Method for recycling recovered polyester resins

Abstract

To provide a method for recycling polyester resin-containing compositions recovered from automobiles. [Solution] A method for regenerating recovered polyester resin, comprising solid-phase polymerization of a polyester resin-containing composition recovered from an automobile at a temperature T (°C) that satisfies the following formula (1). (Melting point of polyester resin -70°C) ≤ T(°C) ≤ (Melting point of polyester resin -5°C) ... (1)

Description

Technical Field

[0004] , , , , ,

[0001] The present invention relates to a method for recycling polyester-based resins recovered from automobiles.

Background Art

[0002] In recent years, automobiles have been promoted to be lightweight, such as replacing metal parts with resin molded products to reduce fuel consumption. For example, resin molded products are used in many in-vehicle parts, such as exterior panels, engine-related parts, mechanism parts, door linings, around the dashboard, consoles, meter panels, monitors, switches, etc. Various resins such as polyethylene terephthalate, polystyrene, polycarbonate, polypropylene, polyurethane, and polyamide are used for resin molded products. In particular, polyester-based resins are widely used as interior and exterior parts because they are lightweight, have high weather resistance, and are excellent in moldability. From the viewpoints of reducing waste and lightening the burden on the environment, recycling and reuse of resin molded products recovered from scrapped cars have become important issues. As a method for recycling resin molded products, for example, Patent Document 1 proposes a technique of heating parts at a predetermined temperature to separate reinforcing materials from a polymer matrix. Further, Patent Document 2 proposes a technique of solubilizing and decomposing waste materials of automobile carpets.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] Polyester resin molded products recovered from automobiles exhibited degraded polyester resin quality. When recycled resin obtained by crushing and pelletizing after recovery was used as a material for automotive plastic molded products, its physical properties and quality, such as strength and heat resistance, were inferior compared to novel polyester resin compositions (virgin resin compositions). Furthermore, the resin molded products recovered from automobiles often contain multiple types of polyester resins with different compositions, as well as resins other than polyester resins. They also contain large amounts of various additives such as stabilizers, flame retardants, and colorants. This complicates the recycling process, requiring adjustments to the compatibility between resins and decomposition conditions, or the additives may interfere with the structure and chemical reactions of the polyester resins. Therefore, the recycling of polyester resin molded products recovered from automobiles as plastic molded articles for automotive and home appliance applications, which require a high degree of polymerization, has not progressed. The present invention has been made in view of the above problems, and its object is to provide a method for regenerating polyester resin-containing compositions recovered from automobiles. [Means for solving the problem]

[0005] The regeneration method of the present invention that achieves the above objective has the following configuration. [1] A method for regenerating recovered polyester resin, comprising solid-phase polymerization of a polyester resin-containing composition recovered from an automobile at a temperature T (°C) that satisfies the following formula (1). (Melting point of polyester resin -70°C) ≤ T(°C) ≤ (Melting point of polyester resin -5°C) ... (1) [2] The recycling method according to [1] above, wherein the recovered polyester resin-containing composition contains two or more polyester resins with different basic structures. [3] The recycling method according to [1] or [2] above, wherein the recovered polyester resin-containing composition contains at least one selected from the group consisting of resins other than polyester resins, inorganic reinforcing agents, stabilizers, flame retardants, and colorants. [4] The recycling method according to any one of [1] to [3] above, wherein the recovered polyester resin-containing composition does not contain a polyfunctional reactive compound, or contains one in an amount of 1.0% by mass or less based on 100% by mass of the polyester resin. [5] The recycling method according to any one of [1] to [4] above, wherein the recycled polyester resin-containing composition obtained by solid-phase polymerization of the polyester resin-containing composition is used as a plastic molded article for automobiles or home appliances. [6] The recycling method according to [5] above, wherein the polyester resin-containing composition contains a polystyrene resin, and the recycled polyester resin is used for automotive applications as a structural member. [7] The recycling method according to [5] or [6] above, wherein the polyester resin-containing composition contains glass fibers, and the recycled polyester resin is used in plastic materials for automobiles or home appliances other than structural members. [8] A polyester resin composition in which the content of polyfunctional reactive compounds is suppressed to 1.0% by mass or less is used to manufacture polyester automotive parts. A method for recycling polyester resin, comprising recovering the used polyester automotive parts from an automobile, and solid-phase polymerizing the recovered polyester automotive parts at a temperature T (°C) that satisfies the following formula (1), while keeping the amount of polyfunctional reactive compounds in the recovered material to 1.0% by mass or less relative to 100% by mass of the polyester resin. (Melting point of polyester resin -70°C) ≤ T(°C) ≤ (Melting point of polyester resin -5°C) ... (1) [Effects of the Invention]

[0006] The present invention provides a method for regenerating polyester resin-containing compositions recovered from automobiles. According to a preferred embodiment of the present invention, the regeneration method makes it possible to restore the molecular weight of a polyester resin-containing composition recovered from an automobile to, for example, a level equivalent to that of the polyester resin-containing composition before use. [Modes for carrying out the invention]

[0007] Polyester resin-containing compositions recovered from automobiles (hereinafter referred to as "recovered resin compositions") may contain multiple types of polyester resins, as well as various additives such as mold release agents and resins other than polyester resins. When multiple types of polyester resins are present, the reactivity of each resin differs due to differences in their basic structures, which has been a factor in making the recycling of recovered resin compositions difficult. Furthermore, in the regeneration of recovered resin compositions by solid-phase polymerization, if there are many additives, such as additives and resins other than polyester resins, the solid-phase polymerization of the polyester resin may be hindered, or the additives themselves may delay the reaction. In particular, if additives decompose due to heating, the polyester resin may oxidize or its physical properties may deteriorate. Therefore, in order to regenerate the recovered resin composition targeted by the present invention, it is necessary to consider not only the composition of the polyester resin but also the influence of additives such as additives.

[0008] As a result of our investigations, we found that by solid-phase polymerization of the recovered resin composition at a temperature T (°C) that satisfies the following formula (1), we can solve the above problems and regenerate the recovered resin composition, leading to the present invention. (Melting point of polyester resin -70°C) ≤ T(°C) ≤ (Melting point of polyester resin -5°C) ... (1) In the present invention, "regeneration" means increasing the molecular weight of the recovered resin composition. In a preferred embodiment of the present invention, the above regeneration means restoring the molecular weight to the same state as, or close to, that of the polyester resin-containing composition (hereinafter referred to as the virgin resin composition) before use, i.e., before molding into a resin molded product (sometimes referred to as regenerating the molecular weight to its original state). Hereinafter, the polyester resin-containing composition regenerated by solid-phase polymerization of the recovered resin composition will be referred to as the regenerated resin composition.

[0009] In another preferred embodiment of the present invention, the regeneration described above may involve increasing the reduced viscosity of the recovered resin composition to restore it to the reduced viscosity required for reuse. For example, the increase in the reduced viscosity recovered by solid-phase polymerization from the reduced viscosity of the recovered resin composition is preferably 5% or more, more preferably 10% or more, and even more preferably 15% or more. Furthermore, the reduced viscosity can be measured by dissolving 0.1 g of the sample in 25 ml of a phenol / tetrachloroethane mixed solvent (mass ratio 6 / 4) and measuring it at 30°C using an Ubbelohde viscometer (unit: dl / g).

