Multilayered container and method for producing recycled polyester

Abstract

This multilayered container has a polyester layer that contains a polyester resin (X) and a polyamide layer that contains a polyamide resin (Y), a phenol-based antioxidizing agent (A), and a phosphorus-based antioxidizing agent (B), wherein: the phosphorus-based antioxidizing agent (B) is a compound having a pentaerythritol skeleton and an aromatic ring; and the total content of the phenol-based antioxidizing agent (A) and the phosphorus-based antioxidizing agent (B) in the polyamide layer is 0.040-0.250 mass%.

Description

Multilayer container and method for producing recycled polyester

[0001] The present invention relates to a multilayer container and a method for producing recycled polyester.

[0002] Aromatic polyester resins obtained using an aromatic dicarboxylic acid compound and an aliphatic diol compound as monomers are characterized by excellent transparency, mechanical properties, melt stability, solvent resistance, aroma retention, gas barrier properties, recyclability, etc. Therefore, aromatic polyester resins such as polyethylene terephthalate (PET) are widely used in various packaging materials such as films, sheets, and hollow containers. Although polyester resins have high gas barrier properties, they are not necessarily sufficient for applications requiring additional gas barrier properties against oxygen, carbon dioxide, etc. Therefore, methods for improving the gas barrier properties of polyester resins have been used, such as vapor deposition of aluminum oxide or silicon oxide onto molded articles or packaging containers made of polyester resin, or coating, laminating, or melt-mixing a resin having high gas barrier properties onto molded articles or packaging containers made of polyester resin.

[0003] Examples of gas barrier resins include polyamide resins such as nylon 6 and nylon 66, and ethylene-vinyl alcohol copolymers. Among polyamide resins, xylylene group-containing polyamide resins obtained by polymerizing a diamine component primarily composed of xylylene diamine with a dicarboxylic acid component primarily composed of an aliphatic dicarboxylic acid have particularly excellent gas barrier properties. Xylylene group-containing polyamide resins not only have high gas barrier properties, but also have similar glass transition temperatures, melting points, and crystallinity to polyethylene terephthalate, a widely used polyester resin, making them easy to laminate and melt-mix with polyester resins. For this reason, xylylene group-containing polyamide resins are highly suitable as materials for improving the gas barrier properties of polyester resins.

[0004] However, multilayer polyester containers having a polyamide layer are more susceptible to yellowing due to thermal history than polyester alone. Therefore, yellowing occurs particularly during the recycling process in which the containers are recovered and the resin is reused. Since this reduces the commercial value of the packaging container, efforts to suppress yellowing have been underway. For example, Patent Document 1 discloses a multilayer container having a polyester resin composition layer containing a polyester resin and a specific amount of an antioxidant, and a polyamide resin composition layer containing a specific polyamide resin and a specific amount of a cobalt salt, with the aim of suppressing yellowing of recycled polyester during recycling.

[0005] JP 2018-043773 A

[0006] As described above, containers made of polyester resins containing polyamide tend to yellow, and recycled polyesters obtained by recycling these containers also tend to have a yellowish tinge. Methods for suppressing this yellowing include adding an antioxidant to the container, as described in Patent Document 1, but the colorlessness of the resulting recycled polyester is still insufficient. Furthermore, recycled polyesters are prone to cloudiness due to the recycling process, and improved transparency is also required. Furthermore, adding a large amount of additives, particularly to containers with a multilayer structure, can sometimes result in whitening during molding, resulting in poor moldability, and therefore a need for both recyclability and moldability. Therefore, an objective of the present invention is to provide a multilayer container that can suppress yellowing of recycled polyesters obtained by recycling multilayer containers, and that has excellent transparency and moldability.

[0007] The present inventors have conducted extensive research in light of the above-mentioned problems and have found that a multilayer container having a polyester layer and a polyamide layer containing a phenolic antioxidant and a specific phosphorus-based antioxidant can solve the above-mentioned problems, thereby completing the present invention. The present invention provides the following [1] to

[19] .

[0008] [1] A multi-layer container having a polyester layer containing a polyester resin (X) and a polyamide layer containing a polyamide resin (Y), a phenolic antioxidant (A), and a phosphorus-based antioxidant (B), wherein the phosphorus-based 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-based antioxidant (B) in the polyamide layer is 0.040 to 0.250 mass%. [2] The multi-layer container according to [1] above, wherein the mass ratio [(A) / (B)] of the content of the phenolic antioxidant (A) to the content of the phosphorus-based antioxidant (B) in the polyamide layer is 2 / 8 to 5 / 5. [3] The multi-layer container according to [1] or [2] above, wherein the polyester layer contains the phenolic antioxidant (A) and the phosphorus-based antioxidant (B). [4] The multi-layer container according to [3] above, wherein the total content of the phenolic antioxidant (A) and the phosphorus-based antioxidant (B) in the polyester layer is 0.050 to 0.220 mass%. [5] The multi-layer container according to [3] above, wherein the mass ratio [(A) / (B)] of the content of the phenolic antioxidant (A) to the content of the phosphorus-based antioxidant (B) in the polyester layer is 2 / 8 to 5 / 5. [6] The multi-layer container according to any one of [1] to [5] above, wherein the polyester layer contains anthranilamide. [7] The multi-layer container according to any one of [1] to [6] above, wherein the polyamide resin (Y) has structural units derived from a diamine containing 80 mol% or more of structural units derived from xylylenediamine and structural units derived from a dicarboxylic acid containing 80 mol% or more of structural units derived from adipic acid. [8] The multilayer container according to any one of [1] to [7], wherein the content of the polyamide resin (Y) is 0.05 to 10.0 mass% relative to the total amount of all polyamide layers and all polyester layers. [9] The multilayer container according to any one of [1] to [8], wherein the content of the polyamide layer is 0.05 to 10.0 mass% relative to the total amount of all polyamide layers and all polyester layers.

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

[11] The multilayer container according to any one of [1] to

[10] above, wherein the multilayer container is a hollow container.

[12] The multilayer container according to any one of [1] to

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

[13] The multilayer container according to any one of [1] to

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

[14] The multilayer container according to any one of [1] to

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

[15] A method for producing recycled polyester, comprising a step of recovering polyester from the multilayer container according to any one of [1] to

[14] above.

[16] A method for producing recycled polyester, comprising a step of recovering polyester from the multilayer container according to any one of [1] to

[14] above, wherein the polyamide layer is removed in whole or in part from the multilayer container to recover the polyester.

[17] A method for producing recycled polyester according to

[16] above, wherein the polyamide layer is removed by crushing the multilayer container and then winnowing.

[18] A method for producing recycled polyester according to any one of

[15] to

[17] above, comprising a step of washing the multilayer container according to any one of [1] to

[14] above or the crushed product thereof with an alkaline aqueous solution to recover the polyester.

[19] A method for producing recycled polyester according to any one of

[15] to

[18] above, wherein the polyester recovery step is followed by one or more steps selected from a crystallization step and a solid-state polymerization step.

[0009] According to the present invention, it is possible to provide a multilayer container in which yellowing of the recycled polyester obtained by recycling a multilayer container can be suppressed, and the recycled polyester has excellent transparency and moldability.

[0010] [Multilayer Container] The multilayer container of the present invention comprises a polyester layer containing a polyester resin (X) and a polyamide layer containing a polyamide resin (Y), a phenolic antioxidant (A), and a phosphorus-based antioxidant (B), wherein the phosphorus-based 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-based antioxidant (B) in the polyamide layer is 0.040 to 0.250 mass %. The reasons why the multilayer container of the present invention can inhibit yellowing of recycled polyester obtained by recycling and also exhibits excellent transparency and moldability are unclear, but are thought to be as follows. While yellowing during recycling is thought to be caused by oxidized polyamide being mixed into the recycled polyester, the multilayer container of the present invention contains an antioxidant in the polyamide layer, which is thought to effectively inhibit polyamide oxidation. Furthermore, introducing a small amount of antioxidant into the polyamide layer, which serves as a barrier layer and has a low mass ratio, is highly effective, and therefore does not affect moldability, resulting in excellent container moldability. Furthermore, by using a phenolic antioxidant in combination with a phosphorus-based antioxidant having a pentaerythritol skeleton and an aromatic ring, the effects of hydrolysis and the like can be suppressed, and hydrolysis and spillage during use of the container and during cleaning during recycling can also be suppressed, and it is believed that a higher yellowing suppression effect can be achieved.

[0011] <Polyamide Layer> The polyamide layer contains a polyamide resin (Y), a phenolic antioxidant (A), and a phosphorus-based antioxidant (B), wherein the phosphorus-based 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-based antioxidant (B) in the polyamide layer is 0.040 to 0.250 mass%.

[0012] (Polyamide Resin (Y)) Examples of the polyamide resin (Y) include xylylene group-containing polyamide resins, nylon 6, nylon 66, nylon 666, nylon 610, nylon 11, nylon 12, and mixtures thereof. Among these, xylylene group-containing polyamide resins are preferred because they can improve gas barrier performance and are easily separated from the polyester layer during recycling. The xylylene group-containing polyamide resin is preferably a polyamide resin containing a structural unit derived from xylylene diamine.

[0013] The xylylene group-containing polyamide resin is obtained by polycondensation of a diamine, including xylylene diamine, with a dicarboxylic acid, and contains structural units derived from xylylene diamine and structural units derived from dicarboxylic acid. The xylylene group-containing polyamide resin preferably contains 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% of structural units derived from xylylene diamine among the structural units derived from diamine (diamine units). The xylylene diamine is preferably meta-xylylene diamine, para-xylylene diamine, or both, with meta-xylylene diamine being more preferred. The diamine units constituting the xylylene group-containing polyamide resin 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% of structural units derived from meta-xylylene diamine. When the metaxylylenediamine-derived structural unit in the diamine unit is within the above range, the polyamide resin has better gas barrier properties.

[0014] The diamine units in the xylylene group-containing polyamide resin may consist solely of structural units derived from xylylene diamine, or may contain structural units derived from diamines other than xylylene diamine. Examples of diamines other than xylylene diamine include aliphatic diamines having a linear or branched structure, such as ethylene diamine, tetramethylene diamine, pentamethylene diamine, 2-methylpentane diamine, hexamethylene diamine, heptamethylene diamine, octamethylene diamine, nonamethylene diamine, decamethylene diamine, dodecamethylene diamine, 2,2,4-trimethyl-hexamethylene diamine, and 2,4,4-trimethyl-hexamethylene diamine; 1,3-bis(amino alicyclic diamines such as bis(4-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)decalin, and bis(aminomethyl)tricyclodecane; and diamines having an aromatic ring such as bis(4-aminophenyl)ether, paraphenylenediamine, and bis(aminomethyl)naphthalene.

[0015] In the xylylene group-containing polyamide resin, examples of compounds that can constitute dicarboxylic acid units include α,ω-linear aliphatic dicarboxylic acids having 4 to 20 carbon atoms, such as succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, and dodecanedioic acid; alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid; other aliphatic dicarboxylic acids such as dimer acid; and aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, orthophthalic acid, xylylenedicarboxylic acid, and naphthalenedicarboxylic acid. Of these, α,ω-linear aliphatic dicarboxylic acids having 4 to 20 carbon atoms are preferred, with adipic acid and sebacic acid being more preferred, and adipic acid being even more preferred from the viewpoint of improving barrier performance. The xylylene group-containing polyamide resin preferably contains 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% of structural units derived from adipic acid among structural units derived from dicarboxylic acids (dicarboxylic acid units).

