Method for recovering recycled polyolefin resin composition

Abstract

A method for recovering a recycled polyolefin resin composition according to the present disclosure comprises: a step for melting waste plastic containing a polypropylene resin and a polyethylene resin; a step for mixing an organic peroxide and a crystal nucleating agent with the waste plastic; and a step for separating the polypropylene resin from the waste plastic after the melting step and the mixing step.

Description

Method for recovering recycled polyolefin resin compositions

[0001] This disclosure relates to a method for recovering recycled polyolefin resin compositions.

[0002] Currently, thermoplastic resin compositions, including olefin, styrene, and polycarbonate resins, are commonly used in home appliances, office automation equipment such as photocopiers, and computer casings and components. When these products reach the end of their lifespan, they are treated as waste, and much of it is incinerated, landfilled, or processed as other fuels. However, in recent years, environmental pollution caused by incineration and landfilling, as well as a shortage of landfill sites, have become social problems. In response to this problem, the Act on Promotion of Resource Recycling Related to Plastics (Plastics Resource Recycling Promotion Act) came into effect in April 2022, and efforts are being made to reduce waste by aiming for a circular economy, or so-called circular economy, based on the principle of "3R + Renewable" throughout the lifecycle of plastic products.

[0003] Furthermore, the majority of the resin compositions in used home appliances consist of polyolefin resins such as polypropylene resin (PP) and polyethylene resin (PE), polystyrene resins such as high-impact polystyrene resin (HOPS) and transparent polystyrene resin (GPPS), and acrylonitrile resins such as acrylonitrile-butadiene-styrene resin (ABS) and acrylonitrile-styrene resin (AS). The majority of the resin compositions in used office automation equipment and computers consist of acrylonitrile resins, polycarbonate resins (PC), polycarbonate / acrylonitrile resins, and flame-retardant resin compositions.

[0004] Among these, polypropylene resin has the second-highest production volume after polyethylene resin. It has the lowest density among thermoplastic resins and is used in many plastic products because of its excellent heat resistance, chemical resistance, mechanical strength, insulation, and heat insulation properties. Therefore, it is possible to manufacture other plastic products from plastic products that would otherwise be discarded, and to enjoy the excellent properties of polypropylene resin again in those other plastic products.

[0005] However, container and packaging plastics contain polyethylene resin in addition to polypropylene resin. Therefore, when attempting to manufacture another plastic product from container and packaging plastics, the purity of the polypropylene resin decreases, which may prevent the other plastic product from enjoying the excellent properties of polypropylene resin.

[0006] Furthermore, when crushing plastic products such as container and packaging plastics containing polypropylene resin and polyethylene resin, and separating the polypropylene resin and polyethylene resin, it is difficult to separate them by specific gravity because their densities are similar. For this reason, separation is performed by analysis using near-infrared light. However, in order to produce resin pellets for resin composition, it is necessary to separate the polypropylene resin from the material obtained by melting and kneading polypropylene resin and polyethylene resin, but it is considered difficult to separate the polypropylene resin with high precision.

[0007] As a conventional method for separating resin from used plastic products, for example, Patent Document 1 (International Publication No. 2022 / 230331) discloses a method for producing a recyclable resin, which includes a separation step of subjecting a resin composition containing recyclable resin A and resin B having a higher melting point than recyclable resin A to a filter treatment to separate the recyclable resin A.

[0008] Patent Document 2 (Japanese Patent No. 7446038) discloses a method for recycling a composite resin material containing a polyamide resin and a polyolefin resin, in which the composite resin material and a solvent containing a polyol are heated, the polyamide resin solution is separated by utilizing the viscosity difference between the polyamide resin solution dissolved in the solvent and the polyolefin resin melt that melted without dissolving in the solvent, and the obtained polyamide resin solution is rapidly cooled using the latent heat of vaporization to recover the polyamide resin.

[0009] Patent Document 3 (Japanese Patent Publication No. 10-258427) discloses a method for obtaining polypropylene resin and polyethylene resin by using a specific gravity separation apparatus that uses a specific gravity liquid, introducing waste plastic into the specific gravity separation apparatus, heating the specific gravity liquid to a temperature above the melting point of polyethylene resin but below the melting point of polypropylene resin, melting the polyethylene resin contained in the waste plastic and separating the polyethylene resin by specific gravity separation, and then heating the specific gravity liquid from the remaining waste plastic to a temperature above the melting point of polypropylene resin, melting the polypropylene resin and separating the polypropylene resin by specific gravity separation.

[0010] International Publication No. 2022 / 230331 Patent No. 7446038 Publication JP 10-258427 Publication

[0011] According to the method described in Patent Document 1, a large difference in the melting points of the two resins is required for the separation of recycled resin A and resin B, and it is considered unsuitable for separating polypropylene resin and high-density polyethylene resin, which have relatively similar melting points. The method described in Patent Document 2 is a method for recovering polyamide resin dissolved in a solvent, and the method described in Patent Document 3 is a method for separating a mixture of granular polypropylene resin and polyethylene resin. Therefore, there is room for improvement in the method of removing polyethylene resin and separating polypropylene resin from waste plastic containing polypropylene resin and polyethylene resin mixed in a molten state.

[0012] This disclosure aims to provide a method for recovering recycled polyolefin resin compositions that can remove polyethylene resin from waste plastics containing polypropylene resin and polyethylene resin with a high removal rate.

[0013] The method disclosed herein is a method for recovering a recycled polyolefin resin composition, comprising the steps of: melting waste plastic containing polypropylene resin and polyethylene resin; mixing the waste plastic with an organic peroxide and a crystal nucleating agent; and separating the polypropylene resin from the waste plastic after the melting step and the mixing step.

[0014] According to this disclosure, a method for recovering a recycled polyolefin resin composition that can remove polyethylene resin from waste plastics containing polypropylene resin and polyethylene resin with a high removal rate is provided.

[0015] Figure 1 is a flowchart showing an example of a method for recovering a recycled polyolefin resin composition according to Embodiment 1.

[0016] A method for recovering a recycled polyolefin resin composition according to one embodiment of this disclosure will be described below with reference to the drawings.

[0017] Embodiment 1. [Method for recovering recycled polyolefin resin composition] The method for recovering recycled polyolefin resin composition according to Embodiment 1 comprises a step of melting waste plastic containing polypropylene resin and polyethylene resin (hereinafter also referred to as the "melting step"), a step of mixing organic peroxide and a crystal nucleating agent with the waste plastic (hereinafter also referred to as the "mixing step"), and a step of separating the recycled polyolefin resin composition from the waste plastic after the melting step and the mixing step (hereinafter also referred to as the "separation step").

[0018] The method for recovering recycled polyolefin resin compositions described in this disclosure allows for the removal of polyethylene resin with a high removal rate. According to this disclosure, the removal rate of polyethylene resin described later can be 10% or more, 20% or more, 30% or more, or 40% by weight or more. This makes it possible to recover recycled polyolefin resin compositions containing high-purity polypropylene resin. The reason for this is presumed to be as follows.