[0010] The recycling method of the present invention is intended for polyester resin compositions recovered from automobiles. An automobile is a vehicle that travels on land using wheels driven by a power source such as an engine or motor, and includes not only four-wheeled vehicles but also two-wheeled and three-wheeled vehicles. The recovered resin composition is not limited to that recovered from end-of-life vehicles (ELVs), but may also include material discarded during the manufacturing or repair process.

[0011] The recovered resin composition is a composition containing a high molecular weight polyester resin composed of a polycarboxylic acid component and a polyhydric alcohol component, with the remainder being at least one of the additives described later. The polyester resin is a crystalline resin.

[0012] The polycarboxylic acid component includes dicarboxylic acid components, tricarboxylic acid components (which are trivalent polycarboxylic acids), and polycarboxylic acid components with tetravalent or higher valencies. The polyhydric alcohol component includes diol components and polyhydric alcohol components with tetravalent or higher valencies. The polycarboxylic acids exemplified below include not only the polycarboxylic acid itself, but also its esters and anhydrides. The polyester resin preferably has a chemical structure obtained by polycondensation of a dicarboxylic acid component and a diol component. The dicarboxylic acid component and the diol component may each consist of one or more selected components.

[0013] The dicarboxylic acid component is not particularly limited, and examples thereof include aliphatic dicarboxylic acids, alicyclic dicarboxylic acids, aromatic dicarboxylic acids, and the like. Examples of the aliphatic dicarboxylic acid include adipic acid, sebacic acid, dimer acid, fumaric acid, maleic acid, succinic acid, and the like. Examples of the alicyclic dicarboxylic acid include 1,3 - cyclohexanedicarboxylic acid, 1,4 - cyclohexanedicarboxylic acid, tetrahydrophthalic acid, hexahydrophthalic acid, methyltetrahydrophthalic acid, and the like. Examples of the aromatic dicarboxylic acid include terephthalic acid, isophthalic acid, orthophthalic acid, naphthalenedicarboxylic acid, 2,5 - furandicarboxylic acid, 5 - sodium sulfodimethylisophthalic acid, and esters and acid anhydrides thereof.

[0014] In a preferred embodiment of the present invention, the dicarboxylic acid component is preferably an aliphatic dicarboxylic acid or an aromatic dicarboxylic acid, more preferably contains at least an aromatic dicarboxylic acid, and even more preferably an aromatic dicarboxylic acid. Among the above - exemplified aromatic dicarboxylic acids, terephthalic acid, isophthalic acid, orthophthalic acid, and 2,5 - furandicarboxylic acid are more preferred, and terephthalic acid and isophthalic acid are even more preferred. When containing an aromatic dicarboxylic acid, in 100 mol% of the dicarboxylic acid component constituting the polyester - based resin, the aromatic dicarboxylic acid is preferably 40 mol% or more, more preferably 50 mol% or more, even more preferably 60 mol% or more, and particularly preferably 70 mol% or more. Terephthalic acid and isophthalic acid as the aromatic dicarboxylic acid may be used alone or in combination. For example, when terephthalic acid and isophthalic acid are used in combination, the content ratio (terephthalic acid:isophthalic acid) is preferably 5:95 to 95:5, more preferably 20:80 to 80:20, even more preferably 30:70 to 70:30, and particularly preferably 40:60 to 60:40 on a molar basis.

[0015] The diol component is not particularly limited, but examples include aliphatic diols, alicyclic diols, aromatic diols, and monomers containing a bisphenol skeleton. Aliphatic diols include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2-methyl-1,3-propanediol, neopentyl glycol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, 1,8-octanediol, 2-methyl-1,3-hexanediol, 2-methyl-2-ethyl-1,3-propanediol, and 2,2-diethyl-1,3-propanediol. Examples include 2-ethyl-2-n-propyl-1,3-propanediol, 2,2-di-n-propyl-1,3-propanediol, 2-n-butyl-2-ethyl-1,3-propanediol, 2,2-di-n-butyl-1,3-propanediol, 2,4-diethyl-1,5-pentanediol, 2-ethyl-1,3-hexanediol, dimer diol, diethylene glycol, triethylene glycol, dipropylene glycol, polyethylene glycol, polytetramethylene glycol, and polypropylene glycol. Among these, linear aliphatic diols having 2 to 9 carbon atoms, such as ethylene glycol, diethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, and 1,9-nonanediol, are preferred, linear aliphatic diols having 4 or fewer carbon atoms, such as ethylene glycol, diethylene glycol, 1,3-propanediol, and 1,4-butanediol, are more preferred, and ethylene glycol and 1,4-butanediol are even more preferred.

[0016] Examples of alicyclic diols include 1,4-cyclohexanedimethanol and tricyclodecanedimethanol.

[0017] Examples of aromatic diols include diphenolic acids.

[0018] Examples of bisphenol skeleton-containing monomers include bisphenol A, bisphenol B, bisphenol E, bisphenol F, bisphenol AP, bisphenol BP, bisphenol P, bisphenol PH, bisphenol S, bisphenol Z, 4,4'-dihydroxybenzophenone, bisphenol fluorene and their hydrogenated derivatives, and glycols such as ethylene oxide adducts and propylene oxide adducts obtained by adding 1 to several moles of ethylene oxide or propylene oxide to the hydroxyl group of bisphenols.

[0019] As the diol, aliphatic diols and alicyclic diols are preferred. When aliphatic diols and alicyclic diols are included, the total amount of aliphatic diols and alicyclic diols in 100 mol% of the diol component constituting the polyester resin is preferably 50 mol% or more, more preferably 70 mol% or more, even more preferably 80 mol% or more, particularly preferably 90 mol% or more, and may be 100 mol%.

[0020] The polyester resin may be a homopolymer or a copolymer. Examples of copolymerization components include polycarboxylic acid components and polyhydric alcohol components. Examples of polycarboxylic acid components include aromatic dicarboxylic acids such as isophthalic acid, orthophthalic acid, 2,6-naphthalenedicarboxylic acid, 4,4′-diphenyldicarbon, 2,5-franciocarboxylic acid, and 5-sodium sulfodimethylisophthalic acid; aliphatic dicarboxylic acids such as succinic acid, adipic acid, azelaic acid, sebacic acid, dimer acid, fumaric acid, and maleic acid; and 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, and 4-methyl-1,2 Examples include alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid, tetrahydrophthalic acid, hexahydrophthalic acid, and methyltetrahydrophthalic acid; trivalent aromatic carboxylic acids such as trimellitic acid, trimesic acid, and trimellitic anhydride (TMA); trivalent aliphatic carboxylic acids such as citric acid and citric anhydride; and trivalent alicyclic tricarboxylic acids such as 1,2,4-cyclohexanetricarboxylic acid, 1,3,5-cyclohexanetricarboxylic acid, and cyclohexane-1,2,4-tricarboxylic acid-1,2-anhydride. These copolymerization components may be used individually or in combination of two or more. The copolymerization ratio of the copolymerization component (polycarboxylic acid) is preferably 40 mol% or less, more preferably 30 mol% or less, even more preferably 20 mol% or less, even more preferably 10 mol% or less, and particularly preferably 5 mol% or less, when the total polycarboxylic acid component of the polyester resin is taken as 100 mol%, and may also be 0 mol%.