[0016] That is, the polyamide resin (Y) preferably has diamine-derived structural units containing 50 mol% or more of xylylenediamine-derived structural units and dicarboxylic acid-derived structural units containing 50 mol% or more of adipic acid-derived structural units; more preferably has diamine-derived structural units containing 80 mol% or more of xylylenediamine-derived structural units and dicarboxylic acid-derived structural units containing 80 mol% or more of adipic acid-derived structural units; and even more preferably has diamine-derived structural units containing 90 mol% or more of xylylenediamine-derived structural units and dicarboxylic acid-derived structural units containing 90 mol% or more of adipic acid-derived structural units. Metaxylylenediamine is preferred as the xylylenediamine. Furthermore, when the dicarboxylic acid-derived structural units include structural units derived from a dicarboxylic acid other than adipic acid, the remaining dicarboxylic acid units excluding adipic acid are preferably structural units derived from an α,ω-linear aliphatic dicarboxylic acid having 4 to 20 carbon atoms.

[0017] Further, preferred xylylene group-containing polyamide resins include polyamide resins in which 70 mol% or more of the diamine units are derived from xylylene diamine (preferably meta-xylylene diamine), 70 to 99 mol% of the dicarboxylic acid units are derived from adipic acid, and 1 to 30 mol% are derived from isophthalic acid. The polyamide resin is preferably a polyamide resin in which 80 mol% or more of the diamine units are derived from xylylene diamine (preferably meta-xylylene diamine), 80 to 99 mol% of the dicarboxylic acid units are derived from adipic acid, and 1 to 20 mol% are derived from isophthalic acid, and more preferably a polyamide resin in which 90 mol% or more of the diamine units are derived from xylylene diamine (preferably meta-xylylene diamine), 80 to 99 mol% of the dicarboxylic acid units are derived from adipic acid, and 1 to 20 mol% are derived from isophthalic acid. By adding isophthalic acid units as dicarboxylic acid units, the melting point is lowered, and the molding temperature can be lowered, thereby suppressing thermal degradation during molding. In addition, the crystallization time is delayed, thereby improving stretch moldability.

[0018] In addition to the above-mentioned diamines and dicarboxylic acids, 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 can also be used as copolymerization components to constitute the xylylene group-containing polyamide resin, provided that the effects of the present invention are not impaired.

[0019] Xylylene group-containing polyamide resins are preferably produced by a polycondensation reaction in a molten state (hereinafter sometimes referred to as "melt polycondensation"). For example, a nylon salt composed of a diamine and a dicarboxylic acid is preferably produced by increasing the temperature under pressure in the presence of water and polymerizing the mixture in a molten state while removing the water. Alternatively, the diamine may be directly added to a molten dicarboxylic acid and polycondensed under normal 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, and during this time, to increase the reaction temperature so that it does not fall below the melting points of the resulting oligoamide and polyamide while polycondensation proceeds. Furthermore, if necessary, the molecular weight of the xylylene group-containing polyamide obtained by melt polycondensation can be increased by further solid-state polymerization.

[0020] The xylylene group-containing polyamide resin is preferably polycondensed in the presence of a phosphorus atom-containing compound. When the xylylene group-containing polyamide resin is polycondensed in the presence of a phosphorus atom-containing compound, the processing stability during melt molding is improved and coloration is more easily suppressed. As the phosphorus atom-containing compound, a hypophosphorous acid compound or a phosphorous acid compound is preferred, and a hypophosphorous acid compound is more preferred. As the phosphorus atom-containing compound, an organic metal salt is preferred, and among these, an alkali metal salt is more preferred.

[0021] Examples of hypophosphite compounds include hypophosphorous acid, metal hypophosphites, metal phenylphosphonite, ethyl hypophosphite, dimethylphosphinic acid, phenylmethylphosphinic acid, phenylphosphonite, and ethyl phenylphosphonite, with metal hypophosphites being preferred, from the viewpoint of promoting the polymerization reaction and preventing discoloration. Examples of metal hypophosphites include sodium hypophosphite, potassium hypophosphite, lithium hypophosphite, and calcium hypophosphite, with sodium hypophosphite being more preferred. Examples of metal phenylphosphonite include sodium phenylphosphonite, potassium phenylphosphonite, and lithium phenylphosphonite.

[0022] Examples of phosphorous compounds include phosphorous acid, pyrophosphorous acid, metal phosphites, metal ethylphosphonates, metal phenylphosphonates, triethyl phosphite, triphenyl phosphite, ethylphosphonic acid, phenylphosphonic acid, and diethyl phenylphosphonate. Examples of metal phosphites include sodium hydrogen phosphite, sodium phosphite, potassium phosphite, and calcium phosphite. Examples of metal ethylphosphonates include sodium ethylphosphonate and potassium ethylphosphonate. Examples of metal phenylphosphonates include sodium phenylphosphonate, potassium phenylphosphonate, and lithium phenylphosphonate. The phosphorus atom-containing compound may be used alone or in combination of two or more.

[0023] Furthermore, polycondensation of the xylylene group-containing polyamide resin is preferably carried out in the presence of a phosphorus atom-containing compound and an alkali metal compound. Using a large amount of the phosphorus atom-containing compound may result in gelation of the polyamide resin. Therefore, in order to adjust the amidation reaction rate, it is preferable to use an alkali metal compound. 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. When an alkali metal compound is used in polycondensing the polyamide resin, 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, calculated by dividing the number of moles of the alkali metal compound by the number of moles of the phosphorus atom-containing compound, in order to suppress gel formation.

[0024] The number-average molecular weight of the polyamide resin is selected appropriately depending on the application and molding method of the multilayer container, but from the viewpoint of the moldability and strength of the multilayer container, it is preferably 10,000 to 60,000, and more preferably 11,000 to 50,000. The number-average molecular weight of the polyamide resin is calculated using the following formula (2): Number-average molecular weight = 2 × 1,000,000 / ([COOH] + [NH2]) ... (2) (In the formula, [COOH] represents the terminal carboxy group concentration (μmol / g) in the polyamide resin, and [NH2] represents the terminal amino group concentration (μmol / g) in the polyamide resin.) Here, the terminal carboxy group concentration is the value calculated by neutralization titration of a solution of polyamide in benzyl alcohol with aqueous sodium hydroxide solution.

[0025] In the present invention, from the viewpoint of suppressing yellowing of the recycled polyester, the terminal amino group concentration of 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. The terminal amino group concentration of the polyamide resin (Y) is determined by precisely weighing the polyamide resin, dissolving it in a phenol / ethanol=4 / 1 volume solution with stirring at 20 to 30°C, completely dissolving it, rinsing the inner wall of the container with 5 mL of methanol while stirring, and neutralizing titrating it with a 0.01 mol / L aqueous hydrochloric acid solution. The method for adjusting the terminal amino group concentration of the polyamide resin (Y) is not particularly limited, but the terminal amino group concentration can be kept low by, for example, a method of carrying out a polycondensation reaction by adjusting the charge ratio (molar ratio) of a diamine and a dicarboxylic acid, a method of carrying out a polycondensation reaction by charging a monocarboxylic acid that caps the amino group together with a diamine and a dicarboxylic acid, or a method of carrying out a polycondensation reaction and then reacting the amino group with a carboxylic acid that caps the amino group.

[0026] (Phenol-based antioxidant (A)) The polyamide layer constituting the multilayer container of the present invention contains a phenol-based antioxidant (A). The content of the phenol-based 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, based on the entire polyamide layer, from the viewpoint of effectively improving the colorlessness and transparency of the recycled polyester and improving moldability. In particular, from the viewpoint of improving moldability, the content 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.

[0027] The phenolic antioxidant (A) is an antioxidant having a phenol structure in which a hydroxyl group is bonded to an aromatic ring in the molecule. The number of phenol structures (phenolic hydroxyl groups) contained in the molecule is preferably two or more, and more preferably three or more.

[0028] Specific examples of the phenolic antioxidant (A) include pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (Irganox 1010, manufactured by BASF), 3,9-bis[2-[3-(3-t-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, thiodiethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and the like. nate], N,N'-hexane-1,6-diylbis[3-(3,5-di-tert-butyl-4-hydroxyphenylpropionamide)], 2,4-dimethyl-6-(1-methylpentadecyl)phenol, diethyl [[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]methyl]phosphate, 3,3',3",5,5',5"-hexa-tert-butyl-a,a',a"-(mesitylene-2,4,6-triyl)tri-p-cresol, 4,6-bis(octyl) N,N'-hexamethylenebis(3,5-di-tert-butyl-4-hydroxy-hydrocinnamamide), 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)-1,3,5-triazine- Examples include 2,4,6(1H,3H,5H)-trione, 2,6-di-tert-butyl-4-(4,6-bis(octylthio)-1,3,5-triazin-2-ylamino)phenol. These may be used alone or in combination of two or more. Among these, from the viewpoint of effectively improving the colorless transparency of the recycled polyester, pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (Irganox 1010, manufactured by BASF) is preferred.

[0029] (Phosphorus-Based Antioxidant (B)) The polyamide layer constituting the multilayer container of the present invention contains a phosphorus-based antioxidant (B). The phosphorus-based antioxidant (B) used in the present invention is a compound having a pentaerythritol skeleton and an aromatic ring. The content of the phosphorus-based antioxidant (B) in the polyamide layer is preferably 0.018 to 0.270 mass%, more preferably 0.018 to 0.240 mass%, and even more preferably 0.030 to 0.150 mass%, based on the entire polyamide layer, from the viewpoint of effectively improving the colorlessness and transparency of the recycled polyester and improving moldability. In particular, from the viewpoint of improving moldability, the content is even more preferably 0.030 to 0.120 mass%, even more preferably 0.030 to 0.090 mass%, and even more preferably 0.060 to 0.090 mass%. The total content of the phenolic antioxidant (A) and the phosphorus-based antioxidant (B) in the polyamide layer is 0.040 to 0.250% by mass, preferably 0.040 to 0.200% by mass, from the viewpoint of effectively improving the colorlessness and transparency of the recycled polyester and improving moldability, and is 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. The mass ratio [(A) / (B)] of the content of the phenolic antioxidant (A) to the content of the phosphorus-based antioxidant (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, from the viewpoint of effectively improving the colorlessness and transparency of the recycled polyester and improving moldability.

[0030] The phosphorus-based antioxidant (B) is a compound having a pentaerythritol skeleton and an aromatic ring, and may be any compound having a pentaerythritol skeleton and an aromatic ring in the molecule, but is 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) may be used alone or in combination of two or more. (In the formula, R 1 ~R 6 are each a hydrogen atom or a hydrocarbon group having 1 to 10 carbon atoms.

