Method for producing recycled polystyrene-based resin composition, recycled polystyrene-based resin composition, and molded body

Abstract

The present invention addresses the problem of providing a novel method for producing a recycled polystyrene-based resin composition, with which it is possible to provide a recycled polystyrene-based resin composition wherein physical properties deteriorated by processing are sufficiently recovered. This method for producing a recycled polystyrene-based resin composition comprises a mixing step for melt-mixing polystyrene-based resin waste and a high molecular weight polystyrene-based resin so as to obtain a resin composition, wherein the weight average molecular weight of the high molecular weight polystyrene-based resin is 500,000 to 5,000,000 inclusive.

Description

Method for producing recycled polystyrene-based resin composition, recycled polystyrene-based resin composition and molded article

[0001] The present invention relates to a method for producing a recycled polystyrene-based resin composition and a recycled polystyrene-based resin composition.

[0002] Each time a resin is processed (e.g., melt-mixed), its molecular chains may shorten due to heat, etc., and the resin may deteriorate, resulting in a decrease in its physical properties. Resins with decreased physical properties have limited processing applications compared to the resin before processing, or may not be processable at all.

[0003] Therefore, conventionally, polystyrene-based resin waste obtained by melt-mixing products made of polystyrene-based resin has had limited uses, such as being mixed in small amounts with virgin polystyrene-based resin (for example, Patent Document 1).

[0004] Japanese Patent Application Publication No. 5-230263

[0005] The above-mentioned conventional techniques are not sufficient in terms of restoring physical properties that have been deteriorated by processing, and there is room for further improvement.

[0006] One embodiment of the present invention has been made in consideration of the above-mentioned problems, and its object is to provide a novel method for producing a recycled polystyrene-based resin composition, which can provide a recycled polystyrene-based resin composition in which physical properties that have been reduced by processing have been fully restored.

[0007] The present inventors have conducted extensive research to solve the above problems and have completed the present invention.

[0008] That is, a method for producing a recycled polystyrene-based resin composition according to one embodiment of the present invention includes a mixing step of melt-mixing polystyrene-based resin waste and a high-molecular-weight polystyrene-based resin to obtain a resin composition, and the weight-average molecular weight of the high-molecular-weight polystyrene-based resin is 500,000 or more and 5,000,000 or less.

[0009] According to one embodiment of the present invention, it is possible to provide a method for producing a recycled polystyrene-based resin composition, which can provide a recycled polystyrene-based resin composition in which physical properties that have been reduced by processing have been fully restored.

[0010] An embodiment of the present invention will be described below, but the present invention is not limited thereto. The present invention is not limited to the respective configurations described below, and various modifications are possible within the scope of the claims. Furthermore, embodiments or examples obtained by combining the technical means disclosed in different embodiments or examples are also included in the technical scope of the present invention. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment. All academic and patent literature described in this specification is incorporated herein by reference.

[0011] In this specification, the term "X unit" contained in a polymer, copolymer, or resin refers to a "structural unit derived from an X monomer." For example, the term "styrene-based unit" refers to a "structural unit derived from a styrene-based monomer."

[0012] Unless otherwise specified in this specification, the structural unit is X １ Unit, X ２ Units, ... and X ｎ A copolymer containing units (n is an integer of 2 or more) is referred to as "X １ / X ２ / ・・・ / X ｎ Also referred to as "copolymer". X １ / X ２ / ・・・ / X ｎ Unless otherwise specified, the polymerization mode of the copolymer is not particularly limited, and the copolymer may be a random copolymer, an alternating copolymer, a block copolymer, or a graft copolymer.

[0013] [1. Technical Concept of One Embodiment of the Present Invention] As described above, conventionally, the use of polystyrene-based resin waste has been limited, for example, by being limited to a small amount when blended with virgin polystyrene-based resin. This is because the greater the amount of polystyrene-based resin waste blended with virgin polystyrene-based resin, the lower the physical properties of the resulting resin composition, limiting the processing applications of the resin composition. In other words, when virgin polystyrene-based resin is blended with polystyrene-based resin waste, the physical properties of the resulting resin composition are improved compared to those of the polystyrene-based resin waste, but are still lower than those of the virgin polystyrene-based resin. In other words, virgin polystyrene-based resin has not been able to fully restore the physical properties of the polystyrene-based resin waste that have been reduced by processing. In this specification, "virgin polystyrene-based resin" refers to a polystyrene-based resin that has never been commercialized. "Virgin polystyrene-based resin" is sometimes referred to as "virgin polystyrene-based resin."

[0014] Therefore, the present inventors have conducted extensive research with the aim of fully restoring the properties of polystyrene-based resin waste that have been deteriorated by processing, and as a result, have independently obtained the following novel finding, which has led to the completion of the present invention: by melt-mixing polystyrene-based resin waste with a high-molecular-weight polystyrene-based resin having a weight-average molecular weight of 500,000 or more and 5,000,000 or less, it is surprisingly possible to obtain a resin composition in which the properties of the polystyrene-based resin waste that have been deteriorated by processing are fully restored.

[0015] Common applications of polystyrene-based resins include foam sheets, foam beads, and foamed molded articles (e.g., in-mold foamed articles and extruded foamed articles). These applications require foaming of the polystyrene-based resin. In these foaming applications, the physical properties of the resin in its molten state (e.g., melt viscosity and melt tension) can significantly affect the density of the final foamed molded article. Therefore, polystyrene-based resins with a weight-average molecular weight of 400,000 or less have generally been used as raw materials to ensure foamability. In other words, polystyrene-based resins with a weight-average molecular weight of 500,000 or more have not been used in general applications and have been used in limited applications, such as as a reference material for gas chromatography. Through extensive research, the present inventors surprisingly achieved the above-described novel findings by using polystyrene-based resins with a weight-average molecular weight of 500,000 or more, which are rarely used in general applications.

[0016] 2. Method for producing recycled polystyrene-based resin composition A method for producing a recycled polystyrene-based resin composition according to one embodiment of the present invention includes a mixing step of melt-mixing polystyrene-based resin waste and a high-molecular-weight polystyrene-based resin to obtain a resin composition, and the weight-average molecular weight of the high-molecular-weight polystyrene-based resin is 500,000 or more and 5,000,000 or less.

[0017] In this specification, a "recycled polystyrene-based resin composition" may be referred to as a "composition," a "method for producing a recycled polystyrene-based resin composition" may be referred to as a "production method," and a "method for producing a recycled polystyrene-based resin composition according to one embodiment of the present invention" may be referred to as the "present production method."

[0018] Because this manufacturing method has the above-mentioned configuration, it has the advantage of being able to provide a recycled polystyrene-based resin composition in which physical properties deteriorated by processing have been fully restored. The following is presumed to be the mechanism by which this manufacturing method can provide the above-mentioned advantages. That is, it is presumed that the entanglement of molecules of the high-molecular-weight polystyrene-based resin with molecules of the polystyrene-based resin waste results in improved physical properties (e.g., melt viscosity and melt tension) in the molten state of the polystyrene-based resin waste that has been deteriorated by processing. However, one embodiment of the present invention is in no way limited to this presumption.

[0019] In this specification, the phrase "physical properties deteriorated by processing have been sufficiently restored" in relation to a recycled polystyrene-based resin composition or a polystyrene-based resin composition means that the value of at least one of the physical properties of the recycled polystyrene-based resin composition or the polystyrene-based resin composition is equal to or greater than the value of the physical property of the polystyrene-based resin before processing. For example, with regard to the melt volume rate (hereinafter sometimes referred to as "MVR"), if the MVR value of the recycled polystyrene-based resin composition or the polystyrene-based resin composition is equal to or less than the MVR value of the polystyrene-based resin before processing, the recycled polystyrene-based resin composition is considered to have sufficiently restored the physical properties deteriorated by processing. As an example, if the MVR of unused polystyrene-based resin that has never been subjected to an extruder after production is 14.1 cm ３ / 10 minutes, and the MVR of pellets (corresponding to polystyrene resin waste) obtained by melt-mixing unused polystyrene resin in an extruder was 16.5 cm ３ The case where the pellets are melt-mixed with a high molecular weight polystyrene resin and the MVR of the recycled polystyrene resin composition obtained is 14.1 cm ３ / 10 minutes (the MVR value of virgin polystyrene resin corresponding to the polystyrene resin before processing) or less, the recycled polystyrene resin composition is considered to have sufficiently recovered the physical properties that were reduced by processing.３ / 10 minutes, and the polystyrene resin was further subjected to the extruder once more (i.e., a total of three times) to melt-mix and obtain pellets (corresponding to polystyrene resin waste). The MVR of the pellets was 22.9 cm ３ The case where the pellets are melt-mixed with a high molecular weight polystyrene resin and the MVR of the recycled polystyrene resin composition obtained is 19.3 cm ３ / 10 minutes (the MVR value of the polystyrene resin obtained by melt-mixing after production and feeding it twice in an extruder, which corresponds to the polystyrene resin before processing), the recycled polystyrene resin composition is considered to have sufficiently restored the physical properties that were reduced by processing. ３ / 10 minutes, and the polystyrene resin was further subjected to the extruder once more (i.e., a total of five times) to melt-mix and obtain pellets (corresponding to polystyrene resin waste). The MVR of the pellets was 31.1 cm ３ The case where the pellets are melt-mixed with a high molecular weight polystyrene resin and the MVR of the recycled polystyrene resin composition obtained is 27.0 cm ３ / 10 minutes (the MVR value of the polystyrene resin obtained by melt mixing after production and feeding it through an extruder four times, which corresponds to the polystyrene resin before processing) or less, the recycled polystyrene resin composition is considered to have sufficiently recovered the physical properties that were reduced by processing.

