JP2015101701A - Method for producing expandable polystyrene-based resin particle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing an expandable polystyrene-based resin particle that can produce a polystyrene-based resin expansion molded article having an excellent fire retardant property as well as that is excellent in expansion moldability and has a high product yield.SOLUTION: A method for producing an expandable polystyrene-based resin particle comprising fire retardant, includes: first, mixing a fire retardant comprising brominated butadiene-styrene copolymer, and a polystyrene-based resin by kneading to produce a polystyrene-based resin seed particle and dispersing the same in an aqueous medium; then, feeding a styrenic monomer into the aqueous medium to impregnate the styrenic monomer into the polystyrene-based resin seed particle and polymerizing the same; and impregnating a physical blowing agent into the resin particle during or after the polymerization to produce an expandable polystyrene-based resin particle.

Description

  The present invention relates to a method for producing expandable polystyrene resin particles containing a flame retardant.

  Polystyrene resin foam moldings are used for heat insulating materials for buildings, cold storage boxes, and the like due to their excellent heat insulation performance. The polystyrene-based resin foam molding is produced using expandable polystyrene-based resin particles. Specifically, first, foamed polystyrene-based resin particles are obtained by foaming expandable polystyrene-based resin particles. Next, a polystyrene resin foam molded article is obtained by fusing the polystyrene resin particles to each other in the mold.

  In applications such as heat insulating materials for buildings that require flame retardancy, polystyrene-based resin foam moldings containing flame retardants are used. Such a polystyrene-based resin foamed molded article is produced as described above from expandable polystyrene-based resin particles containing a flame retardant. Conventionally, hexabromocyclododecane (hereinafter also referred to as “HBCD” as appropriate) has been used as a flame retardant. However, HBCD is known to inhibit the polymerization of styrenic monomers. That is, when suspension polymerization of a styrene monomer in the presence of HBCD, there is a problem that many styrene monomers remain in the resulting expandable polystyrene resin particles. Further, the molecular weight of the polystyrene resin cannot be increased, and there is a problem that a foamed particle molded body having sufficient mechanical strength cannot be obtained.

  Then, the method (refer patent document 1) which produces the expandable polystyrene resin particle containing a flame retardant by impregnating the polystyrene resin particle produced previously with HBCD is developed. Also, a method of producing expandable polystyrene resin particles containing a flame retardant by impregnating and polymerizing polystyrene resin particles with a styrene monomer in which a flame retardant such as tetrabromocyclooctane is dissolved (seed polymerization method, patent Reference 2) has been developed. Also, a method of producing expandable polystyrene resin particles containing a flame retardant by suspension polymerization of a styrene monomer in which a brominated bisphenol A flame retardant having a specific structure is dissolved (suspension polymerization method, patent document) 3) has been developed.

JP-A-4-132746 JP 2008-239709 A Japanese Patent Laid-Open No. 2007-9018

  However, in the methods of Patent Documents 1 and 2 described above, it is difficult for the flame retardant to impregnate the resin particles. Therefore, in order to uniformly impregnate the flame retardant, it is necessary to impregnate the flame retardant with a solvent such as toluene. However, in consideration of environmental influences, it is not preferable that the content of volatile organic compounds such as toluene in the expandable polystyrene resin particles is increased. On the other hand, if no solvent is used, expandable polystyrene resin particles in which the flame retardant is uniformly impregnated into the resin particles as described above cannot be obtained. The polystyrene resin foam molded article obtained by using such expandable polystyrene resin particles has a problem that the fusibility deteriorates and a problem that the number of voids on the surface increases. Moreover, there exists a problem that the surface of a polystyrene-type resin foaming molding will fuse | melt. On the other hand, according to the method of Patent Document 3, the above-described problem can be solved. However, since the expandable polystyrene resin particles obtained by this method tend to have a wide particle size distribution, there is room for improvement in terms of product yield of the expandable polystyrene resin particles.

  The present invention has been made in view of such a background, and is capable of obtaining a polystyrene-based resin foam molded article having excellent flame retardancy, and is excellent in foam moldability and having a high product yield. An object is to provide a method for producing particles.

One aspect of the present invention is a method for producing expandable polystyrene resin particles containing a flame retardant,
A dispersion step of dispersing polystyrene-based resin seed particles obtained by kneading a brominated butadiene-styrene copolymer as a flame retardant and a polystyrene-based resin in an aqueous medium;
A polymerization step of supplying a styrene monomer into the aqueous medium, impregnating and polymerizing the polystyrene resin seed particles with the styrene monomer; and
A foaming agent impregnation step of impregnating a physical foaming agent into resin particles during or after the polymerization in the polymerization step to obtain the expandable polystyrene resin particles. is there.

  As described above, the production method includes a dispersion step, a polymerization step, and a blowing agent impregnation step. That is, in the above production method, first, a specific flame retardant and a polystyrene resin (hereinafter referred to as “PS resin” as appropriate) are kneaded to thereby prepare polystyrene resin seed particles (hereinafter referred to as “seed particles” as appropriate). ) Is produced. Next, the seed particles are impregnated with a styrene monomer, polymerized, and further impregnated with a physical foaming agent to obtain expandable polystyrene resin particles (hereinafter referred to as “expandable resin particles” as appropriate).

  In the above production method, the specific flame retardant is kneaded into the seed particles as described above. Therefore, by using the foamable resin particles obtained by the above production method, a polystyrene-based resin foam molded article that can exhibit excellent flame retardancy even if the amount of flame retardant added is reduced (hereinafter, appropriately referred to as “foam molded article”). In the above production method, the seeding particles are impregnated and polymerized by performing the polymerization step, so that the particle size distribution of the expandable resin particles is narrow. Thus, the product yield of the expandable resin particles is improved.

  In addition, brominated butadiene-styrene copolymers are used as flame retardants. Since the brominated butadiene-styrene copolymer hardly inhibits the polymerization of the styrene monomer, expandable resin particles having excellent foam moldability can be obtained. Therefore, by using the foamable resin particles, it is possible to obtain a foamed molded article having a high fusion rate, few surface voids, and almost no surface melting. Moreover, since the said specific flame retardant is used, the moisture content of an expandable resin particle can be decreased.