[0031] In formula (1), R 1 and R 4 may be the same or different, but are preferably the same. 2 and R 5 may be the same or different, but are preferably the same. 3 and R 6 may be the same or different, but are preferably the same. 1 and R 4 is a hydrogen atom or a hydrocarbon group having 1 to 10 carbon atoms, preferably an alkyl group having 1 to 4 carbon atoms, a benzyl group, a phenylethyl group, or a cumyl group, more preferably an alkyl group having 4 carbon atoms or a cumyl group, even more preferably a tert-butyl group or a cumyl group, and still more preferably a cumyl group. 2 and R 5 is a hydrogen atom or a hydrocarbon group having 1 to 10 carbon atoms, preferably an alkyl group having 1 to 4 carbon atoms, a benzyl group, a phenylethyl group, or a cumyl group, more preferably an alkyl group having 1 to 3 carbon atoms or a cumyl group, even more preferably a methyl group or a cumyl group, and still more preferably a cumyl group. 3 and R 6 R is a hydrogen atom or a hydrocarbon group having 1 to 10 carbon atoms, and is preferably a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, a benzyl group, a phenylethyl group, or a cumyl group. 1 and R 4 is a tert-butyl group, R 3 and R 6 is preferably a tert-butyl group, and R 1 and R 4 is a cumyl group, R 3 and R 6 is preferably a hydrogen atom.

[0032] Examples of the phosphorus-based antioxidant (B) include bis(nonylphenyl)pentaerythritol diphosphite, bis(2,4-di-t-butylphenyl)pentaerythritol diphosphite, bis(2,6-di-t-butyl-4-methylphenyl)pentaerythritol diphosphite, bis(2,4-dicumylphenyl)pentaerythritol diphosphite, etc. Among these, from the viewpoint of effectively improving the colorless transparency of the recycled polyester, bis(2,6-di-t-butyl-4-methylphenyl)pentaerythritol diphosphite and bis(2,4-dicumylphenyl)pentaerythritol diphosphite are preferred, and bis(2,4-dicumylphenyl)pentaerythritol diphosphite is more preferred.

[0033] (Other Components) The polyamide layer may contain other components. Examples of other components include a heat stabilizer, a light stabilizer, a moisture-proofing agent, a waterproofing agent, a lubricant, and a spreading agent. The polyamide layer may contain a resin other than the main component, polyamide resin (Y), as long as the effects of the present invention are not impaired. The content of polyamide resin (Y) is preferably 80 to 100% by mass, more preferably 90 to 100% by mass, based on the total resin amount of the polyamide layer, and the polyamide layer may consist solely of polyamide resin (Y).

[0034] The total content of the polyamide resin (Y), the phenolic antioxidant (A), and the phosphorus-based antioxidant (B) in the polyamide layer is preferably 70 to 100% by mass, and from the viewpoint of gas barrier properties and suppressing yellowing of the recycled polyester, is more preferably 90 to 100% by mass, even more preferably 95 to 100% by mass, and still more preferably 99 to 100% by mass. The polyamide layer may consist of the polyamide resin (Y), the phenolic antioxidant (A), and the phosphorus-based antioxidant (B), or may consist only of the polyamide resin (Y), the phenolic antioxidant (A), and the phosphorus-based antioxidant (B). 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, and from the viewpoint of gas barrier properties and suppression of yellowing of recycled polyester, 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. The content of 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, and from the viewpoint of gas barrier properties and suppression of yellowing of recycled polyester, 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.

[0035] (Polyamide resin composition used in polyamide layer) The polyamide layer constituting the multilayer container of the present invention contains a polyamide resin (Y), a phenolic antioxidant (A), and a phosphorus-based antioxidant (B). Therefore, when forming the multilayer container, it is preferable to use a polyamide resin composition containing these. The method for producing the polyamide resin composition is not limited, but it is preferable to produce it by the following method.

[0036] It is preferable to obtain a polyamide resin composition by melt-mixing the polyamide resin (Y), the phenolic antioxidant (A), the phosphorus-based antioxidant (B), and, if necessary, any other components (additives).

[0037] The phenolic antioxidant (A), the phosphorus-based antioxidant (B), and any other optional components (additives) may be added to the resin as they are and melt-mixed, or may be dissolved in a liquid component and added to the resin as an additive solution and melt-mixed. Forming the components into a solution is preferred because it facilitates metering and addition. It is also preferred because it can be added using a dosing system, etc. The additive solution may be added when dry-blending the masterbatch and polyamide resin (Y), or after melting the polyamide resin (Y).

[0038] The liquid component used in the additive solution is preferably 0.01 to 1% by mass, more preferably 0.01 to 0.5% by mass, relative to the resin (such as polyamide resin (Y)) constituting the polyamide layer. The liquid component used in the additive solution is preferably 0.01 to 1% by mass, more preferably 0.01 to 0.5% by mass, relative to the polyamide resin (Y) constituting the polyamide layer. The liquid component is preferably a liquid resin or a liquid oil component. Examples of the liquid resin include epoxy resins such as epoxidized soybean oil and epoxidized linseed oil, fatty acid polyester resins, polyalkylene glycol resins, polyether ester resins, and acetyl tributyl citrate. Examples of the liquid oily component include vegetable oils such as olive oil, castor oil, jojoba oil, macadamia nut oil, crab rose fruit oil, cacao butter, and lanolin; animal oils such as horse oil, turtle oil, wild boar oil, mink oil, and shark oil; hydrocarbon oils such as petrolatum, liquid paraffin, isodecane, isododecane, octyldodecyl, and hydrogenated polyisobutene; isotridecyl isononanoate, isopropyl isostearate, neopentyl glycol dicaprate, isotridecyl isononanoate, glyceryl diisostearate, and triisostearate. Examples of suitable additives include ester oils such as glyceryl stearate, diisostearyl malate, and di(phytosteryl / 2-octyldodecyl) N-lauroyl-L-glutamate; silicone oils such as dimethylpolysiloxane and phenylmethylpolysiloxane; dimer acid esters, dimer diol derivatives, cholesterol fatty acid esters, phytosterol fatty acid esters, polyglycerin fatty acid esters, pentaerythritol fatty acid esters, glyceryl tri-2-ethylhexanoate, and octyldodecanol. The method for producing the additive solution is not particularly limited. For example, the additive solution can be obtained by adding the liquid components and various additives, mixing them in a Henschel mixer, tumbler, disperser, or the like, and dispersing them using a Silverson mixer (manufactured by Silverson). In addition to the above, any suitable dispersion device can be used, such as a kneader, roll mill, ball mill, or sand mill.

[0039] Examples of the melt-mixing method include melt blending (melt kneading). Furthermore, when producing a multilayer container as described below, the polyamide resin (Y), the phenolic antioxidant (A), the phosphorus-based antioxidant (B), and any other components (additives) may be dry-blended and then melt-mixed in the process of obtaining a multilayer preform. Examples of melt-blending include the masterbatch method and the full compound method, and the masterbatch method is preferred from the viewpoint of preventing deterioration of the resin and the antioxidant.

[0040] The masterbatch method is a method in which a small amount of resin is mixed with a phenolic antioxidant (A), a phosphorus-based antioxidant (B), and any other components (additives) to form a masterbatch, which is then mixed with the remaining polyamide resin (Y). From the viewpoint of miscibility with the polyamide resin (Y), the resin used in the masterbatch is preferably the polyamide resin (Y), and more preferably the same as the remaining polyamide resin (Y). The amount of resin used in the masterbatch is preferably 1 to 20% by mass, more preferably 3 to 15% by mass, based on the amount of resin in the entire polyamide resin composition.

[0041] When a masterbatch is obtained by kneading a resin, a phenolic antioxidant (A), a phosphorus-based antioxidant (B), and any other components (additives), the kneading 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, from the viewpoint of sufficient mixing, where Tm is the melting point of the resin used in the masterbatch. Specifically, 245 to 300°C is more preferable, 250 to 290°C is even more preferable, and 255 to 280°C is even more preferable. Furthermore, from the viewpoint of sufficient mixing, the kneading time is preferably 10 to 600 seconds, more preferably 20 to 400 seconds, and even more preferably 30 to 300 seconds. Examples of equipment used for kneading include open-type mixing rolls, closed-type Banbury mixers, kneaders, continuous kneaders (single-screw kneaders, twin-screw kneaders, multi-screw kneaders, etc.), and the like.

[0042] The masterbatch and the remaining polyamide resin (Y) may be melt-mixed by melt blending (melt kneading). When producing a multilayer container as described below, the masterbatch and the remaining polyamide resin (Y) may be dry-blended in advance, and then melt-mixed in the step of obtaining a multilayer preform.

[0043] The full compounding method is a method in which the entire amount of polyamide resin (Y) used in the resin composition is kneaded and mixed with the phenolic antioxidant (A), the phosphorus-based antioxidant (B), and any other components (additives). From the viewpoint of thorough mixing, the kneading temperature is more preferably 245 to 300°C, even more preferably 250 to 290°C, and even more preferably 255 to 280°C. Furthermore, from the viewpoint of thorough mixing, the kneading time is preferably 10 to 600 seconds, more preferably 20 to 400 seconds, and even more preferably 30 to 300 seconds. Examples of equipment used for kneading include open-type mixing rolls, closed-type Banbury mixers, kneaders, continuous kneaders (single-screw kneaders, twin-screw kneaders, multi-screw kneaders, etc.), and the like.

[0044] <Polyester Layer> The polyester layer contains a polyester resin (X).

[0045] (Polyester Resin (X)) The polyester resin (X) contained in the polyester layer is preferably a polycondensation polymer of a dicarboxylic acid and a diol, and preferably has a structural unit derived from a dicarboxylic acid (dicarboxylic acid unit) and a structural unit derived from a diol (diol unit).

[0046] Examples of dicarboxylic acid units 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. Examples of aromatic dicarboxylic acids include terephthalic acid, isophthalic acid, orthophthalic 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 viewpoints of cost and ease of production, terephthalic acid, isophthalic acid, orthophthalic acid, naphthalenedicarboxylic acid, and 4,4'-biphenyldicarboxylic acid are preferred, with terephthalic acid, isophthalic acid, and naphthalenedicarboxylic acid being more preferred. From the viewpoint of moldability, terephthalic acid and isophthalic acid are even more preferred, with terephthalic acid being even more preferred. When recycling the multilayer container of the present invention, it may be melt-kneaded with a conventional single-layer container made of a polyester resin. By including a unit derived from terephthalic acid as the dicarboxylic acid unit, the compatibility of the multilayer container of the present invention with conventional single-layer containers is improved, and recyclability is also improved.

[0047] As the aromatic dicarboxylic acid, sulfophthalic acid or a metal sulfophthalate may be used. The metal sulfophthalate is a metal salt of sulfophthalic acid, and the metal atom may be an alkali metal or an alkaline earth metal. As the alicyclic dicarboxylic acid, cyclohexanedicarboxylic acid, norbornenedicarboxylic acid, tricyclodecanedicarboxylic acid, etc. may be used. As the aliphatic dicarboxylic acid, malonic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, etc. may be used.

[0048] Examples of diol units 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. Examples of aliphatic diols include ethylene glycol, 2-butene-1,4-diol, trimethylene glycol, tetramethylene glycol, hexamethylene glycol, neopentyl glycol, methylpentanediol, and diethylene glycol. Of these, ethylene glycol is preferred. Examples of alicyclic diols include cyclohexanedimethanol, isosorbide, spiroglycol, 2,2,4,4-tetramethyl-1,3-cyclobutanediol, norbornene dimethanol, and tricyclodecane dimethanol. Examples of aromatic diols include bisphenol compounds and hydroquinone compounds.