[0021] Examples of polyhydric alcohol components include diethylene glycol, 2-methyl-1,3-propanediol, 1,3-propanediol, 1,2-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, 1,8-octanediol, neopentyl glycol, neopentyl glycol hydroxypivalate, dipropylene glycol, 2,2,4-trimethyl-1,3-pentanediol, 2-methyloctanediol, 2-butyl-2-ethyl-1,3-propanediol, dimer diol, 2-methyl-1,3-hexanediol, and 2-methyl-2-ethyl-1,3-propanediol. Aliphatic diols such as ol, 2,2-diethyl-1,3-propanediol, 2-ethyl-2-n-propyl-1,3-propanediol, 2,2-di-n-propyl-1,3-propanediol, 2-n-butyl-2-ethyl-1,3-propanediol, 2,2-di-n-butyl-1,3-propanediol, 2,4-diethyl-1,5-pentanediol, 2-ethyl-1,3-hexanediol, dimer diol, diethylene glycol, triethylene glycol, dipropylene glycol, polyethylene glycol, polytetramethylene glycol, and polypropylene glycol; and alicyclic diols such as 1,4-cyclohexanedimethanol, cyclohexanedimethanol, and tricyclodecanedimethanol. These copolymer components may be used alone or in combination of two or more. The copolymerization ratio of the copolymerization component (polyhydric alcohol) is preferably 40 mol% or less, more preferably 30 mol% or less, even more preferably 20 mol% or less, even more preferably 10 mol% or less, and particularly preferably 5 mol% or less, when the total polyhydric alcohol component of the polyester resin is considered to be 100 mol%, and may also be 0 mol%.

[0022] The following are examples of polyester resin homopolymers, but are not limited to: polyethylene terephthalate (PET), polytrimethylene terephthalate (PTT), polybutylene terephthalate (PBT), polycyclohexylenedimethylene terephthalate (PCT), polybutylene isophthalate (PBI), polycyclohexanedimethylene isophthalate (PCHT), polybutylene orthophthalate (PBO), polyethylene naphthalate (PEN), polybutylene naphthalate (PBN), and others. Preferably, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polycyclohexylenedimethylene terephthalate (PCT) are used. The copolymers of polyester resins are not limited to those listed below, but examples include copolymers of neopentyl glycol and polyethylene terephthalate (PET); copolymers of neopentyl glycol, isophthalic acid (copolymer component) and polyethylene terephthalate (PET); copolymers of diethylene glycol and polyethylene terephthalate (PET); copolymers of isophthalic acid, diethylene glycol (copolymer component) and polyethylene terephthalate (PET); various copolymerized polyethylene terephthalates such as copolymers of 1,4-cyclohexanedimethanol and polyethylene terephthalate (PET); copolymers of neopentyl glycol and PBT; copolymers of neopentyl glycol, isophthalic acid (copolymer component) and PBT; copolymers of diethylene glycol and PBT; copolymers of isophthalic acid, diethylene glycol (copolymer component) and PBT; and various copolymerized polybutylene terephthalates such as copolymers of 1,4-cyclohexanedimethanol and PBT. The same copolymers can also be applied to the above-mentioned single copolymers other than PET and PBT.

[0023] The number-average molecular weight (Mn) of the recovered resin composition and the recycled resin composition is not particularly limited, but is, for example, 1,000 to 100,000, preferably 2,000 to 90,000, and more preferably 3,000 to 80,000. The weight-average molecular weight (Mw) of the recovered resin composition and the recycled resin composition is not particularly limited, but is, for example, 2,000 to 300,000, preferably 3,000 to 200,000, more preferably 4,000 to 150,000, and even more preferably 5,000 to 100,000. The degree of dispersion (Mw / Mn) of the recovered resin composition and the recycled resin composition is preferably 1.0 to 7.0, more preferably 1.1 to 6.0, and even more preferably 1.2 to 5.0.

[0024] The glass transition temperature (Tg) of the recovered resin composition and the recycled resin composition is preferably -100 to 150°C, more preferably -80 to 120°C, even more preferably -50 to 100°C, and particularly preferably 0°C to 90°C.

[0025] The melting points of the recovered resin composition and the recycled resin composition are preferably 130 to 320°C, more preferably 140 to 300°C, and even more preferably 150 to 290°C.

[0026] The cooling crystallization temperature (hereinafter sometimes referred to as the crystallization temperature) of the recovered resin composition and the recycled resin composition is preferably 100 to 230°C, more preferably 110 to 220°C, and even more preferably 120 to 210°C.

[0027] The reduced viscosity (ηsp / c) of the recovered resin composition and the recycled resin composition is preferably 0.4 to 2.0 dl / g, more preferably 0.5 to 1.8 dl / g, and even more preferably 0.6 to 1.5 dl / g.

[0028] In one embodiment of the present invention, the recovered resin composition may contain two or more polyester resins. According to the regeneration method of the present invention, the recovered resin composition can be regenerated even if it contains two or more polyester resins.

[0029] The two or more polyester resins may preferably be two or more polyester resins with different basic structures. Different basic structures mean that the repeating units [(-CO-R-CO-O-R'-O-)] linked by ester bonds are different. In the repeating units, R represents a polyhydric carboxylic acid component and R' represents a polyhydric alcohol component, preferably R is a dicarboxylic acid component and R' is a diol component, more preferably R is the preferred dicarboxylic acid component and R' is the preferred diol component.

[0030] The combination of two or more polyester resins may be any combination of two or more polyester resins with different basic structures, and the combination and proportions are not particularly limited as they will vary depending on the material to be recovered. As one embodiment, for example, the combination of two or more polyester resins may be appropriately selected from the above-mentioned homopolymers and copolymers. Other embodiments include, for example, a mixture of polybutylene terephthalate (PBT) and polyethylene terephthalate (PET), a mixture of PBT and isophthalic acid copolymer PET, a mixture of PET and polyester elastomer (a copolymer consisting of PBT and polytetramethylene glycol), a mixture of PBT and neopentyl glycol copolymer PET, a mixture of PBT and dimer ol copolymer PET, and a mixture of PET and dimer ol copolymer PBT. In one embodiment, polyester resins with the same basic structure, even if their composition differs, may be excluded from the group of two or more polyester resins. For example, a mixture of isophthalic acid copolymer PBT and PBT cannot be distinguished because they have the same basic structure (PBT), and are therefore treated as one type.

[0031] The recovered resin composition contains additives, and examples of additives include resins other than polyester resins (hereinafter referred to as "other resins"), inorganic reinforcing materials, stabilizers, flame retardants, and colorants. In one embodiment, the recovered resin composition may contain at least one selected from the group consisting of other resins, inorganic reinforcing agents, stabilizers, flame retardants, and colorants. According to the regeneration method of the present invention, regeneration is possible even if the recovered resin composition contains a large amount of additives. The amount of additives in the recovered resin composition is not particularly limited as it varies depending on the type of automobile and molded parts, but considering regeneration by solid-phase polymerization, the amount of additives per 100% by mass of the recovered resin composition is preferably 60% by mass or less, more preferably 50% by mass or less, even more preferably 40% by mass or less, and particularly preferably 30% by mass or less.

