Method for producing foamed styrene-based resin particles and method for producing a molded styrene-based resin foam particle article

Abstract

The present invention provides a method for producing foamed styrene-based resin particles, which exhibit minimal shrinkage even when foamed at high magnification, yield foamed particles with low bulk density, and easily produce lightweight molded articles. [Solution] The method for producing foamed styrene resin particles includes a polymerization step in which styrene resin seed particles dispersed in an aqueous medium are impregnated with styrene monomers and organic compounds having a boiling point of 200°C or higher, and the styrene monomers are polymerized to obtain styrene resin particles. The seed particles contain saturated hydrocarbons having 6 to 7 carbon atoms. The content of saturated hydrocarbons having 6 to 7 carbon atoms in the seed particles is 0.5% to 3% by mass per 100% by mass of the seed particles.

Description

[Technical Field]

[0001] The present invention relates to a method for producing foamed styrene-based resin particles and a method for producing foamed styrene-based resin particles. [Background technology]

[0002] Styrene-based foam molded articles are lightweight and have excellent thermal insulation, flexibility, and compressibility properties, making them suitable for various applications such as thermal insulation and cushioning materials. Styrene-based foam molded articles are manufactured by foaming foamable styrene-based resin particles to obtain styrene-based foam particles, and then molding these styrene-based foam particles in a mold (for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 63-182353 [Overview of the project] [Problems that the invention aims to solve]

[0004] From the perspective of making the molded product lighter, it is desirable to foam the foamed styrene resin particles at a higher magnification and lower the bulk density of the foamed styrene resin particles. However, when the foamed styrene resin particles described in Patent Document 1 are foamed at a high magnification, there is a problem that the foamed particles tend to shrink immediately after foaming. Furthermore, even if the shape of the foamed particles is restored by curing processes, etc., once the foamed particles have shrunk, there is a risk that the physical properties of the molded product, such as the compressive properties and flexural properties, will deteriorate.

[0005] This invention has been made in view of the above background, and aims to provide a method for producing foamed styrene-based resin particles and a method for producing styrene-based resin foamed particles that do not shrink easily even when foamed at a high magnification, yield foamed particles with low bulk density, and easily produce lightweight molded articles. [Means for solving the problem]

[0006] One aspect of the present invention relates to a method for producing foamed styrene-based resin particles according to the following [1] to [6].

[0007] [1] A method for producing foamed styrene resin particles containing a foaming agent, The process includes a polymerization step in which styrene resin particles dispersed in an aqueous medium are impregnated with a styrene monomer and an organic compound having a boiling point of 200°C or higher, and the styrene monomer is polymerized to obtain styrene resin particles. The aforementioned seed particles contain saturated hydrocarbons having 6 to 7 carbon atoms. A method for producing foamed styrene-based resin particles, wherein the content of the saturated hydrocarbon in the seed particles is 0.5% by mass or more and 3% by mass or less based on 100% by mass of the seed particles.

[0008] [2] The method for producing foamed styrene resin particles according to [1], wherein the amount of the organic compound added to the aqueous medium in the polymerization step is 0.1 parts by mass or more and 0.6 parts by mass or less with respect to 100 parts by mass of the total amount of styrene resin in the seed particles and the amount of styrene monomer added. [3] A method for producing foamed styrene-based resin particles according to [1] or [2], wherein the organic compound is liquid paraffin. [4] A method for producing foamed styrene resin particles according to any one of [1] to [3], wherein in the polymerization step, 0.1 parts by mass to 3 parts by mass of a brominated flame retardant is added to the aqueous medium in proportion to 100 parts by mass of the sum of the amount of styrene resin in the seed particles and the amount of styrene monomer added, thereby impregnating the seed particles with the brominated flame retardant.

[0009] [5] A method for producing foamable styrene-based resin particles according to any one of [1] to [4], wherein the foaming agent consists of a saturated hydrocarbon having 3 to 5 carbon atoms, including n-butane, and the mass proportion of n-butane in the foaming agent is 40% by mass or more. 〔6〕The method for producing foamed styrenic resin particles according to any one of 〔1〕~〔5〕, wherein in the polymerization step, the blowing agent is impregnated into the seed particles while the styrenic monomer is being polymerized.

[0010] One aspect of the present invention relates to a method for producing styrenic resin foamed particles according to 〔7〕below.

[0011] 〔7〕A method for producing styrenic resin foamed particles including a foaming step of foaming the foamed styrenic resin particles according to any one of 〔1〕~〔6〕, where the bulk density of the foamed particles is 15 kg / m 3 or less, which is a method for producing styrenic resin foamed particles.

Advantages of the Invention

[0012] According to the above aspect, a method for producing foamed styrenic resin particles and a method for producing styrenic resin foamed particles can be provided, in which even when foamed at a high magnification, the foamed particles are less likely to shrink, foamed particles with a low bulk density can be obtained, and a lightweight molded body can be easily obtained.

Brief Description of the Drawings

[0013] [Figure 1] FIG. 1 is an enlarged photograph of the cross-section of the foamed particles in Example 1. [Figure 2] FIG. 2 is an enlarged photograph of the cross-section of the foamed particles in Comparative Example 1. [Figure 3] FIG. 3 is an enlarged photograph of the cross-section of the foamed particles in Comparative Example 2.

Embodiments for Carrying Out the Invention

[0014] (Method for Producing Foamed Styrenic Resin Particles) In the method for producing the foamable styrene resin particles (hereinafter referred to as "foamable particles"), a polymerization step is performed in which styrene resin seed particles (hereinafter referred to as "seed particles") containing the specific saturated hydrocarbon (hereinafter referred to as "saturated hydrocarbon A") in the specific mass ratio are polymerized while impregnating them with styrene monomers and the specific organic compound. This polymerization method, in which styrene monomers are polymerized while impregnating seed particles with styrene monomers, is sometimes called the "seed polymerization method." The foamable particles obtained by the above production method can suppress the shrinkage of styrene resin foam particles (hereinafter referred to as "foamed particles") even when foamed at a high magnification. Furthermore, by performing in-mold molding using such foam particles, lightweight styrene resin foam molded articles (hereinafter referred to as "molded articles") can be easily obtained.

[0015] The reasons why the aforementioned effects can be obtained by the above manufacturing method are thought to be, for example, the following: The seed particles used in the production of the foaming particles contain saturated hydrocarbon A. The styrene resin constituting the foaming particles is obtained by impregnating the styrene resin constituting the seed particles with styrene monomers and the specific organic compound, and then polymerizing the styrene monomers. The polymer chain of the styrene resin obtained in this way has a different structure from the polymer chain of the styrene resin obtained by a method of polymerizing styrene monomers in one step, such as suspension polymerization. Therefore, it is thought that the foaming particles obtained by this method are less likely to shrink after foaming compared to styrene resin foaming particles obtained by a method of polymerizing styrene monomers in one step, possibly due to the difference in the structure of the polymer chain of the styrene resin. Furthermore, it is thought that such styrene resin can improve the compressible and flexible properties of molded articles.

[0016] Furthermore, in the above manufacturing method, seed particles are impregnated with a specific proportion of saturated hydrocarbon A in advance to appropriately plasticize the seed particles, and then the styrene resin particles are plasticized by impregnating them with an organic compound having a boiling point of 200°C or higher during the polymerization process. Both the saturated hydrocarbon A contained in the seed particles and the specific organic compound impregnated into the seed particles during the polymerization process have the property of plasticizing styrene resin, but it is thought that they differ slightly in their ease of impregnation into the seed particles and their plasticizing ability. Therefore, it is thought that by using saturated hydrocarbon A for plasticizing the seed particles and the specific organic compound for plasticization during the polymerization process, the effects of saturated hydrocarbon A and organic compound can be balanced well. By adding such saturated hydrocarbon A and organic compound at different stages in the manufacturing process of foamed particles, the amounts of saturated hydrocarbon A and organic compound can be easily reduced while maintaining the foaming properties of the foamed particles. As a result, shrinkage after foaming of the foamed particles can be suppressed.

[0017] As described above, in the above manufacturing method, by using saturated hydrocarbon A and the organic compound in different processes, it is believed that foamed particles can be obtained that can suppress shrinkage of foamed particles even when foaming at a high magnification. Furthermore, it is believed that foamed particles obtained by foaming the foamed particles can improve the compressible and flexural properties of the molded article. The method for manufacturing the foamed particles will be described in more detail below.

[0018] [Styrene-based resin particles] The seed particles used in the production of the foaming particles are composed of a styrene-based resin. In this specification, "styrene-based resin" refers to a styrene homopolymer and a styrene copolymer containing 50% by mass or more of structural units derived from styrene. Examples of styrene homopolymers include general-purpose polystyrene (so-called GPPS). Examples of styrene copolymers include styrene-acrylic acid copolymer, styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-butyl acrylate copolymer, styrene-methacrylic acid copolymer, styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene-butyl methacrylate copolymer, styrene-maleic anhydride copolymer, styrene-acrylonitrile copolymer, acrylonitrile-butadiene-styrene copolymer, styrene-methylstyrene copolymer, styrene-dimethylstyrene copolymer, styrene-ethylstyrene copolymer, and styrene-diethylstyrene copolymer. The seed particles may contain one type of styrene-based resin selected from the group consisting of these styrene-based resins, or they may contain two or more types of styrene-based resins.

[0019] The seed particles may contain resins or elastomers other than styrene-based resins, as long as they do not hinder the effects described above. Examples of polymer components other than styrene-based resins that may be included in the seed particles include resins and elastomers such as low-density polyethylene, linear low-density polyethylene, high-density polyethylene, polypropylene, polyester, polyamide, polycarbonate, and acrylic resin. The mass percentage of styrene-based resin in the seed particles is preferably 90% by mass or more, more preferably 95% by mass or more, even more preferably 97% by mass or more, and particularly preferably 99% by mass or more.

[0020] The seed particles may contain additives such as antistatic agents, antioxidants, ultraviolet absorbers, and light stabilizers, to the extent that they do not impair the effects described above. Examples of antistatic agents include alkyldiethanolamine, glycerin fatty acid esters, and sodium alkylsulfonate. Examples of antioxidants include phenolic, phosphorus-based, and sulfur-based antioxidants. Examples of ultraviolet absorbers include benzotriazole-based and benzophenone-based ultraviolet absorbers. Examples of light stabilizers include hindered amine-based light stabilizers.

