Composite resin particles, composite resin foam particles, and foam molded article

Abstract

The purpose of the present invention is to provide composite resin particles in which the amount of powder produced when manufacturing composite resin foam particles is reduced, to provide composite resin foam particles which can be foam-molded under low vapor pressure and have excellent moldability, to provide a foam molded body with excellent bending strength, to provide a foam molded body with excellent impact resistance, and to provide a foam molded body with excellent heat resistance.　The present invention pertains to composite resin particles containing a polyethylene resin, an ethylene copolymer, and a polystyrene resin, wherein: the polyethylene resin has a density of 930 kg / m3 to 970 kg / m3; the ethylene copolymer has a carbonyl group, has a melting point of 100°C to 120°C, has a melt flow rate (MFR) of 0.5 g / 10 min to 5.0 g / 10 min, and a mass average molecular weight (Mw) to number average molecular weight (Mn) ratio (Mw / Mn) of 1.0 to 5.5; the ethylene copolymer content in the composite resin particles is 100 to 1,000 parts by mass with respect to 100 parts by mass of the polyethylene resin content; and the total content mass of the polyethylene resin and the ethylene copolymer in the composite resin particles / the content mass of polystyrene resin in the composite resin particles is 5 / 95 to 50 / 50.

Description

[Technical Field]

[0001] The present invention relates to composite resin particles, expanded composite resin beads, expanded molded articles, and the like. [Background technology]

[0002] It is known that foam molded articles made from polystyrene-based resins are excellent in rigidity, heat insulation, light weight, water resistance, and foam moldability, but have poor chemical resistance and impact resistance. On the other hand, foam molded articles made from polyolefin-based resins are excellent in chemical resistance and impact resistance, but are expensive to produce due to poor retention of the blowing agent, and are inferior in rigidity compared to foam molded articles made from polystyrene-based resins. Therefore, in order to utilize the excellent properties of both resins, foam molded articles obtained from composite resin particles of polystyrene-based resin and polyolefin-based resin have been devised.

[0003] Composite resin particles are generally produced by using a base resin such as a polyethylene-based resin as seed particles (also called core particles) and adding a styrene monomer to the seed particles, followed by polymerization. However, composite resin particles using polyethylene-based resin as seed particles have high temperature dependence of the mechanical properties of the resulting foamed molded article. For this reason, composite resin particles using high-density polyethylene as the polyethylene-based resin have been reported, with the aim of suppressing this temperature dependence (Patent Document 1).

[0004] However, the use of high-density polyethylene as a base resin has the drawback of reducing moldability or impact resistance of foamed molded articles. To overcome this drawback, attempts have been made to produce foamed molded articles from composite resin particles consisting of high-density polyethylene-ethylene copolymer-polystyrene resin, which are obtained using as seed particles a base resin in which high-density polyethylene is blended with an ethylene copolymer (Patent Document 2). Patent Documents 3 and 4 also disclose technologies using ethylene-vinyl acetate copolymer.

[0005] Patent Document 3 describes a method for producing expandable polyethylene-based resin particles, in which core particles containing linear low-density polyethylene and ethylene-vinyl acetate copolymer are polymerized with a styrene-based monomer or a mixed monomer containing a styrene-based monomer, and the core particles are impregnated with a blowing agent.

[0006] Patent Document 4 discloses linear low-density polyethylene-based resin particles containing a mixed resin of linear low-density polyethylene having a softening point of 115 to 130°C and a copolymer of a (meth)acrylic acid alkyl ester and ethylene.

[0007] In Patent Document 5, since there is room for improvement in the mechanical strength and heat resistance of the foamed molded article described in Patent Document 2 and in the moldability during production of the foamed molded article, an attempt is made to control the location of the ethylene copolymer in the composite resin particles. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-025347 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-189912 [Patent Document 3] Patent No. 5352233 specification [Patent Document 4] Patent No. 6251103 specification [Patent Document 5] Japanese Patent Publication No. 2020-050784 Summary of the Invention [Problem to be solved by the invention]

[0009] In the method described in Patent Document 5, powder is generated during the production of expanded composite resin beads obtained by pre-expanding composite resin particles, and this powder adheres to the mold surface during expansion molding, shortening the mold life. Also, the expanded molded articles described in Patent Document 5 often have room for improvement in bending strength. Furthermore, expanded molded articles containing high-density polyethylene and ethylene copolymer as resin components have low flexibility and are prone to cracking.

[0010] An object of the present invention is to provide composite resin particles that generate a reduced amount of powder during production of expanded composite resin beads.An object of the present invention is to provide expanded composite resin beads that can be expanded and molded at low water vapor pressure and have excellent moldability.An object of the present invention is to provide an expanded molded product with excellent bending strength.An object of the present invention is to provide an expanded molded product with excellent impact resistance.An object of the present invention is to provide an expanded molded product with excellent heat resistance (low rate of dimensional change upon heating). [Means for solving the problem]

[0011] In view of the above problems, the inventors of the present invention have discovered that at least one of the above problems can be solved by using particles containing a specific polyethylene-based resin and an ethylene-based copolymer as seed particles, and have completed the present invention.

[0012] The present invention typically encompasses the following measures. Section 1. Composite resin particles containing a polyethylene-based resin, an ethylene-based copolymer, and a polystyrene-based resin, The polyethylene resin has a viscosity of 930 kg / m 3 ~970kg / m 3 and has a density of the ethylene copolymer has a carbonyl group, a melting point of 100°C to 120°C, a melt flow rate (MFR) of 0.5g / 10 min to 5.0g / 10 min, and a ratio (Mw / Mn) of mass average molecular weight (Mw) to number average molecular weight (Mn) of 1.0 to 5.5; the ethylene copolymer content in the composite resin particles is 100 parts by mass to 1000 parts by mass per 100 parts by mass of the polyethylene resin content; the total mass content of the polyethylene-based resin and the ethylene-based copolymer in the composite resin particles / the mass content of the polystyrene-based resin in the composite resin particles is 5 / 95 to 50 / 50; Composite resin particles. Section 2. Item 2. The composite resin particles according to Item 1, wherein the ethylene copolymer is an ethylene-vinyl acetate copolymer. Section 3. Item 3. The composite resin particles according to item 1 or 2, wherein the polyethylene resin has a softening temperature of 115°C to 135°C. Section 4. Item 4. Composite resin particles according to any one of Items 1 to 3, wherein the polyethylene resin has a melt flow rate (MFR) of 0.1 g / 10 min to 10.0 g / 10 min. Section 5. Item 5. Composite resin particles according to any one of Items 1 to 4, wherein the polyethylene resin is high-density polyethylene. Section 6. Item 6. Composite resin particles according to any one of Items 1 to 5, wherein the ratio (MFR1 / MFR2) of the melt flow rate (MFR1) of the polyethylene resin to the melt flow rate (MFR2) of the ethylene copolymer is 2 to 20. Section 7. Item 7. The composite resin particles according to any one of Items 1 to 6, further comprising a flame retardant. Section 8. Item 8. The composite resin particles according to any one of Items 1 to 7, further comprising an inorganic component. Section 9. Item 9. The composite resin particles according to Item 8, wherein the content of the inorganic component in the composite resin particles is 0.01 to 5% by mass. Section 10. Item 10. The composite resin particles according to Item 8 or 9, wherein the inorganic component is talc or silica. Section 11. Item 11. Expanded composite resin particles according to any one of items 1 to 10, having a bulk density of 15 kg / m 3 ~200kg / m 3 Composite resin foam particles. Section 12. Item 12. A foamed molded article of the composite resin foam beads according to item 11. [Effects of the Invention]

[0013] The composite resin particles of the present invention reduce the amount of powder (also referred to simply as "powder amount" in this specification) generated during the production of expanded composite resin beads, thereby extending the life of the mold. The expanded composite resin beads of the present invention can be expanded and molded at a high thermal fusion rate 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. Thus, the composite resin particles and expanded composite resin beads of the present invention provide excellent productivity for expanded molded articles. The foam molded article of the present invention has excellent bending strength, excellent impact resistance, and excellent heat resistance due to its low rate of dimensional change caused by heating. DETAILED DESCRIPTION OF THE INVENTION

[0014] As used herein, the phrase "comprising" is intended to encompass the phrases "consisting essentially of" and "consisting of."

[0015] 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 a polyethylene-based resin and an ethylene-based copolymer.

