Expandable styrene resin particles, pre-expanded styrene resin particles, styrene resin foam molded article, and method for producing expandable styrene resin particles

Abstract

To provide expandable styrenic resin particles high in environmental contribution, capable of developing excellent spheroidizing and excellent in moldability and its manufacturing method, a pre-expanded styrenic resin particles obtained from such expandable styrenic resin particles, and a styrenic resin foam molding molded from such expandable styrenic resin particles or pre-expanded styrenic resin particles.SOLUTION: Expandable styrenic resin particles are expandable styrenic resin particles obtained by injecting a volatile blowing agent into the styrenic resin particles (A) obtained by adding a styrene-based monomer to the recycled styrenic resin particles and polymerizing them. wherein a content of the regenerated styrene resin particles with respect to a total amount of the regenerated styrene resin particles and the styrene monomer is 10 mass% to 90 mass%, an injection temperature when press fitting the volatile foaming agent is 40°C to 89°C.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to expandable styrene-based resin particles, pre-expanded styrene-based resin particles, a styrene-based resin foamed molded article, and a method for producing expandable styrene-based resin particles. [Background technology]

[0002] Because foamed molded articles are lightweight and have excellent thermal insulation and mechanical strength, they are widely used as insulation materials for homes and automobiles, thermal insulation materials for building materials, embankment materials used in polystyrene foam civil engineering, transport packaging materials for fish boxes and food containers, cushioning materials, etc. Among these, in-mold foamed molded articles produced using expandable particles (typically expandable polystyrene-based resin particles or pre-expanded styrene-based resin particles obtained by pre-expanding them) as a raw material are widely used because of advantages such as the ease of obtaining the desired shape. Such foamed molded articles are composed of multiple expandable particles fused to each other.

[0003] On the other hand, the amount of plastic waste is increasing year by year. Most plastic waste is disposed of by incineration or landfilling, but this has become a major social problem, causing environmental pollution, global warming, and a shortage of landfill sites. For this reason, there is a strong social demand for the reuse of plastic waste, and various methods for recycling plastic waste are being considered, including the enforcement of the Home Appliance Recycling Law. Among the various recycling methods proposed, material recycling, in which plastic waste is reused as plastic components for products, has attracted attention from the perspectives of resource circulation and reducing environmental impact, and such material recycling is also being considered for styrene resin foam molded products.

[0004] As a material recycling method for styrene-based resin foam moldings, several methods have been proposed in the past, in which recovered raw materials are melted and extruded to form recovered pellets, which are then impregnated with a blowing agent to obtain recycled expandable styrene-based resin particles.

[0005] A method for obtaining recycled expandable styrene resin particles by impregnating recycled resin pellets molded from recovered styrene resin foam molded articles with a blowing agent at a temperature of 100°C to 140°C has been reported (Patent Documents 1 and 2). Also, a method for obtaining recycled expandable styrene resin particles by impregnating recycled resin pellets molded from recovered styrene resin foam molded articles with a blowing agent at a temperature of 90°C to 130°C has been reported (Patent Document 3).

[0006] A method has been reported in which a blowing agent is injected into recycled resin pellets molded from recovered styrene-based resin foam moldings at a temperature of 95°C to 130°C, followed by impregnation (in the examples, the impregnation temperature is 118°C), and then the particles are sphericalized at 110°C to 130°C to obtain recycled expandable styrene-based resin particles (Patent Document 4).

[0007] A method has been reported in which recycled expandable styrene resin particles (containing 70% or less by mass of recycled resin pellets) are obtained by adding styrene monomer to recycled resin pellets molded from recovered styrene resin foam molded articles, polymerizing at 60°C to 105°C, then injecting a blowing agent (injection temperature of 100°C in the examples), and then impregnating the blowing agent at an impregnation temperature of 100°C or higher (Patent Document 5). Another method has been reported in which recycled expandable styrene resin particles (containing 20% ​​to 70% by mass of recycled resin pellets) are obtained by adding styrene monomer to recycled resin pellets molded from recovered styrene resin foam molded articles, polymerizing at 60°C to 105°C, then injecting a blowing agent (injection temperature of 100°C in the examples), and then impregnating the blowing agent at an impregnation temperature of 100°C to 140°C (Patent Document 6). In addition, a method has been reported in which recycled expandable styrene resin particles (containing 30% to 70% by mass of recycled resin pellets) are obtained by adding styrene monomer to recycled resin pellets molded from recovered styrene resin foam molded articles, polymerizing the mixture at 60°C to 105°C, and then injecting a blowing agent (in the examples, the injection temperature is 100°C), followed by impregnation with the blowing agent (in the examples, the impregnation temperature is 115°C). It has also been reported that a flame retardant may be impregnated during the impregnation with the blowing agent (Patent Document 7). In addition, a method has been reported in which recycled expandable styrene resin particles (containing 20% ​​to 70% by mass of recycled resin pellets) are obtained by adding styrene monomer to recycled resin pellets molded from recovered styrene resin foam molded articles, polymerizing the mixture at 60°C to 105°C, and then injecting a blowing agent (in the examples, the injection temperature is 100°C), followed by impregnation with the blowing agent at an impregnation temperature of 90°C or higher (Patent Document 8).

[0008] However, the recycled expandable styrene resin particles obtained by conventional methods have problems such as particle shapes that deviate from spherical, poor filling properties into molding dies, poor surface elongation of the molded body, and a low fusion rate between the foamed particles of the molded body. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Patent No. 3044942 [Patent Document 2] Patent No. 4234832 [Patent Document 3] Patent No. 4261676 [Patent Document 4] Patent No. 6788428 [Patent Document 5] Patent No. 4052193 [Patent Document 6] Japanese Patent Application Laid-Open No. 2006-160905 [Patent Document 7] Patent No. 4912567 [Patent Document 8] Patent No. 5128246 Summary of the Invention [Problem to be solved by the invention]

[0010] The present invention has been made to solve the above-mentioned problems of the related art, and its main object is to provide expandable styrene-based resin particles that are highly environmentally friendly, can exhibit good spheroidization, and have excellent moldability, and a method for producing the same. It is also an object of the present invention to provide pre-expanded styrene-based resin particles obtained from such expandable styrene-based resin particles. It is also an object of the present invention to provide a styrene-based resin foam molded article molded from such expandable styrene-based resin particles or pre-expanded styrene-based resin particles. [Means for solving the problem]

[0011] The expandable styrene-based resin particles according to an embodiment of the present invention are Expandable styrene-based resin particles obtained by adding a styrene-based monomer to recycled styrene-based resin particles and polymerizing the resulting styrene-based resin particles (A) and then injecting a volatile blowing agent into the styrene-based resin particles (A), the content of the recycled styrene-based resin particles relative to the total amount of the recycled styrene-based resin particles and the styrene-based monomer is 10% by mass to 90% by mass, The injection temperature when injecting the volatile foaming agent is 40°C to 89°C.

[0012] In one embodiment, the styrene monomer is added at a temperature of 40°C to 109°C.

[0013] In one embodiment, the recycled styrene-based resin particles are pellets obtained by a melt extrusion method.

[0014] In one embodiment, the pellets obtained by the melt extrusion method are at least one type selected from extruded strand pellets obtained by extruding a used styrene foam-based resin using an extruder and strand-cutting it; underwater-cut pellets obtained by an underwater cutting method in which a used styrene foam-based resin is extruded using an extruder and simultaneously cut in water; and hot-cut pellets obtained by a hot-cut method in which used styrene foam-based resin particles are cut and cooled immediately after emerging from a die of an extruder.

[0015] In one embodiment, a flame retardant is added before the volatile blowing agent is injected.

[0016] The pre-expanded styrene-based resin particles according to an embodiment of the present invention are Pre-expanded styrene-based resin particles obtained by pre-expanding the expandable styrene-based resin particles, The bulk expansion ratio of the pre-expanded foam is 2 to 150 times.

[0017] In one embodiment, the pre-expanded styrene-based resin particles are for use in a cushioning material.

[0018] The styrene-based resin foam molded article according to the embodiment of the present invention is molded from the expandable styrene-based resin particles.

[0019] The styrene-based resin foamed molded article according to the embodiment of the present invention is molded from the pre-expanded styrene-based resin particles.

[0020] In one embodiment, the styrene-based resin foam molded article is a molded article for banking, a molded article for food containers, a molded article for cushioning material, or a molded article for returnable containers.

[0021] A method for producing expandable styrene-based resin particles according to an embodiment of the present invention includes: A method for producing expandable styrene-based resin particles, comprising: a step of adding a styrene-based monomer to recycled styrene-based resin particles and polymerizing the resulting mixture to obtain styrene-based resin particles (A); and a step of injecting a volatile blowing agent into the styrene-based resin particles (A), the content of the recycled styrene-based resin particles relative to the total amount of the recycled styrene-based resin particles and the styrene-based monomer is 10% by mass to 90% by mass, The injection temperature when injecting the volatile foaming agent is 40°C to 89°C.

[0022] In one embodiment, the styrene monomer is added at a temperature of 40°C to 109°C.

[0023] In one embodiment, the recycled styrene-based resin particles are pellets obtained by a melt extrusion method.

[0024] In one embodiment, the pellets obtained by the melt extrusion method are at least one type selected from extruded strand pellets obtained by extruding a used styrene foam-based resin using an extruder and strand-cutting it; underwater-cut pellets obtained by an underwater cutting method in which a used styrene foam-based resin is extruded using an extruder and simultaneously cut in water; and hot-cut pellets obtained by a hot-cut method in which used styrene foam-based resin particles are cut and cooled immediately after emerging from a die of an extruder. [Effects of the Invention]

[0025] According to the present invention, it is possible to provide expandable styrene-based resin particles that are highly environmentally friendly, can exhibit good spheroidization, and have excellent moldability, and a method for producing the same. It is also possible to provide pre-expanded styrene-based resin particles obtained from such expandable styrene-based resin particles. It is also possible to provide a styrene-based resin foam molded article molded from such expandable styrene-based resin particles or pre-expanded styrene-based resin particles. DETAILED DESCRIPTION OF THE INVENTION

[0026] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to these embodiments.

[0027] In this specification, "(meth)acrylic" means acrylic and / or methacrylic, and "(meth)acrylate" means acrylate and / or methacrylate.

[0028] <<A. Expandable styrene resin particles>> The expandable styrene-based resin particles according to an embodiment of the present invention have a particle shape as a whole. The expandable styrene-based resin particles preferably have an average particle diameter of 0.40 mm to 2.0 mm, more preferably 0.6 mm to 1.8 mm. The average particle diameter can be measured in accordance with JIS Z 8815. Specifically, the average particle diameter is the value measured as a particle diameter at 50% of the cumulative value from the particle size distribution according to the JIS Z 8815 sieving test.

[0029] The shape of the expandable styrene-based resin particles according to an embodiment of the present invention can be any appropriate shape as long as it does not impair the effects of the present invention. Specific examples of such shapes include spherical, approximately spherical, and oval spherical (egg-shaped). In terms of achieving the effects of the present invention, the shape of the expandable styrene-based resin particles according to an embodiment of the present invention is preferably spherical or approximately spherical, and more preferably spherical. However, in reality, it is difficult to distinguish between spherical and approximately spherical, and therefore, in this specification, both are collectively referred to as spherical.

[0030] The expandable styrene-based resin particles according to an embodiment of the present invention preferably have a weight average molecular weight of 100,000 to 450,000, more preferably 110,000 to 400,000, even more preferably 120,000 to 350,000, and particularly preferably 130,000 to 320,000.

[0031] The expandable styrene-based resin particles according to an embodiment of the present invention are obtained by injecting a volatile blowing agent into styrene-based resin particles (A).