[0021] The seed particles contain saturated hydrocarbon A having 6 to 7 carbon atoms. The seed particles may contain one type of saturated hydrocarbon A, or two or more types of saturated hydrocarbon A. As mentioned above, the saturated hydrocarbon A contained in the seed particles has the effect of moderately plasticizing the styrene resin that constitutes the seed particles. In addition, the saturated hydrocarbon A contained in the seed particles has the effect of further enhancing the foaming properties of the foamable styrene resin particles. Therefore, by using seed particles containing the saturated hydrocarbon A, it is possible to easily obtain foamable particles that are uniformly foamed throughout and that do not shrink easily even when foamed at a high magnification.

[0022] The saturated hydrocarbon A contained in the seed particles may be a chain-type saturated hydrocarbon such as n-hexane, n-heptane, 2-methylpentane, or 2-methylhexane, or a cyclic saturated hydrocarbon such as cyclohexane and cycloheptane. From the viewpoint of more reliably obtaining the effect of suppressing the shrinkage of foamed particles even when foaming at a high magnification, it is preferable that the seed particles contain a cyclic saturated hydrocarbon, and more preferably cyclohexane.

[0023] The content of saturated hydrocarbon A in the seed particles is 0.5% by mass or more and 3% by mass or less per 100% by mass of seed particles. By setting the content of saturated hydrocarbon A in the seed particles within the specified range, foaming particles that do not shrink easily after foaming can be easily obtained. The content of saturated hydrocarbon A per 100% by mass of seed particles can be determined by preparing a sample solution by dissolving the seed particles in a solvent such as dimethylformamide, and then analyzing this sample solution by gas chromatography.

[0024] If the seed particles do not contain the saturated hydrocarbon A, locally insufficiently foamed areas tend to form inside the foamed particles formed by foaming the foamed particles. Furthermore, if such foamed particles are molded in a mold, it may lead to a decrease in the compressible properties of the molded article. Similarly, if the content of the saturated hydrocarbon A in the seed particles is too low, the foaming ability of the foamed particles will be insufficient, and locally insufficiently foamed areas tend to form inside the foamed particles. By setting the content of the saturated hydrocarbon A in the seed particles to 0.5% by mass or more, preferably 0.7% by mass or more, more preferably 0.9% by mass or more, and even more preferably 1.1% by mass or more, based on 100% by mass of the seed particles, these problems can be easily avoided, the entire foamed particle can be sufficiently foamed, and foamed particles with reduced variation in bubble diameter can be obtained, for example, as shown in Figure 1, which will be described later.

[0025] On the other hand, if the content of saturated hydrocarbon A in the seed particles is too high, the styrene resin constituting the foamed particles tends to become excessively plasticized when the foamed particles are foamed. As a result, the bubble structure of the foamed particles becomes difficult to stabilize, and there is a risk that the foamed particles will shrink after foaming. By setting the content of saturated hydrocarbon A in the seed particles to 3% by mass or less, preferably 2.7% by mass or less, more preferably 2.4% by mass or less, and even more preferably 2.1% by mass or less, based on 100% by mass of the seed particles, the above-mentioned problems can be easily avoided, and the shrinkage of the foamed particles after foaming can be easily suppressed.

[0026] In determining the preferred range for the content of saturated hydrocarbon A in the seed particles, the upper and lower limits of the saturated hydrocarbon A content described above can be arbitrarily combined. For example, the preferred range for the content of saturated hydrocarbon A in the seed particles may be 0.7% by mass or more and 2.7% by mass or less, 0.9% by mass or more and 2.4% by mass or less, or 1.1% by mass or more and 2.1% by mass or less, based on 100% by mass of the seed particles.

[0027] The seed particles may contain plasticizers other than saturated hydrocarbon A, to the extent that they do not impair the effects described above. Examples of plasticizers that may be included in the seed particles include glycerin tristearate. From the viewpoint of more easily suppressing the shrinkage of the foamed particles, it is preferable that the seed particles do not contain organic compounds having a boiling point of 200°C or higher. From a similar viewpoint, it is preferable that the seed particles do not contain liquid paraffin.

[0028] The method for producing seed particles is not particularly limited, and known methods such as suspension polymerization and extrusion can be employed. For example, when producing seed particles by suspension polymerization, a method can be employed in which styrene monomers suspended in an aqueous medium are polymerized to form seed particles and saturated hydrocarbon A is impregnated into the seed particles. When producing seed particles by extrusion, a method can be employed in which molten styrene resin extruded from an extruder is cut by methods such as hot cutting, strand cutting, or underwater cutting to produce seed particles, and then saturated hydrocarbon A is impregnated into the seed particles. From the viewpoint of making it easier to impregnate the seed particles with saturated hydrocarbon A, it is preferable to produce seed particles by suspension polymerization. Furthermore, from the viewpoint of making it easier to uniformly impregnate the seed particles with saturated hydrocarbon A, it is preferable to impregnate the seed particles with saturated hydrocarbon A in the reaction vessel in the suspension polymerization method, and then perform the polymerization step described later using the seed particles removed from the reaction vessel.

[0029] [Polymerization process] In the polymerization process, the seed particles dispersed in an aqueous medium are impregnated with a styrene monomer and an organic compound having a boiling point of 200°C or higher, and the styrene monomer is polymerized. This yields styrene resin particles. As the aqueous medium used in the polymerization process, water, a water-soluble organic solvent, and a mixed solvent of water and the organic solvent can be used.

[0030] A suspending agent and / or surfactant may be added to the aqueous medium as needed. Examples of suspending agents include hydrophilic polymers such as polyvinyl alcohol, methylcellulose, and polyvinylpyrrolidone, as well as poorly water-soluble inorganic salts such as tricalcium phosphate, magnesium pyrophosphate, hydroxyapatite, aluminum oxide, talc, kaolin, and bentonite. These suspending agents may be used individually or in combination of two or more.

[0031] Examples of surfactants that can be used include anionic surfactants, nonionic surfactants, cationic surfactants, and amphoteric surfactants. The aqueous medium preferably contains anionic surfactants among these surfactants, and more preferably contains one or more anionic surfactants selected from the group consisting of sodium alkyl sulfonate, sodium dodecylbenzenesulfonate, and disodium alkyldiphenyl ether disulfonate. By using the above surfactants, the stability of the dispersion state of seed particles, etc., in the aqueous medium can be further enhanced.

[0032] The amount of suspension agent used is preferably 0.01 parts by mass or more and 5 parts by mass or less per 100 parts by mass of styrene monomer. When using a suspension agent consisting of a poorly water-soluble inorganic salt in combination with an anionic surfactant, it is preferable to use 0.05 parts by mass or more and 3 parts by mass or less of the suspension agent and 0.0001 parts by mass or more and 0.5 parts by mass or less of the anionic surfactant per 100 parts by mass of styrene monomer.

[0033] In the polymerization process, seed particles can be impregnated with styrene monomers and organic compounds having a boiling point of 200°C or higher by adding styrene monomers and organic compounds to an aqueous medium. When impregnating seed particles with styrene monomers and organic compounds, the aqueous medium may be heated as needed to promote the impregnation of the seed particles with styrene monomers and organic compounds.

[0034] In the polymerization process, by adding an organic compound having a boiling point of 200°C or higher to an aqueous medium, foamable particles can be obtained that can suppress shrinkage of foamed particles even when foaming at a high magnification. Furthermore, since the organic compound having a boiling point of 200°C or higher does not easily vaporize during in-molding of the foamed particles, shrinkage of the molded foamed particle body after in-molding can be suppressed. From the viewpoint of further enhancing these effects, the boiling point of the organic compound is preferably 230°C or higher, and more preferably 250°C or higher. There is no upper limit to the boiling point of the organic compound, but it is usually 600°C or lower, and more preferably 500°C or lower. The boiling point of the organic compound is determined from the value of the initial boiling point measured according to JIS K0066-1992.

[0035] The addition of styrene monomers to the aqueous medium may be done in a single step or in multiple steps. The styrene monomers added to the aqueous medium may be in the form of an oily liquid mainly composed of styrene monomers, or in the form of a suspension in water or the like.

[0036] Furthermore, the impregnation of seed particles with styrene monomers and the impregnation of the organic compound may be carried out in parallel or separately. When the impregnation of seed particles with styrene monomers and the impregnation of the organic compound are carried out in parallel, for example, the organic compound may be dissolved in the styrene monomer beforehand, and then the styrene monomer containing the organic compound may be added to the aqueous medium. From the viewpoint of more reliably impregnating the seed particles with the organic compound, it is preferable to complete the step of adding the organic compound to the aqueous medium before the step of adding the styrene monomer to the aqueous medium is completed. Also, from the viewpoint of further promoting the impregnation of the organic compound into seed particles, it is preferable to dissolve the organic compound in the styrene monomer beforehand, and then add the styrene monomer containing the organic compound to the aqueous medium.

[0037] In the polymerization process, the amount of the organic compound added to the aqueous medium is preferably 0.1 parts by mass or more and 0.6 parts by mass or less, more preferably 0.15 parts by mass or more and 0.5 parts by mass or less, even more preferably 0.18 parts by mass or more and 0.4 parts by mass or less, and particularly preferably 0.2 parts by mass or more and 0.35 parts by mass or less, based on 100 parts by mass of the total amount of styrene resin in the seed particles and the amount of styrene monomer added. In this case, foamable particles that can suppress shrinkage of foamed particles even when foaming at a high magnification can be obtained more easily.

[0038] Examples of organic compounds to be added to the aqueous medium in the polymerization process include carboxylic acid esters such as dioctyl adipic acid and butyl stearate, and mineral oils such as liquid paraffin. The organic compounds may be used individually. Alternatively, two or more of the organic compounds may be used in combination.

[0039] The organic compound is preferably composed of mineral oil. In this case, foaming particles that can suppress the shrinkage of foaming particles even when foaming at a high ratio can be obtained more reliably. Examples of mineral oil include atmospheric residue obtained by atmospheric distillation of crude oil such as paraffinic crude oil (including liquid paraffin), intermediate crude oil, and naphthenic crude oil; distillates obtained by vacuum distillation of these atmospheric residues; mineral oil obtained by subjecting the distillates to one or more refining treatments such as solvent delamination, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, and hydrorefining; and mineral oil obtained by isomerizing wax (GTL wax) produced by the Fischer-Tropsch process, etc. These mineral oils may be used individually. Two or more types of mineral oil can also be used in combination.