[0019] In Embodiment 1, an organic peroxide is mixed with molten waste plastic. In the molten waste plastic, the polypropylene resin has hydrogen atoms extracted from its tertiary carbon atoms, making it more susceptible to auto-oxidation reactions. Here, the polypropylene resin reacts with the organic peroxide, which has free radicals generated by the decomposition of peroxide bonds, causing its molecular chains to break and its molecular weight to decrease. As a result, the viscosity of the molten polypropylene resin decreases. On the other hand, the polyethylene resin reacts with the organic peroxide, and the free radicals of the organic peroxide extract hydrogen atoms from the main chain or side chains constituting the polyethylene resin, generating carbon radicals. The carbon radicals of the polyethylene resin combine with carbon radicals generated by another reaction, forming a cross-linked structure throughout the polyethylene resin. As a result, the viscosity of the molten polyethylene resin increases.

[0020] As a result of the above reaction, the viscosity of the polypropylene resin decreases and the viscosity of the polyethylene resin increases in the molten waste plastic. Therefore, it is believed that the viscosity difference between the two resins enables the separation of the polypropylene resin from the molten waste plastic. In addition, a crystal nucleating agent is mixed with the molten waste plastic. The crystal nucleating agent is an additive that promotes the crystallization of the polypropylene resin. Therefore, it is believed that this facilitates the separation of the polypropylene resin from the waste plastic. Thus, according to the method of this disclosure, polyethylene resin can be removed from waste plastic with a high removal rate, and a recycled polyolefin resin composition containing high-purity polypropylene resin can be recovered.

[0021] An overview of the method for recovering a recycled polyolefin resin composition according to Embodiment 1 will be described with reference to the figures. Figure 1 is a flowchart showing an example of the method for recovering a recycled polyolefin resin composition according to Embodiment 1. As shown in Figure 1, the method for recovering a recycled polyolefin resin composition according to Embodiment 1 comprises a melting step S10, a mixing step S20, and a separation step S30. In this disclosure, the melting step S10 and the mixing step S20 may be performed in any order. That is, the mixing step S20 may be performed after the melting step S10, or the melting step S10 may be performed after the mixing step S20. In this disclosure, it is preferable that the mixing step S20 be performed after the melting step S10 in order to stably carry out the reaction of the organic peroxide.

[0022] <Melting Process> In the melting process S10, waste plastics containing polypropylene resin and polyethylene resin are melted. In the melting process S10, the waste plastics can be melted by heating them to a temperature above the melting point of the resin components contained in the waste plastics. In the melting process S10, the waste plastics may be kneaded while being heated. The melting temperature and melting time of the waste plastics can be selected according to the resin components and other components contained in the waste plastics. The melting temperature in the melting process S10 may be, for example, 170°C to 220°C, or 180°C to 200°C. The melting time in the melting process S10 may be, for example, 1 minute or more, or 10 minutes or less. This is because the 1-minute half-life temperature of organic peroxides is 175 to 194°C, and organic peroxides decompose almost completely in 7 to 8 times the half-life, so the reaction will not proceed even if the organic peroxides are reacted for 10 minutes or more. The melting process S10 can be carried out using a heating device that can melt the waste plastics. The melting step S10 can also be carried out using a kneading apparatus equipped with the heating device.

[0023] (Waste Plastics) In this disclosure, waste plastics include polypropylene resin and polyethylene resin. Waste plastics include plastics used in home appliances, office automation equipment, container and packaging plastics, and automobiles, etc. Waste plastics can be obtained by washing, drying, and crushing the above-mentioned plastics.

[0024] Waste plastics may include used plastics or unused plastics. Unused plastics include unused plastic products and plastics that are discarded without being used as a result of the manufacturing process.

[0025] The waste plastic may contain polypropylene resin and polyethylene resin. For example, it may be composed of a plastic whose resin component contains polypropylene resin and a plastic whose resin component contains polyethylene resin, or it may be composed of a plastic whose resin component contains both polypropylene resin and polyethylene resin.

[0026] Examples of polypropylene resins contained in waste plastics include homopolypropylene; block copolymers such as propylene-ethylene block copolymer, propylene-butene block copolymer, and propylene-α-olefin block copolymer; block copolymers such as propylene-ethylene random copolymer, propylene-butene random copolymer, and propylene-α-olefin random copolymer; and graft copolymers such as propylene-α-olefin graft copolymer. These polypropylene resins may be present in waste plastics individually or in combination of two or more types.

[0027] The polypropylene resin content in the waste plastic may be 60% by weight or more, or 70% by weight or more, based on 100% by weight of the waste plastic. The polypropylene resin content in the waste plastic is preferably 80% by weight or more, more preferably 90% by weight or more, even more preferably 95% by weight or more, even more preferably 97% by weight or more, and even more preferably 99% by weight or more, since a recycled polyolefin resin composition containing high-purity polypropylene resin can be recovered. The polypropylene resin content in the waste plastic is less than 100% by weight, based on 100% by weight of the waste plastic.

[0028] Examples of polyethylene resins contained in waste plastics include high-density polyethylene (HDPE), low-density polyethylene (LDPE), and linear polyethylene (LLDPE). These polyethylene resins may be present in the waste plastic alone or in combination of two or more types.

[0029] The polyethylene resin content in the waste plastic may be 40% by weight or less, or 30% by weight or less, based on 100% by weight of the waste plastic. The polyethylene resin content in the waste plastic is preferably 20% by weight or less, more preferably 10% by weight or less, even more preferably 5% by weight or less, even more preferably 3% by weight or less, and most preferably 1% by weight or less, since a recycled polyolefin resin composition containing high-purity polypropylene resin can be recovered. The polyethylene resin content in the waste plastic is greater than 0% by weight, based on 100% by weight of the waste plastic.

[0030] Waste plastics may contain other components besides polypropylene resin and polyethylene resin. These other components may include other thermoplastic resins other than polypropylene resin and polyethylene resin, inorganic fillers, organic fillers, etc. These other components may be present in the waste plastics individually or in combination of two or more types.

[0031] Other thermoplastic resins include polycarbonate resin, alkyd resin, amino resin, bismaleimidotriazine resin, chlorinated polyether, allyl resin, epoxy resin, ethylene-vinyl acetate-vinyl chloride copolymer, ethylene-vinyl chloride copolymer, nitrile resin, olefin vinyl alcohol copolymer, phenol resin, polyacetal, polyacrylate, polyallyl sulfone, polybenzimidazole, polybutylene terephthalate, polyetheretherketone, polyetherketone, polyethernitrile, polyethersulfone, polyethylene terephthalate, polyketone, methacrylic resin, polymethylpentene, polyphenylene ether, polyphenylene sulfide, polysulfone, polyurethane, polyvinyl acetal, polyvinyl chloride, polyvinylidene chloride, silicone resin, xylene resin, ethylene propylene rubber, chloroprene rubber, butyl rubber, and nitrile rubber.