[0032] <A-1. Styrene-based resin particles (A)> The styrene-based resin particles (A) are obtained by adding a styrene-based monomer to recycled styrene-based resin particles and polymerizing the mixture.

[0033] The recycled styrene resin particles may be of one type only, or may be of two or more types.

[0034] Any appropriate recycled styrene resin can be used as the recycled styrene resin as long as it does not impair the effects of the present invention. Examples of such recycled styrene resins include recycled products of plastic materials used in polystyrene foam (molded products, block molded products, etc.), foam sheets (tray containers, sheet waste, etc.), home appliances, packaging containers, cushioning materials (foam granules filling the inside of cushions), etc.

[0035] The recycled styrene-based resin may contain any suitable recycled resin other than the recycled styrene-based resin, provided that the effects of the present invention are not impaired. Examples of such recycled resins include recycled resins of AS resin, ABS resin, HIPS (high impact polystyrene); polyester resins such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polycarbonate (PC); polyamide resins such as nylon (PA); and polyolefin resins such as polyethylene (linear low-density polyethylene (LLDPE), low-density polyethylene (LDPE), high-density polyethylene (HDPE), polypropylene (PP), and EVA (ethylene-vinyl acetate copolymer). The other resins may be one type only, or two or more types. In this specification, the recycled AS resin, recycled ABS resin, and recycled HIPS (high impact polystyrene) resin are not included in the category of recycled styrene-based resins.

[0036] As the recycled styrene-based resin, a molded product made from "EPSREM" manufactured by Sekisui Plastics Co., Ltd. may be used.

[0037] The recycled styrene resin particles may be pulverized material obtained by heating and / or reducing the volume of used expanded styrene resin and then pulverizing the recycled resin. The recycled styrene resin particles may be pellets obtained by extruding the pulverized material and then pelletizing it, or may be particles obtained by further pulverizing the pellets. Alternatively, the recycled styrene resin particles may be particles obtained by reducing the volume and recovering the resin using a solvent such as limonene.

[0038] The recycled styrene resin particles are preferably pellets obtained by melt extrusion, which is a method in which crushed styrene resin particles, ingots, foamed styrene resin particles, etc., are fed to a resin feeder, melted in the resin feeder, extruded through small holes in a die attached to the tip of the resin feeder, and then cooled to obtain pellets.

[0039] The pellets obtained by the melt extrusion method are preferably at least one type selected from extruded strand pellets obtained by extruding used styrene foam resin using an extruder and strand cutting the extruded pellets; underwater cut pellets obtained by an underwater cutting method in which used styrene foam resin is extruded using an extruder and simultaneously cut in water; and hot cut pellets obtained by a hot cutting method in which used styrene foam resin particles are cut and cooled immediately after emerging from the die of the extruder.

[0040] As the recycled styrene-based resin particles, the pellets obtained by the above-mentioned melt extrusion method may be used as they are, or they may be subjected to a melt extrusion method again to form so-called "mini-pellets" in order to obtain pellets of a smaller size.

[0041] The recycled styrene-based resin particles may be a shrinkage or melting product of a foamed styrene-based resin obtained by coarsely crushing used foamed styrene-based resin to an appropriate size as needed, and then subjecting the resin to heat shrinkage, bubble destruction shrinkage due to compression, shrinkage due to frictional heat, melting, or the like.

[0042] Examples of used foamed styrene resins include molded articles obtained by molding foamable styrene resins into molds, and those obtained by heating and foaming these.

[0043] The recycled styrene resin particles may contain finely divided inorganic and / or organic lubricants, which typically function as cell control agents.

[0044] Examples of finely powdered inorganic substances include talc, calcium carbonate, and silica. Here, talc typically refers to a mixture containing silicon oxide and magnesium oxide as main components, with trace amounts of aluminum oxide, iron oxide, etc.

[0045] The average particle size of the finely powdered inorganic material is preferably 100 μm or less, more preferably 30 μm or less. If the average particle size of the finely powdered inorganic material exceeds 100 μm, the effect of reducing the bubble size of the pre-expanded styrene-based resin particles may be reduced.

[0046] The content of the finely powdered inorganic material relative to the recycled styrene-based resin particles is preferably 0.1% to 5% by mass, more preferably 0.5% to 2% by mass. If the content of the finely powdered inorganic material relative to the recycled styrene-based resin particles is less than 0.1% by mass, the effect of reducing the cell size of the pre-expanded styrene-based resin particles may be reduced. If the content of the finely powdered inorganic material relative to the recycled styrene-based resin particles exceeds 5% by mass, the cell size of the pre-expanded styrene-based resin particles may become extremely small, causing the pre-expanded styrene-based resin particles to melt during molding, which may deteriorate the appearance of the molded product.

[0047] Examples of organic lubricants include liquid paraffin; polyethylene glycol; silicone oils such as dimethylpolysiloxane, methylphenylpolysiloxane, and methylhydrogenpolysiloxane; higher fatty acid bisatomids such as methylene bisstearylamide, ethylene bisstearylamide, and ethylene bisoleic acid amide; and metal salts of higher fatty acids such as zinc stearate, magnesium stearate, and zinc oleate.

[0048] The content of the organic lubricant relative to the recycled styrene-based resin particles is preferably 0.01% to 2.0% by mass, more preferably 0.02% to 1.8% by mass, and in some cases even more preferably 0.02% to 0.2% by mass, and particularly preferably 0.02% to 0.1% by mass. If the content of the organic lubricant relative to the recycled styrene-based resin particles is less than 0.01% by mass, the effect of reducing the cell size of the pre-expanded styrene-based resin particles may be reduced. If the content of the organic lubricant relative to the recycled styrene-based resin particles exceeds 2.0% by mass, the cell size of the pre-expanded styrene-based resin particles becomes extremely small, causing the pre-expanded styrene-based resin particles to melt during molding, which tends to result in poor appearance of the molded product.

[0049] A specific method for incorporating a fine powder inorganic material and / or organic lubricant into recycled styrene-based resin particles includes, for example, kneading the fine powder inorganic material and / or organic lubricant during extrusion molding. In this case, the pulverized material and the cell control agent are preferably mixed in advance and then extrusion molded. The pulverized material and the cell control agent can be mixed by any appropriate method as long as the effects of the present invention are not impaired. Examples of such methods include mixing using a mixer such as a tumbler, ribbon blender, V blender, Henschel mixer, or Redige mixer.

[0050] The recycled styrene-based resin particles are preferably heat-melted to adjust their specific gravity. In this process, the specific gravity of the recycled styrene-based resin particles is preferably adjusted to 0.6 or greater, more preferably 0.9 or greater. If the specific gravity of the recycled styrene-based resin particles is less than 0.6, the dispersion of the recycled styrene-based resin particles will be unstable, which may result in excessively large particles during the subsequent polymerization process and reduced yield. The heat-melting of the recycled styrene-based resin particles can be carried out by any appropriate method as long as it does not impair the effects of the present invention. Examples of such methods include methods using an extruder or a heated roll. It is preferable to perform the heat-melting process by cooling and solidifying the resulting resin while leaving no or only minimal strain. If strain remains in the resin particles, the strain may be relaxed in the subsequent process, causing shrinkage in the stretching direction, resulting in the resulting expandable styrene-based resin particles becoming flat rather than spherical. Therefore, heat-melting without stretching using an extruder is preferred. If the resin is melted in a stretched state, distortion may remain in the stretched resin obtained after cooling and solidifying. However, even if distortion remains in the resin due to melting, it can be alleviated by curing the resin for a certain period of time at a temperature above its softening point.

[0051] For the pulverization to obtain the recycled styrene-based resin particles, any pulverizer can be used as long as it does not impair the effects of the present invention. For example, a pulverizer for plastics can be used, and a pulverizer for polystyrene is preferred.

[0052] The recycled styrene resin particles can be sieved as necessary and subjected to melting again in an extruder or the like.

[0053] The average particle size of the recycled styrene-based resin particles is preferably 0.2 mm to 3.0 mm, more preferably 0.3 mm to 2.5 mm, even more preferably 0.4 mm to 2.0 mm, and particularly preferably 0.5 mm to 1.7 mm. If the average particle size of the recycled styrene-based resin particles exceeds 3 mm, the shape of the resulting expandable styrene-based resin particles may be difficult to achieve. If the average particle size of the recycled styrene-based resin particles is less than 0.2 mm, the average particle size of the resulting expandable styrene-based resin particles may be too small.

[0054] The L (long side) / D (short side) ratio of the recycled styrene-based resin particles is preferably 1.0 to 6.0, more preferably 1.0 to 5.0, even more preferably 1.0 to 4.0, particularly preferably 1.0 to 3.0, and most preferably 1.0 to 2.5. If the L (long side) / D (short side) ratio of the recycled styrene-based resin particles is outside the above range, the shape of the resulting expandable styrene-based resin particles may be difficult to achieve.

[0055] The recycled styrene-based resin particles preferably contain less than 1% by mass of particles with an average particle size of 200 μm or less. Recycled styrene-based resin particles containing 1% by mass or more of particles with an average particle size of 200 μm or less may result in a deterioration in the appearance of the expandable styrene-based resin particles obtained using the recycled styrene-based resin particles.

[0056] The weight-average molecular weight of the recycled styrene-based resin particles is preferably 100,000 to 510,000, more preferably 100,000 to 490,000, even more preferably 100,000 to 400,000, and particularly preferably 150,000 to 350,000. If the weight-average molecular weight of the recycled styrene-based resin particles is less than 100,000, sufficient strength may not be obtained. If the weight-average molecular weight of the recycled styrene-based resin particles is more than 510,000, the recycled styrene-based resin particles may not be easily formed into a spherical shape, or the foaming properties may be reduced, resulting in poor appearance of the molded product.

[0057] The styrene-based monomer may be one kind or two or more kinds.

[0058] The styrene-based monomer includes styrene or a styrene derivative. Examples of the styrene derivative include α-methylstyrene, vinyltoluene, chlorostyrene, ethylstyrene, i-propylstyrene, dimethylstyrene, and bromostyrene. The styrene-based monomer may be one type or two or more types. The styrene-based monomer preferably contains at least styrene. The content of styrene relative to the total amount of the styrene-based monomer is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more.

[0059] The styrene monomer may contain any suitable vinyl monomer other than the styrene monomer, as long as the effects of the present invention are not impaired. Examples include polyfunctional monomers, (meth)acrylic acid ester monomers, maleic acid ester monomers, and fumaric acid ester monomers. Such vinyl monomers may be used alone or in combination of two or more types.

[0060] Specific examples of polyfunctional monomers include divinylbenzenes such as o-divinylbenzene, m-divinylbenzene, and p-divinylbenzene; and alkylene glycol di(meth)acrylates such as ethylene glycol di(meth)acrylate and polyethylene glycol di(meth)acrylate. Specific examples of (meth)acrylic acid ester monomers include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, pentyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and hexyl (meth)acrylate. Specific examples of maleic acid ester monomers include dimethyl maleate. Specific examples of fumaric acid ester monomers include dimethyl fumarate, diethyl fumarate, and ethyl fumarate.

[0061] The content of the recycled styrene-based resin particles relative to the total amount of the recycled styrene-based resin particles and the styrene-based monomer is preferably 10% to 90% by mass, more preferably 15% to 85% by mass, even more preferably 20% to 80% by mass, particularly preferably 25% to 80% by mass, and most preferably 30% to 80% by mass. If the content is too low outside the above range, environmental contribution may be reduced. Furthermore, if the content is too low or too high outside the above range, the expandable styrene-based resin particles according to the embodiment of the present invention may not be able to exhibit good spheroidization, and moldability may be reduced.