FIG. 3 is a photographic substitute diagram showing a digital photograph of the appearance of the foam molded article in Example 1; The photograph substitute figure which shows the digital photograph of the external appearance of the foaming molding in the comparative example 1. FIG. The photograph substitute figure which shows the digital photograph of the external appearance of the foaming molding in the comparative example 3. FIG. The photograph substitute figure which shows the digital photograph of the external appearance of the foaming molding in the comparative example 4. FIG.

Next, a preferred embodiment in the method for producing the expandable resin particles will be described.
The foamable resin particles are foamed to produce polystyrene-based resin foamed particles (hereinafter referred to as “foamed particles” as appropriate), and these foamed particles are molded in-mold to obtain a foamed molded product. Used for manufacturing. As described above, the expandable resin particles are produced by performing a dispersion step, a polymerization step, and a blowing agent impregnation step.

  In the dispersion step, seed particles obtained by kneading a PS resin and a flame retardant are used. The seed particles are produced by mixing a PS resin and a flame retardant, melting and kneading them, and then refining. The temperature at the time of melt kneading is preferably 200 ° C to 250 ° C, more preferably 210 ° C to 230 ° C. In mixing the flame retardant and the PS resin, the flame retardant may be directly mixed with the PS resin, or a master batch obtained by melting and kneading the flame retardant into the PS resin may be mixed with the PS resin. Good. Further, in mixing the flame retardant and the PS resin, a flame retardant composition obtained by kneading a stabilizer described later into the flame retardant may be mixed with the PS resin. Melt kneading is performed by, for example, an extruder.

  The blending amount of the flame retardant in the expandable resin particles can be appropriately adjusted according to the desired flame retardancy. For example, from the viewpoint of imparting high flame retardancy that satisfies the flammability standard of 5.13.1 of JIS A9511 (2006R) to the foamed resin molded product, 100 mass of PS resin of the foamable resin particles It is preferable to blend the flame retardant with the seed particles so that the blending ratio of the flame retardant with respect to the part is 0.3 parts by mass or more. On the other hand, from the viewpoint of obtaining desired in-mold moldability and mechanical properties, it is difficult for the seed particles so that the blending ratio of the flame retardant with respect to 100 parts by mass of the PS resin of the expandable resin particles is 3 parts by mass or less. It is preferable to add a flame retardant. From the same viewpoint, the blending amount of the flame retardant is more preferably 0.4 to 2.5 parts by mass with respect to 100 parts by mass of the PS resin of the expandable resin particles.

  The blending amount of the flame retardant in the seed particles is preferably 0.4 to 10% by mass. In this case, a foamed molded article excellent in flame retardancy can be obtained more reliably. Further, it is possible to more reliably obtain expandable resin particles having excellent foam moldability. The blending amount of the flame retardant in the seed particles is more preferably 0.5 to 5% by mass, and further preferably 0.6 to 3% by mass.

  A brominated butadiene-styrene copolymer is used as the flame retardant. The brominated butadiene-styrene copolymer is produced, for example, by brominating a styrene-butadiene copolymer. Examples of the styrene monomer in the brominated butadiene-styrene copolymer include styrene, brominated styrene, chlorinated styrene, 2-methylstyrene, 4-methylstyrene, 2,4-dimethylstyrene, α-methylstyrene, and the like. It can be illustrated. Among these, styrene, brominated styrene, 4-methylstyrene, α-methylstyrene, or a mixture thereof is preferable, and styrene is more preferable. The brominated butadiene-styrene copolymer may be a block copolymer, a random copolymer, or a graft copolymer. Preferably, the brominated butadiene-styrene copolymer is a block copolymer.

  The brominated butadiene-styrene block copolymer is represented by the following general formula (1). In the general formula (1), X, Y, and Z are positive integers. The block copolymer in the general formula (1) is a triblock copolymer, but may be a diblock copolymer.

Preferable examples of the brominated butadiene-styrene block copolymer include commercially available products such as “Emerald 3000” manufactured by Chemtura and “FR122P” manufactured by ICL-IP.
The average molecular weight in terms of polystyrene of the brominated butadiene-styrene block copolymer is preferably 1,000 or more and 300,000 or less, more preferably 10,000 or more and 200,000 or less, and further preferably 100,000 or more and 150,000 or less. .

  As long as the effects of the present invention are not impaired, other flame retardants can be used in combination with the brominated butadiene-styrene block copolymer. Examples of other flame retardants include brominated organic compounds and brominated polymers. Examples of the brominated organic compound 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, 1,3,5-tris (2', 3'-dibromopropyl) isocyanurate, 2,4,6-tribromophenol-2 ', 3 '-Dibromo-2'-methylpropi Ether, 2,4,6-tribromophenol-2 ′, 3′-dibromopropyl ether, 1,2,5,6,9,10-hexabromocyclododecane, 1,2,5,6-tetrabromocyclo For example, brominated polystyrene, brominated epoxy resin, etc. are used as the brominated polymer, and one or more of these substances are used as the flame retardant.

From the viewpoint that higher flame retardancy can be imparted with a small addition amount, the bromine content in the flame retardant is preferably 60% by mass or more, and more preferably 63% by mass or more. The bromine content can be determined based on JIS K7392 (2009).
Further, from the viewpoint of suppressing decomposition of the flame retardant during the production of seed particles, the 5% weight reduction temperature of the flame retardant is preferably 250 to 280 ° C, and more preferably 255 to 270 ° C. The 5% reduction temperature of the flame retardant can be determined by a thermogravimetric method (TG method).

  Moreover, in order to improve the thermal stability of the flame retardant during the production of seed particles, a stabilizer such as an epoxy compound or an antioxidant can be used in combination with the flame retardant.

  The epoxy compound has a property of capturing HBr derived from bromine released from the flame retardant when the seed particles are extruded. Utilizing this property, the epoxy compound can suppress the decomposition of the PS resin by HBr. Examples of the epoxy compound include a bisphenol type epoxy compound and a novolac type epoxy compound. More specifically, for example, commercially available products such as “F2200HM” manufactured by ICL-IP, “EPICLON series” manufactured by DIC, and “Araldite ECN1280” manufactured by HUNTUMAN are listed. As these epoxy compounds, 1 type (s) or 2 or more types can be used together. It is preferable that the usage-amount of an epoxy compound is 1-30 mass parts with respect to 100 mass parts of flame retardants, and it is more preferable that it is 5-20 mass parts.