[0016] (Polyethylene resin) The polyethylene resin is not particularly limited, and known resins can be used. The polyethylene resin may be crosslinked. Examples of polyethylene-based resins include branched low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, and crosslinked polymers of these polymers. These polyethylene-based resins may be used alone or in combination. As the polyethylene-based resin, high-density polyethylene is preferred because it can reduce the amount of powder by-produced during the production of composite resin foam beads. Commercially available polyethylene resins can be used, such as those available from Tosoh Corporation, Japan Polyethylene Corporation, and Prime Polymer Corporation. Low-density polyethylene (LDPE), linear low-density polyethylene (L-LDPE), and high-density polyethylene (HDPE) are generally distinguished from one another in terms of molecular structure as follows: low-density polyethylene has short-chain branches and long-chain branches, linear low-density polyethylene has short-chain branches (and may have some long-chain branches) and is therefore somewhat linear, while high-density polyethylene has almost no branches and is therefore considered to be almost linear. Low-density polyethylene and linear low-density polyethylene generally have a relatively lower density than high-density polyethylene. However, some low-density polyethylene and linear low-density polyethylene are commercially available that have high densities and are indistinguishable from high-density polyethylene. For example, Nipolon Z ZF260 (manufactured by Tosoh Corporation) and Nipolon L M50 (manufactured by Tosoh Corporation) have a density of 930 kg / m 3 The above linear low-density polyethylene resins are commercially available. These linear low-density polyethylenes are distinguished from high-density polyethylenes in terms of the molecular structure described above. High-density polyethylenes are preferred because they can suppress powder generation more effectively than linear low-density polyethylenes.

[0017] Polyethylene resin is 930 kg / m 3 ~970kg / m 3 When the density is within this range, the composite resin particle expanded molded article can be imparted with excellent molding processability while maintaining its heat resistance and strength. The density is 938 kg / m 3 ~965kg / m 3is preferred, and 940 kg / m 3 ~965kg / m 3 More preferably, 950 kg / m 3 ~965kg / m 3 The density can be determined by the method described in the Examples.

[0018] The softening temperature of the polyethylene resin is preferably 115°C to 135°C, more preferably 117°C to 132°C, and even more preferably 120°C to 132°C. A softening temperature within the above range is advantageous in terms of improving heat resistance (reducing the rate of dimensional change upon heating) or improving flame retardancy. The softening temperature can be determined by the method described in the examples.

[0019] The melt mass flow rate (also referred to herein as MFR) of the polyethylene resin is not particularly limited, but can be 0.1 g / 10 min to 10.0 g / 10 min, 0.1 g / 10 min to 2.6 g / 10 min, 1.8 g / 10 min to 8.0 g / 10 min, or 1.8 g / 10 min to 2.6 g / 10 min, with 2.0 g / 10 min to 8.5 g / 10 min being preferred, 4.0 g / 10 min to 8.0 g / 10 min being more preferred, and 5.0 g / 10 min to 8.0 g / 10 min being particularly preferred. An MFR within the above range is advantageous in that it provides excellent expandability, facilitates sphericity of the composite resin particles, and improves mold filling during molding. The MFR can be determined by the method described in the Examples.

[0020] The melting point of the polyethylene resin is not particularly limited, but is preferably 122°C to 140°C, more preferably 124°C to 135°C, and even more preferably 125°C to 134°C. A melting point within the above range is advantageous in terms of heat resistance and molding processability of the foamed molded article. The melting point can be determined by the method described in the examples.

[0021] The content of the polyethylene resin in the base resin can be, for example, 9 to 50 mass%, 9.1 to 50 mass%, 9 to 45 mass%, 9.1 to 45 mass%, 10 to 50 mass%, 10 to 45 mass%, 10 to 40 mass%, etc., with 20 to 45 mass% being preferred, and 20 to 40 mass% being more preferred, relative to the total mass of the base resin. A content of the polyethylene resin within the above range is advantageous in that impact resistance can be improved.

[0022] (ethylene copolymer) The ethylene copolymer is, for example, a copolymer of ethylene and an ester monomer. The ethylene copolymer preferably has a carbonyl group in the molecule and a —COO— bond or an —OCO— bond.

[0023] The ethylene copolymer is preferably a copolymer of ethylene and at least one ester monomer such as an alkyl acrylate, an alkyl methacrylate, or a saturated aliphatic vinyl monocarboxylate. The ester monomer is preferably at least one selected from the group consisting of an alkyl acrylate, an alkyl methacrylate, and a saturated aliphatic vinyl monocarboxylate, more preferably at least one selected from the group consisting of an alkyl acrylate and a saturated aliphatic vinyl monocarboxylate, and even more preferably a saturated aliphatic vinyl monocarboxylate. Among the ethylene copolymers, an ethylene-vinyl acetate copolymer is particularly preferred because it can reduce the amount of powder.

[0024] The alkyl acrylate is, for example, a C1-C4 alkyl ester of acrylic acid, and is preferably at least one selected from the group consisting of methyl acrylate and ethyl acrylate.

[0025] The alkyl methacrylate is, for example, a C1-C4 alkyl ester of methacrylic acid, and is preferably at least one selected from the group consisting of methyl methacrylate and ethyl methacrylate.

[0026] The saturated aliphatic vinyl monocarboxylate is preferably at least one selected from the group consisting of vinyl acetate and vinyl propionate, and more preferably vinyl acetate.

[0027] The proportion of the component derived from the ester monomer in the ethylene copolymer is preferably 1 to 20 mass %, more preferably 1 to 14 mass %, and even more preferably 1 to 10 mass %.

[0028] The melting point of the ethylene copolymer is preferably 100°C to 120°C, more preferably 102°C to 115°C, and even more preferably 103°C to 110°C. A melting point within the above range is advantageous in terms of reducing the amount of powder, improving heat resistance (lower rate of dimensional change upon heating), and improving impact resistance. The melting point can be determined by the method described in the examples.

[0029] The ratio (Mw / Mn) of the mass-average molecular weight (Mw) of the ethylene copolymer to the number-average molecular weight (Mn) of the ethylene copolymer is important and is preferably 1.0 to 5.5. Having Mw / Mn within the above range is advantageous in that the amount of powder can be reduced and the cell diameter is homogenized. The homogenized cell diameter is advantageous in that the amount of cell regulator used can be reduced, and moldability at low vapor pressure (high fusion rate) is improved, strength is improved, heat resistance (low thermal dimensional change rate is reduced), or impact resistance is improved. Mw / Mn is more preferably 3.0 to 5.5, and particularly preferably 3.5 to 5.5. The number-average molecular weight and mass-average molecular weight can be determined by the methods described in the examples.

[0030] The MFR of the ethylene copolymer is not particularly limited, but is preferably 0.5 g / 10 min to 5.0 g / 10 min. An MFR within this range is advantageous in that it reduces the amount of powder, improves moldability at low vapor pressure (high fusion rate), improves strength, improves heat resistance (decreased rate of dimensional change upon heating), and improves impact resistance. The MFR is more preferably 0.5 g / 10 min to 4.0 g / 10 min, and even more preferably 0.5 g / 10 min to 3.0 g / 10 min. The MFR can be determined by the method described in the Examples.

[0031] The ratio (MFR1 / MFR2) of the melt flow rate (MFR1) of the polyethylene resin to the melt flow rate (MFR2) of the ethylene copolymer is not particularly limited, but can be 1 to 20, or 2 to 20, for example. MFR1 / MFR2 within the above range is advantageous in that the amount of powder generation can be suppressed. MFR1 / MFR2 is preferably 2.5 to 17, more preferably 5 to 17, and even more preferably 7 to 17.

[0032] The content of the ethylene copolymer in the base resin, relative to the total mass of the base resin, can be, for example, 50 to 91 mass%, 50 to 90.9 mass%, 55 to 91 mass%, 55 to 90.9 mass%, 50 to 90 mass%, 55 to 90 mass%, 60 to 90 mass%, etc., and is preferably 55 to 80 mass%, more preferably 60 to 80 mass%. Having the content of the ethylene copolymer within this range is advantageous in terms of improving impact resistance.

[0033] The content of the ethylene copolymer in the base resin or composite resin particles is preferably 100 to 1,000 parts by mass per 100 parts by mass of the polyethylene resin. The content of the ethylene copolymer within this range is advantageous in that impact resistance can be improved.