[0062] The styrene-based resin particles (A) are obtained by adding a styrene-based monomer to recycled styrene-based resin particles and polymerizing them. Any appropriate method can be used as this polymerization method as long as it does not impair the effects of the present invention. One preferred embodiment of this polymerization method is a method in which recycled styrene-based resin particles are dispersed as nuclei in an aqueous medium to obtain a suspension, to which an emulsion containing a polymerization initiator and a styrene-based monomer is added to impregnate the recycled styrene-based resin particles, and then a styrene-based monomer is added and polymerized.

[0063] When obtaining the styrene-based resin particles (A), the addition temperature when adding the styrene-based monomer to the recycled styrene-based resin particles is preferably 40° C. to 109° C., more preferably 60° C. to 108° C., even more preferably 65° C. to 107° C., and particularly preferably 70° C. to 106° C., in order to further demonstrate the effects of the present invention. If the addition temperature when adding the styrene-based monomer to the recycled styrene-based resin particles is adjusted within the above range, the styrene-based monomer can be incorporated while maintaining the recycled styrene-based resin particles at an appropriate hardness, thereby achieving good spheroidization of the styrene-based resin particles (A), and ultimately achieving good spheroidization and excellent moldability of the expandable styrene-based resin particles obtained. If the temperature at which the styrene monomer is added to the recycled styrene resin particles is too low and outside the above range, the recycled styrene resin particles become too hard. When the styrene monomer is incorporated in this state, the styrene resin particles (A) become difficult to spheroidize, which may result in poor moldability of the final expandable styrene resin particles. If the temperature at which the styrene monomer is added to the recycled styrene resin particles is too high and outside the above range, the recycled styrene resin particles become too soft and the styrene monomer is difficult to spheroidize, which may result in poor moldability of the final expandable styrene resin particles. Note that the "addition temperature at which the styrene monomer is added to the recycled styrene resin particles" refers to the temperature during the addition of the emulsion containing the polymerization initiator and the styrene monomer, and the subsequent addition of the styrene monomer.

[0064] When dispersing recycled styrene-based resin particles as nuclei in an aqueous medium to obtain a suspension, any suitable method can be used to disperse the recycled styrene-based resin particles in the aqueous medium as long as it does not impair the effects of the present invention. A preferred dispersion method is one that uses an apparatus equipped with stirring blades. A method for more fine dispersion is to use a homomixer.

[0065] When dispersing recycled styrene-based resin particles as nuclei in an aqueous medium to obtain a suspension, it is preferable to use a dispersant to disperse the recycled styrene-based resin particles in the aqueous medium. Any suitable dispersant can be used as long as it is suitable for suspension polymerization and does not impair the effects of the present invention. Examples of such dispersants include organic dispersants such as polyvinyl alcohol, polyvinylpyrrolidone, and methylcellulose; sparingly soluble inorganic salts such as magnesium phosphate, magnesium pyrophosphate, and tricalcium phosphate; and surfactants such as sodium dodecylbenzenesulfonate. Among these, magnesium pyrophosphate is preferred as the dispersant, as it can more effectively demonstrate the effects of the present invention.

[0066] Any suitable emulsification method can be used to obtain an emulsion containing a polymerization initiator and a styrene-based monomer, as long as it does not impair the effects of the present invention. A preferred dispersion method is dispersion using an apparatus equipped with a stirring blade. A method using a homomixer is an example of a method for more fine dispersion. In this case, it is preferable to disperse the styrene-based monomer until the oil droplet diameter of the dispersion becomes equal to or smaller than the particle diameter of the nuclei. If the oil droplet diameter is larger than the particle diameter of the nuclei when the dispersion is added to an aqueous medium, multiple recycled styrene-based resin particles will be incorporated into the oil droplets of the dispersion, causing adhesion, plasticization, and coalescence of the recycled styrene-based resin particles, which is likely to result in the generation of excessively large particles.

[0067] The polymerization initiator used to obtain an emulsion containing a polymerization initiator and a styrene-based monomer may be any suitable polymerization initiator used in suspension polymerization, as long as it does not impair the effects of the present invention. Examples of such polymerization initiators include organic peroxides such as benzoyl peroxide, t-butylperoxy-2-ethylhexyl carbonate, and t-butyl perbenzoate; and azo compounds such as azobisisobutyronitrile. The polymerization initiator may be one type or two or more types.

[0068] The amount of the polymerization initiator used is preferably 0.1% by mass to 0.8% by mass, and more preferably 0.1% by mass to 0.5% by mass, based on the styrene-based monomer.

[0069] The polymerization initiator is preferably added after being dissolved in the styrene-based monomer or a solvent. Examples of the solvent include aromatic hydrocarbons such as ethylbenzene and toluene; and aliphatic hydrocarbons such as heptane and octane. When a solvent is used, it is usually used in an amount of 10% by mass or less based on the styrene-based monomer.

[0070] After adding an emulsion containing a styrene monomer to a suspension containing recycled styrene resin particles to impregnate the particles, any suitable method for adding the styrene monomer may be used as long as the effects of the present invention are not impaired. Examples of such methods include divided addition and continuous addition. The addition rate is appropriately selected depending on the capacity, shape, polymerization temperature, etc. of the polymerization apparatus.

[0071] After adding an emulsion containing a styrene monomer to a suspension containing recycled styrene resin particles to impregnate them, the styrene monomer may be added and then the polymerization reaction may be continued at any appropriate temperature and time, as necessary.

[0072] The suspension containing recycled styrene-based resin particles and the emulsion containing styrene-based monomers may contain a cell regulator, such as fatty acid monoamides such as oleic acid amide, stearic acid amide, and hydroxystearic acid amide; and fatty acid bisamides such as methylene bisstearic acid amide and ethylene bisstearic acid amide.

[0073] <A-2. Injection and impregnation of volatile foaming agent> The expandable styrene-based resin particles according to an embodiment of the present invention are obtained by injecting a volatile blowing agent into styrene-based resin particles (A).

[0074] The volatile foaming agent may be of one type only, or may be of two or more types.

[0075] Any suitable volatile blowing agent can be used as long as it does not impair the effects of the present invention. The volatile blowing agent is preferably an organic compound whose boiling point is equal to or lower than the softening point of the styrene-based resin and which is gaseous or liquid at normal pressure. Specific examples include aliphatic hydrocarbons such as propane, n-butane, isobutane, pentane (n-pentane, isopentane, neopentane), and n-hexane; alicyclic hydrocarbons such as cyclopentane and cyclopentadiene; ketones such as acetone and methyl ethyl ketone; alcohols such as methanol, ethanol, and isopropyl alcohol; low-boiling ether compounds such as dimethyl ether, diethyl ether, dipropyl ether, and methyl ethyl ether; and halogen-containing hydrocarbons such as trichloromonofluoromethane and dichlorodifluoromethane. Inorganic gases such as carbon dioxide, nitrogen, and ammonia may also be used as the volatile blowing agent. Among these, in terms of being able to further exhibit the effects of the present invention, the volatile blowing agent is preferably at least one selected from n-butane, isobutane, n-pentane, isopentane, neopentane, cyclopentane, and cyclopentadiene, more preferably at least one selected from n-butane, isobutane, n-pentane, and isopentane, and even more preferably at least one selected from n-pentane and isopentane.

[0076] The content of the volatile blowing agent can be appropriately set depending on the purpose as long as it is an amount sufficient to form pre-expanded styrene resin particles and a styrene resin foam molded article. The content of the volatile blowing agent is preferably 2 to 15 parts by mass when the total amount of the recycled styrene resin particles and the styrene monomer is 100 parts by mass.

[0077] The temperature at which the volatile blowing agent is injected into the styrene-based resin particles (A) is preferably 40°C to 89°C, more preferably 40°C to 88°C, even more preferably 40°C to 87°C, particularly preferably 40°C to 86°C, and most preferably 40°C to 85°C. The temperature at which the volatile blowing agent is injected into the styrene-based resin particles (A) may be varied within the above range. When the temperature at which the volatile blowing agent is injected into the styrene-based resin particles (A) is within the above range, the volatile blowing agent can be injected at a low temperature. Injecting the volatile blowing agent at such a low temperature and then raising the temperature prevents the volatile blowing agent from being rapidly impregnated into the styrene-based resin particles (A), enabling uniform impregnation. For example, this reduces the number of areas that shrink and melt when molded into a styrene-based resin foam. If the temperature at which the volatile blowing agent is injected into the styrene-based resin particles (A) is too low and outside the above range, the volatile blowing agent is not easily impregnated into the styrene-based resin particles (A) when the volatile blowing agent is injected, and the volatile blowing agent is rapidly impregnated when the temperature is raised, which may result in the styrene-based resin particles (A) not being uniformly impregnated with the volatile blowing agent, which may result in uneven cell formation and surface shrinkage during molding. If the temperature at which the volatile blowing agent is injected into the styrene-based resin particles (A) is too high and outside the above range, the volatile blowing agent is rapidly impregnated into the styrene-based resin particles (A) when the volatile blowing agent is injected, which may result in the styrene-based resin particles (A) not being uniformly impregnated with the volatile blowing agent, which may result in uneven cell formation and surface shrinkage during molding.

[0078] The temperature for impregnating the styrene-based resin particles (A) with a volatile blowing agent is preferably equal to or higher than the temperature for injecting the volatile blowing agent into the styrene-based resin particles (A), and is preferably 93°C to 130°C, more preferably 94°C to 129°C, even more preferably 95°C to 128°C, particularly preferably 96°C to 127°C, and most preferably 97°C to 126°C. The temperature for impregnating the styrene-based resin particles (A) with a volatile blowing agent may be varied within the above range. When the impregnation temperature for the styrene-based resin particles (A) with a volatile blowing agent is within the above range, in combination with the adjustment of the injection temperature, rapid impregnation of the volatile blowing agent into the styrene-based resin particles (A) is suppressed, enabling uniform impregnation. For example, portions that shrink and melt when molded into a styrene-based resin foam can be reduced. If the temperature for impregnating the styrene-based resin particles (A) with the volatile blowing agent is too low and outside the above range, the volatile blowing agent may not penetrate deep into the center of the styrene-based resin particles (A), leaving unfoamed areas, and it may not be possible to obtain a good molded product.If the temperature for impregnating the styrene-based resin particles (A) with the volatile blowing agent is too high and outside the above range, the volatile blowing agent may be impregnated too deeply into the styrene-based resin particles (A), causing them to melt during molding.

[0079] The impregnation time of the styrene-based resin particles (A) with the volatile blowing agent can be any appropriate time within the range that does not impair the effects of the present invention, and is preferably 1 hour to 10 hours.

[0080] <A-3. Other ingredients> The expandable styrene-based resin particles according to an embodiment of the present invention may contain any appropriate other component within the scope of not impairing the effects of the present invention. Such other component may be one kind only or two or more kinds.

[0081] The expandable styrene-based resin particles according to an embodiment of the present invention may contain a flame retardant to enhance flame retardancy. The flame retardant may be of one type only or of two or more types.

[0082] As the flame retardant, any appropriate flame retardant can be used as long as it does not impair the effects of the present invention. As such a flame retardant, a bromine compound compatible with polystyrene is preferred, and examples thereof include tetrabromoethane, tetrabromocyclooctane, hexabromocyclododecane, hexabromocyclohexane, trisdibromopropylphosphate, tetrabromobisphenol A, tetrabromobisphenol F, tetrabromobisphenol A-bis(2,3-dibromo-2-methylpropyl ether), tetrabromobisphenol A-bis(2,3-dibromopropyl ether), tetrabromobisphenol A-diglycidyl ether, 2,2-bis[4'(2'',3''-dibromoalkoxy)-3',5'-dibromophenyl]-propane, tris(tribromophenoxy)triazine, 2,2-bis(4-allyloxy-3,5-dibromo)propane, and hexabromobenzene.