[0032] Other resins The type of resin other than polyester resin is not particularly limited, but in one preferred embodiment, the other resin may be a thermoplastic resin. Other resins include, for example, polyphenylene sulfide (PPS), liquid crystal polymer (LCP), aramid resin, polyether ether ketone (PEEK), polyether ketone (PEK), polyetherimide (PEI), thermoplastic polyimide, polyamideimide (PAI), polyether ketone ketone (PEKK), polyphenylene ether (PPE), polyethersulfone (PES), polysulfone (PSU), polycarbonate (PC), polyoxymethylene (POM), polypropylene (PP), polyethylene (PE), polymethylpentene (TPX), polystyrene (PS), polymethyl methacrylate, acrylonitrile-styrene copolymer (AS), acrylonitrile-butadiene-styrene copolymer (ABS), styrene-acrylic acid copolymer, styrene-methacrylic acid copolymer, polyamide (PA), styrene-ethylene-butadiene-styrene copolymer (SEBS), and styrene-ethylene-butadiene-styrene copolymer (SEPS). The other resins included in the recovered resin composition may be one type or two or more types. If the recovered resin composition contains other resins, the polyester resin and the other resin (e.g., polystyrene resin) may have different melting points. However, the recovered resin composition can be regenerated by performing solid-phase polymerization under temperature conditions that satisfy formula (1) above. The content of other resins in the recovered resin composition is not particularly limited as long as it does not impair the regeneration of the polyester resin within the range of formula (1) above. The content of other resins is preferably less than 50% by mass (including 0% by mass, the same applies hereinafter), more preferably 30% by mass or less, and even more preferably 10% by mass or less, based on 100% by mass of the polyester resin (total if multiple are included).

[0033] Inorganic reinforcement Inorganic reinforcing materials are additives used to improve the strength of resin molded products for automobiles, and examples include long inorganic materials and inorganic materials other than long inorganic materials (hereinafter referred to as inorganic fillers). Examples of long inorganic materials include fibrous materials such as glass fibers, carbon fibers, aramid fibers, alumina fibers, silicon carbide fibers, and zirconia fibers; whiskers such as aluminum borate and potassium titanate; needle-shaped wollastonite; and milled fibers. Examples of inorganic fillers include asbestos, glass beads, glass flakes, glass balloons, silica, talc, kaolin, wollastonite, mica, alumina, hydrotalcite, montmorillonite, graphite, carbon nanotubes, fullerenes, zinc oxide, indium oxide, tin oxide, iron oxide, titanium oxide, magnesium oxide, aluminum hydroxide, magnesium hydroxide, red phosphorus, calcium carbonate, potassium titanate, lead zirconate titanate, barium titanate, aluminum nitride, boron nitride, zinc borate, aluminum borate, barium sulfate, magnesium sulfate, and layered silica that has been organically treated for the purpose of delamination. The shape of the inorganic filler is not particularly limited and can be short granules, powder, flakes, spheres, or any other shape other than elongated. In 100% by mass of the recovered resin composition, the total amount of inorganic materials (total if multiple are included) is preferably 80% by mass or less (including 0% by mass, the same applies hereinafter), more preferably 60% by mass or less, even more preferably 40% by mass or less, and even more preferably 20% by mass or less.

[0034] Stabilizer Stabilizers are additives that suppress the decomposition of resins and contribute to ensuring stable processability. Examples of stabilizers include antioxidants, heat stabilizers, light stabilizers, mold release agents, lubrication improvers, metal corrosion inhibitors, ultraviolet absorbers, antistatic agents, lubricants, plasticizers, crystallization accelerators, and crystal nucleating agents. These examples of stabilizers are not limited to those listed below, and various known stabilizers used in automotive plastic molded products may be included in the recovered resin composition.

[0035] Examples of antioxidants include organic antioxidants such as hindered phenol antioxidants, sulfur-based antioxidants, phosphorus-based antioxidants, phosphite compounds, and thioether compounds. Examples of heat stabilizers include 2,6-di-tert-butyl-4-methylphenol, dibutyldithiol, and triphenyl phosphate. Examples of light stabilizers include hindered amine light stabilizers, benzophenone light stabilizers, and imidazole light stabilizers. Examples of release agents include long-chain fatty acids or their esters or metal salts, amide compounds, polyethylene wax, silicone, and polyethylene oxide. Examples of sliding properties improving materials include high molecular weight polyethylene, acid-modified high molecular weight polyethylene, fluororesin powder, molybdenum disulfide, silicone resin, silicone oil, zinc, graphite, and mineral oil. Examples of metal corrosion inhibitors include hydrotalcite compounds. Examples of UV absorbers include triazine-based UV absorbers, benzotriazole-based UV absorbers, and cyanoacrylate-based UV absorbers. Examples of antistatic agents include polyoxyethylene-based antistatic agents, aminosilicone-based antistatic agents, and fatty acid ester-based antistatic agents. Examples of lubricants include paraffinic waxes, carnauba waxes, and fatty acid ester lubricants. Examples of plasticizers include phthalate ester plasticizers, triphenyl phosphate ester plasticizers, dioctyl phthalate plasticizers, and polyethylene glycol plasticizers. Examples of crystallization accelerators include phosphate ester metal salt-based crystallization accelerators and titanate-based crystallization accelerators. Examples of nucleating agents include titanium dioxide-based nucleating agents and borate-based nucleating agents. In 100% by mass of the recovered resin composition, the total amount of stabilizers (total if multiple stabilizers are included) is preferably 10% by mass or less (including 0% by mass, the same applies hereinafter), more preferably 8% by mass or less, and even more preferably 6% by mass or less.

[0036] While there are no particular restrictions on the flame retardants used, examples include halogenated compound flame retardants, halogenated phosphate ester flame retardants, halogenated bisphenol flame retardants, antimony flame retardants, inorganic phosphorus flame retardants, organic phosphate ester flame retardants, nitrogen flame retardants, boron flame retardants, metal salt flame retardants, inorganic flame retardants, and silicon flame retardants. In 100% by mass of the recovered resin composition, the total amount of flame retardants (total if multiple are included) is preferably 20% by mass or less (including 0% by mass, the same applies hereinafter), more preferably 15% by mass or less, and even more preferably 10% by mass or less.

[0037] The colorants are not particularly limited, but examples include various known colorants such as carbon black, organic pigments, inorganic pigments, and dyes. The colors are not particularly limited and include any color such as black, gray, brown, blue, and green. In 100% by mass of the recovered resin composition, the total amount of colorants (total if multiple are included) is preferably 5% by mass or less (including 0% by mass, the same applies hereinafter), more preferably 3% by mass or less, and even more preferably 1% by mass or less.

[0038] If a polyfunctional reactive compound is present, even if the desired molecular weight can be restored by solid-phase polymerization, the reaction between the polyfunctional reactive compound and the polyester resin may form a branched structure. This branched structure can lead to a decrease in crystallinity and a decrease in the melting point. Therefore, in one embodiment, the recovered resin composition may contain a polyfunctional reactive compound, but in a preferred embodiment, the polyfunctional reactive compound contained in the recovered resin composition is either present in small amounts or not present at all. The content of polyfunctional reactive compounds in the recovered resin composition is preferably 1.0% by mass or less, more preferably 0.5% by mass or less, and even more preferably 0% by mass, based on 100% by mass of the polyester resin, i.e., it does not contain polyfunctional reactive compounds.

