Regenerated expandable styrene-based resin particles, regenerated prefoamed styrene-based resin particles, and regenerated styrene-based resin foam molding

Abstract

Provided are regenerated expandable styrene-based resin particles which are obtained using a recycled raw material, have stable quality, and exhibit excellent moldability. Also provided are regenerated prefoamed styrene-based resin particles obtained from such regenerated expandable styrene-based resin particles. Also provided is a regenerated styrene-based resin foam molding formed from such regenerated prefoamed styrene-based resin particles.　The regenerated expandable styrene-based resin particles according to an embodiment of the present invention contain 0.001 mass% or more of propane.

Description

Recycled expandable styrene resin particles, recycled pre-expanded styrene resin particles, and recycled styrene resin foam molded article

[0001] The present invention relates to recycled expandable styrene-based resin particles, recycled pre-expanded styrene-based resin particles, and recycled styrene-based resin foam molded articles.

[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 styrene-based resin particles or pre-expanded styrene-based resin particles obtained by pre-expanding expandable styrene-based resin particles) 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 a plurality of 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 landfill, 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.

[0004] Material recycling as described above is also being considered for styrene-based resin foam molded articles. For example, the following reports have been made. Several reports have been made on recycled expandable styrene-based resin particles using recycled raw materials. One reported method involves impregnating recycled resin pellets molded from recovered styrene-based resin foam molded articles with a blowing agent, or by pressurizing and then impregnating the pellets (Patent Document 1). Another reported method involves adding styrene monomer to recycled resin pellets molded from recovered styrene-based resin foam molded articles, nuclear polymerizing the pellets, and then impregnating or by pressurizing and then impregnating the pellets with a blowing agent (Patent Documents 2 to 4). Recently, reports have been made on recycled expandable styrene-based resin particles containing a predetermined amount of normal butyric acid to improve moldability (Patent Document 5) and on recycled expandable styrene-based resin particles that suppress the odor characteristic of recycled materials (Patent Document 6).

[0005] However, conventionally, recycled expandable styrene-based resin particles made from recycled raw materials have varied in quality, and it may not be possible to provide recycled expandable styrene-based resin particles of stable quality. For example, recycled expandable styrene-based resin particles made from recycled polystyrene foam tend to have unstable quality. Furthermore, such recycled expandable styrene-based resin particles with unstable quality have the problem of poor moldability. Note that this unstable quality typically refers to a state in which the quality of the recycled expandable styrene-based resin particles produced as a product varies. For example, when the recycled expandable styrene-based resin particles produced as a product are expanded, the foaming state varies depending on the product lot, and as a result, the quality of the resulting recycled pre-expanded styrene-based resin particles and recycled styrene-based resin foam molded articles is also unstable.

[0006] Japanese Patent No. 6788428 Japanese Patent No. 4052193 Japanese Patent No. 4912567 Japanese Patent Application Laid-Open No. 2022-153315 Japanese Patent Application Laid-Open No. 2023-143856 Japanese Patent Application Laid-Open No. 2023-147272

[0007] The present invention has been made to solve the above-mentioned problems of the related art, and its main object is to provide recycled expandable styrene-based resin particles using recycled raw materials, which have stable quality and excellent moldability. It is also an object of the present invention to provide recycled pre-expanded styrene-based resin particles obtained from such recycled expandable styrene-based resin particles. It is also an object of the present invention to provide recycled styrene-based resin foam molded articles molded from such recycled pre-expanded styrene-based resin particles.

[0008] The present inventors have investigated the reason why the quality of recycled expandable styrene resin particles made from conventional recycled raw materials is unstable.

[0009] First, analysis of the styrene-based resin foam molded products collected as recycled raw materials revealed that, compared to unused virgin raw materials, there were differences in quality depending on the lot, and that there was a high level of contamination with foreign matter (for example, additives used in the production of virgin raw materials, and proteins contained in collected items such as fish boxes and agricultural product boxes).

[0010] Therefore, further investigation was conducted into the relationship between the quality differences of recycled raw materials, the inclusion of foreign matter, and the quality of recycled expandable styrene-based resin particles. The blowing agent injected and impregnated during the production of recycled expandable styrene-based resin particles should diffuse uniformly throughout the resin particles. However, the quality differences of recycled raw materials and the inclusion of foreign matter prevent the uniform diffusion of the blowing agent, resulting in variations in quality and unstable recycled expandable styrene-based resin particles. As a result, the quality of recycled pre-expanded styrene-based resin particles and recycled styrene-based resin foam molded articles produced from the resulting recycled expandable styrene-based resin particles also varies, making it impossible to maintain stable quality.

[0011] Therefore, the present inventors have conducted extensive research into technical means for promoting the diffusion of a blowing agent in resin particles made from recycled raw materials, and have focused on the use of propane, which has not traditionally been actively used as a blowing agent due to reasons such as safety and ease of handling. Propane has a higher vapor pressure, is more volatile, and is more flammable than butane and pentane, which have traditionally been used as blowing agents. However, the inventors have found that by utilizing this high vapor pressure and high volatility, the quality of the resulting recycled expandable styrene-based resin particles made from recycled raw materials is stable and excellent in moldability, and have thus completed the present invention.

[0012] [1] The recycled expandable styrene-based resin particles according to an embodiment of the present invention have a propane content of 0.001% by mass or more. [2] The recycled expandable styrene-based resin particles described in [1] above may be obtained by injecting a blowing agent into recycled styrene-based resin particles (A). [3] The recycled expandable styrene-based resin particles described in [2] above may have the injected blowing agent contain propane, and the amount of propane injected may be 0.01% by mass or more relative to the recycled styrene-based resin particles (A). [4] The recycled expandable styrene-based resin particles described in [2] or [3] above may have the recycled styrene-based resin particles (A) obtained by nuclear polymerization of a styrene monomer using recycled styrene-based resin raw material particles (a) as nuclei. [5] The recycled expandable styrene-based resin particles described in [2] or [3] above may have the recycled styrene-based resin particles (A) be recycled styrene-based resin raw material particles (a). [6] The recycled pre-expanded styrene-based resin particles according to an embodiment of the present invention are recycled pre-expanded styrene-based resin particles obtained by pre-expanding the recycled expandable styrene-based resin particles according to any one of [1] to [5] above, wherein the pre-expanded particles have a bulk expansion ratio of 2 to 150. [7] The recycled styrene-based resin foam molded article according to an embodiment of the present invention is molded from the recycled pre-expanded styrene-based resin particles according to [6] above.

[0013] According to the present invention, it is possible to provide recycled expandable styrene-based resin particles using recycled raw materials, which have stable quality and excellent moldability. It is also possible to provide recycled pre-expanded styrene-based resin particles obtained from such recycled expandable styrene-based resin particles. Furthermore, it is also possible to provide a recycled styrene-based resin foam molded article molded from such recycled pre-expanded styrene-based resin particles.

[0014] FIG. 1 is a schematic cross-sectional view showing an example of an apparatus suitable for producing recycled expandable styrene-based resin particles according to an embodiment of the present invention.

[0015] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to these embodiments.

[0016] In this specification, "(meth)acrylic" means acrylic and / or methacrylic, and "(meth)acrylate" means acrylate and / or methacrylate.

[0017] <<A. Recycled Expandable Styrenic Resin Particles>> The recycled expandable styrenic resin particles according to an embodiment of the present invention have a particle shape as a whole. The average particle diameter of the recycled expandable styrenic resin particles is preferably 0.4 mm to 2.0 mm, and 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 the particle diameter at 50% of the cumulative value from the particle size distribution obtained by the sieving test of JIS Z 8815.

[0018] The shape of the recycled 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 recycled 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, so in this specification, both shapes are collectively referred to as spherical.

[0019] The weight-average molecular weight of the recycled expandable styrene-based resin particles according to an embodiment of the present invention can be any appropriate weight-average molecular weight within a range that does not impair the effects of the present invention. Such a weight-average molecular weight is preferably 100,000 to 510,000, more preferably 110,000 to 490,000, even more preferably 120,000 to 470,000, and particularly preferably 130,000 to 450,000.

[0020] The recycled expandable styrene-based resin particles according to an embodiment of the present invention have a propane content of 0.001% by mass or more. That is, the recycled expandable styrene-based resin particles according to an embodiment of the present invention contain 0.001% by mass or more of propane in the resin particles. The recycled expandable styrene-based resin particles according to an embodiment of the present invention can exhibit the effects of the present invention by having a propane content of 0.001% by mass or more. The recycled expandable styrene-based resin particles according to an embodiment of the present invention preferably have a propane content of 0.005% by mass to 5.0% by mass, more preferably 0.008% by mass to 4.5% by mass, even more preferably 0.010% by mass to 4.0% by mass, even more preferably 0.012% by mass to 3.5% by mass, particularly preferably 0.015% by mass to 3.0% by mass, and most preferably 0.020% by mass to 2.5% by mass.

