Composite resin particles, foam particles, foam molded body, and automotive member

Abstract

The purpose of the present invention is to provide composite resin particles and the like suitable for producing foam particles with improved service life.　The present invention relates to composite resin particles containing a polypropylene-based resin, an ethylene-vinyl acetate copolymer, and a polystyrene-based resin, wherein the composite resin particles have a mass average molecular weight Mw of 100,000 to 330,000 inclusive in terms of polystyrene, the composite resin particles do not contain any carbon components or contain less than 0.50 mass% of carbon components with respect to the total mass of the polypropylene-based resin content and the ethylene-vinyl acetate copolymer content, and the surface absorbance ratio of the composite resin particles is in the range of 1.0-5.0.

Description

Composite resin particles, expanded particles, expanded molded articles, and automotive components

[0001] The present invention relates to composite resin beads, expanded beads, foamed molded articles, automotive components, and the like.

[0002] Foamed molded articles made from polystyrene-based resins are known to have excellent rigidity, thermal insulation, light weight, water resistance, and foam moldability, but poor chemical resistance and impact resistance. To compensate for this, composite foamed molded articles obtained from composite resin particles of polystyrene-based resins and polyolefin-based resins are used. Composite resin particles are generally produced by using a base resin of a polyolefin-based resin, such as a polyethylene-based resin, as seed particles (also called core particles), adding a styrene-based monomer to the seed particles, and then polymerizing them. This polymerization is also called seed polymerization. The composite resin particles are generally blended with a foaming gas and then expanded (also called pre-expanded) to form expanded particles (expanded particles). The expanded particles are then filled into a mold and heated to produce a foamed molded article.

[0003] The properties of composite resin foam molded products can be altered by changing the type of polyolefin-based resin that constitutes the composite resin particles. For example, using a polypropylene-based resin improves heat resistance, while using linear low-density polyethylene improves impact resistance. Highly heat-resistant composite resin foam molded products are in demand, primarily for automotive components, and composite resin foam molded products with excellent heat resistance obtained from composite resin particles composed of polypropylene-based resin and polystyrene-based resin have been used (Patent Document 1). However, if the steam pressure used for foam molding is not high, foaming is insufficient, making it difficult to obtain molded products with the desired shape, density, and other properties. High steam pressure required for foam molding requires more energy for molding, and further requires the use of a molding machine that is compatible with that pressure, which increases the cost of molding.

[0004] For this reason, composite resin particles obtained by compounding a base resin made of high-density polyethylene and an ethylene copolymer (e.g., ethylene-vinyl acetate copolymer) with a polystyrene resin by seed polymerization have been used as an alternative. Using these particles, foam molding is possible without requiring a high steam pressure (Patent Documents 2 and 3). Furthermore, because foam molded articles used as automotive components are often required to be flame retardant, these foam molded articles have been incorporated with a flame retardant.

[0005] However, when a flame retardant is blended into a composite resin obtained by compounding a base resin made of high-density polyethylene and an ethylene-vinyl acetate copolymer with a polystyrene-based resin by seed polymerization, the foam molded article obtained from this composite resin becomes reddish in an accelerated storage stability test.It has been reported that foam molded articles that do not become discolored in an accelerated storage stability test can be obtained by foam molding composite resin particles containing a polypropylene-based resin, an ethylene-vinyl acetate copolymer, and a polystyrene-based resin, and the foamed particles obtained from this composite resin (Patent Document 4).

[0006] Japanese Patent No. 4718645 Japanese Patent Application Laid-Open No. 2015-189912 Japanese Patent No. 6251409 International Publication No. 2022 / 202680

[0007] Expandable beads, in which composite resin beads are blended with a foaming gas, are pre-expanded (primary expansion) to produce expanded beads (also called pre-expanded beads). The expanded beads are then filled into a mold and heated to form a foamed molded article. For this reason, after production of the expanded beads, the expanded beads are stored for a period until the expansion molding step. If this storage period is long, the expandability of the expanded beads will be insufficient in the expansion molding step, and the appearance of the resulting foamed molded article will be impaired (for example, the foamed molded article will shrink). Therefore, a usage period is set for the expanded beads.

[0008] The present inventors have found that the use life of expanded beads produced from composite resin beads containing a polypropylene-based resin, an ethylene-vinyl acetate copolymer, and a polystyrene-based resin is short.

[0009] An object of the present invention is to provide composite resin particles and the like suitable for producing expanded beads having an improved shelf life.

[0010] The present inventors have discovered that composite resin particles containing a polypropylene-based resin, an ethylene-vinyl acetate copolymer, and a polystyrene-based resin, which have a molecular weight and a surface absorbance ratio within specific ranges, can provide expanded resin particles with a long usable period, and have completed the present invention.

[0011] The present invention typically includes the following aspects: Item 1. Composite resin particles containing a polypropylene-based resin, an ethylene-vinyl acetate copolymer, and a polystyrene-based resin, wherein the composite resin particles have a polystyrene-equivalent mass average molecular weight Mw of 100,000 to 330,000, and the composite resin particles contain no carbon component or contain less than 0.50 mass% of a carbon component relative to the total mass of the polypropylene-based resin content and the ethylene-vinyl acetate copolymer content, and the surface absorbance ratio of the composite resin particles, as specified by the following method, is within the range of 1.0 to 5.0. (Surface absorbance ratio) The surface absorbance ratio of the composite resin particles is determined by the infrared absorption spectrum obtained by infrared spectroscopic analysis of the surface of the composite resin particles using an ATR method. －１ Absorbance (D1380) and 698 cm －１The absorbance (D698) of the composite resin particles is calculated, and the value obtained by applying the formula D698 / D1380 to the surface absorbance ratio is used as the surface absorbance ratio. Item 2. The composite resin particles according to Item 1, wherein the content of the polypropylene resin is 3.0 to 50 mass%, the content of the ethylene-vinyl acetate copolymer is 2.0 to 45 mass%, and the content of the polystyrene resin is 40 to 95 mass%, relative to the mass of the composite resin particles. Item 3. The composite resin particles according to Item 1 or 2, wherein the content of the ethylene-vinyl acetate copolymer in the composite resin particles is 10 to 95 parts by mass, relative to 100 parts by mass of the polypropylene resin content. Item 4. Item 5. The composite resin particle according to any one of Items 1 to 4, wherein the total mass of the polypropylene resin and the ethylene-vinyl acetate copolymer in the composite resin particle is 5 / 95 to 60 / 40, based on the mass of the polystyrene-based resin. Item 6. The composite resin particle according to any one of Items 1 to 5, wherein the ethylene-vinyl acetate copolymer has a melting point of 100 to 120°C. Item 7. Item 6. The composite resin particle according to any one of Items 1 to 6, wherein the ethylene-vinyl acetate copolymer has a ratio (Mw / Mn) of its mass average molecular weight (Mw) to its number average molecular weight (Mn) of 1.0 to 7.0. Item 8. The composite resin particle according to any one of Items 1 to 7, wherein the ethylene-vinyl acetate copolymer has a melt flow rate of 0.50 g / 10 min to 10 g / 10 min. Item 9. The composite resin particle according to any one of Items 1 to 8, wherein the polypropylene-based resin has a melting point of 125 to 145°C. Item 10. The composite resin particle according to any one of Items 1 to 9, wherein the polypropylene-based resin is a random polypropylene.Item 11. The composite resin particle according to any one of Items 1 to 10, wherein the composite resin particle further contains a flame retardant, and the content thereof is 0.50 to 10 mass% of the mass of the composite resin particle excluding the flame retardant. Item 12. The composite resin particle according to Item 11, wherein the flame retardant is a halogen-based flame retardant. Item 13. The composite resin particle according to any one of Items 1 to 12, wherein the composite resin particle is a seed-polymerized particle obtained by impregnating and polymerizing a styrene-based monomer into a seed particle containing the polypropylene-based resin and the ethylene-vinyl acetate copolymer. Item 14. The composite resin particle according to any one of Items 1 to 13, wherein the composite resin particle does not contain a carbon component. Item 15. An expanded particle made of the composite resin particle according to any one of Items 1 to 14. Item 16. The composite resin particle has a bulk density of 10 kg / m. ３ ~200 kg / m ３ Item 17. The expanded beads according to Item 15. Item 18. A foamed molded article comprising the expanded beads according to Item 15 or 16. Item 19. A foamed molded article having a density of 20 kg / m ３ ~50 kg / m ３ Item 19. An automobile component comprising the foam molded article according to item 17 or 18.

[0012] An object of the present invention is to provide expanded beads with an improved usable life, or to provide composite resin beads that can provide such expanded beads. A long usable life of expanded beads eliminates the need to prepare expanded beads for each expansion molding, and as a result, large quantities of expanded beads can be produced at one time. An object of the present invention is to provide a foamed molded product that has a small rate of dimensional change relative to the mold and excellent surface expansion, even when using a low-vapor-pressure medium (e.g., water vapor), to provide expanded beads that can provide such a foamed molded product, or to provide composite resin beads that can provide such expanded beads. Being able to perform expansion molding using a low-vapor-pressure medium reduces the energy required for expansion molding. This allows for simplification of the equipment required for expansion molding and reduces the costs required for expansion molding.

[0013] As used herein, the phrase "comprising" is intended to encompass the phrases "consisting essentially of" and "consisting of."

[0014] In this specification, the term "foaming" is used to mean "in-mold foaming" using foam particles, unless otherwise specified.

[0015] With respect to the numerical ranges described in this specification, the symbol "to" means greater than or equal to the leftmost numerical value and less than or equal to the rightmost numerical value. For example, "0.50 to 10% by mass" and "0.50% to 10% by mass" both mean "0.50% by mass or greater and 10% by mass or less." Furthermore, with respect to numerical ranges, "greater than or equal to" means "the same as or greater than," and "less than or equal to" means "the same as or less than."