[0034] (Inorganic component) The seed particles may contain an inorganic component in addition to the polyethylene resin and the ethylene copolymer. When the seed particles or the composite resin particles contain an inorganic component, the bubbles become finer. Examples of the inorganic component include inorganic bubble adjusters such as talc, silica, calcium silicate, calcium carbonate, sodium borate, and zinc borate. Talc and silica are preferred in that they homogenize the bubble size. The inorganic component can be, for example, 0.01 to 5% by mass, and preferably 0.1 to 1% by mass, based on the total mass of the polyethylene resin and the ethylene copolymer. The inorganic component may be added when the polyethylene resin and the ethylene copolymer are mixed, or may be added to a mixed resin in which the polyethylene resin and the ethylene copolymer are mixed.

[0035] (Other ingredients) The seed particles may contain other components in addition to the polyethylene resin and ethylene copolymer. 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, weather stabilizers, anti-fogging agents, anti-blocking agents, slip agents, coating agents, and neutron shielding agents. The content of other components may be 10% by mass or less, preferably 5% by mass or less, and particularly preferably 0% by mass (no other components) relative to the total mass of the seed particles.

[0036] (Seed particle manufacturing method) 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 (polyethylene resin, ethylene copolymer, etc.) is melt-kneaded in an extruder and extruded to obtain strands, and the obtained strands are cut in air, in water, or while being heated to form granules. The resin components may be mixed in a mixer before being charged into the extruder.

[0037] The seed particles may have any known shape, but are preferably cylindrical, oval-spherical (egg-shaped), or spherical, and more preferably oval-spherical or spherical, from the viewpoint of the ease with which the expanded beads obtained from the seed particles can be filled into a mold. The seed particles preferably have an average particle size of 0.5 to 1.4 mm.

[0038] (composite resin particles) The composite resin particles contain, as resin components, a polyethylene resin and an ethylene copolymer derived from a base resin, and a polystyrene resin derived from a styrene monomer. The composite resin particles can be obtained, for example, by a seed polymerization method (impregnating seed particles with a styrene monomer and polymerizing the same).

[0039] In the seed polymerization, the amount of styrene-based monomer used is preferably such that the ratio of the total mass of the polyethylene-based resin and ethylene-based copolymer contained in the seed particles to the amount of styrene monomer used is 5 / 95 to 50 / 50. The content of polystyrene-based resin in the composite resin particles corresponds to the amount of styrene-based monomer used. Therefore, the ratio of the total mass of the polyethylene-based resin and ethylene-based copolymer contained in the composite resin particles to the mass of the polystyrene-based resin contained in the composite resin particles is preferably 5 / 95 to 50 / 50. Having the amount of styrene-based monomer used or the mass of the polystyrene-based resin contained within the above ranges is advantageous in terms of improved moldability at low vapor pressure (high fusion rate), improved strength, and improved impact resistance. The above range is more preferably 5 / 95 to 45 / 55, even more preferably 10 / 90 to 45 / 55, even more preferably 20 / 80 to 45 / 55, and particularly preferably 20 / 80 to 30 / 70.

[0040] 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 composed of 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 alkyl esters that do not contain a benzene ring in their structure, such as butyl (meth)acrylate. Components derived from these other monomers may be contained in the styrene-based polymer in an amount not exceeding 5% by mass.

[0041] The composite resin particles may contain a flame retardant. Furthermore, since the composite resin particles have relatively high flame retardancy even without a flame retardant, they do not need to contain a flame retardant (e.g., a halogen-based flame retardant).

[0042] Examples of the flame retardant include known halogen-based flame retardants, phosphorus-based flame retardants, inorganic flame retardants, etc. One type of flame retardant may be used alone, or two or more types may be used in combination. When the composite resin particles contain a flame retardant, halogen-based flame retardants such as bromine-based flame retardants, chlorine-based flame retardants, and chlorine-bromine-containing flame retardants are preferred as the flame retardant, as they can impart high flame retardancy to the foamed molded article with a small amount.

[0043] Examples of halogen-based flame retardants include tetrabromobisphenol A, its derivatives (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.

[0044] Generally, when a halogen-based flame retardant is contained in a foam molded article, the flame retardancy of the foam molded article tends to improve, but the heat resistance of the foam molded article tends to decrease. However, the foam molded article of the present invention has a low rate of dimensional change upon heating, and the decrease in heat resistance is small.

[0045] The content of the flame retardant can be, for example, 1.5 to 6.0 mass %, preferably 1.5 to 4.0 mass %, and more preferably 2.0 to 3.5 mass %, relative to the total mass of the polyethylene resin and the ethylene copolymer.

[0046] When the composite resin particles contain a flame retardant, they preferably contain a flame retardant synergist. The flame retardancy provided by the flame retardant can be further enhanced by the inclusion of a flame retardant synergist. Examples of the flame retardant synergist include organic peroxides such as dicumyl peroxide (DCP), cumene hydroperoxide, and diacyl peroxide, 2,3-dimethyl-2,3-diphenylbutane (also known as biscumyl), and 3,4-dimethyl-3,4-diphenylhexane. The flame retardant synergist 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 synergist is within the above range, deterioration in impact resistance and heat resistance of the foamed molded article is suppressed.

[0047] 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 the composite resin foamed beads formed from the composite resin particles can be filled into a mold.The average particle diameter of the composite resin particles is preferably 0.6 mm to 1.8 mm.

[0048] (Method for producing composite resin particles) The method for producing the composite resin particles is not particularly limited as long as it can produce the composite resin particles described above. As an example, the composite resin particles can be produced by the following production method. That is, the composite resin particles can be produced by polymerizing a styrene-based monomer impregnated into seed particles. This method is a so-called seed polymerization method.

[0049] An example of a method for producing composite resin particles using seed polymerization will be described below. First, seed particles, a styrene-based monomer, and, if necessary, a polymerization initiator are dispersed in an aqueous suspension. When a polymerization initiator is used, the styrene-based monomer and the polymerization initiator may be mixed in advance.

[0050] 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. Examples of aqueous media that constitute the aqueous suspension include water and mixed media of water and a water-soluble solvent (for example, a lower alcohol).

[0051] The amount of the polymerization initiator used is preferably 0.01 to 0.9 parts by mass, more preferably 0.1 to 0.5 parts by mass, relative to 100 parts by mass of the styrene-based monomer.

[0052] A dispersant may be added to the aqueous suspension 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. Furthermore, a surfactant such as sodium dodecylbenzenesulfonate may also be used.

[0053] Next, the obtained dispersion is heated to a temperature at which the styrene-based monomer does not substantially polymerize, and the styrene-based monomer is impregnated into the seed particles. The time for impregnating the seed particles with the styrene-based monomer is not particularly limited, but is preferably 20 minutes to 4 hours, and more preferably 30 minutes to 2 hours.

[0054] Next, the styrene-based monomer is polymerized. The polymerization temperature is not particularly limited, but it is preferable to carry out the polymerization at 115°C to 150°C, preferably 120°C to 140°C, for 1.5 to 5 hours. The polymerization is usually carried out in a pressurizable sealed container. It is preferable to carry out the impregnation of the styrene-based monomer and the polymerization in multiple steps. By carrying out the polymerization in multiple steps, the generation of polymer powder of the styrene-based resin can be minimized. Furthermore, taking into consideration the decomposition temperature of the polymerization initiator, the polymerization may be carried out while the styrene-based monomer is being impregnated into the seed particles, rather than initiating the polymerization after the styrene-based monomer has been impregnated into the seed particles. When the polymerization is divided into multiple steps, it is preferable to carry out the polymerization while adding the styrene-based monomer at a rate of 0.1 parts by mass / second or less per 100 parts by mass of seed particles in the second and subsequent polymerization steps.

[0055] Composite resin particles containing a flame retardant and a flame retardant aid can be produced by a method of impregnating seed particles with the flame retardant and the flame retardant aid together with a styrene-based monomer, or by a method of impregnating particles after polymerization.

[0056] (expandable particles) The expandable particles contain the composite resin particles and a foaming agent. Examples of the blowing agent that can be used 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 of two or more. Suitable organic gases are n-butane, isobutane, n-pentane, and isopentane, or a combination thereof. The content of the foaming agent is preferably 5 to 25 parts by mass with respect to 100 parts by mass of the composite resin particles.