[0021] The propane contained in the recycled expandable styrenic resin particles according to an embodiment of the present invention may be the propane used as the blowing agent injected, and may be the propane contained (remaining) in the final recycled expandable styrenic resin particles. Propane has a high vapor pressure, high volatility, and flammability, and has not been actively used as a blowing agent due to safety and handling reasons, such as the high internal pressure of the reaction vessel during production. In the recycled expandable styrenic resin particles according to an embodiment of the present invention, the high vapor pressure and high volatility of propane are utilized appropriately as a gas for expressing foamability, and by incorporating a predetermined amount of propane into the resin particles, the effects of stable quality and excellent moldability can be achieved. If the propane content in the recycled expandable styrenic resin particles is too low, the effects of the present invention may not be achieved, and for example, the aging process during the production of recycled expandable styrenic resin particles may take time, resulting in inconsistent quality. If the propane content in the recycled expandable styrene resin particles is too high, the effects of the present invention may not be achieved. For example, the high vapor pressure may cause a large amount of propane to escape from the recycled expandable styrene resin particles, which may result in poor appearance of the molded product and other variations in quality.

[0022] The recycled expandable styrene-based resin particles according to an embodiment of the present invention may contain, in addition to propane, an organic compound or inorganic gas other than propane that has a boiling point below the softening point of the styrene-based resin and is in a gaseous or liquid state at atmospheric pressure, in order to further enhance the effects of the present invention. Examples of such organic compounds include aliphatic hydrocarbons such as butane (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. Examples of such inorganic gases include carbon dioxide, nitrogen, and ammonia. Among the above organic compounds and inorganic gases, in order to further exhibit the effects of the present invention, preferred are organic compounds whose boiling points are equal to or lower than the softening point of the styrene-based resin and which are gaseous or liquid at normal pressure, more preferably at least one selected from the group consisting of butane and pentane, and particularly preferably pentane. Therefore, in order to further exhibit the effects of the present invention, the recycled expandable styrene-based resin particles according to an embodiment of the present invention preferably contain propane and at least one selected from the group consisting of butane and pentane, more preferably propane and pentane.

[0023] When the recycled expandable styrene-based resin particles according to an embodiment of the present invention contain at least one selected from the group consisting of propane and butane and pentane, the recycled expandable styrene-based resin particles according to an embodiment of the present invention preferably contain at least one selected from the group consisting of butane and pentane in an amount of 20% by mass or less, more preferably 0.5% by mass to 18% by mass, even more preferably 1% by mass to 17% by mass, particularly preferably 2% by mass to 16% by mass, and most preferably 3% by mass to 15% by mass.

[0024] The recycled expandable styrene-based resin particles according to the embodiments of the present invention are preferably obtained by injecting a blowing agent into recycled styrene-based resin particles (A), and the following two embodiments can be mentioned as representative examples. Embodiment (1): Recycled expandable styrene-based resin particles obtained by injecting a blowing agent into recycled styrene-based resin particles (A), wherein the recycled styrene-based resin particles (A) are obtained by nuclear polymerization of a styrene monomer using recycled styrene-based resin raw material particles (a) as nuclei. Embodiment (2): Recycled expandable styrene-based resin particles obtained by injecting a blowing agent into recycled styrene-based resin particles (A), wherein the recycled styrene-based resin particles (A) are recycled styrene-based resin raw material particles (a).

[0025] The recycled expandable styrene-based resin particles according to the embodiment of the present invention have a high environmental contribution. The recycled expandable styrene-based resin particles in the above embodiment (1) have a recycling rate of preferably 10% or more, more preferably 20% or more, and even more preferably 25% or more. The recycled expandable styrene-based resin particles in the above embodiment (2) have a recycling rate of preferably 50% or more, more preferably 70% or more, even more preferably 90% or more, particularly preferably 95% or more, and most preferably 100%. The recycling rate is the proportion of recovered styrene-based resin in the styrene-based resin contained in the recycled expandable styrene-based resin particles.

[0026] First, the above-mentioned embodiment (1) and embodiment (2) will be described below.

[0027] <A-1. Preferred embodiment (1) of recycled expandable styrene-based resin particles> One preferred embodiment (1) of the recycled expandable styrene-based resin particles of the present invention is recycled expandable styrene-based resin particles obtained by injecting a blowing agent into recycled styrene-based resin particles (A), and the recycled styrene-based resin particles (A) are recycled expandable styrene-based resin particles obtained by nuclear polymerization of a styrene-based monomer using recycled styrene-based resin raw material particles (a) as nuclei.

[0028] <A-1-1. Recycled styrene-based resin particles (A) in embodiment (1)> The recycled styrene-based resin particles (A) in embodiment (1) are obtained by nuclear polymerization of a styrene-based monomer using the recycled styrene-based resin raw material particles (a) as nuclei.

[0029] The recycled styrene-based resin raw material particles (a) may be of one type only or of two or more types.

[0030] Any suitable recycled styrene resin can be used as the material for the recycled styrene resin raw material particles (a) as long as the effects of the present invention are not impaired. Examples of such recycled styrene resins include recycled products of plastic materials used in polystyrene foam (molded products such as fish boxes and agricultural product boxes, cushioning materials, block molded products, etc.), foam sheets (tray containers, sheet waste, etc.), home appliances, packaging containers, cushion beads, etc.

[0031] The recycled styrene-based resin raw material particles (a) may contain any suitable recycled resin other than the recycled styrene-based resin, as long as the effects of the present invention are not impaired. Examples of such other 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), and 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.

[0032] As the recycled styrene-based resin raw material particles (a), molded products made from "EPSULEM" or "ESLEM BEAD RNW" manufactured by Sekisui Plastics Co., Ltd. may be used.

[0033] The recycled styrene-based resin raw material particles (a) may be pulverized material obtained by pulverizing recycled resin obtained by heating and / or reducing the volume of used expanded styrene-based resin. The recycled styrene-based resin raw material particles may be pellets obtained by extruding the pulverized material and pelletizing it, or may be pellets obtained by further pulverizing the pellets. Alternatively, the recycled styrene-based resin raw material particles may be particles obtained by reducing the volume and recovering the resin using a solvent such as limonene.

[0034] The recycled styrene resin raw material particles (a) are preferably pellets obtained by melt extrusion, which is a method in which crushed styrene resin, ingots, foamed styrene resin particles, etc., are fed into 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.

[0035] 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.

[0036] As the recycled styrene-based resin raw material particles (a), the pellets obtained by the above-mentioned melt extrusion method may be used as they are, or they may be made into so-called "mini-pellets" by melt extrusion or the like again to obtain smaller pellets.

[0037] The recycled styrene-based resin raw material particles (a) may be a shrinkage or melting product of a styrene-based resin, which is obtained by coarsely crushing used 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.

[0038] 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.

[0039] The recycled styrene-based resin raw material particles (a) may contain at least one selected from the group consisting of finely powdered inorganic substances and organic lubricants, which can typically function as a cell regulator.

[0040] Examples of finely powdered inorganic substances include talc, calcium carbonate, silica, mica, and sodium bicarbonate. Here, talc typically refers to a mixture containing silicon oxide and magnesium oxide as main components and trace amounts of aluminum oxide, iron oxide, etc.

[0041] 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 recycled pre-expanded styrene-based resin particles may be reduced.

[0042] The content of the finely powdered inorganic material relative to the recycled styrene-based resin raw material particles (a) 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 raw material particles (a) is less than 0.1% by mass, the effect of reducing the bubble size of the recycled 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 raw material particles (a) exceeds 5% by mass, the bubble size of the recycled pre-expanded styrene-based resin particles may become extremely small, causing the recycled pre-expanded styrene-based resin particles to melt during molding, which may deteriorate the appearance of the molded product.

[0043] Examples of organic lubricants include liquid paraffin; polyethylene glycol; silicone oils such as dimethylpolysiloxane, methylphenylpolysiloxane, and methylhydrogenpolysiloxane; higher fatty acid bisatomids such as methylene bisstearic acid amide, ethylene bisstearic acid amide, and ethylene bisoleic acid amide; and metal salts of higher fatty acids such as zinc stearate, magnesium stearate, and zinc oleate.

[0044] The content of the organic lubricant relative to the recycled styrene-based resin raw material particles (a) 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 raw material particles (a) is less than 0.01% by mass, the effect of reducing the cell size of the recycled pre-expanded styrene-based resin particles may be reduced. If the content of the organic lubricant relative to the recycled styrene-based resin raw material particles (a) exceeds 2.0% by mass, the cell size of the recycled pre-expanded styrene-based resin particles becomes extremely small, which tends to cause the recycled pre-expanded styrene-based resin particles to melt during molding, resulting in poor appearance of the molded product.

[0045] A specific method for incorporating at least one selected from the group consisting of finely powdered inorganic materials and organic lubricants into the recycled styrene-based resin raw material particles (a) is, for example, a method of kneading at least one selected from the group consisting of finely powdered inorganic materials and organic lubricants during extrusion molding. In this case, preferably, the pulverized material and the cell control agent are 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.