[0016] In the numerical ranges described herein, the upper or lower limit of a certain numerical range can be arbitrarily combined with the upper or lower limit of another numerical range described in the same paragraph or another step. In addition, in a certain numerical range described herein, the upper or lower limit of that numerical range can be replaced with a value shown in an example or a value that can be unambiguously derived from an example.

[0017] The composite resin particles are typically obtained by impregnating base resin particles (seed particles) with a styrene-based monomer and polymerizing the styrene-based monomer. The base resin contains at least a polypropylene-based resin and an ethylene-vinyl acetate copolymer. The total content of the polypropylene-based resin and the ethylene-vinyl acetate copolymer in the seed particles may be, for example, 80 to 100% by mass, 85 to 100% by mass, 90 to 100% by mass, or 95 to 100% by mass, based on the mass of the seed particles.

[0018] (Polypropylene Resin; PP) The polypropylene resin is not particularly limited, and known resins can be used. Examples of polypropylene resins include homopolymers, random copolymers, and block copolymers. Random copolymers (also called random polypropylenes) are preferred because of their high moldability (i.e., the foam particles have high fusibility at low vapor pressure, allowing for foam molding and increasing the expansion ratio during foaming). As the polypropylene resin, recycled products, such as polypropylene resins used as packaging materials, can be recovered and recycled, and recycled resins can also be used.

[0019] The copolymer may contain an olefin other than propylene (e.g., ethylene, butene, etc.). Examples of random copolymers include ethylene-propylene random copolymers, propylene-butene random copolymers, and ethylene-propylene-butene random copolymers. Examples of block copolymers include ethylene-propylene block copolymers, propylene-butene block copolymers, and ethylene-propylene-butene block copolymers. The proportion of components derived from olefins other than propylene in the copolymer may be, for example, 0.010 to 10% by mass, 0.010 to 8.0% by mass, 0.10 to 8.0% by mass, or 0.20 to 8.0% by mass, preferably 1.0 to 8.0% by mass, and more preferably 2.0 to 7.0% by mass. Commercially available polypropylene resins can be used. For example, they are available from Prime Polymer Co., Ltd., SunAllomer Co., Ltd., Sumitomo Chemical Co., Ltd., and the like.

[0020] The melting point of the polypropylene resin is not particularly limited, but can be, for example, 125 to 145°C, and preferably 130 to 145°C. A melting point within this range is advantageous in that the expanded beads have a longer usable life, are excellent in foam moldability at low vapor pressure, and tend to achieve a high expansion ratio during foaming. The melting point can be determined by the method described in the examples.

[0021] The melt flow rate (also referred to as MFR in this specification) of the polypropylene-based resin is not particularly limited, but is preferably 0.10 g / 10 min to 20 g / 10 min, more preferably 1.0 g / 10 min to 10 g / 10 min, and particularly preferably 4.0 g / 10 min to 8.0 g / 10 min. An MFR within the above range is advantageous in that it provides excellent foam moldability at low vapor pressure. The MFR can be determined by the method described in the examples.

[0022] Polypropylene resin has a strength of 880 kg / m ３ ~950 kg / m ３ The density within this range is advantageous in terms of impact resistance and molding processability of the foamed molded article. ３ ~930 kg / m ３ is preferred, and 890 kg / m ３~920 kg / m ３ More preferably, 890 kg / m ３ ~910 kg / m ３ is particularly preferred. A density within the above range is advantageous in terms of foam moldability at low vapor pressure. The density can be determined by the following method. (Density of Polypropylene Resin) The density of the polypropylene resin is measured by the density gradient tube method in accordance with JIS K6922-1:1998.

[0023] The content of the polypropylene resin in the base resin or seed particles can be, for example, 10 to 90 mass%, 10 to 88 mass%, 10 to 85 mass%, 10 to 80 mass%, 10 to 75 mass%, 30 to 90 mass%, 30 to 80 mass%, 30 to 75 mass%, 40 to 90 mass%, 40 to 80 mass%, 40 to 75 mass%, 50 to 90 mass%, 50 to 80 mass%, 50 to 75 mass%, etc., more preferably 50 to 80 mass%, and particularly preferably 60 to 80 mass%. The content of the polypropylene resin in the composite resin particles can be, for example, 3.0 to 50 mass%, 3.0 to 35 mass%, etc., preferably 4.0 to 30 mass%, more preferably 5.0 to 25 mass%, and particularly preferably 10 to 25 mass%, based on the mass of the composite resin particles. When the content of the polypropylene resin in the base resin, seed particles, or composite resin particles is within the above range, it is advantageous in that the expanded beads have a longer usable life or that the expanded molded articles are excellent at low vapor pressure.

[0024] (Ethylene-vinyl acetate copolymer) Ethylene-vinyl acetate copolymer is a copolymer of ethylene and vinyl acetate. Ethylene-vinyl acetate copolymer is superior to copolymers of ethylene and other ester monomers (e.g., alkyl acrylate esters, alkyl methacrylate esters, and vinyl aliphatic saturated monocarboxylates (excluding vinyl acetate)) in that it generates less powder during the production of foamed composite resin beads and has a small rate of dimensional change upon heating. As the ethylene-vinyl acetate copolymer, recycled resins obtained by recovering recycled products, for example, ethylene-vinyl acetate copolymers used as packaging materials, etc., can also be used.

[0025] The proportion of vinyl acetate-derived components in the ethylene-vinyl acetate copolymer is preferably 1.0 to 20% by mass, more preferably 1.0 to 14% by mass, and even more preferably 1.0 to 10% by mass.

[0026] The melting point of the ethylene-vinyl acetate copolymer is not particularly limited, but can be, for example, 85 to 120°C, preferably 100 to 120°C, more preferably 100 to 115°C, and even more preferably 100 to 110°C. A melting point within the above range is advantageous in that the expanded beads have a longer usable life, the expanded molded article is excellent at low vapor pressure, and the compatibility with polypropylene resins is good, resulting in excellent fusion properties during expansion molding. The melting point can be determined by the method described in the examples.

[0027] The ratio (Mw / Mn) of the mass average molecular weight (Mw) of the ethylene-vinyl acetate copolymer to the number average molecular weight (Mn) of the ethylene-vinyl acetate copolymer is not particularly limited, but can be, for example, 1.0 to 7.5, and is preferably 1.0 to 7.0. Mw / Mn within the above range is advantageous in that the strength of the foamed molded article is high or the impact resistance is improved. Mw / Mn is more preferably 3.0 to 6.0, and even more preferably 3.5 to 5.5. The number average molecular weight and mass average molecular weight can be determined by the following method, and more specifically, can be determined by the method described in the examples.

[0028] (Number-average molecular weight (Mn) and mass-average molecular weight (Mw) of ethylene-vinyl acetate copolymer) Specifically, the molecular weight is measured as follows. 6 mL of o-dichlorobenzene was added to a container containing 6 mg of sample, and the container was sealed to prepare a solution. The solution was prepared by heating at 160°C for 1 hour using a DF-8200 manufactured by Tosoh Corporation to dissolve the sample. This solution was used as the measurement sample and measured using gel permeation chromatography under the following measurement conditions. Standard polystyrene was measured in advance, and the average molecular weights (Mn, Mw) of the sample were determined from a calibration curve of the standard polystyrene that had been prepared. Instrument used: Tosoh Corporation "HLC-8321GPC / HT" gel permeation chromatograph Guard column: Tosoh Corporation TSKgel guard column HHR(30)HT2 (7.5mmI.D. x 7.5cm) x 1 Column: Tosoh Corporation TSKgel GMHHR-H(20)HT2 (7.8mmI.D. x 30cm) x 3 Mobile phase: O-dichlorobenzene Sample flow rate: 1.0mL / min Reference flow rate: 0.5mL / min Detector: RI Sample concentration: 0.1wt% Injection volume: 300µL Measurement time: 34min (Temperature settings for each part of the instrument) Solvent stocker: 40°C Column oven (column temperature): 160°C Sample table: 160°C Injection valve: 160°C Detector: 160°C The standard polystyrene samples used for the calibration curve are those manufactured by Tosoh Corporation under the trade names "High polymer kit" and "oligomer kit," and have mass average molecular weights of 8,420,000, 5,480,000, 2,110,000, 1,090,000, 706,000, 427,000, 190,000, 96,400, 37,900, 17,400, 5,060, 2,550, 1,013, and 589. The standard polystyrene for the calibration curve was divided into groups A (8,420,000, 1,090,000, 190,000, 17,400, 1,013), B (5,480,000, 706,000, 96,400, 5,060, 589), and C (2,110,000, 427,000, 37,900, 2,550). 10 mg of each of A was weighed out and dissolved in 30 mL of o-dichlorobenzene. 10 mg of each of B and C was also weighed out and dissolved in 30 mL of o-dichlorobenzene.A standard polystyrene calibration curve is prepared by injecting 300 μL of each of the solutions A, B, and C, and creating a calibration curve (cubic equation) from the retention times obtained after measurement. The average molecular weight is calculated using this calibration curve.

[0029] The MFR of the ethylene-vinyl acetate copolymer is not particularly limited, but can be, for example, 0.30 g / 10 min to 10 g / 10 min, 0.50 g / 10 min to 10 g / 10 min, or 0.30 g / 10 min to 5.0 g / 10 min, with 0.50 g / 10 min to 5.0 g / 10 min being preferred, 0.50 g / 10 min to 4.0 g / 10 min being more preferred, and 0.50 g / 10 min to 3.0 g / 10 min being even more preferred. An MFR within the above range is advantageous in that the foamed molded article is excellent at low vapor pressure, the strength of the foamed molded article is high, or impact resistance is improved. The MFR can be determined by the method described in the examples.