[0032] Examples of inorganic fillers include talc, mica, wollastonite, calcium carbonate, barium sulfate, magnesium carbonate, clay, alumina, silica, calcium sulfate, carbon fiber, glass fiber, metal fiber, silica sand, poppy stone, carbon black, titanium dioxide, zinc oxide, antimony trioxide, magnesium hydroxide, asbestos, zeolite, molybdenum, diatomaceous earth, sericite, shirasu, calcium hydroxide, calcium sulfite, sodium sulfate, bentonite, kaolinite, and graphite.

[0033] Examples of organic fillers include cellulose nanofibers and cellulose microfibers.

[0034] The content of the above-mentioned other components may be 10% by weight or less, 5% by weight or less, or 1% by weight or less, based on 100% by weight of the waste plastic. The content of the above-mentioned other components may be more than 0%, 0.001% by weight or more, 0.01% by weight or more, or 0.05% by weight or more, based on 100% by weight of the waste plastic.

[0035] <Mixing Process> In mixing process S20, the waste plastic is mixed with an organic peroxide and a crystal nucleating agent. Mixing process S20 can be carried out using a known kneading apparatus. Examples of kneading apparatuses include a single-screw extruder, twin-screw extruder, tumbler, Henschel mixer, rotary mixer, super mixer, ribbon tumbler, V blender, gelation mixer, Banbury mixer, roll mixer, Brabender plastograph, kneader, etc. The kneading apparatus used to carry out mixing process S20 may be the same apparatus used to carry out melting process S10, or it may be a different apparatus. From the viewpoint of operational efficiency, it is preferable that it be the same apparatus used to carry out melting process S10.

[0036] The temperature in the mixing step S20 can be selected according to the resin components and other components contained in the waste plastic. For example, it may be 170°C to 220°C, or 180°C to 200°C.

[0037] Organic peroxides are activated at high temperatures, which accelerates the decomposition rate of the polypropylene resin. Therefore, the temperature of the mixing step S20 is preferably 200°C or lower, more preferably 190°C or lower, and even more preferably 180°C or lower.

[0038] (Organic Peroxide) As described above, organic peroxide reduces the viscosity of polypropylene resin in waste plastics and increases the viscosity of polyethylene resin. Examples of the organic peroxide include dialkyl peroxides such as 2,5-dimethyl-di-t-butylperoxyhexane, di(2-t-butylperoxyisopropyl)benzene, dicumyl peroxide, di-t-hexyl peroxide, and 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3. The organic peroxide is preferably a dialkyl peroxide, because it enables recovery of a regenerated polyolefin-based resin composition containing high-purity polypropylene resin; more preferably contains one or more selected from the group consisting of 2,5-dimethyl-di-t-butylperoxyhexane, di(2-t-butylperoxyisopropyl)benzene, and 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3; and still more preferably contains 2,5-dimethyl-di-t-butylperoxyhexane.

[0039] Commercially available products can be used as the organic peroxide. For example, the following commercially available products can be used. As 2,5-dimethyl-di-t-butylperoxyhexane, Perhexa 25B manufactured by NOF CORPORATION and Luperox 101 manufactured by Arkema Yoshitomi, Ltd. can be used. As di(2-t-butylperoxyisopropyl)benzene, Perbutyl P manufactured by NOF CORPORATION and Luperox F manufactured by Arkema Yoshitomi, Ltd. can be used. As dicumyl peroxide, Percumyl D manufactured by NOF CORPORATION can be used. As di-t-hexyl peroxide, Perhexyl D manufactured by NOF CORPORATION can be used. As 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3, Perhexyne 25B manufactured by NOF CORPORATION and Luperox 130 manufactured by Arkema Yoshitomi, Ltd. can be used.

[0040] Regarding the above organic peroxides, only one type may be used alone, or a combination of two or more types may be used.

[0041] The mixing ratio of the organic peroxide may be 0.05 parts by weight or more and 1.00 parts by weight or less, or 0.1 parts by weight or more and 0.5 parts by weight or less, relative to 100 parts by weight of the waste plastic. When the mixing ratio of the organic peroxide exceeds 1.00 parts by weight, the durability of a molded article of the recycled polyolefin-based resin composition may decrease. When the mixing ratio of the organic peroxide is less than 0.05 parts by weight, separation of the polypropylene resin and the polyethylene resin may become insufficient.

[0042] (Crystal Nucleating Agent) As described above, the crystal nucleating agent promotes crystallization of the polypropylene resin. Since the crystal nucleating agent enables recovery of a recycled polyolefin-based resin composition containing high-purity polypropylene resin, it preferably contains one or more selected from the group consisting of α-crystal nucleating agents and β-crystal nucleating agents. Examples of the α-crystal nucleating agent include carboxylic acid metal salts such as calcium stearate, magnesium stearate, sodium benzoate, and hydroxyaluminum di-p-tert-butylbenzoate; and phosphoric acid ester metal salts such as sodium 2,2'-methylenebis-(4,6-di-tert-butylphenol) phosphate. Examples of the β-crystal nucleating agent include amide compounds such as N,N'-dicyclohexyl-2,6-naphthalenedicarboxamide, N,N'-dicyclohexylterephthalamide, and N,N'-diphenylhexanediamide; tetraoxaspiro compounds; and quinacridones such as quinacridone and quinacridonequinone.

[0043] In the crystal nucleating agent, the α-crystal nucleating agent preferably contains one or more selected from the group consisting of sodium benzoate, hydroxyaluminum di-p-tert-butylbenzoate, and sodium 2,2'-methylenebis-(4,6-di-tert-butylphenol) phosphate. In the crystal nucleating agent, the β-crystal nucleating agent is preferably an amide compound, and more preferably N,N'-dicyclohexyl-2,6-naphthalenedicarboxamide.

[0044] A commercially available nucleating agent can be used. For example, the following commercially available products can be used: As di-p-tert-butylbenzoate hydroxyaluminum, AL-PTBBA manufactured by Oxalis Chemicals Co., Ltd. can be used. As 2,2'-methylenebis-(4,6-di-tert-butylphenol) sodium phosphate, ADEKA Stab NA-11 manufactured by ADEKA Corporation can be used. As N,N'-diclohexyl-2,6-naphthalenedicarboxamide, NJester NU-100 manufactured by Shin Nippon Rika Co., Ltd. can be used.

[0045] The above-mentioned nucleating agents may be used individually or in combination of two or more.

[0046] The mixing ratio of the nucleating agent may be 0.05 parts by weight or more and 1.00 parts by weight or less, or 0.1 parts by weight or more and 0.5 parts by weight or less, per 100 parts by weight of waste plastic. If the mixing ratio of the nucleating agent is less than 0.05 parts by weight, a sufficient viscosity difference may not be obtained between the polypropylene resin and the polyethylene species, resulting in insufficient separation of the polypropylene resin and the polyethylene resin.

[0047] (Other components) In mixing step S20, other components besides the organic peroxide and crystal nucleating agent may be mixed. Examples of other components include degradation inhibitors, antioxidants, metal deactivators, ultraviolet absorbers, light stabilizers, antistatic agents, plasticizers, mold release agents, flame retardants, flame retardant aids, dyes, and pigments. In mixing step S20, the mixing ratio of the other components should be adjusted as appropriate so that the molded product of the recycled polyolefin resin composition obtains the desired physical properties. In mixing step S20, in addition to mixing the organic peroxide and crystal nucleating agent, it is preferable to further mix in a degradation inhibitor from the viewpoint of further improving the durability of the molded product of the recycled polyolefin resin composition.