[0049] The polyester resin (X) may have a structural unit derived from a hydroxycarboxylic acid. Examples of the hydroxycarboxylic acid include aliphatic hydroxycarboxylic acids, alicyclic hydroxycarboxylic acids, and aromatic hydroxycarboxylic acids. Examples of the aliphatic hydroxycarboxylic acids include 10-hydroxyoctadecanoic acid, lactic acid, hydroxyacrylic acid, 2-hydroxy-2-methylpropionic acid, and hydroxybutyric acid. Examples of the alicyclic hydroxycarboxylic acids include hydroxymethylcyclohexanecarboxylic acid, hydroxymethylnorbornenecarboxylic acid, and hydroxymethyltricyclodecanecarboxylic acid. Examples of the aromatic hydroxycarboxylic acids include hydroxybenzoic acid, hydroxytoluic acid, hydroxynaphthoic acid, 3-(hydroxyphenyl)propionic acid, hydroxyphenylacetic acid, and 3-hydroxy-3-phenylpropionic acid.

[0050] The polyester resin (X) may have a structural unit derived from a monofunctional compound and a structural unit derived from a polyfunctional compound. Examples of the monofunctional compound include monocarboxylic acids and monoalcohols, specifically aromatic monocarboxylic acids, aliphatic monocarboxylic acids, aromatic monoalcohols, aliphatic monoalcohols, and alicyclic monoalcohols. Examples of the polyfunctional compound include aromatic polycarboxylic acids, alicyclic polycarboxylic acids, aliphatic polyalcohols, alicyclic polyalcohols, and esters thereof.

[0051] The polyester resin (X) preferably has a dicarboxylic acid-derived structural unit containing a terephthalic acid-derived structural unit and a diol-derived structural unit containing an ethylene glycol-derived structural unit, more preferably a dicarboxylic acid-derived structural unit containing 80 mol% or more of terephthalic acid-derived structural units and a diol-derived structural unit containing 80 mol% or more of ethylene glycol-derived structural units, even more preferably a dicarboxylic acid-derived structural unit containing 90 mol% or more of terephthalic acid-derived structural units and a diol-derived structural unit containing 90 mol% or more of ethylene glycol-derived structural units, and even more preferably a dicarboxylic acid-derived structural unit containing 98 mol% or more of terephthalic acid-derived structural units and a diol-derived structural unit containing substantially 100 mol% of ethylene glycol-derived structural units. A specific example of the polyester resin (X) is polyethylene terephthalate (PET).

[0052] Polyethylene terephthalate (PET) may contain structural units derived from aromatic dicarboxylic acids other than terephthalic acid. The aromatic dicarboxylic acid other than terephthalic acid is preferably one or more selected from isophthalic acid, orthophthalic acid, naphthalenedicarboxylic acid, and 4,4'-biphenyldicarboxylic acid. These are low cost, and copolymerized polyester resins containing them are easy to produce. Among these, isophthalic acid and naphthalenedicarboxylic acid are preferred, with isophthalic acid being more preferred. Polyethylene terephthalate containing structural units derived from isophthalic acid is excellent in moldability and, due to its slower crystallization rate, prevents whitening of molded articles. Furthermore, polyethylene terephthalate containing structural units derived from naphthalenedicarboxylic acid increases the glass transition point of the resin, improving heat resistance and absorbing ultraviolet light, making it suitable for use in the production of multilayer containers requiring ultraviolet resistance. Among naphthalenedicarboxylic acids, 2,6-naphthalenedicarboxylic acid is preferred due to its ease of production and high economic efficiency. When polyethylene terephthalate contains constituent units derived from aromatic dicarboxylic acids other than terephthalic acid, the proportion of constituents derived from aromatic dicarboxylic acids other than terephthalic acid is preferably 1 to 20 mol %, more preferably 1 to 10 mol %, even more preferably 1 to 5 mol %, and still more preferably 1 to 2 mol %, of the dicarboxylic acid units.

[0053] The polyester resin (X) may be used alone or in combination of two or more resins. The polyester resin (X) can be produced by a known method such as a direct esterification method or a transesterification method.

[0054] The intrinsic viscosity of the polyester resin (X) is preferably 0.5 to 2.0 dL / g, more preferably 0.6 to 1.5 dL / g. When the intrinsic viscosity is 0.5 dL / g or higher, the resulting container has excellent mechanical properties. The intrinsic viscosity is measured at 25°C using an automatic viscosity measuring device (Viscotek, manufactured by Malvern Instruments, Inc.) by dissolving the polyester resin in a mixed solvent of phenol and 1,1,2,2-tetrachloroethane (6 / 4 mass ratio) to prepare 0.2, 0.4, and 0.6 g / dL solutions.

[0055] (Phenol-based antioxidant (A)) The polyester layer constituting the multilayer container of the present invention preferably contains a phenol-based antioxidant (A). The phenol-based antioxidant (A) is the same as the phenol-based antioxidant (A) contained in the polyamide layer, and the preferred phenol-based antioxidants are also the same. The phenol-based antioxidant (A) contained in the polyamide layer and the phenol-based antioxidant (A) contained in the polyester layer may be the same or different, but are preferably the same.

[0056] From the viewpoint of effectively improving the colorlessness and transparency of the recycled polyester, the content of the phenolic antioxidant (A) in 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, still more preferably 0.015 to 0.050% by mass, still more preferably 0.015 to 0.040% by mass, and still more preferably 0.015 to 0.030% by mass, based on the total mass of the polyester layer.

[0057] The phenolic antioxidant (A) contained in the polyester layer is an antioxidant having a phenol structure in which a hydroxyl group is bonded to an aromatic ring in the molecule. The number of phenol structures (phenolic hydroxyl groups) contained in the molecule is preferably two or more, and more preferably three or more.

[0058] Specific examples of the phenolic antioxidant (A) contained in the polyester layer include pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (Irganox 1010, manufactured by BASF), 3,9-bis[2-[3-(3-t-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, thiodiethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and methyl ... nate], N,N'-hexane-1,6-diylbis[3-(3,5-di-tert-butyl-4-hydroxyphenylpropionamide)], 2,4-dimethyl-6-(1-methylpentadecyl)phenol, diethyl [[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]methyl]phosphate, 3,3',3",5,5',5"-hexa-tert-butyl-a,a',a"-(mesitylene-2,4,6-triyl)tri-p-cresol, 4,6-bis(octyl) N,N'-hexamethylenebis(3,5-di-tert-butyl-4-hydroxy-hydrocinnamamide), 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)-1,3,5-triazine- Examples include 2,4,6(1H,3H,5H)-trione, 2,6-di-tert-butyl-4-(4,6-bis(octylthio)-1,3,5-triazin-2-ylamino)phenol. These may be used alone or in combination of two or more. Among these, from the viewpoint of effectively improving the colorless transparency of the recycled polyester, pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (Irganox 1010, manufactured by BASF) is preferred.

[0059] (Phosphorus-based antioxidant (B)) The polyester layer constituting the multilayer container of the present invention preferably contains a phosphorus-based antioxidant (B), more preferably a phenolic antioxidant (A) and a phosphorus-based antioxidant (B). The phosphorus-based antioxidant (B) is the same as the phosphorus-based antioxidant (B) contained in the polyamide layer, and the preferred phosphorus-based antioxidants are also the same. The phosphorus-based antioxidant (B) contained in the polyamide layer and the phosphorus-based antioxidant (B) contained in the polyester layer may be the same or different, but are preferably the same. The phosphorus-based antioxidant (B) contained in the polyester layer is a compound having a pentaerythritol skeleton and an aromatic ring.

[0060] From the viewpoint of effectively improving the colorlessness and transparency of the recycled polyester, the content of the phosphorus-based antioxidant (B) in the polyester layer is preferably 0.015 to 0.450 mass%, more preferably 0.030 to 0.300 mass%, even more preferably 0.045 to 0.240 mass%, still more preferably 0.045 to 0.150 mass%, still more preferably 0.050 to 0.120 mass%, and still more preferably 0.050 to 0.090 mass%, based on the total mass of the polyester layer. In addition, the total content of the phenolic antioxidant (A) and the phosphorus-based 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. In addition, the mass ratio [(A) / (B)] of the content of the phenolic antioxidant (A) to the content of the phosphorus-based antioxidant (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, from the viewpoint of effectively improving the colorlessness and transparency of the recycled polyester.

[0061] The phosphorus-based antioxidant (B) contained in the polyester layer is a compound having a pentaerythritol skeleton and an aromatic ring, and may be any compound having a pentaerythritol skeleton and an aromatic ring in the molecule, but is 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) may be used alone or in combination of two or more. (In the formula, R 1 ~R 6 are each a hydrogen atom or a hydrocarbon group having 1 to 10 carbon atoms.

[0062] In formula (1), R 1 and R 4 may be the same or different, but are preferably the same. 2 and R 5 may be the same or different, but are preferably the same. 3 and R 6 may be the same or different, but are preferably the same. 1 and R 4 is a hydrogen atom or a hydrocarbon group having 1 to 10 carbon atoms, preferably an alkyl group having 1 to 4 carbon atoms, a benzyl group, a phenylethyl group, or a cumyl group, more preferably an alkyl group having 4 carbon atoms or a cumyl group, even more preferably a tert-butyl group or a cumyl group, and still more preferably a cumyl group. 2 and R 5 is a hydrogen atom or a hydrocarbon group having 1 to 10 carbon atoms, preferably an alkyl group having 1 to 4 carbon atoms, a benzyl group, a phenylethyl group, or a cumyl group, more preferably an alkyl group having 1 to 3 carbon atoms or a cumyl group, even more preferably a methyl group or a cumyl group, and still more preferably a cumyl group. 3 and R 6 R is a hydrogen atom or a hydrocarbon group having 1 to 10 carbon atoms, and is preferably a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, a benzyl group, a phenylethyl group, or a cumyl group. 1 and R 4 is a tert-butyl group, R3 and R 6 is preferably a tert-butyl group, and R 1 and R 4 is a cumyl group, R 3 and R 6 is preferably a hydrogen atom.

[0063] Examples of the phosphorus-based antioxidant (B) contained in the polyester layer include bis(nonylphenyl)pentaerythritol diphosphite, bis(2,4-di-t-butylphenyl)pentaerythritol diphosphite, bis(2,6-di-t-butyl-4-methylphenyl)pentaerythritol diphosphite, bis(2,4-dicumylphenyl)pentaerythritol diphosphite, etc. Among these, from the viewpoint of effectively improving the colorless transparency of the recycled polyester, bis(2,6-di-t-butyl-4-methylphenyl)pentaerythritol diphosphite and bis(2,4-dicumylphenyl)pentaerythritol diphosphite are preferred, and bis(2,4-dicumylphenyl)pentaerythritol diphosphite is more preferred.

[0064] (Aldehyde Catcher) The polyester layer preferably contains an aldehyde catcher.

[0065] Examples of aldehyde catchers include compounds that have the ability to suppress yellowing of polyester resins and contain an amino group. Specifically, at least one compound selected from the group consisting of aminobenzamide, aminobenzoic acid, diaminobenzoic acid, and nylon 6I / 6T is preferred, and at least one compound selected from the group consisting of anthranilamide, anthranilic acid, and nylon 6I / 6T is more preferred. The aminobenzamide may have the amino group substituted at any of the 2- to 4-positions, but is preferably substituted at the 2- or 3-position, more preferably at the 2-position, and more preferably anthranilamide (2-aminobenzamide). The aminobenzoic acid may have the amino group substituted at any of the 2-, 3-, or 4-positions, but is preferably substituted at the 2- or 3-position, more preferably at the 2-position, and more preferably anthranilic acid (2-aminobenzoic acid). The diaminobenzoic acid may be substituted in any of 2,3-, 2,4- and 3,4-positions, but 3,4-diaminobenzoic acid is preferred.