[0083] When a flame retardant is used, a flame retardant aid may be used in combination. Examples of the flame retardant aid include cumene hydroperoxide, dicumyl peroxide, t-butyl hydroperoxide, 2,3-dimethyl-2,3-diphenylbutane, and 3,4-dimethyl-3,4-diphenylhexane.

[0084] The total amount of the flame retardant and the flame retardant aid may be any appropriate amount within the range that does not impair the effects of the present invention, and is preferably 0.1 to 5% by mass, more preferably 0.2 to 3% by mass, based on the recycled styrene resin particles.

[0085] The flame retardant may be added at any appropriate timing as long as the effects of the present invention are not impaired. In order to further demonstrate the effects of the present invention, it is preferable that the flame retardant be added before the volatile blowing agent is injected. By adding the flame retardant before the volatile blowing agent is injected, the flame retardant can be added at a low temperature equivalent to the temperature at which the volatile blowing agent is injected, and therefore the resulting expandable styrene-based resin particles can be well spherical and exhibit excellent moldability.

[0086] The temperature at which the flame retardant is added is preferably 40°C to 89°C, more preferably 40°C to 87°C, even more preferably 40°C to 85°C, particularly preferably 40°C to 83°C, and most preferably 40°C to 80°C, in order to better exhibit the effects of the present invention.

[0087] When producing expandable styrene-based resin particles according to an embodiment of the present invention, a partial ester of a higher fatty acid and an alcohol may be used as the cell control agent. That is, the expandable styrene-based resin particles according to an embodiment of the present invention may contain a partial ester of a higher fatty acid and an alcohol. The partial ester of a higher fatty acid and an alcohol may be one type or two or more types. Examples of higher fatty acids include fatty acids having 15 or more carbon atoms, such as palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, and behenic acid, and monoglycerides and diglycerides thereof can be used. Examples of the partial ester of a higher fatty acid and an alcohol include stearic acid monoglyceride and stearic acid diglyceride. The content of the partial ester of a higher fatty acid and an alcohol is preferably 0 to 3.0 parts by mass, more preferably 0.5 to 3.0 parts by mass, per 100 parts by mass of the expandable styrene-based resin particles. The partial ester of a higher fatty acid and an alcohol may be added, for example, together with a volatile blowing agent, or by a commonly used method such as a dry blending method, a masterbatch method, or a melt injection method.

[0088] When producing the expandable styrene-based resin particles according to an embodiment of the present invention, a foaming aid may be used. That is, the expandable styrene-based resin particles according to an embodiment of the present invention may contain a foaming aid. The foaming aid may be one type or two or more types. Examples of the foaming aid include diisobutyl adipate, toluene, cyclohexane, ethylbenzene, liquid paraffin, and coconut oil.

[0089] When producing the expandable styrene-based resin particles according to an embodiment of the present invention, a cell regulator may be used. That is, the expandable styrene-based resin particles according to an embodiment of the present invention may contain a cell regulator. The cell regulator may be one type or two or more types. Examples of the cell regulator include fatty acid monoamides such as oleic acid amide, stearic acid amide, and hydroxystearic acid amide; and fatty acid bisamides such as methylene bisstearic acid amide and ethylene bisstearic acid amide.

[0090] The expandable styrene-based resin particles according to an embodiment of the present invention may contain a cell regulator such as talc, calcium carbonate, mica, citric acid, sodium bicarbonate, etc. The cell regulator may be one type or two or more types.

[0091] In addition to the above, other additives include, for example, pigments, radiant heat transfer suppressing components, crosslinking agents, plasticizers, stabilizers, fillers, lubricants, colorants, antistatic agents, spreading agents, weather resistance agents, antioxidants, anti-fogging agents, and fragrances.

[0092] <A-4. Surface treatment> The expandable styrene-based resin particles according to an embodiment of the present invention may be surface-treated, preferably with at least one selected from silicone oil, antistatic agents, fatty acid metal salts, and fusion accelerators.

[0093] When the expandable styrene-based resin particles according to an embodiment of the present invention are surface-treated with silicone oil, the amount of silicone oil used per 100 parts by mass of the expandable styrene-based resin particles before surface treatment is preferably 0.001 to 0.3 parts by mass, more preferably 0.003 to 0.28 parts by mass, even more preferably 0.005 to 0.25 parts by mass, particularly preferably 0.008 to 0.23 parts by mass, and most preferably 0.01 to 0.23 parts by mass. If the amount of silicone oil used is too small outside the above range, for example, when an antistatic agent is used, the affinity with the antistatic agent during pre-expansion may be insufficient, making static electricity more likely to be generated. If the amount of silicone oil used is too large outside the above range, the surface may melt during molding, resulting in a loss of surface properties.

[0094] The silicone oil may be of one type only, or of two or more types.

[0095] As the silicone oil, any suitable silicone oil can be adopted as long as it does not impair the effects of the present invention.In terms of being able to further exhibit the effects of the present invention, as the silicone oil, for example, straight silicone oil such as dimethylpolysiloxane, methylphenylpolysiloxane, methylhydrogenpolysiloxane, etc. can be mentioned, and preferably methylphenylpolysiloxane.

[0096] When the expandable styrene-based resin particles according to an embodiment of the present invention are surface-treated with an antistatic agent, the amount of the antistatic agent used per 100 parts by mass of the expandable styrene-based resin particles before surface treatment is preferably 0.001 to 0.3 parts by mass, more preferably 0.005 to 0.28 parts by mass, even more preferably 0.01 to 0.27 parts by mass, particularly preferably 0.015 to 0.26 parts by mass, and most preferably 0.02 to 0.25 parts by mass. If the amount of the antistatic agent is too small outside the above range, static electricity may be easily generated during pre-expansion. If the amount of the antistatic agent is too large outside the above range, the surface of the pre-expanded styrene-based resin particles or the styrene-based resin foam molded article may become sticky.

[0097] The antistatic agent may be of one type only, or may be of two or more types.

[0098] Any appropriate antistatic agent may be used as long as it does not impair the effects of the present invention. In order to further enhance the effects of the present invention, the antistatic agent may be at least one selected from a nonionic surfactant and a fatty acid glyceride, and preferably a combination of a nonionic surfactant and a fatty acid glyceride.

[0099] The nonionic surfactant may be one type only, or two or more types may be used.

[0100] As the nonionic surfactant, any appropriate nonionic surfactant may be used as long as it does not impair the effects of the present invention. Examples of nonionic surfactants that can further enhance the effects of the present invention include polyethylene glycol, glycerin, polyoxyethylene alkyl ethers, polyoxyethylene alkyl esters, polyhydric alcohols, and 1-amino-2-hydroxy compounds. Specific examples of polyoxyethylene alkyl ethers include polyoxyethylene cetyl ether, polyoxyethylene oleyl ether, and polyoxyethylene stearyl ether. Specific examples of polyoxyethylene alkyl esters include polyoxyethylene laurate, polyoxyethylene palmitate, polyoxyethylene stearate, and polyoxyethylene oleate. Specific examples of polyhydric alcohols include glycerin and propylene glycol. Specific examples of the 1-amino-2-hydroxy compound include N-hydroxyethyl-N-(2-hydroxyalkyl)amine, N,N-bis(hydroxyethyl)dodecylamine, N,N-bis(hydroxyethyl)tetradecylamine, N,N-bis(hydroxyethyl)hexadecylamine, N,N-bis(hydroxyethyl)octadecylamine, N-hydroxyethyl-N-(2-hydroxytetradecyl)amine, N-hydroxyethyl-N-(2-hydroxyhexadecyl)amine, N-hydroxyethyl-N-(2-hydroxyoctadecyl)amine, N-hydroxypropyl-N N,N-bis(2-hydroxyethyl)dodecylamine, N,N-bis(2-hydroxyethyl)tetradecylamine, N,N-bis(2-hydroxyethyl)hexadecylamine, N,N-bis(2-hydroxyethyl)octadecylamine, and salts thereof.As the nonionic surfactant, polyethylene glycol is preferred in that it can more effectively exhibit the effects of the present invention.

[0101] When a nonionic surfactant is used as at least a part of the antistatic agent, the amount of the nonionic surfactant used per 100 parts by weight of the expandable styrene-based resin particles before surface treatment is preferably 0.001 to 2.0 parts by weight, more preferably 0.001 to 1.5 parts by weight, even more preferably 0.001 to 1.0 parts by weight, even more preferably 0.001 to 0.5 parts by weight, even more preferably 0.001 to 0.3 parts by weight, even more preferably 0.005 to 0.28 parts by weight, even more preferably 0.01 to 0.27 parts by weight, particularly preferably 0.015 to 0.26 parts by weight, and most preferably 0.02 to 0.25 parts by weight. If the amount of nonionic surfactant is too small, outside the above range, static electricity may be easily generated during pre-expansion. If the amount of nonionic surfactant is too large and outside the above range, the surface of the pre-expanded styrene resin particles or the foamed styrene resin molded article may become sticky.

[0102] The fatty acid glyceride may be one kind or two or more kinds.

[0103] As the fatty acid glyceride, any appropriate fatty acid glyceride can be used as long as it does not impair the effects of the present invention. Specific examples of the fatty acid glyceride that can further demonstrate the effects of the present invention include stearic acid monoglyceride and linoleic acid monoglyceride. As the fatty acid glyceride, stearic acid monoglyceride is preferred in terms of further demonstrating the effects of the present invention.

[0104] When a fatty acid glyceride is used as at least a part of the antistatic agent, the amount of the fatty acid glyceride relative to 100 parts by mass of the expandable styrene-based resin particles before surface treatment is preferably 0.001 to 0.3 parts by mass, more preferably 0.005 to 0.28 parts by mass, even more preferably 0.01 to 0.27 parts by mass, particularly preferably 0.015 to 0.26 parts by mass, and most preferably 0.02 to 0.25 parts by mass. If the amount of fatty acid glyceride is too small outside the above range, static electricity may be easily generated during pre-expansion. If the amount of fatty acid glyceride is too large outside the above range, the surface of the pre-expanded styrene-based resin particles or the styrene-based resin foam molded article may become sticky.

[0105] When the expandable styrene-based resin particles according to an embodiment of the present invention are surface-treated with a fatty acid metal salt, the amount of fatty acid metal salt used per 100 parts by mass of the expandable styrene-based resin particles before surface treatment is preferably 0.005 to 0.5 parts by mass, more preferably 0.007 to 0.45 parts by mass, even more preferably 0.01 to 0.4 parts by mass, particularly preferably 0.015 to 0.35 parts by mass, and most preferably 0.02 to 0.3 parts by mass. If the amount of fatty acid metal salt is too small outside the above range, blocking may occur frequently during pre-expansion, making it difficult to obtain a good styrene-based resin foam molded article. If the amount of fatty acid metal salt is too large outside the above range, too much metal salt may be present during pre-expansion, making the particles more likely to be charged, generating static electricity, and potentially resulting in poor fusion of the molded article.

[0106] The fatty acid metal salt may be of one type only, or of two or more types.

[0107] As the fatty acid metal salt, any appropriate fatty acid metal salt can be used as long as it does not impair the effects of the present invention. Examples of fatty acid metal salts that can further demonstrate the effects of the present invention include metal stearates and metal laurates. Specific examples of metal stearates include magnesium stearate, calcium stearate, zinc stearate, barium stearate, aluminum stearate, and lithium stearate. Specific examples of metal laurates include zinc laurate and barium laurate. As fatty acid metal salts, magnesium stearate and zinc stearate are preferred in terms of further demonstrating the effects of the present invention.