[0057] The expandable particles can be obtained, for example, by impregnating composite resin particles with a blowing agent during or after polymerization. Impregnation can be performed by a method known per se. For example, impregnation during polymerization can be performed by carrying out the polymerization reaction in a sealed container and injecting a blowing agent into the container under pressure. Impregnation after polymerization can be performed, for example, by injecting a blowing agent under pressure into a sealed container containing the composite resin particles.

[0058] (Composite resin foam particles) Expanded beads (also commonly referred to as pre-expanded beads) are particles obtained by pre-expanding composite resin particles. For example, expanded beads can be obtained by expanding expandable beads impregnated with a blowing agent. By using the composite resin particles as a raw material, the expanded beads are fused together in a low vapor pressure medium (e.g., water vapor), which reduces the energy required for expansion molding and simplifies the equipment required for expansion molding, thereby reducing the cost required for expansion molding.

[0059] The bulk density of the foam particles is 15 kg / m 3 ~200kg / m 3 is preferable, and 20 kg / m 3 ~100kg / m 3 is more preferable, and 20 kg / m 3 ~50kg / m 3 A bulk density within this range is advantageous in that the foamed molded article has high strength and is lightweight.

[0060] 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.

[0061] The expanded particles can be obtained by expanding the expandable particles to a desired bulk density by a known method, preferably using heated steam at a gauge pressure of 0.05 MPa to 0.20 MPa, more preferably 0.06 MPa to 0.15 MPa.

[0062] (foam molded body) The foamed molded article is a foamed article composed of a fused body of foamed beads, and is obtained, for example, by foam-molding the foamed beads. Since the foamed molded article uses the composite resin particles as a raw material, it has excellent bending strength, impact resistance, and heat resistance.

[0063] The density of the foamed molding is 15 kg / m 3 ~200kg / m 3 is preferable, and 20 kg / m 3 ~100kg / m 3 is more preferable, and 20 kg / m 3 ~50kg / 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 is determined by the method described in the Examples.

[0064] The flexural strength of the foamed molded article can be, for example, 0.40 MPa or more, 0.40 MPa to 0.60 MPa, 0.40 MPa to 0.50 MPa, etc., and is preferably 0.40 MPa to 0.45 MPa. The flexural strength is determined by the method described in the Examples.

[0065] The bending breaking point of the foamed molded article can be, for example, 20 mm or more, 20 mm to 50 mm, 20 mm to 40 mm, etc., preferably 20 mm to 35 mm, more preferably 25 mm to 35 mm. The bending breaking point is determined by the method described in the examples.

[0066] The thermal dimensional change rate of the foamed molded article can be, for example, 1.5% or less, 0.5 to 1.5%, preferably 0.7 to 1.5%, and more preferably 0.7 to 1.0%. The thermal dimensional change rate is determined by the method described in the examples.

[0067] The falling ball impact value of the foamed molded article can be, for example, 32.5 cm or more, such as 32.5 cm to 60 cm, preferably 32.5 cm to 50 cm, more preferably 35 cm to 50 cm, and particularly preferably 38 cm to 50 cm. The falling ball impact value is determined by the method described in the examples.

[0068] The foamed molded article can be obtained by filling the foamed beads into a mold of an expansion molding machine, heating the foamed beads to expand them, and heat-fusing the foamed beads together. Steam is preferably used as a heating medium.

[0069] The expanded composite resin beads of the present invention can be sufficiently expanded and fused even in a medium (e.g., water vapor) with a low pressure (e.g., gauge pressure of 0.11 MPa or less, 0.10 MPa or less, or 0.09 Pa or less), thereby reducing the energy required for expansion molding and simplifying the equipment required for expansion molding, thereby reducing the cost required for expansion molding (i.e., achieving excellent productivity). Other production conditions such as process temperature, process pressure and process time in each production step are appropriately set depending on the production equipment, raw materials and the like to be used.

[0070] The foamed molded article can be used for cushioning materials, packaging materials, building materials, shoe components, and sporting goods. Specifically, it can be used for shoe midsole components, insole components, or outsole components; core materials for hitting implements 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; tire core materials for bicycles and wheelchairs; interior materials, seat core materials, shock absorbing members, vibration absorbing members, etc. for transportation equipment such as automobiles, railroad cars, and airplanes; fenders; floats; toys; underfloor materials; wall materials; beds; cushions; transport containers for electronic components, various industrial materials, and foods, etc. Preferably, it can be used for automobile interior materials, shock absorbing members, vibration absorbing members, or parts packaging materials. [Example]

[0071] Hereinafter, one embodiment of the present invention will be described in more detail with reference to examples, but the present invention is not limited to these. The methods for determining various physical properties in the examples are as follows.

[0072] (Density of polyethylene resin) The density of the polyethylene resin is measured by the density gradient tube method in accordance with JIS K6922-1:1998.

[0073] (Melt flow rate (MFR) of polyethylene resin and ethylene copolymer) The MFR was measured at 190°C under a load of 2.16 kg in accordance with JIS K6922-1:1998.

[0074] (Melting points of polyethylene resins and ethylene copolymers) The melting point was measured according to the method described in JIS K7122:1987 "Method for measuring heat of transition of plastics." Specifically, a differential scanning calorimeter RDC220 (Seiko Electronics Industries, Inc.) was used. 7 mg of sample was filled into the 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. When there were two or more melting peaks, the lower peak temperature was taken as the melting point.

[0075] (Softening temperature of polyethylene resin (Vicat softening point)) The softening temperature was measured by the method described in JIS 7196:1991 "Test method for softening temperature by thermomechanical analysis of thermoplastic plastic films and sheets." That is, the resin particles were hot-pressed and crushed to a thickness of 2 mm, and then a flat rectangular film test piece measuring 10 mm long x 20 mm wide x 2 mm thick was prepared. The test piece was then subjected to a thermal stress and strain measurement in a needle insertion test mode (needle tip area 1 mm) using a thermal stress and strain measurement device (Seiko Instruments Inc., product name "TMA / SS6200"). 2 ), a load of 50 g was applied, and a needle was placed on the film-like test piece, and the temperature was raised at a rate of 5°C / min. The temperature at which the film-like test piece began to distort was taken as the softening temperature (Vicat softening point) of the resin particles.

[0076] (Number average molecular weight (Mn) and mass average molecular weight (Mw) of polyethylene resin and ethylene 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 the measurement sample and measured using gel permeation chromatography under the following measurement conditions. The average molecular weight (Mn, Mw) of the sample was determined from a calibration curve of standard polystyrene that had been measured and prepared in advance. Equipment used: Tosoh Corporation "HLC-8321GPC / HT" gel permeation chromatograph Guard column: TSKgel guard column HHR(30)HT2 (7.5mm I.D. x 7.5cm x 1) manufactured by Tosoh Corporation Column: Tosoh Corporation TSKgel GMHHR-H(20)HT2 (7.8 mm I.D. x 30 cm) x 3 Mobile phase: O-dichlorobenzene Sample flow rate: 1.0 mL / min Reference flow rate: 0.5 mL / min Detector: RI Sample concentration: 0.1 wt% Injection volume: 300μL Measurement time: 34 min (Temperature settings for each part of the device) Solvent stocker: 40℃ Column oven (column temperature): 160°C Sample table: 160℃ Injection valve: 160℃ Detector: 160℃ The standard polystyrene samples used for the calibration curve were "High polymer kit" and "oligomer kit" manufactured by Tosoh Corporation, 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. 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). Ten milligrams of each of A was weighed and dissolved in 30 mL of o-dichlorobenzene. Ten milligrams of B and C were also weighed and dissolved in 30 mL of o-dichlorobenzene. A cubic calibration curve was constructed from the retention times obtained after injecting 300 μL of each of A, B, and C solutions. The average molecular weights were calculated using the calibration curve.

