Multilayer container and method for manufacturing a recycled polyester

Abstract

A multilayer container comprising: a polyester layer containing polyester resin (X), and a polyamide layer containing polyamide resin (Y), a phenolic antioxidant (A), and a phosphorus antioxidant (B), wherein the phosphorus antioxidant (B) is a compound having a pentaerythritol backbone and an aromatic ring, and the total content of the phenolic antioxidant (A) and the phosphorus antioxidant (B) in the polyamide layer is 0.040~0.250% by mass.

Description

Technical Field

[0001] This invention relates to a method for manufacturing multilayer containers and recycled polyester. Background Technology

[0002] Aromatic polyester resins, obtained using aromatic dicarboxylic acid compounds and aliphatic diol compounds as monomers, possess excellent advantages such as transparency, mechanical properties, melt stability, solvent resistance, aroma retention, gas barrier properties, and recyclability. Therefore, aromatic polyester resins such as polyethylene terephthalate (PET) are widely used in various packaging materials such as films, sheets, and hollow containers. While polyester resins have high gas barrier properties, this may not be sufficient for applications requiring even higher gas barrier properties against oxygen and carbon dioxide. Therefore, as methods to improve the gas barrier properties of polyester resins, the following have been implemented: vapor deposition of alumina and silica onto molded bodies and packaging containers formed from polyester resins; and coating, laminating, or melt-mixing resins with high gas barrier properties onto molded bodies and packaging containers formed from polyester resins.

[0003] Examples of gas-barrier resins include polyamide resins such as nylon 6 and nylon 66, and ethylene-vinyl alcohol copolymers. Among polyamide resins, those containing phthalimide, obtained by polymerizing a diamine component mainly composed of phenylenediamine with a dicarboxylic acid component mainly composed of aliphatic dicarboxylic acid, exhibit excellent gas barrier properties. Phthalimide-containing polyamide resins not only possess high gas barrier properties but also share similarities with polyethylene terephthalate (PET), a widely used polyester resin, in terms of glass transition temperature, melting point, and crystallinity, making them easy to laminate and melt-mix into polyester resins. Therefore, phthalimide-containing polyamide resins are highly suitable as materials for improving the gas barrier properties of polyester resins.

[0004] However, yellowing caused by thermal processes is more likely to occur in multilayer polyester containers with polyamide layers than in polyester itself. Therefore, yellowing particularly occurs during the recycling process where containers are recycled and the resin is reused. This is a major reason for the reduction in the commercial value of packaging containers, hence research has been conducted to inhibit yellowing.

[0005] For example, Patent Document 1 discloses a multilayer container for the purpose of suppressing yellowing of recycled polyester during recycling, comprising: a polyester resin composition layer containing polyester resin and a specific amount of antioxidant; and a polyamide resin composition layer containing a specific polyamide resin and a specific amount of cobalt salt.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2018-043773 Summary of the Invention

[0009] The problem the invention aims to solve

[0010] As mentioned earlier, containers made of polyester resin containing polyamide are prone to yellowing, and recycled polyester obtained from its recycling also has a yellowish tint. Methods to suppress this yellowing include, for example, adding antioxidants to the container, as listed in Patent Document 1; however, the resulting recycled polyester is not sufficiently colorless. Furthermore, because recycled polyester undergoes a recycling process, it is prone to fogging, and improved transparency is required.

[0011] In addition, especially by adding a large amount of additives to containers with multi-layered structures, whitening and poor formability sometimes occur during the molding process, so it is also necessary to take into account both recyclability and formability.

[0012] Therefore, the objective of this invention is to provide a multilayer container that can suppress yellowing of recycled polyester obtained by recycling multilayer containers, and that the recycled polyester also has excellent transparency and formability.

[0013] Solution for solving the problem

[0014] In view of the above-mentioned problems, the inventors conducted in-depth research and found that a multilayer container having a polyester layer and further containing a phenolic antioxidant and a specific phosphorus antioxidant in the polyamide layer can solve the above-mentioned problems, thereby completing the present invention.

[0015] The present invention provides the following [1]~

[19] .

[0016] [1] A multilayer container comprising: a polyester layer containing polyester resin (X) and a polyamide layer containing polyamide resin (Y), a phenolic antioxidant (A) and a phosphorus antioxidant (B), wherein the phosphorus antioxidant (B) is a compound having a pentaerythritol skeleton and an aromatic ring, and the total content of the phenolic antioxidant (A) and the phosphorus antioxidant (B) in the polyamide layer is 0.040 to 0.250 by mass.

[0017] [2] According to the multilayer container described above [1], the mass ratio of the content of phenolic antioxidant (A) in the polyamide layer to the content of phosphorus antioxidant (B) [(A) / (B)] is 2 / 8 to 5 / 5.

[0018] [3] According to the multilayer container described in [1] or [2] above, wherein the aforementioned polyester layer contains a phenolic antioxidant (A) and a phosphorus antioxidant (B).

[0019] [4] According to the multilayer container described above [3], the total content of phenolic antioxidant (A) and phosphorus antioxidant (B) in the polyester layer is 0.050~0.220 by mass.

[0020] [5] According to the multilayer container described in [3] or [4] above, the mass ratio of the content of phenolic antioxidant (A) in the polyester layer to the content of phosphorus antioxidant (B) [(A) / (B)] is 2 / 8 to 5 / 5.

[0021] [6] The multilayer container according to any one of [1] to [5] above, wherein the polyester layer contains o-aminobenzamide.

[0022] [7] The multilayer container according to any one of [1] to [6] above, wherein the polyamide resin (Y) has: a diamine-derived structural unit containing 80 mol% or more of a phenylenediamine-derived structural unit; and a dicarboxylic acid-derived structural unit containing 80 mol% or more of a dicarboxylic acid-derived structural unit.

[0023] [8] The multilayer container according to any one of [1] to [7] above, wherein the content of polyamide resin (Y) is 0.05 to 10.0 by mass relative to the total amount of all polyamide layers and all polyester layers.

[0024] [9] The multilayer container according to any one of [1] to [8] above, wherein the content of the polyamide layer is 0.05 to 10.0 by mass relative to the total amount of all polyamide layers and all polyester layers.

[0025]

[10] The multilayer container according to any one of [1] to [9] above, wherein the polyester resin (X) has: a structural unit derived from dicarboxylic acid, the structural unit derived from dicarboxylic acid containing more than 80 mol% of structural units derived from terephthalic acid; and a structural unit derived from diol, the structural unit derived from diol containing more than 80 mol% of structural units derived from ethylene glycol.

[0026]

[11] The multi-layer container according to any one of [1] to

[10] above, wherein the multi-layer container is a hollow container.

[0027]

[12] The multi-layer container according to any one of [1] to

[11] above, wherein the multi-layer container has a 3 to 5-layer structure, and the outermost layer and the innermost layer are polyester layers.

[0028]

[13] The multi-layer container according to any one of [1] to

[12] above, wherein the multi-layer container has a 3-layer structure.

[0029]

[14] The multi-layer container according to any one of [1] to

[13] above, wherein the multi-layer container does not have an adhesive layer.

[0030]

[15] A method for manufacturing recycled polyester, comprising a step of recovering polyester from a multi-layer container as described in any one of [1] to

[14] above.

[0031]

[16] A method for manufacturing recycled polyester, comprising a step of recovering polyester from a multilayer container as described in any one of [1] to

[14] above, wherein the method for manufacturing recycled polyester comprises a step of removing all or part of the polyamide layer from the multilayer container to recover the polyester.

[0032]

[17] In the method for manufacturing recycled polyester described above

[16] , after crushing the aforementioned multilayer container, the aforementioned polyamide layer is removed by air separation.

[0033]

[18] The method for manufacturing recycled polyester according to any one of

[15] to

[17] above includes the following steps: cleaning the multilayer container or its pulverized material according to any one of [1] to

[14] above with an alkaline aqueous solution and recovering the polyester.

[0034]

[19] The method for manufacturing recycled polyester according to any one of

[15] to

[18] above, wherein, after the step of recycling polyester, one or more steps selected from the crystallization step and the solid-state polymerization step are performed.

[0035] The effects of the invention

[0036] According to the present invention, a multilayer container can be provided that can suppress yellowing of recycled polyester obtained by recycling multilayer containers, and the recycled polyester also has excellent transparency and formability. Detailed Implementation

[0037] Multi-layer containers

[0038] The multilayer container of the present invention comprises: a polyester layer containing polyester resin (X), and a polyamide layer containing polyamide resin (Y), a phenolic antioxidant (A), and a phosphorus antioxidant (B), wherein the phosphorus antioxidant (B) is a compound having a pentaerythritol backbone and an aromatic ring, and the total content of the phenolic antioxidant (A) and the phosphorus antioxidant (B) in the polyamide layer is 0.040 to 0.250% by mass.

[0039] The reasons why the multilayer container of the present invention can suppress yellowing of recycled polyester obtained from recycling, and also has excellent transparency and formability, are not yet certain, but are believed to be as follows. Yellowing during recycling is thought to be caused by the incorporation of oxidized polyamide into the recycled polyester, but in the multilayer container of the present invention, it is believed that because antioxidants are contained in the polyamide layer, the oxidation of polyamide can be effectively suppressed. Furthermore, it is believed that by introducing a small amount of antioxidant into the polyamide layer, which serves as a barrier layer and has a low mass ratio, a high effect can be achieved, thus not affecting formability, and the formability of the container is excellent. Furthermore, it is believed that by combining phenolic antioxidants and phosphorus-based antioxidants having a pentaerythritol backbone and aromatic rings, the effects of hydrolysis can be suppressed, and hydrolysis and leakage during container use and during cleaning during recycling can also be suppressed, resulting in an even higher yellowing suppression effect.

[0040] <Polyamide layer>

[0041] The polyamide layer contains polyamide resin (Y), phenolic antioxidant (A) and phosphorus antioxidant (B). The phosphorus antioxidant (B) is a compound with a pentaerythritol backbone and an aromatic ring. The total content of phenolic antioxidant (A) and phosphorus antioxidant (B) in the polyamide layer is 0.040~0.250 by mass.

[0042] (Polyamide resin (Y))

[0043] Examples of polyamide resins (Y) include polyamide resins containing phthalimide, nylon 6, nylon 66, nylon 666, nylon 610, nylon 11, nylon 12, and mixtures thereof. Among these, polyamide resins containing phthalimide are preferred from the perspective of improving gas barrier properties and facilitating separation from the polyester layer during recycling. Polyamide resins containing phthalimide are preferably polyamide resins containing structural units derived from diphenylene oxide.

[0044] The phenylenediamine-containing polyamide resin is formed by the condensation polymerization of a diamine containing phenylenediamine and a dicarboxylic acid, and has structural units derived from phenylenediamine and structural units derived from dicarboxylic acid. In the phenylenediamine-containing polyamide resin, the phenylenediamine-derived structural units (diamine units) preferably contain 50 mol% or more, more preferably 70 mol% or more, even more preferably 80 to 100 mol%, and even more preferably 90 to 100 mol%.

[0045] The preferred dimethylamine is m-phenylenediamine, p-phenylenediamine, or both, with m-phenylenediamine being more preferred. Furthermore, the diamine unit constituting the dimethyl diamine-containing polyamide resin preferably contains 50 mol% or more of structural units derived from m-phenylenediamine, more preferably 70 mol% or more, even more preferably 80-100 mol%, and still more preferably 90-100 mol%. By ensuring that the m-phenylenediamine-derived structural units in the diamine unit are within the above-mentioned range, the gas barrier properties of the polyamide resin are improved.

[0046] The diamine units in polyamide resins containing diphenylene oxide can be composed solely of structural units derived from diphenylene diamine, or they can contain structural units derived from diamines other than diphenylene diamine. Examples of diamines other than phenylenediamine include ethylenediamine, tetramethylenediamine, pentamethylenediamine, 2-methylpentanediamine, hexamethylenediamine, heptamethylenediamine, octamethylenediamine, nonamethylenediamine, decamethylenediamine, dodecamethylenediamine, 2,2,4-trimethyl-hexamethylenediamine, and 2,4,4-trimethyl-hexamethylenediamine, which are straight-chain or branched aliphatic diamines; 1,3-bis(aminomethyl)cyclohexane, 1,4-bis(aminomethyl)cyclohexane, 1,3-diaminocyclohexane, 1,4-diaminocyclohexane, bis(4-aminocyclohexyl)methane, 2,2-bis(4-aminocyclohexyl)propane, bis(aminomethyl)decahydronaphthalene, and bis(aminomethyl)tricyclodecane, which are alicyclic diamines; and bis(4-aminophenyl) ether, p-phenylenediamine, and bis(aminomethyl)naphthalene, which are diamines with aromatic rings.