[0108] When the expandable styrene-based resin particles according to an embodiment of the present invention are surface-treated with a fusion accelerator, the amount of the fusion accelerator used per 100 parts by mass of the expandable styrene-based resin particles before surface treatment is preferably 0.01 to 0.8 parts by mass, more preferably 0.01 to 0.7 parts by mass, even more preferably 0.01 to 0.6 parts by mass, particularly preferably 0.01 to 0.55 parts by mass, and most preferably 0.013 to 0.5 parts by mass. If the amount of the fusion accelerator is too small outside the above range, the fusion properties may decrease during molding, making it impossible to obtain a good styrene-based resin foam molded article. If the amount of the fusion accelerator is too large outside the above range, blocking may occur during pre-expansion.

[0109] The fusion promoter may be of only one type, or of two or more types.

[0110] Any appropriate fusion promoter may be used as the fusion promoter as long as it does not impair the effects of the present invention. Examples of fusion promoters that can further demonstrate the effects of the present invention include fatty acid triglycerides, fatty acid diglycerides, fatty acid monoglycerides, and vegetable oils. Specific examples of fatty acid triglycerides include lauric acid triglyceride, stearic acid triglyceride, linoleic acid triglyceride, and hydroxystearic acid triglyceride. Specific examples of fatty acid diglycerides include lauric acid diglyceride, stearic acid diglyceride, and linoleic acid diglyceride. Specific examples of fatty acid monoglycerides include lauric acid monoglyceride. Specific examples of vegetable oils include hydrogenated castor oil. Specific examples of stearic acid triglyceride and hydroxystearic acid triglyceride are preferred as fusion promoters in that they can further demonstrate the effects of the present invention.

[0111] <A-5. Method for producing expandable styrene resin particles> The expandable styrene-based resin particles according to an embodiment of the present invention can be produced by any appropriate method as long as the effects of the present invention are not impaired. In terms of being able to further demonstrate the effects of the present invention, the method for producing expandable styrene-based resin particles according to an embodiment of the present invention includes a step of adding a styrene-based monomer to recycled styrene-based resin particles and polymerizing them to obtain styrene-based resin particles (A), and a step of injecting a volatile blowing agent into the styrene-based resin particles (A), wherein the content of the recycled styrene-based resin particles relative to the total amount of the recycled styrene-based resin particles and the styrene-based monomer is 10% by mass to 90% by mass, and the injection temperature when injecting the volatile blowing agent is 40°C to 89°C.

[0112] Regarding the process of adding a styrene-based monomer to recycled styrene-based resin particles and polymerizing them to obtain styrene-based resin particles (A), the explanation in the above section <A-1. Styrene-based resin particles (A)> can be typically used.

[0113] For the step of injecting a volatile blowing agent into the styrene-based resin particles (A), the explanation given in the above section <<A-2. Injection and impregnation of volatile blowing agent>> can be typically applied.

[0114] <<B. Pre-expanded styrene resin particles>> The pre-expanded styrene-based resin particles are obtained by pre-expanding expandable styrene-based resin particles.

[0115] The pre-expanded styrene-based resin particles preferably have an average cell diameter of 0.02 mm to 0.80 mm, more preferably 0.03 mm to 0.70 mm, even more preferably 0.03 mm to 0.60 mm, particularly preferably 0.03 mm to 0.50 mm, and most preferably 0.03 mm to 0.40 mm. When the average cell diameter of the pre-expanded styrene-based resin particles is within the above range, blocking during expansion and molding can be more effectively prevented. Furthermore, pre-expanded styrene-based resin particles can be provided that exhibit better fusion properties and surface properties while further suppressing electrostatic charge during expansion and molding, thereby enabling the molding of styrene-based resin foam molded articles with less static electricity. If the average cell diameter of the pre-expanded styrene-based resin particles is less than 0.02 mm, there is a risk of the surface melting and shrinking during molding.

[0116] The pre-expanded styrene-based resin particles according to an embodiment of the present invention are obtained by pre-expanding expandable styrene-based resin particles. The pre-expanding process involves expanding the expandable styrene-based resin particles to a desired bulk expansion ratio (bulk density) using steam or the like. The bulk expansion ratio of the pre-expanded styrene-based resin particles is preferably 2 to 150 times, more preferably 2 to less than 100 times, more preferably 5 to 90 times, even more preferably 10 to 85 times, and particularly preferably 15 to 83 times. The bulk density is the reciprocal of the bulk expansion ratio. When the bulk expansion ratio of the pre-expanded styrene-based resin particles is within the above range, blocking during expansion and molding can be further prevented. Furthermore, the pre-expanded styrene-based resin particles can exhibit better fusion properties and surface properties while further suppressing electrostatic charge during expansion and molding, thereby enabling the molding of styrene-based resin foam molded articles with less static electricity.

[0117] In one representative embodiment, the pre-expanded styrene-based resin particles can be used to form a styrene-based resin foamed molded article. In another embodiment, the pre-expanded styrene-based resin particles can be used as they are as a cushioning material, a heat insulating material, or the like. When the pre-expanded styrene-based resin particles are used as they are, the pre-expanded styrene-based resin particles can preferably be used as a filler in which a large number of pre-expanded styrene-based resin particles are filled into a bag. Such pre-expanded styrene-based resin particles are suitable for, for example, cushioning materials (expanded particles filled inside a cushion). That is, one embodiment of the pre-expanded styrene-based resin particles according to the present invention is for use in cushioning materials.

[0118] <<C. Styrene-based resin foam molded body>> A styrene-based resin foam molded article according to one embodiment of the present invention is a styrene-based resin foam molded article molded from expandable styrene-based resin particles. Another styrene-based resin foam molded article according to another embodiment of the present invention is a styrene-based resin foam molded article molded from pre-expanded styrene-based resin particles obtained by pre-expanding expandable styrene-based resin particles.

[0119] The styrene-based resin foam molded article typically contains expanded styrene-based resin particles (hereinafter sometimes simply referred to as "expanded particles") obtained by further expanding pre-expanded styrene-based resin particles.

[0120] A styrene-based resin foam molded article is typically composed of a plurality of foam particles fused together.

[0121] Styrenic resin foam molded articles can typically be produced by placing pre-expanded styrene-based resin particles in a mold having a predetermined shape depending on the purpose and performing in-mold foam molding. More specifically, in-mold foam molding includes (i) filling pre-expanded styrene-based resin particles into a closed mold having a large number of small holes, (ii) heating and expanding the pre-expanded styrene-based resin particles with a heat medium (e.g., pressurized steam, etc.) to obtain expanded particles, and (iii) filling the voids between the expanded particles and fusing the expanded particles together to integrate them by the heat expansion. The density of the styrene-based resin foam molded article can be appropriately set depending on the purpose. The density of the styrene-based resin foam molded article can be adjusted, for example, by previously adjusting the bulk expansion ratio of the pre-expanded styrene-based resin particles to be filled in the mold or by adjusting the amount of pre-expanded styrene-based resin particles filled in the mold.

[0122] The heat-foaming temperature (substantially the temperature of the heat transfer medium) is preferably 90°C to 150°C, more preferably 110°C to 130°C. The heat-foaming time is preferably 5 to 50 seconds, more preferably 10 to 50 seconds. The molding vapor pressure of the heat-foaming (gauge pressure of the heat transfer medium blown in) is preferably 0.04 MPa to 0.1 MPa, more preferably 0.06 MPa to 0.08 MPa. Heat-foaming under these conditions allows the expanded particles to be well fused to each other.

[0123] If necessary, the pre-expanded styrene-based resin particles may be aged before molding into a styrene-based resin expansion molded article. The aging temperature of the pre-expanded styrene-based resin particles is preferably 20°C to 60°C. If the aging temperature is too low, an excessively long aging time may be required. If the aging temperature is too high, the blowing agent in the pre-expanded styrene-based resin particles may dissipate, resulting in a decrease in moldability.

[0124] The expansion ratio of the expanded beads in the styrene resin expansion molded article is preferably 2 times or more and less than 110 times, more preferably 5 times to 90 times, even more preferably 10 times to 85 times, and particularly preferably 15 times to 80 times.

[0125] The styrene-based resin foam molded article according to the embodiment of the present invention is lightweight and has excellent heat insulating properties and mechanical strength, and is therefore suitable for use as wall insulation, floor insulation, roof insulation, automobile insulation, hot water tank insulation, piping insulation, solar system insulation, water heater insulation, containers for food and industrial products (e.g., food containers such as fish boxes, returnable boxes), cushioning materials, floats, blocks, packaging materials for fish and agricultural products, etc., embankment materials (embankment molded articles, embankment blocks, etc.), core materials for tatami mats, core materials for cushions, concrete aggregate, etc. Preferred examples of the styrene-based resin foam molded article according to the embodiment of the present invention are embankment molded articles, food container molded articles, cushioning molded articles, and returnable box molded articles. [Example]

[0126] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. The methods for measuring and evaluating each property are as follows.

[0127] <Evaluation of spheroidization> Ten particles of expandable styrene-based resin particles or styrene-based resin particles were randomly selected, and the ratio of their long side (L) to their short side (D) was calculated. The sphericity was calculated using the following formula based on this ratio, and evaluated according to the following criteria. Sphericity=1 / (L / D) 〇:1 / (L / D)=0.9 or more △: 1 / (L / D) = 0.7 or more and less than 0.9 ×: 1 / (L / D)=less than 0.7

[0128] <Moldability> The evaluation was made comprehensively based on the elongation of the surface of the molded body and the fusion rate between the foam particles when the molded body was broken. The evaluation of the elongation of the surface of the molded body was performed by visually inspecting the appearance of the obtained foamed molded body. Specifically, the state of the boundary where the foam particles on the surface of the foamed molded body were joined was visually inspected. The fusion rate between the foam particles when the molded body was broken was evaluated by breaking the obtained plate-shaped foamed molded body by impact, counting the total number of foam particles (A) on the fracture surface and the number of particles broken within the particles (B), and calculating the fusion rate (%) using the following formula: Fusion rate (%) = {(B) / (A)} x 100 The evaluation was based on the following criteria. ◯: The appearance is smooth and the fusion rate is 70% or more. △: Most of the appearance is smooth, but there are some unevenness at the boundaries, and the fusion rate is 60% or more but less than 70%. ×: The boundary portion of the appearance is uneven, the smoothness is poor, and the fusion rate is less than 60%.

[0129] <Environmental contribution> The evaluation was carried out as follows based on the content ratio of the recycled styrene resin particles to the total amount of the recycled styrene resin particles and styrene monomer, which are raw materials for the expandable styrene resin particles. 〇: Recycled styrene resin particle content is 20% by mass or more △: The content of recycled styrene resin particles is 10% by mass or more but less than 20% by mass ×: The content of recycled styrene resin particles is less than 10% by mass

[0130] <Criteria for overall evaluation> Particularly good (〇): All items, including spheroidization evaluation, moldability, and environmental contribution, were rated 〇. Good (△): One or more △ marks in the evaluation of spheroidization, moldability, and environmental contribution, but no × marks. Poor (×): There is an × in any of the items of spheroidization evaluation, moldability, and environmental contribution.