[0039] Polyfunctional reactive compounds are thought to bond with multiple molecular chains of polyester resins via reactive groups, forming a branched structure. However, when the polyfunctional reactive compound is present in a concentration of 1.0% by mass or less (excluding 0% by mass), considering the addition ratio, the polyfunctional reactive compound will be scattered throughout the polyester resin, resulting in a difference in the degree of branching between the vicinity of the polyfunctional reactive compound and other areas. When the degree of branching is high, molecular mobility generally decreases, the crystallization rate decreases, and the melting point decreases. In other words, a difference in the degree of branching will result in a difference in melting point, and it is conceivable that two melting points may be observed: one equivalent to that of virgin material and another lower than that. If the melting point is similar to that of virgin material, or lower, and the melting point is predominantly similar to that of virgin material (indicated by a large peak area in DSC melting point measurements), then it may be usable depending on the application.

[0040] A polyfunctional reactive compound is a compound that contains two or more functional groups in a single molecule that can react with carboxylic acid termini, alcohol termini, or ester groups. In one embodiment, a polyfunctional reactive compound may be used as a stabilizer. Examples of polyfunctional reactive compounds include, but are not limited to, the following compounds, and may include various known polyfunctional reactive compounds used in automotive plastic molded articles. Functional groups that can react with carboxylic acid or alcohol termini and ester groups include glycidyl groups, oxazoline groups, oxetane groups, and carbodiimide groups. Compounds containing two or more of these functional groups in a single molecule are exemplified as polyfunctional reactive compounds. Compounds containing carbodiimide groups and compounds containing glycidyl groups are particularly frequently used due to their availability.

[0041] For compounds containing a carbodiimide group, polycarbodiimide compounds having two or more -N=C=N- structures in one molecule can be used from a handling perspective. Commercially available products that can be used as polycarbodiimide compounds are listed below. Examples include aromatic polycarbodiimide compounds (product names: "Stavaxol P", "Stavaxol P100", "Stavaxol P400", etc., manufactured by Rhein Chemie), aliphatic polycarbodiimide compounds (product names: "Carbodilite LA-1", "Carbodilite HMV-8CA", "Carbodilite HMV-15CA", etc., manufactured by Nisshinbo Chemical), and carbodiimide-modified diphenylmethane diisocyanate (product names: "Cosmonate LK", "Cosmonate LL", manufactured by Mitsui Chemicals, or product name: "Luplanate MM-103", manufactured by BASF INOAC Polyurethane).

[0042] Compounds containing glycidyl groups can be used, for example, as polymers containing two or more glycidyl groups in one molecule, which are formed by copolymerizing an unsaturated monomer containing glycidyl groups with an aromatic monomer having vinyl groups. Examples of unsaturated monomers containing a glycidyl group include unsaturated carboxylic acid glycidyl esters and unsaturated glycidyl ethers. Examples of unsaturated carboxylic acid glycidyl esters include glycidyl acrylate, glycidyl methacrylate, and monoglycidyl itaconic acid ester. Examples of unsaturated glycidyl ethers include vinyl glycidyl ether, allyl glycidyl ether, 2-methylallyl glycidyl ether, and methacrylate glycidyl ether. Examples of aromatic monomers containing a vinyl group include styrene monomers such as styrene, methylstyrene, dimethylstyrene, and ethylstyrene. Polymers containing two or more glycidyl groups in one molecule, obtained by copolymerizing an unsaturated monomer containing a glycidyl group with an aromatic monomer having a vinyl group, include, for example, compounds with a weight-average molecular weight (Mw) of 1000 or more and an epoxy value of 0.5 meq / g or more.

[0043] One embodiment of the present invention also includes a method for recycling polyester resins, which involves manufacturing polyester automotive parts from a polyester resin composition in which the content of polyfunctional reactive compounds is suppressed to 1.0% by mass or less, recovering the used polyester automotive parts from automobiles, and solid-phase polymerizing the recovered polyester automotive parts at a temperature T (°C) that satisfies formula (1) while maintaining the amount of polyfunctional reactive compounds in the recovered material to 1.0% by mass or less relative to 100% by mass of the polyester resin.

[0044] Analysis of recovered resin composition In this invention, a preferred embodiment is to perform compositional analysis of the recovered resin composition. The compositional analysis may target all components contained in the recovered resin composition, such as polyester resins, other resins, reinforcing materials, and additives, or specific components. By performing compositional analysis, processing conditions such as temperature at each stage of the recycling process, such as pelletization and solid-phase polymerization, can be optimized, thereby standardizing quality and performance. In one embodiment, compositional analysis may be performed before the pretreatment step described below, or before any step after the pretreatment step. Compositional analysis can be performed at any stage, but it is preferable to perform it at least before the solid-phase polymerization step. Also in one embodiment, if pelletizing is performed as needed, compositional analysis may be performed before the pelletizing step.

[0045] For compositional analysis, various known methods can be employed depending on the target component, such as NMR (nuclear magnetic resonance) analysis, DSC (differential scanning calorimetry) analysis, IR (infrared absorption spectroscopy) analysis, X-ray diffraction analysis, thermogravimetric analysis, and gas chromatography-mass spectrometry. For example, NMR analysis can quantify the resin composition and its component species. DSC analysis can measure the melting point and crystallization temperature during cooling of the resin. Furthermore, if the resin contains reinforcing materials such as glass fibers, carbon fibers, or other inorganic materials, or additives such as release agents, the type and influence of these reinforcing materials and additives can be inferred. IR analysis, X-ray diffraction analysis, and thermogravimetric analysis can also be used to infer the type of reinforcing material and additives. Gas chromatography-mass spectrometry can quantitatively identify volatile additives such as release agents and solvents. Combining multiple analytical methods is also a preferred embodiment.

[0046] The following describes preferred processing steps for the method of regenerating the recovered resin composition of the present invention.

[0047] Pre-treatment process If the recovered resin composition contains contaminants or foreign materials (impurities), it can negatively affect the solid-phase polymerization reaction and lead to problems such as a decrease in the quality after regeneration. Therefore, it is preferable to perform pretreatment steps such as removing contaminants and foreign materials from the recovered resin composition as needed, before performing pulverization and solid-phase polymerization treatment.

[0048] Contaminant removal process The recovered resin composition may have contaminants such as oil, paint, and dust attached to it. The method for removing the attached contaminants is not particularly limited, and various known cleaning methods can be used, such as water washing and chemical cleaning. Multiple cleaning methods may also be combined.

[0049] Foreign object removal process The recovered resin composition may contain foreign matter other than resin, such as metal parts like iron and aluminum, reinforcing materials like glass fibers, and reinforcing materials like rubber. The method for removing foreign matter is not particularly limited, and various known sorting methods can be employed, such as visual manual sorting, air sorting, specific gravity difference sorting, infrared analysis, X-ray sorting, metal detector sorting, magnetic sorting, electrostatic sorting, and sieving. Multiple sorting methods may be combined. Furthermore, the foreign matter removal process may be performed multiple times as needed, as described later. Depending on the intended use after recycling, the recovered resin composition containing glass fibers may be subjected to solid-phase polymerization without removing the glass fibers. Even if reinforcing materials such as glass fibers are included in the recovered resin composition, the recovered resin composition can be recycled by solid-phase polymerization under conditions that satisfy formula (1).