[0030] The content of the ethylene-vinyl acetate copolymer in the base resin or seed particles can be, for example, 10 to 90 mass%, 12 to 90 mass%, 15 to 95 mass%, 20 to 90 mass%, 25 to 90 mass%, 10 to 70 mass%, 20 to 70 mass%, 25 to 70 mass%, 10 to 60 mass%, 20 to 60 mass%, 25 to 60 mass%, 10 to 50 mass%, 20 to 50 mass%, or 25 to 50 mass%, with 20 to 50 mass% being more preferred, and 20 to 40 mass% being particularly preferred, relative to the mass of the base resin or seed particles. An ethylene-vinyl acetate copolymer content within the above range is advantageous in that the expanded beads have a long service life, excellent expansion moldability at low vapor pressure, and excellent heat resistance. The content of the ethylene-vinyl acetate copolymer in the composite resin particles can be, for example, 2.0 to 45 mass %, preferably 2.0 to 40 mass %, and more preferably 2.0 to 30 mass %, relative to the mass of the composite resin particles. When the content of the ethylene-vinyl acetate copolymer is within this range, it is advantageous in that the expanded beads have a long service life or excellent expansion moldability at low vapor pressure.

[0031] The ethylene-vinyl acetate copolymer content in the seed particles or composite resin particles can be, for example, 10 to 95 parts by mass, 20 to 80 parts by mass, or 10 to 75 parts by mass, preferably 20 to 75 parts by mass, and more preferably 20 to 70 parts by mass, relative to 100 parts by mass of the polypropylene resin content. An ethylene-vinyl acetate copolymer content within the above range is advantageous in that the expanded beads have a long service life or are excellent in expansion moldability at low vapor pressure.

[0032] Examples of polystyrene-based resins include polymers derived from styrene-based monomers such as styrene, α-methylstyrene, p-methylstyrene, and t-butylstyrene. Furthermore, the styrene-based polymer may be a polymer formed from a styrene-based monomer and another monomer copolymerizable with the styrene-based monomer. Examples of other monomers include polyfunctional monomers such as divinylbenzene and (meth)acrylic acid esters that do not contain a benzene ring in their structure, such as butyl (meth)acrylate. The resin components derived from these other monomers may be contained in the styrene-based polymer in an amount not exceeding 5% by mass, for example, 0.001 to 5% by mass, 0.001 to 4% by mass, 0.001 to 3% by mass, 0.001 to 2% by mass, 0.001 to 1% by mass, 0.01 to 5% by mass, 0.01 to 4% by mass, 0.01 to 3% by mass, 0.01 to 2% by mass, 0. ... or 0.050 to 5.0% by mass.

[0033] A polystyrene-based resin in which a (meth)acrylic acid ester is copolymerized with a styrene-based monomer is composed of a component derived from the (meth)acrylic acid ester and a component derived from the styrene-based monomer. This component derived from the (meth)acrylic acid ester is also referred to as a (meth)acrylic acid ester-derived resin component. The (meth)acrylic acid ester may be either an acrylic acid ester or a methacrylic acid ester, but an acrylic acid ester is preferred. Examples of the (meth)acrylic acid ester include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate. Methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, pentyl acrylate, hexyl acrylate, and 2-ethylhexyl acrylate are preferred, with butyl acrylate being more preferred.

[0034] The content of the polystyrene-based resin in the composite resin particles can be, for example, 50 to 95 mass%, 50 to 90 mass%, or 50 to 85 mass%, preferably 55 to 85 mass%, and more preferably 60 to 85 mass%, relative to the mass of the composite resin particles. Setting the content of the polystyrene-based resin within this range is advantageous in that the expanded beads have a long service life or are excellent in expansion moldability at low vapor pressure.

[0035] In the composite resin particles, the ratio of the total mass content of the polypropylene-based resin and the ethylene-vinyl acetate copolymer to the mass content of the polystyrene-based resin may be, for example, 5:95 to 60:40, 5:95 to 50:50, or 10:90 to 50:50, and is preferably 15:85 to 45:55, more preferably 15:85 to 40:60, and even more preferably 20:80 to 40:60.

[0036] (Carbon Component) The base resin or seed particles may contain a small amount of carbon component in addition to the polypropylene resin and the ethylene-vinyl acetate copolymer, but preferably do not contain any carbon component. Examples of the carbon component include carbon black (CB) such as furnace black, ketjen black, channel black, thermal black, and acetylene black, graphite, and carbon fiber.

[0037] The carbon component is preferably particulate, and its average particle size may be 5.0 nm to 100 nm, preferably 15 nm to 35 nm. The average particle size of the carbon component is the average value of particle diameters observed under an electron microscope. However, when the carbon component is carbon black, the average particle size of the carbon black is the average value of particle diameters measured and calculated using an electron microscope photograph of small spherical (crystallite-shaped and inseparable) components that make up the carbon black aggregate.

[0038] When the base resin, seed particles, or composite resin particles contain a carbon component, the content thereof can be, for example, less than 0.50% by mass, less than 0.40% by mass, less than 0.30% by mass, less than 0.20% by mass, less than 0.10% by mass, 0.00010 to 0.50% by mass, 0.00010 to 0.40% by mass, 0.00010 to 0.30% by mass, 0.00010 to 0.20% by mass, 0.00010 to 0.10% by mass, 0.0010 to 0.50% by mass, 0.0010 to 0.40% by mass, 0.0010 to 0.30% by mass, 0.0010 to 0.20% by mass, 0.0010 to 0.10% by mass, and the like, relative to the total mass of the polypropylene resin and the ethylene-vinyl acetate copolymer. The carbon component may be added to and mixed with the base resin, or may be added to and mixed with the base resin as a carbon masterbatch.

[0039] (Other Resins) The base resin or seed particles may or may not contain other resins in addition to the polypropylene resin and ethylene-vinyl acetate copolymer, as long as the amount is within a range that does not impair the usage period of the expanded beads or the expansion moldability at low vapor pressure. Examples of other resins include acrylic acid ethyl ester copolymers and polyester-based resins. The content of the other resin in the base resin or seed particles is, for example, 0.10 to 30% by mass, preferably 0.20 to 20% by mass, and more preferably 0.30 to 10% by mass, relative to the total mass of the polypropylene resin and ethylene-vinyl acetate copolymer.

[0040] (Inorganic Component) The base resin or seed particles may contain an inorganic component (excluding carbon components) in addition to the polypropylene resin and the ethylene-vinyl acetate copolymer. The inclusion of an inorganic component in the seed particles facilitates the formation of fine bubbles. Examples of inorganic components include inorganic bubble regulators such as talc, silica, calcium silicate, calcium carbonate, sodium borate, and zinc borate. Talc and silica are preferred because they facilitate the homogenization of bubble size. The inorganic component in the base resin, seed particles, or composite resin particles may be, for example, 0.010 to 5.0% by mass, preferably 0.10 to 1.0% by mass, relative to the total mass of the polypropylene resin and the ethylene-vinyl acetate copolymer. The inorganic component may be added when the polypropylene resin and the ethylene-vinyl acetate copolymer are mixed, or may be added to a mixed resin in which the polypropylene resin and the ethylene-vinyl acetate copolymer are mixed.

[0041] (Other Components) The base resin or seed particles may contain other components in addition to the polypropylene-based resin, ethylene-vinyl acetate copolymer, polystyrene-based resin, and the above-mentioned materials. Examples of other components include colorants, nucleating agents, stabilizers, fillers (reinforcing materials), metal salts of higher fatty acids, antistatic agents, lubricants, natural or synthetic oils, waxes, UV absorbers, weathering stabilizers, anti-fogging agents, anti-blocking agents, slip agents, coating agents, and neutron shielding agents. When the base resin or seed particles contain other components, the content thereof may be 0.0010 to 10% by mass, preferably 0.0010 to 5.0% by mass or less, and more preferably 0.0010 to 3.0% by mass, relative to the mass of the base resin or seed particles.

[0042] (Method for producing seed particles) The seed particles can be obtained by a known method used for producing seed particles for forming foamed molded articles. For example, a base resin containing a polypropylene resin and an ethylene-vinyl acetate copolymer is melt-kneaded and extruded in an extruder to obtain strands, and the obtained strands are cut in air, in water, or while being heated to form granules. The resins may be mixed in a mixer before being charged into the extruder.

[0043] The seed particles may have any known shape, but are preferably cylindrical, oval-spherical (egg-shaped), or spherical. The shape is more preferably oval-spherical or spherical, since the expanded beads obtained from the seed particles have good mold-filling properties. The seed particles preferably have an average particle size of 0.50 to 1.4 mm.

[0044] (Composite Resin Particles) The composite resin particles contain a polypropylene-based resin, an ethylene-vinyl acetate copolymer, and a polystyrene-based resin as resin components. The polypropylene-based resin and the ethylene-vinyl acetate copolymer may be derived from a base resin, and the polystyrene-based resin may be derived from a styrene-based monomer. The total content of the polypropylene-based resin, the ethylene-vinyl acetate copolymer, and the polystyrene-based resin in the composite resin particles may be, for example, 80 to 100% by mass, 85 to 100% by mass, 90 to 100% by mass, 95 to 100% by mass, etc., relative to the mass of the composite resin particles. The composite resin particles can be produced, for example, by a seed polymerization method (impregnating seed particles with a styrene-based monomer and polymerizing them).

[0045] (Mass average molecular weight (Mw) of composite resin particles) In this specification, the mass average molecular weight of the composite resin particles means the mass average molecular weight in terms of polystyrene. The mass average molecular weight of the polypropylene resin is preferably 100,000 to 330,000, more preferably 200,000 to 330,000, and even more preferably 250,000 to 330,000. Having the mass average molecular weight within the above range is advantageous in that the service life of the expanded beads is improved, moldability at low vapor pressure is excellent, and the expansion ratio during expansion is likely to be high. The mass average molecular weight can be determined by the method described in the examples.