[0048] [Degradation Inhibitor] When waste plastics include used plastic products, the resin composition recovered in this disclosure may not contain a degradation inhibitor because the degradation inhibitor contained in the unused plastic products is consumed by the market's thermal history. Therefore, in the mixing step S20, by further mixing a degradation inhibitor in addition to mixing the organic peroxide and the crystal nucleating agent, the durability of the recycled polyolefin resin composition molded article can be further improved.

[0049] The mixing ratio of the degradation inhibitor may be 0.01 parts by weight or more, or 0.05 parts by weight or more, per 100 parts by weight of waste plastic, from the viewpoint of further improving the durability of the recycled polyolefin resin composition molded product. The mixing ratio may be 0.1 parts by weight or more, 0.15 parts by weight or more, 10 parts by weight or less, 3.0 parts by weight or less, 2.0 parts by weight or less, 1.5 parts by weight or less, 1.0 part by weight or less, 0.7 parts by weight or less, or 0.5 parts by weight or less, per 100 parts by weight of waste plastic.

[0050] The degradation inhibitors, used to improve the thermal stability of molded products of recycled polyolefin resin compositions, include 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane, 4,4'-butylidenebis(6-t-butyl-m-cresol), 3,9-bis{2-[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy]-1,1-dimethylethyl}-2,4,8,10-tetraoxaspiro[5.5]undecane, 2,2'-methylenebis(6-t-butyl-4-ethylphenol), tris(4-t-butyl-3-hydroxy-2,6-dimethylbenzyl)isocyanuric acid, and bis(4-t-butyl-3-hydroxy-2,6-dimethylbenzyl)isocyanuric acid. Preferably, the product contains one or more selected from the group consisting of hydrogenated tallow alkyl hydroamine, bis(hydrogenated palm oil alkyl) hydroamine, tetrakis(1,2,2,6,6-pentamethylpiperidine-4-yl)butan-1,2,3,4-tetracarboxylate, tetrakis(2,2,6,6-tetramethyl-4-piperidyl)butan-1,2,3,4-tetracarboxylate, bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate, bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate, and 2,2,6,6-tetramethyl-4-piperidinyl stearate.

[0051] The above degradation inhibitors can be commercially available products, for example, the following products can be used: 1,1,3-Tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane can be ADEKA STABE AO-30 manufactured by ADEKA Corporation. 4,4'-Butylidenebis(6-t-butyl-m-cresol) can be ADEKA STABE AO-40 manufactured by ADEKA Corporation. 3,9-Bis{2-[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy]-1,1-dimethylethyl}-2,4,8,10-tetraoxaspiro[5.5]undecane can be ADEKA STABE AO-80 manufactured by ADEKA Corporation. As 2,2'-methylenebis(6-t-butyl-4-ethylphenol), Cheminox 179 manufactured by Chemipro Chemical Co., Ltd. and Cyanox 1790 manufactured by Sun Chemical Co., Ltd. can be used. As tris(4-t-butyl-3-hydroxy-2,6-dimethylbenzyl)isocyanuric acid, Cheminox 9425 manufactured by Chemipro Chemical Co., Ltd. can be used. As bis(hydrogenated tulose alkyl) hydroamine, Revonox 420 manufactured by Chitec Technology Co., Ltd. can be used. As bis(hydrogenated palm oil alkyl) hydroamine, Revonox 420V manufactured by Chitec Technology Co., Ltd. can be used. As tetrakis(1,2,2,6,6-pentamethylpiperidine-4-yl)butan-1,2,3,4-tetracarboxylate, ADEKA LA-52 manufactured by ADEKA Corporation can be used. As tetrakis(2,2,6,6-tetramethyl-4-piperidyl)butan-1,2,3,4-tetracarboxylate, ADEKA LA-57 manufactured by ADEKA Corporation can be used. As bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate, ADEKA LA-72 manufactured by ADEKA Corporation can be used. As bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate, ADEKA LA-57 manufactured by ADEKA Corporation and TINUVIN 770 manufactured by BASF Japan Ltd. can be used.As 2,2,6,6-tetramethyl-4-piperidinyl stearate, ADEKA LA-40 manufactured by ADEKA Corporation can be used.

[0052] [Antioxidants] Antioxidants can be used to improve the thermal stability of molded articles of recycled polyolefin resin compositions. Examples of antioxidants include hindered phenol-based, phosphorus-based, and sulfur-based antioxidants. Antioxidants may be used individually or in combination of two or more types.

[0053] Examples of hindered phenol-based antioxidants include 2,6-di-tert-butyl-p-cresol, tetrakis[methylene-3-(3',5'-di-tert-butyl-4'-hydroxyphenyl)propionate]methane, stearyl β-(3',5'-di-tert-butyl-4-hydroxyphenyl)propionate, 1,3,5-trimethyl-2,4,6-tris(3',5'-di-tert-butyl-4-hydroxybenzyl)benzene, and triethylene glycol bis[3-(3-tert-butyl-5-methyl-4-hydroxyphenyl)propionate]. The hindered phenol-based antioxidant is preferably one or more selected from the group consisting of tetrakis[methylene-3-(3',5'-di-tert-butyl-4'-hydroxyphenyl)propionate]methane, stearyl β-(3',5'-di-tert-butyl-4-hydroxyphenyl)propionate, and 3,9-bis[1,1-dimethyl-2-[β-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionyloxy]ethyl]-2,4,8,10-tetraoxaspiro(5,5)undecane, in order to further improve the thermal stability of the molded product of the recycled polyolefin resin composition.

[0054] Among antioxidants, phosphorus-based antioxidants include, for example, tris(2,4-di-tert-butylphenyl) phosphite, diphenyl mono(2-ethylhexyl) phosphite, diphenyl monodecyl phosphite, pentaerythritol bis(2,6-di-tert-butyl-4-phenyl phosphite), 2,2'-methylenebis(4,6-di-tert-butylphenyl)-2-ethylhexyl phosphite, distearyl pentaerythritol diphosphite, tri(mononylphenyl) phosphite, and alkanol (C=12-16) 4,4'-isopropylidenediphenoltriphenylphosphate. Examples include polycondensates, bis[2,4-di-tert-butyl-6-methylphenyl]ethyl phosphite, pentaerythritol bis(2,4-di-tert-butylphenyl phosphite), triallyl phosphite, tetrakis(2,4-tert-butylphenyl)-4,4'-biphenyl diphosphonate, 3,9-bis(2,6-di-tert-butyl-4-methylphenoxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane, and 3,9-bis(octadecyloxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane. The phosphorus-based antioxidant is preferably one or more selected from the group consisting of tris(2,4-di-tert-butylphenyl) phosphite, diphenyl mono(2-ethylhexyl) phosphite, diphenyl monodecyl phosphite, pentaerythritol bis(2,6-di-tert-butyl-4-phenyl phosphite), 2,2'-methylenebis(4,6-di-tert-butylphenyl)-2-ethylhexyl phosphite, 3,9-bis(2,6-di-tert-butyl-4-methylphenoxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane, and 3,9-bis(octadecyloxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane, in order to further improve the thermal stability of the molded product of the recycled polyolefin resin composition.