[0047] Among polyamide resins containing phthalimide, compounds that can form dicarboxylic acid units include α,ω-linear aliphatic dicarboxylic acids with 4 to 20 carbon atoms, such as succinic acid, glutaric acid, adipic acid, pimelic acid, octanoic acid, azelaic acid, sebacic acid, undecanoic acid, and dodecanoic acid; alicyclic dicarboxylic acids, such as 1,4-cyclohexanedicarboxylic acid; other aliphatic dicarboxylic acids, such as dimer acids; and aromatic dicarboxylic acids, such as terephthalic acid, isophthalic acid, phthalic acid, phthalimide dicarboxylic acid, and naphthalene dicarboxylic acid. α,ω-linear aliphatic dicarboxylic acids with 4 to 20 carbon atoms are preferred, and adipic acid and sebacic acid are more preferred. From the viewpoint of achieving good barrier properties, adipic acid is further preferred.

[0048] In polyamide resins containing dimethyl phthalate, the structural units derived from dicarboxylic acid (dicarboxylic acid units) preferably contain more than 50 mol%, more preferably more than 70 mol%, further preferably 80 to 100 mol%, and even more preferably 90 to 100 mol%.

[0049] That is, the polyamide resin (Y) preferably has: structural units derived from diamine, the structural units derived from diamine containing 50 mol% or more structural units derived from phenylenediamine; and structural units derived from dicarboxylic acid, the structural units derived from dicarboxylic acid containing 50 mol% or more structural units derived from acetic acid; more preferably it has: structural units derived from diamine, the structural units derived from diamine containing 80 mol% or more structural units derived from phenylenediamine; and structural units derived from dicarboxylic acid, the structural units derived from dicarboxylic acid containing 80 mol% or more structural units derived from acetic acid; and even more preferably it has: structural units derived from diamine, the structural units derived from diamine containing 90 mol% or more structural units derived from phenylenediamine; and structural units derived from dicarboxylic acid, the structural units derived from dicarboxylic acid containing 90 mol% or more structural units derived from acetic acid.

[0050] m-Phenylenediamine is preferred as the phenylenediamine.

[0051] Furthermore, when the structural unit derived from a carboxylic acid includes a structural unit of a carboxylic acid other than adipic acid, the structural unit of the carboxylic acid remaining in addition to adipic acid is preferably derived from a structural unit of an α,ω-linear aliphatic carboxylic acid with 4 to 20 carbon atoms.

[0052] Alternatively, as a preferred polyamide resin containing phthalimide, examples may include polyamide resins in which 70 mol% or more of the diamine units are structural units derived from phthalic acid (preferably m-phthalic acid), 70-99 mol% of the dicarboxylic acid units are structural units derived from acetic acid, and 1-30 mol% of the diamine units are structural units derived from isophthalic acid. The aforementioned polyamide resin is preferably a polyamide resin in which 80 mol% or more of the diamine units are structural units derived from phthalic acid (preferably m-phthalic acid), 80-99 mol% of the dicarboxylic acid units are structural units derived from acetic acid, and 1-20 mol% of the dicarboxylic acid units are structural units derived from isophthalic acid. More preferably, a polyamide resin in which 90 mol% or more of the diamine units are structural units derived from phthalic acid (preferably m-phthalic acid), 80-99 mol% of the dicarboxylic acid units are structural units derived from acetic acid, and 1-20 mol% of the dicarboxylic acid units are structural units derived from isophthalic acid.

[0053] By adding isophthalic acid units as dicarboxylic acid units, the melting point is lowered, which can reduce the forming processing temperature and thus suppress thermal degradation during forming. In addition, the crystallization time is delayed, thereby improving stretch formability.

[0054] In addition to the aforementioned diamines and dicarboxylic acids, as components constituting the polyamide resin containing dimethyl phthalate, lactams such as ε-caprolactam and laurolactam, aliphatic aminocarboxylic acids such as aminocaproic acid and aminoundecanoic acid, and aromatic aminocarboxylic acids such as p-aminomethylbenzoic acid may also be used as copolymerizing components, without impairing the effects of the present invention.

[0055] Polyamide resins containing dimethyl phthalate are preferably manufactured via a molten polycondensation reaction (hereinafter, sometimes referred to as "melt polycondensation"). For example, they are preferably manufactured by heating a nylon salt composed of a diamine and a dicarboxylic acid under pressure in the presence of water, while removing water and polymerizing in the molten state. Alternatively, they can be manufactured by directly adding the diamine to the molten dicarboxylic acid and carrying out polycondensation at atmospheric pressure. In this case, to maintain the reaction system in a homogeneous liquid state, it is preferable to continuously add the diamine to the dicarboxylic acid while simultaneously heating the reaction system at a temperature not lower than the melting points of the resulting oligoamide and polyamide, and carrying out polycondensation. Furthermore, the molecular weight of the polyamide containing dimethyl phthalate can be increased by further solid-state polymerization of the material obtained from melt polycondensation, as needed.

[0056] Polyamide resins containing phthalimide are preferably polycondensed in the presence of phosphorus-containing compounds. When polyamide resins containing phthalimide undergo polycondensation in the presence of phosphorus-containing compounds, the processing stability during melt molding is improved, and coloring is more easily suppressed.

[0057] As a phosphorus-containing compound, hypophosphorous compounds and phosphorous compounds are preferred, and hypophosphorous compounds are even more preferred.

[0058] The phosphorus-containing compound is preferably an organometallic salt, and more preferably an alkali metal salt.

[0059] From the viewpoints of promoting polymerization and preventing discoloration, hypophosphite, metal hypophosphite, metal phenylphosphonate, ethyl hypophosphite, dimethyl phosphite, phenylmethyl phosphite, phenylphosphonate, and ethyl phenylphosphonate are examples of hypophosphite compounds, with metal hypophosphite being preferred.

[0060] Examples of metal hypophosphite salts include sodium hypophosphite, potassium hypophosphite, lithium hypophosphite, and calcium hypophosphite, with sodium hypophosphite being a more preferred choice.

[0061] Examples of metal salts of phenylphosphonite include sodium phenylphosphonite, potassium phenylphosphonite, and lithium phenylphosphonite.

[0062] Examples of phosphorous compounds include phosphorous acid, pyrophosphorous acid, metal salts of phosphite, metal salts of ethylphosphonic acid, metal salts of phenylphosphonic acid, triethyl phosphite, triphenyl phosphite, ethylphosphonic acid, phenylphosphonic acid, and diethyl phenylphosphonic acid.

[0063] Examples of metal phosphites include sodium hydrogen phosphite, sodium phosphite, potassium phosphite, and calcium phosphite.

[0064] Examples of metal salts of ethylphosphonic acid include sodium ethylphosphonate and potassium ethylphosphonate.

[0065] Examples of metal salts of phenylphosphonic acid include sodium phenylphosphonate, potassium phenylphosphonate, and lithium phenylphosphonate.

[0066] A phosphorus-containing compound may be one type or two or more types may be used together.

[0067] Furthermore, the polycondensation of polyamide resins containing phthalimide is preferably carried out in the presence of phosphorus-containing compounds and alkali metal compounds. If a large amount of phosphorus-containing compound is used, the polyamide resin may gel. Therefore, from the viewpoint of adjusting the amidation reaction rate, it is preferable to have the alkali metal compound coexisting.

[0068] Examples of alkali metal compounds include alkali metal hydroxides and alkali metal acetates. Examples of alkali metal hydroxides include lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, and cesium hydroxide. Examples of alkali metal acetates include lithium acetate, sodium acetate, potassium acetate, rubidium acetate, and cesium acetate.

[0069] When an alkali metal compound is used during the polycondensation of polyamide resin, from the viewpoint of suppressing gel formation, the amount of alkali metal compound used is preferably 0.5 to 1, more preferably 0.55 to 0.95, and even more preferably 0.6 to 0.9.

[0070] The number average molecular weight of the polyamide resin can be selected according to the application and molding method of the multilayer container. From the viewpoint of the formability and strength of the multilayer container, it is preferably 10,000 to 60,000, and more preferably 11,000 to 50,000.

[0071] It should be noted that the number-average molecular weight of polyamide resin is calculated by the following formula (2).

[0072] Number average molecular weight = 2 × 1,000,000 / ([COOH] + [NH2]) … (2)

[0073] (In the formula, [COOH] represents the concentration of terminal carboxyl groups in the polyamide resin (μmol / g), and [NH2] represents the concentration of terminal amino groups in the polyamide resin (μmol / g).)

[0074] Here, the concentration of the terminal carboxyl group is calculated using a titration of a substance obtained by neutralizing polyamide dissolved in benzyl alcohol with an aqueous sodium hydroxide solution.

[0075] In this invention, from the viewpoint of suppressing yellowing of recycled polyester, the concentration of terminal amino groups in the polyamide resin (Y) is preferably 50 μmol / g or less, more preferably 45 μmol / g or less, even more preferably 40 μmol / g or less, even more preferably 30 μmol / g or less, and even more preferably 20 μmol / g or less.

[0076] The concentration of the terminal amino group of polyamide resin (Y) is determined as follows: The polyamide resin is accurately weighed and dissolved in a phenol / ethanol = 4 / 1 volumetric solution at 20~30℃ with stirring. After complete dissolution, the inner wall of the container is rinsed with 5mL of methanol while stirring, and then neutralized and titrated with 0.01mol / L hydrochloric acid aqueous solution.

[0077] There is no particular limitation on the method for adjusting the terminal amino concentration of polyamide resin (Y). The terminal amino concentration can be suppressed to a low level by adjusting the feeding ratio (molar ratio) of diamine and dicarboxylic acid to carry out polycondensation reaction, by adding amino-terminated monocarboxylic acid together with diamine and dicarboxylic acid to carry out polycondensation reaction, or by reacting with amino-terminated carboxylic acid after polycondensation reaction.

[0078] (Phenolic antioxidants (A))

[0079] The polyamide layer constituting the multilayer container of the present invention contains a phenolic antioxidant (A).

[0080] From the viewpoint of effectively improving the colorlessness and transparency of recycled polyester and enhancing its formability, the content of phenolic antioxidant (A) in the polyamide layer is preferably 0.006 to 0.090% by mass, more preferably 0.006 to 0.080% by mass, and even more preferably 0.010 to 0.050% by mass, and particularly from the viewpoint of improving formability, it is even more preferably 0.010 to 0.040% by mass, even more preferably 0.010 to 0.030% by mass, and even more preferably 0.020 to 0.030% by mass.

[0081] Phenolic antioxidants (A) are antioxidants that have a phenolic structure due to the bonding of hydroxyl groups to an aromatic ring in the molecule. Preferably, the phenolic structure (phenolic hydroxyl groups) contained in the molecule consists of two or more hydroxyl groups, more preferably three or more.

[0082] Specific examples of phenolic antioxidants (A) include pentaerythritol tetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (Irganox 1010, manufactured by BASF), 3,9-bis[2-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionyloxy]-1,1-dimethylethyl]-2,4,8,10-tetraoxaspiro[5.5]undecane (Sumilizer GA-80, manufactured by Sumitomo Chemical Co., Ltd.), octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, thiodiethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], N,N'-hexane-1,6-dimethylbis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and others. 5-Di-tert-butyl-4-hydroxyphenylpropionamide), 2,4-dimethyl-6-(1-methylpentadecanyl)phenol, diethyl[[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]methyl]phosphate, 3,3', 3”, 5, 5', 5”-hexa-tert-butyl-a, a', a”-(trimethylbenzene-2,4,6-triyl)tri-p-cresol, 4,6-bis(octylthiomethyl)-o-cresol, ethylenebis(oxyethylene)bis[3-(5-tert-butyl-4-hydroxy-m-tolyl)propionate], hexamethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], N, N'-hexamethylenebis(3,5-di-tert-butyl-4-hydroxy-hydrogenated cinnamamide), 1,3,5-tris(3, 5-Di-tert-butyl-4-hydroxybenzyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, 2,6-di-tert-butyl-4-(4,6-bis(octylthio)-1,3,5-triazine-2-ylamino)phenol, etc. These can be used alone or in combination of two or more. From the viewpoint of effectively achieving good colorlessness and transparency of recycled polyesters, pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (Irganox 1010, manufactured by BASF) is preferred.

[0083] (Phosphorus-based antioxidants (B))

[0084] The polyamide layer constituting the multilayer container of the present invention contains a phosphorus-based antioxidant (B). It should be noted that the phosphorus-based antioxidant (B) used in the present invention is a compound having a pentaerythritol backbone and an aromatic ring.

[0085] From the viewpoint of effectively improving the colorlessness and transparency of recycled polyester and enhancing its formability, the content of phosphorus-based antioxidant (B) in the polyamide layer is preferably 0.018 to 0.270% by mass, more preferably 0.018 to 0.240% by mass, and even more preferably 0.030 to 0.150% by mass, especially from the viewpoint of improving formability, and even more preferably 0.030 to 0.120% by mass, even more preferably 0.030 to 0.090% by mass, and even more preferably 0.060 to 0.090% by mass.