[0046] (Surface absorbance ratio of composite resin particles) In order to obtain the surface absorbance ratio, first, the surface of the composite resin particles is subjected to infrared spectroscopic analysis by the ATR method. －１ Absorbance (D1380) and 698 cm －１ The absorbance (D698) is obtained. The value calculated by applying the obtained absorbance to the formula D698 / D1380 is the surface absorbance ratio. Specifically, it is specified by the method described in the Examples. D698 is the absorbance corresponding to the absorption spectrum derived from the out-of-plane bending vibration of the benzene ring contained in the polystyrene-based resin. Therefore, D698 reflects the proportion of polystyrene-based resin on the surface of the composite resin particle. D1380 is the absorbance corresponding to the absorption spectrum derived from the methyl group contained in the polypropylene-based resin. Therefore, D1380 reflects the proportion of polypropylene-based resin on the surface of the composite resin particle.

[0047] The surface absorbance ratio may be 1.0 to 5.0, preferably 1.5 to 5.0, more preferably 1.5 to 4.0, and particularly preferably 1.5 to 3.6. A surface absorbance ratio within the above range is advantageous in terms of excellent moldability at low vapor pressure and excellent heat resistance.

[0048] (Flame Retardant) The composite resin particles may contain a flame retardant. In addition, the composite resin particles have relatively high flame retardancy even without a flame retardant, so they do not necessarily need to contain a flame retardant.

[0049] Examples of halogen-based flame retardants include tetrabromobisphenol A, derivatives thereof (e.g., tetrabromobisphenol A-bis(2,3-dibromo-2-methylpropyl ether), tetrabromobisphenol A-bis(2,3-dibromopropyl ether), tetrabromobisphenol A-bis(allyl ether)), triallyl isocyanurate hexabromide, tris(2,3-dibromopropyl)isocyanurate, tetrabromocyclooctane, and hexabromocyclododecane.

[0050] The content of the flame retardant, relative to the mass of the composite resin particles excluding the flame retardant, can be, for example, 0.50 to 10 mass%, 1.5 to 6.0 mass%, etc., preferably 1.5 to 4.0 mass%, more preferably 2.0 to 3.5 mass%. A flame retardant content within this range is advantageous in that the foamed molded article can achieve high levels of both flame retardancy and heat resistance.

[0051] When the composite resin particles contain a flame retardant, they preferably contain a flame retardant aid. The inclusion of a flame retardant aid can further enhance the flame retardancy provided by the flame retardant. Examples of flame retardant aids include organic peroxides such as dicumyl peroxide (DCP), cumene hydroperoxide, and diacyl peroxide, as well as 2,3-dimethyl-2,3-diphenylbutane (also known as biscumyl) and 3,4-dimethyl-3,4-diphenylhexane. The flame retardant aid is preferably contained in an amount of, for example, 50 parts by mass or less, preferably 10 to 40 parts by mass, and more preferably 15 to 25 parts by mass, per 100 parts by mass of the flame retardant. When the content of the flame retardant aid is within the above range, deterioration in the strength and heat resistance of the foamed molded article is suppressed.

[0052] The shape of the composite resin particles may be any known shape, but cylindrical, approximately spherical, and spherical shapes are preferred, and approximately spherical or spherical shapes are more preferred in terms of the ease with which expanded beads formed from the composite resin particles can be filled into a mold.The average particle diameter of the composite resin particles is preferably 0.60 mm to 1.8 mm in terms of the ease with which the expanded beads can be filled into a mold.

[0053] (Method for Producing Composite Resin Particles) The method for producing composite resin particles is not particularly limited as long as it can produce the composite resin particles described above, and may be a commonly used seed polymerization method. For example, composite resin particles can be obtained by step (A) of impregnating and polymerizing seed particles containing a polypropylene resin and an ethylene-vinyl acetate copolymer with a styrene monomer to obtain composite resin particles. Therefore, the present invention may include a method for producing composite resin particles, including step (A) of impregnating and polymerizing seed particles containing a polypropylene resin and an ethylene-vinyl acetate copolymer with a styrene monomer to obtain composite resin particles. In the present invention, in step (A), the styrene monomer is slowly added in the presence of a water-soluble polymerization inhibitor while controlling the addition rate (e.g., 0.1 parts by weight / second or less per 100 parts by weight of seed particles), which is preferred in terms of making it easier to achieve the above-mentioned surface absorbance ratio, prolonging the service life of the expanded particles, and providing excellent expansion moldability at low vapor pressure.

[0054] In step (A), it is preferable to polymerize the styrene-based monomer in multiple batches. This is because the particle shape can be made approximately spherical in the initial polymerization step (step 1). In step 1, seed particles in an aqueous medium are impregnated with a styrene-based monomer in the presence of a water-soluble polymerization inhibitor, and then the mixture is heated to a polymerization temperature to polymerize the styrene-based monomer. The styrene-based monomer is added to the aqueous medium containing the seed particles and impregnated into the seed particles. At this time, the temperature of the aqueous medium may be a temperature at which polymerization of the styrene-based monomer does not proceed, for example, 30 to 130°C. Since the styrene-based monomer does not substantially polymerize at this temperature, the addition rate of the styrene-based monomer is not limited; for example, the entire amount of the styrene-based monomer can be added to the reaction system at once, or it can be added slowly in multiple batches. When the styrene-based monomer is added to the aqueous medium containing the seed particles, an additional polymerization inhibitor may be added. The styrene-based monomer is polymerized by heating the aqueous medium to which the styrene-based monomer has been added to a temperature at which polymerization proceeds. This temperature can be 10 to 50°C higher than the melting point of the seed particles (e.g., 125 to 165°C), preferably 20 to 30°C higher than the melting point of the seed particles (e.g., 135 to 145°C). The polymerization can be carried out in the presence or absence of a polymerization initiator. The melting point of the seed particles can be determined in the same manner as the melting point of the polypropylene-based resin. In the first step, the seed particles in which the styrene-based monomer has been polymerized can be made approximately spherical by treating them as described above.

[0055] In the first step, the amount of the polymerization inhibitor used may be 0.010 to 0.20 parts by mass, and preferably 0.040 to 0.10 parts by mass, per 100 parts by mass of the styrene-based monomer used in the first step.

[0056] The first step may be carried out in the presence or absence of a polymerization initiator. When a polymerization initiator is used, the amount of the polymerization initiator used may be 0.050 to 0.50 parts by mass, and preferably 0.10 to 0.30 parts by mass, per 100 parts by mass of the styrene-based monomer used in the first step.

[0057] In the next polymerization step (second step), a styrene-based monomer is slowly added to the reaction solution obtained in the first step (containing the seed particles that have undergone the first polymerization), and the seed particles in the reaction solution are impregnated with the styrene-based monomer and polymerized. The second step may be carried out in the presence or absence of a polymerization inhibitor. The second step may be carried out in the presence or absence of a polymerization initiator. The second step may be carried out in the presence or absence of a chain transfer agent. In the second step, the styrene-based monomer is added at a rate of 0.010 to 0.10 parts by mass / second, preferably 0.010 to 0.060 parts by mass / second, relative to 100 parts by mass of the seed particles. The temperature at which the styrene-based monomer is added is a temperature at which the polymerization of the styrene-based monomer proceeds. For example, the temperature may be 110 to 140°C. The added styrene-based monomer is polymerized while impregnating the particles in the reaction solution.

[0058] The second step may be carried out in the presence or absence of a polymerization inhibitor. When a polymerization inhibitor is used in the second step, the amount of the polymerization inhibitor used may be 0.010 to 0.20 parts by mass, preferably 0.020 to 0.10 parts by mass, per 100 parts by mass of the styrene-based monomer used in the second step.

[0059] The second step may be carried out in the presence or absence of a polymerization initiator. When a polymerization initiator is used in the second step, the amount of the polymerization initiator used may be 0.10 to 0.50 parts by mass, preferably 0.20 to 0.50 parts by mass, based on 100 parts by mass of the styrene-based monomer used in the second step.

[0060] The second step can be carried out in the presence or absence of a chain transfer agent. When a chain transfer agent is used in the second step, the amount of the chain transfer agent used can be 0.010 to 0.50 parts by mass, and preferably 0.050 to 0.40 parts by mass, per 100 parts by mass of the styrene-based monomer used in the second step. Polymerization in the presence of a chain transfer agent is preferred in that low-temperature polymerization can be suppressed even at low polymerization temperatures, allowing the molecular weight of the composite resin particles to be controlled low.

[0061] Furthermore, one or more polymerization steps similar to the second step may be carried out following the second step.

[0062] The polymerization inhibitor is not particularly limited as long as it is the polymerization inhibitor used in the technical field, but is preferably a water-soluble polymerization inhibitor.Examples of the water-soluble polymerization inhibitor include nitrites such as sodium nitrite, potassium nitrite, ammonium nitrite, calcium nitrite, silver nitrite, strontium nitrite, cesium nitrite, barium nitrite, magnesium nitrite, lithium nitrite, dicyclohexylammonium nitrite, etc., thiocyanates such as ammonium thiocyanate, zinc thiocyanate, sodium thiocyanate, potassium thiocyanate, aluminum thiocyanate, etc., mercaptoethanol, monothiopropylene glycol, thioglycerol, thioglycolic acid Examples of suitable water-soluble polymerization inhibitors include water-soluble sulfur-containing organic compounds such as thiohydroacrylic acid, thiolactic acid, thiomalic acid, thioethanolamine, 1,2-dithioglycerol, and 1,3-dithioglycerol, ascorbic acid, sodium ascorbate, and 2,2-methylenebis(4-methyl-6-t-butylphenol), and among these, nitrites and 2,2-methylenebis(4-methyl-6-t-butylphenol) are preferred, nitrites are more preferred, and sodium nitrite is particularly preferred, in that they have little effect on the physical properties of the composite resin particles after polymerization. These water-soluble polymerization inhibitors can be used alone or in combination of two or more.