[0020] In one embodiment of the present invention, the MVR value of the recycled polystyrene-based resin composition or polystyrene-based resin composition is preferably equal to or less than the MVR value of the polystyrene-based resin before processing. In one embodiment of the present invention, the value of at least one of the physical properties of the recycled polystyrene-based resin composition or polystyrene-based resin composition is preferably equal to or greater than the physical property value of the virgin polystyrene-based resin. In one embodiment of the present invention, the MVR value of the recycled polystyrene-based resin composition or polystyrene-based resin composition is preferably equal to or less than the MVR value of the virgin polystyrene-based resin. In one embodiment of the present invention, the MVR value of the recycled polystyrene-based resin composition or polystyrene-based resin composition is preferably at least 6 times the MVR value of the virgin polystyrene-based resin and at most 6 times the MVR value of the virgin polystyrene-based resin. In one embodiment of the present invention, the melt tension value of the recycled polystyrene-based resin composition or polystyrene-based resin composition is preferably at least -0.2 times the melt tension value of the virgin polystyrene-based resin and at most +0.2 times the melt tension value of the virgin polystyrene-based resin. In one embodiment of the present invention, the proportion (%) of resins having a molecular weight of 700,000 or more contained in the recycled polystyrene-based resin composition is preferably at least 4% less than the proportion of resins having a molecular weight of 700,000 or more contained in the virgin polystyrene-based resin, and is preferably at most 4% greater than the proportion of resins having a molecular weight of 700,000 or more contained in the virgin polystyrene-based resin. The "proportion of resins having a molecular weight of 700,000 or more contained in the recycled polystyrene-based resin composition" will be described in detail later. In one embodiment of the present invention, the weight average molecular weight of the recycled polystyrene-based resin composition or the polystyrene-based resin composition is preferably at least 100,000 less than the weight average molecular weight of the virgin polystyrene-based resin and at most 100,000 greater than the weight average molecular weight of the virgin polystyrene-based resin.

[0021] As described above, in the production of conventional recycled polystyrene-based resin compositions, only a small amount of polystyrene-based resin waste is used to mix with virgin polystyrene-based resin. In other words, in conventional methods for producing recycled polystyrene-based resin compositions, virgin polystyrene-based resin is the primary raw material. The amount (wt%) of polystyrene-based resin waste used to produce a 100% recycled polystyrene-based resin composition is sometimes referred to as the "recycle ratio (%)." Conventional techniques have had the problem of low recycle ratios (less than 50% at most). On the other hand, in a preferred embodiment of the present invention, the primary raw material is polystyrene-based resin waste. In a preferred embodiment of the present invention, a recycled polystyrene-based resin composition can be produced by blending a smaller amount of high-molecular-weight polystyrene resin with the polystyrene-based resin waste than with the polystyrene-based resin waste, thereby providing a recycled polystyrene-based resin composition whose physical properties, which have been reduced by processing, are fully restored. In other words, the preferred embodiment of the present invention also has the advantage of a high recycle ratio (at least 50% or more).

[0022] In this manufacturing method, both the polystyrene resin waste and the high-molecular-weight polystyrene resin are polystyrene resins. Therefore, this manufacturing method also has the advantage that the resulting recycled polystyrene resin composition has excellent optical properties. When a recycled polystyrene resin composition has "excellent optical properties," it means, for example, that an injection-molded article obtained from the recycled polystyrene resin composition is not opaque.

[0023] (Mixing step) The mixing step is a step of melt-mixing polystyrene-based resin waste and high-molecular-weight polystyrene-based resin, and as a result, a resin composition can be obtained. The resin composition obtained in the mixing step is a recycled polystyrene-based resin composition.

[0024] <Polystyrene-based resin> In the following, this section will describe a polystyrene-based resin that is common to both polystyrene-based resin waste and high-molecular-weight polystyrene-based resin. Therefore, the following embodiments in this section can be applied independently to each of polystyrene-based resin waste and high-molecular-weight polystyrene-based resin.

[0025] The polystyrene-based resin may be (i) a homopolymer composed only of structural units derived from any one monomer selected from the group consisting of styrene-based monomers, (ii) a copolymer composed only of two or more structural units derived from two or more monomers selected from the group consisting of styrene-based monomers, or (iii) a copolymer composed of one or more structural units derived from one or more monomers selected from the group consisting of styrene-based monomers and one or more structural units derived from one or more monomers selected from the group consisting of monomers other than styrene-based monomers that are copolymerizable with the styrene-based monomer.

[0026] Examples of styrene-based monomers include styrene and styrene derivatives, etc. Examples of styrene derivatives include, but are not limited to, α-methylstyrene, p-methylstyrene, m-methylstyrene, o-methylstyrene, t-butylstyrene, and chlorostyrene.

[0027] The monomer other than the styrene-based monomer that is copolymerizable with the styrene-based monomer is not particularly limited, but examples thereof include unsaturated fatty acids, unsaturated fatty acid esters, vinyl cyanide-based monomers, and polyfunctional monomers.

[0028] The unsaturated fatty acid is not particularly limited, but examples thereof include (meth)acrylic acid and maleic anhydride. In this specification, "(meth)acrylic acid" means "acrylic acid and / or methacrylic acid."

[0029] The unsaturated fatty acid ester is not particularly limited, but examples thereof include (meth)acrylates and fumarates.

[0030] Examples of (meth)acrylates include alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, dodecyl (meth)acrylate, stearyl (meth)acrylate, and behenyl (meth)acrylate; and aromatic ring-containing (meth)acrylates such as phenoxyethyl (meth)acrylate and benzyl (meth)acrylate. Examples of suitable (meth)acrylates include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate; glycidyl (meth)acrylates such as glycidyl (meth)acrylate and glycidyl alkyl (meth)acrylate; alkoxyalkyl (meth)acrylates; allyl alkyl (meth)acrylates such as allyl (meth)acrylate and allyl alkyl (meth)acrylate; and polyfunctional (meth)acrylates such as monoethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, and tetraethylene glycol di(meth)acrylate. In this specification, "(meth)acrylate" refers to "acrylate and / or methacrylate." For example, "methyl (meth)acrylate" refers to "methyl acrylate and / or methyl methacrylate."

[0031] The fumarate is not particularly limited, but examples thereof include dimethyl fumarate and diethyl fumarate.

[0032] The vinyl cyanide monomer is not particularly limited, but examples thereof include acrylonitrile and methacrylonitrile.

[0033] A polyfunctional monomer is a monomer having two or more polymerizable unsaturated bonds in its molecule. The polymerizable unsaturated bond is preferably a carbon-carbon double bond (ethylenically unsaturated double bond). The term "polymerizable unsaturated bond" can also be referred to as a "polymerizable unsaturated bond" and refers to an unsaturated bond that can serve as the starting point for a polymerization reaction by radicals or the like. Examples of polyfunctional monomers include (meth)acrylates having an ethylenically unsaturated double bond, such as allyl alkyl (meth)acrylate and allyloxy alkyl (meth)acrylate, and do not include butadiene. Examples of monomers having two (meth)acrylic groups include ethylene glycol di(meth)acrylate, butylene glycol di(meth)acrylate, butanediol di(meth)acrylate, hexanediol di(meth)acrylate, cyclohexanedimethanol di(meth)acrylate, and polyethylene glycol di(meth)acrylate. Examples of the polyethylene glycol di(meth)acrylate include triethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, and polyethylene glycol (600) di(meth)acrylate. Examples of monomers having three (meth)acrylic groups include alkoxylated trimethylolpropane tri(meth)acrylate, glycerol propoxy tri(meth)acrylate, pentaerythritol tri(meth)acrylate, and tris(2-hydroxyethyl)isocyanurate tri(meth)acrylate. Examples of the alkoxylated trimethylolpropane tri(meth)acrylate include trimethylolpropane tri(meth)acrylate and trimethylolpropane triethoxy tri(meth)acrylate. Further, examples of monomers having four (meth)acrylic groups include pentaerythritol tetra(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, etc. Furthermore, examples of monomers having five (meth)acrylic groups include dipentaerythritol penta(meth)acrylate, etc.Furthermore, examples of monomers having six (meth)acrylic groups include ditrimethylolpropane hexa(meth)acrylate, etc. Examples of polyfunctional monomers also include diallyl phthalate, triallyl cyanurate, triallyl isocyanurate, divinylbenzene, etc.

[0034] The polystyrene resin preferably contains 50 mol% or more of styrene units, more preferably 60 mol% or more, more preferably 70 mol% or more, even more preferably 80 mol% or more, still more preferably 90 mol% or more, and particularly preferably 95 mol% or more, of all structural units (100 mol%). The polystyrene resin may contain 100 mol% of styrene units, of all structural units (100 mol%).

[0035] The polystyrene resin preferably contains 50 mol% or more of styrene units, more preferably 60 mol% or more, more preferably 70 mol% or more, even more preferably 80 mol% or more, still more preferably 90 mol% or more, and particularly preferably 95 mol% or more, of all structural units (100 mol%). The polystyrene resin may contain 100 mol% of styrene units, of all structural units (100 mol%).

[0036] Specific examples of polystyrene-based resins include styrene / butadiene copolymers, high-impact polystyrene, styrene / butadiene / styrene block copolymers, hydrogenated styrene / butadiene / styrene block copolymers, and styrene / acrylonitrile copolymers (sometimes referred to as "SAN," "SAN (based) resin," or "AS (based) resin"), acrylonitrile / butadiene / styrene resins (sometimes referred to as "ABS resin"), and styrene / acrylonitrile / α-methylstyrene copolymers.

[0037] The polystyrene resin in the waste and the polystyrene resin used as the high molecular weight resin may have the same composition or different compositions.