[0086] Furthermore, from the viewpoint of effectively improving the colorlessness and transparency of the recycled polyester and enhancing its formability, the total content of phenolic antioxidant (A) and phosphorus antioxidant (B) in the polyamide layer is 0.040 to 0.250% by mass relative to the total content of the polyamide layer, preferably 0.040 to 0.200% by mass, and more preferably 0.040 to 0.160% by mass, even more preferably 0.040 to 0.120% by mass, and even more preferably 0.080 to 0.120% by mass, from the viewpoint of improving formability.

[0087] Furthermore, from the viewpoint of effectively improving the colorless transparency and formability of recycled polyester, the mass ratio of phenolic antioxidant (A) to phosphorus antioxidant (B) [(A) / (B)] is preferably 1 / 9 to 6 / 4, more preferably 1 / 9 to 5 / 5, even more preferably 2 / 8 to 5 / 5, and even more preferably 2 / 8 to 4 / 6.

[0088] The phosphorus-based antioxidant (B) is a compound having a pentaerythritol skeleton and an aromatic ring. It is acceptable as long as the molecule contains both a pentaerythritol skeleton and an aromatic ring, but preferably a compound represented by the following general formula (1). The compound represented by the following general formula (1) is a bis(substituted phenyl) pentaerythritol diphosphite. The phosphorus-based antioxidant (B) can be used alone or in combination with two or more compounds.

[0089]

[0090] (where R) 1 ~R 6 These are either hydrogen atoms or hydrocarbon groups with 1 to 10 carbon atoms.

[0091] In equation (1), R 1 and R 4 They can be the same or different, but the same is preferred. In equation (1), R 2 and R 5 They can be the same or different, but the same is preferred. In equation (1), R 3 With R 6 They can be the same or different, but the same is preferred.

[0092] R 1 and R 4 It is a hydrocarbon group with 1 to 10 carbon atoms, preferably an alkyl, benzyl, phenylethyl, or cumyl group with 1 to 4 carbon atoms, more preferably an alkyl or cumyl group with 4 carbon atoms, further preferably a tert-butyl or cumyl group, and even more preferably a cumyl group.

[0093] R 2 and R 5 It is a hydrocarbon group with 1 to 10 carbon atoms, preferably an alkyl, benzyl, phenylethyl, or cumyl group with 1 to 4 carbon atoms, more preferably an alkyl or cumyl group with 1 to 3 carbon atoms, further preferably a methyl or cumyl group, and even more preferably a cumyl group.

[0094] R 3 and R 6 It is a hydrogen atom or a hydrocarbon group having 1 to 10 carbon atoms, preferably a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, a benzyl group, a phenylethyl group, or a cumyl group. R 1 and R 4 When it is tert-butyl, R 3 and R 6 Preferred to be tert-butyl, R 1 and R 4 When it is a dry base, R 3 and R 6 Hydrogen atoms are preferred.

[0095] Examples of phosphorus-based antioxidants (B) include bis(nonylphenyl) pentaerythritol diphosphite, bis(2,4-di-tert-butylphenyl) pentaerythritol diphosphite, bis(2,6-di-tert-butyl-4-methylphenyl) pentaerythritol diphosphite, and bis(2,4-dicumylphenyl) pentaerythritol diphosphite. From the viewpoint of effectively achieving good colorlessness and transparency of recycled polyester, bis(2,6-di-tert-butyl-4-methylphenyl) pentaerythritol diphosphite and bis(2,4-dicumylphenyl) pentaerythritol diphosphite are preferred, and bis(2,4-dicumylphenyl) pentaerythritol diphosphite is more preferred.

[0096] (Other ingredients)

[0097] The polyamide layer may contain other components. Examples of other components include heat stabilizers, light stabilizers, moisture-proof agents, waterproof agents, lubricants, and spreading agents.

[0098] Without impairing the effects of the present invention, the polyamide layer may contain resins other than polyamide resin (Y) as the main component. The content of polyamide resin (Y) relative to the total resin amount of the polyamide layer is preferably 80 to 100% by mass, more preferably 90 to 100% by mass, or may consist solely of polyamide resin (Y).

[0099] The total content of polyamide resin (Y), phenolic antioxidant (A), and phosphorus antioxidant (B) in the polyamide layer is preferably 70-100% by mass relative to the total amount of the polyamide layer. From the viewpoint of gas barrier properties and inhibition of yellowing of recycled polyester, it is more preferably 90-100% by mass, further preferably 95-100% by mass, and even more preferably 99-100% by mass. The polyamide layer may contain polyamide resin (Y), phenolic antioxidant (A), and phosphorus antioxidant (B), or it may contain only polyamide resin (Y), phenolic antioxidant (A), and phosphorus antioxidant (B).

[0100] The content of polyamide resin (Y) contained in the polyamide layer is preferably 0.05 to 10.0% by mass relative to the total amount of all polyamide layers and all polyester layers. From the viewpoint of gas barrier properties and suppression of yellowing of recycled polyester, it is more preferably 0.5 to 9.0% by mass, even more preferably 1.0 to 8.0% by mass, and even more preferably 2.5 to 7.0% by mass.

[0101] The content of the polyamide layer relative to the total amount of all polyamide layers and all polyester layers is preferably 0.05 to 10.0% by mass, and from the viewpoint of gas barrier properties and suppression of yellowing of recycled polyester, it is more preferably 0.5 to 9.0% by mass, even more preferably 1.0 to 8.0% by mass, and even more preferably 2.5 to 7.0% by mass.

[0102] (Polyamide resin composition for polyamide layer)

[0103] The polyamide layer constituting the multilayer container of the present invention contains polyamide resin (Y), a phenolic antioxidant (A), and a phosphorus antioxidant (B). Therefore, when forming the multilayer container, a polyamide resin composition containing these antioxidants is preferably used. The method for manufacturing the polyamide resin composition is not limited, but it is preferably manufactured by the following method.

[0104] Preferably, a polyamide resin (Y), a phenolic antioxidant (A), a phosphorus antioxidant (B), and any other components (additives) as needed are melt-mixed to obtain a polyamide resin composition.

[0105] Phenolic antioxidants (A), phosphorus antioxidants (B), and any other components (additives) can be directly added to the resin for melt mixing, or dissolved in the liquid component and added to the resin as an additive solution for melt mixing. Preparing a solution facilitates metering and addition, which is therefore preferred. Furthermore, the ability to use a dosing system or similar method for addition is also preferred. The additive solution can be added during the dry mixing of the masterbatch and polyamide resin (Y), or after the polyamide resin (Y) has been melted.

[0106] The liquid component used in the aforementioned additive solution is preferably 0.01 to 1% by mass relative to the resin (polyamide resin (Y) etc.) constituting the polyamide layer, more preferably 0.01 to 0.5% by mass.

[0107] The aforementioned liquid components are preferably liquid resins or liquid oily components.

[0108] Examples of liquid resins mentioned above include epoxy resins such as epoxidized soybean oil and epoxidized linseed oil, fatty acid polyester resins, polyalkylene glycol resins, polyether ester resins, or tributyl acetyl citrate.

[0109] Examples of liquid oily components include plant-based oils such as olive oil, castor oil, jojoba oil, macadamia nut oil, rosehip oil, cocoa butter, and lanolin; animal-based oils such as horse oil, turtle oil, wild boar oil, mink oil, and shark oil; hydrocarbon oils such as petrolatum, liquid paraffin, isodecane, isodecane, octyldodecane, and hydrogenated polyisobutylene; ester oils such as isotriadecyl isononanoate, isopropyl isostearate, neopentyl glycol didecanoate, isotriadecyl isononanoate, glyceryl diisostearate, glyceryl triisostearate, diisostearate malate, and N-lauroyl-L-glutamic acid di(phytosterol / 2-octyldodecyl) ester; silicone oils such as dimethylpolysiloxane and phenylmethylpolysiloxane; dimer esters, dimer glycol derivatives, cholesterol fatty acid esters, phytosterol fatty acid esters, polyglycerol fatty acid esters, pentaerythritol fatty acid esters, tri-2-ethylhexanoate, and octyldodecyl alcohol.

[0110] The method for manufacturing the aforementioned additive solution is not particularly limited. For example, liquid components and various additives can be added, mixed using a Henschel mixer, drum mixer, disperser, etc., and dispersed using a Silverson mixer (manufactured by Silverson Corporation) to obtain the additive solution. In addition to the above, any device such as a kneader, roller mill, ball mill, or sand mill can be used for dispersion.

[0111] As a method of melt mixing, melt blending (melt mixing) can be cited. In addition, in the case of manufacturing the multilayer container described later, the polyamide resin (Y), phenolic antioxidant (A), phosphorus antioxidant (B) and any other components (additives) can be dry-mixed in advance, and then melt-mixed in the process of obtaining the multilayer preform.

[0112] As a melt blending method, masterbatch method and full compounding method can be cited. From the point of view of preventing the deterioration of resin and antioxidant, masterbatch method is preferred.

[0113] The masterbatch method involves mixing a small amount of resin, phenolic antioxidant (A), phosphorus antioxidant (B), and any other components (additives) to form a masterbatch, which is then mixed with the remaining polyamide resin (Y).

[0114] From the perspective of miscibility with polyamide resin (Y), the resin used in the masterbatch is preferably polyamide resin (Y), and more preferably the same resin as the remaining polyamide resin (Y).

[0115] The amount of resin used in the masterbatch is preferably 1 to 20% by mass relative to the total amount of resin in the polyamide resin composition, and more preferably 3 to 15% by mass.

[0116] As a method for obtaining masterbatch, when mixing resin, phenolic antioxidant (A), phosphorus antioxidant (B), and any other components (additives), if the melting point of the resin used in the masterbatch is set as Tm, then from the viewpoint of thorough mixing, the mixing temperature (°C) is preferably Tm+5 to Tm+60, more preferably Tm+10 to Tm+50, and even more preferably Tm+15 to Tm+40. Specifically, it is more preferably 245 to 300°C, even more preferably 250 to 290°C, and even more preferably 255 to 280°C. In addition, from the viewpoint of thorough mixing, the mixing time is preferably 10 to 600 seconds, more preferably 20 to 400 seconds, and even more preferably 30 to 300 seconds. As for the apparatus used in mixing, examples include open-type mixing rollers, non-open-type Banbury mixers, kneaders, and continuous mixers (single-screw mixers, twin-screw mixers, multi-screw mixers, etc.).

[0117] In addition, as a method for melt mixing the masterbatch with the remaining polyamide resin (Y), melt blending (melt mixing) can be listed. In addition, in the case of manufacturing the multilayer container described later, the masterbatch and the remaining polyamide resin (Y) can be dry-mixed in advance, and then melt-mixed in the process of obtaining the multilayer preform.

[0118] The full compounding method is a method of mixing and blending all the polyamide resin (Y), phenolic antioxidant (A), phosphorus antioxidant (B) and any other components (additives) used in the resin composition.

[0119] From the viewpoint of ensuring thorough mixing, the mixing temperature is more preferably 245~300°C, further preferably 250~290°C, and even more preferably 255~280°C. Furthermore, from the viewpoint of ensuring thorough mixing, the mixing time is preferably 10~600 seconds, more preferably 20~400 seconds, and even more preferably 30~300 seconds. Examples of apparatus used for mixing include open-type mixing rollers, closed-type Banbury mixers, kneaders, and continuous mixers (single-screw mixers, twin-screw mixers, multi-screw mixers, etc.).

[0120] <Polyester layer>

[0121] The polyester layer contains polyester resin (X).

[0122] (Polyester resin (X))

[0123] The polyester resin (X) contained in the polyester layer is preferably a condensation polymer of dicarboxylic acid and diol, and preferably has structural units derived from dicarboxylic acid (dicarboxylic acid unit) and structural units derived from diol (diol unit).

[0124] As a dicarboxylic acid unit, examples include structural units derived from aromatic dicarboxylic acids, structural units derived from alicyclic dicarboxylic acids, and structural units derived from aliphatic dicarboxylic acids, with structural units derived from aromatic dicarboxylic acids being preferred.

[0125] Examples of aromatic dicarboxylic acids include terephthalic acid, isophthalic acid, phthalic acid, biphenyl dicarboxylic acid, diphenyl ether dicarboxylic acid, diphenyl sulfone dicarboxylic acid, diphenyl ketone dicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, and 2,7-naphthalenedicarboxylic acid. From the viewpoint of cost and ease of manufacture, terephthalic acid, isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, and 4,4'-biphenyl dicarboxylic acid are preferred, and terephthalic acid, isophthalic acid, and naphthalenedicarboxylic acid are more preferred. From the viewpoint of formability, terephthalic acid and isophthalic acid are even more preferred, and terephthalic acid is even more preferred.