[0063] As the polymerization initiator, those generally used as initiators for suspension polymerization of styrene-based monomers can be suitably used. Examples include organic peroxides such as benzoyl peroxide, di-t-butyl peroxide, t-butyl peroxybenzoate, dicumyl peroxide, 2,5-dimethyl-2,5-di-t-butylperoxyhexane, t-butylperoxy-3,5,5-trimethylhexanoate, and t-butyl-peroxy-2-ethylhexyl carbonate, and azo compounds such as azobisisobutyronitrile and azobisdimethylvaleronitrile. These polymerization initiators can be used alone or in combination. Dicumyl peroxide can also function as a flame retardant aid.

[0064] Examples of aqueous media include water and mixed media of water and a water-soluble solvent (for example, a lower alcohol).

[0065] A dispersant may be added to the aqueous medium as needed. The dispersant is not particularly limited, and any known dispersant can be used. Specific examples include poorly soluble inorganic substances such as calcium phosphate, magnesium pyrophosphate, sodium pyrophosphate, and magnesium oxide. A surfactant such as sodium dodecylbenzenesulfonate may be added to the aqueous medium.

[0066] In step (A), the amount of styrene-based monomer used may be such that the ratio of seed particle mass to styrene monomer mass is 5 / 95 to 50 / 50. The content of polystyrene-based resin in the composite resin particles may be an amount corresponding to the amount of styrene-based monomer used. The ratio of seed particle mass in the composite resin particles to polystyrene-based resin mass in the composite resin particles is preferably 5 / 95 to 50 / 50. Having the amount of styrene-based monomer used or the polystyrene-based resin mass content within the above ranges is advantageous in terms of a long service life of the expanded beads or excellent foam moldability at low vapor pressure. The above range is more preferably 10 / 90 to 50 / 50, even more preferably 15 / 85 to 45 / 55, and particularly preferably 15 / 85 to 40 / 60.

[0067] Composite resin particles containing a flame retardant or a flame retardant and a flame retardant auxiliary can be produced by a method of impregnating seed particles with the flame retardant or the flame retardant and the flame retardant auxiliary together with a styrene-based monomer, or by a method of impregnating particles after polymerization.

[0068] (Expandable Particles) The expandable particles contain the composite resin particles and a blowing agent. Examples of the blowing agent include organic gases such as propane, n-butane, isobutane, n-pentane, isopentane, cyclopentane, n-hexane, and isohexane, and inorganic gases such as carbon dioxide, nitrogen, helium, argon, and air. These blowing agents can be used alone or in combination. Suitable organic gases include n-butane, isobutane, n-pentane, and isopentane, or combinations thereof. Suitable blowing agents include n-pentane, isopentane, cyclopentane, n-hexane, and isohexane, which are advantageous in that they provide a long service life for the expanded particles or excellent foaming moldability at low vapor pressure. The content of the blowing agent in the expandable particles is preferably 5.0 to 25 parts by mass per 100 parts by mass of the composite resin particles.

[0069] The expandable particles can be obtained, for example, by impregnating composite resin particles with a blowing agent during or after the polymerization of a styrene-based monomer. The impregnation can be carried out by a method known per se. For example, impregnation during the polymerization of a styrene-based monomer can be carried out by carrying out the polymerization reaction in a sealed container and injecting a blowing agent into the container. Impregnation after the polymerization of a styrene-based monomer can be carried out, for example, by injecting a blowing agent into a sealed container containing the composite resin particles.

[0070] (Expanded beads) Expanded beads (also commonly referred to as pre-expanded beads) are particles obtained by pre-expanding composite resin beads. For example, expanded beads can be obtained by expanding expandable beads impregnated with a blowing agent. Expanded beads produced from the composite resin beads of the present invention can maintain their expandability for a long period of time, allowing for a long usage period. Furthermore, expanded beads produced from the composite resin beads of the present invention fuse together using a low vapor pressure medium (e.g., water vapor), thereby reducing the energy required for expansion molding and simplifying the equipment required for expansion molding, thereby reducing the cost required for expansion molding.

[0071] The bulk density of the expanded particles is, for example, 10 kg / m ３ ~200 kg / m ３and 15 kg / m ３ ~200 kg / m ３ is preferable, and 20 kg / m ３ ~100 kg / m ３ is more preferable, and 20 kg / m ３ ~50 kg / m ３ If the bulk density is within this range, it is advantageous in that the foamed molded article will be lightweight.

[0072] The expanded beads preferably have a spherical or nearly spherical shape, and the average particle diameter is preferably 1.0 mm to 9.0 mm, more preferably 2.0 mm to 6.4 mm.

[0073] The expanded beads can be obtained by expanding the expandable beads to a desired bulk density by a known method. For example, the expanded beads can be obtained by expanding the expandable beads using heated steam at a gauge pressure of 0.010 to 0.20 MPa, 0.010 to 0.12 MPa, 0.010 to 0.1 MPa, etc., preferably 0.050 MPa to 0.20 MPa, more preferably 0.060 MPa to 0.12 MPa, and even more preferably 0.060 MPa to 0.11 MPa.

[0074] (Molded foam) A molded foam is an in-mold foam composed of a fused body of a plurality of foamed beads integrated by thermal fusion, and is obtained, for example, by foam-molding the foamed beads in a mold. By using the composite resin particles as a raw material, the molded foam can be produced at a low vapor pressure and has high strength or sufficient heat resistance.

[0075] The density of the foamed molded body is 15 kg / m ３ ~200 kg / m ３ is preferable, and 20 kg / m ３ ~100 kg / m ３ is more preferable, and 20 kg / m ３ ~50 kg / m ３ When the density is within the above range, the foamed molded article is excellent in both lightness and strength. The density of the foamed molded article can be determined by the method described in the Examples.

[0076] The dimensional change rate of the foamed molded article relative to the mold may be 0 / 1000 to 8 / 1000. When the dimensional change rate relative to the mold is within this range, it can be evaluated that shrinkage of the foamed molded article is suppressed. The dimensional change rate relative to the mold can be determined by the method described in the examples.

[0077] The fusion rate of the foamed molded article may be 70% or more, 80% or more, and preferably 90% or more. A fusion rate within this range is advantageous in terms of the strength of the foamed molded article. The fusion rate can be determined by the method described in the Examples.

[0078] Other production conditions such as process temperature, process pressure and process time in each production step can be appropriately set depending on the production equipment, raw materials and the like to be used.

[0079] The foamed molded article can be used, for example, for automobile components, cushioning materials, packaging materials, construction materials, shoe components, sporting goods, etc. Specifically, it can be used for tire core materials for bicycles, wheelchairs, etc.; interior materials, seat core materials, shock-absorbing materials (e.g., bumper core materials), vibration-absorbing materials, etc. for transportation equipment such as automobiles, railroad cars, and airplanes; midsole materials, insole materials, or outsole materials for shoes; core materials for hitting implements for sporting goods such as rackets and bats; protective gear for sporting goods such as pads and protectors; medical, nursing care, welfare, or health care products such as pads and protectors; fenders; floats; toys; underfloor materials; wall materials; beds; cushions; transport containers for electronic components, various industrial materials, and food, etc. Preferred examples include automobile interior materials, shock-absorbing materials, vibration-absorbing materials, and parts packaging materials.

[0080] Hereinafter, one embodiment of the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto. Methods for determining various physical properties in the examples will be described below.

[0081] (Polystyrene (PS)-equivalent mass average molecular weight Mw of composite resin particles) The mass average molecular weight was measured as follows. 0.5 mL of hexafluoroisopropanol (HFIP) and 0.5 mL of chloroform were added to 5 mg of sample, in that order, and dissolved (immersion time: 6.0±1.0 hr (complete dissolution)) to obtain a sample solution. After confirming that the sample was completely dissolved in the solution, chloroform was added to the sample solution to dilute it to a volume of 10 mL, and the solution was mixed by shaking. The sample solution was filtered through a non-aqueous 0.45 μm syringe filter manufactured by Shimadzu GLC Corporation to obtain a filtrate. The filtrate was measured using a chromatograph under the following measurement conditions. The mass average molecular weight (Mw) was determined from a standard polystyrene calibration curve prepared in advance. Apparatus used: Tosoh Corporation "HLC-8320GPC EcoSEC" gel permeation chromatograph (built-in RI detector and UV detector) (GPC measurement conditions) Columns: Sample side: Guard column = Tosoh Corporation TSK guard column HXL-H (6.0 mm x 4.0 cm) x 1 Measurement column = Tosoh Corporation TSKgel GMHXL (7.8 mm I.D. x 30 cm) x 2 in series Reference side: Resistance tube (0.1 mm inner diameter x 2 m) x 2 in series Column temperature = 40°C Mobile phase = chloroform Mobile phase flow rate: Sample side pump = 1.0 mL / min Reference side pump = 0.5 mL / min Detector: UV detector Wavelength: 254 nm Injection volume: 15 μL Measurement time: 10 min - 32 min Runtime: 20 min Sampling pitch: 500 msec. Standard polystyrene samples for the calibration curve were "STANDARD SM-105" and "STANDARD SH-75" manufactured by Showa Denko K.K., with mass average molecular weights of 5,620,000, 3,120,000, 1,250,000, 442,000, 151,000, 53,500, 17,000, 7,660, 2,900, and 1,320.The polystyrene standards for the calibration curve were grouped into A (5,620,000, 1,250,000, 151,000, 17,000, 2,900) and B (3,120,000, 442,000, 53,500, 7,660, 1,320). A (2 mg, 3 mg, 4 mg, 4 mg, 4 mg) was weighed and dissolved in 30 mL of chloroform. B (3 mg, 4 mg, 4 mg, 4 mg, 4 mg) was also weighed and dissolved in 30 mL of chloroform. The polystyrene standards were obtained by injecting 50 μL of each of the prepared A and B solutions and creating a calibration curve (cubic equation) from the retention times obtained after measurement. The mass-average molecular weight was calculated using the calibration curve.