[0046] The recycled styrene-based resin raw material particles (a) are preferably heat-melted to adjust their specific gravity. In this process, the specific gravity of the recycled styrene-based resin raw material particles (a) is preferably adjusted to 0.6 or more, more preferably 0.9 or more. If the specific gravity of the recycled styrene-based resin raw material particles (a) is less than 0.6, the dispersion of the recycled styrene-based resin raw material particles (a) will be unstable, which may result in excessively large particles during the subsequent polymerization process, resulting in reduced yield. The recycled styrene-based resin raw material particles (a) can be heat-melted by any appropriate method as long as the effects of the present invention are not impaired. Examples of such methods include methods using an extruder or a heated roll. The heat-melting is preferably performed by cooling and solidifying the resulting resin with no or minimal residual strain. If residual strain remains in the resin particles, the strain may be relieved in the subsequent process, causing shrinkage in the stretching direction, resulting in the resulting recycled expandable styrene-based resin particles being flat rather than spherical. Therefore, it is preferable to use an extruder for the thermal melting without stretching. If the thermal melting is performed in a stretched state, distortion may remain in the stretched resin obtained by cooling and solidifying. Even if distortion remains in the resin due to the thermal melting, the distortion can be alleviated by curing the resin for a certain period of time at a temperature above the softening point of the resin.

[0047] For the pulverization to obtain the recycled styrene-based resin raw material particles (a), any pulverizer can be used as long as it does not impair the effects of the present invention. As such a pulverizer, for example, a pulverizer for plastics can be used, and a pulverizer for polystyrene is preferred.

[0048] The recycled styrene resin raw material particles (a) can be sieved as necessary and subjected to melting again in an extruder or the like.

[0049] The average particle diameter of the recycled styrene-based resin raw material particles (a) 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 diameter of the recycled styrene-based resin raw material particles (a) exceeds 3 mm, the shape of the resulting recycled expandable styrene-based resin particles may be difficult to obtain as a sphere. If the average particle diameter of the recycled styrene-based resin raw material particles (a) is less than 0.2 mm, the resulting recycled expandable styrene-based resin particles may coalesce.

[0050] The L (long side) / D (short side) ratio of the recycled styrene-based resin raw material particles (a) 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 raw material particles (a) is outside the above range, the shape of the resulting recycled expandable styrene-based resin particles may be difficult to achieve.

[0051] The recycled styrene-based resin raw material particles (a) preferably contain less than 1% by mass of particles having an average particle size of 200 μm or less. Recycled styrene-based resin raw material particles (a) containing 1% by mass or more of particles having an average particle size of 200 μm or less may deteriorate the appearance of the recycled expandable styrene-based resin particles obtained using the recycled styrene-based resin raw material particles (a).

[0052] The weight-average molecular weight of the recycled styrene-based resin raw material particles (a) is preferably 100,000 to 510,000, more preferably 150,000 to 490,000. If the weight-average molecular weight of the recycled styrene-based resin raw material particles (a) is less than 100,000, sufficient strength may not be obtained. If the weight-average molecular weight of the recycled styrene-based resin raw material particles (a) is more than 510,000, the recycled styrene-based resin raw material particles may not be easily spherical, or the foaming properties may be reduced, resulting in poor appearance of the molded product.

[0053] The styrene-based monomer used in the nuclear polymerization may be one kind or two or more kinds.

[0054] The styrene-based monomer includes styrene or a styrene derivative. Examples of styrene derivatives 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.

[0055] 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.

[0056] 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.

[0057] In embodiment (1), the content ratio of the recycled styrene-based resin raw material particles (a) to the total amount of the recycled styrene-based resin raw material particles (a) and the styrene-based monomer is the higher the better from the viewpoint of environmental contribution. However, from the viewpoint of producing the recycled styrene-based resin particles (A) by nuclear polymerization, the content ratio of the recycled styrene-based resin raw material particles (a) to the total amount of the recycled styrene-based resin raw material particles (a) and the styrene-based monomer is preferably 5% by mass to 90% by mass, more preferably 10% by mass to 85% by mass, even more preferably 15% by mass to 80% by mass, even more preferably 20% by mass to 75% by mass, and particularly preferably 25% by mass to 70% by mass.

[0058] In embodiment (1), the recycled styrene-based resin particles (A) are obtained by nuclear polymerization of a styrene-based monomer using recycled styrene-based resin raw material particles (a) as nuclei. Any appropriate method can be used as this nuclear polymerization method as long as it does not impair the effects of the present invention. One preferred embodiment of this nuclear polymerization method is a method in which an emulsion containing a polymerization initiator and a styrene-based monomer is added to a suspension obtained by dispersing recycled styrene-based resin raw material particles (a) as nuclei in an aqueous medium, thereby impregnating the recycled styrene-based resin raw material particles (a), and then a styrene-based monomer is added and polymerization is carried out.

[0059] When obtaining recycled styrene-based resin particles (A), the addition temperature when adding the styrene monomer to the recycled styrene-based resin raw material particles (a) is preferably 40°C to 119°C, more preferably 40°C to 118°C, even more preferably 40°C to 117°C, particularly preferably 50°C to 117°C, and most preferably 60°C to 115°C, in order to further demonstrate the effects of the present invention. If the addition temperature when adding the styrene monomer to the recycled styrene-based resin raw material particles (a) is adjusted within the above range, the styrene monomer can be incorporated while maintaining the recycled styrene-based resin raw material particles (a) at an appropriate hardness, thereby achieving good spheroidization of the recycled styrene-based resin particles (A), and the final recycled expandable styrene-based resin particles can exhibit good spheroidization and excellent moldability. If the addition temperature when adding the styrene monomer to the recycled styrene resin raw material particles (a) is too low outside the above range, the recycled styrene resin raw material particles (a) will become too hard, and when the styrene monomer is incorporated in this state, the recycled styrene resin particles (A) will be difficult to spheroidize, and the finally obtained recycled expandable styrene resin particles may be difficult to spheroidize and may have poor moldability. If the addition temperature when adding the styrene monomer to the recycled styrene resin raw material particles (a) is too high outside the above range, the recycled styrene resin raw material particles (a) will become too soft, and when the styrene monomer is incorporated in this state, the recycled styrene resin particles (A) will be difficult to spheroidize, and the finally obtained recycled expandable styrene resin particles may be difficult to spheroidize and may have poor moldability. The "addition temperature when adding a styrene-based monomer to the recycled styrene-based resin raw material particles (a)" means the addition temperature during the addition of the emulsion containing the polymerization initiator and the styrene-based monomer, and the subsequent addition of the styrene-based monomer.

[0060] When dispersing the recycled styrene-based resin raw material particles (a) as nuclei in an aqueous medium to obtain a suspension, any suitable method can be adopted as a method for dispersing the recycled styrene-based resin raw material particles (a) in the aqueous medium as long as it does not impair the effects of the present invention. As a dispersion method, a dispersion using an apparatus equipped with a stirring blade is preferred. A method for more fine dispersion can be mentioned, for example, a method using a homomixer.

[0061] When dispersing recycled styrene-based resin raw material particles (a) as nuclei in an aqueous medium to obtain a suspension, it is preferable to use a dispersant to disperse the recycled styrene-based resin raw material particles (a) in the aqueous medium. Any suitable dispersant can be used as long as it can be used in 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; and sparingly soluble inorganic salts such as magnesium pyrophosphate and calcium triphosphate. Among these, magnesium pyrophosphate is preferred as the dispersant because it can better demonstrate the effects of the present invention.

[0062] The blending ratio of the dispersant per 100 parts by mass of the recycled styrene-based resin particles (A) is preferably 0.1 to 2.0 parts by mass, more preferably 0.1 to 1.5 parts by mass, and even more preferably 0.1 to 1.0 part by mass.

[0063] When dispersing recycled styrene-based resin raw material particles (a) as nuclei in an aqueous medium to obtain a suspension, it is preferable to use a surfactant when dispersing the recycled styrene-based resin raw material particles (a) in the aqueous medium. Any suitable surfactant that can be used in suspension polymerization can be used as long as it does not impair the effects of the present invention. Examples of such surfactants include sodium dodecylbenzenesulfonate, sodium alkanesulfonate, sodium alkylsulfonate, sodium alkyldiphenyletherdisulfonate, and sodium α-olefinsulfonate. Among these, sodium dodecylbenzenesulfonate is preferred as the surfactant, as it can more effectively demonstrate the effects of the present invention.

[0064] The blending ratio of the surfactant to 100 parts by mass of the recycled styrene-based resin particles (A) is preferably 0.005 parts by mass to 0.1 parts by mass, more preferably 0.005 parts by mass to 0.08 parts by mass, and even more preferably 0.005 parts by mass to 0.06 parts by mass.

[0065] 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 raw material particles (a) will be incorporated into the oil droplets of the dispersion, causing adhesion, plasticization, and coalescence of the recycled styrene-based resin raw material particles (a), which is likely to result in the generation of excessively large particles.

[0066] As the polymerization initiator used to obtain an emulsion containing a polymerization initiator and a styrene-based monomer, any appropriate polymerization initiator can be used as long as it is one that is 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.

[0067] The amount of the polymerization initiator used is preferably 0.1% by mass to 1.0% by mass, more preferably 0.1% by mass to 0.8% by mass, and even more preferably 0.1% by mass to 0.5% by mass, based on the styrene-based monomer.

[0068] 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.