  Examples of the antioxidant include a phenolic antioxidant, a hindered amine antioxidant, and a phosphite antioxidant. These antioxidants can be used alone or in combination of two or more. The antioxidant has a property of capturing halogen radicals or halogen ions generated by decomposition of the brominated butadiene-styrene copolymer during the extrusion process of the seed particles. Utilizing this property, the antioxidant can suppress a decrease in molecular weight and coloring of the PS resin. From such a viewpoint, it is preferable to use a phenol-based antioxidant and a phosphite-based antioxidant in combination as the antioxidant. It is preferable that the usage-amount of antioxidant is 0.2-20 mass parts with respect to 100 mass parts of flame retardants, and it is more preferable that it is 1-15 mass parts.

  In addition to the above-described epoxy compound and antioxidant, other stabilizers can be used in combination. Examples of such stabilizers include metal soaps, organotin compounds, lead compounds, hydrotalcite, polyhydric alcohols, β-ketones, and sulfur compounds.

  From the viewpoint of further improving the flame retardancy of the foamed molded article obtained from the expandable resin particles, it is preferable to uniformly disperse the flame retardant in the polystyrene resin of the seed particles. For that purpose, it is preferable to perform melt-kneading using a single-screw extruder or a twin-screw extruder having a high kneading type screw such as a dull image type, a Maddock type, or a unimelt type. Further, the seed particles are made fine by cutting the kneaded material by, for example, a strand cut method, a hot cut method, an underwater cut method or the like after melt kneading. The seed particle refining method may be other methods as long as a desired particle diameter can be obtained.

  From the viewpoint of improving the productivity of seed particles and improving the filling properties of the foamed particles obtained from the seed particles into the mold, the particle weight of the seed particles is preferably 0.1 to 3 mg, and 0.3 to 1 More preferably, it is 5 mg. In the case of using an extruder, the weight of seed particles can be adjusted by extruding a resin from a hole having a diameter of, for example, about 0.5 to 2 mm and changing the cutting speed at the time of extrusion.

As long as the effects of the present invention are not impaired, additives such as a bubble adjusting agent, a plasticizer, a heat ray shielding agent, a pigment, a slip agent, and an antistatic agent may be further added to the seed particles.
Examples of the air conditioner include ethylene bis fatty acid amide, fatty acid mono amide, fatty acid bis amide, talc, silica, polyethylene wax, methylene bis stearic acid, methyl methacrylate copolymer, and silicone. Preferably, ethylene bis fatty acid amide is used. The bubble regulator may be kneaded into the seed particles, but may be added to the aqueous medium during the polymerization process. In addition, the bubble regulator may be impregnated into the seed particles together with styrene. The addition amount of the cell regulator is adjusted to be 0.01 to 1 part by weight with respect to 100 parts by weight of the expandable polystyrene resin particles, for example. Thereby, the bubble diameter of a foaming molding can fully be stabilized.

Examples of the plasticizer include fatty acid esters such as glycerin tristearate, glycerin trioctanoate, glycerin trilaurate, sorbitan tristearate, sorbitan monostearate, butyl stearate, and glycerin diacetomonolaurate. In addition, organic compounds such as cyclohexane and liquid paraffin are also used.
Examples of the heat ray shielding agent include carbon particles such as graphite powder, carbon black, graphene, and carbon nanotube. As the heat ray shielding agent, metal particles such as aluminum powder are also used. Furthermore, as the heat ray shielding agent, inorganic particles such as titanium oxide, iron oxide, silicon oxide, aluminum oxide, aluminum nitride, and silicon nitride are also used. The heat shielding agent is preferably graphite powder. It is preferable that the addition amount of a heat ray shielding agent is 0.1-6 mass parts with respect to 100 mass parts of expandable polystyrene resin particles. Thereby, the heat insulation of the foaming particle molded object obtained from an expandable resin particle can be improved. As the pigment, slip agent, and antistatic agent, commercially available products and known products can be used.

  In the dispersion step, seed particles are dispersed in an aqueous medium. Dispersion in an aqueous medium is performed using a closed container such as an autoclave equipped with a stirrer, for example. As the aqueous medium, for example, deionized water or the like is used. In the dispersing step, it is preferable to disperse seed particles in an aqueous medium containing a suspending agent. As the suspending agent, for example, hydrophilic polymers such as polyvinyl alcohol, methyl cellulose, polyvinyl pyrrolidone and the like are used. Further, as the suspending agent, for example, poorly water-soluble inorganic salts such as tricalcium phosphate and magnesium pyrophosphate are also used. Further, if necessary, a surfactant may be used in combination with the suspending agent. In addition, when using a poorly water-soluble inorganic salt as a suspending agent, it is preferable to use an anionic surfactant together. As the anionic surfactant, for example, at least one selected from sodium alkyl sulfonate, sodium dodecylbenzene sulfonate, disodium dodecyl diphenyl ether sulfonate, sodium α-olefin sulfonate and the like is used.

  It is preferable that the usage-amount of a suspending agent is 0.01-5 mass parts with respect to 100 mass parts of seed particles. When using a sparingly water-soluble inorganic salt and an anionic surfactant in combination as described above, the amount of sparingly water-soluble inorganic salt used is 0.05 to 3 parts by weight with respect to 100 parts by weight of the seed particles. The amount of the anionic surfactant used is preferably 0.0001 to 0.5 parts by mass. The surfactant is preferably an alkali metal alkyl sulfonate having 8 to 20 carbon atoms. Thereby, a more stable suspension can be realized. Further, the alkali metal alkyl sulfonate is more preferably a sodium salt. In the aqueous medium in which the seed particles are dispersed, an electrolyte such as lithium chloride, potassium chloride, sodium chloride, sodium sulfate, sodium nitrate, sodium carbonate, sodium bicarbonate, sodium acetate, sodium succinate, etc. Is added.

Next, in the polymerization step, a styrene monomer is supplied into an aqueous medium in which seed particles are dispersed. Then, the styrene monomer is impregnated into the seed particles and polymerized.
Examples of the styrene monomer include styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, vinyltoluene, p-ethylstyrene, 2,4-dimethylstyrene, p-methoxystyrene, p-phenylstyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, 2,4-dichlorostyrene, pn-butylstyrene, pt-butylstyrene, pn-hexylstyrene, p- At least one selected from octyl styrene, divinylbenzene, styrene sulfonic acid, sodium styrene sulfonate and the like is used. Of these, styrene is preferred.