[0066] Nylon 6I / 6T is a hexamethylenediamine-isophthalic acid-terephthalic acid copolymer polyamide, i.e., a hexamethylene isophthalamide / hexamethylene terephthalamide copolymer. Commercially available products may be used as nylon 6I / 6T, such as Selar (registered trademark) PA 3426 (manufactured by DuPont) and NOVAMID X21 (manufactured by DSM). 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 measured by gel permeation chromatography and converted into a polystyrene equivalent value. When the weight-average molecular weight of nylon 6I / 6T is within the above range, it has excellent compatibility with polyester resins, is less likely to leach into the contents when used in a container, and is effectively inhibited from yellowing. Furthermore, the amino end group concentration of nylon 6I / 6T is preferably 50 to 350 μmol / g, more preferably 100 to 300 μmol / g, and even more preferably 150 to 250 μmol / g. When the amino end group concentration of nylon 6I / 6T is within the above range, it exhibits excellent inhibition of yellowing of recycled polyester. The amino end group concentration is determined by precisely weighing nylon 6I / 6T, stirring and dissolving it in a phenol / ethanol = 4 / 1 volumetric solution at 20 to 30°C, completely dissolving it, and then rinsing the inner wall of the container with 5 mL of methanol while stirring, followed by neutralization titration with 0.01 mol / L aqueous hydrochloric acid solution.

[0067] Furthermore, examples of aldehyde catchers other than the above-mentioned aminobenzamide, aminobenzoic acid, diaminobenzoic acid, and nylon 6I / 6T include salicylamide, salicylanilide, o-phenylenediamine, 1,8-diaminonaphthalene, o-mercaptobenzamide, N-acetylglycinamide, malonamide, 3-mercapto-1,2-propanediol, histidine, tryptophan, 4-amino-3-hydroxybenzoic acid, biuret, 2,3-diaminopyridine, 1,2-diaminoanthraquinone, dianilinoethane, allantoin, and 2-amino-2-methyl-1,3-propanediol.

[0068] The aldehyde catcher may be used alone or in combination of two or more. The aldehyde catcher is preferably at least one compound selected from the group consisting of anthranilamide and nylon 6I / 6T, more preferably anthranilamide or nylon 6I / 6T, and even more preferably anthranilamide. That is, it is more preferable that the polyester layer contains anthranilamide.

[0069] From the viewpoint of effectively suppressing yellowing and improving transparency, the content of the aldehyde catcher in the polyester layer is preferably 0.003 to 0.150 mass%, more preferably 0.005 to 0.150 mass%, even more preferably 0.005 to 0.100 mass%, still more preferably 0.005 to 0.090 mass%, still more preferably 0.010 to 0.080 mass%, still more preferably 0.030 to 0.070 mass%, and still more preferably 0.030 to 0.060 mass%, based on the total mass of the polyester layer.

[0070] When the aldehyde catcher is anthranilamide, the content of anthranilamide in the polyester layer is preferably 0.003 to 0.150 mass%, more preferably 0.005 to 0.150 mass%, even more preferably 0.005 to 0.100 mass%, still more preferably 0.005 to 0.090 mass%, still more preferably 0.010 to 0.080 mass%, still more preferably 0.030 to 0.070 mass%, and still more preferably 0.030 to 0.060 mass%, based on the total mass of the polyester layer, from the viewpoints of effectively suppressing yellowing and improving transparency.

[0071] (Other Components) The polyester layer may contain other components. Examples of other components include a heat stabilizer, a light stabilizer, a moisture-proofing agent, a waterproofing agent, a lubricant, and a spreading agent. The polyester layer may contain a resin other than the polyester resin (X) that is the main component, as long as the effects of the present invention are not impaired. The content of the polyester resin (X) is preferably 80 to 100% by mass, more preferably 90 to 100% by mass, based on the total resin amount of the polyester layer, and the polyester layer may consist solely of the polyester resin (X).

[0072] (Polyester resin composition used in polyester layer) When the polyester layer constituting the multilayer container of the present invention contains components other than the polyester resin (X), it is preferable to use a polyester resin composition containing these components when forming the multilayer container. The method for producing the polyester resin composition is not limited, but it is preferable to produce it by the following method.

[0073] It is preferable to obtain a polyester resin composition by melt-mixing the polyester resin (X) with optional components such as the phenolic antioxidant (A), the phosphorus-based antioxidant (B) and other components.

[0074] The phenolic antioxidant (A), the phosphorus-based antioxidant (B), and other components (additives) may be added to the resin as they are and melt-mixed, or may be dissolved in a liquid component and added to the resin as an additive solution and melt-mixed. Forming them into a solution is preferred because it facilitates metering and addition. It is also preferred because it can be added using a dosing system, etc. The additive solution may be added when dry-blending the masterbatch and polyester resin (X), or it may be added after melting the polyester resin (X).

[0075] The liquid component used in the additive solution is preferably 0.01 to 1% by mass, more preferably 0.01 to 0.5% by mass, relative to the resin (such as polyester resin (X)) constituting the polyester layer. The liquid component used in the additive solution is preferably 0.01 to 1% by mass, more preferably 0.01 to 0.5% by mass, relative to the polyester resin (X) constituting the polyester layer. The liquid component is preferably a liquid resin or a liquid oil component. Examples of the liquid resin include epoxy resins such as epoxidized soybean oil and epoxidized linseed oil, fatty acid polyester resins, polyalkylene glycol resins, polyether ester resins, and acetyl tributyl citrate. Examples of the liquid oily component include vegetable oils such as olive oil, castor oil, jojoba oil, macadamia nut oil, crab rose fruit oil, cacao butter, and lanolin; animal oils such as horse oil, turtle oil, wild boar oil, mink oil, and shark oil; hydrocarbon oils such as petrolatum, liquid paraffin, isodecane, isododecane, octyldodecyl, and hydrogenated polyisobutene; isotridecyl isononanoate, isopropyl isostearate, neopentyl glycol dicaprate, isotridecyl isononanoate, glyceryl diisostearate, and triisostearate. Examples of suitable additives include ester oils such as glyceryl stearate, diisostearyl malate, and di(phytosteryl / 2-octyldodecyl) N-lauroyl-L-glutamate; silicone oils such as dimethylpolysiloxane and phenylmethylpolysiloxane; dimer acid esters, dimer diol derivatives, cholesterol fatty acid esters, phytosterol fatty acid esters, polyglycerin fatty acid esters, pentaerythritol fatty acid esters, glyceryl tri-2-ethylhexanoate, and octyldodecanol. The method for producing the additive solution is not particularly limited. For example, the additive solution can be obtained by adding the liquid components and various additives, mixing them in a Henschel mixer, tumbler, disperser, or the like, and dispersing them using a Silverson mixer (manufactured by Silverson). In addition to the above, any suitable dispersion device can be used, such as a kneader, roll mill, ball mill, or sand mill.

[0076] Examples of the melt-mixing method include melt blending (melt kneading). Furthermore, when producing a multilayer container as described below, the polyester resin (X), the phenolic antioxidant (A), the phosphorus-based antioxidant (B), and the like may be dry-blended in advance and melt-mixed in the process of obtaining a multilayer preform. Examples of melt-blending include the masterbatch method and the full compound method, and the masterbatch method is preferred from the viewpoint of preventing deterioration of the resin and the antioxidant.

[0077] The masterbatch method is a method in which a small amount of resin is mixed with a phenolic antioxidant (A), a phosphorus-based antioxidant (B), etc. to form a masterbatch, which is then mixed with the remaining polyester resin (X). From the viewpoint of miscibility with the polyester resin (X), the resin used in the masterbatch is preferably the polyester resin (X), and more preferably the same as the remaining polyester resin (X). The amount of resin used in the masterbatch is preferably 1 to 20 mass%, more preferably 3 to 15 mass%, based on the amount of resin in the entire polyester resin composition.

[0078] In a method for obtaining a masterbatch, a resin, a phenolic antioxidant (A), a phosphorus-based antioxidant (B), and the like are kneaded together. When the melting point of the resin used in the masterbatch is Tm, the kneading 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, from the viewpoint of sufficient mixing. Specifically, 245 to 300°C is more preferable, 250 to 290°C is even more preferable, and 255 to 280°C is even more preferable. Furthermore, from the viewpoint of sufficient mixing, the kneading time is preferably 10 to 600 seconds, more preferably 20 to 400 seconds, and even more preferably 30 to 300 seconds. Examples of kneading equipment include open-type mixing rolls, closed-type Banbury mixers, kneaders, continuous kneaders (single-screw kneaders, twin-screw kneaders, multi-screw kneaders, etc.), and the like.

[0079] The masterbatch and the remaining polyester resin (X) may be melt-mixed by melt blending (melt kneading). When producing a multilayer container as described below, the masterbatch and the remaining polyester resin (X) may be dry-blended in advance, and then melt-mixed in the step of obtaining a multilayer preform.

[0080] The full compounding method is a method in which the entire amount of polyester resin (X) used in the resin composition is kneaded and mixed with the phenolic antioxidant (A), the phosphorus-based antioxidant (B), and the like. From the viewpoint of sufficient mixing, the kneading temperature is preferably 255 to 310°C, more preferably 265 to 300°C, and even more preferably 270 to 290°C. From the viewpoint of sufficient mixing, the kneading time is preferably 10 to 600 seconds, more preferably 20 to 400 seconds, and even more preferably 30 to 300 seconds. Examples of devices used for kneading include open-type mixing rolls, closed-type Banbury mixers, kneaders, continuous kneaders (single-screw kneaders, twin-screw kneaders, multi-screw kneaders, etc.), and the like.

[0081] <Structure and Characteristics of Multilayer Containers> The multilayer container of the present invention comprises a polyester layer containing a polyester resin (X) and a polyamide layer containing a polyamide resin (Y), a phenolic antioxidant (A), and a phosphorus-based antioxidant (B), wherein the phosphorus-based 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-based antioxidant (B) in the polyamide layer is 0.040 to 0.250 mass%. The multilayer container of the present invention may contain resin layers other than the polyester layer and the polyamide layer. However, from the viewpoints of facilitating separation during recycling and improving the color tone of the container and the recovered polyester, the content of the resin layers other than the polyester layer and the polyamide layer is preferably low, and preferably substantially free of resin layers other than the polyester layer and the polyamide layer. Furthermore, an adhesive layer made of an adhesive or an inorganic layer made of an inorganic material may be provided. However, from the viewpoints of facilitating separation during recycling and improving the yellowing suppression effect, the content of the adhesive layer or inorganic layer is preferably low, and preferably substantially free of the adhesive layer or inorganic layer. In particular, it is preferable that the multilayer container of the present invention does not have an adhesive layer.