[0040] From the viewpoint of more reliably obtaining the aforementioned effects, it is more preferable that the mineral oil is liquid paraffin. Liquid paraffin refers to paraffins, that is, mixtures of saturated hydrocarbons represented by CmHn (where n and m are natural numbers satisfying n < 2m + 1), which are liquid at room temperature and pressure (e.g., 25°C, 1 atm). As liquid paraffin, liquid paraffin as defined in JIS K2231-1993 is particularly preferred. From the viewpoint of further suppressing the shrinkage of foamed particles even when foaming at a high magnification, it is preferable that the average carbon number of the liquid paraffin is 20 or more and 35 or less. From a similar viewpoint, the kinematic viscosity of the liquid paraffin at 40°C measured by the method in accordance with JIS K2283:2000 is 1 mm². 2 / s or more 80mm 2 It is preferable that the speed be less than or equal to 2 mm 2 / s or more 60mm 2 It is more preferable that the value be less than or equal to / s.

[0041] Furthermore, the styrene monomer may contain additives such as polymerization initiators, foaming nucleating agents, chain transfer agents, antistatic agents, antioxidants, ultraviolet absorbers, and light stabilizers, as needed.

[0042] As chain transfer agents, for example, octyl mercaptan, dodecyl mercaptan, α-methylstyrene dimer, etc. can be used. As antistatic agents, alkyldiethanolamine, glycerin fatty acid ester, sodium alkylsulfonate, etc. can be used. As antioxidants, phenol-based, phosphorus-based, sulfur-based, etc. antioxidants can be used. As UV absorbers, benzotriazole-based, benzophenone-based, etc. UV absorbers can be used. As light stabilizers, hindered amine-based, etc. light stabilizers can be used. These additives may be used individually. Alternatively, two or more additives can be used in combination.

[0043] As polymerization initiators, for example, organic peroxides with a 10-hour half-life temperature of 65°C to 90°C, or organic peroxides with a 10-hour half-life temperature of over 90°C and 110°C or less can be used.

[0044] Organic peroxides with a 10-hour half-life temperature of 65°C to 90°C include, for example, t-butylperoxy-2-ethylhexanoate, t-hexylperoxy-2-ethylhexanoate, 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate, t-amylperoxy-2-ethylhexanoate, 1,1-bis(t-hexylperoxy)cyclohexane, 1,1-bis(t-butylperoxy)-2-methylcyclohexane, 1,1-bis(t-butylperoxy)cyclohexane, and benzoyl peroxide. These organic peroxides may be used individually, or two or more organic peroxides may be used in combination.

[0045] Furthermore, as organic peroxides with a 10-hour half-life temperature exceeding 90°C and below 110°C, for example, t-butylperoxy-2-ethylhexyl monocarbonate, t-butylperoxyisopropyl carbonate, t-butylperoxyacetate, t-butylperoxy-3,5,5-trimethylhexanoate, t-butylperoxylaurate, t-amylperoxy-2-ethylhexyl carbonate, t-hexylperoxyacetate, 2,2-bis(4,4-di-t-butylperoxycyclohexyl)propane, and 2,2-bis(t-butylperoxy)butane can be used. These organic peroxides may be used individually. In addition, two or more organic peroxides can be used in combination.

[0046] In the polymerization process, it is preferable to use in combination an organic peroxide with a 10-hour half-life temperature of 65°C to 90°C and an organic peroxide with a 10-hour half-life temperature of over 90°C and under 110°C as polymerization initiators. In this case, the proportion of styrene monomers remaining in the foamed particles is low, and foamed particles with the desired molecular weight can be obtained more easily. From the viewpoint of more reliably obtaining the effects described above, it is preferable to use in combination in the polymerization process benzoyl peroxide as an organic peroxide with a 10-hour half-life temperature of 65°C to 90°C and t-butylperoxy-2-ethylhexyl monocarbonate as an organic peroxide with a 10-hour half-life temperature of over 90°C and under 110°C.

[0047] The amount of organic peroxide added is preferably 0.01 parts by mass or more and 2 parts by mass or less per 100 parts by mass of the total amount of styrene resin and styrene monomer constituting the seed particles. In this case, productivity can be sufficiently increased by increasing the polymerization rate while suppressing the increase in manufacturing costs associated with the use of organic peroxide. From a similar viewpoint, the amount of organic peroxide added is more preferably 0.05 parts by mass or more and 1 part by mass or less, and even more preferably 0.1 parts by mass or more and 0.5 parts by mass or less, per 100 parts by mass of the total amount of styrene resin and styrene monomer constituting the seed particles.

[0048] When t-butylperoxy-2-ethylhexyl monocarbonate is used as a polymerization initiator, it is preferable to add a polymerization inhibitor to the aqueous medium to the extent that it does not inhibit the polymerization of the styrene monomer. In this case, the variation in the average particle size of the foaming particles can be reduced. Examples of polymerization inhibitors include oil-soluble polymerization inhibitors such as 4-t-butylcatechol (p-TBC), hydroquinone, p-benzoquinone, chloro-p-benzoquinone, 2,5-dichlorobenzoquinone, 2,6-dichlorobenzoquinone, 2,3-dimethyl-p-benzoquinone, 2,5-dimethyl-p-benzoquinone, methoxy-p-benzoquinone, tetrabromo-p-benzoquinone, tetrachloro-p-benzoquinone, dimethyl-p-benzoquinone, o-dinitrobenzene, m-dinitrobenzene, p-dinitrobenzene, 2,4-dinitrotoluene, 1,3,5-trinitrobenzene, 1,3,5-trinitroanisole, and 2,4,6-trinitrophenol; and water-soluble polymerization inhibitors such as sodium nitrite, potassium nitrate, ammonium nitrite, L-ascorbic acid, and citric acid.

[0049] There are no particular restrictions on the timing of adding the polymerization inhibitor to the aqueous medium, but when using an oil-soluble polymerization inhibitor, it is preferable to add a styrene monomer, which is a mixture of the polymerization initiator and the polymerization inhibitor, to the aqueous medium. The amount of polymerization inhibitor to be added is preferably 0.0001 parts by mass or more and 0.01 parts by mass or less per 100 parts by mass of the total of the styrene resin and styrene monomer constituting the seed particles.

[0050] In the polymerization process, if necessary, 0.1 to 3 parts by mass of a brominated flame retardant may be added to the aqueous medium per 100 parts by mass of the total amount of styrene resin in the seed particles and the amount of styrene monomer added, thereby impregnating the seed particles with the brominated flame retardant. In this case, the flame retardancy of the molded article obtained using the foamed particles can be further improved.

[0051] Furthermore, conventionally, when a brominated flame retardant is added to foamed particles, the foamed particles tend to shrink after foaming. In particular, when using foamed particles obtained by foaming foamed particles at a high magnification for in-mold molding, it was difficult to obtain a molded article that possessed both high flame retardancy and high compressibility. In contrast, in the above manufacturing method, as described above, by impregnating the specific seed particles with the specific organic compound and impregnating them with a styrene monomer, foamed particles that do not shrink easily can be obtained even when foamed at a high magnification. Therefore, in the above manufacturing method, by impregnating the seed particles with a brominated flame retardant, foamed particles can be obtained that can improve the balance between high flame retardancy and high compressibility of the molded article. From the viewpoint of suppressing the shrinkage of foamed particles after foaming and obtaining a molded article that exhibits high flame retardancy, the amount of brominated flame retardant added is more preferably 0.3 parts by mass or more and 2 parts by mass or less, and even more preferably 0.4 parts by mass or more and 1 part by mass or less, per 100 parts by mass of the total amount of styrene resin in the seed particles and the amount of styrene monomer added.

[0052] Brominated flame retardants include 2,2-bis[4'-(2",3"-dibromo-2"-methylpropoxy)-3',5'-dibromophenyl]propane, 2,2-bis[4'-(2",3"-dibromopropoxy)-3',5'-dibromophenyl]propane, 2,2-bis[4'-(2",3"-dibromo-2-methylpropoxy)-3',5'-dibromophenyl]sulfone, 2,2-bis[4'-(2",3"-dibromopropoxy)-3',5'-dibromophenyl]sulfone, 1,3,5-tris(2',3'-dibromo-2'-methylpropyl)isocyanurate, and 1,3,5-tris(2',3'-dibromo Brominated organic compounds such as pyruthyl isocyanurate, 2,4,6-tribromophenol-2',3'-dibromo-2'-methylpropyl ether, 2,4,6-tribromophenol-2',3'-dibromopropyl ether, 1,2,5,6,9,10-hexabromocyclododecane, and 1,2,5,6-tetrabromocyclooctane can be used. In addition, brominated polymers such as brominated styrene-butadiene copolymer, brominated polystyrene, and brominated epoxy resin can be used as brominated flame retardants. These brominated flame retardants may be used alone. In addition, two or more brominated flame retardants can be used in combination.

[0053] As the brominated flame retardant, it is preferable to use one or more compounds selected from the group consisting of 2,2-bis[4'-(2",3”-dibromo-2”-methylpropoxy)-3',5'-dibromophenyl]propane, 2,2-bis[4'-(2",3”-dibromopropoxy)-3',5'-dibromophenyl]propane, and brominated styrene-butadiene copolymer, and it is more preferable to use 2,2-bis[4'-(2",3”-dibromo-2”-methylpropoxy)-3',5'-dibromophenyl]propane.

[0054] In the polymerization process, insofar as the effects described above are not impaired, flame retardants other than brominated flame retardants may also be added to the aqueous medium in addition to the brominated flame retardants. Examples of flame retardants other than brominated flame retardants include halogenated flame retardants such as perchlorocyclopentadecane and chlorinated polyethylene; non-halogenated phosphorus flame retardants such as trimethyl phosphate, triethyl phosphate, tributyl phosphate, trioctyl phosphate, tributoxyethyl phosphate, triphenyl phosphate, tricresyl phosphate, and tri(isopropylphenyl) phosphate; halogenated phosphorus-containing flame retardants such as tris(chloroethyl) phosphate, tris(dichloropropyl) phosphate, tris(chloropropyl) phosphate, tris(2,3-dibromopropyl) phosphate, and tris(tribromoneopentyl) phosphate; and inorganic flame retardants such as aluminum hydroxide, magnesium hydroxide, calcium carbonate, calcium aluminate, antimony trioxide, expandable graphite, and red phosphorus.