It is also possible to use a vinyl monomer copolymerizable with the styrene monomer in combination with the styrene monomer. Examples of such vinyl monomers include acrylic acid esters, methacrylic acid esters, vinyl compounds containing hydroxyl groups, vinyl compounds containing nitrile groups, organic acid vinyl compounds, olefin compounds, diene compounds, halogenated vinyl compounds, Examples thereof include vinylidene halide compounds and maleimide compounds.
Examples of the acrylate ester include methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate.
Examples of the methacrylic acid ester include methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, and 2-ethylhexyl methacrylate.
Examples of the vinyl compound containing a hydroxyl group include hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, and hydroxypropyl methacrylate.
Examples of the vinyl compound containing a nitrile group include acrylonitrile and methacrylonitrile.
Examples of the organic acid vinyl compound include vinyl acetate and vinyl propionate.
Examples of the olefin compound include ethylene, propylene, 1-butene, and 2-butene.
Examples of the diene compound include butadiene, isoprene, chloroprene and the like.
Examples of the vinyl halide compound include vinyl chloride and vinyl bromide.
Examples of the vinylidene halide compound include vinylidene chloride.
Examples of maleimide compounds include N-phenylmaleimide and N-methylmaleimide.
As these vinyl monomers, a single substance can be used, but a mixture of two or more kinds can also be used.

  The PS resin refers to a resin having the styrene monomer component unit of 50% by mass or more. That is, the PS resin is not only a homopolymer of a styrene monomer, but a copolymer of two or more styrene monomers, as well as one or more styrene monomers and copolymerizable therewith. It is a concept including a copolymer with a vinyl monomer. The styrene monomer component unit in the PS resin is preferably 80% by mass or more, and more preferably 90% by mass or more.

  The seed particles are composed of PS resin. As the PS-based resin for seed particles, polystyrene is particularly preferable from the viewpoint of enhancing foamability. The seed particles may contain other thermoplastic resins other than polystyrene resins such as polyethylene resins, polypropylene resins and polyester resins, and thermoplastic elastomers such as styrene elastomers and olefin elastomers. it can. When these thermoplastic resins and thermoplastic elastomers are blended, the blending amount is preferably 20 parts by mass or less with respect to 100 parts by mass of the PS-based resin of the seed particles, and is 10 parts by mass or less. Is more preferable, and it is further more preferable that it is 5 mass parts or less.

The weight average molecular weight of the PS resin constituting the expandable resin particles is preferably 100,000 to 600,000.
In this case, when foaming resin particles are foamed, shrinkage of the foamed particles can be prevented. Furthermore, it is possible to improve the fusibility between the foamed particles during molding of the foamed particles obtained after foaming. As a result, the dimensional stability of the foamed molded product can be improved. From the same viewpoint, the PS-based resin preferably has a weight average molecular weight of 150,000 or more, and more preferably 200,000 or more. The weight average molecular weight of the PS resin is more preferably 500,000 or less, and further preferably 400,000 or less. The range of the weight average molecular weight of the PS-based resin can be determined from all combinations of the above preferred upper and lower preferred ranges, more preferred ranges, and even more preferred ranges.

  When the seed particles are impregnated with a styrene monomer and polymerized, the entire amount of the styrene monomer used can be added at once. Moreover, the styrene-type monomer of the whole usage-amount can be divided | segmented into plurality, and these can also be added at a different timing. As in the latter case, by adding the styrene monomer divided into a plurality of times, it becomes possible to sufficiently suppress the condensation of the resin particles during the polymerization.

  It is preferable that the addition amount of the styrene-type monomer in a superposition | polymerization process is 30-300 mass parts with respect to 100 mass parts of seed particles. In this case, the foam moldability of the expandable resin particles can be further improved. As for the addition amount of a styrene-type monomer, it is more preferable that it is 100-250 mass parts with respect to 100 mass parts of seed particles. Moreover, when adding a styrene-type monomer separately as mentioned above, it is preferable that the amount of styrene added initially is 15-50 weight part with respect to 100 weight part of seed particles. In this case, mutual adhesion of seed particles during polymerization can be suppressed, and spherical polystyrene resin particles can be obtained. The amount of styrene added initially is more preferably 20 to 40 parts by mass with respect to 100 parts by weight of the seed particles.

  In the polymerization step, in order to uniformly polymerize styrene in the seed particles, it is preferable to impregnate the seed particles with a polymerization initiator together with styrene. The polymerization initiator may be added after being dissolved in styrene, or the polymerization initiator may be added alone. It is preferable that the usage-amount of a polymerization initiator is 0.01-3 mass parts with respect to 100 mass parts of styrene-type monomers.

  Examples of the polymerization initiator include organic peroxides and azo compounds that are soluble in styrene and have a 10-hour half-life temperature of 50 to 120 ° C. Examples of the organic peroxide include t-butylperoxy-2-ethylhexanoate, t-butylperoxybenzoate, benzoyl peroxide, t-butylperoxyisopropyl monocarbonate, t-amylperoxy-2-ethylhexyl. Monocarbonate, t-butylperoxy-2-ethylhexyl monocarbonate, hexylperoxy-2-ethylhexyl carbonate, lauroyl peroxide, dicumyl peroxide, 2,5-t-butylperbenzoate, 1,1-bis-t -Butylperoxycyclohexane, cumene hydroxyperoxide, etc. are used. As the azo compound, azobisisobutyronitrile or the like is used. As the polymerization initiator, one or more of these substances are used.

  Next, in the foaming agent impregnation step, the resin particles are impregnated with a physical foaming agent (hereinafter referred to as “foaming agent” as appropriate). Impregnation with the foaming agent can be performed during or after the polymerization of the styrenic monomer. Specifically, a foaming agent is press-fitted into a container that accommodates resin particles during or after polymerization, and the resin particles are impregnated with the foaming agent. In addition, the above-mentioned resin particle is the concept containing the particle | grains in the middle of the impregnation polymerization of the styrene-type monomer in a seed particle, and the particle | grains after an impregnation polymerization.

  As the blowing agent, for example, a saturated hydrocarbon compound having 3 to 6 carbon atoms, a lower alcohol having 5 or less carbon atoms, an ether compound, or the like can be used. Specifically, as the saturated hydrocarbon compound, for example, propane, n-butane, isobutane, cyclobutane, n-pentane, isopentane, neopentane, cyclopentane, n-hexane, cyclohexane and the like can be used. As the lower alcohol, methanol, ethanol or the like can be used. Moreover, as an ether compound, dimethyl ether, diethyl ether, etc. can be used. These foaming agents can be used alone or in a mixture of two or more. In addition, as an ether compound, a C6 or less thing can be used, for example. Preferably, as a foaming agent, it is good to use 1 type, or 2 or more types chosen from a C3-C6 saturated hydrocarbon compound.