[0077] (Bulk density of composite resin foam particles) Put 500cm of composite resin foam particles into a measuring cylinder. 3 However, the measuring cylinder was visually inspected from the horizontal direction to ensure that even one composite resin foam particle did not exceed the 500 cm mark. 3 When the scale reached the mark, the filling was completed. Next, the mass of the expanded composite resin beads filled in the measuring cylinder was weighed to two decimal places, and this mass was designated as W (g). The bulk density of the expanded composite resin beads was calculated using the following formula. Bulk density (kg / m 3 )=(W / 500)×1000

[0078] (Amount of powder generated during the production of composite resin foam beads) Bulk density 0.025g / cm 3 Five kg of pre-expanded composite resin foam particles were classified using a sieve with a nominal mesh size of 0.9 mm. The mass (D (g)) of the powder that passed through the 0.9 mm mesh size was measured, and the amount of powder (P) per 5 kg of composite resin foam particles was calculated using the following formula: P(%) = D / (5 x 1000) x 100 If the powder content is too high, it may be necessary to remove the powder during the production of the composite resin foam beads. In particular, removal of a large amount of powder exceeding 0.5% is necessary. Although a powder content of 0.2% or less is desirable, a powder content between 0.2% and 0.5% is also practical.

[0079] (Density of foamed molded product) The mass (a) and volume (b) of a test piece (75 mm x 300 mm x 35 mm) cut out from a foam molded product (dried at 50°C for at least 4 hours after molding) were measured to three or more significant figures, and the density (g / cm) of the foam molded product was calculated using the formula (a) / (b). 3 ) was sought.

[0080] (Flexural strength and flexural breaking point of foam molded product) The bending strength (average maximum bending strength) and bending breaking point were measured according to the method described in JIS K7221-1:2006, "Rigid cellular plastics - Bending test - Part 1: Determination of deflection properties." Specifically, a Tensilon universal testing machine UCT-10T (manufactured by Orientec Co., Ltd.) and universal testing machine data processing software UTPS-237 (manufactured by Softbrain Co., Ltd.) were used to measure rectangular parallelepiped specimens measuring 25 mm wide x 130 mm long x 20 mm thick (with a skin surface only on the pressure surface), with a test speed of 10 mm / min, a pressure wedge of 5R, a support base of 5R, and a support distance of 100 mm. The specimens were pressurized so that the non-skinned side of the specimen was stretched. Five test pieces were used, and they were conditioned for 16 hours in a standard atmosphere of grade 2, designated "23 / 50" (temperature 23°C, relative humidity 50%), according to JIS K7100:1999 "Plastics - Standard atmospheres for conditioning and testing," and then the above-mentioned measurements were carried out in the same standard atmosphere. The bending strength (MPa) was calculated using the following formula. R=(1.5F R ×L / bd 2 ) x 10 3 R: Bending strength (MPa) F R : Maximum load (kN) L: Distance between fulcrums (mm) b: width of test piece (mm) d: thickness of test piece (mm) A bending strength of 0.40 MPa or higher can be evaluated as having excellent bending strength. In this test, the break detection sensitivity was set to 0.5%, and when the decrease in the load compared to the immediately preceding sampling point exceeded the set value of 0.5% (deflection: 30 mm), the immediately preceding sampling point was measured as the bending break displacement (mm), and the average of 5 tests was calculated to determine the bending break point (mm). A bending break point of 20 mm or higher can be evaluated as having flexibility.

[0081] (Dimensional change rate of foam molded body due to heating) The thermal dimensional change of the foamed molded article was measured using Method B described in JIS K 6767:1999 "Foamed Plastics - Polyethylene - Test Methods." Test specimens measuring 150 mm long x 150 mm wide x 20 mm high were cut from the foamed molded article. Three 50 mm long lines parallel to each other were drawn on the surface of the test specimen at 50 mm intervals, and three 50 mm long lines parallel to each other were drawn on the surface of the test specimen at 50 mm intervals. The test specimen was then placed in a hot air circulation dryer at 80°C for 168 hours, then removed and placed under standard conditions (20±2°C, 65±5% humidity) for 1 hour. The lengths of the six lines drawn on the surface of the test specimen were then measured, and the arithmetic mean value L1 of the six line lengths was calculated. The degree of change S was calculated using the following formula, and the absolute value of the degree of change S was taken as the thermal dimensional change (%). S=100×(L1-50) / 50 If the rate of dimensional change upon heating is 1.5% or less, it can be evaluated that the rate of dimensional change is low and the dimensional stability is good.

[0082] (Burning rate and flame retardancy of foam molded products) The burning rate (mm / min) was measured in accordance with the US automobile safety standard FMVSS 302. The test specimen (bulk expansion ratio 40 times) was 350 mm × 100 mm × 12 mm (thickness), and at least two sides of the 350 mm × 100 mm area had a skin. The flame retardancy was evaluated based on the burning rate according to the following criteria. If the fire is extinguished before reaching the measurement starting point, the burning rate is set to 0 mm / min and the material can be evaluated as self-extinguishing. If the burning rate is less than 80 mm / min, the material can be evaluated as having excellent flame retardancy. If the burning rate is more than 80 mm / min and less than 100 mm / min, the material can be evaluated as having flame retardancy. If the burning rate is greater than 100 mm / min, it is difficult to evaluate the material as having flame retardancy.

[0083] (Falling ball impact value) A sample was prepared by cutting the foamed molded body to a size of 215 mm x 40 mm x 20 mm. This sample was placed on a pair of holding members arranged with a span of 155 mm. A steel ball weighing 321 g was then dropped from a specified height onto the midpoint between the two holding members and the center position in the width direction of the sample, and the presence or absence of damage to the sample was confirmed. This test was repeated by changing the height from which the steel ball was dropped, and the lowest height at which the sample was broken was taken as the falling ball impact value, and the impact strength was evaluated. Therefore, the higher the falling ball impact value, the higher the impact strength. If the ball impact value is 35cm or more, it can be evaluated as having excellent shock absorption properties.

[0084] (Fusion rate of foam molded product) 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 in the horizontal direction on the upper surface of the foam molded article, with a length of 300 mm and a depth of about 5 mm. The foam molded article was then divided into two along this cut line, and the fracture surface was observed. An arbitrary range containing 50 or more expanded beads was set, and within this range, the number (a) of expanded beads that had broken internally rather than on the surface (strongly heat-fused expanded beads) and the number (b) of expanded beads that had broken at the interface between the expanded beads (weakly heat-fused expanded beads) were counted, and the fusion rate (%) was calculated using the following formula. Fusion rate (%) = (a / (a+b)) x 100

[0085] (Moldability of foamed molded products; water vapor pressure) The composite resin foam particles were filled into a 300mm x 400mm x 30mm mold of a foam molding machine, and heated with steam to expand the composite resin foam particles, while thermally fusing the composite resin foam particles together. When heated with steam (for 50 seconds), the steam pressure 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 for each pressure. The moldability was evaluated based on the lowest steam pressure (minimum steam pressure) at which the fusion rate was 90% or higher. Obtaining foamed molded articles with good fusion at low steam pressures allows for simpler molding equipment and reduces manufacturing energy, resulting in lower manufacturing costs and improved productivity. If a foamed molded product with a fusion rate of 90% or more can be obtained at a steam pressure of 0.11 MPa or less, a foamed molded product with good fusion can be obtained at a low steam pressure, resulting in good moldability and high productivity.

[0086] (Polyethylene resin) The polyethylene resins used in the examples are as follows: The physical properties of the polyethylene resins are shown in Table 1. 10S65B: High-density polyethylene (Tosoh Corporation, product number 10S65B) HY350: High-density polyethylene (manufactured by Japan Polyethylene Co., Ltd., product number HY350) 2500: High-density polyethylene (Tosoh Corporation, product number 2500) SP4020: Linear low-density polyethylene (Prime Polymer, product number SP4020) NF444A: Linear low-density polyethylene (manufactured by Japan Polyethylene Co., Ltd., product number NF444A)

[0087] [Table 1]

[0088] (ethylene copolymer) The ethylene copolymers used in the examples are as follows: The physical properties of the ethylene copolymers are shown in Table 2. EF0510: Ethylene-vinyl acetate copolymer (manufactured by Asahi Kasei Corporation, product number EF0510, vinyl acetate content 5% by mass) EF0505: Ethylene-vinyl acetate copolymer (manufactured by Asahi Kasei Corporation, product number EF0505, vinyl acetate content 4% by mass) VF105: Ethylene-vinyl acetate copolymer (Ube Maruzen Oil Co., Ltd., product number VF105, vinyl acetate content 6% by mass) LV115: Ethylene-vinyl acetate copolymer (manufactured by Japan Polyethylene Co., Ltd., product number LV115, vinyl acetate content 4% by mass) A1100: Ethylene-ethyl acrylate copolymer (manufactured by Japan Polyethylene Corporation, product number A1100, ethyl acrylate content 10% by mass) LV430: Ethylene-vinyl acetate copolymer (manufactured by Japan Polyethylene Co., Ltd., product number LV430, vinyl acetate content 15% by mass) 514R: Ethylene-vinyl acetate copolymer (manufactured by Tosoh Corporation, product number 514R, vinyl acetate content 5% by mass)