[0055] Examples of sulfur-based antioxidants include pentaerythritol tetrakis[3-laurylthiopropionate], distearyl thiodipropionate, and dilauryl thiodipropionate.

[0056] The mixing ratio of the antioxidant may be 0.01 parts by weight or more, 0.05 parts by weight or more, 10 parts by weight or less, or 3.0 parts by weight or less, per 100 parts by weight of waste plastic.

[0057] [Metal deactivators] Examples of metal deactivators include 2',3-bis[[3-[3,5-di-t-butyl-4-hydroxyphenyl]propionyl]]propionohydrazide, 3-(N-salityloyl)amino-1,2,4-triazole, decamethylenedicarboxylic acid disalityloylhydrazide, N-formylsalityloylhydrazine, benzotriazole, methylbenzotriazole, methylbenzotriazole potassium salt, N,N-dibenzal(oxalylhydrazide), and N,N-bis(3,5-di-t-butyl-4-hydroxyhydrocinnamate). A single metal deactivator may be used alone, or a combination of two or more may be used.

[0058] The mixing ratio of the metal deactivator may be 0.01 parts by weight or more, 0.05 parts by weight or more, 10 parts by weight or less, or 3.0 parts by weight or less, per 100 parts by weight of waste plastic.

[0059] [UV absorbers] UV absorbers are used to suppress yellowing of molded products due to ultraviolet light when used outdoors. Examples of UV absorbers include hydroxybis(dimethylbenzyl)phenylbenzotriazole, 2-(2'-hydroxy-5'-tert-octylphenyl)benzotriazole, 2,2'-methylenebis[6-(2H-benzotriazole-2-yl)-4-tert-octylphenol], 2-(2'-hydroxy-5'-methylphenyl)benzotriazole, 2-(2'-hydroxy-3'-tert-butyl-5'-methylphenyl)-5-chlorobenzotriazole, 2-(4,6-diphenyl-1,3,5-triazine-2-yl)-5-[2-(2-ethylhexanoyloxy)ethoxy]phenol), and 2,4,6-tris(2-hydroxy-4-hexyloxy-3-methylphenyl)-1,3,5-triazine). Regarding the ultraviolet absorber, one type may be used alone, or two or more types may be used in combination. In order to further improve the thermal stability of the molded product of the recycled polyolefin resin composition, it is preferable that the ultraviolet absorber is one or more selected from the group consisting of 2-(2'-hydroxy-5'-tert-octylphenyl)benzotriazole, 2,2'-methylenebis[6-(2H-benzotriazole-2-yl)-4-tert-octylphenol], 2-(4,6-diphenyl-1,3,5-triazine-2-yl)-5-[2-(2-ethylhexanoyloxy)ethoxy]phenol), and 2,4,6-tris(2-hydroxy-4-hexyloxy-3-methylphenyl)-1,3,5-triazine).

[0060] The mixing ratio of the ultraviolet absorber may be 0.01 parts by weight or more, 0.05 parts by weight or more, 10 parts by weight or less, or 3.0 parts by weight or less, per 100 parts by weight of waste plastic.

[0061] [Light stabilizers] Light stabilizers can be used to suppress yellowing of molded products due to ultraviolet light when used outdoors. Examples of light stabilizers include mixed esters of 1,2,3,4-butanetetracarboxylic acid, 1,2,3,6,6-pentamethyl-4-piperidinol, and 3,9-bis(2-hydroxy-1,1-dimethylethyl)-2,4,8,10-tetraoxaspiro[5.5]undecane. Light stabilizers may be used individually or in combination of two or more.

[0062] The mixing ratio of the light stabilizer may be 0.01 parts by weight or more, 0.05 parts by weight or more, 10 parts by weight or less, or 3.0 parts by weight or less, per 100 parts by weight of waste plastic.

[0063] [Antistatic Agent] Examples of the antistatic agent include, but are not limited to: tributyldodecylphosphonium bis(trifluoromethanesulfonyl)imide (IL-AP3, manufactured by Koei Chemical Industry Co., Ltd.), tributyldodecylphosphonium bromide (manufactured by Fujifilm Wako Pure Chemical Corporation), tetrabutylphosphonium dodecylbenzenesulfonate (manufactured by Takemoto Oil & Fat Co., Ltd.), trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl)imide, triethylpentylphosphonium bis(trifluoromethylsulfonyl)imide, triethyloctylphosphonium bis(trifluoromethylsulfonyl)imide, tri-n-butylmethylphosphonium bis(trifluoromethylsulfonyl)imide, phosphonium salt-based ionic liquids such as tetrabutylphosphonium tetraphenylborate; ammonium salt-based ionic liquids such as tributylmethylammonium bis(trifluoromethylsulfonyl)imide (FC-4400, manufactured by 3M Japan Limited); pyridinium salt-based ionic liquids such as N-butyl-3-methylpyridinium bis(trifluoromethylsulfonyl)imide (CIL-312, manufactured by Nippon Carlit Co., Ltd.); imidazolium salt-based ionic liquids; pyrrolidinium salt-based ionic liquids; and ionic liquid antistatic agents such as lithium ion liquids including lithium bistrifluoromethanesulfonylimide / polyether polyol (PEO-20R, manufactured by Sanko Chemical Industry Co., Ltd.); polymer-type antistatic agents having a quaternary ammonium salt in a side chain thereof (1SX-1090 and 1WX-1020-NS manufactured by Taisei Fine Chemical Co., Ltd.); diglycerin monolaurate which is a glycerin fatty acid ester (Poem DL-100 manufactured by Riken Vitamin Co., Ltd.); polymeric permanent antistatic agents including Peletron HS, Peletron AS manufactured by Sanyo Chemical Industries, Ltd. and Pelestat NC6321; Adekastab AS-302 manufactured by ADEKA Corporation; Biomisel BN-105 manufactured by Boron Research Institute Co., Ltd. (chemical formula: C ４２ H ８１ O ８ B・C ２３ H ４８ ON ２ ) and Biomisel BN-77 (chemical formula: C ４２ H ８１ O ８ B・C ２３ H４８ Examples include donor-acceptor compounds that are ON. The antistatic agent may be used alone or in combination of two or more types.

[0064] [Plasticizers] Examples of plasticizers include polyethylene glycol, polyamide oligomers, ethylene bis-stearoamide, phthalate esters, adipic acid esters, polystyrene oligomers, polyethylene wax, and mineral oil. A single plasticizer may be used alone, or a combination of two or more may be used.