[0038] <Polystyrene-based resin waste> "Polystyrene-based resin waste" refers to waste from polystyrene-based resins. More specifically, "polystyrene-based resin waste" refers to (ai) products containing or made of polystyrene-based resins, for example, products that have been used and are to be discarded, or (aii) products that are generated during the manufacturing process of products containing or made of polystyrene-based resins, for example, products that have been removed from their intended use and are to be discarded. The waste (ai) is sometimes referred to as "post-consumer" and the waste (aii) is sometimes referred to as "pre-consumer."

[0039] In this production method, polystyrene-based resin waste is used as a raw material without being discarded. In this specification, "polystyrene-based resin waste" can also be said to be the waste (post-consumer) of (ai) and the waste (pre-consumer) of (aii), which would have been discarded in the past.

[0040] Polystyrene-based resin waste such as the waste (post-consumer) (ai) and the waste (pre-consumer) (aii) may be processed into particles to form resin particles (pellets). In one embodiment of the present invention, resin particles (pellets) obtained by processing polystyrene-based resin waste into particles are also considered to be "polystyrene-based resin waste." In one embodiment of the present invention, resin particles (pellets) obtained by processing polystyrene-based resin waste into particles may be used as "polystyrene-based resin waste." The method for converting polystyrene-based resin waste into particles is not particularly limited, and known methods can be appropriately adopted. For example, particulate polystyrene-based resin waste can be obtained by the following method: (1) shredding or pulverizing polystyrene-based resin waste such as the waste (post-consumer) (ai) and the waste (pre-consumer) (aii) as needed; (2) then melting and mixing the shredded or pulverized material and forming it into particles (pellets). Resin particles (pellets) obtained by processing polystyrene-based resin waste into particles may also be commercially available. In one embodiment of the present invention, resin particles (pellets) obtained by processing polystyrene-based resin waste into particles may be obtained from the market and used as the "polystyrene-based resin waste."

[0041] <Weight-Average Molecular Weight> As mentioned above, polystyrene resins can deteriorate each time they are processed, resulting in a decrease in the weight-average molecular weight of the polystyrene resin. Therefore, polystyrene resin waste tends to have a lower weight-average molecular weight than the polystyrene resins used as raw materials for the products from which they are derived. The weight-average molecular weight of polystyrene resins used as raw materials for common polystyrene resin products such as packaging containers, cushioning materials, insulated containers, and insulating materials is approximately 200,000 to 400,000. Therefore, the weight-average molecular weight of polystyrene resin waste, which is waste from these products, can be, for example, 50,000 to 350,000, 100,000 to 300,000, 100,000 to 250,000, or 100,000 to 200,000. A method for measuring the weight-average molecular weight of polystyrene resin waste will be described in detail in the Examples below.

[0042] <Melt Volume Rate> As mentioned above, polystyrene resins can deteriorate and become lower in molecular weight each time they are processed, which can result in an increase in the melt volume rate of the polystyrene resin. Therefore, polystyrene resin waste tends to have a higher melt volume rate than the polystyrene resins that are the raw materials for the products from which they are derived. The melt volume rate of polystyrene resins, which are the raw materials for general polystyrene resin products such as packaging containers, cushioning materials, heat-insulating containers, and heat-insulating materials, is approximately 5 cm ３ / 10 minutes or more, 20cm ３ Therefore, the melt volume rate of the polystyrene resin waste, which is the waste of these products, is, for example, 10 cm ３ / 10 minutes or more, 40cm ３ / 10 minutes or less, 15cm ３ / 10 minutes or more, 40cm ３ / 10 minutes or less, 20cm ３ / 10 minutes or more, 35cm ３ / 10 minutes or less or 25 cm ３ / 10 minutes or more, 35cm ３ The method for measuring the melt volume rate of the polystyrene-based resin waste will be described in detail in the examples below.

[0043] <Melt Tension> As mentioned above, polystyrene-based resins can deteriorate and become lower in molecular weight each time they are processed, which can result in a decrease in the melt tension of the polystyrene-based resin. Therefore, polystyrene-based resin waste tends to have a lower melt tension than the polystyrene-based resins that are the raw materials for the products from which they are derived. The melt tension of polystyrene-based resins, which are the raw materials for common polystyrene-based resin products such as packaging containers, cushioning materials, insulated containers, and insulating materials, is approximately 0.1 N or more and 0.2 N or less. Therefore, the melt tension of polystyrene-based resin waste, which is waste from these products, can be, for example, 0.01 N or more and 0.18 N or less, 0.03 N or more and 0.18 N or less, or 0.03 N or more and 0.15 N or less. A method for measuring the melt tension of polystyrene-based resin waste will be described in detail in the Examples below.

[0044] <High-molecular-weight polystyrene-based resin> The "high-molecular-weight polystyrene-based resin" is a resin that is melt-mixed together with the polystyrene-based resin waste in the present production method.

[0045] <Weight-Average Molecular Weight> In one embodiment of the present invention, the weight-average molecular weight of the high-molecular-weight polystyrene-based resin is preferably higher than the weight-average molecular weight of the polystyrene-based resin waste. According to this configuration, the present production method can obtain a recycled polystyrene-based resin composition in which physical properties deteriorated by processing are more fully restored. The weight-average molecular weight of the high-molecular-weight polystyrene-based resin is preferably 500,000 or more and 5,000,000 or less, more preferably 500,000 or more and 4,000,000 or less, even more preferably 500,000 or more and 3,500,000 or less, and particularly preferably 700,000 or more and 3,500,000 or less. According to this configuration, the present production method has the advantage of being able to obtain a recycled polystyrene-based resin composition in which physical properties deteriorated by processing are more fully restored. The method for measuring the weight-average molecular weight of the high-molecular-weight polystyrene-based resin will be described in detail in the Examples below.

[0046] In one embodiment of the present invention, the difference obtained by subtracting the weight average molecular weight of the polystyrene resin waste from the weight average molecular weight of the high molecular weight polystyrene resin is not particularly limited, but is preferably 400,000 to 2,500,000, more preferably 500,000 to 2,400,000, and even more preferably 600,000 to 2,350,000. This configuration has the advantage that the present production method can produce a recycled polystyrene resin composition in which the physical properties that have been reduced by processing have been further fully restored.

[0047] In one embodiment of the present invention, when an attempt is made to measure the MVR of a high-molecular-weight polystyrene-based resin by the method described in detail in the Examples below, the viscosity may be too high to be measurable. In one embodiment of the present invention, it is preferable that the MVR of a high-molecular-weight polystyrene-based resin is not measurable by the method described in detail in the Examples below.

[0048] In one embodiment of the present invention, the shape of the high-molecular-weight polystyrene-based resin is not particularly limited, and may be, for example, particulate. When the high-molecular-weight polystyrene-based resin is particulate, the high-molecular-weight polystyrene-based resin may have a layer structure. The high-molecular-weight polystyrene-based resin may have, for example, a single-layer structure or a multi-layer structure of two or three or more layers.

[0049] The method for producing the high molecular weight polystyrene resin is not particularly limited, and examples thereof include emulsion polymerization, suspension polymerization, and bulk polymerization.

[0050] <Amount Used> In this production method, the amount of high-molecular-weight polystyrene-based resin used is not particularly limited. In this production method, the smaller the amount of high-molecular-weight polystyrene-based resin used in the total amount of polystyrene-based resin waste and high-molecular-weight polystyrene-based resin, the greater the amount of polystyrene-based resin waste used, which is preferable. In this production method, the amount of high-molecular-weight polystyrene-based resin used is preferably 50% by weight or less, more preferably less than 50% by weight, more preferably 40% by weight or less, more preferably 30% by weight or less, even more preferably 25% by weight or less, even more preferably 20% by weight or less, and particularly preferably 15% by weight or less, based on 100% by weight of the total of polystyrene-based resin waste and high-molecular-weight polystyrene-based resin. The amount of high-molecular-weight polystyrene-based resin used in this production method can also be said to be the content of high-molecular-weight polystyrene-based resin in the resulting recycled polystyrene-based resin composition.

[0051] As described above, a conventional technique for recycling polystyrene-based resin waste involves melt-mixing the polystyrene-based resin waste with virgin polystyrene-based resin. In the conventional technique, more than 50 wt% of virgin polystyrene-based resin is often used out of a total of 100 wt% of the polystyrene-based resin waste and virgin polystyrene-based resin. In other words, the recycling rate in the conventional technique is low. However, even in recycled polystyrene-based resin compositions obtained using 50 wt% or more of virgin polystyrene-based resin, the physical properties deteriorated by processing are not fully restored. However, according to the present production method, even when, for example, 1 wt% of high-molecular-weight polystyrene-based resin is used out of a total of 100 wt% of the polystyrene-based resin waste and the high-molecular-weight polystyrene-based resin, a recycled polystyrene-based resin composition can be obtained in which the physical properties deteriorated by processing are fully restored. In other words, according to this production method, even when, for example, 99% by weight of the polystyrene resin waste is used out of a total of 100% by weight of the polystyrene resin waste and the high molecular weight polystyrene resin, a recycled polystyrene resin composition can be obtained in which the physical properties deteriorated by processing have been fully restored. That is, the method for producing a recycled polystyrene resin composition according to a preferred embodiment of the present invention also has the advantage of a high recycling rate. In this production method, the lower limit of the amount of high molecular weight polystyrene resin used may be 1% by weight or more, 2% by weight or more, 3% by weight or more, 4% by weight or more, 5% by weight or more, 6% by weight or more, 7% by weight or more, 8% by weight or more, 9% by weight or more, or 10% by weight or more out of a total of 100% by weight of the polystyrene resin waste and the high molecular weight polystyrene resin.

[0052] <Apparatus> In the mixing step, the apparatus used to melt-mix the polystyrene-based resin waste and the high-molecular-weight polystyrene-based resin is not particularly limited. Examples of the apparatus include an extruder, a Banbury mixer, and a kneader. Examples of the extruder include a single-screw extruder and a multi-screw extruder such as a twin-screw extruder. In the case of a multi-screw extruder, the multiple screws may or may not intermesh. In the case of a multi-screw extruder, the multiple screws may rotate in the same direction or in opposite directions.