[0069] After adding an emulsion containing a styrene monomer to a suspension containing recycled styrene resin raw material particles (a) to impregnate the particles, any suitable method can be used to add the styrene monomer as long as it does not impair the effects of the present invention. 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.

[0070] After adding an emulsion containing a styrene monomer to a suspension containing recycled styrene resin raw material particles (a) to impregnate the particles, the styrene monomer may be added, and then the polymerization reaction may be continued at any appropriate temperature and for any appropriate time, as necessary.

[0071] The suspension containing the recycled styrene-based resin raw material particles (a) and the emulsion containing the styrene-based monomer 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.

[0072] <A-1-2. Injection of a blowing agent in embodiment (1)> The recycled expandable styrene-based resin particles in embodiment (1) are obtained by injecting a blowing agent into the recycled styrene-based resin particles (A). Typically, the blowing agent is injected and impregnated into the resin particles.

[0073] A typical method for injecting the blowing agent in embodiment (1) is to place the recycled styrene-based resin particles (A) in a reactor such as an autoclave and inject the blowing agent under pressure.

[0074] The foaming agent may be one kind or two or more kinds.

[0075] In embodiment (1), the blowing agent to be injected preferably contains propane, and the amount of propane injected is preferably 0.01% by mass or more, more preferably 0.05% by mass to 10% by mass, even more preferably 0.08% by mass to 7.0% by mass, particularly preferably 0.10% by mass to 5.0% by mass, and most preferably 0.15% by mass to 3.5% by mass, relative to the amount of recycled styrene-based resin particles (A).

[0076] In embodiment (1), if the amount of propane injected relative to the recycled styrene-based resin particles (A) is too small or too large, the effects of the present invention may not be achieved, and for example, there may be variations in quality, leading to a decrease in moldability.

[0077] In embodiment (1), the blowing agent to be injected preferably contains 0.1 mass% or more of propane relative to the total amount of the blowing agent to be injected. That is, the total amount of propane used for injection is 0.1 mass% or more. In embodiment (1), the effects of the present invention can be achieved by the blowing agent containing 0.1 mass% or more of propane. In embodiment (1), the content of propane in the blowing agent is preferably 0.1 mass% to 50 mass%, more preferably 0.2 mass% to 45 mass%, even more preferably 0.3 mass% to 40 mass%, particularly preferably 0.4 mass% to 38 mass%, and most preferably 0.4 mass% to 35 mass%.

[0078] In the embodiment (1), if the content of propane in the entire blowing agent to be injected is too small or too large, the effects of the present invention may not be exhibited, and for example, there may be variations in quality, leading to a decrease in moldability.

[0079] In embodiment (1), the blowing agent to be injected may contain, in addition to propane, an organic compound or inorganic gas other than propane whose boiling point is equal to or lower than the softening point of the styrene-based resin and which is in a gaseous or liquid state at normal pressure, in order to further enhance the effects of the present invention. Examples of such organic compounds include aliphatic hydrocarbons such as butane (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. Examples of such inorganic gases include carbon dioxide, nitrogen, and ammonia. Among the above organic compounds and inorganic gases, in order to further exhibit the effects of the present invention, preferred are organic compounds having a boiling point equal to or lower than the softening point of the styrene-based resin and being gaseous or liquid at normal pressure, more preferably at least one selected from the group consisting of butane and pentane, and particularly preferably pentane. Therefore, in order to further exhibit the effects of the present invention, in embodiment (1), the blowing agent to be injected preferably includes at least one selected from the group consisting of propane and butane and pentane, more preferably propane and pentane. Furthermore, in embodiment (1), the total content of propane and at least one selected from the group consisting of butane and pentane in the blowing agent to be injected is preferably 50% by mass to 100% by mass, more preferably 70% by mass to 100% by mass, even more preferably 90% by mass to 100% by mass, particularly preferably 95% by mass to 100% by mass, and most preferably substantially 100% by mass.

[0080] In embodiment (1), when the blowing agent to be injected contains at least one selected from the group consisting of butane and pentane, the amount of the at least one selected from the group consisting of butane and pentane to be injected is preferably 0.01% by mass or more, more preferably 0.1% by mass to 30% by mass, even more preferably 0.5% by mass to 20% by mass, particularly preferably 1.0% by mass to 15% by mass, and most preferably 2% by mass to 13% by mass, relative to the recycled styrene-based resin particles (A).

[0081] In embodiment (1), the content of at least one selected from the group consisting of butane and pentane in the blowing agent to be injected (in the total amount of blowing agents used) is preferably 99.9 mass% or less, more preferably 50 mass% to 99.9 mass%, even more preferably 55 mass% to 99.8 mass%, particularly preferably 60 mass% to 99.7 mass%, and most preferably 65 mass% to 99.6 mass%.

[0082] In embodiment (1), the total amount of blowing agent injected can be appropriately set depending on the purpose, as long as it is an amount sufficient to form recycled pre-expanded styrene-based resin particles and recycled styrene-based resin foam molded articles. The amount of blowing agent injected is preferably 0.1 to 40% by mass, more preferably 0.5 to 27% by mass, even more preferably 1 to 20% by mass, and particularly preferably 2 to 17% by mass, relative to the recycled styrene-based resin particles (A).

[0083] In embodiment (1), the temperature at which the blowing agent is injected into the recycled styrene-based resin particles (A) is preferably 40°C to 150°C, more preferably 50°C to 140°C, even more preferably 60°C to 130°C, even more preferably 70°C to 123°C, even more preferably 80°C to 115°C, particularly preferably 90°C to 110°C, and most preferably 95°C to 105°C. The temperature at which the blowing agent is injected into the recycled styrene-based resin particles (A) may be varied within the above range. If the temperature at which the blowing agent is injected into the recycled styrene-based resin particles (A) is within the above range, the blowing agent is prevented from being rapidly impregnated into the recycled styrene-based resin particles (A), allowing for uniform impregnation. For example, this can reduce areas that shrink and melt when molded into a recycled styrene-based resin foam, and can also make it easier to remove odors unique to recycled raw materials. If the temperature at which the blowing agent is injected into the recycled styrene-based resin particles (A) is too low and outside the above range, the blowing agent will not be easily impregnated into the recycled styrene-based resin particles (A) when the blowing agent is injected; for example, the blowing agent will be rapidly impregnated when the temperature is raised, and the recycled styrene-based resin particles (A) will not be uniformly impregnated with the blowing agent, which will likely cause variations in the bubbles and lead to surface shrinkage during molding. If the temperature at which the blowing agent is injected into the recycled styrene-based resin particles (A) is too high and outside the above range, the blowing agent will be rapidly impregnated into the recycled styrene-based resin particles (A) when the blowing agent is injected, and the recycled styrene-based resin particles (A) will not be uniformly impregnated with the blowing agent, which will likely cause variations in the bubbles and lead to surface shrinkage during molding.

[0084] In embodiment (1), one embodiment of the temperature for impregnating the recycled styrene-based resin particles (A) with the blowing agent is preferably 40°C to 150°C, more preferably 40°C to 140°C, even more preferably 40°C to 130°C, even more preferably 40°C to 123°C, still more preferably 40°C or higher but lower than 110°C, particularly preferably 40°C to 105°C, and most preferably 40°C to 102°C.

[0085] In embodiment (1), another embodiment of the impregnation temperature of the blowing agent into the recycled styrene-based resin particles (A) is preferably a temperature equal to or higher than the injection temperature of the blowing agent into the recycled styrene-based resin particles (A) (which may be the same as the injection temperature of the blowing agent into the recycled styrene-based resin particles (A)), 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.

[0086] The impregnation temperature of the blowing agent into the recycled styrene-based resin particles (A) may be varied within the above range. When the impregnation temperature of the blowing agent into the recycled styrene-based resin particles (A) is within the above range, in combination with the adjustment of the pressure-injection temperature, the blowing agent is prevented from being rapidly impregnated into the recycled styrene-based resin particles (A), enabling uniform impregnation. For example, areas that shrink and melt when molded into a recycled styrene-based resin foamed molded article can be reduced. If the impregnation temperature of the blowing agent into the recycled styrene-based resin particles (A) is too low outside the above range, the blowing agent may not be impregnated to the center of the recycled styrene-based resin particles (A), leaving unfoamed areas, which may result in an unsatisfactory molded article. If the impregnation temperature of the blowing agent into the recycled styrene-based resin particles (A) is too high outside the above range, the blowing agent may be impregnated too far into the recycled styrene-based resin particles (A), causing the blowing agent to melt during molding.

[0087] In embodiment (1), a particularly representative embodiment of the temperature for impregnating the recycled styrene-based resin particles (A) with the blowing agent is preferably 40°C to 150°C, more preferably 50°C to 130°C, even more preferably 60°C to 120°C, even more preferably 70°C or higher but lower than 110°C, even more preferably 80°C or higher but lower than 110°C, particularly preferably 90°C or higher but lower than 110°C, and most preferably 95°C to 105°C.

[0088] The time for impregnating the recycled styrene-based resin particles (A) with the blowing agent can be any appropriate time within the range that does not impair the effects of the present invention, and is preferably 1 to 10 hours.