  Further, the content of the foaming agent in the foamable resin particles can be appropriately adjusted according to the desired apparent density, but when the content of the foaming agent is too small, for example, a low density of 16 kg / m3 or less. It may be difficult to foam the expandable resin particles. On the other hand, when there is too much content of a foaming agent, the bubble diameter of the foaming particle obtained after foaming will become coarse, and there exists a possibility that the intensity | strength of a molded object may fall. In this case, there is a possibility that the heat insulating property may be adversely affected. Therefore, the content of the foaming agent in the expandable resin particles is preferably 2 to 15% by mass, and more preferably 3 to 10% by mass. Content of a foaming agent is calculated | required by the gas-chromatography analysis of the melt | dissolution thing obtained by melt | dissolving a foamable resin particle in dimethylformamide (DMF).

  In addition, after the foaming agent impregnation step, the foamable resin particles can be dehydrated and dried, and if necessary, the surface coating agent can be coated on the foamable resin particles. As the surface coating agent, metal soap, fatty acid ester of polyhydric alcohol, antistatic agent and the like are used. For example, zinc stearate is used as the metal soap. Examples of the fatty acid ester of polyhydric alcohol include stearic acid triglyceride, stearic acid monoglyceride, castor oil and the like. As the antistatic agent, for example, diethanol alkylamine is used. It is preferable that the addition amount of a surface coating agent is 0.01-2 mass parts with respect to 100 mass parts of expandable resin particles.

Expandable resin particles are used to obtain a foamed molded article as follows. First, foamed particles are obtained by heating and foaming the expandable resin particles. Subsequently, the foamed particle molded body is obtained by fusing the obtained foamed particles to each other in a mold. As a method of heating and foaming the expandable resin particles, for example, there is a method of supplying a heating medium such as steam to the expandable resin particles. Thereby, expandable resin particles are expanded to obtain expanded particles. Incidentally, it is preferable that the bulk density of the resulting expanded beads is 10 to 100 kg / m ^3, more preferably 12~30kg / m ^3.

Example 1
Next, the manufacturing method of the expandable resin particle concerning an Example is demonstrated.
(1) Preparation of seed particles First, using a φ30 mm single screw extruder, 98.5 parts by mass of a polystyrene resin (“680” manufactured by PS Japan) and 1.5 parts by mass of a flame retardant composition were heated to 210 ° C. Melt-kneaded at ~ 230 ° C. Next, the melt-kneaded product was extruded in a strand form from a die having a hole diameter of 1.4 mm of an extruder. The extrudate was immediately introduced into a water bath and cooled, and then the extrudate was cut by strand cutting. As a result, 0.9 mg / pellet was obtained. This pellet is the seed particle of this example (hereinafter, the seed particle of this example is referred to as “seed particle A”). In addition, the flame retardant composition in this example is a brominated butadiene-styrene block copolymer ("Emerald 3000" manufactured by Chemtura), which is a flame retardant having a bromine content of 64 mass% and a 5% weight reduction temperature of 262 ° C. 10 parts by mass of a novolak type epoxy resin (“EPICLON N680” manufactured by DIC) as a stabilizer (epoxy compound) and pentaerythritol tetrakis [3- (3 as a stabilizer (phenolic antioxidant) , 5-di-t-butyl-4-hydroxyphenyl) propionate] ("Irganox 1010" manufactured by BASF) and bis (2,6-di-) as a stabilizer (phosphite antioxidant). t-Butyl-4-methylphenyl) pentaerythritol diphosphite (“PEP36” 5 product made by ADEKA) The flame retardant used in this example is hereinafter appropriately referred to as “flame retardant a”.

(2) Production of expandable resin particles First, 580 g of deionized water, 4.6 g of sodium pyrophosphate, and 11.4 g of magnesium nitrate are charged into an autoclave having a 3 L internal volume equipped with a stirrer to perform salt exchange. Thus, magnesium pyrophosphate as a suspending agent was synthesized in an autoclave. Next, 0.09 g of sodium alkyl sulfonate as a surfactant and 345 g of seed particles A were added to the suspension. In this way, seed particles A were dispersed in the aqueous medium.

  Next, after the air in the autoclave was replaced with nitrogen, the autoclave was sealed. Next, the dispersion was heated to a temperature of 72 ° C. while stirring the dispersion in the autoclave at 350 rpm. In addition, 145 g of deionized water, 0.12 g of sodium alkyl sulfonate, 35 g of styrene, t-butylperoxy-2-ethylhexyl monocarbonate (“Trigonox 117” manufactured by Kayaku Akzo Co., Ltd., 10 hour half-life temperature: A mixture of 2.6 g of 98 ° C.) and 3.5 g of dicumyl peroxide (“PARK Mill D” manufactured by NOF Corporation, 10 hour half-life temperature: 116 ° C.) was mixed with a homogenizer to obtain an emulsion A. Produced.

  And after the temperature of the dispersion liquid in an autoclave reached the above-mentioned 72 degreeC, the emulsion A was thrown into the autoclave. Also, a mixture of 145 g of deionized water, 0.12 g of sodium alkyl sulfonate, 35 g of styrene, and 1.7 g of benzoyl peroxide (“NIPER BW” manufactured by NOF Corporation, 10 hour half-life temperature: 74 ° C.) Was mixed with a homogenizer to prepare an emulsion B. One hour after the temperature of the dispersion in the autoclave reached 72 ° C., the emulsion B was charged into the autoclave.

  The inside of the autoclave was held at a temperature of 72 ° C. for 2 hours, and then heated to 93 ° C. over 4 hours. After reaching the temperature of 93 ° C., the temperature was maintained at 93 ° C. for 4 hours, and the temperature was further increased to 112 ° C. over 3 hours. Next, this temperature was maintained at 112 ° C. for 3 hours, and then cooled to room temperature. Then, 2 hours after reaching the temperature of 72 ° C., 276 g of styrene was continuously added into the autoclave over 4 hours. When the temperature reached 93 ° C., 46 g of pentane (n-pentane 80%, i-pentane 20%) was added to the autoclave over 30 minutes, and then butane (n-butane 60%, i-butane 40%). ) 10 g was added over 10 minutes. Thereby, the foaming agent was impregnated in the resin particles.