[0053] In the mixing step, the conditions for melt-mixing the polystyrene-based resin waste and the high-molecular-weight polystyrene-based resin are not particularly limited, and general conditions for melt-mixing resins may be appropriately adopted. The temperature for melt-mixing the polystyrene-based resin waste and the high-molecular-weight polystyrene-based resin may be, for example, 170°C or higher and 270°C or lower, or 200°C or higher and 250°C or lower. The "temperature for melt-mixing the polystyrene-based resin waste and the high-molecular-weight polystyrene-based resin" refers to the set temperature of the extruder's cylinder (barrel), for example, when an extruder is used as the device. The time for melt-mixing the polystyrene-based resin waste and the high-molecular-weight polystyrene-based resin may be, for example, 1 minute or longer and 5 minutes or shorter, or 1 minute or longer and 3 minutes or shorter. The "time for melt-mixing the polystyrene-based resin waste and the high-molecular-weight polystyrene-based resin" refers to the time for which the polystyrene-based resin waste and the high-molecular-weight polystyrene-based resin are present in the extruder, for example, when an extruder is used as the device.

[0054] (Selection Step) In this production method, the amount of high-molecular-weight polystyrene resin used is preferably set (selected) appropriately based on the amount of polystyrene resin waste used, its weight-average molecular weight, and physical properties (e.g., melt volume rate and melt tension), and / or the weight-average molecular weight and physical properties of the high-molecular-weight polystyrene resin used. This configuration has the advantage that the production method can provide a recycled polystyrene resin composition in which physical properties deteriorated by processing are more fully restored. Furthermore, in this production method, the weight-average molecular weight and physical properties of the high-molecular-weight polystyrene resin used are preferably set (selected) appropriately based on the amount of polystyrene resin waste used, its weight-average molecular weight, and physical properties (e.g., melt volume rate and melt tension), and / or the amount of high-molecular-weight polystyrene resin used. In other words, it is preferable to appropriately select the high-molecular-weight polystyrene-based resin to be used from a plurality of high-molecular-weight polystyrene-based resins having different weight-average molecular weights and physical properties, etc., depending on the amount of polystyrene-based resin waste used, the weight-average molecular weight and physical properties, and / or the amount of high-molecular-weight polystyrene-based resin used, etc. According to this configuration, the present production method has the advantage of being able to provide a recycled polystyrene-based resin composition in which the physical properties that have been reduced by processing have been more fully restored.

[0055] In one embodiment of the present invention, it is preferable to further include a selection step of selecting one or more of the weight average molecular weight and the amount of the high molecular weight polystyrene-based resin based on one or more of the weight average molecular weight, melt volume rate, and melt tension of the polystyrene-based resin waste before the mixing step. This configuration has the advantage of being able to provide a recycled polystyrene-based resin composition in which the physical properties that have been reduced by processing are further fully restored.

[0056] In the selection step, "selecting the weight-average molecular weight of the high-molecular-weight polystyrene resin" refers to examining what weight-average molecular weight of high-molecular-weight polystyrene resin is suitable or optimal for obtaining a recycled polystyrene resin composition in which the physical properties deteriorated by processing have been sufficiently restored, and selecting (determining) a high-molecular-weight polystyrene resin with a specific weight-average molecular weight (within a specific range) that is deemed suitable or optimal from among various high-molecular-weight polystyrene resins with different weight-average molecular weights. Furthermore, in the selection step, "selecting the amount of high-molecular-weight polystyrene resin to be used" refers to examining what amount of high-molecular-weight polystyrene resin is suitable or optimal for obtaining a recycled polystyrene resin composition in which the physical properties deteriorated by processing have been sufficiently restored, and selecting (determining) the amount of high-molecular-weight polystyrene resin to be used.

[0057] In the selection step, when both the weight average molecular weight and the amount used of the high-molecular-weight polystyrene-based resin are selected, the weight average molecular weight of the high-molecular-weight polystyrene-based resin may be selected first, and then the amount used of the high-molecular-weight polystyrene-based resin may be further selected while also taking into consideration the weight average molecular weight of the high-molecular-weight polystyrene-based resin.

[0058] The weight-average molecular weight and physical properties (e.g., melt volume rate and melt tension) of polystyrene-based resin waste can vary significantly depending on the number of times it has been processed (e.g., the number of times it has been recycled). Therefore, multiple types of polystyrene-based resin waste with significantly different weight-average molecular weights and physical properties are circulating on the market. Therefore, the weight-average molecular weight and physical properties of the polystyrene-based resin waste used are not necessarily constant each time the present production method is performed. When the present production method includes a selection step, selecting the weight-average molecular weight and / or amount of high-molecular-weight polystyrene-based resin depending on the weight-average molecular weight and / or physical properties of the polystyrene-based resin waste used has the advantage of providing a recycled polystyrene-based resin composition in which the physical properties reduced by processing are fully restored without being significantly affected by the weight-average molecular weight and physical properties of the polystyrene-based resin waste used. Furthermore, when selecting the amount of high-molecular-weight polystyrene-based resin used in the selection step, excessive and / or insufficient use of the high-molecular-weight polystyrene-based resin can be avoided.

[0059] The melt volume rate (MVR) of polystyrene-based resin waste will be described. The more high-molecular-weight polystyrene-based resin is used, the lower the MVR of the resulting recycled polystyrene-based resin composition. For example, for every 5 wt% increase in the amount of high-molecular-weight polystyrene-based resin with a weight-average molecular weight of 500,000 or more used, based on a total of 100 wt% of the polystyrene-based resin waste and the high-molecular-weight polystyrene-based resin, the MVR of the recycled polystyrene-based resin composition can be reduced by approximately 20%. For example, consider a case where the MVR of the polystyrene-based resin waste used is 25, and a recycled polystyrene-based resin composition with an MVR of 15 is to be obtained. In this case, the MVR can be reduced by approximately 40%. Therefore, the high-molecular-weight polystyrene-based resin with a molecular weight of 500,000 or more can be used in an amount of approximately 10 wt% based on a total of 100 wt% of the polystyrene-based resin waste and the high-molecular-weight polystyrene-based resin.

[0060] The melt tension of polystyrene-based resin waste will now be described. The greater the amount of high-molecular-weight polystyrene-based resin used, the higher the melt tension of the resulting recycled polystyrene-based resin composition. For example, if the amount of high-molecular-weight polystyrene-based resin with a weight-average molecular weight of 1.9 million or more used is (i) 5% by weight, based on a total of 100% by weight of the polystyrene-based resin waste and the high-molecular-weight polystyrene-based resin, the melt tension of the resulting recycled polystyrene-based resin composition can be approximately twice the melt tension of the polystyrene-based resin waste used. If (ii) 10% by weight is used, the melt tension of the resulting recycled polystyrene-based resin composition can be approximately three times the melt tension of the polystyrene-based resin waste used. Furthermore, for example, if the amount of high-molecular-weight polystyrene-based resin with a weight-average molecular weight of 500,000 or more and 1,500,000 or less is (i) 5 wt% based on a total of 100 wt% of the polystyrene-based resin waste and the high-molecular-weight polystyrene-based resin, the melt tension of the resulting recycled polystyrene-based resin composition can be approximately 1.5 times that of the polystyrene-based resin waste used. (ii) If the amount is 10 wt%, the melt tension of the resulting recycled polystyrene-based resin composition can be approximately 2.5 times that of the polystyrene-based resin waste used. For example, consider the case where the melt tension of the polystyrene-based resin waste used is 0.10 N, and a recycled polystyrene-based resin composition with a melt tension of 0.15 N is obtained. In this case, it is sufficient to improve the melt tension by approximately 50%. Therefore, out of a total of 100% by weight of polystyrene resin waste and high molecular weight polystyrene resin, (i) 3.5% by weight of high molecular weight polystyrene resin having a weight average molecular weight of 1,900,000 or more may be used, or (ii) 5% by weight of high molecular weight polystyrene resin having a weight average molecular weight of 500,000 or more and 1,500,000 or less may be used.

[0061] As described above, by selecting one or more factors selected from the group consisting of the weight average molecular weight and the amount used of the high molecular weight polystyrene resin to be used in accordance with one or more factors selected from the group consisting of the melt volume rate and melt tension of the polystyrene resin waste to be used, it is possible to adjust the processability and / or physical properties of the resulting recycled polystyrene resin composition.

[0062] (Measurement Process) As described above, multiple types of polystyrene-based resin waste with significantly different weight-average molecular weights and physical properties are available on the market. The weight-average molecular weight and physical properties of the polystyrene-based resin waste available on the market may not be disclosed. If the weight-average molecular weight and / or physical properties (e.g., melt volume rate and melt tension) of the polystyrene-based resin waste to be used are unknown, the weight-average molecular weight and / or physical properties of the polystyrene-based resin waste to be used may be measured before the selection process. For example, in one embodiment of the present invention, the mixing process may further include a measurement process for measuring one or more selected from the group consisting of the weight-average molecular weight, melt volume rate, and melt tension of the polystyrene-based resin waste. When the present production method further includes a measurement process, the amount and / or physical properties of the high-molecular-weight polystyrene-based resin to be used can be appropriately selected based on the measurement results. As a result, the present production method has the advantage of being able to provide a recycled polystyrene-based resin composition in which physical properties deteriorated by processing are further fully restored.

[0063] When the above-mentioned selection step is carried out, it is preferable that the selection step is carried out after the measurement step. When the present production method includes the measurement step and the selection step, even if the weight average molecular weight and / or physical properties of the polystyrene-based resin waste to be used are unknown, the weight average molecular weight and / or amount of the high-molecular-weight polystyrene-based resin can be appropriately selected according to the weight average molecular weight and / or physical properties of the polystyrene-based resin waste to be used. As a result, the present production method has the advantage of being able to provide a recycled polystyrene-based resin composition in which the physical properties deteriorated by processing are further fully restored.