[0082] (Melting Points of Polypropylene Resin and Ethylene-Vinyl Acetate Copolymer) The melting points were measured by the method described in JIS K7122:1987 "Method for Measuring the Heat of Transition of Plastics." That is, using a differential scanning calorimeter RDC220 (manufactured by Seiko Electronics Industries, Inc.), 7 mg of sample was filled into a measurement container, and the temperature was increased, decreased, and increased again from room temperature to 220°C at a rate of 10°C / L under a nitrogen gas flow rate of 30 mL / min. The melting peak temperature on the DSC curve during the second temperature increase was taken as the melting point. In addition, when there were two or more melting peaks, the lower peak temperature was taken as the melting point.

[0083] (MFR of Polypropylene Resin and Ethylene-Vinyl Acetate Polymer) The MFR was measured at 190° C. under a load of 2.16 kg in accordance with JIS K6922-1:1998.

[0084] (Number-average molecular weight (Mn) and mass-average molecular weight (Mw) of ethylene-vinyl acetate copolymer) Specifically, the molecular weight was measured as follows. 6 mL of o-dichlorobenzene was added to a container containing 6 mg of sample, and the container was sealed to prepare a solution. The solution was prepared by heating at 160°C for 1 hour using a DF-8200 manufactured by Tosoh Corporation to dissolve the sample. This solution was used as a measurement sample and measured using gel permeation chromatography under the following measurement conditions. Standard polystyrene was measured in advance, and the average molecular weights (Mn, Mw) of the sample were determined from a calibration curve of the standard polystyrene that had been prepared. Instrument used: Tosoh Corporation "HLC-8321GPC / HT" gel permeation chromatograph Guard column: Tosoh Corporation TSKgel guard column HHR(30)HT2 (7.5mmI.D. x 7.5cm) x 1 Column: Tosoh Corporation TSKgel GMHHR-H(20)HT2 (7.8mmI.D. x 30cm) x 3 Mobile phase: O-dichlorobenzene Sample flow rate: 1.0mL / min Reference flow rate: 0.5mL / min Detector: RI Sample concentration: 0.1wt% Injection volume: 300µL Measurement time: 34min (Temperature settings for each part of the instrument) Solvent stocker: 40°C Column oven (column temperature): 160°C Sample table: 160°C Injection valve: 160°C Detector: 160°C The standard polystyrene sample for the calibration curve was manufactured by Tosoh Corporation under the trade name "High polymer kit" and "oligomer kit" with mass average molecular weights of 8,420,000, 5,480,000, 2,110,000, 1,090,000, 706,000, 427,000, 190,000, 96,400, 37,900, 17,400, 5,060, 2,550, 1,013, and 589 were used. The polystyrene standards for the calibration curve were divided into groups A (8,420,000, 1,090,000, 190,000, 17,400, 1,013), B (5,480,000, 706,000, 96,400, 5,060, 589), and C (2,110,000, 427,000, 37,900, 2,550). 10 mg of each of A was weighed out and dissolved in 30 mL of o-dichlorobenzene. 10 mg of each of B and C were also weighed out and dissolved in 30 mL of o-dichlorobenzene.A standard polystyrene calibration curve was obtained by injecting 300 μL of each of the solutions A, B, and C, and plotting a calibration curve (cubic equation) from the retention times obtained after measurement. The average molecular weight was calculated using the calibration curve.

[0085] (Surface absorbance ratio of composite resin particles) The surface absorbance ratio (D698 / D1380) of composite resin particles was measured as follows. Ten composite resin particles were randomly selected. An infrared absorption spectrum was obtained for each particle surface by ATR infrared spectroscopy. This analysis obtained an infrared absorption spectrum within a depth range of 1 μm from the sample measurement surface. The absorbance ratio (D698 / D1380) was calculated from each infrared absorption spectrum. The minimum and maximum absorbance ratios were excluded from the absorbance ratio, and the arithmetic mean of the remaining eight absorbance ratios was taken as the surface absorbance ratio.

[0086] The method for determining the absorbance is as follows in more detail. Infrared spectroscopic analysis of the surface of the measurement sample was carried out under the following conditions to obtain an infrared absorption spectrum. From the obtained infrared absorption spectrum, the peak heights of D698 and D1380 were determined, and the polystyrene resin ratio was calculated from a calibration curve prepared using a standard sample.

[0087] Infrared spectroscopic analysis conditions: Measurement equipment: "Nicolet iS5" Fourier transform infrared spectrophotometer manufactured by Thermo SCIENTIFIC and single-reflection horizontal ATR Smart-iTR manufactured by Thermo SCIENTIFIC. ATR crystal: Ge (angle = 45°). Measurement method: single-reflection ATR method. Measurement wavenumber range: 4000 cm －１ ~675cm －１ Wavenumber dependence of measurement depth: Uncorrected. Detector: Deuterated triglycine sulfate (DTGS) detector and KBr beam splitter. Resolution: 4 cm －１ - Number of accumulations: 16 (same for background measurement).

[0088] The absorbance D698 obtained from the infrared absorption spectrum is the wavenumber 698 cm resulting from the out-of-plane bending vibration of the benzene ring contained in the styrene-based resin. －１ ±5cm －１The absorbance D698 corresponds to the absorption spectrum in the region of 1130 cm －１ and 880 cm －１ 710 cm when the line connecting the －１ and 685 cm －１ This absorbance measurement means the maximum absorbance between 698 cm －１ Even if other absorption spectra overlap, peak separation is not performed. In addition, the absorbance D1380 obtained from the infrared absorption spectrum is the absorbance of CH contained in the polypropylene resin. ３ The wave number 1380 cm originates from the methyl symmetric bending vibration －１ ±5cm －１ The absorbance D1380 corresponds to the absorption spectrum in the region of 1410 cm －１ and 1275 cm －１ 1400 cm when the line connecting －１ and 1350 cm －１ This absorbance measurement means the maximum absorbance between 1380 cm －１ Even if other absorption spectra overlap, peak separation is not performed.

[0089] Preparation of Standard Samples Standard samples (mixtures of polystyrene resin / polypropylene and ethylene vinyl acetate copolymer) were prepared so that the composition ratio was as follows. The mixing ratio of the polypropylene and ethylene vinyl acetate copolymer mixture was 8 / 2, with the polypropylene / ethylene vinyl acetate copolymer ratio being 8 / 2. Composition ratios (mixtures of polystyrene / polypropylene and ethylene vinyl acetate copolymer; mass ratio): 2 / 8, 4 / 6, 5 / 5, 6 / 4, 7 / 3, 8 / 2, 9 / 1. These were heated and kneaded in a small injection molding machine under the following conditions, and molded into cylindrical shapes with a diameter of 25 mm and a height of 2 mm, to obtain standard samples. The small injection molding machine used can be, for example, one sold by CSI under the trade name "CS-183," and molding can be performed under the following conditions, for example. Injection molding conditions: heating temperature 200 to 250°C, kneading time 10 minutes

[0090] The surfaces of the standard samples were subjected to infrared spectroscopy to obtain infrared absorption spectra. From the infrared absorption spectra obtained in each measurement, the absorbance ratios of the standard samples having the above ratios were measured using the measurement device and under the measurement conditions. A calibration curve was created by plotting the relationship between the polystyrene resin ratio (mass%) and the absorbance ratio (D698 / D1380).

[0091] (Bulk density of expanded particles) The expanded particles were placed in a measuring cylinder with a volume of 500 cm ３ However, the measuring cylinder was visually inspected from the horizontal direction, and even one foam particle was found to be within 500 cm ３ If the weight reaches the mark, the filling is complete. Next, the mass of the expanded composite resin beads filled in the measuring cylinder is weighed to two decimal places, and this mass is designated as W (g). The bulk density of the expanded beads is calculated using the following formula: Bulk density (kg / m ３ )=(W / 500)×1000

[0092] (Expanded particle usage period (life)) Bulk density 25 kg / m ３ The pre-expanded foam particles were placed in a molding die measuring 400 mm x 300 mm x 30 mm, and heated by introducing steam at 0.11 MPa for 30 seconds to obtain a fusion rate of 60% or more and a density of 25 kg / m ３A foamed molded article was produced. The foamed molded article was produced on the 7th (1 week), 14th (2 weeks), 21st (3 weeks), 28th (4 weeks), 35th (5 weeks), 42nd (6 weeks), 49th (7 weeks), and 56th (8 weeks), with the day of pre-expansion of the foamed beads being designated as day 0. The foamed molded articles were then molded on the 7th (1 week), 14th (2 weeks), 21st (3 weeks), 28th (4 weeks), 35th (5 weeks), 42nd (6 weeks), 49th (7 weeks), and 56th (8 weeks), respectively. The dimensional change relative to the mold and surface expansion (smoothness) of the resulting foamed molded articles were measured (measurement methods described below). A dimensional change relative to the mold of 0 / 1000 to 8 / 1000 and a surface expansion (smoothness) of 4 or greater were used as the standard. The week between the 7th and 56th days in which the last foamed molded article that satisfied the standard was obtained was recorded as the usage period. For example, if a molded article that met the standard was obtained on the 35th day of molding and a molded article that did not meet the standard was obtained on the 42nd day of molding, the usage period was recorded as 5 weeks (35 days). The foamed beads were stored in an environment of 25°C ± 2°C. The longer the period of use of the expanded beads, the more industrially advantageous it is because it becomes possible to produce a large amount of expanded beads at one time.