[0055] Furthermore, in the polymerization process, in addition to the brominated flame retardant, it is preferable to add one or more flame retardant aids selected from the group consisting of 2,3-dimethyl-2,3-diphenylbutane and dicumyl peroxide to the aqueous medium, and it is more preferable to add dicumyl peroxide to the aqueous medium.

[0056] The timing of impregnating the seed particles with the brominated flame retardant can vary. For example, the impregnation of the seed particles with the brominated flame retardant may be performed before, in parallel with, or after impregnation with the styrene monomer.

[0057] When impregnating seed particles with styrene monomers and impregnating them with brominated flame retardants in parallel, for example, the brominated flame retardant may be dissolved in the styrene monomers beforehand, and then the styrene monomers containing the brominated flame retardant may be added to the aqueous medium. Alternatively, the impregnation with the brominated flame retardant may be performed before polymerization of the styrene monomers, or it may be performed in parallel with the polymerization of the styrene monomers. From the viewpoint of more reliably impregnating the seed particles with the brominated flame retardant, it is preferable to complete the step of adding the brominated flame retardant to the aqueous medium before the step of adding the styrene monomers to the aqueous medium is completed. Furthermore, from the viewpoint of further promoting the impregnation of seed particles with the brominated flame retardant, it is preferable to dissolve the brominated flame retardant in the styrene monomers beforehand, and then add the styrene monomers containing the brominated flame retardant to the aqueous medium.

[0058] In the polymerization process, the styrene monomers within the seed particles can be polymerized by heating the seed particles after impregnating them with a styrene monomer and a polymerization initiator. The heating of the seed particles may be carried out in one stage or in two or more stages. Furthermore, the polymerization temperature and holding time in each stage can be appropriately set according to the 10-hour half-life temperature of the polymerization initiator used for polymerization.

[0059] More specifically, the polymerization of styrene monomers in the polymerization process can be carried out in two stages: a pre-polymerization stage in which styrene monomers are polymerized at a first polymerization temperature, and a post-polymerization stage in which styrene monomers are polymerized at a second polymerization temperature higher than that of the pre-polymerization stage. In this case, the pre-polymerization stage is a stage in which most of the styrene monomers are polymerized at a relatively low temperature to form a styrene resin, and the post-polymerization stage is a stage in which the remaining unreacted styrene monomers are polymerized. By performing the polymerization of styrene monomers in two stages in this way, styrene resin particles with desired properties and a low content of unreacted styrene monomers can be obtained more easily.

[0060] The polymerization temperature in the preliminary polymerization step is preferably 110°C or lower, and more preferably 105°C or lower. In this case, the weight-average molecular weight of the styrene resin can be moderately increased. Then, by in-mold molding of foamed particles composed of such styrene resin, the flexural and compressible properties of the molded article can be further improved. On the other hand, from the viewpoint of polymerization efficiency, the lower limit of the polymerization temperature in the preliminary polymerization step is generally around 70°C. Furthermore, the holding time of the polymerization temperature in the preliminary polymerization step may be, for example, 3 hours or more, and preferably 4 hours or more. From the viewpoint of increasing productivity, the holding time of the polymerization temperature in the preliminary polymerization step is preferably 6 hours or less, and more preferably 5 hours or less.

[0061] In the above manufacturing method, it is more preferable to change the polymerization temperature between the initial and later stages of the preceding polymerization process, and to divide the preceding polymerization process into two stages. In this case, for example, the polymerization temperature in the initial stage of the preceding polymerization process can be set to 60°C or higher and 80°C or lower, and the polymerization temperature in the later stage of the preceding polymerization process can be set to over 80°C and 110°C or lower.

[0062] When the pre-polymerization process is carried out in two stages, it is preferable to add the brominated flame retardant and the organic compound to the aqueous medium in the initial stage of the pre-polymerization process. In this case, the impregnation of the brominated flame retardant and the organic compound into the seed particles can be further promoted. From the viewpoint of further promoting the impregnation of the styrene monomer into the seed particles, it is preferable to add the styrene monomer to the aqueous medium after the initial stage of the pre-polymerization process is completed and while the polymerization temperature is rising from the temperature at the initial stage to the temperature at the later stage. Furthermore, from the viewpoint of further promoting the impregnation of the foaming agent into the resin particles, it is preferable to add the foaming agent to the aqueous medium in the later stage of the pre-polymerization process.

[0063] The polymerization temperature in the subsequent polymerization step is preferably greater than 115°C and 135°C or less, and more preferably between 118°C and 130°C. In this case, the amount of unreacted styrene monomers can be further reduced. The amount of unreacted styrene monomers in the subsequent polymerization step can be controlled by the holding time of the polymerization temperature. The holding time in the subsequent polymerization step may be, for example, 1 hour or more, and preferably 1.5 hours or more. Furthermore, from the viewpoint of increasing productivity, the holding time of the polymerization temperature in the subsequent polymerization step is preferably 4 hours or less, and more preferably 3 hours or less.

[0064] The ratio of the mass of styrene resin in the seed particles to the mass of styrene monomers added in the polymerization process is preferably styrene resin:styrene monomer = 30:70 to 70:30 (where the sum of the mass of styrene resin and the mass of styrene monomers is 100% by mass), and more preferably 40:60 to 60:40. In this case, it becomes easier to impregnate the seed particles with organic compounds having a boiling point of 200°C or higher in the polymerization process, and the proportion of styrene monomers remaining in the foamed particles can be further reduced.

[0065] [Foaming agent] In the above manufacturing method, to obtain foamed particles, seed particles or styrene resin particles may be impregnated with a foaming agent. More specifically, in the above manufacturing method, seed particles that have been pre-impregnated with a foaming agent may be impregnated with a styrene monomer. Alternatively, polymerization of the styrene monomer may be carried out after impregnating the seed particles with both the foaming agent and the styrene monomer, or the foaming agent may be impregnated into the seed particles while the styrene monomer impregnated into the seed particles is polymerization. Furthermore, the foaming agent may be impregnated into styrene resin particles after the polymerization of the styrene monomer is completed. The number of times the foaming agent is impregnated may be once or two or more times.

[0066] The amount of foaming agent added can be appropriately set, for example, within the range of 5 parts by mass to 20 parts by mass per 100 parts by mass of the total of the styrene resin and styrene monomer constituting the seed particles.

[0067] Examples of blowing agents that can be used include saturated hydrocarbons with 3 to 5 carbon atoms (hereinafter referred to as "saturated hydrocarbon B") such as propane, n-butane, isobutane, n-pentane, cyclopentane, isopentane, and neopentane; ethers such as dimethyl ether, diethyl ether, and furan; alcohols such as methyl alcohol, ethyl alcohol, and propyl alcohol; and halogenated hydrocarbons such as HCFC-141b, HCFC-142b, HCFC-124, HFC-152a, and HFC-134a. These blowing agents may be used alone, or two or more blowing agents may be used in combination.

[0068] From the viewpoint of further shortening the curing time of the molded article, it is preferable that the blowing agent consists of the saturated hydrocarbon B containing at least n-butane, and that the mass percentage of n-butane in the blowing agent is 40% by mass or more, and more preferably 50% by mass or more. By keeping the mass percentage of n-butane in the blowing agent within the above-mentioned specific range, the blowing agent remaining on the foamed particles after foaming is made to dissipate more easily to the outside of the foamed particles. As a result, the time required for the curing process of the molded article can be further shortened. Furthermore, if the seed particles are impregnated with a flame retardant, it is possible to more easily obtain a molded article that exhibits good flame retardancy even with a shorter curing time for the molded article.

[0069] (Method for manufacturing styrene-based foamed particles) By foaming the aforementioned foamable particles, styrene-based resin foamed particles can be obtained. One method for foaming the foamable particles is to heat them using a heating medium such as steam.

[0070] The bulk density of styrene-based foamed resin particles is 15 kg / m³. 3 Preferably, the foaming particles have a bulk density of 15 kg / m³. 3Even when foaming at a relatively high magnification as described below, shrinkage of the foamed particles can be suppressed. Therefore, by foaming the expandable particles and obtaining foamed particles with a bulk density of 15 kg / m 3 or less, a molded body having excellent compression physical properties, being difficult to shrink, and being lightweight can be more easily obtained by performing in-mold shaping. Further, since the expandable particles are excellent in foamability, foamed particles with a bulk density of 15 kg / m 3 or less can be obtained by one-step foaming. According to the manufacturing method, even when foaming at a high magnification, foamed particles that are difficult to shrink and have a low bulk density can be obtained, but it is also possible to manufacture foamed particles at a low magnification by the manufacturing method.

[0071] The method for measuring the bulk density of the foamed particles is as follows. First, the foamed particles are left standing for 24 hours under conditions of a relative humidity of 50%, a temperature of 23°C, and an atmospheric pressure of 1 atm to adjust the state of the foamed particles. Next, the conditioned foamed particles are filled into a graduated cylinder so as to naturally accumulate, and the bulk volume (unit: L) of the foamed particles in the graduated cylinder is read from the scale of the graduated cylinder. Then, the mass (unit: g) of the foamed particles in the graduated cylinder is divided by the aforementioned bulk volume, and further unit conversion is performed to calculate the bulk density (unit: kg / m 3 ) of the foamed particles.

[0072] (Method for manufacturing a styrene resin foamed particle molded body) The styrene resin foamed particles obtained by foaming the expandable particles are used in the manufacture of a styrene resin foamed particle molded body. More specifically, a styrene resin foamed particle molded body can be obtained by performing in-mold shaping using the foamed particles. In the in-mold shaping of the foamed particles, first, the foamed particles are filled into the molding cavity of the mold. Then, a heating medium such as steam is supplied into the mold to heat the foamed particles in the mold. The foamed particles heated in the mold fuse with each other while undergoing secondary foaming. Thereby, the foamed particles in the mold can be integrated to form a molded body. The molded body in the mold is taken out of the mold after being cooled in the mold.

[0073] The shape of the molded article obtained using the foamed particles is not particularly limited, but by performing in-mold molding using the foamed particles, for example, a density of 15 kg / m³ is obtained. 3 The following conditions allow for easy acquisition of molded bodies with a thickness greater than 10 cm. The thickness of the molded body is preferably 15 cm to 100 cm, and preferably 20 cm to 100 cm.