[0064] In this production method, for example, a virgin polystyrene-based resin may be further used in the mixing step. Furthermore, in this production method, various additives such as flame retardants, blowing agents, foam nuclei, dispersants, and pigments may also be used depending on the desired purpose. That is, a method for producing a recycled polystyrene-based resin composition according to one embodiment of the present invention includes a mixing step of melt-mixing polystyrene-based resin waste, a high-molecular-weight polystyrene-based resin, and optionally virgin polystyrene-based resin and optional additives (e.g., flame retardants, blowing agents, foam nuclei, dispersants, pigments, etc.) to obtain a resin composition, and the weight-average molecular weight of the high-molecular-weight polystyrene-based resin may be 500,000 or more and 5,000,000 or less.

[0065] [3. Recycled Polystyrene Resin Composition] A recycled polystyrene resin composition according to one embodiment of the present invention contains polystyrene resin waste and a high-molecular-weight polystyrene resin, and the recycled polystyrene resin composition contains 3.0% or more of a resin having a molecular weight of 700,000 or more.

[0066] In this specification, the "recycled polystyrene resin composition according to one embodiment of the present invention" may also be referred to as the "composition."

[0067] Because the present composition has the above-mentioned structure, it has the advantage that the physical properties of the polystyrene-based resin waste contained in the recycled polystyrene-based resin composition that have been reduced by processing are fully restored. In other words, because the present composition has the above-mentioned structure, it has the advantage that it can have better physical properties than the physical properties of the polystyrene-based resin waste contained in the recycled polystyrene-based resin composition.

[0068] The present composition is, for example, a recycled polystyrene-based resin composition obtained by the present production method described in the above section [2. Method for Producing a Recycled Polystyrene-Based Resin Composition]. As described above, the present production method uses a high-molecular-weight polystyrene-based resin. When the present composition is a recycled polystyrene-based resin composition obtained by the present production method, the composition may contain a high-molecular-weight polystyrene-based resin. The high-molecular-weight polystyrene-based resin that can be contained in the present composition may have a weight-average molecular weight higher than that of polystyrene-based resin waste. Through extensive research, the present inventors discovered that recycled polystyrene-based resin compositions obtained using high-molecular-weight polystyrene-based resins contain an increased proportion of resins with high weight-average molecular weights. For example, the recycled polystyrene-based resin composition obtained by the present production method, i.e., the present composition, contains 3.0% or more of resin with a molecular weight of 700,000 or more. In other words, polystyrene-based resins, polystyrene-based resin compositions, or recycled polystyrene-based resin compositions containing 3.0% or more of resin with a molecular weight of 700,000 or more can be considered to contain a high-molecular-weight polystyrene-based resin. Here, "containing 3.0% or more of resins with a molecular weight of 700,000 or more" means that in the integrated molecular weight distribution obtained by integrating the molecular weight distribution measured by gel permeation chromatography (GPC) of the recycled polystyrene resin composition, the proportion of resins with a molecular weight of 700,000 or more is 3.0% or more. The method for calculating the proportion of resins with a molecular weight of 700,000 or more contained in the recycled polystyrene resin composition by GPC measurement will be explained in detail in the Examples below.

[0069] The higher the proportion of resins with a molecular weight of 700,000 or more in the composition, the greater the amount of high-molecular-weight polystyrene-based resin used in the production of the composition, i.e., in the production method. In one embodiment of the present invention, the higher the proportion of resins with a molecular weight of 700,000 or more in the composition, the better the physical properties of the composition will be compared to those of the polystyrene-based resin waste contained in the recycled polystyrene-based resin composition. The composition preferably contains 3.0% or more of resins with a molecular weight of 700,000 or more, more preferably 3.3% or more, even more preferably 3.5% or more, and particularly preferably 3.8% or more.

[0070] The upper limit of the proportion of resins having a molecular weight of 700,000 or more in this composition can be appropriately set depending on the desired physical properties of the resulting recycled polystyrene-based resin composition, taking into account the foaming application, etc. In one embodiment of the present invention, the composition preferably contains 15.0% or less, more preferably 13.0% or less, even more preferably 10.0% or less, and particularly preferably 8.0% or less, of resins having a molecular weight of 700,000 or more. This configuration has the advantage that the resulting recycled polystyrene-based resin composition has good foaming properties.

[0071] Regarding matters relating to the present composition other than those mentioned above (e.g., polystyrene resin waste and high-molecular-weight polystyrene resin), the description in the above section [2. Method for producing recycled polystyrene resin composition] is appropriately incorporated by reference. The amount of high-molecular-weight polystyrene resin used described in the above section [2. Method for producing recycled polystyrene resin composition] can also be read as the content of high-molecular-weight polystyrene resin in the present composition.

[0072] A molded article can be obtained by molding this composition. A molded article obtained by molding this composition can also be said to be one embodiment of the present invention. In other words, a molded article according to one embodiment of the present invention is obtained by molding the recycled polystyrene-based resin composition according to one embodiment of the present invention. It can also be said that a molded article according to one embodiment of the present invention contains the recycled polystyrene-based resin composition according to one embodiment of the present invention.

[0073] The method for molding the composition, in other words, the method for producing the molded article according to one embodiment of the present invention, is not particularly limited. For example, the molded article according to one embodiment of the present invention can be obtained by molding the composition by known methods such as injection molding, blow molding, extrusion molding, and injection blow molding.

[0074] The composition may further contain a virgin polystyrene-based resin. Furthermore, the composition may further contain various additives such as a flame retardant, a blowing agent, a foam core material, a dispersant, and a pigment, depending on the desired purpose. That is, a recycled polystyrene-based resin composition according to one embodiment of the present invention contains polystyrene-based resin waste, a high-molecular-weight polystyrene-based resin, optionally a virgin polystyrene-based resin, and optionally an additive (e.g., a flame retardant, a blowing agent, a foam core material, a dispersant, a pigment, etc.), and the recycled polystyrene-based resin composition may contain 3.0% or more of a resin having a molecular weight of 700,000 or more.

[0075] An embodiment of the present invention may include the following configuration.

[0076] [1] A method for producing a recycled polystyrene-based resin composition, comprising a mixing step of melt-mixing polystyrene-based resin waste and a high-molecular-weight polystyrene-based resin to obtain a resin composition, wherein the weight-average molecular weight of the high-molecular-weight polystyrene-based resin is 500,000 or more and 5,000,000 or less.

[0077] [2] The method for producing the recycled polystyrene-based resin composition described in [1], further comprising a measurement step of measuring one or more selected from the group consisting of the weight average molecular weight, melt volume rate, and melt tension of the polystyrene-based resin waste before the mixing step.

[0078] [3] The method for producing a recycled polystyrene-based resin composition according to [1] or [2] further comprises, before the mixing step, a selection step of selecting one or more selected from the group consisting of the weight average molecular weight and the amount used of the high molecular weight polystyrene-based resin based on one or more selected from the group consisting of the weight average molecular weight, melt volume rate, and melt tension of the polystyrene-based resin waste.

[0079] [4] The method for producing a recycled polystyrene-based resin composition according to any one of [1] to [3], wherein the amount of the high-molecular-weight polystyrene-based resin used is 50% by weight or less, based on a total of 100% by weight of the polystyrene-based resin waste and the high-molecular-weight polystyrene-based resin.

[0080] [5] A method for producing a recycled polystyrene-based resin composition described in any one of [1] to [4], wherein the weight average molecular weight of the polystyrene-based resin waste is 100,000 or more and 250,000 or less.

[0081] [6] A method for producing a recycled polystyrene-based resin composition according to any one of [1] to [5], wherein the difference obtained by subtracting the weight-average molecular weight of the polystyrene-based resin waste from the weight-average molecular weight of the high-molecular-weight polystyrene-based resin is 400,000 or more and 2,500,000 or less.

[0082] [7] A recycled polystyrene-based resin composition comprising polystyrene-based resin waste and a high-molecular-weight polystyrene-based resin, wherein the recycled polystyrene-based resin composition contains 3.0% or more of a resin having a molecular weight of 700,000 or more.

[0083] [8] The recycled polystyrene resin composition according to [7], wherein the recycled polystyrene resin composition contains 3.5% or more of a resin having a molecular weight of 700,000 or more.

[0084] [9] The recycled polystyrene resin composition according to [7] or [8], wherein the weight average molecular weight of the high molecular weight polystyrene resin is 500,000 or more and 5,000,000 or less.

[0085]

[10] The recycled polystyrene-based resin composition according to any one of [7] to [9], wherein the recycled polystyrene-based resin composition contains 50% by weight or less of the high-molecular-weight polystyrene-based resin in a total of 100% by weight of the polystyrene-based resin waste and the high-molecular-weight polystyrene-based resin.

[0086]

[11] A recycled polystyrene resin composition according to any one of [7] to

[10] , wherein the weight average molecular weight of the polystyrene resin waste is 100,000 or more and 250,000 or less.

[0087]

[12] A recycled polystyrene-based resin composition according to any one of [7] to

[11] , wherein the difference obtained by subtracting the weight-average molecular weight of the polystyrene-based resin waste from the weight-average molecular weight of the high-molecular-weight polystyrene-based resin is 400,000 or more and 2,500,000 or less.

[0088]

[13] A molded article obtained by molding the recycled polystyrene resin composition according to any one of [7] to

[12] .

[0089] Hereinafter, one embodiment of the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited thereto. One embodiment of the present invention can be carried out by appropriately modifying the following examples within the scope of the above and below-described aims. All embodiments carried out by appropriately modifying the following examples are included within the technical scope of the present invention.