[0089] <A-1-3. Other Components in Embodiment (1)> The recycled expandable styrene-based resin particles in embodiment (1) may contain any appropriate other components as long as the effects of the present invention are not impaired. Such other components may be one type only, or two or more types.

[0090] In producing the recycled expandable styrene-based resin particles in embodiment (1), a foaming aid may be used. That is, the recycled expandable styrene-based resin particles in embodiment (1) 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.

[0091] The recycled expandable styrene-based resin particles in embodiment (1) may contain a flame retardant to enhance flame retardancy. The flame retardant may be one type or two or more types.

[0092] 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.

[0093] 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.

[0094] 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. Such an amount is preferably 0.1% to 15% by mass, more preferably 0.2% to 10% by mass, even more preferably 0.2% to 5% by mass, and particularly preferably 0.2% to 3% by mass, based on the recycled styrene-based resin raw material particles (a).

[0095] The flame retardant may be added at any appropriate timing as long as the effects of the present invention are not impaired. To further enhance the effects of the present invention, the flame retardant is preferably added before the blowing agent is injected. Adding the flame retardant before the blowing agent can allow the flame retardant to be added at a low temperature equivalent to the temperature at which the blowing agent is injected, thereby enabling the resulting recycled expandable styrene-based resin particles to be well spherical and have excellent moldability.

[0096] The addition temperature when adding the flame retardant is preferably 5°C to 120°C, more preferably 5°C to 118°C, even more preferably 5°C to 115°C, even more preferably 5°C to 113°C, even more preferably 5°C to 110°C, even more preferably 40°C to 89°C, even 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, from the viewpoint of being able to further exhibit the effects of the present invention.

[0097] In producing the recycled expandable styrene-based resin particles of embodiment (1), a partial ester of a higher fatty acid and an alcohol may be used. That is, the recycled expandable styrene-based resin particles of embodiment (1) 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 partial esters of higher fatty acids and alcohols 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 per 100 parts by mass of the recycled styrene-based resin particles (A). The partial ester of a higher fatty acid and an alcohol may be added, for example, together with a blowing agent, or by commonly used methods such as dry blending, masterbatch, and melt injection.

[0098] When producing the recycled expandable styrene-based resin particles in embodiment (1), a cell regulator may be used. That is, the recycled expandable styrene-based resin particles in embodiment (1) 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; fatty acid bisamides such as methylene bisstearic acid amide and ethylene bisstearic acid amide; citric acid; and finely powdered inorganic substances such as talc, calcium carbonate, silica, mica, and sodium bicarbonate. Here, talc typically refers to a mixture mainly composed of silicon oxide and magnesium oxide and containing trace amounts of aluminum oxide, iron oxide, etc.

[0099] The amount of the cell regulator used may be any appropriate amount within the range that does not impair the effects of the present invention. Such an amount is preferably 0 to 5.0 parts by mass, more preferably 0 to 3.0 parts by mass, even more preferably 0 to 2.0 parts by mass, particularly preferably 0 to 1.0 parts by mass, and most preferably 0 to 0.1 parts by mass, relative to 100 parts by mass of the recycled styrene-based resin particles (A).

[0100] In the production of the recycled expandable styrene-based resin particles in embodiment (1), by including a predetermined amount of propane, which has a high vapor pressure as the blowing agent, even without using a cell regulator, recycled expandable styrene-based resin particles with stable quality and excellent moldability can be provided. In particular, when propane is used in combination with at least one selected from the group consisting of butane and pentane, the above-mentioned effects of propane can provide recycled expandable styrene-based resin particles with more stable quality and excellent moldability.

[0101] 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.

[0102] <A-1-4. Surface Treatment> The recycled expandable styrene-based resin particles in embodiment (1) may be surface-treated. Such surface treatment is preferably performed with at least one selected from silicone oil, antistatic agents, fatty acid metal salts, and fusion accelerators.

[0103] When the recycled expandable styrene-based resin particles in embodiment (1) are surface-treated with silicone oil, the amount of silicone oil used per 100 parts by weight of the recycled expandable styrene-based resin particles before surface treatment is preferably 0.001 to 0.3 parts by weight, more preferably 0.003 to 0.28 parts by weight, even more preferably 0.005 to 0.25 parts by weight, particularly preferably 0.008 to 0.23 parts by weight, and most preferably 0.01 to 0.23 parts by weight. 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-foaming 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.

[0104] The silicone oil may be used alone or in combination of two or more kinds.

[0105] 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.

[0106] When the recycled expandable styrene-based resin particles in embodiment (1) are surface-treated with an antistatic agent, the amount of antistatic agent used per 100 parts by weight of the recycled expandable styrene-based resin particles before surface treatment is preferably 0.001 to 0.3 parts by weight, 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 antistatic agent is too small outside the above range, static electricity may be easily generated during pre-expansion. If the amount of antistatic agent is too large outside the above range, the surfaces of the recycled pre-expanded styrene-based resin particles and recycled styrene-based resin foam molded articles may become sticky.

[0107] The antistatic agent may be used alone or in combination of two or more kinds.

[0108] As the antistatic agent, any appropriate antistatic agent can be used 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, 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.

[0109] The nonionic surfactant may be used alone or in combination of two or more kinds.

[0110] As the nonionic surfactant, any appropriate nonionic surfactant can be used as long as it does not impair the effects of the present invention. Examples of nonionic surfactants that can further exhibit 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-(2-hydroxytetradecyl)amine, N-hydroxybutyl-N-(2-hydroxytetradecyl)amine, N-hydroxypentyl-N-(2-hydroxytetradecyl)amine, N-hydroxypentyl-N-(2-hydroxyhexadecyl)amine, N-hydroxypentyl-N-(2-hydroxyoctadecyl)amine, 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.

[0111] 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 recycled 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 surfaces of the recycled pre-expanded styrene resin particles and the recycled styrene resin foam molded article may become sticky.

[0112] The fatty acid glyceride may be one kind or two or more kinds.

[0113] 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.

[0114] When a fatty acid glyceride is used as at least a part of the antistatic agent, the amount of the fatty acid glyceride per 100 parts by weight of the recycled expandable styrene-based resin particles before surface treatment is preferably 0.001 to 0.3 parts by weight, 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 fatty acid glyceride is too low outside the above range, static electricity may be easily generated during pre-expansion. If the amount of fatty acid glyceride is too high outside the above range, the surfaces of the recycled pre-expanded styrene-based resin particles and the recycled styrene-based resin foam molded articles may become sticky.

[0115] When the recycled expandable styrene-based resin particles in embodiment (1) are surface-treated with a fatty acid metal salt, the amount of fatty acid metal salt used per 100 parts by weight of the recycled expandable styrene-based resin particles before surface treatment is preferably 0.005 to 0.5 parts by weight, more preferably 0.007 to 0.45 parts by weight, even more preferably 0.01 to 0.4 parts by weight, particularly preferably 0.015 to 0.35 parts by weight, and most preferably 0.02 to 0.3 parts by weight. If the amount of fatty acid metal salt is too low 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 high outside the above range, too much metal salt may be present during pre-expansion, making the particles more likely to become charged, generating static electricity, and potentially resulting in poor fusion of the molded article.

[0116] The fatty acid metal salt may be of one kind or of two or more kinds.

[0117] 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.

[0118] When the recycled expandable styrene-based resin particles in embodiment (1) are surface-treated with a fusion accelerator, the amount of fusion accelerator used per 100 parts by mass of the recycled 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 fusion accelerator is too small outside the above range, the fusion properties may be reduced during molding, and it may be impossible to obtain a good recycled styrene-based resin foam molded article. If the amount of fusion accelerator is too large outside the above range, blocking may occur during pre-expansion.

[0119] The fusion promoter may be of one kind or of two or more kinds.

[0120] 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.

[0121] <A-2. Preferred embodiment (2) of recycled expandable styrene-based resin particles> One preferred embodiment (2) of the recycled expandable styrene-based resin particles of the present invention is recycled expandable styrene-based resin particles obtained by injecting a blowing agent into recycled styrene-based resin particles (A), wherein the recycled styrene-based resin particles (A) are recycled styrene-based resin raw material particles (a).

[0122] <A-2-1. Recycled styrene-based resin particles (A) in embodiment (2)> The recycled styrene-based resin particles (A) in embodiment (2) are recycled styrene-based resin raw material particles (a). That is, in embodiment (2), recycled styrene-based resin raw material particles (a) are used as the recycled styrene-based resin particles (A). In embodiment (2), the description of the recycled styrene-based resin raw material particles (a) in the above section <A-1-1. Recycled styrene-based resin particles (A) in embodiment (1)> can be used for the recycled styrene-based resin raw material particles (a) that can be used as the recycled styrene-based resin particles (A).

[0123] <A-2-2. Injection of a blowing agent in embodiment (2)> The recycled expandable styrene-based resin particles in embodiment (2) are obtained by injecting a blowing agent into recycled styrene-based resin particles (A) that are made directly from recycled styrene-based resin raw material particles (a). Typically, the blowing agent is injected and impregnated into the resin particles.