[0074] As described above, the foamed particles obtained by the above manufacturing method can suppress shrinkage of the foamed particles even when foamed at a high magnification. Furthermore, by performing in-mold molding using such foamed particles, a molded body that is lightweight and has good compressible and flexural properties can be easily obtained. Therefore, the foamed particles are suitably used in the manufacture of such lightweight and large molded bodies. Examples of such large molded bodies include those having a length of 1 m to 3 m, a width of 0.5 m to 1.5 m, and the aforementioned thickness, and used in EPS civil engineering construction. The density of the molded body is determined by dividing the mass of the molded body by its volume. [Examples]

[0075] Examples of the method for producing the foamed styrene-based resin particles and the method for producing the foamed styrene-based resin particles are described below.

[0076] (Example 1) The seed particles used in the method for producing foamed particles in this example are composed of polystyrene as a styrene-based resin and contain cyclohexane as saturated hydrocarbon A. In the polymerization step, the seed particles are impregnated with styrene as a styrene-based monomer and liquid paraffin as an organic compound with a boiling point of 200°C or higher, and the styrene is polymerized. The method for producing foamed particles in this example is described in detail below.

[0077] [Seed particle] Seed particles were prepared by suspension polymerization as follows: First, a container with a volume of 1.05 m³ equipped with a stirring device was used. 3An aqueous medium was prepared by adding 350.0 kg of deionized water, 1.90 kg of suspension agent, 0.54 kg of electrolyte, and surfactant to an autoclave. Tricalcium phosphate slurry (concentration 20.5% by mass) was used as the suspension agent, and sodium acetate was used as the electrolyte. In addition, 0.131 kg of sodium dodecylbenzenesulfonate (Hard DBSNA, manufactured by Tokyo Chemical Industry Co., Ltd.) and 0.044 kg of a 50% aqueous solution of disodium alkyldiphenyl ether disulfonate (Perex SSH, manufactured by Kao Corporation) were used as surfactants.

[0078] Next, 390.0 kg of styrene, a polymerization initiator, 5.91 kg of cyclohexane, 2.87 kg of glycerin tristearate, 0.015 kg of polymerization inhibitor, and 0.039 kg of chain transfer agent were added to an aqueous medium. As the polymerization initiator, 0.21 kg of t-butyl peroxy-2-ethylhexyl monocarbonate ("Perbutyl® E," manufactured by NOF Corporation) and 1.03 kg of t-butyl peroxy-2-ethylhexanoate ("Perbutyl O," manufactured by NOF Corporation) were used. 4-tert-butylcatechol was used as the polymerization inhibitor. α-methylstyrene dimer was used as the chain transfer agent.

[0079] After purging the autoclave with nitrogen, the autoclave was sealed, and the temperature inside the autoclave was raised to 90°C while stirring at a rotation speed of 110 rpm. From the point where the temperature reached 90°C, it was raised to 100°C over 5 hours, and then to 110°C over 1.5 hours. After maintaining the temperature at 110°C for 2 hours, the autoclave was cooled to room temperature, thereby forming styrene resin seed particles containing cyclohexane in an aqueous medium.

[0080] The seed particles removed from the autoclave were washed with water, and then the water adhering to the seeds was separated from the seeds using a centrifuge. The dehydrated seeds were mixed with 0.005 parts by mass of an antistatic agent per 100 parts by mass of seeds to coat the surface of the seeds with the antistatic agent. A 5% aqueous solution of polyoxyethylene lauryl ether (Kao Corporation's "Emulgen® 108") was used as the antistatic agent.

[0081] After applying an antistatic agent to the seed particles, the seeds were sieved, and seed particles with a particle size of 0.76 mm to 1.24 mm were extracted. This yielded seed particles consisting of polystyrene as a styrene-based resin and containing cyclohexane as saturated hydrocarbon A. In this example, the cyclohexane content relative to the mass of the seed particles was 1.5% by mass.

[0082] [Method for producing foaming particles] Next, using the seed particles obtained by the above method, foamy particles were produced by carrying out a polymerization process as follows. First, a container with a volume of 1.5 m³ equipped with a stirring device was used. 3 297.3 kg of deionized water and 2.56 kg of suspension agent were placed in an autoclave. Then, 6.41 kg of magnesium nitrate hexahydrate was added, and the mixture was stirred at room temperature for 30 minutes to prepare an aqueous medium. Magnesium pyrophosphate was used as the suspension agent.

[0083] In addition to the aqueous medium, a first dispersion was prepared by adding 0.18 kg of surfactant, 59.2 kg of styrene monomer, 0.51 kg of polymerization initiator, 3.09 kg of brominated flame retardant, 1.54 kg of flame retardant aid, and 0.13 kg of foaming agent to 92.5 kg of deionized water and emulsifying this mixture using a homogenizer. A 40% aqueous solution of sodium alkyl sulfonate (Kao Corporation's "Latemul® PS") was used as the surfactant. Styrene was used as the styrene monomer. t-butyl peroxy-2-ethylhexyl monocarbonate (NOF Corporation's "Perbutyl E") was used as the polymerization initiator. 2,2-bis(4-(2,3-dibromo-2-methylpropoxy)-3,5-dibromophenyl)propane (Daiichi Kogyo Seiyaku Co., Ltd.'s "SR130") was used as the brominated flame retardant. Dicumyl peroxide ("Perkmyl® D," manufactured by NOF Corporation) was used as a flame retardant. Polyethylene wax ("Polywax1000-80M," manufactured by Baker Petrolite) was used as a foaming agent.

[0084] Furthermore, separate from the aqueous medium and the first dispersion, a second dispersion was prepared by adding 0.13 kg of surfactant, 40.1 kg of styrene monomer, 0.38 kg of polymerization initiator, and 1.16 kg of liquid paraffin (RCM-S, manufactured by Sanko Chemical Industry Co., Ltd., 20-35 carbon atoms, initial boiling point 280°C, dry point 440°C) to 87.4 kg of deionized water and emulsifying this mixture using a homogenizer. A 40% aqueous solution of sodium alkyl sulfonate (Latemul PS, manufactured by Kao Corporation) was used as the surfactant. Styrene was used as the styrene monomer. Benzoyl peroxide (Niper® BW, manufactured by NOF Corporation) was used as the polymerization initiator.

[0085] Next, 0.13 kg of surfactant and 235 kg of seed particles were placed in the autoclave. A 40% aqueous solution of sodium alkyl sulfonate (Kao Corporation's "Latemul PS") was used as the surfactant. After purging the autoclave with nitrogen, it was sealed, and the temperature inside the autoclave was raised to 72°C while stirring at a rotation speed of 100 rpm. The temperature inside the autoclave was then maintained at 72°C for 2 hours. At the same time, a first dispersion containing a brominated flame retardant was added to the autoclave, impregnating the seed particles with styrene and the brominated flame retardant. Furthermore, one hour after the temperature reached 72°C, a second dispersion containing liquid paraffin was added to the autoclave, impregnating the seed particles with styrene and the liquid paraffin.

[0086] The autoclave was maintained at 72°C for 2 hours, then the temperature was increased to 93°C over 4 hours, during which 132.2 kg of styrene was supplied to the autoclave over 4 hours. This impregnated the seed particles with styrene and initiated the polymerization of styrene, forming styrene-based resin particles in the aqueous medium. After the supply of styrene to the autoclave was complete, an additional 9.7 kg of deionized water was supplied to the autoclave from the styrene supply pipe to clean the styrene in the pipe.

[0087] The temperature inside the autoclave was maintained at 93°C for 3 hours from the moment it reached 93°C. Furthermore, the supply of the foaming agent was started 1 hour after the temperature inside the autoclave reached 93°C, and the foaming agent was added to the autoclave over 1 hour. This impregnated the resin particles with the foaming agent. The foaming agents used were 7.9 kg of pentane (more specifically, a mixture of 80% by mass of n-pentane and 20% by mass of isopentane) and 30.1 kg of butane (more specifically, a mixture of 70% by mass of n-butane and 30% by mass of isobutane).

[0088] The polymerization of styrene was promoted by maintaining the autoclave at 93°C for 3 hours, and then gradually increasing the temperature to 120°C over 3 hours. After maintaining the temperature at 120°C for 2 hours, it was cooled to room temperature. Subsequently, by cooling the autoclave to room temperature, foamy particles containing a foaming agent were formed in the aqueous medium.

[0089] The foaming particles removed from the autoclave were washed with dilute nitric acid to dissolve and remove the suspension agent adhering to the surface of the resin particles. The foaming particles were then washed with water, and the water adhering to the foaming particles was separated using a centrifuge. The dehydrated foaming particles were mixed with 0.008 parts by mass of an antistatic agent per 100 parts by mass of foaming particles to coat the surface of the foaming particles with the antistatic agent. A 5% aqueous solution of stearyl bis(hydroxyethyl)amine lactate ("Dasper 324DS" manufactured by Miyoshi Oil & Fat Co., Ltd.) was used as the antistatic agent.

[0090] After applying an antistatic agent to the foaming particles, 0.01 parts by mass of alkyldiethanolamine was added per 100 parts by mass of foaming particles. Subsequently, 0.1 parts by mass of zinc stearate, 0.03 parts by mass of glycerin monostearate, and 0.07 parts by mass of silica were added per 100 parts by mass of foaming particles to coat the surface of the foaming particles with this mixture.

[0091] Subsequently, the foaming particles were dried by fluid drying using 60°C hot air for 40 minutes. Table 1 shows the mass ratio of each substance when the total amount of styrene resin in the seed particles and styrene added to the aqueous medium is 100 parts by mass. In Tables 1 and 2, t-butyl peroxy-2-ethylhexyl monocarbonate contained in the first dispersion is referred to as "tBPC", 2,2-bis(4-(2,3-dibromo-2-methylpropoxy)-3,5-dibromophenyl)propane is referred to as "SR130", and benzoyl peroxide contained in the second dispersion is referred to as "BPO".

[0092] (Example 2) The method for producing effervescent particles in this example is generally the same as the method for producing effervescent particles in Example 1, except that the amount of liquid paraffin added to the second dispersion is changed as shown in Table 1, and the mixed butane in the foaming agent is changed to isobutane.

[0093] (Example 3) The method for producing the foaming particles in this example is generally the same as the method for producing foaming particles in Example 1, except that the amount of polymerization initiator added to the second dispersion is changed as shown in Table 1.