[0090] <Measurement Methods and Evaluation Methods> Measurement methods and evaluation methods are shown below.

[0091] (Polymerization Conversion Rate of High-Molecular-Weight Polystyrene-Based Resin) A portion of the high-molecular-weight polystyrene-based resin latex was sampled, and the weight of the latex was precisely weighed, and the obtained value was taken as the "latex amount." Next, the precisely weighed latex was dried in a hot air dryer at 120°C for 1 hour. The weight of the obtained dried product was precisely weighed, and the obtained value was taken as the "solid content amount." Next, the solid content amount was divided by the latex amount, and the obtained quotient was taken as the "solid component ratio" in the latex. Finally, the polymerization conversion rate was calculated by the following formula: Polymerization conversion rate = (total weight of charged raw materials × solid component ratio - total weight of raw materials other than water and monomers) / charged monomer weight × 100 (%).

[0092] (Weight-average molecular weight and proportion of resins with a molecular weight of 700,000 or more) The pellet-shaped recycled polystyrene resin composition obtained in the examples and comparative examples was dissolved in tetrahydrofuran (THF) to obtain a THF-soluble portion of the recycled polystyrene resin composition. Also, unused polystyrene resin, polystyrene resin waste, and acrylic resin were each dissolved in tetrahydrofuran (THF) to obtain the THF-soluble portion of the unused polystyrene resin, polystyrene resin waste, and acrylic resin. Also, white resin powder of high molecular weight polystyrene resin was dissolved in tetrahydrofuran (THF) to obtain the THF-soluble portion of the high molecular weight polystyrene resin. These obtained THF-soluble portions were used as samples and subjected to GPC measurement using polystyrene as a reference material using gel permeation chromatography (Tosoh Corporation, HLC-8220GPC) to measure the weight-average molecular weight. For the recycled polystyrene resin composition, the molecular weight distribution of the recycled polystyrene resin composition was further obtained by the GPC measurement, and the molecular weight distribution was integrated to obtain an integrated molecular weight distribution. From the obtained integrated molecular weight distribution, the proportion of resins with a molecular weight of 700,000 or more contained in the recycled polystyrene resin composition was calculated. The measurement conditions for the GPC measurement were as follows: mobile phase: THF, column: Tosoh TSKgelSuper HZM-H, sample solution: 20 mg sample / 10 mL THF, measurement temperature: 25°C, detector: differential refractive index system, injection volume: 1 mL.

[0093] (MVR) The pellet-shaped recycled polystyrene resin compositions obtained in the examples and comparative examples were dried in a dryer at 80°C for 4 hours. The resulting dried products were used as samples and measured for MVR values ​​(cm) in accordance with ISO 1133-1 at a measurement temperature of 200°C and a load of 5 kg. ３ / 10 min) was measured.

[0094] The MVRs of the unused polystyrene resin C-1 and the polystyrene resin waste were measured by the same method and under the same conditions as the above-mentioned method for measuring the MVR of the recycled polystyrene resin composition, except that each resin was used as a sample instead of the dried product of the recycled polystyrene resin composition. The MVR of the high molecular weight polystyrene resin was measured by the same method and under the same conditions as the above-mentioned method for measuring the MVR of the recycled polystyrene resin composition, except that a white resin powder of the high molecular weight polystyrene resin was used as a sample instead of the dried product of the recycled polystyrene resin composition.

[0095] (Melt Tension) The pellet-shaped recycled polystyrene resin compositions obtained in the Examples and Comparative Examples were dried in a dryer at 80°C for 4 hours. The resulting dried material was used as a sample and the melt tension was measured under the following measurement conditions. The melt tension value was determined as the value at a take-up speed of 500 mm / sec under the following measurement conditions. Apparatus name: RHEOGRPH 25 manufactured by GOTTFERT Measurement temperature: 175°C Extrusion speed: piston speed 0.22 mm / sec Take-up speed: from 10 mm / sec to 1000 mm / sec Wheel acceleration: 12 mm / sec ２ Cylinder diameter: 15 mm Capillary die length: 20 mm Capillary die diameter: 2 mm.

[0096] The melt tensions of the unused polystyrene resin C-1 and the polystyrene resin waste were measured in the same manner and under the same conditions as the method for measuring the melt tension of the recycled polystyrene resin composition described above, except that each resin was used as a sample instead of the dried recycled polystyrene resin composition.

[0097] (Test Piece (Molded Body) Preparation Conditions) The pellet-shaped recycled polystyrene resin composition obtained in the Examples and Comparative Examples was dried in a vacuum dryer at 70 ° C. for 4 hours to sufficiently reduce the moisture content. In addition, unused polystyrene resin (C-1) or polystyrene resin waste (A-1 to A-3) was dried in a vacuum dryer at 70 ° C. for 4 hours to sufficiently reduce the moisture content. Subsequently, the dried recycled polystyrene resin composition, unused polystyrene resin (C-1) and polystyrene resin waste (A-1 to A-3) were each molded using an injection molding machine (e-mac 50 manufactured by ENGEL) to prepare a molded body (test piece) with a thickness of 3.0 mm. The temperature conditions were: nozzle temperature 220 ° C, cylinder temperature 225 ° C, 220 ° C, 210 ° C from the side closest to the nozzle, and mold temperature 40 ° C. The test pieces obtained from the recycled polystyrene resin composition in this manner can also be considered as molded articles of the recycled polystyrene resin composition. Therefore, the test pieces obtained by injection molding the recycled polystyrene resin compositions of Examples 1 to 14 can also be considered as molded articles according to one embodiment of the present invention.

[0098] (YI and Haze) The yellow index (YI) and transparency (haze) of the 3.0 mm thick test specimen obtained in the above section (Test Specimen (Molded Article) Preparation Conditions) were measured in an absolute dry state at 23° C. The measuring instrument used was an UltraScan VIS Spectrophotometer manufactured by HunterLab.

[0099] <Materials> The materials used in the Examples, Comparative Examples, and Reference Examples are listed below.

[0100] (Polystyrene-based resin) C-1: Polystyrene-based resin (Styron™ 678E, manufactured by Trinseo Corporation) C-1 can be said to be a "virgin polystyrene-based resin" or a "virgin polystyrene-based resin."

[0101] (Polystyrene-based resin waste) A-1: ​​Resin particles (pellets) obtained by subjecting C-1 to an extruder once and melt-mixing it at 210° C. or higher and 220° C. or lower.

[0102] A-2: Resin particles (pellets) obtained by feeding the resin particles of A-1 again into an extruder and melt-mixing them at 210°C or higher and 220°C or lower. A-2 can also be said to be resin particles (pellets) obtained by feeding C-1 twice into an extruder and melt-mixing them at 210°C or higher and 220°C or lower. A-2 can also be said to be the "polystyrene-based resin before processing" compared to A-3 below.

[0103] A-3: Resin particles (pellets) obtained by subjecting the resin particles of A-2 to an extruder again and melt-mixing at 210° C. or higher and 220° C. or lower. A-3 can also be said to be resin particles (pellets) obtained by subjecting C-1 to an extruder a third time and melt-mixing at 210° C. or higher and 220° C. or lower.

[0104] A-4: Resin particles (pellets) obtained by subjecting the resin particles of A-3 to an extruder again and melt-mixing at 210°C or higher and 220°C or lower. A-4 can also be said to be resin particles (pellets) obtained by subjecting C-1 to an extruder a fourth time and melt-mixing at 210°C or higher and 220°C or lower. A-4 can also be said to be the "polystyrene-based resin before processing" for A-5 below.

[0105] A-5: Resin particles (pellets) obtained by subjecting the resin particles of A-4 to an extruder again and melt-mixing at 210° C. or higher and 220° C. or lower. A-5 can also be said to be resin particles (pellets) obtained by subjecting C-1 to an extruder five times and melt-mixing at 210° C. or higher and 220° C. or lower.

[0106] A twin-screw extruder (ZE 25Ax49D manufactured by Krauss Maffei) was used for melt mixing during the production of polystyrene-based resin waste. The temperatures of the extruder during melt mixing were as follows: C1 / C2 / C3 / C4 / C5 / C6 / C7 / C8 / C9 / C10 / ADAPTER / DIE = 40 / 210 / 210 / 210 / 210 / 210 / 210 / 210 / 220 / 220 / 220°C. The screw rotation speed of the extruder was 200 rpm.

[0107] (High-Molecular-Weight Polystyrene Resin) White resin powders B-1 to B-5 of high-molecular-weight polystyrene resin obtained by the production method described below were used.

[0108] (Acrylic resins) D-1: Acrylic copolymer (a copolymer of 40% by weight of methyl methacrylate, 21.3% by weight of butyl acrylate, and 38.7% by weight of styrene, with a weight-average molecular weight of 432,000). D-2: Acrylic copolymer (a copolymer of 87% by weight of methyl methacrylate and 13% by weight of butyl acrylate, with a weight-average molecular weight of 946,000). D-3: Acrylic copolymer (a copolymer of 80.5% by weight of methyl methacrylate and 19.5% by weight of butyl acrylate, with a weight-average molecular weight of 2,315,000). D-4: Acrylic copolymer (a copolymer of 77% by weight of methyl methacrylate and 23% by weight of butyl acrylate, with a weight-average molecular weight of 5,900,000). The weight-average molecular weights of the acrylic resins were measured using the method described above.

[0109] <Production of High Molecular Weight Polystyrene Resins> The following describes the production methods for High Molecular Weight Polystyrene Resins 1 (B-1) to 5 (B-5). A glass reactor equipped with a thermometer, a stirrer, a reflux condenser, a nitrogen inlet, and a device for adding monomers and an emulsifier was used as the production equipment. Table 1 shows the types and amounts of monomers and initiators used.