[0093] (Fusion Ratio of Foam Molded Article) A rectangular parallelepiped foam molded article having an upper surface of 400 mm long x 300 mm wide and a thickness of 30 mm was cut with a cutter along the horizontal direction with a length of 300 mm and a depth of approximately 5 mm. The foam molded article was divided into two along the cut line, and the fracture surface was observed. An arbitrary area containing 50 or more foamed beads was set on the fracture surface, and within this area, the number (a) of foamed beads that were broken internally rather than on the surface (strongly heat-fused foamed beads) and the number (b) of foamed beads that were broken at the interface between the foamed beads (weakly heat-fused foamed beads) were counted, and the fusion ratio (%) was calculated using the following formula: Fusion ratio (%) = (a / (a+b)) x 100

[0094] (Dimensional change rate of foamed molded body relative to mold) Bulk density 25 kg / m ３ The pre-expanded foam particles were placed in a molding die measuring 400 mm x 300 mm x 30 mm, and heated by introducing steam at 0.11 MPa for 30 seconds to obtain a fusion rate of 60% or more and a density of 25 kg / m ３ The dimensions of the foam molded article corresponding to the 400 mm long surface of the molding mold were measured, and the dimensional change rate relative to the mold was calculated using the following formula: Dimensional change rate relative to the mold = (mold dimension - molded article dimension) / mold dimension

[0095] (Smoothness (Smoothness) of the Surface of Foam Molded Article) A 50 mm x 50 mm test piece having a skin was randomly cut out from a foam molded article with a bulk ratio of 40. The number of interparticle gaps on the skin surface of the test piece was visually counted. Here, "interparticle gaps" refers to contact points where three or more expanded particles are in contact on the skin surface. Next, the number of pinholes (depressions) between particles was counted. Here, "pinholes between particles" refers to depressions that occur between adjacent expanded particles on the skin surface. From the above measurement results, the smoothness (smoothness) of the surface of the foam molded article was calculated using the following formula: Smoothness of the surface of the foam molded article = (1 - (number of interparticle pinholes / total number of interparticle gaps)) x 5 The evaluation criteria were as follows: A surface smoothness of 4 or more was considered pass, and a surface smoothness of less than 4 was considered fail.

[0096] (Moldability of Foamed Molded Articles: Minimum Steam Pressure) The foamed beads were filled into a 400 mm x 300 mm x 30 mm mold of a foam molding machine, and heated with steam introduced into the mold to expand the foamed beads, while thermally fusing the foamed beads together. During heating with steam (50 seconds), the steam pressure of the steam was varied in 0.01 MPa increments from 0.08 MPa to 0.25 MPa, and the fusion rate of the resulting foamed molded article was determined. The moldability was evaluated as the lowest steam pressure value (minimum steam pressure value) at which the fusion rate was 90% or higher. Obtaining foamed molded articles with good fusion at low steam pressures can simplify molding equipment and reduce production energy, thereby contributing to lower production costs and improving productivity.

[0097] (Density of foam molded article) A test piece (75 mm × 300 mm × 35 mm) was cut out from a foam molded article (dried at 50°C for 4 hours or more after molding). The mass (a) and volume (b) of the test piece were measured to have three or more significant figures, and the density (g / cm) of the foam molded article was calculated using the formula (a) / (b). ３ ) was sought.

[0098] (Polypropylene Resin) The polypropylene resin (PP) used in the examples was F744NP manufactured by Prime Polymer Co., Ltd. This PP is a random copolymer having a melting point of 140°C, an MFR of 7 g / 10 min, and an ethylene content of 7 mass%.

[0099] (Ethylene-vinyl acetate copolymer) The ethylene-vinyl acetate copolymer (EVA) used in the examples and the like is EF0505 manufactured by Asahi Kasei Corp. This EVA has a melting point of 108°C, an MFR of 0.5 g / 10 min, a vinyl acetate content of 4.7 mass %, and a molecular weight ratio (Mw / Mn) of 5.3.

[0100] (Polymerization inhibitor) The polymerization inhibitors used in the examples were sodium nitrite (polymerization inhibitor a) and 2,2-methylenebis(4-methyl-6-t-butylphenol) (polymerization inhibitor b).

[0101] (Polymerization Initiator) The polymerization initiator used in the examples was dicumyl peroxide.

[0102] (Chain Transfer Agent) The chain transfer agent used in the examples was 2,4-diphenyl-4-methyl-1-pentene.

[0103] Other materials used in the examples are as follows: TAIC-6B: Tris(2,3-dibromopropyl)isocyanurate (manufactured by Nippon Kasei Co., Ltd.) Biscumyl: 2,3-dimethyl-2,3-diphenylbutane (manufactured by Kayaku Nouryon Co., Ltd., product number Perkadox 30)

[0104] Example 1 [Preparation of seed particles] F744NP as a polypropylene-based resin (A) and EF0505 as an ethylene-vinyl acetate copolymer (B) were charged into a tumbler mixer in a mass ratio of 60:40 and mixed for 10 minutes (base resin). The resulting resin mixture was fed into an extruder and melt-kneaded at a temperature of 230 to 250°C, granulated by an underwater cutting method, and cut into oval spherical (ovular) particles to obtain polypropylene-based resin particles (seed particles, average mass 0.6 mg) modified with the ethylene-vinyl acetate copolymer.

[0105] [Preparation of Composite Resin Particles] (Step 1) A 5-liter autoclave equipped with a stirrer was charged with 40 g of magnesium pyrophosphate (dispersant), 0.6 g of sodium dodecylbenzenesulfonate (surfactant), 0.15 g of sodium nitrite (polymerization inhibitor a), and 2 kg of pure water to obtain a dispersion medium. 600 g of seed particles were dispersed in the dispersion medium at 30°C and maintained for 10 minutes, followed by heating to 60°C to obtain a suspension. While maintaining this suspension at 60°C, a solution prepared by dissolving 0.03 g of 2,2-methylenebis(4-methyl-6-t-butylphenol) (polymerization inhibitor b) and 0.6 g of dicumyl peroxide (polymerization initiator) in 300 g of styrene monomer was added dropwise over 30 minutes, followed by heating to 143°C over 40 minutes and maintaining this temperature for 2 hours to polymerize the styrene monomer (first polymerization). The rate at which the styrene-based monomer was added was 0.17 parts by mass / second relative to 100 parts by mass of the seed particles.

[0106] (Second Step) Next, a dispersion of 3 g of sodium dodecylbenzenesulfonate dispersed in 20 g of pure water was added dropwise over 10 minutes to the reaction solution cooled to 125°C. Next, a solution of 10 g of butyl acrylate and 5 g of dicumyl peroxide (polymerization initiator) dissolved in 1,090 g of styrene monomer was added dropwise at a styrene monomer addition rate of 0.05 parts by mass / second per 100 parts by mass of seed particles. After the dropwise addition, 2 g of ethylene bisstearamide dispersed in 100 g of water was added dropwise over 30 minutes, and the mixture was then held at 125°C for 30 minutes to impregnate the composite resin particles with the styrene monomer. After the impregnation, the mixture was heated to 140°C and held at this temperature for 3 hours to polymerize the styrene monomer (second polymerization).

[0107] 60 g of TAIC-6B as a flame retardant and 20 g of biscumyl as a flame retardant aid were added to this reaction solution. After addition, the temperature of the reaction system was raised to 140°C, and stirring was continued for 3 hours to produce composite resin particles containing a flame retardant (seed particle mass to polystyrene mass ratio of 30:70). Next, the mixture was cooled to 30°C or below, and the composite resin particles were removed from the autoclave. The obtained composite resin particles were subjected to various tests. The results are shown in Table 1.

[0108] [Preparation of Expandable Granules] 2 kg (100 parts by mass) of composite resin particles, 2 kg of water, and 2.0 g of sodium dodecylbenzenesulfonate (surfactant) were added to a 5-liter autoclave equipped with a stirrer. Furthermore, 360 g (620 mL, 18 parts by mass per 100 parts by mass of composite resin particles) of butane (normal butane:isobutane = 7:3 (volume ratio)) was added as a blowing agent, and the mixture was heated to 70°C and stirred for 4 hours to obtain expandable granules. The mixture was then cooled to below 30°C. After cooling was complete, the autoclave was depressurized, and the surfactant was immediately washed with distilled water. The mixture was then dehydrated and dried to obtain expandable granules.

[0109] [Preparation of Expanded Beads] The obtained expandable resin beads were placed in a cylindrical pre-expander equipped with a stirrer and had an internal volume of 50 L, and heated with steam at 0.02 MPa while stirring to a bulk density of 25 kg / m ３ The expanded beads (sometimes generally referred to as pre-expanded beads) were prepared. The resulting expanded beads were subjected to various tests. The results are shown in Table 1.

[0110] [Preparation of foamed molded article] The obtained foamed beads were left at 23°C for 1 day and then filled into a molding die (molding space dimensions: length 400 mm × width 300 mm × thickness 30 mm) of an automatic foamed bead molding machine (DABO Japan, DPM-7454). Steam at 0.11 MPa was introduced into the die for 30 seconds to heat and foam the foamed beads, and then the foamed molded article was cooled until the maximum surface pressure of the foamed molded article decreased to 0.01 MPa, resulting in a density of 25 kg / m ３ The foamed molded article was obtained. The appearance and fusion of the obtained foamed molded article were good. The obtained foamed molded article was also subjected to various tests. The results are shown in Table 1.