[0050] Drying process Since solid-phase polymerization of a recovered resin composition containing moisture may cause hydrolysis, it is preferable to perform a drying treatment as needed. If solid-phase polymerization can be carried out after moisture has been removed, the drying treatment can be performed at any time. Drying conditions such as drying temperature and drying time are not particularly limited; as long as moisture can be removed from the recovered resin composition, they can be adjusted as appropriate. Furthermore, known drying tanks or the like can be used for the drying process.

[0051] Grinding process Since the recovered resin composition may undergo uneven solid-phase polymerization in its original form, it is preferable to perform pulverization as needed. Pulverizing the recovered resin composition reduces the size of the resin clumps, improving heating efficiency and allowing solid-phase polymerization to proceed more uniformly. Furthermore, since the crushing process makes it easier to remove foreign matter, the above-mentioned foreign matter removal process may be performed after crushing as needed. The size and shape of the resin after crushing are not particularly limited and can be determined appropriately according to the recycling purpose and solid-phase polymerization conditions. Examples include coarsely crushed flakes and powders such as crushed granules. From the viewpoint of ensuring uniform solid-phase polymerization, it is desirable that the particles are uniform in size and shape, and the particle size may be adjusted after the grinding process. In another preferred embodiment of the present invention, for example, pellets obtained by crushing the recovered resin composition to an appropriate size and then melt-extruding it at a high temperature may be used. The size of the resin after crushing or particle size adjustment, and the size of the pellets, are not particularly limited, but it is preferable that, for example, one side or diameter is within 1.5 to 5 mm. Furthermore, in cases where the recycled resin after solid-phase polymerization is mixed with other resin materials, it is also preferable in certain embodiments to adjust the pellets or the like to have the same shape and size as the other resin materials.

[0052] Various known devices can be used for the crushing process, such as grinders, shredders, hammer mills, cutter mills, rotary mills, ball mills, and disc mills. Various known devices can be used to adjust the particle size after grinding, such as vibrating sieves, air separators, electrostatic separators, screw conveyors, size classifiers, and centrifugal separators. Various known methods can be used for the pelletizing process; the crushed resin can be melted, extruded into a uniform shape using an extruder, and then cut into pellets. The following describes an example of pelletization treatment of the recovered resin composition. However, the present invention is not limited to the method described below, and it is possible to obtain desired pellets by changing the conditions as appropriate.

[0053] In a preferred embodiment of the present invention, the recovered resin composition is crushed to a size that can be fed into an extruder, for example, to a few millimeters to a few centimeters using the above-mentioned crushing device, then fed into the extruder, and the temperature inside the twin-screw is heated to, for example, above the melting point of the resin and below the melting point + 40°C to melt the resin, then extruded into pellets through a nozzle, and cut to the desired size with a pellet cutter. If necessary, moisture is removed from the pelletized resin using a dryer or other drying device.

[0054] In another preferred embodiment of the present invention, the recovered resin composition may be subjected to the above-mentioned foreign matter removal process after the grinding process before being fed into the extruder. Alternatively, foreign matter in the molten resin may be removed by installing a filter downstream of the screw or immediately before the nozzle.

[0055] The method for pelletizing the molten resin is not particularly limited, and any method such as water cutting or dry cutting can be used. For example, after the molten resin is extruded from the extruder, it can be solidified by water cooling or air cooling, and then cut to the desired size using a cutting tool such as a cutter. The pellets after cooling and cutting may be dried in a dryer or other means as needed.

[0056] After adjusting the particle size of the recovered resin composition, washing, drying, sorting, and other treatments may be performed as needed. For example, a sorting process may be performed to remove foreign matter such as remaining metal fragments, glass fibers, rubber, and paint. The sorting method is not particularly limited, but examples include vibrating sieve sorting, air sorting, magnetic sorting, flotation sorting, optical sorting, centrifugal sorting, X-ray sorting, infrared sorting, electrostatic sorting, specific gravity sorting, and color sorting. Multiple sorting methods may be used in combination as needed.

[0057] Solid-phase polymerization process The recovered resin composition, after undergoing the above processing steps, is subjected to a solid-phase polymerization reaction under reduced pressure or vacuum to restore its molecular weight. The following describes a solid-phase polymerization treatment of a pellet-shaped recovered resin composition (hereinafter referred to as "recovered pellets"), which is one embodiment of the present invention, as a representative example. However, the present invention is not limited to this and can be applied to recovered resin compositions other than recovered pellets, and the solid-phase polymerization conditions can be changed as appropriate.

[0058] Pre-crystallization process The recovered pellets may be pre-crystallized before solid-phase polymerization if necessary. Pre-crystallizing the recovered pellets increases their crystallinity, thereby improving the reaction efficiency during solid-phase polymerization. It is preferable that the recovered pellets undergoing pre-crystallization are dried to remove moisture and remain dry. The degree of crystallinity after the preliminary crystallization treatment is preferably 20% to 60%, more preferably 30% to 50%. It is preferable to appropriately adjust processing conditions, such as heating temperature and processing time, to achieve the desired degree of crystallinity. The preliminary crystallization treatment may be performed at a temperature lower than the crystallization temperature of the recovered pellets, but if the temperature is too low, crystallization may be insufficient. Conversely, if the temperature is too high, the degree of crystallization may become excessively high, which may adversely affect the solid-phase polymerization reaction. If the heating time is too short, crystallization may be insufficient. If the heating time is too long, excessive crystallization may occur. In one preferred embodiment, an example of the heating temperature for the pre-crystallization treatment is preferably 120 to 200°C, more preferably 130 to 180°C. In one preferred embodiment, an example of the pre-crystallization treatment time is preferably 1 minute to 4 hours, more preferably 30 minutes to 2 hours. The atmosphere during the precrystallization treatment can be any of the following: air, vacuum, or inert gas. For example, performing the precrystallization treatment under a vacuum or inert gas atmosphere can suppress oxidation of the recovered pellets.

[0059] Solid-phase polymerization process The solid-phase polymerization of the present invention is carried out within a temperature range that satisfies the following formula (1). (Melting point of polyester resin -70°C) ≤ T(°C) ≤ (Melting point of polyester resin -5°C) ... (1) In the formula, T (°C) is the solid-phase polymerization temperature. The melting point of polyester resins is determined by the endothermic peak temperature of a thermogram obtained using a differential scanning calorimeter (DSC) at a heating rate of 20°C / min under a nitrogen atmosphere. If multiple endothermic peaks appear, the peak temperature originating from the resin with the highest content is adopted. The recovered pellets used for measurement are samples taken from the recovered resin composition. Other conditions are as described in the examples.

[0060] The solid-phase polymerization temperature T (°C) is preferably [(melting point of polyester resin) -10°C] to [(melting point of polyester resin) -50°C], and more preferably [(melting point of polyester resin) -20°C] to [(melting point of polyester resin) -40°C]. By setting the solid-phase polymerization temperature T (°C) within the above range, regeneration is possible even if the recovered pellets are composed of multiple polyester resins or contain additives. If the solid-phase polymerization temperature T (°C) is too low, solid-phase polymerization will be incomplete, and the molecular weight cannot be restored to the desired level. If the solid-phase polymerization temperature T (°C) is too high, not only will the molecular weight not be restored to the desired level, but problems such as fusion may occur. In addition, the removal of contained additives (e.g., heat stabilizers, light stabilizers, mold release agents, etc.) may reduce properties such as heat resistance, weather resistance, and mold release after molecular weight restoration.