[0131] <Measurement of bulk density and bulk expansion ratio of pre-expanded styrene resin particles> The bulk density and bulk expansion ratio of the pre-expanded styrene-based resin particles were measured as follows. (Method for measuring bulk density) The pre-expanded styrene resin particles were allowed to fall naturally into a measuring cylinder as a sample, and the bottom of the measuring cylinder was struck to make the sample volume constant. The volume and mass were measured and calculated using the following formula. Bulk density (g / mL) = sample mass (g) / sample volume in measuring cylinder (mL) (Method for measuring bulk expansion ratio) The pre-expanded styrene resin particles were allowed to fall naturally into a measuring cylinder as a sample, and then the bottom of the measuring cylinder was struck to make the sample volume constant. The volume and mass were measured and calculated using the following formula. The resin specific gravity was set to 1.0 for styrene resins. Bulk expansion ratio (times) = sample volume in measuring cylinder (mL) / sample mass (g) x resin specific gravity The bulk expansion ratio may be calculated as the reciprocal of the bulk density.

[0132] <Measurement of density and expansion ratio of styrene resin foam molded products> (Method of measuring density) The density of the styrene resin foam molded article was calculated by measuring the dimensions and mass of the test piece to three or more significant figures and using the following formula. Density (g / cm 3 ) = mass of test piece (g) / volume of test piece (cm 3 ) (Method for measuring expansion ratio) The expansion ratio of the styrene resin foam molded product was calculated by measuring the dimensions and mass of the test piece to three or more significant figures and using the following formula: The resin specific gravity was set to 1.0 for styrene resin. Expansion ratio (times) = test piece volume (cm 3 ) / test piece mass (g) x resin specific gravity

[0133] [Production Example 1]: Production of recycled styrene resin particles (A) using used polystyrene resin from home appliances Used polystyrene resin from home appliances was fed into a single-screw extruder, heated and melted at 200°C, and cut underwater from a mold to obtain recycled styrene resin particles (A) with an average particle diameter of 0.95 mm (approximately spherical).

[0134] Example 1 <Preparation of Expandable Styrenic Resin Particles> 38.5 kg of pure water, 5 g of sodium dodecylbenzenesulfonate, and 180 g of magnesium pyrophosphate were placed in a 100-liter reactor equipped with a stirrer, and 5 kg of recycled styrene-based resin particles (A) (made from used polystyrene-based resin from home appliances) were added. The mixture was stirred at 160 rpm to form a suspension, thereby preparing suspension (1). Separately, 2 kg of styrene monomer in which 143 g of benzoyl peroxide (purity 75%) as a polymerization initiator and 41 g of t-butylperoxy-2-ethylhexyl monocarbonate were dissolved was added to a dispersion of 2 kg of pure water and 0.8 g of sodium dodecylbenzenesulfonate, and the mixture was emulsified by stirring with a homomixer to prepare emulsion (1). The above suspension (1) in a 100 liter reactor equipped with a stirrer was kept at 80° C., and the above emulsion (1) was added thereto. The mixture was then kept at 80°C for 30 minutes to allow the styrene monomer and polymerization initiator to be fully absorbed into the recycled styrene-based resin particles (A), and immediately after this, 39 kg of styrene monomer was added dropwise over 179 minutes. The addition temperature was kept constant at 80°C. Thereafter, the temperature was increased to 125°C over 30 minutes, maintained at 125°C for 1 hour, and then cooled to 60°C over 1 hour. Separately, 23 g of ethylene bis(stearic acid amide) and 160 g of dicumyl peroxide were added to a dispersion of 3.5 kg of pure water, 0.8 g of sodium dodecylbenzenesulfonate, and 19 g of magnesium pyrophosphate, and the mixture was emulsified by stirring with a homomixer to prepare an emulsion. This emulsion was then added to the reactor cooled to 60°C. Ten minutes after this addition, 710 g of tetrabromobisphenol A-bis(2,3-dibromo-2-methylpropyl ether) was added. After the addition, stirring was continued at 60°C for 30 minutes. Next, 2760 g of pentane (isopentane / normal pentane = 20% by mass / 80% by mass) as a blowing agent was injected at an injection temperature of 60°C, and after maintaining this state for 15 minutes, the temperature was raised to 100°C over 30 minutes and then maintained at 100°C for 5 hours, thereby slowly impregnating the blowing agent. The temperature inside the reactor was then cooled to 30°C. Thereafter, the contents were removed from the reactor, dehydrated, dried and classified to obtain expandable styrene resin particles (1). <Surface treatment of expandable styrene resin particles> 40 kg of the obtained expandable styrene-based resin particles (1), 8 g of polyethylene glycol, 44 g of zinc stearate, 12 g of fatty acid triglyceride, and 16 g of fatty acid monoglyceride were placed in a tumbler mixer, stirred for 30 minutes, and surface-treated to obtain surface-treated expandable styrene-based resin particles (1'). <Preparation of pre-expanded styrene resin particles> The obtained expandable styrene resin particles (1') were stored in a refrigerator at 15°C for 7 days, then placed in a cylindrical batch type pressure foaming machine with a volume of 340 liters and heated with steam for 2 minutes to obtain pre-expanded styrene resin particles (1). The bulk density of the pre-expanded styrene resin particles (1) was 0.02 g / cm. 3 The bulk expansion ratio was 50 times. <Production of styrene-based resin foam molded body> The obtained pre-expanded styrene resin particles (1) were left for 24 hours under room temperature atmosphere, and then the pre-expanded styrene resin particles (1) were filled into the cavity of a molding machine having a mold with a cavity size of 400 mm in height, 500 mm in width, and 300 mm in depth, and heated at a vapor pressure of 0.04 MPa (gauge pressure) for 40 seconds, and then cooled until the pressure inside the mold became -0.002 MPa. After that, the mold was released, and a block-shaped styrene resin foam molded product (1) corresponding to the mold was obtained. The density of the styrene resin foam molded product (1) was 0.02 g / cm. 3 The expansion ratio was 50. Thereafter, the styrene resin foam molded article (1) was stored in a drying room at 50°C for one day. The results of various evaluations are shown in Table 1.

[0135] Example 2 36.5 kg of pure water, 5 g of sodium dodecylbenzenesulfonate, and 180 g of magnesium pyrophosphate were placed in a 100-liter reactor equipped with a stirrer, and 9 kg of recycled styrene-based resin particles (A) (made from used polystyrene-based resin from home appliances) were added. The mixture was stirred at 160 rpm to form a suspension, thereby preparing suspension (2). Separately, 4 kg of styrene monomer in which 127 g of benzoyl peroxide (purity 75%) as a polymerization initiator and 37 g of t-butylperoxy-2-ethylhexyl monocarbonate were dissolved was added to a dispersion of 4 kg of pure water and 0.8 g of sodium dodecylbenzenesulfonate, and the mixture was emulsified by stirring with a homomixer to prepare emulsion (3). The suspension (2) in a 100-liter reactor equipped with a stirrer was kept at 80° C., and the emulsion (2) was added thereto. The mixture was then kept at 80°C for 30 minutes to allow the styrene monomer and polymerization initiator to be fully absorbed into the recycled styrene-based resin particles (A), and immediately after this, 33 kg of styrene monomer was added dropwise over 149 minutes. The addition temperature was kept constant at 80°C. Thereafter, the temperature was increased to 125°C over 30 minutes, maintained at 125°C for 1 hour, and then cooled to 60°C over 1 hour. Thereafter, the same procedures as in Example 1 were carried out to obtain expandable styrene-based resin particles (2), surface-treated expandable styrene-based resin particles (2'), pre-expanded styrene-based resin particles (2), and styrene-based resin foam molded articles (2). The results of various evaluations are shown in Table 1.

[0136] Example 3 34.5 kg of pure water, 5 g of sodium dodecylbenzenesulfonate, and 180 g of magnesium pyrophosphate were placed in a 100-liter reactor equipped with a stirrer, and 14 kg of recycled styrene-based resin particles (A) (made from used polystyrene-based resin from home appliances) were added. The mixture was stirred at 160 rpm to form a suspension, thereby preparing suspension (3). Separately, 6 kg of styrene monomer in which 111 g of benzoyl peroxide (purity 75%) as a polymerization initiator and 32 g of t-butylperoxy-2-ethylhexyl monocarbonate were dissolved was added to a dispersion of 6 kg of pure water and 0.8 g of sodium dodecylbenzenesulfonate, and the mixture was emulsified by stirring with a homomixer to prepare emulsion (3). The above suspension (3) in a 100 liter reactor equipped with a stirrer was kept at 80° C., and the above emulsion (3) was added thereto. The mixture was then kept at 80°C for 30 minutes to allow the styrene monomer and polymerization initiator to be fully absorbed into the recycled styrene-based resin particles (A), and immediately after this, 26 kg of styrene monomer was added dropwise over 119 minutes. The addition temperature was kept constant at 80°C. Thereafter, the temperature was increased to 125°C over 30 minutes, maintained at 125°C for 1 hour, and then cooled to 60°C over 1 hour. Thereafter, the same procedures as in Example 1 were carried out to obtain expandable styrene-based resin particles (3), surface-treated expandable styrene-based resin particles (3'), pre-expanded styrene-based resin particles (3), and styrene-based resin foam molded articles (3). The results of various evaluations are shown in Table 1.

[0137] Example 4 32.5 kg of pure water, 5 g of sodium dodecylbenzenesulfonate, and 180 g of magnesium pyrophosphate were placed in a 100-liter reactor equipped with a stirrer, and 18 kg of recycled styrene-based resin particles (A) (made from used polystyrene-based resin from home appliances) were added. The mixture was stirred at 160 rpm to form a suspension, thereby preparing suspension (4). Separately, 8 kg of styrene monomer in which 95 g of benzoyl peroxide (purity 75%) as a polymerization initiator and 28 g of t-butylperoxy-2-ethylhexyl monocarbonate were dissolved was added to a dispersion of 8 kg of pure water and 0.8 g of sodium dodecylbenzenesulfonate, and the mixture was emulsified by stirring with a homomixer to prepare emulsion (4). The suspension (4) in a 100-liter reactor equipped with a stirrer was kept at 80° C., and the emulsion (4) was added thereto. The mixture was then kept at 80°C for 30 minutes to allow the styrene monomer and polymerization initiator to be fully absorbed into the recycled styrene-based resin particles (A), and immediately after this, 20 kg of styrene monomer was added dropwise over 90 minutes. The addition temperature was kept constant at 80°C. Thereafter, the temperature was increased to 125°C over 30 minutes, maintained at 125°C for 1 hour, and then cooled to 60°C over 1 hour. Thereafter, the same procedures as in Example 1 were carried out to obtain expandable styrene-based resin particles (4), surface-treated expandable styrene-based resin particles (4'), pre-expanded styrene-based resin particles (4), and styrene-based resin foam molded articles (4). The results of various evaluations are shown in Table 1.

[0138] Example 5 30.5 kg of pure water, 5 g of sodium dodecylbenzenesulfonate, and 180 g of magnesium pyrophosphate were placed in a 100-liter reactor equipped with a stirrer, and 23 kg of recycled styrene-based resin particles (A) (made from used polystyrene-based resin from home appliances) were added. The mixture was stirred at 160 rpm to form a suspension, thereby preparing suspension (5). Separately, 10 kg of styrene monomer in which 79 g of benzoyl peroxide (purity 75%) as a polymerization initiator and 23 g of t-butylperoxy-2-ethylhexyl monocarbonate were dissolved was added to a dispersion of 10 kg of pure water and 0.8 g of sodium dodecylbenzenesulfonate, and the mixture was emulsified by stirring with a homomixer to prepare emulsion (5). The above suspension (5) in a 100 liter reactor equipped with a stirrer was kept at 80°C, and the above emulsion (5) was added. The mixture was then kept at 80°C for 30 minutes to allow the styrene monomer and polymerization initiator to be fully absorbed into the recycled styrene-based resin particles (A), and immediately after this, 13 kg of styrene monomer was added dropwise over 60 minutes. The addition temperature was kept constant at 80°C. Thereafter, the temperature was increased to 125°C over 30 minutes, maintained at 125°C for 1 hour, and then cooled to 60°C over 1 hour. Thereafter, the same procedures as in Example 1 were carried out to obtain expandable styrene-based resin particles (5), surface-treated expandable styrene-based resin particles (5'), pre-expanded styrene-based resin particles (5), and styrene-based resin foam molded articles (5). The results of various evaluations are shown in Table 1.