[0089] [Table 2]

[0090] Other materials used in the examples are listed below. Finely divided silica: Silica (manufactured by Nippon Aerosil Co., Ltd., product number AEROSIL200) Talc: Talc masterbatch manufactured by Nitto Funka Co., Ltd. (trade name "Talpet 70P"), average particle size (D50) 12 μm, specific surface area 8.5 m 2 / g, talc purity 70% by mass TAIC-6B: Tris(2,3-dibromopropyl) isocyanurate (manufactured by Nippon Kasei Co., Ltd.) DCP: Dicumyl peroxide (NOF Corporation, product number Percumyl D)

[0091] Example 1 [Preparation of seed particles] 10S65B as the polyethylene resin (A) and EF0510 as the ethylene copolymer (B) were charged into a tumbler mixer in a mass ratio of 40:60 and mixed for 10 minutes. Finely divided silica as an inorganic component was added in an amount of 0.25 mass% relative to the total mass of the polyethylene resin (A) and the ethylene copolymer (B), and the mixture was mixed for an additional 10 minutes to obtain a resin mixture. The obtained resin mixture was fed into an extruder and melt-kneaded at a temperature of 230°C to 250°C, granulated using an underwater cutting method, and cut into oval spherical (egg-shaped) particles of polyethylene-based resin modified with an ethylene-based copolymer (seed particles, average mass 0.6 mg).

[0092] [Preparation of composite resin particles] A dispersion medium was prepared by adding 40 g of magnesium pyrophosphate (dispersant), 0.6 g of sodium dodecylbenzenesulfonate (surfactant), and 2 kg of pure water to a 5-liter autoclave equipped with a stirrer. 600 g of seed particles were dispersed in the dispersion medium at 30°C and held for 10 minutes. The temperature was then raised to 60°C to obtain a suspension. While holding the suspension at 60°C, a solution of 0.6 g of dicumyl peroxide (polymerization initiator) in 300 g of styrene monomer was added dropwise over 30 minutes, and the suspension was then held for 30 minutes to impregnate the seed particles with the styrene monomer. After impregnation, the temperature was raised to 140°C, and polymerization (first polymerization) was carried out at this temperature for 2 hours.

[0093] Next, a dispersion of 3 g of sodium dodecylbenzenesulfonate in 20 g of pure water was added dropwise to the reaction solution cooled to 115°C over 10 minutes. Next, a solution of 5 g of t-butyl peroxybenzoate (polymerization initiator) dissolved in 1100 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, the mixture was maintained at 115°C for 1 hour, thereby impregnating the modified high-density polyethylene resin particles with the styrene monomer. A dispersion medium prepared by dispersing 3 g of ethylene bisstearic acid amide (cell bubble control agent) in 100 g of pure water was then added dropwise over 30 minutes. After the dropwise addition, the mixture was maintained at 115°C for 1 hour, thereby impregnating the seed particles with the styrene and cell bubble control agent. After the impregnation, the mixture was heated to 140°C and maintained at this temperature for 3 hours to allow polymerization (second polymerization).

[0094] 50 g of TAIC-6B as a flame retardant and 10 g of DCP as a flame retardant aid were added to this reaction solution. After addition, the temperature of the reaction system was raised to 130°C, and stirring was continued for 3 hours to produce flame retardant-containing composite resin particles (the ratio of the total mass of the polyethylene resin (A) and the ethylene copolymer (B) to the mass of polystyrene was 30:70). Next, the mixture was cooled to below 30°C, and the composite resin particles were removed from the autoclave.

[0095] [Preparation of expandable particles] A 5-liter autoclave equipped with a stirrer was charged with 2 kg (100 parts by mass) of composite resin particles, 2 kg of water, and 2.0 g of sodium dodecylbenzenesulfonate (surfactant). 300 g (15 parts by mass, 520 mL) of butane (normal butane:isobutane = 7:3 (volume ratio)) was then added as a blowing agent, and the autoclave was pressurized until the internal pressure reached 3.0 MPa (gauge pressure). The autoclave was heated to 70°C while maintaining the internal pressure at 3.0 MPa, and stirring was continued for 4 hours to obtain expandable particles. The contents were then cooled to below 30°C. After cooling was complete, the autoclave was depressurized, and the surfactant was immediately washed with distilled water. The expandable particles were then dehydrated and dried to obtain expandable particles.

[0096] [Preparation of foam particles] The obtained expandable resin particles were placed in a 50 L cylindrical pre-expander equipped with a stirrer, and heated with steam at 0.02 MPa while stirring to a bulk density of 25 kg / m 3 The expanded particles (sometimes generally referred to as pre-expanded particles) were produced. The expanded particles were classified using a 0.9 mm mesh sieve, and the mass of the powder discharged as the classified off-particle was measured to determine the powder amount.

[0097] [Production of foam molded products] The resulting expanded beads were left at 23°C for 1 day and then packed into a molding die (length 400 mm × width 300 mm × thickness 30 mm) of an automatic foam bead molding machine (DABO Japan, DPM-7454). Steam at 0.09 MPa was introduced into the die for 50 seconds to heat and expand the expanded beads, and the foam was then cooled until the maximum surface pressure of the foamed molded product decreased to 0.01 MPa, resulting in a density of 25 kg / m. 3 A foamed molded article of this size was obtained. The foamed molded article obtained had good appearance and fusion. The foamed molded article obtained was subjected to various tests. The results are shown in Table 3.

[0098] Examples 2 to 5, 8 to 9, and 11 and Comparative Examples 1 to 6 The foamed molded articles of Examples 2 to 5, 8, 9, and 11 and Comparative Examples 1 to 6 were produced in the same manner as in Example 1, except that the materials and amounts shown in Tables 3 and 4 were used. The resulting foamed molded articles were subjected to various tests. The results are shown in Tables 3 and 4. The meanings of the terms in Tables 3 and 4 are as follows: MFR ratio (A / B): The ratio of the melt flow rate (MFR1) of the polyethylene resin (A) to the melt flow rate (MFR2) of the ethylene copolymer (B) (MFR1 / MFR2) A:B mass ratio: mass ratio of polyethylene resin (A) to ethylene copolymer (B) Inorganic component content (%): The proportion of inorganic components added to the total mass of the polyethylene resin (A) and the ethylene copolymer (B) (mass%) A+B:PS mass ratio: the ratio of the total mass of the polyethylene resin (A) and the ethylene copolymer (B) to the mass of polystyrene Amount of flame retardant added: The proportion (mass%) of flame retardant added to the total mass of the polyethylene resin (A) and the ethylene copolymer (B) Amount of flame retardant synergist added: The proportion (mass%) of flame retardant synergist added to the total mass of the polyethylene resin (A) and the ethylene copolymer (B) Gas type A: butane as a blowing agent (normal butane: isobutane = 7:3 (volume ratio)) Gas type B: Isopentane as a blowing agent

[0099] Example 6 [Preparation of seed particles] Seed particles were produced in the same manner as in Example 1, except that the materials and amounts shown in Table 3 were used.

[0100] [Preparation of composite resin particles] A 5-liter autoclave equipped with a stirrer was charged with 40 g of magnesium pyrophosphate (dispersant), 0.6 g of sodium dodecylbenzenesulfonate (surfactant), and 2 kg of pure water to obtain a dispersion medium. 900 g of seed particles were dispersed in the dispersion medium at 30°C and held for 10 minutes. The temperature was then raised to 60°C to obtain a suspension. While holding the suspension at 60°C, a solution of 450 g of styrene monomer and 0.9 g of dicumyl peroxide (polymerization initiator) was added dropwise over 30 minutes, and the suspension was then held for 30 minutes to impregnate the seed particles with the styrene monomer. After impregnation, the temperature was raised to 140°C, and polymerization (first polymerization) was carried out at this temperature for 2 hours.