[0126] When recycling the multilayer container of the present invention, it is sometimes melt-blended with conventional single-layer containers made of polyester resin. By having units derived from terephthalic acid as dicarboxylic acid units, the multilayer container of the present invention exhibits good compatibility and recyclability with conventional single-layer containers.

[0127] As aromatic dicarboxylic acids, sulfophthalic acid and its metal salts can be used. Sulfophthalic acid metal salts are the metal salts of sulfophthalic acid; examples of metals that can be used are alkali metals and alkaline earth metals.

[0128] Examples of alicyclic dicarboxylic acids include cyclohexane dicarboxylic acid, norbornene dicarboxylic acid, and tricyclodecane dicarboxylic acid.

[0129] Examples of aliphatic dicarboxylic acids include malonic acid, succinic acid, adipic acid, azelaic acid, and sebacic acid.

[0130] As diol units, examples include structural units derived from aliphatic diols, structural units derived from alicyclic diols, and structural units derived from aromatic diols, with structural units derived from aliphatic diols being preferred.

[0131] Examples of aliphatic diols include ethylene glycol, 2-buten-1,4-diol, trimethylene glycol, tetramethylene glycol, hexamethylene glycol, neopentyl glycol, methylpentyl glycol, and diethylene glycol. Among these, ethylene glycol is preferred.

[0132] Examples of alicyclic diols include cyclohexanediol, isosorbide, spirodiol, 2,2,4,4-tetramethyl-1,3-cyclobutanediol, norbornenediol, and tricyclodecanediol.

[0133] Examples of aromatic diols include bisphenol compounds and hydroquinone compounds.

[0134] Polyester resin (X) can have structural units derived from hydroxycarboxylic acids.

[0135] Examples of hydroxycarboxylic acids include aliphatic hydroxycarboxylic acids, alicyclic hydroxycarboxylic acids, and aromatic hydroxycarboxylic acids.

[0136] Examples of aliphatic hydroxycarboxylic acids include 10-hydroxyoctadecanoic acid, lactic acid, hydroxyacrylic acid, 2-hydroxy-2-methylpropionic acid, and hydroxybutyric acid.

[0137] Examples of alicyclic hydroxycarboxylic acids include hydroxymethylcyclohexanecarboxylic acid, hydroxymethylnorbornenecarboxylic acid, and hydroxymethyltricyclodecanecarboxylic acid.

[0138] Examples of aromatic hydroxycarboxylic acids include hydroxybenzoic acid, hydroxytoluic acid, hydroxynaphthoic acid, 3-(hydroxyphenyl)propionic acid, hydroxyphenylacetic acid, and 3-hydroxy-3-phenylpropionic acid.

[0139] Polyester resin (X) can have structural units derived from monofunctional compounds and structural units derived from polyfunctional compounds.

[0140] Examples of monofunctional compounds include monocarboxylic acids and monohydric alcohols. Specifically, examples include aromatic monocarboxylic acids, aliphatic monocarboxylic acids, aromatic monohydric alcohols, aliphatic monohydric alcohols, and alicyclic monohydric alcohols.

[0141] Examples of multifunctional compounds include aromatic polycarboxylic acids, alicyclic polycarboxylic acids, aliphatic polyols, alicyclic polyols, and their esters.

[0142] The polyester resin (X) preferably has: structural units derived from dicarboxylic acids, the structural units derived from dicarboxylic acids containing structural units derived from terephthalic acid; and structural units derived from diols, the structural units derived from diols containing structural units derived from ethylene glycol. More preferably, it has: structural units derived from dicarboxylic acids, the structural units derived from dicarboxylic acids containing 80 mol% or more of structural units derived from terephthalic acid; and structural units derived from diols, the structural units derived from diols containing 80 mol% or more of structural units derived from ethylene glycol. Further preferably, it has: structural units derived from dicarboxylic acids, the structural units derived from dicarboxylic acids containing 90 mol% or more of structural units derived from terephthalic acid; and structural units derived from diols, the structural units derived from diols containing 90 mol% or more of structural units derived from ethylene glycol. Even more preferably, it has: structural units derived from dicarboxylic acids, the structural units derived from dicarboxylic acids containing 98 mol% or more of structural units derived from terephthalic acid; and structural units derived from diols, the structural units derived from diols containing substantially 100 mol% of structural units derived from ethylene glycol.

[0143] As a specific example of polyester resin (X), polyethylene terephthalate (PET) can be cited.

[0144] Polyethylene terephthalate (PET) may contain structural units derived from aromatic dicarboxylic acids other than terephthalic acid. Preferably, the aromatic dicarboxylic acids other than terephthalic acid are selected from one or more of isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, and 4,4'-biphenyl dicarboxylic acid. These are low in cost, and the copolyester resins containing them are easy to manufacture.

[0145] Among these, isophthalic acid and naphthalenedicarboxylic acid are preferred, with isophthalic acid being more preferred. Polyethylene terephthalate containing structural units derived from isophthalic acid exhibits excellent formability and a slower crystallization rate, thus providing excellent protection against whitening of molded articles. Furthermore, polyethylene terephthalate containing structural units derived from naphthalenedicarboxylic acid not only increases the glass transition temperature and heat resistance of the resin but also absorbs ultraviolet light, making it suitable for manufacturing multilayer containers requiring UV resistance. It should be noted that, from the perspective of ease of manufacture and high economic efficiency, 2,6-naphthalenedicarboxylic acid is preferred as the naphthalenedicarboxylic acid component.

[0146] When polyethylene terephthalate contains structural units derived from aromatic dicarboxylic acids other than terephthalic acid, the proportion of structural units derived from aromatic dicarboxylic acids other than terephthalic acid is preferably 1 to 20 mol% of the dicarboxylic acid units, more preferably 1 to 10 mol%, even more preferably 1 to 5 mol%, and even more preferably 1 to 2 mol%.

[0147] It should be noted that polyester resin (X) can be used alone or in combination with two or more resins.

[0148] Polyester resin (X) can be manufactured by direct esterification and transesterification, which are known methods.

[0149] The intrinsic viscosity of the polyester resin (X) is preferably 0.5~2.0 dL / g, more preferably 0.6~1.5 dL / g. When the intrinsic viscosity is 0.5 dL / g or higher, the container exhibits excellent mechanical properties.

[0150] It should be noted that the intrinsic viscosity was determined as follows: 0.2, 0.4, and 0.6 g / dL solutions were prepared by dissolving polyester resin in a phenol / 1,1,2,2-tetrachloroethane (6 / 4 mass ratio) mixed solvent, and the solutions were measured at 25°C using an automatic viscosity measuring device (Malvern, Viscotek).

[0151] (Phenolic antioxidants (A))

[0152] The polyester layer constituting the multilayer container of the present invention preferably contains a phenolic antioxidant (A).

[0153] It should be noted that the phenolic antioxidant (A) is the same as the phenolic antioxidant (A) contained in the aforementioned polyamide layer, and the preferred phenolic antioxidant is also the same.

[0154] The phenolic antioxidant (A) contained in the aforementioned polyamide layer can be the same as or different from the phenolic antioxidant (A) contained in the polyester layer, but they are preferably the same.

[0155] From the viewpoint of effectively achieving good colorlessness and transparency of recycled polyester, the content of phenolic antioxidant (A) in the polyester layer relative to the total content of the polyester layer is preferably 0.005 to 0.150% by mass, more preferably 0.010 to 0.100% by mass, even more preferably 0.015 to 0.080% by mass, even more preferably 0.015 to 0.050% by mass, even more preferably 0.015 to 0.040% by mass, and even more preferably 0.015 to 0.030% by mass.

[0156] The phenolic antioxidant (A) contained in the polyester layer is an antioxidant with a phenolic structure formed by bonding hydroxyl groups to the aromatic ring in the molecule. Preferably, the phenolic structure (phenolic hydroxyl groups) contained in the molecule has two or more hydroxyl groups, more preferably three or more.

[0157] Specific examples of phenolic antioxidants (A) contained in the polyester layer include pentaerythritol tetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (Irganox 1010, manufactured by BASF), 3,9-bis[2-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionyloxy]-1,1-dimethylethyl]-2,4,8,10-tetraoxaspiro[5.5]undecane (Sumilizer GA-80, manufactured by Sumitomo Chemical Co., Ltd.), octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, thiodiethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], N,N'-hexane-1,6-dimethylbis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and N,N'-hexane-1,6-dimethylbis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]. 5-Di-tert-butyl-4-hydroxyphenylpropionamide), 2,4-dimethyl-6-(1-methylpentadecanyl)phenol, diethyl[[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]methyl]phosphate, 3,3', 3”, 5, 5', 5”-hexa-tert-butyl-a, a', a”-(trimethylbenzene-2,4,6-triyl)tri-p-cresol, 4,6-bis(octylthiomethyl)-o-cresol, ethylenebis(oxyethylene)bis[3-(5-tert-butyl-4-hydroxy-m-tolyl)propionate], hexamethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], N, N'-hexamethylenebis(3,5-di-tert-butyl-4-hydroxy-hydrogenated cinnamamide), 1,3,5-tris(3, 5-Di-tert-butyl-4-hydroxybenzyl)-1,3,5-triazine-2,4,6(1H, 3H, 5H)-trione, 2,6-di-tert-butyl-4-(4,6-bis(octylthio)-1,3,5-triazine-2-ylamino)phenol, etc. These can be used alone or in combination of two or more. From the viewpoint of effectively achieving good colorlessness and transparency of the recycled polyester, pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (Irganox 1010, manufactured by BASF) is preferred.

[0158] (Phosphorus-based antioxidants (B))

[0159] The polyester layer constituting the multilayer container of the present invention preferably contains a phosphorus-based antioxidant (B), and more preferably contains a phenolic antioxidant (A) and a phosphorus-based antioxidant (B).

[0160] It should be noted that the phosphorus-based antioxidant (B) is the same as the phosphorus-based antioxidant (B) contained in the aforementioned polyamide layer, and the preferred phosphorus-based antioxidant is also the same.

[0161] The phosphorus-based antioxidant (B) contained in the aforementioned polyamide layer can be the same as or different from the phosphorus-based antioxidant (B) contained in the polyester layer, but they are preferably the same.

[0162] The phosphorus-based antioxidant (B) contained in the polyester layer is a compound with a pentaerythritol backbone and an aromatic ring.

[0163] From the viewpoint of effectively achieving good colorlessness and transparency of recycled polyester, the content of phosphorus-based antioxidant (B) in the polyester layer relative to the total content of the polyester layer is preferably 0.015 to 0.450% by mass, more preferably 0.030 to 0.300% by mass, even more preferably 0.045 to 0.240% by mass, even more preferably 0.045 to 0.150% by mass, even more preferably 0.050 to 0.120% by mass, and even more preferably 0.050 to 0.090% by mass.

[0164] Furthermore, from the viewpoint of effectively achieving good colorlessness and transparency of the recycled polyester, the total content of phenolic antioxidant (A) and phosphorus antioxidant (B) in the polyester layer is preferably 0.040 to 0.400% by mass, more preferably 0.050 to 0.400% by mass, even more preferably 0.050 to 0.320% by mass, even more preferably 0.050 to 0.220% by mass, even more preferably 0.070 to 0.160% by mass, and even more preferably 0.070 to 0.120% by mass.

[0165] Furthermore, from the viewpoint of effectively achieving good colorlessness and transparency of recycled polyester, the mass ratio of phenolic antioxidant (A) to phosphorus antioxidant (B) [(A) / (B)] is preferably 1 / 9 to 6 / 4, more preferably 1 / 9 to 5 / 5, even more preferably 2 / 8 to 5 / 5, and even more preferably 2 / 8 to 4 / 6.

[0166] The phosphorus-based antioxidant (B) contained in the polyester layer is a compound having a pentaerythritol skeleton and an aromatic ring. It is acceptable as long as the molecule contains a pentaerythritol skeleton and an aromatic ring, but preferably a compound represented by the following general formula (1). The compound represented by the following general formula (1) is bis(substituted phenyl) pentaerythritol diphosphite. The phosphorus-based antioxidant (B) can be used alone or in combination with two or more types.

[0167]

[0168] (where R) 1 ~R 6 These are either hydrogen atoms or hydrocarbon groups with 1 to 10 carbon atoms.

[0169] In equation (1), R 1 and R 4 They can be the same or different, but the same is preferred. In equation (1), R 2 and R 5They can be the same or different, but the same is preferred. In equation (1), R 3 and R 6 They can be the same or different, but the same is preferred.

[0170] R 1 and R 4 It is a hydrocarbon group with 1 to 10 carbon atoms, preferably an alkyl, benzyl, phenylethyl, or cumyl group with 1 to 4 carbon atoms, more preferably an alkyl or cumyl group with 4 carbon atoms, further preferably a tert-butyl or cumyl group, and even more preferably a cumyl group.