  After the inside of the autoclave was cooled to room temperature, the expandable resin particles were taken out from the autoclave. The foamable resin particles were washed with dilute nitric acid to dissolve and remove the suspending agent attached to the surface. Next, the foamable resin particles were washed with water, and the foamable resin particles were dehydrated using a centrifuge. Next, 0.01 parts by mass of alkyldiethanolamine as an antistatic agent was added to 100 parts by mass of the expandable resin particles, and the surface of the expandable resin particles was coated with the antistatic agent. Then, the water | moisture content on the surface of the expandable resin particle was removed by performing fluid drying for 10 minutes using the air of room temperature. To 100 parts by mass of the obtained expandable resin particles, 0.1 part by mass of zinc stearate as an antiblocking agent and 0.05 parts by mass of glycerin monostearate as an antistatic agent are added, and the expandable resin particles The surface of was coated with these antiblocking agents and antistatic agents. Thus, expandable resin particles (expandable polystyrene resin particles) were obtained.

(3) Production of Foam Molded Body 500 g of the expandable resin particles obtained as described above was charged into a 30 L atmospheric pressure batch foaming machine. Next, by supplying steam into the foaming machine, the foamable resin particles were heated and foamed to obtain foamed particles having a bulk density of about 16 kg / m ³ . The obtained expanded particles were aged at room temperature for 1 day. Thereafter, the expanded particles were filled into a mold cavity attached to a mold molding machine (“DSM-0705VS” manufactured by DABO). The mold has a rectangular parallelepiped cavity of 300 mm × 75 mm × 25 mm. A large number of foam particles filled in the mold with steam having a gauge pressure of 0.07 MPa were heated for 10 seconds. Thereby, the expanded particles were fused to each other in the mold. Subsequently, after cooling, a foamed molded product (polystyrene resin foamed molded product) in which the foamed particles were fused to each other was taken out from the mold. In this way, a foamed molded product was obtained.

(Example 2)
In this example, the content of the flame retardant contained in the seed particles and the blending ratio of the seed particles and styrene were changed from those in Example 1 to produce expandable resin particles.
Specifically, first, seed particles (hereinafter referred to as seed particles of this example) were used in the same manner as in Example 1 except that 97 parts by mass of polystyrene resin and 3 parts by mass of the flame retardant composition were melt-kneaded. (Referred to as “seed particles B”). The polystyrene resin and the flame retardant composition are the same as in Example 1. Next, using the seed particles, the amount of sodium pyrophosphate used was changed to 5.5 g, the amount of magnesium nitrate used was changed to 13.7 g, the amount of seed particles used was changed to 207 g, and the temperature was 72 ° C. Expandable resin particles and a foam-molded article were produced in the same manner as in Example 1 except that the amount of styrene added after 2 hours was reached to 414 g.

(Comparative Example 1)
In this example, the method for adding a flame retardant is different from that in Example 1, and foamable resin particles are produced.
Specifically, first, seed particles (hereinafter, referred to as Example 1) were used except that 100 parts by mass of polystyrene resin (PS Japan, 680) was used without adding the flame retardant composition. The seed particles of this example were prepared as “seed particles C”). This seed particle C does not contain a flame retardant. Further, using the seed particles C, expandable resin particles and a foamed molded product were produced in the same manner as in Example 1 except that the following emulsion C was used instead of the emulsion A. Emulsion C is 145 g of deionized water, 0.12 g of sodium alkyl sulfonate, 4.14 g of flame retardant a, 35 g of styrene, t-butylperoxy-2-ethylhexanoate (Kayaku Akzo) It was obtained by mixing a mixture of 2.6 g of “Trigonox 117” manufactured by the company and 3.5 g of dicumyl peroxide (“Park Mill D” manufactured by NOF Corporation) with a homogenizer.

(Comparative Example 2)
This example is an example in which expandable resin particles were produced by changing the polymerization method and the addition method of the flame retardant from Example 1. In this example, expandable resin particles were prepared by suspension polymerization without using seed particles.
Specifically, first, 761 g of deionized water, 2.7 g of sodium pyrophosphate, and 5 g of magnesium nitrate were charged into an autoclave having a 3 L internal volume equipped with a stirrer. Next, a composition containing a styrene monomer was added to the autoclave while stirring the autoclave. This composition is composed of 99 g of polystyrene, 5 g of flame retardant a, 2.3 g of dicumyl peroxide (“Park Mill D” manufactured by NOF Corporation), and benzoyl peroxide (“NIPER BW” manufactured by NOF Corporation). It was obtained by dissolving 0.8 g in 661 g of styrene.

  Next, after the air in the autoclave was replaced with nitrogen gas, the autoclave was sealed. Next, the contents of the autoclave were heated to 80 ° C. over 1 hour and 40 minutes. When this temperature reached 80 ° C., 0.14 g of sodium alkyl sulfonate was added. Next, the content of the autoclave was heated to 90 ° C. over 20 minutes, and then further heated to 134 ° C. over 4 hours. The contents were held at this temperature of 134 ° C. for 4 hours, and then cooled to room temperature. Then, 2 hours after the temperature of the contents reached 90 ° C., 65 g of isobutane as a blowing agent was added, and the resin particles were impregnated with the blowing agent. Thereafter, the same operation as in Example 1 was performed to produce expandable resin particles and a foamed molded product.

(Comparative Example 3)
In this example, the type of flame retardant was changed from that in Example 1 to produce expandable resin particles.
Specifically, 98.7 parts by mass of polystyrene resin (“680” manufactured by PS Japan) and 1.3 parts by mass of a flame retardant composition having a composition different from that of Example 1 were melt-kneaded. Produced seed particles (seed particles D) in the same manner as in Example 1. The flame retardant composition of this example is 2,2-bis [4 ′-(2 ″, 3 ″), which is a flame retardant (flame retardant b) having a bromine content of 65.8 mass% and a 5% weight reduction temperature of 260 ° C. -Dibromo-2 "-methylpropoxy) -3 ', 5'-dibromophenyl] propane (" SR130 "manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), bromine content 67.8% by mass, 5% 2,2-bis [4 ′-(2 ″, 3 ″ -dibromopropoxy) -3 ′, 5′-dibromophenyl] propane (Daiichi Kogyo Seiyaku), a flame retardant having a weight loss temperature of 296 ° C. (flame retardant c) "SR720" manufactured by Co., Ltd.) 40 parts by mass and bis (2,2,6,6-tetramethyl-4-piperidyl) sebacate (manufactured by Ciba Japan Co., Ltd.) as a stabilizer (hindered amine antioxidant) TINUVIN770DF ") and 0.2 parts by mass. Also, except that the seed particles D were used, expandable resin particles and a foamed molded product were produced in the same manner as in Example 1.