[0094] (Example 4) The method for producing the effervescent particles in this example is generally the same as the method for producing effervescent particles in Example 2, except that the amount of liquid paraffin added to the second dispersion is changed as shown in Table 1.

[0095] (Examples 5-6) The method for producing these effervescent particles is generally the same as that for producing effervescent particles in Example 1, except that the amount of polymerization initiator added to the second dispersion and the amount of cyclohexane contained in the seed particles are changed as shown in Table 2.

[0096] (Example 7) The method for producing the foamed particles in this example is generally the same as the method for producing foamed particles in Example 1, except that a brominated flame retardant was not added to the first dispersion.

[0097] (Example 8) The method for producing the foaming particles in this example is generally the same as the method for producing foaming particles in Example 3, except that 2,2-bis[3,5-dibromo-4-(2,3-dibromopropoxy)phenyl]propane (FCP-680, manufactured by Suzuhiro Chemical Co., Ltd.) was used as a brominated flame retardant in the first dispersion. In Tables 1 to 4, 2,2-bis[3,5-dibromo-4-(2,3-dibromopropoxy)phenyl]propane is referred to as "FCP-680".

[0098] (Comparative Example 1) The method for producing the foamed particles in this example is generally the same as the method for producing the foamed particles in Example 1, except that foamed particles without cyclohexane were used, and the amount of polymerization initiator added to the second dispersion was changed as shown in Table 3.

[0099] The method for producing the seed particles used in this example is as follows: First, a container with a volume of 1.05 m³ equipped with a stirring device. 3 An aqueous medium was prepared by adding 350.0 kg of deionized water, 2.09 kg of suspension agent, 0.54 kg of electrolyte, and surfactant to an autoclave. A slurry of tricalcium phosphate (concentration 20.5% by mass) was used as the suspension agent, and sodium acetate was used as the electrolyte. In addition, 0.158 kg of sodium dodecylbenzenesulfonate (Hard DBSNA, manufactured by Tokyo Chemical Industry Co., Ltd.) and 0.053 kg of a 50% aqueous solution of disodium alkyldiphenyl ether disulfonate (Perex SSH, manufactured by Kao Corporation) were used as surfactants.

[0100] Next, 400.0 kg of styrene, a polymerization initiator, 0.04 kg of a foaming nucleating agent, and 0.015 kg of a polymerization inhibitor were added to an aqueous medium. As the polymerization initiator, 0.28 kg of t-butyl peroxy-2-ethylhexyl monocarbonate ("Perbutyl E," manufactured by NOF Corporation) and 0.98 kg of t-butyl peroxy-2-ethylhexanoate ("Perbutyl O," manufactured by NOF Corporation) were used. Polyethylene wax ("Polywax1000-80M," manufactured by Baker Petrolite) was used as the foaming nucleating agent. 4-tert-butylcatechol was used as the polymerization inhibitor.

[0101] After purging the autoclave with nitrogen, the autoclave was sealed, and the temperature inside was raised to 90°C while stirring at a rotation speed of 110 rpm. From the point where the temperature reached 90°C, it was raised to 100°C over 5 hours, and then to 120°C over 1.5 hours. After maintaining the temperature at 120°C for 2 hours and 40 minutes, the autoclave was cooled to room temperature to form cyclohexane-free styrene resin seed particles.

[0102] The seed particles removed from the autoclave were washed with water, and then the water adhering to the seeds was separated using a centrifuge. The dehydrated seed particles were mixed with 0.005 parts by mass of an antistatic agent per 100 parts by mass of seed particles to coat the surface of the seed particles with the antistatic agent. A 5% aqueous solution of polyoxyethylene lauryl ether (Emulgen 108, manufactured by Kao Corporation) was used as the antistatic agent.

[0103] After applying an antistatic agent to the seed particles, the seeds were sieved, and seed particles with a particle size of 0.85 mm to 1.38 mm were extracted. Thus, seed particles consisting of polystyrene as a styrene-based resin and free from saturated hydrocarbon A were obtained.

[0104] (Comparative Example 2) The method for producing the effervescent particles in this example is generally the same as the method for producing effervescent particles in Comparative Example 1, except for the amount of polymerization initiator added to the second dispersion and the amount of cyclohexane shown in Table 3 added to the second dispersion.

[0105] (Comparative Example 3) The method for producing effervescent particles in this example is generally the same as the method for producing effervescent particles in Example 1, except that liquid paraffin was not added to the second dispersion and the mixed butane in the foaming agent was changed to isobutane.

[0106] (Comparative Example 4) The method for producing the effervescent particles in this example is generally the same as the method for producing effervescent particles in Example 1, except that seed particles containing liquid paraffin were used instead of cyclohexane.

[0107] (Comparative Example 5) The method for producing the effervescent particles in this example is generally the same as the method for producing effervescent particles in Example 1, except that the amount of cyclohexane shown in Table 4 is added to the second dispersion instead of liquid paraffin.

[0108] (Comparative Example 6) The method for producing effervescent particles in this example is generally the same as the method for producing effervescent particles in Example 1, except that seed particles containing both cyclohexane and liquid paraffin were used, and liquid paraffin was not added to the second dispersion.

[0109] (Reference example 1) Reference Example 1 is an example of foamed styrene resin particles produced by suspension polymerization. The method for producing the foamed styrene resin particles in Reference Example 1 is as follows: A container with a volume of 1.05 m³ equipped with a stirring device. 3 An aqueous medium was prepared by adding 370.0 kg of deionized water, 1.60 kg of suspension agent, 0.56 kg of electrolyte, and surfactant to an autoclave. A slurry of tricalcium phosphate (concentration 20.5% by mass) was used as the suspension agent, and sodium acetate was used as the electrolyte. In addition, 0.139 kg of a 37% aqueous solution of sodium α-olefin sulfonate (Lion Corporation's "Liporan® LB-440") and 0.046 kg of a 50% aqueous solution of disodium alkyl diphenyl ether disulfonate (Kao Corporation's "Perex SSH") were used as surfactants.

[0110] Next, 370.0 kg of styrene, a polymerization initiator, 2.40 kg of brominated flame retardant, 1.19 kg of flame retardant aid, 0.12 kg of foaming nucleating agent, and 3.00 kg of liquid paraffin (RCM-S, manufactured by Sanko Chemical Industry Co., Ltd.) were added to the aqueous medium. As the polymerization initiator, 0.59 kg of t-butyl peroxy-2-ethylhexyl monocarbonate (Perbutyl E, manufactured by NOF Corporation) and 0.89 kg of benzoyl peroxide (Niper® BW, manufactured by NOF Corporation) were used. As the brominated flame retardant, 2,2-bis[4'-(2",3”-dibromo-2”-methylpropoxy)-3',5'-dibromophenyl]propane (SR130, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) was used. As the flame retardant aid, dicumyl peroxide (Permil D, manufactured by NOF Corporation) was used. Polyethylene wax (Baker Petrolite's "Polywax1000-80M") was used as the foaming agent.

[0111] After replacing the inside of the autoclave with nitrogen, the autoclave was sealed, and the temperature inside the autoclave was raised to 90°C while stirring at a rotation speed of 110 rpm. From the point where the temperature reached 90°C, it was raised to 100°C over 6.5 hours, and then to 115°C over 2.0 hours.

[0112] Furthermore, the supply of the foaming agent was started 5.5 hours after the temperature inside the autoclave reached 90°C, and the foaming agent was added to the autoclave over a period of 1 hour. This allowed the foaming agent to impregnate the resin particles. The foaming agents used were 8.3 kg of pentane (more specifically, a mixture of 80% by mass of n-pentane and 20% by mass of isopentane) and 22.6 kg of butane (more specifically, a mixture of 70% by mass of n-butane and 30% by mass of isobutane).

[0113] After the temperature inside the autoclave reached 115°C, this temperature was maintained for 4.5 hours. Subsequently, by cooling the autoclave to room temperature, foaming particles containing the foaming agent were formed in the aqueous medium.

[0114] The foaming particles removed from the autoclave were washed with water, and then the water adhering to the foaming particles was separated from the foaming particles using a centrifuge. The dehydrated foaming particles were mixed with 0.008 parts by mass of an antistatic agent per 100 parts by mass of foaming particles to coat the surface of the seed particles with the antistatic agent. A 5% aqueous solution of stearyl bis(hydroxyethyl)amine lactate ("Dasper 324DS" manufactured by Miyoshi Oil & Fat Co., Ltd.) was used as the antistatic agent.

[0115] After applying an antistatic agent to the foamed particles, the foamed particles were sieved to extract foamed particles with a particle size of 0.76 mm to 1.30 mm. After applying the antistatic agent to the foamed particles, 0.12 parts by mass of zinc stearate was added per 100 parts by mass of foamed particles. Subsequently, 0.07 parts by mass of glycerin tristearate, 0.05 parts by mass of glycerin monostearate, 0.03 parts by mass of silica, and 0.003 parts by mass of talc were added per 100 parts by mass of foamed particles to coat the surface of the foamed particles with this mixture. Then, the foamed particles were dried by fluid drying using hot air at 40°C for 60 minutes.

[0116] (Reference example 2) Reference Example 2 is an example of foamed styrene resin particles produced by suspension polymerization. The method for producing the foamed particles in this example is generally the same as the method for producing foamed particles in Reference Example 1, except that a brominated flame retardant was not added to the first dispersion, the mixed butane blowing agent was changed to isobutane, and the amount of mixed pentane added was changed as shown in Table 4.

[0117] Tables 1 to 4 show the properties of foamed particles obtained by foaming the foamed particles of the examples, comparative examples, and reference examples, as well as the properties of molded articles obtained using these foamed particles. The measurement and evaluation methods for the properties shown in Tables 1 to 4 are as follows.

[0118] (seed particle) [Cyclohexane content per 100% by mass of seed particles] A sample solution was prepared by dissolving seed particles in N,N-dimethylformamide (DMF). The cyclohexane content per 100% by mass of seed particles was then quantified using gas chromatography.

[0119] The quantitative analysis of cyclohexane by gas chromatography was performed using the following procedure. First, approximately 5 g of cyclopentanol, used as an internal standard, was placed in a 100 mL volumetric flask, and the mass Wi (in grams) of the cyclopentanol in the flask was accurately weighed to three decimal places. Then, DMF was added to the volumetric flask until the volume of liquid in the flask reached 100 mL. An internal standard solution was prepared by further diluting this DMF solution 100-fold with DMF.