[0065] [Release Agents] Examples of release agents include polyethylene wax, silicone oil, stearyl phosphite, long-chain carboxylic acids, long-chain carboxylic acid metal salts, and higher fatty acid esters of monohydric or polyhydric alcohols. One release agent may be used alone, or a combination of two or more may be used.

[0066] [Flame Retardants] Examples of flame retardants include phosphorus-based flame retardants such as bisphenol A bis(diphenyl phosphite), tricresyl phosphate, triphenyl phosphate, and tris-3-chloropropyl phosphate; bromine-based flame retardants such as 2,2-bis[3,5-dibromo-4-(2,3-dibromopropioxy)phenyl]propane (abbreviated as TBA-BP), bis[3,5-dibromo-4-(2,3-dibromopropioxy)phenyl]sulfone (abbreviated as TBS-BP), ethylenebispentabromobenzene, and hexabromocyclododecane; silicone-based flame retardants; and hydroxide-based flame retardants such as magnesium hydroxide and aluminum hydroxide. Furthermore, if the addition of a bromine-based flame retardant causes deterioration or discoloration of the resin due to hydrogen bromide from the bromine-based flame retardant, hydrotalcite, which is a metal double chloride, may be further mixed in. Flame retardants may be used individually or in combination of two or more types.

[0067] [Flame retardant additives] Examples of flame retardant additives include antimony compounds such as antimony trioxide, antimony pentoxide, metallic antimony, PTFE (polytetrafluoroethylene), and melamine cyanurate (MC-4000 manufactured by Nissan Chemical Corporation). Flame retardant additives may be used individually or in combination of two or more.

[0068] <Separation Step S30> The separation step S30 is performed after the melting step S10 and the mixing step S20, and separates polypropylene resin from the waste plastic. The waste plastic after the melting step S10 and the mixing step S20 is in a molten state, in which the polyethylene resin, which has formed a cross-linked structure and become highly viscous, is dispersed in the polypropylene resin, which has become less viscous. In the separation step S30, the separation of polypropylene resin from the waste plastic is preferably performed by at least one selected from the group consisting of filtration and temperature-controlled extrusion, and more preferably by filtration or temperature-controlled extrusion.

[0069] (Filtering) In the separation step S30, by subjecting the molten waste plastic to filtering, the low-viscosity polypropylene resin can pass through the filter, while the cross-linked polyethylene resin cannot. Therefore, polypropylene resin can be efficiently separated from the molten waste plastic, and a recycled polyolefin resin composition containing high-purity polypropylene resin can be recovered.

[0070] The filter can take any shape that has pores through which the resin can pass, such as wire mesh, perforated plates, and grids. The filter may also be in the form of a sheet or a container. The filter material can be any material that is not affected by the high temperature of the resin, such as metal, glass, carbon, and plastic.

[0071] Examples of filter mesh sizes include #60 (wire diameter: 0.19 mm, mesh opening: 0.233 mm), #80 (wire diameter: 0.14 mm, mesh opening: 0.178 mm), #100 (wire diameter: 0.10 mm, mesh opening: 0.154 mm), #120 (wire diameter: 0.08 mm, mesh opening: 0.132 mm), #150 (wire diameter: 0.06 mm, mesh opening: 0.109 mm), and #200 (wire diameter: 0.05 mm, mesh opening: 0.077 mm). The "#" number in the mesh size indicates the number of mesh holes per inch square, and the higher the "#" number, the finer the mesh opening. Therefore, a mesh size of #120 or higher is preferred for filtration, as it makes it difficult for polyethylene resin to pass through, facilitates the separation of polypropylene resin, and allows for the recovery of a recycled polyolefin resin composition containing high-purity polypropylene resin.

[0072] The shape of the filter pores can be any shape, such as square, rectangular, trapezoidal, rhombus, triangular, hexagonal, polygonal, circular, or elliptical.

[0073] The filtering process can be carried out by installing a filter in the die at the tip of the extrusion section of the kneading apparatus where the melting process S10 and the mixing process S20 are performed. For example, it can also be carried out continuously using an apparatus equipped with a filter screen changer. Examples of continuous processing apparatuses equipped with a screen changer include plate type using metal mesh, backflush type with backwashing, and laser filter type using a flat plate or drum-shaped metal filter and a scraper.

[0074] When filtering is performed using a plate type with a metal mesh, the metal mesh is preferably made of stainless steel. Examples of stainless steel mesh include woven wire mesh as specified in JIS G3555 and industrial woven wire mesh as specified in JIS G3556.

[0075] In the separation step S30, filtering can be performed not only once, but two or more times. When filtering is performed twice, the first filter can be designated as the first filter and the second filter as the second filter. In this case, it is preferable to make the mesh opening of the first filter larger than that of the second filter, as this allows for more precise separation of the polypropylene resin and polyethylene resin in the second filter.

[0076] The filtering process can be carried out using a kneading apparatus that has undergone the melting process S10 and the mixing process S20.

[0077] (Temperature-Increased Extrusion Treatment) In separation step S30, first, the molten waste plastic is further heated to further reduce the viscosity of the polypropylene resin, and the molten waste plastic is extruded to remove the high-viscosity polyethylene resin. At this time, the polypropylene resin, which has been further reduced in viscosity, moves in the opposite direction to the extrusion direction due to its low viscosity. Then, the temperature of the remaining waste plastic is lowered and the polypropylene resin is separated by extruding it. As a result, a recycled polyolefin resin composition containing high-purity polypropylene resin can be recovered.

[0078] In the temperature-increasing extrusion process, the temperature may be raised by 10°C to 20°C from the molten waste plastic in order to further reduce the viscosity of the polypropylene resin. When the temperature is raised by 10°C to 20°C from the molten waste plastic, for example, it may be between 180°C and 240°C, or between 190°C and 220°C.

[0079] In a temperature-controlled extrusion process, polyethylene resin can be separated from waste plastic using an extruder. For example, a metal plate that the resin cannot pass through can be attached to the extruder's die to separate the polyethylene resin.

[0080] In the temperature-increasing extrusion process, the temperature of the remaining waste plastic after the polyethylene resin has been separated may be lowered by 20°C to 30°C in order to reduce the temperature of the low-viscosity polypropylene resin. If the temperature of the remaining waste plastic is lowered by 20°C to 30°C, the temperature may be between 160°C and 210°C, or between 170°C and 190°C.

[0081] The temperature-increasing extrusion process can be carried out using a kneading apparatus that has performed the melting process S10 and the mixing process S20.

[0082] Embodiment 2. [Recycled Polyolefin Resin Composition] The recycled polyolefin resin composition according to Embodiment 2 (hereinafter also referred to as "the composition according to Embodiment 2") can remove polyethylene resin contained in waste plastic with a high removal rate. Here, the polyethylene resin removal rate (%) is expressed as (X - Y) / X × 100, where X is the concentration of polyethylene resin in the waste plastic and Y is the concentration of polyethylene resin in the recycled polyolefin resin composition. For the recycled polyolefin resin composition, the polyethylene resin removal rate is preferably 10% by weight or more, more preferably 20% by weight or more, even more preferably 30% by weight or more, and even more preferably 40% by weight or more.