(Comparative Example 4)
In this example, expandable resin particles were produced by changing the type and addition method of the flame retardant from Example 1. Specifically, in place of flame retardant a in emulsion C in Comparative Example 1, flame retardant b (2,2-bis [4 ′-(2 ″, 3 ″ -dibromo-2 ″ -methylpropoxy)- Except for the point of using 3 ′, 5′-dibromophenyl] propane), expandable resin particles and an expanded molded article were produced in the same manner as in Comparative Example 1.

(Experimental example)
Regarding the seed particles of Example 1, Example 2, Comparative Example 1, Comparative Example 3, and Comparative Example 4, the types of seed particles (seed particles A to D) used are shown in Tables 1 and 2 described later. Moreover, about Example 1, Example 2, and the comparative example 3, the kind (flame retardants ac) of the flame retardant contained in a seed core and the compounding quantity (mass%) of the flame retardant in a seed particle are shown in Table 1. And in Table 2. Moreover, about Example 1, Example 2, and Comparative Examples 1-4, polymerization conditions (The polymerization method, the addition method of a flame retardant, the addition amount of a styrene-type monomer) are shown in Table 1 and Table 2. Moreover, about the expandable resin particle of Example 1, Example 2, and Comparative Examples 1-4, the compounding quantity (mass part) of the flame retardant with respect to 100 mass parts of flame retardant types (flame retardants ac) and PS resin. Are shown in Tables 1 and 2.

Moreover, about the expandable resin particle of Example 1, Example 2, and Comparative Examples 1-4, a particle size distribution, content (mass%) of a foaming agent, water content (mass%), and molecular weight are as follows. Measured and evaluated for foamability. In addition, the apparent density (kg / m ³ ) and the fusion rate (%) of the foamed molded products of Example 1, Example 2, and Comparative Examples 1 to 4 were measured, and surface voids, surface melting, difficulty Flammability was evaluated. These results are shown in Tables 1 and 2. In addition, about the foaming molding of Example 1, Comparative Example 1, Comparative Example 3, and Comparative Example 4, the external appearance was image | photographed with the digital camera, and the result is shown in FIGS. 1-4, respectively.

`` Particle size distribution ''
The particle size distribution of the expandable resin particles obtained in each of Examples and Comparative Examples was examined using a particle size distribution measuring apparatus “Millitrack JPA” manufactured by Nikkiso Co., Ltd. Specifically, first, 40 g of the expandable resin particles were freely dropped from the sample supply feeder of the measuring apparatus. The projected image at this time was taken with a CCD camera. Next, calculation / combination processing was sequentially performed on the captured image information, and measurement was performed under conditions of an image analysis method for outputting a particle size distribution / shape index result. Thereby, in the particle size distribution, the particle size (d90) at the volume integrated value 90%, the particle size (d63) at the volume integrated value 63%, the particle size (d50) at the volume integrated value 50%, and the volume integrated value 10%. The particle size (d10) was determined. And particle size ratio ((d90-d10) / d50) was computed.

"Content of foaming agent"
First, the expandable resin particles obtained in each Example and Comparative Example were dissolved in dimethylformamide (DMF). The content of each added blowing agent component was measured by performing gas chromatography on the obtained dissolved matter. The content of the foaming agent was determined by summing the content of each foaming agent component. Specifically, the gas chromatograph was quantified by the following procedure.

First, about 5 g of cyclopentanol was accurately weighed to the third decimal place in a 100 mL volumetric flask. This weight is Wi. Next, DMF was added to cyclopentanol in the volumetric flask to adjust the total volume to 100 mL. This DMF solution was further diluted 100 times with DMF to prepare an internal standard solution. Next, about 1 g of the expandable resin particles to be measured was accurately weighed to the third decimal place. This weight is Ws (g). The weighed expandable resin particles were dissolved in about 18 mL of DMF. To the obtained lysate, 2 mL of an internal standard solution was added using a whole pipette. 1 μL of this solution was collected with a microsyringe and introduced into a gas chromatography apparatus to obtain a chromatogram. From the obtained chromatogram, the peak area of each foaming agent component and internal standard was determined, and the concentration of each component was determined by the following equation.
Concentration of each component (mass%) = [(Wi / 10000) × 2] × [An / Ai] × Fn ÷ Ws × 100
Wi: Weight of cyclopentanol used for preparation of internal standard solution (g)
Ws: Weight of expandable resin particles dissolved in DMF (g)
An: Peak area of each foaming agent component at the time of gas chromatographic measurement Ai: Peak area of the internal standard substance at the time of gas chromatographic measurement Fn: Correction coefficient of each foaming agent component obtained from a calibration curve prepared in advance

The conditions for the gas chromatograph analysis were as follows.
Equipment used: Gas chromatograph GC-6AM manufactured by Shimadzu Corporation
Detector: FID (hydrogen flame ionization detector)
Column material: Glass column with an inner diameter of 3 mm and a length of 5000 mm Column filler: [Liquid phase name] FFAP (free fatty acid), [Liquid phase impregnation rate] 10 mass%, [Carrier name] Diatomaceous earth Comasorb W for gas chromatography, [Carrier Particle size] 60/80 mesh, [carrier treatment method] AW-DMCS (washing, baking, acid treatment, silane treatment), [filling amount] 90 mL
Inlet temperature: 250 ° C
Column temperature: 120 ° C
Detector temperature: 250 ° C
Carrier gas: N ₂ , flow rate 40 ml / min

"amount of water"
Using a Karl Fischer moisture meter, the moisture content of the expandable resin particles of each Example and Comparative Example was determined.