[0082] The multilayer container of the present invention has a multilayer structure of two or more layers, preferably a 2- to 5-layer structure, more preferably a 3- to 5-layer structure, even more preferably a 3-layer or 5-layer structure, and even more preferably a 3-layer structure. The outermost layer of the multilayer container of the present invention is preferably a polyester layer. The innermost layer is also preferably a polyester layer, and more preferably the outermost and innermost layers are polyester layers. When the outermost layer is a polyester layer, the multilayer container has excellent impact resistance, appearance, and design. Therefore, the structure of the multilayer container is preferably a 2- to 5-layer structure with the outermost layer being a polyester layer, and more preferably a 3- to 5-layer structure with the outermost and innermost layers being polyester layers.

[0083] In the case of a two-layer structure, the structure is preferably a polyamide layer / polyester layer from the innermost layer, in the case of a three-layer structure, the structure is preferably a polyester layer / polyamide layer / polyester layer from the innermost layer, and in the case of a five-layer structure, the structure is preferably a polyester layer / polyamide layer / polyester layer / polyamide layer / polyester layer from the innermost layer.

[0084] The multilayer container of the present invention is preferably a hollow container. When the multilayer container is a hollow container, at least the body portion has a multilayer structure. The ratio of the thickness (W) of the polyester layer to the thickness (S) of the polyamide layer in the body portion (thickness ratio W / S) is preferably 2.5 or more and 200 or less. The thickness of the polyester layer refers to the average thickness. When the body portion has multiple polyester layers, the thicknesses of the multiple layers are averaged to determine the average thickness per layer. The same applies to the thickness of the polyamide layer. A thickness ratio W / S of 2.5 or more is preferable because it facilitates separation of polyamide resin from polyester resin in the separation step in the production of recycled polyester, particularly winnowing and gravity separation. Furthermore, a thickness ratio W / S of 200 or less provides excellent gas barrier properties for the hollow container, allowing for long-term storage of the contents. From the viewpoint of improving the gas barrier properties of the hollow container while enhancing separability in the separation step, the thickness ratio (W / S) is more preferably 3 to 50, and even more preferably 4 to 15.

[0085] Furthermore, when the multilayer container is a hollow container, the total thickness of the body of the hollow container (i.e., the total thickness of all layers of the body) is preferably 100 μm to 5 mm, more preferably 150 μm to 3 mm, and even more preferably 200 μm to 2 mm. Furthermore, 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 the present 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 in the separation step.

[0086] When the multilayer container of the present invention is a hollow container, it is more preferably a liquid packaging container that is used by filling the interior of the hollow container with a liquid, and even more preferably a beverage packaging container. Examples of liquids that can be filled include beverages, liquid seasonings, chemicals, pharmaceuticals, detergents, etc., and beverages that can be effectively prevented from deteriorating due to oxygen by the multilayer container of the present invention are preferred. Examples of beverages include water, carbonated water, oxygenated water, hydrogenated water, milk, dairy products, juice, coffee, coffee drinks, carbonated soft drinks, tea, and alcoholic beverages. Examples of liquid seasonings include sauces, soy sauce, syrup, mirin, dressings, etc. Examples of chemicals include pesticides and insecticides.

[0087] <Method for manufacturing multilayer container> The method for manufacturing a multilayer container of the present invention is not particularly limited as long as it is a method for manufacturing a multilayer container having a polyester layer containing polyester resin (X) and a polyamide layer containing polyamide resin (Y), a phenolic antioxidant (A), and a phosphorus-based antioxidant (B) in specific amounts, but is preferably a manufacturing method including the following steps 1 and 2. In other words, the method for manufacturing a multilayer container of the present invention is preferably a manufacturing method that includes the following steps 1 and 2, and produces a multilayer container having a polyester layer containing polyester resin (X) and a polyamide layer containing polyamide resin (Y), a phenolic antioxidant (A), and a phosphorus-based antioxidant (B) in specific amounts. Step 1: A step of coinjecting a polyamide resin composition containing polyamide resin (Y), a phenolic antioxidant (A), and a phosphorus-based antioxidant (B), or a polyamide resin mixture containing polyamide resin (Y), a phenolic antioxidant (A), and a phosphorus-based antioxidant (B), used in the polyamide layer, with a 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. Step 2: A step of blow-molding the multilayer preform.

[0088] (Step 1 (Step of Obtaining a Multilayer Preform)) In step 1, the polyamide resin composition or the polyamide resin mixture, polyester resin (X), and the polyester resin composition or the polyester resin mixture are co-injection molded to obtain a multilayer preform. The polyamide resin composition is a composition containing polyamide resin (Y) as a main component and a phenolic antioxidant (A) and a phosphorus-based antioxidant (B), and may contain resins other than polyamide resin (Y) and other components, etc., as described in the <Polyamide Layer> section. The polyester resin composition is a composition containing polyester resin (X) as a main component and containing the phenolic antioxidant (A), phosphorus-based antioxidant (B), an aldehyde catcher, resins other than polyester resin (X), and other components, etc., as described in the <Polyester Layer> section. The polyamide resin mixture refers to a mixture obtained by dry-blending polyamide resin (Y), phenolic antioxidant (A), phosphorus-based antioxidant (B), resins other than polyamide resin (Y), and other components, or a mixture obtained by dry-blending a masterbatch containing phenolic antioxidant (A), phosphorus-based antioxidant (B), resins other than polyamide resin (Y), and other components with the remainder being polyamide resin (Y). These polyamide resin mixtures become the polyamide resin composition by melt-mixing the components in this process. The polyester resin mixture refers to a mixture obtained by dry-blending polyester resin (X), phenolic antioxidant (A), phosphorus-based antioxidant (B), an aldehyde catcher, resins other than polyester resin (X), and other components, or a mixture obtained by dry-blending a masterbatch containing the above components with the remainder being polyester resin (X). These polyester resin mixtures become the polyester resin composition by melt-mixing the components in this process. In co-injection molding, a polyester resin (composition, mixture) and a polyamide resin (composition, mixture) are separately extruded into a mold and co-injected to form a multi-layer preform.

[0089] (Step 2 (Blow Molding Step)) In Step 2, the multilayer preform is blow molded. In the method for producing a multilayer container of the present invention, it is preferable to mold the multilayer preform (multilayer parison) obtained in Step 1 by stretch blow molding. Among these, in Step 2, it is preferable to stretch blow mold the multilayer preform obtained by coinjection molding, and it is more preferable to biaxially stretch blow mold the multilayer preform obtained by coinjection molding. Note that the conditions for biaxial stretch blow molding are preferably a preform heating temperature of 95 to 110°C, a primary blow pressure of 0.5 to 1.2 MPa, and a secondary blow pressure of 2.0 to 2.6 MPa, which suppresses the occurrence of thickness unevenness and stretch unevenness and allows a multilayer container with excellent strength to be obtained.

[0090] [Method for producing recycled polyester] The method for producing recycled polyester of the present invention is a method for producing recycled polyester, which includes a step of recovering polyester from the multilayer container. The method for producing recycled polyester of the present invention will be described in detail below.

[0091] In this production method, a used multilayer container is usually used, but an unused one may also be used. Examples of used multilayer containers include those that have been once distributed on the market and then recovered. In this production method, if a lid is attached to the multilayer container, it is preferable to first remove the lid from the multilayer container. Next, it is preferable to crush the container, and if necessary, separate the polyester to selectively extract and recover it as recycled polyester (recovery step). In the recovery step, it is preferable to wash the container or the crushed material with an alkaline aqueous solution (washing step). Next, if necessary, it is granulated to form pellets (granulation step). Furthermore, if necessary, a crystallization step and a solid-state polymerization step are performed (crystallization / solid-state polymerization step). Each step is described below.

[0092] <Washing Step> In the method for producing recycled polyester of the present invention, it is preferable to wash the multilayer container or its pulverized product with an alkaline aqueous solution to recover the polyester. Washing with an alkaline aqueous solution can efficiently remove not only the contents stored in the multilayer container but also adhesives and the like. Washing with an alkaline aqueous solution may be performed with the container as is, simultaneously with pulverization, after pulverization, or after separation into polyester and polyamide resin. Washing may also be performed multiple times. Washing after pulverization is preferable, but for convenience, the washing step will be described before the recovery step described below.

[0093] The solvent for the alkaline aqueous solution used to wash the multilayer container or its pulverized product is water in terms of cleaning efficiency and cost. In addition to water, the solution may contain an aqueous organic solvent. Examples of the aqueous organic solvent include lower alcohols such as methanol, ethanol, and isopropyl alcohol, and diols. 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. The alkaline aqueous solution contains an alkaline substance in addition to the solvent. The alkaline substance is preferably at least one selected from the group consisting of alkali metal hydroxides and alkaline earth metal hydroxides, and from the standpoints of cleaning efficiency and cost, alkali metal hydroxides are more preferred. Examples of alkali metal hydroxides include sodium hydroxide, potassium hydroxide, and lithium hydroxide. From the standpoints of cleaning efficiency and cost, at least one selected from the group consisting of sodium hydroxide and potassium hydroxide is preferred, and sodium hydroxide is more preferred. The content of the alkaline substance 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, based on the total amount of the alkaline aqueous solution.

[0094] Any type of washing device may be used, but it is preferable to use a container equipped with a stirrer, especially when washing pulverized material. The temperature during washing is preferably 30 to 95°C, more preferably 50 to 90°C, and even more preferably 70 to 90°C. The washing time is preferably 5 minutes to 10 hours, 5 minutes to 1 hour, or 10 to 30 minutes. The washing temperature and washing time can be appropriately selected depending on the amount and shape of the multilayer container or the pulverized material, etc.

[0095] The method for producing recycled polyester of the present invention includes a washing step of washing with an alkaline aqueous solution, but may also include a step of washing with a liquid other than the alkaline aqueous solution. Preferably, washing with water is further performed. After washing, it is preferable to heat and dry the polyester as needed. By performing the drying step, the moisture content of the recycled polyester obtained by this method can be reduced, making it possible to provide a high-quality recycled polyester with high thermal stability. The drying step can be performed using, for example, air blown by a dryer or hot air.

[0096] <Recovery Process> The recovery process is a process of crushing the multilayer container to recover the recycled polyester. It is particularly preferable to crush the multilayer container and then remove all or part of the polyamide layer to selectively extract the polyester, and it is more preferable to separate the polyester from the polyamide resin constituting the polyamide layer. The multilayer container can be crushed using a crusher such as a single-shaft crusher, a double-shaft crusher, a triple-shaft crusher, or a cutter mill. The crushed material obtained by crushing is, for example, in the form of flakes, powder, or lumps. However, since the majority of the multilayer container has a thin, multilayer laminate structure with a thickness of several mm or less, such as the body, the majority of the crushed material is usually in the form of flakes. Note that a crushed material in the form of flakes refers to a thin or flat material with a thickness of about 2 mm or less.

[0097] Furthermore, in multilayer containers, the polyester layer and the polyamide layer are structurally integrated, but they are not usually adhered to each other, and the polyester and polyamide resin are easily separated as separate pulverized materials during the pulverization process. Furthermore, by forming them into flakes, they are easily separated by being lifted up by the airflow during the winnowing separation process described below. However, the polyester and polyamide resin are not necessarily completely separated during the pulverization process, and the pulverized material is separated into those with a relatively high polyester content and those with a relatively low polyester content and a relatively high polyamide resin content. Hereinafter, for the sake of convenience, those with a relatively high polyester content will be simply referred to as polyester, and those with a relatively high polyamide resin content will be simply referred to as polyamide resin.