[0083] The composition according to Embodiment 2 contains high-purity polypropylene resin because the polyethylene resin contained in the waste plastic is removed with a high removal rate. Containing high-purity polypropylene resin means that the recycled polyolefin resin composition contains, for example, 60% by weight or more, preferably 70% by weight or more, and more preferably 80% by weight or more of polypropylene resin in 100% by weight of the recycled polyolefin resin composition. The polypropylene resin contained in the recycled polyolefin resin composition is the same as the polypropylene resin contained in the waste plastic described above.

[0084] The recycled polyolefin resin composition may contain thermoplastic resins other than polypropylene resin and polyethylene resin, but the content of such thermoplastic resins is preferably low, and may be, for example, 20% by weight or less, 10% by weight or less, 5% by weight or less, or 1% by weight or less in 100% by weight of the recycled polyolefin resin composition.

[0085] The recycled polyolefin resin composition may contain other components mixed in the mixing step S20 from the viewpoint of improving the durability of the molded article, for example, it may contain other components such as degradation inhibitors, antioxidants, metal deactivators, ultraviolet absorbers, light stabilizers, antistatic agents, plasticizers, mold release agents, flame retardants, flame retardant aids, dyes, and pigments. The content of the components mixed in the mixing step S20 may be 10% by weight or less, 5% by weight or less, 1% by weight or less, 0.001% by weight or more, 0.01% by weight or more, or 0.1% by weight or more.

[0086] Embodiment 3. [Recycled Polyolefin Resin Composition Molded Article] The recycled polyolefin resin composition molded article is formed using the recycled polyolefin resin composition according to Embodiment 2. Because the polypropylene resin in the composition according to Embodiment 2 is of high purity, the molded article has excellent durability.

[0087] The molded product can be obtained by molding using an extruder. Examples of molding methods include injection molding, injection compression molding, extrusion molding, shape extrusion, transfer molding, hollow molding, gas-assisted hollow molding, blow molding, extrusion blow molding, IMC (in-mold coating) molding, rotational molding, multilayer molding, two-color molding, insert molding, sandwich molding, foam molding, and pressure molding. The molding method may be used alone or in combination of two or more methods.

[0088] The shape of the molded product is not particularly limited and can be selected according to the application and purpose of use of the molded product. Examples of molded product shapes include plate-like, rod-like, sheet-like, film-like, cylindrical, annular, circular, elliptical, polygonal, hollow, frame-like, box-like, and panel-like shapes. The molded product may be, for example, a housing and parts for various devices such as home appliances and office automation equipment, an interior panel for automobiles, a headlamp lens for automobiles such as motorcycles, and a lighting cover. The surface of the molded product may have a transferred uneven shape or may have a three-dimensional curved surface. The molded product may have a single-layer structure or a multi-layer structure. If the molded product has a multi-layer structure, at least one layer may be formed using the composition according to Embodiment 2, or all layers may be formed using the composition according to Embodiment 2.

[0089] The present disclosure will be further described below with reference to examples and comparative examples, but the present disclosure is not limited to these examples.

[0090] <Examples 1-21, Comparative Examples 1-3> Waste plastics were prepared to have the compositions of components A and B shown in Tables 1-4. Using a twin-screw compounding extruder (TEX-26SX, manufactured by Shibaura Industries Co., Ltd.), the materials were melt-kneaded at a screw rotation speed of 120 rpm and a material supply rate of 10 kg / h, and then pelletized to obtain waste plastic pellets. The columns for components A and B in Tables 1-4 show the percentage content of each component in 100% by weight of the waste plastic. The temperature during the mixing process is shown in the "Temperature" column.

[0091] The above-mentioned waste plastic pellets were mixed with components C, D, E, and other additives to achieve the compositions shown in Tables 1 to 4. Melt-mixing was then carried out using a twin-screw extruder at a screw rotation speed of 120 rpm and a material feed rate of 10 kg / h. The columns for components C, D, E, and other additives in Tables 1 to 4 indicate the mixing ratio (parts by weight) of each component relative to 100% by weight of the waste plastic. The temperature during the melting process was the same as that during the mixing process.

[0092] Subsequently, polypropylene resin was separated from the molten waste plastic, and the resin composition was recovered. Separation was carried out by either separation method A or B, as described below. In separation method A, filtering was performed using a stainless steel wire mesh. The stainless steel wire mesh had a mesh size of #120. In separation method B, a temperature-controlled extrusion treatment was performed. Specifically, the temperature of the molten waste plastic was further increased to 200°C to remove the polyethylene resin, and the temperature of the remaining waste plastic was lowered to 160°C to 170°C to separate the polypropylene resin. In the separation process column, "A" is indicated if separation method A was performed, and "B" is indicated if separation method B was performed.

[0093] The components indicated by each symbol in Tables 1 to 4 are as follows: (Component A: Polypropylene resin) A1...Polypropylene resin (Novatec BC03B manufactured by Nippon Polypropylene Co., Ltd.) A2...Polypropylene resin (Novatec MA3H manufactured by Nippon Polypropylene Co., Ltd.) A3...Used plastic containing polypropylene resin (manufactured by Green Cycle Systems Co., Ltd.) A4...Used plastic containing polypropylene resin (manufactured by Toyama Environmental Services Co., Ltd.)

[0094] (Component B: Polyethylene resin) B1...Polyethylene resin (Novatec HJ360 manufactured by Nippon Polyethylene Co., Ltd.) B2...Used plastic containing polyethylene resin (manufactured by Green Cycle Systems Co., Ltd.)

[0095] (Component C: Organic peroxide) C1: 2,5-dimethyl-di-t-butylperoxyhexane (Perhexa 25B, manufactured by NOF Corporation) C2: di(2-t-butylperoxyisopropyl)benzene (Perbutyl P, manufactured by NOF Corporation) C3: 2,5-dimethyl-2,5-di(t-butylperoxy)hexyn-3 (Luperox 130, manufactured by Arkema Yoshitomi Co., Ltd.)

[0096] (Component D: Crystallization nucleating agent) D1: N,N'-Diclohexyl-2,6-Naphthalenedicarboxamide (NJester NU-100, manufactured by Shin Nippon Rika Co., Ltd.) D2: Sodium 2,2'-Methylenebis-(4,6-di-tert-butylphenol) phosphate (ADEKA NA-11, manufactured by ADEKA Corporation)

[0097] (Component E: Degradation inhibitor) E1...3,9-bis{2-[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy]-1,1-dimethylethyl}-2,4,8,10-tetraoxaspiro[5.5]undecane (ADEKA Corporation, Adekastab AO-80) E2...1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane (ADEKA Corporation, Adekastab AO-30) E3...4,4'-butylidenebis(6-t-butyl-m-cresol) (ADEKA Corporation, Adekastab AO-40) E4...tris(4-t-butyl-3-hydroxy-2,6-dimethylbenzyl)isocyanuric acid (Cheminox 9425, Chemipro Chemical Co., Ltd.) E5...Bis(hydrogenated tallowalkyl)hydroamine (Revonox 420, manufactured by Chitec Technology Co., Ltd.) E6...Bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate (ADEKA Corporation's ADEKA Stab LA-72) E7...Tetrakis(2,2,6,6-tetramethyl-4-piperidyl)butane-1,2,3,4-tetracarboxylate (ADEKA Corporation's ADEKA Stab LA-57) E8...2,2,6,6-tetramethyl-4-piperidinyl stearate (ADEKA Corporation's ADEKA Stab LA-40)

[0098] The resin compositions recovered in Examples 1 to 21 and Comparative Examples 1 to 3 were evaluated as follows.