[0101] Next, a dispersion of 3 g of sodium dodecylbenzenesulfonate in 20 g of pure water was added dropwise to the reaction solution, which had been cooled to 115°C, over 10 minutes. Next, a solution of 3 g of t-butyl peroxybenzoate (polymerization initiator) dissolved in 650 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, the mixture was maintained at 115°C for 1 hour, thereby impregnating the modified high-density polyethylene resin particles with the styrene monomer. Subsequently, a dispersion medium prepared by dispersing 3 g of ethylenebisstearamide (cell bubble control agent) in 100 g of pure water was added dropwise over 30 minutes. After the dropwise addition, the mixture was maintained at 115°C for 1 hour, thereby impregnating the seed particles with the styrene and cell bubble control agent. After impregnation, the temperature was raised to 140°C and maintained at this temperature for 3 hours to polymerize (second polymerization) to produce composite resin particles (ratio of total mass of polyethylene resin (A) and ethylene copolymer (B) to polystyrene mass: 45:55). Next, the temperature was cooled to 30°C or below, and the composite resin particles were removed from the autoclave.

[0102] [Production of Expandable Particles, Expanded Particles, and Expanded Molded Articles] Expandable beads, expanded beads, and foamed molded articles were produced in the same manner as in Example 1. The obtained foamed molded articles were subjected to various tests. The results are shown in Table 3.

[0103] Example 7 [Preparation of seed particles] HY350 as the polyethylene resin (A) and EF0510 as the ethylene copolymer (B) were charged into a tumbler mixer in a mass ratio of 40:60 and mixed for 10 minutes. Talc as an inorganic component was added thereto in an amount such that the pure talc content was 0.17 mass% relative to the total mass of the polyethylene resin (A) and the ethylene copolymer (B), and the mixture was mixed for an additional 10 minutes to obtain a resin mixture. The obtained resin mixture was fed into an extruder and melt-kneaded at a temperature of 230°C to 250°C, granulated using an underwater cutting method, and cut into oval spherical (egg-shaped) particles of polyethylene-based resin modified with an ethylene-based copolymer (seed particles, average mass 0.6 mg).

[0104] [Preparation of composite resin particles] A dispersion medium was prepared by adding 40 g of magnesium pyrophosphate (dispersant), 0.6 g of sodium dodecylbenzenesulfonate (surfactant), and 2 kg of pure water to a 5-liter autoclave equipped with a stirrer. 200 g of seed particles were dispersed in the dispersion medium at 30°C and held for 10 minutes. The temperature was then raised to 60°C to obtain a suspension. While holding the suspension at 60°C, a solution of 0.2 g of dicumyl peroxide (polymerization initiator) in 100 g of styrene monomer was added dropwise over 30 minutes, and the suspension was then held for 30 minutes to impregnate the seed particles with the styrene monomer. After impregnation, the temperature was raised to 140°C, and polymerization (first polymerization) was carried out at this temperature for 2 hours.

[0105] Next, a dispersion of 3 g of sodium dodecylbenzenesulfonate in 20 g of pure water was added dropwise over 10 minutes to the reaction solution, which had been cooled to 115°C. Next, a solution of 9 g of t-butyl peroxybenzoate (polymerization initiator) dissolved in 1700 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, the mixture was maintained at 115°C for 1 hour, thereby impregnating the modified high-density polyethylene resin particles with the styrene monomer. A dispersion medium prepared by dispersing 3 g of ethylene bisstearic acid amide (cell bubble control agent) in 100 g of pure water was then added dropwise over 30 minutes. After the dropwise addition, the mixture was maintained at 115°C for 1 hour, thereby impregnating the seed particles with the styrene and cell bubble control agent. After the impregnation, the mixture was heated to 140°C and maintained at this temperature for 3 hours to allow polymerization (second polymerization).

[0106] 50 g of TAIC-6B as a flame retardant and 10 g of DCP as a flame retardant aid were added to this reaction solution. After addition, the temperature of the reaction system was raised to 130°C, and stirring was continued for 3 hours to produce flame retardant-containing composite resin particles (the ratio of the total mass of the polyethylene resin (A) and the ethylene copolymer (B) to the polystyrene mass was 10:90). Next, the mixture was cooled to below 30°C, and the composite resin particles were removed from the autoclave.

[0107] [Production of expandable particles, expanded particles, and foamed molded articles] Expandable beads, expanded beads, and foamed molded articles were produced in the same manner as in Example 1. The obtained foamed molded articles were subjected to various tests. The results are shown in Table 3.

[0108] Example 10 [Preparation of seed particles] Seed particles were produced in the same manner as in Example 1, except that the materials and amounts shown in Table 3 were used.

[0109] [Preparation of composite resin particles] A 5-liter autoclave equipped with a stirrer was charged with 40 g of magnesium pyrophosphate (dispersant), 0.6 g of sodium dodecylbenzenesulfonate (surfactant), 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 held for 10 minutes. The temperature was then raised to 60°C to obtain a suspension. While holding the suspension at 60°C, a solution of 400 g of styrene monomer and 0.8 g of dicumyl peroxide (polymerization initiator) was added dropwise over 30 minutes, and the suspension was then held for 30 minutes to impregnate the seed particles with the styrene monomer. After impregnation, the temperature was raised to 140°C, and polymerization (first polymerization) was carried out at this temperature for 2 hours.

[0110] Next, a dispersion of 3 g of sodium dodecylbenzenesulfonate in 20 g of pure water was added dropwise over 10 minutes to the reaction solution, which had been cooled to 120°C. Next, a solution of 2.4 g of dicumyl peroxide (polymerization initiator) dissolved in 800 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, the mixture was maintained at 120°C for 1 hour, thereby impregnating the modified high-density polyethylene resin particles with the styrene monomer. A dispersion medium prepared by dispersing 3 g of ethylenebisstearamide (cell bubble control agent) in 100 g of pure water was then added dropwise over 30 minutes. After the dropwise addition, the mixture was maintained at 120°C for 1 hour, thereby impregnating the seed particles with the styrene and cell bubble control agent. After the impregnation, the mixture was heated to 140°C and maintained at this temperature for 3 hours to allow polymerization (second polymerization).

[0111] 50 g of TAIC-6B as a flame retardant and 10 g of DCP as a flame retardant aid were added to this reaction solution. After addition, the temperature of the reaction system was raised to 130°C, and stirring was continued for 3 hours to produce flame retardant-containing composite resin particles (the ratio of the total mass of the polyethylene resin (A) and the ethylene copolymer (B) to the polystyrene mass was 40:60). Next, the mixture was cooled to below 30°C, and the composite resin particles were removed from the autoclave.

[0112] [Production of expandable particles, expanded particles, and foamed molded articles] Expandable beads, expanded beads, and foamed molded articles were produced in the same manner as in Example 1. The obtained foamed molded articles were subjected to various tests. The results are shown in Table 3.

[0113] Example 12 A foamed molded article was produced in the same manner as in Example 10, except that the materials and amounts shown in Table 3 were used. The resulting foamed molded article was subjected to various tests. The results are shown in Table 3.

[0114] Comparative Example 7 [Preparation of seed particles] Seed particles were produced in the same manner as in Example 1, except that the materials and amounts shown in Table 4 were used.

[0115] [Preparation of composite resin particles] A 5-liter autoclave equipped with a stirrer was charged with 40 g of magnesium pyrophosphate (dispersant), 0.6 g of sodium dodecylbenzenesulfonate (surfactant), and 2 kg of pure water to obtain a dispersion medium. 1,200 g of seed particles were dispersed in the dispersion medium at 30°C and held for 10 minutes. The temperature was then raised to 60°C to obtain a suspension. While holding the suspension at 60°C, a solution of 0.6 g of dicumyl peroxide (polymerization initiator) in 400 g of styrene monomer was added dropwise over 30 minutes, and the suspension was then held for 30 minutes to impregnate the seed particles with the styrene monomer. After impregnation, the temperature was raised to 140°C, and polymerization (first polymerization) was carried out at this temperature for 2 hours.

[0116] Next, a dispersion of 3 g of sodium dodecylbenzenesulfonate in 20 g of pure water was added dropwise to the reaction solution cooled to 115°C over 10 minutes. Next, a solution of 2 g of t-butyl peroxybenzoate (polymerization initiator) dissolved in 400 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, the mixture was maintained at 115°C for 1 hour, thereby impregnating the modified high-density polyethylene resin particles with the styrene monomer. A dispersion medium prepared by dispersing 3 g of ethylene bisstearic acid amide (cell bubble control agent) in 100 g of pure water was then added dropwise over 30 minutes. After the dropwise addition, the mixture was maintained at 115°C for 1 hour, thereby impregnating the seed particles with the styrene and cell bubble control agent. After the impregnation, the mixture was heated to 140°C and maintained at this temperature for 3 hours to allow polymerization (second polymerization).