[0110] (High Molecular Weight Polystyrene Resin 1 (B-1)) A glass reactor was charged with 140 parts by weight of deionized water, 0.03 parts by weight of sodium carbonate, and 0.5 parts by weight of dioctyl sodium sulfosuccinate. While stirring the charged raw materials in a nitrogen stream, the temperature inside the glass reactor was raised to 80°C. Next, a first monomer mixture shown in Table 1 was added to the glass reactor over 5 minutes. One minute after the addition of the first monomer mixture was completed, 0.0008 parts by weight of disodium ethylenediaminetetraacetate, 0.0002 parts by weight of ferrous sulfate, and 0.05 parts by weight of sodium formaldehyde sulfoxylate were charged to the glass reactor. A seed layer (first layer) was formed by a 20-minute post-reaction.

[0111] Next, 0.2 parts by weight of dioctyl sodium sulfosuccinate was charged into the glass reactor. Subsequently, the second monomer mixture shown in Table 1 was added to the glass reactor over 150 minutes. After the start of the addition of the second monomer mixture, 0.1 parts by weight of dioctyl sodium sulfosuccinate was added to the glass reactor four times (at 20, 40, 60, and 80 minutes) every 20 minutes. Immediately after the completion of the addition of the second monomer mixture (150 minutes after the start of the addition of the second monomer mixture), 0.005 parts by weight of cumene hydroperoxide was added to the glass reactor. A 40-minute post-reaction allowed to occur, forming an intermediate layer (second layer).

[0112] Next, a third monomer mixture shown in Table 1 was added to the glass reactor over 45 minutes. A third layer was formed by a post-reaction for 60 minutes, and a latex containing high-molecular-weight polystyrene-based resin 1 was obtained. The polymerization conversion rate after polymerization was 99.7%.

[0113] Subsequently, the latex was diluted with deionized water so that the solid content of the obtained latex was 25%. Next, the diluted latex was spray-dried under the conditions of a hot air inlet temperature of 135°C, an outlet temperature of 60°C, and an atomizer rotation speed of 17,000 rpm, to obtain a white resin powder (B-1) of high-molecular-weight polystyrene-based resin 1.

[0114] The weight average molecular weight of the obtained white resin powder (B-1) of high molecular weight polystyrene-based resin 1 was measured by the method described above. The weight average molecular weight of high molecular weight polystyrene-based resin 1 was 1,926,000.

[0115] (High Molecular Weight Polystyrene Resin 2 (B-2)) A glass reactor was charged with 140 parts by weight of deionized water, 0.03 parts by weight of sodium carbonate, and 0.5 parts by weight of dioctyl sodium sulfosuccinate. While stirring the charged raw materials in a nitrogen stream, the temperature inside the glass reactor was raised to 80°C. Next, a first monomer mixture shown in Table 1 was added to the glass reactor over 5 minutes. One minute after the addition of the first monomer mixture was completed, 0.0008 parts by weight of disodium ethylenediaminetetraacetate, 0.0002 parts by weight of ferrous sulfate, and 0.05 parts by weight of sodium formaldehyde sulfoxylate were charged to the glass reactor. A seed layer (first layer) was formed by a 20-minute post-reaction.

[0116] Next, 0.2 parts by weight of dioctyl sodium sulfosuccinate was charged into the glass reactor. Subsequently, the second monomer mixture shown in Table 1 was added to the glass reactor over 150 minutes. After the start of the addition of the second monomer mixture, 0.1 parts by weight of dioctyl sodium sulfosuccinate was added to the glass reactor four times (at 20, 40, 60, and 80 minutes) every 20 minutes. Immediately after the completion of the addition of the second monomer mixture (150 minutes after the start of the addition of the second monomer mixture), 0.005 parts by weight of cumene hydroperoxide was added to the glass reactor. A 40-minute post-reaction allowed to occur, forming an intermediate layer (second layer).

[0117] Next, a third monomer mixture shown in Table 1 was added to the glass reactor over 45 minutes. A third layer was formed by a post-reaction for 60 minutes, and a latex containing high-molecular-weight polystyrene-based resin 2 was obtained. The polymerization conversion rate after polymerization was 99.9%.

[0118] Subsequently, a white resin powder (B-2) of high molecular weight polystyrene-based resin 2 was obtained by spray drying in the same manner as described in the section <High molecular weight polystyrene-based resin 1 (B-1)> above.

[0119] The weight average molecular weight of the obtained white resin powder (B-2) of high molecular weight polystyrene-based resin 2 was measured by the method described above. The weight average molecular weight of high molecular weight polystyrene-based resin 2 was 2,492,000.

[0120] (High Molecular Weight Polystyrene Resin 3 (B-3)) A glass reactor was charged with 140 parts by weight of deionized water, 0.03 parts by weight of sodium carbonate, and 0.5 parts by weight of dioctyl sodium sulfosuccinate. While stirring the charged raw materials in a nitrogen stream, the temperature inside the glass reactor was raised to 80°C. Next, a first monomer mixture shown in Table 1 was added to the glass reactor over 5 minutes. One minute after the addition of the first monomer mixture was completed, 0.0008 parts by weight of disodium ethylenediaminetetraacetate, 0.0002 parts by weight of ferrous sulfate, and 0.05 parts by weight of sodium formaldehyde sulfoxylate were charged to the glass reactor. A seed layer (first layer) was formed by a 20-minute post-reaction.

[0121] Next, 0.2 parts by weight of dioctyl sodium sulfosuccinate was charged into the glass reactor. Subsequently, the second monomer mixture shown in Table 1 was added to the glass reactor over 150 minutes. After the start of the addition of the second monomer mixture, 0.1 parts by weight of dioctyl sodium sulfosuccinate was added to the glass reactor four times (at 20 minutes, 40 minutes, 60 minutes, and 80 minutes) every 20 minutes. Immediately after the completion of the addition of the second monomer mixture (150 minutes after the start of the addition of the second monomer mixture), 0.01 parts by weight of cumene hydroperoxide was added to the glass reactor. A 40-minute post-reaction allowed to occur, forming an intermediate layer (second layer).

[0122] Next, a third monomer mixture shown in Table 1 was added to the glass reactor over 45 minutes. A third layer was formed by a post-reaction for 60 minutes, and a latex containing high-molecular-weight polystyrene-based resin 3 was obtained. The polymerization conversion rate after polymerization was 99.0%.

[0123] Subsequently, a white resin powder (B-3) of high molecular weight polystyrene resin 3 was obtained by spray drying in the same manner as described in the section <High molecular weight polystyrene resin 1 (B-1)> above.

[0124] The weight average molecular weight of the obtained white resin powder (B-3) of high molecular weight polystyrene-based resin 3 was measured by the method described above. The weight average molecular weight of high molecular weight polystyrene-based resin 3 was 1,310,000.

[0125] (High Molecular Weight Polystyrene Resin 4 (B-4)) A glass reactor was charged with 140 parts by weight of deionized water, 0.03 parts by weight of sodium carbonate, and 0.5 parts by weight of dioctyl sodium sulfosuccinate. While stirring the charged raw materials in a nitrogen stream, the temperature inside the glass reactor was raised to 80°C. Next, the first monomer mixture shown in Table 1 was added to the glass reactor over 5 minutes. One minute after the addition of the first monomer mixture was completed, 0.0008 parts by weight of disodium ethylenediaminetetraacetate, 0.0002 parts by weight of ferrous sulfate, and 0.05 parts by weight of sodium formaldehyde sulfoxylate were charged to the glass reactor. A seed layer (first layer) was formed by a 20-minute post-reaction.

[0126] Next, 0.2 parts by weight of dioctyl sodium sulfosuccinate was charged into the glass reactor. Subsequently, the second monomer mixture shown in Table 1 was added to the glass reactor over 150 minutes. After the start of the addition of the second monomer mixture, 0.1 parts by weight of dioctyl sodium sulfosuccinate was added to the glass reactor four times (at 20, 40, 60, and 80 minutes) every 20 minutes. Immediately after the completion of the addition of the second monomer mixture (150 minutes after the start of the addition of the second monomer mixture), 0.02 parts by weight of cumene hydroperoxide was added to the glass reactor. A 40-minute post-reaction allowed to occur, forming an intermediate layer (second layer).

[0127] Next, a third monomer mixture shown in Table 1 was added to the glass reactor over 45 minutes. A third layer was formed by a post-reaction for 60 minutes, and a latex containing high-molecular-weight polystyrene-based resin 4 was obtained. The polymerization conversion rate after polymerization was 99.1%.

[0128] Subsequently, a white resin powder (B-4) of high molecular weight polystyrene resin 4 was obtained by spray drying in the same manner as described in the section <High molecular weight polystyrene resin 1 (B-1)> above.

[0129] The weight average molecular weight of the obtained white resin powder (B-4) of high molecular weight polystyrene-based resin 4 was measured by the method described above. The weight average molecular weight of high molecular weight polystyrene-based resin 4 was 1,011,000.

[0130] (High Molecular Weight Polystyrene Resin 5 (B-5)) A glass reactor was charged with 140 parts by weight of deionized water, 0.03 parts by weight of sodium carbonate, and 0.5 parts by weight of dioctyl sodium sulfosuccinate. While stirring the charged raw materials in a nitrogen stream, the temperature inside the glass reactor was raised to 80°C. Next, the first monomer mixture shown in Table 1 was added to the glass reactor over 5 minutes. One minute after the addition of the first monomer mixture was completed, 0.0008 parts by weight of disodium ethylenediaminetetraacetate, 0.0002 parts by weight of ferrous sulfate, and 0.05 parts by weight of sodium formaldehyde sulfoxylate were charged to the glass reactor. A seed layer (first layer) was formed by a 20-minute post-reaction.