[0099] <Evaluation Method> Evaluation Method 1: Concentration of Polypropylene Resin in Resin Composition The concentration of polypropylene resin in the resin composition recovered by the above procedure was calculated using a Differential Scanning Calorimetry (DSC). First, the melting point of the recovered resin composition was measured using the DSC in accordance with the method of JIS K7121, and the polypropylene resin and polyethylene resin in the resin composition were identified from the measured melting point. Next, the heat of fusion (ΔH) of the polypropylene resin and polyethylene resin was determined, and the ratio of the recovered resin composition was calculated from the area ratio of each, and the concentration of polypropylene resin in the resin composition was determined. The measurement conditions for the DSC were as follows: first, the temperature was increased from 20°C to 250°C at a rate of 10°C / min, and then the temperature was decreased from 250°C to 20°C at a rate of 10°C / min. This constituted one set. After completing the first set, the sample was measured again under the same conditions as described above, and the results from the second set were used. This procedure was also performed on molten waste plastics.

[0100] In Tables 1 to 4, "Pre-purity of PP" indicates the percentage of polypropylene resin concentration in the waste plastic calculated using the above DSC. In Tables 1 to 4, "Pre-purity of PE" indicates the percentage of polyethylene resin concentration in the waste plastic calculated using the above DSC. In Tables 1 to 4, "Pre-purity of foreign matter" indicates the percentage of concentration of components other than polypropylene resin and polyethylene resin (e.g., thermoplastic resins such as polystyrene resin, polyamide resin, and polyethylene terephthalate resin, as well as additives) in the waste plastic calculated using the above DSC. In Tables 1 to 4, "Post-purity of PP" indicates the percentage of polypropylene resin concentration in the resin composition calculated using the above DSC.

[0101] Evaluation Method 2: Polyethylene Resin Removal Rate Based on the results obtained by Evaluation Method 1 above, the polyethylene removal rate (%) is calculated using the following formula, which is derived from the concentration of polyethylene resin in the waste plastic (X) and the concentration of polyethylene resin in the resin composition (Y). This value is shown in the "PE Removal Rate" column of Tables 1 to 4. (X - Y) / X × 100

[0102] Evaluation Method 3: Durability of Resin Composition Molded Products To evaluate the durability of the recovered resin composition molded products, a multipurpose test specimen of type A of the resin composition was first prepared using an injection molding machine in accordance with JIS K7139. This test specimen was subjected to the method in accordance with JIS K7368. In this JIS standard, when estimating the relationship between lifespan and temperature, the recommended test temperature is set to 100°C to 150°C. Therefore, in this evaluation, the test temperature was set to 140°C and the test time to 500 hours. The presence or absence of cracks in the resin composition molded products after heating was confirmed by visual inspection and optical microscope.

[0103] In Tables 1-4, the "Durability Test" column was evaluated according to the following criteria: "+" ... No cracks occurred; "-" ... Cracks occurred; "N.D." ... No resin composition molded product was obtained.

[0104] As an overall evaluation, an evaluation was conducted based on the results of evaluation methods 1 to 3, and is shown in the "Overall Evaluation" column in Tables 1 to 4. The evaluation was conducted according to the evaluation criteria shown below. Note that in evaluations A to C, if the condition that no cracks occur in the resin composition molded product is not met, it means that cracks occur in the resin composition molded product, or that no resin composition molded product can be obtained. "A"...The concentration of polypropylene resin in the resin composition is 80% by weight or more, the removal rate of polyethylene resin is 40% or more, and no cracks occurred in the resin composition molded product. "B"...At least one of the above evaluation criteria A is not met. "C"...At least two or more of the above evaluation criteria A are not met.

[0105]

[0106]

[0107]

[0108]

[0109] The embodiments and examples of the present invention should be considered in all respects to be illustrative and not restrictive. The scope of this disclosure is indicated by the claims rather than the foregoing description, and all modifications within the meaning and scope of the claims are intended to be included.

[0110] S10 Melting process, S20 Mixing process, S30 Separation process.

Claims

1. A method for recovering a recycled polyolefin resin composition, comprising the steps of: melting waste plastics containing polypropylene resin and polyethylene resin; mixing the waste plastics with an organic peroxide and a crystal nucleating agent; and separating the polypropylene resin from the waste plastics after the melting and mixing steps.

2. A method for recovering a recycled polyolefin resin composition according to claim 1, wherein the separation in the separation step is performed by filtration.

3. A method for recovering a recycled polyolefin resin composition according to claim 1 or claim 2, wherein the separation in the separation step is carried out by a temperature-increasing extrusion treatment.

4. A method for recovering a recycled polyolefin resin composition according to any one of claims 1 to 3, wherein the organic peroxide comprises one or more selected from the group consisting of 2,5-dimethyl-di-t-butylperoxyhexane, di(2-t-butylperoxyisopropyl)benzene, and 2,5-dimethyl-2,5-di(t-butylperoxy)hexyn-3.

5. A method for recovering a recycled polyolefin resin composition according to any one of claims 1 to 4, wherein the nucleating agent comprises one or more selected from the group consisting of α-nucleating agents and β-nucleating agents, the α-nucleating agent comprises one or more selected from the group consisting of sodium benzoate, di-p-tert-butylaluminum hydroxybenzoate, and sodium 2,2'-methylenebis-(4,6-di-tert-butylphenol) phosphate, and the β-nucleating agent is N,N'-dicyclohexyl-2,6-naphthalenedicarboxamide.

6. In the mixing step, a degradation inhibitor is further mixed, the degradation inhibitor being 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane, 4,4'-butylidenebis(6-t-butyl-m-cresol), 3,9-bis{2-[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy]-1,1-dimethylethyl}-2,4,8,10-tetraoxaspiro[5.5]undecane, 2,2'-methylenebis(6-t-butyl-4-ethylphenol), tris(4-t-butyl-3-hydroxy-2,6-dimethylbenzyl)isocyanuric acid, bis(hydrogenated tulose alkyl)hydroamine, bis(hydrogenated palm oil A method for recovering a recycled polyolefin resin composition according to any one of claims 1 to 5, comprising one or more selected from the group consisting of lucyl hydroamine, tetrakis(1,2,2,6,6-pentamethylpiperidine-4-yl)butan-1,2,3,4-tetracarboxylate, tetrakis(2,2,6,6-tetramethyl-4-piperidyl)butan-1,2,3,4-tetracarboxylate, bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate, bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate, and 2,2,6,6-tetramethyl-4-piperidinyl stearate.

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