[0171] R 2 and R 5 It is a hydrocarbon group with 1 to 10 carbon atoms, preferably an alkyl, benzyl, phenylethyl, or cumyl group with 1 to 4 carbon atoms, more preferably an alkyl or cumyl group with 1 to 3 carbon atoms, further preferably a methyl or cumyl group, and even more preferably a cumyl group.

[0172] R 3 and R 6 It is a hydrogen atom or a hydrocarbon group having 1 to 10 carbon atoms, preferably a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, a benzyl group, a phenylethyl group, or a cumyl group. R 1 and R 4 When it is tert-butyl, R 3 and R 6 Preferred to be tert-butyl, R 1 and R 4 When it is a dry base, R 3 and R 6 Hydrogen atoms are preferred.

[0173] Examples of phosphorus-based antioxidants (B) contained in the polyester layer include bis(nonylphenyl) pentaerythritol diphosphite, bis(2,4-di-tert-butylphenyl) pentaerythritol diphosphite, bis(2,6-di-tert-butyl-4-methylphenyl) pentaerythritol diphosphite, and bis(2,4-dicumylphenyl) pentaerythritol diphosphite. From the viewpoint of effectively achieving good colorlessness and transparency of the recycled polyester, bis(2,6-di-tert-butyl-4-methylphenyl) pentaerythritol diphosphite and bis(2,4-dicumylphenyl) pentaerythritol diphosphite are preferred, and bis(2,4-dicumylphenyl) pentaerythritol diphosphite is more preferred.

[0174] (Aldehyde scavenger)

[0175] The polyester layer preferably contains an aldehyde scavenging agent.

[0176] Examples of aldehyde scavengers include compounds containing amino groups that have the ability to inhibit yellowing of polyester resins. Specifically, at least one compound selected from the group consisting of aminobenzoamide, aminobenzoic acid, diaminobenzoic acid, and nylon 6I / 6T is preferred, and at least one compound selected from the group consisting of o-aminobenzoamide, o-aminobenzoic acid, and nylon 6I / 6T is more preferred.

[0177] The amino group of aminobenzamide can be substituted at any position from 2 to 4, preferably at 2 or 3, more preferably at 2, and even more preferably o-aminobenzamide (2-aminobenzamide).

[0178] In addition, the amino group of aminobenzoic acid can be substituted at any position of 2, 3 or 4, preferably at 2 or 3, more preferably at 2, and even more preferably o-aminobenzoic acid (2-aminobenzoic acid).

[0179] In addition, diaminobenzoic acid can be substituted at any position in 2,3-, 2,4-, or 3,4-, with 3,4-diaminobenzoic acid being preferred.

[0180] Nylon 6I / 6T is a hexamethylenediamine-isophthalic acid-terephthalic acid copolyamide, specifically a hexamethylene isophthalamide / hexamethylene terephthalamide copolymer. Commercially available products can be used as Nylon 6I / 6T, such as Selar (registered trademark) PA 3426 (manufactured by DuPont) and NOVAMID X21 (manufactured by DSM).

[0181] The weight-average molecular weight of nylon 6I / 6T is preferably 10,000 to 50,000, more preferably 15,000 to 45,000, and even more preferably 20,000 to 40,000. The weight-average molecular weight is determined by gel permeation chromatography and converted using polystyrene. If the weight-average molecular weight of nylon 6I / 6T is within the above range, in addition to excellent compatibility with polyester resins, it inhibits leaching into the contents when used to make containers, and also effectively suppresses yellowing.

[0182] Furthermore, the concentration of amino-terminal groups in nylon 6I / 6T is preferably 50-350 μmol / g, more preferably 100-300 μmol / g, and even more preferably 150-250 μmol / g. If the concentration of amino-terminal groups in nylon 6I / 6T is within the above range, the inhibition of yellowing of the recycled polyester is excellent.

[0183] The concentration of the aforementioned amino-terminal groups was determined as follows: Accurately weigh nylon 6I / 6T, dissolve it in a phenol / ethanol = 4 / 1 volumetric solution at 20~30℃ with stirring. After complete dissolution, rinse the inner wall of the container with 5mL of methanol while stirring, and then perform neutralization titration with 0.01mol / L hydrochloric acid aqueous solution.

[0184] In addition, examples of aldehyde scavengers other than the aforementioned aminobenzoamide, aminobenzoic acid, diaminobenzoic acid, and nylon 6I / 6T include salicylamide, salicylaniline, o-phenylenediamine, 1,8-diaminonaphthalene, o-mercaptobenzoamide, N-acetylglycine amide, malondiamide, 3-mercapto-1,2-propanediol, histidine, tryptophan, 4-amino-3-hydroxybenzoic acid, biuret, 2,3-diaminopyridine, 1,2-diaminoanthraquinone, diphenylamine ethane, allantoin, and 2-amino-2-methyl-1,3-propanediol.

[0185] Aldehyde scavengers can be used alone or in combination with two or more.

[0186] As an aldehyde scavenger, it is preferably at least one compound selected from the group consisting of o-aminobenzamide and nylon 6I / 6T, more preferably o-aminobenzamide or nylon 6I / 6T, and even more preferably o-aminobenzamide. That is, it is more preferable that the polyester layer contains o-aminobenzamide.

[0187] From the viewpoint of effectively suppressing yellowing and improving transparency, the content of aldehyde scavenger in the polyester layer relative to the total polyester layer is preferably 0.003~0.150% by mass, more preferably 0.005~0.150% by mass, even more preferably 0.005~0.100% by mass, even more preferably 0.005~0.090% by mass, even more preferably 0.010~0.080% by mass, even more preferably 0.030~0.070% by mass, and even more preferably 0.030~0.060% by mass.

[0188] When the aldehyde scavenger is o-aminobenzoamide, from the viewpoint of effectively suppressing yellowing and improving transparency, the content of o-aminobenzoamide in the polyester layer relative to the total polyester layer is preferably 0.003 to 0.150% by mass, more preferably 0.005 to 0.150% by mass, even more preferably 0.005 to 0.100% by mass, even more preferably 0.005 to 0.090% by mass, even more preferably 0.010 to 0.080% by mass, even more preferably 0.030 to 0.070% by mass, and even more preferably 0.030 to 0.060% by mass.

[0189] (Other ingredients)

[0190] Other components may also be included in the polyester layer. Examples of such components include heat stabilizers, light stabilizers, moisture-proof agents, waterproof agents, lubricants, and spreading agents.

[0191] Without impairing the effects of the present invention, the polyester layer may contain resins other than polyester resin (X) as the main component. The content of polyester resin (X) relative to the total resin amount of the polyester layer is preferably 80 to 100% by mass, more preferably 90 to 100% by mass, or may consist solely of polyester resin (X).

[0192] (Polyester resin composition for polyester layer)

[0193] When the polyester layer constituting the multilayer container of the present invention contains components other than polyester resin (X), it is preferable to use a polyester resin composition containing them when forming the multilayer container. The method for manufacturing the polyester resin composition is not limited, but it is preferably manufactured by the following method.

[0194] Preferably, polyester resin (X) is melt-mixed with phenolic antioxidant (A), phosphorus antioxidant (B) and other components as optional components to obtain a polyester resin composition.

[0195] Phenolic antioxidants (A), phosphorus antioxidants (B), and other components (additives) can be directly added to the resin for melt mixing, or they can be dissolved in the liquid component and added to the resin as an additive solution for melt mixing. Preparing a solution makes metering and addition easier, which is therefore preferable. Furthermore, it is preferable that a metering supply system or similar method can be used for addition. The additive solution can be added during the dry mixing of the masterbatch and polyester resin (X), or it can be added after the polyester resin (X) has been melted.

[0196] The liquid component used in the aforementioned additive solution is preferably 0.01 to 1% by mass relative to the resin (polyester resin (X) etc.) constituting the polyester layer, more preferably 0.01 to 0.5% by mass.

[0197] The aforementioned liquid components are preferably liquid resins or liquid oily components.

[0198] Examples of liquid resins mentioned above include epoxy resins such as epoxidized soybean oil and epoxidized linseed oil, fatty acid polyester resins, polyalkylene glycol resins, polyether ester resins, or tributyl acetyl citrate.

[0199] Examples of liquid oily components include plant-based oils such as olive oil, castor oil, jojoba oil, macadamia nut oil, rosehip oil, cocoa butter, and lanolin; animal-based oils such as horse oil, turtle oil, wild boar oil, mink oil, and shark oil; hydrocarbon oils such as petrolatum, liquid paraffin, isodecane, isodecane, octyldodecane, and hydrogenated polyisobutylene; ester oils such as isotriadecyl isononanoate, isopropyl isostearate, neopentyl glycol didecanoate, isotriadecyl isononanoate, glyceryl diisostearate, glyceryl triisostearate, diisostearate malate, and N-lauroyl-L-glutamic acid di(phytosterol / 2-octyldodecyl) ester; silicone oils such as dimethylpolysiloxane and phenylmethylpolysiloxane; dimer esters, dimer glycol derivatives, cholesterol fatty acid esters, phytosterol fatty acid esters, polyglycerol fatty acid esters, pentaerythritol fatty acid esters, tri-2-ethylhexanoate, and octyldodecyl alcohol.

[0200] The method for manufacturing the aforementioned additive solution is not particularly limited. For example, liquid components and various additives can be added, mixed using a Henschel mixer, drum mixer, disperser, etc., and dispersed using a Silverson mixer (manufactured by Silverson Corporation) to obtain the additive solution. In addition to the above-mentioned dispersion device, any device such as a kneader, roller mill, ball mill, or sand mill can be used.

[0201] As a method of melt mixing, melt blending (melt compounding) can be cited. In addition, in the case of manufacturing the multilayer container described later, polyester resin (X), phenolic antioxidant (A) and phosphorus antioxidant (B) can be dry-mixed in advance, and then melt-mixed in the process of obtaining the multilayer preform.

[0202] As a melt blending method, masterbatch method and full compounding method can be cited. From the point of view of preventing the deterioration of resin and antioxidant, masterbatch method is preferred.

[0203] The masterbatch method involves mixing a small amount of resin with phenolic antioxidants (A) and phosphorus antioxidants (B) to form a masterbatch, which is then mixed with the remaining polyester resin (X).

[0204] From the perspective of miscibility with polyester resin (X), the resin used in the masterbatch is preferably polyester resin (X), and more preferably the same resin as the remaining polyester resin (X).

[0205] The amount of resin used in the masterbatch is preferably 1 to 20% by mass relative to the total amount of resin in the polyester resin composition, and more preferably 3 to 15% by mass.

[0206] As a method for obtaining masterbatch, when mixing resin, phenolic antioxidant (A), and phosphorus antioxidant (B), if the melting point of the resin used in the masterbatch is set as Tm, then from the viewpoint of thorough mixing, the mixing temperature (°C) is preferably Tm+5 to Tm+60, more preferably Tm+10 to Tm+50, and even more preferably Tm+15 to Tm+40. Specifically, it is more preferably 245 to 300°C, even more preferably 250 to 290°C, and even more preferably 255 to 280°C. In addition, from the viewpoint of thorough mixing, the mixing time is preferably 10 to 600 seconds, more preferably 20 to 400 seconds, and even more preferably 30 to 300 seconds. As an apparatus used for mixing, examples include open-type mixing rollers, non-open-type Banbury mixers, kneaders, and continuous mixers (single-screw mixers, twin-screw mixers, multi-screw mixers, etc.).

[0207] Another method for melt mixing the masterbatch with the remaining polyester resin (X) is melt blending (melt mixing). In addition, in the case of manufacturing the multilayer container described later, the masterbatch and the remaining polyester resin (X) can be dry-mixed in advance, and then melt-mixed in the process of obtaining the multilayer preform.

[0208] The full compounding method is a method of mixing and blending all the polyester resin (X) used in the resin composition with phenolic antioxidant (A) and phosphorus antioxidant (B).

[0209] From the viewpoint of ensuring thorough mixing, the mixing temperature is preferably 255~310°C, more preferably 265~300°C, and even more preferably 270~290°C. Furthermore, from the viewpoint of ensuring thorough mixing, the mixing time is preferably 10~600 seconds, more preferably 20~400 seconds, and even more preferably 30~300 seconds. Examples of apparatus used for mixing include open-type mixing rollers, closed-type Banbury mixers, kneaders, and continuous mixers (single-screw mixers, twin-screw mixers, multi-screw mixers, etc.).

[0210] <Structure and Characteristics of Multi-Layer Containers>

[0211] The multilayer container of the present invention comprises: a polyester layer containing polyester resin (X), and a polyamide layer containing polyamide resin (Y), a phenolic antioxidant (A), and a phosphorus antioxidant (B), wherein the phosphorus antioxidant (B) is a compound having a pentaerythritol backbone and an aromatic ring, and the total content of the phenolic antioxidant (A) and the phosphorus antioxidant (B) in the polyamide layer is 0.040 to 0.250% by mass.