[0098] As described above, the crushed material is separated into polyester and polyamide resin (separation step). Gravity separation, which takes advantage of the difference in specific gravity between polyester and polyamide resin, is preferred as a separation method. That is, the polyamide layer is preferably removed by winnowing after crushing the multilayer container. Specific examples of gravity separation include winnowing, which separates crushed material using wind power. Winnowing, for example, involves separating crushed material exposed to the airflow generated by a separator capable of generating a rotating airflow inside the separator, into material with a high specific gravity or a small specific surface area that falls naturally under its own weight and material with a low specific gravity or a large specific surface area that is lifted up by the airflow. In this method, crushed polyester material falls naturally under its own weight, while crushed polyamide resin material is lifted up, allowing for the separation and recovery of polyester and polyamide resin. In this type of winnowing, the same operation may be repeated on the same crushed material. For example, the polyester content in the recycled polyester may be increased by further separating the particles that have fallen naturally through wind separation. Note that the separation method is not limited to wind separation, and examples include a method in which the crushed material is immersed in a liquid such as water and separated based on the difference in specific gravity of the crushed material relative to the liquid, and a method in which the crushed material is subjected to a certain amount of vibration to separate and separate crushed material with different specific gravities.

[0099] <Granulation Process> The recovered recycled polyester is preferably granulated into pellets to facilitate handling during molding and other processes. Granulation may be performed before or after the crystallization / solid-state polymerization process described below, but is preferably performed before the crystallization / solid-state polymerization process. Performing granulation before the crystallization / solid-state polymerization process also improves handling during the crystallization / solid-state polymerization process. In the granulation process, the pulverized material is preferably plasticized and granulated by melt blending. Examples of granulation devices for plasticization and granulation include single-screw extruders, twin-screw extruders, and multi-screw extruders, but any known device can be used. The pellets are preferably cylindrical, spherical, or elliptical. For granulation, for example, the plasticized recycled polyester is preferably extruded into strands, cooled in a water bath, and cut into pellets using a pelletizer. The pellets removed from the water bath are usually dried to remove moisture adhering to the surface.

[0100] <Crystallization / Solid-State Polymerization Step> After the polyester recovery step, it is preferable to carry out one or more steps selected from a crystallization step and a solid-state polymerization step, and it is more preferable to carry out both the crystallization step and the solid-state polymerization step. The crystallization / solid-state polymerization step is preferably carried out on the pelletized polyester described above, but may also be carried out on an unpelletized material (e.g., a pulverized product). When both crystallization and solid-state polymerization are carried out, it is preferable to crystallize the polyester and then carry out solid-state polymerization. The polyester is crystallized by maintaining the polyester under a constant heating condition. The crystallization is preferably carried out by heating the polyester at, for example, 100 to 230°C. Crystallization of the polyester prevents the polyester from fusing with itself or adhering to the inner surface of the apparatus during solid-state polymerization or molding processing.

[0101] The solid-state polymerization is preferably carried out by maintaining a temperature equal to or higher than (melting point of polyester - 80°C) and lower than the melting point of the polyester for a certain period of time. By maintaining the temperature below the melting point, melting of the polyester is prevented, and for example, the polyester is prevented from adhering to the surface of the apparatus, which would reduce the efficiency of the work. Furthermore, by maintaining the temperature at or higher than (melting point of polyester - 80°C), the polymerization proceeds at a sufficient rate, making it easier to obtain the desired physical properties. Here, "(melting point of polyester - 80°C)" means "a temperature 80°C lower than the melting point of the polyester."

[0102] Solid-state polymerization may be carried out under vacuum or in an inert gas stream such as nitrogen or argon. When carried out under vacuum, the pressure is preferably 1.0 torr or less, more preferably 0.5 torr or less, and even more preferably 0.1 torr or less. In addition, whether under vacuum or in an inert gas stream such as nitrogen or argon, it is preferable to reduce the oxygen concentration remaining in the system as much as possible, and the oxygen concentration is preferably 300 ppm or less, more preferably 30 ppm or less. By keeping the oxygen concentration at 30 ppm or less, poor appearance such as yellowing is less likely to occur. When solid-state polymerization is carried out under vacuum, it is preferable to maintain uniform heat transfer by constantly repeating stirring or mixing of the polyester. When carried out in the presence of an inert gas, it is preferable to always keep the polyester surface in contact with the dry gas under a dry gas stream.

[0103] Examples of solid-state polymerization apparatuses for carrying out the crystallization / solid-state polymerization process include tumbler-type batch apparatuses equipped with a heating jacket, dry silo-type apparatuses equipped with an inert gas flow system, and crystallization apparatuses and reactors equipped with an internal stirring blade and discharge screw. It is preferable that crystallization and solid-state polymerization are carried out continuously or simultaneously in the same apparatus. The heating time for solid-state polymerization is determined appropriately based on the apparatus and other conditions, as long as it is a time that allows the polyester to obtain sufficient physical properties. Since solid-state polymerization involves maintaining the polyester at high temperatures for a long period of time, the presence of impurities in the polyester can deteriorate quality, such as color tone. It is preferable that most of the polyamide resin is removed in the removal process described above, in which case deterioration in quality that may occur during solid-state polymerization is minimized.

[0104] When the method for producing recycled polyester includes a polyamide resin removal step, the content of polyamide resin in the obtained recycled polyester is preferably less than 1 mass%, more preferably less than 0.8 mass%, and even more preferably less than 0.6 mass%. By reducing the polyamide resin content in this way, the quality of the recycled polyester is improved. Furthermore, in the method for producing recycled polyester of the present invention, steps other than the steps described above may be carried out.

[0105] The recycled polyester obtained by this production method can be used for various purposes such as resin moldings and fibers.

[0106] EXAMPLES The present invention will be explained in more detail below using examples and comparative examples, but the present invention is not limited to these examples.

[0107] [Raw Materials] The polyester resins and antioxidants used in the Examples and Comparative Examples are as follows: The polyamide resin used was that produced in Production Example 1 below. <Polyester Resins> PET 1101: Polyclear Refresh PET 1101, polyethylene terephthalate (manufactured by Indorama) <Phenol-Based Antioxidants (A)> Irganox 1010: Pentaerythritol Tetrakis[3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate] (trade name: Irganox 1010, manufactured by BASF) <Phosphorus-Based Antioxidants (Phosphorus-Based Antioxidants (B) and Phosphorus-Based Antioxidants Other Than (B))> Doverphos S9228: Bis(2,4-di-cumylphenyl) pentaerythritol diphosphite (trade name: Doverphos S9228, manufactured by Dover Chemical Co., phosphorus-based antioxidant (B)) Irgaphos 168: Tris(2,4-di-tert-butylphenyl)phosphite (a phosphorus-based antioxidant having an aromatic ring but not a pentaerythritol skeleton, trade name: Irgaphos 168, manufactured by BASF, a phosphorus-based antioxidant other than (B))

[0108] <Polyamide Resin> Production Example 1 (Production of Polyamide Resin (Y1)) Into a 50-liter reaction vessel equipped with a stirrer, a partial condenser, a total condenser, a thermometer, a dropping funnel, a nitrogen inlet tube, and a strand die, 15,000 g (102.6 mol) of adipic acid, sodium hypophosphite monohydrate (NaH ２ P.O. ２ ・H ２ 13.06 g (123.3 mmol, 151 ppm as phosphorus atom concentration in polyamide) of sodium acetate (O) and 6.849 g (83.49 mmol, 0.68 as molar ratio to sodium hypophosphite monohydrate) of sodium acetate were added, and the mixture was thoroughly purged with nitrogen. The mixture was then heated to 170°C with stirring under a small amount of nitrogen flow. 13,896 g (102.0 mol, 0.994 as molar ratio to adipic acid) of metaxylylenediamine was added dropwise with stirring, and the temperature of the mixture was continuously raised while removing the resulting condensed water from the mixture. After completion of the dropwise addition of metaxylylenediamine, the internal temperature was raised to 260°C and the reaction was continued for 40 minutes. The mixture was then pressurized with nitrogen, and the polymer was removed from the strand die and pelletized to obtain approximately 24 kg of polyamide. Next, the polyamide was loaded into a jacketed tumble dryer equipped with a nitrogen gas inlet tube, a vacuum line, a vacuum pump, and a thermocouple for measuring the internal temperature. While rotating at a constant speed, the interior of the tumble dryer was thoroughly purged with nitrogen gas having a purity of 99% by volume or higher. The tumble dryer was then heated under the nitrogen gas flow, and the pellet temperature was raised to 150°C over approximately 150 minutes. When the pellet temperature reached 150°C, the pressure in the system was reduced to 1 torr or less. The temperature was further increased to 200°C over approximately 70 minutes, and then maintained at 200°C for 30 to 45 minutes. Nitrogen gas having a purity of 99% by volume or higher was then introduced into the system, and the tumble dryer was cooled while rotating to obtain polyamide resin (Y1). The amino end group concentration was measured and found to be 14.4 μmol / g.

[0109] Example 1 [Production of multilayer container and recycled polyester] <1. Production of polyamide resin mixture> A polyamide resin mixture was obtained by dry-blending in advance 0.0120 parts by mass of Irganox 1010 as the phenolic antioxidant (A) (120 ppm in the polyamide layer), 0.0360 parts by mass of Doverphos S9228 as the phosphorus-based antioxidant (B) (360 ppm in the polyamide layer), and 99.952 parts by mass of the polyamide resin (Y1) obtained in Production Example 1 (the remainder when the total is taken as 100 parts by mass).

[0110] 2. Production of Multilayer Containers (Preform Molding) Using an injection molding machine (Sumitomo Heavy Industries, Ltd., Model DU130CI) with two injection cylinders and a two-cavity mold (Kortec), the polyamide resin mixture was injected from one injection cylinder and polyester resin (PET 1101) from the other injection cylinder, and a three-layer preform (set to correspond to 25 g per preform) consisting of a polyester layer / polyamide layer / polyester layer was produced by injection molding under the conditions shown below, with the weight of the polyamide layer relative to the total weight of the preform being as shown in Table 1. The shape of the preform was a total length of 95 mm, an outer diameter of 22 mm, and a wall thickness of 4.0 mm. The three-layer preform molding conditions were as shown below. Skin side injection cylinder temperature: 285°C Core side injection cylinder temperature (3 layers only): 265°C Mold resin flow path temperature: 285°C Mold cooling water temperature: 15°C Cycle time: 40 seconds

[0111] (Bottle Molding) The preform obtained in the (Preform Molding) step was biaxially stretched and blow molded using a blow molding machine (EFB1000ET, manufactured by Frontier) to obtain a bottle (hollow multilayer container). The bottle had a total length of 223 mm, an outer diameter of 65 mm, an internal volume of 500 mL, and a petaloid bottom. No dimples were provided on the body. The biaxial stretch blow molding conditions were as follows: Preform heating temperature: 103°C, stretch rod pressure: 0.7 MPa, primary blow pressure: 1.1 MPa, secondary blow pressure: 2.5 MPa, primary blow delay time: 0.30 seconds, primary blow time: 0.30 seconds, secondary blow time: 2.0 seconds, blow exhaust time: 0.6 seconds, mold temperature: 30°C.