[0120] Next, approximately 1 g of seed particles were prepared for measurement. The mass Ws (in g) of these seed particles was accurately weighed to three decimal places, and then the seed particles were dissolved in approximately 18 mL of DMF. A sample solution was prepared by adding 2 mL of internal standard solution, accurately collected using a volumetric pipette, to this solution. Subsequently, 1 μL of the sample solution, collected using a microsyringe, was introduced into a gas chromatograph to obtain a chromatogram. The peak area An derived from cyclohexane and the peak area Ai derived from the internal standard were determined in the obtained chromatogram. Then, using these values ​​and the correction coefficient Fn for the cyclohexane component determined based on a previously prepared calibration curve, the concentration of cyclohexane in the seed particles was quantified according to the following formula (1). Cyclohexane concentration (mass%) = [(Wi / 10000)×2]×[An / Ai]×Fn÷Ws×100 ···(1)

[0121] The measurement conditions for the chromatogram are as follows: Measurement device: Shimadzu Corporation gas chromatograph "GC-2014" Column: SUS column (inner diameter 3mm, length 3000mm) Liquid phase name: PEG-20M Liquid phase impregnation rate: 25% Carrier name: "Chromosorb W NAW" manufactured by GL Sciences Co., Ltd. Carrier particle size 60 / 80 mesh Carrier treatment method: AW-DMCS (water washing, calcination, acid treatment, silane treatment) Detector: FID (Flame Ionization Detector) Inlet temperature: 200℃ Column temperature: 100℃ Detection unit temperature: 200℃ Carrier gas: N2, flow rate 40 ml / min Quantification: Internal standard method

[0122] (Foaming particles) [Molecular weight of styrene resins] Using foamed particles as a sample, the weight-average molecular weight Mw and z-average molecular weight Mz of the styrene-based resin constituting the foamed particles were measured by gel permeation chromatography (GPC) using polystyrene as the standard substance.

[0123] Specifically, a sample solution with a concentration of 0.1% by mass was prepared by dissolving foaming particles in tetrahydrofuran (THF). The styrene-based resin in the sample solution was separated by molecular weight using a column consisting of one TSKguardcolumn SuperH-H and two TSK-GEL SuperHM-H columns connected in series, under separation conditions of tetrahydrofuran (THF) as the eluent and a THF flow rate of 0.6 ml / min, and a chromatogram was obtained. Then, the retention time in the chromatogram was converted to molecular weight using a calibration curve prepared with standard polystyrene, and a differential molecular weight distribution curve was obtained. The weight-average molecular weight Mw of the measured sample was calculated from this differential molecular weight distribution curve. The HLC-8320GPC EcoSEC manufactured by Tosoh Corporation was used to acquire the chromatograms.

[0124] (Foaming particles) [Shrinkage immediately after foaming] The foaming particles were placed into a 30L atmospheric pressure batch foaming machine. Steam was then supplied into the foaming machine to heat the foaming particles, causing them to foam up to a bulk density of approximately 10-12 kg / m³. 3We obtained foamed particles. These foamed particles were observed visually for several minutes to evaluate whether or not they contracted.

[0125] [Variation in bubble size] In the evaluation of shrinkage immediately after foaming described above, the presence or absence of variation in bubble diameter was evaluated for foamed particles that did not shrink immediately after foaming using the following method. First, the foamed particles were cut into approximately two equal parts. Then, the cut surfaces of the foamed particles were visually observed to evaluate whether or not there was variation in bubble diameter within the foamed particles.

[0126] [Bulk density] In the evaluation of shrinkage immediately after foaming described above, the bulk density of foamed particles that did not shrink immediately after foaming was measured using the following method. First, the foamed particles were aged at room temperature for one day. Then, the aged foamed particles were filled into a 1L graduated cylinder up to the 1L mark, and 1L of foamed particles was weighed out. The mass of the foamed particles in the graduated cylinder (unit: g) was then divided by the aforementioned bulk volume, and the bulk density of the foamed particles (unit: kg / m³) was obtained by converting the units. 3 The bulk density was calculated. For foamed particles for which bulk density was not measured, the symbol "-" is entered in the "Bulk Density" column of Tables 1 to 4.

[0127] (Molded body) [Moldability] The foaming particles from the examples and reference examples were placed into a 30L atmospheric pressure batch foaming machine. Steam was then supplied into the foaming machine and heated to foam the particles, resulting in a bulk density of approximately 10-12 kg / m³. 3 Foamed particles were obtained. After aging these foamed particles at room temperature for one day, a rectangular parallelepiped mold measuring 300 mm in length, 300 mm in width, and 50 mm in thickness was filled into a moldable mold. Then, using a mold molding machine (PEONY "AD-0907"), steam was supplied into the mold to perform in-mold molding. The pressure of the steam supplied into the mold was 0.06 MPa (G) in gauge pressure, and the supply time was 15 seconds.

[0128] Subsequently, the fusion rate and surface properties of the molded articles removed from the mold were evaluated using the following method, and the moldability of the foamed particles was evaluated based on these results. Note that for Comparative Examples 1 and 3, moldability was not evaluated because foamed particles with low bulk density could not be obtained. Furthermore, for Comparative Examples 2, 4-6, significant shrinkage occurred immediately after foaming, making it impossible to obtain molded articles. Therefore, for these comparative examples, the symbol "-" is indicated in the "Moldability" column of Tables 3 and 4.

[0129] • Fusion rate The molded body was fractured so that it was divided into roughly equal sections laterally. More than 100 foam particles were randomly selected from the foam particles exposed on the fracture surface and visually observed to determine whether they were foam particles that fractured internally (i.e., foam particles that underwent material failure) or foam particles that fractured at the interface between foam particles. The ratio of the number of foam particles that fractured internally to the total number of foam particles observed was then calculated as a percentage (i.e., material failure rate), and this value was recorded in the "Fusion Rate" column of Tables 1 to 4.

[0130] ·Superficiality A 100mm x 100mm square was drawn in the center of one skin surface in the thickness direction of the molded body (i.e., the surface that was in contact with the inner surface of the mold during in-mold molding), and then a diagonal line was drawn from one of the corners of this square. The number of voids existing along the diagonal line, i.e., gaps formed between foam particles, that have a size of 1mm x 1mm or larger were then counted. The number of voids obtained in this way is recorded in the "Surface Properties" column of Tables 1 to 4.

[0131] [Maximum bending stress] The foaming particles from the examples and reference examples were placed into a 30L atmospheric pressure batch foaming machine. Steam was then supplied into the foaming machine and heated to foam the particles, resulting in a bulk density of approximately 10-12 kg / m³. 3Foamed particles were obtained. After aging these foamed particles at room temperature for one day, a rectangular parallelepiped-shaped mold measuring 350 mm in length, 75 mm in width, and 25 mm in thickness was filled into a moldable mold. Then, using a mold molding machine (DABO "DSM-0705VS"), in-mold molding was performed by supplying steam into the mold. The pressure of the steam supplied into the mold was 0.07 MPa (G) in gauge pressure, and the supply time was 10 seconds.

[0132] Using this molded body as a test specimen, a stress-strain curve was obtained by performing a three-point bending test in accordance with the bending test method described in JIS K7221-2 (2006). The bending stress at the maximum load calculated based on this stress-strain curve was defined as the maximum bending stress of the test specimen. The maximum bending stress was then measured for five test specimens, and the arithmetic mean of these measurements was recorded as the maximum bending stress of the molded body in the "Maximum Bending Stress" column of Tables 1 to 4. A universal testing machine (Shimadzu Corporation's "Autograph®") was used for the three-point bending test, and the test was conducted under the conditions of a lower support distance of 200 mm and a test speed of 10 mm / min.

[0133] [10% compressive stress] A molded body was prepared using the same method as the molded body used to evaluate the maximum bending stress. A rectangular parallelepiped specimen measuring 50 mm in length, 50 mm in width, and 25 mm in thickness was taken from the central part of this molded body. A compression test was performed on the specimen according to the method specified in JIS K7220:2006, and a stress-strain curve was obtained. The compression test was performed in a laboratory at 23°C. The 10% compressive stress was defined as the value obtained by dividing the compressive load at 10% strain by the pressure-receiving area of ​​the specimen.

[0134] [Flame retardant] First, a molded body was prepared using the same method as the molded body used to evaluate the maximum bending stress. This molded body was cured at 60°C for three days to prepare molded body a. Next, five rectangular parallelepiped test pieces measuring 200 mm in length, 25 mm in width, and 10 mm in thickness were cut from molded body a. Then, the average value of the extinction time of the five test pieces was calculated according to the flammability test method A described in C.14 of Annex C of JIS A9521:2022, and this value was taken as the average burning time of molded body a.

[0135] Furthermore, molded body b was prepared by fabricating a molded body using the same method as the molded body used to evaluate the maximum bending stress, and then curing the molded body at a temperature of 60°C for 6 days. Using this molded body b, the average burning time of molded body A was calculated using the same method as described above.

[0136] The flame retardancy was evaluated based on the average burning times of molded bodies a and b calculated above. The meanings of the symbols shown in the "Flame Retardancy" column in Tables 1 to 4 are as follows. A: Both the average burning time of molded body a and the average burning time of molded body b were 3 seconds or less. B: The average burning time of molded body a exceeded 3 seconds, while the average burning time of molded body b was 3 seconds or less. C: Both the average burning time of molded body a and the average burning time of molded body b exceeded 3 seconds.

[0137] [Surface fusion rate] 9.8 kg of the foaming particles from the examples and reference examples were placed into a pressurized batch foamer (DAISEN Corporation's "DYHL-1000"). While stirring the foaming particles, steam was supplied to the foamer so that the pressure inside the foamer was 0.025 MPa(G) gauge pressure. By maintaining this pressure for 100 seconds and heating the foaming particles, the particles were foamed up to a density of approximately 10-12 kg / m³. 3 We obtained foamed particles.

[0138] Using these foamed particles, a block-shaped molded body (hereinafter referred to as "block molded body") was produced by in-mold molding using the following method. First, the foamed particles were left at room temperature for one day, and then filled into the molding cavity of a block molding machine (PEONY-P205DS, manufactured by Kasahara Industries Co., Ltd.). The internal dimensions of the molding cavity were 2.0 m in length, 1.0 m in width, and 0.54 m in thickness. A surface pressure gauge was installed in the center of the mold wall facing the end face in the thickness direction of the molded body, that is, the face enclosed by the 2.0 m side and the 1.0 m side, to measure the pressure the mold receives during in-mold molding.