[0212] The multilayer container of the present invention may include a resin layer other than the aforementioned polyester layer and polyamide layer. From the viewpoint of facilitating separation during recycling and improving the color of the container and the recycled polyester, it is preferable that the content of the resin layer other than the aforementioned polyester layer and polyamide layer is low, and preferably that it substantially does not contain any resin layer other than the aforementioned polyester layer and polyamide layer. Furthermore, an adhesive layer made of an adhesive and an inorganic layer made of inorganic material may be provided. Regarding these, from the viewpoint of facilitating separation during recycling and improving the yellowing inhibition effect, it is preferable that the content of the adhesive layer and inorganic layer is low, and preferably that it substantially does not contain any adhesive layer and inorganic layer. In particular, the multilayer container of the present invention preferably does not have an adhesive layer.

[0213] The multi-layer container of the present invention has a multi-layer structure of 2 or more layers, preferably a structure of 2 to 5 layers, more preferably a structure of 3 to 5 layers, even more preferably a structure of 3 layers or 5 layers, and even more preferably a structure of 3 layers.

[0214] The outermost layer of the multilayer container of the present invention is preferably a polyester layer. Additionally, the innermost layer is also preferably a polyester layer, and both the outermost and innermost layers are more preferably polyester layers.

[0215] When the outermost layer is a polyester layer, the multilayer container has excellent impact resistance, appearance, and design.

[0216] Therefore, as a structure for a multi-layer container, it is preferable that the multi-layer container has a structure of 2 to 5 layers, with the outermost layer being a polyester layer; more preferably, the multi-layer container has a structure of 3 to 5 layers, with the outermost and innermost layers being polyester layers.

[0217] In the case of a 2-layer structure, it is preferable that the innermost layer is a polyamide layer / polyester layer; in the case of a 3-layer structure, it is preferable that the innermost layer is a polyester layer / polyamide layer / polyester layer; and in the case of a 5-layer structure, it is preferable that the innermost layer is a polyester layer / polyamide layer / polyester layer / polyamide layer / polyester layer.

[0218] The multi-layer container of the present invention is preferably a hollow container, and in the case of a hollow multi-layer container, the main body has at least a multi-layer structure. Furthermore, the ratio (thickness ratio W / S) of the thickness (W) of the polyester layer to the thickness (S) of the polyamide layer in the main body is preferably 2.5 or more and 200 or less. It should be noted that the thickness of the polyester layer refers to the average thickness; when the polyester layer in the main body is multi-layered, the average thickness of each layer is calculated by averaging the thicknesses of the multiple layers. The same applies to the thickness of the polyamide layer.

[0219] If the thickness ratio W / S is 2.5 or higher, the polyamide resin is easily separated from the polyester resin in the separation process of the recycled polyester manufacturing method, especially in air classification and gravity separation, which is therefore preferred. Furthermore, if the thickness ratio W / S is 200 or lower, the hollow container exhibits excellent gas barrier properties, enabling long-term preservation of the contents.

[0220] From the viewpoint of improving the separability in the separation process and ensuring good gas barrier properties of the hollow container, the thickness ratio (W / S) is more preferably 3 to 50, and even more preferably 4 to 15.

[0221] Furthermore, when the multilayer container is a hollow container, the total thickness of the main body of the hollow container (i.e., the total thickness of all layers in the main body) is preferably 100 μm to 5 mm, more preferably 150 μm to 3 mm, and even more preferably 200 μm to 2 mm. Additionally, the thickness (W) of each polyester layer is preferably 30 μm to 2 mm, more preferably 40 μm to 1 mm, and even more preferably 50 μm to 500 μm. The thickness (S) of each polyamide layer is preferably 1 to 200 μm, more preferably 3 to 100 μm, and even more preferably 8 to 50 μm. In this invention, by setting the thickness of the polyamide layer within this range, gas barrier properties are ensured, and the polyamide layer is easily separated from the polyester during the separation process.

[0222] In the case where the multi-layer container of the present invention is a hollow container, it is more preferable to use a liquid packaging container for filling the interior of the hollow container with liquid, and even more preferably a beverage packaging container. Examples of liquids that can be filled inside include beverages, liquid seasonings, chemicals, pharmaceuticals, detergents, etc., and beverages that can be effectively prevented from deteriorating due to oxygen are preferred by the multi-layer container of the present invention.

[0223] As beverages, examples include water, carbonated water, oxygenated water, hydrogen-containing water, milk, dairy products, fruit juice, coffee, coffee drinks, carbonated soft drinks, tea, and alcoholic beverages.

[0224] Examples of liquid seasonings include sauces, soy sauces, syrups, mirins, and seasoning sauces.

[0225] Examples of chemicals include pesticides and insecticides.

[0226] <Manufacturing Method of Multi-Layer Containers>

[0227] The manufacturing method of the multilayer container of the present invention is not particularly limited as long as it is a manufacturing method of a multilayer container having a polyester layer containing polyester resin (X) and a polyamide layer containing polyamide resin (Y), phenolic antioxidant (A) and phosphorus antioxidant (B) in a specific amount. Preferably, it is a manufacturing method including step 1 and step 2 described below.

[0228] That is, the manufacturing method of the multilayer container of the present invention preferably includes the following steps 1 and 2, wherein the multilayer container is a multilayer container having a polyester layer containing polyester resin (X) and a polyamide layer containing polyamide resin (Y), phenolic antioxidant (A) and phosphorus antioxidant (B) in a specific amount.

[0229] Step 1: A process of co-injection molding a polyamide resin composition containing polyamide resin (Y), phenolic antioxidant (A), and phosphorus antioxidant (B) used in the polyamide layer, or a polyamide resin mixture containing polyamide resin (Y), phenolic antioxidant (A), and phosphorus antioxidant (B), with polyester resin (X), a polyester resin composition containing polyester resin (X), or a polyester resin mixture containing polyester resin (X) used in the polyester layer to obtain a multilayer preform.

[0230] Step 2: Blow molding the aforementioned multi-layer preform.

[0231] (Process 1 (process for obtaining multi-layer preforms))

[0232] In step 1, the aforementioned polyamide resin composition or the aforementioned polyamide resin mixture is co-injected with polyester resin (X), the aforementioned polyester resin composition or the aforementioned polyester resin mixture to obtain a multilayer preform.

[0233] The aforementioned polyamide resin composition is a composition with polyamide resin (Y) as the main component and containing phenolic antioxidant (A) and phosphorus antioxidant (B). It may include resins other than polyamide resin (Y) and other components as described in the <Polyamide Layer> section.

[0234] The aforementioned polyester resin composition is a composition with polyester resin (X) as the main component and including phenolic antioxidant (A), phosphorus antioxidant (B), aldehyde scavenger, resin other than polyester resin (X), and other components as described in the <Polyester Layer> section.

[0235] It should be noted that the polyamide resin mixture refers to a mixture obtained by dry mixing polyamide resin (Y), phenolic antioxidant (A), phosphorus antioxidant (B), resins other than polyamide resin (Y), and other components, or a mixture obtained by dry mixing a masterbatch containing resins other than phenolic antioxidant (A), phosphorus antioxidant (B), and polyamide resin (Y), and other components, with the remaining polyamide resin (Y). These polyamide resin mixtures are melt-mixed with each component in this process to form the aforementioned polyamide resin composition.

[0236] Furthermore, the polyester resin mixture refers to a mixture obtained by dry mixing polyester resin (X), phenolic antioxidant (A), phosphorus antioxidant (B), aldehyde scavenger, resins other than polyester resin (X), and other components, or a mixture obtained by dry mixing a masterbatch containing the aforementioned components with the remaining polyester resin (X). These polyester resin mixtures are melt-mixed with each component in this process to form the aforementioned polyester resin composition.

[0237] In co-injection molding, polyester resin (composition, mixture) and polyamide resin (composition, mixture) are extruded into a mold separately and co-injected to form a multi-layer preform.

[0238] (Process 2 (blow molding process))

[0239] In step 2, the aforementioned multi-layer preform is blow-molded.

[0240] In the manufacturing method of the multi-layer container of the present invention, it is preferable to form the multi-layer preform (multi-layer blank) obtained in step 1 by stretch blow molding.

[0241] In step 2, it is preferable to perform stretch blow molding on the multi-layer preform obtained by co-injection molding, and more preferably to perform biaxial stretch blow molding on the multi-layer preform obtained by co-injection molding. It should be noted that, as conditions for biaxial stretch blow molding, it is preferable to set the preform heating temperature to 95~110°C, the primary blow molding pressure to 0.5~1.2 MPa, and the secondary blow molding pressure to 2.0~2.6 MPa. This can suppress the generation of uneven thickness and uneven stretching, resulting in a multi-layer container with excellent strength.

[0242] [Manufacturing method of recycled polyester]

[0243] The method for manufacturing recycled polyester of the present invention is a method for manufacturing recycled polyester that includes a step of recovering polyester from the aforementioned multi-layer container.

[0244] The following describes in detail the method for manufacturing the recycled polyester of the present invention.

[0245] In this manufacturing method, multilayer containers are typically used multilayer containers, but unused multilayer containers can also be used. Examples of used multilayer containers include recycled containers that are temporarily circulating in the market.

[0246] In this manufacturing method, firstly, when a multi-layer container is fitted with a lid, it is preferable to remove the lid from the multi-layer container.

[0247] Next, the container is preferably crushed, and the polyester is selectively separated as needed for recycling (recycling process).

[0248] In the aforementioned recycling process, it is preferable to clean the container or pulverized material with an alkaline aqueous solution (cleaning process).

[0249] Next, the material is granulated as needed to produce pellets (granulation process).

[0250] Then, crystallization and solid-state polymerization processes (crystallization / solid-state polymerization processes) are carried out as needed.

[0251] The following is a description of each process.

[0252] <Cleaning Process>

[0253] In the method for manufacturing recycled polyester of the present invention, it is preferable to clean the aforementioned multilayer container or its pulverized form with an alkaline aqueous solution and then recover the polyester.

[0254] Cleaning with an alkaline aqueous solution can effectively remove not only the contents stored in multi-layered containers, but also adhesives and other contaminants.

[0255] Cleaning with an alkaline aqueous solution can be performed while the container is in operation, during crushing, after crushing, or after separation into polyester and polyamide resins. Furthermore, multiple cleaning operations can be performed. Cleaning after crushing is preferred, but for convenience, the cleaning process will be described before the recovery process described later.

[0256] From the perspective of cleaning efficiency and cost, the alkaline aqueous solution used in the cleaning of multi-layer containers or their pulverized materials is water. Besides water, it may also contain aqueous organic solvents. Examples of aqueous organic solvents include lower alcohols such as methanol, ethanol, and isopropanol, as well as glycols.

[0257] The pH of the alkaline aqueous solution is preferably 8 or higher, more preferably 10 or higher, and even more preferably 12 or higher. There is no upper limit, but it is preferably 14 or lower.

[0258] In addition to the solvent mentioned above, the alkaline aqueous solution also contains an alkaline substance. As an alkaline substance, it is preferably selected from at least one of the group consisting of alkali metal hydroxides and alkaline earth metal hydroxides, and from the perspective of cleaning efficiency and cost, alkali metal hydroxides are more preferred.

[0259] Examples of alkali metal hydroxides include sodium hydroxide, potassium hydroxide, and lithium hydroxide. From the perspective of cleaning efficiency and cost, at least one of the group consisting of sodium hydroxide and potassium hydroxide is preferred, and sodium hydroxide is more preferred.

[0260] The content of alkaline substances relative to the total amount of alkaline aqueous solution is preferably 0.1 to 10% by mass, more preferably 0.5 to 8% by mass, and even more preferably 1 to 5% by mass.

[0261] The cleaning device can be made by any method, but in particular, when cleaning pulverized materials, a container equipped with a mixer is preferred.

[0262] Furthermore, the preferred cleaning temperature is 30~95℃, more preferably 50~90℃, and even more preferably 70~90℃. The preferred cleaning time is 5 minutes~10 hours, 5 minutes~1 hour, or 10~30 minutes. The cleaning temperature and cleaning time can be appropriately selected according to the multi-layer container or the amount and shape of the pulverized material.

[0263] Furthermore, in the method for manufacturing recycled polyester of the present invention, a cleaning step is included, which involves cleaning with an alkaline aqueous solution. However, a further cleaning step using a liquid other than an alkaline aqueous solution may also be included. Cleaning with water is preferred. After cleaning, heating and drying are preferably performed as needed. By performing the drying step, the moisture content of the recycled polyester obtained by this method can be reduced, thus resulting in high thermal stability and providing high-quality recycled polyester. The drying step can be performed, for example, using the air supply or hot air from a dryer.

[0264] <Recycling Process>

[0265] The recycling process involves crushing multi-layer containers to recover recycled polyester.