[0117] 50 g of TAIC-6B as a flame retardant and 10 g of DCP as a flame retardant aid were added to this reaction solution. After addition, the temperature of the reaction system was raised to 130°C, and stirring was continued for 3 hours to produce flame retardant-containing composite resin particles (a ratio of the total mass of the polyethylene resin (A) and the ethylene copolymer (B) to the polystyrene mass of 60:40). The mixture was then cooled to below 30°C, and the composite resin particles were removed from the autoclave.

[0118] [Production of expandable particles, expanded particles, and foamed molded articles] Expandable beads, expanded beads, and foamed molded articles were produced in the same manner as in Example 1. The obtained foamed molded articles were subjected to various tests. The results are shown in Table 4.

[0119] [Table 3]

[0120] [Table 4]

[0121] The foam molded article of Example 6 had a burning rate of 76 mm / min, which was flame-retardant. If a flame retardant and a flame-retardant auxiliary are contained, it is expected that self-extinguishing or a very low burning rate will be obtained. Furthermore, the foam molded article of Example 7 had a burning rate of 88 mm / min, which was flame-retardant, but if an inorganic component is contained, it is expected that self-extinguishing or a very low burning rate will be obtained (see Example 9).

[0122] In Comparative Example 1, in which LV115 was used as the ethylene copolymer, the amount of powder generated during the production of the expanded composite resin beads was as high as 0.24%, making it necessary to remove the powder. Furthermore, in Comparative Example 1, the flexural strength, flexural breaking point, and falling ball impact value of the expanded molded article were low, indicating poor mechanical properties. As shown in the examples, excellent results were obtained in terms of powder amount and mechanical properties when the Mw / Mn and MFR of the ethylene copolymer were within the specified ranges.

[0123] In Comparative Example 2, in which A1100 was used as the ethylene copolymer and the mass ratio of the polyethylene resin (A) to the ethylene copolymer (B) was 60:40, the amount of powder generated during the production of the expanded composite resin beads was as high as 0.55%, making it necessary to remove the powder. As shown in the examples, excellent results were obtained in terms of the amount of powder when the MFR of the ethylene copolymer and the mass ratio of the polyethylene resin (A) to the ethylene copolymer (B) were within the specified ranges.

[0124] In Comparative Example 3, in which LV430 was used as the ethylene copolymer, the amount of powder generated during the production of the expanded composite resin beads was as high as 0.25%, making it necessary to remove the powder. Furthermore, in Comparative Example 3, the thermal dimensional change rate of the expanded molded article was as high as 1.7%, indicating low heat resistance (dimensional stability). Furthermore, in Comparative Example 3, the falling ball impact value of the expanded molded article was as low as 31.5, indicating low impact resistance. As shown in the examples, excellent results were obtained in terms of the amount of powder, the thermal dimensional change rate, and the falling ball impact value, provided that the melting point of the ethylene copolymer was within the specified range.

[0125] In Comparative Example 4, in which 514R was used as the ethylene copolymer, the minimum steam pressure during molding was as high as 0.12, requiring a large amount of energy for molding. Furthermore, in Comparative Example 4, the flexural strength, flexural breaking point, and falling ball impact value of the foamed molded article were low, indicating poor mechanical properties. Furthermore, in Comparative Example 4, the dimensional change upon heating of the foamed molded article was as high as 1.6%, indicating poor heat resistance (dimensional stability). As shown in the examples, excellent results were obtained in terms of dimensional change and mechanical properties when the Mw / Mn of the ethylene copolymer was within the specified range.

[0126] In Comparative Example 5, in which NF444A was used as the polyethylene resin, the amount of powder generated during the production of the expanded composite resin beads was very high at 0.76%, making it difficult to remove the powder. Furthermore, in Comparative Example 5, the dimensional change rate upon heating of the expanded molded article was very large at 2.8%, resulting in low heat resistance (dimensional stability). Furthermore, in Comparative Example 5, despite the inclusion of a flame retardant and a flame retardant aid, the burning rate was very high at 120 mm / min, resulting in low flame retardancy. As shown in the examples, excellent results were obtained in terms of dimensional change rate and burning rate when the density and softening temperature of the polyethylene resin were within the specified ranges.

[0127] In Comparative Example 6, in which the mass ratio of polyethylene resin (A) to ethylene copolymer (B) was 70:30, the minimum steam pressure during molding was as high as 0.13, requiring a large amount of energy for molding. Furthermore, in Comparative Example 6, the bending breaking point and falling ball impact value of the foamed molded article were very low, resulting in poor mechanical properties. As shown in the examples, excellent results were obtained in the minimum steam pressure value, bending breaking point, and falling ball impact value when the mass ratio of polyethylene resin (A) to ethylene copolymer (B) was within the specified range.

[0128] In Comparative Example 7, in which the ratio of the total mass of the polyethylene resin (A) and the ethylene copolymer (B) to the mass of polystyrene was 60:40, the amount of powder generated during the production of the expanded composite resin beads was very high at 0.80%, making it difficult to remove the powder. Furthermore, in Comparative Example 7, the minimum steam pressure during molding was very high at 0.15, requiring a large amount of energy for molding. Furthermore, in Comparative Example 7, the flexural strength and falling ball impact value of the expanded molded article were very low, resulting in poor mechanical properties. As shown in the examples, excellent results were obtained in terms of the amount of powder, minimum steam pressure value, flexural strength, and falling ball impact value when the ratio of the total mass of the polyethylene resin (A) and the ethylene copolymer (B) to the mass of polystyrene was within the specified range.

Claims

1. Composite resin particles containing a polyethylene-based resin, an ethylene-based copolymer, and a polystyrene-based resin, the composite resin particles are particles obtained by polymerizing a styrene-based monomer impregnated into seed particles containing the polyethylene-based resin and the ethylene-based copolymer, The polyethylene resin has a strength of 930 kg / m 3 ~970 kg / m 3 and a melting point of 122°C to 140°C, the ethylene-based copolymer has a carbonyl group, a melting point of 100°C to 120°C, a melt flow rate (MFR) of 0.5 g / 10 min to 5.0 g / 10 min, and a ratio (Mw / Mn) of mass average molecular weight (Mw) to number average molecular weight (Mn) of 1.0 to 5.5; the ethylene-based copolymer content in the composite resin particles is 100 parts by mass to 1000 parts by mass per 100 parts by mass of the polyethylene-based resin content; the total mass of the polyethylene-based resin and the ethylene-based copolymer in the composite resin particles / the mass of the polystyrene-based resin in the composite resin particles is 5 / 95 to 50 / 50; Composite resin particles.

2. 2. The composite resin particle according to claim 1, wherein the ethylene copolymer is an ethylene-vinyl acetate copolymer.

3. 3. The composite resin particles according to claim 1, wherein the polyethylene resin has a softening temperature of 115°C to 135°C.

4. 4. The composite resin particles according to claim 1, wherein the polyethylene resin has a melt flow rate (MFR) of 0.1 g / 10 min to 10.0 g / 10 min.

5. 5. The composite resin particles according to claim 1, wherein the polyethylene resin is a high-density polyethylene.

6. The composite resin particles according to any one of claims 1 to 5, wherein the ratio (MFR1 / MFR2) of the melt flow rate (MFR2) of the polyethylene resin to the melt flow rate (MFR1) of the ethylene copolymer is 2 to 20.

7. The composite resin particles according to any one of claims 1 to 6, further comprising a flame retardant.

8. The composite resin particle according to any one of claims 1 to 7, further comprising an inorganic component.

9. 9. The composite resin particle according to claim 8, wherein the content of the inorganic component in the composite resin particle is 0.01 to 5% by mass.

10. The composite resin particle according to claim 8 or 9, wherein the inorganic component is talc or silica.

11. Expanded composite resin particles according to any one of claims 1 to 10, having a bulk density of 15 kg / m ３ ~200 kg / m ３ Composite resin foam particles.

12. A foamed molded article made from the expanded composite resin beads according to claim 11.

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