[0139] Example 6 28.5 kg of pure water, 5 g of sodium dodecylbenzenesulfonate, and 180 g of magnesium pyrophosphate were placed in a 100-liter reactor equipped with a stirrer, and 28 kg of recycled styrene-based resin particles (A) (made from used polystyrene-based resin from home appliances) were added. The mixture was stirred at 160 rpm to form a suspension, thereby preparing suspension (6). Separately, 12 kg of styrene monomer in which 63 g of benzoyl peroxide (purity 75%) as a polymerization initiator and 18 g of t-butylperoxy-2-ethylhexyl monocarbonate were dissolved was added to a dispersion of 12 kg of pure water and 0.8 g of sodium dodecylbenzenesulfonate, and the mixture was emulsified by stirring with a homomixer to prepare emulsion (6). The above suspension (6) in a 100 liter reactor equipped with a stirrer was kept at 80°C, and the above emulsion (6) was added. The mixture was then kept at 80°C for 30 minutes to allow the styrene monomer and polymerization initiator to be fully absorbed into the recycled styrene-based resin particles (A), and immediately after this, 7 kg of styrene monomer was added dropwise over 30 minutes. The addition temperature was kept constant at 80°C. Thereafter, the temperature was increased to 125°C over 30 minutes, maintained at 125°C for 1 hour, and then cooled to 60°C over 1 hour. Thereafter, the same procedures as in Example 1 were carried out to obtain expandable styrene-based resin particles (6), surface-treated expandable styrene-based resin particles (6'), pre-expanded styrene-based resin particles (6), and styrene-based resin foam molded articles (6). The results of various evaluations are shown in Table 1.

[0140] Example 7 26.5 kg of pure water, 5 g of sodium dodecylbenzenesulfonate, and 180 g of magnesium pyrophosphate were placed in a 100-liter reactor equipped with a stirrer, and 32 kg of recycled styrene-based resin particles (A) (made from used polystyrene-based resin from home appliances) were added. The mixture was stirred at 160 rpm to form a suspension, thereby preparing suspension (7). Separately, 14 kg of styrene monomer in which 48 g of benzoyl peroxide (purity 75%) as a polymerization initiator and 14 g of t-butylperoxy-2-ethylhexyl monocarbonate were dissolved was added to a dispersion of 14 kg of pure water and 0.8 g of sodium dodecylbenzenesulfonate, and the mixture was emulsified by stirring with a homomixer to prepare emulsion (7). The suspension (7) in a 100 liter reactor equipped with a stirrer was kept at 80°C, and the emulsion (7) was added thereto. Thereafter, the mixture was kept at 80° C. for 30 minutes so that the styrene monomer and the polymerization initiator were well absorbed into the recycled styrene-based resin particles (A), and then kept at 80° C. for 30 minutes to allow polymerization. Thereafter, the temperature was increased to 125°C over 30 minutes, maintained at 125°C for 1 hour, and then cooled to 60°C over 1 hour. Thereafter, the same procedures as in Example 1 were carried out to obtain expandable styrene-based resin particles (7), surface-treated expandable styrene-based resin particles (7'), pre-expanded styrene-based resin particles (7), and styrene-based resin foam molded articles (7). The results of various evaluations are shown in Table 1.

[0141] Example 8 31.5 kg of pure water, 5 g of sodium dodecylbenzenesulfonate, and 180 g of magnesium pyrophosphate were placed in a 100-liter reactor equipped with a stirrer, and 37 kg of recycled styrene-based resin particles (A) (made from used polystyrene-based resin from home appliances) were added. The mixture was stirred at 160 rpm to form a suspension, thereby preparing suspension (8). Separately, 9 kg of styrene monomer in which 32 g of benzoyl peroxide (purity 75%) as a polymerization initiator and 9 g of t-butylperoxy-2-ethylhexyl monocarbonate were dissolved was added to a dispersion of 9 kg of pure water and 0.8 g of sodium dodecylbenzenesulfonate, and the mixture was emulsified by stirring with a homomixer to prepare emulsion (8). The suspension (8) in a 100 liter reactor equipped with a stirrer was kept at 80°C, and the emulsion (8) was added. Thereafter, the mixture was kept at 80° C. for 30 minutes so that the styrene monomer and the polymerization initiator were well absorbed into the recycled styrene-based resin particles (A), and then kept at 80° C. for 30 minutes to allow polymerization. Thereafter, the temperature was increased to 125°C over 30 minutes, maintained at 125°C for 1 hour, and then cooled to 60°C over 1 hour. Thereafter, the same procedures as in Example 1 were carried out to obtain expandable styrene-based resin particles (8), surface-treated expandable styrene-based resin particles (8'), pre-expanded styrene-based resin particles (8), and styrene-based resin foam molded articles (8). The results of various evaluations are shown in Table 1.

[0142] Example 9 35.5 kg of pure water, 5 g of sodium dodecylbenzenesulfonate, and 180 g of magnesium pyrophosphate were placed in a 100-liter reactor equipped with a stirrer, and 41 kg of recycled styrene-based resin particles (A) (made from used polystyrene-based resin from home appliances) were added. The mixture was stirred at 160 rpm to form a suspension, thereby preparing a suspension (9). Separately, 5 kg of styrene monomer in which 16 g of benzoyl peroxide (purity 75%) as a polymerization initiator and 5 g of t-butylperoxy-2-ethylhexyl monocarbonate were dissolved was added to a dispersion of 5 kg of pure water and 0.8 g of sodium dodecylbenzenesulfonate, and the mixture was emulsified by stirring with a homomixer to prepare emulsion (9). The suspension (9) in a 100 liter reactor equipped with a stirrer was kept at 80°C, and the emulsion (9) was added. Thereafter, the mixture was kept at 80° C. for 30 minutes so that the styrene monomer and the polymerization initiator were well absorbed into the recycled styrene-based resin particles (A), and then kept at 80° C. for 30 minutes to allow polymerization. Thereafter, the temperature was increased to 125°C over 30 minutes, maintained at 125°C for 1 hour, and then cooled to 60°C over 1 hour. Thereafter, the same procedures as in Example 1 were carried out to obtain expandable styrene-based resin particles (9), surface-treated expandable styrene-based resin particles (9'), pre-expanded styrene-based resin particles (9), and styrene-based resin foam molded articles (9). The results of various evaluations are shown in Table 1.

[0143] Comparative Example 1 39.5 kg of pure water, 5 g of sodium dodecylbenzenesulfonate, and 180 g of magnesium pyrophosphate were placed in a 100-liter reactor equipped with a stirrer, and 2 kg of recycled styrene-based resin particles (A) (made from used polystyrene-based resin from home appliances) were added. The mixture was stirred at 160 rpm to form a suspension, thereby preparing suspension (C1). Separately, 1 kg of styrene monomer in which 150 g of benzoyl peroxide (purity 75%) as a polymerization initiator and 44 g of t-butylperoxy-2-ethylhexyl monocarbonate were dissolved was added to a dispersion of 1 kg of pure water and 0.8 g of sodium dodecylbenzenesulfonate, and the mixture was emulsified by stirring with a homomixer to prepare emulsion (C1). The above suspension (C1) in a 100 liter reactor equipped with a stirrer was kept at 80° C., and the above emulsion (C1) was added thereto. The mixture was then kept at 80°C for 30 minutes to allow the styrene monomer and polymerization initiator to be fully absorbed into the recycled styrene-based resin particles (A), and immediately after this, 43 kg of styrene monomer was added dropwise over 194 minutes. The addition temperature was kept constant at 80°C. Thereafter, the temperature was increased to 125°C over 30 minutes, maintained at 125°C for 1 hour, and then cooled to 60°C over 1 hour. Thereafter, the same procedures as in Example 1 were carried out to obtain expandable styrene-based resin particles (C1), surface-treated expandable styrene-based resin particles (C1'), pre-expanded styrene-based resin particles (C1), and styrene-based resin foam molded articles (C1). The results of various evaluations are shown in Table 1.

[0144] Comparative Example 2 39.5 kg of pure water, 5 g of sodium dodecylbenzenesulfonate, and 180 g of magnesium pyrophosphate were placed in a 100-liter reactor equipped with a stirrer, and 44 kg of recycled styrene-based resin particles (A) (made from used polystyrene-based resin from home appliances) were added. The mixture was stirred at 160 rpm to form a suspension, thereby preparing suspension (C2). Separately, 1 kg of styrene monomer in which 8 g of benzoyl peroxide (purity 75%) as a polymerization initiator and 2 g of t-butylperoxy-2-ethylhexyl monocarbonate were dissolved was added to a dispersion of 1 kg of pure water and 0.8 g of sodium dodecylbenzenesulfonate, and the mixture was emulsified by stirring with a homomixer to prepare emulsion (C2). The above suspension (C2) in a 100 liter reactor equipped with a stirrer was kept at 80° C., and the above emulsion (C2) was added. The mixture was then kept at 80°C for 30 minutes to allow the styrene monomer and polymerization initiator to be fully absorbed into the recycled styrene-based resin particles (A), and immediately after this, 1 kg of styrene monomer was added dropwise over 5 minutes. The addition temperature was kept constant at 80°C. Thereafter, the temperature was increased to 125°C over 30 minutes, maintained at 125°C for 1 hour, and then cooled to 60°C over 1 hour. Thereafter, the same procedures as in Example 1 were carried out to obtain expandable styrene-based resin particles (C2), surface-treated expandable styrene-based resin particles (C2'), pre-expanded styrene-based resin particles (C2), and styrene-based resin foam molded articles (C2). The results of various evaluations are shown in Table 1.

[0145] [Table 1]

[0146] Example 10 The same procedure as in Example 5 was carried out except that the blowing agent injection temperature was changed to 40°C, and expandable styrene-based resin particles (10), surface-treated expandable styrene-based resin particles (10'), pre-expanded styrene-based resin particles (10), and styrene-based resin foam molded articles (10) were obtained. The results of various evaluations are shown in Table 2.

[0147] Example 11 The same procedure as in Example 5 was carried out except that the blowing agent injection temperature was changed to 80°C, and expandable styrene-based resin particles (11), surface-treated expandable styrene-based resin particles (11'), pre-expanded styrene-based resin particles (11), and styrene-based resin foam molded articles (11) were obtained. The results of various evaluations are shown in Table 2.

[0148] Example 12 The same procedure as in Example 5 was carried out except that the blowing agent injection temperature was changed to 89°C, and expandable styrene-based resin particles (12), surface-treated expandable styrene-based resin particles (12'), pre-expanded styrene-based resin particles (12), and styrene-based resin foam molded articles (12) were obtained. The results of various evaluations are shown in Table 2.

[0149] Comparative Example 3 The same procedure as in Example 5 was carried out except that the injection temperature of the blowing agent was changed to 35°C, and expandable styrene-based resin particles (C3), surface-treated expandable styrene-based resin particles (C3'), pre-expanded styrene-based resin particles (C3), and styrene-based resin foam molded articles (C3) were obtained. The results of various evaluations are shown in Table 2.