[0266] Preferably, after crushing the multi-layer container, all or part of the polyamide layer is removed, and the polyester is selectively removed. More preferably, the polyester and the polyamide resin constituting the polyamide layer are separated.

[0267] Multi-layer containers can be pulverized using single-screw mills, twin-screw mills, triple-screw mills, shredders, and other pulverizers. The resulting pulverized material can be in the form of flakes, powder, or lumps. However, since the main body of a multi-layer container is mostly composed of thin, multi-layered structures with a thickness of only a few millimeters or less, the majority of the pulverized material is usually in flake form. It should be noted that flake-shaped pulverized material refers to thin, flat pieces of material with a thickness of approximately 2 millimeters or less.

[0268] Furthermore, in multi-layer containers, the polyester layer and the polyamide layer are structurally integrated, but they are usually not bonded together. During the crushing process, the polyester and polyamide resins can be easily separated as independent crushed materials. Additionally, by forming them into sheets, they can be easily separated by the airflow used in the air separation process described later.

[0269] However, polyester and polyamide resin may not be completely separated during the pulverization process. The pulverized material may separate into two parts: a substance with a relatively high polyester content and a substance with a relatively low polyester content and a relatively high polyamide resin content. It should be noted that, for ease of explanation, the substance with a relatively high polyester content will be referred to simply as polyester, and the substance with a relatively high polyamide resin content will be referred to simply as polyamide resin.

[0270] As mentioned earlier, the pulverized material is separated into polyester and polyamide resins (separation process).

[0271] As a separation method, gravity screening, which utilizes the difference in specific gravity between polyester and polyamide resin, is preferred.

[0272] That is, preferably, the polyamide layer is removed by air separation after the aforementioned multi-layer container is crushed.

[0273] As a specific gravity screening method, wind separation can be specifically used to screen pulverized materials based on wind force. Wind separation can be exemplified by methods such as separating pulverized materials in contact with the airflow generated by a separation device within which a rotating airflow is generated: pulverized materials with a high specific gravity or small specific surface area that fall naturally due to their own weight, and pulverized materials with a low specific gravity or large specific surface area that are lifted by the airflow and then recovered.

[0274] In this method, the polyester fragments fall naturally due to their own weight, while the polyamide resin fragments are lifted up, thereby enabling the separation and recycling of the polyester and polyamide resin.

[0275] In this type of air separation, the same operation can be repeated on the same pulverized material. For example, naturally falling materials can also be further separated by air separation to increase the polyester content in recycled polyester.

[0276] It should be noted that the separation method is not limited to air separation. Other methods include immersing the pulverized material in a liquid such as water and separating it by utilizing the difference in specific gravity between the pulverized material and the liquid, or applying a certain vibration to the pulverized material to separate pulverized materials with different specific gravities and then recovering them.

[0277] <Granulation Process>

[0278] To facilitate processing during molding and other procedures, recycled polyester is preferably granulated into pellets.

[0279] Granulation can be performed before or after the crystallization / solid-state polymerization process described later, but it is better to perform it before the crystallization / solid-state polymerization process. By performing it before the crystallization / solid-state polymerization process, the processability in the crystallization / solid-state polymerization process is also improved.

[0280] In the granulation process, it is preferable to plasticize and granulate the pulverized material through melt blending. Examples of granulation equipment for plasticizing and granulation include single-screw extruders, twin-screw extruders, and multi-screw extruders; any known equipment can be used. The preferred shape of the granules is cylindrical, spherical, or ellipsoidal.

[0281] Granulation, for example, preferably involves extruding plasticized recycled polyester into filaments, which are then granulated by cutting them with a granulator while being cooled in a water bath. The granules removed from the water bath are typically dried to remove any moisture adhering to their surfaces.

[0282] <Crystallization / Solid-phase Polymerization Process>

[0283] After the aforementioned polyester recycling process, it is preferable to perform one or more processes selected from the crystallization process and the solid-state polymerization process, and more preferably both the crystallization process and the solid-state polymerization process. The crystallization / solid-state polymerization process is preferably performed on the aforementioned granulated polyester, but it can also be performed on non-granulated materials (e.g., pulverized materials).

[0284] It should be noted that, in the case of both crystallization and solid-state polymerization, it is preferable to perform solid-state polymerization after crystallization of the polyester.

[0285] Polyester crystallization is carried out by holding the polyester under a certain temperature. Crystallization is preferably carried out by heating the polyester, for example, at 100~230°C. By crystallizing the polyester, it is possible to prevent the polyester from fusing together or adhering to the inner surface of the apparatus during solid-state polymerization and molding processing.

[0286] Solid-state polymerization is preferably carried out for a certain period of time at a temperature above and below the melting point of the polyester (-80°C). Setting the temperature below the melting point prevents the polyester from melting, for example, preventing the polyester from adhering to the surface of the apparatus and reducing operating efficiency. Furthermore, setting the temperature above the melting point (-80°C) allows polymerization to proceed at a sufficient polymerization rate, making it easier to obtain the desired physical properties. Here, "(melting point of polyester -80°C)" refers to a temperature 80°C lower than the melting point of the polyester.

[0287] Solid-phase polymerization can be carried out under vacuum or under a stream of inert gases such as nitrogen or argon. When carried out under vacuum, the gas flow rate is preferably 1.0 torr or less, more preferably 0.5 torr or less, and even more preferably 0.1 torr or less. Furthermore, whether under vacuum or under a stream of inert gases such as nitrogen or argon, it is preferable to minimize the residual oxygen concentration in the system, preferably 300 ppm or less, more preferably 30 ppm or less. By keeping the oxygen concentration below 30 ppm, it is less likely to cause undesirable appearances such as yellowing.

[0288] When solid-state polymerization is carried out under vacuum, it is preferable to maintain uniform heat transfer while continuously and repeatedly stirring or mixing the polyester. When carried out in the presence of an inactive gas, it is preferable to keep the surface of the polyester in contact with the dry gas at all times under a dry gas flow.

[0289] Examples of solid-phase polymerization apparatus used for crystallization / solid-phase polymerization processes include: drum-type intermittent apparatus with heating jackets, drying silo-type apparatus with inactive gas flow equipment, crystallization apparatuses and reactors with internal stirring blades and discharge screws, etc. It should be noted that crystallization and solid-phase polymerization are preferably carried out continuously or simultaneously in the same apparatus.

[0290] The heating time for solid-state polymerization is determined according to the equipment and other conditions, but it is sufficient to allow the polyester to obtain sufficient physical properties.

[0291] Solid-state polymerization involves holding the polyester at high temperatures for extended periods, which can sometimes lead to quality deterioration, such as color, if impurities are present in the polyester. It is preferable to remove most of the polyamide resin in the aforementioned removal process, in which case the potential quality deterioration that may occur during solid-state polymerization can be minimized.

[0292] When the method for manufacturing recycled polyester includes a polyamide resin removal step, the polyamide resin content in the obtained recycled polyester is preferably less than 1% by mass, more preferably less than 0.8% by mass, and even more preferably less than 0.6% by mass. By reducing the polyamide resin content in this way, the quality of the recycled polyester becomes good.

[0293] In addition, in the method for manufacturing recycled polyester of the present invention, processes other than those described above may also be performed.

[0294] The recycled polyester obtained by this manufacturing method can be used for various applications such as resin moldings and fibers.

[0295] Example

[0296] The present invention will now be described in more detail through examples and comparative examples, but the present invention is not limited to these examples.

[0297] [raw material]

[0298] The polyester resin and antioxidant used in the examples and comparative examples are described below. Additionally, the polyamide resin used is the polyamide resin manufactured in Manufacturing Example 1 below.

[0299] <Polyester Resin>

[0300] PET 1101: Polyclear Refresh PET 1101, polyethylene terephthalate (manufactured by Indorama).

[0301] <Phenolic Antioxidant (A)>

[0302] Irganox 1010: Pentaerythritol tetra[3-(3',5'-di-tert-butyl-4'-hydroxyphenyl)propionate] (trade name: Irganox 1010, manufactured by BASF)

[0303] <Phosphorus-based antioxidants (phosphorus-based antioxidants (B) and other phosphorus-based antioxidants)>

[0304] Doverphos S9228: Bis(2,4-dicumylphenyl) pentaerythritol diphosphite (trade name: Doverphos S9228, manufactured by Dover Chemical, phosphorus-based antioxidant (B))

[0305] Irgaphos 168: Tris(2,4-di-tert-butylphenyl) phosphite (a phosphorus antioxidant with an aromatic ring but without a pentaerythritol skeleton, trade name: Irgaphos 168, manufactured by BASF, a phosphorus antioxidant other than (B))

[0306] <Polyamide resin>

[0307] Manufacturing Example 1 (Manufacturing of Polyamide Resin (Y1))

[0308] In a 50-liter reaction vessel equipped with a stirrer, partial condenser, total condenser, thermometer, dropping funnel, nitrogen inlet pipe, and wire die, accurately weighed 15,000 g (102.6 mol) of adipic acid, 13.06 g (123.3 mmol, equivalent to 151 ppm phosphorus concentration in polyamide) of sodium hypophosphite monohydrate (NaH2PO2·H2O), and 6.849 g (83.49 mmol, equivalent to 0.68 molar ratio to sodium hypophosphite monohydrate) were added. After thorough nitrogen purging, the system was further heated to 170°C while stirring under a small nitrogen flow. Then, 13,896 g (102.0 mol, equivalent to 0.994 molar ratio to adipic acid) of m-phenylenediamine was added dropwise under stirring, while continuously heating the system to remove the generated condensation water. After the addition of m-phenylenediamine was completed, the reaction was continued at an internal temperature of 260°C for 40 minutes. Then, the system was pressurized with nitrogen, and the polymer was removed from the die head and granulated to obtain approximately 24 kg of polyamide.

[0309] Next, the aforementioned polyamide was placed into a jacketed rotary drum dryer equipped with a nitrogen inlet pipe, vacuum line, vacuum pump, and thermocouple for internal temperature measurement. While rotating at a constant speed, the inside of the dryer was fully purged with nitrogen gas of 99% by volume or higher purity. The dryer was then heated under this nitrogen gas flow, raising the granule temperature to 150°C in approximately 150 minutes. At the moment the granule temperature reached 150°C, the pressure within the system was reduced to below 1 torr. The temperature was further increased, raising the granule temperature to 200°C in approximately 70 minutes, and then maintained at 200°C for 30–45 minutes. Next, nitrogen gas of 99% by volume or higher purity was introduced into the system, and cooling was performed while the dryer was rotating to obtain polyamide resin (Y1). The concentration of amino-terminal groups was measured, and the result was 14.4 μmol / g.

[0310] Example 1 [Manufacturing of Multilayer Containers and Recycled Polyester]

[0311] <1. Manufacturing of Polyamide Resin Blends>

[0312] Irganox 1010 0.0120 parts by weight (120 ppm in the polyamide layer) as phenolic antioxidant (A), Doverphos S9228 0.0360 parts by weight (360 ppm in the polyamide layer) as phosphorus antioxidant (B), and polyamide resin (Y1) obtained in Manufacturing Example 1 (the remainder when the total is set to 100 parts by weight) were pre-dry mixed to obtain a polyamide resin mixture.

[0313] <2. Manufacturing of Multi-Layer Containers>

[0314] (Preform forming)

[0315] Using an injection molding machine (Sumitomo Heavy Industries, Ltd., model DU130CI) with two injection barrels and a two-cavity mold (Kortec), the aforementioned polyamide resin mixture is injected from one injection barrel, and polyester resin (PET 1101) is injected from the other injection barrel. Under the conditions shown below, a three-layer preform consisting of a polyester layer / polyamide layer / polyester layer (each preform is set to 25g) is manufactured by injection molding with the mass of the polyamide layer relative to the total preform as described in Table 1. The preform has a total length of 95mm, an outer diameter of 22mm, and a wall thickness of 4.0mm. The molding conditions for the three-layer preform are as follows.

[0316] Injection barrel temperature on the skin side: 285℃

[0317] Core-side injection barrel temperature (3 layers only): 265℃

[0318] Resin flow path temperature inside the mold: 285℃

[0319] Mold cooling water temperature: 15℃

[0320] Loop time: 40 seconds

[0321] (Bottle forming)

[0322] The preform obtained in the aforementioned (preform forming) step was biaxially stretched and blow-molded using a blow molding apparatus (EFB1000ET, Frontier). This resulted in a bottle (a hollow multi-layered container). The bottle has a total length of 223 mm, an outer diameter of 65 mm, an internal volume of 500 mL, and a petal-shaped bottom. No dimples were provided in the main body. The biaxial stretch blow molding conditions are shown below.