[0124] Representative methods for injecting the blowing agent in embodiment (2) include: Injection method (1): a method in which a suspension containing recycled styrene-based resin particles (A) (recycled styrene-based resin raw material particles (a) are used as they are) is placed in a reactor such as an autoclave, and a blowing agent is injected into the suspension; and Injection method (2): a method in which recycled styrene-based resin particles (A) (recycled styrene-based resin raw material particles (a) are used as they are) are placed in an extruder, a blowing agent is injected midway through the extruder, and the particles are extruded from the extruder and simultaneously cut underwater.

[0125] For the injection method (1), the explanation in the above section <A-1-2. Injection of the blowing agent in embodiment (1)> can be used. However, the injection temperature and impregnation temperature of the blowing agent into the recycled styrene-based resin particles (A) are as follows.

[0126] Regarding the injection method (1) in embodiment (2), the temperature at which the blowing agent is injected into the recycled styrene-based resin particles (A) is preferably 40°C to 150°C, more preferably 60°C to 145°C, even more preferably 80°C to 140°C, particularly preferably 100°C to 135°C, and most preferably 110°C to 130°C. The temperature at which the blowing agent is injected into the recycled styrene-based resin particles (A) may be varied within the above range. If the temperature at which the blowing agent is injected into the recycled styrene-based resin particles (A) is within the above range, for example, the recycled styrene-based resin particles (A) can be easily spheroidized even if they are irregularly shaped particles, particle adhesion can be reduced, and odors specific to recycled raw materials can be easily removed. If the temperature at which the blowing agent is injected into the recycled styrene-based resin particles (A) is too low outside the above range, spheroidization may be difficult. If the temperature at which the blowing agent is injected into the recycled styrene-based resin particles (A) is too high and outside the above range, the particles may become flattened or the number of coalesced particles may increase.

[0127] Regarding the injection method (1) in embodiment (2), the temperature for impregnating the recycled styrene-based resin particles (A) with the blowing agent is preferably 40°C to 150°C, more preferably 60°C to 130°C, even more preferably 80°C to 120°C, even more preferably 90°C or higher but less than 110°C, particularly preferably 95°C or higher but less than 110°C, and most preferably 100°C or higher but less than 110°C. The temperature for impregnating the recycled styrene-based resin particles (A) with the blowing agent may be varied within the above range. If the impregnation temperature for the recycled styrene-based resin particles (A) with the blowing agent is within the above range, for example, the blowing agent is more efficiently impregnated into the recycled styrene-based resin particles (A), and the blowing agent is more uniformly absorbed, making it easier to control subsequent foaming and molding, and also making it easier to remove odors specific to recycled raw materials. If the temperature for impregnating the recycled styrene-based resin particles (A) with the blowing agent is too low and outside the above range, the blowing agent may not be absorbed into the center of the recycled styrene-based resin particles (A), or only a portion of the blowing agent injected may be absorbed into the recycled styrene-based resin particles (A).If the temperature for impregnating the recycled styrene-based resin particles (A) with the blowing agent is too high and outside the above range, the particles may become flattened or the number of coalesced particles may increase.

[0128] The injection method (2) in the embodiment (2) is a method in which recycled styrene-based resin particles (A) (recycled styrene-based resin raw material particles (a) are used as they are) are placed in an extruder, a blowing agent is injected midway through the extruder, and the particles are extruded from the extruder and simultaneously cut underwater (underwater cutting method).

[0129] In more detail, in the injection method (2) in embodiment (2), recycled styrene-based resin particles (A) (recycled styrene-based resin raw material particles (a) are used as they are) are supplied to an extruder, heated and melted, a blowing agent is injected midway through the extruder, the resulting resin composition is extruded through a multi-hole die into water, and simultaneously with extrusion, the resin composition is cut in water to form resin particles.

[0130] As for the foaming agent, the explanation of the foaming agent in the above section <A-1-2. Injection of foaming agent in embodiment (1)> can be used.

[0131] Regarding the injection method (2) in embodiment (2), the temperature at which the blowing agent is injected into the recycled styrene-based resin particles (A) is preferably 100°C to 300°C, more preferably 120°C to 290°C, even more preferably 150°C to 280°C, particularly preferably 160°C to 280°C, and most preferably 170°C to 260°C. The temperature at which the blowing agent is injected into the recycled styrene-based resin particles (A) may be varied within the above range. If the temperature at which the blowing agent is injected into the recycled styrene-based resin particles (A) is within the above range, for example, the blowing agent is more easily injected into the recycled styrene-based resin particles (A) efficiently, and the blowing agent is uniformly absorbed, making it easier to control subsequent foaming and molding. If the temperature at which the blowing agent is injected into the recycled styrene-based resin particles (A) is too low outside the above range, the blowing agent may not be uniformly absorbed into the recycled styrene-based resin particles (A). If the temperature at which the blowing agent is injected into the recycled styrene-based resin particles (A) is too high and outside the above range, there is a risk that the particles will become more likely to coalesce or flatten.

[0132] When cutting in water simultaneously with extrusion, the water temperature is preferably 15°C to 60°C, more preferably 20°C to 50°C. If the water temperature is lower than 15°C, the die surface will be cooled too much, the die holes will be easily clogged, and the pressure inside the die will increase, which may make extrusion difficult. If the water temperature is higher than 60°C, it may be difficult to suppress foaming, and if the water temperature exceeds 80°C, the resin particles obtained by cutting may be prone to coalescence.

[0133] The temperature of the water is preferably 100° C. to 200° C. lower than the temperature of the resin composition when it flows into the die. If the temperature difference between the water temperature and the resin composition temperature is less than 100° C., the resulting resin particles may not be sufficiently cooled, making it difficult to suppress foaming, and if the temperature difference between the water temperature and the resin composition temperature exceeds 200° C., the resulting resin particles may be deformed due to the temperature difference between the surface and interior of the resin particles, and may not become perfectly spherical.

[0134] In the underwater cutting method, a mold with 50 to 500 discharge holes in the multi-hole die is used, and the water pressure is preferably adjusted to 0 MPa to 2.00 MPa and the discharge rate to 50 kg / hour to 300 kg / hour. In the underwater cutting method, the water pressure corresponds to the resistance force when the resin is extruded from the die into the water, and the discharge rate corresponds to the force in the extrusion direction when the resin composition is extruded from the die into the water. Therefore, in the underwater cutting method, expandable styrene-based resin particles can be successfully produced by appropriately adjusting the water pressure and discharge rate. In particular, when recycled styrene-based resin is used as the resin component, the molecular weight tends to decrease and the fluidity tends to increase due to the thermal history of the recycled styrene-based resin during recycling. In addition, the fluidity and viscoelasticity change due to the inclusion of an arbitrary amount of additives derived from recycled raw materials, requiring strict adjustment of the water pressure and discharge rate in the underwater cutting method.

[0135] The water pressure in the underwater cutting method is preferably 0.12 MPa to 1.90 MPa, more preferably 0.13 MPa to 1.85 MPa, even more preferably 0.15 MPa to 1.80 MPa, and particularly preferably 0.20 MPa to 1.60 MPa.

[0136] The discharge rate in the underwater cutting method is preferably 60 kg / hour to 280 kg / hour, more preferably 80 kg / hour to 270 kg / hour, even more preferably 100 kg / hour to 260 kg / hour, and particularly preferably 120 kg / hour to 250 kg / hour.

[0137] An example of an apparatus suitable for producing recycled expandable styrenic resin particles in embodiment (2) by the underwater cutting method of pressure injection method (2) is shown in Figure 1. This production apparatus includes an extruder 1 equipped with a raw material supply hopper 11 for introducing resin component (B) upstream in the resin flow direction (from left to right in Figure 1), a blowing agent supply port 12 having a high-pressure pump 13 downstream of the raw material supply hopper 11 in the resin flow direction, and a multi-hole die 2 at the end of the resin flow direction, a cutting chamber 3 arranged to cover the outlet of the multi-hole die 2 and having a cutter 31 rotatably disposed therein and configured to circulate water therein, a water tank 6 and a water pump 4 for supplying water to the cutting chamber 3, a dehydrator 5 for introducing the recycled expandable styrenic resin particles cut in the cutting chamber 3 together with water and separating the water from the recycled expandable styrenic resin particles, and a container 7 for storing the recycled expandable styrenic resin particles separated in the dehydrator 5.

[0138] The extruder 1 can be a known extruder used in extrusion molding of resin compositions. Examples of such extruders include a single-screw extruder, a twin-screw extruder, and a tandem extruder. The extruder 1 receives the resin component (B) from a raw material supply hopper 11, heats and kneads the mixture, and transports the resulting molten mixture downstream in the resin flow direction. When the molten mixture reaches the blowing agent supply port 12, a blowing agent pumped by a high-pressure pump 13 is mixed into the molten mixture. The resulting resin composition is then extruded through the multi-hole die 2 into the cutting chamber 3, where it comes into contact with water and is cut underwater by a cutter 31. The cut resin composition becomes spherical particles of approximately uniform particle size and is transported from the cutting chamber 3 to the dehydrator 5 by the circulating water flow. The recycled expandable styrene-based resin particles obtained after separation and drying in the dehydrator 5 are stored in a container 7, while the water is sent to a water tank 6.