[0139] Next, in-mold molding of foam particles was performed by supplying steam into the molding cavity. During in-mold molding, the steam pressure was adjusted so that the surface pressure on the mold reached 0.08 MPa (G) and this pressure was maintained for 8 seconds. After that, the mold was water-cooled for 3 seconds, and the pressure inside the molding cavity was further reduced until the pressure inside the molding cavity reached -0.08 MPa (G) in gauge pressure. After maintaining the pressure inside the molding cavity until the surface pressure reached -0.010 MPa (G), the mold was opened and the molded body was removed. The obtained molded body was then cured by leaving it at a temperature of 60°C for 3 days, and then at room temperature for 1 day.

[0140] Using the block molded body obtained in this way, the surface bonding rate was evaluated by the following method. First, the block molded body was sliced ​​using a nichrome wire to create nine thin plates, dividing it into nine equal parts in the thickness direction. Of these thin plates, the plates including the end faces in the thickness direction of the block molded body were fractured so that they were divided into approximately equal parts in the longitudinal direction. Next, more than 100 foam particles randomly selected from the foam particles exposed on the fracture surface were visually observed to determine whether they were foam particles that had fractured inside the particle (i.e., foam particles that had undergone material fracture) or foam particles that had fractured at the interface between foam particles. The ratio of the number of foam particles that fractured inside the particle to the total number of foam particles observed was expressed as a percentage and defined as the bonding rate on the surface of the molded body.

[0141] [Internal fusion rate] The method for evaluating the internal fusion rate is the same as the method for evaluating the surface fusion rate described above, except that it uses a thin plate that was positioned in the center of the block molded body in the thickness direction.

[0142] [Shrinkage after molding] The amount of shrinkage of the molded block was measured using the following method. A ruler was placed on one end face in the thickness direction of the molded block (i.e., the face enclosed by the 2.0m side and the 1.0m side) parallel to the 1.0m side and passing through the center of the molded block in the vertical direction. The maximum value of the gap between the ruler and the end face (i.e., the distance from the ruler to the end face of the molded block in the thickness direction) was measured. Similar measurements were performed by changing the position of the ruler so that it was parallel to the 1.0m side and passed through one of two locations 0.5m away from the center of the molded block in the vertical direction. Furthermore, the same measurements were performed on the other end face in the thickness direction of the molded block.

[0143] When the end face in the thickness direction of a block molded body is curved in a concave shape due to shrinkage, a gap is formed between the ruler and the end face of the block molded body when the ruler is brought into contact with both of the two outer edges of the end face in the thickness direction. The "Shrinkage Amount of the Molded Body" column in Tables 1 to 4 shows the largest value among the maximum values ​​of the gap between the ruler and the end face of the molded body measured at six measurement positions. Note that if the value shown in the "Shrinkage Amount of the Molded Body" column in Tables 1 to 4 is a negative value, it indicates that a gap has been formed between the ruler and the end face of the block molded body, and that the end face in the thickness direction of the block molded body is curved in a concave shape. Note that if the value shown in the "Shrinkage Amount of the Molded Body" column in Tables 1 to 4 is a positive value, it indicates that the end face in the thickness direction of the block molded body is curved in a convex shape.

[0144] [Table 1]

[0145] [Table 2]

[0146] [Table 3]

[0147] [Table 4]

[0148] As shown in Tables 1 and 2, the manufacturing methods in Examples 1 to 8 involve impregnating seed particles containing cyclohexane with styrene and liquid paraffin during the polymerization step, while simultaneously polymerizing the styrene. Furthermore, the cyclohexane content in the seed particles is between 0.5% and 3% by mass per 100% by mass of the seed particles. Therefore, the foamed particles obtained by these manufacturing methods have a bulk density of 15 kg / m³. 3 Even when foaming was performed at high magnifications as shown below, the shrinkage of the foamed particles could be suppressed.

[0149] Figure 1 shows a magnified photograph obtained by observing a cross-section of foamed particles obtained by foaming the foamed particles of Example 1 using a scanning electron microscope, as an example. As shown in Figure 1, the foamed particles E1 obtained by foaming the foamed particles of Example 1 had a good bubble structure with little variation in bubble diameter.

[0150] Furthermore, a comparison between Examples 1-6 and 8, which produced foamed particles containing a flame retardant by seed polymerization, and Reference Example 1 (see Table 4), which produced foamed particles containing a flame retardant by suspension polymerization, shows that the foamed particles produced by seed polymerization in the examples improved the maximum bending stress and 10% compressive stress of the molded article compared to the foamed particles produced by Reference Example in a single polymerization step. Similarly, a comparison between Example 7, which produced foamed particles without a flame retardant by seed polymerization, and Reference Example 2 (see Table 4), which produced foamed particles without a flame retardant by suspension polymerization, shows that the foamed particles produced by seed polymerization in the examples improved the maximum bending stress and 10% compressive stress of the molded article compared to the foamed particles produced by Reference Example in a single polymerization step. Therefore, these results indicate that the bending and compressive properties of a molded article can be improved by producing foamed particles by seed polymerization.

[0151] Furthermore, as shown in Examples 1 to 6 and Example 8, it can be understood that the above manufacturing method suppresses the shrinkage of foamed particles even when a brominated flame retardant is impregnated into the seed particles during the polymerization process, and the aforementioned effects can be easily obtained.

[0152] In contrast, as shown in Table 3, the manufacturing method of Comparative Example 1 uses seed particles that do not contain saturated hydrocarbons with 6 to 7 carbon atoms in the polymerization process. As a result, the foamed particles C1 obtained by foaming the foamed particles of Comparative Example 1 have low foaming properties in the center, as shown in Figure 2, making it difficult to foam them at a high ratio.

[0153] In the manufacturing method of Comparative Example 2, seed particles that did not contain saturated hydrocarbons with 6 to 7 carbon atoms were used, and the seed particles were impregnated with cyclohexane and liquid paraffin during the polymerization process. However, the foamed particles obtained by foaming the foamed particles of Comparative Example 2 shrank significantly after foaming. Furthermore, as shown in Figure 3, the foamed particles C2 obtained by foaming the foamed particles of Comparative Example 2 had excessively small bubble diameters near the surface, and the variation in bubble diameters within the foamed particles was large.

[0154] In the polymerization step of the manufacturing method for Comparative Example 3, organic compounds with a boiling point of 200°C or higher were not impregnated into the seed particles. As a result, the foaming particles of Comparative Example 3 underwent insufficient plasticization during foaming, resulting in low foaming ability and low bulk density.

[0155] In the manufacturing method of Comparative Example 4, seed particles containing liquid paraffin were used instead of saturated hydrocarbons having 6 to 7 carbon atoms. In the manufacturing method of Comparative Example 4, since the seed particles also contained liquid paraffin, the resulting foaming particles were excessively plasticized during foaming. As a result, the foamed particles obtained by foaming the foaming particles of Comparative Example 4 shrank significantly after foaming, and it was not possible to obtain foamed particles with low bulk density.

[0156] As shown in Table 4, in the polymerization step of the manufacturing method for Comparative Example 5, cyclohexane was impregnated into the seed particles instead of an organic compound with a boiling point of 200°C or higher. As a result, the foamed particles obtained by foaming the foamed particles of Comparative Example 5 shrank significantly after foaming.

[0157] In the manufacturing method of Comparative Example 6, seed particles containing both cyclohexane and liquid paraffin were used, and the seed particles were not impregnated with an organic compound with a boiling point of 200°C or higher during the polymerization process. As a result, the foamed particles obtained by foaming the foamed particles of Comparative Example 6 shrank significantly after foaming.

[0158] Although the methods for producing foamed styrene-based resin particles and the embodiments of the method for producing foamed styrene-based resin particles have been described above based on the examples, the specific embodiments of the method for producing foamed styrene-based resin particles and the method for producing foamed styrene-based resin particles according to the present invention are not limited to the embodiments of the examples, and the configuration can be appropriately changed without impairing the spirit of the present invention. [Explanation of Symbols]

[0159] E1 Styrene-based foamed resin particles

Claims

1. A method for producing foamed styrene-based resin particles containing a foaming agent, The process includes a polymerization step in which styrene resin particles dispersed in an aqueous medium are impregnated with a styrene monomer and an organic compound having a boiling point of 200°C or higher, and the styrene monomer is polymerized to obtain styrene resin particles. The aforementioned seed particles contain saturated hydrocarbons with 6 to 7 carbon atoms. A method for producing foamed styrene-based resin particles, wherein the content of the saturated hydrocarbon in the seed particles is 0.5% by mass or more and 3% by mass or less based on 100% by mass of the seed particles.

2. The method for producing foamed styrene-based resin particles according to claim 1, wherein the amount of the organic compound added to the aqueous medium in the polymerization step is 0.1 parts by mass or more and 0.6 parts by mass or less with respect to 100 parts by mass of the total amount of styrene-based resin in the seed particles and the amount of styrene-based monomer added.

3. A method for producing foamed styrene-based resin particles according to claim 1 or 2, wherein the organic compound is liquid paraffin.

4. A method for producing foamed styrene-based resin particles according to claim 1 or 2, wherein in the polymerization step, 0.1 parts by mass to 3 parts by mass of a brominated flame retardant is added to the aqueous medium in proportion to 100 parts by mass of the sum of the amount of styrene-based resin in the seed particles and the amount of styrene-based monomer added, thereby impregnating the seed particles with the brominated flame retardant.

5. A method for producing foamed styrene-based resin particles according to claim 1 or 2, wherein the foaming agent comprises a saturated hydrocarbon having 3 to 5 carbon atoms, including n-butane, and the mass proportion of n-butane in the foaming agent is 40% by mass or more.

6. A method for producing foamable styrene resin particles according to claim 1 or 2, wherein the foaming agent is impregnated into the seed particles while the styrene monomer is polymerized in the polymerization step.

7. A method for producing foamed styrene resin particles, comprising a foaming step of foaming foamed styrene resin particles obtained by the manufacturing method described in claim 1 or 2, The bulk density of the foamed particles is 15 kg / m³ 3 The following is a method for producing styrene-based resin foam particles.

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