[0323] Preform heating temperature: 103℃

[0324] Pressure required for tension rod: 0.7 MPa

[0325] Single blow molding pressure: 1.1 MPa

[0326] Secondary blow molding pressure: 2.5MPa

[0327] Delay time for one blow molding cycle: 0.30 seconds

[0328] Blow molding time per cycle: 0.30 seconds

[0329] Second blow molding time: 2.0 seconds

[0330] Blow molding venting time: 0.6 seconds

[0331] Mold temperature: 30℃

[0332] <3. Manufacturing of Recycled Polyester>

[0333] (Cleaning, recycling, and granulation process)

[0334] 10 kg of the hollow multilayer container obtained in <2. Manufacturing of Multilayer Containers> was pulverized using a pulverizer with a mesh diameter of 10 mm. The pulverized material was placed in a container equipped with a mixer at a ratio of 1 kg to 4 L of 1% sodium hydroxide aqueous solution, and washed while stirring. The washing temperature was 85°C, and the washing time was 15 minutes. After removing the washing water, the pulverized material was placed in 4 times its mass of water at 45°C and stirred for 5 minutes. After dehydration, 8 times its mass of water was added and stirred. After dehydration, the washed pulverized material was dried at 50°C.

[0335] For this sheet, add the sheet of polyester monolayer container obtained in the same steps and dry mix, then dilute to 2 times.

[0336] The dried pulverized material was extruded using a twin-screw extruder (Toshiba Machine Co., Ltd., TEM26SX) at a heater temperature of 280°C and an extrusion speed of 20 kg / h to form filaments. These filaments were then granulated using a granulator while being cooled in a water bath. It should be noted that no polyamide layer was subjected to air separation.

[0337] (Crystallization / solid-phase polymerization process)

[0338] The granules obtained in the aforementioned granulation process are heated at 200°C under vacuum reduced to below 1 torr for 7 hours. The heat-treated granules are then removed to produce recycled polyester.

[0339] Examples 2-3 and Comparative Examples 2-6 [Manufacturing of Multilayer Containers and Recycled Polyester]

[0340] In Example 1, the multilayer container and recycled polyester were manufactured in the same manner as in Example 1, except that the phenolic antioxidant (A) and phosphorus antioxidant used in the polyamide resin mixture (polyamide resin composition, polyamide layer) were of the types and amounts shown in Table 1. It should be noted that in Table 1, the content of the phenolic antioxidant (A) and phosphorus antioxidant is expressed in "ppm" (parts per million, mass ppm). 1 ppm is 0.0001 mass.

[0341] Comparative Example 1 [Manufacturing of Multilayer Containers and Recycled Polyester]

[0342] In Example 1, the multilayer container and recycled polyester were manufactured in the same manner as in Example 1, except that polyamide resin (Y1) was used instead of the aforementioned polyamide resin mixture.

[0343] Comparative Example 7 [Manufacturing of Multilayer Containers and Recycled Polyester]

[0344] <1. Manufacturing of Polyester Resin Blends>

[0345] A polyester resin mixture was obtained by pre-dry mixing 99.99387 parts by weight of polyester resin (PET 1101), 0.00153 parts by weight of Irganox 1010 (15.3 ppm in the polyester layer) as a phenolic antioxidant (A), and 0.0046 parts by weight of Doverphos S9228 (46 ppm in the polyester layer) as a phosphorus antioxidant (B).

[0346] <2. Manufacturing of multi-layer containers and 3. Manufacturing of recycled polyester>

[0347] Except that the aforementioned polyester resin mixture was used instead of polyester resin (PET 1101), the multilayer container and recycled polyester were manufactured in the same manner as in Comparative Example 1.

[0348] Example 4 [Manufacturing of Multilayer Containers and Recycled Polyester]

[0349] <1. Manufacturing of Polyester Resin Blends>

[0350] A polyester resin mixture was obtained by pre-dry mixing 99.928 parts by weight of polyester resin (PET 1101), 0.0180 parts by weight of Irganox 1010 (180 ppm in the polyester layer) as a phenolic antioxidant (A), and 0.0540 parts by weight of Doverphos S9228 (540 ppm in the polyester layer) as a phosphorus antioxidant (B).

[0351] <2. Manufacturing of multi-layer containers and 3. Manufacturing of recycled polyester>

[0352] The multilayer container and recycled polyester were manufactured in the same manner as in Example 1, except that the aforementioned polyester resin mixture was used instead of polyester resin (PET 1101).

[0353] Examples 5, 6 and Comparative Example 8 [Manufacturing of Multilayer Containers and Recycled Polyester]

[0354] In Example 4, the multilayer container and recycled polyester were manufactured in the same manner as in Example 4, except that the phenolic antioxidant (A) and phosphorus antioxidant used in the polyamide resin mixture (polyamide resin composition, polyamide layer) were set to the types and amounts shown in Table 1.

[0355] It should be noted that in Example 6, when dry-mixing polyester resin, phenolic antioxidant (A) and phosphorus antioxidant (B), the amount of o-aminobenzamide shown in Table 1 was added as an aldehyde scavenger and dry-mixed.

[0356] [Evaluation Method]

[0357] <Bottle Formability>

[0358] The whitening of the bottle obtained by forming using the method described in Example 1, <2. Manufacturing of Multi-Layer Containers>, is evaluated as follows.

[0359] Cut a section from the main body of the bottle (3-13 cm from the bottom) of the bottle, visually observed as whitened (using a resin film with a haze of 5% as a standard, measured according to JIS K 7136:2000; the portion with a haze higher than the standard) and measure its mass. Calculate the percentage of the whitened portion according to the following criteria to evaluate its formability. The smaller the percentage of the whitened portion, the higher the transparency of the multi-layered container and the better the formability.

[0360] (Evaluation Criteria)

[0361] A: The percentage of the whitened portion is less than 1% of the total volume of the bottle body, and it is transparent. It has extremely good formability.

[0362] B: The percentage of whitened portion is more than 1% but less than 10% of the overall bottle body, with slight whitening observed. Formability is good.

[0363] C: The percentage of whitened portion is more than 10% but less than 50% of the overall bottle body; whitening is observed in some areas. Formability is slightly poor.

[0364] D: The proportion of the whitened portion is more than 50% of the entire bottle body, resulting in overall whitening. Poor formability.

[0365] <Sample Preparation for Evaluation>

[0366] The following were prepared and measured for the following haze and L. * value, b * Value and Δb * Samples used to evaluate the value of recycled polyester.

[0367] The heat-treated granules from the examples and comparative examples were used to manufacture a plate with a length of 60 mm, a width of 90 mm, and a wall thickness of 3.0 mm by injection molding using an injection molding machine (manufactured by Sumitomo Heavy Industries, Ltd., model SE130DU-HP) equipped with an injection barrel, under the molding conditions shown below.

[0368] Injection barrel temperature: 280℃

[0369] Mold cooling water temperature: 15℃

[0370] Loop time: 45 seconds

[0371] <Haze>

[0372] The haze of the aforementioned plate was measured based on JIS K 7136:2000 using a haze meter COH7700 (manufactured by Nippon Denshoku Kogyo Co., Ltd., with a white LED light source), and the result was expressed as the average of four measurements. A lower haze value indicates better transparency of the recycled polyester, and is therefore preferred.

[0373] <L * Value >

[0374] According to JIS K 7105:1981, the halogen content of the evaluation sample was measured using a COH400 haze meter (manufactured by Nippon Denshoku Kogyo Co., Ltd.). * value.

[0375] It should be noted that L * The value represents brightness. L * The higher the value, the better the colorlessness, and therefore the preferred value.

[0376] * Value >

[0377] According to JIS K 7105:1981, the haze was measured using a COH400 haze meter (manufactured by Nippon Denshoku Kogyo Co., Ltd.), and the b of the evaluation sample was measured. * value.

[0378] It should be noted that b * The value represents chromaticity. +b * Indicates the yellow direction, -b * Indicates the blue direction. (b) * The smaller the absolute value of b, the better. * The smaller the value, the more yellowing is suppressed, the better the colorlessness, and the better the hue.

[0379] <Δb * Value >

[0380] The polyester resin (Polyclear Refresh PET 1101) used in the above raw materials was used to manufacture a sheet with a length of 60 mm, a width of 90 mm, and a wall thickness of 3.0 mm under the molding conditions shown in <Sample Preparation for Evaluation>. Next, according to JIS K 7105:1981, a haze meter COH400 (manufactured by Nippon Denshoku Kogyo Co., Ltd.) was used to measure the b... * value (b) * Value 4.1).

[0381] The above * The evaluation of the examples and comparative examples obtained in the value> was based on the b value of the sample. * The value of b is related to the polyester resin used in the raw materials. * The difference between the values ​​(4.1) is taken as Δb. * Value. Δb * The smaller the value, the more suppressed the yellowing, the less discoloration from the raw polyester resin, and the better the colorlessness, thus it is preferred. It should be noted that in this evaluation, Δb... * When the value is less than 5.0, it is judged to have good colorlessness, especially Δb. * When the value is less than 4.5, it is judged to be extremely colorless.

[0382] [Table 1]

[0383]

[0384] As shown in Table 1, the recycled polyester obtained from the multilayer container of the present invention exhibits low yellowness, excellent colorlessness, and excellent transparency. Furthermore, it can be seen that the multilayer container of the present invention achieves these effects by adding a very small amount of antioxidant, thus also exhibiting excellent formability.​​

Claims

1. A multi-layered container, comprising: A polyester layer containing polyester resin X, and A polyamide layer containing polyamide resin Y, phenolic antioxidant A, and phosphorus-based antioxidant B. Phosphorus-based antioxidant B is a compound with a pentaerythritol skeleton and an aromatic ring. The total content of phenolic antioxidant A and phosphorus-based antioxidant B in the polyamide layer is 0.040~0.250% by mass.

2. The multi-layer container according to claim 1, wherein, The mass ratio of phenolic antioxidant A to phosphorus antioxidant B in the polyamide layer, i.e., A / B, is 2 / 8 to 5 / 5.

3. The multi-layer container according to claim 1 or 2, wherein, The polyester layer contains phenolic antioxidant A and phosphorus-based antioxidant B.

4. The multi-layer container according to claim 3, wherein, The total content of phenolic antioxidant A and phosphorus antioxidant B in the polyester layer is 0.050~0.220% by mass.

5. The multi-layer container according to claim 3 or 4, wherein, The mass ratio of phenolic antioxidant A to phosphorus antioxidant B in the polyester layer, i.e., A / B, is 2 / 8 to 5 / 5.

6. The multi-layer container according to any one of claims 1 to 5, wherein, The polyester layer contains o-aminobenzamide.

7. The multi-layer container according to any one of claims 1 to 6, wherein, The polyamide resin Y has: a diamine-derived structural unit containing more than 80 mol% of a phenylenediamine-derived structural unit; and a dicarboxylic acid-derived structural unit containing more than 80 mol% of a dicarboxylic acid-derived structural unit.

8. The multi-layer container according to any one of claims 1 to 7, wherein, The content of polyamide resin Y is 0.05~10.0% by mass relative to the total amount of all polyamide layers and all polyester layers.

9. The multi-layer container according to any one of claims 1 to 8, wherein, The content of the polyamide layer is 0.05 to 10.0% by mass relative to the total amount of all polyamide layers and all polyester layers.

10. The multi-layer container according to any one of claims 1 to 9, wherein, Polyester resin X has: structural units derived from dicarboxylic acid, wherein the structural units derived from dicarboxylic acid contain more than 80 mol% of structural units derived from terephthalic acid; And structural units derived from diol, wherein the structural units derived from diol contain more than 80 mol% of structural units derived from ethylene glycol.

11. The multi-layer container according to any one of claims 1 to 10, wherein, Multi-layer containers are hollow containers.

12. The multi-layer container according to any one of claims 1 to 11, wherein, Multi-layer containers have a 3-5 layer structure, with the outermost and innermost layers being polyester layers.

13. The multi-layer container according to any one of claims 1 to 12, wherein, The multi-layer container has a 3-layer structure.

14. The multi-layer container according to any one of claims 1 to 13, wherein, Multi-layer containers do not have an adhesive layer.

15. A method for manufacturing recycled polyester, comprising a step of recovering polyester from a multi-layer container according to any one of claims 1 to 14.

16. A method for manufacturing recycled polyester, comprising a step of recovering polyester from a multi-layer container according to any one of claims 1 to 14. The method for manufacturing recycled polyester includes a step of removing all or part of the polyamide layers from a multi-layer container to recycle the polyester.

17. The method for manufacturing recycled polyester according to claim 16, wherein, After crushing the multi-layer container, the polyamide layer is removed by air separation.

18. A method for manufacturing recycled polyester according to any one of claims 15 to 17, comprising the following steps: cleaning the multilayer container or its pulverized form according to any one of claims 1 to 14 with an alkaline aqueous solution, and recovering the polyester.

19. The method for manufacturing recycled polyester according to any one of claims 15 to 18, wherein, After the polyester recycling process, one or more processes selected from the crystallization process and the solid-state polymerization process are carried out.

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