[0112] <3. Production of Recycled Polyester> (Washing, Recovery, and Granulation Steps) 10 kg of the hollow multilayer containers obtained in <2. Production of Multilayer Containers> above were crushed using a crusher with a mesh size of 10 mm. Each kg of the resulting crushed flakes was placed in a container equipped with a stirrer, and 4 L of 1% sodium hydroxide aqueous solution was added. The mixture was washed while stirring. The washing temperature was 85°C, and the washing time was 15 minutes. After removing the washing water, the crushed material was placed in 45°C water in an amount four times the mass of the crushed material and stirred for 5 minutes. After dehydration, an additional eight times the mass of water was added and stirred. After dehydration, the washed crushed material was dried at 50°C. The flakes from polyester single-layer containers obtained using the same procedure were added to the crushed flakes, dry blended, and diluted twice. The dried pulverized material was extruded into strands using a twin-screw extruder (TEM26SX, manufactured by Toshiba Machine Co., Ltd.) at a heater temperature of 280°C and a discharge rate of 20 kg / hour, and the strands were cooled in a water tank while being cut into pellets using a pelletizer. Note that the polyamide layer was not separated by winnowing.

[0113] (Crystallization / Solid-Phase Polymerization Step) The pellets obtained in the granulation step were heated at 200° C. for 7 hours under a vacuum reduced to 1 torr or less. The pellets after the heat treatment were taken out and used as recycled polyester.

[0114] Examples 2 to 3 and Comparative Examples 2 to 6 [Production of Multilayer Containers and Recycled Polyester] Multilayer containers and recycled polyesters were produced in the same manner as in Example 1, except that the types and amounts of the phenolic antioxidant (A) and phosphorus-based antioxidant used in the polyamide resin mixture (polyamide resin composition, polyamide layer) in Example 1 were changed to those shown in Table 1. In Table 1, the contents of the phenolic antioxidant (A) and phosphorus-based antioxidant are shown in "ppm" (parts per million by mass, ppm by mass). 1 ppm is 0.0001% by mass.

[0115] Comparative Example 1 [Production of multilayer container and recycled polyester] A multilayer container and recycled polyester were produced in the same manner as in Example 1, except that polyamide resin (Y1) was used instead of the polyamide resin mixture.

[0116] Comparative Example 7 [Production of multilayer container and recycled polyester] <1. Production of polyester resin mixture> A polyester resin mixture was obtained by dry-blending in advance 99.99387 parts by mass of polyester resin (PET 1101), 0.00153 parts by mass of Irganox 1010 as a phenolic antioxidant (A) (15.3 ppm in the polyester layer), and 0.0046 parts by mass of Doverphos S9228 as a phosphorus-based antioxidant (B) (46 ppm in the polyester layer).

[0117] <2. Production of multilayer container, and 3. Production of recycled polyester> A multilayer container and recycled polyester were produced in the same manner as in Comparative Example 1, except that the polyester resin mixture was used instead of the polyester resin (PET 1101).

[0118] Example 4 [Production of multilayer container and recycled polyester] <1. Production of polyester resin mixture> A polyester resin mixture was obtained by dry-blending in advance 99.928 parts by mass of polyester resin (PET 1101), 0.0180 parts by mass of Irganox 1010 as a phenolic antioxidant (A) (180 ppm in the polyester layer), and 0.0540 parts by mass of Doverphos S9228 as a phosphorus-based antioxidant (B) (540 ppm in the polyester layer).

[0119] <2. Production of multilayer container, and 3. Production of recycled polyester> A multilayer container and recycled polyester were produced in the same manner as in Example 1, except that the polyester resin mixture was used instead of the polyester resin (PET 1101).

[0120] Examples 5 and 6 and Comparative Example 8 [Production of multilayer container and recycled polyester] Multilayer containers and recycled polyester were produced in the same manner as in Example 4, except that the types and amounts of the phenolic antioxidant (A) and phosphorus-based antioxidant used in the polyamide resin mixture (polyamide resin composition, polyamide layer) were changed as shown in Table 1. In Example 6, anthranilamide was added as an aldehyde catcher in the amount shown in Table 1 when the polyester resin, phenolic antioxidant (A), and phosphorus-based antioxidant (B) were dry-blended.

[0121] [Evaluation Method] <Bottle Moldability> The whitening of bottles obtained by molding using the method described in <2. Manufacturing of Multilayer Containers> in Example 1 was evaluated as follows. A visually whitened portion (a portion with a haze equal to or greater than that of a resin film with a haze of 5% measured according to JIS K 7136:2000 as a standard) was cut out from the body of the bottle (a portion 3 to 13 cm from the bottom surface of the bottle), and the mass was measured. The proportion of the whitened portion was calculated using the following criteria to evaluate moldability. The smaller the proportion of the whitened portion, the more transparent the multilayer container obtained and the better the moldability. (Evaluation Criteria) A: The proportion of the whitened portion was less than 1% of the entire bottle body, and it was transparent. The moldability was extremely good. B: The proportion of the whitened portion was 1% or more but less than 10% of the entire bottle body, and slight whitening was observed. The moldability was good. C: The proportion of the whitened portion was 10% or more but less than 50% of the entire bottle body, and some whitening was observed. D: The proportion of whitened areas was 50% or more of the entire bottle body, and the entire bottle was whitened.

[0122] <Preparation of evaluation samples> The following haze, L * value, b * value and Δb* The evaluation samples of the recycled polyester for measuring the values ​​were prepared as follows. The pellets after heat treatment of the Examples and Comparative Examples were injection-molded into plates measuring 60 mm in length, 90 mm in width, and 3.0 mm in thickness using an injection molding machine (manufactured by Sumitomo Heavy Industries, Ltd., model SE130DU-HP) with an injection cylinder under the molding conditions shown below. Injection cylinder temperature: 280°C Mold cooling water temperature: 15°C Cycle time: 45 seconds

[0123] <Haze> The haze of the plate was measured based on JIS K 7136: 2000 using a haze meter COH7700 (manufactured by Nippon Denshoku Industries Co., Ltd., white LED light source) and calculated as the average value of four measurements. The smaller the haze value, the better the transparency of the recycled polyester, which is preferable.

[0124] <L * The L value of the evaluation sample was measured using a haze meter COH400 (manufactured by Nippon Denshoku Industries Co., Ltd.) in accordance with JIS K 7105:1981. * The value was measured. * The value represents the lightness. * The higher the value, the better the colorlessness, and therefore the more preferable.

[0125] <b * The haze value of the evaluation sample was measured using a haze meter COH400 (manufactured by Nippon Denshoku Industries Co., Ltd.) in accordance with JIS K 7105:1981. * The values ​​were measured. * The value represents the chromaticity. * is yellow direction, -b * represents the blue direction. * The absolute value of the value is small, and b * The smaller the value, the more suppressed the yellowing, the better the colorlessness and the better the color tone.

[0126] <Δb *The polyester resin (Polyclear Refresh PET 1101) used as the raw material was molded under the conditions shown in <Preparation of Evaluation Sample> to produce a plate measuring 60 mm in length, 90 mm in width, and 3.0 mm in thickness. Next, the haze was measured using a haze meter COH400 (manufactured by Nippon Denshoku Industries Co., Ltd.) in accordance with JIS K 7105:1981. * The values ​​were measured (b * Value 4.1). Above <b * The values ​​of the evaluation samples of the examples and comparative examples obtained * value and the b value of the polyester resin used as the raw material * The difference in value (4.1) is Δb * The value was Δb * The smaller the value, the more the yellowing is suppressed, the less discoloration from the raw polyester resin occurs, and the more excellent the colorlessness is, which is preferable. * When the value is less than 5.0, the colorlessness is good, and in particular, Δb * A value of less than 4.5 was judged to indicate very good colorlessness.

[0127]

[0128] As shown in Table 1, the recycled polyester obtained by recycling the multilayer container of the present invention has a low yellowness index, excellent colorlessness, and excellent transparency. Furthermore, the multilayer container of the present invention can exhibit the above effects with the addition of an extremely small amount of antioxidant, which shows that it also has excellent moldability.

Claims

1. A polyester layer containing polyester resin (X), The material comprises a polyamide resin (Y), a polyamide layer containing a phenolic antioxidant (A), and a phosphorus-based antioxidant (B), The phosphorus-based antioxidant (B) is a compound having a pentaerythritol skeleton and an aromatic ring. A multilayer container in which the total content of phenolic antioxidant (A) and phosphorus-based antioxidant (B) in the polyamide layer is 0.040 to 0.250% by mass.

2. The multilayer container according to claim 1, wherein the mass ratio [(A) / (B)] of the content of phenolic antioxidant (A) to the content of phosphorus-based antioxidant (B) in the polyamide layer is 2 / 8 to 5 / 5.

3. The multilayer container according to claim 1 or 2, wherein the polyester layer contains a phenolic antioxidant (A) and a phosphorus-based antioxidant (B).

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

5. The multilayer container according to claim 3, wherein the mass ratio [(A) / (B)] of the content of phenolic antioxidant (A) to the content of phosphorus-based antioxidant (B) in the polyester layer is 2 / 8 to 5 / 5.

6. A multilayer container according to claim 1 or 2, wherein the polyester layer contains anthranilamide.

7. The multilayer container according to claim 1 or 2, wherein the polyamide resin (Y) has a constituent unit derived from a diamine containing 80 mol% or more of constituent units derived from xylylenediamine, and a constituent unit derived from a dicarboxylic acid containing 80 mol% or more of constituent units derived from adipic acid.

8. The multilayer container according to claim 1 or 2, wherein the content of polyamide resin (Y) is 0.05 to 10.0% by mass relative to the total amount of the total polyamide layer and the total polyester layer.

9. The multilayer container according to claim 1 or 2, wherein the polyamide layer content is 0.05 to 10.0% by mass relative to the total amount of the polyamide layer and the total polyester layer.

10. The multilayer container according to claim 1 or 2, wherein the polyester resin (X) has a constituent unit derived from a dicarboxylic acid containing 80 mol% or more of constituent units derived from terephthalic acid, and a constituent unit derived from a diol containing 80 mol% or more of constituent units derived from ethylene glycol.

11. The multilayer container according to claim 1 or 2, wherein the multilayer container is a hollow container.

12. The multilayer container according to claim 1 or 2, wherein the multilayer container has a 3 to 5-layer structure, and the outermost layer and innermost layer are polyester layers.

13. The multilayer container according to claim 1 or 2, wherein the multilayer container has a three-layer structure.

14. The multilayer container according to claim 1 or 2, wherein the multilayer container does not have an adhesive layer.

15. A method for producing recycled polyester, comprising the step of recovering polyester from a multilayer container as described in claim 1.

16. A method for producing recycled polyester, comprising the step of recovering polyester from a multilayer container according to claim 1, A method for producing recycled polyester, comprising the step of removing all or part of the polyamide layer from a multilayer container and recovering the polyester.

17. The method for producing recycled polyester according to claim 16, wherein the removal of the polyamide layer is performed by wind separation after crushing the multilayer container.

18. A method for producing recycled polyester according to claim 15 or 16, comprising the step of washing the multilayer container or pulverized material thereof according to claim 1 with an alkaline aqueous solution to recover polyester.

19. A method for producing recycled polyester according to claim 15 or 16, wherein, after the step of recovering polyester, one or more steps selected from a crystallization step and a solid-phase polymerization step are performed.