[0061] The solid-phase polymerization time can be adjusted as needed to obtain the desired degree of polymerization. If the polymerization reaction time is too short within the above temperature range, insufficient polymerization may occur. Conversely, if the polymerization reaction time is too long, the reduced viscosity may decrease significantly. Since the solid-phase polymerization time varies depending on the size of the recovered pellets and processing conditions, for example, the solid-phase polymerization time and viscosity may be measured by sampling at regular intervals while fixing the size of the recovered pellets, the machine setup, the vacuum level, and the temperature, and the reaction time may be set based on the relationship between the solid-phase polymerization time and the viscosity. In one embodiment, the reaction time may be set so that the viscosity of the recovered pellets is about the same as the reduced viscosity of the virgin resin composition, or it is preferable to set the reduced viscosity of the recovered pellets to a value suitable for melt molding in the subsequent process. In one preferred embodiment, an example of the solid-phase polymerization treatment time is preferably 1 to 12 hours, more preferably 2 to 10 hours. In one preferred embodiment, an example of the atmospheric pressure during solid-phase polymerization is -0.1 MPa or less.

[0062] The atmosphere for solid-phase polymerization is under the flow of an inert gas such as nitrogen, argon, or helium, or under high vacuum. These conditions allow for the efficient removal of volatile components that detach from the recovered pellets during the solid-phase polymerization reaction.

[0063] Crystallization temperature during cooling Since the crystallization temperature during cooling affects the cycle time during injection molding, it is preferable that the crystallization temperature of the recycled resin composition during cooling be the same as that of the virgin resin composition. The difference is preferably 5°C or less, and more preferably 3°C or less. The crystallization temperature during cooling is a value measured based on the measurement conditions of the example. According to the solid-phase polymerization of the present invention, the crystallization temperature of the recycled resin composition during cooling is basically the same as that of the virgin resin composition during cooling. In other words, the cycle time during injection molding of the recycled resin composition is almost the same as that of the virgin resin composition, and therefore it can be said that there is no adverse effect on productivity.

[0064] The solid-phase polymerization apparatus is not particularly limited, and various known apparatuses can be used, such as vertical hopper-type continuous solid-phase polymerization tanks, batch-type solid-phase polymerization apparatuses, air-jet type solid-phase polymerization apparatuses, and screw-type solid-phase polymerization apparatuses.

[0065] The recovered resin composition of the present invention can have its molecular weight restored by solid-phase polymerization. Therefore, it is also a preferred embodiment that the recycled resin composition can be used as a material for plastic molded articles for automobiles or home appliances.

[0066] As the material for the plastic molded article, only the recycled resin composition, or a mixture of the recycled resin composition and the other resins and / or virgin resin composition, can be used. The mixing ratio of the recycled resin composition to the other resins and / or virgin resin composition is not particularly limited. Reinforcements and various additives may also be added as needed.

[0067] The following describes one embodiment of recycling using a recycled resin composition, but it is not limited to the example shown below and can be used for various known molded articles. In one embodiment, the recycled resin composition may be the mixture described above. The molding method using the recycled resin composition is not particularly limited, and plastic molded articles can be formed by known methods such as injection molding, extrusion molding, and blow molding. In one embodiment, the plastic molded article is preferably a plastic molded article for automobiles or a plastic molded article for home appliances. Examples of plastic molded articles for automobiles include electrical and electronic component-related parts such as instrument cluster cases, connectors, switches, and buttons; engine-related parts such as air cleaner boxes, engine covers, and radiator fans; cover-related parts such as airbag covers, gearbox covers, and transmission component covers; glass-related parts such as side mirror cases; exterior parts such as bumpers, fenders, hoods, door panels, grilles, and window moldings; interior parts such as dashboards, seat covers, seat cushions, center consoles, door panels, floor mats, trunk linings, headliners, and glove boxes; and structural parts such as vehicle frames, door frames, roof frames, and window frames. In one embodiment, the recycled resin composition is also suitable for automotive applications as a structural member.

[0068] As plastic molded parts for home appliances, they are useful as plastic molded parts used in various home appliances, including exterior components such as door panels, housings, back covers, outer covers, and external panels; interior components such as shelves, filter cases, various connecting parts, and circuit boards; functional components such as fan motor cases, pump cases, cooling plates, and cooling fins; and connector components such as switches and connecting parts. [Examples]

[0069] The present invention will be described in more detail below with reference to examples, but the present invention is not limited by the following examples, and it is certainly possible to implement it with appropriate modifications within the scope that is consistent with the spirit of the preceding and following descriptions, and all such modifications are included within the technical scope of the present invention.

[0070] The measurement method for each characteristic in this embodiment is as follows.

[0071] Reduced viscosity (ηsp / c) 0.1 g of the sample was dissolved in 25 ml of a phenol / tetrachloroethane mixed solvent (mass ratio 6 / 4) and measured at 30°C using an Ubbelohde viscometer (unit: dl / g).

[0072] Melt flow rate (MFR) Measurements were performed using Method A in accordance with ISO 1133-1:2022. The temperature was set according to the conditions in the table for each material, and the load condition was 2160g (unit: g / 10 min). Materials with a moisture content of 0.05% by weight or less were used for the measurements.

[0073] Melting point, crystallization temperature when cooling down The melting point of the polyester resin was determined using a differential scanning calorimeter (DSC) and the endothermic peak temperature of the thermogram obtained by heating the resin at a rate of 20°C / min under a nitrogen atmosphere. The crystallization temperature of polyester resins during cooling was determined using DSC. The resin was heated to a temperature at which it completely melted under a nitrogen atmosphere at a heating rate of 20°C / min, held at that temperature for 5 minutes, and then cooled at a rate of 10°C / min. The exothermic peak temperature obtained from the resulting thermogram was then measured. For the measurements, flat plates manufactured by injection molding were used. An injection molding machine (J-100ADS, manufactured by Japan Steel Works) was used to form flat plates measuring 100 mm x 100 mm x 2 mm thick. The cylinder temperature / mold temperature conditions were as follows: Material A1, D1: 250°C / 50°C; Material B1: 260°C / 60°C; Material C1: 270°C / 90°C. The cylinder temperature was set based on the melting point of the base resin + 10 to 30°C. If another resin with a higher melting point than the base resin was added, and / or if the molecular weight was higher, the temperature was set to the base + 10 to 20°C, and if fillers were included, an additional 10 to 30°C was added. Similarly, the mold temperature was set based on the glass transition temperature (Tg) of the base resin + 10 to 30°C. If another resin with a higher Tg than the base resin was added, the temperature was set to the base + 10 to 20°C, and if fillers were included, an additional 10 to 30°C was added. If the Tg was below room temperature, no mold temperature control was used.

[0074] The following describes some examples. Recovery process Automotive parts were recovered from end-of-life vehicles (ELVs), and polyester resin molded products contained in these parts were used. The recovered automotive parts were molded using a polyester resin composition (virgin resin composition) manufactured by Toyobo MC Co., Ltd., and the physical properties of the Toyobo MC Co., Ltd. polyester resin composition (virgin resin composition) before molding are shown in Table 1. Since the above-mentioned polyester resin molded product does not use a polyester resin composition containing a polyfunctional reactive compound, a resin molded product was prepared using a separately prepared polyester resin composition containing a polyfunctional reactive compound (Material E). This product was then treated under conditions simulating use in automobiles (accelerated moist heat decomposition treatment in a constant temperature and humidity chamber at 80°C and 90% RH until it had the same molecular weight as Material A1). This product was then used as a reference example, equivalent to the polyester resin molded product recovered from a scrapped vehicle.