[0139] <A-2-3. Other Components in Embodiment (2)> The recycled expandable styrene-based resin particles in embodiment (2) may contain any appropriate other components as long as the effects of the present invention are not impaired. Such other components may be one type only, or two or more types.

[0140] As for the other components, the explanation in the above section <A-1-3. Other components in embodiment (1)> can be cited.

[0141] <A-2-4. Surface Treatment> The recycled expandable styrene-based resin particles in embodiment (2) may be subjected to a surface treatment. The explanation in the above section <A-1-4. Surface Treatment> can be used for such surface treatment.

[0142] B. Recycled Pre-Expanded Styrenic Resin Particles The recycled pre-expanded styrenic resin particles according to an embodiment of the present invention are obtained by pre-expanding the recycled expandable styrenic resin particles according to an embodiment of the present invention.

[0143] The recycled pre-expanded styrene-based resin particles preferably have an average cell diameter of 0.01 mm to 1.10 mm, more preferably 0.01 mm to 1.00 mm, even more preferably 0.01 to 0.90 mm, particularly preferably 0.01 mm to 0.80 mm, and most preferably 0.01 mm to 0.70 mm. When the average cell diameter of the recycled pre-expanded styrene-based resin particles is within the above range, blocking during foaming and molding can be more effectively prevented. Furthermore, the recycled pre-expanded styrene-based resin particles exhibit better fusion properties and surface properties while further suppressing electrostatic charge during foaming and molding, thereby enabling the molding of recycled styrene-based resin foam molded articles with less static electricity. If the average cell diameter of the recycled pre-expanded styrene-based resin particles is less than 0.01 mm, there is a risk of the surface melting and shrinking during molding.

[0144] Pre-expansion involves expanding recycled expandable styrene-based resin particles to a desired bulk expansion ratio (bulk density) using steam or the like. The bulk expansion ratio of the recycled pre-expanded styrene-based resin particles is preferably 2 to 150, more preferably 2 to less than 100, more preferably 5 to 90, even more preferably 10 to 85, and particularly preferably 15 to 83. The bulk density is the reciprocal of the bulk expansion ratio. When the bulk expansion ratio of the recycled pre-expanded styrene-based resin particles is within the above range, blocking during expansion and molding can be further prevented, and further, electrostatic charge during expansion and molding can be further suppressed while exhibiting better fusion properties and surface properties, making it possible to provide recycled pre-expanded styrene-based resin particles that can mold recycled styrene-based resin foam molded articles with less static electricity.

[0145] In one exemplary embodiment, the recycled pre-expanded styrene-based resin particles can be used to form recycled styrene-based resin foamed molded articles. In another embodiment, the recycled pre-expanded styrene-based resin particles can be used as they are as cushioning material, heat insulating material, concrete aggregate, etc. When the recycled pre-expanded styrene-based resin particles are used as they are, they can preferably be used as a filler in which a large number of recycled pre-expanded styrene-based resin particles are filled into a bag. Such recycled pre-expanded styrene-based resin particles are suitable, for example, for the core material of a cushion (the foam particles filled inside the cushion).

[0146] C. Recycled styrene-based resin foam molded product A recycled styrene-based resin foam molded product according to one embodiment of the present invention is a recycled styrene-based resin foam molded product molded from recycled expandable styrene-based resin particles according to an embodiment of the present invention. A recycled styrene-based resin foam molded product according to another embodiment of the present invention is a recycled styrene-based resin foam molded product molded from recycled pre-expanded styrene-based resin particles according to an embodiment of the present invention.

[0147] The recycled styrene-based resin foam molded article typically contains recycled expandable styrene-based resin particles (hereinafter sometimes simply referred to as "expanded particles") obtained by further expanding recycled pre-expanded styrene-based resin particles.

[0148] A recycled styrene-based resin foam molded article is typically composed of a plurality of foam particles fused together.

[0149] Recycled styrene-based resin foam molded articles can typically be produced by loading recycled pre-expanded styrene-based resin particles into a mold having a predetermined shape according to the purpose and performing in-mold foam molding. More specifically, in-mold foam molding includes (i) filling the recycled pre-expanded styrene-based resin particles into a closed mold having a large number of small holes, (ii) heating and expanding the recycled 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 form a single integrated product by the heat expansion. The density of the recycled styrene-based resin foam molded article can be appropriately set depending on the purpose. The density of the recycled styrene-based resin foam molded article can be adjusted, for example, by adjusting the bulk expansion ratio of the pre-expanded styrene-based resin particles filled into the mold in advance or by adjusting the amount of recycled pre-expanded styrene-based resin particles filled into the mold.

[0150] 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 seconds to 50 seconds, more preferably 10 seconds to 50 seconds. The molding vapor pressure (gauge pressure of the heat transfer medium blowing in) of the heat-foaming 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.

[0151] If necessary, the recycled pre-expanded styrene-based resin particles may be aged before molding into a recycled styrene-based resin foamed molded article. The aging temperature of the recycled 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 recycled pre-expanded styrene-based resin particles may dissipate, resulting in a decrease in moldability.

[0152] The expansion ratio of the expanded beads in the recycled styrene-based resin foamed 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.

[0153] The recycled styrene-based resin foam molded article according to an embodiment of the present invention is lightweight and has excellent heat insulation 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 material, floats, blocks, packaging material for fish and agricultural products, etc., earth filling moldings, core material for tatami mats, core material for cushions, concrete aggregate, etc.

[0154] 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.

[0155] <Measurement of Blowing Agent Content> The blowing agent content (mass%) in the recycled expandable styrene resin particles was measured using a gas chromatograph and gas chromatogram as follows. Approximately 6 mg of recycled expandable styrene resin particles was precisely weighed as a sample and placed at the inlet of a PYR-1A pyrolysis furnace manufactured by Shimadzu Corporation. The furnace was purged with nitrogen for approximately 15 seconds to discharge the mixed gases present when the sample was placed. After sealing, the sample was inserted into the furnace core at 180°C to 200°C and heated for 120 seconds to release the gas. This released gas was measured using a GC-14B (detector: FID) gas chromatograph manufactured by Shimadzu Corporation. The blowing agent content was quantified using the peak areas of the resulting gas chromatogram. <Measurement conditions> Measurement device: "GC-14B" manufactured by Shimadzu Corporation Gas chromatograph column: "Shimalite 60 / 80NAW (Squalane 25%) 3m x 3φ (I.D. SUS)" manufactured by Shinwa Kako Co., Ltd. Detector: FID (Flame Ionization Detector) Measurement conditions: Column temperature (70°C), injection port temperature (110°C), detector temperature (110°C), furnace temperature (180°C to 200°C), carrier gas (N2), N2 flow rate (50mL / min), absolute calibration curve method

[0156] <Moldability Evaluation> Moldability was evaluated by visually inspecting the appearance of the resulting foamed molded article. Specifically, the moldability was evaluated based on the appearance of the surface (300 mm x 400 mm surface) of a plate-shaped recycled styrene-based resin foamed molded article measuring 300 mm long x 400 mm wide x 30 mm thick. The evaluation criteria were as follows: ◯: Depressions in the foamed beads occurred over 10% or less of the surface area. Δ: Depressions in the foamed beads occurred over 20% to less than 30% of the surface area. ×: Depressions in the foamed beads occurred over 30% or more of the surface area. Fewer depressions in the foamed beads indicate a foamed molded article with better moldability, and indicates that the raw recycled expandable styrene-based resin particles and recycled pre-expanded styrene-based resin particles are of stable quality.

[0157] [Production Example 1]: Production of recycled styrene-based resin raw material particles (a) Recovered pellets from used fish boxes were fed into a single-screw extruder, heated and melted at 200°C, extruded through a mold, and cut underwater to produce recycled styrene-based resin raw material particles (a).

[0158] Example 1 Preparation of Recycled Expandable Styrenic Resin Particles (1) A 100-liter reactor equipped with a stirrer was charged with 36 kg of water, 3.5 g of sodium dodecylbenzenesulfonate, and 150 g of magnesium pyrophosphate. 12.6 kg of the recycled styrenic resin raw material particles (a) obtained in Production Example 1 was added and stirred at 150 rpm to prepare suspension (1). Separately, a dispersion of 2.5 kg of water and 0.8 g of sodium dodecylbenzenesulfonate was added with 125 g of benzoyl peroxide (75% purity) as a polymerization initiator and 2.3 kg of styrene monomer dissolved with 20 g of t-butylperoxy-2-ethylhexyl monocarbonate, and the mixture was emulsified by stirring with a homomixer to prepare emulsion (1). The suspension (1) in the 100-liter reactor equipped with a stirrer was maintained at 75°C, and the emulsion (1) was added. The mixture was then held at 75°C for 30 minutes to ensure that the styrene monomer and polymerization initiator were fully absorbed into the recycled styrene-based resin raw material particles (a). Immediately after this, 27.1 kg of styrene monomer was added dropwise over 120 minutes. The addition temperature was gradually increased from 75°C to 105°C. The mixture was then heated to 125°C over 30 minutes, held at 125°C for 30 minutes, and then cooled to 60°C over 1 hour. This produced recycled styrene-based resin particles (A1) in a reaction vessel. Next, 189 g of dicumyl peroxide and 35 g of ethylenebisstearamide were added to a separate dispersion of 3.5 kg of water, 1.5 g of sodium dodecylbenzenesulfonate, and 20 g of magnesium pyrophosphate, and the mixture was emulsified by stirring with a homomixer to prepare emulsion (2). This emulsion (2) was then added to the reactor cooled to 60°C. Ten minutes after this addition, 756 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, the temperature was raised to 100 ° C, and 7.5 mass% of pentane (isopentane / normal pentane = 20 mass% / 80 mass%) and 0.01 mass% of propane were pressurized into the recycled styrene-based resin particles (A1) as a blowing agent, and the blowing agent was slowly impregnated by maintaining this state for 5.5 hours. Then, the temperature inside the reactor was cooled to 30 ° C.Thereafter, the contents were removed from the reactor, dehydrated, dried, and classified to obtain resin particles (1). The obtained resin particles (1) were stored in a refrigerator at 15°C to obtain recycled expandable styrene-based resin particles (1).

