) = (Vx - W / ρ) × 100 / (Va - W / ρ) ··· (1) Vx: True volume of the foamed particle group measured by the above method (cm 3 ) Va: Apparent volume of the foamed particle group measured from the rise in the water level when the foamed particle group is submerged in water in a graduated cylinder (cm 3 ) W: Mass of the foamed particle group (g) ρ: Density of the resin constituting the foamed particles (g / cm 3 )

[0105] <Average value of the major diameter of the foamed particles / minor diameter of the foamed particles> Measurement and analysis were performed using a dynamic image analysis type particle shape and particle size distribution measuring device and analysis software (trade name: PARTAN 3D, software version: 7.1.3.80) manufactured by Microtrap Bell Co., Ltd. Approximately 2,000 foamed particles obtained above were supplied to the device as samples, and three-dimensional image analysis was performed. The major axis and minor axis of each foamed particle were measured, and the ratio of the major axis to the minor axis of the foamed particle was calculated. Incidentally, the major axis of each foamed particle is the maximum value of the diameter where the distance between two parallel lines sandwiching one particle is the largest by image analysis. Also, the minor axis of each foamed particle is the minimum value of the diameter where the distance between two parallel lines sandwiching one particle is the smallest. The value obtained by arithmetically averaging the ratios of the supplied foamed particles was taken as the average value of the major axis of the foamed particle / the minor axis of the foamed particle. In the measuring method using this measuring device, the major axis of the foamed particle corresponds to the Feret Length, and the minor axis of the foamed particle corresponds to the Feret Thickness.

[0106] <Density of the foamed particle molded body> The density (kg / m 3 ) of the foamed particle molded body was calculated by dividing the mass of the obtained foamed particle molded body by the volume calculated based on the dimensions.

[0107] <Evaluation of the fusion property of the foamed particle molded body> The foamed particle molded body was bent and broken, and the number of foamed particles (C1) present on the fracture surface and the number of broken foamed particles (C2) were counted, and the ratio of the number of broken foamed particles to the number of foamed particles present on the fracture surface [(C2 / C1)×100] was calculated as the material fracture rate. The above measurement was performed 5 times using different test pieces, the material fracture rate of each was determined, and the arithmetic mean value was calculated. The arithmetic mean value was evaluated according to the following evaluation criteria. A: The material fracture rate is 70% or more B: The material fracture rate is 50% or more and less than 70% C: The material fracture rate is less than 50%

[0108] <Evaluation of the surface property of the foamed particle molded body> As an evaluation of the surface appearance, a 100 mm × 100 mm range was cut out from the central part of the expanded particle molded body as a test piece, a line was drawn diagonally from the corner of the test piece, and 1 mm on that line 2 or larger voids (gaps) were counted, and the evaluation was carried out as follows. Good: The number of voids is less than 10 Bad: The number of voids is 10 or more

[0109] <Flame retardancy evaluation of expanded particle molded body> UL94V test (judgment): The flame retardancy of the expanded particle molded body was evaluated based on the results of a vertical combustion test (20 mm vertical combustion test) conducted in accordance with the UL94 standard. The specific test method is as follows. (Preparation of measurement sample) Five test pieces with dimensions of 125 mm in length, 13 mm in width, and 13 mm in thickness were cut out from near the central part of the expanded particle molded body so that all surfaces of the test pieces were cut surfaces. (Test method) By fixing the upper part of the test piece with a fixing clamp to keep the longitudinal direction of the test piece vertical, absorbent cotton was placed below the test piece. After indirectly heating the lower end of the test piece with a burner for 10 seconds, the burner was moved away from the test piece, and the combustion time (first combustion time) until the combustion of the test piece stopped was measured. Again, after indirectly heating for 10 seconds, the burner was moved away from the test piece, and the combustion time (second combustion time) and red heat time (second red heat time) until the combustion of the test piece stopped were measured. The flame retardancy of the expanded particle molded body was evaluated by performing the above test on each of the five test pieces. Here, the combustion time refers to the time during which the combustion state where flames are visible from the test piece continues, and combustion refers to the state where the gas near the surface part and the surface part of the test piece burns and flames are visible from the test piece. Also, the red heat time refers to the time during which the test piece is red-hot after the combustion state where flames are visible ends. Red heat refers to the state where only the surface part of the test piece burns and the red-hot state of the test piece surface can be visually confirmed without the flames being visible. (Evaluation criteria) The test was conducted on five test pieces of each molded body and evaluated according to the V-0, V-1, and V-2 standards of the UL94 standard. If the V-0, V-1, and V-2 standards of the UL94 standard were not met, it was evaluated as unqualified. Note that as the evaluation of flame retardancy, higher flame retardancy is indicated in the order of V-0, V-1, and V-2. When the test piece meets the evaluation criteria of both V-0 and V-1, it was determined as V-0 evaluation, and when it meets only the V-1 standard, it was determined as V-1 evaluation. V-0: The combustion time of the first and second times in each test run is 10 seconds or less respectively, and The total of the combustion time of the first and second times in each test run, that is, the total of the combustion time for 10 times is less than 50 seconds, and The sum of the combustion time of the second time and the afterglow time of the second time in each test run is 30 seconds or less respectively, and There is no test run in which the combustion of the test piece reaches the fixing clamp, and There is no test run in which the absorbent cotton placed under the test piece burns due to the dripping matter dropped by the combustion of the test piece. V-1: The combustion time of the first and second times in each test run is 30 seconds or less respectively, and The total of the combustion time of the first and second times in each test run, that is, the total of the combustion time for 10 times is less than 250 seconds, and The sum of the combustion time of the second time and the afterglow time of the second time in each test run is 60 seconds or less respectively, and There is no test run in which the combustion of the test piece reaches the fixing clamp, and There is no test run in which the absorbent cotton placed under the test piece burns due to the dripping matter dropped by the combustion of the test piece. V-2: The combustion time of the first and second times in each test run is 30 seconds or less respectively, and The total of the combustion time of the first and second times in each test run, that is, the total of the combustion time for 10 times is less than 250 seconds, and The sum of the combustion time of the second time and the afterglow time of the second time in each test run is 60 seconds or less respectively, and There is no test run in which the combustion of the test piece reaches the fixing clamp, and There is a test in which absorbent cotton placed under the test piece is burned by the drippings that have fallen due to the burning of the test piece.