[0150] Comparative Example 4 The same procedure as in Example 5 was carried out except that the injection temperature of the blowing agent was changed to 90°C, and expandable styrene-based resin particles (C4), surface-treated expandable styrene-based resin particles (C4'), pre-expanded styrene-based resin particles (C4), and styrene-based resin foam molded articles (C4) were obtained. The results of various evaluations are shown in Table 2.

[0151] Comparative Example 5 The same procedure as in Example 5 was carried out except that the injection temperature of the blowing agent was changed to 95°C, and expandable styrene-based resin particles (C5), surface-treated expandable styrene-based resin particles (C5'), pre-expanded styrene-based resin particles (C5), and styrene-based resin foam molded articles (C5) were obtained. The results of various evaluations are shown in Table 2.

[0152] [Table 2]

[0153] Example 13 The suspension (5) in a 100-liter reactor equipped with a stirrer was kept at 40°C, and the emulsion (5) was added. Thereafter, the temperature was kept at 40°C for 30 minutes so that the styrene monomer and polymerization initiator were well absorbed in the recycled styrene-based resin particles (A). Immediately after the temperature was kept at 40°C, 13 kg of styrene monomer was continuously added dropwise at 40°C over 60 minutes. Thereafter, the temperature was raised to 125°C over 60 minutes, and the temperature was kept at 125°C for 1 hour. Thereafter, the temperature was cooled to 60°C over 1 hour. Except for this, the same procedure as in Example 5 was carried out to obtain expandable styrene-based resin particles (13), surface-treated expandable styrene-based resin particles (13'), pre-expanded styrene-based resin particles (13), and styrene-based resin foam molded articles (13). The results of various evaluations are shown in Table 3.

[0154] Example 14 The suspension (5) in a 100-liter reactor equipped with a stirrer was maintained at 60°C, and the emulsion (5) was added. The temperature was then maintained at 60°C for 30 minutes to ensure that the styrene monomer and polymerization initiator were fully absorbed into the recycled styrene-based resin particles (A). Immediately after this temperature was reached, 13 kg of styrene monomer was continuously added dropwise at 60°C over 60 minutes. The temperature was then raised to 125°C over 60 minutes, maintained at 125°C for 1 hour, and then cooled to 60°C over 1 hour. Except for this, the procedure was carried out in the same manner as in Example 5 to obtain expandable styrene-based resin particles (14), surface-treated expandable styrene-based resin particles (14'), pre-expanded styrene-based resin particles (14), and styrene-based resin foam molded articles (14). The results of various evaluations are shown in Table 3.

[0155] Example 15 The suspension (5) in a 100-liter reactor equipped with a stirrer was kept at 100°C, the emulsion (5) was added, and then the temperature was kept at 100°C for 30 minutes so that the styrene monomer and polymerization initiator were well absorbed into the recycled styrene-based resin particles (A). Immediately after the temperature was kept at 100°C, 13 kg of styrene monomer was continuously added dropwise at 100°C over 60 minutes. The temperature was then raised to 125°C over 30 minutes, kept at 125°C for 1 hour, and then cooled to 60°C over 1 hour. Except for this, the same procedure as in Example 5 was carried out to obtain expandable styrene-based resin particles (15), surface-treated expandable styrene-based resin particles (15'), pre-expanded styrene-based resin particles (15), and styrene-based resin foam molded articles (15). The results of various evaluations are shown in Table 3.

[0156] Example 16 The suspension (5) in a 100-liter reactor equipped with a stirrer was maintained at 109°C, the emulsion (5) was added, and the temperature was then maintained at 109°C for 30 minutes so that the styrene monomer and polymerization initiator were well absorbed into the recycled styrene-based resin particles (A). Immediately after this maintenance, 13 kg of styrene monomer was continuously added dropwise at 109°C over 60 minutes. The temperature was then raised to 125°C over 30 minutes, maintained at 125°C for 1 hour, and then cooled to 60°C over 1 hour. Except for this, the same procedures as in Example 5 were carried out to obtain expandable styrene-based resin particles (16), surface-treated expandable styrene-based resin particles (16'), pre-expanded styrene-based resin particles (16), and styrene-based resin foam molded articles (16). The results of various evaluations are shown in Table 3.

[0157] Example 17 The suspension (5) in a 100-liter reactor equipped with a stirrer was kept at 80°C, and the emulsion (5) was added. The temperature was then kept at 80°C for 30 minutes so that the styrene monomer and polymerization initiator were well absorbed into the recycled styrene-based resin particles (A). Immediately after this, the temperature was raised from 80°C to 109°C at a rate of 0.48°C / min as the styrene monomer addition temperature, while 13 kg of styrene monomer was continuously added dropwise over 60 minutes. The temperature was then raised to 125°C over 30 minutes, kept at 125°C for 1 hour, and then cooled to 60°C over 1 hour. Except for this, the procedure was carried out in the same manner as in Example 5 to obtain expandable styrene-based resin particles (17), surface-treated expandable styrene-based resin particles (17'), pre-expanded styrene-based resin particles (17), and styrene-based resin foam molded articles (17). The results of various evaluations are shown in Table 3.

[0158] Comparative Example 6 The suspension (5) in a 100-liter reactor equipped with a stirrer was kept at 35°C, and the emulsion (5) was added. The mixture was then kept at 35°C for 30 minutes to ensure that the styrene monomer and polymerization initiator were well absorbed into the recycled styrene-based resin particles (A). Immediately after this, 13 kg of styrene monomer was continuously added dropwise at 35°C over 60 minutes. The mixture was then heated to 125°C over 60 minutes, kept at 125°C for 1 hour, and then cooled to 60°C over 1 hour. Except for this, the same procedure as in Example 5 was carried out to obtain expandable styrene-based resin particles (C6), surface-treated expandable styrene-based resin particles (C6'), pre-expanded styrene-based resin particles (C6), and styrene-based resin foam molded articles (C6). The results of various evaluations are shown in Table 3.

[0159] Comparative Example 7 The suspension (5) in a 100-liter reactor equipped with a stirrer was maintained at 110°C, and the emulsion (5) was added. The temperature was then maintained at 110°C for 30 minutes to ensure that the styrene monomer and polymerization initiator were fully absorbed into the recycled styrene-based resin particles (A). Immediately after this temperature was reached, 13 kg of styrene monomer was continuously added dropwise at 110°C over 60 minutes. The temperature was then raised to 125°C over 30 minutes, maintained at 125°C for 1 hour, and then cooled to 60°C over 1 hour. Except for this, the procedure was carried out in the same manner as in Example 5 to obtain expandable styrene-based resin particles (C7), surface-treated expandable styrene-based resin particles (C7'), pre-expanded styrene-based resin particles (C7), and styrene-based resin foam molded articles (C7). The results of various evaluations are shown in Table 3.

[0160] Comparative Example 8 The suspension (5) in a 100-liter reactor equipped with a stirrer was maintained at 115°C, and the emulsion (5) was added. The temperature was then maintained at 115°C for 30 minutes to ensure that the styrene monomer and polymerization initiator were fully absorbed into the recycled styrene-based resin particles (A). Immediately after this temperature was reached, 13 kg of styrene monomer was continuously added dropwise at 115°C over 60 minutes. The temperature was then raised to 125°C over 30 minutes, maintained at 125°C for 1 hour, and then cooled to 60°C over 1 hour. Except for this, the procedure was carried out in the same manner as in Example 5 to obtain expandable styrene-based resin particles (C8), surface-treated expandable styrene-based resin particles (C8'), pre-expanded styrene-based resin particles (C8), and styrene-based resin foam molded articles (C8). The results of various evaluations are shown in Table 3.

[0161] [Table 3]

[0162] Example 18 The same procedures as in Example 17 were carried out except that the flame retardant aid (dicumyl peroxide) and the flame retardant (tetrabromobisphenol A-bis(2,3-dibromo-2-methylpropyl ether)) were not used, to obtain expandable styrene-based resin particles (18), surface-treated expandable styrene-based resin particles (18'), pre-expanded styrene-based resin particles (18), and styrene-based resin foam molded articles (18). The results of various evaluations are shown in Table 3.

[0163] Example 19 The same procedures as in Example 17 were carried out except that the amount of pentane (isopentane / normal pentane = 20% by mass / 80% by mass) used as the blowing agent was 4150 g, to obtain expandable styrene-based resin particles (19), surface-treated expandable styrene-based resin particles (19'), pre-expanded styrene-based resin particles (19), and styrene-based resin foam molded articles (19). The bulk density of the pre-expanded styrene resin particles (19) is 0.0125 g / cm 3 The bulk expansion ratio was 80 times. In addition, a styrene resin foam molded product (19) was also molded in the same manner as in Example 17, and the density was 0.0125 g / cm 3 The expansion ratio was 80 times. The results of various evaluations are shown in Table 4.

[0164] Example 20 The same procedures as in Example 17 were carried out except that recycled polystyrene foam pellets (B) were used instead of recycled styrene resin particles (A) (made from used polystyrene resin from home appliances) as the recycled styrene resin particles, and expandable styrene resin particles (20), surface-treated expandable styrene resin particles (20'), pre-expanded styrene resin particles (20), and styrene resin foam molded articles (20) were obtained. The results of various evaluations are shown in Table 4.

[0165] [Table 4] [Industrial Applicability]

[0166] The expandable styrene-based resin particles, pre-expanded styrene-based resin particles, and styrene-based resin foam molded articles according to embodiments of the present invention are suitable for use as insulation materials for homes and automobiles, thermal insulation materials for building materials, transport packaging materials for fish boxes and food containers, and cushioning materials. The pre-expanded styrene-based resin particles according to embodiments of the present invention are preferably used as a filler in which a large number of pre-expanded styrene-based resin particles are filled into a bag, and are suitable for use as cushioning materials (expanded particles filling the inside of a cushion). More specifically, the styrene-based resin foam molded articles according to embodiments of the present invention are suitable for use as wall insulation materials, floor insulation materials, roof insulation materials, automotive insulation materials, hot water tank insulation materials, piping insulation materials, solar system insulation materials, water heater insulation materials, containers for food and industrial products (e.g., food containers such as fish boxes, returnable containers), cushioning materials, floats, blocks, packaging materials for fish and agricultural products, embankment materials (e.g., embankment molded articles and embankment blocks), tatami mat core materials, cushion core materials, concrete aggregates, and the like.

Claims

1. A method for producing expandable styrene-based resin particles, comprising: a step of adding a styrene-based monomer to recycled styrene-based resin particles and polymerizing the resulting mixture to obtain styrene-based resin particles (A); and a step of injecting a volatile blowing agent into the styrene-based resin particles (A), the content of the recycled styrene-based resin particles relative to the total amount of the recycled styrene-based resin particles and the styrene-based monomer is 20% by mass to 70% by mass, the styrene-based monomer is added at a temperature of 60°C to 108°C; The injection temperature when injecting the volatile blowing agent is 40°C to 88°C. A method for producing expandable styrene-based resin particles.

2. The method for producing expandable styrene-based resin particles according to claim 1, wherein the recycled styrene-based resin particles are pellets obtained by melt extrusion.

3. 3. The method for producing expandable styrene-based resin particles according to claim 2, wherein the pellets obtained by the melt extrusion method are at least one selected from extruded strand pellets obtained by extruding used expandable styrene-based resin using an extruder and strand-cutting the extruded pellets; underwater-cut pellets obtained by an underwater cutting method in which used expandable styrene-based resin is extruded using an extruder and simultaneously cut underwater; and hot-cut pellets obtained by a hot-cut method in which used expandable styrene-based resin particles are cut and cooled immediately after emerging from a die of an extruder.

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