[0159] <Surface treatment of recycled expandable styrene resin particles (1)> 0.02 mass % of polyethylene glycol, 0.1 mass % of zinc stearate, 0.03 mass % of fatty acid triglyceride, and 0.04 mass % of fatty acid monoglyceride were added to a tumbler mixer to the obtained recycled expandable styrene resin particles (1) after aging, and the mixture was stirred for 30 minutes to perform a surface treatment, thereby obtaining surface-treated recycled expandable styrene resin particles (1′).

[0160] <Preparation of Recycled Pre-Expanded Styrenic Resin Particles (1)> The obtained surface-treated recycled expandable styrene-based resin particles (1') were placed in a cylindrical batch type expansion machine with a volume of 25 liters and heated with steam to obtain recycled pre-expanded styrene-based resin particles (1). The bulk density of the recycled pre-expanded styrene-based resin particles (1) was 0.017 g / cm. ３ The bulk expansion ratio was 60 times.

[0161] <Preparation of Recycled Styrenic Resin Foam Molded Article (1)> A molding machine having a mold with a cavity of 300 mm length x 400 mm width x 30 mm thickness was used. After leaving the recycled pre-expanded styrene-based resin particles (1) in a room temperature atmosphere for 24 hours, they were filled into the cavity of the mold of the molding machine and heated at a vapor pressure of 0.07 MPa (gauge pressure) for 30 seconds. Then, they were cooled until the pressure inside the mold became 0.01 MPa, and then released from the mold to obtain a plate-shaped recycled styrene-based resin foam molded article (1) corresponding to the mold. The density of the recycled styrene-based resin foam molded article (1) was 0.017 g / cm ３ The expansion ratio was 60. Thereafter, this recycled styrene-based resin foam molded article (1) was stored in a drying room at 50° C. for 1 day. The results are shown in Table 1.

[0162] [Examples 2 to 9] Recycled styrene-based resin particles (A1), recycled expandable styrene-based resin particles (2) to (9), recycled pre-expanded styrene-based resin particles (2) to (9), and recycled styrene-based resin foam molded articles (2) to (9) were obtained in the same manner as in Example 1, except that the blowing agent was changed as shown in Table 1. The results are shown in Table 1.

[0163] Comparative Example 1 Recycled styrene-based resin particles (A1), recycled expandable styrene-based resin particles (C1), recycled pre-expanded styrene-based resin particles (C1), and recycled styrene-based resin foam molded articles (C1) were obtained in the same manner as in Example 1, except that the blowing agent was changed as shown in Table 1. The results are shown in Table 1.

[0164] Example 10 Preparation of Recycled Expandable Styrenic Resin Particles (10) A 100-liter reactor equipped with a stirrer was charged with 42 kg of water, 5.7 g of sodium dodecylbenzenesulfonate, and 295 g of magnesium pyrophosphate. 42 kg of the recycled styrene-based resin raw material particles (a) obtained in Production Example 1 as recycled styrene-based resin particles (A10) was added and suspended by stirring at 150 rpm to prepare suspension (3). The suspension (3) in the 100-liter reactor equipped with a stirrer was maintained at 60°C, and 189 g of dicumyl peroxide and 35 g of ethylenebisstearamide were added. Ten minutes after this addition, 756 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. After that, the temperature was raised to 120 ° C. over 60 minutes, and then 7.5% by mass of pentane (isopentane / normal pentane = 20% by mass / 80% by mass) and 0.01% by mass of propane were pressurized into the recycled styrene-based resin particles (A10) as a blowing agent. The temperature was raised to 108 ° C. over 10 minutes, and then the temperature was maintained at that state for 5 hours, allowing the blowing agent to be slowly impregnated. Then, the temperature in the reactor was cooled to 30 ° C. The contents were then removed from the reactor, dehydrated, dried, and classified to obtain resin particles (10). The obtained resin particles (10) were stored in a refrigerator at 15 ° C. to obtain recycled expandable styrene-based resin particles (10).

[0165] <Surface treatment of recycled expandable styrene resin particles (10)> 0.02 mass% of polyethylene glycol, 0.1 mass% of zinc stearate, 0.03 mass% of fatty acid triglyceride, and 0.04 mass% of fatty acid monoglyceride were added to the obtained recycled expandable styrene resin particles (10) after aging in a tumbler mixer, and the mixture was stirred for 30 minutes to perform a surface treatment, thereby obtaining surface-treated recycled expandable styrene resin particles (10′).

[0166] <Preparation of Recycled Pre-Expanded Styrenic Resin Particles (10)> The obtained surface-treated recycled expandable styrene-based resin particles (10') were placed in a cylindrical batch type expansion machine with a volume of 25 liters and heated with steam to obtain recycled pre-expanded styrene-based resin particles (10). The bulk density of the recycled pre-expanded styrene-based resin particles (10) was 0.017 g / cm. ３ The bulk expansion ratio was 60 times.

[0167] <Preparation of Recycled Styrenic Resin Foam Molded Article (10)> A molding machine having a mold with a cavity of 300 mm length x 400 mm width x 30 mm thickness was used. After leaving the recycled pre-expanded styrene-based resin particles (10) in a room temperature atmosphere for 24 hours, they were filled into the cavity of the mold of the molding machine and heated at a vapor pressure of 0.07 MPa (gauge pressure) for 30 seconds. Then, they were cooled until the pressure inside the mold became 0.01 MPa, and then released from the mold to obtain a plate-shaped recycled styrene-based resin foam molded article (10) corresponding to the mold. The density of the recycled styrene-based resin foam molded article (8) was 0.017 g / cm ３ The expansion ratio was 60. Thereafter, this recycled styrene-based resin foam molded article (10) was stored in a drying room at 50° C. for 1 day. The results are shown in Table 2.

[0168] [Examples 11 to 18] Recycled styrene-based resin particles (A10), recycled expandable styrene-based resin particles (11) to (18), recycled pre-expanded styrene-based resin particles (11) to (18), and recycled styrene-based resin foam molded articles (11) to (18) were obtained in the same manner as in Example 10, except that the blowing agent was changed as shown in Table 2. The results are shown in Table 2.

[0169] Comparative Example 2 Recycled styrene-based resin particles (A10), recycled expandable styrene-based resin particles (C2), recycled pre-expanded styrene-based resin particles (C2), and recycled styrene-based resin foam molded articles (C2) were obtained in the same manner as in Example 10, except that the blowing agent was changed as shown in Table 2. The results are shown in Table 2.

[0170]

[0171]

[0172] The recycled expandable styrene-based resin particles, recycled pre-expanded styrene-based resin particles, and recycled 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, cushioning materials, etc. More specifically, the recycled expandable styrene-based resin particles, recycled pre-expanded styrene-based resin particles, and recycled 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 blocks), tatami mat core materials, cushion core materials, concrete aggregates, etc.

Claims

1. Recycled expandable styrene-based resin particles having a propane content of 0.001% by mass or more.

2. The recycled expandable styrene-based resin particles according to claim 1, which are obtained by injecting a blowing agent into recycled styrene-based resin particles (A).

3. The recycled expandable styrene-based resin particles according to claim 2, wherein the blowing agent to be injected contains propane, and the amount of the propane injected is 0.01 mass% or more relative to the recycled styrene-based resin particles (A).

4. The recycled expandable styrene-based resin particles according to claim 2, wherein the recycled styrene-based resin particles (A) are obtained by nuclear polymerization of a styrene-based monomer using recycled styrene-based resin raw material particles (a) as nuclei.

5. The recycled expandable styrene-based resin particles according to claim 2, wherein the recycled styrene-based resin particles (A) are recycled styrene-based resin raw material particles (a).

6. Recycled pre-expanded styrene-based resin particles obtained by pre-expanding the recycled expandable styrene-based resin particles according to any one of claims 1 to 5, wherein the pre-expanded bulk expansion ratio is 2 to 150 times.

7. A recycled styrene-based resin foamed molding produced from the recycled pre-expanded styrene-based resin particles according to claim 6.

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