[0131] Next, 0.2 parts by weight of dioctyl sodium sulfosuccinate was charged into the glass reactor. Subsequently, the second monomer mixture shown in Table 1 was added to the glass reactor over 150 minutes. After the start of the addition of the second monomer mixture, 0.1 parts by weight of dioctyl sodium sulfosuccinate was added to the glass reactor four times (at 20, 40, 60, and 80 minutes) every 20 minutes. Immediately after the completion of the addition of the second monomer mixture (150 minutes after the start of the addition of the second monomer mixture), 0.035 parts by weight of cumene hydroperoxide was added to the glass reactor. A 40-minute post-reaction allowed to occur, forming an intermediate layer (second layer).

[0132] Next, a third monomer mixture shown in Table 1 was added to the glass reactor over 45 minutes. A third layer was formed by a post-reaction for 60 minutes, yielding a latex containing high-molecular-weight polystyrene-based resin 5. The polymerization conversion rate after polymerization was 99.5%.

[0133] Subsequently, a white resin powder (B-5) of high molecular weight polystyrene resin 5 was obtained by spray drying in the same manner as described in the section <High molecular weight polystyrene resin 1 (B-1)> above.

[0134] The weight average molecular weight of the obtained white resin powder (B-5) of high molecular weight polystyrene-based resin 5 was measured by the method described above. The weight average molecular weight of high molecular weight polystyrene-based resin 5 was 804,000.

[0135] In Table 1, "St" represents "styrene," "BA" represents "butyl acrylate," and "CHP" represents "cumene hydroperoxide."

[0136] When an attempt was made to measure the MVR of the obtained high molecular weight polystyrene resins 1 to 5 by the method described above, the viscosity was too high to be measured.

[0137] <Reference Examples 1 to 6> The weight average molecular weight, MVR, melt tension, YI and haze of unused polystyrene resin (C-1) were measured by the methods described above. The results are shown in Table 5.

[0138] The weight average molecular weight, MVR, melt tension, YI, and haze of the polystyrene resin wastes (A-1 to A-5) were measured by the methods described above. The implementation of such measurements can also be considered as the implementation of a measurement step. The results are shown in Table 5.

[0139] <Examples 1 to 15, Comparative Examples 1 to 8, Reference Examples 1 to 4> (Selection Step) In Examples 1, 2, and 3, based on the weight average molecular weight and MVR of the polystyrene resin waste (A-1), (i) a high molecular weight polystyrene resin 1 (B-1) having a weight average molecular weight of 1,926,000 was selected as the high molecular weight polystyrene resin to be used, and (ii) the amount of the high molecular weight polystyrene resin 1 (B-1) used was selected to be the amount shown in Table 2. In Example 4, based on the weight average molecular weight and MVR of the polystyrene resin waste (A-5), (i) a high molecular weight polystyrene resin 1 (B-1) having a weight average molecular weight of 1,926,000 was selected as the high molecular weight polystyrene resin to be used, and (ii) the amount of the high molecular weight polystyrene resin 1 (B-1) used was selected to be the amount shown in Table 2. In Example 5, based on the weight average molecular weight and MVR of the polystyrene resin waste (A-5), (i) high molecular weight polystyrene resin 2 (B-2) having a weight average molecular weight of 2,492,000 was selected as the high molecular weight polystyrene resin to be used, and further (ii) the amount of high molecular weight polystyrene resin 2 (B-2) was selected to be the amount used as shown in Table 2. In Examples 6 and 7, based on the weight average molecular weight and MVR of the polystyrene resin waste (A-3), (i) high molecular weight polystyrene resin 1 (B-1) having a weight average molecular weight of 1,926,000 was selected as the high molecular weight polystyrene resin to be used, and further (ii) the amount of high molecular weight polystyrene resin 1 (B-1) was selected to be the amount used as shown in Table 2. In Examples 8 and 9, based on the weight average molecular weight and MVR of the polystyrene resin waste (A-3), (i) high molecular weight polystyrene resin 2 (B-2) having a weight average molecular weight of 2,492,000 was selected as the high molecular weight polystyrene resin to be used, and further (ii) the amount of high molecular weight polystyrene resin 2 (B-2) to be used was selected to be the amount shown in Table 2 or 3.In Examples 10 and 11, based on the weight average molecular weight and MVR of the polystyrene resin waste (A-3), (i) high molecular weight polystyrene resin 3 (B-3) having a weight average molecular weight of 1,310,000 was selected as the high molecular weight polystyrene resin to be used, and further (ii) the amount of the high molecular weight polystyrene resin 3 (B-3) was selected to be the amount used as shown in Table 3. In Examples 12 and 13, based on the weight average molecular weight and MVR of the polystyrene resin waste (A-3), (i) high molecular weight polystyrene resin 4 (B-4) having a weight average molecular weight of 1,011,000 was selected as the high molecular weight polystyrene resin to be used, and further (ii) the amount of the high molecular weight polystyrene resin 4 (B-4) was selected to be the amount used as shown in Table 3. In Examples 14 and 15, based on the weight average molecular weight and MVR of the polystyrene resin waste (A-3), (i) high molecular weight polystyrene resin 5 (B-5) having a weight average molecular weight of 804,000 was selected as the high molecular weight polystyrene resin to be used, and further (ii) the amount of high molecular weight polystyrene resin 5 (B-5) used was selected to be the amount shown in Table 3. The type and amount of high molecular weight polystyrene resin selected in the selection process are shown in Tables 2 and 3.

[0140] (Mixing step) According to the selection in the above-mentioned selection step, i.e., according to the composition shown in Table 2 or 3, polystyrene resin waste (A-1, 3 or 5) and high molecular weight polystyrene resin 1 (B-1) to high molecular weight polystyrene resin 5 (B-5) were melt-mixed to obtain a particulate (pellet-shaped) recycled polystyrene resin composition (Examples 1 to 15). According to the composition shown in Table 4, polystyrene resin waste (A-3) and unused polystyrene resin (C-1) or acrylic resin (D-1) to acrylic resin (D-4) were melt-mixed to obtain a particulate (pellet-shaped) recycled polystyrene resin composition (Comparative Example 1 to Comparative Example 8). Here, a twin-screw extruder (ZE 25Ax49D manufactured by Krauss Maffei) was used for melt mixing. The temperatures of the cylinders and the die of the extruder during melt mixing were as follows: C1 / C2 / C3 / C4 / C5 / C6 / C7 / C8 / C9 / C10 / ADAPTER / DIE = 40 / 210 / 210 / 210 / 210 / 210 / 210 / 210 / 210 / 220 / 220 / 220° C. The screw rotation speed of the extruder was 200 rpm.

[0141] The weight average molecular weight, MVR, melt tension, YI and haze of the resulting recycled polystyrene resin composition were measured according to the methods described above. The results are shown in Tables 2 to 4.

[0142] An embodiment of the present invention can be suitably used in fields such as foam sheets, foam beads, and foam molded articles (e.g., in-mold foam molded articles, extruded foam molded articles, etc.) using polystyrene-based resins.

Claims

1. A method for producing a recycled polystyrene-based resin composition, comprising a mixing step of melt-mixing polystyrene-based resin waste and a high-molecular-weight polystyrene-based resin to obtain a resin composition, wherein the weight-average molecular weight of the high-molecular-weight polystyrene-based resin is 500,000 or more and 5,000,000 or less.

2. The method for producing a recycled polystyrene-based resin composition according to claim 1, further comprising a measuring step of measuring one or more selected from the group consisting of weight average molecular weight, melt volume rate and melt tension of the polystyrene-based resin waste before the mixing step.

3. A method for producing a recycled polystyrene-based resin composition according to claim 1 or 2, further comprising, before the mixing step, a selection step of selecting one or more selected from the group consisting of the weight average molecular weight and the amount used of the high molecular weight polystyrene-based resin based on one or more selected from the group consisting of the weight average molecular weight, melt volume rate, and melt tension of the polystyrene-based resin waste.

4. A method for producing a recycled polystyrene resin composition as described in claim 1 or 2, wherein the amount of high molecular weight polystyrene resin used is 50% by weight or less out of a total of 100% by weight of the polystyrene resin waste and the high molecular weight polystyrene resin.

5. A method for producing a recycled polystyrene resin composition according to claim 1 or 2, wherein the weight average molecular weight of the polystyrene resin waste is 100,000 or more and 250,000 or less.

6. A method for producing a recycled polystyrene-based resin composition as described in claim 1 or 2, wherein the difference obtained by subtracting the weight-average molecular weight of the polystyrene-based resin waste from the weight-average molecular weight of the high molecular weight polystyrene-based resin is 400,000 or more and 2,500,000 or less.

7. A recycled polystyrene-based resin composition comprising polystyrene-based resin waste and a high-molecular-weight polystyrene-based resin, wherein the recycled polystyrene-based resin composition contains 3.0% or more of a resin having a molecular weight of 700,000 or more.

8. The recycled polystyrene resin composition according to claim 7, wherein the recycled polystyrene resin composition contains 3.5% or more of a resin having a molecular weight of 700,000 or more.

9. The recycled polystyrene resin composition according to claim 7 or 8, wherein the weight average molecular weight of the high molecular weight polystyrene resin is 500,000 or more and 5,000,000 or less.

10. A recycled polystyrene-based resin composition according to claim 7 or 8, wherein the recycled polystyrene-based resin composition contains 50% by weight or less of the high molecular weight polystyrene-based resin out of a total of 100% by weight of the polystyrene-based resin waste and the high molecular weight polystyrene-based resin.

11. A recycled polystyrene resin composition according to claim 7 or 8, wherein the weight average molecular weight of the polystyrene resin waste is 100,000 or more and 250,000 or less.

12. A recycled polystyrene resin composition according to claim 7 or 8, wherein the difference obtained by subtracting the weight average molecular weight of the polystyrene resin waste from the weight average molecular weight of the high molecular weight polystyrene resin is 400,000 or more and 2,500,000 or less.

13. A molded article obtained by molding the recycled polystyrene resin composition according to claim 7 or 8.

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