[0075] [Table 1]

[0076] The materials A~ in the table are as follows: Materials B and C are PBT / PET composite materials. Material A: A PBT-based resin composition containing 96.2% by mass of polybutylene terephthalate (hereinafter referred to as PBT), 3% by mass of acrylonitrile-styrene copolymer ("AP-20", manufactured by UMG-ABS), 0.2% by mass of antioxidant ("IRGANOX1010", manufactured by BASF), 0.3% by mass of mold release agent ("Recolb WE-40", manufactured by Clariant), and 0.3% by mass of pigment (carbon black: hereinafter referred to as CB). Material B: Mineral-reinforced PBT / PET resin composition containing 60% by mass of PBT, 19% by mass of polyethylene terephthalate (PET), 20% by mass of talc ("KCM7500", manufactured by Hayashi Chemical Co., Ltd.), 0.2% by mass of antioxidant ("IRGANOX1010", manufactured by BASF), 0.5% by mass of release agent ("Ricowax OP", manufactured by Clariant), and 0.3% by mass of pigment (CB). Material C: Glass-reinforced PBT / PET resin composition containing 49% by mass of PBT, 20% by mass of PET, 30% by mass of glass fiber, 0.2% by mass of antioxidant ("IRGANOX1010", manufactured by BASF), 0.5% by mass of release agent ("Rikester EW-440A", manufactured by Riken Vitamin), and 0.3% by mass of pigment (CB). Material D: A PBT-based resin composition obtained by adding 0.5% by mass of a polyfunctional reactive compound ("Carbodilite LA-1," manufactured by Nisshinbo Chemical Co., Ltd.) to Material A (Note that the mass percentage of each component is 100 / 100.5 times the percentage of each component in Material A).

[0077] Sorting process The recovered automobile parts were manually disassembled, and foreign materials such as metals and rubber other than resin were removed to produce polyester resin molded products, which were designated as materials A1 to D1. Since the polyester resin molded products did not have paint or topcoats applied, these removal processes were not performed.

[0078] Pelletization process The obtained material was fed into a pulverizer and crushed into flakes. After that, it was fed into an extruder (Shibaura Machinery TEM-26SS) for melt-mixing and then pelletized using a pelletizer. The cylinder temperature was adjusted to the following temperatures. The screw rotation speed was set to 120 rpm for all materials. The cylinder temperature was adjusted according to the composition, as was done during molding. Specifically, the base resin's melting point + 10 to 30°C was used as the baseline. When another resin with a higher melting point than the base resin was added, and / or when the molecular weight was higher, the temperature was set to baseline + 10 to 20°C, and when fillers were included, it was set to an additional + 10 to 30°C. Material A1, D1: 250℃ Material B1: 260℃ Material C1: 270℃ Twenty pellets were randomly selected from the obtained pellets, their sizes were measured, and the average value was defined as the pellet size. The sizes of pellets A1 to D1 obtained from each material were all 3.2 mm in length, 2.5 mm in major diameter, and 2.3 mm in minor diameter. The characteristics of pellets A1 to D1 are shown in Table 2.

[0079] Solid phase polymerization process The obtained pellets were placed in a tray and solid-phase polymerization was carried out using a vacuum constant-temperature dryer (DP610, manufactured by Yamato Scientific Co., Ltd.) under conditions of -0.1 MPa or lower. The solid-phase polymerization temperature and time were as shown in Table 2. After solid-phase polymerization, the pellets were removed from the vacuum constant-temperature dryer and their properties were measured. The pellets before solid-phase polymerization are designated as pellets A1 to D1, and the pellets after solid-phase polymerization are designated as pellets A2 to D2 (corresponding to pellets A1 to D1). The properties of pellets A2 to D2 are shown in Table 3.

[0080] [Table 2]

[0081] [Table 3]

[0082] Table 3 shows that Examples 1-4, which satisfy the requirements of the present invention, contain many additives but can restore their molecular weight and have properties equivalent to virgin materials. The reference example contained a polyfunctional reactive compound, and while the target molecular weight was recovered, DSC measurements after solid-phase polymerization revealed a new peak in a temperature range lower than the melting point of the base resin. This suggests that the polyfunctional reactive compound bonded to multiple molecular chains of the polyester resin via reactive groups, forming a branched structure. However, because the polyfunctional reactive compound is scattered throughout the polyester resin, a difference in the degree of branching occurs near the polyfunctional reactive compound and elsewhere. It is thought that this structural difference resulted in the observation of two different melting points. Furthermore, since the difference in melting points is only slight compared to the melting points of the materials before solid-phase polymerization, it can be used depending on the application. Comparative Examples 1 and 2 failed to recover their molecular weight because the solid-phase polymerization temperature was too low. Furthermore, in Comparative Example 3, the solid-phase polymerization temperature was too high, causing the pellets to stick together. [Industrial applicability]

[0083] According to the present invention, the molecular weight of polyester resins recovered from automobiles with high levels of additives can be restored, thereby dramatically increasing the recycling rate of resin materials. As a result, it can contribute to reducing waste, reducing carbon dioxide emissions, and lowering manufacturing costs.

Claims

1. A method for regenerating recovered polyester resin, comprising solid-phase polymerization of a polyester resin-containing composition recovered from an automobile at a temperature T (°C) that satisfies the following formula (1). (Melting point of polyester resin - 70°C) ≤ T (°C) ≤ (Melting point of polyester resin - 5°C) ... (1)

2. The recycling method according to claim 1, wherein the recovered polyester resin-containing composition contains two or more polyester resins with different basic structures.

3. The recycling method according to claim 1, wherein the recovered polyester resin-containing composition comprises at least one selected from the group consisting of resins other than polyester resins, inorganic reinforcing agents, stabilizers, flame retardants, and colorants.

4. The recycling method according to claim 3, wherein the recovered polyester resin-containing composition does not contain a polyfunctional reactive compound, or contains it in an amount of 1.0% by mass or less relative to 100% by mass of the polyester resin.

5. The recycling method according to claim 1, wherein the recycled polyester resin-containing composition obtained by solid-phase polymerization of the polyester resin-containing composition is used as a plastic molded article for automobiles or home appliances.

6. The recycling method according to claim 5, wherein the polyester resin-containing composition contains a polystyrene resin, and the recycled polyester resin is used for automotive applications as a structural member.

7. The recycling method according to claim 5, wherein the polyester resin-containing composition contains glass fibers, and the recycled polyester resin is used in plastic materials for automobiles or home appliances other than structural members.

8. Polyester automotive parts are manufactured from a polyester resin composition in which the content of polyfunctional reactive compounds is suppressed to 1.0% by mass or less. A method for recycling polyester resin, comprising recovering the used polyester automotive parts from an automobile, and solid-phase polymerizing the recovered polyester automotive parts at a temperature T (°C) that satisfies the following formula (1), while keeping the content of polyfunctional reactive compounds in the recovered material to 1.0% by mass or less relative to 100% by mass of the polyester resin. (Melting point of polyester resin - 70°C) ≤ T (°C) ≤ (Melting point of polyester resin - 5°C) ... (1)

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