"Molecular weight"
The average molecular weight (number average molecular weight, weight average molecular weight, Z average molecular weight) of the expandable resin particles of each Example and Comparative Example was measured by a gel permeation chromatography (GPC) method using polystyrene as a standard substance. Specifically, using HLC-8320GPC EcoSEC manufactured by Tosoh Corporation, measurement was performed under the measurement conditions of eluent: tetrahydrofuran (THF), THF flow rate: 0.6 ml / min, and sample concentration: 0.1 wt%. As a column for GPC, a column in which TSK guard column Super H-H × 1 and TSK-GEL Super HM-H × 2 were connected in series was used. That is, expandable resin particles were dissolved in tetrahydrofuran (THF), and the molecular weight was measured by gel permeation chromatography (GPC). And the number average molecular weight, the weight average molecular weight, and the Z average molecular weight were calculated | required by calibrating a measured value with standard polystyrene, respectively.

"Evaluation of foamability"
Evaluation of foamability was performed by measuring the bulk density of foamed particles obtained by foaming foamable resin particles with a shelf-type foaming machine. Specifically, first, expandable resin particles obtained in each of the examples and comparative examples were expanded in a shelf-type foaming machine to obtain expanded particles. Foaming was performed by supplying steam with a gauge pressure of 3 kPa into the foaming machine for 270 seconds and heating the foamable resin particles. The obtained expanded particles were air-dried for 1 day. Thereafter, the expanded particles were filled to a 1 L mark in a 1 L graduated cylinder. The mass (g) of the 1 L volume of expanded particles was weighed to the first decimal place. Subsequently, the bulk density (kg / m ³ ) of the expanded particles was calculated by converting the mass of the volume of 1 L into units.

"Apparent density"
Volume was calculated | required from the external dimension of the foaming molding obtained in each Example and the comparative example, and the mass of the foaming particle molding was then measured. And the apparent density (kg / m < ³ >) of the foaming molding was computed by remove | dividing mass by volume.

"Fusion rate"
The rectangular parallelepiped foam molded body obtained in each of the examples and comparative examples was divided, and the fractured surface was visually observed. Then, the number A of foam particles peeled from the surface of the foam molded body and the number B of foam particles peeled from the inside of the foam molded body were measured. The fusion rate is obtained from the ratio (100 × B / (A + B)) of the number (B) of the foam particles peeled from the inside to the total number (A + B) of the peeled foam particles.

"Surface void"
The appearance of the foamed molded product obtained in each example and comparative example was visually observed. And based on the following criteria, the space | gap (void) between the foaming particles in the surface of a foaming molding was evaluated.
◯: When there are almost no gaps between the foamed particles on the surface of the foamed molded product and the surface is smooth Δ: When there are few gaps between the foamed particles on the surface of the foamed molded product but the surface is not smooth ×: Foamed molded product When there are many gaps between expanded particles on the surface of the surface, and the surface is not smooth

"Surface melting"
The appearance of the foamed molded product obtained in each example and comparative example was visually observed. And based on the following criteria, the molten state in the surface of a foaming molding was evaluated.
○: When the foamed particles do not melt on the surface of the foamed molded product Δ: When the foamed particles have little melted on the surface of the foamed molded product ×: When the foamed particles melt much on the surface of the foamed molded product

"Flame retardance"
The evaluation of flame retardancy was performed according to the combustion test (Method A) of JIS A 9511 (2006R). First, the foamed molded products in each Example and Comparative Example were allowed to stand at a temperature of 40 ° C. for 3 days. Next, each foamed molded product was cured at room temperature for 1 day. Thereafter, a plate-shaped test piece of 200 mm × 25 mm × 10 mm was cut out from each foamed molded body. Next, using the candle, the test piece was ignited to the ignition limit indicator line and the combustion limit indicator line, and then the candle was quickly retracted from the test piece. The time (extinguishing time) from when the candle was retracted until the flame of the test piece extinguished was measured. This measurement was performed for each of five test pieces, and an average value was calculated.

In Examples 1 and 2, expandable resin particles were produced using seed particles in which a specific flame retardant was kneaded in resin particles. In such expandable resin particles, as known from Table 1, the particle size distribution was narrow, and the product yield of the expandable resin particles was improved. In addition, expandable resin particles with a small amount of water were obtained.
In Examples 1 and 2, expandable resin particles having excellent foam moldability were obtained. That is, by using these expandable resin particles, a foamed molded article having a high fusion rate, few surface voids and almost no surface melting was obtained (see Table 1 and FIG. 1). Moreover, in Examples 1 and 2, a foamed molded article excellent in flame retardancy was obtained even with a small flame retardant addition amount.

  On the other hand, in Comparative Example 1 in which the method of adding the flame retardant was changed from that of the example, the fusion rate of the foamed molded product was lowered, and voids were observed between the foamed particles (see Table 2 and FIG. 2). ). This is presumably because the flame retardant was unevenly distributed on the surface of the expandable resin particles in the expandable resin particles of Comparative Example 1. That is, the foamable resin particles of Comparative Example 1 had a problem with foam moldability. Moreover, in the comparative example 2 produced without using a seed particle, the particle size distribution of the expandable polystyrene-type resin particle was wide, and the product yield of the expandable polystyrene-type resin particle was falling (refer Table 2). Moreover, in Comparative Example 3 in which the type of flame retardant was changed from Example 1, and in Comparative Example 4 in which the method and type of addition of the flame retardant were changed from Example 1, the fusion rate of the foamed molded product was reduced. Further, voids between the expanded particles and melting at the surface were observed (see Table 2, FIG. 3 and FIG. 4).

Claims (3)

A method for producing expandable polystyrene resin particles containing a flame retardant,
A dispersion step of dispersing polystyrene-based resin seed particles obtained by kneading a brominated butadiene-styrene copolymer as a flame retardant and a polystyrene-based resin in an aqueous medium;
A polymerization step of supplying a styrene monomer into the aqueous medium, impregnating and polymerizing the polystyrene resin seed particles with the styrene monomer; and
And a foaming agent impregnation step of impregnating the resin particles with a physical foaming agent during or after the polymerization in the polymerization step to obtain the expandable polystyrene resin particles.   The method for producing expandable polystyrene resin particles according to claim 1, wherein the addition amount of the styrene monomer is 30 to 300 parts by weight with respect to 100 parts by weight of the polystyrene resin seed particles. .   The method for producing expandable polystyrene resin particles according to claim 1 or 2, wherein a blending amount of the flame retardant in the polystyrene resin seed particles is 0.4 to 10% by mass.