[0111] Examples 2 to 5 and Comparative Examples 1 to 4: Foamed molded articles of Examples 2 to 5 and Comparative Examples 1 to 4 were produced in the same manner as Example 1, except that the materials, amounts, polymerization conditions, etc. shown in Tables 1 to 4 were used. When a chain transfer agent (2,4-diphenyl-4-methyl-1-pentene) was used in the second step, the chain transfer agent was dissolved in the styrene monomer and added during polymerization in the second step. For example, in Example 2, 1.04 g of chain transfer agent, corresponding to 0.07% by mass, was dissolved in the styrene monomer (1,090 g) used in the second step, based on a total amount of 1,390 g of styrene monomer used (300 g in the first step and 1,090 g in the second step). The resulting composite resin particles, foamed beads, and foamed molded articles were subjected to various tests. The results are shown in Tables 1 to 4. The meanings of the terms in the tables are as follows: A+B:PS mass ratio: ratio of the total mass of the polypropylene resin (A) and the ethylene-vinyl acetate copolymer (B) to the mass of polystyrene. Carbon component amount (%): ratio of the carbon component contained in the carbon master batch to the total mass of the polypropylene resin (A) and the ethylene-vinyl acetate copolymer (B) (mass %). Chain transfer agent addition amount (%): ratio of the chain transfer agent used in the second step to the total mass of the styrene monomer used in the first and second steps (mass %). Butyl acrylate addition amount (%): ratio of butyl acrylate added to the mass of the composite resin particles (mass %). Flame retardant addition amount: ratio of the flame retardant added to the total mass of the polypropylene resin (A) and the ethylene-vinyl acetate copolymer (B) (mass %). Flame retardant synergist addition amount: ratio of the flame retardant synergist added to the total mass of the polypropylene resin (A) and the ethylene-vinyl acetate copolymer (B) (mass %).

[0112] Example 6: Seed particles, expandable particles, expanded particles, and foamed molded articles were prepared in the same manner as in Example 1, except that the composite resin particle preparation procedure was changed as follows. The obtained composite resin particles, expanded particles, and foamed molded articles were subjected to various tests. The results are shown in Table 2.

[0113] [Preparation of Composite Resin Particles] (Step 1) A 5-liter autoclave equipped with a stirrer was charged with 40 g of magnesium pyrophosphate (dispersant), 0.6 g of sodium dodecylbenzenesulfonate (surfactant), 0.15 g of sodium nitrite (polymerization inhibitor a), and 2 kg of pure water to obtain a dispersion medium. 800 g of seed particles were dispersed in the dispersion medium at 30°C and maintained for 10 minutes, followed by heating to 60°C to obtain a suspension. Furthermore, while maintaining this suspension at 60°C, a solution prepared by dissolving 0.04 g of 2,2-methylenebis(4-methyl-6-t-butylphenol) (polymerization inhibitor b) and 0.7 g of dicumyl peroxide (polymerization initiator) in 400 g of styrene monomer was added dropwise over 30 minutes, and the temperature was then raised to 143°C over 40 minutes, and the styrene monomer was polymerized at this temperature for 2 hours (first polymerization). The rate at which the styrene-based monomer was added was 0.22 parts by mass / second relative to 100 parts by mass of the seed particles.

[0114] (Second Step) Next, a dispersion of 3 g of sodium dodecylbenzenesulfonate dispersed in 20 g of pure water was added dropwise over 10 minutes to the reaction solution cooled to 125°C. Next, a solution of 10 g of butyl acrylate and 4 g of dicumyl peroxide (polymerization initiator) dissolved in 790 g of styrene monomer was added dropwise at a rate of 0.05 parts by mass / second per 100 parts by mass of seed particles. After the dropwise addition, 2 g of ethylene bisstearamide dispersed in 100 g of water was added dropwise over 30 minutes, and the mixture was then held at 125°C for 30 minutes to impregnate the composite resin particles with the styrene monomer. After the impregnation, the mixture was heated to 140°C and held at this temperature for 3 hours to allow polymerization (second polymerization).

[0115] 60 g of TAIC-6B as a flame retardant and 20 g of biscumyl as a flame retardant aid were added to this reaction solution. After addition, the temperature of the reaction system was raised to 140°C, and stirring was continued for 3 hours to produce composite resin particles containing the flame retardant (seed particle mass to polystyrene mass ratio of 30:70). Next, the mixture was cooled to 30°C or below, and the composite resin particles were removed from the autoclave.

[0116] Comparative Example 5 Seed particles, expandable particles, expanded particles, and a foamed molded article were prepared in the same manner as in Example 1, except that the seed particle preparation procedure was changed as follows. The obtained composite resin particles, expanded particles, and foamed molded article were subjected to various tests. The results are shown in Table 4.

[0117] [Preparation of Seed Particles] F744NP as the polypropylene resin (A), EF0505 as the ethylene copolymer (B), and a carbon masterbatch containing carbon black as the carbon component (C) were charged into a tumbler mixer in a mass ratio of 71:17.8:11.2 and mixed for 10 minutes to obtain a resin mixture (base resin). The following product was used as the carbon masterbatch. Carbon masterbatch: PPRM-10H381 manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd., containing 45% by mass of carbon black and 55% by mass of linear low-density polyethylene. The resulting resin mixture was fed into an extruder and melt-kneaded at a temperature of 230 to 250°C. The resulting mixture was granulated by an underwater cutting method and cut into oval (ovular) spheres to obtain polypropylene resin particles (seed particles, average mass 0.6 mg) modified with low-density polyethylene.

[0118]

[0119]

[0120]

[0121]

[0122] The expanded beads of Comparative Examples 1 to 5 were used for 1 or 2 weeks, whereas the expanded beads of Examples 1 to 6 were used for 3, 4, or 5 weeks. When the expanded beads of Examples 1 to 5 were used, the minimum steam pressure value in expansion molding was 0.08 or 0.09 MPa, and expansion molding was possible at a low steam pressure (in other words, with low energy) for expanded beads using PP.

Claims

1. Composite resin particles containing a polypropylene-based resin, an ethylene-vinyl acetate copolymer, and a polystyrene-based resin, wherein the composite resin particles have a polystyrene-equivalent mass average molecular weight Mw of 100,000 to 330,000, and the composite resin particles contain no carbon component or contain less than 0.50 mass% of a carbon component relative to the total mass of the polypropylene-based resin content and the ethylene-vinyl acetate copolymer content, and the surface absorbance ratio of the composite resin particles, as determined by the following method, is within the range of 1.0 to 5.

0. (Surface absorbance ratio) The surface absorbance ratio is determined by the infrared absorption spectrum obtained by infrared spectroscopic analysis of the surface of the composite resin particles using an ATR method. －１ Absorbance (D1380) and 698 cm －１ The absorbance (D698) of the sample is calculated, and the value obtained by applying the value to the formula D698 / D1380 is used as the surface absorbance ratio.

2. Composite resin particles according to claim 1, wherein the content of the polypropylene-based resin is 3.0 to 50 mass %, the content of the ethylene-vinyl acetate copolymer is 2.0 to 45 mass %, and the content of the polystyrene-based resin is 40 to 95 mass %, relative to the mass of the composite resin particles.

3. Composite resin particles according to claim 1, wherein the content of said ethylene-vinyl acetate copolymer in said composite resin particles is 10 to 95 parts by mass per 100 parts by mass of said polypropylene-based resin.

4. Composite resin particles according to claim 1, wherein the content of the ethylene-vinyl acetate copolymer in the composite resin particles is 10 to 75 parts by mass per 100 parts by mass of the polypropylene-based resin content, and the polystyrene-based resin contains a resin component derived from a (meth)acrylic acid ester and a resin component derived from a styrene-based monomer, and the content of the resin component derived from the (meth)acrylic acid ester is 0.05 to 5% by mass of the mass of the resin component derived from the styrene-based monomer.

5. Composite resin particles according to claim 1, wherein the total mass content of the polypropylene-based resin and the ethylene-vinyl acetate copolymer in the composite resin particles / the mass content of the polystyrene-based resin in the composite resin particles is 5 / 95 to 60 / 40.

6. The composite resin particles according to claim 1, wherein the ethylene-vinyl acetate copolymer has a melting point of 100 to 120°C.

7. The composite resin particles according to claim 1, wherein the ethylene-vinyl acetate copolymer has a ratio (Mw / Mn) of the mass average molecular weight (Mw) to the number average molecular weight (Mn) of 1.0 to 7.

0.

8. The composite resin particles according to claim 1, wherein the ethylene-vinyl acetate copolymer has a melt flow rate of 0.50 g / 10 min to 10 g / 10 min.

9. The composite resin particles according to claim 1, wherein the polypropylene resin has a melting point of 125 to 145°C.

10. The composite resin particles according to claim 1, wherein the polypropylene resin is a random polypropylene.

11. The composite resin particles according to claim 1, wherein the composite resin particles further contain a flame retardant in an amount of 0.50 to 10% by mass of the composite resin particles excluding the flame retardant.

12. The composite resin particle according to claim 11, wherein the flame retardant is a halogen-based flame retardant.

13. The composite resin particles according to claim 1, which are seed polymerized particles obtained by impregnating and polymerizing seed particles containing the polypropylene resin and the ethylene-vinyl acetate copolymer with a styrene monomer.

14. The composite resin particles according to claim 1, which do not contain a carbon component.

15. Expanded particles made from the composite resin particles according to claim 1.

16. Bulk density is 10 kg / m ３ ~200 kg / m ３ 16. The expanded particles of claim 15, wherein:

17. A foamed molded article made from the foamed beads according to claim 15.

18. The density is 20 kg / m ３ ~50 kg / m ３ The foamed molded article according to claim 17, 19. An automobile component containing the foamed molded article according to claim 17 or 18.

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