[0110]

Table 1

[0111]

Table 2

[0112]

Table 3

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

Claims

1. Polyolefin-based resin foam particles comprising a foam layer, wherein the base resin of the foam layer is composed of a polyolefin-based resin, and the foam layer contains a phosphonate compound and a NOR type hindered amine compound; the blending amount of the phosphonate compound in the foam layer is 5 parts by mass or more and 25 parts by mass or less with respect to 100 parts by mass of the base resin, and the blending amount of the NOR type hindered amine compound in the foam layer is 0.3 parts by mass or more and 5 parts by mass or less with respect to 100 parts by mass of the base resin; the closed cell ratio of the foam particles is 60% or more, polyolefin-based resin foam particles.

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

3. The polyolefin-based resin foam particles according to claim 1 or 2, wherein the foam particles have a coating layer covering the foam layer, and the mass ratio of the foam layer to the coating layer is 95:5 to 70:

30.

4. The polyolefin-based resin foam particles according to claim 1 or 2, wherein in the foam layer, the ratio of the blending amount of the NOR type hindered amine compound to the blending amount of the phosphonate compound is 0.04 or more and 0.4 or less.

5. The base resin of the foam layer is composed of a linear polypropylene-based resin (A), a branched polypropylene-based resin (B) having a melt tension of 50 mN or more measured under the condition of 230 °C, and / or a polyethylene-based resin (C) having an MFR of 3 g / 10 min or less measured under the conditions of a temperature of 190 °C and a load of 2.16 kg, and the total content of the branched polypropylene-based resin (B) and the polyethylene-based resin (C) with respect to the total content of 100% by mass of the linear polypropylene-based resin (A), the branched polypropylene-based resin (B), and the polyethylene-based resin (C) is 5% by mass or more and 30% by mass or less. The polyolefin-based resin foam particles according to claim 1 or 2.

6. The polyolefin-based resin foam particles according to claim 1 or 2, wherein the foam layer contains a conductive carbon material, and the blending amount of the conductive carbon material in the foam layer is 1 part by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the base resin.

7. The foamed layer contains a phenolic antioxidant, and the compounding amount of the phenolic antioxidant in the foamed layer is 0.01 part by mass or more and 0.5 part by mass or less with respect to 100 parts by mass of the base resin of the foamed layer. In the foamed layer, the ratio of the compounding amount of the phenolic antioxidant to the compounding amount of the NOR type hindered amine compound is 0.03 or more and 0.9 or less. The polyolefin resin foamed particles according to claim 1 or 2. **Claim 8** The foamed layer contains a sulfur-based antioxidant, and the compounding amount of the sulfur-based antioxidant in the foamed layer is 0.01 part by mass or more and 0.5 part by mass or less with respect to 100 parts by mass of the base resin of the foamed layer. In the foamed layer, the ratio of the compounding amount of the sulfur-based antioxidant to the compounding amount of the NOR type hindered amine compound is 0.03 or more and 0.9 or less. The polyolefin resin foamed particles according to claim 1 or 2. **Claim 9** A foamed particle molded body obtained by in-mold molding of the polyolefin resin foamed particles according to claim 1 or 2.

Images